QA155I 1363 Columbia ©ntoeisitp inttjeUTttpctfl^rttjJIork College of logicians; anb gsmrgeons Htbrarp A TEXT-BOOK OF HISTOLOGY INCLUDING MICROSCOPIC TECHNIC BY A. A. BOHM, M. D., and M. VON DAVIDOFF, M. D. of the Anatomical Institute in Munich Edited, with Extensive Additions to both Text and Illustrations BY G. CARL HUBER, M.D. Junior Professor of Anatomy and Director of the Histological Laboratory University of Michigan Authorized Translation from the Second Revised German Edition BY HERBERT H. CUSHING, M.D. Demonstrator of Histology and Embryology, Jefferson Medical College, Philadelphia WITH 351 ILLUSTRATIONS PHILADELPHIA AND LONDON W. B. SAUNDERS & COMPANY 190J Copyright, 1900, By W. B. SAUNDERS & COMPANY Q M «r/ 13 t3 PRE8B OF W. B. 8AUN0ER8 & COMPANY TO THEIR TEACHER PROFESSOR C VON KUPFFER THIS BOOK IS DEDICATED BY THE GRATEFUL AUTHORS Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons (for the Medical Heritage Library project) http://www.archive.org/details/textbookofhistol1901bh EDITOR'S PREFACE. The " Text-book of Histology " by Bohm and v. Davidoff, as stated by the authors in the preface to the first edition, presents as fully as possible, from both the theoretic and technical standpoints, the subject- matter of the lectures and courses in histology given to students in the University of Munich. The authors further state that in the completion of their work they had the constant aid and advice of Professor von Kupffer, and had at their disposal the sections in the collection of the histologic laboratory in Munich, which were freely used in the selection and preparation of the illustrations accompanying the text. The excellence of the text and illustrations of the German edition, attested by all familiar with the work, and the cordial reception which it has received from both students and investigators, justify the belief that an English translation will meet with approval from American and English teachers and students. In the preparation of this American edition the editor has retained substantially all the subject-matter and illustrations of the second German edition, although certain minor changes in the arrangement of the text seemed desirable. Additions to the German text have been freely made. The sections on the Motor and Sensory Nerve-endings and on the Spinal and Sympathetic Ganglia have been greatly expanded, and the Innerva- tion of Glands and Organs has been considered much more fully than in the original. Our knowledge of the normal function of tissues and organs is so dependent on a correct understanding of their innervation that this subject seemed deserving of fuller consideration than is generally given it in text-books of this scope. The glands with internal secretion have also been considered more fully than in the original text, their im- portance necessitating such treatment. More than one hundred illustra- tions, the majority of them from original drawings, have also been added. In making these and other minor additions the editor has striven to stamp his own work with the excellent features of the German text, and trusts that his endeavors may have added to the usefulness of the book. The editor acknowledges with pleasure his indebtedness to I ft. Herbert H. Gushing for his excellent and accurate translation, and for suggestions received from him. The publishers, Messrs. Saunders & Company, have shown throughout the greatest interest in the work, and deserve the gratitude of the editor for their ready acquiescence in all suggestions made by him, for the excellent reproduction of his drawings, and for the suggestions made to him. The editor is particularly in- debted to his able assistant, Dr. Lydia M. De Witt, for valuable assistance rendered, more especially in the tedious work of proof-correction, for which he expresses his sincere appreciation and gratitude. G. Carl Huber. University of Michigan, Ann Arbor, Mich. October, igoo. CONTENTS. INTRODUCTION TO MICROSCOPIC TECHNIC. PAGE Microscope and Its Accessories 17 Microscopic Preparations 20 Fixing Methods 22 Infiltration and Imbedding , 25 Paraffin 26 Celloidin 28 Celloidin-paraffin 30 Microtomes and Sectioning 30 Further Treatment of the Section 38 Fixation to the Slide and Removal of Paraffin 38 Staining 40 Section Staining 40 Staining in Bulk 45 Preparation of Permanent Specimens 46 Introduction to Methods of Injection 48 GENERAL HISTOLOGY. L THE CELL. Cell-body \ . 5 2 Nucleus 55 Nuclear and Cell-division 56 Mitosis or Karyokinesis (Indirect Cell-division) 57 Prophases 60 Metaphases 62 Anaphases 63 Telophases 64 Heterotypic Form of Mitosis 64 Amitosis 64 Process of Fertilization 65 Chromatolysis 68 Technic for the Cell 68 II. TISSUES. Epithelial Tissues 74 Simple Epithelium 76 Simple Squamous Epithelium 76 Simple Cubic Epithelium 76 Simple Columnar Epithelium 76 Pseudost ratified Columnar Epithelium 77 Stratified Epithelium 77 Stratified Squamous Epithelium 7& Transitional Epithelium 79 Stratified Columnar Epithelium 79 Glandular Epithelium 81 Gland-cell 81 General Consideration of the Structure and Classification of Glands ... 82 7 8 CONTENTS. Epithelial Tissues — Glandular Epithelium {Continued). PAGE Remarks on the Process of Secretion 85 Neuro-epithelium 85 Mesothelium and Endothelium 85 Technic for Epithelial Tissues 87 Connective Tissues 89 ■ Mucous Connective Tissue 92 Reticular Connective Tissue 92 Fibrous Connective Tissue 93 Adipose Tissue 99 Cartilage 99 Bone 103 Structure of Bone 103 Development of Bone 107 Technic for Connective Tissues 117 Muscular Tissues 123 Nonstriated Muscle-cells 124 Striped Muscle-fibers 124 Cardiac Muscle-cells 132 Technic for Muscular Tissue 132 Nervous Tissues 133 Nerve-cells or Ganglion Cells ; Cell-bodies of Neurones 134 Nerve-fibers 142 Peripheral Nerve Terminations 147 Technic for Nervous Tissues 164 SPECIAL HISTOLOGY. L BLOOD AND BLOOD-FORMING ORGANS, HEART, BLOOD-VESSELS, AND LYMPH-VESSELS. Blood and Lymph 168 Formation of Blood 168 Red Blood-corpuscles 169 White Blood-corpuscles 173 Blood Platelets and Blood Plasma 176 Behavior of Blood-cells in the Blood Current 177 Lymphoid Tissue, Lymph-nodules, and Lymph-glands 177 Spleen . 180 Bone-marrow 185 Thymus Gland 188 II. CIRCULATORY SYSTEM. Vascular System 190 Heart 190 Blood-vessels 193 Arteries 194 Veins 197 Capillaries 198 Anastomoses, Retia Mirabilia, and Sinuses 199 Lymphatic System 200 Lymph-vessels 200 Lymph-capillaries, Lymph-spaces, and Serous Cavities 201 Carotid Gland (Glandula Carotica, Glomus Caroticum) 202 Technic for Blood and Blood-forming Organs 203 Technic for Circulatory System 210 III. DIGESTIVE ORGANS. Oral Cavity 211 Teeth 213 Structure of the Adult Tooth 213 CONTENTS. 9 Oral Cavity — Teeth {Continued). page I )evelopment of the Teeth 217 Tongue 221 Lingual Mucous Membrane and Its Papillae 221 Taste-buds 223 Lymph-follicles of the Tongue (Folliculi Linguales) and the Tonsils . . 225 Glands of the Oral Cavity 227 Salivary Clauds 228 Parotid ( Hand (Serous Gland) 228 Sublingual Gland (Mucous Gland) 228 Submaxillary Gland (Mixed Gland) 230 Small Glands of the Mouth 231 Pharynx and Esophagus 233 Stomach and Intestines . . . 235 General Structure of the Intestinal Mucous Membrane 235 Stomach 237 Small Intestine 243 Large Intestine, Rectum, and Anus 249 Blood, Lymph, and Nerve Supply of the Intestine 251 Secretion of the Intestine and the Absorption of Fat 256 Liver 257 Pancreas 265 Technic for Digestive Organs 269 IV. ORGANS OF RESPIRATION. Larvnx 275 Trachea 276 Bronchi, their Branches, and the Bronchioles 277 Respiratory Bronchioles, Alveolar Ducts, and Infundibula 279 Thyroid Gland 284 Parathyroid Glands 285 Technic for Organs of Respiration 286 V. GENITO-URINARY ORGANS. Urinary Organs 287 Kidney 28 7 Pelvis of the Kidney, Ureter, and Bladder 300 Suprarenal Glands 3 01 Technic for Urinary Organs and Suprarenal Body 305 Female Genital Organs 3°^ Ovum 3° 6 Ovary 3° 6 Fallopian Tubes, Uterus, and Vagina 316 Male Genital Organs 3 2 3 Spermatozoon 3 2 3 Testes 3 2 4 Excretory Ducts 3 2 9 Spermatogenesis 334 Technic for Reproductive Organs 34° VI. THE SKIN AND ITS APPENDAGES. Skin (Cutis) 341 Hair 35° Nails 355 Glands of the Skin 357 Sweat-glands 357 Sebaceous Glands 35 8 Mammary Glands 359 Technic for the Skin and Its Appendages 3^ 2 VII. THE CENTRAL NERVOUS SYSTEM. Spinal Cord 3 6 5 Cerebellar Cortex 37 2 IO CONTENTS. PAGE Cerebral Cortex 375 Olfactory Bulb 379 Epiphysis and Hypophysis 380 Ganglia 382 General Survey of the Relations of the Neurones to One Another in the Central Nervous System 389 Neuroglia 392 Membranes of the Central Nervous System 393 Blood-vessels of the Central Nervous System 397 Technic for Central Nervous System 397 VIIL EYE. General Structure 407 Development of the Eye 407 Tunica Fibrosa Oculi 409 Sclera 409 Cornea 410 Vascular Tunic of the Eye 412 Choroid, Ciliary Body, and Iris , 412 Internal or Nervous Tunic of the Eye 418 Pigment Layer 418 Retina * . 418 Region of the Optic Papilla 420 Region of the Macula Lutea 421 Ora Serrata, Pars Ciliaris Retina;, and Pars Iridica Retinse • 422 Miiller*s Fibers of the Retina 422 Relations of the Elements of the Retina to One Another 423 Optic Nerve 425 Blood-vessels of the Optic Nerve and Retina 426 Vitreous Body 427 Crystalline Lens 428 Fetal Blood-vessels of the Eye 429 Interchange of Fluids in the Eyeball 429 Protective Organs of the Eye . 430 Lids and Conjunctiva 430 Lacrimal Apparatus 432 Technic for the Eye 433 IX. ORGAN OF HEARING. External Ear Middle Ear 435 437 Internal Ear 439 Utriculus and Sacculus 441 Semicircular Canals 442 Cochlea 443 Organ of Corti ...... 447 Nerves and Blood-vessels of the Cochlea 452 Development of the Labyrinth 454 Technic for Organ of Hearing 455 X. ORGAN OF SMELL. Technic for Nasal Mucous Membrane 457 XI. GENERAL CONSIDERATIONS OF THE SPECIAL SENSE-ORGANS. References to Literaturk 461 Index "483 ILLUSTRATIONS. FIG. PAGE i. Microscope 18 2. Box for imbedding tissues 26 3. Laboratory microtome 3 1 4 Sliding microtome of Jung 33 5. Apparatus for cutting tissues frozen by carbon dioxid 36 6. Movements in honing 37 7. Diagram of cell (Huber) 5 2 8. Cylindric ciliated cells from the primitive kidney of Petromyzon planeri . . . . 53 9-19. Processes of mitotic cell- and nuclear division 58, 59 20-27. Mitotic cell-division of fertilized whitefish eggs (Huber) 60, 61 28. Mitotic division of cells in testis of salamander (Benda and Guenther) .... 63 29-34. Process of fertilization (Boveri) 66, 67 35. Pigment cell from the skin of the head of a pike 71 36. Isolated cells of squamous epithelium (Huber) 76 37. Surface view of squamous epithelium from skin of a frog 76 38. Simple columnar epithelium from the small intestine of man (Huber) .... 77 39. Pseudostratified columnar epithelium 77 40. Stratified pavement epithelium 78 41. Cross-section of stratified squamous epithelium from esophagus of man (Huber) 78 42. Isolated transitional epithelial cells from bladder of man (Huber) 79 43. Cross-section of transitional epithelium from the bladder of a young child ( Huber) 79 44. Stratified columnar epithelium 80 45. Ciliated cells from bronchus of dog 80 46. Cross-section of stratified ciliated columnar epithelium from trachea of rabbit (Huber) 80 47. Goblet cells from bronchus of dog 81 48. Simple tubular glands 82 49. Excretory ducts and lumina of the secretory portion of a compound tubular gland 83 50. Lumina of the secreting portion of a reticulated tubular gland 83 51. Glandular classification 83 52. Mesothelium from pericardium of rabbit ( Huber) 85 53. Mesothelium from mesentery of rabbit (Huber) 86 54. Mesothelium from peritoneum of frog 86 55. Mesothelium covering posterior abdominal wall of frog (Huber) 86 56. Endothelial cells from small artery of mesentery of rabbit (Huber) 86 57. Mesenchymatous tissue from the subcutis of a duck embryo 89 58. White fibrils and bundles from teased preparation of a fresh tendon from tail of rat (Huber) 9 1 59. Elastic fibers from ligamentum nuchas of ox 9 1 60. Reticular connective tissue from lymph-gland of man 93 61. Areolar connective tissue from subcutaneous tissue of rat (Huber) 94 62. Cell-spaces in the ground-substance of areolar connective tissue of young rat (Huber) 94 63. Connective-tissue cells from pia mater of dog (Huber) 94 64. Pigment cells found on the capsule of sympathetic ganglion of frog (Huber) . . 95 65. Leucocyte of frog with pseudopodia 95 66. Fibrous connective tissue from great omentum of rabbit 96 67. Longitudinal section of tendon 97 68. Cross-section of secondary tendon bundle from tail of rat (Huber) 97 69. Tendon cells from tail of rat (Huber) . 98 70. Cross-section of ligamentum nuch;\> of ox (Huber) 98 71. Fat-cell 99 11 12 ILLUSTRATIONS. fig. PAGE -2 Hyaline cartilage l°o 73. Section through cranial cartilage of squid 100 74. Insertion of the ligamentum teres into the head of the femur 101 75. Elastic cartilage from external ear of man 102 76. Longitudinal section through a lamellar system (v. Ebner) 104 77. 7S. Lamellae seen from the surface (v. Ebner) 104 79. Segment of a transversely ground section from the shaft of a long bone, showing lamellar system . . 105 80. Portion of a transversely ground disc from the shaft of a human femur . . . 106 81. Longitudinal section through a long bone of a lizard embryo 108 82. Longitudinal section of the proximal end of a long bone of a sheep embryo . 109 83. Longitudinal section through area of ossification from long bone of human embryo (Huber) . . no 84. Longitudinal section through epiphysis of arm bone of sheep embryo ... 113 85. Section through the lower jaw of an embryo sheep 1 14 86. Cross-section of developing bone from leg of human embryo, showing endo- chondral and intramembranous bone development (Huber) 115 87. Cross-section of shaft (tibia of sheep) 116 88. Smooth muscle from intestine of cat 124 89. Cross-section of striated muscle-fibers 125 90. Muscle-fiber from ocular muscles of rabbit 125 91. Striated muscle-fiber of frog, showing sarcolemma (Huber) 125 92. Diagram of structure of fibrils of a striated muscle-fiber (Huber) 125 93. Transverse section through striated muscle-fiber of rabbit 1 26 94. Diagram of transverse striation in the muscle of an arthropod 127 95. Striated muscle fiber of man 128 96. Cross-section through the trapezius muscle of man 128 97. Branched, striated muscle-fiber from tongue of frog (Huber) . 129 98. Cross-section of rectus abdominis of child, under low magnification (Huber) . 130 99. Longitudinal section through the line of junction between muscle and tendon 130 100, 101. Longitudinal and cross-section of muscle-fibers from the human myo- cardium 131 102. Bipolar ganglion cell from the ganglion acusticum of a teleost 135 103. Chromatophile granules of a ganglion cell from the Gasserian ganglion of a teleost 136 104. Nerve-cell from the anterior horn of the spinal cord of an ox 136 105. Motor neurones from anterior horn of the spinal cord of new-born cat (Huber) 137 106. A nerve cell with branched dendrites (Purkinje's cell), from cerebellar cortex of rabbit 137 107. Pyramidal cell from cerebral cortex of man 138 108. Nerve-cell with dendrites ending in claw-like telodendria 139 109. Ganglion cell with a T-shaped process 139 HO. Ganglion cell from Gasserian ganglion of rabbit (Huber) 140 111. Ganglion cells from spinal ganglion of rabbit embryo 140 112. Neurone from inferior cervical sympathetic ganglion of rabbit (Huber) . . . 141 113. Longitudinal section of nerve-fiber ... 14 2 114. Transverse section through sciatic nerve of frog 143 115. Medullated nerve-fibers from rabbit 144 116. Remak's fibers from pnemno^astric nerve of rabbit 144 117. Diagram to show composition of a peripheral nerve-trunk ( Huber) I46 118. Cross-section through a peripheral nerve 146 119. Peripheral motor neurone (Huber) 148 120. Motor nerve-ending in voluntary muscle of rabbit (Huber-De Witt) . . . 149 121-125. Motor endings in striated voluntary muscles 15° 126. Motor nerve-ending in striated voluntary muscle of frog 1 Huber-De Witt) . . 151 127. Motor nerve-ending on heart muscle-cells of cat (Huber-De Witt) . . 151 Motor nerve-ending on involuntary nonstriated muscle-cell from intestine of cat (Huber-De Witt) ' 151 129. Peripheral none (Huber) 15 2 130. Termination of -ensory nerve-fibers in the mucosa and epithelium of urethra 153 131. End-bulb of Krause from conjunctiva of man (Dogiel) 154 132. Meissner's tactile cor] iel) '55 133. Genital corpuscle from glans penis of man (Dogiel) 156 ILLUSTRATIONS. 1 3 PAGS 134. < ylindric end-bulb of Krause Horn intermuscular fibrous tissue septum of cat i Huber) 157 35. Pacinian corpuscles from mesorectom of kitten 1 Sala) 158 36. Corpuscle of Herbst from bill of cluck ... 159 37. Intrafusal muscle -fiber from neuromuscular nerve end-organ of rabbit (Huber) 160 38. Cross-section of a neuromuscular nerve end-organ from interosseous muscle of man 1 Huber) ... 160 39. Neuromuscular nerve end-organ from plantar muscles of dog ( Huber-De Witt) 161 40. Neurotendinous nerve end-organ from rabbit ( Huber- L)e Witt) ... 162 41. Cross-section of neurotendinous nerve end-organ of rabbit (Huber-De Witt) . 163 42. Rainier* s crosses from sciatic nerve of rabbit 165 43. Medullated nerve-fiber from sciatic nerve of frog 165 44. Ganglion cell from anterior horn of spinal cord of calf 166 45. Human red blood-cells 170 40. Rouleau formation of human erythrocytes 170 47. Hemin, or Teichmann's crystals, from blood stains on a cloth (Huber) . . 170 48. Crenated human red blood-cells 170 40. Reel blood -corpuscles subjected to the action of water 170 50. Red blood-corpuscles from various vertebrate animals 171 51. White blood-corpuscles from normal blood of man 173 52. Ehrlich's leucocytic granules 174 53. Solitary lymph-nodule from human colon 178 54. Section through mesenteric lymph-gland of cat, with injected blood-vessels . 179 55- Section from human lymph-gland 180 56. Section through the human spleen 181 57. Lobule of the spleen (Mall) 183 58. Cells containing pigment, blood-corpuscles, and hemic masses from spleen of dog 184 59. Section through human spleen showing reticular fibrils 184 60. Cover-glass preparation from bone-marrow of dog 186 61. Section through human red bone-marrow 187 Small lobule from thymus of child, with well-developed cortex 189 63. Hassall's corpuscle and a small portion of medullary substance from thymus of child ten days old (Huber) 189 64. Cross-section of human carotid artery 194 65. Section through human artery, one of the smaller of the medium-sized . . . 195 66. Precapillary vessels from mesentery of cat (Huber) 195 67. Cross-section of human internal jugular vein 196 68. Section of small human vein 197 69. Endothelial cells of capillary and precapillary from mesentery of rabbit (Huber) 198 70. Small artery from oral submucosa of cat with nerve- terminations 199 71. Section of a cell-ball from glomus carodcum of man . 203 72. Fibrin from laryngeal vessel of child 207 73. Section through lower lip of man 212 74. Longitudinal section through a human tooth, showing lines of Retzius . . . 214 75. Portion of ground tooth from man, showing enamel and dentin 215 76. Longitudinal section through human molar from the center of the enamel layer 216 77. Cross-section of human tooth, showing cement and dentin 217 78. Nerve termination in pulp of rabbit's molar ( Huber) 218 70-1S2. Four stages in the development of tooth in sheep embryo 219 83. Portion of cross-section through developing tooth 220 84. Fungiform papilla from human tongue (Huber) 221 85. Cross-section of human tongue showing filiform papillae 222 v ". Longitudinal section of foliate papilla of rabbit, showing taste-buds (Huber) 223 87. Longitudinal section of a human circumvallate papilla 224 88. Schematic representation of a taste-goblet (Hermann) 225 89. 100. Section through tonsil of dog 226 91, Scheme of salivary gland 227 93. Section through salivary gland of rabbit, with injected blood-vessels .... 229 93. Section from parotid gland of man 230 94. Section of human sublingual gland 230 \lveoli from submaxillary gland of dog (Huber) 231 96. Section of esophagus of dog 234 97. Section of human esophagus, showing duct of mucous gland 235 14 ILLUSTRATIONS. FIG. PAGE 198. Epithelium of human stomach, covering fold of mucosa between two gastric "ypts 237 199. \ ertical section through fundus of human stomach 238 200. Gastric glands from fundus of stomach of young dog (Huber) 238 201. Section through junction of human esophagus and cardia 239 202. Vertical section through human pylorus 240 203. Section through human pylorus 241 204. Section through fundus of human stomach in condition of hunger 242 205. Section through fundus of human stomach during digestion . ...... 242 206. Section through mucous membrane of human small intestine 244 207. Longitudinal section through summit of villus from human small intestine . . 245 208. Section through the junction of the human pylorus and duodenum 247 209. Section of solitary lymph-nodule from vermiform appendix of guinea-pig . . 248 210. Section through colon of man, showing glands of Lieberkiihn . 249 211. Solitary lymph follicle from human colon 250 212. Section through fundus of injected cat's stomach . . 251 213. Schematic transverse section of human small intestine (Mall) 253 214. Portion of the plexus of Auerbach from stomach of cat (Huber) 254 215. Section of esophagus of cat showing nerve-terminations (Huber) 255 210. Section through liver of pig, showing chains of liver-cells 257 217. Section through injected liver of rabbit 258 218, 219. Human bile capillaries 259 220. Diagram of hepatic cord in transverse section 260 221. Section through the human liver, showing the beginning of bile-ducts . . . 260 222. Injected blood-vessels in liver lobule of rabbit ... 261 223. Reticulum of dog's liver 262 224. Connective tissue from liver of sturgeon, showing reticulum 263 225. Section through liver lobule from dog, showing stellate cells 264 226. Transverse section through alveolus of frog's pancreas 265 227. 228. Section through human pancreas 266, 267 229. Relation of three adjoining alveoli to excretory duct, illustrating origin of centro-acinal cells 268 230. Section of human pancreas, showing gland alveoli surrounding an area of Langerhans (Huber) 268 231. Vertical section through mucous membrane of human larynx 275 232. Longitudinal section of human trachea (Huber) 277 233. Transverse section through human bronchus 278 234. 235. Sections of cat's lungs 279 236. Internal surface of human respiratory bronchiole (Kolliker) .... . 280 237. Inner surface of human alveolus, showing respiratory epithelium (Kolliker) . 281 238. Respiratory epithelium in amphibia 282 239. Section of human lung, showing elastic fibers (Huber) 283 240. Section through injected rabbit's lung 283 241. Section through thyroid gland of child 284 242. Section from parathyroid of man (Huber) 286 243. Kidney of new-born infant 287 244. Isolated uriniferous tubules 288 245. Median longitudinal section of adult human kidney 289 246. Section of cortical substance of human kidney 290 247. Section of proximal convoluted tubules from man 291 248. Epithelium from proximal convoluted tubule of guinea-pig, with surface and lateral views 292 249. Cortical portion of longitudinal section of kidney of child (Huber) 292 250. Section of medulla of human kidney 293 251. Longitudinal section through papilla of injected kidney 294 252. Section through junction of two lobules of kidney 295 253. Diagrammatic scheme of uriniferous tubules and blood-vessels of kidney . . 297 254. Dinct anastomosis between an artery and vein in a column of Bertini of child 298 255. Section of lower pari of human ureter 300 256. Section of suprarenal cortex of dog 302 257. Arrangement of intrinsic blood-vessels in cortex and medulla of dog's adrenal (Flint) 303 258. Section from ovary of adult dog (Waldeyer) 307 259. Section from ovary of young girl 308 260-263. Sections from cat's ovary 310 ILLUSTRATIONS. 1 5 FIG. PACE 264. Representation of behavior of the chromatin during the maturation of the ovum (Ruckert) 312 265. Scheme of the development and maturation of an nscaris ovum (lioveri) . . 314 266. Section of fully developed Graafian follicle from pig 315 267. Section of oviduct of young woman 317 268. Section from uterus of young woman 3'9 269. Section of human vagina (Huber) 3 2 ° 270. Section of human labia minora (Huber) .... 321 271. Diagram showing characteristics of spermatozoa of vertebrates 323 272. Human spermatozoa 3 2 4 273. Longitudinal section through human testis and epididymis 325 274. 275. Sustentacular cells 326 276. Section of human testis (Iluber) 327 277. Section through human vasa efferentia 328 278. Cross-section of vas epididymidis of human testis (Iluber) 328 279. Section of dog's testis with injected blood-vessels 329 280. Cross-section of vas deferens near epididymis (human) (Iluber) 330 281. Cross-section of wall of seminal vesicle (human) (Huber) 331 282. Section of prostate gland of man (Iluber) 331 283. Schematic diagram of spermatogenesis as it occurs in ascaris (Boveri) .... 335 284. Schematic diagram of section through convoluted seminiferous tubule of mammal (Hermann) 337 285. Section of convoluted tubule from rat's testicle 338 286. Under surface of the epidermis 342 287. Cross-section of skin of child with injected blood-vessels 343 288. Prickle cells from the stratum Malpighii of man 344 289. Cross-section of human epidermis 345 290. Cross-section of negro's skin 34^ 291. Nerves of epidermis and papilla? from ball of cat's foot 34& 292. 293. Meissner's corpuscle from man 349 294. Grandry's corpuscles from duck's bill 35° 295. Longitudinal section of human hair and follicle 35 2 296. Cross-section of human hair with follicle 353 297. Longitudinal section of cat's hair and follicle, showing nerve-termination . . 354 298. Longitudinal section through human nail and its groove . 355 299. Transverse section through human nail and its sulcus 356 300. Cross-section of coiled tubule of sweat-glands from human axilla 357 301. Tangential section through coiled tubule of sweat-glands from human axilla . 357 302. Section of alveoli from sebaceous gland of human scalp (Huber) 359 303. Section of mammary gland of nullipara (Nagel) 3^° 304. Transverse section through human skin 363 305. Cross-sections of human spinal cord 366 306. Schematic diagram of spinal cord in cross-section (von Lenhossek) .... 368 307. Schematic cross-section of spinal cord (Ziehen) 3^9 308. Section through human cerebellar cortex vertical to the surface of the convolution 372 309. Schematic diagram of cerebellar cortex 373 310. Cell of Purkinje from human cerebellar cortex 374 311. Granular cell from the granular layer of the human cerebellar cortex . . . . 374 312. Schematic diagram of cerebral cortex 377 313. Large pyramidal cell from human cerebral cortex 377 314. Schematic diagram of cerebral cortex 378 315. Olfactory bulb 380 316. Longitudinal section of spinal ganglion of cat (Huber) 382 317. Ganglion cell from the Gasserian ganglion of a rabbit (Huber) 3S3 318. Diagram showing the relations of the neurones of a spinal ganglion (Dogiel) 384 319. Neurone from inferior cervical sympathetic ganglion of a rabbit (Huber) . . 385 320. From section of semilunar ganglion of cat (Huber) 386 321. From section of stellate ganglion of dog (Huber) 3^7 322. From section of sympathetic ganglion of turtle (Huber) 388 323. From section of sympathetic ganglion of frog (Huber) 388 324. Schematic diagram of a sensorimotor reflex arc according to the modern neu- rone theory 389 325. Schematic diagram of a sensorimotor reflex cycle 390 326. Schematic diagram of the reflex tracts between a peripheral organ and the brain cortex 39 l 1 6 ILLUSTRATIONS. FIG. PAGE 327. Neurogliar cells (Huber) 392 Section through injected cerebral cortex of rabbit 395 329. Schematic diagram of the eye (Leber and Flemming) 408 330. Section through the anterior portion of human cornea 410 331. Corneal spaces of dog 4 11 332. Section through the human choroid . 413 333. Meridional section of the human ciliary body 415 334. Injected blood-vessels of the human choroid and iris 417 335. Section of the human retina 419 336. Section through point of entrance of human optic nerve 421 337. Section through human macula lutea and fovea centralis 421 338. Schematic diagram of the retina (Ramon y Cajal) 424 339. Injected blood vessels of the human retina 426 340. Injected blood-vessels of human macula lutea 426 341. Cross-section of upper eyelid of man 431 342. Schematic representation of the complete auditory apparatus (Schwalbe) . . 436 343. Cross-section of the Eustachian tube 438 344. Right bony labyrinth (Quain, after Sommering) 439 345. Membranous labyrinth from five-month human embryo (Schwalbe, after Retzius) 440 346. Transverse section through an osseous and membranous semicircular canal of an adult human being 441 347. Vertical section through the anterior ampulla 443 34S. Section through a turn of the osseous and membranous cochlear duct of the cochlea of guinea-pig 445 349. Organ of Corti (Retzius) 448 350. Surface of organ of Corti, with surrounding structures (Retzius) 451 351. Scheme of distribution of blood-vessels in labyrinth (Eichler) 453 INTRODUCTION TO MICROSCOPIC TECHNIC. I. THE MICROSCOPE AND ITS ACCESSORIES. A detailed description of the microscope and its accessory appa ratus hardly lies within the scope of this book. If, notwithstanding, a few points be touched upon, it is done only that the beginner may have a working knowledge of the different parts of the instru- ment which he must use. A more intimate knowledge of the theory of the microscope may be acquired by studying such works as those of Uippel, A. Zimmermann, and Carpenter. i. Histologic specimens are examined with the aid of the micro- scope, an instrument V hich magnifies the objects by means of its optic apparatus. For this purpose simple microscopes, consisting usually of a single lens, are not sufficient ; the aid of the compound microscope, which contains a combination of two systems of lenses, is necessary. These systems may be changed according to the needs of the case, and thus a variation in the magnification of the object obtained. The rest of the instrument consists of a frame- work called the stand, the lower portion of which consists of a foot- plate or base, which should rest firmly on the table. From the base rises the column or pillar, to which the other parts of the microscope are attached. From below upward come the movable mirror, the stage and substage with diaphragm and condenser, and the tube with pinion and fine adjustment. One side of the mirror is concave, and serves to concentrate the rays of light in the direction of a central opening in the stage. The other side is plane, and is seldom used. If the objects are to be ex- amined by direct illumination, and not by transmitted light, the mirror is so placed that the rays are reflected away from the open- ing in the stage. 2. The specimen to be examined is placed on the stage, over the central opening. If the light be too strong, the opening may be diminished in size by means of a diaphragm. In some instru- ments these diaphragms are placed in the opening of the stage, and consist of plates with different sized apertures. A better form is composed of one large disc containing several apertures of different sizes. This is fastened to the under surface o( the stage in such a way that by revolving the disc the apertures may be brought one 2 17 i8 THE MICROSCOPE AND ITS ACCESSORIES. after the other opposite the opening in the stage. A much better diaphragm, constructed on an entirely different principle, is the so- called iris diaphragm. Although its opening is not exactly circu- lar, vet it has the advantage of being easily enlarged or contracted by manipulating a small handle controlling the metal plates sliding over one another. 3. The tube, which is contained in a close-fitting metal sheath, is attached to the upright of the microscope. In the simpler forms Ocular or eyepiece. Draw-tube. Tube. Triple nose-piece. Objectives. Stage. Iris diaphragm and Abbe condenser. Screw for focusing condenser. Mirror. Rack and pinion for coarse adjustment. Micrometer screw for fine adjustment. Pillar. Stand. Fig. I. — Microscope. of microscopes the tube is raised, lowered, or twisted by hand. In more complicated instruments the upward and downward move- ments arc accomplished by means of a rack and pinion — coarse adjustment. A micrometer screw — fine adjustment — situated at either the upper or the lower end of the upright, controls the fine adjustment. The tube possesses an upper and a lower opening, into which lenses may be laid and screwed. 4. The ocular, into the ends of which lenses are inserted, fits into I l N \F FRESH HSS1 ES. 21 needle is thrust into the substance to hold it in plat e, while the other is used to tear the fibers apart. This method is used in examining iiiin les, nerves, tendons. et< . Some tissues are >o constituted that they can only be investigated by means of sections, which permit a study of their elements and the rela- tionship of the same to each other. In this method an ordinary razor, moistened in some fluid, may lie employed. As a rule, it is not the of the section, hut the thinness, \vhi< h is important. This latter i^ obtained only by practice. Every microscopisl ought to become ao tomed to making free-hand sections with the razor. It is the simplest o\ all methods, is very rapid, and is especially useful in the quick identifica- tion of a tissue. In cutting fresh so-called parenchymatous tissues, such as liver and kidney, an ordinary razor is not sufficient. Here a double knife is necessary. This consists of two blades, whit h are so placed one above the other that their distal ends touch, while their proximal ends are slightly separated. The distance of the blades from each other is regulated by a screw. If this be removed the knives may be separated for cleaning. In making sections, only those portions of the b are of importance which are very close together but do not actually touch. Sections are cut by drawing the moistened instrument quickly through an organ, as, for instance, a fresh liver. As the organ is cut in two. a very thin section of the tissue remains between the blades. This is removed by taking out the screw and separating the blades in normal salt solution. Organs of a similar consistence can be fro/en and then cut with an ordinary razor the blade of which has been cooled. Sometimes good results may be obtained by drying small pieces of tissue, as, for instance, tendon. 13. As sections or small pieces of fresh tissue would soon become dry when placed on the slide, they must be kept moist during examina- tion. They are therefore mounted in so-called indifferent fluids (placed on the slide and immersed in a few drops of the indifferent fluid and covered with a cover-slip ). These have the power of preserving even living organs for some time without change. Such fluids, for instance, are the lymph, the aqueous humor, serous fluids, amniotic fluid, etc. Artifi- cial indifferent fluids are much used and should always be kept in stock. Of this class, the following are useful : 1. Physiologic saline solution: A 0.75'/,' solution of sodium chlorid in distilled water. 2. Schultze's iodized serum : A saturated solution of iodin or tincture of iodin in amniotic fluid. 3. Ranvier's solution of iodin and potassium iodid : A satu- rated solution of iodin in a 2'/, solution of potassium iodid. 4. Kronecker's fluid : Distilled water, 1000 c.c. : sodium chlorid, 6 gm. ; sodium carbonate, 0.06 gm. 5. Solution of Ripart and Petit : Copper chlorid, 0.3 gm. : cop- per acetate, 0.3 gm. ; aqua camphone, 75 c.c. ; distilled water, 75 c.c. ; and glacial acetic acid, 1 c.c. After mixing, this solution is yellow, but clears up within a few hours, and should then be filtered. 14. The examination of fresh tissues comes far from revealing all the finer details of their structure. This is partly due to the fact that the indices of refraction of the different elements of the tissues are too nearly 2 2 THE MICROSCOPIC PREPARATION. alike, in consequence of which the outlines are somewhat dimmed; and also, that changes occur, even during the most careful manipulation of the tissues, which result in pictures somewhat different from the normal. These difficulties may be lessened by the use of fixing fluids. By these we mean those reagents which we know by experience possess the power of preserving entirely fresh (living) tissues or organs in such a way that accurate conclusions as to their condition and qualities during life may be obtained. Even this can be attained only after a careful series of control observations. In general, fixing fluids act differently on dif- ferent tissues, some preserving better one set of elements, while others give better results with another set. It is therefore always advisable to fix in different fluids pieces of the tissues or organs to be examined. A. FIXING METHODS. The fixing fluids most used for general purposes are the following : 15. Alcohol. — The most common fixing fluid is alcohol. It is at the same time a hardening fluid, as the water of the tissues is withdrawn and their albumin coagulated. Small or thin pieces are put immediately into absolute alcohol, in which they remain for from twelve to twenty- four hours. The period required for fixation may be greatly shortened by changing the absolute alcohol at the end of one or two hours. In the case of larger pieces, a successive immersion in gradually increasing strengths of alcohol (S°/f, 7°%, 90%) is the method chosen. Pieces 1 c.c. in size remain for twenty-four hours in each grade of alcohol, larger pieces for a proportionately longer time. Alcohol used in this way is a hardening fluid rather than a fixing fluid. 16. Osmic acid is a reagent that kills quickly, fixes exceedingly well, and even colors certain tissues. Only small pieces can be fixed in this fluid, as it does not easily penetrate the tissues. It is ordinarily used in a \ ( /c aqueous solution, the objects remaining immersed twenty-four hours. They are then washed in running water for the same length of time, after which they are transferred to 90^ alcohol. Very small objects may be treated with osmic acid in the form of vapor (vaporiza- tion). This is done as follows : A very small quantity of osmic acid so- lution is put in a small dish. The object is then suspended by a thread in such a way that it does not come in contact with the fluid. The dish should be covered with a well-fitting lid. 17. Flemming's Solution. — A solution with a similar action, but fixing nuclear structures even better than osmic acid, is the chromic- osmic-acetic acid solution of Flemming (82) : Osmic acid, 1 fc aqueous solution . . 10 parts. Chromic acid, i'/ aqueous solution ... 25 " Glacial acetic acid, \'/i, aqueous solution . 10 " Distilled water 55 " Small pieces are fixed in a small quantity of the fluid for at least twenty-four hours, sometimes for a longer period, extending even to weeks. They are then washed for twenty-four hours in running water and ed through 70% and 80'/, each twenty-four hours, into 90^, alco- hol. Flemming (84; also recommends a stronger solution, which is made as follows : FIXING METHODS. 23 Osmic acid, 2'// aqueous solution (.parts. Chromic acid, 1 '. aqueous solution ... 15 " Glacial acetic acid 1 part. Fol's Solution. — Fol has recommended the following modification of Flemming's solution : Osmic acid, 1 ' ', a<|iieous solution .... 2 pe Chromic acid, 1 ', aqueous solution . . .25 Glacial acetic acid, 2$ aqueous solution . 5 Distilled water 68 •• In fixing with osmic acid and its mixtures it is always advisable to transfer the objects from water into a weak alcohol (50^ ), as by this means the shrinking and tearing of the tissues which sometimes occur on account of the too rapid diffusion between the water and alcohol are avoided. 18. Hermann's Solution. — Very good results sometimes follow the use of the platinum-acetic-osmic acid solution of Hermann (89, 1). Jt is employed as is Flemming's solution : Osmic acid, 2 r ' r aqueous solution .... 4 part-. Platinum chlorid, l f / c aqueous solution . . 15 Glacial acetic acid I part. After fixing with this solution, Flemming's solution, or any other osmic mixture, the subsequent treatment with alcohol may be followed by crude pyroligneous acid. The objects are placed for from twelve to twenty-four hours in the latter and then again immersed in alcohol. The result is a peculiar coloring of the specimen which often makes subsequent staining (see below) unnecessary (Hermann). ig. Corrosive Sublimate. — An excellent fixing fluid is made by saturating distilled water or a physiologic saline solution ( see p. 21) with corrosive sublimate ; saline solutions keep better. Small pieces, about 0.5 cm. in diameter, are immersed in this fluid for from three to twenty- four hours, are then washed in running water for twenty-four hours, and then transferred into 70'/ alcohol. After twenty-four hours the tissues are placed in 80^ for the same length of time, and then preserved in 9 alcohol. It often occurs that after changes in temperature crystals of sub- limate are formed on the surface or in the interior of the object. For their removal a few drops of a solution of iodin and potassium iodid are added to the alcohol (P. Mayer, 87). It is a matter of indifference whether the 70^, 80% or 90'^ alcohol is thus iodized. In the further treatment of the object, as well as in sectioning, any such crystals of sub- limate will not be found to be a hindrance. Indeed, in the case of very delicate objects it is often more advantageous to undertake their removal after sectioning by adding iodin to the absolute alcohol then used. 20. Picric Acid. — Small and medium-sized objects (up to 1 c.c.) are fixed in twenty-four hours in a saturated aqueous solution of picric acid (about 0.75^ ), although an immersion lasting for weeks is not detrimental, especially if the objects be of considerable size. The tissues are transferred to 70^ or 80$ alcohol, in which they remain until the alcohol is not colored by the picric acid. They are then preserved in 90^ alcohol. 21. Instead of a pure solution of picric acid, the picrosulphuricacid of Kleinenberg or the picric=nitric acid of P. Mayer (81) may be used. 24 THE MICROSCOPIC PREPARATION. The first is made thus: i c.e. of concentrated sulphuric acid is added to ioo c.c. of a saturated aqueous picric acid solution. This is allowed to stand for twenty-four hours, then filtered, and diluted with double its volume of distilled water. • The picric-nitric acid solution is made by adding 2 c.c. of pure nitric acid to 100 c.c. of a saturated picric acid solution. Filter after standing for twenty-four hours. 22. Rabl's Solutions. — C. Rabl (94) recommends the following mixtures, especially for embryos : (1) Concentrated aqueous solution of corrosive sublimate, 1 vol. ; concentrated aqueous solution of picric acid, 1 vol. ; distilled water, 2 vols. (2) 1 per cent, aqueous solution of platinum chlorid, 1 vol. ; concentrated aqueous solution of corrosive sublimate, 1 vol. ; distilled water, 2 vols. In both cases, after being washed twelve hours in water (in the first preferably in alcohol) the specimens are transferred to gradually increased strengths of alcohol. 23. Acetic Sublimate Solution. — This is an excellent fluid, and at present much used for embryonic tissues and for organs containing only a small quantity of connective tissue. To a saturated aqueous solution of sublimate, 5% to 10% of glacial acetic acid is added. After remaining two or three hours or more in this solution, the objects are transferred to 35^ alcohol, after which they are passed through the higher grades. 24. O. vora Rath (95) recommends, among others, the following two solutions: (1) Picric=osmic=acetic acid solution. Add to 1000 c.c. of a cold saturated picric acid solution 1 gm. of osmic acid, and after several hours 4 c.c. of glacial acetic acid. Objects are fixed, according to their size, in four, fourteen, and forty-eight hours, and then transferred to 75% alcohol. (2) Picric=sublimate=osmic acid solution. A mix- ture of 100 c.c. of a cold saturated aqueous picric acid solution with 100 c.c. of saturated sublimate solution is made, into which is poured 20 c.c. of a 2 r / c osmic acid solution. 2 c.c. of glacial acetic acid may also be added. Tissues fixed by either of these fluids may be treated with pyroligneous acid or tannin. The crystals of sublimate must be removed by iodized alcohol. 25. Nitric Acid. — Small objects may be fixed in about six hours in 3 ft to 5% nitric acid (sp. gr. 1.4). A longer immersion is injurious, as certain nuclear structures are affected. After washing thoroughly in running water, the tissues are treated as usual with alcohols of increasing concentration. 26. Chromic acid is used in a y3% to i r / f aqueous solution. Small pieces are fixed for twenty-four hours, larger ones for a longer time, even weeks. The quantity of the fixing fluid should be at least more than fifty times the volume of the tissues to be fixed. The objects are subsequently washed in running water and run through the ascending alcohols. This last should be done in the dark. Two or 3 drops of formic acid may be advantageously added to each 100 c.c. of chromic acid solution (C. Rabl, 85). 27. Muller's Fluid. — ium bichromate 2 to 2.5 gm. Sodium sulphate 1 " Water 100 c.c. With this solution it rcf|iiires several weeks for proper fixation, and the process must be conducted in the dark. During the first few weeks the solution should be changed every few days, and later once a week. INFILTRATION AND IMBEDDING. 25 According to the results desired, the pieces are either washed out in run- Ding water and subsequently treated in the usual manner with alcohol, or they are placed directly in 70'/, which is later replaced by 80 '/, and 90'/ alcohol. It is important that all these prcx edures should take p in the dark. 28. Zenker's Fluid. — Potassium bichromate 2.5 ^m. Sodium sulphate 1 Corrosive sublimate 5 " Glacial acetic acid 5 c.c. Water IOO " It is advisable to add the glacial acetic acid in proper proportion to the quantity of the solution to he used, and not to add it to the stock solution. The tissues are allowed to remain for from six to twenty-four hours in this mixture, in which they float for a short time. They are then washed in running water for from twelve to twenty-four hours, and transferred to gradually concentrated alcohols. Crystals of sublimate which may be present are removed with iodized alcohol. Zenker's fluid penetrates easily, and fixes nuclear and protoplasmic structures equally well without decreasing the staining qualities of the elements. 29. The use of Erlicki's fluid (potassium bichromate, 2^ gm.; cupric sulphate, 0.5 gm., and water, 100 c.c.) is quite similar to that of Midler's, except that it acts much more quickly. A temperature of 30 C. to 40 C. shortens the process in both cases considerably, Midler's fluid fixing in eight and Erlicki's in three days. 30. Formalin (Formol). — Of recent years formalin, which is a 40% solution of the gas formaldehyd in water, has been much used as a fixing fluid. It is best employed in the form of a solution made by add- ing 10 parts of formalin to 90 parts of water or normal saline solution. Small pieces of tissue remain in this solution for from twelve to twent] - four hours, larger pieces or organs a number of days or weeks, and are then transferred to go r / alcohol. We have attempted to give only the fixing and hardening fluids com- monly employed for general purposes. There are numerous other fluids used for special purposes ; these will be noticed under the headings of the corresponding tissues and organs. B. INFILTRATION AND IMBEDDING. 31. To obtain sections from objects already fixed, it is above all necessary that they should have a certain consistency, which they obtain in go r / alcohol. It is not advisable to attempt the free-hand sectioning of objects that have not previously been especially prepared for this treat- ment, as crumbling of the sections and falling apart of the loosely con- nected tissues are the results. To avoid this, infiltration masses are used. The tissue is placed in a fluid medium which penetrates it throughout and then hardens into a solid mass on cooling or on the evaporation of the solvent. The object thus infiltrated and imbedded can then be cut, the natural position of its different elements being preserved in the section. The commonest infiltration masses are paraffin and celloidin (collo- dion or photoxylin). 26 THE MICRCOSOPIC PREPARATION. J. PARAFFIN. 32. In describing the method of paraffin infiltration and imbedding it is assumed that the tissues have been previously fixed and hardened and are in alcohol ready for further manipulation. From the hardened tissues small flat pieces are cut with a sharp knife or razor. If possible, they should be square, rectangular, or triangular in shape, their surfaces not exceeding y 2 square inch, and their thickness from y% to y± of an inch. Pieces of larger size may be imbedded, if desired, provided the requisite care be exercised. The pieces selected are placed in absolute alcohol, in which they remain until thoroughly dehydrated. From the latter they can not be passed directly into paraffin, as alcohol is not a solvent of that substance, and, consequently, the preparation would not be infil- trated with the imbedding mass. The pieces of tissue are therefore first placed in some fluid which mixes with absolute alcohol and at the same time dissolves the paraffin. There are many such reagents, as xylol, toluol, chloroform, and a number of oils (oil of turpentine, oil of cedar, oil of origanum, etc.). Of these reagents xylol may be recommended for general use. In the xylol the tissues remain for from two to twelve hours, the time depending somewhat on the size of the pieces and on the density of the tissue. When thoroughly permeated by the xylol, they are transparent. From the xylol (toluol, chloroform, or oils) the tissues are placed in melted paraffin. Two kinds of paraffin are used, one having a melting point of 38 to 40 C. — soft paraffin — and another with a melt- ing point of 50 to 58 C. — so-called hard paraffin. The paraffin should always be filtered before using. It is essential that melted paraffin have a constant temperature while the tissues are being infiltrated. This is attained by placing the receptacle containing the paraffin in a paraffin oven regulated by means of a thermostat to a temperature about two degrees above the melting point of the hard paraffin. Filtered hard and soft paraffin may be kept in suitable glass beakers in respective compartments in the paraffin oven. After the tissues are thoroughly permeated with the xylol, this is poured off and melted soft paraffin added, and the dish replaced in the paraffin oven. In the soft paraffin the tissues remain from one to four hours, at the end of which time the soft paraffin is poured off and hard paraffin added, and the dish again placed in the oven. In the hard paraffin the tissues remain from Fig. 2 .-Box for imbedding u ^ ^ ^^ ^^ d ndJng Qn the size of the pieces. They are now ready to be imbedded. Two metallic L's are placed together on a glass or metal plate in such a way as to make a rectangular box. 2. ) This is filled with melted hard paraffin taken from the oven. Uefore the paraffin cools, the piece of tissue to be imbedded is taken from the hard paraffin in the oven and placed with one of its flat surf 11st one end of the box. If several pieces of tissue are to be imbedded, a piece may thus be placed in each end of the box. While transferring the tissues from the hard paraffin to the imbedding box they should be handled with forceps, the blades of INFILTRATION AND IMBEDDING. 2J which have been wanned in a flame. As soon as the paraffin in which the u>sucs are imbedded has cooled sufficiently to allow the formation of a film over the melted paraffin, the imbedding box is placed in a dish of cold water. This cools the paraffin quickly and prevents its becoming brittle. A stay of from five to ten minutes in the < old water hardens the paraffin so that the L's may he removed, and the paraffin blo< k < ontaining the imbedded tissue may be taken from the plate. It is well to place the paraffin block thus obtained back into the cold water for a short timi that it may become hard all the way through. As the paraffin often adheres closely to the glass or metal plate and the L's, it is advisable to cover these parts with a very thin layer of glycerin before imbedding. There is then no difficulty in separating them from the paraffin block. 33. If a large number of small pieces of tissue are to be imbedded, it is often advantageous to carry on their infiltration with hard paraffin in a flat dish of suitable size. This may then be taken from the paraffin oven after thorough infiltration has been attained and the several pieces of tissue arranged on the bottom of the dish. As soon as a film forms over the paraffin the dish is placed carefully in cold water and the paraffin allowed to harden. The large piece of paraffin thus obtained may then be cut into several smaller pieces, each containing a piece of the imbedded tissue. The dish used for this purpose should be coated on the inside with a thin layer of glycerin. 34. On transferring an object from one fluid into another, so-called currents of diffusion occur, which produce, especially in such tissues as contain cavities, shrinkage and tearing. This often results in totally changing the finer structure of the tissues. It is therefore necessary to proceed with greater caution than in the method above indicated. Mixtures containing different percentages of alcohol and the inter- mediate fluid (xylol, toluol, chloroform | may be prepared, and the object, according to its delicacy, passed through a greater or smaller number of such solutions. In ordinary cases a single mixture of alcohol and the in- termediate fluid is sufficient, the object remaining in the solution for a length of time varying with its size before being passed into the pure in- termediate fluid. This part of the treatment may of course be slowed or hastened according to the number of such mixtures, eai h succeeding one containing more and more of the intermediate fluid. 35. After the object has been passed into the pure intermediate fluid it should be just as carefully passed into the infiltrating fluid. If paraffin is to be used and the object be delicate, the following method is advisable : The object is placed in a glass vessel half filled with the intermediate fluid, into which a few pieces of soft paraffin are dropped. The vessel is then covered and allowed to remain at the temperature of the room. When the paraffin is dissolved the cover is removed and the vessel placed in a par- affin oven kept at a temperature corresponding to the melting point of the paraffin. The volatile intermediate fluid evaporates gradually, and in a few hours the object is infiltrated with an almost pure soft paraffin. It may now be transferred into pure melted hard paraffin. In this the tissue remains for a longer or shorter time, according to its size. 36. High temperatures are, as a rule, injurious to tissues. This should always be borne in mind, and the student should aim to keep his specimens at the lowest possible temperature conducive to proper infiltra- tion. If for any reason higher temperatures become necessary, the ex- 28 THE MICROSCOPIC PREPARATION. posure of the tissues to their action should be as brief as possible. The paraffins most used have a melting point of 40 to 6o° C. The kind of paraffin used should depend upon the temperature of the room in which the sectioning is to be done. It is even well to have different mixtures of hard and soft paraffins at hand, so that, if the temperature of the room be low, tissues may be imbedded in a softer mixture, and vice versa. 37. The process of infiltrating and imbedding in paraffin is repre- sented by the following diagram (instead of xylol, other intermediate fluids may be used) : Alcohol, 90^ t Abs. alcohol t Alcohol xylol mixture t Xylol <- t Xylol-paraffin (cold) t =*- Xylol-paraffin (in paraffin oven) t Soft paraffin -^ t Hard paraffin Imbedding 38. The size and density of the tissues must necessarily regulate the length of time necessary for their proper infiltration. It is therefore hardly possible to give any definite figures. In presenting the following table we have taken as a standard any tissue that has the general consistency of liver fixed in alcohol. The time is given in hours, and should in each case be regarded as a minimum. A longer stay in any one fluid will, under favorable circumstances, do no harm. Absolute alcohol Xylol From now on affin 1 Soft paraffin . Hard paraffin par- Smai.l Ob- jects under I MM. IN Diameter. I Middle-sized Objects up to 5 MM. IN Diameter. Large Ob- jects up to 10 MM. IN Diameter. 24 6 Very Large Ob- jects, although not More than a Few cm. in Di- ameter. For a longer or shorter time in the fluids, ac- cording to the size of the object. 2. CELLOIDIN. The best and most convenient celloidin to use in microscopic work is Schering's granular celloidin, put up in t -ounce bottles. Of this a sto< k or thii k solution is prepared by dissolving 6 gm. of the celloidin in 100 c.C. of equal parts of absolute alcohol and ether. Of this, when required, a thin solution is prepared by diluting a quantity of the stock solution with an equal quantity of the ether and alcohol solution. INFILTRATION AM) IMBEDDING. 29 39. The hardened tissues arc 1 ut into small pie es, which should not be much more than ^ of an inch in thickness and not have a surface area of more than ^4 of a square inch. Much larger pieces of tissue may be imbedded in celloidin. This is not advised, however, unless it is necessary to show the whole of the structure to be studied. The pieces to be imbedded are placed for twenty-four hours in absolute alcohol, and are then transferred for twenty-four hours to a mixture of equal parts of abso- ute alcohol and ether. Then they go into the thin celloidin solution, where they remain for from twenty-four hours to several days, depending on the size and density of the pieces to be imbedded. The pieces of tissue are then transferred to the thick celloidin solution, where they again remain for from twenty-four hours to several days. If it is desired to imbed large pieces, especially if these be of the medulla or brain, the stay in the cel- loidin solutions should be lengthened to several weeks. The hardening of the celloidin may now be obtained by one of several methods. 40. A sufficient quantity of the stock or thick celloidin solution to cover well the tissues to be imbedded is poured into a flat dish large enough to allow the pieces to be imbedded to be arranged on its bottom and leave a space of about % of an inch between adjacent pieces. The dish is then covered, not too tightly, and set aside to allow the ether and alcohol to evaporate. In one or two days the celloidin is usually hard enough to cut into small blocks, each block containing a piece of the imbedded tissue. The blocks of celloidin are now further hardened by placing them in 80 c / c alcohol. A stay of several hours in this alcohol is usually sufficient to give them the hardness required for section cutting. After the celloidin pieces have obtained the right degree of hardness they are to be stuck to small pieces of pine wood or vulcanized fiber so that they may be clamped into the microtome. This is done in the following way : A piece of celloidin containing a piece of tissue is trimmed with a sharp knife so that only a rim of celloidin about ^ of an inch in thickness surrounds the piece of tissue. It is now placed for a few moments in the ether and alcohol solution. This is to soften the surfaces of the celloidin. One end of a small pine-wood or vulcanized-fiber block about one inch long, the cut end of which has a surface area slightly larger than the celloidin block, is dipped for a few moments into the ether and alcohol solution and then into the thick celloidin. The celloidin block is now taken from the ether and alcohol solution, dipped into the celloidin, and pressed against the end of the wooden or vulcanized-fiber block, which has been coated with the celloidin. The whole is now set aside for a little while to allow the celloidin to harden slightly, and is then placed in 80 f /< alcohol. In the alcohol it may remain indefinitely ; it may, however, be used for cutting as soon as it again becomes hard. 41. The piece of tissue to be imbedded may be mounted at once on pine-wood or vulcanized-fiber blocks from the thick celloidin solution by pouring a small amount of thick celloidin over one end of the block and placing the piece of tissue from the thick celloidin solution onto the layer of celloidin on the block. In three to four minutes a layer of the thick celloidin solution is poured over the piece of tissue and the end of the block. It may be necessary to do this several times if the piece of tissue is large or of irregular shape. The block is now set aside for about five minutes, and is then placed in 80^ alcohol, where it remains until the celloidin is hard, or until it is desired to cut sections. 30 THE MICROSCOPIC PREPARATION. 42. The tissues may be imbedded by pouring the thick celloidin, to- gether with the objects, into a small box made of paper. The surface of the celloidin hardens in about an hour (preliminary hardening), after which the whole is transferred to 80^ alcohol, in which the final hardening takes place. The paper is then removed, the block of celloidin trimmed to a convenient size and fastened on a block. While being cut, celloidin preparations are kept moistened with 8o#> alcohol. Organs consisting of tissues of varying consistency, as well as very dense objects, can be cut with better results in celloidin than in paraffin. On the other hand, celloidin sections can never be cut as thin as paraffin sections, and the after-treatment (see below), fixation on the slide, etc., are much more complicated than in the case of paraffin sec- tions. 43. The following is a diagram showing the process of infiltration and imbedding in celloidin. go c /c alcohol t Abs. alcohol t Abs. alcohol and ether (in equal parts) t Thin celloidin solution t Thick celloidin solution t Imbedding t 80% alcohol 3. CELLOID1N-PARAFFIN. 44. To combine the advantages which infiltration in celloidin and in paraffin offer, a method of celloidin-paraffin infiltration is recommended. Preparations that have been imbedded in celloidin and hardened in 80$ alcohol are placed for about twelve hours in 90$ alcohol, from which the}" are transferred to a mixture of equal parts of oil of origanum and go<% alcohol. They are then immersed for a short time in pure origa- num oil, then in a mixture of equal parts of origanum oil and xylol, and finally in pure xylol. From this point the regular method of infiltrating with paraffin is followed, care being taken that the pieces remain for as short a time as possible in the different fluids, in order that the celloidin may not become brittle. Very thin sections may be obtained by painting the cut surface with a thin layer of a very dilute celloidin solution. This hardens and gives the tissue a greater consistency. This treatment is useful in the combined celloidin-paraffin method, as well as when paraffin alone is used. C. THE MICROTOME AND SECTIONING. Instruments known as microtomes have been devised in order that tting maybe rendered as independent as possible of the skill of the individual, but more especially to obtain series of sections of uni- form thi< kness. Their construction varies greatly. Some of these in- I ill. \M< R( (TOME AND 3E< l [I INING. 31 struments, as the so 1 ailed rocking mi< rotomes, are so spe< ialized that they only cut paraffin objects when the knife is transversely placed. Others have a more general function, celloidin as well as paraffin objects being sectioned with the knife in any position. To the latter (lass belong the sliding microtomes. Of these, two types are in general use in this country, and may therefore be more thoroughly discussed. 45. In figure 3 is shown an instrument which may be recommended for general laboratory work. This instrument consists of a horizontal base which rests on the table, and a vertical plate | a 1, and a slide | b ) whi< h supports a block 1 c 1, to which is fastened a knife by mean-, of a thumb- screw 1 1/ i. On the other side of the vertical plate is a metal frame into which are fastened the paraffin and celloidin blocks ; this frame is attached to a slide 1 / 1, which may be elevated or lowered by a feed ( g). This feed consists of a micrometer screw acting on the lower surface of the slide. The micrometer screw is provided with a milled head, divided into a definite number of parts which bear a definite rela- F« -Laboratorj mien tion to the pitch of the micrometer screw. The instrument shown in the figure is further provided with a lever (//), which may be so adjusted as to move the milled head on the micrometer si rew 1 or any given number of notches at each movement of the lever ; and as each notch on the milled head has a value of 5 microns ( T „ , (lir of an inch), every time the milled head is moved 1 notch (toward the manipulator) the slide carrying the clamp holding the tissue is elevated 5 microns; 2 notches would elevate the tissue 10 microns ,, r of an inch) ; 4 notches, 20 microns ( n ^ of an inch |, etc. It is not essential to have a lever attached to the instrument as above described, although this is very convenient ; if not present, the milled head is moved the desired number of notches with the hand. 46. In cutting paraffin sections with the sliding microtome the knife is placed at an angle of about 35 to 40 to the horizontal plate of the microtome. Sections are cut more easily with the knife in this posi- 32 THE MICROSCOPIC PREPARATION. tion than when the knife is placed at right angles to the microtome, as is often recommended, and it does not seem that the tissues suffer materially from distortion when they are cut with the knife at an angle, as is some- times claimed. Before fastening the paraffin blocks into the clamp on the microtome, preparatory to cutting sections, the paraffin is trimmed with a sharp knife from the end of the paraffin block until the tissue is nearly exposed, care being taken, however, to leave a flat surface. The top of the paraffin block is then beveled off on three sides to within a very short distance of the tissue. The fourth side, that which faces the knife when the block is clamped in the microtome, should be trimmed only to within about y% of an inch of the tissue. This edge of paraffin is made use of, as will be seen in a moment, for preventing the sections from curling while they are being cut. The paraffin block is now ready to be clamped in the microtome. This is done in such a way that the paraffin block just escapes the knife when drawn over it. A number of rather thick sections (20 to 40 microns) are cut by moving the micrometer screw from right to left 4 to 8 notches every time the knife has been drawn over the paraffin block and has been brought back again, until it is noticed that the knife touches all parts of the top of the paraffin block, or until the tissue is fairlv exposed. The succeeding sections may now be kept. It may per- haps be well to state that it is better not to try to cut very thin sections at the beginning ; sections 20 to 15 microns in thickness will answer very well. To begin with, then, the milled head of the micrometer screw is turned 4 notches from left to right, and the knife is drawn over the block with a steady, even pull, and without using undue pressure. Usually the sections will curl up as they are being severed from the paraffin block. This may very readily be prevented by holding the tip of a camel's-hair brush, which has been pointed by drawing it between the lips, against the edge of the section as soon as it begins to curl. A little practice will enable one to do this almost automatically. The sections are transferred to paper by means of the camel's-hair brush, which process is facilitated if the brush has been slightly moistened with saliva, as the section will then adhere lightly to the brush. 47. If the tissues are well imbedded and not too hard, and if the knife is sharp and properly adjusted, paraffin sections may be cut in such a way that each succeeding section adheres to the preceding one, so that actual ribbons of paraffin sections may be made. In order to do this, the knife should be at right angles to the microtome. The paraffin block should be trimmed in such a way that when clamped in the microtome ready for cutting sections, the surface of the paraffin block facing the knife should be exactly parallel to its edge, also to the opposite side of the block. In other words, 2 sides of the paraffin block should be parallel to each other and to the knife ; then if the paraffin is of the right consistency, which must be ascertained by trying, the sections as they are cut will ad- here to each other and form a ribbon. If the sections do not adhere to each other it is quite probable that the paraffin is a little too hard. This may often be remedied by holding an old knife or other metallic instru- ment which has been heated in a flame near the two parallel surfaces for a few moments. Care should be taken not to allow this instrument to touch the paraffin. This is a very convenient and rapid way of cutting par- affin sections. To facilitate the cutting of a paraffin possessing a rela- THE MICROTI >MK AND SK( 1 h iNTNO. 33 tively low melting point in a room with a high temperature, the cooled knife of Stoss may be used. This is so made that a stream of ice water may be passed through a tube running through the entire length of the back of the blade. 48. Celloidin Sections. — before fastening the block of wood or vul- canized fiber to which the^celloidin blocks have been fixed in the clam]) on the microtome, the celloN^xshould be trimmed with a sharp knife from the top of the block until uik tissue is nearly exposed, care being taken to leave a flat surface. The sides of the celloidin block are then trimmed down, if necessary, to within about ,',. of an inch of the tissue. The block is now clamped in the microtome at such a level that it just escapes the knife when drawn over it. The knife is placed at an angle of about 45 , or at even a greater angle. During the process of cutting, the knife, as also the tissue, must be kept constantly moistened with 80% alcohol. This is perhaps most easily accomplished by taking up the 80% alcohol with a rather large camel's-hair brush and dipping this on the Pig. 4. — Sliding microtome of Jung. Medium-sized model No. IV. The instrument is shown from the left. On the right side is the plate placed at an acute angle, as a carrier for the sliding block to which the knife is fastened. Both are partly visible. The screws c serve to fix the knife (absent in the figure) in place. The /') serves to turn the screws. On the left . ide of the microtome is fastened the diagonally placed side plate. On this, behind, rc-ts (in the figure to the right 1 the microm- eter screw, and in front (in the figure to the left) the object carrier. celloidin block and on the knife. A number of rather thick sections are cut until the knife touches the entire surface of the block or until the tis- sue is well exposed. The sections may now be kept. The block is raised 20 to 15 microns, and the knife, which should be well moistened with 80% alcohol, is drawn over the block with a steady pull, not with a jerk. The sections are transferred from the knife to distilled water. This is perhaps most conveniently done by placing the ball of one of the fingers of the left hand under the edge of the knife, in front of the sec- tion, and drawing the section down onto the finger with the camel's-hair brush. The finger is then dipped into the distilled water when the sec- 3 34 THE MICROSCOPIC PREPARATION. tion floats off. If the sections can not be stained within a few hours after they are cut, they are best transferred to a dish containing &o c / c alcohol, in which they may be left until it is desired to stain them. 49. The other type of sliding microtome to be specially mentioned is that suggested by Professor Thoma and made by R. Jung, of Heidelberg. (Fig. 4.) The immovable portions of this microtome consist of four plates, of which the lower rests as a horizontal base on a table. A second vertically, placed plate rests along the middle of this base. The other two are fastened one on each side of the second plate in such a way that they are directed diagonally outward and upward, forming with the vertical plate acute angles whose apices are directed downward. One of these is attached horizontally to the vertical plate, the other obliquely, one end being attached lower than the other, thus forming an incline. Into the angles formed by the side and vertical plates fit solid metal bodies, which can be easily slid backward and forward on the smooth sur- faces arranged for this purpose. On these metal blocks the knife and the object are fastened, and they are therefore called the knife- and object-car- riers. The former runs on the horizontal, the latter on the inclined plane. The several holes bored in the upper surface of the knife-carrier are for the screw which fastens the knife in whatever position is most convenient. The knife is clamped down by the screw -head. The object-holder con- sists of an arrangement for the fixation of the object. This may be a simple clamp, into which the block of wood is fastened. It is, however, often necessary to move the object to be cut in different directions to obtain proper orientation, especially in the sectioning of embryos. In such cases an object-carrier provided with an arrangement for orientation is used. In the carrier is fastened a rectangular frame of metal which, by means of screws, may be turned on two axes at right angles to each other and thus fixed in any given position. In the middle of this revolv- ing frame of metal is an aperture into which a cylinder is fitted. In the case of paraffin preparations, this is filled with paraffin and the imbedded object attached to its upper end by heating. A special mechanism is pro- vided for the raising and lowering of the cylinder. The newer instru- ments are made on the same principle except that they have a screw at one side by means of which the whole apparatus may be raised or lowered, an arrangement that is especially adapted for long objects. Instead of containing a cylinder, the clamp may be made to fit a block of wood ; in this case the object is melted on to the upper surface of the block. In sectioning, the microtome is so placed before the operator that the plate upon which the knife-carrier moves is to the right. The object-car- rier should be at the end of the microtome nearest the worker. A for- ward motion of this carrier on its ascending path will cause the object to be raised. As the knife-carrier always moves in a horizontal direction, the blade will cut from the object a section the thickness of which will correspond to the distance which the object has been raised, and this is regulated by the distance that the object-carrier is moved forward. To measure this, the vertical plate of the microtome and the object-carrier are provided with a scale and nonius or vernier. To obtain ries of sections of exactly equal thickness, the arrangement by which the objei t carrier is moved forward by hand is not sufficiently accurate. Very exact results are obtained with the help of a micrometer screw, which is attached behind the object-carrier and moves the object a a fain distance at every turn. In the Thoma-Jung microtome a single THE MICROTOME AND SB HONING. 35 revolution of the screw raises the object 15 <>■■ A drum attached to the screw is marked off at its periphery into fifteen equal parts; the- turning of the screw one degree, therefore, raises the object 1 //. 15y means of a cog arrangement it is possible to regulate automatically the raising of the object and consequently the thickness of the sections in the series. Before cutting, the paths Upon which the knife- and object-carriers slide must be carefully cleaned and oiled; so-called machine oil (four parts of bone oil to one part of petroleum ) is the best for this purpose. Enough oil should be used, and care should be taken that the knife-car- rier moves easily from one end to the other of its pathway- The micro- tome knife should now be fastened into its holder, and the blade placed in such a position that it forms an acute angle with the upper edge of the vertical plate. The object is placed on the object-carrier, and fixed at the desired height, with the micrometer screw resting against the agate- plate of the object-carrier. The knife-carrier with its knife is now brought toward the operator, the slightest pressure being avoided, as otherwise the layer of oil disappears and the sections become irregular in thickness. The newest Jung microtomes have a rod pointing downward on the side of the knife-holder. The operator, resting a finger on the anterior surface of this rod, can pull the knife toward him, thus avoiding the possibility of any pressure on the apparatus. The knife having brought with it a section, it is often seen that the latter is not flat on the blade, but rolled. This condition may be avoided, as has been stated, by holding down the free edge of the section with a camel's-hair brush held in the left hand. There are also so-called section stretchers, which consist of rollers of different diameters. They are so attached above the blade of the knife that between them and the knife is a very narrow space through which the section must pass. These section stretchers are very difficult to put into position, and their action is uncer- tain, so that it is advisable to accustom one's self to the brush method, which affords good results after a little practice. After cutting the section the knife is pushed back to the opposite end of the instrument and again brought forward after turning the micrometer screw, thus producing a second section. After continued section-cutting the micrometer screw passes through its attachment to its full length and must then be screwed back and adjusted anew against the agate-plate. During this procedure the object-carrier should not be moved. R. Jung has re- cently produced a micrometer screw provided with a reversible arrange- ment by which the tedious process of turning backward is avoided. The knife may be fastened transversely to the long axis of the microtome, and if the paraffin and room temperature be favorable, ribbons can be cut. Celloidin sections may also be cut with this instrument. 50. The sliding microtomes may be provided with an arrangement for freezing tissues — a so-called freezing apparatus. This consists of a metal plate on which the tissue is laid ; an ether-atomizer plays upon its lower surface, cooling and finally freezing the object, which is then cut. A drop of fluid (physiologic saline solution, water, etc. ) is placed upon the knife, in which the section thaws out and spreads. A better and more rapid method of freezing tissues consists in the use of compres carbon dioxid. as recommended by Mixter. Cylinders containing about twenty pounds of the liquid gas may be obtained from Bausch & bomb, who also make a small microtome designed for this purpose. In figure 5 is shown the lower third of a cylinder for compressed carbon dioxid 36 THE MICROSCOPIC PREPARATION. firmly fastened to a thick board, and connected by means of a short piece of strong rubber tubing with the freezing box of the microtome. The handle of the escape valve is from 8 to 10 inches long, so that the quantity of escaping gas may be readily controlled. The pieces of tis- sue are placed on the freezing box of the microtome and the escape valve slowly opened until a small quantity of the gas escapes. Small pieces of tissue are frozen in about thirty seconds to a minute ; tissues taken from alcohol should be washed for a short time in running water before freez- ing. A strong razor may be used for cutting sections ; or better, a well- sharpened blade of a carpenter's plane, as suggested by Mallory and Wright. Sections are transferred to distilled water or normal salt solu- tion, and if fixed may be stained at once. Sections of fresh tissue should be taken from the normal salt solution and transferred to a fixing fluid. 51. It is impossible to cut thin sections with a knife that is not sharp, or with one that is nicked. A few directions as to sharpening a micro= tome knife may therefore not be out of place. For this purpose a good Fig. 5. — Apparatus for cutting tissues frozen by carbon dioxid. Belgian hone is used, which should be moistened or lubricated with filtered kerosene oil as necessity demands. While sharpening the knife it is grasped with both hands — with one by the handle, with the other by the end. The hone is placed on a table with one end directed toward the person sharpening. If the knife is very dull, it is ground for some time on the concave side only fall microtome knives are practically plane on one side and concave on the other j, with the knife at right angles to the stone. It is carried from one end of the stone to the other, edge foremost, giving it at the same time a diagonal movement, so that with each sweep the entire edge is touched (see Fig. 6). In drawing back the knife, the edge is slightly raised. The knife is ground on the concave side until a fine thread ( feather edge; appears along the entire edge. It is then ground on both sides, care being taken to keep the knife at right angles to the stone, to keep it flat, and to use practically no pressure. It is a good plan to turn the knife on its back when the end of the stone is reached. On the return stroke, the knife is again held at right angles to the stone, the same diagonal sweep is used (see Fig. 6), so that the THE MICROTOME AND SECTIONING. 37 whole edge of the knife is touched with ea< h sweep. The grinding on both sides is continued until the thread above mentioned has disappeared. The knife should now be carefully cleaned and stropped, with the back of the knife drawn foremost. The strop should be flat and rest on a firm surface. Very good microtomes are manufactured by August Becker in Gottin- gen. Of these, Model A (after Spengel ) is constructed on the same prin- ciple as the Thoma-Jung microtome. The knife-carrier rests on thick plates of glass in place of metal. The knife is moved by means of a crank. Model B (after Schiefferdecker, 86) is peculiar in that the specimen to be cut is raised by a micrometer screw in a vertical rather than a hori- zontal plane. The knife-carrier runs mechanically on horizontal glass plates. This microtome also possesses an automatic arrangement for the cutting of sections of equal thickness, so that when the micrometer screw is once regulated the knife-holder needs only to be moved back and forth Fig. 6 — Diagram showing direction of the movements in honing. to make sections of a uniform thickness. With the help of both models (A and B), celloidin as well as paraffin objects can be cut. Instruments giving especially good results in the serial sectioning of paraffin objects are : (i) The Minot microtome, which can be obtained from Becker and from E. Zimmermann of Leipzig ( Model D, Becker). Here the knife is station- ary, with the edge of the blade upward, while the object is moved up and down by means of a crank, and at the same time pushed forward toward the blade. The thickness of the section is regulated automatically, and by merely turning the wheel a long series of sections may be made in a short time. (2) An ingenious and well-built instrument is the im- proved rocking microtome of R. Jung, in Heidelberg | Cambridge rocking microtome). The knife is stationary, with the edge upward. By means of a clever arrangement the object is advanced toward the knife. A lever causing a slight rotation of the axis upon which the object rests moves 38 THE MICROSCOPIC PREPARATION. the object up and down. As a result, every section has not a plane sur- face, as is the case with other microtomes, but appears as a peripheral sec- tion of a cylinder the radius of which corresponds to the distance of the blade from the axis bearing the object-holder. (This drawback limits the use of the instrument.) The mechanism has one advantage : excellent serial sections can be made, having a thickness of only 1 p {vid. Schieffer- decker, 92). Bausch & Lomb, of Rochester, N. Y., make excellent sliding microtomes. (Fig. 3.) They have recently constructed for Minot an instrument in which the knife is fixed at both ends. The object-car- rier is elevated by a screw, and moves back and forth under the knife. D. THE FURTHER TREATMENT OF THE SECTION. U FIXATION TO THE SLIDE AND REMOVAL OF PARAFFIN. Sections obtained by means of the microtome undergo further treat- ment either loose or, better, fixed to a slide or cover-glass, thus making further manipulation much easier. 52. The simplest, surest, and most convenient method of fixing par- affin sections to the slide is by means of the glycerin=albumen of P. Mayer (83.2). Egg -albumen is filtered and an equal volume of glycerin added. To prevent decomposition of the fluid a little camphor or sodium salicylate is placed in the mixture. A drop of this fluid is smeared on the slide or cover-slip as evenly and thinly as possible. A section or a series of sections arranged in their proper sequence is then placed upon the slide so prepared. Any folds in the section are smoothed out with a brush, and the section or the whole series gently pressed down upon the glass. When the desired number of sections are on the slide or cover-slip, they are warmed over a small spirit or gas flame until the paraffin is melted. At the same time the albumen coagulates. The sections are now fixed, and are loosened from the glass only when agents are used which dissolve albumen, as, for instance, strong acids, alkalies, and certain staining fluids. If it is desired that a given space, say the size of a cover-slip, be filled up with sections as far as possible, an outline of the cover-slip to be used may be drawn upon a piece of paper and placed under the slide in the required position. 53. A second and in many respects better method is the fixation of the section with distilled water (Gaule). The paraffin sections are spread in proper sequence on a thin layer of water placed on the slide. There should be sufficient water to float the sections. The slide is then dried in a warm oven kept at 30 to 35 C, or gently heated by holding it at some distance from a spirit or gas flame (the paraffin should not melt). By this treatment the sections are entirely flattened out. The superfluous water is either drained off by tilting or drawn off with blot- ting-paper, the sections are definitely arranged with a brush, and the whole is placed for several hours in a warm oven at 30 to 35 C. The sections thus dried are exposed, over a flame, to a temperature higher than the melting point of the paraffin, and from now on can be subjected to almost any after-treatment. The slide or cover-slip should be thor- oughly cleaned (preferably with alcohol and ether), as otherwise the water does not remain in a layer, but gathers in drops. The advantage of this method lies in the fact that the evaporated water can have no possible influence on the subsequent staining of the THE FURTHER TREATMENT <>F THE SECTION. 39 sections, while albumen, especially it" it be in a thick layer, is somel stained, thus diminishing the transparency of the preparation. ( For fix- ation with the stain <-/e the alum is precipitated on the section by the alcohol. Partsch recommends the following solution of coc hineal : Finely pow- dered cochineal is boiled for some time in a 5^ aqueous solution of alum, and filtered on cooling, after which a trace of hydrochloric arid is added. It stains sections in two to five minutes. 60. Alum=carmin (Grenadier). — 100 c.c. of a 3 ( / c to $ r / f solution of ordinary alum, or preferably ammonia-alum, are mixed with o. 5 gm. to 1 gm. of carmin, boiled for one-fourth of an hour, and after cooling filtered and enough distilled water added to replace that lost by evaporation. This fluid stains quickly but does not overstain. Wash the sections in water. Hematoxylin. — 61. Bohmer's Hematoxylin: Hematoxylin crystals I gm. Absolute alcohol 10 c.c. Potassium alum IO gm. Distilled water 200 c.c. Dissolve the hematoxylin crystals in the alcohol, and the alum in the distilled water. While constantly stirring, add the first solution to the second. The whole is then left for about fourteen days in an open jar or dish pro- tected from the dust, during which time the color changes from violet to blue. After filtering, the stain is ready for use. Sections, either loose or fixed to the slide or cover-slip, are placed in this solution, and after about half an hour are washed with water. If the nuclei are well stained the further treatment with alcohol may be commenced. Should the sections be over- stained, a condition showing itself in the staining of the cell -protoplasm as well as the nuclei, the sections are then washed in an acid alcohol wash (six to ten drops of hydrochloric acid to 100 c.c. of 70^ alcohol) until the blue color has changed to a reddish-brown and verv little stain comes from the section — usually about one to two minutes. They are then washed in tap-water, and passed into distilled water before placing in alcohol. 62. Delafield's Hematoxylin: Hematoxylin crystals 4 gm. Absolute alcohol 25 c.c. Ammonia alum, saturated aqueous solution 400 " Alcohol, 95'* 100 " Glycerin 100 " Dissolve hematoxylin crystals in absolute alcohol and add to the alum solution, after which place in an open vessel for four days, filter, and add the 95 % alcohol and glycerin. After a few days it is again filtered. This fluid is either used pure or diluted with distilled water. Staining is the same as with Bohmer's hema- toxylin. 42 THE MICROSCOPIC PREPARATION. 63. Friedlander's Glycerin=hematoxylin : Hematoxylin crystals 2 gm. Potassium alum 2 " Absolute alcohol 100 c.c. Distilled water IOO " Glycerin IOO " Dissolve the hematoxylin crystals in the absolute alcohol and the alum in the water; mix the two solutions and add the glycerin. The mixture is filtered and exposed for several weeks to the air and light, until the odor of alcohol has disappeared, and then again filtered. It stains very quickly. Sections are afterward washed in water and are placed for a short time in acid alcohol if the nuclei are to be especially brought out. Ehrlich's Hematoxylin : Hematoxylin crystals 2 gm. Absolute alcohol 60 c.c. Glycerin "I saturated with .... 60 " Distilled water ) ammonia alum . . . .60 " Glacial acetic acid 3 " The solution is to be exposed to light for a long time. It is ready for use when it acquires a deep-red color. Stain as above. 64. liemalum (P. Mayer, 91). — 1 gm. of hematein is dissolved by heating in 50 c.c. of absolute alcohol. This is poured into a solu- tion of 50 gm. of alum in 1 liter of distilled water and the whole well stirred. A thymol crystal is added to prevent the growth of fungus. The advantages of hemalum are as follows : The stain may be used im- mediately after its preparation, it stains quickly, never overstains, especially when diluted with water, and penetrates deeply, making it useful for staining in bulk. After staining, sections or tissues are washed in distilled water. 65. Heidenhain's Iron Hematoxylin. — Good results, particu- larly in emphasizing certain structures of the cell (centrosome), are ob- tained by the use of M. Heidenhain's iron hematoxylin (92. 2). Tissues are fixed in saline sublimate solutions in twelve to twenty-four hours (-•id. T. 19), after which they are washed for the same length of time in running water and then placed in the ascending alcohols. Very thin sec- tions f in case of amniota not over 4 /;.) are fixed to the slide with water and put into a 2.5^ aqueous solution of ammonium sulphate of iron for four to eight hours (not longer). After careful rinsing in water, the sections are brought into a solution of hematoxylin prepared as fol- lows : Hematoxylin crystals 1 gm., absolute alcohol 10 c.c, and dis- tilled water 90 c.c. This solution should remain in an open vessel for about four weeks, and, before using, should be diluted with an equal volume of distilled water. Staining takes place in twelve to twenty-four hours, after which the sections are rinsed in water and again placed in a like solution of ammonium sulphate of iron, until black clouds cease to be given off from the sections. They are rinsed in distilled water, passed through alcohol into xylol, and mounted in balsam. Should a protoplas- mic stain lie desired, rubin in weak acid solution may be employed {vid. also M. Heitlenhain, 96). Coal-tar or anilin stains. — Ehrlich classifies all anilin stains as salts having basic or acid properties. The basic anilin stains, such as safra- STAINING. 43 nin, methylene-blue, methyl-green, gentian violet, methyl-violet, llis- marck brown, thionin, and toluidin-blue are nuclear stains, while the acid anilin stains, such as eosin, erythrusin, benzopurpurin, acid fuchsin, lichtgriin, aurantia, orange G, and nigrosin stain diffusely and are used as protoplasmic stains. 66. Safranin : Safranin i gm. Absolute alcohol 10 c.c. Anilin water . . • 90 " Anilin water is prepared by shaking up 5 c.c. to 8 c.c. of anilin oil in 100 c.c. of distilled water and filtering through a wet filter. Dissolve the safranin in the anilin water and add the alcohol. Filter before using. Stain sections of tissues fixed in Flemming's or Hermann's solutions for twenty-four hours, and decolorize with a weak solution of hydrochloric acid in absolute alcohol (1 : 1000). After a varying period of time (usu- ally only a few minutes) all the tissue elements will be found to have become bleached, only the chromatin of the nucleus retaining the color. 67. Bismarck Brown. — A very convenient color to handle is Bismarck brown. Of this, 1 gm. is boiled in 100 c.c. of water, filtered, and i/j of its volume of absolute alcohol added. Bismarck brown stains quickly without overstaining, and is also a purely nuclear stain. Wash in absolute alcohol. 68. Methyl-green stains very quickly (minutes). 1 gm. is dis- solved in 100 c.c. of distilled water to which 25 c.c. of absolute alcohol is added. Rinse sections in water, then place for a few minutes in ~o f / alcohol, transfer to absolute alcohol for a minute, etc. 69. Other so-called basic anilin stains can be used in a similar manner. Thionin or toluidin-blue in dilute aqueous solutions are espe- cially useful. Nuclei appear blue and mucus red. 70. Double Staining. — When certain stains are used in mixtures or in succession, all portions of the section are not stained alike, but certain elements take up one stain, others another. This elective affin- ity of tissues is taken advantage of in plural staining. \i two stains are employed, one speaks of double staining. 71. Picrocarmin of Ranvier. — Two solutions are prepared, a satu- rated aqueous solution of picric acid and a solution of carmin in ammonia. The second is added to the first to the point of saturation. The whole is evaporated to one-fifth of its volume and filtered after cooling. The solution thus obtained is again evaporated until the picrocarmin remains in the form of a powder. A \ r / solution of the latter in distilled water is the fluid used for staining. To stain with this solution, one or two drops are placed on the slide over the object and the whole put in a moist chamber for twenty-four hours. A cover-slip is then placed over the preparation, the picrocarmin drained off with a piece of blotting-paper, and a drop of formic-glycerin 1 1 : 100) brought under the cover-slip by irrigation. Proper differentia- tion takes place only after a fev, r days, and the acid-glycerin may then be replaced by the pure glycerin. In objects fixed with osmic acid, the nuclei appear red, connective tissue pink, elastic fibers canary yellow, muscle tissue straw color, keratohyalin red, etc. 72. Weigert's Picrocarmin. — The preparation of Weigert's picro- carmin is somewhat simpler. 2 gm. of carmin are stirred in 4 c.c. 44 THE MICROSCOPIC PREPARATION'. of ammonia and allowed to remain standing in a well-corked bottle for twenty-four hours. This is mixed with 200 c.c. of a concentrated aqueous solution of picric acid to which a few drops of acetic acid are added after another twenty-four hours. The result is a slight precipitate that does not dissolve on stirring. Filter after twenty-four hours. Should the precipitate also pass through the filter, a little ammonia is added to dis- solve it. Both picrocarmin solutions dissolve off sections fixed to the slide with albumen. 73. P. Mayer's Picric=magnesia=carmin. 1. Magnesia-carmin ; Carmin 1 gm. Magnesia usta o. 1 " Distilled water 20 c.c. 2. Ficrate of magnesia ; Carbonate of magnesia 0.25 gm. Picric acid, 0.5 r r in distilled water . . .200 c.c. Heat to boiling, cool and filter. One volume of the first solution is mixed with 9 volumes of the second. Another formula is magnesia-carmin solution 1 volume, magnesia- picrate solution 4 volumes, weak magnesia-carmin solution 5 volumes, magnesia water 100 c.c. The latter is made by allowing 0.1 gm. of magnesia usta to remain for one week in 100 c.c. of water, shaking from time to time. Sections are washed in either distilled or magnesia water. Staining takes place quickly ; the solution may be used for stain- ing in bulk. 74. Carmin=bleu de Lyon (of Rose). — Sections or pieces of tis- sue are first stained with carmin (alum- or borax-carmin ) . Bleu de Lyon is dissolved in absolute alcohol and diluted with the latter until the solu- tion is of a light bluish color. In this the sections or pieces of tissue are after-stained for twenty-four hours (developing bone stains, for instance, blue;. 75. Picric acid is often used as a secondary stain, either in aque- ous (saturated solution diluted 1 to 3 times in water) or in alco- holic solution (weak solutions in 70^, 80^-, and absolute alcohol). Sections previously treated with carmin or hematoxylin are stained for two to five minutes, washed in water or alcohol, and transferred to abso- lute alcohol, etc. Sections stained in safranin can be exposed to the ac- tion of an alcoholic picric acid solution. A solution of picric acid in 7o r / f alcohol may be used to wash sections stained in borax-carmin. This often gives a good double stain. Sections can also be first treated with picric acid and afterward stained with alum-carmin. 76. Hematoxylin=eosin. — Sections already stained in hematoxylin are placed for two to five minutes in a 1 ^ to 2 r / ( aqueous solution of eosin or in a 1 r / f solution of eosin in 60% alcohol. They are then washed in water until no more stain comes away, after which they remain for only a short time in absolute alcohol. 77. Hematoxylin-safranin of Rabl (85). — Sections of prepara- tions fixed with chromic-formic acid or with a solution of platinum chlorid are stained for a short time with Delafield's hematoxylin (jvid. I . 62 ), then ( ounterstained for twelve to twenty-four hours with safranin and washed with absolute alcohol until no more color is given off. STAINING IN BULK. 45 78. Ehrlich-Biondi Triple Stain. — Of the many triple stains in use we mention only the most important, the rubin S — orange G — methyl- green mixture of Ehrlich and Biondi, employed according to the modifi- cation of M. rleidenhain (92. 2). The best results are obtained with objects fixed in saline sublimate solution. The three stains just mentioned arc prepared in concentrated aqueous solutions (rubin S dissolves in the proportion of 1:5, orange G and methyl green about 1:8). These con- centrated solutions are combined in the following volumes : rubin S 4, orange G 7, methyl-green 8. The stock solution thus obtained is diluted with 50 to 100 times its volume of distilled water before using. The tions should be as thin as possible and fixed to the slide by the water method. They remain for twenty-four hours in the stain, and are then washed either in pure 90$ alcohol or in such with the addition of a little acetic acid ( 1 to 2 drops to 50 c.C. ), until the rinsing fluid is no longer colored. Before staining it is occasionally of advantage to treat the section^ with acetic acid (2 : 1000 J for one to two hours. 79. P. Mayer (96) advises fixation of the sections to the slide with the staining solution instead of water. On heating the slide the sections stain very energetically, and results are obtained which would otherwise be difficult to produce. Before the sections are placed in xylol to remove the paraffin, they must be thoroughly dried. STAINING IN BULK. Instead of staining in sections, entire objects can be stained before cutting. This method is in general much slower, and demands, there- fore, special staining solutions, as, for instance : 80. Alcoholic borax-carmin solution (77V/. T. 57). — Pieces }4 cm. in diameter remain in the stain at least twenty-four hours, are then decolorized for the same length of time in acid alcohol (0.5^ to i'/ n hydrochloric acid in 70'/ alcohol), and after washing in 70'/ alcohol are transferred to 90% alcohol. Larger objects require a correspondingly longer time. 81. Paracarmin. — Treatment as in section staining, length of time according to size of object (vid. T. 58). 82. Alum-carmin of Grenacher (vid. T. 60). This never overstains. Time of staining according to size of object. Wash in water, then trans- fer to 70'/ and ()o'/c alcohol. 83. Hemalum (vide T. 64), when diluted with water, is very useful for staining in bulk. After staining, objects should be washed with dis- tilled water. 84. Bohmer's hematoxylin (vid. T. 61) stains small pieces very sharply. Use the same as hemalum. 85. Hematoxylin staining according to R. Heidenhain's method is especially recommended for staining in bulk. Stain objects fixed in alcohol or picric acid twenty-four hours in a °-33 f /c aqueous solution of hematoxylin ; transfer for an equal length of time to a 0.5$ aqueous solution of potassium chromate, changing often until the color ceases to run. Wash with water and pass into strong alcohol. This stain also colors the protoplasm, and is so powerful that very thin sections are an absolute condition to the clearness of the prepa- ration. 4 6 THE MICROSCOPIC PREPARATION. 86. If the objects have been fixed with picric acid and the latter has not been entirely washed out, staining in bulk by the above methods pro- duces very striking differentiation. 87. Pieces of tissue stained in bulk may be infiltrated, imbedded, and cut according to the ordinary methods. Under these circumstances, section staining is not necessary unless a still further differentiation be desired. 88. In general, then, the treatment of the object is somewhat as fol- lows : First, it is fixed in some one of the fixing fluids already described, then carefully washed, and in certain cases stained in bulk before infiltrat- ing with paraffin or celloidin ; or the staining may be postponed until the tissue has been cut. In the latter case, the sections are subjected to the stain either loose or fastened to the slide or cover-slip. 8g. In all cases it is absolutely essential that the paraffin be entirely removed. After the sections have been stained and washed, they are transferred to absolute alcohol in case it be desired to mount them in some resinous medium. They may also be mounted in glycerin or acetate of potash, into which they may be passed directly from distilled water. 90. The method of staining tissues in sections or in bulk is shown in the following: diagrams : In Btdk. 90', alcohol Water Wash in water Wash in acid alcohol I I 70$ alcohol ^ 70 '/, alcohol Absolute alcohol In Sections. Celloidin sections Paraffin sections in 90 % alcohol I Remove paraffin Absolute alcohol 4- 90 $> alcohol Distilled water Wash in Wash in acid water alcohol 4. + 70', alco- 70'/ alco- hol hoi Absolute alcohol E. PREPARATION OF PERMANENT SPECIMENS. The resinotis media used in the final mounting of preparations are Canada balsam and damar. 91. Commercial Canada balsam is usually dissolved in turpentine ; it should be slowly evaporated in casserole and then dissolved in xylol, toluol, or chloroform, etc. The proper concentration of the solution is found with a little experience. A thick solution penetrates the in- PREPARATION OF PERMANENT SPECIMENS. 47 terstices of the section with difficulty, and usually contains air-bubbles which often hide the best areas of the preparation, and can only be re- moved with difficulty by heating over a flame. Thin solutions, on the other hand, have also their disadvantages ; thej evaporate very quickly, and the empty space thus created between the covet slip and slide must again be filled with Canada balsam. This is best done by dipping a glass rod into the solution and placing one drop at the edge of the cover-slip, whereupon the fluid spreads out between the cover-slip and slide as a result of capillary attraction. Canada balsam dries rather slowly, the rapidity of the process depending upon the temperature of the room. To dry quickly, the slides may be held for a few moments over a gas or alcohol flame, or they may be placed in a warm oven, where the prepara- tions become so dry in twenty-four hours that they can be examined with an oil-immersion lens. The oil used for this purpose should be wiped away from the cover-slip after examination. This can only be done, with- out moving the cover-slip, when the balsam is thoroughly dry and holds the cover-slip firmly in place. 92. Damar is dissolved preferably in equal parts of oil of turpentine and benzin. It has the advantage of not rendering the preparation as translucent as does Canada balsam. Otherwise it is used as the latter. 93. Since alcohol does not mix with Canada balsam and damar, an intermediate or clearing fluid is used in transferring objects from the former into the latter. Xylol, toluol, carbol-xylol (xylol, 3 parts; car- bolic acid, 1 part), oil of bergamot, oil of cloves, and oil of origanum are ordinarily used. 94. The process is somewhat simpler where sections are fixed to the slide. Xylol is dropped onto the surface of the slide, or better, the whole preparation is placed for a few minutes in a vessel containing xylol until the diffusion currents have ceased (which may be seen with the naked eye). The slide is then taken out, tilted to allow the xylol to run off, wiped dry around the object with a cloth, and placed upon the table with the specimen upward. A drop of Canada balsam is now placed on the section (usually on its left side), and a clean cover-slip grasped with a small forceps. It is then gently lowered in such a way that the Canada balsam spreads out evenly and no air-bubbles are im- prisoned under the glass. When this is done the preparation is finished. 95. If one is dealing with loose sections, a spatula or section-lifter is very useful in transferring them from absolute alcohol into the clearing fluid — carbol-xylol or bergamot oil (xylol evaporates very rapidly) — and from this onto the slide. In doing this it is necessary that the sec- tion should lie well spread out on the section-lifter, wrinkles being re- moved with a needle or small camel's-hair brush. In sliding the section off the spatula (with a needle or brush) a small quantity of the clearing fluid is also brought onto the slide. This must be removed as far as possible by tilting or with blotting-paper. The section can now be mounted in Canada balsam as before. For esthetic and practical reasons the student should see that during the spreading of the drop of Canada balsam the section remains under the middle of the cover-slip. Should it float to the edge, it is best to raise the cover-slip and lower it into place again. The cover-slip should never be slid over the specimen. 97. To mount in glycerin or acetate of potash (33$- solution in dis- tilled water), the sections are transferred from water to the slide, covered 48 THE MICROSCOPIC PREPARATION. with a drop of glycerin or acetate of potash, and the cover-slip applied. These methods are employed in mounting sections colored with a stain that would be injured by contact with alcohol, and where clearing is not especially necessary. 98. Farrant's Gum Glycerin. In place of pure glycerin the following mixture may be used : Glycerin 50 c.c. Water 50 " Gum-arabic (powder) 50 gm. Arseoious acid 1 " Dissolve the arsenious acid in water. Place the gum-arabic in a glass mortar and mix it with the water; then add the glycerin. Filter through a wet filter-paper or through line muslin. 99. To preserve such preparations for any length of time the cover- glasses must be so fixed as to shut off the glycerin or acetate of potash from the air. For this purpose cements or varnishes are employed which are painted over the edges of the cover-slip. These masses adhere to the glass, harden, and fasten the cover-slip firmly to the slide, hermetically sealing the object. The best of these is probably Kronig's varnish, pre- pared as follows : 2 parts of wax are melted and 7 to 9 parts of colophonium stirred in, and the mass filtered hot. Before employing an oil-immersion lens it is advisable to paint the edge with an alcoholic solution of shellac. F. INTRODUCTION TO METHODS OF INJECTION. 100. A few remarks on the injection of the vascular system will not here be amiss, as it is only by this method that the relations of the blood- vessels to the neighboring tissue elements can be clearly brought out. The process consists in filling the vessels with a mass that can be injected in a fluid state but hardens readily, and is at the same time suitable for microscopic purposes and for sectioning methods. Of such substances there are a large number, and the technic of injection has been developed to such a degree that it has become a very important part of anatomic technic in general. Gelatin masses of different composition have come into general use for injecting the vascular system ; of these, we shall here mention a red and a blue mass. 101. Gelatin=carmin. — The first is a gelatin -carmin mass, and is prepared as follows: (1) 4 gm. of carmin are stirred into 8 c.c. of water and thoroughly ground. Into this a sufficient quantity of ammonia is poured to produce a dark cherry color and render the whole transpar- ent. (2) 50 gm. of finest quality gelatin is placed in distilled water for twelve hours until well soaked. It is then pressed out by hand and melted at a temperature of 70 C. in a porcelain evaporating dish. The two solutions are now slowly mixed, the whole being constantly stirred until a complete and homogeneous mixture is obtained. To this mass is added, drop by drop, a 25% acetic acid solution until the color begins to rhange to a brick red and the mass becomes slightly opaque. This should be very carefully done, as a single drop too much may spoil the whole. During this procedure the substance should be kept at 70 C. and constantly stirred. The change in color indicates that the reaction of the mass has become neutral or even slightly acid (an ammoniac solu- tion should not be used, since the stain diffuses through the wall of the INTRODUCTION tO METHODS OF I N 1 1 .* HON. 49 I and colors the surrounding tissues) ; the whole is filtered through flannel while stiil warm. 102. The blue mass is prepared from an aqueous solution of Berlin blue. A saturated solution is made and poured (as above) into a solution of gelatin wanned to 70 C. until the desired intensity of color is ob- tained. 103. Injection masses already prepared are to be had in commerce. Besides those already mentioned, Still others colored with China ink, et< ., are in general use. 104. Small animals are injected as a whole by passing the cannula of a syringe into the left ventricle or aorta. In the case of large animals, or where very delicate injections are to be made, the cannula is inserted into one of the vessels of the respective organs. The proper ligation of the remaining vessels should not be omitted. 105. Before injecting, the animals or organs are kept warm in water heated to about 38 C. in order to prevent the injection mass from hard- ening before passing into the smaller vessels. 106. before injecting, it is always desirable to thoroughly bleed the animal, or press out as carefully as possible all the blood contained in the organ. 107. Organs injected with carmin are fixed in alcohol and should not be brought in contact with acids or alkalies. Such parts as are injected with Berlin blue are less sensitive in their after-treatment. Pieces or sec- tions that have become pale regain their blue color in oil of cloves. 108. If objects or sections injected with Berlin blue be treated with a solution of palladium chlorid, the bluish color changes to a dark brown which afterward remains unchanged (Kupffer). 109. In thin membranes and sections the vessel -walls can be rendered distinct by silver-impregnation, which brings out the outlines of their en- dothelial cells. This may be done either by injecting the vessel with a 1 ' , solution of silver nitrate, or, according to the process of Chrzon- szczewsky. with a 0.25^ solution of silver nitrate in gelatin. This method is of advantage, since, after hardening, the capillaries of the in- jected tissue appear slightly distended. Organs thus treated can be sec- tioned, but the endothelial mosaic of the vessels does not appear definitely until the sections have been exposed to sunlight. no. By means of the above injection methods other lumina can be filled, as, for instance, those of the glands. As a rule, these are only par- tially filled, since they end blindly, and their walls are less resistant and may be damaged by the pressure produced by the injection. in. The injecting of lymph -channels, lymph -vessels, and lymph- spaces is usually done by puncture. A pointed cannula is thrust into the tissue and the syringe emptied by a slight but constant pressure. The injected fluid spreads by means of the channels offering the least resist- ance. For this purpose it is best to employ aqueous solutions of Berlin blue or silver nitrate, as the thicker gelatin solutions cause tearing of the tissues. 112. To bring out the blood capillaries and the lymphatic channels, Altman's process ( 79 ), in which the vessels are injected with olive oil, is useful. The objects are then treated with osmic acid, sectioned by means of a freezing microtome, and finally treated with eau de Javelle 4 50 THE MICROSCOPIC PREPARATION. (a concentrated solution of hypochlorite of potassium). By this process all the tissues are eaten away, the casts of the blood-vessels remaining as a dark framework (corrosion). The manipulation of these preparations is extremely difficult on account of the brittleness of the oil casts. For lymph-channels Altman {ibid.') used the so-called oil-impregnation. Fresh pieces of tissues, thin lamellae of organs, cornea, etc., are placed for five to eight days in a mixture containing olive oil i part, absolute alcohol •_> part, sulphuric ether )/ 2 part (or castor oil 2, absolute alcohol 1, etc. ). The pieces are then laid for several hours in water, where the externallv adherent globules of oil are mechanically removed and those in the lymph-canalicular system are precipitated. The objects are now treated with osmic acid, cut by means of a freezing microtome, and corroded. In this case, the corrosive fluid (eau de Javelle) should be diluted two or three times. GENERAL HISTOLOGY. I. THE CELL. During the latter part of the seventeenth century, Hooke, Mal- pighi, and Grew, making observations with the simple and imperfect microscopes of their day, saw in plants small compartment-like spaces, surrounded by a distinct wall and filled with air or a liquid ; to these the name cell was applied. These earlier observations were extended in various directions during the latter part of the seven- teenth and the eighteenth century. Little advance was made, however, until Robert Brown (183 1) directed attention to a small body found in the cell, previously mentioned by Fontana, and known as the nucleus. In the nucleus Valentin observed (1836) a small body known as the nucleolus. In 1838 Schleiden brought forward proof to show that plants were made up wholly of cells, and especially emphasized the importance of the nuclei of cells. In 1839 Schwann originated the theory that the animal body was built up of cells resembling those described for plants. Both Schleiden and Schwann defined a cell as a small vesicle, surrounded by a firm membrane inclosing a fluid in which floats a nucleus. This conception of the structure of the cell was destined, however, to undergo important modification. In 1846 v. Mohl recognized in the cell a semifluid, granular substance which he named protoplasm. Other investigators (Kolliker and Bischoff) observed animal cells devoid of a distinct cell membrane. Max Schultze (1861) attacked vigorously the older conception of the structure of cells, proclaim- ing the identity of the protoplasm in all forms of life, both plant and animal, and the cell was defined as a nucleated mass of protoplasm endowed with the attributes of life. In this sense the term cell is now used. The simplest forms of animal life are organisms consisting of only one cell {protozoa). Even in the development of the higher animals, the first stage of development, the fertilized egg, is a single cell. This by repeated division gives rise to a mass of similar cells, which, owing to their likeness in shape and structure, are said to be undifferentiated. As development proceeds, the cells of this mass arrange themselves into three layers, the germ layers, the outer one of which is the ectoderm, the middle one the mesoderm, and the inner one the entoderm. In the further development, the cells of the germ layers change their form, assume new qualities, adapting 51 5-' THE CELL. themselves to perform certain definite functions ; a division of labor ensues, — the cells become differentiated. Cells having similar shape and similar function are grouped to form tissues, and tissues are grouped to form organs. We shall now consider the structure of the cell. Every cell consists of a cell-body and a nucleus. A. THE CELL-BODY, The body of the cell consists of a substance known as proto- plasm or cytoplasm. This is not a substance having uniform Vacuoles. Chromatin network. Linin network. Nuclear fluid. Nuclear membrane. Cell-membrane. Exoplasm. Spongioplasm. Hyaloplasm. Nucleolus. Chromatin net-knot. Centrosome. " Centrosphere. Foreign inclosures. Metaplasm. Fig. 7. — Diagram of a cell. physical and chemical qualities, but a mixture of various organic compounds concerning which knowledge is not as yet conclusive, but which in general are proteid bodies or albumins in the widest sense. In spite of the manifold differences in its composition, proto- plasm exhibits certain general fundamental properties which are always present wherever it is found. Ordinarily, protoplasm ex- hibits certain structural characteristics. In it are observed two con- stituents, — threads or plates, which are straight or winding, which branch, anastomose, or interlace, and which are generally arranged in a regular framework, network, or reticulum. These threads probably consist of small particles arranged in rows, called cell-microsomes (vid. van Beneden, 83 ; M. Heidenhain, 94 ; and others). This sub- THE CELL-BODY 53 stance- is known as protoplasm in the Stricter sense ( Knpffcr, 75) ; also as spongioplasm, or the fibrillar mass of Flemming (82). 1 he other constituent of the cytoplasm is a more fluid substance lying between the threads in the meshes of the spongioplastic network, and is known as paraplasm (Kupffer), hyaloplasm, cytolymph, or the interfibrillar substance of Flemming. According to most investigators, the more important vital pro- cesses of the cell are to be identified with the spongioplasm, and are controlled by the nucleus, while the paraplasm assumes an inferior or passive role. Protoplasm displays phenomena of motion, shown on the one- hand by contraction, ami on the other by the formation of processes that take the form either of blunt projections or lobes, or of long, pointed, and even branched threads or processes known as pseudo- podia. The extension and withdrawal of the pseudopodia enable the cell to change its position. The point of such a process fastens to some object and the rest of the cell is drawn forward, thus giving the cell a creeping motion — wandering cells. Certain cells take up and surround foreign bodies by means of their pseudopodia. If these Fig. 8 1 Cell-body. Nucleus. — Cylindric ciliated cells from the primitive kidney of Petromyson planeri , X 1200. bodies are suitable for nutrition, they are assimilated ; if not, they can, under certain circumstances, be deposited by the cell in cer- tain localities ( Metschnikoff 's phagocytes). Similar thread-like processes which, however, can not be drawn into the cell, occur in some cells in the shape of cilia, which are in constant and energetic motion — ciliated cells. Certain cells possess only a single long pro- cess, by means of which unattached cells are capable of direct or rotating motion — -flagellate cells, spermatozoa. Inside of the cell-body the protoplasm also shows phenomena of motion, the streaming of the protoplasm. In plant cells there is often a noticeable regularity in the direction of the current. Men- tion should not be omitted of the so-called molecular or Brownian movement in the cells, which consists in a rapid whirling motion of particles or granules suspended in the protoplasm (Brown). Living protoplasm is irritable in the highest degree, and reacts very strongly to chemic and physical agents. It is very sensitive to changes in temperature. All the phenomena of life occur in greater intensity and more rapidly in a warm than in a cold temperature, 54 THE CELL. this fact being very strikingly shown by the phenomena of motion in the cell, as also in its propagation. By subjecting protoplasm to different temperatures, its various movements can be slowed or quickened. It dies in too. high or too low a temperature. Certain substances coming in contact with the cell from a given direc- tion have on it an attracting or repelling action. These phenomena are known as positive and negative chemotropism (chemotaxis) . The action of chemic agents on the different wandering cells of the body and on cer- tain free-swimming unicellular organisms naturally varies to a great degree. Among these phenomena must be included those produced by water ( hydrotropism ) and light (heliotropism). It is very probable that all these phenomena are of importance to the proper appreciation of some of the processes going on in the vertebrate body (as, for instance, in the origin of diseases caused by micro-organisms). Protoplasm may contain various structures. Of these, the vacuoles deserve special mention. They are more or less sharply defined cavities filled with fluid, and vary considerably in number and size. The fluids that they contain differ somewhat, but are always secreted by the protoplasm, and are, as a rule, finally emp- tied out of the cell. As a consequence, vacuoles are best studied where the function of the cell is a secretory one. Here they are often large, and sometimes fill up the whole cell, the contents of which are then emptied out {glandular cells). Contents of a solid nature, such as fat, pigment, glycogen, and crystals, are peculiar to certain cells. By these deposits the cell is more or less changed, the greatest variation in form taking place in the production of fat. The latter, as a rule, takes the shape of a globule, and greatly modifies the position of the normal con- stituents of the cell. Deposits of pigment alter the cells to a less degree. This substance occurs in the protoplasm either in solution or in the form of fine crystalline bodies. Glycogen is more gener- ally diffused, occurring very generally in embryonal cells and in the liver- and cartilage-cells of the adult. Occasionally we find larger crystals in animal cells, as, for instance, in the red blood-corpuscles of the teleosts. So-called margarin crystals sometimes occur in large numbers as stellate figures in dead fatty tissues kept at low temperatures. By employing certain methods the existence of granules can generally be demonstrated in protoplasm. Some authors even refer the vital qualities of protoplasm to these particular bodies (Alt- mann's bioblasts, 94). In some cases the outer layer of the cell-protoplasm shows dif- ferentiation, leading to the formation of a distinct cell-membrane (as in fat-cells, cartilage-cells, goblet-cells, etc.). F. K. Schulze has given it the name pellicula in cases where the entire cell is surrounded by a homogeneous layer, and cuticula or cuticle where only one side of the cell is supplied with the membrane (as in the intestinal epithe- THK NUCLEUS. 55 Hum). It is assumed that both spongioplasm and paraplasm are concerned in the formation of this membrane. In the protoplasm of many cells there is found a small body known as the centrosome. This is usually situated near the nucleus of the cell, occasionally in the nucleus. Generally, it has the appear- ance of a minute granule, sometimes scarcely larger than a micro- some. It is often surrounded by a small area of a granular or finely reticular or radially striated cytoplasm, known as the attraction- sphere or centrosphere. B. THE NUCLEUS. The second constant element of the cell is the nucleus. As a rule, it is sharply defined, and in its simplest form consists of a round vesicle of a complicated structure composed of several sub- stances. The form of the nucleus corresponds in general to the shape of the cell ; in an elongated cell, it is correspondingly long, and flattened where the cell is plate-like in shape. The nucleus of a wandering cell that is in the act of passing through a narrow inter- cellular cleft adapts itself to the changes of form in the cell without being permanently altered in shape. In other words, the nucleus is soft, and can be easily distorted by any solid substances within or without the protoplasm, only to resume its original form when the pressure is removed. It possesses, then, a certain amount of elas- ticity. Movements of certain nuclei, entirely independent of the sur- rounding protoplasm, have often been observed. It is only rarely that the form of the nucleus differs materially from that of the cell. This, however, occurs in the nuclei of leucocytes, which are often irregular, and may even be ring-shaped. In certain arthroz< >a, branching forms of nuclei occur, as also in the skin glands of turtles. The proportionate size of nucleus to cell-body varies greatly in different cells. Especially large nuclei are found in immature ova, in certain epithelial cells, etc. The contents of the nucleus consist of a framework or reticu- lum, in the meshes of which there is found a semifluid substance. In treating the nuclei with certain stains, the nuclear reticulum will be seen to consist of two constituents, a substance appearing in the form of variously shaped, minute granules, which stains deeply, and is, therefore, known as chromatin. This is imbedded in and deposited on a less stainable network, the linin. The meshes of this network are occupied by a transparent, semifluid substance, which does not stain easily, and is known as the achromatic portion of the nucleus. It is also known as paralinin, nuclear sap, karyolymph, or nucleoplasm. Chemically, chromatin belongs to those albuminous substances known as nucleins. In well-stained nuclei of considerable size the chromatin gran- ules are seen closely placed in a continuous row throughout the net- work of linin, which penetrates the nuclei in all directions. In 56 THE CELL. every resting nucleus one or more small round bodies are found imbedded in the nucleoplasm. These are known as true nucleoli, and do not stain quite so deeply as the chromatin. The fact that certain reagents dissolve the chromatin, but not the true nucleoli, proves that the substance of which the latter are composed is not identical with chromatin, — and is, therefore, known as paranuclein (F. Schwartz). In many cases we find in the linin, granules of a substance known as lanthanin, which displays a marked affinity for the so- called acid anilin stains, in contradistinction to chromatin, which stains principally with the basic anilin colors. These are known as oxychromatin granules in contradistinction to the basichromatin granules of the chromatin (M. Heidenhain, 94). The true nucleoli should not be confused with the slight swell- ings of the chromatin network found at the junction of the threads, and known as net-knots, or karyosomes. Surrounding the resting nucleus is usually a nuclear membrane resembling in many respects chromatin. As a rule, it does not form a continuous layer, but is perforated, having openings that contain nuclear fluid. We have, then, both substances, chromatin and nucleoplasm, as elements of the nuclear membrane. Besides this, the nuclear membrane receives an outer layer, differentiated from the protoplasm. Later investigations have shown that even during a period of rest the relationship of the nucleus to the protoplasm of the cell is much more intimate than was heretofore believed (vid. B. Reinke, 94). A resting nucleus — i.e., one not in process of division — usually consists, therefore, of a sharply defined membrane, which has in its interior a chromatic (nuclein) and an achromatic (linin) network, a nuclear fluid (paralinin), and nucleoli (paranuclein). The chromatin of the nucleus is not always in the form of a net- work. In some cases — as, for instance, in the premature ova of certain animals (O. Hertwig, 93. II) and in spermatozoa — it is col- lected in compact bodies. In the ova it may often be mistaken for a true nucleolus (germinal spot). In this case, however, it consists of nuclein, and not of paranuclein. C. NUCLEAR AND CELL-DIVISION. The founders of the cell theory believed in what may be known as a modification of the theory of spontaneous generation, stating that cells might originate from a structureless substance known as kyto- blastema or blastema, in which a nucleus was formed by precipita- tion. I Icnle ( 1 S 4 1 ) drew attention to the fact that cells might mul- tiply by the separation of small portions of the cell-body, a process known as budding; and Harry ( 1 841 ) stated that during the multi- plication of cells the nuclei divided. The same year Remak NUCLEAR AND CELL-DIVISION. 57 observed division of cells in the blood of embryos. Goodsir ( 1 84 -, ) originated the theory that all cells were developed from preexisting cells. This was first clearly stated as a general law by Virchow (1855), and his saying, " Omnis cellula a cellula" is constantly being verified. Our more accurate knowledge of cell-division dates, how- ever, from more recent times ( 1873—80), when Schneider, Fol, Stras- burger, Flemming, and many others demonstrated that during the division of the cell the nucleus passed through a series of compli- cated changes which resulted in an exact division of the chromatin. The phenomena which usher in cell-division are especially noticeable in the nucleus, the elements of which are arranged and transformed in a typic manner. During the division of the nucleus the nuclear membrane is lost, and the relationship of the substances of the nucleus to the protoplasm of the cell is a very intimate one. As a consequence, during the middle phases of division there is no well-defined demarcation between the nucleus and the cell-bod}-. As a rule, the mother cell and nucleus divide into two daughter cells, each having a nucleus, alike in every particular. It was early observed, however, that occasionally cells divided by a much sim- pler process, in which case the nucleus did not pass through such complicated changes. Accordingly, two distinct types of cell- division are recognized, which are distinguished as mitosis, karyoki- iicsis, or indirect cell-division, and amitosis, or direct cell-division. Both lead to the formation of two nuclei, which are known as daughter nuclei as distinguished from the original mother nucleus. J. MITOSIS OR KARYOKTNESIS (INDIRECT CELL-DIVISION). The description of the process of mitotic cell-division is compli- cated by the fact that structural changes are observed which occur simultaneously in the nucleus, centrosome, and cytoplasm. This fact should be borne in mind, as, for the sake of clearness, a sepa- rate description of the changes involving each of these structures seems demanded. The process of mitotic cell-division may be divided into four periods or phases, which follow one another with- out clearly defined limits : The prophases, in which the nuclear membrane disappears, the chromatin is transformed into definite threads, and the centrosome and centrosphere undergo important changes. This is the prepar- atory stage. The metaphases, in which the division and the separation of the chromatin take place. The anaphases, in which the daughter nuclei are formed and the cell-protoplasm begins to divide. The telophases, in which the division of the cell is completed. To give abetter understanding of this process, we have inserted a series of diagrammatic figures (9—19), giving the cells the shape of an ellipsoid. We can then distinguish a long axis, two polar 58 THE CELL. Fig. 9. Fig. 10. Chromosomes. Crown of chromo- some. Fig. 11. Fig. 13. Fig. 14. Figs, 9-14. — Diagrammatic representation of the processes of mitotic cell- and nuclear division. 12, Prophases; Figs. 13, 14, metaphases. Fig. 9, Resting nucleus; Fig. I O, coarse skein or spin m ; Fig. II, fine skein or Bpirem; Fig. 12, segmentation of the spirem into single chromosomes; Fig. 13, longi- tudinal division of the chromosomes; Fig. 14, bipolar arrangement of the separated chromosomes. NUCLEAR AND CELL- DIVISION. 59 Uniting filami nt~. Fig. 15. Fig. i^>. - Cell-plates. Chromo- somes. Fig. 17- Fig. iS. 1 Nucleolus. Fig. 19- Figs. 15-19. — Diagrammatic representation of the processes of mitotic cell- and nuclear division. Figs. 15-18, Anaphases; Fig. 19, telophases. Fig. 15, wandering of the chromosomes toward the poles; Fig. 16, chaster; Figs. 17 and 18, formation of the dispirem ; Fig. 19, two daughter cells with resting nuclei. To simplify the figures 1 2-1 7, we have sketched in only a few chromosomes. In Fig. 16 it is seen that the cell-body is also beginning to divide. 6o THE CELL. Fig. 23. Fig. 24. Figs. 20-24. — Mitotic cell-division of fertilized whitefish eggs — Coregonns albus. Fig. 20, Cell with resting nucleus, centrosome, and centrosphere to the right of the nucleus; Fig. 21, cell with two centrospheres, with polar rays at opposite poles of nucleus; Fig. 22, spirem ; Fig. 23, monaster; Fig. 24, metakinesis stage. regions corresponding to the ends of the axis, and an equatorial plane. The latter is horizontal to the axis, equally distant from both poles, and passes through the middle of the nucleus. The division of the cell takes place in this plane. A series of figures (20-27), showing the different phases of mitotic cell-division of the fertilized eggs of the whitefish (Coregonus albus), is given ; the changes involving the centrosome, centrosphere, and cytoplasm are clearly illustrated. Figure 28, showing a small portion of a sec- tion through the testis of the salamander, the object in which Flem- ming first observed this complicated series of changes, presents the appearance more generally seen during mitotic cell-division of the tissue cells of the higher vertebrates. (a) Prophases. — The changes occurring in the nucleus will be considered first. At the beginning of the process of mitosis, the chromatin network, consisting of chromatin granules, is transformed into a twisted skein of threads, beginning at the periphery of the NUCLEAR AND CELL-DIVISION. 6l Fig. 25. Fig. 26. Fig. 27. Figs. 25-27. — Mitotic cell-division of fertilized whitefish eggs — Coregomu; albus. Fig. 25, Metakinesis stage ; Fig. 26, diaster ; Fig. 27, late stage of dispirem, the cell-protoplasm almost divided. nucleus. This skein of threads is known as the spircm or mother skein, and may appear as a single thread, which breaks up into a definite number of segments, or the segments may appear as such when the skein is forming. At first the threads are coarse and often somewhat irregular, staining much more deeply than the linin network. The separate segments of chromatin are known as chromosomes (Waldeyer, 88). They appear, as a rule, in the form of rods varying in length and thickness, and staining very deeply, and often bent into characteristic U-shaped loops. The bent portion of each loop is called its crown. " Every species of plant or ani- mal has a fixed and characteristic number of chromosomes, which regularly recurs in the division of all its cells ; and in all forms arising by sexual reproduction the number is even " (Wilson, 96). In man the number of chromosomes is given as sixteen by Barde- leben (92) and Wilson (96), and as twenty-four by Flemming (98). During the formation of the spirem the nuclear membrane, as a rule, disappears. The nucleolus is also lost sight of, although the manner of its disappearance can not be definitely stated. The net- knots are no doubt taken up by the chromosomes. The chromo- 62 THE CELL. somes are now free in the protoplasm ; gradually the crown of each chromosome approaches the center of the space occupied by the .nucleus, and the chromosomes form a characteristic, radially arranged stellate figure, known as the monaster, in the equatorial plane of the cell. During the progress of the changes affecting the chromatin of the nucleus and resulting in the formation of the chromosomes, important phenomena are observed, connected partly with the achromatic substance of the nucleus, more especially with the centrosome, centrosphere, and cytoplasm of the cell. These phenomena result in the formation of a complicated structure known as the achromatic spindle or amphiaster. Its development is as fol- lows : The centrosome and centrosphere, as has been stated, usu- ally lie in the protoplasm to one side of the nucleus. If, at the be- ginning of the division, the centrosome be single, it divides, and the two centrosomes begin to separate, causing a division of the centro- sphere. Between the centrosomes are usually seen finely drawn-out connecting threads. The centrosomes, each of which is surrounded by a centrosphere, now move apart, and a structure known as the central spindle, and consisting of fine threads arranged in the form of a spindle, develops between them. At each end of the central spindle is found a centrosome surrounded by a centrosphere from which radiate into the cytoplasm fine fibers known as polar rays. During the formation of the achromatic spindle the nuclear mem- brane disappears and the chromosomes develop, as above described. Some fibers, which seem to have their origin from the centrosphere, grow into the spirem formed of chromosomes, which they appear to pull into the equatorial plane of the cell, which is also the equator of the central spindle. Thus, the nuclear figure above described as the monaster is formed. In other cases the centrosomes and centrospheres continue moving apart until opposite each other and separated by the nucleus (Figs. 21, 22). As the nuclear membrane disappears and the spi reins and chromosomes are form- ing, the central spindle develops, its fibers running from centro- sphere to centrosphere. The polar rays also develop in the cyto- plasm at the same time. As the central spindle develops, the chromosomes arrange themselves or are arranged about its equator — monaster. (b) Metaphases. — Usually, during the formation of the monaster, or immediately after its formation (sometimes in the spirem stage or even earlier), the most important process of cell -division takes place. Each chromosome divides longitudinally into two daughter chromosomes. The loops first divide at the crown, the cleft extend- ing up either limb until the' free ends are reached. The smallest particle of chromatin divides, retaining the exact relative position in the twin chromosomes that it possessed in the mother chromo- some. The daughter chromosomes now wander over the central spindle, their crowns presenting, in opposite directions toward the poles of the cell. This process is known as metakiuesis. Two stel- NUCLKAR AND CELL-DIVISION. 63 late figures are developed about the respective poles of the central spindle. The appearance presented is known as a diaster. Our knowledge of the part taken by the amphiaster or achromatic spindle in metakinesis is not above controversy. It would appear, however, that certain cytoplastic fibers, which arise from the cen- trosphere and hang over the central spindle and chromosomes, designated as mantle fibers^ assist in drawing the daughter chromo- somes toward the poles of the central spindle. (c) Anaphases. — After the formation of the diaster, the loops be- longing to each stellate figure are joined together to form a skein, thus forming the dispirem. The chromatin threads of the two skeins gradually assume the disposition found in the resting nucleus. This process takes place in such a way that the threads ot the I (ispirem. Diaster. s Diaster. Monaster. — Resting nucleus. -- Metakinesis. - Diaster. - Daughter cells. S| litem. Fig. 28. — Mitotic division of cells in testis of salamander (IJenda and Guenther). skeins (or the single thread) send out lateral processes. These interlace, and little by little reproduce the network of the resting nucleus ; at the same time the nuclear membrane and the nucleolus reappear. In this stage the changes that lead to the division of the cell-body are observed. In some cases the division of the cell-body is ushered in by an equatorial differentiation of the connecting threads of the central spindle. Chains of granules, arranged in double rows, are seen to appear in this region. The cell now begins to contract at its equator, the contraction extending between the two chains of granules until the cell is completely divided. At this time, also, the threads of the amphiaster disappear or are drawn into the nucleus. The centrosomes, with centrospheres, again lie by the side of the daughter nuclei. 64 THE CELL. According to the opinion of C. Rabl (85), there remains in the nucleus, even after it has fully returned to a state of rest, a polar arrangement of the chromatin loops — that is, an arrangement of the axis of the loops in the direction of the centrosphere. The area toward which the crowns of the loops point is known as the polar field. The equatorial differentiation of the connecting threads of the central spindle, above mentioned, was first observed in vegetable tissue, and is known as the cell-plate. (Fig. 27.) In animal cells such a plate is relatively rare, and, when seen, is found developed in a rudimentary form (v. Kostanecki 92, I). (d ) Telophases (M. Heidenhain 94). — In these phases of mitosis the cell divides completely. The daughter nuclei and centrospheres, which do not yet occupy their normal position in the daughter cells, show movements that result in their assuming their normal positions. From our description it is seen that the anaphases represent the same stages as the prophases, only in an inverted sequence. In the latter case, the result is the resting nucleus, while the prophases lead to the metaphases. The fertilized ovum also divides by indirect nuclear division. (Figs. 20-27.) From it are derived, by this process, the seg- mentation cells, or blastomercs, from which the whole embryo is developed. (e) The Heterotypic Form of Mitosis. — The above-described type of indirect or mitotic nuclear division {Jwmcotypic mitosis) is the usual one. Variations, however, occur, as, for instance, in the so-called Jietcrotypic form of division (Flemming 87), which occurs in certain cells of the testes (spermatocytes). In this form the first stages are lacking, the nucleus possessing from the beginning a skein-like structure. The longitudinal splitting and division of the chromatin threads take place during the first spirem stage, after which there is a phase in which the figure may be compared with an aster of ordinary mitosis, although the free ends of the threads in this case are seldom observed. The latter is due to the fact that after the longitudinal splitting, the ends of the chromosomes remain united, or, if entire separation occurs, they are again joined. In this way closed loops are formed extending from pole to pole. Later the threads break at the equator and move toward the poles, again dividing to form the daughter stars. 2. AMITOSIS. Very different from the indirect form of nuclear division is the direct or amitotic. It appears to occur seldom as a normal process, and is only exceptionally followed by a subsequent cell-division {vid. Flemming, 91, 111). As a consequence, this process, in most cases, results in the formation of polynuclear cells (polynuclear leu- cocytes, giant-cells, etc.). The complicated nuclear figures of PROCESS OF FERTILIZATION. 65 indirect division arc here entirely absent. The nucleus merely con- tracts at a certain point and separates into two or more fragments (direct fragmentation , Arnold) ; often the nucleus first assumes an annular form and then breaks up into several fragments, which remain loosely connected (polynuclear cells). Centrospheres are also present, and appear to take a prominent part in the whole pro- cess, although the exact relationship between the achromatin and chromatin has not as yet been determined. Arnold (83) gives the following comparison of indirect and direct nuclear division : (1) Segmentation. Division of the nuclei in the equa- torial plane into two or more equal parts; (« ) direct segmentation without, (/') indirect segmention witli, increase and changed arrangement of the 'chromatic substance (mitosis). (2) Fragmentation. Contraction of the nucleus at some point, forming two or more equal, but oftener un- equal, nuclear fragments; (c) direct fragmentation without, (V ) indirect fragmentation with, increase and changed arrangement of the chromatic substance. D. PROCESS OF FERTILIZATION. The sexual cells form a special group among cells in general. Before the division of the egg-ceil leading to thd development of the embryo can take place, the ovum must be impregnated (the so- called parthenogenetic ova are an exception to this rule). Fertili- zation is produced by the male sexual cell, the spermatozoon. The process of fertilization consists in a conjugation of two sex- ual cells, and in this process certain peculiarities in the behavior of both cells must be mentioned. The cell forming the ovum and the one forming the spermato- zoon must pass through certain stages before fertilization can be accomplished. These consist in the loss of half their chromosomes by the nuclei of both sexual cells. In this way are produced the matured sexual cells (ova and spermatozoa), which retain only half of the number of chromosomes of a somatic (body-) cell. In the conjugation of the male and female sexual cells their nuclei unite to form a single nucleus, known as the segmentation nucleus. Consequently, this nucleus contains the same number of chromo- somes as does that of a somatic cell. In its earlier developmental stages the ovum is an indifferent cell, the nucleus of which is known as the germinal vesicle. As the ovum matures the germinal vesicle approaches the periphery, and a peculiar metamorphosis, which may be regarded as a double, un- equal division of the egg-cell, takes place. One portion, in the case of both divisions, is much smaller than the other, and is known as a polar body. At the close of these divisions, during which the chromosomes have been reduced to half the original number.^there are, therefore, two polar bodies and the matured ovum, which is now ready for impregnation. 5 66 THE CELL. Membrane of ovum. Nucleus of ovum. Spermatozoon entering. Protoplasm of ovum with deutoplastic granules. Fig. 29. Female pronu- cleus. Head of spermato- zoon with centro- some. Female pronu- cleus. SbJ~ Male pronu- cleus. Fig. 30- Fig. 31. Figs. 29-31. — Diagrams of the process of fertilization, after Boveri (88). Figure 29, the ovum is surrounded by spermatozoa, one of which is in the act of penetration. Toward it the yolk is pushed forward in a short, rounded process. Figure 30, the tail of the spermatozoon has disappeared. Beside the head is a centrosome with polar radiation. Figure 31, the pronuclei approach each other. The development of the male sexual cell in its earlier stages is sim- ilar to that of the ovum. They are derived from cells known as sper- matogones. These divide into equal parts, forming the cells of a second generation, the spermatocytes. From a further division of the spermatocytes, during which division the chromosomes are reduced to half the number, the spermatids are produced. These latter are then changed directly into spermatozoa. The reduction division of the egg-cell and that of the spermatocytes is in principle the same, except that in spermatogenesis all cells become matured sexual cells (spermatozoa). In short, there is here an absence of structures analogous to the polar bodies, which degenerate after maturation of the ovum. 'I he spermatozoa are flagellate cells. The head consists prin- cipally of nuclear substance, to which is added a smaller middle- piece containing, according to the investigations of Fick, the centro- some. These two portions of the male sexual cell, the head- and PKOCKSS ol I KKI1I.IZATION. 67 ■^v^ifH — Centrosome. . Male pronu- cleus. Chromo som egg-nil- Chromo- somes of male |hm- nucleus. Centrosome. ■ Fig. 3i- Chromosomes from e^g-iiu- cleus. Chromosomes in mi sperm- nucleus (male pronucleus). S&ftSE"*ijrw Centrosome. Fig- 34- Figs. 32-34. — Diagrams of the process of fertilization, after Boveri (88). Figure 32, from the spirems in the pronuclei, chromosomes have been formed. The centrosphere has divided. Figure ^^, the double chromosomes of the two pronuclei lie in the equatorial plane of the ovum. Figure 34, the ovum has divided. Chromosomes from the male and female elements are seen in equal numbers in both daughter nuclei. middle-piece, are the most important, and are exclusively con- cerned in fertilization, the flagellum or tail playing no part in this process. The spermatozoon usually penetrates the ovum after the first polar body has been extruded. The tail disappears during this process, being either left at the periphery of the egg or dissolved in the protoplasm. From this time the head represents the so-called male pronucleus, and the middle-piece the centrosome. From tin's stage the male pronucleus undergoes changes, the first of which consists of a loosening of the chromatin. Chromatin granules are formed, which later arrange themselves in the form of chromo- somes. After the second polar body has been extruded, the chro- matin remaining in the ovum is transformed into the female pro- nucleus. The latter then approaches the male pronucleus, the membranes of both nuclei disappearing. The chromosomes of 68 THE CELL. the two nuclei thus formed arc of equal number, and now come to lie together. After a longitudinal division of the chromosomes, the daughter chromosomes glide along the filaments of the achro- matic spindle, developed from the centrosome of the male pronu- cleus, toward its two poles, as in ordinary mitosis. This they do in such a manner that an equal distribution of the male and female daughter chromosomes results. Then follow the stages of the ana- phase. From the above description of the process of fertilization it is seen that it consists, in the end, of a union of the nuclei of both sexual cells. If paternal qualities are inherited by the offspring, this can only take place through the nucleus, or through the centrosome of the male sexual cell. In other words, it can be safely said that these structures, or the nucleus alone, are the principal means of trans- mitting inherited qualities. The same may also be said of the female pronucleus. There is no doubt that the first two seg- mentation cells of the ovum are equally provided with male and female nuclear elements. Since all future cells are derivatives of these two, it is possible that the nucleus of every somatic cell (body-cell) is hermaphroditic. E. CHROMATOLYSIS. In the living organism many cells are destroyed during the various physiologic processes and replaced by new ones. On the death of a cell, changes take place in its nucleus which result in its gradual disappearance. These processes, which seem to follow certain definite but as yet unfamiliar laws, have been known since their study by Flemming (85, I) by the name of chromatolysis (karyolysis). The nuclei during the course of these changes show many varied pictures. TECHNIC. 113. In a fresh condition, cells do not show much of their internal structure. Epithelial cells of the oral cavity, which can easily be ob- tained and examined in the saliva, show really nothing except the cell outlines and the nuclei. More, however, can be seen in young ova iso- lated from the (Graafian follicles of mammalia ; or the examination may be facilitated by using the ovary of a young frog. Tissues that are especially adapted for the observation of cells in a fresh condition are small ova, blood-corpuscles, and epithelia of certain invertebrate animals (shellfish, etc.). Unicellular organisms such as amebae, infusoria, and many low forms of vegetable life make also good material for this purpose. Protoplasmic currents are best seen in the tactile hairs of the net- tle. Should fresh animal cells be desired, amebae can occasionally be found in muddy or marshy water. The same phenomena may be ob- served in the leucocytes of the frog or, better still, in the blood of the crab. < IIKDM vroi.vsis. 69 114. In order to make a detailed study of the minute relationship Of the different cellular structures, it is necessary to fix the cells j the same is true of nuclear division and cell proliferation. Although this process has been observed in Living < ells, it was not until it had been thoroughly worked out in preserved preparations. The best results in the study of the eell are obtained by methods that will be subsequently deS( ribed. Fresh tissues are absolutely essential. According to Hammer, mitosis in man does not cease immcdiat.b after death. The nuclei suffer chromatolytic destruction, and the achro- matic spindle is the last element to disappear. 115. Flemming's solution (vid. T. 17) here deserves first men tion as a fixative. The tissues are imbedded, sectioned, and stained with safranin (vid. T. 66). An equally good fixative is Hermann's solution, which may be combined with a subsequent treatment with pyro- 1 igneous acid {vid. T. 18). Rabl fixes with a o. 1-0. 1 2 '/, solution of ehlorid of platinum, washes with water, passes into gradually stronger alcohols, then stains with Delafield's hematoxylin (vid. T. 62), and finally examines the preparation in methyl alcohol. 116. Mitoses can also be seen by fixing in corrosive sublimate, picric acid, chromic acid, etc., and staining in bulk with hematoxylin or carmin, although perhaps not so well as by the preceding method. The objects to be examined are best when obtained from young and grow- ing animals, especially those possessing large cells. Above all are to be recommended the larva? of amphibia, like the frog, triton, and sala- mander. If examination by means of sections be undesirable, thin structures should be procured, such as the mesentery, alveoli of the lungs, epithelium of the pharynx, urinary bladder, etc. These have the advan- tage of enabling one to observe the whole cell instead of parts or frag- ments of cellular structures. In sections of a larva that has been fixed in toto, mitotic figures can be seen in almost all the organs, and are particu- larly numerous in the epithelium of the epidermis, gibs, central canal of the brain and spinal cord, etc. Other organs, such as the blood, liver, and muscle, also show mitoses. 117. Certain vegetable cells are peculiarly adapted to the study of mitosis, as, for instance, those in the ends of young roots of the onion. The onion should be placed in a hyacinth glass filled with water and kept in a warm place. After two or three days numbers of small roots will be found to have developed. Beginning at the points, pieces 5 milli- meters in length are cut, which are treated in the same manner as animal tissues. These are then cut, either transversely or longitudinally, into very thin sections ( not over 5 ft in thickness ). In one plane, polar views of the mitoses are obtained ; in the other, lateral views. 118. The methods used for demonstrating the remaining parts of the cell and its nucleus (except the chromatin) are, as a rule, more compli- cated, and consequently less reliable. In order to see the centrosome, the spindle fibrils, the linin threads, and the polar rays, one of the methods already described may be used ; viz., the treatment with pyro- ligneous acid of objects previously fixed in osmic acid mixtures. 119. According to Hermann | 93, II |, sections from such preparations can be double=stained as well as those that have not been treated with pyroligneous acid. They are accordingly stained with safranin in the usual manner, and afterward treated from three to five minutes with "O THE CELL. the following solution of gentian violet : 5 c.c. of a saturated alco- holic solution of the stain is dissolved in 100 c.c. of anilin water. The latter is composed of 4 c.c. of anilin oil in 100 c.c. of distilled water. This is shaken in a test-tube and then filtered through a wet filter. The sections are then placed in a solution of iodin and iodid of potassium (iodin 1 gni., iodid of potassium 2 gni.. water 300 c.c.) until they have become entirely black, after which they are immersed in alcohol until they receive a violet tinge with a slight dash of brown. By this means the chromatin network, the resting nuclei, and the chromo- somes in both of the spirem stages appear bluish -violet, while the true nucleoli are pink. The chromosomes of the aster and diaster are col- ored red. 120. Hemming (91, III) recommends the following method : Fixation by his mixture ( T. 17 ) ; the specimens or thin sections are then placed in safranin from two to six days (T. 66), washed for a short time in distilled water, and then immersed in absolute alcohol weakly acidulated with hydrochloric acid ( 1 : 1000), until no more color is given off. They are then washed again with distilled water and placed in a concentrated solution of anilin-water-gentian-violet from one to three hours. After a third rinsing in distilled water, they come into a concentrated aqueous solution of orange G, until they begin to assume a violet color. Then wash with absolute alcohol, clear in clove or bergamot oil, and mount in Canada balsam. 121. A comparatively simple method showing the different structures of the cell and its nucleus with great clearness consists in staining with Heidenhain's hematoxylin (vid. T. 65). 122. Solger (89, I and 91 ) has discovered that both chromosomes and polar rays are shown in an exquisite manner in the pigment cells of the skin (corium ) of the frontal and ethmoidal regions of the common pike (rid. Fig. 35 ). The preliminary treatment is optional, Flemming's solution or corrosive sublimate being the best. These cells illustrate the stabilitv of the radiate structures of protoplasm, the polar rays showing as parallel rows of pigment granules. 123. The various structures of resting and dividing nuclei and cells are of such a complicated nature that they can be observed only with great difficulty in ordinary objects, because of the crowding of so many elements into a comparatively small space. For example, salamandra maculosa, which has become a classic histologic object through the researches of Flemming, possesses somatic cells whose nuclei have no less than twenty-four chromosomes. (It may here be remarked that, curiously enough, salamandra atra has only half this number. ) Consequently, van Beneden's discovery (83 ), that the somatic cells of ascaris megalocephala have only four primary chromosomes, is a fact of considerable import- ance. Boveri (87, II and 88) has even found an ascaris showing only two chromosomes. As these animals also show distinct achromatic fig- ures in the protoplasm of their ova and sperm cells, they are certainly worthy of being regarded as typic specimens for laboratory purposes. The processes of cell-proliferation are almost diagrammatic in their dis- tinctness. After opening the abdominal wall of the animal, the ovisacs are removed, their numerous convolutions separated as much as possible, and then fixed for twenty-four hours in a picric-acetic acid solution ( 1 1 ROM ATO LYSIS. 71 (a concentrated aqueous solution of picric acid diluted with 2 vols, of water to which 1 per cent, glacial acetic acid is added). Then fol- lows washing for twenty-four hours with water, after which the spe< imen is transferred to increasing strengths of alcohol (lioveri, ibid.). Differ- ent regions of the ovisacs contain ova in various stages of development, those nearest the head containing cells ripe and ready for fecundation, while in the more posterior regions are ova in varying stages of segmen- tation showing mitoses. Specimens fixed in the manner above described can be stained with a borax-tannin solution. After staining, the ova arc- gently pressed out with needles upon a slide, separated, covered with a cover-glass, and cleared by gradual irrigation with glycerin. The ova, especially the segmentation spheres, are very small, and can be examined only under high magnification. In spite of the minuteness of the ob- ject and the fact that the yolk does not take the stain, and, on account of .:•'•'■■ Centrosphere. ' ■"'.*r> — Nucleus. Fig. 35. — Pigment cell from the skin of the head of a pike ; X 650. T. No. 122. its high refractive index, distorts the picture to a considerable extent, the mitotic figures are beautifully distinct. 124. Certain methods of treatment bring out in both cells and nuclei the presence of peculiar granules. The latter have been especially studied and described by v. Altmann (94, 2ded.). The methods that he applies are as follows : The specimens of organs of recently killed animals are fixed in a mixture consisting of equal volumes of a 5^ aqueous solution of potassium bichromate and a 2 r / r solution of osmic acid, remaining in the mixture for twenty-four hours. They are then washed for several hours in water and treated with ascending strengths of alcohol ; viz., 70, 90, and 100%. The specimens are now placed in a solution of 3 parts of xylol and 1 part of absolute alcohol, then in pure xylol, and finally in paraffin. The tissues imbedded in paraffin must not be cut thicker than 1 to 2 p.. Altmann mounts according to the following method : A rather thick J 2 THE CELL. solution of caoutchouc in chloroform (the so-called traumaticin of the Pharmacopeia — i vol. guttapercha dissolved in 6 vols, chloroform) is diluted before use with 25 vols, of chloroform and the resulting mixture poured upon a slide. The latter is tilted, and after evaporation of the chloroform, heated over a gas flame. The paraffin sections are mounted upon the slides so prepared and then painted with a solution of guncotton in aceton and alcohol (2 gm. guncotton dissolved in 50 c.c. of aceton, 5 c.c. of which is diluted with 20 c.c. of absolute alcohol ). After painting with this solution, the sections are firmly pressed upon the slide with tissue paper, and after drying are made to adhere more closely by slight warming. Fixation to the slide with water is equally good. The sections can now be treated with various staining solutions without becoming detached from the slides. The paraffin is gotten rid of by immersing in xylol, after which the specimens are placed in absolute alcohol. Fuchsin S. can be used as a stain ( 20 gm. fuchsin S. dissolved in 100 c.c. anilin water). A small quantity of this solution is placed upon the section, and the slide warmed over a flame until its lower surface becomes quite perceptibly warm and the staining solution begins to evaporate. The slide is then allowed to cool, washed with picric acid (concentrated alcoholic solution of picric acid diluted with 2 vols, of water), after which it is covered with a fresh quantity of picric acid, and again, but this time vigorously, heated (one-half to one minute). Occasionally the same results can be obtained by covering the section for five minutes with a cold solution of picric acid of the above strength. This last procedure has a decided influence upon the granula, and gives rise to a distinct differentiation between them and the remaining portions of the cell, the latter appearing grayish-yellow, while the granula themselves appear bright red. In some cases where the granula can not be sharply differentiated from the remaining structures, it may be necessary to repeat the staining process. Xylol-Canada balsam should not be used for mounting, as it has a bleaching effect upon the osmic acid in the specimen. Mount either in liquid paraffin (Altmann) or in undiluted Canada balsam, which is easily reduced to a fluid state, whenever needed, by heating. There is another method used by Altmann which deserves mention, but practical application of which must be improved upon in the future ; this consists in freezing the specimens and drying them for a few days in the frozen condition in a vacuum over sulphuric acid at a temperature of about — 30 C. According to Fischer, dilute solutions of pepton when treated with various reagents (especially with a potassium bichromate-osmium mix- ture; form precipitates and granules which are remarkable in that they react to stains exactly as do Altmann's granula. It is, therefore, doubt- ful whether Altmann's granules should be regarded as vital structures. 125. Altmann (92; has also devised a simpler negative method for demonstrating the granula. Fresh specimens are placed for twenty-four hours in a solution consisting of molybdate of ammonium 2.5 gm., chromic acid 0.35 gm., and water 100 c.c. ; then treated for several days with absolute alcohol, sectioned in paraffin, and colored with a nuclear stain such as hematoxylin or gentian. The intergranular network ilored, while the granula remain colorless. The amount of chromic a' id used ("0.25 to i r / ) varies according to the object treated ; if molyb- date of ammonium alone be used, the nuclei will appear homogeneous, THE I [SSI ES. 73 while if an excess of chromic acid be employed, the nuclei will appear . oarsely reticulated. This method leads to the formation of granula in the cells as well as in the nucleus. 126. By fixing and staining cells of widely different vegetable and animal types Biitschli believes he has demonstrated the existence of proto- plasmic structures having the form of bubbles and termed by him mi< ro scopic foam-structures. Fixing is done either in picric acid solution or in weakly iodized alcohol. The specimens are then stained with iron -hema- toxylin — 1. c, first treated with acetate of iron, rinsed in water, and trans- ferred to a o.-,'// aqueous solution of hematoxylin 1 similar to the method of R. Heidenhain 1 vid. T. 85 i. Very thin sections are required ( : 1 1). Mounting is done, when the lighting is good, in media having low refractive indices, which emphasize the alveolar or foam -like structure of the protoplasm. Of various animal objects, Biitschli especially recom- mends young ovarian eggs of teleosts, and blood-cells and intestinal epi- thelium of the frog, etc. It is still a matter of uncertainty whether or not the structures are actually present in Living protoplasm. II. THE TISSUES. The first few generations of cells which result from the segmen- tation of the fertilized ovum have no pronounced characteristics. They are embryonic cells of rounded form, and are known as blas- tomeres. As they increase in number they become smaller and of polygonal shape, owing to the pressure to which they are subjected. From the mass of blastomeres, known as the morula mass, there- are formed, under various processes described under the name of gastndatiou, two layers of cells, the so-called primary genu layers, of which the outer is the ectoderm, the inner the entoderm. To the primary germ layers is added still a third layer, called the meso- derm ; it is derived from both the ectoderm and entoderm, but principally from the latter. From these three layers of cells, known as the primary blastodermic layers, are developed all the tissues, each layer developing into certain tissues that are distinct for this layer. In their further development and differentiation the cells of the blas- todermic layers undergo a change in shape and structure character- istic for each tissue, and there is developed an intercellular substance varying greatly in amount and character in the several tissues. In the tissues developed from the ectoderm and entoderm the cellular elements give character to the tissue, while the intercellular sub- stance is present in small quantity ; in the majority of the tissues developed from the mesoderm, the intercellular substance is abun- dant, while the cellular elements form a less conspicuous portion. The tissues derived from the ectoderm are : The epidermis of the skin, with the epidermal appendages and glands ; the epithelium lining the mouth, with the salivary glands and the enamel of the teeth ; the epithelium and glands of the nasal tract and the cavities opening into it ; the lens of the eye and retina, 74 THE TISSUES. and the epithelium of the membranous labyrinth of the ear ; and finally, the entire nervous system, central and peripheral. Fr< >m the entoderm : The epithelium lining' the digestive tract, and all glands in con- nection with it, including the liver and pancreas ; the epithelium of the respiratory tract and its glands ; the epithelium of the bladder and urethra (in the male, only the prostatic portion, the remainder being of ectodermal origin). The cells of the mesoderm are early differentiated into three groups (Minot, 99) : (a) Mesothelium. — The mesothelial cells retain the character of epithelial cells. They form the lining of the pleural, pericardial, and peritoneal cavities, and give origin to the epithelium of the uro- genital organs (with the exception of the bladder and urethra), and striated and heart muscle tissue. (b) Mesenchyme, from which are derived all the fibrous connective tissues, cartilage, and bone, involuntary muscle tissue, the spleen, lymph-glands, and bone-marrow ; and cells of an epithelioid charac- ter, lining the blood and lymph-vessels and lymph-spaces, known as endothelial cells. (c) Mesameboid cells, comprising all red and white blood-cells. It would be extremely difficult to attempt a classification of tis- sues according to their histogenesis, as identical tissue elements owe their origin to different germinal layers. The classification adopted by us is based rather on the structure of the tissues in their adult stage. We distinguish : A. Epithelial tissues with their derivatives. B. Connective tissues ; adipose tissue ; supporting tissues (car- tilage, bone). C. Muscular tissue. D. Nervous tissue. E. Blood and lymph. A. EPITHELIAL TISSUES. Epithelial tissues are nonvascular, and composed almost wholly of epithelial cells, united into continuous membranes by a substance known as intercellular cement. They serve to protect exposed surfaces, and perform the functions of absorption, secretion, and excretion. The epithelia are developed from all of the three layers of the blastoderm. They secrete the cement-substance found between their contigu- ous surfaces. This takes the form of thin lamellae between the cells, gluing them firmly together. In certain regions the epithelial cells develop short lateral processes (prickles), which meet like structures EPITHELIAL ll-- 7 5 from neighboring cells, thus forming intercellular bridges. Between these bridges are intercellular spaas filled with lymph-plasma for the nourishment of the cells. Epithelia do not, as a rule, poss processes of any length. However, it would appear that the base- ment membranes, situated beneath the epithelia, consist chiefly of processes from the basal portion of the cells. Some authors ascribe to them a connective-tissue origin, a theory which conflicts with the that such membranes are present in the embryo before connective tissue, as such, has been developed {inembrana prima, Hensen, } The free surfaces of epithelia often support cuticular structures which are to be regarded as the products of the cells. The cutic- ula,* of neighboring cells fuse to form a cuticular membrane or mar- ginal cone which can be detached in pieces of considerable size (cuticula). In longitudinal sections the cuticula show, in many cases, a striatum which would seem to indicate that they are com- posed of a large number of rod-like processes cemented together by a substance possessing a different refractive index. The cell-bod)' is also striated for more than half its length, corresponding to the rods of the marginal zone. In the region of the nucleus at the basal por- tion the striation disappears, the cell here consisting of granular pro- toplasm of a more indifferent character. Since one surface of each epithelial layer lies free, and is conse- quently exposed to other conditions than the inner surface, certain differences are noticed between the two ends of each cell. The cells may develop cuticular structures as above stated. In other cases motile processes (cilia) are developed on their exposed surface, which move in a definite direction in the medium surrounding them, and by means of this motion sweep away foreign bodies. It is not strange that the free surface of the epithelia, exposed as it is to stimulation from without, should develop special structures for the reception of sensations (sense cells). On the other hand, the inner or basal surfaces of the cells usually retain a more indifferent character, and serve for the attachment oi the cells and the conveyance of their nourishment. For this reason the nuclei of such cells are usually situated near the basal surface. From the above it is seen that the two ends of the epithelial cell undergo waning processes of differentiation, the outer being adapted more to the animal, the inner more to the vegetative functions. This differentiation has recently been known as the polarity of the cell. This polarity appears to be retained even when the cell loses its epithelial character and assumes other functions (Rabl, 90). With few exceptions, blood- and lymph-vessels do not penetrate into the epithelia, but the latter are richly supplied with nerves. The finer morphology of the epithelia wall be described in the chap- ters on the different organs in Part II. Epithelia are classified according to the shape and relation of the epithelial cells. y6 THE TISSUES. We give the following classification : 1. Simple epithelia (with or without cilia). () Transitional Epithelium. — Transitional epithelium is a stratified epithelium occurring in the pelvis of the kidney, the ure- ters, bladder, and the posterior portion of the male urethra. It is composed of four to six layers of cells and rests on a connective tissue free from papillae. In sections the cells of the deeper layers appear to be of irregularly columnar, cubic or triangular shape. The Fig. 42. — Isolated transitional epithe- lial cells from the bladder of man : a, i>, c, J, Large surface cells, < and J presenting the pitted undersurface ; c, variously shaped cells from the deeper layers. Fig. 43. — Cross-section of transitional epithelium from the bladder of a young child. cells forming the superficial layer are large, somewhat flattened cells, with convex free surfaces, often possessing two, sometimes three, nuclei. They cover a number of the cells of the layer just beneath them, their under surfaces being pitted to receive the upper ends of the deeper cells. In teased preparations the cells of the deeper layers appear very irregular, often showing ridges or variously shaped processes. (See Fig. 42.) (c) Stratified Columnar Epithelium. — In this type the super- ficial layer consists of columnar cells, the basal ends of which are usually somewhat pointed, or may branch. The deeper cells, which may be arranged in one or more layers, are of irregular, triangular, polyhedral, or spindle shape. It is found in the larger gland ducts, olfactory mucous membrane, palpebral conjunctiva, portions of the So THE TISSUES. male urethra and the vas deferens, and in certain regions of the larynx. The ciliated variety of this epithelium differs from the foregoing in that the superficial columnar cells are provided with cilia. Strati- fied ciliated columnar epithelium is found in the respiratory portion r::: I f jfji '%;-, m '-§S' / HP Fig. 44. — Schematic dia- gram of stratified columnar epi- thelium. Fig. 45. — Ciliated cells from the bronchus of the dog, the left cell with two nuclei ; X °°o. Technic No. 126. of the nose, larynx, trachea, and larger bronchi, in the Eustachian tube, epididymis, and a portion of the vas deferens. All epithelial cells are probably joined together by short pro- cesses forming intercellular bridges, the lymph supplying them with nourishment circulating in the intercellular spaces thus formed. Toward the surface, these intercellular spaces are roofed over, thus preventing the escape of the fluid. When seen from the surface, epithelia treated by certain methods (iron-hematoxylin) show the cells joined together by very minute, clearly defined and continuous Goblet cell. -Cilia. Fig. 46. — Cross se< tion of stratified ciliated columnar epithelium from the trachea of a rabbit. cement-lines. Bonnet has called them terminal ledges or bars (Schlussleisten). The function of this structure would seem to consist in its power to prevent the escape of lymph from the sur- face, and the penetration of micro-organisms (M. Heidenhain, 92; J ion net, 95). EPITHELIAL TISSUES. 3. GLANDULAR EPITHELIUM. (a) The Gland-cell. — Certain cells lying scattered among other epithelial cells produce substances that are extruded and utilized in the body economy. The protoplasm of such a cell elaborates in its interior a substance that takes the form of vacuoles, or granules, which gradually distend the cell ; the substance thus produced is finally given off as the secretion. All these phases of the activity of a gland-cell are included under the term secretion. Isolated glandular cells are frequently met with in epithelia, and are known in general as unicellular glands. They occur especially in the intestinal and respirator)' epithelium, where, owing to their shape, they are termed goblet cells. All the intestinal epithelial cells and many of the cells of respiratory epithelium, have the power of changing into goblet cells. These are distinguished from the neigh- boring cells by the fact that their free ends are clearer and more Cilia. — Mucin Nucleus Basal process Fig. 47. — Goblet cells from the bronchus of a dog. The middle cell still possesses its cilia ; that to the right has already emptied its mucous contents (collapsed goblet cell) ; X 600. Technic No. 128. vesicular, while their basal portions, containing the nuclei, are narrow and pointed. The clear substance elaborated by the protoplasm of the cell, but not yet extruded, is mucin. On closer examination it is seen that this substance fills the interspaces of a very fine proto- plasmic network continuous with the protoplasm surrounding the nucleus. Thus we have, during the phases of secretion, two distinct sub- stances in the cell-body : the one the original protoplasm of the cell — protoplasm (Kupffer) ; the other its product, in this case mucin — paraplasm (Kupffer). When the secretion is extruded the goblet cell collapses and then appears as a thin cord between the neighbor- ing cells. There is as yet some question as to whether a collapsed goblet cell dies after the expulsion of its contents, or whether it may again become stored with mucin. Should it be destroyed, its place is soon occupied by the closing in of contiguous cells. 6 82 THE TISSUES. Multicellular glands originate by the metamorphosis of a num- ber of adjacent cells into glandular cells. This is usually accom- panied by a more or less marked dipping down of the epithelial layer into the underlying connective tissue. The simplest form of such an invagination is a cylindrical tube lined entirely by glandular cells. A further differentiation may take place in that all the in- vaginated cells do not assume a secretory function, those at the upper portion of the tube forming the lining membrane pf an excre- tory duct. The originally uniform tube is thus differentiated into an excretory and a secretory portion. Multicellular glands may lie entirely within the epithelium, and are then known as intra-epithelial glands, in contrast to the extra-epithe- lial or ordinary type, the greater part of which lies imbedded in the under- Lumen of gland. Gland-cells. T. propria. Muse, mucosae. Fig. 48. — Simple tubular glands. Lieberkiihn's glands from the large intestine of man. Sublimate fixation ; X 9°- lying connective tissue. Glands of the former type have been studied in amphibian larvae, and, according to Sigmund Mayer, occur also in the epididymis, conjunctiva, etc., of mammals. {(>) General Consideration of the Structure and Classifica- tion of Glands. — Variations in glandular types affect principally the secretory portions of glands, while the excretory ducts are more or less uniform. Glands are classified, according to their shape, into tubular and saccular glands ; each of these types is further divided into simple and compound tubular, and simple and com- pound saccular (racemose) glands. Tubular Glands. — The simplest form is a tubule of uniform diameter, as in the simple tubular glands of the cardiac region of EPITHELIAL TISSUES. 83 the stomach and in the crypts of Lieberkuhn in the intestine. Without losing the shape of a tubule, the glands of this type may be mi ne or less coiled (pyloric glands, sweat glands, and the ceru- Fig. 49. — Excretory ducts and lumina of the secretory portion of a compound tubular gland. Lingual gland of the rabbit. Chrome-silver prepara- tion ; X 215- Fig. 50. — Lumina of the secreting portion of a reticulated tubular gland ; from the human liver. Chrome-silver preparation ; X 1 2 °- minous glands of the external ear). Again, the secretory portions of the glands may divide, forming branched tubular glands (pyloric glands, uterine glands). A compound tubular gland is one in which two or more secre- tory tubules empty into each branch of a system of excretory Alveus. Alveus. Alveolus. Alveolus. Alveus. Fig. 51. — Schematic diagram of glandular classification: , branched tubular; e, simple alveolar; ./, compound alveolar (without alveoli); e and _/", alveolar (with alveoli). ducts, as the result of repeated division of the primary duct (kid- ney). The secretory tubules may anastomose with each other, forming a reticulated tubular gland (liver). S4 THE TISSUES. In alveolar or saccular glands the secretory portion usually takes the form of a winding tube, the caliber of which is somewhat enlarged at its extremity (alveus). Glands of this class are divided into simple and compound types, as in the case of the tubular glands. To the former belong Ebner's glands of the tongue and Brunner's glands .of the duode- num ; to the latter, the salivary and the larger mucous glands. Certain glands have the shape of a flask, the neck representing the excretory duct of the gland (integumentary glands of salaman- dra). To these the term saccular is often restricted. Still more Complicated forms of alveolar or saccular glands are produced. by the bulging here and there of the walls of the tube or alveus. The protrusions thus formed are known as alveoli. According to the above description, multicellular glands may be classified as follows : Glands. Tubular. • Alveolar or saccular. Simple. Compound (here Simple (with or Compound (with belong also the reticu- without alveoli). or without alveoli). lated glands). The secretory and excretory epithelia rest upon a thin membrane (membrana propria), which has, according to some authors, a con- nective-tissue origin, while, according to others, it is the product of the glandular cells themselves. In some cases it appears structure- less, in others a cellular structure can be distinguished ; in the latter case the cells are flattened, with very much flattened nuclei, and show irregular outlines. Macroscopically, compound glands present a more or less lobular structure, the separate lobules being held together by connective tissue. In the immediate neighborhood of the gland and its larger lobes, the connective tissue is thickened to form the so-called tunica albuginea or capsule. In this fibrous-tissue sheath are found numer- ous blood-vessels which penetrate between the lobes and lobules of the gland and form a dense capillary network about the tubules and alveoli immediately beneath the membrana propria. Nerve-fibers are also plentiful. (c) Remarks on the Process of Secretion. — The gland-cell varies in its microscopic appearance according to its functional con- dition. In its phases of activity it shows vacuoles filled with secre- tion fas in the liver-cell), or a granulation (pancreas), or even a dis- tinct striation of its protoplasm (kidney). I lie secretory process varies. In one case the cell remains intact throughout the process (salivary glands) ; in another a por- tion of its own substance is used up in the production of the secre- tion, only the basal portion containing the nucleus being preserved. When this occurs, the upper part of the cell is reconstructed from the remaining basal portion, and the cell is ready to renew the EPITHELIAL TISSUES. 85 process (mammary glands). In a third type the whole cell is destroyed, and is replaced by an entirely new cell (sebaceous glands). 4. NEURO-EPITHELIUM. In certain of the organs of special sense (inner ear and taste-buds) the epithelial cells about which the nerves terminate undergo a high degree of specialization. This differentiation is moreapparent in the outer portions of these cells, resulting in the formation of one or sev- eral stiff, hair-like processes, which appear especially receptive to stimuli. Such cells are known as neuro-efrithelial cells. In the epithelia in which they occur they are surrounded by supporting or sustentacula)- cells. 5. MESOTHELIUM AND ENDOTHELIUM. The pleural, pericardial, and peritoneal cavities are lined by a single layer of flattened epithelioid cells which develop from the mesothelium lining the primitive body cav- ity (celom). For this reason, as has been suggested by Minot (90), the term mesothe- lium may with propriety be applied to this layer in its developed condition. A meso- thelial cell is a very much flattened cell, resembling those of squamous epithelium, with faintly granular protoplasm, possessing a flattened, oval, or nearly round nucleus. These cells are of polyhedral shape, and are united into a single layer by a small amount of intercellular cement substance. The borders of these cells maybe quite . Fi ? . 52 -Mesothelium * * from pericardium 01 rabbit regular Or slightly Wavy (Fig. 52) ; more Silver nitrate preparation, often they are serrated (Figs. 53, 54). The stained in hematoxylin. quantity of intercellular cement substance is so small in amount, and the cell boundary so indistinct, that it is necessary to resort to special staining methods to bring out clearly their outline (silver nitrate or intra vitam methylene-blue method). The cavities lined by mesothelium communicate directly with lymph-vessels or -spaces beneath the lining membrane by means of small openings known as stomata. The stomata are surrounded by a layer of cubical cells with granular protoplasm, spoken of as ger- minal cells. They are numerous in the diaphragm, and may be readily demonstrated in the frog in the membrane separating the abdominal lymph-space from the peritoneal cavity (in the region of the kidneys). Small accumulations of the intercellular cement substance, found at the place of union of several mesothelial cells, are described as pseudostomata or stigmata. S6 THE TISSUES. Endothelial cells are differentiated mesenchymal cells. They line the blood- and lymph-vessels and lymph-spaces (arachnoidal and Fig. 53. — Mesothelium from mesentery of Fig. 54. — Mesothelium from peritoneum of rabbit. frog; X 4°°- Technic No. 123. Fig. 55. — Mesothelium covering posterior abdominal wall of frog. Stained with silver nitrate and hematoxylin. Fig, 56. — Endothelial cells from small artery of the mesentery of a rabbit. Stained with silver nitrate and hematoxylin. synovial spaces, anterior chamber of the eye, bursa', and tendon sheaths). Endothelial cells are in structure like those of the meso- I l'l I 111. I I \l. I [SSI I -. 87 thelium. In blood- and lymph-vessels they arc of irregular, oblong shape, with serrated borders. The boundaries of these cells are clearly brought out by silver nitrate. TECHNIC. 127. Epithelium may be examined in a fresh condition. The sim- plest method consists in placing some saliva under a cover-glass and examining it with a moderate power. In it will be found a number of isolated squamous epithelial cells, suspended in the saliva singly and in groups. The cells that are cornified still show the nucleus and a small granular area Of protoplasm. 128. In order to examine isolated epithelial cells of organs, it is necessary to treat the epithelial shreds or whole epithelial layers with the so-called isolating or maceration fluids. These are: (1) Iodized serum; (2) very dilate osmic acid (o.\'/ ( to 0.5'/ 1: (3) very weak chromic acid solution (about 1:5000 of water) ; (4) 0.5'/ or \'/ ( solution of ammonium or potassium bichromate ; and, above all, the one-third alcohol recommended by Ranvier (28 vols, absolute alcohol, 72 vols, distilled water). The mixture recommended by Soulier (91), consist- ing of sulphocyanid of potassium or ammonium, and the mixture of Ripart and Petit {rid. T. 13) serve the same purpose. All these solu- tions are used by allowing a quantity of the isolation fluid to act upon a small fresh piece of epithelium for from twelve to twenty-four hours, according to the temperature of the medium and quality of the tis- sue. As soon as the isolation fluid has done its work, it is easy to com- plete the isolation of the cells by shaking the specimen or teasing it with needles. Separation of the elements may be accomplished either in the isolation solution itself or in a so-called indifferent fluid 1 vid. T. 13 ), or in gum-glycerin (vid. T. 98). The macerated preparation may be stained in a hematoxylin or carmin solution before teasing and mounting in gum -glycerin. 129. The movement of the cilia can be observed in mammalian tissues by scraping the epithelium from the trachea with a scalpel and examining it in an indifferent fluid. As the ciliated epithelium of mammals is very delicate and sensitive, specimens with a longer duration of ciliary move- ment are more desirable. They can be obtained by using the mucous membrane from the palate of a frog ( examine in normal salt solution, vid. T. 13). Particularly large epithelial cells, as well as very long cilia, are found on the gill-plates of mussels or oysters. 130. In order to study the relations of mesothelial and endothe= lial cells, the silver method is the most satisfactory. The outlines of the mesothelial cells may be clearly brought out by placing pieces of the peri- cardium, central tendon of the diaphragm, or the mesentery in a 0.75^ to 1 r / f solution of silver nitrate. Before placing in this solution, they should be rinsed in distilled water in order to remove any adherent foreign bodies, such as blood-corpuscles, etc. In this solution they remain until opaque, which occurs in from ten to fifteen minutes. They are then again rinsed with distilled water, in which they are exposed to sunlight until they begin to assume a brownish-red color. ( Mice again they are washed with distilled water, and either placed in glycerin, in which they may be mounted, or dehydrated and mounted in Canada balsam, according to the 88 THE TISSUES. usual methods. The margins of the cells subjected to this treatment will appear black. Endothelial cells may be demonstrated after the following method : A small mammal ( rat, Guinea-pig, rabbit, or cat) is narcotized. Before the heart's action is completely arrested, the thorax is opened and the heart incised. As soon as the blood stops flowing, a cannula is inserted and tied in the thoracic aorta a short distance above the diaphragm, and 50 to 80 c.c. of a i ( '/ c aqueous solution of silver nitrate injected through the cannula. About fifteen minutes after the injection of the silver nitrate solution, there is injected through the same cannula 100 to 150 c.c. of a 4', solution of formalin (formalin 10 parts, distilled water 90 parts). The abdominal cavity is then opened, loops of the intestine with the attached mesentery removed and placed in a 4^1 solution of formalin, in which the tissue is exposed to the sunlight. As soon as the reduction of the silver nitrate has taken place, which is easily recognized by the reddish- brown color assumed by the tissues, the mesentery is divided into small pieces, dehydrated first in 95%, then in absolute alcohol, cleared in oil of bergamot, and mounted in balsam. As a rule, the mesothelial cells covering the two surfaces of the mesentery, and the endothelial cells lining the arteries, veins, and capillaries are clearly outlined by the reduced silver nitrate. If desired, the tissue may be further stained in hematoxylin (we have used Bohmer's hematoxylin solution) or in a carmin solution after dehy- dration in 95% alcohol, after which they are dehydrated, cleared, and mounted in balsam. In preparations made after this method the endo- thelial cells are outlined by fine lines of dark brown or black color. Silver nitrate may also be dissolved ina 2^ to 3% solution of nitric acid, in osmic acid, and various other fluids. Stratified epithelia can also be impregnated with silver nitrate, but only after prolonged immer- sion. They are exposed to sunlight after sectioning on the freezing microtome, or after hardening and imbedding, followed by sectioning. After the reduction of the silver the sections are dehydrated and mounted in balsam. 131. Kolossow has devised the following excellent method for demon- strating intercellular bridges : Fine membranes, or even minute frag- ments of previously fixed tissues, are placed for about a quarter of an hour ina 0.5% to i f /c< osmic acid (or in a mixture composed of 50 c.c. abso- lute alcohol, 50 c.c. distilled water, 2 c.c. concentrated nitric acid, and 1 to 2 gm. osmic acid) and then into a io ( / f aqueous solution of tannin for five minutes, or into a developer consisting of the following : water, 450 c.c. ; 85^ alcohol, 100 c.c. ; glycerin, 50 c.c. ; purified tannin, 30 gm., and pyrogallic acid, 30 gm. In the latter case they are subse- quently rinsed in a weak solution of osmic acid, washed with distilled water, and then carried over into alcohol. 132. There are, of course, special methods of fixing and subsequently examining epithelial structures; these, and the methods of examining gland tissue, will be discussed in the chapters devoted to the various organs. THE CONNECTIVE TISSUES. 89 B. THE CONNECTIVE TISSUES. In the connective tissues, the intercellular substance gives char- acter to the tissue, the cellular elements forming a less conspicuous portion. All the members of this group are developed from the mes- enchyme, .m embryonic tissue differentiated early in embryonic life from the mesoderm, and consisting of variously branched cells, possessing a small amount of protoplasm and relatively large nuclei. The branches of neighboring cells are united by threads of proto- plasm ; between the cells is found a homogeneous ground-substance or matrix. In their fully developed condition some of the members of the connective-tissue group are only slightly altered from embryonic con- nective tissue. This is the case in mucous connective tissue, which Cell process. Nucleus. Fig- 57- — Mesenchymatous tissue from the subcutis of a duck embryo ; X 650. Technic No. 17. resembles closely mesenchymal tissue. In other members there are developed in the ground-substance, in less or greater number, fibers, known as connective -tissue fibers, thus forming reticular con- nective tissue and the looser and denser forms of fibrous connective tissue. A more marked condensation of the intercellular substance is observed in cartilage ; and in bone and dentin a still greater de- gree of density is obtained by the deposition of calcareous salts in the intercellular matrix. The role played by the connective tissues in the economy of the body is largely passive, depending on their physical properties. Bone and cartilage serve as supporting tissues ; the looser fibrous tis- sues for binding and holding the organs and parts of organs firmly in place. The denser fibrous connective tissues come into play 9<3 THE TISSUES. where strength and pliability are desired, as in ligaments, or else are used in the transmission of muscular force, as in tendons. Another important characteristic of connective tissue is that its various members are capable of undergoing transformation into wholly different types ; bone, for instance, being developed from fibrous connective tissue and from cartilage. Certain structures are represented by different members of the connective-tissue group in the different classes of vertebrates. In certain fishes the skeleton is cartilaginous, and in certain birds the leg tendons are formed of osseous tissue, etc. In the different types of connective tissue the cellular elements are morphologically very similar, and do not differ materially from the mesenchymal cells from which they are developed. The connective tissues receive their nutrition from the lymph. In the denser connective tissues this permeates the tissues through clefts or spaces in the ground-substance, in which the connective- tissue cells are found and which are united by means of fine canals into a canalicular system. In the looser fibrous tissues and in mucous connective tissue the system of lymph-channels is not present ; here the lymph seems to pass through the ground-sub- stance. Certain connective-tissue cells have the function of producing fat. In various parts of the body, masses of fat tissue are formed as a protection to various organs and as a reserve material upon which the body can call when necessary. This type can hardly be con- sidered a separate class of connective tissues, as it can be demon- strated that it is merely modified connective tissue, and can occur wherever the latter is found. Finally, certain elements of the middle germinal layer are capa- ble of producing colored substances known as pigments. To this class belong the pigment cells and the red blood-corpuscles. From the above account it will be seen that we have to distin- guish between the following kinds of connective tissue : (i) mucous connective tissue, (2) reticular connective tissue, (3) fibrous con- nective tissue, (4) adipose tissue, (5) cartilage, (6) bone. The fibrous connective tissues are composed of a ground-sub- stance or matrix in which are imbedded the cellular elements and two kinds of connective-tissue fibers, namely, white and elastic fibers. As the character of the fibrous connective tissue depends largely on the arrangement of the fibers and on the relative propor- tion of the white and elastic fibers, these will be considered prior to a description of the several types of fibrous connective tissue. White Fibers. — White fibrous connective tissue consists of ex- lingly fine homogeneous fibrilhe, cemented by a small amount of an interfibrillar cement substance into bundles varying in size. In the bundles these fibrilhe have a parallel course, although the bun- dles are often slightly wavy. The fibrilhe of white fibrous connective tissue vary in size from 0.25 to I it, and neither branch nor anasto- THE CONNECTIVE TISS1 I S. 91 mose. The)- become transparent and swollen when treated with acetic acid, are not at all or only very slowly digested by pancreatin, and yield gelatin on boiling. Elastic Fibers. — These are homogeneous, highly refractive, dis- tinctly contoured fibers, varying in size from l // to (>//., and in some animals are even larger. They branch and anastomose, and are not cemented into bundles. When extended, they appear straight; when relaxed, they show broad, bold curves, or are arranged in the form of a spiral. The broken ends of the fibers are bent in the form of a hook. F. P. Mall has shown that elastic fibers are com- posed of two distinct substances — an outer delicate sheath which does not stain in magenta, and an interior substance which is intensely colored in this stain. The interior substance is highly refractive. Elastic fibers are not affected by acetic acid, but are readily digested in pancreatin and less readily in pepsin. They yield elastin on boiling. Our knowledge concerning the development of the connective- Fig. 58.- — White fibrils and small bun- dles of white fibrils from teased preparation of a fresh tendon from the tail of a rat. Fig. 59. — Elastic fibers from the liga- mentum nuchre of the ox, teased fresh ; X 500. At a the fiber is curved in a char- acteristic manner. tissue fibers is not as yet conclusive ; two distinct views are held at the present time. One group of observers maintains that the fibers are developed in the cells of the embryonic connective tissue. These cells are thought to change into fibrous connective tissue by the formation in their interior of thread-like structures — the con- nective-tissue fibrils — a process which is always accompanied by active nuclear division (Flemming,9i, II; Lwoff, Rcinke). The cells thus become polynuclear and considerably lengthened, and the fibrils gradually increase in number at the expense of the cell-bodies, so that on examining the tissue the fibrils appear to predominate, and give the impression of forming the ground-substance. Ac- cording to the other view, the fibers are at all times intercellular, developing in the ground-substance. Mall believes their develop- ment to be due to a kind of coagulation, certain cells being held Q2 THE TISSUES. responsible for the formation of special fluids or ferments which briny; about this coagulation. The formation of the ground-sub- stance in which the fibers develop is also attributed to the cellular elements. The intercellular mode of formation of connective- tissue fibers would appear to be the more usual, although some of them may have an intracellular origin. We shall now discuss the several types of fibrous connective tissue. U MUCOUS CONNECTIVE TISSUE. Mucous connective tissue is a purely embryonal type, and scarcely represented in the adult human body. It consists of branched, anastomosing cells imbedded in a gelatinous ground-sub- stance, containing here and there white fibers. The latter as well as the mucous matrix are, directly or indirectly, the products of the .cells. During the development of the embryo this tissue is found in large quantities in the umbilical cord, and is here known as Whar- ton's jelly. It also occurs in the embryo in the cutis, in the region of the semicircular canals of the cochlea, in the vitreous humor, etc. 2. RETICULAR CONNECTIVE TISSUE. Reticular connective tissue is a fibrous connective tissue in which the intercellular substance has disappeared. The tissue is often described as being composed of anastomosing branched cells, ar- ranged in the form of a network with open spaces. The obser- vations of Ranvier and Bizzozero, and more recently those of Mall, have shown that the framework of reticular tissue is composed of very fine fibrils or bundles of fibrils. These interlace in all planes to form a most intricate network, surrounding spaces of varying size and shape. According to F. P. Mall, the fibrils of reticular tissue differ chemically from both the white and elastic fibers, although their composition has not been fully determined. Like white fibrous tissue, reticular tissue is not digested by pancreatin, but, unlike white fibrous tissue, it does not appear to yield gelatin upon boiling in water. The cells of reticular connective tissue, which are flattened and often variously branched, lie on the reticular network, being often wrapped about the bundles of fibrils. Unless they are removed, the reticulum has the appearance of a network composed of branched and anastomosing cells. Reticular connective tissue is found in adenoid tissue and lymph- glands, in the spleen, and in the mucous membrane of the intestinal canal, and in these locations the meshes of the reticulum arc filled with lymph-cells and other cellular elements, which, unless removed, obscure' the reticulum. Connective-tissue fibrils giving the same reaction as those found in the adenoid reticulum are found associ- ated with white and elastic fibers in the liver, kidneys, and THE CONNECTIVE TISSUES. 93 lung. In bone-marrow a reticulum is found, in the meshes of which are the cellular elements of this tissue. 3. FIBROUS CONNECTIVE TISSUE. Fibrous connective tissue can be divided morphologically into two groups: In one the bundles of fibers cross and interlace in all directions, forming a network with meshes of varying size — formless or areolar connective tissue. In the other the bundles of fibers are parallel to each other, as in tendon and many of the apo- neuroses and ligaments, or less regularly arranged, yet very densely Reticulum. • • * * * « * <© ... i ' *£ f 0* - % 9 $ X. as ■ i i - Nucleus of connec- tive-tis- sue cell. Blood- vessel. Fig. 6o. — Reticular connective tissue from lymph-gland of man ; X 2 %°- Brush preparation. woven, as in fascias, the dura mater, and the firm, fibrous capsules of some of the organs. (a) In areolar connective tissue the bundles of white fibers, which vary greatly in size and which often divide and anastomose with portions of other branching bundles, intercross and interlace in all directions. If the bundles of fibers are numerous, the interlacement is more compact, thus forming a dense areolar connective tissue ; if less numerous, the network is more open, as in loose areolar connective tissue. Elastic fibers are always found in areolar connective tissue, though in varying quantity. They anastomose to form a network with large, irregular meshes, and run on or between the bundles of white fibers. The meshes between the bundles of fibers, and the minute spaces between the fibrils in these bundles, are occupied by a semifluid, homogeneous substance known as the ground-substance, or matrix. The fibrous elements of areolar connective tissue are, 94 THE TISSUES. therefore, imbedded in this ground-substance, in which they develop. In dense areolar connective tissue the fibrous elements appear to have nearly displaced the ground-substance. In the ground-sub- stance are found irregular, branched spaces, — cell-spaces, — in which lie the cellular elements of this connective tissue. These spaces anastomose by means of their branches, thus forming part of a system of spaces and small chan- nels, known as the lymph canal- icular system. These spaces and channels permeate the ground- substance in all directions, and serve to convey lymph to the tissue elements. The cell -spaces and their anastomosing branches can be demonstrated by immers- ing areolar connective tissue (preferably from a young animal), spread out in a thin layer, in a solution of silver nitrate (i fc) until the tissue becomes opaque. If then the tissue is exposed to sunlight, the silver is reduced in the ground-substance, giving it a brown color, while the cell-spaces remain unstained. The ground- substance of areolar connective tissue contains mucin. The cellular elements of areolar connective tissue, which, as above stated, are imbedded in the cell-spaces, are either fixed CO/l- Fig. 6l. — Areolar connective tissue from the subcutaneous tissue of a rat. Elastic libers not shown. » .,«'' a '■ ;; ' -*- .-/I., ._./'?.';:>-,' ,- ^0m^ §e- ,-:•>•■ Fig. 62. — Cell -spaces in the ground- Fig. 63. — Three connective-tissue substance of areolar connective tissue (sub- cells from the pia mater of a dog. Stained cutaneous) of a young rat. Stained in silver in methylene-blue {intra vitam). nitrate. ncctive-tissue cells or wandering or migratory cells. The former are again divided, according to their shape and structure, into true connective-tissue cells or corpuscles, granular cells, plasma cells, and pigment cells. The connective-tissue cells or corpuscles are flattened, variously shaped cells of irregular form, usually having many branches. The THE CONNECTIVE II-- 95 protoplasm is free from granules ; the nucleus, situated in the thicker portion of the cell-body and of oval shape, shows a nuclear net- work and one or several nucleoli. The cells assume the shape of t 1 k^r~i^&r^\ s tYY I v \ I' 4 i' 9 Fig. 64. — Two pigment cells found on the capsule of a sympathetic ganglion of a frog. the space that they occupy and nearly fill. The branches of neigh- boring cells often anastomose through the fine channels uniting the cell-spaces. Granular cells are thus named because in their protoplasm are found rather coarse granules of an albuminous nature which stain Protoplasm. Nucleus. - Bacterium in a vacuole. 1 If Fig. 65. — Leucocyte of a frog with pseudopodia. The cell has included a bacterium which is in process of digestion. (After Metschnikofi", from O. Hertwig, 93, II). readily in many anilin stains, notably eosin. They are of irregular form, and are generally found in the neighborhood of blood-vessels. The nucleus is relatively large and of round or oval form. 96 THE TISSUES. Plasma cells, first described by Waldeyer, show large vacuoles in their protoplasm. Pigment cells are branched connective-tissue cells, in the proto- plasm of which arc found brown or nearly black granules. In man they occur in the choroid and iris and in the dermis. In the lower animals they have, however, a much wider distribution, and in the frog and other amphibia they are very large and irregular. These cells have the power of withdrawing their processes and, to a limited degree, of changing their location (dermis). The wandering or migratory cells are described in this connec- tion not because they form one of the structural elements of areolar connective tissue, but because they are always associated with it. They are lymph- or white blood-cells, which have left the lymph- or blood-vessels and have migrated into the lymph canalicular system. They possess ameboid movement, and wander from place to place, Fibrils. Nucleus. ■#"" Fig. 66. — Fibrous connective tissue (areolar) from the great omentum of the rabbit ; X 400. Technic No. 17. and are the phagocytes of Metschnikoff. They seem to be intrusted with the removal of substances either superfluous or detrimental to the body (as bacteria). These are either digested or rendered harm- less. The wandering cells even transport substances thus taken up to some other region of the bod)', where they are deposited. In the peritoneum and other serous membranes the network formed by the fibrous tissue lies in one plane, and does not branch and intercross in all directions, as where areolar tissue is found in larger quantity. (Fig. 66.) (/>) Tendons, aponeuroses, and ligaments represent the densest variety of fibrous connective tissue, and are composed almost wholly of white fibrous tissue. This is found in the form of rela- tively large bundles of white fibrils, having a parallel or nearly parallel course. In tendons these bundles are known as primary tendon bundles or tendon fasciculi. The fibrils of white fibrous con- 1 III. CONM.CTIVK 97 nective tissue forming the fasciculi arc cemented together by an iu- terfibrillar cement substance. Here and there the fasciculi branch at very acute angles and anastomose with other fasciculi. The fas- ciculi are grouped into larger or smaller bundles, the secondary tendon bundles, which are surrounded by a thin layer of areolar con- nective tissue, and in part covered by endothelial cells. Between the tendon fasciculi there is found a ground-substance, interfascicu- lar ground-substance, identical with the ground-substance in areolar connective tissue. In this there are cell-spaces occupied by the tendon cells, morphologically similar to the branched cells of areolar connective tissue. The tendon cells are arranged in rows between the tendon fasciculi. The}' have an irregular, oblong body, containing a nearly round or oval nucleus. Two, three, or even more wing- M : * Tendon cell. Tendon fibers. ' > ^ Tendon * cell. : "" Tendon fasciculus. Fig. 67. — Longitudinal section of tendon ; Fig. 68. — Cross-section of secondary X 270. tendon bundle from tail of a rat. like processes (lamellae) come from the cell-body and pass between the tendon fasciculi. In cross-section the tendon cells have a stellate shape. The secondary tendon bundles are grouped to form the tendon, and the whole is surrounded and held together by a layer of areolar connective tissue, called the peritendineum. From this, septa pass in between the secondary tendon bundles, forming the internal peri- tendineum. The blood- and lymph-vessels and the nerve-fibers reach the interior of the tendon through the external and internal peritendineum. The structure of an aponeurosis and a ligament is like that of a tendon. The structure of a fascia, the dura mater, and the more fully 7 98 THE TISSUES. developed gland capsules, differs from that of the formed connective tissues above described, in that the fasciculi are not so regularly arranged, but branch and anastomose and intercross in several planes. (c) Elastic Fibrous Tissue. — In certain connective tissues the elastic fibers predominate greatly over the fibers of white fibrous connective tissue. These are spoken of as elastic fibrous tissues and their structural peculiarities warrant the making of a special sub- group. The ligamentum nuchae of the ox consists almost exclu- sively of elastic fibers, many of which attain a size of about 10 /i. The elastic fibers branch and anastomose, retaining, however, a generally parallel course. They are separated by a small amount of areolar connective tissue, in which a connective-tissue cell is here and there found, and are grouped into bundles surrounded by thin layers of areolar connective tissue ; the whole ligament receives an Areolar con- nective tis- sue. Nucleus of con- nective-tissue cell. Fig. 69. — Tendon cells from the tail of a rat. Stained in methylene- blue (intra vitam). Fig. 70. — Cross-section of ligamentum nuchre of ox. investment of this tissue. In cross-sections of the ligamentum nuchae, the larger elastic fibers have an angular outline ; the smaller ones are more regularly round or oval. (Fig. /O.) In man the ligamenta subflava, between the laminae of adjacent vertebra;, are elastic ligaments. In certain structures (arteries and veins), the elastic tissue is arranged in the form of membranes. It is generally stated that such membranes are composed of fiat, ribbon -like fibers or bands of elastic tissue arranged in the form of a network, with larger or smaller openings ; thus the term fenestrated membranes. F. P. Mall has reached the conclusion that such membranes are composed of three layers — an upper and a lower thin transparent layer in which no openings are found and which are identical with the sheaths of clastic fibers described by this observer, and a central layer, contain- ing openings, and staining deeply in magenta. This substance is identical with the central substance of clastic fibers. THE CONNECTIVE TISSUES. 99 4. ADIPOSE TISSUE. In certain well-defined regions of the body occur typical groups of fixed connective-tissue cells which always change into fat-cells | fat organs,Toldt). Connective-tissue cells in various other portions of the body mayalso change into fat-cells, but in this case the fat, as such, sometimes disappears, allowing the cells to resume their original con- nective-tissue type, only again to appearand a second time change the character of the tissue. The formation of fat is very gradual. Very fine fat globules are deposited in the cell; these coalesce to form larger ones, until finally the cell is almost entirely filled with a large globule {vid. also II. Rabl, 96). As the fat globule grows larger and i^ 5 ^*?* v,„-i»„ g larger, the protoplasm of the cell, to- A& B^. Protoplasm, gether with its nucleus, is crowded to fm N> the periphery. The protoplasm then H Hf- Fat drop. appears as a thin layer just within the wp Ceii-membrane. clear cellular membrane. The nucleus ^^H^^^ becomes flattened by pressure, until Fig. 71.— Scheme of a rat-cell. in profile view it has the appearance of a long, flat bod)-. In regions in which large masses of fat- cells arc developed, they are seen to be gathered into rounded groups of various sizes (fat lobules) separated by strands of con- nective tissue. Numerous blood-vessels are imbedded in this con- nective tissue, penetrating into the lobules and there breaking up into a rich capillar)- network. Microscopically, fat is easily recognized by its peculiar glistening appearance (by direct light). It has a specific reaction to certain reagents. It becomes black on treatment with osmic acid, and is stained red by Sudan III. 5. CARTILAGE. The simplest type is hyaline cartilage, so named because of its homogeneous and transparent ground-substance. Cartilage cells, as such, are of various shapes, and have no typical appearance. They are usually scattered irregularly throughout the matrix, but are often arranged in groups of two, three, four, or even more cells. At the periphery of cartilage, either where it borders upon a cavity (articular cavity) or where it joins the perichondrium, the cells are arranged in several rows parallel to the surface of the tissue. Cartilage cells often contain glycogen, either in the form of drops or diffused throughout their protoplasm. The matrix of cartilage is the product of the cell. It is not present in the so-called precartilage (embryonal cartilage), in which the cells lie close together with their membranes touching. The ground-substance is gradually formed as follows : The membranes of the cells thicken, pressing the cells apart. Inside of the mem- branes the cells divide, and each resulting cell again forms a mem- IOO THE TISSUES. brane. Membranes of the mother cells fuse to form the ground- substance or matrix. The newly created membranes of the daughter cells pass through the same process, and fuse not only with each •' Matrix Cartilage cell. Fig. 72. — Hyaline cartilage (costal cartilage of the ox). Alcohol preparation ; o. The cells are seen inclosed in their capsules. In the figure a are represented frequent but by no means characteristic radiate structures. other, but also with the matrix. The cartilage thus gradually as- sumes the appearance of its adult stage. The youngest cells also possess membranes which separate them from the ground-sub- stance. These are known as the capsules. The spaces occupied by the cells are called lacuna. Fig. 73. — From a section through the cranial cartilage of a squid (after M. Furbringer, from Bergb \. From the description just given it would seem that cartilage grows only by intussusception, but as a matter of fact an apposi- tional growth, although in a lesser degree, also takes place. It THE CONNECTIVE TISS IOI occurs where the cartilage borders upon its connective-tissue .sheath or perichondrium, a vascular, fibrous-tissue membrane composed of white and elastic fibers, which covers the cartilage except where it forms a joint surface. The relations of the cartilage and peri- chondrium are extremely intimate Fibers are seen passing from the perichondrium into the cartilaginous matrix, and the connective- tissue cells appear to change directly into cartilage-cells. White fibrous connec- tive tissue. ;»>\Vliile lib]. n a: : "«} V . •* n i ertion of liga- lentum teres. Hyaline cartilage. Fig. 74. — Insertion of the ligamentum teres into the head of the femur. Longitudinal section ; X 650. It is an interesting fact that the cartilage of certain invertebrate animals, the cephalopoda, shows cells with anastomosing processes. (Fig. 73.) In this case the cartilage-cell is similar to a bone-cell, thus theoretically allowing of the possibility of the metamorphosis of the elements of cartilage into those of bone ( M. Fi'irbringer). Hyaline cartilage occurs as articular cartilage, covering joint surfaces, as costal cartilage and in the nose, larynx, trachea, and 102 THE TISSUES. bronchi. All bones except those of the vault of the skull and the majority of the bones of the face are preformed in hyaline cartilage. In white fibrocartUage (Fig. 74) there are from the beginning, even in precartilage, fibrous strands in the ground-substance. They preponderate over the matrix and, as a rule, have a parallel direc- tion. White fibrocartilage is found in the intervertebral and inter- articular disks, the symphysis pubis, and in the insertion of the ligamentum teres ; it deepens the cavity of ball-and-socket joints, and lines the tendon grooves. In some places elastic fibers are found imbedded in hyaline car- tilage — fibro-elastic cartilage. The elastic fibers send off at acute angles finer or coarser threads which interlace to form a delicate or spaf- -Cartilage-cell. • r/yy Fig. 75. — Elastic cartilage from the external ear of man ; • 760. Technic No. 149. a, Fine elastic network in the immediate neighborhood of a capsule. dense network which permeates the hyaline matrix (Fig. 75), pass- ing over into the corresponding elements of the perichondrium. Elastic cartilage is found in the external ear, the cartilage of the Eustachian tube, the epiglottis, a portion of the arytenoid cartilages, and the cartilages of \\ risbcrg and Santorini. The hyaline ground-substance of all three forms of cartilage, ther with the contained fibers, may undergo calcification, es- pecially in old age. This renders the tissue brittle and easily broken. The nutrition of cartilage is partially supplied by blood-vessels in the matrix, which, however, are not numerous. Wry fine lymph- THE ( ONNE< I l\ I. riSSUl 5. IO3 canals are probably also present in the matrix, uniting the lacunae, through which lymph plasma circulates {vid. researches of Flesch, Budge, Solger (88, \l). van der Stricht (87), etc.). To obtain chondrin, a piece of cartilage matrix is placed in a tube containing water. This is hermetically closed and heated to 120° C, alter which it is opened and the fluid filtered and treated with alcohol. A precipitate of chondrin is the result. This sub- stance is insoluble in cold water, alcohol, and ether, but soluble in hot water, although, on cooling, it gelatinizes. In contrast to gel- atin, chondrin is precipitated by acetic acid. This precipitate does not redissolve in an excess of this acid but disappears in an excess of certain mineral acids. 6. BONE. (a) Structure of Bone. — Bone nearly always develops from a connective-tissue foundation, even where it occurs in places formerly occupied by cartilage. The inorganic substance of bone is deposited in or between the fibers of connective tissue, while the cells of the latter are trans- formed into bone-cells. As in connective tissue, so also in bone, the ground-substance is fibrous. Between the fibers remain uncalcified cells, bone-cells, each of which rests in a cavity of the matrix — lacuna. Primarily, bone consists of a single thin lamella, its later com- plicated structure being produced by the formation of new lamella,- in apposition to the first. During its development the bone becomes vascularized, and the vessels are inclosed in especially formed canals known as vascular or Haversian canals. The bone-cells have processes that probably anastomose, and that lie in special canals known as bone canaliculi. Whether, in man, all the processes of bone-cells anastomose is still an open question. The appearance presented by a transverse section of the shaft of a long bone is as follows : In the center is a large marrow cavity, and at the periphery the bone is covered by a dense connective- tissue membrane, the periosteum. In the new-born and in young in- dividuals the periosteum is composed of three layers — an outer layer, consisting mainly of rather coarse, white fibrous-tissue bundles that blend with the surrounding connective tissue ; a middle fibro-elastic layer, in which the elastic tissue greatly predominates ; and an inner layer, the osteogenetic layer, vascular and rich in cellular elements, containing only a few smaller bundles of white fibrous tissue. In the adult the osteogenetic layer has practically disappeared, leav- ing only here and there a few of the cells of the layer, while the fibro-elastic layer is correspondingly thicker (Schulz, 96). A large number of Haversian canals containing blood-vessels, seen mostly in transverse section, are found in compact bone-substance. 104 THE TISSUES. Lamellae of bone arc plainly visible throughout the ground-sub- stance, and arc arranged in the following general systems : First, there is a set of bone lamellae running parallel to the ex- ternal surface of the bone, while another set is similarly arranged around the marrow cavity. These are the so-called fundamental, or outer and inner circumferential lamella; (known also as periosteal and marrow lamella). Around the Haversian canals are the con- centrically arranged lamellae, forming systems of Haversian or con- centric lamelUc. Besides the systems already mentioned, there are found interstitial or ground lamellce wedged in between the Haversian H V ,-v X s a ng, 6 it to 1 5 fi wide, and 4 a to 9 a thick) have, in common with the canaliculi, walls which present a greater resistance to the action of strong acids than the rest of the solid bone-substance. In each lacuna there is found a bone-cell, the nucleated body of which practically fills the lacuna, while its processes extend out into the canaliculi. The Haversian canals contain blood-vessels, either an artery or a vein or both. Between the vessels and the walls of the canals are perivascular spaces bounded by endothelial cells, resting on the adventitious coats of the vessels and the sides of the canals. Into these spaces empty the canaliculi of the Haversian system. Lymph- spaces beneath the periosteum and at the periphery of the marrow Canaliculi. - Haversian canal. •• Fig. 80. — Portion of a transversely ground disc from the shaft of a human femur ; X 400. Technic No. 154. cavity communicate directly with the canaliculi of the circumferen- tial systems. All the lacunae and canaliculi should be thought of as filled by lymph plasma which circulates throughout, bathing the bone-cells and their processes. The formed elements of the lymph are prob- ably too large to force their way through the very small canaliculi. The plasma current probably flows from the periosteal and marrow regions toward the Haversian canals. Between the lamellae are bundles of fibers (some of which are calcified), which can be demonstrated by heating the bone, or in de- calcified preparations on staining by certain methods. These are the so-cal led fibers of SJiarpcy ; in the adult they contain elastic fibers. In the circumferential lamellae are found canals, not surrounded by concentric lamella,-, which convey blood-vessels from the perios- teum to the Haversian canals. These are called Volkmann's canals. The structure of bone-marrow will be discussed with the blood- forming organs. THE CONNECTIVE TISSUES. 107 (b) Development of Bone. — Nearly all the bones of the adult body arc, in the earlier stages of embryonic life, preformed in embry- onic cartilage. As development proceeds, this embryonic cartilage assumes the character of hyaline cartilage, its cells becoming vesic- ular, and probably disappearing. In the matrix, however, there an- formed spaces that are soon occupied by cells and vessels which grow in from a fibrous-tissue membrane (the future periosteum) sur- rounding the cartilage fundaments of the bones. These cells deposit a bone matrix in the cartilage spaces. Bone developed in this man- ner is known as endochondral ox intracartilaginous bone. In certain bones — namely, those of the vault of the skull and nearly all the bones of the face — there is no preformation in cartilage, these bones being developed from a connective-tissue foundation. They are known as intramembranojts bones. ^ As will become evident upon further discussion of the subject, the formation of fibrous-tissue bone (intramembranous) is not confined to bones not preformed in cartilage. In bones preformed in cartilage, fibrous-tissue bone de- velops from the connective-tissue membrane surrounding the carti- lage fundaments, the two types of bone-development going on simul- taneously in such bones. Attention may further be drawn to the fact that nearly all endochondral bone is absorbed, so that the greater portion of all adult bone, even that preformed in cartilage, is developed from a foundation of fibrous tissue. The two modes of ossification — endochondral or intracartilaginous and intramem- branous — even though appearing simultaneously in the majority of bones, will, for the sake of clearness, be discussed separately. 1 . Endochondral Bone=development. — The cartilage that forms the fundaments of the bones preformed in cartilage has at first the appearance of embryonic cartilage, consisting largely of cells with a small amount of intercellular matrix. These fundaments are sur- rounded by a fibrocellular membrane — the perichondrium. Ossifi- cation is initiated by certain structural changes in the embryonic cartilage, in one or several circumscribed areas, known as centers ot ossification. In the long bones a center of ossification appears in the middle of the future diaphysis. In this region the intercellular matrix increases in amount and the cells in size ; thus the embry- onic cartilage assumes the character of hyaline cartilage. This is followed by a further increase in the size of the cartilage-cells, at the expense of the thinner partitions of matrix separating neighbor- ing cells, while at the same time lime granules are deposited in the matrix remaining. During this stage the cells appear first vesicu- lar, distending their capsules, then shrunken, only partly filling the enlarged lacunae. They stain less deeply, and their nuclei show- degenerative changes. The center of ossification, in the middle of which these changes are most pronounced, is surrounded by a zone in which these structural changes are not so far advanced and which has the appearance at its periphery of hyaline cartilage. Simultaneouslv with these changes in the cartilage, a thin laver ioS THE TISSUES. of bone is deposited by the perichondrium (in a manner to be described under the head of intramembranous bone-development) and the perichondrium becomes the periosteum. This in the mean- time has differentiated into two layers — an outer, consisting largely ol fibrous tissue with few cellular elements, and an inner, the osteogenetic layer, vascular and rich in cellular elements and con- taining few fibrous-tissue fibers. Ossification in the cartilage begins after the above-described ■*?•*•• I : -Vesicular cartilage- cells. -Primary periosteal bone lamella. 'Periosteal bud. - Periosteum. lallered hyaline cartilage. Fig. 81. — Longitudinal section through a long bone (phalanx) of a lizard embryo. The primary bone lamella originating from the periosteum is broken through by the peri- osteal bud. Connected with the bud is a periosteal blood-vessel containing red blood- corpuscles. structural changes have taken place at the center of ossifica- tion. Its commencement is marked by a growing into the cartilage of one or several buds or tufts of tissue derived principally from the osteogenetic layer of the periosteum. As the periosteal buds grow into the cartilage, some of the septa of matrix separating the altered cartilage-cells disappear, and the cells become free and probably degenerate. In this way the cartilage at the center of ossi- THE CONNECTIVE TISSUES. IO9 fication becomes hollowed out, and there are formed irregular anas- tomosing spaces, primary marrow spaces, separated by partitions or trabeculae of calcified cartilage matrix. Into these primary mar- row spaces grow the periosteal buds, consisting of small blood- vessels, cells, and some few connective-tissue fibers, forming embry- onic marrow tissue. Some of the cells which have thus grown into j^'y-. ■ •••'...■' '*■' . '$%& ^■M^4M&%-- Groove of l"v.ViY*M*fi8B ossificatioi Periosteum. Periosteal bone lamella. Primary marrow spaces. Fig. 82. — Longitudinal section of the proximal end of a long bone (sheep embryo) ; X3°- the primary marrow spaces arrange themselves in layers on the trabecular of calcified matrix, which they envelop with a layer of osseous matrix formed by them. The cells thus engaged in the formation of osseous tissue are known as osteoblasts. Ossification proceeds from the center of ossification toward the no THE TISSUES. extremities of the diaphysis (in a long bone), and is always preceded, as at the center of ossification, by the characteristic structural changes above described. Beginning at the center of ossification and proceeding tow aid either extremity of the diaphysis, the enlarged and vesicular cartilage-cells will be observed to be arranged in quite reg- ular columns, separated by septa or tra- becular of calcified cartilage matrix. The cells thus arranged in columns show the degenerative changes above described. They are shrunken and flattened, and their nuclei, when seen, stain less deeply than the nuclei of normal cartilage-cells. Beyond this zone of columns of altered cartilage-cells are found smaller or larger groups of less changed cartilage-cells, and beyond this zone, hyaline cartilage. The arrangement of the cartilage- cells in the columns above mentioned is, according to Schiefferdecker, mainly due to two factors — the current of lymph plasma which flows from the center of ossification toward the two extremities of the cartilage fundament, and the mutual pressure exerted by the groups of carti- lage-cells in their growth and prolifera- tion. Ossification proceeds from the cen- ter of the diaphysis toward its two ex- tremities by a growth of osteoblasts and small vessels into the columns of carti- lage-cells. Here, also, these degenerate, leaving in their stead irregular, oblong, anastomosing spaces, separated by septa and trabecular of calcified cartilage ma- trix on which the osteoblasts arrange themselves in layers, and which they envelop in osseous tissue. In a longi- tudinal section of a long bone, preformed in cartilage, the various steps of endo- chondral bone-development may, there- fore, be observed by viewing the prepa- ration from either end to the center of the diaphysis, as may be seen in figures 82, 83. The former represents the appear- ance as seen under low magnification, the latter a small portion of such a section from the area of ossification, more highly magnified. Adjoining the primary marrow spaces is vesicular cartilage and columns and groups of cartilage-cells and finally hyaline car- tilage. Fig- 83. — Longitudinal sec- tion through area of ossification from long Lone of human em- bryo. THE C0NNEC1 IVE I rSSl ES. I I I In the upper portion of figure 83 is observed a zone composed of groups of cartilage-cells, adjoining this a zone composed of columns of vesicular and shrunken cartilage-cells, the nuclei of which are indistinctly seen. These columns are separated by septa and trabecular of calcified matrix. This zone is followed by one in which the cartilage-cells have disappeared, leaving spaces into which the osteoblasts and small blood-vessels have grown. In cer- tain parts of the figure, the osteoblasts are arranged in a layer on the trabecular of calcified cartilage, some of which are enveloped in a layer of osseous matrix, less deeply shaded than the darker car- tilage remnants. As the development of endochondral bone proceeds from the center of ossification toward the extremities of the diaphysis in the manner described, the primary marrow spaces at the center of ossi- fication are enlarged, a result of an absorption of many of the smaller osseous trabecular and the remnants of calcified cartilage matrix enclosed by them. In this process are concerned certain large and, for the most part, polynuclear cells, which are differentiated from the embryonic marrow. These are the osteoclasts (bone break- ers) of Kolliker (73). They are 43 fi to 91 u long and 30/4 to 40 ;i broad, and have the function of absorbing the bone. The spaces which they hollow out during the beginning of the process appear as small cavities or indentations, containing osteoclasts either single or in groups, and are known as Howship's lacuna. All bone- absorption goes hand in hand with their appearance. At the same time, the osseous trabecular not absorbed become thickened by a deposition of new layers of osseous tissue (by osteoblasts), during which process some of the osteoblasts are enclosed in the newly formed bone and are thus converted into bone-cells. In this wax- there is formed at the center of ossification a primary or embryonic spongy or cancellous bone, surrounding secondary marrow spaces or Haversian spaces, filled with embryonic marrow. This process of the formation of embryonic cancellous bone follows the primary ossification from the center of ossification toward the extremities of the diaphysis. It should be further stated, that long before the developing bone has attained its full size — indeed, before the end of embryonic life — the embryonic cancellous bone is also absorbed through the agency of osteoclasts. The Haversian spaces are thus converted into one large cavity, which forms a portion of the future marrow cavity of the shaft of the fully developed bone. The absorption of the embryonic cancellous bone begins at the center <>l "ssification and extends toward the ends of the diaphysis. Some time after the beginning of the process of bone develop- ment at the center of ossification of the diaphysis, centers of ossification appear in the epiphyses, the manner of the develop- ment of bone being here the same as in the diaphysis. Several periosteal buds grow into each center of ossification, filling the irregular spaces formed by the breaking down of the degener- I I 2 THE TISSUES. ated cartilage-cells. Osteoblasts are arranged in rows on the trabecular of cartilage thus formed, which they envelop in osseous tissue. As development proceeds, the primary osseous tissue is converted into embryonic cancellous bone as above described. In the development of the epiphyses, as in the development of the smaller irregular bones, the formation of bone proceeds from the center or centers of ossification in all directions, and not only in a direction parallel to the long axis of the bone as described for the diaphysis. The epiphyses grow, therefore, in thickness as well as in length, by endochondral bone-development. There remains between the osseous tissue developed in the dia- physis and that in the epiphyses, at each end of the diaphysis, a zone of hyaline cartilage in which ossification is for a long time delayed ; this is to permit the longitudinal growth of the bone. These layers of cartilage constitute the epiphyseal cartilages. Here the periosteum (perichondrium) is thickened and forms a raised ring around the cartilage. As it penetrates some distance into the substance of the cartilage, the latter is correspondingly indented. (Fig. 82.) The im- pression thus formed appears in a longitudinal section of the bone as an indentation, — the ossification groove {encoche d 'ossification, Ranvier, 89). That portion of the perichondrium filling the latter is called the ossification ridge. The relation of the elements of the perichondrium to the cartilage in the region of the groove just described is an extremely intimate one, both tissues, perichondrium and cartilage, merging into each other almost imperceptibly. It is a generally accepted theory that so long as the longitudinal growth of the bone persists, new cartilage is constantly formed at these points by the perichondrium. In the further production of bone this newly developed cartilage passes through the preliminary changes necessary before the actual commencement of ossification — i. c, it goes through the stages of vesicular cartilage and the formation of columns of cartilage-cells, in place of which, later, the osteoblasts and primary marrow cavities develop. By the development of new cartilage elements from the encoche the longitudinal growth of the bone is made possible ; at the same time, those portions of the cartilage thus used up in the process of ossification are immediately replaced. (Fig. 84.) The following brief summary of the several stages of endochon- dral bone-development may be of service to the student : 1. The embryonic cartilage develops into hyaline cartilage, beginning at the centers of ossification. 2. The cartilage-cells enlarge and become vesicular. In the diaphysis of long bones such cells are arranged in quite regular columns, while in the epiphyses and irregular bones this arrange- ment is not so apparent. 3. Calcification of the matrix ensues ; the cartilage-cells disap- pear (degenerate) ; primary marrow spaces develop. 4. Ingrowth of periosteal buds. The osteoblasts are arranged THK CONNECTIVE TIS 113 in layers on the trabecular of calcified cartilage, which they envelop with osseous tissue. 5. Osteoclasts cause the absorption of many of the smaller osseous trabecular ; others become thickened by a deposition of new layers of osseous tissue. Osteoblasts are enclosed in bone- tissue and become bone-cells. In this way there is formed embry- onic cancellous bone, bounding Haversian spaces inclosing embry- onic marrow. 6. In the diaphysis, the greater portion of the embryonic can- cellous bone is also absorbed (by osteoclasts) ; the Haversian spaces unite to form a part of the marrow space of the shaft of the bone. 2. Intramembranous Bone. — This, the simpler type of ossifi- cation, occurs in bone developed from a connective-tissue founda- tion, and is exemplified in the formation of the bones of the Fig. 84. — Longitudinal section through epiphysis of arm bone of sheep embryo ; a, (>, Primary marrow spaces and bone lamellae of the diaphysis. cranial vault and the greater number of the bones of the face, and also in bone developed from the periosteum (perichondrium) sur- rounding the cartilage fundaments of endochondral bone. All fibrous-tissue bone is developed in the same way. The intramembranous bone-development begins by an approxi- mation and more regular arrangement of the osteoblasts of the osteogenetic layer of the periosteum about small fibrous-tissue bundles. The osteoblasts then become engaged in the formation of the osseous tissue which envelops the fibrous-tissue bundles. In this way a spongy bone with large meshes is formed, consisting of irregular osseous trabecular, surrounding primary marrow spaces. These latter are filled by embryonic marrow and blood-vessels de- veloped from the tissue elements of the periosteum not engaged in the formation of bone. 8 H4 THE TISSUES. Intranicmbranous bone first appears in the form of a thin lamella of bone, which increases in size and thickness by the formation of trabecular about the edges and surfaces of that previously formed and in the manner above described. A layer of intramembranous bone thus surrounds the endochondral bone in bones preformed in hyaline cartilage. The two modes of ossification may, therefore, be observed in either a cross or a longitudinal section of a develop- ing bone preformed in hyaline cartilage. In such preparations the endochondral bone can be readily distinguished from the intra- B bjjy —Primary marrow Osteo v blast. P Fig. 85. — Section through the lower jaw of an embryo sheep (decalcified with picric acid) ; / 300. At a and immediately below are seen the fibers of a primitive marrow cavity lying close together and engaged in the formation of the ground-substance of the bone, while the cells of the marrow cavity, with their processes, arrange themselves on either side of the newly formed lamella and functionate as osteoblasts. membranous bone by reason of the fact that remnants of calcified cartilage matrix may be observed in the osseous trabecular of the former. It will be remembered that these osseous trabecular de- velop about the calcified cartilage matrix remaining after the dis- appearance of the cartilage-Cells. In figure 86, which shows a cross-section of a bone from the leg of a human embryo, these facts an- clearly shown. A study of this figure shows the endochondral bone, with the remnants of the cartilage matrix (shaded more THE CONNE< n\ E TISS1 ES. "5 deeply) inclosed in osseous tissue, making up the greater portion of the section and surrounded by the intramembranous bone. In figure 87, more highly magnified, the relations of endochon- dral to intramembranous hone and the details of their mod development are shown ; also the structure of the periosteum. As was stated in the previous section, soon after the formation of the endochondral hone, this is again absorbed; the process ot endochondral bone-formation and absorption extending from the center of ossification toward the ends of the diaphysis. Before the absorption of the endochondral bone, the intramembranous bone has attained an appreciable thickness and surrounds the marrow cavity formed on the absorption of the endochondral bone. Before, - -■."-.- :• ■'-'•' ■■■'.'.'.: 77T..: -...' Fig. 86. — Cross-section of developing hone from leg of human embryo, showing endo- chondral and intramembranous hone-development. however, the marrow cavity can attain its full dimensions, much of the intramembranous bone must also undergo absorption. While intramembranous bone is being developed from the periosteum and thus added to the outer surface of that already formed, osteoclasts are constantly engaged in its removal from the inner surface of the intramembranous bone. The marrow cavity is thus enlarged, the process continuing until the shaft attains its full size. The compact bone of the shaft is developed from the primary spongy intramembranous bone after the following manner : The primary marrow spaces are enlarged by an absorption, through the agency of osteoclasts, of many of the smaller trabecular of osse- u6 THE TISSUES. ous tissue and by a partial absorption of the larger ones, the primary marrow spaces thus becoming secondary marrow spaces, or Haversian spaces. The osteoblasts now arrange themselves in layers Connective-- lissue. Osteoblasts. rtfi. Remnants of cartilage matrix. Bone-cells.--^ matrix.' Osteoblasts., ' Fig. 87. — From a cross- sect ion of a shaft (tibia of a sheep) ; / 550. In the lower part of the figure is endochondral hone formation (the black cords are the remains of the cartilaginous matrix, ; in the upper portion is bone developed from the periosteum. about the walls of the Haversian spaces and deposit lamella after lamella of bone matrix, concentrically arranged, until the large Haversian spaces have been reduced to Haversian canals. During THE CONNECTIVE TISS I \~ this process many of the osteoblasts become inclosed in bone matrix, forming bone-cells and the blood-vessels of the Haversian spaces remain as the vessels found in the Haversian canals. The spongy intramembranous hone not absorbed at the commencement of the formation of the system of concentric lamellae, remains between the concentric systems as interstitial lamellae. The circum- ferential lamellae are those last formed by the periosteum. Calcifica- ation of the osseous matrix takes place after its formation by the osteoblasts. From what has been stated it may be seen that the shafts of the long bones and bones not preformed in cartilage develop by the process of intramembranous bone-formation, while the cancellous bone in the ends of the diaphysis and in the epiphyses is endochon- dral bone. Further, that long bones <^row in length by endo- chondral bone-development, and in thickness by the formation of intramembranous bone. In the development of the smaller irreg- ular bones, both processes may be engaged ; the resulting bone can not, however, be so clearly defined. TECHNIC 133- O ne of the methods for examining connective-tissue cells and fibers is that recommended by Ranvier i 89 > ; it is as follows : The skin of a recently killed dog or rabbit is carefully raised, and a o.\'/ ( aqueous solution of nitrate of silver injected subcutaneously by means of a glass syringe. The result is an edematous swelling in which the connective- tissue cells and fibers | the latter somewhat stretched; come into imme- diate contact with the fixing fluid and are consequently preserved in their original condition. In about three-quarters of an hour the whole eleva- tion should be cut out | it will not now collapse 1 and small fragments placed upon a slide and carefully teased. Isolated connective-tissue cells with processes of different shapes, having the most varied relations to those from adjacent cells, are seen. The fibers themselves either consist of several fibrils, or, if thicker, are often surrounded by a spirally encir- cling fibril. By this method numerous elastic fibers and fat-cells are also brought out. If a drop of picrocarmin be added to such a teased prepa- ration and the whole allowed to remain for twelve hours in a moist chamber, and formic glycerin (a solution of 1 part formic acid in 100 parts glycerin 1 be then substituted for twenty-four hours, the following in- structive picture is obtained : All nuclei are colored red. the white fibrous connective-tissue fibers pink, the fibrils encircling the latter brownish - red. and the elastic fibers canary yellow. The peripheral protoplasm of the fat-cells is particularly well preserved, a condition hardly obtain- able by any other method. 134. Connective tissue with a parallel arrangement of its fibers is best studied in tendon, those in the tails of rats and mice being particularly well adapted to this purpose. If one of the distal vertebra? of the tail be loosened and pulled away from its neighbor, the attached tendons will become separated from the muscles at the root of the tail and appear as thin orlisteninEr threads. These are easily teased on a slide into fibers and IlS THE TISSUES. fibrils. Such preparations are also useful in studying the action of reagents (see below >. The substance resembling mucin which cements the fibrillse together is soluble in lime-water and baryta-water — a circumstance made use of and recommended by Rollet (72, II) as a method for the isolation .of connective-tissue fibrils. In necrotic tissue the fibers show a degenera- tion into fibrils (Ranvier, 89). If connective tissue be heated in water or dilute acids to 120 C, and the fluid then filtered, a solution is obtained from which collagen can be precipitated by means of alcohol. This is insoluble in cold water, alcohol, and ether, but is soluble in hot water and when dissolved in the latter and cooled, becomes transformed into a gelatinous substance. Unlike mucin and chondrin this substance does not precipitate on the addition of acetic and mineral acids. Tannic acid and corrosive sublimate will cause pre- cipitation, as also in the case of chondrin, but not with mucin (vid. also Hoppe-Seyler). 135. Elastic tissue may be obtained by treating connective tissue with potassium hydrate solution, and if the alveoli of the lungs be treated for some time with this reagent, very small elastic fibers can be obtained. By this means the connective-tissue fibers are dissolved, but not the elastic fibers. Particularly coarse fibers are found in the ligamenta subflava. 136. According to Kuhne, connective and elastic tissues are differ- ently affected by trypsin digestion — /. e., alkaline glycerin-pancreas extract at 35 C. — white fibrous connective tissue being resolved into fibrils, while elastic tissue is entirely dissolved. 137. Elastic fibers remain unchanged in acetic acid, and even when boiled in a 20^ solution they only become slightly brittle. They are, however, rapidly destroyed by concentrated hydrochloric acid, although in a \o ( /c solution at ordinary temperature no change is seen. In a 50^ solution the fiber is dissolved in seven days, and in a concentrated solu- tion in two days. The inner substance of the fiber is first attacked, then the membrane. To demonstrate this membrane, the fibers are boiled several times in concentrated hydrochloric acid and the whole then poured into cold water. Occasionally, a longitudinal striation of the membrane is seen, indicating a fibrillar structure. Concentrated solutions of potassium hydrate disintegrate the fibers in a few days : weak solutions, more slowly. A 1 f / f solution of potassium hydrate requires months to produce the effect; a 2 r / c solution, one month; a 5%, three days; a io f /c , one day ; and 20^ to 40^, only a few hours. A weak solution of potassium hydrate, even when brought to the boiling-point, does not dissolve elastic fibers, nor does it cause them to become brittle. If, how- ever, they be boiled in a 5% or io r / f solution of potassium hydrate, the membranes of the fibers will be isolated. A cold 20^ solution has the same effect in one or two days. Pepsin induces a disintegration of the contents of the fiber, leaving the membranes intact (F. P. Mall). 138. Orcein, if correctly applied, colors elastic fibers a dark brown, and can be used to demonstrate them in sections ( Unna, 91). The solution is made as follows: T ' ff gm. of orcein is dissolved in 20 c.c. 95'/ alcohol and 5 c.c. distilled water. This is then diluted one-half by adding a solution composed of 0.1 c.c. hydrochloric acid, 20 c.c. 95$j alcohol, and 5 c.c. distilled water. The sections are stained for twenty-four hours and differentiated in acid alcohol for about a THE ( ONNE( riVE TISSU] 3. I 19 minute. Then the nuclei may be stained either witn hematoxylin or methylene-blue, and the spec imens carried over into absolute alcohol, next into xylol, and finally mounted in Canada balsam. 139. Trypsin quickly dissolves clastic fibers, but not tendon and reticulated tissue, the latter remaining unchanged for days. Putrefaction disintegrates the ligamentum nuchae in a i'vw days, the internal structure of the fibers suffering first, the membranes last. 140. To demonstrate the inner substance of elastic fibers and their membranes, magenta red has been recommended (a small granule is added to 50 c.c. glycerin and 50 c.c. water). By this method the internal substance is colored red while the enveloping sheath remains colorless. 141. To F. I'. Mall also belongs the credit for a few data, which we insert, as to the different reactions which various connective-tissue sub- stances show when treated by the same reagents. When a tendon is boiled it becomes shorter, but if it be fixed before boiling, there is no change. Adenoid reticulum shrinks when boiled, but after a short time swells, and finally dissolves. Both tendon and adenoid reticulum shrink at 70 C. If, however, they be first treated with a 0.5^ solution of osmic acid, the shrinkage will not take place until 95 C. is reached. If the reticulum or the tendon has become shrunken through heat, they are easily digested with pancreatin, and putrefy very readily. Tendon fibers do not become swollen in glacial acetic acid, either concentrated or in strengths of 0.05^ or less, but in strengths of 0.5'/ to 25^ they swell, and if placed in a 25^ solution they will dissolve in twenty-four hours. They also swell in hydrochloric acid in strengths of o.i f / c to 6 r /< . In strengths of Q> r /< to 25$ the fibers remain unchanged for some time, and only dissolve in a concentrated solution of this acid. Reticulated tissue, on the other hand, swells in a $ ( / c hydrochloric acid solution, but remains unchanged in strengths of 3% to \o'/< . It dissolves in twenty-four hours in solutions of 25^ and over. After treatment with a dilute solution of acid, tendon dissolves more rapidly on boiling than does reticular tissue. Tendon exposed to the action of the gastric juice of a dog does not dissolve more rapidly than elastic tissue ; but if placed in an artificial solu- tion of gastric juice, tendon dissolves first, then reticular tissue, and finally elastic fibers. 1'ancreatin affects neither tendon nor reticulated tissue, but if boiled, both tissues are easily digested by its action. If taken out of the body, neither tendon nor reticulum will become affected by putre- faction. In the body, however, and especially at high temperatures (37° C.), both tissues are decomposed within a few days. 142. Fresh adipose tissues can be obtained in lobules and in small groups of cells from the mesenteries of small animals. As a rule, the highly refractive fat globule hides from view the nucleus and protoplasm of the cell. The latter structures can be brought out by the subcutaneous injection of silver nitrate solution, this forming the edematous elevation previously described (vid. T. 133). Fresh fat is soluble in ether and chloroform, especially if the latter be heated. Strong sulphuric acid does not dissolve fat. The stains made from the root of the henna plant color fat red (the color disappearing in ethereal oils). Quinolin-blue, dissolved in dilute alcohol, stains fat a dark blue. If a \o'/ ( potassium hydrate solution be then added, everything will become decolorized except 120 THE TISSUES. the fat. The most important reagent for demonstrating adipose tissue is osmic acid (and its mixtures). Small pieces of adipose tissue are treated for twenty-four hours with a 0.5^ to i'/c osmic acid solution ; if mixtures containing osmic acid be used, the specimens are generally im- mersed for a somewhat longer period. The pieces are then washed with water, and should not be placed directly into alcohol of full strength, as all the structures would then become intensely black (Hemming, 89), but carried into alcohols of ascending strength. When treated in this way the globules of fat take a more intense stain than the other tissues, which, nevertheless, are blackened to some extent. 143. Fat that has been subjected to osmic acid treatment dissolves readily in turpentine, xylol, toluol, ether, and creosote, with difficulty in oil of cloves, and not at all in chloroform. Such preparations are best carried from chloroform into paraffin. Fat that has been stained with osmic acid can be decolorized by nascent chlorin. The specimens are placed in a jar of alcohol in which crystals of potassium chlorid have been previously placed. Hydrochloric acid is then added (to i c /o) and the vessel tightly sealed ( P. Mayer, 81). 144. L. Daddihas recently recommended Sudan III as a stain for fat. This reagent can be applied in two ways : ( 1 ) Either the animals are fed with the coloring matter for some days, in which case all the fat will be colored red, or (2) either fresh or fixed pieces of tissue or sections are stained. Fixation before staining must be done in media that do not dis- solve fat, as, for instance, Miiller's fluid. A saturated alcoholic solution of the stain is used and allowed to act from five to ten minutes. The specimen is then washed with alcohol and mounted in glycerin. The author's experiments with Sudan have been very satisfactory. 145. Thin lamella; of fresh cartilage are examined after separating them from the soft parts and placing them in indifferent fluids. Cartilage removed from the hyposternum or episternum or scapula of a frog is especially adapted for examination. Larger pieces of uncalcified carti- lage may be used if cut into sufficiently thin sections with a razor moist- ened with an indifferent fluid. Under the microscope such sections show a finely punctated background with capsules containing cartilage -cells, provided the latter have not fallen out in the process of cutting, in which case lacuna; will be observed. 146. Osmic acid and corrosive sublimate are by far the best fix- ing agents for cartilage. If the cartilage be calcified, it is fixed for some time in picric acid, which at the same time acts as a decalcifying agent. Although alcohol fixes cartilage fairly well, it causes shrinkage of the cells. The ground substance may be specifically colored by certain reagents, safranin producing an orange and hematoxylin a blue stain. 147. On treating cartilage by certain methods, systems of lines appear in its ground substance, possibly indicating a canalicular sys= tern in the cartilage. In order to make these structures visible, Wolters recommends staining thin sections for twenty-four hours in a dilute solu- tion of Delafield's hematoxylin (violet blue) (vid. T. 62). They are then treated with a concentrated alcoholic solution of picric, acid. 148. The capsules are seen to best advantage if small pieces of car- tilage are treated with a \'/ (i solution of gold chlorid. 149. < 'onnective-tissue and elastic fibers in cartilage are easily THE CONNECTIVE TISSUES. 121 demonstrated by staining the specimens with picrocarmin. The con- nective-tissue fibers are colored a pale pink, the elastic fibers yellow. The latter may also be stained with a \'/,, aqueous solution of a< id fuchsin. 150. If a section of fresh cartilage be placed in a weak solution of iodo=iodid of potassium 1 Lugol's solution), glycogen can sometimes be seen in the cartilage-cells, stained a peculiar mahogany brown. If elastic fibers be present, they also are stained brown, but of a different shade. 151. Thin bone lamellae, such as occur in the walls of the ethmoidal cells, can be (leaned of all the soft parts and examined without further manipulation. If larger bones are scraped with a sharp knife, pieces suitable for microscopic examination are sometimes obtained. 152. If, however, the denser structure of the large bones is to be more closely examined, the following is the best procedure : A long bone is thoroughly freed from fat and other soft parts by allowing it to macerate, after which it is thoroughly washed and dried, thus freeing it from its organic material. Then, by means of two parallel cuts with a saw, as thin a disc as possible is cut out. The section is now ground still thin- ner, either between two hones or upon a piece of glass covered with emery. One surface of the bone is then polished and fastened by means of heated Canada balsam to a thick square plate of glass with the polished side toward the glass. Care should be taken that no air-bubbles are inclosed between the section and the glass. As soon as the specimen is firmly adherent, the other side is ground upon the emery plate or hone, during which manipulation the glass to which the bone has been fastened is held between the fingers. As soon as the section is sufficiently thin and transparent, it is polished. In order to remove the Canada balsam and powdered bone from the section, the glass and bone are dried and placed in some solvent of Canada balsam, such as xylol. This loosens the specimen from the glass, after which it is immersed in absolute alcohol, thoroughly washed, and dried in the air. On examining the bone through the microscope, its lacunae will appear black on a colorless back- ground. The reason is, that the air has taken the place of the evapo- rated alcohol and the spaces appear black by direct light. 153. Sections thus prepared may be permanently mounted as follows : Small pieces of dry Canada balsam are placed both upon a slide and a cover-glass and warmed until they have become fluid, then allowed to cool until a thin film forms over the balsam ; the bone disc is then placed upon the balsam on the slide and quickly covered with the cover-glass. A firm pressure will evenly distribute the balsam, and if the whole has been done with sufficient rapidity the air will have been caught in the open spaces of the bone before the Canada balsam has had a chance to enter these spaces. 154. Other substances may be used to demonstrate the spaces in bone. Ranvier (75) recommends the following method: A few c.c. of a concentrated alcoholic solution of anilin blue (which is soluble in alcohol and not soluble in water and sodium chlorid solution ) are placed in an evaporating dish containing the dry bone. The solution is very carefully evaporated, as the alcohol may otherwise ignite. The specimen, which will soon be covered on both surfaces by a blue powder, is taken out and ground upon a rough glass plate until thoroughly clean. While being 122 THE TISSUES. polished the bone should be kept moist by a solution of sodium chlorid (yid. T. 13). On heating in the evaporating dish, the air is driven from the spaces and replaced by the anilin blue. As already stated, anilin blue is insoluble in sodium chlorid solution, and it therefore remains un- affected by the latter during the process of grinding and cleaning. Hence it remains in the lacunae and canaliculi of the bone, which then appear blue. The specimen may either be mounted in glycerin-sodium chlorid and the edge of the cover-glass sealed with varnish (yid. T. 99), or the section may be washed for a short time in water (in order to remove the sodium chlorid), dried, and finally mounted in Canada balsam as directed. 155. In bone, as also in cartilage, there sometimes occur amorphous as well as crystalline deposits of lime-salts. Upon the addition of acetic acid the carbonate of calcium gives off bubbles ; upon the addition of sulphuric acid, short, thin needles will be formed — crystals of gypsum. Hematoxylin stains the lime-salts blue, with the exception of the oxalate of lime. Alkaline solution of purpurin stains calcium carbonate red. Caustic potash does not affect lime. 156. In order to study the organic constituents of bone, it must first be decalcified and thus rendered suitable for sectioning — i.e., the lime-salts must first be removed, and that without destroying the cellular elements of the bone. The process of decalcification consists in substi- tuting the acids of the decalcifying fluids for those of the bone salts. As a consequence, new combinations are formed, soluble in water or in an excess of the decalcifying acids themselves. 157. The decalcifying fluids most frequently used are : (a) Hydrochloric acid (1% aqueous solution), used in quantities amounting to about fifty times the volume of the specimen. The solution is changed daily, and the bone remains immersed until it is soft enough to be cut. This stage is reached when a needle can be introduced with no resistance. (/>) An aqueous solution of nitric acid in strengths of 3^ to ioV , ac- cording to the delicacy of the specimen, and of a specific gravity of 1.4. Instead of water, 70^-, alcohol may be used as a solvent for the acid. Thoma has recommended for this purpose a solution consisting of 1 vol. nitric acid of a specific gravity of 1.3, and 5 vols, alcohol. This fluid is changed daily and decalcifies small objects in a few days. The specimens are then washed several times in 70^, alcohol to remove as much as possible of the acid. 95% alcohol, with the addition of a little precipitated calcium carbonate, has been recommended for washing sections that have been treated by Thoma's method. After from eight to fourteen days the specimens are again washed with clear 95% alcohol. I c 1 The process of decalcification recommended by v. Ebner (75) is of considerable value, as it also reveals the fibrillar structure of the bone lamellae. A cold saturated solution of sodium chlorid is diluted with 2 vols, of water, and 2 r / r of hydrochloric acid added. This fluid decalcifies very slowly, and must either be changed daily or a small quantity of hydrochloric acid occasionally added. As soon as the speci- men is thoroughly decalcified, it is washed with a half-saturated solution of sodium chlorid. A little ammonia is now added from time to time until the reaction of the fluid and bone is neutral. MUSCULAR 123 Very anal] pieces that contain very little lime-salts, as, for in- stance, bone- in an embryonal condition where calcification has only just begun, can be deprived of their lime-salts by means of a< id fixing solu- tions like Flemming's fluid, chromic acid, picric arid. etc. (*) Bone should be first fixed in some one of the fixing fluids and then decalcified. 158. A method adapted to the study of the hard and soft parts together is that first used by von Koch in studying corals. The specimen is first fixed, and if it be a long bone, the marrow cavity should first be opened to permit the fixing agent to come in contact with all parts of the tissue. After fixing, the bone is stained and then placed in absolute alcohol, and when completely dehydrated the pieces are placed in chloro- form, then in a thin solution of Canada balsam in chloroform, and finally put into an oven kept at a temperature of about 50 C. for from three to four months. By this means the pieces are completely penetrated by the Canada balsam, and as the latter becomes very hard on cooling, the sections may be afterward ground without difficulty. Long as this pro- cedure may seem, it is still the one which enables us to see the soft and hard parts of bone in a relationship the least changed by manipu- lation. 159. Sections treated by Ranvier's method {vid. T. 154) show the perforating fibers of Sharpey as bright, sharply defined ribbons, appearing oaks or circles, according to the section made (longitudinal or trans- verse). If decalcified specimens be first rendered transparent by glacial acetic acid, and then immersed for a minute in a concentrated aqueous solution of indigocarmin, washed with water, and then mounted in gly- cerin or Canada balsam, the fibers of Sharpey will appear red and the remaining structures blue. Thin sections of bone can be deprived of their organic elements by bringing them for from one-half a minute to a minute into a platinum crucible at a red heat. In such preparations cal- cified Sharpey*s fibers may be seen (Kolliker, 86). 160. Airchow's bone corpuscles may be isolated in the following manner : Aerv thin fragments or discs of bone are immersed for some hours in concentrated nitric acid. They are then placed on a slide and covered with a cover-glass : pressure with a needle upon the latter will isolate the lacunae, and occasionally also their numerous processes, the canaliculi. C. MUSCULAR TISSUE. Almost all the muscles of vertebrates have their origin from the middle germinal layer. In the simplest type the protoplasm of the formative cell changes into contractile muscle substance, the cell in the meantime undergoing a change in shape (unstriped muscle-cell). In other cases contractile fibrils are formed which are separated by the remains of the undifferentiated protoplasm (striped muscle-cells). In this case the cells either increase very little in length and possess only a single nucleus (heart muscle), or they grow considerably longer and develop many nuclei (voluntary skeletal and skin muscles). 124 THE TISSUES. A peculiarity of muscle-substance is that it contracts in only one direction, while undifferentiated protoplasm contracts in all directions. I. NONSTRIATED MUSCLE-CELLS. The smooth, unstriped, nonstriated or vegetative muscle-cells belong to involuntary muscle, and are found in the walls of the intestine, trachea, and bronchi, genito-urinary ap- paratus, blood-vessels, in certain glands, and also in connection with the hair fol- licles of the skin. The involuntary mus- cle-cells are spindle-shaped cells, whose substance either appears homogeneous or shows a faint, longitudinal striation. They are 40—200 ;jl long and 3—8 fx broad. The longest are found in the pregnant uterus, where they attain a length of 500//. At the thickened middle portion of the cell is a long rod-like nucleus, typic of this class of cells. Surrounding it, and especially at its ends, is a small quantity of undifferentiated protoplasm. Nonstriated muscle-cells are doubly re- fractive — anisotropic. Nonstriated mus- cle-cells are cemented together, by a small amount of intercellular cement, to form membranes or small bundles (fas- ciculi) surrounded by a thin layer of fibrous connective tissue. They are often joined by longitudinal ridges similar to the prickles of epidermal cells. These fit edge to edge and form connecting bridges (Kultschitzky, Barfurth). -- Nucleus. — Protoplasm. c b a Fig. 88.— Smooth muscle- cells from the intestine of a cat : In I, isolated; in 2 and 3, in cross-section ; X 3°°- Technic No. 172. At a the cell is cut in the plane of the nucleus ; at (•, in the neighborhood of the pointed end. In 3 (from Bar- furth ) is seen the manner in which neighboring cells are joined to each other by inter- cellular bridges. 2. STRIPED MUSCLE-FIBERS. Soon after the segmentation of the mesoderm begins, certain cells of the mesoblastic somites commence the formation of muscle -sub- stance in their interior, a process which is accompanied by in- crease in the number of nuclei, the formation of a membrane, a lengthening of the cells, and the appearance of fibrils in the per- ipheral protoplasm of the cells. Voluntary or striated muscle-cells are large, highly' differen- tiated, polynuclear cells, which may attain a length of 12 cm., with a width of 10— 100 u.. They are consequently known as muscle-fibers. Their free ends are usually pointed ; the ends attached to tendon rounded (Fig. 90). MUSCULAR TISS1 I . 125 Each striated muscle-fiber consists of a delicate membrane, the sarcolemma, a muscle protoplasm, in which arc recognized very fine --» Nucleus. > Muscle substance. Sarcolemma. Fig, Si). — ( rnss- section of striated muscle-fibers : I, Of man ; 2, of the frog. The relations of the nuclei to the muscle-substance and sarcolemma are clearly visible ; X 670. Free ending. Fig. 90. — Muscle-fiber from one of the ocular muscles of a rabbit, showing its free end; Xi75- fibrils and a semifluid interfibrillar substance (the sarcoplasm) and the muscle nuclei. The sarcolemma is a very delicate, transparent, and apparently structureless membrane, winch resists strong acetic acid, even after boiling for a long time. If we examine in an indif- ferent fluid fresh muscle-fibers, the contents of which have been Fig. 91. — Striated muscle-fiber of frog, showing sarcolemma. Fig. 92. — Diagram of the structure of the fibrils of a stri- ated muscle-fiber. The lighl spaces between the fibrils may represent the sarcoplasm. broken without rupturing the sarcolemma, we may see this sheath as a fine glistening line. (Fig- 91.) 126 THE TISSUES. Ffc The fibrils of the muscle-protoplasm constitute the contractile part of the muscle-fiber. They are exceedingly fine and extend the entire length of the muscle-fiber, and consist of a series of minute, rod-shaped segments with attenuated ends {sarcous elements), united by shorter and much thinner thread-like bridges, on each of which there is found a small granule or globule. Their structure may be expressed in the form of a diagram (Fig. 92) giving the view of Rollett, whose account has here been followed. The ultimate fibrils are grouped into small bundles (0.3-0.5 \i in diameter), forming the mus- .^rTgr-i cle-columus of Kolliker. In ^ fl^^ ppppl^ 1 the muscle-columns the fibrils are so placed that the larger segments fall respectively in the same plane. (See Fig. 92.) The same disposition of the fibrils prevails in all the nu- merous muscle-columns form- ing a muscle-fiber, and all the muscle-columns bear such a relation to each other that the lamer segments of the fibrils fall in the same plane. The semifluid, interfibrillar substance, the sarcoplasm, penetrates between the fibrils of the muscle-columns and separates these from each other and from the sarcolem- ma. In fresh preparations the substance forming the fibrils appears somewhat darker and dimmer, while the sarcoplasm appears clearer. Accordingly, the narrow zone formed by the larger segments of the fibrils appears slightly darker and dimmer than the zones in the regions of the uniting bridges, where the sarcoplasm is more abundant (see Fig. 92), giving these zones a clearer appearance. This gives the striated muscle- fibers their characteristic cross-striation. The sarcoplasm is found in greater abundance between the muscle-columns than between the fibrils in the columns. The sarcoplasm between the muscle- columns appears in the form of narrower or broader lines, parallel to the long axis of the muscle-fibers, giving the cross-striated muscle-fiber also a longitudinal striation. The sarcoplasm between the muscle-columns is seen to best advantage in cross-sections x* Sarcoplasm. Cohnheim's area. .^Sarcolemma. • Sarcoplasm. .Cohnheim's area. Sarcoplasm. -Fibrils. -Sarcolemma. Fig- 93- — Transverse section through striated muscle-fibers of a rabbit. 1 and 3, from a muscle of the lower extremity ; 2, from a lingual muscle ; / 900. Technic No. 163. In 2, Cohnheim's fields are distinct ; in I, less clearly shown : in 3, the muscle- fibri Is are more evenly distributed. Ml -i ri.AK 'I i 127 of the muscle-fiber. Here it appears in the form of a network inclosing the muscle-columns. Thus, we have in a cross-section slightly darker areas, the cross-sections of the muscle-columns, known as Cohnheim's fields or areas, separated by the network of sarcoplasm. (Fig. 93.) In a striated muscle-fiber the darker and fainter hands (larger seg- ments of the fibrils) are doubly refracting, anisotropic, while the clearer bands (sarcoplasm) are singly refracting, isotropic. The relative group- ing of the two unequally refracting substances is, however, somewhat complicated, a condition which has given rise to much discussion as to the liner structure of the muscle-fiber. It should be remembered that the anisotropic and isotropic substances of the fiber are respectively placed in the same plane, so that the cross-striation of the entire fiber is fairly regular. The thickness of the bands varies considerably, often appearing as fine lines. In a definite segment the grouping is very regular, and the structure of such a segment is exactly repeated throughout the entire length of the fiber. A segment of this description contains in its center a broad disc of aniso- tropic substance — the transverse disc (Q) (Fig. 94); this is di- vided through its middle by a less refractive (isotropic) narrow- band, known as the median disc of Hensen (//). Above and below the transverse disc ( Q) is a disc of isotropic substance 1 / 1; these in turn border upon itermediate discs of Krause (/). There are consequently in each segment or muscle-casket four discs — the transverse disc ( Q) divided into two parts by the median disc of Hensen (li), with above and below the two isotropic discs (/), outside of which lie the intermediate discs of Krause ( /. |. One of the best objects for the study of transverse striation is the muscle of some of the arthropods (beetles). Here it will be noticed that the disc (_/) is separated by an anisotropic disc through its center into three: | 1 | an isotropic disc (y) ; (2) an anisotropic disc (A~), the "accessory disc" of Engelmann, Krause's "transverse membrane"; and (3) still another disc of anisotropic substance (E~), Merkel's "ter- minal disc." In other words, the number of discs in a segmental unit is increased to six: Q divided by //, two /'s, two 7:'s, and Z. It should be remarked here that all the doubly refracting substances appear as light, Fig- 94. — Diagrams of the transverse striation in the muscle of an arthropod ; to the right with the objective above, to the left with the objective below its normal focal dis- tance (after Rollett, 85): Q, Transverse disc; h, median disc (Hensen); E, terminal disc (Merkel); A', accessory disc (Engelmann); J, isotropic substance. 128 THE TISSUES. and the singly refracting as dark, bands when the objective is raised just a trifle above its focal distance. The contrary is the case on lowering the objective to a point just below its focal distance. (Fig. 94.) In figure 95 is shown a portion of a striated muscle-fiber of man very highly magnified. The larger and darker transverse disc (Q) formed by the larger segments of fibrils is divided by a light line (//), I Iensen's median disc ; the clearer band, largely sarcoplasm, is divided by a dark line, the intermediate disc of Krause ; this falls in the plane of the granules on the fine bridges uniting the larger segments of the fibrils. After a prolonged treatment with 98 fo alcohol the muscle-fibers of the w'ater beetle {Hydrophilus pic cits) can be made to separate into transverse discs (Rollet, 85). One of these discs would correspond to the segment O, and it is very probable that this is the portion which has long been known under the name of Bow- Fig. 95. — From a striated muscle of man ; obtained by teasing ; X 1200. Technic No. 166 : //, A median disc lying in the transverse disc Q ; s, the interme- diate disc borders above and below on the light isotropic discs. Fig. 96. — From a cross-section through the trapezius muscle of man, showing dark fibers rich in protoplasm, and light fibers containing very little protoplasm (after Schaffer, 93, II) : •"■.' .-, substance. .-•.• ,£.■'? *•". \ • . Contractile substance. I •-•''.'•'•'" %\ ■■■■ '-'Jj'~ — Nucleus. © *»'-. ■;.'•::. % m 1 mmi 'V H^^i.» Fig. ioj. Fig. 101. Longitudinal and cross-section of muscle-fibers from the human myocardium, hard- ened in alcohol ; X 64°- The muscle cells in the longitudinal section are not sharply defined from each other, and appear as polynuclear fibers blending with each other. Between them lie, here and there, connective-tissue nuclei. consequently to be regarded as in a perpetual stage of transition, the destruction and compensatory reproduction of its elements going on hand in hand. Its destruction is ushered in by a process which can be compared to a physiologic contraction. Nodes or thickened rings are formed, and at these points the muscle-substance separates into fragments with or without nuclei (sarcolytes), which are then absorbed, in most cases without phagocytic aid. This loss of sub- stance is replaced by new elements developed from the free sarco- plasm, which is characterized by rapid growth and increase in the number of its nuclei. The result is that new elements are formed which have been called myoblasts. The process by which myo- blasts are changed into the finished muscle-fibers is exemplified in the embryonal type of development of the tissue. I3 : THE TISSUES. CARDIAC MUSCLE-CELLS. The muscle-cells of the heart differ in structure from the ordi- nary type of transversely striated muscle-fibers. The heart muscle- cells are short, irregularly oblong cells, often branched, possess no sarcolemma, and have one, occasionally two, centrally placed nuclei. In the smaller muscle-cells a cross-section often shows an arrange- ment of the fibrils radiating from the axis. The heart muscle-cells are cemented end to end to form anastomosing heart muscle-fibers ; these are arranged in bundles or in the form of a network. The muscle-cells of the so-called fibers of Purkinje lie immediately beneath the endocardium, and are remarkable in that their proto- plasm is only partially formed of transversely striated substance, and that only at their periphery. Such cells are found in great numbers in some animals (sheep), but rarely in man. Heart muscle has a rich blood supply, which will be considered more fully when the heart is discussed as an organ. For the nerve-endings in smooth and striated muscle-fibers see the chapter on Nervous Tissues. TECHNIC. 161. Fresh, striated muscle-fibers may be isolated by teasing them in an indifferent fluid (yid. T. 13). After a short time the sarcolemma may separate as a very fine membrane. If a freshly teased muscle be placed in a cold saturated solution of ammonium carbonate, the sar- colemma will become detached in places within five minutes (Solger, 89, III). 162. Striated muscle-fibers may be examined in an extended condi- tion by placing an extremity in such a position as to stretch certain groups of muscles. A subcutaneous injection of 0.25-0.5 c.c. of a \°fc osmic acid solution is then made. The acid penetrates between the fibers and fixes them. Pieces of muscle are then cut out and washed in dis- tilled water. Teased fibers, even if not stained, will show the stria- tion plainly if mounted in glycerin. Muscles thrown into a state of tetanic contraction by electric stimulation may also be fixed in this state and later examined. 163. Cross-sections of muscles, extended and fixed in osmic acid, also show the relation of the fibrils to the sarcoplasm (Cohnheim's fields). A remarkable quantity of sarcoplasm in proportion to the number of fibrils is seen, for instance, in the muscles which move the dorsal fin of hippocampus ; among the mammalia a similar condition is found in the pectoral muscles of the bat (Rollett, 89). 164. In the muscles of all adult vertebrates (except the mammalia) the nuclei lie between the fibrils. In young mammalia they also have this position, but in the adult animals only the nuclei of red muscles are found between the fibrillar ; in all other muscles the nuclei are under the sarcolemma. 165. The fibrillar structure of muscle-fibers can be seen by teasing old alcoholic preparations, or tissue treated with weak chromic acid (0.1%) or one of its salts. THE NERVOUS TISSUES. 133 166. In alcoholic preparations of mammalian muscle, the cross- striation is clearly seen, and is intensified by staining with hematoxylin. This stain colors everything anisotropic in the muscle, but does not affe< I the remaining structures. Similar results may be obtained with other stains, such as basic anilin dyes, but not with the same precision as with hematoxylin. 167. A certain species of beetle ( Hydrophilus) is admirably adapted for the study of the finer details of striation. The beetle is first wiped dry and then immersed alive in 93'/ alcohol. On examining in dilute- glycerin after from twenty-four to forty-eight hours, the substance of its muscles will show disintegration into Bowman's discs (vid. p. 128). The latter swell up in acids and are finally dissolved, as may be seen, by adding a drop of formic acid to a specimen prepared as above (Rollet, 85). 168. In order to study the relation of muscle to tendon, small mus- cles with their tendons are put into a 35'/ potassium hydrate solution for a quarter of an hour, after which the specimen is placed upon a slide and teased at the line of junction of the two tissues. This will separate the muscle-fibers from their respective tendon-fibrils (Weismann). 169. Similar results may be obtained by immersing a frog in water at a temperature of 55 C, in which the animal soon dies with muscles perfectly rigid. As soon as the water begins to cool (one-quarter hour) the frog is removed and a small piece of its muscle cut out and teased in water on a slide (Ranvier). 170. Cardiac muscle-cells are isolated by maceration for twenty-four hours in a 20^ solution of fuming nitric acid (potassium hydrate with a specific gravity of 1.3 will do the same in one-half or one hour). The margins of the cells may be brought more clearly into view by placing pieces of heart muscle for twenty-four hours in a 0.5% aqueous solution of silver nitrate and then cutting into sections. 171. Isolated fibers of Purkinje are obtained by immersing pieces of endocardium (0.5 mm. in size) in zZ c /o alcohol and then teasing them on a slide. The sheep's heart is especially well adapted for this purpose. 172. Nonstriated muscle-fibers are isolated in the same way as heart muscle. In thin cross -sections (under 5 n in thickness) of intestinal muscle, preferably of a cat, fixed in osmic acid, the 'intercellular bridges may be seen here and there between the fibers. D. THE NERVOUS TISSUES. The entire nervous system, peripheral as well as central, is com- posed of cells possessing one or many processes. These cells develop early in embryonic life from certain ectodermal cells (neuro- blasts) of the neural canal, which is formed by a dorsal invagination of the ectoderm. The neuroblasts soon develop processes, — many of them in loco, others only after wandering from the neural canal. The processes of the nerve-cells are of two kinds: (1) 1111- branched processes having a nearly uniform diameter throughout, 154 THE tissues. with lateral offshoots known as collateral branches ; these, as we shall see, generally form the central part of a nerve-fiber, and are known as neuraxes (Deiters' processes, axis-cylinder processes, neurites, neuraxones or axones) ; and (2) processes which branch soon after leaving the cell-body and break up into many smaller branches ; these are the dendrites, or protoplasmic branches. In the spinal ganglia and the homologous cranial ganglia these morpho- logic differences in the processes are not observed, theneuraxis and the dendrites of each presenting essentially the same structure. To the entire nerve-cell, cell-body and processes the term neurone (Waldeyer, 91) has been applied ; neura (Rauber), or neu- rodendron (Kolliker, 93). The neuraxes of many neurones attain great length. Those of some of the neurones, the cell-bodies of which are situated in the lower part of the spinal cord, extend to the foot. In other regions neuraxes nearly as long are to be found, and in the majority of neu- rones the neuraxes terminate some distance from the cell-body. It is therefore manifestly impossible in the majority of cases to see a neu- rone in its entirety. Usually, only a portion of one can be studied in any one preparation. Consequently, the more detailed descrip- tion which follows will deal with the neurone in this fragmentary manner. The cell-bodies of the neurones, to which the term " nerve-cells " or "ganglion cells" is usually restricted, the den- drites and neuraxes, often forming parts of nerve-fibers, and their mode of terminating, will receive separate consideration. NERVE-CELLS, OR GANGLION CELLS ; THE CELL-BODIES OF NEURONES. The cell-bodies of nerve-cells are usually large. The bodies of the motor neurones of the human spinal cord measure 75 to 150 \x y their nuclei 45 /x, and their nucleoli 15 p.. The smallest nerve-cells, the neurones of the granular layer of the cerebellum, are 4 to 9 fi in diameter. The protoplasm of nerve-cells shows a distinct fibrillar structure and the fibrils may be followed into the processes. (Fig. 102.) Their nuclei are also large, with very little chromatin, but as a rule are supplied with a large nucleolus. After treatment by certain special methods, the protoplasm of the ganglion cells shows granules or groups of granules which show special affinity to certain stains, consequently known as chromato- phile granules ; these are densely grouped around the nucleus, so that the cell-body shows an inner darker and an outer lighter por- tion. These chromatophile granules, also spoken of as tigroid granules or as the tigroid substance, as a rule are not arranged in concentric layers, but lie mostly in groups, giving to the protoplasm a mottled or reticular appearance. In the cells of the anterior horns (man, ox, rabbit) the granules join to form flakes, which are also more numerous in the region of the nucleus. In all cases the THE NERVOUS TISSUES. I 3 5 granules or flakes are continued into the dendrites of the cell. I [ere they change their shape into long pointed rods, with here and there nodules, which are probably the chief causes of the varicosities so often seen in dendrites (Golgi's method). The cell usually has a clear, nongranular peripheral border (not a membrane), and in the case of large cells there is a similar area around the nucleus, the inner border of which belongs to the nuclear membrane. H. Meld has found that the chromatophile granules are brought out by treat- ment with alcohol and acid fixing fluids, but not in alkaline or neu- tral. They appear, according to the treatment, as fine or coarse granules. They can not be seen in fresh nerve-cells. He conse- quently regards them as artefacts — precipitations of the protoplasm due to reagents (vid. A. Fischer, T. 124). At its junction with the cell the neuraxis spreads out into a cone which is entirely free from granules, and apparently fitted into a depression in the granular substance of the cell (implantation cone). The cellular substance between the chromatophile granules con- sists also of very fine, highly refractive granules, which appear to be arranged in a reticulum surrounding the chromatophile granules Nucleus. Nucleolus. Fibrillar structure. Medullary sheath. Fig. 102. — Bipolar ganglion cell from the ganglion acusticum of a teleost (longi- tudinal section). The medullary sheath of the neuraxis and dendrite is continued over the ganglion cell ; X 800. Technic No. 175. (vid. Nissl, 94, and v. Lenhossek, 95), and the recent observations of Apathy and Bethe make it very probable that in the intergranular substance of the protoplasm of the nerve-cell there exist very fine fibrils which may be traced into the processes of the cell. It requires, however, further observation before more positive statements may be made concerning them. Besides the granules above mentioned, and which are revealed by special methods, there are found in the protoplasm of many of the larger nerve-cells pigment granules of a yellow or brown color which stain black with osmic acid. The dendrites are usually relatively thick at their origin, but gradually, as a result of repeated divisions, taper until their widely distributed arborescent endings appear as minute threads of widely different shapes. When treated by certain methods, they present uneven surfaces studded with varicosities and nodules, in contradis- tinction to the neuraxes, which are smooth and straight. Their ter- minal branches end either in points or in small terminal thickenings. The groups of terminal end-branches of a dendrite (also of a neur- axis) are known as telodendria (Rauber), or end-branches. The 136 THE TISSUES. branches of the dendrites form a dense feltwork, which, together with the cell-bodies of the neurones and with other elements to be described later, constitute the gray substance (gray matter) of the brain and spinal cord. All neurones, with possibly a k\v exceptions, possess only a sinsrle neuraxis. Neurones without a neuraxis have never been found in vertebrates. The neuraxis usually arises from a cone- shaped extension of the cell-body free from chromatophile granules, the implantation cone, more rarely from the base of one of its dendrites, or from a dendrite at some distance from the cell-body. Its most important characteristics are its smooth and regular contour and its uniform diameter. At some distance from the cell- body, usually near its termination, now and then in its course, a neuraxis may divide into two equal parts. Golgi (94) called attention to the fact that the neu- raxes of certain neurones (Pur- kinje's cells in the cerebellum, pyramidal cells of the cerebral cortex, and certain cells of the spinal cord) give off lateral pro- cesses, the collateral branches. Fig. 103. — Chromatophile granules of a ganglion cell from the Gasserian ganglion of a teleost : a, Nucleus ; b, implantation cone. Fig. 104. — Nerve-cell from the ante- rior horn of the spinal cord of an ox, showing coarse chromatophile flakes. Two types of cell are recognized according to the disposition of their neuraxes : In the first the neuraxis is continued as a nerve- fiber ; in the second and rarer type it does not long preserve its independence, nor is it continued as a nerve-fiber, but soon breaks up into a complicated arborization, the ncuropodia of Kolliker (93). The latter type of cell occurs in the cortex of the cerebrum and cerebellum and in the gray matter of the spinal cord. The cells of the two types can be simply described as having long (type I) or short, branched neuraxes (type II). The neuraxes of the cells of type I possess the collateral branches which end in small branching tufts. In its simplest form, a neurone consists of a cell-body and a neu- raxis with its telodendrion. In more complicated types one or several THE NERVOUS TISSUES. 137 dendrites may be present, as also collaterals from the neuraxis, and in rare cases even several neu raxes. According to the number of its processes, a ganglion cell is known as unipolar, bipolar, or multipolar. Dendrite. Neuraxis. Neuraxis. Dendrite. Fig. 105. — Motor neurones from the anterior horn of the spinal cord of a new-born cat. Chrome-silver method. Although neurones present a great variety of morphologic dif- ferences, — large and variously shaped cell-bodies or small ones scarcely larger than the nucleus ; large and numerous dendrites or - Telodendrion. Dendrite. Cell-body. — Neuraxis. Fig. 106. — A nerve-cell with branched dendrites (Purkinje's cell), from the cerebellar cortex of a rabbit ; chrome-silver method ; X I2 5- few and less conspicuous ones, — and although these various forms are widely distributed and intermingled in the different parts of the nervous system, yet in many regions there are found nerve-cells of fixed and characteristic morphologic appearance, which would I38 THE TISSUES. enable a determination of their source. A few of the most charac- teristic types are here figured and may receive brief consideration. In the anterior horn of the spinal cord are found large multipolar neurones (motor neurones), with numerous dendrites, which termi- nate after repeated branching in the neighborhood of the cell-body, while the neuraxis with its collateral branches proceeds from the cell-body and becomes a part of a nerve-fiber. (Fig. 105.) In the cerebellum are found large neurones, discovered by Pur- kinje, and known as Purkinje's cells, with flask-shaped cell-body, from the lower portion of which arises a neuraxis with collateral branches, b --■ Branching of a dendrite. Xeuraxis and collaterals. Fig. 107. — Pyramidal cell from the cerebral cortex of man ; chrome-silver method : «, b, c, Branches of a dendrite. from the upper portion one or two very large and typic dendrites the smaller branches of which are beset with irregular granules. (Fig. 106.) In the cortex of the cerebrum occur large neurones, each with a cell-body the shape <>f a pyramid (pyramidal cell of the cerebral cortex), from the apex of which arises one large dendrite, and from angles at the base, or from the sides of the cell-body, several smaller dendrites. The neuraxis arises from the base directly or from one of the basal dendrites. (Fig. 107. J THE NERVOUS TISSUES. 139 In figure 10S is shown a neurone with relatively small cell-body and short dendrites, from the granular layer of the human cere- bellum. The function of the dendrites has given rise to considerable dis- cussion. Grolgi and his school regard them as the nutrient roots of the cell, a theory which is opposed by Ramon y Cajal (93, I ), van Gehuchten (93, I), and Retzius {(j2, II). According to the latter, all the processes of the nerve-cell are analogous structures ; they pass out from a sensitive element, and probably have a correspond- ingly uniform function. In the spinal ganglia and the homologous cranial ganglia, are grouped the cell-bodies of neurones (peripheral sensory neurones, peripheral centripetal neurones) which differ in many respects from those above described. In the peripheral sensory neurones the Neuraxis. — Ti luclendrion. Fig. 108. — Nerve-cell with dendrites ending in claw-like telodendria ; from the granular layer of the human cerebellum ; chrome-silver method ; X 110 ' Fig. 109. — Ganglion cell with a pro- cess dividing at a (T-shaped process); from a spinal ganglion of the frog ; X 230. Technic No. 178. neuraxes and dendrites have essentially the same structure, both forming part of a nerve-fiber. From a relatively large, nearly round, oval, or pear-shaped cell-body there arises a single process, which, at a variable distance from the cell-body, divides into two branches forming a right or obtuse angle with the single process (T-shaped or Y-shaped division of Ranvier, 78). Both of these branches form the central axis of a nerve-fiber ; one of the branches passing as a nerve-fiber to the spinal cord or brain, as the case may be ; the other forming a nerve-fiber which passes to the periphery. (Figs. 109 and 1 10.) The ganglion cells of the spinal ganglia and homodynamic structures of the brain are therefore apparently unipolar cells, but, as Ranvier has shown, their processes are subject to a T-shaped or Y-shaped division. The branches going to the periphery are re- I-|0 THE TISSUES. garded as dendrites, the others as neuraxes. As to the significance to be attached to the single process, the theory of v. Lenhossek Fig. no.— Ganglion cell from the Gasserian ganglion of a rabbit ; stained in methylene- blue {intra vitatn). (94, I) that it represents an elongated portion of the cell, and that therefore the origin of the dendrite and that of the neuraxis are in this case close together, is very plausible. In the embryo these ganglion cells are at first bipolar, a process arising from each end of a spindle-shaped cell ; as de- velopment proceeds, the two pro- cesses approach each other and ultimately arise from a drawn-out portion of the cell - body, the single process. (Fig. ill.) The sympathetic ganglia are composed mainly of the cell- bodies and dendrites (also some structures to be mentioned later) of neurones of the sympathetic nervous system. In nearly all vertebrates, and with but few ex- ceptions in any one ganglion, these neurones are multipolar and resemble morphologically the multipolar ganglion cells of the anterior horn of the spinal cord, though they are somewhat smaller. In the cell-body there may be ob- Fig. in. — Three ganglion cells from a spinal ganglion of a rabbit embryo. The cells are still bipolar. Their processes come together in later stages, and finally form the T-shaped structure seen in the adult animal; chrome - silver method; /170. THE NKK VOL'S TISSUES. I 4 I served fine chromatophile granules and a large nucleus and nucleolus. From the cell -body there proceed a varying number of dendrites which branch and rebranch and terminate, as a rule, near the cell- body, forming plexuses in the ganglia. The neuraxis arises either directly from the cell-body from an implantation cone, or from one of the dendrites at a variable distance from the cell-body. (Fig. 1 12.) In nearly all ganglia a few unipolar or bipolar cells are to be found. In the sympathetic nervous system of amphibia the sympathetic neurones are unipolar ; the single process present is the neuraxis. A most important result of the more recent investigations on the nervous system is the theory of the independence of the neurone. Each neurone develops from a single cell (neuroblast), and func- tionates as an independent cell under physiologic and pathologic conditions. Only very rarely has any direct connection between two neighboring neurones been demonstrated, so rarely that the Fig. 112. — Neurone from inferior cervical sympathetic ganglion of a rabbit ; methylene- blue stain. scattered observations at hand do not vitiate the above statement. Recent investigations have, however, shown that, while a neurone is a distinct anatomic unit, it is always found associated with other neurones. Nowhere in the body of a vertebrate does one find a neurone completely disconnected from other neurones. This asso- ciation of one neurone with one or several other neurones is always effected by a close contiguity existing between the telodendria (end-branches) of the neuraxis of one neurone with the cell-body or dendrites of one or several other neurones. The telodendron of the neuraxis of one neurone may form a feltwork inclosing the cell- body of one or several neurones, forming structures known as terminal baskets or end-baskets, or the end ramifications of the neuraxis of a neurone may come in very close proximity to the end-branches of the dendrites of one or several neurones. By this contiguity of the telodendria of the neuraxis of one neurone with 142 THE TISSUES. the cell-bodies or the dendrites of other neurones, they are, without losing their identity, linked into chains, so that a physiologic conti- nuity exists between them. In such neurone chains the dendrites are regarded as cellulipetal, transmitting the stimulus to the cell ; the neuraxes as cellulifugal, transmitting the impulse imparted by the cell to the motor nerve-endings or central organs (Kolliker, 93). The entire nervous system may therefore be said to be made up of such neurone chains, the complexity of which varies greatly according to the number of neurones which enter into their construction. This subject will be considered more fully in a chapter on the nervous system. Fibrils of axial cord. Neurilemma. Segment of Lantermann. THE NERVE-FIBERS. The neuraxes of the cells of type I, and the dendrites of the peripheral sensory neurones (spinal ganglia and homologous cranial ganglia), form the chief elements in all the nerve-fibers. In the nerve-fibers they pos- sess a distinctly fibrillar structure. The fibrils composing them, the axis-fibrils, are imbedded in a semifluid substance, the neuroplasm (Kupffer, 83, II) the whole being surrounded by a very delicate membrane, the axolemma. In the nerve- fibers, the axis-fibrils and the neuroplasm form axial cords which are surrounded by a special membrane or membranes, the presence or absence of which serves as a basis for a classification of nerve- fibers. Two kinds are medullated and nonmedullated fibers. In medullated nerve-fibers, the axial cords (neuraxes of cells of type I, and dendrites of spinal ganglion cells) are sur- rounded by a highly refractive substance very similar to fat, which is blackened in osmic acid, the so-called medullary or myelin sheath. In a fresh condition this sheath is homogeneous, but soon changes and presents segments separated from each other by clear fissures. These seg- ments vary in size and are known as " Schmidt-Lantermann-Kuhnt's segments." On boiling in ether or alcohol the entire medullary sheath of a nerve-fiber does not dissolve, but a portion is left in the shape of a fine network which is not affected by exposure to the action of trypsin. From the latter circumstance it has been thought that this network consists of a substance very similar to horn, and is therefore known as neurokeratin (horn-sheath, Ewald and Kuhne). On burning isolated neurokeratin, an odor exactly like that of burn- distinguished, nerve - 'IliJ'j Fig. 113. — Longitudinal section through a nerve-fiber from the sciatic nerve of a fr°g > / 83°- Technic No. 175- TIIK NERVOUS TISSUES. H3 ing horn is given off. It is thought that the meshes of this neuro- keratin network contain the highly refractive substance similar to fat, composing the greater portion of the medullar}- sheath. The medullary sheath is interrupted at intervals of from 80 to 900 fi, the constrictions thus formed being known as the nodes of Ranvier. The smaller the liber, the less the distance between the nodes. In a fiber with a diameter of 2 /x the internodal segments are usually about 90 fi in length. In peripheral nerves the medullar}- sheath is in its turn sur- rounded by a clear, structureless membrane, the neurilemma or sheath of Schwann. Nerve-fibers contain here and there relatively long, oval nuclei (neurilemma-nuclei) which are surrounded by a small quantity of protoplasm, and are situated in small excavations between the neurilemma and the medullar}- sheath. In the higher vertebrates a single nucleus is found midway between each two Fibrils of axial cord. Medullary sheath. -/-- Fibrils. Fi^. 1 14. — Transverse section through the sciatic nerve of a frog ; X 820. Technic Xo. 175 : At a and b is a diagonal fissure between two Lantermann's segments ; as a result, the medullary sheath here appears double. (Compare Fig. 113.) nodes ; in the lower vertebrates (fishes) several scattered nuclei (5—16) may be found in each internodal segment. At the nodes, where the medullary sheath is interrupted, the neurilemma is thickened and contracted down to the axial cord (contraction-ring). Just beneath the contraction-ring, Ranvier found that the axis- cylinder presents a slight, biconic swelling (renjfement bieonique). Thus the sheath of Schwann represents a continuous tube through- out the length of the fiber in contrast to the medullary sheath. In the nerve-fibers of the spinal cord and brain there is no neurilemma, although the medullary sheath is present. In the fresh nerve-fiber the axial cord fills the space (axial space) within the medullary sheath, and appears transparent. After treatment with many fixing fluids the neuroplasm coagulates and shrinks, no longer filling the entire axial space, but appears in the latter as a wavy cord composed of an apparently homogeneous 144 THE TISSUES. mass, the fibrillar of which are no longer recognizable. Such pic- tures, which formerly were supposed to represent the normal condi- tion of the nerve-fibers, gave rise to the conception of an axis-cyl- inder (vid. Technic). That which is known as an axis-cylinder is therefore, in reality, the changed contents of the axial space. It may be stated, however, that the term axis-cylinder is still much used, since the methods commonly employed in the investigation of the nervous system do not preserve the axial cord in its integrity, but nearly always result in the for- mation of an axis-cylin- der. Consequently, al- though we shall make use of the term, its limit- ations are to be kept in mind. Medullated nerve - fibers vary greatly in di- Ranvier's node. Fig. 115. — Medullated nerve-fibers from a rabbit, varying in thickness and showing internodal segments of different lengths. In the fiber at the left the neuri- lemma has become slightly separated from the under- lying structures in the region of the nucleus ; X I 4°- Technic No. 173. Nucleus. Fig. 116. — Remak's fibers (nonmedullated fibers) from the pneumogastric nerve of a rabbit ; X 360. Technic No. 179. ametcr, but whether this points to a corresponding variation in function has not been fully decided. Fine fibers possess a diameter of 2-4//, those of medium size 4—9//., and large fibers 9— 20 fi (Kolliker, 93). A division of medullated fibers during their course through a nerve is relatively rare. The greater number of fibers pass unbranched from their central origin to the periphery, and only when in the neighborhood of their terminal arborization do they begin to divide. A point of division is always marked by a node of Ranvier. THE NERVOUS TISSUES. 145 The segmental structure of nerve-fibers would seem to give the impression that they are formed by a number of cells fused end t<> end. After what has been said with regard to ganglion cells and their processes, this can be the ease only SO far as the nerve-sheaths are concerned. According to this theory, the formative cells of the latter gather in chains along the neuraxes or dendrites, forming a mantle around them, and in the adult nerve-fibers taking the shape of the segments or internodes just described (His, 87 ; Boveri, X5). The points at which the sheath-cells are joined would then corre- spond to the nodes of Ranvier. Other investigators have concluded that the whole nerve-fiber is developed from a terminal apposition of ectodermal cells. In this case not only the sheaths of the fibers but also the corresponding portions of the nerve processes are formed by them (Kupffer, 90). In both theories the neurilemma corresponds to the cell-membrane ; in the former the neurilemma nucleus corresponds to that of the sheath-forming cell, in the latter to that of the formative cell, of the whole nerve segment. It should be noticed that, according to the second theory, a fiber segment is the product of a single cell, while according to the first it is evolved from at least two cells (ganglion cell (process) and sheath-forming cell). The former theory is now very generally accepted. The nonmedullated nerve-fibers, Remak's fibers, possess no medullary sheath ; the axial cord shows nuclei which can be re- garded as belonging to a thin neurilemma. The majority of the neuraxes of the neurones of the sympathetic nervous system are of this structure, although small medullated nerve-fibers (the neuraxes of sympathetic neurones) are found in certain regions. All nerve-fibers, medullated as well as nonmedullated, in the central and peripheral nervous systems lose the sheaths here de- scribed before terminating ; the axis-cylinders (axial cords) ending without special covering (naked axis-cylinders). These terminal branches are, in fixed and stained preparations, beset with small thickenings — varicosities — which vary greatly in size and shape. Nerve-fibers presenting such appearances are spoken of as varicosed fibers. The varicose enlargements may be regarded as small masses of neuroplasm ; the fine uniting threads, as representing the axial fibrils. In the peripheral nervous system the nerve-fibers are grouped to form nerve-trunks. The nerve-fibers, as has been stated and as will be seen from the diagram (Fig. 117) on the next page, are the neuraxes of neurones, the cell-bodies of which are situated in the spinal cord or brain and in the sympathetic ganglia, and the den- drites of peripheral sensory neurones, the cell-bodies of which are found in the spinal and homologous cranial ganglia. In the nerve-trunks the nerve-fibers are gathered into bundles termed funiculi. The nerve-fibers constituting such a bundle are separated by a small amount of fibro-elastic tissue, containing here and there connective-tissue cells, the endoneurium. This is continu- 146 THE TISSUES. ous with a dense, lamellated fibrous sheath surrounding each funicu- lus, the perineurium. Between the lamellae of this sheath are lymph- spaces, communicating with the lymph-clefts found between the Neuraxis of peripheral sensory neurone. Spinal ganglion. Dendrite of per- ipheral sen- sory neurone. Anterior horn of gray matter of spinal cord. ~" Neuraxis of peripheral motor neurone. — Sympathetic ganglion. Nerve-trunk. Neuraxis of sympathetic neurone. Fig. 117. — Diagram to show the composition of a peripheral nerve-trunk. ^HHg Epineurium. Axis-cylinder. Neurilemma. ;/ W v',# ■-,■:#■ m Endoneurium -Perineurium. X f . . . - *"■ ■.....• -■ 1 Fig. 118. — Part of a cross-section through a peripheral nerve treated with alcohol. The small circles represent the cross-sections of medullated nerve fibers; the axis-cylin- inta in their centers. The nerve is separated by connective tissue into large and small bundles — funiculi ; X 75- MOTOR NERVE-ENDINGS. 147 nerve-fibers of the funiculi ; consequently, the lamellae arc covered by a layer <>f endothelial cells. In the larger funiculi, septa of fibrous connective tissue pass from the perineuria! sheath into the funiculi, dividing them into compartments varying in shape and size ; these are spoken of as compound funiculi. The funiculi of a nerve- trunk are bound together by an investing sheath of loose fibro-elastic tissue, continuous with the perineuria! sheaths, which penetrates between the funiculi, and which contains fat-cells, blood-vessels, and lymph-vessels; the latter are in communication with the lymph- spaces of the perineu rial sheaths. When a nerve-trunk divides, the connective-tissue sheaths above mentioned are continued on to the branches, and this even to the smallest offshoots. Thus, single fibers even possess a connective- tissue sheath, — Italics sheath, — which consists of a few connective- tissue fibers and of flattened cells. PERIPHERAL NERVE TERMINATIONS. According to the character of the peripheral organs in which the telodendria of nerve-fibers (neuraxes of type I cells and dendrites of spinal ganglion cells) occur, the nerve-fibers are known as motor and sensory nerve-fibers, the terminations as motor and sensory nerve-endings. Motor Nerve-endings (the Telodendria of Nerve-fibers Ending in Muscle Tissue). — The motor nerve -endings in striated, voluntary muscle tissue will first be considered. The motor nerve-endings in voluntary muscle tissue are the endings of neurones (peripheral motor neurones), the cell-bodies of which are situated in the ventral horns of the spinal cord and in the medulla. The neuraxes of these cells leave the cerebrospinal axis as medullated nerve-fibers (motor fibers) which, after branching, end in the muscle-fibers in the so-called motor endings. . In figure 119 is represented, by way of diagram, a complete peripheral motor neurone. Each motor nerve - fiber branches repeatedly before terminating, although this branching does not often take place until near the termination of the nerve- fiber. Kolliker estimates that in the sternoradialis of the frog, each motor fiber innervates about twenty muscle-fibers ; but whether this number may be regarded as the average number of muscle-fibers receiving their motor nerve-supply from one motor neurone can not be stated with any degree of certainty at the present time. Each motor ending represents the termination of one of the ter- minal medullated branches of a motor nerve-fiber. The ncuraxis of this fiber passes under the sarcolemma and terminates in a teloden- dron (end-brush) in an accumulation of sarcoplasm, in which are found numerous muscle nuclei, forming a more or less distinct ele- vation on the side of the muscle-fiber, Doyere's elevation. The medullary sheath accompanies the nerve-fiber until it passes under the sarcolemma, when it stops abruptly. The neurilemma of the 148 THE TISSUES. nerve-fiber becomes continuous with the sarcolemma of the muscle- fiber at the place where the neuraxis passes under the sarcolemma. Hulk's sheath continues over the motor ending as a thin sheath, containing here and there flattened nuclei, the telolemma nuclei. With the majority of the reagents used to bring to view the motor endings, notably chlorid of gold, the sarcoplasm, in which Dendrite. Neuraxis. - Medullary sheath. Nucleus of neurilemma. Internodal segment. Motor ending. =^- Collateral branch. Neurilemma. Node of Ranvier. Axis-cylinder of medullated nerve-fiber. Muscle-fibers. Fig. 119. — Diagram of peripheral motor neurone. the telodendrion of the nerve-fiber is found, has a granular appear- ance, and is consequently differentiated from the remaining sarco- plasm of the muscle-fiber. To this the term granular sole plate has been applied, the nuclei contained therein being known as sole nuclei, the whole ending as the motor end-plate. If the above interpreta- MOTOR NERVE-ENDINGS. I49 tion of the structure of the motor nerve-ending is correct, there would seem to be no reason why the sarcoplasm in which the telo- dendria occur should be considered other than the sarcoplasm of the muscle-fiber, the nuclei as muscle-nuclei ; the terms motor end- plate, granular sole plate, and sole nuclei would therefore seem un- necessary and misleading. In figures 121 to 125 are shown motor nerve-endings from several vertebrates as seen when stained with gold chlorid. The mass of sarcoplasm in which the neu raxes terminate as above described is about 40 to 60 ji long, 40/1 broad, and 6 to 10 /i thick ; these dimensions vary greatly, however ; they may be greater or less than the averages here given. In amphibia the motor nerve-endings are not so localized as in the majority of vertebrates, as above described, but are spread over a relatively greater surface of the muscle-fiber, and there is no distinct accumulation of the sarcoplasm, and the muscle-nuclei are Fig. 120. — Motor nerve-ending in voluntary muscle of rabbit, stained in methylene- blue [intra vitani) 1 Huber, DeYYitt, "lour. Comp. Neurol.," vol. vn) : A, Surface view ; B, longitudinal section through motor ending ; C, cross-section : a, < >n after entering the capsule, divide into two, three, or tour branches, which form several circular or spiral turns in the same i>r in opposite directions. These fibers then divide into varicose branches, which undergo further division, the resulting branches interlacing to form a bundle of variously tangled fibers which may be loosely ortightly woven. Between the nerve-fibers and their branches, within the capsule, there is found a semifluid sub- stance, which is granular in fixed preparations. Meissner's ( 'orpuscles, — These corpuscles are found in man in the subepidermal connective tissue of the hand and foot and outer surface of the forearm, in the nip- ple, border of the eyelids, lips, glans penis and clitoris. They are most numerous in the palmar sur- face of the distal phalanx of the fingers. They are oval in shape, sometimes somewhat irregular, and vary in size, being from 45 //. to 50 n broad and from 1 10 ;x to 180/^ long. They possess a thin connective-tissue capsule, in which are found round or oval nuclei, some of which have an oblique position to the axis of the corpus- cle. One medullated nerve ends in the smaller corpuscles, two or , Fig; /32. -Meissner's tactile corpus- 1 ' cle ; methylene-blue stain (Dogiel, " In- three or even more in the larger ternat Monatsschr. f. Anat. u. Phys.," ones. After piercing the capsule, to1.dc). the medullated nerves lose their medullary sheaths, the naked axis-cylinders making a variable number of circular or spiral turns, some of which are parallel, others crossing at various angles. These larger branches are all beset with large, spindle-shaped, round, or pear-shaped varicosities. The larger branches, after making the windings mentioned, break up into many varicose branches, which interlace and form a most com- plex network. One usually finds one or several larger naked axis- cylinders, which pass up through the axis of the spiral of fibers thus formed ; these give off branches which contribute to the spiral formation. Genital Corpuscles. — These corpuscles are found in the deeper part of the mucosa of the glans penis and the prepuce of the male and the clitoris and neighboring structures of the female. Their shape varies ; they may be round, oval, egg- or pear- 1 5 6 THE TISSUES. shaped, or even slightly lobulated. Their size varies from 0.04 to o. 10 mm. in breadth and from 0.06 to 0.40 mm. in length. They are surrounded by a relatively thick fibrous capsule, consisting of from three to eight quite distinct lamellae, between which irregu- lar flattened cells with round or oval nuclei are found. Within this capsule, there is found a core, which seems to consist of a semi- fluid substance, slightly granular in fixed preparations, the nature of which is not fully known. The number of sensory nerves going to each corpuscle varies from one to two for the smaller ones, and from eight to ten for the larger corpuscles. The medullated nerves, after entering the corpuscle, divide dichotomously, the resultant branches assuming a circular or spiral course, and interlacing in various ways, within the capsule. After a few turns, the medullated branches lose their medullary sheaths and undergo further di- vision, often dividing repeatedly. The nonmedullated nerves re- sulting from these divisions, the majority of which are varicose, form a most complicated net- work, the whole nerve network presenting a structure which re- sembles a tangle of fine threads. In the meshes of this network is found the semifluid substance of the core. Now and then some of the larger fibers of the network leave the corpuscle and terminate in neighboring corpuscles, or pass to the epi- thelium, where they end be- tween the cells. These three sensory nerve- endings — end-bulbs of Krause, Meissner's tactile corpuscles, genital corpuscles — are, as Dogiel has stated, very similar in structure. Each has a thin connective-tissue capsule, surrounding a core, consisting of a semifluid substance, concerning which our knowledge is as yet imperfect. One or sev- eral medullated nerves go to each corpuscle, which, after losing their medullary sheaths, divide and subdivide into numerous fine varicose branches, which arc variously interwoven, forming a more or less dense plexus of interlacing and, according to Dogiel, anas- tomosing fibers. The chief differences are those of form and size, and of position witli reference to the epithelium. Of the three forms of endings, the genital corpuscle is the largest, and occupies the deep- est position in the subepithelial connective tissue ; Meissner's cor- puscle is intermediate in size, and is found immediately under the epithelium ; while the end-bulbs of Krause are the smallest of these Fig. 133. — Genital corpuscle from the glans penis of man ; methylene-blue stain (Dogiel, "Arch. f. mik. Anat.," vol. XLl). SENSORY NERVK-ENDINGS. I 57 three forms of sensor}- endings and may be found in the papilla' or in the deeper connective tissue. A somewhat smaller nerve-ending of long, oval, or cylindric form, known as the cylindric end-bulb of Krause, is found in various parts of the skin and oral mucous membrane, in striated muscle and in tendinous tissue. These corpuscles consist of a thin nucle- ated capsule, investing a semifluid core. The nerve-fiber, after losing its medullar)' sheath and fibrous sheath (the latter becomes continuous with the capsule), passes through the core, generally without branching, as a naked axis-cylinder, terminating at its end, usually in a small bulb. (Fig. 134.) The majority of the sensory nerve-endings with well-developed lamellated capsules are relatively large structures. We shall con- sider especially the Vater-Pacin- ian corpuscles, the neuronitis- . ^ ... >.. ■■^ ra cular end-organs, and the neuro- tendinous end-organs. Vater-Pacinian C *orpuscles. — These corpuscles are of oval shape and vary much in size, the largest being about o. 10 of an inch long and 0.04 of an inch Fig . i 34 . _ Cylindric end-bulb of broad. The greater portion of Krause from intermuscular fibrous tissue the corpuscle is made up of a upturn of cat ; methylene-blue stain. series of concentric lamellae, vary- ing in number from twenty to sixty. These lamellae are made up of white fibrous tissue fibers, rather loosely woven, between which is found a small amount of lymph, containing usually a few leucocytes. The lamellae are covered on both surfaces by a layer of endothelial cells (Schwalbe). Between two consecutive lamellae there is found an interlamellar space, also containing lymph. The axis of the cor- puscle is occupied by a core, consisting of a semifluid, granular substance, in the periphery of which oval nuclei are said to be found. Usually one large medullated nerve-fiber goes to each cor- puscle. The fibrous tissue sheath of this nerve-fiber becomes con- tinuous with the outer lamellae of the capsule. The medullary sheath accompanies the axis-cylinder through the concentric lamel- lae until the core is reached, where it disappears. The naked axis- cylinder usually passes through the core to its distal end, where it divides into three, four, or five branches which terminate in large, irregular end-discs. The axis-cylinder may, however, divide soon after it enters the core into two or three or even four branches, these passing to the distal end of the core before terminating in the end-discs above mentioned. Both Retzius and Sala state that the naked axis-cylinders, after entering the core, give off numerous short side branches, terminating in small knobs, which remind these ob- servers of the fine side branches or thorns seen on the dendrites of Purkinje's cells and of the pyramidal cells of the cortex, when stained 1 5 8 THE TISSUES. after the Golgi method. In company with the large nerve-fibers here mentioned, Sala has described other nerve-fibers, quite independent of them and much finer, which after entering the corpuscle divide repeatedly, the resulting fibers forming a plexus around the central fiber. A small arteriole enters the corpuscle with the nerve-fiber, dividing into capillary branches found between the lamellae of the capsule. The Vater-Pacinian corpuscles have a wide distribution. They are numerous in the deeper parts of the dermis of the hand and foot, and also near the joints, especially on the flexor side. They have been found in the periosteum of certain bones and in tendons and intermuscular septa, and even in muscles. They are further found in the epineurial sheaths of certain nerve-trunks and near Fig- 135- — Pacinian corpuscles from mesorectum of kitten : A, Showing the fine branches on central nerve-fiber; B, the network of fine nerve-fibers about the central fiber; methylene-blue preparation (Sala, " Anat. Anzeiger," vol xvi). large vessels. They are numerous in the peritoneum and mesentery, pleura and pericardium. In the mesentery of the cat, where these nerve-endings are large and numerous, the)- are readily seen with the unaided eye as small, pearly bodies. In the bill and tongue of water birds, especially of the duck, are found nerve-endings, known as the corpuscles of I Icrbst, which re- semble the Vater-Pacinian corpuscles ; they differ from the latter in having cubic cells in the core. (Fig. 136.) Neuromuscular Nerve End-organs. — These nerve end-organs consist of a small bundle of muscle-fibers, surrounded by an invest- SENSORY NERVE-ENDINGS. 159 ing capsule, within which one or several sensory nerves terminate. They are spindle-shaped structures varying in length from O.75 to 4 mm., and in breadth, where widest, from So to 200 ji (Sherrington, 94). In them there is recognized a proximal polar region, an equatorial region, and a distal polar region. The muscle-fibers of this nerve-ending, known as the intrafusal fibers \ which may vary in number from 3 or 4 to 20 or even more, are much smaller than the ordinan' voluntary muscle-fibers and differ from them structur- ally, and result from a division of one or several muscle-fibers ol the red variety. In the proximal polar region the intrafusal fibers present an appearance which is similar to that of voluntary muscle- fibers of the red variety; in the equatorial region they possess rela- - Nucleus of lamellae. Axis-cylinder of nerve-fiber. Medullary sheath of nerve-fiber. Neurilemma and sheath of Henle. Fig. 136. — Corpuscle of Herbst from bill of duck ; X °°o. Technic No. 296. tively (c\v muscle-fibrils and are rich in sarcoplasm and the muscle- nuclei are numerous ; the striation is here indistinct. In the distal polar region the intrafusal fibers are again more distinctly striated and, a short distance beyond the end-organ, become greatly reduced in size, and terminate as very small fibers, still showing, however, a cross-striation. In figure 1 37 is shown a single intrafusal muscle- fiber. Owing to the length of such a fiber it was necessary to rep- resent it in several segments. The intrafusal muscle-fibers are surrounded by a capsule con- sisting of from four to eight concentric layers of white fibrous tissue. At the proximal end this capsule is continuous with the connective i6o THE TISSUES. tissue found between the muscle-fibers — endo- and perimysium. It attains its greatest diameter in the equatorial region of the nerve end-organ, and becomes narrower again at its distal end, where it mav end in tendon or become continuous with the connective tissue Fig. 137. — Intrafusal muscle-fiber from neuromuscular nerve end-organ of rabbit: A, From proximal polar region ; B, equatorial region ; C, distal polar region. of the muscle. Immediately surrounding the intrafusal fibers is found another connective -tissue sheath known as the axial sheath, and between this and the capsule there is found a lymph-space bridged over by trabecular of fibrous tissue, to which the name periaxial lymph-space has been given. (Fig. 138.) By degenerating the motor nerves going to a muscle, Sherrington Fig. 138. — Cross-section of a neuromuscular nerve end-organ from interosseous (foot) muscle of man ; fixed in formalin and stained in hematoxylin and eosin. determined that the nerve-fibers ending in the neuromuscular nerve end-organs were sensory in character. The manner of termination in these end-organs of the nerve-fibers ending therein has been studied by Kerschner, Kolliker, Rufftni, Huber and DcWitt, and others. SENSORY NERVE-ENDINGS. 161 One or several (three or four) large medullated nerves, surrounded by a sheath of Henle, terminate in each neuromuscular end- Fig- I39. — Neuromuscular nerve end-organ from the intrinsic plantar muscles of dog; from teased preparation of tissue Stained in methylene-blue. The figure shows the intrafusal muscle-fibers, the nerve-fibers and their terminations ; the capsule and the sheath of Henle are not shown ^Huber and DeWitt, "Jour. Comp. Neurol.," vol. vn). organ. As these nerves enter the capsule, the sheath of Henle blends with the capsule. The medullated nerve-fibers now and l62 THE TISSUES. ■A i r-< mb$j tt- 1 5 w then divide before reaching the nerve end-organs, and divide several times as they pass through the capsule, periaxial space, and axial sheath. Within the axial sheath, the medullary sheath is lost, and the naked axis-cylinders terminate in one or several ribbon - like branches which are wound circularly or spirally about the intrafusal fibers (anmilospiral % ending) or they may terminate in a S number of larger branches which again fi divide, these ending in irregular, round, oval, or pear-shaped discs (flower-like endings), which are also on the intra- g fusal fibers. These flower-like endings | are usually at the ends of the annulo- I spiral fibers. In the smaller end- ^ organs only one area of nerve-termi- nation has been observed ; in the larger, two, three, or even four such areas may be found. Neuromuscular nerve end-organs are found in nearly all skeletal muscles (not in the extrinsic eye muscles nor in the intrinsic muscles of the tongue), but the}" are especially numerous in the small muscles of the hand and foot. They are found in amphibia, reptilia, birds, and mammalia, presenting the same general structure, although the ultimate termination of the nerve-fibers varies somewhat in the different classes of vertebrates. Neurotendinous Nerve End -organ (Golgi Tendon Spindle). — In 1880 Golgi drew attention to a new nerve end-organ found in tendon, describing quite fully its general structure and less fully the nerve termination found therein. These nerve end-organs are spindle-shaped structures, which in man vary in length from 1.28 mm. to 1.42 nun., and in breadth from 0.17 mm. to 0.25 mm. (Kolliker). Ciaccio mentions a neurotendinous nerve end- .m found in a woman, which was 2 Fig. 140. - • Neurotendinous or 3 nun. long. A capsule consisting of nerve end-organ from rabbil ; teased from 2 to 6 fibrous tissue lamellae, and preparation of tissue tained in broadest at the equatorial part of the methylenc-DluefHuber and De Witt, ' . , . . "Jour. Comp. Neurol ," vol. x). end-organ, surrounds a number of m- ife H « <#■ i Mi m KY NERVE-ENDINGS. 163 trafusal tendon fasciculi. The capsule is continuous at the prox- imal and distal ends of the end-organ with the internal periten- dineum of the tendon in which it is found. The number of the intrafusal tendon fasciculi varies from eight to fifteen or even more. They are smaller than the ordinary tendon fasciculi, from which they originate by division, and structurally resemble embryonic tendon, in that they stain more deeply and present many more nuclei than fully developed tendon. The intrafusal tendon fasciculi are surrounded by an axial sheath of fibrous tissue, between which and the capsule there is found a periaxial lymph-space. m ■ J m y :, l_ t ^ — =^0* Fig. 141. — Cross-section of neurotendinous nerve end-organ of rabbit ; from tissue stained in methylene-blue : in, Muscle-fibers ; t, tendon ; < , capsule of neurotendinous end-organ ; m n, medullated nerve-fiber (Huber and DeWitt, " Jour, of Comp. Neurol.," vol. X). The termination of the nerve-fibers ending in these end-organs has been studied by Golgi, Cattaneo, Kerschner, Kolliker, Pansini, Ciaccio, Huber and DeWitt. One, two, or three large medullated nerve-fibers, surrounded by a sheath of Henle, end in each end- organ ; as they pass through the capsule, the sheath of Henle blends with the capsule. The medullated nerve-fibers before enter- ing the capsule usually branch several times, branching further within the capsule and axial sheath. Before the resultant branches terminate on the intrafusal tendon fasciculi, the medullary sheath is 164 THE TISSUES. lost, the naked axis-cylinder further dividing into two, three, or four branches, each of which runs along on the intrafusal fasciculi, giving off numerous short, irregular side branches, which partly enclasp the tendon fasciculi and end in irregular end-discs. Some of the ter- minal branches pass between the smaller fibrous tissue bundles of the fasciculi, ending between them. In these end-organs, the larger nerve-branches are found near the center of the bundle of intrafusal tendon fasciculi, the terminal branches and the end-discs nearer their periphery. The neuroten- dinous nerve end-organs are widely distributed, being found in all tendons although not equally numerous in all. Like the neuromus- cular nerve end-organs, they are especially numerous in the small tendons of the hand and foot. Sensory nerve end-organs, which resemble in structure the neurotendinous end-organs here described, though somewhat smaller than these, have been found in the tendons of the extrinsic eye-muscles. In this brief account of the mode of ending of the telodendria of the dendrites of peripheral sensory neurones (sensory nerve-fibers) it has not been possible to discuss any but the more typical varie- ties of sensory nerve-endings. Other nerve -endings will be consid- ered in connection with the several organs to be treated later. For a fuller discussion of this subject, the reader is referred to special works and monographs. TECHNIC. 173. Fresh medullated nerve-fibers, when teased in an indifferent fluid {rid. T. 13), show the peculiar luster of the medullary sheath, and also the nodes of Ranvier, the neurilemma with its nuclei, and the seg- ments of Lantermann. At the cut ends of the fibers, the typical coagula- tion of their medullary portions is seen in the form of drops of myelin. All these structures can also be seen after using 1 c / c osmic acid. A nerve (not too thick j is placed in a \ c / c aqueous osmic acid solution, then washed for a few hours in distilled water, and finally carried over into absolute alcohol. After dehydration, small pieces are cleared with oil of cloves and the fibers teased apart upon a slide. The medullary sheath is stained black and hides the axial space, the nodes are clear, the neu- rilemma is sometimes seen as a light membrane, and the nuclei of the fibers are of a lenticular shape, and stained brown. 174. The nodes of Ranvier may also be demonstrated by means of silver nitrate solution. Fresh nerve-fibers are either teased in distilled water to which a trace of 1% silver nitrate solution has been added (the nodes of Ranvier appear after a short time as small crosses^, or whole nerves are placed for twenty-four hours in a 0.5^ aqueous solution of. silver nitrate, washed for a short time with water, hardened in alcohol, after which they are imbedded in paraffin and cut longitudinally. Exposure to light will soon bring out the "crosses of Ranvier" at the nodes. The appearance of these crosses is due to the fact that the silver nitrate solution first penetrates at the nodes of Ranvier, and then - by capillary attraction along the axial cord for some distance. After the reduction of the silver, the cruciform figures appear colored Till'. NKRVOUS TISSUES. i6i black. Occasionally, a peculiar transverse striation is seen in the longi- tudinal portions of the crosses. These are known as Frommann's lines. Their origin and significance have not as yet been satisfactorily ex- plained. 175. To demonstrate the fibrils of the axial cord a piece of a small nerve is stretched on a match or toothpick and fixed for four hours in a o.$'/o osmic acid solution, after which it is washed in water for the same length of time and immersed in 90$ alcohol for twenty-four hours. The preparation is now stained for another twenty-four hours in a saturated aqueous solution of fuchsia S and then placed for three days in abso- lute alcohol. Finally, the nerve is passed as rapidly as possible through toluol, toluol -paraffin, and then im- bedded in paraffin. The proper orientation of the specimen is of the greatest importance, as is also the cutting of thin sections. In a lon- gitudinal section red fibrils of almost uniform thickness and evenly dis- tributed throughout the axial space are seen lying in the colorless neuro- Medullary sheath. Axis-cylin- der. Fig. 142. — Ranvier's crosses from sci- atic nerve of rabbit ; \ 120. Technic No. 174. Frommann's lines can be seen in a few fibers. Fig. 143. — Medullated nerve-fiber from sciatic nerve of frog. In two places the medullar}' sheath has been pulled away by tea-inn;, showing the " naked axis-cylin- der" ; X 212 - Technic No. 176. plasm, and parallel to the long axis of the nerve-fiber. In cross-section the axial fibrils appear as evenly distributed dots. Attention must be called to the fact that the fibrils are not equally well stained in all cases (Kupffer, 83, II ; compare also Jacobi and Joseph). 176. When the fiber is less carefully treated, the fibrils fuse with the neuroplasm to form the "axis-cylinder" of authors. As the appearance of the latter is due to a shrinkage of the contents of the axial space, it is easy to understand that one reagent may have a greater effect in this re- spect than another. The thinnest axis-cylinders are produced by chromic acid and its salts, while thicker ones are seen in nerve-fibers fixed in alcohol. These variations are best seen in cross-sections, in which the 1 66 THE TISSUES. Dendrite. axis-cylinders sometimes appear as round dots and again as stellate figures. The latter are due to pressure on the shrinking axial cord by the unevenly coagulated medullary sheath. As the medullary sheath in such preparations crumbles away in many places, large areas of the axis-cylinder may often be isolated by teasing ( Fi g- J 43)- 177. If freshly teased fibers be treated with glacial acetic acid, the axis-cylinders swell up and issue from the ends of the fibers in irregular masses showing fine longitudinal striation (Kolliker, 93). The structures of the axial space dissolve in x'j ( hydrochloric acid, as well as in a 10% solution of sodium chlorid (Halliburton). 178. For the isolation of ganglion cells, 33^ alcohol, 0.1 to 0.5% chromic acid, or 1 '/ (: solution of potassium bichromate may be used. Small pieces of the spinal cord and brain containing ganglion cells are treated with a small quantity of one of the above solutions for one or two weeks. After this interval the prepara- tions may be teased and the isolated ganglion cells stained on a slide and mounted in glycerin. They may even be fixed in situ by injecting a 1 ) white blood-corpuscles (leucocytes) ; and (0) the blood platelets of Bizzozero (82), Hayem. Besides these, there are present particles of fat, and, as H. F. Miiller (96) has recentlv shown, also hemokonia. 2. RED BLOOD-CORPUSCLES. In man and nearly all mammalia the great majority of the red blood-corpuscles are nonnucleated, biconcave circular discs with rounded edges. They have smooth surfaces, are transparent, pale yellow in color, and very elastic. No method has as yet been devised to demonstrate a nucleus in these cells, and there is no doubt that the red blood-discs of the human adult and of mammalia are devoid, in the histologic sense, of a nucleus capable of differen- tiation (compare Lavdowsky ; Arnold, 96). They are therefore peculiarly modified cells. If fresh blood be left for some time undisturbed, the blood-discs adhere to each other by their flattened surfaces, grouping them- selves in rouleaux. By certain reagents the clear and transparent contents of the blood-corpuscles can be separated into two substances — a staining and a nonstaining. The first consists of the blood pigment, or hemoglobin, which can be dissolved ; the second of a colorless sub- stance, the stroma, which presents itself in various forms (protoplasm of the cell). Hemoglobin is a very complex proteid which may be decom- posed into a globulin and a pigment hcviatiti. The hemoglobin of the majority of animals crystallizes in the form of rhombic prisms ; in the squirrel, however, in hexagonal plates, and in the guinea-pig in tetrahedra. Hematin combines with hydrochloric acid to form hemin, or Teichmann's crystals, of brownish color, rhombic shape, and microscopic size. They are of much value in lego-medical I70 BLOOD AND BLOOD-FORMING ORGANS. work, since they may be obtained from blood, no matter how old, and are characteristic of hemoglobin. They may be obtained from very small quantities of blood pigment. The stroma probably contains the hemoglobin in solution. The question as to whether the erythrocytes possess a membrane or not is difficult to answer, although in all probability they do (Lav- dowsky). If a small drop of blood pressed from a small puncture is placed on a slide and covered with a cover-glass, the red blood- cells soon become changed. This is due to the evaporation of water in the blood plasma, causing an increased concentration of the sodium chloride contained, which in turn draws water from the blood-cells The shrinkage which follows produces a characteristic Fig. 145.— Hu- man red blood-cells ; 1 500 : a, As seen from the surface ; b, as seen from the edge. Fig. 146. — So-called "rouleau" formation of human erythrocytes ; X 1500. Fig. 147. — Hemin, or Teichmann's crystals, from blood stains on a cloth. Fig. 148.- Crenated " human red blood- cells ; X '500. Fig. 149.— Red blood-corpuscles sub- jected to the action of water ; X I 5°° : a > Spheric blood-cell ; b, "blood shadow." change in the form of the cells, which assume a crenated or stellate shape. The red blood-cells of blood mounted in normal salt become crenated in a short time for the same reason. Red blood- cells are variously affected by different fluids. In water they become spheric and lose their hemoglobin by solution. Their remains then appear as clear, spheric, indistinct blood shadows, which may, how- ever, be again rendered distinct by staining with iodin. Dilute acetic acid has a similar but more rapid action, with this peculiarity, that before becoming paler the blood-cells momentarily assume a darker hue. Bile, even when taken from the animal furnishing the blood, exerts a peculiar influence upon the red blood-cells ; they first become distended, and then suddenly appear to explode into BLOOD AND LYMPH. 171 small fragments. Dilute solutions of tannic acid cause the hemo- globin to leave the blood-cells, and coagulate in the form of a small globule at the edge of the blood-cell. In alkalies of moderate strength the red blood-cells break down in a few moments. Besides the disc-shaped red blood-cells, every well-made prep- aration shows a few small, spheric, nonnucleated cells containing hemoglobin. These, however, have received as yet but little attention. M. Bethe makes the statement that human blood and the blood of mammalia contain corpuscles of different sizes, bearing a definite numerii al relationship to each other. " If they be classified according to their size, and the percentage of each class be calculated, the result will show a nearly constant proportional graphic curve varying hut slightly, according SOG? Fig. 150. — Red blood-corpuscles from various vertebrate animals ; V 1000 (YYelker's model) : a, From proteus (Olm) ; /', from frog ; c, from lizard ; d, from sparrow ; e, from camel ; fa.n&g, from man ; //, from myoxus glis ; i, from goat ; k, from musk-deer. to the animal species." According to M. Bethe, dry preparations of human and animal blood may be distinguished from each other, with the exception of the blood of the guinea-pig which presents a curve identical with that of human blood. The red blood-cells of mammalia, excepting those of the llama and camel species, are in shape and structure similar to those of man. The red blood-cells of the llama and camel have the shape of an ellipsoid, flattened at its short axis, but also nonnucleated. We have already made mention of the fact that the embryonal erythrocytes are nucleated ; the question now arises as to how, in the course of their development, they lose their nuclei. Three pos- sibilities confront us : First, either the embryonal blood-cells are destroyed and gradually replaced by previously existing nonnucle- \J2 BLOOD AND BLOOD-FORMING ORGANS. ated elements ; or, second, the nonnucleated red cells are formed from the nucleated by an absorption of the nucleus (or what appears to be such to the eye of the observer, Arnold, 96) ; or, finally, the nucleus is extruded from the original nucleated cell. According to recent investigations (Howell) the third possibility represents the change as it actually takes place. In all vertebrate animals except mammalia, the red blood- corpuscles are nucleated. They are elliptic discs with a biconvex center corresponding to the position of the nucleus. The blood- cells of the amphibia (frog) are well adapted for study on account of their size. They are long and, as a rule, contain an elongated nucleus with a coarse, dense chromatin framework, which gives them an almost homogeneous appearance. The cell-body may be divided, as in mammalia, into stroma and hemoglobin. When sub- jected to certain reagents, the contour of the cells appears double and sharply defined. This condition is, however, no proof of the existence of a membrane ; yet, as modern observers have demon- strated, a membrane may be totally or partly isolated (Lavdow- sky). The blood-cells of birds, reptiles and fishes are similarly constructed. The diameter of the erythrocytes varies greatly in different ver- tebrate animals, but is constant in each species. We append a table of their number in a cubic millimeter and size in man and certain animals as compiled by Rollett (71, II) and M. Bethe : Species. Man {Homo) . . . Monkey (Cercopith. rubt Hare (Lepus cuniculus) Guinea-pig (Cavia cob.) . . Dog . (Cants fa in.) . . Cat (Felts do fit. Horse (Equuscab.) . Musk-deer (Moschtts jar.} Spanish goat (Capra his.) Domestic chaffinch .... (Fringilla clout. Dove (Columba) . . . Chicken ( Gallus dont. ) . Duck (Anas bosch.) Tortoise (Testudo gnrca) Lizard (Lacerla agil.) . Snake (Coluber natr.) . Frog (Rana temp. ) Toad (Bufo vulg.) . . Triton (Triton crist.) . Size. 5-58 2-5 4-25 • Length, Breadth, L. B. L. B. L. B. I.. B. L. I:. L. is. I.. B. I.. B. L. B. 11. 9 6.8 14-7 6.5 12. 1 7.2 12.9 8.0 21.2 12.45 15-75 0.1 22.0 13.0 22.3 15-7 21.8 15-9 29-3 19-5 No. IN Cubic Milli- meter. 5,000,000 6,355, °°° 6,410,000 5,859,500 6,650,000 9,900,000 7,403,500 19,000,000 2,010 000 629,000 1,292,000 829,400 393,200 389,000 103,000 BLOOD AND LY.MI'H. i/3 Sim . n s. Salamander {Salamandra mac. ) I Proteus angu.) Sturgeon {Acipenser St.) . . Carp [Cyprinus Gobio) . Size, • Length, 37.8 Breadth, 23.8 I. 58 B. 35 • I- 13-4 II. IO.4 I.. 17.7 B. 10. 1 No. IN Milli Ml-. I I R, 80,000 35.O0O 3. WHITE BLOOD-CORPUSCLES. The white blood-cells contain no hemoglobin and arc nucleated elements which, under certain conditions, possess ameboid move- ment. Their size varies from 5 u to 10//, and they are less numer- ous than the red blood-corpuscles, one white blood-cell to from three hundred to five hundred red cells being a normal proportion. In / c Fig. 151. — From the normal blood of man; X I2 °° (from dry preparation of H. F. Miiller) : a, Red blood-cell; />, lymphocyte; c and & "* - Epithelium "•-ra»ei?«»n examining a section of the spleen with the low-power mag- nifying glass, sections of the trabecular, and round or oval masses of cells, having a diameter of about 0.5 mm., and in structure and ntv.'A " - - _~ - ' - - " '- J^J^'^i Trabecula. i-X'j >»tfty. " SnU'en ]iul|i. ^m^ fi m Trabecula. •fr^- -Artery. iY: i h|_ Malpighian c .'".'■ '•'■•■'' '"■■ ■ ■:■'•'.■■•.■' ': ^'/^''^r^''"'- : . ■?:.': L'crm centei TV ■ v. cor- th perm center. - or Fig. 156. — Part of a section through the human spleen ; X 75- (Sublimate fixation.) At a is an oblong Malpighian body with a blood-vessel. appearance similar to the lymph-nodules (Malpighian corpuscles), are clearly defined ; between and around these structures is a tissue rich in cells, blood-vessels and blood-corpuscles, known as the spleen pulp. The organ has a very typical blood supply. Its arteries enter at the hilum, or indented surface, and its veins pass out at the same place. On the penetration of the vessels through the capsule, the latter forms sheaths around them (trabecular), but as soon as the arteries and veins separate, the trabecular envelop the veins alone. 1 82 BLOOD AND BLOOD-FORMING ORGANS. The arteries break up into smaller branches, which in turn divide into a large number of tuft-like groups of arterioles. Soon after their separation from the veins, the adventitia (outer fibrous tissue coat) of the arteries begins to assume a lymphoid character. This lymphoid tissue increases here and there to form true lymphoid nodules, pos- sessing all the characteristics already mentioned — reticular tissue, germ centers, etc. These are the Malpighian bodies, or corpuscles ; they are not very plentifully represented in man. The Malpighian bodies with their germ centers are formative centers for the lympho- cytes. The newly formed cells pass into the pulp and mix with its elements, which are then bathed by the blood emptying from the arterial capillaries into the channels of the pulp. The lymphoid sheaths and nodules derive their blood supply from arteries which arise from the lateral branches of the splenic vessels, and which divide into capillaries inside of the lymph sheaths or nodules, and only assume a venous character outside of the lymphoid substance. These vessels constitute the nutritive vascular system of the spleen. The small arterial branches above mentioned break up into very fine arterioles which gradually lose their lymphoid sheath, so that branches with a diameter of 0.02 mm. no longer possess a lymphoid sheath, but again assume an adventitia of the usual type. The smallest arterioles now pass over into capillaries which are for a time accompanied by the adventitia (capillar) 7 sheath), while the terminal branches have the usual structure of the capillary wall and are gradually lost in the meshes of the pulp. (See below.) On the other hand, the beginnings of the venous capillaries may be dis- tinctly seen in the pulp spaces. Groups of these capillaries com- bine to form larger vessels, which, however, still retain a capillary structure, and these again form small veins which unite to form the larger veins. F. P. Mall, whose recent contributions on the structure of the spleen have greatly extended our knowledge of the microscopic anatomy of this organ, states that the trabecular and vascular systems together outline masses of spleen pulp about 1 mm. in diameter, which he has named spleen lobules. Each lobule is bounded by three main in- terlobular trabecular, each of which sends three intralobular trabe- cular into the lobule which communicate with each other in such a manner as to divide the lobule into about ten smaller compartments. An artery enters at one end of the lobule and, passing up through its center, gives off a branch to the spleen pulp found in each of the ten compartments formed by the intralobular trabeculae. The spleen pulp in these compartments is arranged in the form of anastomosing columns, or cords, to which Mall has given the name of pulp cords. The branches of the main intralobular artery, going to each compartment, divide repeatedly ; the terminal branches course in the spleen-pulp cords, and in their path give off numerous small side branches which end in small expansions known as the ampulla of Thoma. "The first two-thirds of the ampulla are lined THK SPLEEN. 183 with spindle-shaped cells lying on a delicate framework of reticulum. Through the last third, at the junction with the vein, no cell bound- aries can be demonstrated. In fact, it appears as if this portion of the ampulla were cut up by fibrils of the reticulum passing across it " ( F. P. Mall). The veins of the lobule begin in a system of venous -paces surrounding the pulp cords. These are in communication with intralobular veins, often asso< iated with intralobular trabecular, and the latter empty into the interlobular veins found in some of the interlobular trabecule. F. P. Mall further states that " the ampullae and venous plexus have very porous walls, which permit fluids to pass through with great ease and granules only with difficult) - . In life the plasma constantly flows through the intercellular spaces of the pulp cords, while the blood-corpuscles keep within fixed channels." The accompanying diagram (Fig. 157), slightly, though immate- Intralobular trabecula. Artery to one of the ten compartments. Intralobular artery. Interlobular trabecula Intralobular trabecula. Malpighian corpuscle. Capsule. Intralobular venous spaces. Intralobular vein. Ampulla of Thoma. — Spleen pulp cord. Interlobular vein. - Intralobular vein. Fig- 157. -Diagram of lobule of the spleen (Mall, " Johns Hopkins Hospital Bulletin," Sept., Oct., 1898)." rially, modified from one given by Mall, shows clearly the trabecular and vascular systems of a spleen lobule. In larger spleens there may be some two hundred thousand of these lobules. In a dog weighing 10 kg. there are on an average some eighty thousand (F. P. Mall). The splenic pulp consists of a very delicate reticulum, in the meshes of which are found ( [) fully developed red blood-cells ; (2) now and then nucleated red blood-cells ; (3) in many animals giant cells ; (4) cells containing red blood-corpuscles and the remains of such, with or without pigment ; (5) the different varieties of white blood-cells, especially a relatively large proportion of mononuclear leucocytes. Pigment granules, either extra- or intracellular, also occur in the splenic pulp. The pigment probably originates from disintegrating erythrocytes. Besides these are found, especially in 1 84 BLOOD AND BLOOD-FORMING ORGANS. teased preparations, long, spindle-shaped and flat cells, which are probably derivatives of the connective-tissue cells of the pulp and of the endothelium and muscular fibers of the vessels. 7 .-- 8 V Fig. 15S. — Cells containing pigment, blood-corpuscles, and hemic masses from the spleen of dog; X '800 (from cover-glass of II. F. Miiller). Fig. 159. — From the human spleen ; Y 80 (chrome-silvn method): , lymphocyte; c, eosinophile cell; d, red blood-cell ; e, erythroblast in process of division ; f, _/", normoblast ; g, erylhroblast. Myelocyte not shown in this figure. larly by the presence of neutrophile granules not found in the mononuclear leucocytes. 2. Nucleated Red Blood-cells containing Hemoglobin. — Two varieties of these cells are recognized structurally, with interme- diary stages, as one variety is developed from the other. The crytlirablasts, being genetically the earlier cells, possess relatively large nuclei with distinct chromatin network, surrounded by a protoplasm tinged with hemoglobin, and are often found in a stage of mitosis. The other variety of nucleated red blood-cells, the normoblasts, are developed from the erythroblasts. They contain globular nuclei, staining deeply, in which no chromatin network- is recognizable, and surrounded by a layer of protoplasm containing hemoglobin. The normoblasts are changed into the nonnucleated THE BONE-MARROW. 1S7 red blood-discs by the extrusion of the nucleus. This pro occurs normally in the red bone-marrow, or in the venous sp of the bone-marrow (see below). In certain pathologic conditions, nucleated red blood-cells are found in the circulation. 3. Cells with Eosinophile Granules. — In the red bone-marrow are found numerous eosinophile (acidophile) cells, some with round or oval nuclei (mononuclear eosinophile cells), others with horse- shoe-shaped nuclei (transitional eosinophile cells), and still others with polymorphous nuclei. The latter, which are the most numer- ous, are no doubt the mature cells, and are identical with those elements of the blood having the same structure. %*/"''' J # „ lr< 7 f A. * v ' m : S O s Fig. 161. — From a section through human red bone-marrow; .' 680. Technic No. 216 : a,f, Normoblasts ; b, reticulum ; c, mitosis in giant cell ; d, giant cell ; e, A, myelocytes ; g, mitosis ; /', space containing fat-cells. 4. The various forms of leucocytes and the lymphocytes found in blood and lymph. 5. The giant cells (myeloplaxes), which are situated in the center of the marrow, and contain simple or polymorphous nuclei, or lie adjacent to the bone in the form of osteoclasts, which are, as a rule, polynuclear (compare p. 1 1 1 ). The physiologic significance of the giant cells is still obscure. They probably originate from single leucocytes by an increase in size of the latter, and not, as many assume, from a fusing of several leucocytes. The giant cells are endowed with ameboid movement, and often act as phagocytes (the latter quality is denied them by M. Heidenhain, 94). BLOOD AND BLOOD-FORMING ORGANS. M. Heidenhain (94) has made a particular study of the giant cells. According to him the nuclei of these cells take the form of per- forated hollow spheres whose thick walls contain "endoplasm." The latter is continuous with the remaining protoplasm of the cell, the " exo- plasm " through the "perforating canals" of the nuclear wall. The exoplasm is arranged in three concentric layers, separated from each other by membranes, the external membrane of the outer zone being the membrane of the cell. The outer layer or marginal zone is of a transient nature, but is always renewed by the cell. Thus, the cell-membrane is replaced by the secondary membrane situated between the second and third zone. According to the same author the functions of the giant cells appear to consist in " the selection and elaboration of certain albu- minoid substances of the lymph and blood currents, which are later returned to the circulation." The number of centrosomes occurring in the mononuclear giant cells of the bone-marrow is very large, and in some cases, as in a pluripolar mitosis, may even exceed one hundred in number. The distribution of the blood-vessels in the bone-marrow is as follows : On entering the bone the nutrient arteries divide into a large number of small branches, which then break up into small arterial capillaries. The latter pass over into relatively large venous capillaries, whose walls either finally disappear entirely or are broken through in many places so that the venous blood pours into the spaces of the red bone-marrow where the current is very slow. The blood passes out by means of smaller veins formed by the conflu- ence of the capillaries which collect the blood from the marrow. It is worth mentioning that the venous vessels, while inside of the bone-marrow, possess no valves ; but, on the other hand, they have an unusually large number of valves immediately after leaving the bone. Yellow bone-marrow is derived from red bone-marrow by a change of the marrow-cells into fat-cells. The gelatinous marrow, on the contrary, is characterized by the small quantity of fat which it contains. Neither the yellow nor the gelatinous bone-marrow is a blood-forming organ (compare Neumann, 90; Bizzozero, 91 ; H. F. Muller, 91 ; van der Stricht, 92). E. THE THYMUS GLAND. The thymus gland is usually considered as belonging to the lymphoid organs, although in its earliest development it resembles an epithelial, glandular structure. In the epithelial stage, this gland develops from the entoderm of the second and third gill clefts. Mesoderm ic cells grow into this epithelial structure, proliferate and then differentiate into a tissue resembling adenoid tissue. It retains this structure until about the end of the second year after birth, when it slowly begins to retrograde- into a mass of fibrous tissue, adipose tissue, and cellular debris, which structure it presents in adult life. THE TIIYMI S '.LAND. IS9 By means of connective-tissue septa, the thymus is divided into larger lobes, and these again into smaller lobes, until finally a number of very small, almost spheric structures are formed — the lobules of" the gland. These consist of a reticular connective tissue- much more delicate at the periphery than at the center of the • W fm Fig. 162. — A small lobule from the thymus of child, with well-developed cortex, presenting a structure -imilar to thai of the cortex of a lymph-gland; ■ 60: se, n< mmedullated nerve-fibers — form intricate plexuses situated under the pericardium and, penetrating the myo- cardium, surround the bundles of heart muscle-fibers. From the varicose nerve-fibers constituting these plexuses, fine branches are given off, which terminate on the heart muscle-cells in a manner previously described (see p. 149 and Fig. 127). The cell-bodies of the sympathetic neurones, the neuraxes of which thus terminate on the heart muscle-fibers, are surrounded by end-baskets, the telodendria of small medu Hated nerve-fibers which reach the heart through the vagi. The slowed and otherwise altered action of the heart-muscle, produced on stimulating directly or indirectly the vagus nerves is therefore due not to a direct action of these nerve- fibers on the heart muscle-cells, but to an altered functional activity produced by vagus stimuli in at least some of the sympathetic neu- rones situated in the heart, the neuraxes of which convey the im- pulse to the heart muscle. The heart receives further nerve supply through sympathetic neurones, the cell-bodies of which are situated in the inferior cervical and stellate ganglia, the neuraxes of which enter the heart as the augmentor or accelerator nerves of the heart. The mode of ending of these nerve-fibers has not as yet been fully determined. It may be suggested as quite probable that they ter- minate on the dendrites of sympathetic neurones, the cell-bodies of which are not inclosed by end-baskets of nerves reaching the heart through the vagi, as above described. It is also possible that they end directly on the heart muscle-cells. The cell-bodies of the sympathetic neurones, the neuraxes of which form the augmentor nerves, are surrounded by the telodendria of small medullated fibers, forming end-baskets, which leave the spinal cord through the anterior roots of the upper dorsal nerves. Besides the nerves here described, nonmedullated nerves (whether the neuraxes of sympa- thetic neurones, the cell-bodies of which are situated inside or out- side of the heart has not been fully determined), form plexuses in the walls of the coronary vessels, terminating, it would seem, on the muscle-cells of the media (vasomotor nerves). 2. THE BLOOD-VESSELS. A cross-section of a blood-vessel shows several coats. The inner consists of flattened endothelial cells, and is common to all vessels. The second varies greatly in thickness, contains most of 13 194 THE CIRCULATORY SYSTEM. the contractile elements of the arterial wall, and is known as the media, or tunica media. Its elastic fibers have in general a circular arrangement and are fused at the inner and outer surfaces to form fenestrated membranes, the lamina elastica interna and externa. Outside of the media lies the adventitia or tunica externa, consist- ing in the arteries almost entirely of connective tissue and in the veins principally of contractile elements, smooth muscle-fibers. Between the internal elastic membrane and the endothelial layer is a fibrous stratum which varies in structure in the different vessels of larger caliber. This is the subendothelial layer, or the inner fibrous layer, and forms, together with the endothelium, the intima Intima. Endothelium of the intima. > Media. Fenestrated elastic mem- brane. Elastica ex- terna. Inner layer of adventitia. Outer layer of adventitia. Yasa vasorum. '. Fig. 164. — Cross-section of the human carotid artery ; X I 5°* or tunica intima. Bonnet (96), as a result of his own investigations, suggests a somewhat different classification of the layers composing the arterial wall. According to him, the endothelium alone con- stitutes the intima. The elastic membranes, both internal and external, together with the tissue lying between them, and that between the internal elastic membrane and the intima, constitute the media. The tissue layers outside the external elastic membrane form the tunica externa (adventitia). (a) Arteries. — In the great arterial trunks, such as the pulmo- nale, carotis, iliaca, etc., the tunica media possesses a very typical structure. It is divided by means of elastic fibers and membranes THE VASC1 I \l< SYSTEM '95 (fenestrated membranes) into a large number of concentric layers containing but few muscle-fibers. Here also the tunica media is separated from the intima by an elastic limiting membrane, the fenestrated membrane of Henle, or the lamina elastica interna. In the aorta this membrane as such is not recognizable. The intima presents three distinct layers — the inner composed of flattened endo- thelial cells, and the other two consisting chiefly of elastic tissue (fibrous layers). Of these latter the inner is the richer in cellular Endi ithelium of the intima, [ntima. . Media. Adventitia with nonstriated mus- c!e-fib. Precapillary artery ; /', precapillary vein possessing no muscu- lar tissue. 196 THE CIRCULATORY SYSTEM. the media is limited externally by the external elastic membrane. The adventitia, which becomes looser externally, is not so well de- veloped as in the larger vessels, but presents in general the same structure. In certain arteries (renal, splenic, dorsalis penis) it shows in its inner layers scattered longitudinal muscle-cells, which, how- ever, may also occur in other arteries at their points of division. With regard to the elastic tissues, the arteries of the brain differ to some extent from those of the remainder of the body. The elastica interna is much more prominent, the elastic fibers in the Intima. Elastica interna. S „ r Media. ~ ' - <• ■ '■' **».•%.«*■. - »_-^ «■ -- _ Blood- -IJ^/tfU „ ' .. " -'• - S •*• «. . ••<>■ t -t m Fenestrated elastic membrane. Inner layer of the adventitia with . ■ longitudinally ar- ranged muscle- cells. Connective tissue of the adventitia. ^•V^-Nerve. Fig. 167. — Cross-section of human internal jugular vein. At the left of the nerve are two large blood-vessels with a smaller one between them (vasa vasorum) ; X I S°- circular muscular layer are few r, and the longitudinal strands are almost entirely lacking (H. Triepel). The walls of the smaller arteries consist mainly of the circular muscular layer of the media. The intima is reduced to the endo- thelium, which rests directly on the elastic internal limiting mem- brane. Outside of the external limiting membrane is the adventitia, which now consists of a small quantity of connective tissue. The vasa vasorum have disappeared. To this type belong the supra- orbital, central artery of the retina, etc. In the so-called precapillary vessels the intima consists only THE VASCULAR SYSTEM. 1 97 of the endothelial layer. The internal clastic membrane is very delicate. The media no longer forms a continuous layer, but is made up of a few circularly disposed muscular fibers. The adven- titia is composed of a small quantity of connective tissue, and con- tains no vasa vasorum. (/>) Veins. — In the foregoing account of the structure of the arteries we have described the structure of their walls according to the caliber of the vessels. Such a differentiation in the case of the veins would be impossible, since sometimes veins of the same cali- ber present decided differences in structure in various parts of the body. For the sake of convenience, we will commence with the de- scription of a vein of medium size. Its intinia consists of three layers : (i) Of an inner layer of endothelium ; (2) of an underly- ing layer of muscle-cells, interrupted here and there by connective tissue ; and (3) of a fibrous connective-tissue layer containing fewer elastic but more white fibrous connective-tissue fibers than is the case in the arteries. Externally, the intima is limited by an in- ternal elastic layer. The media is in general less highly developed than that of a corresponding artery, and contains muscle-cells 'f^«§/ 1 W^^Ji&? ~r'H^\- Adventitia with .... , r - r .- .-- .-' - - nonstriated which have a circular ar- .. muscle-ceils , I in cross-sec rangement and in some t k>n. veins form a continuous layer, although they some- times OCCUl" as isolated fi- Fig. 168. — Section of small vein (human); > 640. bers. The adventitia shows an inner longitudinal muscular layer, which may be quite promi- nent and even form the bulk of the muscular tissue in the wall of the vein. Otherwise the adventitia of the veins belonging to this class corresponds in general to that of the arteries of the same size ; but here also we have, as in the intima, a preponderance of white fibrous connective-tissue elements. In the crural, brachial, and subcutaneous veins, the muscula- ture of the media is prominent ; while in the jugular, subclavian, and innominate veins, and in those of the dura and pia mater, the muscular tissue of the media is entirely wanting, and, as a conse- quence, the adventitia with its musculature, if present, is joined directly to the intima. In the smaller veins the vascular wall is reduced to an endothe- lial lining, an internal elastic membrane, a media consisting of interrupted circular bands of smooth muscle-fibers (which may be absent), and an adventitia containing a few muscle-fibers. The precapillary veins, which possess in general thinner walls than the corresponding arteries, present a greatly reduced intima and ad- ventitia, while the media has completely disappeared. io8 THE CIRCULATORY SYSTEM. The valves of the veins are reduplications of the intima and vary slightly in structure at their two surfaces. The inner surface next to the blood current is covered by elongated endothelial cells, while the outer surface possesses an endothelial lining composed of much shorter cellular elements. The greater part of the valvular structure consists of white fibrous connective-tissue and elastic fibers. Flattened and circularly arranged muscle-cells are met with at the inner surface of many of the larger valves. The elastic fibers are more numerous beneath the endothelium on the inner surface of the valves ( Rainier, 89). ( <) The Capillaries. — The capillaries consist solely of a layer of endothelial cells, accompanied here and there by a very delicate struc- tureless membrane, and rarely by stellate connective-tissue cells. The connective tissue in the immediate neighborhood of the capillaries is modified to such an extent that its elements, especially those of a cellular nature, seem to be arranged in a direction parallel with the Fig. 169. — Endothelial cells of capillary [a) and precapillary (/;) from the mesentery of rabbit ; stained in silver nitrate. long axis of the capillaries. When examined in suitable prepara- tions, the endothelium of the capillaries is seen to form a continuous layer, the cells of which are, as a rule, greatly flattened and present very irregular outlines. It is a well-known fact that a migration of the leucocytes occurs from the capillaries and smaller vessels (compare p. 175). In this connection arises the question as to whether or not the cells pass through certain preformed openings in the endothelium of these vessels, the so-called stomata, or through the stigmata and intercel- lular cement uniting the endothelial cells. The latter seems more probable, as stomata do not occur normally in the capillary wall. This subject will be further touched upon in the description of the lymphatic system. The capillaries connect the arterial and venous precapillary ves- sels, and in general accommodate themselves to the shape of the elements of tissues or organs in which they are situated. In the I in VASCU1 \i< SYS1 I M. 199 muscles and nerves, etc., they form a network with oblong meshes, while in structures having a considerable surface, such as the pul- monary alveoli, the meshes are more inclined to be round or oval ; such small examinations of tissue as the papillae of the skin contain capillaries arranged in the shape of loops. In certain organs — as, for instance, in the lobules of the liver — the capillaries form a distinct network with small meshes. (f cellular cords, or trabecular, the elements of which are extremely sensitive to the action of reagents. The cells are round or irregularly polygonal and separated from each other by a scanty reticular connective tissue. The capillaries already mentioned come in direct contact THE CAROTID (.LAND. 203 with the cells of the cell-balls. The organ contains a relatively large number of nerve-fibers and a few ganglion cells. As the individual grows older, the organ undergoes changes which finally make it unrecognizable. The former belief that the carotid gland was developed as an evagination of one of the visceral pouches has been replaced by a newer theory which gives it an origin solely from the vessel-wall (;■!>(. Schaper). The structure of the coccygeal gland is in general like that of the carotid gland here described. Septum. Fig. 171. — Section of a cell-ball from the glomus enroticum of man ; X IDO - (Injected specimen, after Schaper.) TECHNIC (BLOOD AND BLOOD-FORMING ORGANS^. 184. Red blood-corpuscles may be examined in the blood fluid without special preparation. The tip of the finger is punctured and a small drop of blood pressed out, placed upon a slide, and immediately covered with a cover-glass and examined. In such preparations the red blood- cells soon become crenated. The evaporation causing the crenation may be prevented by surrounding the cover-glass with oil (olive oil). A fluid having but a slight effect upon the red blood-cells is Hayem's solution, which, however, is not adapted to the examination of leucocytes. It consists of sodium chlorid 1 gm.. sulphate of soda 5 gm., corrosive subli- mate 0.5 gm., and water 200 gm. The fresh blood is brought directly into this solution, the amount of which should be at least one hundred times the volume of the blood to be examined. The fixed blood-cells sink to the bottom, and after twenty-four hours the fluid is carefully poured off and replaced by water. The blood-corpuscles are then removed with a pipet and examined in dilute glycerin. They may be stained with eosin and hematoxvlin. 204 THE CIRCULATORY SYSTEM. 185. Fresh red blood-corpuscles may also be fixed in osmic acid and other special fixing agents. 'This is done by dropping a small quantity of blood into the fixing fluid ; the blood-cells immediately sink and allow the osmic acid to be decanted ; they are then washed with water, drawn up with a pipet, and examined in dilute glycerin. 186. A method almost universally used consists in preserving the blood-corpuscles in dry preparations. A drop of fresh blood is placed between two thoroughly cleaned cover-glasses, which are then quickly drawn apart, leaving on the surface of each a thin film of blood which dries in a few moments at ordinary room temperature. The specimens are further dried for several hours at a temperature of i2o°C. After they have been subjected to this process, they may be stained, etc. 187. The same results may be obtained by treating specimens dried in the air with a solution of equal parts of alcohol and ether for from one to twenty-four hours, after which they are again dried in the air, and are then ready for further treatment. 188. A cover-glass preparation of fresh blood may also be treated for a quarter of an hour with a concentrated solution of corrosive sublimate in saline solution, then washed with water, stained, dehydrated with alcohol and mounted in Canada balsam. A concentrated aqueous solution of picric acid may also be used, but in this case the specimen should remain in it for from twelve to twenty-four hours. 189. The elements of the blood may also be examined in sections. Small vessels are ligated at both ends, removed, fixed with osmic acid, corrosive sublimate, or picric acid, and imbedded in paraffin. igo. After fixation by any of the above methods the blood-cells may be stained. Eosin brings out very well the hemoglobin in the blood- cells, coloring it a brilliant red ; the stain should be used in very dilute aqueous or alcoholic solutions (i°/v or less), or in combination with alum (eosin 1 gm., alum 1 gm., and absolute alcohol 200 c.c, E. Fischer). Eosin may also be used as a counterstain subsequent to a nuclear stain — for instance, hematoxylin. The preparation is stained for about ten min- utes, then washed in water or placed in alcohol until the blood-cells alone remain colored ; the cover-glass preparation should then be thoroughly dried between filter-paper and mounted in Canada balsam. Besides eosin, other acid stains — as orange G, indulin, and nigrosin — have the property of coloring blood-cells containing hemoglobin. igi. Blood platelets are best fixed with osmic acid, and may be seen without staining. They may also be stained and preserved in a sodium chlorid solution to which methyl-violet is added in a proportion of 1 : 20000 (Bizzozero, 82). Afanassiew adds o.(y ( '/ ( , of dry peptone to the solution (this fluid must be sterilized before using). 192. The leucocytes of the circulating blood and those found in certain organs possess granulations which were fust studied by Ehrlich and his pupils, and which may be demonstrated by certain methods. The names given to these granulations are based upon Ehrlich's classifica- tion of the anilin stains, whi< h differs from that of the chemist. This author distinguishes acid, basic, and neutral stains. By the acid stains he understands those combinations in which the acid is the active staining principle, as in the case of the picrate of ammonia. Among these are Congo, eosin, orange d, indulin, and nigrosin. The basic stains are TECHNIC (BLOOD AND BLOOD-FORMING ORGANS). 205 those which, like the acetate of rosanilin, consist of a color base and an indifferent acid. To these belong fuchsin, Bismarck brown, safranin, gentian, dahlia, methyl-violet, methylene blue, and toluidin. Finally, the neutral anilins may be considered as those stains which, like the pi< - rate of rosanilin, arc formed by the union of a color base with a color acid. The granula may be demonstrated in dry preparations as well as in those fixed with alcohol, corrosive sublimate, glacial acetic acid, and sometimes even Flemming's solution. Five kinds of granules are distin- guished, and designated by the Greek letters from alpha to epsilon. 193. The ^-granules 1 acidophile, eosinophile) occur in leucocytes of the normal blood, in the lymph, and in the tissues, ami are differen- tiated from the others by their peculiar staining reaction to all acid stains. They are fust treated for some hours with a saturated solution of an acid stain 1 preferably eosin ) in glycerin, washed with water, subsequently col- ored with a nuclear stain (as hematoxylin or methylene-blue), and then dried and mounted in Canada balsam. Sections may be treated in the same way, with the exception that after being washed with water, they are first dehydrated with absolute alcohol before mounting in balsam. 194. Another method by which both nuclei and granules are stained consists in the use ofEhrlich's hematoxylin solution (,-/, Two layers in which the direction of the enamel prisms changes; in c is seen a dentinal fiber with its sheath ; e, groups of fibrils ; d, dentinal tubules. the former are found here and there peculiar masses of epithelial cells representing the remains of the enamel organs. The tooth-pulp has a rich blood supply. A small artery enters the pulp cavity through the apical foramen, which, as it passes up through the pulp, gives off numerous smaller branches which end in a capillary network situated under the layer of odontoblasts. Numerous medullated nerve-fibers (dendrites of sensory neurones) inter the pulp cavity through the apical foramen. Some of these lose their medullary sheaths soon after entering, or just before entering, the pulp, and divide into long, fine, varicose fibers which interlace to form a loose plexus under the odontoblasts. Other TIIK TEETH. 217 Cementiini. medullated fibers, grouped into small bundles, ascend in the pulp for variable distances ; the nerve-fibers of the bundles then sepa- rate and as single fibers approach the superficial portion of the pulp, and, after losing their medullary sheaths, divide into fine varicose fibers forming under the odontoblasts a plexus continuous with the plexus above mentioned. from the varicose nerve-fibers of this plexus small terminal branches are given off which termi- nate between the odontoblasts, or pass through the layer of odontoblasts, to end between these and the dentin (Retzius, 94; Huber, 98). Medullated nerve-fibers also terminate in free end- ings in the peridental membrane. Development of the Teeth. — In the second month of fetal life the first traces of the teeth are seen in the development of a groove along the inner edge of the fetal jaw, the dentinal or en- amel groove. From the floor of the latter an epithelial ridge- is formed constituting the anlage of the enamel organs and known as the dentinal ridge, or enamel ledge. At those points at which the milk-teeth later appear, the enamel ledge develops solid protuberances corre- sponding in number to the temporary teeth. These are known as the dentinal bulbs or enamel germs. In their first stage of development the enamel germs are knob- like, but later their bases spread, and they become flattened and finally cup- shaped by the pushing up into them of connective - tissue projections, the den- tinal papilla*. At the same time they gradually sink- deeper into the underlying tissue, but still remain con- nected, by means of a thin cord, with the epithelium of the enamel ledge, which now lies on the inner side of the enamel germs. The enamel germs now differentiate into enamel organs. In this stage they consist of an outer layer of columnar epithelial cells, which are to be regarded as a direct continuation of the basal cells from the epithelium of the oral mucous membrane, or still better, of the enamel ledge ; the epithelium in the interior of the organ is derived from the stratum Malpighii of the oral epithe- lium. The cells of this layer, however, undergo a change in shape and structure, in that an increased quantity of lymph-plasma or intercellular substance collects in the interspinous spaces between the cells, pushing the cells apart, and allowing their processes to Dentin. ) Fig. 177. — Cross-section of human tooth, showing cement and dentin; X 212 - Technic No. 225 [vid. also Technic 152). At a are seen small interglobular spaces (Tomes' granular layer). 218 THE DIGESTIVE ORGANS. develop until the cells finally assume a stellate shape. In this way the enamel pulp is gradually formed. The next stage is character- ized by a vertical growth of the dentinal papillae, which soon be- come surrounded on all sides by the cap-like enamel organs. The cvlindric cells (enamel cells) of the enamel organs lying next to the papillae become lengthened, and after passing through further changes, finally develop into the enamel prisms of the teeth. At the periphery of the dentinal papillae, there is differentiated a layer of columnar cells, the odontoblasts, which have a connective-tissue origin, and later form the dentin. During these processes a connective -tissue mantle, the dental sac, rich in cellular and fibrous elements, is formed around each tooth anlage. The earliest appearance of the enamel is in the form of a cuticu- lar membrane, developed from the ends of the enamel cells resting on the dentinal papilla, this cuticular membrane appearing in the form of a thin layer covering the top of the dentinal papilla. Sometime later, short striated processes — Tomes' processes — appear on the Odontoblasts. Terminal nerve- fiber. Odontoblasts. Terminal nerve- fiber. Fig. 178. — Nerve termination in the pulp of a rabbit's molar, stained in methylene- blue [intra vitavi) : a, Odontoblasts seen in side view ; b, a number of odontoblasts seen in end view, showing a terminal branch of a nerve-fiber situated between the odonto- blasts and the dentin (Huber, "Dental Cosmos," October, iF lower end of each of the enamel cells (the end toward the dentinal papilla). These are imbedded in a cement-substance, forming a continuous layer. The Tomes' processes are regarded as the be- ginnings of the enamel prisms. Calcification begins in the middle of these processes ; they thicken at the expense of the cement- substance surrounding them, which later also calcifies. The enamel as a whole thickens by the elongation of the Tomes' processes of the enamel cells and by their subsequent calcification. The process ends finally in the death and partial absorption of the enamel cells and the remaining elements of the enamel organs ; these structures persist for a short time after the eruption of the tooth as a cuticular s heath. The dentin is developed by the odontoblasts by a process analogous to that observed in the formation of bone by the osteo- blasts. These epithelioid cells secrete at their outer surfaces a ■'.'■ ■ ""'V vp?? Fig. 179. ;}w^ - c P '. -■■■'•'.• ;';'■:■■., ■ . .. "•- : ;;^ ;.: : ■. <*>?»•:''' Fi^. (8o. ^"* r ^^ Fig. 181. % ' .•1 ■ •■':■ fj I ig. 182. .- S Figs. 179-182. — Four stages in the development of a tooth in a sheep embryo (from the lower jaw) : Fig. i~n, Anlage of the enamel germ connected with the oral epithelium by the enamel ledge ; Fig. 180, first trace of the dentinal papilla; Fig. 181, advanced stage with larger papilla and differentiating enamel pulp ; Fig. 182, budding from the enamel ledge of the anlage of the enamel germ, which later goes to form the enamel of a permanent tooth ; at the periphery of the papilla the odontoblasts are beginning to differentiate. Figs. 179, 1S0. and 181, X IIO '» Fig- '< s -- 4°- «» o, a, a, Epithelium of the oral cavity ; 6,6,6,6, its basal layer; c,c,c, the superficial cells of the enamel organ; d, //, ,/>, dentinal papilla ; >, r, enamel-forming elements (enamel cells) ; 0, odontoblasts ; S, enamel germ of the permanent tooth ; 7', part of the enamel ledge of a temporary tooth ; u, surrounding connective tissue. 219 220 THE DIGESTIVE ORGANS. Enamel pulp. --- Enamel cells. ' homogeneous substance which fuses to form a continuous layer, the membrana prceformativa. The further development of the dentin is as follows : Its ground-substance is deposited at the cost of the lateral portions of the odontoblasts (under the membrana praeforma- tiva), the axial portion of the cells remaining intact as the dentinal fibers ; the basal portions of the cells containing the nuclei persist, later constituting the odontoblasts of the adult pulp. By the fusion of the segments of the ground-substance formed by each cell, it becomes a homogeneous mass, but soon displays connective-tissue fibrils which gradually undergo a process of calcification. The mem- g brana praeformativa has no fibers and calcifies much later. It lies im- mediately beneath the enamel or the cementum, and in the normal tooth always contains small in- terglobular spaces. In the adult tooth this mem- brane in its entirety is known as Tomes' gran- ular layer. The cementum is merely a periosteal growth of bone originat- ing in the tissue of the dental sac and adhering to the dentin. Although at first the enamel or- gan almost entirely sur- rounds the dentinal pa- pilla, later a portion of that part of it in the re- gion of the fang is ab- sorbed in order to allow the cementum to reach the surface of the dentin. Remains of this regressive portion persist as the epithelial nests of the dental root (compare p. 216). The contents of the dentinal papillae change into the tissue of the dental pulp. As early as the third month outgrowths appear on the inner side of the enamel ledge next to the partly developed milk-teeth, which represent the anlagen of the enamel organs of the permanent teeth. Their further development is similar to that of the milk teeth. The enamel organs of the molars are also developed from an enamel ledge which is practically a backward continuation of the embryonic enamel ledge. With their crowns presenting, the temporary teeth ~ Odontoblasts. Fig. 183. — A portion of a cross-section through a developing tooth (later stage than in Fig. 182) ; / 720 : The dentin is formed, but has become homo- geneous from calcification. Bleu de Lyon differen- tiates it into zones -(a and b). At c is seen the in- timate relationship of the odontoblasts to the tissue of the dental pulp. THE ORAL CAVl'l V. 221 at last break through the epithelium of the gums. When the de- velopment of the permanent teeth is so tar advanced that the}- are read}- t<> perforate, regressive processes begin at the roots of the milk-teeth, which are due, as in like conditions of the bone, to the action of certain cells, which are here known as "odontoclasts." Ill-' ciowns of tin- milk-teeth are then thrown off, oik- by one, by the growing permanent teeth. For further information as to the teeth and their development, see the articles by Ebner (91), whose studies we have to a great ex- tent followed on this subject. 2. THE TONGUE. The Lingual Mucous Membrane and its Papillae. — The mucous membrane of the tongue differs in general very little from •■«;*' 4& I Fig. 184. — Fungiform papilla from human tongue. that lining the rest of the oral cavity. It must, however, be borne in mind that in the greater part of the tongue the submucosa is poorly developed, and as a consequence the mucous membrane on the upper surface and base of the tongue is scarcely movable. Other peculiarities of the lingual mucous membrane are the absence of glands in the mucosa on the upper surface of the tongue, — although glands are found in the musculature of the tongue, their ducts passing through the mucosa, — the presence of epithelial papilla?, and of lymph-follicles at the base of the tongue. The upper surface of the tongue is roughened by the presence of epithelial projections, the Ungual papilla. The latter are almost entirely epithelial structures, and should not be confused with those papillae which are composed exclusively of connective tissue. There 222 THE DIGESTIVE ORGANS. are several classes of lingual papillae — the filiform, the fungiform, and the circumvallate papillae. The most numerous are the thread- like or filiform papilla (from 0.7 to 3 mm. long). These are scat- tered over the entire upper surface of the tongue, and consist of conic projections of the epithelium and of the mucosa. The con- nective-tissue portions of these papillae are very thin and long. The basal layers of the epithelium can not be distinguished from the same layers covering the surrounding mucosa, but the more super- Papilla filiformis. iSU Tongue epithe- lium. , , j, ■ . ,. . • ; , , . a. . . Connective-tissue :'. , papilla. ''4JA- ■ V : ' .' ';, ■' ' •% I,-. J, ,.- -■,. ,, ,* • ; » « yj.iucosa. ,. j;J; X1J ■ 1 KW 1 '.'',',< W- Basal epithelial ■ - layer. Fig, 185. — From a cross-section of the human tongue, showing short, thread-like papillae (filiform) ; X I 4°- ficial layers are differentiated, in that their cells are arranged parallel to the long axes of the papillae and overlap each other like tiles (Fig. 185). Their free ends are often continued into several spine- like processes. Less numerous than the filiform are the fungiform papilla (from 0.7 to 1.8 mm. in height) scattered here and there between the former. They are nearly hemispheric in shape, and are joined to the surface of the tongue by a slightly constricted base. At times they are even partly sunk into the mucous membrane. The mucosa is raised under the epithelium to form connective-tissue papillae (Fig. 1 84). On the free surface of the fungiform papillae THE mm. i avi rv. 223 are sometimes found taste-buds, <>r taste-goblets, which lie im- bedded in the epithelium and extend through its entire thick ri The circumvallate papilla occupy a definite region <>n the upper surface of the tongue, and arc arranged in two rows, forming almost .1 right angle, with the apex directed backward and situated just in front of the foramen caecum (Morgagni). These papillae are few in number, about eight to fifteen in all. In shape they are similar to those of the fungiform type, but are much larger (about I or 2 mm. in diameter), and sunk so deeply into the mucous membrane that the latter forms a wall around their sides. Here also the mucosa passes up into the papilla: and forms con- nective-tissue papillae of its own at the upper surface, while at the sides it merely adheres to the smooth inner surface of the epithelial layer. Taste-buds are found in the epithelium at the sides of the papillae, and also in that of the ridges surrounding the papillae. At the sides of the human tongue and near its base are the so-called fimbricc lingua. These are irregular folds of mucous membrane, Fig. 186. — Longitudinal section of foliate papilla of rabbit, showing taste-buds. the sides of which also contain taste-buds. In the rabbit they are more regular in structure and consist of parallel folds of mucous membrane thickly dotted with taste-buds, and are termed the foliate papil/tc. In place of the circumvallate papilla?, the guinea-pig pos- sesses structures similar to the foliate papilla; of the rabbit. Into the depressions in which the circumvallate papillae lie and into those between the folds of the fimbria? lingua? open the ducts of numerous serous glands, the glands of Ebner (see below). The Taste-buds. — The gustatory organs in the form of taste- buds are found on the surface of the tongue, principally on the lateral surfaces of the circumvallate papilla? and the fimbria? lingua? (foliate papilla?). They are also occasionally met with in the epithelium of the fungiform papillae and the soft palate, and on the posterior surface of the epiglottis. They always lie imbedded in the epithelium and extend through its entire thickness ; they are ovoid in form, with base downward and the smaller pole at the 124 THE DIGESTIVE ORGANS. surface. The whole structure is surrounded by the epithelium of the mucous membrane of the regions in which they occur, except at the attenuated outer end of the taste -bud, where, by means of a small opening, the taste-pore, it communicates with the oral cav- ity. Most of the cells constituting the taste-buds are elongated, spindle-shaped structures, extending from one end of the organ to the other, with spaces between them. There are four varieties of these cells : (i) The outer sustentacula?' or tegmental cells, lying at the periphery of the organ with a nucleus in their center, and having a short, cone-shaped cuticular projection ; (2) the inner sustentacula)- or rod-shaped cells, which are more slender structures with basally situated nuclei and without a cuticular projection ; between the latter are (3) elongated, spindle-shaped, neuro-epithe- Epithelium Taste-buds. Ebner's gland. Fig. 187. — Longitudinal section of a human circumvallate papilla; X 2 °- lial cells, with the nucleus of each in the thickest portion of the cell, and with slender, stiff processes projecting into the taste -pore ; (4) a few broad basal cells, communicating with each other as well as with the sustentacula cells by numerous processes. We have, therefore, in the cells of the first, second, and probably fourth varieties, elements which belong exclusively to the sustentacular apparatus of the organ (Hermann, 85, 88). Von Rbner found in the taste-buds of the circumvallate papillae of man, monkey, and cat, as well as of the papillae foliatoe of the rabbit, an open space situated between the taste-pore and the tip of the taste-bud (Fig. 188). These spaces vary according to the species, and are bounded above by the summits of the tegmental cells and laterally and below by the more centrally situated sus- I III ORAL CAVITY. "5 Epithe- lium. Nei \ fibrils. neuro-epi thelial cell. Taste- pure. W tentacular cells. The cavities are often 10 />. in depth, and are filled with a fluid apparently in communication with the fluid of the depression into which the circumvallate papillae arc sunk. The processes of the neuro-epithelial cells project into the cavity from its floor and lateral walls, but do not extend as far as the taste- pore. The circumvallate papilla- are differentiated from the adjacent surface of the tongue by the development of a solid encircling epithelial ridge. Nu- merous taste-buds ap- pear on the surface quite earl_\- in the his- tory of the embryo. These, however, dis- appear completed)' when the permanent taste - bin Is develop from the basal cells of the epithelial ridge. Similar phenomena occur in the fungiform papillae ( Hermann, 88). The neural epith- elia of the taste-gob- lets were formerly re- garded as directly connected with the nerve-fibers by means of long processes, but the latest researches have shown that dendrites of sensory neurones (sensory nerves) enter the taste-buds and end free in telodendria. The latter sur- round the neuro-epithelial and, to some extent, the sustentacular cells, their relations depending upon contact. The Lymph-follicles of the Tongue (Folliculi linguales) and the Tonsils. — At the root of the tongue, and especially at its sides, are numerous elevations due to the increased quantity of lymphoid tissue found in the mucosa of these regions, the lingual tonsils, or lingual follicles. In the center of each follicle is a cavity communicating with the exterior and caused by an invagination of the epithelium. The lymphoid tissue contains a number of more or less distinctly defined lymph-nodules, some even showing germ centers {yid. p. 178). The whole structure is surrounded by a connective -tissue capsule. The epithelial walls of the follicular cavities often show extensive degenerative changes, which are accompanied by increased migration of leucocytes into the oral cavity. These leucocytes change (according to Stohr, 84) into the so-called mucous or salivary corpuscles of the saliva. The pharyn- geal tonsils may be regarded as clusters of small lymph-follicles, 15 nental zr "'ii. JuNuuio-ipilhe- ST lial cell. Sustentacular cell. Terminal branches of nerves. Fig. 1 J . — Schematic representation of a taste-goblet (partly after Hermann, 88). 226 THE DIGESTIVE ORGANS. similar to those found in the tongue. They are covered by a stratified pavement epithelium, resting on a mucosa possessing papillae folded to form pits or crypts of irregular shape. The adenoid tissue of the tonsil is found in the form of diffuse ade- noid tissue and a varying number of more or less clearly defined follicles of adenoid tissue often showing germ centers of Flemming. Epithelium. Lymph-follicle. . _ c/---- — Epithelial crypt. Connective-tis- sue capsule. Fig. 189. — Section through tonsil of dog; X 2 ° : At rt and at the opposite side the epithelium is composed of a very thin layer of cells. " fsSSf ~ ■«s£@: $e -- b "i if? '- 7 • - » a'' ^v(* ''® J^ >* f - 19 • & <3>,*>,, one of the spaces in the epithelium filled with leucocytes and more or less changed epithelial cells ; c, blood-vessel ; d, normal epithelium ; e, basal cell of the same. The epithelium lining the crypts or cavities of the tonsils shows, as in the lingual follicles, extensive degenerative changes, resulting mainly in the formation of variously shaped, communicating spaces filled with lymphocytes and leucocytes. (See Fig. 190.) Besides the nerves terminating in the taste-buds, the tongue is 1 in: okAL CAVITY, 227 richly supplied with sensory nerves which terminate in free sen- sory endings, which may be traced into the epithelium, and which are especially numerous in the fungiform and circumvallate papillae; or in smaller or larger end-bulbs of Krause found in the mucosa of the fungiform papillae. The motor nerves of the tongue terminate in motor-endings. Interlobular duct. Intralobular - duct. Intermediate duct. GLANDS OF THE ORAL CAVITY. The glands of the oral cavity comprise numerous lobular, tubulo-acinous glands situated in the mucosa and submucosa of the lips, cheeks, and tongue, and three pairs of lobar, tubulo-acinous glands — the parotid, submaxil- lary, and sublingual glands. These are classified according to their secretions into those secreting principally mucus (human sublin- gual and man\ r of the smaller oral glands), and known as mucous glands ; those secreting a fluid al- buminoid substance containing no mucus, the serous glands (parotid glands and the small glands near the circumvallate papillae) ; and those having a mixed secretion, mucous and serous glands (human submaxillar)'). The ducts of all these glands open into the cavity of the mouth. The ducts of the smaller oral glands are, as a rule, short and pass up through the mucosa and the epithelium to open on the free surface. The principal excretory ducts of the salivary glands are Steno's ducts(Stenson's ducts), passing from the parotid glands to the mouth ; Wharton's ducts, the ducts of the submaxillar)- glands, and Bartholin's ducts for the sublingual glands. The salivary glands consist of numerous lobules and small lobes of glandular tissue, surrounded by a thin fibrous-tissue capsule which sends septa and trabecular between the lobules and lobes. The duct of each gland on reaching the gland divides into smaller ducts, which penetrate the gland between the lobes, the interlobar ducts ; these in turn divide into ducts of the next order, which pass between the lobules, the interlobular ducts. The interlobular ducts pass over into short cylindric tubes which enter the lobules, and are known as intralobular ducts. These are followed by very short, narrow tubules, the intermediate ducts or tubules, Acinus. Fig. 191. — Scheme of a salivary gland. 228 THE DIGESTIVE ORGANS. which finally terminate in the alveoli or acini, irregular and some- what tortuous tubular structures with a lumen and possessing an epithelium characteristic of the particular variety of the gland (see below). The epithelium lining the different portions of the large excretory ducts varies somewhat. For a short distance from their oral end they arc lined by a stratified columnar epithelium con- sisting of two layers of cells (Wharton's ducts are now and then lined for a short distance by a stratified pavement epithelium continuous with that lining the mouth). Beyond this stratified columnar epithelium, which extends for a variable distance, the larsre excretorv ducts, the interlobar and interlobular ducts are lined by a pseudostratified columnar epithelium, possessing two rows of nuclei (Steiner). Outside of the epithelial lining there is found a firm fibro-elastic covering, forming the wall of the ducts. The intralobular ducts are lined by a single layer of columnar cells, the basal half of each cell showing a distinct striation. The interme- diate portions of the ducts are lined by a low, cubic, or flattened epithelium. Between the membrana propria and the secreting epithelium of the tube, and more especially in the acini, are branched cells which anastomose with each other, the so-called basket cells. Their processes penetrate between the glandular cells and form a sup- porting structure for them. The homogeneous membrana propria surrounding the entire glandular tube is in close relationship to these cells. We shall now consider more in detail the structure of the alveoli or acini of the salivary glands. SALIVARY GLANDS. The Parotid Gland (Serous Gland). — The epithelial cells lining the acini of this gland are short, irregularly columnar or cubic cells, their structure changing according to their physiologic condi- tion. When at rest the secreting cells are only slightly granulated and contain a large quantity of clear secretion (paraplasm), while the nuclei arc irregular and indented. As soon as the protoplasm of the cells commences the formation of secretion, the cells become smaller, more granular and opaque, and their nuclei assume a spheric shape ; when, however, the cells throw off a portion of the granular material, an immediate increase in their protoplasm is noticed. After a long period of secretion the cells become still smaller and their contents still more turbid. They now contain very little protoplasm. These phenomena can only be regarded as due to the fact that the granular paraplasm is formed at the expense of the protoplasm of the cell during the period of rest. The Sublingual Gland (Mucous Gland). — In the acini of mucous glands there are found two varieties of cells: (i) True mucous cells, which, when filled with secretion, are large and SALIVARY GLANDS. 2 29 clear, with their nuclei always at the periphery. During the ex- pulsion of the secretion the mucous cells decrease in size and become cloudy, wink- the nuclei leave the periphery and increase in si/.e. (2) Cells rich in protoplasm, situated in close apposition to the membrana propria. These cells resemble in structure serous cells, and are found either singly Or in groups of crescentic shape. They are known as the crescents of Gianuzzi or the demilunes of Heidenhain. The margins of the individual cells composing the crescents are often so faintly outlined that the whole structure has the appearance of a large polynuclear giant cell. . Acini. Intralobu- lar duct. 21 - - Connective ~^< i.^ .■- '■■: •*. tissue be- lobules. Fig. 192. — Section through salivary gland of rabbit, with injected blood-vessels ; X 7°- The demilunar cells have been variously interpreted by different observers. They have been regarded as permanent cells with a special secretion, as transitional structures, and again as cells des- tined to replace the degenerated mucous cells. Stohr (87) be- lieves that the cells of the acini are never destroyed in the process of mucous secretion, and that the crescents of Gianuzzi are there- fore merely a complex of cells containing no secretion, which have been crowded to the wall by the adjacent enlarged and distended cells. Solger (96), on the other hand, does not regard the demi- lunes as transitional structures whose function is to replace the 230 THE DIGESTIVE ORGANS. destroyed cells, but considers them to be permanent secreting cells — an opinion which he bases on the results of special methods of investigation. According to him, then, the mucous salivary glands are mixed glands, in that the demilunes consist of cells of a serous type, while the remaining elements are mucous in character. The destruction of mucous cells during secretion is not admitted by him Connective — tissue. (fc Gland cell _ of acinus. Intralobu- lar duct. Intermedi- ate duct. Fig. 193. — Section from parotid gland of man. (compare also R. Krause). This latter view seems more in accord with recent observations. The Submaxillary Gland (Mixed Gland). — With regard to the mixed glands it is sufficient to say that there is a simultaneous secretion of serous and mucous fluids, and that these two sub- stances are produced in separate but adjacent acini, of which the Intermediate duct. Crescents of Gianuzzi. Fig. 194. — From section of human sublingual gland. one type possesses a structure identical with that found in the parotid and the other with that in the sublingual. By means of various methods the existence of a network of tubules surrounding the glandular cells may be demonstrated both in the serous and mucous glands. The same arrangement may be SALIVARY GLANDS. 231 Fig. 195. — A number of alveoli from ihe submaxillary gland of ilo^, stained in ch le- silver, showing some of the fine intercellular tubules. observed in the case of the cells forming the demilunes. '1 lie course of these tubules may be followed to their junction with the lumen of the secreting portion of the gland tubule, and the whole structure would seem to indicate that the entire surface of the cells is concerned in the act of secretion (Erik M uller, 95 ; Stdhr, 96, II). As to the part that the intermediate tubules and the intralobular tubes play in the process of secretion, Merkel's (83) theory is of interest. He believes that the former yield a part of the water in the saliva, while the salts are furnished by the rod -shaped epithelium of the intralobular tubes. These views of Merkel have been questioned, as it has been shown by chemic analysis that the relative quantity of water and salts in the secretion of the salivary glands is not at all proportionate to the number of the intermediate tubules and intralobular tubes. For exam- ple, Werther funis that although a great many intermediate tu- bules are present in the par- otid gland of the rabbit and none at all in the submaxillary gland of the dog, nevertheless the secretionsofthe.se glands contain equal quantities of water. Furthermore, the secretions of the parotid of the rabbit and of the sublingual of the dog show equal quantities of salts, in spite of the fact that in the former there are large numbers of intralobular tubes with rod-shaped epithelium and in the latter none at all. THE SMALL GLANDS OF THE MOUTH. Besides the larger glands, there are in the oral cavity numerous small lobular, tubulo-acinous and simple branched tubulo-acinous glands. They are mostly of the mixed type, and are called, accord- ing to their location, glanduhe labiales, palatinae and linguales. Serous glands, known as v. Ebner's glands, occur in the tongue, their ducts opening into the depressions of the circumvallate and foliate papilkne. The absence of intralobular tubes and well-defined intermediate tubules is characteristic of all the smaller glands of the oral cavity. As a consequence the secreting tubules are composed almost entirely of those parts corresponding to the acini of the larger glands. It appears that the smaller mucous glands, except those of the lips (J. Nadler), do not, as a rule, contain typical demilunes. The salivary glands and smaller glands of the mouth have a -o- T1IE DIGESTIVE ORGANS. rich blood supply. In the salivary glands the arteries follow the ducts through their repeated branching, ultimately ending in capil- laries which form a network inclosing the acini and the terminal portions of the system of ducts. The lymphatics begin in clefts in the connective tissue surround- ing and separating the acini. Larger lymph-vessels are found in the connective tissue separating the lobules and lobes of the gland. The nerve supply of the salivary glands, ma}-, owing to the im- portance of these structures, receive somewhat fuller consideration. Their nerve supply is from several sources. That of the sublin- gual and submaxillary glands will be considered first. Sensory nerve-fibers (no doubt the dendrites of sensory neurones, the cell- bodies of which are situated in the geniculate ganglion) terminate in free sensory endings in the large excretory ducts and their branches. These medullated fibers accompany the ducts in the form of small bundles. From place to place one or several fibers leave these bundles and, after dividing a number of times, lose their medullary sheaths. After further division the nonmedullated branches form plexuses under the epithelial lining of the ducts. From the fibers of these plexuses terminal fibrils are given off, which enter the epithelium, to end, often near the free surface, on the epithelial cells (Arnstein, 95; Huber, 96). The secretory cells of the acini receive their innervation from sympathetic neurones. The cell-bodies of those supplying the sublingual glands are grouped in a number of small, sympathetic ganglia situated in a small triangle formed by the lingual nerve, the chorda tympani and Wharton's duct, the chorda- lingual triangle. These ganglia may be known as the sublingual ganglia (Langley). The cell-bodies of the sympathetic neurones supplying the secretory cells of the submaxillary glands are grouped in small ganglia situated on Wharton's duct just before it enters the gland, in the hilum of the gland, and on the interlobar and inter- lobular ducts ; they may be spoken of collectively as the submax- illar)' ganglia. In the glands under discussion, the neuraxes of the sympathetic neurones are grouped to form small bundles, which divide repeatedly, the resulting divisions joining to form plexuses situated in the outer portion of the walls of the ducts, and as such may be followed along the ducts, the bundles of nerve-fibers be- coming smaller and the division of the bundles of fibers and the individual fibers occurring oftener as the smaller divisions of the system of ducts are reached. On reaching the acini, the terminal branches of the nerve-fibers form a plexus outside of the basement membrane, epilaiucllar plexus ; from this branches are given off which penetrate the basement membrane, some forming a hypolam- ellar plexus, others ending on the gland-cells in small granules or clusters of granules (Arnstein). Throughout their entire course the neuraxes of the sympathetic neurones are varicose, nonmedullated nerve-fibers. The nerve-fibers of the chorda tympani end in ter- minal end-baskets, inclosing the cell-bodies of the sympathetic THE PHARYNX AND ISoPHAGUS. 233 neurones found in the sublingual and submaxillary ganglia, and not in the glands, as generally stated by writers, The increase of secre- tion from the submaxillary and sublingual glands on direct or indi- rect stimulation of the chorda tympani is due, therefore, not to a direct stimulation of the gland-cells by the fibers of this nerve, but to a stimulation of the sympathetic neurones of the sublingual and submaxillary ganglia, the neuraxes of which convey the impulse to the gland-cells. These glands have a further nerve supply from the superior cervical ganglia of the cervical sympathetic. The neuraxes of sympathetic neurones, the cell-bodies of which are situated in the superior cervical ganglia, accompany the blood-vessels to the sub- lingual and submaxillary glands ; their mode of termination is, however, not as yet determined. The cell-bodies of the sympathetic neurones here in question are surrounded by end-baskets of nerves which leave the spinal cord through the second, third, and fourth dorsal spinal roots. The blood-vessels of the salivary glands arc also richly supplied with vasomotor nerves, the neuraxes of sympa- thetic neurones, which terminate on the muscle-cells of their walls. The nerve supply of the parotid glands is, in the main, like that of the other salivary glands here described, although it has not been worked out with the same detail. The cell-bodies of the sympathetic neurones, the neuraxes of which innervate the gland-cells, are, it would appear, situated in the otic ganglia. The nerve-ending in the smaller glands of the mouth is similar to that given for the salivary glands, as has been shown by Retzius and other observers. It is very probable that the cell-bodies of the sympathetic neu- rones, the neuraxes of which innervate the glands of the tongue, are situated in the small sympathetic ganglia found on the lingual branches of the glossopharyngeal and lingual nerves. B. THE PHARYNX AND ESOPHAGUS. The mucous membrane of the pharynx and esophagus is similar in structure to that of the oral cavity. The epithelium is of the stratified squamous variety, and also contains prickle cells and keratohyalin. (See Skin.) A stratified ciliated epithelium is present only in the fornix in the region of the posterior nares. The area covered by this type of epithelium is more extensive in the fetus and new-born, and extends over the whole nasopharyngeal vault. In the human embryo the superficial epithelial cells' of the esophagus possess cilia up to the thirty- second week (Neumann, 76). The papillae of the mucosa are loosely arranged and are in the form of slender cones. The mucosa of the pharynx contains diffuse adenoid tissue rich in cells which in some places forms accessory tonsils {vid. p. 225). There are but few mucous glands in the submucous tissue of the esoph- agus, but when present they contain well-marked demilunes. In 234 THE DIGESTIVE ORGANS. man the ducts of these glands do not reach the surface between the connective-tissue papillae, as in the external skin, but pass up through them into the epithelium and thus to the surface. A layer consisting of nonstriated muscle-fibers, the muscularis mucosa, the majority of the cells of which show a longitudinal arrangement, is found between the mucosa and submucosa in the esophagus, but not in the pharynx. The external muscular coat of the pharynx is made up of transversely striated muscle-fibers, arranged in a complicated man- ner. This tissue extends downward to about the middle of the m Fig. 196. — Section of esophagus of dog ; 1 S. - Epithelium. - Mucosa. - Muscularis mucosas. -.- — "" Submucosa. Circular layer of muscle. Longitudinal muscle layer. Outer connec- tive - tissue coat. esophagus, in which it consists of an outer longitudinal and an inner circular layer. In the lower half of the esophagus nonstriated muscle-fibers alone are present. There is no sharply defined line of demarcation between the two types of muscular tissue, as the fibers of the unstriped variety penetrate for some distance upward into the substance of the striated muscle, giving the tissue here a mixed character. THK STOMACH AND INTESTINE. 235 G THE STOMACH AND INTESTINE. I. GENERAL STRUCTURE OF THE INTESTINAL MUCOUS MEMBRANE. The mucous membrane of the stomach and intestine, unlike that of the esophagus and oral cavity, p< an epithelium of the simple columnar variety with elongated cells (about 22 // in . . . >" Alveolus of gland. Mucosa. Lumen. •>-^. .. ■. ^-i- - .\..^.v:-\^.-".: -;_;.-- - '" ','r- , '- Branched papilla of mu- cosa. Fig. 197. — Part of section of human esophagus, showing duct of mucous gland ; V I2 °- height). In the intestine the epithelium shows a well-marked striated cuticular border, striated protoplasm in the outer ends of the cells, extending to the immediate vicinity of the nuclei, which are situated in the basal portions of the cells. The basal portion of each cell consists of nonstriated protoplasm, ending in a longer or shorter process which extends to the basement membrane, or possibly 2 $6 THE DIGESTIVE ORGANS. even penetrates it. The epithelial cells have the power of produc- ing mucus, a phenomenon which, in the normal condition, rarely embraces whole areas of epithelium ; these cells (goblet cells) are usually surrounded by others which are unchanged (for details about goblet cells see General Histology, p. 81). Throughout the entire intestinal tract the epithelium forms simple, branched, and compound tubular and alveolar glands. These are depressions lying in the mucosa, and only in the duodenum extend beyond it into the sub- mucosa. The mucosa consists of adenoid tissue, containing relatively few cells. It fills the interstices between the glands, and often forms a thin but continuous layer (granular layer of F. P. Mall) below the glands. It is therefore obvious that the development of the mucosa is inversely proportionate to the number and the density of arrangement of the glands ; when the latter are present in large numbers, as, for instance, in the stomach, the mucosa is reduced to a minimum. In the small intestine it forms not only the perma- nent folds, but also certain finger-like elevations known as villi, which are covered with epithelium and project into the lumen of the intes- tine, thus increasing to a considerable extent the surface area of the mucous membrane. In the mucosa are found small nodules of adenoid tissue. These are spoken of as lenticular glands when occurring in the stomach, as solitary glands when found in the upper portion of the small intestine and in the large intestine. In the lower portion of the small intestine they are grouped to form the agminated glands, or Peyer's patches, which, when large, extend into the submucosa. Beneath the stratum proprium is a layer consisting of two or three strata of unstriped muscle- fibers, the muscularis mucosce. As a rule, it is composed of an inner circular and an outer longitudinal layer. This arrangement is interrupted only where the larger glands and follicles penetrate into the sub- mucosa. The epithelium with the glands, the mucosa with its lymph-nodules, and the muscularis mucosa; form together the mucous membrane, or tunica mucosa. Below the mucous membrane is the connective-tissue submucosa. This is characterized by its loose structure, and consequently affords considerable mobility to the mucous membrane. In the small intes- tine it forms a large number of permanent transverse folds known as valvules conniventes (Kerkring). In the submucosa of the duodenum occur the secreting portions of Brunner's glands (gland- ule: duodenales), and in the small intestine the larger lymph-nodes and Peyer's patches. External to the submucosa is the muscular coat, which generally consists of two layers of unstriped muscle-tissue. The inner layer is composed of circular fibers (stratum circulare) ; the outer layer, of longitudinal fibers (stratum longitudinale). In the colon the longi- tudinal layer forms definite bands, the t(C>ii Fundus. : i"f fW^W^-* Fig. 109. — From vertical section through fundus of human Stomach ; / 60 : aand /*, Inter- lacing fibers of the muscularis mucosae ; from a and b muscular fibers enter the mucosa. The fibers of the layer b penetrate those of layer a. Fig. 200. — A number of gastric glands from the fundus of the stom- ach of young dog, stained after the chrome silver method, showing the system of fine canals surrounding the parietal cells and communica- ting with the lumen of the glands. of the remaining cells, thus forming, together with the membrana propria, a protuberance (particular])- noticeable in the pig, where almost the- entire cell may be enveloped by the basement membrane, giving it an appearance of being entirely extraglandular). Toward the lumen of the gland the contour of these cells is modified by pressure on the part of the adjacent cells belonging to the other variety, and they arc indented according to the number of the latter. THE STOMACH AND INTESTINE. 239 Occasionally, a process is seen extending from a parietal cell to the lumen of the gland. The parietal cells are larger than the cells of the other variety and richer in protoplasm ; the}- are of an irregular oval or triangular shape and possess, as a rule, a single nucleus. According to Erik Midler and ( rolgj (93 }, there exists in the peripheral protoplasm of each parietal cell a system of eanals in the form of a network communicating with the lumen of the gland and varying in structure according to the physiologic condition of the cell — wide-meshed in a state of hunger and fine-meshed during — Epithelium of esophagus. Mucous cardiac gland. — Junction of esophagus and stomach. *" Epithelium of stomach. Fig. 201. — From a section through the junction of the human esophagus and cardia ; X5o. digestion. A peripheral zone differing from the rest of the cell- body may occasionally be demonstrated in the parietal cells (mouse) by using the method of von Altmann (vid. T. 125). The second variety of glandular cells is represented by the central, chief, peptic, or adelomorphous cells. These are short, irregular, columnar structures whose narrower portions point toward the lumen of the gland. They are situated either directly between the lumen and the basement membrane of the ___: c ^< i' Fig. 204. — Section through fundus of human stomach in a condition of hunger ; X 5°°' Technic No. 242. Lumen. -- Chief cell. Fig. 205. — Section through fundus of human stomach during digestion; X 5°°- Technic No. 242. to the center of the cells. Since chemic examination has shown that the amount of pepsin found in the gastric mucous membrane increases with the enlargement of the chief and pyloric cells, and decreases with their diminution in size, there can be hardly any THE STl IM UII AND IM'l.-l [NE. 243 doubt that this ferment is elaborated by these cells. The pro- cess consists either in a direct change of the cellular protoplasm into the ferment, or in a preliminary stage before its final trans- formation into the finished ferment. It is assumed that the parietal cells secrete the acid of the gastric juice, although, in spite of all efforts, it has not yet been definitely proved that these cells possess an acid reaction. The vascular and lymph-vessels <»f the stomach, and also its nerve supply, will be considered in a general discussion of these structures pertaining to the entire intestinal canal. 3. THE SMALL INTESTINE. The mucous membrane of the small intestine is characterized by the presence of villi. These are more or less elongated elevations of the mucous membrane projecting into the lumen of the intestine. They greatly increase the surface of this portion of the intestine and are actively concerned in the absorption of its contents. The mu- cous membrane also forms permanent folds in both the duodenum and the remainder of the small intestine, the valvulae conniventes (Kerkring). Upon these the villi rest, and, indeed, it is probable that the very existence of the plicae is due to the blending of the basilar ends of the villi. The latter are leaf-shaped in the duod- enum, columnar in the jejunum, and club-shaped in the ileum. The epithelium of the intestinal mucous membrane covers the villi in a continuous layer, and penetrates into the mucosa to form the glands. Its structure is essentially the same in all regions of the small intestine, the cells being of the high columnar variety with free surfaces covered by wide, striated cuticular borders. The basilar portions of these cuticular borders are nearly always homo- geneous, and upon vertical section give the appearance of a fine line. The cuticular borders of adjacent cells blend with each other, form- ing a continuous membrane, lar "" Lymph- Villus. ^55?- ':. ,dule. - - Muscularis mucosae. ■bb s§S% -- Submucosa. Villus. Brunner's glands. .Blood-vessel. '••Glands of Lieberkuhn. Fig. 208. — Section through the junction of the human pylorus and duodenum; X about 15 : At a the pyloric glands extend into the duodenum. near their axes around the lacteal vessels. The contraction of these fibers causes a contraction of the entire villus. Lymph-nodules are distributed throughout the mucosa of the small intestine, occurring either singly, as solitary follicles, or aggregated, as Peyer's patches. At the points where they occur, 2 4 S THE DIGESTIVE ORGANS. the villi are absent and a lateral displacement of the glands of Lieberkiihn is observed. The lymph-nodule is usually pyriform in shape. The thinner portion protrudes somewhat in the direction of the lumen of the intestine, while the thicker portion extends outward to the muscularis mucosae, the latter being frequently in- dented or even perforated if the lymph-nodules be markedly devel- oped. Their structure is similar to that of the lymph-follicles (see under these), and consists of reticular adenoid tissue, supporting lymph-cells. It should be remembered that every nodule may possess a germ center. Peyer's patches are collections of these lymph-follicles. The surface of the nodule presenting toward the lumen of the intestine is covered with a continuous layer of intestinal epithelium. In man the summit of that portion of the Leucocyte in epithe- lium. Epithelium. Crypt. . Intermedi- ary zone. -;.-.r,-' 3 5 ■ , J ,&®>& s> *■ c v- B n — :- ■ - — -a Submucosa. — H Fig. 209. — Section of solitary lymph-nodule from vermiform appendix of guinea- pig, showing ciypt ; X about 400 (Flemming's fluid). nodule projecting into the lumen of the intestine presents but a slight depression of the intestinal epithelium, while in some animals (guinea-pigs), and especially in the nodules composing Peyer's patches, there is a deeper depression, even leading to the formation of a so-called "crypt" or "lacuna" (vid. Fig. 209). At the summit, the intestinal epithelium where it comes in contact with the lymph-nodule, is peculiarly altered. In most cases there is an absence of a basement membrane, the epithelium resting directly upon the lymphoid tissue. No clearly defined boundary between the two is distinguishable (intermediate zone of v. David- off ) ; they are therefore in the closest relationship to each other. The basal surfaces of the epithelial cells arc fibrillar, the fibrils seeming to penetrate into the adenoid reticulum of the follicles. THE STOMACH AND INTESTINE. 249 4. THE LARGE INTESTINE, RECTUM, AND ANUS. The small intestine ends at the ileocecal valve. At some dis- tance from the margin of the valve the villi of the ileum become broad and low. In the immediate vicinity of the valve their basilar portions Income continent, forming a honeycomb structure which supports a few villi. At the base of the honeycomb open the glands of Lieberkuhn. On the cecal side of the valve the villi become fewer in number and finally disappear, while the folds which give the honeycomb appearance persist for a considerable distance. In Intestinal epithelium. — Lumen of gland. — Goblet cell. Mucosa. Mucosa. Muscularis mucosae. Fig. 2IO. — From colon of man, showing glands of Lieberkuhn ; X 2 °°- the adult cecum the villi are absent. The mucosa and glands pre- sent a structure similar to that of the remainder of the large intes- tine. In the mucosa of the vermiform appendix is found a relatively large number of solitary lymph-follicles, occasionally forming a continuous layer. The marked development of the lymph-follicles encroaches upon the glands of Lieberkuhn, so that many are obliterated ; they are penetrated by the adenoid tissue, the epithe- lial cells of the glands mingling with the lymph-cells. What finally 250 THE DIGESTIVE ORGANS. becomes of the secretory cells has not been definitely ascertained (Rudinger, 91). In the colon the villi are wanting, while the glands of the mucosa arc densely placed and distributed with regularity. The glands of Lieberkiihn in the colon are somewhat longer, and as a rule contain many more goblet cells than those in the small intestine. Only the neck and fundus of the glands show cells de- void of mucus. Transitional stages between the latter and the goblet cells have been observed in man (Schaffer, 91). Solitary lymph-follicles are found throughout the colon. They are situated in the mucosa, only the larger ones extending into the submucosa. The glands of Lieberkiihn are displaced in the regions of the lymph- follicles. Gland. Submu- cosa. Fig. 211. — A solitary lymph-follicle from the human colon : At a is seen a pronounced concentric arrangement of the lymph-cells. The teenies and plica; semilunares cease at the sigmoid flexure, and are replaced in the rectum by the plica transversales recti. Permanent longitudinal folds, the so-called cohimnce rcctalcs Mor- gagni, are present only in the lower portion of the rectum. Here the intestinal glands are longest but disappear simultaneously with the rectal columns. At the anus the mucous membrane of the rectum forms a narrow ring devoid of glands, covered by stratified pavement epithelium, and terminating in the skin in an irregular line. The transition from the mucous membrane to the skin is gradual, yet reminding one of the appearance presented at the junction of the esophagus with the cardiac end of the stomach. External to the anus, and at a distance of about one centimeter from it, are numerous highly developed sweat-glands, the circum- anal glands, which are almost as large as the axillary glands. THE STOMACH AND INTESTINE. 251 5. BLOOD, LYMPH, AND NERVE SUPPLY OF THE INTESTINE. In general, the following holds true with regard to the blood- vessels of the intestinal tract (further details will be discussed in dealing with the vessels of the various regions of the intestine) : The arteries enter along the line of the mesenteric attachment and penetrate the longitudinal muscular layer. Between the two mus- cular layers branches are given off which form an intermuscular plexus, from which, in turn, smaller branches pass out to supply the muscles themselves. The arterial trunks penetrate the circu- lar muscular layer and form an extensive network of larger vessels in the deeper layer of the submucosa. This is known as Heller s plexus ( F. P. Mall). From this, radiating branches are Epithelium of stomach. Recriini of the bodies of the gastric glands. ^cyS^ -S Musculai is mucosae. Fig. 212. — Section through fundus of cat's stomach. The blood-vessels are injected ; X 60. given off which supply the muscularis mucosae, forming under the latter a close network of finer vessels. This plexus, together with that of Heller, gives rise to vessels which penetrate the mus- cularis mucosae and break up into capillaries in the mucous mem- brane. The veins of the mucous membrane form beneath the muscularis mucosae a plexus with small meshes, giving off many radiating branches ; these in turn unite to form an extensive net- work of coarser vessels. Veins extend from the latter and unite to form larger trunks, which then lie side by side with the arteries. According to F. P. Mall, delicate retia mirabilia occur here and there in the venous network in the submucosa of the intestine of the dog. In the esophagus the arteries end in a capillary network situated 2; J THE DIGESTIVE ORGANS. in the mucosa and extending into the connective -tissue papillae of the mucosa. The vessels of the stomach are arranged in plexuses in the muscular coat, submucosa, and beneath the muscularis mucosae, as previously described. From the plexus beneath the muscularis mu- cosae, small branches are given off which pass through this layer and in the mucosa form a capillary network, consisting of relatively small capillaries, which surround the gastric glands, this plexus being par- ticularly well developed in the region around the body and neck of the glands, where the parietal cells are most numerous. The capil- laries of this network are continuous with capillaries of a much larger size, forming a network surrounding the gastric crypts and situated immediately under the epithelium lining the mucosa of the stomach. The blood is collected from this capillary plexus by small veins which pass nearly perpendicularly through the mucosa, forming a plexus above the muscularis mucosae, from which small veins pass through the muscularis mucosae to the venous plexus in the sub- mucosa. The blood-vessels of the mucosa of the small intestine may be divided into (i) the arteries of the villi and (2) the arteries of the intestinal glands. The former arise principally from the deep arterial network in the submucosa, then penetrate the muscularis mucosae and give off branches at acute angles which continue without further branching into the summits of the villi. Within the villi themselves the arteries lie in the axes. The broader villi may contain two arteries. The circular muscle-fibers of the arteries gradually disappear inside of the villi (dog), and at the summit of the latter the vessels break up into a large number of capillaries. These form a dense network extending beneath the basement mem- brane and into its marginal layer. These networks give rise to venous capillaries which unite to form small vessels and finally end in two or more larger veins inside of the villi. These latter are con- nected with the venous network in the mucosa. The glandular arteries, derived principally from the superficial network of the submucosa, also pass through the muscularis mucosae and break up internally into capillar)' nets which encircle the intestinal glands ; these give rise to small veins which empty into the venous plexus of the mucosa. The veins of the plexus in the mucosa unite to form larger branches, which connect with the plexus in the submucosa (compare Fig. 213). In the dog these trunks inside of the muscularis mucosa,- arc encircled by bundles of muscle-fibers (sphincters, F. P. Mall). The capillaries of the solitary lymph-nodules do not always penetrate into the centers of the latter, but often leave a central nonvascular area. The blood-vessels of the mucosa of the large intestine are, in their distribution, similar to the glandular vessels of the small intes- tine and stomach. The lymph-vessels begin in the mucosa near the epithelium, pass THE STOMACH AND INTESTINE. ^53 cl«>wn between the glands, and arc arranged in the form of a net- work just above the muscularis mucosae, but with coarser meshes than that formed by the blood-vessels. Here the valves begin to make their appearance. The lymph-vessels pass through the mus- cularis mucosa' and in the outer portion of the submucosa form a plexus with open meshes, from which arc derived the efferent ves- sels which penetrate the muscular co.it and thus gain access to the mesentery. In their course through the muscular coat they com- municate with the branches of a plexus of lymph-vessels situated between the two muscular layers, and also with lymph-vessels found in the serous coat. "" Central chyle- vessel of vil- lus. - Chvle-vessel. Gland of Lieber- kuhn. Base of villus. Artery Mucosa. &' Muscularis mucosae. - Sutunucosa. "^=-=^>- " -_■_ z ^~*~jz^\^J~^ <£- Vein. Plexus of lymph -ves- sels. Circular mus- cular layer. Plexus of lymph-ves- sels. Long', muse. layerwiththe serous coat. Fig. 213. — Schematic transverse section of the human small intestine (after F. 1'. Mall). The lymphatics of the small intestine begin in the axes of the villi. When filled, these lymph-vessels are conspicuous, irregularly cylindric capillary tubules, lined by endothelial cells, and known as the axial canals, the chyle-vessels, or the lacteals of the villi. They are hardly discernible when collapsed. If the villus be broad, it may contain two chyle-vessels, which then join at the apex of the villus, and may also be connected with each other by a few anasto- moses. At the base of the villus the chyle-vessel enters a lymphatic capillary network, the structure of which is due to the confluence ^54 THE DIGESTIVE ORGANS. of similar canals. Numerous lymph-vessels from this network penetrate the mucous membrane in a vertical direction, uniting at the bases of the intestinal glands to form a second plexus — sub- glandular plexus of the mucosa. A few of the lymph-vessels pene- trating the mucous membrane directly perforate the muscularis mucosa; to join the lymphatic network of the submucosa. The subglandular plexus also communicates with the submucous lymphatic plexus by means of small radiating branches {2nd. Fig. 213). The solitary lymph-nodules themselves contain no lymphatic vessels, but are encircled at their periphery by a network of lymph capillaries. The same is true of the nodules in Peyer's patches. It is an interesting fact that in the rabbit lymph-sinuses exist around Peyer's patches, giving to the latter a still greater similarity to the nodules of lymph-glands. The solitary nodules of the same Fig. 214. — A portion of the plexus of Auerbach from stomach of cat, stained with methylene-blue (intra vitani), as seen under low magnification. animal are not surrounded by the sinuses just mentioned (Stohr, 94)- The structures of the alimentary canal receive their innervation mainly from sympathetic neurones, the cell-bodies of which are grouped to form small ganglia, located at the nodal points of two plexuses, one of which is situated between the two layers of the muscular coat, the other in the submucosa. These two plexuses are found in the entire digestive tract, although not equally well developed in its different regions. The outer plexus, the more prominent of the two, situated between the two layers of the muscu- lar coat, is known as the plexus myentericus, or the plexus of Auer- bach. It consists of innumerable small sympathetic ganglia, united by small bundles of nonmcdullated fibers, containing here and there a much smaller number of medullated nerve-fibers. The cell-bodies of the sympathetic neurones of this plexus are grouped to form the THE STOMACH AND INTESTINE. H sympathetic ganglia. The dendrites, the number of which varies for the different cells, divide and re-divide in the ganglia, some ex- tending into the nerve bundles uniting the ganglia. The neuraxes of the sympathetic neurones of the ganglia form nonmedullated nerve-fibers, which leave the ganglia by one of the several roots possessed by each ganglion, and, after repeated division and forming intricate plexuses in the circular and longitudinal layers of the mus- cular coat, terminate on the involuntary muscle-cells of these layers. The plexus in the submucosa, known as the plexus of Meissner, is similarly constructed, although it contains fewer and much smaller ganglia and the meshes of the plexus are much finer. It commu- nicates by numerous anastomoses with the plexus of Auerbach. The neuraxes of the sympathetic neurones of this plexus have not been traced, with any degree of certainty, to their terminations. Numerous nonmedullated nerves enter the muscularis mucosa; and, according to Berkley (93, I), form in the dog terminal bulbs and nodules which perhaps rep- resent the endings of motor (sympathetic) nerves in this layer. Nerve-fibers have also been traced into the mucosa, and in the vicinity of the glands and in the villi are found numerous exceedingly fine nerve-fibers which inter- lace, but in the greater por- tion of the intestinal tract the endings of these fibers have not been full}- worked out. That they end on the gland- cells seems very probable from observations made by Kvtmanow (96), who was able, by means of the methylene-blue method, to stain plexuses of fine nerve-fibrils surrounding the gastric glands of the cat, some of these fibrils being traced through the basement membrane of the glands and to and between the gland-cells, where they ter- minated in clusters of small nodules on both the chief and parietal cells. The plexus of Meissner is not so well developed in the esophagus as in the remaining portions of the digestive tract. That the cell-bodies of many of the sympathetic neurones of Auerbach's and Meissner's plexuses are capable of being stimulated by cerebrospinal nerves seems certain from observations made by Dogiel (95), who has shown that many small medullated nerve- fibers which enter the digestive tract through the mesentery (small and large intestines) terminate after repeated division in terminal end-baskets which surround the cell -bodies of many of the sympa- thetic neurones of these plexuses. Similar nerve-fibers ending in Fig. 215. — From thin section of esopha^u^ of cat, showing the epithelium and a portion of the mucosa and the terminal nerve-fibrils in the epithelium (from preparation of Dr. DeWitt). 256 THE DIGESTIVE ORGANS. baskets have also been observed in the ganglia of the plexuses of the stomach and esophagus. Large medullated nerve-fibers, the dendrites of sensory neurones, have also been traced to the alimen- tary canal. In the esophagus these pass to the mucosa, where, after repeated division, they lose their medullar)- sheaths, the non- medullated terminal branches forming a subepithelial plexus from which terminal, varicose branches, further dividing, enter the strati- fied epithelium and may be traced to near the surface of the epithe- lium. Large medullated nerve -fibers may be traced through the ganglia of Auerbach's and Meissner's plexuses in the stomach and intestinal canal and through the nerve bundles uniting these ganglia (Dogiel, 99), but the termination of these fibers has not been deter- mined. 6. THE SECRETION OF THE INTESTINE AND THE ABSORPTION OF FAT. The cells of Brunner's glands are similar in many respects to those of the pyloric glands. During digestion they show analogous changes — i. c, the secretory cells are large and clear during a state of hunger, and become smaller and opaque during the process of secretion. Another and still greater similarity between Brunner's glands and the pyloric glands is established by the fact that the cells of the former, especially during hunger, have been shown to be rich in pepsin. It is well known that the goblet cells of the intestinal glands are very numerous during starvation, and that they nearly disappear after continued functional activity ; furthermore, they en- tirely disappear in certain portions of the rabbit's intestine after pilocarpin-poisoning. It would therefore appear that the principal physiologic function of the glands of Lieberkuhn is to secrete mucus, although the possibility of the production of another secretion, especially in the small intestine, must not be excluded (compare R. I leidenhain, 83). Until recently it was believed that the fat contained in the food was emulsified in the intestine, and furthermore that the bile acted upon the cuticular margins of the epithelial cells in the villi in such a manner that an assimilation of the emulsified fat by the cells of the villi (not by the goblet cells) was made possible. It has been re- peatedly observed that the epithelial cells contained fat granules during absorption. Hence a mechanism was sought for which would account for an assimilation of globules of emulsified fat on the part of the cells. It seemed most probable that protoplasmic threads (pseudopodia) were thrown out from each cell through its cuticular zone, which, after taking up the fat, withdrew with it again into the cell. But when it was shown that, after feeding with fatty acids or soaps, globules of fat still appeared in the epithelial cells as before, and that the chyle also contained fat, the hypothesis was THE LIVER. 257 suggested that the fat is split up by the pancreatic juice into glycerin and fatty acids, and that the fatty acids arc then dissolved by the bile and the alkalies of the intestinal juice, only again to combine with the glycerin to form fat within the epithelial cells. It remains for the histologist to ascertain the exact mechanism in the cell which changes the fatty acids into fat Altmann (94) claims that certain granules of the cells (elementary organisms) offer a solution to this problem. The manner in which the fat globules gain access to the central vessels of the villi is a question which has not as yet been settled. D. THE LIVER. In the adult the liver is a lobular, tubular gland with anastomos- ing tubules. When viewed with the unaided eye or under low magnification the liver is seen to be composed of a large number Intralobular vein. Branch of portal vein. Bile-duct. Branch of hepatic artery. Interlobular connective tissue. Fig. 216. — Section through liver of pig, showing chains of liver-cells; X 7°« of nearly spheric divisions of equal size ; this is particularly notice- able in some animals, especially in the pig. These divisions are the liver lobules and have a diameter of from 0.7 to 2.2 mm. They are separated from each other by a varying amount of interlobular con- nective tissue, which is a continuation of the eapsule of Glisson, a fibro-elastic layer surrounding the entire liver and covered for the greater portion by a layer of mesothelium. In the interlobular septa are found the larger blood-vessels, bile passages, nerves and lymph-vessels. On examining a thick section of the liver with a low power, a radiate structure of the lobule is noticeable, and an open space is seen in its center, which according to the direction of the section, is either completely surrounded by liver tissue or con- nected with the periphery of the lobule by a canal. This open 17 258 THE DIGESTIVE ORGANS. space represents the central or intralobular vein of the lobule which belongs to the system of the inferior vena cava. From the center of the lobule toward its periphery extend numerous radiating strands of cells, which branch freely and anastomose with each other, and are known as the trabecules, or cords of hepatic cells. Be- tween the latter are small, clear spaces occupied partly by blood capillaries and partly by the intralobular connective tissue. The above description is in some respects not a true statement of the appear- ance presented by the human liver, as in the latter one or more lobules may blend with each other, thus rendering the individual lobules less distinct. The Jicpatic cords consist of rows of hepatic cells. The cells Portal inter- — lobular branch, cut longitudi- nally. The same, cut -£ transversely. ^3 Fig. 217. -Section through injected liver of rabbit. The boundaries of the lo"bules are indistinct ; X about 35. are usually polyhedral in form, witli surfaces so approximated that a cylindric capillary space, known as the bile capillary remains be- tween them. The angles of the cells also show grooves which join those of the neighboring cells to form canals in which lie the blood capillaries. A closer examination of the hepatic cells reveals the fact that they possess no distinct membrane, and, in a resting state, usually contain a single nucleus, although some possess two. It is an interesting fact that nearly all the hepatic cells of some animals — as, for instance, the rabbit — contain two nuclei. The cell-bodies of the hepatic cells, which average from 18// to 26 ft in diameter, show a differentiation into protoplasm and paraplasm. This is especially manifest in a state of hunger. In this condition TIIK LIVER. 259 it is seen that the network of protoplasm around the nucleus is un- usually dense, and becomes looser in arrangement as it extends toward the periphery of the cell-body. The paraplasm is slightly granular, and contains glycogen and bile drops during the func- tional activity of the cell (secretion vacuoles). The vacuoles in the paraplasm play an important part in the secretion of the cell, and are Intralobular vein. Fig. 218. — Human bile capillaries. The capillaries of one lobule are seen to anas- tomose with those of the adjoining lobule (below, in the figure) ; X IIG (chrome-silver method). Vacuole of secretion. -~^s jr^ Tubule of same. \- Bile capillary. Fig. 219. — Human bile capillaries as seen in section ; \ 480 (chrome-silver method). due to the confluence of minute drops of bile into a large globule. As soon as the vacuole has attained a certain size it tends to empty its contents into the bile capillary through a small tubule connect- ing the vacuole with the bile capillary (Kupffer, 73, 89). The bile capillaries are, as we have remarked, nothing but tubu- lar, capillary spaces between the hepatic cells, with no distinct indi- 26o THE DIGESTIVE ORGANS. vidual walls. They may be compared to the lumen of a tubular gland, although in the human liver their walls consist of only two rows of hepatic cells. In the lower vertebrates the walls of the bile capillaries appear in transverse section to consist of several cells (in the frog generally three, in the viper as many as five). The bile capillaries naturally follow the course of the hepatic cords — i. e., in man extending radially. They form networks, the meshes of which correspond to the size of the hepatic cells. At the periphery of the lobule the hepatic cells pass directly over into the epithelial cells of the smaller interlobular bile-ducts. The epithelium of the latter is of the cubical variety, its cells being considerably smaller than the hepatic cells. At the point where the hepatic cells become J^Lss "i Biie.capMaries. continuous with the walls of the smaller passages we find a few cells of gradually decreasing size which represent a transition stage from the cells of the bile capil- Fig. 220. — Schematic diagram of he- patic cord in transverse section. At the left the bile capillar}' is formed by four cells, at the right by two ; the latter type occurs in the human adult. Fig. 221. — From the human liver, showing the beginning of the bile-ducts ; X 90 (chrome-silver). laries (hepatic cells) to those of the interlobular bile passages. The vascular system of the liver is peculiar in that, besides the usual arterial and venous vessels common to all organs, there is found another large afferent vein — the portal vein. It arises from a confluence of the superior and inferior mesenteric, the splenic, coronary veins from the stomach, and cystic veins. It divides into two branches, the right supplying the right lobe of the liver, the left the remaining lobes. These branches again divide into numerous smaller branches, the smallest of which finally reach the individual lobules. While still within the inter- lobular tissue, the branches of the portal vein receive the venous blood from the hepatic arterial system. These smaller divisions constitute the internal radicals of the portal vein, since they are within the liver itself. Along its whole course through the inter- lobular connective tissue the portal vein and its branches are accom- panied by divisions of the hepatic artery and bile passages. In a transverse section of the liver the arrangement of these structures in the interlobular tissue is such that the cross-sections of the vessels THE LIVER. 26l belonging to the hepatic vein are seen to be at some distance from the closely approximated branches of the portal vein and bile pas- sages. Branches of the portal vein encircle the liver lobules at different points, and while they remain within the interlobular con- nective tissue, are known as interlobular veins. From these, small offshoots are given off to the lobules which, on entering, divide into capillaries and form a closely reticulated network between the hepatic cords. The meshes of this network arc about as large as an hepatic cell, each cell coming in repeated contact with the blood capillaries. All of these capillaries pass toward the central or intralobular vein of the lobule, which during its efferent passage through the lobule continues to receive capillaries from the portal Blood capillaries. Intralobular vein. Cord of hepatic cells. Interlobular vessel. Fig. 222. — Injected blood-vessels in liver lobule of rabbit ; X IO °- system. The intralobular veins unite to form the sublobular veins, situated in the interlobular connective tissue, and these unite to form the larger hepatic veins which empty into the inferior vena cava. The relations of the various blood-vessels within the lobule are in themselves somewhat difficult of comprehension, but the whole be- comes still more complicated when the reciprocal relations of the vessels and bile capillaries are taken into consideration. In order to understand the structure of the liver lobule, with its hepatic cords, vessels, and bile capillaries, the following points should be borne in mind : The course of the bile capillaries is along the sur- faces, and that of the blood-vessels along the angles of the hepatic cells ; every cell comes in contact with a bile capillary and a blood 262 THE DIGESTIVE ORGANS. capillary. The latter, however, do not come in contact with the former, but in man are separated by at least half the breadth of a hepatic cell. In animals in which the bile capillaries are bounded by more than two cells, the blood-vessels extend along the outer sides of the hepatic cells ; here the bile and blood capillaries are separated from each other by the breadth of a whole cell. The connective tissue within the hepatic lobules presents points of interest which, however, are not demonstrable in organs treated by ordinary methods. But when the liver tissue is treated by a certain special method {vid. T. 258), an astounding number of fibers are seen extending in regular arrangement from the periphery toward the central vein. These fibers are extremely delicate, of nearly equal size, and intermingle in such a manner as to form an envel- oping network about the blood capillaries (Gitterfasern ; Kupffer ; - Intralobular vein. Boundary of - lobule. Fig. 223. — Reticulum (Gitterfasern) of dog's liver; X l2 ° (gold-chlorid method). Oppel, 91 ; vid. Fig. 223). A few coarser fibers (radiate fibers, Kupffer, 73) seem to enter in a less degree into the formation of the sheath around the blood capillaries ; they also extend from the periphery toward the center of the lobule and form a coarse reticu- lum, the meshes of which are drawn out radially. The radiate fibers are less prominent in man, but are numerous and well devel- oped in animals (rat, dog). With what exuberance the intralobular connective tissue may develop, is seen in the accompanying sketch of a sturgeon's liver, which is taken from one of Kupffer' s prepara- tions. ( a rtain peculiar cells — the so-called stellate cells of Kupffer (76) — occur exclusively in the lobule, and are seen only after a special method of treatment. They are uniformly distributed, of differ- ent shapes, elongated, and end in two or three pointed projee- THE LIVER. 263 tions. They arc smaller than the hepatic cells, and contain one or two nuclei. In a recent communication Kupfler (99) states that the stellate cells belong to the endothelium of the intralobular capillaries of the portal vein. In such cells blood-corpuscles and fragments of such were often found. The endothelium of these capillaries possesses, therefore, a phagocytic function, taking up particles of foreign mat- ter, blood-corpuscles, etc. The efferent ducts of the liver, the bile-ducts, are lined by col- umnar epithelium, varying in height in direct proportion to the cal- iber of the passage. The smallest ducts possess a low, the: medium sized a cubical, and the larger a columnar epithelium. The smaller bile-ducts have no clearly defined external walls other than the membrana propria ; the larger ones, on the other hand, possess a Connective- tissue fibers. Fig. 224. — Connective tissue from liver of sturgeon. At a is an open space from which the hepatic cells were mechanically removed during treatment. connective-tissue sheath which ma}- even present two layers in the larger passages. Unstriped muscular fibers occur in the large ducts, but do not form a continuous layer until the gall-bladder is reached, where two layers are found. The epithelium of the gall-bladder is of the columnar variety, with nuclei in the lower thirds of the cells ; a cuticular zone is either absent or very poorly developed. The mucous membrane of the gall-bladder is raised into folds having a peculiar reticular arrangement. The gall-bladder contains a few mucous glands ; these are, however, more numerous in the hepatic, cystic, and common bile-ducts. Besides the network of lympli-vcsscls accompanying the portal vein and hepatic artery, there are also lymphatic networks about the branches of the hepatic vein (v. Wittich). The lymph-ves- sels penetrate the liver lobules and pass between the hepatic cells 264 THE DIGESTIVE ORGANS. and the blood capillaries to form perivascular capillary lymph- spaces. Berkley (94) has described several divisions of the intrinsic nerves of the liver, all connected and morphologically alike. These nerves are no doubt the neuraxes of sympathetic neurones, the cell-bodies of which are located in ganglia outside of this organ. No medul- lated fibers were found by him, although it seems probable that the nerve-fibrils terminating between the" cells of the bile-ducts (see be- low) are terminal branches of sensory nerve-fibers. The nerves of the liver accompany the portal vessels, the hepatic arteries, and the bile-ducts. The first division of the nerves, embracing the larger number of the intrinsic hepatic nerves, accompany the branches of the portal vessels, form plexuses about them, and end in inter- lobular and intralobular ramifications, the latter showing here and there knob-like terminations on the liver-cells, and, in their course, give off here and there branches which end on the portal vessels. Intralobular vein. -Interlobular con- nective tissue. "Stellate cells. Fig. 225. — Part of a section through liver lobule from dog, showing stellate cells ; X 168 (7V./. T. 257). . The nerve-fibers following the hepatic arteries are in every respect like the vascular nerves in other glands. Some of the terminal branches seem, however, to end on hepatic cells. The nerve-fibers following the bile-ducts may be traced to the smaller and medium-sized ducts, forming a network about them, and ending here and there in small twigs on the outer surface of the cells, and occasionally, it would seem, between the epithelial cells lining the ducts. The suggestion seems warranted that these terminal fibrils are the end- ings of sensory nerves. Some of the nerve-fibers following the bile-ducts may be traced into the hepatic lobules. The intralobu- lar plexus is formed, therefore, by the terminal branches of the non- medullated nerve-fibers accompanying the portal and hepatic ves- sels and the bile-ducts. In the wall of the gall-bladder are found numerous small sympathetic ganglia formed by the grouping of the cell-bodies of sympathetic neurones (Dogiel). The neuraxes of these THE PANCREAS. J,, 5 innervate the nonstriated muscle of this structure. Large, medul- lated nerve-fibers may be trai ed through these ganglia which appear to end in free sensory endings in and under the epithelium lining the gall-bladder (Huber). In the human embryo the liver originates from the intestine during the second mouth as a double ventral diverticulum. Later solid trabecular masses are developed which then unite and become hollow. At this stage the whole gland is uniform in structure, as a division into lobules dors not take place until later. The bile capillaries are surrounded by more than two rows of cells. In this stage the embryonal liver suggests a condition which is permanent during the life of certain animals. Only later when the venae ad- vehentes, which later represent the branches of the portal vein, penetrate the liver, is there a secondary division into lobules (about the fourth month), by which process the primitive type gradually changes to that characteristic of the adult. N'iu leus :m) Alcoholic solution — 0.2 gm. hematein, 0.1 gm. aluminium chlorid, 100 c.c. 70'/, alcohol, and 1 or 2 drops of nitric acid. Both of these solutions are used for staining mucin in sections and thin membranes. By the use of these methods the mucous acini of mixed glands are shown with ease and pre- cision. Under favorable conditions the whole secretory and excretory system of the gland may be brought out by Golgi's method (see this). 240. In order to obtain a general structural view of the esophagus a small animal may be selected, in which case small pieces of tissue are fixed and imbedded in paraffin. H a large animal is used, the tissue is imbedded in celloidin. 241. The mucous membrane of the stomach should be fixed while still fresh and warm, the best fixative for this purpose being corrosive sub- limate. Mixtures of osmic acid are also serviceable, but fixing with cor- rosive sublimate increases the staining power of the tissue. In order to preserve the stomach and intestine in a dilated condition, they should be filled with the fixing fluid and after ligation placed whole in the fixing agent. 242. In gastric mucous membrane that has been fixed either with cor- rosive sublimate or alcohol, the parietal cells are easily differentiated from the chief cells by staining. The most reliable and convenient rhethod is as follows : Sections fastened to the slide by the water-albumin fixative method are stained with hematoxylin and then placed in a dilute aqueous solution of Congo red until they assume a red color (minutes); they are then washed with dilute alcohol until the parietal cells appear red and the chief cells bluish (Stintzing). Almost all acid anilin dyes have an affinity for the parietal cells ; hence the red stains may be com- bined with hematoxylin and the blue ones with carmin. The chief cells then take the color of the carmin or hematoxylin, and the parietal cells that of the anilins. 243. An accurate fixation of that portion of the small intestine pos- sessing villi is attended with great difficulty, since the axial tissue of the villi shows a tendency to retract from the epithelial layer surrounding it (the latter becoming fixed first ); and as a consequence spaces are formed at the summits of the villi which undoubtedly represent artefacts. A good method is to cut pieces from tissue while still warm and fix in osmic acid. If portions of the intestine be filled with alcohol or corrosive sub- limate and thus dilated, both the glands and villi are shortened. The 2/2 THE DIGESTIVE ORGANS. methods above mentioned for staining mucin may be used to stain the goblet cells. The villi may also be examined in a fresh condition in one of the indifferent fluids (vid. T. 13). For this purpose the intestine of the mouse is especially well adapted. 244. The absorption of fat is best studied in preparations fixed in osmic acid, and especially in those treated by Altmann's method {yid. T. 124). 245. The technic for the solitary lymph-follicles and Peyer's patches is the same as that for lymph -glands. For this purpose the cecum of a rabbit or guinea-pig is the best material. 246. The nerves of the intestinal mucous membrane are best demon- strated by means of the methylene-blue method or Golgi's method (yid. Technic), and the coarser filaments of Auerbach's and Meissner's plexuses may also be stained by the gold method (Lowit's procedure, T. 182). Good results are also obtained by staining with hematoxylin such speci- mens as have been previously fixed and distended with alcohol. The plexuses then appear somewhat darker than the remaining tissue of the isolated mucous membrane or muscular layer. 247. The arrangement of the liver lobules is best seen in the pig's liver. In the human liver and in most domestic animals the lobules are not sharply defined, two or three adjacent lobules merging into each other. In the liver of the fetus, of the new-born, and of children, the lobules are seen indistinctly Or not at all, although the perivascular spaces of the blood-vessels are better seen than in the adult. 248. The liver-cells are best examined by treating small pieces of tissue with 1 n the epithelial cells in small nodules, or small clusters of nodules. In the trachea of the dog, such fibrils were traced to the ciliary border of the columnar ciliated cells before terminating. Numerous sympathetic ganglia are found in the larynx and trachea. In the latter they are especially numerous in the posterior wall. The neuraxes of the sympathetic neurones forming these ganglia were traced to the nonstriated muscular tissue of the trachea. The cell- bodies of these sympathetic neurones are surrounded by end-baskets of small medullated fibers terminating in the ganglia. Medullated Fig. 232. — From longitudinal section of human trachea, stained in orcein. nerve-fibers, ending in the musculature of the trachea in peculiar end-brushes, were also described by Ploschko. C THE BRONCHI, THEIR BRANCHES, AND THE BRONCHIOLES. The primary bronchi and their branches show the same general structure as the trachea. The epithelium of the bronchi of medium size (up to 0.5 mm. in diameter) consists of a ciliated epithelium having three strata of nuclei. Kollikcr (81) distinguishes a deep layer of basilar cells, a middle layer of replacing cells, and a super- ficial zone consisting of ciliate and goblet cells. The number of the last varies greatly. Glands are found only in bronchial twigs that are not less than i mm. in diameter ; as in the trachea, they are branched tubulo-acinous glands of the mucous variety. 2 7 8 ORGANS OF RESPIRATION. In these structures the mucosa contains a large number of elastic fibers, the greater part of which have a longitudinal direction. Furthermore, numerous lymph-cells are found, and here and there a lymph-nodule. The muscularis presents, as a rule, circular fibers, which do not, however, form a continuous layer. The cartilaginous framework here no longer consists of symmetrically arranged rings, but of irregular platelets, which are absent in bronchial twigs less than 0.85 mm. in diameter. The smaller bronchi subdivide into still finer tubules of less than 0.5 mm. in diameter (bronchioles), which contain neither car- stratified cili- ated columnar epithelium. — Elastic fibers, cut trans- versely. - Gland. Mucosa. i %•' --%*■ — Cartilage. Connective tissue. Fig. 233. — Transverse section through human bronchus ; X 2 7« tilage nor glands. The stratum proprium, as well as the external connective-tissue sheath, becomes very thin ; and the epithelium now consists of but one layer, but is still ciliated. RESPIRATORS BRONCHIOLES AND [NFUNDIBULA. 279 D. THE RESPIRATORY BRONCHIOLES, ALVEOLAR DUCTS, AND INFUNDIBULA. The bronchioles arc continued as the respiratory bronchioles. ---•; Artery ' Lung tissue. Respiratory /j bronchiole. Fig. 234- ,.% '■■: - ■ ■ • ■ Lung tissue. Alveolar duct. v*V Fig. 235. Figs. 234 and 235.— Two sections of cat's lung : Fig. 234, X 5 2 5 F 'g- 2 35> X 35- The epithelium of the latter is ciliated in patches, but ultimately be- comes nonciliated, and assumes the character of the respiratory epi- 28o ORGANS OF RESPIRATION. thelium. (See below.) The fine tubular segments of the respiratory- passages, lined by an epithelium which marks the transition from the mixed to the respirator)- epithelium, are known as the alveolar ducts. The muscle-fibers may be traced as far as these segments, where they are lost. Both in the walls of the respiratory bron- chioles and along the alveolar ducts there occur diverticula called alveoli. Each alveolar duct is continuous with a so-called infundibulum. Section of al veolus of lung. U Respiratory bronchiole with two kinds of epithelium. «! -Respiratory bronchiole. Fig. 236. — Internal surface of a human respiratory bronchiole, treated with silver nitrate; / 234 (after KSlliker). The general shape of the latter is conical, the base of the cone be- ing turned away from the duct. Numerous diverticula are present in the walls of the infundibula, known as the air-sacs or alveoli of the lung. The epithelium of the infundibulum (i i //. to i 5 /i in diam- cterj and of its alveoli (the so-called respiratory epithelium) con- sists of two varieties of cells (F. E. Schulze) — smaller nucleated elements and larger nonnucleated platelets (the latter derived very probably from the former). The arrangement of the epithelial cells RESPIRATORY I5KONCH IDLES AND INFUNDIBULA. 281 nerally such that the nonnucleated platelets rest directly upon the blood capillaries, while nucleated cells lie between them. The basement membrane beneath the epithelium of the respiratory pas- sages gradually becomes thinner as it approaches the infundibula, and in the latter is scarcely to be seen. In amphibia the epithelium of the alveoli consists of cells, of whi< h the portion containing the nucleus forms a broad cylindric base ; from the free end of each cell a lateral process extends over the adjoining capillary to meet a similar process from the neighboring cell. When viewed from above, the basal portion of the (ell appears dark and granular, while the processes are clear and transparent. These cells, together with their prolongations, are about 50 ,u in diameter. The surface view greatly re- sembles that of the human respiratory epithelium (Duval, Oppel, 89]. *J$.l Nonnucleated epi- thelial cell. . Nucleated epithelial cell. Fig- 237. — Inner surface of human alveolus treated with silver nitrate, showing respira- tory epithelium ; X 2 4° (after Kolliker). The walls of the infundibulum and its alveoli are encircled by vet')' delicate elastic fibers. The lung tissue is arranged in small lobules, which form defi- nite units in its anatomy and pathology (Councilmann, 1900). These lobules have a diameter of from 1 to 3 cm. in the adult, and from 0.5 to 1.5 cm. in the child from two to eight years old. They are of pyramidal shape, the apex of the lobule being formed by a small bronchus. They are separated from one another by a small amount of interlobular fibrous tissue. The small bronchus entering the apex of each lobule divides within the lobule several times, each bronchiole becoming a respiratory bronchiole, alveolar duct, and infundibulum, with alveoli or air-sacs associated with them. The visceral and the parietal layers of the pleura consist of a layer of fibro-elastic tissue covered by a layer of mesothelium. The blood-vessels of the lung have been described by Miller 282 ORGANS OF RESPIRATION. (93) working under Mall's direction. His account is closely fol- lowed in the following description : The pulmonary artery follows closely the bronchi through their entire length. An arterial branch enters each lobule of the lung at its apex in close proximity to the bronchus. After entering the lobule the artery divides quite ab- ruptly, a branch going to each infundibulum ; from these branches the small arterioles arise which supply the alveoli of the lung. " On reaching the air-sac the artery breaks up into small radicals which pass to the central side of the sac in the sulci between the air-cells, and are finally lost in the rich system of capillaries to which they give rise. This network surrounds the whole air-sac and communicates freely with that of the surrounding sacs." This capillary network is exceedingly fine and is sunken into the epi- thelium of the air-sacs so that between the epithelium and the capil- lar)' there is only the extremely delicate basement membrane. The infundibula, the alveolar ducts and their alveoli, and the alveoli of the respiratory bron- chioles are supplied with similar capillary networks. The veins collecting the blood from the lobules lie at the periphery of the lobules in the interlobular con- nective tissue, and are as far dis- tant from the intralobular arteries as possible. These veins unite to form the larger pulmonary veins. The bronchi, both large and small, as well as the bronchioles, derive their blood supply from the bronchial arteries, which also partly supply the lung itself. Capillaries derived from these ar- teries surround the bronchial system, their caliber varying according to the structure they supply — finer and more closely arranged in the mucous membrane, and coarser in the connective-tissue walls. In the neighborhood of the terminal bronchial tubes the capillary nets anastomose freely with those of the respiratory capillary system. From the capillaries of the bronchial arteries, veins are formed which empty cither into the bronchial veins or into the branches of the pulmonary veins. The lymphatics of the lung originate between the alveoli. They form two sets of vessels (Councilmann, 1900) — the one found in the interlobular connective tissue, which communicates with lymph- vessels in the pleura, forming a rich plexus, terminating in several lymphatic vessels, provided with valves, which end in the lymph- glands at the root of the lung, and " a central set which accompa- Fig. 238. — Scheme of the respiratory epithelium in amphibia : The upper figure gives a surface view : l>, Basilar portion ; a, the thin process. The lower figure is a sec- tion : a, Respiratory epithelial cell ; />, blood- vessel ; a > The irregular interlacing pro- jections. ***** ■ Fig. 249. — Prom cortical portion of longitudinal section of kidney of young child. often be separated as a whole from the underlying basement mem- brane. The distal convoluted or intercalated portion, from 39/* to 45 /i in THE URINARY ORGANS. '■93 diameter, is only slightly curved (2 to 4 convolutions). Its epi- thelium is relatively high, though not so high as that lining the proximal convoluted portion and not SO distinctly striated. The cells are provided with large nuclei and their basal portions are- joined by interlacing projections. The next important segment is the short arched collecting portion^ which has nearly cubical epithelial cells and a lumen somewhat wider than that of the intercalated tubule. The smaller straight collecting tubules have a low columnar epithelium with cells of somewhat ir- regular shape, the basal portions of which are provided with short, irregular, intertwining processes, which serve to hold the cells in " Wf(l -4H ■<•.? I medulla of human kidney limb of Henle's loop ; b, b, b, blood-vessels ; c, c, c, descending limb of Ilenle's loop. Fig. 250. — Section of medulla of human kidney ; X about 300 : o, a, a, Ascending place. The diameter of the collecting tubules measures from 45 />. to 75/^. In the larger collecting tubules the epithelium is more regular and becomes higher as the tube widens. These tubules gradually unite within the Malpighian pyramid and the regions adjacent to the columns of Bertini to form about 20 papillary ducts from 200 it to 300// in diameter. The latter have a high columnar epithelium, and empty into the pelvis of the kidney at the apex of the papilla, forming the foramina pa pill aria. Besides the epithelium, the uriniferous tubules possess an ap- 2 9 4 THE GENITO-UKINAKV ORGANS. parently structureless membrana propria, that of the collecting tubules being very thin. According to Riihle (97), the membrana propria of the uriniferous tubules consists of fine circular and longi- tudinal fibers which are at no point connected with the cells, and which represent nothing more than a thickened and more regularly distributed layer of the interstitial reticular tissue. The basement membrane of the vascular loops in the glomeruli also appears to have a fibrous structure and presents numerous fine openings. Between the Malpighian pyramids are found the columns of Bertini, presenting a structure similar to that of the cortex of the kidney, and extending to the hilum of the kidney. Between the uriniferous tubules and surrounding the blood- vessels of the kidney there is found normally a small amount of connective tissue. Between the convoluted portions of the tubules this is present only in small quantity, a somewhat greater amount Papillary duct. I r 7 /t/u-v-- -' : ' Blood-vessel. Fig. 251. — From longitudinal section through papilla of injected kidney; X 4° : a > Epi- thelium of collecting tubule under greater magnification. being found in the neighborhood of the Malpighian corpuscles, in the boundary zone between the cortex and medulla and between the larger collecting tubules in the apices of the Malpighian pyra- mids. From what has been said concerning the uriniferous tubule it must be evident that its course is a very tortuous one. Beginning with the Malpighian corpuscles, situated in the cortex between the medullary rays, the tubule winds from the cortex to the medulla and back again into the cortex, where it ends in a collecting tubule, which passes to the medulla to terminate at the apex of a Malpig- hian pyramid. The different portions of the tubules have the following positions in the kidney : In the cortex between the medul- lary rays are found the Malpighian corpuscles, the neck, the proxi- mal and distal convoluted portions of the uriniferous tubule, and the I in. URINARY ORGANS. 295 arched collecting tubules. The medullary rays arc formed by the cortical portions of the straight collecting tubules and a portion of the ascending limbs of Henle's loops. The medulla is made up mainly of straight collecting tubules of various sizes and of the de- scending limbs and loops of Henle's loops, the latter being often found in the boundary zone between the cortex and medulla. (See Fig. 250.) The blood-vessels of the kidney have a characteristic distribu- tion, and are in the closest relationship to the uriniferous tubules. — Boundary line bet\\' Malpighian pyramids. Uriniferous tubules. Glomerulus. Fig. 252. — Section through junction of two lobules of kidney, showing their coalescence; from new-born infant. The renal artery divides in the neighborhood of the hilum into two branches, — a dorsal and a ventral, — which again divide, the result- ing trunks giving off lateral branches to the renal pelvis, supplying its mucous membrane and then breaking up into capillaries which extend as far as the "area cribrosa." The venous capillaries of this region empty into veins which accompany the arteries. Besides these, other arteries originate from the principal branches, or from their immediate offshoots, and pass backward to supply the walls of the renal pelvis, the renal capsule, and the ureter. The main 296 THE GENITOURINARY ORGANS. trunks themselves penetrate at the hilum, and divide in the columns of Bertini to form arterial arches (arteriae arciformes) which extend between the cortical and medullary substances. Numerous vessels, the intralobular arteries, originate from the arteriae arciformes and penetrate into the cortical pyramids between the medullary rays. Here they give off numerous twigs, each of which ends in the glomerulus of a Malpighian corpuscle. These short lateral twigs arc the vasa afferentia. Each glomerulus is formed by the breaking down of its afferent vessel, which, on entering the Malpighian cor- puscle, divides into a number of branches, each in turn subdividing into a capillar}' net. From each of these nets the blood passes into a somewhat larger vessel constituting one of the branches of the efferent vessel which carries the blood awav from the glomerulus. Since the afferent and efferent vessels lie in close proximity, the capillary nets connecting them are necessarily bent in the form of loops. The groups of capillaries in a glomerulus are separated from each other by a larger amount of connective tissue than separates the capillaries themselves, so that the glomerulus may be divided into lobules. In shape the glomerulus is spheric, and is covered by a thin layer of connective tissue over which lies the inner mem- brane of the capsule, the glomerular epithelium. On its exit from the glomerulus the vas efferens separates into a new system of capillaries, which gradually becomes venous in character. Thus, the capillaries which form the glomerulus, together with the vas efferens, are arterial, and may be included in the category of the so-called arterial retia mirabilia. Those capillaries formed by the vas efferens after its exit from the Malpighian corpuscle lie both in the medullary rays and in the cortical pyramids. The meshes of the capillary net- works distributed throughout the medullar}- rays are considerably longer than those of the networks supplying the cortical pyramids and labyrinth, the latter being quadrate in shape. The glomeruli nearest the renal papillae give off longer vasa efferentia which extend into the papillary region of the Malpighian pyramids (arteriolar rectae spuriae) and form there capillaries which ramify throughout the papiike with oblong meshes. Arterial retia mirabilia also occur in the course of the vasa afferentia between the intralobular arteries and the glomeruli, but nearer the latter. Each is formed by the breaking down of the small afferent vessels into from two to four smaller branches, which then reunite to pass on as a single vessel. In structure these retia differ greatly from the glomeruli in that here the resulting twigs are not capillaries and have nothing to do with the secretion of urine (Golubew). From the vasa afferentia arterial twigs are occasionally given off, which break down into capillaries within the cortical substance. Other arteries originate from the lower portion of the intralob- ular arteries or from the arciform arteries themselves and enter the medullar}- substance, where the}' form capillaries. These THE URINARY ORGANS. 297 vessels constitute the so-called "arteriolae rectae verae." Their capillary system is in direct communication with the capillaries of the vasa afferentia and " vasa recta spuria." The intralobular arteries are not entirely exhausted in supplying the vasa affeientia which pass to the glomeruli. A few extend to the surface of the kidney and penetrate into the renal capsule, where they termin- ate in capillaries which communicate with those of the recur- rent, suprarenal, and phrenic arteries, etc. Smaller branches Arched collecting tubule. Straight collect- ing tubule. Distal convoluted tubule. Malpighian cor- puscle. Proximal convo- luted tubule.. Loop of Henle. Collecting tubule. Arteria arcuata. Large collecting tubule. Papillary duct. — Glomerulus. Vena arcuata. Fig- 253. — Diagrammatic scheme of uriniferous tubules and blood-vessels of kidnev. Drawn in part from the descriptions of Golubew. from these latter vessels may penetrate the cortex and form glomeruli of their own in the renal parenchyma (arteriae capsulares glomeruliferae). These relations, first described by Golubew, are of importance not only in the establishment of a collateral circula- tion, but also as a partial functional substitute in case of injury to the renal arteries. The same author also confirms the statements of Hover (jy) and Geberg, that between the arteries and veins of the kidney, in the cortical substance, in the columns of Bertini, and 298 THE GENITOURINARY ORGANS. at the bases of the Malpighian pyramids, etc., direct anastomoses exist by means of precapillary twigs. From the capillaries the venous blood is gathered into small veins which pass out from the region of the medullary rays and cortical pyramids and unite to form the "intralobular veins." These have an arrangement similar to that of the corresponding arteries. The venous blood of the labyrinthian capillaries also flows into the intralobular veins, and as a result a peculiar arrangement of these vessels is seen at the surface of the kidney where the capillaries pass radially toward the terminal branches of the intralobular veins and form the stellate figures known as the vence stcllatcc. This sys- tem is also connected with those venous capillaries of the capsule which do not empty into the veins ac- companying the arteries of the capsule. The capillary system of the Malpighian pyramids unites to form veins, the " venulae rectae," which empty into the venous arches (venae arciformes) which lie parallel with and adjacent to the corresponding arteries. The larger veins are found side by side with the arteries and pass out at the hilum of the organ. The lymph-vessels of the kidneys need to be investigated further. Lymph clefts have been observed in the cortex between the convoluted tubules ; these have been traced into larger vessels found in the capsule. The kidneys receive their innerva- tion through nonmedullated and medul- lated nerve-fibers. The former accom- pany the arteries and may be traced along these to the Malpighian corpus- cles. From the plexuses surrounding the vessels small branches are given off, which end on the muscle-cells of the media. According to Berkley, small nerve-fibrils may be traced to the uriniferous tubules, which pierce the membrana propria and end on the epithelial cells. Dogiel has shown that medullated (sensory) nerve-fibers terminate in the adventitia of the arteries of the capsule. The most important investigations into the secretory processes of the uriniferous tubules are those of R. Hcidcnhain (83) who used indigo-carmin in his researches. If a saturated aqueous solution of indigo-carmin be injected into the blood-vessels of a rabbit, the elimination of the substance will be found to take place through the kidneys as well as by means of the other excretions. Microscopic examination of such a kidney reveals the fact that the proximal convoluted tubules and ascending limbs of the loops of Fig. 254. — A, Direct anasto- mosis between an artery and vein in a column of Bertin of child ; B, bipolar rete mirabile inserted in the course of an arterial twig. Dog's kidney (after Golubew). THE URINARY ORGANS. 299 Hcnle arc alone concerned in the elimination of the substance, while apparently water alone is filtered through the remaining seg- ments of the uriniferous tubules. Among others, Disse has recently taken up the subject of cellular secretion in the uriniferous tubules. According to him, we may distinguish in the convoluted tubules (1) those with a wide lumen, having low cells apparently with no cell limits and no distinct basilar zone, but with peculiar structures which may be likened to cuticuke, so called, or a striated border (Tornier) (Fig. 247) ; (2) tubules with a narrow lumen and wedge-shaped epithelial cells, with indistinct cell limits and diffusely granular protoplasm ; (3) tubules with an extremely narrow lumen and high epithelial cells with differentiated protoplasm, the basal portion of which is dark and striated, the upper clear and contain- ing the nucleus. These results are not, however, confirmed by the painstaking researches of Sauer. This author finds that the secre- tory portions of the uriniferous tubules (convoluted portions of the tubules and part of the loops of Henle) always have the same un- changed epithelium, but that, during secretion, the lumina of the tubules are subject to great variation ; in tubules with scarcely recognizable lumina the epithelial elements are high and narrow ; in those with wide lumina, low and broad. In the former the stria- tion of Heidenhain is naturally fine ; in the latter, somewhat coarser. The peculiar terminations of Tornier are found by Sauer during all phases of secretion. According to this view, then, neither the striation of Heidenhain nor the terminations of Tornier are tem- poral'}' appearances due to a particular phase of secretion, but represent permanent structural peculiarities of the cells in certain definite portions of the uriniferous tubules. The volumetric changes in the uriniferous tubules also probably influence the form and number of the indentations in the epithelial cells described on page 291. The permanent kidney is developed as early as the fifth week of embryonic life. The renal anlagen, from which the epithelium of the ureter, renal pelvis, and uriniferous tubules is formed, originate from the median portion of the posterior wall of the Wolffian duct. These buds grow with their blind ends extending anteriorly, and are soon surrounded by cellular areas, the blastema of the kidneys. After the renal bud has become differentiated into a narrow tube (the ureter) and a wider central cavity (the renal pelvis) hollow epithelial buds are developed from the latter. These extend radi- ally toward the surface of the renal anlagen, where the}- undergo a T-shaped division. These latter are the first traces of the papillary ducts and collecting tubules. The cup-shaped capsules are formed by the invagination of the ends of the tubules by the glomeruli which originate separately and in this way become connected with the uriniferous tubules. The remaining portions of the adult urin- iferous tubules are gradually formed from the tubes connecting the glomeruli with the collecting tubules. 300 THE GENITOURINARY ORGANS. 2. THE PELVIS OF THE KIDNEY, URETER, AND BLADDER. The renal pelvis, ureter, and urinary bladder are lined by strati- fied transitional epithelium. Its basal cells are nearly cubical ; these support from two to five rows of cells of varying shape. They may be spindle-shaped, irregularly polygonal, conical, or sharply angular, and provided with processes. Their variation in form is probably due to mutual pressure. The superficial cells are large fgsg fV. 11 --\^ = V ', fit mi ._ Superficial epi- thelial cells. Mucosa. Epithelium. Inner longitud- inal muscular layer. Middle circular muscular layer. Outer muscular layer. Fig. 255. — Section of lower part of human ureter; X I 4°- and cylindric, a condition characteristic of the ureter and bladder. Their free ends and lateral surfaces are smooth, but their bases pre- sent indentations and projections due to the irregular outlines of the underlying cells. The superficial cells often possess two or more nuclei. The mucosa often contains diffuse lymphoid tissue, which is more highly developed in the region of the renal pelvis. A few THE SUPRARENAL GLANDS. 301 mucous glands are also met with in the pelvis and in the upper por- tion of the ureter. The ureter possesses two layers of nonstriated muscle-fibers — the inner longitudinal, the outer circular. From the middle of the ureter downward a third external muscular layer is found with nearly longitudinal filters. The urinary bladder has no glands, and its musculature appar- ently consists of a feltwork of nonstriated muscle bundles, a condi- tion particularly well seen in sections of the dilated organ. But even here three indistinct muscle layers may be distinguished, the outer and inner layers being longitudinal and the middle circular. A remarkable peculiarity of these structures is the extreme elasticity of their epithelium, the cells flattening or retaining their natural shape according to the amount of fluid in the cavities which they line (compare London, Kann). The nerve supply of the bladder has been studied by Retzius, Huber, and Grunstein in the frog and a number of the smaller mammalia. Numerous sympathetic ganglia are observed, situated outside of the muscular coat, at the base and sides of the bladder. The neuraxes of the sympathetic neurones of these ganglia are grouped into smaller or larger bundles which interlace and form plexuses surrounding the bundles of nonstriated muscle-cells. From these plexuses nerve-fibers are given off, which penetrate the muscle bundles and end on the muscle-cells. The cell-bodies of the sym- pathetic neurones are surrounded by the telodendria of small medullated fibers, which terminate in the. ganglia. Passing through the ganglia large medullated fibers (sensory nerves) may be ob- served which pass through the muscular coat, branch repeatedly in the mucosa, and lose their medullary sheaths on approaching the epithelium in which they end in numerous telodendria, the small branches of which terminate between the epithelial cells. The ureters are surrounded by a nerve plexus containing non- medullated and medullated nerve-fibers. The former end on cells of the muscular layers ; the latter pass through the muscular layer, and on reaching the mucosa branch a number of times before losing their medullary sheaths. The nonmedullated terminal branches form telodendria, the terminal fibers of which have been traced between the cells of the lining epithelium (Huber). B. THE SUPRARENAL GLANDS. The suprarenal gland is surrounded by a fibrous-tissue capsule containing nonstriated muscle-cells, blood- and lymph-vessels, nerves, and sympathetic ganglia. The glandular structure is divided into a cortical and a medullary portion. In the former are distin- guished three layers, according to the arrangement, shape, and structure of its cells — an outer glomerular zone, a middle broad fas- cicular zone, and an inner reticular zone. According to Flint, who 302 THE GENITOURINARY ORGANS. worked in Mall's laboratory, and whose account will here be fol- lowed, the framework of the gland is made up of reticulum. In the glomerular zone this reticulum is arranged in the form of septa, derived from the capsule, which divide this zone into more or less regular spaces of oval or oblong shape. In the fascicular zone the reticulum is arranged in processes and fibrils running at right angles to the capsule. In the reticular zone the fibrils form a dense network, while in the medulla the reticular fibrils are arranged in processes and septa which outline numerous spaces. Capsule. Zona glomerulosa. ,. Zona fasciculata. Zona reticularis. Fig. 256. — Section of suprarenal cortex of dog ; X I2 °- The gland-cells of the glomerular zone are arranged in coiled col- umns of cells found in the compartments formed by the septa of reticulum above mentioned. The cells composing these columns are irregularly columnar, with granular protoplasm and deeply stain- ing nuclei. In the fascicular zone the cells are arranged in regular columns, consisting usually of two rows of cells, and situated be- tween the reticular processes, which run at right angles to the cap- TIM'. SUPRARENAL GLANDS. 303 sulc. The cells of this zone are polyhedral in shape, with gran- ular protoplasm often containing fat droplets and with nuclei containing little chromatin. Similar cells are round in the reticular zone, but here they are found in small groups situated in the me of the reticulum. The cells of the medullar}' substance are less granular and smaller in size than those of the cortex, and are grouped in irregular, round, or oval masses hounded by the septa of reticulum. These cells stain a deep brown with chromic acid and its Fig- 257. — Arrangement of the intrinsic blood-vessels in the cortex and medulla of the dog's adrenal (Fig. 17, Plate V, of Flint's article in "Contributions to the Science of Medicine," dedicated to Professor Welch, 1900). salts, and the color can not be washed out with water — a peculiarity which shows itself even during the development of these elements, and which is possessed by few other types of cells. Numerous ganglion cells, isolated and in groups, and many nerve-fibers occur in this portion of the organ. The blood-vessels of the suprarenal glands are of special interest, since it has been shown that the secretion of the glands passes directly or indirectly into the vessels. The following statements 304 THE GENITOURINARY ORGANS. we take from Flint : The blood-vessels, derived from various sources, form in the dog a poorly developed plexus, situated in the capsule. From this plexus three sets of vessels are derived, which arc distributed respectively in the capsule, the cortex, and the medulla of the gland. The vessels of the capsule divide into capillaries, which empty into a venous plexus situated in the deeper portion of the capsule. The cortical arteries divide into capillaries which form networks, the meshes of which correspond to the arrangement of the cells in the different parts of the cortex, encircling the coiled columns of cells in the glomerular zone, while in the fascicular zone the capillaries are parallel with occa- sional anastomoses. These capillaries form a fine-meshed plexus in the reticular zone and unite in the peripheral portion of the medulla to form small anastomosing veins, from which the larger veins are derived. The latter do not anastomose, and are therefore terminal veins. The arteries of the medulla pass through the cortex without giving off any branches until the medulla is reached, where they break up into a capillary network surrounding the cell masses situated here. The blood from this plexus may be col- lected into veins of the medulla which empty into the terminal vein or some of its larger branches, or may flow directly into branches of the venous tree. The endothelial walls of the capil- laries rest directly on the specific gland cells, with the intervention here and there of a few reticular fibrils. According to Pfaundler, the walls of the blood-vessels of the entire suprarenal body consist solely of the tunica intima. The nerves of the suprarenal glands have been studied recently by Fusari and Dogiel (94) ; the description given by the latter will here be followed. Numerous nerve-fibers, both nonmedullated and medullated, arranged in the form of a plexus containing sym- pathetic ganglia, are found in the capsule. From this plexus numerous small bundles and varicose fibers enter the cortex, where they form plexuses surrounding the columns of cells or groups of cells found in the three zones of the cortex and about the vessels and capillaries of the cortex. The nerve-fibers of these plexuses are on the outside of the columns and cell groups and do not give off branches which pass between the cells. The nerve supply of the medullary substance is very rich, and is derived mainly from large nerve bundles which pass from the plexus in the capsule to the medulla, where they divide and form dense plexuses which surround the groups of gland-cells and veins ; from these plexuses fine varicose fibers pass between the gland-cells, forming intercel- lular plexuses. In the medulla there are found in many animals large numbers of sympathetic cells, some isolated, others grouped to form small ganglia. Pericellular networks surround the cell- bodies of certain of these sympathetic cells. (For further informa- tion concerning the suprarenal glands consult Gottschau, Wcldon, Hans Rabl, C. K. Hoffmann (92), Pfaundler, Flint, and Dogiel.) TECHNIC. 305 TECHNIC. 270. The arrangement of the cortical and medullary portions of the kidney is best seen in sections of the kidney of small mammalia, cut in the proper direction, and, if possible, embracing the whole organ. If, on the other hand, the liner epithelial structures are to be examined, small pie< es are first fixed in osmic acid mixtures or in corrosive sublimate. 271. Impregnation with silver nitrate (method of Golgi or Cox ) reveals some points as to the relation of the cells of the uriniferous tubules to each other. 272. In order to isolate the tubules, thin strips of kidney tissue are treated for from fifteen to twenty hours with pure hydrochloric acid having a specific gravity of 1. 12 I for this purpose kidney tissue is used taken from an animal killed twenty-four hours previously). It is then washed, teased, ami examined in glycerin (Schweiger-Seidel ). Fuming nitric acid l ao'/f ), applied for a few hours to small pieces of tissue, occa- sionally isolates the uriniferous tubules very extensively. The further treatment is then the same as after hydrochloric acid. A 35^ potassium hydrate solution may also be employed. The isolated pieces are, however, not easily preserved permanently. 273. The epithelium of the uriniferous tubules may be isolated either in yi alcohol <<-/, <■, c, ova; >/, ft /> /> fnecae folliculorum ; g, beginning of formation of the cavity of the follicle (compare Fig. 266]. 310 Till. FEMALE GENITAL ORGANS. 3 I I ova of the primitive or primordial follicles attain a size: (in fresh tissue teased in normal salt solution) varying from 48 // to 69//. They 1 possess a nucleus varying in size from 20// to 32//, presenting a doubly contoured nuclear membrane, and containing a distinct chromatin network with a nucleolus and several accessory nucleoli. The protoplasm shows a distinct spongioplastic network containing a clear hyaloplasm. The primitive ova, until they undergo further development, retain this size and structure, irrespective of the age of the individual. They are numerous in embryonic life and early childhood, always found during the ovulation period, but not observed in the ovaries of the aged. Changes in the size and structure of the ova accompany the proliferation of the follicular cells in the growing follicles. As soon as the follicular cells of a primitive follicle proliferate, as above described, the ovum of the follicle increases in size until it has attained the size of a fully developed ovum. The zona pcllucida now makes its appearance, and after this has reached a certain thickness, yolk granules (deuto- plastic granules) develop in the protoplasm of the ovum. In a fully developed Graafian follicle the ovum presents an outer clearer protoplasmic zone and an inner fine granular zone containing yolk granules ; in the former lies the germinal vesicle. Between the protoplasm of the ovum and the zona pellucida is found a narrow space known as the perivitelline space. The germinal ' vesicle (nucleus), which is usually of spheric shape, possesses a doubly contoured membrane and a large germinal spot (nucleolus), which shows ameboid movements. The origin of the zona pellucida has not as yet been fully de- termined. It probably represents a product of the egg epithelium, and may be regarded in general as a cuticular formation of these cells. At all events it contains numerous small canals or pores into which the processes of the cells composing the corona radiata ex- tend. These processes are to be regarded as intercellular bridges (Retzius, 90) ; and, according to Palladino, they occur not only betw r een the ovum and the corona radiata, but also between the follicular cells themselves. In the ripe human ovum the pores are apparently absent (Nagel), and it is very probable that they have to do with the passage of nourishment to the growing egg. Retzius believes that the zona pellucida is derived from the processes of the cells composing the corona radiata, which at first interlace and form a network around the ovum. Later, the matrix of the membrane is deposited in the meshes of the network, very probably by the egg .itself. Further developmental changes are, however, necessary before a fully developed ovum (ripe ovum) may be fertilized. These are grouped under the head of maturation of the ovum. They have in part been described in a former section (p. 65), but may receive further consideration at this time. During maturation the chromo- somes are reduced in number, so that the matured ovum presents 3 12 THE GENITOURINARY ORGANS. only half the number found in a somatic cell of the same animal. The manner in which this reduction takes place has been described for many invertebrates and vertebrates, and in all ova studied with reference to this point essentially the same phenomena have been observed. In this account we shall follow the process as it occurs in the Copepoda (Ruckert, 94). During the period of growth the cells composing the last gen- eration of oogonia (primitive ova) increase in size, and are then Fig. 264.- Schematic representation of the behavior of the chromatin during the maturation of the ovum (from Ruckert, 94). Instead of 12 chromosomes we have drawn, for the sake of simplicity, only four : a, a, a, First, and (l>) second polar body. known as "oocytes" (the ripe ova). These then undergo mitotic division, and in each a spirem is formed which divides into 12 chromosomes, and not into 24 as in the case of the somatic cells. These 12 chromosomes split longitudinally, so that the germinal vesicle is seen to contain 12 pairs of chromosomes, or daughter loops. By this process the oogonia have become egg mother cells (O. Hertwig, 90) or oocytes of the first order. The loops now begin to shorten and each soon divides crosswise into two equal THE FEMALE GENITAL ORGANS. 313 rods, thus giving rise to 12 groups of 4 chromosomes, or 12 tetrads. The mother cell now divides into 2 unequal parts, the process con- sisting in a distribution of the rods composing the tetrads in such a way that the pairs of rods derived from one set of daughter loops pass to the <>ne daughter cell, and those derived from the other set to the second daughter cell. In this manner are formed the large egg daughter ceils (( ). Hertwig) or oocytes of the second order, and a smaller cell, the first polar body. From this it is seen that the daughter cell still retains 1 2 pairs of rods. A second unequal division immediately follows without a period of rest, hut in this case the com- ponent parts of the pairs of rods are so divided that each separate- rod moves away from its fellow, although they both originated from the same daughter loop. In this manner a cell of the third gen- eration is formed, the oocyte of the third order, or mature ovum, as well as a second polar body. The second division in the period of maturation is peculiar in that here daughter chromosomes are formed, not by a longitudinal splitting of the chromosomes, but by a transverse division. In the process of development of the ova, three periods are therefore distinguishable. The first, or period of proliferation, rep- resents a stage of repeated mitotic division in the oogonia, during which the latter become gradually reduced in size. In the second, or period of growth, the oogonia increase in size and are then ready for the third, or period of maturation. In the latter, by means of a modified double mitotic division, uninterrupted by any resting stage, the matured ovum and the polar bodies are formed. These several periods are represented in figure 265. The manner in which the full)- developed Graafian follicle bursts and its ovum is freed is still a subject of controversy ; the following may be said regarding it : By a softening of the cells forming the pedicle of the discus proligerus, the latter, together with the ovum, are separated from the remaining granulosa, and lie free in the liquor folliculi. At the point where the follicle comes in contact with the tunica albuginea of the ovary, the latter, with the theca folliculi, becomes thin, and in this region, known as the stigma, the blood-vessels are obliterated and the entire tissue grad- ually atrophies ; thus a point of least resistance is formed which gives way at the slightest increase in pressure within the follicle, or in its neighborhood. The increase of pressure within the follicle, leading to its rup- ture, is, according to Nagel (96), due to a thickening of the tunica interna of the theca of the follicle. The cells of this layer prolif- erate and increase in size and show yellowish colored granules. This cell-proliferation leads to a folding of the tunica interna, the folds encroaching on the cavity of the follicle, and causing its contents to be pushed toward the stigma. When the ovum is released, the rest of the follicle remains be- hind to form a corpus luteutn. In the formation of the much larger 314 THE GENTTO-URIXARV ORGANS. corpus luteum verum — i. c, one whose ovum has been fertilized and is in process of further development — the regressive metamorphosis is much slower than is the case with the corpora lutea spuria, whose ova have not been impregnated. In place of the liquor folliculi the corpus luteum usually contains a blood coagulum which is formed as a result of the rupture of the adjacent blood-vessels. Then follows a prolifera- tion of the tissue composing the tunica interna of the theca folliculi. This ingrowth gradually surrounds and finally penetrates into the coagulum and the few granulosa cells remaining, while the latter degenerate and are eventually absorbed. The proliferating tissue contains cells filled with pigment, the lutein cells, and it is these which give rise to the characteristic yellow color of the bodies. The inner wall of the corpus luteum is gradually folded in and the Primordial egg-cell. Oogonia -^ Germinal zone. Zone of mitotic division. (The number of genera- tions is much larger than here represented.) Zone of growth. Zone of maturation. Oocyte 1. order Oocyte II. order Matured ovum II. P.B. Fig. 265. — Scheme of the development and maturation of an ascaris ovum (after Boveri) P. B., Polar bodies. (From " Ergebn. d. Anat. u. Entw.," Bd. I.) degenerating central portion is finally penetrated by vessels and absorbed by the proliferating cells from the outer wall. In the folds of the tunica interna, composed of lutein cells, there is found a vari- able amount of fibrous connective tissue carrying blood-vessels which break up into capillaries, the latter penetrating between the lutein cells. According to Sobotta (96 and 97), the corpus luteum of both the mouse and the rabbit is formed chiefly by a hypertrophy of the epithelial cells, while the vascular connective tissue of the inner thecal layer penetrates between the epithelial cells in the shape of processes accompanied by leucocytes, which form a cellular net- work around the central coagulum. The blood is finally absorbed Till: ITM \I.I. (iKMTAI. ORGANS. J 1 ) without the formation of hematoidin crystals, and a mucoid* nective-tissue mass is the result. There is then no further prolifera- tion of connective tissue and the corpus luteum is fully developed in this condition. Later, fat globules are deposited in the greatly enlarged epithelial cells. In the mouse there is no difference as to structure or size between corpora lutea derived from follicles whose ova have been impregnated and those whose ova have not been fertilized. After a variable time the tissue of the corpus luteum itself undergoes hyaloid defeneration, a process which may be compared to the formation of scar tissue, and which finally results in the formation of the corpus albicans. The latter is then in its turn '-..•-- Ovum. Germinal vesicle. "■-• Blood-vessel. Fig. 266. — Section of fully developed Graafian follicle from injected ovarv of pig ; X50- absorbed, and in the end there remains in its place only a connec- tive tissue containing very few fibers. Not all of the eggs and follicles reach maturity; very many are destroyed by a regressive process known as atresia of (he fol- licles. This process may begin at any stage, even affecting the primitive ova while still imbedded in the germinal epithelium — first attacking the egg itself and later the surrounding follicular epithe- lium, although in both the degenerative process is identical. The germinal vesicle and the nuclei of the follicular cells usually undergo a chromatolytic degeneration, although they sometimes disappear without apparent chromatolysis (direct atrophy), while 316 THE GENITOURINARY ORGANS. the cell-bodies are generally subjected to a fatty degeneration or may even undergo what is known among pathologists as an albu- minous degeneration — i. <\, one characterized by granulation and showing no fat reaction but numerous reactions such as are ob- served where albumin is present. These two forms of metamor- phosis result in a liquefaction of the cell-body, and finally lead to a hyaline swelling, which renders the substance of the cell homo- geneous. The zona pellucida softens, increases in volume, becomes wrinkled, and after some time is absorbed. A further stage in the regressive process consists in the formation of scar tissue, as in the case of the corpus luteum. Here leucocytes accompany the proliferation from the tunica interna of the theca folliculi, and assist in absorbing the products of degeneration, the result being a connective-tissue scar {vid. G. Ruge, and Schottlander, 91, 93). The blood-vessels of the ovary enter at the hilum and branch in the medullary substance of the ovary. From these medullar}' vessels branches are given off which penetrate the follicular zone, giving off branches to the follicles and terminating in a capillary network in the tunica albuginea (Clark, 1900). The relations of the branches to the follicles are such that in the outer layer of the theca folliculi the vessels form a network with wide meshes while the inner layer contains a fine capillary network (Fig. 266). The veins are of large caliber and form a plexus at the hilum of the ovary. The lymphatics of the ovary are numerous. They begin in clefts in the follicular zone, which unite to form vessels lined by endothelial cells in the medulla. They leave the ovaiy at the hilum. The nerves accompany and surround the blood-vessels, while very few nerve-fibers penetrate into the theca folliculi ; those doing so form a network around the follicle and end often in small nodules without penetrating beyond the theca itself. Ganglion cells of the sympathetic type also occur in the medulla of the ovary near the hilum (Retzius, 93 ; Riese, Gawronski). 3. THE FALLOPIAN TUBES, UTERUS, AND VAGINA. The Fallopian tubes consist of a mucous membrane, muscular coat, and peritoneal covering. The mucous membrane presents a large number of longitudinal folds which frequently communicate with one another. Very early in the development four of these folds are particularly noticeable in the isthmus ; these may also be recognized at times in the adult. These are the chief folds, in contradistinction to the rest, which are known as the accessory folds 1 Frommel). The accessory folds are well developed in the isthmus, and are here so closely arranged that no lumen can be seen with the naked eye. The epithelium lining the tubes is composed of a single layer of ciliated columnar THE l 1-M \i I Gl Nl i \l. ORGANS. 3'7 cells which entirely cover the folds as well as the tissue between them. Glands do not occur in the oviducts, unless the crypts between the folds may be considered as such. The mucosa beneath the epithelium contains relatively few connective-tissue fibers, but numerous cellular elements. In the isthmus it is com- pact, but in the ampulla and infundibulum its structure is looser. The mucosa contains a few nonstriated muscle-fibers, which have a longitudinal direction and extend into the chief folds, but not into the accessory folds. External to the mucosa is found the muscular coat, consisting of an inner circular ami an outer and thinner longitudinal layer. Tin; latter is imperfectly developed in the ampulla and may be Mucosa. '^W^i^^^^0^M-^0^$ Fig. 267.— Section of oviduct of young woman. To the left and above are two enlarged ciliated epithelial cells from the same tube ; X l 7°- entirely absent in the infundibulum. The peritoneal layer consists of a loose connective tissue covered by mesothelium. The uterus is composed of a mucous, a muscular, and a peri- toneal coat. The mucosa of the body of the uterus and cervix is lined by a single layer of columnar ciliated epithelial cells ; these are some- what higher in the cervix than in the corpus. Barfurth (96) has found intercellular bridges between the cells of the uterine epithelium in the guinea-pig and rabbit. In the cervix of the virgin the ciliated columnar epithelium extends as far as the external os, at which point this usually changes to a stratified squamous epithelium. In 3 18 THE GENITO-URINARY ORGANS. multipara; the squamous epithelium extends into the cervical canal and may be found, with occasional exceptions (islands of ciliated epithelium), throughout its entire lower third. This arrangement is subject to considerable variation, so that even in children the lower portion of the cervical canal may sometimes be lined by stratified epithelium. In the bod}- of the uterus the mucosa is com- posed of a reticular connective tissue, resembling in structure that of the mucosa of the intestinal canal. This reticular connective tissue consists of connective-tissue fibers and branched connective- tissue cells arranged in the form of a network, in the meshes of which are found lymphocytes and leucocytes. The mucosa of the cervix is somewhat denser, containing more fibrous tissue. In the cervical canal the mucosa of the anterior and posterior walls is elevated to form numerous folds, extending laterally from larger median folds. These folds are known as the plic ■JZCPp-'y ;fjCx Fig. 269.— From section of human vagina. In the vagina we distinguish also three coats — the mucous membrane, the muscular layer, and the outer fibrous covering. The epithelium of the mucous membrane is of the stratified squamous type, and possesses, as usual, a basal layer of cylindric cells. The mucosa of the vagina consists of numerous connective- tissue fibers mingled with a number of exceptionally coarse elastic fibers. Papillae containing blood-vessels are present everywhere ex- cept in the depressions between the columns rugarum. It is generally stated that the vagina has no glands, but according to the observa- tions of von Preuschen and C. Ruge, a few isolated glands occur in THE FEMAI.I. GENITAL ORGANS. 321 the vagina. They are relatively simple in structure, form irregular tubes, and are lined by ciliated columnar epithelium. The ex tory ducts are lined by stratified squamous epithelium. Diffuse adenoid tissue is met with in the mucosa, which sometimes assumes the form of lymphatic nodules. The muscular coat, which in the lower region is quite prominent, may be separated indistinctly into an outer longitudinal and an in- ner circular layer ; the latter is, as a rule, poorly developed, and may be entirely absent. The muscular coat is especially well developed anteriorly in the neighborhood of the bladder. ERMM W (Ml mmm 1 ■ Fig. 270. — From section of human labia minora. The outer fibrous layer consists of dense connective tissue loosely connected with the adjacent structures. At its lower end the vagina is partially closed by the hymen which must be regarded as a rudiment of the membrane which in the embryo separates the lower segment of the united Miillerian ducts from the ectoderm of the sinus urogenitals. Accordingly, the epithelium on the inner surface of the hymen partakes of the character of the vaginal epithelium ; that on the outer surface re- sembling the skin in structure (G. Klein). 322 THE GENITOURINARY ORGANS. The epithelium of the vestibulum gradually assumes the char- acteristics of the epidermis ; its outer cells lose their nuclei and sebaceous glands occur here and there in the neighborhood of the urethral orifice and on the labia minora. Hair begins to appear on the outer surface of the labia majora. The clitoris is covered by a thin epithelial layer, resembling the epidermis. This rests on a fibrous-tissue mucosa having numerous papillae, some of which contain capillaries, others special nerve- endings. In the clitoris of the adult no glands are found. The greater portion of the clitoris consists of cavernous tissue, homol- ogous to the corpora cavernosa of the penis ; ' the corpus spongi- osum is not present in the clitoris. The glands of Bartholin the homologues of the glands of Cowper in the male, are mucous glands situated in the lateral walls of the vestibule of the vagina. The terminal portions of their ducts are lined by stratified squamous epithelium. Free sensory nerve-endings, with or without terminal enlarge- ments, have been demonstrated in the epithelium of the vagina (Gawronski). The sensory nerve-fibers form plexuses in the mucosa, and lose their medullary sheaths as they approach the epithelium. Sympathetic ganglia are met with along the course of these nerves, and nonmedullated nerves terminate in the involuntary muscular tissue of the vaginal wall. In the connective-tissue papillae and in the deeper portions of the mucosa of the glans clitoridis are found, besides the ordinary type of tactile corpuscles and the spherical end-bulbs of Krause, the so- called genital corpuscles (see p. 155). Numerous Pacinian cor- puscles have been observed in close proximity to the nerve-fibers of the clitoris and the labia minora. In varying regions of the medullary substance of the ovary, but more usually in the neighborhood of the hilum, there occur irregular epithelial cords or tubules provided with columnar epithe- lium, ciliated or nonciliated, which constitute the paroopJioron. These are the remains of the mesonephros, and are continuations of that rudimentary organ — the cpooplwron — of similar structure which lies within the broad ligament. The separate tubules of the epoophoron communicate with the duct of Gartner (Wolffian duct), which in the human being is short, ends blindly, and never, as in certain animals, opens into the lower portion of the vagina. These derivatives of the primitive kidney consist of blindly ending tubules of varying length lined by a ciliated epithelium, the cells of which are often found in process of degeneration. The hydatids of Morgagni arc duplications of the peritoneum. Till-: MALE GENITAL ORGANS. 323 D. THE MALE GENITAL ORGANS. 1. THE SPERMATOZOON. The semen, or sperma, is a fluid that, as a whole, consists of the secretion of several sets of glands in which the sexual cells, the SpermatOSOmes, or spermatozoa, which are formed in the testes, are suspended. We shall first consider the structure of the typical adult spcrma- tosome, taking up consecutively its component parts. Three prin- cipal parts may be distinguished — the head, the middle piece, and the tail or flagellum. The round or oval body of the head termi- nates in a lanceolate extremity. The former consists of chromatin, and is most intimately associated with the phenomenon of fertiliza- tion. The middle piece, which is attached to the posterior end oi the head, is composed of a protoplasmic envelop which surrounds a portion of the so-called axial thread. The latter is enlarged ante- riorly just behind the head to form the terminal nodule , which fits into a depression in the head. From the middle piece on, the axial thread Fig. 271. — Diagram showing the general characteristics of the spermatozoa of various vertebrates: u. Lance; t>, segments of the accessory thread; r, accessory thread ; form the mediastinum testis, or the corpus Highmori, which projects as a fibrous-tissue ridge for a variable distance into the substance of the testis. The gross structure of the testis is best seen in a sagittal longitudinal section. Even a low magnification will show that the testis is composed of lobules. These are produced by septa which extend into the substance of the organ ami are derived from the investing tunics of the testis and diverge in a radiate manner from the mediastinum testis. The lobules an- of pyramidal shape, with their bases directed toward the capsule and their apices toward the mediastinum. They consist principally of the seminiferous tubules, whose transverse, oblique, and longitudinal Lobule of testis. Tunica albuginea. BaL— Caput epidi- ~^E£k dvminis. s Corpus Highmori and rete testis. Tubuli recti. Vasepididymidis. Fig. 273. — Longitudinal section through human testis and epididymis. The light areas between the lobules are the fibrous- tissue septa of the testis ; X 2 - sections may be observed in sections of the testis. When isolated, these tubules are seen to begin in the testis as closed canals, which are closely coiled upon each other (convoluted tubules) ami describe a tortuous course, until they finally reach the corpus Highmori. Immediately before they reach the latter, the convoluted tubules change into short, straight and narrow segments — the straight tubules, or tubuli recti. Within the corpus Highmori, all the straight tubules of the testis unite to form a tubular network — the rete testis (Haller). From this network about fifteen tubules — the vasa efferentia — 126 THE GENITOURINARY ORGANS. arise. The latter, at first straight, soon begin to wind in such a man- ner that the various convolutions of each canal form an independent system, invested by a fibrous sheath of its own — com vasculosi Halleri. These lobules constitute the elements of the globus major of the epididymis. In cross-section the vasa efferentia are seen to be stellate in shape. The vasa efferentia gradually unite to form one canal — the vas epididymidis. This is markedly convoluted and is situated in the body and tail of the epididymis itself. The epithelium of the convoluted seminiferous tubules consists of sustentacular cells (cells or columns of Sertoli) and of sperma- togenic elements. The former are high, cylindric structures (see below), the basilar surfaces of which are in contact. They do not form a continuous layer, but their basal processes are interwoven to form a superficial network surrounding the epithelium of the \_Vc-— ■ b Fig. 274. Fig. 275- Sustentacular cells (cells of Sertoli) of the guinea-pig (chrome- silver method). Figure 274, surface view of the seminiferous tubules ; figure 275, profile view; X 220: ■/, Basilar surface of a cylindric sustentacular cell ; b, flattened sustentacular cell ; c, c, depressions in the sustentacular cells due to pressure from the spermatogenic cells ; d, basilar portion of sustentacular cells. seminiferous tubules. (Fig. 275.) In the meshes of the reticulum are deposited numbers of plate-like cells, which lie in contact with the basement membrane and also represent sustentacular elements {vid. Merkel, 71). Between the sustentacular cells are found from four to six rows of cells, possessing relatively large nuclei, rich in chromatin, and derived from cells of the deeper strata by mitotic cell division. The epithelium of the convoluted portion of the seminiferous tubules is, therefore, a stratified epithelium. The cells of this epithelium present various peculiarities according to their stage of development, and will be considered more fully in discussing spermatogenesis. Externally, the walls of the convoluted tubules are limited by a single layer or several layers of spindle-shaped, epithelioid cells. A basement membrane is present, but very thin, and in some cases THE MAI 1. GEN] 1'AI. ORGANS. 327 hardly capable of demonstration. The convoluted tubules are separated from each other by a small amount of connective tissue, in which, in addition to the vessels, nerves, etc, are found peculiar groups of large cells containing large nuclei, and known as interstitial cells. Nothing definite is known regarding the significance of these cells ; but they are probably remains of the Wolffian body. Retake (96) found repeatedly crystalloids of problematic significance in the interstitial cells of the normal testis. The stratified epithelium of the convoluted tubules changes in :%x|ftJ #? /'W ::.-H:™-%a^ %;->!•§ WMi '■■'■■'" w?S Fig. 276. — From section of human testis, showing convoluted seminiferous tubules. the tubuli recti to art epithelium consisting of a single layer of short columnar or cubical cells resting on a thin basement membrane. The canals of the rete testis (Haller) are lined by nonciliated epithelium, which varies in type from flat to cubical. Communicat- ing with the rete testis is a blind canal, the vas aberrans of the rete testis, lined with ciliated epithelium. The vasa efferentia are lined partly by ciliated columnar and partly by nonciliated cubical epithelium. The two varieties form groups which alternate, giving rise to nonciliated depressions, which represent gland-like structures (Schaffer, 92), but do not 3-^8 THE GENITOURINARY ORGANS. cause corresponding evaginations of the mucosa. Outside of the mucosa, which consists of fibrous connective tissue, there are found several layers of nonstriated muscle-fibers circularly disposed. The vas epididymidis is lined by stratified ciliated columnar epithelium, resting on a thin mucosa, outside of which there is Fig. 277. — Section through human vasa efferentia : a, Glands; b, ciliated epithelium; c, glandular structure ; d, connective tissue. Fig. 278. — Cross-section of vas epididymidis of human testis. found an inner circular rind an outer, though thin, longitudinal layer of nonstriated muscular tissue. An aberrant canaliculus also communicates with the vas epi- didymidis, and is here known as tin- vas aberrans Hallcri. Num- I III. M \l I. GENIT \I. ORGANS. 329 bers of convoluted and blindly ending canaliculi arc frequently found imbedded in the connective tissue around the epididymis. These constitute the paradidymis, or organ of Gir aides. The blood-vessels of the testis spread out in the corpus High- mori and in the tunica vasculosa of the connective-tissue septa and of the tunica albuginea, their capillaries encircling the seminal tu- bules in well-marked networks. The lymphatic vessels begin in clefts in the tunica albuginea and in the connective tissue between the convoluted tubules. They con- verge toward the corpus Highmori and pass thence to the spermatic cord. Rctzius (93) and Tim- ofeew (94) have described plexuses of nonmedul- lated, varicose nerve-fibers surrounding the blood- vessels of the testis. From such plexuses single fibers, or small bundles of such, could be traced to the seminiferous tubules, about which they also form plexuses. Such fibers have not been traced into the epithelium lining the tubules. In the epididymis Timofeew found numerous sympa- thetic ganglia, the cell- bodies of the sympathetic neurones of which were surrounded by pericellular plexuses. In the wall of the vas epididymidis and the vasa efferentia were observed numerous varicose nerve-fibers, arranged in the form of a plexus, many of which seemed to terminate on the nonstriated muscle cells found in these tubes. Some of the nerve-fibers were traced into the mucosa, but not into its epithelial lining. Fig. 279 — Section of 'log's testis with in- jected blood-vessels (low power) : a, Seminifer- ous tubule ; b, connective-tissue septum ; c, blood- vessel. 3. THE EXCRETORY DUCTS. The vas deferens possesses a relatively thick muscular wall, con- sisting of three layers, of which the middle is circular and the other two longitudinal. The subepithelial mucosa is abundantly supplied with elastic fibers and presents longitudinal folds. The lining epi- thelium is in part simple ciliated columnar and in part stratified ciliated columnar, with two rows of nuclei. The cilia are, however, often absent, beginning with the lower portion of the vas epidi- 330 THE GENITOURINARY ORGANS. dymidis. According- to Steiner, the epithelium of the vas deferens varies. It may be provided with cilia in the lower segments, or it may even be similar to that found in the bladder and ureters. The inner muscular layer is wanting in the ampulla of the vas deferens ; here the epithelium is mostly simple columnar and pig- mented. Besides the folds, there are also evaginations and tubules which sometimes form anastomoses — structures which may be re- garded as glands. The seminal vesicles are also lined, at least when in a distended condition, by simple, nonciliated columnar epithelium containing yellow pigment. In a collapsed condition the epithelium is pseudo- stratified, with two or even three layers of nuclei. The arrange- ment of the epithelial cells in a single layer would therefore seem to be the result of distention. The mucous membrane shows Epithelium. Mucosa. Inner longi- tudinal muscular layer. Fig. 280. — Cross-section of vas deferens near the epididymis (human) numerous folds, which, in the guinea-pig for instance, present a delicate axial connective -tissue stroma. Besides scanty subepithe- lial connective tissue, the seminal vesicles are provided with an inner circular and an outer longitudinal layer of muscle-fibers. Sperma- tozoa are, as a rule, not met with in the seminal vesicles. The epithelium of the cjaculatory ducts is composed of a single layer of cells ; the inner circular muscle-layer is very poorly devel- oped. In the prostatic portion of the ejaculatory ducts the longi- tudinal muscle-layer mingles with the musculature of the prostate and loses its individuality. The ejaculatory ducts empty either directly into the urethra at the colliculus seminalis, or indirectly into the prostatic portion of the urethra through the vesicula prostatica. The prostate is a compound branched alveolar gland. Its capsule THE MALE GENITA1 ORGANS. 331 consists of dense layers of nonstriated muscle-fibers, connective tissue, and yellow elastic fibers. Processes and Lamellae composed of all these elements extend into the interior of the -land, converg- ing toward the base of the colliculus seminalis. Between the larger trabecular are situated numerous glands, consisting of lai /7 s *5u. /C_ ^ & Fig. 281. — Cross-section of wall of seminal vesicle, showing the folds of the mucosa (human). ^nS * ^BaSS &&t '■ -■■■■ ■"■' V Fig. 282. — From section of prostate gland of man. irregular alveoli, separated by fibromuscular septa and trabecular The alveoli are lined by simple columnar epithelium, the inner portion of the cells often showing acidophile granules. Now and then the alveoli present a pseudostratified epithelium, with two rows of nuclei (Rudinger, 83). A basement membrane, although 33^ THE GENITO-URINARY ORGANS. present, is difficult to demonstrate. The numerous excretory ducts, lined by simple columnar epithelium, become confluent and form from 15 to 30 collecting ducts which empty, as a rule, either at the colliculus seminalis or into the sulcus prostaticus. Near their terminations the larger ducts are lined by transitional epithelium similar to that lining the prostatic portion of the urethra. In the alveoli of the glands, peculiar concentrically laminated concrements are found, known as prostatic bodies or concretions (corpora amylacea). They are more numerous in old men, but are found in the prostates of young men and also of young boys. The secretion of the prostate (succus prostaticus) is not mucous in character, but resembles a serous secretion and has an acid reac- tion. The vesicula prostatica (sinus pocularis) is lined by stratified epithelium, consisting of two layers of cells and provided with a dis- tinct cuticular margin upon which rest cilia. In its urethral region occur short alveolar glands. The glands of Cowper are branched tubular alveolar glands, the alveoli being lined by mucous cells. Crescents of Gianuzzi are, however, seldom seen. The smaller excretory ducts, lined by cubical epithelium, unite to form two ducts, one on each side of the urethra ; these are 1 y 2 inches long, and are lined by stratified epi- thelium consisting of two or three layers of cells. The blood-vessels of the prostate ramify in the fibromuscular trabecular and form capillary networks surrounding the alveoli. The veins collecting the blood pass to the periphery of the gland, where they form a plexus in the capsule. The lymphatics begin in clefts in the trabecular and follow the veins. The terminal branches of the vessels supplying Cowper's glands are, in their arrangement, like those of other mucous glands. Numerous sympathetic ganglia are found in the prostate under the capsule and in the larger trabecular near the capsule. The neuraxes of the sympathetic cells of these ganglia may be traced to the vessels and into the trabecular ; their mode of ending has, however, not been determined. Small medullated nerve-fibers terminate in these ganglia in pericellular baskets. Timofeew has described peculiar encapsulated sensory nerve-endings, found in the prostatic and membranous portions of the urethra of certain mam- malia. They consist of the terminal branches of two kinds of nerves, inclosed within nucleated laminated capsules : one large medul- lated nerve-fiber, after losing its medullary sheath, breaks up into a small number of ribbon-shaped branches with serrated edges, which may pass more or less directly to the end of the nerve-ending or may be bent upon themselves ; and very much smaller medullated nerve-fibers which, after losing their medullary sheaths, divide into a large number of varicose fibers which form a dense network en- circling the ribbon-shaped fibers previously mentioned. The penis consists of three cylindric masses of erectile tissue — the two corpora cavernosa, forming the greater part of the penis THE MALE GENITAL ORGANS. 333 and lying side by side, and the corpus spongiosum, surrounding the urethra and lying below and between the corpora cavernosa. The two latter are surrounded by a dense connective-tissue sheath, the tunica albuginea. These erectile bodies are surrounded by a thin layer of skin, containing no adipose tissue and no hair-follicles. The corpus spongiosum is enlarged anteriorly to form the glans penis. The principal substance of the erectile bodies is the so-called erectile tissue : septa and trabecular, consisting of connective tissue, elastic fibers, and smooth muscle-cells inclosing a sys- tem of communicating spaces. These latter may be regarded as venous sinuses, the walls of which, lined by endothelial cells, are in apposition to the' erectile tissue. Under certain conditions the venous sinuses are distended with blood, but normally they are in a collapsed state and form fissures which simulate the clefts found in ordinal'}' connective tissue. In other words, there is here such an arrangement of the blood-vessels within the erectile tissue that the circulation may be carried on with or without the aid of the cavernous spaces. The arteries of the corpora cavernosa possess an especially well-developed musculature. They ramify through- out the trabecular and septa of the erectile tissue and break up within the septa into a coarsely meshed plexus of capillaries. A few of these arteries empty directly into the cavernous spaces. On the other hand, the arteries give off a rich and narrow-meshed capillary network immediately beneath the tunica albuginea. This is in com- munication with a deeper and denser venous network, which, in turn, gradually empties into the venous sinuses. Aside from these there are anastomoses between the arterial and venous capillaries, which later communicate with the venous network just mentioned. The blood current, regulated as it thus is, may pass either through the capillaries alone, or may divide and flow through both these and the venous sinuses. These conditions explain both the erec- tile and quiescent state of the penis. The relations are somewhat different in the corpus spongiosum urethras and in the glans penis. The epithelium of the urethra varies in the several regions. The prostatic portion possesses an epithelium similar to that of the bladder. In the membranous portion, the epithelium may be simi- lar to that found in the prostatic portion, but more often pre- sents the appearance of a pseudostratified epithelium with two or three layers of nuclei. The cavernous region is lined by pseudo- stratified epithelium, except in the fossa naviculars, where a stratified squamous epithelium is found. Between the fibro-elastic mucosa and the epithelium there is a basement membrane. There occur in the urethra, beginning with the membranous portion, ir- regularly scattered epithelial sacculations of different shapes. Some of these show alveolar branching, and are then known as the glands of Littre. The submucosa of the cavernous portion of the urethra, which 334 THE GENITOURINARY ORGANS. contains nonstriated muscle-tissue arranged circularly, is richly sup- plied with veins, and contains pronounced plexuses communicating with cavernous sinuses, which correspond in general to those of the corpora cavernosa penis. In the glans penis the cavernous spaces are small and of more regular shape than in the corpora cavernosa. The glans is covered by a layer of stratified squamous epithelium, often possessing a thin stratum corneum (see Skin). Near the corona of the glans penis there are now and then found small sebaceous glands (see Hair), known as glands of Tyson. The prepuce is a duplication of the skin, the inner surface present- ing the appearance of a mucous membrane. The nerves terminating in the glans penis have recently been studied by Dogiel, who made use of the methylene-blue method in his investigation. He finds Meissner's corpuscles in the connective- tissue papillae under the epithelium, Krause's spheric end-bulbs somewhat deeper in the connective tissue, and the genital corpuscles situated still deeper (see Sensory Nerve-endings). In the epithelium are found free sensory nerve-endings. Pacinian corpuscles have also been found in this region. 4. SPERMATOGENESIS. In order that the student may obtain an understanding of the com- plicated process of spermatogenesis we shall give a description of it as it occurs in salamandra maculosa, which of all vertebrate animals presents the phenomena in their simplest and best known form. The student should understand, however, that many of the details here described have not been observed in the testes of mammalia ; and, since the spermatozoa of many of the mammalia are of simpler structure than those of the salamander, the development of the spermatozoa of the former is consequently simpler. It should also be noticed that the general structure of the testes of the salamander differs in some respects from that of the testes of mammalia, as given in the preceding pages. At first the seminiferous tubules consist of solid cellular cords, and it is only during active production of spermatozoa that a central lumen is formed, in which the spcrmatosomes then lie. The cells which compose these solid cords may be early differentiated into two classes — those of the one class being directly concerned in the pro- duction of the spcrmatosomes ; those of the other appearing to have a more passive role. The cells of the first class — the spermatogo- nia, or primitive seminal cells — undergo a process of division accom- panied by an increase in size. In this way they soon commence to press upon the cells of the second class — the follicular or sustentacu- la cells. The result is that the nuclei of the latter arc forced more or less toward the wall of the seminal tubule, while their proto- plasm is so indented by the adjacent spermatogonia that the cells SPERMATOGENESIS. 335 assume a flattened cylindric shape presenting indentations and processes <>n all sides. In this stage the spermatogonia have a radiate arrangement and entirely surround the elongated susten- tacular cells. At present three periods are distinguished in the development of the male sexual cells (spermatosomes) from the spermatogonia. The first period embraces a repeated mitotic divi- sion of the spermatogonia — the period of proliferation. In the sec- ond, the spermatogonia, which have naturally become smaller from repeated division, begin to increase in size — the period of growth. The third is characterized by a modified double mitotic division without intervening period of rest, and results in the matured sper- matozoa — the period of maturation, figure 283. During the third period, a very important and significant process takes place — the Primordial sexual cell. •-■ Spermatogonia. proliferation. I hi ^oierations are much larger. ) Zone of grow th. Zone of maturation. Spermatocyte I order. Spermatocytes II order. Spermatids. Fig. 283. — Schematic diagram of spermatogenesis as it occurs in ascaris (after Boveri). ("Ergebn. d. Anat. u. Entw.," Bd. I.) reduction in the number of chromosomes, so that in the spermatids, the chromosomes are reduced to half the number present in a somatic cell of the same animal. The manner in which this reduc- tion in the number of chromosomes takes place will be described as it occurs in salamandra maculosa. After the cells composing the last generation of spermato- gonia have attained a certain size (period of growth), they under- go karyokinetic division. First, the usual skein or spirem is formed, but instead of dividing into twenty-four chromosomes, as in the somatic cell, the filament of the skein segments into, only twelve loops. The cell thus provided with twelve chromosomes now enters upon the period of maturation, and is known as a spermatocyte of the first order, or a " mother cell " (O. Hert- 336 THE GENITOURINARY ORGANS. wig, 90). The division of these cells is heterotypic (vid. p. 64) ; the chromosomes split longitudinally and in such a way that the division begins at the crown of the loops, extending gradually toward their free ends. In this case the daughter chromosomes remain for some time in contact, so that the metakinetic figure resembles a barrel in shape. Finally, the daughter chromosomes separate and wander toward the poles. As soon as the daughter stars (diaster) are developed, the number of chromosomes is again doubled by a process of longitudinal division. The spermatocyte of the first order thus divides into two spermatocytes of the second order, or daughter cells (O. Hertwig, 90). The nuclei of the daughter cells now contain twenty-four chromosomes, as is the case in the somatic cell, and, without undergoing longitudinal split- ting, the daughter chromosomes are distributed to the two nuclei of the spermatids. In other words, the latter contain only twelve chromosomes. The spermatozoa are formed from the spermatids by a rearrangement of the constituent elements of these cells. It may thus be said that even in the stage of the segmenting skein in the mother cells, the spermatocytes of the first degree contain twice as many chromosomes as a somatic cell, a condition which is first clearly seen in the stage of the diaster (here only an apparent duplication in the diaster stage). As a result, there is, first, a de- crease in the double number of chromosomes found in the sperma- tocytes of the second degree to the normal number ; second, a decrease in the number of chromosomes in the spermatocytes of the third degree (spermatids) to one-half the number present in a somatic cell, a condition probably due to the fact that here there is no stage of rest nor longitudinal splitting of the chromosomes. This is the general process in heterotypic division. Besides the heterotypic form, there occurs in the division of the spermatocytes another (homeotypic) form of karyokinetic cell-division. This dif- fers from the heterotypic in the shortness of the chromosomes, the absence of the barrel phase, the late disappearance of the aster, and the absence of duplication in the chromosomes of the diaster. According to Meves (96), the spermatocytes of the first degree undergo heterotypic, those of the second degree, homeotypic division. The spermatids develop into the spermatozoa, beginning imme- diately after the close of the second division of maturation. This process has been fully described for salamandra maculosa by Her- mann, Flemming, Benda, and others, but need not engage our attention at this point beyond the statement that the chromatin of the nuclei of the spermatids develops into the heads of the sperma- tozoa, while the remaining structures are developed from the proto- plasm. " The mature spermatozoon of the salamander represents a completely metamorphosed cell ; in the course of its develop- ment no portion of the original cell is cast off" (Meves, 97). Spermatogenesis in mammalia may be compared to the foregoing SPERMAT0GEN1 SIS. 337 process, with the exception that here the different stages are seen side by'side in the seminiferous tubule and without any apparent sequence, making the successive stages more difficult to demon- strate. The various generations of cells form columns, and are arranged in such a manner that the younger are found near the lumen and the older close to the wall of the tubule. (Figs. 284 and -~d Fig. 284.— Schematic diagram of section through convoluted seminiferous tubule of mammal, showing the development of the spermatosomes. The number of chromo- somes is not shown in the various generations of the spermatogenic cells. The pro- gressive development of the spermatogenic elements is illustrated in the eight sectors of the circle : a, Young sustentacular cell ; />, spermatogonium ; c, spermatocyte ; d, spermatid. In I, 2, 3, and 4 the spermatids rest on the enlarged sustentacular cell in the center of the sector ; on both sides of the sustentacular cells are the spermatogenic or mother cells in mitosis. In the sectors 5, 6, 7, and 8 spermatozoa are seen in ad- vanced stages resting on the sustentacular cells, with new generations of spermatids on each side. [From Rauber (after Brown) with changes (after Hermann).] 285.) These columns are separated from each other by high sus- tentacular cells, or Sertoli's cells or columns. The metamorphosis of the cells into spermatids and spermatosomes is accomplished by the changing of the cells bordering upon the lumen and then of those in the deeper layers, etc., into spermatids and then into spermatosomes. During this process the spermatids arrange 33^ THE GENITOURINARY ORGANS. themselves around the ends of Sertoli's columns, a phenomenon which -was formerly regarded as representing a copulation of the two elements, although it was clearly understood that no real fusion or interchange of chromatin occurred, but that the close relations of the two were for the purpose of furnishing nourishment to the developing spermatosomes. The whole forms a spermato- blast of von Ebner. Since the spermatids lining the lumen are changed into spermatozoa, and the process is repeated in the cells of the deeper layers as they come to the surface, the result is that the entire column is finally used up. The compensatory elements are supplied by the proliferation of the adjacent spermatogonia. The resulting products again divide, and thus build up an entirely new generation of spermatogenic cells. Hand in hand with these progressive phenomena occurs an extensive destruction of the cells taking part in spermatogenesis. This is shown by the presence of so-called karyolytic figures in the cells, wdiich later suffer complete demolition. These developmental changes are represented in the preced- t, / 1 I / mUUmLi "•/ ; ' lit, 'o^ . ■ Fig. 285. — Section of convoluted tubule from rat's testicle (after von Ebner, 88). The pyramidal structures are the sustentacular cells, together with spermatids and spermatosomes. Between these are spermatogenic cells, some of which are in process of mitotic division. Below, on the basement membrane and concealing the spermato- gonia, are black points representing fat-globules, a characteristic of the rat's testicle. Fixation with Flemming's fluid. ing schematic figure (Fig. 284), and may in part be observed in figure 285. In mammalia it has been possible to trace the development of the spermatids into the spermatosomes. These phenomena have been studied and described by numerous writers, and although many conflicting views have been expressed, the essential steps of this process seem quite clearly established. The account here given is based in part on the recent observations of v. Lenhossek and the observations of Benda. Before considering the method of development of the spermatosomes from the spermatids, a few words concerning the structure of the latter may be useful. The sharply outlined spermatid possesses a slightly granular protoplasm and a round or slightly oval nucleus with a delicate chromatic network. In the protoplasm there is found a sharply defined globule, known as the sphere or sphere substance, which lies near the nucleus and SPERM \ l' (GENESIS. 339 presents throughout a nearly homogeneous structure. This sub- stance is first noticed in the spermatocytes, disappears during the cell-divisions resulting in the spermatids, and reappears in the latter. In the protoplasm of the spermatid, lying near the nucleus, there is further found a small globular body, the chromatoid accessory nucleus of Benda, smaller than the sphere and staining very deeply in Heidenhain's hematoxylin. A true centrosome may also be found in the spermatid. The nucleus of the spermatid develops into the head of the spermatosome, tin ring which change the originally spheric nucleus becomes somewhat flattened and at the same time assumes a denser structure and moves toward that portion of the spermatid pointing away from the lumen of the seminiferous tubule. Accompanying these changes in the nucleus, marked changes are observed in the shape and structure of the sphere, which marks the position of the future anterior end of the head of the spermatosome, and applies itself to the nucleus on the side pointing away from the lumen of the tubule. In this position it differentiates into an outer clear homogeneous zone and a central portion which stains more deeply and to which v. Lenhossek has given the name akrosome. From these structures are developed the head-cap and the lance of the spermatosomes, which differ in shape and relative size in the sper- matosomes of the different vertebrates. Recent investigation seems to establish quite clearly that the axial thread of the tail is devel- oped from the centrosome (from the larger, if two are present), which is situated at some distance from the nucleus. Soon after the begin- ning of the development of the axial thread the centrosome wanders to the posterior part of the future head of the spermatosome (the pole of the nucleus opposite the head-cap) and becomes firmly attached to the nuclear membrane in this position (observations made on the rat by v. Lenhossek, and on the salamander by Meves). The middle piece and the undulating membrane, it would appear, are differentiated from the protoplasm, although the question of the mode of their development is still open to discussion. The chro- matoid body assumes a position near the axial thread at its junc- tion with the cell membrane ; its fate has not, however, been fully determined. According to Hermann (97), the end-piece in the selachia is derived from the centrosome, the ring-shaped body from the invagi- nated half of the intermediate body of the spermatid formed during the last spermatocytic division, and the axial thread from filaments of the proximal half of the central spindle. The lance, according to him, represents a modified portion of the nuclear membrane of the spermatid. For further particulars regarding spermatogenesis see the in- vestigations of v. la Valette St. George, 67-87 ; v. Brunn, ^4 ; Biondi, Benda, Meves, and v. Lenhossek. 340 THE GENITOURINARY ORGANS. TECHNIC. 278. The ovaries of the smaller animals are better adapted to study than those of the human being, since the former are more easily fixed. 279. The germinal epithelium and its relations to the egg-tubes of Pfliiger are best studied in the ovaries of young or newly born animals — cats, for instance, being especially well adapted to this purpose. 280. Normal human ovaries are usually not easily obtainable. Human ovaries very often show pathologic changes, and in middle life frequently contain but few follicles. 281. Fresh ova may be easily procured from the ovaries of sheep, pig, or cow in the slaughter-houses. On their surfaces are prominent trans- parent areas — the larger follicles. If a needle be inserted into one of these follicles and the liquor folliculi be caught upon a slide, the ovum may as a rule be found, together with its corona radiata. That part of the preparation containing the ovum should be covered with a cover-glass under the edges of which strips of cardboard are laid. If no such strips are employed, the zona pellucida of the ovum is likely to burst in the field of vision, giving rise to a funnel-shaped tear. These tears have often been pictured and described as preformed canals (micropyles). 282. The best fixing fluid for ovarian tissue is Flemming's or Her- mann's (yid. T. 17, 18), either of which may be used for small ovaries or pieces of large ovaries ; safranin is then used for staining. Good results are also obtained with corrosive sublimate (staining with hematoxylin according to M. Heidenhain), and also with picric acid (staining with borax -carmin). 283. The treatment of the Fallopian tubes is the same as that of the intestine ; in order to obtain cross-sections of a tube it is advisable to dis- sect away the peritoneum near its line of attachment and then distend the tube before fixing. It is instructive to dilate the tube by filling it with the fixing agent, thus causing many of the folds to disappear. 284. Xo special technic is necessary in fixing the uterus and vagina. The epithelium is, however, best isolated with one-third alcohol {yid. T. 128). 285. Seminal fluid to which normal salt solution has been added may be examined in a fresh condition. The effect upon the spermatozoa of a very dilute solution of potassium hydrate (1% or weaker) or of a very dilute acid (acetic acid) is worth noticing. The spermatozoa of sala- mandra maculosa show the different structural parts very clearly (lance, undulating membrane, marginal thread, etc.). In macerated prepara- tions (very dilute chromic acid), or in those left for some time in a moist chamber, the fibrillar structure of the marginal and axial threads may be seen quite distinctly. The spermatozoa may also be examined in the form of dry preparations (treatment as for blood), stained, for instance, with safranin. Osmic acid, its mixtures, and osmic vapors are useful as fixing agents, certain structures being better brought out so than by employing the dry methods. 286. In examining the testicle (spermatogenesis) it is advisable to begin with the testis of the salamander, which does not show such com- plicated structures as do the testes of mammalia. Here also either Flem- ming's or Hermann's fluid may be used as a fixing agent, the latter being THE SKIN. 341 followed by treatment with crude pyroligneous acid {yid. T. 18). I oi the salamander Hermann recommends a mixture composed of \'/< plati- num chlorid 15 c.c, 2 1 /, osmic acid 2 c.c, and glacial acetic arid 1 c.c, and for mammalia the same solution with double the amount of osmic acid. This fluid is allowed to act for some days, the spei mien then being washed for twenty-four hours in running water and carried over into all <> hols of ascending strengths. Paraffin sections are treated as follows : Pla< e for from twenty-four to forty-eight hours in safranin (safranin 1 gm. is dissolved in 10 c.c. of absolute alcohol and diluted with 90 c.c. of anilin water: vid. T. 119). After decolorizing with pure or acidulated absolute alcohol the sections are placed for three or four hours in gentian-violet (saturated alcoholic solution of gentian-violet 5 c.c. and anilin water 100 c.c), and are then placed for a few hours in iodo-iodid of potassium solution until they nave become entirely black (iodin 1, iodid of potas- sium 2, water 300); finally, they are washed in absolute alcohol, until they become violet with a dash of brown. The various structures appear differently stained : for instance, the chromatin of the resting nucleus and of the dispirem, bluish-violet ; the true nucleoli, red ; while, on the other hand, in the aster and diaster stages the chromatin stains red. It is of especial importance that small testicles should not be cut into pieces before fixing, as this causes the seminal tubules to swell up and show marked changes, even in regions at some distance from the cut (Hermann, 93, I). The treatment of the remaining parts of the male reproductive organs requires no special technic. VI. THE SKIN AND ITS APPENDAGES. A. THE SKIN (CUTIS). The skin consists of two intimately connected structures — the one, of mesodermic origin, is the true skin, corium or dermis ; the other, of ectodermic origin, is the epidermis or cuticle. The super- ficial layer of the corium is raised into ridges and papillae which penetrate into the epidermis, the spaces between the papillae being filled with epidermal elements. Thus, the lower surface of the epidermis is alternately indented and raised into a system of furrows and elevations corresponding to the molding of the corium. In the epidermis two layers of cells may be observed — the stratum Malpighii, or stratum gcrminativum ( ITemming), and the horny layer, or stratum corneum. According to the shape and characteristics of its cells, the stratum germinativum may also be divided into three layers — first, the deep or basal layer, consisting of columnar cells resting immediately upon the corium ; second, the middle layer, consisting of polygonal cells arranged in several strata, the number of the latter varying according to the region of the body ; and third, the upper layer, or stratum granulosum, which is composed, at most, of two or three strata of gradually flattening cells characterized by their peculiar granular contents. 3-P THE SKIN AND ITS APPENDAGES. All these cell layers consist of prickle cells, and for this reason the stratum Malpighii is sometimes known as the stratum spinosum. When these cells are isolated by certain methods, their surfaces are seen to be provided with short, thread-like processes. In section the cells appear to be joined together by their processes. Since it has been proved that the processes of adjacent cells do not lie side by side, but meet and fuse, they must be regarded as belonging alike to both cells. Between the fused processes, which are known as intercellular bridges, there exists a system of channels which is in communication with the lymphatic system of the corium. The prickles just mentioned are variously regarded by different investi- gators ; some considering them to be exclusively protoplasmic in 1 Fig. 286. — Under surface of the epidermis, separated from the cutis by boiling. The sweat-glands may be traced for a considerable part of their length ; X 4° : «> Sweat- gland ; b, longitudinal ridge ; c, depression ; d, cross-ridge. processes of the cells, others regarding them as derived from the membranes of the cells composing the stratum Malpighii. Ranvier and others ascribe a fibrillar structure to the peripheral portion of the cellular protoplasm, and, according to them, these fibrillae, surrounded by a small quantity of indifferent protoplasm, form the processes. Ranvier has also shown that such fibrillae may extend from one cell around several others before reaching their ultimate destination in other cells at some distance. (Fig. 288.) The cells of the stratum granulosum contain peculiar deposits of a sub- stance to which Waldeyer has given the name of keratohyaliu. This substance occurs in the form of irregular bodies varying in size and imbedded in the protoplasm. The nuclei of such cells always THE .-KIN*. 343 show degenerative processes, which are possibly due to the forma- tion of the keratohyalin (Mertsching, Tettenhamer). These karyo- lytic figures and keratohyalin possess in common many apparently identical microchemic peculiarities, and it is very probable that karyolysis and the formation of keratohyalin are processes origin- ally very closely allied — i. c, that the keratohyalin is derived from the fragments of the dying nucleus. The stratum corncum forms the outer layer of the epidermis and presents, as a rule, a somewhat differentiated lower stratum. This Strj Stratum corneum. Stratum Malpighii. Duct of sweat- gland. Corium. Subcutis. , Fig. 287. — Cross-section of skin of child, with blood-vessels injected ; X 3°- latter is more especially noticeable in those regions in which the stratum corneum is highly developed, and is known as the stratum lucidum. It is quite transparent, this property being due to the presence in its cells of a homogeneous substance, the eleidin. Hleidin is in all probability a derivative of the more solid keratohy- alin of the stratum granulosum. The cells of the stratum corneum are more or less flattened and cornified, especially at their periphery. This applies more particularly to the superficial cells. In the inte- rior of each cell a more or less degenerated nucleus may be seen, but otherwise its contents are homogeneous, or, at most, arranged 344 THE SKIN AND ITS APPENDAGES. in concentric lamellae (Kolliker, 89). Here and there between the cornified cells structures may be seen which probably represent the remains of intercellular bridges. The thickness of the epidermis varies greatly according to the locality, and is directly proportionate to the number of its cell layers. As a rule, the stratum Malpighii is thicker than the stratum corneum, but in the palm of the hand and the sole of the foot the latter is considerably the thicker. The various layers of the epidermis are in close genetic relation- ship to one another. The constant loss to which the epidermis is subjected by desquamation is compensated by a continuous upward pushing of its lower elements ; cell-proliferation occurs in the basal cells and adjacent cellular strata of the stratum germinativum (Malpighii), where the elements are often seen in process of mitotic division. The young cells are gradually pushed outward, and dur- ing their course assume the general characteristics of the elements the layers Fibrils which pass from one cell to another. Nucleolus. Intercellular bridges. Nucleus of cell. composing through which theypass. For instance, such a cell changes first into a cell of the stratum germina- tivum ; then, when it commences the forma- tion of keratohyalin, into a cell of the stratum granulosum ; later, into a cell of the stratum lu- cidum, and finally into an element of the stra- tum corneum, where it loses its nucleus, corni- fies, and at last drops off. The mesodermic por- tion of the skin, the co- rium, consists of a loose, subcutaneous connective tissue containing fat, the subcutaneous layer, with the panniculus adiposus, and of the true skin, or corium proper. The amount of adipose tissue in the subcutaneous layer is subject to great variation ; there are, however, a few re- gions in which there is normally very little or no fat (external ear, eyelids, scrotum, etc.). To the subcutaneous connective tissue is due the mobility of the skin. The corium may be compared to the mucosa of a mucous membrane, and consists of two layers — of a deeper and looser pars reticularis, and of a superficial pars papillaris supporting the papillae. The transition from the one to the other is very gradual. Elastic fibers are present in the connective tissue of both layers. The pars reticularis is made of bundles of connective-tissue fibers arranged in a network, nearly all of the strands of which have a direc- Fig. 2I -Prickle cells from the stratum Malpighii of man ; X 4&0. THE SKIN. 345 tion parallel with the surface of the skin and are surrounded by a retic- ulum of rather coarse clastic fibers. In that portion of the pars papil- laris bordering upon the epidermis, the interlacing strands of con- nective tissue, as well as the surrounding reticulum of elastic fibers, are finer, so that the whole tissue is denser. This stratum supports the papillae — knob-like or conical elevations of still denser tissue end- ing in one or more points. We accordingly speak of simple or com- pound papillae. These structures are especially numerous and well developed in the palm of the hand and sole of the foot, where they are from I io u to 220 u long. Here the} - rest upon ridges of the corium, which are nearly always arranged in double rows. Accord- ing to whether the papilke contain blood-vessels alone, or special nerve-endings also, they are known as vascular or tactile papillae. Stratum corneum. Lower border of stratum lucidum. Stratum granu- losum. Stratum Mal- pighii. L 1 : -:(?}' o m^. >r®> ms>: w www* Fig. 289. — Cross-section of human epidermis ; the deeper layers of the stratum Malpighii are not represented ; \ 750. The smallest papillae are found in the mammae and scrotum — from 30 (J. to 50 ft long. The surface of the pars papillaris is covered by an extremely delicate membrane — the basement membrane. Accord- ing to most authors, the basal cells of the epidermis arc simply cemented to this structure. Others believe that the epithelial cells are provided with short basilar processes which penetrate into the basement membrane and meet here with similar structures from the connective-tissue cells of the corium. This would give the base- ment membrane a fibrillar structure (Schuberg). The subcutaneous layer contains numerous more or less verti- cal strands of connective tissue, containing numerous large elastic- tissue fibers and joining the stratum reticulare of the corium to the 346 THE SKIN AND ITS APPENDAGES. superficial fascia of the body or underlying structure, whatever that may be. These strands are the retinaculce cutis, and inclose in their meshes masses of fatty tissue which form the panniculus adiposus. The latter varies greatly in thickness in different parts of the bod}-. The vertically arranged cords of connective tissue are accompanied by blood-vessels, nerves, and the excretory ducts of glands. Smooth muscle-fibers are also present in the skin, and around the hair follicles are grouped into bundles. Nearly continuous layers of smooth muscle tissue are found in the subcutaneous layer of the scrotum (forming here the tunica dartos), in the perineum, in the areolae of the mammae, etc. In the face and neck striated muscle-fibers also extend outward into the corium. Even in the white race certain regions of the epidermis always contain pigment — as, for instance, the areolae and mammillae of the , ... ,,i:> as well as toward the hair shaft. Below, in the region of the thick- ened hair bulb, the root-sheaths begin to lessen in thickness, their layers becoming more and more indistinct toward the base of the hair papilla. Finally, all differentiation is lost in the region where they encircle the neck of the papilla. Toward the shaft of the hair, the root-sheath also undergoes changes. In the region into which the sebaceous glands empty, the inner root-sheath disappears, while the outer becomes continuous with the stratum germinativum of the epidermis ; the outer layers of the latter — the stratum granu- losum, stratum lucidum, and stratum corneum — push downward between the outer root-sheath and the hair to the openings of the sebaceous glands. Regarding the growth of the hair, two theories are prevalent. Glassy layer. Cortex of hair. Medulla of hair. Cuticle of innei root- sheath. - Henle's layer. ' Fibrous-tis- sue sheath. Fig. 296. — Cross-section of human hair with its follicle ; >( about 300. The one theory assumes that the elements destined to form the epithelial root-sheaths are derived from the epidermis by a constant process of invagination. The component parts of the hair would thus be continuous with the layers of the root -sheaths, and conse- quently with those of the epidermis. Thus the basal cells of the external root-sheath would extend over the papilla, and be continu- ous with the cells of the medulla of the hair (these relations are especially well defined in the rabbit), and the stratum spinosum (middle layer of stratum Malpighii) of the outer root-sheath would be continuous with the cortical substance of the hair. According to this theory also, the layer of Henle would correspond to the stratum lucidum of the epidermis, and at the base of the hair 23 354 THE SKIN AND ITS APPENDAGES. would become its cuticle, while the layer of Huxley would form the cuticle of the inner root-sheath (Mertsching). The other theory assumes that the hair is derived from a matrix, consisting of proliferating cells situated on the surface of the papilla. From these germinal cells would be derived the medullary and cortical substance of the hair, its cuticle, and the inner root-sheath (Unna). The shedding of hair is common to all mammalia, a phenomenon occurring periodically in the majority of species. In man the pro- cess is continuous. Microscopic examination shows that the hair destined to be shed becomes loosened from its papilla by a cornifi- cation of the cells of its bulb. At the same time the cortical por- tion of the hair bulb breaks up into a brush-like mass. Such hairs are called bulb hairs, in contradistinction to papillary hairs. In the region of the former papilla there arises, by a proliferation of the external root-sheath, a bud which grows downward, from which a new hair with its sheaths and con- nective-tissue papilla is developed. The result is that the developing new hair gradually pushes the old hair outward until the latter fin- ally drops out. The exact details of this process have given rise to considerable discussion {vid. Gotte and Stieda, 87). Adjacent to the hair follicles are bundles of smooth muscle- fibers, known as the arrectores pi- lorum. They originate from the papillary layer of the corium and extend to the lower part of the connective-tissue sheath of the hair follicles. In their course they not infrequently encircle the sebace- ous glands of the follicle. Since the hair follicles have a direction oblique to the skin surface, forming with it an acute and an obtuse angle, and since the muscle is situated within the obtuse angle, its function may easily be conceived as being that of an erector of the hair. The hair papillae are very vascular. The nerve-fibers of the hair follicles have recently been studied by a number of investigators, with both the Golgi and the methylene- blue methods. It has been shown that the hair follicles receive their nerve supply from the nerve-fibers which terminate in the immediate skin area. Each follicle receives, as a rule, only one nerve-fiber, which reaches the follicle a short distance below the mouth of the sebaceous gland. The nerve-fiber, on reaching the Fig. 297. — Longitudinal through hair and hair follicle X 160. Technic No. 291. section of cat : THE NAILS. 355 follicle, loses its medullar}' sheath and divides into two branches, which surround it in the form of a ring. From this complete or partial ring of nerve-fibers numerous varicose fibers proceed upward parallel to the axis of the follicle for a distance about equal to the cross diameter of the follicle, to terminate, it would seem, largely outside of the glassy layer (Retzius). In certain mammalia the nerve-fibers end in tactile discs, found in the external root-sheaths of the so-called tactile hairs. The muscles of the hairs receive their innervation through the neuraxes of sympathetic neurones, which reach the periphery from the chain ganglia through the gray rami communicantes. These nerves are known as pilomotor nerves, and when stimulated, excite contraction of the erector muscles of the hairs, causing these to assume an upright position and producing the appearance termed goose skin, or cutis anserina. Langley and Sherrington have made interesting and important observations on the course and distribution of the pilomotor nerves. C THE NAILS. The nails are a peculiar modification of the epidermis. The external arched portion is called the body of the nail ; that area upon Fig. 298. — Longitudinal section through human nail and its nail groove (sulcus) ; X 34- which the latter rests, the nail bed, or matrix ; and the two folds of epidermis which overlap the nail, the nail walls. The groove which exists between the nail wall and nail bed is known as the salens of the matrix, and the proximal imbedded portion of the nail as the nail root, since all growth of the nail takes place in this region. The nail bed consists of the corium, which is here made up of a dense felt-work of coarse connective-tissue fibers. Immediately beneath the nail the corium is raised into a number of more or less symmetric longitudinal ridges, which again become con- tinuous with the connective-tissue papillae of the skin at the line where the nail projects beyond its bed. The depressions between the ridges are occupied by epidermal cells, which also form a thin covering over the ridges themselves. 356 THE SKIX AND ITS APPENDAGES. These cells correspond here to the basilar layer of the stratum Mal- pighii. The stratum granulosum is not uniformly present, although occurring as isolated areas in the region of the nail root and lunula, the white area of demilunar shape at the proximal portion of the nail. Unna has demonstrated that the pale color of the lunula and root of the nail is due to the presence of keratohyalin. Formerly, this peculiarity was attributed to a difference in the distribution of the vessels in the various portions of the nail bed. The body of the nail, with the exception of the lunula, is transparent — a con- dition which ma}- be explained by the fact that the elements of the nail correspond to those of the stratum lucidum. As a consequence, the vessels of the matrix shine through, except at the lunula, where the keratohyalin granules render the nail opaque. The nail itself consists of elements homologous to those of the stratum lucidum. They are flat, transparent cells, closely approxi- mated, and all contain nuclei. The cells overlie each other like tiles, and are so arranged that each succeeding lower layer projects Nail.- Stratum Mai- - ,—- - pighii. ' ,** Nail wall Nail groi ■•• ■:.. _ C 01 mm. -Blood-vtissel. Fig. 299. — Transverse section through human nail and its sulcus ; X 34- a little further distalward than the preceding. At the period when the nails are formed, about the fourth month of fetal life, sulci are already present. The first trace of the nail is seen as a marked thickening of the stratum lucidum in the region which later be- comes the body of the nail ; in this stage the structure is still cov- ered by the remaining layers of the stratum corneum, constituting the eponychium. The embryonal nail then spreads in all directions until it finally reaches the sulcus. Henceforward the growth is uniform. The eleidin normally present in the stratum lucidum of the skin also occurs in the nail, and is derived, as we have already seen, from the keratohyalin. It may readily be conceived that later, when growth is confined to the root of the nail, keratohyalin is also present. As soon as the nail begins to grow forward, in the ninth month, the greater part of the eponychium is thrown off; but during the entire extrauterine life, a portion of the eponychium is retained at the nail wall, and as hyponychium on the anterior and under surface of the nail. THE GLANDS <>l THE SKIN. 357 Nonsti iated muscle-cell. (".land-cell. Fig. 300. — Cross- section of tubule of coiled portion of sweat-gland from human axilla. Fixation with sublimate ; X o0 °- D. THE GLANDS OF THE SKIN. The glands in the skin arc of two kinds — sweat-glands and sebaceous glands. A modification of the latter is seen in the mam- mary glands. 1. The Sweat-glands. — The sweat-glands, or sudoriparous glands, are distributed throughout the entire skin, but are especially numerous in certain re- gions — as, tor instance, the axilla, palm of the hand, and sole of the foot. They lie imbedded either in the adipose tis- sue of the true skin, or still deeper in the subcu- taneous connective tissue (axilla). To this group of glands belong also the ceruminous glands of the ear, the glands of Moll in the eyelid, and the cir- cumanal glands. The sweat-glands are simple tubular in type, and their secreting portion is coiled ; hence the name coil-glands. The coil is, as a rule, 0.3 or 0.4 mm. in di- ameter, but in the axilla reaches from 3 to 7 mm. The excretory duct (the su- doriferous duct) is nearly straight during its course up- ward through the corium, and always enters the epider- mis between two papillae of the corium. From here on, its course is spiral, and it should be borne in mind that in its passage through the epidermis it has no other wall than the epidermal cells of the various layers through which it passes, although these cells are arranged con- centrically around the lumen of the duct. The lining of the secretory or coiled portion of the sweat- gland consists of cubical cells with finely granular protoplasm and round or oval nuclei possessing one or two nucleoli. In the excre- Nucleus of nonstriated muscle-cell. Fig. 301. — Tangential section through coiled portion of sweat-gland from human axilla. Sublimate fixation; X 7°°- 3 5^ THE SKIN AND ITS APPENDAGES. ton- segments, the cells are arranged in two layers. The membrana propria is very delicate, and in both regions of the gland apparently structureless. External to the basement membrane is a fine con- nective-tissue sheath. A marked peculiarity of the secretory por- tion of the gland consists in a longitudinal layer of smooth muscle- fibers between the membrana propria and the glandular epithelium. The presence of this structure can be accounted for only by assuming that it is an epithelial derivative. The changes in the gland cells during secretion have not been sufficiently studied, but this much is certain, that the secretory phe- nomena are not similar to those in the sebaceous glands (see below). To the glandular secretion must be added also the serum-like fluid oozing from the canalicular lymph-spaces in the stratum Mal- pighii into the epidermal portion of the excretory duct (Unna). The development of the sweat-glands begins in the fifth month of fetal life. At first solid cords grow from the stratum germi- nativum of the epidermis into the corium. Later, in the seventh month, these become hollow. Capillary networks surround the secreting portions of the sweat-glands. The nerves of the sweat-glands have been studied with the aid of the methylene-blue method by Ostroumow, working under Arnstein's direction. These glands receive their innervation through the neuraxes of sympathetic neurones, the terminal branches of which form an intricate network just outside of the basement membrane, known as the epilamellar plexus. From this plexus fine, varicose nerve-fibers pass through the basement membrane, and, after coursing a shorter or longer distance with or without further division, end on the gland-cells, often in clusters of small terminal granules united by delicate threads. 2. The Sebaceous Glands. — The distribution of the sebaceous glands in the skin is closely connected with that of the hair follicles into which they pour their contents. Exceptions to this rule occur in only a kw regions of the body, as, for instance, in the glans penis and foreskin (Tyson's glands), in the labia minora, angle of the mouth, glandulse tarsales, and the Meibomian glands of the eyelids, etc. As a rule the sebaceous gland empties by a wide excretory duct into the upper third of the hair follicle. The walls of the duct also produce secretion, and can therefore hardly be differentiated from the rest of the gland. At its base the duct widens and is pro- vided with a number of simple or branched alveoli. The sebaceous glands are therefore of the type of compound alveolar glands, vary- ing in length from o. 2 mm. to 5 mm. They are surrounded by connective-tissue sheaths, which at the same time cover the hair follicles. Inside of the sheath is the membrana propria, which is a continuation of the glassy membrane of the follicle. The two or three basal strata of glandular cells must be regarded as a direct continuation of the elements of the external root-sheath. In the THE (.LANDS OF THE SKIN. 359 more centrally placed strata the cells arc distinctly changed in char- acter ; their contents consist of fat globules, varying in size and distributed throughout the protoplasm, giving this a reticular appearance, while the nuclei suffer compression from the accumu- lation of the fat globules and gradually become smaller and more angular. Finally, the cells change directly into secretion, which is then poured into the hair follicle as sebum. It is thus seen that in the secretion of sebum the cells are consumed and must be re- placed. This renewal takes place by the constant proliferation of the basilar cells, which push the remains of the secreting cells upward and finally take their places. The final disintegration of the cells occurs either within the gland itself or between the hair follicle and the hair. The secretion contains fatty globules of varying size, which occur either free or attached to cellular detritus. 4m i^^ic '§m0S[ Fig. 302. — Section of alveoli from sebaceous gland of human scalp. 3. The Mammary Glands. — The mammary glands are also included among the cutaneous glandular structures. They are developed early, but not until the fifth month is it possible to dis- tinguish a solid central portion, with radially arranged tubules terminating in dilatations. The structures are all derived from the basal layers of the epidermis. From birth to the age of puberty the organs are in a state of constant growth, and are early sur- rounded by a connective-tissue sheath. The alveoli, which have been developed in the mean time, .ire still solid and relatively small. Up to the twelfth year the glands remain identical in structure in boys and girls. In the female the mammary glands continue to develop from the age of puberty ; in the male, on the other hand, they undergo a retrograde metamorphosis, ending, finally, in the atrophy of all except the excretory ducts. The mammary glands 360 THE SKIN AND ITS APPENDAGES. do not attain their full stage of development in women until the last months of pregnane}', and are functionally active at parturition. The human mammary gland when fully developed has the fol- lowing structure : It consists of about twenty lobes, separated from each other by connective-tissue septa. These lobes are again divided into a larger number of lobules, and these in turn are com- posed of numerous alveoli, which, as in the case of the lung, pre- sent lateral sacculations. The alveoli are provided with small excretory passages, which unite and finally form the larger ducts. Shortly before terminating at the surface of the mammilla, each I s ,V$^'ffc^>^U^.4Si- Alveolus. mmm .v.. m Connective- tissue stroma. Duct and alveoli. Adipose tissue. Fig. 303. — From section of mammary gland of nullipara. (From Nagel's " Die weiblichen Geschlechtsorgane," in " llandbuchs der Anatomie des Mcnschen," 1896.) mammary duct widens into a vesicle, the sinus lactifcrus. The number of excretory ducts corresponds to that of the larger lobes. The ducts are lined by simple cubical epithelium, except near the termination in the nipple, where they are lined by stratified pave- ment epithelium, and surrounded by a fibrous tissue sheath. The epithelium of the alveoli differs according to the state of functional activity. In a state of rest it consists of a single layer of glandular cells of nearly cubical shape which stain deeply, the internal surfaces projecting into the lumen. At the beginning mi. '.lands OF THE SKIN. 361 of secretion the cells increase in length and fat globules make their appearance in their distal ends. At the same time a corresponding increase in size occurs throughout the entire alveolus. Finally, the free ends of the cells, which contain the most tat globules, are con- stricted off, after which the fat globules are freed in the lumen. The secretorv portion of the alveolus is then composed of low epithelial cells, in which the process begins anew. The- process of milk secre- tion therefore consists in throwing off the inner hakes of the cells containing the tat globules, and in regeneration of the cells from the nucleated remains of the glandular epithelium. Whether a k;i isokinetic division of the nuclei occurs in this process is not known, and how often the process of regeneration may be repeated in a single cell is not capable of demonstration. It is certain, how- ever, that entire cells are destroyed, to be replaced later by new elements. The membrana propria of the alveoli appears homo- geneous. Between it and the glandular cells are so-called basket cells, similar to those in the salivary glands. Benda regards the basket cells as nonstriated muscle elements, having a longitudinal direction, making the structure of the alveoli of the mammary inland similar in this respect to that of the secreting portion of the sweat-glands. The skin of the mammilla is pigmented, and the papillae of its corium are very narrow and long. In the corium are also found large numbers of smooth muscle-fibers, which form circular bun- dles around the excretory ducts. In the areolae of the mamma' are the so-called glands of Montgomery, which very probably repre- sent accessor}- mammary glands. These are especially noticeable during lactation. The mammai}- glands possess many lymphatics. These are especially numerous in the connective-tissue stroma between the lobules and alveoli. The vessels form capillar}' networks surround- ing the alveoli. The lymph-vessels collect to form two or three- larger vessels, which empty into the axillary glands. The mam- mar}- gland receives its nerve supply from the sympathetic and cerebrospinal nervous systems through the fourth, fifth, and sixth intercostal nerves. The terminations of the nerves in the mammary gland have been studied by means of the methylene-blue method by Dmitrewsky, working in the Arnstein laboratory, who finds that the terminal branches form epilamellar plexuses outside of the base- ment membrane of the alveoli, from which fine nerve branches pass through the basement membrane and end on the gland cells in clusters of terminal granules united by fine filaments. The nipple has a rich sensor}- nerve supply. In the connective-tissue papilla- are found tactile corpuscles of Meissner. The milk consists of fat globules of varying size, which, how- ever, do not coalesce — an attribute due to the presence of albu- minous haptogenic membranes surrounding the globules. Shortly before, and for some days after, parturition the milk contains true 362 THE SKIN AND ITS APPENDAGES. nucleated cells in which are fat globules ; these are known as the colostrum corpuscles. They probably represent cast-off glandular cells in a state of fatty degeneration. Some authors regard them as leucocytes which have migrated into the lumen of the gland and there undergone fatty degeneration. This milk is known as colostrum. TECHNIC. 287. Good general views of the skin can be obtained only from sections. Any fixation method may be employed, although alcohol is preferable on account of the better subsequent staining. For detail work Flemming's solution, corrosive sublimate, or osmic acid is the best. Sectioning of the skin is attended with many difficulties, and large pieces can be cut only in celloidin. Small and medium-sized pieces may be cut in paraffin ; but even in this case the skin must be rapidly imbedded in the paraffin — i. e., it must not remain too long in either alcohol or toluol — and the paraffin must have only the consistency necessary to cut well (about 50 C. melting- point). In order to obtain good paraffin sections of the skin the follow- ing procedure is recommended : Pieces fixed in Flemming's solution or osmic acid are kept in 96% alcohol, then placed for not more than twenty- four hours in absolute alcohol and imbedded in paraffin by means of the chloroform method. In the chloroform, chloroform -paraffin, and pure paraffin they remain for one hour each. The paraffin used should consist of two parts paraffin of 42 ° C. , and one part paraffin of 50 C. melting-point. The thermostat must be kept at 50 C. (R. Barlow). The sections should not be mounted by the water-albumen method. 288. In sections of epidermis which have been freshly fixed with osmic acid, the stratum corneum may be clearly differentiated into three layers (probably because of the defective penetration of the reagent) — into a blackened superficial, a middle transparent, and a still lower black layer (yid. Fig. 304). 289. In tissue fixed in alcohol or corrosive sublimate the stratum lucidum stains yellow with picrocarmin, but is very weakly colored by basic anilin stains. In unstained preparations the stratum lucidum is glass-like and transparent. Eleidin is diffusely scattered throughout both the stratum lucidum and stratum corneum. Like keratohyalin, it stains with osmic acid and also with picrocarmin, but not with hematoxylin. Nigrosin stains eleidin, but not keratohyalin. 290. Keratohyalin is insoluble in boiling water and is not attacked by weak organic acids. It dissolves, however, in boiling acetic acid, but is not changed by the action of pepsin or trypsin. The keratohyalin granules of the stratum granulosum swell in from i ( /, to <^'/ ( potassium- hydrate solution ; under the influence of heat these granules together with the cells containing them are finally dissolved. They are not attacked by ammonia, and remain unaffected for a long time in strong acetic acid. As ammonia and acetic acid render the remaining portions of the tissue transparent, these reagents may be employed for die rapid identification of keratohyalin. The larger flakes of keratohyalin swell in sodium car- bonate solution ( 1 '/, ), but not the smaller granules, and it would seem that the larger granules have less power of resistance than the smaller. Keratohyalin remains unchanged in alcohol, chloroform, and ether, but I E< HNIC. 363 is digested in trypsin and pepsin (not, however, the keratin). kerato- hyalin can be stained with hematoxylin and most of the basic anilin dyes. 291. The prickles of the cells composing the stratum Malpighii may be seen in very thin sections (not over 3 ft in thickness) of skin previ- ously fixed in osmic acid. In this case it is best to employ not Canada balsam, but glycerin, which does not have so strong a clearing action. Isolation of the prickle cells is best accomplished as follows ( Schieffer- decker) : A fresh piece of epidermis is macerated for a few hours in a filtered, cold-saturated, aqueous solution of dry pancreatin ; the whole may then be preserved for any length of time in equal parts of glycerin, Outer dark laser. Stratum corneum. Middle lik'ht layer. Inner dark la\ ei . Stratum lucidum. Stratum Malpighii. jSfc '»0 Fig. 304. — Transverse section through the human skin. Treated with osmic acid ; X 30 : , duct of same sweat-gland in the corium. Cutis and sub- cutis. Fat cell. water, and alcohol. Small pieces taken from such specimens are readily teased and show both isolated and small groups of attached prickle cells. 2g2. The distribution of the pigment in the skin is best studied in unstained sections. With a nearly closed diaphragm and under medium magnification the pigment granules appear darker on raising the tube and lighter upon lowering it. 293. In sections of skin treated with Flemming's fluid, the structure of the cutis also may be studied. The medullary sheaths of the nerve- fibers and the fat appear black. In preparations stained with safranin the 364 THE SKIN AND ITS APPENDAGES. elastic fibers are colored red and are very distinct (Stohr and O. Schultze). For the orcein method according to Unna, see T. 138. 294. Hair may be examined in water without further manipulation. The cuticle is then seen to consist of polygonal areas, the border-lines of which correspond to the limits of the flattened cells. By slightly lower- ing the objective the cortical substance comes into view with its indistinct striation and occasional pigmentation. The medullary substance, if pres- ent, may also be seen with its vesicles containing air. Both the cortical and cuticular cells may be isolated, the process consisting in treating the hairs for several days with 33 ( / c potassium hydrate solution at room tem- perature, or in heating the whole for a few minutes. Concentrated or weak sulphuric acid produces the same result. On warming a hair in sul- phuric acid until it begins to curl and then examining it in water, we find that the cortical and medullary layers as well as the cuticle are separated into their elements. Treatment of the skin with Miiller's fluid, alco- hol, or sublimate is recommended for the examination of hair and hair follicles. The orientation of the specimen should be very precise, in order to obtain exact longitudinal or cross-sections of the hair. There is hardly a structure of the body which is more suitable for staining with the numerous coal-tar colors than the hair and its follicle (Merkel). 295. The corpuscles of Meissner may be best obtained from the end of the finger. After boiling a piece of fresh skin from the finger-tip for about a quarter of an hour, the epidermis may be easily removed ; the papillae are now seen on the free surface of the cutis. A portion of the latter is cut away with a razor and examined in a 3 % solution of acetic acid. The corpuscles are readily distinguished. Their relations to the nerves should be studied in specimens fixed with osmic acid or gold chlorid. The terminations of the nerves in these end-organs are best seen in preparations stained after the intra vitam methylene-blue method. 296. The corpuscles of Herbst and Grandry are found in the waxy skin covering the bill, and in the palate of the duck (especially numerous in the tongue of the woodpecker). For the study of the nervous ele- ments the following method is useful : Pieces of the waxy skin are removed with a razor and placed for twenty minutes in 50% formic acid. After washing the specimens for a short time in distilled water they are transferred to a small quantity of 1% gold chlorid solution (twenty min- utes), then again rinsed in distilled water, and placed for from twenty- four to thirty-six hours in the dark in a large quantity (j/3 liter) of Pichard's solution (amyl alcohol 1 part, formic acid 1 part, water 100 parts j. After again washing in water the specimens are transferred to alcohols of gradually increasing strengths and finally imbedded in celloidin or celloidin-paraffin. 297. The Pacinian corpuscles occur in the mesentery of the cat and may be examined in physiologic saline solution. 298. The nerves of the epidermis are demonstrated by the gold- chlorid method ( see |>. 166 j. But even here the < hrome-silver method and the intra vitam mclhyleiie-bluc method yield extremely good results, and may be used with great advantage in the study of the nerves in the cutis. 299. The so-called tactile menisci are very numerous in the snout of the pig and the mole. Bonnet recommends for these structures fixation in 0.33$ chromic acid solution (vid. T. 26), overstaining with hematoxylin, and differentiation in an alcoholic solution of potassium ferricyanid. THE SPINAL CORD. 365 VII. THE CENTRAL NERVOUS SYSTEM. I\ .1 study of the minute anatomy of the central nervous system consideration should be given to the arrangement of the nerve-cells and nerve-fibers in the various regions, and to the mutual relations which the elements of the nervous system bear to one another. In a text-book of this scope, however, we shall be unable to enter into the consideration of these subjects in detail, but must content our- selves with a very general discussion of the structure of certain regions of the central nervous system and an account of a few typical examples illustrating the mutual relationship of the nerve-elements to one another. We shall, therefore, give a general description of the structure of the spinal cord, cerebellum, cerebrum, olfactory lobes, and ganglia. In this description we have drawn freely from the results of the researches of Golgi (94), Ramon y Cajal (93, 1), von Lenhossek (95), Kolliker (93), and van Gehuchten (96). • A. THE SPINAL CORD. The spinal cord extends from the upper border of the atlas to about the lower border of the first lumbar vertebra. It has the form of a cylindric column, which at its lower end becomes quite abruptly smaller, to form the conus medullaris, and terminates in an attenu- ated portion — the filuiu terminate. It presents two fusiform enlarge- ments, known as the cervical and lumbar enlargements respectively. The spinal cord is partly divided into two symmetric halves by an anterior median fissure and by a septum of connective tissue, extend- ing into the substance of the cord from the pia mater (one of the fibrous tissue membranes surrounding the cord), and known as the posterior median septum. Structurally considered, the spinal cord consists of white matter (mainly medullated nerve-fibers) and gray matter (mainly nerve-cells and medullated nerve-fibers). The white and the gray matter present essentially the same general features at all levels of the spinal cord, although the relative proportion of the two substances varies somewhat at different levels. The different portions of the cord present also certain structural peculiarities. The distribution of the gray and the white substances of the spinal cord is best seen in transverse sections. The varying shape of the spinal cord in the several regions and the changing relations of the gray to the white substance are shown in the illustrations of cross-sections of the adult human spinal cord (see p. 366). The gray substance is arranged in the form of two crescents, one in each half of the cord, united by a median portion extending from one half of the cord to the other, the whole presenting some- what the form of an H. The horizontal part contains the commis- 3 66 THE CENTRAL NERVOUS SYSTEM. s^ m^m % -:■" P>& 305.— Four cross sections of the human spinal cord ; / 7 : A, Cervical region in the plane of the sixth spinal nerve-root; 3, lumbar region ; C, thoracic region • D sacral region (compare with Fig. 306). (From preparation's of 11. Schmaus.) Tin: SPINAL CORD. }<>7 sures and the central canal of the spinal cord, while the vertical limbs or crescents extend to the ventral and dorsal nerve-roots, forming the anterior and posterior horns. The former are, .1- .1 rule, the larger, and at their sides (laterally) the so-called lateral horns maybe seen, varying in size in different regions. In each anterior horn are three main groups of ganglion cells : the ventro- lateral, made up of root or motor nerve-cells ; the ventromesial, composed of commissural cells; and the lateral (in the lateral horn), containing column cells. At the median side of the base of each posterior horn we find a group of cells and fibers known as the column of Clark, most clearly defined in the dorsal region, while in the posterior horn itself is the gelatinous substance of Rolando. Aside from these, numerous cells and fibers arc scat- tered throughout the entire gray substance. The motor nerve-cells lie in the ventrolateral portion of the ante- rior horn, their neuraxes extending into the anterior nerve-root. Their dendrites are distributed in a lateral, dorsal, and mesial direc- tion, the two former groups ending in the anterior and lateral col- umns, the mesial in the region of the anterior commissure. Some of the mesial dendrites extend beyond the median line and form a sort of commissure with the corresponding processes of the other side. The commissural cells lie principally in the mesial group of the anterior horn, but occur here and there in other portions of the gray substance. Their neuraxes form the anterior gray commis- sure with the corresponding processes from the other side. After entering the white substance of the other side, these neuraxes undergo a T-shaped division, one branch passing upward and the other downward. The column cells are small multipolar elements, represented by the cells of the lateral horns, although they are also found throughout the entire gray mass. Their neuraxes pass directly into the anterior, lateral, and posterior horns. The cells of the column of Clark, or nucleus dorsalts, arc of two kinds — those in which the neuraxes pass to the anterior commis- sure (commissural cells) and those in which the neuraxes pass into the direct cerebellar tract of the same side. The plurifunicular cells are cells the neuraxes of which divide two or three times in the gray substance, the branches then passing to different columns of the white matter on the same or opposite side of the cord. In the latter case the branches must necessarily extend through the commissure. The cells of the substantia gelatinosa (Rolando) are cells with short, freely branching neuraxes, which end after a short course in the gray mass (Golgi's cells). The posterior horn con- tains marginal cells, spindle-shaped cells, and stellate cells. The first are situated superficially near the extremity of the posterior horn, their neuraxes extending for some distance through the gela- tinous substance of Rolando and then into the lateral column. The spindle-shaped cells are the smallest in the spinal cord and possess a rich arborization of dendrites extending to the nerve-root of the pos- 3 68 THE CENTRAL NERVOUS SYSTEM. tenor horn. Their neuraxes, which originate either from the cell- body or from a dendrite, pass over into the posterior column. The stellate cells are supplied with dendrites, which either branch in the substance of Rolando or extend into the column of Burdach. The gray matter contains, further, numerous medullated nerve- fibers, in part the neuraxes of the nerve-cells previously mentioned, and in part collateral and terminal branches of the nerve-fibers of the white matter with their telodendria ; also supporting cells, known as neuroglial - cells (to be discussed later), and blood-vessels. The white matter of the spinal cord consists of medullated fibers, which are devoid of a neurilemma, of neurogliar tissue, and of fibrous connective tissue. In each half of the cord the white substance, which surrounds the gray, is separated by the gray matter and its nerve -roots into Posterior horn cell. Crossed pyram- idal column. Golgi cell of posterior horn. Direct cerebel- lar column. Column cells. Golgi'scommis- sural cells. Gowers' column. Motor cells. - Collaterals of crossed pyramidal column. Collaterals ending in the gray matter. Direct pyramidal column. Fig. 306. — Schematic diagram of the spinal cord in cross-section after von Lenhos- sek, showing in the left half the cells of the gray matter, in the right half the collateral branches ending in the gray matter. three main divisions or columns: The first division, lying between the anterior median fissure and the anterior horn, is the anterior column ; the second, lying between the anterior and posterior horns, is the lateral column (since the anterior and lateral columns belong genetically to each other, the term anterolat- eral column is often used) ; and the third, lying between the poste- rior nerve-root and the posterior median septum, is the posterior column. By means of certain methods it has been possible to separate the white substance into still smaller divisions, the most important of which may here be described. In each anterior column is found a narrow median zone extend- ing along the entire length of the anterior median fissure and con- THE SPINAL CORD. 3 r >9 B 2 2 a fcd ftd u •a = « 5 h o H O ■=■3 S ■a g J; B 4) 5j *i» in w 3 C HI'S N 24 37° THE CENTRAL NERVOUS SYSTEM. taining nerve-fibers which come from the pyramids of the medulla. The majority of the pyramidal fibers cross from one side of the cord to the other in the lower portion of the medulla, at the crossing of the pyramids, and form a large bundle of nerve-fibers found in each lateral column, which will receive attention later. Some of the pyramidal fibers descend into the cord on the same side, to cross to the opposite side at different levels in the cord. These latter fibers constitute the narrow median zone, on each side of the anterior median fissure previously mentioned, forming the anterior or direct pyramidal tract, or the column of Tiirck. Between the direct pyramidal tract and the anterior horn lies the anterior ground bundle. In the lateral columns are found a number of secondary col- umns, which may now be mentioned. In front of and by the side of the posterior horn in each lateral column lies a large group of nerve-fibers, forming a bundle which varies somewhat in size and shape in the several regions of the spinal cord, but which has in general an irregularly oval outline. These nerve-fibers are the pyramidal fibers, previously mentioned, which in the lower part of the medulla cross from one side to the other, and for this reason are known as the crossed pyramidal fibers, forming the crossed pyramidal columns. External to these columns and to the poste- rior horns, and extending from the posterior horns half-way around the periphery of the lateral columns, lie the direct cerebellar col- umns, consisting of the neuraxes of the cells of the columns of Clark, which have an ascending course. Lying just external to and between the anterior and posterior horns is a somewhat irregular zone, the mixed lateral column, containing several short bundles of fibers, the anterior of which are probably motor ; the posterior, sensory. In the ventrolateral portions of the lateral columns, between the mixed lateral and the direct cerebellar columns and extending as far backward as the crossed pyramidal columns, lie two not well-defined columns, known as the ascending anterolat- eral or Gowers's columns and the descending anterolateral col- umns ; the former are nearer the outer portion of the cord. In the posterior column we distinguish a median and a lateral column. The former lies along the posterior median septum, and may even be distinguished externally by an indentation ; its upper portion tapers into the fasciculus gracilis. This is the column of Goll, and it contains ascending or centripetal fibers. The lateral tract lies between the column of Goll and the posterior horn, and is known as the column of Burdach, posterior ground-bundle, or posterolateral column. It contains principally the shorter tracts, or bundles of longitudinal fibers connecting the adjacent parts of the spinal cord with one another. .Many of the nerve-fibers of the posterior column are the ncu- - of spinal ganglion cells which enter the spinal cord through the posterior roots. The cell-bodies of the spinal ganglion or sen- THE SPINAL CORD. 3/1 BOry neurones are situated in the .spinal ganglia found on the pos- terior roots of the spinal nerves. In the embryo they an- distinctly bipolar, but during further development their two processes approa< h each other, and then fuse for a certain distance, forming finally single processes which branch like the letter T. In reality, then, there are two processes which are fused for a certain distance from the cell-body of each neurone. The peripherally directed process is regarded as the dendrite of the cell, and the proximal as the neuraxis passing to the spinal cord. The neuraxes enter the spinal cord through the posterior roots and pass to the posterior columns, where they divide, Y-shaped, into ascending and much shorter descending branches, from each of which numerous collateral branches are given off. From the preceding account of the white matter of the spinal cord, it may be seen that it consists of longitudinally directed neu- raxes arranged in so-called short and long tracts or columns. The neuraxes constituting the former, after a short course through the gray matter, emerge from it, and after giving off various collaterals, again penetrate into the gray matter, where their telodendria enter into contact with the ganglion cells. The long columns consist of the neuraxes of neurones the cell-bodies of which are situated in the cerebrum or cerebellum, and of neurones the cell-bodies of which are in the spinal cord or spinal ganglia and the neuraxes of which terminate in the medulla or cerebellum. The nerve-fibers ot the various columns give off numerous collaterals which enter the gray matter to end in telodendria. The collaterals of the posterior col- umns end : (i) between the cells of the gelatinous substance of the posterior horns ; (2) in the columns of Clark ; (3) in the anterior horns, these constituting the principal portion of the so-called reflex bundles ; (4) in the posterior horn of the opposite side. The col- laterals of the lateral columns pass horizontally toward the central canal, some ending in the anterior horn, others closely arranged near the columns of Clark, and some arching around the central canal, forming with the corresponding fibers of the other side the anterior bundles of the posterior commissure. The collaterals of the anterior columns form well-marked plexuses in the anterior horns of the same and opposite sides. We have still to describe the two commissures. The anterior consists of: first, neuraxes from the commissural cells; second. dendrites from the lateral group of the anterior horn cells ; and, third, the collaterals of the anterolateral column, which end in the gray substance of the other side of the cord. The posterior com- missure is probably composed of the collaterals from all the remain- ing columns. The posterior bundle of this commissure comes from the posterior column ; the middle, from the posterior portion of the lateral column ; and the anterior, or least developed, from the anterior portion of the lateral column, possibly also from the anterior column. 372 THE CENTRAL XEKVOl:> SYSTEM. In the gray commissure, nearer its anterior border, is situated the central canal of the spinal cord, continuous above with the ventricular cavity of the medulla and terminating caudally in the filum terminale. This canal is not patent in the majority of adults, being occluded from place to place. The canal is lined by a layer of columnar cells, developed from columnar cells, known as spongio- blasts, lining the relatively larger canal of the embryonic spinal cord. In young individuals these cells are ciliated and their basal portions terminate in long, slender processes. B. THE CEREBELLAR CORTEX. In the cerebellar cortex we distinguish three general layers — the outer molecular, the middle granular (rust-colored layer), and the inner medullary tract. Blood-vessel.- msmssm —Nerve-fiber layer. Fig. 308. — Section through the human cerebellar cortex vertical to the surface of the con- volution. Treatment with Miiller's fluid; • 115. The molecular layer contains three varieties of nerve-cells, those of Purkinje, which border upon the granular layer, the stel- "Su oS^ "i — II u o-~ _ ea.5 ■« - 2=-s I/I afuSSJ ^T, E m v 73 "3 j -j 3 ,3 -y O .O « u J fc t- ■ oq 5 O £' ■5-3 a -5 cq — C O - i/> O PJ >- ° 3 -. X -; C o -3 a o a u pq u 5 crt -- r. *-» — 41 ,- — — 41 O O ■ - S o j/ 4 THE CENTRAL NERVOUS SYSTEM. late cells, and the small cortical cells. The cells of Purkinje pos- sess a large flask-shaped body (about 60 ll in diameter), from which one or more well-developed dendrites pass toward the periphery. The latter branch freely and the main arborization has in each case the general shape of a pair of deer's antlers. These dendrites extend nearly to the periphery of the cerebellar cortex. In a section horizontal to the surface of the organ the dendrites of the Purkinje's cells are seen to lie in a plane very nearly vertical to the surface of the convolutions, so that a longitudinal section through the latter would show a profile view of the cells. In other words, they have an appearance much like that of a vine trained upon a trellis. The neuraxes of the cells of Purkinje arise from their basal Dendrite.. Cell-body. -— Neuraxis. — Claw-like telo- dendron of dendrite. Fig. 310. — Cell of Purkinje from the human cerebel- lar cortex. Chrome-silver method ; / 120. Fig. 311. — Granular cell from the granular layer of the hu- man cerebellar cortex. Chrome- silver method ; X IO °- (inner) ends and extend through the granular layer into the medul- lary substance. During their course they give off a few collaterals, which pass backward to the molecular layer and end in telodendria near the bodies of the cells of Purkinje. The stellate cells lie in various planes of the molecular layer. Their peculiar interest lies in the character of their neuraxes. The latter are situated in the same plane as the dendrites of the cells of Purkinje, run parallel to the surface of the convolution, and possess two types of collaterals. Those of the first are short and branched ; those of the second branch at a level with the cells of Purkinje, and form, together with their telodendria, basket-like nets around the bodies of these cells. The small cortical cells of the molecular layer are found llll. CEREBRAL CORTEX. 375 in all parts of this layer, but are more numerous in its peripheral portion. They are multipolar cells with neuraxes which are not readily stained and concerning the fate of which little is known. The granular layer contains two varieties of ganglion ele- ments, the so-called granular cells (small ganglion cellsj and the large stellate cells. The dendrites of the granular cells are short, few in number (from three to six), branch but slightly, and end in short, claw-like telodendria. Their neuraxes ascend vertically to the surface and reach the molecular layer. At various points some of them are seen to undergo a T-shaped division, the two branches then running parallel to the surface of the cerebellum in a plane vertical to that of the dendrites of the cells of Purkinje. Large numbers of these T-shaped neuraxes produce the striation of the molecular layer of the cerebellum. It is very probable that during their course these parallel fibers come in contact with the dendrites of the cells of Purkinje. The large stellate cells are fewer in number and lie close to the molecular layer, some of them even within this layer. Their dendrites branch in all directions, but extend principally into the molecular layer. Their short neuraxes give off numerous collaterals which end in telodendria among the granular cells. The medullary substance is composed of the centrifugal neu- raxes of the cells of Purkinje and of two types of centripetal neu- raxes, the mossy and the climbing fibers. The position of their corresponding nerve-cells is not definitely known. The mossy fibers branch in the granular layer into numerous twigs, and are not uniform in diameter, but are provided at different points with typical nodular swellings. These fibers do not extend beyond the granular layer. The climbing fibers pass horizontally through the granular layer, giving off in their course numbers of collaterals, which extend to the cells of Purkinje, up the dendrites of which the}' seem to climb. In the medullary portion of the cerebellum are found a number of groups of ganglion cells known as central gray nuclei. The nerve-cells of these nuclei are multipolar, with numerous, oft- branching dendrites and a single neuraxis. C THE CEREBRAL CORTEX. The cell-bodies of the neurones of the cerebrum are grouped in a thin layer of gray matter, varying in thickness from 2 to 4 mm., — which, as a continuous sheet, completely covers the white matter of the hemispheres, — and in larger and smaller masses of gray mat- ter, known as basal nuclei. In our account of the histologic struc- ture of the cerebral hemispheres we shall confine ourselves in the main to a consideration of the cerebral cortex, the thin layer of gray matter investing the white matter. 37^ THE CENTRAL NERVOUS SYSTEM. From without inward the following layers may be differentiated in the cerebral cortex : (i) a molecular layer ; (2) a layer of small pyramidal cells ; (3) a layer of large pyramidal cells ; (4) a layer of polymorphous cells ; and (5) medullar)' substance or underlying nerve-fibers. Aside from neuroglial- tissue, we find in the molecular layer a large number of nerve-fibers, which cross one another in all direc- tions, but, as a whole, have a direction parallel with the surface of the brain. Within this layer there are found : (1) the tuft-like telo- dendria of the chief dendritic processes of the pyramidal cells ; (2) the terminations of the ascending neuraxes, arising mostly from the polymorphous cells ; and (3) autochthonous fibers — i. c, those which arise from the cells of the molecular layer and terminate in this layer. The cells of the molecular layer may be classed in three general types — polygonal cells, spindle-shaped cells, and triangular or stellate cells. The polygonal cells have from four to six den- drites, which branch out into the molecular layer and may even penetrate into the underlying layer of small pyramidal cells. Their neuraxes originate either from the bodies of the cells or from one of their dendrites, and take a horizontal or an oblique direction, giving off in their course a large number of branching collaterals, which terminate in knob-like thickenings. The spindle=shaped cells give off from their long pointed ends dendrites which extend for some distance parallel with the surface of the brain. These branch, their offshoots leaving them at nearly right angles, the majority passing upward, assuming as they go the characteristics of neuraxes having collaterals. The arborization is entirely within the molecular layer. The triangular or stellate cells are similar to those just described, but possess not two, but three, dendrites. The triangular and spindle-shaped cells, with their numerous den- dritic processes resembling neuraxes, are characteristic of the cere- bral cortex. The elements which are peculiar to the second and third layers of the cerebral cortex are the small (about 10 fi in diameter) and large pyramidal cells (from 20 p. to 30 fi in diameter). They are composed of a triangular body, the base of the triangle being down- ward and parallel to the surface of the brain, of a chief, principal, or primordial dendrite ascending toward the brain-surface, of several basilar dendrites arising from the basal surface of the cell-body, and of a neuraxis which passes toward the medullary substance and which has its origin either from the base of the cell or from one of the basilar dendrites. The ascending or chief dendrite gives off a number of lateral offshoots which branch freely and end in terminal filaments. The main stem of the dendrite extends upward to the molecular layer, in which its final branches spread out in the form of a tuft. The neuraxis, during its course to the white substance, gives off in the gray substance from six to twelve collaterals, which divide two or three times before terminating. THE CEREBRAL CORTEX. 377 Aside from the fact that the layer of polymorphous cells con- tains a few Large pyramidal cells, it consists principally of (i) mul- tipolar cells with short neuraxes (Golgi's cells) and (2) of cells with only slightly branched dendrites and with neuraxes passing toward the surface of the brain (Martinotti's cells). Both these types of cells are, however, not found exclusively in the layer of polymorphous cells, but may be met with here and there in the layers of the small and large pyramidal cells. The dendrites of the cells of Golgi are Molecular layer. Layer of small pyr- amidal cells. Layer of large pyr- amidal cells. Layer of polymor- phous cells. Medullary substance. Fig. 312. — Schematic diagram of the cerebral cortex, after Golgi and Ramon y Cajal. Basal den drite. Neuraxis with col- laterals. F'g- 313. — Large pyramidal cell from the human cerebral cortex. Chrome-silver method ; X I 5°- projected in all directions, those in the neighborhood of the medul- lary substance even penetrating into this layer. The neuraxes break up into numerous collaterals, the telodendria of which lie ad- jacent to the neighboring ganglion cells. The cells of Martinotti, which, as we have seen, occur also in the second and third layers, are either triangular or spindle-shaped. The neuraxis of each cell originates either from the cell-body or from one of its dendrites, and 3/8 THE CENTRAL NERVOUS SYSTEM. ascends (giving off collaterals) to the molecular layer, in which it finally divides into two or three main branches ending in telo- dendria. Occasionally it divides in a similar manner in the layer of small pyramidal cells. In the medullary substance the following four classes of fibers are recognized : [i) The projection fibers (centrifugal) — i. e., those which indirectly connect the elements of the cerebral cortex with the periphery of the body ; their course may or may not be interrupted during their passage through the basal nuclei ; (2) the commissural fibers, which, according to the original definition, pass through the corpus callo- sum and anterior commis- sure, thus joining corre- sponding parts of the two hemispheres ; (3) the asso= ciation fibers, which con- nect different parts of the gray substance of the same hemispheres ; and (4) the centripetal or terminal fibers — i.e., the terminal arborizations of those neu- raxes, the cells of which lie in some other region of the same or opposite hemi- sphere, or even in some more distant portion of the nervous system. The pro- jection fibers originate from the pyramidal cells, some of them perhaps from the polymorphous cells. The commissural fibers are also derived from the pyramidal cells, and lie somewhat deeper in the white sub- stance than the association fibers. With the exception of those which join the cunei and those which lie in the anterior commissure, all the commissural fibers are situated in the corpus callosum. They give off during their passage through the hemispheres large num- bers of collaterals, which penetrate at various points into the gray substance and end there in terminal filaments. In this respect their arborization is contrary to the old definition of these fibers, and the latter must be completed by the statement that, besides joining symmetric points of the two hemispheres, they also, by means of mkmty SB Fig. 314. — Schematic diagram of the cerebral cortex : a, Molecular layer with superficial (tan- gential) fibers; 6, striation of Bechtereff-Kaes ; c, layer of small pyramidal cells ; d, stripe of Bail- larger; e, radial bundles "f the medullary sub- stance ; /, layer of polymorphous cells. THE OLFACTORY BULB. 379 their collaterals, may connect other areas of the gray substance with the peripheral regions supplied by their end-tufts (Ramon y Cajal, 93). The association fibers have their origin also in the pyramidal cells. In the medullary substance their neu raxes divide T-shaped, and after a longer or shorter course penetrate into the gray substance of the same hemisphere, where they end as ter- minal fibers. A few collaterals are, however, previously given off, which also terminate in the same manner in the gray substance. The association fibers form the bulk of the medullar}' rays. ' )n examining a vertical section through one of the cerebral convolutions a number of successive striations may be seen. These are more or less distinct, according to the region, and consist of strands of medullated nerve-fibers between the layers of cells, and parallel with the surface of the convolution. The most superficial form a layer of tangential fibers. Between the molecular layer and the layer of small pyramidal cells is the striation of Bechtereff and Kaes, and in the region of the large pyramidal cells the striation of Baillarger (Gennari) corresponding to the striation of Vicq d'Azyr in the cuneus. In figure 314 the medullary substance is seen below, with rays, composed of parallel bundles of fibers, passing upward into the gray substance ; in reality these fibers penetrate much higher than is shown in the illustration. D. THE OLFACTORY BULB. The olfactory bulb is composed of five layers, which are espe- cially well marked on its ventral side : first, the layer of peripheral nerve-fibers ; second, the layer of olfactory glomeruli ; third, the stratum gelatinosum, or molecular layer; fourth, the layer of pyr- amidal cells (mitral cells) ; and, fifth, the granular layer with the deeper nerve-fibers. The layer of peripheral fibers is composed of the nerve- bundles of the olfactory nerve which cross one another in various directions and form a nerve-plexus. The glomerular layer con- tains peculiar, regularly arranged, round or oval, and sharply defined structures, which were first accurately studied by Golgi. They are known as glomeruli (from 100 u to 300 n in diameter), and are in reality complexes of intertwining telodendria. As we shall see, the epithelial cells of the olfactory region of the nose must be regarded as peripheral ganglion cells and their centripetal (basal) processes as neuraxes. The telodendria of these neuraxes, together with those of the dendrites from the mitral or other cells, come in contact with each other within the olfactory glomeruli. The molec- ular layer consists of small, spindle-shaped ganglion cells. Their neuraxes enter the fifth layer and their short dendrites end in ter- minal ramifications in the glomeruli. The mitral cells give off neuraxes from their dorsal surfaces which also enter the granular ;So THE CENTRAL NERVOUS SYSTEM. layer, but the majority of their dendrites break up into terminal ramifications in the olfactory glomeruli, as just described. The granular layer (absent in the illustration) is made up of nerve-cells and nerve-fibers ; but, aside from these, we find also large numbers of peculiar cells with a long peripherally and several short centrally directed dendrites. No neuraxes can be demonstrated in these cells (granular cells). This layer also contains the stellate ganglion cells. The latter are not numerous, but lie scattered, and each pos- sesses several short dendrites and a peripherally directed neuraxis which ends in the molecular layer in a rich arborization. The deep nerve-fibers are grouped into bundles which inclose between them the granular and stellate cells just mentioned. These nerve-fibers Mitral cells. Molecu- lar layer. ' Large nerve- cell. Small nerve-- - cell. Layer of glomeru olfactory 4 i. Peripheral nerve- fibers. Fig- 3i5- -The olfactory bulb, after Golgi and Ram6n y Cajal. The granular layer is not shown. are derived partly from the neuraxes of the pyramidal or mitral cells and partly from the cells of the molecular layer, while some of them arc centripetal fibers from the periphery, which end between the granules of the fifth layer. E. EPIPHYSIS AND HYPOPHYSIS. In mammalia the epiphysis, or pineal gland, consists of a fibrous capsule derived from the pia mater, from which numerous fibrous tissue septa and processes pass into the gland, uniting to form quite regular round or oval compartments in which closed follicles or alveoli, whose walls consist of epithelial cells, are found. EPIPHYSIS AND HYPOPHYSIS. 381 The epithelial cells forming the walls of the follicles arc of cubic or short columnar shape, and may be arranged in a single layer or may be pseudostratified or stratified. Follicles completely filled with cellular elements are found. Other follicles contain peculiar con- cretions, known as brain-sand or acervulus, of irregular round or oval or mulberry shape. Medullated nerve-fibers have been traced into the epiphysis, but their mode of termination is not known. The hypophysis, or pituitary body, consists of two lobes. The posterior or infundibular lobe is developed from the floor of the first primary brain-vesicle, and remains attached to the floor of the third ventricle by a stalk, known as the infundibulum ; the anterior or glandular lobe develops from a bud derived from the primary oral ectoderm, known as Rathke's pouch. The distal end of this pouch comes in contact with the anterior surface of the lower portion of the infundibulum, and becomes loosely attached to it. As the bones at the base of the skull develop, the attenuated oral end of Rathke's pouch atrophies, the distal end becoming finally completely severed from the buccal cavity. In the infundibular lobe of the hypophysis of the dog, Berkley (94) described three portions presenting different microscopic struc- ture. His -account will here be followed : (1) An outer stratum consisting of three or four layers of cells resembling ependymal cells, which are separated into groups by thin strands of fibrous tissue entering from the fibrous covering of this lobe. (2) A zone consisting of glandular epithelial cells which in certain places are arranged in the form of alveoli, often containing a colloid substance. This zone merges into the central portion, (3), containing variously shaped cells and connective-tissue partitions with blood-vessels. In this portion neurogliar cells (see these) and nerve-cells were stained by the chrome-silver method. The glandular or anterior lobe resembles slightly in structure the parathyroid. This lobe is surrounded by a fibrous tissue capsule and within it are found variously shaped alveoli or follicles, or, again, columns or trabecular of cells separated by a very vascular connective tissue. In the alveoli or columns of cells are found two varieties of glandular cells, which may be differentiated more by their staining reaction than by their size and structure, although they present slight structural differences. One variety of cells pos- sesses a protoplasm which shows affinity for acid stains ; these are known as chromophilic cells. They are of nearly round or oval shape, with nuclei centrally placed, and have a protoplasm present- ing coarse granules. The other variety of cells, known as chief cells, are more numerous than the chromophilic. They are of cubic or short columnar shape, with nuclei placed in the basal portions of the cells and with protoplasm showing a fine granulation and with an affinity for basic stains. Now and then alveoli containing a colloid substance, similar to that found in the alveoli of the thy- roid gland, may be observed. The blood-vessels of the glandular 332 THE CENTRAL NERVOUS SYSTEM. portion are relatively large, the majority of them having only an endothelial lining. In the glandular portion of the hypophysis of the dog, Berkley (94) found small varicose nerve-fibers belonging to the sympathetic system. From the larger bundles, which follow the blood-vessels, are given off single fibers or small bundles of such, which end on the glandular elements in numerous small nodules. F. GANGLIA. In the course of peripheral nerves are found numerous larger and smaller groups of nerve-cells, known as ganglia. The neurones of these ganglia are in intimate relation with the neurones of the cen- Fig. 316. — Longitudinal section of spinal ganglion of cat. tral nervous system, and may, therefore, be discussed with the lat- ter. According to the structure and function of their neurones, the ganglia arc divided into two groups — (1) spinal or sensory ganglia and (2) sympathetic ganglia. The spinal ganglia are situated on the posterior roots of the spinal nerves. Certain cranial ganglia — namely, the Gasserian, geniculate, and auditor}' ganglia, the jugular and petrosal gan- glia of the glossopharyngeal nerves, and the root and trunk ganglia of the vagi — are classed with the spinal ganglia, since they present the same structure. The spinal and sensory cranial ganglia are surrounded by firm connective- tissue capsules, continuous with the perineural sheaths of the incomingand outgoing nerve-roots. From GANGLIA. 3M3 these capsules connective-tissue septa and trabecular pass into the interior of the ganglia, giving support to the nerve-elements. The cell-bodies (ganglion cells) of the neurones constituting these ganglia are arranged in layers under the capsule and in rows and groups or clusters between the nerve-fibers in the interior of the ganglia. More recent investigations have shown that several types of neurones are to be found in the spinal and cranial sensory gan- glia; of these, we may mention the following: (1) Large and small unipolar cells with T- or Y-shaped division of the process. These neurones, which constitute the greater number of all the neurones of the ganglia under discussion, consist of a round or oval cell-bod)-, from which arises by means of an implantation cone Fig. 317. — Ganglion cell from the Gasserian ganglion of a rabbit ; stained in methylene- blue [intra vitain). a single process, which, soon after it leaves the cell, becomes in- vested with a medullary sheath and usually makes a variable num- ber of spiral turns near the cell-body. According to Dogiel, this process divides into two branches, usually at the second or third node of Ranvier, sometimes not until the seventh node is reached. Of these two branches, the peripheral is the larger, and enters a peripheral nerve-trunk as a medullated sensory nerve-fiber, termi- nating in one of the peripheral sensory nerve-endings previously described. The central process, the smaller of the two, becomes a medullated nerve-fiber, which enters the spinal cord or medulla in a manner described in a former section. The cell-body of each of these neurones is surrounded by a nucleated capsule, continuous with 3 84 THE CENTRAL NERVOUS SYSTEM. the neurilemma of the single process. (2) Type II spinal ganglion cell of Dogiel. Dogiel has recently described a second type of spinal ganglion cell which differs materially from the type just described. The cell-bodies of these neurones resemble closely those of the typ- ical spinal ganglion neurones. Their single medullated processes divide, however, soon after leaving the cells into branches which divide further and which do not pass beyond the bounds of the gan- glia but terminate, after losing their medullary sheaths, in compli- cated pericapsular and pericellular end-plexuses surrounding the capsules and cell-bodies of the typical spinal ganglion cells. (3) Mul- tipolar ganglion cells ; in nearly all spinal and cranial ganglia there are found a few multipolar nerve-cells, which in shape and struc- ture resemble the nerve-cells of the sympathetic system. Fig. 318. — Diagram showing the relations of the neurones of a spinal ganglion ; /. r., posterior root; a. r., anterior root; p. s., posterior branch and a. s., anterior branch of spinal nerve ; w. r., white ramus communicans ; a, large, and l>, small spinal ganglion cells with T-shaped division of process ; c, type II spinal ganglion cells (Dogiel); s, multipolar cell ; d, nerve-fiber from sympathetic ganglion terminating in pericellular plexuses (slightly modified from diagram given by Dogiel). Entering the spinal ganglia from the periphery are found a rel- atively small number of small, medullated or nonmedullated nerve- fibers, probably derived from sympathetic ganglia. These nerve- fibers, medullated and nonmedullated, the former losing their medullary sheaths within the ganglia, approach a spinal ganglion cell, and after making a few spiral turns about its process, termi- nate in pericapsular and pericellular end-plexuses. Dogiel believes that the cell-bodies and capsules thus surrounded by the terminal branches of the sympathetic fibers terminating in the spinal ganglia belong to the spinal ganglion cells of the second type first described by him. In figure 318 is represented by way of diagram the structure of a spinal ganglion. In the medium-sized cells (from 30 ji to 45 /x in diameter) of the GANG! [A. 38! spinal ganglia of the frog, von Lenhossek (95) found centrosomes surrounded by a clear substance (centrospheres). The entire struc- ture lay in a depression of the nucleus and contained more than twelve extremely minute granules (centrosomes), which showed a staining reaction different from that of the numerous concentrically laminated granules present in the protoplasm. This observation is interesting in that it proves that centrosome and sphere occur also in the protoplasm of cells which have not for a long time under- gone division and in which there is no prospect of future division. Sympathetic Ganglia. — The ganglia of the sympathetic ner- vous system comprise those of the two great ganglionated cords, found on each side of the vertebral column and extending from its cephalic to its caudal end, with which may be grouped certain cranial ganglia having the same structure, — namely, the sphenopalatine, otic, ciliary, sublingual, and submaxillary ganglia ; also three un- Fig- 319. — Neurone from inferior cervical sympathetic ganglion of a rabbit ; methylene- blue stain. paired aggregations of ganglia, found in front of the spinal column, of which the cardiac is in the thorax, the semilunar in the abdomen, and the hypogastric in the pelvis ; and further, large numbers of smaller ganglia, the greater number of which are of microscopic size and are found in the walls of the intestinal canal and bladder, in the respiratory passages, in the heart, and in or near the majority of the glands of the body. The sympathetic ganglia are inclosed in fibrous tissue capsules continuous with the perineural sheaths of their nerve-roots. The thickness of the capsule bears relation to the size of the ganglion, being thicker in the larger and thinner in the smaller ones. From these capsules thin connective-tissue septa or processes pass into the interior of the ganglia, supporting the nerve elements. The sympathetic neurones, the cell-bodies and dendritic processes of which are grouped to form the sympathetic ganglia, are variously 25 3 86 THE CENTRAL NERVOUS SYSTEM. shaped unipolar, bipolar, and multipolar cells, the cell-bodies of which are surrounded by nucleated capsules, continuous with the neurilemma of their neuraxes. In the sympathetic ganglia of mam- malia and birds the great majority of sympathetic neurones are multipolar, although in nearly all ganglia a small number of bipolar and unipolar cells are to be found, usually near the poles of the ganglia. The dendrites of the sympathetic neurones in any one ganglion branch repeatedly. Of these branches, some extend to the per- iphery of the ganglion, where they interlace to form a peripheral subcapsular plexus, while others interlace to form plexuses between the cell-bodies of the neurones in the interior of the ganglion — pericellular plexuses. These pericellular plexuses are external to the capsules surrounding the cell-bodies of the sympathetic neurones. Fig. 320. — From section of semilunar ganglion of cat ; stained in methylene-blue, intra vitam (Huber, Journal of Morphology, 1899). The neuraxes of the sympathetic neurones, the majority of which are nonmcdullated, the remainder surrounded by delicate medullary sheaths, arise from the cell-bodies either from implanta- tion cones or from dendrites at variable distances from the cell- bodies, leave the ganglion by way of one of its nerve-roots, and terminate in heart muscle tissue, nonstriated muscle, and glandular tissue, and to some extent in other ganglia, both sympathetic and spinal. Terminating in all sympathetic ganglia are found certain small medullated nerve-fibers, varying in size from about 1.5 p. to 3 it. The researches of Gaskell, Langley, and Sherrington have shown that these small medullated nerve-fibers leave the spinal cord through the anterior roots of the spina] nerves from the first dorsal to the third or fourth lumbar and reach the sympathetic GANf.I.IA. 387 ganglia through the white rami communicantes. Similar small medullated nerve-fibers arc found in certain cranial nerves. These small medullated nerve-fibers, which ma}- be spoken of as white rami fibers, after a longer or shorter course, in which they may pass through one or several ganglia without making special con- nection with the neurones contained therein, terminate in some sympathetic ganglion in a very characteristic manner. After enter- ing the sympathetic ganglion in which the}- terminate, the)- branch repeatedly while yet medullated. The resulting branches then lose their medullary sheaths and divide into numerous small, varicose nc.-ve-fibers, which interlace to form intracapsular plexuses, which surround the cell-bodies of the sympathetic neurones. In the sympathetic ganglia of mammalia such intracapsular pericellular cS> Fig. 321. — From section of stellate ganglion of dog, stained in methylene-blue and alum carmin : a, white ramus fiber ( Huber, Journal of Morphology, 1899). plexuses may be very simple, consisting of only a few varicose nerve-fibers, or very complicated, consisting of main- such fibers. In the sympathetic ganglia of reptilia, in which are found very large sympathetic neurones, the white rami fibers are wound spirally about the cell-bodies of such neurones before terminating in com- plicated pericellular plexuses. In the frog and other amphibia the sympathetic neurones are unipolar nerve-cells. The white rami fibers terminating in the sympathetic ganglia of amphibia are wound spirally about the single processes of these unipolar cells while yet medullated fibers, but they lose their medullary sheaths before ter- minating in the intracapsular pericellular plexuses. From what has been said concerning the white rami fibers and their relation to the sympathetic neurones, it is evident that the sympathetic neu- 3 8S THE CENTRAL NERVOUS SYSTEM. rones, the cell-bodies and dendrites of which are grouped to form the sympathetic ganglia, form terminal links in nerve or neurone chains ; the second link of these chains is formed by neurones the cell-bodies of which are situated in the spinal cord or medulla, the m ^m^ Fig. 322. — From section of sympathetic ganglion of turtle, showing white rami fibers wound spirally about a large process of a unipolar cell, and ending in pericellular plexus (Huber, Journal of Morphology, 1 899). neuraxes leaving the cerebrospinal axis through the white rami as small medullated nerve-fibers, which terminate in pericellular plex- uses inclosing the cell-bodies of the sympathetic neurones. Large medullated nerve-fibers, the dendrites of spinal ganglion neurones, reach the sympathetic ganglia through the white rami. Fig. 323. — From section of sympathetic ganglion of frog, showing spiral fiber (white ramus fiber) and pericellular plexus (Huber, Journal of Morphology, 1899). They make, however, no connection with the sympathetic neurones, but pass through the ganglia to reach the viscera, where they ter- minate in special sensor)' nerve-endings or in free sensory nerve- endings. RELATIONSHIP OF NEURONES. 3< s 9 G. GENERAL SURVEY OF THE RELATIONS OF THE NEURONES TO ONE ANOTHER IN THE CENTRAL NERVOUS SYSTEM. The following figures illustrate the modern theories with re- gard to the relationship of the neurones in a sensorimotor reflex- cycle. The pathway along which the impulse from the stimulated area of the body is transmitted to the motor nerve end-organ tra- verses two neurones (primary neurones) which are in contact by means of their telodendria situated within the gray matter of the spinal cord. The cell-body of the sensory neurone lies within the spinal ganglion ; that of the motor neurone, in the anterior horn of the spinal cord. The dendrite of the sensory neurone commences c ^\ mN _ Fig. 324. — Schematic diagram of a sensorimotor reflex arc according to the modern neurone theory ; transverse section of spinal cord : mX, Motor neurone ; sN, sensory neurone ; C 1 , nerve-cell of the motor neurone ; C' 2 , nerve-cell of the sensory neurone ; >f its ascending branch through the posterior column to the medulla. Although here the relationship is not so clearly defined as in the motor tract, it may nevertheless be assumed that the cellu- lifugal (but centripetally conducting) neuraxis at some point or other terminates in telodendria (sensory neurone of the first order), which enter into contact with the corresponding structures of a cell of the spinal cord or medulla oblongata. These cells would then KKLATIONSHII' OF NEURONES. 391 constitute the sensory neurones of the second order. Exactly how their cellulifugal neuraxes end has not as yet been fully determined, hut it is very probable that in this case the telodendria are repre- sented by the coarse end-fibers which penetrate into the brain cor- tex, and here seem to come in contact with the dendrites of the pyr- amidal cells. sN* -sW Fig. 326. — Schematic diagram of the reflex tracts between a peripheral organ and the brain cortex : //, Cerebral cortex; miV 1 , motor neurone of the first, .c.V 2 , sensory neurone of the second, degree ; C 1 , motor cell of the spinal cord ; C 2 , sensory cell of a spinal ganglion ; C 3 , pyramidal cell of the brain cortex (pyschic cell) ; C*, nerve-cell of a sensory neurone of the second degree ; «, //, ;/, >/, neuraxes ; ,/, keep the fixative below ordinary room-temperature. After fixation the tissues are washed for an hour in distilled water. They are then hard- ened and dehydrated in absolute alcohol. It is advisable to hasten this step as much as possible, though not at the risk of imperfect dehydration. The tissues are then transferred to xylol and imbedded in paraffin, sec- tioned, fixed to the slide or cover-glass with albumin fixative, and may be double stained in alum-carmin or alum-cochineal. After staining in either of these stains, the sections are thoroughly dehydrated and cleared in oil ofbergamot. The oil is washed off with xylol and the sections are mounted in Canada balsam. 312. In staining nerve-fibers with methylene-blue by local application of the stain to the tissues, the tissues to be studied are removed from an animal which has just been killed, divided in small pieces, and placed on a slide moistened with normal salt solution. A few drops of a ^ ( / ( to TH% solution of methylene-blue in normal salt solution are added from time to time — sufficient to keep the tissues moistened by the solution, but not enough to cover them. The preparations are examined from time to 4O4 THE CENTRAL NERVOUS SYSTEM. time, under the microscope, to see whether the nerve elements are stained. The length of time required for staining by this method varies. Some- times the nerve elements are stained in half an hour ; again, it may re- quire two and one-half hours ; on an average, about one hour. As soon as the tissues seem well stained they are fixed as previously directed. Dogiel has found that sympathetic ganglia and sensory nerve-fibers of the heart removed from the human body several hours after death may be stained by means of the foregoing method. In order to obviate the necessity for the low temperature of the pre- vious method, Bethe (96) has recommended the following procedure : According to the method of Smirnow and Dogiel, he first employs as a preliminary fixing agent a concentrated aqueous solution of ammonium picrate. In this he places the tissue, previously treated with methylene- blue, for from ten to fifteen minutes. Without further washing the larger objects are immersed in a mixture composed of ammonium molybdate (or sodium phosphomolybdate) 1 gm., distilled water 20 c.c, and pure hydrochloric acid 1 drop. The following mixtures may also be employed for the same purpose : ammonium molybdate (or sodium phosphomo- lybdate) 1 gm., distilled water 10 c.c, 2% solution of chromic acid 10 c.c, and hydrochloric acid 1 drop ; or, for very thin gross specimens or sections, ammonium molybdate (or sodium phosphomolybdate) 1 gm., distilled water, 10 c.c, 0.5% osmic acid 10 c.c, and hydrochloric acid 1 drop. Small objects are permitted to remain no longer than from three quarters of an hour to one hour in either of the first two mixtures, and not more than from four to twelve hours in the third. After fixing, the specimens are washed with water, carried over into alcohol, then into xylol, and finally imbedded in paraffin. Subsequent staining with alum-carmin, alum-cochineal, or one of the neutral anilin dyes gives good results. 313. A very promising method recommended by Meyer (95) consists in injecting subcutaneously about 20 c.c. of normal salt solution contain- ing from 1% to 4% of methylene-blue into a young rabbit, and repeating the operation in one to two hours. Within the next two hours the animal usually dies and the central nervous organs are then removed and small pieces fixed according to Bethe' s method. 314. Apathy (97) demonstrates the fibrillar elements of the nervous system in invertebrates and vertebrates by means of his gold method. Fresh tissue may be used, or tissue already fixed. In the first case thin membranes are placed for at least two hours inai^ solution of yellow chlorid of gold in the dark, then carried over without washing into ai^ solution of formic acid (sp. gr. 1.223), an ^ finally exposed for from six to eight hours to the light (the formic acid may have to be changed). These specimens are best mounted directly in syrup of acacia or in con- centrated glycerin. In his second method Apathy fixes vertebrate tissues for twenty-four hours in sublimate-osmic acid (1 vol. saturated solution of corrosive sublimate in 0.5% sodium chlorid solution combined with 1 vol. \°Jc osmic acid solution ), washes repeatedly in water, and places for twelve hours in an aqueous iodo-iodid of potassium solution (potassium iodid i c /(j and iodin 0.5%). The further treatment is the same as after or- dinary corrosive sublimate fixation. Finally, the specimens are imbedded in paraffin with the aid of chloroform, cut, and mounted by the water method. The whole process, up to the point of imbedding in paraffin, is carried out in the dark. The sections are then passed through chloro- TECHNIC. 4O5 form and alcohol into water, where they are allowed to remain for at least six hours ; or they may be washed in water, placed for one minute in 1% formic acid, again washed in water, immersed for twenty-four hours in a \'/c solution of gold chlorid, rinsed in water, and finally placed in a 1% formic acid solution and exposed to the light. For the latter purpose glass tubes are employed in which the slides are placed obliquely, with the sections downward. A uniform illumination of the section with "as intense a light and low a temperature " as possible are conditions indis- pensable to the attainment of successful results. The sections are then again washed in water and mounted in glycerin or syrup of acacia, or in Canada balsam after being dehydrated. Thin membranes are stretched upon small frames of linden wood especially prepared for this purpose. Their further treatment is then the same as that of sections fixed to the slide. If successful, the nerve-fibrils appear dark violet to black. The large ganglia in the spinal cord of lophius, the calf, etc., are especially recom- mended as appropriate vertebrate material. Bethe (1900) has recommended the following method for staining neurofibrils and Golgi-nets in the central nervous system of vertebrates : The perfectly fresh tissue is cut in thin lamellae, varying in thickness from 4 to 10 mm. These are placed on pieces of filter-paper and then in 3 to l-S r /f nitric acid, in which they remain twenty-four hours. From the hardening fluid the pieces of tissue are transferred into 96% alcohol, where they remain for from twelve to twenty-four hours. They are then placed in a solution of ammonium-alcohol, — ammonium (sp. gr. 0.95 to 0.96), 1 part ; distilled water, 3 parts ; 96% alcohol, 8 parts, — in which they remain for from twelve to twenty-four hours. The temper- ature of this solution should not exceed 20 C. The tissues are then placed for from six to twelve hours in 96^ alcohol, and next in a hydro- chloric acid-alcohol solution, — concentrated hydrochloric acid (sp. gr. !.i8 — 37^-), 1 part; distilled water, 3 parts; and 96^ alcohol, 8 to 12 parts, — in which they remain for several hours. The temperature of this solution should not exceed 20 C. The tissues are then again placed in 96^ alcohol for from ten to twenty-four hours, and next in distilled water for from two to six hours. The tissues are now placed for twenty -four hours in a 4$- aqueous solution of ammonium molybdate. (This solution should be kept at a temperature varying from io° to 15 C, if it is de- sired to stain the neurofibrils ; or at a temperature varying from io° to 30 C, if it is desired to bring out the Golgi-nets.) After the ammo- nium molybdate treatment, the tissues are rinsed in distilled water, placed in 96 r / c alcohol for from ten to twenty- four hours, then in absolute alco- hol for a like period, cleared in xylol or toluol, and imbedded in par- affin. Sections having a thickness of 10 p are now cut and fixed to slides with Maver's albumin-glycerin. Since the various solutions used in the fixation and further treatment of the tissues do not act with the same in- tensitv on all parts of the piece of tissue to be studied, and since the differ- entiation and staining depend on a relative proportion (not yet fully de- termined) of the mordant (ammonium molybdate) and the stain in a given section, it is advised by Bethe to cut large numbers of sections and fix to each slide about three sections from different parts of the series. After fixation of the sections to the slide the paraffin is removed with xylol ; and they are then carried through absolute alcohol into distilled water, in which, however, the sections remain only long enough to re- 406 THE CENTRAL NERVOUS SYSTEM. move the alcohol. The slides (with the sections fixed to them) are then taken from the water and rinsed with distilled water from a water-bottle. The slide is then wiped dry on its under surface and edges with a clean cloth, and about i c.c. to 1.5 c.c. of distilled water placed on the slide over the sections. The slides are now placed in a warm oven with a tem- perature of 55 C. to 6o° C. for a period of time varying from two to ten minutes. No definite time can here be given ; sections from each block of tissue need to be tested until the right stay in the warm oven is ascertained. The slides are then taken from the warm oven and rinsed two or three times in distilled water and again dried as previously directed. They are then covered with the following staining solution and again placed in the warm oven for about ten minutes : toluidin-blue, 1 part ; distilled water, 3000 parts. The stain is washed off with dis- tilled water and the sections are placed in 96^ alcohol until no more stain is given off — usually for from three-fourths to two minutes. They are then dehydrated in absolute alcohol, passed through xylol twice, and mounted in xylol balsam. For a fuller discussion of this method the reader is referred to Bethe's account in " Zeitsch. f. Wissensch. Mikrosk. , ' ' vol. xvii, 1900. 315. For staining neuroglia Weigert (95) has recommended a method, from which we give the following : A solution is made consisting of s r /( neutra l acetate of copper, 5% ordinary acetic acid, and 2.5% chrome-alum in water. The chrome-alum and water are first boiled together, the acetic acid then added, and finally the finely pulverized neutral copper acetate, after which the mixture is thoroughly stirred and allowed to cool. To this solution 10% formalin may be added. Objects not over 0.5 cm. in diameter are placed in this fluid for eight days, the mixture being changed at the end of a few days. By this means the pieces of tissue are at the sarnie time fixed and prepared for subsequent staining by the action of the mordant. If separation of the two processes be desired, the specimens are fixed for about four days in a 10% formalin solution (which is changed in a k\v days), and then placed in the chrome-alum mixture without the addition of formalin. Specimens thus fixed may be preserved for years without disadvantage, and may then be subjected to further treatment by other methods, Golgi's for instance. Washing with water, dehydration in alcohol, and imbedding in celloidin are the next steps. The sections are then placed for about ten minutes in a 0.33% solution of potassium permanganate, washed by pouring water over them, and placed in the reducing fluid (5% chromogen and 5% formic acid of a specific gravity of 1.20; then filter carefully, and add 10 c.c. of a 10^ solution of sodium sulphite to 90 c.c. of the fluid). The sections, rendered brown by the potassium permanganate, readily decolorize in a k\v minutes, but it is better to leave them for from two to four hours in the solution. If it be desirable to decolorize entirely the connective tissue, no further steps need be taken preliminary to staining ; if not, the reducing fluid is poured off and the sections are rinsed twice in water and then placed in an ordinary saturated solution of chromogen ( 5% chromogen in distilled water, carefully filtered). The sections are left in this solution overnight, and the longer they remain in it, the more marked will be the contrast, as far as stain is concerned, between the con- ne< live and nervous tissues ; then water is again twice poured upon the Ions and they are ready for staining. This process consists in a DEVELOPMENT OF THE EYE. 407 modified fibrin stai] The iodo-iodid of potassium solu- tion is the same saturated solution of iodin in a $'/ f iodid of potassium solution t. Instead of the customary gentian-violet solution, a hot satu- rated alcohol - 'iution of methyl -violet is made, anil, after cooling, the clear portion decanted off: to even,- ioo c.c. of this fluid 5 c.c. 01 .ueous solution of oxalic acid is added. The staining takes place in a very short time. The sections are then rinsed and normal salt solution and the iodo-iodid of potassium solution poured over them ;', iodid of potassium solution saturated with iodin >, and washed off with water and dried with filter-paper and decolorized in the anilin oil-xylol solution in the proportion of i :i. The reactions are rapid, and the thickness of the section should not excee«i i method is best adapted to the central nervous system of the human adult ; it has as yet not been sufficiently tested for other vertebrates. VIII. THE EYE. A. GENERAL STRUCTURE. The organ of vision consists of the eyeball, or bulbus oculi, and the entering optic nerve. In the eyeball we distinguish three tunics : (l) a dense external coat, the tunica fibrosa or externa, which may be regarded as a continuation of the dura mater, consisting of an anterior transparent structure, called the eoruea. and the remaining portion, known as the tunic r:ea, or, briefly, the 5 : within the tunica fibrosa a vascular tunic, the tunica vasculosa or media, subdivided into the chor and iris; (5 s ) an inner coat, the tunica interna, which consists of two layers, the inner being the the outer, the pigment membrane. The latter lines the internal surface of the tunica vasculosa throughout. Within the eyeball are the aqueous humor, th ind the vitreous body. The lens is attached to the ciliary body by a special accessory apparatus — the •Maris. These two structures — the lens and its fixation apparatus — divide the cavity of the eyeball into two principal cham- bers, the one containing the aqueous humor and the other the vitreous. The former is further subdivided by the iris into an anterior and a posterior chamber. During life the latter is only a narrow capillar}- cleft. B. DEVELOPMENT OF THE EYE. In man the eyes begin to develop during the fourth week of embryonic life, and at first consist of a pair of ventrolateral diver- ticula, projecting from the anterior brain vesicle. T: - ^inations gradually push outward toward the ectoderm, and are then known as the prim,: .'es. The slender commissural segments 408 THE EYE. connecting the vesicles with the developing brain are termed the optic stalks. Very soon a process of invagination takes place ; that portion of the vesicular wall nearest the ectoderm is pushed inward, thus forming a double-walled cup — the secondary optic vesicle, or optic cup. An internal and an external wall may now be differentiated, continuous at the margin of the cup. At the same time a disc-like thickening of the adjacent ectoderm sinks inward toward the mouth of the cup-shaped optic vesicle, forming the first trace of the lens. During the development of the secondary optic vesicle a groove Blood-vessels Sphincter Vein. Canal of Petit, of the iris. Cornea, pupillse. Iris. Fontana's spaces. — Pigment layer. Choroid. Physiologic excavation. Macula lutea. Fig. 329. — Schematic diagram of the eye (after Leber and Flemming) : a, Vena vorti- cosa ; b, choroid ; /, lens. is formed on its ventral side, extending from the marginal ring into the optic stalk. This is the embryonic optic fissure, or the choroi- dal fissure. At the edges of the groove the two layers of the optic cup are continuous. This groove serves for the penetration of mesoblastic tissue and blood-vessels into the interior of the optic cup, and in its wall the fibers of the optic nerve develop. The outer layer of the secondary optic vesicle becomes the pig- ment metnbranc ; the inner, the retina. The optic nerve-fibers con- sist not only of the centripetal neuraxes of certain ganglion cells in TUNICA FIBROSA OCULI. 409 the retina, but also of centrifugal neuraxes, which pass out from the brain ( Froriep). The invaginating ectoderm which later constitutes the lens is constricted off from the remaining ectoderm in the shape of a vesi- cle, the mesial half of which forms the lens fibers by a longitudinal growth of its cells, while the lateral portion forms the thin anterior epithelial capsule of the lens. The epithelium of the ectoderm external to the lens differentiates later into the external epithelium of the cornea and conjunctiva, neither of which structures is at this stage sharply defined from the remaining ectoderm. It is only during the development of the eyelids that a distinct demarcation is established. All the remaining portions of the eye, as the vitre- ous body, the vascular tunic with the iris, the sclera with the substantia propria of the cornea and the cells of Descemet's layer, are products of the mesoderm. C TUNICA FIBROSA OCULI. U THE SCLERA. The sclera is the dense fibrous tissue covering of the eyeball, and is directly continuous with the transparent cornea. At the poste- rior mesial portion- of the eyeball, the sclera is perforated for the en- trance of the optic nerve, this region being known as the lamina cribrosa. The sclera consists of bundles of connective-tissue fibers arranged in equatorial and meridional layers. " At the external scleral sulcus, in the vicinity of the cornea, the arrangement of the fibers is principally equatorial. The tendons of the ocular muscles are continuous with the scleral fibers in such a manner that those of the straight muscles fuse with the meridional fibers, while those of the oblique muscles are continuous with the equatorial fibers. In the sclera are man}' lymph-channels communicating with those of the cornea. Thev are much coarser and more irregularlv arranged than those of the cornea, and in this respect simulate the lymph- channels found in aponeuroses. Pigmentation is constantly present at the corneal margin, in the vicinity of the optic nerve entrance, and also on the surface next the choroid. The innermost pigment layer of the sclera is lined by a layer of flattened endothelial cells, and is regarded by some as a separate membrane, known as the lamina fusca. The external surface of the sclera also presents a layer of flattened endothelial cells, belonging to the capsule of Tenon. Anteriorly, the mobile scleral conjunctiva is attached to the sclera by a loose connective tissue containing elastic fibers. The cornea is inserted into the sclera very much as a watch- crystal is fitted into its frame. At the sclerocomeal junction is found an annular venous sinus, the canal of Schlemm, which may appear as a single canal or as several canals separated by incom- plete fibrous septa. Anteriorly and externally this canal is bounded 4io THE EYE. by the cornea and sclera ; internally, it is partly bounded by the origin of the ciliary muscle. The sclera comprises, therefore, one- half of the canal-wall, and presents a corresponding circular sulcus, the so-called inner scleral sulcus. The blood-vessels of the sclera are derived from the anterior ciliary vessels. The capillaries enter either into the ciliary veins or into the venae vorticosae. The numerous remaining vessels traverse the sclera, extending to the choroid, iris, or scleral margin. At the corneal margin the capillaries form loops. Corneal epithelium. Basal cells. Anterior elastic membrane. Substantia propria. 2. THE CORNEA. The cornea is made up of the following layers : (i) the ante- rior or corneal epithelium ; (2) the anterior elastic membrane, or Bowman's membrane ; (3) the ground-substance of the cornea, or substantia propria ; (4) Des- cemet's membrane ; (5) the endothelium of Descemet's membrane. At the center of the human cornea the epithe- lium consists of from six to eight layers of cells, being somewhat thicker near the corneal margin. Its basilar surface is smooth and there are no connective-tissue pa- pillae. The basal epithelial layer is composed of cylin- dric cells of irregular height ; the following layers contain irregular polygonal cells, while the two or three most superficial layers consist of flattened cells. The cells of the corneal epithelium are all provided with short prickles, which are, however, very difficult to demon- strate, and between are found lymph-canaliculi. The lower surfaces of the basal cells also possess short processes which penetrate into the anterior basement membrane. In man the anterior elastic or Bowman's membrane is quite thick and apparently homogeneous, but may be separated into fibrils by means of certain reagents. In structure it belongs neither to the elastic nor to the white fibrous type of connective tissue, and must be regarded as forming a class by itself. Numerous nerve- fibers penetrate its pores to enter the epithelium. The thickness of this membrane decreases toward the sclera, and it finally disap- pears about 1 mm. from the latter. The substantia propria consists of connective-tissue fibrils Fig. 330. — Section through the anterior portion of human cornea ; X 5°°- TUNICA FIBROSA 0C1 LI. 411 Lymph-canal iculi. Corneal space. grouped into bundles and lamellae. Chemically they do not differ from true connective-tissue fibers (Morochowetz), but arc doubly refracting. There are about sixty lamella.: in the human cornea. The fibrils composing each lamella are cemented together and run parallel to one another as well as to the surface of the cornea, but they are so arranged that the fibrils of each lamella cross those of the immediately preceding one at an angle of about twelve degr The lamellae themselves are likewise closely cemented to one another. The most superficial lamella, lying immediately beneath the anterior elastic membrane, is composed of finer fibers, the course of which is oblique to the surface of the cornea. Between the anterior and posterior elastic membranes are bundles of fibers, which perforate the various lamellae of the cornea and are conse- quently known as the perforating or arcuate fibers. Between the lamella; are peculiar, flattened cells, possessing irregular or lamella -like processes, the corneal cor= puscles ; these lie in spe- cial cavities in the ground substance of the substan- tia propria, which are known as corneal spaces. By means of various meth- ods {vid. T. 3 19 and 320), these corneal spaces may be shown to be part of a complicated lymphatic system, comparable to the lymph-canalicular system of fibrous connective tis- sue. This system of can- als is also in communica- tion with the lymph-chan- nels at the corneal margin. The posterior elastic or Descemet's membrane is not so inti- mately connected with the substantia propria as Bowman's mem- brane. It is thinnest at the center of the cornea, and becomes thicker toward the margin. It may be separated into finer lamellae, is very elastic, resists acids and alkalies, but is digested by trypsin. The endothelium of Descemet's membrane consists of low, quite regular, hexagonal cells, which in certain vertebrates (dove, duck, rabbit) are peculiar in that a fibrillar structure may be seen in that portion of each cell nearest the posterior elastic membrane By means of these fibers, not only adjacent cells, but also those further apart, are joined together. Thus we have here to a marked degree the formation of fibers which penetrate the cells and connect them with one another, conditions already met with in the prickle-cells of the epidermis. (Fig. 288.) Fig. 331. — Corneal spaces of a dog ; X 640 (Technic No. 320). 412 THE EYE. The cornea is nonvascular. In fetal life, however, the capil- laries from the anterior ciliary arteries form a precorneal vascular network immediately beneath the epithelium, a structure which is obliterated shortly before birth and only rarely seen in the new- born. Its remains are found at the corneal limbus either as an episcleral or conjunctival network of marginal capillary. loops. Fine branches of the anterior ciliary arteries extend superficially along the sclera to the corneal margin, and form here a network of capil- laries also ending in loops, from which numerous veins arise, con- stituting a corresponding network emptying into the anterior ciliary veins. The conjunctival vessels likewise form a network of mar- ginal loops at the corneal limbus, and are connected with the epi- scleral vessels (Leber). Under pathologic conditions the cornea may become vascularized from the marginal episcleral network. The nerves of the cornea are derived from the sensory fibers of the ciliary nerves, which form a plexus at the corneal margin ; from this, nonmedullated fibers penetrate the cornea itself and form two plexuses, a superficial and a ground plexus ; the latter is distributed throughout the whole substantia propria with the exception of its inner third (Ranvier, 81). The two plexuses are connected by numerous anastomoses. At one time it was supposed that direct communication existed between the corneal corpuscles and the nerve- fibers of both plexuses. This view, however, contradicts the gen- erally accepted neurone theory. Nerve-fibers from the superficial plexus pass through the ante- rior elastic membrane and form a plexus over the posterior surface of the epithelium, known as the subepithelial plexus. From the lat- ter nerve-fibers extend between the epithelial cells, terminating in telodendria with long slender nerve-fibrils, which end in small nodules. Many of the fibrils reach almost to the surface of the epi- thelium (Rollett, 71; Ranvier, 81). D. THE VASCULAR TUNIC OF THE EYE. THE CHOROID, THE CILIARY BODY, AND THE IRIS. From without inward the following layers may be differentiated in the choroid : (1) the lamina suprachoroidea ; (2) the lamina vas- culosa Hallcri ; (3) the lamina choriocapillaris ; and (3) the glassy layer, or vitreous membrane. The lamina suprachoroidea. consists of a number of loosely arranged, brandling and anastomosing bundles and lamellae of fibrous tissue, joined directly to the lamina fusca of the sclera. These bundles and lamellae consist of white fibrous connective tissue containing numerous elastic fibers, among which a few connective- tissue cells are distributed. Pigment cells arc also present in varying numbers. The bundles and lamellae are covered by endothelial THE VASCULAR TUNIC OF THE EYE. 413 cells, and the spaces and clefts between them, and between the lamina suprachoroidea and the lamina fusca, constitute a system of lymph-channels — the perichoroidal lymph-spaces. The lamina vasculosa of the choroid is also composed of simi- lar lamellae, which, however, are more closely arranged. The blood- vessels constitute the principal portion of this layer, the vessels being of considerable caliber, not capillaries. They are so distrib- uted that the larger vessels, the veins, occupy the outer layer of the lamina vasculosa. The venous vessels converge toward four points of the eyeball, forming at the center of each quadrant one of the four voice vorticosic. The arteries, on the other hand, describe a more meridional course. In the inner portion of this layer is found a narrow zone, — in the human eye only about 10 7. 27 41 8 THE EVE. E. THE INTERNAL OR NERVOUS TUNIC OF THE EYE. This tunic is composed of two layers : the outer, or stratum pig- menti ; and the inner, or retina. l. THE PIGMENT LAYER. The pigment layer develops, as we have seen, from the outer layer of the secondary optic vesicle. It consists of regular hexa- gonal cells, 12 n to 1 8 }i in length and g }x in breadth, which con- tain black pigment in the form of granules. The inner surfaces of these cells possess long, thread-like and fringe-like processes, between which project the external segments of the rods and cones of the retina, yet to be described. The nuclei of the pigment cells lie in the outer ends of the cells, the so-called basal plates, and are not pigmented. The distribution of the pigment varies according to the illumination of the retina. If the latter be darkened, the pig- ment collects at the outer portion of each cell ; if illuminated, the pigment is evenly distributed throughout the whole cell. The pig- ment granules are therefore mobile (Kiihne, 79). 2. THE RETINA. The retina has not the same structure throughout. In certain areas peculiarities are noticeable which must be described in detail ; such areas are : (1) the macula lutea ; (2) the region of the papilla (papilla nervi optici) ; (3) the ora serrata ; (4) the pars ciliaris retinae ; and (5) the pars iridica retinae. We shall begin with the consideration of that portion of the retina lying between the ora serrata and the optic papilla (exclusive of the macula lutea). From without inward, we differentiate: (1) the layer of vis- ual cells, including the outer nuclear layer ; (2) the outer molecu- lar (plexiform) layer ; (3) the inner nuclear or granular layer ; (4) the inner molecular (plexiform) layer ; (5) the ganglion-cell layer ; (6) the nerve-fiber layer. Besides these, we must also consider the supporting tissue of the retina and Muller's fibers, together with the internal and external limiting membranes. The visual cells are cither rod-visual cells or cone-visual cells. The rod-visual cells consist of a rod and a rod-fiber with its nucleus. The rod (40 fi to 50 ft in length) consists of two seg- ments, an outer and an inner, the former of which is doubly refrac- tive and may be separated into numerous transverse discs by the action of certain reagents. The inner is less transparent than the outer segment, and its inner end shows a fine superficial longitu- dinal striation due to impressions from the fiber-baskets formed by Muller's fibers. In the lower classes of vertebrates a rod-ellipsoid THE INTERNAL OR NERVOUS TUNIC OF THE EVE. 419 (a fibrillar structure) may easily be demonstrated in the outer region of each inner portion ; in many mammalia and in man the demon- stration of this is more difficult. This structure is a planoconvex, longitudinally striated hod)-, the plane surface of which is coincident with the external surface of the inner segment, its inner convex sur- face Lying at the junction of the outer and middle thirds of the inner segment The rod- fibers extend as far as the outer molecular layer of the retina, where they end in small spheric swellings. The nuclei of the rod-visual cells are found at varying points within the rod- fibers, but rarely close to the inner segment. When treated with certain fixing agents and stains, the rod-nuclei are seen to show several zones, which stain alternately light and dark (striation of the rod-nuclei). Layer of nerve- fibers. Ganglion-cell layer. Inner molecular layer. Inner nuclear layer. Outer molecular layer. Outer nuclear layer. Ext. limiting mem- brane. Inner segment of rod. Inner segment of cone. Outer segment of cone. Outer segment of rod. Fig. 335. — Section of the human retina ; X 7°°- The cone-visual cells consist, similarly to the rod-visual cells, of a cone and a cone-fiber with its nucleus. The cone ( 1 5 u to 25 fi in length) is, as a whole, shorter than the rod, and its inner segment is considerably broader than that of the rod. The cone ellipsoid comprises the outer two-thirds of the inner segment, and the outer segment has a more conical shape. The conc-fibcr like- wise extends as far as the outer molecular layer, where it ends in a branched basal plate. Its somewhat larger nucleus is always found in the vicinity of the inner segment of the cone. The inner surfaces of the inner segments, not only of the cone-cells, but also of the rod-visual cells, lie in one plane, corresponding to the 420 THE EYE. external limiting membrane ; a structure composed of the sustenta- cular fibers of Miiller. The rod-fibers and cone-fibers, with the nuclei of the rod- and cone-visual cells, lie between the external limiting membrane and the outer molecular layer. It will be observed, therefore, that the visual cells include the layer of rods and cones and the outer nuclear layer. The outer molecular layer consists : (i) of the ramifications of Miiller's fibers ; (2) of the knob and tuft-like endings of the visual cells ; and (3) of the dendritic processes of the bipolar cells of the inner nuclear layer. These structures will be considered more in detail in discussing the relations of the elements comprising the retina. The inner nuclear layer contains: (1) the nucleated stratum of Miiller's sustentacular fibers ; (2) ganglion cells situated in the outer region of the layer and extending in a horizontal direction ; (3) bipolar ganglion cells with oval nuclei, densely placed at various depths of the layer and vertical to it ; (4) amacrine cells (neurones, apparently without neuraxes) lying close to the inner margin of the layer and forming with their larger nuclei a nearly continuous layer of so-called spongioblasts. The numerous processes of these spongioblasts lie in the inner molecular layer, the composition of which will be further discussed later. The ganglion=cell layer of the optic nerve consists, aside from centrifugal neuraxes and the fibers of Miiller, which are here present, of multipolar ganglion cells, the dendrites of which extend outward and the neuraxes of which are directed toward the optic nerve-fiber layer. These cells vary in size, and their nuclei are typical, being relatively large, deficient in chromatin, and always provided with large, distinct nucleoli. In man the optic nerve- fibers of the retina are nonmedullated. All these structures are typical of that portion of the retina lying behind the ora serrata. The retina in the vicinity of the optic papilla and macula lutea must be taken up separately. 3. REGION OF THE OPTIC PAPILLA. The optic papilla is the point of entrance of the optic nerve into the retina. At the center of the papilla, in the region where the nerve-fibers spread out radially in order to supply the various areas of the retina, is a small, funnel-shaped depression, the physi- ologic excavation. The fibers of the optic nerve lose their medullary sheaths during their passage through the sclera and choroid, and then continue, penetrating the various layers of the retina, to the inner surface of the latter, over which they spread in a layer which grad- ually becomes thinner toward the ora serrata. On account of the de- flection of the nerve-fibers, and because, during their passage through the sclera, they lose their medullary sheaths at one and the same point, the optic nerve becomes suddenly thinner. The result is a THE INTERNAL OK NERVOUS TUNIC OF THE EVE. 421 deeply indented circular depression in this region. On this depres- sion border the three ocular tunics. At this point the retina is interrupted, the outer layers extending to the bottom of the de- pression, while the inner cease at its margin. In many cases the outer layers of the retina are separated from the optic nerve by a thin lamina of supporting tissue (intermediate tissue). Sclera. Fig- 336-- /Pigment layer. ^..-Hods and cones. -- 1 later naolear layer. •*J --Outer molecular layer. r nuclear layer. "Iun.r molecular layer. "•Layer of nerve-fibers. Blood-vessels. Physiologic excavation. -Section through point of entrance of human optic nerve ; X 4°- 4. REGION OF THE MACULA LUTEA. At the center of the macula lutea is a trough-like depression, the fovea centralis, the deepest part of which, the fundus, lies very close to the visual axis. Here the layers of the retina are practic- ally reduced to the cone-visual cells. The margin of this depression is somewhat thickened, owing to an increase in the thickness of the nerve-fiber and ganglion-cell layers. Toward the fundus of the fovea Fovea centralis. Layer of nerve-fibers Ganglion-cell . layer. Inner molecu- lar layer Inner nuclear layer. Outer molec- ular layer. , !3 C f C T3 :3 "3 •a ° »£a IS l _. £ C ,.* °- c !r, -C -T3 13 C fiio 01 — 01 V S3 j^ fc *** — cD eral or in all of the strata of the inner molecular layer. Besides the ramifications of the spongioblasts just mentioned, autochthonous cells are also present. These lie in one of the interstices of the molecular layer, their ramifications spreading out in a horizontal direction. Besides all these structures the dendrites of the cells THE INTERNAL OR NERVOUS TUNIC OF THE EYE. 425 in the ganglion-cell layer also ramify throughout the inner molec- ular Layer. 4. The gang/ion - cell layer. The cell-bodies are irregularly oval ; their dendrites extend into the inner molecular layer, and their neuraxes into the nerve-fiber layer. According to the manner of their dendritic termination, the ganglion cells may be divided into three groups: (1) those the dendrites of which ex- tend into but one stratum of the molecular layer ; (2) those the dendrites of which extend into several strata of the molecular layer ; and ( 3 ) those the dendrites of which are distributed throughout the entire thickness of the molecular layer. Thus, these three groups are made up of the so-called mono-stratified, poly-stratified, and diffuse cells ; by means of their dendrites they come in contact with one or several of the neuraxes of the bipolar cells of the inner nuclear layer. 5. The nerve-fiber layer of the retina. This layer consists of centripetal neuraxes from the ganglion cells of the ganglion-cell layer, and of centrifugal nerve -fibers ending in various layers of the retina, including the outer molecular layer. 8. THE OPTIC NERVE. Within the orbit the optic nerve possesses an external sheath, which is an extension of the dura mater and is continuous with the scleral tissue, and an inner sheath, which is a prolongation of the pia mater. Between these two sheaths is a fissure, divided into two smaller clefts by a continuation of the arachnoid. Both these clefts are traversed by connective-tissue trabecular. The inner cleft com- municates with the subarachnoid space ; and the outer narrower cleft, with the subdural space. The fibers of the optic nerve are medullated, but there is no neurilemma (sheath of Schwann), the latter being represented by the neuroglia. In the region of the sclera and choroid the optic nerve- fibers lose their myelin, and the septa of the inner or pial sheath become better developed and relatively more numerous. Connec- tive-tissue fibers from the sclera and choroid also traverse this region of the optic nerve, giving rise to what is known as the lamina cribrosa. At from I ]/ 2 to 2 cm. from the eyeball there enter into the optic nerve laterally and ventrally (according to J. Deyl, mesially) the central artery and vein of the retina, which very soon come to lie within the axis of the nerve. Here they are surrounded by a common connective-tissue sheath which is in direct connec- tion with the perineurium. The optic nerve-fibers extend through the lamina cribrosa into the retina, where they spread out as the nerve-fiber layer in the manner previously described. 426 THE EYE. 9. BLOOD-VESSELS OF THE OPTIC NERVE AND RETINA. The blood-vessels of the optic nerve are principally derived from the vessels of the pial sheath. In that portion of the nerve con- taining the central vessels of the retina the latter anastomose with the pial vessels, so that this por- tion of the optic nerve is also supplied by the central vessels. At their entrance through the sclera the short posterior ciliary arteries form a plexus around the optic nerve, the arterial circle of Zinn, which communicates, on the one hand, with the vessels of the pial sheath, and, on the other, with those of the optic nerve. At the level of the choroid the vessels of the latter communicate by means of capillaries with the central vessels of the optic nerve. The central artery and vein of the retina enter and leave the retina at the optic papilla, dividing here, or even within the nerve itself, into the superior and inferior papillary artery and Fig. 339. — Injected blood-vessels of the human retina ; surface preparation ; X i8. - - Vascular plexus of macula huea with wide meshes. Fovea centra- lis, free from vessels. Fig. 34°- — Injected blood-vessels of human macula lutea ; surface preparation ; X 2 %- vein. Both the latter again divide into two branches, the nasal and temporal arteriole and venule, known, according to their posi- THE VITREOUS BODY. 427 tions, as the superior and interior nasal and temporal artery and vein. Besides these vessels, two small arteries also arise from the trunk of the central artery itself, and extend to the macula. Two similar vessels extend toward the nasal side as the superior and inferior median branches. Within the retina itself the larger ves- sels spread out in the nerve-fiber layer, forming there a coarsely meshed capillary network connected by numerous branches with a finer and more closely meshed network lying within the inner nuclear layer. The venous capillaries of this network return as small venous branches to the nerve-fiber layer, in which they form a venous plexus, side by side with the arterial plexus. The arteries of the retina are of smaller caliber than the veins. The larger arteries possess a muscular layer ; the smaller, only an adventitia. All the vessels possess highly developed perivascular sheaths. The visual-cell layer is nonvascular, as are also the fovea centralis and the rudimentary retinal layers lying anterior to the ora serrata. The arteries of the retina anastomose with one another solely by means of capillaries (end-arteries), and it is only in the ora serrata that coarser venous anastomoses exist. F. THE VITREOUS BODY. The vitreous body consists of a semifluid tissue containing very few fixed cellular elements and only a small number of leucocytes. The latter are found only on the surface of the vitreous humor, be- tween it and the retina. Thin structureless lamella; and fibers occur throughout the entire vitreous body, with the exception of the hyaloid canal. These are particularly numerous at the per- iphery and especially in the region of the ciliary body. The outer or hyaloid membrane of the vitreous bod}-, separating the latter from the retina, is somewhat thicker in the region of its close attachment around the physiologic excavation of the optic nerve and to the ex- ternal limiting membrane of the retina in the ciliary region. In the latter region the hyaloid membrane is closely connected with the epithelium of the pars ciliaris retina:. It does not, however, pene- trate into and between the ciliary processes, but extends like a bridge over the furrows between them. This arrangement gives rise to spaces, the reeessus camera posterioris, which form a division of the posterior chamber, and are inclosed between the hyaloid membrane, the ciliary processes, the suspensory ligament of the lens, and the lens itself; these spaces are filled with aqueous humor. In the region of the ciliary processes the hyaloid membrane splits up into numerous fibers, which diverge fan-like toward the lens and become blended with the outer lamella of the lens-capsule. Those coming from the free ends of the ciliary processes become attached 428 THE EVE. along the equator of the lens and to the adjacent posterior portion of the lens-capsule. On the other hand, the fibers originating be- tween the ciliary processes attach themselves to the anterior sur- face of the lens-capsule in the immediate vicinity of the equator. Together these fibers constitute the zonula ciliaris, zonule of Zinn, or the suspensory ligament of the lens. Between these fibers of the zonula and the lens itself there is, consequently, a circular canal divided by septa, the canal of Petit, which communicates by open- ings with the anterior chamber. G. THE CRYSTALLINE LENS. As we have already seen, the crystalline lens originates as an ectodermic invagination, which then frees itself from the remaining ectoderm in the shape of a vesicle and becomes transformed into the finished lens. In this process the cells of the inner wall of the vesicle become the lens-fibers, while those of the outer portion re- main as the anterior epithelium of the lens. The lens is surrounded on all sides by the lens-capsule. The lens capsule is a homogeneous membrane, nearly twice as thick on the anterior surface of the lens as on the posterior. Its chemic reactions differ from those of connective tissue, and in this respect it may be compared with the membranse proprise of glands. In sections the lens capsule appears to possess a tangen- tial striation ; under the influence of certain reagents, and under proper preliminary treatment, lamellae may be detached from its surface which are found to be directly connected with the fibers of the suspensory ligament. The anterior epithelium consists, in the fetus, of columnar cells ; in children, of cells approaching the cubic type ; and in the adult, of decidedly flattened cells. Toward the equator of the lens, in the so-called transitional zone, the cells increase in height and gradually pass over into the lens fibers. The lens fibers are also derivatives of epithelial cells ; they are long, flattened, hexagonal prisms, which extend through the entire thickness of the lens. In the adult the lens may be differentiated into a resistant peripheral and a softer axial substance. The sur- faces of the fibers present irregularities, and it is with the help of these serrations and a cement substance that the fibers are bound together. Each fiber possesses one or more nuclei, which, although they have no constant position, are usually found in the middle of the fibers situated near the lens-axis, and in the anterior third of those at some distance from the axis. The course of the fibers in the lens is extremely complicated. INTERCHANGE OF FLUIDS IN THE EYEBALL. 429 H. THE FETAL BLOOD-VESSELS OF THE EYE. In the eye of the embryo the vitreous body and the capsule of the lens contain blood-vessels. The vessel which later becomes the central artery of the retina passes through the space sub- sequently occupied by the vitreous body as far as the posterior sur- face of the lens (anterior hyaloid artery) and branches in the region of the posterior and anterior lens-capsule. The anterior vascular membrane of the lens capsule of the embryo is known as the mentbrana capsitlopupillaris, and that portion corresponding to the pupil, as the mentbrana papillaris. In the embryo numerous other vessels arise at the papilla and extend over the surface of the vitreous body close to the hyaloid membrane ; these are the pos- terior hyaloid arteries. These vessels later disappear. In place of the anterior hyaloid artery there remains in the vitreous humor a transparent cylindric cord containing no fibers nor lamelke, as is the case in the remaining portion of the vitreous body, and consisting of a more fluid substance ; this is the hyaloid canal, or the canal of Cloquet. With regard to the posterior hyaloid vessels, the generally ac- cepted theory is that they later enter into the formation of the retinal vessels. Little is known as to the details of this process ; but the fact remains that, in the rabbit, for instance, the larger branches of the retinal vessels are internal to the inner limiting membrane, and, therefore, within the vitreous body, and that they send smaller branches into the retina (His, 80). L INTERCHANGE OF FLUIDS IN THE EYEBALL. The anterior lymph-channels of the eye comprise (1) the lymph-canaliculi of the cornea, which communicate with similar structures in the sclera ; ( 2) the system of the anterior chamber, which is indirectly connected, on the one hand, with the canal of Schlemm by means of the spaces of Fontana, and with the stroma iridis, into which the ligamentum pectinatum extends ; while, on the other hand, it communicates with the posterior chamber and its recesses, and with the canal of Petit. In the posterior region of the eyeball are the lymph-channels of the retina (the perivascular spaces), those of the optic nerve, the space between the pigment layer and the remaining portion of the retina (interlaminar space, Rauber), and the lymph-spaces of the choroid and sclera. The influx and efflux of intraocular fluid occur principally by means of filtration. The influx takes place through the ciliary processes ; that the choroid has to do with this process is very improbable. The efflux takes place through the veins of the canal of Schlemm. into which the fluid filters through the cement lines of the endothelial lining of the canal of Schlemm, 430 THE EVE. finally emptying into the anterior ciliary veins. A posterior efflux from the vitreous body probably does not exist, or at least occurs to a very limited extent. The anterior chamber possesses no efferent lymph-vessels (Leber, 95). J. THE PROTECTIVE ORGANS OF THE EYE. J. THE LIDS AND THE CONJUNCTIVA. At the end of the second month of embryonic life the eyelids begin to develop in the shape of two folds of skin. At the end of the third month these folds come in contact in the region of what is later the palpebral fissure, and grow together at their outer epithelial margins. Shortly before birth the two lids again separate and the definitive palpebral fissure is formed. The eyelids show three distinct layers : (1) the external cutis, which presents special structures at its free margin and continues about 1 mm. inward from the inner border of the free margin ; (2) the mucous membrane, or palpebral conjunctiva, beginning from this line and covering the entire internal surface ; and (3) a middle layer. 1 . The cuticular portion of the eyelid consists of a thin epider- mis and a dermis poorly supplied with papillae. Fine lanugo-like hairs with small sebaceous glands and a few sweat-glands are distributed over its entire surface. The cutaneous connective tissue is very loose, contains very few elastic fibers, and is supplied with pigment cells in the superficial layers. At the lid-margin the papillae are well developed and the epidermis is somewhat thickened. The anterior margin supports several rows of larger hairs, the cilia, the posterior row of which possesses, besides the sebaceous glands, modified sweat-glands, the ciliary glands of Moll, which also empty into the hair follicles. The eyelids are further provided with numer- ous glands, known as the Meibomian or tarsal glands. About thirty of these glands are found in the upper, a slightly smaller number in the lower, lids. They lie within the tissue of the tarsus vertical to the palpebral margin. Each gland consists of a tubular duct, lined by stratified squamous epithelium, beset with numerous simple or branched alveoli lined by a stratified, cubic epithelium in every respect similar to that lining the alveoli of sebaceous glands. The ducts of these glands terminate at the palpebral margin poste- rior to the cilia. 2. The conjunctival portion of the eyelids is lined by a simple pseudostratified columnar epithelium, possessing two strata of nuclei. This is continuous with the bulbar conjunctiva at the conjunctival fornix, and is characterized by the occasional presence of folds and sulci. Longitudinal folds in the upper portion of the upper lid running parallel with the lid-margin are frequently present. Goblet cells are usually found in the epithelium. According to W. Pfitz- THE I'KOI'KCI'IVE ORGANS OF T1IK EYE. 431 ner (97), the epithelium of the conjunctiva consists of two <»r three strata of cells, of which the more superficial possess a cuticular margin. Certain structures which have always been regarded as goblet cells are in all probability similar to the cells of Leydig — i. e., mucous cells, which do not pour their secretion out over the sur- face of the epithelium. Some lymphoid tissue is always found in the stratum proprium of the mucous membrane, and occasionally it Hair and sebace- ous gland. Conjunctiva. Loose connective tissue. - Meibomian glands. Cilium Fig. 34I. — Cross-section of upper eyelid of man ; the blood-vessels injected. By reason of the characteristic arrangement of the capillaries in the several layers of tissue, the extent and arrangement of these may be readily ascertained. is seen to form true lymph-nodules. It is of some interest to note that a marked production of these lymph-nodules occurs in certain diseases. Such lymph-nodules are usually associated with epithe- lial crypts, which fact led Henle to regard them as glandular forma- tions. Small glands with a structure similar to that of the lacrimal glands are also present in the palpebral conjunctiva ; they are found 43 2 THE EVE. in the upper eyelid, at the outer angle of the conjunctival fornix. Similar glands occur also at the mesial angle of the fornix. 3. Besides the tarsus (fibrocartilage)the middle layer of the eye- lid contains : (1) The musculus orbicularis oculi, which lies beneath the subcutaneous tissue. At the margin of the lid this structure gives off the musculus ciliaris Riolani, which is composed of two fasciculi separated by the tarsus. (2) The connective tissue be- tween the bundles of the musculus orbicularis oculi. (3) The con- nective tissue lying behind the latter and the tarsus. In the upper lid the connective tissue mentioned under 2 and 3 is connected with the tendon of the musculus palpebralis superior. The latter is composed of smooth muscle-fibers, and is regarded as a continua- tion of the middle portion of the striated, voluntary musculus leva- tor palpebral superioris. The middle layer of the lower lid is struc- turally analogous, except that here the inferior rectus muscle takes the place of the levator palpebral. The blood-vessels of the eyelid lie directly in front of the tarsus, and from this region supply adjacent parts ; they reach the poste- rior portion of the lid either by penetrating the tarsus or by encir- cling it (Waldeyer, 74). The "third eyelid," the plica semilunaris, contains, when well developed, a small plate of hyaline cartilage. At the fornix the epithelium of the palpebral conjunctiva be- comes continuous with the two- or three-layered squamous epithe- lium of the conjunctiva bulbi. Beneath this epithelium is found a loose fibro-elastic connective tissue, presenting subepithelial papillae, and quite vascular. In it are found medullated nerve-fibers, some of which terminate in free sensory nerve-endings in the conjunctival epithelium ; others terminate, especially near the corneal margin, in end-bulbs of Krause ; and still others may be traced to the cornea, to terminate in a manner previously described. 2. THE LACRIMAL APPARATUS. The lacrimal apparatus consists of the lacrimal glands, their ex- cretory ducts, the lacrimal puncta and canaliculi, the lacrimal sac, and the nasal duct. The lacrimal gland is separated into two portions, of which the one lies laterally against the orbit and the other close to the upper lateral portion of the superior conjunctival fornix. The structure of the gland is, on the whole, that of a serous gland (parotid), with the difference that the intralobular ducts are not lined by a striated epithelium such as is found in the salivary tubules, and that those cells which are wedged in between the secretory elements and functionate as sustentacular cells (basket- cells) are here much more highly developed. The excretory ducts of the orbital division generally pass by the conjunctival half of the gland, taking up a few ducts from the latter TECHNIC. 433 as they go, and finally empty on the surface of the conjunctiva. Aside from these, the lateral portion of the gland possesses also independent ducts. All the excretory ducts are lined by columnar epithelium and surrounded by a relatively thick connective-tissue wall having inner longitudinal and outer circular fibers. From the lateral portion of the conjunctival culdesac, into which the secre- tion is brought by the excretory ducts of the lacrimal gland, the secretion passes into the capillary space of the sac, and is then evenly distributed by means of the sulci and papillx over the con- junctival surface of the lid. In this manner the secretion reaches the mesial angle of the lid, whence it passes through the lacrimal puncta into the lacrimal canals. The nerve supply of the lacrimal glands is from the sym- pathetic nervous system. The neuraxes of sympathetic neurones accompany the gland ducts and form plexuses about the alveoli, the terminal branches of which ma}' be traced to the gland cells. The lacrimal canals are lined by stratified squamous epi- thelium, and possess a basement membrane as well as a con- nective-tissue layer containing circularly disposed elastic elements. Externally we find a layer of transversely striated muscle-fibers. The lacrimal sac is provided with a simple pseudostratified columnar epithelium having two strata of nuclei. In it goblet cells are also found. The nasal duct is lined by a similar epithelium. The connective-tissue wall of the latter and that of the lacrimal sac come in contact with the periosteum ; between them is a well- developed vascular plexus. Stratified squamous and ciliated epi- thelium have been described as being present in the nasal duct, as well as mucous glands in both nasal duct and lacrimal sac. (See works of M. Schultze, ~2 ; Schwalbe, 87.) TECHNIC 316. The eyes of the larger animals, after having been previously cleaned by removing the muscles and loose connective tissue, are placed in the fixing fluid and cut into two equal parts by means of an equa- torial incision. Smaller eyes with thin walls may be fixed whole. Muller's fluid T. 2- >. nitric acid ( T. 25), and Flemming's fluid I.17 are usually employed as fixing agents. After fixing in one of these fluids, different parts of the eyeball are imbedded in celloidin or cel- loidin-paraffin and then sectioned. 317. The corneal epithelium is best macerated in 33$ alcohol : the membrane of Descemet may be impregnated with silver. In order to bring the fibers of the latter into view, Xuel recommends an injection of 1 ' , \o :' , formic acid into the anterior chamber of the eye of a dove or a rabbit, after having drawn off the aqueous humor. The cornea is then cut out, and fixed for from three to five minutes in osmic acid. 318. The substantia propria is examined either by means of sections or by means of teased preparations from a cornea macerated in lime- water or potassium permanganate. The sections are stained with picro- 28 434 THE EYE - carmin (Ranvier). The corneal spaces and canaliculi may be demon- strated in two ways with the aid of silver nitrate ; either the fresh cornea of a small animal is stripped of its epithelium, cauterized with a solid stick of silver nitrate, and then examined in water, in which case the corneal spaces and their canaliculi show light upon a dark ground (neg- ative impregnation) ; or the corner of larger animals are treated in the same manner, after which tangential sections are made with a razor, and placed in water for a few days ; in this. case the corneal spaces and their canaliculi show dark upon a light ground (positive impregnation, Ran- vier, 89). 319. By means of Altmann's oil method (T. 112) casts of the corneal spaces and their canaliculi may be made. Treatment by the gold method often brings out not only the nerves, but also the corneal corpuscles and their processes. 320. Ranvier (89) especially recommends a 1% solution of the double chlorid of gold and potassium for the corneal nerves. The cor- nea of the frog is treated for five minutes with lemon-juice, then for a quarter of an hour with 1 c / potassium-gold chlorid solution, and, finally, for one or two days with water weakly acidulated with acetic acid (2 drops to 30 c.c. of water), the whole process taking place in the light. Golgi's method may also be used, but the gold method is more certain. 321. The sclera is treated in a similar manner. 322. The pigmentation of the vascular layer interferes with examina- tion, and albinotic animals should therefore be selected ; or the pigment may be removed from the previously fixed eyeball with hydrogen peroxid or nascent chlorin. The latter method is applied exactly as in cases where the removal of osmic acid is desired (T. 144). 323. The adult lens is sectioned with difficulty, as it becomes very hard in all fixing fluids. The anterior capsule of the lens may be removed from previously fixed specimens and examined by itself. The lens-fibers are demonstrated by maceration in y'i alcohol (twenty-four hours) or in strong nitric acid. Before immersion the lens-capsule is opened by a puncture. 324. The retina can rarely be kept unwrinkled in eyes that have been fixed whole. The eyeball should therefore be opened in the fixing fluid and the latter permitted to act internally ; or the external tunics are removed, thereby enabling the fixing fluid to act externally. 325. Ranvier recommends subjecting the eyes of smaller animals (mouse, triton) for a quarter or half hour to the action of osmic acid fumes (vid. T. 16), after which the eyes are opened in ^3 alcohol with the scissors. At the end of three or four hours the posterior half of the eye is stained for some time in picrocarmin (T. 67), then carried over into \ ( /c osmic acid for twelve hours, washed with water, treated with alcohol, and cut. In osmic acid preparations the rod-nuclei show dark transverse bands, a condition due to the fact that the end-regions of the nuclei stain more deeply. The retina is a good object for differential staining, as, for instance, with hematoxylin-eosin, hematoxylin-orange (), etc. The latter combina- tion is particularly successful in staining the rod- and cone-ellipsoids. The examination of tangential sections should not be omitted. THE EXTERNAL EAR. 435 326. Willi the retina the besl results are obtained by means of Golgi s method. Attention must be (ailed to the fact that the supporting stnu - turesofthe retina are more easily impregnated than the nervous elements, and that the latter can be demonstrated to any extent only in very young eyes. 327. Ramon y Cajal (94) recommends the following method, modi- fied after (iolgi : After the removal of the vitreous humor the posterior half of the eyeball is placed for one or two days in a mixture containing 3'/ potassium bichromate 20 c.c. and \'/< osmic acid 5 or 6 c.c. The pieces are then dried with tissue paper and placed in a 0.75'/ silver nitrate solution for an equal length of time. Without washing, the piei es are immersed for from twenty-four to thirty-six hours in a mixture con- taining y/, potassium bichromate 20 c.c, and 1 f /„ osmic acid 2 or 3 c.c, and then again carried over into a 0.75^ silver nitrate solution for twenty-four hours. In order to prevent precipitation it is advisable to roll up the retina before treating, and to cover it with a thin layer of a thin celloidin solution, which prevents it from again unrolling. 328. The methylene-blue method (T. 312) will also bring out the nervous elements of the retina, although the results are not quite so satis- factory as those obtained by Golgi 's method. JX. THE ORGAN OF HEARING. The ear, the organ of hearing-, consists of three parts : (1) The external ear, including the pinna or auricle and the external audi- tory canal; (2) the middle, ear, tympanum, or tympanic cavity, containing" the small ear bones and separated from the external auditory canal by the tympanic membrane, but communicating with the pharynx by means of the Eustachian tube ; (3) the inner ear, or labyrinth, consisting of a bony and a membranous portion, the latter lined by epithelial cells, especially differentiated in certain regions to form a neuro-epithelium, in which the auditory nerves terminate. The first two parts serve for the collection and trans- mission of the sound-waves ; the complicated labyrinth, with its differentiated neuro-epithelium, for the perception of the same. Figure 342 presents in a schematic way the relationships of the parts here mentioned. A. THE EXTERNAL EAR. The cartilage of the ear, including that of the external auditory passage, is of the elastic variety, but differs from typical elastic carti- lage in that it contains areas entirely free from elastic fibers. The elastic reticulum is, however, never absent near the perichondrium. The skin covering the pinna is thin, and in it are found hairs with relatively large sebaceous glands ; sweat-glands are found on the outer surface. 436 THE ORGAN OF HEARING. The skin lining the cartilaginous portion of the external auditory- canal possesses very few pronounced papillae, and is characterized by the presence of so-called ceruminous glands, which represent modified and very highly differentiated sweat-glands. Two or three of the latter sometimes become confluent, and then possess only a single excretory duct, which, as a rule, empties into a hair follicle near the surface of the skin. The cbrium is somewhat mobile. The skin lining the osseous portion of the external auditory canal is supplied with neither hair nor glands, and possesses slender papillae, especially in the neighborhood of the tympanic membrane. The corium is closely attached to the periosteum. The tympanic membrane consists of a tense and a flaccid portion. Pinna Fig. 342. — Schematic representation of the complete auditory apparatus (Schwalbe). It forms a part of both the external and the middle ear. From without inward, the following layers may be differentiated : (1) the cutaneous layer ; (2) the lamina propria ; and (3) the mucous layer. The epidermis of the cutaneous layer is identical in structure with that of the outer skin, except that the superficial layers of the stratum corneum contain nucleated cells. The corium is very thin, except along the course of the manubrium of the malleus, where it is thickened, forming the so-called cutkular ridge t which possesses papillae and is supplied with vessels and nerves. The lamina propria ends peripherally in a thickened ring of fibro- cartilaginous tissue, the awiulus fibrosus, which unites at the sulcus THE MIDDLE EAR. 437 tympanicus with the periosteum of the latter. The lamina propria is composed of connective-tissue fibers, in which two layers may be distinguished — extern. ill}-, the radiate fibers, the stratum radiatum, and internally, the circular fibers, the stratum circularc. The ex- ternal radiate layer extends from the annul us to the umbo and manubrium, and is interrupted in the flaccid portion of the tympanic membrane by the upper fourth of the manubrium and the short process of the malleus; it gradually thins out toward the center until it finally disappears in the vicinity of the umbo. The fib ra of the inner (circular) layer are circularly disposed. This layer is thickest at the periphery of the tympanic membrane, becoming gradually thinner toward the lower end of the manubrium, where it disappears. Between the two layers of the lamina propria is a small quantity of loose connective tissue. The manubrium of the malleus is inclosed within the tympanic membrane. This is due to the union of the fibers of the radial layer with the outer strata of the manubrial perichondrium, the handle of the malleus being here covered by a thin layer of cartilage. In the posterior upper quad- rant of the tympanic membrane the two layers of the lamina propria intermingle, forming irregularly disposed bundles and trabecular, the dendritic fibrous structures of Grubcr. The mucous layer of the tympanic membrane consists of sim- ple squamous epithelium separated from the lamina propria by a thin connective-tissue layer containing but few cells. It likewise extends over the handle of the malleus. In the flaccid portion of the tympanic membrane the lamina propria disappears, so that in this region the cutaneous layer and the mucous membrane are in direct contact. B. THE MIDDLE EAR. The middle ear, or tympanum, is a small irregular cavity, filled with air, situated in the petrous portion of the temporal bone be- tween the bony wall of the inner ear and the tympanic membrane, and communicates with the pharynx through the Eustachian tube. It contains the small bones of the car, their ligamentous attach- ments, and, in part, the muscular apparatus moving them. The mucous membrane lining the tympanic cavity is folded over the ossicles and ligaments of the tympanum and is joined to that of the tympanic membrane and the Eustachian tube, the line of junction with the former being marked by the presence o r papilla-like eleva- tions. The epithelium of this mucous membrane is a simple pseudo- stratified ciliated epithelium, having two strata of nuclei. Cilia are, however, lacking on the surface of the auditory ossicles, on their ligaments, and on the promontory of the inner wall, as well as on the tympanic membrane. The mucosa of the mucous membrane is in- timately connected with the periosteum, and contains short isolated 438 THE ORGAN OF HEARING. alveolar glands, especially in the neighborhood of the opening of the Eustachian tube. The "auditon- ossicles" are true bones with Haversian canals and lamellae ; with the exception of the stapes, they contain no marrow-cavity. Very distinct perivascular spaces are seen sur- rounding the vessels in the canals (Rauber). The malleus articu- lates with the incus, both articular surfaces being covered with hyaline cartilage. Within this articulation we find a fibrocartilagin- ous meniscus, and at the summit of the short limb of the incus another small cartilage plate. Between the lenticular process of the incus and the capitulum of the stapes is another articulation, also provided with cartilaginous articular surfaces. The basal plate of Portion of Eusta- chian tube free from glands. Cartilage. -* Glands. _ Mucosa of the pharynx. Glands. Fig. 343. — Cross-section of the Eustachian tube with its surrounding parts ; X I2 (from a preparation by Professor Riidinger). the stapes is covered both below and at its edges with cartilage, as are also the margins of the fenestra ovalis (fenestra vestibuli). The basal plate is held in place within the fenestra by an articulation, provided with tense ligamentous structures on the tympanic and vestibular sides. Between these the connective tissue is quite loose. All the cartilaginous portions of the auditory ossicles, with the ex- ception of the articular cartilages, rest on the periosteum (Riidin- ger, 70). The fenestra rotunda (fenestra cochlear) is closed by the secon- dary or inner tympanic membrane, a connective-tissue membrane containing vessels and nerves, the outer wall of which is covered by THE INTKKNAI. EAR. 439 ciliated epithelium, the inner (the surface toward the scala tympani) by flattened endothelial cells. In the antrum and mastoid cells, the mucosa of the mucous membrane is immovably fixed to the periosteum. The epithelium is of the simple squamous variety and is nonciliated. The mucous membrane of the osseous portion of the Eustachian tube is very thin, and its mucosa is intimately connected with the periosteum. Its epithelium is of the simple pseudostratified ciliated variety, having two strata of nuclei. There are no glands. The mucous membrane of the cartilaginous portion of the Eustachian tube is thicker, and its epithelium, which is of the stratified ciliated variety, is higher, and often contains goblet-cells. Lymphoid tissue may be demonstrated in the mucosa of this portion, and occasion- ally structures resembling lymph-nodules are found, especially in the vicinity of the pharyngeal opening of the tube. In the cartilaginous portion of the tube are mucous glands, which are particularly numerous in the vicinity of the pharyngeal opening (Riidinger, 7-\ 2). G THE INTERNAL EAR. The internal ear consists of an osseous and a membranous por- tion, the osseous and the membranous labyrinths; the latter is con- tained within the former, and, although smaller, presents the same Superior semicircular canal. Horizontal semi- circular canal. Posterior semi- circular canal. Ampulla. Ampullae. Fenestra oralis. Bony cochlea. Vestibule. Fenestra rotunda. Fig. 344. — Right bony labyrinth, viewed from outer side : The figure represents the appearance produced by removing the petrous portion of the temporal bone down to the denser layer immediately surrounding the labyrinth (from Quain, after Sommering). general shape. The two structures are separated by a lymph-space containing the perilymph. In the bony labyrinth we recognize a central portion of ovoid shape, known as the vestibule, the outer wall of which forms the inner wall of the tympanum and presents two openings, the fenestra ovalis and the fenestra rotunda, separated by a ridge known as the promontory. This ridge becomes continuous with the lower portion 440 THE ORGAN' OF HEARING. of the bony cochlea, anterior and mesial to the vestibule and having the shape of a blunt cone. From the posterior portion of the ves- tibule arise three semicircular canals, known respectively as the external or horizontal semicircular canal, the anterior superior vertical, and the posterior inferior vertical semicircular canals. The canals communicate with the vestibule by means of five openings, the superior contiguous portions of the anterior and posterior canals uniting to form the caualis communis before reaching the vestibule. The three canals present near their origin from the vestibule enlarge- ments known as the osseous ampullae. The osseous labyrinth is lined throughout by a thin layer of periosteum, covered by a layer of endothelial cells. The membranous labyrinth, differs in shape from the osseous Auditory nerve with its vestibu- lar and cochlear branches. Ant. semicircular canal. Ampulla. Cochlear duct. Canalis reuniens. Ductus Ampulla. Horizontal semicir- endolymphaticus. cular canal. Fig. 345. — Membranous labyrinth of the right ear from five-month human embryo (from Schwalbe, after Retzius). labyrinth in that, in place of the single chamber (vestibule) of the latter, the membranous labyrinth presents two sacs, the utriculus and the sacculus, united by a narrow duct, the utriculosaccular duct. The utriculus is the larger, and from it arise the membran- ous semicircular canals. These present ampullae, situated within the osseous ampullae previously mentioned. The sacculus com- municates with the cochlear duct by means of the canalis reuniens (Hensen). From the utriculosaccular duct arises the ductus endolymphaticus, which passes through the aqueductus vestibuli and ends in a subdural saccus endolymphaticus on the posterior sur- face of the petrous portion of the temporal bone. In the membranous labyrinth the nerves are distributed over certain areas known as the macules, crista;, and papilla spiralis. THE INTERNAL EAR. 441 There is a macula within the recess of the utriculus, the macula acustica utriculi ; and another within the sacculus, the macula acustica sacculi ; crista; are present in the ampullae of the upper, posterior, and lateral semicircular canals, the crista ampullar es sup., post., ct la/. Besides these, we have the terminal arborization of the acoustic nerve in the membranous cochlea, the papilla spiralis cochlcw, or the organ of Corti. 1. UTRICULUS AND SACCULUS. Only the inner wall of the utriculus is connected with the peri- osteum of the vestibule. In this region lies the corresponding Membranous semicircular canal. V:- .- ■.■!■■■■■€< ■ \ ■■:,•',.■■ Blood-vessel. -- Wall of mem- branous canal. Epithelium of the membranous canal. — Ligament of canal. Bone. Perilymphatic spaces. Blood-vessel. Fig. 346. — Transverse section through an osseous and membranous seniici of an adult human being; ■ 50 (after a preparation by Dr. Scheibe): ,/, tissue strand representing a remnant of the embryonic gelatinous connective strands serve to connect the membranous canal with the osseous wall. macula cribrosa, through which the nerves penetrate to the macula of the utriculus. The utriculus and sacculus fill only a part of the inner cavity of the osseous vestibule. Between the osseous and membranous portions remains a space traversed by anastomosing connective-tissue trabecular, and lined by endothelium, which also forms an investing membrane around the trabecular. These trabe- cular pass on the one side into the periosteum lining the vestibule, 44 2 THE ORGAN OF HEARING. and on the other, into the wall of the utriculus and sacculus. The cavity which they thus traverse represents a perilymphatic space. (Compare Fig. 346, which shows analogous relations in the semi- circular canals.) The wall of the utriculus, especially its inner portion, consists of dense fibrous connective tissue, most highly developed in the region of the macula acustica. In the immediate vicinity of the macula utriculi the epithelium of the utriculus is high columnar in type ; in the remaining portion it consists of a single layer of low columnar cells, with a distinct basement membrane ; the epithelium of the macula itself is also high, and is composed of two kinds of elements — of sustentacular elements and of the so-called auditory hair-cells. The sustentacula)' cells are tall epithelial cells resting on the basement membrane by means of their single or cleft basal plates. Each possesses an oval nucleus lying at or beneath the center of the cell. The hair-cells are peculiar cylindric elements with somewhat thickened and rounded bases. One end extends to the surface of the epithelium, while the other, which contains the nucleus, extends only to the center of the epithelial layer. The free end is provided with a cuticular zone supporting a number of long, stiff hairs, which often coalesce to form single threads. On the surface of the epithelium, which must be regarded as a neuro-epithelium, are crystals of calcium carbonate, known as oto- liths, each of which incloses a minute central vacuole (Schwalbe). The otoliths are inclosed in a homogeneous substance, the otolithic membrane, which coagulates in a network of filaments when sub- jected to the action of fixing agents. The nerve-fibers going to the macula penetrate the wall, and, under the epithelium, undergo dichotomous division, and, after fur- ther division, form, in the region of the basilar ends of the auditory cells, a plexus consisting of fine ramifications, and embracing the lower ends of the auditory cells. A few fibers extend still further upward, where their telodendria enter into intimate relations with the acoustic cells (v. Lenhossek, 94, 1). The structure of the sacculus is in every respect like that of the utriculus, and a further description of it is therefore unnecessary. 2. THE SEMICIRCULAR CANALS. The membranous semicircular canals are attached at their con- vex surfaces to the periosteum of the bony canals, which they only partly fill, the remaining cavity being occupied by an eccentrically situated perilymphatic space traversed by connective-tissue trabecular. The walls of the perilymphatic spaces of the semicircular canals, like those surrounding the utriculus and the sacculus, are lined by endothelium, which covers, on the one hand, the periosteal surface of the bony semicircular canals, and, on the other hand, the outer wall of the membranous canals, together with the connective-tissue THE INTERNAL EAR. 443 trabecular The connective-tissue walls of the membranous canals are structurally similar to those of the utriculus and sacculus. Hensen compares their structure to that of the substantia propria of the cornea. In the adult, the inner layer of the wall of the canals supports here and there papillary elevations, which, however, disappear along its attachment to the bony semicircular canal (Riidinger, 72, 88). The epithelium lining the membranous semicircular canals is simple squamous in character and very evenly distributed over the entire inner surface, including the papillae previously mentioned. On the concave side of each semicircu- lar canal the epithelial cells are some- what narrower and higher. This inner and higher epithelium (raphe), extending along the concave side into the ampullae, marks the region at which the semicir- cular canals were constricted off from the pocket-like anlagen. The epithe- lium oi~ the ampulla: (Fig. 347), with the exception of that in the region of the raphe, is of the squamous type. At the crista; of the ampullae, however, there is found a neuro-epithelium similar to that of the maculae. The cells adjoining both ends of the cristas are high columnar, and to these the squamous epithelium is joined. The columnar cells just men- tioned form the so-called semilunar fold. Otoliths are also present upon the neu- ro-epithelium of the cristae. Here the structure corresponding to the otolithic membrane of the utriculus and sacculus is called the cupula. In preserved spec- imens it presents the appearance of a coagulum, showing a faint striation ; in the fresh condition, it has never been recognized as a distinct struc- ture, at least in the lower classes of vertebrates. BK I mm Fig. 347. — Part of a verti- cal section through the anterior ampulla, showing the membran- ous wall, a portion of the "cri-ta acustica," and the "planum semilunatum" (after Retzius) : a, Semilunar fold ; i>. crista acus- tica ; 1, nerve-fibers ; d, blood- vessels. 3. THE COCHLEA. The cochlea consists of an osseous portion, the bony cochlea, a membranous portion, the cochlear duct, and two perilymphatic canals. The bony cochlea consists of a central bony axis of conical shape, the modiolus, around which is wound a spiral bony canal, having in man a little over two and one-half turns, the modiolus forming the inner wall of this canal. The summit of the cochlea, which has the shape of a blunt cone, is formed by the blind end of this bony canal, and is known as the cupola. The modiolus further 444 THE ORGAN OF HEARING. gives support to a spiral plate of bone, the lamina spiralis ossca, which extends from the lower part of the modiolus, and, forming two and one-half spiral turns, reaches its top, where it ends in a hook-like process, the hamulus. This bony spiral lamina partly divides the bony cochlear canal into two parts, the division being completed by a fibrous tissue membrane, the lamina spiralis mem- brauacea, which extends from the free edge of the osseous spiral lamina to a thickened periosteal ridge, the ligamentum spirale, lining the outer wall of the bony cochlear canal. The canal above the lamina spiralis (bony and membranous) is known as the scala vestibuli, that below as the scala tympani. Both are perilymphatic canals, and communicate in the region of the last half-turn of the cochlea, by means of a narrow canal, the hclicotrcma, partly sur- rounded by the termination of the bony spiral lamina, the hamulus. The scala vestibuli is in free communication with the perilymphatic space of the vestibule ; while the scala tympani communicates with perivascular spaces surrounding the veins of the cochlear aqueduct, which latter empty into the jugular veins. The scala tympani ter- minates at the secondary tympanic membrane, closing the fenestra rotunda. The cochlear duct, which, as will be remembered, communicates with the sacculus by means of the canalis reuniens, is a long tube closed at both ends, the one end representing the vestibular sac, or ccecum vestibularc, and the other the cupolar extremity, or ccecum cupolare, also known as the lagena. The cochlear duct forms about two and three-fourths spiral turns, its length being about 3.5 mm. Its diameter gradually increases from its lower to its upper or distal extremity. The cochlear duct lies above the lamina spiralis, and, in a section of the cochlea parallel to the long axis of the modiolus, it is of nearly triangular shape, with the somewhat rounded apex of the triangle attached to the osseous lamina spiralis. In the cochlear duct we may distinguish the following parts : (1) the outer wall, which is intimately connected with the periosteum of the bony cochlear canal ; (2) the tympanal wall, resting on the membranous basilar membrane, with its highly differentiated neuro-epithelium, the spiral organ of Corti ; and (3) the vestibular wall, bordering on the scala vestibuli, the intervening structures forming a veiy delicate membrane — the vestibular or Rt issuer's membrane. From the account given thus far, it may be seen that within the bony cochlear canal there are found three membranous canals, running parallel with one another and with the osseous lamina spi- ralis about which they are grouped. Two of these membranous canals, the scala vestibuli and the scala tympani, are perilymphatic spaces, and are consequently lined by endothelial cells ; between them is found the cochlear duct, from its position known also as the scala media, lined by epithelial cells. These three membranous canals retain their relative position in their spiral course about the modiolus, and, in a section through the cochlea parallel to the bony THE INTERNA! EAR 445 axis of the modiolus, would be met with at each turn, and at ea< h turn present essentially the same relative position and structure. Figure 34S is sketched from such a section, and shows the appear- ance presented by a section through one of the turns of the bony cochlear canal as well as a section of the contained osseous lamina spiralis, the scalae, and the cochlear duct. We may now proceed with a fuller consideration of the structures mentioned. ]■. ■ ■ •« ©<*'•>. ' • . ".-V'V.'.V. "\ •- - Dc _'-■- -- d ■• • •■'••■ - ~ i Fig. 348. — Section through one of the turns of the osseous and membranous coch- lear ducts of the cochlea of a guinea-pig ; ■ 90: /, Scala vestiboli ; m, labium vestibu- lare of the limbus ; //, sulcus spiralis interims; 0, nerve-fibers lying in the lamina spi- ralis ; p, ganglion cells ; q, blood-vessels ; a, bone ; ''. Reissner's membrane ; Dc, ductus cochlearis ; , epithelium of the sulcus spiralis internus ; k, labium ves- tibular ; e, tympanic investing layer ; m, outer auditory cells ; n, n, nerve-fibers which extend through the tunnel of Corti ; o, inner pillar cell ; q, nerve-fibers ; b, b, basilar mem- brane ; a, epithelium of the sulcus spiralis externus ; ;-, cells of Hensen ; s, inner audi- tory cell ; /, ligamentum spirale (after Retzius). union of their free ends, a space which, as seen in figure 349, appears triangular in section. This is the tunnel of Corti. According to their position, we distinguish inner and outer pillars, the inner being more numerous than the outer. Including the entire extent of the lamina spiralis membranacea, we find that there are about 6000 of the inner and 4500 of the outer pillar cells. Each pillar cell originates from an epithelial cell, and is found to be composed of a protoplasmic portion containing the nucleus, which may be regarded as a remnant of the primitive cell, and of a cuticular formation derived from the primitive cell, forming the elongated body of the pillar cell — the pillar. The free adjoining ends are called the heads of the pillars. The head of the inner pillar is provided with a flattened process, the head-plate, which extends outward and forms an obtuse angle with the axis of the THE INTERNAL EAR. 449 pillar. Under this plate, and at the outer side of the head of the inner pillar, is a depression into which fits the head of the outer pillar. The latter also extends outward in the shape of a phalan- geal plate, with a thinner process, the phalangeal process, at its end. The phalangeal plate and process lie under the head-plate of the inner pillar, the process extending a little beyond this, forming an acute angle with the head of the outer pillar. At the inner side of the head of the outer pillar is a convex articular surface, with which, as a rule, two, and occasionally even three, articular sur- faces of the inner pillars come in contact. The outer and inner pillars appear to possess an indistinct longitudinal striation, and their basilar plates are continuous with the extremely fine cuticula covering the basilar membrane. The inner margins of the basilar plates belonging to the inner pillars border on the foramina ner- vosa ; while the outer margins of the basilar plates belonging to the outer pillars come in contact with the basal end of the inner- most row of the cells of Deiters in the outer region of Corti's organ. The protoplasmic portions of the pillar cells, constituting what are known as basal cells, lie against the basilar plates of the corresponding pillars, — i. e., on the basilar membrane, — and partly cover the bodies of the pillars, especially the surfaces toward the tunnel. In order to comprehend the relative position of the inner audi- tory cells to the inner pillars, it may be stated that one auditory cell rests upon every two inner pillars. The outer region of Corti's organ is joined directly to the outer pillar cells, and consists of four rows of auditory cells alternating with an equal number of sustentacular cells or Deiters's cells. Following these structures and in contact with them are the outer- most sustentacular cells, known as Hensen's cells. The outer auditory cells have a structure similar to that of the inner auditory cells, but possess a more slender body. They do not extend as far as the basilar membrane, but end at a distance from the latter equal to about double their own length. The cutic- ular zone of each outer auditor}' cell likewise assumes the form of an ellipse, with its long axis pointing radially. The surface of this zone also is provided with about twenty stiff auditory hairs, arranged in the form of a decidedly convex arch, the convexity of which points outward. At a short distance from the cuticular zone of each outer auditory cell is a peculiar round body, found only in these cells, the significance of which is unknown. Deiters's cells rest on the basilar membrane, and in shape resem- ble a flask with a narrow neck, known as the phalangeal process, the latter lying between the auditor}- cells. The nuclei of Deiters's cells lie in the upper parts of the thickened basal portions of these cells. With each Deiters's cell there is associated a cuticular structure, which extends along the surface of each cell in the form of a thin 29 450 THE ORGAN OF HEARING. fiber, the sustentacula? fiber, and which is found partly within and partly without the cell. The sustentacular fiber begins near the center of the thicker basal portion of the cell-body and extends first into the cell itself, then passes to the surface, and, entering the phalangeal process, passes to the top of the cell and expands as a plate, to which the name phalangeal plate has been given. The latter is broader than the phalangeal process, and since, as we shall see, the phalangeal plates are joined to one another, as well as to the elliptically shaped cuticular zones of the outer auditory cells, there remains a space between the cells of Deiters and the auditory cells, as also between the outer pillars and the innermost of the outer auditory cells, known as NueVs space. To the basal regions of the inner row of the cells of Deiters is joined the basal plate of the outer pillars of the arches of Corti. Next to the outer row of Deiters's cells are the cells of Hensen, arranged in about eight radially disposed rows. They form an eminence which is high internally, but gradually decreases in height externally. The somewhat narrowed bases of Hensen's cells prob- ably extend, without exception, to the basilar membrane. The free surfaces of these cells are likewise covered by a thin cuticular mem- brane. In man the cells of Hensen usually contain yellow pigment ; in the guinea-pig, as a rule, fat ; and in the rabbit, generally rudi- ments of sustentacular fibers. Externally the cells of Hensen gradu- ally change into elements of a more cuboid type — the cells of Claudius, of which there are about ten rows, radially disposed. The surfaces of the latter also possess a cuticular margin ; the nucleus is at the center of each cell and pigment is also present. Darker elements with more basally situated nuclei sometimes occur be- tween these cells, giving rise to the appearance of a double-layered epithelium (Bottcher's cells). Thus far we have considered in detail the cells comprising the organ of Corti, and described their relative positions and sequence from within outward. In order to give a clearer understanding of the mutual relations of these cells, from within outward and in the direction of the spiral turning of the cochlea, we shall now consider the appearance presented in a surface view of the organ of Corti. From within outward a surface view of the organ of Corti pre- sents the following characteristics : The somewhat broadened hex- agonal outlines of the inner sustentacular cells adjoin the epithelial elements of the sulcus spiralis internus and terminate externally in a spiral undulating line (if seen for only a short distance, this line appears straight). On this line border the contours of the cuticular zones belonging to the inner auditory cells. The outer margins of the cuticular zones come in contact with the head-plates of the inner pillars, the cuticular zone of one inner auditory cell coming in contact with at least two head-plates. The externally directed pro- cesses of the head-plates belonging to the inner pillars come in contact with one another and end in a spiral line which for a short THE INTERNAL EAR. 451 (fc^ distance is apparently straight. The head-plates of the inner pillars cover the head-plates of the outer pillars (which also come in con- tact with each other), also their phalangeal plates, but not their phalangeal processes, which thus pro- ject beyond the line formed by the outer borders of the head-plates of the inner pillars. It should be men- tioned that about three head-plates belonging to the inner pillar cells are in apposition to every two head-plates and their phalangeal processes of the outer pillar cells. The succeeding four rows, from within outward, are made up of alternately placed cutic- ular zones of the outer hair cells and the phalangeal plates of the Deiters's cells, alternating like the squares of a chess-board. This regular arrange- ment is lost in the outer row of Deiters's cells. The cells of Hensen adjoin this row, and when viewed from the surface, present the appearance of irregular polygons. This arrangement is, however, sel- dom found to be as typical as that just described ; although the relations of the cells to one another always correspond in general to the forego- ing scheme. In the cupolar and vestibular sacs the neuro-epithelium changes into an epithelium of an indifferent type. The lamina reticularis is formed by the cementing together of the pha- langeal processes of the outer pillars and the phalangeal plates of Deiters's cells, and is continued externally by a cuticular membrane which covers the cells of Hensen and, as a much thin- ner cuticular membrane, extends over the cells of Claudius. In this mem- brane there are found three or four rows of small apertures, into which the outer hair cells project. The membrana tectoria Cortii is attached to the limbus spiralis, but becomes free at the margin of the labium vestibulare and thick ens considerably, again becoming thinner toward its free end Fig. 350. — Surface of the organ of Corti, with the surrounding struc- tures, from the basal turn of the cochlea of a new-born child ; the original drawing reduced one-half (after Retzius, 84): T. 7. — 89, I, Ueber die Loslichkeit osmirten Fettes und Myelins in Terpentinol, in Zeitschr. Wiss. Mikroskopie, Bd. vi, S. 39, 40. — 89, 2, Weiteres iiber die Entfarbung osmirten Fettes in Terpentin und anderen Substanzen, ibid., 178-181. — 91,1, Neue Beitrage zur Kenntniss der Zelle, 2. Theil, in Arch. mikr. Anat., Bd. xxxvii, S. 685-751, T. 38-40. — 91, 2, Zur Entwickelungsgeschichte der Bindegewebsfibrillen, in Intemat. Beitr. wiss. Med., Bd. 1, S. 213-222, T. 9. — 91, 3, Ueber Theilung und Kernformen bei Leukocyten und iiber deren Attrak- tionsspharen, in Arch. mikr. Anat., Bd. XXXVII, S. 249-298, T. 13, 14. — 95, Zur Farbung mit sehr verdiinntem Hematoxylin, in Anat. Anzeiger, Bd. XI, S. 504. — - 98, Ueber die Chromosomenzahl beim Menschen, Anat. Anzeiger, Bd. xiv, S. 171. Flesch, Max, 80, Untersuchungen iiber dei Grundsubstanz des hyalinen Knorpels, S. 1-102, 5 T., Wiirzburg. Flint, J. M., 1900, The Blood-vessels, Angiogenesis, Organogenesis, Reticulum, and Histology of the Adrenal, Contributions to the Science of Medicine, pp. 153-228, Johns Hopkins Press, 1900. Fol, Hermann, 84, Lehrbuch der vergleichenden mikroskopischen Anatomie, u.s.w., I. Lief; Die mikroskopisch-anatomische Technik, S. 1-208, 84 Fig. (2. Lief, S. 209-452, 136 Fig., ist von M. Bedot, 96, herausgegeben. ) Leipzig. Foster, M., und F. M. Balfour, 74, The Elements of Embryology, London, 1. Theil (Hiihnchenj, Deutsch von N. Kleinenberg, 267 Sn., 71 Fig., Leipzig, 1876. Fottinger, Alex., 80, Sur les terminaisons des nerfs dans les insectes, Arch. Biol., Tome 1, pp. 279-304, T. 10. Frommel, R., 86, Beitrag zur Histologic derEileiter, in Miinchener med. Wochenschr. , 33. Tahrg., Nr. 26. FUrbringer, Max, 77, Ueber das Gewebe des Kopfknorpels der Cephalopoden, in Morph. Jahrb., Bd. m, S. 653-658, 1 Fig. Fusari, R., 91, De la terminaison des fibres nerveuses, dans les capsules surrenales des Mammiferes, in Arch. Ital. Biol., Tome xvi, pp. 262-275, l Pi- Gad, J., 95, Ueber eine leichte and sichere Methode (von Chr. Sihler) die Nerven- endigung an Muskelfasern und Gefassen nachzuweisen, Verh. Phys. Ges., Berlin, in Arch. Anat. u. Phys., Phys. Abth., S. 202-208. Gardner, M., 97, Zur Frage iiber die Histogenese des elastichen Gewebes, in Biol. Centralbl., Bd. xvn, S. 394-418. Gaule, J., 81, Das Flimmerepithel der A ricia fcetida, in Arch. Anat. u. Phys., Phys. Abth., S. 153-159, 1 T. Gawronski, X. von, 94, Ueber Verbreitung und Endigung der Nerven in den weib- lichen Genitalien, Vorlaufige Mittheilung, in Centralbl. Gynak., Nr. II. Geberg, A., 85, Ueber direkte Anastomosen zwischen den Arterien und Venen in der Nierenkapsel, in Internat. Monatsschr. Anat. Hist., Bd. II, S. 223-229, T. 13, 14. (Die Tafelerklarung bezieht sich falschlich auf : T. 15 und die T. 13 und 14 tragen die Nummern des 1. Bandes der Zeitschrift.) Gegenbaur, C. , 64, Ueber die Bildung des Knochengewebes, in Jena. Zeitschr. Naturw., Bd. I, S. 363-369, I T. — 67, Ueber die Bildung des Knochengewebes, in ibid. , Bd. Ill, S. 206-246, 2 T. Gehuchten, A. van, 93, Les terminaisons nerveuses intra-epidermiques chez quelques mammiferes, in La Cellule, Tome IX, pp. 301-331, 2 PI. REFERENCES TO LITERATURE 467 (iehuchten, A. van, 97, Le Systeme nerveux de l'homme, pp. XXVI und 941, 619 Fig., Louvaio (z Autlage). Qensch, II., 81, Die Blutbildung auf dem Dottersack bei Knochenfischen, in Arch. mikr. Anat., Bd. XIX, S. 144-146. Gerlach, J., 58, Mikmskopische Studien aus dem Gebiete der menschlichen Mor- phologic, S. vi und 1-72, ST., Erlangen. — 71, 72, Von dem Rfickenmark, in Handbuch, Lehre von den Geweben, Strieker, S. 665-693, Fig. 217-229, Leipzig. Gerota, D., 96, (Jeber Lymphscheiden des Auerbach'schen Plexus myentericus der Darmwand, in Sitz-Ber. Akad. Berlin, S. 887 und 888. Gibbes, Heneage, 80, On the Structure of the Spermatozoon, in Quart. Journ. Micr. Sc. (X. S. 1, Nr. 63, pp. 320, 321, 1 Fig. Giesbrecht, YV. Vergl. Andres. Golgi, Camillo, 89, Annotazioni intorno all' istologia dei reni dell' uomo e di altri mam- miferi e sull' istogenesi dei canalicoli oriniferi, in Atti. Accad. Lincei Rend. (4) vol. v, sem. 1, pp. 324-342, 3 Fig. — 93, Sur la fine organisation des glandes peptiques des Mammiferes, in Arch. Ital. Biol., Tome xix, pp. 448-453, 7 Fig., auch in Gazz. Med. Pavia, Anno 2, pp. 241, 247. — 94, Untersuchungen iiber den feineren Bau des centralen und peripherischen Xerven- systems, S. 1-272, 30 T., Ueutsch v. R. Teuscher, Jena (enthalt sammtliche Unter- suchungen Golgi's iiber das obige Thema seit 1871 ). Golubew, W. Z., 93, Ueber die Blutgefasse in der Niere der Saugethiere und des Menschen, in Internat. Monatsschr. Anat. u. Phys., Bd. X, S. 541-598, T. 22-24. Goppert, E. , 94, Ueber die Herkunft des Wrisberg'schen Knorpels, Ein Beitrag zur vergleichenden Anatomie des Saugethierkehlkopfes, in Morph. Jahrb., Bd. xxi, S. 68-151, T. 3 und 4, 13 Textfig. Gotte, Alexander, 68, Zur Morphologie der Haare, in Arch. mikr. Anat., Bd. iv, S. 273-322, T. 19, 20. Gottschau, M., 83, Struktur und embryonale Entwickelung der Nebennieren bei Saugethieren, in Arch. Anat. u. Phys., Anat. Abth., S. 412-458, 2 T. Grenacher, M., 79, Einige Notizen zur Tinktionstechnik, besonders zur Kernfarbung, in Arch. mikr. Anat., Bd. XVI, S. 463-471. Griinstein, 99, Zur Innervation der Hamblase, Arch. mikr. Anat., Bd. i.v. Gscheidlen, Richard, 76-79, Physiologische Methodik, Ein Handbuch der prak- tischen Physiologie, Braunschweig, S. I-640, 462 Fig. (nicht vollendet). Haeckel, Heinrich, 94. Vergl. Bardeleben. Halliburton, W. I)., 93, Lehrbuch der chemischen Physiologie und Pathologie, S. xii und 1-883, 104 Fig., Deutsch von K. Kaiser, Heidelberg. Hamburger, Ove, 90, Ueber die Entwickelung der Saugethierniere, in Arch. Anat. u. Phys., Anat. Abth., Suppl. Bd., S. 15-51, T. 3, 4. Hammer, Bernh., 91, Ueber das Verhalten von Kerntheilungsfiguren in der mensch- lichen Leiche, Inaug. -Diss. , Berlin, 39 Sn. Harz, W-, 83, BeitrSge zur Histologic des Ovariums der Saugethiere, in Arch. mikr. Anat., Bd. XXII, S. 374-407, T. 15. Hay em, Georges, 89, Du sang et de ses alterations anatomiques, pp. xxvi und 1-1035, 126 Fig., Pari-. Heidenhain, M., 92, 1, Ueber die Riesenzellen des Knochenmarkes und ihre Cen- tralkSrper, in Sitz. -Ber. Phvsik.-Med. Ges., Wiirzburg, S. 130-133. — 92, 2, Ueber Kern und Protoplasma, in Festschr., Kolliker, Leipzig, S. 109-166, T. 9-1 1. 468 REFERENCES TO LITERATURE. Heidenhain, M., 94, Neue Untersuchungen iiber die Centralkorper und ihre Bezieh- ungen zum Kern- und Zellprotoplasma, in Arch. mikr. Anat., Bd. XLIII, 423-758, T. 26-31. — 96, Noch einmal iiber die Darstellung der Centralkorper durch Eisenhamatoxylin nebst einigen allgemeinen Bemerkungen iiber die Hamatoxylinfarben, in Zeitschr. Wiss. Mikroskopie, Bd. XIII, S. 1S6-199. 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Schweigger=Seidel, F. , 65, Die Nieren des Menschen und der Saugethiere in ihreni feineren Baue, S. I-92, 4 T., Halle. — 71, Das Herz, in Handb. Lehre von den Geweben, Strieker, S. 177-190, 5 Fig., Leipzig. Seipp, Ludwig, 95, Das elastische Gewebe des Herzens, in Anat. Hefte, Bd. vi, S. 63-116, T. 3, 4. Sherrington, 94, On the Anatomical Constitution of Nerves of Skeletal Muscles, with Remarks on Recurrent Fibers in the Ventral Spinal Nerve-root, Journ. Phys., vol. XVII. Smirnow, A., 88, Ueber die Zellen der Descemet'schen Haut der Cornea bei Vogeln, in Protokoll Ges. Naturf. Universitat Kasan (Beilage), Nr. 101, 4 Sn. (russisch). Smirnow, 95, Ueber die sensiblen Nervenendigungen im Herzen bei Amphibien und Siiugethieren, Anat. Anzeiger, Bd. x. Sobotta, J., 91, Beitrage zur vergleichenden Anatomie und Entwickelungsgeschichte der Uterusmuskulatur, in Arch. mikr. Anat., Bd. xxxvni, S. 52-100, T. 1. — 96, Ueber die Bildung des Corpus luteum bei der Mans, in Arch. mikr. Anat., Bd. xlvii, S. 261-308, T. 15-17. — 97, Ueber die Bildung des Corpus luteum beim Kaninchen, u.s.w., in Anat. Hefte, 1. Abth., Bd. VIII, S. 471-521, T. 42-48, 1 Textfig. Solger, B., 89, I, Zur Struktur der Pigmentzelle, in Zool. Anzeiger, 12. Jahrg. , S. 67»- 6 73. * F »g- — 89, 2, Ueber Knorpelwachsthum, in Fortschr. Med., Bd. vii, S. 849-855, 1 Fig.; auch in Verh. Anat. Ges., 3. Vers., Berlin, 1890, S. 67-71. — 89, 3, Kohlensaures Ammoniak, ein Mittel zur Darstellung des Sarkolemmas, in Zeit. Wiss. Mikroskopie, Bd. VI, S. 189. — 91, Zur Kenntniss der Pigmentzellen, in Anat. Anzeiger, 6. Jahrg., S. 162-165, 2 Fig. — 92, Zelle und Zellkern, in Thiermedizin. Vortrage, 61 Sn., I T., Leipzig. — 96, Ueber den feineren Bau der Glandula submaxillaris beim Menschen, mit beson- derer Beriicksichtigung der Driisengranula, in Festschrift f. C. Gegenbaur, Bd. II, S. 181-248, 2 T. Spalteholz, W., 93, Die Vertheilung der Blutgefasse in der Haut, I. in Arch. Anat. u. Phys., Anat. 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REFERENCES I<> LITERATURE. 48 1 Waldeyer, \\\, 71, Ficr>tuck unOuble knife, 21 staining, 43 of cells, 69 Doyere's elevation, 147 Ductus endolymphaticus, 440, 454 Dura mater, 393 EAR, 435 external, 435 internal, 439 middle, 437 technic of, 455 vestibule of, 439 Ectoderm, 51, 73 tissues derived from, 73 Egg tubes, primary, of Pfliiger, 307 Ehrlich-Biondi triple stain, 45 Ehrlich's hematoxylin, 42 leucocytic granules, 174 methylene-blue method for ganglion cells and nerve-fibers, 402 neutrophile mixture, 206 Ejaculatory ducts, 330 Elastic fibers, 91 fibrous tissue, 98 membrane, anterior, of cornea, 410 posterior, of cornea, 411 Eleidin, 343 Embryonal cartilage, 99 Enamel, 213 germs, 217 prisms, 213 Encoche d' ossification, 1 12 End-brush, 147, 15 1 End-bulb of Krause, 1 54 cylindric, 157 Endocardium, 190 Endolymph of membranous labyrinth, 453 Endomysium, 1 29 Endoneurium, 1 45 Endoplasm, 188 End-organs, nerve, neuromuscular, 158. See also Nerve end-organs, neuro- muscular. neurotendinous, 162 Endosteum, 185 Endothelial and mesothelial cells, relations of, 87 cells, 74, 86 demonstration of, 88 Endothelium, 85 anterior, of iris, 416 End-piece of Retzius, 323 Engelmann's accessory disc, 127 Entoderm, 51, 73 tissues derived from, 74 Eosinophile cell. 187. See also Cell, eosin- ophil. 488 INDEX. Eosinophile granules, 174. See also Gran- ules, eosinophile. Ependymal cells, 392 Epicardium, 191 Epidermis, 341 compensation for desquamation of, 344 layers of, 341 nerves of, technic of, 364 pigment in, 346 technic of, 362 Epidural space, 394 Epilamellar plexus, 232, 358 Epimysium, 1 29 Epiphysis, 380 Epithelial cells, isolated, examination of, 87 tissue, 74 technic of, 87 Epithelium, anterior, of crystalline lens, 428 ciliated, islands of, in cervical canal, 318 columnar, pseudostratified, 77 simple, 77 examination of, 87 germinal, of ovary, 307 glandular, 81 neuro-, 85 of urethra, 333 posterior, of iris, 416 respiratory, 280 simple, 76 cubic, 76 squamous, 76 stratified, 77 columnar, 79 squamous, 78 technic of, 87 transitional, 79 Eponychium, 356 Epoophoron, 322 Erlicki's fluid, 25 Erythroblasts, 186 Erythrocytes, 169 Esophagus, 233 technic for, 271 Eustachian tube, 438, 439 Excretory duct of testis, 329 ducts, membrane of, 82 Exoplasm, 188 External auditory canal, 435, 436 limiting membrane of retina, 420, 422 Eye, 407 anterior lymph-channels of, 429 development of, 407 fetal blood-vessels of, 429 general structure of, 407 pigment layer of, 418 protective organs of, 430 technic for, 433 tunics of, 407 Eyeball, 407 interchange of fluids in, 429 Eyelids, 430 conjunctival portion of, 430 cuticular portion of, 430 middle layer of, 432 " third," 432. Fallopian tubes, 316 nerve-supply of, 320 technic for, 340 Farrant's gum glycerin, 48 Fasciculus gracilis, 370 Fat, absorption of, by intestine, 256 lobules, 99 Fat-cell, scheme of, 99 Fat-marrow, 185,188 Female genital organs, 306 pronucleus, 67 Fenestra cochleae, 438 rotunda, 438 Fenestrated membranes, 98 Ferrein's pyramids, 289 Fertilization, diagram of, 66 process of, 65 Fetal blood-vessels of eye, 429 Fiber, cone-, of retina, 419 dentinal, 215 elastic, 91 intrafusal, of neuromuscular nerve end- organs, 159 Kupffer's reticular, 185 lens, 428 Miiller's, of retina, 422 muscle-, striped, 124 nerve-, 142. See also Nerve-fiber. Purkinje's, 190 muscle-cells of, 132 Remak's, 145 rod-, of retina, 419 Sharpey's, 106 sustentacular, of Deiters's cells, 450 tunnel-, 452 white, of connective tissue, 90 Fiber-baskets of retina, 423 Fibrae circulares, 415 Fibrillar mass of Flemming, 53 Fibrils of axial cord, demonstration of, 1 65 Fibrin, 176, 207 demonstration of, 208 Fibrocartilage, white, 102 Fibro-elastic cartilage, 102 Filiform papillae, 222 Filum terminale, 365 Fimbriae linguae, 223 Fixation to slide, of sections, 38 Fixing methods, 22 solutions, 22 acetic sublimate, 24 alcohol, 22 chromic acid, 24 corrosive sublimate, 23 for cartilage, 120 Erlicki's, 25 Flemming' s, 22 Fol's, 23 formalin, 25 formol, 25 Hayem's, 203 Hermann's, 23 Miiller's, 24 nitric acid, 24 osmic acid, 22 for cartilage, 1 20 INDEX. 489 Fixing solutions, picric acid, 23 picric-nitric acid, 23 picric-osmic-acetic acid, 24 picric- sublimate-osmic acid, 24 picrosulphuric acid, 23 Rabl's, 24 Zenker's, 25 Flagellate cell, 53 Flagellum of spermatosome, 323 Flemming's fibrillar mass, 53 interfibrillar substance, 53 solution, 22 for fixing cells, 69 Flower-like nerve-ending, 162 Fluids in eyeball, interchange of, 429 Foam-structures, 73 Foliate papillce, 223 Follicles, simple, of adenoid tissue, 177 Follicular cells, 334 Folliculi linguales, 225 Fol's solution, 23 Fovea centralis, 421 Fontana's spaces, 415 Foramen apicis dentis, 213 Foramina nervosa, 446 papillaria, 293 Formalin as fixing solution, 25 Formol as fixing solution, 25 Fragmentation, direct, 65 Free-hand sectioning, 21 Freezing apparatus for sliding microtome, 35 Friedlander's glycerin-hematoxylin, 42 Front lens, 19 Fundus of fovea centralis, 421 Fungiform papillae, 222 Funiculi of nerve-trunk, 145 compound, 147 Ganglia, 382 spinal, 382 sympathetic, 385 Ganglion cell, 134 bipolar, 135, 137 chromatophile granules of, 134 demonstration of, 1 66 layer of retina, 420, 425 multipolar, 137 of Dogiel, in spinal ganglia, 384 sympathetic, 140 technic of, 399 unipolar, 137 spiral, of cochlea, 452 Gartner's duct, 322 Gastric crypts, 237 glands, 237 body of, 238 fundus of, 238 neck of, 238 Gastrulation, 73 Gelatin-carmin as injection fluid, 48 Gelatinous substance of Rolando, 367 Genital corpuscles, 155 organs, female, 306 Genital organs, male, 323 Genito-urinary organs, 2S7 Germ centers of lymphoid tissue, 1 75, 178 layers, 51 Germinal cells, 85 epithelium of ovary, 307 spot, 56 vesicle, 65 Germs, enamel, 217 < liant-cells, 64, 187 ( lianuzzi's crescents, 229 Giraldes, organ of, 329 Gland-cell, 81 Glands, alveolar, 84 Brunner's, 236, 246 capsule of, 84 carotid, 202 ceruminous, 357, 436 ciliary, 414 Moll's, 430 circumanal, 250, 357 classification of, 82 coil-, of skin, 357 gastric, 237. See also Gastric glands. lacrimal, 432 lenticular, 241 Lieberkuhn's, 245 lymph-, 177, 178. See also Lymph- glands. mammary, 359. See also Mammary glands. mixed, 230 mucous, 228 multicellular, 82 of Bartholin, 322 of Bowman, 457 of Cowper, 332 of Littre, ^^^ of Moll, 357 of Montgomery, 361 of mouth, small, 231 of oral cavity, 227 of skin, 357. See also Skin, glands of. of Tyson, 334 parotid, 228 pineal, 350 saccular, 84 salivary, 228. See also Salivary glands. sebaceous, 358 serous, 228 structure of, 82 sublingual, 228 submaxillary, 230 sudoriparous, 357 suprarenal, 301. See also Suprarenal glands. sweat-, 357 thymus, 188 thyroid, 284 tubular, 82 branched, 83 compound, 83 reticulated, S3 Glandula carotica, 202 490 INDEX. Glandulas buccales, 211 duodenales, 236 labiates, 211 Glandular cells, 54, 239. See also Cell, glandular. epithelium, 81 Glassy layer of choroid, 412, 414 membrane, 352 Glia covering of pia mater, 396 Glisson's capsule, 257 Glomeruli arteriosi cochleae, 453 Glomerulus, 287 Glomus caroticum, 202 Glossary of literature, 460 Glycerin, Farrant's gum, 48 mounting in, 47 Glycerin-albumen for fixing paraffin sec- tions to slide, 38 Goblet cells, 81 Gold chlorid as stain for capsules of car- tilage, 120 Golgi-Mazzoni corpuscle, 350 Golgi's cell of cerebral cortex, 377 methods for demonstration of ganglion cells, 399 mixed, 401 rapid, 401 slow, 400 preparations, methods of mounting, 402 tendon spindle, 162 Goll's column, 370 Gowers's columns, 370 Graafian follicle, 309 antrum of, 309 bursting of, 313 Grandry's corpuscles, 350 technic for, 364 Granular cells, 95 of cerebellar cortex, 375 layer, Tomes', 220 sole plate, 148 Granules, acidophile, technic for, 205 amphophile, technic for, 205 basophile, 174 technic for, 206 demonstration of, in cells, 71 deutoplastic, 31 1 eosinophile, 174 cells with, 187 technic for, 205 interstitial, of Kolliker, 129 leucocytic, Ehrlich's, 174 mast-cell, technic for, 205 neutrophile, 174 technic for, 206 yolk, 311 Gray matter, 136 substance of spinal cord, 365 Ground bundle, anterior, 370 plexus of cornea, 412 Ground-substance, interfascicular, 97 of areolar connective tissue, 93 of cartilage, 99 Gruber's dendritic fibrous structures, 437 Gustatory organs, 223 Hair, 350 auditory, 448 bulb, 35 1, 354 cells of utriculus, 442 cortical layer of, 35 1 cuticle of, 351 follicle, 351 nerve-fibers of, 354 germ, 351 glassy membrane of, 352 growth of, 353 medullary substance of, 35 1 olfactory, 457 papilla, 351 root, 351 root-sheaths of, 351 inner, 351 outer, 351 shaft, 351 shedding of, 354 technic for, 364 Hamulus, 444 Hassall's corpuscles, 189, 190 Haversian canals, 103 spaces, III Hayem's solution, 203 Hearing, organ of, 435 technic for, 455 Heart, 168, 190 coats of, 190 elastic tissue of, distribution in, 191 muscle-cell, 149 nerve supply of, 1 92 Heidenhain's demilunes, 229 iron-lack hematoxylin, 42 Helicotrema, 444 Heliotropism, 54 Heller's plexus, 251 Hemalum as stain, 42 Hematin, 169 Hematoidin, demonstration of, 207 Hematoxylin as stain, 41. See also Stains. Delafield's, for demonstrating canalicular system in cartilage, 120 Hematoxylin-eosin as stain, 44 Hematoxylin-safranin of Rabl as stain, 44 Hemin, 169 isolation of, 207 Hemoglobin, 169 demonstration of, 206 Hemokonia, 176 Henle's layer, 351 loop, 288, 291 ascending limb of, 288, 291 descending limb of, 288, 291 sheath, 147 Hensen's cells, 449, 450 median disc, 127 Hepatic cells, cords of, 258 cords, 258 Herbst's corpuscles, 158, 350 technic for, 364 Hermann's solution, 23 Heterotypic form of mitosis, 64 Highmore, body of, 325 Ililum of lymph-gland, 178 INDEX. 491 Histology, general. 51 special, 16S Homeotypic mitosis, 64 Honing microtome knife, 36 Horn-sheath of nerve-fibers, 142 1 [owship's lacunae, 1 1 1 Huber's method for mounting Golgi's pre- parations, 402 Huschke's auditory teeth, 446 Huxley's layer. 351 Hyaline cartilage, 99 Hyaloid arteries, posterior, 429 canal, 429 membrane, 427 [asm, 53 Hydatid* of Morgagni, 322 Hydrochloric acid as decalcifying fluid, 122 Hydrotropism, 54. Hymen, 321 Hypolamellar plexus, 232 Hypophysis, 3S1 Imbedding, 25 celloidin, 2S. See also Celloidin imbed- ding. celloidin-paraffin, 29 paraffin, 26. See also Paraffin imbed- tissues, box for, 26 Immersion lens, 19 Implantation cone, 135 I ndifferent fluids, 21 Kronecker's, 21 physiologic saline solution, 21 Ranvier's iodin and potassium iodid, 21 Ripart and Petit'-. 21 Schultze's iodized serum, 21 Indirect cell-division, 57 Inferior nasal artery of retina, 427 vein, 427 papillary artery, 426 vein, 426 Infiltration, 25 celloidin, 28. See also Celloidin infil- tration. celloidin-paraffin, 29 paraffin, 26. See also Paraffin infiltra- tion. Infundibula, 279 Injection fluids. 4S Berlin blue, 49 gelatin-carmin, 48 methods of. introduction to, 48 of lymph-channels. 49 of lymph-spaces, 49 of lymph-vessels, 49 Inner molecular layer of retina, 420, 423 nuclear layer of retina, 420. 423 Intercellular bridges, 75, 342 demonstration of, 88 space-. 7; substance. 73 Interfascicular ground-substance, 97 Interfibrillar substance of Flemming, 53 Interglobular spaces, 215 Interlobular duct <>f pancreas, 266 Intermediate disc of Krause, 127 tubule of pancreas, 266 Internal auditory artery, 452 limiting membrane, 422 Interpapillary epithelial processes, 79 Interstitial granules of Kolliker, 129 Intertubular cell-masses of pancreas, 267 Intestine, 235 absorption of fat by, 256 blood supply, 251 large, 249 lymph supply of, 25 1 mucous membrane of, structure of, 235 nerve supply of, 251 secretion of, 256 small, 243 axial canals of, 253 crypt of, 248 lacuna of, 248 technic for, 271 Intracapsular plexuses, 387 Intralobular arteries of kidney, 296 vein, 258, 261, 298 Iodo-iodid of potassium stain to demon- strate glycogen in cartilage, 121 Iris, 407, 412, 415 diaphragm, 18 layers of, 415, 416 nerve supply of, 417 Islands of ciliated epithelium in cervical canal, 318 Isolating fluids, 87 Japanese method for fixing paraffin sec- tions to slide, 39 Jung's sliding microtome, ^2t 34 Karyokinesis, 57 Karyokinetic cell-division, heterotypic, 336 homeotypic, 336 Karyolytnph, 55 Karyolysis, 68 technic of, 68 Keratohyalin, 342 technic for, 362 Kidney, 287 arched collecting portion of tubules, 288, 293 blood-vessels of, 295 cortical substance of, 288 distal convoluted portion of tubules, 288, 292 intercalated portion of tubules, 2S8, 292 medullary substance of, 288 pelvis of, 300 proximal convoluted portion of tubules, 288. 290 straight collecting tubules of, 288 Knife, double, 21 Kolliker' s interstitial granules, 129 muscle columns, 126 492 INDEX. Kopsch's technic for ganglion cells, 402 Krause's end-bulb, 154 cylindric, 157 intermediate disc, 127 transverse membrane, 127 Kronecker's fluid, 21 Kronig's varnish, 48 Kupffer's method of treating liver tissue, 273 reticular fibers, 185 Kytoblastema, 56 Labium tympanicum, 446 vestibulare, 445 Labyrinth, bony, 439 development of, 454 membranous, 439, 440 osseous, 439 Lacrimal apparatus, 432 gland, 432 sac, 433 Lacteals of villi, 253 Lacuna of small intestine, 248 Lacunae, Howship's, III of bone, 103, 104 of cartilage, IOO Lagena, 444 Lamellae, 97 marrow, 104 of bone, 104 periosteal, 104 Lamina basilaris propria, 447 choriocapillaris, 413 cribrosa, 409, 425 elastica interna, 195 fusca, 409 propria of oral cavity, 211 reticularis, 447, 451 spiralis membranacea, 444, 447 ossea, 444, 445 suprachoroidea, 412 vasculosa Halleri, 413 Langerhans, areas of, 267 cells of, 266 Lanthanin, 56 Large intestine, 249 Larynx, 275 Lateral column, 367 mixed, 370 Layer of Henle, 351 of Huxley, 351 Leucocytes, 173, 187 polynuclear, amitotic division of, 64 Lens, 407 apochromatic, 19 capsule, 428 collective, 19 crystalline, 428 fibers, 428 front, 19 immersion, 19 ocular, 19 suspensory ligament of, 428 technic of, 434 Lenticular glands, 241 Leydig's cells, 431 Lieberkiihn's crypts, 245 glands, 245 Ligaments, 96 Ligamentum pectinatum iridis, 415 spirale, 444, 446 Limbus spiralis, 445 Limiting membrane, external, 420, 422 internal, 422 Lingual mucous membrane, 221 papillae of, 221 papillae, 221 Linin, 55 Liquor folliculi, 309 Literature, glossary of, 460 Littre's glands, ^2 Liver, 257 development of, 265 lobules, 257 lymph -vessels of, 263 nerves of, 264 technic of, 274 technic of, 272 Kupffer's method, 273 vascular system of, 260 Lobes, renal, 287 Lobules, fat, 99 liver, 257 spleen, 182 Loop of Henle, 288, 291. See also Henle 1 s loop. Lowit's method of demonstrating nerve- fibers, 167 Lung, blood-vessels of, 281 lymphatics of, 282 tissue, 281 Lunula, 356 Lutein cells, 314 Lymph, 168 canalicular system, 94 capillaries, 201 Lymphatic glands, capsule of, 178 technic for, 208 system, 200 Lymph-channels, anterior, of eye, 429 injection of, 49 Lymph-follicles of tongue, 225 of tonsils, 225 solitary, 177 Lymph-glands, 177, 178 Lymph-nodules, 177 agminated, 177 Lymphocytes, 173, 175, 187 Lymphoid tissue, 177 Lymph-sinus, 179 Lymph-spaces, 201 injection of, 49 periaxial, of neuromuscular end-organ, 160 perichoroidal, 413 Lymph-vessels, 168, 200 injection of, 49 Macerating fluids, 87 Macula acustica sacculi, 441 utriculi, 441 INDEX. 493 Macula lutea, 421 region of, 421 Magenta red as --tain for connective tissue, 119 Male genital organs, 323 pronucleus, 67 Malpighian bodies, 180, 182 corpuscles, 180, 182, 287, 289 layer, technic of, 363 Mammary glands, 359 human, structure of, 360 lymphatics of, 36 1 , milk of, 361 Mantle fibers, 63 Marginal thread of spermatosome, 323 zone, 75 Marrow, bone-, 185. See also Bone-mar- row. cell, 186 fat-, 185, 188 spaces, primary, 109 secondary, III Martinotti's cells of cerebral cortex, 377 Ma>t-cell granules, technic of, 205 Matrix of areolar connective tissue, 93 of cartilage, 99 of nail, 355 sulcus of, 355 Mayer's picric-magnesia-carmin, 44 Median disc of Hensen, 127 Mediastinum testis, 325 Medullary cords, 179 cortex, projection fibers of, 378 rays, 288 sheath, 142 technic, 397-399 substance, association fibers of, 378 centripetal fibers of, 378 commissural fibers of, 378 of cerebellar cortex, 375 climbing fibers of, 375 messy fibers of, 375 of cerebral cortex, 378 of hair, 351 of kidney, 288 of ovary, 306 terminal fibers of, 378 Medullated nerve-fibers, 144 Meissner's corpuscles, 155 technic of, 364 plexus, 255 Membrana capsulopupillaris, 429 praeformativa, 220 prima of epithelium, 75 propria, 84 papillaris, 429 tectoria Cortii, 447, 451 Membranous labyrinth, 439, 440 Meninges of central nervous system, 393 Merkel's terminal disc, 127 Mesameboid cells, 74 Mesenchyme, 74 Mesoderm, 51, 73 cells of, 74 Mesothelial and endothelial cells, relations of, 87 Mesothelium, 74, 85 Metakinesis, 62 Metaphases, 57, 62 Methylene-blue for staining of nerve-fibers, 403 Methyl-green, 43 Metschnikoff' s phagocytes, 53 Microscope and its accessories, 17 coarse adjustment of, 18 compound, 17 description of, 17 fine adjustment of, 18 parts of, 17 simple, 17 Microscopic preparation, 20 technic, introduction to, 1 7 Microtome, 30 knife, honing of, 36 sharpening of, 36 laboratory, 31 rocking, 31 sliding, 31 cutting celloidin sections with, 33 paraffin sections with, 31 freezing apparatus for, 35 of Jung, 33, 34 varieties of, 37 Migratory cells, 94, 96, 1 75 Milk, 361 Mitosis, 57 demonstration of, 69 heterotypic form of, 64 homeotypic, 64 Mitotic cell-division, diagrammatic, 58 of fertilized whitefish eggs, 60 Mixed gland, 230 lateral column, 370 Modiolus, 443 Molecular movement of cells, 53 Moll's ciliary glands, 430 glands, ciliary, 357 Monaster, 62 Mononuclear eosinophile cells, 187 Monostratified cells of retina, 425 Montgomery's glands, 361 Morgagni's hydatids, 322 Morula mass, 73 Mother skein, 61 Motor endings in striated voluntary mus- cle, 150 end-plate, 148 nerve-endings, 147 neurones, 138 peripheral, diagram of, 148 Mounting, 21, 46 Altmann's method of, 71 Mouth, small glands of, 231 Muchematein, 271 Mucicarmin, 271 Mucosa of oral cavity, 211 Mucous glands, 228 membrane of intestine, 236 Midler's fibers, 415 of retina, 422 fluid, 24 Multicellular glands, 82 494 INDEX. Muscle-casket, 127 Muscle-cell, 123 cardiac, 132 heart, 149 nonstriated, 124, 149 of fibers of Purkinje, 132 smooth, 124 striped, 123 unstriped, 123 Muscle-columns of Kolliker, 126 Muscle-fasciculi, 129 Muscle-fibers, striped, 124 Muscular tissue, 123 technic of, 132 Muscularis mucosae of intestine, 236 of pharynx, 234 of small intestine, 246 Myelin sheath, 142 Myelocytes, 186 Myeloplaxes, 187 Myoblasts, 13 1 Myocardium, 191 Nail, 355 bed, 355 sulcus of, 355 body of, 355 lunula of, 356 matrix, 355 sulcus of, 355 root, 355 walls, 355 Nasal artery, inferior, of retina, 427 superior, of retina, 427 cavity, 456 technic of, 457 duct, 433 vein, inferior, of retina, 427 superior, of retina, 427 Nerve, auditory, 452 end-organs, neuromuscular, 158 axial sheath of, 159 distal polar region of, 159 equatorial region of, 159 intrafusal fibers of, 159 proximal polar region of, 159 neurotendinous, 162 end-organs of Golgi-Mazzoni, 350 of Grandry, 350 of Herbst, 159 of Krause, 154 of Meissner, 155 of Ruffini, 350 optic, 425. See also Optic nerve. pilomotor, 355 Nerve-cell, 134. See also Ganglion cell. Nerve-ending, annulospiral, 162 flower-like, 162 motor, 147 sensory, 151 encapsulated, 152, 154 free, 152 Nerve-fiber layer of retina, 425 Nerve-fibers, 142 Nerve-fibers ending in muscle tissue, telo- dendria of, 147 medullated, 144 nonmedullated, 145 staining of, with methylene-blue, 403 Nerve-trunk, peripheral, diagram to shew composition of, 146 Nervous system, central, 365 blood-vessels of, 397 membranes of, 393 technic of, 397 tissue, 133 technic of, 164 tunic of eye, 407, 418 Neura, 134 Neuraxones, 134 Neurilemma, 143 nuclei, 143 Neurites, 134 Neuroblasts, 133 Neurodendron, 134 Neuro-epithelial cells, 85 Neuro-epithelium, 85 Neuroglia, 392 staining of, 406 Neurogliar cells, 393 Neurokeratin, 142 Neuromuscular nerve end-organs, 158. See also Nerve end-organs, neuromuscular. Neurone, 134 cell-bodies of, 134. See also Ganglion cell. centripetal, peripheral, 139 motor, 138 peripheral, diagram of, 148 relationship of, 389 sensory, peripheral, 139 diagram of, 152 Neuroplasm, 142 Neuropodia, 136 Neurotendinous nerve end-organs, 162 Neutrophile granules, 174 technic of, 206 mixture, Ehrlich's, 206 Nitric acid, aqueous solution of, as decal- cifying fluid, 122 as fixing solution, 24 Nodes of Ranvier, 143 demonstration of, 164 Nodules, 177 cortical, 179 lymph-, 177. See also Lymph-nodules. secondary, 175, 178 terminal, of spermatosome, 323 Nonmedullated fibers, demonstration of, 166 nerve-fibers, 145 Nonstriated muscle-cell, 124, 149 Normoblasts, 186 Nuclear division, 56 membrane, 56 sap, 55 stains, 40 Nucleated red blood-cells containing hemo- globin, 186 Nucleolus, 51 true, 56 Nucleoplasm, 55 INDEX. 495 Nucleus, 51, 55 dorsal is, 367 segmentation, 65 Nuel's space, 450 Objective system, 19 Ocular lens, 19 Odontoblasts, 215, 216, 218 Oil of bergamot as clearing fluid, 47 of cloves as clearing fluid, 47 of origanum as clearing fluid, 47 Olfactory bulb, 379 glomerular layer, 379 granular layer, 380 layer of mitral cells, 379 of peripheral fibers, 379 of pyramidal cells, 379 molecular layer of, 379 stratum gelatinosum, 379 cell, 456 hairs, 457 region of nasal cavity, 456 Oocytes, 312 Oppel method for demonstrating reticular liver libers, 274 Optic cup, 408 nerve, 407, 425 blood-vessels of, 426 papilla, 420 region of, 420 stalks, 408 vesicles, primary, 407 secondary, 408 Ora serrata, 422 Oral cavity, 211 glands of, 227 technic of, 269 Orbiculus ciliaris, 414 Orcein as stain for connective tissue, 1 18 Organ of Corti, 447. See also Cor/i's organ. Organs, blood-forming, 168 Osmic acid as fixing solution, 22 for cartilage, 1 20 Osseous labyrinth, 439 Ossification, 107 centers of, 107 groove, 112 ridge, 112 Osteoblasts, 109 Osteoclasts, 1 1 1 Otolithic membrane, 442 Otoliths, 442 Outer fiber layer of retina, 420 molecular layer of retina, 420, 423 Ova, 65 primitive, 307 Ovary, 306 blood-vessels of, 316 cortex of, 306 germinal epithelium of, 307 medullary substance of, 306 stroma of, 306 technic of, 340 Ovula Nabothi, 318 Ovum, 306 Ovum, changes in, during development, 311 ripe, 312 technic of, 340 I >xyi 'hromatin granules, 56 Oxyntic cells, 238 Pacchionian bodies, 395 Pacinian corpuscles, technic of, 364 Pal's method for demonstration of medul- lary sheath, 398 Pancreas, 265 blood supply of, 268 interlobular duct of, 266 intermediate tubule of, 266 intertubular cell-masses of, 267 nerve supply of, 268 technic of, 274 Pancreatic duct, 265 Panniculus adiposus, 346 Papilla spiralis cochleae, 441 Papillae, 78 circumvallate, 223, 225 dentinal, 217 filiform, 222 foliate, 223 fungiform, 222 hair, 351 lingual, 221 optic, 420 region of, 420 tactile, 345 vascular, 345 Papillary artery, inferior, 426 superior, 426 vein, inferior, 426 superior, 426 Paracarmin as stain, 40 Paradidymis, 329 Paraffin imbedding, 26 diagram for, 28 infiltration, 26 diagram for, 28 removal of, 40 sections, cutting of, with sliding micro- tome, 31 distilled water for fixing of, to slide, 3 8 fixing of large number to cover-slips, 39 . glycerin-albumin for fixing of, to slide, 38 Japanese method of fixing to slide, 39 Paralinin, 55 Paranuclein, 56 Paraplasm, 53, 81 Parathyroid glands, 285 Parenchymatous tissues, sectioning of, 21 Parietal cells, 238 Paroophoron, 322 Parotid gland, 228 Pars ciliaris retina-, 414,422 iridica retinae, 422 papillaris, 344 reticularis, 344 Partsch's cochineal solution, 41 496 INDEX. Pellicula, 54 Pelvis of kidney, 300 renal, 299, 300 Penis, 332 erectile tissue of, 333 nerve supply of, 334 Perforating fibers of cornea, 411 Periaxial lymph-space, 160 Pericardium, 191 Pericellular plexuses, 386 Perichondrium, 101 Perichoroidal lymph-spaces, 413 Perilymph of cochlea, 454 Perilymphatic spaces, 201 Perimysium, 129 Perineurium, 146 Periosteum, 203 Peripheral centripetal neurones, 139 motor neurone, diagram of, 148 nerve terminations, 147 sensory neurones, 139 diagram of, 152 Peritendineum, 97 Perivascular spaces, 201 Petit and Ripart's solution, 21 Petit' s canal, 428 Pfliiger's primary egg tubes, 307 Phagocytes, 1 75 Metschnikoff' s, 53 Phalangeal plate, 449, 450 process, 449 Pharynx, 233 Physiologic excavation of retina, 420 Pia intima, 395 mater, 395 Pial funnels, 396 Picric acid as fixing solution, 23 for cell, 69 as stain, 44 Picric-magnesia-carmin as stain, Mayer's, 44 Picric-nitric acid as fixing solution, 23 Picric-osmic-acetic acid solution as fixing fluid, 24 Picric-sublimate-osmic acid solution as fix- ing fluid, 24 Picrocarmin as stain for connective tissue in cartilage, 120 for elastic fibers in cartilage, 1 20 of Ranvier, 43 of Weigert, 43 Picrosulphuric acid as fixing solution, 23 Pigment, 90 cell, 71, 95, 96 in epidermis, 346 layer of eye, 418 membrane, 408 of eye, 407 origin of, 346 Pillar cells, 448 heads of, 448 Pilomotor nerves, 355 Pineal gland, 380 Pituitary body, 381 Plasma cells, 96 Plexus, choroid, 396 Plexus, epilamellar, 232 ground, of cornea, 412 hypolamellar, 232 intracapsular, 387 myentericus, 254 of Auerbach, 254 of Heller, 251 of Meissner, 255 pericellular, 386 subepithelial, of cornea, 412 superficial, of cornea, 412 Plicre palmatae, 318 semilunares, 250 sigmoidea;, 237 transversales recti, 250 Plural staining, 43 Polar body, 65 field, 64 rays, 62 Polarity of cell, 75 Polygonal cells of cerebral cortex, 376 Polykaryocyte, 1 75 Polymorphous cells of cerebral cortex, 377 Polynuclear cells, 64 leucocytes, 64 Polystratified cells of retina, 425 Portal vein, 260 Posterior elastic membrane of cornea, 41 1 epithelium of iris, 416 hyaloid arteries, 429 Potassium bichromate-osmic acid solution, 400 Precapillary arteries, 196 veins, 197 Precartilage, 99 Primary blastodermic layers, 73 germ layers, 73 marrow spaces, 109 optic vesicles, 407 tendon bundles, 96 Primitive ova, 307 seminal cells, 334 Primordial ova, 307 Prominentia spiralis, 446 Promontory ridge, 439 Pronucleus, female, 67 male, 67 Prophases, 57, 60 Prostate, 330 blood-vessels of, 332 nerve supply of, 332 secretion of, 332 Prostatic bodies, 332 concretions, 332 Protoplasm, 51, 8 1 Protoplasmic currents, 68 stains, 40 Protozoa, 51 Pseudopodia, 53 Pulp cords of spleen, 182 Pupil, dilator muscle of, 416 sphincter muscle of, 416 Purkinje's cells, 138 of cerebellar cortex, 374 fibers, 190 muscle-cells of, 132 INDEX. 497 Purkinje's vesicle, 306 Purpurin, alkaline, as stain for calcium carbonate in bone, 122 Pyramidal cells, large, of cerebral cortex, 376 of cerebral cortex, 138 small, of cerebral cortex, 376 columns, crossed, 370 tract, direct, 370 Pyramids of Ferrein, 289 QuiNTUFU hydroquinon developer, 401 Rabl's hematoxylin-safranin stain, 44 solution, 24 Rami cochleares, 452 vestibulares, 452 Ramon y Cajal's technic for retina, 435 Rainier' s crosses, 164, 165 iodin and potassium iodid solution, 21 method for demonstrating spaces in bone, 121 for examination of connective tissue, "7 nodes, 143 demonstration of, 164 picrocarmin, 43 Real image, 19 Recessus camene posterloris, 427 cochlere, 454 Rectum, 249 Red blood-cells, nucleated, containing hemoglobin, 1 86- blood-corpuscles, 169 bone-marrow, 185 Reissner's membrane, 444, 447 Relationship of neurones, 389 Remak's fibers, 145 demonstration of, 166 Renal lobes, 287 pelvis, 299, 300 Renflement biconique, 143 Respiration, organs of, 275 technic of, 286 Respiratory bronchioles, 279 epithelium, 280 region of nasal cavity, 456 accessory cavities of, 456 Rete testis, 325, 327 Retia mirabilia, 199 Retina. 407, 408, 418 blood-vessels of, 426 layers of, 418-420, 423 macula lutea of, 421 Mailer's fibers of, 422 optic papilla of, 420 ora serrata of, 422 pars ciliaris retinae, 422 iridica retinae, 422 relation of elements of, to one another, 423 technic of, 434 Retinaculae cutis, 346 Retzius, end-piece of, 323 32 Ribbon sectioning, 32 Ripart and Petit's solution, 21 Ripe ova, 312 Rocking microtome, 31 Rod -fibers of retina, 419 Rod-visual cells, 418 Rolando's gelatinous substance, 367 Root-sheaths of hair, 351. See also Hair, root-sheaths of. Rose's carmin-bleu de Lyon, 44 Rouleaux, 169, 170 Rudder membrane of spermatosome, 323 Saccular glands, 84 Sacculus, 440, 441, 454 Saccus endolymphaticus, 440, 454 Safranin as stain, 43 Salivary glands, 228 blood-supply of, 232 lymphatics of, 232 nerve supply of, 232 scheme of, 227 Sarcolemma, 125 Sarcolytes, 131 Sarcous elements, 126, 128 Scala media, 444 tympani, 444 vestibuli, 444 Schlemm's canal, 409 Schmidt - Lantermann-Kuhnt's segments, 142 Schultze's iodized serum, 21 Schwann's sheath, 143 Sclera, 407, 409 blood-vessels of, 410 technic of, 434 Scleral conjunctiva, 409 sulcus, inner, 410 Sebaceous glands, 358 Secondary marrow spaces, III nodule, 175, 178 optic vesicle, 408 tendon bundles, 97 Secretion of intestine, 256 process of, 84 vacuoles, 259 Section staining, 40 stretchers, 35 Sectioning, 21, 30 double knife for, 2 1 free-hand, 21 of parenchymatous tissues, 21 ribbon, 32 Segmentation cell, 64 nucleus, 65 Selective stains, 40 Semen, 323 technic of, 340 Semicircular canals, 442 anterior superior vertical, 440 external, 440 horizontal, 440 posterior inferior vertical, 440 Semilunar fold, 443 valves, 191 498 INDEX. Seminal cells, primitive, 334 vesicles, 330 Sense cells, 75 Sense-organs, special, general considera- tions of, 458 Sensory nerve-endings, 151 encapsulated, 152, 154 free, 152 neurones, peripheral, diagram of, 152 Septa renis, 289 Septum posticum, 395 Serous cavities, 201 gland, 228 Sertoli's cells, 326 Sexual cells, matured, 65 Sharpening microtome knife, 36 Sharpey, fibers of, 106 Sheath of Schwann, 143 Sihler's method of demonstrating nerve- endings, 167 Silver-impregnation of thin membranes, 49 Simple epithelium, 76. See also Epithe- lium, simple. microscopes, 17 Sinus, 199 blood, 199 lactiferus, 360 pocularis, 332 Skin, 341 and appendages, 341 technic of, 362 blood-vessels of, 350 glands of, 357 nerve-endings in, 348 nerves of, 348 pigment of, technic of, 363 structure of, technic of, 363 technic of, 362 true, 341 vascular system of, 347 Slides, 20 Sliding microtome, 31. See also Micro- tome, sliding. Small intestine, 243. See also Intestine, small. Smell, organ of, 456 technic of, 457 Sole nuclei, 148 plate, granular, 148 Solitary lymph-follicles, 177 Somatic cell, 65 Soudan III as stain for fat, 120 Special histology, 168 sense-organs, general considerations of, 458 Specimens, drawing of, 20 examination of, 19 permanent, preparation of, 46 Sperma, 323 Spermatids, 66, 336 development of, into spermatosomes, 336 Spermatoblast, 338 Spermatocytes, 66 of first order, 335 Spermatogenesis, 334 Spermatogones, 66 Spermatogonia, 334 Spermatosome, 323 accessory thread of, 323 axial thread of, 323 sheath of, 323 development of, from spermatids, 336 flagellum of, 323 head of, 323 marginal thread of, 323 middle piece of, 323 rudder membrane of, 323 tail of, 323 terminal nodule of, 323 undulating membrane of, 323 Spermatozoa, 53, 65, 66 Spermatozoon, 323. See also Spermato- some. Sphincter muscle of pupil, 416 Spider-cells, 393 Spinal cord, 365 anterior median fissure of, 365 gray substance of, 365 horns of, 367 posterior median septum of, 365 structure of, 365 white substance of, 365 ganglia, 382 ganglion cell of Dogiel, 384 Spindle cells of cerebral cortex, 376 Spiral ganglion of cochlea, 452 Spirem, 6 1 Spleen, 180 lobules, 182 Splenic pulp, 183 Spongioblasts, 392 diffuse, 424 stratum of, 424 Spongioplasm, 53 Staining, 40 double, 43 in bulk, 45 diagram showing method, 46 in section, diagram showing method, 46 neurofibrils and Golgi-nets, Bethe's method for, 405 of cells, 69 of nervous tissue, 402 of neuroglia, 406 plural, 43 purpose of, 40 section, 40 Stains, 40 acid, 40 alkaline purpurin, for calcium carbonate in bone, 122 alum-carmin, 41 anilin, 42 basic, 40 Bismarck brown, 43 borax-carmin, alcoholic, 40 aqueous, 40 carmin, 40 carmin-bleu de Lyon, of Rose, 44 coal-tar, 42 Czocor's cochineal solution, 41 Ehrlich-Biondi triple, 45 INDEX. 499 Stains for adipose tissue, 119 gold chlorid, for capsules of cartilage, 120 hemalum, 42 hematoxylin, 41 Hohmer's, 41 Delafield's, 41 for demonstrating canalicular sys- tem in cartilage, 1 20 Ehrlich's, 42 for liroe-salts in bone, 122 Friedlander's glycerin-, 42 Heidenhain's iron, 42 hematoxylin-eosin, 44 hematoxylin-safranin of Rabl, 44 iodo-iodid of potassium, to demonstrate glycogen in cartilage, 121 magenta red, for connective tissue, 119 methyl-green, 43 nuclear, 40 orcein, for connective tissue, 1 18 paracarmin, 40 Partsch's cochineal solution, 41 picric acid, 44 picric-acid-fuchsin, Van Gieson's, 399 picric-magnesia-carmin, Mayer's, 44 picrocarmin, for connective tissue in car- tilage, 120 for elastic fibers in cartilage, 120 Ranvier's, 43 Weigert's, 43 protoplasmic, 40 safranin, 43 selective, 40 Soudan III, for fat, 120 Stellate cells, 262 large, of cerebellar cortex, 375 of cerebellar cortex, 374 of cerebral cortex, 376 Stellular vasculosis, 414 Stomach, 235, 237 technic of, 271 Stomata, 85 Straight tubules of testis, 325 Stratified epithelium, 77 Stratum circulare, 437 corneum, 343 gelatinosum, 379 germinativum, 341 granulosum, 309, 341 lucidum, 343 technic of, 362 Malpighii, 341 technic of, 363 proprium of oral cavity, 211 radiatum, 437 spinosum, 342 spongioblasts, 424 submucosum of oral cavity, 212 Stria vascularis, 446 Striation of Baillarger, 379 of Bechtereff and Kaes, 379 Striped muscle-cell, 123 muscle-fibers, 1 24 Stroma of red blood-cells, 169, 170 of iris, 416 Stroma of ovary, 306 Subarachnoid space, 394 Subdural space, 394 Subepithelial plexus of cornea, 412 Sublingual gland, 228 Submaxillary gland, 230 Submucosa of intestine, 236 of oral cavity, 212 Subpia, 396 Substantia gelatinosa, 367 propria of cornea, 410 Succus prostaticus, 332 Sudoriferous duct, 357 Sudoriparous glands, 357 Sulcus of matrix of nail, 355 scleral, inner, 410 spiralis internus, 446 Superficial plexus of cornea, 412 Superior nasal artery of retina, 427 vein, 427 papillary artery, 426 vein, 426 Suprarenal glands, 301 blood-vecsels of, 303 nerves of, 304 technic for, 305 Suspensory ligament of lens, 428 Sustentacular cells, 85, 224, 334 fiber of Deiters' cells, 450 Sweat-glands, 357 nerves of, 358 Sympathetic ganglia, 140, 385 Tactile papillx, 345 Taeniae coli, 236 of large intestine, 250 Tapetum cellulosum, 413 fibrosum, 413 Taste-buds, 223 Taste-pore, 224 Teasing, 20 Technic, microscopic, introduction to, 1 7 Teeth, 213 adult, structure of, 213 auditory, 446 development of, 217 pulp of, 215 Tegmental cells, 224 Teichmann's crystals, 169 isolation of, 207 Tela submucosa, 212 Telodendria, 135 of nerve-fibers ending in muscle tissue, 147 Telodendrion, 147, 151 Telolemma nuclei, 148 Telophases, 57, 64 Temperature, effects of, on tissues, 27 Tendons, 96 bundles, primary, 96 secondary, 97 fasciculi, 96 spindle, Golgi, 162 Tenon's capsule, 409 Terminal disc of Merkel, 127 500 INDEX. Terminal ledges, 80 nodule of spermatosome, 323 Testes, 324 blood-vessels of, 329 lymphatics of, 329 nerve-supply of, 329 technic of, 340 Theca folliculi, 309 Thoma's ampullae, 182 Thymus gland, 188 Thyroid gland, 284 Tigroid granules, 134 Tissue, 73 adipose, 99 stains for, 119 connective, 89 areolar, 93 cellular elements of, 94 ground-substance of, 93 matrix of, 93 fibrous, 93 mucous, 92 Ranvier' s method for examination of, 117 reticular, 92 technic of, 1 17 effects of temperature on, 27 epithelial, 74 erectile, of penis, 333 fibrous, elastic, 98 frozen with carbon dioxid, cutting of, 35, 36 lymphoid, 177 muscular, 123 technic of, 132 nervous, 133 technic of, 164 Toluol as clearing fluid, 47 Tomes' granular layer, 220 processes, 218 Tongue, 221 lymph-follicles of, 225 Tonsils, lymph-follicles of, 225 Tooth-pulp, 215 Trabeculse of liver, 258 Trachea, 276 Transitional eosinophile cells, 187 Transverse disc, 1 27 membrane of Krause, 127 Triangular cells of cerebral cortex, 376 Trophoplasts, 347 Trypsin digestion for differentiating con- nective and elastic tissues, 118 Tubular glands, 82. See also Glands, tubular. Tubule, dentinal, 214 intermediate, of pancreas, 266 straight collecting, of kidney, 288 uriniferous, 287, 293 schematic diagram of, 297 Tubuli recti of testis, 325 Tunica albuginea, 84, 324 dartos, 346 externa of eye, 407 fibrosa oculi, 407, 409 interna of eye, 407, 418 Tunica media of eye, 407, 412 mucosa of intestine, 236 propria of oral cavity, 211 sclerotica, 407, 409. See also Sclera. vaginalis, 324 vasculosa, 324 of eye, 407, 412 Tunnel of Corti, 448 Tunnel-fibers, 452 Tiirck's column, 370 Tympanic investing layer of basilar mem- brane, 447 membrane, 436 layers of, 436 Tympanum, 437 Tyson's glands, 334 Undulating membrane of spermatosome, 323 Unstriped muscle-cell, 123 Ureter, 299, 300 Urethra, epithelium of, 333 submucosa of cavernous portion of, 2>ZZ Urinary organs^ 287 technic for, 305 Uriniferous tubules, 287, 293 schematic diagram of, 297 Uterus, 317 blood supply of, 319 layers of, 318 lymphatics of, 319 nerve supply of, 320 technic of, 340 Utriculosaccular duct, 440 Utriculus, 440, 441, 454 wall of, 442 Vacuoles, 54 secretion, 259 Vagina, 320 sensory nerve-endings in, 322 technic of, 340 vestibule of, 322 Valvulse conniventes, 236 Van Gieson's picric-acid-fuchsin stain, 399 Vas aberrans Halleri, 328 deferens, 329 epididymidis, 326, 328 spirale, 447 Vasa afferentia, 178, 296 efferentia, 178, 325, 327 recta spuria, 297 Vascular canals, 103 papillae, 345 system, 190 tunic of eye, 407, 412 Vater-Pacinian corpuscles, 157 Veins, 197 central, 258 intralobular, 258, 261, 298 portal, 260 precapillary, 197 • smaller, 197 valves of, 198 INDEX. 50I Venre arci formes, 298 stellate, 298 vorticosre, 413 Ventrolateral column, 367 Ventromesial column, 367 Venuloe rectce, 298 Vesicula prostatica, 332 Vestibular membrane, 444, 447 Vestibule of ear, 439 of nasal cavity, 456 of vagina, 322 Villi of mucous membrane of small in- testine, 243 of small intestine, lacteals of, 253 Virchow's bone corpuscles, 104 isolation of, 123 Virtual image, 19 Visual cells, 418 Vitreous body, 407, 427 membrane, 412, 414 Volkmann's canals, 106 von Ebner's process of decalcification, 122 von Koch's technic for bone, 123 Wagner's spot, 306 Wandering cells, 53, 94, 96 Water, distilled, for fixing paraffin sections to slide, 38 Weigert's methods for demonstration of medullary sheath, 397, 398 picrocarmin, 43 Wharton's jelly, 92 White blood-corpuscles, 173 fibers, 90 fibrocartilage, 102 rami communicantes, 387 fibers, 387 substance of spinal cord, 365 Wirsungian duct, 265 Wolffian duct, 322 Xylol as clearing fluid, 47 as intermediate fluid, 26 Yellow bone-marrow, 185, 188 Yolk granules, 311 Zenker's fluid, 25 Zinn's arterial circle, 426 zonule, 428 Zona pellucida, 311 Zonula ciliaris, 407, 428 Zonule of Zinn, 428 Catalogue SL Medical Publications OF W. 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Schmitson, and r 25 pages of text. additional volumes in preparation. 19 NOTHNAGEL'S ENCYCLOPEDIA OF PRACTICAL MEDICINE AMERICAN EDITION Edited by ALFRED STENGEL, M. D. Professor of Clinical Medicine in the University of Pennsylvania; Visiting Physician to the Pennsylvania Hospital IT is universally acknowledged that the Germans lead the world in Internal Medicine ; and of all the German works on this subject, Nothnagel's " Speci- elle Pathologie und Therapie " is conceded by scholars to be without question the best System of Medicine in existence. So necessary is this book in the study of Internal Medicine that it comes largely to this country in the original German. In view of these facts, Messrs. W. B. Saunders & Company have arranged with the publishers to issue at once an authorized American edition of this great ency- clopedia of medicine. For the present a set of ten volumes, representing the most practical part of this excellent encyclopedia, and selected with especial thought of the needs of the practical physician, will be published. These volumes will contain the real essence of the entire work, and the purchaser will therefore obtain at less than half the cost the cream of the original. Later the special and more strictly scientific volumes will be offered from time to time. The work will be translated by men possessing thorough knowledge of both English and German, and each volume will be edited by a prominent specialist on the subject to which it is devoted. It will thus be brought thoroughly up to date, and the American edition will be more than a mere translation of the Ger- man ; for, in addition to the matter contained in the original, it will represent the very latest views of the leading American and English specialists in the various departments of Internal Medicine. The whole System will be under the edi- torial supervision of Dr. Alfred Stengel, who will select the subjects for the American edition, and arrange for the editing of the different volumes. Unlike most encyclopedias, the publication of this work will not be extended over a number of years, but five or six volumes will be issued during the coming year, and the remainder of the series at the same rate. Moreover, each volume will be revised to the date of its publication by the eminent editor. This will obviate the objection that has heretofore existed to systems published in a number of volumes, since the subscriber will receive the completed work while the earlier volumes are still fresh. The usual method of publishers, when issuing a work of this kind, has been to compel physicians to take the entire System. This seems to us in many cases to be undesirable. Therefore, in purchasing this encyclopedia, physicians will be ^iven the opportunity of subscribing for the entire System at one time ; but any single volume or any number of volumes may be obtained by those who do not de ire the complete scries. This latter method, while not so profitable to the pub- lisher, offers to the purchaser many advantages which will be appreciated by those who do not fare to subscribe for the entire work at one time. This American edition of Nothnagel's Encyclopedia will, without question, fortn the greatest System of Medicine ever produced, and the publishers are con- fident that it will meet with general favor in the medical profession. 20 NOTHNAGELS ENCYCLOPEDIA OF PRACTICAL MEDICINE. AMERICAN EDITION. VOLUMES JUST ISSUED AND IN PRESS. TYPHOID AND TYPHUS FEVERS. By Dr. II. I U« i HMANN, of Lcipsic. or, William Osier, M.D., F.R.C.P., Professor of the Principli - and Practice of MediciDe in Johns Hopkins University, Baltimore, Handsome <•< I . pages, 72 valuable text illustrations, ami two lithographic plates. Cloth, 85. 00 net; Half Morocco, 56.00 net. Just Ready. VARIOLA (induing VACCINATION 1. By J»k. II. I.mmi.kmann. of Basle. VARI- CELLA. By Dr. Th. von JOrgensen, of Tubingen. CHOLERA ASIATICA and CHOLERA NOSTRAS. By Dr. C. Liebermeister, of Tubingen. ERY- SIPELAS and ERYSIPELOID. By Dr. II. Lenhartz, of Hamburg. PER- TUSSIS ml HAY-FEVER. By Dr. . Rosenbaum, of Berlin. PNEUMONIA. By Dr. E. Aufrecht, of Magdeburg. Editor, John H. Musser, M. D., Professor of Clinical Medicine, University of Pennsyl- vania. Handsome octavo, 700 pages, 7 full-page lithographs in colors. Cloth, 35.00 net ; Half Morocco, S^.oo net. just Ready. DISEASES OF THE LIVER. By Drs. H. Quincke and G. Hoppi Seyler, of Kiel. DISEASES OF THE PANCREAS. By Dr. L. I >SER, of Vienna. DISEASES OF THE SUPRARENALS. By Dr. E. NEUSSER.of Vienna. Editors. Frederick A. Packard, M.D., Physician to the Penna. and the Children's Hospitals, Phila. ; and Reginald H. Fitz, A. M., M. D., Hersey Prof, of the Theory and I'ractice of Physic, Harvard L'niv. Handsome octavo of 750 pages, illustrated. Cloth, $5.00 net; Half Morocco, $6.00 net. Just Ready. INFLUENZA AND DENGUE. By Dr. O. Leichtenstern, of Cologne. MALA- RIAL DISEASES. By Dr. J. Mannaberg, of Vienna. Editor, Ronald Ross, F.R.C.S.. Eng., D.P.H., F.R.S., Major, Indian Medical Service, retired; Walter Myers, Lecturer, Liverpool School of Tropical Medicine, Liverpool. Handsome octavo, 700 pages, 7 full-paye lithographs in colors. ANEMIA. LEUKEMIA. PSEUDOLEUKEMIA, HEMOGLOBINEMIA. By Dr. I. Emrlich, of Frankfort-on-the-Main, Dr. A. Lazarus, of Charlottenburg, and Dr. Felix Pinkus, of Berlin. CHLOROSIS. B) Dr. K. von Noorden, of Frank- fort-on-the-Main. Editor, Alfred Stengel, M.D., Professor "f Clinical Medicine, University of Pennsyl- vania. Handsome octavo, 750 pages, 5 full-page lithographs in d TUBERCULOSIS AND ACUTE GENERAL MILIARY TUBERCULOSIS. By Dr. ( ',. ( !ornet, of Berlin. Editor to be announced later. Handsome octavo, 700 pages. DISEASES OF THE STOMACH. By Dr. F. RlEGEL, of < dessen. Editor, Charles G. Stockton, M.D., Professor of Medicine, University of Buffalo. Handsom pag -. with 29 text-cuts and 6 full-page plates. DISEASES OF THE INTESTINES AND PERITONEUM. By Dr. Hermann X' 'i hnagi 1., of Vienna. Edit. r. Humphry D. Rolleston, M.D., F.R.C.P., Physician to and Lecturer on Pathol- ogy at St. George's Hospital, London. Handsome octavo, Soo pages, finely illustrated. 21 CLASSIFIED LIST OF THE MEDICAL PUBLICATIONS or W. B. SAUNDERS & COMPANY ANATOMY, EMBRYOLOGY, HISTOLOGY. Bbhm, Davidoff, andHuber — Histology, . 4 Clarkson — A Text-Book of Histology, . . 5 Haynes— A Manuai of Anatomy, .... 8 Heisler — A Text-Book of Embryology, . . 8 Leroy — Essentials of Histology 16 McClellan — Art Anatomy, 10 McClellan — Regional Anatomy, Nancrede — Essentials of Anatomy Nancrede — Essentials of Anatomy and Manual of Practical Dissection, .... Sobotta — Atlas of Normal Histology, . . 16 19 BACTERIOLOGY. Ball — Essentials of Bacteriology 16 Eyre — Bacteriologic Technique, 7 Frothingham — Laboratory Guide, .... 7 Gorham — Laboratory Bacteriology, ... 7 Lehmann and Neumann — Atlas of Bacte- riology, 19 Levy and Klemperer's Clinical Bacteri- ology 10 Mallory and Wright— Pathological Tech- nique 10 McFarland — Pathogenic Bacteria 11 CHARTS, DIET-LISTS, ETC. Griffith— Infant's Weight Chart 8 Keen — Operation Blank, 9 Laine — Temperature Chart 10 Meigs — Feeding in Early Infancy 11 Starr — Diets for Infants and Children, . . 13 Thomas — Diet-Lists 14 CHEMISTRY AND PHYSICS. Brockway — Essentials of Medical Physics, 16 Jelliffe and Diekman — Chemistry, ... 9 Wolf — Urine Examination, 15 Wolff — Essentials of Medical Chemistry, . 16 CHILDREN. American Text-Book Dis. of Children, . . 1 Griffith— Care of the Babv 8 Griffith— Infant's Weight Chart, 8 Meigs —Feeding in Early Infancy n Powell— Essentials of Diseases of Children, 16 Starr —Diets for Infants and Children, . . 13 DIAGNOSIS. Cohen and Eshner— Essentials of Diag- nosis 16 Corwin — Physical Diagnosis, 5 Vierordt — Medical Diagnosis 15 DICTIONARIES. The American Illustrated Medical Dic- tionary 3 The American Pocket Medical Dictionary, 3 Morten — Nurses' Dictionary 11 EYE, EAR, NOSE, AND THROAT. An American Text-Book of Diseases of the Eye, Ear, Nose, and Throat 1 Brtihl and Politzer— Atlas of otology, . 19 DeSchweinitz — Diseases of the Eye, . . 6 Friedrich and Curtis — Rhinology , Laryn- gology and Otology 7 Qleason — Essentials of Diseases of the Ear, 16 Gleason— Ess. of Dis. of Nose and Throat, 16 Gradle — Ear, Nose, and Throat 7 Grant — Surgery of Face, Mouth, and Jaws, 8 Griinwald — Atlas of Mouth, Throat, and Nose 19 Griinwald — Atlas of Diseases of the Larynx 17 Haab — Atlas of External Diseases of the Eye 17 Haab — Atlas of Ophthalmoscopy 18 Jackson — Manual of Diseases of the Eye, 9 Jackson — Essentials of Diseases of Eye, 16 Kyle— Diseases of the Nose and Throat, . 9 GENITO-URINARY. An American Text-Book of Genito-Uri- nary and Skin Diseases, 2 Hyde and Montgomery— Syphilis and the Venereal Diseases, 8 Martin — Essentials of Minor Surgery, Bandaging, and Venereal Diseases, . . Mracek— Atlas of Syphilis and the Vene- real Diseases, Saundby — Renal and Urinary Diseases, . . 12 Senn — Genito-Urinary Tuberculosis, ... 13 Vecki — Sexual Impotence 15 GYNECOLOGY. American Text-Book of Gynecology, . . 2 Cragin — Essentials of Gynecology 16 Garrigues— Diseases of Women 7 Long— Syllabus of Gynecology 10 Penrose — Diseases of Women u Schaeffer — Atlas of Operative Gynecology, iq Schaeffer — Atlas of Gynecology 18 HYGIENE. Abbott— Hygiene of Transmissible Diseases 4 Bergey — Principles of Hygiene 4 Pyle — Personal Hygiene 12 MATERIA MEDICA, PHARMACOL- OGY, AND THERAPEUTICS. American Text-Book of Therapeutics, . Butler— Text-Book of Materia Medica Therapeutics, and Pharmacology, . Morris— Ess. of M. M. and Therapeutics Saunders' Pocket Medical Formulary, . Sayre — Essentials of Pharmacy Sollmann— Text- Book of Pharmacology Stevens — Manual of Therapeutics, . . Stoney — Materia Medica for Nurses, . Thornton— Prescription-Writing, . . . 16 17 5 16 12 16 13 14 15 MEDICAL mil /CATIONS OF If. />'. SA C.\ />/-. A'.S o- CO. 23 MEDICAL JURISPRUDENCE AND TOXICOLOGY. Chapman --M i-