Qf^\ Columtiia ?Hnibers(itp in tljE Citp of ^eto gorfe CoUfge of ^fjpsitianK anb burgeons l^eference Hitjrarp > . ^ .^-^y^ L^Oyrn ^^ -..{ '^ I ( Digitized by tine Internet Arciiive in 2010 witii funding from Columbia University Libraries http://www.archive.org/details/textbookofhistoOOst TEXT-BOOK HISTOLOGY STOH R TEXT-BOOK H ISTOLOGY INCLUMINi; THE MICROSCOPICAL TECHNIQUE DR. PHILIPP STOHR rtlCAL INSTITl'TR IN ZURICH SIXTH EDITION rRANSLATEI) U\ KMMA L. BILLSIEIN, M. D. i;i)l IKI), WITH ADDITIONS 11 V DR. ALFRED SCHAPER TlGitb 20S Ullustvations I'HII.ADKLI'HIA I', i; 1. .\ K 1 S T O N, so X c\: C O I O 1 2 W A I. .N U r S l' K H K 1' 1 s'.m; CoPYKinHT, 1896, BY Dr. Alfred Schapek. Press of Wm. F. Fell & Cc 1220-24 SANSOM ST.. EDITOR'S PREFACE. Stiihr's text-book is well known to the histologists of all nations and held in high esteem by them. To the German medical student it has become an in- dispensable guide. During the ten years of its existence it has reached an ex- traordinary sale and pa.ssed through six revised editions. It has been translated into Italian (1887), French (1890), and Russian (1891), and has thus come into the hands of the students of these nations. These facts are sufficient to guarantee the value of the work without further recommendation, .\lthough excellent text-books of Histology already exist in English, still the peculiarity and special superiority of Stohr's text-book justifies, in our opinion, its transla- tion into English for the convenience of .\merican and English students. * It is especially intended for the use of students, but even professional histol- ogists and physicians will find in it much valuable information, as well as sug- gestions for technical purposes. The chief merit of the work lies, on the one hand, in the brevity and perspicuity of the descriptive text, elucidated by illustrations which have thus far never been excelled ; and, on the other hand, in the simplicity and certainty of the methods for preparing the most important microscopical specimens. The young .student is thus enabled to practice histological methods privately, at a minimum cost, in connection with his courses in the university. The preparation of almost all of the specimens enumerated in the book can be made simply by means of teasing, isolation, or cutting with the razor, but those .students who have a microtome at their disposal will also find, in an .\|)pendix, brief directions tor the preparatory treatment (embedding in paraffin and celloidin) of specimens for sectioning with the microtome. With the permission of Prof. Stohr we have made several immaterial, but for an American edition very desirable, changes in the text, and have considered it more preferable to place the technical part as a whole at the end of the book rather than in sections after the several chapters. Furthermore, we have enlarged the cha])ter on the I'terus, in order to give detailed consideration to the various functional conditions of the organ, and added to the book an entirely new chapter on the I'lacenta. Eight new illustrations (Fig. 200, 201, 202, 203. 204, 205, 206, 207) were neces.sary for these additions. * In 1888 Stohr's Text-book was utilized in Kendrick's Physiology, but in such a frag- mentary form and so intermingled with selections from other .luthors thai its chief merits wero entirely lost. This use of the book cannot be considered as an Knglish translation proper. VI EDITOR S PKEFACK. The editor is under great obligation to the translator, Dr. Billstein, for her successful efforts in reproducing the conciseness and clearness of the German original. Further, he desires to express his gratitude to Professor Philipp Stohr for placing at his disposal the original electrotypes, and to Drs. Bohm and von Davidoff for the illustration of the virginal uterus (Fig. 200) from their " Lehrbuch der Histologic." He also feels deeply indebted to Professor Charles S. Minot for kind assistance, valuable criticism, and for permission to use two illustrations (Fig. 202 and 205) from his text-book of "Human Embryology "; and finally to Messrs. P. Blakiston, Son & Co., Philadelphia, for the very satisfactory reproduction of the new drawings, and for their many courtesies during the preparation of the American edition. Alfred Schaper. Harvard Medical School, Boston, Juiii, iSgb. CONTENTS. PART I. GENERAL TECHNIQUE. The Labokatiiky Ai'coint- MENTS Instrumenls. Reagents. The Pkei'akation ok Mi- (_'Rosci)i'iCAi. Specimens, . Introduction. Nature of the Materia). Killing and Dissecting tlie Animals. Isolating. Fixation, Hardening, Decalcifying. The Preparation of Microscopical Speci- r^cK mens. — Continued. Sectioning. Staining. Injecting, Mounting and Preser\ing of the I'reparations. Examination of Fresh Objects. Storing of I'ermanent Speci- mens, III. Management ok the Micro- scope, 43-46 Drawing, Measurement. PART II. MICROSCOPICAL ANATOMY. I, }llsTOl,oi;v. A. — Cells 4X-54 Parts, Form, Size. Vital Properties. Phenomena of Motion. Reproduction and Multi- plication. Phenomena of Secretion, Length of Life. Growth, Secretory Products. H. — Tissues, The Epithelial Tissues, . 55-63 Secretory .-Xctivitv. Histology. — Continued. The Glands. The Connective Tissues, 64-72 Connective Tissue, Cartilage, Bone. The Muscular Tissues, , 72-76 Involuntary. Voluntary, The Nervous Tissues, . 76-.S3 Nerve-Cells. Nerve-Fibers. II. MlCROSCOrlCAl, .\NATOMV OF THE Organs. The Circulatory System, , , S4-93 CONTENTS. Microscopical Anatomy of ilie gans. — Coiitinitc'i/. The Heart. Tlie Arteries. The Veins. The Capillaries. The Blood. The Lymphatic System, The Lymph-vessels. The Lymph-nodes. The * >rgans of the Nervous Sys- tem. — Contitiued. The Peripheral Nerve Endings. Terminations of Sei-.- sory Nerves. Tactile-Cells. End-Bulbs. Terminations of Motor Nerves. The Peripheral I.ympli- The Suprarenal Body. . . . U3- 144 nodules. The lA-raph. \1. The DiGESTixE Orc;.\n>. . . 14-;- I.S4 The Spleen. Mucous Membranes. The Teeth. 111. The Org.\ns of tiik, Skki.i-,- ialSystkm 100-113 The Bones. The Articulations. The Cartilages. Development of Bone. Development of Primary Bone. Secondary or Intt-i mem- The Tongue. The Pharynx. The Esophagus. The Stomach. The Intestines. The Salivary Glands. The Liver. The Peritoneum. branous Bone. Vn. The Kesi'Iratory Organs. I,S4- lot IV. The Oko.w.s of the Mi ^- em,.\R System ii.s-iiS The Muscles. The Tendons. The Fascix. The Larynx. The Trachea. 1 I'he Bronchi and the 1 .ung>. The Thyroid Gland. The Thymus Body. The Organs of iiie .\],k- vous System. The Central Nervous System. 116-134 The Spinal Cord. Topography. Mmute Structure. The Brain. The Cerebrum. The Cerebral Ganglia. The Gray Substance of the Ventricles. The Cerebellum. The Membranes of the Central Nervous Sys- tem. The Blood-vessels of the Central Nervous Sys- tem. The Peripheral Nervous Sys- tem, 134-14.1 The Nerve Trunks. The Ganglia. VIU. The Urinary Organs, . . 191-198 The Kidneys. The Ureters. The Urinary Bladder. The I'rethr.n. IX. The Rei'RoiU'I rivE Or GANS, icjS-223 The Male Reproductive Or- gans. The Testicle. The Semen. The E.xcretory Ducts of the Testicle. The Prostate Body. The Penis. The Female Reproductive Organs. The Ovaries. The Oviduct. The Uterus. The Placenta. The Vagina and the Genitali.T. CONTENTS. X. TiiK Skin and its Ani.Ni> ■'*<;'' AGES, 223-236 The Skin. The Nails. The Hair. The Glanils of the Skin. The Bloodvessels, Lymph- Vessels, and Nervrs of the Skin. The Manimarv (iland. The Eyk anh iis Aithnd- .v;ks 23I1-259 The Eyeball. The Tunica liMerna. The Tunica Media. The Iridocorneal .Angle. The Tunica Interna. The Cerebral Layer. The Neuro-Epitlielial Layer. The Optic Nerve. The Lens. The Vitreous Body. The Suspensory Ligami-ni. The Eye and its .Appendages. — Con- fack tiniifii. The Blood ■ \'essels of the Eyeball. The Lymph-Channels of the Eyeball. The Nerves of the Eyeball. The Eyelids. The Lacrymal Glands. Ml Tim Organ df Hkakinh, . 260-269 The Internal Ear. The .Saccule, The Utricle, and the Semicircular Canals. The Cochlea. The Middle Ear. The External Ear. XIII. The Nasal Mucuih Mkm- BRANE, 26()-27; The Vestibular Region. The Respiratory Region. The Olfactory Region. XIV. TlIF, TaSTE-HL'DS 27^-27S PART III. SPfEClAL TKCHNIQUE. I. Karyokinesis II. Cll.I.\TED Er 1 T II K I. I A 1. Cells Connective-Tissue. . . . Muscle-Fibers Nerve-Cells and Nerve- Fibers, The Heart and the b1.00d-vessei.s, . . . The Blood, VIII. The Lymphatic System, IX. Bone, III. IV. V. VII. 277 277-279 279-280 2S0-282 X. \1. Muscles and Tendon, . The Organs of the .Ner- vous System 282-284 284-287 287-289 289-292 292-293 293-300 XII. Ihe Digestive Tkact, . XI II. The Respiratory Or- gans, XIV. The Urinary Organs, XV. The Testicle and the Ovary, XVI. The Skin and its .Append- ages, XVII. I'he Eve and its Append- 308-310 -Will. The Organ ok Hearing, \I\. The Mucous Membrane ciFTiiE Nose APPENDIX. M iCROTO.\iK Tech n njf e. . 326-330 Preservation of Secfions LIST OF ILLUSTRATIONS. 1. I.eitz Microscope . . 44 2. Diagram of a Cell, 49 3. Cell of Bone-Marrow of Rabbit, 50 4. Leucocyles of Frog, 5° 5. Karyokinelic Figures — Epithelium of Salamander, 5^ 6. Epithelial Cells of Ral)bit. Isolated, 55 7. I'rickle-Cells of Stratum Mucosum of Epidermis . 5*^ 8. Pigmented Epithelium 56 9. Simple Columnar Epithelium 56 10. Stratified Sc|uamous Epithelium, 57 11. Stratified Ciliated Epithelium, 57 12. Secreting Epithelial Cells, 5*^ 13. Crypt of I-ieberkiihn, 59 14. Diagram of the Different Gland Forms, 60 15. Section of Mucous Glands of Tongue of Rabbit . 62 16. Section of Fundus Gland of Mouse, 62 17. Diagram of Origin of Crescents, 63 18. Cross-Section of Umbilical Cord of Human Embryo, 64 19. Connective-Tissue Bundles 64 20. Elastic Fibers 65 21. Network of Elastic Fibers, 65 22. Connective-Tissue Cells, Bundles of Connective-Tissue Filers 65 23. Fat-Cells, 66 24. Reticular Connective Tissue 67 25. Hyaline Cartilage, 68 26. Elastic Cartilage, 69 27. Section of Intervertebral Disk of Man, 70 28. Ground Section of Dried Bone of Adult Man 70 29. Sections of Humerus of Human Embryo, and of middle Turbinal of Man, . . 70 30. Section of Diaphysis of Humerus of Human Embryo 71 31. Smooth Muscle- Fibers from Small Intestine of Frog 72 32. Section of Circular Layer of the Muscular Coat of Intestine 73 33. Muscle- Fibers of Man 74 34. Isolated Striated Muscle- Fibers of Frog 75 35. Muscle-Fibers of Heart 7'> 36. Diagram of a Neuron, 77 37. Various Fonns of Ganglion-Cells 78 38. Nerve-Cell 79 39. Nerve-Cells from the Spinal Cord of Embryo Chick 80 40. Teased Preparation from the Sympathetic Nerve of Rabbit, . . Si 41. Medullated Nerve- Fibers 82 42. Medullated Nerve-Fibers, Treated with Silver Nitrate Solution. . S3 XU LIST OF ILLUSTRATIONS. 43. Section of Papillary Muscle of Human Heart 84 44. Small Arteries of Man, 85 45. Cross-Section of Brachial Artery of Man, ... 86 46. Endothelium of Mesenteric Artery of Rabbit, 87 47. Cross- Section of Thoracic Aorta of Man, 87 48. Cross-Section of Vein of Man, 88 49. Cross-Section of Renal Vein of Man, Sg 50. Surface View of tlreater Omentum of a Seven-Days'-Old Kabliit 90 51. Blood Corpuscles 91 52. Colorless Blood-Cells of Man, . . 92 53. Hemin, Hematoidin, Hemoglobin Crystals; Crystals of Common Salt, 93 54. Lymphatic Vessel of Mesentery of Rabbit, 94 55. Section of Lymphatic Nodule of Nine-Days'-Old Cat 95 56. .Section through Medulla of Lymphatic Nodule of Ox, 96 57. Cross-.Section of Human Spleen, 97 58. Elements of Human Spleen, 98 59. Reticular Connective Tissue of Humnn .Spleen .... 98 60. Three Karyomitotic Figures from Sjileen of Dog, . 98 61. Section of .Spleen of Mouse, 98 62. A. Section of Injected Spleen of Cat, 99 62. B. Schematic Drawing of Section 62, A. .. 99 63. Longitudinal Section through Human Metacarpus, . . 64. Cross-Section of Metacarpus of Man 65. Elements of Human Bone-Marrow ... 66. Cross-Section of Femur of Adult Man 67. Section through Head of Metacarpus of Adult Man 104 68. Synovial Villi with Blood-Vessels from Human Knee-joint 106 69. Section of Oreat Toe of Human Embryo, 107 70. Section of Finger of Human Embryo, loS 71. Section of Phalanx of First Finger of Human Embryo, tog 72. Cross-Section of U|iper Half of Diaphysis of Humerus of Human Embryo. . . 73. Cross-Section of Lower Jaw of Newborn Dog 74. Section of Parietal Bone of Human Embr)0, 75. Cross-Section of Humerus of Newborn Cat • . 76. Cross-Section of Adductor Muscle of Rabbit, 77. Cross-Section of Dried Tendon of Adult Man 114 78. Tendons from Rat's Tail 115 79. Section of Gastrocnemius of Frog 115 So. Cross- Section of Cervical Enlargement of Human Spinal Cord, . . ■ 117 81. Cross-Section of Spinal Cord of Embryo Chick, 82. .Scheme of Spinal Cord, showing the Nerve-Cells, . . 83. Longitudinal .Section of Spinal Cord of Newborn Rat. 84. Cross- Section of Spin.al Cord of Newborn Rat 85. Glia-Cells from Spinal Cord 86. Cross-Section of Human Spinal Cord, 87. Section of Human Cerebral Corte.t, 124 88. Scheme of Cerebral Cortex, 124 89. Pyramidal Cell from Cerebral Cortex of .^dult Man, 125 90. Glia-Cells of Human Brain, 126 91. Section through Cortex of Cerebellum of Adult Man. . . 127 92. Small Granule-Cell from Cerebellum of Cat 1 28 93. Large Granule-Cell from Cerebellum of Cat, 128 94. Scheme of Cerebellar Cortex . LIST OK ILI.U.STRAI IONS. Xlll 10. PAGE 95- Basket-Cell from Cerebellar Cortex of Cat, . 1 50 96. Section of Cerebellar Cortex of Adult Man ... 131 97. GliaCells from Cerebellar Cortex of .\tluli Man 132 98. Section of Human Pituitary liody, 132 99. Acervulu.s Cerebri from I'ineal Body, • .■ • '33 00. Gray-Sul 'Stance from \V;iIi of a Ventricle of Human Br.\in 133 01. Cross-Section of Human Median Nerve, X 20, 135 02. Cross-Section of Human Median Nerve, X 220, 135 33. Cross Section of the Gasserian Ganglion of Man 136 04. Section of the Superior Cervical Ganglion of .Man 137 05. Section through Skin of Great Toe of Man, 138 06. Section through Skin of Great Toe of Man, showing Tactile-Cells, . . 139 07. Section through Skin of Beak of (ioose, 139 08. Cylindrical Knd-Bulb from Conjunctiva of Calf, ... , . . , 140 09. Small Corpuscle of Vater from Mesentery of Cat, 140 10. Tactile Corpuscle from Great Toe of Man 141 11. Motor Nerve-Ending of Intercostal Muscle-Fibers of Rabbi- 142 12. Motor Nerve-Ending in a Fiber of an Ocular Muscle, 142 13. Section of Suprarenal Body of Child, 143 14. Section of Mucous .Membrane of I.ip of .Adult Man, . . 145 15. Section of Human Tooth 146 16. Section of Lateral Part of Crown of Human Molar Tooth ... 147 17. Section of Fang of Human Molar Tooth 147 18. Section of Tooth of Infant, t|7 19. Odontoblasts with Dentinal Fibers, 14S 20. Scheme of the Initial Processes in the Development of the Teeth, 149 21. Frontal Section of Head of Embryo Sheep, .149 22. Cross- Section of Lower Jaw of Human Embryo, 150 23. Cross-Section of Upper Jaw of Human Embryo, 151 24. Section of Voung Milk-Toolh of Newborn Dog 152 25. Section of Mucous Membrane of Dorsum of Human Tongue, . . 153 26. Section of Mucous Membrane of Human Tongue, ... 153 27. Section of a Circumvallate Papilla of Man, 154 28. Section of Lymph- Follicle from Root of Human Tongue. 155 29. Serous Gland of Root of Tongue of Mouse 155 30. Section of Mucous Gland of Root of Human Tongue, 156 31. Cross-Section of Middle Third of Human Esophagus, 15S 32. Transverse Section of Human Stomach I5, p). As secretion progresses, more and more of the protoplasm is trans- formed, and the nucleus and remnant of unaltered protoplasm are pushed to the bottom of the cell. As a consequence of this gradual compression, the nucleus is rounded or even flattened. The volume of the secreting cell when filled is considerably enlarged. Finally, the cell-wall bursts at its free surface. The secretion gradually escapes, and simultaneously the protoplasm is regen- erated, the nucleus moves upward to its original position, and the cell, dim- inished in size, is restored to its previous condition and appearance. The '•'•-4-- Fig. 12. — Sbcrhting Epithelial Cells. From a thin section of mucous membr.-tne of the stomach of n X 5''0- /■ ProtopKism. s. Secretion, a. Two cells empty of secretion: the cell between them sh beginning mucoid metamorphosis, c. The cell on the right is discharging its contents, its upper free having ruptured; the granular protoplasm has increased, and the nucleus has become round ag majority of glandular cells do not degenerate in the act of secreting, but are able to repeat the process again and again. The cells of the sebaceous glands furnish an exception, for, like the goblet-cells, their secretion is formed by the disintegration of cells.* In the case of the latter the processes of elab- oration and expulsion of the secretion occur simultaneously ; at first the secretion is produced more rapidly than it is discharged, and it accumulates in the cell, but at the last expulsion exceeds production, the cell gradually empties itself completely, and dies (Fig. 13). The glandular cells lie isolated between other epithelial cells f or are united in groujis and form glandular tissue. * The testicle and ovary furnish a peculiar instance, the gland cells of which, after secre- tion, undergo further development. t They are then called unicellular glands, and are very common among invertelirates, but a]ipcar also in man as goblet-cells. TISSUES. 59 Supplement. — The Glands. — The glands are composed almost ex- clusively of epithelium fglandular), and therefore, although they are organs, they may be described with the epithelial tissues. Connective tissue and blood- vessels are present, and though very important physiologically, are less so morphologically. The glands occur in two principal forms : as cylindrical tubules or as rounded saccules. The tubular glands occur either singly or combined into groups ; there- fore thev are divided into — Secretion. Protoplasm with nucleus. GLind lumen. 3. 13. — CBVtT OF LlBBftRKi'-HN FROM A Sf.CTION OF THR LarGK InTESTINH OF MaN. X 165. secretion formed in the goblet-cells is dark in color. In zone i Ihc goblet-cells show the beginning of secre- tion. That a part of the secretion is already given off here is evident from the presence of secretion in tht form nf drops in the lumen of the crypt. 2. Goblet-cells with much secretion. 3. Cells containing a smal amount of secretion. 4. Degenerating goblet-cells, some of which still contain remnants of secretion Tcchn. 10. The I. Simple tubular glands, which have the form of simple or branched tubules (Fig. 14) ; the latter may be called a " duct-system." * * The true form of such glands can be recognized only on the most exact investigation, because the branched tubules are twisted about one another or coiled in a dense convolution. They were fonnerly called "racemose glands." 6o HISTOLOGY. 2. Compound tubular glands, which consist of a large and variable number of "duct-systems" (Fig. 14). The same division is applicable to alveolar glands. They occur as — Tiilnibr Gland Simple Glands. Compound Glands Saccular (Alveol.-ir) Glands. Terminal compartments. Simple Glands, Fig. 14.— Diagram o Saccules (Alveoli). Compoimd Glands. Different Gland. Forms, a. Excretory duct. I. Simple saceular (^alveolar) glands, which, similarly, are simple or branched saccules having an excretory duct ; the latter are termed ''alveolar system." • TISSUES. 6 1 2. Compound saccular {alveolar) glands, which consist of a combination of several " alveolar systems " (Fig. 14J. Simple unbranchcd tubular s'ands: the peptic or fundus glands, the sweat- glands, and the glands of Lieberkiihn. Simple branched tubular glands : the pyloric glands, the glands of Brunner, the smallest glands of the oral cavity, the glands of the tongue, and the glands of the uterus. Compound tubular glands : the mammary, the salivary, the lacrymal and the larger mucous glands,* the kidneys, the glands of Cowper, the prostatic glands, the thyroid gland, the testicle, and the liver. The branches in the last two anasto- mose and form networks, and hence are also called "reticular glands." Simple unbranched saccular glands: the smallest sebaceous glands and the follicles of the ovary. Simple branched saccular glands : the larger sebaceous glands and the Meibo- mian glands. Compound saccular glands : the lungs. In the majority of glands, especially in those visible to the naked eye, a sheath is formed by the surrounding connective tissue, which sends septa into the gland and divides it into compartments of varying size, the gland lobules. The septa carry the larger blood-vessels and nerves. The glands may secrete throughout their entire e.xtent, but usually only that part lying near the blind end {gland follicle) is specialized for this purpose, while the part forming the connection with the surface serves for the conveyance of the secretion, and is called excretory duct. Glands without excretory ducts are the thyroid body and the ovary. The former has an excretory duct in the embryonic period, which disappears, how- ever, in the course of development. The gland follicles of the ovary, in the embryonic period, are in communication with the sujierficial epithelium; these connections, which might be called e.xcretory ducts, disappear, and the expul- sion of the products formed in the ovary (the ova) takes place by the bursting of the follicles. The ovary is a dehiscent gland. All gland follicles are composed of a usually simple layer of gland cells, which bound the lumen of the gland and are in turn surrounded by a special modification of the connective tissue, a membrana propria or basement mem- brane (see p. 67). Occasionally, instead of this, the gland tubules are em- braced by stellate, nucleated cells (" basket-cells "). On the outer side of the *The cross-sections of the coiled and closely-packed branching tubules of the last three glands were for a long time regarded as vesicular evaginatioiis of the terminal ends of the tubules, and were named acini. Such evaginations (except in a few isolated parts of the sub- lingual gland do not really occur; the diameter of the lumen is not larger here than in other portions of the tubules. Un the other hand, a thickening of the wall of terminal parts of tubules, by taller cells, is not uncommon in some tubular glands, e. g., in the parotid and the pancreas. Such thickenings, however, must not be called " acini," since we understand by acinus an evagination, a distention of the lumen. To avoid misunderstanding, the term "aci- nus " was dropiwd and that of " alveolus " selected for glands of the saccular form. Likewise the much-used term "acinous" or "racemose" (alveolar) has been discarded, because the cross-sections of lulmlar glands also exhibit a " racemose " appearance. 62 HISTOLOGY. basement membrane the blood-vessels are situated (Fig. 15). The gland-cells are inserted between the blood-vessels and the lumen of the gland, and on the one side receive from the blood-vessels (or the surrounding lymph-vessels) the crude materials necessary to secretion, and on the other side give off" the elaborated materials as secretion. In some glands, e. g., the fundus glands of the stomach, the cell dis- charges the secretion not only on the free surface but on all sides. The secre- tion then passes into a network of canaliculi that envelopes the cell and com- municates with the lumen by a single wider canal. These canaliculi are called secretory capillaries. The microscopic appearance of the gland-cells changes with their peri- odic functional condition. In many glands all the cells exhibit simul- taneously the same functional condition. In other glands, however, dif- ferent functional conditions are encountered at the same time, even within the Mucous Glands Blood-vessels in- id-cells were only . X 180. Techn. Fig. 16. — Section of Fundus Gland op Mouse. Left upper half drawn after an alcohol preparation {Techn. No. 102), right upper half after a Golgi preparation (Techn. No. 119). The entire lower portion is a diagrammatic combination of both prepa- same tubule or alveolus. The latter is the case in many mucous glands, the cells of which have delicate walls. In these, cells in a condition of activity and of exhaustion are found side by side in the same tubule. The loaded cells push the empty ones away from the gland-lumen ; the latter then lie at the periphery of the tubule, and represent in this form the so-called "demilunes of Heiden- hain " or "crescents of Giannuzzi" (Fig. 17). It must be remarked here that other authors regard the crescentic cells as young gland-cells destined to replace those that disintegrate in the secretory process. The absence of rem- nants of disintegrated cells contradicts this interpretation, as does also the impossibility of demonstrating karyokinetic figures. The nuclei of many glandular cells also exhibit a variable appearance according to the functional condition. In an empty cell the nucleus exhibits a delicate chromatin network and a conspicuous nucleolus (Fig. 17 /;), while in loaded cells the nucleolus is invisible, and the chromatin network appears in the form of coarse fragments (Fig. 17 «). TISSUES. 63 The smaller branches of the ducts of many tubular glands must be regarded as belonging to the secretory follicles, since they are characterized by the spe- cialized epithelium lining their walls, and participate in the function of secre- tion by eliminating certain materials (salts). They are thus not merely excre- tory ducts, but belong to the actively secreting portion of the glands. The difference in structure of these branches renders their division into two parts desirable. The first portion, jiroceeding from the terminal compartments, is narrow, and lined sometimes with flat, sometimes with cubical, cells. This is called the infenalatcd or iiifermcdiatc tubule. The adjoining portion is wider Fig. 17.— Diagram op ti IB Okigin op the Crhschnts. Protoplasm shown darkly shaded. shaded, the secretion less I. Cross-section of a tubule of a mucous gland, with 6 gland cells. 3 («i. a., a.^) are filled with se- cretion, and have pressed the three cells \hx,bz,b^ 11. Same section some- what later. The cells. ai. rt2> "3) liave discharged a part of their secretion, and become smaller. The ceils, by. I'a, ^3, again III. Same section still later. The cells, ay a«, rt3, have discharged the bulk of their secretion, and become still smaller. In the cells, b^^b^, ^3, the IV. Same section still later. The cells, rtj, do, «i3, are now entirely cm p"- ly, and pushed entirely away from the gland lu- men by bu b.., ba, now empty of secretion, away from the gland lumen. Comp. Fig. 146. extend to the lumen and begin to secrete. lated to such an extent that they have become larger and compress tlicir neighbors, Uy, flg, full of secretion. In I thecells/-, inlV the cells a are the crescents. and clothed with tall columnar cells, the bases of which show distinct longi- tudinal striation. These are called ititralohula?- tubes or secretory {salivary or mucous) tubes. The relative length of the intercalated tubules and the intra- lobular tubes varies greatly in the different glands. The excretory ducts consist of a simple or stratified columnar epithelium lining a wall of connective ti.ssue mingled with elastic fibers. The most complex glands consist of the following sections : (i) the ex- cretory duct, which divides into (2) the secretory tubes, which lead into (3) the intercalated tubules, which pass into (4) the terminal compartments, which, finally, take uj) (5) the secretory capillaries. 64 HISTOLOGY. II. THE CONNECTIVE TISSUES. While in the epithelial tissues the cells constitute the principal mass, in the connective substances they are less noticeable, and instead the intercellu- lar substance is conspicuously develojied and variously differentiated. The predominance of the intercellular substance, which also functionally plays the more important part, is characteristic of the group of connective tissues. According to the nature of the intercellular substance they are divided into : I. Connective tissue. 2. Cartilage. 3. Bone. I. Connective Tissue. — The matri.x or intercellular substance of con- nective tissue is more or less soft ; the cells are few in number. Several varieties are distinguished : (a) mucous connective tissue, (^) fibrillar connective tissue, and {c) reticular connective tissue. (a) Mucous connective tissue consists of round or stellate branched cells and a great quantity of undifferentiated, muciferous intercellular substance con- ^IG. 18. — From a Cross-Se Cord of a Four Months' Human Embryo. X 240. I. Cells. 2. Intercellular substance. 3. Connec- tive-tissue bundles, cut obliquely, but at 4 directly cross-sectioned. Techn, No. 3. ivE-TissUE Bundles of V FHE Intermuscular Conn X 240. Techn. No. 4. taining a few minute bundles of fine fibrils. In the higher animals it is found only in the umbilical cord of very young embryos, but is very common in many lower animals. (J)) Fibrillar (^areolar) connective tissue consists of an abundant inter- cellular substance and cells. The intercellular substance is differentiated into connective-tissue fibers, exquisitely fine (o.6/t) filaments united by a small quantity of homogeneous cement into bundles of varying thickness — connective-tissue bundles. These bundles are soft, flexible, slightly e.\tensible, and characterized by their pale and indistinct contours, their longitudinal striation, their wavy course, and also by their chemical properties. On treatment with picric acid, they separate into their fibrils, swell up on the addition of dilute acids, e. g., acetic acid, and become transparent. They are destroyed by alkaline fluids, and yield glutin on boiling. TISSUES. 65 The matrix of fibrillar connective tissue always contains elastic fibers, but in varying quantities (Fig. 20). In contrast to the connective-tissue bundles, they are characterized by their shar]) dark outlines, their strong refractive '"^^'Q^^ Fig. 20.— Elastic Fibfrs. X 560- A. Fine elastic fibe connective-tissue bundles swelled by treatment wit fibers, y", from ligamentum nuchae of ox ; b, connective- section of the ligamentum nucha; of ox ; /, clastic fibe , y, from intermuscul issue of man; *, _jhn. No. 10. B. Very thick elastic issue bundles. Techn. No. 11. C From a cross- s; b, connective-tissue bimdles. Techn. No. 12. power, and their cons])icuous resistance to acids and alkalies. The elastic fibers vary from immeasurably fine to ii i>., and occur usually in the form of finer or coarser networks, the meshes of which are sometimes narrow, sometimes large (Fig. 21). Fig. 21.— Network («) of thick elastic fibers, on the left p:issing into a fenestrated 'mem- brane (w/). From the endocardium of man. X 560. Techn. No. 13. '' "-^K «i© 9 ; ^ h Fig. 22 — A. Connective>tissue cells from intermuscular ncctive tissue. X s6o. i. Flat cell lying partly on a nective-tissue bundle : 2, folded cell : 3. cell of whicl protoplasin is not_visible; b, connective-tissue bundles. Techn. No. 5. B, Coimective-tissue bundle: circling fibers: *, nucleus. Techn. No. 8. C. PI cells from the eye-lid of a child. Techn. No. 182 th Narrow-meshed networks composed of thick elastic fibers form the tran- sition to elastic membranes, which are either homogeneous or finely .striated and perforated with apertures of different sizes (hence the name fenestrated 5 66 membranes) and probably are produced by the merging of broad elastic fibers (Fig. 2i). When elastic fibers predominate over the connective-tissue bundles, the tissue is spoken of as elastic tissue. The elastic fibers are derived neither from cells nor from nuclei, but are a transformation of the matrix. In the be- ginning of their development they are thin, but thicken in the progress of their growth. The connective-tissue cells are irregularly polygonal or stellate, flattened, and variously bent or folded (Fig. 22, A'). The flattening and bending are explained by the adaptation of the cells to the narrow spaces between the connective-tissue bun- dles. Flattened cells not infrequently form sheaths about the connective-tissue bundles. If such a bundle be treated, with acetic acid it swells and bursts the ensheathing cells, of which encir- cling pieces are often retained and constrict the swelled bundle. Formerly these remnants of cells were considered fibers, and were called "encir- cling fibers" (Fig. 22, B'). Other connective- tissue cells are rounded, rich in protoplasm, coarsely granular, and comparatively of large size. These are termed plasma-cells, and are found especially in the neighborhood of small blood- vessels (Fig. 22, ^). Others again, the " Mast- zellen, ' ' are characterized by the affinity of their protoplasm for certain anilin dyes (<-. ^g'., dahlia) but do not stand, as their name might suggest, in any demonstrable relation to the processes of nutrition. [They are also known as granule- cells.'\ The protoplasmic body of the connective- tissue cells encloses a nucleus and often contains pigment-granules ; in the latter case they are called pigment-cells. These are found in man only in certain parts of the skin and in the eye, but in the lower animals they are very common. Con- nective-tissue cells may contain fat-globules which, if very large, coalesce and give a spherical form to the cell, which is then designated a fat-cell (Fig. 23, A'). In such cells the protoplasm occupies only a narrow peripheral zone, in which lies the extremely flattened nucleus. This protoplasmic zone is often so thin as to be invisible. Aggregations of fat-cells are abundantly sup- plied with blood- and lymph-vessels and nerves, and form what is called adipose tissue, which bears a very important relation to metabolism. In cases of extreme emaciation the fat in fat-cells is reduced to a few small globules. In place of the fat which has disappeared there is a pale protoplasm mixed with a mucoid fluid. The cell is no longer spherical, but has become flattened, and Fig. 23. — Fat-Cblls from the Ax- illa, /I, OF A Lean Individual. X 240. I. In focusing the equator of the cell ; 2, objective somewhat elevated ; 3, 4. forms changed by pressure ; /. traces of protoplasm in the vicinity of the flat nucleus, k. B. Of an emaciated individual ; k, nucleus ; y", fat-drops ; c , blood- capillaries, bundles. Techn. No. 9 TISSUES. 67 is known as a serous fat-cell (Fig. 23, B). In many fat-cells after death spheri- cal masses of needle-shaped crystals appear — the so-called margarin crystals. In addition, smaller irregularly-spherical cells are found in connective tissue that are not connective-tissue elements, but leucocytes that have passed out of the blood-vessels. They are described as "wandering cells," in dis- tinction to those of the connective tissue, which are designated as "fixed; " but this cla,ssification cannot be rigidly carried out, since in certain conditions (mainly pathologic) the fixed connective-tissue cells, and also epithelial and glandular cells, can migrate, and it is therefore better to term the latter " his- togenetic," the leucocytes " hematogenetic " wandering cells. The number and distribution of the different kinds of cells is subject to considerable fluctuation. The different elements of fibrous connective tissue are united either with- out any definite arrangement, as in areolar tissue, or are regularly disposed in definite structures. Areolar tissue is distinguished by its loosely-con- nected bundles of fibers interlacing in every direction ; it occurs be- Connective-tissue tween neighboring organs, and serves to connect them and fill in the interspaces. For this reason it '^ . . Network. is also called "interstitial" tissue. The cells of areolar tissue not in- frequently contain fat. The fibrous connective tissues characterized by Leucocytes, closer connection and regular ar- rangement of the bundles comprise : F.G. 24.-RETICULAR CONNECTIVE TISSUE. From a .1 ■ .1 t shaken section of a human lymph-gland. X 560. Techn. the cormm, the serous membranes, no. 48. j f b . ^ sou the periosteum, the perichondrium, the tendons, fasciae, and ligaments ; the compact sheaths of the central nervous system, of the blood-vessels, of the eye, and of many glands. The fibrous connective tissue in immediate contact with epithelium is usu- ually modified, forming a structureless membrane called basement-membrane or membrana propria, also hyaloid membrane. The membrana projiria of many glands — for example, salivary glands — consists of basket-works of flattened, often stellate, cells, which surround the gland -tubules. {c) Reticular Connective Tissue. — The views in regard to the structure of reticular connective tissue are divided. According to an opinion formerly widely entertained, it consists of a delicate network of anastomosing stellate cells, and to this may be traced the name " cytogenous," that is, formed of cells. Accordingly, mucous tissue may be termed cytogenous tissue. There is no doubt but that such networks occur in lower animals and in embryonic stages of higher animals. In the higher vertebrates, however, the relations are changed ; in these the network consists of slender bundles of fibrillar connective tissue, upon which lie flattened, nucleated cells (Fig. 24). By means of com- 68 HISTOLOGY. plicated methods the outlines of the cells on the fibers can be demonstrated. Finally, the fact that fibrillar connective tissue, even in the adult, may change into reticular tissue can only be comprehended on the assumption that the lat- ter is a network of delicate fiber-bundles. The meshes of reticular connective tissue are usually crowded with leucocytes. It occurs principally in lymph- glands (better, lymph-nodules), and is then called adenoid tissue. 2. Cartilage.— The matrix of cartilage is dense, elastic, easily cut, and milk-white or yellowish in color. The cells present little that is characteristic in form ; they are usually spherical or, from being flattened on one side, some- what angular. They lie in the spaces or lacuncB of the matrix, which they fill completely. Whether, as in bone, the matrix is penetrated by a system of minute channels communicating with and connecting the lacunse is extremely 6 ^ \l Fig. 25. — Hyalinf Caki il \<,e. X 240. A. Surface view of the ensiform process of frog, fresh; /, proto- plasm of cartilage-cell, which entirely fills the lacuna ; k, nucleus ; g, hyaline matrix. Techn. No. 14. B. Portion of cross-section of human rib-cartilage several days after death ; examined in water: the protoplasm, 2, of the cartilage-cells has withdrawn from the walls of the lacimEe.A; the nuclei are invisible, i. Two cells within one capsule, k: x, a developing partition. 2. Five cartilage-ccUs within one capsule ; the low- est cell has fallen out, and here only the empty space is seen. 3. Capsule cut obliquely, and apparently thicker on one side. 4. Capsule not cut, but showing the cell within, g. Hyaline matrix transformed into rigid fibers,,/". Techn. No. 15. doubtful. Many observations, in which such channels were apparently seen, have been acknowledged as erroneous; the supposed channels were a result of shrinkage, and can be produced by treating cartilage with absolute alcohol or ether. Not infrequently the matrix immediately surrounding the lacunse is specialized, and forms a strongly refractive, occasionally concentrically-striated capsule. The otherwise homogeneous matrix may be free from admixture of fibrous tissue, or it may be penetrated by elastic fibers or by bundles of white fibers. Accordingly, three varieties are distinguished : {a) hyaline cartilage, (d) elastic cartilage, (r) fibro-cartilage. (a) Hyaline cartilage is of a faint bluish, pearly, transparent color. It occurs as the cartilages of the respiratory organs and of the nose, as the costal and the articular cartilages, also in the synchondroses, and in the embryo in TISSUES. 69 many situations where it is later replaced by bone. It is characterized by the homogeneity of its matrix, which in the ordinary methods of investigation appears amorphous throughout, but after special processes, e.g., artificial diges- tion, falls apart into bundles of fibers. Further evidence in confirmation of its fibrillar structure is afforded by its appearance when examined in polarized light. It is very firm, very elastic, and on boiling yields chondrin. In certain cases the matrix may undergo a peculiar modification. In the thyroid and costal cartilages it is transformed patchwise into rigid fibers, which impart an a.sbestos-like lustre, perceptible on macroscopic inspection. In ad- vanced age deposition of calcareous salts may take place in the hyaline matrix, in the beginning appearing in the form of minute granules, siib.sequently as complete husks, surrounding and enclosing the cells. In the cartilages of the larynx this may occur as early as the twentieth year. The cells of hyaline cartilage frequently occur in groups or nests, an arrangement explained by the conditions and processes of growth. Two cells may lie in one lacuna and be enclosed within the same capsule (Fig. 25, £ i) ; i^jmHi^lJim WL^ji \' !kk!\yjl Fig. 26. — Elastic Cartilage. X 240. i- Portion of section of vocal process (anterior cartilage of a woman thirty years old ; the elastic substance in the form of granules, sections of epiglottis of a woman sixty years oltl : a fine network of elastic fibers in : X. Cartilage-celi, nucleus not visible; A, capsule. Techn. No. 16. glc) of ar>'tel nd ,. Portion network i they are the descendants of the original cell, which has undergone division by the indirect mode ; in other cases, a thin partition of hyaline substance may be seen between them. In still other cases, the septum does not develop im- mediately, and the process of cell-division may be repeated, until groups of four, eight, and even more cells may be enclosed within one capsule (Fig. 25, B 2~). Such phenomena were supposed to establish a special theory of cell- division, the so-called endogenous cell-formation. Not infrequently the car- tilage-cells in adults contain oil-globules. (J)) Elastic cartilage has a faint yellowish color. It occurs as the cartilages of the external ear, of the epiglottis, of Wrisberg and Santorini, and of the vocal process (anterior angle) of the arytenoid cartilages. It pre- sents the same structural peculiarities as hyaline cartilage, but is distinguished by the networks of finer or coarser elastic fibers that penetrate the matrix. The elastic fibers do not arise directly from the cartilage-cells, but by a transforma- tion of the matrix, and appear in the vicinity of the former as minute granules, 70 histolo(;y. J!l\ \ which later are disposed in linear rows and fuse into fibers. This phenomenon, according to an opposite view, is regarded as an indication of post-mortem dis- integration of the elastic fibers. (f ) Fibro-cartilage is found in the intervertebral disks, the pubic symphysis, the inferior maxillary and sterno-clavicular articulations. The matrix contains an abundance of fibrous connective tissue in loose bundles extending in all directions (Fig. 27,^). The cartilage-cells are few in number, have thick capsules, and occur in small groups or rows at com- paratively wide intervals. 3. Bone. — -The matrix of bone, osse- ous tissue, is distinguished by its hardness, solidity, and elasticity, properties due to an intimate blending of organic and inorganic substances. This union is of such a nature that either part may be removed without destroying the tissue. On treatment with acids, the inorganic substances are with- drawn ; the bone is decalcified, is rendered flexible, and is easily cut, like cartilage. On the other hand, the organic substances may be removed by cautious heating ; the bone is tlien said to be calcined. Fossil bones, similarly, are deprived of the organic substances through the prolonged action of moisture. The matrix or ground-substance is composed of calcium salts, especially basic calcium phosphate, and of collagenous fibrils, united by a Fig. 27.^Fbom a Hori: Fibrilla r connective ti* isue; z. cartilage-cell (nucleii s invisible) ; k , caps ■ule surroundeti by calc lareous granul< < 240. Techn. 'iG. 29. — From Sections, «, of the Humerus of a Four Months' Human Embryo ; h, of the middle turbinal bone of man ; z, bone-cells lying in the lacunae, h ; the canalicuU are only slightly visible ; g, matrix. X 560. Techn. No. 61. small amount of cement-substance in finer or coarser bundles ; accordingly, a compact, or lamellar, and a spongy matrix are distinguished. It appears homogeneous or faintly striated and contains numerous spindle-shaped spaces 15 to 27 // in length — the lacuna' — from which minute branched channels — the canaliciili — radiate in all directions ; the lacunae, with their minute canals, form an intercommunicating system of lymph-spaces throughout the matrix. Within the lacunce, sometimes improperly called "bone-cells," lie nucleated TISSUES. 7 1 flattened bodies, the real hone-cells. It is extremely doubtful whether in the adult bone the cells are connected by means of jjrocesses extending through the canaliculi, although such connection is readily observed in developing bone. The skeleton of the adult is formed principally of compact bone, which is characterized by the arrangement of the fiber-bundles in lamellas ; the matrix contains elastic fibers. Spongy bone occurs in the fetus as periosteal and intermembranous bone, and is found in the adult along sutures and at the points of insertion of tendons ; it always contains uncalcified connective-tissue bundles, the so-called Sharpey's fibers, which, however, are also found in the circumferential and interstitial lamella; of compact bone, the remains of the primary or periosteal bone. Fibrous connective tissue and cartilage may be converted directly into osseous tissue by calcification of the matrix ; and the connective tissue and Bone-cell. — Fic. 30. — Portion of Cross-Section of thb Diaphysis of thb Humerus of a Four Months' H cartilage-cells then become bone-cells. This, however, is of comparatively rare occurrence ; usually, the formation of osseous ti.ssue follows the calcifica- tion of the matrix of the embryonal cartilage and connective tissue, in which young, still indifferent, connective-tissue cells arrange themselves upon the surface of the calcified trabecuhi; and produce bone-substance. Dentine is a modification of bone, from which it is distinguished by its developmental history ; the formative cells, the odontoblasts, are not enclosed within the matrix, but penetrate the latter with their processes. Further details will be found in connection with the structure of teeth. Blood-vessels, Lymphatics, and Nen'es. — Connective-tissue structures are, in general, poorly supplied with blood-ves.sels, lymph-vessels, and nerves. An exception occurs in adipose tissue, which has a rich vascular supply. Connec- tive tissue plays a very important i)art, however, in the transference of nutritive 72 HISTOLOGY. fluids — tissue jidics, lymph — passing from the blood-vessels to the tissues. When the matrix is soft, as in mucous tissue, the lymph permeates the entire sub- stance ; when on the other hand, it is denser, the lymph circulates in a system of intercommunicating channels formed by the cell-spaces — lymph-spaces — and the minute canals connecting them — lymph-caiialiculi. This is the case in bone and the more compact connective tissues. Whether the tissue-juice is diffused throughout the matrix of hyaline cartilage or conveyed in definite channels is still undetermined. The intercellular substance of epithelium is in direct connection with the lymph-capillaries of the subjacent connective-tissue, and may be regarded as being similarly permeated by the lymph. III. THE MUSCULAR TISSUES. The structural elements of the muscular tissues, the inusclc-fibers. occur in two forms, the smooth and the striatcJ. Both are cells whose body is extraor- dinarily elongated. I. Smooth, Non-striated, or Involuntary Muscle. — This consists of contrac- tile fiber-cells, spindle-shaped, cylindrical, or slightly-flattened elements with tapering extremities (Fig. 31). They vary in length from 45 tq 225 //. in G. 31.— Two s potash-lye. The I. Isolated with 35 per t n of the lye. Techn. No. 24 width from 4 to 1 jj.; in the gravid uterus fibers measuring 0.5 mm. have been found. They are composed of homogeneous protoplasm and an elongated or rod -shaped nucleus ; the latter is characteristic of the smooth muscle- fiber. The protoplasm of certain fibers, those, for example, of the vas deferens, exhibits longitudinal striation, which has led some authors to regard the smooth muscle-fiber as composed of minute contractile fibrillar. In fishes and amphibians muscle-fibers containing pigment have been found in the iris. [According to many histologists the smooth muscle-fiber is invested by an exceedingly delicate structureless hyaline sheath, corresponding to the sarco- lemma of the striated fiber.] The fibers are collected into fasciculi, and firmly held together by a homo- geneous cement-substance. Communication between neighboring fibers by means of protoplasmic processes or intercellular bridges, like those occurring in certain ephithelia, has been observed in the muscular tunic of the intestine of the dog and cat, and also of man. Septa of connective tissue are found only at comparatively wide intervals (Fig. 32 ). The fasciculi are united to form strata or membranes, in which their dis- position is parallel, as in the muscular coat of the intestine, or they cross and interlace forming complicated networks, as in the urinary bladder and the uterus. The larger blood-vessels run in tlie connective-tissue septa ; but the TISSUES. 73 capillaries penetrate the fasciculi, within which thev Ibrm networks with elonga- ted meshes. The lymph-vessels follow the course of the blood-vessels, and are present in considerable numbers. For the nerves of smooth muscle, see Peripheral Nerve-endings. Smooth muscle-tissue occurs in the alimentary canal, in the trachea and bronchial tubes, in the gall-bladder, in the capsule and pelvis of the kidneys, in the ureters and the urinary bladder, in the reproductive organs, in the vascu- lar channels and lymph -vessels, in the eye, and in the skin. The contraction of smooth muscle-fiber is slow, and is not under the control of the will. 2. Striated or Voluntary Muscle. — It is only by the study of their develop- ment that the striated muscle-fibers can be recognized as the morphologic equivalents of cells. As a result of the extraordinary elongation of the em- bryonal elements, the proliferation of their nuclei, and the peculiar differentia- tion of their protoplasm they have become highly-specialized structures. The fibers are cylindrical in shape, and in the interior of the larger muscles have rounded or pointed ends ; on the other hand, at the extremities of the muscle they possess a pointed inner end, while the outer end, in contact with the tendon, is broad. The latter is blunt or notched, often step-like and tapering. Anastomoses, septun divisions, and fissures occur; branched fibers are found in the muscles of the eye, the tongue, and the skin (Fig. 34, 4). smooth^mulcie- They vary in length from 5.3 to 12.3 cm., «rsVs«"oT in width from 10 to 100 11. It is probable Fig. 32 -Srction of thb Circular Layer .\.^\ ri -L • .. 1 ..1- OF THE Muscular Coat of the Human that there are fibers having greater length. Intestine, x 560. Tcchn. No. 103. but their isolation entire is very difficult to accomplish. In the embryo the fibers differ but little in width, but after birth their development in this dimension varies, and is dependent on the functional activity of the muscle ; in the adult, robust muscles possess thick fibers, delicate muscles have thin fibers. Apart from this, their diameter depends also on the nutritional condition of the individual. Furthermore, larger animals possess thicker fillers than smaller ones. The difference in caliber is, therefore, of a threefold nature. Under the microscope each fiber exhibits alternate broad dim and narrower light transverse strife. The substance of the dim stripes is doubly refracting or anisotropic, that of the light stripes singly refracting or isotropic. High amplifi- cation shows that both the dim and light strise are transversely divided ; in the light zone a delicate dim interrupted line may be seen, the intermediate disk (Fig. 33, q). Each part of the light zone, above or below the intermediate disk, constitutes a lateral disk. In the dim transverse band a clear stripe, the median disk, has been observed. [In certain forms of invertebrate muscles the lateral disk is crossed, above and below the intermediate disk, by a dark stripe, the secondary disk.'] Owing to their extreme variation and their instability, these disks are of subordinate significance. Besides the cross-marking, a more 74 HISTOLOGY. or less distinct longitudinal striation maybe observed. Treatment with chromic acid solutions renders this striation more evident, and may even effect the dis- integration of the fibers, which fall apart lengthwise into delicate fibrils, each of which exhibits the cross-striae. These fibrils are the contractile structural elements, and are called -ultimate fibrilla. The muscle-fibers of some animals, after treatment with certain reagents, cleave transversely into disks. Both fibrillae and disks may be further separated into smaller prismatic anisotropic particles called sarcous elements. Certain authors have interpreted the disks, others the sarcous elements, as the true structural units. [According to the theory of Rollett regarding the structure of voluntary muscle, the fiber is composed of the dim anisotropic contractile substance and the light isotropic, relatively passive sarcoplasm. The highly-specialized con- tractile substance is in the form of slender spindles, the ends of which are pro- longed into extremely fine filaments and terminate in a minute knob. The spindles, arranged end to end, form the continuous contractile fihrillce, which grouped in parallel bundles constitute the sarcostyles, and extend throughout the length of the fiber. The thicker parts of the apposed spindles form the dim transverse bands, the knobs the dim intermediate disks in the light trans- verse bands. The spindles correspond to the sarcous elements.] The contractile fibrillas are grouped into bundles — sarcostyles or viuscle- columns ; they are arranged parallel to one another and held together by the sarcoplasm, which also surrounds and unites the bundles. The disposition of the sarcoplasm is best seen in cross-section ; high amplification is required. It presents the appearance of a clear network, and within the meshes are the muscle-columns in section, — small dark polygonal areas known as C(3/i///;d'/'w'i- yields. The sarcoplasm contains the interstitial granules — consisting partly of fat and probably also partly of lecithin — and the nuclei. The latter are oval bodies placed parallel to the long axis of the fiber ; in mammals, bony fishes, and some birds they are chiefly situated immediately beneatli the sarcolemma. TISSUES. 75 upon the surface of the muscle-substance ; in other vertebrates they are embedded within the sarcoplasni. Each muscle-fiber is closely invested by a structureless sheath, the sarco- lemma, which represents the cell-membrane. Thus the fiber of striated muscle comprises the fibrillar, the sarcoplasni, the muscle- nuclei, and the sar- colemma. The striated fibers are found in the muscles of the trunk and the extremi- ties, of the eye and the ear, also in the tongue, the pharynx, the upper half of the fjesophagus, in the larynx and the diaphragm, the genital organs, and the rectum. In some animals, the rabbit, for example, two varieties of striated muscles are distinguished, the ?-ed (semitendinosus, soleus) and the white or pale (adductor magnus) ; and correspondingly, two varieties of muscle-fibers: i, Fig. 34. — Portions op IsoLATRD Striated MuscLB-FiBBRS OF Fkog. X 50. i. After treatment with water : ji, sarcolemma ; at x the musclc-5:ubstance is torn : the cross-striation not apparent, the longitudinal striation distinct. Techn. No. 19. 2. After treatment with acetic acid : k, nuclei : the minute punctations repre- sent interstitial granules. Techn. No. 20. 3. After the action of concentrated potash solution ; e, rounded ends: the numerous nuclei are swollen and vesicular in appearance. With tnis amplification the cross- striation in a and 3 is not visible. Techn. No. 32. 4. Branched muscle-5ber from the tongue of the frog. dim fibers, rich in sarcoplasni, less regularly cross-striped, exhibiting distinct longitudinal striation, and possessing in general a smaller diameter (found in the soleus of the rabbit) ; 2, pale fibers, poor in protoplasm, more distinctly cross-striated, and having in general a greater diameter. The latter represent the more highly-differentiated fibers. While in certain animals the two varie- ties of fibers occur separately, each in particular muscles, in others — also in man — they are found intermingled in the same muscle. As a rule, the more functionally active muscles — cardiac, ocular, masticatory, and respiratory — contain the greater number of red fibers. The pale fibers, on the other hand, respond more rapidly to electric stimulation. The contraction of the striated fibers, as compared with that of smooth muscle, is quick, and is under the control of the will. The striated fibers are united into bundles by areolar tissue, which serves also to convey the numer- 76 HISTOLOGY. ous ramifications of the blood-vessels and nerves supplying the muscular tissue. The lymphatic vessels are few in number. 3. Cardiac Muscle. — The muscle-fibers of the heart occupy a peculiar position. Although transversely striated, in the history of their development, as well as histologically, they must be regarded as modifications of the smooth muscle-fibers. In the lower vertebrates, in frogs for example, they are spindle- shaped, possess elongated nuclei, and are often more distinctly striated trans- versely than longitudinally (Fig. 35, A'). The cardiac muscle of mammals consists of short, cylindrical fibers, the ends of which are often step-like. The protoplasm is partially differentiated into cross-striated fib)illcz, which not infrequently are grouped into muscle- columns radially arranged to the axis of the fiber (Fig. 35, Z>). The remnant of undifferentiated protoplasm — sarcoplasm — proportionately consid- ~ffl C ,« auricles, where they form a close-meshed network or are ^ '-,C^> blended in a fenestrated membrane (Fig. 21). The free ^.■^m— i. surface, that directed toward the cavity of the heart, is ^ " clothed with a simple layer of irregularly polygonal epithe- lial (endothelial) cells. The naked miiscle-fihcrs, whose structure has been '"/""erimysfum dcscribcd, are surrounded by a delicate perimysium, and sw'ined il^ciei ; r'.btood'- are United by numerous lateral processes. The arrange- No^al! ^^-t"- '^ ='=''"• ment of the muscle-fibers is very intricate. The muscle tissue of the auricles is entirely separate from that of the ventricles. In the former an outer transverse layer, common to both, and an independent longitudinal layer in each can be distinguished. In addition, numerous small bundles pursue independent courses in other directions. The muscle tissue of the ventricles is much more irregularly distributed. The bundles extend in all directions, often describing a figure-of-eight in their course. Between the auricles and ventricles lie firm tendinous ligaments, the annuli fihrosi, of which the right is .stronger than the left. Similar but less developed ligaments lie at the arterial orifices of the ventricles. Numerous muscle-fibers take their origin in these ligaments. The pericardium is a connective-tissue membrane penetrated by elastic 84 Muscle-fiber; THE CIRCULATORY SYSTEM. 85 fibers, clothed on its outer (visceral layer) and inner (parietal layer) surfaces by a single stratum of epithelium. The parietal pericardium is considerably thicker than the visceral. Between the latter and the heart fat-cells are found. The valves of the heart are composed of fibrous connective tissue, contin- uous with that of the annuli fibrosi, and their surfaces are clothed by the endo- cardium. Muscle-fibers are found only in the roots or attached edges of the valves. The numerous blood-vessels of the muscular wall of the heart form typical capillary networks with elongated meshes (see the Muscular System). The pericardium and endocardium, the latter in its deeper strata, also possess blood-vessels. The lymph-vessels are extremely numerous in the heart. They form a comprehensive system embracing all the lymph-spaces in the clefts between the muscle-fibers, and accompany the blood-vessels in their course. The nerve supply of the heart includes medullated nerve-fibers derived from the pneumo- gastric and nonmedullated sympathetic nerve-fibers from the cervical ganglia ; along their course numerous ganglion-cells occur. ^?^^H Fig. 44.— Small Aktbribs of Man. i. Nuclei ot intima, the outlines of the cells are invisible; m, nucle of circuLirly-disposed musclc-fibers of media; a, nuclei of the adventitia ; A, artery with the surface ir focus ; B, artery with the lumen in focus ; at m' the nuclei of the muscle-fibers of the media are seen ii optical section ; C, small artery shortly before transformation into capillaries. The media here consists of a few isolated muscle-fibers. X 240. Techn, No. 34 a. The Arteries. The walls of the arteries comprise three coats : i, tunica intima ; 2, tunica media; 3, tunica adventitia. The elements of the tunica media are transversely disposed, those of both the other tunics chiefly longitudinally. The structure and thickness of these coats varies with the size of the artery. This renders their classification as small, medium, and large arteries desirable. The small arteries include the terminal branches shortly before their trans- formation into capillaries. The intima consists of elongated, spindle-shaped epithelial cells and a structureless membrane, the so-called internal elastic mem- brane, which in somewhat larger arteries assumes the character of a fenestrated membrane. The media is formed of a single layer of circularly-disjiosed smooth muscle-fibers. The adventitia, the external coat, is composed of Ion- 86 HISTOLOGY. gitudinally-disposed bundles of connective tissue and fine elastic fibers. It blends insensibly with the surrounding connective tissue. The arteries of medium size comprise all the arteries of the body with the exception of the aorta and the pulmonary artery. The intima of these vessels has increased in thickness owing to the interposition between the endothelium and internal elastic membrane of delicate fibrous connective tissue, flattened corpuscles, and networks of elastic fibers. This subendothelial layer is absent in the uterine arteries of young individuals, in the coeliac, external iliac, the renal, and the mesenteric arteries. The media, in addition to .several super- imposed layers of circularly-arranged smooth muscle-fibers, comprises wide- FiG. 45.— Portion of Cross-Section of the Brachial Artehv op Man. X loo. Techn. No. 33. meshed networks of elastic fibers. At the inner boundary of the media of some arteries longitudinally-disposed muscle-fibers occur; these are especially well-developed in the subclavian artery. The proportion of the two tissues in the different arteries is extremely variable. In the coeliac, femoral, and radial arteries the muscle tissue preponderates ; in the carotid, axillary, and common iliac, the elastic tissue. The adventitia has also become stouter. Thick elastic fibers occur in especial profusion at the boundary of the media and in many arteries form a continuous layer designated the external elastic membrane. New elements in the adventitia of medium size arteries are smooth muscle- THE CIRCULATORY SYSTEM. 87 fibers, which appear in single longitudinally-disposed bundles, and never form a continuous layer. In the large arteries (aorta and pulmonary artery) the epithelial cells of the intima are broader and more polyhedral in outline than in medium-sized vessels. The subepithelial layer consists of fibrous connective tissue, elastic networks, and flattened, stellate, or spherical cells. The elastic network is closer meshed the nearer to the intima it is, and finally passes into a fenestrated membrane corresponding to the internal elastic membrane of small and medium- FlG. 46. — ENUnxHBLIUH OF A MkS- Fig. 47. — Pll BNTBKic Aktrryop Raubit. Sur- face vicw. X260. Tcchn, No. 35. ■ Cross-Sbction op Thoracic Aokta op Ma X 100. Techn. No. 33. sized arteries. The media of the large arteries is characterized by the prepon- derance of elastic tissue over the muscular elements. The thin elastic networks of the media of medium-sized arteries is here replaced by close networks of broad elastic fibers or by fenestrated membranes, which alternate regularly with the lamellne of smooth muscle-fibers. The elastic elements, like the muscle- fibers, are circularly arranged. The muscular lamellae are penetrated in an oblique direction by elastic fibers which connect all the elastic elements of the media. The media of the larger medium-sized arteries possess the elastic »S HISTOLOGY. membrane; it is well-marked in the carotids, which closely approach in struct- ure the large arteries. The adventitia of large arteries presents no essential peculiarity and differs but slightly from that of the medium-sized arteries. It does not possess the external elastic membrane. In the lower animals smooth muscle-fibers are present. The Veins. There is no definite proportion between the size of the veins and the thickness of their walls, and no basis for a division into groups as with the arteries. The veins are characterized by the preponderance of fibrous connec- tive tissue, and the slighter development of the muscular and elastic elements. Three coats, as in the arteries, may be distinguished. Owing to the meager development of the media some histologists have suggested that only two coats are present, the tunica intima and tunica adventitia, and that the layers usually regarded as tunica media belong to the latter. The intima consists of a single Smooth muscle-fibers of the adventitia. Cross-Section through a Vein op Lime of Man. X loo. Techn. No. 33. layer of endothelial cells which are elongated only in the smallest veins, in others are polygonal in outline. In medium-sized veins, 2 to 9 mm. in diame- ter, nucleated connective-tissue elements occur in the subendothelial layer, which in large veins (femoral, popliteal, and superior cava) is arranged in distinct lamellag. Surrounding this is the internal elastic membrane, which is structureless in small veins, but in medium-sized and large veins it is represented by elastic networks. Oblique and longitudinally-disposed smooth muscle- fibers occur in the intima of the iliac, femoral, saphenous, and mesenteric veins. The media exhibits great variation. It is composed of circular muscle- fibers, elastic networks, and fibrous connective tissue, and is best developed in the veins of the lower extremities (especially in the popliteal), less in the veins of the upper extremities, still less in the large veins of the abdominal cavity, and is absent in many veins (those of the pia and dura, the bones, and the THE CIRCULATORY SYSTEM. 89 retina, in the superior cava, and also in the veins proceeding from the capil- laries). The usually well-developed adventitia consists of intercrossing bundles of connective tissue, elastic fibers, and longitudinally-disposed smooth muscle- fibers, which are more highly develo])ed in the veins than in the arteries. The adventitia of certain veins (the trunk of the portal and the renal) possesses an almost complete membrane of longitudinally-arranged muscle-fibers (Fig. 49)- The valves of the veins are folds of the intima, covered on both surfaces by epithelial cells, which, on the surface directed toward the vascular stream, are elongated in the direction of the current ; on the opposite surface, toward the wall of the veins, they are elongated transversely. The Capillaries. The capillaries establish the communication between the arteries and veins. There are a few exceptions, as for example in the corpora cavernosa. In the transformation of the arteries into capillaries a gradual simplification of the structure of the vessel-wall follows (Fig. 44). The media grows continu- imima. ^ — —-^—-^----^^^^ ally thinner, until in the vessels between ' " ' 'Cy's?^ /~^i,t^ _^ the smallest arteries and capillaries it is Adventiiiawithcro«.j ', '^'^^«^a . represented by a few isolated circular n" fiTe's. °"^' " ' j ■^^-^■^^'^M muscle-fibers, at.wide intervals, that ulti- ~ -~^-^- mately disappear entirely. The advcn- ■■' o;*Ji7J:"°^o.^">e'hi°NlT3- '*'"''*'' ^"^ titia becomes correspondingly attenu- ated until it consists of a thin layer of connective-tissue fibers and corpuscles that also ultimately vanish, so that at the last the only part of the vessel-wall that remains is the intima. This is also reduced to a stratum of plate-like, nucleated endothelial cells. The walls of the capillaries, therefore, consist of a simple layer of endothelial cells, spindle-shaped, and united at their edges by a small amount of cement-substance. The capillaries divide without decrease in caliber and by anastomosis with neighboring capillaries form networks differing widely in the size of their meshes. The closest meshes occur in the capillary networks of secretory organs, as in the lung and the liver ; wide-meshed networks in the muscles, the serous membranes, and the special sense organs. The reverse obtains with regard to the caliber of the capillaries ; the widest capillaries are found in the liver, the narrowest in the retina and in the muscles. Development of Capillaries. — Only the developmental processes in the post- embryonic epoch will be considered here. A minute conical mass appears on the wall of an existing capillary, resting with a broad base on the latter and having a tapering, sharp-pointed free end. In the further course of develop- ment this pointed free end unites with another off-shoot arising from a different point on the capillary wall. They are solid at first but gradually become hoi- 90 HISTOLOGY. low by an extension of the lumen of the capillary, and subsequently the walls of the new vessels become differentiated to endothelial cells. The development of new capillaries is always consummated in connection with existing capillaries. These blind capillary sprouts may be hollowed out at an early period ; corpus- cles that flow into them disintegrate because they are excluded from the circu- lation and the interchange of gases. They fall into fragments, which have been erroneously interpreted as hematoblasts ; they have no connection with the true hematoblasts. All medium and large blood-vessels possess small blood-vessels (vasa vasorum) that provide for the nutrition of their walls ; they run almost exclusively in the adventitia. The intima is always without blood-vessels. All blood-vessels are furnished with nerves, which form a plexus of medul- lated fibers in the media of the arteries and veins. From these, nonmedullated fibers arise which are distributed to the muscle-fibers. The capillaries are 55=0.0 C)°''g O Fig. 50. — Surface View of a Portion of the Greater Omentum of a Seven-Days* Rabbit, c. Blood capill.*ries, some containing blood-corpusclcs ; j, capillary sprout tapering to a free solid point; :', voung capillary, the greater part of which is hollow ; at s' still solid ; k, nuclei of peritoneal endothelium. X 240. Techn. No. 37. accompanied by encircling networks of delicate nonmedullated nerve-fibers. Many blood-vessels are surrounded by lymph channels ; occasionally the lymph- spaces in the adventitia unite to form a complete ensheathing sinus, the adven- titial or perivascular lymph-space. The carotid gland is really no gland but consists essentially of blood- vessels. The capillaries arising from the division of the single arterial vessel differ greatly in width, and are surrounded by numerous cells resembling the plasma-cells of connective tissue, arranged in rounded groups forming the so- called secondary nodules. The veins are collected at the periphery of the organ, which besides contains fibrous connective tissue, isolated ganglion-cells, and a conspicuous number of medullated and nonmedullated nerve-fibers. Similar in structure is the coccygeal gland, the blood-vessels of which are char- acterized by hemispherical evaginations. the circulatory system. 9i The Blood. The blood is a slightly clammy, red-colored liquid which consists of a fluid substance, the blood-plasma, and formed elements, the blood-cells, the blood-platelets, and elementary granules. The blood-cells are of two kinds : colored blood-cells and colorless blood-cells. The colored blood-cells are soft, flexible, highly-elastic elements, and pos- sess smooth, slippery surfaces. In man and in other mammals they have the form of a flat-circular disk, slightly concave on each surface, and therefore re- semble biconcave lenses. (Exceptions occur in the llama and the camel, in which the colored blood-cells are oval. ) The average diameter in man is 7. s /t, the thickness 1.5 11. The colored blood-corpuscles of domesticated mammals are all smaller, the largest are those of the dog (7.3 //)• The colored blood- cells consist of a stroma (protoplasm), the spaces of which are filled with the blood-coloring matter, the hemoglobin. The hemoglobin imparts to the cor- puscle its yellow or yellowish-green color. A nucleus and a proper cell-mem- FlG. 51. — Blood. Corpuscles Magnified 560 Times. /I. Of man: 1-6. Discoidal cotored blood-ccIU; i, seen with close focus; 2, with distant focus; 3 and 4, viewed edgewise; 5, crenaled In consequence of evapo- ration ; 6. after treatment with water ; 7, spherical colored blood^corpuscle ; 8. colorless blood-corpuscle ; 9, blood-platelets. />. Of frog: 10-13. Colored blood-cells; 10, fresh nucleus, indistinct; 11, a few minutes later, nucleus plainly visible ; 12, seen from the side ; 13, after treatment with water; 14, living ; 15, dead colorless blood-corpuscle. Techn. Nos. 38-41. brane are wanting. The colored blood-corpuscles ol fishes, amphibians, rep- tiles, and birds are distinguished from those of mammals by their oval, bicon- vex form, their generally greater size (22 ,« long by 15 /m broad in the frog), as well as by the presence of a round or oval nucleus ; in other respects they exhibit the same properties as those of mammals. The white or colorless blood-cells (leucocytes) occur not only in the blood but also in the lymphatic vessels, where they are termed lymph-corpuscles. They are also found outside of the vessels, in bone-marrow, in adenoid tissue, in fibrous connective tis.sue, and also between epithelial and gland-cells, where they have wandered by their power of amoeboid movement, and are therefore described as " wandering cells." The colorless blood-cells consist of a clammy protoplasm and a nucleus, and are without a cell-membrane. A definite form cannot be described, because during life they are engaged in amoeboid activity. In a condition of rest they are spherical (Fig. 52). 92 HISTOLOGY. Their size and the properties of the nucleus and protoplasm have led to the following classification : 1. The smallest leucocytes, measuring 4 to 7.5 /i. They possess a propor- tionately large round nucleus surrounded by a narrow zone of protoplasm, so small in amount that it can scarcely be demonstrated by the usual methods (Fig. 52, a). These are regarded as young forms; they exhibit little activity and are found chiefly in adenoid tissue. 2. The second kind have a diameter of 7.8 to 10 p. ; their nucleus is spheri- cal and surrounded by a larger amount of granular protoplasm. The nucleus may be cleft or lobulated (Fig. 52, i). Occasionally several disjoined nuclei are present ; the slender filaments uniting the several parts of the lobulated nucleus are frequently overlooked, which then simulates several separate nuclei. The latter form is very active ; the lobulation of the nucleus is in fact the expression of this activity ; seventy-seven per cent, of the leuco- cytes of the blood are of this form. 3. The third kind of leucocytes measure from 8 to 14 p., and are charac- terized by their granular protoplasm ; the granules are variable in quantity and react differently to stains. According to their affinity for @acid, basic, or neutral dyes, oxyphile, basophile, and (*^ neutrophile leucocytes are distinguished.* "^ ' -C"^^*^ '"'^'^ determination of the proportionate number of, as '©' ^5^ ^2^ well as the ratio between, the colored and colorless Fig. 52.— Colorless blood-corpuscles is coupled with considerable difficultv, Blood-CellsofMan. y t- ]■: c. Cell with neutrophile and oulv approximately-correct estimates can be siven. granules. X 600. Tcchn. ,. No. 39. In man one cubic millimeter of blood contains about 5,000,000 colored corpuscles. The white blood-cor- puscles are present in the blood in much smaller number, about i to 300 to 500 colored. The blood-platelets are very unstable, colorless, round or oval disks having a diameter one-third to one-fourth less than that of the colored blood-cells ; at times they are present in the blood in large numbers. A leading role in the process of coagulation of the blood is ascribed to them. The elementary granules are for the most part fatty granules transferred from the chyle to the blood. They are frequently observed in the blood of the lower mammals, but are not normally present in the blood of man. After death, or as a result of changes within the vessel-walls, the blood, under the influence of two substances which pass into solution in the plasma, fibrinoplastin and fibrinogen, coagulates, and fibrin is formed. The coagulated blood separates into two parts, the clot and the serum. The clot is red, and contains all the colored and the majority of the colorless blood -corpuscles and the fibrin, which microscopically consists of a feltwork of fine, straight, *Ehrlich, who made this classification, proceeds therein from a different standpoint than that of the chemist ; acid colors are those, for example, with which acids develop the coloring principle. THE LYMPHATIC SYSTEM. 93 interlacing filaments. Chemically fibrin resembles glutinous connective tissue. The supernatant serum is colorless and contains a few colorless blood-cells. The coloring substance contained in the colored corpuscles, x!nt hemoglobin, crystallizes under certain conditions, and in nearly all vertebrates the crystals belong to the rhombic system. Their form in the different animals varies greatly ; in man it is usually prismatic. Hemoglobin is readily decomposed. One of the decomposition products is hematin, which yields hematoidin and hemin. Crystals of hematoidin occur within the body in old extravasated blood, for example, in the corpus luteum, and are rhombic prisms of orange- red color. The hemin crystals, when well-developed, are rhombic plates or needles of a mahogany-brown color. They are often very irregular in form, and as a positive indication of the presence of blood have an important legal relation. Development of Colored Corpuscles. — From the earliest period of embryonic development and during the whole of life nucleated colored blood-cells (hema- toblasts, erythroblasts) are found in certain situations. Their number fluctu- ates and runs parallel to the energy of the blood-forming processes. By indi- FlG. 53. — I. Hemin crystals of man; whetstone forms on the right. 3. Crystals ol ( toidin crystals of man, magnified 560 times. 4. Hemoglobin crystals of the dog, magnified ico times; *T, a crystal showing a tendency to fall apart lengthwise. Techn. No. 44. rect division they give rise to the nonnucleated colored blood -corpuscles, which at first contain a nucleus, but lose it later. As centers for the formation of blood in the embryo the liver and, later, the spleen, in the adult exclusively the bone-marrow, may be mentioned. 2. THE LYMPHATIC SYSTEM. THE LVMPH-VESSELS. The walls of the larger lymph-vessels, from 0.8 to 0.2 mm., like the blood-vessels, are composed of three coats. The intima consists of endothelial cells and a network of delicate elastic fibers with elongated meshes. The media is formed of circularly-disposed smooth muscle-fibers and a few elastic fibers. The walls of the smallest lymph-vessels and the lymph-capillaries are composed exclusively of extremely delicate endothelial cells, often having sinuous outlines. The lymph-capillaries, unlike the blood-vessels, present at frequent intervals constrictions and dilatations, and where they branch are often considerably widened ; the networks they form are more irregular. 94 HISTOLOGY. The question as to the origin of the lymph-vessels is not yet satisfactorily determined ; while some authors are of the opinion that the lymph-capillaries form a closed system, according to another view, widely entertained, the lymph-capillaries are open toward the periphery, and are in direct con- nection with the system of intercommunicating cell-spaces of connective tissue. These interfascicular clefts are by some set apart as " lymph canaliculi " from the lymph-vessels with well-defined walls composed of continuous layers of cells ; other authors include the lymph-canaliculi in the lymph-vessels. According to the first opinion the surplus of nutritive fluids (tissue-juices) diffused through the walls of the blood -capillaries, and not used in the nutrition of the tissues, is returned to the closed lymph-capillaries by endosmosis ; the second view holds that the tissue-juices pass directly from the tissue into the patent orifices of the lymph- capillaries. It is a significant fact that the lymph-vessels of the pleura and of the peritoneum are in open com- munication with their respective cavities through small openings — stomata — between the endothelial cells, which in the pleura are found at the intercostal 1^^ spaces, and in the peritoneum on the central tendon of the diaphragm. BIT, showing the boundaries of the endothelial cells. X 50. Techn. No. 35. The Lymph-Nodes. The lymph-nodes (incorrectly "lymph-glands") are macroscopic, encapsuled bodies found along the course of the lymph-vessels ; they are usually rounded, oval, or flat, kidney-shaped structures, and differ greatly in size. At one side there is often a scar- like depression, the hikes, at which the efferent lymph-vessels emerge. The afferent lymph-vessels penetrate the nodes at various points. Their con- struction becomes intelligible if we proceed from the following conception : in certain localities three to six lymph-vessels divide and anastomose, forming a kind of rete mirabile, and then reunite into the same or a less number of usually narrower lymph-vessels.* The dividing lymph-vessels are called afferent (vasa afferentia), the reunited, efferent vessels (vasa efferentia). Within the meshes of this reticulum lie spherical and elongated masses that consist of adenoid tissue. The spherical masses, the scco?idary nodules (follicles), occupy the periphery ; the elongated masses, the medullary cords, the center of the lymph-node. * Retia mirabilia were first described in connection with the blood-vessels. They occur along the course of both arteries and veins ; the vessel suddenly breaks up into branches and these into capillaries, which reunite into a single vessel. Exquisite examples of such networks occur as the glomeruli of the kidneys. THE LYMPHATIC SYSTEM. 95 The node is enveloped in a capsule of fibrous connective tissue, which sends into the interior of the organ stout fibrous bundles, the trabeciilce (Fig. 55). Finer extensions from the trabecule form a reticulum which breaks through the walls of the lymph-vessels, penetrates the secondary nodules and the medullary cords, and forms a support for the numerous leucocytes present. The lymph-nodes consist of a cortical and a medullary region that vary greatly in their proportionate extent. The cortex contains the secondary nodules, which are directed toward the center of the organ and merge into the medullary cords (Fig. 55). The secondary nodules and medullary cords are surrounded by the sinus-like continuations of the afferent lymph-vessels. The latter, in this situation, are greatly expanded and are termed lymph-sinuses ; they are interwoven with the connective-tissue reticulum. The lymph-vessels never penetrate the interior of the secondary nodules. The secondary nodules and the medullary cords are composed of adenoid tissue ; that is, of a reticulum of connective tissue the meshes of which are crowded with leucocytes. In many of the secondary nodules there is a light, rounded area, xht germinal center, in Medullary cords. " Follicle." Lyniph-s Fig. 55. — Section op a Lymphatic Nodulb op ' Cat. X 30. Techn. No. 47. which karyokinetic figures are always to be found. Multiplication of cells also occurs in the medullary cords, but in a much slighter degree. The secondary nodules are, therefore, centers for the formation of the leucocytes, which pass into the lymph-sinuses and thence into the vasa efferentia. The ca])sule consists of fibrous connective tissue and smooth muscle-fibers, which in the large lymph-nodes of some animals are arranged in bundles. The trabeculae have the same structure ; they pass between the secondary nodes and medullary cords but do not come into contact with them, being separated from them by the lymph-sinuses. The walls of the lymph-sinuses are formed of a simple layer of plate-like cells ; similar cells clothe the surface of the nodules and the cords, and are applied to the trabeculae and the connective-tissue reticulum. The structure of the lymph-nodes is difficult to recognize, owing to several complications. These consist in: i, the merging of neighboring secondary nodules ; 2, the anastomosis of the medullary cords in the form of a coarse network ; 3, the network formed by the trabeculx ; 4, the interlacing of 96 HISTOLOGY. the networks formed by the medullary cords and the trabecular ; 5, the pres- ence of leucocytes in the lymph-sinuses, which must be removed by special methods. The secondary nodules, the medullary cords, and the leucocytes in the lymph-sinuses form a soft mass, \ht pulp or parenchyma of the lymph-node. The majority of the blood-vessels enter at the hilus, the others at various points on the surface of the node. The latter are smaller vessels and divide in the capsule and in the large trabecule, in the axes of which they run. The large artery entering at the hilus divides into a number of branches, which are surrounded by a richly-developed connective tissue. The branches are prin- cipally distributed to the adenoid tissue, only a few entering the trabeculae ; they pass through the lymph-sinuses, to the medulla and to the cortex, and in both situations break up into rich capillary networks, which supply the oxygen needed in the formation of leucocytes. The veins emerge at the hilus. — ^ Medull.-^ry cords. Fig. 56— From a Section through the Medulla of a Lymphatic Nodule of Ox. X 5°- '" '•": upper half the trabeculae and medullary cords are cut lengthwise, in the lower half crosswise. Both form an anas- tomosing network. In the lymph-sinuses fine fibers of reticular connective tissue are seen, which still in part contain leucocytes. Drawn with change of focus, 'lechn. No. 48. The nerves are few in number, the supply including bundles containing both meduUated and nonmedullated fibers ; their ultimate distribution is still undetermined. The Peripheral Lymph-Nodules. Adenoid tissue is not confined to the lymph-nodes, but, in different degrees of development, occurs widely distributed in many mucous membranes ; sometimes as diffuse, sometimes as definitely-circumscribed infiltrations of leuco- cytes. These formations are not included in the lymphatic system. More highly-specialized structures, nodules with germinal centers, resembling exactly the secondary nodules of the lymph-nodes, are also found in the mucous mem- branes ; these are termed the peripheral lymph-nodes, and included in the lymph- atic system. In many mucous membranes they occur isolated, as the solitary nodules (solitary follicles), or grouped, as " Peyer's patches," and lie always in a simple layer in the membrana propria close to the epithelium (see the THE LYMPHATIC SYSTEM. 97 DigestiYC Organs). The number and distribution of the peripheral lymph- nodes is subject to considerable fluctuation, not only in the different species of animals, but in different individuals ; since their mass varies and there are fre- cjuent transitions from circumscribed to diffuse infiltration, it is probable that they are temporary structures, that arise and disappear during life. The follicles are distinguished from the real lymph-nodes by the absence of the encircling lymph-sinus. The only exceptions occur in the rabbit, in which the sinus is present in the Peyer's patches, but not in the solitary follicles. But the possession of a germinal center, a brooding-place for young leucocytes, appears in so far to entitle them to a place in the lymphatic system. The young leucocytes only in part enter the Ivmijh-vessels : many wander through ,. , the epithelium to the surface of the mucous membrane. Tin; Lymph. The lymph is a colorless fluid in which leucocytes ( lymph-corpuscles) and granules are suspertded. The latter are immeasurably small, consist of fat, and M.iipighi.in -: ' are found principally in the lymph- (or corpusccs. chyle-) vessels (lacteals) of the intestine ; frequently they are present in enormous ''"'p-' numbers ; they impart the white color to ' fl the chyle. In other Ivmph-vessels the „ ii fatty granules occur but sparingly. -.-Il The Spleen. ' . ''' The spleen is a "blood-vessel gland ■ • consisting of a connective-tissue ^'t.^i^^Z.^Js^^^t^^.^^^^^cZ capsule and of a soft red mass, the spleen ^'fTe'Hgiu ta'^;ch"o'fTh""V«?y*'har"cS pulp, which is composed of blood-vessels no!V='^"''' "^ "''""''' "''"■ ^ '°' ' "''"' and adenoid tissue. The capsule is invested by a reflection of the ]jeritoneum, with which it is firmly united. It is composed of dense fibrous connective tissue and a net- work of elastic fibers. In some animals (the dog, cat, pig, etc.), but not in man, smooth muscle-fibers are also present. Numerous cylindrical or band-like prolongations, the irabecuhe, extend into the interior of the organ, where they form a framework in the spaces of which lies the spleen pulp. In the lower mammals the trabeculte also contain smooth muscle-fibers. At the hilum of the spleen the capsule furnishes special sheaths for the blood-vessels — adven- titial sheaths — which blend with the adventitia of the latter and accompany them for long distances. The sheaths of the arteries are the seat of numerous leucocytes, which form a continuous envelope along the entire course of the 7 HISTOLOGY. vessel, as in the guinea-pig, or, as in man, the cat, etc., are limited to certain points where they form spherical masses, 0.2 to 9.7 mm. in size, the so-called Malpighian corpuscles. Between these many intermediate forms exist, as in the mouse and rabbit. Fig. 58. — Elbm Spleen. X 560. i. Color- less blood cells 2. Epitheli.il cells. 3. Colored blood-corpus- cles. 4. Cells ■ _ ule.s : the upper one enclosing also a blood -corpuscle, b. Techn. No. 49. X 560, the edge ot a shake tion. Techn. No. 51 X s6o. 1 he fi iblc with this Techn. No. 52. The Malpighian corpuscles are usually situated in the forks of the smaller arteries, and in such wise that the artery pierces them through the center or near the periphery. In their minute structure they agree entirely with the secondary nodules of the lymph-nodes, and occasionally even contain germinal centers. ... Surface blackened by silv Malpighian corpuscle. 3. 61. — Section of Splbfn of Mouse, Magnifi artery The sheath of the artery is infiltrated its the pulp and the artery is indicated by a dotted hi 85 Times, showing the ne :nt!re length by lymphoid ( Techn. No. 54. The Malpighian corpuscles are also temporary structures, continually disin- tegrating and developing anew. The spleen pulp forms a network of cords which, like that of the lymph- nodes, occupies the interstices of the trabecular framework. Occasionally THE LYMPHATIC SYSTEM. 99 the cords are attached to the Malpighian corpuscles. The spleen piilp is com- posed of a delicate connective-tissue reticulum and numerous cellular elements. Venous capillarie (•■imermediat lacuna;" ofothc; authors). Splenic pulp. Fig. 62, A. — Section Cat. Techn. No. 53- The latter are in part leucocytes, in part slightly larger nucleated cells ; also cells containing colored blood-corpuscles and free colored blood-corpuscles. Pig- ment-granules are also present. Transition of venous capillaries into — Flc. 62, B.— Schematic Drawing op Section 62, A. The Blood-vessels. — The arteries of the spleen give off branches to the trabecule and to the pulp, and contribute to the dense capillary network of loo HISTOLOGY. the jMalpighian corpuscles. The veins proceed from a wide-meshed network of capillaries (venous spaces, venous capillaries) occupying the intervals between the trabeculse and the pulp cords (Fig. 62). The larger veins run alongside the arteries. The precise mode of communication between the arteries and the veins is not yet determined. The arteries break up into slender capillaries which do not anastomose with one another. According to one view, these arterial capillaries are directly continuous with the "venous" capillaries, and the blood-vessels are closed on all sides. Other authors hold that the arterial capillaries pass into spaces without definite walls, " inter- mediate lacunae," which connect with veins with perforated sieve-like coats, and that the latter establish the communication with the veins with closed walls. The superficial lymphatics on the surface of the spleen, numerous in the lower mammals, are scantily developed in man. The deep lymphatics in the interior of the spleen are also .few in number ; the exact relations of the latter have not yet been fully investigated. The nerves, which comprise a few meduUated fibers and many naked axis- cylinders, follow the course of the trunks and branches of the arteries, supply- ing the muscular coats of the latter, and in the lower mammals the smooth muscle-fibers of the trabecule (Fig. 61). Plexuses of nonmedullated nerve- fibers occur in the spleen pulp, partly sensory in their nature, and probably proceed from the branches of the medullated nerve-fibers just mentioned. 111. THE ORGANS OF THE SKELETAL SYSTEM. The skeletal system consists of a large number of hard parts, the bones, which are joined together by special structures and form in their entirety the skeleton. In the embryo the greater part of the skeleton consists of cartilage, which in the course of development is supplanted by bone, and with the exception of a few remnants disappears ; such remnants are the costal cartilages and the cartilages of the joints, which cover the opposed surfaces of many bones. Skeletal cartilages are also found in the respiratory passages and the organs of special sense. THE BONES. On sawing through a fresh long bone, it will be seen at once that its texture is not everywhere alike, but that the osseous tissue appears in two forms: the one, a dense, firm, apparently structureless substance, constitutes the principal portion of the periphery and is termed compact bone (sub- stantia compacta) ; the other, toward the axial cavity, appears as an irregular THE HONES. lOI reticulum of thin osseous lamella: and slender trabeculfe, and is called s/iongy bone (substantia spongiosa). The interstices of the spongy bone, as well as the central marrow-cavity, are filled by a soft mass, the hone-marrow ; the surface of the bone is enveloped in a fibrous membrane, the periosteum. The pro- portion between the compact and the spongy substance is different in the short hones, which consist chiefly of the latter, the compact substance being limited to a narrow zone at the periphery. Flat bones have sometimes thicker, sometimes thinner outer shells or crusts of compact substance, while the interior is filled with spongy substance. In the epiphyses of the long bones, as in the short bones, the spongy substance preponderates. H.iversian Can.iU. Fig. 63.— Piece op , LoNGiTUOiNAi. Section through Human Met canals. At x Haversian canals open on the outer. The Spongy siihsfance consists entirely of osseous tissue ; the compact substance, on the other hand, contains besides the bone canaliculi and lacunje, a second system of coarser channels, 22 to no /x wide, which divide dichotomously and form a wide-meshed network. These channels contain the blood-vessels and are named Haversian canals. In the long bones, in the ribs, the clavicle, and the inferior maxilla their course is parallel to the long axis of the bone; in short bones they run mainly in one direction, for example, vertically in the vertebra: ; in the flat bones their course is parallel to the sur- face, not infrequently along lines that radiate from a point, as in the tuberosity of the parietal bone. The Haversian canals open on the outer surface of the bone, as well as on the inner surface, directed toward the substantia spongiosa. The ground-substance or matrix of bone is arranged in lamellae. The fibrillte are joined in bundles, and these placed side by side form the lamellse. I02 HISTOLOGY. According to the disposition of these strata three lamellar systems may be distinguished : an annular or Haversian system, in which in cross-sections eight to fifteen lamellae are seen to be concentrically arranged around an Haversian canal; these lamellae are called Haversian or special lamella (Fig. 64). Between the Haversian systems, which come into contact only here and there, are irregularly-disposed lamellae, the interstitial or ground lamella; these are con- nected with the third lamellar system, the circumferential or fundamental lamellce, in which the osseous strata encircle the outer and inner free surfaces of the bone. The circumferential lamellae contain a variable number of canals, which, unlike the Haversian canals, are not the centers of annular systems of lamellae; they are called Volkmann's canals, and contain the " perforating vessels." The latter frequently connect with the vessels of the Haversian canals ; the passage of the Volkmann's canals into the latter is a gradual one. The bone lacuna in the compact substance extend in a definite direction. In the Haversian systems their long axis is parallel to the long axis of the Haversian canals, and they are bent so that cut transversely in the cross-section of an Haversian system they appear concentrically curved. In the interstitial lamellae the lacunae are placed irregularly ; in the circumferential lamellae so that their surfaces extend parallel to the surfaces of the lamellae. The bone canaliculi open into the Haversian canals, and also on the free outer and inner surfaces of the bone. The bone-marrow occupies the axial cavity of the tubular bones, fills the interstices of the spongy substance, and is also found in the larger Haversian canals. It is of a red or yellow color, and therefore two varieties are recog- nized — the red marrow and the yellow marroto. The red marrow is found in the vertebrae, the bones of the skull, the sternum, and the ribs — in all young bones (also in the long bones of some animals) ; the yellow marrow occurs in the short and the long bones of the extremities. In old and in sick persons the marrow is mucoid and reddish-yellow, and is characterized by its poverty in fat. THE BONES. 103 The elements of red marrow comprise a delicate connective-tissue retic- ulum which supports a few fat-cells, larger and smaller marrow-cells, and giant-cells (myeloplaxes). In the larger marrow spaces the connective tissue forms a membrane, the endosteum, which lines the free surface. The marrow- cells exhibit forms resembling leucocytes ; the giant-cells are structural anom- alies representing leucocytes enlarged and altered in form ; they are huge, 1.. ; Hematoblasts. \ (*/ ( Colored blood-corpuscle. --- Giant-cell. Fig. 65. — Elements OF Human Bone.Marrow. X600: 1-5. Various forms of bone-cells. 6. Eosinophilous cell. Techn. No. 57 b. extremely irregular, multinucleated masses of protoplasm. The shape of the nucleus varies greatly ; it may be round, lobulated, band- or hoop-shaped, or it may fashion a network. A uninuclear giant-cell may become multinuclear through the division of the nucleus by constriction, or a corresponding part of the protoplasm may be set free with the nucleus and the result is a uninuclear cell. The view interpreting these indications of division as the phenomena of Outer fundamental la Sharpey's fibc Interstitial lamellsc o Fig. 66.— Piece CHriss-SttCTioN OP Frmur OP Adult Man. X 80. Techn. No. 56. The la be recognized by the disposition ot the lacuna:. a reversed series of processes — the merging of several cells into one — has very little probability, since the process of budding has been observed in living cells. There are also found in the red marrow nucleated cells with yellow- colored protoplasm like that of the colored blood-corpuscles ; the.se are the hematoblasts ( erythrohlasts) (Fig. 65). Yellow pigment-granules that appear in the different cells are regarded as the remains of disintegrated colored blood- cor|)uscles. I04 HISTOLOGY. The yellow marrow consists of a connective-tissue reticulum containing much fat. Marrow-cells and hematoblasts in yellow marrow are found only in the head of the humerus and the femur. The periosteum is a compact connective-tissue membrane, in which two layers can be distinguished. The outer is characterized by its richness in blood-vessels and forms the connection with adjacent structures, tendons, fascise, etc.; the inner layer contains few blood-vessels, but is rich in elastic fibers and spherical or spindle-shaped connective-tissue cells. At places on the inner surface a layer of cubical elements may be found, which are of importance in the development of the bone. The periosteum is sometimes firmly, some- times loosely attached to the bone ; the attachment is secured by the blood Harrow (fat-cells). Blood-vessel. Section thkough Head of a Metacarpus <'F Adult Man. X 50. Techn. No. 59. vessels passing to and from the bone and by Sharpey's fibers, which pierce the circumferential and interstitial lamellae and extend in all directions (Fig. 66 ). The blood-vessels of the bone, the marrow, and the periosteum are in the closest connection with one another, and also with surrounding structures. Small branches (not capillaries) of the numerous arteries and veins of the periosteum enter the Haversian and Volkmann's canals, and on the inner surface of the bone are in communication with the blood-vessels of the marrow. The latter is supplied by the nutrient artery, which in its course through the compact substance gives off branches to the same, and in the marrow breaks up into a rich capillary network. The veins that take up the capillaries of the THE BONES. I05 marrow have no valves. Lymph-vessels with well-defined walls occur only in the superficial layer of the periosteum. The nerves are numerous and consist partly of medullated, partly of gray fibers. They enter the Haversian canals and are distributed to the bone-mar- row and the periosteum, and in the latter occasionally terminate in Pacinian corpuscles. The Articul.ations of Bones. Two forms of articulations are recognized: synarthroses, joints character- ized by immobility; diarthroses, joints in which the bones are movable, one upon the other. In synarthroses the bones are joined either by ligaments, the union consti- tuting a synifesmosis ; or by the intervention of cartilage, forming a synchon- drosis. The ligaments are fibrous bands possessing a structure like that of tendon, or they are composed of elastic tissue. The latter are distinguished by the possession of numerous robust elastic fibers which are never arranged in bun- dles or lamellse, but are always separated by loose connective tissue. The ligamentum nuchse, ligamenta subflava, and ligamentum stylohyoideum are elastic ligaments. The sutures also belong to the syndesmoses ; short fibrous ligaments extend from one serrated osseous edge to the other. The cartilage in synchondroses is rarely only of the hyaline variety, but usually is in part fibro -cartilage (especially at the borders in contact with the bone) and in part hyaline, in which the cell capsules are frequently calcified. The intervertebral ligaments, which belong to the synchondroses, possess a soft, jelly-like center, the "gelatinous nucleus," which contains groups of cartilage cells ; it is the remains of the notochord, the embryonic precursor of the vertebral column. At the periphery of the intervertebral ligaments there is a narrow tendinous zone. In diarthroses the parts entering into a joint are the articular ends of the bones, the capsular ligament, the marginal fibro-cartilages, and the inter- articular cartilages. 'l"he articular ends of the bones are from 0.2-5 mm. thick and are covered by a stratum of cartilage thinning out at the edges. The superficial cartilage cells are flattened and placed parallel to the surface ; those in the median plane are rounded and are often collected in groups ; in the deepest plane, the groups of cells are partly arranged in longitudinal rows, vertical to the surface of the cartilage ; adjoining this, but separated by a narrow striated belt, is a small zone of calcified cartilage interjiosed between and connecting the hyaline car- tilage with the osseous tissue ( Fig. 67). Not all the articular cartilages ex- hibit the same structure; the cartilages of the costo-vertebral, the sterno-clavi- cular, the acromio-clavicular, and the maxillary articulations, and the head of the ulna are not hyaline, but fibro-cartilage ; the distal articular surface of the radius is covered with dense fibrous tissue. io6 HISTOLOGY. The glenoid ligament and the interarticular cartilages do not exhibit the characteristic cartilage matrix, but consist of a compact fibrous connective tissue and of spherical cells. To the same category belong the so-called sesa- moid cartilages; that of the tendon of the peroneus longus, however, contains genuine cartilage. In the adult, nerves and blood-vessels are wanting in the articular carti- lages, as also in the interarticular cartilages and the glenoid cartilage. The capsular ligaments consist of an external fibrous membrane, K\\% fibrous capsule, of varying thickness, possessing a structure like that of the ligaments, and of an internal membrane, the synovial membrane, the free inner surface of which is smooth and glossy ; the outer layer of the latter is composed of loose elastic fibers and fibrillar tissue containing fat-cells; within this is a thin lamella of parallel connective-tissue bundles, in which, toward the interior, there are spherical or stellate nucleated cells, 11-17 ,a in size;' they are not numerous except at points subjected to great pressure, where they occur in large numbers and form an endothelial membrane three or four strata thick. The synovial membranes often send free pro- cesses containing fat into the synovial cavity, and bear on their free surfaces the synovial fringes or villi, variously shaped processes, mostly of micro- scopic size, which closely beset the edges of the joint surfaces, and bestow upon the synovial mem- brane a reddish, velvety appearance. They consist of connective tissue and are clothed by a single or a double layer of cells. The larger blood-vessels of the synovial mem- branes lie in the loose connective-tissue layer ; the capillaries extend through the inner thin connec- tive-tissue stratum and form vascular tufts in the villi. Some of the villi are without vessels. The lymph-vessels lie close under the endothelium. The nerves run in the loose connective tissue and terminate in part in Pacinian corpuscles. The synovia consists principally of water ; it contains only six per cent. of solids and no formed elements. Fig. 68,— SY^ JOVIAL Villi v ^MTH Blood -Vbs: SELS FKOM Hu MAN Knee-Jo.ni •. Magnified f;o ti mes Theepitheh urn has fallen fror nthe apex of ihe left villus. ex-p( jsine theconnecti' ^■e tissue. Techn .No The Cartilages. The costal cartilages are of the hyaline variety ; the matrix exhibits the usual characteristics ; the cells frequently contain fat. The surface is envel- oped by a compact fibrous membrane, the perichondrium, which consists of interlacing fibrous bundles and elastic fibers. THE BONES. 107 The articular cartilages are covered by the perichondrium only at their edges, not on their free surface. Where the cartilage and the perichondrium are in contact there is a gradual transition of the one tissue into the other, and consequently the attachment between the two is very firm. The perichondrium carries the nerves and the blood-vessels; the latter also run in canals within growing cartilage. In the adult, cartilage is devoid of blood-vessels ; the nutrition of the tissue depends upon diffusion from adjoining structures. The costal cartilages in advanced life are often extensively ossified and contain blood-vessels. The cartilages of the special-sense and the respiratory organs will be described in the corresponding chapters. Usteogenetic tissue. Perichondnil bone. ::. 69. — Khom a Dokso-Plantar Longitudinal Section op Grbat Ton op Fouk-Months' Human Em- BKVt). TwO'thirds of the first ph;tlaiix represented. X 50. i. Lnctinae enhirged ntid containing many carli- laeC'Cells, I'hc cells cannot be distinguished with this magnification, only their nuclei, which appear as minute dots. At 2, developing cartilage : cells in groups of three and four, each group produced by re- peated division from one cartilage.cell. Techn, No. 61. Development of Bone. The bones are comparatively late structures in their appearance. The development of the muscles, nerves, blood-vessels, brain, spinal cord, etc., is alreaily well advanced in the embryo at a time when not a trace of bone is present. M that period the skeleton is formed of hyaline cartilage. With the exception of certain parts of the cranium and nearly all the bones of the face, the entire skeleton is mapjied out in cartilage. In the upper e.xtremity, for example, the humerus, radius, ulna, carpus, and the skeletal jjarts of the hand, consist of cartilaginous pieces, which, however, are not hollow like the bones by which they are subsequently rejilaced, but are solid throughout. The io8 HISTOLOGY. osseous skeleton then gradually appears in the place of the cartilaginous. All the osseous parts that in the embryo were preceded by cartilage are called primary or endochondral bone : all other bones, not preformed in cartilage, secondary or interinenihranous bone. The primary bones include all the bones of the trunk and extremity, the greater part of the cranium (the occipital bone with the exception of the upper portion of the tabular part, the sphenoid with the exception of the internal pterygoid plate, the temporal bone with the exception of the squamous portion and the annulus tympanicus, the ossicles of the ear, the ethmoid bone, the inferior turbinal), and the hyoid. The secondary bone includes the bones forming the sides and vertex of the cranium and nearlv all the bones of the face. Osteogenet Endochondral bone Blood-vessels. Perichondral bone. Enlarged I Perichondral bon Fig. 70.— From a Dorso-Palmar Loncitudinal Section of Kingkk of Four-Months' Human Embr Tu'o-thirds of second phalanx represented. X 50- 'A'he calcified trabeculae are covered by a thin laye endochondral bone. (More highly magnified in Fig. 71.) Techn. No. 61. Development of Prim.^rv Bone. Two modes of bone formation are here to be considered: i, endochon- dral ossification, formation of osseous tissue within the cartilage, and 2, perios- teal (better perichondral ) ossification, formation of osseous tissue immediately surrounding and also on the cartilage. The phylogenetically older perichon- dral ossification usually begins earlier, but for didactic reasons will be described subsequently to the process of endochondral formation. I. Endochondral Ossification. — The first indications of this process consist in changes at certain places within the cartilage ; the cells enlarge and divide, so that several lie in one lacuna ; a deposition of lime-salts takes place within the matrix, in consequence of which it becomes granular and dull — it THE BONES. & calcifies. Such places may be recognized with the unaided eye, and are called centers of ossification (better, centers of calcification). The portions of the cartilage remote from the centers of calcification continue to grow in Hyaline cartil- age (cells re. arranged in thickness and length, while at the center growth ceases, and consequently the cartilage at this point appears constricted (Fig. 69). Meanwhile, on the surface of the center of calcification, a tissue rich in blood-vessels and young no HISTOLOGY. cells — ostcogenetic tissue,-^ his made its appearance. This penetrates into the cartilage, the calcified matrix is absorbed, the cartilage-cells are set free and disintegrate; a little space — \\\t. primary marrow-cavity — is excavated in the center of calcification. These processes are repeated in the immediately surrounding cartilage; that is, the matrix calcifies, the cartilage-cells enlarge, new portions of the car- tilage break down, and as a result the primary marrow-space is gradually and continuously extended. At the same time the capsules of many cartilage- cells are opened, the cells degenerate, and the intervening calcified matrix pro- jects into the marrow-space in the form of irregular processes or trabeculre. Fig. 72.— Ck //. Developing H, The primary marrow-cavity is now filled with blood-vessels and young cells. The fate of these cells in the further course of development varies. They retain their original form and become marrow-cells, or they become fat-cells, or — most important — they become bone-forming cells, osteoblasts. In the latter event, a number of cells arrange themselves in a single layer on the walls of the marrow-cavity and on the surface of the calcified trabecule, and produce the matrix of true osseous tissue. As a result of this activity, the trabeculee and the walls of the marrow- * This is not a good name, inasmuch as the tissue has not orig become bone. lated from bone, but is to THE HONES. Ill cavity are soon covered with a thin layer of bone-substance, which gradually increases in thickness. Thus step by step the former solid cartilage is trans- formed into spongy bone, the trabeculas of which still contain a residue of cal- cified matrix (Fig. 72). 2. Perichondral Ossification. — This mode of bone formation is also ac- complished through the agency of the osteoblasts derived from the osteogenetic tissue at the surface of the center of calcification ; they form strata of spongy osseous tissue on the surface of the cartilage, which is distinguished from the endochondral bone in the absence of remnants of calcified cartilaginous matri.x, because the perichondral bone is formed at the circumference and not in the interior of the cartilage. The formation of the first Haversian canals may be observed in the perichondral bone (Fig. 72). The latter is not formed in a con- tinuous layer of uniform thickness, but at frequent intervals depressions or recesses may be observed containing blood-vessels surrounded by osteoblasts (Fig. 72 hit) ; at first the recesses are open toward the periphery, but with the advancing development of the osseous strata they are closed in, and then rep- resent Haversian canals. The osteoblasts enclosed within the canals produce new osseous strata, the Haversian lamells. 1 '->;!. Carlilagc-cell. Transitional form of a cartilage- cell undergoing conversion into Dug. X 240- Metaplastic type. By the absorption of the cartilage and its substitution by o.sseous tissue, also by the deposition of bone-substance on its e.Kterior, the piece of cartilage has become a bone. The essence of the foregoing processes consists in an absorption of the parts of the primordial skeleton and in the new formation of the same by the development of bone-substance. This mode of bone formation is termed neo- plastic in contradistinction to the rarer vietaplastic mode, in which the cartilage is not destroyed but ossified, and the cartilage matrix becomes the bone matrix, the cartilage-cells the bone-cells (as for example, in the angle of the inferior maxilla) (Fig. 73). Secondary or Interme.mbranocs Bone. In this the fundament on which the forniation of bone occurs is not carti- lage but connective tissue. Isolated bundles of connective ti.ssue calcify ; on these osteolilasts derived from embryonal cells arrange themselves and produce bone, in the manner above described (Fig. 74). The intermembranous HISTOLOGY. ;-tissue bundles. bone is enclosed on all sides by connective tissue : when osseous tissue is in direct contact on one side with cartilage, without the intervention of con- nective tissue, the resulting formation is not intermembranous, but perichon- dral bone. Growth of Bone. — In tubular bones ossification in the diaphysis begins much earlier than in the epiphyses (\\\ the humerus the center of ossification in the diaphysis appears in the eighth fetal week, in the epiphyses in the first year of life) ; blood-vessels grow into the calcified cartilage which is trans- formed at first by endochondral, later by perichondral, formation into bone. The articular surfaces of the bone re- main permanently cartilaginous ; and a narrow zone between the diaphysis and each epiphysis, the epiphyseal carti- lage, persists until the growth of the bone is completed. An active growth of cartilage is maintained here, which by e-\tension of the primary marrow-cavities of the diaphysis and the epiphyses is continually being supplanted by bone. In this way the bone grows in length. Increase in thickness takes place by the "apposition" of new peri- osteal strata. In the short bones ossification takes place, as in the epiphyses, at first by endochondral formation ; after the absorption of the superficial remnant of cartilage, a perichondral osseous shell is formed. In they?ir/ bones perichondral precedes endochondral formation. Intermembranous bones grow in superficies and thickness by the formation of new osseous masses at their edges and their surfaces respectively. As a '"' consequence of the abundant deposition of bone-substance on the surface, the outer and the inner tables of compact Bone bone are formed, which enclose between /, them spongy bone ; the latter is termed diploe in this situation. The osseous masses at first possess a coarse-fibered, and later (from about the first year of ^^\ life) a fine-fibered matrix. Re.sorption of Bone. — Immedi- ately following the initial formation of osseous tissue a contrary process, resorption, becomes perceptible, by which the calcified cartilage matrix and many parts of the primary or endochondral bone are removed. Resorption is actively carried on in the tubular bones in the formation of the marrow-spaces (in a lesser degree in other bones) and on the surface of bones until their tyi)ical form is completed. The femur of a three-year-old child, for example. ells lying in Howship's lacunx. —From a Cross-Section of Humerus Newborn Cat. X 240. H. Haver- pace, containing two blood-vessels and THE ORGANS OF THE MUSCULAR SYSTEM. "3 contains scarcely any of the osseous tissue present at birth. In the interior of the compact bone irregular excavations may be seen, the so-called Haversian spaces, formed by the absorption of the innermost Haversian lamellae, which, however, may be partly filled again by the deposition of new- osseous substance. Wherever resorption of bone takes place, multinucleated giant-cells may be seen lying in depressions or pits — ffawship's lacuna — which they have excavated in the bone. In this situation the giant-cells bear the name of osteoclasts (Fig. 75). Even in the fully-developed skeleton the processes of apposition and resorption still occur at isolated places. IV. THE ORGANS OF THE MUSCULAR SYSTEM. y The muscular system is composed of a large number of contractile organs, the muscles, which consist of cross-striated muscle-tissue and are joined to the skeleton, the skin, the viscera, etc., by the intervention of special con- ^w^ ' nective-tissue formations, the /.fWf/c/w, ■ ^ and accessory parts of similar struc- ture, the fascia, tendon-sheaths, and ^ - bursa. „ Each muscle is composed of striated muscle-fibers which, as a rule, are disposed parallel and lengthwise in bundles surrounded by a connective- tissue sheath, tht perimysium. Interlacing is rare, but occurs, for example, in the tongue. Neigh- boring muscle-fibers are never in direct contact, but each individual fiber is enveloped in a delicate connective- tissue sheath, the endomysium, which is joined to neighboring sheaths (Fig. 76). A number of muscle bundles form a muscle, the surface of which is covered by a robust connective-tissue membrane, the epimysium. The sev- eral sheaths are connected with one another. The grouping of the primary bundles into secondary bundles, which in. a certain number of instances are grouped into tertiary bundles, and finally united to form a muscle, is an arbi- trary division, and in many preparations cannot be recognized. "0" Fig. 76. — From a Cross-Section ..f the Adductor MfscLE OF A Rabbit. P. Fcrimysium, conuining two blood-vessels, at ^ ; m, muscle-fibers ; many are shrunken and between them the endomysium, /, can be seen ; at x the section of muscle-fiber has fallen out. X 60. Techn. No. tt. 114 HISTOLOGY. The perimysium is composed of fibrillar connective tissue and numerous fine elastic fibers, and occasionally contains fat-cells ; it conveys the nerves and lymph- vessels. The endomysium contains only capillaries and terminal branches of nerves. The post-embryonal increase in the thickness of the muscle depends less on the division than on the growth in thickness of the already existing muscle- fibers. The tendons are characterized by the parallel course of their fibers, their firm union, and the scarcity of elastic fibers. They are composed of bundles of fibrous tissue, the primary or tendon-bundles, which are held together by looser connective tissue and form secondary bundles. Each primary bundle consists of a number of parallel fibrillae, running a straight course and united by a small amount of cement-substance. Between the primary bundles lie the Tendon-bundk. Fig. 77. — A. From a Cross-Sbction of Dried Tendon of Adult Man. X 50. Techn. No. 63. B. From a cross-section of tendon fixed with chromic acid (adult man). Tcchn. No. 64. cellular elements of the tendon, fusiform, stellate, polygonal, or flat cells, arranged in longitudinal rows. They partially clasp the primary bundles and unite with one another by means of processes. Elastic fibers are found chiefly in the loose connective tissue ; in the dense tendon-bundles they are scarce and occur in the form of a fine wide-meshed network. The union of muscles with tendons and fibrous membranes is effected by the extension of the endomysium of the muscle-fiber to these structures, and the blending of the tissues ; the sarcolemma takes no part in this, but as a con- tinuous sheath, with pointed or obliquely blunted ends, closely invests the mus- cle-fibers. When the muscle-fibers are spread out in a membrane they attach themselves to the connective tissue ,by pointed or forked ends. 'X\\^ fascia in part exhibit the same structure as the tendons, and in part they are fibrous membranes richly provided with elastic fibers. The latter is THE ORGANS OF THE MUSCULAR SYSTEM. "5 the case where they form sheaths for the muscles and do not furnish surfaces for the attachment of the muscle-fibers. The tendon-sheaths and the biirsce consist of a layer of connective tissue and elastic fibers, varying in thickness, the inner surface of which is covered patch- wise by polygonal endothelial cells. Where the endothelium is wanting the connective tissue is dense and rich in rounded elements resembling cartilage- cells. The majority of the tendon-sheaths have small vascular processes exactly like the synovial fringes. The blood-vessels of striated muscles are very numerous and uniformly dis- tributed ; the capillaries are among the thinnest in the human body, and form networks characterized by elongated rectangular meshes, closely surrounding the individual fibers. Nucleus. - Protoplasm. — U -<^ Fig. 78. — Tendons fkom Rat's Tail. X 240. A. TenHon-ce! in profile, B, from the surface. At X the nucleus is bent so seen partly tn profile (the shaded portion) and partly from th (the light portion). Tcchn. No. 65. Muscle-/, W/ fibers.^^-T'W^ 11 viewed that it is e surface Fig. 79. — From a Sagittal Longitudinal Section op THE Gastrocnemius OF Frog. X 50 The uppermost trans- verse line represents the endo- mysium seen from the surface. Techn. No. 66. The veins are provided with valves throughout their course, even in their smallest branches. The lymph-vessels are few in number and follow the branches of the smaller blood-vessels. For the nerves, partly sensory and partly motor, see the Peripheral Nerve- Endings. The blood-vessels of the tendons and the thinner fascis are very scarce, and run in the loose tissue between the fibrous bundles ; the tendon-sheaths, on the other hand, and the bursK have a rich vascular supply. Lymph-vessels are found only on the surface of the tendon. The medullated nerves of tendons terminate in part in a close plexus of gray nerve-fibers, and in part in tendon-spindles, a formation resembling the motorial end-plates. End-bulbs and Pacinian corpuscles also are found in ten- dons, fasciffi, and tendon-sheaths. V. THE ORGANS OF THE NERVOUS SYSTEM. I. THE CENTRAL NERVOUS SYSTEM.* THE SPINAL CORD. Topography. — The spinal cord consists of a white and a gray substance, distinguishable by the unaided eye. The arrangement and the relation of these two substances are best recognized in cross-sections of the spinal cord. The white substance encircles the gray matter, and is partially divided by a deep anterior cleft, the anterior median fissure, and a posterior septum (formerly called the posterior median fissure) into a right and a left half. Each half is subdivided by the furrows marking the exit of the anterior and the posterior roots of the spinal nerves into a large lateral column, an anterior col- umn, and a posterior column. In the lower cervical and the upper thoracic regions two divisions may be distinguished in the posterior column, of which the median portion is named the column of Goll (funiculus gracilis), and the lateral portion the column of Burdach (funiculus cuneatus). The anterior columns are united by the icihife commissure at the bottom of the anterior median fissure. The gray substance appears in cross-section in the form of an H, and consists of two lateral columns or masses connected by a horizontal bridge, the gray commissure. On each mass thick anterior cornua and slender posterior cornua may be distinguished. Adjoining the lateral portions of the anterior horns, and horizontally even with the central canal, are the lateral cornua, which are especially well-developed in the upper thoracic region. From the front boundary of the anterior cornua, the anterior roots of the spinal tien'es emerge in several bundles, while the posterior roots enter at the postero-median side of the posterior cornua. At the base of the posterior cornua, laterally, a net- like mass of gray substance, the reticular process, is found ; at the median side, near the gray commissure, lies the well-defined column of Clark (dorsal nucleus), visible in the whole length of the thoracic and in the upper part of the lumbar regions of the cord ; and capping the summit, a glistening, jelly- * I shall confine myself here to a brief account of the topography and histology of the spinal cord and the brain. An exhaustive presentation of the architecture of the central nervous system, the paths of the nerve-fibers, and the complicated origins of the cranial nerves in the "nuclei" of the oblongata would exceed the limits of this "Histology." The student is referred to special text-books, of which Edinger's " Vorlesungen iiber den Bau der nervSsen Centralorgane " is recommended. Il6 THE CENTRAL NERVOUS SYSTEM. "7 like mass, the suhstantia gelatinosa Rolandi may be distinguished. Posteriorly to this is the small zona spongiosa, at the dorsal edge of which is found the zona termiiialis, an area of cross-sectioned thin nerve-fibers. In the gray commis- sure lies, in section, the central canal, which extends through the whole length of the cord and is surrounded by the substantia gelatinosa centralis. The cen- tral canal is from 0.5 to i mm. in diameter; not infrequently it is impervious. The portions of the gray commissure in front of and behind the canal are named respectively the anterior znd xhe. posterior gray commissure. From all points of the periphery of the gray substance coarser or finer processes, the septula meilullaria, radiate into the white substance. 'In the cervical and Lateral posterior Mcdi.1l anter Groups of ncrve-cclls. erior median Anterior „„ . ^ iissure, column. White commissure. ' commi! _ _. lich is the canal. Fig. 80. — Cross-Section of the Cervical Enlargement of the Hvman Spinal Cord. X 7. Techn No 68 the lumbar enlargements of the cord the gray matter is more powerfully devel- oped than in the thoracic region, and there is a corresponding variation in the form of the H. The end of the cord, the conns mcdullaris, consists almost wholly of gray substance. Minute Structure. — The gray substance will be first considered, a knowl- edge of its composition being essential to the comprehension of the structure of the white substance. It consists of multipolar ganglion-cells, which with their ramifying and axis-cylinder processes form a dense nervous tangle, the " nerve- felt," which is penetrated by nerve-fibers proceeding in part from the white columns and in part from the posterior roots, and the whole is supported by a framework of neuroglia. ii8 HISTOLOGY. The iien - cells occurring here. f^ ,^ " ■ J ledullated erve-fibers onsisting of— ■ .\x is-cylinder and ■- Me dullary sheath. ,Gli a-cells. Blood-vessels. Techn. No. 69. THE BRAIN. Fig. 86.-From Spinal Coku : The brain, like the spinal cord, Column, x .s is composed of a white and a gray matter, which in their minute structure agree on the whole with the same substances in the cord. But the arrangement of the two substances in the brain is a much more diversified one than in the spinal cord. The gray substance of the brain occurs in four aggregations: i, as the cerebral cortex, the outer sheet covering the surface of the cerebral hemi- spheres ; 2, in the form of discrete masses in the cerebral ganglia, — the corpora striata, the optic thalami, the corpora quadrigemina ; 3, as the lining of the ven- tricles, which is the direct continuation of the gray substance of the spinal cord ; 4, as the cerebellar cortex, the sheet covering the surface of the cerebellum. Discrete masses also occur in the interior of the cerebellum. All these aggregations have numerous connections with one another by means of fiber- tracts. Layer ol small pyramidal miiiiju^^i m Superra- -- ^ M ' * "*^ ^ i . A dial > J * : i fcj rcticulu .Ui- 1 Layer ot \ large ' pyramidal I I Interra- y^ dial -— ' reticulum. :\.'i' Layer ot polymor- phous "iG. 88.— Scheme of Cerebral Cortex, sketched from specimens prepared according to Techn. No. 73 b. I. CellofCajal. 2, 2'. Small pyramidal cells. 3. Large pyramidal cell. 4. Polymorphous cell. 5, 5'. Cells of the second type. 6. Nerve-fiber ending in the superficial zone ; a, mossy-cell ; i, spider-cell. THE CENTRAL NERVOUS SYSTEM. 125 The Cerebrum. In vertical sections of the cerebral cortex four zones, not sharply defined from one another, may be distinguished : — 1. The molecular layer (neuroglia layer), the most superficial, in ordinary preparations appears finely granular or reticulated, and contains, besides a few cells, an interlacement of medullated nerve-fibers running horizontally, the tan- gential fibers (Fig. 87). By means of Golgi's method, it may be seen that the reticulum is formed in part by the dendrites of the pyramidal cells (of the second and third zones) and in part by the processes of glia-cells. Besides the latter there are in the molecular zone the cells of Cajal ; these possess an irregularly- shaped cell-body and processes nmning parallel to the surface, from which ascending lateral twigs diverge (Fig. 88, i). In the lower animals four or more processes have been described ; in man these cells have only been ob- served in the embryo, and evidence of the nerve- processes was not obtainable. The nervous nature of Cajal's cell is, therefore, not yet determined. 2. 'Y\\t zotte of the small pyramidal cells (Y'xg. 87 and 88) is characterized by ganglion-cells 10 to 12 /i in size and of a pyramidal form ; the apex of the pyramid is prolonged into a long ramifying proto- plasmic process, which after giving off minute lateral twigs enters the molecular zone, where it terniinates in numerous, often serrulate, branches (Fig. 88, 2) ; smaller dendrites spring from the lateral and inferior surfaces of the cell. The axis-cylinder process pro- ceeds from the base and after giving off branched collateral fibers passes, as a rule, toward the white substance to become the axis-cylinder of one or, by division, of two nerve-fibers ; occasionally, however, it bends and runs to the molecular layer, where it divides and enters the web formed by the tangential fibers (Fig. 88, 2'). The nerve-processes and also the collateral fibers are enveloped in a medullated sheath. The size of these cells is difficult to determine because of the extension of the cell-body into the apical process. 3. 'Y\\Q zone of the large pyramidal cells \i A\i\\x\g\wi\\^A from the second zone by the greater size of its elements (20 to 30 //) ; the robust axis- cylinder process, after giving off in the gray substance several collateral fibrils, always goes to the white substance (Fig. 88, 3). 4. In the layer of the polymorphous nerve-cells the majority of the elements are oval or polygonal ; an apical dendrite is wanting, but the delicate nerve- process, after sending off a number of lateral twigs, enters the white substance, where it passes into one, or, dividing into T-branches, into two nerve-fibers (Fig. 88, 4). Nerve-process. IG.89, — PvramidalCell fkom A Fbkpendicl'lak Section op THE CbkRDRAL CoKTEX OP Adult Man. X 120. 1 he terminal branches of the den- drites running toward the mole- cular layer aie not visible. Techn. No. 73 b. 126 HISTOLOGY. In the last three zones ganglion-cells of the second type are also found. Their branching axis-cylinder process is either confined to the gray matter in the vicinity of the cell, or extends to the molecular zone, where after rapid branching it terminates (Fig. 88, 5, 5'). The last two zones both contain nmiierous meduUated nerve-fibers arranged in part in thick "radiating" bundles, which split up into single fibers near the zone of the small pyramidal cells (Fig. 87). The bundles are formed by the descending medullated nerve-processes of the large and small pyramidal cells, and by thick medullated nerve-fibers of unknown source, that ascend from the white substance toward the cortex (Fig. 88, 6), where they divide repeatedly and form the " superradial " and the tangential interlacement (Fig. 88), and finally end in free branches ; another set of medullated nerve-fibers runs transversely to the radiating bundles and forms the interradial reticulum. Blood-vessel Mossy-cells. go.^FROM Sections of Br Spider-cell. X 280. Techn. No. 73 b. which is somewhat condensed toward the "superradial" reticulum, and rep- resents the stripes of Gennari or Bai/Iarger (Fig. 87). This and the interra- dial reticulum are composed of the medullated collateral fibrils of the nerve- processes of the pyramidal cells. The structure of the cerebral cortex is modified in certain localities. In the hippocampal and uncinate convolutions the tangential fibers are present in large numbers and form a net-like extended white layer, the substantia re- ticularis alba. In the vicinity of the calcarine fissure the stripes of Gennari are developed into the bundle of Vicq d'Azyr, which may be seen by the unaided eye. Greater or lesser deviations occur in many other localities, which render a division of the above description much more difficult. Finally, extensions of the pia that penetrate the cerebral cortex in company with the blood-vessels participate in its construction, as also the neuroglia, which like that of the spinal cord consists of ependymal cells and Deiters's cells. ir THE CENTRAL NERVOUS SYSTEM. 1 27 In the embryo the peripheral processes of the former extend to the free surface. Of the latter two varieties are distinguished, as in the spinal cord : the spider- cells, which occur chiefly in the white substance, and the mossy-cells, which are found mainly in the gray substance, where they are in intimate relation with the blood-vessels, to the walls of which they are often attached by one thick process (Fig. 90). On the surface of the cerebral cortex there is a glia-zone composed essentially of the processes of the glia-cells. The Cerebral Ganglia. The gray substance of the cerebral or basal ganglia consists of ganglion- cells varying in size, medullated nerve-fibers, and neuroglia. Macroscopical variations in color depend on the proportions in which the ganglion-cells and nerve-fibers are mingled : wealth of ganglion-cells is rendered perceptible by a dark red-brown color, profusion of ner\'e-fibers by a pale yellow-gray color. The Gray Substance of the Ventricles. The gray substance extends from the floor of the fourth ventricle through the aqueduct of Sylvius into the third ventricle, to the tuber cinereum and the infiindibulum. It is of especial interest as the place of origin of the cranial nerves. It is composed of neuroglia, nerve-fibers, and ganglion-cells ; the majority of the latter are multipolar, and in certain localities are dis- tinguished by their size (as in the nucleus of the hypoglossal nerve), or by their peculiar form (as the spherical ganglion-cells in the upper pair of the corpora quadrigemina). An extension of the neuroglia and ependyma lining the central canal of the spinal cord lines the floor of the fourth ventricle, the aqueduct of Sylvius, the inner surface of the third and the lateral ventricles ; it is composed of similar elements. The columnar or cubical cells of the ependyma of the ventricles in the newborn, and in part also in the adult, possess cilia. The Cerebellum. The cerebellum consists of a cortical layer of gray substance composed of three well-defined strata, of which the outer and the inner are macroscopically, the middle, on the contrary, only microscopically perceptible: they are from within outward, the granule layer, the layer of the cells of Piirkiiije, and the molecular layer. The granule layer, the innermost, is characterized by its rust color and consists of numerous strata of small cells, which by the ordinary methods ex- - Outer layer 128 HISTOLOGY. hibit a proportionately large nucleus and a small amount of protoplasm. By the aid of Golgi's method it becomes apparent that, apart from the glia-cells, two kinds of ganglion-cells are present : small granule-cells and large granule-cells (Fig. 92 and 94, i). The former are multipolar ganglion-cells with short proto- plasmic processes, with claw-like endings, and a delicate nerve-process, with- out a medullary sheath, which passes vertically into the outermost or molecular layer ; there it divides into longitudinal T-branches running parallel to the sur- face and terminating in free unbranched ends. The small granule-cells are the Fig. 93.— Large Granule-cell from a Section Through the Cortex OF THE Cerebellum of a Six-Webks'-Old Cat. X "oo. Techn. No. 74. through the cortex of the cere- bellum of .1 six-weeks'-old cat. X 400. Techn. No. 74. principal elements of the granule-layer. Less numerous are the large granule- cells, multipolar ganglion-cells more than twice the size of the smaller elements, whose ramifying protoplasmic processes extend into the outermost layer, and whose nerve-process, running in the opposite direction, rapidly divides and terminates in a rich ramification penetrating within the granule-layer (Fig. 93 and 94, 2). A dense plexus of medullated nerve-fibers occurs in the granule-layer ; the greater part of the fibers come from the white substance of the cerebellum, and THE CENTRAL NERVOUS SYSTEM. 129 at the boundary of the granule and middle layers they form a horizontal band, transverse to the longitudinal axis of the convolution, from which fibers run into the molecular layer. A small portion of this plexus is formed by the medullated nerve-processes of the cells of Purkinje (Fig. 94, 3, 3', 3"). The middle stratum of the cerebellar cortex consists of a simple layer of very large multipolar ganglion-cells, the cells of Purkinje. Their somewhat pear-shaped bodies send two robust protoplasmic processes into the molecular layer, where they terminate in an imcommonly rich arborization extending to Molecular l.iyi Granulclaycr. Fig. 94.— Sciibmb of the Ci 74. 1. Small grantilc-celli V', fibers of the molecular layer. 4. l_ell 01 rurlcinie. Glia-cells ; a, of the molecular layer ; ^, mossy-cell; f, spldei BBBLLAR CoRTEX, skctchccl from a specimen prepared according to Techn. No. ». Large granule-cells. 3. Network of nerve fibers ; 3', horizontal bundles: Cell of Purkinje. 5. BaskeKell. 6. Small cortical cells. the free surface (Fig. 94, 4). The ramification does not extend in all direc- tion, but only in planes transverse to the long axis of the convolution. The entire ramification can, therefore, only be seen in sections at right angles to the long axis of the convolution. From the opposite pole of the cell the axis- cylinder process proceeds, which soon acquires a medullated sheath and, pass- ing through the granule-layer, enters the white substance of the cerebellum ; while still within the granule-layer it sends off collateral fibrils, which branch and, in part, run hack between the cells of Purkinje (Fig. 94). 9 13° HISTOLOGY. The molecular-layer is distinguished by its gray color and contains two kinds of multipolar ganglion-cells : the lai-ge cortical cells or basket-cells and the small cortical cells. The large cortical cells lie in the deeper half of the molecular-layer ; their protoplasmic processes extend mainly toward the surface. Their longer nerve-process runs horizontally near the inner margin of the molecular-layer, transversely to the axis of the convolution, sends toward the surface a few collateral fibrils, and in the deeper portions of the layer gives off at successive intervals delicate branches whose terminal ramifications form a basket-like network — fiber-basket — around the bodies of Purkinje's cells (Fig. 95). The "basket" often also embraces the beginning of the axis-cylinder process of Purkinje's cell. Nearer to the surface lie the small cortical cells (Fig. 96) ; their nerve-process is difficult to find, and consequently has been but little investigated. Fig. 95. — Baskbt-Cbll, from a Section ■ X 240. The five cells of Purkinje were not blackened, but plainly ■ are sketched. Techn. No. 74. The medullated nerve-fibers in the molecular-layer are extensions of the reticulum of the granule-layer, and pass in part to the surface, where after los- ing the medullary sheath they terminate in free branches between the arboriza- tion of the protoplasmic processes of the cells of Purkinje, and in part they run horizontally between the bodies of these cells, parallel to the axis of the convolution. The neuroglia of the cerebellum consists of two kinds of cells : the one kind lie at the boundary of the granule-layer, and have small bodies which send a few short processes inward, but many long processes in a straight course toward the free surface, where they terminate in a triangular expansion (Fig. 97, left), and form in this way a relatively thick peripheral glia-layer ; the other kind, stellate cells, resemble the mossy-cells of the cerebral cortex (Fig. 97, right) ; they occur in all the strata. In the white substance typical spider-cells are found. THE CENTRAL NERVOUS SVSTEM. 131 So long as the cerebellum is not fully developed it is characterized by a series of peculiarities which are wanting in the adult. In embryos and young animals there is over the as yet slightly-developed molecular-layer a superficial granule stratum ; the structures in the granule-layer described under the name of " moss-fibers " are developmental forms of meduUated nerve-fibers ; and of like significance are the "climbing plexuses" found in the environs of the ramifying protoplasmic processes of the cells of Purkinje. The union of the elements of the cerebellum — as everywhere in the central nervous system — is by contact, not by direct connection. Small cortical cells. Cell of Purkinje. .. Ascending i Fig. 96. — Fkom a Srction of thb Cbrsbgllar Cortex op Adult Man. X 240. nerve-processes of bitsket-cells. The cell at Purkinje and the glia-cell are drawr specimen for the purpose of demonstrating the difference in size. Techn. No. 74. The white substance — the medulla — of the cerebrum and of the cerebel- lum, apart from the elements of the supporting framework (connective tissue and neuroglia), consists throughout of medullated nerve-fibers without a neuri- lemma and varying in thickness from 2.5 to 7/1. The hypophysis cerebri (pituitary body) is composed of two genetically different jiarts : (i) a. sma/l posterior /obe i\\3X belongs to the brain, its stalk the infundibulum ; it however contains but few nerve-fibers, and consists prin- cii)ally of connective tissue, blood-vessels, and cells which closely resemble bipolar or multipolar ganglion-cells; (2) an anterior larger lobe derived as a 132 HISTOLOGY. diverticulum from the primary oral cavity ; it contains tubular acini embedded in loose vascular connective tissue, the majority of which are solid and filled with pale or dark cubical epithelial cells (Fig. 98). Only a few of the acini at the edge of the smaller lobe are hollow ; occasion- ally they contain colloid substance resembling that in the tubules of the thyroid body. The piiicaU'ody (epiphysis, conarium,) isderived from a diverticulum of the primitive brain-vesicle and consists of epithelial cells, some of which have delicate processes, and of a connective-tissue envelope from which septa extend into the interior of the body, in which almost invariably the so-called "brain-sand" is found, rounded concretions vary- ing in size and having uneven, mulberry-like sur- faces (Fig. 99). They are composed of an organic basis and calcium phosphate with magnesium phos- phate. Not infretpiently (especially in advanced life) there occur in the brain substance round or discoid bodies exhibiting distinct concentric striation, stain- ing violet on treatment with iodine and sulphuric acid, and therefore related to amylum (Fig. 100, «). These corpora amylacea are almost constant within the walls of the ventricles of the brain, and are also present in many other localities, as well in the gray as in the white substance. IN. X 90. On the right the body, P, and the dendrites, P' , of a cell of Pur- kinje are sketched to demon- strate the difference between this element and the glia-cells. Techn. No. 74. Blood-vessel taining bit corpuscles. *-.»f 'tt.^.sr— ** Colloid " sub- FiG. 08 Tech Portion of Horizontal Shction of Human Pituitary Body, showing the boundary line betw iterior and posterior lobe. Two gland-tubules on lire left contain each a dark epithelial cell. X n. No. 75. The Me.mbr.^nes of the Central Nervous SvsTE^L Two connective-tissue membranes envelop the brain and the spinal cord : the dura and the//t;. THE CENTRAL NERVOUS SYSTEM. I33 The dura of the spinal cord consists of compact connective tissue and numerous elastic fibers, flat connective-tissue cells and plasma-cells (Fig. 103). The inner surface is covered by a simple layer of flat epithelial cells (endothe- lium). The nerves and the blood-vessels are not numerous. The dura of the brain forms also the periosteum of the inner surface of the cranium and consists of two lamellae ; an inner, corresponding to the dura of the cord, and of like structure, and an outer, corresponding to the periosteum of the vertebral canal. It is composed of the same elements as the inner lamella, with the exception that the outer fiber-bundles are disposed trans- versely to the inner. The outer lamella is rich in blood-vessels, which pass from it into the cranial bones. The pia of the brain and spinal cord is a two-layered sack. The outer layer, the arachnoid of authors, is covered on its free surface by a simple layer of epithelium (endothelium), and is not closely attached to the dura. The inner layer (pia) closely invests the surface of the brain and cord, and sends Fig. 99. — AcBRvuLus C Body op a Woma Techn. No. 76. ^WiW \i f ^IG. 100. — From a Tbased Preparation of Gray SUBSTAN'CB FROM THE WaLL OF A VbNTRICLB OF Human Brain. X 240. a. Corpora amylacca ; b, myelin drops ; c, red blood-corpuscles ; d, epcndy- mal cells : ^, meduUated ell. Techn. No. 77. :-fibers ; _/", ganglic into their substance processes carrying blood-vessels. The arachnoid and the pia are joined together by numerous trabeculae extending from the inner surface of the former to the outer surface of the latter. Hernia-like evaginations occur on the outer surface of the arachnoid in certain localities, in particular near the superior longitudinal sinus, and push the attenuated dura before them into the venous sinus. These are the so-called villi of the arachnoid, which under the name Pacchionian bodies were long regarded as pathologic. The pia is composed of delicate connective-tissue bundles and plate-like cells which cover the inner surface of the arachnoid and the trabeculre. The telm cltoroidca and plexus choroidece are highly vascular villous pro- cesses on the margin of a fold of the pia that hang like a fringe within the ven- tricles ; they consist of connective tissue and blood-vessels, whose fine ramifi- cations are united into tufts or lobules. They are covered by a simple layer of cubical epithelial cells, ciliated in the newborn, which enclose pigment -granules or oil-elobules. 134 histology. The Vessels' of the Central Nervous System. The blood-vessels of the central nervous system form a narrow-meshed capillary network in the gray, a wide-meshed network in the white substance. The blood-vessels possess a so-called adventitial sheath (perivascular lymph- sheaths) often consisting of only a simple stratum of endothelial cells. The walls of the intradural venous sinuses are composed of a simple endothelial membrane. The Lymph Channels. — Between the dura and the arachnoid there is a capillary cleft or fissure, the subdural space, which communicates with the deep cervical lymph- vessels and lymph-nodes (at least in the rabbit and the dog), with the lymph channels of the peripheral nerves, with the lymph-vessels of the nasal mucous membrane, with the smaller clefts (juice-canals) in the dura, and finally, round the arachnoidal villi, with the intradural venous sinuses. The fluid in the subdural space is very scanty. The subarachnoidal space, that between the two layers of the pia — (arach- noid and pia) — communicates with the "juice channels" of the peripheral nerves, the lymph-vessels of the nasal mucous membrane, the interior of the ventricles of the brain and of the central canal of the spinal cord. The fluid in the subarachnoid space is very abundant ; it is called the cerebrospinal fluid. The perivascular lymph-spaces are also in communication with the subarach- noid spaces, and may be injected from the latter. The spaces filled only by injecting the brain substance itself cannot be included in the system of lymphatic channels. These spaces occur as pericel- lular spaces surrounding the larger ganglion-cells of the cerebral cortex, also many glia-cells ; as perivascular spaces of the blood-vessels, that formed by the adventitial sheath excepted ; and between the pia and the cerebrum, as the epicerebral space. These may be regarded as a separate juice-canal system. 2. THE PERIPHERAL NERVOUS SYSTEM. The Nerve-Trunks. The cerebro-spinal neme-trunks are composed chiefly of medullated nerve- fibers varying in thickness and only a few gray nerve-fibers, and therefore by reflected light appear white. Their mode of union agrees in many respects with that of the striated muscle-fibers. A sheath formed of loose connective tissue and elastic fibers, often containing clusters of fat-cells, surrounds the entire nerve-trunk. It is called the f//>/f//r////« (Fig. loi). E.xtensions of the epineurium into the interior of the nerve surround the so-called secondary nerve-fiber bundles (funiculi), each of which is enveloped by the concentri- cally lamellated connective-tissue perineurium. From the latter connective- tissue septa extend into the interior of the secondary nerve-fiber bundles ; they THE PERIPHERAL NERVOUS SYSTEM. 135 constitute the eiidoneurium. Finally, delicate offsets from the endoneurium, the fibrillar septa, corresponding to the endomysium of the single muscle-fiber, surround each individual nerve-fiber. These sheaths are in direct connection with the tissue of the dura and the pia. Perineurium and endoneurium are composed of bundles of fibro-elastic tissue arranged in a number of lamellae Artery. Epineurium. -Portion of Ckoss-S Human Median Nbrve. X 20. Techn. No. 79. concentrically disposed ; each lamella is lined by a simple layer of flattened connective-tissue cells, whose outlines can be demonstrated by silver staining. The fibrillar septa also consist of delicate connective-tissue bundles lined by endothelioid plates. Fibrillar sheath. The nerve-fiber bundle not infrequently divides; a variable number of nerve-fibers branch off from one funiculus to join another, and the result is a plexus of nerve-fiber bundles. Division of the nerve-fibers does not occur until at the periphery. The sympathetic iiervc-tninks are in part white and in part gray in color, depending upon the greater or lesser number of meduUated nerve-fibers present : 136 HISTOLOGY. for example, the splanchnic nerves contain many medullated nerve-fibers, while the gray branches of the abdominal and pelvic plexuses contain only a few of the thinnest medullated and, on the other hand, numerous nonmeduUated nerve-fibers. The nerve-fibers are held together and grouped into bundles by connective tissue. The blood-vessels run lengthwise within the epineurium, and form within the perineurium and endoneurium capillary networks with elongated meshes. The lymph channels are represented by the spaces between the lamellae of the perineurium and between the individual nerve-fibers ; these are in commu- nication with the sub-dural and the sub-arachnoidal spaces, but not with the lymph- vessels accompanying the nerve-trunk. Nucleated sheath Is^^^ i. 103. — Pi 11 he °ee, OF CROi 1 in such ;s-Shct1( aprocess. In the axis of the t HE Gassbrian Ganglion of Man. X 240. The cell-processes At X the protoplasm of the ganglion-cell has retracted and simulates ly cut nerve-fibers the axis-cylinders are seen in section. Techn. The Gangli.\. Ganglia are groups of nerve-cells occurring along the course of the nerve- trunks. They are usually macroscopic in size, and contain small bundles of nerve-fibers between which lie ganglion-cells arranged in rounded groups or in longitudinal rows. A connective-tissue capsule, an extension of the epineurium, covers the outer surface of the ganglion and sends into the interior delicate processes for the support of the nerve-fibers and ganglion-cells. The blood- vessels are very numerous and form a capillary network which surrounds the individual cells. The cells of the spinal ganglia are bipolar in the embryo ; the processes spring from opposite poles of the cell. In the course of development the two processes gradually approach until finally they proceed from a com- mon stalk ; the cell thus becomes unipolar. (In amphibians and birds THE PERIPHERAL NERVOUS SYSTEM. 137 isolated multipolar ganglion-cells occur; their dendrites are, however, short and only slightly branched. ) The process of the adult cell receives a medullary sheath and a neurilemma very near its exit, and after a short course divides at a node of Ranvier into twoT" or Y-branches. One branch — the cellulipetal — passes as the axis-cylinder of a sensory nerve-fiber to the periphery of the body, the other — the cellulifugal — usually the thinner, enters the spinal cord as a constituent of a posterior nerve-root, and terminates in free branches in the gray substance. Thus each spinal ganglion-cell, by its undivided process, is in a manner intercalated in the course of a sensory nerve-fiber. The cells of the spinal ganglia are large, round, often pigmented, and their vesicular nucleus contains a conspicuous nucleolus. Each ganglion-cell is enveloped in a nucleated cajisule consisting of concentric strata of flat connective-tissue cells, which is prolonged on to the process of the cell as l\iz fiber- sheath (neurilemma). Whether any nerve-fibers pass through the spinal ganglia that do not enter into relation with the ganglion-cells is uncertain. In young embryo chicks such fibers have been seen coming from the cells of the anterior cornua, but they have not been found in mammals. Artcrj' in transvei Nuclcaled sheath Fig. 104. — Portion Nucleated sheath (from the surface). X 240. Techn. No. 81 Gray nerve-fibers from the sympathetic occur in the spinal ganglia ; they branch and form a plexus in the connective-tissue capsule of the ganglion-cells. Other ganglia possessing the same structure as the spinal ganglia are : the Gasserian, the jugular, the plexus nodosus of the vagus, the petrosal, and the geniculate ; the ganglion of the auditory nerve (ganglia nervi cochlepe et nervi vestibuli) contains bipolar cells. The sympathetic ganglia consist of nerve-fibers and small, often pigmented, cells surrounded by a nucleated capsule and possessing one or two nuclei (two in the rabbit and the guinea-pig). The cells are multipolar ; the axis-cylinder process passes directly into a nerve-fiber ; the varicose ramifications of the pro- toplasmic processes surround the neighboring ganglion-cells. The nerve-fibers are partly thin medullated, partly nonmedullated fibers; their terminal ramifi- cations in part surround the ganglion -cells. The nerve-cells of the symjia- thetic ganglia of fishes are bipolar. In amphibians ganglion-cells occur in which the single process with T-branches is surrounded by a spiral fiber. 138 HISTOLOGY. THE PERIPHERAL NERVE-ENDINGS. Terminations of Sensory Nerves. The peripheral terminal branches of the sensory nerves are distributed naked, as free endings, or they are enclosed by epithelial or connective-tissue cells and terminate as special endings (terminal corpuscles, end-organs). Free endings are formed as follows : a medullated nerve-fiber in passing to its ultimate distribution loses its medullated sheath, divides repeatedly, and forms a plexus of primitive fibrils which terminate in pointed or club-shaped ends. These endings occur more particularly in stratified epithelium. They Epideri THROUGH T Yba'rs of Age. X 200. The cell-nuclei of the stratuci Cells ot LangcrhansT n. intr.iepilhelial nerve-fibtrs. /■,/>!. capillary loop, c, of which only one limb is visil ' ing meduUaled nerve-fibers. Both papilUc contain nonmedullated r distinct only in the deepest layer. /. 1 papillae of the corium ; P, contains a tactile corpuscle, /, with two approach- :rve-fibers. Techn. No. 82. have been demonstrated in the cornea, in the oral mucous membrane, and in the deeper strata of the epidermis. In the latter cells with long branched pro- cesses — the cells of Langcrhans — occur; these were formerly regarded as migrated wandering cells from the corium, and it is possible that some of them may have such an origin ; the majority, however, are transformed epithelial cells; all the transitional forms from the typical epithelial cells to the stellate bodies in question may be found. Sensory nerves have also been found in the muscles. The nerve-fibers lose their medullated sheath and, invested only by the nerve-nuclei, divide dicho- tomously ; the delicate naked fibrillae extend lengthwise between the muscle- fibers and terminate in free endings. THE PERIPHERAL NERVOUS SYSTEM. 139 The terminal corpuscles ox special endings may be divided into two groups : tactile-cells and end-bulbs. In the tactile-cells the nerve-fiber terminates in relation with one or two cells; in end-bulbs it terminates in the interior of a finely granular body, the so-called inner bulb. Tactile-cell , Nerve-fiber Connective-tissue sheath Fig. 106.— From a Pbrpendici;lar Section through the Skin of the Great Toe of FIVE Vbaks Old. X 240. The outlines of the cells and nuclei of the epidermis can onl3M>e X. Tactile-ceiU in tile corium, resting upon the ramifications of a delicate nerv( Man Twbntv- :en indistinctly. Techn. No. 82. Tacth.e-Cells. These may be either simple or compound. The simple tactile-cells are oval nucleated bodies measuring 6 to 12 m (Fig. 106); they occur in the deeper strata of the epidermis or adjacent portion of the corium, and are embraced by the tactile meniscus, a crescentic expansion in relation with a nonmedullated nerve-fiber. '\:\\e compound tactile-cells H^randry'i and Merkel's) consist of two or more somewhat flattened cells, each larger than a simple tactile-cell (15 At deep :-fiber :re, in profile, B. Two com- ic corpuscle " section. Fig. 107.— FnfjM Perpendicular Sections Throl'Ch the Skin of the Beak of a Goose. ^ 240. A Compound tactile-cell (simple tactile corpuscle), cut parallel to the course of the entering ne -^"^ - medullated nerve-fiber only partially met by the section; a, axis-cylinder; its division is h< invisible; /f, tactile disks cut perpendicularly ; h, connective-tissue sheath ; /s, tactile-cells, pound tactile-cells cut transversely to the plane of the entering nerve-fiber ; I. "Simple tact consisting of four tactile cells ; 2, twin tactile-cells ; ts, tactile disks ; a, axis-cylinders in trans before divitling; if, medullated nerve fibers; c, corium. Techn. No. 83. by 50 II wide) and containing a vesicular nucleus. Between the cells is a flat- tened tactile disk, which is embraced between the forks of the divided axis- cylinder of a medullated nerve-fiber. The medullary sheath terminates at the point where the fiber enters the corpuscle and the neurilemma becomes fused with the connective tissue of the capsule surrounding the tactile-ceUs (Fig. 107). The compound forms containing three or four tactile-cells have been I40 HISTOLOGY. designated "simple tactile corpuscles." The compound tactile corpuscles have only been found in the epidermis of the beak and in the tongue of birds, espe- cially in web-footed birds; they are situated almost exclusively in the upper- most strata of the corium. End-Bulbs. The end-bulbs are spheroidal or oval bodies in the interior of which a nerve-fiber terminates in a simple or branched ending. There are various forms of end-bulbs. The so-called cylindrical end-bulbs, the simplest form, consist chiefly of a modified extension of the entering nerve-fiber and comprise three parts, the axis-cylinder, the inner bulb, and the capsule. The capsule is a continua- tion of the connective-tissue sheath of the nerve-fiber. The inner bulb is a is-cylinde er bulb. r^' Fig. 108. — Cylindrical End-Bulb from th: JUNCTIVA OF Calf. X 240. Tcchn. No. . Corpuscle of Vater from thb Cat. >C 50. The cells lining the capsules may be recognized by their prominent nuclei. The medulla of the nerve-fiber may be traced to the inner bidb. Techn. No. 85. finely granular mass exhibiting concentric striations and a few nuclei at the periphery. The nerve-fiber loses its medullary sheath before entering the inner bulb, into which the axis-cylinder ascends as a flat band and terminates at the upper pole in a free or club-shaped ending. The cylindrical end-bulbs are found in the tunica propria of mucous membranes ; for e.xample, in the scleral conjunctiva and the oral mucous membrane. The corpuscles of ^ Vater, or Pacinian bodies, are transparent, elliptical forms, 2 to 3 ram. long and i to 2 mm. thick, and like the cylindrical end- bulbs consist of a capsule, an inner bulb, and an axis-cylinder; the two latter possess the same structure as in the end-bulbs, but the capsule is differently formed. It consists of twenty-five to fifty concentric lamellje, each lined by a simple layer of endothelioid cells and separated from neighboring lamelloe by a serous fluid. Each lamella consists of an outer transverse and an inner loneitudi- THE PERIPHERAL NERVOUS SYSTEM. I4I nal layer of connective- tissue fibers. They are thinner and closer together near the inner bulb. Along the course by which the entering nerve passes to the inner bulb the lamellae are not infrequently united by a longitudinal strand of tissue, the iiiterlamellar ligament. A small artery accompanies the nerve-fiber into the interior of the corpuscle and breaks up into a capillary network between the concentric lamella;. The Pacinian bodies or corpuscles of Vater are found in the subcutaneous connective tissue of the palm of the hand and the sole of the foot, on the pudic nerves of the penis and the clitoris, in the vicinity of joints, in the neighbor- hood of the pancreas, in the mesentery, and elsewhere. Not infre(iuently the axis-cylinder terminates in a forked ending or in a number of twisted and interlacing branches. The corpuscles of Herbst and Key-Retzius, h-vesse/s also form two networks, a coarser in the submucosa, a finer in the tunica propria. The medullated nerve-fibers form a wide-meshed reticulum in the submucosa, from which many ramifying fibers ascend to the tunica propria where they terminate in endbulbs, or lose their medullary sheath and as nonmedullated nerve-fibers penetrate the epithelium, where after repeated division they terminate in free endings between the epithelial cells. 146 HISTOLOGY. THE TEETH. The teeth of man and the higher animals are soHd structures, possessing a central cavity — tht pulp-cavity — filled with a soft mass, the pi/ /p. The portion of the tooth within the alveolus or socket is called the/an^, the exposed por- tion, the crown; the juncture of these portions forms the neck ; the latter is covered by the gums. The hard substance of the tooth consists of three different parts: (i) the dentine, (2) the enamel with the enamel cuticle, and Fig, 115. — Longitudinal S Human Tooth. X 4- Techn. No. 92. (3) the cementum. The distribution of the parts is as follows : the dentine contributes the chief bulk of the tooth and determines its form ; it completely encloses the pulp-cavity except where a small nutrient canal at the apex of the fang admits the numerous blood-vessels to the pulp ; the dentine of the crown is covered by the enamel, of the fang by the cementum, so that its surface is nowhere exposed (Fig. 115). The dentine or i71 bulbs. Denial furrow. Dcnt.-il ridge. Fig. 120. — Schematic Reprbsbntation op thb Initial Procp.sses in showing the formation of three teeth. The anlage of each anterior t is stippled, k. Free edge of the dental ridge. lowing the direction of the gums a longitudinal groove has appeared, the dental f arrow, \\\)\c\\ indicates the line along which the dental ridge progressed backward toward the mandibular articulation. The time of the appearance of the dental furrow varies ; it is frequently present in the initial stages. It disappears later. Dental ridge of upper jaw. Fig. 121.— Frontal Section of the Head op an Embryo Sheep 4 cm. long. X 15. Techn. No. 95. The original broad attachment between the dental ridge and the enamel organ is diminished by partial constriction, and is finally reduced to a slender cord, the isthmus. Meanwhile, the papilla and enamel organ have developed beyond the 150 HISTOLOGY. dental ridge, so that the free edge of the latter does not extend to half the depth of the enamel organ (Fig. 120 and Fig. 123). At the same time the elements of the enamel organ undergo differentiation. The inner layer of cells, resting upon the papilla, develop into tall columnar elements, the inner enamel-cells ; their inner surface is provided with acuticular border. The outer cells, on the other hand, steadily decrease in height, until finally they are reduced to thin plates, the outer enamel-cells ; the cells between the inner and outer enamel-ceils, by an abundant increase of the intercellular substance, become transformed into stellate anastomosing elements, and form the enamel-pulp. At the point where the inner enamel-cells bend over into the outer layer, the enamel organ grows down until it has reached the extremity of the anlage of the tooth, thus form- ing, in a measure, the mould or matrix in which the tooth develops. The deter- mination of the shape of the future tooth is the first function of the enamel ''^ e^^ — " r. "' - Osseous trabecuisc ^^ U V-'K ' of lower jaw. Four Months Old. X 42 organ ; the second, the production of the enamel, which only takes place in that portion of the inner layer covering the crown of the tooth. This portion may be named the enamel membrane. Each cell of this membrane deposits a substance which subsequently calcifies and becomes an enamel prism. The enamel-cells surrounding the fang take no part in the production of the enamel ; they decrease in height and (as here the enamel-pulp soon disappears) apply themselves directly against the outer enamel-cells, the two layers forming the epithelial sheath of the fang (Fig. 124). Before the production of enamel has begun, the first lamina of dentine has been formed (about the twentieth week). The superficial cells of the dental papillae elongate and become the odontoblasts, the agents which produce the at first uncalcified dentine. These cells do not develop beyond the extent of the epithelial sheath. As soon as the first dentine is formed, the epithelial THE DICESTIVE ORGANS. 151 sheath undergoes retrogressive change ; connective-tissue ingrowths from the alveolar periosteum penetrate between the epithelial cells. This retrogression begins at the lower border of the enamel organ, thus severing the connection between the latter and the deeper parts of the epithelial sheath. With the completed growth of the tooth the last remnant of the epithelial sheath dis- appears. Even before the production of enamel and dentine the connection between the dental ridge and the oral epithelium is severed, and the mesodermic tissue % Thickened epilheliiiniof Upprr Jaw of a Techn. No. 95. surrounding the anlage of the tooth forms a compact membrane, the dental sack, in which subsequently an inner looser, and an outer denser, stratum can be distinguished. =f= The enamel cuticle and the cementum do not appear until after birth, shortly before the irruption of the teeth. The former is produced by the merging of the cuticular borders of the enamel-cells into a firm homo- geneous membrane ; the latter is a product of the alveolar periosteum. •The dental ridge has previously become a perforated plate, beset on all sides with short, j.igged excrescences. Remains of the dental ridge may be found in the gums of newborn chil- dren, and were formerly erroneously regarded as glands (glanduloe tartarica;). 152 The permanent teeth develop in the same manner as the temporary teeth ; in the twenty-fourth week new protuberances develop on the growing ledge of the dental ridge, which embrace new papillae arising from the sides. The anlage of the permanent tooth lies at first in the same alveolus with the temporary Dental papilla (fut Blood-vessel. ' Bony trabeculse of lo Fig. 124. — Longitudinal Section ; 42. Techn. No. 95. tooth ; a separate alveolus is developed later. The completed tooth is in part of epithelial origin (the enamel), and in part derived from the connective- tissue dental papilla (the dentine), the remains of which persist in the adult as the pulp. The cementum is in a measure an accessory formation contributed by neighboring tissues. THE DIGESTIVE ORGANS. 153 THE TONGUE. The bulk of the tongue is formed of striated muscles, the separate bundles and fibers of which interlace in various directions. The unattached surfaces of the organ are covered by a reflection of the oral mucous membrane. The bundles of the muscular tissue are disposed in three planes : (i) vertically, and somewhat radially (geniohyoglossus, lingualis, and hyoglossus) ; (2) transversely (lingualis) ; and (3) longitudinally (lingualis and styloglossus). Since the muscle-bundles cross one another for the most part at right angles sections exhibit a regular, beautiful network. A median septum, the septum lingua, divides the muscular tissue into a right and a left half. The septum begins at the hyoid bone and gradually increases in height, reaching its great- est elevation in the middle of the tongue, then gradually slopes downward and , Srctios op t THE Dorsum op the Human Tongue. X 30. 1. Section of two filiform papillae, each of which bears, 2, three secondary papillse : 3, compound : 4, simple pro. cess of epithelium, the surface of which is cov- ered with masses of loosely-attached scaly epi- thelial cells. IG. 126. — LONGITUC iiNAL Section OF THE M ICOUS .Mem form 4. Sn papilla w tail filiform Hu ith, pap MAN lilla." Tongue. lecondary Techn. N X 30. papillae ; 0.96. I. 1 3. sufk. forward and disappears ; it does not extend through the entire half of the tongue, but ceases at a distance of about 3 mm. from the dorsum of the organ. The .septum is composed of compact connective tissue. The mucous membrane of the tongue, like that of the oral cavity, consists of an epithelium and a tunica i)ropria, and rests on a submucosa. It is char- acterized by the conspicuous development and complicated form of the papillze. Three kinds of papillae are distinguished : \\\q filiform or conical, the fungiform , and the circumvallate papillcE. The filiform papilla are cylindrical or conical elevations of the tunica propria, bearing on the summit five to twenty small secondary papillae. They are composed of distinctly fibrillated tissue and numerous elastic fibers, and are covered by a thick layer of stratified scaly epithelium that not infrequently, over the secondary papilla:, forms a number of filamentous horny processes. 154 HISTOLOGY. The filiform papillae are very numerous, and are distributed over the entire dorsum of the tongue ; they vary in height from 0.7 to 3 mm. (Fig. 125). The fungiform papillcE are rounded elevations connected with the tunica propria by a slightly-constricted stalk ; their entire surface is beset with sec- ondary papillK. They consist of a distinct feltwork of connective-tissue bundles which contain but few elastic fibers. The epithelial cover is thinner than that on the filiform papilla and is not cornified. The fungiform papillae are also distributed over the entire surface of the tongue, but are not so numerous as the filiform ; they vary in height from 0.5 to 1.5 mm. They are usually easily distinguished by their red color, due to the capillaries shimmering through the transparent epithelium (Fig. 126). The circumvallate papilla resemble broad, flattened fungiform papillae, and are separated from the surrounding epithelium by a circular furrow varying in depth and bounded by a ridge designated the wall. The papillse are com- Secondar> papilla Epitheliun V '^^ Taste- buds (inaistinci). X 30. Techn, No. 96. posed of connective tissue, like that of the fungiform papillae. Secondary papillae are found only on the upper surface. In the epithelium covering the sides, and occasionally also the wall, lie the end-organs of the special sense of taste — the taste-buds. The circumvallate papillae are i to 1.5 mm. high and I to 3 mm. broad. They are eight to fifteen in number, and occur on the posterior end of the dorsum of the tongue. At the lateral margins of the tongue, just in front of the anterior pillars of the fauces, is a group of parallel folds of the mucous membrane — papilla foliata — containing numerous taste- buds. The papillae foliatae are especially well developed in the rabbit. The suhmucosa at the tip and at the edges of the tongue is firm and re- sistant and intimately connected with the underlying parts. The Lymph-follicles of the Tongue. — The mucous membrane extend- ing from the circumvallate papillae to the epiglottis is peculiarly modified by the development of lymph-nodules. They are spherical aggregations of THE DIGESTIVE ORCANS. 15s adenoid tissue 1 to 4 mm. in size, embedded in the uppermost strata of the tunica propria, and form easily perceptible macroscopic elevations. In the center a punctate opening may be seen, the entrance to a deep central crypt, I Epilhelii 128. — Vrrtical Sfction 01 < 20. 1 Cjyptof Ihe f.llicli mh leucocyie> on the Wt .-ind at the h:\~c. :ilnir>sl i aiiiing ticrminal centers ; y. nodules cm through th . Kibrous sheath. 5. Section of excretory duct of THE Root of thh Tongue of Aiiult Man. :ytes. 2. Epithelium of the crypt ; infiltrated ^n the right. 3, Nodules of adenoid tissue con- le: /•, through the side: /^, at the periphery, gland. 6. Blood-vessel. Techn. No. 96. lined by a continuation of the stratified epithelium of the oral mucous mem- brane. The epithelium bordering the crypt is surrounded by diffuse adenoid tissue, which contains a variable number of the lymph-nodules, with germinal centers, and is separated by a sharp line of demarcation from the subjacent fibrillar connective tissue of the tunica propria ; when well developed, the fibrous bundles of the tunica propria are circularly disposed about the adenoid tissue and form a fibrous capsule (Fig. 128, 4). Under normal conditions numerous leucocytes of the adenoid tissue wander through the epithelium into the central crypt and thence to the oral cavity ; they are readily found in the saliva, as "mucous" and " salivary " corpuscles. The epithelium is often greatly expanded in consequence and destroyed, or is infiltrated with leucocytes to such a degree that its boundary can- not be definitely determined. The Glands. — Two kinds of branched tubular glands occur in the mucous membrane and in the super- ficial muscular strata of the tongue. The gland-cells of the one kind produce a mucigenous secretion (mucin) ; such glands are named mucous glands. The secretion of the second kind is a thin, watery, serous fluid, distinguished by the large amount of albumin it contains ; such glands are called serous glands. Fig I?; ,.— Fro M A Sbction TH llfOtJf.H TH IE Rc.OT OF TH :b ' lONGUH : of MoirSE. X 90. A s. erous gland; th. :du ct-sysle m silvered by k reaction/' Gi -Igi' s " blac th( Libular stniclMre is ea: sily recogn ized. Tech. 156 HISTOLOGY. The mucous glands are of the same structure as those of the oral mucous membrane, and occur along the edges and — in larger numbers — at the root of the tongue, where not infrequently their excretory ducts open into the crypts of the follicles. The ducts are lined by columnar epithelium, which occasion- ally is ciliated ; the walls of the tubules consist of a structureless membrana propria and gland-cells ; the latter are columnar elements possessing a firm cell- membrane, and vary in appearance with their functional condition. The ex- hausted cell is smaller, the transverse-oval nucleus near the base of the cell ; the cell loaded with secretion is broader, and the nucleus is pressed flat against the cell-wall. Generally the same gland, often the same tubule, exhibits vary- ing phases of secretion ; demilunes are however not formed here, because the rigid membrane of the gland-cells resists the pressure exerted by neigh- boring cells. Only the mucous glands of the tongue of the cat and of the uvula of man exhibit demilunes. Nuhn's glands occurring in the tip of the tongue are likewise mucous glands. The serous glands are limited to the vicinity of the papillae circumvallatK and foliatK ; the excretory ducts open into the furrows between the papilla: •"■ d- N^ Fig. 130 — /, //. From a Section of a Mucous Gland of the Root of Human Tongue. /. Section of a tubule with (b\ gland-cells empty of secretion, and (c) gland-cells filled with secretion ; d, lumen. //. Cross- section of a tubule containing only cells loaded with secretion. /// and IV. From the mucous membrane of the tongue of rabbit. ///. Tubule of a mucous gland in transverse section. IV. Several tubules of a serous gland, at rfthe very small lumen. V. Several tubules of a human serous gland, with large (af') and small \d) lumen. All the sections are magnified 240 times, 1 echn. No. 96. and the wall, and are lined by simple or stratified columnar epithelium, not infrequently ciliated. The tubules consist of a delicate membrana propria and short cylindrical or conical cells, destitute of a membrane, whose dim granular protoplasm encloses a round nucleus. The lumen of the tubules is, especially in animals, very narrow. The blood-vessels of the mucous membrane of the tongue form networks disposed parallel to the surface, from which twigs ascend to supply the papillae and the secondary papillse. At the root of the tongue small arteries pierce the fibrous envelopes of the lymph-follicles, and break up into capillaries that penetrate to the interior of the nodules. The blood-vessels of the glands form networks around the gland-tubules. The lymph-vessels of the tongue are arranged in two sets ; a deep set con- sisting of larger vessels, and a superficial set, which takes up the lymph-vessels of the papillae. The lymph-vessels at the root of the tongue are very numerous ; they form networks encircling the lymph-nodules. The nerves of the mucous membrane of the tongue, the glosso-pharyngeal THE DIGESTIVE ORGAN'S. I57 and the lingual branch of the fifth, end in part as in other portions of the oral mucous membrane, and in part in intimate relation with the taste-buds. THE PHARYNX. The wall of the pharynx is composed of three coats : a miiious, a muscular, and 2, fibrous coat. The mucous coat, like the oral mucous membrane, possesses a stratified scaly epithelium, a tunica propria beset with papillae, and also numerous mucous glands. The upper or respiratory part of the pharynx is clothed by stratified ciliated columnar epithelium ; the lower limit of the latter is variable. Very richly developed is the adenoid tissue. Between the pillars of the fauces it forms conspicuous accumulations, one on either side, known as the tonsils, which in respect to their structure in man and many animals correspond to an aggregation of lymph-nodules like those of the root of the tongue. The leucocytes that wander through the epithelium of the tonsils are so numerous that the latter may be regarded as the most fertile source of the salivary corpuscles. The adenoid tissue is also vigorously developed in the respiratory portion of the pharynx, where on the posterior wall between the orifices of the Eustachian tubes it forms a conspicuous mass, the " pharyngeal tonsil," which agrees in its structure with the palatine tonsils, excepting that the lymphoid tissue is less sharply circumscribed. Here, too, many leucocytes migrate through the epithelium. The development of the adenoid tissue of the oral cavity and of the pharynx is subject to considerable variation. The muscular coat (constrictor muscles of the pharynx) consists of striated muscle-fibers, the description of which belongs to the province of macroscopic anatomy. The fibrous tunic is a stout membrane composed of a dense feltwork of fibro-elastic tissue. Blood -ves.sels, lymph-vessels, and nerves are distributed in the same manner as in the oral mucous membrane. THE ESOPHAGUS. The walls of the esophagus comprise a mucous, a muscular, and a fibrous coat. The mucous coat is composed of a stratified squamous epithelium, of a tunica propria beset with papillM, and following thisof a stratum of longitudinally disposed smooth muscle-fibers, the muscularis mucosa ; subjacent to the latter is the submucosa, which consists of loosely-joined bundles of connective tissue, and in the upper half of the esophagus contains small mucous glands. The muscular tunic, in the upper portion of the tube, is composed of striated muscle- fibers, which in the lower portion are replaced by smooth muscle-fibers. The latter are arranged in two strata, an inner circular and an outer longitudinal layer. The fibrous coat consists of compact connective-tissue bundles inter- spersed with numerous elastic fibers. The distribution of the blood-vessels, lymph-ve.ssels, and nerves is the same as in the jiharynx. Between the circular and the longitudinal layers of the muscular coat the nerves form a plexus, at the nodal points of which minute groups of ganglion-cells occur (see Auerbach's [ilexus, p. 170). iS8 HISIOLOGY. THE STOMACH. The wall of the stomach is 2 to 3 mm. tliick and comprises four coats : a mucous, a submucous, a muscular, and a serous or fibrous tunic. Fig. 131.— Fkom a Cross-Suction of the Middle Third of Human Esophagus. X lo. i. Stratified squamous epnheliuin. 2. Tunica propria. 3. Muscularis mucosa:. 4. Submucosa. 5. Circular muscles. 6. Longitudinal muscles, g. Blood-vessel. Teclin. No. 98. Epithelium rtlf.^ \ Tunica prop Fig. 132. — Transverse Sec so close togeltier that its Techn. No 99. [ Inner circular ! layer of muscle ^ Outer longitiid nal .*"--,! -- layer of mu^cle I -v^^-fj^. ble onl) at the b c of The mucous coat, sharply contrasted with the white esophageal mucous membrane by its reddish-gray color, consists of an epithelium, a tunica pro- pria, and a muscularis mucosa; (Fig. 132). THE DIGESTIVE ORGANS. 159 The epithelium is a simple columnar epithelium, whose elements produce a mucoid secretion. Two zones can usually be distinguished, an upper mucoid Epithelium of the surface. 1 \ Gastric pil i Body. and a lower proto])lasmic ; the latter contains the oval, round, or flattened nucleus. The extent of the mucoid zone varies considerably with the func- l6o HISTOLOGY. tional condition of the cells. After the discharge of their mucoid contents the epithelial elements closely resemble goblet-cells. The tunica propria is com- posed of a mixture of fibrillated and reticular connective tissue, and of an ex- tremely variable number of leucocytes, that occasionally lie closely aggregated and form solitary lymphatic nodules. The tunica propria contains so many glands that its tissue is limited to delicate septa between, and to a thin stratum below, the tubules. In the pyloric end the glands are far apart, the tunica propria is conspicuously developed, and not infrequently elevated in filamentous or leaf-like villi. Two kinds of gastric glands are recognized : fundus glauds,'^^ situated chiefly in the middle and cardiac thirds of the stomach, and pyloric glands, con- fined to the narrow pyloric region. Both kinds are simple tubular glands, often branched, especially in the pyloric region, and open singly or in groups into minute, pit-like depressions in the mucous membrane of the free surface. The portion of the gland adjoining these depressions is called the neck, the following portion the body, and the blind end the fundus (Fig. 133). Each gland consists of a membrana propria and of gland-cells. The fundus glands contain two kinds of cells: cliief- or central-cells and parietal- or (?(7(/-cells. The former are clear, cubical or short columnar cells. Portion of a parietal-cell. Parietal-cell adjoining a lateral \'^ ,, n. branch of the lumen. ^-^-■' Fig. 134. — Transverse Section of a Human Fundus Gland. X 240. Techn. No. 102. whose granular protoplasm surrounds a spherical nucleus. The chief-cells are very unstable. The parietal-cells are marked by their affinity for anilin dyes, with which they react intensely. The two kinds of cells are not equally dis- tributed ; the chief-cells form the principal portion of the fundus, the parietal- cells are irregularly distributed, but are especially numerous in the neck and the body of the tubule. Here they lie in rows beside the chief-cells, but toward the fundus they are pressed to the periphery, without, however, being shut off from the lumen, with which they communicate by a short lateral canal e.xtend- ing between the chief-cells from the lumen to the parietal-cells. The lateral canal is the only one of the system of canaliculi enveloping the parietal-cells that can be seen in ordinary preparations. By the aid of Golgi's " black re- action," which also blackens the secretion, it may be seen that from the axial lumen of the fundus glands minute lateral twigs branch off at right angles, divide and anastomose, forming a fine-meshed network of " secretory capil- laries" that, basket-like, embrace each parietal-cell. The secretion is discharged from all sides of the cell, passes into the secretory capillaries, then into one or * In the earlier text-books the fundus glands were called peptic glands, a name based upon , function of the glands now called into question. THE UKJESTIVK ORGANS. i6i more short lateral canals, and finally into the lumen of the gland (Fig. i6 and Fig. 135). The assertion upheld on various sides that the chief- and the parietal-cells are different functional appearances of one kind of cell, as also the statement that during digestion the parietal-cells multiply, but disappear after prolonged fasting, are very much in need of thorough investigation. The stomach of an animal killed after a long winter hibernation still contains parietal-cells. The pyloric glands are furnished almost throughout with columnar cells containing a spherical nucleus situated near the ba.se of the cell, which in the rr^s^.f\ Tunica propria with gLinds. FlC. 135. — CkOSS-SBCTION THROUGH THR M IICOUS MbMBRANH OP THE FONDOS OF StOMACH OP MOUSB (DURING DlGKSTloN). X 234. In 'he gland to the right the entire system of canjiliculi, in the other glands only a portion of the same, is silvered. The " baskets " formed by the secretory capillaries can be distinguished. Tcchn. No. iiy. intermediate zone, that is, the border zone between the pyloric and the fundu.s mucous membrane, resemble very closely the chief-cells, with which they have been compared. In man isolated parietal-cells are found; in animals, e.g., the dog, a few dark conical cells occur, that owe their appearance to the com- pression e.xerted by neighboring cells. The foregoing description applies to the stomach as seen after a period of fasting ; during digestion the parietal-cells are larger, the chief-cells, as also l62 HISTOLOGY. the cells of the pyloric glands, are darker, the nuclei of the latter are nearer to the middle of the cell, and the secretory capillaries expanded with increased contents are wider than in the fasting organ. The miiscularis mucosce consists of smooth muscle-fibers arranged in two or three layers interlacing in various directions, from which single strands branch off" and ascend vertically between the gland-tubules (Fig. 133). The stibmttcosa is composed of loosely-united connective-tissue bundles and elastic fibers, and occasionally contains small clusters of fat-cells. It is only in the pyloric region that two separate layers can be distinguished in the muscular coat, a thicker inner circular and a thinner outer longitudinal layer. In the other regions of the stomach the arrangement of the muscle- tissue is very comijlicated, owing to the extension of the muscular strata of the esophagus to the stomach, as well as by the curving of the organ that ensues in the course of development ; sections exhibit bundles of fibers extending in every possible direction. The serous coat will be described with the peri- toneum. THE INTESTINES. The wall of the intestines, like the stomach, is composed of four tunics ; a mucous, a submucous, a muscular, and a serous. The mucosa is thrown into folds, the valvulse conniventes, especially well marked in the upper part of the small intestine, the object of which is to in- crease the superficial extent of the membrane. In addition to these readily perceptible plications there are still other contrivances serving a similar purpose, that stand at the limit of macroscopic perception. These are minute ele- vations and depressions of the raucous membrane. The former, the villi, are present only in the small intestine ; in the large intestine of man they are wanting; they are processes about i mm. high, in the duodenum of leaf- like, in the remainder of the small intestine of cylindrical form. The depressions begin at the pylorus, and are found throughout the whole length of the intestine. They occur in their most primitive form in fishes, and originate in parallel folds running lengthwise that are connected by small transverse folds. In vertical sections these shallow depressions appear as short, wide sacks, called crypts. In mammals the crypts are deeper, their lumen narrower, and placed in rows close beside one another they have the appearance of simple tubular glands ; but they could only be regarded as such if the epithelial cells lining them produced a specific secretion, which is not the case. Whether the isolated granular cells that occur in the fundus of the crypts are gland-cells is a question. The crypts are known as the follicles or cr)'pts of Licberkiilin. The mucous membrane consists of an epithelium, a tunica propria, and a muscularis mucosae. The epithelium, which clothes the entire free surface, THE MUCOU OF Human St X 240. Techn. No. lo: THE DIGESTIVE ORGANS. 163 including the villi, and lines the crypts is a simple columnar epithelium, the elements of which in their mature condition consist of a granular protoplasm containing numerous resorbed fat-particles, a usually oval nucleus, and a cell- membrane. On the free surface of the cells there is a homogeneous or finely- striated iasa/ iion/er chaTa.cteTht\c of the intestinal epithelium. The regeneration of the epithelium takes place only in the crypts of Lieberkuhn, where by mitotic division new cells are constantly formed, which gradually move upward and replace the cells that disintegrate on the upper' surface of the mucous membrane. Therefore the youngest generation of epi- Fic. 137. — Longitudinal Section op thr Jejuncm op Adult Man. X i6- The circular fold (valvula conniventcs) on the right supports two small solitar)' nodules, that do not extend into the submucosa, and of which the left exhibits .-% germinal center, X. The epithelium is slightly loosened from the connectiv core of many of the villi, so that a clear space, X X, exists between the two. The isolated bodies lying r the villi (more numerous to the left of the valvtilz conmventes) are partial sections of villi that were bent, therefore not cut through their entire length. Techn. No. 105. thelial cells is found in the crypts, the oldest on the free upper surface — in the small intestine on the apices of the villi. Goblet-cells in extremely variable numbers occur in the intestinal epithelium ; they possess an elliptical or, not infrequently, a chalice form ; the upper portion, that directed toward the surface of the intestine, undergoes different degrees of distention as the proto- plasm is transformed into mucus, and the nucleus with the remainder of the unaltered protoplasm lies at the base of the cell ; a basal border is wanting, in place of which a sharply-defined circular orifice is found, through which the mucus is p>oured out on the surface (Fig. 139, A). 164 HISTOLOGY. The goblet-cells are derived from the ordinary epithelial cells of the in- testine. In certain conditions each young intestinal epithelial cell may assume the functions of a aroblet-cell. Tangential sections ofvilli. , I Eplthelii Tunica piopri Lieberkiihn's crypts. Oblique sections of Lieberkiihn rypts. Fig. 138. — Section of thb Mucous Mbmbrane of Jeju.num op .Adult Man. X 80. The empty space, a, between the tunica propria and the epithelium of the villi is an artificial product, the result of the shrink- ing action of the fixing fluid. Not infrequently within the space lie cells that have been pressed out of the tunica propria. In its retraction the epithelium often tears, and then the villus appears to have an opening, d, at its apex. The goblet-cells have been sketched on one side of the villus to the right. Techn. No. 105. The several phases of secretion appear in regular sequence, and so that the later phases are always to be seen in the apices of the villi or near the upper surface of the mucous membrane, the initial phases in the crypts of Lieberkiihn (Fig. 140). Fig. 139. — Intestina piTHELiuM. X 560. A. Isolated goblet-cells of rabbit. Techn. No. a section of the mucous membrane of human intestine. Techn. No. r cells. X. Escap- A goblet- Ill the crypts of the small intestine the number of goblet-cells is propor- tionatel}' less than in the large intestine ; this is explained by the fact that the THE DIGESTIVE ORGANS. 165 young epithelial cells of the crypts move more rapidly to the surface, the greater superficies of the small intestine, so much increased by the villi, necessitating a greater supply of young cells to replace those that disintegrate on the surface ; the elaboration of mucus often does not take place in the crypts, but first begins in the cells on the villi. In the large intestine, where the villi are absent, the passage to the surface takes place slowly, and the cells have time to produce secretion while they are within the crypts. Out of this arose the misconcep- tion that the crypts of the small intestine produced a serous fluid ; those of the large intestine a mucoid secretion. Between the epithelial cells migratory leucocytes from the underlying tunica propria are found in varying numbers. . - Tunica propria. ^ ? -7 . S -J t, . ^ '^iU-v^i' l'"rtion ot a capilUrj' f*/^^ V€^'^:i" ; Mood- vessel ■ ** ^ ' ) C^ _ jBi 1 §^ •%. *^« '-'-- N'jcleus of a wandering leucocyte. Tangential section of a goblet-cell. 't 'Y\it. tunica propria consists chiefly of fibrillated and reticular connective tissue which contains an e.xtremely variable number of leucocytes. Owing to the numerous crypts present the tunica propria of the large intestine is confined to the spaces between, and to a narrow zone below, the tubules, as in the stomach ; throughout the small intestine the tunica propria extends into the villi. The muscularis miicosiz consists of an inner circular and an outer longi- tudinal layer of smooth muscle-fibers. Fibers derived from the muscularis 1 66 HISTOLOGY. mucosae extend within each vilhis nearly to its apex. Their contraction effects a shortening of the villus. The submiuosa consists of loose fibrous connective tissue, and in the upper half of the duodenum contains branched tubular glands — the glands of Brunner. The excretory ducts of these glands are clothed with columnar cells, pierce the muscularis mucosje, and run in the tunica propria parallel with the crypts of Lieberkiihn. The walls of the tubules are formed of columnar gland-cells and a structureless membrana propria. The Lymph-nodules. It has been previously mentioned that the tunica propria of the mucous membrane contains leucocytes or lymphoid cells in variable numbers, occurring Lieberkiihn's crypls. -==*- Ganglion-cells of Auerbach's pie left. ;. 141. — Longitudinal Section thkough the Duodb loosened from the connective tissue of the villus on the cut obliquely. The epithelium has fallen from the middle villus, s posed. The serosa is represented by a line beneath the longitudi cular layer. J Cat. X 30. The epithelii The two villi at the ex that the ccnnective-tiss l1 layer of the muscular either as diffuse adenoid tissue or a.s circumscribed masses 0.5 to 2 mm. in size. The latter are lymph-nodules which occur singly as the solitary nodules (soli- tary follicles) or in groups as Peyer' s patches. The solitary nodules vary greatly in number in the gastric mucous mem- brane ; they are more numerous in the intestines. They usually possess an oval form, and in the beginning of their development always lie in the tunica pro- pria, close under the epithelium, with their base directed toward the muscularis mucosae. With advancing growth (in cats at birth) they break through the muscularis mucosEE and expand in the submucosa, where the loose tissue offers but little resistance. The part of the nodule lying in the submucosa has a spherical outline, and soon becomes considerably larger than that within the tunica propria. The completed solitary nodules, therefore, are in general pear- THE DIGESTIVE ORGANS. 167 shaped, with the small end turned toward the epithelium. Where the nodules are situated the villi are wanting and the crypts are pushed aside. The solitary nodules are composed of adenoid tissue and usually contain a germinal center. The young leucocytes formed in them pass in part into the neighboring Of muscularis. The . Patch of Pbvrr or thb Small Intbstinb of Cat. ■ilhin the pl.lne of the section. X '»■ Techn. No. 107. *^i^iii/c/ies of Peyerzx^ groups of ten to sixty nodules that lie side by side, never over one another, each of which has the structure of a solitary i68 HISTOLOGY. nodule. Occasionally the outline of an individual nodule is altered by the pressure of adjacent nodules (Fig. 142). They occur principally in the lower portion of the small intestine, and are either isolated from one another or embedded in diffuse adenoid tissue, in which case only the germinal centers can be distinguished. This is not infrequently the case in the vermiform process of man. The muscular layer of the intestine consists of an inner robust circular, and an outer thinner longitudinal stratum of smooth muscle-fibers. In the large intestine the longitudinal muscular layer is only well developed at the folds corresponding to the intervals between the sacculi ; between these folds it is extremely thin. The structure of the serosa will be described with the Peritoneum. Lymph-follicle Circular muscles. Longitudinal muscles. Artery. ;. 144.— From a Cross-Sbction of an Injected Small Intestine of Rabbit. X 5°- Th": lymph-nodule is sectioned so that in the upper half the superficial capillary network is visible, in the lower half, the capil- lary loops occurring within the interior of the nodule The section is thick and unstained, and the crypts of Lieberkuhn cannot be distinguished, i. The network of blood-vessels within the muscularis; 2, within the submucosa ; 3, within the tunica propria. Techn. No. 110. The Blood-vessels of the Stomach and Intestines. The blood-vessels of the stomach and the large intestine have a precisely similar distribution, which is modified in the small intestine by the presence of the villi. In the stomach and the large intestine the entering arteries first give off small branches to the serosa, then pierce the muscularis, which they also supply, and form in the submucosa a network extending parallel to the sur- face. From this small twigs ascend through the muscularis mucosa, and in the tunica propria at the base of the glands form another network parallel to the surface. Fine capillaries (4.5 to 9 ix wide) arise from the latter, and form THE DIGESTIVE ORGANS. 1 69 plexuses surrounding the gland-tubules and crypts; wider capillaries (9 to iS !i) form a subepithelial plexus, which lies wreath-like about the mouths of the glands. Venules take their origin from the wide capillaries, pass vertically down between the gland-tubules, and of)en into a venous plexus lying parallel to the surface in the tunica propria ; in their further course the veins run along- side the arteries. The veins arising from the venous plexus in the submucosa are furnished with valves to the point where they meet the veins of the small intestine approaching along parallel paths. The larger branches and the trunk of the portal vein are without valves. In the small intestine only the arteries supplying the crypts are distributed in the same manner as in the large intestine. A special artery passes to the base of each villus (more than one when the villus is wide), breaks up into a capillary network extending beneath the epithelium, and terminates in a venous stem which descends almost vertically to the mucosa, taking up in its course the capillaries from the crypts. In the dog the artery enters the villus along- side the vein ; it then breaks up into a subepithelial capillary plexus, that passes vertically or obliquely to the long axis of the villus over into the vein. The further course of the veins is the same as in the large intestine. The duodenal glands (glands of Brunnerj are enveloped in a capillary plexus supplied by the blood-vessels of the submucosa. The lymph-nodules are surrounded by a superficial capillary network, from which fine capillaries extend into the interior ; often these do not pene- trate to the center, which is then without blood-vessels (Fig. 144). The Lvmph-ve.ssels of the Sto.m.\ch and the Intestines. The lymph- (chyle) vessels of the stomach and the large intestine begin in the mucous membrane as blind capillaries about 30 ;i wide, and descend between the gland-follicles. In the mucous membrane of the small intestine the lymph -\-essels begin in the a.\es of the villi ; in cylindrical villi they are simple (in leaf-shaped villi multiple) canals(27to 36 ;u wide) closed at their upper ends — lymph-radicles or lacteals. All these vessels descend to a narrow-meshed capillary plexus lying at the base of the glands and extending parallel to the surface, which communicates by numerous anastomoses with a wide-meshed plexus in the submucosa ; the lymph-vessels proceeding from this network l^enetrate the muscular coat and take up the vessels of a plexus lying between the circular and the longitudinal muscular strata, called the intramuscular lymphatic plexus, which takes up the lymph-capillaries of both muscular layers. The vessels then run beneath the serosa to the edge of the mesentery and pass onward between its folds. Many of the vessels are provided with valves. In certain localities the course of the lymph-vessels in the mucosa is modi- fied ; the nodules of the patches of Peyer never contain h-mph-vessels. They press aside the capillaries, which run in the interstices between them, constantly decreasing in number but increasing in caliber. It is probable that the lymph- 170 HISTOLOGY. sinuses of the rabbit (p. 97) are nothing else than immensely widened, flat- tened capillaries. The Nerves of the Stomach and the Intestines. The numerous nerves, consisting mainly of gray fibers, form a plexus be- neath the serosa, then penetrate the longitudinal layer of the muscular tunic and between this and the circular layer are arranged in a conspicuous network, the intramuscular ganglionic plexus or Auerbacli s plexus ; numerous groups of multipolar ganglion-cells are found along the course of the nerves, usually at the nodal points of the network, the meshes of which are angular or elliptical. From this network bundles of pale fibers are given off, usually at right angles, which in part supply the longitudinal and the circular strata of the muscular tunic, while another portion pierces the latter and enters the submucosa. In the muscu- FiG. 145. — A. Surface View of Auebbach's Plexus of Infant r, layer of circular muscle-fibers, recognized by their rod-shaped n B. Surface View of Meissner's Pi.e.\us of the Same Infant. blood-vessel shimmering through the overlying tissue, 'I'echu. No X 50. s^. Groups of ganglion-cells ; lei. Techn. No. in a. ' 50. g. Groups of ganglion-cells ; b, lar coat the nerves form a rich rectangular-meshed network, from which nerve- fibers turn aside and after repeated division approach the muscle-fibers, on which (not within) they terminate in free club-shaped endings. The nerves in the submucosa form a delicate ple.xus, Meissner's plexus, whose meshes are narrower and whose groups of ganglion-cells are smaller. From this spring numerous fibers which enter the tunica propria, and in part weave a nervous net about the crypts, and in part enter the villi, where they terminate free in the parenchyma or close beneath the epithelium, without connection with the epithelial cells. A network corresponding to the intramuscular ganglionic ple.xus occurs between the layers of the muscular coat of the esophagus. THE DIGESTIVE ORGANS. 171 THE SALIVARY GLANDS. The salivary glands are the submaxillary, the sublingual, the parotid, and the pancreas. They are compound tubular glands, which elaborate either a mucoid or a serous fluid rich in albumin, or both the mucoid and the serous secretion, .\ccordingly we distinguish : (i) mucous sa/irarv ^/a/u/s (suhWngual in man, the rabbit, dog, and cat ; submaxillary in the dog and cat) ; (2) serous sa/tTary g/am/s (the parotid in man, the rabbit, dog, and cat; submaxillary in the rabbit, and the pancreas) ; (3) mixed salivary glands (submaxillary in man, the ape, guinea-pig, and mouse). The Sublingual Gland. — The excretory duct (duct of Bartholin) consists of a two- layered cylindrical epithelium and fibro-elastic tissue. It is continued as the intralobular or mucous tubes, whose low columnar epithelium exhibits the characteristic striation only in a few places. Intercalated tubules cannot be demonstrated with certainty, and it is much more probable that the mucous tubes pass directly into the terminal compartments. The latter are com]5osed of a membrana propria and of gland-cells. The membrana propria is formed t)y stellate connective-tissue cells ; the empty glandular cells occur in groups, and the "demilunes" therefore appear very large. The connective tissue between the tubules and the lobules is rich in leucocytes (Fig. 146). The Parotid Gland. — The excretory duct (duct of Stenson) is distinguished by its broad, compact membrana propria close beneath the epithelium, but is otherwise like that of the sublingual gland. It divides and passes into Xk\t inlralolmlar Xwhz?,, whose columnar cells exliibit at the base distinct ver- tical striation. Following these are the intermediate tubules, which are lined by elongated, often spindle-shaped cells. The intermediate tubules con- tinue into the terminal compartments, which consist of a delicate mem- brana projjria of stellate connective-tissue cells and of cubical serous glandu- lar cells. In a condition of exhaustion the cells are small, dark, and granu- lar ; in a condition of activity they appear larger and somewhat lighter. The Submaxillary Gland. — The excretory duct (duct of Wharton) pos- sesses likewise a two-layered columnar epithelium, a connective-tissue layer rich in cells, and outside of this a thin stratum of longitudinally-disposed muscle-fibers ; it continues as the intralobular tubes lined with characteristic " rodded " epithelium, which pass into the short intermediate tubules clothed with cubical cells. The latter lead into the acini, which are clothed with ic:. 146. — From a Thin Cuoss-Section OF HumanSublingualGland. X 240. Of the seven tubules represented, only three (1,2,3) are sectioned so as to be suitable for study. In 2 are six cells loaded with secretion {s.g) ; and two empty cells (j./) are crowded to the peri- fhery, where they form a "crescent." n 3 all the cells are filled with secretion, and have deeply slamcd contents : 4, tangential section of a similar tubule. 5, 6, 7. Oblique sections of tubules like I ana 2, which show the crescents, but not the lumen of the gland, mp. Mem- brana propria. b. Connective tissue with numerous leucocytes, z. Tcchn. 172 HISTOLOGY. either serous gland-cells (as in the parotid) or with mucous gland-cells and demilunes. The Pancreas. — The excretory duct (duct of Wirsung and Santorini) is formed of a simple columnar epithelium and fibrous connective tissue, which latter is denser beneath the epithelium, looser toward the periphery. The walls Fic. 147.— From a ThinSectioi OF Human Pakotid Gland X 240. .?. Intercalated tiibule the outlines of the cells canno be distinguished. The vcr' narrow lumen of the gland tubule is seen only at /: th remaining gland-tubules are cu obliquely. Techn. No. 112. •'iG. 148. — From a Thin Sbction of Huivian SuBtflAJ X 240. A. Cross-sectionof salivary tube: the epithelial- are partially loosened from the surrounding connect! same side the striation in the outer zone of the cells i of wandering leucocytes ; j, secretion. B. Tubul gland-cells showing four lumina ; e, tubules with set ing one lumen ; b, blood-vessels, of which the \~ dinally and contains colored blood-corpuscles. Tech >n the right . * : on the I ; k, nuclei (m) with mucous i gland-cells show- ut longitu- No. 112. of the main e.xcretory duct and its larger branches contain minute mucous glands. Intralobular tubes with their characteristic epithelium are wanting. The branches of the excretory duct continue directly into the intermediate divisions. The columnar epithelial cells of the former steadily diminish in height and B -£r7^57»^^^(I^^_N_ Terminal compartment (tangen- , ^ * ^ "'' ^c^ \:K. • ^ ^'^* section). Intermediate tubule (longitudi- ~ nal section). . Acinus (halved). Intermediate tubule (t n). -Acinus (halved). Fig. 149.— .-^. Gland-Cells of Pancreas of C below, two isolated cells. B. From a Cross-Se irmediate tubule. X 560. Above, groups of cells as they usually appear; N op Pancreas of AN Infant. X 240. Techn. No. 113. eventually pass over into the flattened cells, placed parallel to the long axis, of the intermediate tubules. These tubules are very long and narrow ; toward the acini they divide and then terminate abruptly. The epithelium of the acini is composed of short cylindrical or conical cells, which are characterized by the highly refracting granules — "zymogen THE DIGESTIVE OROANS. 173 granules " — occupying the zone adjoining the lumen, and are thus distinguished from all other glandular cells (Fig. 149 A). The clearer peripheral zone con- tains the round nucleus. The granular and clear divisions of the cell vary in proportionate extent with the functional condition of the cell. In the beginning of digestion the granules disappear and the clear belt becomes deeper. Sub- sequently the granular zone increases to such an extent that it occupies nearly the whole of the cell. In a fasting condition the two zones are of equal size. In glands treated by the method of Golgi, the secretion often stains and the duct-system in its entire extent appears black. It may then be seen that strife radiate out from the central lumen, but do not quite extend to the membrana propria ; they branch, and without anastomosing terminate in free ends. They must not, without further consideration, be compared with the secretory capillaries of the parietal-cells, for these form a network embracing the cell, while here, at the most, the stria;, not their branches, lie upon the gland-cells ; the latter lie rather within the cell and, in my opinion, indicate the residue of elaborated secretion that remains in the otherwise empty cell (also in the submaxillary, in the "demilunes"). (Fig. 150 and Fig. 151.) X 320. Techn. No. 119. -From a Section t OF Dog. X 3=o. ' The blood-vessels of the salivary glands are richly developed. The arterial stems run, as a rule, along the main excretory duct,_ divide into numerous branches which pass between the lobules and finally penetrate within the latter, where they break up into capillaries and form close networks embracing the tubules. The capillaries lie in immediate proximity to the gland-cells. The larger veins follow the course of the arteries. With regard to the lymph-vessels little is known with certainty. The interfascicular clefts between the lobules and the tubules have been described as lymph-channels. The salivary glands are profusely supjjlied with meduUated and nonmedul- lated nerves, along the courseof which microscopic groupsof ganglion-cells occur. The fine meduUated nerve-fibers form networks around the gland-tubules, but do not penetrate them, and ramify in the walls of the blood-vessels. 174 HISTOLOGY. THE LIVER. The liver is a compound tubular gland. On making an incision into a liver or on examining its outer surface, it will be observed that it is divided into irregular polygonal areas, well defined, as in the hog, or poorly defined, as in man and the majority of mammals. These areas are the lobules of the liver (incorrectly named acini). Their real form is somewhat like that of a prism with a rounded upper end and a transversely-blunted base (Fig. 152). They are 2 mm. high and i mm. broad. Close under the capsule of the liver the lobules are often arranged with their apices looking toward the surface, and a section taken parallel to the surface will pass through the lobules transversely (Fig. 154) ; in the interior of the liver the lobules extend in different direc- tions. Each lobule consists of gland- cells and blood-vessels and is separated from neighboring lobules by the inter- lobular connective tissue — the capsule of Glisson — which supi)orts the branches of the excretory duct — the hepatic duct — the branches of the portal vein and the hepatic artery, the lymph-vessels and the nerves. The demarcation of the lobules depends on the development of the inter- ^_ , lobular connective tissue. |^,^<~»-> ^ The main excretory duct, the //c/(7//f duct, and its larger branches are com- posed of a single stratum of columnar epithelium, occasionally containing gob- let-cells, and of fibrous connective tissue separated into a tunica propria and sub- mucosa. The tunica propria contains glands, chiefly short pear-shaped follicles lined with mucous gland-cells, and also isolated longitudinally- and transversely-disposed plain muscle-fibers. The cystic duct, the ductus choledochus, and the gall-bladder exhibit the same structure ; the tunica propria is elevated into minute anastomosing ruga;, and the mucosa is supplemented by a thin layer of smooth interlacing muscle- fibers. The columnar epithelial cells of the gall-bladder are distinguished by their height (0.05 mm.) from those of the ductus choledochus (0.024 mm.). The vasa aherrantia or blind bile-ducts, that occur chiefly at the left border of the liver, at the portal fissure, and surrounding the vena cava, are em- bryonal remains of liver-substance (isolated bile-ducts) and do not occur in the parenchyma of the organ. The branches of the hepatic duct — inter- lobular bile-ducts — exhibit thinner walls as they diminish in caliber ; the larger are composed of simple columnar epithelium and fibro-elastic tissue ; the small- HEME OF A Hepatic Lobuli I tninsverse section below an partial leveling, in longitudinal section : In the left half the blood-vessels are drav the right half only the cords of hepatic d, by THE DIGESTIVE ORGANS. 175 est possess only a structureless membrana propria and a simple layer of low epithelial cells, often showing a cuticular border, which as they enter at the margin of the lobules annex themselves directly to the true glandular cells. This transition is very difficult to see, and can only be distinctly perceived in sections in which the bile-ducts have been injected or blackened by Golgi's silver method. Fig. 153. — Livbr-Cells op Man. X 560. A. Isolated liver-cells containing smaller and larger fat-drops,/"; b, impression resulting from a blood-vessel. Techn. No. 114. B. I'rom a section ; i . Exhausted cells ; 2, active cells, filled with secretion. Techn. No. 116. The glandular-cells of the liver, the hepatic cells, are irregular polyhedral elements consisting of a granular protoplasm and of one or more nuclei ; they have no cell-membrane. The protojilasm contains granules of pigment and globules of fat of various sizes. The cells vary in size from i8 to 26 ,a. The ■< '\ *'' ' ,' * ~ ".! ' 'y • p"^'. ^Interlobular bile-duct. ;-■■->•'.•;".■•.•"-•'■'.. / ",'■,'• •■''VI' ^•''- . Interlobular ^^^^|;:v:-'!;v: I ■-■■ '■^:^'% '■ ''i^ir-^ Fic. 154— From a Horizontal Section i>i l^•,l^N Iivik. ^■, I l.n.- ciitial veins, cut transversely, represent each a center of as many hepatic lobules, which at the periphery are but slightly defined from their neighbors. Helow and to the right of the section the lobules are cut obliquely and their boundaries cannot be distinguished. I'echn. No. 116. appearance of the hepatic cells depends, as in other glands, on the phase of functional activity. In a fasting condition they are small and dark, and have indistinct contours ; during digestion they are larger, have a clear center, and at the periphery a coarsely-granular zone. In man the two conditions are frequently e.xhibited in the same liver (Fig. 153 B). 176 HISTOLOGY. In the lower vertebrates (amphibians and reptiles) the hepatic cells form typical tubes, but in the higher vertebrates their arrangement is a very peculiar one, and not a trace of tubular structure is to be seen, as might be presupposed from the tubular character of the liver. The cells are united in small trabeculse or cords, the so-called conls of cells, which are radially disposed around a small vein (the central vein) situated in the axis of the lobule, and by lateral branches anastomose with neighboring cords of cells. A lumen cannot be distinguished in sections prepared by the usual methods ; it can only be shown by injecting the system of canals from the hepatic duct or by employing Golgi's method, which blackens the bile. In such preparations it may be seen that Small interlobu- lar bile -duel, bile-capiUa- Boundary, toward central > method of Golgi. the minutest interlobular bile-ducts are continued directly into the lobules, where they form, apparently, a network with polygonal meshes. In reality there are but few true meshes ; the network is simulated by the zigzag course of the bile-canaliculi and the crossing in different planes of the blind lateral twigs with which they are furnished (Fig. 155). The ramifications of the intralobular system of canaliculi appear to have little relation to the branching of the cords of hepatic cells. The latter branch much less than the former and thus, apparently, the intralobular canaliculi have attained a certain degree of independence, as implied in the name Inle-caftillaries bestowed upon them. This also accounts for the hitherto always fruitless THE DIGESTIVE ORGANS. 177 endeavor to demonstrate a special wall for the bile-capillaries. There can be no wall other than that formed by a modification of the exoplasni of that side of the hepatic cells at which the capillary is situated. Thin sections show clearly that the bile-capillaries stand in the same rela- tion to the hepatic cells as the lumina of other glands do to the surrounding gland-cells, at least in most cases. But nevertheless certain differences exist. The first difference is this, that only a few, usually two, hepatic cells bound the bile-capillaries, while in other glands the lumen is surrounded by several cells. The explanation of this may be found in the conspicuous difference between the diameter of the lumen (bile-capillary) and that of the hepatic cell ; two cells are sufficient to completely surround the lumen. The capillary is thus formed by the apposed furrow-like depressions of two contiguous hepatic cells (Fig. 162). A second difference consists in the relation of the surfaces of the hepatic cells to the bile-capillaries ; they are in contact with the bile-capillaries not only on one, but on several surfaces. This momentarily confusing fact, though not a frequent, is nevertheless not an isolated phenomenon. One need but recall the relations in the fundus glands, where lateral twigs leave the chief lumen, branch and form a complete basket-work of fine canals embrac- ing the parietal-cells, and where each parietal-cell presents not only one but all surfaces to the gland- lumen ; but there the phenomenon is not so striking, because the branching off of the small lateral canals from the main lumen is easily recognized ; in the liver the lateral branches of the bile-cajjillaries are of the same diameter as the main lumen and are often of considerable length, subdivide, and may even anastomose directly with neighboring bile-capillaries, although this does not commonly occur, and thus every possibility of distinguishing between bile-capillaries, main lumen, and lateral canals vanishes. The fact tiiat the hepatic cells are in contact with the bile-capillaries not only on one but on several surfaces, renders compre- hensible the luxuriant ramification of the latter, despite the fact that few cells are required to circumscribe them. Not infrequently it may be seen that short fine lateral twigs leave the bile- capillaries and terminate in a minute knob-shaped end. The knob corresponds to a small vacuole in the liver-cell, which communicates with the bile-capillary by means of the minute lateral twig. These are undoubtedly transient forma- tions occurring in connection with certain functional phases; the proof of this I detect therein that entire areas of the system of canaliculi may be free from these knobs, while close beside every capillary is beset with them (Fig. 156). Of the blood-vessels of the liver, the portal vein assumes the role that falls to the artery in other glands, while the hepatic artery is assigned the subordi- 178 HISTOLOGY. nate part of the maintenance of the interlobular branches of the bile-ducts, of the portal vein, and of the nerves. From the branches of the portal vein, which because they run in the inter- lobular connective tissue are called interlobular veins, spring numerous capil- laries, possessing a width of lo to 14 //. They penetrate within the lobules, anastomose repeatedly during their course, and finally empty into a small vein lying in the axis of the lobule, the central {intralobular') vein visible in trans- verse and longitudinal sections even in the uninjected liver (Fig. 154). The central veins represent the radicles of the hepatic veins and empty into the sublobular veins, which run along the slightly-flattened side, the so-called base, of the hepatic lobules (Fig. 159). nterlobulares. Vense intralobuldres (i entral). 'iG. 157.— Horizontal Section of Liver of Rab- bit. Injected through the portal vein. X 40. Three hepatic lobules are represented. The injec- tion mass filled only the branches of the portal vein (interlobular veins) ; in the upper lobule it penetrated to the central vein. Techn. No. 118. Fig. 158. — Horizontal Section of Liver of Injected through vena cava inferior. X 40- iiepatic lobules are shown. The injection masj the central vein and the capillaries emptying i l)ut did not penetrate to the interlobular Techn. No. 1.8. The relations between the portal capillaries on the one side and the he- patic cells and bile-capillaries on the other calls for especial consideration. Between the meshes of the portal-capillary network lie the cords of hepatic cells, and the relation of the blood-vessels and gland-cells is consequently a very intimate one ; sections show that a hepatic cell is in contact with capillar- ies, not only on one but on several sides (Fig. i6o). This is a peculiar phe- nomenon ; it does not occur in other glands, in which the blood-vessels touch the cells only at one surface, and is only comprehensible when we recall that in cross-sections the lumen (bile-capillary) is bounded by two cells, while in other glands the lumen is bounded by six or more cells (Fig. i6i). But as in other glands, so also in the liver, the cells are inserted between the lumen on THE DIGESTIVE ORGANS. 179 the one hand and the blood vessels on the other. Nowhere do blood-capil- laries and bile-capillaries lie close beside one another; they are always separated by an intervening portion of the cell. The most convincing demonstration of this is afforded bv thin sections of rabbit's liver, in which Central (intralobular) ''*iA. Fig. 159. — Fhom a Vertical Section op Liveu op vein cut longitudinally ; it takes up the central vci the wide blood-vessels. X iS- Techn. No. 118. r. Injection through vena cava The greater part of the injecti( the blood-vessels have been cut transversely ; these show plainly that the bile- capillaries run along the surfaces, the vascular capillaries at the corners of the hepatic cells (Fig. 162); however, this is not invariably the case; the bile- i, i6o.^From a Section op Livek of Rabbit. X 340. The portal-capillaries were injected w mass, the bile-capillaries with a blue mass. The hepatic cells are in contact with the blood-capillarie sides. At a few points the red mass has retracted and given rise to a space (/), between the hepatic portal-capillaries. The bile-capillaries are nowhere in contact with portal-capillaries but arc alwa rated from them by half the breadth of a cell. The dark spots on the portal-capillaries are optit sections of blood-capillaries which run vertically to the plane of the section. capillaries sometimes run along the edges, a disposition that occurs e.specially in man (Fig. 162 X). The branches of the hepatic artery follow the course of the portal vein and ramify only in the interlobular tissue ; they form capillary networks about i8o HISTOLOGY. the larger bile-ducts, the branches of the portal and the hepatic veins. These capillaries are taken up by the portal interlobular veins or by the portal capil- laries at the margin of the lobules. In the capsule of the liver the hepatic artery forms a wide-meshed capillary plexus. The course of the blood-vessels Gland-lumen (bile-capil- lary). ll,R,. is therefore as follows: The portal vein enters at the transverse fissure, divides repeatedly into branches that steadily decrease in size and run in the connective tissue between the lobules as the interlobular veins ; these break up into capilla- ries which pass toward the axis of the lobule and terminate in the central vein. Flu. 162. — Thin Section- of Liver of R nut schematic.) Two of the hepatic capillary at the edge of a hepatic cell. Injected Bile-Capillaries. X 560. (The t contact with four blood-capillanes (i, 2, 3, 4). Several of the latter' unite in the formation of each of the sublobular veins, which, like the larger hepatic veins they form by their union, run between the lobules. The capsule of the liver is composed of fibre-elastic tissue, which is espe- cially well developed at the transverse fissure, where it is called the capsule of THE DIGESTIVE ORGANS. l8l ^W^ [G 163. — From a Shake Human Livek. X 240. c. Blood- capillaries, at X still containing blood- corpuscles, d. Interlobular connective tissue. On the right are five hepatic cells : the others nave fallen out of the meshes of the capillary network. I'echn. No. 117. Glisson, and in the form of special sheaths for the different channels penetrates the interior of the liver, where it is usually found in such small amounts between the lobules that the boundaries of the latter are very imperfectly defined. The walls of the veins are firmly attached to the liver substance by the interlobular connective tissue, and for this reason do not collapse when cut. Delicate fibers (" lattice- fibers") derived from the interlobular connec- tive tissue penetrate into the interior of the lobule, where they are arranged in the form of a delicate, radially-placed "latticework." The lymph-vessels accompany the branches of the portal vein, which they embrace in their ramifications; with the portal capillaries they enter the interior of the hepatic lobules, ac- company them close up to the central vein, then pursue a divergent course. The deep lymphatics communicate with a superficial net- work of lymph-vessels, which occur in the capsule. The nerves consist largely of nonmcdul- lated fibers with which a few meduUated nerve- fibers are mingled; they enter the interior of the liver in company with the hepatic artery and follow its ramifications ; the exact mode of their termination is unknown. Ganglion-cells occur along the course of the nerves. The secretion of the liver, the bile, frequently contains drops of fat, also granu- lar masses of bile-pigment. Columnar cells from the bile-ducts are incidental admix- tures. That the structure of the liver really follows the type of the tubular glands, and that the cords of hepatic cells, with certain modifications, are comparable to the acini of other glands, the foregoing considerations have shown. The hepatic lobules, on the other hand, cannot without explanation be compared with the lobules of other glands ; the latter, as a rule, consist of a duct-system, of which the excretory duct leaves the lobule at one place and continues into a larger duct. In the hepatic lobules the ducts emerge at many points on the surface. 'I'he acconijianying schematic representations may serve to elucidate the relations of the lobules. Imagine a system of ducts ; along- side the excretory duct an artery, whose capillaries surround the terminal com- partments and i)ass into a vein running along the base of the latter (Fig. 164). Excretory duct compartments F A System of Ex (" DUCT-SVSTEM "). HISTOLOGY. Excretory ducts. Branch of portal > Terminal comparti Fig. 165. — Scheme of the Liver. Two lobules areshown, of which the left is only half carried of the capillaries and the cords of hepatic cells have been omitted for the sake'of Branch of portal Fig. 166. — Scheme of Transverse Section of Liver. Four lobules represented. The separate systems ol ducts are indicated by the difference in shading, A. Excretory ducts. £. Terminal compartments. THE DIGESTIVE ORGANS. 183 This is the principle of each of the many systems of ducts of which the liver con- sists ; but there is one peculiarity : the somewhat tortuous terminal compartments extend in certain different directions (Fig. 165). At the base as well as above runs a vein, but — another variation — the vein takes up not only these capillaries but also those of the other side, where lies another system of ducts whose acini are in contact at the base with the same vein. The vein, therefore, lies in the axis of a complex or aggregation of terminal compartments, and such a complex is termed an hepatic lobule. (In the liver of the rabbit the central veins lie close under the surface, and only take up capillaries from one side. ) If we now draw a comparison with the scheme Fig. 164, the artery corresponds to the portal vein in scheme Fig. 165, and the vein in Fig. 164 is the equivalent of the central vein of Fig. 165 ; one hepatic lobule corresponds not to one duct- system, but to parts of several systems. The simijlicity of this schematic Grratbr Omentum of Ti/t ve tissue. The wavy striatic IS mounted in damar. At X lb hn. No. 120. BIT. X 240. The network is formed by large and small of the bundles can only be indistinctly seen, because the cells from the opposite surface can be seen shimmering presentation is based in part on the conception of well-defined lobules, as they occur in the hog. In other animals the distribution of the terminal ramifi- cations is less regular; the latter bend into neighboring lobules, to which in part is owing their less distinct demarcation. Each system of ducts partici- pates in the formation of several lobules. THE PERITONEUM. The i)eritoneum consists principally of bundles of fibrous connective tissue and numerous elastic networks ; the free surface is covered by a simple layer of flat polygonal epithelial (endothelial) cells. The connection with subjacent parts (the parietes, the viscera, etc.) is effected by loose (subserous) connec- tive tissue. The connective-tissue bundles are arranged in thinner (in the visceral lieritoneum) or thicker (in the parietal peritoneum, in the mesentery) layers 184 HISTOLOGY. parallel to the surface, and interlace in various directions ; in certain localities (in the greater omentum, in the middle of the lesser omentum) the bundles form a beautiful network with polygonal or rectangular meshes. The strands of the network are covered by plate-like epithelial cells (Fig. 167). The number of connective-tissue cells among the fibrous bundles is on the whole not large; only in young animals are larger groups of cells found; they resemble plasma-cells and probably bear a close relation to the formation of blood-vessels. The elastic fibers in the deeper layers of the peritoneum, particularly in the parietal portion, are profuse and vigorously developed. The subserous tissue consists of loose connective tissue, many elastic fibers, and fat varying greatly in quantity ; it is plentiful where the peritoneum is easily shifted over the underlying parts, but on the liver and the intestine it is so much reduced that it cannot be demonstrated as a special layer. At certain places, e.g., in the broad ligaments, numerous bands of smooth muscle-fibers are found. Blood-vessels and nen'es are scantily represented ; the latter terminate in part in Pacinian corpuscles. Lymph-vessels occur in the superficial and the deeper layers of the peri- toneum. VI. THE RESPIRATORY ORGANS. THE LARYNX. The mucous vtembmiie of the larynx is a continuation of the pharyngeal mucous membrane and like this is composed of an epithelium, a tunica propria, and a submucosa which binds the mucous membrane with underlying parts. The mucous membrane over nearly the whole of the organ is covered by a stratified ciliated columnar epithelium ; the ciliary wave is directed toward the cavity of the pharynx. On the true vocal cords, on the anterior surfaces of the arytenoid cartilages and on the posterior surface of the epiglottis the epithelium is of the stratified scaly variety. The tunica propria consists of numerous elastic fibers and of white fibrous connective tissue, which in the lower animals is con- densed to a membrana propria immediately beneath the epithelium. The tunica propria is the site of a varying number of leucocytes ; in dogs and cats, solitary nodules are found in the mucous membrane of the ventricle of Morgagni. Papillae occur mainly in the mucous membrane clothed with strati- fied squamous epithelium. The submucosa contains branched tubular mucous glands from 0.2 to i mm. in size. The cartilages of the larynx are principally of the hyaline variety, which in a measure exhibit the peculiarities of the costal cartilages ; to this belong the thyroid, the cricoid, the greater portion of the arytenoid and often the THE RESPIRATORY ORCANS. 1 85 triticeous cartilages. The epiglottis, the cartilages of Wrisberg and Santorini, the median portion of the thyroid, and the apex and vocal process of the arytenoid cartilages are of the yellow elastic variety. Occasionally the tritice- ous cartilages are composed of white fibro-cartilage. Between the twentieth and thirtieth years of life ossification (chiefly endochondral) begins in the thyroid and the cricoid cartilages. The larynx is richly supplied with blood-vessels and nen'es. The blood- vessels form two or three networks in planes i>arallel to the surface, and a close subepithelial capillary plexus. The lymph-vessels also form two communicating networks in horizontal planes, of which the superficial has the narrower channels and lies beneath the vascular capillary network. The nerves in their course include microscopic ganglia. In ])art they terminate in end-bulbs and taste-buds. The latter are found on the posterior surface of the epiglottis. THE TR.\CHE.\. The ciliated mucous membrane of the trachea possesses a structure like that in the larynx, excepting that the elastic fibers form a close network in which the fibers pursuing a longitudinal direction predominate. This network lies immediately beneath the epithelium and above the glands. The cartilages are of the hyaline variety. The ])osterior wall of the trachea is composed of a layer of transversely-arranged jjlain muscle-fibers, which is usually covered by a stratum of fibers extending longitudinally. The mucous glands of the poste- rior wall are distinguished by their size (2 mm.); they not infrequently penetrate the muscular layer, and lie in part in the fibrous tissue behind it. The behavior of the blood-vessels, lymph-vessels, and nerves is the same as in the larynx. THE BRONCHI .\ND THE LUNGS. Tile lungs may be regarded as compound alveolar glands, in which, as in all glands, excretory and secretory (in this case respiratory) portions may be distinguished. The excretory division comprises the larynx, the trachea, and the bronchi. Each bronchus on entering the lung divides repeatedly and within the same undergoes continual subdivision, giving off small lateral twigs and branching at acute angles, with gradual decrease in the caliber of the branches, finally breaking up into minute twigs that now'here anastomose with one another and that retain the characteristics of the bronchus to a diameter of 0.5 mm. At this point the respiratory division begins. Isolated hemispherical evaginations, the alveoli, appear at irregular intervals on the walls of the minute bronchi. Such bronchi are called respiratory or terminal bronchioles. These divide and lead into the alveolar ducts, which differ from the terminal bron- chioles only in the larger number of alveoli in their walls. The alveolar ducts divide at right or acute angles, and pass without sharp demarcation into 1 86 HISTOLOGY. the slightly-expanded terminal vesicles (less correctly, infundibula), whose walls are thickly beset with alveoli. The entire respiratory division is separated by areolar tissue into lobules 0.3 to 3 cm. in size. All the branches of the excretory division to a diameter of 1.5 to I mm. and less lie between the lobules — as "interlobular ducts." The minute structure of the bronchi in the largest branches does not differ from that of the trachea. Gradually, however, modifications appear, which first involve the cartilages and the musculature. The C-shaped ring cartilages Fig. i63.— Ckoss-Se Two MiLLiMETEKS Thick, OF Child. X 30- Techii. No. 123. are replaced by irregular plates lying on all sides of the bronchial wall. They diminish in size and thickness with the decrease in the diameter of the bronchi and disappear altogether in bronchioles 1 mm. in diameter. The smooth muscle-fibers are circularly disposed in a continuous layer lying within the cartilages and form a complete investment for the tube. The thickness of the muscular layer decreases with the diameter of the bronchi ; but muscle-fibers are still found as far as the alveolar ducts. In the infundibula thev are wanting. IHE RESPIRATORY ORGANS. ■ 87 The miiioiis iiiemliranc is thrown into longitudinal folds and consists of a stratified ciliated epithelium containing goblet-cells, which in the smaller bronchi becomes gradually reduced to a single stratum, and of a connective- tissue tunica pro[)ria. The latter contains numerous longitudinal networks of Fig. 169.— From a Section of Lung of Adult Man. X 50. The terminal bronchiole divides into two branches (on the right). A portion of the wall of the bronchiole fell within the plane of the section. Above the entrance to the alveoli can be seen ; below the alveoli are viewed from the side. The epithelium of the V. ..k:..!. ;^ "'=xed. The epithelial lining of the alveoli is only partially visible with this magnification. the entr^.- __ ichiole Techn. No. 1 elastic fibers and leucocytes in greatly varying numbers. Occasionally solitary nodules occur, from the crest of which leucocyte* wander through the epithe- lium into the bronchial tubes. Cnbical and flat epithelial cells. Fig. 170- — From Sections op Human Ll'ng (.\ and B), and fC), op Lung op t X 540 A. Mixed epithelium of terminal bronchiole. B and C. Alveoli drawn margin of the alveolus is shaded ; it can he seen that the epithelium covering it i alveolus (the light portion) ; the nuclei of the cells are not visible. Techn. No. Kitten Nine Days Old. with change of focus. The like that in the base of the Branched tubular mucous glands occur as far as the cartilages extend ; they are situated outside of the muscular layer (Fig. i68). They are numer- ous and do not disappear until at the beginning of the respiratory bronchioles. F.xternal to the cartilages is z^fibro-elastic tunic which envelops the entire bronchus including the accompanying vessels and nerves. iSa / HISTOLOGY. The minute structure of tlie respiratory division, after the gradual disap- pearance of the cartilages and glands, is distinguished especially by the nature of the epithelium. The respiratory bronchioles following the smallest excretory bronchi still contain a single layer of ciliated columnar epithelium, but as they proceed the cilia are lost, the cells become cubical, and between these another kind of epithelial cells appears, in the form of thin nonnucleated plates of different sizes. These plates and isolated or small groups of cubical cells form an epi- thelium called respiratory epithelium. The transition of the cubical into the respiratory epithelium is not abrupt and sharply defined, but occurs in such wise that at one extremity of the bronchiole cubical, at the other extremity respiratory epithelium is found ; or that groups of cubical cells are surrounded by respiratory epithelium or the reverse. The respiratory bronchioles contain, therefore, a mixed epithelium (Fig. 169 and Fig. i']oA). The epithelium of the alveolar ducts and of the alveoli is the same as the respiratory epithelium of the bronchioles. The developmental history^teaches that the smaller nonnucleated plates originate from cubical cells which become flattened by inspiration, that is, by the inflation of the alveoli. The larger plates are formed by the subsequent blending of several smaller ones. The alveoli of old embryos and in stillborn children contain only cubical cells. The walls of the alveolar ducts and the alveoli, in addition to the previously mentioned muscle-fibers in the former, are composed of a delicate fibrous framework and many elastic fibers. The latter are circularly arranged in the alveolar ducts, and encircle the entrance to the alveolus (the mouth or base) ; delicate fibers spring from this annular bundle and form a network surround- ing and supporting the entire wall of the alveolus. The elastic rings of neigh- boring alveoli grow together at the points of contact and thus constitute the alveolar septa. The areolar tissue between the lobules of the lung — the interlobular con- nective tissue — contains extremely fine elastic fibers and a few connective-tissue cells, and in the adult black pigment-granules and inhaled carbonaceous parti- cles. In children the interlobular connective tissue is more richly developed and the demarcation of the lobules more distinct. The surface of the lung is covered by the visceral pleura ; this is composed of connective-tissue, numerous fine elastic fibers, and on its free surface is clothed by a simple stratum of flat polygonal epithelial (endothelial) cells. The parietal pleura has the same structure, but contains fewer elastic fibers. The blood-vessels of the lungs, the branches of the pulmonary artery, enter at the hilus of the lung and run beside the bronchi, bronchioles, alveolar ducts, and between the infundibula, where they break up into a very narrow-meshed capillary network, placed immediately beneath the respiratory epithelium of the terminal bronchioles, the alveolar ducts, and the alveoli. The veins arise each at the base of an alveolus, and unite into branches that follow the bronchi and arteries. The walls of the bronchi are supplied by the bronchial arteries, which furnish a deep capillary plexus for the muscles and the glands, a superficial THE RESPIRATORY ORGANS. 1S9 plexus for the tunica propria. These capillaries are taken up in part by the bronchial veins, in part by the pulmonary veins. Of the lymphatic vessels two groups are recognized, a well-developed superficial plexus beneath the pleura and a wide-meshed deep plexus in the interlobular connective tissue. From these networks small stems furnished with valves proceed, which follow the bronchi and emerge at the hilus, where they connect with the bronchial lymph-nodules. The numerous nerves of the lungs, derived from the symi)athetic and the vagus, contain meduUated and nonmedullated nerve-fibers and small groups of ganglion-cells. The nerve-endings stand in especial relation to the walls of the blood-vessels. Capillari Fig. 171. — From a Section op Lung of Child, InJBCTFD THKOUr.H PuLMONARY ArTBRY. X 80. Of the five alveoli ilrawn the three upper ones are fully injected. Techn. No. 126. THE THYROID GLAND. The thyroid body is a compound tubular gland, whose excretory canal, the thyro-glossal duct, opening at the foramen cecum of the tongue, with Colloid substa Fig. 172.— a Lob Thin Section Thvkoid Kodv op Icchn. No. 127. Tangential seciion of lubiile ; ihc cpiihc- Hum viewed from the free surface. the exception of a few atrophic remains was obliterated in the embryonic stages of the organ. It consists, therefore, of completely closed tubules , which are united into lobules by loose connective tissue. The tubirles differ greatly in size (40 to 120 /i in diameter) and are lined by a simple layer of cubical epithelial cells. Their contents consists of a characteristic, homogeneous, vis- 19° HISTOLOGY. cid mass, the colloid substance, which is found also in the lymph-vessels of the organ. The blood-vessels are exceptionally numerous, and break up into capil- laries which form a network close beneath the epithelium. The lymphatics, like- wise profuse, form a network lying between the tubules. The nen-es follow the Blood-vessels. Fig. 173.— Section of Sbcondary Lobiiles of Thymus Body of The lower lobules are sectioned tangentially, so that chiefly only ( Techn. No. 128. ramifications of the blood-vessels and form networks distributed especially to the vascular walls, some of which also surround the gland-tubules. The pene- tration of the terminal twigs into the epithelium has not been observed. THE THYMUS BODY. The thymus body, in its first anlage an epithelial organ, consists in child- hood of lobes 4 to 1 1 mm. large, which are enveloped by a fibrous connective- tissue sheath containing fine elastic fibers. The capsule sends septa into the lobes, by which a subdivision into smaller (secon- dary) lobules, I mm. large, is effected. Each of the lobules consists of adenoid tissue, denser at the periphery than in the center, so that a darker cortical zone and a lighter medullary substance may be dis- tinguished. In the medullary substance con- centrically striated bodies, varying greatly in number and size (15 to 180 /i in diameter), are found ; they are masses of altered epithelial cells [the remains of the epithelial structures which in the embryonic stages constituted the principal bulk of the organ]. They are called Hassair s corpiisdes. THE URINARY OROANS. I9I The blood-vessels are richly developed and supply the cortex and the medulla with capillary networks. The lymphatics, likewise, are very numerous ; the larger vessels lie on the surface of the organ, their branches run in the in- terlobular septa and penetrate into the medullary substance. At a later period the tissue of the thymus undergoes retrogressive change ; the greater jjart of the adenoid structures disai)pear and are replaced by fat. VII. THE URINARY ORGANS. THE KIDNEYS. The kidneys are compound tubular glands, which consist e.Kclusively of minute tubes, the uriniferous tubules. The niacroscopically perceptible dif- ferences between the peripheral and central portions of the organ, the so-called cortica/ 3ini\ meilulhify regions, are princijially determined by the course of the uriniferous tubules, the divisions within the cortex pursuing a tortuous, those within the medulla a straight course. Each uriniferous tubule begins in the cortex a.s a spherical dilatation, the Malpighian corpuscle, which is marked off by a constriction, the neck, from the greatly convoluted succeeding division, the proximal convoluted tubule. This passes into a straight portion, which is at first centrally directed, but soon turns back and forms a loop, Henle's loop, in which a descending and an ascend- ing limb may be distinguished. The latter passes into a convoluted portion, the intercalated tubule {irregular and distal convoluted portions), that as it pro- ceeds assumes a straight course, and is then called collecting tubule (Fig. 175). The collecting tubules, during their centrally-directed course, take up other distal convoluted tubules, unite under acute angles with neighboring collect- ing tubules, and converge toward the apex of a renal papilla, where, diminished in number but greatly increased in diameter, they terminate in the papillary duct or duct of Bellini, which opens on the free surface of the papilla. Henle's loop-tubules and the collecting tubules are named straight tubules (tubuli recti). Each uriniferous tubule pursues a completely isolated course until it is taken up by a collecting tubule. The loops of Henle and the peripheral portions of the collecting tubules are grouped into bundles as they ])ass toward the medulla, and form the familiar strife in the cortex known as medullary rays or pyramids of Ferrein. The minute structure of the uriniferous tubules varies so greatly in the sev- eral divisions that a special consideration of each is necessary. The Malf>igliian corpuscles, from 0.13 to 0.22 mm. in size, consist of a spherical mass of convoluted blood-vessels, the glomerulus, and the expanded and invaginated blind initial extremity of a uriniferous tubule, the capsule of 192 HISTOLOGY. Boivinaii. The glomerulus lies within the invaginated portion of the capsule, and is almost completely enveloped by it. Accordingly, two layers are distin- guished in the capsule of Bowman, an inner (quasi visceral) which lies close Fig. 17s.— Scheme of ti IFEROUS Tubules (Le - (Righ: of kidney of an infant Cortex. M. Medulla. 7n.s. Medullary rays, /i, l^Jz- Three renal lobules, a ftlalpighian corpuscle ; ^, proximal convoluted tubule; c, descending, rf, as- cending limb of Henle's loop-tube ; e, distal convo- luted tubule; /", collecting tubule ; yi, portions of col- lecting tubules; ^, excretory duct. i. Branch of renal artery. 2. Interlobular artery. 3. Afferent artery. 4. Efferent artery. 5. Interlobular vein. 6. Branch of renal vein, x and xx. Branches sup- plying the medulla. Fig. 176. — Urin Weeks'-Old F pighian corpuscle, f. Henle's loop, de f. Collecting tubule. No. g. Papillary d [29. upon the glomerulus, and an outer (quasi parietal) layer ; the former, in young animals, is composed of cubical cells, which later become more and more flat- tened, the latter of flat polygonal cells (Fig. 178). At the neck of the capsule the outer layer passes over into the walls of the proximal convoluted titlmle, THE URINARY ORGANS. 193 which is 40 to 60 .a thick. The cells in a condition of functional activity are tall and exhibit a clear central zone surrounding the nucleus, while the outer zone or ba.se is striated, with the strife placed radially to the narrow lumen ; in i *^Jti'.—' ' '^ Renal (Malpighian) corpuscle Medullary ray. Running at the boundary be- Compare Fig. '75- Henle's loop. k Section of Human Kidney. Including a Portion op the Cortex At X two renal cor|)UScles iiave fallen out. X ao. Techn. No. 130. an exhausted condition the cells are lower, dim, their boundaries arc indis- tinctly defined, and the free surface presents a striated border. Both stages of secretion occur simultaneously. The de- sceitdiiii; limb of Henle's loop is 9 to 15 /i thick, and the lumen is very wide ; it is lined by squamous epithelial cells whose nuclei often protrude into the lumen. The ascendiiii; limh is 23 to 28 11 thick, and the lumen relatively narrower ; the epithelial cells resemble those of the convoluted divi- sions, but are somewhat lower. The transi- tion of the narrow descending limb into the thicker ascending portion does not always occur at the loop. The intercalated or distal convoluted portion is from 39 to 46 ft. thick, and the epithelial cells are cylindrical or conical in shape and have a peculiar luster. The collecting ttibiiles increase in thickness as they approach theajjcx of the pajjilla ; the thinnest have a diameter of 45 n, the thickest (duct Urinlfen tubule 'lo. 178— Scheme. On the left an artery which eives off an afferent vessel toward the rit;ht ; this breaks up into branches, which turn into the radicles of the efferent vessel (directed toward the right). The three loops are intended to represent the glomerulus: this lies in Bowman's capsule, of which both layers are visible : below, th<: latter passes into the uriniferous tubule. 194 HISTOLOGY. of Bellini) of from 200 to 300 11. Their epithelial cells are in part clear, in part granular columnar elements, which increase in height with the increase of the diameter of the tubule (Fig. 181, 3). The uriniferous tubules are covered in their entire length by a structureless membrana propria situated outside of the epithelium, which is thickest in the descending limb of Henle's loop. The tubules are enveloped by a small V?-^,('A'V!»*/'','«-» Jjrmri. cowman s c Bowman's capsule Fig. 179. — Fr Mouse. X 240- amount of loose connective tissue (interstitial connective tissue), which at the surface of the kidney becomes condensed and forms a fibrous investment con- taining plain muscle-fibers. The blood-vessels run in the interstitial connective tissue. The blood-vessels of the kiJneys. The renal artery divides in the hilus of the kidney into branches, which after giving off small twigs to the capsule and IG. 180.- -A. I so LATED Ch; VO LUTED T UBUl LE. Theb; into min ute rods >. B. Trai mai convoluted tubule : th cate stri: e. Both preparati ney. X 24( rechn. No. ; from a cat's kid- ''iG. 181. — From a Transverse Section of the Medulla of Human Kidney, through the Base OF A Papilla. X 240. 1. Descending; 2, ascend- ding limb of Henle's loop; 3, collecting tubule ; 4, blood-vessel filled with blood-corpuscles. Techn. No. 130. to the calices of the kidney, enter the parenchyma of the organ at the circum- ference of the papillae, and without branching pass to the boundary between the cortex and the medulla. Here they bend at right angles and form arches with the convexity toward the periphery. From the convex side of the arches, at regular intervals, spring branches running toward the periphery ; these are the THE URINARV ORGANS. 195 interlobular arteries,^- which give off short lateral twigs, each one of which sup- plies the afferent vessel oi a glomerulus. The glomeruli ari.se by the rapid division of the afferent artery into groups of convoluted capillaries, which reunite into a single vessel, the efferent artery, which is somewhat smaller than the entering ves- sel. The efferent artery breaks up into a capillary network with round meshes in Interlobular vein. Interlobular arterj'. Afferent vessel. Efferent vessel. Capillary network of a n ray, with elongated meshe: KiG. 182. — From a Longitudinal Suction op Injected Kidnf.y of Guinea-Pic. Techn. No. 133, ^•^■^i,. M.ilpighian corpuscle Nervous network of an interlobular artery. ... Silvered uriniferous tubule. Fic. 183.— Section of Kidney ti/s of C(m>/>er are compound tubular glands, whose wide tubules are clothed with a simple layer of clear columnar cells, and whose excretory duct is lined with two to three strata of cubical cells. THE PENIS. The penis consists of three cylindrical bodies : the two corpora cavernosa and the corpus spongiosum, which are enveloped by fascia and skin. Each corpus cavernosum is composed of a fibrous sheath, the tunica albuginea, and of erectile tissue. The tunica alhuginea is a stout connective- tissue membrane, i mm. thick, in which an outer longitudinal and an inner circular layer may be distinguished ; the bundles are intermingled with many Epilhelil Fig. 103. — From a Transverse Section of the Cavernous Portion op the Human Urethra. X 20. /. Littrc's glands; the lowermost line indicates the body of the gland, the upper lines, portions of the excre- tory duct: ^.blood-vessels: wi. transverse section of longitudinally-disposed muscle-fibers; r, superficial cortical capillary network. Tcchn. No. 148. elastic fibers. The erectile tissue consists of connective-tissue trabeculoe con- taining bundles of smooth muscle-fibers, which by means of numerous anasto- nio.ses form a network the spaces of which are lined by a single stratum of flat epithelial cells. The spaces are filled with venous blood. The thick- walled arteries pass in part into capillaries, in part open directly into the deep cortical plexus. The capillaries form a network beneath the tunica albuginea, iht su/>erjicia/ {fine) cortical plexus, which is connected with a many-layered net of wide venous channels, the Jeep {coarse) cortical plexus. This lies in the superficial strata of the erectile tissue and passes gradually into the venous spaces of the latter. The so-called lielicine arteries are small branches within slender trabecule;, which protrude as loops in the cavernous spaces, and in an imperfect injection a|)pear to terminate in blind ends. The veins which return the blood from the corpora cavernosa arise mostly from the deep 2o6 HISTOLOGY. cortical plexus, in part out of the deeper portions of the erectile tissue. They penetrate the tunica albuginea and empty into the dorsal vein of the penis. The corpus spongiosum consists of two different divisions ; the central por- tion is a venous network formed by the conspicuously-developed veins of the submucosa of the urethra ; the peripheral portion resembles in structure the corpora cavernosa, excepting that there is no direct communication of the arteries with the venous spaces. The tunica albuginea is composed of a layer of circularly-arranged bundles of fibrous tissue. The glans consists of greatly- convoluted veins, held together by a well-developed connective tissue which supports the arterioles and capillaries. THE FEMALE REPRODUCTIVE ORGANS. THE OVARIES. The ovaries consist of connective tissue and glandular substance. The compact connective tissue, the ovarian stroma, is arranged in several strata ; : Year: s 0: LD X lO. .. Germi inal epi imost z one of'th artex containi ngn 6, medulla with nui Tieroi js tortuo igerus n ot w ithin th< :plar leofthe sect ion ._E Section of the Ovary of a Child E , _, a albuginea, as yet but slightly developed ; 3, erous minute follicles : 4, larger follicle; 5, inner division of cor ies : 7, follicle cut at the periphery : 8, large follicle, the cumulu 9, hilus, containing wide veins. Techn. No. 149. the outermost, the tunica albuginea, is composed of two or more lamella; of variously-disposed bundles, which pass by imperceptible gradations into the stroma of the cortex ; the latter encloses the glandular substance and is contin- uous with the medulla, which contains numerous convoluted blood-vessels and strands of smooth muscle-fibers accompanying them. 'l\\e: glandular substance is formed by a profusion of spherical epithelial sacs, the Graafian follicles, each of which contains an ovum. In the human ovary there are about 36,000 follicles. The majority of the follicles are microscopic in size (4 ti) and in the outermost stratum of the cortex form an arched zone embracing the entire organ except at the hilus, where the vessels and nerves enter. The larger follicles occupy THE FEMALE REPRODUCTIVE ORGANS. 207 the deeper portions of the cortex. The largest, those readily perceptible by the unaided eye, when fully matured extend from the medulla to the tunica albuginea. The surface of the ovary is covered by a simple layer of very small, short cylindrical cells, X}cit germinal epithelium. Only tlie initial stage in the development of the ova takes place during the embryonal period ; their subsequent development, from the primordial to the fully-ripened follicle, may be observed in every functionally active Gerinin.1l cpiihcl Egg-tubes Germinal spot Germinal vesicle Follicular epithelium r A Vertical Section has a large nucleus wi Techn. No. 14Q. >F AH Ovary OF AN Infant Four Weeks Old. X 240. The prim- li a nucleolus. The egg-tube contains three ova, surrounded by cylin- ovary. In the fetal i)eriod, and also after birth, there may be seen be- tween the columnar elements of the germinal epithelium larger spherical cells with nucleolated nuclei, the sexual cells, specially differentiated elements of the germinal ei)ithelium. In the course of development groups of cylindrical epi- thelial cells enclosing several sexual cells grow into the ovarian stroma. These groups are the primary egg-tubes. Each ovum becomes enveloped by a single layer of the small columnar cells and separated by constriction from the Germinal epithcliuni Fig. 196 Rabbit. X 90. Techn. No. 149. remaining ova. It is now a spherical body, the pi imary follicle, which thus_^ consists of the ovum and the epithelial cells — the so-called follicular epithelium — enclosing it. So far the developmental processes are chiefly fetal. . The cells of the follicular epithelium now grow taller, multiply, and become strati- fied ; the ovum increases in size, takes up an eccentric position within the follicle, and acquires a ])rotecting membrane, the zona pellucida, which exhibits delicate radial striatioii and gradually augments in thickness. .\s the ovum HISTOLOGY. develops in size a modification of the protoplasm occurs ; the greater part of it is transformed into a granular mass, the deiitoplasm ; of the original egg- Theca foiliculi Ovum with zona pellucida.. germ- inal vesicle, and germinal spot. Fig. 197.— Section of a Large Graafian Follicle of a Child Eight Years Old. X 9°. Th' <:'=; space wilhin ihe follicle contains the liquor foiliculi. Techn. No. 149. Zona pellucida Vitellus. Zona pellucid.i. Vitellu.. • ^^^^ Germinal vesicle. Germinal spot. (cells of the mulus). Fig. 198.— An Ovl Graafian Follicl of the zona and the perivitelline space c Cow. A magnified 50, B magnified 240 tii protoplasm there remains only a small zone surrounding the eccentrically-situ- ated nucleus and a thin stratum on the surface of the ovum. The deutoplasm and egg-protoplasm are together named viUllus. The nucleus is called the I'HE FEMALE REPRODUCTIVE ORlJANS. 209 germinal vesicle : it contains the germinal spot.* Amceboid movements have been observed in the latter. Between the vitelhis and zona pelhicida a narrow fissure, 1.3 /i wide, the pcrivitelline space, has been described. The follicle develops further by continual multiplication of the cells of the follicular epithelium and a cleft appears in their midst that becomes filled with a fluid substance, the liquor folliculi. This liquid is in part a transudate from the blood-vessels surrounding the follicle, and is in part derived from the liquefaction of some of the cells of the follicular epithelium; it increases pro- gressively in quantity and the follicle expands to a vesicle — the Graafian fol- licle — having a diameter of from 0.5 to 12 mm. Around the larger follicles the connective tissue of the stroma is arranged in circular lamellae forming a sheath called the theca folliculi, in which an outer fibrous layer — tunica fibrosa — and an inner va.scular layer rich in cells — tunica propria — may be distinguished. 'I'he stratified follicular epithelium has long been known as the membrana granulosa ; at one point it presents a thickening, the discus proligerus or cumulus oi'igerus, which encloses the ovum. The cells of the cumulus which lie next to the zona pellucida are radially placed to the ovum and form the corona radiala (Fig. 198). The greater part of the interior space of the follicle is occupied by the liquor folliculi. When the Graafian follicle has attained its fiill development, it bursts at the pole directed toward the surface of the ovary, where its site is indicated by the attenuated and arched overlying tissue, and the ovum surrounded by the discus escapes into the pelvic cavity ; the empty follicle becomes converted into the yellow body — corpus luteuni. When fertilization does not follow the dis- charge of the ovum the yellow body disappears after a few weeks ; it is called the false corpus luteum. When the escape of the ovum is followed by pregnancy, the ruptured follicle develops into \.\\t true yellon.' body, which possesses a diameter of about one centimeter and endures for years. It consists of a fibrous membrane ( the former tunica fibrosa) enclosing a yellow mass formed principally by pro- liferation of the cells of the tunica propria, and of the metamorphosed remains of the follicular e])ithelium, in the center of which is a cavity filled with blood. The blood is derived from the torn vessels of the tunica propria. Later the cells become in part converted into new connective tissue, the center becomes decolored, and in place of the blood-clot a granular ma.ss occasionally con- taining hematoidin crystals appears. Not all the primitive follicles attain complete development. Many undergo retrogressive change. Retrograde metamorphosis of mature follicles also occurs. This process is effected as follows : first the ovum dies and then cells — in l)art elements of the membrana granulosa, in part leucocytes — wander Into the ovum and li(iuefy and absorb its substance. Having completed the disinte- gration and resorption of the vitelhis, the migrated cells perish. The arteries of the ovary, branches of the ovarian and uterine arteries, * Tlie germinal spot cannot be regarded as a nucleolus, since itdiflers from this in its chem- al relations. It is not composed of paranuclein, but of a substance resembling nuclein. 2IO HISTOLOGY. enter at the hilus, divide in the medulla, and are characterized by their tortuous course (Fig. 194). From the medulla they pass to the cortex, where they are principally distributed to the Graafian follicles in which they form capillary net- works in the tunica propria. The veins form a dense plexus at the hilus of the ovary. The lymph-vessels are numerous, and may be traced to the tunica propria of the follicles. Medullated and nonmedullated nerves in large num- bers enter at the hilus in company with the blood-vessels, to the walls of which the majority of them are distributed. A few of the nerves proceed to the cortex ; these form a dense plexus of delicate, mostly gray fibers, which em- braces the follicles and sends minute fibrils to the walls of the blood-vessels and (in the cat) between the epithelial cells of the larger follicles. The cpoophoron ox parovarium and Xht paroophoron are embryonal remains. The former lies within the broad ligament between the ovary and oviduct and consists of a group of convoluted blind tubules, lined with ciliated columnar epithelium. The parovarium is the remdins of the middle or sexual segment of the Wolffian body. The paroophoron consists of branched tubules lined with ciliated columnar epithelium, and is embedded in the broad ligament between the ovary and uterus ; it represents the posterior segment of the Wolffian body. THE OVIDUCT. The walls of the oviduct or Fallopian tube consist of three coats : an inner mucous, a middle muscular, and an outer serous. The tnucous membrane is thrown into numerous longitudinal folds, so that on tranverse section the lumen of the narrow portion of the oviduct has a stellate outline. The folds corre- spond in amplitude to the size of the tube and are highest in the ampulla, where they are united to one another by minute oblique secondary plications. The thick mucous coat is composed of a fibro-elastic tunica propria con- taining numerous connective-tissue cells, and of a layer of simple ciliated columnar epithelium ; the ciliary wave is directed toward the uterus. Outside of the tunica propria is an extremely thin muscularis mucosae consisting of longitudinally-disposed bundles of smooth muscle-fibers. The submucosa is represented by a thin layer of fibrillar connective-tissue. The muscular coat consists of an inner thicker circular and an outer very thin longitudinal layer of involuntary muscle-fibers. The serous tunic is formed by the peritoneum and a considerable layer of loosely-united connective-tissue bundles. The blood-vessels are especially abundant in the mucosa, where they form a narrow-meshed capillary network. The larger veins run along the bases of the longitudinal folds of the mucosa. The knowledge of the relations of the lymph-vessels and the ultimate distribution of the nerves is still imperfect. THE UTERUS.* The walls of the uterus, like those of the oviduct, consist of a mucosa, a muscularis, and a serosa. * This chapter has been revised and considerably enlarged by the editor. THE FEMALE REPRODUCTIVE ORGANS. 211 The serosa exhibits no special characteristics. The mtiscularis consists of smooth nniscle-fibers, united into bundles which interlace in all directions, so that a .sharp demarcation of single layers is not possible ; still, in general, three strata, more or less well-defined, may be distinguished: (i) an inner layer (stratum submucosum), composed chiefly of bundles disposed in a longitudinal direction; (2) a middle layer, the most robust, consisting of bundles having in general a circular dis- position, and containing the principal ramifications of the arteries and also a well-developed venous plexus, hence the name stratum vasculare ; (3) and an outer layer (stratum supravasculare), formed partly of bundles extending in a circular, partly in a longitudinal direction, the latter close beneath the serosa, with which it is intimately united. The stratification of the muscular tissue is more pronounced in tlie cervix, where an inner and an outer longitudinal may ;. 199.— From a Transverse Section of thb Middle op the Uterus op a Girl Fifteen Years Old. X 10. a. Epithelium; ^, tunica propria ; c, glands ; i, inner muscular layer (stratum submucosum) ; 2, mid- dle muscular layer (stratum vasculare) ; 3, outer muscular layer (stratum supravasculare). Techn. No. 153. be distinguished from a middle circular layer. The volume of the muscularis is subject to great variation, dependent on the functional condition of the uterus. Tlie miiscle-Jihers differ somewhat from the elements of smooth muscle- tissue as found in other organs. They are elongated cells, usually spindle- shaped, or are blunted and frayed at the ends. Frequently they are forked at their extremities. Their length varies greatly ; in the virgin uterus from 40 to 60 !x ; during pregnancy they increase excessively, and at the end of the same attain a size of from 300 to 600 /i. The nucleus (not infrequently two or more are present in one cell) is usually oval, and lies embedded in a granu- lar substance. 212 HISTOLOGY. The mucosa is sharply defined from the muscularis. It is the coat which in the different functional conditions of the uterus undergoes the profoundest, and physiologically the most important changes. A description of the histo- logic structure of the mucosa of the uterus can, therefore, only answer to the corresponding functional condition of the organ, and in consideration hereof will be presented in separate sections. It is desirable to consider : — 1. The mucosa of the virgin resting organ. 2. The muco.sa of the menstruating uterus. ^. The mucosa of the erravid uterus. j» - -- Gland-lubule. L , Utekvs of a Davidoff.) X li-(A/ter Boh» The mucosa of the virgin resting uterus (Fig. 200), after the advent of puberty, has a thickness of from i to 2 mm. and bears on its surface a single layer of ciliated columnar epithelium, 30 /j. in height in the middle regions ; the ciliary wave is directed toward the cervix. The tunica propria is formed of a fine fibrous tissue closely resembling embryonal connective tissue ; it con- sists of elongated cells furnished with oval nuclei, which send out in all direc- tions branched processes which unite with those of neighboring cells and form a cellular network, the meshes of which are occupied by lymph and numerous leucocytes. The tunica propria supports many simple or forked gland-tubules, the upper part of which pursues a course more or less vertical to the surface of the THE KE.MAI.F. REPRODl'CTIVE ORGANS. 213 mucosa, while the lower half usually appears irregularly spiral. The glands extend clo.se up to the muscularis, and here not infrequently they are bent at right angles, so that the fundus runs parallel to the muscular coat. The glands of the uterus are to be regarded as invaginations of the superficial epithelium, and consist likewise of a simple layer of ciliated epithelium resting upon a delicate basement membrane composed of anastomosing connective-tissue cells. The blood-vessels run in a winding manner from the muscularis to the surface of the muco.sa, and the arteries, especially, are characterized by their extremely convoluted, corkscrew-like course. At the surface they break up into capillaries and form a clo.se network. A similar network surrounds the gland- ds..^^;>.r, " Superficial epithelii Excretory duct. ---j Fig. aoi.— Mucous .Memdranb op a Vikgi integrating surf:ice ; pd, pit-like depress! larged. X 3= —{Schafier.) Utbrus During thr First Day op Mbnstruation. ds. Dis- 1 of the mucous membrane ; gl, glandular lumen very much en- tubules. The veins ])roceeding from the capillaries form a plexus in the deeper strata of the muccsa, that is especially well developed in the cervix and par- ticularly around the external orifice. In the cen'ix the mucous membrane is thicker, and in its upper two-thirds is clothed with a single layer of tall ciliated cells (60 .a high in the middle por- tion),* while toward the external orifice papilla; covered by a stratified squam- ous epithelium appear. In addition to a few scattered tubular glands, mucous follicles, the so-called mucous crypts, occur; they are i mm. wide, possess * Transformation of these cells into goblet-cells occurs. 214 HISTOLOGY. many evaginations, and by retention of their secretion are converted into cysts, the ovula Nabothi. During the period of iiicnstniation a number of progressive and retrogres- sive changes take place in the mucosa of the uterus, which may be grouped in three phases : — ((?) Thickening of the mucosa, accompanied by changes in its histologic structure. (iJ) Menstruation proper. (;:) Regeneration. The initial phase is characterized by a considerable increase in the thick- ness of the mucosa (up to 6 mm.), in consequence of which the surface Excretory duct. Cavernous layer. ^ -" Gland'tubiiles. becomes irregular and the orifices of the glands ojien in deep depres- sions. The thickening of the mucosa depends in a measure on an actual increase of the tissue, produced by proliferation of the connective-tissue cells and leucocytes and by growth of the gland-tubules, which in the process take up an irregular course and become essentially wider. Simultaneously the blood-vessels, especially the veins and capillaries, undergo enormous disten- tion, whereby the blood-supply of the organ is extraordinarily augmented. In this condition the mucosa is designated decidiia menstrua lis. These changes are followed by a partial disintegration of the superficial strata of the mucosa, accompanied by an infiltration of blood into the sub- epithelial tissues. The molecular disintegration (associated with fatty degen- THE FEMALE REPRODUCTIVE ORGANS. 215 eration) of the surface advances rapidly, the greath'-dilated superficial blood- vessels become exposed, rupture, and cause hemorrhages within the uterine cavity, which flow into the vagina and give rise to the external phenomena of men- struation. After this discharge of blood the mucosa becomes rapidly reduced in thickness. The surface is now entirely devoid of epithelium, and consists of con- nective tissue and exposed blood-vessels. This condition is immediately suc- ceeded by the stage of regeneration. The hyperemia disappears rapidly, the extravasated blood is partly resorbed, partly cast off, a cellular network grows upward and restores the lost tunica propria, while from the gland-cells the epithelial covering of the mucosa is regenerated. New subepithelial capil- laries are formed. The histology of the mucosa of the uterus during pregnancy (decidua graviditatis) (Fig. 202 and Fig. 203) is, on the whole, like that of the decidua Fig. 203. — Vertical Sbction thkough the Wall THE Fetal Membranes i.s Situ. Between il gelatinous connective tissue. X y>. — {.Schajter.) menstrualis, with the alterations more pronounced. It, however, undergoes considerable modification because of its intimate relations with the developing ovum in the uterus. These relations vary, and thus in the course of develop- ment three essentially different parts of the mucosa may be distinguished : — ((r) The Jecidiia serotina (decidua basalis), the area of the mucosa to which the ovum is attached (placenta uterina). (/') The decidua vera, which comprises all the remaining portion of the mucosa attached to the wall of the uterus. (c) The decidua reflexa (decidua capsularis), the portion of the mucosa which ])rojects into the cavity of the uterus and encapsules the ovum. The decidua .serotina and vera undergo progressive development during the entire course of jiregnancy and ]iersist until its close ; the decidua reflexa becomes graduallv attenuated and disapiiears in the course of the fifth month. 2l6 HISTOLOGY. A section of the greatly thickened mucosa (decidua vera and serotina) shows the same histologic details that have been described in the menstrual decidua, but with this difference, that the progressive alterations (proliferation of the connective-tissue elements, distention of the blood-vessels and glands) attain much greater proportions. A superficial compact zone and a deep spongy zone can always be distinguished (Fig. 202). The cavities in the latter are produced by the lower divisions of the gland -tubules, which have become greatly widened and very tortuous. At a later stage of pregnancy, owing to the great distention of the uterus, the lumina of the glands appear compressed and straighter (parallel to the muscular coat) (Fig. 203). Between the glands are numerous blood-vessels, spindle-cells, and multinucleated giant-cells. The epithelium of the glands begins early to loosen, and in great part the cells lie irregularly scattered in the lumen of the tubule, where they disintegrate. The orifices of the glands are gradually obliterated, since \ ^^ the walls, after the loss of the epithelium, become adherent and grow together. The blood-vessels of the mucosa are all dilated, especially the superficial veins and capillaries ; the latter often form distended sinus-like cavities in the upper layer of the decidua. In the decidua serotina the arteries and veins open on the surface of the mucosa (Fig. 205 and Fig. 206), so that here the maternal blood circulates between the chorionic villi of the placenta (see Placenta, page 217). In the decidua vera the blood-vessels, toward the end of pregnancy, are less conspicuous. Of especial interest are peculiar, typical cells, decidual cells, which appear in large numbers in the mucosa of the gravid uterus. They are flattened, spherical, oval, or branched cells of conspicuous size (0.03 to o. I mm.), which, in the latter half of pregnancy, assume a characteris- tic brown color. They possess usually but one nucleus, though occasionally two, three, or more are present, and in rare cases as many as 30 or 40. The decidual cells are most numerous and most densely aggregated in the upper compact zone of the serotina (Fig. 203), which owes its typical character and brown color to these elements. Occasionally cells are found that are united with one another by means of protoplasmic processes. According to Minot, the decidual cells originate from connective-tissue elements, and therefore may be regarded as a modified embryonal or so-called anastomosing connective tis- sue. In a cross-section of the decidua vera, in the latter half of pregnancy, it will be seen that the surface of the mucosa is covered by two distinct mem- branes — fetal membranes — the chorion and the amnion (Fig. 203). The cho- rion lies next to the decidua vera, and is intimately united with it. It consists of two layers, an epithelial and a connective-tissue layer, of which the former is Fig. 204. — Oi ECIDUAL Crlls FROM THE Mucous Mhm- BRANB OF HUMAN Utbrus ABOUT SEVE^ 1 MoNTf [S Prbg- NANT. Belo' IV a "gia Lnt-cell," above to the right a cell with akaryokincti c figure. X 250 — (Sdu.per.) THE FEMALE REPRODUCTIVE ORGANS. 217 turned toward the uterine wall, the latter toward the amnion. Two similar layers may be distinguished in the amnion, but of these the epithelial layer, which consists of cubical cells, is turned toward the cavity of the uterus, while the connective-tissue stratum faces the chorion. The amnion and chorion are loosely united to each other by mucous connective tissue, in which delicate fibrils may be .seen extending from one membrane to the other. The /vmph-vesse/s of the uterus form in the mucosa a wide-meshed network ])rovided with blind branches. From this small stems proceed through the muscularis, and communicate with a close subserous network of larger chan- nels. The nerves of the uterus, medullated as well as nonmedullated, are very numerous. They branch — the medullated nerves after losing their medullary sheath — in the muscularis, and form a dense ple-xus in this and in the mucosa. From the latter delicate fibrils may be traced between the epithelial cells. THE I'L.VCKNTA.* The placenta is an organ which from a morphologic standpoint is com- ])o.sed of two heterogeneous parts, of which the one is produced by the mother (placenta uterina ), the other by the embryo (placenta foetalis). It is the result of the intimate union of a circumscribed area of the chorion (chorion fron- dosum), with that portion of the mucosa of the uterus known as the decidua serotina. The placenta serves the purpose of bringing the fetal and maternal blood into the closest proximity, to render possible the interchange of materials between them. To subserve this function the organ possesses a peculiar histologic construction, in which the blood-vessels, especially in their arrange- ment and structure, take a i)rominent part. In the histologic investigation of the placenta various obstacles are encountered, owing to its being an extremely soft spongy mass, traversed by numerous wide blood-vessels. The comprehension of the minute structure will be considerably facilitated by proceeding from the previously-mentioned fact that the finished organ is the product of two originally heterogeneous struc- tures, the chorion on the one side, the decidua serotina on the other, and that this union is substantially effected in that the chorion, by means of numerous villous-like proliferations, penetrates the underlyitig serotina, the surface of which is peculiarly modified and fiirther regressively altered for its reception, and as it were takes root in the same. For the investigation of these relations sections through the wall of the uterus with the placenta in situ, toward the end of pregnancy, are most instructive. In such a section two sharply-defined zones may be recognized : an outer compact stratum consisting of the greatly-thickened muscular coat of the uterus, covered externally by the serosa, and an inner spongy zone containing numerous inter-communicating spaces filled with blood. The latter is the placenta ; that is, the united decidua serotina and chorion frondosum. *This chapter is an entirely new addition liy the editor. v"°^i,'-'"" A?~'^^ Ve Fig. 205. — Section through a Normal Human Placenta of about Sevb nion : Cho, Chorion; Vi, villus trunk; vi, sections of villi in the substan. basalis; Mc, muscularis ; D', compact layer of decidua ; Ve, uterine artery fetal blood-vessels are drawn black : the maternal blood-spaces are left whit' xcept the canalized fibrin, which is shaded by lines ; the remnants of the | dark.— (^/j'^r Mitwt.) N Month s N Situ Am . Am- ce of the p'l icenta ■ D, d :cidua opening i nto the plk ceiUa. The e ; the cho rio nic tissu e is St ppled gland cav tie 5 in D" are st ppled 218 THE 1-EMAI.F, REPRODUCTIVE ORGANS. 219 The accompanying illustration (Fig. 205) shows their relations under low mag- nification, which will be elucidated by referring to the schematic representation in Fig. 206. The surface of the placenta directed toward the cavity of the uterus is covered by a compact stratum, X\\Qmeml>rana choiii, which is composed chiefly of fibrillar connective tissue, and in which the main branches of the umbilical blood-vessels run. The outer surface of the chorion is covered by a delicate membrane, the placental portion of the amnion, which, as previously stated, consists of an inner epithelial and a connective-tissue layer, and is con- nected with the chorion by means of embryonicconnective tissue. The other sur- face of the membranachorii, that directed toward the wall of the uterus, is closely beset with innumerable villous-like structures, large and small, which in the Chorionic villi. Intervillous spaces. "^^'TnO-O^A^^^-^ no.in.v Attached villi. Spiral artery. Gland. upper part of the placenta form a dense tangle, and whose terminal ramifica- tions are embedded in the cleft, uneven substance of the serotina. On closer study of this villous tangle it will be seen that the larger stems run a more or less direct course from the chorion to the serotina, in order to secure a firm union with the latter, while their many much-branched lateral twigs usually establish no connection with the uterine portion of the placenta, but terminate free in the blood-spaces, the so-called iiiterfillous spaces, between the chorion and serotina. Dependent upon these relations the branches of the chorionic villi are divided into " roots of attachment" or main stems, and free processes or floathh:; villi. From the chorion a branch of the umbilical artery enters each main stalk and, within the terminal ramifications of the villus, breaks up into a dense capillary network from which the umbilical veins take their origin and carry hack the blood from the chorion through the umbilical cord to the 2 20 HISTOLOGY. fetus. Accordingly, the blood-vessel system of the fetal placenta is entirely closed. Notuhei-e does a direct intermingling of maternal and fetal blood occur. A cross-section of one of the smaller chorionic villi, highly magnified, shows that it is chiefly composed of mesenchymal tissue (mucous tissue), in which the blood-vessels are embedded (Fig. 207). This central supporting substance is covered by an irregular and not everywhere continuous stratum of epithelium. In the earlier months of development two distinct strata may be distinguished in the epithelium of the villi : an inner, lying immediately upon the supporting tissue, in which the cells possess large nuclei and definite contours, so that in the main they are distinctly separated from one another ; and an outer layer, consisting of a continuous protoplasmic mass — syncytium — containing numerous small irregularly-scattered nuclei. Toward the end of pregnancy, however, the epithelium of the villi undergoes great alteration, as appears in the Protopl: Epithelial nucleus. , Capillaries *'-''l^ Cell-patch (Zeilkncten) - '1V''«*».^ __»/ Capillarv. Cell- patch (Zellknoten). : (.A) AND Lakgek IB) Chokionic Vi: Precnanlv. X 2io.—{Scha/€r.) illustration (Fig. 207). On the larger villi a true epithelial investment has almost entirely disappeared and instead, isolated accumulations of large round nuclei are found ; they stain intensely, are embedded in a clear, homogeneous substance, and form protuberances {Zellknoten, cell-patches') on the surface of the villi. Between these cell-patches the connective tissue of the villi is fre- quently covered only by a thin, homogeneous stratum, or in other cases (espe- cially in smaller villi) this stratum still retains more or less the character of the protoplasm containing scattered nuclei. There are many indications that the latter is the remains of the syncytium, while the cell-patches probably originated in the primitive inner stratum of the epithelium of the villi. In many places the syncytium becomes transformed into a peculiar hyaline sub- stance, permeated by fissures, which often lies upon the chorion in dense strata, and is called canalized fibrin.* * It has not been as yet determined with certainty whether the epithelium of the villi of the human placenta is derived entirely from the epithelium of the chorion, or whether the epithe- THE FEMALE REPRODUCTIVE ORGANS. 221 The histologic structure of the maternal portion of the placenta — placenta uten'iia — in its essential features has been described in connection with the decidua in the preceding chapter. Certain peculiarities, however, as well as the union of the maternal and fetal placenta in a functional whole require a brief consideration. The placental portion of the decidua (Fig. 205), that forming the lower stratum of the placenta (basal-plate), becomes greatly thinned (0.5 to i.o mm.), however, as in the e.\traplacental portion, an upper compact layer, and a lower cavernous layer (gland lumina) may be distinguished. The decidual cells are extremely numerous and lie closely crowded. .\ honeycombed structure of connective-tissue septa {septa placentce) arises from the surface of the serotina, directed toward the intervillous spaces, and penetrates between the villi of the chorion, separating the latter into lobes or cotyledons. Only in the peripheral regions of the placenta do these septa reach to the membrana chorii, where frequently they form on the inferior surface of the latter a thin membranous stratum, the decidua placentalis siibchorialis. On the margin of the placenta the serotina gradually increa.ses in thickness and pa.sses into the vera, at which point it is closely applied to, and firmly united with, the chorion. Within the area of the placenta, however, the chorion and serotina are far apart, and the space between them is filled with the above-described chorial villi and the blood circulating between them ; it is maternal blood that surrounds the villi on all sides, and is thus brought into the closest relation with the fetal circulation. Of especial interest is the behavior of the blood-vessels within the placenta uterina (Fig. 205 and Fig. 206). Numerous ed appear in cross-seclion like papillae. Techn. No. 155. inserted. The posterior border of the nail, the nail-root, rests in a similar but deeper groove, the tnatrix, in which the principal growth of the nail takes place. (Some authors name the whole nail-bed matrix, which is in a measure justified by the growth of the nail in thickness which occurs here.) The anterior free edge of the nail projects over the nail-ridge, a small seam-like prominence at the distal end of the nail-bed. The nail-bed consists of corium and of epidermis. The fibro-elastic bundles of the corium are in part disposed parallel to the long axis of the fingers, in part vertically from the periosteum of the phalanx to the surface. There are no papilte on the corium, but minute longitudinal ridges. They begin low at the matrix, increase in height toward the front of the nail, and terminate abruptly at the point where the latter leaves its bed. The epithelium is of the stratified scaly variety, of the same structure as that of the rete mu- cosum of the epidermis. It covers the ridges of the nail-bed, fills up the fur- rows between them, and is sharply defined from the substance of the nail. The matrix, likewise, consists of corium and epidermis: the corium is distinguished THE SKIN AND ITS APPENDAGES. 227 by its tall papillae, the stratified scaly epithelium is very thick and is not sharply defined from the nail-substance, but passes gradually into the latter. This is the place where by continual division of the epithelial cells the material for the growth of the nail is furnished. The extent of the matri.x is indicated by the It/ nil /a, a white convex area, visible to the unaided eye, produced by the thick, uniform rete mucosum. The nail-wall 3X\A the nail-fold (the margin of the groove overhanging the root of the nail) exhibit the same general structure as the skin ; the rete mucosum blends gradually with the epithelium of the nail- bed, while the horny stratum extends into the nail-groove and as " epony- chium " covers a small portion of the edge of the nail, but soon diminishes in thickness and disappears (Fig. 210). The «<7// itself consists of horny epithelial scales, very firmly united with one another, which possess a nucleus and differ in this respect from the horny cells of the stratum corneum of the epidermis (Fig. 211). THE HAIR. The hairs are flexible, elastic horny threads, which are distributed over nearly the entire surface of the body and on the integument of the cranium are united in small groups. The part of the hair which pro- jects beyond the free surface of the skin is called the shaft; the portion obliquely embedded within the in- tegument, the root; at its lower extremity the latter terminates in a bulbous expansion, the hair-bulb, which embraces a formation of the corium, the hair-papilla (Fig. 212). Each hair-root is inserted in the hair-follicle, a modi- ^^^ 211 -Elembhtsop fication of the skin in the formation of which both corium T«:hn''No*'i'' 6 ^ '^°' and epidermis participate ; the parts furnished by the latter are the epithelial root-sheaths, the portion originating from the corium is the dermal or fibrous sheath. Into the follicle, laterally, two to five glands open, the sebaceous glands. Bundles of smooth muscle-fibers, the arrectores pilorum, pass obliquely from the upper surface of the corium and attach themselves to the fibrous sheath of the hair-follicle, beneath the .sebaceous glands ; the point of insertion of these fibers is always on the side toward which the hair inclines ; when they contract, the follicle and the shaft become erect. The hair consists entirely of epithelial cells, arranged in three well-defined strata : the cuticle, which covers the surface ; the cortical substance, which contributes the chief bulk ; the medulla, which occupies the axis of the hair. The cuticle consists of a single layer of transparent imbricated scales — horny epithelial cells without nuclei. The cortical substance of the shaft consists of elongated horny epithelial cells with attenuated nuclei, which are intimately united with one another ; on the root the cells become softer and rounder, their nucleus correspondingly more spherical, as they approach the hair-bulb. 2 28 HISTOLOGY. The incchtlla is absent in many hairs ; when it is present it does not extend through the entire length of the hair. It consists of cubical, finely-granular epithelial cells, which contain a nidimentary nucleus and are usually disposed in twofold rows. The colored hairs contain pigment, diffused and in the form of granules, which occurs in part between and in part within the cells of the cortical sub- stance. In every hair which has attained its full development minute air- vesicles occur; they are found in the cortical substance as well as in the medulla, and also in the intercellular clefts. The follicle of fine (lanugo) hairs is formed alone by the epidermal root- sheaths, but in coarser hairs the corium participates in its construction. In the follicles of the latter the following strata may be distinguished : an outer loiii^i- Fat-cclls Fig. 212. — From a Thick Cross-Section i Techn. No. 160. tiidinal stratum formed of loosely-united, longitudinally-disposed bundles of white fibrous tissue, mingled with elastic fibers and richly supplied with blood- vessels and nerves ; a middle circular stratum, thicker, and consisting of small fibrous bundles circularly arranged ; and an inner clear, homogeneous, narrow belt, the glassy or hyaline membrane, resembling in character the elastic mem- branes. Elastic fibers do not occur in the middle layer nor in the papilla. These three strata are derived from the corium and together constitute the der- mal 'l* \ Arachnoidal sheath HHiiiiim^"' Fig. 235. — Longitudinal Section of Optic Entranxk of Human Eye. X 15. Above the lamina cribrosa the narrowing of the optic nerve is visible. The central artery and vein have been for the most part cut longitndinally, but above at several points, transversely. Techn. No. 169 rf. its anterior border, breaks up into fibers, so that the subdural space lying to its outer side communicates with the subarachnoidal space on its inner side. The pial sheath blends with the sclera, which here is pierced with numerous aper- tures for the nerve-fibers passing through it ; this portion of the sheath is called lamina cribrosa. The choroid also participates, though in a slight degree, in the formation of the lamina cribrosa. The nerve-fibers lose their medullary sheaths at the point of entrance, and consequently the nerve becomes consid- erably reduced in size. In the distal half of the optic nerve, the central artery and vein of the retina lie in its axis ; the connective-tissue investing these vessels is connected at many points with the pial sheath, as well as with the lamina cribrosa. THE EYE AND ITS APPENDAGES. 251 THE LENS. The crystalline lens consists of a substantia propria which on its anterior surface is covered by the epithelium of the lens ; the whole is enveloped by the lens-capsule. In the substantia pi-opria a soft cortical substance and a firm core may be distinguished ; it consists throughout of colossal, greatly-elongated epithelial-cells, the li'iis-fibcrs. They have the form of six- sided prismatic bands, which are thickened at their posterior extremities. The lens-fibers of the cortical zone have smooth borders, and in the vicinity of the equator lies an oval nucleus. The lens-fibers of the central portion of the lens have dentated outlines and are without nuclei. .\11 the fibers are united and held together by a small amount of cement-substance, which is accumulated in larger quantities at the anterior and pos- terior poles of the lens and produces the so-called anterior and posterior lens-stars, stellate forms seen in macerated prepara- tions. All the lens-fibers, beginning at the anterior lens-star, run in a meridional direction to the posterior lens-star; but no lens-fiber spans the entire half of the lens ; the nearer the fibers arise to the anterior pole, the more remote from the posterior pole do they find their termination. IG. 236.-LENS-F1BEKS OF AN Ivp ANT. A. Isolated lens-fibers, thi ree with sm 00th, one with dcnt.ttcd border? ■■■ X 240. Tcchn. No. 178. B. Human lens-fibers cut irans- versely ; f , section through club-shaped ends. X 560. TechD. No. 179. ;. 337. — Capsulr and Epithblii'M op Adult Human Lbns. C Inner aspect. 180 a. D. Lateral aspect, from a meridional section through the equator of the lens Hum : 3, lens-fibers. X 240. Techn. No. 180 d. X 240. Techn, No /, capsule : 2, epithe The leiis-epitlieliiiiii consists of a simple layer of cubical cells, which covers the anterior surface of the lens and extends as far as the equator ; here the 252 HISTOLOGY. epithelium, by gradual elongation of its elements, becomes transformed into the lens-fibers (Fig. 237, D). The lens-capsule is a transparent, glassy, elastic membrane ; the anterior capsule, the portion covering the anterior surface of the lens, is 1 1 to 1 5 /j thick, the corresponding posterior portion, the posterior capsule, only 5 to 7 ,a. The lens-capsule comprises two genetically distinct parts ; the one is a cuticular formation, a product of the epithelium of the lens, the other, of the nature of connective tissue, is a transformation product of the embryonal connective- tissue sheaths. THE VITREOUS BODY. The vitreous hody consists of a fluid substance — the vitreous sul'staiice — and oi Jitters which extend in all directions through the former. The surface of the vitreous body is covered by a somewhat firmer membrane, the hyaloid membrane, and in certain localities contains a limited number of fibrillse and a few cells ; of the latter two forms may be distinguished, round elements, resembling leucocytes, and stellate or fusiform cells. Cells containing clear vacuoles are probably degenerating forms. THE SUSPENSORY LIGAMENT. The suspcnsoiy ligament (zonula ciliaris, zone of Zinn), consists of deli- cate homogeneous fibers which extend from the surface of the hyaloid mem- brane, in the vicinity of the era serrata, in a meridional direction toward the lens. They are attached to the inner surface of the ciliary processes and extend from the apices of the same over to the equator of the lens, where they are attached to the anterior and posterior surfaces and to the equator of the lens- capsule. The fibers do not form a continuous membrane, but are radially plicated e.xtensions of the hyaloid membrane that find attachment and support on the lens. The annular cleft between the zonula ciliaris behind and the vitreous body in front is designated canal of Petit. Other authors describe the triangular space included between the anterior and posterior zonula fibers and the lens-capsule as the canal of Petit. The canal is not completely closed on the side toward the posterior chamber of the eye. THE BLOOD-VESSELS OF THE EYEB.\LL. The blood-vessels of the eyeball are separated in two sharply-defined regions, which are in communication only at the entrance of the optic nerve. Territoiy of the Vasa Centralia Retina. — The central arteiy of the retina, at a distance of 15 to 20 mm. from the eyeball, enters the axis of the optic nerve and runs within it to the surface of the optic entrance. Here it divides into two main branches, of which the one is directed upward, the other down- ward, each of which subdivides and supplies the entire pars optica retinae to the ora serrata. During its course in the optic nerve the artery gives ofif numerous small branches, which run within the processes of the pial sheath THE EYE AND ITS APPENDAGES. 253 between the nerve-fiber bundles, and anastomose with small arteries that have entered the sheath of the nerve from the surrounding adipose tissue and also with twigs from the short ciliary arteries. In the retina itself the artery breaks up into capillaries, which extend into the outer reticular layer. The cerebral layer of the retina alone contains blood-vessels; in the fundus foveje the cere- bral layer is wanting, and with it the blood-vessels. The veins proceeding from the capillaries run parallel with the branches of the arteries and finally unite in the vena centralis retina; enclosed within the axis of the optic nerve (Fig. 238). In the embryo a twig from the central artery of the retina, the hyaloid artery, passes through the vitreous body to the posterior surface of the lens. This artery atrophies before birth, but the canal which transmits it may still be found in the vitreous body of the adult ; it is called the hyaloid canal. Territory of the Vasa Ciliaria. — This region is characterized by the com- plementary veins taking a course entirely different from that of the arteries. Of the arteries, the short ciliary arteries supply the smooth portion of the choroid, while the long ciliary arteries and the anterior ciliary arteries are des- tined chiefly for the ciliary body and the iris. The branches, about twenty, of the short ciliary arteries penetrate the sclera in the vicinity of the optic entrance; after giving off twigs which sup- |)ly the posterior half of the surface of the sclera, the arteries break up into a narrow-meshed capillary network, the choriocapillaris. At the optic entrance the arteries anastomose with branches of the arteria centralis retinse and there form the circular artery of the optic nenie ; at the ora serrata they anastomose with recurrent twigs of the long ciliary and the anterior ciliary arteries. The two lon^ ciliary arteries likewise penetrate the sclera at the optic entrance ; the one artery passes to the nasal, the other to the temporal side of the eyeball between the choroid and the sclera to the ciliary body, where each artery divides in two diverging branches running along the ciliary margin of the iris ; by the anastomoses of the branches of the two arteries a vascular ring is formed, the larger arterial circle of the iris (circulus iridis major) from which numerous twigs are given off to the ciliary processes and the iris. Near the pupillary margin of the iris the arteries form an incomplete ring, the smaller arterial circle (circulus iridis minor). The anterior ciliary arteries come from the arteries supplying the recti muscles of the eye, penetrate the sclera near the corneal margin, communicate with the larger arterial circle of the iris, supply the ciliary muscle, and send recur- rent branches to unite with the choriocapillaris. Before the anterior ciliary arteries penetrate the sclera, they give off twigs behind for the anterior half of the sclera, and in front to the conjunctival sclera and to the corneal limbus. The cornea itself is without blood-vessels ; only at the margin, in the anterior lamellce of the substantia propria, is there a circumferential network of capillary loops. The veins all run toward the equator, where they converge to four (more rarely five or six ) small stems, the whorl veins or vence vorticosce, which forth- 354 HISTOLOGY. with pierce the sclera and empty into one of the ophthahnic veins. In addition to these there are small complemental veins that run parallel to the short ciliary arteries and the anterior ciliary arteries ; the anterior ciliary veins receive twigs Vessels op the Eye, accoeding to Leber. External tunic stippled, middle ernal tunic and optic nerve dotted crosswise. Arteries light. Veins dark. Region of the central vessels of the retina (small Italic letters) : a. Artery : a', central vein of retina : i, anastomosis with vessels of the sheath ; c, anastomosis with branches of the posterior short ciliary arteries : d, anasto- mosis with choroidal vessels. Region of the vessels of the sheath (large Italic letters): A. Inner; B, outer vessels of the sheath. Region of the posterior short ciliary vessels (Italic numerals): /. Arteries: /', veins (short posterior ciliarj): //. episcleral arterial: //', episcleral venous branches of the same; ///, capillaries of the choriocapillaris. Region of the posterior long ciliary vessels (.Arabic numerals): i. Pos- terior long ciliary arterj'; 2, circulus iridis major cut transversely: 3. branches to the ciliary body: 4, branches to the iris. Region of the anterior ciliary vessels (Greek letters) : a. Artery : a', vein (anterior ciliary): 3, connection with the circulus iridis major; 6', venous episcleral branches: e, arterial; e', venous brai venous branches to the corneal limbus ; V, vena vorticosa ; Fig. 238. — Scheme ' th the chori to the scleral conjunctii 3ss-section of the venous from the ciliary muscle, from the episcleral vascular network, from the con- junctival sclera, and from the circumferential capillary loops of the cornea. The episcleral veins communicate with the vena; vorticos?e at the equator. THE EVE AND ITS APPENDAGES. 255 The anterior ciliary veins eventually communicate also with the canal of Schlemm. This canal is an annular cleft encircling the cornea, but lying just within the sclera. It is by some regarded as a lymph-space in open com- munication with the anterior chamber, by others held to be a venous channel. THE LYMPH-CHANNELS OF THE EYEBALL. The eye possesses no proper lymph-vessels, but a series of intercommuni- cating lymph-spaces. Two complexes of such spaces may be distinguished, an anterior and a posterior tract. The anterior tract comprises : — 1. The lymph-canalkuli of the cornea and sclera. 2. The anterior chamber of the eye, which, with Schlemm's canal, by means of the capillary clefts between the iris and the lens, communicates with — 3. The /'os/ericr c/iamfier of the eye. The latter is in open connection with — 4. The canal of Petit. The last three spaces stand in close relation to one another, and may be injected from the anterior chamber. The posterior tract includes: — 1 . The hyaloid canal. 2. The lymph-clefts between the sheaths of the optic nen-e (the subdural and the subarachnoidal spaces), the narrow cleft between the choroid and the sclera — the perichoroidal space — and Tenon's space, which extends from the dural sheath of the optic nerve to the optic foramen. These spaces may be filled from the subarachnoidal space of the brain. The contents of these spaces is a filtrate from the blood-vessels, which also permeates the vitreous body. The quantity of this fluid in the perichoroidal space, also in Tenon's space, is normally exceedingly scanty. Both these spaces serve to facilitate the move- ments of the choroid and of the eyeball, and may be regarded as synovial spaces. THE NERYES OF THE EYEBALL. The nerves of the eyeball penetrate the sclera in the vicinity of the entrance of the optic nerve and run forward between the outer tunic and the choroid ; after giving off bundles accompanied by ganglion-cells to the choroid, they form an annular plexus intermingled with ganglion-cells lying upon the ciliary body — the ciliary ganglionic ple.xiis (orbiculus gangliosus ciliaris), from which branches go to the ciliary body, the iris, and the cornea. The nerves of the ciliary boiiv terminate in delicate pointed ends in the blood-ves.sels, in the ciliary muscle between the muscle-bundles in the form of branched ends, which perhaps subserve the muscular sense, and on the scleral surface of the ciliary body in the form of a delicate plexus. The medullated nerves of the iris form net- works and lose their medullary sheath as they pass to the pupillary margin : their terminal ramifications are in part distributed to the smooth muscle-fibers and the blood-ves-sel walls ; another jjortion forms a dense sensory plexus lying close 256 HISTOLOGY. beneath the anterior iridal surface. The nerves to the cornea first enter the sclera and form a circular plexus — plexus aniiiilaiis — surrounding the corneal margin, from which branches are distributed to the sclera and to the cornea. In man the twigs in the sclera terminate in spherical end-bulbs lying close under the epithelium; they are also found in the substance proper of the cornea for a distance of from i to 2 mm. within the corneal limbus. The branches that go to the cornea, after their entrance in the substance proper lose their medullary sheath and as naked a.xis-cylinders penetrate the entire structure. They form networks, which, according to the plane they occupy, are described as — the stroma or gnnitid-J'/exus, which lies in the deeper strata of the cornea; the siil'hasilar plexus, situated beneath the anterior basal membrane ; the sub- epithelial plexus, lying close under the epithelium. From the latter plexus exquisitely-delicate nerve-fibrillse pass up into the epithelium between its elements, and form the exceedingly fine intraepithelial plexus, whose naked axis-cylinders terminate in free ends between the epithelial cells (Fig. 239). -^r Fig. 239. — From a Vertical Section through the Human Cornea. X 240. penetrating the anterior basal membrane ; s, subepithelial plexus beneath the the intraepithelial plexus ascending betweett the epithelial cells. Techn, No. 1 I propria. ^^__^^^ THE EYELIDS. The eyelids are folds of the integument, which enclose muscles, loose and compact connective tissue, and glands. The outer fold of the eyelid retains the usual characteristics of the skin ; the inner fold, that toward the eye, is considerably modified and is called \k\R palpebral conjunctiva. The skin on the external surface of the eyelid extends over the lower free margin and does not pass into the palpebral conjunctiva until it reaches the posterior border, /a^f/'z-i?/ bonier. The eyelid is best studied in a sagittal section, in which, counting from before backward, the following strata are found : — I. The ////'<'^'v//// ;. 242 .-Otolith lechn THE Saccui.u iNPANT. X56C . No. 184 THE ORGAN OF HEARING. 261 drical elements occupying only the upper half of the thickness of the epithe- lium, which in the lower rounded portion contain a spherical nucleus and bear on their free surface a bundle of long, delicate agglutinated filaments, the "auditory hairs." The hair-cells are the terminal apparatus of the auditory nerve. The nerve-fibers lose their medullary sheaths on entering the epithe- lium, divide, and ascend to the base of the hair-cells as naked axis-cylinders where each fiber divides into three to four varicose twigs, which run be- neath several hair-cells parallel to the surface of the epithelium, and finally turn upward and terminate in contact with the lateral surface of a hair-cell in a free pointed end.=*= During their horizontal course they send upward a few twigs, which end in the same manner in contact with the hair-cells. These ends do not reach to the surface of the epithelium. The free surface of the neuro-epithelium is covered by a continuation of the cuticular zone, which is perforated by the auditory hairs. The maculae acusticse are covered by a soft, gelatinous substance (a cuticula?), in which innumerable prismatic crystals of calcium carbonate, the otoliths, i to 15 // in size, are embedded ; they form the otolith meml>raiie. On the crista acusticK the so-called cupola occurs; in fresh ])rei)arations it is an invisible substance; on the application of fixation fluids it coagulates and thus becomes visible. The wall of the bony labyrinth is covered by a thin iieriosteum and flat- tened connective-tissue cells. The saccules and semicircular canals are secured to the walls of the bony labyrinth by means of connective-tissue trabeculse. The Cochlea. The membranous cochlea, the ductus cochlearis, does not entirely fill the space within the bony cochlea. It lies with one wall in contact with the outer wall \ of the bony cochlea ; the upper or vestibular wall (^membrane of Reissner) bounds the scala vestibuli ; the lower or tympanic wall {membran- ous spiral lamina') is directed toward the scala tympani. The angle in which the vestibular and tympanic wall meet lies on the free end of the osseous spiral lamina. There the periosteum and the fibrous coat of the ductus cochlearis are especially well developed and form a prominence, the limbus, which rests with a broad surface on the bony spiral lamina, slopes upwards, and terminates in a sharp edge. This edge is called the labium vestibulare ; the free margin of the bony spiral lamina is called the labium tympanicum ; between the labia is a recess, iht sulcus spiralis (Y\g. 249). The inner surfaces of the ductus cochlearis are covered by an epithelium that varies greatly in different localities ; the outer surfaces — toward the scala vestibuli and scala tympani — are covered by a deli- * The horizontal branches interlace and form a small, but direct " lattice- work," which also in other methods than that of Golgi appears to consist of a Kiyer of strongly-refracting granules. The granules are the varicosities and the optical cross-sections of the horizontal fibers. 1 1 follow here the customary description, in which the cochlea is placed in such a manner that the base is directed downward, the summit upward; accordingly, " inner " is toward the axis of the cochlea, " outer " toward the periphery. 262 HISTOLOGY. cate continuation of the periosteum which clothes both scalie. On the outer wall of the cochlea the periosteum becomes greatly thickened, and in cross- section appears as a crescentic mass, the ligamenttim spirale, which extends both above and below the attached surface of the ductus cochlearis. The structure of the outer and the vestibular wall of the membranous cochlea is comparatively simple, that of the tympanic wall, on the other hand, is extremely complicated. The outer wall and the spiral ligament together consist of epithelium and connective tissue. The latter, next to the bone, is a dense fibrous tissue ; this passes into a loose connective tissue which contributes the chief bulk of the spiral ligament. The epithelium is composed of a row of cubical epithelial cells. A dense network of blood-vessels, the stria vascularis, occupies three- fourths of the height of the outer cochlear wall. At its lower end a vein Bony axis of cochlea (modiolus). Organ of Corti (organon spirale). [^ Outer bony wall of ^ cochlea. Vas prominens. Ligamentum spirale. Fig. 243. — Sfction through contains longitudinal canal cochlea. The membrana ^ tectoria can not be seen. 1 THE Second Turn of the Coch ; cut obliquely, j. Bony wall betw estibularis is torn, the upper fragn echn. No. 1S6. nfant. X 25. The modiolus nd and third (half) turns of the ned upwards. The membrana projects into the lumen of the cochlea, the proiiiincntia spiralis (vas promi- nens) (Fig. 243). The capillaries of the stria vascularis lie close beneath the epithelium ; they are the source of the endolymph. The vestilnilar wall {Reissner' s membrane), consists of a process of the periosteum of the scala vestibuli, that is of delicate fibrous tissue and flattened cells, which on the surface turned toward the ductus cochlearis is clothed with a simple layer of polygonal epithelial cells. The tympanic wall consists of two portions : the limbiis, with the free margin of the bony spiral lamina, and Hn^ lamina spiralis membranacea. The limbiis consists of compact connective tissue, containing an abundance of spindle-shaped cells, which below is continuous with the tissue of the periosteum, and on its free surface is beset with peculiarly-shaped papillre. THE ORGAN OF HEARING. 263 They have the form of an irregular hemisphere ; toward the labium vestibulare they become small elongated plates, the so-called auditory teeth, which lie in a single row next to one another. The surface of the limbus is covered by a simple layer of flattened epithelial cells, which at the edge of the labium ves- til)ulare passes into the cubical epithelium of the sulcus spiralis (Fig. 247, A). Labium tympanicum. Labium vcsttbutare. Zona perforata. Auditory teeth. k, °C5ci>S:r=r=:3=*- Papilla:. Pic. 244.— a Surface View op Lamina Spiralis op Cat. X 240. The vestibular lamina is seen from above. Between the auditorj' icelh two nuclei of the epithelial cells are visible. On the left of the picture the upper surface of the auditory teeth is in focus, on the right, the plane of the zona perforata. Tcchn. No. 185. The upper surface of the free margin of the osseous spiral lamina is per- forated by a single row of slit-like openings, the foramina nervina, through which the nerves enclosed within the bony lamina emerge, to penetrate within the epithelium of the basilar membrane. This portion of the osseous spiral lamina is called zona perforata. The membranous spiral lamina comprises : ( i ) the memhrana basilaris, an extension of the limbus and of the periosteum of the osseous spiral lamina : (2) the tympanic lamella, which is a process of the periosteum of the scala tympani and clothes the lower surface of the basilar membrane ; and (3) the epithelium of the ductus cochlearis, which rests upon the upi)er surface of the basilar membrane. The membraiia basilaris consists of a structureless substance which contains rigid, perfectly straight fibers, extending from the labium tympanicum to the spiral ligament, and also oblong nuclei. The membrane has a finely striated appearance (Fig. 245,7"). The tympanic lamella is composed of a delicate connective tissue containing spindle-cells, the fibers of which are dis[)0sed vertically to the elements of the ^cttnata'"^*drawn'''° wi"h basilar membrane (Fig. 245, b). fe'renf e°pi,hei;::m (cem oi The epithelium of that half of the membranous S?£rU in'foi!^:/"''^^ spiral lamina toward the axis of the cochlea is differ- f.iarisl'ibcirsTvEe nil: entiated as the highly-specialized neuro-epithelium, the ti'^focLl'^' '^S"' No"'!^^ spiral organ (organ of Corti), while that occupying the outer half, toward the spiral ligament, consists of indifferent epithelial elements. The spiral lamina is therefore divided into two zones : an inner, occupied by the spiral organ, zona tecta — and an outer, zona pectinata — so called because of the striations of the basilar membrane shimmering through it. The most remarkable elements of the spiral organ are the pillar-cells or rods of Corti, peculiarly-shaped and for the greater part rigid forms, arranged 264 HISTOLOGY. in two rows throughout the entire length of the cochlea ; an inner row, the inner pillars^ and an outer row, the outer pillars (Fig. 247). The two rows of pillars converge and form an arch, the arctis spiralis, which spans a triangular Cells of Claud Fibe tympanicum. -i vestibulare. > Ganglion spirale. Fig. 246. — Lamina Spiralis op Cat seen prom thi been removed. X 50. to. Lamina spiralis ossea, inner half cleft and broken at s< spiral ganglion project from the posterior border of the same. hti. Lamina spiralis of Claudius have partly fallen off, so that the fibers of the membrana basilaris are tion. Techn. No. 1S5. : membrana tcctoria has eral points. Cells of the nembranacea. The cells isible as a delicate stria- FiG. 247.— Scheme of the Structure op the Tympanic Wall of the Duct of the Cochlea. A. Seen from the side. B. Seen from the surface. In the latter, the free upper surface is in focus. It is evident that the epithelium of the sulcus spirahs, lying in other planes, as well as the cells of Claudius, can only be distinctly shown by depressing the tube. The membrana tectoria has not been drawn. The spiral nerve- fibers are indicated by dots. space, the tunnel, the base of which is directed toward the basilar membrane. The tunnel is nothing more than a very large intercellular space, filled with a soft mass, the intercellular substance. THE ORGAN OF HEARING. 265 Regarding the histology of the pillar-cells, the following details are to be considered : The inner pillar-cells are rigid bands in which a three-sided ex- panded base, a slender body, and concave head, with the concavity directed out- ward, may be distinguished. The head is furnished with a thin process, the " head-plate " (Fig. 247). The body and base of the cell are surrounded by a scant amount of protoplasm, which only to the outer side of the base, in the vicinity of the nucleus, is present in somewhat larger amount. The outer pil- lar-cells exhibit the same details, e.xcepting that the portion containing the nucleus lies to the inner side of the base; the rounded articular head rests in the concave facet of the head of the inner pillar-cells ; the broader head-plate is covered in its greater part by the head-plate of the inner pillars. To the inner side of the inner pillars lies a simple row of cells, the inner hair-cells, short cylindrical elements that do not extend to the basilar membrane ; they possess a rounded base and about twenty stiff hairs on their free surface. To the inner side of the inner hair-cells lies the cubical epithelium of the sulcus spiralis. On Fig. 348. — SuRFACB Vibw op Lamina Spiralis Mbmbkanacea op Cat. X 340. A. Outer pillar-cells : k, head- plates of the same, upper surface in focus ; ap, body and inferior extremity drawn with gradual depression of the tube ; ktp, portions of the head-plates of the inner pillar-cells. B. It. Labium tympanicum partly covered by the epithelium of the sulcus spiralis: ih, inner, ah, outer hair-cells, between these the phalanges ph, forming the membrana reticularis; ap, head-plates of the outer, //, of the inner pillar-cells. Techn. No. 185. the outer side of the outer pillars lie \.\ie. outer hair-cells; they resemble the inner hair-cells, but are characterized by a dark body occupying the upper half of the cell, the spiral body. ^ The outer hair-cells are arranged in several ( usually four) rows ; they do not lie in contact with one another, but are held apart by Deiters's cells ; these are elongated cells that contain a rigid fila- ment and possess at their upper ends a cuticular end-plate ; this has the form of a digital phalanx. The free spaces between the " phalanges " are occupied by the upper ends of the outer hair-cells (Fig. 248). The cells of Deiters are sustentacuiar elements that exhibit much in common with the pillar-cells; like these they consist of a rigid filament and a protoplasmic portion ; like these they have a head-plate (named phalanx). The difference consists only in this, that the transformation into rigid parts is not so far advanced. The pha- langes are joined to one another and form a beautiful netted membrane, the membrana reticularis. * In the scheme (Fig. 247, A\ this liody is indic.itcd by a (Ltrk dot close licneath the aulitory hairs. 266 HISTOLOGY. The outer hair-cells do not extend to the basilar membrane, but occupy only the upper half of the spaces between the cells of Deiters ; the lower divi- sions of these spaces remain unoccupied, and are called NueV s spaces (or, since they communicate with one another, the space of Nuel), which are inter- cellular clefts, like the tunnel, with which they connect. External to the last row of Deiters's cells lie the cells of Heusen, elongated cylinders, that gradually decrease in height and pass into the indifferent epithe- lium of the duct of the cochlea, whose elements over the remaining part of the basilar membrane are called the cells of Claudius. A soft, elastic cuticular formation, the mem/irana tectoria, extends over the sulcus spiralis and the organ of Corti (Fig. 249). It is attached to the vestibular lip of the sulcus and extends to the outermost row of hair-cells. The cochlear hninch of the auditory neife penetrates into the axis of the cochlea and in its spiral uninterrupted course gives off branches which pass to the root of the osseous spiral lamina ; here each medullated nerve-fiber loses its medullated sheath and passes into a nerve-cell which like those of the spinal ganglia possesses a connective-tissue capsule ; these nerve-cells collectively form the ganglion spirale,* which winds along the entire peripheral spiral canal of the cochlea (Fig. 243). From the opposite pole of each cell springs a second nerve-fiber, that soon acquires a medullated sheath and unites with neighbor- ing fibers in a wide-meshed plexus enclosed within the osseous spiral lamina ; it extends near to the labium tympanicum, where the fibers lose their medul- lated sheath, escape through the foramina nervina, and end in the epithelium in the following manner : they bend in the direction of the turns of the cochlea and run in spiral bundles, of which the first passes to the inner side of the inner pillar-cells, the second to the tunnel, the third between the outer * The ganglion spirale possesses the same structure as the spinal ganglia, with a single difference, — the ganglion-cells are not unipolar, but bipolar, as in the embryonal ganglia. THE ORGAN OF HEARING. 267 pillar-cells and the first row of the cells of Deiters, the remaining three between the cells of Deiters. From these bundles delicate fibers proceed to the hair- cells, on which (not within) they terminate. The arteries of the labyrinth come from the auditory and the styloma-stoid artery, which send a branch through the fenestra rotunda to the cochlea. The auditory artery sends branches to the saccules and to the semicircular canals, which in general supply a wide-meshed capillary network, but a close-meshed network on the maculse and cristfe ; and a branch to the cochlea, which on en- tering the same breaks up into a number of small branches. These in part enter the first turn, in part ascend in the axis of the cochlea. From the latter branches small twigs diverge successively and enter the bony wall of the modio- lus, where they form the radicles of smaller and larger masses of coiled blood- vessels, the glomeruli cochlea minores et majores. The smaller glomeruli are situated somewhat above the point of origin of the osseous spiral lamina and supply capillaries to the limbus and to the vestibular membrane. The larger glomeruli lie at the root of the septum between the adjoining turns of the cochlea and supply two independent vascular territories — the stria vascularis and the lamina spiralis membranacea. The x'eins unite in the vas prominens and in the vas spirale, which empty into the vena spiralis modioli lying beneath the ganglion spirale within the modiolus. The latter probably empties through the aqujeductiis cochleae into the internal jugular vein. The arrangement of the blood-vessels of the cochlea is such that the scala vestibuli is encircled by arteries, the scala tympani by veins. The upper por- tion of the scala tympani bounding the membranous spiral lamina is thus com- pletely removed from the influence of arterial pulsation. The Lymph-channels. — The endolymph in the interior of the membranous labyrinth communicates with the subdural lymph-sijaces by means of minute tubules passing from the ba,se of the ductus endolymphaticus. The perilym- phatic spaces connect with the subarachnoidal sjiaces by means of the "ductus jierilymphaticus." a lymph-vessel running through the aquasductus cochleiE. The Middle Ear. The mucous membrane of the tympanic cavity is intimately united with the underlying periosteum. It consists of a thin connective-tissue tunica propria and a single stratiun of cubical epithelial cells, that sometimes on the floor, occasionally also in larger areas of the tympanic cavity, is ciliated. Glands (short, 0.1 mm. long follicles) occur sparingly in the anterior half of the tym- panic cavity. The mucosa of the Eustachian tube consists of a fibrous tunica propria (containing numerous leucocytes near the pharyngeal orifice) and of a stratified ciliated columnar epithelium ; the ciliary wave is directed toward the pharynx. Mucous glands occur in especial abundance in the pharyngeal half of the tube. The cartilage of the Eustachian tube, where it adjoins the bony tube, is of the hyaline variety, and here and there contains rigid (not elastic) fibers; in the anterior portion the matrix is penetrated by dense networks of 268 HISTOLOGY. elastic fibers. The /'lood-vesse/s in the mucosa of the tympanic cavit)' form a wide-meshed, in the mucosa of the Eustachian tube a narrow-meshed super- ficial capillary network, and a deep capillary plexus surrounding the glands. The lymph-vessels run in the periosteum of the tympanic cavity. With regard to the terminations of the nerves, exact information is still wanting. Excretorj duct The External E.ar. The tympanum consists of a lamina of connective tissue, lamina propria, in which the fibrous bundles on the outer surface are radially arranged and connected with the periosteum of the sulcus tympanicus ; while on the inner surface, toward the tympanic cavity, they are cir- cularly arranged. On its inner surface the membrane tympani is covered by the mucous membrane of the tympanic cavity, on its outer surface by the integument of the exter- nal auditory canal. Both investments are very firmly attached to the lamina propria, are smooth, and are without papillae. Where the malleus lies against the tympanum, the latter is provided with a superficial stratum of hyaline cartilage. The external auiUfojy canal, as far as it is cartilaginous and on the whole length of its upper wall, is clothed with an extension of the skin characterized by its thickness and by a great abundance of peculiar coil-glands, the cerinninous glands. In some respects these glands correspond with the ordinary larger coil-glands (sweat-glands) of the skin ; like these, they possess an ex- cretory duct, lined by several layers of epithelial cells, and the tubules of the coil contain a simple layer of cubical gland -cells, resting on smooth muscle- 250. — From a Vertical Section B Skin of the External Auditory Meatus of an Infant. X 50' The excretory duct opens into the hair- follicle. Techn. No. 189. ■Section op the Coil-Tubulk from of a COIL-TUBULE FROM THE EXTER X 240. Techn. No. 189. Cuticular border. Gland-cells. Nuclei of smooth i Membrana propri; fibers and a conspicuous basement membrane ; they are distinguished from the sweat-glands by the very wide lumen of the coiled tubule, that, especially in adults, is greatly dilated, and by numerous pigment-granules and fat-droplets within the gland-cells, which frequently exhibit a distinct cuticular border. THE NASAL MUCOUS MEMBRANE. 269 The excretory ducts are narrow, and in children open in the hair-follicles; in adults, close beside the hair-follicles on the free surface. The secretion, the cerumen, consists of pigment-granules, oil-globules, and cells containing fat ; the latter probably come from the sebaceous glands. In the (remaining) region of the bony external auditory meatus, the integument is thin and with- out ceruminous glands. The cartilage of the external auditory canal and of the pinna is of the yellow elastic variety. The blood-vessels and nen'es are distributed as in the skin elsewhere; only on the tympanum do they exhibit peculiarities. Along the handle of the malleus an artery descends, which breaks up into radially-disposed branches; the blood is returned by a vein that, likewise, runs along the handle of the malleus. The vessels lie in the integumentary covering of the tympanum. The mucous membrane of the tympanum is provided with a dense capillary network, which anastomoses with the integumentary vascular network by means of perforating branches. The lymph-vessels a.re ioun^ principally in the cutaneous stratum of the tympanum. The nerves form delicate networks beneath both the mucous and the cuta- neous lavers. XII. THE NASAL MUCOUS MEMBRANE. The nasal mucous membrane is composed of three divisions differing in structure : that of the vestihiilar region, that of the respirator}' region, and that of the olfactory region. THE VESTIBULAR REGION. The mucous membrane of the vestibular region (that lining the movable nose) is a modified continuation of the integument and consists of a tunica propria beset with papillaj and covered by a stratified squamous epithelium. Nuuierous sebaceous glands and the hair-follicles of the stiff nasal hairs (vibris- sje) are embedded in the tunica propria. THE RESPIR.\TORY REGION. The respiratory region of the nasal mucous membrane in man includes that lining all parts of the nasal fossre (and the accessory nasal spaces), except that upon the median portion of the superior turbinal and the corresponding part of the nasal septum. It consists of a stratified ciliated epithelium, some- times containing few goblet-cells, sometimes many, and of a conspicuous tunica propria. 4 mm. thick on the inferior turbinal, which is composed of 270 HISTOLOGY. fibrillar connective tissue and a large, variable number of leucocytes ; occasion- ally the latter form solitary nodules. Migration of leucocytes through the epithelium into the nasal fossse also occurs. The tunica propria in man contains branched tubular glands, which pro- duce both mucous and serous secretion, and are therefore mixed glands. Not infrequently they open in funnel-shaped depressions, which are lined by an extension of the superficial epithelium, and on the inferior turbinal are per- ceptible by the unaided eye. In the accessory nasal spaces the epithelium and tunica propria are con- siderably thinner ( — o. 02 mm.), but otherwise of the same structure; the glands are small and few in number. THE OLFACTORY REGION. The olfactory division of the nasal mucous membrane in man is limited to the median portion of the superior turbinal and the corresponding part of the Fig. 252. — Thick Vertical Section of Respiratory Mucous M X 20. The excretory ducts of two glands are visible. /. Funnel-shaped depl No. 191. nasal septum, and is distinguished, macroscopically, from the rosy mucosa of the respiratory division by its yellowish-brown color. It consists of an epithe- lium, the olfactory epithelium, and of a tunica propria. In the olfactory epithelium, two forms of cells occur. The one form is cylindrical in its upper half and contains a yellowish pigment and minute granules, often arranged in longitudinal rows. The lower half is slenderer, the edge is serrated and in- dented, the inferior end is forked, and is said to unite with the similar ends of neighboring cells to form a protoplasmic network. These elements are called si/s- tentacular cells. Their nuclei are usually oval and lie at the same level ; in ver- tical sections they are seen to occupy a narrow belt, the zoiie of the oval nuclei (Fig. 255). The second form of cells possesses a spherical nucleus and only in the vicinity of the latter an appreciable amount of protoplasm ; from this a slender ciliated cylinder, the attenuated cell-body, extends upward, while from the opposite pole a very delicate process continues directly into the axis-cylin- der of a nerve-fiber. These cells, the olfactory cells, are ganglion-cells, and their louer i)rocess a centripetal nerve-fiber. Their round nucleolated nuclei THE NASAL MLXOUS MEMBRANE. 271 lie at different levels and occupy a broad belt, the zone of the round nuclei. Occasionally, in the nonnucleated ei)ithelial territory, round nuclei in varying number are found above the zone of the oval nuclei ; they belong to dislocated olfactory cells, or are the nuclei of wandering, often pigmented, leucocytes. In addition to these two kinds of cells, there are intermediate forms, which sometimes resemble the olfactory elements, some- times the sustentacular cells. At the border of the epithelium, toward the connective tissue, is a protoplasmic network furnished with nuclei, the so-called basal cells (Fig. 256, ^). The surface of the epithelium is covered by an extremely delicate homo- geneous membrane, the membrana litnitans olfactoria ; it is pierced by the ciliated ex- tremities of the olfactory cells and is covered by a peculiar substance, regarded by some authors as a cuticular formation similar to the basal border of the intestinal epithelium, by others as delicate cilia, by still others interpreted as minute jiarticles of discharged mucus (Fig. 253, s). The tunica propria consists of a loose feltwork of rigid connective-tissue fibers intermingled with delicate elastic fibers, which in some animals toward the epithelium (for example, in the cat) is condensed to a structureless mem- brane. Numerous glands, the so-called olfactory (^Bowman' s) glands, are em- 53, — Isolated Cblls of the Olpac- ^ Mucosa of Rabbit. X 560. st. Sus- tenucttU bling ( . . process has been torn oflf;y". 1 ^, cells of olfactorj' glands. . olfactory' < r' the lower ilialcd cells ; :hn. No. 190. Bundles of fibers of olfactory nerve. KiG. 354. — Vrrtical Section thkough the Olfactory Re ripetal process of an olfactorj' cell. 3F A Vouxc Rat. X 480. lechn. No. 193. bedded in the tunica propria; they are either sim|)le or (for example, in man) branched tubules, in which an excretory duct, situated in the epithelium, a body and a fundus may be distinguished. The cells of the body of the glands are pigmented. The glands were until recently regarded as serous glands, but latterly they have been pronounced mucous glands. The olfactory glands fre- 272 HISTOLOGY. quently advance beyond the territory of the olfactory mucous membrane, and are found in the adjoining portions of the respiratory mucous membrane. The tunica propria also carries the ramifications of the nerves. The branches of the olfactory nerve are accompanied by processes of the dura and consist ■«?;,,# ) Tunica propri Fig. 255. — Vertical Section of Olfactorv Mucosa of Kahbit. X 50. zo. Zone of oval nuclei ; zr, zont round nuclei ; dr, olfactory glands ; a, excretory duct ; k, body ; ^, fundus ; n, branches of olfactory ne cut transversely ; z*, veins ; ar, arteries ; 6, bundles of connective tissue in cross-section. Techn. No. 19 throughout of nonmeduUated fibers, that readily separate into their component fibrillse ; the fibers are the inferior processes of the olfactory cells, grouped in bundles, which pass in horizontal arches from the epithelium, descend into %>-•'■ Fig. 256. — Vertical Section through the Olfactory Mucosa of Rabbit. X 560. s. Cuticular border zo, zone of oval nuclei ; zr, zone of round nuclei . i, b.-is.il cells ; dr, portions of olfactory glands, on ihc right the lower portion of the excretory duct is visible ; «, branch of the olfactory nerve. Techn. No 192 the tunica propria, and by union with neighboring bundles form the branches of the olfactory nerve. The terminal ramifications of the trifacial nerve lie within the tunica propria ; delicate fibers that ascend to the epithelium and there ter- minate in free ends possibly belong to the trifacial nerve. THE TASTE-BUDS. 273 Of the l>/o(hi-vi-ssels of the nasal mucosa the stems of the arteries run in the deeper strata of the tunica propria ; they break up into a rich subepithelial capillary network. The veins are remarkable for their size, and over the poste- rior end of the inferior turbinal form so dense a network as to give the tunica propria the character of cavernous tissue (Fig. 252 and Fig. 255). The lymph-vessels form a coarse-meshed net lying in the deeper strata of the tunica propria. The lymph-vessels of the olfactory mucosa may be injected from the subarachnoidal space, through the perineuria! sheaths of the branches of the olfactory nerve, acquired from the cerebral membranes on passing through the cribriform plate. Medullated twigs of the trifacial nerve may be found in the respiratory as well as in the olfactorv mucosa. XIII. THE TASTE-BUDS. The tastc-hiids or gustatory organs are oval bodies, about 80 /x long and 40 // broad, which are completely embedded in the epithelium of the oral mucous membrane ; their base rests upon the tunica propria, the upper end reaches to the surface of the epithelium, which at this point exhibits a funnel-shaped de- KlG. 257.— Vkktical Section of Two Rinr.Rs ,,r 1'aiilla Foliata of Rabbit. X 80. Ea.:h ridge. /, bears secondary ridges, /'; ^, taste-buds; «, medullated nerves; d, serous gland; a, portion of an ex- cretory duct of a serous gland ; m, muscle-fibers of tongue. Tcchn. No. 195. pression, the taste-pore. Each taste-bud consists of two kinds of elongated epithe- lial cells ; the one are either of the same diameter throughout, or they taper at the basal end, which occasionally is forked, while the upper end is prolonged to a fine pointed e.\tremity ; their protoplasm is clear. These cells constitute the bulk of the ta.ste-bud, are princi|)ally situated at the periphery, and are called 2 74 HISTOLOGY. tegmental cells. They serve as support and sheath for the gustatory cells, which are the real percipient epithelial elements. The gustatory cells are small, and only slightly enlarged where the nucleus is situated ; the latter is sometimes near the lower or central end, sometimes in the middle, rarely at the upper or peripheral end of the cell. The upper division of the cell is cylindrical, or more frequently conical, and bears on its free end a stiff, refractile, hair-like process, a cuticular formation (Fig. 258) ; the lower division is sometimes slender, sometimes thick and blunted at the end or expanded into a triangular Tunica propria. Fig. 258.— From a Vertical Section of Papilla Foliata of Rabbit. X 560. Techn. No. 195. foot, which does not however extend into the fibrous tissue of the mucosa. Their protoplastn is granular. Not infrequently many leucocytes are found in the interior of the taste-bud. The taste-buds occur chiefly in the lateral walls of the circumvallate pa- pillae and on the ridges of the papillae foliatse, also occasionally on the papillae fungiformes, on the soft palate, and on the posterior surface of the epiglottis. Taste-pore. ~1 I \ Taste-bud. ', X'Sv"^' . I \^ " Gustatory cells. Epithel Inlergemmal nerve-fibers. Intragemmal nerve-fibers. Fig. 259. — From a Vertical Section of a Circumvallate P.apilla of Monkey. X 240. Techn. No. 196. The conjecture that the terminal ramifications of the glossopharyngeal nerve have the same anatomical relation to the gustatory cells that the olfactory nerve-fibers have to the olfactory cells has been shown to be erroneous. The terminal branches of the glossopharyngeal nerve consist of medullated and gray nerve-fibers beset with microscopic (sympathetic) ganglia,* which form a dense plexus in the tunica propria, from which numerous branches spring. * Whether the so-called "taste-granules " beneath the epithelium of the papillse foliatse are multipolar nerve-cells is very questionable ; a nerve-process has not as yet been demonstrated. THE TASTE-BUDS. 275 Some of the latter terminate, possibly, in the connective tissue in end-bulbs, but the majority of the gray fibers penetrate into the epithelium. Here two kinds of fibers may be distinguished. The one kind, the " intragemmal " fibers, enter the taste-buds, divide, and form a plexus beset with numerous conspicuous varicosities that extends up to the taste-pore ; these fibers do not anastomose with one another, nor do they connect with the gustatory cells, but all terminate in free ends. The other, the smoother " intergemmal " fibers, penetrate the epithelial areas between the taste-buds and, usually without dividing, extend to the uppermost strata of the epithelium. PART 111. SPECIAL TECHNIQUE. Protopla Nucleus. );—:. t Nuclear membrai 2 Chromatin cords. 3 Nucleoli. I. KARYOKINESIS. Xo. I. — For the study of nuclear structure and karyokinesis amphibian larvK are most suitable. Those most readily procured are the larvae of the water salamander, which in the months of June and July abound in every pool. Place freshly-caught specimens, 3 to 4 cm. long, in about 100 c.c. of chromo- acetic acid (p. 21). After 3 hours place the larvae in running water for 8 hours, and then in 70 per cent, alcohol. At the expiration of 4 hours, or later, the objects are ready for further treatment. a. Nuclear Stnicttirc. — With a scalpel carefully scrape the epithelium from the skin of the abdomen, with two pairs of delicate forceps strip off the thin corium, stain it i to 3 minutes in , 5 c.c. of Bohmer's hematoxylin (p. 31), and mount in damar-varnish (p. 38). Between the round glands beautiful con- nective-tissue cells with large nuclei may be seen. The structure of the protoplasm, the centrosome and attraction-sphere, also the structure of the nucleus can only be recognized by the employment of com- plicated methods and high magnification. The results obtained by ordinary methods are like that pictured in Fig. 260. The cross-striped muscles of the tail and the membranes of smooth muscle-fiber ( the latter may be readily obtained by stripping off the muscularis of the intes- tine) also furnish instructive slides. b. Kaiyokinesis. — With a pair of fine scissors cut round the margin of the cornea, and strip off the same ; stain and preserve like a. The preparation must be placed on the slide with the convex surface of the cornea upward ; in the epithelium, even with the low-power objective, many karyomitotic figures may be seen, which may be recognized by their intense color. By this method the nuclear spindle and polar radiation, as in Fig. 5, can only be perceived (with higher magnification) in especially favorable preparations, e. g., eggs of siredon and the trout. The delicate lamellae suspended from the convex side of the cartilaginous- gill-arch, as well as the epithelium of the floor of the oral cavity, are very suitable objects. Occasionally not a single karyokinetic figure is found. Isolated figures may sometimes be observed in preparation a. 276 Fig. 260. — Connective-tissue Cell from Corium of Triton T-^niatus. Surface View. X 560. Only the coarser filaments of the nuclear network can be distinctly seen : with this magnification the finer filaments ap- pear as minnie dots, the niicleoH as parts of the nuclear network. SPECIAL TECHNIQUE. 277 II. CILIATED El'ITHEI.IAL CELLS. No. 2. — To obtain living ciliated cells, kill a frog (p. 25), place it on its back and with scissors cut off the lower jaw, so that the roof of the cavity of the mouth is exposed. From the mucosa of the roof cut out a small strip about 5 mm. long, place it on the slide in adroj; of salt solution, and apply a cover-gla.ss. Examine with the high power and search the edges of the pre- paration. At first the movement of the cilia is very lively, so that the observer cannot see the individual cilia ; the entire ciliated border waves ; the motion ha.s been compared to a cornfield swayed by the wind. After a few moments the rapidity of the movement diminishes and the cilia can be plainly seen. If the movement ceases, it can be restored by the application of a drop of concentrated potash solution (p. 41); the effect is transient, so that the eye of the observer must not be removed from the ocular while the fluid passes under the cover-glass. The addition of water soon suspends the movement. III. CONNECTIVE TISSUE. No. 3. — Mucous Connective Tissue. — Place the umbilical cord of a 3 to 4 months' human embryo (or pig embryo 3 to 6 cm. long) in 100 c.c. of Miiller's fluid (p. 20) 3 to 4 weeks; harden in 30 c.c. of gradually strengthened alcohols (p. 29). The cord will still be very soft; in order to obtain good sections it must be embedded in liver, and in cutting must be somewhat com- pressed with the fingers. The section may be stained in picrocarmine (12 hours) or in hemato.xylin ( 5 minutes j, and should be examined in a drop of distilled water. In glyceflne and damar-varnish the delicate proces.ses of the cells and the bundles of connective tissue are invisible. In the vicinity of the blood- ves.sels the network of cells is less fine ; therefore a field remote from the blood-vessels should be selected for study. The older the embryo, the greater is tiie number of the connective-tissue bundles. Mount in diluted glycerine (p. 21). No. 4. — Fibrous Connective Tissue ; Connective-tissue Bundles. — Prcjiare small strii)s, i to 2 cm. long, of intermuscular connective tissue, for examjile, of the thin septum between the serratus and intercostal muscles ; place a small piece on a dry slide and quickly spread it out with teasing needles (see " half- drying method," No. 27 a, p. 281 ), add a drop of salt solution and apply a cover-glass. The bundles of connective tissue appear wavy and pale; with a little jjractice the sharply-contoured, highly-refracting elastic fibers may be dis- tinguished, and also, in favorable situations, the nuclei of the connective-tissue cells. No. 5. — The cells of fibrous connective tissue may be rendered visible by the addition of a drop of picrocarmine to preparation No. 4, under the cover- glass (p. 41). In most cases only the red nucleus can be perceived, especially when the cell lies wholly upon the fibrous bundles. In rare cases the jiale yellow, variously-shaped body of the cell can be seen (Fig. 22, A, i, 2, 3). No. 6. — Afastzellen (granule-cells). — Fix small pieces, i to 2 cm. square, of mucous membrane (of the mouth, of the pharynx, or of the intestine) in absolute alcohol ( p. 27). In from 3 to 8 days cut thin sections and stain them in 10 c.c. of alum-carmine dahlia for 24 hours (p. 23). Transfer them to 10 c.c. of ab.solute alcohol for 24 hours, which must be renewed once or twice during this time. Mount in damar (p. 38). The protoplasm of the Mastzellen then exhibits granules stained an intense blue. 2 76 HISTOLOGY. No. 7. — Fibril/a. — Place a piece of tendon about 2 cm. long in a saturated aqueous solution of picric acid. On the following day, with two pairs of forceps, \m\\ the tendon apart along its length, take from the interior a bundle about 5 mm. long, and tease the same on a dry slide {cf. No. 27 a, p. 281), add a drop of distilled water, apply a cover-glass, and examine with the high-power objec- tive. The ultimate fibrillce appear as exceedingly fine, silky filaments. No. 8. — "Enci/r/ing Fibers." — With the scissors cut out a piece about i cm. square of the connective tissue within the arterial circle of Willis, wash it in a watch-glass in salt solution, with needles spread it out in a drop of the same solution on a slide, and cover. With the low power, in addition to numerous delicate blood-vessels and ordinary bundles of fibrous tissue, sharply-contoured, refracting bundles, in distinct contrast to the remaining connective tissue, will be found, which, on the use of the high power and a diaphragm of narrow aperture, show that they, likewise, consist of fibrillar connective tissue. Place such a bundle in the field and treat it with a drop of acetic acid under the cover-glass (p. 41). As soon as the acid reaches the bundle, it swells, the fibrillation vanishes, and instead elongated nuclei appear. The swell- ing is not uniform ; at irregular intervals the bundle is constricted. With dim illumination the "fibers" (cell remnants) producing the constrictions mav be seen (Fig. 22, B). No. 9. — Fat-cells. — Take a small piece of the reddish-yellow, gelatinous fat from the axilla of an emaciated individual ; spread out rapidly a piece the size of a split pea in the thinnest possible layer on a dry slide, add imtneJiately a drop of salt solution, and apply a cover-glass. In thin places atrophic fat- cells, like those shown in Fig. 23 B, will be seen. This pjeparation may be stained under the cover-glass with picrocarmine (p. 41) and preserved in diluted glycerine. Ordinary (normal) fat-cells, taken from any part of the body, are likewise to be examined in salt solution. The spherical cells should be studied with change of focus {^cf. Fig. 23, A^. No. 10. — Fine elastic fibers may be readily obtained by treating prepara- tion No. 4, under the cover-glass, with a few drops of acetic acid. The con- nective-tissue bundles swell and become transparent, the elastic fibers, on the contrary, remain unaltered, and stand out sharply contoured (Fig. 20, A'). No. II. — Thicker elastic fibers may be obtained by teasing in a drop of salt solution a slender piece, about 5 mm. long, of the fresh ligamentum nuchre of an ox (Fig. 20, j9). The piece should not be taken from the loose, envelop- ing tissue, but from the tough, yellowish fibrous portion. The preparation may be stained in picrocarmine and mounted in glycerine. No. 12. — Cross-sections of thick elastic fibers may be obtained by drying a piece (10 cm. long and i to 2 cm. thick) of the ligamentum nuchse (it will be ready to use in 4 to 6 days) and treating it like No. 63. No. 13. — Fenestrated Membranes. — Take a small piece (about 5 mm. square) of endocardium, place it in a drop of water on a slide, and add, under the cover-glass, i to 2 drops of potash-lye. Examine the edges of the preparation (Fig. 21). Good specimens may also be obtained from the basilar artery ; place a ]nece of the artery cut open lengthwise in 10 c.c. of concentrated potash solu- tion. After 6 hours take a small piece, about i cm. long, and separate the lamellae in a drop of water on a slide ; this is easily done by scraping it with a scalpel. Cover and examine with the high power. The small apertures in the membrane have the appearance of shining nuclei. SPECIAL TECHNIQUE. 279 With the low power the membrane is to be recognized by its dark outlines. To preserve, wash it well in lo c.c. of water (5 minutes), stain it in 3 c.c. of Congo red from 12 to 20 hours (p. 23), and mount in damar. No. 14. — Hyaline Cartilage. — Cut off the extremely thin episternum of the frog, place it on a dry slide, cover it with a cover-glass, and examine at once with the high power. The cartilage-cells completely fill the lacunre (Fig. 25, A). For prolonged study, add a drop of saline solution. No. 15. — Hyaline Costal Cartilage. — Without any previous preparation fine sections of costal cartilage may be cut with a dry razor, and examined in a drop of water. Search for one of the glossy areas containing rigid fibers (Fig. 25, .5). The preparation may be preserved by adding a few drops of dilute glycerine. Fresh cartilage does not stain readily. The tissue must first be placed in Kleinenberg's picrosulphuric-acid mixture or in Miiller's fluid and then in alcohol (p. 29) and subsequently stained with Bohmer's hematoxylin (p. 22). Mounted in damar, which clears vigorously, the finer details vanish. No. 16. — Elastic Cartilage. — Take a piece of the arytenoid cartilage of man (better still of the ox) — the elastic cartilage of the anterior angle is recognized by its yellowish color. Cut a section that includes the boundary line between the elastic and hyaline cartilage, and examine it in water. Preserve like No. 15. The development of the elastic fibers may often be studied in the cartilages of adults, especially in the epiglottis and in tlie vocal process of the arytenoid cartilage (Fig. 26, i). No. 17. — ]V}iite Fibro-cartilage. — Cut the intervertebral disks of adult man in pieces from i to 2 cm. square ; fix in 100 c.c. of picrosulphuric acid (p. 20). for 24 hours and harden in 50 c.c. of gradually strengthened alcohols (p. 29). Stain sections in Bohmer's hematoxylin (p. 22) and mount in damar (p. 38). Sections through the edges yield hyaline cartilage ; sections through the central portions of the disk exhibit large groups of cartilage-cells. IV. MUSCLE-FIBERS. No. 1 8. — Striated Mtisclc-filiers. — a {of the frog') . — With the scissors placed flat and parallel to the course of the fibers, cut a piece about i cm. long from the adductor muscle of a recently-killed frog. Take a fragment from the inner surface of this piece and tease it in a small droj) of salt solution, add a second larger drop of the same liquid and, without />ressing, cover the prepara- tion with a cover-glass. With low magnification (50 diameters) the cylindrical form, the difference in thickness, occasionally also the cross-striation of the isolated fibers may be seen (Fig. 34). With higher magnification (240 diameters) the cross-striation is distinctly visible, and occasionally pale nuclei and refracting granules. The presence of numerous granules within the muscle- fibers is probably an indication of active metabolic processes. Where the muscle-fibers are cut acro.ss, the muscle-substance not infrequently protrudes from the sarcolemma. /' {of man). — I have found beautiful striated fibers in muscles taken from the human cadaver injected with carbolic acid. To i)reserve, stain under the cover-glass with picrocarmine (p. 41) for about 5 minutes, and then displace the staining fluid with diluted glycerine. No. 19. — The Sarcolemma. — Treat preparation No. 18 a with a couple of drops of ordinary water. In 2 to 5 minutes it will be seen, with the low power ( tO diameters^, that the sarcolemma is raised from the muscle-substance in the 2 So HISTOLOGY. form of transparent blebs, and at other places, where the torn muscle-substance has retracted, the sheath appears as a delicate line spanning the interval (Fig. 34, I, s, s'). No. 20. — Muscle Nuclei. — Prepare muscle-fibers like Xo. iS a. Treat with a drop of acetic acid (p. 41). The shrunken but sharply-outlined nuclei, with the lower power, have the appearance of spindle-shaped streaks (Fig. 34, 2). No. 21. — Fibrilla. — Place the fresh muscle of a frog in 20 c.c. of o. i per cent, chronaic-acid solution (p. 20). In about 24 hours the tissue may be teased in a drop of water, and fibers will be found whose ends have separated into their ultimate fibrillffi (Fig. 34, 2 ). If it is desired to make a permanent preparation, place the muscle in water for i hour, then in 20 c.c. 33 per cent, alcohol, 10 to 20 hours ; tease at once or preserve in 70 per cent, alcohol until wanted, and then isolate (p. 25). If the chromic acid be removed by allowing the tissue to remain in alcohol (frequently renewed) for several weeks, the teased preparation may then be stained with picrocarmine in the moist chamber and this replaced by glycerine (p. 41). No. 22. — The Ends of the Muscle-Ji/>e?-s. — Place the fresh gastrocnemius muscle of the frog in 20 c.c. of concentrated potash-lye, and cover the watch- glass. In about 30 to 60 minutes (in a cold room, somewhat later) the muscle, if lightly moved with a glass rod, falls into its fibers. Should this fail, the solution is not strong enough (see p. 26). Transfer a number of the fibers in a drop of the same solution to a slide and carefully apply a cover- glass. With the low power the ends of the muscle-fibers and numerous nuclei may be seen (Fig. 34, 3). The fibers should not be examined in water or glycerine, since the lye, thus diluted, soon destroys them. No. 23. — Branched Muscle-fibers. — Remove the tongue from a recently- killed frog (it is attached in front to the lower jaw, is free behind) and place it in 20 c.c. of pure nitric acid, to which about 5 gm. of ])otassium chlorate have been added (some undissolved chlorate must remain in the bottom of the vessel). In a few hours, with glass rods carefully transfer the tongue to 30 c.c. of distilled water, which must be frequently changed. In this the tissue can remain a week, though it may be used at the end of 24 hours. For this purpose put it in a test-tube half filled with water and shake it several minutes ; the tongue will fall to pieces. Turn the contents of tlie test-tube into a capsule, and in an hour or later place -a little of the sediment that has been deposited in the meanwhile in a drop of water on a slide. The tissue may be further isolated with the teasing needles, but in most cases this is superfluous. Examine with the low power. Stain under the cover-glass with picrocarmine (p. 41). Mount in dilute glycerine (p. 21). (Fig. 34, 4.) No. 24. — Smooth Musclefibers. — These are best isolated by placing a piece of the stomach or intestine of a frog, just killed, in 20 c.c. of potash solution and treating like No. 22 (Fig. 31). V. NERVE-CELLS AND NERVE-FIBERS. No. 25. — Ganglion-cells, Fresh. — Tease a small piece of the Gasserian ganglion in a drop of salt solution, and stain under the cover-glass with picro- carmine for 2 minutes (p. 41). The processes of the cells usually tear off. The ganglion-cells of the cerebral and cerebellar cortex may be prepared in the same way ; the processes likewise are easily lost. SPECIAL TECHNIQUE. 281 i cylinde Medullary sheath. No. 26. — Multif>olar Ganglion of the Spinal Cord. — Remove with the scissors as much as jjossible of the white substance of the spinal cord of an ox. and i)tace the gray remnant in pieces i to 2 cm. in length in 30 c.c. of 33 jJer cent, alcohol (p. 19, 3, ers. — Expose the sciatic nerve of a frog just killed, and with delicate scissors cut it at the level of the popliteal space and about i cm. higher. Isolate in a drop of salt solution. No. 27 a. — Better still, tease on a dry slide by the "half-drying" method. Hold the linocr end of the nerve with one needle, with another needle separate the nerve-bundles along half the length of the nerve; a thin shining membrane will span the interval between the sejiarated bundles. Add a drop of salt solution and apply a cover-glass. The membrane contains numer- ous isolated nerve-fibers. The mani- pulation must be done very rapidly (in a1)ont 15 seconds), so that the nerve- fibers do not become dry ( Fig. 41, 6, 7, 8, 9)- No. 28. — Alterations in the Med- ullary Sheath. — Treat No. 27 a with water ( place a drop at the edge of the cover-glass and let it flow under). In a few minutes the formation of the myelin drops begins (Fig. 41, 10). No. 29. — The Axis-cylinder. — Tea.se dry (like No. 27 (/) and stain with methylene blue { p. 34) ; the nodes of Ranvier stain first, and often (■ic. s6i.— Serve fiukk of Rabbit. X 560- so deeply that the axis-cylinder cannot be recognized there. The axis-cylinder frequently shrinks and becomes dis- ]>laced within the medullary sheath, or it contracts and becomes convoluted. ( )n the addition of glycerine the medullary substance can no longer be dis- tinctly recognized as such, but the nuclei of the neurilemma are often rendered plainly visible. No. 30. — E.yhihition of the A.xis-iylinder -luith Chromic Acid. — Kxpose the sciatic nerve of a rabbit recently killed, hciiig careful not to touch it ; place a match-stick parallel to the long axis of the nerve, and secure it by means of ligatures at the uj^per and lower ends; cut the nerve on the further side of each ligature, and place it, with the wood, in 100 c.c. of a o. i per cent, chromic- acid .solution (p. 20). In about 24 hours cut the ligatures and tease a piece of the ner\e, 0.5 to I cm. long, separating it into bundles, not libers. Put the bundles back into the rhromic-acid solution : in 24 hours transfer them to 50 c.c. of distilled water, and in 2 to 3 hours to 30 c.c. of gradually strengthened alcohols to harden (p. 29). It is advantageous to leave the bundles for a long time, i to 8 weeks, in 90 per cent, alcohol, as they are then more readily stained. .After Node of R Biconical enlar:gei 252 HISTOLOGY. the hardeniBg is completed, the bundles are to be teased in a drop of picro- carmine, placed in the moist chamber, and after the staining is completed, (which, according to the length of time the tissue was allowed to harden in the alcohol, requires from 3.^ to 3 days) preserved in acidulated glycerine (p. 41). The nodes of Ranvier are not as distinct as in fresh and in osmic-acid prepara- tions, but appear as delicate transverse lines (Fig. 261). The somewhat shrunken axis-cylinder and the nuclei are stained a fine red. The intensity of the color depends on the quality of the picrocarmine, which unfortunately varies greatly. No. 31. — Nodes of Ranvier and Axis-cylinders. — Add 10 c.c. of a i per cent, solution of silver nitrate to 20 c.c. of distilled water. Kill a frog, open the abdomen by a crucial incision, turn out the viscera, and expose the nerves descending on either side of the vertebral column. Wash out the abdominal cavity with distilled water, and pour over the nerves about one-third of the silver solution, .\fter two minutes carefully cut out the delicate nerves, put them for a half-hour in the remainder of the silver solution, placing them in the dark. Then transfer them to 10 c.c. of distilled water, in which they may remain for from i to 24 hours. If the nerves are now examined in a drop of water, with the low power, the endothelial sheath of the nerve and numerous pigment-cells will be seen ; frequently a blood-vessel lies along the nerve. On examination with the high power, little will be seen of the nodes and axis- cylinders, but if the preparation be exposed for several hours to daylight (or a {liw minutes to sunlight) the reaction takes place and the parts mentioned be- come silvered. The biconical swelling on the axis-cylinder often becomes dis- placed in teasing, and cannot always be readily found by the beginner (Fig. 42). No. 32. — Nonmedullated Nerz'e-fibers. — Tease a portion of the pneumo- gastric nerve of a rabbit on a dry slide (No. 27 a), and add a few drops of a yi, per cent, osmic-acid solution ; in 5 to 10 minutes the meduUated nerve-fibers become blackened (which may be ascertained by examination with the low power). Remove the osmic-acid solution and add a few drops of distilled water, which should be renewed in 5 minutes. In 5 minutes more remove the water, add a few drops of picrocarmine, apply a cover-glass, and place in the moist chamber for from 24 to 48 hours ; then displace the picrocarmine with acidulated glycerine (p. 41). The tissue may be teased again after the staining is completed, which is now more easily done because the elements are more dis- tinctly seen. With high magnification the medullated nerve-fibers appear blue- black, the nonmedullated pale gray and finely striated longitudinally. The sympathetic nerve treated in the same way exhibits more numerous non- medullated nerve-fibers. But this nerve is somewhat more difficult to find. Cut through the greater cornu of the hyoid bone, also the hypoglossal nerve, and push them aside ; behind the pneumogastric nerve lies the sympathetic, which may be recognized by its 3 to 4 mm. in size, ellipsoidal, yellowish, and trans- parent superior cervical ganglion. If the piece of the nerve lying close under the ganglion be teased, ganglion-cells, the majority of which contain two nuclei, will be obtained ; it is difficult to isolate the cells so that their processes can be seen. In Fig. 41, accideutallv, only the more unusual uninucleated ganglion- cell is to be seen. VI. THE HEART AND THE BLOOD-VESSELS. No. 33. — The Heart and the Large Blood-vessels. — Cut out a papillary muscle from a human heart, a piece of the aorta 2 cm. long, a piece i to 2 cm. long of the bronchial arterv with its veins and tlie surrounding connective SPECIAL TECHNIQUE. 283 tissue, and a piece of the renal vein i cm. long, and suspend them on a thread in a bottle containing 40 c.c. of absolute alcohol. In 24 to 48 hours the objects are ready to section. Embed them in liver (the artery and vein maybe embedded together and will not be injured by strong compression), cut thin cross-sections and stain in Bohmer's hematoxylin 2 to 5 minutes (p. 31). Mountindamar (Fig. 43,45,47, 48, 49). Theelastic fibers do not stain, but with the high power can often be distinctly recognized. The arrangement of the elements of the adventitia cannot be satisfactorily appreciated in cross-sections — often they all appear to be circularly disposed (a portion of them are circularly arranged — for example, those of the inner- most strata of the external elastic membrane). The exact arrangement can only be seen in longitudinal sections, which al.so show the muscle-fibers of the adventitia plainl\ . No. 34. — Small Blood-vessels ami Capillaries. — From the base of a human brain strip off slowly ])ieces of the pia i to 3 cm. in length (in this way delicate blood-vessels that penetrate the brain vertically are obtained), shake them in Miiller's fluid to free them from adherent fragments of brain-tissue, and place them in 50 c.c. of Miiller's fluid for from 3 to 10 days ; then trans- fer them for from i to 3 hours to water (for i hour to running water), and harden them in about 40 c.c. of gradually strengthened alcohol (p. 29). Kxamine one of these pieces in a watch-glass on a black background, and it will be seen that small vessels are isolated. a. With a fine scissors cut off small twigs with their ramifications, stain them 2 to 5 minutes in Bohmer's hematoxylin (p. 31) and mount in damar (Fig. 44)- b. From the larger twigs of the cerebral blood-vessels cut pieces about 5 mm. long, slit them open lengthwise, stain them in Bohmer's hematoxylin, and place them on the slide with the adventitia side down. Mount in damar. By changing the focus the three coats of the vessels and their general arrange- ment can be seen. Capillaries may also be found on examining fresh brain tissue. They may be recognized by their parallel outlines and the oval nuclei of their endothelial cells; they may be found in other preparations, for example in No. 9. No. 35. — Epithelium (Endothelium) of the Blpod-ressels. — Decapitate a rabbit, open the abdomen by a crucial cut made with the scissors ; insert under the mesentery a cork frame about 2 cm. square, span it smoothly over this and fasten it with quills or hedge-hog spines, taking care to touch the memlirane as little as possible with the fingers. Cut it off all around the frame and place the stretched membrane with the frame in 20 to 30 c.c. of i per cent, silver solution. In about 30 seconds the solution becomes turbid and milky ; remove the frame, carefully wash the membrane with distilled water, place the whole in a white capsule containing 100 c.c. of distilled water and expose it to direct sunlight. In a few minutes a brown coloration appears. Now transfer the whole to 50 c.c. of 70 per cent, alcohol (the membrane must be submerged in the alcohol) ; in a half-hour cut out small pieces, 5 to 10 mm. long, and mount them in damar. In the absence of sunlight, take the preparation from the silver solution, wash it; place it for about 20 hours in about 30 c.c. of 70 per cent, of alcoliol, then in a like quantity of 90 per cent, alcohol, and expose.it to sunlight on the first opportunity. It must not l)e forgotten that the whole blood-vessel and not a section of it is present, so that in order to obtain a view such as that in Fig. 46, the surface of the vessel must be in focus. 284 HISTOLOGY. No. 36. — Elastic Fenestrated Membranes. — See Techn. No. 13. ^'o- 37- — Development of Ca/'tllaries. — Chloroform a seven-days' -old rabbit, fasten it with pins on a cork-plate, open the abdomen by a crucial incision, quickly remove the spleen, stomach, and attached greater omentuui and place these parts in 80 c.c. of a saturated aqueous solution of picric acid (p. 20). In this solution the omentum, otherwise difficult to separate, spreads out easily. After i hour cut it off, transfer it to 60 c.c. of distilled water, and divide with the scissors into pieces about i cm. square. Place such a piece on a dry slide (remove the water with filter-paper) and with needles spread it out as smooth as possible, which is the more easily done, the less moisture there is present. Put i to 2 drops of Bohmer's hematoxylin on the preparation. In from I to 5 minutes drain off the hematoxylin and place the slide with the pre- paration in a flat dish containing distilled water ; the membrane will soon float from the slide, but will remain smooth, and in 5 minutes should be trans- ferred with the section-lifter to a watch-glass containing eosin (p. 23), in which It should remain 3 minutes. It should then be washed for i minute in distilled water and placed on a slide ; the water should be absorbed with filter-paper, any wrinkles smoothed out with needles, and a cover-glass with a drop of dilute gly- cerine suspended from its lower surface applied. The preparation may be mounted in daraar instead of glycerine (that is, dehydrated in absolute alcohol, cleared in oil of bergamot, and then mounted in damar), but the finer struc- tural details are apt to be lost. The colored blood-corpuscles are stained a bright red by the eosin (Fig. 50). In spreading out the membrane on the slide, delicate young capillaries may be easily torn loose from the older capillaries and then simulate " isolated cells containing blood-corpuscles ; " such artificial products have been described as " vasoformative cells. ' ' VII. THE BLOOD. No. 38. — Colored Blood-corpuscles of Man. — Carefully cleanse a slide and a small cover-glass (finally with alcohol). With a clean needle prick the tip of the finger, at the side ; with the cover-glass lightly touch the first drop of blood that exudes, and without the addition of any reagent place it imme- diately on the slide. With the high power many colored corpuscles adhering to one another by their broad surfaces, forming the so-called rouleaux, may be seen, as well as isolated colored and colorless blood-corpuscles. The distor- tion of many of the colored corpuscles is due to evaporation ; the corpuscles are beset with minute spines, a condition which is known as crenation. If a drop of water be placed at the edge of the cover-glass, the corpuscles soon become decolorized and the water acquires a yellowish tinge ; the corpuscles become spherical, have the appearance of pale circles, and finally disappear entirely. The student is advised to study the decolorization of a single corpuscle. In Fig. 51, 6, the tinged area surrounding the bleached corpuscles is somewhat too deeply shaded. No. 39. — Permanent preparations of colored cind colorless blood-corpuscles are made by Ehrlich's dry method. The method accurately carried out, after some practice, yields good results, but with unskilful manipulation many cari- catures arise and mislead the inexperienced. The employment of this method for purposes of investigation and discovery re.quires great skill and great caution in judgment. Preliminary Manipulations. — For each preparation two thin cover-glasses are required (they must not be over o.i mm. thick). Place them for a few SPECIAL TECHNIQUE. 285 minutes in dilute hydrochloric acid, then in distilled water, and finally in alcohol. It is best to take cover-glasses that have never been used. Prepare a mixture of equal parts of absolute alcohol and ether (about 5 c.c. of each). Cleanse the tip of the finger first with soap and water, and then with a tuft of clean cotton-wool moistened in the alcohol-ether mixture. With a clean needle (not previously used for anatomic purposes) prick the pad of the finger, made slightly hyjieremic by compression ; take up a cover-glass with the forceps (not with the fingers) press it lightly upon the blood that exudes, and place it on the second cover-glass, with one edge projecting slightly. The drop of blood will spread out in a thin film between the two glasses, which are then slipped apart by means of two forceps. By this manipulation the influence of the insensible perspiration on the blood -corpuscles is prevented, which otherwise would shrink or lose their hemoglobin. Exposed to the air, the blood on the cover-glasses dries in a few minutes : the glasses are then to be placed in the alcohol-ether mixture for fixation. In from ]l to 2 hours they should be removed, dried again in the air, when they are ready for further treatment, which may be applied immediately or later, since the preparations thus fixed may be preserved for a long time. a. O.xyphile {Eosinop/ii/f, a) Granules. — Place the cover-glass prepara- tion for 24 hours in about 4 c.c. of distilled water, to which about 10 drops of eosin solution have been added. Rinse i minute in distilled water and stain 1 to 5 minutes in a watch-glass with hemalum (p. 32). Transfer to distilled water ; remove in 5 minutes and let the preparation dry in air under a bell- glass. Mount in damar. The colored blood-corpuscles and the oxyphile granules of the colorless corpuscles are stained a bright red, the nuclei are blue. The oxyphile granules occur in the leucocytes of normal blood, of the Ivmph, and in the tissues, but are uncommon in normal blood. A magnifica- tion of 400 diameters is sufficient to find them. /'. Basophik Granules. — Two groups are distinguished, the ^-granules and the o-granules. The ygraniiles (Masfzellen Granulationen), which occur only in the leiicocytes of pathologic blood, are to be stained according to the method given in No. 6. When the staining is completed, proceed as in a. The blue- violet granules are coarser than the — en though here and there actual lymph-vessels may be thus filled, in most ca.ses the injection-mass is simply driven forcibly into the interfascicu- lar clefts of the connective tissue. From this the value of any decision with regard to " lyniph-ves.sels " and "lymph-spaces" thus exhibited may be inferred. No. 47. — Lymph-nodes. — For a general view the mesenteric glands of kittens are suitable. For fixation and hardening place them in 30 c.c. of abso- lute alcohol ; in three days thin sections can be readily made, and should be taken so that they pass through the hilus, which may be easily recognized macro- .scopically by an external depression. Longitudinal sections passing through the poles of the node are best, though transverse sections are also useful. Stain 6 to 8 sections in Bcihmer's hematoxylin for from 2 to 3 minutes, then in eosin, at the most i minute (p. 32, 3 /<), then transfer them to a test-tube half filled with distilled water and shake them for from 3 to 5 minutes. Pour the shaken sections into a flat dish ; the cortex and medulla can be distinguished macroscopically by the uniformly blue color of the former and the variegated appearance of the latter. Mount in damar. With the lower |)Ower fields similar to that in Fig. 55 may be seen in favorable places. The trahecuhne are but slightly developed. The adipose tissue adhering to the nodes must not be taken for reticular tissue. High magnification is of no advantage; the sharp outlines disappear and the picture loses in distinctness. No. 48. — Lymph-nodes of mature animals and of man are difficult to understand, because the entire cortex is transformed into a continuous mass sprinkled with irregular germinal centers. In shaking the sections the germinal centers are apt to fall out, and leave round spaces recognizable macroscopically. The lymph-sinuses can only be indistinctly made out. The mesenteric fol- 288 HISTOLOGY. Holes of the ox are well adapted for the representation of the network of the mcdiillaty cords and trabecula. Place pieces 2 cm. long in 200 c.c. of concen- trated aqueous picric-acid solution, and after 24 hours, with a sharp knife moist- ened with water, endeavor to cut thin sections. This is not so easily done as after alcohol fixation, but slightly thicker sections can be used. Place the sec- tions for one hour in 100 c.c. of distilled water, which must be changed fre- quently, then stain with Bohmer's hematoxylin and eosin and shake them (see No. 47). Mount in damar (p. 38). The trabeculse are red, the medullary cords blue ; with low magnification the appearance of the section is like Fig. 56 ; with high magnification the reticular connective tissue of the lymph-sin- uses can be seen ; the majority of the leucocytes occupying the meshes become loosened by tiie treatment with picric acid and lost in the shaking. No. 49. — Elements of the Spleen. — Make an incision through a fresh spleen ; with a scalpel obliquely applied scrape the cut sm-face and examine a little of the red mass adhering to the blade in a drop of salt solution. Use the high power. Often, especially in animals, only colored and colorless blood- corpuscles are found ; some of the latter contain minute granules. In human spleens, in addition to the numerous colored blood-corpuscles altered in form, en- dothelial cells of the blood-vessels maybe found : the latter were formerly called "spleen-fibers" (Fig. 58, 2, 3). In many human spleens, multinucleated cells and cells containing colored blood-corpuscles often cannot be found (Fig. 58, 4). No. 50. — The Spleen. — Without cutting it, fix the entire spleen in Mailer's fluid, using one liter for a human, 200 to 300 c.c. for a cat's spleen. After 2 weeks for the cat's, 5 weeks for the human spleen, wash for from i to 2 hours in, if possible, running water, cut out pieces 2 cm. square and harden them in 60 c.c. of gradually strengthened alcohol (p. 29). Sections not too thin are to be stained in Bohmer's hematoxylin and mounted in damar. If it is desired to stain the trabecule, after staining in hematoxylin is completed place the sections for y^ minute in eosin. In successful preparations the pulp and the Malpighian bodies are blue, the trabeculse rosy, the vessels, distended with blood- corpuscles, brown. If the staining in eosin be prolonged beyond 30 seconds the blood-corpuscles become brick-red, the trabecular dark red, and the distinc- tion between them is apt to be lost. The sections are most satisfactory when examined with a very low power (Fig. 57) ; with the high power the outlines are often indistinct. No. 51. — Reticular Connective-tissue of the Spleen. — Shake a thin sec- tion fixed and stained like No. 50 for about 5 minutes in a test-tube half filled with distilled water. Mount in glycerine. The leucocytes are difficult to dis- lodge ; the narrow-meshed network can only be seen at the edges of the preparation (Fig. 59). No. 52. — Karyoinitotie Figures in the Spleen and Lymph-nodes. — For this purpose small pieces (5 to 10 mm. long) of Tvarm living spleen and lymph-node should be fixed in chromo-aceto-osmic acid (p. 21), and hardened in alcohol. Stain thin sections in saffranin (p. 33). Mount in damar. The karyomitotic figures of mammals are so small that, with the usual magnification (560 diam- eters), they can only be found by the practiced microscopist. They may be recognized by their deep red color (Fig. 60). No. 53. — Blood-vessels of the Spleen may be obtained, incidentally, by injecting the stomach and intestine (compare with No. no). No. 54. Nei-t'cs of Spleen. — For this purpose the spleen of the mouse is best suited. Halve it, and apply Golgi's method for demonstration of the ele- SPECIAL TECHXIlJUE. 289 merits of the nervous system (p. 35). It is sometimes sufficient to place the object in the osmio-bichromate mixture (in a warm chamber) for 3 days and for the same length of time in the silver solution ; often a repetition of the whole process once or twice yields good results. IX. BONE. No. 55. — Dried Bone. — The bone must not be dried before maceration, but must be placed fresh for several months in water, which should be fre- quently changed. Then it is to be dried and a piece held between two pieces of cork or cloth clamped in a vice, and with a compass-saw sections i to 2 mm. thick, transverse or longitudinal, are to be cut. Secure a section with sealing- wax to the under surface of a cork -stopper, dip the whole for a moment in water and then file it, first with a coarse, then with a fine file, until it is perfectly smooth : the file must be dipped in water frequently, in order to wash off the adherent particles of bone and to prevent the heating of the sealing-wax by friction. The section of bone should then be loosened by heating the sealing-wax, and the smooth side stuck fast to the stopper. It must now be filed until it is so thin that the sealing-wax can be seen through it. The whole should then be placed in 90 per cent, alcohol, in which within a few minutes the section becomes loosened from the cork. Moisten a coarse whetstone with water, rub it with a second whet- stone until the surface is covered with a little grinding-paste ; lay the section in it, place a smooth cork upon it (one without cracks), and with a circular motion grind it on both sides ; it is not necessary to glue the section to the cork. The section when sufficiently thin is transparent ; this is to be ascer- tained by drying it between pieces of filter-paper and examining with the low power. It should then be ground on a fine whetstone, in the .same manner as on the coarse, and when both sides are smooth, dried with filter-pa|jer and polished. To do the latter, nail a piece of wa.sh-leather smoothly on a board, sprinkle it with chalk, and with the tip of the finger rub the section to and fro on it. In this way the previously dull section acquires shining sur- faces. The adherent powder may be removed by rubbing the section on fresh wash-leather. The finished section is to be placed dry on a slide and the cover-gla.ss secured by means of cement ( p. 38). Examine first with the low, then with the high power. (If the section is thick, it may be impossible to e.xamine it with the high power, since then the objective cannot be brought near enough to the preparation.) The bone lacunae and bone canaliculi are filled with air. and with the customary illumi- nation of the object from below aj^pear black (Fig. 28). No. 56. — Sharpcy' s I-il>eis. — Pre]»re a cross-section of the middle of the shaft of a tubular bone, preferably of a young individual, according to the method given in No. 55. Place the finished dry section for from 2 to 5 minutes in 4 c.c. of turpentine and then mount in dainar. The fibers, invisi- ble in the sections produced by other methods (No. 55 and 57), can be plainly seen, even with the low power ( Fig. 66). No. 57. — Haversian Canals and Lamellm. — Select the metacarpal bone of an adult ; after 4 weeks' fixation in Miiller's fluid, and hardening in alcohol, decalcify in nitric acid (p. 29), harden again, and cut transverse and longi- tudinal sections. The compact structure of larger bones (the femur, for ex- ample) require too much time (several weeks) for decalcification. The jieri- osteum should be allowed to remain on the bone. For longitudinal views of Haversian canals very thick sections (0.5 mm. and more) must be cut. •9 290 HISTOLOGY. Mount in dilute glycerine (Fig. 63). Neither are very thin sections neces- sary for transverse views and lamellar systems ; the lamellae are best seen if the section be examined in a drop of distilled water and the mirror turned so that the object is only half illuminated ; thus, too, the strife produced by the bone canaliculi, running vertical to the lamellae, are best seen (Fig. 64). Mount in dilute glycerine ; this, however, renders the lamellar systems par- tially indistinct. Not every part of the bone exhibits all the lamellar systems ; the outer and also the inner ground lamellae are frequently wanting. In sec- tions taken near the epiphyses the continuation of the compact substance into the trabeculae of the spongy bone may be seen. The bone lacunae and bone canaliculi are much less distinct in moist preparations than in dried ground sections, because the contained air has been displaced by the mounting medium. (Compare Fig. 28 and 29.) Not infreciuently the concentric lamellae of the Haversian systems are found to be interrupted by an irregular line. Up to this line the osseous tis- sue previously formed has been again resorbed. All that which lies within the line is newly-deposited bone-substance. These formations are, therefore, partially filled Haversian spaces (Fig. 64, h). o ® 9 ^ : 262.— Isolated Elements o V Fresh Bonf-marrow FROM A Vertebra of Calf. X 560. 1. In salt solution. 2- Stained wiih picrc .carmine. 3. After treatm ent with acidulaied glyct :rine. k. Marrow-ceils; >f, two marrow-cells containing m a'^ses of pigment-granules ,. the cell on the right se en from the Mde. the cell on the lefi, from the surface ; 6, no nnucleated colored blood-( lorpuscles ; r, giant-cells ; in the one oiil he right the niiclr-u. F"or specimens of the cortex, treat pieces of the brain of an 8- to 30- days'-old mouse with the Golgi mixture for from 2 to 3 days, or of a i- to 15- days'-old rabbit, or a kitten under 6 weeks old, for 5 days. Pieces of the brain of adults must remain in the Golgi mixture S to 15 days. Further treat- ment like No. 70. No. 74. — The Cortex 0/ the CereMli/m ; Golgi Staining. — Remove the cerebellum from the cranium of a newborn guinea-pig (or a kitten less than 6 weeks old) and treat it according to the method given in No. 70. The staining of the elements of the cerebellum is more difficult to accomplish than of the cerebrum and the spinal cord. Failures are frequent. The sections shotild he princijwlly made vertically to the axis of the convolutions. (For embedding, see Microtome Technique.) -^'^- 75- — Hypophysis Cerebri. — Treat like No. 80. No. 76. — Brain-sand, AeerTiiliis Cerebri. — Tease the epiphysis in a drop 296 HISTOLOGY. of salt solution. If much brain-sand is present, a gritty sound will be heard on teasing and the larger concretions can be perceived by the unaided' eye. Ex- amine with the low power, without a cover-glass (Fig. 99). Often the irregularity of the surface is indistinct. Push aside the larger granules with a needle, cover a few of the smaller ones with a cover-glass and treat with 2 to 3 drops of hydrochloric acid (p. 20). Bubbles of gas develop and the sharp outlines of the granules disappear. No. 11.— Corpora Amylacea. — Select the brains of elderly individuals. With a scalpel scrape the mesial surface of the optic thalamus — that directed toward the third ventricle — and spread the scrapings with a needle in a drop of salt solution ; apply a cover-glass. The corpuscles when present are easily found, and are recognized by their bluish-green color and their stratification (Fig. 100, a). They should not be confused with drops of extruded myelin (/'), which are always clear and have a double contour. In addition there may be found in such preparations numerous red blood-corpuscles, ependymal cells (;/), medullated nerve-fibers varying in thickness, and ganglion-cells; the latter are very pale and often can only be detected by their pigmentation (y). Human brains, even though not absolutely fresh, can still be used. ^ J ERiPHERAL (Spinal) Nbrve OF Rabp.it. X 50. In the srse sections of nerve-fibers have fallen out. others are lying endoneurium is but slightly developed in the rabbit. No. 78. — Spread out a piece i cm. long of the choroid plexus in a drop of salt solution and apply a cover-glass. The convoluted red blood-vessels and the epithelium of the plexus can be seen. No. 79. — Transverse Sections of Neroe-Ji/'er Bundles. — Treat a piece of nerve, if possible the sciatic of man, which possesses a well-developed endo- neurium, according to the method given in No. 30. Place it for 6 days in a 0.1 per cent, solution of chromic acid, then wash it for from 3 to 4 hours in running water, and harden it in gradually strengthened alcohol. When the hardening is completed, cut thin sections with a sharp razor. It is advisable to embed the tissue in liver ; better still, in elder pith, or in the pith of the sun- flower. For this purpose, make a hole in the dry elder jiith with a needle, and then carefully insert the nerve. Place the whole for about a half-hour in water ; the pith swells and firmly grasps the nerve. Stain the sections in picrocar- mine, and mount in glycerine. The length of time required for staining varies greatly. The sections must be very carefully handled and pressure with the SPECIAL TECHNIQUE. 297 cover-glass must be scrupulously avoided, lest the sections of the fibers, which are not disks but short cylinders, be turned on their sides, and not a fiber in section be seen. If successful, the section will show a somewhat shrunken axis-cylinder, resembling a red nucleus, surrounded by the yellow medulla, enclosed by the reddish neurilemma. The cross-section of the nerve-fiber has been compared to a picture of the sun {SonnenbilJchenfigidr) (Fig. 102 j. No. 80. — Spinal Ganglia. — These are difficult to obtain. Therefore re- move the Gasserian ganglion from the depression in which it is lodged (on the anterior surface of the ])etrous jwrtion of the temjjoral boiiej, and place it in about 100 c.c. of Miiller's fluid for fixation. .After 4 weeks wash it for 3 hours in running water, and harden it in 50 c.c. of gradually strengthened alcohol (p. 29). Cut the thinnest possible transverse and longitudinal sec- tions ; stain them 30 seconds in hematoxylin, and then 2 to 5 minutes in eosin (]). 32, 3 F), and mount in damar. The ganglion-cells are pale red ; the axis- cylinder deep red : the medullary sheath brownish ; the nuclei blue ( Fig. 103). If the section is not sufficiently thin, the large number of deeply-stained nuclei will render it difficult to see the other stnictures. For this reason it is better to stain thick sections in picrocarmine, 2 to 3 days, and mount them in damar. The nuclei are then not so intensely stained. Occasionally the protoplasm of the ganglion-cell contracts, and thus acquires a stellate outline (Pig. 103 x), which the beginner may easily confiise with a multipolar ganglion-cell. Fixa- tion in Kleinenberg's picrosulphuric acid gives very good results. T-shaped branches may be seen in preparations of thes|)inal cord treated as in No. 70. In young embryo chicks the s|)inal ganglion-cells are still bipolar. Unipolar cells are found in embryo chicks about i 7 days old ; transition forms between the 9th and 14th days, and in embryo rabbits 5 to 12 cm. long. Xo. 81. — Sympathetic Ganj^/ia. — Fix and harden the large superior cervi- cal ganglion of the sympathetic nerve like Xo. 80. Here, too, on account of the abundance of nuclei, nuclear staining is ap]jlicable only to very thin sec- tions. Treated according to the method given in Xo. 80, the processes of the multijiolar ganglion-cells are not rendered distinct. For this purpose place the thinnest jjossible sections for 24 hours in 5 c.c. of nigrosin solution (pre- pared like the methyl-violet solution, p. 23 ) ; then transfer them to 5 c.c. of absolute alcohol for 5 minutes, and preserve in damar. The characteristic bundles of nonmedullated nerve-fibers, cut oblicjuely and transversely, can be recognized with the low power; also the ganglion-cells; but to see their pro- cesses high magnification and careful scrutiny are necessary. In many sec- tions the ])roce.sses of the ganglion-cells cannot be seen ; the latter may be best exhibited according to the method given in No. 70, and a suitable object is the cervical portion of a 10- to i5-days'-old embryo chick. No. 82. — Simple Tactile-cells; Intra-epitlielial Nei~'e-fibers ; Cells of Langerhans ; Tactile Corpuscles. — Prepare a mixture of gold chloride and formic acid ('p. 37), boil it and let it cool ; then cut from the volar side of a freshly-amputated finger or toe (with scissors a])piied flatwise) several small |)ieces of the e])idermis and uppermost layers of the corium, about 5 mm. long and i mm. broad. Carefully remove any fat attached to the under surface of the corium and place the |)ieces in the gold and formic acid mixture for i hour, /// the dark. Then, with glass rods, transfer the pieces to 10 c.c. of distilled water and in a few minutes to fresh distilled water to which formic acid has been added, and expose the whole to daylight (sun- light is unnecessary). In 24 to 48 hours the tissue becomes dark violet. It 290 HISTOLOGY. is now to be hardened in 30 c.c. of gradually strengthened alcohol. In 8 days the pieces may be embedded in liver and sectioned ; mount in damar. The epi- dermis is red-violet in different tints ; the nuclei are only to be seen in places and often are not perceptible ; the corium is white ; the capillaries, the excre- tory ducts of the coil-glands, and the nerves are dark violet to black. For tactile-cells the thinnest possible sections are necessary. They may often be found near the excretory ducts of the coil-glands. Care must be taken not to confuse them with shrunken epithelial cells (Fig. 106). The intra-cpltlielial nerve-fibers appear as delicate filaments ; their connec- tion with the nerve-fibers in the corium is difficult to trace. Processes of the cells of Langerhans, in thin sections, are apt to be confused with the intra- epithelial nerve-fibers (Fig. 105). The cells of Langerhans and the tactile corpuscles may be easily seen ; in thick sections the tactile corpuscles are black (Fig. 105), in thin sections red- violet (Fig. no). No. 83. — Compound Tactile-cells. — Cut the yellowish wax-like skin, or cere, from the lateral edges of the upper beak of a duck or goose and treat pieces i to 2 mm. thick and i cm. long with 3 c.c. of 2 per cent, osmic-acid solution plus 3 c.c. of distilled water; place the whole in the dark 18 to 24 hours ; then wash the pieces for i hour in running water and transfer them to 20 c.c. of 90 per cent, alcohol. In 6 hours the objects maybe sectioned. Embed them in liver and make the sections from the corium toward the epithelium, not the reverse. The sections may be mounted unstained in damar. The olive- green tactile-cells may be readily seen, but the entrance of the nerve- fiber is difficult to find (Fig. 107). In addition, Herbst's corpuscles occur in the sections. If it is desired to stain the sections, use a nuclear staining solution (P- 31)- No. 84. — Cylindrical End-bulbs. — ^With scissors and forceps cut out pieces I cm. square of the scleral conjunctiva near the corneal margin of the fresh eye of a calf, taking care not to roll them. It is better to let them lie smooth on the sclera. Carefully slip the pieces, epithelial side up, from the sclera on to a cork-plate, and span them out with needles. Moisten the surface with a {i\i drops of the vitreous humor obtained from the eye ; with scissors and forceps dissect off a thin layer consisting of connective tissue and the epithelium resting upon it. This operation must be done with great care ; folding and torsion of the membrane must as far as possible be avoided. The pieces, with the epithelial side up, should now be slipped on to a dry slide and spread out flat. At first they draw together, but in a moment or two the edges dry some- what and adhere to the glass, and they can then be extended without much dif- ficulty. The slide with the preparation is next to be placed in a glass jar contain- ing 65 c.c. of distilled water to which 2 c.c. of acetic acid have been added. In about an hour (or later), during which time the pieces swell considerably and float from the slide, with a clean needle endeavor to remove the epithe- lium ; it may be loosened without much trouble and floats off in fine white shreds. If this is not done cautiously the end-bulbs lying close beneath the epithelium mav be torn off with it. After the pieces have lain 4 to 5 hours in dilute acetic acid transfer them with a few drops of the same fluid to a slide, apply a cover- glass and make slight pressure upon it with the outspread branches of the forceps. On examination with the low power the blood-vessels may be distinctly seen — they may be recognized by their prominent nuclei — and also the medullated nerve-fibers. Trace such a fiber until the medulla ceases ; examine such places with the high power, for there the end-bulbs are most apt to be found. In most SPECIAL TF.CHNIQUE. 299 cases nothing will be seen but the numerous nuclei, and even when a favorable situation is found the end-bulbs are so pale that it is very difficult to perceive them ; the axis-cylinder, too, is often very difficult to see. Only the practised microscopist will have much success in finding them. Beginners are advised not to attempt this jireparation. Xo. 85. — Corpuscles of Valcr. — These are best obtained from the mes- entery of a cat, where they may be seen with the unaided eye. They appear as milky, glass-like, transparent oval spots between the strands of adipose tis.sue of the mesentery. Their number varies greatly. Occasionally they are very scarce and of such small size that to find them requires close searching. Cut out the portion of the mesentery containing the corpuscles, and spread them out in a drop of salt solution on a slide lying on a black background. Endeavor to remove the attached clusters of fat-cells, taking care not to prick the corpuscles. Ascertain with a low power, without a cover-glass, whether the corpuscles have been sufficiently isolated. Cover them with another drop of .salt solution and a cover-gla.ss. Pressure must be carefully avoided. The corpuscle rejiresented in Fig. 109 was of very small size. With the high power one can distinctly see the nuclei of the cells lining the capsules ; on the other hand, the oval nuclei of the inner bulb are often indistinct and pale. If it is desired to ]>reserve the preparation, treat it under the cover-glass with i to 2 drops of I per cent, osmic acid and, after the medulla is blackened and the inner- bulb has become brown, displace the acid with very dilute glycerine. Methylene- blue staining (p. 34) is recommended. No. 86. — Afotor Nen'c-cniii>i};s — a. Terminal Ramifications. — Prepare a mi.vture of 24 c.c. of i per cent, gold chloride solution plus 6 c.c. of formic acid, boil it and let it cool ; cut out small pieces, 3 to 4 cm. long, of the intercostal muscles of a rabbit, and treat them like No. 82 ; after the dark-violet pieces have lain 3 to 6 days in 70 per cent, alcohol, tease a muscle-bundle about 5 mm. broad in a drop of dilute glycerine to which a very small drop of formic acid has been added. It is of advantage to make slight pressure on the cover-glass. To find the terminal ramifications, trace with the low power the easily recognized black nerve-fibers (Fig. 1 1 1 ). The addition of another drop of acetic or formic acid often renders the elements more distinct. h. iViielei of the. Motor-plates. — Place the anterior halves of the eye-muscles of a recently-killed rabbit in 97 c.c. of distilled water plus 3 c.c. of acetic acid. After 6 hours transfer the muscles to distilled water ; with the scissors cut a thin flat piece and spread it out on a slide; the ramifications of the whitish nerves can be plainly seen with the unaided eye. With low magnifica- tion (50 diameters), the anastomoses of the nerve-bundles, as well as the blood-vessels (easily recognized by the transversely-jjlaced nuclei of their smooth muscle-fibers) can be seen. On account of the large number of sharplv-contoured nuclei belonging to the muscles and the intramuscular con- nective tissue, the end-plates are not easy to find. If a nerve-fiber be traced it will soon be seen that the double-contoured medullary-sheath cea.ses abruptly and loses itself in a grouj) of nuclei ; these are the nuclei of the motor-plate, whose other details are not distinctly visible. The cross-striation of the muscle- fibers, which are very pale, is often indistinct (Fig. 112). Xo. 87. — The Suprarenal Bodies ; General Vie70. — Fi.K the entire su|jra- renal body of a child in 200 c.c. of o.i per cent, chromic acid, and after 8 days harden it in 150 c.c. of gradually strengthened alcohol ; mount unstained sections in dilute glycerine (Fig. 113 A\ 300 HISTOLOGY. No. 88. — Elements of the Suprareiiat Body. — Tease portions of the fresh organ in a drop of salt solution. The elements are very delicate and in- jured cells are therefore of frequent occurrence. No. 89. — For the study of the minute structure of the suprarenal bodies, place 2 cm. cubes of the fresh organs in 100 c.c. of Kleinenberg's picrosul- phuric acid, and after 12 to 24 hours in an equal quantity of gradually strengthened alcohol ; cut fine sections, stain them in Bohmer's hematoxylin and mount in damar (Fig. 113 B). XII. THE DIGESTIVE TRACT. No. 90. — Isolated Squamous Cells from the Oral Cavity. — -With a scalpel gently scrape the upper surface of the tongue and mix the scrapings with a drop of salt solution on a slide ; apply a cover-glass ; in addition to isolated, pale, squamous epithelial cells, leucocytes (" salivary corpuscles ") maybe found; also, with more vigorous scraping, the torn apices of filiform papillae, which not infrequently are surrounded by finely granular, dark masses of micrococci to which tufts of leptothrix buccalis are attached. The preparation may be stained under the cover-glass with picrocarmine and then treated with dilute acidulated glycerine, provided too many air-bubbles do not make the preserva- tion of the preparation impossible (Fig. 6, i). No. 91. — Mucous Glands of the Lips. — These are millet-sized nodules macroscopically perceptible to touch and sight. For microscopic preparations cut from the mucous membrane of a human lower lip (not the margin of the lip) I cm. cubes; fix them in 50 c.c. of Kleinenberg's picrosulphuric acid and in 24 hours harden in 50 c.c. of gradually strengthened alcohol. In 3 days the tissue may be sectioned. C\it many sections, not too thin, and stain them with Bohmer's hematoxylin ; place the sections in water, and with the naked eye select those which include the excretory duct and preserve them in damar ; examine with a low power (Fig. 114). No. 92. — Dried Tooth. — To prepare dried ground sections of teeth they should be obtained immediately after they are extracted, sawed into transverse disks 2 mm. thick, and glued with sealing-wax upon cork and treated like No. 55. If longitudinal sections are desired the entire tooth should be glued to the cork. Longitudinal sections are to be i)referred, since thev show all parts of the tooth in a single preparation. If it is desired to decalcify the teeth of an adult, treat like No. 57. The enamel contains only 3 to 5 per cent, of organic substances and dissolves completely, so that only the dentine and cementum remain (Fig. 115, 116, 117). No. 93. — Odontoblasts. — Remove the teeth from the jaws of a newborn child ; place them in 60 c.c. of Miiller's fluid ; after 6 days the pulp can be easily withdrawn in toto by means of forceps. With the scissors cut from the upper surface of the pulp a piece the size of a lentil, and tease it a little in a drop of Miiller's fluid ; it is moderately tenacious; apply a cover-glass, press lightly upon it, and examine with the high power. At the edges of the pre- paration the long processes of the odontoblasts will be seen ; also scattered completely isolated odontoblasts (Fig. 119). In order to preserve, treat under the cover-glass with distilled water for 2 minutes, then with picrocarmine ; when the staining is completed, add dilute acidulated glycerine. No. 94. — Enamel Prisms. — These may be obtained by teasing portions of the lateral surface of the teeth of No. 93 in a drop of Miiller's fluid. Examine SPECIAL TECHXIQUK. 30I with a high power. The enamel prisms will be found in groups of 3 and 4 and are distinguished by their dark outlines and usually indistinct cross-striation (Fig. ii8j. Mount in glycerine. The prismatic form of the enamel i)risms may be seen in thin sections cut parallel to the surface of the teeth. Only portions of a section exhibit regular hexagonal prisms, that is, cross-sections of the prisms (Fig. 118). The enamel of younger teeth may be sectioned without previous decalcification. No. 95. — Development of Teeth. — For the study of the early stages select pig and shee[) embryos ; these are the most easily obtained at the slaughter houses ; for the first stages the pig embryos should have a size of about 6 cm., for the second stage a size of about 10 to 11 cm. For later stages the inferior maxilla of newborn dogs or cats are very suitable. Place the heads (or the lower jaws) in 100 c.c. of Kleinenberg's picrosulphuric acid, 12 to 24 hours, and harden in 80 to 120 c.c. of gradually strengthened alcohol. After the heads have lain 6 to 8 days in 90 per cent, alcohol, they are to be decalcified in 100 c.c. of distilled water plus i or 2 c.c. of nitric acid. When the de- calcification is completed, in 3 to 8 days, harden again in alcohol. In 5 to 6 days cut off the lower jaw and divide it in front in the middle (larger jaws should be cut vertically into pieces i to 2 cm. long) ; stain the pieces in bulk in borax-carmine. When the staining and decolorization are completed, the tissue is to be transferred to absolute alcohol, in which it must remain for sev- eral days ; it is then to be embedded in liver and sectioned. It is necessary to cut many (20 to 40) thick sections, since only those which pass through the middle of the tooth, or the anlage of the tooth, can be used. Blount in damar. Not infrequently in sectioning the enamel organ separates from the papilla, so that a free space exists between the two. The dentine is often stained in dif- ferent tones of red ; this is due to the different ages of the calcified and uncal- cified strata of the dentine. The objects may also be fixed in Miiller's fluid ; section-staining in hematoxylin is not advisable, since too many sections must be stained which on investigation are found to be useless. No. 96. — Papill(Z Fillformes, Fiingiformes, Circiimvallata: ; Follicles of the Tongue. — Cut pieces 2 cm. square from the mucous membrane of the surface of a human tongue. Each piece should have some of the muscle tissue at- tached to its lower surface; for fungiform papillte cut the piece from the tip of the tongue; for filiform, from the middle of the dorsum of the tongue; for circumvallate, from the root of the tongue, and for follicles (the puncti- form openings of which can be seen with the naked eye) from the root of the tongue, and place them in 100 to 200 c.c. of Miiller's fluid. The fluid must be changed several times ; after 2 weeks wash the tissue and harden it in 50 c.c. of gradually strengthened alcohol. For filiform papillce cut thick sag- gital sections of the tongue and do not stain them ; stain the other sections in Bohmer's hematoxylin and mount in damar (Fig. 125, 126, 127). For the preparations represented in Fig. 12S and Fig. 130 the tissue was fixed and hardened in 50 c.c. of absolute alcohol. Rabbits' tongues may be placed in toto in 200 c.c. of Miiller's fluid; the subsequent treatment is the same. Thick cross-sections through the anterior half of the entire tongue are suitable for the study of the arrangement of the muscles of the tongue. Thin sections of the root of the tongue show beautiful mucous and serous glands. No. 97. — The Tonsils. — The tonsils of adult man do not furnish instruc- tive preparations. They should be treated like No. 96. The tonsils of the rabbit and the cat are to be recommended ; to find these proceed as follows : — Dissect the skin from the anterior surface of the neck and remove 302 HISTOLOGY. the structures lying over the trachea and esophagus ; with a pair of stout scissors cut through both tubes above the sternum, grasp the cut ends with for- ceps, and with scissors dissect them up to the head of the pharynx, keeping close to the anterior surface of the vertebral column (at the same time the cornua of the hyoid bone will be divided). Cut through the musculature close to the median edges of the inferior maxilla, and also through the ligaments of the tongue (glosso-epiglottic). (In the rabbit it is advisable to divide both angles of the mouth, and with scissors introduced within the slit to sever the ligaments and the genio-hyoglossus muscle.) Draw the trachea and attached structures downward, press the tongue down between the rami of the inferior maxilla, and divide its remaining attachments (to the palate) close to the bone. Put the tongue down with its free surface looking upward. With delicate scissors divide the posterior wall of the pharynx in the median line down to the larynx and pull the walls apart ; the tonsils will then be seen as a pair of oval prominences, about 5 mm. long, on the lateral walls of the phar- ynx. They may be fixed in 60 c.c. of Kleinenberg's picrosulphuric acid (p. 28), and hardened in 50 c.c. of gradually strengthened alcohols (p. 29), stained with hematoxylin or with eosin and hematoxylin (p. 31), and mounted in damar. No. 98. — The Esophagus. — Pieces of human esophagus 2 cm. square and of that of the rabbit and cat 2 cm. long of the entire tube are to be fixed in 60 c.c. of Miiller's fluid and in 2 weeks hardened in 50 c.c. of gradually strengthened alcohol; stain with Bohmer's hematoxylin; mount in damar (Fig. 131). No. 99. — The Mucous Membrane of the Stomach. — For topographical preparations place pieces 2 to 5 cm. square for 6 hours in 100 c.c. of 3 per cent, nitric acid. Remove the gastric contents adhering to the mucous membrane by moving it slowly to and fro in the acid. In a half hour renew the acid, and harden in 60 c.c. of gradually strengthened alcohol. Mount thick unstained sections in damar (Fig. 132). No. 100. — Fresh Gastric Glands. — From the fundus of the stomach of a rabbit just killed cut pieces about 2 cm. square and separate the loosely- attached muscular coat from the mucous membrane. Grasp the latter with for- ceps at the left edge and with fine scissors cut very thin strips, 0.5 to 1 mm. thick; tease them in a drop of 0.5 salt solution. The body and fundus of the fundus glands can be satisfactorily isolated without much trouble. The bodies of the parietal-cells may be distinctly seen (Fig. 265, B), the chief-cells are not visible. The nuclei may be stained with picrocarmine and the prepa- ration mounted in dilute glycerine. The isolation of the pylorus glands can only be accomplished by very careful teasing. No. loi. — Isolated Gastric Epithelium. — Place pieces i cm. square of gastric mucous membrane for about 5 hours in 30 c.c. of Ranvier's alcohol (see further p. 26 a). In the majority of the cells the mucous portion occupies a large division, and they have the appearance of those pictured in Fig. -12 c. The preparation may be stained under the cover-glass with picrocarmine, and mounted in diluted acidulated glycerine. No. 102. — Gastric Glands. — -The stomach of a cat or dog that if possi- ble has been fasting for one or two days is especially to be recommended. The stomach of the rabbit, on account of the very small size of the chief-cells, is less suitable. Dissect off the mucous membrane from the muscular coat and place pieces of the former about i cm. square in about 10 c.c. of absolute SPECIAL TECHNIQUE. 303 alcohol. In about a half-hour transfer them to 20 c.c. of fresh alcohol. The outlines of the glands can be recognized in moderately thin sections ; the only difficulty is the circumstance that the gland-tubules are placed very close together. The beginner may not recognize the glands and may mistake for them the gastric pits lined with clear epithelium. The stomach of man, which however is suitable for use only for a few hours after death, exhibits this diffi- culty in a less degree. For the study of the minute structure of the glands and of the superficial eijithelium, embed the tissue in liver and cut the thinnest pos- sible sections. a. For fundus glands, chief- and parit-tal-cflls, cut vertical or better hori- zontal sections of the mucous membrane and stain them with Bohmer's hema- toxylin, 2 to 4 minutes. Wash the sections thoroughly in 30 c.c. of distilled water, which must be changed as often as it becomes bluish — about once or twice. Transfer them to 5 c.c. of a ^^ per cent, solution of Congo red (p. 23), 3 to 6 minutes, wash 2 minutes in distilled water, and mount in damar. If the sections are too thick, everything appears red; the large red parietal- cells cover the smaller chief-cells ; e.xamine the thinnest parts of the sections, especially the fundi of the glands, where the parietal-cells are not so exceedingly profuse. l fiy\_£ The parietal-cells can be recognized with the low power ^'-^'Y as isolated red spots on a rosy-red ground. With the r" ' high power the pale blue smaller chief-cells can be '' seen. The very narrow lumen of the fundus glands may be best seen in cross-sections of the follicle (sections parallel to the surface of the mucosa). The lateral twigs of the chief lumen can only be perceived in very favorable sections (Fig. 134). Fig. 133 is a com- bination of several thin longitudinal sections. b. For pylonis glands, stain vertical and horizontal sections of the mucosa with Bohmer's hematoxylin and mount in damar. The lumen of the pyloric glands is wider (Fig. 136). ^t^ No. 103. — Brunner s Glands. — Cut out the stomach and duodenum of a cat about i hour after death. Open both along their length, remove the con- tents by swaying them gently to and fro in salt solution (p. 19), and place the pyloric end of the stomach and the upper half of the duodenum, that is, in all a piece 5 to 6 cm. long, for 6 hours in 100 c.c. 3 per cent, nitric acid. Further treatment like No. 99. Cut longitudinal sections, which pass simultaneously through the pylorus and duodenum. Stain with Bohmer's hematox\lin. Mount in glycerine or in damar (Fig. 136). If the tissue be placed in the acid immediately after death the smooth muscle of the intestine contracts so that a rigid curving of the intestinal wall takes place. No. 104. — Epilhclium and Villi of the Small Intestine. — From the small intestine of a rabbit just killed, cut a jiiece i cm. long, open it along its length and remove the contents by carefully pouring over it i/^ per cent, salt solution. Then grasp the piece at the left edge with the forceps, with fine scissors cut off a small strip, and spread it out in a drop of salt solution on a slide on a black background. With the unaided eye one can see the villi projecting froni the edge of the preparation. Examine the preparation without a cover-f;lass, with the low power. The villi will be seen partly extended, partly contracted ; Fic. 265.- -LOWBR Half OP AN clii Iso !" B ef-ccll OF Ra) Haricl:.: hUNUUS- BBir. X l-ccll; M, 304 HISTOLOGY. the latter condition may be recognized by transverse folds running across the villi (Fig. 266). Details cannot be detected. Apply a cover-glass; the villi thus become flattened and appear clearer; the cylindrical epithelium, and close beneath this the loops of the capillary blood-vessels, can be distinctly seen. If the epithelium contains goblet-cells, these appear as bright shining rounded spots. For the investigation of the epithelium, proceed as follows : — a. Tease the piece a little ; in this way columnar cells, singly and in groups, may be isolated, which are to be examined with the high power. Not infrequently a few columnar cells are found inflated and of a spherical form. The basal border sometimes shows very distinct rods. Goblet-cells, when present, may be recognized by their homogeneous appearance, and if carefully focused the sharply-outlined orifice may be perceived. Occasionally the epithelial cells are difficult to loosen from the basement-membrane ; in such cases make a sec- ond investigation an hour later, when the epithelium will be suificiently macer- ated to be brushed off. /'. F"or permanent preparations place pieces ( i cm. square) of the intes- tine in 30 c.c. of Miiller's fluid. In 3 to 5 days take the tissue out, scrape it with the tip of a scalpel, and distribute a little of the scraping in a drop of diluted glycerine ; cover-glass; high power (Fig. 139, K). No. lot;. — Secfioiis of the Small Intestine. — Place pieces 2 to 4 cm. long of the intestine of a rabbit, better, of a puppy or a kitten, in 100 to 200 c.c. of 3 per cent, nitric acid. After 6 hours the pieces are to be hardened in 100 c.c. of gradually strengthened alcohol. Sections can be made through the entire in- testinal tube ; in most cases, only fragments of the villi are thus obtained ; to obtain entire villi cut ojien the hardened intestine along its length with a razor, pin it with needles on a cork-plate, with the mucosa upper- most. The villi can then be seen with the unaided eye. Cut thick cross-sections, stain them for one. minute with Bohmer's hemato.xylin, and mount in daraar. Goblet-cells are very frequently found in the epithelium (Fig. 139, B). Staining in bulk with borax-carmine is to be strongly recommended. The human intestine, before being placed in the nitric acid, must be cut open and washed in the same fluid. It is advisable to pin pieces about 5 cm. square to a cork-plate and thus to place them in the fixing and hardening fluids. If the intestine is not absolutely fresh, the entire superficial epithelium loosens so that the naked connective-tissue villi lie exposed. Horizontal sections of the intestine furnish very beautiful pictures. Not infrequently the cross-sections of the glands drop out and then only the con- nective-tissue tunica propria remains. In these preparations the goblet-cells all appear as clear bodies of equal size, and therefore afford no clue in regard to the functional condition of the cell. For the latter purpose the following is to be recommended :— No. 106. — -Triple Staining of the Intestine. — Small pieces of tissue are to be fixed in Flemming's mixture (p. 21), hardened in gradually strengthened alcohol, and subsequently treated according to the method given on p. 34, 10. No. 107. — The Patches of Fever. — These can be seen shimmering through the uninjured fresh intestinal wall of the rabbit, but in the dog and in the cat they are often (on account of the thickness of the muscular coat) not at all perceptible. In the latter animals patches are constant at the point SPECIAL lECHNIuLE. 305 where the small intestine opens into the large. Cut out the portion of the intestine of a rabbit containing the Peyer's patches and proceed according to the method given in No. 105. In the cat take the lowermost portion of the ileum (about 2 cm. long) with a piece of the cecum of the same length ; open both along their length and span them out on a cork-plate, with the muco.sa uppermost. Usually the mucosa is covered with a tenaceous excrement, dif- ficult to remove by washing, and which glues the villi together, so that only oblique sections of the villi can be obtained. Further treatment like No. 105. Closely-placed nodules are found in the blind half of the vermiform pro- cess of the rabbit, which encroach upon the muco.sa and compress it to such narrow areas that cross-sections exhibit very complicated pictures, scarcely in- telligible to the beginner. Fi.xation in o.i per cent, chromic acid and hardening in gradually strengthening alcohols renders the germinal centers very distinct, but is not so good for the remaining elements as the nitric acid. No. 108. — The Large Intestine. — Treat empty pieces like No. 105 or 106 (compare with Fig. 13, p. 59). Pieces filled with feces must be cut open, washed, and spanned on cork. No. 109. — Fresh Crypts of the Large Intestine (yf the Rahhit. — Cut a piece I cm. long from the lowermost portion of the large intestine (between two s])herical masses of feces ) place it on a dry slide, open it with the scissors, and spread it out with the mucous surface uppermost ; add a drop of J4^ per cent, salt solution, grasp the piece with for- ceps at the left edge, and with fine scissors cut off an extremely thin strip. Transfer this with a drop of the salt solution to another slide ; with needles se])arate the muscularis from the mucosa and tease the latter a very little; apply a cover-glass with slight pressure. \\'ith a low power the follicles of the crypts can be readily seen, but it is difficult to detect their orifices ( F"ig. 267). The epithelial cells are often granular in the '"ryptJ of''Lieberkah " ' x portion bordering the lumen. With the high power the ^°- superficial eiiithelium can be very well seen from the side and from the surface. The contents of the goblet-cells are often not clear, as in sections, but dark and granular. No. no. — Bloihi-vessels of the Stomaeh anJ the Intestines. — A stomach and intestine injected from the descending aorta, are to be fi.xed in 50 to 200 c.c. of Miiller's fluid and hardened in gradually strengthened alcohols. One portion should be cut into thick (up to i mm.) sections, stained, and mounted in daniar (Fig. 144), and another part used for horizontal preparations, which with the low power and change of focus are very instructive. For this purpose pieces of the large intestine, i cm. square, may be transferred from absolute alcohol to 5 c.c. of turpentine for clearing, and mounted in damar. It is easy to strip the muscularis from the mucosa and to mount the separate coats in damar. No. III. — Aiierbach' s and Meissnei' s Ple.xtis. — For this purpose the intes- tine of the rabbit and guinea-pig (not of the cat) are especially suitable. It is not necessary that the object be absolutely fresh ; the small intestines of chil- dren several days after death can still be used. Prepare 200 c.c. of a dilute solution of acetic acid (10 drops of glacial acetic acid to 200 c.c. of distilled water). Then separate a piece (10 to 30 cm. long) of the small intestine from the mesentery. Cut it open and brush out the contents lightly with the finger ; 3o6 HISTOLOGY. tie the lower end of the intestine and fill it from the upper end with the diluted acetic acid ; tie it above and place the whole piece in the remainder of the acetic acid. In i hour change the fluid. In 24 hours transfer the intes- tine to distilled water, with scissors open it along one side of the line of attach- ment of the mesentery, and cut off a piece 1 cm. long. The muscularis can be readily separated from the mucosa with the aid of forceps ; they are only firmly united at the line of attachment of the mesentery. a. AuerbacJi s Plexus. — If a piece of black paper be placed under the glass dish containing the tissue, the white nodal points of Auerbach's plexus can be seen by the unaided eye. Transfer a piece of the muscularis, about i cm. square, in a drop of the diluted acetic acid to a slide ; examined with the low power it furnishes a very pretty picture (Fig. 145, A). If it is desired to preserve the preparation, place the tissue for i hour in 30 c.c. of distilled water, which must be changed several times, and then for from 8 to 16 hours in 5 to 10 c.c. of a i per cent, osmic acid solution, in /he dark ; wash the piece quickly in distilled water and mount in diluted glycerine. The osmium preparations are not as beautiful as the fresh ones in the acetic acid. In the guinea-pig both strata of the muscularis can be readily separated (if the intestine is absolutely fresh on being filled with the dilute acid) : the plexus remains attached to one stratum. Pieces of this should be placed for i hour in distilled water, then treated with gold chloride (p. 37), and mounted in damar. The gold-chloride treatment is less adapted to human intestines, since both the muscular layers are likewise stained red and partially conceal the plexus. The firm union of the muscular strata in the human organ may be due to the age of the object. b. Afeissner's Plexus. — With a scalpel scrape the epithelium from the isolated mucosa ; place a piece about i cm. square on a slide ; apply a cover- glass, press upon it slightly, and examine with the low power (Fig. 145, B). To preserve the preparation, proceed as in No. in, a; but it is advisable to span the pieces on cork and before transferring them from the absolute alcohol to the bergamot oil, to press them somewhat, in order that the alcohol may be completely removed from the spongy mucosa. In addition to nerves, many blood-vessels are present, which may be easily recognized by the structure of their walls, in part by the transversely-placed nuclei of the muscle-fibers. No. 112. — The Parotid, Siil/maxillary, and Sublingual Glands. — From human glands (still useful in winter after 3 or 4 days) cut a number of pieces 0.5 to I cm. square, and place them in 30 c.c. of absolute alcohol, which should be changed in 5 to 20 hours. In 3 days the tissues are ready to be sectioned, and can be used at once or later. Stain i piece in bulk in borax-carmine. Embed another in liver and cut the thinnest possible sections ; small fragments about 2 mm. long can be used ; stain them in Bohmer's hematoxylin, 2 to 3 minutes ; the transfer of the sections to the staining solution must be done slowly, or the most delicate sections will be destroyed ; then stain with eosin (p. 32), and mount in damar. (Very thin sections should be examined in water after the staining in hematoxylin is completed, since the cell boundaries are then very much more distinct.) If the staining is successful, the salivary tubules and the crescents are red. In the sublingual gland and in the mucous cells of the submaxillary the membrana propria also stains red ; it must not be confused with the sections of the crescents, which latter are granular, while the membrana propria has a homogeneous appearance. The mucous cells in the borax -carmine preparations are clear throughout. In the sections stained with hematoxylin they are sometimes clear, sometimes a pale blue of different shades (Fig. 146) ; the portion which stains is a reticulum which occurs in SPECIAL TECHNKJfE. 307 certain functional stages of each mucous cell. The very short intercalated pieces of the submaxillary gland are difficult to find ; on the other hand, they may be easily seen in the parotid (also in that of the rabbit). Of the end- pieces only certain portions, those which have been accurately halved and the lumen of which is visible, are suitable for study. The numerous oblique and tangential sections are often very difficult to understand (Fig. 146, 4, 5, 6, 7). No. 113. — The Pancreas. — The human pancreas as a rule cannot be used. The treatment is the same as for the parotid gland, Xo. 112. The character- istic granular zone of the gland-cells, bordering the lumen, is not to be seen by this method (Fig. 149. B). Tease a i)inhead-sized piece of the fresh pan- creas of a cat in a drop of Y^ per cent, salt .solution. With the low power the acini appear spotted ; this is due to the partly clear and partly granular divi- sions of the cell. With high magnification the tissue appears like Fig. 149, A. No. 114. — Liver Cells. — Make an incision in a fresh liver and with the blade of the scalpel obliquely placed scrape the cut surface. The brown liver- tissue attached to the blade is to be transferred to a slide and a drop of salt solution added. Apply a cover-glass. Examine first with the low power then with the high (Fig. 153, A). The jireparation contains, in addition to the liver-cells, numerous colored and colorless blood -corpuscles. Xo. 115. — Hepatic Lobules. — Place small pieces (about 2 cm. cubes) of a l)ig's liver in 30 to 50 c.c. of absolute alcohol. The majority of the lobules are hexagonal ; they can be seen on the surface of the liver by the unaided eye, and after a moment become distinctly visible on the cut surface. The section of the central vein also becomes visible. In about 3 days sections can be made ; stain them with Bohmer's hematoxylin. The division into lobules can be well seen with the low |)ower, but the hepatic cells as well as the bile-ducts are less satisfactory for study. Better for this purpose is the following. No. 116. — Human Liver. — Place pieces about 2 cm. square, as fresh as possible, for 4 weeks in 200 c.c. of Miiller's fluid for fixation and then in 100 c.c. of gradually strengthened alcohols for hardening. Examine unstained sections (parallel and also vertical to the surface) and stain others with Bohmer's hematoxylin and also with eosin ; mount in damar. The de- marcation of the lobules is not distinct, because of the slight development of the interlobular connective tissue. The division into lobules may be more readily perceived on macroscopic inspection, than on investigation with the microscope. For orientation the beginner should recall that isolated sections of blood-vessels always represent intralobular veins ; while numbers of sections together rejiresent branches of the ])ortal vein, of the he|)atic artery, and of the bile-duct. Exact transverse sections of central veins may also be recog- nized by the cords of hepatic cells radiating from them (Fig. 154). For the study of the structure of the gall-bladder as well as of the larger bile-ducts, only absolutely fresh livers can be used, since the alkaline bile permeates the walls of the gall-bladder soon after death, stains the tissue yellow, and renders it unfit for microscopic investigation. Xo. 117. — To demonstrate iht: capillaries astd X\\t intralobular connective tissue, which in ordinary preparations are scarcely visible, shake a number of thin double-stained sections of human liver (Xo. 116) for from 2 to 3 minutes in a test-tube half filled with distilled water. The liver-cells in part fall out: the edges of the preparation are then to be examined in a drop of water (Fig. 163). This preparation can be mounted in damar, but the more delicate con- nective-tissue fibers disappear therein. 3o8 HISTOLOGY. No. 1 18. — Blood- Vessels of the Liver. a. Chloroform a rabbit and quickly place a 2 cm. cube of the liver (with- out allowing much blood to flow from it) in 50 c.c. of absolute alcohol. In 2 days the natural injection can be seen on the surface ; it is indicated by brown spots within the centers of the lobules. Cut thick sections parallel to the sur- face, and mount them unstained in damar. Examine with a low power. Very frequently only the superficial strata of the liver contain filled blood- vessels. /'. Of all injections that of the liver is most easily accomplished. Inject Berlin blue (p. 37), either through the [lortal vein or the inferior vena cava; in the latter case it is advisable to make an incision above the diaphragm, to allow the heart to rest upon it, and to insert the canula through the right auri- cle into the inferior cava. The injected liver is to be placed in toto in about 500 c.c. of Miiller's fluid ; after 6 days pieces about 2 cm. square of the por- tions best injected are to be cut out, placed again for 2 to 3 weeks in about 150 c.c. of Miiller's fluid, and finally hardened in 100 c.c. of gradually strengthened alcohols. Cut thick sections and mount them unstained in damar (Fig. 157, 158, 159)- No. 119 — Exhibition of Glaiui Lumina hv Golgi's '^ Black Reaction.''' — Place small pieces of stomach, of salivary glands, and of liver for 3 days in the osmio-bichromate mixture (in winter, in the warm chamber, p. 36), and for the same length of time in the silver solution. For further treatment see p. 35. Very often the staining does not succeed until after the procedure has been reiieated once or twice. After-staining (p. 37) is to be advised. In the liver the "lattice-fibers" stain occasionally. No. 1 20. — The Endothelium of the Peritoneum. — Proceed as in No. 35, but instead of taking the mesentery, which also yields instructive pictures, use the greater omentum. The pieces may be stained in Bohmer's hematoxylin and mounted in damar (Fig. 167). No. 121. — The Connective-tissue Reticulum. — This may be obtained by spreading out a fragment of a fresh human omentum in a few drops of picro- carmine. Mount in diluted glycerine (not acidulated). XIII. THE RESPIRATORY ORGANS. No. 122. — The Larynx, the Bronchi, and the Thyroid Gland. — Of animals, the cat is especially suitable. Expose the bronchi above the manubrium, cut them and the esophagus through transversely and dissect both loose upwards (see No. 97). The tongue maybe removed with these parts. The thyroid gland should be allowed to remain attached to the larynx. The whole is to be placed for from 2 to 6 weeks in 200 to 400 c.c. of Miiller's fluid, then washed for i hour in running water and hardened in 200 c.c. of gradually strengthened alcohol. In about 8 days cut sections, transverse and longitu- dinal, through the vocal cords and portions of the trachea ; stain them for 5 minutes in Bohmer's hematoxylin, and mount in damar. Especially instructive are sections taken transversely through the vocal cords, in which the mucous membrane, glands, muscles, blood-vessels, nerves, and cartilage furnish material for the most varied study. No. 133. — The Bronchi. — From an animal just killed (rabbit) remove the lungs, fix them in Miiller's fluid and harden them in gradually strengthened alcohol, like No. 122. In 8 davs cut out of the lung i cm. cubes, which SPECIAL TECHNIQUE. 309 contain a portion of a longitudinally-disposed bronchus. With the scissors remove the greater part of the attached lung tissue ; embed the bronchus in liver, and make thin transverse sections, which may be stained in Bohmer's hematoxylin and mounted in daniar (Fig. i68). The lungs of cat.s are less suitable than those of the rabbit, owing to the often considerable masses of fat surrounding the bronchi. This method is also applicable for the exhibition of the alveoli and the alveolar pa.ssages. Xo. 124. — The Respiratory Epithelium. — For the demonstration of this tis- sue only animals just killed can be used. Young kittens (not newborn) are suitable ; they should be killed by decajiitation. The trachea and lungsshould then be carefully taken out and filled by means of a glass pipet with a previously- prepared solution of silver nitrate ( 50 c.c. of a i per cent, solution to 200 c.c. of distilled water). The trachea should then be tied fast and the whole placed ( I to 12 hours) in the remainder of the silver solution and stood in the dark. On removing them from the silver solution, the lungs should be quickly washed with distilled water and transferred to 150 c.c. of gradually strengthened alcohol, in which they may remain (in the dark) for an indefinite length of time. The reduction can be undertaken in an hour after the silver injection, or later. For this purpose the lungs in the alcohol should be exposed to sunlight, in which they become a deep brown in a few minutes. With a zvvt sharp razor cut thin sections, taking care not to compress the tissue. Despite the hardening in alcohol the lung tissue is still soft and allows only thick sections to be cut. Sections may be most easily cut in a direction parallel to the surface. Place the sections for from 10 to 60 minutes in 5 to 10 c.c. of distilled water to which a crystal of common salt about the size of a lentil has been added, and then mount them unstained indamar. It is not advisable to employ nuclear staining, since not only the nuclei of the epithelial cells, but also those of the cai)illaries and other tissues are colored, and consequently the picture becomes very complicated. Orientation in such .sections is not altogether easy. The investigation should be begun with the low power. The small alveoli are easily recognized ; the somewhat larger spaces correspond to alveolar ducts. The demarcation of the epithelium is on the whole finer with medium magnification (So diameters ), and by no means eciually good in all places. The cubical epithelial cells are usually colored a somewhat deeper brown. Find a good place, study it with the high power (240 diameters), and by changing the focus (elevating and depressing the tube) note the relief of the preparation ; with high magnification, either only the ba.se or the edge of an alveolus can be dis- tinctly seen. Fig. 170 was drawn with change of focus. Xi). 125. — Elastic Fibers of the Lungs. — With the scissors placed flatwise on the lung (the lung need not be fresh ), cut a flat piece i cm. square, spread it out with needles on a dry slide, apply a cover-glass and treat with 2 drops of potash lye diluted 'j with water ; the diluted lye destroys all parts except- ing only the elastic fibers, who.se thickness and arrangement may l)e easily in- vestigated with the high i)ower (240 diameters). * Xo. 126. — Blood-vessels of the Lungs. — Inject the lung from the pulmo- nary artery with Herlin blue ; fix it in Miiller's fluid, and harden it in alcohol. Cut thick sections, principally parallel to the surface of the lung (Fig. 171). Xo. 127. — The Thyroiii Gland. — Thin sections of the gland, hardened in toto (see No. 122 ), are to be stained with picrocarmine and mounted in damar (Fig. 172). The retracted colloid ma.sses stain an intense yellow. Examine thick sections in glycerine, in which the lyniiih-vessels filled with colloid sub- stance are often distinctly visible. 3IO HISTOLOGY. No. 128. — The Thymus Body. — Place the thymus body of a young animal, for from 2 to 5 weeks, in Miiller's fluid and harden it in gradually strengthened alcohol. Stain sections with Bohmer's hematoxylin ; mount them in damar (Fig. 173). Care should be taken not to confuse the cross-sections of the blood-vessels, the lumina of which change in elevating and depressing the tube (when they are not true cross-sections), with the concentrically-striated cor- puscles of Hassall. The preparation represented in Fig. 174 is from a thymus bodv fixed in Flemming's mixture and stained with safl'ranin. XIV. THE URINARY ORGANS. No. 129. — Isolated Urinifemis Tubules. — The most suitable for this pur- pose are the kidneys of young animals, for example newborn kittens. Divide the kidney in halves ; place one half (arations. Insurmountable difficulties are often encountered, especially in rendering the gland-tubules evident. In the two-horned uterus of many animals, the often greatly-convoluted follicles 314 HISTOLOGY. may be more readily seen ; the arrangement of the muscular strata is more regular, and dififerent from that of the human organ. The specimens are to be prepared like No. 152. XVI. THE SKIN AND ITS APPENDAGES. No. 154. — Strata of the Skin; Coil-glands. — Cut from the pad of the finger, from the palm of the hand, or the sole of the foot, pieces of skin i to 2 cm. square together with a thin stratum of subjacent fat and place them in 30 c.c. of absolute alcohol. To prevent curling of the pieces pin them on a small cork-plate with the epidermis turned toward the cork, and place the whole in absolute alcohol. On the following day remove the pieces from the cork- plate and place them for from 3 to 4 weeks in 50 c.c. of 90 per cent, alcohol. Cut thin and thick sections. The latter are indispensable in order to see the excretory ducts of the coil-glands in their entire length. The most suitable for this purpose is the skin of the sole of the foot of children, because the ducts of the coil-glands here run vertically (Fig. 208). Stain with alum carmine, 10 minutes (p. 32) ; the red coils can be seen with the unaided eye ; mount in damar. Examine with the low power. In thick sections the papillae are often indistinct, because they are surrounded by the red colored stratum mucosum ; the screw-like twisted ends of the excretory ducts may be most distinctly seen when the object is faintly illuminated or with obli(|ue illumination (see p. 43, remark*). To render the stratum granulosum visilile, bulk staining with borax- carmine, 2 to 3 days (p. 32), is to be recommended. The granules of this stratum are then stained an intense red. No. 155. — For preparations of the nails fix the distal phalanx of a child 8 to 12 years of age (in adults, that of the little finger, if possible of women), 2 to 4 weeks in 100 to 200 c.c. of Miiller's fluid, and harden in about 100 c.c. of gradually strengthened alcohol ; decalcify (p. 29) ; harden again, and stain thick cross-sections 10 minutes in alum carmine (p. 32). In cutting sections place the knife on the volar side (not on the nail side) of the phalanx. The substance of the nail frequently shows diflerently-colored strata. In the nails of old cadavers the epithelium often becomes loosened from the ridges. No. 156. — Elements of the Nails. — Place pieces of cut nail i to 2 mm. broad in a test-tube containing 5 c.c. of concentrated potash-lye and heat over a flame until it boils up once. Transfer the nail with a drop of the lye to a slide and scrape off some of the softened surface ; apply a cover-glass. On examination with a high power, cells will be found like those in Fig. 211. For comparison, , investigate the horny cells of the stratum corneum, which may be obtained by lightly scraping the pad of the finger with the handle of a scalpel. Examine the polygonal scales in a drop of distilled water, with a high power. No. 157. — Hairs. — Place a hair in a drop of salt solution on a slide and examine it with the low and the high power ; the most suitable for study are white hairs and the hairs of the beard. The hair-cuticle of man is very delicate and the transverse markings produced by the imbrication of the cells are often very indistinct; usually only fine wavy lines are visible. The hairs of many animals, on the other hand, show the cuticula very well, for example, sheep's wool. No. 158. — For the demonstration of the elements of the hairs, place a piece of hair i to 2 cm. long in a drop of pure sulphuric acid on a slide and apply a cover-glass ; press lightly on the glass with a needle and the cortical substance will split up into fibers, which consist of adherent cortical cells. SPECIAL TECHNIgUE. 315 Slightly warm the slide, press again with a needle, so that the cover-glass becomes slightly displaced ; numerous free elements, superficial scales, and cortical cells will then be seen. Xo. 159. — For the exhibition of the elements of the hair-follicles (and the hairs) cut from a mustachioed human upper lip a piece 2 cm. square and place it in dilute acetic acid (5 c.c. of acetic acid to 100 c.c. of distilled water). In 2 days the individual hairs with their sheaths can be easily withdrawn and their elements separated by teasing in a drop of distilled water (Fig. 213). The cells of Henle's sheath float in small complexes in the prejjaration and closely resemble fenestrated membranes (Fig. 213, 5). Not infrequently a hair-follicle is obtained at the base of which anew hair is developing (compare with Fig. 126). No. 160. — For the study of hair ami hairfollicles place pieces 2 to 3 cm. square of the fresh skin of the scalp in about 200 c.c. of a 2.5 per cent, solution of pota.ssium bichromate (p. 20, 9) for from 4 to 8 weeks; wash them I to 3 hours in running water and harden in the dark in about 100 c.c. of gradually strengthened alcohol. Longitudinal sections which include the entire length of the follicle are very difficult to cut. Macroscopic orientation as to the direction of the hair is first necessary. To obtain preparations like that in Fig. 212 thick sections, unstained, are to be mounted in glycerine. Thin sections usually include only a portion of the hair-follicle. It is much easier to cut thin cross-sections, but care must be taken to make the cut vertical to the longitudinal direction of the hair, not parallel to the surface of the skin. In this way a single section shows different levels of the hairs and hair-follicles ; such sections are to be stained in dilute carmine (p. 32), and Bohmer's hema- toxylin (p. 31), or better, first with hematoxylin and then with picrocarmine (P- 33) 1° minutes, and mounted in damar. I-"specially instructive are the sections through the hair-follicle close to the hair-bulb (Fig. 214). No. 161. — For the development of hair cwi pieces about 2 cm. scjuare of the skin of the forehead (not of the hairy scalp) of a 5- to 6-months'-old human embryo ; s[)an them out (see No. 154) ; ])lace them for 14 days in too to 200 c.c. of Miiller's fluid and harden in about 100 c.c. of gradually strengthened alcohol. Stain the tissue in bulk in bora.\ -carmine (p. 32). The sections may also be stained in Bohmer's hematoxylin (p. 31). Embed the tissue in liver ; endeavor to cut sections exactly in the direction of the hair-follicle, which is much more easily done than in the hairy scalp of the adult. Mount in damar. The sections exhibit all stages of development (Fig. 215). The epidermal thickenings are only to be seen in well-preserved epidermis, which in embryos is often somewhat macerated. They are more easily found in em- bryos of the lower animals. No. 162. — Shedding and Replacement of Hair. — The eyelids of new- born children are most suitable. Treat like No. 182, Cut sagittal sections. Vertical sections of the hairy scalp often yield good results (Fig. 216). No. 163. — The Sebaceous Glands. — Fix and harden the alse nasi of an infant in 100 c.c. of 2.5 per cent, solution of potassium bichromate (like No. 160). Cut thick and thin sections ; stain them with dilute carmine (p. 32), and with Bohmer's hematoxylin (p. 31), and mount in damar. Sec- tions lengthwise to the dorsum of the nose often show both sebaceous glamls and hair-follicles, but they must be made exactly vertical. The alK of the nose of adults, on account of the very large sebaceous glands with their wide excretory ducts, do not furnish good microscopic specimens. Small seba- 3l6 HISTOLOGY. ceous glands with hair-follicles can be seen with the unaided eye in stripping off the macerated epidermis of old cadavers. No. 164. — Blood-Tcsseh of tlic Skin. — Inject with Berlin blue the entire hand of a child through the ulnar artery (or a foot through the posterior tibial artery) and place it in i to 2 liters of Miiller's fluid ; after several days cut pieces 2 to 3 cm. square of the palm of the hand or of the sole of the foot, place them (2 to 4 weeks) in 100 to 200 c.c. of Miiller's fluid for fi.xation, and harden them in 100 c.c. of gradually strengthened alcohol. Cut thick sections and mount them, unstained, in damar. The papillfe in such sections are only to be recognized by the capillary loops. To the beginner it appears as if the loops extend into the stratum mucosum. No. 165. — For a general view of f/w maiininirv g/aiitis place the nipple and a portion of the gland (3 to 4 cm. square) in 60 to 100 c.c. of absolute alcohol. If possible, obtain the glands of an individual that was pregnant not too long a time before ; also the glands of virgins, etc. Make vertical sections through the nipple and in any direction through the gland-substance, and stain them with Bohmer's hematoxylin ; mount in damar. No. 166. — For the minute structure of the mammary glands place the warm living tissue (3 to 5 mm. cubes) of a pregnant mammal in 5 c.c. of Flemming's mixture (p. 21), and harden after i to 2 days in 30 c.c. of gradually strength- ened alcohol. Cut very thin sections, stain them with saffranin (p. 32, 4), and mount in damar (Fig. 219). The structure is often difficult to understand on account of the small size of the gland-cells (in the rabbit). No. 167. — FJemen/s of Milk. — Put a drop of salt solution on a clean slide, and add to it a drop of milk. The milk is to be obtained by placing the cover-glass upon the nipple and then pressing out a drop. Examine with a high power (Fig. 221). No. 168. — Eletnents of the Colostrum. — Proceed as in No. 167. Be careful to avoid pressure on cover-glass. The nuclei of the colostrum corpuscles can rarely be distinctly seen without further treatment ; on the addition of a drop of picrocarmine they appear as dull-red spots. XVII. THE EYE AND ITS APPENDAGES. No. 169. — Carefully cut the fresh eye-ball out of the optic cavity, and secure as much as possible of the optic nerve ; then with the scissors cut off the attached fat and muscle, and with a sharp razor make an incision at the equator, about i cm. long, through all the coats of the eye. Place the eye-ball in 150 c.c. of 0.05 percent, chromic acid solution (p. 20) ; after 12 to 20 hours, beginning at the incision already made, divide the eye-ball with the scissors completely into an anterior and posterior half, and change the fluid. After 12 to 20 hours more, wash the pieces and harden them in 100 c.c. of gradually strengthened alcohol. a. Carefully remove the lens from the anterior half of the eye-ball and treat it further like No. 179 ; then cut out a quadrant and with the attached ciliary body and iris embed it in liver and cut sections thro\igh tlie iridocorneal angle. The thick sections are to be stained with Bohmer's hematoxylin and mounted in damar (Fig. 227). /'. From the remaining three-fourths of the anterior half of the eye-ball cut out a piece of the cornea, 5 to 10 mm. square, embed it in liver and make sections through the layers of the cornea (Fig. 222 ). The alternating lamellas of SPECIAL TECHN1(,)UE. 3I7 the substantia propria can only be well seen in unstained sections mounted in dilute glycerine. c. From the posterior half of the eye-ball cut pieces including the three coats, 5 to 10 mm. square, and cut sections, not too thin, for the study of the strata of the sclera and choroid {Y\%. 225). Stain them with Bohmer's hema- to.\yiin and mount in damar. In sectioning, the retina usually becomes loosened. (/. For i)reparations showing the entrance of the optic-nerve cut around the point of entrance at a distance of about 5 mm. from the same through all tiie coats of the eye ; embed this jjortion with about i cm. of the optic-nerve in liver and cut sections (not too thin). Place the knife so that it strikes the retina first, then the choroid and sclera, and passes through the optic-nerve longitudinally; stain with dilute carmine (p. 32) and with Bohmer's hema- to.xylin (p. 31), and mount in damar. Examine with very low magnification (Fig. 235). No. 170. — Remove a fresh eye-ball according to the method given in No. 169; make an incision at the eiiuator. and jilace it in 100 to 200 c.c. of Miiller's fluid. In 12 to 20 hours divide it with the scissors into an anterior and posterior half In 2 to 3 weeks carefully wash both halves in slowly running water for from i to 2 hours. Then cut pieces including all the coats, about 8 mm. long, and use for them the following i)reparations : — a. Teased Preparation of the Choroid. — Tease and mount a fragment in a drop of dilute glycerine; it exhibits large blood-vessels, the ca|)illaries of the choriocapillaris, branched pigment-cells, elastic fibers, sometimes also the gla.ssy membrane; the "lattice-work " of the latter is only partially distinct. The isolated membranes may be stained with Bohmer's hematoxylin and mounted in damar, but the more delicate structures are thus rendered indistinct (Fig. 226). /'. Elements of the Retina. — Tease a small piece of the retina in a drop of Miiller's fluid, carefully, with needles. Along with many fragments of the elements, a few more or less well-preserved parts will be found. Human eyes have very large, beautiful cone-visual cells, while those of many mammals are very small ; wholly unsuitable in this respect are the eyes of the rabbit ; unfortunately, human eyes are usually no longer in a sufficiently fresh condition when the investigation is made. The outer segments of the cones, also of the rods, are extremely delicate and rapidly disintegrate after death, falling into transverse plates and at the same time curving like a shepherd's crook. Later they disappear entirely. In order to see beautiful cone-visual cells, examine, according to the method just given, the eyes of fishes. (See furtiier No. 171 and 172.) c. The remaining parts of the eye-ball are to be transferred from the water to 80 c.c. of gradually strengthened alcohol for hardening: when the hardening is com|)leted, cut out the iris, embed it in liver, and make meridional sections; stain them in Bohmer's hematoxylin and mount in damar (Fig. 228). (/. Cut out a portion i cm. long of the retina, including the ora serrata. which is macroscopically visible as a wavy line, embed it in liver, and make meridional sections; stain them in hematoxylin and mount in damar (Fig. 234)- e. Treat in the same manner a |)iece of tjie retina taken from the posterior portion of the eye, where the optic-fiber stratum is thickest. The radial fibers of Miiller can only be seen in their entire length in accurate vertical sections (Fig. 229 and Fig. 230). f. In the same manner treat meridional sections through the macula and 3l8 HISTOLOGY. fovea. It is not difficult to cut sections of the macula, but on the other hand very difficult to obtain satisfactory sections through the extremely delicate fovea. The retina should not be loosened from the choroid, but the two should be sectioned together. (Among the lower mannnals only the ape pcssesses a yellow macula and a central fovea ; on the other hand, the majority — insectivora and certain rodents excepted — have an " area centralis," without yellow pigmenta- tion, but similar in structure to the macula. A simple or multiple fovea is always present in birds and reptiles ; a fovea has also been found in bony fishes. ) No. 171. — Fresh Elements of the Retina. — Select the warm eyes of animals lust killed. Divide the eye-ball at the equator and carefully remove the vitreous body from the posterior half; cut small pieces about 3 mm. square from the transparent retina and tease in a drop of the vitreous humor; place two thin strips of paper on either side of the preparation (p. 41), and apply a cover- glass. Isolated elements will be found only here and there ; on the other hand, very good surface views are not infrequently obtained in which the rods and cones are perceptible in optical cross-section, the first as small, the latter as large circles. If at the same time a little piece of the pigmented epithelium has been transferred to the slide, the regular hexagonal cells of the same can be plainly seen with the low power. The light spots in these cells are their nuclei (Fig. 8). These cells are also very unstable and soon lose their sharp contours ; molecular motion of the pigment-granules may be very fre- quently observed. No. 172. — -The best method for isolating the elements of the retina is the following : Place the eye unopened, but freed from fat and muscle, in i per cent, osmium solution. In 24 hours cut the eye open at the equator and place it for maceration for 2 to 3 days in distilled water ; then with scissors cut out a piece of the retina about 2 mm. long and tease it in a drop of water ; the prep- aration may be stained with picrocarmine, under the cover-glass, and mounted in dilute glycerine. With the high power, in addition to many fragments whose source is not always to be determined with certainty, elements like those pic- tured in Fig. 232 may be found. It is advisable to select the eyes of small animals — e. g., a small salaman- der (Triton tasniatus), whose sclera is thin and allows the osmium solution to penetrate easily. For such an eye i to 2 c.c. of the solution will be sufficient. The form of the rods is quite different from those of mammals ; they are thick and are provided with long outer segments ; the cones are small. No. 173. — Corneal Spaces and Canaliculi. — Select an eye as fresh as pos- sible ; of the eyes of animals, that of the ox is most suitable ; with the handle of a scalpel scrape away the epithelium of the cornea ; spray the denuded sur- face with distilled water ; cut the eye through in front of the attachment of the ocular muscles and place the anterior segment, containing the entire cornea, down on the epithelial side ; then with forceps and scalpel remove the ciliary body, the lens, and the iris, so that only the anterior portion of the sclera and cornea remain, which are to be placed in 40 c.c. of a i per cent, solution of silver nitrate. The whole is then to .be placed in the dark, 3 to 6 hours, and then transferred to 50 c.c. of distilled water and exposed to sunlight (see further p. 35). Harden the objects in 50 c.c. of gradually strengthened alcohol and cut horizontal sections, which is most easily done if the cornea is held over the left index-finger. It is best to take the sections on the posterior surface of the cornea, since the spaces and canaliculi are more regular there. The sections may be stained in Bohmer's hematoxylin and mounted in damar. The pic- tures are negative, the spaces and canaliculi white on a brown or brown-yellow SPECIAL TECHNIQUE. 319 surface (Fig. 223). Examine carefully the usually somewhat thinner margins of the section ; in sections stained in hematoxylin the nuclei of the fixed cor- neal corpuscles are a dull blue ; the contours of the cells can seldom be per- ceived. No. 174. — Fixed Corneal Corpuscles by the Gold Method. — The method described on p. 35 is to be somewhat modified, as follows : Express the juice from a fresh lemon ; filter it through flannel. Kill the animal, cut out the cornea and place it for 5 minutes in the lemon-juice, in which it becomes trans- jjarent ; then wash it in 5 c.c. of distilled water for i minute; transfer it to 10 c.c. of gold-chloride solution and place it in the dark for 15 minutes. With glass rods transfer the cornea to 10 c.c. of distilled water for i minute, then to 50 c.c. of distilled water to which 2 drops of acetic acid have been added, and expose it to daylight ; in 24 to 48 hours the reduction is completed. The object is then to be placed in 10 c.c. of 70 per cent, alcohol (in the dark) ; on the following day cut out a little piece of the cornea, hold it with needle and scalpel at the edges and sejiarate the thin lamella from the posterior surface ; this can be done successfully without much trouble. Mount the lamellae in damar. In frogs the canaliculi are very regular and the posterior lamellae easy to strip off. No. 175. — Very good preparations oi fixed corneal cells are obtained by the method of Drasch. The objects are not to be taken from the animal re- cently killed, but 12 to 24 hours after death, during which time the cadaver must be kept in a cool place. Small pieces of the cornea are to be cut out, about 6 mm. long, placed in 5 c.c. of 1 per cent, gold-chloride solution plus 5 c.c. of distilled water and stood in the dark for i hour. During this time stir the fluid often with a gla.ss rod ; then with glass rods transfer the pieces to 30 c.c. of distilled water, in which they should remain (in the dark) 8 to 16 hours. They are then to be transferred to 25 c.c. of distilled water plus 5 c.c. of formic acid and exposed to daylight. When the reduction is completed (p. 35) the dark-violet pieces are to be hardened in gradually strengthened alcohol, and in about 6 days thin sections, parallel to the surface, can be cut and mounted in damar (Fig. 224). No. 176. — Nen'es and Blood-vessels of the Fresh Cornea. — Select the eye of an ox and cut out the cornea and the portion extending from the limbus to the attachment of the ocular muscles; remove, with scalpel and forceps, the ciliary body, iris, and lens, cut out a quadrant of the cornea, place it with the epithelial side up on a slide, and apply a cover-glass ; a drop of the vitreous humor may be added. The very thick preparation must be examined with a low ])ower. .\t the scleral margin the loops formed by the blood-vessels as they bend back can be seen when the surface of the cornea is in focus ; the most of them still contain blood-corpuscles. Medullated nerve-fibers are also found here, as well as in the deeper strata ; they are arranged in bundles and within the cornea can only be traced for a short distance. The elongated pigment-streaks found in the eye of the ox have no relation to the nerves. This method is not serviceable for the exhibition of the finer distribution of the nerves. No. 177. — Nerves of the Cornea. — a. Gold Method. — Cut out the cornea I 2 to 24 hours after death, remove the ciliary body and iris, and treat it accord- ing to the method given in No. 175. When the hardening is completed cut horizontal sections, which contain the epithelium and the uppermost strata of the cornea, and vertical sections through the thickness of the cornea. Mount in damar (Fig. 239). 320 HISTOLOGY. b. Methylene Blue Staining. — Kill a rabbit; remove the entire eye-ball; free it from the attached remnants of ocular muscles and connective-tissue ; place it in a watch-glass and with a sharp scalpel make a deep incision through all the coats of the eye at the equator. The vitreous humor thus escapes into the watch-gla.ss ; then with scissors separate, at the incision, the entire cornea, place it on a slide with the concave surface upward, and scrape off with the handle of the scalpel the ciliary body, iris, and lens, which is easily done ; transfer the cornea thus cleansed to a second watch-glass containing 3 to lo drops of the vitreous humor and 3 to 4 drops of a J^ per cent, methylene blue solution. The fluid must cover the concave surface of the cornea. The time required for staining cannot be given with certainty ; it is there- fore advisable after several hours to place the cornea with the convex surface up on a clean slide and, without a cover-glass, to examine it with the low power ; if it is not sufficiently stained return it to the watch-glass and examine it again in about 10 minutes. So soon as the nerves can be distinctly seen the cornea is to be transferred for from 18 to 20 hours to 20 c.c. of ammonia; then cut out a quadrant and mount it in dilute glycerine, to which a drop of ammonia has been added ; after being kept for 24 hours in the dark the preparation will be sufficiently transparent and can be investigated with the high power. No. I 78. — Lens-fibers. — Cut the eye-ball open back of the equator; remove the vitreous body and lens ; thus the pigment covering the ciliary processes remains attached to the margin of the lens. Loosen the lens from the vitreous body and place it in 50 c.c. of Ranvier's alcohol (p. 19). In about 2 hours thrust needles into the anterior and posterior surfaces of the lens and strip the capsule up from a small area ; this is easily done ; if lens-fibers are attached to the capsule it does not matter. On pricking the lens a turbid white fluid escapes; shake the alcohol and let the lens remain in it 10 to 40 hours. .\t the expiration of this time the lens can be easily separated into shell-like pieces. Tease a small strip of one of these pieces in a small drop of salt solution on a slide (p. 25). Apply a cover-glass, taking care to avoid pressure ; if it is desired to preserve the fibers, stain with picrocarmine (staining usually occurs in a few minutes), and mount in dilute acidulated glycerine (Fig. 236, A). No. 179. — Lens-fibers in Transverse Section. — Place a lens in 50 c.c. of 0.05 per cent, chromic acid. A cloth or a little cotton must be placed on the bottom of the bottle or the lens will adhere to the glass and burst. This may also be prevented by frequently shaking the bottle. In 24 to 48 hours break up the lens into shell-like pieces with a needle, transfer them after 10 to 15 hours to 30 c.c. of 70 per cent, alcohol, which is to be replaced on the fol- lowing day by an equal quantity of 90 per cent, alcohol. With the scissors cut the pieces through in the region of the equator, and so embed them in liver that the first sections shall pass through the zone lying next to the equator. If the section, which need not be very thin, has passed through the fibers trans- versely they will appear as sharply-defined hexagons ; if, on the contrary, the section is oblique, the single fibers will appear to be separated from one another by irregular zigzag lines ; they may even be cut partially lengthwise. The sections are to be transferred directly from the blade to the slide and mounted in dilute glycerine (Fig. 236, £). No. 180. — The Lens Capsule and t/ie Lens Epithelium. — Place the eye- ball, free from muscle and fat, in 100 to 200 c.c. of Miiller's fluid. Treat it further as follows : — SPECIAL TECHNIQUE. 32I liC )■ If it is desired to obtain the lens capsule alone strip off a portion of the posterior lens capsule. /'. Sections of the Capsule and Epithelium. — Let the eye-ball remain in iMiiller's fluid for 2 weeks ; remove the lens, wash it for i hour in running water and harden it in 50 c.c. of gradually strengthened alcohol (p. 29) ; cut meridional sections through the anterior surface and the equator of the lens ; stain them with Bohmer's hematoxvlin (p. 31 ) and mount in damar (Fig. No. 181. — The Blood-vessels of the Eye. — For this purpose surface prep- arations are especially suitable. Open a fresh eye at the equator. The course of the central artery of the retina is macroscopically perceptible. For the exhibition of the blood-vessels of the choroid place an eyeball completely freed from attached muscle and fat on a small glass funnel which has been thrust into a low glass bottle, and, with scissors and forceps, begin at the eijua- tor and carefully dissect off the sclera. With a little practice the entire sclera can be removed beyond the ora serrata up to the optic entrance without injury to the choroid ; care must be taken not to tear it. (Beginners should be con- tent to remove only one quadrant of the sclera.) All the firmer points of attachment between the sclera and choroid (the venaj vorticosre) must be cut through. Then by careful brushing with a sable pencil moistened in water remove the attached portions of the lamina suprachoroidea from the choroid ; by this manipulation the course of the larger blood-vessels is brought to view. Thus far the investigation may be pursued on the uninjected eye (compare with No. 170, a). For the study of the blood-vessels of the ciliary body and the iris it is necessary to use an injected eye, divided anterior to the equator, fixed in Miiller's fluid and hardened in alcohol. The iris and ciliary body may be easily stripped from the sclera ; remove the lens and mount in damar. E,\amine first with the low power. No. 182. — Place the upper eyelid oi a child in 100 c.c. of 0.5 per cent, chromic acid, i to 3 days, wash it 2 hours in running water, and harden in 50 c.c. of gradually strengthened alcohol. For a general view cut thick (F"ig. 240), for the finer details thin sections (Fig. 22, C). Staining with Bohmer's hema- toxylin is at first difficult, l)ut more readily accomplished after the object has lain in alcohol several months (compare p. 31, remark*). Mount in damar. No. 183. — The Lacrymal Glands. — The lower tear-gland m man can be easily removed, without visible external injury, from the fornix of the conjunc- tiva. In the rabbit this gland is very small and when fresh resembles pale muscle tissue. It must not be confiised with Harder's gland lying in the median angle of the eye. Treat like No. 112. Small pieces i mm. square can be used. The excretory duct and tubules may be easily seen ; difficult, on the other hand, it is to see the intercalated tulniles, whose epithelium differs greatly in height and occasionally is so low that care must be taken not to con- fuse tliem with blood-vessels. 32 2 HISTOLOGY. XVIII. THE ORG.W OF HEARING. A fundamental condition is an exact knowledge of the macroscopic an- atomy of the labyrinth. The difficulties, the failures, depend in the main on inaccurate knowledge of the bony labyrinth. As a preliminary all parts lying lateral to the promontory (os tympanicum and ossicles of the ear) must be removed, so that this is distinctly visible. No. 184. — Otoliths. — Chisel out the promontory, beginning at the upper margin of the fenestra stapedii, to the lower margin of the fenestra rotunda. Then, especially if the bone has been placed in water, the white spots (maculje) in the sacculus and utriculus can be detected. With delicate forceps lift out the sacculus and spread out a small piece in diluted glycerine on a slide. The otoliths are present in large numbers, but are very small, so that their shape can only be distinctly seen with the high power ( 240 diameters). The gly- cerine must not be too thick, or it will render the otoliths completely invisible (Fig. 242). In taking out the saccules portions of the semicircular canals not infre- quently may be removed ; stain these with picrocarmine and mount them in dilute glycerine. Only the epithelium, and here and there in optical section the delicate glassy membrane, can be seen. The connective tissue is scanty. No. 1 85. — The Cochlea. — The base of the cochlea lies in the bottom of the internal auditory meatus, the apex is directed toward the Eustachian tube, and therefore the axis of the cochlea is horizontal and trans\-erse to the long axis of the petrous bone. Open the free portion of the cochlea, that is, remove the promontory close to the fenestra rotunda, open the apex of the cochlea and, having removed the superfluous osseous mass as far as practicable, place the ])reparation in 20 c.c. of 0.5 percent, osmicacid (5 c .c. of 2 per cent, osmic acid to 15 c.c. of distilled water). In 12 to 20 hours wash the preparation for about i hour, and then place it in 200 c.c. of Miiller's fluid. In 3 to 20 days (or later) open up the cochlea and examine it in water. The osseous spiral lamina can be seen as a delicate lamella, the membranous spiral lamina as a delicate membrane, attached to the axis of the cochlea; with fine forceps break off pieces of the osseous spiral lamina; do not lift them with the forceps, but carefully with needle and section-lifter remove them from the fluid and transfer them to a drop of dilute glycerine on a slide. It is advisable to break off the axial por- tion of the spiral lamina on the slide with needles, because the relatively thick osseous process renders it difficult to apply a cover-glass. The vestibular sur- face must be directed upward ; it may be recognized by the auditory teeth, which are visible when the upper surface is in focus (Fig. 244), while the other portions are not distinct until the tube is depressed and the lower planes are focused. With the low power only the interstices of the auditory teeth are at first visible, as dark lines (Fig. 246); the papilte likewise cannot be seen immediately, even with the high power, but become distinct after the second or third day. The chief difficulty lies not in the finishing, but in the proper examination of the object ; the picture alters with the slightest change in focus. In Fig. 247, B, the membranous sjjiral lamina is drawn schemati- cally, as seen with the upper surface in focus, and, therefore, only the free sur- face of the structure, drawn as seen from the side in A, is visible. It is clear that in depressing the tube the head-plates of the pillar-cells are no longer visible, but their bodies (as circles in optical section) ; the reticular membrane, SPECIAL TECHNIQUE. 323 likewise, disappears, and can only be seen when the tube is elevated. The jjreparation may be stained with picrocarmine and preserved in dilute glycerine. The foregoing directions are intended to apply to the human ear and that of the cat. The labyrinths of children are to be recommended. Xo. 186. — Sections of the Bony and Membranous Cochlea. — Remove the cochlea of a child from the labyrinth. The compact osseous substance of the cochlea is surrounded by spongy bone so soft that the latter may be removed with a stout penknife. With a chisel make small openings in the cochlea at two or three places, about i mm. square, in order to facilitate the penetration of the fixation fluid ; then place it in 15 c.c. of distilled water plus 5 c.c. of 2 per cent, osmic acid. After 24 hours remove the object, wash it for a quarter of an hour in running water, and harden it in about 60 c.c. of gradually strengthened alcohol. When the hardening is completed, decalcify the cochlea in the following mixture : i c.c. of a i percent, aqueous solution of ])alladium chloride, lo c.c. of hydrochloric acid, and 100 c.c. of distilled water. Place the cochlea in 100 c.c. of this mixture, which must be changed often. When the decalcification is completed, the object should be hardened again, embedded in liver, and sectioned. The sections must be made in the long axis of the cochlea. Stain them with picrocarmine; mount in damar. It is not difficult to obtain preparations furnishing a good general view ; the vestibular membrane is usually torn, so that the ductus cochlearis and .scala vestibuli appear as a com- mon space (Fig. 243). The organ of Corti leaves most to be desired ; only very thin sections which pa.ss through the organ vertically furnish intelligible jiictures ; usually a section contains several inner and outer pillar-cells, also fragments of them ; the cells of Hensen appear pale and swollen- (Fig. 249) ; orientation presents many difficulties to the beginner. .\niong animals, the cochlea of the guinea-pig and of the bat are to be recom- mended ; it is not embedded in spongy bone and does not need to be chiselled out and punctured, but can be placed at once in the fixing fluid. Xo. 187. — The Nerves of the Maciilce, Cristie, and Cochlea. — For this purpo.se the ear of the newborn mouse is recommended, treated according to the method given on p. 35. The base of the cranium, after removal of the vertex, the brain, and lower jaw, is to be placed for from 3 to 4 days in the osmio- bichromate mixture and for 2 days in the silver solution. As a rule it is necessary to employ the double method (p. 36). Cut horizontal and frontal sections through the cranium, without decalcifying it. The former are the more readily made. Xo. 188. — The Eustachian Tube. — To obtain transverse sections (includ- ing cartilage and mucosa) the oblique direction of the tube downward, for- ward, and inward must be ascertained. Cut out the ])haryngeal division of the tube together with the surrounding muscles and fix it in 200 to 300 c.c. of Miiller's fluid (p. 27). In 3 to 6 weeks wash it in running water and harden it in 100 c.c. of gradually strengthened alcohol (p. 29). The sections may be stained in Bohmer's hematoxylin (p. 31) and mounted in daniar (p. 38). For a general view, examine with the low power. No. 189. — The Ceruminous G/ands. — Cut out the ear with the cartilagin- ous auditory passage close t6 the bony auditory passage. From the carti- laginous ])ortion cut a jjiece i cm. square and ])lace it in 30 c.c. of absolute alcohol. The tissue may be sectioned on the following day. If it is desired to see the coil and the excretory duct the sections must be tolerably thick ( — 0.5 mm.). Nuclear staining with Bohmer's hematoxylin (p. 32) may be em- ployed (Fig. 250). Examine thin unstained sections in diluted glycerine ; in 324 HISTOLOGY. these the fat-globules and pigment-granules can be seen. The organs of new- born children are especially suitable for this purpose. In adults the tubules are widely dilated and do not furnish good general views. On the other hand, the cuticular border of the gland-cells is distinct in the adult, which in the newborn I miss (compare with Fig. 251). XIX. THE MUCOUS MEMBRANE OF THE NOSE. Xo. 190. — Olfactory Cells. — Saw open the head of a rabbit in the median line. The olfactory mucosa is easily recognized by its brown color. With fine scissors cut out a small piece, about 5 mm. long, of the nuicosa, together with the corresponding portion of the turbinal bone, and place it in 20 c.c. of Ranvier's alcohol (p. 19). In 5 to 7 hours transfer the same to 5 c.c. of picrocarmineand on the following day to 10 c.c. of distilled water. In about 10 minutes remove the piece and lightly strike it against a slide on which a drop of diluted glycerine has been placed ; stirring with the needle is to be avoided. Carefully apply a cover-glass. In addition to many fragments of cells many well-])reserved sus- tentacular elements may be obtained. Very frequently the delicate central process of the olfactory cells is wanting (Fig. 253). No. 191. — The Miuoiis Membrane of the Respiratory Region.- — Cut out a small piece, about 5 to 10 mm. long, from the lower half of the nasal septum; strip off the mucosa and fi.x and harden it in about 20 c.c. of absolute alcohol (p. 27). Use the nasal mucous membrane of the rabbit's head (No. 190) for thin sections ; embed the pieces in liver (p. 31), and stain sections with Bohmer's hemato.xylin ; mount in damar. For general views the mucous membrane of human cadavers answers, which is to be treated in the same manner; thick, unstained sections are to be mounted in diluted glycerine (Fig. 252). No. 192. — The Alitcous Membrane of the Olfactory Region. — Remove pieces 3 to 6 mm. long of the brown mucosa from the upper portion of the nasal septum of a rabbit (No. 190), and place them for 3 hours in 20 c.c. of Ran- vier's alcohol, which loosens somewhat the elements of the olfactory epithelium. Transfer the pieces carefully to 3 c.c. of 2 per cent, osmium solution plus 3 c.c. of distilled water, and place the whole for from 15 to 24 hours in the dark. At the expiration of this time the pieces are to be placed for a half hour in 20 c.c. of distilled water and then hardened in 30 c.c. of gradually strengthened alcohol. The hardened pieces are to be embedded in liver and sectioned. Stain the sections 20 to 30 seconds in Bohmer's hematoxylin : mount them in damar. In order to obtain good views of the glands make thick sections transverse to the course of the Jierve-fibcrs (Fig. 255). For the exhibition of the nerve- libers and the epithelium thin sections parallel to the course of the fibers are suitable (Fig. 256). No. 193. — The neiTe-processes of the olfactory cells may be obtained in preparations made according to No. 178. In these the duct-system of the olfactory glands is often blackened. No. 194. — For orientation "with regard to the number and position of the taste- buds proceed according to the method in No. 96. Suitable objects are the cir- cumvallate i)apillae of any animal and the papillae foliatse of the rabbit. The latter consist of elevated groups of parallel folds of the mucosa, found one on either edge of the root of the tongue. In moderatelv thin sections vertical to SPECIAL TECHNIQUE. 325 the long axis of the folds, examined with the low power, the taste-buds may be recognized as clear spots. No. 195. — The Structure of the Taste-buds. — Dissect off with scissors a papilla foliata of a rabbit, with as little as possible of the subjacent muscle substance. Pin the piece with spines on a cork-stopper, the muscle side toward the cork, and expose it for i hour to the vapor of osmic acid (see further p. 28, 6). Thin sections of the hardened preparation embedded in liver are to be stained 30 seconds in Bohmer's hematoxvlin and mounted in damar (Fig. 258)- Xo. 196. — Exhibition of the Xer-ces. — Cut out with scissors a circumvallate papilla (without the wall), and place it for 10 minutes in the filtered juice of a lemon; then transfer it to 5 c.c. of a i per cent, gold-chloride solution and place the whole for i hour in the dark. Lift the papilla with wooden rods from the gold-chloride solution into a watch-glass with distilled water and wash it by moving it to and fro. Transfer it to 20 c.c. of distilled water to which 3 drops of acetic acid have been added. In this expose the pa[>illa to daylight until the reduction is completed, which usually requires 3 days. Harden the papilla, in the dark, in 30 c.c. of gradually strengthened alcohol. Embed the object and make the thinnest possible sections. Mount in damar. The nerve-fibers are dark-red to black, the gustatory cells are also dark (compare with Fig. 259). The papillae foliatse of the rabbit are not suitable for such preparations, but yield successful preparations byGolgi's method (p. 35 ). Place the papillae for 3 days in the osmio-bichromate mixture, for 2 days in the silver solution. The double method is to be recommended. The intergemmal fibers are more numerous and more readily blackened than the intragemmal fibers, which are ■ exceedingly delicate. Frequently single cortical and gustatory cells become blackened. APPENDIX. MICROTOME TECHNIQUE. THE MICROTOME. The most useful microtomes are constructed according to two different principles. The principle of the one kind consists therein, that the object to be sec- tioned is elevated by the shifting of the object-holder up an inclined plane. In the other form, the object is elevated in a vertical direction by a micrometer-screw. pjoth kinds are excellent instruments.* All parts of the microtome should be kept as clean as possible. It should be protected from dust, when not in use, by covering it with a light wooden case. The slideway in which the knife moves must be kept scrupulously clean. It should be cleansed occasionally with a cloth moistened in benzine and should then be freely lubricated with vase- line, so that the sliding-block will pass evenly throughout the entire slideway at the lightest touch. Especial care must be bestowed upon the knife. Only with a very sharp knife can very thin sections be made or ribbon cutting be done. A really sharp knife should pass easily through a thin hair held at one end between the fingers. EMBEDDING. P.ARAFFiN Method. The following materials and apparatus are required : — I. Paraffin: two kinds, a soft (melting point 45° Celsius) and a hard (melting point 52° Celsius). Of this prepare a mixture which melts at 50° Celsius. On the proper proportions of the two sorts of paraffin in the mixture much depends. Many a failure is due to an unsatisfactory mixture. The precise proportions cannot be given because the consistence of the paraffin depends in a great measure on the outer temperature. Then, too, hard objects, as well as the cutting of very thin sections, require a harder mixture than usual. For winter, at a room-temperature of 20° Celsius, a mixture of 30 grams of soft and 25 grams of hard paraffin f answers for most purposes. * The workmanship of tlie sliding microtomes of Thoma, made by Jung in Heidelberg, is exquisite, as I know from my own experience. The size No. IV is especially to be recom- mended. For several years I have used the microtome of .Schanze in Leipzig, Model B, No. 9, the construction of which leaves nothing further to be desired. The microtomes constructed on the same principle, byG. Mihe in Hildesheim, are also to be highly recommended ; and very good are those of A. Becker in Gottingen. [A very satisfactory sliding microtome is made by the Bausch and Lomb Optical Company of Rochester, N. Y.] f To be obtained of Dr. Griibler, Leipzig. 1:26 MICROTOME TECHNIQUE. 327 2. Chloroform : 20 c.c. 3. Paraffin-chlflrofonn : a saturated solution (5 grams of the paraffin mixture and 25 c.c. of chloroform). This solution is litiuid- at room- temperature. 4. An emhcdding oven of block-tin with double walls, between which is a space to be filled with water. * A small gas-burner is to be placed beneath the oven. On top there are two openings ; the one leads into the space between the walls, and into this a Reichert thermo-regulator f is to be inserted ; the sec- ond Oldening leads into the air-space or oven, and into this a thermometer is to be inserted. The front wall consists of a glass plate which slides up and down in grooves. The interior of the oven is divided into three compartments by means of two adjustable shelves. The oven should be 25 cm. long, 23 cm. high, and 16 cm. deep. The embedding oven, with its accessories, is indisjiensable if much embedding in paraffin is to be done; however, the paraffin may be melted on a water-bath and kept liquid with a small spirit- flame. 5. An Embedding Frame. — This consists of two adjustable bent metal frames, placed together thus ^^ Instead of this frame little paper trays madeofstiff])aper or cardboard can be used. The objects to be embedded must be absolutely free from water, and to this end should have lain 3 days in absolute alcohol, which has been changed several times ; they are then to be transferred to a bottle containing 20 c.c. of chloro- form, in which they should remain until the following day. From this the objects should be carried to the solution of paraffin in chloroform and, in from 2 to 8 hours, according to their size, transferred to a capsule containing melted (but not too hot ) paraffin. In about a half hour the objects are to be transferred to a second capsule with melted paraffin, + where, according to their size, they are to remain from i to 5 hours. § The paraffin should not be heated more than 2 to 3 degrees above its melting point ; for the mixture advised the air in the oven should have a temperature of 50° Celsius. When the ob- jects have been in the i)araffin bath the required length of time, place a slide in a broad dish and on this the embedding frame, into which the paraffin and object are now to be poured. Then, while the paraffin is still fluid, with a heated needle place the object in the desired position ; so soon as this is done carefully pour cold water into the dish until it reaches the upper margin of the frame ; the paraffin will begin at once to harden, whereupon more water may Ite added until the entire frame is submerged. By this manipulation the paraffin hardens into a homogeneous mass, whereas otherwise it is apt to crys- tallize and is then difficult to cut and also has an injurious influence on the struc- ture of the embedded tissues. In about 10 minutes the metal frames maybe removed ; the paraffin block should be allowed to remain in the water on the slide until it is completely hard. The embedded object may be sectioned in a half hour. In case it is to be used later mark it with a needle. In the paraffin the object can be kept for an indefinite period. * Made by R. Jung, Heidelberg. t To be obtained of Reichert, Vienna. % If the paraffin has been melted on a water-bath, place the flame at such a distance that the surface of the paraflfin remains covered by a thin film. \ This is sufficient for all cases ; for small objects from I to 2 hours will be enough. 328 HISTOLOGY. Celloidin Method. Two solutions are required : — a. A thin solution of about 30 grams of celloidin cut into cubes are to be dissolved in 60 c.c. of a mixture of equal parts of absolute alcohol and ether. d. A somewhat thicker solution of 30 grams of celloidin dissolved in 40 c.c. of a mixture of equal parts of absolute alcohol and ether. This solu- tion has the consistence of a thick syrup. Both solutions should be kept in wide-necked bottles. If they become too thick they may be thinned by the addition of some of the alcohol-ether mix- ture. After a time the solutions become turbid and milky ; it is better then to let them dry completely and to redissolve the pieces in the alcohol-ether mixture. The tissues to be embedded must be completely free from water and must have lain i to 2 days in absolute alcohol, which has been changed several times. From this the objects should be transferred to the thin, and on the follow- ing day to the thick, celloidin solution. In the latter, the objects may remain for an indefinite length of time. Usually they are sufficiently permeated after 24 hours, but large objects enclosing many spaces must remain in the thick solution about 8 days. The object should then be quickly placed on a cork-stopper and some celloidin poured over it. In doing this care must be taken not to press the object against the cork, lest it become detached. There should be a stra- tum of celloidin I to 2 mm. thick between the cork and the object.* Now the whole is to be placed under a bell-glass to dry slowly ; the bell-glass should not be air-tight, and to avoid this should be supported on one side on a needle or something similar. Delicate objects dry in a half hour, larger objects in 4 hours; they are then to be placed in a glass jar with 30 c.c. of 80 per cent, alcohol. In order that the objects may be submerged, glue the under surface of the cork-stopper by means of celloidin to the inner surface of the lid of the jar. On the following day the alcohol should be replaced by 70 per cent. alcohol, in which the tissue may remain an indefinite length of time. In order to cut thin sections the celloidin must be hardened : for this pur- pose transfer the objects embedded in celloidin from the 80 per cent, alcohol for 2 days or longer into an alcohol-glycerine mixture (80 per cent, alcohol one part, pure concentrated glycerine 6 to 10 parts). The larger the propor- tion of glycerine to alcohol, the harder the celloidin becomes. This mixture may be differently prepared ; an extreme limit is i part of alcohol to 30 parts of glycerine. Still greater difference in the proportions produces strong curl- ing of the sections. In order to prevent the yielding of the elastic cel- loidin block, dry it carefully with filter-paper on removing it from the alcohol- glycerine mixture ; make a pair of lateral incisions and dip it into liquid paraffin ; such blocks cannot be preserved dry — they must be returned to the alcohol-glycerine mixture. Preparations fixed by Golgi's method reijuire special treatment, since the absolute alcohol has an injurious influence if the object remains in it bevond i hour. When the tissue is taken from the silver solution it is to be placed in 30 c.c. of 96 per cent, alcohol, 15 to 20 minutes, then hardened in absolute alcohol for 15 minutes, and then .placed in the thin celloidin solution for 5 minutes. Meanwhile, in the previously smoothed lateral surface of a broad piece of elder- * This stratum must not be thicker ; even well-hardened celloidin is elastic, and a thick layer would cause the object to give in sectioning. MICROTOME TECHNInl'K. 329 pith, make an excavation just large enough to take in the whole preparation ; in- sert it, cover it with celloidin solution, and then fit a second piece of elder-pith on the first, pour on more celloidin, and place the whole for 5 minutes under a bell-glass to dry ; then transfer it to 80 per cent, alcohol for 5 minutes, and cut sections with a knife flooded with 80 per cent, alcohol. The microtome is altogether unneces.sary ; satisfactory sections can easily be cut free-hand. If the microtome be used, the thickness of the sections should vary from 40 to 120 IX. The elder-pith should be trimmed off so that only a small border (i mm.) surrounds the celloidin. SECTIONING. Paraffin Ohjecis wi/h llie Knife Placed Obliquely. — The paraffin block con- taining the ti.ssue is to be secured in a hollow cylinder coated with hard ])araffin (in the Thoma microtome) or (in the microtome of Schanze) to a little plate adjoining the clamp. With the latter the plate is simply warmed and the paraffin block glued to it by pressure. In the case of the cylinder, warm it and also the base of the paraffin block ; press the latter lightly into the cylin- der and by means of a heated needle inserted between them establish a firm union. In order to cool the paraffin quickly place the cylinder or the ])late for 5 minutes in cold water. The projecting portion of the paraffin block containing the object should then be trimmed to a four-sided column, the ba.se of which is a right-angled i)arallelogram. The column must not be taller than i cm., and the object should be cov- ered by a layer of paraffin not over i to 2 mm. thick. The cylinder (or the plate) with the object should now be placed in the microtome. Sections are to be cut with the blade of the knife dry. The position of the knife depends on the nature of the object. Sectioning with the Knife Placed Ohliqiiely. — If the object is large and of unequal resistance the knife should be so clamped that it forms a very acute angle with the long axis of the microtome. The paraffin block should stand so that the knife strikes it first on one corner. The knife should be moved slowly in the slideway and pressure upon it should be carefully avoided. Sectioning li'ith the Knife Placed Transversely. — Screw the knife down jierpendicular to the long axis of the microtome, turn the i)araffin block so that the blade will strike it first on a flat surface. The knife should be moved rapidly with a ])laning movement and then the sections will adhere to one another at their edges and form long ribbons. When the paraffin is of the right consistence the first section lies smooth on the blade and is shoved by the second section in the direction of the back of the blade. If however the first sections show an inclination to curl and fall over the edge, they must then be carefully held with a delicate sable brush and led back to the right direction. Ribbon cutting is most successful when the sections have a thickness of o. 01 of a mm. ; thicker sections curl easily and do not readily adhere to one another at their edges. Ol'stacles in Sectioning and their Remedy. — P^very one who has worked with paraffin is probably able to explain many an unsuccessful attempt. I. The knife glides over the object and cuts a partial section or none. The reason for this may lie in the microtome ; the slideway may not be clean ; examine the vertical portion of the slideway. Or the knife is not sharp enough, or the under surface has paraffin attached to it ; in the latter case remove the knife and with a cloth wetted with turpentine carefully cleanse it. Knives with thin backs buckle when the distal end of the blade is used ; thus it happens that when the knife is obliquely placed the blade strikes the 330 HISTOLOGY. tissue at first and glides over the rest without cutting it. In microtomes of earlier construction the cause of this often lies in the unsatisfactory manner in which the block of paraffin is secured. Secondly, the trouble may be found in the object ; it may be too hard, or of very unequal resistance, or poorly embedded ; in' the latter case there are two possibilities. Either the preparation was not thoroughly dehydrated, in which case it e.xhibits opaque spots, or it still contains chloroform ; in this case it is soft, and light pressure with a needle on the surface leaves a mark or even presses out fluid. In both cases the procedure of embedding must be repeated, reversing the series of processes to the absolute alcohol (in the latter case to the paraffin bath). Finally, the consistence of the paraffin may be at fault. 2. The sections curl. This can be prevented by holding a small sable brush or bent needle lightly against the curling sections.* The cause of this curling lies in the hardness of the paraffin, which is also responsible for— 3. The sections break. The serviceableness of the paraffin depends in a high degree on the outer temperature. If the paraffin is too hard do not endeavor to reduce its consistence by the admixture of soft paraffin, — this is the last resource, — but employ simpler measures. Cut the sections near a stove or near a lamp ; often slight warming of the knife is sufficient. Even very good paraffin crumbles when cut with a cold knife. 4. The sections fold and become pressed together. As a result of this the sectioned objects acquire a false form. The reason for this lies in a too soft paraffin. This difficulty may be overcome by placing the block frequently in cold water or by cutting the sections in a cold room (in summer, in the morn- ing hours). Cclloidin Objects. — The embedded object is to be trimmed so tliat it is sur- rounded by a stratum of celloidin only i to 2 mm. thick ; clamp the knife obliquely, so that it makes a very acute angle with the long axis of the micro- tome. The knife must be moistened with 70 per cent, alcohol, by means of a sable brush ; this must be repeated after every second or third section. The sections should be removed with a sable brush and transferred to a dish contain- ing 70 per cent, alcohol. Very thin sections (less than 0.02 mm.) cannot be cut unless the celloidin has been hardened. PRESERV.VnON OF THE SECTIONS. Paraffin Objects. — If the sections are not very thin and are not in ribbons, they may be placed in a capsule with 5 c.c. of turpentine, and when the paraffin is dissolved transferred to a second capsule with turpentine. From this the sec- tions, if the tissue has been stained in bulk, are brought on to a slide and mounted according to the directions given on p. 38. If the sections are un- stained, transfer them from turpentine to 5 c.c. of absolute alcohol, which is to be changed in 5 minutes. In another 2 minutes the sections may be stained. In the case of serial sections and very thin sections, it is necessary to fasten the dry sections on the slide. The slide must be absolutely clean ; wash it with alcohol and dry it with a clean, not oily, cloth, or place it for a half hour in cold soap-suds. On the well-dried slide arrange the sections (or por- tion of the " ribbon "), and at the edge of the same place a drop of distilled * .\ " section-smoother " Tor microtomes in which the object is elevated vertically is made by Kleinert of Breslau. See further Born, " Zeitschr. f. wissensch. Mikroskopie," Bd. .x, p. 157. MICROTOME TECHNIQUE. 33 1 water by means of a sable brush. Another section (or portion of the ribbon) is now to be ])laced on the slide, another drop of water added, and so on until the slide is covered. It does not matter if the sections float. Pass the slide through a spirit-flame or place it i to 3 minutes in the oven ;* on being slightly warmed, the sections spread out flat and smooth. Then arrange them with a needle, and by slightly inclining the slide let the water flow off, or absorb it with a strip of filter-paper and, protected from dust, let the whole dry. On the following day ])0ur tnrjientine over the slide and, if the sections are already stained, mount them in damar. In case the sections are not stained the turpentine is to be wiped off and the slide ]jlaced in absolute alcohol. y After 5 minutes take the slide from the alcohol, which is to be quickly wiped off around the sections, and either placed in the stain or covered with a drop of the solution. Then slowly transfer the slide to a dish with distilled water and preserve it in dilute glycerine (p. 37), or with the cus- tomary preliminary treatment with absolute alcohol and oil of bergamot (p. 38), mount it in damar. Celloidiii Ohjects. — Place the sections in a dish containing 20 c.c. of 90 per cent, alcohol. If the tissue has not been previously stained in bulk, staining in bulk is to be preferred, the sections maybe subsequently stained ; but aniline colors cannot be used, as these also stain the celloidin ; even hematoxylin imparts a light blue tint to the celloidin. The sections must not be placed in alii^olute alcohol, since this dissolves the celloidin ; they are to be taken from the 90 per cent, alcohol and jjlaced in chemically jmre amyl alcohol and then transferred to xylol ; when the clearing is completed (p. 38) mount them in xylol-balsam. Serial sections of celloidin objects are only used for special purposes, for example, for the central nervous system. See the articles by Wiegert in the " Zeitschrift fiir wissenschaftliche Mikroskopie," Bd. ii., p. 490, Bd. iii.,p. 480, Bd. iv., p. 209. The negative varnish recommended in the article is to be obtained of Dr. Griibler. • The paraffin must not be allowed to melt ; the resulting mixture of melted paraffin and water is not soluble in turpentine. t The turpentine, also the alcohol, must be quickly wiped ofT, because the sections are ren- dered useless if they are allowed to become dry. Care must also be exercised in placing the staining fluid on the sections, which it should completely cover. Loosening of the sections occurs when there is not enough water between the section and the slide — the water must be evenly diffused between the two. The sections may also be fastened to the cover-glass, but ihis method necessitates the use of larger quantities of the staining solution, alcohol, and other reagents. INDEX. A. Acervulus cerebri, 295 Acetic acid. 30 Acbromatin, 48 Acid alcohol, 23 mixture, 22 Adenoid tissue, 68 diffuse, 96 of the intestines, 166, 167 of the lymph-nodes, 95 of the pharynx, 157 of the tongue, 155 Adipose tissue, 66 Alcohol, absolute, 19, 27 acid, 23 gradually strenj^thened, 29 ninety per cent., 19 Ranvier's thirty-three per cent. seventy per cent., 19 Alum-carmine, 23 Alveolar ducts, 185 Ammonium picrate, 23 Amoeboid movement, 51 Amphypyrenin, 48 Anaphase, 53 Anisotropic substance, 73 Arachnoid, 133 villi of, 133 Arcuate fibers, 237 Arcus tarseus, 258 tarseus externus, 258 Areolar tissue, 64, 67 Arrectores pilorum, 227 Arteries, 85 classification of, 85 Attraction-sphere, 52 Auerbach's plexus, I70, 305 Axis-cylinder, 77, 81,281, 282 Haillarger's stripes, 126 Basement membrane, 61, 67 liergamot oil, 21 Uerliii blue, 37 liile, iSi Hile-capillaries, 176 Bioplasts, 48 Bismarck brown, 23 Blood, 91 elementary granules, 91 examination of, for legal purposes, 286 fibrin, 92 hematoblasts, 93 permanent preparation of, 284 plasma, 91 lilood-cells, 91 colored, 91 colorless, 91 Blood-crystals, 93, 286, 287 Blood-platelets, 92, 2S6 Blood-vessels, 85, 283 arteries, 85 blood-vessels of, 90 capillaries, 89 epithelium (endothelium) of, 283 external clastic membrane, 88 internal elastic membrane, S5 large, 282 lymph-spaces of, 90 nerves of, 90 small, 283 tunica adventilia, 85 tunica intima, 85 tunica media, 85 valves, 89 vasa vasorum, 90 veins, 88 Bone, 70, 100 articulations of, 105 blood-vessels of, 104 canaliculi, 70 cells, 71, no circumferential lamella;, 71, 102 compact matrix, 70 development of, 107, 291 dried, 289 endochondral, I08 fundamental lamellx. 102 ground lamella', 102 growth of, n 2 Haversian canals, loi, 2S9 Haversian lamella", 102, 2S9 Haversian systems, 102 Howship's lacunce, X13 inlerinembranous, 71, III interstitial lamellx, 71, 102 lacuna;, 70 lymph-vessels of, 105 333 Bone, marrow of, I02 nerves of, 105 osteoblasts, no osteoclasts, 113 perichondral. III periosteal, 71, 108 periosteum, 104 primary, 108 resorption of, 112 secondary, in Sharpey libers, 71, I04, 289 spongy matrix, 70 Volkmann's canals, 102 Bowman's membrane, 237 Brain, 123, 295 cells of, 295 cerebellum, 123 cerebrum, 1 23 corpora quadrigemina, 123 corpora striata, 1 23 ganglia of, 1 27 Golgi staining of, 295 gray substance of, 12 J hypophysis cerebri, 131 optic thalami, 123 pineal body, 1 32 staining of niedullated nerve-fibers of, 295 ventricles of, 127 white substance of, 1 23 Brain-sand, 132, 295 Bronchi, 185, 30S blood-vessels of, 188 cartilages of, 186 excretory division, 185 glands of, 187 mucosa of, 1S7 muscle-fibers of, 186 respiratory division, iSS Brunner's glands, 166 Bursa;, 113, 115 Cajal's cell, 125 Calcification, center of, 109 Canada balsam, '22 Canalized fibrin, 220 Capillary blood-vessels, 89 development of, 89, 2S4 Cardiac muscle, 76 Carmine, alum-, 23 borax-, 23 neutral solution of, 23 Carotid gland, 90 Cartilage, 68, 279 articular, 106, 291 bronchial, 186 capsule, 68 cells, 68 costal, hyaline, 279 elastic, 68, 279 epiphyseal, 112 fibrous, 68, 279 hyaline, 68, 279 lacunas of, 68 matrix of, 68 Cartilage, perichondrium, 107 varieties of, 68 Cell-division, 51 direct, 5 1 duration of, 53 indirect, 51 Cell-membrane, 50 Cells, 47 basket, 61 bone, 71 Cajal's, 125 cartilage, 68 chief, 160 column, ilS commissure, I18 concentric, 245 cone-visual, 246 decidual, 216 Deiters's 122, 126, 265 endothelial, 56 ependymal, 122, 126 epithelial, 55 fat, 66, 278 fat, serous, 67 fiber, 260 fixed, 67 forms of, 50 ganglion, 77 giant, 103 glandular, 57 glia, 122 goblet, 58, 163, 164, 187 granule, 66, 277 growth of, 54 gustatory, 274 hair, 260 interior, 120 interstitial, 199 Langerhans's 138, 297 length of life of, 54 liver, 175, 307 marrow, 103 mossy, 123 motion of, 51 multiplication of, 51 nerve, 77, 118 olfactory, 270 parietal, 160 pigment, 66, 225, 239 pillar, 263 plasma, 66, 235 pluricordonal, 120 prickle, 56, 224 Purkinje's, 129 reproduction of, 51 rod-visual, 246 secretory activity of, 54 secretory products of. 54 sexual, 207 size of, 50 spider, 122 structure of, 48 sustentacular, 200, 245, 270, 273 tegmental, 274 tendon, 293 undiflferentiated, 47 vasoformative, 2S4 335 Cells, vita! properties of, 51 wandering of, 67 Cement-substance, 54 Central spindle, 53 Centrosome, 49 Cerebellum, 1 27, 295 basket-cells of, 130 cells of I'urkinje, 129 Golgi staining of, 295 granule layer of, 12S molecular layer of, 130 neuroglia of, 130 while substance of, 131 Cerebrum, 125, 295 bundle of Vic(| d' Azyr, 126 cells of Cajal, 125 hippocampal convolution, 1 26 inlerradial reticulum, 126 layer of polymorphous cells, 125 molecular layer, 125 radiating bundles of, 126 stripes of liaillarger, 126 stripes of Gennari, 126 superradial reticulum, 126 tangential libers, 125 zone of large pyramidal cells, 125 zone of small pyramidal cells, 125 Cerumen, 269 Ceruminous glands, 323 Chondrin, 69 Choriocapillaris, 239 Choroid, 239, 317, boundary zone of, 239 choriocapillaris, 239 layer of capillary networks, 239 layer of large blood-vessels, 239 stroma of, 239 tapetum cellulosum, 239 tapetum fibrosum, 239 teased preparation of, 317 vitreous lamina, 240 Chromatin, 48 Chromic acid, 20 Chromoacetic acid, 21 Chromoaceto-osmic acid, 21, 2S Chromosomes, $2 Ciliary body, 236, 240 muscle, 257 Ciliated epithelial cells, 277 Cle.iring, 39 Close skein, 52 Coccygeal gland, 90 Cochlea, 261. 322, 323 Cohnheim's fields, 74 Coil-glands, 232, 314 distribution of, 233 secretion of, 233 Collateral fibrils, 77 Colored blood-corpuscles, 91 development of, 93 hemoglobin, 91 of frog, 286, of man, 284 stroma of, 91 Colorless blood-corpuscles, 2S6 basophilc granules of, 285 nculrophile granules of. 2S5 Colorless blood-cor|)Uscles, oxyphile granules of, 28s Colostrum, 236 corpuscles of, 236 elements of, 316 Column-cells, 118 Conarium, 132 Cone-fibers, 246 -granules, 246 Congo red, 23 Coni vasculosa, 202 Conjunctiva, palpebral, 256 scleral, 25S Connective tissue, 64, 277 arrangement of elements of, 76 blood-vessels of, 71 cells of, 66, 67, 277 cell-spaces of, 72 elastic, 66 fibrillar, 64, 277 intercellular substance of, 64, 65 interstitial, 199 lymph-spaces of, 72 mucous, 64, 277 nerves of, 71 reticular, 97 varieties of, 64 wandering cells of, 67 Conus meduUaris, 1 17 Corium, 223 Cornea, 239, 31S anterior basal membrane, 237 anterior epithelium, 237 arcuate fibers of, 237 bloodvessels of, 319 canaliculi of. 31S corpuscles of, 237, 319 methylene-blue staining of, 320 nerves of, 319 posterior basal membrane. 238 posterior endothelium, 23S spaces of, 237 substance proper, 237, 318 Corona radiata, 209 Corpora amylacea, 132, 296 quadrigemina, 123 striata, 123 Corpus Highmori, 199 Coipuscles, articular, 141 concentric, 190 corneal, 237 Grandry's, 139 genital, 14I Hassall's, 190 Herbst and Key-Retzius's. 141 Malpighian, 98, 191 Merkel's, 139 Pacini.in, 140 salivary, 155, 157 tactile, 297 Wagner and Meissner's. 14I Corpus luteum. 209 Corti's organ, 263 Cover-glass cement, 22 Cover-glasses, iS Crescents of Giannuzzi, 62 Crypts of Lieberkiihn, 162 33^ Cumulus ovigerus, 209 Cytoblastema. 51 Cytogenous tissue, 67 Dahlia, alum-carmine, 23 Damar-varnish, 21, 3S Daughter-stars, 53 Decalcifying, 29 Decidua graviditatis, 215 menstrualis, 214 placentalis subchorialis, 221 reflexa, 215 serotina, 215 vera, 215 Demilunes, 62, 156, 171 Dendrites, 77 Dentinal ligament, circular, 148 Dentine, 146 Descemet's membrane, 238 Deutoplasm, 208 Diarthroses, 105 Diaster, 53 Direct cell-division, 51 Discus proligerus, 209 Drawing, 45 Duct of Hartholin, 171 of Bellini, I9I of Stenson, 171 of Wharton, 171 of Wirsung and Santorini, 172 Duct-system, 59 Duodenal glands, 169 Dura, 133 E. Ear, 260 arcus spiralis, 264 arteries of, 267 auditory hairs, 261 auditory teeth, 263 blood-vessels of, 267 bony labyrinth, 260 cells of Claudius, 266 cells of Deiters, 265 cells of Hensen, 266 ceruniinous glands, 26S cochlea, 261 cristas acusticie, 260 cupola, 261 ductus cochlearis, 261 ductus endolymphaticus, 260 ductus perilymphaticus, 267 endolymph, 260 epithelium of cochlea, 263 external, 260 fiber-cells, 260 foramina nervina, 263 glands of, 267, 26S hair-cells, 260 internal, 260 labium tympanicum, 261 labium veslibulare, 261 Ear, lamina spiralis membranacea. 262 ligamentum spirale, 262 limbus, 262 lymph-channels of, 267 maculie cribrosse, 260 membrana basilaris, 263 membranous labyrinth, 260 middle, 260 mucosa of Eustachian tube. 267 mucosa of tympanic cavity, 267 nerves of, 266, 326 Nuel's space, 266 organ of Corti, 263 otoliths, 261 perilymph, 260 pillar-cells, 263 prominentia spiralis, 262 Reissner's membrane, 262 saccule, 260 scala tympani. 261 scala vestibuli, 261 semicircular canals, 260 spiral organ, 263 stride vascularis, 262 sulcus spiralis, 261 tunnel. 264 tympanic lamella, 263 utricle, 260 veins of, 267 vestibular membrane, 262 zona pectinati, 263 zona perforata, 263 zona tecta, 263 Egg-protoplasm, 208 Elastic fibers, 278 section of thick, 27S tissue, 66 Eleidin, granules of, 224 Elementarj' granules, 91 organism, 48 Embedding, 326 in celloidin, 328 in paraffin, 327 Enamel prisms, 300 Encircling fibers, 66, 27S End-bulbs, 139, 140, 298 Endogenous cell-formation, 53, 69 Endothelium, 56 Eosin, 23 Ependyma of the ventricles. 127 Epidermis, 223 strata of, 224 Epididymis, 203, 313 Epiglottis, 185 Epiphysis, 132 Epithelium, 55 ciliated, 55 columnar, 55 cuticular zone of. 55 cylindrical. 55 distribution of, 56 germinal, of ovary. 207 glandular, 59 isolation of, 26 of lens, 251 of mucous membranes. 144 of sense organs, 56 337 Kpillielium, pigmented, 55, 225, 226, 24 prickle-cells of, 56, 224 respiratory, 188, 309 rod, 55, 171, 193 secretor)- activity of, 57, 58 transitional, 196 varieties of, 56, 57 Kponychium, 227 l*-poophoron, 2IO Krythroblasts, 93, 103 Ksophagus, 157, 302 Kustachian tube, 267, 323 Exoplasm, 48 Kye, 236, 316 blood-vessels of, 252, 321 canal of Petit, 252, 255 canal of Schlemm, 255 choriocapillaris, 239 choroid, 239 ciliary body, 240 ciliary muscle, 241 ciliary processes, 240 color of iris, 241 conjunctiva, 256 cornea, 236 fovea centralis, 248 ganglion retina, 245 glassy membrane, 240 hyaloid canal, 255 hyaloid membrane, 252 iridocorneal angle, 255 iris, 241 lacrymal canaliculi, 259 lacrymal caruncle, 25S lacrymal glands, 259 lacrymal sac, 259 lamina cribrosa, 250 lamina fusca sclera-, 239 lamina suprachoroidea, 239 lens, 251 ligamentum pectinatum iridis, 242 macula, 248 naso-lacrymal duct, 259 optic nerve, 249 era serrata, 243, 248 perichoroidal space, 255 pigment layer of iris, 241 plica semilunaris, 258 retina, 242 sclera, 238 sheaths of optic nerve, 249 spaces of Kontana, 242 suspensory ligament of lens, 252 tapetum cellulosum, 239 tapetum fibrosum, 239 Tenon's space, 255 tunica externa, 236 tunica interna, 242 tunica media, 239 venae vorticosa;, 253 vitreous body, 252 vitreous lamina, 252 zone of Zinn, 252 zonula ciliaris, 252 Eyeball, coats of, 236 contents of, 236 lymph-channels of, 255 Eyeball, nerves of, 255 Eyelids, 256, 321 blood vessels of, 258 caruncula lacrymalis, 258 cilia, 256 fornix conjunctiva-, 25S glands of, 257, 25S integument of, 256 lymph-vessels of, 259 muscle-fibers of, 257 nerves of, 259 palpebral conjunctiva, 256 plica semilunaris, 258 tarsus, 258 Fallopian tube, 210 ' Fasciae, 1 13, 114 Fenestrated membranes, 65, 278 I Fiber-body, 246 I Fiber- crates, 243 ' Fibers, arcuate, 237 I cone-, 246 j encircling, 66 intergemmal, 275 intragemmal, 275 lattice-, 181 lens-, 251 moss-, 133 Fixation of tissues, 27 Flemming's solution, 21, 28 Formic acid, 21 Fresh objects, examination of, 41 Frommann's lines, 83 Fundus foveas, 248 Galactophorous ducts, 235 Gall-bladder, 174 Ganglia, 136 cerebral, 127 spinal, 136, 297 sympathetic, 137, 297 Ganglion-cells, fresh, 280 apolar, 78 bipolar, 78 multipolar, 78 unipolar, 78 Ganglion nervi optici, 249 retime, 245 spirale, 266 Gastric glands, 160 Gemmation, 54 Generatio x-quivoca, 51 Genitalia, 222 glands of, 222 Gennari's stripes, 126 Germinal center, 95, 167 Germ-layers, 47 Glacial acetic acid, 20 Glands, 59 accessory mammary, 235 accessory tear-, 258 alveolar, 60 338 Glands, alveolar system of, 60 Bartholin's, 222 basement membrane of, 6 1 blood-vessels of, 62 Bowman's, 271 Brunner's, 166 ceruminous, 268 classification of, 59 coil, 232 compound saccular, 60 compound tubular, 59 Cowper's, 205 dehiscent, 61 duct-system of, 59 duodenal, 166 excretory duct of, 61 follicle of, 61 forms of, 59 fundus, l5l Harder' s, 321 lacrymal, 259 Littre's, 198 lobules of, 61 lumen of, 308 membrana propria of, 61 mammary, 234 Meibomian, 258 mixed, 171 Moll's, 257 Montgomery, 235 mucous, 171 Nuhn's, 156 olfactory, 271 periurethral, 198 pyloric, 161 salivary, 171 sebaceous, 227, 231 serous, 171 simple saccular, 60 simple tubular, 59 structure of, 61 sudoriparous, 232 sweat-, 232 tear, 258 trachoma, 258 Tyson's, 232 Glycerine, 21, 38 Gold chloride, 21 Golgi's " black reaction," 36 method, 20 mixture, 35 Graafian follicle, 209 cumulus ovigerus, 209 discus proligerus, 209 liquor folliculi. 209 membrana granulosa, 209 theca folliculi, 209 Granula, 48 Ground-substance, 54 H. Hair, 227, 314, 315 -bulb, 227 color of, 228 cortical substance of, 227 cuticle of, 227 Hair, development of, 230, 315 distribution of, 227 elements of, 314 follicle of, 227 growth of, 230 medulla of, 227 -papilla, 227 renewal of, 231, 3 15 roots of, 227 shaft of, 227 shedding of, 230, 315 Hair-follicle, 227 elements of, 315 Hardening of tissues, 29 Heart, 85, 282 annuli fibrosi, 85 blood-vessels of, 86 endocardium, 85 lymphatics of, 86 muscle-fibers of, 85 nerves of, 86 valves of, 86 Hemalum, 22, 32 Hematoblasts, 93, 103 Hematoxylin, Bohmer's, 22, 31 Delafield's, 22, 34 Weigert's, 22 Hemoglobin, 91 Henn.ann's solution, 21, 29 Howship's lacuna:, 1 13 Hyaloid canal, 255 membrane, 67, 252 Hyaloplasm, 48 Hydatid of Morgagni, 204 sessile, 204 stalked, 204 Hydrochinous developer, 20 Hydrochloric .acid, 20, 27 Hypophysis cerebri, 131, 295 I. Illumination, central, 43 lateral, 43 oblique, 43 Indirect cell-division, 51 Injecting, 37 Instruments, 17 Intercellular bridges, 56, 225, 72 substance, 47, 54 Intermediate lacun.'e, 100 Internodal segments, 83 Internode, 83 Interstitial cells,'l99 granules, 74 tissue, 67 Intestine, 162, 304, 305 basal border of, 163 blood-vessels of, 16S, 305 Brunner's glands, l56, 303 crypts of large, 305 epithelium of small, 303 goblet-cells of, 163, 164 Lieberkiihn's follicles, 162 lymph-nodules of, 166 lymph-vessels of, 169 339 Intestine, mucosa of, 163 muscular tissue of, 165, 16S nerves of, 170 I'eyer's patches, 166 regeneration of epithelium, 163 sohtary follicles of, 166 triple staining of, 304 vaivula conniventes, 163 villi, 162, 303 Intraepithelial nerve-fibers, 297 Involuntary muscle, 72 Iridocorneal angle, 242 Iris, 236 Isolating, 25 Isotropic substance, 73 K. Karyokinesis, 51, 276 Keratohyaline tyrannies, 224 Kidney, 19I, 310 bloodvessels of, 194, 311 Bowman's capsule, 191,311 connective tissue of, 194 cortex of, igi, 310 duct of Hcllini, 191 epithelium of, 193 llenle's loop, 310 lymph-vessels of, 196 Malpighian corpuscles of, 191 medulla of, 191 medullary rays, 310 nerves of, 196, 311 papilliv of, 191 uriniferous tubules, 191, 310 Kleinenberg's solution, 20, 28 L. I.acrymal glands, 259, 321 Lamina cribrosa, 250 fusca sclera.', 239 suprachoroidea, 239 Lanugo, 228, 232 Larynx, 184, 30S blood-vessels of, 185 cartilages, 1S4, 1S5 lymph-vessels of, 185 nerves of, 185 solitary n(xlules of, 184 vocal cords, 184 Lens, 236 epithelium of, 320, 321 Lens-capsule, 252, 320, 321 Lens-fd)ers, 251, 320 Leucocytes, 91, 95 classification of, 92 formation of, 95 granules of, 95 l.igamentum iridis pectinatum, 242 Linin, 48 Lithium carbonate, solution of, 22 Littre's glands, 19S Liver, 174, 307 bile-capillaries, 176 blood-vessels of, 177, 308 Liver, capsule of, 180 capsule of (Ilisson, 171, 181 cells of, 175, 307 cords of cells, 176 hepatic duct, 174 interlobular bile-ducts, 174 interlobular connective tissue, 174 lobules of, 174, 183, 307 lymphatics of, 181 nerves of, I Si relation of bile-capillaries to cells of, 177 secretion of, 181 tubular structure of, 181, 183 vasa aberrantia, 174 Loose skein, 52 Lumen of glands by Golgi's black reaction, 308 Lungs, 185, 309 alveolar ducts, 185 alveoli, 155 blood-vessels of, 188, 309 elastic fibers of, 188, 309 infundibula of, 186 interlobular tissue of, 188 lobules of, 1 86 lymph-vessels of, 1S9 nerves of, 1 89 pigmentation of, 1 88 respiratory bronchioles, 1S5 respiratory epithelium, 188 terminal bronchioles, 185 terminal vesicles, 186 Lunula of nail, 227 Lymph, 97 canaliculi, 72 corpuscles, 72 spaces, 72 Lymph-spaces, adventitial, 90 perivascular, 90 Lymphatic tissue, 95 diffuse, 96, 166 Lymph-channels of the central nervous sys- tem, 134 Lymph-nodes, 94, lOfi, 287 blood-vessels of, 96 bronchial, 189 distribution of, 97 germinal center, 95 hilus of, 94 medullary cords, 94 nerves of, 96 peripheral, 96 pulp of, 96 secondary nodules, 94 -sinus, 95 solitai-y, 96, 1 66, 184 trabecuhv of, 95 Lymph- vessels, 93, 287 origin of, 94 stomata, 94 Macula lutea, 24S Mammary glands, 234, 316 accessory, 235 34° Mammary glands, ampulla of, 234 ducts of, 235 nipple, 235 secretion of. 236 sinus lactiferus, 234 Margarin crystals, 67 Marrow, cells of, 103 elements of, 103 red, 102, 290 yellow, 102 Mastzellen, 66, 277 Measurement, 45 Medullary rays, 191 segments, 82 Meissner's plexus, 170, 305 Membrana chorii, 219 choriocapillaris, 239 granulosa, 209 limitans iridis, 241 limitans olfactoria, 271 propria, 144 reticularis, 265 tectoria, 266 vestibularis, 262 Metakinesis, 53 Metaphase, 53 Methyl -violet B, 23, ;i;i Methylene blue, 23 for axis-cylinders, 34 Microscope, care of, 17 management of, 43 Microsomes, 48 Microtome, 326 ' Mikron, 50 Milk, human, 236, 316 Mitotic cell-division, 51 in the intestine, 163 in the lymph-nodes, 95 Molecular motion, 51 Monaster, 53 Mother-star, 53 Motor nerve-endings, 299 Mounting, 38 Mucous glands of lips, 300 Mucous membranes, structure of, 144 of the oral cavity, 144, 145 Muller's fluid, 20, 28 Muscle, 72, 113, 293 bundles of striped, 292 cardiac, 76 endomysiuni, 113 epimysium, II3 nonstriated, 72 perimysium, 113 striated, 73 Muscle-columns, 74 Muscle-fibers, 72, 279 branched, 280 ends of, 280 librillje of, 74, 280 isolation of, 26 nuclei of, 74, 280 pale, 75 red, 75 sarcolemma, 75 smooth, 72, 280 striated, 73, 279 Myelin, 82 Myeloplaxes, 103 N. Nails, 226, 314 elements of, 314 growth of, 226 lunula, 227 matrix of, 226 substance of, 227 Nasal mucous membrane, 269 basal cells, 271 blood-vessels of, 273 lymph-vessels of, 273 membrana limitans olfactoria, 271 nerves of, 272, 324 olfactory cells, 270, 324 olfactory glands, 271 olfactory region of, 270, 324 respiratory region of, 269, 324 sustentacular cells of, 270 tunica propria of, 27 1 vestibular region of, 269 Nerve-cells, 77 of the first type, 79 of the second type, 79 processes of, 78 Nerve-endings, 138, 297 end-bulbs, 139 in epithelium, 138 in striated muscle, 142 motor, 142, 299 tactile-cells, 139, 297, 298 tactile corpuscles, I40 sensory, 138 Nerve-fibers, 78, 281 axis-cylinder, 81 bundles of, 296 medullary sheath of. Si, 2S1 medullated, Si, 2S1 neurilemma, S3 nodes of, 83 nonmeduUated, 80, 282 Nerve-process, 76 Nerve-trunks, 134 blood-vessels of, 136 cerebro-spinal, 134 endoneurium, 135 epineurium, 134 fibrillar septa of, 135 lymphatics of, 136 perineurium, 134 sympathetic, 135 Neuroblasts, 76 Neurodendron, 77 Neuro-epithelium, 56 of ear, 260 of nose, 270 of retina, 246 of tongue, 273 Neuroglia, 83, 117, 122, 126 Neuron, 77 Neuroplasm, 82, S3 Nitric acid, 20, 28 Node of Ranvier, 83, 282 Normal salt solution, 19 341 Xuclear spindle, 53 structure, 276 Nuclei of motor-plates, 299 Nuclein, 48 Nucleolus, 49 Nucleus, 48 matrix of, 48 membrane of, 49 network of, 49 nucleolus, 49 Nulin's glands, 156 O. Odontoblasts, 71, I48, 150,300 Ocular-micrometer, 45 Olfactory cells, nerve-process of, 324 (Jmentum, 308 Ora serrata, 243, 248 Organ of Giraldds, 204 Osmic acid, 21, 28 Osmio-bichromate mixture, 20 Ossification, loS centers of, 109 endochondral, 109 metaplastic mode of, 1 1 1 neoplastic mode of, 1 1 1 perichondral , I n periosteal, ill Osteoblasts, no Osteoclasts, 113 Otoliths, 261, 322 Ova of frog, 313 Ovary, 206, 311, 313 blood-vessels of, 2io corpus luteum, 209 cortex of, 206 germinal epithelium, 207 glandular substance of, 206 Graafian follicles, 206 lymph-vessels of, 210 medulla of, 206 nerves of, 210 primary egg- tubes, 207 primary follicles, 207 sexual cells of, 207 tunica albuginea of, 206 f)viduct. 210, 313 Ovula Nabothi, 214 Ovum, 207, 313 corona radiata, 209 deuloplasm, 208 germinal spot, 209 germinal vesicle, 209 perivitelline space, 209 vitellus, 20S zona pellucida, 207 P. Pacchionian bodies, 133 Pacinian bodies, 140 Pal's mixture, 22 Pancreas, 172. 307 z)Tnogcn granules of, 172 Panniculus adiposus. 223 Papillx, circumvallate, 154 filiform, 153 foliate, 154, 274 fungiform, 154 Paradidymis, 204 Paranuclcin, 48 Paroophoron, 210 Parotid, 171, 306 Parovarium, 210 Pars retinae ciliaris, 249 iridica, 241 optica, 243 Pelvis of kidney, 311 epithelial cells of, 311 Penis, 205 arteries of, 205 corpora cavernosa, 205 corpus spongiosum, 206 erectile tissue of, 205 helicine arteries, 205 tunica albuginea of, 205 venous spaces of, 205 Perichondrium, 106 Perichoroidal space, 255 Periosteum, loi, 104 Peritoneum, 183 endothelium of, 308 Perivascular lymph-spaces, 90 Permanent preparations, storing of, 42 Peyer's patches, 96, 166, 167,304 Pharyngeal tonsil, 157 Pharynx, 157 Picric acid, 20 Picrocaniiine, 23, ^^ Picrosulphuric acid, 20, 28 Pigmentation of skin, 225 theories of, 225, 226 Pineal body, 132 Pituitary body, 131 Placenta, 217 amnion, 219 arteries of, 212 blood-vessel system of, 212 canalized fibrin, 220 cell-patches, 220 chorion, 217 chorionic villi, 217, 219 decidua serotina, 217 foetal is. 217 intervillous spaces, 217. Jin septa of, 221 syncytium, 220 uterina, 217, 221 Plasma-cells, 66 Plastin, 48 Platino-aceto-osmic mixture, 21. 2q Platinum chloride, 21 Pleura, 188 Plexus choroideiv, 133 Polar field, 52 radiation, 53 Potash lye, 21, 26 Potassium bichromate, 20 permanganate, 22 Prophase, 52 342 Prostate body, 204, 313 glandular tissue of, 205 muscular tissue of, 204 secretion of, 204 Prostatic crystals, 204 Protoplasm, 48 Pyramids of Kerrein, 191 Pyrenin, 48 Radial fibers of Muller, 243 Reagents, 19 Reissner's membrane, 262 Remak's fibers, 80 Respiratory epithelium, 309 Rete testis, 199 Retia mirabilia, 94 Retina, 243, 317 cerebral layer, 243 cone-visual cells, 246 elements of, 317 fovea, 248 macula, 248 neuro-epithelial layer, 246 era serrata, 24S pigmented epithelium of, 248 rod-visual cells, 246 Rod-fibers, 246 Rod-granules, 246 Saccule, 260 Saflfranin, 23, 33 Salivary corpuscles, 155, 157 Salivary glands, 171 blood-vessels of, 173 demilunes, 171 excretory ducts of, 171, 172 intercalated tubules, 171 intralobular tubes, 172 membrana propria of, 171 mixed, 171 mucous, 171 nerves of, 173 rod epithelium of, 171 secreting cells of, 171, 172 serous, 171 Salt solution, normal, 19 Sarcolemma, 75, 279 Sarcoplasm, 74 Sarcostyles, 74 Sarcous elements, 74 Schmidt-Lantermann segments, 82 Sclera. 23S Sebaceous glands, 231, 315 distribution of, 232 secretion of, 232 Secretory capillaries, 62, 160 Sectioning, 30, 329 Sections, preservation of. 330 Segments, cylindro-conical, 82 internodal, 73 medullary, 82 Schmidt-Lantermann, 82 Semen, 201 elements of, 312 Semicircular canals, 260 ampuUoe of, 260 crista; acusticLU, 260 Seminal filaments of frog, 312 vesicles, 203, 313 Seminiferous tubules, 312 Septula medullaria, 117 Sertoli's columns, 200 Sharpey's fibers, 71, 104, 148 Silver nitrate, 20, 21 Sinus lactiferus, 234 Sister-loops, 53 Skin, 223 arrector pili, 227 blood-vessels of, 223, 316 coil-glands, 232, 314 color of, 225, 226 corium, 223 cuticle, 223 derma, 223 eleidin granules, 224 epidermis, 223 glands of, 23 1 hair, 227 hair-follicles, 228 lymph-vessels of, 233 nails, 226 nerves of, 233 panniculus adiposus, 223 papillae of, 223 pigment of, 225 rete mucosum, 224 sebaceous glands, 232 stratum corneum, 224 stratum granulosum, 224 stratum lucidum, 225 stratum Malpighii, 224 stratum papillare, 223 stratum reticulare, 223 stratum subcutaneum, 223 striated muscle-fibers of, 224 Slides, 18 Smooth muscle, 72 Sodium carminate, 23 hyposulphite, 20 Solitary follicles, 166 Spaces of Fontana, 242 of Nuel, 266 Spermatids, 200 Spermatogenesis, 200 Spermatozoa, 201 Spinal cord, 116, 293 anterior column, 1 16 anterior cornua, I16 anterior gray commissure, 117 anterior medi.in fissure, 116 anterior roots of nerves of, 116 central canal, 1 17 collateral fibers, 1 18, 119, 120 column of Burdach, :i6 column-cells, 1 18 column of Clark, 116, 119, I20 column of GoU, II6 commissure-cells, 118 conus medullaris, 117 343 Spinal cord, Dciters's cells, 122 dorsal nucleus, Il6 epcndymal cells, 122 funiculus cuneatus, Il6 funiculus gracilis, Il6 glia-cells, 122 (jolgi's method of staining, 294 gray commissure, 116 gray substance of, 117 interior cells, 120 lateral column, 116 lateral cumua, 116 motor nerve-cells, llS multipolar ganglion-cells, 2S1 nerve-fibers of, 120 neuroglia, 117, 122 posterior column, 116 posterior comua, Ii6 l>osterior gray commissure of, 117 iwsterior roots of nerves of, 1 16 posterior septum, 116 pluricordonal cells, 120 reticular process, 116 septula meduUaria, 117 stem-fiber, 118 staining of axis-cylinders of, 294 staining of cells of, 294 staining of medullated fibers of, 294 sul>stantia gelatinosa centralis, 1 23 substantia gelatinosa Rolandi, 123 white commissure, 116 white substance of, 121 zona spongiosa, 117 zona terminalis, 1 17 Spiral organ, 263 Spleen, 97, 288 blood-vessels of, 99, 288 capsule of, 97 elements of, 288 intermediate lacuna', lOO karyomitotic figures in, 288 lymphatics of, 100 Malpighian corpuscles of, 98 pulp of, 97 reticular connective tissue of, 288 trabecula- of, 97 Spongioplasm, 48 Stage-micrometer, 45 Staining, 31 bulk, 32 diffuse, 32 double, i^ gold, 37 mucous, 34 nuclear, 31, 33 silver, 35 triple, 34 under the cover-glass, 41 Stomach, 158, 302 Auerbach's plexus, 170 bloodvessels of, 168, 305 epithelium of, isolated, 302 glanils of, 160, 302 lymph-vessels of, 169 Meissner's plexus, 170 nmcous membrane of, 302 muscular tissue of, 162 Stomach, ner\es of, 170 Strangzellen, liS Strata of skin, 314 Striated muscle, 73 Sublingual gland, 171, 306 Submaxillary, 171, 306 Substantia compacta, loo gelatinosa centralis, 1 1 7, 123 gelatinosa Rolandi, 117, 123 propria, 237 spongiosa, of bone, loi Sudoriparous glands, 232 Suprarenal body, 143, 299, 300 blood-vessels of, 144 elements of, 300 nerves of, 144 zona fasciculati, 1 43 zona glomerulosa, 143 zona reticularis, 143 Sutures, 105 Svk-eat-glands, 232 Synarthroses, 105 Synchondrosis, 105 Syncytium, 220 Syndesmosis, 105 Synovial membranes, 105 villi, 105, 291 Tactile-cells, compound, 139, 298 simple, 139, 297 Tapetum cellulosuin, 239 tibrosum, 239 Taste-buds, 154, 185, 273, 324, 325 gustatory cells, 274 ner\'es of, 325 orientation of, 324 taste-pore, 273 tegmental cells, 274 Teasing, 25 Teeth, 146, 300 blood-vessels of, 148 cementum, 146, 148, 151 crown, 146 dental bulb, 148 dental furrow, 149 dental papilla, 14S dental ridge, 148 dental sack, 151 dentinal fibers, 147, 14S dentinal globules, 147 dentinal sheath, 147 dentinal tubules, 147 dentine, 146 development of, 148, 301 dried, 300 enamel, 146 enamel cuticle, 151 enamel organ, 149 enamel prisms, 300 epithelial sheath, 150 fang, 146 interglobular spaces, 147 isthmus, 149 neck, 146 nerves of, 148 344 Teeth, odontoblasts, 148, 150 pulp of, 146, 14S Telre choroide;!:, 133 Tendon, 1 13, 1 14, 292, 293 cells of, 293 Tendon-sheath, 113, 115 Tendon-spindles, 1 15 Tenon's space, 255 Terminal bronchioles, 1S5 vesicles, 186 Testicle, 198, 311 blood-vessels of, 201 cells of, 200 corpus Highniori, 199 ducts of, 202 elements of, 312 hydatids of, 204 lobules of, 198 lymph-vessels of, 201 mediastinum of, 199 nerves of, 201 rete testis, 199 secretion of, 201 seminiferous tubules, 199 Sertoli's columns, 200 tubuli recti, 200 tunica albuginea of, 19S tunica vasculosi of, 199 Thymus body, 190, 310 blood-vessels of, 191 corpuscles of Hassall, 190 Thyro-glossalduct, 189 Thyroid gland, 61, 189, 309 duct of. 189 colloid substance of, 189 Tissue juices, 72, 94 Tissues, 47 animal, 48 vegetative, 47 Tongue, 153, 301 blood-vessels of, 156 glands of, 155 lymph-follicles of, 154, 301 lymph-vessels of, 156 mucosa of, 153 muscles of, 153 nerves of 156 papilla: of, 153, 301 •ronsils, 157, 301 " Trachea, 185 cartilages of, 1 85 elastic fibers of, 185 glands of, 1 85 Transitional epithelium, 296 Triacid solution, 2S5 Tympanum, 268 U. Ureters, 196, 311 transitional epithelium of, 19 Urethra, 198, 311, 313 blood-vessels of, 19S female, 198 glands of, 198 male, 198, papillce of, 19S Urinary bladder, 197, 311 internal vesical sphincter, 197 Urogenital sinus, 198 Uterus, 210, 313 blood-vessels of, 213, 215, 216 cervix, 213 decidual cells, 216 glands of, 212 lymph-vessels of, 217 mucosa of the gravid, 215 mucosa of the menstruating, 214 mucosa of the virgin resting, 212 mucous crypts, 213 nerves of, 217 ovula Nabothi, 214 Utricle, 260 Vagina, 222 blood-vessels of, 223 lymph -vessels of, 223 secretion of, 223 tunics of, 222 Valvula; conniventes, 162 * Vas aberrans Halleri, 204 Vas deferens, 203, 313 ampulla of, 203 Vasa aberrantia, 174 efierentia, 202 vasorum, 90 Vasoformative cells, 284 Vater's corpuscles, 140 Veins, 88 valves of, 89 Ventricle of Morgagni, 1S4 Vesuvin, 23, 33 Vicq d'Azyr's bundle, 126 Villi of arachnoid, 133 of intestine, small, 162 of placenta, 217 synovial, 106, 291 Vitellus, 208 Vitreous body, 236 Vocal cords, 184 Volkmann's canals, 102 Voluntary muscle, 73 W. Wagner and Meissner's corpuscles, i Wandering cells, 91, 238 hematogenetic, 67 histogenetic, 67 Westphal's alum-carmine dahlia, 23 Xylol, 21 -balsam, 22 Zell-knoten, 220 Zona pellucida, .207 Zone of Zinn, 252 Zonula ciliaris, 252 Zymogen granules, 172 COLUMBIA UNIVERSITY LIBRARY This book is due on the date indicated below, or at the expiration of a definite period after the date of borrowing, as provided by the rules of the Library or by special ar- rangement with the Librarian in charge. DATE BORROWEO DATE DUE DATE BORROWED DATE DUE 194S •m - c2el29e)Mioo .i:.!551 Stohr St61 1896 / Text-book of histology 1