HX64089193 QP34 .OtS 1 907 A text-book of physi av3^ Ot^g ■amummmms^ai^mMtai^ti!- i< Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/textbookofphysioOOotti A Text-book OF PHYSIOLOGY BY Isaac Ott, A.M., M.D. Profkssor of Physiology in the Medico-Chirurgical College of Philadelphia; Kx-Fellow in Bkilogy,. Johns Hopkins University ; Consulting Neurologist, NoRRisTOWN Asylum, Penna.; Ex-President of American Neurological Association, etc. SECOND EDITION, REVISED AND ENLARGED Illustrated With 393 Half=Tone and Other Engravings Many in Colors PHILADELPHIA F. A. DAVIS COMPANY, PUBLISHERS 1907 W34 fC)*l ^ R,c. l^ COPYRIGHT, 1904 and 1907, BY F. A. DAVIS COMPANY. [Registered at Stationers' Uall, London, Kng.] Philadelphia, Pa., U. S. A. : Press of F. A. Davis Company 19U-1G Clierry Street. Oo> DEDICATED TO THE Memory of my Mother SARAH A. OTT PREFACE TO THE SECOND EDITIOI^, The second edition of tliis l)oo]%; has been enlarged by the addi- tion of two hundred and forty pages. Considerable new matter has been inserted, for Physiology is a science undergoing continuous development. The sul)ject of electro-physiology has 1:»een treated more com- prehensively than in the first edition. The article upon the sympa- thetic system has been nearly entirely re-written. The latest acqui- sitions in this direction have been incorporated. The chapter on Vision has Ijeen entirely recast. In fact, nearly every page has l)een subjected to alterations and emendations. The work ujion peristalsis of intestines in the Medico-Chirurgical laboratory has been incorpor- ated. Over two hundred and fifty additional figures, many of them entirely original, have been included in this edition. In the chapter on Reproduction, the first eleven pages and the part headed "Evolution" have 1)een contril)uted l)y Dr. P. Fischelis. Demonstrator of, Histology and Eml)ryology, ]\Iedico-Chirurgical College, My cordial thanks are due to Dr. E. T. Rehrig for the com- plete index. Isaac Ott. (V) CONTENTS. CHAPTER I. PAGE The Cell 1 CHAPTER II. Chemical Constituents of the Body and Food 24 CHAPTER III. Digestion 45 CHAPTER IV. ABSORrTION 130 CHAPTER V. The Blood 160 CHAPTER VI. The Circulation 201 CHAPTER VII. Respiration . 298 CHAPTER VIII. Secretion ; 355 CHAPTER IX. ^rETAHOLTSM 419 CHAPTER X. Animal Heat 434 CHAPTER XI. The Muscles 456 CHAPTER XII. Voice and Speech 491 CHAPTER XIII. Electro-phtsiology ... 503 CHAPTER XIV. jSTervous System 534 (Yii) viii CONTENTS. CHAPTER XV. PAGE Tactilk Sense C50 CHAPTER X\'l. 'I\\sTi; G65 C:iIAPTER XVII. Smelt G70 CHAPTER XVI] I. Hearing G77 CHAPTER XIX. Vision 099 CHAPTER XX. Cranial Nerves 748 CHAPTER XXL REPRODrcTioN 7G9 Index • 797 LIST OF ILLUSTRATIOE'S. PIG. PAGE 1. Vegetable Cell. (Duval) 6 2. Cell with Reticulum of Protoplasm Radially Disposed, p-rom Intestinal Epi- thelium of a Worm. (Carnoy) 8 3. Amceba Proteus. (Leidy) 9 4. To Show the Changes in the Nerve-coll Due to Age. (Prom Howell) 2.3 5. Yeast Fungus. (After Harley) 28 6. Specimens of Milk, viewed through the Microscope. (Landois) 40 7. Longitudinal Section of a Molar Tooth of Man. X S. (Sobotta) 51 8. Portion of the Crown of a Longitudinal Section of a Human Premolar. X 200. (Sobotta) 52 9. Portion of a Longitudinal Section of the Root of a Human Molar Tooth. X 200. (Sobotta) 53 10. Histology of the Salivary Glands. (Landois) 54 11. Parotid of Cat. (L. MOller) G3 12. Parotid of a Rabbit in Fresh State. (Langley) 64 13. Human Stomach. (After Sappey) GG 14. Vertical Section through the Gastric Mucous Membrane. (Landois) GT 15. Gastric Contents. Collective Microscopic Picture. X 350. (Lenhartz) G9 IG. Hourly Variations of the Secretion of Gastric Juice in the Dog after a Meal of Meat, Dread, and Milk. (Pawlow) 74 17. Hourly Variations of the Digestive Power of the Gastric Juice in the Dog after a Meal of Meat, Bread, and Milk. (Pawlow, Gley) 75 18. Dog's Stomach. (Pawlow) 77 19. Dogs to whom a Fictitious Meal is Given. They have a fistula in the oesoph- agus and a fistula in the stomach. After a photograph taken in the labora- tory of Pawlow. (Gley) 79 20. Portion of the Wall of the Small Intestine Laid Open to Show the Valvulce Conniventes. (Brinton, Raymond) SG 21. Blood-vessels of an Intestinal Villus. (Landois) 87 22. Mucous Membrane of the Jejunum, Highly Magnified. (Schematic.) (Testut, Raymond) 88 23. Effect of Albumose, increasing Peristalsis 92 24. The Pancreas. (Posterior View.) (Bourgery) 93 25. Schematic Section of Pancreas. (Vialleton) 94 26. Pancreas of Rabbit Observed During Life. (KOhne and Lea) 95 27. Hourly Variations of the Pancreatic Secretion after a Meal of Meat, Bread, and Milk. (After a curve obtained in the laboratory of Pawlow by one of his pupils, A. Walther) 96 28. Liver of Man. (Duval) 105 29. Diagrammatic Representation of an Hepatic Lobule. (L.\ndois) 107 30. Glyeocholic Acid. (Duval) 110 31. Taurin. (Duval) Ill 32. Crystals of Cholesterin. (Duval) 113 33. Curves Showing the Velocity of Secretion of Bile into the Duodenum on (1) a diet of milk, uppermost curve; (2) a diet of meat, middle curve; (3) a diet of bread, lowest curve. The divisions on the abscissa represent inter- vals of thirty minutes; the figures on the ordiuates represent the volume of secretion in cubic centimeters. (Howell, after Bruns) 114 2i. A, Liver-cells during fasting. B, Cells filled with Glycogen. (Heidenhain). . 117 35. Aspect of an Intestinal Loop before and after Section of its Nerves. (Armand Moreau, after Gley) 123 36. Stool. Collective Microscopic Picture. X 350. (Partly after Nothnagel.) (Lenhartz) 125 37. Inhibitory Apparatus of Ano-spinal Center 127 38. Osmometer. (Cohen) 133 39. A, Section of Villus of Rat killed during Fat Absorption. (Schafer.) B, Mucous Membrane of Frog's Intestine during Fat Absorption. (Schafer). 141 40. Lacteals of a Dog during Digestion. (Colin) 143 41. The Superficial Lymphatics of the Internal Surface of the Lower Limb. ( Sappey) 144 42. Topography of the Thoracic Duct (Zuckerhandl.) (Raymond) 145 43. Section of Dog's Intestine, showing Villi. (Cadiat) 149 44. Diagram to Show Relation of the Secreting Cell of a Gland to the Blood and Lymph-supply. (Starling) 152 45. Diminution of the Flow of Lymph under the Influence of the Slowing of the Heart. Dog narcotized with morphia and chloroform. (L. Camus) 154 46. Dog with Medulla Divided. (L. Camus and E. Gley) 155 47. Blood-corpuscles of Different Animals. (Th.^nhoffer) 164 48. y4, Progressive Pernicious Amcmiii. iJ, Llenal (Splenic) Leukieiuia. <7, Lien :il (Splenic) Lpukfeniia. D, Acute I.eukiciuin. Facing 164 49. Human and Amphibian Blood-corpuscles. (Landois) 1C5 50. Hfemacytometer of Thoma-Zeiss. (Lahousse) 167 51. Daland's Hasmatocrit 1G8 (ix) X LIST OF ILlASTRATrONS. Fia. PAGE 52. Uc'd niood-porpusclps. (Landois) I(j9 53. Leucocytes of Man, showing Ama?boid Movement. (Landois) IT:? 54. Blood-plates and their Derivatives. (Lanuois) 175 55. lUood-erystals of Man and DilTcrent Animals. (Thanhoffer and Fkey) 17S 56. Teichmanii's IliEmin-erystals. (Lahousse) 181 57. Sorby-Browning Microspeetroscoix- 182 58. Spectra of Oxyhccmoglobin, Ueduced Haemoglobin, and CO Haemoglobin. (Gamgre) 184 59. Von Flcischl IIa;mometcr. (Lahousse) 188 CO. Relative Proportion of Corpuscles and of Plasma. (Human Blood.) (Lang- I.OIS) 189 CI. Delicate Fibrin Coagulum (from Croupous Pneumonia.) X 3.50. (Lenhartz).. 191 C2. Anterior Surface of the Heart. (Bourgb:ry) 204 63. Heart of the Cow, with Left Auricle and Ventricle Laid Open. (MOli.er) 205 64. Diagram of Mammalian Heart. (Beclard) .' 206 65. Valves of Heart 207 66. Course of Muscular Fibers of Heart. (Landois) 209 67. Course of the Ventricular Muscular Fibers. (Landois) 210 68. Diagram of the Circulation. (Duval) 212 C9. A Cardiac Cycle. (Starling) 213 70. Sanderson Cardiograph 216 71. Cardiogram (li) with Simultaneous Record of Heart-sounds (A). (Hijrthlr, Starling) 217 72. Magnified curve of the course of pressure within the left ventricle and the aorta of the dog, the chest being open; to be read from left to right. Recorded simultaneously by two elastic manometers with transmission by liquid. (Porter) 219 73. The Action of the Semilunar Valves. (Chauveau) 222 74. The Action of the Tricuspid Valve. (Chauve.\u) 223 75. Heart of the Frog. (Livon) 229 76. Schema of Ligatures of Stannius. (Hedon) 231 77. Cardiac Plexus and Stellate Ganglion of the Cat. (Landois) 233 78. Course of Vagus fJerve in Frog. (Stirling) 234 79. Tracing by Lever Attached to Frog's Heart on Stimulation of the Pneumo- gastric Nerve. (Foster) 235 SO. Arrest of the Heart of a Rabbit by Irritation of the Peripheral End of the Pneumogastric in the Neck. (Glet) 23C 81. Irritation of Nervous Depressor in a Rabbit, Causing a Fall of Arterial Tension. (Gley) 237 82. Scheme of the Cardiac Nerves in the Rabbit. (Landois) 238 83. Diagram of the connections of the Depressor Nerve in the Rabbit and Dog, according to Cyon. It will be noticed that in the latter animal the depressor nerve runs in the vagus trunk for the greater part of the course. (Starling) 2.39 84. Schema of Innervation of the Heart of a Dog. (Morat) 240 85. Curve of Blood-pressure in the Cat, recorded by a mercury manometer, show- ing the increase in frequency of heart-beat from excitation of the aug- mentor nerves. (From HoWELL) 241 86. Increase in the Force of the Ventricular Contraction (curve of pressure in right ventricle) from stimulation of augmentor fibers. (Howell) 242 87. Staircase Contractions of a Frog's Ventricle in Response to a Series of like Stimuli, written on a regularly revolving drum by the float of a water manometer connected with the chamber of the ventricle. (Howell, after BOWDITCH) 243 88. Refractory Period of Heart-muscle of Frog, with Compensatory Pause 244 89. To Illustrate the Varying Excitability of the Frog's Heart at Different Periods of Systole and Diastole. (Waller) 245 90. Weber's Schema 251 91. Marey's Intermittent Afflux Apparatus. (Lahousse) 254 92. Marey's Sphygmograph. (Yeo.) 257 93. Dudgeon's Sphygmograph. (Lahousse) 258 94. Sphygmogram Magnified. (Lahousse) 259 95. Frog's Web, Highly Magnified. (Yeo, after Hlixley) 260 96. Showing the Relative Heights of Blood-pressure in Different Blood-vessels. (Yeo) 263 97. Variations in Pressure. (Landois) 264 98. Manometer of Mercury for Measuring and Registering Blood-pressure. (Yeo). 266 99. Ludwig's Kymograph. (Yeo) 267 100. Blood-pressure Curve Recorded by the Mercurial Manometer. (Yeo) 268 101. Cardiac Manometer. (Lahousse) 269 102. Riva-Rocci Sphygmomanometer 270 103. Traube-Hering Curves. (Fredericque) 272 104. Ludwig's Stromuhr. (Landois) 275 105. Curves Obtained by Enclosing the Hind Limb of a Cat in the Plethysmograph and Stimulating the Peripheral End of the Cut Sciatic Nerve (Bowditch and Warren, 1886). (Howell) 282 106. Effect of Irritation of the Splanchnic Nerve on the Aortic Pressure. (Glet).. 283 107. Carotid Pressure in Curarized Dog after Section of Medulla .4, and after Destruction of the Cord /?. (Glet) 287 108. Elevation of Arterial Pressure by Vasoconstriction. A result of irritation of the central end of sciatic in curarized dog. (Hedon) 289 LIST OF ILLUSTRATIONS. xi FIG. PAGE 109. Pick's Plethysmograph 290 110. Stages iu Widal Reartion. (After Robin) 293 111. Human Respiratory Apparatus. (Duval) 302 112. Bronchia and Lungs, Posterior View. (Sappey) 303 113. Mold of a Terminal Bronchus and a Group of Air-colls Moderately Distended by Injection, from the Human Subject. (Robin) 305 114. Termination of a Bronchus in an Alveolus 306 115. Section of the Parenchyma of the Human Lung, Injected Through the Pulmo- nary Artery. (Schulze) 307 116. Diagrammatic Representation of the Action of the Diaphragm. (Beclard). .. . 309 117. The Action of the Ribs in Man in Inspiration. (Beclard) 310 118. Schema of Respiratory Mechanism in Inspiration. (Laulanie) 311 119. Schema of Respiratory Mechanism iu Expiration. (Laulanie) 312 120. Schema of Action of Intercostal Muscles. (Landois) 313 121. Tracing of a Respiratory Movement. (Foster) 315 122. Marey's Tympanum and Lever. (Sanderson) 316 123. Spirometer. (Fredericque) 317 124. Gad's Aeroplethysmograph. (Krusich) 320 125. Number of Respirations by Man at Different Ages. (Quetelet) 321 126. Carotid Pressure in Dog. Acceleration of Heart at the Moment of Inspiration is Well Marked. (Langlois) 322 127. Apparatus to Illustrate Relations of Intra-thoracic and External Pressures. (After Beaunis) 323 128. Illustrating Atmospheric Pressure During Respiration 324 129. Comparison of Blood-pressure Curve with Curve of Intra-thoracic Pressure. (M. Foster) 324 130. Illustrating Arterial Blood-pressure During Respiration 325 131. Illustrating Venous Blood-pressure During Respiration 326 132. Rabbit (morphine gr. Vn injected hypo.). (Dr. W. H. Good) 330 133. Scheme of the Chief Respiratory Nerves. (Landois, after Rutherford) 331 134. Arrest of Respiration in State of Expiration. (Hedon) 332 135. Apparatus for Taking Tracings of the Movements of the Column of Air in Respiration. (Foster) 334 136. Shows the Position to be Adopted for Effecting Artificial Respiration in Cases of Drowning. (Schaefer, Howell) 3.37 137. Cheyne-Stokes Respiration. (Waller) 340 138. Ludwig's Mercurial Air Pump to Extract Blood Cases. (Lahousse) 341 139. Schema of the Large Respiration Apparatus of Pettenkofer. (Fredericque).. 342 140. Showing Constituents of Air Inspired and Expired. (Langlois) 343 141. Variations of Respiratory Quotient According to Food Taken. (L.\nglois). .. . 345 142. Variations of Respiratory Quotient According to the Food Taken. (Langlois). 346 143. Relative Proportion of Gases of Blood. (Langlois) 347 144. Structure of the Thyroid (Morat and Doyon). Lobule of the Thyroid after an Injection of the Lymphatic Vessels with Nitrate of Silver. Semi-schematic. (Vialleton) 358 145. Parathyroid of Dog (Morat and Doyon). (Vialleton) 359 146. Illustrating Nicholson's Article on Thyroid Treatment in a Cretin (Arch, of Ped., .June, 1900). (Raymond) 360 147. Effect of lodothyrin on Intestinal Peristalsis 363 148. Effect of Extract of Spleen on Intestinal Peristalsis 365 149. Adrenal Capsules of a Rabbit. (Morat and Doyon) 365 150. Section of Adrenal. (Vialleton) 360 151. Effect of Adrenalin on the Volume of Inspired and Expired Air. Tracing with Gad's Aeroplethysmograph 3G7 152. Effect of Adrenalin on Intestinal Peristalsis 368 153. Cat. One drop of adrenalin solution and ten drops of 1-per-cent. solution of nitroglycerin, mixed and then injected per jugular 368 154. Turtle Heart, Suspended by Lever 369 155. Effect of Suprarenal Extract upon Muscle-contraction in the Frog. (Schafer). 370 156. Mammary Gland of Human Female. (After Liegeois) 373 157. Dog's Mammary Gland in First Stage of Secretion. (Heidenhain) 375 158. Mammary Gland of the Dog, Second Stage of Secretion. (Heidenhain) 376 159. Sweat Gland. (Hedon) 377 160. Section of Sweat-glands of Cat 379 161. Relations of the Kidnev. (After Sappey) 384 162. Section of Kidney. (Landois) 386 163. Diagram of the Course of Two Uriniferous Tubules. (Landois) 3S'7 164. Structures of Kidney. (Landois) 388 165. Longitudinal Section of a Malpighian Pyramid. (Landois) 389 166. Blood-vessels and Uriniferous Tubules of the Kidneys. (Semidiagrammatic.) (Landois) 390 167. Urea from Human Urine. (Funke) 395 168. Micrococcus Ureae. X 500. (After von Jaksch) 396 169. Uric-acid Crystals with Amorphous Urates. (Purdy, after Peyer) 398 170. Uric Acid. Effect of on Intestinal Peristalsis 399 171. Urate of Soda and Crystals of Uric Acid (h). Oxalate of Lime (o), and Cystin (r). X 350. (Lenhartz) 400 172. Effect of Xanthin on Muscle Curve, Causing an Extra Contraction during the Relaxation. (J. F. Ulman) 402 173. Leucin in Balls; Tyrosin in Sheaves. (Peter) 403 174. Crystals of Ammonio-magneslum Phosphate. (After Ultzmann) 408 xii LIST OF ILLUSTRATIONS. FIG. PAOE 175. Feathery Crystals of Triple Phosphate. X 350. (After Tyson) 409 17G. Crystals of PhenylKlucosazono. (I'URDY, after v. Jak.scii) 412 177. Blood-pressure ami Volume of Kidney. (STiiu.lNn, after Roy) 414 178. Diagram, of Nerve-supply to Itladder. (Nawkocki, Skabitchewsky, and Starling) 417 179. Variations in the Bodily Temperature during Health within Twenty-four Hours. (Landois) 438 180. Human Calorimeter 442 181. Bilateral Puueture of the Tuber Cineroum of Rabbit Through Roof of Mouth.. 445 182. Puncture of Tuber Cinereum in Rabbit, Showing Effect on Respiration, Arte- rial Tension, Pulse, and Temperature 44G 183. Cortex of Cat's Brain 418 184. Lesions of Cortex in Man, Causing Elevations of Temperature 449 185. Curves of Temperature and Respiration when Cortex is Removed and the Animal is Artificially Heated '. 450 186. Curve of Temperature and Respiration when the Tuber Cinereum is Destroyed and the Animal is Artificially Heated 451 187. Heat Production and Heat Dissipation in Man during a Paroxysm of Malarial Fever— a Great Increase of Heat Production 453 188. Histology of Muscular Tissue. (Ellenberger) 459 189. Unstriped Muscular Tissue. (Ellenberger) 40.') 190. The Pendulum Myograph. (Foster) 473 191. A Muscle-curve Obtained by Means of the Pendulum Myograph. (Foster) 475 192. Arrangement of Apparatus in Conducting Experiments on Nerve and Muscle. (Stirling) 476 193. Fatigue-curves of Frog's Muscle. (Waller) 477 194. Effect of Increase of Current on Efficiency of Breaking Induction Shocks. (Howell, after Fick) 477 195. An Experiment to Show that a Contracting Muscle does not Change its Vol- ume. (Hedon) 478 19G. Apparatus for Measuring the Velocity of the Wave of Muscular Contractions. (Marey) 479 197. Rate of Conduction of the Contraction Process along a Muscle as shown by the Difference in the time of Thickening of the two Extremities. (Marey, Howell) 480 198. Tracing of a Double Muscle-curve. (Foster) 480 199. Progress in Fusion of Contraction. (Laulanie) 481 200. 1. Imperfect Tetanus, 15 Contractions per second. 2. Perfect Tetanus. (Lau- lanie) 482 201. Extensibility of Elastic Band and Muscle. (Waller) 484 202. Extensibility of Muscle in Various States. (Waller) 485 203. Mosso's Ergograph 487 204. Ergographic Curves. (After Mosso) 488 205. Ergographic Curve of a Case of Addison's Disease, Showing Rapid Exhaustion of Muscle. (Langlois) 489 206. Fick's Work Adder. (Laulanie) 489 207. Curve of Contraction of the Unstriped Muscle of Miiller in Dog. (Laulanie).. 490 208. The Larynx as Seen with the Laryngoscope. (Landois) 492 209. Action of the Muscles of the Larynx. (Beaunis) 493 210. Schematic Horizontal Section of Larynx. (Landois) 494 211. Schematic Closure of the Glottis by the Thyro-arytenoid Muscles. (Landois). 495 212. The Posterior Rhinoscopic Image. (Bosworth) 497 213. Position of Vocal Cords on Uttering a High Note. (Landois) 498 214. Daniell Cell 504 215. DuBols Nonpolarizable Electrodes. (Lahousse) 507 216. Tetanizing Key of DuBois-Reymond. (After Rosenthal) 508 217. Pohl's Commutator. (Lahousse) 509 218. DuBois-Reymond's Induction Apparatus. (Waller) 511 219. Principle of Simple Rheocord 512 220. Schema of Apparatus to Study Influence of Rapid Variations of the Constant Current by the Rheonome of von Fleischl. (Lahousse) 513 221. Schema of Experiment to Measure the Rapidity of the Muscle Current by the Aid of the Differential Rheotome of Bernstein. (Lahousse) 514 222. The Nerve-muscle Preparation. (Stirling) 515 223. Thompson Galvanometer 516 224. Diagram of Capillary Electrometer. (Starling) 517 225. Direction of Current of Daniell Cell 518 226. Direction of Current of Injured Muscle. (Waller) 518 227. Schema Representing the Inequalities of Electric Tensions upon the Natural Longitudinal Surface and upon the Artificial Transverse Surface of a Muscle-cylinder. Also the direction of the electric currents from the exterior to the interior of the muscle. (Lahousse) 519 228. The Negative Variation (Frog's Gastrocnemius). (Waller) 520 229. Arrangement of Parts to Show Secondary Contraction in Muscle. (After Rosenthal) 521 230. Effect of Chloroform upon the Electrical Responses of Isolated Nerve. (Waller) 522 231. The Structure of Nervous Tissue. (Landois) 525 232. Cells from Anterior Horn of Human Spinal Cord. Ganglion Cells. (Ramon t Cajal.) Neuroglia. (Weigert) 526 LIST OF ILLUSTRATIONS. xiii FIG. PAGE 233. Ganglion Cell from Sympathetic Ganglion of Frog; Greatly Magnified, and Showing Both Straight and Coiled Fibers. (After Quain) 527 234. A Piece of MeduUated Nerve-fibril of Man, Nucleus and Axis Cylinder Stained by Carmine. (Sobotta) 52y 235. A Piece of MeduUated Nerve of Man. It shows Ranvier's Constrictions and Lantermanu's Incisures. (Sobotta) 529 236. Two Nerve-pairs at Their Origin in the Spinal Cord — Anterior and Posterior Roots. (MORAT) 540 237. Transverse Section of the Spinal Cord 546 238. Section of Spinal Cord, Showing the Less Well-known Tracts 549 239. Medulla Oblongata, Pons, Cerebellum, and Pes Pedunculi. Anterior View, to Demonstrate E.xits of Cranial Nerves. (Edinger) 551 240. The Three Pairs of Cerebellar Peduncles. (After Hirschfeld and Leveille). 552 241. Metencephalon, Mesencephalon, and Thalamencephalon, from the Dorsal Sur- face. (Gordinier, after Obersteiner) 554 242. Diagrammatic Transverse Section of the Spinal Bulb X 3, at about the middle of the olivary body, to illustrate the principal nuclei and tracts at that level. (Waller, after Schwalbe) 555 243. Cross-section of the Oblongata through the Decussation of the Pyramids. (After Henle) 556 244. Section of Medulla Oblongata at the Level of the Decussation of the Pyramids —Motor Decussation. (M. Duval.) Section of Medulla Oblongata at the Upper Part — Sensory or Fillet Decussation. (M. Duval) 558 245. The Base of the Brain. The Left Lobus Temporalis is in Part Represented as Transparent in Order that the Entire Course of the Optic Tract Might be Seen. (Edinger) 561 246. Diagram to Illustrate Some of the Connections of the Nuclei of the Nerves to the Ocular Muscles. (Starling, after Held) 563 247. Diagrammatic Transverse Section Through the Crus Cerebri and Anterior Cor- pora Quadrigemina. (Waller, after Obersteiner) 564 248. Section of the Crus Cerebri. (Morat) 565 249. The Mesial Fillet, Ending Chiefly in the Ventral Nucleus of the Optic Thala- mus and then United by New Neuraxons (Upper P^illet) to Parietal Cortex.. 5G8 250. View from the Side and Slightly from Above and Behind of the Right Hemi- sphere of a Simply Convoluted European Brain. (Quain) 569 251. Lateral Aspect of Brain. (Edinger) 571 252. Mesial Aspect of Left Hemisphere of a European Brain. (Quain) 572 253. Longitudinal Section Through the Middle of an Adult Brain. The posterior portion of the thalamus, the crura cerebri, etc., have been removed, in order to expose the inner surface of the temporal lobe. (Edinger) 573 254. Section Through the Cerebral Cortex of a Mammal. (Edinger and Cajal)... 574 255. The Brain-structures from the Thalamus to the Spinal Cord (the "Brain- stem"). (Edinger) 575 256. Thalamus and Corpora Quadrigemina Seen from the Side. (Edinger) 576 257. Median Sagittal Section Through the Interbrain and the Structures Posterior to it. (Edinger) 577 258. Median Section of the Brain. (Quain) 579 259. So-called Ganglionic Gray Matter of the Cerebral Trunk. (After Charpy.) Gray Masses Superadded to the Scnsori-motor Nuclei. (Morat) 580 260. Ideal Horizontal Section Through the Right Hemisphere and Basal Ganglia. (Waller, after Charcot) 581 261. Internal Capsule. (Sherrington) 582 262. Motor Tract. (Morat) 583 263. Sensory Tract. (Morat) 585 264. D, Dubois-Reymond's Spring Myograph to Measure the Rapidity of the Nerve Current in Motor Nerves. (Lahousse) 589 265. Curves Illustrating the Measurement of the Velocity of a Nervous Impulse (Diagrammatic). (Poster) 590 266. Method of Studying Physiological Electrotonus. (Lahousse) 592 267. Schema of Apparatus for the Study of the Law of Contractions in the Frog. (Lahousse) 593 268. Scheme of Electrotonic Excitability 594 269. Pfliigor's Law of Contraction of Nerve-muscle Preparation 595 270. Anelectrontonic Current. Polarizing Current. Katelectrotonic Current. (Waller) 598 271. Elementary Reflex Arc. Course of Senscu-y Injpressions and a Motor Impulse, Passing Through the same Level of tne Spinal Cord. (Morat) 599 272. Diagram of the Roots of a Spinal Nerve, Showing Effect of Section. (Landois). 604 273. Floor of Fourth Ventricle of Rabbit. (Hedon) 611 274. Horizontal Section Through the Cerebellum. (After B. Stilling) 613 275. Section of Cerebellum of Man Treated by Golgi Method. (Sobotta) 615 276. Schema Showing the Origin and Course of the Fibers of the Peduncles of the Cerebellum. (Edinger) 616 277. Connections of the Cerebellum with Cerebrum, Pons, and Spinal Cord. (Schema of Charpy.) (Morat) 618 278. Effects of Removal of Cerebellum. (Dalton) 619 279. The Motor Area and its Subdivisions on the Lateral Aspect of the Hemicere- brum of the Chimpanzee. (Grunbaum and Sherrington) C24 280. The Motor Areas and Centers on the Mesial Aspect of the Hemicerebrum of the Chimpanzee. (GrOnbaum and Sherrington) 625 xiv L1«T OF ILLUSTRATIONS. FIG. PAGE 281. Areas and Centers of the Lateral Aspect of the Human Ilemicerebrum. (Mills) C26 282. Areas and Centers of the Mesial Aspect of the Human Hemicerebrum. ( M ILLS) 627 283. Lateral View of a Human Hemisphere, Showing the Bundles of Association Fibers. (Stakr) 630 284. Effects of Ablation of Cerebrum. (Dalton) 63^ 285. Curve of the Depth of Sleep. (Piesbergen) 635 2S6. Pyramidal Cells of the Marmot In Two Different Conditions. (After Querton). 636 287. Diagram of the Origin, in Man, of the Efferent Autonomic Fibers from the- Central Nervous System. (Langley) 640 288. Gungli.'i and Fibers. (Langley) 641 289. Diagram of the Main Distribution of the Bulbar and Sacral Autonomic Fibers. (Langley) 642 200. Diagram of the Great Sympathetic, Representing its Viscecal Distribution. (Morat) (i-l^ 291. Diagram of the Great Sympathetic, Representing its Cutaneous Distribution and its Two Orders of Fibers of Projection C44 292. An Afferent Sympathetic Fiber 615 293. Efferent Sympathetic Fiber 646 294. Cross-section of Neurotendinous Nerve End-organ of Rabbit from Tissue Stained in Methylene Blue. (Huber and Dewitt) 652 295. Histology of the Skin and the Epidermoidal Structures. (Landois) 654 296. Cutaneous Papilla; Deprived of Their Epidermis and the Vessels Injected. (Landois) 656 297. Vater-Pacinian Corpuscle from the Mesentery of the Cat, Fixed in a Platinum Chlorid-osmic Acid Solution. X 45. (Sobotta) 657 298. Krause's Corpuscle. (Hedon) 658 299. Transverse Section of Two Grandry's Corpuscles from the Tongue of a Duck. X 450. (Sobotta) 659 300. Topography of Sensibility to Cold and Heat in the same Region of the Ante- rior Surface of the Thigh. (Goldschbider, Hedon) 661 301. Structure of the Taste-organs. (Landois) 667 302. Sternberg's Gustometer 668 303 Innervation of the External Wall of the Nasal Fossa. (Testut) 670 304. Internal Structure of Nose. (Bishop) 671 305. Diagram of the Connections of Cells and Fibers in the Olfactory Bulb. (Schafer, in Quain's Anatomy) 672 306. Zwaardemaker's Olfactometer 675 307. Diagram of the External Surface of the Left Tympanic Membrane. (Hensen). 678 308. Tympanic Membrane and Auditory Ossicles, seen from the Tympanic" Cavity. (Landois) 679 309. Left Tympanum and Auditory Ossicles. (Landois) 680 310. Scheme of the Organ of Hearing. (Landois) 681 311. Scheme of the Labyrinth and Terminations of the Auditory Nerve. (Landois). 683 312. Section through the Uncoiled Cochlea (I) and through the Terminal Nerve Apparatus of the Cochlea (II). (Munk, after Hensen) 684 313. Section of the Ductus Cochlearis and the Organ of Corti. (After Landois) 685 314. Connections of Cochlea with Central Nervous System. (Baton) 686 315. Connections of Semi-circular Canals with Central Nervous System. (Paton). 687 316. I. The Mechanics of the Auditory Ossicles. (After Helmholtz.) II. Section of the Middle Ear. (Munk, after Hensen) 691 317. Schema of the Semi-circular Canals, the Posterior Part of the Skull Removed. (Hedon, after Ewald) 695 318. Semi-circular Canals on Right Side Destroyed Commencing rotation of head of pigeon about five days after operation. (After Ewald) 696 319. Twisting of the Head of a Pigeon twenty days after removal of all the semi- circular canals on the right side. (Ewald, J. R.) 697 320. Position of Pigeon's Head after removal of all the semi-circular canals on both sides. (Ewald, J. R.) 698 321. Diagram of Horizontal Section through the Human Eye. (Yeo) 700 322. Anterior-posterior Section of the Eyeball. (Leveille) 701 323. Section through the Human Cornea. (Bohm and Davidoff) 702 324. Corneal Corpuscles of Dog. (Bohm and Davidoff) 702 325. Corneal Nerves of the Pig. (Rollet) 703 326. Diagram of the Vessels of the Eye. (Leber) 704 327. Meridional Section of the Human Ciliary Body. (Bohm and Davidoff) 705 328. Dissection of the Zonula. (After Schultze) 706 329. Lateral View of the Orbit, Showing the Nerves. (Deaver) 707 330. The Nervous Mechanism of the Iris 708 331. Isolated Lens Fibers. (J. Arnold) 709 332. Transverse Section of Lens Fibers. (.1. Arnold) 710 333. Anterior Surface of the Lens of an Adult. (J. Arnold) 710 334. Diagram of the Structure of Human Retina According to Golgi's Method. (Greeff) 711 335. Hexagonal Cells from the Pigment Layer of the Retina of a Rabbit. (Ball).. 712 336. Action of the Light on Retina. Section of retina of frog. (Englemann) 713 337. Right Eye, Normal Fundus Oculi. (Ball) 714 338. Diagram of Occipital Region of Right Cerebral Hemispheres. (Ball) 715 339. Diagram of the Lymph Spaces of the Eyeball. (After Fuchs) 717 LIST OF ILLUSTRATIONS. xv FIG. PAGE 340. Schematic Ej'o Three Times Natural Size. (Landolt) 718 341. Diagram Illustrating Spherical Aberrations. (Ganot) 722 342. Scheme of Accommodation for Near and Distant Objects. (Landois, after Helmholtz) 723 343. Refraction of Parallel Rays of Light in Emmetropia (E), Hypermetropia (//), and Myopia (Ji). (Ball) 725 344. Different Kinds of Lenses. (Ganot) 726 345. Refraction of Rays in Regular Astigmatism. (Ball) 726 346. Diagram Showing Refraction by a Double Convex Lens. (Ganot) 727 347. Concave Lens Diverging Parallel Rays of Light. (Lahousse^- 727 348. Purkinje-Sanson Images. (Ball) 728 349. Diagram to show the Blind Spot in the Visual Field. (Ball) 72S 350. Scheiner's Experiment — an experiment to determine the minimum distance of distinct vision 729 351. Diagram to show that the visual angle and size of the retinal image vary with the distance of the object from the eye. (Ball) 729 352. Diagram Showing the Corneal Axis, U-E; the Optic Axis, O-A; the Visual Line, R-Y; the Line of Fixation, R-J ; and the Three Angles. (Ball)... 730 353. The Horopteric Circle of Muller. (Ball) 731 354. The Visual Angle 732 355. Optogram on the Rabbit's Retina of a Window Four Meters Distant. (Kuhne). 732 356. Diagram Illustrating the Decomposition of White Light into the Seven Colors of the Spectrum in Passing Through a Prism. (Beclard) 733 357. Wools for the Detection of Color Blindness. (Oliver) 734 358. Diagram Illustrating Irradiation. (Stirling) 736 359. Diagram to show (1) the primary position of the right eye; (2) the eye turned upward and inward, and (3) downward and outward. (Ball) 736 360. Muscles Associated in Moving the Eyeballs in the Directions Indicated by the Arrows. (Ball) 737 361. Positions of Images in Ocular Paralyses. (Ball) 738 362. Capsule of Tenon. (Ball, after Merkel) 738 363. Diagram Illustrating Binocular Vision. (Beclard) 739 364. Lacrymal and Meibomian Glands, the latter viewed from the posterior surface of the eyelids. The conjunctiva of the upper lid has been partially dis- sected off, and is raised so as to show the Meibomian glands beneath. (Raymond, after Testut) 740 365. Loring's Ophthalmoscope 741 366. Direct Ophthalmoscopy. (Ball) 742 367. Indirect Ophthalmoscopy. (Ball) 742 368. The McHardy Perimeter. (Brown) 743 369. Diagram of the Normal Visual Field for White and Colors. (Jennings) 744 370. Diagram of the Visual Tract. (Ball) 745 371. Diagram of Right Homonymous Hemianopsia and of the sites of lesions which may cause it. (Ball) 746 372. Position of the Nuclei of the Cranial Nerves. (After Edinger) 750 373. Distribution of the Third and Sixth Nerves in the Orbit. (Leveille) 752 374. Nuclei of Origin of the Third and Fourth Nerves. (Poirier and Charpt) 754 375 The Origin of the Trigeminal Nerve 757 376. Ophthalmic Division of the Fifth Nerve. (Leveille) 758 377. Distribution of the Sensory Nerves of the Head, together with the Situation of the Motor Points on the Neck. (Landois) 760 378. Graafian Follicle from Ovary of a New-born Child. (After P. Strassman) 770 379. Human Spermatozoon. (Manton) 771 380. Transection of Chick Embryo, Showing the Three Plastodermic Layers. (Manton) 772 381. Diagram Showing Development of Spermatozoa in a Seminal Tubule. (Mc- MURRICH) 773 382. Schema to Indicate the Process of Maturation of the Spermatozoa. (Boveri, Howell) 774 383. Diagram Showing Essential Facts in the Maturation of the Egg. (Wilson)... 774 384. Schema to Indicate Process of Maturation of Ovum. (Boveri, Howell) 775 385. Schenjatic Representation of the Process Occurring During Cell-division. (Boveri. Howell) 776 386. Schematic Representation of the Process Occurring During the Fertilization and Subsequent Segmentation of the Ovum. The cromatin (chromosomes) of the ovum is represented in blue, that of the spermatozoon in red. (Boveri, Howell) 778 387. Formation of Decidua (the decidua is colored black, the ovum is represented engaged between two projecting folds of membrane). (After Dalton) 781 388. Projecting Folds of Membrane Growing Around the Ovum. (After Dalton)... 781 389. Showing Ovum Completely Surrounded by the Decidua Reflexa. (After D.\L- TON) 781 390. Diagram of an Early Stage of a Primate Embryo. (Minot) 782 391. Uterus at Menstrual Period, Showing Congested Area and Destruction of Mucous Membrane. (Photomicrograph by Gramm.) (Gilliam) 786 392. Virginal Uterus. (Grandin and Jarman) 788 393. The Foetal Circulation. (Grandin and Jarman) 789 CHAPTER I. THE CELL. Observation and experience tell us that all tangible or material things about us are either dead or alive ; that is, matter is either life- less or living. The conception of life in its simplicity is limited to a few ele- mentary phenomena, such as nutrition, evolution, reproduction, sen- sibility, and motion. These properties taken together distinguish the living from every form of lifeless substance. Combinations of these simple, elementary phenomena give us every complex function of our present life. If the study of life is the study of these elemen- tary phenomena, it is necessary that our working force be Ijrought to their seat and home — the cell. Everywhere there is a sharp line or division between living and lifeless matter, although the two are frequently so closely allied that first oljservations seem to show no distinctions. This is particularly true of those things that are not seen with the naked eye — micro- scopical things. When one's attention is brought to such objects as quartz, iron, the earthworm, or the dog. the distinction is very evident. On the other hand, long and tireless observation and inves- tigation are required to determine whether some of the bodies found in water are dead or alive. And although so closely associated, scientists have found that a living substance never comes of its own accord from a lifeless one, but only through the influence of some other living matter. For example, no vegetation springs up from the soil until the seed (a form of dormant life) becomes buried in it; no colony appears for the bacteriologist on the sterilized medium until the surface is impregnated with the germ. Although the sharp distinction exists, nevertheless the two mate- rials are very closely associated, as is shown by a little observation. Plants and animals are kept alive and nourished by the food they consume, and it consists, in the main, of lifeless matter. While in the body it seems to be transformed, as it were, to a living state, and it forms part of the body. After it has served the needs of the economy of the plant or animal it dies, and is gotten rid of as waste- matter. (1) 2 PHYSIOLOGY. A living plant or animal is like a fountain into which and out of which material is constantly ])assing, but the fountain maintains its form and general appearance. Hu.xley's simile of a whirlpool in a stream is very striking. The pool remains the same in the stream, but water enters it, becomes a part of it as it is whirled around, then passes out and gives place for other to enter. The pool retains its identity all the while that its elements are being changed. The contrast between living and lifeless matter' forms the basis of the separation of the natural sciences into two divisions : the biological and physical divisions, biology dealing with living and physics with lifeless matter. Biology is the science that treats of living things, whether ani- mal or vegetable, normal or abnormal. It deals with the forms, structures, and origin, together with the functions and activities of the whole animal or plant or its various parts. In fact, its scope is so wide and comprehensive that it becomes necessary to divide it into two branches : morphology and physiology. Morphology is that part of the science that deals with the form and structure of living things, together with their arrangements. Physiology is the science that treats of the functions, or work, of the various parts of the living organism, and what each one does toward the economy of the whole. For instance, the study of the form, growth, and development of the different parts of the brain, beginning with the lamper-eel, then the higher fishes, birds, and mammals, belongs to the science of morphology. By comparisons we see that in the lamper there is merely the semblance of a brain in its crudest form, showing no development as compared with the brain of the higher fishes and birds. In the latter we notice a stronger development in one department — the optic lobes. The cerebral por- tion is very weak. In mammals the reverse is true, and it reaches its most striking size in man, in whom the cerebral portions are extremely large and well developed, while the optic lobes are relatively small. The study of the functions, for instance, of the heart and kid- neys belongs to the science of physiology; which tells how the heart by its alternate contractions and relaxations forces the blood through the circulatory system to the peripheral parts of the body for its sus- tenance and nutrition and to the lungs for its purification by the elimination of the carbonic acid and the absorption of the oxygen ; and how the kidneys by means of their mass of tubes and cells take from the blood those parts that are no longer of any use, fit only to be expelled from the body. When physiology is applied to man, THE CELL. 3 it is called human physiology, for the great and ultimate end and aim of all physiological studies is the understanding of the functions of ourselves. Morphology and physiology are treated as though they were ahsolutely distinct sciences, yet they are so closely related that the division is made only for convenience. Morphology includes in its category such subdivisions as anat- omy, histology, and embryology. Anatomy is the science that treats of the situation, form, and structure of the various parts of the organism. Anatomy from its root keeps in mind the idea of cutting or dissecting, and as com- monly used at the present time deals with the grosser work done upon the more common and apparent structures of the body with scalpel and forceps. When we describe in all their detail the different organs of the body and the position of the organs to one another, we call it descriptive anatomy. Contrasted with anatomy is histology, sometimes called micro- scopical anatomy. Histology is the science that deals with the inti- mate structure of the various tissues of an organism. It takes up the work where anatomy ends; as it brings to its aid the microscope, it can delve down deeper and deeper until it gives us knowledge of the component parts of the various organs. Histology is a tissue- study. Its separation from anatomy is only for convenience, and is not absolute. Embryology is the science of the development of the adult from the ovum or germ. It gives a history of the various stages of develop- ment from the moment of impregnation of the ovum, until the adult is reached. Its field is more closely associated with morphology than physiology. Living things are usually found in separate masses and these have peculiarities and structures of their own which give to them the name "organisms." This is true equally of the large masses, such as the elephant or whale, as of the small bodies found in water or the bacteria of disease. All the structures of the latter have as yet not been discovered nor dissected, as it were, since the microscope is not powerful enough and our supply of reagents not adequate enough to lay bare all of their properties and forms. When we examine some of the contrivances found in the mechan- ical world, such as a watch or a machine, thoy at first sight appear to us, as regards their identity, single individual units; that is, as one watch or as one machine, each capable of doing its own peculiar work. Upon closer investigation, we perceive that each is com- 4 PHYSIOLOGY. posed of a variety of individual parts, each of which has its own [jcculiar share of the work to be done and bears an essential relation to tlie working of the whole. In the watch, the springs, pinions, levers, and niinierous little wheels all bear certain relations to one another and assist in the running of the watch. Similarly we find that it is characteristic of any living body or organism — say, a dog or a rose — that it- should be made up of a number of diifercnt and distinct parts which are so constructed that they may assist in the life of the whole organism. The animal has a head, a trunk, limbs, eyes, ears, etc., externally; heart, lungs, liver, stomach, intestines, brain, etc., internally. To these parts the name organs has been applied. Thus, the organism is composed of distinct parts called organs. The division of the body into organs is purely artificial. An organ is a particular part of the organism that has a certain specified work to do. For example, the liver is a certain structure found in a particular situation in the animal and has assigned as its share of the work of the general economy, the manufacture of the bile to aid digestion. So, also, the eye and the stomach are organs. They are particular parts of the organism concerned in particular work; the eye, in sight, or vision; the stomach, in digestion. The work that any organ does is called its function. Since the appearance and structure of the various organs of a living body are so varied, therefore we do not expect that their functions are any more the same than the functions of the watch and locomotive. Thus, the function of the heart is to pump the blood to all parts of the body; of the blood, to carry nutritious foods to all parts, and at the same time to carry away certain waste-products ; of the kidneys, to excrete waste-matters from the blood ; of the brain, to have a general over- sight and to govern the functions of the whole organism, etc. Anatomy is the forerunner of physiology and must pave the way for it. For how are we to study the functions of the various organs and their relations to one another, unless we are acquainted with the structure, form, and position in the body of the various organs? Even while studying physiology, anatomy must run hand in hand with it, particularly that modified form of anatomy — histology, or microscopical anatomy — which deals with the minute structures and their components — the cells. We have learned that the various portions of the living body are called organs. As we know, each organ has its own particular work to do. By careful dissection, we find that an organ — a human arm. THE CELL. 5 for instance — is made up of a variety of substances called tissues. There are bone-tissues, cartilaginous tissues, muscle-tissues, nerve- tissues, etc.. all different in structure, yet all bundled up in the mem- ber called the arm and essential to it to perform its various functions. The brain is composed of two distinct tissues — the gray and white tissues. So, in like manner, any of the organs of the body may be resolved into various parts known as tissues. Thus far anatomy has aided us in our analysis of the various parts of the body, for it has to deal with only the grosser, coarser, and more obvious forms of the body. So, for a long time, physiology was the study of those large and more evident organs. Physiology could not go further until it had more exact and intimate knowledge of the organs. How can we gain correct knowledge of the working of any machine unless we first know and understand the construc- tion of the parts of the machine? Chemistry and physics teach us that matter is made up of simple forms, called elements and molecules, respectively. It is assumed that the units, ultimately, of these elements and molecules are definite, though exceedingly small, material particles. These particles are called atoms — the word meaning that the particles are unable to be divided without losing their identity. The atom of the chemist and the cell of the physiologist are the final divisions of matter. In the physical world it was found that all phenomena were due to the movements of these small particles — the atoms. The fact that animals and plants, although very different ex- ternally, are made up of the same anatomical units was not brought to light until the invention of the microscope. These structural units were called cells. The theory that organisms were made up of cells was suggested by the study of plant-structure. At the end of the seventeenth century, scientists, by means of their low-power micro- scopes, discovered in plants small, roomlike spaces, provided with firm walls and filled with a fluid. Because of their similarity to the large cells of the honeycomb these small structures received the name of cells. To the scientists, however, the principal feature seemed to l^e the firm walls. By study, they found that the cell absorbed nutri- ent material, assimilated it. and produced new material. Although plants were composed of a mass of cells, or even a single cell, it was found that each cell was an isolated Avhole ; that it nourished itself and built itself up. The cell-theory was also applied to animal tis- sues. By its use it was found that many of the tissues were formed also of cells and that these cells appeared to be of similar construction 6 PHYSIOLOGY. to those in plant life. Thus we find that every tissue is composed of minute parts known as cells and which in a particular tissue are nearly or (|uite similar. For instance, in examining a muscular fiber, we find tliat it is composed of very small, ribbonlike units called muscle-cells. Although differing somewhat in size and development, yet they are otherwise similar ; that is, muscular tissue is composed of muscular units, or cells. Cartilage is composed of oystershell-shaped cells; mucous-membrane cells are gobletlike, and secrete, or give off, mucus. Even though these cells are self-supporting and grow and form other cells, in the higher animals they are grouped and held together by means of a kind of cement, spoken of as "intercellular material.'' Hence a tissue may be defined as a group of similar cells having a similar function. Tissues are different only because they are com- Ip Fig. 1.— Vegetable Cell. (Duval.) up, Cell-wall of cellulose, n, Nucleus, ch, Chlorophyll bodies. posed of different kinds of cells having functions peculiar to them- selves. An aggregation of cartilage- and muscle- cells gives us, respectively, cartilage- and muscle- tissues. As the result of this knowledge, physiology is beginning to develop from a science of the organ and its functions to that of the cell and its functions. But this is only natural as a form of develop- ment, since we first consider the greater and more active functions of the organs and then delve down deeper and deeper until we reach the functions of the cell. Cells are characterized by the presence of the elementary func- tions or phenomena of nutrition, growth, reproduction, etc. If physiology has to deal with them, it can do it most successfully by studying them in their seat — the cell. THE CELL. 7 The vegetable cell is known from the animal cell by the presence of cellulose. The cell of the vegetable kingdom in its respiration takes in oxygen and gives off carbonic acid, as we do, but in its nutrition the action of the suns rays u]X)n the chlorophyll causes it to break up the carbon, to fix it in the tissues, and to give off oxygen. This fixation of carbon overshadows in daylight the ordinary respiration of the plant, which goes on both by day and by night. Yeast-cells break up sugar into alcohol and carbonic acid. Besides this action, they have in them a ferment, invertin, which changes cane-sugar into invert-sugar, which is a mixture of dextrose and Isevulose. CELLS. We have learned that the higher forms of life, whether plants or animals, may be resolved into a vast number of very small, structural units, called cells. The skin, muscles, bone, brain, etc., appear to the naked eye to be composed of one kind of substance respectively. The microscope, however, has told us that each tissue is composed of colonies of units, held together by intercellular cement, and that the units or cells of a particular tissue are similar in structure and func- tions. For example, upon examination, wo find that muscular tissue is made up of ril)bonlike fibers, similar in appearance and structure and all engaged in the same function — contraction. Thus, the cell is not only tlie unit of structure, but also of function, diseased or normal. Animal cells are of various sizes. Although differing very much in shape and ajjpearance in various parts of the body, nevertheless every cell consists of the following parts: (1) protoplasm. (2) mi- cleiis, (3) centrosomes, and (4) various matters commonly called "special cell-const ituen ts." Max Schultze's definition of a cell, enlarged by later research, is : "A mass of protoplasm containing a nucleus." The term cell as employed to-day is a misnomer, but from its constant use since the seventeenth century, it has gained such a hold upon the minds of those engaged in the study of science that the attempt to supersede it with a more appropriate term has been unsuc- cessful. However, the idea that it originally conveyed has been some- what modified. The term originated among the botanists of the seventeenth and eighteenth centuries, and was applied to chamberlike elements, separated from one another and containing a fluid. Their characteristic and most important feature was the wall, or membrane. 8 PHYSIOLOGY. in which were supposed to lie active properties of the coll. Tlio liquid, originally called plant-slimc, was named protoplasm by von Mohl, and was thought to be a waste-])roduct. That the wall, or inenibrane, was not of vital importance was clearly dcmonsti'ated by later researches. The study of the ama'lja and of the white blood-corpuscle, one-celled organisms, was the chief means. These organisms are capable of extending their Ijodies into ])rocesses — fine threads and networks — as they move about from place to place, taking up and giving off matter as they go. They pos- sess all the elementary vital functions, and yet at no time do they possess a cell-membrane, showing that the protoplasm, not the niem- Cell-inenibrane Reticulum of cell** Membrane of nucleus Nuclear achromatic substance Nuclear chromatic substance Fig. 2. — Cell with Reticulum of Protoplasm Radially Disposed. From Intestinal Epitlielium of a Worm. (Carxoy. ) brane, was the seat of the functions. An immense number of other unicellular organisms were examined, together with the develop- ment of other plants and animals, and many cells devoid of a mem- brane were found. PROTOPLASM. The protoplasm of unicellular organisms appears as a viscid sub- stance, which is almost always colorless and which will not mix readily with water. The term protoplasm is constantly in the mouths of the physiologists, and it is difficult to give it a rigid definition, since it is used in so many different senses. Hence, we commonly describe protoplasm as a living substance surrounding a nucleus, which substance may or may not be limited by a cell-wall. THE CELL. 9 Its refractive power is greater than that of water and in it, as a medium, very delicate threading of protoplasm may be distin- guished. It was formerly supposed to be composed of a homogeneous material, and destitute of any structure and to ccmtain a number of minute granules of a solid nature. Under the high powers of the microscope, when properly stained with reagents, it has l)een found that the protoplasm consists of two parts: (1) a fine network of fibers, like a sponge, called the reti- ciiJuni, or spoil gioplasm; and (2) the more fluid ])ortion in the meshes, called the envlnjlcma, or liyaloplasm. However, it must be Fig. 3 n, Nucleus, rr, Contractile vacuole. A", Food-vacuoles. en, Endoplasm. ck. Ectoplasm. mentioned that the views concerning the structure of protoplasm dif- fer, several theories being .offered. According to the first idea, the protoplasm forms the network, the nodal points of which appear as individual granules. It is very probable that many of the larger and more obvious granules are inert bodies, such as glycogen, mucin, fat-g"lol)ules, albuminous substances, etc., suspended in the network. The glycogen granules are found in the liver-cells, the fat-globules in the cells of the lacteal glands, and the pigment-granules in the skin-cells of many colored animals. Sometimes, in unicellular ani- mals, calcareous matters are found, although those most uniformly found are of the same general nature as the protoplasm. All these particles, or granules, are termed microsomes. Besides, tliere are 10 PHYSIOLOGY. occasionally found indigestible bodies, such as grains of sand, indi- gestible residue of foodstuil's, and excretory substances, waiting to be expelled from the body. Otiier substances found within the pi'otoiiiasm and supposed to be of great importance to cell-life are drops of liquid — vacuoles, as they are commonly called. Specific Gravity of Living Protoplasm. Living protoplasm has the physical property of having a greater specific gravity than water. When cells of the most varied kinds are allowed to fall into water they sink to the bottom. In some cases the protoplasm contains a considerable quantity of fat; so that, although the substratum of protoplasm is heavier than water, the floating of the cell is due to the lighter specific gravity of the fat-particles over- coming the heavier specific gravity of the protoplasm. The chemical composition of protoplasm (a living substance) can be obtained only after it has been killed. However paradoxical this may seem, it is found impossible to apply the methods of chem- istry without killing it. Every reagent that comes in contact with it disturbs and changes it and eventually kills it. Thus, our ideas of the chemical composition of living ])roto])lasms are the ideas we get from the chemical composition of dead protoplasm. The substances of which it is comjDosed are : — 1. Water. — Water is that element in a living substance that gives it its liquid nature, allowing its particles to move about with a cer- tain degree of freedom. In the cell, water occurs, either chemically combined with other constituents or in the free state. Salts occur dissolved in the water. Protoplasm is semifluid, and about three- fourths of its weight is due to water. The molecules of protoplasm are thought to be separated from one another by layers of water. 2. Proteids. — The proteids take a very active and essential part in the functions of all cells. The proteids consist of the elements carbon, hydrogen, sulphur, nitrogen, and oxygen. Proteids occur both in the protoplasm and in the nucleus, but with this difference: that found in the nucleus has combined with it phosphoric acid, forming the so-called nucleins. To show this fact is very easy, for the nuclein of cells resists the action of digestion hy the gastric juice. All kinds of cells in artificial gastric juice have their protoplasm digested and only the nuclei remain ; that is. nuclein. If, now, this nucleus is treated with stains, it shows that the nuclear bodies consist THE CELL. 11 of niiclein, while the protopUism of the cell is constructed from other albuminous bodies. Protoplasm is composed principally, then, of simple proteids and compound proteids that lack phosphorus. Our most common and typical type of an albuminous substance, or proteid, is the white of an egg. This contains 12 per cent, of actual proteid substance, the remainder being chiefly water. The albumins are the only bodies that can safely be said to be found in all cells. Although the albu- mins contain only five elements, — C, H, N, S, and 0, — yet the num- ber of their atoms often exceeds a thousand. 3, Various Other Substances occur in smaller proportions as car- bohydrates; as glycogen in protoplasm of liver-cells; fats, seen in protoplasm as fats or oil-drops ; and simpler substances which are the result of decomposition of the proteids, or are concerned in its for- mation; and also, inorganic salts, such as phosphates, and chlorides of calcium, sodium, and potassium. NUCLEUS. From an examination of the protoplasm, we pass on to the nucleus. As we have said before, "a cell is a mass of protoplasm con- taining a nucleus." Various properties and functions of an import- ant nature have been assigned to protoplasm, but it is found that the nucleus is equally as important. The classical experiments of the old observers upon protoplasm led them to believe that the protoplasm was the embodiment of all the functions of life. To them the nucleus w^as unessential as regards the activities of life. The ruling power of the protoplasm was dismissed when it was found that the nucleus in reproduction of cells by division or impregnation underwent extra- ordinary changes, while the protoplasm remained passive and quiet. Within recent years there has set in a reaction, and the happy mean 'twixt the two extremes is now held to be correct: the two are of equal importance. By extended research and with staining reagents such as carmin, hematoxylin, etc., a distinct nucleus was found imbedded in the pro- toplasm of most animal cells. For a long time, and until the micro- scope was greatly improved, two classes of organisms appeared to be the exceptions. They were, monera, the lowest and sim])lost organ- isms, and bacteria. Gradually the number of each class was reduced until at the present day it may safely be said that every cell contains a distinct nnclens. Every cell may thus be said to be characterized by two general cell-constituents, protoplasm, and at least one nucleus. 12 PHYSIOLOGY. The form of the nucleus is different in various cells. Usually it is a round or oval body situated in the middle of the cell. Its rounded ionu is considerably expanded in young cells, as in tlie ovaries in their evolution. Very fre(|U('nlly the form of the element influences that of the nucleus. Thus, in muscle- and nerve- cells the nucleus is generally elongated. In the lower organisms it sometimes assumes the shape of a horseshoe or a twisted strand, or is very much branched, the processes running out in every direction into the sur- rounding protoplasm. The size of the nucleus is usually in proportion to the mass of protoplasm enveloping it. Thus, in the large ganglion-cells of the spinal cord the nuclei are correspondingly large. Also in cells en- gaged in active work, the nuclei are generally of good size, as in the secreting cells of the salivary and mucous glands. As to the number of nuclei present in a cell, the general condition of the presence of but one in a cell seems to prevail. There are ex- ceptions, however, as liver-cells very frequently contain two, and the immense cells of bone-marrow, many. General Substance, or Structure. The nucleus is no more of a homogeneous nature than the proto- plasm and presents several distinct substances and structures. The different constituents that are known are not always present in all cells, at all times, or in the same pro{)ortions. Among some cells one element may l)e very conspicuous, while in some otliers it is scarcely to be found. According to Verworn, the following substances occur most constantly : (1) nuclear sap, (2) acliromatic nuclear substance, (3) chromatic nuclear substance, and (-1) the nucleolus. The nuclear sap may be present in larger or smaller quantities and is the liquid ground-substance which fills up the interstices left among the solid nuclear constituents. In many cells under the in- fluence of certain reagents, and even in life, it is known to be of a very fine granular nature. The achromatic nuclear substance is a structure of fine threads found in the nuclear sap, and it is characterized, as is also the latter, by not staining with the usual reagents; carmin, htematoxylin, etc. It contains achromatin or linin. Lantanin is found in linin in the form of fine granules, which stain by acid anilin dyes, as opposed to chromatin, which takes up only basic anilin dyes. Hence lantanin is called oxychromatin, whilst chromatin is known as basichromatin. THE CELL. 13 The cliromatic nuclear substance, as its name implies, has an affinity for coloring-matter in the form of different stains. It is usually in the form of a continuous network, but sometimes appears in small granules, or particles. It contains chromatin or nuclein. The nucleolus, if it appears at all, is found in the network of the nucleus, as a rounded or irregularly shaped body. It contains para- nuclein or pyrenin and has an especial affinity for color, and stains more deeply than the network. The nucleoli are thought to be passive bodies that hold in reserve different constituents which are essential to the life of the nucleus. Sometimes the nucleus is enveloped in a membrane, called the nuclear membrane, Avhicli marks it distinctly from the protoplasm. This, however, as Avith the cell-membrane, is not universal and is not classed as a general constituent of the nucleus. The sharpness of the contour which distinguishes the nucleus in the midst of protoplasm led many histologists firml}^ to believe that the nucleus always does possess a membrane. The truth is between the two extreme opinions. The nucleus can very readily exist without one. The nuclear meml)rane consists of an achromatic substance, amphipyrenin. A portion of a cell deprived of its nucleus may live for a time, but it evinces no activities or functions other than that of move- ment. It neither absorbs food, nor grows, nor reproduces, but seems gradually to dwindle away and die. From this it is believed that the nucleus exercises some powers with regard to the building up, or con- structive metamorphosis. Regarded chemically, the nucleus is composed principally of pro- teid and a substance like proteid. which contains as much as 10 per cent, of phosphorus. Xo doubt there are others, but even the most delicate chemical reagents kill the constituents and so lessen the opportunities for careful investigation. CENTROSOME. About twenty years ago, when nuclear cell-division was being investigated, a small body other than the nucleus was noticed during the division of the cell and was called by various names : polar corpuscle, central corpuscle, or centrosomc. The last name seems to be more generally used at the present time. The centrosome in its simplest form is a body of extreme min- uteness, frequently not larger than a microsome, but which exerts an active influence on the protoplasmic structure during cell-division. 14 PHYSIOLOGY. Because of its influence in the cell, it lias aroused more interest among investigators than any other conij)onent of the celL By some it is considered to he a part of the nucleus, and by others, of the pro- toplasm. As a rule, it lies in the protoplasm just outside of the nucleus, even during the resting stage, and in certain conditions of tlie cell is clearly indicated by a radiation of protoplasm, attraction sphere, or archoplasm, the fibers of which are arranged in the form of a star, the centrosome heing at the center. In size the centrosome ranges between that of the ordinary micro- some and the smallest micro-organism. No structure has been as yet discovered in it. It cannot be classed as a general cell-constituent, since many forms of the cell and unicellular organisms have been examined and no centrosome found, due probably to the inadequacy of the microscope. Most authors consider the centrosome as an essen- tial part of the cell. The centrosome does not absorb the ordinary stains suitable for the nucleus, but requires acid anilin dyes, as acid fuchsin and orange. By them it is colored vividly. As a rule, there is one centrosome in a cell, lying close to the nucleus and surrounded by a raylike or rodlike structure of the pro- toplasm. As the cell prepares for division, the centrosome divides into two distinct parts, both lying passively within the starlike net- work. When tlie daughter-cells are examined, each is found to pos- sess one of the centrosomes, which, as the cell grows, passes through the same process as its antecedents. The centrosome is regarded as the particular organ of cell-division. PROTOPLASMIC MOVEMENT. The movements of protoplasm are movements in currents and the amoeboid movement. In certain vegetable cells protoplasm moves and causes a true rotation of its substance, as in Chara ; or the move- ment may be in opposite direction and the paths even cross over each other. In this movement all parts of the protoplasm do not move with the same rapidity. The rate in protoplasm is about V50 inch per minute. Movements differ according to whether the protoplasm is nal-ed — without any enveloping membrane — or inclosed ivithin a firm wall, or membrane. THE CELL. 15 I. Movement of the Naked Protoplasm. Probably our most common and typical form of naked proto- plasm is presented to us by the fresh-water anwha, found in stagnant water. The anireba is a unicellular organism, about Viooo i^^^'^^ i^^ diameter, possessing one or more nuclei, and is almost continually in motion, due to its extending numerous protoplasmic projections, called pseudopodia (false feet). It then rolls its entire mass into the pseudopodium, or fingerlike projection, only to continue the same operation repeatedly during its life. The pseudopodia assume different forms and shapes in the differ- ent kinds of cells, and in this way the establishment of the identity of a cell is frequently aided by an observation of the processes. For example, most of the fresh-water amoeba possess broad, lobate or finger-shaped pseudopodia; leucocytes, white blood-corpuscles, divided and pointed pseudopodia; some of the rhizopods and pigment- cells, threadlike and reticular pseudopodia which flow into one another. In the human body some of the cells — such as white blood- corpuscles, lymph-corpuscles, and connective-tissue cells — possess movements, which, because of their likeness to those of the amoeba, are called amcehoid. 1. Ciliary Movement. There have been discovered cells and unicellular organisms possessing delicate, hairlike processes, which extend in greater or less numbers from their surfaces. They are called flagella, or cilia. These resemble very thin pseudopodia when they are composed of hyaloplasm alone, as the cilia and flagella are homogeneous and nongranular in nature. However, they differ from pseudopodia in that their movements are very energetic and always definite, and also that, unlike pseudopodia, their structures are not temporary, but permanent, being neither protruded nor withdrawn. The ciliary cells lining the trachea are subjects for examination. The deep back part of the throat of a frog is gently scraped and the scrapings placed in a dro]i of water upon a warm stage. When we examine the cells under the microscope, we see upon their surface a constant rapid movement ; l)ut the movement is so rapid that we see onlv the motion, and not tlie vibrating cilia. If, however, the vibrations be lowered to about a dozen per second, we are then able to see the cilia themselves. Ciliary movements are of various kinds. More 16 PHYSIOLOGY. frequently it is a movement of elevation and deju'ession of tlic cilia; sometimes it is like the extension and flexion of our fingers, at other times a sort of wave or whirlpool-like movement. In these move- ments all the cilia on the surface move in the same direction, like a field of grain before tlie wind. Each completed movement of the cilia is composed of two movements of unequal duration, the longer corresponding to contraction, and the shorter to relaxation of the cilia. Ciliary movements may be of a high rapidity, as many as 960 to about 1000 per minute, and entirely independent of the circu- lation and the nervous system. These movements are able to con- tinue after death as long as a day, while in frogs they have been observed for many days. Cilia are about '^/sooo i'lch in length and are able to perform some work. By their movements they are able to float a cell in a liquid, such as water, even though the cell and cilia are composed, in a great part, of protoplasm, whose specific gravity is heavier than water and naturally inclined to sink, and at the same time they pro- pel the cell in some definite direction at a much faster speed than that obtained by the protrusion and retraction of pseudopodia. The function of the ciliated cells does not appear to be of any particular importance in man except that in the trachea their movements bring to the larynx foreign substances that have been inhaled into the lungs, such as dust, etc., and to bring up for expectoration the thickened mucus that is formed during the stages of a cold. A practical illustration of the effects of the protoplasmic move- ments of leucocytes (white blood-corpuscles) can be observed when an injury occurs to any part of the body. As a result of the injury and as an attempt at repair, more blood is sent to the injured part. This result, called congestion, gives to it its red color. With the additional quantity of blood comes an additional numl)er of leucocytes. They, by protoplasmic movements, pass through the walls of the capillaries to the seat of the injury, to take up dead portions. Sometimes bac- teria lodge in the wound, which the leucocytes approach and kill by ingestion, as it were, thus rendering them harmless. This process of ingesting bacteria and other foreign substances is called phagocytosis, and hence the leucocytes are sometimes termed phagocytes. The phenomenon of a leucocyte in active movement, which by one-sided action of the chemical products of bacteria, as toxins, moves toward (positive) or away (negative) from the bacteria, is called chemotaxis. THE CELL. 17 CELL=DIVISION. We have learned that organs are composed of various structures, called tissues. A tissue may be defined as "a group of similar cells having similar functions." For example, muscular tissue is made up of ribbonlike muscle-cells; mucous tissue of secreting, goblet-shaped cells; nervous tissue of ganglion-cells, with their numerous project- ing dendrons, etc. By observation we notice a variety of tissues due to a variety of kinds of cells; also that all tissues of a kind are not necessarily of the same bulk, size, or weight. The chick contains, in its body, a number of organs of a definite size and consistency. It has a head, limbs, muscles, a heart, lungs, intestines, a liver, etc. We see, of course, that these organs are of a size and weight in proportion to their age— none of them large or heavy. Upon examination, we find the tissues of the various organs to be composed of cells such as we should expect them to contain; that is, the muscles of muscle-cells, 'the bones of osseous cells, the brain of ganglion-cells, etc. Furthermore, although cells are of dif- ferent sizes and forms, yet there is very little difference in respect to size between the cells of a particular tissue, as compared with one another, or with those of the adult animal; for the size of every cell is definite. When we observe the same animal one year after its birth, we notice some striking differences : it is much larger and heavier, the various organs are fuller, more compact, and show the effects of the development as it approached maturity. The head, brain, muscles, heart, lungs, intestines, etc., are all much larger and better developed than those found in the small chick. However, if a microscopical examination be made of the various tissues in this, the adult animal, what do we find and how do the cells compare with those of the chick ? Nothing remarkable in the individual cells themselves. The liver- cells of the adult are no larger than those of the chick, nor are the ganglion-, muscle-, or other cells. What we do perceive is a great increase in the mimler of the cells in any particular tissue. The liver and brain of the adult animal contain many more cells than the same organs of the chick. Thus we see that there has been a growth due, not to larger cells, but to a greater number of cells. That is. the cells have multiplied. Similarly, as the infant passes through the various stages of boy- hood, youth, and manhood, we say that he grows, for there is an 2 18 PHYSIOLOGY. increase in the size and weight of the various organs of his body. This means that there is a greater number of cells composing tlie tissues of his various organs. The power to multiply — that is, pro- ducing new forms similar to itself — is one of the most important and characteristic functions of the cell. By this attribute, it not only is able to maintain its own particular kind, or species, but can undergo constructive metamorphosis: building up, or growing, until any part, or organ, is matured. A cell multiplies by dividing into two or more parts. Each part is, of course, smaller than the original or mother-cell, but, by assimilating nutrient material from the surrounding tissues, it grows until each part is the size of the mother-cell, when it also is ready for division, or reproduction. No cell exists that has not had its origin in some pre-existing cell. In animals whose tissues are composed of many cells, these same tissues can be traced back to single cells, of which they are developments. The animal itself, with all its many and various parts and structures, originated • from a single cell, the germ-cell, or ovum, which have existed in the parent-body, is also derived from a cell. Schleiden, the botanist and accredited discoverer of the cell- theory among plants, and Schwann, to whom Schleiden confided his views and ideas of plant-structure, and who then reduced animal tis- sues to their structural units, the cells, were anxious to know the origin of the cells. To them the presence of the nucleus was known, and even the nucleolus; but their instruments were not powerful enough to allow of their penetrating deeper, and of getting the cor- rect ideas of cell-division. It was proved in 1858 that cells multiplied as a result of the divi- sion of the two equally essential parts of the cell, the nucleus and protoplasm. Our present conception, that the two are of equal im- portance and value, dates from this time. It was asserted that the division began within and proceeded to the outer parts of the cell. That is, the nucleolus was divided, its division was followed by sepa- ration of the nucleus, and this, in turn, followed by constriction and division of the protoplasm with its enveloping membrane. These views were confirmed liy Virchow, who formulated the doctrine "Omnis cellula e cellula" (every cell from a cell). Later, it was discovered, by the investigation of some of the tissue-cells, that the process of division was not so simple as expected. In some cases, it was found that the nucleus became star-shaped, or THE CELL. 19 lobed, or even seemed to disappear altogether before cell-division. A few years later, it was seen that the process of division was compli- cated in the extreme, and that the cell-nucleus underwent a variety of transformations, assuming different shapes and figures until two daughter-cells were formed from the mother-cell. This process was afterward named kanjokinesis. By experiment, it was demonstrated that, if a cell in a living organism or tissue was so divided that one of the parts was composed of protoplasm only, none of the nucleus being present, the proto- plasmic part continued to live for a considerable time, but that, of the vital phenomena exhibited by the normal cell, it possessed only that of movement. It was unable to take up from the surrounding tissues a proper amount of nutrition, so that growth and reproduc- tion never occurred, and after a time it died. Thus it was concerned only in destructive, not constructive, metamorphosis. It was totally unable to build itself up, to grow, or reproduce others of its species. On the other hand, the part containing the nucleus grew and repro- duced its kind, forming daughter-cells, that in turn formed other cells, etc. Thus, in order that the daughter-cell may possess the same properties, form, and functions of the mother-cell, — in a word, in order that it may live, — it becomes necessary, in the division, that both the nucleus and the protoplasm must divide. The disposition of any cell to divide, or reproduce, is usually announced by changes in its nucleus, both physical and chemical. In fact, the division of any cell is preceded by division of the nucleus. This process in the cells of most organisms is very complicated, whereas the division of the protoplasm is most simple, consisting of the appearance of a con- striction, which becomes deeper and deeper, forming a groove, or fissure, until eventually the mass is divided into two parts. The evident importance of the relation of the nucleus to cell- division has led to extended study of the nucleus and its transforma- tions during the process of reproduction, with the result that, upon its function in this respect, three forms of division are recognized: (1) direct cell-division. (2) indirect cell -division, and (3) endogenous nuclear multiplication. I. Direct CelNdivision (Amitosis). Direct cell-division is very rare, and present only in some of the unicellular organisms and leucocytes. In pathological formations, however, such as tumors, this form of division occurs very frequently. 20 PHYSIOLOGY. To get a better conception of the direct form of division, we will study one of the infusorians, the typical amoeba, and the changes occurring in it during reproduction. The first intimation of a divi- sion is noted in the spherical nucleus, which becomes elongated, the middle portion of it being indented by a constriction, which gives to the nucleus a dumb-bell shape. The constricted portion becomes gradually narrower and slenderer until the two heads of the ball sepa- rate and each assumes the same shape as its mother — spherical. The cell thus contains two distinct nuclei. Following the division of the nucleus is that of the protoplasm by constriction also. The indenta- tion always appears between the two nuclei. Eventually two cells are thus formed, each with a separate nucleus; each daughter-cell is, of course, smaller than its mother, but by the assimilation of the nutrient material surrounding it. it soon grows to the normal, definite size. Tliis process often requires several hours for its completion, the various stages being frequently accomplished in an uncertain manner. 2. Indirect Cell=division (Mitosis, or Karyokinesis). By far the greater number of animal- and plant- cells follow the more complicated and intricate method of indirect, or Tcary akinetic, form of division. The division of the protoplasm is simple enough, following only the laws of constriction until the mass is completely separated into two parts, by means of a furrow, or fissure. It is the nucleus which undergoes very remarkable and typical changes, very complicated in their nature, but which in plants and animals are con- stant and agree very much in regard to essentials. Thus the indirect method is very nearly, though not quite, universal. As a cell prepares for division the most evident and important fact noticed is a change in its nucleus, both physical and chemical. The nucleus becomes somewhat enlarged, and its chromatic nuclear substance, or chromoplasm, — so called because it has an affinity for stains, — ^begins to become changed little by little, from the netlike arrangements of its minute granules and particles, until the substance is arranged in the form of threads loosely rolled up, like a coil or convolution, called the sl-ein or spirem. These consist principally of nuclein, and stain more deeply than the surrounding parts, and are, hence, more easily discerned. It is the presence of these threads that gives to the process the name mitosis. In most cases there is but a single thread, which is coiled or convoluted throughout its entire length ; occasionallv. there occur several such threads. The THE CELL. 21 threads are somewhat thicker than before, and more separated than during the resting stage. With the formation of the spirem, or wreath, the nucleoli and membrane, if any, disappear. In some cases the nucleoli are dissolved and cast into the hyaloplasm, where they degenerate and have no further function. The thread of the spirem becomes divided transversely into nearly equal parts, or bodies, known as chromosomes, which, in most cases, are in the form of rods, straight or curved. The ground- substance of the nucleus now becomes a part of the surrounding hyalo- plasm. The chromosomes at first are placed rather irregularly, but they soon begin to arrange themselves into a more definite form, that of a rosette. The curved chromosomes now become more angular and V-shaped, the angle pointing toward the center of the nuclear space while the free ends are directed toward the circumference, this figure being called the aster, or garland. While in the form of the aster each chromosome splits longitudinally into halves, so that we have just again as many, though thinner, chromosomes. Before the membrane has been dissolved, there appear in the protoplasm, but very near the nuclear membrane,, two small granules lying side by side. These are the centrosomes. They are of a sub- stance that stains with difficulty. Gradually they begin to separate from one another, moving in a semicircle, until they are diametrically opposite one another, or at the nuclear poles. While they have been in motion, the nuclear membrane has been dissolving, so that, by the time they are again at rest, the membrane has disappeared. The achromatic nuclear spindle develops between the centrosomes. When they begin to separate, the spindle is small, scarcely discernible, and like a band in form. As the centrosomes separate more widely, the fibers become more plainly visible and assume the form of a spindle — broad in the middle and converging at either end, toward and end- ing in the centrosomes. The protoplasm now arranges itself around the centrosomes in the form of ravs of a star, as though the filaments of protoplasm were attracted by the centrosomes in the manner of iron filings by a magnet. At first these fibers are small, but increase in length and numbers as the division of the cell progresses, until they run throughout the entire protoplasmic mass. The V-shaped filaments, called chromosomes, are now collected in the plane of the equator, called the equatorial plate. While the chromosomes have been arranging themselves in the plane of this plate, they have been growing somewhat shorter and thicker, their angles pointing to the axis of the spindle and their ends to the cir- 22 PHYSIOLOGY. eiimference. By the contraction of the spindle fibers the daughter- chi'oinosomes (the result of the original chromosomes being divided Jongitiidinally into two separate halves by means of fission) are divided into two equal groups, which are moved toward the points, or poles, of the spindle, but never reach it absolutely. Between these groups fine "connecting fibrils" stretch. This figure is called the double star, or diaster. The star shape is formed by the angles of the chromosomes being arranged next to the centrosomes, with their free ends extending out radially. There now follows a retransforming of the daughter-chromo- somes, arranged in the form of a star, into a genuine resting nucleus. The angles begin to disappear, the threads draw more closely to one another, becoming more bent and roughened at the same time that little processes appear on their surfaces. A very delicate nuclear membrane develops and surrounds the group of threads. The radi- ating fibers of protoplasm around the centrosomes become more and more indistinct until they finally disappear. The same thing occurs with the "connecting fibrils." When the two daughter-stars are separated as far as possible there appears on the surface of the cell-body a fissure, cutting into the protoplasm in the line of the equatorial plate, imtil the cell is completely divided into two parts, each containing a nucleus. The duration of this process has been seen in man to he half an liour, while in the larvce of the salamander it has been known to take as long as five hours. The whole process of mitosis may be divided into five stages: — 1. Prophase (skein stage). 2. Mother-star stage (monaster). 3. Metaphase-Metakinesis (diaster). 4. Anaphase (daughter skeins). 5. Telophase (daughter nuclei). 3. Endogenous Nuclear Multiplication. A third rare mode of nuclear multiplication, to which is given the above-named title, was discovered in the thalassicola. The thalassicola, which is the largest in size of the radiolarians and the diameter of whose central capsule is nearly equal to that of the frog's egg, has, during the major portion of its life, one single, highly differentiated, giant nucleus, called the internal vesicle. This nucleus, or internal vesicle, usually attains to V,^ inch in diameter, THE CELL. 23 and possesses a thick, porous, nuclear meniljrane. It is very similar to the multinucleated germinal vesicle of the ovum of an amphibian. Simultaneously with the advent of the centrosome into the proto- plasm, there appeared in the latter, which heretofore has been entirely free and clear, a large number of very small nuclei. These act as centers, around each one of which there develop nucleated zoospores, which may amount finally to as many as some hundreds of thousands of separate cells. JV---- Fig. 4. — To Show the Changes in the Nerve-cell Due to Age. (From Howell.) A, Spinal ganglion cell of a still-born child. B, Spinal ganglion cell of a man dying at 92 years of age. N, Nuclei. In the old man the cells are not large, cytoplasm is pigmented, the nucleus is small and the nucleolus much shrunken or absent. Both sections taken from the cervical ganglion. 250 diameters. (Hodge.) Fatigue of Cells. — Hodge, of Clark University, has found changes in the cell corresponding to rest or activity. Thus the nerve- cell in the morning has a clear, round nucleus, while in the evening, being tired from work, the nucleus has an irrccrular contour. LlTER.\TURE COXSULTED. Verworn, "General Physiologj^" 1899, Hertwig, "The Cell," 1895. CHAPTER II. (a) CHEMICAL CONSTITUENTS OF BODY AND FOOD, (b) ALIMENTARY SUBSTANCES. Digestion has been described as the physical and chemical alter- ation of the foodstuffs into forms better lifted for absorption by the action of certain soluble ferments, the digestive enzymes. The animal organism had its birth in a single ovum or cell, which, under certain favoring circumstances and conditions, developed into a mass of simple cells. As development proceeded, this aggregation became differentiated into tissues, l)y the grouping of tlie cells, altered by chemical changes in the substance of the cells themselves, by alterations in their shapes, and by deposits of intercellular substances. As the organism continued to grow, the various parts became more and more complex by use and development until it presented a highly complex unit. In the metabolism of the cell it was learned that the various cells while performing their various vital phenomena must constantly maintain a very nice balance in respect to waste and repair. That is, the various kinds of cells took out from their environuients those sub- stances that were necessary for their economy to build themselves up and grow, while the waste-products were excreted. A distinctive property of the cells was the selective power exercised in regard to different nutrient materials with which they came into contact. Al- though the surrounding media might contain many kinds of food, yet cells of a particular kind took only that for themselves which was best adapted to their wants, disregarding entirely all the others. As there was a great variety of cells, there must necessarily be a cor- responding variety of foodstuffs. What is true of the cells is true of that of which they are but components or units : the body. Among the phenoniena produced by the waste of the solid constituents of the body and the loss of the fluid or watery parts of the tissues are the sensations of hunger and thirst. These sensations of appetite excite the desire to take food, which by the processes of digestion is prepared for absorption and cir- culation in the blood, to supply the various needs of the organism. The term food includes all those substances received into the (24) CHEMICAL CONSTITUENTS OF BODY AND FOOD. 25 alimentary canal and used /for the support of life, by supplying the waste continually occurring in the living animal tissues, and also weight, heat, and energy. Food contains substances that have a cer- tain chemical relation to the tissues which it supports. The sub- stances out of which the complex adult tissues are constructed are chemical elements, chemical compounds, or unions of these elements. The food taken in by the animal consists of the same or similar com- position, in its nature very complex. Animals are either carnivorous or herbivorous. The carnivora, or flesh-eating species, consume food possessing apparently the same chemical components as the tissues and fluids of their own bodies. The food of the herbivora, or vegetable-eating species, contains prin- ciples resembling very closely those found in the animal body. No matter what the source or nature of the food for animals might be, their chemical constituents or principles are similar, since it is through the agency of the vegetable kingdom with the aid of light and heat from the sun that the simpler combinations of inorganic nature are woven together and elaborated to form the complex organ- isms in the shape of plants and vegetables. Thus, the animal king- dom is dependent on the vegetable for its existence ; numerous experi- ments have proven that the animal organism does not possess the power to any great extent of constructing complex from simple mate- rials. Yet complex foods it must have to supply its own complex con- stituents. However, it is also necessary that the food should possess, besides the complex constituents, a proper proportion of the various principles, and these must be in a digestible form. It is well known that beans, peas, and other vegetables contain a very considerable percentage of proteid, but it is m such indigestible form, that much of it passes off in the ftpces. The various digestive juices had been unable properly to dissolve their nutritive elements. Of the 74 elements known to the chemist, but 20 are found in the body. They are: carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, fluorin, chlorine, iodine, silicon, sodium, potassium, cal- cium, ammonium, magnesium, lithium, iron, and occasionally man- ganese, "Copper, and lead. These elements are rarely found in the free state, being usually in the form of compounds. The compounds, or. as they are sometimes termed, proximate principles, are divided into: (1) tnineral, or inorganic, compounds; (2) organic compounds, or compounds of carbon. The organic com- pounds may again lie divided very conveniently into two groups: the nitrogenous and nonnitrogenous. 26 I'lIVSIULOGY. The inorganic compounds are water; the various acids, sucli as (he hydrochhiric acid of the pistric juice; and nunicrous salts. Sinc(! the |)r().\imat(' principles (if Ixttli food and tlie hody are the same, mention of the princij)les will he known to refer to hoth. A very convenient method of grouping the principk's of hoth food and the hody is that hy Hallihurton, as follows : — Inoiifiinic. Wafer. Sails, as oliloridos .and pliospliatos of sodium and falcium. Prolcids: albumin, myosin, etc. Nitrogenous. ... <( Alhuminoids : gelatin, keratin, etc. Bimpli'v ')iilro(iriioiis bodies: lecilliin, urea, etc. I Fats: butter, adipose tissue. Nonnitrogenous <^ Vaihohydratcs : sugar, starch. I Hhiijdc organic bodies: aleoliol, lactic acid. Although all (if lliese elements are })resent, yet not all are of equal importance or occur in the same proportions. Among the inor- ganic group, irater and mils are prominent; among the organic, car- huliy(Iraies\ fats, and proteids. WATER. Water forms more than one-half of the hody-weight. The value of water to the economy can he readily appreciated hy the student when he considers that the various processes and stages of digestion, absorption, and assimilation are dependent upon hydration and dehy- dration. About fifty ounces of urine are excreted daily, this being the main avenue for the escape of watery elements from the body. In addition, considerable water is given off by the skin as sensible and insensible perspiration, while expired air is heavily laden with moisture. With so much water making its escape from the body, at least as much must find its way into the economy. About two and a half quarts of water are ingested daily as food. The water we drink ought to be fresh, limpid, without smell, and of an agreeable taste. When complete and exact analysis is impossible, the taste is the only safe criterion or judge as to its fitness. Drinking-water should always contain a certain percentage of air. The palatability is due to the presence of carbonic acid gas in the water. Besides gaseous constitu- ents, solid substances are also present. These are both mineral and organic, and should be present in but very small amount. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 27 Somewliat more water is excreted daily tlian is ingested, since some water is formed in tlie tissues by the oxidation of hydrogen. SALTS. The most important salts fonnd are the sulphates and chlorides of sodium; the phosphates of sodium, potassium, calcium, and mag- nesium; and the carbonates of sodium and calcium. Of these various salts, sodium chloride is the most important and the most common one found. In the fluids — blood, serum, lymph, and urine — this salt is high in percentage. While in the body it favors aljsorption by increasing the endosmosis of the tissues and so aids metabolic processes, the absence of sodium chloride for an extended time causes disturbances and disorders in the constitu- tion. There are about 3000 grains of common salt present in the body. About 180 grains are excreted daily in the urine, wdiile some finds its exit as a component of the faeces, sweat, and tears. A practical illustration of its value to animal life may be gained by noticing how wild animals repair to the so-called '^salt licks" at various times, traveling for many miles to procure it. The Africans in the interior of their country do not have NaCl, but use the ashes of certain plants. These ashes chiefly contain KCl and K2SO4 and one-twentieth per cent, of sodium salts. Calcium phosphate is a very prominent factor of the mineral solids of the body. It forms about one-half of the bony skeleton. where it is most abundant, although it occurs to some extent in all other solids and fluids. This salt is particularly conspicuous in milk. Iron is an important element of hemoglobin. It is this iron in the red blood-corpuscles that is the means of holding the oxygen without being itself oxidized. A want of it causes the pathological condition called anemia. In the blood of an adult are found forty- five grains. In small proportions it is found in the liquids of the body, — as the chyle, lymph, bile, urine, etc., — in the feces, and traces in the liver and spleen. I. CARBOHYDRATES. Tlie car])ohydrates are found principally in the vegetable king- dom. They are, however, not indigenous to the vegetable kingdom, but are found and formed in animal tissues ; notably, glycogen, or animal starch; dextrose; and lactose, or milk-sugar. For the sake of a clearer conception of the term carbohydrate the components of the name are used when it is defined as a compound of 28 PHYSIOLOGY. carbon, hydrogen, and oxygen, the last two in tlie proportion occurring in the formation of water, two to one. The carboliydrates are: — Glucoses (CgHjaOe), or monosaccharides. Saccharoses (C12 H22 On), or disaccharides. Amvloses (CcHkjO-), or polysaccharides. The Glucoses are glucose; or dextrose, or grape-sugar; Igevulose, and galactose. The glucoses have three properties which are im- portant for the physiologist to know: physical, chemical, and bio- logical. From the fact that it deviates the plane of polarization to the right, its physical property is demonstrated, whence its name, dextrose. Its chemical property is the reducing of certain metallic salts in the presence of alkalies. Biologically, it ferments under the influence of the zymase of yeast to form carbonic acid and ethylic alcohol. The zymase, an intracellular ferment, is formed in the body of the cell. Fig. 5. — Yeast Fungus. (After Harley.) Saccharoses. — The saccharoses are saccharose, or cane-sugar; lac- tose, or milk-sugar; and maltose. When saccharose, or cane-sugar, is boiled with a dilute mineral acid, the right-handed polarizing solu- tion of saccharose is transformed into invert-sugar, or is said to be inverted. Invert-sugar is a mixture of equal weights of glucose, a right-handed polarizing agent, and Isevulose, which is a left-handed polarizing body. The saccharoses do not reduce the copper salts. The saccharoses are not directly fermentable by yeast except in this way : ( 1 ) when yeast is added, the saccharoses take up water and the soluble ferment of yeast, invertin, changes the saccharoses into glu- cose and laevulose; then (2) the zymase fermentation of the glucose and laevulose by the yeast-cell, which is not a vital act. Lactose, or sugar of milk, is a right-handed polarizing sugar. It reduces the copper salts, but is not fermentable either directly or in- directly by the yeast-ferment. Lactose ferments in the presence of the lactic acid bacillus to form lactic acid. Maltose is a right-hand polarizing sugar, reduces copper salts, CHEMICAL CONSTITUENTS OF BODY AND FOOD. 29 and ferments by yeast. Maltose has the same properties as glucose, but is distinguished in two ways: (1) the light-rotating power of glucose is 56 degrees, while maltose is 150 degrees; (2) the reducing of metallic salts by glucose is equal to 100, while that of maltose is but 66. The sugar in blood is a glucose. By moistening barley and germinating it in heaps at a constant temperature, the starch of the barley is converted into dextrose and maltose. This change is brought about by the ferment called dias- tase, which is found in barley. This product, when dried, is denom- inated malt, which, when it is acted upon by yeast, produces the malted beverages, beer and ale. Maltose by invertin of yeast is changed into glucose. Amyloses, or Polysaccharides. — Under the influence of dilute mineral acids the amyloses are changed by boiling or are transformed into glucose. Starch presents a polarizing cross: black cross upon a white ground or a white cross upon a black ground. Starch does not reduce copper solution nor is it fermentable by yeast. When iodine is added to starch it gives a blue color. Glycogen, or animal starch, does not reduce copper salts nor is it fermentable by yeast. During the hydrolysis of starch dextrin is formed as an intermediate product. Dextrins colored red l^y iodine are called erythrodextrins ; those not colored by iodine are called achroodextrins. 2. FATS. Fats form a more or less variable proportion of the animal economy. They come to us principally in the form of animal food, but to some extent in vegetable food, also, especially in seeds, nuts, fruit, and roots. The fats contain in their substances a fatty principle having acid properties — a sort of fatty acid. When acted upon by alkalies and ferments, this acid becomes separated and a sweet principle known as glycerin makes its appearance. Thus fats may be said to be compounds of fatty acids with glycerin. It would seem, however, that the glycerin had not pre-existed in the fats, as the united weight of the glycerin and the fatty acid produced exceeds that of the fat originally employed. In bone-marrow, adipose tissue, and milk, the fats are very prominent components. The adipose tissue consists of nucleated vesicles filled with fatty matter. The vesicles are closely packed together and are surrounded by a network of blood-vessels which 30 PHYSIOLOGY. draw out from this source a supply for nutrition. This fatty tissue is found between the muscles, bones, vessels, etc., and, by its accumu- lation under the skin, gives to the surface of the body its full and regular outline. By reason of its bad conducting power, it helps to keep the various structures of the body warm by a coating of it lying under the skin. This fact is best illustrated in warm-blooded aquatic ani- mals, such as the seal, porpoise, or whale. The normal fats found in the body and used for food are divided into three compounds : stearin, palmitin, and olehi. Stearin is the most solid of the three. It is typically illustrated in mutton suet, and is the element which makes this fat so hard and firm, and characterizes it at once. Its melting-point is 145° F., so that at ordinary temperatures it is solid. Palmitin occupies a position midway between stearin and olein as regards consistency. It is the principal constituent of most animal fats, and occurs largely in vegetable fats also. Olein is always found in a fluid state unless the temperature be very low. When the olein ingredients predominate in a body it is then in a liquid state, as in the case of the oils. Olein is found in both animal and vegetable fats, but the vegetable fats are richer in it than the animal. The oils used in food — olive-oil, oil of sweet almonds, etc. — are derived from the vegetable kingdojn. Human fat contains about 75 per cent, of olein plus a small quantity of fatty acids in a free state. All are soluble in hot alcohol, ether, and chloroform, but insoluble in water. Saponification. When fat is boiled with alcoholic soda or potash, the particles of fat are broken up into a small quantity of glycerin and a large quan- tity of fatty acid. The fatty acid unites with the soda or potash, forming, as a result, soap. This process of soap-forming is known as saponification. Emulsification. If oil and water are well shaken together the fatty particles do not form a part of the water, but are held in suspension and come to the surface in the form of small globules. A mixture of an oil, a soap, and water is spoken of as an emulsion. No emulsion is per- manent, for even in milk, the most perfect of emulsions, the fatty particles in the form of cream rise to the surface in a few hours. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 31 Emulsification is a physical or mechanical rather than a chemical change. Both soaps and emulsions are continually being formed in the body during the digestion of fats. 3. PROTEIDS, OR PROTEINS. The principal constituents forming the muscular, nervous, and glandular tissues, as well as the serum, blood, and lymph, are proteids. In normal urine there are found no proteids, or, if any, only traces. In a great measure the various phenomena of life are present and due to the protoplasm in the cells. On analyzing protoplasm chemically its substance is, of course, killed by the reagents used, but proteids invariably result in the process. Whether the proteids exist as such in the protoplasm, or occur only after the death of the protoplasm, has not been fully established, but they are believed to be the con- stituents of it. However, none of the phenomena of life occur with- out their presence. Proteids are very complex, comprising compounds of carbon, hydrogen, nitrogen, oxygen, and sulphur. They may be either solid or liquid, as they are found in the different tissues of the body. The different classes of proteids present both physical and chemical pecu- liarities, although all have certain common reactions. Some are sol- uble, others are insoluble, in water, while nearly all are soluble in ether and alcohol. Strong acids and alkalies are also capable of dis- solving the proteids. but in the process of dissolution decomposition almost invariably occurs. The supply of proteids in our bodies is obtained from the vege- table kingdom, being taken in as vegetables directly, or indirectly in the form of meat which is derived from animals that live on vege- tables. Thus the proteids are built up from the simpler inorganic compounds taken from the soil and air and elaborated in plant-struc- ture. The chemical composition of the proteids is variable, depending upon the products analyzed by the different investigators, as the purity of the substances cannot be definitely determined. From in- vestigations we have the following average percentages: 0, 21.50 to 23.50; H, 6.5 to 7.3; K, 15.0 to 17.6; C, 50.6 to 54.5; S, 0.3 to 2.2. The nitrogen and sulphur are each contained in the molecule in two forms, the one loosely combined, the other firmly combined. The basis of construction of all proteids is, according to Kossel. a body called protamin (C3oH.-N"i-Og), which on hydrolysis gives three basic substances each containing six carbon atoms, hence called hexone 32 PllYSJULUCiY. bases, lysin, histidin, and arginin. Protamin has been found loosely combined with nucleic acid in the spermatozoa of fishes. In the pro- teid molecule it is firmly combined with the amido acids, like leucin, glycin, and usually with tlie aromatic bodies, like tyrosin, etc., and in- organic elements, like sulphur and phosphorus.^ The proteids of different animals seem, to rough chemical tests, to be the same; but the precipitin test shows a difference between tliem. The casein of cow's milk is not exactly similar to that of wonum's milk. More is required than a mere equivalent of nitrogen to cover the loss of nitrogen from the body. Polypeptids. When proteids are split up by either ferments or chemical agents, the general order of the products is the same. Tlie first action is to produce proteids which have smaller molecules than the original native albumin. These products are denominated albu- moses. The next stage is the formation of still smaller molecules of peptone, and finally the peptone breaks up into smaller crystalline materials of known composition, which do not give typical proteid reactions. The above chemical reactions are hydrolyses. These bodies can be arranged into groups : — (1) Monoamino acids, such as glycin or glycocoll, leucin, aspar- tic acid, glutaminic acid, etc. (2) Diamine acids, as lysin, arginin, valeric acid, containing a urea radical like creatin and histidin. The introduction of a second amino or NH. group confers basic properties upon the acid ; hence the name hexone bases — hexone because all contain six atoms of carbon. (3) Aromatic amino-acids, such as phenylalanin, tyrosin. and tryptophan, the mother substance of indol and skatol. (4) Pyrimidin bases, such as thymin (cytosin) and pyrroli- din derivatives. (5) The sulphur-containing substance, cystin. (6) Ammonia. The amido-acids have been shown by Fischer to possess the prop- erty of combining with one another to nuike complex molecules con- ^ Beddard, "Practical Physiology'." CHEMICAL CONSTITUENTS OF BODY AND FOOD. 33 taining two, three, or more groups of amido-acids. Thus, two mole- cules of amido-acid (glycocoll) may be made to unite to form a com- pound, glycylgljcin, which Fischer calls a peptid. When formed from the union of two amido-acids, they are called dipeptids; from three, tripeptids; from more complicated compounds of this kind, the polypeptids, which have a reaction similar to that of proteids. The polypeptids occupy in proteolysis a stage between the peptones and the final simpler amido-acids, and can be found in peptic and tryptic digestion of albumin. ^Ye may write the formulaa for the three typical amino-acids as follows : — Glycin— HNH, CH,, COOH (amino-acetic acid). Alanin — HXH, C.H^. COOH (amino-propionic acid). Leucin — HXH, CgH^o, COOH (amino-caproic acid). In each, the first and last groups are the same, the middle group varies and may l)e represented by E. The general formula of the mono-amino acids is. therefore: HNH, E, COOH. If now we link these two together, we get HXH, E, CO, |0H H| NH, E, COOH. What happens is that tlie hydroxyl (OH) of the carboxyl (COOH) group of one acid unites with one atom of the hydrogen in the next amino (HXH) group, and water is thus formed, as shown in the oblong, and the rest of the chain closes up and the water is eliminated. In this way we get a dipep- tid. The names glycyl, alanyl, leucyl. etc., are given by Fischer to the XH2, E, CO groups which replace the hydrogen atom of the nexb XH, group.^ Thus : glycyl-glycin, glycyl-leucin, leucyl-alanin, alanyl-leucin, and numerous other combinations and permutations are obtained. If the same operation is repeated, we obtain tripeptids (leucyl- glycyl-alanin, alanyl-leucyl-tyrosin, etc.) ; then we have the tetra- peptids and so on ; and in the end, by coupling the chains sufficiently often and in appropriate order, Fischer has already obtained sub- stances which give the reaction of a peptone. Hence we may consider proteids as essentially polypeptid com- pounds of greater or less complexity ; that is, they are acid-amids formed by the union of a number of amido-acid compounds. Many of the polypeptids have l)cen produced synthetically, and these facts lead to the hope that the actual synthesis of the proteid molecule may be finally accomplished. British ^Medical Journal. 34 PHYSIOLOGY. Classification of Proteids or Proteins. For tlic sake of convenience and study the proteids have been divided into various groups and classes by dill'erent autliorities. They are almost universally divided into the two niain <;r()U})s of animal and vegetable origin. Tbe amount of proteid matter in plants, par- ticularly the full-grown ones, is less than in animals. It is found dis- solved in their juices, in the protoplasm, or deposited in the form of grains called aleuron granules. Vegetable proteids are divisible into the same classes as the animal, but, since human physiology deals with animal proteids, the vegetables are disregarded. A convenient classification is: (1) native albumins, (2) derived albumins, or albuminates, (3) compound proteids, (4) globu- lins, (5) peptones, (6) albuminoids, (7) histons, and (8) protamins. I. Native Albumins. The proteids of this class are those that are found in an unal- tered, natural state or condition in the solids of the body. They are soluble in water and are not precipitated by the dilute acids. The two main forms are egg-albumin and serum -albumin. The egg- albumin occurs in the part of the egg known as tlie white. The serum-albumin is found not only in the blood-serum, but also in the lymph as it is found in its proper lymphatic channels and diffused throughout the tissues, in the chyle, milk, and transudations. 2. Derived Albumins, or Albuminates, or Meta=proteins. To this class belong two divisions: acid-albumin and all-ali- albumin. The derived albumins are formed from the native albumins by the action of weak alkalies or acids. Thus, when a native albumin, such as serum-albumin, is treated for a while with dilute hydro- chloric acid its properties become entirely changed. The solution is no longer able to be coagulated by heat, and when the solution is care- fully neutralized the whole of the proteid is thrown down as a pre- cipitate. The substance into which the native albumin was changed by the action of an acid is called an acid-albumin, or s\Titonin. This acid-albumin is insoluble in distilled water and neutral saline solu- tions, but readily soluble in dilute acids and alkalies. This is the process through which albumins pass when undergoing gastric diges- tion and when acted upon by the HCl of the gastric juice. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 35 If serum-albumin, egg-albumin, or washed muscle is acted on by an alkali, instead of an acid, the proteid undergoes changes similar to those i^roduced by the acid, except that the product formed is an alkali-albumin instead of an acid one. 3. Compound Proteids, Conjugated Protein, or Proteides of Germans. These are native proteids with another organic substance, in contrast to albuminates, which are compounds of native proteids with inorganic substances. The compound proteins include (1) glucoproteins. like mucin, consisting of a proteid combined with a carbohydrate group; (2) nucleoproteins are built up of albumins, nucleic acid, and always contain iron. They exist in the cell-nu- cleus; (3) phosphoproteins, like casein of milk and vitellin of yelk of eggs; (4) chromoproteins, like haemoglobin. Tests for Proteids. — (A) Color Tests. — (1) The biuret test of Eose and Wiedemann, — when a solution of albumin is made strongly. alkaline with caustic potash, and a solution of copper sulphate is added drop by drop, then a pink-violet color is produced. (2) The xanthoproteic test of Fourcroy and Yauquelin. Add nitric acid, and a white precipitate ensues, which, on being boiled, turns yellow ; on cooling, add ammonia ; the yellow-colored precipitate becomes orange. This reaction depends upon the presence of the benzol ring in the proteid molecule (phenylalanin, tyrosin, indol).. (3) Millon's reagent. This reagent is a solution of mercuric nitrate in -water containing free nitrous acid. On adding it to a solution of albumin, a whitish precipitate ensues, which becomes a brick-red on boiling. This reaction indicates the presence of oxy- phenol group (tyrosin). (B) Precipitation of Proteids by I^eutral Salts. — (1) Saturation with ammoniimi sulphate precipitates all proteids except peptones. (C) Precipitatio>t of Proteids by Acids. — (1) Add a drop or two of strong nitric acid, a white precipitate ensues. 4. Globulins. The globulins are quite abundant. The globulins differ from the albumins in that they are not soluble in distilled water. There must be present an appreciable amount of sodium chloride or mag- nesium sulphate. Globulins are insoluble in saturated solution of all the neutral 86 PHYSIOLOGY. salts. They are also insoluble in a half-saturated solution of ammo- nium sulpluite. They are coagulated by heat. The different members of this group are : serum-globulin (para- (jlohuVm), and pbrinugcn in blood, myusmogen in muscle, etc. I'araglobulin is a ])recipitate that can be formed from blood- serum by diluting it tenfold with water, and passing through it a current of carbon anhydride. A flocculent, and finally a granular, precipitate results, which is the paraglobulin. The coagulated proteids are fibrin, myosin, and casein. The coagulation is produced by ferments. Fibrinogen is present in the blood, chyle, serous fluids, 'and transudations. Myosinogen is the principal proteid found in muscle. 5. Peptones. In the body peptones are the final results of the action of the gas- tric and pancreatic juices upon the native proteids, and, as peptones, are ready for absorption by the cells. Although formed in large quantities in the stomach and intestine, they are absorbed as soon as formed, since none are left in these organs. Peptones can, how- ever, be produced outside the body by the action of dilute acids at medium temperatures. The peptones are soluble in water, not coagulated by the pres- ence of heat, cannot be precipitated by the usual proteid precipitants, and diffuse very readily through membranous tissues. Siegfried has recently isolated peptones of a basic character by hydrolysis of all)umins with about 12 per cent, of hydrochloric acid. He calls these bodies kyrines. Intermediate products between the native proteids and peptones are the proteoses. True peptones are not found in the circulating juices of plants, but the product found is very likely proteose. The proteoses are only slightly diffusible, they are not coagulated by heat, but can lie precipitated. A characteristic feature of their pre- cipitates is that they can be dissolved by heating, but reappear when the solution cools. 6. Nitrogenous Bodies Allied to Proteids, or Albuminoids, or Sclero= proteins. Besides the proteids there are other nitrogenous, noncrystalline bodies that are allied to the former, having many general points in common. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 37 Gelatin is the substance produced by heating in dilute acetic acid for several days, the collagen of connective-tissue fibers. It possesses the property of setting into a jelly when its concentration is greater than 1 per cent. When digested it is converted into a peptone, and, although readily absorbed, is not a1)le to take the place of a true proteid, since it cannot build up nitrogenous tissue, being valuable only as a means of storing up energy. Keratin is the horny material forming the outer layer of the epidermis, hair, wool, nails, hoofs, etc. Elastin of elastic tissue belongs to this group. 7. Histones. To the histones belong globin, the proteid which is separated from hammglobin by decomposing acids and alkalies. 8. Protamins. The protamins are salmin, clupein, scombrin, sturin, etc. ALIMENTARY SUBSTANCES. We have learned that the body is composed of the chemical con- stituents or proximate principles, carbohydrates, fats, and proteids comprising the organic group, and water and salts the inorganic class. In order that the nutrition of the body may proceed normally, it is very apparent that those principles must be supplied in the food, in the proper proportions and quantities. So, a proper diet for man is one containing the proximate principles in their ])roper proportions, the value of it depending mainly on the amount of carbon and nitro- gen present. The elements, as elements, are not valual)le; it is only when they are in combination that they serve their proper ends as foods. For the elements, to constitute an organic product, must be united previously by some living organism. It is not often that the alimen- tary substances are used by us as Nature furnishes them, even though they contain the proper ingredients. One requisite is that they should be presented in a digestible form. Water, heat, and condi- ments are the three agents used to make food more palatable and digestible. Water helps to soften the insoluble substances, and to dissolve the principal substances. Heat modifies the foods still more, so that they acquire different cliaracters. Condiments give physical satisfaction and enjoyment, and, at the same time, they please the taste. 38 PHYSIOLOGY. A diet, to be sufficient, must be adapted to tlie particular indi- vidual's need, keeping in mind, also, the climate, age of person, and the amount of work done by him. We make changes of clothing to suit the weather conditions in order that the body may not suffer in regard to the surrounding tem- perature, and our diet should be regulated with the same ends in view. In cold weather we eat more, to furnish an extra amount of heat; in warm weather we eat less than usual. A growing youth's body must not only repair the daily waste, but also assist in con- structive metamorphosis, or growth, so that he requires relatively more food per diem than the adult. Because of the waste attending action, the workingman requires more than the ordinary supply of food. There are some single foods which contain all the necessary proximate principles in proper proportions, but they are the excep- tions, rather than the rule. Thus milk and eggs are classed as per- fect foods. It is usually necessary for a proper diet to contain a vari- ety of substances in this list. For a man doing a moderate amount of work, it has been com- puted that it is necessary that the daily diet should contain the fol- lowing amounts :— Proteid 125 grams. Fat ; 50 grams. Carboliydrates 500 grams. Alimentary substances comprise products of both animal and vegetable kingdoms. The principal ones are animal substances, with cereals, potatoes, drinks, condiments, cocoa, coffee, tea, etc. The animal substances, or foods, comprise: (1) meat, (2) eggs, and (3) milk, with its derivatives — cream, butter, and cheese. The parts of animals used for food are the various portions of their muscular system. They comprise the general term meat. Ani- mal food. 1:)eing identical with the body structures, requires nothing to be added or subtracted to make it fit to give proper nourishment. MEAT. The more compact the fiber, the less digestible the meat. Hence ham is much less digestible than other meats. The more fat that is combined intimately with the fibers, so much less is the digestibility of the meat, because the fat melts and coats the fibers of the meat with a layer of oil which prevents the ferment from acting upon it. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 39 Meat is noted for the large quantity of nitrogenous matter which it contains, containing four times the amount of proteid compared with the same weight of milk. The proteid in meat is myosin, the main constituent. Beef-tea is a solution of gelatin, salts, extracted matters, a little albumin, together with some fat. The value of beef-tea as an ali- mentary substance has been much disputed, some claiming great results from it, others none. However, one thing is certain; it possesses a stimulant and restorative value, though it must not be depended iipon as a food and administered as such. Liebig's Beef Tea. — It contains novain, oblitin, ignotin, and neosin. Oblitin increases the tonus and peristaltic movements of the intestine. It also increases the salivary secretion and lowers arterial tension. Novain has a similar action to oblitin. Neosin lowers the arterial tension. Neosin is also obtained from fresh muscle, and is not due to putrefactive changes in beef-tea. The process of cooking meat loosens up the various fasciae and enveloping membranes, thereby separating the fibers; at the same time parasitic growths are killed. Thus the digestive juices are given more ample opportunity for acting upon all parts of the foods, even penetrating into the innermost parts. EGGS. The white of an egg is a faint-yellowish, albuminous fluid in- closed in a framework of thin membranes, and this fluid itself is very liquid, but seems viscid, because the membranes are entangled. Oval- bumin, or the egg-albumin of the egg-white, is the chief constituent. The mineral bodies in the white of the egg are potash, soda, lime, magnesia, iron, chlorine, phosphoric acid, and sulphuric acid. The principal part of the yelk is an orange-yellow, alkaline emul- sion of a mild taste. Tlie yelk contains vitellin as its principal con- stituent. Besides vitellin, the yelk contains alkali albuminate and albumin. The yelk also contains a phosphorized fat (lecithin) with cholesterin, fats, and a small quantity of sugar and of mineral bodies, chiefly lime and phosphoric acid. Iron exists in the yelk in an or- ganic combination. As the egg is so easily digested it is prized highly as a food. However, the more that an egg is boiled, the more insoluble do the proteids become and so are more indigestible. In cases where eggs are difficult of digestion the white of egg may be given. In some persons the yelks of eggs cause headache and 40 PHYSIOLOGY. drowsiness. The caloric value of two eggs is about twenty calories, about equal to the heat-value of a tumbler of milk. MILK. Like eggs, milk contains all the elements necessary for the main- tenance of life, and hence it is regarded as a type of alimentary sub- stances and classed as a perfect food. It serves very well as an infant-food. The quantitative composition of cow's milk and human milk is as follows, according to Bunge: — Carbo- Proteid. Fat. Hydrate. Salt. Cows' milk 3.5 3.7 4.9 0.7 Human milk 1.7 3.4 6.2 0.23 Fig. G. — Specimens of Milk, viewed tliroiigh the Microscope. (Landois.) M, Milk. C, Colostrum. The amount of fat and cai-l)oliydrate is nearly the same in both. there being, however, twice as much proteid and nearly three times as much salt in cows' milk as in human milk. To bring cows' milk to the same condition as human milk, it is necessary to dilute with an equal amount of water, and, at the same time, to add some cream and sugar. Milk is a watery solution of various proteids, a carbohydrate and salt, containing in suspension emulsified fat. Cows' milk is an opalescent solution, with a characteristic taste and an amphoteric reaction. The specific gravity varies between 1028 and 1034. Micro- scopically, it consists, like blood, of plasma and corpuscles, or glob- ules, of fat. Boiling does not coagulate fresh milk, but forms a skin CHEMICAL CONSTITUENTS OF BODY AND FOOD. 41 on its surface, which is chiefly composed of caseinogen innieshing some fat-particles. This film is formed by the drying of proteid at the siarface of the milk. The chief proteid of milk is a phospho-proteid called caseinogen, which can be precipitated by adding to the diluted milk a weak acid or by saturating it with a neutral salt. The chief peculiarity of caseinogen is its coagulating power when treated with a ferment, rennin, in the .presence of lime salts. The coagiilation of milk depends upon the change of a soluble proteid, caseinogen, into an insoluble body, casein, by means of the enzyme, rennin, and the presence of lime salts is necessary. It is probable that the rennin first splits the caseinogen into two bodies, the more important being soluble casein, which then combines with the calcium salts to form a caseinate of calcium, while the other passes into solution in the whey as whey proteid, or lacfoserum proteose. The casein thus generated inmeshes the fat-granules and forms milk-curd. This curd, like the blood-clot, shrinks after a few hours and an opalescent fluid, or serum, called whey, is expressed. This whey contains, besides the whey-proteid, or lactoserum pro- teose, traces of other proteids and also lactose and milk salts. The casein of cows' milk forms large masses on coagulation, while women's milk forms very fine flakes. The lactose, or sugar of milk, does not readily ferment with yeast, but it is capable of undergoing a special fermentation, by which it is changed by the lactic acid bacillus into lactic acid, and this lactic acid is further split up into butyric acid. These two acids, lactic and butyric, precipitate the caseinogen and produce the curd in sour milk; but this curd is quite a different body from that pro- duced by rennin, for it can be dissolved by a weak alkali, and then the rennin will clot it. Potassium oxalate, which precipitates the cal- cium in the milk, prevents the clotting of the milk. The other pro- teids in milk, besides caseinogen, are lactalbumin and lactoglobulin. Kumiss is mare's milk fermented. It contains 10 per cent, of solids. 3 per cent, of alcohol, 2 per cent, of fat, 2 per cent, of sugar, 1 per cent, of lactic acid. 1 to 2 per cent, of casein, and 1 volume per cent, of carbonic acid. Kephir is cows' milk fermented by kephir grains. Matzoon is prepared by adding to milk a ferment consisting of some form of yeast and the lactic acid bacilli. It. however, contains very much less alcohol and carbonic acid than kumiss. Plasmon is prepared by precipitating casein from fresh milk. Then it is dis- solved in sodium bicarl)onate in the presence of free carbon dioxide, 42 PHYSIOLOGY. which prevents the alkali from decoiiiposing the casein. It is then dried, and is a yeiiovvish-white body. It contains 2 per cent, of fat and milk-sugar and 7 per cent, of salts. It is used as a substitute for milk when a large amount of water is not desirable. The fats of milk are olein, palmitin, stearin, caproin, and buty- rin. The milk of women contains twice as much olein as palmitin and stearin, but these bodies are about the same in quantity in cows' milk. In cowls' milk two-fifths is olein, one-third is palmitin, one- sixth stearin and butyrin, and caproin one-fourteenth of the total fat. Buttermilk contains about 10 per cent, of solids, including casein; lactose; and about 1 per cent, of fats. Butter is formed in churning by making the fat-particles adhere to each other, forming a yellow, fatty mass. The salts of milk average 0.6 per cent, and they consist chiefly of phosphate of lime with calcium chloride, magnesium phosphate, and traces of iron. Milk also contains about 7.G per cent, of carbonic acid and traces of oxygen and nitrogen. The quantity of milk daily secreted by a woman is about one quart. The quantity of milk changes during lactation, wdiich lasts in the woman about ten months. In the case of the woman, the percentage of casein and fat increases to the end of the second month, but sugar lessens even in the first month. During the fifth to the seventh month there is a diminution of fat, and between the ninth and tenth months a decrease of casein. In the first five months the salts increase; after that they diminish. Colostrum is the milk secreted for a few days after parturition, and it has peculiar characteristics. It contains large corpuscles called colostrum-corpuscles, which are large cells full of colorless, fatty par- ticles. A poisonous principle is sometimes generated in milk by microbes. It is called tyrotoxicon. VEGETABLE FOODS. Vegetable substances differ very much from animal bodies in their physical appearances, and, in some respects, also chemically. The vegetable matters are capable of being transformed into the various animal components and thereby nourish the animal body, since they contain all the elements, or proximate principles, that are necessary CHEMICAL CONSTITUENTS OF BODY AND FOOD. 43 for the maintenance of life. They need a more complex apparatus for their transformation, and, as a consequence, the digestive organs of the herbivora are better developed and more complex than those of the carnivora. The cereals have the same general composition, all containing the same proximate principles, but not all possess the same relative amounts, because of which some are more valuable as food than others. The most important of the cereals is wheat. ^Vlleat, as a source of food, occupies a very important place and is one of the most widely cultivated of the cereals. The wheat- grains by grinding have their cellulose coats burst, and the resulting powder is called flour. This contains, on an average. 70 per cent, of 'carbohydrates, 8 per cent, of proteid, and 1 per cent, of fat. The coverings of the grain still contain some albumin and starch and thus form l:)ran, a substance used for feeding the herbivora. Bread is made by a mixture of wheat-flour and water, forming dough. The body which, on the addition of water, becomes viscid is called gluten, and is a tough, sticky mass. This is made more porous by carbonic acid, which is generated in the dough by the action of the yeast-plant on sugar. The sugar is produced l^y the diastase in the flour, which hydrates the starch into sugar. Baking kills the yeast-action and makes the vesicles filled with carbonic acid expand, so the dough is filled with little cavities. The crust of bread is formed by the heat coagulating the gluten, and at the same time the heat transforms the starch into dextrin and soluble starch. The glazing of the crust is due to dextrin. The color of the crust and its taste are due to a caramel generated by the action of heat on the sugar produced by the diastase. ACCESSORY FOODS. In addition to the ordinary foods there is a series of articles which are not necessary to the maintenance of life, but which are fre- quently used. They are : alcohol, tea, coffee, and cocoa. Of these accessory foods, alcohol is the predominant one and is used in a vari- ety of drinks. Alcohol. — Beer contains from 3 to 5 per cent, of alcohol. It also has from 5 to 7 per cent, of extractives, which consist mainly of dextrin and maltose, with all)uniinope. which give it nutrient proper- ties. Each ounce usually holds about two cubic inches of carbon dioxide. It is an infusion of malt fermented, to which a bitter prin- ciple foimd in hops is added. It is frequently adulterated with sali- 44 PHYSIOLOGY. cylic acid and benzoic acid to preserve it. In excess it gives rise to rheumatism, gout, and bilious attacks, due to diminished excretion of waste-materials from the economy. Wines contain from G to 25 per cent, of alcohol. Port holds 10 per cent, and sherry IG to 25 per cent, of alcohol. Besides, the aroma is due to ethers. Champagnes contain in addition, 10 per cent, of sugar, which upsets the stomach. Wines also have free acids, especially tartaric, which also disagree with certain stomachs. Spirits contain about 50 per cent, of alcohol. Alcohol is a nutrient and heat-generator. One gram of alcohol produces more heat than one gram of proteid or carbohydrate. Ordinarily the sys- tem can oxidize dail}^ about one and one-half ounces of alcohol. When alcohol is oxidized it spares the fats and carbohydrates and probably the proteids. It is w^ell known that the continuous drinking of alcohol makes a person fat. The persistent use of alcohol also increases the dangers of infection from infectious diseases. In fevers its use prevents the loss of fat and stimulates the secretion of gastric juice. It dilates the capillaries of the skin either by a local or central action, favoring heat-dissipation. Its habitual use gives rise to chronic gastritis and cirrhosis of the liver. The odor of spirits in the breath is due to fusel-oil. Alcohol in the blood is changed into carbonic acid and water. Coffee. — Each cup of coffee contains about two grains of caffeine. Coffee also contains a volatile substance called coffeon, which resem- bles an oil. The exhilaration after the drinking of coffee and the increased peristalsis are due to the coffeon. Tea. — Tea contains caffeine and th(>ophyllino and about 7 per cent, of tannin. Tea induces constipation and chronic gastritis .when used in excess. Neither tea nor coffee diminishes metabolic changes. Cocoa. — This body is a nutrient because it contains fat (50 per cent.) and an all)uminous substance. It contains theobromine. Caffeine and theobromine belong to the purin group. CHAPTER 111. DIGESTION. Anatomy and Structure of the Mouth, Pharynx, and (Esophagus, together with the Digestive Processes Occurring in Them. Digestion has for its aim the separating of the principles of growth and repair from the aliments and the fitting of them for absorption into the circulation. The process is both mechanical and chemical, accomplished mainly through the action of certain soluble ferments called digestive enzymes. Some form of digestion is found to take place in all animal organ- isms no matter how low we proceed in the zoological scale. It is essential to every one of them that they be able to take from their environments those elements that are necessary to maintain their economy and to give off those substances termed waste-products that are no longer fit for use. for only by this exchange of the elements outside of their own organisms are they able to live, grow, and pro- duce others of their kind. In the higher grades of animal life, as the articulata and verte- brata, the number of organs concerned in digestion is increased, and, of course, in direct ratio the various stages and acts in the whole process are multiplied. In their bodies it is a long tube, in some parts much folded on itself ; in and along the outside of this tube there are numerous glands which empty their products, called secretions, into the long tube; at the' beginning of which there is an apparatus for crushing and grinding the solid parts of the food. Intimately con- nected with this apparatus is the system of blood- and chyle- vessels for absorbing the digested products, thus allowing them to circulate through the entire l^ody and come into contact with every part of the organism. In the vertebrata there are modifications and forms of develop- ment dependent upon the class, and even in mammalia there are differences, as the animal may be insectivorous, carnivorous, herbivor- ous, or omnivorous. Man, the highest of the mammalia, is the real and intimate study upon which all our phvsiological researches bear. He is omnivorous, (45) 46 PHYSIOLOGY. and naturally wc expect to lind liis digestive apparatus suited to dis- integrating and dissolving all kinds of food. In him the digestive apparatus consists of a long tube, called the alimentary canal, about thirty feet in length, with its accessories, the teeth and the various glands which empty their products into the tube by means of little ducts. The alimentary canal is the long tube beginning with the mouth and ending with the anus, composed of muscle and mucous membrane, the latter lining it throughout its entire length and giving to the interior of the canal its characteristic smoothness and redness. In this lining membrane, as also in the submucosa, are located some of the glands whose secretions aid digestion. The alimentary canal in its extent of about thirty feet has received various names for its several parts. They are : mouih, pharynx, o'sophagus, stomach, small and large intestines. The mouth is an oval box situated at the commencement of the canal, in which, by the action of the jaws with their two rows of teeth, the hard parts of the food are masticated. While the food is being masticated, it is at the same time being mixed with a watery fluid, the saliva, the secretion of the salivary glands; this mixing of food and saliva has been termed insalivation. In the pharynx and oesophagus occurs the act of deglutition, or swallowing of the masticated mouthful, in the form of a large, moist bolus. It is by the contraction of the muscles in these parts, that the food is quickly passed on to the stomach. The course of the tube, beginning with the mouth and ending at the opening of the stomach, is comparatively straight, and measures about fifteen or eighteen inches in length. This part of the tube is found in the head, neck, and thorax, ending just below the transverse muscular wall of the trunk, the diaphragm. The stomach is the muscular pouch in which occur some of the chemical changes of the food, converting it into a grayish-brown soup- like mass. From thence it passes into the small intestine, where the nutrient materials are separated from the waste-residue; the latter is passed on into the large intestine to be later expelled from the body. The stomach and the large and small intestines are located in the abdomen and pelvis, differing from that part of the canal above the diaphragm in that the intestines are much folded and convoluted in their course ; so that the major portion of the entire length of the canal is contained here. In the mucous membrane and submucosa are located micro- DIGESTION. 47 scopical glands whose ducts open directly upon the lining, interior surface. Outside the canal, their secretions emptying into the canal by small ducts, are the larger glands, salivary, liver, and pancreas. The ducts of the salivary glands open into the mouth ; the common duct of the liver and pancreas opens into the first fold of the small intestine, the duodenum. Although digestion in its entirety, as it occurs in the alimentary canal, is in its nature very complex, yet there are three natural divi- sions of the whole process based upon the changes as they occur (1) in the mouth (including the pharynx and oesophagus), (2) in the stomach, and (3) in the intestines. It is the intention to consider the changes and alterations of the foodstuffs, whether mechanical or chemical, in each, together with the anatomy of the parts of each division and the structure of the accessory glands, with their secretions and the functions they bear to the completion of the entire work. However, the fact must not be lost sight of that these divisions are only arbitrary and for conve- nience, as no real line can be drawn at the various stages, since all parts, structures, and functions work in harmony, on the plan of division of labor : having in mind one common end — the dissolving of the food so that it can become a part of the circulation. PREHENSION. Before the processes of digestion can begin, it is essential that the food should be brought to and placed in the mouth, the beginning of the alimentary canal, for only in some of the infusoria does diges- tion of the food take place outside the organism, due to the influence of ferments secreted by the organism to be nourished. The act of bringing the food to the mouth has been termed prehension. Nature has admirable contrivances for this act wherever we look among the lower animals. The monkey, squirrel, rat, etc.. usually make use of their anterior extremities for grasping and bringing to their mouths the food, while they sit upon their haunches. The horse makes use of his teeth and lips; indeed, his upper lip is very movable, long, and endowed with extreme sensibility. It is his means of gathering together his grain and bringing it to the incisors which cut it up, then to be passed along by tlie tongue to the molars for grinding. In the cow, the tongue, in the cat and dog. the teetli and jaws, are the main organs of prehension. The frog, by protruding his long, thin tongue, the surface of which is covered with a viscid mucus, catches insects as they fly. 48 PHYSIOLOGY. By far the most complicated and best developed prehensile instru- ment in animal mechanics is that employed by iiuin — the human upper limb. The extreme perfection of all its parts, and particularly of its terminal portion., the hand, makes it admirably fitted, not only for the prehension of food, but also for the execution of all the various caprices and designs of the human will. Thus it not only simply raises the food to the mouth (prehension), but also, with the human intelligence as the real potent factor, aids in the preparation of food by means of fire (cooking). Thus we learn that the first real step in digestion is prehension: bringing the food to the mouth. THE MOUTH. The space included between the lips in front, the pharynx behind, and the cheeks at the side is the mouth. Above the roof of the mouth we have the palate; below, its floor, upon which rests the tongue. The cavity of the mouth, excepting the teeth, is everywhere invested with a highly vascular mucous membrane, with an investment of squamous epithelium. Conical papillae, for the larger part minute and concealed beneath the epithelium, are found. The lips are separated by the oral fissure. They are composed of various muscles converging to and surrounding the oral fissure. The cheeks have a composition similar to the lips, and their principal muscle is the buc- cinator. At their back part they include the ramus of the jaw and its muscles, and usually between these aud the buccinator muscle is a mass of soft, adipose tissue. Beneath the mucous memljrane of the lips and cheeks, there are a number of small, racemose glands, with ducts which open into the mouth. These glands are, in the lips, called labial and. in the cheeks, buccal. They secrete mucus. There are two parts to the palate: a hard and a soft palate. The hard palate is deeply vaulted and lined with a smooth mucous membrane, except at its anterior part, where it is roughened l)y trans- verse ridges. The soft palate is a doubling of the mucous membrane, inclosing a fibromuscular layer, also containing racemose glands. It hangs down obliquely from the hard palate between the mouth and posterior nasal orifices. It is a freely movable partition. The uvula is an appendage like a tongue projecting from the middle of the soft palate, and consists of a pair of muscles inclosed in a pouch of mucous membrane. Palate. — The palate has two crescentic folds of mucous mem- DIGESTION. 49 brane inclosing muscular fasciculi and diverging from the base of the uvula, on each side of the palate outward and downward, one to the side of the tongue, the other to the side of the pharynx. These folds are known as the half -arches of the palate. The one in front is known as the anterior palatine arch, the one posterior as the posterior pala- tine arch. The Fauces. — The fauces is the strait, or passage, leading from the mouth to the pharynx, and corresponds with the space included between the half-arches of the palate. The Tongue. — The tongue is composed of muscle and is covered with a mucous membrane. It is composed of two symmetrical halves joined in the middle line. By the freedom of its movements it aids in mastication and deglutition ; it is also a great help in articulation, and by the papillas on its surface forms an organ of taste. The root, or base, is the posterior part, where it is attached to the hyoid bone and inferior maxilla. The body is the great bulk of the organ. Its tip is the anterior free extremity. On the anterior two-thirds of the upper surface of the tongue, we find a mucous membrane, which adheres most intimately to the muscles beneath. Its surface is rough- ened by the presence of a number of little papilla. On the surface of the tongue there are many mucous glands. Papillae. — The papillse are the fungiform, filiform, and circum- vallate. These are more minutely described in the section on the sense of taste. Nerves. — The nerves of the tongue are the lingual of the fifth pair, the glosso-pharATigeal, and the hypoglossal. THE TEETH. In form, structure, and number, the teeth vary very considerably in different animals : this is markedly shown in the classes, car- nivora and herbivora. In most animals the teeth are worn down by use and eventually decay. The exception is found in that class of animals that constantly nibble ; their incisors are peculiar in that there are deposits of fresh dentine within and upon the pulp and of enamel upon the anterior surface, thus giving a continuous growth. They are the rodentia. Among mammalia, and particularly in man, the teeth are devel- oped in two sets: (1) the frst, less numerous and smaller set. called the Umpomry. or mWk. teeth; (2) the second set. larger and more numerous, called the permanent teeth. The temporary, or millc. teetli are usually 20 in number. 10 in 4 50 PHYSIOLOGY. each jaw. In each jaw there are Jf. incisors, 2 canines, and k molars. When the milk teeth drop out they are followed by the permanent teeth. The permanent teeth are 32 in number, 16 in each jaw, consisting of Jf. incisors, 2 canines, 1^ bicuspids, and 6 molars. There are three distinct parts in a tooth : crown, root, and neck. The crown, or body, is the protruding portion of the tooth; the portion inserted in the alveolus of the jaws is the root, or fang. The slightly constricted part enveloped by the gum, is the neck. The fang is firmly fastened to the sides of the alveolus, in which it is inserted by fibrous tissue, which is continuous with the periosteum of the jaws. When the jaws are closed the under incisors are inclosed by the upper ones. Init the grinding surfaces of the molars are in contact. Temporary Teeth. — There are 20 milk teeth, 10 in each jaw, or 5 on each side of the jaw; that is, 2 incisors, 1 canine, and 2 molars. The temporary set resembles the permanent in form and structure. The teeth are, however, fewer in number, smaller in size, and charac- terized by the bulging out of the crown close to the neck, making the latter very sharply defined. Lower central incisors are the first to appear. They appear about the seventh month. The milk teeth die off and so give room for the second and more permanent set. They die partly in accordance with the rule of epi- thelial tissues and drop off, since all such tissues are expelled after their death ; then, too, the jaws grow as the being passes from infancy to adult life, when larger and more numerous teeth must replace the smaller ones, so as not to impair the efficiency necessary to masticate quantities of food proportionate to the demands of the growing body. Permanent Teeth. — They are 32 in number. There are 8 in- cisors and they form the 4 front teeth in each jaw, and are named incisors because they divide the food. The upper incisors are the larger. The lower molar is the first to appear in the permanent set. It appears about the sixth year. The canine teeth are 4 in number, larger than the incisors. The upper canines are usually called the eye teeth, and they are longer and larger than the canine teeth in the lower jaw. In the carnivorous animals, like the dog, the canine teeth are usually large; hence the name of canine. The lower canines are popularly known by the name of stomach teeth. There are 4 premolars, or bicuspids, in each jaw. They are shorter and smaller than the canines. The bicuspids of the upper jaw are larger than those of the lower jaw. The functions of the bicuspids are to cut and grind the food. The molars are 12 in DIGESTION. 51 Fig. 7. — Longitudinal Section of a Molar Tooth of Man. ( SOBOTTA. ) X 8. The figure gives a general view of the structure of the tooth. The pulp cavity is not cut its whole length in the two roots seen in the section. We recognize the three main elements of the tooth— dentine, enamel, and cemen- tum— and their division into crown and root. On account of the low magnifica- tion, the interglobular spaces appear only as a dark zone on the surface of the dentine. C, Cementum. D, Dentine. P, Pulp cavity. 8. Enamel. 52 PHYSIOLOGY. number, 3 on each side above and below. Their large crown and their groat width are the chief distinguishing characteristics. The u])per molars have 3 conical fangs, the lower ones 3. Tlie last molar is the wisdom tooth, so called because it appears about the twentieth year, when the individual is assumed to have acquired wisdom. The molars are intended for the grinding of food. Structure of the Teeth. — If a tooth is split in its long axis the surface exhibits, besides the pulp-cavity, th^-ee different kinds of materials. Dentine forms the greater part of the yellowish-white So Dk Fig. 8. — Portion of the Crown of a Longitudinal Section of a Human Premolar. X 200. (Sobotta. ) The figure shows the structure of a tooth at the border of enamel and dentine. In the region of the dentine two larger and two smaller interglobular spaces are shown. The dentinal fibers branch and fork and with their processes pass beyond the limits of the enamel. In the figure, the enamel prisms show partly wavy curves and partly alternating stripes of darker and brighter prisms (the parallel stripes of Retzius). D, Dentine. Dk, Dentinal tubules. J , 1 -^ \ \ 1 \ ■5^ 6 \ / 1 \ =^ V / 1 \ 1 4- \ / \ ' \ \ / \ j 2 \ / \ A \ \ \ / \ \ 0 \ \ 1 \ lours 1 Ji :> ^ s 6 7 3 ; z 2> 4 S 6 1 S 3 10 1 Z d ^ 3 6 Fig. IG. — Hourly Variations of the Secretion of C4astric Juice in the Dog after a Meal of Meat, Bread, and Milk. (Pawlow.) same juice the dilferont ferments nuiy suffer variations, running courses independently of each other, a fact which undoubtedly shows that the pancreas, which has a complex chemical activity, is able to furnish, during given periods of its secretory work, now one pro- duct and now another. That which may be said of the ferments may also be applied to the quantities of the salts in the juices. The gastric juice always has the same acidity as poured out by the glands, but on leaving the glands and running over the walls of the stomach, the mucus can neutralize 25 per cent, of it. The food also neutralizes the acid. At the beginning of digestion, when the quantity of food is large and its external structure still coarse, the strongest juice should be poured out when most needed. The greatest digestive power belongs to the juice poured out on bread, which mio;ht, for brevity, be called DIGESTION. 75 "bread-juice"; the next strongest is "flesh-juice/' and then comes "milk-juice." In other words, "bread-juice" contains four times as much ferment as "milk-juice." Xot alone the digestive power, but likewise the total acidity, varies according to the nature of the diet. Comparing equivalent weight, flesh requires the most and milk the least gastric juice; but taking equivalents of nitrogen, bread needs the most and flesh the least. The hourly intensity of gland work is almost equal in the case of milk and flesh diets, but far less with bread. The bread, however, exceeds all others in the time required for its digestion, and the duration of the secretion is correspondingly protracted. s .^ 1^ Fig. 17. — Hourly Variations of the Digestive Power of the Gastric Juice in the Dog after a Meal of Meat, Bread, and Milk. (Pawlow, Gley. ) M cnf I hei id. MilJc ■ /f / \ 6 A \ \ y K' / 4 J — ^ \ / \ / f, ■"" '' \ f \ ^^ — - 0 / -e 3 4- 5 6 7 t 2 3 4' 3 6 7 d / i 3 4 s Each separate kind of food corresponds to a definite hourly rate of secretion, and calls forth a characteristic alteration of the proper- ties of the juice. Thus, with flesh diet, the maximum of secretion occurs during the first or second hour, and in both the quantity of juice furnished is approximately the same. With bread diet we have always a sharply indicated maximum in the first hour, and with milk a similar one during the second or third hour. On the other hand, the most active juice occurs with flesh in the flrst hour, with bread in the second and third hours, and with milk in the last hour of secre- tion. The point of maximvim outflow as well as the whole curve of secretion is always characteristic for each diet. On proteid in the form of bread, five times more pepsin is poured out than on the same quantity of proteid in the form of milk, and the flesh-nitrogen re- quires 25 per cent, more pepsin than that of milk. These different 7(3 PHYSIOLOGY. kinds of protoid receive, therefore, quniitities of ferment correspond- ing to the dilferences in llieii- digestil)ility, which we already know from experiments in pliysiological chemistry. Excitants of Flow of Gastric Juice. Before the dog adapted for sham feeding, Pawlow cut up meat and sausage, when he obtained a great flow o,f gastric juice, more so than when he fed the dog with them ; they escaped by the oesophagus. Here is a psychic excitation of the gastric secretion, which plays a considerable part in the production of gastric juice in the sham feed- ing experiment. The appetite is, then, the first and mightiest exciter of the secre- tory nerves of the stomach. A good appetite in eating is equivalent from the outset to a vigorous secretion of the strongest gastric juice. Sham feeding of five minutes does not call forth a secretion for longer than three to four hours. Mechanical excitation of the mucous membrane of the stomach does not cause the flow of gastric juice. Sodium bicarbonate in the stomach inhibits its secretion. Liebig's extract or meat-broth intro- duced into the stomach increases the secretion of gastric juice. Fat in the stomach inhibits the psychic secretory action of the stomach upon meat. The fat of milk can inhibit its digestion to a certain extent. The secretory activity of the stomach depends on nervous pro- cesses. In the immense majority of cases gastric digestion begins by a strong central excitation of the secretory and trophic fibers of the glands. Popielski has shown that a stomach with all nervous connections severed will secrete gastric juice, if extracts of meat are placed in the stomach. Edkins believes this secondary secretion of gastric juice to be due to the action of the products of digestion on the pyloric mucous membrane. They produce in the membrane a chemical sub- stance, which is absorbed into the circulation, and, conveyed to the glands of the stomach, it acts as a specific excitant of their secretory activity. Starling calls it a gastric secretion or gastric hormone, similar to the secretin-exciting pancreatic secretion. Secretory Nerves of the Stomach. In a dog with a cannula in the stomach and the oesophagus opened so that food leaving the mouth goes through the opening in the oesophagus, and not into the stomach ("sham feeding"), the swal- DIGESTION. lowing of food caused a great increase of flow of gastric juice. If, now, the pulmonary and abdominal vagi are divided on both sides, then sham feeding causes no flow of gastric juice. These experiments show that the gastric glands receive their normal impulses to activity by means of nerve-fibers in the vagi. Pawlow believes that secretory nerves of the stomach run in the vagi. Pawlow also excited the vagi after a previous section for some days and obtained an increase of Pylorns Plexus gastricui Anterior vagi CEsophagns II. Fig. 18. — Dog's iStomaeh. (Pawlow.) I. A-B, Line of incision. C, Flap for forming stomach-pouch of Pawlow. II. 1', Cavity of large stomach. S, Pawlow's pouch, or small stomach. A, A, Abdominal wall. gastric secretion. Atropine paralyzes the secretory nerves of the stomach. By the secretory fibers we mean those, according to Heid- enheim, which stir up the secretion of water and inorganic salts of the gastric juice. The trophic fibers are concerned in the secretion of the ferment of the gastric juice. Sooner or later after the taking of food the influence of the reflex excitant comes into play, while the 78 PHYSIOLOGY. psychic effect dies out. If meat has been eaten, the secretory center will still be strongly excited in a reflex manner from the stomach and intestine, while, at the same time, the trophic center receives only weak impulses from the peripheral terminations of the nerves in ques- tion. When bread is eaten the reverse happens. After the cessa- tion of the psychical stimulus, the secretory fibers are now only weakly excited through the end-apparatus; the trophic, on the other hand, are strongly influenced. In the case of fat foods reflex inhibitory impulses proceed to the centers which affect the activity of both secre- tory and trophic nerves. ACTION OF AGENTS ON THE STOMACH. When absolute alcohol or a strong emulsion of oil of mustard was introduced in the small stomach (Pawlow), there was an enormous secretion of mucus. Ice-cold water in the large stomach (Pawlow) causes the secre- tion, which is subsequently produced by an ordinary meal, to be less than normal, more especially in the first hour; here is a special inhibitory reflex. When alcohol is poured into the large stomach (Pawlow) an extremely free secretion of gastric juice Ijegins in the small stomach (Pawlow). The secretion in the small stomach was compensatory for the arrested secretion in the large stomach. In hypersecretion of the stomachs of dogs he found sodium bicar- bonate to have a good effect. In hyposecretion he found water a good agent. Borrisow has shown that bitter substances, such as gentian, excite the flow of gastric juice. Hydrochloric acid, when secreted in considerable quantity, pre- vents further secretion of gastric juice. Phosphoric acid does not inhibit. Butyric acid strongly excites gastric secretion. ACTION OF THE GASTRIC JUICE. The amylolytic action of the saliva, the conversion of starch into maltose, is dependent upon the presence of ptyalin, an organic fer- ment whose actipn is best carried on in a neutral or alkaline medium. The proteolytic action of the gastric juice is due to the presence of its organic ferment, or enzyme, — pepsin, — in an acid medium. A par- tial digestion of certain foodstuffs can be accomplished in an acid solution, if given sufficient time and the proper temperature. There is, however, a strong tendency toward putrefaction during the pro- DIGESTION. 79 cess. On the other hand, pepsin alone is unable to perform any dis- solution or digestion of the foods with which it comes into contact. But, if to it a 0.2-per-cent. solution of hydrochloric acid is added, proteolysis proceeds quickly and energetically. The powers of the gastric juice cannot ])e attributed to the presence, then, of its acid or pepsin alone, but to a combination which may be termed pepsin-acid. Thus gastric digestion is an acid digestion, and demands a knowledge Fig. 19. — Dogs to whom a Fictitious Meal is Given. They have a fistula in the ossophagus and a fistula in the stomach. After a photo- graph taken in the laboratory of Pawlow. (Gley. ) of chemistry, for it is in many respects a chemical act. The result of the action of gastric juice on food is essentially the same whether the act takes place within the body or outside of it. Life has nothing to do with it, for it is a chemical action on the protcids of the food. In the stomach, then, the main process of digestion is the conversion of the proteids, through intermediate stages, into peptones, for pro- 80 PHYSIOLOGY. teids are incapable of diffusion through animal meml>ranes in the act of absorption. Thus it can safely be stated tliat tlie prime and essential func- tion of the gastric secretion is to dissolve the proteids present and convert them inio peptones. Gastric juice exercises no amylolytic influences upon any starch present; in fact, three-fourths of an hour after a meal, the action going on due to the saliva swallowed with the food is stopped alto- gether by reason of traces of free hydrochloric acid secreted by the oxyntic cells. There is a fat-splitting ferment in the gastric juice of the fundus. Those mineral matters which can be dissolved in hydrochloric acid of the strength of that found in the gastric juice are also dis- solved in the stomach. The degree of solubility and efficiency at- tained by the gastric secretion far surpasses that of simple, diluted acid, probably because of the pepsin found in the former. Although the amylolytic action of the saliva on starch takes place for a definite interval, the gelatinous envelopes of the fat-globules and mineral substances are dissolved within the receptacle of the stomach, yet the essential and characteristic feature of the work to be done there is on the proteids: converting them into peptone through the action of proteolysis. The proteids found in Nature are very complex and as yet not thoroughly known. However much they, as individuals, may difEer in composition, reactions, etc., yet they all possess an inherent ten- dency to undergo hydrolytic decomposition when conditions are favor- able. Hydration and cleavage can be induced by simple heating in water alone raised to the temperature of 100° C, for there results par- tial solution of the proteids during the process. The proteolytic pro- cess of the gastric secretion in its converting proteids into peptones is also one of Jiydration and cleavage. The final products are not the result of one simple step, not the formation of one simple body or substance, as when the proteids are acted on by heated water alone. The acid in gastric digestion induces a row of chemical changes and products, each separate and distinct, and capable of being recognized by certain reagents. By the action of pepsin-acid the proteid is first changed into (1) syntonin, or acid-alhumin. By further action of the ferment, the acid-albumins are changed into (2) proteoses, with their divisions into primary and secondary proteose. The proteoses are the intermediate products between acid-albumins and peptones. These are found un- DIGESTION. 81 der various names in this group; as, the proteoses may be derived from albumin, when they are called albumoses; or from globulin, when the name globuloses is used. The proteoses are soluble in warm water, acids, and the alkalies. They are only slightly diffusible and not coagulated by the action of heat. Nitric acid produces a white precipitate, which is colored yellow by heat and dissolved again. When cool, the precipitate occurs again ; this recurrence of the pre- cipitate upon cooling is a distinctive feature of proteoses. Ammo- nium sulphate precipitates proteoses and leaves the peptones in solution. By the continued proteolytic action of the gastric juice, the proteoses are changed into (;3) peptones, the final, diffusible products of gastric digestion. They are simply the result of a process of hydration. The peptones are very diffusible, particularly in acid solution. The utility and benefit to be derived from that characteristic is very evident when we keep in mind the chief aim of digestion, which is to render foodstuffs into soluble conditions so that they may be readily absorbed and so become a component of the blood and eventually of the tissues. The peptones are soluble in water, but not precipitated from their aqueous solutions by the addition of acids or alkalies, or by boil- ing. In fact, peptones are never coagulated by heat. They are not precipitated by nitric acid, copper sulphate, ammonium sulphate, and a number of other reagents usually held as precipitants of proteids. To differentiate albumoses from peptones, add a few drops of salicyl-sulphonic acid to several cubic centimeters of the original fluid. A white precipitate may indicate native proteid or proteoses. Boil, then the proteoses dissolve, whereas the native proteid becomes coagulated. Filter hot. If a precipitate forms in the filtrate on cooling, it indicates proteoses. Filter off this precipitate and apply the biuret test to filtrate. A rose-pink coloration indicates peptone. However, the chief and striking feature of peptones is their great diffusibility. Other forms of proteid matter pass through animal membranes with very great difficulty, if at all. When the proteids have lieen reduced to peptones, they are ready for absorption into the blood through the capillary walls. However, proteoses, the intermediate products, although less diffusible than peptones, find their way, to souie extent, also, through the capillary walls. Experiment has demonstrated that pure proteoses, or even peptones, introduced directly into the blood are more or less toxic, 6 82 PHYSIOLOGY. and the system behaves toward them as foreign bodies, striving to get rid of them as speedily as possible. From this it is evident that there must be some transformation in the very act of diffusion through the capillary walls, else the nutritions proteid matters are not used in constructive metamorphosis, but expelled as foreign matters. The agencies which act upon these proteoses and peptones, in some manner destroy their toxic tendencies and, probably, convert them into the serum-albumin, or globulin, of the blood. The fact that peptones are not found in the blood and lymph during or directly after digestion confirms this idea, since peptones are absorbed as soon as manu- factured. An excess of peptone in the stomach-contents would have the power to arrest proteolysis by its mere presence. A preparation on the market is somatose, a mixture of albumoses produced by the action of a ferment on meat. It is a predigested beef, and readily absorbed. It dispenses with the large amount of fluid which is neces- sary in peptonized milk. Weinland has shown that the epithelium of the stomach and of the intestines forms antipepsin and antitrypsin, which prevent diges- tion of the stomach itself or of the intestine, by the ferments, pep- sin and trypsin. Antiseptic Action of the Hydrochloric Acid in Gastric Juice. Besides the function which hydrochloric acid exercises as a com- ponent of the gastric secretion. — namely: of rendering the pepsin in it active, — it possesses another very powerful property as a dis- infectant and germicide in that it can kill many bacteria that are taken in with the food. By means of it the bacteria producing putrefaction are killed, and thus disorders in the entire constitution as a result of abnormal digestion are prevented. Even when putre- faction has occurred in the food previous to its entrance into the stomach, upon reaching this receptacle it is stopped. Many pathological bacteria are likewise destroyed by the acid in the juice, although some, as the bacillus of tuberculosis and that of splenic fever, are unaffected. It is interesting to note that experi- ment has shown that just about the amount and strength of hydro- chloric acid as that in the stomach is needed outside the body to ac- complish the death of putrefactive and many pathological germs. Acetic and lactic fermentations are arrested by mere traces of hydro- chloric acid. To epitomize: The general action of gastric juice is to convert DIGESTION. 83 the proteids into peptones by various stages. The fats are split up b}^ a gastric lipase. Starch is unaffected. The general result is the formation of a pouplike mass in the stomach. This undigested food is passed through the pylorus into the duodenum of the small intestine, and is called chyme. The average time that food remains in the stomach is about three hours. Giinzburg's Test for Hydrochloric Acid. — With a solution of phlorogluciu and vanillin in alcohol mix a drop of a solution of hydrochloric acid. 0.2 per cent. ; evaporate slowly in a porcelain cap- sule, when a red color will appear. TJffelmann's Test for Lactic Acid. — Add a trace of solution of ferric chloride to a 1-per-cent. solution of carbolic acid. This ame- thyst-colored solution will change to canary yellow on the addition of lactic acid. VOMITING. Vomiting is a spasmodic rejection of food from the stomach, and is usually a sign of some malady. The ease with which animals vomit is dependent upon the conformation of the stomach, particularly with regard to the fundus, as well as the condition of its contents. Thus, a child vomits easily, since its fundus is not very well developed; with the adult the act is one of great difficulty. When the person is conscious, vomiting is usually preceded by a sensation of nausea, during which the saliva flows very freely into the mouth. While the food is being swallowed considerable air enters the stomach, and later assists actual vomiting by helping to dilate the cardiac orifice. Before the real expulsion occurs, and during the efforts to accomplish the same, a very deep inspiration is taken just as in the act of coughing. Immediately the glottis closes, and the muscles of the abdomen commence to contract very actively. In- stead of the glottis opening to permit an expiration, it remains tightly closed, thereby holding the diaphragm immovably fixed, and so furnishing an unresisting plane against which the stomach is pressed. Immediately preceding the pressure brought to bear upon the stomach by the contraction of the abdominal muscles, there occurs a shortening of the longitudinal fibers of the oesophagus, thereby bringing the cardiac orifice of the stomach nearer the diaphragm, to form a straight passageway for the vomit to the phar}Tix. The muscles of the sphincter at the cardiac orifice are rather suddenly dilated, forming a funnel-shaped opening at the beginning of escape, since the pylorus usually remains closed. By the abdominal con- 84 PHYSIOLOGY. tractions and slightly assisted by gastric movements also, some of the contents of the stomach is forced into the opening of the oesophagus, where its movement toward the pharynx and mouth is aided by con- tractions of the oesophageal circular fibers : the reverse of what occurs when a bolus of food is swallowed. Thus there are two separate and distinct acts occurring during vomiting: (a) the dilating of the cardiac sphincter and (b) the expulsive movements of the abdominal muscles. The absence of either act is detrimental to the accomplishment of vomiting. The pyloric gate is usually closed during vomiting; so that little or no substances find their way into the duodenum. However, when the gall-bladder is very full, the movements of the surrounding organs force its contents into the duodenum and very frequently some of the bile finds its way into the stomach, from whence it passes out through the oesophagus, pharynx, and mouth in bilious vomiting, That the expulsive impetus is mainly given by the contractions of tlie abdominal walls and not the gastric movements alone has been proved by experiment. The stomach of an animal was excised and replaced with a bladder filled M'ith water and attached to the oesoph- agus by means of a rubber tul)e. When tlie wound was closed and an emetic injected, the contents of the bladder were immediately expelled through the mouth. Vomiting is normally considered to be a reflex action, although in some instances vomiting may proceed at will or be acquired after some practice. The afferent nerves are principally the fiftJi. the glosso-pharyngeal, and the vagus. The center of vomiting is located in the medulla oblongata. The efferent impulses are conveyed by the vagi to the stomach, phrenics to the diaphragm, and various spinal nerves to the abdominal muscles. Thus vomiting may arise: — 1. From irritation of the stomach, as when this organ is too full. 2. From tickling the vault of the palate. 3. From intestinal irritation by worms. 4. From irritation of the uterine mucous membrane during the first three months of pregnancv. 5. The remembrance or siglit of disgusting sights, or pathological- disorders of the brain may cause it, which proves that the brain is united to a vomiting center. 6. The use of emetics, which do not all act alike. Thus, some emetics, as copper sulphate, mustard, etc., produce emesis because of their irritating effects upon the peripheral nerves DIGESTION. 85 in the mucous membrane lining the stomach. Others, like tartar emetic, apomorphine, etc., attain the same results by reason of their • stimulating the vomiting center in the medulla. DIGESTION IN THE INTESTINES. When the food is converted into chyme and partially dissolved by the gastric juice, it passes into the small intestine, where it is subjected to new reagents: the bile, pancreatic juice, and intestinal juices. Here the food is prepared for absorption, forming what is called chyle, which is rapidly taken up by the chyliferous vessels. Because of the small and large calibers of the two parts of the intestinal tract, the portions have received the names of sinall and large intestines, respectively. The small intestine, the continuation of the stomach, opens into the large intestine by an orifice which is guarded by the ileo-ccecal valve. Under ordinary and normal condi- tions this valve allows the passage of the remnants of active digestion to pass through from the small into the large intestine; very rarely does the reverse occur, except in some cases of hernia and other ob- structions in the large intestine. THE SMALL INTESTINE. This tube is cylindrical and much convoluted. It occupies the umbilical region and is suspended from the vertebral column by the mesentery. It measures about twenty-five feet in length, and its diameter is about one and three-fourths inches. As it continues to join the large intestine it becomes slightly narrower. It consists of three parts: the duodenum, jejunum, and ileum.. The duodenum is twelve fingers' breadth in length, and it is the widest part of the small intestine. It commences at the pyloric end of the stomach and opposite the second lumbar vertebra; it terminates in the jejunum. The common bile-duct and the pan- creatic duct perforate the inner side of the duodenum. The jejunum constitutes about two-fifths of the small intestine. It is wider than the ileum and is characterized by the absence of the agminated glands. The ileum constitutes three-fifths of the small intestine, and terminates in the right iliac region by joining the large intestine at a right angle. 8G PHYSIOLOGY. Structure of the Small Intestine. Like the stomach, the intestine has four coats: (1) the external serous, (2) the muscular, (3) the submucous, and (4) the mucous coat. The serous coat is furnished by the peritoneum. The mus- cular coat is composed of two layers of pale, unstriped fibers, the ex- ternal layer of longitudinal fibers, and the internal layer of circular fibers. The submucous coat is thinner than that in the stomach, but is also extensible. The mucous coat is thinner and redder than that of the stomach, and, like it, has a columnar epithelium. It has folds of mucous and submucous tissue, running in a transverse direction and in the shape of a crescent, which are called the valvule conniventes. These valv- ulse are more abundant in the upper part of the small intestine. Fig. 20. — Portion of the Wall of the Small Intestine, Laid Open to Show the ValvultB Conniventes. (Brinton, Raymond.) where they overlap the edges. As you go down the small intestine you find the numl)er of the valvule gradually lessen, and in the ileum they disappear. These folds are permanent. The minute elevations called villi beset the mucous membrane of the small intestine and even the valvulre conniventes. They give a velvety appearance to the surface of the small intestine. In the upper part of the small in- testine the villi appear as fine folds, but farther down the intestine they appear as flattened, conical projections. The villi are V40 inch in height, and in structure are appendages of the intestinal mucous membrane. Villi.* Upon the surface of the villi you find an epithelium of regular cylindrical cells. The border cells of the epithelium of the villi have a broad, finely striated border which spreads over their ends like a cuticle or mosaic. The other end of the cell often ends in a point * Szymonowics's Histology has been drawn upon in the description of the villi. DIGESTION. 87 and is separated from the underlying tissues by a thin basal mem- brane. Each cell consists of a granular protoplasm containing an oval, well-defined nucleus lying in its lower half, in which a distinct nucleolus appears. The epithelial cells are joined together in bridges of a protoplasmic nature, with spaces between the bridges filled with cement substance. In cholera and in poisoning by arsenic these cells are shed. Between the epithelial cells roundish structures, either single or in small groups, and of a diameter greater than the epithelial cells, appear. They are quite transparent, have no true Fig. 21. — Blood-vessels of an Intestinal Villii.g. (Landois.) Un, Capillaries. A, Artery, CI, Cylindrical epithelium. O, Surface of the epithelium. V, Vein. cell-membrane, and only a thickened ectoplasm, which undergoes no mucoid change. These cells are goblet-shaped, full of protoplasm, containing a compressed nucleus. It is generally considered that these two kinds of cells, the cylindrical and the goblet, are separate in origin ; that is, a young epithelial cell cannot become changed into a goblet cell. The goblet cells discharge mucin, which goes to form the mucus. Fasting, active digestion, and excessive doses of pilo- carpin increase their number. Going inward from these cells we meet in the villus a base- ment membrane, immediately beneath it the blood-vessels, then the 88 PHYSIOLOGY. fibers of the muscularis mucosa and a single lacteal or lymphatic vessel. The body of the villus is composed of adenoid tissue, closely invested with small and numerous bundles of smooth muscular fibers arranged in a longitudinal and in an oblique direction, and derived from the muscularis mucosa. The longitudinal fibers, when they contract, shorten the villus and with the valves in the lacteal empty it, whilst the oblique fibers keep the lacteal open. These muscular fibers are attached to the sub-epithelial basal membrane. The lymph-spaces in the adenoid tissue form a network of channels com- municating with each other, and contain leucocytes and fine globules of fat, which have passed through the spaces between the epithelial Fig. 22. — Mucous Membrane of the .Jejunum, Highly Magnified, (schematic). (Testut, Raymond.) 1, 1, Intestinal viUi. 2, 2, Closed or solitary follicles. 3, 3, Orifices of the follicles of Lieberkiihn. cells on the border, then through the basal membrane, through the lymph-spaces of the parenchyma of the villus, and finally enter the lacteal. The lymph-vessels end in the upper part of the villus, in a blind extremity, and show a certain degree of anastomosis, and when joined form the central chyle-vessel or lacteal. The lacteal lies in the center of the villus, whilst the artery enters to one side of it and spreads out into a network of capillaries, like an umbrella, over the lacteal immediately underneath the epithelium of the villus. The number of the villi has been estimated to be about four millions. DIGESTION. 89 Glands of the Small Intestine. There are four kinds of glands in the mucous membrane of the small intestine. They are: duodenal, or Brunner's; glands of Lieberkuhn ; solitary ; and agminated glands, or Peyer's patches. Brvmner's glands are small, racemose glands situated in the sub- mucous tissue of the duodenum. Toward the end of the duodenum they gradually disajjpear. The glands of Lieberkiihn are the most numerous of all the glands of the small intestine, and they exist from the pyloric end to the ileo-c£ecal valve. They are placed in a vertical direction in the thickness of the mucous membrane and open between the villi. They are about Vioo inch in length. They have thin walls lined with a columnar epithelium. The solitary glands are found in all parts of the mucous mem- brane of the small intestine. They are minute, whitish, oval or rounded bodies scattered singly in the intestine. They are closed vesicles, and are situated in the submucous tissue. They are lymph- nodules composed of retiform tissue and lymphocytes. The agminated glands (Peyer's) are formed of solitary glands, disposed in oval patches. Usually there are fifteen to thirty of these patches, from one-half to two inches in length, and one-half inch in breadth. The ileum is their usual habitat, and they are seated oppo- site the attachment of the mesentery. In the neighborhood of the ileo-csecal valve they are larger and more numerous. As the duo- denum is approached they are smaller and fewer. In youth they are distinct, less so in adult life, and in old age may disappear. They are the seat of ulceration in typhoid fever. The arteries of the small intestine are the superior mesenteric and pyloric. The lymphatics are numerous. The nerves are given off by the solar plexus. Be- neath the mucous coat in the areolar tissue of the small intestine are Meissner's ganglia. Between the muscular coats the ganglia of Auer- bach can be found. THE LARGE INTESTINE. This is a cylindrical tube differing from the small intestine in having a greater capacity and a sacculated appearance. It is about five feet in length and extends from the ileo-csecal valve to the anus. It nearly encircles the abdomen in its course. Like the small intes- tine, it is divided into three parts: the caecum, colon, and rectum. The head of the colon, the c»cum, is a wide, blind pouch, or cul-de- 90 PHYSIOLOGY. sac,, about two and one-half inches in length and breadth. Toward its bottom it curves inwardly and backward and is abruptly reduced to a wormlike prolongation — the vermiform appendix. The small intestine opens into the csecum, the orifice being guarded by the ileo- ca3cal valve. The second and largest part of the large intestine is the colon, and it extends from the caecum to the rectum. It consists of four parts : the ascending, transverse, and descending colon, with the sigmoid flexure. Its diameter is greatest at its commencement, being about two and one-half inches; but it gradually lessens to an inch. The sigmoid flexure is shaped like the letter S. It is the nar- rowest part of the colon. The rectum extends from the sigmoid flex- ure to the anus. It is about seven inches in length. When distended the rectum is club-shaped, being narrow above and expanded just before it contracts to the anus. The anus is completely surrounded by a sphincter muscle. Structure of the Large Intestine. The caecum and colon, like the small intestine, have four coats : the (1) serous, (2) muscular, (3) submucous, and (4) mucous. The mucous membrane contains two kinds of glands: the glands of Lie- berkiihn and the solitary glands. The glands of Lieberkiihn are closely set together and give a peculiar sievelike appearance to the surface of the mucous membrane. Experiments upon the CECcum of the cadaver prove that the action of the ileo-caecal valve is not dependent upon muscular con- traction, for fluid forced through the large intestine rarely passes into the ileum. When the cscum is filled the dilatation of the same presses upon the folds of the valve so as to press them tightly together and thus prevent any reflux into the small intestine. MOVEMENTS OF THE INTESTINES. As was the case with the oesophagus, the intestines are com- posed of two muscular coats : an outer longitudinal one and an inner circular one. Movements in them are caused by alternate contrac- tions and relaxations of adjoining portions of the tube. To the characteristic movements of the intestines two names have been given to describe two separate forms: (1) peristaltic and (2) pendular. Peristalsis. — By this term is implied the alternate contractions and dilatations of adjoining segments to produce a wavelike motion which proceeds from its point of origin anywhere along the intestinal tract aivay from the stomach. "Antiperistalsis" is the term used to DIGESTION. 91 designate the movements running in an exactly opposite direction: that is, toward the stomach. Pendular Movements. — These are the very slight swinging to- and-fro oscillations, probably caused by the contractions of the longi- tudinal fibers. Cannon has shown that in the cat, when fed, a portion of the small intestine may be seen, with its continuous contents, to sud- denly be divided into segments. These segments are then also sub- divided. This segmentation of the intestinal contents does not move the food along. A peristaltic wave does that. These movements incor- porate the food with the ferments. When a peristaltic wave reaches the ileo-colic sphincter, it relaxes and permits the intestinal con- tents to pass into the colon. If a reflux wave of the colon takes place, it contracts, when the proximal part of the colon is distended - Then contractions, an antiperistaltic wave, travel from the point of union of the ascending and transverse colon tow^ards the caecum. Then peristaltic Avaves drive the contents into the distal colon. In the large intestine, the distal part of the colon and its adjacent sigmoid flexure are a resting place for the faeces, and are concerned in defecation. The chief point about the distal colon is its complete subordination to the spinal cord. The ileo-colon, the transverse colon, and the descending colon are a place for the pro- pulsive peristalsis, as the descending colon is never distended. NERVE=SUPPLY OF THE INTESTINES. The small intestine receives fibers from the greater and smaller splanchnic nerves, which pass through the semilunar and superior mesenteric ganglia, and then pass along the mesenteric arteries to their destination. The right vagus also supplies the intestine with fibers. The sympathetic ganglia of Auerbach lie between the two mus- cular coats and extend from the oesophagus down throughout the small and large intestine. Meissner's ganglia, also belonging to the sympathetic system, lie in the submucous coat. The vagi convey motor impulses to the intestine, while the sympathetics mainly con- vey inhibitory, although they also carry motor, impulses. Slight stimulation of the splanchnic ealls out motion, strong stimulation inhibition of the intestinal movements. I have found that, when the right vagus is divided in a rabbit and the cardio-inhibitory fibers are allowed to degenerate for five days, electric stimulation of the cut vagus slows the pendular movement. 92 PHYSIOLOGY. Stimulation of any portion of the intestine causes contraction above the place of irritation, and inhibition or relaxation below the point of irritation. This causes the food to move onward, and is due to Auerbach's plexus. This is the "kw of the intestines," accord- ing to Bayliss and Starling. ^m^^ki^-^^^'^''' mm w'vm:wmMi}BM!ESSmmm Fig. 23. — Effect of Albumose, increasing Peristalsis. The descending colon has its nerve-supply from two sources: (1) fibers from lumbar nerves to sympathetic chain and mesenteric ganglia, and from the mesenteric ganglia, by fibers running in the hypogastric nerves and plexus; (2) fibers from sacral nerves, run- ning in the nervi erigentes and entering the pelvic plexuses, which are motor and antagonize the preceding fibers, which are inhibitory. When the small or large intestine is excised, it has peristaltic move- ments, which are due to Auerbach's plexus acting as a reflex center. DIGESTIOX. 93 I have found that albiimoses and peptones increase peristalsis. This has been confirmed by Eoger. Atropin increases the peristaltic movements, probably by an action on the post-ganglionic fibers. Langley believes that nicotine and curare, in intestinal peristalsis, act on a substance intervening between the nerve-ends and the muscle, a mvoneural substance. Fig. 24. — The Pancreas. (Posterior View. [ BOURGERY. ) 1, Duodenum. 2, Duct, choledicus. 3, Duct of Wirsung. 5, Union of the two ducts. 7, Accsssory duct. The distension of the al)domen, in many diseases of this region, is probably due to a reflex inhibition by the way of the splanchnic nerve, which has power over the tonus of the caliber of the intes- tine. Salines are supposed to act as aperients by their presence in the blood, causing an increased secretion to be poured out by the blood- vessels into the intestinal canal. The theory of endosmosis has been abandoned. 94 PIIYSIOLOCY. PANCREAS. The pancreas is a long gland, of a reddish-cream color, and is situated behind the stomach. Its pointlike extremity comes in con- tact with the spleen. It closely adheres to the duodenum. It is about seven inches in length, its width about one and one-half inches, and its thickness about one-half inch. The right and large end is the head; its left free end is its tail. The duct of Wirsung, or the pancreatic duct, the size of a goose-quill, runs the entire length of the gland. Upon leaving the pancreas the duct penetrates the wall of the duodenum, opening in conjunction with the common biliary duct, about three inches from the pylorus. 7 (> Fig. 25. — Schematic Section of Pancreas. (Vialletox.) 1, Origin of excretory canal. 2, Centro-acinar cell. 3, Pancreatic cell. 4, Granular internal zone, zymogen granules. 5, External zone, clear part of cell. 6, Nucleus. 7, Accessory nucleus. Structure. In structure the pancreas is an acino-tubular gland, resembling the salivary glands. In fact, it has very frequently been called the abdominal salivary gland. The lobes are composed of ducts which have been convoluted, terminating in alveoli or sacs and which unite with other tubules so as to communicate with the main duct. The small ducts are lined with short columnar epithelial cells which are smaller than those of the salivary glands. The secretory cells of the pancreas are large and rounded, being distinctive in that they possess an outer portion which is nearly or quite homogeneous, stain- ing readily with dyes, and an inner portion, very granular, which does not stain easily. The latter forms about two-thirds of the cell. When the gland is inactive the cells are heavily charged with DIGESTION. 95 granules and the lumen is almost invisible. When active, the cells first swell up and press outward against the basement membrane; later they diminish in size as the granules pass out through the now opened lumen, and so leave a large, clear zone. The presence of these numerous small granules marks the presence, in tlie cells, of a zymogen, termed tnjpsinogen, which is the precursor of trypsin, the active ferment of the pancreatic juice. In the interalveolar tissue are islets of small cells permeated with a close network of convoluted capillaries. These cells are also met with in the carotid and coccygeal glands. In the pancreas they are called cells of Lan- gerhans, centro-acinar cells, and are often degenerated in pancreatic diabetes. A B Fig. 26. — Pancreas of Ral)bit Observed During Life. (KuHJfE and Lea.) (From Tigerstedt's "Human Physiology-," copyright, 1906, by D. Appleton and Company.) A, Resting glaud. B, Secreting gland. The pancreatic blood-vessels are derived from the splenic and branches of the hepatic and superior mesenteric. Its nervous suppl}'' comprises networks of fibers from the splenic plexus. Pancreatic Secretion (Pawlow). Each kind of food determines the secretion of a definite quan- tity of pancreatic juice, while the result as regards ferments is truly striking. The greatest amount of proteid ferment is foun hretxcL m/lfc. ; J I 0 it f 1 ' '* Zn 3 « 3 / \ 1 - 1 ■ ' - \ \ / \ / \ \ \ 1 s / \ ^ \ \ \ / Xr^ i 2 3 * 5 1 t 3 * 5 f 7 a "1 J ^ J i Fig. 27. — Hourly Variations of the Pancreatic Secretion after a Meal of Meat, Bread, and Milk. (After a curve obtained in the lab- oratory of Pawlow by one of his pupils, A. Waltheb. ) also that administration of like quantities of proteid in the form of bread, flesh, and milk calls forth a secretion as regards the first of 1978, as regards the second of 1503, and as regards the third of 1085 ferment units ; that is to say, vegetable proteid likewise demands from the pancreas the most, milk and milk proteid the least, ferment. The difference between the stomach and the pancreas is limited to this : that the former pours out its ferment in very concentrated form upon bread, the latter in a very dilute condition. This fact strengthens the supposition that in the digestion of bread a large accumulation of hydrochloric acid has to be avoided. DIGESTION. 97 When in feeding animals the kind of food is altered and the new diet maintained for a length of time, it is found that the ferment- content of the juice becomes from day to day more and more adapted to the requirements of the food. If, for example, a dog has been fed for weeks on nothing but milk and bread and is then put on an exclusive flesh diet, which contains more proteid, but scarcely any carbohydrate, a continuous increase of the proteid ferment in the juice is to be observed. The capability of digesting proteid waxes from day to day, while, on the contrary, the amylolytic power of the juice continuously wanes. When under the influence of a given diet this or that condition of the pancreas had been established in experiment-animals in char- acteristic form, Pawlow was al)le, by altering the feeding, to reverse it several times in the same animal. It seems then that the gastric and pancreatic glands have what may be called a form of instinct. They pour out their juice in a manner which exactly corresponds both qualitatively and quantitatively to the amount and kind of food partaken of. Besides, they secrete precisely that quantity of fluid which is most advantageous for the digestion of the meal. Hydrochloric acid of gastric juice acts on pro-secretin in the epithelium of duodenal mucous membrane, producing secretin, a hormone^ which, when absorbed, greatly excites pancreatic secretion. Fats in the stomach retard stomachic secretion, but increase pan- creatic secretion, chiefly by a reflex action through the duodenum, and not from the mucous membrane of the stomach. Sleep does not arrest pancreatic secretion. Psychical effect, strong craving for food and water, are common excitants for both gastric and pancreatic secretion. The extractives of meat excite the gastric secretion, while acids and fats excite the pancreas. Sodium bicarbonate and alkalies inhibit pancreatic secretion. Secretory Nerves of Pancreas. In nonnarcotized dogs whose vagus was divided four days pre- viously and whose cardio-inhibitory fibers had lost their irritability. Pawlow irritated the vagus without pain and obtained an increased pancreatic secretion. He found that vasoconstriction of the pan- creatic vessels prevented the action of the vagus on the pancreas, as did compression of the aorta and pain. He also found in the vagus ^Hormone is derived from a Greek word, meaning to excite. 7 98 PHYSIOLOGY. inhibitory fibers of the secretion, as well as secretory. He believes that secretory fibers also run in the symj^athetic, not only for the pancreas, but also for the stomach. The usual method of obtaining pancreatic juice for experimental purposes is by insertion of a cannula or by a fistula into the duct of Wirsung. By this method practically normal secretion is procured, whose composition is variable at difEerent times, depending upon whether the fluid is collected three or four hours, or two or three days, after the operation. The secretion examined shortly after the operation is meager in quantity, though rich in solids; that collected a day or two later is more copious, but contains a smaller proportion of solid constituents. This is })robably due to inflammatory changes in the pancreas as a result of the operation. The pancreatic juice examined is usually obtained from dogs, human secretions of the gland having been but rarely analyzed, and it has never been obtained under quite normal conditions. Most experiments are performed with the aid of an artificial juice made by mixing a weak solution (1 per cent, sodium carbonate) with a glycerin extract of pancreas. It is usual to treat the pancreas with a dilute acid several hours previous to its being mixed with glycerin to convert the zymogen, or mother- substance, trypsinogen, into the ferment, trypsin. Normally, the pancreatic juice is colorless, viscid, and gummy; it flows in large, pearl-like drops, which become foamy on agitation. The fluid is without odor, and gives to the tongue an impression of a viscid liquid and a taste like that of salt. The reaction is always alkaline; its specific gravity about 1.030. In consequence of the removal of a pancreatic tumor Zawadski obtained human pancreatic juice through the fistula remaining, whx'h possessed powerful digestive properties, and found it to be made up of the following composition in a thousand parts: 135.9 parts were of solid nature, the remaining ones being water. Of the solid portions, 92 were proteids. 3.4 parts were inorganic in nature, while the re- mainder were organic substances soluble in alcohol. The figures rep- senting the quantities of secretion in twenty-four hours are very various as given by difl^erent observers, but it has been roughly esti- mated to average about 8 ounces. The flow of pancreatic juice is somewhat as follows : Before the meal is finished there begins the secretion, wliich reaches its maximum point at about the third hour. After this the secretion sinks till about the sixth or seventh hour, when it increases to the ninth or eleventh hour, only to sink gradually to the eighteenth or twentieth. When DIGESTION. 99 the quantity is greatest the quality is poorest, and vice versa. Thus the function of the jiancreas in man is intermittent. During secre- tion the ghmcl is very red, and its vessels dilated, and the venous blood red. During repose the gland is flat and of a pale-yellow color, while its blood-vessels are contracted. The secretion is probably caused by secretin and the reflex action due to the contact of the foods. The pancreatic secretion can be moderated or suppressed equally by reflex action, notably in vomiting. Of the 3.4 parts of an inorganic nature, the most abundant is sodium chloride, with alkaline and earthy phosphates and alkaline carbonates. The alkalinity of the Juice is due principally to the phosphates of sodium. Pilocarpine increases the secretion, while atropine diminishes it. The organic matters of the pancreatic juice comprise four prin- cipal enzymes or ferments. They are: (1) trypsin, (2) amylopsin, (3) steapsin, and (4) a mill: -curdling ferment. Trypsin, a very important constituent of the pancreatic secretion, is much like pepsin of the gastric juice, in that it is a proteolytic enzyme acting on the proteids and transforming them into peptones through intermediate stages. However, its fermentative powers are much stronger and its range of activity extends over more space than do those of pepsin. Atlhough pepsin and trypsin possess many prop- erties in common, yet they are distinctly different and separate bodies. The main, characteristic difference is that pepsin requires an acid medium for its activity, while trypsin acts and performs its functions best in an alkaline solution whose strength ranges from 0.5 to 1 per cent. Experiment has proved that trypsin can act in a neutral or very slightly acid medium. A remarkable feature of trypsin is the large and rapid transfor- mation of proteid matter of any kind into peptone. This it produces when in only a moderately strong solution. Thus, it is a very capable body to take up the work of proteolysis where the pepsin of the gastric juice left it. since it is particularly a peptone-forming ferment. As the final products of proteolysis, there result peptones. When these come into contact with the pancreatic juice, they are quickly broken down into simple, crystalline bodies, as leucin. tyrosin, aspartic acid, arginin, and a polypeptid. Like pepsin, the proteolytic action of trypsin is one of contact also, only it displays its powers more remarkably an. — AciTE Leik.emia. The upper portion is stained Avith Ehrlich's stain with eosin-hematoxylin : the lower portion is stained with the Plehii-C'henzin- sky's stain. (Lenliartz-lirooks. i THE BLOOD. 165 combination with the haemoglobin, with which the gas unites very readily. Because of this fact it falls to the lot of these little bodies to perform a very important function for the economy, viz. : to con- vey oxygen from the lungs to the tissues to be distributed to them. The 0 is held by the hcemoglobin so lightly that it can be very readily extracted from the corpuscles by the cells of the tissues. Upon the blood depends the internal respiration of the tissues and all oxidation processes. While there is undoubted active oxidation occurring in the blood itself, yet the blood is not the place of the oxidation in the body. The cause is in the living cells of the tissues. In addition to an inherent affinity possessed by the tissues Fig. 49. — Human and Ampliibian Blood-corpuscles. (Landois.) A, Human red blood-corpuscles: 1, on the flat; 2, on the edge; 3, rouleaux of red corpuscles. B, Amphibian red corpuscle: 1, on the flat; 2, on edge. C, Ideal transverse section of a human red corpuscle, magnified 5000 times. a-h, linear diameter; c-d, thickness. for oxygen, its passage from the blood to the tissue-cells, as also the passage of carbon dioxide from the cells back to the blood- stream, depend very materially upon differences of pressure of these two gases in the blood and tissues. The direction is always from a higher pressure to a lower one. A peculiar inherent power and property of red corpuscles is to arrange themselves, when withdrawn from their retaining vessels, in the form of rolls of coin, adhering to one another by some peculiar affinity. To describe this condition the term rouleaux has been used. This peculiarity becomes particularly marked when 166 PHYSIOLOGY. there is an inflammatory state of tlie s3'steni. Formation of rouleaux can ))(■ ])reveiited by the iiijeclioii of physiological saline solution. Parasites of Blood-corpuscles. — In the red corpuscles of some birds and fishes the microscopist frequently notices small, trans- parent spots. These are "pseudovacuoies/"' in which may be devel- oped and later shed into the blood-stream small parasites. Within the red corpuscles of man, when affected by malaria, are developed the riasmodium malariw. Their passage into the patient's blood- plasnui marks a paroxysm. The number of the corpuscles is usually spoken of in terms of cul)ic millimeters; thus, in man there are about 5,000,000 per cubic millimeter; in woman, about 4,500,000. These figures represent the average number per cubic millimeter, but even in health and in the same individual there may be wide variations from this standard given, to say nothing of the extreme diminution experienced in cer- tain pathological conditions. As the corpuscles are small bodies floating in a liquid medium, the student can easily understand why their number should be in inverse ratio to the quantity of plasma, when the unit, cubic milli- meter, is considered. Copious sweating and the loss of much water by way of the bowels and kidneys occasion a temporary increase in their number. Normally, there is no difference as to the number of corpuscles in arteries and veins, provided there be no congestion in the latter. A most interesting variation is that produced by habitation in high altitudes. A two weeks' sojourn in a high mountain has been known to show an increase from 5,000,000 to 7,000,000 per cubic millimeter. This is accounted for Ijy a real increase in the manufac- ture of corpuscles. In chlorosis and pernicious anaemia the corpus- cular count falls considerably. A decrease to half a million per cubic millimeter is the lowest limit compatible with life. Life-cycle of the Red Corpuscles. — The life of the red corpuscle is unknown. In experimental transfusion the red corpuscles disap- pear at the end of a variable period. The destruction of blood- corpuscles in extravasations does not give us any precise results. Observing the differences in color, consistency, and chemical reac- tion, it is found that they correspond to the different degrees of development. This shows that in the blood there is a constant destruction and renewal of the corpuscles. As to the place of destruction of the red corpuscles, certain THE BLOOD. 167 facts show that the liver and spleen seem to he places for the accom- plishment of it. Counting- Red Corpuscles. — Various methods have been devised for connting- the number of corpuscles, the instruments used receiv- ing the name lia'macijtometers. Modifications are numerous, but underlying all of them is one main principle, namely: the actual counting of the corpuscles within a certain measured bulk. To Fig. 50. — Ilasmacytometer of Thoma-Zeiss. (L.\housse.) -l, Capillary glass tube. B, A glass slide upon which is a covered disc accurately ruled so as to present 1 square millimeter divided into 100 squares of ^/oQ millimeter each. 1, Blood is drawn up to this point. 101 represents normal saline-solution drawn up the tube, mixed with the blood drawn up to 1. In 101 parts the blood forms 1 part. preserve the shape and integrity of these little bodies during the technique it is necessary to dilute the sample of blood with some solution whose specific gravity exactly equals that of the blood- serum. Some of this blood-solution is then placed upon a grad- uated slide beneath a microscope for counting, when the number per cubic millimeter is easily computed. 1G8 PHYSIOLOGY. At this point the attention of tlie student will be directed' to but two instruments: (1) the Thoma-Zeiss apjiaratus, aiid {2) the Daland hu'iiiatocrit. 1. Tuoaia-Zkiss Apparatus. — The apparatus consists of two separate and distinct parts: a capillary tube and a counting cham- ber. The tube is for the purpose of measuring the amount of blood whose corpuscles are to be counted. By it also is accomplished the proper dilution in the upper, bulbed chamber. The capillary por- tion of the tube is graduated to 0.5 and 1.0 marks. Just above the capillary portion of the instrument is the bulbous portion, contain- ing a small glass ball to assist in the thorough mixing of blood and diluting normal saline fluid. Just above the bulb is the 101 mark. For drawing both blood and the diluting saline into the apparatus there is attached a piece of rubber tubing with a suitable mouth- piece. With the blood up to the 1.0 mark and enough diluting saline to bring the whole quantity of liquid to 101, the dilution is 1 to 100. Fig. 51. — Daland's lisematocrit. The second portion of the instrument, known as the counting chanihcr, is constructed so as to enable one to count under the micro- scope all the cells in a known bulk of the diluted blood. In the center of a thick glass slide is cemented a cover-glass of accurately measured thickness with a hole in the center of about 1 centimeter in diameter. In the central area of this cover-glass there is also cemented to the glass slide a glass disc about 2 millimeters smaller in diameter and exactly V^q millimeter thinner than the cover-glass. The glass shelf being exactly ^/^o millimeter thinner than the cover- glass, it will readily be seen that if a second loose cover-glass be laid upon the first, the under surface of this loose cover-glass will be exactly ^/^q millimeter above the upper surface of the glass disc. In this way there is secured a layer of fluid ^/k, millimeter in depth. Furthermore, 1 square millimeter of the surface of the disc is out- lined and subdivided by intersecting lines into 400 small squares. For convenience in counting, every fifth row of squares is divided into two by an additional line. The volume of diluted blood above each square of the micrometer will be ^Aooo cubic millimeter. The average of 10 or more squares is then ascertained, which result is THE BLOOD. 169 multiplied by 4000 times 100 to give the number of corpuscles in a cubic millimeter of undiluted blood. The H.iiMATOCRiT. — A rapid approximate determination of the relative percentage of the corpuscles may be made by Daland's iiistrument. The blood is sucked up the graduated tube without dilution and then centrifuged. The corpuscles rapidly accumulate at the end of the tube in an almost solid mass, and their collective volume can be directly read off. The estimate can be made with a small quantity of l)lood, and is, therefore, capable of being used for clinical jnirposes. Daland found that 50 was normal; this, multi- plied by 100,000, gives the number of corpuscles in 1 cubic milli- meter. Fig. 52. — Red Blood-corpuscles. (Landois.) a, 1), Normal human red corpuscles with the central depression more or less in focus, c, (I, e, Mulberry forms. y, li, Crenated corpuscles. k. Pale decolored corpuscles, i, Stroma. /, Frog's corpuscles acted upon by a strong saline solution. Experiments Upon the Blood. — Points of interest to the physiol- ogist particularly and to the clinician incidentally have been dis- closed as the results of some simple experimental work upon the blood-corpuscles. Each red corpuscle is seen to be composed of a fine meshwork, or stroma, consisting of noncolored, homogeneous protoplasm. Scattered throughout this framework is the iron- holding pigment, which gives color to the corpuscle and is the sub- stance with which the oxygen-gas enters into loose combination. Any reagent which is able to sever the union between stroma and haemoglobin causes the latter to pass into solution in the plasma. The once-red corpuscles then appear as transparent bodies. This makes the blood dark red, but transparent, since the coloring mat- ter is in solution. When the blood is in this condition it is said to be 'lake-colored." Laky blood may also be produced upon the injection of the blood-serum of one animal into the blood of another 170 PHYSIOLOGY. kind, the serum having the i)ower to destroy the red corpuscles. 'JMie term "globulicithii action" covers tliis property of the serum. The first elTect of pure ivaler upon red corpuscles is to produce a very obvious change in shape. From a discoid form, they hecome spherical, or nearly so. After sojne time the luenioglobin becomes dissolved out, leaving the corpuscles transparent: shadow-corpuscles. The knowledge thus gained led to further research to find some solution which will not all'eet the corpuscles. Isotonic Solutions. — To prevent "laking" of the blood normally there must be a certain degree of concentration of the medium immediately surrounding the corpuscles so that just sufficient water is maintained within tlie corpuscles as is needed. If by the addi- tion of distilled water or other reagents this degree of concentration is changed so that the balance is broken, then too much water enters the corpuscle. There immediately follows a change in shape, with forcing out of the pigment. A solution, containing just enough of salts so that the corpuscles are neither altered in shape nor lose their haemoglobin, is said to be "isotonic." The percentage of jSTaCl necessary to generate such a solution is, for frogs' blood, 0.65 per cent.; for blood of man, 0.95 per cent. The action of certain organic substances is of considerable importance. Thus, bile and the alkaline salts of the biliary acids have the power to dissolve and destroy the red corpuscles with phenomena which resemble those produced by the action of chloro- form. Urea in solution, digitalin, saponin, and venom of snakes also destroy them. As to vitality, it is known that the corpuscles of the blood that have escaped from the circulatory system, as well as those from defibrinated blood, when reintroduced into the living blood-stream, retain their vitality. THE WHITE CORPUSCLES, The white corpuscles are colorless, spherical little bodies which are a little larger than the red ones and much less numerous. Each is about V0500 inch in diameter and is composed of granular proto- plasm that is highly retractile and without any enveloping mem- brane. In striking contrast to the erythrocytes, the leucocytes possess not only one, but usually three nuclei; even four are not uncom- mon. Within the nuclei may be defined several distinct nucleoli. THE BLOOD. 171 When examining a section of blood, it is at once a striking fea- ture how few are the white as compared with the red corpuscles. In the average field but three or four are found, while at the same time hundreds of erythrocytes are noticed. The average is biit 1 white for every 500 or 600 red ones. This proportion does not pretend to convey an accurate idea of their relationship because of the frequent fluctuations of the white corpuscles even in a single day. They increase during digestion and diminish during abstinence. Bleeding, lactation, quinine, local suppuration, pregnancy, and leucocythsemia increase the white corpuscles; their number is dimin- ished by large doses of mercury. The proportionate number of leucocytes that is found in blood drawn from its containing vessels is no criterion of the number found within the blood-stream. As soon as blood is drawn from the body, for no accountable reason as yet known, an immense number of white corpuscles disappears. It is stated that there remains but one-tenth of the number previously found in circulation. Colorless corpuscles are not essentially peculiar to the blood- stream nor to be found only in it, for similar corpuscles are found in lymph, chyle, adenoid tissue, the marrow of the long bones, and also as wandering cells in connective tissue, drawn thither by inflam- mation and by bacteria. Varieties. — According to Ehrlich, they may be separated into tliree groups, the basis of classification depending upon the staining prodivities of the granules held within the cytoplasm. To the first group he gave the name eosinophiles, because the granules of this class of corpuscles stain best with acid aniline dyes. The hasophiles comprise the second group and include those staining best with hasic dyes. Last come the neutrophiUs; their granules are capable of being colored only by the presence of neutral dyes. This classifica- tion is a very popular one, and holds a very prominent position in pathological circles. White blood-corpuscles are classified in two varieties: — I. Lymphocytes are without granules in the cell and without amoeboid movement. (a) Small mononuclear lymphocytes are about the size of a red blood-corpuscle, have a large, round, concentric nucleus, a small amount of cytoplasm, and are strongly l)asophilic, 20 per cent. 172 PHYSTOLOnY. (h) Large mononuclear lymphocytes have a large, oval nucleus, located excentrically ; cytoplasm relatively considerable, not granular, and are weakly basophilic, 1 per cent. II. Leucocytes have a granuhir cytoplasm and amoeboid move- ment. (a) Transitional are mononuclear leucocytes, having a large nucleus, considerable granular cytoplasm, and neutrophilic granules. They are a transitional form between the large lymphocytes and the polymorphonuclear leucocytes, 7 per cent. (h) Polymorphonuclear leucocytes have the amoeboid movement well developed; the granules in the cytoplasm are neutro- philic; and the nucleus is divided into lobes, connected by bands. (c) Eosinophiles have a segmented nucleus, the granules in the cy toplasjn are large and stain with eosin ; they are oxyphilic, (d) Mast cells are small in number, with a polymorphic nucleus and basophilic granules. Amoeboid Movement. — All the leucocytes have in common a very remarkable attribute of spontaneously changing their shape and thereby executing certain movements, which, from their great similarity to those performed by the micro-organism, amoeba, have been termed amoehoid. When the conditions of temperature and moisture are maintained at the proper standard, the leucocytes will be seen slowly to alter their shapes and to send out from their cyto- plasm little processes into which the remainder of the leucocytes seem to flow, thereby causing a slight movement with change of position. This process repeated successively gives to the cell its power slowly to move from place to place, after having worked its way through the vessel-walls into the surrounding connective tissues. This locomotion is frequently termed the "wandering" of the cell. To their sticky exteriors there are frequently seen adhering fine pieces of broken-down cells, bacteria, and other foreign par- ticles. By reason of certain internal circulatory movements in the protoplasm of the leucocytes, these adherent foreign particles may be drawn into the interior of the cell, where some are absorbed, and others excreted as effete matters. Functions of the Leucocytes. — It is definitely known that the leucocytes play an important role in the process of blood-coagula- tion. Their relation to this most important process will be dis- THE BLOOD. 173 cussed under the head of "Coagulation." They are believed to help maintain the needed proportion of proteids. Their most evident function is the protection of the economy from both harmless and pathogenic bacteria. This they accomplish by two methods. The first is by generating a defensive proteid which, when imbibed by the bacteria, kills them. The second and more usual method is that of drawing into their interiors the various bacteria, together with the debris resulting from lesions, and, as it Fig. .5.]. — LeiR'ocytes of ^lan, showing Aina'boid Movement. (Landois.) were, eating them. From this apparent consumption of foreign par- ticles they have gained for themselves the name of phagocytes, and the act is known as phagocytosis. The seat of the presence of the bacteria marks a miniature battlefield, with the hosts of bacteria drawn up on one side in battle array against the leucocytes, the two armies to become engaged in a death-struggle. If the leucocytes, now termed phagocytes, are victorious, they not only kill their adver- saries, but even remove every vestige of the combat, aided by the fixed connective-tissue cells. Those leucocytes which come out of 174 PHYSIOLOGY. the affray iinharnicd and are no longer needed, find their way back into the blood-stream. If, however, the bacteria, with their toxic secretions and excre- tions, are too powerful for the phagocytes, the latter succumb, to become pus-corpuscles. When the pus has been removed by drain- age and the action of other leucocytes, the broken-down tissues are replaced by regenerating connective tissues. Bacteria alone are not the provocation for attack by the phago- cytes, for the presence of other foreign matters will also call out an assault. It is well known that surgical ligatures of gut and silk that are allowed to remain wiiliin the body-cavity and tissues are gradually removed, particle by particle, by the phagocytic action of the leucocytes. The absorption of the tails of tadpoles and other batrachians is due to phagocytic action. Diapedesis. — By reason of their locomotive tendencies the leu- cocytes and red corpuscles are able to make their way through the walls of the capillaries; this emigration has been styled diapedesis. There are several stages before the leucocyte finally makes its exit, namely: slowing of the current with the adherence of the cell to the side of the blood-vessel, and projection of processes, to be fol- lowed by the gradual exit of the entire leucocyte. This process occurs to some extent in health, but is greatly exaggerated by inflammation, presence of bacteria, etc. Circumscribed collections outside of the vessels often form abscesses; the leucocytes then receive the name pus-corpuscles. The leucocytes in this condition usually are dead and show signs of fatty degeneration. Frequently red corpuscles follow in the wake of the white ones, passing through the openings in the vessel-walls made by the former. In acute fevers and septic processes, as the temperature rises there follows a decrease in the number of erythrocytes, with a corre- sponding increase of leucocytes. Origin of Leucocytes. — The source of the colorless corpuscles seems to be rather extended. They originate in the bone-marrow and spleen, but the credit for greatest production belongs to the lymphoid tissues and lymphatic glands. From these latter sources the leucocytes enter the lymph-circulation, from thence to be emptied into the blood-stream. After having once gained entrance to the blood-circulation there is rapid multiplication to keep up the proper supply, since many succumb to the poisons secreted and excreted by the various bacteria. THE BLOOD. 175 Blood-plates and Elementary Granules. — In addition to tlie erytlirocytes and leucocytes found floating in the liquor sanguinis, there have been discovered other numerous, smaller bodies, termed blood-plates and elementary granules. The blood-plates are pale yellow or colorless discs; round, oval, or crescentic in shape; and varying within wide ranges as to size, although always smaller than red corpuscles. In blood that has been drawn from the vessels they diminish very rapidly both in numbers and size, becoming gradually dissolved in the plasma, and are believed to assist in coagulation. As to their nature, there is Fig. 54. — Blood-plates and their Derivatives. (Landois.) 1, Red corpuscle on the flat. 2, On the side. 3, Unchanged blood-plates. ■4, Lymph-corpuscle surrounded by blood-plates. 5, Altered blood-plates. 6, Lymph-corpuscle with two heaps of blood-plates and threads of fibrin. 7, Group of fused blood-plates. 8, Small group of partially dissolved blood-plates with fibrils of fibrin. some diversity of opinion, but the consensus of thought seems to be in favor of the plates being formed bodies, and not precipitates. They have been found to contain the same elements chemically as do the nuclei of the leucocytes, so that they are probably fragments of the nuclei of disintegrated leucocytes. In nmnber, their range is very extensive: from 15,000 to 200,000 in a cubic millimeter of blood. They take part in the formation of thrombi and in coagu- lation of blood. The elementary granules are smaller than the blood-plates and appear to be composed of portions of the protoplasm of leucocytes. They contain proteid and fatty matters. 176 PHYSIOLOGY. FORMATION OF RED BLOOD=CORPUSCLES. The red corpuscles, as every other portion of the economy, per- form their allotted task and round of existence, to finally die and disappear. Just how long the red corpuscle lives is yet unknown, but that it cannot be very long lived is probable when we consider that its haemoglobin is the parent-body of the bile-pigments which are constantly being expelled from the body as portion of the faeces. Hence there must constantly be manufactured a new supply of cor- puscles to replace those that die. The origin of the red corpuscle as to time may be spoken of as that which occurs during intra-uterine life and that occuring during extra-uterine life. During Intra-uterine Life. — The corpuscles which first appear in the human embryo owe their existence to a very simple origin. They differ in some resj)ects from those that appear later during intra-uterine life, and very materially from those formed during life outside of the uterus. The wall of the yelk-sac, situated entirely outside of the body of the embryo, is the seat of the first vessels and blood. In the chick the corpuscles appear during the first days of incubation and before the appearance of a heart. At the end of the first day, sur- rounding the early embryo there appears a circular, vascular area made up of cords of cells in which are developed the first evidences of the vessels and corpuscles. The corpuscles appear in groups within this branched network of mesoblastic cells, where they f onn the ''blood-islands'^ of Pander. Presently the cords of mesoblastic cells which compose this network begin to become vacuolated and hollowed out to constitute a system of branching canals, at the same time that their cells acquire the endothelial type. The small, nucleated masses of protoplasm, known as the "blood-islands," undergo disintegration, whereby their nuclei are set free soon to collect around themselves a thin envelope of protoplasm. These constitute the primitive red corpuscles, and are the only bodies con- tained within the blood during the first month. In the meantime they have been acquiring a reddish hue, which marks the advent of the haemoglobin. As the canals become extended and branched eventually to connect with the heart as its system of vessels, there appears within them a fiuid into which are emptied the red cor- puscles. Thus is completed the circulation. According to Klein, the nuclei of the protoplasmic vessel-walls multiply to form new cells. The primitive corpuscles are spherical in shape, nucleated, THE BLOOD. I77 and possess amoeboid movements. They undergo multiplication by karyokinesis. During the foetal period the protoplasm of the connective-tissue corpuscles, derived from the mesoblast, contains ceils of the size and appearance of blood-corpuscles. The mother-cells elongate, throw out processes which become hollowed out and branched until they reach the regular circulatory vessels, with which they unite to empty into them their fluid and cells. During this period also they seem to be developed from the liver, spleen^ and red bone-marrow. During- Extra-uterine Life. — For some time after the birth of the mammal, nonnucleated corpuscles are still formed in the spleen, liver, and connective-tissue cells, but by far the most important and prolific seat is in the red marroiv of hones. It is in the bones of the skull, trunk, and ends of the long bones that blood-fonnation is most extensive, since the shafts of these bones contain a yellow, fatty substance which is nonproductive. Within the marrow are seen numbers of nucleated, red cells, which are very similar to the corpuscles of the embryo, and which, like them, multiply by karyo- kinesis. From these repeated divisions there result nonnucleated red corpuscles which are washed into the circulation. The blood- forming cells have received the name of erythroilasts, or hwmato- hlasts, and are particularly numerous after copious ha?morrhage, when the lost blood is being replaced by more active formation. At such times some erythroblasts may appear in the blood-stream, hav- ing been forced out prematurely, so active is the function of the red marrow in striving to repair the damage done. These soon lose their nuclei while in the blood-stream. If the loss by hsemorrhage has been particularly severe, the yellow bone-marrow and spleen assist in blood-manufacture, for in the latter and in the splenic vein are found nucleated, red corpuscles identical with those of the red marrow of bone. DESTRUCTION OF THE RED CORPUSCLES. No exact time can be given as the life-period of an erythrocyte, but it is usually estimated to be in the neighborhood of three or four weeks. The student can gain some comprehension of the num- ber of corpuscles which must constantly be undergoing disintegra- tion when he recalls the fact that all of the pigmentary matters in the body owe their existence, directly or indirectly, to the haemo- globin of these little bodies. The quantities of urinary and biliary pigments alone that are excreted from the economy are considerable. 12 178 PHYSIOLOGY. Physiologists have proved that there are fewer red corpuscles in the hepatic than in the portal vein. The bile-pigments are formed by the liver-cells; these coloring matters contain only traces Fig. 55. — Blood-crystals of Man and Dilleieiit Animals. (Tuan- HOFFEB and Frey.) 1, Hsemoglobia crystals: Mo, squirrel; Tr, guinea-pig; M, groundmole; L, Horse; Em, man; H, Marmot; Ma, cat; T, cow; mv, from venous blood of a cat. 2, Hsematin crystals; E, man; Vb, sparrow; M, cat. 3, Haematoidin crystals from an old extravasation of blood in man. of iron, while the hepatic cells are rich with it. They give the char- acteristic test for. iron when treated with hydrochloric acid and potassium f errocyanide. THE BLOOD. 179 Only traces of the iron are excreted as a constituent of the bile. The presence of iron in the spleen has long made this organ seem a cradle to many physiologists where erythrocytes are born and nour- ished. But the presence of this same element advances an argu- ment equally as strong in favor of the spleen being the grave for these same little bodies. Pathologically, masses of iron substances are found within the spleen, liver, and red bone-marrow when aljnormal disintegration occurs, as in anwmia. CHEMISTRY OF THE CORPUSCLES. The red corpuscles consist of a stroma containing in its meshes a peculiar proteid haemoglobin. Chemically they are made of 60 per cent, of water and 36 per cent, of haemoglobin, the remaining -f per cent, representing the stroma, which is made up of lecithin, choles- terin, and nulceo-proteid. The white corpuscles consist of solids and water. The solids are gluco-proteids and nucleo-proteids and a small amount of albumin and globulin. The protoplasm may also contain glycogen and fat. The nuxileus is made up of nucleo-pro- teids, nuclein, and nucleic acid. The phosphorus content of the nucleus is greater than that of the protoplasm. The table on page 180 is the result of the analyses reported by Halliburton. The other named constituents are common to the two kinds of corpuscles. The mineral components are principally the chlorides of potassium and sodium and the phosphates of calcium and mag- nesium, the phosphates being in greater proportion. Water forms 90 "per cent, of the corpuscular contents. It will be remembered that the sodium salts assume greater proportions in the plasma. The nucleo-proteid obtained from the white corpuscles is the pre- cursor of the fibrin-ferment of coagulation. It is believed that the proteid is converted into fibrin-ferment through the activity of the calcium salts of the plasma. Haemoglobin. — This is the pigment matter of the red corpuscles. Haemoglobin is a proteid composed of globin, a histon. and haematin. Its principal characteristics are : (1) its ability to combine chem- ically with oxygen and other gases, (3) its spectroscopic phenomena, (3) its crystallization, and (4) the fact of its containing iron. It is by virtue of the presence of this haemoglobin that the red corpuscles are capable of performing the function of oxygen-carry- ing— carrying it from the external respiration in the lungs to the 180 PHYSIOLOGY. Chemicai Composition of Blood. PLASMA. ' "Wat.pr . . 90.29% vv diuci ......••...•• ' Serum- Average, 52% Maximum, 56.7% Minimum, 45.6% Take 100 parts ' Organic (8.86%)^ ^ Proteids < albumin Serum- | globulin . Fibrin . . 7.9 % 0.4 % ^ Extractives : Fats, etc. . 0.56% Solids l- C9-'71%)' Soluble salts . ^ ' NaCl KCl NaHCOg Inorganic ^ . (0.85%) Na^HPO, 0.85% Insoluble J CaHPO, salts 1 CaSO, . V. Average, 48% Maximum, 54.4% Minimum, 43.3% Take 100 parts 100.00% C0EPUSCLE3. Water 68.80% Solids (31.2%) Organic (30.4%) ' Proteids (29.79%) Fats rHiBmoglobinfHaematin] <-^«' 1o,i"l|- ■ "•"^" Globulin 2.43% ° I 0.61% ;erinj f Lecithi \Cholesteri Inorganic (0.8%) KCl NaCl MaCl^ CaHPO^ Mg3(P0,),. Fe (see Haematin). 0.80% 100.00% internal respiration in the cells of the tissues. The liEemoglobin molecule possesses the property of linking to itself an oxygen mole- cule, forming a compound known as oxylicBmogloUn. The union of the two molecules is so unstable that the presence of an easily oxidized body, or of an atmosphere with a lower oxygen pressure, separates the two, the oxidizable body and the atmosphere taking THE BLOOD. 181 up the oxygen. Oxyhasmoglobin, minus oxygen, is usually termed reduced hoimoglobin; better, however, simply hasmoglobin. Oxy- htemoglobin is most abundant in arterial blood; that is, blood that has received its oxygen from the lungs during respiration and is then on its way to supply the needs of the cells of the tissues. Oxy- hsemoglobin behaves as an acid. Ordinary venous blood, upon expo- sure to the air for a considerable length of time, becomes bright red because of the union of the oxygen of the air with the hemoglobin of the blood. Crystallization of Haemoglobin. — The haemoglobin is contained M'ithin the stroma of the corpuscles. In form, the crystals of the blood of man and of the great majority of animals is that of rhombic 0 » / " Fig. 56. — Teichmann's Hsemin-crystals. (Lahousse.) prisms or needles which belong to the rhombic system; in the squirrel there are produced six-sided plates. Haemoglobin crystals are readily broken up by the addition of an acid or an alkali into two parts: hcematin and globin. Hcematin is a brown pigment, representing the cleavage product of haemo- globin in the presence of oxygen. It contains all of the iron of the decomposed crystals, and is not crystallizable. In addition to the iron, it contains the four chief elements of proteid bodies: carbon, hydrogen, oxygen, and nitrogen. Globin is the proteid element of the liEemoglobin. It contains all the sulphur, and constitutes the major proportion of the haemoglobin luolecule, which is 16,000 times heavier than a molecule of hydrogen. Haemin. — Hasmin is the decomposition-product that results from the action of hydrochloric acid upon haematin. The haemin crystals are small rhombic plates and prisms. The finding of the crystals of Teichmann constitutes the best-known clinical test for the detec- tion of blood. The crystals are prepared by adding a small crystal 182 PHYSIOLOGY. of common salt to dry blood on a glass slide, and then an excess of glacial acetic acid. The preparation is then gently heated vintii bubbles of gas are given off. Upon cooling, the characteristic hsemin crystals are formed. By transmitted light the crystals appear as mahogany-brown, but by reflected light they are bluish black. Fig. 57. — Sorby-Biowning Microspectroseope. Chemical Properties. — Hsemin crystals are insoluble in water, alcohol, ether, and chloroform. Very strong sulphuric acid is capable of dissolving them. Should this solution be evaporated to dryness and the residue properly treated, there will be produced a brown, amorphous powder. This product is known as hcEmatopor- phyrin. Haematoporphyrin is iron-free htematin. It is frequently found in pathological urines, while traces of it are to be found in normal urine. THE BLOOD. Ig3 It has the same formula as bilirubin, isomeric, but not identical. Mesoporphyrin, containing one atom of oxygen less than hsemato- porphyrin, is said to be identical with hasmatoidin. Chlorophyll, the pigment of plants concerned in respiration and containing iron, gives a body, phylloporphyrin, on cleavage by acids. It is similar to hsmatoporphyrin. Haematoidin. — In old blood-extravasates in the brain, hgema- toidin is found in crystals. It is an iron-free derivative of hgemo- globin, identical with bilirubin. Methaemoglobin. — Methsmoglobin is prepared chemically by adding amyl nitrite to blood. It contains the same amount of oxy- gen as haemoglobin, but, owing to its different combination, the oxygen cannot be removed even in a vacuum; hence it cannot be a transporter of oxygen to the tissues. Potassium chlorate and the continued use of antipyrin and acetanilid will produce methsemo- globin. Carbon-monoxide Hsemoglobin, or Carboxyhaemoglobin. — With carbon-monoxide gas (CO) ha-mogiobin forms a compound similar to oxyhgemoglobin, but known as carbon-monoxide hcemoglohin. This union is much more stable than the preceding, so that when carbon- monoxide gas is breathed in excess death results from asphyxia, since the tissues are prevented from receiving their proper supply of oxygen. Carbon-monoxide results from the incomplete combustion of carbon in coal and charcoal stoves. Tts poisonous properties are caused by its combining so strongly with the haemoglobin of the corpuscles that it prevents union with oxygen, and so produces asphyxia. The blood of both veins and arteries is bright, cherry- red in color. In poisoning from this gas, artificial respiration with saline transfusion is sometimes of avail. For a better understanding of the import of the absorption bands of the coloring matters in the blood, a brief description will be given of the instrument whereby they are studied. THE SPECTROSCOPE. When ivliite light, or that which reaches us from the sun, passes from one medium into another more dense, it is decomposed into several kinds of light, a phenomenon to which the name dispersion is given. Thus, when a pencil of the sun's rays is passed through a prism of flint glass, it is broken up into the seven colors of the spectrum. This band of colors may be seen naturally in the form 184 PHYSIOLOGY. of the rain'bow. These colors are violet, indigo, blue, green, yellow, orange, and red. The colors of the solar spectrum are not continuous. Several grades of refrangibility of rays are wanting, and, in consequence, throughout the whole extent of the spectrum there is a great num- THE BLOOD. 185 ber of very narrow, dark lines which run at right angles to the longi- tudinal axis of this band of light. They are generally known as Fraunhofer's lines, since the most marked ones were first mapped and indicated by him. They are designated by the letters A, B, and C, in the red; D, in the yellow; E, h, and F, in the green; G and H, in the violet. If the light produced from burning common salt (sodium chlo- ride) be decomposed by means of a prism, it will be found to give one broad yellow line. Artificial light will not give Fraunhofer's lines. The D line in the solar spectrum is due to the volatilizing of the metal sodium in the sun. Other elements account for the remaining dark lines of the spectrum. The spectroscope is combined with the microscope when you wish to make a medico-legal analysis of a small amount of coloring matter resembling blood. The microspectroscope used is usually the Sorby-Browning. As will be seen from the preceding figure, it is a very compact piece of apparatus, very ingenious in construction, and consists of several parts. The prism is contained in a small tube, which can be removed at pleasure. Below the prism is an achromatic eyepiece, having an adjustable slit between the two lenses; the upper lens being furnished with a screw motion to focus the slit. A side slit, capable of adjustment, admits, when required, a second beam of light from any object whose spectrum it is desired to compare with that of the object placed on the stage of the microscope. This second beam of light strikes against a very small prism suitably placed inside the apparatus, and is reflected up through the com- pound prism, forming a spectrum in the same field with that obtained from the object on the stage. ^ is a brass tube carrying the compound direct-vision prism, and has a sliding arrangement for roughly focusing. B, a milled head, with screw motion to adjust finally the focus of the achro- matic eyelens. C, milled head, with screw motion to open and shut slit vertically. Another screw, H, at right angles to C, regulates the slit horizontally. This screw has a larger head, and when once recognized cannot be mistaken for the other. D, D, an apparatus for holding a small tube, that the spectrum given by its contents may be compared with that from any other object on the stage. E, A, screw opening and shutting a slit to admit the quantity of light required to form the second spectrum. Light entering the aperture near E strikes against the right-angled prism which I have 186 PHYSIOLOGY. mentioned as being placed inside the apparatus and is reflected up through the slit belonging to the compound prism. If any incan- descent object is placed in a suitable position with reference to the aperture its spectrum will be obtained and will be seen on looking through it. F shows the position of the field-lens of the eyepiece, (r is a tube made to fit the microscope to which the instrument is applied. To use this instrument, insert G like an eyepiece in the microscope tube, taking care that the slit at the top of the eyepiece is in the same direction as the slit below the prism. Screw on to the microscope the object-glass required and place the object whose spectrum is to be viewed on the stage. Illuminate with stage mirror if transparent. Remove A and open the slit by means of the milled head H at right angles to D, D. When the slit is sufficiently open the rest of the apparatus acts like an ordinary eyepiece, and any object can be focused in the usual way. Having focused the object, replace A and gradually close the slit till a good spectrum is obtained. The spectrum will be much improved by throwing the object a little out of focus. Every part of the spectrum differs a little from adjacent parts in refrangibility, and delicate bands or lines can only be brought out by accurately focusing their own parts of the spectrum. This can be done by the milled head B. When spectra of very small objects are viewed, powers of V2 ™ch to V^o may be employed. These bands represent the light absorbed by the colored medium. For the same substance the bands are always identical and similarly placed. Thus, a solution of oxyhaemoglobin of a certain strength gives two bands, reduced hsemoglobin gives only one. The other derivatives, methjemoglobin, haematin, hgemin, etc., though similar to haemoglobin when viewed with the naked eye, yet each gives char- acteristic absorption bands in various positions. Hsemochromogen is produced by treating an alkaline haematin solution with ammonium sulphide. It is reduced alkaline haematin. Carbon-monoxide haemoglobin, oxyhemoglobin, haemochromo- gen, and haematoijorphyrin all have two characteristic bands in their spectra. By adding ammonium sulphide you can distinguish between oxyhaemoglobin and carbon-monoxide haemoglobin, since the two bands of oxyhaemoglobin disappear, whilst those of carboxyhaemo- globin remain unaltered. Haemochromogen bands are to the violet side and ha&matopor- phyrin to the red side of the bands of oxyhsemoglobin in the spec- THE BLOOD. 187 tram. Acid haematin, alkaline haematin, reduced haemoglobin, and methgenioglobin can each produce a band on the red side of the D line. A reducing agent makes this band vanish in the case of methsemoglobin or alkaline hgematin, and produces reduced hsemoglobin or reduced haematin. Eeduced haemoglobin can be temporarily reoxidized by shaking the solution. Picro-carmine gives a two-banded spectrum, but it differs in position from the double bands of oxyhemoglobin. They are unal- tered by ammonium sulphide, whilst oxyhtemoglobin gives the dou- ble band of reduced hajmatin by the addition of ammonium sulphide. The amount of hsemoglobin as calculated by various methods and instruments has been found to be in man, 13.77 per cent.; in woman, 12.59 per cent. Pregnancy reduces the quantity from 9 to 12 per cent. Normally there are two periods in a person's life when the amount of htemoglobin attains maximum limits — in the blood of the newborn and again between the years twenty-one and forty- five. Pathologically there follows a decrease during recovery from febrile conditions, as also occurs during phthisis, cancer, cardiac disease, chlorosis, anaemia, etc. It is known that dry haemoglobin contains 0.4 per cent, of iron, and that all the iron of the blood is held by the haemoglobin of the red corpuscles. The amount of iron in the blood is about -iS grains. Colorimetric methods consist in making comparisons between a standard solution of a known strength and the test solution of blood to be examined, water being added to the latter until the exact shade of the standard solution is obtained. Von Fleischl's Haemometer. — This instrument consists of A, a cylindrical cell for holding the prepared blood; D, a graduated wedge-shaped piece of colored glass with which to compare the solu- tion of blood; H, a stand with a rack and pinion; and a capillary tube for measuring the quantity of blood required. 1. The cell (.4) is a cylindrical metallic chamber divided by a fixed partition into two equal compartments, open at the top, but closed at the bottom by a base of glass. One of these compartments is to be filled with distilled water, the other with the proper quan- tity of blood dissolved in distilled water. 2. The colored glass wedge {B) is fitted to a metal frame, so that it can be adjusted in the stand and moved from side to side by the rack and pinion. When in position the glass wedge moves directly beneath that part of the cell which contains the distilled water, thus enabling one to compare the color of the glass with that 188 PHYSIOLOGY. of the dissolved blood which fills the adjoining compartment of the cell. The wedge is graduated at E from 1 to 100, the figures repre- senting the percentage of hgenioglobin in the specimen of blood as compared to normal blood containing 13.7 per cent, of haemoglobin. 3. Besides the support for the glass wedge and frame, there is a white plaster mirror (M) which furnishes the diffused light required in the test. 4. The capillary tubes are carefully prepared to hold the pro- per quantity of blood. The size of these tubes varies, and on the handle of each is stamped a number indicating its capacity.^ 59. — Von Fleischl Hsemometer, (Lahousse.) A, Mixing vessel with two compartments: B, for diluted blood; C, for pure water, reposes over the colored prism of glass. D. E, Scale to read off amount of haemoglobin. M, A mirror to reflect light. H, Milled wheel that moves D. PHYSICAL PROPERTIES OF THE PLASMA. Plasma is the fluid part of the blood as it occurs in a healthy condition within the circulatory system. However, upon its removal from the body there is formed in it a solid substance, called fibrin, from elements which it previously held in solution. The fluid which surrounds the clot is termed serum; it is plasma minus fibrin. Plasma is described as a clear, somewhat viscid fluid; that of man, when strata are examined, is colorless; when in bulk it is slightly yellow because of the presence of a pigment. ^ Dare's hsemoglobinometer is most frequently employed. THE BLOOD. 189 CHEMICAL PROPERTIES OF PLASMA AND SERUM. In order to examine plasma, a very great amount of caution is necessary to prevent its coagulation, even after separating the cor- puscles. The most common methods for obtaining it in a liquid state are by the use of the "living test-tube" — an excised piece of jugular of a horse filled with blood, and cold as an environment. It has been found that serum differs from plasma only in respect to certain proteids, and, as it is so much easier to handle the serum, the latter is principally used for experimentation. Chemically the plasma is composed of inorganic and organic substances, with certain gases. In Weight. In Volume. Fig. 60. — Relative Proportion of Corpuscles and of Plasma. (Human Blood.) (Laxglois.) Inorganic Constituents. — The plasma's greatest factor is water. It is this which gives it fluidity and is present to the extent of 90 per cent. There are present many salts : sodium chloride, carbonate of soda, chloride of potassium, sulphate of potassium, phosphate of calcium, phosphate of sodium, and phosphate of magnesium. The first two occur in the greatest amounts, the remaining ones only as traces. It is carbonate of soda that gives to plasma its ability to absorb carbonic acid and it also contributes much to its alkalinity. Organic Constituents. — These components are readily divisible into profeid and nonproteid groups. The Proteids are: — 1. One albumin (serum-albumin). 2. Two globulins, termed serum-globulin and fibrinogen. 3. A nucleo-proteid. The classes of proteids present various soIubilHies in neutral salt solutions, by appreciation of which they are able to be separated from one another. 190 PHYSIOLOGY. The albumins upon liali'-iBatiiration with ammonium sulphate remain in solution, while the globulins and nucleo-proteids are pre- cipitated. The precipitate is removed by filtrations, or the albu- mins may themselves be precipitated by saturation with ammonium sulphate. The gluhuUns almost universally possess the characteristic of coagulating when heat of 75° C. is applied to them. In man the globulins make up about 3 per cent, of the total serum. Fibrinogen is also a globulin. It is precipitated by half -satura- tion with NaCl thus making its differentiation from serum-globulin a comparatively easy task. Upon precipitating with NaCl, if a lime salt be added, the precipitate partakes of the nature of a fibrin-clot or coagulum, but it is not true fibrin, since it is a combination of fibrinogen with lime. Nudeo-proteid of Plasma. — About the only characteristic that is known in connection with the nucleo-proteid is that it is very essential to the formation of fibrin during coagulation. It is formed by the dissolution of the leucocytes and blood-plates after the blood is shed from the body. When hydrocele, pericardial, and ascitic fluids contain no leucocytes, it has been noticed that they lack power of spontaneous coagulation. The nucleo-proteids in the presence of calcium salts form a substance which is identical in every respect with the fibrin-ferment of Alexander Schmidt. This new substance possesses the power of converting fibrinogen into fibrin. The Nonpkoteids of the Plasma. — The nonproteids comprise both nitrogenous and nonnitrogenous elements. The nonnitrogenous consist of carbohydrates and fats, with small amounts of lipochrome and sarco-lactic acid. The nitrogenous elements comprise in their category urea, uric acid, hippuric acid, creatin, and some ferments. Urea, which represents the end-product of nitrogenous combus- tion of either the tissues or the blood itself, and which must be included among the normal elements of this fiuid, is found in the blood in small proportion. But it can accumulate in an abnormal manner within the blood and give rise to the disorder known as uraemia. It is in this way that ablation of the kidneys, acute nephritis, and the terminal feverish period of cholera, in which the ' urinary secretion is suppressed, provoke the accumulation of urea in the blood. Uric acid, which is regarded as the product of a work of com- bustion less advanced than for urea, doubtless owes its existence to THE BLOOD. 191 an incomplete oxidation of the true, immediate principles of the muscles. It may occur in greater proportion than usual in combina- tion with soda, with the urea, in the blood of gouty persons, and in that of albuminuric persons. Gases of the Plasma. — Present knowledge affirms the presence of oxygen, nitrogen, and carbonic anhydride. The first two are simply dissolved in the plasma, but the carbonic anhydride occurs in from 43 to 57 volumes, and then combines chemically with soda to form carbonates and bicarbonates. Fig. 61. — Delicate Fibrin Coagiilum (from Croupous Pneumonia.) X 350. (Lenhaetz.) COAGULATION OF THE BLOOD. Normal blood contained within the body vessels is a fluid. For a very brief period after it makes its exit from a wounded vessel it remains in a liquid state, but mthin two or three minutes its vis- cidity increases until there is formed a solid of the consistency of jelly; to this has been given the name blood-clot. The process whereby the clot is formed is termed coaguJaMon, and is caused by the presence of a body called fihri?i. To best observe the process of coagulation, the blood is drawn into an open vessel as a beaker, care being taken that the atmos- pheric and other conditions are favorable. The initial change, which occurs within the first two or three minutes, is the formation of a jellylike layer over the surface of the blood ; during the next three or four minutes this layer extends to such a degree that the entire 192 PHYSIOLOGY. blood-mass becomes enveloped. If at this time the contents of the vessel be turned out, they f onn a mold of the exact shape of the con- taining vessel, or the vessel may be inverted without the escape of the contents. This jellylike mass is the clot. Within it are impri- soned the serum and corpuscles. A straw-colored fluid, the serum, is expressed, appearing upon the surface to form finally a transparent layer of liquid around the clot. The retraction is complete at the end of from twelve to twenty hours, at which time all of the serum has been expressed and the corpuscles enmeshed within the network of fibrin. The clot, so dense that it may readily be cut with a knife, being heavier than the serum, is found at the bottom of the vessel. It is now just about one-half of its original size. The serum, when examined, is found to be practically free from corpuscles. The character of the clot varies according to the state of the blood. It is large, soft, and tears easily at times. At other times it is small, resistant, and from the energetic contraction of the fibrin the edges of the upper sur- face of the clot curve over so as to form a sort of cup. The clotting of the blood is due to the development in it of fibrin, whose fibrils arrange themselves in the form of a network. In blood within its vessels there are found no such fibrils of fibrin; therefore normally no coagulation occurs within the body. These fibrils then must have been formed by some change, chemical or otherwise, of one or more constituents of the blood. That the corpuscles themselves cannot form a clot excludes them, so that our attention is turned to the plasma. In it is formed the fil^rin, for pure plasma from which the corpuscles have been removed very readily coagulates. When blood is vigorously beaten with twigs, long shreds of a nearly transparent substance are found adhering to them. These are fibrin-fibers, free, or nearly so, from corpuscles. Its structure consists of very delicate, doubly-refractive fibrils of microscopical size. Many theories have been propounded to account for the forma- tion of fibrin and the coagulation of the blood, but the one most widely received is that of Hammersten, a Swedish investigator. In the study of plasma it was learned that one of its constitu- ents was a proteid of the globulin class, to which had been given the name fibrinogen. It is held in solution by the plasma and is believed to be an end-product of the disintegration of useless white corpuscles. Within the circulating fluid there is an immense num- ber of these white cells; when blood is withdrawn from the living THE BLOOD. 193 vessel there is a large and very sudden destruction of them; accord- ing to Alexander Schmidt, 71.7 per cent, are dissolved. When these little bodies are disintegrated in the laboratory they yield nucleo- proteids ; so that it is very probable that practically the same pro- ducts result upon disintegration in the shed blood. To this nucleo- proteid has been given the name prothrombin. By the action of the calcium salts dissolved in the blood-plasma the prothrombin is con- verted into fibrin-ferment, or thrombin. When thrombin comes into contact with the fibrinogen molecule dissolved in the plasma it splits it into two parts: one is a globulin, which is very small in propor- tion and equally unimportant; it remains in solution. The other is the insoluble substance fibrin, which entangles the corpuscles and is so essential to the formation of the blood-clot. The process of fibrin-formation has been neatly tabulated by Dr. J. J. K. Macleod/ as follows: — Living blood Plasma Albumin Globulin Corpuscles White Red Ca salts -\- Prothrombin Fibrinogen + Fibrin ferment Second globulin Fibrin Serum Clot Dead blood '^ "Practical Physiologj'." 13 19i PHYSIOLOGY. To epitomize, it may be said that coagulation depends upon three factors, according to Hammersten's theory: (1) calcium salts to convert the nucleo-proteids in the form of prothrombin into throm- bin, or (2) fibjin- ferment; this latter breaks up the (3) fibrinogen in solution into an unimportant globulin and the all-important fibrin. Fibrin-ferment is a term used simply for convenience and prob- ably is a misnomer. It is a proteid of the globulin group whose sub- stance does not seem to be used up in the process nor to enter into the fibrin formed; a small quantity of it serves to break up an immense amount of fibrinogen. Morawitz thinks that extracts of organs form a proenzyme from a zymogen stage, thrombogen, whence thrombin arises from the pro- enzyme under the influence of the calcium ions. The formation of thrombin is stopped immediately by sodium fluoride, and the course of formation of thrombin can be closely followed by the addition of small quantities of this salt. In the peculiar hereditary^ disease of males only, known as haemophilia, it sometimes happens that diminished coagulability is due to a deficiency of the calcium salts. Consequently the tendency to bleed may in some cases l)e lessened by the internal administra- tion of calcium chloride, or the actual hasmorrhage may be stopped upon its local application or of adrenalin. A condition known as biiffy coat occurs when blood coagulates very slowly. It is most readily seen in horses' blood, being caused by the more rapid sinking of the red corpuscles in slow coagulation, thus leaving the upper stratum to consist of a layer of fibrin and white corpuscles. This whitish layer is elastic, has some resistance, is more or less opaque, and has therefore been designated the buffy coat. The shape of the vessel is also a factor in the production' of "buffy coat." If the vessel be long and straight, the fall of the cor- puscles is facilitated. The buffy coat then appears. No buffiness, however, is seen if the vessel be large and low, and if the blood be received in a vessel which is shaken from time to time. The blood of different parts of the vascular system shows differences as to the time required for complete coagulation. Arterial blood coagulates more quickly than venous ; blood of the hepatic veins coagulates very little, and the same is true of menstrual blood — probably due in the latter to mixture with the alkaline vaginal secretions, for, when menstruation is so abundant that this alkalinity is overcome, then clotting may ensue, THE BLOOD. 195 Certain conditions favor the rapidity of coagulation. Clotting is accelerated by these factors: 1. Calcium salts. 2. A tempera- ture a little higher than that of the body (102° to 107° F.). 3. Pre- sence of foreign bodies. If a needle be made to penetrate the wall of a vessel, fibrin is deposited upon it and so produces coagulation. It seems to be a sort of phenomenon analogous to that which occurs when a thread is suspended in a solution of sugar, when the crystals of sugar are deposited upon it. Injections of laky blood, biliary salts, fibrin-ferment, and rapid venous injection of a strong alkaline solution of a nucleo-proteid also hasten coagulation. 4. Injury to the vessel-walls. 5. Agitation, probably because there is then a more free mixture with oxygen. Gelatin increases the coagulating power of blood, and has been used in haemophilia. Coagulation is retarded by: 1. Oxalates, which combine with calcium. 2. A very low temperature. 3. The saturation of blood with CO2 (thus in asphyxia the blood does not coagulate). 4. Blood received into a vessel filled with oil does not coagulate. 5. Coagula- tion is prevented when the blood is in contact with normal, living, vascular walls. The addition of certain articles retards coagula- tion; thus, feeble doses of alkalies, carbonate of sodium and potas- sium, sugar, water, albumin, injection of peptone, and leech extract. In the disease known as haemophilia, as well as in lightning strokes, the blood does not coagulate. Why Blood does not Normally Coagulate within the Blood-vessels. — Much time and experiment have been given to ascertaining the cause for noncoagulation within living walls, but notwithstanding the question is yet unsettled. By some it is thought that the destruction of the white corpuscles is not extensive enough to fur- nish the proper supply of nucleo-proteid, from which fibrin-ferment is manufactured. According to Schmidt, the blood within the liv- ing vessels is constantly being acted upon by two opposing influences : one with a tendency to promote coagulation, the other to oppose it. In health the former never gains the ascendency. But perhaps the real secret depends upon the intima being alive and intact. Haemorrhage and its Effects. — It is common knowledge that a very abundant loss of 1)lood causes death. The blood has for its functions to insure the physical conditions of the life of the cells as well as to maintain an excitability of the nerve-cells which gov- ern respiration and circulation. Every considerable loss of blood disorders cell-life in the organism, tending to cause death. Necrosis very soon manifests itself when a member has by some procedure 196 PHYSIOLOGY. been deprived of its normal supply of blood. When the loss of blood has been from the whole system, and not confined to any mem- ber, a general death precedes the local death of the cells, because, the oxygen not going to the cardiac and respiratory centers, the functions of the heart and lungs are arrested. The principal symp- toms of great loss of this vital fluid are general paleness and lower temperature of the cutaneous surface, oppression, breathlessness, stoppage of the secretions, with finally general convulsions of anaemia. The quantity of blood which can be lost without causing death varies according to age, sex, temperature, etc. The loss of some cubic centimeters in the newborn, of a half-pound in an infant of one year, or of half the quantity of blood in an adult, is capable of causing death. Women bear the loss of blood much better than men do because of the periodical haemorrhages to which they are subject. The renewal of the blood appears to be accomplished rapidly, although the time of withdrawal plays an important role in determin- ing whether there will l)e attending fatality. If the loss has not been too severe, the fluid part of the blood and its dissolved salts is replenished by withdrawal from the lymph and plasma of the tissues. Later the albumin is restored, but a much longer period is required for replenishment of the corpuscles. The amount of haeonoglobin is diminished in proportion to the amount of bleeding. Shock very materially affects the results of haemorrhage. When the sensibilities are deadened temporarily by anaesthetics, less seri- ous results follow the loss of a given quantity of blood than do those when the same quantity escapes through accident. Transfusion. — This is a process by which blood is conveyed from one animal to the vascular system of another. It was shortly after Harvey's discovery of the circulation of the blood that this operation was first practiced by Denis, of Paris. He transfused with success the blood of a lamb into that of a man. It was believed that a great panacea had been discovered whereby not only blood lost by haemorrhage could be replaced, but a cure effected for many diseases and infirmities. Subsequent attempts proved such miserable fail- ures that the operation was abandoned and even proscribed by law. More than a century later it was revived, but only after much experi- mentation upon the lower animals. The serum of certain animals possesses the property of dis- THE BLOOD. 197 solving the red corpuscles of another species of animals. The serum of a dog destroys the red corpuscles of man; the haemoglobin is dissolved out. The serum, besides its action on the red corpuscles, is also active against the white corpuscles of the same animal, stop- ping their amoeboid movements. The globulicidal action of the serum is related to its poisonous action on microbes. The normal serum of certain animals kills microbes, as the serum of the dog kills the typhoid bacilli. The power to kill red corpuscles and microbes is due to the presence in the serum of a substance, an alexin. In transfusion this plays an important part. The knowledge gained thereby was to the effect that, for the operation to be at all successfully performed, blood of the same species of animal should be used as the one on which it is performed. It was only after the establishment of this rule that it appeared pos- sible to determine the value of transfusion and to make application of it, with some degree of safety, to man. In practice there are two kinds of transfusion: (1) blood with fibrin ; (2) blood without fibrin. In using fibrinated blood the stream is passed directly from the blood-vessel, either artery or vein, into that of the patient. Usually the peripheral end of a vein of the person furnishing the blood is united with the central end of a vein of the patient. The tubing should have been previously filled with a normal salt solution so as to exclude the entrance of air into the circulation, for, if sufficient quantity of it be introduced, it will be carried to the right side of the heart, where, by virtue of the heart's action, a froth will be generated, the bubbles from which, being pumped into the pulmonary arteries, arrest pulmonary circulation and cause death. The danger of coagulation is, however, very great. In using defibrinated blood the shed blood is first whipped in an open vessel with a glass rod so as to separate the fibrin; it is then filtered, heated to the temperature of the body, and injected very slowly into a vein (usually the median basilic) in the direction of the heart. Besides giving a tendency toward intravascular coagulation, there is also danger of introduction of bacteria, whose entrance into the injected blood occurs with the beating in the process of defibrin- ation. It has been learned that the most serious symptoms of rapid haemorrhage follow the sudden diminution in the amount of blood in circulation, accompanied with a moderate fall of blood-pressure. From these data we conclude that the proper measures to take are 198 PHYSIOLOGY. to replenish the amount of fluid regardless of the corpuscles or the soluble nutrient elements of the plasma. A precaution to be taken is that the fluid should be of such a density and nature that no dis- turbance in the vascular system be generated. This knowledge has led to the manufacture of various artificial solutions for infusion, the one most used being a warm, sterilized, physiological salt solution (NaCl, 0.95 per cent.); this is injected either subcutaneously or into any exposed vein. Transfusion is called for after copious hcemorrhage (acute anae- mia), or in such cases of poisoning when the blood-corpuscles are no longer capable of supplying the tissues with their required supply of oxygen. This condition is particularly prominent in carbon- monoxide (CO) poisoning. Plethora. — The old physicians admitted that there was in cer- tain individuals of sanguine temperament an exaggerated richness of the mass of blood as a consequence of too active nutrition. How- ever, it is impossible to verify in an experimental manner if the mass of blood be augmented. Yet plethora is usually accompanied with a swelling of the veins and arteries; an injection of mucous membrane; a full, hard pulse; congestive vertigo, and dyspnoea from pulmonary congestion. Many physicians believe that there is no such condition as too much blood in the body, unless it be introduced experimentally by transfusion. The above symptoms are explained by reason of an increased peripheral circulation at the expense of the more central one. Nevertheless, the above-named symptoms disappear by blood-letting, which would seem to admit the existence of plethora to a certain extent. An experimental plethora may be induced in dogs by trans- fusion; so that the blood may be increased from 80 to 100 per cent, without provoking any trouble. The injected plasma is soon gotten rid of, but the surplus corpuscles remain for a long time. There is also believed to be an increase in the number of red corpuscles in those persons in whom for any reason there should be a suppression of periodically recurring haemorrhages, as in menstruation and bleed- ing from the nose. Plethora of water, or liydrcemia, follows the excessive ingestion of water. The condition is but temporary, however, as an increased diuresis rapidly eliminates the excess of water. There is a physiological excess of red corpuscles in the blood of man and animals who live in hio-h altitudes. THE BLOOD. 199 MEDICO=LEGAL TESTS OF THE BLOOD. To determine that a substance under examination and inspec- tion is blood several tests are employed : — First. — Teichmann's crystals, or hsemin crystals, are a product of decomposition of the coloring matter of the blood. They may be prepared by the addition to the blood of glacial acetic acid and sodium chloride. A few granules of dried blood with a few granules of salt are pulverized on a glass slide; having covered the powder with a glass circle, a drop of the acid is allowed to flow under, when the slide is heated. If the examined substance be blood, the char- acteristic crystals appear. Second. — The Guaiacum Test. — On treating a solution of the coloring matter of the blood with an alcoholic tincture of guaiacum and an ethereal solution of hydrogen peroxide, a deep-blue coloration is produced, due to oxidation of the guaiacum resin. Third. — The Spectkoscope Test, in which characteristic bands appear. Fourth. — Careful measurements of the blood-corpuscles, their diameter, etc., by means of the microscope and photomicrographs. Fifth. — The Precipitin Test. — Strong rabbits are injected subeutaneously with 5 cubic centimeters of sterile human blood, the injections being repeated every two or five days, depending upon the condition of the test animal. The occurrence of a rise of tempera- ture above 101° F. or a decided loss in weight are considered coun- ter-indications to further injections until after this reaction has sub- sided. It is better to give injections of only 5 cubic centimeters each and always with great care as to asepsis, since abscesses often develop at or near the site of puncture. Usually 20 to 30 cubic centimeters make a sufficient quantity for the average-sized rabbit, and with due care a specific anti-serum can always be produced in from three to four weeks. After a sufficient quantity of blood has been injected to insure obtaining an anti-serum, the rabbit is chloro- formed, the chest-cavity opened, and the blood drawn from the heart into a sterile receptacle by means of a sterile trocar and cannula. The drawn blood is placed in an icebox for one hour until well coag- ulated. Carbolic acid is now added to the serum, which has separ- ated sufficiently to make the mixture approximately 0.5 per cent, acid. The serum is then drawn up into sterile pipettes and sealed. It will remain potent indefinitely if kept at a low temperature. 200 PHYSIOLOGY. The test is made as follows : A given amount of the test-serum is diluted to the desired extent with sterile water or normal saline solution. To a few cubic centimeters of this diluted solution in a sterile test-tube is added an equal quantity of a similarly diluted solution of the blood to be tested and the tube left at room tempera- ture or placed in an incubator for two or three hours at 37° C. The reaction, if it occurs, will be more rapid and marked if the tube is exposed to the higher temperature. If the dilution be sufficient the reaction will not occur at room temperature. If the test-serum is used undiluted and pure human blood is added to it, the reaction is immediate. If only the sample of blood to be tested is diluted and pure test- serum is used, the reaction is almost immediate. The reaction is marked by a turbidity of the solution, becoming constantly more intense. If an old stain is to be examined by the serum test, the material containing it is washed in sterile water or in sterile normal saline, the mixture is repeatedly filtered and finally added to some of the test-serum, as in the examination of fresh blood already described. Contamination with monkey blood can be excluded first by a great dilution of the blood tested, and a dilution of the test-serum of 1 to 500, with incubation; second, by a great dilution of the blood tested, the test-serum being used pure and the test made at room temperature. CHAPTER VI. THE CIRCULATION. In animals above the very lowest grades, as also in plants, there exists a particular liquid (nutritive fluid, blood, sap), which is agi- tated into a circular or simply oscillating movement. By reason of this movement it is permitted to reconstitute itself unceasingly, to distribute the materials of nutrition to the different parts of the or- ganism, and at the same time carry away some effete products. In the lowest orders of animal life, as the amoebae and infusoria, where no special organs are manifest and no part therefore has needs differing from any other, there is found no circulatory system — no heart or propelling body or any blood-vessels. Its life depends upon diffusion throughout its parenchyma of substances brought from with- out and of those which must be excreted. It is only as special organs show themselves and the liquids take determined directions toward one or another of them, that blood-vessels are seen to commence; these at the same time become the receptacles of products absorbed for the purposes of nutrition and the distributors of these same materials to the various tissues of the organism. It is, therefore, from complex organisms that the idea of a per- fect circulation is gained, with its admirable mechanism for incessant movement whereby the fluid necessary for its growth, functions, and individual life is forced to every part. Viewed as a whole, the vas- cular system of the higher animals forms a system of branching ves- sels or canals, closed in all parts, and not showing at any point in their course the least perceptible orifice of communication with the external world. Consequently, the fluids which have to penetrate into the closed channels of circulation, as well as those which have to emerge from them for the needs of secretion and nutrition, only do so by passage through the vascular walls; that is, through the finest filters imaginable. At a variable point in this tubular apparatus there exists an organ of propulsion, the heart, which is seconded in its work by auxiliary means and forces which aim to give a determined and con- stant direction to the movement of the circulatory fiuid. (201) 202 PHYSIOLOGY. In the study of comparative anatomy it is found that certain lower organisms are absolutely without any semblance of blood-ves- sels, yet they absorb through the periphery of their bodies the gases as well as the liquids of the fluids in which they are plunged, and, in fact, are nourished and continue to live. It is only as animals with spe- cial organs appear in the scale of animal life that there is developed a system of canals, more or less complete, which are intended to con- tain the nourishing fluid. And where there is a circulatory system there is present some means, composed — in the great majority of cases — of muscle, for the impulsion of the circulatory fluid to every part of the organism. Whenever, in animal organisms, there is transformation of energy into motion or mechanical work, it may nearly always be attributed to muscle. So that in the higher forms of animals there exist one or more rhythmically contractile organs — for the most part muscular in nature — to which is attributed the task of maintaining a definite circulation. Comparative. — Among insects and the lower orders of Crustacea the heart, if such it may be called, is simply the contractile dorsal blood-vessel; among the higher Crustacea, as the lobster, there exists dorsally a well-defined muscular sac. Among the invertebrates in general the blood passes from the arteries into irregular spaces, known as lacunae, which are situated in the tissues and from which it finds its way back into the veins to terminate in the heart for the completion of its cycle. That interesting creature, the amphioxus, the lowest of the vertebrates, possesses a primitive, lacunar vascular system. Its contractile dorsal vessel serves as its systemic heart; a ventral vessel serves as a respiratory heart, vessels proceeding from it to the gills. Fishes contain but a respiratory heart, which sends blood to the gills for aeration. It consists of a venous sinus, an auricle, and a ventricle. From the gills it finds its way to the aorta, to be distributed throughout the tissues without any further impul- sion. Among the amphibians, as the frog, there are found two auri- cles and a single ventricle. Eeptiles possess two auricles with two ventricles, though the latter are but incompletely separated. Among birds and mammals there is a heart which serves a double purpose — it sends blood to the lungs for aeration, to the body in general to serve the needs of its various tissues. The passage of the blood to the lungs is accomplished by the right auricle and ventricle and is known as the pulmonary system. That going to the tissues of the body is propelled by the left auricle and ventricle to constitute the systemic system. THE CIRCULATION. 203 THE CIRCULATORY SYSTEM. This system has for its distinctive function the propulsion of the blood to every part of the economy. It is a closed, vascular apparatus consisting of an impelling agency, or pump, with an outgoing and incoming system of vessels. The central pumping organ is the heart, from which proceed the vessels that carry the blood from the heart to the various organs and parts of the body — the arteries — and the vessels returning the impoverislied blood to the right side of the heart — the veins. Connecting the smallest arterioles and the fine radicals of the beginning veins is a network of microscopical vessels, large enough in many places to admit of but a single row of cor- puscles and whose walls are composed of a single layer of endothelial cells; these are the capillaries. THE HEART. The heart is a hollow, cone-shaped organ of muscle. It is situ- ated in the cavity of the thorax, inclosed by a serous sac : the peri- cardium. It lies between the lungs, rests on the diaphragm, and is located more on the left than on the right side. It is placed obliquely ; its broad end, or base, by attachments to the blood-vessels, is fixed to the front of the vertebral column. The base of the heart extends from the fourth to the eighth dorsal vertebra. The apex is inclined downward, forward, and to the left, where it terminates just behind the interval between the fifth and sixth ribs, ^/^ inch to the inner side of and ly, inches below the nipple. The heart is 5 inches in length; in breadth, Sy, inches; and in thiclmess. Sy^ inches. The heart is brown in color, and on its surface has a longitudinal and a transverse groove, which shows a division of the organ in four parts : the two auricles and two ventricles. The heart increases in all dimensions up to a late period in life, thus augmenting its weight. The auricles are cavities having thin walls. The base of the heart is formed by the auricles. A partition separates them and they are connected with the great veins, — the cavae and pulmonary veins. — by which they receive blood coming from every portion of the system. The aperture of communication between the auricles and ventricles is the auriculo-ventricular opening, which permits the blood to leave the auricle to enter the ventricle, but valves prevent it from running back into the auricle. The thick-walled parts of the heart are the ven- tricles, which become thicker in the direction of the apex. Like the auricles, they are separated by a partition and connected with the 204 PHYSIOLOGY. large arteries, — the pulmonary artery and aorta, — by which they send blood to the entire system. Both ventricles have valves called aortic and pulmonary, which prevent the reflow of the blood from the arteries into the ventricles. The right auricle consists of an oblong part, the sinus. The walls of the right auricle are thin and translucent, but are thickened Fig. 62. — Anterior Surface of the Heart. (Bourgeey.) 1, Right ventricle. 2, Left ventricle. 4, Right auricle. 5, Left auricle. 6, Pulmonary artery. 7, Aorta. 8, Vena cava superior. 9, Anterior coro- nary artery. 10, Posterior coronary artery. 11, Coronary vein. by means of isolated columns of muscle called the pectinate muscles. These pectinate muscles make the interior of the heart present an uneven, ridgelike appearance. On the partition between the auricles there is a shallow, oval fossa, with a border, which is the position of the foramen ovale, by which the two auricles communicated during intra- THE CIRCULATION. 205 uterine life. The openings of small veins, the foramina Thebesii, can be seen at various parts of the inner surface of the right auricle. The auriculo-ventricular orifice of the right side of the heart is a large oval aperture. It is about an inch in diameter. It is guarded by the tricuspid valve, or right auriculo-ventricular ralve. Fig. 63. — Heart of the Cow, with Left Auricle and Ventricle Laid Open. ( MuLLER. ) a, Root of the aorta. 6, Spaces in the wall of the auricle. r, c. Orifices of the pulmonary veins. 1, 1, Pulmonary veins. p, p. Papillary muscles. q, q, Columnae carneae. A, Orifice of the aorta. K, Left ventricle. S, Septum. r, Left auricle. W, Lateral wall of left ventricle. 1, 1, 2, Leaflets of mitral valve. The left auricle has thick walls, and the walls are not so trans- lucent as those of the right auricle. It has a smooth interior surface, except with the auricular appendage, where pectinate muscles are present. It has four openings, which are the pulmonary veins, two in the right and two in the left side of the auricle. At the lower 206 PHYSIOLOGY. anterior part of the cavity is the left aurieulo-ventricular orifice. The right ventricle is in the shape of a pyramid with the base upward and backward. It extends from the right auricle to near the apex of the heart, and occupies more of the front surface of the heart than the left ventricle. The walls of the right ventricle are only one-third the thickness of those of the left. The septum ventriculorum bulges into the right ventricle. There are numerous projecting ridges in the right ventricle which are muscles called the columnaB carneae. Some Fig. 64. — Diagram of Mammalian Heart. (Beclard.) a. Left ventricle. b. Right ventricle. c, Left auricle. d, Right auricle. f, Aorta. {/, {I, Pulmonary arteries. h. Inferior vena cava. i, Superior vena cava. k. Orifice of superior vena cava. /, Orifice of inferior vena cava. m, Orifice of the coronary vein. o, Left pulmonary vein. p. Right pulmonary vein. r. Orifice of the right pulmonary vein. s. Orifice of the left pulmonary vein. of them are named, from their shape, the papillary muscles, which project from the interior surface of the ventricle and end in narrow tendinous cords called the chordae tendineae. The right aurieulo-ventricular orifice opens into the ventricle at its lower back part. From its edges projects a broad, membranous fold divided into three parts and hence called the tricuspid, whose free borders are attached by the chordae tendineae to the papillary muscles and to other points on the interior surface of the ventricle. THE CIRCULATION. 207 When the valve is open the three parts lie against the interior surface of the ventricle. The duplicature of the endocardium with included fibrous tissue makes up the tricuspid valve and the chordae tendineae. The pulmonary artery springs from the base of the right ventricle. Its opening is provided with three semilunar valves. These valves are three crescentric doublings of the endocardium with fibrous tissue and are arranged in a circle. Their convex border is attached around the edge of the orifice of the artery. Behind each valve the artery is dilated into a shallow pouch, called the sinus of Valsalva, which Pulmonary valve. Aortic valve. Bicuspid valve. ■ Fig. 65. — Valves of Heart. prevents the valve. Avhen open, from adhering to the side of the artery and permits the reflow of blood readily to press the valve down to close the opening. At the middle of the free border of the valve there is a thickening of fibrous tissue, making the corpora Arantii. The left ventricle is three times the thickness of the right, and its apex forms the apex of the heart. It is longer and forms more of the posterior surface of the heart than the right ventricle. Like the right ventricle, it has columnjE carneae, papillary muscles, and chords tendines. The left auriculo-ventricular valve is provided with a pair of membranous folds forming the mitral valve, or bicuspid valve. It is larger in size and thicker than the right auriculo-ventricular valve. These mitral segments have the chordae tendineae attached. 208 PHYSIOLOGY. The left ventricle has an opening which is the origin of the great blood-vessel, the aorta. It is provided with semi-lunar or sigmoid valves, of the same character as those of the pulmonary artery. Structure of the Heart. The lining membrane of the heart is called the endocardium. All the valves of the heart are made up by its inclosing fibrous tissue. The endocardium is formed of epithelium and fibro-elastic tissue. The rings to which the valves are attached are also made of endo- cardium and fibro-elastic tissue. Muscular Structure of the Heart. The muscular fibers of the auricles consist of two layers running in different directions. The external fibers are common to both auricles, while some run into the interauricular septum. The internal fibers are not common to both auricles, but are confined to each auricle. The fibers of the internal layer are attached to their respec- tive auriculo-ventricular rings. The external fibers run in a trans- verse direction; the internal fibers cross the direction of the former. There are other muscular fibers, arranged concentrically around the origin of the great veins and auricular appendages. In the ventricles there are several layers of muscles. The outer layer runs from the base, where they are attached to the fibro-car- tilaginous rings around the orifices, toward the apex of the heart, where they run by a sharp twist into the interior of the left ventricle to the papillary muscles. This twisting of the fibers gives rise to the whorl of the fibers at the apex of the heart. Other fibers run obliquely upward in the septum to be attached to the fibro-cartilaginous ring, from which they started. Still other fibers pass in a horizontal direc- tion into the posterior wall of the left ventricle and take a ringlike course in it. The right ventricle in the arrangement of its muscular fibers may be regarded as an appendage of the left. Histology. — The fibers of the heart are striated. Unlike the voluntary muscle, they branch and have their ends united to each other so as to form a network. The open space in the network is filled with connective tissue and lymphatics. The muscle-cells are quadrangular in shape, with clear oval nuclei. There is no sar- colemma in heart-muscle. The muscles of the heart anastomose and divide. As to lymphatics, the heart is very liberally supplied with THE CIRCULATION. 209 The muscu- them. The nerves are nonmedullated near their ends lar mass of the heart is called the myocardium. Pericardium. — This is a fibro-serous sac inclosing the heart, and consists of two leaves, or layers. The internal serous, or visceral, layer closely invests the heart and the commencement of the great blood-vessels. It is an inextensible membrane. n Fig. 06. — Course of Muscular Fibers of Heart. (Landois. ) I. Course of the muscular fibers on the left auricle, with the outer trans- verse and inner longitudinal fibers, the circular fibers on the pulmonary veins (r. p.). T, The left ventricle. (John Reid.) II. Arrangement of the striped muscular fibers on the superior vena cava. a, Opening of the vena .izygos. Y, Auricle. (Elischer.) The external filirous. or parietal, layer is a strong, inelastic mem- brane which embraces the origin of the great blood-vessels at the base of the heart. These two layers unite to make a close sac. Between the pari- etal and visceral layers is the pericardial liquor, which permits the two layers to slide on each other without friction. The elastic fibers 14 210 PHYSIOLOGY. in the parietal layer permit of its following very closely the chang- ing form of the heart. The Auricles. — In examining each half of the heart it is easy to recognize that the auricle, on account of the thinness and the weak- ness of its muscular walls, can scarcely be the important part of that organ. In laying bare the heart of an animal while artificial respira- tion is maintained, it is seen that the action of the auricle is very weak as compared with that of the ventricle. A manometer introduced into the auricular cavity at the moment when it contracts marks a Fig. 67. — Course of the Ventricular Muscular Fibers. (LandOIS.) A, On the anterior surface. B, View of the apex with the vortex. V, Course of the fibers within the ventricular wall. D, Fibers passing into a papillary muscle, P. pressure that is five or six times less than that obtained in the corres- ponding ventricular cavity under the same conditions. The pressure in the auricles is lowest at the period of diastole, and since, then, the pressure in the veins is greater than the pres- sure in the auricles, there is a flow of blood into the auricles, which gradually becomes less. When the ventricles dilate, another fall in the auricular pressure takes place and another rush of venous blood follows. The opening of the great veins is contracted, and this act, THE CIRCULATION. 211 preceding the contraction of the auricle, drives the blood from the veins into the auricles. When the auricles contract, the blood can- not flow back into the veins to any great extent. The Ventricles. — The ventricles represent the parts that are really active in the cardiac circulation. The strength of the contrac- tions proper to the two ventricles reveals itself in the thickness of the muscular walls, the fibers of which are inserted into fibrous rings. These latter are the veritable skeleton of the heart. Manometric observation presents us with proof of the force of the ventricular contractions. GENERAL COURSE OF THE CIRCULATION. Since the main points of the anatomy of the heart have been touched upon, it might be well at this stage roughly to consider the circuit of the blood through it and its vessels. The vascular system is a closed apparatus consisting of a central pump with its vessels leading to every part and organ of the economy. All vessels lead- ing aivay from the heart are arteries; those leading toward it are veins. The entire circuit of the blood is divided into two principal por- tions, which are distinctly separated from one another both ana- tomically and functionally. The one conveys the blood to and from the lungs during the process of aeration; so that to it has been affixed the term pulmonary circulation. The other has for its func- tion the distribution of the blood to all parts and organs of the economy in general, thereby receiving the name systemic circulation. Beginning with the left ventricle, the blood is conveyed to the aorta, from which branches are distributed to every part of the body, through the capillaries to the veins, to be eventually returned as dark, impure blood to the right auricle. This, the greater circuit, has been termed the systemic circulation. During the course of this circulation it has been found that the blood from the capillaries of some of the abdominal viscera is gathered together into a single ves- sel, the portal vein, which again subdivides to form a capillary plexus in the liver. This accessory circulation is commonly designated as the portal circulation. From the right auricle the blood flows into the right ventricle, from which it is expelled through the pulmonary artery to the lungs, to be returned to the left auricle as bright-red, pure blood. This change in color is due to the presence of oxygen in the haemoglobin 212 PHYSIOLOGY. gained during the process of aeration. This shorter circuit is known as the lesser, or pulmonary, circulation. Difference of pressure between the blood of the aorta and pul- monary artery, on the one hand, and that in the venue cavae and pul- monary veins, on the other hand, is responsible for the flow of blood. Fig. 6S. — Diagram of the Circulation. (Duval.) 1, Left ventricle. 2, Left auricle. 3, Right ventricle. 4, Right auricle. 5, Aorta. 6, Systemic capillaries. 7, Inferior vena cava. S, Pulmonary artery. 9, Pulmonary capillaries. 10, Pulmonary vein. 11, Gastric and intes- tinal vessels. 12, Intestine. 13, Portal vein. 14, Portal vein, forming second capillary system in the liver 15, Liver. 16, Hepatic vein. 17, Pulmonary, or lesser, circulation. 18, Systemic, or greater, circulation. Its direction is always in the line of least resistance. The greater the difference of pressure, the greater is the velocity of the blood- stream; the reduction of this difference to nil, as in death, results in no movement. ' THE CIRCULATION. 213 CHANGES IN THE SHAPE OF THE HEART. When the auricles contract, they become smaller. When the ventricles contract, the base of the heart approaches the apex (lur- ing the contraction of the fibers running in a longitudinal direction. As the blood escapes from the ventricles, then the lateral and antero- posterior diameters lessen. CHANGE IN POSITION OF THE HEART. In diastole, the heart hangs downward and to tlie left from the line of its basal attachment. During contraction, it assumes a posi- tion at right angles to its base and presses the heart in contact with the chest more vigorously, producing the impulse of the heart. 01 02 03 04 05 06 07 08 09 lOeecs. I [Heart Sounds dup Lnbb dup Fig. 69. — A Cardiac Cycle. (Starling.) CARDIAC REVOLUTION. The cardiac revolution may be divided as follows: (1) the first sound; (2) the first, or short, silence; (3) the second sound; and, (4) the second, or long, silence. If the cardiac revolution be divided into tenths, then the first sound will be Yio ; the first silence, ^/^^o; the second sound, -/if,; and the long silence, ^/^q. The time of the various acts of the total cardiac movement in man are, according to Gibson, as follows: — Auricular systole 0.112 second. Ventricular systole 0.368 second. Ventricular diastole 0.578 second. Cardiac cycle 1.058 seconds. 214 PHYSIOLOGY. The rhythmica,! succession of these acts constitutes the cardiac revolution. By their function the vital fluid — the blood — is kept in constant circulation within the body so that every portion of the economy receives its proper nourishment. The processes of meta- bolism are balanced, the various organs and glands of the body per- form their needed functions, and the whole animal lives and thrives. The events in a cardiac revolution can be tabulated as follows : — 1st period. Auricular Systole. Accomplishment of ven- tricular diastole. 3d period. General diastole of the heart. Closure of semilunar valves. The blood pours into the auricles, and a little into the ventri- cles. 2d period. Ventricular systole. Closure of mitral and tricuspid valves. Opening of semilunar valves. The blood is thrown in- to the aortic and pul- monary arteries. Cardiac impulse. Diastole of the arteries and the pulse. Auricular diastole. To physiologists, the first period in the movement of the heart coincides with contraction of the auricles. The clinicians take the first period at the moment of ventricular systole. MOVEMENTS OF THE HEART. The heart movements consist of alternate contractions and relaxations, which follow each other with a certain rhythm. Systole is the name for contraction; diastole is the term for relaxation. The two auricles contract and relax synchronously, and these movements are followed by a simultaneous contraction and relaxa- tion of the ventricles. There is a systole and diastole of auricles and a systole and diastole of ventricles. At last there is a very short period in which the heart is in diastole. The succession of move- ments from the commencement of one auricular systole to the com- mencement of one immediately following is known as a cardiac rev- olution. The auricular contraction is less sudden than the ventri- cular. The contraction of the auricle lasts a very short time, while the time of ventricular contraction is considerable, and the relaxa- tion of the ventricle is slow. The time of contraction of the auricle and its repletion are about the same, but the ventricular diastole is nearly twice as long as the ventricular systole. The auricles have a uniform, wavelike move- THE CIRCULATION. 215 ment; the ventricles have a spasmodic action in their movement. If now the venae cava? and pulmonary veins are delivering blood into the two auricles, then at this time the diastole of the auricles is gradually approaching completeness. The swelling of the auricles is due, in part, to the pressure in the veins being greater than in the cavity of the auricles and in part to the inspiratory movement of the thorax sucking the blood from the veins external to the thorax to the interior of the veins of the chest. During this period the ventricles are filling with blood, for both the triscuspid and mitral valves are open. As the cavity of the auricles is smaller tlian that of the ventricles, the auricles are filled sooner, and consequently con- tract before the ventricles, the veins offering a resistance to the backward movement of the blood by a narrowing of their opening. The systole of the auricle forces the blood chiefiy in the line of least resistance into the ventricle, which is not yet completely filled and is undergoing diastole. While the blood is passing from the auricles into the ventricles the auriculo-ventricular valves are floated grad- ually into a horizontal position. The blood by the systole of the auricles has filled the ventricles, already filled in part during the diastole of the auricle. Now the ventricles contract, the mitral and tricuspid valves are tightly pressed together, and regurgitation of blood into the auricles is prevented. Now, as the blood cannot go back into the auricles, it must by the muscular force of the ven- tricles rush into the pulmonary artery and aorta, respectively. The onset of the blood forces open the semilunar valves of the pulmonary artery and aorta, and exerts a pressure in these arteries partially filled with blood before the new rush of blood sets in. Their walls are necessarily considerably distended. Then the ventricles dilate and at the same time the mitral and tricuspid valves open, and the semilunar valves close from the recoil of blood against them. From the time the systole of the ventricles ends to the full distension of the auricles, all the chambers of the heart are in diastole and are being filled with blood. This is the resting of the heart, and is called the pause. Pathological Cardiac Action. — An increase in the heart's action is produced by any resistance either to the heart itself or to any of its blood-vessels. With increased action the heart-muscle under- goes hypertrophy, and frequently, dilatation also. The most common resistance met with in the vessels is narrow- ing of their lumen or want of elasticity in their walls. Within the heart the most usual defects are narrowing of the orifices or incom- 216 PHYSIOLOGY. petency of the valves. On account of the latter condition blood is allowed to escape in the wrong direction so that the heart must do extra work to keep all of it in circulation. Palpitation and syncope are two very common conditions met with, and they are due to faulty heart-action, induced perhaps by causes that are more or less remote. The Cardiac Impulse. — Synchronous with this is "apex-beat,'^ by which is understood that surface movement which is seen or the impulse that can be felt within a circumscribed area and is produced by ventricular systole. This area is located in the fifth left inter- costal space between the mammary and midsteriial lines. The cen- ter of this area is described as being two inches below the nipple and one inch to its sternal side. Fig. 70. — SiiiuIi'iHon Cardiograph. The cause of the impulse of the heart is not the apex but the change in form and consistency of the ventricles, when these pass from the diastole to the systole and in the instantaneous transforma- tion. It is the sudden hardening of the ventricle. The impulse takes place at the same time as the systole of the ventricle, and is caused by the ventricle, which is pressed very firmly against the chest. At the time of the contraction of tlie ventricle the outline of the heart changes; instead of being an oblique cone having an elliptical base, as at rest, it becomes a regular cone with a regular base. For giving more accurate accounts of the heart's movements recourse is had to the instruments called cardiographs. Cardiographs. — These are instruments which give graphic rec- ords of the heart's movements. They register at the same time the movements of the auricles, ventricles, and the beating of the heart THE CIRCULATION. 217 against the walls of the chest. For obtaining these records of ani- mals the heart was exposed, and levers were attached to various parts of it so that their distal ends could make tracings upon a revolving, blackened surface. This apparatus was inapplicable for use upon the human heart, but there are to-day for its study numerous cardiographs, all of them, however, being only modifications of Marey's tambours. Sanderson^s instrument consists of a hollow disc, the rim and back of which are of brass, while the front is of thin rubber. On its back is a flat steel spring bent at right angles, and its unattached end is provided with an ivory button which is directly over the cen- ter of the rubber membrane. The ivory button is applied over the point where the apex-beat is most plainly felt. During the applica- Fig. 71. — Cardiogram (B) witli Simultaneous Record of Heart- sounds (A). ( HuRTHLE, Starling. ) 1, Position of first sound. 2, Position of second heart-sound. The first heart-sound, corresponding to the systole of the ventricle, begins at the notch in the cardiogram near the top of the ascent; hence the ascent of curve pre- ceding this notch is due to auricular systole forcing blood into the ventricle, and the ventricular systole is indicated by the notch. tion of the apparatus the ivory button is kept continually in motion by the surface pulsations. Each movement of the button sets the rubber membrane in motion, and, as the drum is airtight and in communication with a second drum with a recording lever, the diminution of air in the first causes an increase in the content of air in the second, and an elevation of its recording lever on a smoked drum. Each systole of the ventricle causes a sudden rise of the lever, and the end of the systole is noted by a marked gradual descent of it. The cardiogram is read from right to left, and normally shows a small elevation, corresponding to auricular systole, immediatelv suc- ceeded by a very abrupt rise which marks ventricular svstole. This 218 PHYSIOLOGY. is held for 0.3 of a second and presents small vibrations, which are at- tributed to the closure of the semilunar valves. The very abrupt, downward stroke marks the pause, or diastole. Clinically^ changes in the cardiac impulse are best ascertained by using any of the graphic instruments and then studying the curves obtained. From such study the observer is able to get very definite knowledge as to the nature of the cardiac lesion, its severity, etc. The various stenoses, insufficiencies, hypertrophies, and dilatations may by this means be diagnosed with considerable accuracy. Endocardiac Pressure. — The ordinary mercurial manometer, by which the heart's work can be estimated, is unsuitable for determin- ing its ventricular pressure. The objections are the relatively great amount of work required to produce a given displacement of the mer- cury; that it is not susceptible and sensitive to quickly follow differ- ences of pressure; and when once displaced, the mercury possesses enough oscillations of its own which confuse oscillations of blood- pressure. However, when this instrument by the introduction of a properly placed valve is converted into a "maximum and minimum manometer," the actual blood-pressure may be more readily deter- mined. The dog has been very extensively used for the application of this instrument, as a consequence of which the appended figures are given : — Systole. Diastole. Maximum Pressure. Minimum Pressure. Left ventricle 140 millimeters — 30 to 40 millimeters. Right ventricle 60 " — 15 " Right auricle 20 " — 7 to 8 By negative pressure is meant that the mercury in the instru- ment has been sucked toward the heart. The negative pressure, as is seen, occurs only during the diastole of the heart. Moens is of the opinion that this negative pressure within the ventricle happens shortly before the systole has reached its height. During negative pressure the blood from the veins is sucked into the heart. For determination of the duration of the cardiac events, as well as the blood-pressure — that is, to have tracings of the curves for each cavity, to know the time-relations for comparisons, as well as the curves of the great arteries and veins — requires an instrument of some complexity. Only within recent years have these been invented, by Chauveau and Marey, whereby elastic manometers counterbalance the blood-pressure instead of a column of liquid. Many of the in- THE CIRCULATION. 219 struments employed give their tracings from movements transmitted to them from cardiac sounds through a tube to the recording appa- ratus. The sounds were usually appropriately curved cannula?, to one end of which were attached flexible rubber bags, or ampullae. Two were introduced through the jugular vein into the right auricule and ventricle, a third into an intercostal space in front of the heart. These were put into communication with three tambours with their needles, by which were recorded the endocardiac pressure with the duration of the auricular and ventricular contractions. By these levers it was shown without doubt that the apex-beat is due to the systole of the ventricle, as the two were synchronous. ' z .3 4 r' ' . y^-' ~~ — -. — , ~^j ~- — ,J 1 z 3 4 Line of a'mosplieric pressure. Fig. 72. — Magnified curve of the course of pressure within the left ventricle and the aorta of the dog, the chest being open; to be read from left to right. Recorded simultaneously by two elastic manometers with transmission by liquid. (Porter.) In both curves the ordinates having the same numbers have the foHowing meaning: 1, The instant preceding the closing of the mitral valve. 2, The opening of the semilunar valve. 3, The beginning of the "dicrotic wave," regarded as marking the instant of closure of the semilunar valve. 4, The instant preceding the opening of the mitral valve. Pressure Curve in the Ventricle. — Experiments on ventricular pressure have been made with Fick's elastic manometer and the dif- ferential manometer of Hiirthle. Dr. Porter, of Harvard, has made a study of this subject with the instrument of Hiirthle, and I shall follow him in the description of the curves obtained. Porter (Fig. 72), with his predecessors, has shown that the systolic muscular contractions begin quite suddenly, producing a swift rise of pressure. The diastolic fall of pressure is nearly as sudden as the rise. In the fall of diastolic pressure, the pen often reaches below the pressure of the atmosphere. Between the systolic rise and the diastolic fall it is found that the systolic pressure causes its 220 PHYSIOLOGY. curve to bend alternately downward and upward. Between these two points the general direction of the curve approaches the hori- zontal, and thus may be denominated the "systolic plateau." The curve of intraventricular pressure rarely gives any clear indication of the beginning or end of auricular systole. The ventricular pres- sure curve does not give any clear indication of the moment of clos- ing or opening of either auriculo-ventricular or semilunar valves. These instances can, however, be marked upon it after they have been obtained in an indirect manner. In Fig. 72 the ordinate 1 indicates the closing, and ordinate 4 the opening of the mitral valve; ordinate 2 indicates the opening, and ordinate 3 the closing of the aortic valve. In the arterial curve, 2 marks the beginning of the systolic rise and 3 the beginning of the dicrotic wave, which corresponds closely to the closure of the aortic valve. During the period when the bicuspid valve is open, the pres- sure is lower in the ventricle than in the artery, the aortic valve is shut, and blood is entering the ventricle, this being the "period of the reception of blood," During the greater part of the period when the bicuspid valve is shut, the aortic valve is open, the pressure is higher in the ventricle than in the artery, the ejection of blood is taking place, this being the "period of ejection," which lies between the ordinates 2 and 3 (Fig, 72). There are two brief periods, during each of which both valves are shut and the ventricle is a closed cavity; one immediately pre- cedes the period of ejection, the other immediately follows it. The explanation of these periods is that it takes a brief time for the cardiac muscle, contracting upon the blood in the closed ventricle, to raise the pressure to the high point required to overcome the opposing pressure within the artery and to open the aortic valve. Hence the ventricular cycle is composed of four periods: the first, the period of complete closure with strongly rising pressure; the second, the period of ejection, relatively long; the third, a period of complete closure, with swiftly falling pressure; the fourth is the period when the pressure is low and blood is entering the ventricle. Persistence of the Heart Movement. — The heart may continue to beat for some time after its removal from the body. This is par- ticularly noticeable in cold-blooded animals like the turtle, whose heart movements have been known to continue even for days. When the heart dies the ventricles stop first, but the right auricle is the last to be arrested; hence it is called the " ultimum moriens." THE CIRCULATION. 221 50UNDS OF THE HEART. When the ear is placed over the cardiac region, or to a stetho- scope applied to the precordial area, two characteristic sounds are heard. The two sounds are known as the first sound and second sound, and are emitted during every cardiac revolution. Though the sounds occur in quick succession, yet they are each separated by silences. The first sound is the stronger of the two. In nature it is dull. It coincides with the shock of the heart. The first sound is fol- lowed by the first, or short, silence. The second sound is shorter in duration and clearer in character than the first. It conies an instant afterward, at the moment when the whole heart is in relaxation. In pitch, the second sound is from one-fourth to one-third higher than that of the first sound. Following the second sound of the heart there occurs the second, or long, silence. In reality the pause occupies but a fraction of a second, yet it is said to be "long" as compared with the first silence. It must be borne in mind by the student that there occur in reality four sounds during each cardiac cycle. However, the first two normally occur in unison, as do the second two, so that but two sounds are heard by the examiner. From their difference in pitch the two heart-sounds may be expressed graphically upon the musical staff. To the ear they sim- ulate the sounds which are produced in pronouncing the words, "lubb," "dup," the former corresponding to the first heart-sound, the latter to the second. If the two sounds be listened to at some distance from the heart, the first may nearly always be distinguished from the second by com- paring the intervals between them. The time elapsing between the first and second sounds is generally much shorter than that which separates the second sound from the first in the succeeding revolu- tion of the heart. But, in medical practice, too much importance must not be attached to these intervals, since their respective dura- tion is extremely variable. In the absence of the impulse it is bet- ter to depend upon the differences of pitch. Causes of the Sounds. — The nature and causes of the cardiac sounds are best studied in a large mammal whose heart-action is comparatively slow. For this purpose the horse is used. Its pulse averages but forty. The animal is properly prepared by anaesthe- tizing, curarizing, and exposing the viscus to view by placing a win- 222 PHYSIOLOGY. (low in the thorax. With stethoscope and by observation and pal- pation, the experimenter is ready to determine, among the complex actions which make up a cardiac cycle, the one which gives rise to each of the two sounds. Second Sound. — The cause of the second sound is the sudden closure of the sigmoid (semilunar) valves of the aorta and pulmonary artery during relaxation of the ventricle. The sudden closing of the valves is produced during the effort of the arterial blood to escape backward from the elastic reaction of the aorta and pulmon- ary artery. Proofs abound in support of this theory. If the valvular move- ments be hindered in one of the above-mentioned arteries by placing a clamp close to its base, immediately the second sound is suppressed Fig. 73. — The Action of the Semilunar Valves. (Chauveau.) Pp, Tracing of the variations of pressure in the left ventricle. 2, Means second sound. 8, Tracing by the signal magnet, showing the action of the valve which by its movements closes and opens an electric current to the signal magnet. The second sound (closure of the semilunar valves) corresponds to the moment when the ventricle relaxes, that is, at the beginning of the ven- tricular diastole. at that point. If the valvular action of both vessels be suppressed, the second sound may be completely extinguished. Again, should the apex of the heart be cut off and the ventri- cular blood be made to escape to the outside, no second sound occurs. In this experiment the sigmoid valves have neither been lifted up nor allowed to fall back and stretch themselves out with a sound. Physically, one is able to account for the production of the second sound on the principle that it is produced by the clicking of the sigmoid valves. In fact, similar sounds are obtained by produc- ing sudden tension of a membrane under the action of a column of liquid. When the initial stump of an aorta, whose valves are still intact, is attached to a tube and the reflux of the liquid closes the valves, a clear, snappy click is produced. THE CIRCULATION. 223 When pathological conditions occur, the sound is altered, being accompanied by or even altogether replaced by a blowing sound, known as a "munnur." The Cause of the Fisst Sound is more difficult to determine than is that of the second. The nature of this sound is more com- plex, several factors entering into its evolvement. Since it is established that the first sound corresponds in point of time with ventricular systole, it is reasonable to connect it with one or several phenomena which take place in the heart at that moment. They are: The precordial shock, contraction of the ven- tricles, occlusion of the auriculo-ventricular valves, and opening of the sisrmoid valves. Fig. 74. — The Action of the Tricuspid Valve. (Ciiauveau.) Pr, Tracing cf the variations of pressure in the right ventricle. 1, Means first sound S, Tracing by the signal magnet, showing the action of the valve, ■which by its movements closes and opens an electric current to the signal magnet. The first sound (closure of the auriculo-ventricular valves) is simul- taneous with the beginning of the ventricular systole and it produces during the first sound a ra,pid ascent of the curve of ventricular pressure. While the above phenomena are synchronous with the first sound, yet the majority of them are believed to have no action in producing the first sound. Thus, the sound is audible in a heart from before which the chest-wall has been removed, so that precor- dial shock is not the source of the sound. That the opening of the sigmoid (semilunar) valves is not of consequence has long been refuted by experiment. In the case of the second sound we just learned that the pro- duction of it was due to the closure of the sigmoid valves. In like manner the closure of the auriculo-ventricular valves is in part the cause of the first sound. Wintrich, by means of proper resonators, was able to analyze the first sound and so distinguish the clear, snappy valvular component of this so-called solid sound. The very fact that the sound is low and booming in nature demonstrates the fact that there must be some other component entering into its causation. 224 PHYSIOLOGY. The tension and vibration of the chordae tendinea? are factors in producing sound, but the nature of it is similar in every respect to that produced by valvular vibration. Even though the auriculo-ventricular valves and their chordae tendinese be destroyed in an excised heart, yet will there be pro- duced a feeble sound of rather low pitch. This sound is believed to be produced by the contraction of the muscular fibers of ventricular walls, and has been termed ^^muscle-sound." Any muscle whatever, during its contraction, gives rise to a dull sound. It is evident then that, during contraction of the ventricle, this same phenomenon must occur and so contribute its part to the production of the first sound. From new experiments it appears that the role of the muscular contraction is more important than it has generally been thought to be. For verification of this the following experiment seems to be decisive : — The heart is exposed in a dog which has been poisoned with curare and in which artificial respiration has been maintained dur- ing two hours. The left veritricle is cut open in front and at the back with scissors along the intraventricular partition. The incis- ions are rapidly lengthened from the apex toward the base in such a manner as to turn completely outside all the ventricular wall. This portion is no longer held to the rest of the heart except by the auricle. The suspended piece of ventricular wall, under these conditions, continues to contract with force and rhythm for some seconds. If the stethoscope be applied to the internal face of the stump, it per- mits us to hear at the moment of each contraction a sound that is exactly like the one which had been perceived in the nonmutilated. There is, however, a vast difference in intensity, the sound emitted from the experimental heart-muscle being very weak. The contraction of the auricles is not considered at all as being a factor in the production of cardiac sounds. Eepeated experiments have proved the auricular contractions to be inaudible. Position of Valves and the Areas of Audibility. — The pulmonary and tricuspid of the right side lie nearer the surface than the aortic and mitral of the left. The best point to hear the pulmonary valve is chiefly behind the third left costal cartilage. For the aortic valve it is behind the left half of the sternum, on a level with the third space. For the mitral valve it is behind the left half of the sternum, on a level with THE CIRCULATION. 225 the fourth and upper border of the fifth cartilage. For the tricuspid valve, behind the lower fourth of the sternum, to the right of the iniddle line from the fourth right cartilage to a point behind the junction of the sixth right cartilage to the sternum. Variations in Heart-sounds. — Increase in the intensity of the first sound of the heart is indicative of a more vigorous contraction of the ventricles, with, of course, greater tension of the auriculo- ventricular valves. Increase of the second sound denotes a higher tension in the corresponding large arteries. The condition is usually demonstra- tive of overfilling and congestion of the pulmonary circuit. With equal intensity the muscular sound of the left ventricle is appre- ciably longer than that of the right. Weak heart-sounds are indicative of a feeble action of the heart and usually denote degenerations of the heart-muscle. The Coronary Arteries. — The heart-muscle, by reason of its almost constant activity, must be very generously supplied with blood to insure its proper nutrition. In it are found a system of arteries, capillaries, and veins, known as the coronary vessels. The arteries going to the heart-muscle are two in number: the right and left coronary. They are the first branches of the aorta, and take their origin just above the level of the free margins of the semi- lunar valves. The diameter of the coronary arteries is that of a crow's quill. From these main vessels there proceed numerous branches which dip down into the heart-substance, dividing and sub- dividing as they go until a system of capillaries is formed. The effete products are conveyed to the general circulatory sys- tem by the coronary vein, which empties its blood into the right auricle. It, with its branches, is provided with valves, since every auri- cular systole interrupts the venous flow; the ventricular contrac- tions, however, accelerate its flow. The coronary arteries are char- acterized by their very thick connective tissue and elastic intima, which perhaps accounts for the frequent occurrence of atheroma of these vessels. Ligature of the coronaries in the case of dogs is followed by very prompt results, because of the sudden anaemia and inability of the heart to rid itself of its metabolic, decomposition products. Within two minutes the cardiac contractions become very irregular, give place to twitches, and then all movements cease. In those cases of fatty degeneration where alteration of the cor- 15 226 PHYSIOLOGY, onary vessel-walls produces the condition known as atheroma, the symptoms of ligaturing and of sudden death occur because of the sudden arrest of the heart's action. At the beginning of systole the blood rushes into the coronary arteries in the same fashion that it does into other arteries. How- ever, later, during systole, the branches of the coronary arteries are so squeezed by the strong ventricular contractions that the passage of the blood is temporarily obstructed or even made to retrograde. Before the blood can recede to any extent, systole has ended and the blood then flows along as before. It has also been found that, during the beginning of a ventri- cular systole, a cut into the coronary artery of a living animal causes a spurt of blood from the central end of the artery. A shortening of the diastolic period lessens the nutritive supply to the heart. Diastolic distension of the left heart by "back pres- sure" lessens the coronary flow. These facts are of much practical import in diseases of the heart. Frequency of the Heart's Action. — During health the heart acts so smoothly and with so little concern on our part that there is required considerable self-attention before any differences are seen to exist. Its action, as studied from the throbbings (pulse) that are exhibited by some of the more superficial arteries, and each of which corresponds to ventricular systole, is found to lie in very close sym- pathy to the other great functions of the economy and is accordingly influenced by them. The average number of adult beats is 73 per minute. Even in health great deviation on either side of this standard may exist, depending upon age, sex, size, food and drink, 3xercise, posture, etc. That age and sex exercise an influence upon the frequency of the heart's movements must be remembered by the clinician when making his diagnosis. From the annexed table it will be noticed that just before birth the rate, as determined by the stethoscope, is very high, but gradually diminishes until very old age, when there is a slight increase. Sex is very influential, the female heart averaging about eight beats more per minute. It has been noticed that the rule seems to be that smaller ani- mals possess a greater amount of neuro-muscular activity than larger ones. Among human beings this is also applicable, shorter people usually having a pulse that is a trifle more rapid than taller people. Idiosyncrasies are frequently found which are at first very mislead- ing to the diagnostician. Thus, the pulse of Napoleon I often did not exceed 40 beats to the minute, yet he was perfectly well. After THE CIRCULATION. 227 each meal there is an increase of from 5 to 10 beats, while following very violent exercise the figures 140 or 150 may be reached. During health there is found a nearly constant relation existing between the number of heart-beats and of respirations. This pro- portion is four heart-beats for every single respiration. Even when the number is very much increased from violent exercise or any other cause, the proportion still remains constant. Pathological conditions usually alter this relation. Landois gives the following results : — In male adults the pulse-rate is 72, in females 80. Pulsations per Minute. Age Malk. Foetal 130 to 140 1 year 120 to 130 2 years 105 3 years 100 4 years 97 5 years 94 10 years 90 10 to 15 years 78 15 to 50 years 70 80 to 90 years 80 Work of the Heart. — When a force produces acceleration, or when it maintains motion unchanged in opposition to resistance, it is said to do worJc. To convey an impression of the amount of work done by any machine, it is usual to express its efficiency in terms of work-units. This is a comparatively easy task when attempted in the physical world, but becomes extremely difficult when one attempts to express in terms of work-units the force of the heart's action. The work of the heart — central pump, that it is — is so hard to reckon in view of the ill-defined data that we are able to obtain as to the resistance which it overcomes and from the fact that different portions of this human machine are known to exert different degrees of force. Anatomical differences, then, in the heart musculature permit the conclusion that the left heart, the walls of which are thicker, has more force than the right heart. It is reasonable to state from these premises that where the ventricular walls are three times thicker in one-half of the heart than they are in the other, that one must have a thrice greater systolic force than the other half. The work of the heart is usually expressed in kilogrammeters. A kilogrammeter is equal to 7.24 foot-pounds. To estimate the work of the heart according to Dr. Leonard Hill, the mean pressure 228 PHYSIOLOGY. and velocity in the aorta and the volume of blood ejected by the ventricle must be obtained. If W be the work done during systole of the left ventricle in gram centimeters; Q, the volume of the output in cubic centimeters; M, the mass of the output in grams; P, the specific gravity of the blood (.•. M = PQ); V, the mean velocity in the aorta; H, the mean aortic pressure in grams per centimeter; g, the acceleration due to gravity ^981 centimeters per second, then MV 2g . W = QH+ ^^^' 2g The mean aortic pressure may be put down as 12 centimeters of mercury (specific gravity of mercury = 13.5). The volume of the systolic output is about 110 cubic centimeters. Substituting these data in the above equation one obtains: — ■ 1 05 X 110 X 33^ W= 110 + 12 + 13.5 + ~ = 17.880 gram cen- 2 X 981 ^ timeters. If in the case of the right ventricle the mean pressure in the pulmonary artery be taken to be -1 centimeters of the mercury, the work of that ventricle will be one-third of that of the left ventricle. Thus, the total work of each systole of the heart will be 17,880 X Vs = 23,640 gram centimeters, and the total work of the heart will be per day about 24,000 kilogrammeters, or 1000 kilo- grammeters per hour, or the equivalent of about V50 of the whole amount of heat produced in the body. INNERVATION OF THE HEART. If the heart be removed from the chest or all of its nerves be severed, it will still continue to beat for a variable time, dependent upon the class of animal operated upon. In the case of the frog and other cold-blooded animals the beating of the heart will continue for hours under favorable conditions. From this it would seem that there must reside within the heart itself some mechanism whereby the rhythmical movements of the heart are maintained. Like every other organ of the body, the heart receives its pro- per quota of nerve-supply, through whose medium are conducted cer- tain impulses from without and by whose influence its rhythm may THE CIRCULATION. 229 be altered. Yet, in addition there would seem to be nerve-ganglia within the heart-substauce which behave as stimuli to the heart and so maintain its ordinary rhythmical movements. Cardiac Ganglia. — This internal mechanism has been chiefly studied in the frog, where there exist in the heart three distinct ganglia: Remak's, Bidder's, and von Bezold's. From the cells of these ganglia there are discerned numerous small fibers which form a plexus over the surface of the auricles and upper portion of the ventricles. Remah's ganglion is seen at the orifice of the superior vena cava or sinus venosus. Bidder's is located at the jimction of the auricles and ventricles in the auriculo-ventricular groove. Von Bezold's ganglion has its seat in the interauricular septum. The heart of a mammal differs from that of an amphibian only in that there are several groups of ganglia in the mammals, while I A, II ^*^^^fc ^-^ Yri ^^^^T* s«v^^H fw ^ ^^m -YJv' ml^jb ^^^Voi Fig. 75.— He; irt of the Frog. ( Livox. ) I. Anterior view. II. Posterior view. A, A, Aortse. Vc, Superior vena cava. Or, Auricle. F, Ventricle. Ba, Aortic bulb. «S'F, Sinus venosus. Tci, Inferior vena cava. Tb, Hepatic vein. Vh, Pulmonary vein. but one exists in the amphibians. However, these several ganglia of the mammal are believed to be automatically and physiologically equivalent to the homologous single ganglion or group of ganglia of the amphibian. The same general laws may be applied to both. Cause of Cardiac Rhythm. — The rhythm of the ventricle is a property of the cardiac muscle. In the maintenance of this rhythm the nervous system does not intervene except as an ordinary excitant of muscle. It is known that, if the apex of the frog's heart be cut away, it is then separated from all ganglia. The excised por- tion does not beat spontaneously, while the rest of the heart, the auricles and the base of the ventricles, continue their rhythmical action. Thus it seems that the ventricles normally contract under the persuasion of irritations which arise in them from the cardiac ganglionic cells. 230 . PHYSIOLOGY. If now the isolated and immovable portion of the heart be placed under a cardiograph and subjected to opening of the induc- tion current, there will result a pulsation from each isolated induc- tion shock. It is a remarkable fact that, if this same excised portion be excited by frequent breaks (at least thirty per second), the muscle beats rhythmically. Ordinary striped muscle responds to isolated and separate breaks of the induction current by manifesting isolated contractions. Heart-muscle cannot be tetanized. Hence this observation would force us to the conclusion that the heart's rhythm does not depend upon the ganglionic cells of the heart. The rhythm is the property of the cardiac muscle to react to the frequent excitations which it receives. In this respect cardiac muscle is completely differentiated from ordinary striated muscle. It is a mistake to seek to make the rhyth- mical property of the cardiac muscle a property of ordinary muscle. Theory of Cardiac Rhythm. — The heart is not equally excitable during rest and during action ; it is less excitable during action than during waning action; that is, during the beginning than during the end of systole. The comparative want of excitability is so marked during the commencement of systole that this period has been called the refractory period. The auricles and ventricles do not receive excitations except during and at the end of diastole, because of the refractory phase during cardiac contraction. It is during diastole that the cavities of the heart possess greatest excitability. At the end of general diastole the auricles and ventricles are full of blood, particularly the auricles. By reason of this blood-distension the auricles become excited and contract. The blood is rushed into the ventricles, dilating them to their maximum. From distension produced in them and also from ganglionic impulses which were not efficacious except at this moment, the ventricles are made to contract in their turn. With each cardiac cycle the same phenomena are manifested, the result being a rhythmical action of the heart. The warm-blooded heart increases its pulsations with rise of temperature and decreases them correspondingly with fall of tem- perature. The temperature does not act through the endocardium, but directly upon the muscle itself or its ganglia. Direct irritation of the surface of the ventricle with tetanizing currents of electricity shows a marked change in the rhythm. Upon THE CIRCULATION. 231 the human heart the constant current calls out an acceleration of the heart, while an induction current is without effect. Hence, in apparent death the proper current to employ to stir up the heart is the constant current. Numerous experiments have been performed upon the hearts of animals (the frog chiefly) for determihing the causes and means of control of the rhythmical movements of the heart. The experi- ments consist, for the most part, of ligaturing various portions of the heart, and are performed by tightening and then relaxing the ligature so that the physiological connection is destroyed, while its anatomical and mechanical functions are still intact. The most important, as well as best known, of the ligature experiments is the one known as : — A. Ligature below the auriculo-ventricular groove (L) ; the sinus venosus (3) and the auricles (1) continue to beat, but the apex of the isolated ventricle is arrested. B. Ligature of L to sinus (3), which continues its rhythmical beats; 1 and 2 are arrested in diastole (seventh experiment of Stannius). C After the ligature (L) as in B, a second ligature (L') is placed around the auriculo-ventricular groove; the ventricle, which was originally arrested, after some rhythmical contraction, is again arrested (tenth experiment of Stannius). Staxxius's Experiment. — If the sinus venosus of the frog's heart be separated from the auricles by the application of a ligature, then the auricles and ventricles will remain quiet in diastole, while the veins and the remainder of the sinus continue to beat. If a second ligature be applied at the junction of the auricles and ven- tricle, the usual sequence is for the ventricle to begin to beat again while the auricles continue to remain in their diastolic rest. Though the two, sinus venosus and ventricle, continue to beat, their motion is not rhythmical, the ventricular movements being considerably slower. In every case the quiescent portion can be made to give 232 PHYSIOLOGY. single contractions by stimuli, either mechanical or electrical. Thus, when the ventricle remains quiet after the first ligature, it may be made to give single contractions by pin-pricks. To explain the experiment of Stannius it has been asserted that Eemak's and Bidder's ganglia are motor and von Bezold's is inhibi- tory; that the motor influence of Eemak's and Bidder's is greater than the inhibitory influence of von Bezold's; hence, in the absence of all ligatures, the heart beats. That the motor power of Bidder's is less than the inhibitory power of von Bezold's; consequently, the first ligature cutting ofl: the motor power of Eemak's, the auricle and ventricle stand quiescent, while after the second ligature, cut- ting off also the inhibition of von Bezold's ganglia, the ventricle, actuated by Bidder's ganglia alone and unopposed, again commences to beat. According to Gaskell and Englemann, the nerve-ganglia do not play any part in the movements of the frog's heart. According to their ideas the sinus sends out impulse-waves through the muscular structure of the heart. When the first Stannius ligature is applied it blocks the waves running from the sinus to the right auricle. Here the sinus continues beating, but the remainder of the heart is quiet. If, now, you tie a ligature in the auriculo-ventricular groove of this quiescent heart, then the ventricle beats. The ligature or compressor at this point is said to stimulate the ventricle. His has discovered a bundle of muscular fibers which run from the posterior part of the interauricular septum into the intraventri- cular septum, and it is held to be a pathway of myogenic impulses from the auricle to the ventricle. When this bundle of fibers is clamped in animals, the ventricle beats with a slower rhythm and one entirely independent of the auricles. In the Stokes-Adams dis- ease we have a similar block in the heart, where the rhythm of the ventricle is independent of the auricle; the ventricles may be beat- ing 37 per minute and the auricles 90. These facts favor the myo- genic theory of cardiac contractions. Kronecker, however, has liga- tured this bundle of His and has never seen the pulsations of the heart interrupted or modified, and he states that it does not enjoy any role in the conduction of motor impulsions from the auricle to the ventricle, but that they take place only through the nerve-ele- ments. Tawara holds that the cells in the bundle of His are not the ordinary muscular fibers of the heart, but the variety of cardiac mus- cle which has been called Purkinje cells or fibers. He also found THE CIRCULATION. 233 a nervous network in this bundle. Dr. Alfred Stengel discovered an atheromatous lesion in the bundle of His in a case of Stokes- Adams disease. Dogiel and Archangelsky, in a frog's heart, have extirpated the ganglia of Bidder, the intraventricular ganglia, and the ganglion cells and nerves which lie about the auriculo-ventricular groove, and found that the ventricle lost the power to rhythmically contract, although its muscle and nerves were retained up to the ganglion Fig. 77. — Cardiac Plexus and Stellate Ganglion of the Cat. (Landois.) B, Right. L, Left (X li/2)- t, Vagus. 2', Cervical sympathetic and In the annulus of Vieussens. 2, Communicating branches from the middle cer- vical ganglion and the ganglion stellatum. 2", Thoracic sympathetic. 3, Re- current laryngeal. 4, Depressor nerve. 5, Middle cervical ganglion. 5', Com- munication between 5 and the vagus. 6, Ganglion stellatum (first thoracic ganglion). 7, Communicating branches with the vagus. 8, Nervus accelerans. 8, 8', 8", Roots of accelerans. 9, Branch of ganglion stellatum. cells, which had been removed. In such a heart, robbed of its ganglion cells, the law of Bowditch, that a minimal irritation is at the same time a maximal one, fails, for the cardiac muscle gave vary- ing heights of contraction with varying strength of the electrical current. 234 PHYSIOLOGY. Extracardiac Nervous System. The extracardiac nervous system is composed of llie cardiac branches of the vagus, together with the cardiac branches of the sympathetic. The Vagus. — The superficial origin of this nerve is from the groove between the inferior olive and the restiform body. It leaves the skull by passing through the middle compartment of the jugular foramen, presenting, immediately after its exit, an enlargement Fig. 78. — Course of Vagus Nerve in Frog. (Stirling.) SM, Submentalis. LU, Lung. V, Vagus. OP, Glosso-pharyngeal. Hypoglossal. L, Laryngeal. I'H, SH, Gil, OH, Petro-, sterno-, genio- omo- hyoid. EG, Hypoglossus. H, Heart. BR, Brachial plexus. and known as the gangliform plexus. The accesory portion of the spinal accessory nerve joins this ganglion, while the hypoglossal nerve winds around it in a spiral manner. As has been previously stated, the immediate cause of the rhyth- mical contractions of the heart lies in the protoplasm of the muscle- cells themselves, but that the rate and force of its beats are influenced by impulses reaching it through the central nervous system. The effects of these impulses are twofold: inliihition, or diminution in the rate or force of the heart-beat, and acceleration, or increase in THE CIRCULATION. 235 the rate or force. Both the inhibitory and accelerator centers are located within the medulla, fibers from which leave the cranium and reach the heart. Of these efferent fibers of the vagus, the inhibi- tory ones are most prominent and come from the spinal accessory. However, there are accelerator fibers which take their origin in the medulla oblongata and then descend in the spinal cord. They emerge by the anterior roots to the stellate ganglion or first thoracic, then proceed by the annulus of Vieussens to the inferior cervical ganglion of the sympathetic, and then to the heart-muscle. Knowledge of the presence of inhibitory fibers in the vagus is due to the investigation of the Weber brothers, who, about fifty years ago, demonstrated their presence in the vagus of the frog. They showed that stimulation of one or both produces slowing or (llUl/l/lil/lilil^^ iumm Fig. 79.- -Traeing by Lever Attached to Frog's Heart on Stimulation of the Pneumogastric Nerve. (Foster.) a-b shows time of stimulation by electricity. As ttie tracing shows, the heart's movements were arrested for some time. complete stoppage of the beats of the heart. Stimulation not only inhibits the heart's action, but also modifies it in this, that the force of the contraction and the income and output of the ventricle are diminished. The number of ventricular and auricular beats are not in unison, both being less frequent. It makes no difference whether one irritates the center of the pneumogastrics, their trunk, or peripheral ends within the heart, the same result follows: there is a diminution in the number of the heart-beats. A tap upon the abdominal wall is able to throw the pneumogastric into greatly increased action; so that the heart is often stopped and death ensues. In this case the sympathetic nerves of the solar plexus convey the impression up the spinal cord to the center of the pneumogastric in the medulla. From the medulla the impulse is sent down the inhibitory fibers of the pneumogastric. 236 PHYSIOLOGY. which causes arrest of the heart. The arrest always occurs in diastole, never in systole. All of the sensory nerves of the body have a reflex relation to the pneumogastrics. Even pinching the skin of some fishes is suffi- cient to stop the heart. Irritation of the branches of the fifth nerve in the rabbit by ether and other vapors can stop the heart. There are reasons to believe similar results can occasionally be obtained in man. Swallowing Fluids. — Experimenters have demonstrated that Fig. 80. — Arrest of the Heart of a Rabbit by Irritation of the Peripheral End of the Pneumogastric in the Neck. ( Gley. ) PC, Carotid pressure equals 12 centimeters of mercury. E, Excitation of the nerve by an induction current. T, Time every 2 seconds. swallowing interferes with or even may abolish for a short time the cardio-inhibitory action of the vagus. By reason of this the pulse- rate is greatly increased. Sipping a wineglassful of water will raise the pulse-count 30 per cent. In this way water can be made to behave as a powerful cardiac excitant. The course of the impulse is along afferent fibers of the nerves supplying the oesophagus to the cardio-inhibitory center, whose tonus is reduced. Stimulation of the vagus always produces the same result — inhi- THE CIRCULATION. 237 bition — no matter at what point in its course the nerve be stimu- lated. If the pneumogastries be divided in the neck the heart runs with great rapidity. This is due to the removal of the inhibitory power, which comes from the center located within the medulla. A brake, as it were, is taken from the heart, so that all restraint is removed. Inhibition is not perceived immediately after the application of the stimulus. There is present a distinct latent period which pre- cedes the inhibitory effects. Various conditions may modify the Fig. 81. — Irritation of Nerviis Depressor in a Rabbit, Causing a Fall of Arterial Tension. (Gley. ) PC, Carotid pressure. E, Time of irritation of nerve by the induced cur- rent. T, Time recorded every two seconds. length of this period, but the average duration is one or two beats. The stimulus is applied to either side, though the right vagus seems to be more susceptible ; when the stimulus is strong enough to cause complete stoppage, this condition is the result of lengthening the diastole, the most usual occurrence. Peculiarities. — Some of the points of peculiarity of the vagus and its action are: 1. The heart is arrested in diastole; so that the slowing depends upon the period of diastole. 2, The irritation of one nerve alone acts upon the two sets of inhibitory ganglia in the heart by reason of association fibers. 3. After the arrest of the heart by excitation of the vagus, the heart begins its contractions first in the auricles. 238 PHYSIOLOGY. Afferent Nerve of the Heart (Depressor Nerve of Ludwig and von Cyon.) — This nerve in the rabbit usually arises from two branches, one from the trunk of the vagus and the other from the superior laryngeal. It ends in the heart, and, according to some, in the aorta's origin. It is found in man and other animals. When its central end is stimulated, there is a fall of arterial tension to about half its former level. After the stimulation is arrested, the tension returns to normal. With this fall of arterial tension the |V JMD Fig. 82. — Scheme of the Cardiac Nerves in the Rabbit. (Landois.) P, Pons. MO, MeduUa oblongata. Tag, Vagus. SL, Superior Laryngeal. IL, Inferior laryngeal. SC, Depressor or superior cardiac brancii. IL-H, cardio-inhibitory. H, Heart, a, a. Accelerator fibers. S, Cervical sympathetic. beats of the heart are slowed; but if the vagi are divided, there is no change in the frequency of the heart, which shows that the lessening of the number of heart-beats is due to stimulation of the cardio-inhibitory center. Even after curarization, irritation of the central end of the depressor lowers the arterial tension. If the splanchnics are previously divided, stimulation of the depressor has hardly any effect. After an injection of pyocyanin, which para- lyzes the vasodilator centers, irritation of the depressor does not lower arterial tension. THE CIRCULATION. 239 Porter and Beyer have shown that it dilates the arterioles throughout the body, and especially those blood-vessels innervated by the splanchnics. Excessive repletion of the heart stimulates the endings of the depressor nerve in the heart. These afferent impulses inhibit the main vasomotor center and permit the arterioles to dilate, and, opening the flood-gates, thus relieve the systolic strain of the muscular fibers of the heart. The depressor nerve is not in constant action and is not easily fatigued. Sup-, lar. n. Depressor S.C.C. --Sym^. ,.. -Vagus Vagus Sup-, lar. n.-j ... Sup^. Cerv. Gang - Depressor Cerv. symp. n. — Vago. symp RABBIT DOG Fig. 83. — Diagram of the connections of the Depressor Nerve in the Rabbit and Dog, according to Cyon. It will be noticed that in the lat- ter animal the depressor nerve runs in the vagus trunk for the greater part of the course. (Starling.) It has been stated that the depressor nerve acts like a safety- valve to the heart. Von Cyon has shown that iodothyrin augments the irritability of the depressor nerve. The depressor is greatly called into play in the heart of the bicycle-rider, where the abdominal reservoir of blood is compressed by the active abdominal muscles, and the blood is driven into the thoracic cavity and the heart is swollen with blood. The depressor cannot well dilate the abdominal vessels, for they are compressed in bicycle-riding by the violent compression of the muscles of the abdomen. 240 PHYSIOLOGY. Fig. 84. — Schema of Innervation of the Heart of a Dog. (Mobat. ) gg.ca, Cardiac ganglia in which the cardiac nerves terminate, gg.ci. Inferior cervical ganglion, g.cs, Superior cervical ganglion, gg.pl, Plexiform ganglion. sym.th. Thoracic sympathetic. an.Ti, Ansa Vieussenii. pn.g, Pneumogastric. n.re. Vertebral nerve. Vag.symp., Vago-sympathetic. sym.c. Cervical sympa- thetic, sym.cr, Prolongation of the sympathetic in the skull. 6", First cervical pair. D\ First dorsal pair. X, Origin of the pneumogastric. XI, Bulbar origin of the spinal accessory. Accelerators. — When they are irritated they not only accelerate the beat of the heart, but also increase the force, causing a greater output of blood. THE CIRCULATION. 241 The accelerators apparently have less powerful functions, for when the inhibitors and they are simultaneously irritated the effect is inhibition. The phenomenon is less, however, than if the same inhibitors had been stimulated by themselves. Aside from their great and primary differences as to the effects produced, the acceler- ators differ in that they require a greater intensity of stimulus to produce any results ; also in that a comparatively long latent period precedes every effect. In every respect the accelerators seem to be directly opposite to the inhibitors. They are the antagonists of the inhibitors. When the accelerator fibers are divided, the rhythm of the heart remains unchanged. This proves that the accelerator center is not constantly in a state of tonic excitement. When, however, the peripheral ends of the accelerators are stimulated by a faradic cur- j^" £4- ,,,'. 28 ^^. 32 J. 0 Respiration. Fig. 182. — Puncture of Tuber Cinereum in Rabbit, Showing Effect on Respiration, Arterial Tension, Pulse, and Temperature. At the end of 90 minutes the animal was unbound, when a rise occurred in curve of respiration. tion, and vasomotor action, in fact a rapid death, still the tempera- ture rises to 109.5° F. ISfow, if by a puncture of the medulla, pons, ANIMAL HEAT. 447 or crura cerebri, sudden death ensues; 3'et the temperature is but slightly increased. These facts show that the injury of the tuber determines a rise of temperature by some action on the metabolism of the body. (3) When a rabbit is bound down and the respiration, blood-pressure, and pulse are recorded on the kymograph, and the thalamus punctured, then the temperature records its highest point at the time when the respiration, arterial tension, and pulse-rate are falling. In a transverse section of the corpora striata, I have seen a tem- perature of 110° F. and the animal die inside of five minutes. Hence we must attribute the regulation of temperature to special thermogenic and thermo-inhibitory centers. Thermotaxic Centers. — These centers compose the thermogenic, thermo-inhil)itory, and thermolytic centers, as the aim of all is to regulate the temperature. Thermogenic Centers. — Spinal Cord. — Destruction of the spinal cord from the fifth dorsal vertebra down j^ermits the animal to generate as much heat as before the operation. A drug, beta- tetrahydronaphthylamin, when injected by the vein causes a great increase of temperature, l)ut after a section behind the tuber cinereum it fails to cause any rise of temperature. These facts lead to the conclusion that there are no special thermogenic centers in the spinal cord, but that the basal thermogenic centers act through the trophic centers in the anterior cornua. Brain. — When a normal animal is subjected to heat or cold it regulates its temperature and keeps it at a fixed point. If. however, the spinal cord is separated from the brain, the spinal cord is not able to regulate the temperature at a given degree, but its tempera- ture changes with the temperature of the surrounding air. These facts show also the importance of the thermotaxic centers in the brain in the regulation of temperature. As to the medulla oblongata and pons, numerous punctures by a probe two millimeters in width and one millimeter in thickness caused a very slight rise of temperature, which was of a very fugitive nature. Cross-section of the pons is an operation which cuts off the afferent and efferent fibers from the tliermotaxic centers anterior to it and permits heat-production to increase without any regulation. If there are any thermogenic centers in the pons, puncture ought to bring out the fact, as it has done for the thermogenic centers located in the basal ganglia. Any transverse section behind the crura cerebri or pons simply 448 PHYSIOLOGY. cuts out the thermogenic and tliermo-inhibitory centers in front of the section and permits the thermic apparatus beliind the section to elevate the temperature. That a greater rise of temperature should ensue after pontal than after crural section is quite in accord with the well-known fact that successive sections from before backward cause a greater activity of the spinal-cord centers behind the section, and also of the trophic centers. Fig. 18.3— Cortex of Cat's Brain. g. Cruciate thermo-inhibitory center of Eulenberg and Landois. S, Sylvian tliermo-inliibitory center of Ott. Now, I have shown that after the intravenous injection of beta- tetrahydronaphthylamin in the normal animal a great rise of tem- perature ensues. But after section through the crura cerebri this drug is powerless to raise the temperature. A needle-point thrust into the pons or crura causes a fugitive rise, and a feeble one. But if the needle goes into the corpora striata or tuber cinereum there is a quite permanent and considerable elevation of temperature. To as- sume that a different kind of thermogenic center exists in the pons is begging the question. ANIMAL HEAT. 449 In April, 1884, I was the first to make a transverse section of the corpora striata in the cat, which was followed by the temperature rising to llOYo" F. Afterward Drs. Sachs and Aronsohn more exactly localized the center in the caudate nucleus. I also located another thermogenic center in the optic thalami, a bilateral puncture of their anterior ends causing a rapid rise of temperature to 109° F. Von Tangl, of Budapest, has confirmed this fact by experiment upon the brain of a horse. Upon more exact localization this thalamic thermogenic center was found to be located in the tuber cinereum. Hence the conclusion that the thermogenic centers are located in the corpus striatum and tuber cinereum. Fig. 184. — Lesions of Cortex in Man, Causing Elevations of Temperature. Experiments by Ott show that an increased supply of oxygen is not necessary to a rise of temperature. A great increase of arterial tension can not elevate the temperature over 1.5° F., as has been shown by Ott and Scott. The tuber cinereum is also connected with the vasomotor appa- ratus. In experiments to find vasotonic centers in the thalami I have located them in their anterior part. Later experiments have led to more exact data. After puncture of the tuber with a fine probe a gradual fall of arterial tension ensued. In about forty minutes it amounted to one-fourth the absolute pressure. This fall invariably ensued in six experiments; so that there seemed little doubt that vasotonic centers exist in the thahmii. Theemo-inhibitory Centehs. — Eulenberg and Landois discov- ered about the cruciate sulcus a center whose ablation was followed by an increase of temperature. Prof. H. C. Wood has shown that 29 450 PHYSIOLOGY. the increase is due to augmented production of heat. I have also shown in the cat that at the juncture of the suprasylvian and pust- sylvian fissures is another center whose removal is followed by an increase of temperature. This has been confirmed by White. The increased heat-production after injury to the Sylvian and cruciate centers, the fall to normal, and the subsequent rise in some cases indicate that there is a conflict between these centers and those that lie beneath in an effort to gain the mastery. This state of things is seen in the temperature of patients -afflicted with fever. Puncture, like fever poison, excites the thermogenic centers. Antipyretics act as sedatives to them and so reduce their excitability. Albumoses, peptones, skatol, guanine, and neurin have been shown by Ott to produce fever. ISttAP. Fig. 185. — Curves of Temperature and Respiration when Cortex is Removed and the Animal is Artificially Heated. Dr. W. Hale White reports a case in which a bullet from a pistol caused an injury of the anterior extremity of the middle lobe of the right hemisphere and also the third frontal convolution, which was followed by a temperature of 104.4° F. in less than twelve hours after the accident. Dr. Page also reported a case of depressed fracture of the skull which was about the posterior part of the temporo-sphenoidal lobe and which was followed by a temperature of 105° F. This tempera- ture fell after trephining, and it did not rise again. Fig. 184 shows the position of these lesions in man, and they correspond roughly to the position of the cruciate and Sylvian centers in the cat. Thermolytic Centers. — These centers include the cooling ANIMAL HEAT. 451 apparatus of the body: the polypnceic, the sudorific ,and the vaso- motor centers. Polypnaa. — Professor Eichet found that with the elevation of the body-heat of an animal its respirations suddenly increased to 350 or 400 per minute. This form of respiration he termed polyp- noea. It was found that the animal did not do this from want of oxygen. An animal pants to cool himself, while a man perspires for the same purpose. The role of poiypnoea is exclusively to reg- ulate the temperature of the body. I have made numerous experiments to determine the exact seat of the polypnceic center. To establish a center three things are necessary : (1) that its abolition causes the phenomena to disappear. JU^flU Itoyu Fig. 186. — Curve of Temperature and Respiration when the Tuber Cinereum is Destroyed and the Animal is Artificially Heated. (2) that irritation — mechanical, chemical, or electrical — causes the phenomena to be present, and (3) that the part of the nervous sys- tem exhibiting these peculiarities be circumscribed in extent. After numerous observations and experiments it was found that pressure upon the tuber cinereum with a pledget of cotton, or even slight puncture, increased the normal respirations to the point of poiypnoea. Complete puncture in a normal animal was followed by a rise to 106° F. within two hours, even though the animal was bound down and had been subjected to considerable shock. If now the animal whose tuber is punctured be heated, there will result no poiypnoea, even though a temperature of 107° F. be reached. I am convinced that the fnher cinereum is a center of polyp- 452 PHYSIOLOGY. ncea and thermotaxis. When heat is thrown on the body the polyp- nccic center telegraphs the respiratory center to work more rapidly to throw off more moisture by the expired air. The afferent nerves of the thermotaxic apparatus are probably those nerves in the skin administering to the "hot" and "cold" spots. Regulation of Loss of Heat, or Thermolysis. — Heat is lost by an animal in various ways. It may be by direct radiation and conduc- tion from the skin, by the extraction of heat during the process of evaporating perspiration, by warming the respired air, and by the discharge of urine and faeces. Skin Eadiation and Conduction. — The skin is the main means of escape of the bodily heat. Nearly three-fourths of the heat which escapes from the economy does so through the skin as a means. A marked difference between the temperature of the skin and that of the surrounding atmosphere constitutes a prime factor in radiation. When the enveloping medium is very cold radiation from the skin's surface is very rapid. The cutaneous circulation has considerable to do with the dissi- pation of heat. The caliber of the peripheral vessels is governed by the vasomotor system, which is itself under the guidance of the cen- tral nervous system. External heat refiexly causes dilatation of the cutaneous vessels, so that at such times the skin becomes red and engorged. It con- tains more fluids and thus is a better conductor of heat. More blood being at the body surface allows of greater and more rapid loss through radiation. External cold refiexly causes a contraction of the peripheral ves- sels; so that their lumina are narrowed. In consequence there is less blood circulating in the skin, which appears pale and contains less fluid; so that the radiation of heat is markedly hindered. By reason of nervous stimulation the sweat-glands are at times made to functionate very freely; whereupon the skin's surface be- comes bathed in a sensible perspiration. For the conversion of this moisture into vapor heat is necessary. It is by the abstraction of this heat from the underlying tissues that the body owes much of its loss when its parts are hyperpyrexial. One pound of water in evaporating takes up 1047 B. H. U. daily. The covering of the body by clothing during various seasons of the year contributes much to the proper regulation of loss of heat, so that the mean temperature may be maintained fairly constant. Fever. — The process of fever is one of absorbing interest dur- ANBIAL HEAT. 453 DAY AFTER.. CHIL]- PERIODS. 1 Fig. 187. — Heat Production and Heat Dissipation in Man during a Parox\'sm of Malarial Fever— a Great Increase of Heat Production. 454 PHYSIOLOGY. ing every period of a physician's life. The constant level of tem- perature in man is accounted for by two theories: One that it is due to changes in heat-i^roduction ; the otlier, held by a minority, that it is kept so by changes in heat-dissipation under the varying conditions of external temperature. In a case of fever generated by the malarial parasite I found with the human calorimeter an increased production of heat as the primary cause of the fever. In the case of fever generated by the subcutaneous injection of putrid blood I found a fever caused by an increased production of heat in the animal. As a rule, it is true that fever is set up by an increase of heat- production beyond that of heat-dissipation. But when this is once established the fever continues, not from an excessive production, but from an altered relation between heat-production and heat- dissipation. That the basal thermogenic centers, the corpus striatum and tuber cinereum, play a prominent part in the production of fever is proved by the fact that putrid blood and betatetrahydronaphthylamin both produce a rise of temperature. They are powerless after a sec- tion behind the tuber cinereum to elevate the temperature. Antipyrin reduces the temperature by an action upon the cor- pora striata. Experiments in my laboratory by Dr. W. S. Carter proved that whilst the temperature of the body has a rhythm, there was no rhythm in either heat-production or heat-dissipation. All recent researches go to show that fever is not a fire that is continuously kept up by an excessive oxidation of the constituents of the human body. For instance, if the amount of water flowing into a vessel partly filled with water is equal to 2, and the amount going out is equal to 2, the level of the water will be the same. But if the amount of water going into the vessel is equal to 3 and the amount going out equal to 2, the level of the water will rise. If, however, the amount going into the vessel should suddenly fall to 1 and the amount going out should do the same, the level of the water would be nearly the same as before. If, now, you substitute for the amount of water going in the amount of heat produced, and for the water going out the amount of heat dissipated, and the level of the water as the height of temperature, it is easy to see how a dimin- ished production and dissipation of heat due to want of food and the waste of the body by the fever process, may still keep up a high ANIMAL HEAT. 455 fever, although both are dhninished below what is generated and dissipated in a state of health. The physico-chemical cause of death in fever by hyperpyrexia is due to a coagulation of cell-globulin. If heated long enough, a temperature of 42° C. will coagulate it. Postmortem Temperature. — Usually after death the body cools gradually, depending upon the temperature of the external atmos- phere and the body-surface. The body of a child or emaciated sub- ject cools more rapidly than does that of a well-developed and well- nourished adult body. A temporary increase of postmortem temperature is due to the change of myosinogen into myosin and to those series of cliemical changes immediately succeeding death. When death has occurred from tetanus, acute rheumatism., typhoid, small-pox, cholera, or injuries to the brain, there is noxo'I a marked postmortem rise in temperature. CHAPTER XI. THE MUSCLES. Covering np the l^ones and attached to their surfaces at certain definite places is the soft, red, fleshy portion of the body: the mus- cular substance. This consists of not one homogeneous environing mass, but of a great number of distinct fleshy masses, called muscles. These are of various forms and sizes; number about four hundred; and are, for the most part, arranged in pairs. It is mainly to the shape and disposition of these muscles that the body owes the regu- larity of its contour. It is by the power of these skeletal muscles that the animal is able to move about, procure means of sustenance, care for its young, etc. ; but it must be borne in mind that muscles — not so powerful as are the skeletal muscles, but muscles, nevertheless — are contained within the viscera and blood-vessel walls. These muscles have very important functions to perform in aiding tlie processes of metab- olism : that balance which when disturbed produces, not health, but disease. Any animal motion means muscle. Muscular tissue is empowered with contractility; that is, an ability to shorten itself when acted upon by any stimulus. By its shortening it produces movement to parts to which one or both of its ends are attached. The resultant motions may be the very common ones of walking, running, various manual employment, etc., or the peristaltic movements of .stomach and in- testines, or the variations in the sizes of the lumen of the blood- vessels. Any animal movement should at once recall to the mind of the student that it is the resultant of some muscular contractility produced by the influence of a stimulus to it, whether that be nerv- ous, electrical, mechanical, or thermal. Muscular tissue consists of fibers bound together into those dis- tinct organs already mentioned as muscles, and in this condition is known as the meat of animals. In the f.ne anatomy of the muscles I have followed the writings of Professor Shaefer, as they appear in Quain's "Anatomy," of which this is an abstract. Varieties. — When seen under the microscope, these fibers' are found to be cross-striped, or striated; as many of them are under the control of the will, they are usually spoken of as being voluntary. (456) THE MUSCLES. 457 In the coats of the blood-vessels and in the hollow .viscera is another variety of muscular fibers, often making a distinct layer or layers to these organs. In this kind the libers do not have the cross- striped appearance, but are plain, or unstriped. Nearly all of these are not under the control of the will, and are, hence, involuntary. It must here be noted, however, that the muscle of the heart — which, as everyone knows, is an involuntary muscle — is exceptional to this class of muscle in that its fibers are very plainly cross-striped. jSTever- theless, it presents differences from the striped fibers of skeletal muscles; so that it has become customary with very many authors to class it under the separate title cardiac muscular tissue. The muscular fibers of the skeleton are generally collected into distinct organs of various sizes and shapes which have at each end a tendon by which they are attached to the skeleton. The fibers of the muscles are collected together into bundles, called fasciculi. In the fasciculi the fibers are parallel, so that the fasciculi wind from one tendinous end to the other, except in a few muscles like the rectus abdominis. In this instance the body of the muscle is interrupted by interposed tendinous tissue. The fas- ciculi themselves do not mingle with one another and, for the most part, run parallel, although in many cases they converge to their tendinous endings. The covering of the entire muscle is termed the epimysitwi, and is a connective-tissue envelope. The covering of areolar tissue which insheathes the fasciculi of the muscle is spoken of as the perimysium. The latter, a septum from the epimysium. furnishes to each fascicu- lus a special covering as well as furnishing it with blood-vessels and nerves. Within each compartment lie a number of muscle-fibers which are usually parallel to one another and held together by a very delicate reticular connective tissue. This areolar network is called the endomysium, but does not make a continuous covering and so cannot be said to form sheaths for them. Each fiber of the muscle, however, has a tubular sheath, but this sheath is not composed of the areolar tissue just mentioned. The special function of the areolar tissue seems to be to connect the fasciculi and fibers, and to support and conduct the blood-vessels and nerves in their ramifications be- tween the various parts. Fasciculi in form are prismatic, so that a transverse section shows an angular outline. The thickness of a fasciculus, as well as the number of fibers of which it is composed, varies. The texture of a muscle, whether coarse or fine, depends upon the large or small 458 PHYSIOLOGY. fasciculi contained within it; thus, the glutei are coarse, the muscles of the eye fine. The length of the fasciculi is not always the same as the length of the muscle; this characteristic depends upon the arrangement of the tendons to wliieli the muscle is attached. When the tendons are attached to the ends of a long muscle, as the sartorius, the fasciculi run from one end of the muscle to the other and so are of consid- erable length. However, a long muscle may be made up of a series of short fasciculi attached obliquely to one another by beveled ends. Short fasciculi thus attached, as in the rectus muscle of the thigh, have stronger action than where they run the extent of the nmscle. Fibers. — The form of the muscle-fibers is cylindrical or prism- atic with rounded angles. Their diameter varies very considerably, even in each muscle, although a certain standard is found to exist in every muscle. The largest human fibers average one-tenth of an inch in diameter, and fiom that size to one two-hundred-and-fiftieth of an inch fibers may l)e found. Between the size of the muscle and that of its fibers there is no constant relation. The length of the muscular filjers does not generally exceed one and one-half inches. Thus, in a long fasciculus, the fibers do not reach its whole length, but end in a rounded or tapering end invested with sarcolerama and cohering with neighboring fibers. There is, as a rule, no anastomosis or division of the fibers of a muscle, except in the tongue of a frog, where they branch beneath the mucous mem- brane to which they are attached. The same thing has been observed in the tongue of man. Sarcole:mma. — The sarcolemma is a tubular sheath inclosing the soft substance of the muscle. It is an elastic, transparent, homoge- neous memljrane ; it is rather tough and can remain intact even though the muscle be ruptured. Upon its inner side are found nuclei which, however, belong to the muscle rather than to the inclosing membrane. Structure. — With a low magnifying power, the muscle presents clear pellucid fibers which are cross-striped with bands alternately dark and light. That this striation is not on the surface alone, but extends throughout the substance of the muscle, is readily demon- strated by altering the focus of the microscope. The stripes do not occur on the sarcolemma, but throughout the sarcous substance in- closed by the former. The breadth of the bands is about ^/i7ooo inch, so that eight or nine dark bands may be counted in Viooo inch. While this is the THE MUSCLES. 459 1. Diagram of part of a striped muscular fiber. 8, Sarcolemma. Q, Transverse stripes. F, FibrillEe. K, Muscle nuclei. N, Nerve-fibers entering it with A, its axis cylinder, and Kiihnes motorial end-plate, E, seen in profile. 2. Transverse section of part of a muscular fiber, showing Cohnheim's areas, C. 3. Isolated muscular fibrillae. 4. Part of an insect's muscle, greatly magnified. A, Krause-Amici's line limiting the muscular cases. B, The doubly refractive substance. C, Hensen's disc. D, Singly refractive substance. 5. Fibers cleaving transversely into discs. 6. Muscular fiber from the heart of a frog. 7. Development of a striped muscle from a human foetus at the third month. 8. 9. Muscular fibers of the heart. C, Capillaries. B, Connective tissue corpuscles. 10. Smooth muscular fibers. 11. Transverse section of smooth muscular fibers. 12. Muscular fibers with tendon. 13. Interfibrillary muscular nerves. 460 PHYSIOLOGY. common breadth in human muscle, yet they arc much narrower in different parts; s6 that there may be twice as many bands existing in the space just mentioned. This striation is found in all muscles attached to the skeleton, in the heart, pharynx, upper oesophagus, diaphragm, urethral sphincter, external anal sphincter, as well as in the muscles of the middle ear. When a muscle is deeply focused, the appearance of the striae is somewhat altered; a finely dotted line is seen to pass across the middle of each light band. This is supposed to represent Krause's memhrane stretching across the fiber and attached to the surface of the sarcolemma. However, there is reason to believe that the ap- pearance of a dotted line in this position in the fresh fiber is due to tlie peculiar optical condition of the tissue. A fine, clear line is sometimes seen in the middle of each dark band, and is known as the line, or disc of Hensen. Since there seems to be such variance as to muscle-structure and so many different names are met with in text-books, it might be well to call the student's attention to the fact that Dobie's line, Amici's line, and Krause's membrane are terms used to describe the same condition. They designate the dark line bisecting the white band. Hensen's band occurs in the dark bands. In addition to the cross-striping, the fiber of the muscle has longitudinal striation. When a muscle has been very carefully teased with fine needles after having been previously hardened in spirits, an interesting result follows. The muscle-fibers break up into fine, longitudinal elements of a rounded or angular section which run from end to end of the fiber. These have been very aptly termed muscle- columns, or sarcostyles. Each sarcostyle appears to consist of a row of elongated pris- matic particles with clear intervals. These particles are termed sarcous eleinents. The sarcostyles in some muscles are striated longi- tudinally. This appearance has led some authors to believe that they are composed of still finer elements, or fibrils. Under some conditions, the fibers show a tendency to cleave across in a direction parallel to the bands, and even to break up into transverse plates, or discs. The latter are made up by the lateral cohesion of the sarcous elements of adjacent sarcostyles. To the for- mation of such discs, therefore, every sarcostyle furnishes a particle, which coheres with its neighbors on each side, and this with perfect regularity. Sarcoplasm is the intercolumnar substance by which the sarco- THE MUSCLES. 461 styles are united into the muscle-fibers. It is the protoplasm of the muscle-corpuscles, and forms a fine network throughout the whole muscular fiber. From an examination of the aforementioned facts, Bowman was induced to believe that the division of the fiber into fibrils, or sarco- stj^les, was merely a phenomenon of the same kind as the separation into discs, only a more common occurrence. CoHNHEiM''s Areas. — If a transverse section be made of a mus- cular fiber, or the surface of a separated disc be examined with a strong objective, there appear in the field small polygonal areas separated by fine lines. In acid preparations they give the appear- ance of a network. These areas represent sections of the muscle- columns, and are usually designated as Cohnlieim's areas. The line between them represents the sarcoplasm, or intercolumnar substance. When a muscle-fiber placed in fresh serum is examined, fine, longitudinal lines are seen running through the cross-striping. If, now, a weak acid is added to swell the muscular substance and render it more transparent, these lines can be traced from end to end of the fiber. By careful management of the microscope, it is found that these lines are really the optical section of the planes of separation between the sarcostyles ; that is to say, the optical effect of the sarco- plasm, or intercolumnar substance. The sarcoplasm, in transverse section, presents the aspect of network; in longitudinal optical sec- tion it has the appearance of fine, parallel lines. The student can very readily imagine how these effects can he produced by the pres- ence of a small amount of interstitial substance lying between closely packed prismatic columns. In most muscular fibers the sarcoplasm exhibits a peculiarity of arrangement which has a very characteristic influence upon the op- tical appearance of the fiber. In a longitudinal view of fresh muscle, the lines representing intercolumnar sarcoplasm present at regular intervals along their course rather marked enlargements. These en- largements lie in the bright cross-strige, either in their middle or near their junction with the dim cross-stripes. These sarcoplasm nodules have the appearance of dots upon fine longitudinal lines which run through the muscle; in the more extended fibers these dots are in double rows. In less extended parts they are thicker and blend together in the middle of the liright stri-p. Structure of the Wing-muscles of Insects. — The study of these muscles has furnished the key to the comprehension of the intimate 462 PHYSIOLOGY. structure of muscle. As to their structure, the wing-fibers are in complete agreement with ordinary muscles.. Wing-fibers occur in large bundles of muscle-columns or sarco- styles imbedded in considerable amount of granular sarcoplasm, while the whole of the structure is inclosed within a sarcolemma. The nuclei are scattered here and there. The quantity of sarco- plasm in wing-muscle is relatively far greater than in the ordinary muscle. When wing-muscle has been carefully teased into muscle-col- umns, or sarcostylcs, it is found that they contract while the sarco- plasm is quiescent. The muscle-columns can then be very carefully studied, when they show, like other muscles, the alternate bright and dark cross-striping. Each bright stria is bisected by a line which is the optical section of a transverse membrane: the membrane of Krause. These membranes divide the fibers into a series of seg- ments, called sarcomeres. In a muscle hardened by spirits each sarcomere is seen to con- tain: (1) in its middle, a strongly refracting, disclike sarcous ele- ment; (3) at either end (next the membrane of Krause) a clear interval occupied by hyaline substance. With strong lenses the sarcous elements can be made out to be composed of a sarcous sub- stance which stains with logwood ; it is pierced by short, tubular canals which extend from the clear interval as far as the middle of the disc. It is these canals which give to the sarcous element its longitudinal striping. If, for any reason, the sarcostyle becomes extended, the sarcous elements tend to separate into two parts with an interval between them ; vice versa, if the muscle be contracted or retracted the sarcous elements tend to encroach upon the clear intervals. At the same time the sarcous elements become swollen, so that the sarcomeres are bulged out at their middle and contracted at their ends. Changes in Contraction. — When these muscles contract, the sar- cous elements become bulged out and shortened, while the fluid of the clear interval becomes relatively diminished in amount. The ends of the sarcomeres are thereby contracted opposite the membrane of Krause, so that the sarcostyles become moniliform. This altera- tion in the shape of the sarcostyle necessarily affects the sarcoplasm which lies in their interstices. It must become squeezed out of the parts which are opposite the bulgings of the sarcostyles and into those parts which are opposite their constrictions. In other words, the sarcoplasm must accumulate in greater quantity opposite the THE MUSCLES. 463 clear bands and the membranes of Krause, and must necessarily diminirili in amount opposite the sarcous elements. In the living muscle this change in the position of the sarco- plasm during contraction can be observed; the muscle-columns tend to cause the contracted parts to appear dark, the bulged parts bright, in comparison. Appearance of Muscle under Polarized Light. — Briicke was the first to point out that the fiber is not composed entirely of a double refracting, or anisotropous, substance. In addition there is a cer- tain amount of singly refracting, or isotropous, material. This investigator points out that there is a difference between the appear- ances presented by living muscle examined in its own plasma and those of dead and hardened muscle examined in glycerin. In living muscle nearly the entire fiber is doubly refracting, the isotropous substance occurring only as fine transverse lines or as rows of rhom- boidal dots which are united to one another across the anisotropous substance by fine longitudinal lines. Sarcous element is anisotropic ; sarcoplasm is isotropic. Nuclei. — In muscles that are cross-striped are found a number of clear, oval nuclei. They are sometimes spoken of as muscle-cor- puscles. In mammalian muscle they usually lie upon the inner sur- I'ace of the sarcolemma. In the muscles of the frog and reptiles the nuclei lie in the substance of the fiber surrounded by a small amount of protoplasm. When the nuclei lie immediately beneath the sarco- lemma they are more or less flattened. Each nucleus contains one or two nucleoli. Mitotic figures, denoting division of the nuclei, have been observed. The nuclei are not very readily seen in fresh muscle, due to their being of the same refractive index as the sar- cous substance. Only after they have undergone some spontaneous change or acetic acid has been added to the specimen can they be readily discerned. In the rabbit and rays of fishes some of the voluntary muscles present differences from others, both as to appearance and mode of action. Thus, while most of the voluntary muscles are pale and con- tract forcibly when irritated, the soleus and semitendinosus show different characteristics. They are of a deeper color and respond 'with slow, prolonged contractions when stimulated. Thus, in these animals there are red and white muscles. In other animals, this distinction of muscles is not found as regards a whole muscle, but may affect individual fibers. Thus, in the diaphragm many of the fibers have numerous nuclei imbedded 464 PHYSIOLOGY. within the protoplasm so as to form an almost continuous layer beneath the sarcoleimna. Relation to Tendons. — When a muscle terminates in a tendon, it is found that the muscular fibers cither run in the same direction as the fibers of the tendon or Join with the tendon at an acute angle. According to Toldt, the delicate connective-tissue elements covering the several muscular fibers pass from the latter directly into the con- nective-tissue elements of the tendon. According to another author, the ends of the muscular fibers are believed to be fastened to the smooth tendons by means of a special cement. However, it is prob- able that the areolar tissue which lies between the tendon-fibers passes between the ends of the muscular fibers to be gradually lost in the interstitial connective-tissue. Blood-vessels of Muscle. — The blood-vessels to the muscles are very numerous. The average muscle leads such an active life that its nourishment and repair material must be in proportionate rela- tion. Unlike the organs, as the kidney and spleen, which usually are supplied by one artery and vein, muscles receive several branches from various arteries which pierce the muscle at difi:erent points along its course. The artery and vein usually are in close proximity, being held in position by the connective tissue upon the perimysium. The capil- laries lie between the muscle-fibers in the endomysium, but outside of the sarcolemma. Here the capillaries are small, and form a fine network with narrow, oblong meshes, which are stretched out in the direction of the fibers. The capillaries have both longitudinal and transverse vessels. The lymph that is destined to support the sar- cous substance must pass through the sarcolemma to reach the same. Muscle Nerve-supply. — The nerve-supply to muscles is both motor and sensory. Each muscle-fiber receives a motor nerve-fiber. The trunJv of the motor nerve, as a rule, enters the muscle at its geometrical center (Schwalbe) ; thus, the point of entrance in a long, spindle-shaped muscle lies near its middle. At this "geometrical center" there is the point of least disturbance during contraction of the muscle. After the trunk of the nerve pierces the muscle it pro- ceeds to divide dichotomously until there are just as many nerve- fibers as muscle-fibers. A nerve-fiber now enters each muscle-fiber, to do which, of course, it must pierce the sarcolemma. The point of entrance forms an eminence known as Doyere's eminence, or motorial end-plate. At this point the sheath of the nerve-fiber becomes continuous with the sarcolemma. The eminence itself con- THE MUSCLES. 465 sists of a mass of protoplasm (sarcoplasm) containing granules and nuclei. Beneath the sarcolemma the original nerve-fiber is broken up into a number of divisions, spoken of as nerve-endings. These are divisions of the axis-cylinder which are spread over the sarcous substance without piercing it. To this branched arrangement of the nerve-endings Kiihne gave the name motor spray. Fig. 189. — Unstriped Muscular Tissue. (Ellenberger.) A and B, Foetal cells. C, U, Fully formed fiber. /, Bundle of fibers. K, Cross-section of bundle of pale muscular fibers. The nerve-endings are thus confined to very small areas on the muscle-fibers which have been termed by the same author fields of innervation. As a rule, each muscle-fiber has but one such area; it is the exception to find more than one, but as many as eight have been found in very long fibers. Sensory fibers are also found in muscles, for it is through their presence that we obtain muscle sensibility. They seem to be dis- 30 466 PHYSIOLOGY. tributed upon the outer surface of the sarcolemma, where there is formed a plexus. This plexus winds round the muscle-fiber. Cardiac Muscle. — Some mention has previously been made con- cerning cardiac muscle, so that at this point only its most striking peculiarities will be mentioned, and that cursorily, (a) It is a striped muscle. However, its striations are not nearly so distinctly marked as are those of voluntary muscle. Occasionally it is noticed to be marked longitudinally, (b) Cardiac muscle-fibers possess no sarcolemma. (c) Its fibers branch and anastomose, (d) The nucleus is placed in the center of each cell. One author says that cardiac muscle stands, physiologically, midway between striped and unstriped muscle. When stimulated, its contractions occur slowly, but last for a considerable length of time. Nonstriped Muscle. — These muscles are made up of a number of contractile fiber-cells, of an elongated, fusiform shape, usually pointed at the end. These fiber-cells may be readily demonstrated by placing the tissue in a strong alkaline solution or in a solution of strong nitric acid. Upon transverse section they are generally prismatic, but some- times are more flattened. Their muscle-substance is doubly refract- ing. Each cell has a nucleus which is either elongated or oval. It may contain one or more nucleoli. The nucleus is brought into view by means of dilute acetic acid or staining reagents. The involuntary fiber-cells have a delicate sheath, which, like the sarcolemma of voluntary muscle-fiber, is very apt to become wrinkled when the fiber is contracted. By reason of this an indis- tinctly striated appearance may be produced. While fiber-cells do occur singly, yet it is more common for them to be found in groups. Thus, muscular sheets, or bundles, are pro- duced which may cross one another and interlace, being held in posi- tion by enveloping connective tissue. The individual cells are united by the presence of a very delicate cement. The average length of the fiber-cells ranges from Vioo to Voqo of an inch ; those forming the middle coat of the arteries are shorter, those in the intestinal tract and pregnant uterus are considerably longer. Where Found. — The unstriped muscular tissue is more gen- erally distributed within the body than one would suppose. It is found in the lower part of the oesophagus, in the stomach, small and large intestines; in arteries, veins, and lymphatics; in the ureters, bladder, and urethra ; in the internal female generative organs, etc. THE MUSCLES. 467 Blood-supply. — The blood-supply to unstriped muscle is very free, but not nearly so liberal as that to voluntary muscle. The nerve- supply is from the sympathetic system, and comprises both medullated and nonmedullated fibers. The fibers form a main plexus, lying in the connective tissue of the perimysium. From this plexus of fibers there come off numerous fibrils, which traverse the fiber and nucleus. Irritability of Muscle. — Contractility, elasticity, tonicity, and irritability are terms used to designate various properties of muscles. Thus, contractility is the property the muscle possesses of short- ening and of giving a contraction when it is excited. Elasticity is the general property, common to muscles and many other bodies, of stretching under the influence of a weight and of then returning, more or less perfectly, to the first shape. Tonicity is the state midway between extreme contraction and relaxation. It is a condition depending upon the central nervous system. In addition, muscle possesses a property that is common to all live tissues and which is of fundamental importance in general physi- ology. It is irritability. By irritability is meant that property of a living element to act according to its nature under the stimulus of an excitant. Paralyses have been observed which have lasted for several months or even several years and, although the nerves were abso- lutely unexcitable, yet the muscles had retained their irritability. This may be readily demonstrated in cases of paralysis of the seventh pair of nerves. The independence of muscle irritability is formally demonstrated by experiment in which the known action of the drug, curare, upon muscles is taken advantage of. A watery extract of this drug, when injected into the blood of an animal or introduced beneath its skin, acts chiefly upon the motor nerve-endings. It does not, however, affect muscular contractility. Curare is an agent which separates the muscle-element from the nerve-element by a physiological dissection much superior to the coarse anatomical dissections which we could make. When a few milligrams of this drug are injected into the dorsal l}Tnph-sac of a frog, the poison is absorbed within a few minutes. The animal soon ceases to support itself, but lies in any position in which it may be placed by the experimenter. It is paralyzed, produc- ing neither voluntary nor reflex movements. Now, should the brain be destroyed, the skin removed, and the sciatic nerve stimulated by 468 PHYSIOLOGY. electricity, no movements of the muscles of the limb follow. On the other hand, should the stimulus be applied directly to the muscles, they immediately contract. Therefore the muscle is irritable by itself. By this it would seem to be clearly demonstrated that irritability belongs to the muscle, and does not depend upon the nerve-fibers mingled with those of the muscle. In addition to this classical experiment there may be mentioned several other facts which go to corroborate what has been mentioned concerning irritability : — 1. The chemical excitants of the muscle are not the same as the chemical excitants of the nerves. Thus, glycerine excites the nerve, but has no effect upon the muscle. 2. Isolated muscle-fibers have been seen which, according to microscopical examination, contained no nervous elements and which, notwithstanding, were contractile. 3. If the decreasing progress of irritability be followed after death, in the muscle as well as in the nerve, it will be found that the nerve dies long before the muscle. When the nerves have lost all irritabilit}^, the muscle is still alive, and can contract under the influence of excitations directly applied to its tissue. It is at that very moment when the nerves have lost all excitability that the mus- cle is at its maximum of irritability. Influence of Blood Upon Irritability. — It has been demon- strated by experiment upon the frog that when the artery of a mem- ber is ligated the muscle contraction is less high and less strong than if the artery had been left intact. Stenon's experiment of ligating the abdominal aorta of a dog is worthy of mention. In twenty to thirty minutes after the ligation the dog seems paraplegic. He is unable to stand upon his hind limbs. Eeflex and voluntary movements are completely lost ; muscle irritability, however, persists for nearly three hours. When the ligature is removed movement does not return to the limbs at once, but within a very short time the dog is able to stand upon his four feet. Stimuli. — Those extreme forces which bring into play the irrita- bility of the muscle are simply various forms of energy. To them the name stimuli has been applied. By their action the muscle is thrown into a state of excitement whereby the chemical energy of the muscle is transformed into heat and work. These muscle excitants, or stimuli, are of five varieties: (a) nervous, (b) electrical, (c) thermal, (d) mechanical, and (e) chemical. THE MUSCLES. 469 Nervous Stimuli. — The most important of all the excitatory forces of the muscle is innervation. In the normal state there is scarcely any other than this to produce muscle contraction. Our muscles, as well as those of all other animals, contract because the motor nerve transmits to them the spontaneous or reflex excitation of the nervous centers. The nerve impulses average about ten per second. The stimulus is exactly proportioned to the effect which must be obtained. Electrical Stimuli. — Electricity is employed in preference to any other external agent to bring into play the irritability of muscle. Thermal Stimuli. — Thermic excitations also provoke muscular movements. The stomach and intestines are viscera whose muscles are very readily excited by heat and cold. They contract very ener- getically when very cold drinks are taken and their temperature is suddenly modified. On the contrary, striated muscles hardly react to thermic excitants. If heat or cold be applied gradually, there is not produced any muscle contraction. Excitants act only when they are applied suddenly. Mechanical Stimuli. — Mechanical excitants that are capable of producing muscular contraction are rather common. Thus, the surgeon, while performing an operation, notices slight fibrillary tremblings following each stroke of his scalpel. Chemical Stimuli. — It can be stated as a rule that all the substances which are fatal to the life of the muscle are excitants of the muscle. On this ground, distilled water is an excitant, for when it is injected into the arterial system of a frog its muscles show fibrillary twitchings. Not only does the water excite the muscle, but it also kills rapidly. Chemical Constitution of Muscle-tissue. — The chemical study of muscle is one of the most difficult of physiological chemistry. There are in the muscle proteid matters very like one another and which can be distinguished only by superficial characters. This renders results far from being satisfactory or reliable. Besides, it is necessary, in order to know chemical reactions of muscles, to study only living muscle. But from previous study it will be recalled that even the weakest chemical actions produce very decided changes in the muscles, with consequent alteration of its chemical functions. Then, too, muscle-fiber is mingled with many other tissues, arteries, veins, nerves, connective tissues, etc.; the separation of the 470 PHYSIOLOGY. muscular fiber from its enveloping media is almost impossible com- pletely to effect. Reaction. — Living muscle is alkaline; however, after extreme activity and after death its reaction is found to be acid. This is due to the development of sarcolactic acid. The postmortem change in muscular constitution is due to spontaneous coagulation of a pro- teid Avithin the muscle-fibers. Constituents of Muscle. — Proteids. — Most abundant, myosino- gen (pseudoglobulin), paramyosinogen (euglobuiin) of muscle exist- ing as one-fourth in amount of myosinogen. Coloring Matter, — Myohaematin. Ferment. — Myosin ferment, and another ferment in muscle which, with the activitor of the pancreatic juice, destroys sugar. Extractives. — (1) Non-nitrogenous Extractives : — 1. Glycogen. 4. Inosite. 2. Dextrin and sugars. 5. Fat. 3. Lactic acid. (2) Nitrogenous Extractives: — 1. Creatin. 6. Urea. 2. Creatinin. 7. Carnine. 3. Xanthin. 8. Carnic acid. 4. Hypoxanthin. 9. Inosinic acid, 5. Uric acid. 0. Taurine. Carbohydrates of Muscle. — (1) Glycogen. (2) Lactic Acid, (a) The optically inactive acid, ordinary lactic acid of fermentations, as in milk; small quantity in muscle, (b) Dextro-rotary lactic acid. This is paralactic or sarcolactic acid, the chief lactic acid of muscle. The bulk of authority tends to prove that sarcolactic acid mainly comes from proteid. Urea. — A small quantity in muscle (0.07 to 0.02 per cent.). It is supposed that most of the creatin is broken up into ammonia before it leaves the muscle. Myosin. — Myosin is formed from myosinogen, myosin ferment, and calcium salts. Syntonin. — When a solution of myosin is heated it is altered in such a manner that it can no longer be dissolved in NaCl as before. If it be treated with dilute HCl, it becomes altered in still another manner, and produces an important substance which is called synionin. THE MUSCLES. 471 If syntonin in HCl solution have pepsin added to it, the syntonin is transformed into peptone. Muscle-serutn. — In the coagulation of blood two principal com- ponents are noted: the clot and the serum floating upon the clot. Also, after coagulation of the muscular juice, myosin and serum must be distinguished. The muscle-serum which floats upon the surface of the myosin contains several substances. The amount of proteid matters contained in the muscular tissues is very variable. It is usually stated that in 100 parts, by weight, of muscle, there are 20 parts of proteid matters. Extractives. — Creatinin is derived from creatin by dehydra- tion. The amount of creatinin in muscle is small, being but 0.3 per cent. Hypoxanthin and xanthin occur to the extent of about 0.02 per cent. Halliburton found a myosm-fertnent. Its presence would seem to explain the coagulation of myosin. Glycogex. — Among the nonnitrogenized substances must first be classed the sugars and their analogues. Glycogen is the principal muscle-starch. The glycogen in the muscles was discovered by Claude Bernard while looking for the glycogen in the liver of the foetus and newborn. He found in the muscles of the embryo quanti- ties of glycogen that were relatively enormous. Glycogen exists in all of the muscles. The more active the state of a muscle, the less glycogen it con- tains. Therefore, much of it is found in those muscles which con- tract but little. Muscle extract and pancreatic activator when mixed together rapidly destroy sugar in the blood, probably by the formation of a ferment. Either extract alone is powerless to break up glucose. These two extracts resemble the action of enterokinase upon trypsin- ogen. Inosite. — It is a sort of crystallizable body that is unferment- able. That is, it does not ferment to form alcohol, but lactic acid. It is found in the vegetable kingdom also, where it is usually extracted from peas or beans. It is identical with the inosite of muscle. It is not a sugar, but belongs to the aromatic series. Mineral Substances. — Alkaline phosphates predominate. In 100 parts of ash there are about 90 parts of phosphates. The metals found in muscle are potassium, sodium, and calcium; there is also 472 PHYSIOLOGY. a small quantity of mfignesiuin and iron. Phosphoric acid exists in muscle as inorganic phosphates, phosphorus of phosphocarnic acid, and phosphorus of inosinie acid. Carnic acid is identical with anti- peptone. When a muscle works it increases the phosphates in the urine. The gases found in muscle are carbonic-acid gas and oxygen. Adipocere is a waxy substance which replaces muscular tissue if bodies be buried in damp soil. It consists principally of a soap made of calcium with palmitic and stearic acids. Rigor Mortis. — During rigor mortis the muscles become rigid, hard, inextensible, shortened and swollen, as though in a state of contraction. After death, rigor mortis is a constant phenomenon. The muscles to first become rigid are the masseter, temporal, and internal pterygoid. Then it seizes the muscles of the trunk and neck, then the arms and the legs. Tetanus and rigors appear in the same muscles and extend to others in the same way. In rigor mortis the thumb is in the palm of the hand and covered with the other fingers, showing that the flexor muscles overcome their antagonistic muscles, the extensors. The jaws are contracted, the eyes are widely open, the head and neck are drawn backward, the abdomen is depressed, the extremities are half flexed, and the feet are extended. Cause of Eigek Mortis. — It is due to the myosinogen becom- ing myosin by the action of the myosin ferment with calcium salts. During rigor mortis the muscles become acid, due to sarcolactic acid and acid phosphates, the muscle becomes cloudy, and gives off heat and carbonic acid. After some time rigor mortis passes off and the body becomes relaxed. After fatigue the rigor mortis ensues rapidly after death, lasts but a short time, followed by putrefaction. It is well known that butchers do not kill animals tired by a long walk, but wait for a rest of some days. In man it is generally four hours after death that cadaveric rigidity becomes complete. As a rule, it may be said that rigidity begins two hours after death, reaching its maximum two hours later. A particular kind of 7-igor mortis has been observed by military surgeons. Soldiers while in full activity have been struck by pro- jectiles and have been seen to become stiff instantaneously. It is a sort of rigor mortis which seizes all of the muscles of the body imme- diately after death. Influence of Temperature. — Animals which have died in heated chambers become rigid very quickly and the rigidity disappears as quickly. THE MUSCLES. 47-^ Fig. 190. — The Pendulum Myograph. (Foster.) A, Smoked glass plate, swings on the "seconds" pendulum, B, by means of carefully adjusted bearings at C. The contrivances by which the glass plate can be moved and replaced at pleasure are not shown. A second glass plate, so arranged that tho first glass plate may be moved up and down without altering 474 PHYSIOLOGY. Cold, which retards chemical phenomena, retards the appear- ance of cadaveric rigidity and prolongs it enormously. Influence of Fatigue. — The inlluence of prolonged labor of the muscle upon the premature appearance of rigidity is an indisputable fact. Muscular Labor and Urea Excretion.— With the ordinary diet of fats, carbohydrates, and proteids, muscular labor greatly increases the output of carbon by the lungs in the shape of carbon dioxide, whilst the nitrogen excreted as urea is slightly, if at all, increased. In a fasting animal work increases the excretion of both the carbon and the nitrogen. The output of carbon is proportional to the work done, the nitrogen not being so closely proportional. Here the mus- cle procures its energy from the proteids, whilst the animal with an ordinary diet uses up mainly the carbohydrates and fats. Hence, in muscular exertion the chief foods — proteids, fats, and carbohydrates — are metabolized in order to set free heat and work. In doing this the muscle prefers to break up the fats and carbo- hydrates rather than the proteids. Hence when muscle fulfills its two chief functions, to produce work and heat, it uses up the fats and carbohydrates and proteids, but the proteids are chiefly used to build up and repair the muscle-substance itself. Sarcolactic Acid. — ^The production of sarcolactic acid is the more abundant as the muscle has been longer and more strongly excited. Myograph. — The du Bois-Eeymond induction coil is the one most commonly employed in physiological experiments. When it is the swing of the pendulum, is also omitted. Before commencing an experiment the pendulum is raised up (in the figure to the right) and is kept in that position by the tooth (a) catching on the spring-catch (&). On depressing the catch (h^ the glass plate is set free, swings into the new position indicated by the dotted lines, and is held in that position by the tooth (a') catching on the catch (6')- In the course of its swing Ihe tooth (a'), coming into contact with the projecting steel rod (c), knocks it on one side into the position indicated by the dotted line (c')- The rod (c) is in electrical continuity with the wire (x) of the primary coil of an induction-machine. The screw ((7) is similarly in electrical continuity with the wire {y) of the same primary coil. The screw (d) and the rod (c) are armed with platinum at the points at which they are in contact, and both are insulated by means of the ebonite block (e). As long a^ c and d are in contact the circuit of the primary coil to which x and y belong is closed. When in its swing the tooth W) knocks q away from d, at that instant the circuit is broken, and a "breaking" shock is sent through the electrodes connected with the secondary coil of the machine and so through the nerve. The lever (7), the end only of which is shown in the figure, is brought to bear on the glass plate, and when at rest describes a straight line, or more exactly an arc of a circle of large radius. The tuning-fork (f), the ends only of the two limbs of which are shown in the figure placed immediately below the lever, serves to mark the time. THE MUSCLES. 475 necessary to use very rapid breaking of the current, some instrument must be employed for that purpose. The first instrument used in making myograms was that of Helmholtz. Simple Contraction. — If a single induction shock be applied to a muscle there will result a simple muscular contraction; that is, the muscle will respond by a quick contraction, with return to its former relaxed condition. This contraction, when graphically shown, is termed a simple muscle-curve. Muscle-curve, or Myogram. — If the muscle-curve of a single stimulus be analyzed, it will be seen to be composed of various eie- Fig. 191. — A Muscle-curve Obtained by Means of tlie Pendulum Myograph. ( Fosteb. ) To be read from left to right. a indicates the moment at which the induction-shock is sent into the nerve. 6, The commencement; c, the maximum; and (l, the close of the contraction. The two smaller curves succeeding the larger one are due to oscillations of the lever. Below the muscle-curve is the curve drawn by a tuning-fork making 180 double vibrations a second, each complete curve therefore representing i/iso of a second. It will be observed that the plate of the myograph was traveling more rapidly toward the close than at the beginning of the contraction, as shown by the greater length of the vibration-curves. ments, as follows : (1) period of latent stimulation, (2) period of con- traction, and (3) period of relaxation. Latent Period. — The significance of this term is that the muscle experimented with does not respond at the precise moment when the stimulus is applied to it. The response comes later — about ^/joo o^ a second. During the latent period there is no apparent change occurring within the muscle. The latent period may be modified by increased stimulus and heat, when it becomes shortened ; fatigue and cold lengthen the time. The latent period of unstriped muscle may be as long as one or two seconds. Contraction Period. — The muscle-curve comprises two periods: that of the ascent and that of the descent of the muscle. The ascent 476 PHYSIOLOGY. of the curve represents the contraction of the muscle until it has reached its maximum. The rate of contraction is at first a trifle slow, then more rapid and more slow a second time. The extent is Vioo of a second. Relaxation Period. — After the muscle has contracted to its max- imum, it begins to relax — at first slowly, then more quickly, and finally more slowly again. Its duration is ^/loo of a second. It is shorter with a weak stimulus and longer with a strong stimulus. Fig. 192. — Arrangement of Apparatus in Conducting Experiments on Nerve and Muscle. (Stirling.) B, Galvanic battery. K, Electric key in primary circuit. P, Primary coil of induction machine. S, Secondary coil of induction apparatus, from which the current is conducted when the key (£') is open to the electrode (E) on which rests the nerve in). The muscle (M) is supported by a clamp under a glass shade, its tendon being connected by a thread with a lever (L) writ- ing on the smoked surface of a revolving drum. The time-marker (TM) is included in the primary circuit so that when the current passes through P by closing the key (K) it also traverses the electromagnet of the time-marker and causes a record of the instant of stimulation to be made on the surface of the drum. S, Stand supporting moist chamber. W, Weight by which muscle is stretched and which is lifted in the contraction of the muscle. In the myograph we use a light lever and a weight as near its axis as possible to record the contraction. Here the tension of the muscle in its contraction and relaxation remains nearly the same. This contraction is called an isotonic contraction. The isometric contraction is produced when the muscle pulls against a spring. Here the muscle undergoes slight change in length and the energy of change of form is transformed into tension and stored in the spring. An examination of isometric and isotonic curves proves that a muscle which has shortened to a given length will be making a far THE MUSCLES. 477 greater pull when its effort to shorten has been resisted than when it has reached the same during a contraction without resistance, which is an isotonic contraction. Curve of Fatigue. — When a muscle has become fatigued and its myogram studied, at first the contractions improve for a short Fig. 193. — Fatigue-curves of Frog's Muscle. (Waller.) time. This is shown by the successive contractions being higher. Afterward the latent period increases, the curve becomes less high, while the contraction becomes slower and lasts longer. Yeratrine and adrenalin greatly prolong the stage of relaxation in a muscle. Staircase Coxtractioxs. — When electrical stimuli of equal strength are let into a muscle at regular intervals and the contrac- tions registered, it is seen that at first each curve exceeds its pre- decessor in height. It shows that the muscle is benefited within cer- Fig. 194. — Effect of Increase of Current on Efficiency of Breaking Induction Shocks. (Howell, after FiCK.) a, minimal contraction; 6, c, first maximum; d, e, second maximum. tain limits by contraction, and its excitability increased for a new stimulus, just as we can do better muscular work when we have warmed up our muscles. Bowditch first noticed the staircase con- traction in cardiac muscle. Compositiox of Muscle Before axd After Contraction. — Experiments show that constant chemical metabolism is going on in a muscle at rest. It is constantly taking in oxygen, glucose, and 478 PHYSIOLOGY. perhaps fats and proteids, and giving off carbonic acid. When the muscle becomes active and does work, then the chemical changes become more active. The chief differences between resting and acting muscle are: (1) the acting muscle forms more CO, ; (2) more oxygen is consumed ; (3) sarcolactic acid is formed; (4) glycogen is made use of; (5) the substances soluble in water diminish in amount, while those soluble in alcohol increase. Changes in the Volume of the Muscle During Contrac- tion.— Muscular contraction can be defined by its apparent effects: Fig. 195. — An Experiment to Show that a Contracting Muscle does not Change its Volume. (Hedon.) V, Vessel filled with water containing the frog's foot, the nerve upon two electrodes, t, Capillary tube In which the level of the water is observed. P, Battery. a shortening of the muscle. By experiment it has been shown that the muscle on contracting simply shifts its muscular units when it shortens, for the volume of the muscle remains the same. Muscle-wave. — When a muscle is placed beneath two levers some distance apart, and one end of the muscle is stimulated, then a wave of muscular contraction runs through it. The distance between the points at which the two curves begin to rise from the abscissa gives the rate of wave-movement. The continuity of the muscle-fiber is the reason the wave is propagated. The fibers stimulated are set into activity and the THE MUSCLES. 479 evolution of energy in them stimulates the neighboring fibers and the contraction passes along the muscle. The velocity of a contraction-wave in muscle can be measured; in the frog it is from three to four meters per second; in man, about forty feet per second. 480 PHYSIOLOGY. The Effects of Two Successive Stimuli. — Let the student imagine two successive nionieiitary stimuli applied successively to a muscle. The stimuli may l)e either maximal or submaxim,aJ; that is, either the greatest possible contraction the muscle is able to accomplish or only a medium contraction from the applied stimulus. Fig. 197. — Rate of Conduction of the Contraction Process along a Muscle as shown by the DiiTerence in the time of Thickening of the two Extremities. (Marey, Howell.) The tuning-fork waves record ^/mo of a second. If each of the two stimuli be maximal, the effects produced will vary according to the time of application of the two excitants. Thus, (1) if the second stimulus be applied after the relaxation following the effect of the first stimulus, then the myogram shows two maximal Fig. 198. — Tracing of a Double Muscle-curve. (Foster.) To be read from left to right. While the muscle was engaged in the first contraction (whose complete course, had nothing intervened, is indicated by the dotted line), a second induction shock was thrown in at such time that the second contraction began just as the first was beginning to decline. The second curve is seen to start from the first as does the flrct from the base line. contractions; (2) if the second stimulus follow the first with such rapidity that the two occur during the latent period of the muscle- curve, then the recording instrument shows but one maximal con- traction. THE MUSCLES. 481 If the two stimuli be nonmaximal, the effects of the two separate stimuli will be superimposed ; that is, there will be a summation of the contractions. This summation occurs regardless of the time of application of the stimuli. Summation of Stimuli. — As the second stimulation was just seen to add its curve to the first, so does the third add itself to the second, Fig. 199. — Progress in Fusion of Contraction. (Laulanie.) A G, B 7, C 8, per second. the fourth to the third, etc. If the excitations occur with a rhythm that is not too rapid, the various shocks are nearly equal, as shown by the myogram, but yet they do not mingle. These isolated shocks are seen when the rhythm does not exceed six per second. If, now, these same excitations be repeated with a frequency of twenty per second, isolated shocks will not be seen. Each stimulus, lasting but V20 of a second, does not allow the muscle completely to 31 482 niYSIOI.OGY. relax; thus, the second contraction encroaches upon the first, the third upon the second, etc. From the rapid succession of the stimuli, the muscle remains in a condition of continued viljratory contraction. I'hat is, in a stale of Irlanus. Complete Tetanus.— If the excitation rhythm be more frequent, — say, fifty of them per second, — there will no longer be any trace of the primitive shocks. The ascent of the muscle-curve will be Fig. 200. — 1. Imperfect Tetanus, 15 Contractions per second. 2. Perfect Tetanus. (Laulani^.) abrupt and decided; the contraction due to the first shock will not be followed by any relaxation. There will be no oscillation recorded upon the myogram. The upper straight line due to the complete contraction of the muscle is called the plateau. When the muscle is in this condition the tetanus is said to be perfect or complete. The tetanus is spoken of as incomplete when there are still relax- ations and vibrations which indicate the incomplete mingling of the shocks. The number of stimuli that are required to produce tetanus may be very variable. Fifteen to twenty stimuli per second suffice to throw a frog's muscle into tetanus. THE MUSCLES. 483 Duration of Tetanus. — A tetanized muscle cannot be kept con- tracted for a considerable length of time, even though, the stimuli be kept constant. The muscle begins to elongate — at first some- what quickly, but later more slowly. This change is produced by fatigue of tbe muscle. Effect of Temperature on Muscle-curve. — Low temperature makes the contraction longer and lower; the latent period is longer, and the relaxation-curve is greatly not unlike that of a fatigued muscle. When the temperature is raised, the setting free of energy is more rapid; hence the time of contraction is shortened, especially the latent period ard time of shortening of the muscle. Strength of Stimulus. — If you apply a current just sufficient to cause a muscle to contract, and then increase the strength of the current, the muscular contraction will become more rapid and more complete. But the increase in contraction is not proportional to the increase in stimulus. As the stimulus is gradually increased, the increase in contraction becomes smaller and smaller. After a cer- tain strength of stimulus is attained, a further increase of it does not cause any increment in the contraction of the muscle. Amount of Load. — If a muscle is attached to a lever without any weight in the scale-pan, it is ascertained that light weights actually increase the height of the contraction, whilst heavier weights dimin- ish it until a limit is reached, and when a sufficient weight is used the muscle no longer contracts. Muscle-tonus. — This is a condition of a muscle more or less stretched, and is dependent upon the reflex activity of the central nervous system and a sufficient supply of blood to the muscle. If you cut a motor nerve going to a muscle, the muscle loses its tonus. If you divide all the posterior spinal roots, then the muscles also lose their tonus. Muscle-sound. — Helmholtz said that 36 vibrations per second formed the average for the production of muscular tones. To-day this is considered an overtone, and the requisite number of necessary vibrations is placed at 19 per second. First Heart-sound. — It is probable that the first sound of the heart is partly a muscle-sound. It is a dull sound, persisting when the thorax is taken away and the auriculo-ventricular valves are de- stroyed. The sound could not in such an instance be produced by the vibration of the valves. Voluntary Contraction. — The number of single impulses sent to our muscles during voluntary movements are somewhat variable. 484 PHYSIOLOGY. There are from 8 to 12 impulses for a slow movement and from 18 to 20 impulses per second for a rapid movement. Ten vibrations per second ma}^ ))e taken as the average. Elasticity of the Muscle. — Of all the properties of muscle, elas- ticity is the one least well known, the one which is most difficult to explain and understand. Physicists say that a body is perfectly elastic when, after having been removed from its first position, it returns exactly to the original position. Thus, an ivory ball is perfectly elastic; after it has been flattened by an external force it returns exactly to its original shape. Fig. 201. — Extensibility of Elastic Band and Muscle. (Waller.) If a piece of rubber is stretched by adding successive weights it is found that the series of elongations are nearly proportional to the weights. When the weights are successively removed it will be found that the elasticity of the rubber is nearly perfect. But if over- weighted for a long time it does not return completely to its original length, and the elasticity disappears gradually. If now you take a frog's fresh muscle and successively load it, the extension of the muscle for each weight is not proportional to the weight used, but with each increase in weight the muscle stretches rather less, the greater the previous extension. On removing the weights the muscle shortens but it does not return to its original length. A contracted muscle is more extensible than a resting one. This prevents a rup- ture of the muscle in a sudden contraction. Muscular elasticity preserves the tension of the muscle under THE MUSCLES. 485 all usual conditions. The muscles attached to the bones are in a state of elastic tension which is favorable to the action of the muscle, diminishing the danger of rupturing its fibers. The elasticity of muscle favors the economical expenditure of work by the muscle. A muscle is always taut, never in a state of relaxation, and it is then ready to efficiently exert mechanical force the moment it begins to contract. Heating to a certain extent increases and cooling decreases elasticity. The curve of muscle, when stretched by weights, is not a hyperbola, but one peculiar to muscle. In rgor lu tetanus Fatigued Fig. 202.— Extenaibility of Muscle in Various States. (Waller.) Tested by 50 grammes applied for short periods. Muscular Work. — While treating of elasticity and its modifica- tion, tonicity, it might be well to give a brief discussion upon mus- cular work. The amount of mechanical work which a muscle per- forms equals the product of the weight lifted and the height to which the weight is lifted. Thus, the work = height X the weight. When a muscle begins to contract, it is then that it lifts the greatest load; as the contraction continues, the muscle is capable of lifting less and less. 486 PHYSIOLOGY. If the height he expressed in feet and the weight in pounds, then the work performed is measured in units of foot-pounds. Likewise, should the height he measured in meters and the weight in grams, then the work done is expressed in grammeters. In studying tlie heights of contraction in a loaded muscle it is found that the heights of lift continuously diminish, but the actual work done by the muscle increases rapidly and then more slowly until it reaches its maximum with a load of 200 grams. After that point the work done slowly decreases and then more rapidly until it receives a load of 700 grams, when the muscle is unable to contract. Dynamometer. — The common, clinical form of dynamometer is much used to determine the absolute force of certain muscles. The instrument is very useful to determine the difference in grip between the two hands in cases of paralysis. The patient grasps the instru- ment in his hand and squeezes upon it ; the power exerted is regis- tered in kilograms. Muscles are Most Perfect Machines. — They take the best ad- vantage of the fuel supplied to them and give in return a very high percentage of energy in the form of work. They, by legitimate exer- cise, increase in strength and power so that they progressively per- form more work. The steam engine, to which muscles are frequently compared, is inferior in every respect. The best-made steam engine shows as work only about 12 per cent, of the total energy supplied to it by the oxidation of the coal, while about 88 per cent, is transformed into heat. Muscle transforms 25 per cent, of its energy into work and 75 per cent, into heat to warm itself. The proportion of work to heat is not a fixed one. If you gradu- ally increase the stimulus, both work and heat increase ; but the heat- production is increased more rapidly and reaches its maximum sooner. Heat-production decreases more rapidly than the amount of work pro- duced, when the muscle is exhausted. When the muscle is loaded so it cannot contract, or an unweighted muscle is made to contract, no work is produced and all the energy is converted into heat. Fatigue. — Fatigue is due to a chemical and physiological altera- tion of the muscles. It is characterized by a pain, more or less acute, localized in the muscles. The alterations in the muscles fatigued are due to an accumulation of toxic products of the metabolism of the muscle. Sarcolactic acid is one of these fatigue-products, and when applied to a muscle it causes a state of exhaustion. Whatever the fatigue-products may be, a muscle exhausted by a series of con- THE MUSCLES. 487 tractions is saturated with the so-called fatigue-products which have poisonous properties. The chemical theory of fatigue is proved by preparing a watery extract of muscles exhausted by a series of con- tractions, and injecting this into the circulation of a frog. Here it will cause the muscles to show fatigue in the same manner as when spontaneously caused. This fatigue of the muscles in the frog, caused by electric tetanus, can be removed and their irritability re- stored by the injection of solutions of sodium carbonate into the vein. Tliis alkaline solution washes out the fatigue-products from the Fig. 203. — Mosso's Ergngraph. (From Tigerstedt's "Human Physiol- ogy," copyright, 190{), by D. Appleton and Company.) muscle. The circulation of blood normally washes away the toxic products of fatigue. Mosso has shown that the blood of a fatigued dog, when injected into the vein of another dog. caused all the symp- toms of fatigue. In the fatigued muscles of the frog it is not neces- sary to have the blood wash away the products of fatigue, for it has been shown that the oxygen of the air in about half an hour can restore their irritability. If the muscle fatigued is placed in an atmosphere of hydrogen, no restoration of the muscle ensues. Oxida- tion is the restorative agent in fatigued muscles. The Seat of the Fatigue. — When a nerve of a warm-blooded animal is curarized, artificial respiration being kept up, and elec- tricity applied to the nerve, it causes no muscular response until the curare is excreted, when the muscle again contracts, showing that it 488 PHYSIOLOGY. is not tlie nerve or tlie muscle, but the motor end-plates, which are exhausted. Mosso has shown that if, with the ergograph, you lift a weight until the flexor muscle is exhausted, and then induction cur- rents are applied to tiie nerves going to the muscle, the muscle will again lift the weight. This experiment shows that the fatigue- products generated in the muscle are carried by the circulation to the central nervous system and poison it. Hence the central nervous system is shown to be the chief seat of fatigue, and the motor nerve- endings the next. A B Fig. 204. — Ergographic Curves. (After Mosso.) (From Tiger- stedt's "Human Physiolog\'," copyriglit, 1906, by D. Appleton and Com- pany. ) Read from right to left. Ergographic Curves. — The most salient feature seen in them is the rhythmical rise and fall, which is due to the central nervous sys- tem. During the first 180 contractions the height of the ergographic curve decreases, and then becomes nearly constant in the height, which is above 85 per cent, of the original contraction. The curve indicates that during a series of contractions two pro- cesses are at work, the one using of material and the other an accu- mulation of fatigue-products in the first part of the curve. In the subsequent part of the curve, the fatigue-products are removed by the circulation, and the circulation supplies the materials to be used up. THE MUSCLES. 489 Involuntary Muscle. — The same sul)stances are found in plain muscle as in striated muscle, except that plain muscle contains six Fig. 205. — Ergographic Curve of a Case of Addison's Disease, Show- ing Rapid Exhaustion of Muscle. (Langlois. ) Read from right. times more neucleoproteid than striped muscle. In its contraction the latent period is ahout a second, and the contraction lasts several sec- Fig. 20G.— Pick's Work Adder The wheel (rf) bears upon its axle a counterpoised muscle lever (c), ending in a pawl (w), through which the wheel is caused to revolve when the lever is pulled upward by the attached muscle. A second pawl («) prevents the wheel from turning bark when the muscle relaxes. On the other side the axle of the wheel bears a pulley from which a weight (d) is suspended. The turning of the wheel winds the suspending cord upon the pulley and raises the weight ('/). The muscle preparation should be the double adductor, suggested by Fick. onds; it spreads as a wave from filler to fiber. Its irritability is very dependent upon temperature; heat decreases its tonus, cold 490 PHYSIOLOGY. increases it. The stimuli to excite plain muscle are chemical, mechanical, and the opening and closing of a constant current. Organs containing unstriped muscle frequently exhibit involuntary rhythmical movements and a tendency to sustained tonic contrac- tion. The force of the uterus in expelling the child and that of the bladder in expelling the urine show that plain muscle can do con- siderable work. Ordinarily, organs made up of nonstriated muscle are only faintly sensitive. These rhythmic contractions and relaxa- tions, like the tonic contractions, are independent of the action of nerves, but are modified by it. Unstriped fiber does, like striped Fig. 207. — Curve of Contraction of the Unstriped Muscle of Muller in Dog. (Laulanie.) The intervals on the line T are seconds. fiber, increase its height of contraction by increasing the strength of the stimulus. It can not be thrown into a state of tetanus by a series of stimuli. Rapid stimuli simply increase the force and rate of individual contractions. Smooth muscle, as a rule, contains nerve- plexuses and ganglion-cells. It has two kinds of functionally different nerves, motor and inhibitory. Both sets of nerves are connected with nerve-cells in their course, such as the plexuses of Auerbach and Meissner in the intestinal tract. CHAPTER XII. VOICE AND 5PEECH. It has long been established that the sounds of the voice in man and mammalia are produced by the vibratory action of the vocal cords. It is usually the blast of expired air — under certain circumstances the inspiratory blast also — in its passage through the glottis that causes the tense vocal cords to vibrate. These cords vibrate according to tiie laM's which regulate the vibration of stretched membranous cords. As a result of these vibrations sound is produced which, in man, is capable of being so modified as to constitute articulate speech. Experiments upon living animals show that the vocal cords alone are tlie essential factors in the production of sound. For. so long as these remain untouched, although all other parts in the interior of the larynx are destroyed, the animal is still able to emit vocal sounds. The existence of an opening in the larynx of a living animal, or of man, above the glottis in no way prevents the formation of vocal sounds; however, should sueli an opening occur in the trachea, it causes total loss of voice. By simply closing the opening sounds can be again produced. Such openings in man are usually met with as the result of accident, of suicidal attempts, or of operations performed upon the larynx or trachea for the relief of disease. Production and Modification of Sounds. — Whenever a solid body surrounded by air is tlirown into vil)ration the sensation of sound is carried to the ear. The vibrations must, however, be of certain strength and follow one another with certain rapidity. It is usually stated that if the vibrations l)e fewer than 32 or exceed 33,768 per second no effect is produced upon the nerve of hearing. For the production of a musical sound the vibrations must suc- ceed each other at regular intervals ; if the vibrations occur at irregular intervals, only a noise results. The pitch of a sound depends upon the number of vibrations within a given period of time. The pitch becomes higher in direct proportion to the rate of increase in the rapidity of the vibrations. The strength, or intensity, of the sound depends upon the extent of the vibratory action of the sonorous body. Tone, or timbre, is that peculiar character of a musical note whereby it can at once be distinguished from another note of exactly the same pitch and strength. (491) 492 PHYSIOLOGY. THE ORGAN OF VOICE. The special organ of voice in man is that portion of the air- passages called the larynx. It is a sort of hollow chamber which extends from near the root of the tongue to the first ring of the trachea. It is placed in the middle line of the neck, where it forms a considerable ])rojcction, larger above than below. Although the larynx is the proper organ of voice, yet the lungs and the moving parts of the thorax serve to propel the air through this organ. The cavities above it. including the pharynx, mouth, and nasal cavities, assist in modifying the vocal sounds. They are, there- fore, adjunct organs of voice. Fig. 20S. — The Larynx as Seen with the Laryngoscope. (Landois.) L., Tongue. A'., Epiglottis. V., Vallecula. R., Glottis. L. r.. True vocal cords. /R. iM., Sinus Morgagni. L. i\ s.. False vocal cords. P., Position of pharynx. .S'., Cartilage of Santorini. W., Cartilage of Wrisberg. »S'./>., Sinus pyriformis. Anatomy of the Larynx. — The larynx consists of a cartilaginous skeleton which constitutes its walls ; also vocal cords ; muscles which move directly the cartilaginous pieces, and influence indirectly the tension of the cords; and finally, a mucous membrane which lines the internal cavity. Cartilages. — The cartilages of the larynx are four in number: two unlike and two alike. One of the former is inferior and exists in the form of a signet-ring. It is the cricoid. This cartilage is continuous with the rings of the trachea. Its narrower portion is situated anteriorly ; its wider portion is placed posteriorly. It ar- ticulates with the inferior cornua of the thyroid cartilage, forming the crico-thyroid articulation. The other odd cartilage, the superior one, is called the tliyroid. It is composed of two quadrilateral laminae which meet in front VOICE AND SPEECH. 493 at an angle. This projection is popularly known as Adam's apple. Each thyroid lamina terminates posteriorly in two horns: one su- perior, the other inferior. The two cartilages which are alike are the arytenoids. Each one is in the form of a triangular pyramid, whose base is movably articulated at the back on the cricoid cartilage. The apex of each arytenoid cartilage has attached to it, in the shape of a movable point, a cartilage of Saniorini. The true vocal cords are attached to the anterior angles, or vocal processes, of the arytenoids; the crico-aiytenoideus muscles are inserted into the external angles. Fig. 209. — Action of tlie Muscles of tlie Larynx. (Beaunis.) The dotted line indicates the new positions assumed by the thyroid carti- lage in the action of the crico-thyroid muscle. 1, Cricoid cartilage. 2, Arytenoid cartilage. 3, Thyroid cartilage. 4, True vocal cord. 5, New posi- tion of the thyroid cartilage. 6, New position of vocal cords. The cartilages of Wrisberg are found in the aryteno-epiglottic folds. The epiglottis is attached to the inner surface of the anterior portion of the thyroid cartilage. It projects upward behind the base of the tongue. The epiglottis is attached to the tongue by the three glosso-epiglottic folds. The false vocal cords are two folds of the laryngeal mucous mem- brane which pass from the anterior surfaces of the arytenoids to the thyroid cartilage. They are located above the true vocal cords. The true vocal cords extend from the anterior angles of the bases of the arytenoids to the thyroid cartilage. The glottis is the chink between the true vocal cords. The ventricle of the larynx is the pouch between the true and false vocal cords. 494 PHYSIOLOGY. The Muscles. — All of the laryngeal cartilages, joined together by ligaments, are moved by five pairs of muscles. The muscles of the larynx are divided into two groups: intrinsic and extrinsic. To the former group belong those muscles which are attached to the various cartilages. The latter collection comprises the musculature connect- ing the hirynx to other parts like the hyoid bone. Intrinsics. — Of these there are five pairs. 1. TJie Crico-tliyroid Muscles. — Thci^e, which are in the anterior part of the larynx, originate in the front and sides of the cricoid car- tilage below. Outwardly they are attached on each side to the lower Fig. 210. — Schematic Horizontal Section of Larynx. (Landois.) /, Position of horizontally divided arytenoid cartilages during respiration. From their anterior processes run the converging vocal cords. The arrows show the line of traction of the posterior crico-arytenoid muscles. //, //, Position of the arytenoid muscles as a result of this action. edge of the thyroid cartilage. They become fixed by the action of the thyro-hyoid, sterno-thyroid, and laryngo-pharyngeal muscles. Action. — They incline the cricoid cartilage upward and backward and so elongate and stretch the vocal cords, at the same time contract- ing the opening of the glottis. 2. The Posterior Crico-arytenoid Muscles. — These take their de- parture from the posterior surface of the shield of the cricoid cartilage. They then converge and are fastened to the base of the corresponding arytenoid cartilage. Action. — In contracting they turn the anterior ends of the aryte- noids outward, whereby they separate the vocal cords from each other VOICE AND SPEECH. 495 and give a rhomboid form to the glottis. Thus it is materially widened, 3. The Lateral Crico-arytenoids. — These muscles are found upon the inner side of the cricoid. They are carried backward and upward and are fastened to the outside of the posterior ends of the bases of the arytenoid cartilages. Action. — In contracting they rotate the arytenoid cartilage in- ward. They are antagonists of the posterior crico-arytenoid muscles; they narrow the vocal part of the glottis. 4. The Thyro-anjtenoid Muscles. — This pair of muscles is inserted at the anterior end in the middle of the angle of the thyroid cartilage, Fig. 211. — Schematic Closure of the Glottis by the Thyro-arytenoid Muscles. ( Landois. ) //, //, Position of the arytenoid cartilages during quiet respiration. The arrows indicate the direction of muscular traction. I, I, Position of the arytenoid cartilages after the muscles contract. and at the posterior end it is fastened to the inside of the anterior end of the base of the arytenoid cartilages. Each muscle of the pair runs its entire length parallel with the corresponding vocal cord. This muscle has two bundles : an internal and external bundle. The muscle draws the arytenoids toward the thyroid and relaxes the cords. By the internal bundle the anterior part of the vocal cord can be tightened while relaxing the posterior part. It is the muscle concerned in the production of the high notes in the singing voice. 5. The arytenoid constitutes an odd muscle. It extends pos- teriorly between the two arytenoid cartilages. The muscle is divided into two layers: one posterior, of oblique fibers disposed like an X; and one anterior, of transverse fibers. 49b PHYSIOLOGY. Its action is, in contracting, to draw the arytenoid cartilages together so that the respiratory part of the gh)ttis is closed. If the contraction be simultaneous with that of the lateral crieo-arytenoid muscles, respiration is entirely interrupted. The Extrinsic Muscles are those of the anterior region of the neck ; those in the suprahyoid as well as those in the subhyoid region. By the action of these muscles the entire larynx is moved upward and downward. The Cavity of the larynx is lined with a mucous membrane. The mucous membrane is continuous with that of the trachea. It is covered with the prisnuitic or ciliated epithelium in all places ex- cept over the vocal cords and epiglottis. In these special areas it is stratified. The Vocal Cords comprise two sets, as was previously men- tioned; the upi)er, false cords, composed of folds of mucous mem- brane, take no part in voice production; the lower, true cords, are composed of a mucous membrane with pavement epithelium, a lamina of elastic fibers, and the thyro-arytenoid muscle. Opening the cavity of the pharynx and raising the epiglottis, the whole extent of the glottis is seen; that is, the slit left by the two superior cords. This has the shape of a much elongated triangle — apex in front, base at the back. The limited anterior part of the triangle is called the vocal part of the glottis; whereas the posterior part is called the respiratory portion. It does not participate in phonation, but only in the passage of air. Xerve-supply.- — The nerves which are distributed to the larynx come from the pneumogastric. The superior laryngeal nerve supplies the mucous membrane of the larynx and gives the external laryngeal branch to the crico-thyroid muscle. The inferior, or rerurrenf, laryn- geal nerve supplies allof the muscles except the crico-thyroid. The ganglia which preside over the motor innervation of the larynx are seated in the floor of the fourth ventricle. Laryngoscopy. — The laryngoscope is an instrument used to bring to view various parts of the pharynx, larynx, and trachea. It comprises a small mirror fastened to a long handle. The angle that the mirror makes with its handle is from 125 to 130 degrees. Condition of the Vocal Cords. — By observations made with the laryngoscope it has been determined that, while in respiration the vocal cords are inclined from each other, and the glottis is wide open, in speaking or vocalization the cords are seen to approximate and vibrate. In ordinary quiet breathing there is a wide, triangular- VOICE AND SPEECH. 497 shaped opening in the glottis. On the other hand, during the pro- duction of vocal sounds the triangular posterior opening is com- pletely closed, while the anterior portion of the rima glottidis becomes a very fine fissure, or slit. Fig. 212. — The Posterior Rhinoscopic Image. (Bosworth.) VOICE. It is the vibration of the edges of this fissure by the passage of air through it that produces sound: the voice. The air expelled from the lungs acquires a maximum of tension in the narrow tracheal tube, causing it to strike under the true vocal cords and put them into the proper vibrations. But the tone produced will not always be of the same calil)er and height, since the expired air may find the vocal cords in different states, the result of muscular contractions. The Height of the sound produced in the larynx depends upon the number of vibrations of the vocal cords during a given time. 32 498 PHYSIOLOGY. The number of vihralions would then depend upon the slate of tension and the length of the cords themselves. The greater the number of vibrations during a second, the higher will be the tone, and vice versa. The range of the human voice, as regards height, is usually between 87 and 768 vibrations per second. Not all persons have such a range. Each type of voice includes about two octaves. When a man speaks — that is, when he uses the articulate voice — his voice does not exceed the height of a half-octave. When he sings, his vocal range is more extended. The Intensity of sound depends upon the extent of the vibra- tions of the vocal cords, produced especially by the force of the cur- rent of air. The height of the voice depends, to a considerable extent, upon different lengths of the vocal cords. The result is that in adult man Fig. 21.3. — Position of Vocal Cords on Uttering a High Note. (Landois.) the hass, haritone, and tetior voices are found, because of the greater length of the vocal cords in man. On the contrary, the contralto, mezzosoprano, and soprano voices belong to women and boys, for they have cords shorter in length. Timbre of sound depends upon the nature of the vibrating body and of the other parts vibrating at the same time with it for the production of harmonious sounds. Resonance. — The normal voice of man is sonorous; that is, it is composed of vibrations regular in extent and isochronous. Its resonance comes either from the air-tnhe or from the resonators. By the former is understood the trachea, bronchi, walls of the lungs, and thoracic case; by the latter, the ventricles, pharynx, mouth, and nasal cavities. The resonance within the thorax in an adult causes a fremitus of the thoracic wall. This is greatly increased in low sounds and diminishes until it disappears in high sounds. Ordinarily, in speaking and singing, the air put in vibration in the larynx issues from the mouth while the nostrils are open. If VOICE AND SPEECH. 499 they be closed, the air which is held ther© vibrates with the air issuing through the oral cavity and gives the voice a nasal tone. The human voice can assume two different registers. The one is strgng and sonorous and accompanied with vibrations of the thoracic wall (chest-voice). The other is Aveak, without resonance, and of higher pitch (head-voice, or falsetto). Ventriloquy, which by practice can reach great perfection, con- sists only in the possibility of changing the register of the voice. The name derived its origin from the erroneous interpretation of it by the ancients. They claimed that the ventriloquists spoke from the stomach. The performer is able to conduct dialogues in which two persons appear to take part. Speech. — If man had the faculty of making only sounds with the larynx, his vocal organ would not differ greatly from ordinary musical instruments. The voice in such a case would but serve to make others aware of his presence and to call them for the various wants of life, just as happens in animals and in the child itself when just born. But man is endowed with an important means by which he can communicate to his fellows the state of his mind. It forms one of man's noblest characteristics, a distinctive one. The infant at first expresses the state of his mind by cries accompanied by gestures. Then little by little it learns and tries to imitate those sounds which the parents always make corresponding to given objects and persons. It pronounces them without under- standing their meaning. In later years it learns of the correspon- dence of given sounds to given objects and ideas. Speech is articulate voice. It is an ensemble of sounds and noises harmonized by the will and co-ordinated by a particular cor- tico-motor nervous center. Its aim is to make known to the listener the present state of mind of the speaker as well as recollections of the past and tendencies toward the future. Vowels and Coxsoxaxts. — Speech is composed of two ele- ments, namely: vowels and consotiants. The former consist of sounds generated in the larynx and slightly modified in the pharynx and mouth-cavity. The consonants result from noises variously pro- duced by the obstacles encountered by the air in its passage through the pharynx and mouth-cavity. Vowels are produced in the larynx, pharynx, and mouth ; consonants not in the larynx, but in the mouth. The vowels are produced by the different form of the cavity of the pharynx and mouth during the expiration of air through them. 500 PHYSIOLOGY. The principal change in form consists in the lengthening and short- ening of the mouth. The vowels are a, e, i, o, and u. The consonants consist of sounds emitted by the larynx, but which become noises by reason of obstacles they encounter. Accord- ing to the obstructions met with, consonants are termed (jutterals {It, k, q), Unguals {c, d, g, t, s, n, I, r), and labials {b, f, m, p, v). The Unguals are subdivided into palatals and dentals. The very varied union of the vowels with the consonants con- stitutes syllables; union of the latter forms words. Stammering is due to a continued spasmodic contraction of the diaphragm and to the muscles of the larynx not harmonizing the chink of the glottis. Stuttering is due to a want of ability to form the proper sounds by the laryngeal muscles; the breathing and diaphragm are both normal. Pathology. — Paralysis of the motor nerves of the larynx from the pressure of tumors, causes aphonia, or loss of voice. In aneur- ism of the aortic arch the left recurrent nerve may be paralyzed from pressure. The laryngeal nerves may be temporarily paralyzed by overexertion and hysteria. If one vocal cord be paralyzed, the voice is not pure in tone, but falsettolike. Hoarseness may be caused by mucus upon the vocal cords or by roughness or laxness of the cords. Disease of the pharynx or naso- pharynx and uvula may, in a reflex manner, produce a change in the voice. APHASIA. Aphasia means a loss of power to produce or understand spoken or written speech. Aphasia is a disorder of the speech, due to a lesion of the third left frontal convolution. There are four different kinds of word- memory, each having its seat of registration in a well-defined part of the cortex. The first is the (1) auditory word-center, where the sound of words is registered; (3) a visual word-center, where the visual images of letters and words are registered ; (3) a glosso-kinaes- thetic center, where the combined impressions which pass to the brain as a result of the movements of the lips, tongue, palate, larynx, and other parts concerned in articulate speech, are registered; (4) a cheiro-kinaesthetic center, where sensory impressions resulting from the movements made in writing are stored up. From the glosso- VOICE AND SPEECH. 501 kingestbetic and cheiro-kinaesthetic center, fibers descend as part of the pyramidal motor tract, those from the glosso-kina^sthetic center going to the motor-speech apparatus in the medulla, and those from the cheiro-kinEBsthetic center going to the spinal-motor ganglia con- cerned in the act of writing. As is known, the auditory word-center is in the first temporal convolution, the visual word-center in the gyrus angularis and a part of the supramarginal gyrus, the speech- center in the third left frontal convolution, and the writing center in the posterior part of the second frontal convolution. The auditory word-center is the first called into activity; then the speech-center is gradually organized under the influence of excitations coming from the auditory word-center. After a year or two the child's visual word-center becomes organized, and the child recognizes letters and words, and at the same time two sets of asso- ciation-channels, commissural fibers, are laid down between the audi- tory word-center and this visual word-center. Finally, the child reads; then there must be activity first in the visual word-center, then in the auditory word-center, and immediately afterwards in the glosso-kingesthetic center. Then, as the child learns to write, the cheiro-kingesthetic center becomes organized, the guiding influence of the visual center being called into play, and this would lead to a development of commissural channels between the two centers. The visual center holds the same sort of relation to the act of writing that the auditory word-center holds to articulate speech. In writing from dictation, the train of activity starts in the hearing word-cen- ter, spreads to the visual word-center, thence to the cheiro-kinaes- thetic center, where the efferent stimuli pass over to the spinal motor centers (Bastian, Allbutt's System of Medicine, vol. VIII). The chief varieties of aphasia are: — , . { aphemia. Motor aphasia < , . '■ I agraphia. T • f visual. Sensory aphasia < ... -' ^ I auditory. Conduction aphasia. ■ Auditory Aphasia. — Supposing the patient's hearing is perfect, then auditory aphasia is revealed by his inability to put out his tongue. Visual Aphasia (Alexia). — Supposing the patient can see per- fectly, can the patient understand written or printed words ? If he 'fails to do so, he has alexia. 502 PHYSIOLOGY. Motor Aphasia (Aphemia). — 11' he can speak voluntarily, can he repeat words or read aloud? If he cannot, he has aphemia. Agraphia. — Supposing the patient can write voluntarily, can ho write from dictation or from copy? If he cannot, he has agraphia. A symptom found in all cases of aphasia: if he cannot write voluntarily, because of inability to remember words, but can write from dictation, it is sensory agraphia. If he cannot write either voluntarily or from dictation, it is motor agraphia. If he uses one word for another, so that the result is unintelli- gible, then there is paraphasia. If he writes, and he uses one word for another, so that it is unintelligible, then para-agraphia. Paraphasia and paragraphia are symptoms of conduction apha- sia, lesion of commissural fibers, and the lesion is ordinarily in the island of Reil or the convolutions about the fissure of Sylvius. Motor Aphasia. — If the patient can read silently, write volun- tarily, write from dictation, copy and hear and understand spoken words, but cannot speak voluntarily, repeat words or read aloud, then the lesion is in Broca's convolution, tliird frontal (motor apliasia. aphemia). If the patient can hear and understand spoken words, read and understand written or printed words and copy, but cannot speak vol- untarily, repeat words, read aloud, write voluntarily or from dicta- tion (aphemia plus agraphia), there is a lesion of the third left frontal convolution. This is the most frequent form of aphasia. Visual Aphasia. — If the patient can speak voluntarily and under- stand spoken words, but cannot understand written or printed words, write voluntarily or from dictation or from copy (visual aphasia plus agraphia), there is a lesion in the angular gyrus and supramarginal lobe. Auditory Aphasia. — If the patient can speak voluntarily, read intelligently, and write voluntarily, but cannot understand spoken words, repeat words or write from dictation (auditory aphasia), then there is a small subcortical lesion of the first and second temporal convolutions. (Butler's Diagnostics). CHAPTER XIII. ELECTRO=PHYSIOLOQY. ELECTRICITY. Electrical Measurements. The system of electrical measurements now in use is founded on the centimeter as the unit of length, the gramme as the unit of mass, and the mean solar second as the unit of time. This is commonly designated as the C. G. S, system. The amiDere is the unit of current; the unit of electromotive force, the volt; the unit of resistance, the ohm. The ampere is equal to one-tenth of the C. G. S. unit of cur- rent, or approximately the current of an ordinary Daniell cell through an ohm. The volt is 100,000.000 times the C. G. S. unit of electro- motor force, or approximately the electromotive force of a Daniell cell. The ohm is the resistance of a column of pure mercury 1 millimeter square and 1063 millimeters in length, at zero degrees C. To Measure Work. — ^To measure work of contracting muscle, the millimeter-gramme is the unit in the metrical system as that work required to overcome a force equal in weight of one gramme acting through the space of one millimeter. Cells or Batteries. — 1. Daniell Cell. — The first constructed con- stant battery. It consists of a glass jar filled with concentrated solu- tion of snlphate of copper, bathing an unclosed ring of sheet copper around a porous earthen jar filled with sulphuric acid (1 to 10 of water), in which is immersed a rod of zinc. The zinc pole is the negative or the cathode, and the copper pole the positive or the anode, and its electromotive force (E. M. F.) is about 1.07 volts. On ac- count of the constancy of the battery it is the one chiefly used in laboratories of physiology. 2. Dry Cells. — The Just-described wet cell gives off fumes, contains acids, and must be prepared for use. As the dry cell is always ready and without the preceding disadvantages, it is used extensively in the laboratory. The dry cells are usually modified Leclanche batteries. The Leclanche cell consists of a glass jar con- taining a saturated solution of ammonium chloride, into which an amalgamated zinc rod dips. The zinc is negative and the carbon positive. The plate of carbon is fitted into a porous pot packed with (503) 504 PHYSIOLOGY. pieces of carbon and dioxide of manganese. Its electromotive force is 1.5 volts, 'llie dry cell is usually made of a zinc cup lined with plaster of Paris, saturated with amomnium chloride. A carbon plate is placed in the center of tliis and surrounded with black oxide of manganese. Polarization of Plates. — The voltaic battery consists of two metals, zinc and copper, which are surrounded by an electrolyte con- taining various ions. The positive ions, Cu and H, will work their way towards the positive element, the copper plate, and the OH and SO4, being negative ions, will go towards the zinc. The hydrogen gas settles in minute bubbles upon the surface of the copper plate and ^K Fig. 214.— Daniell Cell. at once interferes with the action of the battery. It interferes both by the resistance it offers to the passage of the current, and also by setting up a current in an opposite direction, which tends to weaken the original current by neutralization. This action is called polari- zation of the plates. Besides this, in such an element some of the sulphate of zinc produced in the element is attacked by the hydrogen and deposited on the copper plate, so that the copper plate begins to approach the condition of the zinc plate, and, of course, the difference of potential or electromotive force is reduced. In all these ways the current is diminished and the cell is not of constant strength. Polarization in the Daniell cell is overcome by the solution of copper sulphate, and in the Leclanche cell by the manganese dioxide. Resistances. — There are two kinds of resistance to electric cur- rents: Internal resistance or the resistance of the element, or the ELECTRO-PHYSIOLOGY. 505 resistance the current experiences in passing through the liquid of the cell from one plate to another; and external resistance, or the resist- ance the current meets with in passing through the electrodes and apparatus. Internal resistance is inversely proportional to the size of the cell, and directly proportional to their distance from one another; that is, the larger the plate the less the resistance, and the greater the distance the greater the resistance, the conducting power of the liquid being always the same. External resistance depends on the conductivity of the conductor, which is a constant quantity for each conductor. External resistance is directly proportional to the length of the conductor and inversely proportional to the cross-sec- tion ; that is, the longer the conductor the greater the resistance, and the thicker the (wire) conductor the less the resistance. The thinner the wire the greater is the resistance. Batteries may be united together as positive pole to negative pole. Here the voltage is equal to the voltage of a single cell multi- plied by the number of cells. This method of coupling is used in the medical battery for the application of the galvanic or constant cur- rent to man. Another method is to couple abreast or "in multiple arc." Here the positive poles are on one wire and the negative on another wire. Here we have, as a matter of fact, a single cell with plates as many times larger as we have taken cells. The electromotive force is not altered, since the electromotive force of a cell varies with its chemical constituents and not with the size of the cell. Now, the internal resistance of a cell is inversely proportional to the size of the plates, so that by multiplying the size of the plates by the number of cells, say six, then the internal resistance is practically diminished one-sixth. Increased quantity of current is, therefore, obtained. The human body opposes to the electric current so great an external resistance that the internal resistance of the battery can be overlooked; hence surface extent of the zincs can be neglected. The intensity of the current is determined by the number of the elements and not by their size, hence you couple in series. When, however, you employ electricity to heat the galvano-cautery wire, which is short and of feeble external resistance, you augment the intensity of the current by increasing the surface (size) of the zincs. It is true you do not augment the electromotive force; but as the resistances diminish in proportion to the increase of size of the zinc, the inten- sity of the current increases in proportion to the increase of size of the zincs. You can have an apparatus to heat the cautery wire by coup- 506 PHYSIOLOGY. ling cells abreast or in multiple arc, which amounts to the same thing as having a cell with large-sized zincs. To summarize : to obtain increased intensity of current with small external resistance, as in a cautery wire, either use large cells or couple a number of cells abreast or in multiple are; with great external resistance, as in the application of the galvanic current to the human body or the nerves of an animal, you couple the cells in series, small elements being as good as large. One centimeter of nerve offers a resistance of about 80,000 ohms and nonpolarizable electrodes have a resistance equal to 700 ohms each. Ohm's Law. — G. S. Ohm, in 1827, formulated a law : — Current strength (amperes) C. = E. M. F. = Electromotive force (volts). H =Eesistance (ohms). But, there are two resistances, so let E stand for internal resist- ance and r for external resistance ; the law will be E. M. F. C R + r The ohm, the ampere, and the volt are closely related, and if any two of them are known with reference to any particular electric current, the value of the third may be readily inferred. Currents are measured in amperes, resistances in ohms. Electromotive force is the force which tends to move electricity from a higher to a lower potential. The unit of electromotive force is the volt, and, therefore, is the measure of electrical pressure. Electromotive force is "difference in potential." A volt is that amount of electrical energy which will produce one ampere of current after overcoming one ohm of resistance. Then :— Volts = amperes X ohms. Amperes = volts -^ ohms. Ohms = volts -^- amperes. The small Daniell cell has 4 ohms resistance and a current of ^/^ ampere. "The difference of potential may be compared to the difference of water-level between a reservoir and its distributing pipes. It pro- duces an electromotive force comparable to the force which moves the water from a higher to a lower level. The unit of electrical pres- sure is the volt. The flow through a hydraulic system is measured ELECTRO-PHYSIOLOGY. 507 by the quantity of water passing any point in a given time ; similarly, the quantity of electricity is the amount that iiows through a cross- section of the conductor in a given time. The unit of quantity is the ampere." Eoughly speaking, your bladder filled with urine may be a volt, the ohm may be a stricture, and an ampere the passing stream of urine or the unit of measure of the amount of urine pass- ing through an object in a second of time. Electrodes. — To carry the current from the different metals or carbons we have wires covered with cotton, or silk, or gutta-percha, which are attached to the metals or carbon; they are then called electrodes. Polarization of Electrodes. — In electrolysis of the lymph by the current in a tissue there are produced positive and negative ions in the lymph, which act on the electrodes. If a pair of clean platinum- Fig. 215. — DuBois Xonpolarizable Electrodes. (Lahousse. ) wire electrodes have been immersed in water and have been convey- ing a current for decomposition, the positive pole will, after some time, become covered with bubbles of oxygen, while the negative will have collected on it hydrogen gas. If now these electrodes be sud- denly disconnected with the battery and connected with a galvano- meter, the needle of the galvanometer will deviate in such a way as to show a current in an opposite direction to the original battery current. This is caused by the coating of the negative pole with hydrogen, making it positive, and a current runs from the electrode covered with hydrogen to the electrode covered with oxygen; that is, it runs in an opposite direction to the original current when the battery was attached to the electrodes. This current will naturally weaken the original battery current. This occurrence is called polarization of electrodes. In the same way, if a fresh muscle or nerve be laid across two copper wires carrying a battery current, and these be connected with a galvanometer (previously disconnecting the 508 PHYSIOLOGY. battery), a deviation of the galvaiiometer-neeclle will be apparent, showing a reversal of direction of current, as was the case with the electrodes in water. To get rid of this current, due to polarization of the electrodes by the tissue of the muscle or nerve, it was neces- sary to employ electrodes which were unpolarizable. Eegnault found these to be zinc immersed in a strong solution of zinc sulphate. DuBois-Reymond constructed electrodes upon this plan. They are usually made by taking two small pieces of glass tubing, open at both Fig. 216. — Tetanizing Key of DuBois-Reymond. (After Rosen- thal.) (From Mills's "Animal Physiology," copyright, 1889, by D. Appleton and Company. ) Wires may be attached at 6 and c. When d is down the current is "short- circuited," i.e., does not pass through the wires, but direct from c through il to 6, or the reverse, since b, c, d are of metal and, on account of their greater cross-section, conduct so much more readily than the wires, a Is an insulating plate of ebonite. This form of key is adapted for attachment to a table, etc. ends and curved. One end of the tube is plugged with modeling clay, moistened with salt solution, and then the tube is filled with a saturated solution of sulphate of zinc in which is immersed a rod of amalgamated zinc and to which one of the wires of the circuit is attached. The non-polarizable electrodes of Porter's are porous, boot-shaped cups filled with saturated solution of sulphate of zinc, in which is plunged a zinc rod. After the use of the unpolarizable electrodes the boot should be ELECTRO-PHYSIOLOGY. 509 emptied, rinsed in tap water, cleaned, and placed in several hundred cubic centimeters of normal saline until wanted. If the boot is kept saturated with normal saline, the electrodes will remain non-poiar- izable. Detector, or Galvanoscope, or Current Indicator. — Use a vertical galvanoscope, in which the magnetic needle is so loaded as to rest in a vertical position. It consists of a magnetized needle, sur- mounted by a coil of wire. It indicates the passage and direction of a current. It really is a little galvanometer. Xow, connect the wires from the positive (+) and negative ( — ) poles of a battery with the binding screws, and note, when the circuit is closed, the needle deviates from its vertical poRitinn. Fig. 217. — Polil's Commutator. (Lahousse.) Keys. — When we wish to make or break a current by hand we use keys. DuBois key consists of two metal blocks, each carrying two binding-screws fitted on a base of hard rubber, which acts as an insulator. These two blocks of metal are connected by a metal cross-bar which thus closes the key. It is employed in two ways. In one, it breaks the current going from the cell to the nerve ; when the key is closed the current is made, when the key is open the cur- rent is broken. In the other way, the current from the cell passes through the key when it is closed and then it is a short-circuiting key, because the current going through the electrodes from the short- circuiting key to the nerve meets here a body (the nerve) which opposes a great resistance to the passage of the electrical current, and, as electricity always takes the easiest way home, it goes through 510 PIIYSIOLOGY. the conductor offering the smaller resistance, the brass key. If the key is open, then the whole current pa&ses to the nerve. This method of using the key is known as "short-circuiting.^' In using the key to apply an induction or Faradic current to excite a nerve or muscle, always use this method ; that is, place a short-circuiting key in the secondary circuit to prevent unipolar action. Mercury Key. — Where a fluid contact is required the wires dip into the mercury. It is used in the same way as the DuBois key, for nuike-and-brcak shocks. Commutators.- — PohTs commutator is used for sending (1) a cur- rent into two different pairs of wires; (2) for reversing the direc- tion of the current in a pair of wires; (3) it can also be used as a mercury key. It consist of a round block of wood with six cups, each containing a binding-screw. Between two of these stretches is a bridge insulated in the middle. The battery is attached to the lead- ing-in wires, and, as the bridge is rocked from one side to the other, the current is sent through one or the other pair of wires. To reverse the direction of a current, only one pair of leading-out wires, besides the cell wires, is attached to the binding-screws of the mer- cury cups. Then the cross bars are inserted, which change the direc- tion of the current on rocking the bridge. Induction or Faradic Currents. DuBois-Reymond's Induction Apparatus. — It consists of a pri- mary spiral of aljout 130 coils of a moderately thick silk-covered copper wire, and of a secondary spiral of some 6000 coils of silk- covered copper wire of a thickness of about a tenth of a millimeter. The core inside the primary spiral is formed by a bundle of thin iron wires, each carefully coated with shellac varnish. To graduate the strength of the induced current of the secondary spiral, the sec- ondary spiral is moved in a groove of w^ood from or towards the pri- mary spiral, and the distance between the spirals is graduated in centimeters and millimeters, or the secondary spiral is rotated as by Bowditch. To make or close, or to break or open the circuit coming from the cell through the primary spiral, the electro- magnetic hammer of iSTeef is used to give us repeated shocks, or the interrupted current. When single induction shocks are used, the wires from the battery are connected with a key and this, again, with the two terminals of the primary spiral. The action of the coil of wires depends upon the fact that the strength of a current running along a wire will be altered and an induced ELECTRO-PHYSIOLOGY. 511 current set up in a second wire placed near it. The strength of the induced current may be increased by placing a bundle of soft iron wires in the interior of the primary coil. By using a large number of turns of wire in each coil the effect is greatly increased, because each turn of the primary coil induces a current in each of the turns Fig. 218. — DuBois-ReymoncFs Induction Apparatus. (Waller.) The numbers 1 to 7 indicate the terminals and contact screws connected with the primary coil. For single shocks the two battery wires are to be connected with the termi- nals 4 and 5, which are at the two ends of the primary wire. (a) Unmodified sJwcks are obtained when a key is used to interrupt one of the wiles. (h) Reduced shocks are obtained when a key is used short-circuiting the primary wire. (r) For repeated shocks (ordinary) the two battery wires are to be inserted at 1 and 6. The circuit now includes the spring interrupter and the wire of the electro-magnet by which the circuit is made and broken at the contact screw 3; the contact screw 7 is kept out of use by being lowered. (d) For repeated shocks {modified) the battery wires are left, as before, at 1 and 6. A short, thick side wire is placed between 2 and 4. The contact screw 3 is raised out of range of the spring, and the contact screw 7 is raised until it comes within range of the spring. The electrode wires are in each case connected with two terminals (not seen in figure) forming the two ends of the secondary wire. of the second, and all these small effects summed up produce a single greatly increased effect. The opening shock is stronger than the closing shock, so that if repeated induction shocks are sent through a tissue for some time polarization effects are set up. To 512 PHYSIOLOGY. equalize the shocks, Helmholtz used a modification consisting of a "side wire." Helinholtz's side-wire and the modifications it intro- duces into the induction apparatus should be used when induced cur- rents are applied to nerves. By this contrivance we diminish two possible mistakes: (1) the undesirable predominance of currents in one direction, that is, in that of the break; (2) unipolar stimulation. Helmholtz's side-wire acts by short-circuiting instead of completely breaking the battery current. Unipolar Induction. — If you remove one of the wires of the electrodes of the secondary coil, so that only one electrode is con- nected with that coil, and slide the coil towards the primary coil. r'ig. 219.-^— Principle of Simple Rheocord. G, Galvanometer. R, Rheocord. P, Battery. then send a strong current through Xeef's hammer and the primary coil, shocks will be faintly felt by the tongue, though only one elec- trode is attached to the secondary coil. It is on account of this pos- sibility of stimulating through only one pole that a short-circuiting key is always used in the secondary spiral current. In the primary or battery current a simple key is used, for a short-circuiting key would let the battery quickly run down. Rheocord. — A rheocord is an apparatus for dividing a constant current by offering a circuit of relatively small resistance, which is capable of being varied so that a variable part only of the current shall pass through the experimental circuit. It usually consists of a platinum wire of known resistance, to the ends of which the bat- tery poles are connected. With one of these ends another wire is ELECTRO-PHYSIOLOGY. 513 connected. This forms part of the experimental circuit through which a portion of the battery current is to be conducted. This cur- rent is completed through a wire attached to a rider which slides along the rheocord wire. The other portion of the current goes through unpolarizable electrodes to a nerve lying across them. The amount of current passing through the nerve varies directly with the resistance of the deriving circuit, the rheocord. By increasing this resistance more current is sent through the nerve, and on diminish- ing, less. Fig. 220. — Schema of Apparatus to Study Influence of Rapid Variations of the Constant Current by the Rheonome of von Fleischl. (Lahousse.) P, Daniell cells. E, Key. A. B, Two pieces of zinc to which the wires are attached. C, D, These two points are united by wires to the muscle 31. Suppose, for example, that the resistance of the electrode and nerve is 100,000 ohms and the resistance of the rheocord 5 ohms, 100,000 5 then 77r;rrrTr of the current passes through the rheocord and ~rZn~^Zf. lUU.UOo 100,005 through the nerve. Rheonome of Von Fleischl. — The rheonome of Yon Feischl con- sists of an ebonite plate with a circular groove on its upper surface. This groove is connected at diametrically opposite points to the bind- ing-screws. In the center of the ebonite plate is a vertical rod whose upper extremity articulates with a piece of ebonite, which is mov- able and has on its two surfaces two plates of zinc, which are curved in an archlike form. Their upper extremities are united to the bind- 33 514 PTTYSTOLOCY. Fig. 221. — Schema of Experiment to Measure the Rapidity of the Muscle Current by the Aid of the Differential Rheotome of Bernstein. (Lahousse. ) M, Muscle prepared in such £, manner that by one extremity the muscle current goes to the galvanometer, and to the other extremity electrodes are applied which carry to the muscle an induction current. G, Galvanometer. The rheotome of Bernstein (A) consists essentially of a disc (B), which is set in uniform and rapid motion by the rotation apparatus of Helmholtz (H). At each revolution the needle C, striking the wire C", closes and opens rapidly the primary current of the induction apparatus in such a manner as to excite the muscle by a single induction current. On the opposite side of the disc lie two needles (D, D) which, dipping in the two cups of mercury {D', D'), close for a very short time the circuit of the muscle current. If the rapidity of rotation of the disc is known and the interval which elapses between the time of excitation of the muscle, that is, the time when the needle (C) strikes against the wire (C), and the beginning of the closing of the muscle current, that is, the time when the two needles (D, D) commence to dip into the mercury cups (C, D'), then the rapidity of the propagation of the negative wave or variation is easily calculated. ELECTRO-PHYSIOLOGY. 515 ing-screws, and their lower extremities dip into the groove filled with a saturated solution of sulphate of zinc. The arched plates are called the bridge. Three Daniell cells are connected to the binding-screws, with the interposition of a key. The binding-screws are united to electrodes upon which lie the nerve-muscle preparation. When the key is closed the muscle contracts and in the interval relaxes, except when there is a rotation of the bridge. Then suddenly rotate the handle with its two zinc arms. This is equivalent to a sudden variation of the intensity of the current, the current, of course, continuing to pass all the time. The muscle suddenly contracts. The response of a muscle or nerve to electrical Fig. 222. — The Nerve-muscle Preparation. (Stirling.) S, The nerve-muscle. F, Lower third of femur. /, Tendon of gastrocnemius muscle. stimulation is due not to the simple flow or intensity of a current through the tissues, but rather to the more or less sudden change in the strength of the current. Sudden increase or decrease may act as an efficient stimulus, but the gradual increase or decrease of the current causes no response (Du Bois's law.) Differential Rheotome. — The rheotome of Bernstein is an instru- ment by which a series of stimuli can be led into a nerve or muscle, and the consequent excitatory effects led off to a galvanometer dur- ing definite periods at regular intervals after stimulation. ELECTRO-PHYSIOLOGY. Animals and plants have, as a general phenomenon, electricity, the potential energy of living matter. In the animal the nerves, muscles, and glands are the special seats of the electrical properties. A muscle has three forms of energy — work, heat, and electro-motor 516 PHYSIOLOGY. activity. To study animal electricity, it is necessary to use the instruments employed in the physical laboratory, but they have to be made very sensitive, since the electric potential is feeble in animals. There are usually employed three methods of revealing animal elec- tricity: (1) the physiological rheoscope; (2) the galvanometer; (3) the capillary electrometer. Physiological Rheoscope. — This name has been given to the nerve-muscle preparation of the frog where the greatest possible length of the sciatic nerve attached may be used. The preparation of the nerve requires special care, for the nerve must be removed by a little seeker of glass or bone. No metal must touch it. It is removed from below upward, and if properly done there should be no contraction of the muscle during the operation. If the nerve of this preparation be brought into contact with a segment of separated muscle so as to touch simultaneously the longitudinal and transverse surfaces, a contraction instantly follows. G-alvanometer. — The instru- ment usually employed is Thomp- son's astatic, high-resistance, re- flecting galvanometer. In this in- strument a pair of suspended mag- nets nearly astatic are surrounded by many windings of fine, insulated wire with a resistance equal to 10,- 000 to 20,000 ohms, which explains the name of high-resistance galvano- meter. Because it has on the upper magnet a slightly concave mirror by which a ray of light can be reflected on a scale, it is also called reflecting. By placing the point of the unpolarizable elec- trode on the center of the longitudinal surface of the muscle, and the other electrode over the center of the freshly divided transverse surface of the muscle, and connecting the electrodes with the gal- vanometer, with a shunt interposed between the electrodes and the galvanometer, it will be seen that the needle of the galvanometer Fig. 223. — Thompson Galvanometer. ELECTRO-PHYSIOLOGY. 517 deviates. By noting the deflection of the needle, it is found that the longitudinal surface of the muscle is positive and the transverse section is negative. The deflection of the needle is caused by the current of injury by the transverse section of the muscle. It is called the demarcation current, because the difference of potential appears at the demarcation between the dying and the injured mus- cle. The injured part of the muscle is negative to the uninjured part and the current in the galvanometer is from the longitudinal (positive) surface to the uninjured negative transverse surface. Capillary Electrometer. — This instrument is an electrical mano- meter and shows electrical pressure. It consists mainly of a glass acid Fig. 224. — Diagram of Capillary Electrometer. (Starling.) Hg., Mercury. The two terminals are represented as leading off two points at the base and apex of a frog's heart, a b. tube ending in a fine point, which is partly filled with clean mercury and then placed in communication with a pressure apparatus. The capillary end of the glass tube dips into a tube containing mercury and a 20-per-cent. solution of sulphuric acid. Into the tube with sulphuric acid is fused a platinum wire which forms one connection with the lower column of mercury. Another platinum wire is con- nected with the capillary tube. Anything which alters the surface tension will cause the mercury to move. If now two unpolarizable electrodes are connected with a capillary electrometer with a short- circuiting key, and the center of a muscle is laid on one of the non- polarizable electrodes and the divided transverse end on another non- polarizable electrode, then when the mercury meniscus is watched 518 PHYSIOLOGY, with a low-powor microscope the mercury will move in a direction showing a higher potential at the positive electrode on the longi- tudinal surface. Instead of a transverse section of a muscle its tendon may be taken, which is also negative and has been called the natural trans- Fig. 225.— Direction of Current of Daniell Cell. Through the galvanometer the current is from copper to zinc. Through the ceU the current is from zinc to copper. verse surface. The cut surface of a longitudinal section of muscle presents positive electrization. Tbe laws of electrical currents of muscle have been fully determined by DuBois-Eeymond : — 1. When the conductor unites the longitudinal to the transverse surface there is a well-marked deviation of the needle, and the great- Fig. 226.— Direction of Current of Injured Muscle. (Waller.) Through the galvanometer the current is from normal to injured part, or from resting to active part. Through the muscle the current is from injured to normal part or from active to resting part. est deviation occurs when the middle of the longitudinal surface is connected with the middle of the transverse. 2. When tv^o points are connected on a longitudinal or trans- verse surface which are unequally distant from the middle, or two points unequally distant on opposed surfaces, then there is a slight deflection of the needle. In the case of the longitudinal surfaces the ELECTRO-PHYSIOLOGY. 519 current passes along the conductor from the point nearer the center to the one farther off. The reverse is the case for the transverse. 3. When two points are connected on the same or on opposed surfaces equally distant from the center, or when the centers of two opposite surfaces are joined, there is no movement of the needle of the galvanometer. The parelectronomic part of the muscle is the tendinous part of the muscle, which is negative instead of being positive, as is the rule. Here it is necessary to make an artificial section for the purpose of demonstrating the electrical phenomena of muscle. Fig. 227. — Schema Representing the Inequalities of Electric Ten- sions upon the Natural Longitudinal Surface and upon the Artificial Transverse Surface of a Muscle-cylinder. Also the direction of the electric currents from the exterior to the interior of the muscle. (La- HOUSSE.) Hermann has shown that the muscle-currents (demarcation cur- rents) are the result of the preparation, and do not exist in the nor- mal, intact fibers when in a state of repose. These galvanometrical deviations are due to the traumatic action of air, cold, or chemicals. Electrical Phenomena of Contracting Muscle. — If upon the elec- trodes connecting the poles of the galvanometer a muscle is so placed that the needle deflects, then on tetanizing the muscle by stimulat- ing its nerve, the needle will be seen to retrace its movement of deflection. This reverse of the natural current is known as negative deviation. This has been shown to be due to a weakening of the natural muscle-current, and not to the production of a new one con- 520 PHYSIOLOGY. trary to the current of rest. This negative variation can stimulate the nerve of another muscle if the nerve of the physiological rheo- scope be placed on the contracting muscle in such a man- ner that the first touches both the cut surface and another point on the muscle; then each contraction of the muscle is followed by a contraction of frog's nerve-muscle preparation (secondary con- traction). This negative variation lasts about 0.00-i second and is Time Fig. 228. — The Negative Variation (Frog's Gastrocnemius.) (Waller.) Simultaneous record of a tetanic contraction (white line) and of the accom- panying negative variation of a current of injury (black line), (a) The Current of injury is normally subsiding; (b) it is suddenly diminished during tetanus (negative variation); (c) it subsequently increases (positive after-variation); and (d) it finally resumes its normal decline. propagated along the muscle with the same velocity as the wave of contraction it precedes, vanishing even before the arrival of the lat- ter. Hermann calls the negative variation by the name of current activity or action current. ELECTRO-PHYSIOLOGY. 521 Diphasic Variation. — The base and apex of the heart are con- nected by unpokirizable electrodes to the capillary electrometer. When the heart contracts, there will be a diphasic variation. The contracted portion at first becomes negative, and then positive, to the part not contracted. The first phase, base is negative to the apex ; second phase, apex negative to the base. The diphasic variation fol- lows from the fact that action does not take place at the same time throughout the whole heart, but takes time in its transmission from a point of stimulation. Nerves. The nerve presents differences in electric potential similar to that of the muscle, except it is much weaker. Every part of its cut Fig. 229. — Arrangement of Parts to Show Secondary Contraction in Muscle. (After Rosenthal.) (From Mills's "Animal Physiology," copyright, 1889, by D. Appleton and Company.) transverse surface is negative, whilst its longitudinal surface is electro-positive. You have muscle-currents; also nerve-currents. Negative Variation of the Nerve-current or Action-current. — If you place upon the electrodes connected with the galvanometer a piece of nerve, the deviation of the needle shows the existence of the nerve-current already described so long as the nerve is at rest. If you tetanize the nerve the needle is seen to run back toward zero, and sometimes even beyond it. This takes place in every kind of nerve and in the whole length of the nerve. It can be produced by mechanical or chemical stimuli as readily as with electricity. The greater the stimulus, the greater the negative variation, but there is not a definite proportion between them. Hermann has shown that neither in the nerve nor in the muscle do any of these currents exist so long as the structures are uninjured. To generate a nerve- current in repose it is necessary to make a transverse section. This 522 PHYSIOLOGY. produces death of the superficial layer of a segment next the cut sur- face. The dead tissue behaves negatively with regard to the living, and the electromotor forces accordingly have their seat at the plane of demarcation between the dead and living. As to the action cur- rents, they are explained by admitting that during stimulation the active parts are negative with regard to the parts at rest. Waller has compared the action of ether and chloroform on the electrical currents of a nerve. The movements of the galvanometer mirror are photographed. He has shown that chloroform is more toxic than ether by this method. The nerve had in each case a maximum dose; that is, for a period of one minute, air saturated with the drug, that is about Beiore. Alter. Fig. 230. — Effect of Chloroform upon the Electrical Responses of Isolated Nerve. (Waller.) The electrical response is definitely abolished; there is no recovery during the period of observation. With ether it gradually recovered. 50 per cent, of ether and about 12 per cent, of chloroform. In the case of ether, the effect was quite typical, an abolition of excitability in about three minutes. In the case of chloroform, the excitabi'.ity was promptly abolished, and on testing the nerve a half hour after- wards the nerve has definitely lost its excitability; that is, dead by chloroform. Theories of Muscle and Nerve Electrical Currents. — There are two theories, one of Du Bois-IJeymond, the molecular, the other that of Hermann, that of alteration. Molecular Theory. — The molecules may be considered to be positive on their longitudinal surface, and negative on their trans- verse section. Their negative surface is turned towards the ends of the muscle or nerve, and the positive surfaces directed towards ELECTRO-PHYSIOLOGY. 523 the longitudinal surface. They are surrounded by a non-electrie conducting surface. When an electrode is placed on the longitu- dinal surface and would touch the positive side of the molecules, the other electrode on the transverse section would be in contact with the negative side. Alteration Hypothesis. — It was shown that muscle not injured exhibited no electrical current. Hermann states that these currents are due to the chemical constitution of the tissue at the cross-section. He believes that the current is the result of injury, causing death of a small part of the muscle fiber at the cross-section, and so producing dilferences in potential. The difference of poten- tial arises at the demarcation between dying and injured muscle ; hence the name "demarcation current.^' The dying portion of the cross-section of the muscle behaves negatively to the living, and the electromotive force has its seat in the demarcation zone between the living and dying. Hering is in accord with DuBois-Reymond, that the normal resting muscle is the seat of electromotor forces which are not exhibited. The electrical currents are due to chemical changes in the tissues. Anabolism causes a positive electrical phenomenon. and katabolism a negative condition of the part. The majority of physiologists have accepted the alteration theory as the one explain- ing the majority of the facts observed. Neither theory explains all the facts. CHAPTER XIV. THE ANATOMY AND PHYSIOLOGY OF THE NERV0U5 SYSTEM. ANATOMY OF THE NERVOUS SYSTEM (EXCEPT THE CEREBELLUM).! STRUCTURE OF NERYE=TISSUE. Nerve-tissues present themselves in two varieties: some as white substance and some as gray substance. These two substances are different, not only in color, but also in physical and chemical properties and in anatomical arrangement. The gray substance contains as characteristic elements the nerve- cells; the white substance, the nerve-fibers. These latter emerge from the gray nervous substance to branch out toward the peripheral organs. These two substances, gray and white, possess a common ele- ment known as neuroglia; in addition, each contains blood-vessels. The Nerve-cell, or Neuron. — The nerve-cell is the characteristic fundamental element of the gray substance : it is an independent unit of the nervous system. It is the element which gives to this kind of nervous tissue its gray color. When these units are charged with a strong portion of pigment, they are black, as in the locus niger of the cerebral peduncles. When a little less pigmented they pre- sent a grayish color: the color that is characteristic of the brain and the central portion of the spinal cord. They may be charged with red pigment, then the cells are reddish; such cells constitute the red nucleus of the head of the cerebral crura. Structure of the Nerve-cell. — The nerve-cell is composed of (1) a mass of protoplasm inclosing a nucleus with its nucleolus; (2) of simple or branched prolongations. The protoplasm of a nerve-cell, like that of many other cells, is formed of a very delicate network of bands whose meshes are filled with a clear or finely granu- lar albuminoid substance. The network has been designated by the name of spongioplasm and the intermediate substance is generally termed hyaloplasm. As to these two components the protoplasm of nerve-cells is like that of most other cells. Fibrils. — One peculiarity is the presence in it of fibrils which run through its substance. (524) ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 3 525 Fig. 231. — The Structure of iServous Tissue. (Laxdois.) 1, Primitive fibril. 2, Axis-cylinder. 3, Remak's fiber. 4, Medullated varicose fiber. 5, 6, Medullated fiber with Schwann's sheath. C, Neurilemma. t, t, Ranvier's nodes, b. White substance of Schwann, d, Cells of the endo- neurium. a. Axis-cylinder, x. Myelin drops. 7, Transverse section of nerve- fiber. 8, Nerve-fiber acted on with silver nitrate. /, Multipolar nerve-cell from spinal coid. s, Axial cylinder process. //, Protoplasmic processes; to the right of it a bipolar cell. //, Peripheral ganglionic cell with a connective-tissue cap- sule. ///, Ganglionic cell, with o, a spiral, and n, straight process. »», Sheath. Granules. — The other characteristic feature of uerve-proto- plasm is the existence within it of angular granules. These show a special liking for basic aniline dyes, as methylene blue. By many 526 PHYSIOLOGY. A Fig. 232. A and B, Cells from the anterior horn of a human spinal cord. Fixed with alcohol and stained with methyl-blue. C, Ganglion-cell fixed with alcohol and stained with hEematoxylin. D, Ganglion-cell from anterior horn of foetal dog. (After an original preparation by Ramon y Cajal.) Prepared with Golgi method. E, Neuroglia. (After an original preparation by Weigert.) ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 527 authors they are spoken of as Nissl bodies, after their discoverer and the man who has demonstrated their physiological worth. The gran- ules are found scattered throughout the cell-l)ody and its dendrons, but not in the axis-cylinder and the adjacent area of the cell to which it is attached. The most important relation that these granules bear physiologically to the cell is as follows: Under either normal or abnormal activity of the nerve-cell the granules undergo a change which has been termed chroinatolysis. It is slow dissolution of the granules with diffu- sion of the degenerated product into the protoplasm. At first the cell swells, pushing its nucleus to one side; later the cell diminishes in size, due to a loss of its chromatophilic substance. It is in the hyaloplasm that the pig- ment substance which gives to the cell its particular color is deposited. In the discharge of nerve-energy of a nerve-cell, Nissl granules are used up, hence called by Marinesco, kinetoplasm, a source of energy. Nissl granules dis- appear or undergo chromatolysis after high fever, after epileptic convulsion, or after poisoning by strychnia or the toxins of tetanus germs. During urasmia the cells of the cerebal cortex and of the an- terior horns of the spinal cord show chro- matolysis. Anaemia produces similiar effects. Fatigue in nerve-cells can be demonstrated by chromatolysis. Nucleus. — The nucleus of the nerve- cell forms a small, rounded or oval mass. It is characterized by its relatively large size. This nucleus is strongly colored by all the reagents, such as carmine, methylene blue, etc. Around the nucleus the chromatin forms a sort of cell-wall called the nuclear membrane. Within the nucleus is seen a small refract- ing body called the nucleolus. Its chromatin is relatively great in amount. Fig. 233.— Ganglion Cell from Sympathetic Ganglion of Frog; Greatly Magnified, and Showing Both Straight and Coiled Fibers. (After QuAiN.) (From Mills's "Animal Physiology^" copy- right, 1889, by D. Appleton and Company.) 528 PHYSIOLOGY. Cell-prolongations. — From the researches of Deiters it has been learned that nearly every nerve-cell has protruding from its periphery a greater or less number of prolongations. These are of two vari- eties: one is unique, nonbranching, and prolonged under the form of a cylinder-axis of a nerve. It is known by the various terms, axis- cylinder, neuraxon, Deiters' process, and neurite. The other variety of prolongations is composed of many, though an uncertain, number of processes. This new set of prolongations bears the name of proto- plasmic processes, dendrons, dendrites, or the poles of the cells. Some cells possess no dendrons, others .very many. However, it is believed that no cell is without its neuraxon. According to Cajal, the com- munication of the prolongations of the cells among themselves is no more than that of simple contact. It is analogous to the contact which permits of the passage of the electrical current when the two electrodes of an electrical battery are in contact. Further, the nervous impulses are transmitted only along the neuraxons from cell to cell. This neuraxon, by branching and coming in contact with the dendrons of other and neighboring cells, conveys its impulse to them. They in turn transmit it centripetally to the axis-cylinders of their own cells to be further transmitted to other cells. The nerve-cell, according to this doctrine, would be physiologically unipolar. To denote this close contact existing between the axis-cylinder and dendrons of various cells, Foster has used the term "synapsis." Betlie's Theory of Nerve-cell Connections. — According to Bethe, when a nerve is cut the nuclei of the neurilemma can regenerate a new "band-fiber" without union with the central stump. Hence we believe that the axis-cylinder is only an outgrowth from the nerve-cell. According to Bethe, the neuro-fibrils go through the nerve-cells and by a network are placed in direct communication with the neuro- fibrils of other neurons. Here the cell has no direct activity in the conduction of impulses from one part of the nervous system to the other. The neuro-fibrils alone, and the cellular network within and around the nerve-cells with which they connect, form the conduct- ing track that at all points is in continuity. The nerve-cells of the gray matter are of various sizes and shapes, the branched, stellate, or multipolar form being predominant. Some are more or less bipolar or spindle-shaped; however, at each extremity there is usually a fine plexus of branches. Some are ovoid or pyriform, as in the cortex of the cerebellum, where they have received the name of cells of Purkinje. The cells of the ganglia of the spinal nerves are, in great part, unipolar. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 529 The dimensions of the nerve-cells are very variable ; the smallest are about V4000 iiich in diameter, the cells of the posterior horns of the spinal cord are from V2500 to V1200 inch, and the giant cells of the anterior horns of the spinal cord are about V250 inch in diameter. By employing Golgi's silver-nitrate method of staining, the nerve-cells, with their processes, are stained black from a deposition of the silver. By means of this, the nerve-prolongations may be .sch 23-4 235 Fig. 234. — A Piece of Medullated Nerve-fibril of Man, Nucleus and Axis Cylinder Stained by Carmine. (Sobotta. ) a, Axis cylinder. A-, Nucleus, m. Medulla, n. Neurilemma (Schwann's sheath). Fig. 235. — A Piece of Medullated Nerve of Man. It shows Ranvier's Constrictions and Lantermann's Incisures. (Sobotta.) m. Medulla, sch, Ranvier's constrictions. traced to their ultimate terminations. This method beautifully dem- onstrates the distribution of the neurites, their branching, and man- ner of contact with dendrites of contiguous cells; also, how, as a rule, the neuraxon does no very immediate branching. It must be stated, though, that usually from the neuraxon there proceed numer- ous fine fibrils to which the term collaterals is applied. These are in communication with the dendrites of the neighboring cells. In nerve- centers, the neuraxon, after proceeding for some distance, does really 530 PHYSIOLOGY. branch to form arborizations to come into contact witli nerve-den- drites. The JSTerve-fibers. — Every nerve-fiber is a process of a nerve- cell. It is the neuraxon of some particular cell. It is the medium which conducts impulses to or from the tissues and organs, on the one hand, and the nerve-centers, on the other. In the majority of cells the neuraxon acquires a sheath to be thus converted into a medullated nerve-fiber. Thus, there are two kinds of nerve-fibers: medullated, or those with myelin; and nonmeduUaied, or those without myelin. Medullated Fibers in the fresh condition are bright, glistening cylinders showing a dark, double contour. The essential part of the fiber is the axis-cylinder. This is a soft, transparent rod, or thread, which runs from one end of the fiber to the other. It does not anastomose with its neighbors, and in the average nerve is about V1200 inch in diameter. After the employment of certain reagents the axis-cylinder shows itself to be composed of very fine, homogeneous or more or less beaded fibrillfe. The latter are the elemejitary, or primitive fibrillw. They are held together by a small amount of a faintly granular, interstitial substance. The thickness of the axis- cylinder is in direct proportion to the thickness of the whole nerve- fiber. The axis-cylinder is enveloped in its own, more or less elastic, hyaline sheath. The axis-cylinder is not regularly cylindrical, but is slightly nar- rowed in places. Under the influence of silver nitrate applied to its surface there appear alternate obscure and clear transverse striae. They are the so-called lines of Frommann. Myelin. — Surrounding the axis-cylinder is the myelin, medullary sheath, or the white substance of Schwann. It is a layer of fatty sub- stance, strongly refracting, and of homogeneous aspect. It is colored black by osmic acid. It is the myelin which gives to the nerve its double contour. It is composed of a network of fibrils of a chemical substance called neurol-eratin, which incloses the semi-fluid, fatty sub- stance. The latter contains, among other substances, a complex, phosphorized fat. The sheath of myelin envelops the axis-cylinder everywhere, ex- cept at its termination and at the nodes of Eanvier. In its arrangement the myelin is imbricated in the fashion of tiles on a roof by reason of a series of segments one above the other. They are separated one from the other by clear lines. The lines are ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 531 known as the incisures of Lantermann, and the segments as those of Schmidt. Neurilemma. — The neurilemma or sheath of Schwann, sur- rounds the medullary sheath to form the outer boundary of the nerve- fiber. It is a thin, elastic, very delicate, hyaline, and transparent mem- brane. It is comparable to the cell-wall of a cell. Between the neu- rilemma and medullary sheath there are irregularly scattered ovoid nuclei. They are the nerve-corpuscles, and are analogous to the muscle-corpuscles previously mentioned. Each nerve-corpuscle is sur- rounded by a thin zone of protoplasm. Between the myelin layer and the neurilemma is a thin zone of protoplasm. When this arrives at the level of the annular constric- tions it is reflected upon itself to line the internal surface of the myelin layer (Mauthner's membrane). The protoplasm is also insinu- ated into the incisures of Lantermann and decomposes the layer of myelin into the superposed segments of Schmidt. Nodes of Ranvier. — At intervals of about one micromillimeter along the course of the nerve there appear constrictions : the nodes of Eanvier. At these points the myelin sheath is interrupted so that the neurilemma appears to do the constricting. That portion of the nerve-fiber between any two constrictions is termed an internodal seg- ment. At about the center of each internodal segment is located one, sometimes more, nerve-corpuscles. Such is the composition of a medullated nerve-fiber. This type of nerve is found chiefly in the white matter of the nerve-centers and in the cerebro-spinal nerves, with the exception of the olfactory nerve. NoNMEDULLATED Nerve-fibers. — They occur especially in the S3Tnpathetic system, but are also present to a slight extent in the cerebro-spinal nerves. Each fiber consists of a bundle of fibrils — primitive fibrils — which are inclosed in a delicate, transparent, and elastic sheath. The fibrils are very delicate and somewhat flattened. Here and there along the course of the fibrils will be found oval nuclei. These latter lie between the axis-cylinders and their enveloping neurilemma. As these fibrils contain no myelin, they are not blackened by osmic acid. This allows of a differentiation between medullated and nonmedul- lated nerves when examining the nerve-supply of a tissue. Nerve-trunkS consist of bundles of nerve-fibers. Each bundle, of course, contains a greater or less number of fibrils. Several bun- dles are held together by a common connective-tissue sheath : the epineurium. Delicate fibrils lie between the nerve-fibers to constitute 532 PHYSIOLOGY. the endoneurium. The larger blood- and lymph- vesssls lie in the epincuriiim; the few capillaries of the nerve-fibers lie supported in the endoneurium. Eegeneration of United Nerves. — If a nerve is cut, its peri- pheral end undergoes degeneration. The fiber breaks up into small pieces of myelin, each holding a piece of neuraxon which is finally absorbed. Eepair of the nerve begins wholly during the degenera- tion. The nuclei of the neurilemma increase in number to form around them a layer of protoplasm or cytoplasm. At length the cytoplasm becomes a continuous piece of protoplasm, and the fiber thus produced is known as a "band-fiber." Then there is an arrest of regeneration unless the peripheral fiber is anatomically united to its central connection. If the central and peripheral ends are brought together, then the "band-fiber" becomes changed into a normal nerve- fiber, with a sheet of myelin and a cylinder axis. The axis cylinder in the peripheral end of the nerve is supposed to grow out from the central end of the nerve. Termination of the Nerve. — After a certain course in the trunk of the nerve the nerve-fiber divides at the periphery into a terminal plaque, the motor plaque of muscles; or into a sense-cell, as in the retinal cells or organ of Corti; or into a sense-corpuscle, as a tactile corpuscle; or into numerous fibrils which anastomose to form a terminal plexus, as in the cornea. Nonmedullated Fibers, that is, those that are naked, pale or gray, and reduced to an axis-cylinder and sheath, branch and form networks — their peripheral terminations. This mode of termination occurs in the nerve-fibers of common sensation, as in many of the nerve-fibers of the skin, cornea, and mucous membrane. In all of these cases the peripheral termination fibrils are intra-epithelial : that is, they are situated in the epithelial portions of cornea, mucous membrane, etc. Neuroglia. — In the gray, as well as in the white, substance of the nerve-centers there exists between the cells and nerve-fibers an intervening substance which has been termed neuroglia. It must not be confounded with the true connective tissue along the course of the blood-vessels in the nerve-centers. Its chemical nature is wholly different from the latter, which is always derived from the mesoblast. Ranvier has shown that neuroglia is derived from the primitive neuro- blast or epiblast. Neuroglia sometimes presents itself in the shape of very fine fila- ments assembled in a very close network, as in the gray substance. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 533 Sometimes, again, it is seen imder the aspect of reticulated plates bounding the space in which the nerve-fibers pass. This is beautifully demonstrated in the white substance of the columns of the spinal cord. Elsewhere the neuroglia is found to be a homogeneous, gelatini- form substance, as in the ependyma of the spinal cord or in the gela- tinous substance of Eolando in the postero-lateral groove of the same structure. Besides the fibers and plates already mentioned, neuroglia con- tains cells. These are star-shaped, flat, and nucleated. They have numerous prolongations. By the aid of these prolongations the cells of the neuroglia anastomose freely with one another to form a very complicated network. This incloses in its meshes the nerve-elements. Neuroglia enjoys the role of a true cement which unites all of the fibers and nerve-cells. Classification of Nerve-cells. — According to Schafer, nerve-cells are broadly classified into: "1. Afferent cells, which receive impres- sions at the periphery to convert them into impulses. The latter then pass toward the central nervous system. 2. Efferent cells, which send out nervous impressions toward the periphery. 3. Intermediary cells, which receive impressions from afferent cells to tfansmit them directly or indirectly to efferent cells. 4. Distributing cells, which occur near the periphery, and, receiving impulses from efferent cells, distribute them to involuntary muscles and secreting cells. The cells of this class belong to the so-called sympathetic system. "The afferent and efferent cells are kno^voi as root-cells. The greater number of the nerve-cells of the brain and cord belong to the intermediate class. They serve the purposes of association and coordination and afford a physical basis for psychical phenomena." Efferent fibers are also called cellulifugal. Afferent fibers are also called cellulipetal. Structure of the Gray Substance. — The gray matter is formed (1) of nerve-cells, (2) of neuroglia-cells, (3) of fibril elements repre- senting the prolongations of nerve- and neuroglia- cells, (4) of an intervening network formed by the branching fibrils, and (5) of blood-vessels. Elements 1, 2, and 3 (here enumerated) of the struc- ture have been treated previously in detail. The blood-vessels penetrate the gray substance, and are sur- rounded with a layer of connective tissue coming from the pia mater, which they have received in their passage along and through this membrane. The connective tissue forms sheaths around the capillary network, arterioles, and little veins, in which the vessels seem to float. 534 PHYSIOLOCY. These liavo been termed tlie perivascular .sheaths of His. Between them and the vessels exists a lymph-space : one of the origins of the lymphatics. White-substance Formation. — The white matter is formed by the bundles of white fibers covered by a lamellar investment of neuroglia. These bundles are separated from one another by tracts of connective tissue detached from the pia mater. Axis-cylinders are also found, which come from the gray matter. Blood-vessels anastomose and run in a course parallel with the nerve- fibers. This circulatory network likewise has a perivascular sheath as has that in the gray sul)stance. Chemical Properties of Nervous Substance. — The following table of Landois gives the percentage of the various components of both gray and white matters : — Chemical Composition of Gray Matter. White Matter. Water Solids The solids consist of : — Proteids (globulins) . . . Lecithin ..... Cholesterin and fats .... Cerebrin ... Substances insoluble in ether Salts 81.6 per cent. 18.4 " 55.4 per cent. 17.2 " 18.7 " 0.5 6.7 " 1.5 68.4 per cent. 31.6 " 24.7 per cent. 9.9 52.1 9.5 3.3 0.5 In 100 parts of ash. Breed found potash, 33 : soda, 11 ; magnesia, 2; lime, 0.7; NaCl, 5; iron phosphate, 1.2; fixed phosphoric acid, 39 ; sulphuric acid, 0.1 ; and silicic acid, 0.4. Composition of Nerve-tissue, According to Halliburton. — (a) Proteids. Over 50 per cent, in gray matter. They are : — 1. Neuro-globulin (alpha), coagulates at 47° 0. 2. A nucleo-proteid which, like other proteids. causes ex- tensive intravascular coagulation. 3. A neuro-globulin (beta). (&) Nuclein from nuclei of cells. (c) N"euro-keratin, from neuroglia. (d) Phosphorized fats. 1. Lecithin; when decomposed it gives rise to glycero- phosphoric acid, stearic acid, and choline. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 535 2. Protagon. 3. Kephalins, (e) Cerebrins (nitrogenized substances), or Cerebrosides. The name cerebrosides indicates that they are glucosides, and that the sugar (cerebrose) obtained from them has been identified as galactose. (/) Cholesterin. (g) Extractives: creatin, xanthin, hypoxanthin. inosite, lactic acid, uric acid, and urea. (h) Gelatin. (t) Inorganic salts, of which the alkaline phosphates and chlorides are the most abundant. Haitai has shown that lecithin, when administered to white rats, caused a gain of 60 per cent, in body weight compared with the nor- mal animal. Hence lecithin is a stimulant of normal growth. Eeaction". — When passive, nerve-tissue is neutral or feebly alka- line. When active or dead it is said to be acid. It is found that after death nerves have a more solid consistence. Probably some coagulation occurs which is to be compared to the stiffening of muscle. Simultaneously there is generated and liberated a free acid. Mechanical Properties. — A remarkable property of nerve-fibers is the absence of elastic tension according to the varying positions of the body. Divided nerves do not retract. The cohesion of a nerve is an important property. Oftentimes when a limb is forcibly torn from the body the nerve still remains intact (though considerably stretched), while the other soft tissues are completely severed. The sciatic nerve at the level of the popliteal space requires a force equal to one hundred and ten or one hundred and twelve pounds to rupture it ; the median or ulnar require forces equal to forty or fifty pounds. The latter nerves will stretch six or eight inches before the point of ru])ture is reached. It is upon the knowledge of this fact that the method of nerve-stretching is employed in some forms of neuralgia. Nerve-metabolism. — Some extractives are obtained which are believed to bo decomposition products of the nerve. The Nerve-centers. — The nerve-fibers and nerve-cells comprise the essentials from which the nerve-centers are formed ; the elements must, of course, be held together by enveloping neuroglia. The term center is merely applied to an aggregation of nerve-cells which are so related to one another as to subserve a certain function. These 536 PHYSIOLOGY. cells give off numerous i^'occssos whereby they are brought into direct communication witli one another as well as other parts of the body. These masses thus form structural integrations which per- form corresponding integral functions. If at any time the struc- ture suffers, the function must of necessity suffer also. The nerve-centers comprise the spinal cord, medulla oblongata, pons Varolii, cerebrum, and cerebellum. Common Pkoperties. — There are certain properties which all nerve-centers seem to possess in conunon and which arc of interest to the student: — 1. They all contain nerve-cells. These are the real centers of activity. They both originate and conduct impulses. Nerve-fibers are almost exclusively conductors. 2. Nerve-centers are capable of discharging reflexes. They are motor, secretory, and inhibitory reflexes. 3. They are the seat of automatic excitement when phenomena are manifested without the application of any apparent external stimulus. 4. The nerve-centers are trophic centers for both their nerves and the tissues supplied by them. THE SPINAL CORD. Structure of the Spinal Cord. "The key to the study of the central nervous system is to re- member that it begins as an involution of the epiblast. It is orig- inally tubular with a central canal whose brain-end is dilated into ventricles. In the spinal cord there are three concentrated parts: First, the columnar, ciliated epithelium; outside of this is the cen- tral gray tube ; and, covering all, the outer white, conducting fibers." (Hill.) The spinal cord is that portion of the cerebro-spinal axis which is inclosed within the vertebral canal. It extends in the form of a large, cylindrical cord from the upper level of the atlas to the first or second lumbar vertebra. Above it is continuous with the medulla oblongata. Below it becomes conical, to terminate finally in a slen- der filament : the filam terminalc. It is attached to the base of the coccyx. The filum terminate passes through and is partly concealed by the conical extremity of the spinal cord. The cone is a mass of nerve-roots Avhich, from its striking resemblance to a horse's tail, has been termed the cauda equina. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 537 The average length of the spinal cord is eighteen inches. In the foetus the cord extends the whole length of the vertebral canal. The difference in relative length of the cord in the foetus and in the adult is due to the unequal and more rapid growth of the spinal canal than of the cord. The cord thus seems to ascend in its canal. Instead of the spinal nerves of the lower portion of the cord leaving their points of emergence horizontally, they sweep down like the hairs in the tail of a horse to form the aforementioned cauda equina. Coverings. — Not only is the cord protected by the spinal canal in which it is suspended, but in addition it is enveloped by a triple membranous container. The cord does not more than half fill the lumen of the spinal canal. It is suspended in this cavity surrounded by an aqueous medium : the cerebrospinal fuid. The investing membranes have been termed, from within out- ward, pia mater, arachnoid, and dura rnater. They form a sheath, or theca, which is considerably larger than the cord. It is separated from the bony wall of the spinal canal by venous plexuses and loose areolar tissue. The pia mater is a very delicate covering which is closely adherent to the cord. It sends numerous septa into the substance of the cord as well as into its anterior and posterior median fissures. It is composed of blood-vessels and connective tissue. The arachnoid (spider's web) is, as its name implies, a very deli- cate, reticular membrane. It is nonvascular. Hanging like a cur- tain between the innermost and outermost membranes, it forms two spaces which are termed subdural and suharachnoid. The outermost and toughest membrane is the dura mater. It is a very dense sheath and lies indirectly in contact with the canal- wall. However, unlike the dura of the brain, it does ?iot form the periosteum for the portions of the vertebra constituting the walls of the spinal canal. Diameter of the Cord. — The volume of the cord is not the same throughout its whole extent. Although of a mean diameter of half an inch, yet it presents two decided enlargements. The one enlargement is at the level of the inferior portion of the cervical region; the other at the lower portion of the dorsal region. The first one is the cervical enlargement from which emerge the nerves of the upper extremity. The name brachial enlargement has been given to it. From the lower enlargement arise the nerves which proceed to the lower extremities. It is known as the lumbar enlargement. At 538 PHYSIOLOGY. the site of each enlargement the cord loses its cylindrical form to become somewhat flattened from before backward. The formation of the enlargements is in intimate relation with the development of the members. In fishes we have only rudiment- ary members, the cord is of uniform diameter throughout. In steel- workers the cervical swelling is considerable. The ivelght of the cord is about one and one-fourth ounces; it is equal to about one-forlieth of the weight of the brain. The suspension of the spinal cord within the canal is main- tained laterally by irregular fibrous tracts which form the ligamentum denticulatum. Laterally the roots of the spinal cord give support; below, the filum terminale fastens it to the coccyx; above, its con- tinuation as the medulla furnishes the most important support. Exterior Form of the Cord. — Externally the cord has two longi- tudinal median grooves: one anterior, the other posterior. They traverse the entire length of the cord to divide it into two halves which are usually perfectly symmetrical. The origins of the spinal nerves are situated upon each side of these two parallel, longitudinal lines. The anterior median groove divides the anterior surface of the cord into two perfectly equal parts. It extends from the decussa- tion of the pyramids to the caudal extremity of the cord. In depth it occupies nearly a third of the thickness of this organ. In this groove is folded a layer of pia mater; at its base is seen a layer which passes from one-half of the cord to the other — the white, or anterior, commissure. The posterior median fissure, deeper and narrower than the anterior, extends from the nib of the calamus scriptorius to the termination of the spinal cord. Into this groove the pia mater sends but a simple partition; but it is very adherent to the walls of the groove. The depth of the fissure is bounded by a commissure analog- ous to that which is furnished to the anterior median groove, but of a gray color. This is the gray, or posterior, commissure. Upon each side of the cord are seen two lateral grooves which represent the lines of implantation of the anterior and posterior roots. They are known as the antero- and postero-lateral grooves. The latter is the more apparent of the two, showing itself in the form of a dotted, longitudinal line. The antero-lateral groove corresponds to the line of insertion of the anterior roots of the spinal nerves. The two lateral grooves ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 539 may be regarded as purely artificial; seen only after the spinal nerves are torn from the cord. By virtue of the median and lateral fissures the cord is divided into columns, paired and symmetrical. The portion comprised be- tween the anterior median and the antero-lateral fissures is known as the anterior column. That portion between the two lateral fissures bears the name of lateral column. That part between the postero- lateral and posterior median groove is the posterior column. Anatomy and physiology demonstrate that the separation of the anterior from the lateral column is not complete; hence it is cus- tomary to reunite these two columns under the name of antero- lateral columns. Internal Conformation of the Spinal Cord. — The texture of the cord is best studied by means of transverse section. These sections show that the cord is composed throughout its whole extent of two substances: one, the cortical, white substance; and the other, the central, gray suistarice. The white substance is located peripherally and covers all of the gray substance except at the base of the posterior median groove. It forms the columns which have Just been pointed out. The gray substance forms in each half of the cord a longitudinal column whose transverse section appears in the form of a crescent with its concavity directed externally. The crescent terminates in two swollen extremities, the anterior one having the name of anterior horn; the posterior one, that of the posterior horn. The two crescents are bound to one another at their convexity by the aid of a transverse band of gray substance, the gray commis- sure. This band is pierced centrally by a canal, the central canal of the cord. It runs down the central axis of the cord and is accom- panied on each side by a vein, the central veins of the cord. In all sections the gray matter is vaguely represented by the letter H: per- haps better by the two wings of a butterfly united by a transverse bar. The column of gray matter is not exactly of the same form in its whole length. It is thicker in the cervical and lumbar regions than in the thoracic. The white matter is likewise thicker at the level of the cervico-dorsal and lumbar enlargements. At the level of the Cauda equina the white substance forms but an enveloping layer for the gray matter. In the cervical and lumbar regions the anterior cornua are remarkable for their volume; toward the dorso-lumbar enlargements the posterior cornua increase in size. The anterior cornu of the 540 PHYSIOLOGY. crescent is swollen. The posterior is more slender and reaches to the surface of the cord. Each cornii possesses a swelling (head) and a somewhat restricted portion (cervix). The head of the posterior cornu is remarkable in that it is capped with a layer of neuroglia to which has been given the name of gelatinous substance of Rolando. It is nearly amorphous, and, in section, gives an appearance very similar to the small letter u. The substantia contains a few neuroglia cells, with some fusiform nerve- cells along its margin. Fig. 236. — Two Nerve-pairs at Their Origin in the Spinal Cord — Anterior and Posterior Roots. (Morat.) As regards the upper pair the figure shows the relation of the roots with the gray axis. In the lower pair is seen the emergence of the anterior roots at the surface of cord. In the inferior cervical and superior thoracic region the most lateral portion of the anterior cornu is shaped in a special fashion so as to constitute a particular prolongation. This is known as the lateral cornu, or mtermedio-lateral column. The cells of this column are arranged in groups of from eight to twelve bipolar cells whose long axes are vertical or more or less oblique. It is believed that these give origin to those fine medullated fibers which form the splanchnic efferent fibers. On examination of sections it is seen that the anterior cornua do not reach to the surface of the cord. Hence that portion of the ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 541 white substance which surrounds the anterior cornua reaches from the anterior median groove to tlie posterior cornua. It seems to form a homogeneous column: the antero-Iateral column. In the rear, on the contrary, the posterior cornua sharply sepa- rate the preceding to form posterior columns. They lie between the posterior median groove and the posterior cornua. In the cervical region the posterior column is sharply divided into two secondary columns by the posterior intermediate groove. These are the columns of GoU (next to the posterior median groove) and Burdach (in apposition with the posterior cornu). From measurements by Stilling it seems that the cervical swell- ing results from a localization of superdevelopment of both gray and white matter of the cord. The lumbar enlargement is almost exchi- bively formed by a localized superdevelopment of gray substance. This is readily explained by the constitution of the columns them- selves. Excepting the fibers forming the roots of the spinal nerves, the columns of white matter are formed of (lescenclin-g, or motor, and ascendhuj, or sensory, fibers. The motor bundle successively gives off fibers to the motor roots of the spinal nerves to such a degree that in their descent their volume proportionately diminishes. The sensory, or ascending, bundle, receiving fibers from each posterior root which comes from a sensory nerve, enlarges as it ascends. Hence it results that at the level of the lumbar enlarge- ment the bundles are at a minimum, the ascending bundle just com- mencing, while the descending bundle is nearly spent. Minute Constitution of the Cord. — The spinal cord is composed of fibers, nerve-cells, neuroglia, and blood-vessels. In the white sub- stance there are found only nerve-fibers and neuroglia; in the gray substance, nerve-cells and fibers plunged in a stroma of neuroglia. White Substance. — The white matter is composed principally of m.edulJated fibers without the sheath of Schwann. The fibers in the white substance are, for the most part, arranged longitudinally ; those which pass to the nerve-roots, as well as those fibers which pro- ceed from the gray matter into the columns, possess an oblique course. In addition there are decussating fibers in the white com- missure. On cross-section the fibers (which are of different sizes) present the appearance of small circles with a rounded dark spot in their centers. This latter represents the axis cylinder of the fiber. The diameter of the fibers varies from ^/-,ooo to ^/i2oo inch. The most voluminous are the motor parts of the antero-Iateral 542 PHYSIOLOGY. column and direct cerebellar tract; the finest are in the pos- terior median column. Classification. — The fibers of the cord are classified into two great classes: intrinsic and extrinsic. Intrinsic. — This class of fibers originates in and terminates in the cord, thereby uniting the levels of gray matter. Fixed by their lower extremities upon a given point of gray substance, they follow an ascending course, to become lost by their extremities in a more or less elevated part of the gray column. Thus they are fibers of union or association for the purpose of establishing communication between the different levels of the gray substance of the cord. Extrinsic. — These fibers in the gray matter proceed to the gan- glia of the brain after having traversed the medulla oljlongata, pons, and crura. They unite the cells of the gray substance of the spinal cord to the upper nerve-centers. They are long and gradually diminish in number from the top to the bottom of the cord. Degeneration occupies their whole extent. Some are centripetal and undergo an ascending degeneration. They are contained in the column of Goll, the direct cerebellar bundle, and Gowers's tract. The others are centrifugal fibers, and undergo a descending degen- eration. They are localized in the crossed pyramidal and bundle of Tiirck. They are the last ones to appear in the fcetus. The roots of the nerves arrive at the central gray substance and plunge into it after having passed between the fibers of the peri- pheral white sul)stance. But few of them take part in the constitu- tion of the cortical white matter. Neuroglia. — In addition to the fibers just discussed the white matter of the cord contains neuroglia. From the neuroglia project extremely fine prolongations. These penetrate the cord to form within its thickness an infinity of partitions of extreme thinness. These are united to the adventitious tissue of the vessels and to the tissue w^hich serves as a basement membrane to the epithelium of the ependyma. Thus there is formed (on transverse section) a poly- gonal network whith isolates little colonies of nerve-elements one from the other. This sort of framework has been compared to a sponge in whose interstices are found the fibers and cells of the cord. ISTeuroglia does not belong to the category of connective tissues. It is a special formation which is derived from the primitive epiblast. In the central gray substance the neuroglia does not seem to be any more than amorphous matter with some few cellular elements. The gelatinous substance of Eolando is composed of abundant neuroglia ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 543 in the form of amorphous matter. The only connective tissue pres- ent in the cord is carried in by the blood-vessels. Gkay Matter of the Cord. — The gray substance of the cord is composed of neuroglia, fibrils, and nerve-cells. The cells of the cord are formed by a small mass of protoplasm in which is plunged a nucleus surrounded by pigment-granules. These cells, whose volume varies with the groups, have a certain number of prolongations. Cell-arrangement. — The cells of the cord are not disseminated in the gray substance in a disorderly way. They are grouped at cer- tain points to form nuclei — nuclei of nerves ; these are situated one above the other in a fashion to form columns parallel with the long axis of the cord. There are distinguished three groups in the anterior horns: an interior internal group, an anterior external group, and a posterior external group. In the posterior horns the cells are fewer in number; it is only at the internal part of the neck of these horns that there is found a grouping. It is known as the dorsal nucleus of Stilling or the vesi- cular column of Clarke. The ganglionic cells of the aJiterior horns are very large, star- shaped, and from ^/^^o to Voqo inch in diameter. That is, they are nearly large enough to be visible to the naked eye. Degeyicration. — The nuclei of origin of the anterior roots are seized with degeneration in the various forms of muscular atrophy. The cells, by reason of their function, are known as motor cells. They are motors for the muscles to which their nerves go, and trophic for the same nerves and muscles. Progressive muscular atrophy is ana- tomically cliaracterized by a general atrophy of the motor cells of the anterior horns of the cord. Children's palsy is also characterized by atrophy of these cells. The cells of the posterior horns, irregularly distributed in the neuroglia, are fewer in number and smaller in size than are those of the anterior horns. Their diameters average about V1200 inch. Anatomically, the column of Clarke exists only from the second lumbar to the eighth dorsal pair of nerves. However, there are small, erratic groups of cells and two restiform nuclei at the level of the medulla which are analogous to the two columns of Clarke. The cells of the column of Clarke are very large, star-shaped, and only very meagerly branched. The intermedio-lateral gray column is in the outermost portion of 544 PHYSIOLOGY. gray matter, midway between the anterior and posterior horns. It lies in what is known as the lateral horn. It is the spinal origin of the great sympathetic. A part of the posterior root-fibers are said to end in these columns. Erom this as a source fibers pass into the column of Goll and the direct cerebellar tract; others pass into the columns of Burdach and Gowers. To the degenerative changes within the cells of the column of Clarke have been attributed the vasomotor troubles of paralysis agi- tans. Sclerosis of the lateral columns explains the exaggerated trembling in the reflexes. The fibers of the cells of the gray matter form a spongy sub- stance which unites the two halves of the gray axis of the cord to one another. This, the gray commissure, passes in front of and behind the central canal of the cord. Neuroglia. — The neuroglia of the gray matter has a structure analogous to that of the neuroglia of the white substance of the cord. It is found in particular abundance at the extremity of the posterior horns (gelatinous substance of Rolando) and at the periphery of the central canal. The Central Canal. — This is a canal of very fine caliber located within the center of the gray commissure. It transverses the entire length of the cord, and, at the level of the nib of the calamus scrip- torius, is continuous with the fourth ventricle ; by means of the latter it communicates with the ventricles of the brain. The wall of this canal, known as the ependyma, is composed — from within outward — of: (1) a ciliated epithelium, (3) an amor- phous basal membrane, find (3) a substratum of neuroglia which unites the wall of the canal to the body of the cord. Tlie canal is flanked on each side by a longitudinal vein; the two constitute the central veins. Systemization in the Spinal Cord. — The spinal cord may be con- sidered as formed of a series of segments superposed. They are metameres corresponding to each pair of spinal nerves. Each one of these is a complete center, being supplied with nerve-cells and motor and sensory nerves. Each one is different from its neighbor, since it innervates a particular area of the surface of the body, whether it be tactile surface or muscular group. The nerve-cells are grouped in motor and sensory fields. They are all in perfect communication with one another by reason of numerous fibers; some are longitudinal {longitudinal commissures) which unite the various levels of the cord; others are transverse ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 545 {transverse commissures) whose function seems to be to unite the cells of the right side to those of the left side of each segment. The transverse commissures are but from one to three centimeters in extent. In addition to the spinal commissures just mentioned there are two other kinds formed by the long fibers uniting the spinal cord either to the cerebrum or cerebellum. They are known as the cerehro-spinal and cerehello-spinal fibers. Experimental physiology, pathological anatomy, and oml)ryology all agree very admirably in demonstrating that the apparently homo- geneous cord is composed of distinct and specialized parts. These parts are called systems, which, in the white substance, form sec- ondary columns, or bundles. White Columns of the Cord. Flechsig ascertained that in the foetus the different bundles of nerve-fibers did not all take on myelin layers at the same time. By taking advantage of this fact he was able to trace the bundles of fibers with myelin and thus map out the different tracts of the spinal cord and brain. Gudden extirpated an organ of sense and after waiting a sufficient length of time was able to trace the course of the atro- phied nerve-fibers. The nerve-filiers of the cord enveloping the central gray axis are distributed in different bundles or columns. These have previously been mentioned cursorily, but will now be discussed in detail. Anterior Column. — The anterior column comprises that area be- tween the anterior median groove and the line of implantation of the anterior roots of the spinal nerves. Its most internal fibers are com- missural ; they cross throughout the whole extent of the cord and so contribute in the formation of the white commissure. Other fibers run across at the same level to connect the large cells of the anterior horns of the two halves of the spinal cord. The anterior column comprehends two bundles : one, internal (next to the median groove), is known as TilrcTc's bundle, or direct pyramidal bundle; the other, external, comprises the remainder of the anterior column and is known as the root-bundle of the anterior column, or antero-lateral ground-bundle. The bundle of Tiirck (pyramidal bundle, direct cerebral, direct motor) is formed of centrifugal fibers which descend from the brain into the cord without decussating at the level of the medulla ob- longata. Its fibers are longitudinal and travel along and through 35 546 PHYSIOl.Or.Y. the brain, the anterior pyramid of the medulla and the same side of the corresponding half of the spinal cord. Yet, having arrived in the cord, some of its fibers cross to the opposite side along the path of the white commissure. They finally terminate in the cells of the anterior cornua. This bundle usually terminates about the second lumbar nerve. It undergoes descending degeneration. The antero-lateral ground-bundle (root-bundle of the anterior column) occupies the territory between the preceding and the antero- lateral groove. It is formed in ]-)art by the anterior roots which ax (crescendo and diminuendo) indicate increase and decrease. They are used in electrical formula to show the relationship of one reaction of muscle becoming greater than another. Thus: A. C. C. > K. C. C. == the anodic closure contrac- 598 PHYSIOLOGY. tion becoming greater than the kathodic closure contraction. In neuralgias the anode is placed upon the painful nerve. The Faradic current is a more effective stimulus to nerves than a galvanic current, for the effectiveness of a current as a stimulus depends not only upon the total variations in intensity, but also upon the amount of such variation in the unit of time; that is, the greater the rapidity of the total variation, the more effective is the current as a stimulus. In the Faradic current the kathode is always more active in pro- ducing contractions. The short duration of the opening and closing of the induction currents makes them fused in eff'ects. Electrotonic Variation of Electromotivity. — Electrotonus not only changes the irritability and conductivity, but also the elec- TTSTfVe Anelecirotonic current Polarisim current Ka-telectro tonic current. Fig. 270. (Waixer.) tromotivity of a nerve. If a nerve is connected with nonpolarizable electrodes in such a way that its transverse section is laid on one and its surface on the other, then the galvanometer will show the pres- ence of a strong nerve-current. If, now, a galvanic current is passed through the extremity of the nerve outside the unpolarizable elec- trodes, the polarizing current is established. The electrotonic cur- rent in the nerve always has the same direction as the polarizing current. In the extrapolar kathodic region an electrotonic current is gen- erated when the polarizing current is closed. In the anodic region the electrotonic current is stronger than the kathodic current. These electrotonic currents are only found in medullated nerves, and are only produced by an electrical polarizing current. ISTon- medullated nerves, muscles, and tendons do not show them. The electrotonic currents are not the action-currents of a nerve, and must not be confounded with them. The experiment of paradoxical contraction depends upon elec- trotonic currents. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 599 Reflex Action. — A motor reflex act is the transmission of an irritation by tlie neuraxon of a sensory neuron to the dendrons of a motor neuron and by its neuraxon in turn to the muscle. The functions of the gray substance of the nervous centers can be known only through reflex movements; so that, to study reflex action is to study the nervous centers. From a knowledge of the principles of a reflex action it will be seen that three stages must be considered : 1. The external excita- 3 Fig. 271. — Elementary Reflex Arc. Course of Sensory Impressions and a Motor Impulse, Passing Through the same Level of the Spinal Cord. ( MoRAT. ) 1, Skin. 2, Sensory nerve. 3, Posterior root ganglion. 4, Anterior root. 5, Motor nerve. G, Muscle. tion which goes to excite the nervous centers through the sensitive nerves as a medium. 2. The excitation of the nervous centers which receive the irritation and then transform and modify it; through the medium of the motor nerves it is communicated to the muscles. 3. The contraction of the muscle thus innervated. Other Seats. — It is not only in the spinal cord properly so called that there are reflex acts. There are some in the medulla oblongata, in the pons, and in the gray parts of the brain. The physiological study of strychnine shows what intimate con- GOO Piivsi()L(x;v. nections exist between the different parts of the spinal cord. The irritation of the periphery at any point whatever, being transmitted to the spinal cord by a sensitive nerve, goes to provoke at once the activity of the whole organ. The initial stimulation for a reflex action may arise from any sensory nerve, whether of special sense, touch, or visceral supply. But there are some which generate a more active reflex movement, among which may be mentioned those of the j)alm of the hand and the sole of the foot. The quality and nature of the stimulus used has an influence on the reflex. Thus, tickling the auditory meatus produces cough; excessive sunlight acting on the retina cause* sneezing. Stimulation of a sensory nerve-trunk in any part of its course calls out a reflex action, but the movement in this case is much less energetic and its character altered. In such a case the stim- ulation causes movement in one or more muscles, while stimulation of the skin surface innervated by the same nerve produces movements which have a peculiar character of co-ordination. To produce a reflex action the application of the stimulus must be sufficiently rapid. Any agent which produces a slow and gradual change in the nerve is without effect. Some experimentalists have found a differ- ence between the reflex of chemical and of mechanical stimulation. When the reflex center has a greater or less excitability, then the stimulation produces greater or less results. Every center which gives origin to a motor nerve may be looked upon as a reflex center. The excitability of the reflex centers is increased when their con- nection with the cerebrum is cut off or when the latter centers are inactive. Hence after decapitation, removal of the brain, section of the oblong medulla, or section of the spinal cord, the centers below the section have greatly increased activity in their reflexes. Set- schenow has shown that mainly in the optic thalami and corpora quadrigemina are seated centers inhibiting the activity of the spinal reflex centers. Eeflex excitability is much greater in young animals than in adults. This explains the quickness with which slight causes pro- duce convulsions in the infant. Eeflex activity is greater in the summer than in the winter. Certain toxic agents have an effect on the reflexes. Thus, atropine, bromides, chloral, chloroform, and ether reduce reflex activity, while strychnine greatly excites it. Chloroform is poisonous to every living cell, whether of plant or of ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 601 animal life. Strychnine is only poisonous to the nerve-cell, not to the plant-cell. Every time that intellectual action is suppressed then are the reflexes more manifest. A person asleep has more energetic reflex actions than a person awake. In somnambulism the action of the will is nearly suppressed, while the reflex excitability of the cord is enormously increased. On the other hand, a person by exercising a strong will can arrest certain reflexes. Thus, the conjunctival reflex can be pre- vented by the will of a courageous person. Up to a certain point a person is able to resist sneezing or coughing, which are certainly typical reflex movements. Swiftness of Reflex Actions. — Helmholtz succeeded in meas- uring by the graphic method the swiftness of the spinal actions. B}' him it was ascertained that the excitation travels in the spinal cord at the rate of about twenty-four feet per second. Laws of Reflex Actions. — They are the law of localizatioti and that of irradiation. One other accessory law will be added: the law of co-ordination. Lair of Localization. — If any sensitive region be excited, the first reflex movement which will be produced will bear upon the muscles near the sensitive region excited. Thus, if the foot of a frog be very lightly touched, the muscles of that foot will respond reflexly. If the conjunctiva be touched, the reflex movement will be in the orbicular muscles. Laiv of Irradiation. — When an excitation has produced a reflex movement in the muscles of one side by a first degree of irradiation, there will be reflex movements in the corresponding muscles of the opposite side. Cutaneous constriction by cold applied to the right hand determines constriction by the vasomotors of the left liaud as well. These are examples of the type known as transverse irradiation. If the excitation be more intense, the movement is spread into the muscles situated above and l)elow the point of excitation. This represents the longitudinal irradiation. Laiv of Co-ordination. — The law of co-ordination or adaptation of the reflex actions in decapitated animals is very striking. If a drop of acetic acid be placed upon the back of a decapitated frog the animal will make such movements with the feet that it seems to want to free itself from the substance which irritates it. They are not blind movements, but such as seem to be adapted to an end and are co-ordinated. 602 piiysi()T.()(;y. Reflex Tonus of Spinal Cord. — li cannot be denied that, in the nornial stale, there ii^ always a certain spinal tonus. That is to say, an active state of the cord which is provoked by sensory excitations. All of the muscles of the organism, striated as well as smooth, are always in a state intermediate between relaxation and contraction. This state of semiconstriction, of semiactivity, is governed by the spinal cord. When the spinal cord is destroyed, immediately all of the muscles of the body relax and their tonus ceases. Influence of the Blood. — If a limb be separated from the rest of the organism, and, consequently, receives no nutritive blood-current, the function of the n-erve nevertlietess persists. By making Stenson's experiment (tying the abdominal aorta), at the end of twenty minutes, or an hour at the most, it will l)e found that sensibility and motility disappear in the abdominal mem- bers. Though the deprivation of blood be complete, still there is preservation of the nervous activity for some time. By using on man the ligature and then compressing the limb by an Esmarch bandage interesting observations upon the influence of anaemia are made. During the first twenty minutes the arm is sen- sitive and the cutaneous excitations are plainly perceived. Like- wise the motor nerves can still command the movements of the muscles. Soon, however, the sensibility becomes obtuse; the voluntary movements take place only incompletely, without force, and slowly. Next the sensibility disappears so completely that the strongest elec- trical excitations are not felt. Because of the powerlessness of the motor nerves, the limb feels limp and inert as if it were completely paralyzed. This state of death of the nerves, from ana-mia, contrasts with the survival of the muscles. The nerve dies before the muscle, but much later than the nervous centers. Exciting Effects of Anaemia. — However it may be, ansemia, which makes the functions of the nerve finally disappear, begins at first by overexciting it. Thus, the first effects of anaemia are marked by an increase of excitability. If it be a sensory member, anaemia of it provokes extremely lively pains. Physicians have long been acquainted with painful anaemise. It is anaemia, not absolute, but relative, which is often the cause of intense peripheral pains. Thus, in symmetrical gangrene of the extremities (Raynaud's disease), which is characterized by nearly complete cessation of the circulation in the affected areas, the pain ANATO:\IY AND PHYSIOLOGY OF NERVOUS SYSTEM. G03 is very acute. There is extreme liyperaistliesia, prol)al)ly due to nervous anaemia. Physiology of the Spinal Cord and its Nerves. The spinal cord represents: 1. A great conductor whose extent lies between the brain and periphery of the body. Along it are transmitted centrifugal as well as centripetal actions; the former carry volitional impulses to the muscles, the latter impressions from the sensitive surfaces to the brain. By reason of the spinal cord having in its composition innumerable nervous cells, it becomes a co- ordinator of the actions which pass over it. 2. The spinal cord represents a true iwrvoiis center. It may be either an important center of reflex phenomena in that its cells unite centripetal fibers with centrifugal ones, or it may possess the role of acting as a special center of the special functions. Cord as a Conductor. — The law of Bell is enunciated as follows : "Of the roots which issue from the spinal cord, the anterior are those of motion and the posterior those of sensation." This law is very clearly demonstrated by the so-called Miiller frog. If the last four anterior spinal roots in the cauda equina of a frog are cut off at the right, and the last four posterior roots are cut off at the left, the animal after recovering from the operation will present interesting conditions. The right lower leg will be para- lyzed; that is, deprived of voluntary motion. The left lower leg will be ancBsthetic: that is, deprived of sensation, but still possess motion. Therefore, the anterior spinal roots are motor and the posterior ones sensory. Irritation of the posterior roots, or of their central stumps, determines sensations. These sensations are sharp pains in the regions innervated by the particular nerve. Excitation of the peri- pheral stump is without any effect. Irritation of the anterior roots, or of their peripheral stumps, determines movements. These movements are of the nature of con- vulsive cramps in the particular muscles innervated. Excitation of the central stumps is not followed b}' any effect. Cutting off, or the complete destruction, of the posterior roots causes the loss of tactile, thermic, and painful sensibilities; also of muscular sensation in the parts where they are distributed. Sec- tion of the anterior roots wholly paralyzes the muscles innervated by them. 604 PHYSIOLOGY. Apparent Contradiction. — In demonstrating Bell's law there occasionally are seen results which seem to contradict that law, but instead they really confirm it. It is found that in stimulating the anterior (motor) root with electricity the animal sometimes gives evidences of pain. The same thing may occu^r also after cutting it in the middle and then stimulating, not the central, but the peripheral stump. Bernard has explained the sensibility of the anterior root by admitting that the recurrent sensitive fibers, which, taking their departure from the posterior roots, run back from the periphery towards the center on the anterior root. If the posterior root be cut near to the spinal cord, sensibility in the corresponding anterior root wholly disappears. Fig. 272. — Diagram of the Roots of a Spinal Nerve, Showing Effect of Section. (Landois.) The black represents the degenerated parts. A, Section of the nerve-trunk beyond the ganglion. li. Section of the anterior root. C, Section of the poste- rior root. D, Excision of the ganglion, a, Anterior root, p, Posterior root. g. Ganglion. The spinal roots united, those of sensation with those of motion, constitute the inixed spinal nerves. They furnish the different parts of the body in which they are distributed with both sensibility and motion. Consequently the section of many spinal nerves leads to anaesthesia and paralysis of the parts innervated. In the recently cut nerves, the central as well as peripheral stumps are excitable by stimulants, the former causing pain, the latter contractions. Ganglion. — The posterior root, before joining the anterior, has a ganglion. The function of this ganglion is its trophic infiu- ence, discovered by Waller and afterward proved by Bernard and others. When an anterior root is cut the peripheral stump becomes atrophied, whereas the central stump remains entire. The latter retains its vitality, since it is still in connection with its trophic center in the cells of the anterior horn of the gray matter. On the contrary, when a posterior root is cut between the spinal ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 605 cord and the ganglion the peripheral stump remains entire, while the central stump becomes atrophied. The ganglia of the posterior spinal roots have, therefore, the office of trophic centers over the sensory nerves; the trophic centers for the motor nerves lie within the cord itself and are none other than the large, multipolar cells of the anterior horns. The anterior roots contain different centrifugal fibers — motor fibers, vasomotor fibers, sweat, and inhibitory fibers of the splanch- nics. The motor fibers take their origin in the cells of the anterior horns, while other centrifugal fibers are united to the cereln-al cortex. As to the vasomotor fibers, they have their centers of origin in the medulla oblongata and cord to penetrate the anterior roots. They probably do this without entering into connnunication with the cells of the anterior horns. The posterior roots have centripetal reflex filjers. These leave the skin, muscles, and other organs; penetrate the spinal cord; and are in direct connection with the reflex centers located partly in the cord itself and partly in the medulla oblongata, pons, corpora quadri- gemina, cerebellum, and optic thalami. The other sensory and sense fibers penetrate the cord by way of the posterior roots to ascend toward the cerebral cortex. Here are received the several conscious sensations : touch, pressure, temperature, pain, and mus- cular sense. Path of Transmission of Voluntary Motion. — Voluntary luotor excitation is transmitted from the cerebral cortex to the nerve-cells of the anterior horns by way of the anterior and lateral colunms. These columns, as a whole, do not participate in conduction, but only the anterior pyramidal tracts of the anterior columns and the crossed pyramidal tracts of the lateral columns. As the student knows, the crossed pyramidal tracts do not decus- sate in the cord, but in the medulla oblongata. The direct pyramidal tract does not decussate in the medulla, but in the spinal cord by way of the anterior commissure. "When the spinal cord is completely sererrd the voluntary move- ments for all of the muscles below the point of section are ahsoJutcIy abolished. Path of Conscious Sensations. — The sensations of touch and muscular sense are transmitted I)y the posterior roots and traverse the posterior columns to the brain. Muscular sense is transmitted mainly by the posterior columns. The direct cerebellar tract, and probably Gowers's, also contain fibers 606 PHYSIOLOGY. which conduct muscle-sense to the cerebellum. Tactile and muscular sensations are abolished by locomotor ataxia. One-sided section of the posterior and lateral columns causes : (a) suppression of skin sensations, or ana3sthesia, in the whole half of the body innervated by nerves which enter the cord below the side of section; (b) loss of motion on side of section. There is very fre- quently observed on the side of hemisection a zone of liypera^sthesia ; this is due either to removal of inhibition on that side or inflamma- tory irritation of the central extremity of the cut curd. It has been shown by WoroschilofE in Ludwig's laboratory that the lateral columns are a pathway for sensory impulses. 1 have shown with Dr. Eobert M. Smith similar results in a series of sections of the lumbar part of the spinal cord. Section of the posterior and lateral columns does not exercise any influence upon sensibility to pain and temperature. But this is not the case when the gray matter is cut; so that it must be inferred that these impulses ascend through the gray substance to the brain. kSyriufjoiiri/rlia is the term applied to that condition when there is complete abolition of the conduction of pain and temperature. It is due to vacuolation of the gray matter of the cord. Fibers from the Centers of the Medulla Oblongata. — The vasomotor nerves, which come from a center seated in the medulla oblongata, run down the lateral colnnm to penetrate the gray sub- stance and anterior roots. Hence, section of the lateral columns produces a dilatation of the arterioles innervated by vasoconstrictors, which leave the cord below the point of section. The nerves leaving the respiratory center also run through the lateral columns and enter the gray substance, to communicate with it and leave by the anterior roots. In the middle third of the lateral columns I have found running both sweat and inhibitory fibers. Both sets of fibers, I have discovered, decussate : the former in the spinal cord, the latter in the medulla. Skin Reflexes. — The most important slin reflexes in man are : — 1. The Plantar Eeflex, wliich is caused by tickling the sole of the foot. The involved center lies in the lumbar cord. 2. The Cremasteric Eeflex. — If the skin of the upper and inner surface of the thigh in man be excited, the corresponding testicle will be seen suddenly to rise by contraction of the cremaster muscle. Its center lies between the first and second lumbar nerves. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 607 3. The Abdominal Reflex is a contraction of the abdominal muscles caused by a t^harp push of the finger. Its center lies between the eighth and twelfth dorsal, 4. The Epigastric Keflex. — If the skin between the fourth, fifth, and sixth intercostal spaces be irritated, contractions of the rectus alxlominis of the same side will follow. The center is between the fourth and eighth dorsal. 5. Scapular Keflex. — xA.n irritation of the skin covering the scapulge may cause contraction of the shoulder-muscles. Its center is between the seventh cervical and second dorsal nerves. Tendon Reflexes. — 1. Ankle-clonus. — When the sole of the foot is pressed upon by the hand, then the gastrocnemius contracts, and if the pressure is continued there may be several clonic contrac- tions. Ankle-clonus is never found in health. 3. Patellar Reflex. — AYhen a tap is made on the tendon of the quadriceps just below the patella, the foot jumps upward. Jendrassik found tliat the patellar reflex could be increased if, at the time of tapping the tendon, the patient squeezed his hands together or clenched his jaws. This augmentation has been called, by Mitchell and Lewis, reinforcement of the knee-jerk. Bowditch and Warren found that if the reinforcing act preceded the blow on the patellar tendon by 0.6 second, the knee-jerk was inhibited instead of being increased. Both reinforcement and inhil)ition of the reflex are supposed to be due to "overflow" in the central nervous system. When the cortical motor-center for the foot of a rabbit was irritated, then the patellar reflex caused by stimulation of the paw was in- creased, as shown by Exner. The knee-jerk is absent in locomotor ataxia, and exaggerated in lesions of the brain and of the lateral columns of the cord. This exaggeration is due to removal of inhibitory impulses from the brain travelling down the middle third of the lateral columns, as I have shown in the case of the ano-spinal reflex. Antagonistic Muscles. — Sherrington has shown a relation to exist between the tonic condition of antagonistic muscles; for ex- ample, between the hamstrings and the vastus internus of the quadri- ceps extensor. Division of the hamstring muscles, or even section of their nerv^e, causes a great increase in the knee-jerk, elicited by tapping the patellar tendon. Stretching the liamstring muscles or •weak stimulation of the central end of the cut nerve to the ham- string, abolishes the knee-jerk. Every sensory irritation which calls 608 PHYSIOLOGY. out a contraction of one set of muscles will inhibit the antagonistic muscles. Sherrington has shown that the reflex arc in the knee-jerk is due to nerve-fibers passing to and from the quadriceps extensor by the anterior crural nerve, and to those passing to and from the ham- string muscles by the sciatic. The tendon reflexes are not true reflexes, but are due to a direct stimulant action on the muscle itself. But a reflex arc is necessary to keep the muscles in a state of tonus that the t-endon reflexes may take place. Centers in the Spinal Cord. — The spinal cord presides over the movements of the anus, the bladder, and the genital apparatus by means of three centers located one above the other. The ano-spinal center is found in the dog near the fifth lumbar vertebra. From this center emanate fibers which, with the sacral nerves, go to animate the sphincter of the anus. Irritation of this center, especially by disease, brings on spasm of the sphincter, with difficulty in passing faeces. Destruction of the center causes paralysis of the sphincter and incontinence of faeces. In paraplegics (those afi^ected with paralysis of the lower limbs from cord lesion), spinal incontinence or the involuntary passage of the fgeces may be observed. Or there is a protracted and invincible constipation. The former condition depends upon the destruction of the spinal center, while the latter comes from paresis of the intes- tine in the region of the colon and rectum. The vesicospinal center in dogs is found between the third and fifth lumbar vertebra. When it is stimulated or the nerves which take their departure from it, there are energetic and painful contrac- tions of the body and neck of the bladder. In apoplectics there is often, first, ischuria (retention of urine), which seldom comes from irritative or nervous spasm of the sphincter, but more frequently from paralysis limited to the detrusor nerves only. Afterward there is enuresis (incontinence of urine), from paralysis also of the nerves of the sphincter. The genito-spinal center is to be found in the spinal cord at the level of the fourth lumbar vertebra. If excited by stimuli it pro- duces contractions of the lower part of the rectum, bladder, and, if the animal be a female, the uterus. In addition, if the spinal cord be cut between the dorsal and lumbar parts, tickling of the mucous membrane of the glans penis of the dog determines by reflex action an erection. Erection is no longer obtained if the lumbar cord be ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 609 destroyed. Goltz and Freusburg have observed in a bitch, wliose spinal cord was cut at the level of the last lumbar vertebra, the mani- festations of desire, conception, gestation, delivery, and lactation to take place just as in a sound bitch. In obstetrical wards women are delivered while in the anaes- thetic sleep produced by ether, chloroform, or other anaesthetics. These various facts show that the center of the movements of the uterus is found in the spinal cord, and not in the hrain. The sudorific centers are seated in the spinal cord. The spinal cord has minor vasomotor centers for the vessels of the parts it inner- vates. In fact, cutting the cord produces hyperipmia and eleva- tion of temperature in the paralyzed parts. This is due to the paralysis of the vessels there. The constrictors are paralyzed. Electrical excitation of the peripheral stump lowers the tem- perature in the parts innervated, by constricting the lumen of the corresponding arterioles. The vasomotor fibers, emanating from the spinal column, rejoin the vessels either directly, or, more commonly, by means of branches of the SA'mpathetic. The cilio-spinal center is seated in the medulla oblongata and sends fibers down the dorsal cord to the third dorsal vertebra. These fibers emerge by the anterior root of the two lower cervical and the two upper dorsal nerves and go into tlie cervical sympathetic to the dilating fibers of the iris. Pinching the skin of tlie neck will dilate the pupils : another skin reflex. Physiology of the Medulla and its Nerves. The medulla oblongata, or huJh, like the spinal cord, is an organ of transmission, or conduction-, but at the same time it is a center of particular and very important functions. Double Conduction. — Like the spinal cord, the medulla carries centripetal, or sensory actions, and centrifugal, or motor actions. The former are conveyed by means of its posterior part; the latter by the anterior part. The centripetal, sensory conduction is crossed or decussated along the floor of the fourth ventricle. The centrifugal, motor conduction accomplishes, instead, its decussation in the pyramids of the medulla, where the right, lateral fibers pass to the left, and vice versa. This decussation of the fibers is much more complete in man than in animals. So much is this so that in man a lesion which destroys one-half of the medulla brings on complete hemi- plegia of the opposite side ; in animals a similar lesion never pro- 010 PHYSIOLOGY. duces hemiplegia, but only paresis. Equally, in animals this same lesion does not entirely abolish sensibility in the opposite side of the body. The gray substance of the opposite side connects the parts lying over and under the lesion, and so conducts the sensory im- pressions. Bulbar Nerves. — From the medulla oblongata many pairs of nerves, the bulbar nerves, take their origin and departure. Each nerve has a gray nucleus. The nuclei on the right side are connected with those on the left and all have their location along the gray substance of the floor of the fourth ventricle. The fibers which connect these nuclei of origin with the superior cranial centers are also crossed on the way. Centers. — The medulla, with its gray substance and especially with the gray nuclei of the nerves which issue from it, becomes a center of very important functions. First, it is a respiratory center. This center is found toward the inferior angle of the fourth ventricle, a little back of and lateral to the source of the vagi nerves. It is composed of two lateral halves, each of which, in function, can take the place of the other. This center is about two and one-half millimeters in size. A lesion affecting both respiratory centers causes the sudden death of a warm-blooded animal. Therefore, this region of the fourth ventricle has l)een called the vital Tcnot. In fact, a blow from a stick upon the back part of the head or upon the nape of the neck, also a thrust from a sharp stilleto between the back of the head and the first vertebra, suffices to cause even a large mammal to fall to the ground instantly. Butchers do this because they injure the vital knot. Components of the Center. — The center of respiration in the medulla is composed of an inspiratory center and an expiratory center. From the inspiratory center the excitation for the nerves, and therefore for the muscles of inspiration, takes its departure rhyth- mically. These motor excitations always decussate in the cervical cord. The inspiratory excitation reaches the center by means of the pneumogastric nerves, having been carried along their sensory pulmon- ary fibers. The excitation is originated cither by reason of an accumu- lation of CO2 in the blood or the absence of 0. On the contrary, an excess of oxygen in the blood abolishes excitation of the inspira- tory center. The expiratory center, on the other hand, gives excitation to the ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. gH nerves and muscles of forced expiration (normal expiration is accom- plished by reason of the elasticity of the thoracic case). Experimentally it is observed that exciting the vagus nerves or their central stumps provokes very deep inspirations until tlie thorax stops in the inspiratory movement. Stimulating the superior laryngeal nerves or their central stumps provokes violent and forced expirations until the thorax stops in the expiratory movement. It is said that when a lesion affects the bilateral respiratory cen- ter there follows immediate suspension of breathing, and, therefore, death. Fig. 273. — Floor of Fourth N'entricle of Rabbit. (Hedon.) Puncture at «, a little above the nib of the calamus, produces diabetes. Punoture at h produces polyuria without glycosuria. The medulla oblongata is a moderating center of the movements of the heart. By irritating the medulla near the originating nucleus of the vagus nerve there is caused a stoppage of the cardiac move- ments. The heart first slackens its systole and afterward stops in diastole. The medulla exercises this moderating action upon the heart through the vagus nerve as a medium. Some of its centrifugal fibers put themselves in relation with its inhibitory ganglia. Hence, moderation and suspension of the heart movements is obtained by irritating the peripheral stump of the vagus in the neck. According to Traube, the normal stimulus, capable of exciting this moderating action, is the accumulation of CO, in the blood. In the medulla is found tliis moderating center, whicli is antago- nistic to that other center seated in the medulla oblongata : the accelerator center of the heart. The medulla contains the principal vasomotor center, which is of 612 PHYSIOLOGY. tliG utmost importance to the economy. This general vasomotor center in the medulla may become stimulated directly from the hrain. In short, an emotion or irritation to the cerebral cortex readily brings on ischemia or hypensmia either in the skin or in the internal organs. Thus, there may be pallor from fear or diarrhoea from fright. This organ of the nervous system is a secretory center for the saliva. In the floor of the fourth ventricle at the level of the origin of the facial nerve, and somewhat posterior to it, is found the originating nucleus of the fibers of the intermediary nerve of Wris- berg. This, through the chorda tympani of the facial nerve, is car- ried to the submaxillary gland. Pricking the center or stimulating it electrically provokes a copious secretion of saliva. Certain patho- logical lesions may produce the same thing. Glucose Secretion. — The puncture in tlie fourth ventricle should be limited superiorly by a line joining the origin of the audi- tory nerves, and inferiorly by one Joining the origins of the vagi. This will determine within an hour the condition known as diabetes mellitus — glucose in the urine. The diabetes ceases if the liver be extirpated, and is not pro- duced if the liver has been previously taken away, or its vessels have been previously tied. In the liver of animals rendered diabetic in such a manner there is found an intense vasomotor paralysis. This appears to be the cause of the increased production of glucose. The action of the medulla upon the liver is exercised by means of the spinal cord through the intervention of the great sympathetic. The oblongata centers are : (1) respiratory, (3) vasoconstrictor and vasodilator, (3) cardio-inhibitory , (4) cnrdio-accelerator, (5) diabetic center, (6) vomiting center. (7) deglutition, (8) salivation, (9) mastication, and (10) cilio-spinal. ANATOMY OF THE CEREBELLUM. The cerebellum is situated at the posterior and inferior portion of the brain. It is bounded anteriorly by the cerebrum, which is separated from it by the tentorium of the cerebellum. At the posterior face of the cerebellum are the pons and medulla oblongata, from which structures it is separated by the fourth ventricle. The cerebellum is entirely covered by the occipital lobes of the cerebrum in man, but only incompletely so in monkeys. It is united by the cerebellar peduncles to the cerebrum, pons, and uiodulla. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 613 The peduncles are six in number — three on each side. • They are known as the superior, middle, and inferior cerebellar peduncles. Surface Form. — Tlie cerebellum consists of a median lobe (the vermis) and two lateral lobes (the cerebellar hemispheres) . The supe- rior vermiform process extends from the notch on the anterior to the one on the posterior border. The under surface of the cerebellum is subdivided into two lateral hemispheres by a depression (the valleij). It extends from before backward in the median line. On the floor of the median lobe is the inferior vermiform, process. Fig. 274. — Horizontal Section Through the Cerebellum. B. Stilling.) (After The section passes through the region under the corpora quadrigemina (T), then through the anterior cerebellar peduncle (/?), and between these through the lingula (1). Above this lies the nucleus tegmenti, nucleus fastigii (m), to the left of the nucleus globosus (Xf/), the embolus (Emb), and still farther to the side within the hemisphere the corpus deutatum {Vdc). Internal Structure of the Cerebellum. — The cerebellum, like the spinal cord, is composed of botli wliito and gray substances. The gray is the most abundant, and occupies the periphery of the organ in the form of a thin layer which is from two to three millimeters in thickness. The white substance is placed in the center of the organ and is enveloped in all of its parts liy the gray matter. The white represents 614 PHYSIOLOGY. nearly one-third of the whole cerebellar mass. Its consistency is greater than that of the gray matter. The central nucleus of the white matter sends out an affinity of arborescent prolongations which terminate in the cells of the gray substance of the lamella?. It is this formation which the student knows under the name of arbor vitce. Each one of the leaflike divisions of the white arbor vitge forma- tion is enveloped by a very thin plate of yellowish substance, while above this is the cortical gray substance. The latter sinks into the white substance at the level of the grooves which separate the plates from one another. A horizontal section of the cerebellum shows in the center of each half of the organ an ovoid body. It is very similar to the olive of the bulb in size and structure. This is the corpus dentatum. Corpus Dentatum. — The corpus dentatum is formed by a yellow layer folded upon itself in the form of a purse which opens in front. Within the interior of this purse is found the tissue proper of the corpus dentatum. It is formed of a matter which seems to be a mixture of the white and gray substances. Under the name of accessory nucleus dentatus Meynert has de- scribed two small leaves of gray substance located in front and inward from the corpus dentatum. Tliey are the nucleus globosus and nucleus fastigii. Stilling has discovered two clear gray nuclei at the lower border of the vermis near the median line and the roof of the fourth ventricle. He calls them the nuclei eniholiformes. Part of the fibers of the inferior cerebellar peduncles end within these nuclei. Hence, there are here four gray nuclei: dentate^ globosus, fas- tigii, and emboliforrnis. The last three are in pairs, but the dentate is single. The central white substance passes toward the lateral angles of the sinus rhomboideus in three prolongations on each side. They are the cerebellar peduncles. The superior cerebellar peduncles go forward, and pass under the corpora quadrigemina, where they decussate with one another in the upper level of the cereliral peduncles. They end in the optic thalamus and cortex of the brain. The middle cerebral peduncles pass forward and inward to form the superficial annular fibers of the ])ons. These fibers form a true commissure between the two hemisplieres of the cerebellum; other fibers decussate in the pons to terminate in the islands of gray sub- ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 615 stance ; a last category ascends into the brain after decussating in the pons Varolii. The inferior cereheUar peduncles (corpus restiformis) pass down- ward and inward to the level of the medulla, where the fibers which form them separate into three groups: the frst form the external Fig. 275. — Section of Cerebellum of Man Treated by Golgi Method. { SOBOTTA. ) gl, Glia cells of stratum cinereum. A'c, Basket cells, kk::, Small granular cells. Rz, Small cortical cells, sic, Stratum cinereum. stg)-, Stratum granulosum. arcuaie fibers of the medulhi ; the second are thrown in to the post- pyramidal bodies (nuclei of Coll and Burdach) ; the third are pro- longed directly into the cord under the name of direct cerebellar tract. The cortex of the cerebellum is divided into two layers: the external, or molecular layer; and the interual granular, rust-colored, or nuclear layer. The external layer is made up of two kinds of cells: star-shaped and l)asket cells. The neuraxons of tbe stellate cells enter 616 PHYSIOLOGY. Fig. 276.— Schema Showing the Origin and Course of the Fibers of the Peduncles of the Cerebellum. (Edixger.) ANATO:\IY AND PHYSIOLOGY OF NERVOUS SYSTEM. 617 the upper part of the molecular, or external, layer, forming a net- work of fibers. The basket cells have their dendrons extending into the inner part of the molecular layer, while their neuraxons arborize in a tuftlike manner, forming a '^basket-work" about the cells of Purkinje. The internal layer is made up of multipolar cells whose neuraxons form the horizontal fibers in the external, or molecular, layer. These horizontal fibers divide in a T-shaped manner, arbor- izing about the dendrons of the cells of Purkinje. In the granular layer there are relatively large cells known as the cells of Golgi; their neuraxons end in the nuclear layer, while their dendrons lie in the molecular laypr. Between the external and the internal layers we have the cells of Purkinje. which are supposed to be the cells concerned in the pres- ervation of equilibrium. The dendrons of the Purkinje cells occupy the chief part of the external layer, and have little, clublike projec- tions on them. The neuraxons of the Purkinje cells go into the in- ternal layer, enter the external layer, and arborize al)out the dendrons of the cells of the latter layer. From the white nuitter come fibers, perhaps from the spinal cord, which on entering the granular and molecular layers have at their terminations irregular thickenings; hence called moss- fibers by Cajal, who believes that they conduct impulses to the granular cells. Another kind of fiber from the white matter, perhaps from the spinal cord, goes through the granular layer into the molecular layer, and, like a climbing plant, clings around the dendrons of the cells of Purkinje. and is called the tendril fiber. Foster ho'ds that impulses from the spinal cord or other parts pass along the tendril fibers to the dendrons of the Purkinje cells and by their neuraxons away from the cerebellum to other parts. But other impulses may be carried by the moss-fibers to the cells of the nuclear layer. From here the impulse would be carried to the mole- cular layer and spread along the bifurcating fibrils a long distance, which would carry them to the dendrons of the Purkinje cells. At the same time the arborizations of the just-mentioned bifurcating fibrils running in a longitudinal direction about the basket cells would affect the Purkinje cells in an indirect manner, and. since the neuraxon of each basket cell bears baskets for several Purkinje cells, a number of these Purkinje cells would be "associated" in the same event. The cerebellum has a threefold grasp on the cerebro-spinal axis: 1. By the direct cerebellar tract and the vestibulo-spinal tract; by the restiform bodies and inferior cerebellar peduncles. 2. By the middle 618 PHYSIOLOGY. cerebellar peduncles connecting the nuclei of the pons and indirectly by these nuclei with the frontal lobes. 3. By the superior cerebellar peduncles where the corpus dentatum is connected with the red nucleus and where the cerebellum is connected with the nuclei of y^: Fig. 277. — Connections of the Cerebellum with Cerebrinn, Pons, and 8pinal Cord. (Schema of Charpy. ) (Mokat. ) 1, Red nucleus. 2, Superior peduncle. 3, Path from cortex to pons. 4, Middle peduncle. 5, Pontal nucleus. 6, Inferior peduncle. 7, Olive. 8, Goll and Burdach. 9, Column of Clarke. 10, Anterior horn. the optic thalamus, and through new neuraxons of the optic thalamus to the parietal, ascending frontal, and ascending parietal of the opposite side. In the red nucleus we have a point of union for im- pulses from the cerebellum on one side, and from the cerebrum on the other side. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 619 PHYSIOLOGY OF THE CEREBELLUM AND MESENCEPHALON. Cerebellum. — Mechanical irritation applied to the cortical sub- stance of the cerebellum does not cause the animal to cry out nor are contractions of his members provoked. Even a prick or a wound that IS not very deep in the cerebellar cortex does not cause any noticeable or constant disturbances, particularly in movements. More often the only movements are those of the ocular globes. However, a deep lesion of the cerebellum — a large compression, a tumor, haemorrhage, the removal of all or a large portion of the cerebellum — determines a peculiar ataxia which shows the loss of equilibration. The animal, desiring to move, shows great uncertainty, irregularity, and want of coordination of movement. Often when it wishes to take some steps, it falls backward, slipping with the feet foremost. Fig. 278. — Effects of Ri'iuoval of Cerebellum. (Daltox.) The experiment succeeds best in birds. After removal of the cerebellum they can no longer keep their balance. This is known as cerebellar tottering. Sometimes after several efforts they succeed in remaining upon their feet for a little while, but they soon fall and always in a particular manner. They slip either with the feet spread wide apart laterally, so as to touch the ground with the breast, or else, slipping with the legs extended forward, they support themselves with the wings behind. The head is folded with more or less twisting upon the back. When these animals continue to live for some time with such a lesion they end by presenting characteristic obstructions with the feet, especially in the disposal of the toes. A man with deep lesions of the cerebellum has very noticeably disordered movements in walking and standing erect. He cannot bal- lance himself well. While walking he appears like one who is drunk. 620 PHYSIOLOGY. He suffers intense vertigo, with loss of balance, which renders all wfliis movements ataxic. This is especially so of motions of locoir«otion. From this it would seem that the cerebellum is the center of the coordination of movements. With the cerebellum destroyed, the ani- mal can no longer balance itself. Atrophy of one cereljellar hemi- sphere follows atrophy of the opposite cerebral hemisphere, showing a close relation between them. The function of equilil)ration is regulated by the cerebellum, which receives afferent impulses as follows: — 1. Tactile impressions by the posterior columns to the nuclei of Goll and Burdach and from them by the restiform body to the cere- bellum. To prove that tactile impressions are necessary to coordina- tion it is simply necessary to remove the skin from a frog, when it will not be able to leap, swim, or resume its natural position when placed on its back. Jn locomotor ataxia, where we have a sclerosis of the posterior colunms, there is great difficulty in walking. 2. Visual impressions by optic nerve conveyed by the superior cerebellar peduncle. Ataxics are able to walk much better when they fix their eyes on the ground, and when they close their eyes walking becomes impossible. 3. Muscular-sense impulse through the direct cerebellar tract by the restiform body to the vermis. 4. Impressions from the semicircular canals, which will be con- sidered under the "Semicircular Canals." Here the vestibular nerve carries impressions from the semicircular canals by the restiform body to the nucleus fastigii and nucleus globosus of the cerebellum. Horsley has shown that the cortex cerebelli is the afferent recipient organ, and that the cerebellar nuclei and the paracerebellar or bulbar nuclei are the efferent mechanisms of the cerebellum. The cortex cerebelli sends no direct axons via the cerebellar peduncles to the brain or spinal cord. The cortical efferent axons terminate in the intrinsic nuclei of the cerebellum, that is, the nucleus den- tatus, nucleus fastigii, and nucleus emboliformis vel globosus. These intrinsic nuclei send efferent axons to the cerebral, spinal, and paracerel)ellar, that is, bulbar nuclei. Efferent Tracts of the Cerebellum. — An efferent tract from the cerebellum may be as follows: the fibers of the superior pedun- cles end in the red nucleus ; the rubro-spinal tract runs from the red nucleus, decussates, passes through the medulla and pons, enters the lateral column, and terminates around the cells of the anterior horns. It is also known as Monakow's bundle. Another efferent tract may ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 621 be tlie vestibulo-spinal tract. The nucleus fastigii of the cerebellum has neuraxons passing down to the vestibular nucleus, which is con- nected with Deiters, and these nuclei send neuraxons down the antero- lateral columns to end in the anterior horns. In addition to the tottering walk and vertigo, deep lesions of the cerebellum in man produce a tendency to vomiting. This is probably due to the irritation which spreads to the center of the origin of the vagus nerve in the underlying medulla oblongata. Sometimes there is found a disposition to dyspnoea and syncope for the same reason. Frequently there are changes in the organ of sight, as amaurosis, strabismus, and astigmatism. Middle Peduncles. — Deep lesion of the middle peduncles of the cerebellum (those which pass to the pons Varolii), if made upon one side only, produces in the animal a tendency to turn or rotate upon the principal axis of its body. If the lesion occur in the pos- terior part of the peduncle the rotation is toward the side where the peduncle is cut. The animal may make as many as sixty or more revolutions per minute. The rotation will be toward the opposite side when the anterior portion of the peduncle has been injured. This rotation is explained by Schiff, who admits paralysis of the rotary muscles of the head and one side of the spinal colum. Cutting the middle cerebral peduncle brings on internal strabis- mus in the eye on the side operated upon, but external superior stra- bismus in the eye upon the opposite side. Lesion of the inferior peduncle of the cerebellum or of the bulb becomes painful. Also the animal falls upon the opposite side and is unable to keep itself erect. The animal's body is curved in the form of an arch toward the side of the lesion. Lesion of the superior peduncle does not give characteristic and precise phenomena. The Pons. — The pons represents a crossed way of conductibility between the periphery of the body and the brain, and vice versa. Besides it is a coordinating center of the actions that pass through. The pons Varolii, at its anterior surface, shows itself to be but very little or not at all irritable. Posteriorly, there are signs of great pain and agitation in the animal under stimulation. Deep irritation causes convulsions and pains according to the kind of fibers irritated. The facial nerve is often found paralyzed upon the same side as the lesion and so opposite to the paralysis of the members and trunk. This condition is spoken of as alternate hemiplegia. The pons Varolii is the center of epileptiform convulsions. Deep 622 PHYSIOLOGY. irritation with electricity to the suhstance of the pons causes general cpilej)tiform movements in the animal, Nothnagcl, by irritating with the needle, has defined the limits of the spasmodic territory, or region of cravips. This convulsive center is irritated by excess of CO2 in the blood, or else by absence of the proper proportion of oxygen. Oil of absinthe is cajiahle of irritating this center. Cerebral Peduncles. — The cerebral 'peduncles contain all of the fibers of sensation and motion in the body and direct them (except a few) toward the large ganglia at the base of the brain. Stimulation of a peduncle produces pain and contractions in the opposite half of the body; section or deep lesion from disease produces paralysis and anaesthesia in the opposite half of the body. The cerebral peduncles, therefore, carry: (1) the voluntary exci- tations to the nerves of motion and so to the muscles; and (2) the sensitive impressions made upon the peripheral extremities of the centripetal nerves up to the brain. I have found in the cat that mechanical irritation of the locus niger will cause the bladder to contract, indicating a high detrusor center. Mechanical irritation of any part of the brain in front of this point has no effect on the bladder. In the greater number of unilateral lesions of the cerebral pe- duncle the so-called movement in a circle is oljserved. That is, the animal walks or flies, but always follows the curve of circumference. This is usually to the side opposite the lesion. Corpora Quadrigemina. — In man atrophy of the opposite anterior quadrigeminal body follows removal of an eye. The anterior quad- rigemina are also centers for the reflex movements of the iris. As the student already knows, the pupil contracts in the presence of strong light, but enlarges in a faint light or darkness. If the anterior quad- rigeminal bodies be destroyed, the pupil remains immovable and dilated even in the presence of a strong light. Besides these functions for the eye, the quadrigeminal bodies are believed to serve other reflex actions. The posterior quadrigeminal bodies are pathways of auditory fibers. They are also regarded as centers of coordination of movements; their destruction is accom- panied by disturbances of motility. Physiology of the Optic Thalami and Striated Bodies. The optic thalami, if deeply stimulated or injured, appear to be but slightly irritable and little or not at all sensitive. The animal has shocks or shrinkings. but does not cry out. A deep lesion, made ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 623 in the posterior third of the optic thalamus, determines in the animal movements in a circle from the injured side toward the sound side. If, however, the lesion be made in the anterior part of the thalamus, the circular movement is reversed. Opinion seems to be divided as to the effect produced by lesion of the optic thalamus upon the visual function. It is eonchuled, how- ever, that the surface of the thalamus (in conjunction witli the cor- pora quadrigemina) presides over sight. In addition to the functions just mentioned, the optic thalami have an influence upon the sensibility of the opposite side of the body. That is, not conscious sensibility, but that tactile and muscular sensi- bility necessary for the execution of extended and coordinate move- ments. This is especially so for locomotion without the aid of the will. These movements, then, are none else than reflex. They re- spond to the impressions nuide upon the sensory surface of the body and reflected in the large, excitomotor centers, viz., the thalami. The thalami are relay centers for the sensory tract. Thus, while a normal individual walks along a clear street, per- haps he thinks of his movements but once. During that short time his ivUl directs his volitional impulses; the rest of his walk, on the contrary, is executed almost automatically. In this case the excita- tions take their departure from impressions upon the body by the ground, space, weight of the body, etc. These impressions are all summed up in the optic thalami, from which they return, coordinated, along the nerves of motion. When the striated bodies are irritated they do not provoke any signs of pain. Though the animal remains relatively quiet under ablation of the hemispheres, yet it is seized with violent and con- vulsive contractions in the opposite half of the body when the striated body is hardly reached. This response is especially marked in the lenticulo-striate part of the internal capsule. By stimulating a striated body with electricity, tetanus in the opposite half of the body has been obtained. The corpora striata are motor relay centers. They also contain a thermogenic center. Experimental Physiology of Cerebral Hemispheres. There are two great means that experimental physiology has at its disposal, viz.: stimulation (electrical, mechanical, chemical, and thermal) and removal. These are likewise applied to the most im- portant and noble part of the nervous apparatus: the cerebral hemi- spheres. The experimental results are then compared with those 624 PHYSIOLOGY. observed in clinics from pathological lesions located and circumscribed in various points of tlie same hemis])lieres. Some years ago all physiologists admitted the complete inexcita- bility of the cortical substance of the cerebral hemispheres. Accord- ing to the view then held, mechanical, thermal, chemical, and elec- trical irritation of the convolutions did not determine phenomena of any kind. Abdomen ..CheoC 6 thumbs Cidaure of jam. rt ■' ■ , Opening afj&M Voc&L \ corata. MaAbiceZion Fig. 279. — The Motor Area and its Subdivisions on the Lateral Aspect of the Hemicerebrum of the Chimpanzee. (GRxmBAUM and Sherrington. ) Later, however, it was demonstrated that very slight electrical currents applied to the cerebral convolutions in dogs determined vari- ous movements in the head, limbs, eyes, etc. By this means the operator can cause the execution of various movements to suit his will, as, for example, closing the fist, extending the arm, moving the leg, eyes, face-muscles, etc. These results were best demonstrated in experiments upon apes. By experiments along this line it has become feasible to fix the seat of various cortical motor centers of the brain. In man himself experiments with electricity have been made upon the convolutions exposed for various causes. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 625 Motor and Sensory Centers. By observations upon the chimpanzee, Sherrington and Gruen- baum have shown that the motor area is in the ascending frontal (precentral) convolution and spread over its whole length. The motor area did not, at any point, extend behind the fissure of Eolando (cen- tral fissure) ; on the inner side of the brain they found the motor area extended only a short distance downward, and not to the calloso-mar- ginal fissure. In the motor area they also localized movements of the StilcCsnCral. '^"'^s St Vkgina, SuZccaUoso ^^.^-^^ Sa,to.precentr.7tuarg. SuLcparieto C? 8. dd. Fig. 280. — The IMotor Areas and Centers on the Mesial Aspect of the Hemicerebrum of the Chimpanzee. (Gruxbaum and Sherrington.) . ear, nostril, palate, movements of sucking, mastication, of the vocal cords, of the thorax, abdomen, and the sphincters. The arrangement of the representation of various regions of the muscles follows the exact segmental sequence of the cranio-spinal nerve series; thus, in front of the central fissure from below upward are, first, the center of the face ; next, centers for the upper extremity ; next, those from the trunk ; and last, for the lower extremities. Extirpation of these areas gave positive paralysis. Sherrington and Gruenbaum also found in the middle and inferior frontal convolutions a center which, when irritated, caused conjugate deviation of the eye of the oppo- site side. In accordance with these facts of Sherrington, and from his 40 626 PHYSIOLOGY. clinical experience, Dr. Mills has located the motor centers for man mainly in the ascending frontal and the paracentral convolutions. The posterior central (ascending parietal) is for tactile sensation. Muscle-sensibility is in the superior and inferior parietal convolu- tions. Stereognostic perception is located in the superior parieta.. On the mesial surface of the hemisphere he locates stereognostic per- ception in the precuneus. The center of speech is in the posterior part of inferior left frontal gyrus. CONCRtTE CONCEPT Fig. 281. — Areas and Centers of the I^ateral Aspect of tlie Human Hemicerebrum. { Mills. ) In stereognosis the form of an object is recognized l)y tactile sensibility, although the eyes are closed. The cortical motor center for writing is seated in the base of the left frontal gyrus. There is clinical evidence to substantiate the fact that disease of the left angu- lar gyrus may cause agraphia; for it must be remembered that, in order to write, it is absolutely essential to call to the mind memories of the words previously written. The center of taste and smell is in the uncus. Auditory Center. — This center is seated in the first temporal convolution and in part of the second. Complete deafness is not produced in man when there is total destruction of one center, which proves that there is only a partial decussation of the auditory jjath- ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 627 way. Irritation of the auditory centers produces movements of the ears, rotation and inclination of the head as in hearing sounds. Visual Center. — In man, the visual center is in relation with the corresponding half of each retina. The destruction of one of these centers produces a bilateral hemianopsia, and not a total loss of vision in the opposite half of the eye. The seat of the visual center is in the cuneus. The anterior part of the visual center is in rela- tion with the superior part of the retina; the posterior portion of the same center is in relation with the inferior part of the retina. Fig. 282. — Areas and Centers of the Mesial Aspect of the ±iuman Hemicerebrum. ( Mills. ) Irritation of the occipital lobes produces extensive movements of the eyes. Excitation of the occipital lobe always produces move- ments of the eyes, which are directed to the opposite side : to the left when the right occipital lobe is irritated. It is evident that the occipital lobes, whilst concerned in vision, also have efferent fibers to centers beneath the cortex. The center for the memories of objects seen is located in the right gyrus angularis. Ablation of this area produces in man mind-blindness; that is, the person fails to recall to m.ind the visual image of the appearance of an object, although fully seen. This condition must not be confounded with word-blindness, which is located in the left angular gyrus. 628 PHYSIOLOGY. Cortical Epilepsy.* — Fritsch and Hitzig observed that, through continued irritation of the cortex of the cerebrum, the animal became convulsed not only in the muscles whose centers were irritated, but in all the muscles of the body. The convulsive move- jiient always began in the muscles which were innervated by the cen- ter irritated, and then spread from this in a regular and systematic manner to the remaining muscles. For exam})le: when an animal had the left cortical center for the eyelids irritated, the convulsive movement began in the muscles of the eyelid of the opposite side, and then spread to the other facial muscles ; next, the head was bent to the right; then, first the right anterior and next the right pos- terior extremities were seized with convulsions; after this the con- vulsive movement began in the muscles of the left side and from below upwards, first the left posterior extremity, then the left anterior, and last the muscles of the left eyelid. The convulsive movements are first tonic, and then they become clonic aiul the ani- mal becomes sleepy. If an injury is produced in the motor area and the animal lives, then a spontaneous epilepsy can ensue with cortical irritation. In the cortex of man similar results ensue from an irritation of the motor centers, except that the man usually feels conscious of the attacks in the beginning of the fit and takes care that he shall not be injured by the attack. Cortical epilepsy can ensue from irritation of other convolutions than the motor, but these convolutions must be in a physiological association with the motor centers. The spread of the convulsive movements to different muscles can take place even after extirpation of the opposite motor area. If the motor area of a defined group of muscles is extirpated, and on an adjacent motor area another group of muscles are convulsed by an irritation, then these convul- sions spread to the muscles whose motor area has been extirpated. Hence the irritation can spread to the subcortical centers and cause general convulsions, even when the original motor center which has caused the convulsions is extirpated. Extirpation of the Motor Area.* — When in a dog the motor area of one hemisphere has been extirpated completely or in part, then shortly after the operation there are considerable disturbances of the movements of the opposite side. But soon the animal is able to move the muscles of the opposite side, and after a time the mus- ^ Tigei'sted's "Physiolog\'" has been drawn upon for the data. ANATOMY AXU PHVSlOi.OGY OF NERVOUS SYSTEM. (509 cular disturbance near!}* entirely disappears, except the regulation of the finer muscular movements. Quite otherwise is the result when you extirpate the motor area in apes. If you remove the whole motor area in a monkey there is a nearly complete paralysis of the muscles of arm and face, and a weakness of the muscles of the pos- terior extremity. There is also difficulty in moving the head to the opposite side. The weakness of the posterior extremity is not so great but that the animal can use it in walking or climbing. If in an ape only the motor area of the finger is extirpated, then a permanent weakness in these muscles innervated by this area re- mains, whilst the other muscles are not affected. The result of irritation and extirpation of the cortex in the ape confirms the fact that irritation of a certain motor area always calls out movements of certain muscles, Avhilst extirpation of the same motor center is followed by a paralysis or weakness of the same muscles. The motor area in the ape is much more important in the muscular movements of the body than the motor area in the dog. The subcortical cen- ters in the dog are not so much under the domination of the activity of the motor centers of the cortex as the subcortical centers in the monkey. The motor centers in man have been established (1) by irritation of the cortex, (2) by anatomical investigations, and (3) by clinical studies and pathological anatomy. The motor area in man has about the same extent as in the ape. Flechsig's Association Areas. Flechsig, from a study of sections of 56 human brains, has divided the cerebral cortex into 36 areas, of which 13 are myelinated before birth. He was able to determine these areas by the fact that in the cerebral cortex the fibers take on myelin at different periods, and thus he is enabled to track the fibers. The sensory tracts of the central nervous system take on myelin before birth. The motor tract receives its myelin after birth, but in the spinal nerve roots the anterior are myelinated before the posterior. The first areas to become myelinated are the sense areas — smell, touch, muscle-sense, sight, hearing, and taste. The next series of centers to become medullated have at first only fibers within themselves — that is, neither projection fibers nor association fibers — and Flechsig denom- inates them automatic centers whose function is unknown. The rest of the areas have association bands, and it is most interesting to note that the earlier areas of this group develop as marginal zones around the primary sensory areas and first receive short fibers from 630 PHYSIOLOGY. them. They are without doubt connected with sensory areas in function. The six sense areas in the cortex, namely, those of smell, touch, muscle-sense, sight, taste, and hearing, are proportional in size to the nerve or nerves supplying them. For example, the tactile and muscle sense area is greatest, while the visual area is larger than the auditory. The structure of each area corresponds to the struc- ture of the sense organ. Thus the visual area has many layers of cells, thus corresponding to the many layers in the retina. The olfactory area has the fewest layers, thus being in agreement with Fig. 283. — Lateral View of a Human Hemisphere, Showing the Bundles of Association Fibers. (Starr.) A, A, Between adjacent gyri. B, Between frontal and occipital areas. 0, Between frontal and tempora,l areas, cingulum. D, Between frontal and temporal areas, fasciculus uncinatus. E, Between occipital and temporal areas, fasciculus longitudinalis inferior. C, N, Caudate nucleus. O, T, Optic thalamus. the cells of the olfactory mucous membrane. The area for hearing in the cortex is twice as thick there as in the rest of the temporal convolution. Hence each area is to be considered as a repetition, in the cortex, of a peripheral sense organ. Flechsig suggests the name of projection fields for the seven primary sense areas. As to the great sense area for touch and muscle sense, it is found that the sensory paths for the legs are the first to reach the cortex, and end in the paracentral lobule at the upper third of the ascend- ing parietal convolution, extending on to the posterior surface of ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 631 the ascending frontal convolution. The corresponding motor tract develops from the area of large pyramidal cells in the ascending frontal convolution. Thus the sensory and motor areas in the brain are not mixed, except in the fissure of Rolando. The experiments of Sherrington and Grlinbaum on the chim- panzee are in accord with the results of Flechsig. They found the motor centers to be in the ascending frontal convolution, separate from the sensory centers of touch and muscle-sense in the ascend- ing parietal convolution. Around each primary sense area develops a border zone of association centers. Only about one-third of the brain is composed of sensory and motor areas; the question arises, '"What is the function of the other two-thirds?" The fibers going to the latent, inexcitable area of the brain take on myelin much later than those of the excitable area. The fibers in this latent area do not run downward like the projec- tion fibers, but run in a more or less longitudinal direction, and are known as internuncial or association fibers; they are of both a cen- trifugal and centripetal nature. These internuncial fibers connect the latent cortex with the excitable cortex. According to Flechsig there are three association centers: (1) the frontal, (2) the parieto- occipito-tcmporal, and (3) the insular. These centers are centers to receive impressions, and are the seat of memory. The internuncial fibers are: (1) the superior longitudinal bundle uniting the Eolandic and parieto-occip'tal region; {2) the perpendicular bundle passing between the parietal lobule and the temporo-occipital region; (3) the anterior association bundle connecting the frontal and temporal lobes and traversing the bottom of the sylvian fissure; and (4) the inferior association bundle uniting the temporal and occipital lobes. The frontal association center is in front of the ascending frontal convolution ; the insular, or middle, association center is the cortex of the island of Eeil ; whilst the parieto-occipito-temporal associa- tion center is situated back of the ascending parietal convolution. The anterior association center, or frontal, is made up of the anterior half of the first and a great part of the second frontal con- volution. The middle association center or insular is covered by the insula, whilst the posterior or parieto-occipito-temporal is made up of the pra^cuneus, the parietal convolution, the second and third temporal, and the anterior part of all three occipital s. Disease of the anterior association center, as in idiocy and dementia, changes the character; a man of good and orderly habits becomes irritable and disorderly, and loses his sense of morality; there is a loss of 632 niYsiOLOGY. ideas regarding his own personality, and his relations to what is tak- ing place inside and outside his body. He considers himself enor- mously wealthy, or a genius, or he iiuiy fail to I'eeognize liis own sur- roundings, and perform acts not reconcilable; in other words, he is like one with paresis. When disease attacks the posterior associa- tion centers he is unahle to name correctly objects which he can touch and see, or, if both centers are affected, he may not at all recognize the nature of these objects, so that he loses the power of forming intelligent conceptions of the world around him. He is bankrupt in ideas, although his affections may not be altered. In other words, he has what is called mind-blindness. The posterior association center is highly developed in musicians. PHENOMENA FOLLOWING THE DESTRUCTION OF ONE OR BOTH OF THE CEREBRAL HEMISPHERES. Ablation of the cerebral hemispheres is generally performed in frogs or fowls, who seem to endure the operation sufficiently well. Mammals easily succumb. The skin of the head being cut and the thin cap of the skull removed, the brain is reached. The incision of the meninges is pain- ful, but, after gradually removing the mass of the hemispheres from above downward, the bird shows itself indifferent. In fact, it be- comes more stupid and apathetic as more of the cerebral tissue is removed. When the removal of the hemispheres is completed without injuring the peduncular system, with its ganglia, and the haemorrhage stopped as well as possible, the bird remains in a sleepy state. It has a tendency to bury its head and close its eyes ; it breathes slowly, but does not walk away. Under stimulation the bird reopens its eyes, raises its head, takes a few steps, then suddenly returns to its former position. The bird, having recovered from its traumatism, the following phenomena are observed within a few days : The bird has become an automaton. It does not eat, so that it becomes necessary to put the food into its mouth. It moves not at all of its own volition; if pur- sued it takes some steps; its pupils contract under the influence of the light; it cries or tries to flee when the skin is irritated. It is startled by loud noises. For the rest there are no longer voluntary movements, and the few movements observed are aroused by external excitement, or some internal need. The movements are rubbing the skin with the beak, scratching the head with the foot, etc. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. (533 The vegetative functions (once that eare is taken to nourish the birds and clean them) are performed without disturbances. If the bird lives for some time it shows a general deposit of fat. The skin and musck's in particular are seen to be infiltrated with adipose tissue. In these birds there are only movements of a reflex nature. Sensibility is blunted since the stimuli arc not able to reach the cortical centers. Hence, they cannot provoke volitional acts in them. As Kiiss says, these birds live, but do not perceive; they hear, but do not listen; they are aware of stimuli upon the tongue, but do not taste them. They are just as a human being who is asleep or absorbed in contemplation. He may drive a fly from the face without being conscious of it. Fig. 284. — Effects of Ablation of Cerebrum. (Dalton.) When hut one cerebral hemisphere is removed without in the least injuring the other and the animal recovers, it does not show positive disturbances of intelligence or of conscious sensibility or of voluntary motion. However, the opposite side shows weakness. Should the lesion extend to the underlying basal ganglia or to the peduncular system, there will be complete hemiplegia in the opposite side of the body. The same manifestations are observed in a man who has lost an entire hemisphere from a wound or from disease. There is no posi- tive lesion of intelligence, but there is manifested very marked fatigue from intellectual labors. If the lesion has extended toward the peduncular base of the hemisphere, there is hemiplegia in the oppo- site side of the body. The crowbar case is a much-cited instance. A workman twenty- five years of age was engaged in charging a blast in a rock. The instrument he used was a sharp-pointed bar, forty inches long, one and one-quarter inches in diameter and weighing twelve pounds. The g34 PHYSIOLOGY. charge was suddenly exploded, driving the bar so that it entered the man's lower jaw and came out at the top of the head close to the sagittal suture in the frontal region. It fell at some distance, covered with blood and brains. For the moment the victim remained uncon- scious. An hour after the accident he walked to the house of a sur- geon, where he gave an intelligent account of the accident. For a long time his life was despaired of, but he finally recovered to live twelve and one-half years longer. It may be concluded, therefore, that one cerebral hemisphere only is sufficient for the mobility and sensibility of the two sides of the body, as well as the performance of psychical functions. The indi- vidual with one hemisphere destroyed remains like one who has lost an eye. That is to say, the brain continues to perform its functions, ani- mal as well as psychical, but with noticeahle weahness. greater effort, and fatigue. The frontal lobes are the chief seat of the will, of the memory, and intellectual functions. The irritahility of the cerebral cortex may be diminished or ex- aggerated by various circumstances. Thus, opium, ether, chloroform, chloral, the bromides, cold, asphyxia, etc., diminish it. Inflamma- tion, urea, uric acid, atropine, strychnine, etc., increase its excita- bility. Action of Brain Extracts. — In 1898 I found that infusions of dried brain reduced the heart's frequency and the arterial tension. Section of the vagus or its paralysis by atropine did not prevent this action. Halliburton did not obtain the same results after the use of atropine, but my experiments have been confirmed by Swale Vincent and Sheen. Quite recently Swale Vincent and Cramer have found two substances in brain, both depressing the heart even after the previous use of atropine. They also obtained another substance depressing the circulation, but its effects are abolished by atropine. SLEEP. Sleep is characterized by a suspension of consciousness, a dim- inution of reflex activity of the nerve-centers, a decrease of the excitability of the nerves, and a lessening in all the chief functions of the body. The activity of the cerebral motor centers is nearly sus- pended in the majority of animals as they seek a reclining position. In extreme fatigue sleep is preceded by yawns, a want of atten- tion, a decrease of sensibility in the special senses, a progressive loss of movement, and a dropping of the upper eyelids. The eyes are closed, vision is necessarily then abolished. The pupil is contracted. ANATOMY AND PHYWIOLOGY OF NERVOUS SYSTEM. 635 the eyeball is turned upward and inward ; at the same time hearing disappears and consciousness vanishes. During sleep the metabolic processes of nutrition are slowed, and there is a diminution of the heart-beats, of the arterial tension, and of the movements of respira- tion. Sleep is deepest during the first one and one-half hours; after that its depth greatly diminishes. Durham was the first to show that during sleep the brain is anemic, but it is only an epiphenomenon, and not the cause of sleep. Plethysmographic tests of the arm in a sleeping person show a decrease of volume whenever the subject is disturbed, although the noise may not be sufficient to wake him. Fig. 285. — Curve of the Depth of Sleep. (Piesbergen.) (From Tigerstedt's "Human Pliysiology," copyright, 1906, by D. Appleton and Company. ) Read from left to right. This means that the brain is anemic during sleep, and that the blood-supply of the brain is increased upon waking. The histological theory of Demoor is that during sleep the den- drons are retracted and break the connections between the dendrons and arborizations which are necessary for the action of the nerve- centers, Demoor found that in deep anesthesia there were moniliform varicosities on the dendrons. The chemical theory is that during wakefulness certain fatigue-products (lactic acid, etc.) are generated, which have a somnolent effect upon the brain. If the blood of an exhausted dog is transfused into a dog awake, it will cause him to be fatigued. It is probable that the fatigue of the brain-cells, the law of periodicity of the action of the nerve centers, and a decrease of external stimuli are the main causes of sleep. The intimate cause is not known. 636 PHYSIOLOCY. That the absence of sensory impulse has an important action in promoting sleep is shown by the case of a boy who had only one eye and one ear to keep him in touch with the external world. All other avenues of sensory impulses were abolished. If now, these avenues of impulse were abolished by bandaging the ear and eye, the boy would fall asleep. If a dog is kept awake five days he will die. This wake- -k.--i-:i> Fig. 286. — Pyramidal Cells of the Marmot in Two Difl'erent Conditions. (After QuERTON.) On the left, pyramidal cell of the marmot asleep; on the right, that of the marmot awake. fulness is attended with a lowering of temperature (8° C). dimin- ished reflex activity, and changes in the brain. In man, loss of sleep causes a slight increase in weight. The excretion of nitrogen, and especially that of phosphoric acid, is increased by the want of sleep ; acuteness of vision is also increased. But when the man is permitted to make up for this loss of sleep, there is a complete disappearance of the just-mentioned conditions and a normal state ensues. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 637 NARCOTICS. Meyer and Overton have arrived at the conchision that anggsthesia is caused by the solution of the lipoid (fatty) constitiients of the cells by the absorbed anaesthetic. All the . substances which dissolve fats are anesthetics if they enter the cell, and anaesthetic power is proportional to this factor. The quick recovery which ensues when the anesthetic substances are removed shows that the lipoids are not taken out of the cell, but' merely dissolved within the cell. Wright finds that anaesthetics produce a disappearance of Nissl corpuscles and a shrinkage of the nerve-cells after prolonged anesthesia by either chloroform or ether. Bromides and opium produce sleep by depressing the excitability 01 the cortex cells of the cerebrum. CEREBRO=SPINAL FLUID. The cerebro-spinal fluid is like a lymph-fluid. It is only in the smallest part a transudate, and as such is modified through the specific secretion of the capillaries of the brain. It is chiefly a specific pro- duct of the braiu. It has been shown that this fluid contains 20 to 30 per cent, of potash salts and only 15 per cent, of soda salts, and the brain has also an excess of potash compared with sodium. Spina believes that the cerebro-spinal fluid comes either from its blood- vessels or the brain-substance, and not only from its choroid plexus. It differs from the blood-plasma in containing only 0.2 per cent, of albumin, whilst blood contains 7 per cent, and Ij'mph 4.5 per cent, of albumin. Cerebro-spinal fluid does not contain, like the blood, an agglutinin (it has no globucidal action on foreign blood), nor an alexin. According to Allihin, it contains 0.0461 per cent, of glucose, 0.221 per cent, of proteid, 0.2794 per cent, of organic material, 0.813 per cent, of inorganic, 98.886 per cent, of water; peptones and albumoses were not present, and the proteid seemed to be a globulin. The cerebro-spinal fluid of diseased brains contains poisonous material, which results from a disintegration of nervous tissues. In general paralysis of the insane, Halliburton and IMott found a nucleo- proteid in the cerebro-spinal fluid. It is a nucleo-proteid, which, when injected into the circulation, can cause intravascular clotting. The cerebro-spinal fluid and the blood also contain choline, which depresses the heart. Ponath injected choline into the sensori-motor convolution and produced convulsive attacks. Choline is also found in other diseases of the central nervous svstem. 638 PHYSIOLOGY. Ether and pilocarpin increase flow of cerebro-spinal fluid, whilst atropine slows it, and aniyl nitrite has no particular effect. Medi- cines, as a rule, and the toxins of bacteria, do not appear in the cerebro-spinal fluid when given by the mouth or subcutaneously. Strychnia injected into the cerebro-spinal fluid has a very intense action, as much as when ten times that quantity is injected into the blood. Cocaine injected into the cerebro-spinal fluid causes an anaes- thesia in the lower extremities, lasting forty-five minutes. Whilst chemical substances with difficulty appear in the lymph when in- jected into the blood, they appear quite readily in the blood when injected into the lymph-tracts. REACTION=TIME. When a terminal organ of special sense is irritated, the time between this stimulation and the moment when motion ensues as the result of conscious perception of the irritation is called reaction-time. Midler's law of specific energy of sensory nerves is that irritation of nerves of special sense always causes sensations of the same kind. Thus, when the nerve of hearing is irritated by different agents, it always gives rise to a sensation of sound. Perception-time is the time required, for example, in colors, to decide what color it is and in what part of the visual field it is located. The organs of special sense dift'er from each other as to the number of separate excitations that they can receive in a second. In reaction-time by the auditory nerve the following things are involved: (1) the time consumed in sound reaching the ear; (2) the time taken for the reception of the stimulus by the sensory terminals of the auditory nerve and the transmission to the higher centers, so that volitional impulse may be started in the cerebral motor centers; (3) the time for the convey- ance of those motor impulses to the nerve-colls of tbe spinal cord ; (4) the time necessary for the generation of impulses in the cells and their transit down the motor nerves to the muscles of the hand ; (5) the latent period of the contraction of those muscles. The reaction- time for sound is about 0.150 second; light, 0.195 second; and for touch, 0.145 second. Perception-time varies from about .01 to .02 second. THE GREAT SYMPATHETIC. The ganglia lying on each side of the vertebral column may be divided into four parts, viz. : cervical, thoracic, abdominal, and pelvic. The cervical part of the great sympathetic is composed of three ganglia. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 539 The thoracic portion is composed of twelve ganglia. The abdominal, or lumbar, part consists of four ganglia. The pelvic portion consists of five or six ganglia, including the coccygeal ganglion. Two structures only finally receive the sympathetic fibers; that is, involuntary muscular tissue and secretory epithelium. SYMPATHETIC NERVOUS SYSTEM. The ganglia lying on each side of the vertebral column are lateral or vertebral ganglia. The prevertebral collateral ganglia are the ganglia in advance of the vertebra, as the semilunar, inferior mesenteric, etc. From the prevertebral ganglia, nerves go to the terminal ganglia in the tissues. The efferent fibers of the sympathetic nervous system arise in the intermedio-lateral column of gray cells. They pass out by the anterior root from the spinal cord. From here they go by the white ramus to a sympathetic ganglion. From the sympathetic ganglion they may pass in two directions: (1) they may form synapses about these cells, and from these cells new axons (postganglionic fibers) may arise and pass outwards in the visceral nerves, or back, through the gray ramus connected to the ganglion, into the spinal or somatic nerve to the blood-vessels as vasomotor nerves, or sweat- glands as secretory nerves, or to hairs as pilomotor nerves; (2) or they may pass through the ganglion on to one situated more towards the periphery, in which they form synapses and are continued onward by new axons. These ganglia from which they do not pass back to somatic nerves are called the prevertebral or collateral gan- glia. These nervous fibers, after their interruption, proceed as gray nonmedullated fibers to their termination, where they break up into a network of anastomosing fibers, with cells or a sort of terminal ganglion. When sympathetic nerve-fibers are interrupted in a gan- glion, the fibers, before they meet the ganglia, are preganglionic; after they leave the ganglion, postganglionic. The number of nerves leaving a ganglion is greater than the number of nerves entering it. If the sympathetic fibers pass through the vertebral ganglia to be interrupted in the prevertebral ganglia, then they are preganglionic, and the fibers leaving the prevertebral ganglia are postganglonic. By nicotine it can be determined if fibers end in a ganglion or pass through it, for nicotine paralyzes the preganglionic terminals of the nerve-cells of a ganglion, or, according to Langley, a special recep- tive substance in the nerve-cell. 640 PIlY!SlUL(HiV. Langley calls the sympathetic system an autonomic system, because it is a sort of independent system from the central nervous system. Midbrain autonomic. Bulbar autonomic. ■Sympathelic. ITh. to 11 or 111 L. of mail •Sacral autouomic. Fig. 287. — Diagram of the Origin, in Man, of the Efferent Autonomic Fibers from the Central Nervous System. (Langley.) The sympathetic system proper arises from the dorso-lumbar cord. The cranial and sacral autonomic systems have more in common with one another than either has with the sympathetic, and on this account they may be grouped together as the parasympathetic sys- tem. The parasympathetic system includes the midbrain autonomic ANATOMY AND PHYSIOLOGY OF .NERVOUS SYSTEM. (341 — bulbar autonomic — and sacral autonomic systems. The fibers from the midbrain arise in it, and go out in the third nerve and by the short ciliary nerves to the sphincter of the iris and the ciliary muscles, and cause their contraction. The fibers arising in the bulb travel through the facial, glosso-pharyngeal, vagus, and the spinal accessory. Cranial Ganglia. The ciliary ganglion of the fifth cranial nerve has preganglionic sympathetic fibers from the motor oculi by a short root which arborize about the ganglionic cells and when irritated contract the pupil. The postganglionic fibers of this ganglion start from the superior cervical ganglion through fhe ciliary ganglion to contract the blood-vessels of the iris and retina. Caw'tra'l niert^e cell. Fig. 288. (Langley.) The number of fibers leaving a ganglion is greater than the number of fibers entering it. This is due to the fact that the preganglionic fibers divide. The spheno-palatine ganglion of the fifth cranial nerve obtains its preganglionic fibers from the facial. Its nerve-cells send post- gansiionic fibers to the Ijlood-vessels and glands of the mouth and nose. Stimulation of this ganglion dilates the blood-vessels and aug- ments secretion. The otic ganglion of the fifth cranial nerve obtains its pre- ganglionic fibers from the ninth nerve by the pathway of Jacobson"s nerve and the small petrosal. The postganglionic fibers run in the auriculo-temporal of the fifth, to increase the secretion of the parotid gland and to dilate the blood-vessels. The submaxillary and the sublingual ganglia acquire their pre- ganglionic fibers from the chorda tympani of tlie facial. Their post- (^anglionic fibers dilate the blood-vessels and increase the secretions of these glands. 642 PHYSIOLOGY. As to the bulbar origin, tlic autonomic efferent fibers of the vagus end in the cardiac ganglia, from which postganglionic fibers run to the cardiac muscle. In its course the vagus meets small groups of nerve-cells in the lungs, the external wall of the ceso- pliagus, and the stomach. The vagus sends many fibers to the (enteric nervous system) Meissner-Auerbach ganglia in the stomach, furnishing secretory nerves to the stomach and pancreas; and the number of its fibers in its downward course to the intestine diminish, and are completely absent in the descending colon. The Ijulbar autonomic system innervates the upper part of the digestive tract, from the mouth to Mau*^ f\ 3r ^^^^^^^''^ ^'^^onointc SipnpcJhetiC Sacral /lutoruiTm^ Fig. 289. — Diagram of the Main Distribution of the Bulbar and Sacral Autonomic Fibers. (Langley. ) The bulbar fibers supply the anterior end of alimentary canal and the sali- vary glands. The sacral fibers supply the posterior end of the alimentary canal and the external generative organs. The sympathetic supplies the whole tract and also the skin and the internal generative organs which receive no involun- tary fibers from any other source. the descending colon, and the cavities and organs in connection, as the salivary glands, the lungs, the liver, and the pancreas. The sacral a,utonomic nerves innervate the lower part of the digestive tract, the descending colon, anus, bladder, and, by their nervi erigentes, the external genitals. The sphincter of the iris and ciliary muscle receives no fibers from the spinal thoracic sympathetic, but only cranial autonomic nerves. The bul])ar and sacral autonomic systems are independent of the spinal thoracic sympathetic system as regards development, and are not a part of the spinal sympathetic system. A long series of fibers arise from the thoracic and upper lumbar spinal cord. These are the fibers of the sympathetic nervous system. ANATOMY AM) I'HYSIOLOGY OF ^.ERVOUS SYSTEM. G43 Fig. 290. — Diagram of tiie Great Sympathetic, Representing its Visceral Distribution. (MoRAT. ) On the right, medulla oblongata, spinal cord, and roots. In the middle, ver- tebral chain and ganglia; on the left, second chain (prevertebral) formed by the pneumogastric nerve and the mesenteric nerves, solar ple.xus and hypogastric plexus. On the extreme left, terminal ganglia and plexuses of the viscera. The break between the peripheral and deep neurons is effected either in the catenary, terminal or intermediate ganglia. Symmetrical with regard to a plane, xy, which intersects the thorax. Principal condensed origins in the thoracic region. Supplementary origins arising from the medulla oblongata (nerve of Wrisberg and pneumogastric) and from the sacral spinal cord (erector nerves). 644 PHYSIOLOCtY. & II as Fig. 291. — Diagram of tlie Great Sympathetic, Representing its Cutane- ous Distribution and its Two Orders of Fibers of Projection. On the right of the diagram, the medulla oblongata, the spinal cord and their roots; on the left the cutaneous nerves, containing those roots (chosen ANATOMY AND PHYSIOLOGY OF JMERVOUS SYSTEM. 645 The chief difference between the sympathetic and the parasym- pathetic systems is that the former sends nerve-fibers to all parts of the body, whilst the latter sends fibers only to certain parts. Accord- ing to Langley, when a tissue has a double innervation the effect pro- duced by one set of fibers is, in most cases, the opposite of the main effect produced by the other set of fibers. Thus, if one set causes mainly contraction, the other causes mainly inhibition. PosfRoot (cy^^ Oan^/ion. V ' ~J Fig. 292. — An Afferent Sympathetic Fiber. Adrenalin, when injected, produces all the effects seen from stimulating the sympathetic nerves, but does not produce any of the effect characteristic of stimulation of the parasympathetic nerves. Hence it is a test-agent for the presence of sympathetic fibers. The pilomotor nerves come from the cord, from the fourth on account of their more regularly metameric distribution) ; in the middle the ganglia of the sympathetic chain. These ganglia give off branches of distribu- tion in which join the cutaneous nerve belonging to the same metamere as the branch itself and the ganglion which has given it off. On the other hand, these ganglia receive branches of medullary origin which arise from segments of the spinal cord situated either higher or lower than the corresponding metamere. Spinal origins condensed in the thoracic region, supplementary regions in the medulla oblongata and the sacral spinal cord. Symmetrical arrangement with regard to a plane (.r;/) cutting across the middle of the thoracic region. 64G PHYSIOLOCY. tlioracic to tlic third Iiinil)ar nerves, in the eat, and are distributed to the unstri])e(l niusele about the roots of tlie hairs and cause erec- tion of them. The condition of the skin known as "goose-skin" is due to tliese nerves. Syni])athetic fil)ers, according to their distribution, can be divided into cutaneous or somatic, and visceral or splanchnic. /I rteriole of He.<^cL nerve and cfiionic fiber ghoiiic fiber etic Ga notion fhehc Ganglion. janolioTLic -^ fi rteriole Fig. 293. — Efferent Sympathetic Filler. Afferent fibers take their origin in the ganglion of the posterior root. The efferent fibers arise from the interniedio-lateral column of cells, and pass out by the anterior roots. The efferent fibers of the head and neck come from the upper five dorsal nerves, and run up in the cervical sympathetic to the superior cervical ganglion, where they have their cell station. From this ganglion the following fibers arise: — 1. Vasocontrictors. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 647 2. Pupillo-dilator to the Gasserian ganglion, in the ophthahnic branch and long ciliary nerves to dilator fibers of the iris. 3. Motor to Miiller's smooth muscle of the orbit and Tenon's capsule. 4. Secretory to sweat-glands. If you irritate the cervical portion of the sympathetic, the eye- ball is projected by a contraction of the smooth, muscular fibers of the capsule of Tenon; the pupil dilated. The recti muscles push the eyeball inward. The vasomotor nerves, constrictors, and dila- tors are in the cervical sympathetic, and when it is irritated the blood-vessels of the ear, conjunctiva, iris, tongue, epiglottis, and palate are contracted, whilst we have a dilatation of the vessels of the retina, lips, gums, and nasal mucous membrane. The cervical sympathetic also acts upon the circulation of the brain and that of the thyroid gland. Thorax. — The fibers of the thoracic organs arise from the five upper dorsal nerves, go out through the first thoracic ganglion, then go through the annulus of Vieussens to the inferior cervical ganglion. and pass to the heart and lungs, as the cardio-accelerator and the vasoconstrictors of the lungs. Abdomen. — These fibers come off from the lower six dorsal and upper three lum])ar nerves. The great splanchnic nerve is formed by branches from the fifth to the tenth thoracic ganglia, and termi- nates in the semilunar ganglion of the solar plexus and in the superior mesenteric plexus. The lesser splanchnic is formed by filaments from the tenth to eleventh thoracic ganglia, and goes to the solar and renal plexus. The splanchnic nerves are the greatest vasoconstrictor nerves in the body, and contain inhibitory fibers of the small intestines. They also contain motor fibers to the intestines. Pelvis. — The fibers for the pelvis emerge from the cord by the lower dorsal and upper four lumbar nerves, and have their cell-sta- tion in the inferior mesenteric ganglia, from which they run in the hypogastric nerves to the pelvic ganglia. They contain vasoconstric- tors, inhibit the colon, give motor-power to the bladder, uterus, and vagina. The mesenteric nerves go to the superior mesenteric ganglion, and then to the hypogastric plexus. The coeliac, the superior mesen- teric, and the hypogastric prevertebral ganglia are united amongst themselves by connections parallel to the sympathetic chain. These ganglia form in some sort a second chain anterior to that which fol- 648 PHYSIOLOGY. lows the lumbar vertebral chain. This prevertebral chain receives elements of reinforcement by two remarkable paths. The first is that of the vagus, which carries bulbar influences. The second is that path formed by the nervi erigentes, which come off from the second and third sacral nerves and, like the bulbar and midbrain nerves, do not enter the sympathetic ganglia, but go to the hypo- gastric plexus near the bladder, where the fibers have their cell-sta- tion. They are vasodilator nerves to the pelvic organs, inhibit the retractor penis, and are motor to the bladder, 'colon, and rectum. In the heart and lungs, the vagus is inhibitory and the sympa- thetic is accelerator. For the gastric and intestinal muscles the pneumogastric mainly augments, whilst the sympathetic chiefly inhibits. Arm. — These fibers come out by the fourth to tenth dorsal nerves, and send fibers to the stellate ganglion and from there pass into the spinal nerves, and go to the blood-vessels, sweat-glands, and pilomotor muscles of the skin and limb. Leg. — These fibers take origin from the eleventh dorsal to third lumbar nerves, and come out of the last two lumbar and first two sacral ganglia and go to the leg in the spinal nerves, to supply the blood-vessels and pilomotor muscles and secretory nerves. Langley regards the nerve-cells of Auerbach and Meissner's plexus of the intestinal tract (the enteric nervous system) as differ- ent, both from the sympathetic and parasympathetic system. He does not know if they are connected with the sympathetic or para- sympathetic, but doubts it. Magnus has shown that the nerve-cells of Auerbach's plexus are reflex centers for the rhythmic contractions of the intestines. Langley believes that in the intestine there are two sets of nerve-cells, one motor, the other inhibitory, both acting on the muscular tissue, the state of the muscle depending on the balance of the two forces. Afferent Fibers. — They have their cell-station in the ganglion of the posterior root. They enter the cord largely by the white rami. ISTormally, stimulation of their peripheral endings does not lead to modifications of consciousness, and is therefore not accompanied by pain. In abnormal conditions painful sensations are produced. Head has shown that the sensation of pain from visceral dis- eases is referred to certain points on the surface of the body. Thus, intestinal trouble causes pain in the skin of the back, abdomen, and loins. In stomach troubles, the pain is referred to the ensiform cartilage; in disease of the heart, to the scapular region. Here the ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 649 pain in the skin is due to the segment of the spinal cord from which the organ concerned receives its sensory fibers, there being a spread of it through the nerve-centers, and tlius causing an error in its localization. Blows on the solar plexus reflexly cause arrest of the heart. The splanchnics also have sensory nerves for the intestine, and in intestinal cram}) may give rise to extremely painful sensations. In the colic due to lead-poisoning, we have an affection of the sympa- thetic ganglia. Reflex Action of the Sympathetic Ganglia. — Snkownin has found that when in the cat the nervous connections of the inferior mesenteric ganglion are divided, with the exception of the hypogas- tric nerves, and when the central cut end of one hypogastric is stim- ulated, contraction of the bladder ensues on the opposite side. According to Langley, this is not a true reflex, but an axon reflex. CHAPTER XV. SPECIAL SENSES. TACTILE SENSE. TjiK organs of special sense constitute the periplicral portion of the centripetal part of the nervous system. The nervous system is open to receive the impressions from the external world according to the nature of the different agents which must impress the organs of the special senses. The various kinds of sense-organs have each a different con- struction. They are always adapted to receive an impression of a given agent. Thus, the eye is an organ that is particularly adapted to receive impressions from rays of light; the ear receives sound- waves; the skin is responsive to touch, etc. Man is endowed with five senses. That is. he possesses five kinds of organs which are destined to give him notice of the impressions upon his nervous system from five different agents. To these agents man has assigned special names which recall their relations to the organs of sense, and without which they could not he conceived of. These agents, with the corresponding organs of sense, are (1) contact, which is perceived through the sense of touch, whose highest devel- opment is in the skin; (2) taste, a modification of touch is perceived ^through the sense of taste emhodied in the tongue; (3) odor is recog- nized through the sense of smell as located in the nose; (4) sound- waves are made known to the economy through the sense of hearing, whose peripheral organ is the ear; and (5) light is perceived through sif/ht hy reason of tlie response produced in the eye from the excita- tion of rays of light. Miiller's law of the specific energy of sensory nerves is that irri- tation of the nerves of special sense always causes sensations of the same kind. An induction current upon the skin will produce un- pleasant tactile sensations. Upon the eye it provokes luminous sensa- tions, upon the ear, noise sensations, and upon the tongue there is pro- duced a sensation of taste. Yet in each case the stimulus is always the same. In order that the impressions caused by the external excitants may he able to reach the consciousness of the individual, it becomes necessary that each organ of sense be furnished with centripetal (650) TACTILE SENSE. 651 nerves. These are in direct anatomical relation with the central nervous system. By means of these nerves the cortical portion of the cerebrum, endowed with consciousness, perceives the impressions com- ing from the external world. These are the so-called special, external and objective sensations. Among the parts furnished with nerves of general sensibility are the mucous membrane of the digestive, respiratory , and genito-urinary tracts, and the skeletal muscles. In the digestive tract, the mouth, pharynx, and anus are endowed with tactile nerves; the rest of the tract is furnished with nerves of general sensibility. The mucous membrane of the oesophagus gives us the sensation of thirst, the gastric mucous membrane the sensation of hunger and satiety, while the rectal membrane notifies the individual of the need of defecation. Pulmonary tissue in itself has but very little sensibility; but ab- normal irritations cause cough and painful sensation. The pleura, when invaded by disease, produces very painful sensations. The genito-urinary membrane, besides its exquisite tactile sensi- bility, is also the seat of general sensibility that is doubly modified: in the need of urination and the sexual sense. The kidneys, ureters, testes, Fallopian tubes, and the uterus are endowed only with nerves of general sensibility. The slieletal muscles are furnished with the so-called muscular sense. Muscular Sense. — According to Dr. Sherrington, of Liverpool, this is a specific sensation obtained from specific sense-organs in muscles, tendons, joints, and all the accessory organs of movement. In the muscles of the skeleton there are three sets of sensory organs: muscle-spindles, tendon-organs, and Pacini corpuscles. Muscle-spindles, or neuromuscular spindles, are long, narrow bodies, with a thick sheath of connective tissue enclosing fine striped muscular fibers. Sensory, medullated nerve-fibers enter the spindle, dividing into branches, and losing their medulla fonn endings around and between the muscular fibers. The perception of muscular sense may be grouped into: (1) those of posture; (2) those of passive movement; (3) those of active movement; and (4) those of resist- ance to movement. To the organs of muscular sense is largely traceable a local feeling of fatigue. The nerves of muscle are competent to ]n-oduce pain ; this is proved by the pain of muscular cramp. A proof of muscular sense is the employment of enough force 652 pnYSi()i.()(iv. to overcome resistance. Consciousness is a large factor in this last function, for by it the individual Judges the amount of resistance. He then vohintarily regulates the amount of muscular effort. It is by the sum of all the sensations from the nerves of general sensibility, as well as the sensation produced by muscular movement, that individuals feel that they exist. With these data the individual recognizes the state of different parts of his body, whether in repose or activitv. ^-i ^. mn 1' ig. 2SJ4. — C loss-sectiun of JveuiotciKlinous Nerve Eiid-oigHn of Rabbit from Tissue Stained in Methylene Blue. (Huber and Dewitt. ) m. Muscle fibers, i. Tendon, r, Capsule of neuro-tendinous end-organ. mn, Medullated nerve fiber. Laws of Sensation. — Special sensations are subject to the fol- lowing laws : — 1. For every nerve of sense there is a nominal degree or limit of stimulus which gives no sensation whatever. There is also a max- imum degree beyond which an increase of the intensity of the stim- ulus brings on pain or an unpleasant sensation. TACTILE SENSE. 553 2. The minimum limit varies for the separate sensations, or. rather, the single specific agents. Thus, the minimum for excitation of touch is a pressure of 0.003 milligrams; for temperature, Vg" C; for sensation of movement, a shortening to the extent of 0.044 milli- meters of the internal rectus of the eye ; for hearing, the noise made by a hall of pith one milligram in weight falling one millimeter in height upon a glass plate heard at a distance of ninety-one milli- meters from the ear; for sight, an intensity of light ahout three hundred times feehler than that of the full moon. 3. The intensity of the sensation is proportional to the intensity of the stimulus and the degree of irritability of the nerve at the moment of excitation. As the strength of the stimulus increases, so do the sensations. But the sensations increase equally when the strength of the stimulus increases in relative proportions. Thus, small noises will he distinguished in the silence, not in the midst of loud noises ; a sliglit difference will be noticed between small weights, not between heavy ones. A burning candle in the daytime makes little impression. 4. Sensations do not increase in the same proportion as the stimulus. If the stimulus increases in geometrical progression, then the sensation increases in simple arithmetical progression. Eather, it increases as the logarithm of the stren.gth of the stimulus. (This is Fechner's psycho-physical law.) 5. For the single, specific sense apparatuses, whenever a stimulus takes place, whether at the peripheral terminations of a nerve or in its course, or at its central point, the individual always localizes with his perception the stimulus at the place where the normal stimulus operates. That is, for sight and hearing he refers it to space ; for the nerves of taste, smell, or touch, he refers it to the peripheral regions of his body, even if these be lacking. Thus, in an amputated leg, pain in the stump is referred ■ to the toes. This is the law of eccentric projection of sensation. Touch. The organ of touch is represented by the skin and mucous mem- branes in proximity to the natural orifices of the body. The skin, or common integument, is composed of the following layers: (1) the epidermis; (2) the corium, or cutis vera, with its papilla; and (3) the subcutaneous tissue with the adipose tissue. 1. The Epidermis belongs to the tissues which are composed of simple cells imited to each otlu^r by cement-substance. It in itself consists of several 1 avers. 654 PHYSIOLOGY. Fig. 295. — Histolog}^ of the Skin and the Epidernioidal Structures. (Landois. ) I, Transverse section through the skin, with hair and sebaceous glands (7'), cerium and epidermis are shown in reduced size. 1, External, 2, Internal fibrous layer of the hair-follicle. 3, Cuticula of the hair-follicle. 4, External root-sheath. 5, Henle's layer of the inner root-sheath. 6, Huxley's layer of the Inner root-sheath, p, Hair-root attached to the vascular hair-papilla. .4,, Ar- rector pill muscle. C, Corium. a, Subcutaneous fatty tissue. 6, Horny layer. il, Malpighian mucous layer of the epidermis, g. Vessels of the cutaneous papilla. V, Lymphatics of the cutaneous papillae, h. Horny substance, i. Medullary canal, fr, Epidermis of the hair. A', Sudoriferous gland. E. Epi- dermal scales from the horny layer, viewed partly from the side, partly from the surface. R, Prickle-cells from the Malpighian layer, n. Superficial, deep nail-cells. H, Hair, more highly magnified, e. Epidermis, f. Medullary canal with medullary cells, f, f, Fiber cells of the hair-substance, cc. Cells of Hux- ley's layer. 1, Cells of Henle's layer. S, Transverse section through a sudo- riferous gland of the axillary cavity, a. Adjacent unstriated muscular fibers. /, Cells of a sebaceous gland, in part with fatty contents. TACTILE SENSE. 655 (a) Stratum Corneum. — This is the superficial horny layer and consists of several layers of horny scales, without any nuclei. The layers are separated from one another by narrow clefts containing air. They are in a process of desquamation. The variable thickness of the epidermis is chiefly dependent upon the thickness of this outer layer. The stratum corneum is of greater thickness on the palm of the hand and fingers, and sole of the foot. (b) The stratum lucidum is clear and transparent and consist? of a few layers of clear cells which contain l)ut the remains of nuclei. (c) Stratum Granulosum. — Under this is the (d) rete muco- sum, or rete Malpighii. This layer consists of strata of nucleated, protoplasmic, epithelial cells. In the colored races these contain pigment. Among the fair races this layer of th*e skin of the scrotum and anus contains pigment-granules. The deeper cells are more or less polyhedral, while the deepest ones are columnar. These last are placed vertically upon the papilla? and are provided with spherical nuclei. Granidar leucocytes or wandering cells are occasionally found between these cells. The superficial layers of the epidermis are continually being thrown off, while new cells are just as rapidly being formed in the deep layers. Within them there occurs a proliferation of the cells of the rete Malpighii. Many of the cells exhibit the changes of karyo- kinesis. No pigment is formed within the epidermis itself. But in brunettes and colored races pigment granules of melanin exist within the cells of the lowermost layers of the stratum Malpighii. The pigment-granules owe their presence here to their having been car- ried thither by leucocytes from the subcutaneous tissue. This ex- plains how a piece of white skin transplanted to a colored person becomes black. 2. The Corium, or cutis vera, is a dense network of fibrous con- nective tissue admixed with elastic fibers. Its entire surface is studded with numerous papiUo', the largest of which are upon the volar surface of the hand and foot. The majority of the papillae contain a looped capillary. In some regions of the surface of the body they contain touch-corpuscles. The papilla^ are arranged in groups whose disposi- tion varies in the several parts of the body. The lowermost connective-tissue layers of the corium gradually merge into the subcutan-eous tissue. Its arrangement is such as to leave spaces which contain, for the most part, cells of fat. The sub- cutaneous connective tissue, composed of ordinary connective tissue, is soft, and is rich in adipose cells, vessels, nerves, and lymphatics. (;;")() rilYSiOLOGY. Tactile Corpuscles. — The student well knows that in the epithe- lium of the skill and mucous membranes the nerves of common sen- sation are arranged, for the; most ])art, in nelworlhS of fibrillar. In addition to these there are otiiei- special terminal organs of sensory nerves. These are variously known as tactile corpuscles. These are concerned in the ])erception of some special quality or (juantity of sensory impulses. They have their site, not in tlie surface of the epidermis, but deeper within the tissues. The principal ones among them are the corpuscles of Pacini, the end-bulbs of Kruuse, the cor- puscles of Meissner, and the corpuscles of Merkel. The tactile corpuscles of Meissner in the papilla of the cutis vera are oval bod it's V,„ of an inch in length and nearly the same width. These are tire corpuscles of the palm of the hand and sole of the foot. One or two medullated nerve-fibers are spirally twisted Fig. 29G. — Cutaneous Papillae Deprived of Their Epidermis and the Vessels Injected. (Landois.) a, a, a, Tactile papUlas, eacli containing a Meissner corpuscle. around it, and near the top of the corpuscles the nerves lose their white substance and the axis-cylinders end in flat bodies penetrating the surface of the corpuscle. The corpuscle is composed of flattened cells, which give it a striated appearance. These corpuscles are built up of a great number of tactile discs and of tactile cells. There are about twenty tactile corpuscles to a square millimeter of the skin. The Pacinian or Vater's corpuscles are attached in greatest num- ber along the digital nerves of the fingers and toes and occasionally on other nerves. These bodies are oval or pyriform, about one- eighth of an inch in length and one-twelfth of an inch in thickness. They have a pearly luster and consist of a series of capsules or con- centric layers of fibrous tissue, with here and there a nucleus. The outer capsules are separated more widely than the inner ones and the interspaces are tilled with a colorless liquid. Each corpuscle is attached to a nerve by a pedicle of fibrous tissue through which TACTILE SENSE. 557 extends a single nerve-fiber, wliicli, jDcnetrating the series of capsules, terminates by sending its neuraxon into the central cavity of the cor- puscle, at the top of which it ends in a simple extremity. Each cor- puscle is covered with forty or fifty capsular layers. Krause's End-bulbs. — The tactile corpuscles of Krause are elon- gated, oval bodies, into one end of which a nerve-fiber penetrates. Externally they have a covering of connective tissue, a continuation of the perineurium, and an internal knob of granular matter dis- posed in concentric layers with a few nuclei. In the center of this knob is found the axis-cylinder which runs through it like a ribbon to the upper pole and then ends in a slight thickening. These bulbs Fig. 297. — Vater Paciiiian e uipu.^Llc lioiu the Mesentery of the Cat, Fixed in a Platinvim Chlorid-osmic Acid Solution. X 45. (Sobotta.) The figure gives a general view of the corpuscle and not a cross-section. a. Axis cylinder in the core, ik. Core, mn, Medullated nerve-fibers entering the corpuscle. are found in the basement membrane of certain mucous membranes, as in the corneal conjunctiva, in the mucous membrane of the mouth, in the clitoris, and in the glans penis. They are also to be found in the skin. Corpuscles of Grandry or of Merkel consist of two or more flat- tened cells, each larger than a simple tactile cell. Each cell is nucleated, and the nerve-fiber, before entering the corpuscle, loses its white sheath, and the axis-cylinder ends as a flat disc lying between the two tactile cells. These tactile cells are piled one upon the other so as to form a heap of cells. They are found chiefly in the lioak and tongue of the duck and in the epidemi of man. Other Modes of Ending. — In addition to sensory nerves ending by special structures as those Just described, there are some which 42 658 PHYSIOLOGY. do not possess such elaborate apparatus. In the case of many nerves, the axis-cylinder splits up into fibrils which are arranged in the form of a network. From this somewhat deeply placed network very fine llhrils or fibrillar are given off to terminate in the tissues to be sup- plied. The fibrilla} have their terminus in free ends lying between the epithelial cells. In many cases the free ends are seen to be pro- vided with small enlargements. These latter are known as tactile cells. Knowledge Gained. — By the sense of touch one feels the con- tact of bodies and their temperature, whether these bodies be solid, liquid, or gaseous. This special sense also defines at the same time the locality of the impression made by the external agent. The judg- Fig. 298. — Kiause's Corpuselo. (Hedon.) a, Nerve fiber, b. Corpuscle. ment of locality is not, however, free from error. It is really exact for but a few points; that is, wherever the touch is delicate. On the other parts of the skin the individual never exactly divines the point pressed upon ; so that he makes mistakes of millimeters, centi- meters, and even decimeters. In sensory nerve-trunks there exist different kinds of nerve- fibers; some administer to painful impressions and others to tactile impressions. Sensations of temperature, sensations of pressure, and of muscular sense belong to the latter group. There are, then, four sense qualities in skin-sensations: sensa- tions of pain, temperature, pressure, and muscle-sense, and each one has its own nerve-fiber. Sense Spots. — The surface of the skin is found by experimenta- tion to be composed of very small sensorial areas. Between these TACTILE SENSE. g59 areas are found little fields which are insensitive and which are rela- tively much larger than the sensitive areas, or "spots." It has been demonstrated that each "spot" has its own specific function to per- form, whether that be touch, cold, warmth, or pain. Each little sensitive area no doubt marks the site of single or groups of sensory corpuscles, end-organs, or bulbs, of the terminations of various nerves. Where the nerves terminate, there are the sense-spots rep- resented upon the skin's surface. Some one has very aptly likened the skin with its sense-spots to a pond upon whose surface, as well as just below the same, are seen lily leaves floating. The leaves represent the sense-spots. A pebble thrown into the pond may strike one or more leaves, depend- Tz Tsch Fig. 299. — Transverse Section of Two Grandry's Corpuscles from the Tongue of a Duck. X 450. (Sobotta. ) One of the corpuscles shows two, and the other, four tactile cells, mn, MeduUated nerve-fibers, entering the corpuscle. Tsch, Tactile discs. Tz, Tactile cells. ing upon how close together they are growing. The pebble repre- sents a stimulus, and by its presence temporarily stirs up or throws into a state of excitation the leaves struck as well as some of those adjacent. Upon the skin's surface may be demonstrated "touch-spots," "cold-spots," "warmth-spots," and "pain-spots." These are all mixed up, though those of one kind may be more strongly in evidence in certain areas. As a rule, "pain-spots" are found to be the most numerous; "warmth-spots" are the least likely to be found. Solids. — These act upon the sense of touch either by pressure or by traction: Pressure may be from zero to a maximum whose limit is the disorganization of the tissues. Up to a certain minimum, which depends upon the sensibility of the region, the application of pressure excites no sensation. The minimum pressure corresponds to the sensation of simple contact ; this by degrees gives way to the 600 PHYSIOLOGY. sensation of pressure. When the pressure is sufficiently increased there results pain. This in turn disappears when the pressure is increased to disorganization of the tissues. Pressure varies not only in inicusily, l)ut in extent. No mat- ter how the latter may be limited, the pressui'e always affects at least more than one peripheral nerve-ending. When tactile sensations are very light and succeed one another rapidly, a large number of nerves is stimulated. The sensation ex- cited is a peculiar one : that of ticMing. Traction uj)on the hair and nails determines pain much more rapidly than does pressure. Liquids. — Liquids applied at the temperature of the skin exer- cise a uniform pressure upon all parts of the cutaneous surface excepting those at the level of the surface of the fluid. If a finger he plunged into a heavy fluid, as metallic mercury, the part submerged hears a pressure which decreases from below upward uniformly. It is only at the surface of the liquid that a marked inequality of pressure exists. It follows a circular line which surrounds the finger at this level and can he plainly felt by the individual. If a lighter fluid, as water, be used, the pressure sensation is but very slight. Compound Tactile Sensations. — These may be simultaneous or successive. Simultaneous tactile sensation may be either double or multiple. Double sensations, whether of contact, pressure, or traction, are shown only when the stimuli are applied at a certain distance from one another. If the stimuli be near enough, the sen- sation remains single even though the stimulus has been applied to the skin in two places. The earliest systematic experiments upon this subject were by Weber. He touched the various points of the skin's surface with a pair of carpenter's compasses and then observed the distance of separation necessary to give a distinct impression of two points of contact. The instrument now used for this purpose is the ccstliesiometer. From the table compiled by Weber it is found that the tip of the tongue is most sensitive, while the thigh and arm are least so. In the case of the tongue, the threshold stimulus, the minimum separation necessary for the impression of double contact is but 1.1 millimeter; 67.6 millimeters are necessary in the case of the thigh and arm. The connection between the mental and physical conditions explains certain illusions of tactile sensations. Of these, the Lest known is the so-called experiment of Aristotle. Wlien a pea or small ball is rolled between the crossed index and middle TACTILE SENSE 661 fingers of a blindfolded person there results a sensation of Iwo halls being present instead of one. There are spots of temperature which have been worked out by Goldscheider. They are found to be arranged in a linear manner and generally radiate from certain points of the skin, usually the hair-roots. The chain of "cold-spots" does not coincide with those of "warmth-spots." The sensation of cold occurs at once; that of heat develops gradually. As a rule, the cold-spots are more abund- ant over the entire body surface. The hot-spots may be quite absent. The minimal distance on the forehead for cold-spots is 0.8 milli- meters while for warmth-spots it is 5 millimeters. Fig. 300. — Topography of Sensibility to Cold and Heat in the same Region of the Anterior Surface of tlie Thigh. (Goldscheider, HEDO?f.) a. Cold spots. I, Hot spots. Most sensitive spots in black; moderately sensi- tive spots are hatched; spot feebly sensitive, in points; spots which are white are not sensitive. Protection of the Organs of Touch. The means are the cutaneous oil and the hornij appendages. The cutaneous oil is the product of the sebaceous glands of the skin. They are found in every area of the skin, but are less numerous than the sudorific glands except in the palms of the hands and soles of the feet. They may be large, as in the nose; these usually have fine, downy hairs near their mouths. The sebaceous glands are situated more superficially than the sweat-glands. They are white granules annexed to the hair-follicle. 662 PHYSIOLOGY. in which their excretory duet ends. Their size is, in general, in- verse to the volume of the corresponding hair-follicle. Where the hairs are large the sebaceous glands seem to be appendages, and when the hairs are small its hair-follicle seems to be an appendage of the sebaceous gland. The glands are aciniform, surrounded by a thin, connective tissue with a basement membrane studded with epithelial cells infiltrated with fat, and the cells are more fatty in the direction of the excreting duct, where is found free fat, due to the destruction of the cells. When the sebaceous secretion stagnates, it forms a fatlike mass which, when expressed, as in the nose, forms the comedo, a wormlike body. The black-heads, as they are called, are dirt in the surface of the gland. When the comedo is pressed out of the duct it has been mistaken as the head of the worm. The sebaceous matter contains, even in healthy individuals, the pimple- mite, or Demodex folliculorum. There are three varieties of sebaceous secretions: (1) the seba- ceous secretion proper of the skin, (2) the vernix caseosa of the new- born child, and (3) the smegma of Tyson's glands of the prepuce. Function. — The sebaceous matter anoints the hairs with oil in their progress of growth from the skin. The greasiness of the sur- face of the skin caused by this secretion permits the dust readily to adhere, which makes soap necessary to remove its excess. Seba- ceous secretion is made up of olein, palmitin, cholesterin, and earthy phosphates. The organ of touch is also protected by the horny layer of the epidermis, whose cells are being constantly removed by friction and as constantly renewed by proliferation of the cells of the cutis vera. The modifications of the epidermis in man are the hair and the nails. Hair. — The hairs are threadlike appendages to the skin project- ing from almost every part of its surface except the palms and soles. They are flexible, elastic, and shining, but vary in degree of develop- ment, fineness, color, and form in different races and the sexes as well as in different persons. The color of the hair varies from a light color to a black. The black hairs are found in all parts of the globe and in all latitudes, as in the Esquimaux, negro, Indian, and Malay. All the colored races have black hair, and this is true in some groups of the white race. Red hair is represented in all races. The hair is composed of a projecting part, the stem, terminated by the point, or end. The portion inserted into the skin is the root, which begins in a clublike expansion. The hairs generally project TACTILE SENSE. 663 obliquely from the skin. The hairs of the white race are cylindrical ; the hair of the negro flattened cylindrical. In structure the hairs consist of an exterior cuticle, a cortex, and an interior medulla. The cuticle consists of a single layer of thin, colorless, quadrilateral scales which overlap like the shingles of a roof. The edges of the scales are directed upward and outward along the shaft. The cortex makes the chief part of the hair, and it is that upon which the color of the hair mainly depends in different individuals. The cortical layer is made up of elongated, fusiform cells containing a lineal nucleus. When the coloring matter disappears in the cortex the hair becomes white. The medulla is frequently absent, especially in the dark-colored hairs. It occupies the axis of the hair. It consists of cuboidal cells with granular contents and an indistinct nucleus. The medullary substance is generally mingled with more or less air, in small bubbles, which penetrates from the ends of the hairs and gives to these when white the characteristic silver luster. The root of the hair is lodged in a flask-shaped receptacle of the skin called the hair- follicle, at the bottom of which is a papilla from which the hair grows. "Goose-flesh" is due to minute muscles contracting and causing the hair-follicles to become erect. At the same time the sebaceous glands are compressed, favoring the exudation of the seba- ceous secretion. Chemically, the hairs are mainly composed of an albuminoid derivative, keratin, in which a notable quantity of sulphur is present: about 5 per cent. In the ashes are found the phosphates, earthy sul- phates, oxide of iron, and pigment. FuNCTiox. — The large hairs serve to protect the skin, breaking shocks and preventing a considerable loss of heat. In other places, like the armpits, they prevent friction and attrition of the skin layers. The downlike hairs render the touch more delicate. Nails. — The nails are hard appendages of the skin, and corre- spond to the claws of animals. They are flexible, translucent, square-shaped plates continuous with the epiderm and resting on a depressed surface of the dermis called the matrix, or bed. The exposed part of the nail is the body and its anterior end is its free border. The root of the nail is lodged in a deep groove of the matrix and the lateral borders are received into shallow grooves. The half-moon, or lunule, of the nail is due to a less degree of vascu- larity of the matrix at the root, defined by a semicircular line. The horny layer corresponds to the cuticle of the epiderm, and is com- posed of flattened, nucleated cells. The soft layer of the nails, the 664 PHYSIOLOGY. stratum mucosum, corresponds to that layer of the cpiderm. The nails grow in length by new cells at the root, in thickness by addi- tions beneath the nail. The nails serve to protect the skin at the tips of the phalanges, and, at the same time, perfect the touch of the fleshy parts of the fingers. The average growth of the nails is about one-eighth of an inch per month. CHAPTER XVI. SPECIAL SENSES (Continued.) THE SENSE OF TASTE. Taste is an organ of special sense, by which as a medium the individual perceives savory impressions. Its principal uses to the economy are two: First, it acts as a guide to the individual in his choice of food, at the same time rendering its mastication a matter of some pleasure. Secondly, it excites the salivary glands reflexly, so that they pour out their juices into the mouth. The organ of taste is seated in the oral cavity and in the mucous membrane of the tongue. Its limits are not well defined. The diffi- culty in their determination depends upon the double fact that these organs of taste are endowed with a very delicate sensibility of a tactile nature, and that the gustatory sensibility and the organ of smell are in very close proximity to one another. For these reasons one may very easily believe that certain regions of his mouth are gustatory, when in reality the substances which have touched them have only produced tactile or olfactory impressions. Still it has been shown that the principal regions of the oral mucous membrane designed to perceive taste-impressions are at the base and edges of the tongue. In a secondary degree, also, gustatory impressions are perceived in the anterior surface and edge of the soft palate, and the anterior portion of the tongue. All other por- tions of the mouth are incapable of taste-impressions. The Ton^e. — The principal organ of the sense of taste is un- doubtedly the tongue. Its anatomical structure as a muscular organ has already been described when discussing deglutition and the part it i^layed in the role of that important function. At this time it remains but to review such portions as have a direct bearing upon its role as a gustatory member. There are three kinds of papillae in the mucous membrane of the tongue: the circumvallate, fungiform, and filiform. They extend from the tip of the tongue to the foramen caecum. The papillae con- sist of elevations, visible to the naked eye and covered with strati- fied, squamous epithelium. The central body of each papilla con- tains connective tissue, blood- and lymph-vessels, and nerves. (G65) 666 PIIYSIOLOGY. The circumvallate papilla-, the largest of the varieties and about a dozen in number, J'onu a, \'-like low, defining the papillary layer at the posterior third of the tongue. They have the fomi of an inverted cone surrounded by a ringiike wall-elevation. The fungiform are next in size, and more numerous than the circumvallate. They are small, red eminences scattered over the sur- face of the tongue, but are especially numerous at and near the tip. They are rounded at the free extremity and narrower at the point of attachment to the tongue. The filiform papilla?, smaller and more numerous than the others, are crowded in the spaces between the others, but are ar- ranged in rows diverging from the median line of the tongue. Nerves. — The tongue receives three nerves: one of motion, the hypoglussal, which animates the muscles; and two other sensory branches — the lingual branch of the glosso-pharyngeal and the lingual branch of the trigeminus. The former of the hitter two branches spreads in the mucous membrane at the base and edges of the tongue; the latter is distributed to the mucous membrane of the anterior two- thirds of the tongue. The branches of the glosso-pharyngeal are especially concerned in sensations of hitterriess, while the branches of the trigeminus are affected principally by siveet and acid tastes. Section of the hypoglossal upon both sides causes paralysis of the tongue without injuring its tactile or gustatory sensibilities. Section of the lingual branch of the trigeminus causes only loss of fine tactile sensibility and gustatory sensibility of the anterior two-thirds of the tongue. Section of the glosso-pharyngeal causes loss of tactile and gusta- tory sensibility in the mucous membrane at the base of the tongue. Such an animal can swallow bitter and nauseous substances, like colocynth, with impunity. The gustatory action of the lingual branch of the trigeminus comes from the chorda tympani. The latter is a small nerve which begins in the facial and traverses the middle ear to join the lingual branch at the level of the pterygoid muscles. The chorda tympani nerve passes from the tongue to the nerve- centers through the lingual nerve, the facial, and finally through the intermediate nerve of Wrisberg. Taste-organs. — The terminal branches of the glosso-pharyngeal nerve end in the taste-bulbs. The taste-bulbs are oval bodies imljedded in the epithelial layer. Each taste-bulb is fomied of two kinds of elongated epithelial cells, and their whole outline is barrel-shaped. THE SENSE OF TASTE. 667 The taste-cells are narrow and slightly thickened in the iniddle, where the nucleus is situated. The taste-bulbs occur chiefly on the sides of the circumvallate papilla, although a small number of them are on the fungiform and the soft palate. The ends of the taste-bulbs near the surface have a minute, funnel-like opening called the taste-pore. The number of taste-bodies is very great. If the glosso-pharyngeal nerve is cut, the taste-bodies degenerate. The proper stimuli for the end-bulbs of the gustatory nerves are the savory substances. These must be dissolved in the liquids of the mouth before they can penetrate the outer cells of the mucous mem- brane to come into contact with the nerve-filaments in the imbedded Fig. 301. — Structure of the Taste-organs. (Lais'dois.) I. Transverse section of a circumvallate papilla. W, the papilla, v, r. The wall in sections. R, R, The circular slit, or fossa. A", A', The faste-bulbs in position. N, N, The nerves. II. Isolated taste-bulbs. D, Supporting, or protective, cells. K, Lower end. E, Free end, open with the projecting apices of the taste-cells. III. Isolated protective cell (d) with a taste-cell (r). bulbs. The most suitable temperature for the thorough testing of liquids is 100° F. The intensity of the gustatory impression depends upon various factors: the nature of the substance, the duration of the impression, sensibility of the region touched, and the stimulating action of the substance upon the mucous membrane. The flavor of a substance does not depend upon its chemical properties, for both quinine and sulphate of magnesia are bitter; sugar, chloroform, and glycerin are sweet. Improper stimuli give gustatory impressions. Thus, the galvanic current applied to the tongue gives an acid taste at the positive pole and a weaker, alkaline taste at the negative pole. 668 PHYSIOLOGY. Varieties of Substances. — Of the gustatory substances there are four: (1) sweet, (2) hitter, (3) acid, and (4) saline. In addition to these fundamental substances there are compound gustatory im- pressions, or a confusion of gustatory sensations with those which are tactile or olfactory. Thus, there is known the piquant taste of cheese, the caustic taste of mustard, and the aromatic taste of strawberries. The acid and siveet tastes are best perceived at the tip and edges of the tongue; the salty and hitter tastes are comprehended at the hase. This leads to the result that some substances have a different taste, dependent upon whether they touch the tip or the base of the tongue. Thus, acetate of potassium at the tip of the tongue is acid, and at the base it is bitter. Fig. 302. — Sternberg's Gustometer. The four primitive tastes are not all perceived at the exact time of their impression upon the tongue. The salty is first perceived, then, the sweet, next the acid, and last the bitter. Tactile sensations by astringents (tannic acid) or thermal sensa- tions (mustard) are usually confounded with taste proper. The taste of vanilla is but an olfactory impression. Drugs. — By the action of drugs one is able to abolish certain tastes more readily than others. Cocaine upon the tongue abolishes tactile sensations and the taste for bitter things, but does not inter- fere with voluntary movement. The leaves of Gymnema sylvestre, when chewed, destroy the sense of taste for bitters and sweets, while that for salts and acids remains. The Taste-center, to which the gustatory nerves send their im- pressions, lies in the vnci?iate gyrus. Sternberg's Gustometer. — This instrument consists of a Eichard- son double-bellows rubber bulb, which is attached to a two-way stop- cock. The two-way stopcock is connected by rubber tubes with two glass bulbs fitted with an entrance and an exit tube. Both glass bulbs contain small pieces of sponge, to increase the surface for THE SENSE OF TASTE. 669 evaporation of the volatile fluids. In one glass bulb is placed chloro- form as a sweet substance to be tasted; in the other glass bulb, ether, to represent a bitter-tasting substance. To the exit tubes of each glass bulb are attached, by rubber tubes, two tubes of glass drawn to a fine point. A spring clip is placed on each rubber con- necting-tube. When the apparatus is to be used, the Eichardson rubber bulb is compressed and air is driven through one or the other glass bulb. By this means we can, at our pleasure, test for bitter or sweet substances. Even acetic acid can be placed in one of the bulbs, to test the taste for acids. The pointed glass tubes must be brought near the point on the tongue to be tested, but they must not touch it. Sternberg has also constructed a quantitative gustometer, on the same principle as the olfactometer of Zwaardemaker. CHAPTER XVII. SPECIAL SENSES (Continued.) THE SENSE OF SMELL. The seat of the sense of smell resides in the cavities of the nose. Ivant has very aptly spoken of smell as "taste at a distance.'^ The organ of smell resembles those of sight and hearing in that it consists of a special nerve which ends in a specialized epithelium. In this case the special nerve is the olfactory; the specialized epithe- lium is the mucous membrane of the upper portion of the nasal cavity. It is in this portion the mucous membrane that the fila- i BouLtUAZ Fig. 303. — Innervation of the External Wall of the Nasal Fossa. (Testut.) 1, Olfactory tract. 2, Olfactory bulb. 3, Branches of olfactory nerve. 5, Ganglion of Meckel. 6, Pharyngeal nerve. 7, Vidian nerve. 8, 9, Spheno- palatine. 10, 11, 12, 12', Palatine nerves with, 13, nasal branch. 14, 14', Termina- tion of ethmoidal nerve. 15, Opening of Eustachian tube. 16, Vault of palate. ments of the olfactory nerve are distributed. For that reason it has been termed the ref/io olfacforia, and comprises the upper portion of the septum, the upper turbinated, and part of the middle turbinated regions. All other portions of the nasal-cavity covering is known as the regio respiratoria, or simply the Schneiderian membrane. During ordinary respiration the currents of air in their passage in and out (670) THE SENSE OF SMELL. 671 are, for the most part, confined to this latter region. The mucous membrane which covers this portion of tlie nasal cavity is, in struc- ture and appearance, very similar to that of the trachea. It is com- posed of layers of ciliated epithelium which rest upon a basement membrane rich in blood-vessels and lymphatics. Among the ciliated cells are found numerous goblet and mucous cells, whose secretions keep the surface of the mucous membrane soft and moist. In it are numerous filaments of the trigeminus, which endow it with tactile .^ -^i Fig. 304. (Bishop.) 1, Middle turbinated body turned aside and held by a hook. 2, Nasal duct' and valves. 3, Canal leading to the maxillary and frontal sinuses. 4, Inferior turbinated body showing the location of the mouth of the nasal duct in the ciil-de-sac. sensibility. There are 710 filaments of the olfactory nerve in this region. The olfadorij mucous membrane is thicker than that of the respiratory portion. To the naked eye it presents a yellow or brown- yellow color because of the pigment contained within it. By reason of its color it is very readily distinguished from that of the Schneider- ian membrane. Its surface is covered by a single layer of cylindrical epitheUum whose cells are often branched at their lower ends. 672 PHYSIOLOGY. The olfactory region contains the olfactory cells. These possess a body of spindle shape with a large nucleus containing nucleoli. In the deeper part the olfactory cells pass into and become continuous with fine fibers. These last pass into the olfactory nerve. The olfactory, the nerve of smell, issues by two roots, each from the corresponding hemisphere. The fibers are composed of medul- lated and nonmedullated fibers. These latter fibers proceed from the olfactory bulb. Fig. 305. — Diagram of the Connections of Cells and Fibers in the Olfactory Bulb. (.Schafer, in Quain's Anatomy.) oJf.c, Cells of the olfactory mucous membrane, olf.n, Deepest layer of the bulb, composed of the olfactory nerve-fibers which are prolonged from the olfac- tory cells. {/I, Olfactory glomeruli, containing arborization of the olfactory nerve-fibers and of the dendrons of the mitral cells, me, mitral cells, a. Thin axis-cylinder process passing toward the nerve-fiber layer, n.tr, of the bulb to become continuous with fibers of the olfactory tract; these axis-cylinder proc- esses are seen to give off collaterals, some of which pass again into the deeper layers of the bulb, ii', A nerve-fiber from the olfactory tract ramifying in the gray matter of the bulb. The olfactory bull) is a part of the cerebral cortex and is an oval or club-shaped mass of gray matter which rests on the cribriform plate of the ethmoid bone, through the foramen of which it is con- nected with the olfactory nerves. The olfactory nerves are twenty in number and are the central coursing of the neuraxons of the rod- shaped olfactory nerve-cells in the olfactory region of the nose. They pass through the openings in the cribriform plate and terminate in THE SENSE OF SMELL. 673 arborizations about the dendrons of the mitral cells of the olfactory glomeruli. These bipolar cells greatly resemble the cells of a gan- glion of a posterior root of the spinal cord, one ueuraxon going to the olfactory mucous membrane and the central neuraxon going to the olfactory bulb. The olfactory bulb from without inward consists of four layers : — 1. The nerve-fibers. 2. Stratum glomerulosum. 3. Stratum gelatinosum. 4. Layer of central nerve-fibers. In the first layer each fibril is a central ueuraxon of a rod-shaped nerve-cell from the olfactory mucous membrane. The fibers of the olfactory nerves pass into the glomeruli lying beneath. Within the glomerulus the endings of the olfactory fibrils come in contact with an olfactory end-brush of an apical dendron of a mitral cell. In the stratum glomerulosum each glomerulus consists of the terminal arborizations of an olfactory nerve-fiber, together with the olfactory end-brushes from the apical dendrons of the mitral cells. The stratum gelatinosum in its inner part contains two chief forms of cells: the deep and superficial layers of mitral cells which correspond to the pyramidal cells of the cerebral cortex. The fourth layer in its outer part has a large number of very small granular cells between which pass the descending neuraxons of the mitral cells. The nerve-fibers of the olfactory bulbs collect at their posterior extremities into two bundles: the olfactory tracts. The outer root-fibers of the olfactory tract come into relation with the gyrus hippocampus, the uncus, and cornu ammonis. The inner root-fibers pass into the gyrus fornicatus. Olfactory Sensations. — The student, in order to obtain clear-cut ideas as to the mechanism of the special sense of smell, should bear in mind the principle of the arrangement of the olfactory nerve- terminations. It is recalled that within the mucous membrane lie the olfactory cells. From the peripheral end of each cell project seven or eight ciliumlike processes. These not only project to the surface of the mucous membrane, but even to the surface of the serous fit id moistening the membrane. Thus, the terminal filaments are placed in an exposed position so that they may very readily respond to any irritant. The proper stimulus for olfactory-nerve filaments are odorous siibstances which reach the regio olfactoria through the air and must be in a volatile state. Hence, olfactory sensations are produced by 674 PHYSIOLOGY. volatile, odorous particles coming into direct contact with the exposed nerve-filaments during the act of inspiration. As the regio olfactoria is in the highest position of the nasal cavity, it becomes necessary for the individual to cause the inspired air forcibly to reach this area. This is accomplished by an act ordinarily known as "sniffing." During ordinary respiration the inspired and expired air courses along close to the septum and below the inferior turbinated bone. Should the respired air be heavily charged with odorous particles, of course some will find their way into the regio olfactoria, as the air in this compartment is gradually changed. There will then result a sensation of smell, but it will be faint and not so sharply defined as when the person sniffs. By the latter process the air is changed more quickly and a greater number of volatile particles irritate the exposed nerve-endings, with the result of a sharply defined sensation. The sensation seems to occur at the first moment of contact of the odorous particles with the mucous membrane. The olfactory nerve tires very quickly when an odor acts for a certain time; the effect becomes weaker and weaker little by little, until the odor is finally unperceived. Should the free movement of the air be prevented — as, for example, when nasal catarrh brings on a tumefaction of the mucous membrane of the inferior turbinate, — the odorous impression cannot take place. In case many different odors act simultaneously upon one nasal cavity, the individual receives a mixed sensation. Should but two odors act, the one is perceived on the right half of the mucous mem- brane of the cavity, the other upon the left half. This is not a true mixture, for the person perceives slightly the one odor and slightly the other. One part of vanillin to 10,000,000 can be recog- nized by the sense of smell. Secondaky Sensation. — The olfactory impression having been made, the secondary after-sensation often remains for a long time. This is particularly the case with strong, disagreeable odors. This phenomenon is explained on the supposition that the odorous parti- cles remain in the cavity of the nose, even in the air. It is not believed that the manifestation is due to persistence of excitation of the olfactory nerve-fibers after the stimulus has been removed. There are subjective olfactory sensations which are true hallucina- tions. They are often met with in demented, in hysterical, or in pregnant women. These sensations owe their existence to some material alteration of the nervous apparatus. THE SENSE OF SMELL. 675 From impressions truly olfactory it becomes necessary to dis- tinguish the gustatory as well as tactile or irritative sensations upon the nasal mucous membrane. The irritation and even pain produced by the vapors of ammonia often lead it to be improperly classed as "having a bad odor." Experimentally, a dog with both olfactories divided always starts from the odor of ammonia or of acetic acid. This is due to painful stimulation of his Schneiderian membrane, which gets its sensory nerve-filaments from the second branch of the trigeminus. Uses. — The organ of smell represents an advance sentinel for the functions of respiration and alimentation. Among the lower animals it serves for the recognition of sex. Fig. 306. — Zwaardemaker's Olfactometer. ( Tigerstedt. ) (From Tigerstedt's "Human Physiology," copyright, 1906, by D. Appleton and Company. ) Hyperosmia and Anosmia, — Hyperosmia, or increased sensitive- ness of smell, is a common condition. It is very apt to be found among the hysterical and in many other nervous disorders. Strych- nine is one of the drugs which is capable of producing this condition when it is applied locally in solution. Anosmia is a term used to designate a condition which is the reverse of the beforementioned. It may be complete, when it is usually congenital. In such a case the olfactory nerves are absent. It is more usual, however, to find the condition partial. Its causes may be stenosis of the nasal cavities, disease of the olfactory mucous membrane, or nervous diseases. Strychnine often relieves the con- dition. The local application of a dilute solution of strychnia heightens the sense of smell (hyperosmia). Smoking, the local application of 676 PHYSIOLOGY. morphia and cocain produce partial loss of the sense of smell (anosmia). Certain odors can antagonize another odor when perceived by separate nostrils, so that no odor is perceived, as acetic acid and ammonia. There is also a relationship between smell and the chemico-physical properties of odors; it follows the periodic law of Mendelcjeff. The Center of Smell lies in the tip of the uncinate gyrus upon the inner surface of the cerebral hemisphere. - Zwaardemaker's Olfactometer.— Eubber tubing, two inches in length, is fitted inside a glass tube, which prevents any particles of odor leaving its surface. Another glass tube is closely fitted inside the rubber tube. When the inner glass is drawn out .7 centimeters, then a normal person can perceive the odor of rubber, when air is drawn through the inner graduated glass tube. Hence the inner glass rod was graduated in degrees of .7 centimeters. If a man can only perceive rubber at 1.4 centimeters, he has only half normal olfaction; but in certain cases of considerable want of olfaction the odor of rubber is not strong enough to be perceived. Here he used a tube of "gutta percha ammoniacum," which is twenty-four times more powerful as a stimulus than india rubber. It was found, in many cases of anosmia, that certain odors might be smelt to a nor- mal extent, whilst others barely stimulated the olfactory organs. CHAPTER XVIII. SPECIAL SENSES (Continued.) THE SENSE OF HEARING. By means of the special sense of hearing the individual gains knowledge of a kind differing from the Just-mentioned senses. It does not tell him what is going on in the outer world by actual con- tact, as in touch or taste; nor yet by particles of matter impinging upon the exposed end of nerve-filaments, as in the sense of smell. In the special sense of hearing the impressions conveyed to the cen- tral nervous system are produced by wavelike vibrations in the sur- rounding air. For the reception of these vibrations, so that they may be properly interpreted and the corresponding impressions con- veyed to the brain, it becomes necessary to have a special sense- organ: the ear. The Ear. The organ of hearing in its greatest simplicity may be repre- sented by a small membrane stretched like a drumhead over the bottom of a funnel-shaped tube. The tube opens upon the surface of the body so that it is in direct communication with the enveloping atmosphere. The membrane is so disposed that it is readily thrown into vibrations when the external air becomes undulatory as the result of vibrations of some body. Its vibrations are communicated to an inner vesicle that is filled with a liquid. The liquid is like- wise thrown into waves whose imdulations stimulate the ramifica- tions of the auditory nerve wdiich are spread out upon the walls of the vibrating vesicle. Anatomy. — The apparatus for hearing is composed of three parts: external ear, middle ear, and internal ear. ExTEKNAL Ear. — The external ear is composed of the auricle and external auditory meatus. The auricle has the form of an irregularly shaped shell. It is composed of yellow, elastic cartilage which is covered over with skin. From its shape one might readily believe that the function of the auricle is to collect and reflect sound-waves into the auricle : that is, to behave in the capacity of an ear-trumpet. But it is found that (677) G78 PHYSIOLOGY. hearing is perfectly normal in those persons from whom the external ear has been removed by accident or otherwise. The external auditory meatus and canal extend from the concha of the auricle to the tympanum. The canal is composed partly of cartilage and partly of bone; the bony portion belongs to the tem- poral bone. The canal is lined by skin, which contains modified sebaceous and sudoriferous glands. By the glands is secreted the cerumen, or earwax. The internal end of the auditory canal is bounded by an ellipsoid structure which is composed of three layers of tissue : the tympanic membram. -^ss Fig. 307. — Diagram of the External Surface of the Left Tymimnic Membrane. ( Hensen. ) a, Head of malleus, h, Incus, e, Joint between malleus and incus. Between c and d is the flaccid portion of the membrane, ax, Axis of rotation of ossicles. The umbo is the deeply shaded part. Fimction of the External Ear. — Sound- vibrations strike the ex- ternal ear, some of which go directly into the external auditory meatus. The irregularity of the surface of the pinna permits us to judge more correctly of the direction and the intensity of sound. If these irregularities are filled up with wax, while the meatus is left open, the intensity of sound is diminished, and it is more difficult to judge of the direction. In the external meatus the waves of sound undergo a series of reflections, which conduct them to the membrana tympani. By reason of the obliquity and curves of the membrana tympani, the sound-waves strike it in a nearly perpendicular direc- tion. The external ear has for its function the collection and trans- mission of sounds to the membrana tympani. The horse is con- THE SENSE OF HEARING. 679 stantl_y moving his ears to determine the direction of sounds, but in man this function is greatly subordinated. The twisting of the mouth of the meatus, and the hairs and wax in the external meatus, also keep out dust and insects. Auditory Field. — Like the visual field, we have an auditory field. It is all the points in space from which sound-waves can be collected by the auricle and transmitted by the auditory canal. Its extent and form depend upon the conformation of the auricle. Middle Eae, ok Tympanum. — The tympanum is a space situ- ated within the substance of the petrous portion of the temporal boue. It is composed of tivo hony and four soft parts. Fig. -308. — Tympanic Membrane and Auditory Ossicles, seen from the Tympanic Cavity. (Landois.) M, Manubrium, or handle of the malleus. T, Insertion of the tensor tym- pani. h. Head. IF, Long process of the malleus, or incus-tooth. The short (K) and the long (/) process. 8, Plate of the stapes. Ax is the common axis of rotation of auditory ossicles. 8, The pinion-wheel arrangement between the malleus and incus. The tiro bony parts comprise the walls of the cavity, with the mastoid cells and Eustachian tube; also the ossicles or bones of the ear. The soft structnres are: (1) the ligaments and muscles of the little ossicles, (2) the mucous membrane of the tympanic cavity, (3) the lining of the Eustachian tube, and (4) the membrana tympani and membrane of the round window. In otitis media pus may cause a disintegration of the mastoid cells, from which it frequently extends to the membranes of the brain. 680 PHYSIOLOGY. The cavity of the tympanum forms a dilatation added to the auditory canal. It has an internal wall, an external Avail, and the Eustachian tube. The mastoid cells communicate by a large orifice with the upper, back i)art of the tympanum. They are lined throughout with a delicate mucous membrane. The external wall is occupied in its greatest extent by an open- ing which is nearly circular and closed by the membrana tympani. The latter is semitransparent, concave externally and convex inter- nally. To its inner surface is attached the malkus, one of the three ear ossicles. Fig. .309. — Left Tympanum and Auditory Ossicles. (Lanrois.) A.O., External meatus. .1/, Membrana tympani, which is attached to the handle of the malleus (n) and near its short process (p). h. Head of the malleus. «, Incus. K, Its short process, with its ligament. /, Long process. 8, stapes. The internal ivall is convex and has in its central portion a tubercle known as the promontory. Its base corresponds to the origin of the cochlea. The most prominent of the grooves upon its surface marks the position of the nerve of Jacohson. Above the promonotory is found the oval windoir. Its shape is really reniform; it leads to the vestibule. The round window is situated Just beneatli the oval window. It is closed by a membrane. The ossicles, which form an articulated chain, reach from the THE SENSE OF HEARING. 681 membrana t3'mpani to the oval window. In number they are three: the malleus, or mallet; the incus, or anvil; and the stapes, or stirrup. The three ossicles form a chain suspended across the cavity of the tympanum. The handle of the malleus is inserted into the tym- panic membrane; the base of the stirrup is applied to the oval win- dow. Between these two ossicles is suspended the incus. The ossicles have joints w^hich are lined wdth synovial membrane; there are present suitable ligaments. The mucous membrane of the tympanum is very thin, and either white or rose-colored. It envelops the chain of ossicles. Fig. 310. — Scheme of the Organ of Hearing. (LuVXBOls.) AG, External auditory meatus. T, Tympanic membrane. A", Malleus with Its head (70, short process (Uf), and handle (?«)• «, Incus, with its short process (j-) and long process; the latter Is united to the stapes (.s). P, Middle ear. o. Oval window, r. Round windov?. x, Beginning of the lamina spiralis of the cochlea, pt. Its scala tympani. vt. Its scala vestibuli. V, Vestibule. »Sf, Saccule. U, Tubercle. H, Semicircular canals. TE, Eustachian tube. The long arrow indicates the line of traction of the tensor tympani; the short curved one that of the stapedius. The Eustachian tube is composed of a bony and a cartilaginous part. The canal opens at the anterior upper part of the tympanum; its pharyngeal orifice is situated ten millimeters behind the posterior extremity of the nasal fossa. The Bony Labyrinth, or Internal Ear. — This structure is imbedded within the substance of the petrous portion of the tem- poral bone. Its long axis lies in a position parallel with that of the bone. The labyrinth is composed of three portions: vestibule, semi- circular canals, and cochlea. 682 PHYSIOLOGY. The vcdihule is iin oval, irregular cavity, l.ying between tlie tym- paniini and tlic bottom of the internal anditory meatus. The .semi- circular canals open from it posteriorly and the cochlea opens from it anteriorly. Through its outer wall it communicates with the tym- panum by the oval window. The fovea heniispherica and fovea hemi- elliptica are two depressions upon the inner and superior walls of the vestibule, respectively. They are pierced by numerous fora- mina; through the former pass the filaments of the cochlear branch of the auditory nerve ; through the latter foramina pass the branches of the vestibular branch. Through the latter also pass small veins which communicate with the inferior petrosal sinus. The semicircular canals are three in number. They are located above the inner and back part of the tympanum. From their loca- tion they are named superior, posterior, and external. The canals lie in three distinct planes: the first two are vertical, but nearly at right angles to one another; the last is horizontal. Each canal is rather more than half of a circle, and fonns at one extremity a dilatation called the ampulla. The canals communi- cate with the vestibule by five openings, one of which belongs to both the superior and posterior canal. The interior of the vestibule and semicircular canals is lined with a delicate membrane. The cavity formed by this membrane contains a fluid of serous nature. It is known as the perih/mph, by reason of its surrounding a secondary structure, the labyrinth. This last structure consists of a pair of saccules in the vestibule, and three semicircular saccules whose form is the same as the osseous canals containing them. This membranous labyrinth comprising the sac- cules just mentioned itself contains a serous fluid, the endolymph. The inner portion of the bony labyrinth is the cochlea : so named from its resemblance to a shell. Its base is attached to the internal auditory meatus, while its apex is directed forward and outward. The axis of the cochlea is nearly at right angles to that of the petrous portion of the temporal bone in which it lies. The cochlea is a tube of bone wound around a central axis, each turn successively rising. This bony tube is about one and one-half inches long. Its beginning is connected with the fore part of the vestibule to produce the promontory of the tympanum; it ends in a closed extremity called the infundihulum. The central axis just spoken of is termed the modiolus. The apex of the cochlea is often called the cupola. The bony canal is divided into two passages, or scalce, by a septum known as the lamina spiralis, which projects from the THE SENSE OF HEARING. 683 modiolus. The two scalse commuincate with one another only at the top of the cochlea, by an opening: the hiatus, or helicotrema. That portion of the cochlear canal that is above the septum termi- nates in the vestibule; hence scala ■vestibuli. The lower portion opens into the tympanum through the round window; hence scala tympani. The membranous portion of the septum, or lamina spiralis, con- sists of two layers: The superior layer is the membrane of Corti, or membran-a tedoria; the other is the membrana basilaris. These two membranes are placed parallel with one another to contain between them the orga7i of Corti. The latter rests upon the basilar mem- ])rane. Fig. 311. — Scheme of the Labyrinth and Terminations of the Auditory Nerve. (Landois.) I. Transverse section of a turn of the cochlea. II. Ampulla of a semicircular canal, a, p, Auditory cells, p, Cell provided with a fine hair. T, Otoliths. III. Scheme of the human labyrinth. IV. Scheme of a bird's labyrinth. V. Scheme of a fish's labyrinth. The bony portion of the septum has, upon its superior external surface, a denticulated, cartilaginous substance called the lamina den- ticulata. From the superior surface of the lamina spiralis, and internal to the lamina denticulata, exists a delicate membrane, the membrane of Beissner. This membrane divides the scala vestibuli into two passageways, one of which is the ductus coclilearis. It con- tains the essential portion of the auditory apparatus of the cochlea : the organ of Corti. It forms part of the membranous labyrinth. The membranous labyrinth is a closed sac consisting of semi- circular canals, a vestibular portion, and the membranous part of 684 PHYSIOLOGY. Ihc lamina spiralis. The vestibular portion consists of an expanded body, the ulriele, and a smaller body, the saccule. Within these com- partments are two calcareous bodies: the oiolilhs. The vestibidar filaments of the cochlear nerve are distributed to the ampullge, utricle, and saccule. In the first the fi])ers terminate in elevations called cristce acusticw ; in the last two they end as oval plates, — maculce, — colored by yellow pigment. Organ of Corti. — The organ of Corti contains the following elements : — Sctymv- „„CT aa^a^^ivfea Fig. 312. — Section through the Uncoiled Cochlea (I) and througli the Terminal Nerve Apparatus of the Cochlea (II). (Munk, after Hensen.) I. Fr., Round window. H, Helicotrema. »S<., Stapes. II. IS, Huschke's process, h', Basilar membrane, e, Corti's arch, g, Sup- porting cells, h, Cylindrical cells, i, Deiters's hair-cells, c, Membrana tec- toria. n, Nerve-fibers. «', NonmeduUated nerve-fibers. 1. Arches of Corti. — They are formed of an internal and external pillar whose pedestals rest upon the basilar membrane. The arches intercept the canal of Corti. 2. Internal Auditory Cells. — Inward from the internal pillar of Corti is found a layer of auditory cells. These cells contain nuclei, while their superior extremities terminate in a plateau having long ciliated prolongations; their inferior extremities are in relation with THE SENSE OF HEARING. 685 the basilar membrane and axis-cylinder of the terminal cochlear branches of the auditory nerve. 3. A Granular Layer composed of rounded cells. 4. Cells in the sulcus spiralis which are cubical in shape. 5. The External Auditory Cells, whose structure and arrange- ment are very similar to the internal cells just mentioned. 6. The Cells of Deiters, Hensen, and Claudius, which make a prominence upon the interior of the cochlear canal. Fig. 313. — Section of the Ductus Cochlearis and the Organ of Corti. (After Landois.) N, Cochlear nerve. K, Inner, and P, outer, hair-cells, n. Nerve-fibrils terminating in P. a, a. Supporting cells. (7, Cells in the sulcus spiralis, z, Inner rod of Corti. Mb, Corti, membrane of Corti, or the membrana tectoria. o, The membrana reticularis. H, G, Cells filling up the space near the outer wall. 7. Reticular Mcmhrane. — The membrana reticularis is formed i)y the superior extremity of the cells of Deiters. It possesses lacunae which allow the passage of cilia of the cells. 8. The Memhrane of Corti, or membrana tectoria, is a soft, thick membrane which covers the spiral groove and organ of Corti. Be- neath it adheres to the cilia of the auditory cells. Auditory Nerve. — The auditory nerve consists of two ]iai'ts: the cochlear, the hearing part, and the vestibular, the tonus part. The cochlear part arises in the spiral ganglion of the cochlea, and, like a posterior root ganglion, sends a branch to the auditory cells in the 686 PHYSIOLOGY. organ of Corti and a central branch to the cochlear nucleus in the medulla. The cochlear nucleus consists of two parts : the accessory nucleus and the tuberculum acusticum. Hence the first neuron ex- tends from the spiral ganglion to the cochlear nucleus; then the two divisions of the cochlear nucleus — the accessory nucleus and NVI C^EVE. Oc M. CocU.n. Fig. 314. — Connections of Coclilea with Central Nervons System. (Paton.) Coch.R, Cochlear root of eighth nerve. N.Acr, Tuberculum acusticum and nucleus accessorius sending fibers to the cerebrum (C.B.) and to oculo-motor mechanism {N.VI.). tuberculum acusticum — send out neuraxons to the superior olive; here they are second neurons. The superior olive sends out neuraxons to the lateral fillet; here the third neuraxons make up chiefly the lateral-fillet fibers. These go to the posterior corpora quadrigemina and finally are connected with the seat of hearing in the first tern-, poral convolution. The vestibular root arises in Scarpa's ganglion-cells of the laby- rinth and goes to the vestibular nucleus. THE SENSE OF HEARING. 687 The vestibular nucleus is composed of the medial, the lateral, or Deiters's, the superior, or Bechterew's, and the nucleus of the descending root. There are connections between the nucleus of Deiters and the nucleus fastigii of the cerebellum. Deiters's nucleus £Y£. CCLLS a Ant Hotn. Fig. 'M'). — Connections of Semi-circular Canals with Central Nervous System. ( Paton. ) Ves.R, Vestibular root of eighth nerve sending fibers to C.B (cerebrum) and C.B.L (cerebellum) downwards to center in medulla oblongata (Med), and to Deiters's nucleus (.V.DciO. from which fibers pass to oculo-motor mechanism (N.Vi) and to center in the anterior horn of the spinal cord. is connected with the vestibulo-spinal tract which runs down the cord to the anterior horns. Fibers from the cerebellar nuclei go by the superior cerebellar peduncle and the red nucleus, and end in the 688 PHYSIOLOGY. cortex of the parietal and central convolutions. Some fibers from the nucleus of Deiters and of Bechtcrew go by the posterior longi- tudinal bundle to the nuclei of the motor nerves of the eye. (See equilibratory center of Mills.) The cochlear nerve is the nerve concerned in hearing. The vestibular nerve is the nerve concerned in equilibration. It docs not have anything to do with hearing. Memhrana Tympani. — The membrana tympani is an elastic, very vascular membrane, which protects the delicate organs of the middle ear against the action of cold coming in- from the external ear. It is also specially endowed with a specific sensibility for the contact of special agents, as the scratchings of an insect on its surface cause a peculiar auditory sensation. The membrana tympani is of variable size, according to the species of animal, and is adapted to receive low and high sounds. It is of circular form, and attached by its borders upon a bony circle, the tympanic circle. Its direction is peculiar. It cuts obliquely the axis of the external auditory meatus and this obliquity is favorable to the impact of sound-waves. It is depressed and becomes prominent in the middle, having the arrangement of a depressed cone. Under the shock of sound-waves the membrana tympani vibrates for all sounds in the range of per- ceptible sounds. Its vibration can be measured by a water mano- meter inserted into the external auditory canal. Accommodation of Memhrana Tympani. — Since the membrana tympani vibrates in unison with all the external sounds which strike it, it is inferrable that there is a means capable of regulating the tension of this membrane. The shape of the tympanic membrane is peculiarly adapted for transforming weak movements of wide amplitude into strong ones of wide compass. For it is not simply a depressed cone, but the radii are slightly curved with the convexity outward, a shape mainly caused by the elastic fibers maintaining a tension on its inner surface, these being most numerous toward the circumference. The principal regulator of the tension is the tensor tympani. The membrane of the tympanum has no definite funda- , mental tone ; it vibrates indifferently to every sound. The mem- brana tympani is tense for high sounds and relaxed for low sounds, but these changes in tension are chiefly for the intensity of sound rather than their height, so as to offer a resistance to the shock of sound-waves and obviate the effect of this shock upon the deep and delicate structure of the ear. The adherence of the membrana tympani to the handle of the THE SENSE OF HEARING. 689 malleus, which follows its movements, causes its vibrations to meet with considerable resistance. This diminishes the intensity of the vibrations, and prevents also the continued vibration of the mem- brane after an external vibration has ceased, so that a sound is not heard much longer than the moment when the exciting cause ceases. The tensor tympani at its base arises from the apex of the petrous portion of the temporal bone and the cartilage of the Eustachian tube, and is inserted into the malleus near its root. The membrana tympani has the handle of the malleus inserted into its layers; and as the malleus and incus move around an axis passing through the necK of the malleus from before backward, the action of the tensor tympani is to pull the membrana tympani inwards toward the tympanic cavity in the form of a funnel, the meridians of which are not straight, but curved with the convexity outwards. This making tense and relaxing the membrana tympani is a kind of accommodating apparatus for receiving and transmitting sounds of different pitch. With different tensions it will respond more readily to sounds of one pitch than to sounds of another. The tensor tympani receives its motor fibers from the fifth by the otic ganglion, and its movements are purely reflex. The stapedius muscle is innervated by the facial and exercises an antagonistic action to the tensor tympani. The stapedius draws the stapes outward, whilst the tensor tympani tends to press the stapes into the oval window. The two antagonistic muscles are able to comliine in such a manner as to modify the length of the chain of ossicles, and give an amplitude variable to the vibrations. Hensen has proved that these muscles are reflexly kept in a state of adjustment by the pitch of sound. Transmission of Sound Waves in the Middle Ear. — The normal and regular means of transmission of sounds is by the chain of ossi- cles, but it can take place by the air in the cavity of the tympanum, or by the bones of the skull. The ossicles of the middle ear form, by the articulations which unite them, a broken but rigid chain between the membrana tympani and the oval window. This chain of bones is not always in the same state, for the combined action of the two muscles modifies the length and rigidity of the chain. Pollitzer, by means of very fine pens, has been able to register the movements of the bones. In rarefaction of the air in the auditor}^ meatus, as with the pneumatic speculum, there is no clanger of pulling the stapes out of the oval window, for the incus only follows the malleus for a certain distance, the latter 690 PHYSIOLOGY. completing its motion by gliding in the joint. The destruction of the chain of bones does not necessarily cause deafness, any more than perforation of the membrana tympani, as long as the stapes is pre- served. If the stapes is torn out there is deafness, because the peri- lymph escapes into the middle ear and it is not able to transmit sound-waves to the membranous labyrinth. The bones of the head also conduct sounds, as is easily proved by closing the ears with your fingers and putting a watch between the teeth. The intervention of the bones of the skull in the trans- mission of sounds is made use of in the audiphone for the deaf, where a rod, which terminates in a large disk spread out to receive sounds, is held between the teeth. Transmission of Sounds by the Air in the Middle Ear. — In the normal state the air enclosed in the tympanic cavity plays an insig- nificant part in the transmission of sound-waves, but its interven- tion is inevitable when the chain of ossicles has been destroyed. It is probable that it conveys the sound to the round window. Eustachian Tube. — The air enclosed in the middle ear is con- stantly kept in an equilibrium of pressure with the external air by the intermittent patency of the Eustachian tube, which extends be- tween the cavity of the tympanum and the pharynx. The Eustachian tube is opened in each act of deglutition, by the salpingo-pharyngeus and the dilator tubal muscles. If the air is enclosed in the tympanic cavity, the oxygen goes to the blood and the carbon dioxide is given off, but the amount of carbonic acid given out is less than the amount of oxygen removed, so that the total quantity of gases in the tym- panic cavity is reduced, the air is rarefied, and the membrana tym- pani, on account of the vacuum, presses upon the chain of ossicles, which are immobilized and do not readily transmit any vibrations. By a forced expiration, the oral and nasal cavities being closed, fol- lowed by an act of deglutition, air may be driven into the tympanic cavity and a crackling noise will be heard. This is Valsalva's positive experiment. A forced inspiration accompanied by deglutition will draw air from the cavity, again causing a crackling noise, the nega- tive experiment of Valsalva. In the positive experiment of Valsalva the membrana tympani bulges outward ; in the negative experiment it bulges inward ; and in both, from the extreme tension of the mem- brane, there is a partial deafness for high-pitched sounds. Permanent closure of the Eustachian tube by catarrhal condi- tions is the most frequent cause of deafness. Closure of the tube, except in deglutition, is necessary for the transmission of sound-waves THE SENSE OF HEARING. 691 in tlie middle ear. Deglutitions periodically open the Eustachian tube and form an auxiliary function to that of hearing. These acts follow each other at short intervals and are repeated often during the day, even during sleep. In a deep mine where the atmosphere is considerably more dense than that on the surface, the uninitiated is instructed to swallow every few minutes. By so doing he maintains an equable pressure upon both sides of the membrana tympani. The secretory nerve of the submaxillary gland is the chorda tympani, which passes through the middle ear and may be considered as a proof of the functional unity which belongs to the salivary secre- tion and hearing. Fig. 316. — I. The Mechanics of the Auditory Ossicles. (After Helm- HOLTZ.) II. Section of the Middle Ear. (Munk, after Hensen.) I. a. Malleus, h. Incus, am, Long process of incus, s, Stapes. The arrows show the direction of motion. II. G, E.^ternal auditory canal. M.t., Membrana tympani. C, Tympanum. H, Malleus. L.S., Superior ligament. S, Stapes. Movements of the Osskles. — To the tympanic membrane is at- tached the handle of the malleus, whilst projecting above the edge of the membrane, into the tjTnpanic cavity, is the head of the bone. Helmholtz states that the malleus-incus articulation, in its action, may be compared with the points of the Breguet watch-keys, which have rows of interlocking teeth which offer scarcely any resistance to revolution in one direction, but allow no revolution in the other. Hence, when the handle of the malleus moves inward toward the tympanic cavity, the incus and its long process, which is parallel with 692 PHYSIOLOGY. the handle of the malleus, also passes inward, from the fact that the head of the malleus pulls the articulating surface of the incus out- ward. The long- j^rocess of the incus and the handle of the malleus vibrate in the same direction. When the long process of the incus moves inwaj-d it gives an impression to the stapes, with which it articulates almost at right angles. The stapes cannot he torn out of the oval window by the Sigle pneumatic speculum when the tym- panic membrane is drawn outward, as the incus only follows the malleus for a certain distance, the malleus sliding in the joint to complete its motion. The malleus and incus are fixed by ligaments in such a way that motion is only possible in to-and-fro vibrations around the so-called axis of rotation, one end of which is found at the origin of the anterior part of the anterior ligament of the malleus, and the other end in the short process of the incus. The ossicles of the ear act like a compound lever; the short process of the incus is the fulcrum ; the power is applied to the umbo, in which the handle of the malleus ends; and the resistance is the base of the stapes. The length of the handle below the axis of the malleus is one and one-half times that of the head above the axis. But the range of excursion is only two-thirds that of the handle and drum- head, whilst the power of movement of the head of the malleus will be one and one-half times more than that of the handle. By this means, according to Helmholtz, vibrations are diminished in extent but increased in force. The chain of ossicles vibrates as a whole, and not by molecular vibration. The tympanic membrane is twenty times the size of the oval window; hence the movement of the mem- brane of the oval window is smaller in extent, but about thirty times greater in power. When sound impinges against the tympanum, the tympanic membrane moves inward with the attached handle of the malleus, and the head of the malleus moves outward. The incus fol- lows these movements ; the body of the incus swings outward and the long process moves inward, which pushes the stapes into the oval window. Thus the ossicles and the fluid in the labyrinth do not form a mass vibrating independently, but as one body. Tensor Tympani. — The tensor tympani reflex has its sensory nerves from the trigeminus and its motor nerve from the same source. When one tensor tympani contracts, the tensor of the opposite side also contracts. In rare cases the tensor tympani is under the control of the will. THE SENSE OF HEARING. 693 A man who is absolutely deaf in one ear has great difficulty in recognizing the direction of sound. It will be recalled by the student that all of the spaces and com- partments of the internal ear, or labyrinth, are filled with peril}-mph, and that in this fluid float saccules containing endolymph fluid. So intimately are all of the parts of the labyrinth associated that any vibration of its contained fluid at one part is promptly propagated to every other portion. The vibrations of the fluid striking upon the tiny nerve-filaments act as stimulants whose impressions are carried to the center of hearing, where the impressions are recog- nized as sound. To epitomize: The sonorous waves collected by the auricle to pass through the external auditory meatus and along its canal strike the surface of the membrane of the tympanum. It becomes tense, vibrates in unison, and then communicates its vibrations through the ossicles and contained air in the tympanum to the oval window. From here the vibrations are carried over the vestibule, semi- circular canals, and labyrinth to the perflymph. From this the vibra- tions are transmitted through the membranous walls of the sacculus to the endolymph. Vibrations also pass from the vestibule to the scala vestibuli of the cochlea, and, through the helicotrema, descend- ing the scala tympani, end as an impulse against the membrane of the round window. Most of the organs of special sense contain a "specially modi- fied epithelium" for the reception of the particular kind of stimulus peculiar to each other. Xor is the sense of hearing different from the others. It also has its tissues representing "specially modified epithelium" in which lie the terminal filaments of the auditory nerve. These tissues are so constituted that they receive the "waves of sound" which generate auditory impulses in the auditory nerve. These last, when conveyed to the brain, are developed into auditory sensations. The vibrations of elastic bodies produce condensation and rai'e- faction of the enveloping atmosphere. That is, there are developed waves whose particles vibrate longitudinally. These waves are usually spoken of as sound-waves. iSTormally. then, the auditory nerve may be stimulated by sonor- ous vibrations which set into motion the end-filaments of the acous- tic nerve. The filaments are distributed over the inner surface of the membranous labyrinth, upon the membranous expansions of the cochlea, and in the semicircular canals. The excitement of the fila- 694 PHYSIOLOGY. meuts is really mechanical in nature, due to the wavelike motion of the serous fluid of the membranous labyrinth. It is common to divide auditory stimuli into those which are caused by noises and those caused by musical sounds. It is a feature peculiar to musical sounds that the vibrations which form them are periodical and that they recur at regular intervals. When neither of these two conditions is present, there results a noise. From the sensory impulses to which the several vibrations give rise are gen- erated our sensations of noise or of sound. To produce a sensation certain conditions in the excitation of the auditory nerve are necessary. The sound-wave must exist for a certain length of time ; it must not be greater than ^/^^ nor less than ^Aoooo second. In the piano the lowest base (C, 33 vibrations) and the highest treble (C, 422-i vibrations) exist. A certain number of impulses must be made within a given interval of time to excite a sensation of tone. The lower limit is about 30 vibrations, the upper limit about 40,000, per second. Visual sensations separated by less than a tenth of a second are fused, but auditory sensations separated by V133 second remain distinct. Theory of Hearing. — If you sing a note into a piano, the cords of the piano tuned for this note only respond. Now the basilar membrane is supposed, like a harp, to represent a series of cords which, like the piano-strings, respond to the sounds striking them. This membrana basilaris is striated in a radiating direction, and these striations increase as it ascends toward the helicotrema. Un- like the harp, the cords are joined together by their edges; but, as they are stretched only in a radiating direction, they can vibrate as though they were separate cords. Now, the cords are very short, being at most not over ^/^^ iiich in length; so that they would be expected only to vibrate for high sounds; but it must be remem- bered that these cords are weighted with the arches and cells of Corti, which lower their sound. Hence we have a series of cords in the basilar membrane vibrating separately to musical sounds. We know that there are in man about 3000 arches of Corti, and as at least two of the cords correspond to an arch of Corti, we have 6000 cords. Now, the scale of musical sounds extends to seven octaves, and we have 400 arches of Corti to 1 octave. In 1 octave there are 13 semi- tones, and we have 66 cords corresponding to a semitone; so that we have sufficient cords to vibrate in unison with all possible musical sounds. THE SENSE OF HEARING. 695 When the sound-waves vibrate the cells of Corti they make the terminal filaments of the cochlear nerve vibrate, because they are in relation with the cells of Corti. The analysis of sounds takes place in the brain. Binaural Audition. — The hearing of a single sound with both ears may be due to habit or to the connection in the nerve-centers of the fibers connected with both ears. Undoubtedly binaural audi- tion facilitates our knowledge of the direction of sound, since each ear has its own axis and direction. Fig. 317. — Schema of the Semicircular Canals, the Posterior Part of the' Skull Removed. (Hedon, after Ewald.) In the plane 1 lies the anterior canal. In the plane 2 the external canal. In the plane 3 the posterior canal. We combine binauricular audition, just as we judge of the relief of objects in binocular vision (stereoscopic vision), to determine the direction of sounds. The tympanic membrane may be looked upon as an organ of pressure-sense by variations of air-pressure, even when sound-sensations are not produced. A blind man has been able to state correctly that he has passed a fence, and whether it be of solid board or of open picket. It may be stated that the membrana tympani is the outward organ of pressure- sense, by which we know more or less the position of objects inde- pendent of the sensations of sight and hearing. The air is in endless movement, and its waves, striking against various objects, must be impinged against the drumhead with an intensity dependent upon their position and the physical properties of the bodies reflecting it. 696 PHYSIOLOGY. Auditory Sounds. — All auditory sensations are immediately re- ferred to the external air. When your head is immersed in water, then the auditory sensations are not projected externally, but seem to arise in the ear. Auditory Judgement. — The auditory sensations inform us of the nature, distance, and relative situation of bodies. The Judgments draw their exactness from associations established in previous ex- periences between those of hearing and the other senses. When we hear a particular instrument, the sensation we experience calls up a picture of all its qualities which, from our past experience, we know belong to that instrument. The appreciation of the distance of a "•?S!55a!!;LH|||lci«'(^ Fig. 318. — Semi-circular Canals on Right Side Destroyed. Com- mencing rotation of head of pigeon about five days after the operation. (After EwALD. ) (From Tigerstedt's "Human Pliysiology,' copyright, 1906, by D. Appleton and Company.) body by its sound results from thousands of experiences between audi- tory impressions of that body and the visual impressions. The auricle has an important part in the determination of the direction of sounds, causing an inequality of impressions which strike the two ears. Semicircular Canals. — The semicircular canals are, through the vestibular nerve and the cerebellum, the most important agents in the preservation of equilibrium. When in a pigeon the horizontal canals are divided, the head moves from left to right and from right to left, with nystagmus and a tendency to revolve on its vertical axis. When the inferior vertical or posterior canals are divided, the head oscillates from front to rear; the animal has a tendency to fall back- ward. A section of the superior vertical canal causes the head to THE SENSE OB HEARING. 697 oscillate from front to rear, with a tendency to fall forward. A sec- tion of all the canals is followed by contortions of the most bizarre nature. After a destruction of all the canals the animal cannot main- tain his equilibrium. Similar phenomena have been observed in man in disease of the semicircular canals, known as Meniere's vertigo. In the fixed position of the head there is equilibrium, hut with each movement the vary- ing tension of the liquid in the ampulla changes and irritates the hair-cells. The horizontal, semicircular canals form the arc of a circle, with an ampulla at each end. In rotation of the head to the right, the endolymph in the ampulla of the right horizontal canal will accumu- Fig. 319. — Twisting of the Head of a Pigeon twenty days after removal of all the semi-circular canals on the right side. (Ewald, J. R.) (From Tigerstedt's "Human Physiology," copyright, 1906, by D. Appleton and Company.) late in the ampulla because the membranous canal is very narrow. This will cause a high pressure in the ampulla. These ampullae and canals are, then, sensory organs, and give the animal an idea of the position of his head in space. Now, as the canals are at right angles to each other according to the three dimensions in space, their section makes the animal unable to know the position of his head and thus produces vertigo. Cyon's theory that the semi- circular canals give us a series of unconscious sensations as to the position of our heads in space, (See cerebellum.) Ewald holds that all the muscles of the body are kept in a state of tonus by means of the semicircular canals, and that injury to them affects those muscles whose movements are most delicate, such as those of the eye and larynx. The loss of tonus may be explained for some of the muscles by disturbances in the reflex arc of the vestibular nerve, Deiters's nucleus, and the vestibulo-spinal tract. Here is a 698 PHYSIOLOGY. reflex between the semicireiilar canals and the muscles of the body innervated by the anterior horns which liave the vcstibulo-spinal tract connected with thcni. The fibers from Deitcrs's nucleus go to the nuclei of the motor nerves of the eye by the posterior longitudinal bundle; hence the nucleus of Deiters may be a reflex center, with the semicircular canal on one side and the fibers from Deiters's nucleus to the motor nuclei for the eye-muscles on the other side. Destruction of the semicircular canals would thus cause loss of tonus in the eye-muscles. Fig. 320. — Position of Pigeon's Head after removal of all the semi- circular canals on both sides. (Ewald, J. R.) (From Tigerstedt's "Human Physiology," copyright, 1906, by D. Appleton and Company.) A 20-gram lead baU fastened to beak with wax, which cannot be moved, owing to weakness of the muscles of the neck. TJtriculus and Sacculus. — The utriculus and sacculus. small sacs, also contain hair-cells, and lying among them are the otoliths, con- sisting of crystals of calcium carbonate. Breuer states that these sacs give us information when the head is at rest and when it is making slow rotary movements. Thus they aid the function of the semicir- cular canals. In this view, the otoliths mechanically stimulate the hairs. CHAPTER XIX. SPECIAL SENSES (Concluded.) VISION. Those bodies are said to be liniiinons which especially affect the organ of vision. Some are luminous in themselves, others become so by reflection. Since there is no direct contact between the visual apparatus and the object which makes the impression, and since the distance which separates them is often infinite, it is impossible not to admit the existence of a particular intervening agent between the center of radiation and the eye. This agent is ether. How Does Light Transmit Itself? — The accepted theory to-day with regard to its propagation is the undulatory, or wave, theory. Its doctrines make light, like heat and sound, a mode of motion. A luminous body is one whose particles are in a state of vibration. That they may give rise to a luminous impression it is necessary that they be transmitted to the eye. Ordinarily the atmospheric air is the usual medium for the transmission of the vibrations of a sounding body to our ears. However, a luminous body does not become invisi- ble in a vacuum, as does a sounding body become inaudible. Hence, there must be supposed the existence of a highly elastic medium that pervades all spaces and all bodies. To this especial medium luminous bodies communicate their vibrations to be transmitted with enormous velocity. This medium is known to physicists as ether. Suppose a luminous body isolated in a gas or suspended in a vacuum; it will be visible in all directions. Imagine, also, a point of space lighted up by its radiations. The line which joins this point to one of the elements of the luminous body represents the direction of a ray of light. So long as no obstruction intervenes the ray of light pursues an even, straight course. Should, however, a mirror inter- cept its path, the greater portion of it will be bent out of its regular course. That is, it is reflected. In all cases of reflection it is well to remember that "the angle of reflection always equals the angle of in- cidence." Again, the passage of light through transparent media of various densities presents peculiarities: its straight course is modified — broken. To convey a conception of this phenomenon the term re- fraction is used. (699) , 700 PHYSIOLOGY. The organ of siglit, the eye, is constructed upon the principles of the camera obscura. In the latter the collecting lens unites the light impressions at the back of the apparatus to form upon the ground- glass plate a diminished and reversed image of external objects. Structure. — The (!ye is composed of three concentric coats (scle- rotic, choroid, and retina), the aqueous and vitreous humors and the crystalline lens. Fig. 321. — Diagram of a Horizontal Section through the Human Eye. (Yeo.) 1, Cornea. 2, Sclerotic. 3, Choroid. 4, Ciliary processes. 5, Suspensory ligament of lens. 6, So-called posterior chamber between iris and lens. 7, Iris. 8, Optic nerve. 8', Entrance of cerebral artery of retina. 8", Central depression of retina, or yellow spot. 9, Anterior limit of retina. 10, Hyaline membrane. 11, Aqueous chamber. 12, Crystalline lens. 13, Vitreous humor. 14, Circular venous sinus which lies around the cornea, a-a, Antero-posterior axis of bulb. 6-6, Transverse axis of bulb. The first, or outside, coat of tlie eye is opaque in all of its parts except a small anterior segment. This area, which is about one-sixth of the entire circumference, is perfectly transparent. The dense, opaque part is known as the sclerotic; the transparent portion is the cornea, which is the most anterior portion of the sclerotic. The sclerotic is thickest behind, in the neighborhood of the part pierced by the optic nerve, which is placed about a tenth of an inch inside of the antero-posterior axis. The sclerotic thins a little as it VISION. 701 passes forward, and is weakest about two lines from the cornea; the anterior portion again increases in thickness. Cornea. — It is joined to the sclerotic coat by direct continuity of tissue. The tissue of the cornea absorbs water readily and becomes opaque after death. The cornea has five layers. The first, or anterior, epithelial layer is composed of several layers of epithelial cells; the deepest are cylindrical, which pass over into the lower polygonal cells, which, on the surface, become flat, nucleated cells. At the edge of the cornea this epithelium becomes continuous with that of the conjunctiva. Second layer: the anterior elastic lamina (of Bowman) Vig. 322. — Anterior-postei-ior Section of the Eyeball. (Leveill:^.) 1, Optic nerve. 2, Sclerotic. 3, Cornea. 4, Spaces of Fontana. 5, Choroid. 6, Ciliary muscle. 7, Ciliary processes. 8, Iris. 9, Retina. 10, Jacobs's mem- brane. 11, Anterior chamber. 12, Posterior chamber. 13, Pupillary area. 14, Aqueous humor. 15, Hyaloid membrane. 16, Canal of Stilling. 17, Canal of Petit. 18, Vitreous humor. 19, Capsule of the lens. 20, Fluid of Morgagni. 21, Lens. is formed by the superficial part of the proper structure of the cornea, which is denser than the rest of the tissues and free from cor- puscles. This layer is strongly developed in man and is a homogene- ous refractive membrane. Fibrils can be demonstrated in it by means of certain reagents. Third layer: the substantia propria, or the cornea proper, forms the main mass of the cornea. It consists of fibrils of connective tissue bound together in flat lamella (about 60 in number). The fibrils run in various directions, and cross each other at various angles. Between the lamelhe are canals and spaces which contain a serous fluid. In these spaces are found the connec- tive-tissue cells, having many processes and large nuclei, around which the serous fluid trickles to carry nutriment to the surround- 702 PHYSIOLOGY. ing tissue. By the chloride of gold method a picture is obtained of this system of canals. The fourth layer: the posterior elastic layer, or membrane of Descemet. This lamina is about V2500 of an inch Fig. 323. — Section through the Human Cornea. (BoHM and Davidoff. ) 1, Anterior epithelium. 2, Basal colls. 3, Bowman's layer. 4, Substantia propria. thick, firm, refractive, and homogeneous in structure. When pieces of this layer are separated, they curl up with the attached surface innermost. At its circumference the lamina breaks up into bundles Fig 324. — Corneal Corpuscles of Dog. (BoHM and Davidoff.) of fibers, some of which form the pillars of the iris. To these radiating and anastomosing bundles of elastic fibers prolonged from the circumference of Descemet's membrane has been sriven the name VISION. 703 of pectinate ligament. The fifth layer of the cornea is the posterior epithelial layer, composed of low, hexagonal cells. The epithelium is deficient at the circmnference in the interval between the pillars of the iris. The openings formed are mouths of cavernous spaces (the spaces of Fontana), which lead into the circumferential channel (canal of Schlemm), through the intervention of which the aqueous chamber is placed in connection with the canal of Schlemm, which is a lymphatic channel. The cornea contains no blood-vessels. The corneal nerves enter into the substantia propria of the cornea, where Fig. 325. — Corneal Nerves of the Pig. (Rollet.) 1, 1, Larger nerves. 2, Plexus beneath Bowman's layer. 3, 3, Terminal twigs ascending through the epithelium. 4, Sub-epithelial plexus. they lose their medullary sheaths and form four plexuses at different levels : — 1. The ground plexus, in the deep layer of the substantia propria. 2. The subbasal plexus. 3. The subepithelial plexus. 4. The intraepithelial plexus, which consists of fine fibers run- ning between the epithelial cells, ending in knoblike terminations. Choroid. — The dark-brown choroid coat is the vascular coat of the eye. It consists of two parts, which are continuous with one another — the choroid and the iris. The choroid is composed of sev- eral layers. Externally it is bounded by a nonvascular membrane, the lamina supra choroidca. The arteries groove the sclerotic coat 704 PHYSIOLOGY. before passing into the choroid. After entering its substance they go beneath the veins, while the latter (vasa vorticosa) receive their tributaries as curved branches arranged in a peculiar form, which Fig. 326. — Diagram of the Vessels of the Eye. (Leber.) 1, Cornea. 2, Sclera. 3, Lens. 4, 4, Short ciliary nerves. 5, Long posterior ciliary artery. 6, Anterior ciliary artery and vein. 7, Posterior conjunctival artery and vein. 9, Vessels of the internal optic sheath. 8, Vessels of the external optic sheath. 11, Vena vorticosa. 12, Posterior short ciliary vein. 13, Branch of short posterior ciliary artery to the optic nerve. 14, Anastomosis of choroidal vessels with those of the optic nerve. 15, Chorio-capillaris. 16, Episcleral branches. 17, Recurrent choroidal artery. 18, Large arterial circle of Iris (transverse section). 19, Vessels of iris. 20, Ciliary prccess. 21, Branch of vena vorticosa from the ciliary muscle. 22, Branch of anterior ciliary vein from the ciliary muscle. 23, Canal of Schlemm. 24, Plexus of the corneal margin. 25, Anterior conjunctival artery and vein. has been compared to the branching of a weeping willow, and form four or five large trunks, which pierce the sclerotic half way between the optic nerve entrance and the edge of the cornea. In the inter- VISION. 705 vals between the vessels are elongated, stellate pigment-cells. The inner part of the choroid is formed mainly by capillary blood-vessels (tunica Euyschiana vel chorio-capillaris). This reaches to one- eighth of an inch from the corneal margin, where its vessels join those of the ciliary processes. On the inner surface of the tunica Euyschiana is a structureless membrane, the membrane of Bruch, which lies next to the pigmentary layer of the retina. The choroid Fig. .327. — Meridional Section of the Human Ciliary Body. (BoHM and Davidoff. ) 1, 2, Conjunctiva. 3, Sclera. 4, Meridional fibers of tlie ciliary muscle. 5, Ciliary processes. 6, Circular fibers of the ciliary muscle. 7, Iris pigment. 8, Stroma of iris. 9, Canal of Schlemm. 10, Membrane of Descemet. 11, Cor- nea. 12, Corneal epithelium. coat ends anteriorly in the ciliary processes and the iris. The ciliary processes consist of about seventy to eighty ridgelike pro- cesses running meridionally. They are arranged around the lens, and toward the outside the ground-substance of the processes bor- ders on the ciliary muscle. They have the same structure as the choroid, and contain very numerous blood-vessels, derived from the anterior ciliary arteries. 45 706 PHYSIOLOGY. Uses. — By reason of its vascularity the choroid is destined to nourish the all-important and underlying retina. By reason of its elasticity and contained musculature the choroid maintains intra- ocular pressure. The pigment of the choroid is believed to serve a dioptric purpose: that of absorbing the superfluous rays of light which pass through the eyeball on their way to the retina. Their absorption prevents dazzling and interference with vision. Fig. 328. — Dissection of the Zonula. (After Schultze. ) 1, Lens. 2, Cut surface of iris, 3, Ciliary processes. 4, Choroid. 5, Zonula. Ciliary Muscle. — The libers of this muscle can be divided into three parts: (1) The strongest layer is nearest the sclerotic. It is composed of a thick layer of fibers having a meridional direction, which extend backwards into the choroid. (3) The second part of the muscle contains fibers which are less intimately connected with each other. Their direction deviates more, and they radiate towards the center of the ocular globe. These fibers terminate near the pos- terior surface of the ciliary body. (3) The third part of the ciliary muscle is represented by the ring-muscle of H. Miiller, and is much VISION. 707 developed in hypermetropic eyes, and atrophied or absent in myopic eyes. It is composed of circular fibers, which form a ring parallel with the base of the cornea. The ciliary muscle arises from the sclerotic close to the cornea; its fibers are inserted into the pecti- nate ligament, and extend to be attached to the choroid, as has Just been described. Ciliary Buthj. — This includes the ciliary processes and the ciliary muscle. Fig. 329. — Lateral View of the Orbit, Showing the Nerves. (Deaver.) 1, Antrum. 2, Bristle in the antrum. 3, Loop between orbital and lacrimal nerves. 4, Tarsal plate. 5, Lacrimal gland. 6, Tendon of superior oblique. 7, Pulley of the same. 8, Infundibulum. 9, Frontal sinus. 10, Supra-orbital nerve. 11, Supra-trochlear nerve. 12, Levator palpebrge muscle. O, Lacrymal nerve. J, Superior rectus muscle. A, Frontal nerve. 13, Internal rectus muscle. 14, Optic nerve. 15, Short ciliary nerve. 16, Nasal nerve. 17, Ciliary ganglion. 18, Lacrimal nerve. 19, Motor oculi nerve. 20, Patheticus nerve. 21, Abducens nerve. 22, Ophthalmic division of the fifth nerve. 23, Gasserian ganglion. 24. Fifth nerve. 25, Inferior maxillary nerve. 26, Superior maxillary nerve. 27, Orbital nerve. Iris.- — This body is to be considered as a process of the choroid. It is made up of four layers: (1) The anterior epithelium, made of flat cells, which cover the anterior surface of the iris. (2) The stroma of the iris, which consists of connective tissue which contains numerous blood-vessels, which are radially arranged and have no muscular sheaths. In this part of the iris the smooth muscle-cells are collected to form the sphincter and dilator muscles of the pupil. The sphincter muscles are arranged circularly around the edge of the pupil. The dilating muscles run in a radial manner. The 708 PHYSIOLOGY. coloring inn tier which is found in the connective tissue of the stroma of (he ii'is, and its varying (juantity, give the color to the iris. (3) The posterior limiting layer, or a portion of Bruch's mem- brane. (-1) The pigment layer (uvea). This is made up of two layers of cells; the posterior layer is cubical and full ol' j)igment, the anterior layer is Hat and contains only a small amount of pig- ment. This pigment-layer is a continuation anteriorly of the pig- ment-layer of the retina. The color of the iris is due to pigmented connective-tissue corpuscles, especially in brunettes. The artery and veins of the iris lie at its periphery. OPTIC CENTIie.- /— ~ Fig. 330. — The Nervous Meclianism of the Iris. The pupil is made smaller by contraction of its circular fibers. These belong to the smooth type of muscle-fibers and are innervated by the oculomotor through the medium of its ciliary branches. The pupil enlarges through contraction of the radiating fibers of the iris. It is innervated by the ciliary branches derived from the great sympathetic. Sensory nerves are present, coming from the first branch of the fifth, or trigeminus. Hence, stimulation of the oculomotor and trigeminus, as well as cutting the sympathetic nerve in the neck, produces contraction of the pupil. Irritation of the sympathetic causes the pupil to dilate. The normal contraction and dilatation of the pupil are re/?e;c movements that are caused by the rays of a very strong or very faint light striking the retina. From the retina the impression is con- VISION. 709 veyed by the optic nerve to the anterior corpora (juadrigemina and then to tlie oculomotor nucleus and by its nerves to the iris. It is not due to the direct action of liglit upon the iris itself. The following cause changes in the diameter of the pupil: — Contraction of Pupil. — Stimulation of optic nerve; stimulation of third cranial nerve ; section of fifth cranial nerve ; section or paralysis of the cervical sympathetic; light acting on retina; accom- modation for a near object; myotics (eserin, stimulation of the ends of oculomotor) ; ana?sthetics (at first). Dilatation- of Pupil.- — Section of the optic nerve; paralysis of third cranial nerve; stimulation of fifth cranial nerve; stimulation Fig. 331. — Isolated Lens Fibers. (J. Arxold.) of sympathetic; stimulation of sensory nerves; mydriatics (atropin, by paralyzing the ends of oculomotor); dyspnoea, asphyxia; anaes- thetics (at the end). Meltzer and Auer have shown that, with the superior cervical ganglion present, adrenalin does not act on the pupil. When the ganglion is removed, then adrenalin dilates the pupil. I have con- firmed this statement. The Ceystallixe Lexs. — The lens is situated behind the iris, and enclosed in a distinct capsule. The lens consists, in the begin- ning, of cylindrical cells, which in the course of development in- crease in height, until exceedingly long cells are formed. The lens- fibers are flattened hexagonal prisms, which are thickened at their posterior ends. They run in a meridional direction from the an- 710 PHYSIOLOGY. terior surface backward, joined by a small quantity of cement sub- stance. The outer fibers have oval nuclei, whilst in the center of tlie lens no nuclei are found. The capsule of the lens is thicker on the anterior surface tbi'.n on the posterior. It is a clear, refractive membrane, nonvascular. Between the anterior surface of the lens Fig. 332. — Transverse Section of Lens Fibers. (J. Arxold.) and the capsule there is a single layer of cubical, nucleated cells. The radius of curvature of the anterior surface of the lens varies with the accommodation for distant vision. It is about 10 milli- meters to 0 millimeters in near point of distinct vision. Cataract. — Normally the lens is transparent. When it becomes opaque for any reason, then there results the condition known as cataract. Tliis condition is artificially produced in frogs by the injection of grape-sugar. Cataract in diabetes is from the same cause. Fig. 333. — Anterior Surface of tlie l^cns of an Adult. (J. Arnold.) The Eetina. — The retina contains the terminations of the optic-nerve fibers. It ends at the pupillary border of the iris. The optical part of the retina ends in the ora serrata, a zigzag line in the vicinity of the ciliary body. Bods and Cones. — Each rod consists of a rod and a rod-fiber, the fiber containing the nucleus. The rods are cylindrical and VISION. 711 elongated. The}' are divided into two parts, the outer segment and the inner. Tlie outer segment is doubly refracting, contains the visual purple, and breaks up into many superposed discs when acted Fig. 3.34. — Diagram of the Structure of the Human Retina According to r4olgi's Method. (Greeff.) I, Pigment epithelium layer. II, Rods and cones. Ill, Granules of the visual cells. IV, Outer plexiform layer. V, Layer of horizontal cells. VI, Layer of bipolar cells. VII, Layer of amakrine cells. VIII, Inner plexiform layer. IX. Ganglion cell layer. X, Layer of nerve fiber. 1, Diffuse amakrine cell. 2, Diffuse ganglion cell. 3, Centrifugal nerve fiber. 4, Amakrine association fiber. 5, Neuroglia cells. 6, Miiller's radial fibers. upon by certain reagents. The inner segment is spindle-shaped, granular, and singly refractive. The ellipsoid of Kraus is in the outer part of the inner segment, and exhibits a fibrous structure. 712 PHYSIOLOGY. The rod-fiber is a contiiination at its inner end of the rod. The fiber contains the rod-nnclous. Cones. — Both rods and cones are closely set lilvc a palisade over the whole extent of the retina, between the external limiting mem- brane and the pigmentary layer, except at the macula lutea, where there are only cones. The smallest angular distance at which points can be separately distinguished is 50 seconds, with which the size of a retinal image is 3.G5 micromillimeters. This size coincides closely with the diameter of the cones at the fovea, which are about 3 micromillimeters. Fig. 335. — Hexagonal Cells from the Pigment Layer of the Retina of a Rabbit. (Ball.) The cones, like the rods, consist of two segments, an inner and an outer. The cones are shorter than the rods. The outer seg- ment of the cone has cross striations. The inner segment is much thicker and shorter than the rod, and is rounded. The ellipsoid of the cone is larger than that of the rod, and lies in the peripheral part of the inner segment. A cone-fiber is a continuation of the cone. Between each cone there are usually two or three rods, show- ing the greater abundance of rods. The external limiting mem- brane is a product of the Miiller fibers, the sustentacular tissue of the retina. In the vicinity of the ora serrata the nerve-fiber and VISION. 713 ganglion-cell first disappear. At a certain distance from the ora serrata the rods disappear, and then the cone-cells change and become a layer of cylindrical epithelium. Tlie Pigmentary Layer. — It is composed of hexagonal pigment- cells. The outer surface of the cell, turned towards the choroid, is smooth and flattened, and the part of the cell near this surface is without pigment and is nucleated. The inner boundary of the cell is loaded with pigment and is prolonged into fine, straight, filament- ous processes, which reach for a certain distance into the outer seg- A B Fig. 336. — Action of the liight on Retina. Section of retina of frog. (Englemann.) (From Tigerstedt's "Human Physiology-."' copyright, 1006, by D. Appleton and Company.) A, After two days of rest, animal in dark, pigment concentrated, cones protruded. B, After diffuse daylight, cones retracted, pigment diffused. ments of the rods and cones, which are imbedded in the pigment- cells. The pigment is in the form of small, dark-brown granules and rods. In the dark, the pigment is mainly heaped up in the body of the cell; but when light strikes the pigment, it is drawn in between the rods. The pigment seems to renew the visual purple of the outer segment of the rods after they have been bleached by the light. The eyes of albinos have no pigment in the cells. Macula Lvtea. — The yellow spot of Soemmering is an oval de- pression in the center of the retina. It measures one-twentieth of 714 PHYSIOLOGY. an inch across and is one-tenth of an inch to the outer side of the ])oint of entrance of tlie o])ti(; nerve. Jts center is the fovea cen- iralis. In I lie fovea there are no rods: cones only ai'e |)resent, and these are longer and narrower than those of the other i)arts of the retina. When tlie optic nerve penetrates the eye it projects somewhat beyond the inner surface of the eyeball as a papilla. In this papilla there are none of the essential nerve-elements of the retina, so that rays of lif^iit cannot be perceived l)y this particular area; hence the name of blind spot. The nervous layer of the retina is composed princi])ally of the terminal nerve-elements of the optic nerve. Externally, it is coated Fig. .337.— Riglit Eye, Normal Fundus Oculi. (Ball.) with a pigment-layer; internally, it is lined with a homogeneous, transparent structure, the hyaloid membrane. Histological Structure. — The histological structure of the retina is very complicated. The retina is really an outward expansion of the original forebrain. The retina is usually divided into eight layers : — 1. The layer of nerve-fibers. 2. The layer of ganglionic cells. 3. The inner molecular layer. 4. The inner nuclear layer. o. The outer molecular layer. ('). The outer nuclear layer. 7. The layer of rods and cones. 8. The hexagonal pigment-layer. VISION. 715 The first layer consists of neiiraxons from tho ganglionic cells of the second layer. The second layer consists of a lot of mnlti- polar nerve-cells, and their neuraxons run inward to form most of the fibers of the optic nerve. The dendrons of these multipolar cells are branched and terminate in the inner molecular layer, of which this third layer is chiefly composed. The fourth inner nuclear layer is made up chiefly of round and oval cells with a peripheral neuraxon and a central neuraxon. The peripheral neuraxon arborizes around the dendrons of a ganglionic cell in the inner molecular layer. The fifth outer molecular layer is made up of the arborizations of the neuraxons of the visual cells of the outer nuclear layer. lobuL f. of Rolando intraparietal fissure /. of Sylirius parallel fissure corpus fascia. . denlata A B Fig. 338.— Diagram of Occipital Region of Riglit Cerebral lleiuisplieres. (Ball.) A, From iniior, and li, from outer aspect. The sixth layer, the outer nuclear layer, is the layer of bipolar visual cells. Their central neuraxons end in arborizations in the outer molecular layer about the dendrons of the bipolar cells of the inner nuclear layer. The peripheral processes of these cells are the rods and cones of the retina, which are similar to the dendrons of other nerve-cells. The seventh layer of rods and cones are the dendrons of the visual cells. The eighth layer is the pigment-layer of the retina. The retina is essentially formed by a number of nerve-cell chains, the elements of which are arranged in three series from with- out in. The first is the rod and tlie cone; the second is the bipolar cell, which interlaces with the peripheral dendrons of the ganglonic cells. The third element is the ganglion-cell. 716 PHYSIOLOGY. Tlic optic tract arises in the retinal cells, which are its trophic center. These retinal cells send in fibers which arborize around the cells of the anterior corpora quadrigemina, pulvinar, and the lateral corpus geniculatum. ^Now, from the lateral corpus geniculatum and pulvinar we have a second set of neuraxons running to the occipital cortex, the center of vision. Here the lateral corpus geniculatum and pulvinar are the relay centers in the path of visual impulses. The Vitreous Humor. — The hyaloid membrane, a homogene- ous capsule, encloses the vitreous humor. This hyaloid membrane divides as it cdmes forward over the vitreous, one part going to the capsule of the lens as the zonule of Zinn, and the other passing in front of the vitreous. The free part of the hyaloid, stretching from the capsule of the lens to the ciliary body, is termed the suspensory ligament of the lens. Between these two layers of the hyaloid the canal of Petit is formed, a lymphatic canal. In the center of the vitreous is the canal of Stilling, which, in the foetal state, was the pathway of the artery of Zinn to the posterior part of the capsule of the lens. The vitreous has no blood-vessels, and is composed chemically of water, 98.5 per cent., and salts, extractives, and traces of proteid and nucleo-albumin. The vitreous has fine intercrossing connective-tissue fibers, connective-tissue cells, and leucocytes. Aqueous Humor. — This fluid contains about 2 per cent, of solids, chiefly in the form of sodium chloride. It occupies the anterior chamber in the space back of the cornea and in front of the iris. The so-called posterior chamber lies between the back of the iris and in front of the lens. When by ulceration of the cornea or accident the aqueous humor escapes, it is found to be regenerated very rapidly. The secretion of the aqueous humor has been studied by fluore- scin instilled into the fluids of the eyeball. It has been found that ihe humor is secreted by the posterior surface of the iris and ciliary body. It passes through the pupil into the anterior chamber. Blood-vessels of the Eye. — There are two systems of blood- vessels: the retinal and the ciliary system. These systems are separate, and anastomose only at the j^lace of entrance. The retinal system is the central artery of the retina, which goes through the axis of the optic nerve until it reaches the optic papilla, where it divides into two branches, one running forward and the other in a posterior direction. These vessels are seen with the ophthalmo- scope. VISION. 717 Tha Cilianj System. — These break through the sclera to supply the choroid, the ciliary body, and the iris. The short ciliary, about six to twelve in number, supply the choroid and ciliary processes. The long ciliary, two in number, penetrate the sclerotic, run forward between the choroid and sclerotic to the ciliary muscle, forming a very vascular circle about the iris. Fie 339. — Diagram of the Lymph Spaces of the Eyeball. (After FucHS.) 1, Anterior chamber. 2, Posterior chamber. 3, Canal of Sohlemm. 4, Hya- loid canal. 5, Anterior ciliary vein. 6, Continuation of Tenon's capsule on the ocular tendons. 7, Lymph space around the vena vorticosa. 8, Perichoroidal space. 9, Supra-vaginal space. 10, Inter-vaginal space.' In deep-seated ciliary congestion you have a pus-zone about the cornea, which is much different from the bloodshot eye of conjunc- tivitis. The capsule of Tenon is a thin membrane which envelops the eyeball from the optic nerve to the ciliary region, forming a socket in which it plays. On its inner surface it is smooth, and is in con- tact with the outer surface of tlie sclerotic, tlie perisclerotic lymph- 718 PIIYRTOLOGY. space lying between it and the sclerotic. There are some nnstriped muscular fibers in the capsule of Tenon. These muscular libers are innervated by the cervical sympathetic, and project the eyeball when in action. Intraocular rrcssurc. — The iiiiraocular pressure depends upon the tension of blood in the arteries of the eye. The pressure under- goes oscillations simultaneous with the pulse and respiratory move- ments. The pressure is about 20 to 30 millimeters of mercury. Fig. .'MO. — .Schematic Eye three Times Natural Size. (Landolt.) (j)'. Anterior or principal focus. A, Anterior surface of cornea. //' and H", Principal points. K' and A"', Nodal points. 0", Posterior or second principal focus. F.c, Fovea centralis. <^', (p", Optic axis. The aqueous humor, which is secreted and absorbed with great ease, appears to regulate the pressure. Lymphatics.— The lymphatics of the eye comprise an anterior and posterior set. The former is located in the anterior and posterior chambers of the eye and has communication with the lymphatics of the iris, ciliary processes, cornea, and conjunctiva. The posterior set consists of the perichoroidal spaces lying between the choroid and sclerotic coats of the eyeball. VISION. 719 Optic Nerve. The optic ner\'e contains centripetal and centrifugal tibers. The bundle of centripetal tibers from the second layer of retinal ganglionic cells, which originate in the vicinity of the macula, go into the optic tract of the same and opposite side. Those going into the optic tract of the same side come from the temporal tract of the macuhi, while the decussating fibers come from the nasal side of the macula ; hence each optic tract is made up of fibers from the temporal half of the retina of the same eye and from the nasal half of the opposite eye. The optic tract then goes backward, passing around the cerebral peduncle, and breaks up into two bundles, the external and the internal. The internal bundle is connected with the internal geniculate body and the posterior corpus quadrigeminum, and is a part of Gudden's commissure. It has no connection with vision. The external bundle goes to the external geniculate body, the i^ulvinar and anterior corpus quadrigeminum. The cells in the external geniculate body receive the terminal arborizations, as also do the cells of the pulvinar and corpus quadrigeminum. From these ganglia neuraxons go through the most posterior end of the internal capsule (optic radiations of Gratiolet), to end in the occipital lobe, mainly in the cuneus. The pyramidal cells send centrifugal fibers to the external geni- culate body, to the pulvinar and the anterior corpus quadrigeminum, and from here new centrifugal axons go to the retina. Irritation of the occipital cortex in the monkey, say of the right lobe, causes movement of the eyes to the opposite side, through the action of the efferent fibers. The average dimensions of the dioptric system of the eye are as follows: — Index of refraction of air 1. Index of refraction of cornea, aqueous luinior, and vitreous bod}' 1.3365 Total index of refraction of the crystalline lens 1.4371 Radius of curvature of the cornea 7.829 mm. Radius of curvature of the anterior surface of the crystal- line lens 10.0 mm. Radius of curvature ol the posterior surface of the crystal- line lens (5.0 mm. Distance from the apex of the cornea to tlie anterior sur- face of the crystalline lens 3.G mm. Distance from the apex of the cornea to the posterior sur- face of the crystalline lens 7.2 mm. Thickness of the lens 3.6 mm. 720 PHYSIOLOGY. Using the above values, the positions of the cardinal points of Gauss, of the human eye on the optical axis, calculated from the apex of the cornea, are as follows: — Tlie first principal focus is situated 13.745 millimeters in front of the cornea. The other points ai'c behind the cornea: — The first principal [joint 1.75:32 mm. The second principal point 2.1101 mm. The difference is 0.35U9 mm. The first nodal point '. G.9085 mm. The second nodal point 7.;3254 mm. The second principal focus 2.282;}7 mm. These values are shown in Fig. 340, but are three times as great as in nature. From these data are shown the course of rays through the eye and the position and size of images. Perception of Light. Light is due to vibrations of ether; a proper conception of them gives the sensation of sight. Transmission of light, with air as a medium, is 186,0U0 miles per second. The rapidity of the vibra- tions influences the sensation produced, for color is for luminous sensation what height is for sound. The inferior limit of visible vibrations is represented by the color red; the superior limit is exemplified in violet. For light to be perceived physiologically by any individual it must make an impression ui^on the retina. The light falling upon the retina immediately stirs uj) certain changes in it which in turn give rise to nervous changes in the fibers of the optic nerve. This last change, or "visual impulse," produces a further series of events within the brain, one effect of which is a change in our conscious- ness; that is, there is a sensation. The point upon the retina at which the impressions are strongest and most exact is the macula lutea and its fovea centralis. The anatomical layer designed to be impinged upon by a distinct image is the membrane of Jacobson, the layer of rods and cones. As only the cones, and no rods, are found in the fovea centralis, it is the point where objects are fixed. Hence it must be held that the cones are the specific elements of the retina that are designed to make the individual perceive a luminous impression precisely. Nevertheless, the field of vision, though indistinct toward its periphery, is very much enlarged. VISION. 721 The luminous impression consists of the vibrations of the lumi- nous ether which stimulate the outer portion of the rods and cones. In them there is produced a molecular, mechanical change, or dis- turbance. Whenever the layer of rods and cones is stimulated, the excitation is propagated from without inward to all of the retinal elements. Von Kries holds that the cones alone have the power to per- ceive colors (day vision), whilst the rods are sensitive only to light and darkness. The rods, by their adaptability in the dark through the regeneration of their visual purple, form the special apparatus for vision in dim lights (night vision). The various elements are connected by fibers, and, finally, by the optic nerve with the brain. Physiology of the Eye. The study of the phenomena of the eye may be divided into four parts: (1) dioptrics, {2} accommodation, (3) imperfections and corrections, and (4) vision icith both eyes. Dioptrics. — The eye has previously been mentioned as being like a camera obscura. If a small opening exist in the shutter of a dark room the rays of light from tlie outside passing through the opening will form an inverted image of the external object upon the opposite wall of the chamber. However, unless the opening be very small, the image will be blurred and indistinct. These latter qualities will be due to overlapping of rays of light from various points of the object. If the opening be small enough the overlapping rays will be cut off and a distinct image be formed. Should a convex lens be interposed in the path of the rays of light the opening may be very considerably enlarged, and yet the various rays be brought to a focus so that diffused images will be prevented. The camera obscura is popularly known to-day in the form of the photographic camera. The latter consists of a box blackened on the interior to prevent reflection from the walls. In front is a short tube which contains achromatic lenses. In the back wall of the camera is found a ground-glass plate upon which the image formed by the lens is focused. If the camera be so adapted that parallel rays falling upon the lens are focused upon the ground-glass plate, then divergent rays must have their focal point behind the plate. Should the plate be moved backward or forward the focal point can be made to coincide with the conjugate focus of the rays diverging from the object. 46 •^22 PHYSIOLOGY. Spherical Aberration, which interferes with distinctness, is gotten rid of by cutting off outside rays. In the camera this point is accomplished l)y the insertion of a diaphragm through a slit in the lens-tube. The diaphragm is pierced by holes — a larger or smaller one being used according as the light is feeble or strong. The eye may be very aptly compared to the camera. It has a small opening in front through which pass the rays of light. The sclerotic and choroid coats form its walls. The refracting lenses are the cornea, aqueous humor, crystalline lens,- and vitreous humor. They all tend toward the accomplishment of the same end : to bring parallel rays of light to a focus upon a sensitive plate (the retina), Fig. 341. — Diagram Illustrating Spherical Aberrations. (Ganot.) The rays passing through the edge of the lens have a shorter focal distance than those passing nearer to the center. there to form a real inverted image of the object. Last, the iris with its pupil acts as a diaphragm. Chromatic Aberration. — The edge of the lens of a camera represents the outer angle of a prism. White light falling upon it is decomposed into its spectral components. Objects seen upon the ground-glass plate have an iridescent hue. In the eye this trouble is obviated by the presence of the iris and the fact of the edge of the lens being more angular and less curved. Visual Angle. — It is usually stated to be the angle included by the lines from the extreme points of the object where they cross at the nodal point. The apparent size of the object depends upon the visual angle. Acuteness of vision is inversely as the size of the visual angle. Act of Accommodation. — AYlien a luminous body is brought too near to the eye, the rays which pass from it tend to come to a focus VISION. 723 behind the retina. In this way circles of diffusion form, which would prevent the appearance of a distinct image if a special appar- atus did not exist for the purpose of modifying the degree of refrac- tion. This modification is what is understood by the term accommo- dation. Mechanism of Accommodation. — The ciliary muscle, when it contracts, causes the zone of Zinn to advance, and thus diminishes the tension exercised by the latter upon the capsule of the crystalline lens. The lens, left to itself, assumes the form which the elasticity Fig. 342. — Schemo of Accommodation for Near and Distant Objects. (Landois, after Helmholtz.) The right side of the figure represents the condition of the lens during accommodation for a near object and the left side when at rest. The letters indicate the same parts on both sides; those on the right side are marked with a stroke (or minute mark). A, Left half of lens. B, Right half of lens. C, Cornea. S, Sclerotic. CS, Canal of Schlemm. VK, Anterior chamber. J, Iris. P, Margin of pupil. T', Anterior surface. //, Posterior surface of lens. R, Margin of the lens. F, Margin of ciliary processes, a, h. Space between the two former. The line Z-X indicates the thickness of the lens during accom- modation for a near object. Z-Y, the thickness of the lens when the eye is passive. of its fibers naturally gives it and becomes more convex, especially at its anterior surface. When the action of the oculomotor nerve ceases, the ciliary muscle is relaxed, the ciliary processes become tense and make traction on the zone of Zinn, which in turn flattens the lens by exerting upon it a traction in the direction of its equator. The retina follows along with the choroid in the movement of accommodation. When the traction of the ciliary muscle ceases relaxation of accouimodatiou in tliis way, the border of the retina, being closely attached with the choroid, is stretched and irritated by the siulden relaxation of accommodation until the lens flattens. These locomotor changes of the choroid may generate a choroid- itis, especially in the production and progress of myopia. Atropine, by 724 PHYSIOLOGY. paralyzing the oculomotor nerve and thus the ciliary muscle, has a very favorable influence by putting the affected membranes at rest. The suspensory ligament (zone of Zinn) is not a membrane, but an agglomeration of fibers of the nature of connective tissue. They originate partly at the ora serrata from the intervals between the ciliary processes, and a few of them from the ciliary processes themselves. Accompanying the act of accommodation is a contraction of the pupil, which dilates when the accommodation relaxes, and a conver- gence of the eyeballs due to a contraction of the internal recti. The range of accommodation is as follows: — BARS Range of Accommodation 10 14 D. 15 12 20 10 25 8.0 .30 7 35 5.5 40 4.5 Years Rangk of Accommodation 45 3.5 50 2.5 55 1.75 60 1. 65 0.75 70 0.25 75 0. This table shows that the power to accommodate diminishes rapidly and considerably as we become older. This is due to the decreasing elasticity of the crystalline lens. The crystalline lens commences early to change its physical constitution and becomes more rigid, whilst our other bodily forces are in a state of progres- sive development. In what may be regarded as the normal, or so-called emmetropic, eye, the near point of accommodation is about five inches. The far limit, for all practical purposes, is from 200 feet up to an infinite distance. In this eye the range of distinct vision has wide latitudes. In the myopic, or short-sighted, eye the near point is two and one-half inches from the cornea. The far limit is at a variable, but not very great, distance. The range of vision in this eye is very limited. In this the rays of light are brought to a focus in front of the retina. In the hypermetropic, or far-sighted, eye rays of light coming from an infinite distance are, in the passive state of the eye, brought to a focus behind the retina. The near point is some distance away. The presbyopic, or long-sighted, eye of aged persons resembles the hypermetropic eye, but differs in so far that the former is an essentially defective condition of the mechanism of accommodation. There are two changes which occur when we accommodate for near objects: one is that the pupil contracts to cut off divergent VISION. 725 rays; the other is a change of curvature of the lens. The ciliary muscle is the motive power of accommodation. Its paralysis renders accommodation impossible. The oculomotor innervates the ciliary muscle. Its paralysis by atropine produces both dilatation of the pupil and inability to accommodate. To correct anomalies of refraction it is necessary to use lenses. These are transparent media which seem to refract rays of light Fig. 343. — Refraction of Pai-allel Rays of Light in Emmetropia (E), Hypermetropia {H) , and Myopia {M) . ( Ball. ) passing through them. They have curved surfaces. The direction which the rays take on emerging from the medium depends upon the nature of the curvature. The chief forms of lenses are convex and concave; convex lenses may be doubly convex, plano-convex, or concavo-convex. A concave lens may have equivalent features. A convex lens converges the rays of light; a concave lens diverges the rays of light. In myopia a concave lens is used; in hypermetropia and presbyopia, a convex lens. 726 PHYSIOLOGY. Astigmatism is n defect of refraction due to a want of S3'mmetry in the refracting media of the eye. The result of this is that the rays of light passing through the lens are not l)rought to a focus at the same point. This want of symmetry is usually in the cornea, but may he in the lens. To remedy this defect we use a lens called a cylinder to level up the curvature of one of the meridians of the Fig. .344. — Different Kinds of Lenses. (Ganot. ) A, Double convex. B, Plano-convex. C, Converging concavo-convex. D, Double concave. E, Plano-concave. ¥, Diverging concavo-convex. C and F are also called meniscus lenses. cornea to correspond to the curvature of the others. Cylinders have no curvature in one axis, but more or less considerable curvature in the opposite axis in correspondence with the degree of astigmatism that has to be corrected. Lenses. — Lenses are arranged according to their focal distance in inches, and, as the unit was taken as one inch, all weaker lenses r G ^^e-^) Fig. 345. — Refraction of Rays in Regular Astigmatism. (Ball.) were expressed in fractions of an inch. However, Bonders made the standard in lenses of a focal distance of one meter, and this unit he called a dioptre. Thus the standard in a weak lens and the stronger lens are multiples of these. Hence a lens of two dioptres equals one of about twenty inches' focus. Purktn.te-Sanson's Images.— If you place a lighted candle in front of the eye of a person, three images of the flame are seen. One, which is direct, small, brilliant, and comes from the anterior VISION. 727 surface of the cornea; another, which is in the middle, is direct, larger, hut not so hright, and is due to the anterior surface of the lens, which acts as a convex mirror; and, finally, a third image, small, inverted, and brilliant, due to the posterior surface of the Fig. 34G. — Uiagrani Showing Refraction by a Double Convex Lens. ( Gaxot. ) The incident ray (,L-B) is refracted at the points of incidence (B), and emergence (D), toward the axis (M-N-A), which it cuts at F. lens, which also acts as a convex mirror. If the person experimented on looks fixedly at objects placed at different distances, the only change in the three reflections which we mentioned will be found to take place in that caused by the anterior surface of the crystalline lens. This fact leads to the conclusion that the phenomena of accommodation are dependent upon a change in the anterior surface of the crvstalline lens. Fig. 347. — Concave Lens Diverging Parallel Rays of Light. (Laiiousse. ) In the act of accommodation, when the candle is brought nearer the eye, the image due to the anterior surface of the crystalline lens becomes smaller because the lens becomes more convex. The form and variations in form of the dioptric surfaces of the eye can be measured by Helmholtz's ophthalmometer and the phako- scope of Helmholtz. '28 PlIVSIOLOaY. Blind Spot. — ]\[iU"ri()llc's cxpcriiiiciit jji-ovcs Hint at the en- trance ot the o])tie nerve, w Ihtc rods and cones ai'e not lo Ix; tound, the spot is a blind spot. Thus: make a cross and a cireh' about tliree inches a])art upon ])apcr. With the right eve view the cross, keeping the k'ft eye 12 3 12 3 A B Fig. 34S. — Piirkinje-Sanson Images. (Ball.) A, In the absence of accommodation. IS, In accommodation. 1, Reflection from the cornea. 2, From the anterior surface of the lens. 3, From ihe poste- rior surface of the leas. closed. Hold the paper about a foot from the eye, when both cross and circle will be visible. Let the paper be gradually brought nearer the eye, keeping the right eye steadily fixed on the cross. At a cer- tain moment the circle will disappear, and that time is when the image of the circle falls upon the optic nerve entrance. + Fig. 349. — Diagram to Sliow tlie Blind Spot in tlie Visual Field. (Ball.) The minimum visual angle is fifty seconds; below this limit the extreme points of an object are no longer separate and but one point is perceived. The minimum visual angle corresponds to a retinal image of about .004 millimeter, which is nearly the diameter of one of the cones of the retina. AcuTENESS OF VisiON. — Acutcness of vision is in inverse ratio to the visual angle. It diminishes as the later increases. In favor- able conditions, bodies having a diameter of V^^ to Vioo of an inch are perceived by the naked eye. VISION. 729 Circles of Diffusion. — When rays of light proceeding from a luminous object do not come to a focus directly on the retina, the image is no longer distinct, and circles of diffusion appear about it. In the normal condition, the luminous rays passing to a point of the retina through the pupil form a cone, the base of which is at the pupil and the apex at the retinal focus. But if the focus be placed Fig. 350. — Scheiner's Experiment — an experiment to determine the minimum distance of distinct vision. in front of or behind the retina, the latter intersects the bundle of rays so that, instead of a point on the retina corresponding to one on the luminous object, we have a circle formed. The different points of the retina will be intersected by rays coming from various parts of the object, and the image in this way becomes blurred and Fig. 351. — Diagram to show that the visual angle and size of the retinal image vary with tlie distance of the object from the eye. (Ball.) The image of S-B is seen at 0.8. under the angle g, and the image of T.C. is seen at I-W under the angle Ma. loses its distinctness. The existence of these circles of diffusion explains why it is that we cannot at the same time see clearly objects which are placed at different distances from the eye. Their size varies with the distance of the focus from the retina, being larger as the distance is greater, and also with the size of the pupil, con- 730 PHYSIOLOGY. trad ion of which narrows tlic cone ol' luminous rays and conse- quently the circles of diffusion. SciiEiNEK^s Experiment. — A card is taken in which two small holes are placed close togethePo The card is held close to the eye, and in front of it a needle is held. When you move the needle nearer the card, and then farther from it, a position is found where it is distinctly seen. If it be brought slightly nearer, the needle appears double, and you obtain the double image. The explanation is easily seen from the diagram. Fig. 350. e f represent the holes in the card, a the point of the needle, h a lens, and m n I a screen at varying distances from it. With the TS NA Fig. 352. — Diagram Showing tlip Corneal Axis, IJ-E; the Optic Axis, 0-A; the Visual Line, R-Y ; the Line of Fixation, R-J ; and the Three Angles. (Ball.) The angle between U-E and the visual line R-Y is the angle Alpha, averaging 5 degrees. The angle between the optic axis (O-.l) and the line of regard {R-J) is the angle gamma. The angle between the optic axis (0-A) and the line of vision (R-Y) is the angle beta. T8, Temporal side. NA, Nasal side. screen at n, a distinct single image of the needle is perceived, because the rays e and / coincide and are focused at n n. At the position m the image is blurred and double because the rays from e do not coincide with those from f; while at I the image is also double and blurred because the rays are intercepted after they have diverged from their focus. Let h represent the refractive media of the eye, and m n the retina. The Optic Axis. — This is a line which passes through the nodal point and the center of the cornea. If prolonged backwards, it falls upon the retina on the inner side of the yellow spot. The Visual Line. — The visual line joins the macula lutea with the point on which the eye is fixed. It passes through the cor- VISION. 731 nea a little to the inner side of its center, and therefore forms an angle with the optic axis, which is termed the angle alpha, which normally does not exceed -l to 5 degrees. Horopter. — The horopter represents all those points of the outer world from which rajs of light passing into both eyes fall on identical points of the retina, the eyes being in a certain position. It is a circle of which the chord is formed by the distance between the point of decussation of the rays of light in the eye. Its size is determined by the position of the two eyes and the point towards which their axes converge. All objects not found in the horopter, or which do not form an image on corresponding points of the retina, are seen double. IxvERTED Image of Objects. — The rays proceeding from the surface of luminous bodies above the optic axis cross in the eye so as to be brought to a focus below the axis, and mce versa. Thus an inverted image is formed on the retina. The Acuteness of Vision is tested by Snellen's types. It has been found out that square letters which have limbs and parts equal 732 PHYSIOLOGY. in breadth to two of the height of the letters are distinctly legible to a normal eye under an angle of live minutes. These letters arc numbered, the numbers expressing in meters tlie distance at which the letter can be seen under an angle of five minutes. The eye is tested with letters smaller and smaller at the same distance from the eye, (! meters. Suppose No. 6 type is thus seen; then Ve = l, Fig. .354.— The Visual Angle. If Xo. 'ig. 365. — Loring's Ophthalmoscope. two photographs taken at the same time by two cameras, so placed that their axes* shall form the same angle with each other as that which the axes of the two eyes would form when looking at the same object. "When we look at a solid object near l^y with l:)oth eyes, the right eye sees farther round the object on the right side, and the left eye farther round on the left side. These two slightly different images, when compared in the mind, produce the perception of 742 PHYSIOLOGY. solidity or depth, since experience has taught us that those objects only which have depth can affect the eyes in this way. The photographs are slightly different from each other, for if they were identical no sensation of relief will ensue. The combina- tion of the dissimilar images furnished by the two eyes is a mental act. 0 Fig. .366. — Direct Oplitlialmoscopy. (Ball.) Lacrymal Secretion. — Lately it has been shown by Landolt that in the rabbit and the monkey secretory nerves of the lacrymal gland run in the facial nerve. These nerves leave the geniculate ganglion Eve Lens Fig. .367. — Indirect Ophthalmoscopy. ; Ball. ) and enter the superficial petrosal. We then find them in the supe- rior maxillary and occasionally in the ophthalmic. He believes these fibers run in the glosso-pharyngeal and then in the facial, but he did not locate the nucleus from which they arise. Eserin increases the secretion of tears, atropine decreases it. VISION. 743 Ophthalmoscope. — This is a small concave mirror by means of which rays of light are directed through the pupil of the eye so that the deep parts are illuminated and made visible. There is a hole in the center of the mirror through which the examiner looks. But the ophthalmoscope may be used with or without lenses. Without lenses the ophthalmoscope gives an erect image. If, however, we use a convex lens over the central aperture of the ophthalmoscopic mirror the observer sees a re-inverted image. If a concave lens is used over the aperture of the ophthalmoscopic mirror there is seen an erect image considerably magnified. The instrument is usually fitted with a series of concave and convex mirrors, which can be revolved in front of the central aperture of the mirror. If the observer is myopic he can nse the concave lenses to cor- rect his myopia. If he is long-sighted, he corrects it by means of one of the convex lenses. Fig. 368. — The McHardy Perimeter. (Brown.) If the eye examined be short- or long-sighted, the retinal image could not be brought into focus with the mirror alone, but the examiner can adjust his concave or convex disc, as the case may be, and find a lens to correct the short or long sight of the eye examined. In this way the ophthalmoscope may be used to measure the degree of myopia or hypermetropia of the eye examined. Perimeter. — It has been noted that by the peripheral parts of the retina a person can observe pretty definitely the form and color of objects. To determine just how far this field of indirect vision extends in exevx direction from the visual axis is to locate, bv the 744 PHYSIOLOGY. perimeter, the field of indirect vision. The instrument devised for this purpose is called the perimeter. With the perimeter the eye is made to view a fixed point from Avhich a ([uadrant proceeds so that the eye lies in the center of it. Around the fixed point the quadrant rotates, and this circumscrihes the surface of a hemisphere in the center of which the eye is located. From this fixed point ohjeets are slid on semicircular arms and are 7< 2M^ " X*^' / y\ )ir-^ ' / 1 /\ ^ ,. r,^ ;,■ rli 'A. ^ITJ^ \\ jL? TO \ \\ ^ \ / \ izs\ J/ita- Blue Yellow.. R(2d_._ /s \' \ ^-^\ y^ 2S5' 2SJ' Fig. 369. — Diagram of tlie Normal Visual Field for White and Colors. (Jennings.) The outer continuous line indicates the limit of the field for white, and the broken lines indicate the limits of the color fields. gradually placed more toward the periphery of the field of vision until the ohject is no longer noticed. Then hy moving the semi- circular arm in different meridians of the field of vision we ohtain what is called the field of vision. The field of vision is more extended below and to the outer side. It is narrowed above by the brow; below by the cheek and the nose. VISION. 745 Fig. 370. — Diagram of the Visual Tract. (Ball. R.F., Right visual field. L.F., Left visual field. A'. Nasal side, side. R.R., Right retina. L.R., Left retina. O.C, Optic chiasm nerve. O.T., Optic tract. C.Q., Corpora quadrigemina. geniculate body. T.O., Optic thalamus. C.C, Corpus ca.llosum T, Temporal O.y., Optic Ex.G.B., External 746 PHYSIOLOGY. Visual Field. — 'I'lie Loundary of the visual field of white light crosses the upper vertical meridian at 55°, the median meridian at <;0°, the lower vertical meridian at 70°, and the external meridian beyond !)0°. The field for yellow light is witliin that for white, the Fig. 371. — Diagram of Right Homonymous Hemianopsia and of the sites of lesions which may cause it. ( Ball. ) RE, Right eye. LE, Left eye. ON, Optic nerve. C, Chiasma. OT, Optic tract. Th, Thalaml optici. O, Corpora geniculata. Q, Corpora quadrigemina. RC, Right cuneus. OR, Optic radiations. field for blue light within that for yellow, the field for red within that for yellow, and the field for green is much smaller. Pathological. — Argyll-Eobertsox Pupil. — Here there is no contraction of the pupil to light (no light-reflex) ; but it does con- tract when the accommodation is called into play for near objects,. VISION. 747 it has accommodation-reflex. It occurs in locomotor ataxia and in paresis. Both pupils act, though only one retina is stimulated, owing to the intercentral coupling of the two constricting centers of the pupil. In dyspnoea the pupil dilates, but wheh asphyxia ensues the dilatation diminishes. Atropine paralyzes the oculomotorius terminals (thus paralyzing accommodation), but after its section the dilatation of the pupil is still further increased by atropine; hence it must be an action on the dilating fibers. Eserin, a myotic, contracts the pupil, due to stimulation of the oculomotor. The ansesthetics con- tract the pupil, but when their action is deep they dilate it. Weenicke's Hemiopia Pupillaky Eeaction. — If the light is thrown on the hemianopic half of the retina, the pupil remains inac- tive. Here there is an interruption in the path between the retina and the geniculate bodies; the hemiopia is not central, but due to a lesion in the tract of the optic nerve. If the light is thrown on the sensitive half of the retina, the pupil immediately contracts. CHAPTER XX. CRANIAL NERVES. The cranial nerves are twelve pairs of nerves which reach their respective terminations after passage through foramina located in the base of the cranium. They are designated numerically, begin- ning from the anterior jDortion of the base of the brain backward, as well as by names dependent upon their functions and distribution. They are as follows: — 1. Olfactory. 5. Trifacial. 9. Glosso-pharyngeal. 2. Optic. G. Abducent. 10. Pneuniogastric. 3. !Motor oculi. 7. Facial. 11. Spinal accessory. 4. Pathetic. 8. Auditory. 12. Hypoglossal. Origin of the Cranial Nerves. — Upon examination, each cranial nerve is found to possess a point of superficial orifjin as well as a nucleus of deep origin. The superficial origin is that point upon the brain's surface where each nerve emerges. This is but the apparent origin of each pair of nerves, since their individual fibers may be traced more deeply. Each cranial nerve has a special nucleus of gray matter lying deeply within the brain-substance. The nucleus consists of a col- lection of cells from whose prolongations spring the axis-cylinders which constitute the fibers of the nerves. The gray masses which represent the prolongations of the anterior horns of the cord into the medulla oblongata form the nuclei of origin of the cranial motor nerves. The base, separated from the head of the horn by decussation of the pyramidal columns, remains contiguous to the central canal. It is prolonged in its entirety upon the floor of the fourth ventricle, lying upon each side of the raphe. Beneath the trigonum hypoglossi lies the nucleus of tlie hypoglossal; beneath the eminentia teres is found the common nucleus of the facial and abducent; the nuclei of the oculomotor and pathetic lie upon each side of the aqueduct. Tlxe head of the anterior horn, cut into fragments by the motor decussation, forms that which is known as the antero-lateral nucleus. This is the motor nucleus of the mixed nerves. Bv its most internal (748) CRANIAL NERVES. 749 parts it represents the accessory or anterior nucleus of the hypo- glossus; farther up, tlie proper nucleus of the facial; and in the pons there is found the motor root of the trigeminus. The gray masses of the posterior horns of the cOrd, prolonged into the medulla oblongata and cut by the sensory decussation or fillet, form the sensiiire nuclei of the cranial nerves. The base of the posterior horn forms the sensory nucleus of the mixed nerves, namely : glosso-pharyngeal, vagus, and spinal accessory. Above these nuclei there is a gray layer which represents the oblongata cen- ter of the internal root of the auditory; higher still arises the sen- sory nucleus of the trigeminus. The head of this horn, under the name of gray nucleus of Kolando, ascends in the pons to form the ascending root of the trigeminus. Among the twelve pairs of cranial nerves, ten have their points of origin in cells of the gray nuitter of the cord. This latter has been prolonged into the medulla oblongata and pons in the form of four motor and sensory columns. Thus these cranial nerves are com- parable to spinal nerves. Comparable to Spixal Xerves. — The law of double root is as applicable here as to the spinal nerves. Those nerves destined for movement originate in the prolongations of the anterior horns, while those which preside over sensibility take their origin in gray matter of the medulla and pons which has sprung from the posterior horns of the spinal cord. Point of Difference. — There is this difference, however, between cranial and spinal nerves: In the spinal nerves, the two roots are intimately united just outside of the spinal-cord substance to form a mixed nerve. In the case of the cranial nerves the posterior sen- sory roots and the anterior motor roots remain, for the most part, separated to form nerves that are either exclusively motor or exclu- sively sensory. In other words, the cranial nerves represent the dis- sociated spinal nerves in which the anterior and posterior roots remain habitually isolated to form nerves which are either fine con- ductors of motion or sensation, dependent upon their source. In the hypoglossal alone are fulfilled the true characteristics, for in numerous cases it is fouiid to have a ganglion upon its pos- terior root. The mesencephalon has been considered to possess parallel fea- tures with the spinal cord, in that it is formed of a series of seg- ments corresponding to the cranial nerves. As the student already knows, each spinal nucleus has peripheral conductors which bring to 750 PHYSIOLOGY. the cord its sensory impressions, and motor nerves to conduct to the muscles the motor reactions. In the same way the central conduc- tors of the brain bring to it sensory impressions and by its motor fibers carry out motion. Hence it results that all of the sensory fibers of centripetal course have their origin, not in the gray nuclei of the medulla oblongata, but in the ganglia annexed to the dorsal roots of the cranial nerves. The oblongata nuclei are but terminal nuclei, for in them the sensory fibers terminate by fine arborizations- w^hich surround the central cells without penetrating them. The termination is identical wdth that of the sensory roots Qf the spinal nerve. JX, IS. w. Fig. 372. — Position of the Xuclei of the Cranial Nerves. (After Edinger.) The medulla oblongata and pons are Imagined as transparent. The nuclei of origin (motor), black; the end nuclei (sensory), red. The sensory fibers of the tenth, ninth, seventh, and fifth pairs of cranial nerves, as well as that of the auditory, originate in their respective ganglia. Thus, there is the jugular for the tenth pair, the jugular and petrosal for the ninth pair, the geniculate for the seventh, Gasserian for the fifth, and Scarpa's and spiral ganglia for the eighth pair. On the contrary, the motor fibers of the cranial nerves arise in the central cells of the medulla and pons, just like the motor fibefs of the spinal cord. Thus, fine anatomy demonstrates that the cranial, like the spinal, nerves have dovhie roofs. Decussations. — The afferent or sensory cranial nerves do not decussate. Of the motor cranial nerves, the third and fourth, the CRANIAL NERVES. 751 motor root of the fifth, the seventh, the motor root of the vagus, the giosso-pharyngeal, and the hypoglossal decussate partially. The jjathetic decussates completely in the valve of Vieussens. The last- named nerve springs from the oculomotor nucleus united with that of the pathetic. These portions of gray matter are a direct part of the anterior horn of the spinal cord lying heneath the aqueduct of Sylvius. In Chapters XYII and XIX were considered the olfactory, or first pair of cranial nerves, and the optic, or second pair; so that in this chapter there will be taken up, first, the motor oculi, or third pair of cranial nerves. THIRD PAIR, OR MOTOR OCULI NERVE. This nerve arises from a nucleus situated between the corpora ciuadrigemina and beneath the floor of the aqueduct of Sylvius. Beneath the posterior end of the anterior corpus quadrigeminum this nucleus becomes continuous with the nucleus of the trochlearis or patheticus. The oculomotor nuclei consist (1) of a group of cells concerned in accommodation; (2) those concerned in the reflex action of the iris to light; (3) the innervation of all the muscles of the eye except the external rectus and superior oblique. The neuraxons of these cells pass by and through the red nucleus and emerge at the inner side of the cerebral crura, to pass through the interpeduncular space along the outer boundary of the cavernous sinus; they then enter the sphenoidal fissure, and go to the muscles of the eyeball, except the external rectus and superior oblique. It also gives fibers to the ciliary muscle and the sphincter of the pupil and a branch to the elevators of the upper lid. The posterior longitudinal bundle is also connected with the nuclei of the third, fourth, and sixth nerves. The oculomotor nucleus also has a connection with the optic neurons in the anterior corpora quadrigemina. In the cavernous sinus it receives filaments coming from the carotid branches of the great sympathetic and a branch from the ophthalmic of the trigeminus. Functions.- — From a functional point of view, it may be said that tlie motor oculi is devoted exclusively, in conjunction with the fourth and sixth pairs of nerves, to making the sight perfect. With these nerves it concurs to regulate the varied movements which allow the eye to act as a telescope upon a support that is furnished •«dth numerous articulations. By means of these muscles and nerves of the orbit the individual is enabled to remove the visual field from 752 I'liyyiOLOGY. place to iDlacG and in all directions to any objects which he might wish to examine. For its part, the motor ocnli allows the eye to see particularly objects that are situated high or low or at one side. However, it has a most important function in the harmony of the associated movements by which two images fall upon identical points of the retina of the two eyes, thus causing but one and the same impression. The third pair of nerves manages to regulate the amount of light which falls upon the retina?. Its function in this capacity is to protect the optic nerve against a too intense excitement from Fig. 373. — Distribution of the Third and Sixth Nerves in the Orbit. ( Lf:VEILLE. ) 1, The third nerve. 2, Its superior division. 3, Its inferior division. 4, Branch to the inferior oblique muscle. !J, The sixth nerve distributed to the external rectus muscle. excessive light. By contracting the pupil it lessens the pencil of light which penetrates into the depths of the ocular globe. On the contrary, it is the sympathetic which produces dilatation of the pupil so that the retina may receive all of the light which can be reflected from obscure objects. For the accomplishment of con- traction and dilatation of the pupil it must be remembered that the iris comprises two kinds of muscular fibers: circular and radiating. The former are connected with the motor oculi; the latter with the sympathetic. Finally, the third nerve is considered to have an important function in the act of accommodation. CEANIAL NERVES. 753 Pathology. — The motor oculi is frequently a sufferer by reason of its situation and course. It is often compressed by tumors at the base of the brain. In its passage through the sinus cavernosus it is exposed to compression by a thrombosis of this venous canal. The course of the third nerve through the interpeduncular space makes it play a considerable part in pathology. This is the place of predilection for meningitic deposits. This segment of the nerve is most frequently compressed in the exudates of tubercular meningitis. It is also the point of attack of constitutional syphilis, particularly during the tertiary period; this is a chronic meningitis which has its principal focus at the interpeduncular space as an exudate. Diph- theritic infection often attacks the third pair of cranial nerves. Paralysis of the oculomotor gives rise to external squint. Its irritation causes internal squint, and also contraction of the pupil, or myosis. The eye deviates outward in paralysis, due to the action of the external rectus not being antagonized by the internal rectus. Diplopia. — The deviation of one of the eyes does not permit the maintenance of parallelism of the visual axes. Without this coinci- dence the two images will not fall upon identical points in the retina. Hence all objects seen will be double. This symptom, known as diplopia, renders the sight very uncertain and often produces vertigo. Should the paralysis be general, so that it comprises the elevator of the lid, jSTature brings for itself a remedy for the defect of diplopia by suppressing the vision of one eye. It does this by letting the lid fall over the deviating eye. This drooping of the lid gives the con- dition known as ptosis. Stimulation of the motor fibers of the third can be produced reflexly by teething or intestinal irritations of children; hence their squint. Chronic spasms of the eye-muscles which are involuntary are called by the name nystagmus. Drugs. — Atropine paralyzes the intra-ocular ends of the motor oculi; Calahar bean stimulates them or paralyzes the sympathetic. FOURTH PAIR, OR PATHETIC NERVE. Distribution. — The pathetic supplies the superior oblique muscle. Physiology. — If the peripheral end of the pathetic be electrically irritated, the superior oblique muscle contracts and turns the eyeball downward and outward. The pathetic is a nerve that is especially endowed for the realiza- tion of simple vision with the two eyes in inclined positions of the head. It is impossible for an individual to carry one eye downward 48 -54 PHYSIOLOGY. and outward. That is, he cannot make a movement directed l)y the superior oblique and still keep the Iread perfectly vertical. It becomes necessary that the head be inclined to one side, and at the time this inclination is produced the rotation of the eyeball occurs without the will having the power to prevent it. By the very act of inclination of the head the necessary parallelism of the two eyes is positively destroyed; hence this involuntary action of the supe- rior oblique to place the visual axes upon the same plane. Nucleus of oculo-motor, ' Edinger-Westphal nucleus. Principal nucleus. Median nucleus. Nucleus of fourth nerve. Fig. 374. — Nuclei of Origin of the Third and Fourtli Nerves, (PoiRiER and Charpy.) The fourth pair of cranial nerves arise from a collection of cells beneath the anterior part of the posterior corpus quadrigeminum. It completely decussates in the superior medullary velum. It starts behind the quadrigeminal body and then appears like a white thread winding around the outer side of the crus of the cerebrum. It then pierces the dura mater, runs along the outer wall of the cavernous sinus, and enters the sphenoidal foramen with the oculomotor and abducent. It supplies the superior oblique muscle of the eye. Pathology. — Usually the first sign of any disorder of the pathetic is a giddiness when ascending or descending a stairs, owing to the CRANIAL NERVES. 755 double vision that occurs when the patient, in going down, looks at his steps. To overcome this diplopia he gives to his head a position that is quite characteristic. He holds his head bent forward and directed to the ground. This position overcomes the necessity of moving the eyeballs from above downward aud so minimizes the liability to diplopia. SIXTH PAIR, OR ABDUCENT NERVE. This nerve arises from a collection of ceils seated beneath the floor of the fourth ventricle below the stria acustica^. The loop of the facial incloses it. The abducent emerges between the summits of the pyramidal bodies of the medulla oblongata and the pons. As a threadlike nerve it goes through the cavernous sinus and through the sphenoidal foramen to the external rectus. The nucleus of the abducent has a connection with the posterior longitudinal bundle of fibers to the opposite oculomotor nucleus, thus permitting associated movements of the eyeball. The pontal olives are connected by fibers with the oculomotor nucleus. And these olives are also connected with the auditory nuclei and these nuclei are connected with the cerebellum, so that there is an association between the motor nerves of the eye, the auditory nerves, and the cerebellum. Physiology. — The sixth nerve is exclusively motor. It has for its only aim to excite the external rectus. When the nerve is strongly galvanized the eyeball deviates outward. Its section, on the contrary, produces an internal strabismus. It is especially adapted for seeing objects placed to one side. In general, the abducent is but one of the elements for the exercise of perfect vision. Pathology. — Paralysis is the most common manifestation in the sixth pair. A considerable concussion of the orbital cavity, espe- cially when it is upon the external side, will particularly paralyze the ab'ducent. Unilateral paralyses of this nerve are usually of peri- pheral origin. Bilateral paralysis is generally due to central dis- turbance. The most prominent symptom of this affection is an internal or convergent strabismus. The eye is held inward by the tonus of the rectus intcrnus, so that not more than one part of the cornea is perceived. 756 PHYSIOLOGY. CONJUGATE DEVIATION. Waller explains this as follows: The two eyes arc exactly equal and parallel for different directions of distant vision. Both eyes are turned to the right or to the left, up or down, so that the object lixed gives images on corresj^onding parts of both retina?. In move- ments directly u])ward or downward muscles of the same name in each eye are associated in action; but in lateral movements the asso- ciation is asymmetrical : e.g., the external rectus of one eye acts with the internal rectus of the other, and the peculiarity of this asso- ciated action seems still more striking when it is remembered that the external rectus is supplied by the sixth nerve, while the internal rectus is supplied by the third. A similar, if less striking, associa- tion of asymmetrical muscles on the two sides occurs in the rotation of the head and nock, which arc turned to the right by the right inferior oblique and the left sterno-mastoid muscles, and to the left by the left inferior oblique and the right sterno-mastoid. In look- ing to the right we contract the right external and left internal recti: i.e., impulses pass through the right sixth nerve and the left third, possibly from the left and from the right side, respectively, of the motor cortex, but more probal)ly from only the left motor cor- tex, in. which case we must suppose that certain nerve-fibers cross twice: once between the cortex and bulljar nucleus and a second time between the nucleus and nerve-termination. Unilateral con- vulsions of cortical origin are accompanied by rotation of the head and eyes toward the convulsed side: i.e., away from the cerebral lesion. Thus a discharging lesion of the right motor cortex causes convulsions of the left side of the body, with rotation of the eyes to the left. This is a "conjugate deviation." A destructive lesion of the right motor cortex causes paralysis of the left side of the bod}^ with rotation of the eyes to the right. The peculiarity in this case is that there is a cessation of action along the left sixth nerve (external rectus) and the right third nerve (internal rectus), the deviation of the eyes to the right being caused by the unbalanced action of the muscles, which rotate the eyes to the right. FIFTH PAIR, TRIGEMINUS, OR TRIFACIAL NERVE. The fifth pair of nerves, like a spinal nerve, has two roots: an anterior motor one and a posterior sensory one. The neuraxons of the motor nucleus in the pons make up the motor root. The sen- sory arises in the Gasserian ganglion, and, like a posterior-root CRANIAL NERVES. 757 Fig. 375. — Tlie Origin of the Trigeminal Nerve, 758 PHYSIOLOGY. ganglion, its neuraxons are divided, one j^art going to the skin of the face and the other, running toward the pons, also divides into two parts, one going upward and the other downward. The gela- tinous substance of Kolando on the posterior horn receives the fibers running downward, which arborize around the cells. The descending part of the trigeminus, known as the ascending root, extends down to the second cervical vertebra, continually giv- ing off collaterals as it descends, which arborize around the gelatin- ous substance of Eolando of the posterior horn, thus making the lower trigeminal nucleus a long one. The descending branch also Fig. 37G. — Oplithalmie Division of the Fifth Nerve. (LE^iiiiLL^.) 1, Skin of the forehead turned down. 2, Optic nerve. 3, Third nerve. 4, Fourth nerve. 5, Ophthalmic division of the fifth nerve. 6, Lacrymal branch. 7, Union of the fourth nerve with the lacrymal branch of the fifth. 8, Frontal. 9, Nasal. 10, Internal branch of nasal. has collaterals, which arborize around the motor nuclei of the hypo- glossal, facial, and trifacial. The neuraxons of the sensory nuclei in which the trigeminus ends decussate and go to the cortex in the fillet. Cortical Connection. — The sensory path ends in the inferior part of the central region of the cortex, going up in the fillet and the thalamus. The nucleus of the motor root lies in the pons, near the sensory nucleus of the trigeminus and back of the nucleus of the facial, of which it is probably a part. There is another nucleus, the accessory nucleus of the motor nucleus, which is situated beneath the aqueduct of Sylvius, and which sends descending fibers to the motor nucleus. CRANIAL NERVES. 759 The trigeminus emerges from the pons by two roots: a large sensory root and a small motor root. The large root has the Gas- serian, or semilunar, ganglion, while the small root runs beneath it. From the semilunar ganglion emanate the ophthalmic, superior max- illary, and a third branch, which joins the small root of the trifacial to form the inferior maxillary nerve. The nasal branch of the ophthalmic, ciliary, or lenticular ganglion gives off the ciliary nerves for the ciliary muscle and iris. This ganglion receives motor fibers from the oculomotor nerve and branches from the sympathetic. The superior maxillary branch passes through the rotund foramen of the sphenoid bone and gives off dental nerves and spheno-palatine nerves which go to Meckel's, or the spheno-palatine, ganglion. It gives off nasal, palatine, and pterygoid nerves. The pterygoid nerve gives off a branch, the great petrosal, which enters the cranial cavity through the cavity of the foramen lacerum and enters a canal on the front of the petrous portion of the temporal bone to join the facial nerve. The inferior maxillary nerve is formed of the small motor root of the trigeminus and a third branch of the semilunar ganglion, and makes its exit from the skull by the oval foramen. It gives off the auriculo-temporal and the lingual nerve, which in its course is joined by the chorda tympani of the facial and the inferior dental nerves. On the sensory division of the inferior maxillary nerve is seated the otic, or ganglion of Arnold. From it emanates the small petrosal nerve, which enters the cranium through a fine canal in the spinous process of the sphenoid bone and then courses along a canal in front of the petrous portion of the temporal bone to join the facial. The otic ganglion gives out filaments to the ten- sor palati and tensor tympani muscles. Physiology. — From the point of view of general sensibility the trigeminus possesses a considerable domain. To it alone is intrusted the giving of general sensibility to nearly all parts which enter into the composition of the head. In the external covering of the head but one region escapes it. This is the lateral and posterior part of the hairy scalp, the innervation for the latter coming from the cer- vical nerves. As to mucous-membrane sensibility, trifacial innervation comes only to the posterior third of the tongue, where the glosso-pharyn- geal innervates the palate, with the middle and inferior parts of the phar}'nx. These points being eliminated, it gives tactile sensibility not 7G0 PHYSIOLOGY. only to the skin, bnt also to all of the tissues of the head, compris- ing the glands, meninges, organs of sense, bone, and dental pulp. Reflex Relations. — By reason of the ciliary filaments the trigem- inus is in particular reflex relation with the motor oculi and sympa- HtLit. teraporallJ. HuBC masseter N. hypoplospnii. riatysma inyoide^. Muse, sternohyoideua. Muse, steriiothyreoideui Muse, omohyoideufl. Kd. thuracici anteriores. Unsc splentna. Muse, steriiocleidomaatoideiu. I^. accesaorius Muse. levator anguli scapulae Muse. cueull;irw or trapeziu*. K. dora&lia acapulaa. N. axLllArU. N. thoracinu Ungb. H. pIiTenicus. ErVa BupraclavlcuJIar* Fig. 377. — Distribution of the Sensory Nerves of the Head, together with the Situation of the Motor Points on the Neck. (Landois.) SO, Distribution of the supraorbital nerve. ST, Supratrochlear nerve. IT, Infratrochlear nerve. L, Lacrymal nerve. N, Ethmoid nerve. 10, Infraorbital nerve. B, Buccinator nerve. SM, Subcutaneous malar nerve. AT, Auriculo- temporal nerve. AM, Great auricular nerve. OMj, Greater occipital nerve. OMi, Lesser occipital nerve. C3, Third cervical nerve. CS, Cutaneous branches of the cervical nerves. CW, Situation of the central convolutions of the cere- bral hemisphere. 8C, Situation of the speech-center (third frontal convolution). thetic. Because of the ramifications of the trifacial branches in the mucous membrane of the nose there is established a very intimate relation with the expiratory muscles and nerves. Even the slightest touch may occasion a sudden and violent sneeze. A close relation- CRANIAL NERVES. 761 ship exists betAveen this nerve and the mnscles and nerves of degluti- tion. A remarkable fact in connection with the trigeminus is its great functional resistance to various poisons which are capable of paralyz- ing nerves of sensation. While all other regions of the body show the effects of anEesthetics, those under the dominion of the trigem- inus still preserve a high degree of sensibility. Even though a patient be anaesthetized with chloroform, yet will he perceive punc- tures in the temples and frontal regions. This occurs in spite of the fact that sensations are not perceived elsewhere. Motor Functions. — By its short root the trigeminus holds under its power the movements of elevation, depression, and rotation of the lower jaw. If this root be cut, it is found that the muscles con- cerned in the performance of the above-mentioned movements are paralyzed. The lower jaw remains passively separated from the upper. Trophic Function. — AVithin twenty-four hours after intracranial section of the trigeminus, the cornea becomes opaque. At the end of five or six days the cornea becomes ver}^ white in color. The iris becomes inflamed and covered with false membranes. In about eight days the cornea becomes detached and the contents of the eye escape. The suppression of the fifth pair is followed by remarkable alterations in the Schneiderian membrane. It becomes spongy, and bleeds upon the least touch. The place where the olfactory bulbs lie is completely changed. Thus the acts of olfaction and vision are indirectly affected. Pathology. — By reason of the intimate association of the trigem- inus, and its Gasserian ganglion, with the petrous portion of the temporal bone, it is exposed to all of the shocks and blows that are able to fracture this bone. The relations of the trigeminus with its meninges are very apt to be disturbed seriously by the presence of tumors. The false mem- branes which are found in meningitis compress it and so produce atrophy. The exudates of tubercular meningitis very often produce anaesthesia of the face. The fifth pair is mout often the seat of either excessive sensi- bility or paralysis. It is, perhaps, the one nerve which is the most frequently affected in neuralgia. The relative nearness of the tri- geminus to its sensory center probably explains the acuteness of tlie pains in neuralgia. 702 PHYSIOLOGY. SEVENTH PAIR, FACIAL NERVE, OR PORTIO DURA. The facial nerve arises from a nucleus beneath the floor of the fourth ventricle. This nerve contains a motor and a sensory root. The sensory root comes from the cells of the geniculate ganglion, and is called the nerve of Wrisberg. The motor pontal nucleus gives oft' the neuraxons of the motor root. The motor nucleus is thought to be the upward part of the nucleus ambiguuS;, which originates the motor fibers in the vagus and glosso-pharyngeal nerves. The neu- raxons of the motor nucleus form a distinct knee, which uprising on the floor of the fourth ventricle is known as the eminentia teres. The facial nerve in its course to the periphery makes a peculiar loop, or knee, inclosing the nucleus of the abducent, and emerges from a depression back of the pons between the olivary and restiform bodies, enters the internal auditory meatus with the auditory nerve, leaves the auditory nerve, enters the Fallopian canal, and makes its exit by the stylomastoid foramen to go to the muscles of the face. The nerve of Wrisl)erg, or tlie sensory part of the facial, is made up of neuraxons from the cells of the geniculate ganglion seated in the Fallopian canal. The auditory nerve is also called portio mollis, and it lies to the outer side of the facial, — the portio dura, — and between the two is the pars intermedia portio inter duram et mollem of Wris- berg, which extends from the medulla to join the facial in the internal auditory meatus. It is connected with both auditory and facial nerves, between which it lies. The central neuraxons of the geniculate ganglion or the nerve of Wrisberg go to the fasciculus solitarius or the vagus and glosso-pharyngeal roots. The peripheral neuraxons of the geniculate ganglion join the facial, and Duval states that they go to form the nerve of taste : the chorda tympani. In the hiatus Fallopii the great petrosal nerve branches off from the facial. It, in conjunction with a filament from the glosso-pharyn- geal and another from the sympathetic, passes over to join the gan- glion of Meckel. The S7naU petrosal leaves the aqueduct by a particular opening to end in the otic ganglion. Cortical Connection. — Tlie motor path from the cortex to the facial nucleus arises from the inferior part of the central con- volutions. Chorda Tympani. — A few millimeters above the stylo-mastoid foramen the facial gives off a branch of very considerable size: the chorda tympani. It ascends into the cavity of the tympanum. It CRANIAL NERVES. 763 passes between the malleus and incus, giving a branch to the lat- ter, and then enters the zygomatic fossa. The chorda tympani then descends between the two pterygoid muscles to meet the nerve of .taste. After communicating with the latter it accompanies it to the submaxillary gland. There it joins the submaxillary ganglion to terminate in the lingual nerve. Physiology. — While the trigeminus is responsible for the sen- sibility of the face, the facial presides over the contraction of the facial muscles of expression. The facial nerve is purely motor, and so has nothing to do with the transmission of sensory impressions developed upon the face. After its section the skin still preserves all of its sensibility. On the other hand, after section of the trifacial it completely disap- pears. Though the facial does not transmit sensory impressions, yet in itself it is sensitive because of the branches which it receives from the trigeminus. If the nerve be pinched, the animal shows signs of pain. Pathology. — The facial is the motor nerve which suffers most easily from the influence of cold. Facial paralysis, or Bell's palsy, may occur very easily when draughts from a window blow upon the face. When the paralysis is unilateral, the face is drawn toward the sound side. The labial commissure on the paralyzed side is lower than that on the other side, thus giving to the mouth an oblique direction. Bell's paralysis is usually due to a cold draught of air striking the nerve at its exit from the stylo-mastoid foramen. When the cause is seated in the brain the external rectus is usually affected, because its nerve is also involved and usually there is paralysis of the opposite half of the body, or crossed paralysis. Here the lesion is in the pons. If the lesion is seated in the petrous portion of the temporal bone, there is not only facial palsy, but also loss of taste from an involvement of the chorda tympani. EIGHTH PAIR, OR AUDITORY NERVE. The anatomy and function of this nerve have been discussed in Chapter XVIII. "^ NINTH PAIR, OR QLOSSO=PHARYNGEAL NERVE. The glosso-pharyngeal nerve is a nerve of both motion and sen- sation. 764 PHYSIOLOGY. Cortical Connections. — Tlio sensory ascending path of the ninth nerve ends in the inferior part of the central region of the cortex and in the immediate neighborhood of the posterior part of the sec- ond and third frontal convolutions. The nucleus ambiguus gives off neuraxons to form its motor root. The sensory neuraxons arise 'from the jugular and petrosal ganglions and arborize about two sensory nuclei in the medulla oblongata. The lower sensory end nucleus produces an elevation on the ficor of the fourth ventricle, and is called the ala-cinerea. The upper nucleus is also connected with sensory neuraxons of glosso- pharyngeal nerves, while the lower portion of this nucleus is in rela- tion with the vagus. The second nucleus is called the vertical nucleus, the fasciculus solitarius, the combined descending root of the pneumogastric and glosso-pharyngeal nerves, or the respiratory bundle. This respiratory tract extends from the olive down the spine to the eighth cervical nerve. This respiratory bundle of Gierke may associate the nuclei coordinating the various respiratory muscles. The glosso-pharyngeal nerve arises by a half-dozen cords from the restiform body and goes through the jugular foramen into the vagus, where it has a small ganglion: the jugular. As it emerges from the jugular foramen there is developed the petrosal ganglion, or gan- glion of Andersch. Nerve of Jacobson. — This same ganglion gives origin to the nerve of Jacobson. It enters the cavity of the tympanum by way of an opening in its floor, where it divides into three filaments. These are distributed, one to the round window, another to the oval window, and the third to the lining membrane of the Eustachian tube and tympanum. Physiology. — The ninth is a mixed nerve. Its motor properties are distributed to the middle constrictors of the pharynx and the stylo-pharyngeus muscle. The most important sensory function of the glosso-pharyngeal is the part which it plays in the role of the sense of taste. The ninth nerve has an action upon the blood-vessels of the tongue that is identical with that of the chorda tympani. If the glosso-pharyngeal be cut and its peripheral end stimulated, the tongue becomes a livid red. Pathology. — In man there are no clear cases recorded where there have been uncomplicated affections of the glosso-pharyngeal. CRANIAL NERVES. 765 TENTH PAIR, PNEUMOGASTRIC, OR VAGUS. Of all of the cranial nerves, the vagus is the most important and has the most functions of a varied nature in clinical study. It is a nerve of motion and sensation. Cortical Connection. — The motor path to the nucleus of the vagus is from the inferior part of the central convolutions. The motor neuraxons arise from the nucleus ambiguus. The sensory roots come from the neuraxons of the jugular and petrosal ganglions. The sensory neuraxons have been described under the preceding nerve: the glosso-pharyngeal. The vagus springs by means of from ten to fifteen cords from the groove behind the olivary body and passes through the jugular foramen with the glosso-pharyn- geal and spinal accessor}'' nerves. In the jugular foramen it has a ganglion : the jugular ganglion. After it emerges from the foramen it has an enlargement, the gangliform plexus, or ganglion nodosum. . The plexus gives off the plianjngcal and superior laryngeal nerves. The pharyngeal nerves, three in number, go down the side of the pharynx to supply the mucous membrane and muscles of the pharynx. The superior laryngeal goes down the side of the larynx. This nerve also furnishes a collateral branch, important from a phy- siological standpoint, to the crico-thyroid muscle. It then loses itself in the mucous membrane of the larynx. At the base of the neck the vagus gives off another branch, the recurrent, or inferior laryngeal. The nerve upon the right side descends in front of the subclavian artery and winds around it pos- teriorly from beneath. Upon the left side the nerve winds around the arch of the aorta in the same manner. As collateral branches, the vagus furnishes cardiac fibers, which form the cardiac plexus and are destined to innervate the heart. There are also oesophageal fibers whose terminations are distributed to the ctsophagus and trachea. In the cervical region the tenth pair gives rise to a branch, the nerviis depressor. It results by the fusion of two fibers: one from the superior laryngeal and the other from the vagus itself. The nervus depressor loses itself in the cardiac tissue of the heart at the level of the aortic and pulmonary orifices. During the first portion of its course the vagus forms numerous anastomoses. These are with the spinal accessory, the facial, and hypoglossal cranial nerves and with a great number of branches from the various ganglia of the sympathetic system. 766 PHYSIOLOGY. In the thorax the vagus gives off cardiac and pulmonary branches. These also anastomose with the symimthctics to form numerous plexuses. The terminal branches of the vagus are distributed to the stom- ach, solar plexus, and also to the hepatic plexus of the sympathetic. The most striking feature with regard to the vagus is the great number of its anastomoses. It is a very complex nerve and in no part of its course is it exclusively itself. Physiology. — The relationship existing between the vagus and spinal accessory nerves is a very intimate one by reason of their anastomoses. This makes the determination of the true nature of the vagus one of the difficult problems of physiology. It is certain that the vagus is endowed with sensibility, for the suppression of the spinal accessory does not deprive the parts of any sensibility in any portion of their common distribution. But, as the spinal accessory is motor and the vagus sensory, it does not neces- sarily follow that the latter nerve is exclusively sensory and that all movements realized by association should be the special work of the spinal accessory. It was Bernard who first demonstrated that the vagus in itself is a mixed nerve. After he had torn out all of the root-fibers of the spinal accessory in animals he found that the motor acts of the larynx persisted in the phenomena of respiration. How- ever, while the vagus in itself is a mixed nerve and has a certain amount of motor functions, yet its principal role is of a sensory nature. The mode of distribution of the vagus indicates that the nerve exercises some action upon (1) the digestive apparatus, (2) upon the respiratory apparatus, (3) upon the circulation, (4) upon the hepatic apparatus, and (5) an indirect action upon the kidneys and supra- renal glands. Pathology. — The recurrent is more liable to be pressed upon by reason of its peculiar course and its direct relations with the great vessels and body of the thyroid. As the vagus is a mixed nerve, it is very evident that compression causes troubles in motion and sensi- bility, either isolated or conjointly. Any lesions located at the origin of the vagus cause phenomena of irritation in the whole sphere of distribution of this nerve. Re- flexly the vagus is capable of affecting the chorda tympani and increasing the flow of saliva. It is for this reason that intestinal parasites often cause ptyalism. The sensibility of the branches of the vagus in the stomach CRANIAL NERVES. 767 remains mitonscious during the normal physiological state, when it does not seem to be any greater than that of the sympathetic. Dur- ing pathological conditions, however, it acquires a high degree of intensity. Thus, in simple wounds of the stomach, without haemor- rhage or peritonitis, the impression carried to the medullary center may be of such a nature as to cause rapid death. The great frequency of gastralgia is due to an affection of the terminal branches of the tenth pair. At its cranial end this same nerve is found to be in direct relation with the trigeminus through the intervention of the gray tubercle of Kolando. This fact un- doubtedly furnishes the key to the headache which so often accom- panies gastralgia. The vagus is the chief sensory carrier of the reflex movements of circulation and respiration. Thus, irritation of the renal and hepatic plexuses can produce vomiting. Angina pectoris has its seat in the cardiac plexus. The sensa- tion experienced is like that seen in the renal and hepatic plexuses after renal and hepatic colic. ELEVENTH PAIR, OR SPINAL ACCESSORY NERVE. The eleventh pair of cranial nerves, the spinal accessory, is com- posed of two distinct parts: a spinal portion and an accessory por- tion. A group of cells in the anterior horns of the spinal cord and extending downward to the sixth cervical segment is called the accessory nucleus. There is another group of cells at the exit of the first cervical nerve which extends into the medulla oblongata and is the origin of the hypoglossal nerve. The medulla-oblongata root arises from the nucleus ambiguus, which is connected with the vagus nucleus in the medulla. The superficial origin of the accessory portion is from the groove between the inferior olive and the restiform body. Near the jugular foramen both portions come together, but do not exchange fibers. Very soon both roots separate from one another to form the two distinct branches. The accessory portion of the nerve passes entirely into the plexus gangliformis of the vagus. This branch supplies the vagus with the major portion of its motor fibers and also its cardio-inhibitory fibers. The spinal portion enters the cavity of the cranium by passing through the foramen magnum. The two portions of the spinal accessory leave the cranium together by passing through the middle compartment of the jugular foramen. The spinal portion then 768 PHYSIOLOGY. pierces the sterno-mastoid to supply it and the trapezius. This por- tion oi' the nerve comniuuicates with several cervical nerves. Physiology. — The eleventh nerve is generally considered to be motor. Any observable sensibility must be due to anastomosis with the cervical nerves. From experimentation it has been found that the accessory branch presides, through motor branches in the vagus to the laryn- geal muscles, over the formaiioii of sound and its tone. The spinal branch is concerned in the duration, intensity, and modulation of the vocal sound. Hence it regidates the rhythm of speech and song. Aphonia is often due to hysteria, but may be due to lead-poison- ing, syphilis, or to such reflex causes as intestinal worms. The reflex that is established between the vocal and genital organs is also shown by troubles in the spinal branch of the spinal accessory. The voice may be lost at times during menstruation. TWELFTH PAIR, OR HYPOGLOSSAL NERVE. The nuclei of the hypoglossal nerve are under the floor of the fourth ventricle, on each side of the raphe. Beneath the main nucleus of the hypoglossal nerve is a collection of cells in the for- matio reticularis, called the hypoglossal nucleus of Roller. Cortical Connection. — The motor path is from the inferior part of the central convolutions. Anastomoses. — The connections of the hypoglossal are: 1. With the superior cervical ganglion of the sympathetic, which supplies vasomotor fibers to the vessels of the tongue. 2. The plexus gangli- formis vagi gives a small lingual branch which supplies the tongue with sensory fibers. 3. The hypoglossal is also connected with the upper cervical nerves. Physiology. — The hypoglossus, by itself, is purely motor. It moves the muscles of the tongue. When its original filaments are torn out there is never any pain. Sensibility of its terminal branches is due to anastomoses with the lingual. When the hypoglossus is cut, the tongue remains quiescent in the mouth. In unilateral paralysis of the hypoglossus the tongue, when pro- truded, passes over to the paralyzed side. This phenomenon is occa- sioned by the action of the genio-hyo-glossus of the sound side. Literature Consulted. Gordinier, "Nervous System." CHAPTER XXI. REPRODUCTION. All physiological phenomena described in the previovxs chapters have as their ultimate result the maintenance of the life of the individual itself. Xo matter, however, with what regularity these physiological processes are taking place, the life-period of a given animal is not of an unlimited duration. Sooner or later the more or less complicated mechanism stops its activity, and the individual ceases to exist. With its death, not only all traces of the former existence of the individual, but also, with it, the existence of the entire species to which the individual belonged, would be entirely Aviped out, had nature not j^rovided for a process of rejuvenation, as it were, of all living beings. This very important and peculiar phe- nomenon in the economy of all living organisms, animal as well as plant, is generally known as the process of Reproduction, the ulti- mate aim of which is to maintain the species. We have to confine ourselves to a consideration of animal reproduction only, and, even here, we find this important ju'ocess carried out in various ways. In lower animals, in which a specialization of different parts of the body to different functions is not yet established, the process of reproduc- tion is also more or less simple. The body of an amoeba becomes constricted and finally is divided in two halves, and each of these halves becomes a fully developed animal, capable of multiplying in the same fashion. A portion of a hydra, separated from the living animal, is capable of developing into a complete new hydra. This method of reproduction is called non-sexual. Throughout the greatest part of the animal kingdom, Avhere we find well-defined physiological division of labor in regard to other vital functions, we also find the function of laying the foundation for perpetuating the species assigned to special parts — organs of ■reproduction. The product of these specialized organs is known in modern biology as the germ-plasm, and it is upon this structure that the formation of a new individual and the transmission of all the qualities from the parents to the offspring — the liereditij — are con- sidered to depend. The starting point for the development of every individual we find represented in a typical cell, called an ovum, con- taining the germ-plasm,' and therefore also called germinal cell. ^9 (7G9) 770 PHYSIOLOGY. There are a few instances, however, in which tlie ovum alone is capable of reproducing a new individual. This is observed only among lower animals, and this method of reproduction is known as parthenogenesis. In all more highly organized animals the ovum is not capable of developing into a new individual, unless it comes in contact and fuses with a part of another germinal cell called a sper- matozoon. This method is called sexual reproduction. In it the ovum Fig. .378. — Graafian Follicle from Ovary of a New-born Child. (After P. Strassmax.) It consists of five portions: (1) An external membrane or zona peUucida. (2) An Internal membraru? or vitelline membrane which lies in close to the . yelk; between the two membranes is a slight space, the peri-vitelline space. (3) The yelk or vitellus, containing yelk grains or dentoplasm. (4) The nucleus, germinal vesicle, vesicle of Purkinje. (5) The nucleolus, germinal spot, spot of Wagner, consisting mainly of chromatin. presents the female element, the spermatozoon the male element of reproduction. The process of meeting and ultimate fusion of the two elements to form one, capable of forming a new individual, is called fertilization. The fact that in producing a new individual a union of male and female elements takes place has been known for centuries ; but in regard to the importance, or the predominating influence, of the one or the other of these elements, the views have changed. During REPRODUCTIOX. 771 the eighteenth and part of the nineteenth centuries, we find among investigators and interpreters of this phenomenon two extreme views represented. Some investigators considered the spermatozoon as a very minute hut complete animal — animalculus — containing all the organs of its jDarent animal en miniature. By means of a slender tail they were supposed to move around until they found an appro- priate soil — the ovum — to which they became attached and from which they received the necessary stimulus to grow, and gradually attained the size characteristic to the type. The advocates of this view have been known as animalculists. The advocates of the other, extremely oppo- site, view — the ovists — considered the ovum to be like the bud of the plant, containing all the parts of the future animal wrapped together, and, being met by the spermatozoon, the parts received a stimulus for their unfolding and growth until the typical size has been reached. It is obvious that these both extreme views are based on a common supposition that either the spermatozoon or the ovum represents an already preformed organism, and therefore l^oth of these views have accord- ingly been known as the theory of preformation. A detailed account of other theories on this sub- ject is generally given in text-books of embr}'- ology. For the understanding of the physiology of reproduction, it suffices to state that subsequent Fig. 379. — Human investigations have proven conclusively that Spermatozoon, the ovum as well as the spermatozoon repre- ^^ antox.j sent but single cells. Simultaneously with the astonishing facts, revealed during the last few decades, of the structure and life-his- tory of the cell in general, which are presented in the first chapter of this book, very much light has been thrown on the structure and life-history of the cellular elements specialized for reproduction. According to the facts known at the present time, it is pretty well establislied that both the spermatozoon and the ovum originate from the same source, the germinal epithelium : both undergo a prelim- inary process of ripening, matvrafion, before they are able to par- ticipate in fertilization ; and, while the role assigned to one of them in the latter process is not exactly the same as the role assigned to the other, they are nevertheless equivalents in regard to their ultimate significance for the process of producing a new individual. 772 PHYSIOLOGY. To fully appreciate the different stages of the process of repro- duction mentioned above, a brief account of the origin, formation, and structure of the ovum and spermatozoon is essential. The beginning of the differentiation of the organs of the animal body from the blastoderm, of which we will speak later, we find expressed in the arrangement of tlie building material, so to speak, in three distinct so-called germinal layers — an outer layer, the ecto- derm; an inner one, the entoderm; and between these two a middle layer, the mesoderm. The first two layers we find very well defined in all Metazoa, and from them all vital organs of the body, composed of epithelium, are developed. The middle layer supplies the sup- porting and connective tissues and the vascular system. In the lower types of Metazoa, which require very little supporting material, and in which a special vascular system is not present, we find also the mesoderm very scantily presented. The higher the type of the Fig. 380. — Transection of Chick Embryo, Showing the Three Plastodennic Layers. (Mantox.) animal, the more we find the mesoderm developed, until we finally see it not only as a well-defined single layer, but it becomes split into two secondary layers : one, the parietal mesoderm, which follows and gives support, and supplies blood-vessels and nerves to the ectoderm and its derivatives, and a second one, the visceral mesoderm, which acts in the same way for the entoderm. The space formed between them constitutes the future body cavity or coelom. It is in this middle layer where we find the first traces of the two kinds of the elements of reproduction — the spermatozoa and ova. In the lower types, with scanty mesoderm, we find these elements loosely scattered within it; in the higher types, with well-defined, double- layered mesoderm, we find certain parts of it crystallized, so to say, as organs of reproduction — the ovaries and testicles. It was Waldeyer who first called attention to the fact that a certain part on the visceral layer of the mesoderm becomes thickened and forms the so-called genital ridge, which gives rise to the organs of the primitive genito-urinary apparatus. A part of the ridge-cells be- REPRODUCTION. 773 comes the above-mentioned germinal epithelium of Waldeyer, because it is these cells which, by their down-growth into the subjacent layers, gradually become transformed, first, into indifferent sexual cells, and. ultimately, into spermatozoa or ova, as the case may be. Leaving out the detailed account of the development of the testicle and ovary, to be found in text-books on embryology, we have to consider the formation of the spermatozoa and ova as it takes place in a fully developed ovary or testicle. In the seminiferous tubules of the testi- ng. 381. — Diagram Showing Development of Spermatozoa in a Seminal Tubule. (McMuRRiCH.) 1, Spermatozoon. 2, Spermatid. 3, Secondary spermatocyte. 4, Primary sper- matocyte. 5, Spermatogone. 6, Supporting cell. cle we find five physiologically different kinds of cells. Covering the inner surface of the basement membrane of the tubule we find the so-called layer of parietal cells, consisting of two kinds of cells, of a different physiological character: (1) the sustentacular, and (2) the spermatogenic cells. Both kinds undergo karyokinetic multipli- cation, but the fate of their offspring is different. Each offspring of a sustentacular cell, after attaining its full size, is not only mor- phologically, but also physiologically, fully equivalent to the parent cell, as it is ready to serve its ultimate definite purpose — supporting and generallv uniting with other cells of its kind, it forms stronger 774 PHYSIOLOGY. supporting units, the so-called columns of Sertoli. In regard to the spermatogenic cells, we see an entirely different state of affairs. The function of each spermatogenic cell is nothing else but to undergo • • 4- .^ 4 Fig. 382. — Schema to Indicate the Process of Maturation of the Spermatozoa. ( Boveri. ) ( Howell. ) 1, Primary spermatocytes. 2, Secondary spermatocytes. 3, Spermatids. 4, Spermatozoa. Fig. 383. — Diagram Showing Essential Facts in the Maturation of the Egg. (Wilson.) 1, First polar body. 2, Division of tirst polar body. 3, Three polar bodies. 4, Female pronucleus. karyokinesis and form two cells, called mother-cells. Each mother- cell performs the similar function and gives rise to two other cells^ called daughter-cells ; hut these cells differ from their two consecu- tive predecessors. They do not multiply further, but in the REPRODUCTIOX. 775 material constituting their structure a rearrangement takes place, and gradually each of these daughter-cells becomes transformed into a spermatozoon, with its characteristic parts : the head, middle piece, and tail. It is evident, therefore, that each spermatogenic cell gives rise to four spermatozoa, all equally qualified to take part in the physiological process assigned to them — fertilization. This is dia- gramatically represented in the figure of Boveri (Fig. 382). In the ovary we find the Graafian follicle, containing two dif- ferent kinds of cells: one large one, the ovarian ovum, correspond- ing to the spermatogenic cell of the testicle; and more numerous smaller ones, supporting or protecting the larger by forming a cap- sule, as it were, around it and constituting the memlrana granulosa i Fig. 384. — Schema to Indicate Process of jMaturation of Ovum. , (BovERi. ) (Howell.) 1, Ovarian egg. 2, First polar body. 3, Abortive ova resulting from division of first polar body. 4, Second polar body, abortive ovum. 5, Mature egg. with its discus proligerus. Like the spermatogenic cell, the ovarian ovum also undergoes the karyokinetic division, but with somewhat different result. We find two cells formed, one of which is very large and contains the chromatin substance and the cytoplasm in the same proportion as the egg cell, and another, which is very small and con- tains only chromatin, and little cytoplasm. A second division of the larger cell takes place, with the same result, forming again one large cell and one very small one. The first small cell, in the mean- time, frequently also divides in two, and, because the three small cells are found grouped together on one of the poles of the large cell, they received the name polar bodies. They take no part in the processes following, and gradually disappear. The large remaining cell is the mature ovum, the one which is qualified for fertilization, and the series of changes through which the ovarian ovum has to pass to become so qualified is called maturation. The parallelism in the changes which take place during formation of the two sexual 77G PHYSIOLOGY. Fig. 385. — Schematic Representation of the Processes Occurring During Cell-division. (Boveri.) (Howell.) REPRODUCTION. 777 cells are very lucidly represeutcd by Boveri in the two schematic figures (Figs. 3S5 and 380). The process of maturation is also called reduction division, because it is known at present that the quantity of chromatin sub- stance in the nucleus of either of the sexual cells, or the number of chromosomes which the chroma-tin thread forms, is reduced to one- half of the quantity typical to all other cells of the same animal. In regard to other essential parts, we find the spermatozoon contain- ing only very little cytoplasm, while the mature ovum contains nearly all the cytoplasm of the original ovarian ovum. The centrosome is considered by Boveri to become lost in the ovum, while in the spermatozoon it is retained, and later plays an important part. The process of fertilization itself consists in a union of the male with the female element to form one capable of being the foundation for a new individual, although in regard to the details of this process the facts known at present, and the interpretations given, can by no means be considered conclusive. A very widely and favorably accepted view is presented by Boveri in a to g (Fig. 386), and the essential points are the following: either attracted by chemotaxic force radiating from the ovum, or by their own locomotion, the sper- matozoa come in contactwith the ovum and pierce the zona radiata; but as soon as one spermatozoon penetrates into the cytoplasm of the ovum, a reaction on its surface takes place, making it impermeable for other spermatozoa. During its entrance into the ovum, the spermato- zoon usually loses the tail, while the head, which in reality repre- sents the chromatin substance of the nucleus, becomes expanded, takes on the character of a nucleus, and moves towards the nucleus of the ovum. The egg at this stage obviously contains two nuclei; the one is called male pronucleus, and the other female pronucleus. Gradually both come in contact and form the so-called segmen- tation nucleus. The middle piece of the spermatozoon also enters the ovum. Soon, however, it reveals itself as a centrosome and acts as a dynamic force for a cleavage of the segmentation nucleus, which inaugurates the process of cell-division. With this first cleavage the formation of a new individual has actually begun. Through succes- sive cell-divisions an aggregation of cells is finally formed, which, depending on the amount of nutritive material stored up in the ovum for future purposes, becomes arranged either in form of a spherical mass (morula), which gradually becomes hollow and is then called a lilastula, or as a circular disk, and in either case a uniform layer of cells is gradually formed, which is known as the hlastoderm. 778 PHYSIOLOGY. Fig. 386. — Schematic Reiiresentation of the Processes Occurring During the Fertilization and Subsequent Segmentation of the Ovum. The chromatin (chromosomes) of the ovum is represented in blue, that of the spermatozoon in red. (Boveki. ) (Howell.) REPRODUCTION. 779 Through invagination of the blastula, forming the cnp-shaped gas- trula, or through delaniination from the disklike layer of cells, a blastoderm is gradually formed, which consists of two distinct layers, an outer one, called ectoderm, and an inner one, called entoderm. The next step of advancement in the development is one to which the attention of all distinguished embryologists has been kept engaged for many decades. It is the gradual formation of a distinct tliird layer of cells between the outer two, which is called the middle layer, or mesoderm. Some investigators have proved that in certain animals the mesoderm originates from the entoderm; others, again, have shown that it takes its origin from the ectoderm. The present state of our knowledge leads us to assume that from the morpholog- ical point of view throughout the animal kingdom both modes of origin can be found to take place. The far more important phy- siological aspect and significance of the question is closely correlated with the broader questions of general biolog}', and to them we will turn our attention now. With the differentiation of blastoderms into three distinct, so- called germinal layers, the foundation for a physiological division of labor is established and the formation of the various organs — organogenesis — begins. A description of the details of it, however, are beyond the scope of this text-book. Here it is only necessary to emphasize the important fact that each of the three layers repre- sents not only a morphological, but also a physiological, unit, as each one of them gives rise only to certain tissues and organs of the adult, and neither one can be substituted in that respect by another with- out producing abnormal conditions. This fact is of such great prin- cipal significance that pathologists have adopted a classification of tumors according to the three germinal layers and their derivates. An exceedingly important, as well as interesting, question which occupies the minds of modern biologists is v/hether the physiological differentiation of the germinal layers begins only with the forma- tion of these structural units, or whether it is already present at an earlier stage of the development of the ovum, and becomes more per- ceivable only in the germinal layers. The attempt to answer this ques- tion leads us over to the consideration of the vital problems in general biolog}' — evolution and inheritance — which I will shortly take up.* It has been shown bv Loeb that the unfertilized egs; of the sea * The preceding pages \ipon reproduction have been contributed by Dr. P. Fischelis. 780 PHYSIOLOGY. urchin can develop by chemical agents without spermatozoa. He treats the egg for a minute or more with acetic acid, to cause a membrane to form around it. They are then deposited in a hyper- tonic sea-water, made by the addition of sodium cliloride to ordinary sea-water. Afterwards they are transferred to ordinary sea-water, and soon they multiply and develop into normal larvae. Loeb be- lieves that the unfertilized egg of the sea urchin possesses all the elements for development, and the only reason parthenogenesis in it is prevented is the constitution of the sea-water. Here the pro- cess is mainly ionic. He believes that the nucleus of the sperma- tozoon is not essential, and that it is only a means to stimulate the arrangement of ions surrounding it. How does the ovum arrive in the uterus? There is consider- able obscurity on this point. Most observers believe the ovum is discharged into the pelvic cavity, where the cilia of the Fallopian tube propel it toward the uterus. It is in the tube that the sper- matozoon meets the ovum, which here undergoes fecundation, arrives in the uterus, and develops. The spermatozoon is deposited in the vagina or at the mouth of the uterus, and, by means of its cilium or tail, travels up the uterus and Fallopian tube. Should the ovum not be impregnated, it dies and passes out of the uterus as a constituent of its secretions. On the other hand, should it become fecundated, the ovum becomes attached to the mucous membrane of the uterus, usually occupying the bottom of some little cleft or pouch. The investigations of Peters, of Vienna, and of Webster, of Chi- cago, show that the uterine mucosa does not fold up around the ovum, but that the mucosa at the site of implantation is eroded; so that the ovum eats its way, as it were, into the mucosa, sinking into its depths until the edge of the swollen mucosa closes over it, thus forming the decidua reflexa. The position to which the fecundated egg becomes attached is the decidua serotina, and it eventually forms the placenta, the nutrient organ of the embryo. Before the ovum arrives in the uterus it has formed the amnion and chorion with the villi of the chorion. Some of the ectodermal cells in the chorion become spe- cialized to form what is called the trophoblast, and this probably transfers nourishment from the mother to the ovum. After its formation the mesoderm grows by reason of its own cell-proliferation, and is independent of its dual source. Along either side of the median line the luesoderm presents a thickening REPRODUCTION. 781 of cells (vertebral plate), which becomes laminated laterally (lateral plate). From the vertebral plate develop the somites; the lateral plate splits into two lamella?, of which the outer is the somatic meso- derm; the inner, the splanchnic mesoderm. Fig. 38S. Fig. 387. — Formation of Decidua (the decidua is colored black, the ovum is represented as engaged between two projecting folds of mem- brane). (After Dalton.) Fig. 388. — Projecting Folds of ^lembrane Growing Around the Ovum. (After Daltox.) Fig. 389. — Showing Ovum Completely Surrounded by the Decidua Reflexa. (After Daltox.) The former iinites with the ectoderm to form the somafopleure, while the latter unites with the entoderm to form the splanchnopleure. Between the somatcpleure and the splanchnopleure there is an open- ing, the tody-cavity, from which arise the serous cavities of the adult. 782 PHYSIOLOGY. Derivatives from the Layers. Ectoderm, or Epiblast. — From the epiblast are developed the central nervous system and the epidermal tissues. Mesoderm, or Mesoblast. — From the mesoblast arise most of the organs of the body. These include the vascular, muscular, and skeletal systems; also the generative and excretory organs; but not the bladder, the first part of the male urethra, nor the female urethra. Entoderm, or Hypoblast. — The hypoblast is the secretory layer. From it spring the intestinal epithelium and that of the glands b. 8. All. Fig. 390. — Diagram of an Early Stage of a Primate Embryo. ( MixOT. ) AU, Allantois. Am, Amnion, h.s.. Body-stalk. Clio, Chorion. Emi), Embryo. In, Entodermal Cavity of Embryo, ri, Villi of Chorion. //A", Yelk-sac. which open into the intestines; also the epithelum of the resipra- tory system, the bladder, the prostatic part of the male urethra, and the entire female nrethra. Up to this point the cavity of the germ is one undivided com- partment bounded by splanchnopleure. By infolding of the splanch- nopleure this cavity is divided into two smaller compartments of unequal size. The smaller is the gut-trad; the larger, the yelk-sac, or umbilical vesicle. The communication between the two cavities is the vitelline duct. With the unfolding of the splanchnopleure the somatopleure also follows, to form the body-walls of the embryo. Part of the REPRODUCTION. 783 somatopleure becomes so lifted up as eventually to curl up and over the embryo until the fold of one side fuses with that of the other. That is, there is formed the amniotic membrane and cavity. The amnion is a membranous sac consisting of two layers of embryonal cells. The inner layer is composed of ectodermic cells, the outer layer of mesodermic cells. The false amnion, or serosa, comprises all that part of the somatopleure which does not go to form the body-wall and the true amnion. It is also called the primitive chorion and by some authors the chorion. The allantois growing forth from the gut-tract unites with its inner surface and thus gives it vascularity. It is the outermost envelope of the germ. The amniotic sac is tilled with a fluid in which floats the foetus. The function of the yelk-sac is to furnish nutrition to the embryo for a certain length of time, but is very rudimentary in man. As the yelk-sac disappears by degrees, its place is taken by the aUaniois. The latter then serves as a medium of nutrition and respiration until the formation of the placenta at the end of the third month. Chorion. — The chorion is the membrane which envelops the ovum subsequent to the appearance of the amnion. It results from the fusion of the allantois and false amnion. Upon the surface of the chorion are numerous villi. At first they are uniform in size, but at the latter half of the first month there develops an area the villi of w^hich are noted for their long prolongations: the chorion frondosum. This eventually becomes a portion of the placenta. The remaining villi atrophy and finally disappear. Chemical Constituents of Spermatozoa. — In the head of the spermatozoa of salmon of the Khine is found a chemical body which is a combination of nucleic acid and a protamin. In different fishes the protamin is given a dift'erent name. Thus, we have scrombrin from scromber scrombrius. salmin from salmon, clupein from herring (clupea harengus), sturin from sturgeon (accipenser sturo). The protamins are strong bases and their watery alkaline solutions are intensely akaline, and with acids they form characteristic salts. They all give the biuret reaction, and, it is to be noted, without the addition of an alkali. Protamins are not coagulated by heat, and polarize to the left. These peculiarities place the protamins in a class peculiar to themselves. Clupein, chemically, is identical, according to Kossel, with salmin. A peculiarity of the protamins is the high percentage of nitro- 784 PHYSIOLOGY. gen; in salmon it forms nearly a third of the whole weight. By breaking np the protamins by acids it was found that the chief ele- ment in the protamins is arginin, with the hexone bases. In the semen of the carp (cyprinus carpio) Miescher obtained no protamin, but a "peptonelike" substance with Ijasic properties which is a histon, which makes bases very easily with acids. The histon possesses the usual properties of the albumins. The nucleo-proteids in the heads of all spermatozoa are a nucleic acid compound. The nucleic acids of sperm a?e organic phosphoric acid combinations. The protainins and histon have been found only in the semen of some fishes, and not in that of mammals. — Burian — Asher und Spiro's Ergebnisse der Physiologic, Part I, I'JU-i. Erection. — The erectile tissue of the male is formed by the penis, formed of corpora cavernosa and the corpus spongiosum. During erection the penis is gorged with blood, due to the arterioles, which are supplied by vasodilator nerves in the nervus erigens. Besides the vasodilation, the return flow of blood by the dorsal vein is partially arrested by the muscle of Houston. The smooth mus- cles of the trabeculge also aid in the act of erection. Erection is a reflex phenomenon, and the center is located in the lumbar cord. The sensory nerve concerned is the pudic, for Eckhard found that section of this prevented, in the dog, any erection when the glans penis was irritated. Other irritations, as of the testes or the prostatic urethra, lead to erection. A full bladder in the morning is also frequently accompanied by a passive erection, due to a compression of the ven- ous plexus of Santorini by the bladder. The genito-spinal center in the lumbar region is also affected by impulses coming from the brain, which may be of two kinds, excitatory and inhibitory. The penis also receives vasoconstrictor fibers, which emanate from the second to fifth lumbar nerves, and reach the penis either l)y the pudic or the hypogastric plexus. The surface of the organ, its integument, usually slightly folded, becomes tense, and the engorged subcutaneous veins are seen beneath the surface. During erection the clonic contraction of the bulbo-cavernous muscle pushes the blood towards the glans. These muscles are aided in a similar man- ner l)y the ischio-cavernous muscles. These two muscles have been compared to peripheral hearts in the vascular movement of this organ. In disease of the spinal cord erection is often lost or sup- pressed, so that coitus is impossible. Ejaculation of Semen. — At the moment of erection the urethral canal becomes filled with a secretion of its different glands. REPRODUCTION. 785 All these glands and the seminal vesicles furnish a liquid capable of diluting and liquefying the semi-solid semen as it leaves the vas deferens. The smooth muscles of the vasa deferentia, vesiculae seminales, aided by the dartos and cremaster muscles, which com- press the testicles, make semen accumulate in the urethra between the congested verumontanum (which prevents its regurgitation into the bladder) and the urethral sphincter. The friction of the glans is the cause of the ejaculation. This friction, in a reflex manner, causes the involuntary and spasmodic contraction of the vas deferens and of the seminal vesicles. The escape of semen in jets is due to the rhythmic contraction of the bulbo-cavernous and ischio-cavernous muscles, aided by the other muscles of the perineum. Ejaculation is accompanied by a general excitement of the brain. However, Goltz has shown that after a transverse section of the cord in the dog, ejaculation can still ensue. Castration. — In castrating a bull or a guinea-pig it is found that the thymus is greatly retarded in its stage of atrophy, so that the thymus of an ox exceeds considerably that of a bull. The testes greatly increase in size in guinea-pigs after removal of the thymus. Hence it is probable that the thymus has an internal secretion which controls the growth of the testicles. Prostate. — The secretory nerve of the prostate gland is the descending branch of the inferior mesenteric ganglion. The vaso- dilator fibers of the prostate are contained in the nervus erigens and its two branches. The vasodilation of erection is accompanied by a vasodilation in the prostate. When atropin is given, irritation of the secretory nerves of the prostate is without effect. Pilocarpin increases the secretion. Menstruation. — In the adult female during certain age-limits there occurs a discharge from the genitalia once about every twenty- eight days. This periodical discharge consists of blood, dead and disintegrated epithelium from the uterus, and mucus from the glands of the uterus. With the discharge of the above-named materials there is nsualhj expelled at the same time one or more ova from their follicles. How- ever, ovulation and menstruation may be, and very often are, inde- pendent of one another. The onset of menstruation is usually her- alded and then accompanied by certain constitutional signs of full- ness and pain in the pelvic region. There is a real congestion of all of the pelvic organs; in particular the uterine mucous membrane &o 786 PHYSIOLOGY. is swollen and congested. From it are derived the blood and epithe- lium of the menstrual flux. By some authorities it is claimed that the entire uterine mucous membrane is exfoliated at every flux, to be regenerated in the interim. It has been found by observers that congestion of the ovary coincident with sexual intercourse is capable of rupturing Graafian' follicles and so liberating ova. From this it is reasonable to sup- pose that the congestion and high tension of the generative organs during the time of menstruation would surely accomplish the same end. Fig. 391. — Uterus at Menstrual Period, Showing Congested Area and Desti'uction of Mucous Membrane. (Photomicrograph by Gramm.) (Gilliam.) The usual period of a female's life during which she menstruates is from piiherty (from the thirteenth to the fifteenth year) to the climacteric, or menopause (about the forty-fifth year). Its cessation at the latter period denotes the end of the childbearing period. The cessation of menstruation may be abrupt or gradual, and is frequently accompanied by disturbance of the physical and the mental functions. Eemoval of the ovaries usually causes menstru- ation to cease; occasionally, however, menstruation persists. If after the ovaries are removed and menstruation has ceased; an ovary- is transplanted, then menstruation returns. REPRODUCTION. 787 Theory of Menstruation. — There are two theories. In Pflueger's theory, the discharge of blood is looked upon as a phy- siological freshening of the tissue, like in surgery, for the recep- tion of the ovum and its union with the mucous membrane. In Eeichert's theory, before the discharge of the ovum a change takes place in the uterine mucous membrane, which becomes swollen up, more spongy, more vascular, and more ready to nourish an impregnated ovum. If the ovum is not impregnated, then there is degeneration of the uterine mucous membrane, and a flow of blood ensues. Both theories believe that menstruation is a preparation of the uterine mucous membrane for the reception of the ovum. It is usually recognized that ovulation is arrested during preg- nancy and lactation. The amount of menstrual blood is usually about IVi; ounces, and the flow generally lasts four days. Marshall and Jolly have shown that ovulation cannot be the cause of either heat in animals or menstruation. They show that the whole prooestrous process is of the nature of a preparation for the attachment of the eriibryo to the uterine mucous membrane. The ovary of a mammal elaborates an internal secretion which, at recurring j^eriods, is the cause of the proo?strous and the restrous. The corpora lutea form a ductless gland, which is necessary for the nutrition of the trophoblast during the early stages of pregnancy, and subsequently atrophies. Bond believes the endometrium has a saline secretion peculiar to the ancestrous state; that some substance is elaborated by the pregnant uterus which stimulates the growth of the corpora lutea in transplanted ovaries. He believes the ovary furnishes a secre- tion having an anabolic influence on the uterus and produces the oestrus. The saline uterine secretion is antagonistic to the action of the ovarian secretion. Corpus Luteum. — The place in the ovary where the bursting of a Graafian follicle by the overdistension of the liquor folliculi ensues is usually filled up with what is known as the corpus luteum. The follicle collapses, and in its interior remains a lining of granulosa cells and a clot of blood. Cells of the corpus luteum, containing a yellow body (lutein), are formed from a proliferation of the internal con- nective-tissue cells. If pregnancy ensues, the true corpus luteum is larger, thicker, and deeper in color than the false corpus luteum of menstruation. 788 PHYSIOLOGY. Pregnancy. — With the impregnation of the ovum pregnancy begins. Menstruation is arrested, and nausea or morning sickness ensues. At the end of the second month the nipple swells, becomes more erect, and projects forward. Then the areola of the nipple enlarges, becomes puffy, and deepens in color. Toward the fifth month the mammary glands increase in size. As to the genitals, the mucous membrane of the vagina becomes of a violet hue, the vaginal part of the cervix grows softer, a peculiar velvety softness at the end of the third month. At the end of the third month the uterus is the size of a foetal head, of certain doughy, elastic feel. About the sixteenth week active spontaneous foetal movements are Fig. 392. — Virginal Uterus. (Grandin and Jarman.) felt, popularly known as "quickening." From the eighteenth week up to the end of pregnancy the foetal heart-sounds are heard, which vary from 120 to 160 per minute. During the last three months the uterus becomes more distended, its walls are more muscular and vas- cular. After a period of 380 days of gestation labor begins, and the contents of the uterus are expelled. At birth the ligature of the umbilical cord cuts off the placental circulation. The placenta, being now a foreign body in the uterus, is expelled. The ruptured and opened vessels of the uterus are closed by the contraction of its walls, and haemorrhage is avoided. The mother must eliminate dur- ing pregnancy not only the waste of her own organism, but also that of the foetus. Hence the kidneys, being overworked, are occasionally the cause of urtemic convulsions. Enlargement of Mammaey Glands in Pregnancy. — Starling found that the injections of a part of the dried embryo of rabbits REPRODUCTION. 789 cause an onormons enlargement of the mammary glands of the rabbit, showing that the sympathetic enlargement of the mammary glands in pregnancy is due to some chemical agent, a hormone, act- ing through the blood, and not by the nervous system. Fig. .S93.— The Foetal Circulation. (Grandin and Jarman.) Placenta. — The placenta is the nutritive, excretory, and respir- atory organ of the foetus from the third month to the end of preg- nancy. It is discoid in shape, one side being attached to the uterine wall, the other becoming attenuated, to end in the umbilical cord, which is the medium of exchange between the placenta and the foetus. The villi of the chorion frondosum dip down into the 790 PHYSIOLOGY. mucous membrane of the uterus, to push against the walls of the large vessels found there and whose structure is similar to that of capillaries. The cells comprising the villi act as an osmotic mem- brane through which osmosis occurs. By this means oxygen and nutritive lymph pass from the mother's blood to that of the foetus. On the other hand, the fffital blood gives off carbon dioxide and probably urea. There is no intermingling of the two blood-currents, since there is always a layer of epithelium to act as a limiting mem- brane. Fcetal Circulation. — The blood is brought to the body of the foetus by the umbilical vein. Some of this oxygenated blood passes through the liver to the hepatic veins, to be emptied into the inferior vena cava. The remainder of the umbilical blood passes into the inferior vena cava through the ductus venosus. The blood, mixed with that which is returned from the lower extremities, enters the right auricle. Guided by the Eustachian valve, it passes over into the left auricle through the foramen ovale. The blood now courses through the left ventricle, aorta, the hypo- gastric and umbilical arteries to the placenta. The blood is returned from the head and the upper extremities to the right auricle by the superior vena cava. This stream of blood passes through the auricle and auriculo-ventricular opening directly into the right ventricle, guided by the tubercle of Lower. The blood next passes into the pulmonary artery. Some of it (enough to nour- ish the solid lung-substance) passes to the lungs, but the major por- tion passes into the aorta through the ductus arteriosus. When in the aorta it takes the course of the blood from the left ventricle to finally reach the placenta. The blood to the lungs returns to the left auricle through the pulmonary veins. After hirth the umbilical arteries are obliterated with the excep- tion of their lower portions, which remain as the superior vesical arteries. The umbilical vein becomes obliterated and remains as the round ligament of the liver. The umbilicals become impervious soon after cessation of the placental circulation. The foramen ovale closes, thereby cutting off communication between the right and left hearts. By the second or third day the ductus arteriosus has also become obliterated, to be present in adult life as the ligamentum arteriosum. These changes in the circulatory apparatus are dependent upon the establishment of pulmonary respiration at birth. The first in- spiration is said to be due to a sensory reflex from the colder air REPRODUCTION. 791 striking the sensory skin filaments of the chest and abdomen. After the cord is tied there soon follows an increase of COo in the blood. By its presence the activities of the respiratory center of the medulla are instigated. However, the various centers are but feebly irritable at birth and require somewhat heroic stimulation to bring out their activities. This feeblenetrs accounts for the remarkable vitality of the infant and its intense resistance to asphyxiation. EVOLUTION.* All modern conceptions of the immense multiformity in the animated world are based upon the observed facts of perpetuating established forms by heredity and the arising of new forms by varia- tion. The main points of discussion are how, when, and where the physiological phenomena of heredity and variation, leading ulti- mately to evolution, set in. While the discussion of these problems has been going on for centuries past, a great stimulus for approach- ing them in a more rational way has been given by Darwin with the publication of his views of the "Origin of Species." Having observed the great variety of forms produced by breeders of animals and culti- vators of plants, through artificial selection, he was led to assume that the natural selection has been the cause of the multiformity of animals and plants in nature. It was particularly plausible to accept this view of a gradual development of a new species, if there was taken into consideration the needed adaptation to dominating cir- cumstances; the constantly taking place in nature of the struggle for existence, with its consequence of the survival of the fittest; and last, but not least, the transmission of the changes acquired through the mentioned factors to succeeding generations by heredity. It is evident that Darwun based his views only upon facts available at that time and known from observations of adult forms, but these facts alone could not be considered as sufficient evidence for his views. The theory itself, however, was so fascinating that a great num- ber of enthusiastic investigators were induced to study the de- velopment of individual animals, and the facts revealed by embryo- logists at that period have been astonishing. It has been shown that all metazoa develop from ova, that the ova of all animals undergo a similar process of segmentation, and in every case a blastoderm is formed, first consisting of a single layer, but consecutively changing into one of two, and finally one of three layers of cells. The * Contributed bv Dr. P. Fischelis. 792 PHYSIOLOGY. similarity between those early stages in tlie development of widely dill'erent animals has been i'ound to be so striking that it is impos- sible to distinguish one animal From another at this stage, and these I'aets gave rise to the Uadnvii tneory ol llaeckel in support of the views of Darwin. llaeckel considers that all forms of blastoderms, consisting of two germinal layers, can be looked upon as modifica- tions of the simple gastrula; and as a gastrula is the foundation for the development of a single individual — ontogenesis — so a simply con- structed animal similar to it is to be considered as the ancestor of all metazoa. He even constructed a treelike diagram to illustrate how, from an undifferentiated being, gastrcm, by means of the above- mentioned factors pointed out by Darwin, an evolution to different types, varieties, and species — phylogenesis — observed in the animal world, could take place. Haeckel has published his views not only for scientific readers, but, through his popular publication, he, more than any one else, made the discussion of the problems of evolution and inheritance accessible to the public at large; and the literature, scientific as well as unscientific, called forth by his efforts, for and against this theory, is enormous. The scientific investigations, how- ever, have failed to show as yet a single instance of a gastrula, or its modification, developing into any other animal than one similar to that from which it itself originated. On the other hand, it has been conclusively shown that the physiological differentiation of the cells constitutnig the blastoderm is established long before the germ- inal layers are distinctly differentiated. We must, therefore, con- clude that the lever for lifting the mystery of our phenomena is to be applied at an earlier period than the already formed blastoderm. The facts, which have accumulated within recent years, on the mor- phology of the cell and its physiological manifestations during the process of reproduction have, as we have seen above, been astonish- ing. Particularly the nucleus has attracted the most attention, and it has been shown very conclusively that the chromosomes of the nuclei of the sexual cells are the principal factors in transmitting the hereditary manifestations during reproduction. The most recent studies, particularly those of Conklin, have revealed the fact, how- ever, that the cytoplasm of the egg-cell also has a more highly dif- ferentiated structure than was suspected. It has been conclusively shown that many of the future organs are already mapped out in the two-cell stage, and even in the unsegmentated ovum. It was only natural that these new discoveries should exercise great influence upon the conception of evolution, and therefore a REPRODUCTION. 793 new theory, embod3'ing all the newest achievements, could be expected to be received with favor. This new theory is suggested by De Vries as the "mutation theory," and is founded upon the phenomena of the cell-life. It is a theory of evolution of living organisms through evolution of their germ-cells, and suggests, in the words of Conkliu, that similarities in the character and localization of the material sub- stances of the egg must be the initial causes of all similarities or homologies which appear in the course of development. Modifica- tions of this germinal organization, however produced, are probably the immediate causes of evolution; and if it is to be accepted as probable that certain types of animals have been derived from others, it is evident that such transformations might be accomplished far more easily in the egg than in the adult. Relatively slight modifica- tions in the germinal organization would convert one type into another. We find here the question raised, whether sudden alterations of germinal organization may not lie at the basis of the origin of new types. How much nearer this new theory will bring us to the proper conception of the physiological "phenomenon of life" itself and the "phenomenon of reproduction" of living beings, as a manifestation of the preservation of energy underlying the former, remains to be seen. The solution of the ultimate and most mysterious of all problems — the question of the "origin of life" — seems to be as remote as ever. LiTEBATUBK CONSULTED. Heisler's "Embryology." Boveri, "Das Problem der Befruchtung," 1902. UNITS OF MEASUREMENT. French Measures of Length, Weight, and Volume. 1 millimeter = Vij, centimeter = Viooo meter. 1 centimeter =^ ^/mo meter. 1 micromillimeter (1 /a) = Viooo millimeter. 1 liter = 1000 centimeters cubes (1000 c.c). Relation hettveen Volume and Weight. 1 c.c. = 1 gramme. 1 milligramme = Vioon gramme. 1 kilogramme = 1000 grammes. Length. French to English. 1 centimeter = 0.39371 inch. 1 meter =39.37079 inches. 1 micromillimeter = 0.00003937 inch. {To convert centimeters into inches multiply by ^'Vas-) Weight. English to French. 1 grain = 0.0648 gramme. 1 ounce = 28.3495 grammes. 1 pound = 453.592 1 stone = 6.35 kilogrammes. 1 ewt. = 50.8 1 ton =1016 " Weight. Fren-ch to English. 1 gramme = 15.432349 grains. 1 kilogramme = 2.2046213 pounds, or about 35 ounces. 1 milligramme = 0.015432 grain. (794) UNITS OF MEASUREMENT. 795 Volume. English to French. 1 cubic inch = 16.3861759 centimeters cubes. 1 fluid ounce = 28.3495 1 pint =567 1 cubic foot = 28.3153 liters. Volume. French to English. 1 centimeter cube = 0.061027 cubic inch. 1 liter (1000 c.c.) =61.027 cubic inches, or 35 fluid ounces, or 1^/4 pints. 1 meter cube (1000 liters) = 35.3 cubic feet. Measures of Energy. 1 kilogrammeter = about 7.2-4 foot-pounds. 1 foot-pound = " 0.1381 KgM. Mechanical Equivalent of Heat. 1 kilocalorie = 424 (or 423.985) kilogrammeters. Fahrenheit and Centigrade Scales. To convert Fahrenheit into Centigrade subtract 32 and multiply by Vo- To convert Centigrade into Fahrenheit multiply by ^/., and add 32. i:n^dex. Abdominal reflex, 607 Abducent nerve, 755 distribution, 755 function, 755 origin, 755 pathology, 755 physiology, 755 Aberration, 722 chromatic, 722 spherical, 722 Absorption, 130 by the skin and lungs, 158 by blood vessels, 157 from intestines, 138 stomach, 138 within, 130 without, 130 of alcohol, 138 carbohydrates, 139 fats, 141 proteids, 140 salts, 138, 139 water, 138, 139 rapidity of, 142 time of, 143 Accessory foods, 13 Accessory nucleus dentatus, 614 Acid sodium urate, 399 Acid fermentation of urine, 407 Acid poisoning, 429 Accommodation of the eye, 722 act of, 722 defects of, 722 for distance, 724 mechanism of, 723 Acetic acid fermentation, 124 Acetonaemia, 120 Achromatic nuclear substance, 12 Achroodextrin, 62 Acids in the gastric juice, 71 Acromegaly, 372 Adam's apple, 493 Adaptation, 791 Addison's disease, 367 Adenin, 371 Adipocere, 472 Adrenalin, 291, 354, 367, 369, 645, 709 Adrenal glands, 365 blood supply of, 367 choline secretion, 365 extract of, 369 function of, 367 results of extirpation of, 367 secretory nerves of, 370 structure of, 366 Aeroplethysmograph, 320 iEsthesiometer, 660 Afferent impulses of cerebellum, 620 After-images, 737 Age, influence on capacity of respiration, 321 Agglutinins, 293 Agraphia. 502 Aim of alimentation, 421 Air, 351 complemental, 319 compressed, 352 quantity breathed, 319 rarefied, 353 reserved, 319 residual, 319 tidal, 319 vital capacity of, 319 Air cells, 306 Air passages, 302 Air tubes (see bronchi). Ala cinerea, 556, 567 Alanin, 33 Albumin, 34 alkali, 34 acid, 34 derived, 34 egg, 34 in urine, 321 native, 34 serum, 34 Albuminuria. 411 causes, 411 tests, 411 Albuminates, 34 Albuminoids, 36 Albumoses, 81, 93 Albumosuria, 410 Alcohol, 43 heat value of, 431 Alcoholic fermentation, 124 Aleuron granules, 34 Alexia, 501 Alimentary canal, 46 length, 46 parts of, 46 substances, 24, 37 Alkali albumin. 34 Alternate hemiplegia, 621 Alteration theory of nerve currents, 523 Alveolus, 50 Amido acids, 32, 35, 103, 104 Ammonia, 32, 120, 402 Ammonium carbonate, 397 magnesium phosphate, 410 Amnion, 783 Amtuba. 9, 15 Amoeboid movement, 15 Amphipyrenin, 13 Ampulla, 508 Amyloses or starches, 28 action of saliva upon, 60, 62 pancreatic juice, 100 Amylopsin, 100 Amyloses, 28, 29 Anabolic processes, 420 Anatomy, 3 Animal heat, 436 estimation of, 438, 441 extremes of temperature, 440 post-mortem rises, 455 Animals, 437 cold blooded, 437 temperature of, 437 warm blooded, 437 Anions, 131, 132 Ankle clonus, 607 Anosmia, 675 Anospinal center, 127 Anterior columns, 539, 545 root fibers, 545 pyramids, 553 Antero-lateral ascending cerebellar tract, 547 Antero-lateral ground bundle, 545 Antiferments, 82 Antipepsin, 71, 82 Antiperistalsis, 91 Antiseptic action of hydrochloric acid, 82 Antitoxins, 292 Anus, 90 (797) 798 INDEX. Aphasia, 501 Aphemla, 502 Aphonia, 500 ApnoDa, 333 Aqueductus Sylvius, 567 Aqueous humor, 716, 722 Arachnoid, 537 Aromatic amino acids, 32 Arcuate fibers, 560 superficial, 560 deep, 5C0 Areas of Cohnheim, 461 Arginine, 32, 103, 104, 129, 397 Argyll-Robertson pupil, 746 Arterial blood, 161, 163 Arteries (see names of), 246 bronchial, 307 coats of, 197, 247 contractility of, 255 coronary, 225 elasticity of, 253 lymph spaces of, 148 muscularity of, 247 nerve supply of, 247 pressure of blood in asphyxia, 335 pulmonary, 204 pulse, 255 rate of movement of blood in, 275 structure, 247 tension, 271 vasa vasorum, 247 Artery of cerebral haemorrhage, 587 Articulate sounds, classification of, 499 vowels and consonants, 499 Artificial respiration, 336, 337 Laborde method, 338 Marshall Hall method, 337 Ploman's experiments, 337 Shafer method, 337 Sylvester method, 336 Arytenoid cartilages, 493 Arytenoideus muscle, 495 Ascending loop of Henle, 389 Ase, 60 Aspartic acid, 32, 103 Asphyxia, 335 artificial respiration in, 336 causes of death in, 336 effect upon circulation, 335 stages of, 335 Aspiration of heart and thorax, 279 Association areas of Flechsig, 631 Aster, 21 Astigmatism, 726 Atmospheric air (see air). pressure in relation to respiration, 351 Atoms, 5 Atropine, effects of, on heart, 242 lacrymal gland, 742 respiration, 327 salivary glands, 63 Auditory area, 626 auricle, 678 cells, 684 external, 685 internal, 684 center. 626 field, 679 judgment, 696 nerve, 685 sounds, 696 striae, 565 Auerbach's plexus, 68, 91 Auricle of ear, 677 Auricles of heart, 210 diastole of, 213 systole of, 213 Auriculo-ventricular valves (see heart valves). Automaton, 632 Avogadro-Van't Ho£E law, 134 Axis cylinder, 529 Bacillus coli communis, 61, 124 Bacteria, classification of, 122 digestion by, 123 fermentation by, 124 in intestines, 124 Balance of nutritional exchange, 422 Basophiles, 171 Beckman's differential thermometer, 135 Beef tea, 39 Beef toxic principles, 39 Beer, 43 Bell's law, 60? apparent contradiction, 604 palsy, 763 Bernard's puncture, 119 Betatetrahydronaphthylamin, 448 Bethe's theory of nerve-cell connections, 528 Bicuspid valve, 207 Bicycle heart, 239 Bidder's ganglion, 232 Bile, 109 acids of, 110 action of drugs on, 121 action on muscles and nerves, 115 antiseptic powers of, 115 capillaries, 106 cholesterin, 113 composition of, 110 derivatives of salts and pigments, 111 ducts, 106 mucin, 110 pigments. 111 in urine, 406 properties and constituents of, 108, 110 quantity secreted, 109 reabsorption of salts, 116 salts, 110 specific gravity, 109 tests for, Gmelin's, 112 Hay's, 111 Pettenkofer's, 111 uses of, 114 Bilirubin, 112 Biliverdin, 112 Binaural audition, 695 Biology, 2 Biuret test, 35 Bladder, 417 Blastoderm, 772 Blind spot, 728 Blood, 160, 161 arterial, 161 buffy coat, 194 carbon dioxide in, 191, 350 cause of movement of, 212, 253 circulation of, 211, 249 schema, 251 coagulation of, 191 color of, 160 composition, 180 crystals, 179, 181 distribution of, 162 difference between arterial and venous, 163 experiments upon, 169 fibrin of, 191 function of, 160 globucidal action of, 197 gases of, 191, 343, 344 htpmoglobin, 179 laking, 169 medico-legal tests, 199 odor, 162 oxygen in, 165 pigments in urine, 406 INDEX. 799 Blood, plasma, 1S9 plates of, 175 proteids of, 189 quantity of, 162 reaction, 161 renewal of, 166, 196 serum, 192 specific gravity, 161 spectra, 186 taste, 161 temperature of, 161 estimation of, 162 transfusion, 197 volume of, 189 Welcker's estimation, 162 venous, 163 Blood-corpuscles, 163 blood-platelets, 175 chemical composition of, 180 chemistry of, 179 count of, 167, 168 destruction of, 166 diapedesis of, 174 experiments upon, 169 of different animals, 163 parasites, 166 vitality of, 170 red-corpuscles, action of inorganic sub- stances, 169, 170 destruction of, 167 formation of, 176 in extra-uterine life, 177 in intra-uterine life, 176 function of, 165 life cycle of, 166 methods of counting, 167 number, 166 conditions affecting, 166 parasites, 166 place of destruction, 171 rouleaux, 165 shape, 164 size, 164 white corpuscles, 170 amteboid movements of, 172 disappear when blood is drawn, 171 function of, 173 number of, 171 origin of, 174 structure of, 170 variations in number, 171 varieties, 171, 172 where found, 171 Blood-crystals, 178 Blood-platelets, 175 Blood-pressure, 263 effect of vagus on, 234, 272 extremes of, 271 in man, 271 measurement of, 269, 270 pathological, 273 respiratory wave, 269, 272 causes, 272 Traube-Hering curve of, 272 variations of, 272 venous, 273 Blood-vessels, 252 circulation in, 252 Weber's schema, 25J Body, chemical constituents of, 25 Bowditch stair-ease contraction, 244 Body cavity, 6 Bony labyrinth, 681 Bowman's capsule, 388 Boyle-Van't Hoff law, 134 Boveri on fertilization, 777 Brain (see cerebellum, pons, etc.). action of extracts of, 634 aqueduct of Sylvius, 567 artery of hamorrhage, 587 Brain, blood-supply of, 586 circulation in, 586 claustrum, 581 corpora quadrigemina, 582, 622 corpora striata, 578, 623 external form, 570 extirpation of, 623 fissures of, 570 fourth ventricle, 566 ganglia of, 578 gray matter of, 576 internal capsule, 582 lobes, 573 motor areas, 625 optic thalamus, 578, 623 sensory areas, 625 structure of convolutions of, 577 tracts, cortico-pontal cerebellar, 584 motor, 584 sensory, 586 white matter, 578 Bread, 33 Bread juice, comparative value of, 75, 95, 96 Breathing (see respiration). Bromelin, 100 Bronchial system, 305 Bronchi, 307 blood-supply of, 307 unstriped muscle, 327 Brunner's glands, 89 Buffy coat, 194 Bulb (see medulla). Bulbar nerves, 610 Burdach's column, 549 Butter, 42 Buttermilk, 42 Butyric fermentation, 124 Cachexia strumipriva, 361 Cfecum, 60 Caffeine, 44 Caissons and effect of compressed air, 351 Caisson paralysis, 351 Calamus scriptorius, 555 Calcium carbonate, 410 oxalate, 401 phosphate, 406 Calorie, 431 Calorimeter, 442 Calyces of kidney, 387 Camera obscura, 721 Canal, alimentary, 46 external auditory, 678 function, 679 Petit's. 716 Schlemm's, 703 Stilling's, 716 semi-circular of ear, 696 Cannon's experiments on stomach, 69 Capacity of chest, vital, 319 Capillaries, 248 anatomy of, 248 bile, 107 blood-pressure in, 273 capacity, 249 circulation in, 259, 261 histology, 248 passage of corpuscles through walls, 174 rate of blood in, 276 size. 248 Capillary circulation, 259 blood-pressure, 273 swiftness, 276 Capsule of Bowman, 388 Capsule of Glisson, 106 Capsule of Tenon, 618 Carbamid, Z9b Carbohydrates, 27, 38 absorption of, 139 800 INDEX. Carbohydrates, heat value of, 431 in metabolism, 427 Carboluria, 406 Carbon equilibrium, 424 estimation of, 427 Carbon monoxide, 351 Carbon monoxide haemoglobin, 183 Carbonic acid, 351 in blood, 191, 349 in urine, 407 Cardiac glands, 68, 71 impulse, 216 mucous membrane, 72 pathology, 290 revolution, 213 sphincter in vomiting, 83 sympathetic, 241 Cardinal points of Gauss, 720 Cardiograms, 217 Cardiographs, 216 Sanderson's, 216 Cartilages of larynx, 492 Caseanic acid, 41, 104 Casein (see milk), 41 Caseinogen, 41, 101 Catabolic processes, 420 Cataract, 710 Cathions, 131 Cauda equina, 537 Caudate nucleus, 579 Cell-division, 17 direct, 19 endogenous nuclear multiplication, 22 indirect, 20 Cells. 1, 7 achromatin, 12 afferent, 583 animal and vegetable, differences, 5 blood (see blood-corpuscles). ciliated, 15 constituents, 7 definition, 7 Deiters's, 621 efferent, 533 fatigue of, 23 gustatory, 677 Langerhans's, 95, 102 nerve, 524 Nissl granules, 527 nuclear sap, 12 nucleolus, 13 nucleus, 12 olfactory, 672 oxyntic, 68 parietal, 68 parts of, 7 Purkinje's, 617 selective power of, 24, 130 tactile, 656 theory of, 5 vegetable, 6 wall, 8 Cellulipetal fibers, 533 Cellulifugal fibers, 533 Cement, 53 Center of smell, 626 Central nucleus, 564 Centrosome, 13, 21 definition, 13 division of, 14 number, 14 size, 14 staining of, 14 Cereals, 43 Cerebellum, 612 accessory nucleus dentatus, 614 afferent impulses, 620 arbor vitse, 614 center of coordination, 620 corpus dentatum, 614 Cerebellum, cortex, structure of, 615 efferent impulses, 620 experiments on, 619 function of, 620 general description, 613 internal structure, 615 nuclei of, 614 median lobe, 613 peduncles, 621 Purkinje cells, 615 section of, 621 spinal cord connections, 617 surface form, 613 valley of, 613 Cerebral convolutions, structure of, 577 Cerebral cortex, 577 ablation, 63^; action of brain-extracts on, 634 motor centers, 625 sensory centers, 626 Cerebral detrusor center, 418 Cerebral hemispheres, experimental phys- iology of, 632 effect of destruction, 632 irritability of cortex, 634 Cerebral peduncles, 564 crusta, 565 locus niger, 565 tegmentum, 566 texture, 565 Cerebrins, 535 Cerebrospinal fluid, 637 action of drugs on, 638 composition, 637 differences from plasma, 637 origin, 637 Cerebrum (see brain). Cerumen, 678 Chambers of eye, 716 Champagne, 44 Charcot's artery of hsemorrhage, 587 Cheirokinesthetic center, 501 Chemical composition of the body, 25 Chemiotaxis, 16 Chest in respiration, 313 voice, 491 Cheyne-Stokes respiration, 340 Chlorides in urine, 406 Chlorophyll, 183 Chlolagogues, 121 Chloroform on electrical responses, 522 Cholesterin, 112, 113 Cholin, 113, 366, 637 Chorda tendineae (see heart). Chorda tympani, 63 Chorion, 783 Chorium frondosum, 783 Choroid coat of eye, 703 Chromatic aberration, 722 Chromatic nuclear substance, 12 Chromatolysis, 527 Chromogen, 366 Chromosomes, 21 Chyle, 153 coagulation of, 153 composition, 153 corpuscles, 153 flow, 153 quantity, 157 Chyme, 83, 85, 115 Cilia, 15 Ciliary movement, 15 body, 707 ganglion, 759 muscles, 706 processes, 705 system, 717 Cilio-spinal center, 609 Circles of diffusion, 72 INDEX. 801 Circulation, 201, 211, 215 actiou of heart in, 215 capillary, 259 comparative, 202 course of, 211 early discoveries, 249 in blood-vessels, 252 • brain, 279 frog's foot, 250 lower animals, 202 portal system, 106, 211 pulmonary system, 211 renal system, 391 systemic system, 211 venous system, 277 influence of asphyxia, 335 pathological conditions of, 215, 220 of blood, 249, 215 duration, 277 rapidity, 273 Circulatory system, 211 Circumvallate papilla, 666 Clarke's column, 543 Claudius's cells, 685 Claustrum, 581 Clava, 555 Climacteric, 786 Coagulation of blood, 191 conditions affecting, 195 factors of, 195 of milk, 41 process of, tabulated, 193 rapidity, 191 theories of, 192 why it does not in vessels, 195 Coagulases, 61 Cocoa, 44 Cochlea, 682 Cochlear nerve, 685 Coffee, 44 Coffeon, 44 Cohesion of nerves, 535 Cohnheim's areas, 461 Cold-blooded animals, 437 Cold spots, 661 Colloids, 137 Colon, 89, 90 Colon bacillus, 124 Color-vision, 733 blindness, 735 phenomena of perception, 734 sensations, 734 Colostrum, 40, 376 corpuscles, 42 Comma-tract, 549 Commissures of cord, 550 Complemeutal air, 319 Complementary colors, 735 Compounds, 25 inorganic, 25, 26 organic, 25, 26 Compressed air of caisson, 352 Cones, 712 Conjugate deviation, 537 Conjugated sulphates, 120, 407 Conjunctiva, 701 Conklin's discoveries, 792 Connective-tissue spaces. 148 Contractility of muscle, 467 Contraction of pupil, 709 Convolutions of brain, 573 Cord, spinal (see spinal cord). Corium, 655 Cornea, 701 Coronary arteries, 225 Corona radiata, 582 Corpora quadragemina, 582, 622 Corpora striata, 578, 623 Corpus callosum, 570 Corpus dentatum, 614 Corpus luteum, 787 of menstruation, 787 of pregnancy, 787 spongiosum, 784 Corpus striatum, 578, 623 Corpuscles (see names of). Corti arches, 684 canal, 684 membrane, 685 organ of, 684 Cortical epilepsy, 628 Cortico-pontal-cerebellar tract, 565, 584 Coughing, 339 Cranial ganglia, 578 Cranial nerves, 748 decussations, 748 origin. 750 spinal nerves, comparison with, 749 Creatinin, 402 Cremasteric reflex, 608 Cresol, 120, 124 Cretinism, 361 Crico-arytenoid muscle, 495 Cricoid cartilage, 492 Crista acousticce, 555 Crossed pyramidal tract, 547 Crusta petrosa, 53 Crowbar case, 633 Cruciate centers, 449 Crusta, 565 Cryoscopy, 135 Crystalline lens, 709 Crystalloids, 137 Cuneate nucleus, 556, 560 Cuneus, 627 Cupola, 682 Curdling ferments, 67 Currents, nerve, 521 Cutis vera, 655 Cytotoxins, 294 Cystic duct, 108 Cystine, 32, 410 Daltonism, 735 Darwin on evolution, 791 Descemet's membrane, 702 Decidua reflexa, 780 Decidua serotina, 7S0 Defecation, 126 center, 127 mechanism of, 127 Degeneration of nerves, 604 Deglutition, 57, 58 of fluids, 58 of solids, 57 (see swallowing.) Dehydration, 421 Deiters's process, 528 nucleus, 621 Daland's hsematocrit, 169 Demodex foUiculorum, 662 Dendrons, 528 Depressor nerve, 238 Dermis, 655 Descending tubule of Henle, 389 Development and growth, 432 Devries's mutation theory, 793 Dextrins, 29 erythrodextrin, 29 achroodextrin, 29 Dextrose in urine, 412 Diabetes, 118, 404 adrenalin, 119, 369 experimental, 119 inhalation, 120 irritation of vagus and depressor, 120 pancreatic, 101 phloridzin, 119 section of cord, 120 Diabetic puncture, 119 802 INDEX. D'Jelitzin's artificial respiration, 338 Diamino acids, 32, 103 Diapadcsis, 174 Diaphragm in respiration, 312 Diaster, 22 Diastase, 29, 118 Diastole of heart, 215 Dibasic acids, 103 Dicrotic wave, 258 Diet, 431 Chittenden's experiments, 431 energy table. Hall, 431 Atwater, 431 Diffusion, 132 Digestion, 24, 45 changes in the mouth, 60, 62 divisions of, 47 gastric, 65 intestinal, 85, 121 in large intestines, 122 mechanism of, 79, 124 Dioptrics, 721 Diphtheria toxin (immunity), 291 Diplopia, 738 Direct cell-division, 19 Direct cerebellar tract, 547 Direct pyramidal tract, 545 Discus proligerus, 775 Double vision, 738 Doyere's eminence, 464 Dropsy, 138 Drug pigments in urine, 406 Dubois-Reymond coil, 510 Ductless glands (see names of). Ductus arteriosus, 790 Ductus cochlearis, 683 Ductus communis choledichus, 108 Duodenum, 85 Duplication, 421 Dura mater, 537 Dynamometer, 486 Ear, 677 anatomy, 677 bones, 680 description, 677 external, 678 function, 678 internal, 681 function, 694 middle, 679 transmission by air of, 689 transmission in, 689 Ectoderm, 5, 11 Eck's fistula, 397 Efferent fibers' of sympathetic, 639 Eggs, 39 Ehrlich's theory of immunity, 292 Ejaculation, 562 Elastin, 37 Elasticity, 484 Electrodes, non-polarizable, 507 Electrolytes, 130 Electrometer, 517 Electrophysiology, 503 Dubois-Reymond coil, 511 electrical phenomena of contracting muscle, 519 negative variation of nerve-currents, 521 nerve-muscle preparation, 516 physiological rheoscope, 516 Electrotonic variations, 598 Electromotivity, 515, 596 Electrotonus, 594 Loeb's theory of, 596 phenomena, 1 Elements, 5 in body, 25 Embryology, 773 Emetics, 84 Emmentia teres, 567 Emmetropic eye, 724 Emulsification, 30 Enamel, 53 Eud-bulbs, 657 Endocardiac pressure, 218 Endocardium, 208 Endogenous nuclear multiplication, 22 Endolymph, 693 Endomysium, 457 Endoneurium, 532 Energy, 434 kinetic, 434 potential, 435 Enterokinase, 121 Entoderm, 772, 782 Enuresis, 608 ' Enzymes, 61 classification of, 61 hydrolytic action of, 61, 103 Eosinophiles, 171 Epiblast, 782 Epidermis, 653 Epigastric reflex, 607 Epiglottis, 493 Epineurium, 531 Epimysium, 457 Erection, 784 Ergograph, 487 Erepsin, 121 Erythroblasts, 177 Erythrodextriu, 29, 62 Esophoria, 739 Ether on electrical responses, 522 Eustachian tube, 690 Evolution, 791 Exercise, effect on temperature, 439 Exophoria, 739 Expiration, 314 center, 333 complex, 314 effect on blood-movement, 324 movements of, 314 muscles of, 314 simple, 314 External auditory meatus, 677 capsule, 581 Eye, 700 accommodation for distance, 724 after-images, 737 blood-vessels, 703, 716 coats, 700 co-ordinated movements, 737 general description, 700 imperfections and corrections, 725 lymphatics, 718 measurements, 719, 720 movements, 740 muscles, 740 nerves, 708 phosphenes, 713 structure, 700 Facial, nerve, 762 Bell's palsy, 763 chorda tympani, 762 distribution, '763 function, 763 origin, 762 pathology, 763 physiology, 763 Faeces, 125 amount, 125 color, 126 composition, 125, 126 variations, 125 Falsetto voice, 499 Fasciculi, 457 Fasting, 425 INDEX. 803 Fatigue of cells, 23 Fats, 29, 42 absorption, 141 composition, 29, 30 heat value, 430 human fat, 30 in metabolism, 426 olein, 30 origin, 30, 426 palmatin, 29, 30 stearin, 30 Fauces, 49 Feehner's law, 653 Fchling's test, 422 Female pronucleus, 777 Fenestra ovale, 680 rotundrum, 680 Ferments (see blood, milk, digestive juices), 60 definition of, 61 Fermentation, 124 acetic, 124 alcoholic, 124 butyric, 124 lactic, 41, 124 oxalic, 124 test for sugar, 413 Fertilization, 797 Fever, 454 Fibers, muscular, 458 length of, 458 Fibrin, 191 Fibrin ferment, 193 Fibrinogen, 36, 193 Fifth cranial nerve (see trigeminus). Filiform papillffi, 666 Fillets. 568 Filtration, 155 theory of lymph, 155 Filum terminale, 536 Fistula, gastric, 79 Flechsig's association areas, 629, 631 frontal, 631 parieto-occipito frontal, 631 insular, 631 Flour, wheat as a food, 43 F(T?tal circulation, 790 Foods, 42, 43 accessory, 43 caloric value, 431 chemical constituents, 26 daily amount, 38 definition, 24, 421 vegetable, 42 Formatio reticularis, 557 Fourth cranial nerve (sec trochlear). Fourth ventricle, 561, 566 boundaries, 561 floor, 561 Fovea centralis, 714 Fovea hemielliptica, 682 Fovea hemispherica, 682 Fovea posterior, 567 Fraunhofer's lines, 185 Freezing point, 135 Function, 4 Fungiform papillas, 666 Funiculus cuneatus, 556 gracilis, 556 teres, 567 Gall-bladder, 108 Galvanometer, 516 Ganglia of heart, 232 Gases of intestines, 124 Gastrasa theory of Haeckel, 792 Gastric digestion, 79 Gastric juice, 70 action of, 78, 80 action on bacteria, 82 Gastric juice, chemical analysis, 71 composition of, 71 excitants of flow, 70. 76 effects of bitters, 78 fat-splitting ferment, SO fistula for, 70 flow of, 74 function, 79, 80 methods of securing, 77 mixed, 80 pepsin of, 79 reaction of, 71 secretion of, 71 specific gravity, 71 theory of non-digestion of stomach, 82 varies in, composition and rate of se- cretion, 74, 75 Gastrula, 779 Gay-Lussac-Van't Hoff law, 134 Gelatin, 37, 424 Geniculate bodies, 578 Genito-spiual center, 608 urinary apparatus, 417 Germinal cells, 769 epithelium, 771 Germplasm, 769 Genu, 582 Giantism, 372 Glands (see names of). Glands of intestines, 89 Glass-blower's pulse, 350 Glisson's capsule, 106 Globulins, 35, 36 Glomerules of kidney, 389 Glossokinesthetic center, 501 Glossopharyngeal nerve, 65, 763 distribution, 764 function, 764 origin, 764 pathology, 764 physiology, 764 Glottis, 496 Glucose, 28 secretion, 119, C12 Glycocholic acid, 111 Glycogen, 116, 117, 118 Glycosamin, 104 Glycosuria, 118 Gmelin's test for bile. 112 Golgi stain, 529 GoU's column, 559 Gower's column, 547 Graafian follicle, 787 Gram calorie, 441 Gram molecule solution, 137 Grandry corpuscles, 657 Gray matter (see cerebellum, etc.). Great longitudinal fissure, 570 Great transverse fissure, 570 Growth and development, 432 Guaiac test for blood, 199 Gullet (see oesophagus). Gunsberg's test for hydrochloric acid, S3 Gustometer, Sternberg's, 302 Gyrus fornicatus. 575 hippoeampus, 576 Habenula, 578 Htemacytometers, 167 Thoma-Zeiss, 168 Hwmaglobinuria, 405 Hiemianopsia, 747 Hffimatachometer, 276 Htematoblasts, 177 H;pmatocrit, 169 Daland's, 168 Htematoidin, 183 Haematoporphyrin, 182 Hffimatin, 181 804 INDEX. Hpcmin, 181 chemical properties of, 182 crystals, 181 tests for, 181 Hajmochromogen, 186 ispectrum, 186 Hemoglobin, 179, 181 amount, 187 characteristics, 181 composition, 181 crystallization, 181 estimation of percentage, 187 reduced, 186 variations in amount, 187 HEemolysins, 295 physiological analogy, 290 Hffimometcr, 187 Dare's, 188 Von Fleischl's, 188 Hsemorrhage, 196 effects of, 196 quantity of blood in, 196 Hair, 662 chemical composition, 663 function, G63 general description, 663 Hale's blood-pressure experiments, 265 Hay's test for bile. 111 Hearing, 677 anatomy of organ of, 677 auditory nerve, 685 binaural audition, 695 Eustachian tube, 690 general description, 677, 678 organ of Corti, 684 semi-circular canals, 696 sense of, 653 theory of, 694 Heart, 208 accelerator center, 235 action of vagus on, 234 areas of audibility, 224 arteries, 240 auricles, 210 causes of sounds, 221 changes in shape and position, 213 chordae tendinese, 206 course of blood in, 311 diphasic variation of, 521 effects of drugs on, 242 endocardium, 208 foramen ovale, 204 foramina Thebesii, 205 frequency, 227 ganglia of, 232 His's muscular bundle, 232 histology of, 208 innervation of, 234 lymphatics of, 208 minimal stimuli, 243 moderator center, 235 movements of, 214 to clinicians, 214 persistence of, 220 muscles of, 208 musculi pectinati, 204 myocardium, 208 nerves of, 234 nutrition of, 245 papillary muscle, 206 position of valves, 207 refractory period of, 244 revolution of, 213 rhythm of, 230 sinus of Valsalva, 207 size and shape of, 203 sounds of, 222, 223, 224 stair-case contraction, 244 Stannius's experiments, 231 stimuli, 243 Heart, structure of, 208 sympathetic fibers to, 241 valves of, 207 mitral, 207 position, 224 semilunar, 207 tricuspid, 206 ventricles of, 208 work of, 228 Heat (see temperature), animal, 434 estimation of, 441 latent, 435 other sources, 436 radiant, 435 theory of, 435 Heat-spots, 661 Heat value of food, 431 Heat unit, 441 calorie, 441 calorimeter, 442 Height, relation to lung capacity, 318 Helicotrema, 683 Heller's nitric acid test, 411 Hemianopsia, 471 Heidenhain's lymphagogues, 156 theory of secretion, 156 Hensen's cells, 685 Hensen's disk, 460 Heredity, 791 Hering's theory of color, 735 Hiatus, 683 Hibernation, 438 Hiccough, 339 Hippuric acid, 401 formation of, 401 where secreted, 401 His's muscular bundle of heart, 232 Histology, 3 Histones, 37 Hoarseness, 500 Hormone, 76, 97 Horopter, 731 Hunger, 128 Hyaloplasm, 9, 524 Hydrsemia, 198 Hydrochloric acid, 71 , ion theory of, 73 stimuli for secretion, 73 test for (Gtinsberg), 83 Hydroxamino acids, 104 Hypermetropia, 724 Hyperosmia, 6'75 Hyperphoria, 739 Hyperpyrexia, cause of death, 455 Hypoblast, 782 Hypoglossal nerve, 768 anastomoses, 768 origin, 768 pathology, 768 physiology, 768 Hypoxanthiu in urine, 402 IGNOTIN, 39 Ileocsecal valve, 89 Ilium, 85 Image, formation on retina, 731 Immunity, 291 Inanition or starvation, 425 Incus, 681 Indican, 405 test for, 405 Indigestible residue of fgeces, 126 Indirect cell-division, 20 Indol, 124, 126, 405 Inferior vermiform process, 613 Infundibulum, 306 Inoculation (see immunity). Inorganic salts of faeces, 126 Inoslte, 471 INDEX. 805 Insalivation, E>7, 62 luhcritanc'c, 791 Inspiration, 310 expansion of chest in, 313 extraordinary, 314 movements of, 313 movements of blood in, 325 muscles of, 313 Inspiratory center, 333, 610 Intensity of sound, 491 Intermedio-lateral column, 543 Intermittent afflux apparatus, 253 Internal capsule, oS2 Interpedunculear space, 565 Interstitial slits, 148 Intestinal digestion, 122 Intestine, 85, 89 blood-supply, 88, 89 coats, 86, 90 digestion in, 122 gases, 124 glands, 89 large, 89, 90 length, 85 movements of, 90 nerve-supply of, 91 small, 85 structure, 86 Intracellular ferments, 28 Intraocular pressure, 718 Intrapleural pressure, 323 Intrathoracic pressure, 322 Inunction, 158 Inverted images, 731 Invertin, 28 lodothyrin, 362 Ions, 130 necessary for solution, 131 system of naming, 131 Iris, 707 ciliary processes, 705 nerves, 708 pigment, 708 reflex, 612 reflex movement of, 612 uses, 708 Iron, 27 Irradiation, 736 Irritability. 467 Ischuria, 680 Islets of Langerhans, 95, 102 Isotonic solution, 135, 170, 245 Jacobson's nerve, 764 Jaundice, 121 Jecorin, 113 Jejunum, 85 Juices (see names of). Karyokinesis, 20 stages of, 22 time of, 22 Keratin, 37 Kephir, 41 Kjeldahl process, 395 Kidney, 383 blood-vessels of, 391 calyces of, 387 capillaries of, 392 capsule of, 385 cavity of, 301 cortex of, 388 extirpation of, 414 general description of, 385 glomerules, 389, 391 hilus, 384 lymphatics, 382 Malpighian corpuscles of, 391 pyramids of Ferrein, 391 medulla of, 388 Kidney, minute anatomy of, 388 parenchyma of, 388 position of, 383 sinus of, 385 structure of, 385 urinary tubules of, 389 Knee-jerk or patellar reflex, 608 Krause's end-bulbs, 657 membrane, 462 KumysSj 41 Kymograph, 267 Kyrines, 36 Labyrinth of ear, 681 Lacrymal gland, 740 Lacrymal secretion, 742 Lactalbumin, 41 Lacteals, 88, 142, 143 Lactose, 41 Lactic acid, 41, 401 Uffelman's test, 83 Lactic acid bacillus, 41 Lactic fermentation, 41 Lactose, 28 Lamper eel, 2 Lamina denticulatum, 538 spiralis, 682 Langerhans's cells, 95, 102 Lantanin, 12 Lanterman's incisures, 531 Large intestine, 46, 89, 90 Laryngoscope, 496 Larynx, 492 'anatomy of, 492 cartilages of, 493 cavity of, 496 condition of, 496 muscles of, 494 nerves of, 496 pathology of, 500 vocal cords of, 496 Lateral chain theory of Ehrlich, 292 Lateral columns, 546 Lateritious deposits, 400 Laughing, 339 Law of Fechner, 653 Laws of sensation, 653 Lecithin, 113 Lemniscus, 568 Lens, crystalline, 709 Lenses, 726 Lenticular nucleus, 579 Leucine, 99, 103 Leucocytes, 170 eosinophiles, 171 mononuclear, 172 polymorphonuclear, 172 transitional, 172 Leukocytosis, 171 Levulose, 28 Lieberkiihn's glands, 89 Life period, 1 Ligamentum denticulatum, 538 Light, 699 perception of, 517 theory of, 699 transmission of, 699 Lime salts in metabolism, 428 Linin, 12 Lipase, 61 reversible action of, 61, 101 Liquor sanguinis, 163 Lissauer's tract, 549 Liver, 105 antitoxic function of, 116 blood-supply of, 106 daily secretion, 109 diastase of, 118 extirpation of, 116 function of, 108 806 INDEX. Livor, gall-bladdpr, 108 internal secretion of, 116 reaction of, 100 specific gravity of, 109 structure of, 107 Locus cocruleus, 567 Locus niger, 565, 622 Ludwig's tlieory of lympli, 156 strolimur, 275 Lungs, 304 air-pressure in, 323 air sacs, 306 blood-supply, 307 color, 305 coverings, 308 diffusion of gases within. 343 lobes, 304 lymphatics, 308 medico-legal test, 305 nerves, 308 roots, 304 structure, 306 vital capacity, 319 Luxus consumption, 42G Lymph, 151 coagulation, 151 composition, 152 flow of, 153 formation of, 155 quantity of, 157 relation to nervous system, 154 theories of secretion, 155 Lymphagogues, 156 Lymphatic glands, 150 Lymphatic system, 148 Lymphatic trunk, etc., 146 Lymphatic vessels, 145, 150 capillaries, 147 coats of, 147 development of, 148 distribution of, 146 origin of, 148 structure of, 146 valves of, 147 Lymphocytes, 152, 171 large non-nuclear, 172 small non-nuclear, 171 Maculae, 713 Macula lutea, 713 IVIagnesium salts in metabolism, 428 Malpighian corpuscles, 3 of kidney, 391 of spleen, 364 Malleus, 681 Maltase, 61 Maltose, 28, 29 Maly's theory of gastric secretion, 73 Male pronucleus, 777 Mammary glands, 372 arteries of, 374 during pregnancy, 788 general description, 373 lymphatics, 374 nerves, 374 results of dried, .376, 788 structure of, 375 Manometer, 265 Marey's intermittent afflux apparatus, 254 tympanum, 316 Mastication, 56, 57 Mast cells, 172 Mastoid cells, 680 Matter, 1 living, 1 Maturation of ovum, 775 Matzoon, 41 Meat, 38 Meconium, 126 Medico-legal tests for blood, 199 Medulla oblongata, 551 ala cinerea, 556 anterior pyramids, 553 arcuate fibers, 560 auditory strias, 555 bulbar nerves, 610 calamus scriptorius, 550 centers of, 610 olava, 555 double conduction, 609 external form, 552 fillets, 568 formatio reticularis, 557 fourth ventricle, 566 funiculus cuneatus, 556 gracilis, 556 general description, 552 internal structure, 557 lateral columns, 559 nucleus lateralis, 557 olives, 560 parts added, 560 posterior columns, 559 raphe of Stilling, 557 restiform body, 553, 555 trigonum hypoglossi, 556 weight, 552 white columns, 558 white substance, 558 Meissner's plexus, 91 Melanin, 655, 733 Membrana basilaris, 683, 694 granulosa, 775 tympani, 688 Membranes of cord and brain, 537 Membranes, mucous (see names of). Membranous labyrinth, 683 Memory center, 631 Menopause, 786 Mesoblast, 782 Mesoderm, 782 Mesoporphyrin, 183 Metabolism, 423 anabolic processes, 420 balance of, 422 catabolic, 420 effect of starvation on, 425 effect of work on, 474 equilibrium, 424 general explanation, 420 of carbohydrates, 427 fats, 426 salts, 428 tabulated exchange, 430 Meta-proteins, 34 Metazoa, 772 Methsemoglobin, 183 spectrum of, 187 Mett proteid method, 73 Metric system, 794, 795 Micro-organisms of fteces, 126 Microscopic test for blood, 199 Microspectroscope, 183 Sorby Browning's, 182 Micturition, 418 Midcerebellar peduncles, 562, 621 Middle ear, 679 Milk, 40 clotting of, 41 colostrum of, 42, 376 cow's, 40 fats of, 42 fermentation of, 41 functional variations of, 42, 376 matzoon, 41 microscopically, 40 proteids of, 41 quantitative, 40 quantity secreted, 42 reaction, 40 INDEX. 807 Milk, salts of, 42 secretion of, 42 specific gravity, 40 theory of Ottolcnghi, 370 woman's, 42 Milk-curdling ferments, 41 globults, 40 sugar, 41 teeth, 49 Mitosis, 20 stages of, 22 Modiolus, 682 Mol, 137 Molars, GO Molecular theory of nerve currents, r>22 Molecules, 5 Monamino acids, 32, 103 Mononuclear leucocytes, 172 Monosaccharides, 28 Morphology, 2 Morula, 777 Motion, 1 Motor area, extirpation of, G28 Motor areas, G25 impulses transmitted, 590 speech-center, 501, tract, 584 writing center, 501 Motor oculi nerve, 751 distribution, 751 diplopia, 753 drugs, action upon, 753 function of, 751 origin of, 751 pathology of, 753 Motor spray, 4G5 Motor tract, 584 Mouth, 4(i, 47 Movement in a circle, (121 of protoplasm, 15 Mucin, 35 Mucous membranes (see names of). Miiller's law, G50 Muroxid test, 401 Muscarine, 242 action on heart, 242 on respiration, 328 Muscle-curve, 475 effect of stimuli upon, 477 summations of stimuli, 480, 481 tetanus, 482 Muscles, 456 appearances under polarized light, 4G3 as perfect machines, 4SG blood-vessels of, 464 carbohydrates of, 470 cardiac, 4G6 changes in contraction, 478 chemical excitants, 46 chemistry of, 470 Cohnheim's areas, 461 contraction period, 475 constituents of, 470 contractility of, 467 curve, 475 elasticity of, 484 electrical phenomena of. 518 extractives, 471 fatigue, 477 ferments, 471 fibers. 462 general description, 457 Hensen's disc, 4G0 •influence of blood upon, 467 involuntary, 466 latent period, 475 longitudinal striations, 460 nerve-supply, 464 nerve-stimuli of, 469 chemical. 469 Muscles, nerve-stimuli, electrical, 469 mechanical, 469 thermal, 469 nuclei of, 466 proteids of, 470 rate of contraction of, 478 reaction of, 470 relation to tendons, 464 relaxation period, 476 resting and acting, 478 rigor mortis, 472 sarcous elements of, 460 serum, 471 sounds of, 483 striated, 456 structure, 458 tension of, 484 tetanus of, 482 theories of currents, 519 tonus, 483 unstriped, 466 urea in, 470 varieties of, 456 voluntary, 456 voluntary contractions of, 483 wave, 478 wing muscles of insects, 461 work of, 485 Muscular labor and urea excretion, 474 Muscular sense, 651 center of, 630 Mutation theory, 793 Myelin, 530 Myograph, pendulum, 473 Myogram, 475 Myopia, 724 Myohfematin, 470 Myosin, 470 Myosinogen, 470 Myxcedema, 361 Nails, 663 general description, GG3 function, 664 Narcotics, 637 Near point of eye, 724 Neosin, 39 Neovitalists, school of, 155 Nerve, comparison with muscle, 587 effects of anajmia upon, 602 electricity upon, 594 temperature upon, 588 electrotonus, 594 electrical potential of, 521 current, theories of, 522 excitability of, .587 excitability and conductivity, 591 excitants, 591 chemical, 591 electrical, 594 mechanical, 591 influence of blood upon, 602 irritability of, 588 Kiihne's experiment, 590 Pflueger's contraction laws, 594 regeneration, 532 roots of, 550 stable equilibrium of, 588 table of degenerations, 550 ascending, 550 descending, 550 Nerve-cell, 524 classification of, 533 dendrons of, 528 dimensions of, 529 fibrils, 528 neurite, 528 Nissl's granules, 527 nucleolus of, 527 nucleus of, 527 808 INDEX. Nervc-ccll, prolongations of, r)28 staining, 529 structure, 524 Ncrvc-ccuters, 535 common points of, 536 Ncrve-fibors, 531 centrifugal, 605 centripetal, 605 chenii('al properties of, 534 fatigue of, 4S,S, 5S9 meclianical properties of, 535 niedullated, 531 myelin, 530 neurilemma, 531 nodes of Ranvicr, 531 non-medullated, 531 reaction of, 535 terminations of, 532 Nerve metabolism, 535 Nerve-muscle preparation, 515 Nerve-tissue, 534 composition, 534 gray, 533 reaction of, 535 structure of, 535 trunks, 531 white, 534 Nerve-wave, transmission of, 589 swiftness of, 591 Nerves of deglutition, 59 heart, 234, 236, 23S intestines, 91 larynx, 496 Jacobson, 764 respiration, 331 salivary glands, 55 sweat glands, 381 taste, 666 tongue, 666 vasomotor system, 279 Nervous system, 524 anatomy of, 524 chemistry of, 534 extra-cardiac, 234 lecithin, 534, 535 metabolism of, 535 neuroglia, 542 Neurilemma, 531 Neurites, 528 Neuroglia, 542 Neurokeratin, 534 Neutral fats, 29 Neutrophiles, 171 Ninsen's globules, 376 Nissl bodies, 527 Nitrogen eliminated, 430 equilibrium, 424 estimation, 430 in blood, 349 in respiration, 349 Nodal points of eye, 720 Nodes of Ranvier. 531 Nonsexual reproduction, 770 Nose (see smell). Novain, 39 Nuclear membrane, 13 sap, 12 spindle, 21 substance, 12 Nuclei of cerebellum, 614 Nuclein, 13 Nuclei pontis, 563 Nucleolus, 12 Nucleoproteids, 35 Nucleus, 7, 11, 13 composition, 13 form, 12 number, 12 relative importance of, 11 size, 12 Nucleus, structure, 12 Nucleus, Deiters's, 687, 698 emboliformis, 614 fastigii, 614 globosus, 614 lateralis, 557 Nutrition, 1 Nuttall's guinea-pig foetus, 124 Nystagmus, 753 Obesity, 432 Banting's method, 432 Oertel's method, 432 Oblitin, 39 Oculomotor, 751 diplopia, 753 effect of drugs on, 753 function of, 751, 752 pathology of, 753 Odors, 674 ODsophagus, 46, 56 length, 56 anatomy, 56 nerves, 56 ODstrus, 787 Olein, 30 Olfactory bulb, 673 cells, 673 mucous membrane, 671 nerve, 672 organ, 672 sensations, 673 Olives, 553, 564 Oncometer, 290, 365 Open pores, 149 Ophthalmoscope, 742 Opsonins, 297 Optic angle (eye), 731 axis, 730 commissure of Gudden, 719 nerve, 714 thalamus, 578, 623 Organic compounds in body, 25 Organ of Corti, 684 taste, 665 voice, 492 Organs, 4 Origin of species, 791 of life, 793 Orthophoria, 693 Osmosis, 132 Osmotic pressure, 133 determination of, 134 of lymph, 135 proteids, 135, 137 physiological application, 137 Osseous labyrinth, 682 Ossicles, 681, 691 Otic ganglia, 641 Otitis media, 679 Ovary, 775 internal secretion, 787 Ovists, 771 Ovum, 775 Oxalic acid, 401 fermentation, 124 Oxidation, 349 seat of, 344 Oxybutyric acid, 120 Oxygen in bloofl, 341 Oxyhemoglobin, 181 spectrum, 186 Oxyntic glands, 68 Pacinian corpuscles, 657 Pain, 659 Palate, 48 Palmatin, 43 INDEX. 809 Pancreas, 94 blood-supply of, 95 composition of, 98 daily amount, 98 effects of removal, 101 injection of extract, 104 methods of obtaining the juice, 98 nerve-supply of, 95 reaction of, 98 removal of, 101 secretion of, 95, 96, 97 adaptation of, 97 excitants of, 97 secretory nerves of, 97 specific gravity, 98 structure of, 94 Pancreatic juice, 98 composition of, 98 ferments, 99 quantity, 98 reaction, 98 specific gravity of, 9S Papillte of tongue, 49, GGG Papain, 100 Paracerebellar nuclei, C20 Paraglobulin, 36 Paranuclein, 13 Parasympathetic, 040 Parietal cells, 68 Parieto-occipital fissure, 571 Parathyroid gland, 362 Parotid gland, 54 Parthenogenesis, 770 Pathetic nerve, 753 distribution, 753 function, 754 origin, 754 pathology, 754 Pav.'low's stomach, 77 Peduncles of cerebellum, 621 Pelvis of kidney, 386 Pendular movements, 91 Pendulum myograph, 473 Pepsin, 71, 72 Pepsinogen, 73 Peptic digestion, 80 Peptone, 36, 99 Peptonuria, 410 Perception time, 638 Pericardium, 209 Perilymph, 693 Perimeter, 743 Peristalsis, 90 infiuence of drugs on, 93 of intestines, 90 pendular njovement, 91 Perivascular space of His, 148 Permanent teeth (see teeth). Perspiration, 380 acidity of. 380 constituents, 380 effect of drugs upon, 381 function of, 382 insensible, 378 nerve-centers, 382 nerves of, 381 pathological, 382 relation to lung excretion, 382 role of, 382 sensible, 378 suppression by cold, 382 Petit, canal of, 716 Petrosal nerves, 762 great, 762 small, 762 Pettenkofer's test for bile. 111 Peyer's patches, 89 Pfeiffer's phenomenon, 295 PfJiigcr's contraction laws, 594 Phagocytes, 16, 173 Pharynx, 55 openings, 55 anatomy, 55, 56 Phenol, 124 Phenylhydrazin test for sugar, 413 Phenomena of life, 1 Phrenic nerve, 329, 331 Phloridzin, 119 diabetes, 119 Phosphenes, 737 Phosphoric acid, 406 sediments, 410 Phylogenesis, 792 Phylloporphyrin, 183 Physical heat, 434 Physiology, 2 Pilomotor nerves, 645 Pia mater, 537 Pitch, 498 Picrocarmin spectrum, 187 Pituitary body, 371 extirpation of, 372 extracts of, 372 lobes of, 372 position, 371 size, 371 structure, 372 Placenta, 789 Plantar reflex, 600 Plasma of blood, 189 chemical properties of, 189. 190 gases of, 191, 347 inorganic constituents of, 189 method of examining, 189 organic constituents of, 190 physical properties of, 188 Plasmodium malarias, 166 Plasmon, 41 Plethysmograph, 290 Plethora, 198 Pleura, 308 Plexus (see names of). Pneumogastric nerve (see vagus), 234, 765 branches of, 765 function of, 766 influence on deglutition, 59 gastric secretion, 77 heart, 235 lungs, 331 pancreatic juice, 97 vomiting, 84 pathology of, 766 physiology of, 766 Pneumograph, 315 Poiseuille's still space, 262 Polar bodies, 775 Polymorphonuclear leucocytes, 172 Polypeptids, 32 groups, 33 Polysaccharides, 28 Pons Varolii, 560 center of epileptiform convolutions, 621 central nucleus, 564 faces, 560 general description, 560 stratum complexium, 562 profundum, 562 zonale, 563 structure, 562 trapezoid body, 562 Portal circulation, 106 Portal vein, 106 Posterior columns, 548 Posterior fovea, 567 Posterior perforated spaces, 565 Posterior root-fibers. 550 Postganglionic fibers, 639 Precipitin lest for blood, 199 Precipitins, 294 Preganglionic fibers, 639 810 INDEX. Pregnancy, 788 Prehension, 47 of cow, 47 frog, 47 horse, 47 man, 47 squirrel, 47 Presbyopia, 724 Prostate gland, 785 Proopstrus, 787 Pressure curve of ventricle, 21!) Protamines, 37 Proteases, 61 Proteid compounds, 35 Proteids, 31, 32, 425 absorption of, 140 chemical composition of, 31 chromoproteids, 35 classification of, 34 heat value of, 431 metabolism of, 425 nucleoproteids, 35 of muscle, 486 where found, 34 Proteins, 34 Proteoses, 36, 128 Prothrombin, 193 Protoplasm, 8 chemical composition, 9, 10 constituents of, 10 definition of, 8 importance of, 19 movements of, 14 movements, rate of, 15 specific gravity, 10 Protoplasmic movement of leucocytes, 15 Proximate principles, 26 Ptyalin, 60 Pulmonary artery, pressure, 353 action of drugs upon, 353 Pulse, 255 dicrotic, 258 factors necessary for, 25S qualities of, 256 glass-blower's, 350 Pulse, respiration ratio, 227 Pupil, 70S cause of dilatation of, 709 Purin, 399 Purkinje cells, 617 Purkinje-Sanson images, 726 Putamen, 580 Putrid products of faeces, 126 Pyloric glands, 68 Pylorus, 66 closure of, 70 Pyramidal tracts, 545, 546 Pyramids of kidney, 388 Pyrimidine bases, 32 Pyrenin, 13 Pyrrolidine, 32, 104 Quickening, 788 Quotient of gases, respiratory, 345 Ranvier, nodes of, 531 Rarefied air, 352 Reaction time, 638 of light, 638 of motor impulses, 638 of sound, 638 of touch, 638 Rectum, 127 Reduction division, 777 Referred sensations, 648 Reflex action, seat of, 599 forms of, 606 law of co-ordination, 601 irradiation, 601 Kedex action, laws of, 601 localization, UUl other seats, 599 skin, 609 swiftness of, GDI tendon, 607 Reil, island of, 573 Reissner, membrane of, 683 Remak's ganglion, 232 Renal circulation, 392 oncometer, 414 Rcnnin, 41, 73, 100 Reproduction, 769 among higher animals, 770 among lower animals, 770 chorion, 783 epiblast, 782 fecundation, 777 fertilization, 777 foetal circulation, 790 hypoblast, 782 menstruation, 785 mesoblast, 782 non-sexual, 770 ovum, 775 ovum, maturation of, 775 parthenogenesis, 770 placenta, 789 segmentation, 777 sexual reproduction, 770 spermatozoon, 783 structure of, 783 Reserved air, 319 Residual air, 319 Resonance, 498 Respiration, 308 abdominal type, 315 action of drugs upon, 340 air-passages, 306 alveoli, 307 apparatus, 301 artificial, 327, 336 bronchi, 306 carbon monoxide, 351 center of, 328 chemistry of, 340 Cheyne-Stokes respiration, 340 compressed air in, 352 curious phenomena of, 348 effect on blood-pressure, 324 effect on circulation, 322 effect on pulse, 326 expiration, 314 external, 301 function of, 300, 301 function of unstriped muscular of bron- chi, 327 gases in, 350 inferior costal type, 315 internal, 301 inspiration, 310 lungs, 304 lymphatics, 308 mechanism of, 308 modified movements of, 338 nasal, 327 nerves of, 329, 331 number of, 320 of different forms of life, 300 of chick, 300 of fnetus, 300 pathological, 320, 328 pressure in, 321 quotient of gases, 345 relation to nervous system, 328 rarefied air, 353 sounds of, 317 superior costal type, 315 trachea, 302 Respiratory undulfitions, 272, 323 INDEX. 811 Restiform body, 555 Rete Malpighii, 655 Reticulated nucleus, 563 Retina, 710 blind spot, 728 duration of stimulation, 737 epithelium, 713 histological, 711 hyaloid membrane, 71G lymphatics, 718 pigmentary membrane, 713, 715 rods and cones, 710 terminal nerve elements, 712 Retina! epithelium. 713 Rheonome of Von Fleischl, 513 Rheotome, differential, 514 Rheoscope, physiological, 516 Rhodopsin or visual purple, 713, 732 Ribs, action in respiration, 313 Rigor mortis, 472 and tetanus, 482 cause of, 472 influence of fatigue, 474 influence of temperature, 472 Rolando, fissure of, 571 Rosette, 21 Saccharoses, 28 Saccule, 698 Saliva, 60 action on starch, 60 composition of, 62, 63 ferment of, 60 mechanical function of, 57 reaction of, 62 reflex centers, 65 specific gravity of, 62 temperature variations in, 02 time of activity, 62 Salivary glands, 54, 55, 63 action of, 62 of drugs on, 63 nerves to, 63, 64 Pawlow's experiments, 65 reflex centers of, 65 structure of, 55 trophic and secretory fibers, 64 Salts, 27, 88 in body, 27 in metabolism, 428 in urine, 406 Santorini'a cartilage, 493 Saponification, 30 Sarcolactic acid, 470 Sarcolemma, 458 Sarcomeres, 460 Sarcoplasm, 460 Sareostyles, 460 Scala tympani, 683 Scala vestibuli, 683 Scapular reflex, 607 Schafer's artificial respiration, 337 Schuetz's law, 73 Scheiner's experiments, 730 Schmidt, segments of, 531 Schwann, white substance of, 530 Science, 2 biological, 2 physical, 2 Scleroproteins, 36 Sclerotic coat, 700 Sebaceous glands, 661 function of, 662 Secretin, 97 Secretion, 355 adrenal, 365 by filtration, 355 by filtration proper, 3.56 by glandular desquamation, 356 external. 372 Secretion, external, mammary, 372 sweat, 377 urinary, 383 internal, 357 morphological, 356 pancreas, 95 pituitary body, 371 spleen, 364 thymus, 370 thyroid, 357 Sediments in urine, 410 in acid urine, 410 alkaline urine, 411 amorphous, 399 Segmentation, 777 Segmentation nucleus, 777 Semen, "83 spermatozoon, 773 Semicircular canals, 6S2, 696 Cyon's theory, 697 Ewald's theory, 696 reflex center of, 698 Semilunar valves (see heart-valves). Sensibility, 1 Seminiferous tubules, 773 Sensation of color, 734 Sense spots, 653 Sensory centers, 625 Sensory relay centers, 623 Sensory tract, 586 Serum albumin, 34 of bacteriolytic cholera, 295 of blood, 189 globulin, 189 normal, 188 Sham feeding, 76 Shock, 196 Side-chain theory, 292 Sighing, 33S Sight, 699 Sigmoid flexure, 90 Sinus of Valsalva, 207 Sixth cranial nerve, 755 Skatol, 124 Skin, 653 action of liquids on, 660 action of solids on, 659 cold spots, 661 corium, 655 epidermis, 653 hot spots, 661 Krause's end bulbs, 657 layers of, 654 radiation and conduction, 4.52 reflexes, 606 rete Malpighii, 655 stratum corneum, 655 granulosum, 653 lucidum, 653 touch corpuscles of, 656 Sleep, 6.34 theories of, 635 Small intestine, 85 innervation of, 89, 91 Smell, sense of, 670 anosmia, 675 center of, 626 general description of, 671 hyperosmia, 675 mechanism of, 674 nerves of, 672 olfactory organ, 672 olfactory sensation, 673 proper stimulus of, 673 secondary sensations, 674 subjective sensations, 674 uses of, 675 Snoring, 339 Soap, 30 Sobbing, 339 S12 INDEX. Sodium chloride, 27 in blood, 189 in urine, 40G substitutes for, 27 Solitary glands, 89 Solutions, gram molecule, 137 Somatose, 82 Sound, 497 height of, 497 intensity of, 49 production and modification of, 491 resonance of, 498 timbre, 498 Sound-waves, course of, C93 conduction of, G90 Sounds of heart, 221 variation in, 225 Special cell-constituents, 7 sensation, laws of, G53 senses, 650 Spectra of blood, 184 Spectroscope, 183 Spectroscopic test for blood, 199 Speech, 499 aphonia, 500 center of, 501 defects of, 500 hoarseness, 500 stammering, 500 stuttering, 500 ventriloquy, 499 Spermatogenic cells, 773 Spermatozoon, 774 structure of, 774 Sphenopalatine ganglion, 759 Spherical aberration, 722 Sphincter ani, 127 Sphygmogram, 259 Sphygmograph, 257 Marey's, 257 Sphygmometers, 269 Erlanger's, 271 Mosso's, 270 Riva-Rocci's, 270 Sphygmomanometers, 269 Spinal accessory, 767 distribution, 767 function, 768 origin, 767 pathology, 768 physiology, 768 Spinal cord, 536 anterior median groove, 538 anterior roots, 538, 605 antero-posterior lateral grooves, 538 blood-supply, effect of, 602 centers in, 608 central canal, 544 columns of, 545 conduction of, 603 commissures of, 550 coverings of, 537 degenerations of, 550 diameter of, 537 ependyma, 544 experiments on, 606 exterior form, 538 fibers of, 541 general description of, 538 gray commissure of, 538 gray matter of, 539 Internal conformation of, 539 length of, 537 minute structure of, 541 neuroglia, 542 path of motion in, 605 path of sensation in, 605 posterior median fissure, 538 posterior roots of, 550, 605 recurrent sensibility of, 604 Si)inal cord, reflex action of, 600 forms of, 001 laws of, 601 swiftness of, 601 skin reflexes in, 606 suspension of, 538 systemization of, 544 tendon reflexes in, 607 tonus of, 602 tracts, comma, 549 of lateral column, 547 of Lissauer, 549 of posterior columns, 548 trophic centers of, 536 weight of, 538 ^hite commissure, 538 Spinal ganglion, 604 Spirem, 20 Spirits, 44 Spleen, 364 effect of injection of dried extract, 365 function of, 364 Malpighian corpuscles of, 304 nervous influences of, 365 pulp of, 364 structure of, 364 trabeculae, 364 Spongioplasm, 9, 524 Staircase contraction, 244, 477 Stammering, 500 Stannius's experiments, 231 Stapes, 681 Stapedius, 689 Starch, 27 Starling's theory of lymph, 156 Starvation, effects upon proteid, 425 description, 425 Steapsin, 100 Stearic acid, 30 Stearin, 30 Stereognosis, 62C Stercobilin, 124 Stethograph, 315 Stilling, raphe of, 552 canal of, 716 Stimulants as accessories, 43 Stimulation fatigue, 477 Stimuli, successive, 480 Stokos-Adams disease, 232 Stomach, 66, 68 absorption from, 138 action of agents on, 78 blood-supply of, 68 coats of, 66 glands of, 68 movements of, 68 mucous membrane, 68 nervous control of, 68 Schuetz's law, 73 secretion (see gastric juiee), 71 secretory nerves of, 77 structure of, 66 Stomata, free, 148 Strabismus, 738 Stratum complexium, 562 corneum, 655 granulosum, 655 lucidum, 655 profundum, 562 zonale, 563 Stromhur, Ludwig's, 275 Struggle for existence, 791 Stuttering, 500 Subarachnoidean space, 537 Subdural space, 537 Sublingual glands, 55 Submaxillary ganglion, 763 Substantia gelatinosa of Rolando, 540 Succi's fast, 426 Sugar (see dextrose). INDEX. 813 Succus cntcricus, 121 daily secretion, 121 ferments of, 121, 122 function of, 121 specific gravity of, 121 sugar in urine, 412 tests for, 413 Sulphur, 407 Superior laryngeal nerve, 332, 496 Superior vermiform process, 613 Sulphuric acid in urine, 407 Superior fovea, 562 Suprarenal capsules, 365 Sustentacular cells, 773 Survival of the fittest, 791 Swallowing, 57, 58 of food, 57 three stages of, 57 of fluids, 58 mechanism of, 58 nervous control of, 59 Sweat (see perspiration), 378 Sweat glands, 378 experiments on, 378 nerves of, 381 number of, 377 structure of, 378 Sylvian center, 450 Sylvius, fissure of, 571 Sympathetic, the great, 638 afferent fibers of, 646 efferent fibers of, 639 ganglia of, 639 reflex action of, 649 general description of, 639 of abdomen, 647 of arm, 648 of head and neck, 647 of leg, 648 of pelvis, 647 of thorax, 647 Synthesis, 421 Syntonin, 34 Syringomyelia, 606 Systemic circulation, 211 Systole of heart, 213 Systolic plateau, 220 Tabes dorsalis, 549 Table of oxidation in starvation, 425, 426 Tactile sense, 653 effect of liquids on, 660 effects of solids on, 659 cells, 606 compound sensations, 660 illusions, 660 knowledge gained from, 658 law of Fechner, 653 law of sensation, 653 Taste, 665 center of, 626 drugs, 668 effect of drugs on, 668 general description, 665 improper stimuli, 667 intensity of, 667 nerves of, 65, 666 organs of, 666 substances of, 668 tongue's part in, 665 Taste buds, 667 Taste center, 626 Taurocholic acid, 110 Tea, 44 Tension, arterial, 271 Teeth, 49 milk, 49 number of, 49, 50 parts of, 52 permanent, 50 Teeth, structure of, 52, 53 Tegmentum, 566 Teichmann's crystals, 199 Temperature, 437 at different ages, 439 cause of variations, 439 estimation of, 441 extremes of, 440 modifying influences, 439 nerve-centers of, 448 of animals, 437 blood, 161, 440 man, 437 post mortem, 455 spots, 661 Tendon reflexes, 607 Tendons in relation to muscle, 464 Tenon's capsule, 717 Tensor tympani muscle, 692 Tetanus of muscle, 482 Tetany, 361 Theory of preformation, 771 Thermal unit, 441 Thermogenic center, 447 Thermoinhibitory center, 449 Thermolysis, 452 Thermolytic center, 450 Thermotaxic center, 447 Thirst, 128 Thoma-Zeiss apparatus, 167 Thoracic duct, 146 Thymus gland, 370 chemical composition, 371 extract of, 371 function of, 371 results of extirpation of, 371 structure, 371 Thyro-arytenoideus muscle, 495 Thyroid gland, 357 function of, 359 internal secretion of, 362 lymphatics of, 358 relation to heart, 363 results of extirpation of, 361 structure of, 358 vessels and nerves of, 358 Tidal air, 319 Timbre of voice, 498 Tissues, 6 definition of, 6, 17 Tone, 491 Tongue, 47 in deglutition, 57 in mastication, 56 mucous membrane, 49 nerves of, 49 Tonicity, 483 Touch, 653 Touch center, 630 Touch corpuscles, 656 Toxalbumin, 291 Toxproteins, 291 Toxins, 291 Trachea, 302 Transitional leucocytes, 172 Trapezoid body, 562 Traube-Hering curves, 272 Transfusion, 197 Tricuspid valve, 206 Trifacial, 756 distribution of, 759 function of, 759 irritation of, 761 motor function of, 761 origin, 759 pathology of, 761 physiology of, 759 reflex actions of, 331, 760 trophic function of, 761 Trigonum acustici, 556 814 INDEX. Trigonum hypoglossi, 556 Trigonuni vagi, 556 Trochlear nerve, 753 Trophoblast, 780 Trophic centers, 447 Trypsin, 99, 103 Trypsinogen, 95 Tryptophan, 32 Tube casts, 413 Tuber cinereum, 449 Tiirck's tract, 545 Tympanum, G79 mucous membrane of, G79 Trypsin, 95 Tyrotoxicon, 42 Units of measurement, Ml Uffelmann's test for lactic acid, 83 Uhlenhuth's test for blo6d, 294 Urates, 409 Uraemia, 415 Urea, 395 crystals of, 395 decomposition of, 395 excretion of muscular labor, 396 formation of, 397 properties of, 395 quantity of, 396 Ureters, 416 Uric acid, 398 daily amount of, 400 formation of, 399 increased by food, 399 murexide test for, 401 quantity of, 400 tests, 401 Uric sediments, 409 Urinary apparatus, 415 Urinary bladder, 417 blood, nerve, lymph supply of, 385 capacity of, 385 structure of, 417 Urinary tubules, 389 Urine, 393 acidity of, 394 albumin in, 411 Heller's nitric acid test, 411 bile pigments of, 406 coloring matters of, 404 oomposition of, 407 drug pigments of, 406 fermentation of, 407 inorganic constituents, 406 movements of, 416 nerves, influence of on, 415 pathological pigments, 405 quantity of, 393 reaction of, 393 secretion of, 414 sediments of, 410 oxalic acid, 409 phosphorus, 410 specific gravity of, 394 sugar in, 412 Pehling's test, 412 fermentation test for, 413 phenylhydrazin test for, 413 temperature of, 393 tides, 394 theory of secretion of, 413 toxicity of, 414 tube casts, 413 Urobilin, 404 Urochrome, 404 Uroerythrin, 404 Uterus, 788 secretion, 787 Utricle, 698 Vagina, 788 Vagus, 234 accelerator fibers, 241 depressor fibers, 238 effect of division of accelerator fibers, 241 effect of irritation of accelerator fibers, 241 effect of section of, 237, 331 effect of sipping upon, 236 effect of stimulation of, 235 effect of swallowing liquids upon, 236 peculiarities of, 235 pneumonia, 331 relation to blood-pressure, 272 Valves of heart, 207 Valvules conniventes, 86 Variation, 791 Vasa vasorum, 247 Vasoconstrictors, 281 effect of irritation of, 282 effect of section of, 281 differences from vasodilators, 285 of abdominal viscera, 283 of extremities, 283 of head, 282 of lungs, 284 Vasodilators, 284 path of, 285 recognition of, 285 theory of action of, 286 Vasomotor nerves, 280 effect of section of, 281 effect of stimulation of, 282 pathologic conditions of, 290 Vasomotor system, 279 centers of, 286 function of, 288 nerves of, 280 reflexes of, 288 Vegetable cell, 6 Vegetable foods, 42 Veins, 247 blood-pressure in, 273 coats of, 247 lymph and nerve supply, 248 portal vein, 106 rate of blood in, 276 tension in, 273 valves of, 248 vasa vasorum of, 248 Venom, 266 Venous blood, 163 Venous circulation, 277 Venous pulse, 273 Ventilation, 353 Ventricles of larynx, 493 Ventricles of heart, 211 Ventriloquy, 499 Vermis, 620 Vesicospinal centers, 418 Vessel innervation, advantages of, 288 Vestibular nerve, 687 Vestibular nucleus, 687 Vestibule, 683 Vestibulo-spinal tract, 548 Vibrations in car, 694 Villi, 86, 149 epithelial cells of, 87 goblet cells of, 87 of intestines, 86 structure of, 87, 88 Vision, accommodation, 722 acuteness of, 728 after-images, 738 aqueous humor, 716 astigmatism, 726 binocular vision, 739 center of, 627 chromatic aberration, 722 INDEX. 815 Vision, color vision, 735 complementary colors, 735 crystalline lens, 709 Daltonism, 735 dioptrics, 721 hypormetropia, 724 irradiation, 736 lacrymal secretion, 742 lenses, 726 lymphatics, 718 movements of eyes, 710 myopia, 724 oplithalmoscope, 742 optic nerve, 713 perception of light, 720 perimeter, 743 phosphenes, 737 presbyopia, 724 retina, 710 retinal epithelium, 713 rhodopsin, 713, 732 sensation of color, 734 Snellen's test-types, 731 spherical aberration, 722 transmission of light, 699 visual angle, 370 apparatus (see eye), structure of, 700 purple, 713 area, 743 field, 746 line, 730 Vital capacity, 319 Vitelliu, 39 Vitreous humor, 716 Vocal cords, 493, 496 conditions of, 496 false, 493 true, 493 Voice and speech, 497 height of, 497 organ of, 496 range of, 498 Vomiting, 83 causes, 84, 621 mechanism of, 83, 84 nerve center, 84 Von Bezold's ganglion, 232 Vowels and consonants, 499 Wallerian degeneration, 604 Warm-blooded animals, 437 Water, 26 daily amount, 26 drinking, 26 in faeces, 125 in metabolism, 428 Weber's schema of circulation, 251 Wheat, 43 Whey, 41 Widal reaction, 294 White columns, -545 White corpuscles (see blood-corpuscles), 170 Wine, 44 Wing muscles of insect, 461 Wirsung's duct, 94 Word-centers, 501, 627 auditory, 501, 626 visual. .500, 626 Work, effect upon destruction of proteid, 474 Wrisberg's cartilages, 493 Xanthin in urine, 402 Xanthoproteic test for proteids, 35 Yawn, 339 Zonule of Zian, 723 Zymogen, 95 Zymoids, 291 ^J^_J^,^J^,^QJj|J^^||||^^^^|^^_^^_yi^^ •VvSJViVJ^JiJytiJVJvJV'i'^JvJil