«' B :
CORNELL UNIVERSITY.
THE
llostucll p. S^Iotocr tSbrarg
THE GIFT OF
ROSWELL P. FLOWER
FOR THE USE OF
THE N. Y. STATE VETERINARY COLLEGE.
1^97
Cornell University Library
QM 551.S86 1900
Text-book of histology, including the mic
""1
3 1924 001 029 937
no
The original of this book is in
the Cornell University Library.
There are no known copyright restrictions in
the United States on the use of the text.
http://archive.org/details/cu31924001029937
TEXT-BOOK
HISTOLOGY
INCLUDING
THE MICROSCOPIC TECHNIC
DR. PHILIPP STOHR
PROFESSOR OF ANATOMY AT THE UNIVERSITY OF WURZBURG
THIRD AMERICAN FROM EIGHTH GERMAN EDITION
TRANSLATED BY DR. EMMA L. BILSTEIN [BILLSTEin]
FORMERLY DIRECTOR OF THE LABORATORIES OF HISTOLOGY AND EMBRYOLOGY, WOMAN'S MEDICAL
COLLEGE OF PENNSYLVANIA
EDITED, WITH ADDITIONS
I!Y
DR. ALFRED SCHAPER
"T
PROFESSOR OF ANATOMY, UNIVERSITY OF BRESLAUJ FORMERLY ASSISTANT PROFESSOR OF HISTOLOGY, HARVARD
MEDICAL SCHOOL, BOSTON, MASS : FORMERLY DOCENT OF ANATOMY AND FIRST ASSISTANT
AT THE ANATOMICAL INSTITUTE OF THE UNIVERSITY OF ZURICH
TKHitb 301 flllustrations
PHILADELPHIA
P. BLAKISTON'S SON & CO
IOI2 WALNUT STREET
1900
Copyright, 1900, by Dr. Alfred Schaper.
Press of Wm. F, Fell & Co
1220-24- Sansom St.
philadelphia
EDITOR'S PREFACE TO THE THIRD EDITION,
This edition has been revised in accordance with the eighth, again ^
considerably enlarged, German edition. The many new illustrations
added are from the original electrotypes, placed at our disposal, as
formerly, by the kindness of Professor Stohr. The editor has found it
necessary to make no changes or additions whatever in this edition, but
has retained all those contributions (illustrations as well as text) which
appeared in the former American editions, and which, as previously, dis-
tinctly bear his name. In compliance with the special request of Pro-
fessor Stohr he wishes moreover to emphasize that he takes the sole
responsibility for those additions.
BRESLAU, December, 1900. ALFRED SCHAPER.
EDITOR'S PREFACE TO THE SECOND
EDITION.
The favorable acceptance of the first American edition of Stohr' s
Text-book of Histology has apparently proved the work a welcome
addition to the histological literature of this country. In preparing a
second edition the editor has found the opportunity to revise and com-
plete the book according to the seventh, very much enlarged, German
edition, which has meanwhile been issued. Therefore the present Ameri-
can edition can be considered as offering to the student the latest results
of histological research. With considerable changes and additions in
the text, twenty-one new illustrations have been embodied in the new
American from the last German edition. Beyond this the editor has
ventured to add ten (Figs. 66, 76, 119, 131, 160, 172, 208, 209, 260, 265)
illustrations from original drawings, hoping to contribute further to the
usefulness of the book. Some new editorial remarks and additions
appear, mostly in the form of foot-notes.
The editor is again under great obligation to Dr. E. L. Billstein
for a thorough and very successful revision of the English translation,
and to Prof. Ph. Stohr for placing the electrotypes of the new illustra-
tions of the eighth German edition at his disposal. He also feels deeply
indebted to Messrs. P. Blakiston, Son & Co. for the excellent reproduc-
tion of his new drawings and for the many improvements in the general
arrangement and the printing of the work.
Alfred Schaper.
Harvard Medical School,
Boston, Mass., July, i8g8.
EDITOR'S PREFACE.
Stohr'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 indispensable guide. During the ten years of its exist-
ence it has reached an extraordinary sale and passed 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. Although 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 translation
into English for the convenience of American and English students.*
It is especially intended for the use of students, but even profes-
sional histologists and physicians will find in it much valuable informa-
tion, as well as suggestions 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 speci-
mens. 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 enu-
merated 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 Appendix, brief directions for the pre-
paratory treatment (embedding in paraffin and celloidin) of specimens
for sectioning with the microtome.
With the permission of Prof. Stohr we have made several imma-
terial, but for an American edition very desirable, changes in the text,
and have considered it preferable to place the technical part as a
whole at the end of the book rather than in sections after the several
* 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 authors that its chief merits were
entirely lost. This use of the book can not be considered as an English translation proper.
V
VI EDITOR S PREFACE.
chapters. Furthermore, we have enlarged the chapter on the Uterus,
in order to give detailed consideration to the various functional condi-
tions of the organ, and added to the book an entirely new chapter on
the Placenta. Eight new illustrations (Figs. 229, 230, 232, 233, 234,
236, 237, 238) were necessary for these additions.
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
Prof. 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. 229) from their " Lehrbuch der Histologic" He also feels
deeply indebted to Prof. Charles S. Minot for kind assistance, for valuable
criticism, and for permission to use two illustrations (Figs. 231 and 234)
from his text-book of " Human Embryology " ; and, finally, to Messrs.
P. Blakiston, Son & Co., Philadelphia, for the very satisfactory repro-
duction of the new drawings, and for their many courtesies during the
preparation of the American edition.
Alfred Schaper.
Harvard Medical School,
Boston, June, i8g6.
CONTENTS
PART I
GENERAL TECHNIC.
I. The Laboratory Appoint-
PAGE
The
Preparation of Microscopic Spec-
PAGE
ments, .
17-26
imens. — Continued.
Instrument.
Sectioning.
Reagents.
Staining.
Injecting.
II. The Preparation of Micro-
Mounting and Preserving of the
scopic Specimens, . .
27-52
Preparations.
Introduction.
Examination of Fresh Objects.
Nature of the Material.
Storing of Permanent Speci-
Killing and Dissecting the Ani-
mens.
mals.
Isolating.
III.
Management of the Micro-
Fixation.
scope, .
53-57
Hardening.
Drawing.
Decalcifying.
PAF
T II
Measurement.
MICROSCOPIC ANATOMY
AND SPECIAL TECHNIC
I. HISTOLOGY.
(Microscopic Anatomy of the Cells and the Tissues.)
A. — Cells
59-68
Tissues. — Continued.
Parts of the Cell.
The Glands.
Form of Cells.
Technic No. 3-5,
80
Size of Cells.
II.
The Supporting Tissues,
80-95
Vital Properties of Cells.
Connective Tissue.
Phenomena of Motion in Cells.
Cartilage.
Reproduction and Multiplication
Osseous Tissue.
of Cells.
Technic No. 6-22, .
91-95
Phenomena of Secretion in Cells.
III.
The Muscular Tissues, .
95-101
Length of Life of Cells.
Smooth Muscle-Tissue.
Growth of Cells.
Striated Muscle-Tissue.
Secretory Products of Cells.
Cardiac Muscle.
Technic No. 1,2,
67-68
Technic No. 23-29, . . .
IOO-IOI
B. — Tissues.
IV.
The Nervous Tissues, .
I02-II2
I. The Epithelial Tissues,
68-80
Nerve-Cells.
Secretory Activity of Epi-
Nerve- Fibers.
thelial Tissues.
Technic No. 30-37,
IIO-II2
Vll
CONTENTS.
II. MICROSCOPIC ANATOMY OF THE ORGANS.
PAGE
I. The Circulatory System, . 113-141
1. The Blood- Vessel System, 1 13-126
The Heart.
The Arteries.
The Veins.
The Capillaries.
Development of Capil-
laries.
Glomus caroticum and coc-
cygeum.
The Blood.
Development of Colored
Blood -corpuscles.
Developrrient of Colorless
Blood-corpuscles.
2. The Lymph-vessel System, 126-134
The Lymph-vessels.
The Lymph-glands.
The Peripheral Lymph-
nodules.
The Lymph.
The Spleen.
Technic No. 38-60 134- 141
II. Organs of the Skeletal
System 142-161
The Bones.
Articulations of Bones.
The Cartilages.
Development of Bone.
Development of Primary
Bone.
Development of Second-
ary or Intermembranous
Bone.
Growth of Bone.
Resorption of Bone.
Technic No. 61-67, • - 157-161
III. Organs of the Muscular
System, ... . 162-166
The Muscles.
The Tendons.
The Fasciae.
Tendon-sheaths and BursEe.
Technic No. 68-72, . . . 165-166
IV. Organs of the Nervous
System, ... . 167-214
I. The Central Nervous System, 167-190
PAGE
Organs of the Nervous System. —
Continued.
The Spinal Cord.
Topography.
Minute Structure.
The Brain.
The Cerebral Cortex.
The Cerebral Ganglia.
The Gray Substance of
the Ventricles.
The Cerebellar Cortex.
The White Substance.
The Hypophysis Cere-
bri.
The Epiphysis.
The Membranes of the
Central Nervous System.
The Vessels of the Cen-
tral Nervous System.
2. The Peripheral Nervous
System, . . . 190-205
The Nerves.
The Ganglia.
The Peripheral Nerve-end-
ings.
Terminations of Sensory
Nerves.
Terminations of Motor
Nerves.
The Suprarenal Body.
Technic No. 73-95, ... 206-214
V. The Digestive Organs, . 214-276
A. Headgut.
The Oral Cavity.
Mucous Membranes.
The Mucous Membrane of
the Oral Cavity.
The Teeth.
Development of the Teeth.
The Tongue.
The Soft Palate and the
Pharynx.
B. Rumpgut.
The Foregut.
The Esophagus.
The Stomach.
The Midgut.
The Duodenum and the
Small Intestine.
The Endgut.
CONTENTS.
IX
The Digestive Organs. — Continued.
The Large Intestine.
The Rectum.
The Lymph-nodules of the
Stomach and the Intes-
tines.
The Blood-vessels of the
Stomach and the Intes-
tines.
The Lymph-vessels of the
Stomach and the Intes-
tines.
The Nerves of the Stomach
and the Intestines.
The Salivary Glands.
The Liver.
The Peritoneum.
Technic No. 96-126, .
VI. The Respiratory Organs,
The Larynx.
The Trachea.
The Bronchi and the Lungs.
The Thyroid Gland.
The Thymus Body.
Technic No. 127-133, .
VII. The Urinary Organs, . .
The Kidneys.
The Ureters.
The Urinary Bladder.
The Urethra.
Technic No. 134-144, .
266-276
276-287
285-287
287-298
296-298
VIII. The Reproductive Organs, 299-330
The Male Reproductive Or-
gans.
The Testicle.
The Semen.
The Excretory Ducts of
the Testicle.
The Prostate Body.
The Penis.
The Female Reproductive Or-
gans.
The Ovaries.
The Epoophoron and the
Paroophoron.
The Oviduct.
The Uterus.
The Placenta.
The Vagina and the Ex-
ternal Genitalia.
Technic No. 145-160, . . . 329-330
IX. The Skin and its Append-
ages, 33I-3SI
The Skin.
The Nails.
The Hairs and the Hair-Fol-
licles.
Development of the Hair.
Growth of the Hair and of the
Root-sheaths.
Shedding and Replacement of
Hair.
The Glands of the Skin.
The Blood-vessels, Lymph-
vessels, and Nerves of the
Skin.
The Mammary Gland.
Technic No. 161-176, . 348-351
X. The Organ of Vision, . . 351-386
The Eyeball.
The Tunica Externa.
The Cornea.
The Sclera.
The Tunica Media.
The Choroid.
The Ciliary Body.
The Iris.
The Iridocorneal Angle.
The Tunica Interna.
1 . Pars Optica Retinae.
The Cerebral Layer.
The Neuro - epithelial
Layer.
The Pigmented Epithe-
lium.
The Macula and Fovea
Centralis.
The Ora Serrata.
2. Pars Ciliaris Retina?.
3. Pars Iridica Retinse.
The Optic Nerve.
The Lens.
The Vitreous Body.
The Suspensory Ligament.
The Blood-vessels of the Eye-
ball.
The Lymph-channels of the
Eyeball.
The Nerves of the Eyeball.
The Eyelids.
The Lacrymal Organ.
Technic No. 177-192, . . . 379-386
CONTENTS.
XI. The Organ of Hearing, .
The Internal Ear.
The Saccule, the Utricle,
and the Semicircular
Canals.
The Cochlea.
The Middle Ear.
The Tympanic Cavity.
The Eustachian Tube.
The External Ear.
The Tympanum.
PAGE
386-402
The Organ of Hearing. — Continued.
The External Auditory
Canal.
Technic No. 193-198, . . . 399-4°2
XII. The Olfactory Organ, 402-407
The Vestibular Region.
The Respiratory Region.
The Olfactory Region.
Technic No. 199-202, . 406-407
XIII. The Gustatory Organ, 407-410
Technic No. 203-205, . 410
APPENDIX.
Microtome Technic, . .
I. The Microtome.
II. Embedding.
The Paraffin Method.
The Celloidin Method.
III. Sectioning.
Paraffin Objects.
With the knife placed
obliquely.
With the knife placed
transversely.
411-418
Microtome Technic. — Continued.
Obstacles in Sectioning
and their Remedy.
Celloidin Objects.
IV. Preservation of Sections.
Paraffin Objects.
Celloidin Objects.
Books Recommended for Col-
lateral Study, . . . 419-420
Index, . . . . 421
LIST OF ILLUSTRATIONS.
FIG.
PAGE
1. Leitz Microscope, ..... . . 54
2. Diagram of a Cell . . 60
3. Cell of Bone-Marrow of a Rabbit, ... . . 61
4. Leucocytes of a Frog, . . .62
5. Karyolcinetic Figures — Epithelium of Salamander, . 64
6. Nuclear Structure, Connective-Tissue Cell, . . 67
7. Epithelial Cells of a Rabbit, Isolated, .... . . 68
8. Pigmented Epithelium, .... 69
9. Simple Columnar Epithelium, . .... 69
10. Stratified Squamous Epithelium, . 69
11. Stratified Ciliated Epithelium, . . . 70
12. Terminal Bars, Columnar Epithelium, . 71
13. Scheme of the Network of Terminal Bars, . . . 71
14. Prickle-Cells, ... . . 71
15. Serous Gland-Cells, .... . . 72
16. Secreting Epithelial Cells, . . 73
17. Crypt of Lieberkiihn, . . . . . 74
18. Diagram of the Different Gland-Forms, . 75
19. Mucous Gland of the Tongue of a Rabbit, . . . • 77
20. Fundus Gland of a Mouse, . . 77
21. Diagram of the Origin of Crescents, . 78
22. Schematic drawing of a Tubular Gland, . . 79
23. Umbilical Cord of a human Embryo, . . .81
24. Connective-Tissue Bundles, . . . ... 81
25. Elastic Fibers, 81
26. Network of Elastic Fibers, passing into a Fenestrated Membrane, . . 82
27. Connective-Tissue Cells, Connective-Tissue Bundles, Plasma Cells, 82
28. Fat-Cells, .... ... . 83
29. Adipose Tissue, . . . .84
30. Serous Fat-Cells, . . . ... .84
31. A Piece of the Greater Omentum of Man, . . . . . . 85
32. Reticular Connective Tissue, ... . . . ... 85
33. Hyaline Cartilage, . .... . . 87
34. Elastic Cartilage, . . 88
35. Section of an Intervertebral Disk of Man, . . . 88
36. Ground Section of Dried Bone of Adult Man, . . .... 90
37. Section of the Humerus of a human Embryo and of the Middle Turbinal of Man, 90
38. Section of the Diaphysis of Humerus of a human Embryo, 91
39. Adipose Tissue, human Scalp, . . ... 93
40. Smooth Muscle-Fibers, . . -95
41. Intercellular Bridges of Smooth Muscle-Fibers, 95
42. Intercellular Bridges and Smooth Muscle- Fibers of the human Intestine in Section, 96
43. Striated Muscle-Fibers of Man . ... ... 97
44. Isolated Striated Muscle-Fibers of a Frog, ... .98
45. Muscle-Fibers of Heart, 99
xi
LIST OF ILLUSTRATIONS.
FIG.
PAGE
46. Diagram of a Neuron, io 3
47. Various forms of Ganglion-Cells, . . • ■ io 3
48. Multipolar Nerve-Cells I0 4
49. Cell of Purkinje IO S
50. Nerve-Cells from the Spinal Cord of an Embryo Chick, . . . . • IO °
51. Teased Preparation of the Sympathetic Nerve of a Rabbit, io 7
52. Medullated Nerve-Fibers, • Io8
53. Medullated Nerve-Fibers, treated with Silver Nitrate, . . • ■ • io 9
54. Nerve-Fiber, showing a Node of Ranvier ...... 1 1 1
55. Papillary Muscle of a human Heart, . . . • • IJ 3
56. Small Arteries of Man . . . . . . ■ • • • J1 4
57. Epithelium of a Mesenteric Artery, . . . . • I: S
58. Cross-Section of the Brachial Artery of Man, . . . 116
59. Cross-Section of the Thoracic Aorta of Man, . I! 7
60. Cross-Section of a human Vein, IJ *
61. Elastic Fibers of a human Vein, ... • :I 9
62. Section of the Renal Vein of Man, . . . 12 °
63. Developing Capillaries in the Omentum of a Rabbit, . . .... 1 2 1
64. Human Blood Corpuscles, Amphibian Blood Corpuscles, ... 122
65. Colorless Blood-Cells of Man, .... . 123
66. Hemin and Hematoidin Crystals of Man ; Hemoglobin Crystals of a Dog, . .125
67. Lymph-Vessels from the Mesentery of a Rabbit, . . ... 127
68. Section of a Lymph-Gland of a Rabbit, ... ... 128
69. Section of the Medulla of a Lymph-Nodule of an Ox, . . 129
70. Cross- Section of a human Spleen, ...... I3 1
71. Elements of a human Spleen, . . . .... 131
72. Reticular Connective Tissue of a human Spleen, ... . . . . . 13 1
73. Three Karyomitotic Figures from the Spleen of a Dog, . .131
74 A. Section of Injected Spleen of a Cat, . 13 2
74 B. Schematic Drawing of Section 74 A, . . 132
75. Section of the Spleen of a Mouse . . 133
76. Longitudinal Section of a human Metacarpus, ... . 143
77. Cross-Section of a human Metacarpus, . . ... . . 144
78. Section of Bone-Marrow of a Rabbit, ... . . . . 145
79. Elements of human Bone-Marrow, ... . 146
80. Cross-Section of the Femur of adult Man, . 146
81. Vertical Section of the Head of a Metacarpus of adult Man, . 148
82. Synovial Villi from a human Knee-joint, . 149
83. Section of the Great Toe of a human Embryo Four Months Old, . .151
84. Section of the Finger of a human Embryo Four Months Old, .... . . 152
85. Longitudinal Section of the Phalanx of the first Finger of a human Embryo, 153
86. Cross-Section of the upper half of the Shaft of the Humerus of a human Embryo, 154
87. Cross-Section of the lower Jaw of a newborn Dog, . ... . . . 155
88. Horizontal Section of the Parietal Bone of a human Embryo . 156
89. Osteoclasts and Howship's Lacunae, . . 157
90. Elements of the fresh Bone-Marrow of a Calf, ... . . 159
91. Cross-Section of the Adductor Muscle of a Rabbit, . . 162
92. Cross-Sections of Dried human Tendon, .... . . 163
93. Tendons of a Rat's Tail . . . 164
94. Section of the Gastrocnemius Muscle of a Frog, . 164
95. Cross-Section of the Cervical Enlargement of the human Spinal Cord, . . 168
96. Motor Nerve-Cells from the Spinal Cord of a Rabbit, . .... 170
97. Cross-Section of the Spinal Cord of an Embryo Chick, . .... 171
LIST OF ILLUSTRATIONS.
FIG.
98.
99-
100.
101.
102.
103.
104.
105.
106.
107.
108.
109.
no.
III.
112.
"3-
114.
115.
116.
117.
118.
119.
120.
121.
122.
I23.
I24.
125.
126.
I27.
128.
129.
I30.
I3I-
132.
133-
134-
135-
136-
137-
138.
'39-
140.
141.
142.
143-
144.
145-
146.
'47-
148.
149.
150.
Scheme of the Spinal Cord
Longitudinal Section of the Spinal Cord of a Rabbit, ..
Section of the Spinal Cord of a Rat, showing Collaterals,
Glia-Cells from the Spinal Cord, . . . .
Cross-Section of the Lateral Column of a human Spinal Cord
Vertical Section of the human Cerebral Cortex, . . .
Scheme of the Cerebral Cortex, .... ...
Pyramidal Cell from the Cerebral Cortex of adult Man, .
Glia-Cells from the Brain of Man, ...
Section through the Cerebellar Cortex of adult Man,
Small Granule-Cell from the Cerebellar Cortex of a Kitten, .
Large Granule-Cell from the Cerebellar Cortex of a Kitten, .
Cell of Purkinje from the Human Cerebellar Cortex,
Scheme of the Cerebellar Cortex, . . ...
Basket-Cell of the Cerebellar Cortex of a Cat, .
Section of the Cerebellar Cortex of adult Man, .
Glia-Cells of the Cerebellar Cortex of adult Man, . . .
Horizontal Section of a human Pituitary Body,
Acervulus Cerebri from a human Pineal Body, . . .
Elements of the Gray Substance of the wall of a Ventricle of the human Brain,
Portion of the Plexus Chorioideus of adult Man, . ...
Cross-Section of a human Median Nerve, .
Cross-Section of a human Median Nerve, . . .
Longitudinal Section of the Spinal Ganglion of a Calf, ....
Cross-Section of the Gasserian Ganglion of Man,
Scheme of the Nervous Elements of a Spinal Ganglion,
Section of the Superior Cervical Ganglion of Man, . . ...
Tactile Corpuscle, Cells of Langerhans, Intraepithelial Nerve-Fibers,
Tactile Cells in a Section of the Skin of a human Toe, . . .
Compound Tactile-Cells from the Beak of a Goose,
Cylindrical End-Bulb from the Conjunctiva of a Calf, . . .
Lamellar Corpuscle from the Mesentery of a Cat, . .
Tactile Corpuscle from a Section of a human Toe, .
Motor Nerve-Endings of the Intercostal Muscles of a Rabbit, .
Motor Nerve-Ending in an Ocular Muscle-Fiber of a Rabbit, .
Sections of the human Suprarenal Body,
Section through Cortex and Medulla of the Suprarenal Body of adult Man,
Section of a human Cerebral Cortex, . .
Transverse Section of a Peripheral Spinal Nerve, . . . .
Section of the Mucous Membrane of the Lip of adult Man,
Longitudinal Section of a human Tooth, . . , .
longitudinal Section of a human Molar Tooth ...
Longitudinal Section of the Fang of a human Molar Tooth, .
Enamel Prisms from the Tooth of an Infant, .
Six Odontoblasts with Dentinal Fibers, . .
Schematic Representation of the Initial Processes in the Development of the Teeth
Frontal Section of the Head of an Embryo Sheep, ...
Section of the Lower Jaw of a human Embryo Four Months Old, .
Section of the Upper Jaw of a human Embryo Five Months Old, . .
Section of a Milk- Tooth of a newborn Dog,
Filiform Papillae of the human Tongue,
Fungiform Papilla of the human Tongue,
Vertical Section of a Vallate Papilla of Man ...
PAGE
172
173
174
175
176
178
178
179
180
182
182
182
183
184
185
186
186
187
188
188
189
191
191
192
193
194
196
197
198
199
200
200
201
202
202
203
204
208
210
215
217
218
218
21S
21S
219
220
220
221
222
224
224
225
LIST OF ILLUSTRATIONS.
FIG.
151. Vertical Section of a Lymph-Follicle from the Root of the Tongue of adult Man
152. Thin Section of a Lingual Follicle of Man,
153. A Serous Gland from the Tongue of a Mouse, . .
154. Tubules of Human Mucous and Serous Glands, . . .
155. Cross-Section of the Middle Third of the human Esophagus, .
156. Transverse Section of a human Stomach,
157' Vertical Section of the Cardiac End of a human Stomach, . .
158. Transverse Section of a human Fundus Gland,
159. Section of the Fundus of the Stomach of a Mouse (during digestionl,
160. Section of the human Pyloric Mucous Membrane, .
161. Section of the Jejunum of adult Man,
162. Section of the Mucous Membrane of the Jejunum of adult Man,
163. Intestinal Epithelium, . . • .
164. Longitudinal Section of the Apex of a Villus of a Dog,
165. Longitudinal Section through the Duodenum of a Cat,
166. Mucous Membrane of the Descending Colon of Man,
167. Transverse Section of a Patch of Peyer of the Small Intestine of a Cat,
168. Crest of a Solitary Follicle from the Small Intestine of a Kitten,
169. Section of the Injected Small Intestine of a Rabbit,
170. Plexus Myentericus and Plexus Submucosus of an Infant,
171. Scheme of the human Sublingual Gland,
172. Section of the human Sublingual Gland,
173. Scheme of the human Submaxillary Gland, . . . ■
174. Section of the human Submaxillary Gland,
175. Scheme of the human Parotid Gland, . .
176. Section of the human Parotid Gland, . .
177. Scheme of the human Pancreas,
178. Gland-Cells from the Pancreas of a Cat ; Section of the Pancreas of an Infant,
179. Gland- Tubule of the Pancreas of Necturus, showing Zymogen Granules, . .
180. Section of the Pancreas of adult Man, .
181. Section of the Submaxillary Gland of a Dog, . ....
182. Scheme of an ordinary compound Tubular Gland,
183. Scheme of the Liver, . . . .
184. Scheme of the End-piece of a Tubular Gland,
185. Scheme of an End-piece of the Liver, , . . .
186. Section of a Rabbit's Liver
187. Scheme of an Hepatic Lobule,
188. Section of a human Liver, . . . . .
189. Section of a human Hepatic Lobule, . . .
190. Bile Capillaries, silvered after Golgi, . . .
191. Bile Capillaries, injected, ... . .
192. Section of the Liver of a Dog, after Golgi, .
193. Liver Cells of Man, ..... ...
194. Horizontal Section of the Injected Liver of a Rabbit, . .
195. Horizontal Section of the Injected Liver of a Cat, .
196. Portal Capillaries and Bile Capillaries, injected, . . ...
197. Vertical Section of the Injected Liver of a Cat,
198. Shaken Section of a human Liver
199. Greater Omentum of a Rabbit,
200. Isolated Fundus Gland of a Rabbit, . . '.
201. Intestinal Villus of a Rabbit .
202. Intestinal Crypts of a Rabbit,
203. Section of a Bronchus of a Child, . ... . .
PAGE
225
227
228
228
23 '
232
233
234
234
236
238
239
240
240
241
242
244
244
246
247
248
249
249
250
250
251
251
252
252
253
• 253
254
254
255
255
256
257
258
• 259
259
. 260
. 261
. 261
262
. 262
263
263
. 264
• 265
. 269
270
. 272
• 279
LIST OF ILLUSTRATIONS.
PAGE
FIG '
204. Section of a Lung of adult Man, ^80
205. Respiratory Epithelium of a human Lung and of a Kitten's Lung, . 280
206. Section of Lung of a Rabbit, showing Elastic Fibers, .... 281
207. Section of the Lung of a Child, Injected through the Pulmonary Artery, . 282
208. Section of the Thyroid Gland of adult Man, . . 283
209. Section of the Thymus Body of a Rabbit seven days old, . 284
210. Concentric Corpuscle, . . . . 284
211. Scheme of the Course of the Uriniferous Tubules and of the Renal Blood-Vessels, 288
212. Isolated Uriniferous Tubules of a Rabbit, . . . 288
213. Section of Human Kidney, . . . 289
214. Scheme of a Renal Corpuscle, , 2 8g
215. Section of the Kidney of a Mouse, showing the relation of the Glomerular Cap-
sule to the Uriniferous Tubule, ... , . 289
216. Isolated Cell of a Convoluted Tubule ; Cross-Section of a Convoluted Tubule, . 290
217. Section through the Cortex of a human Kidney, . . . 291
218. Transverse Section through the Medulla of a human Kidney, . . 291
219. Longitudinal Section of the Injected Kidney of a Guinea-Pig, . 292
220. Nerve-Plexus in a Section of the Kidney of a Mouse, . . . 293
221. Transverse Section of the Lower Half of a human Ureter, 294
222. Vertical Section of a human Vesical Mucous Membrane, 294
223. Section of the Testicle of a newborn Child, . 300
224. Section of the Testicle of an Ox, ... . 300
225. Section of Seminiferous Tubules of a Mouse, . 301
226. Human Spermatozoa, . . ... ... ... 303
227. Section of an adult human Ductulus Efferens Testis, . 304
228. Section of a human Ductus Epididymidis, .... . 305
229. Section of the Initial Portion of a human Ductus Deferens, 305
230. Section of the Cavernous Portion of the human Urethra, 307
231. Section of the Ovary of a Child, . . . 308
232. Section of the Ovary of an Infant, . . ... . 309
233. Section of the Cortex of the Ovary of a Rabbit, , . 309
234. Section of a large human Vesicular Follicle of a Child, . . 310
235. An Ovum from the Vesicular Follicle of a Cow, . . 311
236. Corpus Luteum of a Rabbit ; Corpus Luteum of a Cat, . . 312
237. Section of the Middle of the Uterus of a Girl, . 314
238. Mucous Membrane of the Resting Uterus of a Young Woman, . 315
239. Mucous Membrane of a Virgin Uterus during the first day of Menstruation, 317
240. Section of the Mucous Membrane of a human Uterus one month Pregnant, 318
241. Section of the Wall of a Uterus about seven months pregnant, with the Fetal Mem-
branes in situ, . . . . .... . . ... 319
242. Decidual Cells, . . ... „ . 320
243. Section of a normal human Placenta of about seven months, in situ, 322
244. Diagram of human Placenta at the close of Pregnancy, ... . 323
245. Section of a smaller and larger Chorionic Villus of a human Placenta at the end of
Pregnancy, ... ... 324
246. Isolated Elements of the Testicle of an Ox, . 328
247. Section of the Skin of the Finger of adult Man, . . . 332
248. Epidermis from the Skin of the dorsum of the human Foot, 332
249. Section of the Skin of the Sole of the Foot of adult Man, . 334
250. Cross-Section of the Third Phalanx of a Child, 335
251. Elements of a human Nail .' 336
252. Section of a human Scalp, showing a Hair and Hair-follicle, 337
253. Elements of a human Hair and Hair-Follicle, 338
XVI LIST OF ILLUSTRATIONS.
FIG. \ PAGE
254. Cross-Section of a Hair and Hair- Follicle in the lower half of the Root, .... 339
255. Sections showing the development of a Hair and Hair Follicle, . . 340
256. Vertical Section of the Hairy Scalp of adult Man, . 341
257. Vertical Section of the Ala Nasi of a Child, .... . . 342
258. Vertical Section of the Injected Skin of the Sole of a human Foot, . . 344
259. Section of the Mammary Gland of a Pregnant Rabbit 346
260. Section of the Mammary Gland of a Woman last Pregnant two years before, . . . 347
261. Human Milk-Globules ; Elements of the Colostrum of a Pregnant Woman, . 347
262. Vertical Section of a human Cornea, . . . . . 352
263. Corneal Canaliculi and Corneal Spaces, . ... ... 353
264. Corneal Corpuscles, ... . . .... 353
265. Section through the human Sclera and Choroid, . 354
266. Teased Preparation of a human Choroid 355
267. Meridional Section through the right Iridocorneal Angle of Man, . . 355
268. Vertical Section of the Pupillary Portion of a human Iris, ... . 356
269. Vertical Section of a human Retina, . . .... . . 359
270. Vertical Section of the Retina of a Rabbit, . . 360
271. Scheme of the Elements of the Retina, ... . 361
272. Isolated Elements of the Retina of an Ape, . . 363
273. Section of the Macula and the Center of the Fovea, . 364
274. Section of the Ora Serrata and the Pars Ciliares Retinas of a Man thirty-seven
years old, ... ... . . . . 366
275. Section of the Optic Entrance of a human Eye, . 368
276. Lens-Fibers of an Infant, . ... 369
277. Capsule and Epithelium of an adult human Lens, . .... 369
278. Scheme of the Vessels of the Eye, . . . 372
279. Vertical Section of the human Cornea, showing Nerve-Fibers, . 375
280. Sagittal Section of the Upper Eyelid of a Child, . . . . 377
281. Section of a human Lacrymal Gland, . . ... 379
282. Otoliths from the Sacculus of an Infant, 388
283. Section of the Second Turn of the Cochlea of an Infant, 389
284. Surface View of the Lamina Spiralis of a Cat, . 300
285. Surface View of the Lamina Spiralis Membranacea of a Cat, 390
286. Lamina Spiralis of a Cat seen from the vestibular surface, . 391
287. Scheme of the Structure of the Tympanic Wall of the Duct of the Cochlea, . 392
288. Surface View of the Lamina Spiralis Membranacea of a Cat,
289. Section of the Lamina Spiralis Ossea and the Lamina Spiralis Membranacea of an
Infant, . . ,
290. Scheme of the Blood- Vessels of the right human Labyrinth, . . .
291. Scheme of the right half of the first and second turns of the Cochlea,
292. Section of the Skin of the External Auditory Meatus of an Infant,
293. Section of a Coil-Tubule of the External Auditory Meatus of an Infant ; Section of
a Coil-Tubule of the External Auditory Meatus of a twelve-year-old Boy,
294. Section of the Respiratory Mucosa of the human Nasal Septum,
295. Isolated Cells of the Olfactory Mucosa of a Rabbit,
296. Nerves of the Olfactory Region of a young Rat, . .
297. Vertical Section of the Olfactory Mucosa of a Rabbit,
298. Vertical Section of the Olfactory Mucosa of a Rabbit,
299. Vertical Section of two ridges of the Papilla Foliata of a Rabbit,
300. Tastebud of the Papilla Foliata of a Rabbit, .
301. Nerves of the Papilla Foliata of a Rabbit
393
39S
395
390
398
398
403
404
404
405
406
408
409
INTRODUCTION.
The great progress of medical education in America 'during the
past twenty years is marked chiefly by the increased attention given to
the scientific branches, which form the basis of all medical training and
practice. In no respect is this progress more obvious than in the recog-
nition of the value of the microscope as a medical instrument, upon
which in its manifold applications to anatomy, physiology, bacteriology,
pathology, and sanitary science the advance of medicine depends to a
far greater degree than upon any other instrument or apparatus. All
these applications, however, are based upon a knowledge of the normal
microscopic anatomy, or, as it is called, the histology of the human body.
Thus it has come about that the importance of histology in medical
education has grown, until the work in the histological laboratory prob-
ably equals in value the work of the student in the dissecting room.
These circumstances have created a need for a text-book of his-
tology, combining scientific thoroughness with simplicity, conciseness,
and clearness of exposition. These qualities appear to me felicitously
combined in Stohr's manual. The author's style is singularly clear and
succinct, and shows unmistakably that it is based upon a first-hand
acquaintance with the microscopical pictures of the various tissues and
organs to be described. The illustrations are of a very high order,
both for their faithfulness to the actual preparations and for their delicacy,
and this delicacy is fully preserved in the present edition by careful
printing, such as is, unfortunately, rare in American text-books. Pro-
fessor Stohr has kept constantly abreast with progress of histological
research, and thus has given to the successive editions of his work an
authoritative value, rendering it an excellent book of reference, not only
for students but for others.
The translation here presented is very faithful, and is to be 'com-
mended, especially for the correct rendering of the technical terms.
xvii
XV111 INTRODUCTION.
The character of the original has been preserved scrupulously ; but the
editor has added sixteen figures and certain notes, as well as a chapter
on the Uterus and Placenta, which will be found to add to the usefulness
of the volume for American students.
It affords me pleasure to recommend the American edition of
Stohr's Histology to my colleagues and to students of medicine and
biology, for I think it needs only to become known to secure the suc-
cess which its many merits deserve.
Charles Sedgwick Minot.
Harvard Medical School,
August 2q, 1898.
PART I.
GENERAL TECHNIC.
I. THE LABORATORY APPOINTMENTS.
i. INSTRUMENTS.
The Microscope. — From my own experience I can recommend the
microscopes made in the optical works of Leitz in Wetzlar, Seibert in
Wetzlar, and Zeiss in Jena, having repeatedly tested their excellent
workmanship.*
It is not advisable for the beginner to purchase a microscope
without first submitting it to an expert for examination. In order to
preserve the microscope in good working condition it is necessary to
protect it from dust ; when in frequent use, it is best to keep it under a
bell-glass, in a place not exposed to sunlight. The tarnish which forms
on the tube should be rubbed off with a dry piece of soft filter-paper.
* Students of the first semester are advised to refrain from the purchase of high-power
oculars and immersion-systems. These should be bought shortly before entering upon bacterio-
logic work.
The following outfits are recommended :
Leitz. — Catalogue No. 36, 1895. Microscope No. 4 b. Price, 370 M. = $92.00. Without
homogeneous immersion and ocular IV, 265 M.
S«;totf:^Catarogue No. 25, 1895. Microscope 3 c. Price, 449 M. = $112.00. Without
homogeneous immersion, objective 3, and ocular o, 283.50 M. = $71.00.
Zeiss. — Catalogue No. 30, 1895. Combination (p. 116) 7 b. Price, 602 M. = $150.00.
Without homogeneous immersion, 442 M. = $110.00; or 8 b. Price, 559 M. =
$140.00. Without homogeneous immersion, 399 M. = $100.00.
The majority of the work for this book was carried out with a Leitz microscope.
Editor's remark: Of American microscopes, those made by the Bausch & Lomb
Optical Co., Rochester, N. Y., and New York City, are recommended.
For histologic work the following outfit is suitable :
Stand BB. — Oculars, I -inch and 3-inch. Objectives, %-inch and J^-inch. Catalogue
1895. Price, $62.50. For cytologic and bacteriologic work a T 'j-inch oil-immersion objective
(price, $44) and an Abb6 condenser and iris-diaphragm should be added. For convenience a
double or triple revolver for the objectives is desirable.
17
16 HISTOLOGY.
Smirches on the lenses and on the mirrors should be removed with soft
leather, and if this does not answer the purpose, — as, for example, when
a lens is smeared with canada-balsam or damar-varnish, — a small piece of
fine linen moistened with a drop of pure alcohol should be used. In
the latter procedure great care must be exercised lest the alcohol pene-
trate the setting of the lenses and dissolve the balsam with which they
are cemented together. Therefore the balsam should be quickly rubbed
off with the moistened linen and the lens carefully dried. The screws ot
the microscope should be cleaned with benzin. The lenses of the objec-
tive must not be unscrewed.
A good razor, flat on one side. It should always be kept sharp,
and before each use should be drawn without pressure over the strop.
The honing of it should be left to the instrument-maker. The razor
should be used only in the preparation of microscopic sections.
A fine whetstone.
A pair of fine, straight scissors.
A pair of easily-closing fine forceps, with smooth or only slightly
notched points.
Four dissecting needles with wooden holders : two are to be heated,
then slightly bent, heated again and thrust into solid paraffin, by which
they are again hardened. The other two must be kept clean and sharply
pointed ; for delicate dissections the needles must be pointed and polished,
first on the whetstone and then on the strop.
A flexible section-lifter, for the transfer of sections from fluids to the
slide, is very useful but not absolutely necessary. A scalpel having a
broad blade can be used instead.
Pins, quills, cork disks, a fine sable brush.
A crayon, for writing on glass.
Slides, of clear glass and not more than i to 1.5 mm. in thickness.
Cover-glasses. Those measuring 15 to 18 mm. in diameter are
generally large enough ; the thickness may vary from o. 1 to 0.2 mm.
Small wide-mouthed bottles. One dozen, capacity 30 c.c. and over,
with cork stoppers.
Several glass preparation jars (preserve jars), with tightly-fitting
covers. Height, 8 to 12 cm. ; diameter, 6 to 10 cm.
A cylindrical graduate, capacity. 100 to 150 c.c.
A glass funnel, upper diameter 8 to 10 cm.
A pipet. Small pipets may be prepared by heating in a gas-flame
a glass tube 1 cm. thick and 10 cm. long, pulling one end to a point and
placing on the other a small rubber bulb.
A dozen watch-glasses of 5 cm. diameter.
THE LABORATORY APPOINTMENTS.
19
A dozen test-tubes, 10 cm. long and 12 mm. wide.
Glass rods, 3 mm. thick, 1 5 cm. long, some drawn to a point at the
end.
Old bottles that have been thoroughly cleansed will answer as recep-
tacles for reagents. In most cases the bottles can be cleansed with water,
but sometimes it is necessary to rinse them with crude hydrochloric acid
or with potash lye, then with ordinary water, then with distilled water,
and finally with alcohol.
Glass dishes (" Stender " dishes), 6 to 8 cm. in diameter, with ground
covers, are not absolutely necessary, but very useful.* In many cases
they may be replaced by saucers, food dishes for birds, etc.
A few sheets of thin, white filter-paper, large and small gummed
labels, soft pieces of linen (old handkerchiefs), a towel, a large and a
small bottle-brush.
A large earthen jar for refuse.
2. REAGENTS.f
General Rules. — Large quantities of reagents should not be kept
on hand, because many decompose in a comparatively short time. Cer-
tain reagents (see below) should be procured or prepared shortly before
they are to be used. Each bottle should be provided with a large label
on which its contents are designated ; it is advisable to write on the label
not only the formula of the reagent, but also the mode of its application.
All the bottles must be tightly closed with cork or well-made glass
stoppers. The fluid should not reach to the lower surface of the cork.
1. Distilled water, 3 to 6 liters.
2. Normal salt solution, 0.75 per cent, (sodium chlorid, 1.5 gm.,
distilled water, 200 c.c).
The cork must be provided with a glass rod reaching to the bottom
of the bottle. This solution spoils easily and must be frequently pre-
pared afresh.
3. Alcohol. — (a) Ninety-five percent. Alcohol. — About 500 c.c. should
be kept on hand. The alcohol of commerce is 95 per cent, and in the
*Most of the glassware, including slides and cover-glasses, here enumerated may be ob-
tained of W. P. Stender, Leipzig ; or, in the United States, of the Bausch & Lomb Optical
Co. , New York.
f The reagents must be obtained from a reputable dealer. Excellent dyes and reagents
may be had of Dr. Griibler, chemical and physiological laboratory, Leipzig, Bayer'sche Strasse 63.
In the United States Grubler's stains and reagents are sold by Eimer & Amend, New York,
and others.
20 HISTOLOGY.
majority of cases is entirely satisfactory for microscopic purposes. If it
is desired to obtain alcohol free from water (absolute alcohol), drop into
the bottle a few pieces of copper sulfate heated to white heat (15 gm.
to 100 c.c. of alcohol). When these become blue, they must be replaced
by new pieces or be reheated. Fresh quicklime serves the same purpose,
but acts more slowly.*
(6) Ninety per cent. Alcohol. — Prepare 500 c.c. by diluting 475 c.c.
of 95 per cent, alcohol with 25 c.c. of distilled water.
(c) Seventy per cent. Alcohol. — Prepare 500 c.c. by mixing 370 c.c.
of 95 per cent, alcohol with 130 c.c. of distilled water.
(d) Fifty per cent. Alcohol. — Prepare 500 c.c. by mixing 265 c.c. of
95 per cent, alcohol with 235 c.c. of distilled water.
(e) Thirty-three per cent. Alcohol (Ranvier's one-third alcohol). —
This is prepared by mixing 40 c.c. of 95 per cent, alcohol with 60 c.c.
of distilled water.
4. Acetic Acid, 50 c.c. — The official is 30 per cent.
5. Glacial Acetic Acid. — This should be procured shortly before it is
required. The commercial acid is 96 per cent.
6. Nitric Acid. — A bottle holding 100 c.c. of concentrated nitric
acid of 1. 18 sp. gr. (containing 32 per cent, of acid hydroxid) should
be kept in stock.
7. Hydrochloric acid, pure, 50 c.c.
8. Chromic Acid. — A 10 per cent, stock solution should be prepared -
by dissolving 10 gm. of fresh crystalline chromic acid in 90 c.c. of
distilled water. From this can be made :
{a) A O.i per cent, chromic-acid solution (10 c.c. of stock solution
to 990 c.c. of distilled water), and —
(p) A 0.5 per cent, chromic-acid solution (50 c.c. of stock solution
to 950 c.c. of distilled water).
9. Potassium Bichromate. — This should be kept on hand in two
solutions :
(«) Twenty-five gm. to 1000 c.c. of distilled water.
* For the preparation of mixtures containing a smaller percentage of alcohol this equation
will serve :
100 : 95 = x : c / e
e. g. , gofc, 100 : .95 = x : go
95 x = 90 . 100
9000
x = 2 =94.7 or 95.
95
Therefore, to obtain 100 c.c. of 90 per cent, alcohol, 95 c.c. of 95 per cent, alcohol must
be mixed with 5 c.c. of distilled water. For our purposes the errors of this ratio are too insignifi-
cant for consideration.
THE LABORATORY APPOINTMENTS. 21
(b) Thirty-five gm. to iooo c.c. of distilled water (for the Golgi
mixture, No. 12).
At room temperature it dissolves in from three to six days. There-
fore make the solutions with warm water or place the bottles near the
stove.
10. Muller's Fluid. — Dissolve 30 gm. of sodium sulfate and 60
gm. of pulverized potassium bichromate in 3000 c.c. of distilled water.
The solution can be made with the aid of heat, like No. 9.
11. Zenker's Fluid. — Dissolve 25 gm. of potassium bichromate, 10
gm. of sodium sulfate, and 50 gm. of mercuric chlorid in 1000 c.c. of
warm distilled water. Before using add 1 c.c. of glacial acetic acid to
each 20 c.c. of the mixture.
12. Golgi' 's Mixture (osmio-bichromate mixture). — This is prepared
by pouring together 54 c.c. of the 3.5 per cent, solution of potassium
bichromate (9 b) and 6 c.c. of the 2 per cent, osmic-acid solution (No.
21). It should be prepared shortly before it is to be used.
For the "fixation" of the Golgi preparations the following solutions
are required :
13. Strong Hydroquinone Developer. — This consists of 5 gm. of
hydroquinone, 40 gm. of sodium sulfite, 75 gm. of potassium carbo-
nate, and 250 gm. of distilled water. From this prepare a dilution by
adding 20 c.c. of the mixture to 230 c.c. of distilled water. In a well-
closed bottle in a dark place it keeps for weeks. The yellowish coloration
which appears in time does not depreciate it.
14. Sodium Hyposulfite, 10 gm. in 50 c.c. of distilled water. — It
dissolves quickly without the aid of heat.
15. Cox-Golgi Mixture. — This is prepared by pouring together 40
c.c. of a 5 per cent, solution of potassium bichromate, 40 c.c. of a 5 per
cent, solution of corrosive sublimate, 32 c.c. of a 5 per cent, solution of
potassium chromate, and -88 c.c. of distilled water. This mixture may
be kept in stock.
16. Ten per cent. Phosphomolybdic Acid. — Fifty c.c, kept in the dark.
17. Iron Solution. — Dissolve 2.5 gm. of ferric alum — (NH 4 ) 2 Fe 2 -
(SO^ — in 100 c.c. of distilled water.
18. Picric Acid. — Keep on hand 50 gm. of the crystals and 500 c.c.
of a saturated aqueous solution, in which undissolved crystals in a stratum
2 to 3 mm. deep must always lie on the bottom of the bottle. It dissolves
readily.
19. Picrosulfuric Acid (Kleinenberg's solution). — This is prepared
by adding 4 c.c. of pure sulfuric acid to 200 c.c. of a saturated aqueous
solution of picric acid ; a copious precipitate occurs. In about one hour
22 flISTOLOGY.
filter the mixture and dilute the filtrate with 600 c.c. of distilled water.
The residue on the filter is to be thrown into the refuse jar.
20. Chromic-acetic Acid. — To 50 c.c. of the 0.5 per cent, chromic-
acid solution (8 b) add 50 c.c. of distilled water and 3 to 5 drops of
glacial acetic acid.
21. Osmic Acid. — This may be obtained from the dealer — 50 c.c.
of a 2 per cent, solution — shortly before it is needed. It is very
expensive. It should be kept in the dark or in a dark glass bottle and
if well stoppered can be preserved many months.
22. Chromic-acetic-osmic Acid (Flemming's mixture). — Prepare a 1
per cent, chromic-acid solution (5 c.c. of the 10 per cent, solution [No.
8] to 45 c.c. of distilled water) and add 12 c.c. of 2 per cent, osmic acid
and 3 c.c. of glacial acetic acid. This mixture is not injured by light
and can be kept in stock.*
23. Platinum Chlorid. — Prepare a 10 per cent, stock solution, 2gm.
dissolved in 20 c.c. of distilled water.
24. Platinum-acetic-osmic Acid Mixture (Hermann's mixture). — Pour
into 60 c.c. of a 1 per cent, solution of platinum chlorid (6 c.c. of stock
solution and 54 c.c. of distilled water) 8 c.c. of 2 per cent, osmic-acid
solution and 4 c.c. of glacial acetic acid.
25. Saturated Sublimate-salt Solution. — Put 7.5 gm. of common
salt into one liter of distilled water ; after solution add 125 gm. of crys-
talline corrosive sublimate and dissolve by the aid of heat. Filter the
warm solution. On cooling, white acicular crystals form on the bottom
of the bottle.
26. Silver Nitrate. — A 1 per cent, solution (1 gm. of silver nitrate in
100 c.c. of distilled water) should be procured a short time before it is
to be used. In a dark place or in a dark bottle it can be preserved for a
long time.
27. Gold Chlorid. — A solution of 1 gm. of gold chlorid in 100 c.c.
of distilled water should be procured shortly before it is to be used. It
must be kept in the dark or in a dark bottle. For gold-chlorid staining
it is necessary to have No. 28 :
28. Formic acid, 50 c.c.
29. Concentrated potash lye (35 per cent.), 30 c.c. The bottle must
have a rubber stopper that is pierced by a glass rod. It should be pro-
cured from the druggist.
30. Glycerol. — One hundred c.c. of pure glycerol are to be kept in
* Tissues fixed in old Flemming's fluid often stain badly, because the acetic acid has
evaporated ; 5 to 20 drops of acetic acid newly added to the solution removes this defect.
THE LABORATORY APPOINTMENTS. 23
stock; also a solution of 5 c.c. of pure glycerol in 25 c.c. of distilled
water. The growth of fungi, which soon takes place in this mixture,
may be prevented by the addition of a small piece of camphor or thymol.
The cork of the bottle should be provided with a glass rod.
31. Bergamot oil (green), 20 c.c. The bottle should have a cork
pierced by a glass rod. The much-used cheaper clove oil scents the
whole laboratory and its occupants.
(a) Xylol. — This is to be used in special cases instead of bergamot
oil. Xylol clears more strongly and, on account of its sensitiveness in
preparations incompletely dehydrated, is not recommended to beginners.
32. Damar-varnish (of Dr. Fr. Schonfeld & Co. in Diisseldorf)
may be purchased in small bottles containing about 50 c.c. from dealers
in artists' materials. If it is too thick, it may be diluted with pure turpen-
tine. It has the proper consistence when the drops from an immersed
glass rod fall without spinning long threads. Damar is preferable to
canada-balsam (diluted with chloroform), which clears too vigorously
and renders tissues too transparent, but has the disadvantage of drying
more slowly than balsam. The cork of the bottle should be provided
with a glass rod.*
(a) Xylol-balsam. — A solution of canada-balsam in xylol, a sub-
stitute for damar-varnish.
33. Cover-glass Cement. — Dilute Venetian turpentine with enough
ether to make an easily flowing liquid ; then filter warm (in a heated
funnel) and inspissate the filtrate on a sand-bath. The proper con-
sistency is attained when a drop transferred with a glass rod to a
slide hardens at once and becomes so firm that it cannot be indented
with the finger-nail. Because of the danger of fire, it is better to have
the cement prepared by the druggist, f
34. Hansen's Hematoxylin. — (a) Dissolve 1 gm. of crystallized
hematoxylin in 10 c.c. of absolute alcohol and preserve it in a stop-
pered bottle, (b) Dissolve 20 gm. of potassium alum in 200 c.c. of dis-
tilled water, with the aid of heat, and when cold filter, (c) Dissolve 1
gm. of potassium permanganate in 16 c.c. of distilled water, at room
temperature. On the next day pour solutions a and b into a porcelain
capsule, add 3 c.c. of solution c, and, with constant stirring, heat the
mixture to boiling and boil about one minute. Cool quickly by floating
the porcelain capsule in cold water. When cold the mixture should be
^-Editor's remark : Instead of this commercial damar-varnish I recommend a solution
of pure gum damar in xylol, which has the advantage of drying more quickly.
f Editor's remark : In the United States an excellent fluid cover-glass cement is pre-
pared by J. D. King, Cottage City, Mass.
24 HISTOLOGY.
filtered ; it is then ready to use. Cloudiness, or the development of
fungi in the mixture, does not depreciate its effectiveness in the slightest
degree. It is to be kept on hand.
35. Delafield's Hematoxylin. — (a) Dissolve 1 gm. of crystallized
hematoxylin in 6 c.c. of absolute alcohol. (b) Dissolve 1 5 gm. of
ammonia alum in 100 c.c. of distilled water, with the aid of heat, and
when cold filter. Pour the two solutions together and let the mixture
stand three days in a wide-open vessel exposed to the light ; then filter
and mix with 25 c.c. of pure glycerol and 25 c.c. of methyl-alcohol.
After three days filter the mixture. It does not deteriorate with age
and should be kept in stock.
36. Weigert's hematoxylin, for the demonstration of the medullated
nerve-fibers of the brain and the spinal cord. Heat 1 gm. of crystallized
hematoxylin in 10 c.c. of absolute alcohol plus 90 c.c. of distilled water,
and when cold filter. It should be prepared shortly before it is to be
used. The application of this stain demands the aid of the following
three fluids :
37. Saturated Solution of Lithium Carbonate. — Dissolve 3 or 4
gm. of lithium carbonate in 100 c.c. of distilled water. This should be
prepared the day before using.
38. Solution of Potassium Permanganate (0.25 per cent.). — Dissolve
0.5 gm. of potassium permanganate in 200 c.c. of distilled water. This
may be kept on hand.
39. Acid Mixture (Pal's mixture). — Dissolve 1 gm. of pure oxalic
acid and 1 gm. of potassium sulfite (K 2 S0 3 ) in 200 c.c. of distilled
water. This mixture should be prepared one day before using and be
kept in a well-stoppered bottle.
40. Mallory's Hematoxylin. — Pour 10 c.c. of 10 per cent, phospho-
molybdic acid into 200 c.c. of distilled water ; in this dissolve (without
heating) 1.75 gm. of crystallized hematoxylin and add 5 gm. of crystal-
line carbolic acid.
41. Neutral Carmine-solution. — Dissolve 1 gm. of the best car-
mine in 50 c.c. of cold distilled water to which 5 c.c. of a solution of
ammonia (liquor ammonii caustici), have been added. The deep,
cherry-red fluid should stand in an open vessel until it has no odor of
ammonia (about three days) and then be filtered. It is to be kept in
stock. The odor of this solution immediately becomes very disagree-
able, but this does not depreciate its staining power.
42. Picrocarmine . — Pour 5 c.c. of solution of ammonia into 50 c.c.
of distilled water and to this mixture add 1 gm. of the best carmine.
Stir with a glass rod. After complete solution of the carmine (in about
THE LABORATORY APPOINTMENTS. 25
five minutes) add 50 c.c. of a saturated solution of picric acid and let the
whole stand in a wide-open vessel for two days. It is then to be filtered.
Abundant fungous growth does not diminish the staining power of this
excellent medium.
43. Alum-carmine. — Dissolve 5 gm. of alum in 100 c.c. of warm
distilled water and add 2 gm. of carmine. Boil this mixture ten or
twenty minutes and when cold filter ; finally, to the clear, beautiful, ruby-
red fluid add 2 or 3 drops of liquefied carbolic acid.
44. Borax-carmine. — Dissolve 4 gm. of borax in 100 c.c. of warm
distilled water ; when the solution has cooled add 3 gm. of the best car-
mine, stirring meanwhile, and then 100 c.c. of 70 per cent, alcohol. At
the expiration of twenty-four hours the fluid should be filtered. It filters
very slowly, requiring twenty-four hours or more.
Staining with borax-carmine requires after-treatment with 70 per
cent, acid-alcohol, which is prepared by adding 4 or 6 drops of pure
hydrochloric acid to 100 c.c. of 70 per cent, alcohol.
Borax -carmine and acid-alcohol should be kept on hand.
45. Sodium Carminate. — Dissolve 2 gm. of pigment in 200 c.c.
of distilled water.*
46. Safranin. — Dissolve 2 gm. of pigment in 60 c.c. of 50 per
cent, alcohol (32 c.c. of 95 per cent, alcohol in 28 c.c. of distilled water).
It is to be kept in stock.
47. Eosin. — Dissolve 1 gm. of pigment in 60 c.c. of 50 per cent,
alcohol. This should be kept in stock.
48. Congo-red. — Dissolve 1 gm. of pigment in 100 c.c. of distilled
water. From this stock-solution prepare —
(a) A 0.33 per cent, solution: 3 c.c. of stock-solution in 100 c.c.
of distilled water.
49. Vesuvin, or —
50. Methyl-violet B. may be kept in stock in a saturated aqueous
solution (1 gm. in 50 c.c. distilled water).
51. Methylene-blue. — Dissolve 1 gm. in 100 c.c. of distilled water.
This solution keeps well, as does the following, which is required for
after-treatment.
* Editor's remark : Of the carmine stains, alum-cochineal should be highly recommended.
Because of the certainty of its action and the simplicity of its application it is very useful in
the hands of the beginner. It is prepared by boiling 60 gm. of powdered cochineal and 60 gm.
of alum in 800 parts of water for about twenty minutes, filtering the decoction, and adding a
small piece of camphor or thymol to prevent the growth of mold. It can be kept in stock for a
long time.
26
HISTOLOGY.
52. Ammonium Picrate. — Dissolve 3 gm.. in 100 c.c. of distilled
water.
53. Orcein. — Dissolve 1 gm. of pigment in 100 c.c. of absolute
alcohol and add 1 c.c. of pure hydrochloric acid.
54. Westphal' s Alum-carmine Dahlia. — Dissolve 1 gm. of dahlia in
25 c.c. of absolute alcohol, add 12 c.c. of pure glycerol and 5 c.c. ot
glacial acetic acid, and pour into this mixture 25 c.c. of alum-carmine
(No. 43, p. 25). Preserve in a well-stoppered bottle.
II. THE PREPARATION OF MICROSCOPIC
SPECIMENS.
INTRODUCTION.
Very few organs of the animal body are of a structure suitable
for microscopic examination without special preparation. They must
possess a certain degree of transparency, which is attained either by
separating the organs into their elements or by cutting them into thin
sections — that is, either by isolating or by sectioning. Further, very
few organs possess a consistency that, without treatment, allows of the
cutting of sufficiently thin sections ; they are either too soft, in which
case they must be hardened, or too hard (calcified), in which case they
must be decalcified. But fresh objects can be neither hardened nor
decalcified without injury to their structure ; both processes must be pre-
ceded by treatment which rapidly kills the structural elements and at the
same time preserves their natural form. This procedure is called fixation.
Usually, the preparation of thin sections is possible only after fixation and
hardening, followed in some cases by decalcification, of the object. The
sections, too, require further treatment ; they may be forthwith ren-
dered transparent by means of clearing media (which can be also suc-
cessfully applied in the examination of fresh objects), or they may be
stained before being made transparent. The staining materials are in-
valuable agents in microscopic investigations. They can be applied in
the examination of fresh and even of living organs. Many of the most
important facts have been discovered by means of them. Introduced
into the blood-vessels, injected, they enable us to trace the branching and
course of the finest ramifications.
§ i. NATURE OF THE MATERIAL.
For the study of the structural elements and the simplest tissues,
amphibians (frogs, salamanders) are recommended. The best is the
spotted salamander,* the elements of which are very large. For the
^-Editor's remark : Or the American Amblystoma, Necturus, etc.
27
28 HISTOLOGY.
study of organs, mammals should be chosen. In many cases our
rodents (rabbits, guinea-pigs, rats, mice), also young dogs, cats, etc.,
are suitable. Still, no opportunity to secure human organs should be
neglected. Perfectly fresh material can often be obtained at surgical
clinics. Material may also be had at autopsies, if not made too long
after death ; with the exception of the mucous membrane of the intes-
tinal tract, which decomposes very quickly after death, many organs can
be used.
In general it is advisable to place the organs while yet warm in the
fixing fluid. In order to accomplish this the following injunctions must
be observed: Fill the bottles selected for the reception of the objects
with the appropriate fluid and provide them with a label on which is
designated the object, the fluid, the date, and in some cases the hour ;
then place the dissecting instruments near at hand ; then kill the animal.*
§ 2. KILLING AND DISSECTING THE ANIMALS.
In the case of amphibians, cut through the vertebral column of the
neck with strong scissors and destroy brain and spinal cord by means
of a needle introduced through the wound into the spinal canal and the
cranial cavity. In the case of mammals, cut the throat by a deep incision
reaching as far back as the vertebral column, or pour chloroform on a
cloth and press it to the nOse of the animal. f Small animals, up to the
size of four centimeters, and embryos may be placed entire in the fixing
fluid ; after about six hours the thoracic and abdominal cavities should
be opened by incisions. In the dissection, if possible, an assistant should
hold the extremities of the animal. Small animals can be extended on
cork or wax plates and secured by strong pins thrust through the feet.
The organs must be carefully removed. This is best done with scissors
and forceps. Crushing or pressing the parts, or taking hold of them with
the fingers, must be entirely avoided. Only the edge of the object may
be grasped by the forceps. Attached foreign matter — mucus, blood,
contents of the intestines — must not be scraped off with the scalpel, but
should be removed by slow twirling in the respective fixing fluids [or
by gently shaking the object in normal salt solution (p. 19) before
placing it in the fixing medium. — Ed. J
* To take parts from the Irving animal is an entirely needless cruelty !
f Editor's remark: I prefer to kill medium-sized and small animals (rabbits, guinea-
pigs, cats, mice, etc.) by placing them under a sufficiently large bell-glass, together with a wad
of absorbent cotton saturated with chloroform.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 20.
In the following methods it is not possible to avoid moistening scis-
sors, forceps, needles, glass rods, etc., with different fluids — for example,
with acids. Therefore the instruments should be cleaned immediately
after using by rinsing in water and drying. Above all, avoid dipping a
glass rod which, for instance, may be contaminated with an acid or a dye,
into another fluid. Apart from the fact that thereby the reagents will
be spoiled, the success of the preparation is, as a consequence, often
totally frustrated. Beaker-glasses, watch-glasses, etc., are easy to clean
if attended to immediately after using ; but if, for example, any staining
fluid is allowed to evaporate and dry on them, the cleansing then becomes
very tedious. Therefore the cleansing of the glasses immediately after
using should never be neglected ; in case there be no time for this, they
at least should be placed in water.
All vessels used for isolating, fixing, hardening, staining, etc., must
be kept closed, and should not be placed in the sun.
§ 3. ISOLATING.
The process of isolating is accomplished by teasing either the fresh
objects or those previously treated with dissociating fluids, which render
the teasing partially or wholly unnecessary. It is a difficult task to
make a well-teased preparation. Great patience and exact fulfilment of
the following directions are indispensable : The needles must be sharp
and perfectly clean ; they should be previously pointed and polished on
a moistened whetstone. The minute object, at the most 5 mm. in
length, should be placed in a small drop of the dissociating or mount-
ing medium on a slide and teased — on a dark background if it is color-
less, on a white surface if it is dark or colored. If the tissue is fibrous, —
for example, a bundle of muscle-fibers, — apply both needles at one end
and separate the fasciculus along its length into two ; in the same way
divide one of these bundles into two, and so continue until the minute
individual fibers are isolated. At times it is difficult to divide the bundle
along its entire length ; in this case it is often sufficient to divide it for
three-fourths of its length, allowing the isolated fibers to remain attached
at the one end. The uncovered preparation may be examined with the
low power in order to ascertain if the dissection is fine enough.*
The following isolating fluids are recommended :
For Epithelium. — Ranvier's one-third alcohol (p. 20) is an admirable
* Uncovered preparations lying in a small amount of fluid often appear indistinct, exhibit
black borders, etc., errors which may be corrected by the addition of a sufficiently large drop
of fluid and the application of a cover-glass.
30 HISTOLOGY.
dissociating medium. Place small pieces from 5 to 10 mm. in length
(e. g., of the intestinal mucous membrane) in about 10 c.c. of this fluid.
After four hours (in the case of stratified squamous epithelium after ten
to twenty-four hours or later) take out the pieces with the forceps, care-
fully and slowly, and tap them lightly against a slide upon which a drop
of the same fluid has been placed. By this manipulation many isolated
epithelial cells fall off; occasionally shreds are detached, which can be
separated into their elements by teasing them. Then apply a cover-
glass (p. 46) and examine. If it is desired to stain the object, carefully
transfer the entire piece from the alcohol to about 6 c.c. of picrocarmine
(p. 24). In two or four hours place the object very carefully in 5 c.c. of
distilled water, and in five minutes tap it against the slide, which this
time should have on it a drop of diluted glycerol (p. 22). Apply a
cover-glass. The preparation can be preserved.
For Muscle-fibers and Glands. — A 35 per cent, solution of potassium
hydroxid is suitable. Small cubes from 10 to 20 mm. in diameter should
be placed in 10 to 20 c.c. of this fluid. In about an hour the objects fall
apart into their elements, which may then be lifted out with a needle or a
pipet and examined under a cover-glass in a drop of the same lye. The
action of diluted potash lye is totally different ; examined in a drop of
water the elements are rapidly destroyed. If the isolation is not suc-
cessful, and instead a jelly-like softening occurs, the potash solution is
too old. Therefore a freshly-prepared solution should always be used.
The preparations, even when successful, cannot be preserved.*
A mixture of potassium chlorate and nitric acid maybe used. This
is prepared by throwing into 20 c.c. of pure nitric acid so much potassium
chlorate (about 5 gm.) that an undissolved residue will remain on the
bottom of the bottle. In from one to six hours, occasionally later, the
object is sufficiently dissociated, and should then be transferred to dis-
tilled water, in which it should stay for one hour, but may remain for a
week without injury. Then the object is placed on a slide, where, in a
drop of diluted glycerol (p. 22), it can be easily dissected. If the nitric
acid is well washed out, the preparation can be preserved and can also be
stained under the cover-glass (p. 51). Placing the unteased objects in
* Editor's remark: According to S. H. Gage ("Proc. Amer. Soc. Micr.," 1889, p. 36),
the action of the caustic potash may be at any time most satisfactorily checked by replacing it
with a 60 per cent, solution of potassium acetate, or by the additiomof sufficient glacial acetic
acid to neutralize the caustic potash and form acetate of potash. After the action of the caustic
potash is checked the elements may be preserved indefinitely en masse in a 60 per cent, solu-
tion of acetate of potash, or after being treated with a saturated solution of alum, in 40 per cent,
alcohol or glycerol. After the last treatment the elements may even be satisfactorily stained
with hematoxylin or alum-carmine.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 3 1
picrocarmine (see For Epithelium § 3, p. 29) will not be successful, be-
cause this staining fluid renders them brittle.
For gland-tubules pure hydrochloric acid is excellent. Small pieces
about 1 cm. in diameter should be placed in 10 c.c. of the acid and in from
ten to twenty hours transferred to about 30 c.c. of distilled water, which
must be renewed several times during twenty-four hours. The isolation
is then easily accomplished by carefully spreading. out the pieces with
needles in a drop of diluted glycerol. The preparation can be pre-
served.
§ 4. FIXATION.
General Rules. — (1) For fixation a large quantity of the fluid
should be used, exceeding the volume of the object 50 to 100 times.
(2) The fluid must always be clear, and so soon as it becomes turbid must
be replaced by fresh fluid. It often becomes turbid within an hour
after the introduction of the object. (3) The objects to be fixed should
be as small as possible ; in general they should not exceed 1 or 2 c.c.
Should it be necessary to preserve the object entire (e. g., for subsequent
orientation), many deep incisions should be made in it from five to ten
hours after placing it in the fixation medium. The object should not lie
on the bottom of the receptacle, but should be suspended within it or
placed upon a thin layer of cotton- or glass-wool.
1. Ninety-five per cent, alcohol is especially suitable for fixing glands,
skin, blood-vessels, etc. It acts simultaneously as a hardening medium.
Objects fixed in alcohol can be sectioned after twenty-four hours ; * there-
fore it is well adapted for the rapid preparation of specimens. Special
attention should be given to the following details : (1) The alcohol must
be renewed in from three to four hours, even though it is not turbid.
(2) The objects should not lie in contact with the glass, lest they adhere to
it ; f therefore they should be either suspended on a thread in the alco-
hol or placed on a little wad of cotton on the bottom of the vessel.
Weaker alcohol — for example, 90 per cent, alcohol — acts very
differently, shriveling the object, and therefore cannot be used instead of
95 per cent, alcohol.
2. Chromic acid is mainly used in two aqueous solutions :
(a) As a 0.1 or a 0.5 per cent, solution (p. 20), which is especially
* One should not too long delay using objects fixed in absolute alcohol, for the elements
gradually deteriorate ; they should be sectioned in from three to eight days. Sections of objects
that have lain only twenty-four hours in absolute alcohol occasionally stain poorly.
f Such areas appear strongly compressed in the sections.
HISTOLOGY.
suitable for organs that contain much loose connective tissue. This
strong solution imparts a superior consistence to connective tissue, but
has the disadvantage of making the staining' difficult ; it is also suitable
for the fixation of karyokinetic figures. The objects remain in the chro-
mic-acid solution for from one to eight days, are then washed in running
water for from three to four hours or, if this is not possible, placed for the
same length of time in water renewed three or four times, then transferred
to distilled water for a few minutes, and finally hardened in alcohol of
gradually increased strength (§ 5) and protected from daylight (p. 34,
remark *).
(b) As a 0.05 per cent, solution, which may be prepared by dilut-
ing the 0.1 per cent, solution with an equal volume of distilled water.
The application is the same as that of solution a, except that the objects
remain only twenty-four hours in solution b.
Chromic-acid solutions penetrate slowly ; accordingly, if the tissue
is submitted to the action of the medium for so brief a period as twenty-
four hours, only small pieces, 5 to 10 mm. in diameter, should be pre-
served.
3. Nitric acid in a 3 per cent, solution (3 c.c. ot concentrated nitric
acid [p. 20] to 97 c.c. of distilled water), like the strong chromic-acid
solution, is an admirable medium for organs rich in connective tissue.
The objects remain for from five to eight hours in this solution and with-
out the previous use of water are transferred directly into alcohol of
gradually increased strength for hardening (§ 5).
4. Kleinenberg' s Fluid (p. 21). — Delicate objects (embryos) should
be allowed to remain in this fluid for five hours, more solid parts for from
twelve to twenty hours ; then, without previous washing in water, they
are hardened in alcohols of gradually increased strength (§ 5).
5. Miiller's Fluid. — The objects remain for from one to six weeks *
in a large volume (up to 400 c.c.) of this solution, are then washed in
(if possible) running water, rinsed in distilled water, and, finally, hard-
ened in the series of gradually ascending alcohols, under exclusion from
daylight (p. 34, remark *). Who does not follow with painstaking con-
scientiousness the previously specified general rules for fixation will secure
imperfect results, for which even otherwise experienced microscopists
have held the blameless Muller's fluid responsible.
6. Zenker's Fluid. — Metallic instruments must be cleansed imme-
diately after dipping them into this fluid. The objects should remain in
* Objects may be left in Muller's fluid for a longer period — up to six months ; often they
can then be sectioned and stained without the alcohol hardening.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 33
it for from twenty-four to forty-eight hours, allowing about 60 c.c. of the
reagent to each one-centimeter cube of tissue, should be washed in
running water for the same length of time, rinsed in distilled water, and
hardened in the dark in alcohols of gradually increasing strength (p. 34).
For the removal of the sublimate precipitates that occur in the tissues
add to the 90 per cent, alcohol enough tincture of iodin to impart to the
fluid the color of port-wine. The objects remain for from eight to fourteen
days in this iodin-alcohol, the color of which rapidly fades and there-
fore it requires the daily addition of enough of the tincture of iodin to
maintain the tint.* Finally the objects are transferred to pure 90 per
cent, alcohol, which is to be changed two or three times, and in this
they may remain for a week or longer. (See also p. 49.)
7. Osmic-acid Solution (p. 22). — In using this reagent care must be
taken not to inhale the vapor, which is very irritating to mucous mem-
branes. Fixation is accomplished either by immersing very small pieces,
up to 5 mm. cubes, in the acid, which is usually employed in a one per
cent, solution, of which only a small quantity — from 1 to 6 c.c. — need
be used ; or by exposing the moist object to the vapor of the osmic-acid
solution. For the latter purpose pour 1 c.c. of the 2 per cent, solution
into a test-tube about 5 cm. in length and add an equal volume of dis-
tilled water ; fasten the object by means of quills to the under surface of
a cork stopper, with which the test-tube is then to be securely closed.
In from ten to sixty minutes, according to the size of the object, it is
removed from the cork and dropped into the fluid in the test-tube. In
both cases the objects remain in the acid for twenty-four hours, and
during this time the containers must be tightly closed and stood in the
dark. Then the objects are taken out, washed for from one-half to two
hours in running water, rinsed in distilled water, and hardened in gradu-
ally strengthened alcohols (§ 5).
8. Chromic-acetic osmic acid (Flemming's solution) (p. 22) is an
excellent medium for the fixation of karyokinetic figures. Place the
absolutely fresh, still warm pieces, from 3 to 5 mm. in diameter, in 4 c.c.
of this fluid, in which they remain for from one to two days, or even
longer. Then the pieces should be washed in running water for one
hour, better longer, rinsed in distilled water and hardened in alcohols
of gradually ascending strength (§ 5). The effect of this mixture on
the nuclei is different at the periphery of the object than in the interior,
* If, despite this, the sections still show sublimate precipitates, the latter may be removed
by placing the sections in iodin-alcohol for about ten minutes. Then rinse them in pure alco-
hol, transfer them to the staining fluid, etc. Occasionally, the staining is difficult ; this may be
remedied by subsequent treatment with diluted potash lye (p. 37, remark*).
3
34 HISTOLOGY.
where the chromatin networks are more distinct, because at the periphery
the osmic acid, which renders the nuclear sap granular and the nuclear
reticulum indistinct, acts in its purity.
9. Platinum-acetic-osmic acid mixture (p. 22) is very suitable for dis-
playing sharply defined cell-boundaries. It is used like Flemming's
solution.
10. Sublimate-salt Solution. — Place small cubes of tissue, at the most
not over 4 mm. in diameter, for from one to six hours, according to bulk,
in 20 c.c. of sublimate-salt solution (p. 22) ; then transfer directly into
30 c.c. of gradually strengthened alcohols (§ 5, p. 34) for hardening. To
the 70 per cent, alcohol and upward add tincture of iodin, as when
using Zenker's medium (No. 6, p. 32). Avoid the use of metal instru-
ments.
The fluids that have been used for fixation cannot be employed
again and should be thrown away.
§ 5. HARDENING.
Except when alcohol is used, all the fixing methods necessitate a
supplementary process of hardening. The best hardening medium is
alcohol in ascending degrees of strength. Here, too, the rule is to use
abundance of fluid, and to change the alcohol as it becomes turbid or
colored.* The exact application is as follows : After the objects have
been fixed in one of the previously enumerated fluids and washed in
water.f they are placed, under exclusion of daylight, for twelve hours in
50 per cent, alcohol, then transferred for the same period to 70 per cent,
alcohol, and at the expiration of this time to 90 per cent, alcohol, in
which, after another period of from twenty-four to forty-eight hours, the
hardening is completed. In this alcohol the objects may remain for
months before their final preparation. The 90 per cent, alcohol employed
for hardening should be collected and used for burning or for hardening
liver for embedding.
* Objects fixed in chromic acid or in Miiller's fluid, if not subjected to prolonged wash-
ing, — and this must be avoided because of incipient decomposition, — still yield substances to the
alcohol, which with the simultaneous action of daylight appear in the form of precipitates ; on
the other hand, if the object is kept in the dark no precipitates are formed, and though the
alcohol becomes yellow it remains clear. It is on this account that the exclusion of daylight
has been recommended above ; it is sufficient to place the bottles in a dark part of the room.
The 90 per cent, alcohol must be changed once daily so long as it becomes intensely yellow.
f An exception is made in the case of objects that have been fixed in picrosulfuric acid
and in 3 per cent, nitric acid. These should be transferred directly from the fixing fluid to the
70 per cent, alcohol, which must be changed several times during the first day.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 35
§ 6. DECALCIFYING.
The objects to be decalcified must not be placed fresh in the decalcify-
ing fluid ; they must be previously fixed and hardened. For this purpose
place small bones up to the size of a metacarp, teeth entire, and pieces from
3 to 6 cm. long sawed from the larger bones in 300 c.c. of Miiller's fluid
for from two to four weeks and, after previous washing, harden them in
1 50 c.c. of gradually strengthened alcohols (§ 5). After the bone has been
in the 90 per cent, alcohol for three days or longer it is transferred to
the decalcifying fluid — diluted nitric acid, prepared by adding from 9 to
27 c.c. of pure nitric acid to 300 c.c. of distilled water. Large quantities,
at least 300 c.c, of this fluid should be used and changed daily at first,
later every four days, until the decalcification is completed. The pro-
cess is controlled, and the degree of decalcification ascertained, by thrust-
ing in a needle or by making an incision with a scalpel, which should be
at once carefully cleaned. Decalcified bone is flexible, soft, and easily
cut. Fetal bones, heads of embryos, etc., are decalcified in weaker nitric
acid (1 c.c. of pure nitric acid to 90 c.c. of distilled water) or in 500 c.c.
of a saturated aqueous solution of picric acid (p. 21). The process of
decalcification requires several weeks in the case of thick bones, from
three to twelve days in the case of fetal and small bones.
So soon as the decalcification is completed the bones are washed in
running water for from six to twelve hours, and then hardened in gradu-
ally strengthened alcohols (§ 5).
It not infrequently happens to beginners that they transfer the bone
to alcohol before it is fully decalcified, and then in the attempt to section
it they discover that it is not yet ready for use. In such cases the entire
procedure of decalcification must be repeated. If the action of the decal-
cification medium is too prolonged, it eventually leads to the complete
destruction of the objects.
§ 7. SECTIONING.
The razor must be sharp, for success in sectioning depends upon
the sharpness of the knife. In cutting, the blade must be moistened
with alcohol ; water is not suitable, because it does not adhere evenly to
the surface of the blade. Therefore, at each third or fourth section, dip
the knife into a shallow glass dish containing 30 c.c. of 90 per cent,
alcohol, which at the same time serves for the reception of the sec-
tions that are cut. The razor is to be held in a horizontal position,
grasped lightly, with the thumb on the side of the cutting edge, the
$6 HISTOLOGY.
fingers toward the back of the blade, the dorsum of the hand directed
upward. The object to be sectioned must first have a smooth surface,
which is made by cutting off a slice of the necessary thickness with a single
movement of the razor. From this surface the sections may now be
taken, and should be cut with a uniformly light, not too rapid, movement,
as smooth as possible, and of even thinness. The knife must not be
pushed, but should be drawn through the object, and that this may be
done the portion of the blade adjoining the handle should be first applied
to the object. Ten to twenty sections should be made ; they may be
transferred by means of a needle or by immersing the blade in the alco-
hol.* Then place the dish on a black surface and search for the best
sections. The thinnest sections are not always the most useful ; for
many preparations — for example, for a preparation through all the coats
of the stomach — -thick sections are recommended. For a general view,
large, thick sections should be prepared, for the study of ultimate struc-
tures, thin sections ; for the latter purpose small fragments from 1 to 2
mm. on a side are often satisfactory.
If the object to be sectioned is too small to be held with the fingers,
it should be embedded. The simplest method consists in placing the
object in a cleft in a piece of hardened liver.
Ox-liver or, better, human lardaceous or amyloid liver may be
used. The latter may be obtained from the pathologic laboratories.
Dog's liver, to be obtained from the physiologic laboratory, is also
recommended. The liver should be cut into pieces about 3 cm. high,
2 cm. broad, and 2 cm. thick, and these hardened in 90 per cent, alcohol,
which must be changed within twenty-four hours ; in three to five days
the liver attains the necessary hardness. The embedding is then accom-
plished by making an incision in one of these pieces from the top half-way
down and inserting the object into the cleft thus made. If the object is
too thick, furrows can be cut in the liver with a small scalpel and the
object fitted into these. The object requires no further staying except,
perhaps, binding with thread.
As a rule I embed objects in liver ; very thin sections can then be
made so soon as one has a certain amount of skill, and this can be easily
acquired in the course of a few weeks.
*Very thin sections that are not to be stained or that have been stained in bulk may be
transferred directly to the slide by inclining the blade and slipping or rinsing them off.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 37
§ 8. STAINING.
Before using a stain it should always be filtered. A small funnel
may be made by simply twice folding a piece of filter-paper 5 cm. square
and supporting it in a cork frame, which can be made by cutting out a
piece 2 cm. square from a cork plate 5 cm. square. The frame is then
mounted on four long pins. Such a funnel and frame can be used re-
peatedly, but only for the same fluid. The sections should not float
on the surface of the staining fluid ; they should be submerged with
needles.
1 . Nuclear Staining with Hansen's Hematoxylin (p. 23). — Filter from
3 to 4 c.c. of the staining fluid into a watch-glass and in it place the sec-
tions. The time in which the sections stain varies greatly. Sections
fixed and hardened in alcohol stain in from one to three minutes. If
Miiller's fluid was used for fixing, the sections must remain in the staining
fluid somewhat longer — up to five minutes.*
From the stain the sections are transferred to a watch-glass contain-
ing distilled water, in which they are washed, — i. e., gently moved about
with the needle to remove the excess of dye, — and then placed in a glass
containing 30 c.c. of distilled water. In this the sections must remain at
least five minutes, during which their blue-red color changes to a beauti-
ful deep blue, which becomes the purer the longer (up to twenty-four
hours) the sections are allowed to remain in the water. At first the sec-
tions have a faded blue tint ; usually the differentiation occurs in about
five minutes, but sometimes not for hours. When it is completed, certain
details can be recognized even by the unaided eye.
Beginners are recommended to leave the sections for different lengths
of time — one, three, or five minutes — in the stain, in order to learn the
time required to produce successful staining. The chief essential in
hematoxylin staining is thorough washing ; if the water becomes blue, it
must be replaced by fresh. The used stain should be poured back
through the filter into the hematoxylin bottle. The watch-glasses
should be immediately cleaned.
* Sections fixed in the strong solution of chromic acid or in Zenker's fluid, or objects not
entirely free from acid, often stain very slowly, occasionally not at all. This defect can be reme-
died either by keeping the objects from two to three months in 90 per cent, alcohol, which must
be changed two or three times during this period, or by treating the sections from five to ten
minutes with 5 c.c. of distilled water to which from 3 to 7 drops of 35 per cent, solution of
potassium hydroxid have been added. The sections are then to be transferred for from one to
two minutes to a watch-glass containing pure distilled water and from this into the hematoxy-
lin. In from five to ten minutes such sections will also stain.
38 HISTOLOGY.
2. Nuclear Staining with Alum-carmine (p. 25). — Filter from 3 to
4 c.c. of the staining fluid into a watch-glass, place the sections in it, and
allow them to stain for at least five minutes. The advantage of the dye
lies in this, that the sections may be left in it for a longer period without
becoming overstaihed, which is more apt to occur with hematoxylin ; a
disadvantage is that alum-carmine is a pure nuclear stain, while in
hematoxylin staining the protoplasm too acquires color, a gray or gray-
violet tone, and is thereby more easily recognized.
3. Diffuse Staining. — For staining the protoplasm and the inter-
cellular substances.
(a) Slow Staining. — A small drop of neutral carmine solution is
transferred by means of a glass rod to a capsule containing 20 c.c. of dis-
tilled water, on the bottom of which lies a small piece of filter-paper.*
The sections remain over night in this fluid. The paler the rose color of
the fluid, the longer the time required for staining and the more beautiful
the result will be. The beginner is always inclined to regard the pale-
rose fluid as too dilute to secure good staining, until on the following
day the deep pink to red sections teach him better.
This stain can be used alone only in a few cases, but is highly
recommended for double-staining. The sections should be stained first
with the carmine solution, then with hematoxylin.
(b) Rapid Staining. — Add 10 drops of a solution of eosin (p. 25)
to 3 or 4 c.c. of distilled water. In this the sections remain for from one
to five minutes, are then washed in distilled water, and then placed in
30 c.c. of fresh distilled water (see No. 1, p. 37). The stain may be
used alone or combined with hematoxylin ; in the latter case the whole
procedure of hematoxylin staining is to be carried out first, and then that
of eosin staining.
4. Staining of the Chromatin Substance. — For nuclear division.
Place the objects for from five to ten minutes in a watch-glass containing
10 c.c. of distilled water and one drop of pure hydrochloric acid ; wash
them for one minute in distilled water and transfer them to a watch-
glassful of safranin solution (p. 25), in which they should remain five min-
utes. The sections or membranes are then lifted out with the needle and
placed in about 5 c.c. of absolute alcohol for decolorization. When the
sections no longer give off much of the dye (usually in from one to two
minutes), they are transferred to 5 c.c. of fresh absolute alcohol for one
minute, then cleared and mounted (§ 10, 3, p. 48). If the immersion in
absolute alcohol is too prolonged, it may lead to total decolorization of
* If the filter-paper is omitted, the sections stain only on the one side.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 39
the preparation. Failure in staining is usually due to an insufficient
amount of acetic acid in the Flemming's solution (p. 22, remark).
5. Staining in Bulk* — Nuclear staining of the entire object before
sectioning. — The fixed and hardened objects are placed in 30 c.c. of
borax-carmine for twenty-four hours if they are small (5 mm. square), for
from two to three days if they are large. From this they are transferred
directly to 25 c.c. of acid-alcohol (p. 25); the used borax-carmine may
be returned to the bottle. In a few minutes the acid-alcohol acquires a
red color f and must be replaced by fresh, which should be again
renewed in about fifteen minutes ; this renewal must be repeated until
the alcohol no longer becomes red. J The object is then transferred to
90 per cent, alcohol, and if after twenty-four hours it is not sufficiently
hardened to be sectioned, it is placed for twenty-four hours or longer in
absolute alcohol.
6. Picrocarmine. — Double-staining : Nuclei and connective tissue red,
protoplasm yellow. Filter about 5 c.c. of the staining fluid into a watch-
glass. The length of time in which picrocarmine acts differs greatly for
individual objects and can be approximately given only in the special
directions. When the staining is completed, the dye is filtered back into
the bottle and the object transferred for from ten to thirty minutes to 10
c.c. of distilled water. (The latter procedure is omitted in staining under
the cover-glass, p. 51.) If the object, e. g., a section, is to, be dehy-
drated in absolute alcohol (p. 48), it must not be allowed to remain in
this reagent longer than from one to two minutes, because the alcohol
extracts the yellow stain ; or the decolorization can be prevented by
adding a small crystal of picric acid to the absolute alcohol.
Picrocarmine is preferably used in the examination of fresh objects.
If the solution is good, a very pretty stain is obtained, that is improved
by subsequent treatment with acidulated glycerol, which renders it crisp
and clear.
7. Nuclear Staining with Anilin Dyes. — For this purpose the best
anilin dyes are vesuvin and methyl-violet B (p. 25). Filter 5 c.c. of the
* Editor's remark. It is especially for staining in bulk that alum-cochineal (recom-
mended on p. 25, remark) proves very useful. It has the advantage of not overstaining, and
does not need in its application a special discharging fluid. Stain the pieces for about twenty-
four hours and wash them in several changes of water to remove the excess of stain and the
alum ; then transfer to alcohol of gradually increased strength.
f Preparations fixed in Miiller's fluid often give off very little dye.
% This may require from one to three days ; during the first day the fluid should be
changed every two hours, subsequently every four hours. If you wish to be economical, take
a needle and gently push the object out of the area of red fluid in which it lies into an un-
colored portion of the alcohol.
40 HISTOLOGY.
staining fluid into a watch-glass ; in this place the sections, which acquire
a very dark color in from two to five minutes ; they are then washed in
distilled water and transferred to a watch-glass containing absolute
alcohol, in which they give off the dye abundantly. In a few minutes,
from three to five, the sections become paler, and individual parts
(e. g., the glands of the skin) can be detected by the unaided eye. The
sections are now to be transferred to another watch-glass containing
5 c.c. of absolute alcohol, and in about two minutes they may be
cleared and mounted. The result is a very beautiful permanent nuclear
stain. A disadvantage lies in the necessity for using so much absolute
alcohol.
8. Safranin can be similarly employed. The sections stained for five
minutes are washed for thirty seconds in a watch-glass containing 95 per
cent, alcohol and then transferred to absolute alcohol, which must be
replaced by fresh so soon as it becomes intensely red. In from five to
fifteen minutes — the time varies according to the thickness of the sec-
tions — they are sufficiently decolorized and are then to be cleared in oil
and mounted in xylol-damar (p. 48).
9. Methylene-bhie for Staining Axis-cylinders. — This method is
applicable only to perfectly fresh preparations. Prepare a 0.66 per cent,
solution, which may be done by adding 1 c.c. of a 1 per cent, solution
(p. 25) to 1 5 c.c. of distilled water. The fresh preparation is treated on
the slide with a few drops of the diluted staining fluid, and meanwhile
protected with a watch-glass, which must not be so applied as to make
an hermetic cover, since the access of atmospheric air is necessary to the
success of the staining. The reaction occurs in from one to one and a
half hours, and can be rendered more certain by gently moving the prep-
aration to and fro. In order to prevent the drying of the preparation
during this period, a drop of the diluted staining fluid or of normal salt
solution should be added from time to time. When the staining is done,
a cover-glass should be applied. The result is a beautiful blue coloration
of the axis-cylinders. Other elements often are stained, the nuclei, con-
nective-tissue fibers, etc., and with more prolonged action of the reagent
also the medullary sheaths of the nerves. The preparation may be pre-
served as follows : replace the staining fluid with a drop of ammonium
picrate solution (p. 26) according to the method given on page 5 1 ; this
converts the blue color to violet ; then place a drop of glycerol at the
edge of the cover-glass, and it will gradually take the place of the evap-
orating water of the ammonia solution, and thus make the specimen
permanent.
After eighteen to twenty hours secure the cover-glass with cement
THE PREPARATION OF MICROSCOPIC SPECIMENS. 4 1
(p. 47). The preparations must not be exposed to sunlight, in which
they fade ; in any case they soon lose their original beauty.
10. Delafield ' s Hematoxylin for Staining Mucus. — Filter three drops
of this fluid (p. 24) into a watch-glass containing 25 c.c. of distilled
water. In this dilute solution the sections (preferably of objects fixed in
Flemming's mixture*) are placed and remain for two or three hours.
Usually at the end of this period the mucus {e. g., in the goblet-cells) is
stained an intense blue, which can be ascertained by examining with low
magnification the sections as they lie in the solution. It is often neces-
sary for the sections to remain in the solution for a longer time. Then
they are washed for one minute and mounted in damar, according to the
rules given in § 10, 3, p. 48. The nuclei also stain blue. Very pretty
pictures are obtained by a combination with safranin and picric acid, as
in No. 1 1 .
11. Triple-staining is accomplished in the following manner : The
sections stained in Delafield' s hematoxylin are placed for five minutes in
safranin (p. 25) and then transferred to 5 c.c. of absolute alcohol, which
must be changed twice within fifteen minutes. The sections are next
placed for one minute in 5 c.c. of absolute alcohol, to which five drops
of a saturated alcoholic solution of picric acid have been added (1 gm. of
picric acid to 1 5 c.c. of absolute alcohol), washed for thirty seconds in
pure absolute alcohol, and mounted in damar (§ 10, 3, p. 48).
Result : mucus, blue ; nuclei, red ; protoplasm and fibers, yellow.
12. Staining of Elastic Fibers. — Thin sections of tissue fixed in any
medium (preferably in alcohol) are placed for about six hours in orcein
solution (p. 26), then treated for ten minutes or more with 95 per cent,
alcohol, — in which they may remain for twenty-four hours without injury,
— and mounted in damar. Staining in bulk also may be done. The
objects, at the most 2 mm. in thickness, are transferred from 70 per
cent, alcohol to 10 c.c. of orcein solution and after twenty-four hours
are decolorized in 20 c.c. of acid-alcohol (see Borax-carmine, p. 25), in
which, according to their bulk, they remain for from ten to thirty minutes.
If left too long in the acid-alcohol, the color will be extracted from the
fine elastic fibers. Dehydrate for two hours in absolute alcohol, which
should be twice renewed. In successful preparations the elastic fibers
appear brown-red on a clear background.
13. Staining of Connective-tissue Fibrils. — By means of glass rods
place thin sections of objects fixed in any medium (preferably in alcohol)
* Preparations that have been fixed in Mailer's and in Zenker's fluid are also suitable for
mucus-staining.
42 HISTOLOGY.
in 5 c.c. of 10 per cent, phosphomolybdic acid, and aiter a minute or
minute and a half wash for a couple of seconds in distilled water ; stain
for five minutes in 5 c.c. of Mallory's hematoxylin, rinse in distilled
water, and place in 10 c.c. of 50 per cent, alcohol; after another five
minutes dehydrate in absolute alcohol, clear in xylol, and mount in xylol-
balsam (see § 10, 3, p. 48). The connective tissue stains intensely blue.
If it is desired to stain nuclei, the sections must be previously stained
with safranin (p. 25), or with borax-carmine (p. 25). Everywhere, in
glands, mucous membranes, the skin, etc., etc., I have obtained very
instructive pictures.
14. M. Heidenhairi s Iron-hematoxylin. — For staining centrosomes,
cement bars, and gland granules. Fix the object preferably in sub-
limate (p. 34), in Zenker's medium (p. 32), or in Flemming's mixture
(P- 33) > embed in paraffin, cut on the microtome, and fasten the sections
(which should be very thin) to the slide (see Microtome Technic).
Transfer the slide with the sections from the absolute alcohol to a capsule
containing 50 c.c. of the iron solution (p. 21) ; after from six to twelve
hours remove from the mordant, rinse for a couple of seconds in distilled
water, and place for from twelve to thirty-six hours in a mixture of 30
c.c. of Weigert's hematoxylin and 30 c.c. of distilled water.* The sec-
tions, which have become black and wholly untransparent, are now
rinsed in tap-water and then returned into the iron solution for bleach-
ing and differentiation. When this is accomplished, wash them for about
fifteen minutes (not more) in running water, — common water is indis-
pensable, — and, after the customary preliminary treatment, mount in
xylol-balsam. When the decoloration is slowly and carefully done, this
admirable method easily succeeds, but the exact duration of this process
cannot be given ; the slide must be frequently removed from the iron
solution, washed with tap-water, and examined with a high -power objec-
tive, to ascertain if the differentiation is completed.
15. Silver Staining. — For the exhibition of cell-boundaries and the
staining of intercellular cement-substance. \
The use of metallic instruments must be avoided ; glass rods should
be employed, and quills instead of pins.
The object is immersed for from one-half to ten minutes, according
to its thickness, in 10 to 20 c.c. of a 1 per cent, or weaker (see Special
* This diluted hematoxylin can be repeatedly used and should be saved. Old Weigert's
hematoxylin is preferable to the freshly prepared stain.
\ The cross-striations that appear in different tissues and organs when treated with silver
nitrate, particularly in nerve-fibers, blood-vessels, cartilages, etc., are artifacts.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 43
Technic) solution of silver nitrate (p. 22), which meanwhile becomes
milky and turbid ; it is then removed with glass rods, washed, placed in
a porcelain capsule containing 100 c.c. of distilled water, and exposed to
direct sunlight ; in a few minutes a faint brown coloration appears — the
sign of a successful reduction. So soon as the object has become a
deep red-brown (usually in from five to ten minutes) it is taken out,
placed in a watch-glass containing distilled water to which a few grains of
common salt have been added, and at the end of five or ten minutes
transferred to 30 c.c. of 70 per cent, alcohol, and stood in the dark ; in
from three to ten hours the 70 per cent, should be replaced by 90 per
cent, alcohol. The immersion in the silver solution should be done
under exclusion of sunlight ; the reduction, on the other hand, should
be undertaken only with sunlight.* If the sun does not shine, the object,
after treatment with the silver solution and washing in distilled water, is
to be preserved in the dark in 30 c.c. of 70 per cent, (later 90 per cent.)
alcohol, and in this exposed to sunlight at the earliest opportunity.
16. Golgi's "black" reaction for demonstration of the elements of
the nervous system. f
This method unites fixing and staining. The objects must be as
fresh as possible, and in general their diameter should not exceed 4 mm.
It is not easy to cut fresh brain into pieces of this size without bruising
the delicate tissue ; therefore place larger pieces (up to 3 cm. cubes) in
a small glass jar containing freshly prepared Golgi's mixture (p. 21),
which is to be covered and stood in the dark (in winter it must be put in
an oven having a temperature of about 25 ° C). In from one to two
*The reduction takes place in ordinary daylight, but slowly, and yields less satisfactory
results.
f Editor's remark : In American laboratories a modification of Golgi's method by Cox is
often used with excellent results. This modification is particularly recommended to beginners,
because it is very simple and nearly always successful. In its application the following direc-
tions should be observed : Put small cubes, 2 cm. or less, of the organs of the central nervous
system of adult or newborn animals for from six to ten weeks in the Cox-Golgi mixture, the
formula of which is given on page 21 (No. 15), using 10 to 20 times the volume of the object
treated. Change the fluid at the following intervals : after twenty-four hours ; three days ; eight
days ; fifteen days ; twenty-one days ; thirty days. The objects should remain in the mixture
until they are to be sectioned, and will keep in good condition for about ten months. Then
transfer them directly into 95 per cent, alcohol for one hour ; into alcohol-ether (equal parts)
for a half hour ; into thin celloidin solution (in alcohol-ether) for one hour. Mount on a block
with thick celloidin solution (see Microtome Technic) and harden in 80 per cent, alcohol
for from one to two hours. Cut at once sections from 50 to loo /t thick ; clear them in a mixture
of xylol, three parts, and carbolic acid, one part, in which they may remain for weeks without
injury. Mount in balsam and cover the sections with a cover-glass. In time the specimens thus
preserved are not infrequently marred by the appearance of corrosive crystals, but the impreg-
nation of the elements of the nervous tissue remains intact.
44 HISTOLOGY.
hours the pieces can easily be cut into slices about 4 mm. in diameter
The quantity of Golgi's fluid to be used is regulated by the number of
the slices, each slice requiring about 10 c.c. of the mixture. In from
two to six days, less often fifteen days,* the slices are taken out, quickly
washed for a couple of seconds in distilled water, gently dried with filter-
paper, and placed in 0.75 per cent, silver solution (30 c.c. of the 1 per
cent, solution [p. 22] plus 10 c.c. of distilled water, and for each piece
10 c.c. of this fluid). f A brown precipitate immediately surrounds the
pieces. They should be left in the silver solution for two days (which
need not stand in the dark and must not be placed in the oven), and they
may remain in it for six days without injury ; they are then placed for
from fifteen to twenty minutes (not longer) in 20 c.c. of absolute alcohol,
then embedded in elder-pith (or in celloidin, see Microtome Technic) and
cut into thick sections (p. 36).
Each section should be examined, without a cover-glass, with the
low power, in order to ascertain its usefulness ; if it is good, it is placed
for from one to two minutes in a watch-glass containing absolute alcohol,
then in creosote for two minutes, then in oil of bergamot for two minutes ;
from this it is transferred for a few seconds to xylol, then placed upon
the slide. Finally the xylol is removed by light pressure on the section
with clean filter-paper and the preparation covered with a few drops of
canada-balsam diluted with xylol. A cover-glass must not be applied,
because it would prevent evaporation of the moisture in the section,
which when retained destroys the Golgi preparations. Not infrequently
— especially when the xylol has not been satisfactorily removed — the
canada-balsam gradually withdraws from the preparation, which in con-
sequence appears spoiled, but may be fully restored by the application of
a fresh drop of balsam. At first the preparation should be examined
with the low-power objective ; when the balsam has become dry the
high power may be used.
The results obtained by this method, when successful, are admir-
able ; single elements of the nervous system (never all), occasionally also
blood-vessels, lymph-vessels, connective-tissue fibers, secretions, muscle-
fibers, and epithelial cells stand out in full relief — black on a light back-
ground. But the method is subject to various accidents. Almost in-
variably the best sections are disfigured by black precipitates ; these occur
chiefly at the edges of the preparations ; in order to avoid them it has
been suggested that a layer of coagulated blood be applied to the fresh
* See Special Technic.
t The used Golgi mixture is to be thrown away.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 45
object. Very often the reaction fails entirely (especially when the action
of the Golgi mixture was too prolonged) ; then the so-called " double
method " may lead to success. If the first sections show nothing, the
objects should be .again treated with Golgi's fluid for from twenty-four to
thirty-six hours, and for the same length of time with the silver solu-
tion. A second failure may be occasionally crowned with success by a
second repetition of the procedure. In the application of Golgi's method
practice and patience are important factors.
Preparations to which the foregoing method has been applied can
be "fixed." For this purpose the sections are transferred from the
alcohol to a mixture of 10 c.c. of absolute alcohol* and 20 c.c. of
the diluted solution of hydroquinone (p. 21) ; in this they remain five
minutes, during which they become dark gray to black. When the
reduction is completed, the sections are directly transferred for from ten
to fifteen minutes to a glass containing 70 per cent, alcohol. In this
they become paler, then are placed in the sodium hyposulfite solution
(p. 21) for five minutes, and finally in a large capsule containing distilled
water, in which they must remain at least twenty-four hours or longer.
The preparations that have been thus "fixed" can be mounted, like
other preparations, under a cover-glass, and staining with alum-carmine
or hematoxylin is sometimes successful.
17. Gold staining, for the demonstration of nerve terminations.
Steel instruments must not be used ; all manipulations in the gold solu-
tion are to be performed with rods of glass or wood. Put 8 c.c. of a
I per cent, gold-chlorid solution and 2 c.c. of formic acid into a test-tube
and heat the mixture to the boiling-point ; let it boil up three times.
Into the cooled mixture very small cubes of tissue (at most 5 mm. square)
are placed for one hour, during which they must be kept in the dark ;
then they are washed in distilled water and exposed to the light in a
mixture of formic acid, 10 c.c, and distilled water, 40 c.c. Sunlight is
not necessary. The reduction takes place slowly, often not until after
twenty-four or forty-eight hours, the exterior of the cubes meanwhile
assuming a dark violet hue. When the reduction is completed, place the
tissue in 30 c.c. of 70 per cent, alcohol, and on the following day in an
equal quantity of 90 per cent, alcohol, in which, to hinder further reduc-
tion, they must remain in the dark for at least eight days before their final
preparation.
* Excess of alcohol produces a precipitate, which can be promptly removed by the addi-
tion of more hydroquinone solution.
46 HISTOLOGY.
§ 9. INJECTING.
The filling of the blood- and lymph-vessels with colored masses is
a special art that can only be acquired through much practice. The
knowledge of the many little devices employed can scarcely be attained
through didactic teaching, however painstaking and explicit. Here prac-
tical instruction is indispensable. Accordingly, since this book is intended
for beginners, it seems wise to refrain from entering upon a detailed
account of the technic of injecting.
He who desires to attempt injecting must have an accurately closing,
smoothly working hand-syringe, provided with cannulse of different sizes.
For an injecting mass Berlin blue (Grubler) is recommended — 3 gm. dis-
solved in 600 c.c. of distilled water. It is advisable to begin with the
injection of single organs — for example, the liver, which is preferable
because it gives useful results, even though the blood-vessels are but
partially filled. The injected object should be fixed for from two to four
weeks in Miiller's fluid (p. 32) and hardened in gradually strengthened
alcohols (p. 33). The sections should not be very thin.
§ 10. MOUNTING AND PRESERVING OF THE
PREPARATIONS.
The finished sections and other objects prepared according to the
foregoing methods, in order that they may be examined under the micro-
scope, are finally mounted on a slide and covered with a cover-glass.
The media in which the sections are mounted are : (1) water ; or, if the
section is to be cleared and preserved, (2) glycerol ; or (3) xylol-
damar.
The transfer of the object to the slide is usually done in this way :
a small drop of a suitable fluid is placed on the middle of the slide ; the
section is then taken up on the section-lifter, and with the aid of the
needle slipped off onto the slide. Very thin sections are better lifted on
the end of a glass rod and by rolling of the latter transferred to the
slide. When the section is smoothly mounted, it is covered with a
cover-glass.* The latter must be grasped by its edges, not by its sur-
* Examinations with low powers, without a cover-glass, are permissible only for the most
superficial orientation : c. g., to ascertain if an object has been sufficiently teased. In all other
cases the cover-glass is indispensable. In order to convince one's self of this an uncovered sec-
tion should be examined, then covered with a cover-glass and examined again. Many a good
preparation that one neglects to cover appears useless. Examinations with high-power objec-
tives without a cover-glass are in general not allowable.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 47
faces. It should be taken in the left hand, one edge placed in contact
with the slide, and then, supported on its under surface by a needle held
in the right hand, slowly lowered upon the preparation. It is simpler
to suspend a drop of the mounting medium from the inferior surface of
the cover-glass and then to let it softly fall upon the preparation.
The fluid in which the section is mounted must occupy the entire space
between cover-glass and slide. If the amount of fluid is insufficient,
another drop should be placed at one edge of the cover-glass by means
of a glass rod. If there is too much fluid, — and here the beginner
strives to perpetrate impossibilities, — the excess which has escaped from
beneath the edges of the cover-glass should be absorbed with filter-paper.
The upper surface of the cover-glass must always be dry. Small air-bub-
bles under the cover-glass may be removed by cautiously raising and
lowering the cover-glass several times with the needle (see' further,
P- 49)-
1 . The examination of the unstained and the stained sections in water
or normal salt-solution should never be neglected, since many structural
peculiarities — for example, connective-tissue formations — stand out dis-
tinctly in these media, which under the clearing influence of glycerol or
xylol-damar almost entirely elude observation. Preparations mounted
in water or salt-solution cannot be preserved.
2. Preparations mounted in glycerol can be preserved ; in order to pre-
vent the shifting of the cover-glass it should be secured with cover-glass
cement (p. 23). The edge of the cover-glass must be perfectly dry ;
this is an indispensable preliminary condition, because the cement adheres
only to a dry glass surface. The drying is accomplished in this wise :
remove the excess of glycerol surrounding the cover-glass with filter-
paper and then, with a cloth moistened in 90 per cent, alcohol and
turned over the finger-tip, carefully wipe the slide clean all around the
cover-glass without disturbing the latter. Now heat a glass rod and dip
it into the hard cement ; * place a drop at each corner of the cover-glass
and trace a continuous border from 1 to 3 mm. wide, in such a way that
one edge rests on the cover-glass, the other on the slide. Finally, heat
the rod again and smooth the surface of the band of cement. |
Preparations mounted in glycerol often do not become transparent
* Glass rods fracture very easily in this procedure, nevertheless are preferable to metal
rods, because the latter cool too quickly. The fracturing can be prevented in a measure by
heating the glass rod to red heat, meanwhile turning it continuously ; only rods insufficiently
annealed break when they are dipped into the cement.
f Editor's remark; King's fluid cover-glass cement (p. 23, foot-note) is to be applied
with a small brush.
48 HISTOLOGY.
until the second or third day. Hematoxylin and other dyes soon fade
in it ; picrocarmine and carmine, on the contrary, are permanent.
3. The mounting of objects in xylol-damar or in xylol-balsam is the
most popular preserving method. In comparison with glycerol it has the
advantage of keeping the colors, but has one disadvantage : it clears more
vigorously than diluted glycerol, and thus renders many delicate struc-
tures completely invisible. Sections in alcohol or water cannot without
further treatment be mounted in damar ; they must be previously dehy-
drated. For this purpose the sections are lifted with a needle (very thin
sections with needle and section-lifter) and placed in a covered watch-
glass containing 5 c.c. of 95 per cent, alcohol. In making this transfer,
as little as possible of the water should be allowed to adhere to the sec-
tion. If a section-lifter is used, the water clinging to it should be absorbed
with filter-paper ; if the sections are lifted on a needle, the water can be
removed by bringing the filter-paper into gentle contact with them. Thin
sections remain in the 95 per cent, alcohol two minutes ; thick sections,
ten minutes or more.* Then the sections are transferred for clearing to
a watch-glass containing 3 c.c. of oil of bergamot, as much as possible of
the alcohol being removed with filter-paper before placing them in the
clearing agent. f If the watch-glass is placed on a black background, the
effect of the oil can be watched, and it will be seen that the sections grad-
ually become transparent. Care must be taken not to breathe into the
watch-glass, or the oil of bergamot will immediately become turbid. If
some areas of the section do not become transparent within two or three
minutes (such areas appear white and opaque in direct light, black-brown
in transmitted light), this indicates that the section is not dehydrated and
it must be put back into the absolute alcohol. When the clearing is com-
pleted, the section is transferred to a dry slide, the superfluous oil \ absorbed
with filter-paper or carefully wiped up § with a linen cloth turned over the
* Beginners are recommended to transfer the sections from the water to 5 c.c. of 90 per
cent, alcohol, and then to place them in an equal quantity of 95 per cent, alcohol.
f Thin sections may be transferred from the 95 per cent, alcohol directly on to the slide,
the superfluous alcohol wiped off, and a drop of bergamot oil applied. At first the oil will retreat
from the section and must be led back with the needle ; when the clearing is completed, which
can be ascertained under the microscope with the low power, as much as possible of the oil
should be wiped up and a cover-glass with a drop of damar applied. When examining
uncovered sections lying in oil both oil and sections often become clouded by the moisture
exhaled in breathing ; in this case drain off the clouded oil and add a fresh drop.
% The oil in the watch-glass that has been used for clearing may be returned to the
bottle.
jj The removal of the oil is most readily accomplished by inclining the slide and then
wiping it.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 49
index-finger, and a cover-glass, on the under surface of which a drop
of damar is suspended, applied. If several sections are to be mounted
under one cover, arrange them close together with a needle ; then, by
means of a glass rod, apply a thin, even layer of damar to the under
surface of the cover-glass and place it on the sections. Large air-bubbles
are driven out by placing a small drop of damar at the edge of the cover-
glass ; on the following day it will be seen that the air-bubbles have
retreated from beneath the cover. Small air-bubbles disappear spontane-
ously and may be neglected.
It not infrequently happens to beginners to discover that the damar
becomes turbid and finally renders the entire preparation, or parts of it,
untransparent. This is due to incomplete dehydration. If the clouding
is slight, which under the microscope is seen to consist of minute drops
of water, a gentle warming of the slide is often sufficient to remove it.
In the case of much-clouded preparations, place the whole slide in tur-
pentine for half an hour ; then carefully lift off the cover-glass, place the
section for two minutes in turpentine, in order to dissolve off the adhe-
rent varnish, and then dehydrate in 4 c.c. of absolute alcohol, which
should be changed in five minutes ; clear in oil of bergamot and mount
in damar.
The damar dries slowly, therefore the slides must not be stood on
edge, but be kept in a horizontal position.
The series of processes through which a fresh object must pass
until it is preserved as stained sections is a very long one. When, for
example, the directions in the Special Technic require " fixation in
Zenker's fluid, hardening in gradually strengthened alcohols, staining of
sections in carmine and hematoxylin, mounting in damar," the procedure
is as follows :
1. Place the fresh object, about 1 cm. in diameter, in 60 c.c. of
Zenker's fluid * for twenty-four hours.
2. Wash in (if possible running) water for twenty-four hours.
3. Place in 20 c.c. of distilled water for about fifteen minutes.
4. Transfer to 50 c.c. of 50 per cent, alcohol for twenty-four
hours; from now on the object is to be kept in the dark (see p. 33,
remark *).
5. Transfer to 50 c.c. of 70 per cent, alcohol for twenty-four hours.
6. Transfer to 50 c.c. of 90 per cent, alcohol and tincture of iodin
for from eight to fourteen days, daily adding tincture of iodin (p. 32).
* The quantities named are calculated only for this I cm. cube ; for several or for larger
objects more fixing and more hardening fluid must be used.
4
SO HISTOLOGY.
7. Transfer to pure 90 per cent, alcohol, which is to be changed
two or three times.
The object thus fixed and hardened can be sectioned at once or may
remain indefinitely in the go per cent, alcohol, which perhaps should be
once renewed.*
8. Transfer the sections from the alcohol (p. 38) to 20 c.c. of dilute
carmine solution for twenty-four hours.
9. Place them in 5 c.c. of distilled water for ten minutes.
10. Place them in 5 c.c of hematoxylin for five minutes.
11. Place them in 30 c.c. of distilled water for from ten minutes to
two hours.
12. Place them in 5 c.c. of 95 per cent, alcohol for ten minutes.
13. Place them in 3 c.c. of bergamot oil for two minutes.
14. Mount in damar.
§ 11. EXAMINATION OF FRESH OBJECTS.
I have placed this method last because it is the most difficult and
presupposes a somewhat practised eye. This practice is most readily
acquired by previous examination of prepared (hardened, stained, etc.)
objects ; having once clearly perceived and studied peculiarities of struc-
ture, it is then not difficult to detect them in fresh objects, even though
the majority of the details leave something to be desired in point of dis-
tinctness. The following instructions should be observed :
The slide and the cover-glass must not be oily. They should be
cleansed with alcohol and dried with a perfectly clean cloth. f Then
transfer one drop of a 0.75 per cent, salt solution (p. 19) to a slide,
place in it a small piece of the object to be examined, and cover it with
a cover-glass. Pressure must be carefully avoided ; if the structures are
very delicate, support the cover-glass on two strips of thin paper placed
at the sides of the object. If the objeqt requires no further treatment,
the cover-glass should be sealed with paraffin to prevent evaporation.
Melt a small piece of paraffin on the blade of an old scalpel and let it flow,
not from the tip but from the edge, on to the rim of the cover-glass ;
gaps that may occur in this frame of paraffin can be closed with the re-
heated scalpel. In most cases the influence of certain reagents (acids,
* The following quantities are intended for from three to six sections ; for a larger number
of sections the quantity of the absolute alcohol in particular should be increased.
f For removing the oil from new cover-glasses, heating them on a piece of sheet-iron for
five minutes over the flame of a Bunsen burner is recommended.
THE PREPARATION OF MICROSCOPIC SPECIMENS. 5 I
alkalies, stains) is studied directly under the microscope. It is then
necessary to remove a portion of the medium in which the object happens
to be mounted (in the present instance the salt solution) and to replace
it by another fluid. For this purpose place a drop of picrocarmine at
the right edge of the cover-glass. Should the drop not touch the
edge of the cover-glass, do not incline the slide, but lead it with a
needle to the appropriate position. It may now be seen that a little of
the staining fluid mingles with the salt solution, but does not properly
flow under the cover-glass. In order that this may occur, place at the
left edge of the cover-glass a little piece of filter-paper * and presently
the picrocarmine will be seen to diffuse under the cover-glass and
occupy the entire area.f Then remove the filter-paper and let the
stain act ; when the staining is completed, — this can be ascertained under
the microscope, — place at the right edge of the cover-glass a drop of
diluted glycerol to which, in picrocarmine staining, as much acetic acid
is added as will drop from a steel needle (hence a very small drop), and
again apply the filter-paper to the left edge of the cover-glass. In this
way a whole series of fluids can be passed through beneath the cover-
glass and their action on the tissues studied. Some of these fluids —
for example, picrocarmine — must remain in contact with the objects for
a very long time if they have been previously fixed with osmic acid.
In this case evaporation is prevented by placing the object in a moist-
chamber. For the construction of a moist-chamber a porcelain plate
and a small bell-glass 9 cm. in diameter are required. Pour water into
the plate to the depth of 2 cm., and stand in the middle a small glass
dish ; on the latter place the slide with the preparation and cover the
whole with the glass bell, the free edge of which must be submerged in
the water.
§ 12. STORING OF PERMANENT PREPARATIONS.
The finished preparations should be promptly labeled. Labels ot
cardboard about 1.2 mm. thick, glued to the slide with fish-glue (isinglass)
are preferable to those of gummed paper ; the slides can then be placed
one upon the other without injury to the preparations. The labels should
* Cut a strip 4 cm. long and 2 cm. broad, fold it square, and place the paper tent thus
formed on the slide, so that one of the narrow ends, which must be perfectly straight, touches
the left edge of the cover-glass.
f After the first drop has penetrated, place two or three additional drops at the right edge
of the cover-glass.
52 HISTOLOGY.
be as large as possible (2 cm. square for slides of English form) and
should bear the name of the animal, of the organ, and if possible a brief
statement of the methods used. Of the cases * for storing the prepara-
tions only such s_hould be chosen in which the slides lie flat, not those
in which they stand on edge.
*The best and cheapest cases are made by Th. Schroter, Leipzig, Windmiihlenstr. Nr.
46. I recommend for box {arm pattern O (for about 300 slides), price 2 M. (50 cents) ; for
tray form, P, with flat covers for 10 to 20 slides (according to size), price 45 Pfg. (about
12 cents). The tray form has the great advantage of allowing all the specimens to be seen at
once. In the United States Schroter's boxes and trays are supplied by King & Co., New York,
the Bausch and Lomb Optical Co , Rochester and New York, and other dealers.
111. MANAGEMENT OF THE MICROSCOPE.
In conformity with the position taken in the introduction, an exhaus-
tive description of the optic and mechanical parts of the microscope
cannot be entered upon here. Figure I will recall to the reader the usual
names of the several parts of the microscope.
The first requisite in the use of the microscope is perfect cleanliness
of all its parts (see also p. 17). The surface of the mirrors, objectives,
and oculars should not be touched with the fingers. The objective
should be held with the lower end directed toward the window and the
clearness of the reflected image thus tested. Foreign matter on the
ocular can be detected by rotating the latter in the tube, when anything
that is adherent will revolve.
After the ocular has been placed in the upper end of the draw-tube
and a low-power objective screwed on the lower end of the tube (or on
the revolver, if used), the field of view of the microscope should be illu-
minated with light reflected from a suitable source by the concave mirror
placed below the stage. This is best accomplished by moving the mirror
tentatively in all directions (with the diaphragm widely open, and the
front lens of the objective about 1 cm. above the level of the stage) till
the eye, looking simultaneously through the eye-piece into the micro-
scope, sees the field of view brightly and uniformly illuminated.* The
concave mirror should be used with dry lenses, except when a substage
condenser is employed.
The light reflected from a white cloud or from a white window-blind
illuminated by the sun is recommended ; less desirable but still useful as
a source of light is the blue sky. Direct sunlight must be avoided. In
using artificial illumination the light should be taken from the inner sur-
face of a white lamp-shade, not directly from the flame. A screen of blue
*The rays of light reflected from the mirror in this position pass perpendicularly through
the object on the stage. This is called " central illumination.'' 1 For distinguishing slight dif-
ferences of level between adjacent parts of an object it is of advantage to use " oblique or
lateral illumination" to obtain which the mirror is moved to the side so that the rays reflected
from it strike the object obliquely. When lateral illumination is used, the diaphragm and the
cylinder in which it is mounted must be removed, that the opening in the stage be as large as
possible.
S3
54
HISTOLOGY.
• Eye-piece (Ocular)
d pinion adjustment
Tube • •
Triple revolver
Objective ■
• Micrometer Screw
Fig. i.— Leitz Microscope. Stand II (one-half actual size).
glass placed between the mirror and the source of light, or between the
mirror and the object, agreeably subdues artificial light, without essen-
tially injuring the definition of the image. It is obvious that the micro-
MANAGEMENT OF THE MICROSCOPE. 55
scopist should not sit in direct sunlight ; the instrument should be placed
about a meter from the window.
Having secured the light, the examination may begin. Always ex-
amine first with the low-power, then with the high-power, objective ; do not
use strong oculars — they narrow and darken the field of view and render
the examination much more difficult.* The low- and the medium-power
oculars (Leitz, Oc. I) of the usual outfit supplied with the microscope
answer for the great majority of cases.
The increased magnification obtained by drawing out the draw-tube
is seldom necessary. With low-power lenses a diaphragm having a large
opening should be used ; with high-power lenses a diaphragm having a
small opening. In focusing the object, the coarse adjustment by rack
and pinion is used first ; the objective is placed near to the object, but at
a distance greater than its focal length, and then, with the eye applied to
the ocular, the tube should be gradually lowered until the indistinct out-
lines of the image appear, which is then brought into distinct view by
means of the fine adjustment or micrometer-screw. The left hand should
hold the slide, while the right should remain at the micrometer-screw.
Since only the points lying in a single plane of the object can be in focus
and distinctly seen at one time, the preparation must be examined with
slight raising and lowering of the tube — that is, with change of focus by
gently turning the micrometer-screw. In using the microscope the habit
should be formed of keeping both eyes open.
One should never neglect to examine the preparations with a hand-
lens. For this purpose the oculars (e. g., Leitz, Oc. Ill) can be used.
The mounted specimen is held with the cover-glass side toward the
light ; the upper or back lens of the ocular is placed directly against the
slide, the eye applied to the lower or front lens.
DRAWING.
An invaluable aid to study is the drawing of the microscopic object.
The power of observation is made considerably keener, and many
details which otherwise would be completely overlooked are discovered
while the sketch is in progress. Even the most attentive examination
cannot replace the advantage which drawing yields. Those who have
little practice in drawing should nevertheless try to sketch the prepara-
tions under both low- and high-power objectives. For this purpose the
* The majority of the preparations from which the illustrations in this book were taken
were examined and sketched with weak oculars.
56 HISTOLOGY.
drawing-paper should be on a level with the stage, the left eye applied
to the microscope, the right eye directed to the paper and the pencil-point.
At first this is somewhat difficult, but a little practice will soon give the
necessary facility.
MEASUREMENT.
For this purpose an ocular-micrometer and a stage-micrometer are
used.*
The latter is laid on the stage of a microscope provided with an
ocular-micrometer, and the number of divisions of the ocular-micrometer
corresponding to one part of the stage-micrometer is ascertained. f
The dimensions of the spaces of the stage-micrometer being known, the
size of the object, which with a given magnification will occupy one or
more of the divisions of the ocular-micrometer, is easily calculated.
The following illustrations may render the manipulations intelligible :
Ocular I, and draw-tube pushed in, 5 divisions of the ocular-microm-
eter correspond with 1 division of the stage-micrometer. Each division
of the stage-micrometer used = fa mm. Hence 5 divisions of the
ocular-micrometer = fa (0.05 mm.), and 1 division of the ocular-
micrometer = 0.01 mm. If, then, any microscopic object, e. g., a
striated muscle-fiber, the diameter of which is to be measured with this
magnification, occupies 4 divisions, the fiber is 0.04 mm. broad.
It is often difficult, especially with low magnification, to count the
fine divisions of the ocular-micrometer. This can be more easily done
by noting the longer lines marking every fifth or tenth division. For
instance, with Leitz Objective 3, Ocular I, and the draw-tube drawn out,
40 divisions of the ocular-micrometer correspond with 5 divisions of the
stage-micrometer. Therefore, 40 divisions = -fa mm. = 0.25 mm.,
and 1 division of the ocular-micrometer with this magnification =
0.0062 mm., 2 divisions = 0.0 124 mm., and so on.
With Leitz Objective 7, Ocular I, and draw-tube pushed in, 30 divi-
sions of the ocular-micrometer correspond with 1 division of the stage-
* Some ocular-micrometers (Leitz) are made to rest upon the diaphragm inside the ocular ;
others (Seibert) to be inserted through a lateral opening ; or, in some cases, special oculars
(Zeiss) for measuring are made for the microscope. The actual size of the divisions of the
ocular-micrometer need not be known. The stage-micrometer is a glass slide on which I mm.
with 100 subdivisions is engraved. Instead of this a second ocular-micrometer, which usually
contains a mm. with only 20 divisions, may be used. Measurements made with this are not
so accurate, but the errors are so insignificant that they scarcely need consideration.
f Beginners often find it difficult to focus the lines on the stage-micrometer ; faint or
oblique illumination of the object makes it easier to detect the lines.
MANAGEMENT OF THE MICROSCOPE. 57
micrometer ; 30 divisions = 0.05 mm., 1 division = 0.0017 mm., or 17 /ji.
Finally, with Leitz Objective 7, Ocular I, and draw-tube drawn out, 40
divisions of the ocular-micrometer = 1 division of the stage -micrometer.
Therefore, 40 divisions = 0.05 mm., 1 division = 0.0012 mm., or
12 fi.
It is advisable, if one has many microscopic measurements to make,
to prepare a table for each magnification used, in which the equivalent
values of 1, 2, 3 . . . . 20, 30, 40 . . . . 100 scale divi-
sions of the ocular-micrometer are given. It must be emphasized that the
foregoing calculations by no means apply to all the microscopes made by
Leitz. The values must be specially determined for every instrument by
the foregoing method.
In conclusion, the microscopist is advised to be patient, very patient ;
if his preparations are unsuccessful, let him not search for the cause in the
deficiency of the methods recommended, — I have often tested them, — but
in himself; he who cannot accustom himself conscientiously to follow the
written instructions,* who grasps delicate objects with his fingers, who
contaminates the reagents by pouring one into the other, who leaves
objects in fixing fluids exposed to the sun or allows them to become dry,
has not the right to expect good results from his slovenly work.
* The periods of time given for staining, dehydrating, etc., have only an approximate
value. They vary within considerable limits in accordance with the thickness of the sections,
the concentration of the solutions, etc. Experience will soon teach the microscopist to. deter-
mine the precise period of time.
PART II.
MICROSCOPIC ANATOMY AND SPECIAL
TECHNIC.
The animal body consists of cells which are derived from a single
cell by repeated division. At the beginning of development the cells are
of similar form, all are spherical structures, and none is furnished with
special characteristics that distinguish it from its companions. The cells
are still undifferentiated. In the course of development the cells arrange
themselves in flat, superposed layers, the germ-layers. With the sepa-
ration in germ-layers and the formation of organs from these, the cells
cease to resemble one another — they become differentiated. As a rule,
the cells that have developed in the same direction are united in com-
plexes, without definite spatial limitation, and thus form a tissue. A
tissue, therefore, is a complex of similarly differentiated cells. We dis-
tinguish four principal tissues : (i) the epithelial tissues ; (2) the supporting
tissues ; (3) the muscular tissues ; (4) the nervous tissues. So long as these
tissues are still young they consist only of similar elements, of cells ;
but in the course of development this condition is changed in a twofold
manner. First, the cells produce special substances, which, being de-
posited between them, are called intercellular substances. However, by
this process the character of the tissue is not essentially altered. The
definition of tissue given above need be only so far extended that we call
a tissue a complex of similarly differentiated cells and their derivatives.
More radical is the second change, consisting in the penetration of a
tissue of one kind by other tissues. The extent of this change varies
greatly in different cases. It is least marked in the case of the epithelial
tissues, more so in the supporting tissues. Muscular and nervous tissues
in their developed forms are mixed with other tissues to such a degree
that even though among the differentiated elements muscle and nerve
predominate, in the sense of the given definition they can scarcely be
called tissues.* The tissues, therefore, are not equivalent among them-
* For this reason the proposition has been made to omit a division of tissues and to dis-
tinguish only elements and organs.
58
CELLS. 59
selves ; in the lowest rank stand the epithelial tissues and the supporting
tissues ; both, though differing from each other in form and function,
also occur in the plant-world ; therefore we can class them as vegetative
tissues. On a higher level, as well morphologically as physiologically,
stand the muscular and nervous tissues, that, being found only in the
animal body, are called animal tissues.
When different tissues unite in the formation of a body of definite
internal structure and definite external form,* they constitute an organ.
Accordingly our task resolves itself into : (i) the study of the cells
and of the tissues, and (2) the study of the organs. The investigation
of cells and of tissues is the object of histology. Histology is a part of
general anatomy, which, because of the instrument most used in its-
study, is called microscopic anatomy. The investigation of organs, also,
so far as it can be done with the aid of the microscope, is the task of
microscopic anatomy.
I. HISTOLOGY.
(MICROSCOPIC ANATOMY OF CELLS AND TISSUES.)
A. CELLS.
A cell, cellula, is a spatially limited structural element which, under
certain conditions, is able to nourish itself, to grow, and to multiply. In
virtue of these properties the cell is called an elementary organism.
The essential parts of a cell are: 1. The protoplasm, or cell-body,
a soft, semifluid substance of alkaline reaction, insoluble in water, highly
distensible, that consists principally of albuminous substances, much
water, and salts, and contains a special nitrogenous proteid, plastin. In
the protoplasm small granules, microsomes, occur in variable quantity ;
when numerous they may give to the protoplasm a dark appearance.
They are irregularly distributed — namely, are absent in the superficial
layer, the exoplasm, which is somewhat denser and perhaps possesses a
special function. With the aid of very high magnifying powers it is seen
that protoplasm possesses structure : a reticulum, spongioplasm, which is
* Usually in the definition of an organ " the definite function " is included ; but this does
not come within the limits of a morphologic definition, nor is it a special peculiarity of an or-
gan, but may be the property of a cell as well as of a tissue.
6o
HISTOLOGY.
embedded in an amorphous ground-substance, hyaloplasm (Flemming).*
2. The nucleus, a clear, sharply defined, usually vesicular body lying in
the middle of the cell, that consists of several proteid substances, chro-
matin, or nuclein, pyrenin, or paranuclein, linin, " nuclear fluid," or matrix,
and amphipyrenin. Chromatin and pyrenin, by their affinity for stains, are
distinguished from the other three so-called achromatin substances, but
differ chemically from each other. For example, on the addition of dis-
tilled water the structures composed of chromatin disappear, while those
composed of pyrenin remain intact. In the simplest case (in spermatozoa)
the nucleus is a compact mass of chromatin, to which the pyrenin is
attached, but usually it consists of a network of fine linin threads and
coarser chromatin cords. f The chromatin cords are of different caliber,
and at intervals exhibit isolated enlargements (" net-knots," karyosomes)
Nuclear membrane. *
Linin.
Nuclear fluid (matrix). . \
Nucleolus.
Chromatin cords (nuclear
network).
Nodal enlargements of --
the chromatin.
-• Cell-membrane.
■ Exoplasm.
Microsomes.
4— Centrosome.
'. j ^JT-T7 — Spongioplasm.
'■*''C''V~ Hyaloplasm.
"V'V
Foreign enclosures.
Fig. 2. — Diagram of a Cell. Microsomes and spongioplasm are only partly drawn.
that must riot be confused with .the nucleoli. Linin and chromatin form
the nuclear network, the interstices of which are occupied by one or more
nucleoli consisting of pyrenin and by the nuclear fluid. J The nuclear
* The theories concerning the structure of protoplasm are by no means agreed. Accord-
ing to Fromann, Leydig, and others, protoplasm is a spongy structure — that is, it consists of a
network, the meshes of which contain a fluid. According to Biitschli, the structure is froth-like —
that is, it contains small spaces that do not communicate with one another. According to the
much-disputed theory of Altmann, protoplasm is composed of granules (granula, bioplasts),
connected by an indifferent substance, and these are the real elementary organisms.
f In suitable preparations it may be seen that the chromatin cords are composed of rows
of granules which lie in contact with threads of linin. This is shown in the upper half of the
diagram (Fig. 2).
% Recently a special structure has been ascribed to the nuclear sap ; it is said to consist
of a substance in the form of a framework, within which are encamped tumescent Granules,
and of a fluid ; whether this structure is vital is not yet definitely established.
CELLS. 6 1
membrane, not always present, is composed of amphipyrenin ; often a
membrane is simulated by a thin superficial layer of chromatin. The
nuclear network and the nucleoli undergo important changes according to
the age of the cell. 3. The centrosome, a usually diminutive corpuscle
within the nucleus, from which fine threads extend to the chromatin
cords and to the nuclear membrane. Because of its minuteness it can
be seen only in particularly favorable objects (in the spermatocytes of
ascaris megalocephala univalens, in carcinoma cells) ; it becomes more
distinct when it wanders from the nucleus into the protoplasm, which
it does during the division of the cell. In the protoplasm the centro-
some seems to be able to remain for a considerable period and there it
was first discovered (Fig. 3).
Most cells contain but one nucleus ; only a few have several nuclei
(some wandering cells, giant cells, and others). Nonnucleated cells
(horny cells of the epidermis, colored blood-corpuscles of mammals)
originally possess nuclei, but lose them in the course of development.
An unessential element of the cell
is the cell-membrane, which is wanting in
many cells, and when present is either a
transformation of the peripheral zone of
the protoplasm or a secretory product
of the latter. When the membrane sur-
rounds the cell on all sides, it is named FlG - 3--cellof the bone-marrow of
' a Rabbit. X 1500. I he double centro-
Pellicula; when it lies Only On the free some l, es in a clear area, the attracuon-
surface, — namely, only on one side, — it
is named cuticula. By crusta is understood the denser border zone ot
the cell, that without sharp demarcation gradually passes into the
softer protoplasm. The protoplasm of cells may contain adventitious
materials, pigment, glycogen, etc., and globules of fat, of aqueous and
slimy fluids. The term paranucleus has been used to designate various
structures, the significance of which is not yet in each case determined.
A paranucleus is often simulated by the remnants of degenerated cells
that have been incorporated in a living cell. In other cases the para-
nucleus is confused with the centrosome.
Cells differ greatly in form. They may be : spherical, the typical
form of all cells in the embryonal period, and in the adult, for example,
resting leucocytes are spherical ; discoid, e. g., the colored blood-cor-
puscles ; polyhedral, e. g., the liver-cells ; cylindrical or columnar, e. g.,
the epithelium of the small intestine ; cubical, e.g., the epithelium of the
capsule of the crystalline lens ; flattened (so-called squamous epithelium),
e. g., the epithelial cells of the blood-vessels ; spindle-shaped, c. g., many
62 HISTOLOGY.
connective-tissue cells ; elongated into fibers, e. g., smooth muscle-fibers ;
and stellate, e. g., many ganglion-cells. The form of the nucleus usually
corresponds to the form of the cell. It is more or less oval in columnar,
spindle, and stellate cells ; rounded in spherical and cubical cells. Lobu-
lated, so-called polymorphous, nuclei are found in leucocytes and in
giant-cells ; they are a symptom of activity on the part of the cell, tending
either to locomotion or change in form, or to increased metabolic energy.
The size of cells varies from forms microscopically small, 4 fj. *
(colored blood-corpuscles), to macroscopic bodies (eggs of birds, of am-
phibians). The size of the nucleus corresponds in general to that of the
protoplasmic body ; only mature ova, despite their great dimensions,
have minute nuclei.
The vital properties of cells will be discussed here only in so far as
they can be studied by direct microscopic observation ; other details
must be sought in textbooks of physiology. Accordingly, the phe-
nomena of motion in cells, the reproduction of cells, and those micro-
scopic processes which are associated with the secretory activity of cells
will be considered.
/i 1 2 z%
3/i J il 8 HI Minutes.
Fig. 4. — Leucocytes of a Frog. X 560. Changes in form observed during ten minutes. Techn. No. 49.
The phenomena of motion occur in the form of ameboid f activity, ot
ciliary motion, and of contraction of certain fibers (muscle-fibers). The
ameboid movement is the most important ; it has been observed in
nearly all the cells of the animal body. In well-marked cases, e. g., in
leucocytes, the protoplasm of the cells throws out finer or coarser
processes (pseudopodia), which by dividing and flowing together produce
a great variety of forms. These processes may be retracted or they
may become fixed and draw the remainder, of the cell-body after them,
the result of which is locomotion, or the so-called " wandering " of cells.
The wandering cells play an important part in the economy of the animal
body. The processes can flow around and enclose foreign particles or
* A micron, fiiKpav = fi = 0.001 mm.
f This movement is exhibited in its perfection by unicellular organisms named ametee
thence the phrase "ameboid movement."
CELLS.
63
small cells, an incident described as the feeding of the cell.* Ameboid
movements ensue very slowly ; in warm-blooded animals, only on arti-
ficial warming of the object. For ciliary motion and contraction see the
Epithelial Tissues and the Muscular Tissues.
There is still another movement that is observed, not only in the
living, but also in the dead cell. This is the so-called molecular motion,
an oscillation of minute granules in the cell, the result of molecular
currents in the fluid in which they are suspended. It may often be
observed in the salivary corpuscles (see the Lymph-follicles of the
Tongue).
Reproduction and Multiplication of Cells. — Formerly, two kinds of
cell-formation were distinguished — spontaneous generation {generatio
aquivocd) and generation by division. According to the theory of
spontaneous generation, cells originated in a suitable fluid, cytoblastcma.
This view has been utterly abandoned. "Only one kind of^cell-generation
is now recognized — namely, reproduction by division of preexisting cells,
" Omhis cellula e cellula." f
In the division of a cell, first the nucleus and then the protoplasm
divides into two usually equal parts. In this process a special grouping
and rearranging of the nuclear substances take place according to
definite laws. This mode of division is called indirect division, mitosis, %
karyokinesis. Its cycle is usually divided into three phases, as follows :
(1) Prophase. — The centrosome increases in size and migrates
from the nucleus into the protoplasm. There it lies close beside the
nuclear membrane, surrounded by a clear zone from which delicate
threads radiate that collectively are called astrosphere, or attraction-
sphere. The centrosome now divides in halves, each of which is sur-
rounded by an attraction-sphere. Then the nucleus enlarges ; the
nuclear network becomes richer in chromatin, and the chromatin cords
*This must not be confused with the nutrition of the cell, which is effected by a series 01
complicated chemical processes within the cell-: diosmotic currents, imbibition, molecular pres-
sure, etc.
f Likewise, a new nucleus can be formed only by the division of an existing nucleus. The
theory of spontaneous generation of nuclei, according to which nuclei originate directly from the
protoplasm and independently of existing nuclei, lacks convincing evidence.
\Ilitos — thread, because in this process threads are visible in the nucleus. There is a
second mode of division, in which the nuclei divide simply by constriction, without a definite
grouping of the nuclear substances. This is called direct or amitotic division. However, it is
very probable that this kind of division in vertebrates has not the significance of a physiologic
multiplication of cells, but occurs only in those cells which are on the point of disintegrating,
for very often the division of the protoplasm does not follow, so that only » multiplication of
nuclei takes place. This frequently happens in leucocytes, also in epithelial cells — c. g., in the
superficial epithelial cells of the bladder of young animals.
6 4
HISTOLOGY.
assume the form of tortuous segments, chromosomes* transversely dis-
posed to the longitudinal axis of the nucleus, the number of which is
constant for each animal species. The form of these segments is usually
that of a V-shaped loop. The apices or closed ends of the loops are
directed toward a common center, the polar-field, — the area in which the
centrosomes are situated, — their free ends toward the opposite pole of the
cell. This arrangement of the segments is called the close skein. It is
followed by a further thickening of the segments and the formation of the
loose skein, in which the loops are less tortuous and some have their
closed ends turned away from the polar-field.
Meanwhile the two centrosomes move apart and wander along the
Close skein
(viewed from
the side).
Polar-field.
Loose skein (viewed
from above — i. e.,from
the pole).
Mother stars (viewed from the side).
Polar
radiation.
Spindle.
lllP
**
Mother star (viewed
from above).
Daughter star.
Beginning, Completed.
Division of the protoplasm.
Fig. 5. — Karyokinetic Figures Observed in the Epithelium of the Oral Cavity of a Sala-
mander. The picture in the upper right-hand corner is from a section through a dividing egg of
srredon pisciformis. Neither the centrosomes nor the first stages of the development of the spindle
can be seen by this magnification. X 560. Techn. No. 1 b.
nuclear membrane, each through an arc of 90 degrees. The interval
between them is spanned by delicate fibrils, which form the "central
spindle" ; to these the linin filaments, extending from the centrosomes
to the chromosomes (or chromatin cords), become applied (see p. 60).
Toward the completion of the prophase the nuclear membrane vanishes
and the nucleolus becomes invisible.
* These segments are also present in many resting nuclei, but are not easy to distinguish
because of the many lateral branches by which they anastomose with their fellows to form a
network. When the process of division begins, the lateral twigs are retracted, consequently
the segments become thicker and more conspicuous. In some nuclei the chromatin appears as
a single filament, which subsequently divides into chromosomes.
CELLS. 65
(2) Metaphase. — The centrosomes have reached diametrically op-
posite points,* and the threads extending from them to the chromosomes,
with which parts of the nuclear membrane may be associated, now appear
in the figure of a spindle, the nuclear-spindle. At each apex of the
spindle is a centrosome surrounded by an attraction-sphere, which in this
stage is also known as "polar-radiation." f The chromatin-loops move
to the equator of the spindle, in the future plane of division of the
nucleus, and arrange themselves so that their closed ends are directed
toward the axis of the spindle, their free ends toward the equator.
Viewed from the apex of the spindle this grouping of the segments has
the appearance of a star, mother star (monaster).
During the formation ot the mother star, often earlier, in the first
stages of the prophase, the chromatin-loops divide longitudinally and
each forms two " sister-loops." Division of the nucleus exactly into halves
now follows, as a result of the contraction of the threads of the spindle,
by which one sister-loop of a pair is drawn to one pole, the other to the
opposite pole of the spindle. This process is called metakinesis.
In this stage the nuclear segments appear in the form of two daughter
stars (diaster).
(3) Anaphase. — These relations are soon obliterated. The chromo-
somes thrust out lateral twigs for anastomosis with neighbor-chromo-
somes, and thus reproduce the reticulum of the resting nucleus. Mean-
while the spindle and the greater portion of the polar-radiation have be-
come invisible, the nuclear membrane is reformed, the nucleus reabsorbs
the nuclear fluid, swells, and becomes spherical, and the nucleolus reap-
pears. At the same time the hitherto quiescent protoplasm begins to
divide, a furrow appearing at the equator of the cell and deepening until
the separation into halves is accomplished.
In rare cases of mitotic division, especially in those of a pathologic
nature, the nucleus simultaneously divides into more than two nuclei.
The duration of cell-division varies from a half hour (in man) J to
five hours (in amphibians).
Special modifications of cell-division are the so-called endogenous
cell-formation and budding. The former occurs in those cells which are
* The above description of the behavior of the centrosomes Hoes not always hold good.
For example, the centrosome in ascaris megalocephala univalens divides within the nucleus,
which elongates and extrudes a centrosome at each end. During their extrusion the nuclear-
spindle is formed. In succeeding events the processes are identical.
f Remains of the central-spindle still lie in the axis of the nuclear-spindle.
% The disappearance of the mitotic figures in the human cadaver is not complete until after
an elapse of forty-eight hours.
5
66 HISTOLOGY.
enclosed in a firm envelop (eggs, cartilage-cells), and the mode of
division is precisely the same as that previously described, only that all the
descendants of the mother-cell remain enclosed in the common capsule.
Gemmation or budding indicates a kind of unequal cell-division, in which
protoplasmic processes of the cell are set free by constriction and become
independent cells (see Bone-marrow).
The young cells always resemble in character the mother-cells.
Such a case as a connective-tissue cell arising from the division of an
epithelial cell never occurs.
The Phenomena of Secretion. — (See Secretory Activity of Epithelial
Tissue.)
The length of life of all cells is limited. The old elements disin-
tegrate, new ones appear in their places. Formerly these phenomena
were not distinguished from secretory processes, and the erroneous idea
was entertained that the process of secretion terminated in the death of the
cell. Dying cells are characterized by decrease in the volume of both nu-
cleus and protoplasm. The latter often presents a notched edge or stains
deeply, while the chromatin substance of the nucleus decreases or appears
in the form of irregular fragments that stain uniformly. Vacuolization of
the protoplasm or of the nucleus is another symptom of degeneration.
Dying cells in abundance may be observed in epithelia, where formerly
they were often regarded as peculiar kinds of cells (cf also Fig. 17).
The growth of cells preeminently concerns the protoplasm and only
exceptionally takes place equally in all directions, in which case the
original form of the cell is retained (e. g., egg-cell) ; as a rule, an un-
equal growth occurs. As a result of unequal growth the original
form is altered ; the cell becomes elongated, or flattened, or branched,
etc. The majority of cells are soft and susceptible to change in form
from mechanical influences, as, for example, the columnar epithelial cells
in the empty bladder, which are flattened in the distended organ. Epithe-
lial cells of the peritoneum, through stretching, may acquire three times
their original superficies.
Secretory Products of Cells. — The secreted materials are either wholly
removed (as most glandular secretions) or they become rigid and remain
in the vicinity of the cells. To the latter belong certain intercellular
substances, many of which are a secretion of cells ; others are produced
by a transformation of the peripheral layers of the cell-protoplasm, still
others, by a complete metamorphosis of the cells themselves (?). It is
very difficult to decide whether individual intercellular substances were
formed by one process or another ; many points in this matter are still
the subject of lively controversy.
CELLS. 67
The intercellular substances occur either in small amount, as struc-
tureless, soft, perhaps fluid, ccmcnt-substance, between epithelial cells,
connective-tissue cells, smooth muscle-fibers, etc. ; or in large amounts,
exceeding the mass of the cells, and then are called matrix or ground-
substance. The matrix is either formless (homogeneous) or formed ; in
the latter case it is for the most part transformed into fibers or granules
of different kinds. The remnants of formless substance found between
the fibers or granules also are called cement-substance.
TECHN1C.
No. 1. — For the study of nuclear structure and karyokinesis am-
phibian larvae 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 chromic-acetic acid (p. 22). After three hours place
the larvae in running water for eight hours and then in 70 per cent, alco-
hol. At the expiration of four hours, or later, the objects are ready for
further treatment.
(a) Nuclear Structure. — With a scalpel carefully scrape the epithe-
lium from the skin of the abdomen, with two pairs of fine forceps strip off
the thin corium, stain it for from one
to three minutes in K c.c. of Hansen's
hematoxylin (p. 37,) and mount in /
xylol -damar (p. 48). Between the / /
round glands beautiful connective- protoplasm. />-_feSf
tissue cells with large nuclei may be ^\__ t Nuclear membrane
Seen. The reticulum of the pi'OtO- Nucleus. ^-kSJ — 2 Chromatin cords.
plasm, the centrosome and attraction-
sphere, and the finer structure of the
nucleus can be recognized only by the
employment of complicated methods , „
r , . , F ~, Fig. 6.— Connective-tissue Cell from the
and high magnification. The results Corium of Triton tveniatus. surface
, . , . .. .11 i'i View. X 560. Only the coarser filaments
obtained by ordinary methods are like of the nuclear network can be distinctly
,1 • , 1 • r- *- seen; with this magnification the finer fila-
tnose pictured in ngure O. ments appear as minute dots, the nucleoli
The cross-striped muscles of the as P arts of the nuclear ne ^ ork -
tail and the membranes of smooth '
muscle-fibers (the latter may be readily obtained by stripping off the
muscularis of the intestine) also furnish instructive slides.
(b) Karyokinesis. — With a pair of fine scissors cut round the margin
of the cornea and strip off the same ; stain and preserve as in 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 are recognized by their
intense color. By this method the nuclear-spindle and polar-radiation,
as in figure 5, can only be perceived (with higher magnification) in espe-
cially favorable preparations — e.g., eggs of siredon and of trout.
68
HISTOLOGY.
The delicate lamellae suspended from the convex side of the carti-
laginous gill-arch, as well as the epithelium of the floor of the oral cavity,
are suitable objects. Occasionally not a single karyokinetic figure is
found. Isolated figures may sometimes be observed in preparation a.
No. 2. Centrosomes. — Fix small pieces of bone-marrow in sublimate-
salt-solution (p. 34), and harden them in gradually strengthened alco-
hols (p. 34). Embed in paraffin, cut sections from 5 to 8 fj. in thick-
ness, and fasten them to the slide (see Microtome Technic). Stain by
M. Heidenhain's iron-hematoxylin method (p. 42), and mount in xylol-
balsam (p. 48). The centrosomes can be found only with immersion
systems and only by the practised microscopist. Beginners are advised
not to attempt the production of such preparations.
B. TISSUES.
1. THE EPITHELIAL TISSUES.
The elements of epithelial tissue, the epithelial cells, are sharply
defined cells consisting of protoplasm and nucleus. A cell-membrane is
frequently absent, often is represented by a condensation of the peripheral
zone of the protoplasm. The majority of epithelial cells are soft and
plastic, yield readily to the pressure of neighboring cells, the result of
f
Fig. 7.— Isolated Epithelial Cells of the Rabbit. X 560. 1. Squamous cells (mucous membrane
of mouth). Technic No. 96. 2. Columnar cells (corneal epithelium). 3. Columnar cells, with top-
plate, s (intestinal epithelium). 4. Ciliated cells : h t cilia (bronchial epithelium). Technic on page 29.
which is great diversity of outline. In general two principal forms can
be distinguished : the flattened or squamous and the cylindrical or columnar
(better, prismatic). These extremes are united by numerous transitional
forms.
The squamous epithelial cells rarely are symmetrical in form, except-
ing the pigmented epithelium of the retina, which consists of tolerably
regular hexagonal cells ; generally the contour is very irregular.
The cylindrical epithelial cells, cylinder or columnar cells, seen from
the side are elongated elements, the height of which considerably exceeds
the breadth ; seen from above they appear hexagonal ; therefore they are
in reality prismatic.
TISSUES. 69
Cells as high as they are broad are called cubical epithelial cells ;
sometimes, pavement cells.
Many columnar cells have a sometimes homogeneous, sometimes
striated border on their free upper surface (Fig. 7, 3, s), a cuticular
formation, the so-called top-plate.
The striae are the optical expression of minute rods, occasionally
distinctly seen even with medium magnification (Fig. 9, c) ; they are
processes of the protoplasm that penetrate the homogeneous cuticular
zone, and differ greatly in length. To the same category belong the stria-
tions seen in the basal half of the cells lining the smaller ducts of the
salivary glands and in the cells of some of the tubules of the kidneys ;
in the latter they form the so-called " brushborder," and are distinguished
by their greater delicacy.
Other columnar cells are beset with delicate filamentous processes
:•■■-. i'X -■;
WtSy
s _-.-^5 a t^'--^
:■»
Fig. 8:— Pigmented Epithelium of the Retina
z»-
' "'~ K . -. ,
in such a manner that either they present smooth \y
surfaces of contact to one another, — namely by 'u*rj ;, (
the intervention of intercellular substance, — or
they interlock by variously shaped processes,
the latter being pressure-effects. The delicate
spines and thorns visible on the surfaces of
many epithelial cells have been regarded as
similar processes. But these are connecting-filaments/ 1 ' which pierce
the intercellular substance and establish an intimate union with neighbor
epithelial cells. Cells provided with such spikes and ridges are called
prickle-cells ; the processes are aptly designated by the appropriate name
of intercellular bridges (Fig. 14).
. 14. — From a Vertical
Section of the Stratum
Germinativum of the
Epidermis. '/ 560. Seven
prickle-cells united bv in-
tercellular bridges. Tech-
nic like No. 89.
* These filaments, that can be traced in the interior of the cells (the spongioplasm,
p. 59), are the ground on which such epithelium was said to have a " fibrillar " structure, — a
description that can only lead to perplexity, because, for example, it tends to produce confu-
sion with the fibrillar structure of connective tissue, which is something wholly different.
72
HISTOLOGY.
They were first seen on the polygonal cells of stratified squamous
epithelium,* but they also occur on the cells of simple squamous and
columnar epithelium, — for example, of the stomach and of the intestines, —
but there they are extremely delicate and can be demonstrated only by the
application of special methods. The length of the intercellular bridges
and the diameter of the " intercellular clefts " occurring between them
vary greatly in the different forms of epithelium and in the different phy-
siologic states of the tissue.
The epithelium has no blood- and lymph-vessels, but nerves are
found in some situations — for example, in the epithelium of the skin and
of many mucous membranes.
SECRETORY ACTIVITY OF EPITHELIAL TISSUE.
Many epithelial cells are capable of secreting and discharging
certain substances which are not used in the growth and development of
the tissue. Such cells are called gland-cells. The secreted substances
Granule.
Protoplasm.
" Basal filaments." f
Nucleus.
Granule.
Protoplasm.
New granule.
Nucleolus.
Fig. 15.— Two Serous Gland-cells from the Submaxillary Gland of a Guinea-pig. X 1260.
In cell B the granules have passed into the unstainable state ; new stainable granules are begin-
ning to develop in the protoplasm. Technic No. 5.
are either used in the body (secretions) or, those of no further use,
removed from the body (excretions). The performance of the processes
of elaboration and of discharge of secretions (or excretions) is manifested
by certain changes in the appearance of the form and contents of gland-
cells, which indicate states of rest and activity. In many cells, for
example, in the serous gland-cells, the exhausted state, barring certain
*The basal surface of the columnar cells of stratified squamous epithelium is also pro-
vided with short processes, directed toward the subjacent connective tissue, the " rivet-fibers "
{Haftfasern), that are rendered visible only by means of complicated methods.
f The basal filaments occurring in the serous gland-cells and in the chief cells of the gas-
tric glands may be portions of the filar substance (spongioplasm), or possibly they too are
concerned in the production of the secretion.
TISSUES.
73
phenomena of the nucleus (p. 73), is manifested by a smaller volume
and a darker appearance of the cell ; the higher objectives and special
methods reveal granules that stain intensely (Fig. 15 A). These
"granula" lose the faculty of staining (Fig. 15 B) and become trans-
muted into drops of secretion ; thus the cell becomes filled and there-
with passes into the replenished state, which may be demonstrated also
by simple methods and is indicated by an increased volume and a clearer
appearance. The drops of secretion are discharged into the lumen of the
gland. In other gland-cells, for example, in many mucous gland-cells,
the elaboration of secretion is initially likewise associated with granules,
which, however, soon become transformed into a transparent mass, the
mucus (Fig. 16, s) that, lying on the side of the cell adjacent to the
lumen or to the free surface, is more or less sharply defined against the
still unaltered protoplasm (p, p). As the process of secretion progresses,
more and more of the protoplasm is transformed, and the nucleus and
remnant of unaltered protoplasm are pushed to the bottom of the cell ;
Fig. 16. — Secreting Epithelial Cells. From a thin section of the mucous membrane of the stomach of
man. X 560. p. Protoplasm, j. Secretion, a. Two cells empty of secretion ; the cell between them
shows beginning mucoid metamorphosis, e. The cell on the right is discharging its contents, its
upper free wall having ruptured; the granular protoplasm has increased, and the nucleus has be-
come round again. Technic No. 108.
as a consequence of this compression the nucleus gradually becomes
rounded or even flattened. The volume of the cell when filled with
secretion is considerably increased. Finally, the cell-wall bursts at its
free surface. The secretion gradually escapes, simultaneously the proto-
plasm is regenerated, the nucleus moves upward to its original position,
and the cell, diminished in size, is restored to its previous condition and
appearance. The majority of gland-cells do not degenerate in the act
of secretion, but are able to repeat the process again and again. The
sebaceous glands furnish an exception, for their secretion is formed by
the disintegration of cells, like the goblet-cells.* In the case of the latter
the processes of elaboration and of expulsion of secretion occur simul-
taneously (Fig. 17) ; at first the secretion is produced more rapidly than
it is discharged and it accumulates in the cell (Fig. 17, 2), but finally
* The testicle and ovary afford a peculiar instance, the gland-cells of which after secre-
tion undergo further development.
74
HISTOLOGY.
expulsion exceeds production, the cell gradually empties itself com-
pletely and dies (Fig. 17, 4).
The gland-cells lie isolated between other epithelial cells * or are
united in groups and form glandular tissue.
The Glands.
The glands are composed almost exclusively of epithelium. Con-
nective tissue and blood-vessels, so important from a physiologic point
Secretion.
Protoplasm with nucleus.
Gland lumen. —
Fig. 17. — Crypt of Lieberkuhn from a Section of the Large Intestine of Man. X 165. The
secretion formed in the goblet-cells is dark in color. In zone 1 the goblet-cells show the beginning of
secretion. That a part of the secretion is already given off here is evident from the presence of secre-
tion in the form 01 drops in the lumen of the crypt. 2. Goblet-cells with much secretion. 3. Cells
containing a small amount of secretion. 4. Degenerating goblet-cells, some of which still contain
remnants of secretion. Technic on page 31.
of view, are morphologically subordinate. Therefore, although they are
organs, they may be appropriately described with the epithelial tissues.
The glands are secreting epithelial tissue, buried beneath the surface
* They are then called unicellular glands ; they are very common among invertebrates,
also occur in man as goblet-cells.
tissues. 75
of the body and arranged in the form of cylindrical tubules or rounded
saccules. Accordingly, two principal forms of glands are distinguished :
tubular and saccular (alveolar) glands.
The tubular glands occur singly or united in groups ; therefore they
are divided as follows :
1. Simple tubular glands, which have the form of simple or branched
tubules (Fig. 18) ; the latter may be called a " tubular system."
2. Compound tubular glands, which consist of a large, variable
number of "tubular systems " (Fig. 18).
The same division is applicable to alveolar glands. They also may
be distinguished as —
1. Simple saccular {alveolar) glands, which, similarly, are simple or
branched saccules having an excretory duct ; the latter form is termed
an " alveolar system."
2. Compound saccular (alveola?*) glands, which consist of a com-
bination of several " alveolar systems" (Fig. 18).
Simple unbranched tubular glands : the peptic or fundus glands, the sweat-
glands, and the intestinal glands.
Simple branched tubular glands : the pyloric glands, the duodenal glands,
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 lacrimal, and the
larger mucous glands,* the kidneys, the bulbo-urethral glands, the prostate gland, the
thyroid gland, the testicle, and the liver. The branches in the last two anastomose
and form networks, hence they 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 tarsal
glands.
Compound saccular glands : the lungs.
In the majority of glands, particularly 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
*The cross-sections of the coiled and closely packed branching tubules of the last four
glands were for a long time regarded as vesicular evaginations 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 greater here than in other
portions of the tubules. On 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. But such thickenings must not be called " acini," since we understand by
acinus an evagination, a distention of the lumen. To avoid misunderstanding, the term
" acinus " was dropped and that of " alveolus " selected for glands of the saccular form. The
much-used term " acinous " or " racemose " has also been discarded, because the cross-sections
of tubular glands also exhibit a " racemose " appearance.
7 6
HISTOLOGY.
size, the gland lobules. The septa arc the carriers of the larger
blood-vessels and nerves. The glands may secrete throughout their
entire extent, but usually only that part lying near the blind end, the
Tubular elands
Terminal pieces.
Simple glands. Compound glands.
Saccular (alveolar) glands.
Simple saccule.
Alveolar system.
Alveolar system.
Terminal piece.
Saccules (alveoli).
Simple glands. Compound glands.
Fig. 18.— Diagram of the Different Gland-fokms. u. Excretory duct.
TISSUES.
77
fundus, is specialized for this purpose, while the part forming the connec-
tion 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 dis-
appears in the course of development. The gland follicles of the ovary
in an embryonal period also are in connection with the superficial epi-
thelium ; these connections, which might be called excretory ducts,
disappear, and the expulsion of the products formed in the ovary (the
ova) takes place by the bursting of the follicles. The ovary is a
dehiscent gland.
The secreting portion of all glands consists of a usually simple
layer of gland-cells, which bound the lumen of the gland and are in turn
Gland-lumen.
Gland-cells.
Membrana pro-
pria (basement-
membrane).
Blood-vessels.
Fig. 19. — Section of a Mucous Gland of the
Tongue of a Rabbit. Blood-vessels injected.
The nuclei of the gland-cells were only faintly
visible in the preparation. X 180. Technic
like No. 124 b.
Secretory
capillaries.
Fig. 20. — Section of a Fundus Gland of a
Mouse. Left upper half drawn after an alcohol
preparation (Technic No. 108) ; right upper half
after a Golgi preparation (Technic No. 125).
The entire lower portion is a diagrammatic
combination of both preparations.
surrounded by a special modification of the connective tissue, the mem-
brana propria or basement-membrane * (see p. 86). On the outer side of
the basement-membrane the blood-vessels are situated (Fig. 19). Hence
the gland-cells are inserted between the blood-vessels and the lumen oi
the gland, and on the peripheral side receive from the blood-vessels (or
from the neighboring lymph-vessels) the materials necessary for secre-
tion, on the other or central side yield the elaborated substances as
secretion.
In many glands, for example, the mucous and the serous glands of
* Occasionally, instead of this, the gland-tubules are embraced by stellate, nucleated cells
("basket-cells").
7»
HISTOLOGY.
the oral cavity, the glands of the stomach, of the duodenum, and of
the pancreas, the secretion is discharged not only on the side of the cell
directed toward the lumen, but on many sides. Then the secretion
passes into minute canaliculi which, simple or branched, sometimes
without anastomoses, sometimes forming a network, surround the gland-
cell.* These minute canaliculi, the "secretory capillaries, " open indi-
vidually or united in a single larger trunk into the lumen of the gland ;
whether they are always present or only periodically is not yet deter-
mined.
The microscopic appearance of the gland-cells changes with the
periodic functional condition. In some glands all the cells simultaneously
Fig. 21. — Diagram of the Origin of the Crescents. Protoplasm shown deeply shaded, the secre-
tion less shaded.
I. Cross-section of a
tubule of a mucous
gland with six gland-
cells. Three («i, 03,03)
are filled with secretion,
and have pressed the
three cells (d lt b>>, b 3 )
empty of secretion
away from the gland-
lumen. Comp. Fig.
174-
II. Same section
somewhat later. The
cells fli, a2> 03 have
discharged a part of
theirsecretion and have
become smaller. The
cells d\ t b 2l b A again
extend to the lumen
and begin to secrete.
III. Same section
still later. The cells
fli, a 2t as have dis-
charged the bulk of
their secretion and have
become still smaller. In
the cells b\, b 2 , b s the
secretion has accumu-
lated to such an extent
that they are the larger
and compress their
neighbors, a\ y a», a 3 .
IV. Same section still
later. The cells ai, az,
a% are now entirely
empty and pressed
away from the gland-
lumen by & lt #2, £3, now
full of secretion.
In I the cells b, in IV the cells a, are the crescents.
exhibit the same functional appearance. In other glands different func-
tional states are encountered at the same time, even within the same
tubule or alveolus. The latter is the case in many mucous glands, the
cells of which have delicate walls. Tubules occur in these that contain
cells in a condition of activity and of exhaustion. 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 " demi-
lunes of Heidenhain " or " crescents of Gianuzzi " f (Fig. 21). The nuclei
* It may be that single parts of the canaliculi He in the interior of the gland-cell.
f This meaning of the demilunes is by no means undisputed. Other authors interpret the
demilunes as serous gland-cells. According to this conception there are gland-tubules with
mixed epithelium : with gland-cells some of which produce a serous fluid rich in albumin, others
a mucous fluid. This is the less astonishing when it is recalled that glands are known which
TISSUES.
79
of many gland cells also exhibit varying appearances corresponding to
the changing functional state ; in empty cells the nucleus exhibits a
delicate chromatin-network arid a conspicuous nucleolus (Fig. 21, b x ),
while in loaded cells the nucleolus is invisible and the chromatin-cords
appear in the form of coarse fragments (Fig. 21, a x ).
The smaller branches of the ducts of many tubular glands must be
regarded as belonging to the secreting portion, since they are charac-
terized by the specialized epithelium lining their walls and participate in
the function of secretion by eliminating certain materials (salts). They
are not only excretory ducts, but part of the actively-secreting portion
of the gland. The difference in the structure
of these branches renders their division into
two parts desirable : the first portion, proceed-
ing from the terminal compartments, is narrow
and lined sometimes with flat, sometimes with
cubical cells ; it is called the intercalated or
intermediate tubide. The adjoining portion is
wider and clothed with tall columnar cells, the
bases of which show distinct longitudinal stri-
ation ; it is called the intralobular or secretory
(salivary or mucous) tube. The relative length
of the intercalated and the intralobular tubes
varies greatly in the different glands.
The excretory ducts consist of a simple
or stratified columnar epithelium lining a wall
of connective tissue mingled with elastic fibers.
Therefore, the most complex glands consist
of the following divisions : (i) The excretory duct, which divides into (2)
the secretory tubes, which lead into (3) the intercalated tubules, which
pass into (4) the terminal pieces, the axial lumen of which receives
(5) the secretory capillaries (Fig. 22).
Intercalated
tubules.
--= Terminal
pieces.
Fig. 22.— Schematic Drawing
of the Different Divi-
sions of a Tubular Gland.
(Human parotid.)
contain tubules with serous, and tubules with mucous gland-cells {e.g., the submaxillary
gland of man). But in opposition to a theory of this sort stands the fact that in strongly stim-
ulated glands the demilunes are wanting and only one variety of cells is present. When
strongly stimulated all the gland-cells discharge their secretion, and the differences between
empty and loaded cells vanish. In a third theory the demilunes are regarded as young ele-
ments to replace the gland-cells that perish in the act of secretion. The absence of any remains
of perished cells, as also the impossibility of demonstrating any of the mitotic figures invari-
ably associated with reproduction of cells, testify against this interpretation.
8o HISTOLOGY.
TECHNIC.
No. 3. — To obtain living ciliated cells, kill a frog (p. 28), 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 a drop of salt
solution, and apply a cover-glass. Examine with the high power and
search the edges of the preparation. At first the movement of the cilia
is very lively, so that the observer cannot see individual cilia ; the en-
tire ciliated border waves ; the motion has been compared to that of a
corn-field swayed by the wind. After a few moments the rapidity of the
movement diminishes and the cilia can be plainly seen. If the move-
ment ceases, it can be restored by the application of a drop of concen-
trated potash solution (p. 22) ; 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 move-
ment.
No. 4. — Terminal Bars. — Fix small pieces of intestine, from o. 5 to 1
cm. long, in Flemming's mixture (p. 33), or in sublimate-salt solution
(p. 34), and harden in alcohols of gradually increased strength (p. 34) ;
embed in paraffin, cut thin sections (about 10 ji) on the microtome, and
fasten them to the slide (see Microtome Technic). Stain after Heiden-
hain's iron-hematoxylin method (p. 42), and mount in xylol-balsam.
Even with good diy systems the bars can be distinguished as black streaks
or dots.
No. 5. — Gland granules. — Fix in sublimate-salt solution (p. 34)
5 mm. cubes of the submaxillary gland of a guinea-pig just killed.
Further treatment like No. 4. The pancreas, of amphibia in particular,
possesses very large granules ; it may be prepared after the same method.
II. THE SUPPORTING TISSUES.
While in the epithelial tissues the cells constitute the principal mass,
in the supporting tissues the intercellular substance (ground-substance,
matrix) is conspicuously developed and variously differentiated. The
predominance of the intercellular substance, which also functionally
plays the more important part, is characteristic of the group of support-
ing tissues. According to the nature of the intercellular substance they
are divided into : (1) connective tissue ; (2) cartilage ; (3) bone.
1. Connective Tissue.
The matrix or intercellular substance of connective tissue is more
or less soft ; the cells are few in number. Several varieties are distin-
guished : (a) mucous connective tissue, (b) fibrillar connective tissue,
and (c) reticular connective tissue.
TISSUES.
(a) Mucous connective tissue consists of round or stellate branched
cells and a large quantity of undifferentiated, muciferous intercellular
substance containing a few minute bundles of fine fibrils. In the higher
animals it is found only in the umbilical cord of very young embryos, but
it is widely distributed in many lower animals.
I
§>
Fig. 23.— From a Cross-section of the Umbili-
cal Cord of a Human Embryo about Four
Months Old. X 240. 1. Cells. 2. Intercellu-
lar substance. 3. Connective-tissue bundles
mostly in oblique section, at 4 in true cross-
section. Technic No. 6.
Fig. 24. — Connective-tissue Bundles of Vari-
ous Thicknesses from the Intermuscular
Connective Tissue of Man. X 240. Technic
No. 7.
Fig. 25.— Elastic Fibers. X 560. A. Fine elastic fibers: f, from intermuscular connective tissue of
man ; b, connective-tissue bundles swelled by treatment with acetic acid. Technic No. 14. B. Very
thick elastic fibers : /, from ligamentum nuchae of an ox ; *, connective-tissue bundles. Technic No.
15. C. From a cross-section of the ligamentum nuchae of an ox ; f, elastic fibers ; b, connective-
tissue bundles. Technic No. 16.
(b) Fibrillar connective tissue consists of abundant intercellular sub-
stance and of cells.
The intercellular substance is composed of fibrils, that, according to
one view, are a metamorphosis of the matrix ; according to another, a
direct transformation -product of the cell-substance. They are exquisitely
6
82
HISTOLOGY.
fine- filaments (0.6 //), which are united by a small quantity of homogene-
ous cement-substance into bundles varying in thickness, the connective-
tissue bundles. These bundles are soft, flexible, slightly extensible, and
characterized by their pale contour, their longitudinal striation, their
wavy course, and by their chemical properties. On treatment with, picric
acid they separate into their fibrils, swell on the addition of dilute acids,
e. g., acetic acid, and become transparent, are destroyed by alkaline
fluids, and on boiling yield glutin. The first connective-tissue fibrils,
according to the one view, originate inside, according to the other view
outside, of the cell ; hence in the latter case are transformations of the
intercellular substance.*
;&.'-
Fig. 26. — Network (w) of thick elastic fibers,
on the left passing into a fenestrated
membrane, tn. From_the endocardium
of man. X 560. Technic No. 17.
Fig. 27. — A. Connective-tissue cells from intermuscular
connective tissue. X 560. 1. Flat cell lying partly on
a connective-tissue bundle ; 2, folded cell ; 3, cell of
which the protoplasm is not visible; b, connective-
tissue bundles. Technic No. 8. B. Connective-tissue
bundles with encircling fibers ; k, nucleus. Technic
No. 11. C. Plasma-cells from the eyelid of a child.
Technic No. 191.
The matrix of fibrillar connective tissue always contains elastic fibers,
but in different quantities (Fig. 25). In contrast to the connective-tissue
bundles they are characterized by their sharp, dark outlines, their strong
refractive power, and their conspicuous resistance to acids and alkalies.
The elastic fibers vary from immeasurably fine to 1 1 p, and usually ofccur
in the form of finer or coarser networks, the meshes of which are some-
times narrow, sometimes large.
Narrow-meshed networks composed of thick elastic fibers form the
transition to elastic membranes, which are either homogeneous or finely
striated and perforated with apertures of different sizes (hence the name
* Flemming holds that a fibril-containing zone is formed in the peripheral portion of the
cell, which separating becomes intercellular substance and as such can produce new fibrilte.
Perhaps the different opinions are harmonized in this statement.
TISSUES. 83
fenestrated membranes), and probably are produced by the merging of
broad elastic fibers (Fig. 26).
When the quantity of elastic fibers predominates over the number of
connective-tissue bundles, the tissue is spoken of as elastic tissue. The
elastic fibers are derived neither from cells nor from nuclei, but are trans-
formations of the matrix, perhaps of the existing connective-tissue bun-
dles. In the beginning of their development they are thin, but become
thicker with advancing growth.
The connective-tissue cells are irregularly polygonal or stellate,
much flattened, variously bent or folded (Fig. 27 A). The flattening
and bending are explained by the adaptation of the cells to the narrow
spaces occurring between the connective-tissue bundles. Not infrequently
the flattened cells form complete sheaths about the connective-tissue
bundles. If such a bundle be treated with acetic acid it swells and bursts
the ensheathing cells, of which annular or
other-shaped fragments remain and constrict s
the swelled bundle. Formerly these remnants
of cells were considered fibers and were called
" encircling fibers " (Fig. 27 B). Other con-
nective-tissue cells are spherical,* rich in pro-
toplasm, coarsely granular, and relatively of 4
large size ; they are termed plasma cells and fig. 28.— fat-cells from the
t , Axilla of Man. x 240. 1.
are found principally in the neighborhood of The equator of the ceiih. focus;
2. objective somewhat elevated;
Small blood-VeSSels (Fie. 27 C\ Still Others, 3, 4>rm S changed by pressure;
\ o / / A traces of protoplasm in the
the mast-cells, are characterized by the affinity relt'X No'AV"" nuc ' eus ' *"
of their protoplasm for certain anilin dyes (e. g.,
dahlia), but do not, as their name may suggest, stand in any demonstrable
relation to the processes of nutrition. f (They are also known as granule-
cells.) The protoplasmic body of the connective-tissue cells encloses a nu-
cleus and often contains pigment-granules , in the latter case they become
pigment-cells, % that in man are found only in certain parts of the skin and
of the eye, but in the lower animals are very common. Connective-
tissue cells may contain fat-globules, that* when they are very large,
* Hence the form of the connective-tissue cells is not in any respect characteristic; their
resemblance to epithelial cells, especially when connective-tissue cells lie together in groups,
often is complete. Regarding the true nature of such cells, designated by the perilous name
of "epithelioid" cells, the embryonal history only and alone, not the form, can give the clue.
f Possibly the plasma- and mast-cells are not connective-tissue elements, but stand in closer
relation to the leucocytes.
% Not every pigment-cell is a connective-tissue cell ; there are also pigmented epithelial
cells, e.g., in the eye.
8 4
HISTOLOGY.
coalesce and give a spherical form to the cell, which is then designated
a fat-cell (Fig. 28). In such cells the protoplasm occupies only a narrow
Surface-view of fat-cells, in the nuclei of which vacuoles are visible.
tissue Blood-vessel with
blood-corpuscles.
Blood-capillary.
Fibrillar connective tissue.
A fat-cell, with its nucleus
in profile.
Fig. 29. — Adipose Tissue from the Human Scalp. X 240 (about). Technic No. 13.
peripheral zone, in which lies the extremely flattened nucleus that in
well-developed, but not in atrophic, fat-cells invariably contains one or
more sharply-circumscribed vacuoles * (Fig. 29). These finally pass
into the interior of the fat-cell,
whereupon new vacuoles form with-
in the nucleus. The protoplasmic
zone often is so thin as to be invisi-
ble. Aggregations of fat-cells are
abundantly supplied with blood-ves-
sels, lymph-vessels, and nerves, and
form what is called adipose tissue,
which bears a very important physi-
ologic 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. Such cells are named serous fat-
Fig. 30. — Serous Fat-cells from the Axilla
of an Extremely Emaciated Individual.
X 240. k. Nucleus ; f t oil-droplets, c, Blood-
capillaries; A , connective-tissue bundles.
Technic No. 12.
*In the lower mammals these vacuoles ar^ rarer than in man; furthermore, by some-
authors they are regarded as fat-drops lying external to the nucleus in a niche of the latter.
TISSUES.
85
cells (Fig. 30). In many fat-cells after death spherical masses of needle-
shaped crystals appear, the so-called margarin crystals.
Finally, smaller irregularly-spheric cells are found in connective
tissue that are not connective-tissue elements, but leucocytes (seep. 123)
that have passed out of the blood-vessels. They are described as wander-
ing cells, in distinction to those of the connective tissue, which are des-
ignated as fixed cells ; a classification that cannot be rigidly carried out,
since in some conditions (mainly pathologic) the fixed connective -tissue
cells, also epithelial and glandular cells, can migrate, and therefore it is
better to term the latter " histogenetic," the leucocytes " hematogenetic "
Blood-
vessels.
Connective-tissue
cells.
Network.
Fig. 31.— A Piece of the Greater Omentum of
Man. X 60. Technic No. 18.
Leucocytes.
Fig. 32.— Recticular Connective Tissue. From a
shaken section of a human lymph-gland. X 560.
Technic No. 57.
wandering cells. It is self-evident that such wandering cells cannot be
included in the same category with the leucocytes.
The number and distribution of the different kinds of cells are sub-
ject to considerable fluctuation.
The different elements of fibrillar connective tissue are united either
without exact 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 between
neighboring organs and serves to connect them and to fill in the inter-
86 HISTOLOGY.
spaces. For this reason it is also called "interstitial " tissue. The cells
of areolar tissue not infrequently contain fat. The fibrillar connective
tissue characterized by closer connection and regular arrangement of
the bundles comprises the corium, the serous membranes, the peri-
osteum, the perichondrium, the tendons, the fasciae, the ligaments ; the
compact sheaths of the central nervous system, of the blood-vessels, of
the eye, and of many glands.
The fibrillar connective tissue in immediate contact with epithelium
is usually modified, forming a structureless membrane called basement
membrane or membrana propria, also hyaloid membrane. On the other
hand, the membrana propria of many glands, for example, the salivary
glands, consists of flattened, often stellate cells which, basket-like, sur-
round 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 anasto-
mosing stellate cells. To this may be traced the name " cytogenous,"
that is, formed of cells.* There is no doubt that such networks occur
in lower animals and in embryonic stages of higher animals. But in the
higher vertebrates the relations are changed ; here the network consists
of slender bundles of fibrillar connective tissue, upon which lie flattened,
nucleated cells (Fig. 32). By means of complicated methods the outlines
of the cells on the fibers can be demonstrated. In fibrillar connective
tissue the cells almost without exception lie upon the bundles. Finally,
the fact that even in the adult fibrillar connective tissue may change into
reticular tissue can be comprehended only on the assumption that the
latter is a network of delicate fiber-bundles. Therefore reticular connec-
tive tissue really is only a variety of fibrillar connective tissue. The
meshes of reticular connective tissue are usually crowded with leuco-
cytes. It principally occurs in lymph-glands and is then called adenoid
tissue.
2. Cartilage.
The matrix of cartilage is firm, elastic, easily cut, and milk-white or
yellowish in color. The cells present little that is characteristic in form ;
usually they are spherical or, from being flattened on one side, somewhat
angular. They lie in the spaces or lacunce of the matrix, which they
completely fill. Whether, as in bone, the matrix is penetrated by a sys-
tem of minute channels communicating with and connecting the lacunae
is extremely doubtful. Many observations in which such channels appar-
* Accordingly mucous tissue also may be termed cytogenous tissue.
TISSUES. 87
ently were perceived have been acknowledged as erroneous ; the sup-
posed 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 lacunae is specialized, and forms
a strongly refractive, occasionally concentrically-striated capsule. The
matrix is produced by the cartilage- eel Is ; it originates in secretions that
subsequently fuse into a homogeneous mass. The parts lying nearest to
the cells, immediately adjoining the capsule, are the youngest ; they do
not always persist, but during the process of cell-division are resorbed.
Thus the ground-substance is subjected to many changes. It may be
free from fibrous admixture or it may be penetrated by elastic fibers or
a
A
\\;,l
iSSi
Br&m
Fig. 33. — Hyaline Cartilage. X 240. A. Surface view of the ensiform process of a frog; p, proto-
plasm of cartilage-cell, which entirely fills the lacuna ; k, nucleus ; g, hyaline matrix. Technic No. ig.
B. From a cross-section of a human rib-cartilage several days after death, examined in water: the
protoplasm, z, of the cartilage-cells has withdrawn from the walls of the lacunae, h ; the nuclei are
invisible. 1. Two cells within one capsule, k; x, a developing partition. 2. Five cartilage-cells
within one capsule ; the lowest cell has fallen out, so that only the empty cavity 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,/". Technic No. 20.
by connective-tissue bundles. Accordingly three varieties are distin-
guished : (a) hyaline cartilage, (b) elastic cartilage, (c) fibrous cartilage.
(a) Hyaline cartilage is of a faint bluish, pearly 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
many situations where it is later replaced by bone. It is characterized by
the homogeneity of its matrix, which in the ordinary methods of investi-
gation appears amorphous throughout, but after special processes, e. g.,
artificial digestion, falls apart into bundles of fibers. Further evidence
in confirmation of its fibrillar structure is afforded by its appearance when
HISTOLOGY.
examined in polarized light. It is very firm, very flexible, and on boil-
ing yields chondrin.
In certain cases the matrix may undergo peculiar modifications. In
the thyroid and costal cartilages it is transformed patchwise into rigid
Fig. 34. — Elastic Cartilage. X 240. 1. Portion of a section of the vocal process of an arytenoid
cartilage of a woman thirty years old ; the elastic substance in the form of granules. 2 and 3. Por-
tions of sections of the epiglottis of a woman sixty years old ; a fine network of elastic fibers in 2, a
coarser network in 3. z. Cartilage-cell, nucleus not visible ; k, capsule. Technic No. 21.
J \l
5
H
if'
fibers that impart an asbestos-like luster, perceptible on macroscopic in-
spection. In advanced age deposition of calcareous salts may take place
in the hyaline matrix, in the beginning appearing in the form of minute
granules, subsequently as complete husks surrounding and enclosing the
cells. In the cartilages of the larynx
this may occur as early as the twen-
tieth year.
The cells of hyaline cartilage
frequently occur in groups or nests,
an arrangement explained by the con-
ditions and processes of growth. Two
cells may lie in one lacuna and be
enclosed within the same capsule (Fig.
33 B, 1) ; they are the descendants
of one cell which has undergone di-
vision by the indirect mode ; in some
cases a thin partition of hyaline sub-
stance may be seen between two such
cells. In other cases the septum does
not develop immediately, and the pro-
cess of cell- division maybe repeated until groups of four, eight, and even
more cells may be enclosed within one capsule (Fig. 33 B, 2). Such
phenomena were supposed to establish a special theory of cell-division,
z-
7 : v
1:
' 1
;■:/
'■J
Fig. 35. — From a Horizontal Section of
the Intervertebral Disk of Man. g.
Fibrillar connective tissue ; z, cartilage-
cell (nucleus invisible) ; k, capsule sur-
rounded by calcareous granules. X 240.
Technic No. 22.
TISSUES. 89
the so-called endogenous cell-formation. Not infrequently the cartilage-
cells in adults contain oil-globules.
(b) Elastic cartilage has a faint yellowish color. It occurs as the
cartilages of the external ear, of the epiglottis, of Wrisberg and San-
torini, and of the vocal process (anterior angle) of the arytenoid cartil-
ages. It presents 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 transformation of the matrix, and appear in the
vicinity of the former as minute granules (Fig. 34, 1), that later are dis-
posed in linear rows and fuse into fibers. According to an opposite
view, this phenomenon is regarded as an indication of post-mortem dis-
integration of the elastic fibers.
(c) Fibrotts cartilage is found in the intervertebral disks, the pubic
symphysis, the inferior maxillary and the sterno-clavicular articulations.
The matrix contains an abundance of fibrous connective tissue in loose
bundles extending in every direction (Fig. 35,^). The cartilage-cells
are few in number, have thick capsules, and occur in small groups or
rows at comparatively wide intervals.
3. Osseous Tissue.
The matrix of bone, osseous tissue, is distinguished by its hardness,
solidity, and elasticity, properties due to an intimate blending of organic
and inorganic substances.* It is composed of calcium salts, chiefly basic
calcium phosphate, and of collagenous fibrils that are united by a small
amount of cement-substance in finer or coarser bundles ; accordingly, a
fine-textured, or lamellar, and a coarse-textured, or plexiform, matrix are
distinguished. f It appears homogeneous or faintly striated and contains
numerous spindle-shaped spaces 15 to 27 p. in length, the lacunce, which
communicate with one another through numerous branched minute
* This union is of such a nature that either part may be removed without destroying the
structure of the tissue. On treatment with acids, the inorganic substances are withdrawn; the
bone is decalcified, is rendered flexible, and is easily cut, like cartilage. The organic sub-
stances may be removed by cautious heating; the bone then is said to be calcined. Similarly,
fossil bones are deprived of the organic substances through the prolonged action of moisture.
f The skeleton of the adult is principally formed of the fine-textured matrix, which is
characterized by the arrangement of the fiber-bundles in lamellae and contains elastic fibers.
The coarse-textured matrix occurs in the fetus in periosteal and intermembranous bone, and is
found in the adult along sutures and at the point of insertion of tendons ; it always contains
uncalcified connective-tissue bundles, the so-called Sharpey's fibers, which also are found in
the circumferential and interstitial lamella; of fine-textured bone, the remains of the primary
or periosteal bone.
9 o
HISTOLOGY.
canals, the canaliculi. In this way a system of canaliculi that penetrates
the entire matrix is established. Within the lacunae, sometimes im-
properly called " bone-cells," lie nucleated, flattened, oval bodies, the real
bone-cells. It is doubtful whether in the adult the bone-cells are con-
nected by means of processes extending through the canaliculi, although
such connection is readily observed in developing bone (Fig. 38).
Usually the formation of osseous tissue takes place in such a way
that the ground-substance of the connective tissue or of the cartilage
calcifies during embryonic life. Around the trabecular of the calcified
matrix numerous young, still indifferent, connective-tissue cells then
arrange themselves, which produce the at first soft, then calcified,
ground-substance of bone. These cells are called osteoblasts. At first
they lie upon the osseous matrix they have formed, later they come to
lie within it, and gradually become transformed into stellate bone-cells.*
■■W
m0
Fig. 36. — From a Ground Section of Dried
Bone of Adult Man ; h, lacunas ; k, canalic-
uli ; g, bone-matrix. A. Seen from the sur-
face. B. Seen from the side. X ^60. Technic
No. 61.
Fig. 37.— From Sections, a, of the Humerus
of a Human Embryo of Four Months; 6, of
the middle turbinal bone of adult man ; z,
bone-cells lying in the lacunae, h ; the canalic-
uli are only partially visible ; g, matrix. X 560.
Technic No. 67.
Dentine is a modification of bone, from which it is distinguished by
its developmental history ; the formative cells, the odontoblasts, are not en-
closed 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 Nerves. — The supporting tissues are,
in general, poorly supplied with blood-vessels, lymph-vessels, and nerves.
An exception occurs in adipose tissue, which has a rich vascular supply.
But connective tissue plays a very important part as a conveying appa-
ratus in the transference of nutritive fluids — tissue-juices, lymph — from the
blood-vessels to the tissues. When the matrix is soft, as in mucous
* Direct transmutation of developed connective tissue or cartilage into osseous tissue does
not occur. The phenomena collectively designated " metaplasia " are much better interpreted as
signifying that indifferent formative cells of connective tissue, subject to dissimilar influences,
may develop, now into bone-cells, now into cartilage-cells, or into typical tendon cells (see
also the chapter on Development of Bone).
TISSUES. 9 1
tissue, the lymph permeates the entire substance ; when on the other
hand it is denser, the lymph circulates in a system of intercommunicat-
ing channels, a juice-canal-system, formed by the cell-spaces — lymph-
spaces — and the minute canals connecting them — lymph-capillaries .
This is the case in the more compact connective tissues * and in bone.
Whether the tissue-juice is diffused throughout the matrix of hyaline
cartilage or conveyed in definite channels is still undetermined.
" Bone-matrix.
Osteoblasts.
Bone-cell.
Osteoblast chang-
ing to a bone-cell.
Fig. 38. — Portion of a Cross-section of thk Diaphysis of the Humerus of a Human Embryo
Four Months Old. X 560. Technic No. 67.
TECHNIC.
No. 6. — Mucous Connective Tissue. — Place the umbilical cord of a
human embryo of three or four months (or pig embryo from three to six
cm. long) in ioo c.c. of Miiller's fluid (p. 32) for three or four weeks ;
harden in 30 c.c. of gradually strengthened alcohols (p. 34). 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 compressed with the fingers.
The section may be stained in picrocarmine (twelve hours) or in Hansen's
hematoxylin (five minutes), and should be examined in a drop of dis-
tilled water (Fig. 23). In glycerol and in xylol-damar the delicate
processes of the cells and the bundles of connective tissue are invisible.
In the vicinity of the blood-vessels the network of cells is less fine ;
therefore a field remote from the blood-vessels should be selected for
* The lymph capillaries occurring here stand in direct connection with the intercellular
substance of the epithelial tissues, which we must imagine as similarly permeated by the tissue
juices.
92 HISTOLOGY.
study. The older the embryo, the greater is the number of the connec-
tive-tissue bundles. Mount in diluted glycerol (p. 47).
No. 7. — Fibrillar Connective Tissue ; Connective-tissue Bundles. —
Prepare small strips, one or two cm. long, of intermuscular connective tis-
sue, for example, of the thin septum between the serratus and the intercos-
tal muscles ; place a small piece on a dry slide and quickly spread it out
with teasing needles (see " half-drying method " No. 32 a, p. 110), add
a drop of salt solution and apply a cover-glass. The bundles of con-
nective tissue appear wavy and pale (Fig. 24) ; with a little practice the
sharply-contoured, highly-refracting elastic fibers may be distinguished
and also, in favorable situations, the nuclei of the connective-tissue cells.
No. 8. — The cells of fibrillar connective tissue may be rendered visi-
ble by the addition of a drop of picrocarmine to preparation No. 7, under
the cover-glass (p. 51). In most cases only the red nucleus can be per-
ceived, especially when the cell lies wholly upon the fibrous bundles.
In rare cases the pale yellow, variously-shaped body of the cell can be
seen (Fig. 27, A, 1, 2, 3).
No. 9. — Mast-cells (granule-cells). — Fix small pieces, 1 or 2 cm.
square, of mucous membrane (of the mouth, pharynx, or intestine) in
ninety-five per cent, alcohol (p. 31). In from three to eight days cut
thin sections and stain them in 10 c.c. of alum-carmine dahlia for twenty-
four hours (p. 26). Transfer them to 10 c.c. of absolute alcohol for
twenty-four hours, which must be renewed once or twice during this
time. Mount in damar (p. 48). The protoplasm of the mast-cells
exhibits granules stained an intense blue.
No. 10. — Fibrillce. — 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, pull 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. 32 a, p. 1 10) ; add a drop of distilled water, apply a cover-glass,
and examine with the high-power objective. The ultimate fibrillae appear
as exceedingly fine, silky filaments.
No. 11. — Encircling Fibers. — With the scissors cut out a piece
about one 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 bun-
dles 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. S 1). So soon as the acid reaches the bundle, it swells, the fibrillation
vanishes, and instead elongated nuclei appear. The swelling is not
uniform ; at irregular intervals the bundle is constricted. With dim
TISSUES.
93
illumination the "fibers" (cell-remnants) producing the constrictions
may be seen (Fig. 27 B).
No. 1 2. — Fal-cells. — Take a small piece of the reddish-yellow, gelat-
inous fat from the axilla of an emaciated individual ; rapidly spread out
a piece the size of a split pea in the thinnest possible layer on a dry slide,
immediately add a drop of salt solution and apply a cover-glass. In
thin places atrophic fat-cells, like those shown in figure 30, will be seen.
This preparation may be stained under the cover-glass with picrocarmine
(p. 51) and preserved in diluted glycerol. 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. 28).
in superposed VM
layers.
Fig. 39. — Adipose Tissue from a Section of Human Scalp. X 50. Technic No. 168.
No. 13. — Adipose tissue may be seen in sections of many prepara-
tions fixed by any of the usual methods — above all of the skin {cf. Fig.
247, Fig. 252). The oily contents are withdrawn by the treatment with
alcohol and then the clusters of empty cell-envelopes present a picture
that the beginner often finds difficulty in understanding (Fig. 39).
No. 14. — Fine elastic fibers may be readily obtained by treating
preparation No. 7, under the cover-glass, with a few drops of acetic acid.
The connective-tissue bundles swell and become transparent ; the elastic
fibers, on the contrary, remain unaltered and stand out sharply con-
toured (Fig. 25 A).
No. 15. — Thick elastic fibers may be obtained by teasing in a drop
of salt solution a slender piece, about 5 mm. long, of the fresh ligamen-
tum nuchas of an ox (Fig. 25 B). The piece should not be taken from
the loose, enveloping tissue, but from the tough, yellowish, fibrous por-
tion. The preparation may be stained in picrocarmine and mounted in
glycerol.
No. 16. — Cross-sections of thick elastic fibers may be obtained by
drying apiece (10 cm. long and from 1 to 2 cm. thick) of theligamentum
94 HISTOLOGY.
nuchse (it will be ready to use in four or six days) and treating it like
No. 64.
No. 17. — 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, 1 or 2 drops of potash-lye. Examine the edges
of the preparation (Fig. 26).
Good specimens may also be obtained from the basilar artery ; place a
piece of the artery cut open lengthwise in 10 c.c. of concentrated potash
solution. After six hours take a small piece, about 1 cm. long, and
separate the lamellae in a drop of water on a slide ; this is easily done
by scraping with a scalpel. Cover and examine with the high power.
The small apertures in the membrane have the appearance of shining
nuclei. With the low power the membrane is recognized by its dark out-
lines. To preserve, wash it well in 10 c.c. of water (five minutes), stain it in
3 c.c. of congo-red for from twelve to twenty hours (p. 25), and mount
in damar.
No. 18. — A network of connective-tissue bundles may be obtained
by spreading out a little piece of fresh human omentum in a few drops
of picrocarmine. It maybe preserved in diluted, nonacidulated glycerol
(p. 47). Pieces of the omentum fixed in absolute alcohol and stained
with hematoxylin and eosin (p. 38) may be mounted in xylol-damar
(p. 48). (Fig 31, p. 85.)
No. 19. — 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 lacunae (Fig. 33 A). For prolonged study, add a drop of saline
solution.
No. 20. — Hyaline Costal Cartilage. — Without any previous prepara-
tion thin 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 con-
taining rigid fibers (Fig. 33 B). The preparation may be preserved by
adding a few drops of dilute glycerol.
Fresh cartilage does not readily stain. The tissue must be first
placed in Kleinenberg's picrosulfuric-acid or in Muller's fluid (p. 32),
then in alcohol (p. 34), and subsequently stained with Hansen's hema-
toxylin (p. 37). Mounted in damar, which clears vigorously, the finer
details vanish.
No. 21. — 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. 20. The development of elastic fibers may
often be studied in the cartilages of adults, especially in the epiglottis and
in the vocal process of the arytenoid cartilage (Fig. 34, 1).
No. 22. — Fibrous cartilage. — Cut the intervertebral disks of adult
man in pieces from 1 to 2 cm. square ; fix in 100 c.c. of picrosul-
TISSUES.
95
furic acid (p. 32) for twenty-four hours and harden in 50C.C. of gradually
strengthened alcohols (p. 34). Stain sections in Hansen's hematoxylin
(p. 37) and mount indamar (Fig. 35). Sections through the edges yield
hyaline cartilage ; through the central portions of the disk they exhibit
large groups of cartilage-cells.
III. THE MUSCULAR TISSUES.
The structural elements of the muscular tissues, the muscle-fibers,
occur in two forms, the smooth and the striated. Both are cells, the
body of which is extraordinarily elongated.
1. Smooth, Nonstriated, or Involuntary Muscle. — The tissue of
smooth muscle consists of contractile fiber-cells, spindle-shaped, cylin-
Fig. 40.— Two Smooth Muscle-fibers from the Small Intestine of a Frog. X 240. Isolated in 35
per cent, potash-lye. The nuclei have lost their characteristic form through the action of the lye.
Technic No. 29 a.
drical, or slightly-flattened elements with tapering extremities (Fig. 40).
They vary in length from 45 to 225 p., in width from 4 to 7 /u ; in the
gravid uterus fibers measuring o. 5 mm. have been found. They are corn-
End of a muscle-fiber
Fig. 41. — Intercellular Bridges of Smooth Muscle-fibers. From a longitudinal' section of the
circular layer of the small intestine of a guinea-pig. X 420. Technic No. 29 b.
posed of a homogeneous protoplasm* and an elongated, elliptical, or rod-
shaped nucleus ; the latter is characteristic of the smooth muscle-fiber.
The smooth muscle-fibers sometimes lie scattered in the connective
tissue, sometimes are united in complexes. In the latter case they are
* The protoplasm of certain fibers, those, for example, of the ductus deferens, exhibits
longitudinal striation, which has led some authors to regard the smooth muscle-fiber as com-
posed of minute contractile fibrillae. In fishes and amphibians muscle-fibers containing pigment
have been found in the iris.
96 HISTOLOGY.
very firmly secured to one another by delicate thorn-shaped intercellular
bridges (Fig. 41 and Fig. 42 A). Septa of connective tissue occur only
at wide intervals (Fig. 42 B),
The complexes or fasciculi are united in strata or membranes in which
their disposition 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 the connec-
tive-tissue septa, the capillaries penetrate the fasciculi, within which they
form networks with elongated meshes. The lymph-vessels follow the
course of the blood-vessels and are present in considerable numbers.
For the nerves of smooth muscle, see the 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
A
Connective-tissue
septum.
^ic* .: .r>::>VVv Nucleus.
' 5 >^3%^l^-'-'''''~" ; -''' t .V Smooth muscle-fibers
^^^f?*y&^K2§wS^* and nuclei in trans
Fig. 42 A. — Intercellular Bridges. From a Fig. 42 B. — Section of the Circular layer of
cross-section of the longitudinal muscular layer the Muscular Coat of the Human Intes-
of the large intestine of a rabbit. X 600. tine. X 560. The intercellular bridges can-
Technic No. 29 b. not be seen. Technic No. 109.
organs, in the vascular channels and lymph-vessels, in the eye, and in
the skin. The contraction of smooth muscle-fiber is slow and not under
the control of the will.
2. Striated or Voluntary Muscle. — It is only by the study of their
development that the striated muscle-fibers are recognized as the mor-
phologic equivalents of cells. By a colossal growth in length, by pro-
liferation of their nuclei, and by peculiar differentiation of their proto-
plasm, the embryonal elements have become highly-specialized structures.
The fibers are cylindrical in form and in the interior of the larger mus-
cles have rounded or pointed ends ; at the extremities of the muscle
they possess a pointed inner end and a broad outer end, in contact with
the tendon ; the outer end is blunt or notched, often step-like and tapering.
Anastomoses, divisions, and fissures occur ; branched fibers are found in
the muscles of the eye, the tongue, and the skin (Fig. 44, ./). They vary
in length from 5.3 to 12.3 cm., in width from 10 to 100//. It is proba-
tissues. 97
ble that there are fibers having greater length, but their isolation entire
is very difficult to accomplish. In the embryo the fibers differ 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 on the nutritional condition of the indi-
vidual. Furthermore, large animals possess thicker fibers than smaller
ones. Hence the difference in caliber may be of a threefold nature.
Under the microscope each fiber exhibits alternate broad dim and
narrower clear transverse striae. The substance of the dim stripes is
doubly refracting or anisotropic, that of the light stripes singly refracting
or isotropic. High amplification shows that each transverse disk is
transversely divided ; invariably in the clear zone a dim line may be
I 'i
f^P^-MfS-F ~ r 'i . ' ffl II
a —
Fig. 43. — B. Portion of a Muscle-fiber of Man; a, anisotropic, i, isotropic band; q, intermediate
disk ; k t nucleus. X 560. Technic No. 23 b. A. Muscle-fiber of a Frog ; /", fibrillse ; £, nucleus.
X 240. Technic No. 26.
seen, the intermediate disk, and above and below this a dark band, the
accessory disk, or secondary disk. In the anisotropic (dim) band a clear
stripe, the median disk, has been observed. Owing to their extreme
variation and their instability, these disks are of subordinate significance.
Besides the cross-marking, a more or less distinct longitudinal striation
may be observed. Treatment with chromic-acid solutions renders this
striation more evident and even causes the muscle-fiber to fall apart into
delicate longitudinal fibrils, each of which exhibits the cross-striae.
These fibrils are the contractile structural elements of the muscle-fiber *
and are called ultimate fibrillce. They are grouped into bundles, the
* The muscle-fibers of some animals, after treatment with certain reagents, cleave trans-
versely into disks. Fibrillse and disks may be further separated into smaller prismatic, aniso-
tropic particles called sarcous elements. Certain authors have interpreted the disks, others the
sarcous elements, as the true structural units.
7
9 8
HISTOLOGY.
sarcostyles or muscle -columns, in which they are arranged parallel to one
another and held together by the sarcoplasm, which also surrounds and
unites the neighboring bundles. The disposition of the sarcoplasm is
best seen in cross-section ; high amplification is required. It presents
the appearance of a clear network, within the meshes of which are the
muscle-columns in section, — small, dark, polygonal areas known as
Cohnheim 's fields. 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
muscle-fiber ; in mammals, bony fishes, and some birds they are chiefly
situated immediately beneath the sarcolemma, upon the surface of the
Fig. 44.— Portions of Isolated Striated Muscle-fibers of a Frog. X50. 1. After treatment with
water: s l t sarcolemma; at x the muscle-substance is torn, the cross-striation not apparent, the longi-
tudinal striation distinct. Technic No. 24. 2. After treatment with acetic acid: £, nuclei; the fine
stippling represents the interstitial granules. Technic No. 25. 3. After the action of concentrated potash
solution : e, rounded ends ; the numerous nuclei are swollen and vesicular in appearance. With this
amplification the cross-striation ifi 2 and 3 is not visible. Technic No. 27. 4. Branched muscle-fiber
from the tongue of a frog. Technic No. 28.
muscle-substance ; in other vertebrates they are embedded within the
sarcoplasm.
Each muscle-fiber is closely invested by a structureless sheath, the
sarcolemma, which represents the cell-membrane. Therefore the fiber
of striated muscle consists of fibrillae, sarcoplasm, muscle-nuclei, and
sarcolemma.
The striated fibers are found in the muscles of the trunk and the
extremities, of the eye and the ear, also in the tongue, the pharynx, the
upper half of the esophagus, the larynx, the diaphragm, the genital
organs, and the rectum.
In some animals, the rabbit, for example, two varieties of striated
muscles are distinguished, the red (semitendinosus, soleus) and the white
TISSUES.
99
or pale (adductor magnus) ; and correspondingly, two varieties of
muscle-fibers : i, dim fibers, rich in sarcoplasm, less regularly cross-
striped, exhibiting more distinct longitudinal striation, possessing in
general a smaller diameter (for example, those forming the soleus of the
rabbit) ; 2, pale fibers, poor in protoplasm, more distinctly cross-
striated, having in general a greater diameter. The latter represent the
more highly differentiated muscle-fibers. While in certain animals the
two varieties 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, the cardiac, ocular,
masticatory, and respiratory, contain the greater number of red fibers.
The pale fibers contract more rapidly, but are sooner fatigued.
The contraction of the striated fibers, compared with that of smooth
fea®2?
Muscle-
columns.
Sarcoplasm.
n
Of the frog. B. Of the rabbit;
Fig. 45. — A and B t Cardiac Muscle-fibers, isolated in potash-lye. A
x, lateral branch. X 240. Technic like No. 27. C, from a longitudinal section, Z>, from a cross-
section of a papillary muscle of man. C magnified 240, D 560, diameters. Technic No. 38.
muscle-fibers, is rapid and is under the control of the will. The striated
fibers are united into bundles by fibrillar connective tissue, which serves
also to convey the numerous 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 pecu-
liar position. Although transversely striated, in the history of their de-
velopment, as well as microscopically, the musty be regarded as modifi-
cations of the smooth muscle-fibers. In the lower vertebrates, in frogs,
for example, they are spindle-shaped fibers possessing elongated nuclei,
that often are more distinctly striated transversely than longitudinally
(Fig. 45 A).
The cardiac muscle-fibers of mammals are short cylinders, the
ends of which often are step-like (Fig. 45 E). The protoplasm is
IOO HISTOLOGV.
partially differentiated into cross-striated fibrillm, which not infrequently
are grouped into muscle-columns radially arranged to the axis of the fiber
(Fig. 45 D). The remnant of undifferentiated protoplasm, the sarco-
plasm, proportionately considerable in comparison with that of striated
voluntary fibers, is found chiefly in the axial part of the fiber, from
which processes radiate between the muscle-columns. Owing to the
generous amount and to the disposition of the sarcoplasm, longitudinal
striation is often marked. The oval nucleus is embedded in the axial
part of the sarcoplasm, which frequently contains pigment-granules or
oil-droplets. A cell-membrane or sarcolemma is wanting. The cardiac
muscle of the higher animals is characterized by the anastomosis of the
cells by means of short oblique or transverse lateral processes (Fig.
45 B, x).
TECHNIC.
No. 23. — Striated MiLscle-fibers : a (Of the frog). — With the scis-
sors placed flat and parallel to the course of the fibers, cut a piece about
1 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
drop of salt solution, add a second larger drop of the same liquid, and,
without pressing, cover the preparation 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. 43). With higher magnification (240 diameters) the
cross-striation is distinctly seen and occasionally pale nuclei and refract-
ing granules. The presence of numerous granules within the muscle-
fibers is probably an indication of active metabolic processes. Where
the muscle-fibers are cut across, the muscle-substance not infrequently
protrudes from the sarcolemma.
b (Of man). — I have found beautiful striated fibers in muscles taken
from the human cadaver injected with carbolic acid. To preserve, stain
under the cover-glass with picrocarmine (p. 51) for about five minutes,
then displace the staining fluid with diluted glycerol.
No. 24. — The Sarcolemma. — Treat preparation No. 23 a with a
couple of drops of ordinary water. In from two to five minutes it will
be seen, with the low power (50 diameters), that the sarcolemma is
raised from the muscle-substance in the form of transparent blebs ; at
some places, where the torn muscle-substance has retracted, the sheath
appears as a delicate line spanning the interval (Fig. 44, 1, .r s').
No. 25. — Muscle Nuclei. — Prepare muscle-fibers after No. 23 a;
treat them with a drop of acetic acid (p. 51). The shrunken but sharply-
outlined nuclei, with the lower power, have the appearance of spindle-
shaped streaks (Fig. 44, 3).
No. 26. — Fibrillce. — Place the fresh muscle of a frog in 20 c.c. of
TISSUES. I O I
o.i percent, chromic-acid solution (p. 31). In about twenty-four hours
the tissue may be teased in a drop of water and fibers will be found, the
ends of which have separated into their ultimate fibrillae (Fig. 43 A).
If it is desired to make a permanent preparation, place the muscle in
water for one hour, then in 20 c.c. of 33 per cent, alcohol, ten or twenty
hours ; tease at once or preserve in 70 per cent, alcohol until wanted and
then isolate (p. 29). 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 glycerol (p. 51). Beautiful fibrillar can also
be obtained by teasing the muscles of larval salamanders that have been
fixed according to technic No. 1 and stained in bulk [in borax-carmine
(P- 39)-
No. 27. — Ends of the Muscle-fibers. — Place the fresh gastrocnemius
muscle of the frog in 20 c.c. of concentrated potash-lye, and cover
the watch-glass. In from thirty to sixty 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. 30).
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. 44, 3). The fibers
should not be examined in water or glycerol, since the lye thus diluted
soon destroys them.
No. 28. — 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 potas-
sium 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 twenty-four 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 the 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 picro-
carmine (p. 51). Mount in dilute glycerol (p. 47). (Fig. 44, 4.)
No. 29. — Smooth Muscle-fibers, a (Isolated}. — These are best
obtained 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. 27 (Fig. 40).
b {Intercellular Bridges). — Take from a guinea-pig just killed a piece
of the small intestine from 1 to 2 cm. long, fix it in 100 c.c. of Zenker's
fluid (p. 32), harden it in gradually-strengthened alcohols (p. 34), and
stain the sections with safranin (p. 40). The bridges can only be dis-
tinctly seen in very thin sections (5 /j. thick) prepared with the microtome
(see Paraffin Embedding, Microtome Technic).
102 HISTOLOGY.
IV. THE NERVOUS TISSUES.
The elements of the nervous tissues, in an early embryonic stage,
are without exception cells having a spherical form, the so-called
neuroblasts. In the course of development they become elongated and
pyriform ; the narrow part grows out as a long, delicate process, often
extending the length of a meter, and terminates in a free, branched end ;
it is named nerve-process. From the body of the cell, now termed a
nerve- or ganglion-cell, other processes may arise, which, however, are
short and divide dichotomously ; they are called dendrites, or protoplas-
mic processes. Delicate lateral branches, the collateral fibers, may grow
from the nerve-process. The nerve-cell and nerve-process together
form an individual element, the neuron (neurodendron). The dendrites
and collaterals are to be regarded as secondary processes of the neuron.
The nerve-process may remain naked throughout its course, or it
may receive different sheaths ; these are the neurilemma, or sheath of
Schwann, and the medullary sheath* Both invest the nerve-process
only in a portion of its course. There are stretches in which the nerve-
process is entirely without investment, is naked (Fig. 46, a) ; stretches
in which it is enveloped only by the neurilemma (Fig. 46, U) or only by
the medullary sheath (Fig. 46, c), and, finally, stretches in which both
sheaths are present (Fig. 46, d); in this case the medullary sheath is
always the innermost envelope, lies directly upon the cylindrical nerve-
process, and is itself ensheathed by the neurilemma. The nerve-process
always occupies the longitudinal axis ; hence the name, axis-cylinder.
Owing to the often great length of the nerve-process, it is not possible
to investigate the neuron as a whole. As a rule, it is seen only in frag-
ments, either the nerve-cell or the nerve- process, and this explains the
former division of the elements of the nervous tissues into nerve-cells
and nerve-fibers, the latter being the nerve-processes with their sheaths.
There are no independent nerve-fibers, each so-called fiber is a process
of a nerve-cell ; if the connection between the fiber and the cell is broken,
the fiber dies cellulifugalward from the point of solution of continuity.
For practical reasons the old classification is retained.
NERVE-CELLS.
Nerve-cells (ganglion-cells) are found in the ganglia, in the organs
of special sense, along the course of cerebro-spinal, as well as sympa-
* The neurilemma is a. product of connective tissue, the origin of the medullary sheath
requires further investigation ; it is probable that the nerve-process and the nutritive fluid sur-
rounding it play a part in its formation.
TISSUES.
IO3
thetic nerves, but principally in the central nervous system. They differ
greatly in size (4 to 135^ and more) and in form. There are spherical
and spindle-shaped nerve-cells and irregularly-stellate forms are very
common ; the latter are those in
which the protoplasm sends off
several processes and so gives rise
to the stellate outlines. Nerve-
cells having two processes are
termed bipolar, those having several
processes multipolar ganglion-cells
(Fig. 47 and Fig. 48). There are
also unipolar nerve-cells ; these oc-
cur in the sympathetic nerve of am-
phibians and universally in the ol-
factory mucous membrane. They,
in fact, possess but a single pro-
cess. The nerve-cells of the spinal
ganglia, on the other hand, are only-
apparently unipolar ; bipolar in the
embryo, in the course of develop-
ment they become unipolar by the
gradual approach of the processes,
which eventually come off from
the cell by a common stalk, from
.^Terminal branches.
Fig. 46. — Diagram of a Neuron.
Fig. 47. — Various Forms of Nerve-cells.
X 240. 1. Bipolar cell from the ganglion
acusticum of an embryo rat. Technic No. 196.
2. Multipolar cell from the spinal cord of man.
Technic No. 31. 3. Cell from the Gasserian
ganglion of man, axis-cylinder process torn
off. Technic No. 30. 4. Cell with T-branches
from a spinal ganglion of a young rat. Technic
No. 76.
ic>4
HISTOLOGY.
which they then diverge at right or obtuse angles. These are the
cells described as having T-shaped or Y-shaped processes. Apolar
cells, that is, nerve-cells without processes, are either immature forms
or artificial products, the processes in the latter case having been torn off
in the manipulation required for isolation.
Each nerve-cell consists of a granular or faintly-striated protoplasm,*
that not seldom contains granules of yellow-brown pigment (Fig. 47, 2)
and granules f that may be demonstrated by special methods (basophile
staining), and of a vesicular nucleus poor in chromatin, that encloses a
Fig. 48. — Two Forms of Multipolar Nerve-cells from the Ventral Horn of the Spinal
Cord of a Newborn Rabbit, showing the Richly-branched Protoplasmic Processes, n.
Nerve-process. X 60. Technic No. 76. (Schapet.)
conspicuous nucleolus. This nucleus is characteristic for nerve-cells.
A cell-membrane is wanting.
The processes of nerve-cells are of two kinds : i, the nerve-process
(axis-cylinder, axon) and, 2, the branched protoplasmic processes (den-
drites). (Fig. 48 and Fig. 49.) They are most readily distinguished in
the multipolar cells. The nerve-process, usually the only process of the
*See also p. 109, remark *.
f Occasionally the latter granules are present in vast quantities, for example, in the motor-
cells of the anterior horns of the spinal cord, where they form aggregations that extend into the
beginning of the dendrites, but not into the nerve-process. These granules are products of
metabolism.
TISSUES.
I05
kind,* is the first outgrowth from the embryonal spherical cell and is
characterized by its hyaline appearance and smooth outlines ; its course
is cellulifugal — it leads from the cell. The protoplasmic processes, usu-
ally several in number, are a later outgrowth of the embryonal cell and
are thicker, granular or finely striated, and often varicose ; their course is
cellulipetal — toward the cell. They undergo repeated division and finally
terminate in an intricate arborization of extremely fine fibrils ; in this
way the cell acquires an enormous superficial enlargement, which on the
Dendrites.
Cell-body
Nerve-process.
Fig. 49. — Nerve-cell (Cell of Purkinje) from a Section through the Human Cerebellar
Cortex. X 180. Technic No. 80.
one hand exalts the sustentative power, on the other, the susceptibility of
the cell-body to nerve-stimuli — transmitted by the terminal ramifications
of nerve-processes lying between the fibrils.
* It is said there are cells with several nerve-processes, CajaFs cells in the cerebral cor-
tex. In bipolar ganglion-cells, the two processes of which become the axis-cylinders of medul-
lated nerve-fibers (cells of the spinal ganglia of lower vertebrates and of embryos) the central
process running toward the central nervous system corresponds to the nerve-process, the per-
ipheral process to a dendrite.
io6
HISTOLOGY.
According to the behavior of the nerve-process, two kinds of nerve-
cells are distinguished, cells of the first type, having a long nerve-process
which becomes the axis-cylinder of a medullated nerve-fiber, and cells of
the second type, having a short nerve-process which divides and subdi-
vides and terminates in a nervous ramification in the vicinity of the cell
(Fig. 50). The nerve-process of cells of the first type, after giving off a
number of fine, branched twigs, the collateral fibers (paraxons) and run-
ning an extended course, often embracing many centimeters, as the
axis-cylinder of a nerve-fiber, undergoes rapid division and terminates
Nerve-cell of the first type.
Nerve-cell of the
second type. B
Nerve-process
Fig. 50.— Two Nerve-cells from the Spinal Cord of an Embryo Chick Seven Days Old. The
nerve-process of the left cell is not seen in its entire length. X 200. Technic No. 76.
in a plexus of delicate fibrils. It is supposed that all the processes ter-
minate in free endings, without forming anastomoses ; accordingly there
is no connection between the processes of adjacent cells except by
contact. Properly, therefore, there can be no nervous network, but only
a dense feltwork of interlacing fibrils* (iieuropileni).
* There may be some exceptions ; in recent investigations of the retina and of the elec-
tric organ of the torpedo nervous networks formed by the processes of several nerve-cells have
been described. In general, the phrase "nervous network" or "nervous plexus" is to be
interpreted as signifying the disposition of single nerve-fibers that branch off from nerve-fiber
bundles to join other bundles. The transition of one nerve-fiber into another never occurs.
TISSUES.
107
NERVE-FIBERS.
Dependent upon the presence or absence of the medullary sheath,
nerve-fibers are divided into medullated, or white, and nonmedullated, or
gray. Each division is susceptible of a subdivision dependent on the
presence or absence of the neurilemma.
Nonmedullated Nerve-fibers. — Without a Neurilemma. — These
fibers consist of the naked axis-cylinder alone and are found in the
olfactory nerves, where they are held together and grouped into bundles
by connective tissue. Similar are many fibers of the sympathetic nerve,
the so-called Remak's fibers ; * they
are transparent, cylindrical or band-
like in form, from 3 to 7 p. wide,
about 2 /j. thick, and exhibit faint lon-
gitudinal striation ; they are similarly
grouped into bundles of naked axis-
cylinders, that however possess ah
imperfect sheath of isolated, closely
applied, flat connective-tissue cells,
corresponding to the endoneurium
(see the chapter on the Nervous Sys-
tem).
While the fibers so far described
exhibit the same structure throughout
their length, there are nerve-fibers of
which only certain divisions are naked
axis-cylinders ; such divisions occur
as peripheral endings of the nerves
of special sense, of sensory as well as motor nerves ; also the first divi-
sion of the nerve-process proceeding from the nerve-cell is a naked axis-
cylinder (Fig. 46, a).
With a Neurilemma. — Nonmedullated fibers with a neurilemma con-
sist of the axis-cylinder enveloped by a neurilemma and are of the same
structure throughout their length ; they are found in many invertebrates
and in cyclostoma. They occur as limited portions in the course of the
cerebro-spinal nerve-fibers (Fig. 46, b).
Medullated Nerve-fibers. — Without a Neurilemma. — Among
these are no fibers that possess the medullary sheath in their entire
Fig. si- — Teased Preparation of the Sym-
pathetic Nerve of a Rabbit, i. Non-
medullated, 2, thin medullated nerve-
fibers; 3, ganglion-cell; the large nucleus
has lost its characteristic appearance in
consequence of the treatment with osmic
acid ; 4, nuclei of connective-tissue cap-
sule; 5, fine connective-tissue fibers. X
240. Technic No. 37.
* By Remak's fibers some authors understand, not bundles of naked axis-cylinders, but
individual axis-cylinder processes of sympathetic ganglion-cells.
io8
HISTOLOGY.
length ; this always invests only one portion of the axis-cylinder.
Fibers consisting of axis-cylinder and medullary sheath alone occur only
in the central nervous system.
With a Neurilemma. — Medullated fibers possessing a neurilemma
are found in the trunks and branches of the cerebro-spinal nerves, also
in the sympathetic nerve, and vary in thickness from I to 20 //. The
thickness of the nerve-fiber bears no relation to its motor or sensory
nature, but appears to be determined by its length : the longer its course,
the thicker is the fiber. Division of the medullated fibers occurs (1)
throughout the central nervous system, principally where the collateral
Axis- Medullary Axis- Nucleus of
cylinder. sheath. cylinder. neurilemma.
Fig. 52.— Medullated Nerve-fibers from the Sciatic Nerve of a Frog. X 280. 1, Normal, 2,
shrunken, 3, tortuous axis-cylinder ; 4, node ol Ranvier; 5, neurilemma with nucleus. Technic No.
32. 6, 7, 8, and 9, Fresh medullated nerve-fibers ; 10, post-mortem distortion of medullary substance ;
r, annular constriction ; /, notches of Lanterman ; /, medullary segment. Technic No. 32 a.
fibers diverge at right angles into the white substance, and (2) in the
peripheral nervous system shortly before their ultimate distribution
(Fig. 46).
The medullated nerve-fibers have a brief lease of life. They de-
generate by a gradual breaking down of the medullary substance and
axis-cylinder into a granular mass containing numerous nuclei ; in this
mass both parts are regenerated, the axis-cylinder probably by out-
growth of the nerve-process of the nerve-cell. Regarding their finer
structure and peculiar properties, the three constituent parts of nerve-
fibers comport themselves in the following manner.
The axis-cylinder, the essential part of every nerve-fiber, occa-
sionally exhibits a delicate longitudinal striation, the optical expression
TISSUES.
IO9
of its fibrillar structure.* Each fibrilla represents a special conducting
path and is cemented to neighboring fibrillae by a small amount of
finely-granular interstitial substance, neuroplasm.
The medullary sheath is composed of a semi-fluid, highly-refract-
ing, fatty substance, the myelin, which imparts 1 to fresh medullated fibers
the appearance of glistening hyaline cylinders, homogeneous throughout,
the structure of which can only be perceived by the help of reagents.
In favorable conditions it may be seen that the medullary sheath is
not continuous, but is divided at slightly irregular intervals by oblique
incisions or clefts, the Lantermari ' s notches, into small conical or funnel-
shaped pieces (medullary segments, cylindro-conical segments), which
seem to be united by cement-substance f
(Fig. 52, 9). Kolliker has interpreted these
oblique markings as artifacts. After treat-
ment with various reagents, the apparently
homogeneous medullary substance of living
•nerve-fibers in dying undergoes partial trans-
formation, and the fibers exhibit a character-
istic double contour (thence the old designa-
tion, "double-bordered," or "dark-edged"
fibers), and later appear mottled, owing to the
distortion of the medullary substance, which
collects into irregular spheric masses (Fig.
52, 10).
At regular intervals along the medullated
nerve-fibers the medullary substance is inter-
rupted, so that the axis-cylinder and neuri-
lemma come into contact. At these points
the fibers exhibit well-marked annular constrictions, termed nodes of
Ranvier (Fig. 53); they are the localities where the nutritive fluid can
approach the axis-cylinder. These constrictions occur in all peripheral
medullated fibers, at intervals of from 0.08 mm. in thin, to 1 mm. in
thick fibers, dividing them into intemodal segments or internodes. In the
vicinity of the nodes the axis-cylinder frequently shows a biconical en-
FlG. 53
Medullated Nerve-
fibers of a Frog, treated
with Silver Nitrate Solu-
tion. X 560. 1. At ?-, node of
Ranvier; a, axis-cylinder, of
which only a small extent is
silvered ; b, biconical swelling
displaced downward owing to
manipulation. 2. Axis-cylinder
with the silvered portion in situ,
at a. 3. Axis-cylinder with
cross-markings. Technic No.
36.
*The fibrils may be traced (unusually well in the cells of the spinal ganglia) on into the
nerve-cell, where curving they run round the nucleus, partially encircling it — whence the
erroneous teaching of the origin of the nerve-fiber from the nucleus. Upon this also rests the
authority for the fibrillar structure described in nerve-cells, particularly in those of the spinal
ganglia.
f These notches are artifacts, that appear very early, even in fibers recently taken from
the animal.
HO HISTOLOGY.
largement (Fig. 53 and Fig. 54), probably due to a local accumulation
of neuroplasm. After treatment with silver nitrate the nodes are rendered
conspicuous by a dark annular disk called the constricting band, pro-
duced by the staining of the cement-substance collected at these points
and by distinct transverse striae (Frommann's lines), that appear on the
adjacent parts of the axis-cylinder.*
The neurilemma, or sheath of Schwann, is a delicate, structureless
membrane, against the inner surface of which lie oval nuclei surrounded
by a very small amount of protoplasm (Fig. 52, 5).
The union of the elements of the nervous tissues in the peripheral
nervous system is secured by means of connective tissue, which contains
the ramifications of the blood-vessels. In the central nervous system
they are supported and held together, not only by connective tissue, but
by a peculiar form of tissue, the neuroglia.
TECHNIC.
No. 30. — Ganglion-cells, fresh. — Tease a small piece of the Gas-
serian ganglion in a drop of salt solution and stain under the cover-glass
with picrocarmine for two minutes (p. 51). The processes of the cells
usually tear off.
The nerve-cells of the cerebral and the cerebellar cortex may be
prepared in the same way ; the processes likewise are easily lost.
No. 31. — Multipolar Nerve-cells of the Spinal Cord. — Remove with
the scissors as much as possible of the white substance of the spinal cord
of an ox and place the gray remnant in pieces 1 or 2 cm. in length
in 30 c.c. of 33 per cent, alcohol (p. 20, e). After thirty-six or forty-
eight hours transfer the pieces to 20 c.c. of undiluted neutral carmine
solution (p. 24) for twenty-four hours. The now very soft pieces should
be transferred with the section-lifter to 50 c.c of distilled water, in order
to wash out some of the stain, and after ten minutes spread with needles
in a thin layer on a dry slide. With a little practice the nerve-cells can
be distinguished by their bright-red nuclei ; the cell-body and the pro-
cesses are not yet visible. Let the preparation dry thoroughly and
mount it in damar (Fig. 47, 2).
No. 32. — Fresh Medullated Nerve-fibers. — Expose the sciatic nerve
of a frog just killed. With delicate scissors cut it at the level of the
popliteal space and about one cm. higher. Isolate in a drop of salt so-
lution.
No. 32 a. — Better still, tease on a dry slide by the "half-drying"
method. Hold the lower end of the nerve with one needle, with another
needle separate the nerve-bundles along half the length of the nerve ;
* These strife are artifacts ; for their significance, see p. 42, remark f.
TISSUES.
Ill
- Axis-cylinder.
Node of Ranvier.
Biconical enlargement.
Medullary sheath.
\
Neurilemma.
a thin shining membrane will span the interval between the separated
bundles. Add a drop of salt solution and apply a cover-glass. The
membrane contains numerous isolated nerve-fibers. The manipulation
must be done very rapidly (in about fifteen seconds), so that the nerve-
fibers do not become dry (Fig. 52, 6, 7, 8, 9).
No. 33. — Alterations of the Medullary Sheath. — Treat No. 32 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. 52, 10).
No. 34. — The Axis-cylinder. — Tease dry (like No. 32 a) and stain
with methylene-blue (p. 40) ; the nodes of Ranvier stain first, and often
so deeply that the axis-cylinder cannot be recognized there (Fig. 52, 4).
Frequently the axis-cylinder shrinks and becomes displaced within the
medullary sheath, or it contracts and becomes convoluted (Fig. 52, 2, 3).
On the addition of glycerol the
medullary substance can no
longer be distinctly recognized
as such, but the nuclei of the
neurilemma are often rendered
plainly visible (Fig. 52, 5).
No. 35. — Exhibition of the
Axis-cylinder with Chromic Acid.
— Expose the sciatic nerve of a
rabbit recently killed, being care-
ful 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 upper and
lower ends ; cut the nerve on
the farther side of each ligature and place it, with the wood, in 100 c.c.
of a 0.1 per cent, chromic-acid solution (p. 31).
In about twenty-four hours cut the ligatures and tease a piece of the
nerve, from o. 5 to 1 cm. long, separating it into bundles, not fibers. Put
the bundles back into the chromic -acid solution ; after twenty-four hours
transfer them to 50 c.c. of distilled water, and after two or three hours
to 30 c.c. of gradually-strengthened alcohols to harden (p. 34). It is
advantageous to leave the bundles for a long time, one to eight weeks,
in 90 per cent, alcohol, as they are then more readily stained. After the
hardening, the bundles are to be teased in a drop of picrocarmine,
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 one-half to three days), preserved in acidu-
lated glycerol (p. 51). The nodes of Ranvier are not so distinct as in
fresh and in osmic-acid preparations, but appear as delicate transverse
lines (Fig. 54). 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. 36. — Nodes of Ranvier and Axis-cylinders. — Add 10 c.c. of a
Fig. 54. — Nerve-fiber of a Rabbit. X 560.
I I 2 HISTOLOGY.
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 each 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. After two minutes carefully
cut out the delicate nerves, put them for a half-hour in the remainder of
the silver solution, and place them in the dark. Then transfer them to
10 c.c. of distilled water, in which they may remain for from one to
twenty-four hours. If a nerve is now examined in a drop of water,
with the low power, the epithelial 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-cylinder, but if the preparation be exposed for several hours to day-
light (or a few minutes to sunlight) the reaction takes place and the parts
mentioned become silvered. The biconical swelling on the axis-cylinder
often becomes displaced in teasing and is not always readily found by the
beginner (Fig. 54).
No. 37. — Nomnedidlated Nerve-fibers. — Tease a portion of the
pneumogastric nerve of a rabbit on a dry slide (No-. 32, a), and add a
few drops of a 0.5 per cent, osmic-acid solution ; in five or ten minutes
the medullated 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 five
minutes. In five minutes more remove the water, add a few drops of
picrocarmine, apply a cover-glass, and place in the moist chamber for from
twenty-four to forty-eight hours ; then displace the picrocarmine with
acidulated glycerol (p. 51). The tissue maybe teased again after the
staining is completed, which is now more easily done because the ele-
ments are more distinctly 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 nonmedullated nerve-fibers. But this nerve is
somewhat more difficult to find. Cut through the greater cornu of the
hyoid bone, through the hypoglossal nerve, and push them aside ; behind
the pneumogastric nerve lies the sympathetic, which is recognized by its
three or four mm. in size, ellipsoidal, yellowish, and transparent superior
cervical ganglion. If the piece of the nerve lying close under the gan-
glion 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. Accidentally, in figure 51 only the more unusual uninu-
cleated ganglion-cell is seen.
II. MICROSCOPIC ANATOMY OF THE ORGANS.
I. ORGANS OF THE CIRCULATORY SYSTEM.
i. The Blood-vessel System.
The blood-vessels are composed of fibrous connective tissue, elastic
fibers, and smooth muscle-fibers, mingled in widely different proportions
and arranged in strata or tunics. In general, a uniform disposition of
the elements prevails in each tunic, longitudinal in the inner and outer,
circular in the middle tunic. An exception to this occurs in the com-
plicated structure of the heart and in the simple structure of the capil-
laries.
the heart.
The walls of the heart consist of three membranes: i, the endo-
cardium ; 2, the powerfully developed muscular layer, the myocardium ;
3, the epicardium (visceral layer of the pericardium).
The endocardium is a connective-tissue mem-
brane which contains smooth muscle-fibers and
numerous elastic fibers. The latter are especially '/M^fP^ 3
well developed in the auricles, where they form a
close-meshed network or are blended in a fenes-
trated membrane (Fig. 26). The free surface, that ss^
directed toward the cavity of the heart, is clothed Fig ' T ion of papillary
with a simple layer of irregula'rly-polygonal epi- • hSt^'musT
thelial (endothelial) cells. S^i^'wiA
rn t j ,. ., small deeply-
Ihe muscular Layer or myocardium consists stained nuclei; v,
. . . blood-vessel. X 240.
or muscle-nbers (tor their structure, see p. 99) Technic No. 38.
and a delicate perimysium surrounding each ele-
ment. Numerous transverse and oblique processes (see Fig. 45) unite
the muscle-fibers into complexes, the arrangement of which is very com-
plicated. The muscle-tissue of the auricles is entirely separate from that
of the ventricles. In the auricles an outer transverse layer common to
both and an inner longitudinal layer independent in each can be distin-
guished. In addition, numerous small bundles pursue independent
8 "3
114
HISTOLOGY.
courses in other directions. The muscle-tissue of the ventricles is much
more irregularly distributed ; the bundles extend in every direction, often
describing a figure-of-eight in their course.
Within the compass of the auricles the perimysium contains elastic
fibers, that are connected with those of the endocardium and of the
epicardium. The muscular layer of the auricular appendages is poor
in elastic tissue. Between the auricles and ventricles lie firm tendinous
ligaments intermingled with elastic fibers, the anmtli fibrosi, 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 epicardium is a connective-tissue membrane penetrated by elas-
a-M^th
"ft*. ^ A
1 . II ' '
B
Fig. 56.— Small Arteries of Man. i, Nuclei of intima, the outlines of the cells are invisible ; m, nuclei
of circularly-disposed muscle-fibers of media; a, nuclei of externa. A, artery with the surface ifi
focus. B, artery with the lumen in focus ; at m! the nuclei of the muscle-fibers of the media are seen
in optical section. C, small artery shortly before transition into capillaries ; the media consists of a
few isolated muscle-fibers. X 240. Technic No. 40 a.
tic fibers and fat-cells, which on the outer surface is covered with a single
stratum of squamous epithelium.
The elastic fibers of the auricular epicardium pass over into the
adventitia of the large veins ; those of the ventricular epicardium are
lost in the conus arteriosus and do not continue over into the aorta and
the pulmonary artery.
The valves of the heart are composed of fibrous connective tissue,
continuous with that of the annuli fibrosi, and their surfaces are clothed
by the endocardium. They contain muscle-fibers, but only in the
attached margin, and elastic fibers, which are especially abundant in the
nodules of the free edges of the semilunar valves.
The numerous blood-vessels of the muscular wall of the heart form
typical capillary networks with elongated meshes (see the Organs of the
THE CIRCULATORY SYSTEM.
"5
Muscular System). The epicardium and endocardium, the latter in its
deeper strata, also possess blood-vessels.
The semilunar valves contain no blood-vessels, the cuspid valves
have them only at their base, so far as the musculature extends into
them.
The lymph-vessels of the heart are extremely numerous. They
form a comprehensive system embracing all the lymph-spaces in the
clefts between the muscle-fibers and accom-
pany the blood-vessels in their course.
The many nerves, partly medullated and
partly nonmedullated, arising from the vagus
and the sympathetic, form numerous networks
enclosing ganglion-cells ; the branches spring-
ing from these networks are partly motor (on
every muscle-fiber a nerve-fiber terminates in
a small eminence) and partly sensory ; the
latter end in terminal plexuses of varying size,
that spread over a granular lamella furnished
with stellate (connective-tissue ?) cells. The
terminal plexuses all appear to be derived
from medullated nerves and occur in great
number, as well in the epicardium as in the
endocardium.
The pericardium consists of compact con-
nective tissue intermingled with elastic fibers,
which on its inner surface, that directed toward
the heart, is clothed in a simple layer of
squamous epithelium.
THE ARTERIES.
■.~S-~W:
Fig. 57. — Epithelium of the Mes-
enteric Artery of a Rabbit.
Surface view. X 260. Technic
No. 41.
The structure and thick-
The walls of the arteries comprise three
coats: 1 , tunica intima ; 2, tunica media; 3,
tunica externa (adventitia). The elements of
the tunica media are transversely disposed,
those of the other tunics chiefly longitudinally,
ness of these coats vary 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
transition into capillaries. The intima consists of elongated, spindle-
shaped epithelial cells and a structureless elastic membrane, the so-called
internal elastic membrane , that in somewhat larger arteries assumes the
n6
HISTOLOGY.
character of a fenestrated membrane. The media is formed of a single
layer of circularly-disposed smooth muscle-fibers. The externa is com-
posed of longitudinally-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 named 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 interposi-
Epithelium
External
elastic
membrane.
Media.
Vasa ^^Q^C^ V '••■;-.- -"t-
vasorum. \S*i<-. ^.^-^ "V'--
Fig. 58.— Portion of Cross-section of the Brachial Artery of Man. X 100. Technic No. 38.
tion between the epithelium and internal elastic membrane of fibrous
connective tissue, including flattened cells and networks of delicate elastic
fibers.* The media, in addition to several superimposed layers of cir-
cularly-arranged smooth muscle-fibers, comprises wide-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
*This subepithelial layer is absent in the larger branches of the abdominal aorta, in the
external iliac and the uterine arteries of young individuals.
THE CIRCULATORY SYSTEM.
"7
in the different arteries is extremely variable. In the celiac, femoral,
and radial arteries the muscle-tissue preponderates ; in the carotid, axil-
lary, and common iliac, the elastic tissue is in excess. The externa 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 externa
of arteries of medium size are smooth muscle-fibers, that appear in single,
longitudinally-disposed bundles and never form a continuous layer.
Epithelium.
Fibrous connective '
tissue.
Bundles of smooth
muscle-fibers.
Elastic fibers.
SSSi ) a.
Elastic fibers.
Connective-tissue
bundles.
Fig. 59. — From a Cross-section of the Thoracic Aorta of Man. X 100. Technic No. 38.
In the large arteries (aorta and pulmonary artery) the epithelial
cells of the intima are shorter and more polyhedral in outline than in
medium-sized vessels. Immediately beneath is the subepithelial layer,
which consists of fibrous connective tissue enclosing elastic networks and
*In the arteries of the brain the longitudinally disposed elastic fibers of the externa are
very slightly developed ; on the other hand, the internal elastic membrane is very well de-
veloped.
n8
HISTOLOGY.
flattened cells, stellate or spherical in outline. The elastic networks are
closer meshed the nearer to the intima they lie and finally pass into a
fenestrated membrane corresponding to the internal elastic membrane of
small- and medium-sized arteries. The media of the large arteries is
characterized by the preponderance of elastic tissue over the muscular
elements. The thin elastic networks of the media of medium-sized
arteries are here replaced by close networks of richly-developed, broad,
elastic fibers or by fenestrated membranes, which alternate regularly with
lamella? of smooth muscle-fibers. The elastic elements, like the muscle-
fibers, are circularly arranged. The muscular lamella? are penetrated in
an oblique direction by elastic fibers which connect all the elastic
elements of the media.
The elastic membranes already occur in the larger medium-sized
Intima.
Media.
.- Internal elastic
membrane of
the intima.
~- — ^Smooth
/'' muscle-
fibers.
.—' '',-~~~' Connective
tissue.
Smooth muscle-fibers of the externa.
Fig. 60.— Portion of Cross-section of a Vein of a Limb of a Man. X ioo. Technic No. 38.
arteries ; they are especially well-marked in the carotids, which closely
approach in structure the large arteries. The externa of large arteries
presents no essential peculiarity and differs but slightly from that of
medium-sized arteries. It does not possess the external elastic mem-
brane. Smooth muscle-fibers only occur in the externa of the large
arteries of the lower animals.
The foregoing classification of the strata of the wall of the artery
corresponds to present usage. There is a new proposition to regard as
intima simply the epithelial tube alone, as externa all that lies outside
of the external elastic membrane, the latter to be reckoned as belonging
to the media. Between these two, then, lies the media, of which the
external and internal elastic membranes represent the border-lamella?.
The subepithelial layer of the large arteries is to be reckoned as belong-
ing to the media.
THE CIRCULATORY SYSTEM. I 19
THE VEINS.
There is no definite proportion between the size of the veins and the
thickness of their walls, no basis for a division into groups as in the
arteries. The veins are characterized by the preponderance of fibrous
connective tissue and by the slighter development of the muscular
elements. As in the arteries, three coats may be distinguished.*
The intima consists of a single layer of epithelial cells, that are
Intima.
. 1 "-■-•crs^
Medi.
Externa.
Fig. 61. — Cross-section of a Vein of a Human Limb. X 420. The elastic elements are stained.
Technic No. 39.
fusiform only in the smallest veins, in others are polygonal in form. In
veins of medium size, having a diameter of from two to nine millimeters,
the subepithelial layer consists of connective tissue containing nucleated
cells, that in large veins (femoral, popliteal, superior cava) develops in
the form of distinct fibrous lamellae. Surrounding this is the internal
elastic membrane, which is structureless in small veins, in medium-sized
* Owing to the meager development of the media some histologists have suggested that
only two coats are present, tunica intima and tunica externa, and that the layers usually
regarded as tunica media belong to the latter.
120 HISTOLOGY.
and large veins is represented by elastic networks. Obliquely or longi-
tudinally-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 poplit-
eal), less so in the veins of the upper extremities, still less in the large
veins of the abdominal cavity ; it is absent in many veins (in those of the
pia and dura, of the bones, of the retina, in the superior cava, and also
in the veins proceeding from the capillaries).
The usually well-developed externa consists of intercrossing bundles
of connective tissue, elastic fibers, and longitudinally-disposed smooth
muscle-fibers, that are more highly developed in the veins than in the
arteries. The externa of certain
veins (of the trunk of the portal and
of the renal) possesses an almost
Intima.
Media.
E J&™ AS %altfV§|/- complete membrane of longitudin-
al fibers. | '^Pz^k^' ally arranged muscle-fibers (Fig.
*/ 62).
Fig. 62.— Cross-section of the Renal Vein of
man. x 50. Technic No. 38. The valves of the veins are
folds of the intima covered on both
surfaces by epithelial cells, that 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 vein, they are transversely elongated.
THE CAPILLARIES.
The capillaries establish the communication between the arteries
and veins. There are a few exceptions, as, for example, in the corpora
cavernosa of the genital organs. The transition of the arteries into the
capillaries is effected by a gradual simplification of the structure of the
vessel-wall (Fig. 56). The media becomes steadily thinner and finally
is represented by a few isolated, circularly-disposed muscle-fibers occur-
ring at wide intervals, that ultimately disappear. The externa becomes
correspondingly attenuated until it consists of a thin layer of connective
tissue containing cells, that ultimately also vanishes, so that at last the
only part of the vessel-wall that remains is the intima, the layers of
which are likewise reduced until nothing is left but a stratum of plate-
like, nucleated epithelial cells. Hence the walls of the capillaries con-
sist of a simple layer of epithelial cells, the form of which may be most
aptly compared with a steel pen pointed at both ends. These cells are
united at their edges by a small amount of cement-substance.
THE CIRCULATORY SYSTEM. 121
The capillaries divide without decrease in caliber and by anasto-
mosis with neighboring capillaries form networks differing widely in the
size of the meshes. The closest meshes occur in the capillary networks of
secretory organs, for example, in the lung and liver ; wide-meshed net-
works occur in the muscles, the serous membranes, the special-sense
organs. The reverse obtains in 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,
protoplasmic mass appears on the wall of an existing capillary, resting
by a broad base on the latter and terminating in a slender, tapering, free
r»
Fig. 63. — Surface Vikw of a Portion of the Greater Omentum of a Seven-Day-Old Rabbit.
c. Blood-capillaries, some containing blood-corpuscles; j, capillary sprout tapering to a free solid
point; 1', young capillary, the greater part of which is hollow, at s 1 still solid; k, nuclei of perito-
neal epithelium. X 240. Technic No. 43.
end.* In the further course of development this pointed free end unites
with another off-shoot that has arisen in the same way from another
point on the capillary wall. These formations are solid at first, but
gradually become hollow by an extension of the lumen of the capillary,
and subsequently the walls of the new vessels become differentiated to
epithelial cells. The development of new capillaries is always consum-
mated in connection with existing capillaries.
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 externa (Fig. 58). The intima always is
without blood-vessels.
* Such blind capillary sprouts may be hollowed out at an early period ; corpuscles that
happen to flow into them disintegrate, because they are excluded- from the circulation and the
interchange of gases, and fall into fragments that have been erroneously interpreted as hemato-
blasts ; they have no connection with the true hematoblasts.
122 HISTOLOGY.
All blood-vessels are furnished with medullated and nonmedullated
nerves, which form a plexus in the media of the arteries and veins. From
these nonmedullated fibers arise, which are in part distributed to the
muscle-fibers, in part form terminal plexuses lying in the externa and
in the interna and agreeing in every point with those of the heart.
The capillaries are accompanied by encircling networks of delicate
nonmedullated nerve-fibers.
Many blood-vessels are surrounded by lymph-channels , occasion-
ally the lymph-spaces are so wide that they form an ensheathing sinus
for the blood-vessel, the " adventitial " or " perivascular lymph-space."
The glomus caroticum (" glandula carotica ") is no gland, but con-
sists 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, that are
arranged in rounded groups forming the so-called secondary nodules.
The many veins collect at the periphery of the organ, that besides con-
tains fibrous connective tissue, isolated ganglion-cells, and conspicuous
numbers of medullated and nonmedullated nerve-fibers. Similar in
structure is the coccygeal gland {glomus coccygeum), the blood-vessels
of which are characterized by hemispherical evaginations.
Fig. 64. — Blood-corpuscles Magnified 560 Times. A. Of man : 1-6, discoidal colored blood-cells; i,
seen with close focus ; 2, with distant focus ; 3 and 4, viewed edgewise ; 5, crenated in consequence
of evaporation; 6, after treatment with water; 7, spherical colored blood-corpuscle; 8, colorless
blood-corpuscle; 9, blood-platelets. B. Of frog: 10-13, colored blood-cells; 10, fresh, nucleus in-
distinct; 11, a few minutes later, nucleus plainly visible; 12, seen from the side; 13, after treatment
with water ; 14, living, 15, dead colorless blood-corpuscles. Technic No. 44, 45, 47.
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 the elementary granules. The blood-cells are
of two kinds, colored blood-cells and colorless blood-cells.
* The elements of the blood do not form a tissue, but represent a loose union of element-
ary parts, without definite arrangement of the same, — an aggregation of cells.
THE CIRCULATORY SYSTEM. I 23
The colored blood-cells (Fig. 64) are soft, flexible, highly-elastic ele-
ments and possess 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 resemble biconcave lenses. Exceptions
occur in the llama and the camel, in which the colored blood-cells are
oval. The average diameter in man is 7.5 ft, the thickness 1.5 p.. The
colored blood-corpuscles of domesticated mammals all are 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
color substance, the hemoglobin. The hemoglobin imparts to the cor-
puscle its yellow or yellowish-green color. A nucleus and a proper
cell-membrane are wanting. The colored blood-corpuscles of fishes,
amphibians, reptiles, and birds are distinguished from those of mammals
by their oval, biconvex form, their generally greater
size (22 p. long by 15 p broad in the frog), as well as
by the presence of a round or oval nucleus ; in other cr""'*'
respects they exhibit the same properties as those of ||| „
mammals. FlG 6s . _ CoLORLESS
The white or colorless blood-cells (leucocytes) occur MAN. OD c. c ceii L with
not only in the blood but also in the lymphatic vessels, x&^Techmc if". 45.'
where they are termed "lymph-corpuscles." They .
are also found outside of the vessels, in bone-marrow, in masses in
adenoid tissue, scattered in fibrous connective tissue, and between epi-
thelial and gland-cells, where they have wandered by their power of
ameboid movement; therefore they are also called " wandering cells."
In all cases the colorless blood-cells consist of a clammy proto-
plasm and a nucleus, and are without a cell-membrane. A definite form
cannot be described, because during life they are engaged in ameboid
activity. In a state of rest they are spherical (Fig. 65).
The size and properties of the nucleus and protoplasm have led to
the following classification :
1. The smallest leucocytes, measuring from 4 to 7.5 p. They
possess a relatively 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. 65, a). These are regarded as young forms,
exhibit little activity, and are chiefly found in adenoid tissue.
2. Those of the second variety have a diameter of from 7.5 to 10 p ;
the nucleus is spherical or deeply cleft — lobulated — and surrounded by
* In addition, there occur in human blood spherical colored blood-corpuscles, Fig. 64 A,
7 ; they are smaller (5 fi) and few in number.
1 24 HISTOLOGY.
a larger amount of granular protoplasm (Fig. 65, b). Rarely several
separate nuclei are present. Multiplicity of nuclei is often feigned,
the delicate filaments of the deeply cleft nucleus being overlooked.
This form is very active (the lobulation of the nucleus is in fact regarded
as the expression of this activity) and includes "jy per cent, of the leuco-
cytes of the blood.
3. The leucocytes of the third class have a diameter of from 8 to
14 p. and are characterized 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. The granules are probably the
optical expression of metabolic processes and of phases of progressive
development (see further, Technic No. 45).
The determination of the proportionate number of, as well as the
ratio between, the colored and colorless blood-corpuscles is coupled with
considerable difficulty and only approximately-correct estimates can be
given. In man one cubic millimeter of blood contains about 5,000,000
colored corpuscles. The white blood-corpuscles are present in the blood
in much smaller number, about one in from 300 to 500 colored blood-
corpuscles.
The blood-platelets are very unstable, colorless, round or oval disks
having a diameter from one-third to one-fourth less than that of the
colored blood-cells ; at times they are present in the blood in large
numbers. f A leading role in the process of coagulation of the blood is
ascribed to them. In animals that have nucleated colored blood-
corpuscles the blood-platelets also possess nuclei.
The elementary granules are for the most part fatty granules trans-
ferred 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 coagulates under the influence of two substances, fibrin oplastin
and fibrinogen, which pass into solution and unite in the plasma. The
product of this union is fibrin. The coagulated blood separates into
two parts, the clot and the serum. The clot is red and contains all the
* Ehrlich, who made this classification, proceeds therein from other standpoints than the
chemist; acid dyes, c g., are those in which the coloring principle is a molecular combina-
tion existing chemically as an acid.
fin I c.c. of human blood there are said to be 200,000 blood-platelets, a number that
probably is below the truth, since in the methods of estimating some blood-platelets always
adhere to the walls of the pipet.
THE CIRCULATORY SYSTEM. 1 25
colored blood-corpuscles, the majority of the colorless blood-corpuscles,
and the fibrin, which microscopically consists of a feltwork of fine,
straight, 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, the
hemoglobin, possesses the property of crystallizing 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 decompo-
sition 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 ; often they are very irregular in
Fig. 66. — 1. Hemin crystals of man ; whetstone forms on the right. 2. Crystals of common salt. 3. Hema-
toidin crystals of man, magnified 560 times. 4. Hemoglobin crystals of the dog, magnified 100 times ;
a, a crystal failing apart lengthwise. Technic No. 50.
form. As a positive indication of the presence of blood they have a
legal relation of great importance (see Technic No. 50 a).
Development of Colored Corpuscles. — From the earliest period of
embryonic development and during the whole of life nucleated colored
blood-cells (hematoblasts, erythroblasts) are found in certain localities
(see Bone-marrow). Their number fluctuates and runs parallel with the
energy of the blood-forming processes. By indirect division they give
rise to the nonnucleated colored blood-corpuscles, that at first contain a
nucleus, but by a process of internal degeneration (not by extrusion)
subsequently lose it.* As centers for the formation of blood in the
embryo the liver, later the spleen, in the adult almost exclusively the
bone-marrow, may be mentioned.
Development of Colorless Blood-corpuscles. — It is conjectured that
the colorless blood-cells arise from elements having their origin in the
* Transformation products, rudiments of nuclei, may still be demonstrated in nonnucle-
ated elements fixed in osmium solution.
126
HISTOLOGY.
anlage of the embryonal blood and blood-vessels and are transported
with (not in) the blood-vessels to the remotest localities, to the anlages
of the lymph-glands and lymph-nodules, where they multiply by mitosis
and are carried back to the vascular stream by the lymph-vessels. In
early embryonal times the mother-cells of the leucocytes can produce
not only colorless but also colored blood-cells.
2. The Lymph-vessel System.
Valve.
THE lymph-vessels.
The walls of the larger lymph-vessels, from 0.8 to 0.2 mm. in thick-
ness and upward, like the blood-vessels, are composed of three coats.
The intima consists of epithelial cells and a
network of delicate elastic fibers with elon-
gated meshes. The media is formed of cir-
cularly disposed smooth muscle-fibers and a
few elastic fibers. The externa consists of Ion- .
gitudinally arranged bundles of connective'
tissue, elastic fibers, and bundles of smooth
muscle-fibers likewise disposed in a longitu-
dinal direction. The walls of the smallest
lymph-vessels and of the lymph-capillaries
are composed exclusively of extremely deli-
cate epithelial cells, that often have sinuous
outlines. The lymph-capillaries are wider
than the blood-capillaries, at frequent intervals
present constrictions and dilatations, and where
they branch are often considerably expanded ;
the networks they form are more irregular.
The question of the origin of the lymph-
vessels is not yet satisfactorily decided ; while
some authors are of the opinion that the lymph-capillaries form a closed
system, according to another widely-entertained view the lymph-capilla-
ries are open toward the periphery and in direct connection with the
system of intercommunicating cell-spaces of connective -tissue (juice-canal
system, p. 90). These intercellular clefts are by some set apart, as
" lymph-canaliculi," from the lymph-vessels with well-defined walls com-
posed of continuous layers of cells ; other authors include the lymph-
canaliculi among the lymph-vessels.
According to the first opinion the nutritive fluids (tissue-juices)
Fig. 67. — Lymphatic Vessel of
the Mesentery of a Rabbit,
showing the boundaries of the
epithelial cells. X 50. Technic
No. 41.
THE CIRCULATORY SYSTEM. I 27
diffused through the walls of the blood-capillaries that are not used in
the nutrition of the tissues penetrate the closed lymph-capillaries by
endosmosis ; according to the second view 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 communication with their respective cavities
through small openings, the stomata, between the epithelial cells, which
in the pleura are found at the intercostal spaces and in the peritoneum
on the central tendon of the diaphragm.
THE LYMPH-GLANDS.
The lymph-glands (lympho-glandular, lymph-nodes) are macroscopic
bodies intercalated in the course of the lymph-vessels. Usually they
are rounded oval or flat kidney-shaped structures and differ greatly in
size. At one side there is often a scar-like depression, the hihts, at which
the efferent lymph-vessels emerge. The afferent lymph-vessels penetrate
the glands at various points. Their construction becomes intelligible if
we proceed from the following conception : In certain localities from three
to six lymph-vessels divide repeatedly, the branches anastomose, then re-
unite into the same or a lesser number of usually narrower lymph-vessels.
In this way a kind of rete mirabile * is formed. The dividing lymph-
vessels are called afferent vessels (vasa afferentia), the reuniting, efferent
vessels (vasa efferentia). Within the meshes of this reticulum lie spher-
ical and elongated masses that consist of adenoid tissue. The spherical
masses, the secondary nodules (follicles), occupy the periphery, the
elongated masses, the medullary cords, the center of the lymph-gland.
The lymph-gland is enveloped in a capsule of fibrous connective
tissue, which sends processes into the interior of the organ, the trabecule
(Fig. 68). Finer extensions from the trabecular, in the form of reticular
connective tissue, pierce the walls of the lymph-vessels, penetrate the
secondary nodules and the medullary cords, and form a support for the
numerous leucocytes present.
The lymph-glands consequently consist of a cortical and a medullary
substance, the relative proportions of which vary greatly. The cortex
contains the secondary nodules, which continue centralward directly into
the medullary cords (Fig. 68). The secondary nodules and the medullary
cords are surrounded by the sinus-like continuations of the afferent
* 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.
128
HISTOLOGY.
lymph-vessels. The latter here are greatly expanded and arc termed
lymph-sinuses : they are pierced by 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 reticular connective tissue the meshes of which are
crowded with leucocytes. In many of the secondary nodules there is a
light, spherical area, the germinal center, in which karyokinetic figures
are always to be found. Multiplication of cells also occurs in the medul-
lar)- cords, but in a much slighter degree. The secondary nodules are
centers for the formation of leucocytes, which pass into the lymph-
sinuses and thence into the vasa efferentia.
Capsule. Secondary nodule ("follicle"). Blood-vessel.
Hilus. Medullary cord. Lymph-sinus.
Fig. 68. — Section of Lymph-gland of a Rabbit. ;■' 2S. (Schaper.) Technic No. 53
The capsule consists of fibrous connective tissue and smooth muscle-
fibers, which in the large lymph-glands of some animals are arranged
in long strands. The trabecular 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 secondary nodules and
the medullary cords, and are also applied to the trabecular and the con-
nective-tissue reticulum.
The structure of the lymph-glands is difficult to recognize, owing
to several complications. These consist in : 1, the merging of neighbor-
THE CIRCULATORY SYSTEM.
I2 9
ing secondary nodules ; 2, the anastomosis of the medullary cords in the
form of a coarse network ; 3, the network formed by the trabecular ;
4, the interlacing of the networks formed by the medullary cords and the
trabecular (Fig. 69); 5, the presence of leucocytes in the lymph-sinuses,
which must be removed by special methods.* The secondary nodules,
the medullar)' cords, and the leucocytes in the lymph-sinuses form a soft
mass, that has been named the pulp or parenchyma of the lymph-gland.
The majority of the blood-vessels enter at the hilus, the others at
various points on the surface of the gland. The latter are smaller
vessels and divide in the capsule and in the large trabecular, in the axes
of which they run. The large artery entering at the hilus divides into a
number of branches, that are surrounded by richly-developed connective
'•■ '■]'■
Lymph-sinuses.
Trabecule.
y Medullary cords.
Fig. 69.— From a Section through the Medulla of a Lymphatic Nodule of an Ox. X 50. In the
upper half the trabecule and medullary cords are cut lengthwise ; in the lower half, crosswise. Both
form an anastomosing network. In the lymph-smuses the fine fibers of the reticular connective tissue
are seen, which still contains leucocytes. Drawn with change of focus. Technic No. 54.
tissue. The branches are principally distributed to the adenoid tissue,
only a few entering the trabecular ; the}' pass through the lymph-sinuses,
into the medullar)' cords, then into the secondary nodules, and in both
situations break up into rich capillary networks which supply the oxygen
needed in the formation of the leucocytes. The veins emerge at the
hilus.
The nerves are few in number, the supply including bundles con-
taining medullated and nonmedullated fibers ; their ultimate distribution
is still undetermined.
* Editor s remark : In preparations of lymph-glands it is necessary to dislodge the leuco-
cytes to bring the lymph-sinuses into view (see Technic No. 5j)-
9
1 30 HISTOLOGY.
THE PERIPHERAL LYMPH-NODULES.
(Noduli Lymphatici.)
Adenoid tissue is not confined to the lymph-glands ; it occurs in
many mucous membranes, in different degrees of development, some-
times as diffuse, sometimes as definitely circumscribed infiltrations of
leucocytes. These formations are not included in the lymphatic system.
More highly-specialized structures, nodules with germinal centers,
closely resembling the secondary nodules of the lymph-glands, are also
found in the mucous membranes ; these are named peripheral lymph-
nodes and are included in the lymphatic system. In many mucous
membranes they occur isolated, as the solitary nodules (solitary follicles),
or grouped, as the agminated nodules (Peyer's patches), and always lie
in a simple layer in the tunica propria close beneath the epithelium (see
Organs of the Digestive System). The number and distribution of the
peripheral lymph-nodes are subject to considerable fluctuation, not only in
the different species of animals, but in different individuals ; since their
mass also varies and frequent transitions to circumscribed and to diffuse
infiltrations occur it is highly probable that they are temporary structures
that arise and disappear during life. They are distinguished from the real
lymph-glands above all by their less intimate relation to the lymph-
vessels, which do not form an encircling sinus for the follicle.* 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 lymph-vessels ; many wander
through the epithelium to the surface of the mucous membrane.
THE LYMPH.
The lymph is a colorless fluid in which leucocytes (lymph-corpus-
cles) and granules are suspended. The latter are immeasurably small,
consist of fat, and are principally found in the lymph- (or chyle) vessels
(lacteals) of the intestine ; frequently they are present in enormous num-
bers and then they impart the white color to the chyle. In other
lymph-vessels the fatty granules occur sparingly. In the lymph-glands
many leucocytes are found in which the envelope of protoplasm sur-
rounding the nucleus is so thin that its presence can only with difficulty
be demonstrated.
* The only exception exists in the rabbit, in which the sinus occurs in the agminated
nodules ; on the other hand, in the solitary nodules of this animal the sinus is likewise wanting.
THE CIRCULATORY SYSTEM.
131
Capsule
Trabecular
The Spleen.
The spleen is a " blood-vessel gland " and consists of a connective
tissue capsule and a soft red mass,
composed of blood-vessels and aden-
oid tissue, the spleen-pulp.
The capsule is invested by a re-
flection of the peritoneum, with which
it is firmly united, and is composed
of dense fibrous connective tissue,
smooth muscle-fibers, and a network
of elastic fibers. Numerous cylin-
drical or band-like prolongations, the
trabecules, extend into the interior
of the organ, where they form a
framework in the spaces of which lies
the spleen-pulp. The trabecular also
contain smooth muscle-fibers. At the
hilum of the spleen the capsule fur-
nishes special sheaths for the blood-
vessels — adventitial sheaths — which
blend with the externa and accom-
pany them for long distances. The
sheaths of the arteries are the seat of
numerous leucocytes, that in the form
of a continuous envelope accompany the vessel in its entire course, as in
Trabecular.
Artery
Fig. 70. — From a Cross-section of Human
Spleen, showing well-developed spleen-
follicles, each pierced eccentrically by an
artery. The right branch of the artery has
a continuous sheath of adenoid tissue.
X 10. Technic No. 56.
e
Fig. 71. — Elements of Human
Spleen. X560. I. Colorless
blood-cells. 2. Epithelial cells.
3. Colored blood-corpuscles. 4.
Cells containing granules ; the
upper one enclosing a blood-
corpuscle, b. Technic No. 55.
Fig. 72. — Reticular Connec-
tive Tissue of Human
Spleen. X 560. Drawn
from the edge of a shaken
preparation. Technic No.
57-
£&%
Fig. 73. — Three Karyomi-
totic Figures from a
Section of the Spleen
of a Dog. X 560. The
filaments are not visible
with this magnification.
Technic No. 58.
the guinea-pig, or that, as in man, the cat, etc., are confined to certain
localities, where they form spherical masses from 0.2 to 0.7 mm. in size,
HISTOLOGY.
the so-called spleen-follicles (Malpighian corpuscles). Between these
many intermediate forms exist, as in the mouse and rabbit.
The spleen-follicles arc usually situated in the forks of the smaller
Venous capillar-
ies ("intermedi-
ate lacunae " of
other authors).
Transition of
the venous
capillaries
into a—
Spleen-pulp.
Fig. 74 A.— Section through the Injected Spleen of a Cat. Technic No. 59.
Venous capillaries.
Arterial capillaries. )/")■
Transition of venous
capillaries into a
Spleen-follicle.
Splenic pulp.
Fig. 74 B.— Schematic Drawing of Section 74 A.
arteries, in such a manner that the artery pierces the center or the side
of the follicle. In their minute structure they entirely agree with the
secondary nodules of the lymph-glands and even occasionally contain
THE CIRCULATORY SYSTEM.
133
germinal centers. The spleen-follicles are also temporary structures ;
continually some are undergoing regressive change and new ones are
developing.
The spleen-pulp forms a network of cords similar to those of the
lymph-glands, which occupies the interstices of the trabecular frame-
work. Occasionally the cords are connected with the spleen-follicles.
Surface black-
ened by precip-
itates of silver.
Small nerve
bund
Branches for the '
arterial wall.
Fig. 75. — Section of the Spleen of a Mouse. X 85. The boundary between the spleen-pulp and the
artery, the sheath of which is infiltrated in its entire length with leucocytes, is indicated by a dotted
line. Technic No. 60.
The spleen-pulp is composed of a delicate connective-tissue reticulum
and numerous cellular elements. The latter are in part leucocytes, in
part slightly larger nucleated cells, also cells containing colored blood-
corpuscles (Fig. 71), and free colored blood-corpuscles ; finally, a gran-
ular pigment occurs there.
The Blood-vessels. — The arteries of the spleen give off branches to the
1 34 HISTOLOGY.
trabecule and to the pulp-cords and supply the dense capillary network
of the spleen-follicles. There are no anastomoses between the arteries.
The thin-walled veins proceed from a wide-meshed network of capillaries
(venous spaces, venous capillaries) occupying the intervals between
the trabeculse and the pulp-cords (Fig. 74). The medium-sized and
large veins run alongside the arteries and frequently lie in furrow-like
depressions in the trabeculae. The precise mode of communication
between the arteries and the veins is not yet satisfactorily determined.
The arteries break up into slender capillaries which do not anastomose
with one another.* According to one view, the arterial capillaries are
directly continuous with the "venous " capillaries and the vascular chan-
nels of the spleen are closed on all sides. Other authors hold that the
arterial capillaries pass into spaces without definite walls, " intermediate
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 lym-
phatics 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, consisting of a few medullated fibers and many naked
axis-cylinders, follow the course of the trunks and branches of the
arteries, supply the muscle-fibers of the latter and of the trabeculae (Fig.
75). Plexuses of nonmedullated nerve-fibers occur in the spleen-pulp ;
they probably arise from the branches of the medullated nerve-fibers just
mentioned, and are in part sensory in their nature.
TECHNIC.
No. 38. — The Heart and the Large Blood-vessels. — Cut out a papil-
lary muscle from a human heart, a piece of the aorta 2 cm. long, a piece
1 or 2 cm. long of the brachial artery with its veins and the surround-
ing connective tissue, a piece of the renal vein 1 cm. long, and suspend
them on a thread in a bottle containing 40 c.c. of absolute alcohol.
After twenty-four or forty-eight hours the objects are ready to section.
Embed them in liver (the artery and vein may be embedded together
and will not be injured by strong compression), cut thin cross-sections,
stain them in Hansen's hematoxylin, from two to five minutes (p. 37),
and mount in damar (Figs. 55, 58, 59, 60). The elastic fibers do not
stain, but with the high power can be often distinctly recognized.
The arrangement of the elements of the externa cannot be satis-
* In injected and macerated spleens the pulp can be Washed out, and then the slender
terminal branches of the arteries can be seen lying together in a leash or pencil.
THE CIRCULATORY SYSTEM. 1 35
factorily appreciated in cross-sections ; often all appear to be circularly
disposed (a portion of them are circularly arranged, for example, those
of the innermost stratum of the external elastic membrane). The exact
arrangement can be seen only in longitudinal sections, which also show
the muscle-fibers of the externa plainly.
No. 39. — Elastic Fibers of the Blood-vessels. — Stain objects fixed in
absolute alcohol, according to No. 38, with orcein (No. 12, p. 41) and
preserve in damar (Fig. 61).
No. 40. — Small Blood-vessels and Capillaries. — From the base of a
human brain slowly strip off pieces of the pia from 1 to 3 cm. long (in
this way delicate blood-vessels that penetrate the brain vertically are
withdrawn), shake them in distilled water to free them from adherent
fragments of brain-tissue, and place them in 50 c.c. of Zenker's fluid
(p. 32) for one hour ; transfer them for from one to three hours to water
(for one hour to running water), and harden them in about 40 c.c. of
gradually-strengthened alcohols (p. 34). Examine one of these pieces
in a watch-glass on a black background and it will be seen that small
vessels are isolated.
a. With fine scissors cut off small twigs with their ramifications,
stain them for from two to five minutes in Hansen's hematoxylin (p. 37)
and mount in damar (Fig. 56).
b. From the larger twigs of the cerebral blood-vessels cut pieces
about 5 mm. long, slit them open lengthwise, stain them in Hansen's
hematoxylin, and place them on a slide with the externa side down.
Mount in damar. By changing the focus the three coats of the vessel
and their general arrangement can be seen.
Capillaries may be found on examining fresh brain-tissue. They
are recognized by their parallel outlines and the oval nuclei of their
epithelial cells ; they are also found in other preparations, for example
in technic No. 1 1.
No. 4 1 . — Epithelium (Endothelium) of the Blood-vessels. — Decapitate
a rabbit, open the abdomen by a crucial cut made with the scissors ;
insert a cork frame about 2 cm. square under the mesentery, span
the membrane smoothly and fasten it with quills or hedgehog spines,
taking care to touch it as little as possible. Cut around the frame and
place the stretched membrane with the frame in 20 or 30 c.c. of 1 per
cent, silver-nitrate solution. In about thirty seconds the solution be-
comes turbid and milky ; remove the frame, carefully wash the membrane
with distilfed 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 or 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 twenty hours in 30 c.c. of 70 per cent, alco-
hol, then in a like quantity of 90 per cent, alcohol, and expose it to
sunlight on the first opportunity. It must not be forgotten that the
I36 HISTOLOGY.
whole blood-vessel and not a section of it is present, so that in order
to obtain a view such as that in Fig. 57 the surface of the vessel must
be in focus.
No. 42. — Elastic Fenestrated Membranes. — See Technic No. 17.
No. 43. — Development of Capillaries. — Chloroform a seven-day-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 omen-
tum and place these parts in 80 c.c. of a saturated aqueous solution of
picric acid (p. 21). In this solution the omentum, otherwise difficult to
separate, spreads out easily. After one hour cut it off, transfer it to
60 c.c. of distilled water, and divide it with the scissors into pieces about
1 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 one or two
drops of Hansen's hematoxylin on the preparation. In from one to five
minutes drain off the hematoxylin and place the slide with the preparation
in a flat dish containing distilled water ; the membrane will soon float
from the slide, but will remain smooth, and in five minutes should be
transferred to a watch-glass containing eosin (No 3 (d), p. 38), in which
it should remain three minutes. It should then be washed for one
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 glycerol suspended from its lower
surface applied. The preparation may be mounted in damar instead of
glycerol (that is, dehydrated in 95 per cent, alcohol, cleared in oil of ber-
gamot, and then mounted in damar), but the finer structural details are
apt to be lost. The colored blood-corpuscles are stained a bright red by
the eosin (Fig. 63).
In spreading the membrane on the slide, delicate young capillaries
may be easily torn from the older capillaries and then simulate " isolated
cells containing blood-corpuscles"; such artificial products have been
described as "vasoformative cells."
No. 44. — Colored Blood-corpuscles of Man. — Carefully cleanse a slide
and a small cover-glass (finally with alcohol). With a clean needle prick
the finger-tip at one side ; lightly touch the first drop of blood that
exudes with the cover-glass and without the addition of any reagent
immediately place it 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 distortion of many of the colored corpuscles is
due to evaporation, in consequence of which they are beset with minute
spines, are crenated. 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 then become spherical, have
the appearance of pale circles, and finally disappear. In studying this
process of decoloration the student is advised to concentrate his attention
THE CIRCULATORY SYSTEM. I 37
upon a single corpuscle. In Fig. 64, 6, the tinged area surrounding the
bleached corpuscles is somewhat too deeply shaded.
No. 45. — Permanent preparations of colored and 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 caricatures arise and mislead the inexperienced. The
employment of this method for purposes of investigation and discovery
requires great skill and great caution in judgment.
Preliminary Manipidations . — For each preparation two thin cover-
glasses are required (they must not be over o. 1 mm. thick). Place them
for a few 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, then with a tuft of clean cotton-wool moistened with the alcohol-
ether mixture. With a clean needle (not previously used for anatomic
purposes) prick the pad of the finger, that has been made slightly
hyperemic 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 ol
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 pre-
vented, which otherwise would shrink or lose their hemoglobin.
Exposed to the air the blood on the cover-glasses dries in a few
minutes ; they are then to be placed in the alcohol-ether mixture for
fixation. In from one-quarter to two hours they should be removed,
again dried 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.
Further Treatment. a. Oxyphile (Eosinophile, a) Gramdes. — Place
the cover-glass preparations for twenty-four hours in about 4 c.c. of
distilled water to which about 10 drops of eosin solution have been
added. Rinse one minute in distilled water and stain for from one to five
minutes in a watch-glass with Hansen's hematoxylin (p. 37). Transfer
to distilled water ; remove in five minutes and let the preparations 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 leuco-
cytes of normal blood, of lymph, and of the tissues, but are uncommon
in normal blood. They are numerous in the bone-marrow of the rabbit.
A magnification of 400 diameters is sufficient to find them.
b. Basophile Granules. — Two groups are distinguished, the ^-granules
and the ^-granules. The y-granules (mast-cell granules), which occur
only in the leucocytes of pathologic blood, are stained according to the
method given in No. 9. When the staining is completed, proceed as in
a. The blue-violet granules are coarser than the —
8-granules, which occur in the leucocytes with round nuclei in nor-
I38 HISTOLOGY.
mal and other blood. Stain the cover-glass preparations for from five
to ten minutes in 5 c.c. of methylene-blue (p. 25), wash, dry, and mount
in damar. These granules are minute and scarcely to be seen with the
usual high-power dry lenses ; an immersion lens should be used. In
staining with methylene-blue not infrequently the film of blood floats
from the cover-glass ; this may be prevented by passing the dry cover-
glass preparation rapidly through a flame before staining.
c. Neutrophil (e-) Granules. — Dissolve (1) 1 gm. of orange-yellow
extra in 50 c.c. of distilled water ; (2) 1 gm. of acid-fuchsin extra in
50 c.c. of distilled water; (3) 1 gm. of crystalline methyl-green in
50 c.c. of distilled water, and let the three solutions settle. Then mix
11 c.c. of solution (1) with 10 c.c. of solution (2) and add 20 c.c. ol
distilled water and 10 c.c. of absolute alcohol; to this mixture add a
mixture of 13 c.c. of solution (3), 10 c.c. of distilled water, and 3 c.c. of
absolute alcohol. The whole is then allowed to stand for one or two
weeks. In this " triacid solution " the cover-glass should be placed for
fifteen minutes, then washed, dried, and mounted in damar. The neu-
trophile granules, which are found in leucocytes with lobulated nuclei, in
normal and other blood, are of a violet color and are easily seen with
the usual dry high-power lenses ; the oxyphile granules and the colored
blood-corpuscles are of a yellow-brown or chocolate-brown color, the
nuclei a bright blue-green, though their outlines are not so distinct as in
the hematoxylin preparation.
No. 46. — Blood-platelets. — Mix about 5 drops of an aqueous solu-
tion of methyl-violet (p. 25) with about 5 c.c. of salt solution (p. 19).
Filter the mixture and place a drop of it on the tip of the finger ; prick
the finger through the drop ; the blood as it exudes mixes with the
methyl-violet ; take up a drop with the cover-glass and examine with
the high power. The platelets are stained an intense blue, have a peculiar
luster, are disk-shaped, and should not be confused with the white
blood-corpuscles likewise stained blue (Fig. 64, 9). They are numeri-
cally variable elements, occurring in large numbers in the blood of one
individual, while in the blood of another they are only to be found
singly here and there. Care must be taken not to confuse them with
foreign particles, which may occur even in the filtered staining solution.
No. 47. — Colored Blood-corpuscles of the Frog. — Prepare the slide
and treat the blood after No. 44.
No. 48. — For Forensic Purposes. — Since it is usually dried blood that
is to be examined, dissolve small particles of dried blood in 35 per cent,
potash solution on a slide ; blood-stained pieces of linen may be teased
in a drop of the same solution. Although the colored blood-corpuscles
of domestic mammalian animals are smaller than those of man, it is
nevertheless impossible from the size of the blood-cell to determine its
source. On the other hand, it is easy to distinguish the disk-shaped
corpuscles of mammals from the oval elements of other vertebrates.
No. 49. — Colorless Blood-corpuscles {Leucocytes) in Motion. — Pre-
liminary manipulations: Carefully cleanse a slide and cover-°-lass with
THE CIRCULATORY SYSTEM. 1 39
alcohol. Kill a frog, grasp it by its hind legs, dry its back somewhat
with a cloth, and with fine scissors make an incision i cm. long parallel
to and close beside the vertebral column. Introduce a capillary pipet
into the wound (with the tip directed forward) and suck the tip full. A
small drop is sufficient ; blow it on to the slide, cover it quickly, and
seal the edges with melted paraffin (p. 50). Such a preparation shows
colored and colorless blood-cells ; at first the nuclei of the former are
indistinct. The nuclei of living blood-corpuscles are in general not to
be seen. For the study of ameboid movement select leucocytes the
protoplasm of which is partly granular and which are not spherical. The
movements are slow ; of this one may convince one's self by studying a
single leucocyte and making sketches of it at intervals of from one to two
minutes. Study with the high power (Fig. 4).
No. 50. — Blood-crystals. — a. Hemin crystals are easily obtained.
Cut a small strip, about 3 mm. long, from a piece of linen previously
saturated with blood and dried and place it with a pinhead-sized crystal
of common salt on a clean slide ; add a large drop of glacial acetic acid
and with a glass rod stir the linen and salt for about one minute or until
the acid acquires a brownish tinge. Then heat the slide over the flame
until the acetic acid is evaporated. Remove the linen and examine the
dry brown places on the slide with the high power (from 240 diameters
up). Occasionally the brozvn crystals may be seen without the cover-
glass and without a mounting medium, lying next to numerous frag-
ments of white salt-crystals (Fig. 66, 1). To preserve, add a large drop
of damar and apply a cover-glass. The hemin crystals differ greatly in
form and size. In the same slide well-developed crystals lying singly,
crosswise over one another, or in stellate groups are seen, with whet-
stone shapes and minute particles that scarcely exhibit crystallization.
The demonstration of the hemin crystals is of great importance in foren-
sic cases. While it is easy to obtain the crystals in large stains on wear-
ing apparel, it is difficult, when the stains are small, especially on rusty
iron, to prove that they are from blood. The instruments and reagents
employed in such investigations must be absolutely free from contami-
nation.
b. Hematoidin crystals are obtained by teasing old blood extravasa-
tions ; they can be recognized macroscopically by their reddish-brown
color — for example, in the corpus luteum, in cerebral hemorrhages.
c. Hemoglobin crystals are obtained by transferring 5 c.c. of the
blood of a dog to a test-tube, adding a couple of drops of ether, and
shaking vigorously until the blood becomes lake-colored. Then spread
a drop on a slide and let the preparation dry in the cold. When crys-
tallization has occurred, add a drop of glycerol and apply a cover-glass.
The large crystals often exhibit a tendency to cleave lengthwise (Fig.
66, 4 a).
No. 51. — Lymph-vessels. — For the study of the walls of the larger
lymph-vessels select the vessels opening into the inguinal glands, that
are large enough to be taken out with forceps and scalpel. Prepare like
the large blood-vessels, No. 38, or after No. 39 b.
140 HISTOLOGY.
No. 52. — For the exhibition of the more delicate lymph-vessels, of
their course and arrangement, the method of interstitial injection is often
employed. The needle of a hypodermic syringe filled with Berlin-blue
is thrust haphazard into the tissue ; this is a crude method, the results
of which are of very doubtful value. Even though here and there actual
lymph-vessels may thus be filled, in most cases the injection-mass is
simply driven forcibly into the interfascicular clefts of the connective tissue.
The value of any decision with regard to "radicles of lymph-vessels "
and to " lymph-spaces" thus exhibited may be inferred.
No. 53. — Lymph-glands. — For a general view the mesenteric glands
of kittens and young rabbits are suitable. For fixation and hardening
place them in 30 c.c. of absolute alcohol ; in three days thin sections can
be readily made and should be taken, so that they pass through the
hilus, which is easily recognized macroscopically by an external depres-
sion. Longitudinal sections passing through the poles of the gland are
best, though transverse sections are also useful. Stain six or eight sec-
tions in Hansen's hematoxylin for from two to three minutes, then in
eosin for one minute (No. 3 (b), p. 38), transfer them to a test-tube halt
filled with distilled water and shake them for from three to five minutes.
Pour the shaken sections into a flat dish ; the cortex and medulla can be
macroscopically distinguished by the uniformly blue color of the former
and the variegated appearance of the latter. Mount in damar. With
the low power, fields similar to that of Fig. 68 may be seen in favorable
sections. The. trabeculae are but slightly developed. The adipose
tissue adhering to the glands must not be taken for reticular tissue.
High magnification is of no advantage, the sharp outlines disappear and
the picture loses in distinctness.
No. 54. — Lymph-glands of mature animals and of man are difficult
to understand, because the entire cortex is transformed into a continuous
mass irregularly sprinkled with germinal centers. In shaking the sections
the germinal centers are apt to fall out and leave round spaces macro-
scopically recognizable. The lymph-sinuses can be only indistinctly
made out. The mesenteric follicles of the ox are well adapted for the
representation of the network of medullary cords and trabeculce. Place
pieces 2 cm. long in 200 c.c. of concentrated aqueous picric-acid solu-
tion and after twenty-four hours, with a sharp knife moistened 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
sections for one hour in 100 c.c. of distilled water, which must be changed
frequently, stain with Hansen's hematoxylin and eosin (No. 3 (£), p. 38),
and shake them (see No. 53). Mount in damar (p. 48). The trabeculae
are red, the medullary cords blue ; with low magnification the appearance
of the section is like Fig. 69 ; with high magnification the reticular con-
nective tissue of the lymph-sinuses can be seen; the majority of the
leucocytes occupying the meshes become loosened by the treatment with
picric acid and are lost in the shaking.
No. 55. — Elements of the Spleen. — Make an incision through a
THE CIRCULATORY SYSTEM. I4I
fresh spleen ; with a scalpel obliquely applied scrape the cut surface 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 con-
tain minute granules. In human spleens, in addition to the numerous
colored blood-corpuscles altered in form, epithelial cells of the blood-
vessels are found ; the latter were formerly called " spleen-fibers " (Fig.
71,2,3). In many human spleens, multinucleated cells and cells con-
taining blood-corpuscles are often sought in vain (Fig. 71, 4).
No. 56. — The Spleen. — Without cutting it, fix the entire spleen in
Miiller's fluid (p. 32), using one liter for a human, 200 to 300 c.c. for a cat's
spleen. After two weeks for the cat's, five weeks for the human spleen,
wash for from one to two hours in, if possible, running water, cut out
pieces 2 cm. square and harden them in 60 c.c. of gradually-strengthened
alcohols (p. 34). Sections not too thin are to be stained in Hansen's
hematoxylin and mounted in damar. If it is desired to differentiate the tra-
becular, after staining in hematoxylin place the sections for a half minute in
eosin (No. 3 (p), p. 38). In successful preparations the pulp and the
spleen-follicles are blue, the trabeculse rosy, the vessels, distended with
blood-corpuscles, brown. If the staining in eosin is prolonged beyond
thirty seconds the blood-corpuscles become brick-red, the trabecular
dark red, and the distinction between them is apt to be lost. The sec-
tions are most satisfactory when examined with a very low power (Fig.
70) ; with the high power the outlines are often indistinct. Fixation in
Zenker's fluid is also recommended.
No. 57. — Reticular Connective Tissue of the Spleen. — Shake a thin
section fixed and stained like No. 56 for about five minutes'in a test-tube
half filled with distilled water. Mount in glycerol. The leucocytes are
difficult to dislodge ; the narrow-meshed network can only be seen at the
edges of the preparation (Fig. 72).
No. 58. — Karyomitotic Figures in the Spleen and Lymph-glands. —
For this purpose small pieces (5 or 10 mm. long) of warm living spleen
and lymph-gland should be fixed in chromic-acetic-osmic acid (p. 33),
and hardened in alcohol. Stain thin sections in safranin (p. 40). Mount
in damar. The karyomitotic figures of mammals are so small that with
the usual magnification (560 diameters), they can be found only by the
practised microscopist. They are detected by their deep-red color
(Fig. 73)-
No. 59. — Blood-vessels of the spleen are incidentally obtained by
injecting the stomach and intestine (compare with No. 1 16).
No. 60. — Nerves of the Spleen. — For this purpose the spleen of the
mouse is best suited. Halve it and apply Golgi's method for the demon-
stration of the elements of the nervous system (p. 43). It is sometimes
sufficient to place the object in the osmio-bichromate mixture (in a warm
chamber) for three 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.
I42 HISTOLOGY.
II. ORGANS OF THE SKELETAL SYSTEM.
The skeletal system mainly consists of a large number of hard
bodies, the bones, which are joined together by special structures and
in their entirety form 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 articular sur-
faces of many bones. Skeletal cartilages are also found in the respiratory
passages and in the organs of special sense.
The Bones.
On sawing through a fresh bone, at once it will be seen that its
texture is not everywhere alike, but that the osseous tissue appears in
two forms : the one, a very dense, firm, apparently structureless substance,
constitutes the principal portion of the periphery and is termed compact
bone (substantia compacta) ; the other, toward the axial cavity, appears
as an irregular reticulum of thin osseous lamellae and slender trabecular,
and is called spongy bone (substantia spongiosa). The interstices of the
spongy bone, as well as the central marrow-cavity, are filled by a soft
mass, the bone-marrow ; the surface of the bone is enveloped in a fibrous
membrane, the periosteum. The proportion between the compact and
the spongy substance is different in the short bones, 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.
The spongy substance consists entirely of osseous tissue ; the com-
pact substance, on the other hand, contains besides the bone canaliculi
and lacunar, a second system of coarser channels, from 22 to 1 10 /i 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, in the clavicle, and in the inferior maxilla
their course is parallel to the long axis of the bone and in short bones
they run mainly in one direction, for example, vertically in the vertebrae ;
in the flat bones their course is parallel to the surface, 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
THE SKELETAL SYSTEM.
H3
(Fig. "6, x), as well as on the inner surface (Fig. 76, xx) directed toward
the substantia spongiosa.
The ground-substance of compact bone is arranged in lamellae, that
is, the osseous fibrillar are joined in bundles and these placed side by
side form thin plates or lamella;. According to the disposition of these
plates three lamellar systems may be distinguished : an annular or
haversian system, which in cross-section exhibits from eight to fifteen
lamellae concentrically arranged around an haversian canal ; these lamella;
are called haversian or special lamellce (Fig. yy). Some of the haversian
lamellar systems are in partial contact with one another, others are
Haversian canals.
Fat-drops.
Fig. 76. — From a Longitudinal Section of a Human Metacarpus. X 30. Fat-drops are seen in
the haversian canals. At x haversian canals open on the outer, and at xx on the inner surface ol
the bone. Techuic No. 63.
separated by stratified osseous lamella;. These more irregularly-dis-
posed lamella; running between the haversian systems arc named inter-
calated ox interstitial lamella ; they are connected with the third lamellar
system, the general lamellce, in which the osseous strata encircle the
outer and occasionally the inner free surface of the bone and are respec-
tively called outer and inner ground lamella. The general lamellae
contain an extremely variable number of channels for blood-vessels,
which, unlike the haversian canals, are not the centers of annular
systems of lamella; ; they are called Volkmann's canals and the con-
tained vessels, the "perforating vessels." The latter frequently connect
144
HISTOLOGY.
with the vessels of the haversian canals ; the passage' of the Volkmann's
canals into the latter is a very gradual one. The bone lacunae in the
compact substance have a definite position. 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
canal they appear concentrically curved. In the interstitial lamellae the
lacunae are placed irregularly, in the ground lamellae so that their sur-
faces extend parallel to the surfaces of the lamellae. The bone canaliculi
open into the haversian canals and 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 a yellow color and therefore two
Periosteum.
Outer ground lamellae.
Haversian canals.
Haversian lamellae.
Interstitial lamellae.
Inner ground lamellae.
Marrow.
Fig. 77. — From a Cross-section of a Metacarpus of Man. X 50. The haversian canals, h, still
contain marrow (fat-cells). Techuic No. 63.
varieties are distinguished, the red marrow and the yellow marrow. The
red marrow is found in the flat bones, in the vertebrae, in the base of the
skull, in the sternum, in the ribs, and in all young bones (also in all the
long bones of small animals) ; the yellow marrow occurs in the short
and long bones of the extremities. In old and in sick persons the
marrow is mucoid and reddish-yellow and is then called gelatinous bone-
marrow ; it is characterized simply by its poverty in fat.
The elements of red marrow comprise a delicate connective-tissue
reticulum, a few fat-cells, larger and smaller marrow-cells,* and giant-
* The attempt has been made to classify the cells of bone-marrow according to their
source, cells with a slightly-developed cell-body (Fig. 79, 1) having been named " lymphocytes,"
those with a well-developed cell-body (3, 4, 5) "myelocytes." The possibility that the
lymphocytes originate not only in the lymph-glands and related organs, but also in the bone-
THE SKELETAL SYSTEM.
145
cells (mycloplaxes) (Fig. 79). In the larger marrow-cavities the connec-
tive tissue forms a membrane lining the free surface, the endosteum,
which in the marrow-spaces of spongy bone is almost entirely wanting.
The marrow-cells exhibit manifold forms resembling leucocytes ; the
giant-cells are structural anomalies representing leucocytes enlarged and
altered in form, and consist of huge, extremely irregular, uninucleated, or
multinucleated masses of protoplasm. The shape of the nucleus varies
greatly ; it may be round, lobulated, band- or hoop-shaped, or it may
Hematoblast. Eosinophilous cell (granule-cell).
,-ts. Marrow-cell
WWm^ (P'-ma-ce.,).
S?) "^S' Marrow-
& ©^ Wtt, cell (plasma-
m «>_ (j&tJi cell >-
*&-
f
^ Connective-tissue
reticulum.
r
Fat space.
/
Hematoblast. Eosinophilous cell (granule-cell)
Fig. 78. — Section of the Bone-marrow of a Rabbit, showing the Dei icate Connective-tissue
Reticulum Containing the Different Elements of the Marrow. X 400. (Scliaper.)
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 supposition that these processes of division indi-
cate the phenomena of a reversed series ot processes, the merging of
several cells into one, has very little probability since the process of
budding has been observed in living cells. Finally, there are found in
marrow, cannot be excluded; likewise, the occurrence of myelocytes in the spleen and
occasionally in the lymph-glands is certain. Further, if the fact that numerous intermediate
forms exist is considered, the untenableness of this attempted classification is evident.
10
146
HISTOLOGY.
the red marrow nucleated cells with yellow-colored protoplasm like that
of the colored blood-corpuscles ; these are the mother-cells of the colored
blood-corpuscles, the hematoblasts (erythroblasts) (Fig. 78 and Fig. 79).
Yellowish pigment-granules that appear in the different cells are regarded
as the remains of disintegrated colored blood-corpuscles.
Hematoblasts.
C>— Colored blood-corpuscle.
Giant-cell.
Fig. 79. — Elements of Human Bone-marrow. X 600. 1-5. Various forms of marrow-cells.
6. Eosinophilous cell. Technic No. 64 b.
The yellozv marrow consists of a connective-tissue reticulum con-
taining much fat. Marrow-cells and hematoblasts in yellow marrow are
found only in the head of the humerus and of the femur.
The periosteum is a compact connective-tissue membrane, in which
two layers can be distinguished. The outer layer is characterized by its
richness in blood-vessels and forms the connection with adjacent struc-
Volkmann's canals.
Sharpey's fibers.
Outer fundamental
or ground lamellae.
Haversian lamellae.
Haversian canal.
Interstitial lamellae.
Fig. 80.— From a Cross-section of the Femur of Adult Man. X 80. Technic No. 62. The lamellae
can be recognized by the disposition of the lacunae.
tures, tendons, fascia?, etc. ; the inner layer contains few blood-vessels, •
but is very rich in elastic fibers running parallel with the long axis of the
bone and in spheric or spindle-shaped connective-tissue cells. Here and
there on the inner surface a layer of cubical elements may be found,
that are of importance in the development of the bone. The periosteum
THE SKELETAL SYSTEM. 1 47
is sometimes firmly, sometimes loosely attached to the bone ; the attach-
ment is secured by the blood-vessels . passing to and from the bone
and by Sharpey's fibers, which pierce the general and adjacent inter-
stitial lamella; and extend in all directions (Fig. 80). In the tubular
bones elastic elements of the inner layer of the periosteum penetrate the
bone in company with Sharpey's fibers and, without regard to the lamellar
structure, run in the more superficial strata. Elastic fibers also occur
that penetrate independently of Sharpey's fibers. In the bones of the
vertex of the skull elastic elements are wanting.
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 arterial
and venous vessels of the periosteum everywhere enter the haversian and
Volkmann's canals and on the inner surface of the bone are in commu-
nication with the blood-vessels of the marrow. The latter is supplied
by the nutrient artery, which on its way through the compact substance
gives off branches to the same and in the marrow breaks up into a rich
vascular network. The capillaries of the marrow resolve into wide, very
thin-walled,* valveless veins ; of the larger, likewise valveless, veins one
accompanies the nutrient artery, while the others make numerous con-
nections with the veins of the compact substance. Lymph-vessels with
well-defined walls occur only in the most superficial layers of the peri-
osteum.
The nerves are numerous and consist partly of medullated, partly
of gray fibers. They enter the haversian canals, the bone-marrow, and
the periosteum, and in the latter occasionally terminate in lamellar
corpuscles.
Articulation of Bones.
Two forms of articulation are recognized : 1, synarthroses, joints
characterized by immobility ; 2, diarthroses, joints in which the bones
are movable, one upon the other.
In synarthroses the bones are joined either by ligaments, the union
constituting a syndesmosis ; or by the intervention of cartilage, forming a
synchondrosis.
The ligaments are partly fibrous bands, possessing a structure like
that of tendon, partly elastic bands. The latter are distinguished by the
possession of numerous robust elastic fibers, which are never arranged
in bundles or lamellae, but are always separated by loose connective
* These delicate walls were formerly overlooked, whence arose the teaching that blood-
spaces without walls existed in bone-marrow.
148
HISTOLOGY.
tissue. The ligamentum nuchse, ligamenta subflava, and ligamentum
stylohyoideum are elastic ligaments (Fig. 25 C).
The sutures also belong to the syndesmoses ; they are short fibrous
ligaments that 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 fre-
quently calcified.
The intervertebral ligaments, which belong to the synchondroses,
Hyaline cartilage.
Striated zone.
Calcified cartilage.
Bone.
Marrow (fat-cells).
Blood-vessel.
Fig. 81.— Vertical Section through the Head of a Metacarpus of Adult Man. X 50.
Technic No. 65.
possess in their center a soft, gelatinous substance, the nucleus pul-
posus, that contains large 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 ten-
dinous zone.
In diarthroses the parts entering into a joint are the articular ends
of the bones, the capsular ligament, the marginal fibro-cartilages {labra
glenoidalid), and the interarticular cartilages {menisci).
The articular ends of the bones are covered by a stratum of hyaline
cartilage from 0.2 to 5 mm. thick thinning toward the edges. The super-
THE SKELETAL SYSTEM.
149
ficial cartilage-cells are flattened and placed parallel to the surface ; those
in the median strata are rounded * and are often collected in groups ; in
the deepest strata the groups of cells are partly arranged in longitudinal
rows, vertical to the surface of the bone. Attached, but separated by a
narrow striated belt, is a small zone of calcified cartilage interposed
between and connecting the hyaline cartilage and the osseous tissue
(Fig. 81).
Not all the articular cartilages exhibit the structure just described ;
the cartilages of the costo-vertebral, the sterno-clavicular, the acromio-
clavicular, and the maxillary articulations, and the head of the ulna are
not hyaline, but fibro-cartilage ; the distal ar-
ticular surface of the radius is covered with
dense fibrous tissue.
The glenoid ligaments and the interarticu-
lar cartilages do not exhibit the characteristic
cartilage matrix ; they consist of a compact
fibrous connective tissue and of spherical cells.
To the same category belong the so-called
sesamoid cartilages. The tendinous sheath
of the cuboid, however, contains genuine car-
tilage.
In the adult nerves and blood-vessels
are wanting in the articular cartilages, also in
the interarticular cartilages and the glenoid
ligaments.
The capsular ligame?its consist of an ex-
ternal fibrous layer, stratum fibro sum, varying
greatly in thickness, possessing a structure
like that of the ligaments above described,
and of an internal membrane, the stratum
synoviale, the free inner surface of which is smooth and glossy ; the outer
layer of the latter is composed of loose elastic fibers and fibrillar con-
nective tissue here and there containing fat-cells ; within this is a thin
lamella of parallel connective-tissue bundles in which, toward the inte-
rior, there are small spherical or stellate cells, 11 to 17 // in size, con-
taining a large nucleus. These cells are sometimes few in number, — at
points subjected to more pressure — sometimes very abundant, and form
a distinct epithelial membrane three or four strata thick.
Fig. 82.— Synovial Villi with
Blood-vessels from a Human
Knee-joint. X 50. The epi-
thelium has fallen from the apex
of the left villus, exposing the
connective tissue. Technic No.
66.
* Recently, the cells of the articular cartilages have been described as having processes
which extend into the adjacent cartilaginous matrix. The cells of the deeper strata are said to
possess lobulated nuclei.
I50 HISTOLOGY.
The synovial membrane (stratum synoviale) often forms folds contain-
ing fat and projecting into the synovial cavity and on its free surface bears
the synovial fringes or villi (Fig. 82), variously-shaped processes, mostly
of microscopic size, which are particularly closely set on the edges of the
joint-surfaces and bestow upon the membrane a reddish, velvety appear-
ance. They consist of connective tissue and are clothed by a single
or double layer of epithelial cells.
The larger blood-vessels of the synovial membrane lie in the loose
connective-tissue layer ; from here the capillaries extend through the
inner thin connective-tissue stratum and penetrate the villi. Some of the
villi are nonvascular. The lymph-vessels lie close under the epithelium.
The nerves run in the loose connective tissue and in part terminate
in lamellar corpuscles.
The synovia contains more or less profoundly altered cells, fragments
of cells, and oil-globules, all the product of physiologic processes of
waste of the surfaces of the synovial membrane and articular cartilage ; also
albumin, mucus, and salts ; these solid constituents amount only to six per
cent., the remainder consists of water.
The Cartilages.
The costal cartilages are of the hyaline variety ; the matrix exhibits
the peculiarities previously described (p. 87), the cells frequently con-
tain fat. Their surface is enveloped by a compact fibrous membrane, the
perichondrium, which consists of interlacing connective-tissue bundles
and elastic fibers.
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 excavated canals within growing cartilage. In the adult
cartilage is devoid of blood-vessels ; the nutrition of the tissue depends
upon diffusion from the surface. The costal cartilages in advanced life
often contain blood-vessels because of beginning ossification.
The cartilages of the special-sense organs and of the respiratory
organs will be described in the respective chapters.
Development of Bone.
The bones are relatively late structures to appear. The develop-
ment of the muscles, nerves, blood-vessels, brain, spinal cord, etc., is
THE SKELETAL SYSTEM.
ISI
already well advanced in the embryo at a time when not a trace of bone
is present. At 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 represented in cartilage. In the
upper extremity, for example, the humerus, radius, ulna, carpus, and the
skeletal parts of the hand consist of cartilaginous pieces that are not
hollow like the bones by which they are subsequently replaced, but solid
throughout. The osseous skeleton then gradually appears in the place
of the cartilaginous skeleton. All the osseous parts that in the embryo
were preceded by cartilage are called primary or endochondral bone ;
"a?' , =*" ,, *'V "■■'.■ '■■■';'
Hyaline cartilage. ' :-:'.-£■. f*I s?'-* '.'*-/~„~\°' %"-.'V
Center of calcification.
Osteogenetic tissue.
Perichondral bone.
Hyaline cartilage.
Fig. 83. — From a Dorso-plantar Longitudinal Section of the Great Toe of a Human Embryo
of Four Months. Two-thirds of the first phalanx represented. X 50. 1. Lacunas enlarged and
containing many cartilage-cells. The 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 repeated division of one cartilage-cell. Technic No. 67.
the other bones, not preformed in cartilage, are named secondary or
intermembranous bone.
The primary bones include all the bones of the trunk and extremi-
ties, the greater part of the base of the cranium (the occipital bone with
the exception of the upper portion of the tabular part, the sphenoid bone
with the exception of the internal pterygoid plate, the temporal bone with
the exception of the squamous portion, the ossicles of the ear, the eth-
moid bone, the inferior turbinal), and the hyoid bone.
The secondary bones include the bones forming the sides and vertex
of the cranium and nearly all the bones of the face.
152
HISTOLOGY.
DEVELOPMENT OF PRIMARY BONE.
Two modes of bone formation are here to be considered : i, endo-
chondral formation, formation of osseous tissue within the cartilage pres-
ent, 2, periosteal (better perichondral) formation, formation of osseous
tissue immediately surrounding, therefore upon, the cartilage. The phylo-
genetically older perichondral ossification usually begins earlier, but for
didactic reasons will be described subsequently to the process of endo-
chondral formation.
i . Endochondral Ossification. — The first indications of this pro-
cess consist in changes at certain places within the cartilage ; the cells
Enlarged lacuna.
Calcified cartilage trabeculae projecting
into the primary marrow-space.
Perichondral bone.
Osteogenetic tissue.
F.ndochondral bone.
Blood-vessels.
Perichondral bone.
Enlarged lacunte.
Fig. 84. — From a Dorso-palmar Longitudinal Section of the Finger of a Human Embryo of
Four Months. Two-thirds of the second phalanx represented. X 50. The calcified trabecule are
covered by a thin layer of endochondral bone. (More highly magnified in Fig. 85. J Technic No. 67.
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 calcifies. Such places may be recognized by the
unaided eye, and are called centers of ossification (better, centers of cal-
cification). The portions of the cartilage remote from the center of
calcification continue to grow in thickness and length, while at the center
growth ceases and consequently the cartilage at this point appears con-
stricted (Fig. 84). Meanwhile, on the surface of the center of calcifica-
tion a tissue rich in blood-vessels and young cells, the osteogenetic tissue*
*This is>n inaccurate name, inasmuch as the tissue has not originated from bone, but is
to become bone.
THE SKELETAL SYSTEM.
153
has made its appearance. This penetrates into the cartilage and causes
the breaking down of the calcified matrix ; the cartilage-cells are set
Osteogenetic
tissue.
Hyaline carti-
age (cells re-
arranged 111
vertical rows).
Hyaline car-
tilage (cells
enlarged).
Periosteum.
: ■■■$ S\***^wlS -\ V V **s^^?M4\
. V" % ^LX«i -.■'"' »** •• •• .» .*, Mi
. : -\ ijr is y ' .'--■ l-i* -
fr
Perichondral
bone.
Endochondral bone.
Osteoblasts. Osteoblasts. Blood- Giant -eel Is. Marrow-
vessels, cells.
Fig 85— From a Longitudinal Section of the Phalanx of the First Finger of a Human
Embryo of Four Months. X 220. In the endochondral bone irregular lacunae with bone
corpuscles are seen. Technic No. 67.
free and disintegrate. In this way a little excavation arises in the
center of calcification ; it is called the primary marrow-cavity .
These processes are repeated in the immediately surrounding carti-
154
HISTOLOGY.
lage ; that is, the matrix calcifies, the cartilage-cells enlarge, new portions
of the cartilage break down, and as a result the primary marrow-space is
gradually and continuously enlarged. At the same time the capsules of
many cartilage-cells are opened, the cells degenerate, and the intervening
calcified matrix projects into the marrow-space in the form of irregular
processes or trabecular The primary marrow-cavity now is a little bay
filled with blood-vessels and young cells. The fate of these cells in the
further course of development varies greatly. The}' retain their original
form and become marrow-cells, or they become fat-cells, or — and this is
Blood-vessel. Marrow.
0.
H:<3>\-
5^/T
^#
v-~>y^C
m $
X
— Blood-vessel.
>-J?L.
Endochondral
bone.
J: ,.'. . (tf?— l n *«)!?, >.Vf. — ~^^~ Remnant of cal
- j j" U j i , '*- kJ \\ -jXr^ s cified carti-
■■> t\ - -r ~^~~^' ' )' 1'vL ' lage-matrix.
^mm
t^-?
rM
Perichondral
bone.
Boundary line
between en-
dochondral
and perichon-
dral bone.
■ Periosteum.
Fig. 86. — Cross-section of the Upper Half of the Diaphvsis of the Humerus of a Human Embryo
of Four Months, h. Developing haversian spaces; h', blood-vessel. X 35- Technic No. 67.
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 tra-
becular and produce the matrix of osseous tissue.
As a result of the activity of the osteoblasts, the trabecule and
tlie walls of the marrow-cavity are soon covered with a thin layer of
bone-substance, gradually increasing in thickness. Thus step by step
the former solid cartilage is transformed into spongy bone, the trabecular
of which still contain a residue of calcified cartilage-matrix (Fig. S6).
THE SKELETAL SYSTEM. I 55
2. Perichondral Ossification. — This mode of bone-formation is
also accomplished through the agency of the osteoblasts * derived from
the osteogenetic tissue at the surface of the center of calcification (Fig.
83). Through the activity of the osteoblasts strata of plexiform osseous
tissue are periodically formed on the surface of the cartilage ; these osse-
ous masses are distinguished from the endochondral bone by the absence
6f remnants of calcified cartilaginous matrix, 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 peri-
chondral bone (Fig. 86). The latter is not formed in a continuous layer
of uniform .thickness, but at frequent intervals depressions or recesses
may be observed containing blood-vessels surrounded by osteoblasts
(Fig. 86, h fi) ; at first the recesses are open toward the periphery, but
with the progressive development of the osseous strata they are closed
in and then represent haversian canals. The osteoblasts enclosed within
the canals produce new osseous strata, the future haversian lamella?.
Cartilae-e-eell — X-/TV r~< ^^Tff i * v- Bone-cell.
Cartilage-matrix.
Y'$?i ^ K- ~y y ~\ Bone-matrix.
Transitional form of a cartilage-
cell undergoing conversion into
a bone-cell.
Fig. 87. — From a Cross-section of the Lower Jaw of a Newborn Dog. X 240. Metaplastic
type. Technic No. 67.
By the absorption of the cartilage and its substitution by osseous
tissue, also by the deposition of bone-substance on its exterior, 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 a reconstruction of the same
by the development of bone-substance. This mode of bone-formation is
termed neoplastic (Fig. 87).
On the articular fossa of the temporal bone, on the inferior maxilla,
on the tuberosity of the radius, on the spine of the scapula, and on the
tips of the terminal phalanges areas are found in which apparently
a direct transformation of cartilage into bone takes place (Fig. 87).
* In the inner strata of the perichondral osseous cortex the osteoblasts are almost entirely
absent ;■ also in-the region of the endochondral osseous trabecule the number of osteoblasts is
smaller.
1 5 6
HISTOLOGY.
From this the conclusion has been deduced that here a direct metamor-
phosis of the matrix of cartilage into the matrix of bone, of cartilage-cells
into bone-cells, occurs and the process has been named the metaplastic
mode. The conclusion is unwarrantable ; it is not here a question of the
metamorphosis of a developed connective-tissue cell into a bone-cell,
but of the performances of indifferent formative cells of the periosteum,
that sometimes produce cartilage, sometimes bone (see also p. 90,
remark *).
DEVELOPMENT OF SECONDARY OR INTERMEMBRANOUS BONE.
In this the foundation on which the formation of bone occurs is not
cartilage, but connective tissue.
Isolated bundles of connective tissue
calcify ; on these osteoblasts de-
rived from embryonal cells arrange
themselves and produce bone in the
manner above described (Fig. 88).
The intermembranous bone is en-
closed on all sides by connective
tissue ; when osseous tissue is in
direct contact on one side with
cartilage, without the intervention of connective tissue, the resulting
formation is not intermembranous, but perichondral bone.
Connective-tissue bundles.
Osteoblast. Calcified.
Uncalcified.
Fig
From a Horizontal Section of the
Parietal Bone of a Human Embryo. X 240.
Technic No. 67.
GROWTH OF BONE.
Primary Bone. — In tubular bones ossification in the diaphysis begins
much earlier than in the epiphyses (in the humerus the center of ossi-
fication 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 at first is transformed only by endochondral, later also by peri-
chondral, formation into bone. The articular surfaces of the bone remain
permanently cartilaginous ; a narrow zone of cartilage between diaphysis
and epiphysis, the epiphyseal cartilage, persists until the growth of the bone
is completed. Here an active growth of cartilage is maintained that, by
extension 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 constant
"apposition " of new periosteal strata.
In the short bones ossification takes place, as in the epiphyses, at first
by endochondral formation ; after the absorption of the last superficial
remnant of cartilage, a perichondral osseous shell is formed.
THE SKELETAL SYSTEM.
157
In the flat bones perichondral precedes endochondral formation.
Secondary Bone. — Intermembranous bones grow in superficies and in
thickness by the formation ~oi new osseous masses at their edges and on
their surfaces respectively. As a consequence of the abundant deposition
of bone -substance on the surfaces, the outer and inner tables of compact
bone are formed, which enclose between them spongy bone ; the latter in
this situation is termed diploe. The osseous masses at first possess a
coarse fibered, later (from about the first year of life) a fine-fibered matrix.
RESORPTION OF BONE.
Immediately 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 and secondary bone
are removed. Resorption occurs most actively 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 typical form is completed.* In
the interior of the compact bone
. . Giant-cells lying in Howship's lacunae.
irregular excavations may be seen,
the so-called haversian spaces,
formed by the resorption of the in-
nermost 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 pit-like
depressions — Howship's lacuna — which they have excavated in the bone.
In this situation the giant-cells bear the name of osteoclasts (Fig. 89).
Even in the fully-developed skeleton the processes of apposition
and resorption still occur at some places.
Bone.
Fig. 89.— From a Cross-section of the Hu-
merus of a Newborn Cat. X 240. H. Ha-
versian space, containing two blood-vessels
and several marrow-cells. Technic No. 67.
TECHNIC.
No. 61. — Ground Sections of Dried Bone. — The bone must not be
dried before maceration, but must be placed fresh for several months in
water, which should be frequently changed. Then it is dried and a piece
held between two pieces of cork or folds of cloth is clamped in a vice and
with a compass-saw sections I or 2 mm. thick, transverse or longitudinal,
* For example, the femur of a three-year-old child contains scarcely any of the osseous
tissue of the femur of the newborn child.
158 HISTOLOGY.
are cut. Secure a section with sealing-wax to the under surface of a
cork-stopper (the sealing-wax should also surround the section), 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 frequently-
dipped in water, 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. Then moisten
a coarse whetstone with water, rub it with a second whetstone until the
surface is covered with a little grin ding-paste ; lay the section in the paste,
place on it a smooth cork (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 ascertained
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 it should be
dried with filter-paper and polished. To do the latter, nail a piece ot
wash-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 pre-
viously dull section acquires shining surfaces. 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-glass secured
by means of cement (p. 47).
Examine first with the low, then with the high power (Fig. 36). If
the section is thick, it may be impossible to examine it with the high
power, since then the objective cannot be brought near enough to the
preparation. The bone lacuna? and bone canaliculi are filled with air
and with the customary illumination of the object from below appear
black.
No. 62. — Sharpey's Fibers. — Prepare 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. 61. Place the finished dry section for from
two to five minutes in 4 c.c. of turpentine and then mount in damar.
The fibers, invisible in the sections produced by other methods (No. 61
and No. 63), can be plainly seen, even with the lower power (Fig. 80).
No. 63. — Haversian Canals and Lamellce. — Select the metacarpal
bone of an adult ; after four weeks' fixation in Miiller's fluid, and harden-
ing in alcohol, decalcify in nitric acid (p. 35), harden again, and cut trans-
verse and longitudinal sections. The compact structure of larger bones
(the femur, for example) requires too much time (several weeks) for decal-
cification. The periosteum should be allowed to remain on the bone.
For longitudinal views of haversian canals very thick sections (0.5 mm.
or more) must be cut. Mount in dilute glycerol (Fig. 76). Nor are
very thin sections necessary for transverse views and lamellar systems ;
THE SKELETAL SYSTEM. I 59
the lamellae are best seen if the section be examined in a drop of dis-
tilled water and the mirror turned so that the object is only half illumi-
nated ; thus, too, the striae produced by the bone canaliculi, running ver-
tically to the lamellae, are best seen (Fig. 77). Mount in dilute glycerol,
which, however, renders the lamellar systems partially indistinct. Not
every part of the bone exhibits all the lamellar systems ; the outer and
also the inner ground lamellae are frequently wanting. In sections taken
near the epiphyses the transition of the compact substance into the tra-
becular 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. 36 with Fig. 37.)
Not infrequently the concentric lamellae of the haversian systems
are found to be interrupted by an irregular line. Up to this line the
osseous tissue previously formed has been again resorbed. All that which
0% ,. '**0
/ 2 j
Fig. 90. — Isolated Elements of Fresh Bone-marrow from the Vertebra of a Calf. X 560.
1. In salt solution. 2. Stained with picrocarmine. 3. After treatment with acidulated glycerol, k.
Marrow-cells ; k! , two marrow-cells containing masses of pigment-granules, the cell on the right seen
lrom the side, the cell on the left seen from the surface ; b, nonnucleated colored blood-corpuscles ; r,
giant-cells ; in the one on the right the nucleus is dividing by constriction, and two of the future new
nuclei are seen from the side, another, x, from the surface.
lies within the line is newly-deposited bone-substance. These formations
are partially filled haversian spaces (Fig. "jj, /i).
No. 64. — Red Bone-marrow. — a. Compress the vertebra (cut in half)
or the rib of a calf in a vice or with tongs ; with a pipet take up a small
drop of the liquid thus expressed, transfer it to a slide and, without the
addition of any other fluid, apply a small cover-glass or, better, a frag-
ment of a cover-glass. Examined with the high power red blood-
corpuscles, hematoblasts, marrow-cells of different sizes, and giant-cells
will be seen, but not always their nuclei (Fig. 90, 1). Add a drop of
picrocarmine (p. 51); the nuclei become red in from one to two minutes,
but are still pale (Fig. 90, 2). If the picrocarmine is displaced by salt
solution and then by dilute acidulated glycerol, the nuclei acquire a deep
color and sharp contours (Fig. 90, 3). Occasionally giant-cells are
sought in vain. Human ribs are often usable.
b. To make permanent preparations, proceed as follows : With a thin
cover-glass take up a drop of the marrow expressed from a rib and make
two cover-glass preparations as directed in No. 45. Since the marrow
l6o HISTOLOGY.
does not diffuse as readily as blood between the two cover-glasses, make
slight pressure upon them before slipping them apart. They should
not be allowed to dry, but should be placed at once in a concen-
trated aqueous solution of corrosive sublimate (5 gm. in 100 c.c. of
distilled water). At the end often minutes transfer the cover-glasses to
20 c.c. of distilled water, which is to be changed in about five minutes.
In ten minutes place them in 5 c.c. of diluted eosin (p. 38, 3 b) for from
one to five minutes, then wash for a moment in distilled water and trans-
fer them to 5 c.c. of filtered Hansen's hematoxylin ; after one or two min-
utes place them for five minutes in distilled water ; remove the water by
means of filter-paper placed at the edge of the cover-glass and place them
in 95 per cent, alcohol (not longer than one minute, lest the eosin be
extracted), then in pure oil of bergamot for three minutes. With a cloth
carefully remove the oil from the film-free surface of the cover-glass,
place a drop of damar on the surface containing the film of marrow, and
invert the cover-glass on a slide. The colored blood-corpuscles and the
protoplasm of the hematoblasts are stained a brilliant red, the protoplasm
of the remaining cells gray-violet ; all the nuclei are blue. Cells con-
taining oxyphile (eosinophile) granules are often found (Fig. 79). Cells
with neutrophile and basophile granules are obtained by treating bone-
marrow according to technic No. 45.
No. 65. — Articular Cartilage. — Select the head of the metacarpal
bone of an adult, and treat it according to the method given in No. 63.
Cut longitudinal sections and mount them in dilute glycerol (Fig. 81).
The parallel streaks often present in the hyaline cartilage are produced
by the razor. The granules of the calcified cartilage have disappeared
in consequence of the process of decalcification to which the tissue was
subjected.-
No. 66. — Synovial Villi. — From a cadaver, as fresh as possible, cut
out a piece about 4 cm. long of the capsular ligament at the edge of the
patella, and with the scissors cut a strip 2 or 3 mm. broad from the red-
dish, glossy, velvety inner surface of the same, moisten it with a drop
of salt solution, and without a cover-glass examine it with the low power.
At the edges of the tissue the villi may be seen ; their blood-vessels
often still contain blood-corpuscles. The refractive nuclei of the epithel-
ial cells lie close beside one another (Fig. 82).
If it is desired, the preparation may be stained under the cover-glass
with picrocarmine and mounted in diluted glycerol (p. 51), but much of
the original beauty is lost.
No. 67. — Development of Bone. — Human embryos four or five
months old, embryos of the sheep, pig, or cow, from 10 to 14 cm. long
(measured from the tip of the snout to the root of the tail), are suitable.
The latter are readily obtained at the slaughter-house ; the entire uterus
should be ordered. Place the embryos in toto (2 or 3 in 1 liter) in
Zenker's fluid for forty-eight hours. Wash in running water for forty-
eight hours and harden in from 200 to 400 c.c. of gradually-strength-
ened alcohols (p. 34). After the embryos have lain one week or longer
THE SKELETAL SYSTEM. l6l
in 90 per cent, alcohol to which tincture of iodin has been added (p. 32),
cut off the head, the extremities close to the rump, and decalcify them in
200 c.c. of distilled water to which 2 or 4 c.c. of pure nitric acid ha\e
been added. In two or five days, during which the decalcification
medium must be changed about three times, the extremities are to be
taken out (the head is probably not yet decalcified, and must remain in
two per cent, nitric acid for several days more), washed from one to six
hours in running water, and again hardened in gradually-strengthened
alcohols. After they have lain five days in 90 per cent, alcohol, cut the
extremities into pieces 1 cm. long, which, should they still be too soft,
may be placed for one or two days in 30 c.c. of absolute alcohol.
The vertebrae and the ribs also furnish instructive specimens.
To obtain sections showing the first processes in the development of
bone, embed in liver the phalanges and metacarpal bones (the latter are
very long in the animals mentioned), and make longitudinal (sagittal) sec-
tions, from the flexor to the extensor surface ; to be useful the sections
must be taken in the axis of the extremities, those taken from the
margin exhibit pictures that are unintelligible.
For more advanced stages make chiefly transverse sections of the
humerus and femur. Sections through the diaphysis show more peri-
chondral, sections through the epiphyses more endochondral bone.
The most beautiful examples of osteoblasts are obtained in cross-
sections of the inferior maxilla ; they are also valuable as preparations
showing the development of teeth.
For still later stages the skeleton of newborn animals is useful ;
their phalanges show tolerably early stages in the process, their carpal
bones the first stages. The decalcification requires somewhat more time
(up to eight days).
For intermembranous bone select the parietal and frontal bones of
embryos ; make horizontal sections.
The sections are to be stained in 4 c.c. of Hansen's hematoxylin for
from two to ten minutes, transferred to 10 c.c. of distilled water for ten
minutes, then to 4 c.c. of picrocarmine for ten minutes (p. 39), to 20 c.c.
of distilled water for from fifteen minutes to one hour, and mounted in
damar (p. 48).
If the staining is successful, the cartilage (especially the calcified
portions) is blue, the bone red. Occasionally the cartilage does not
stain well ; then place the sections in 5 c.c. of distilled water plus 5 drops
of filtered hematoxylin solution. In from six to fourteen hours the
cartilage will become blue. The picrocarmine staining of bone often is
not uniform ; the youngest portions of the bone, the margins of the
osseous trabecules, for example, are often the more brilliantly stained.
l62
HISTOLOGY.
III. ORGANS OF THE MUSCULAR SYSTEM.
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 connective -tissue formations, the tendons, and by accessory
apparatus of similar structure,
the fascia, tendon-sheaths, and
bursce.
Each muscle is composed ot
striated muscle-fibers, which as
a rule are longitudinally dis-
posed, so that they lie side by
side and behind one another, and
are held together by loose con-
nective tissue, the perimysium.
Interlacing is rare, but occurs,
for example, in the tongue.
Neighboring muscle-fibers never
are in direct contact, but each in-
dividual fiber is enveloped in a
delicate connective-tissue sheath,
the perimysium of the single
muscle-fiber, which is joined to
neighbor sheaths (Fig. 91,/).
A somewhat thicker con-
nective-tissue sheath, the peri-
mysium internum, encloses a large, widely varying number of fibers and in
this way a muscle-bundle is formed. A collection of muscle-bundles *
forms a muscle, the surface of which is covered by a still thicker con-
nective-tissue sheath, the perimysium externum. The several sheaths
are connected with one another.
The perimysium is composed of fibrillar connective tissue and
numerous fine elastic fibers, f occasionally contains fat-cells, and conveys
the nerves, blood-vessels, and lymph-vessels. The perimysium of the
individual muscle-fiber contains only capillaries and terminal branches
of nerves.
Fig. 91.— From a Cross-section of the Adductor
Muscle of a Rabbit. P. Perimysium, containing
two blood-vessels, at g; «, muscle -fibers ; many
are shrunken and between these the perimysium
of the individual muscle-fiber, p, can be seen ; at x
the section of muscle-fiber has fallen out. X 60.
Technic No. 68.
* The grouping of the primary bundles in secondary bundles, that in a certain number
of instances are grouped in tertiary bundles, that finally unite 10 form a muscle, is an arbitrary
division, and in many preparations cannot be recognized.
f In the perimysium externum elastic fibers are present in great abundance.
THE MUSCULAR SYSTEM.
163
The post-embryonal increase in the thickness of the muscles depends
less on the multiplication than on the growth in thickness of the already
existing muscle-fibers.
The tendons are characterized by the parallel course of their fibers,
by .their firm union, and by the scarcity of elastic fibers. They are
composed of dense, fibrous connective-tissue bundles, the "tendon-
bundles," which are held together by looser connective tissue. Each of
these (so-called secondary) tendon-bundles consists of a number of
parallel fibrillar running a perfectly straight course and united by a small
amount of cement : substance in smaller (so-called primary) bundles.
Between the primary bundles lie the cellular elements of the tendon,
Processes of tendon-cells.
Primary bundle, j ~~j
Loose connec-
tive tissue.
Tendon-cell.
Fig. 92.— A. From a Cross-section of Dried Tendon of Adult Man. X 50. Technic No. 69.
B. From a cross-section of tendon fixed with chromic acid of adult man. Technic No. 70.
fusiform-, stellate, quadrate, or flat cells, arranged in longitudinal rows,
which, curved like concave tiles, 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 very scarce and occur in the form of a fine, wide-meshed network.
The union of the muscles with tendons and fibrous membranes
(periosteum, fascia) is effected by an extension of the perimysium of the
individual muscle-fiber into these structures and theblending of the tissues ;
the sarcolemma takes no part in this but, cla'sely investing the- muscle-
fiber, terminates as a closedisheath with pointed or .obliquely blunted ends.
The radiating cross-striped muscle-fibers in the skin attach themselves
toi the connective tissue of the corium by pointed or forked ends.
164
HISTOLOGY.
The fascice 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 case when they form sheaths for the muscles and do not
furnish surfaces for the attachment of the muscle-fibers.
The tendon-sheaths and the bursa consist of a layer of connective
tissue and elastic fibers, varying in thickness, the inner surface of which
is covered patchwise by a simple stratum of polygonal, connective-
tissue epithelial cells. Where the epithelium 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 ex-
actly like the synovial fringes.
Elastic
fiber.
Proto-
plasm.
—
iff
■ 1
£
i 1
1
' .'1
Fig. 93.— Tendons from a Rat's Tail. X 240. A. Tendon-cell
viewed in profile. B. From the surface. At X the nucleus is bent
so that it is seen partly in profile (the shaded portion) and partly
from the surface (the light portion). Technic No. 71.
Fig. 94. — From a Sagittal
Longitudinal Section of
the Gastrocnemius of
a Frog. X 50. The up-
permost transverse line
represents the perimysium
seen from the surface.
Technic No. 72.
The blood-vessels of striated muscles are very numerous and evenly
distributed ; the capillaries are among the thinnest in the human body
and form networks characterized by elongated rectangular meshes,
closely surrounding the individual fibers. The veins are provided with
valves even in their smallest branches. The lymph-vessels are few in
number and follow the ramifications of the smaller blood-vessels.
For the nerves, partly sensory and partly motor, of cross-striped
muscle see the Peripheral Nerve-endings.
The blood-vessels of the tendons and the thinner fascise are very
scarce, and are contained only in the loose connective tissue surrounding
the tendon-bundles ; the tendon-sheaths and the bursae have a rich vas-
cular supply. Lymph-vessels are found only on the surface of the tendons.
THE MUSCULAR SYSTEM. 1 65
The medullated nerves of tendons terminate in part in a close plexus
of gray nerve-fibers and in part pass into spindle-shaped expansions of
the tendon, the so-called tendon-spindles, where they end in structures
resembling, but more richly branched than, the motorial end-plates.
End-bulbs and lamellar corpuscles are found in tendons, fasciae, and
tendon-sheaths.
TECHN1C.
No. 68. — Bundles of Striped Muscle. — Select a muscle in which the
fibers have a parallel disposition (for example, the adductor of the rab-
bit) and with a sharp razor make a deep incision transverse to the course
of the fibers and 2 or 3 cm. below make a second incision ; connect these
by longitudinal incisions and, without traction, carefully remove the piece
thus mapped out. For fixation place it in 100 c.c. of o. 1 per cent,
chromic acid (p. 31). After two weeks wash it in running water and
harden in 50 c.c. of gradually-strengthened alcohols (p. 34). Cut cross-
sections and examine them unstained in diluted glycerol (Fig. 91). The
muscle-fibers vary greatly in thickness ; the smallest are sections through
the ends of the fibers. Although the muscle-fibers are cylindrical and
should therefore in section appear circular, they have an irregularly
polygonal outline due to mutual pressure. The color of the sections is
very different, some are quite dark, others quite clear. The cause of this
phenomenon is unknown to me. The perimysium of the individual
fiber is best seen with the high power (240 diameters).
No. 69. — Tendons. — Cut from a tendon a piece 5 or 10 cm. long,
and let it dry in the air (but not in the sun). Thin tendons [e. g., that
of the flexor digitorum pedis) at room-temperature are sufficiently dry
in twenty-four hours. Thicker tendons require several days. With the
scalpel (not the razor) make a smooth transverse surface and then cut thin
shavings from the tendon, supporting it on the thumb of the right hand and
with the remaining fingers grasping the scalpel (the manipulation is the
same as in sharpening a pencil). Throw the shavings into a capsule con-
taining distilled water and in two minutes examine in a drop of the
same medium (Fig. 92 A). To preserve, stain in 3 c.c. of picrocarmine
for five minutes and mount in dilute glycerol. Very frequently a streak
may be seen extending across the entire section ; this is produced by
the knife.
Place another section, unstained, in a drop of water on a slide ;
treat it under the cover-glass with a drop of acetic acid ; the edge of the
section soon exhibits swollen convoluted bands (acetic-acid reaction ot
connective tissue).
No. 70. — For the study of the minute structure of tendon, its cells
and their processes, place a thin tendon, as fresh as possible (that of the
palmaris longus muscle), in pieces 3 cm. long in 100 c.c. of 0.5 per cent,
chromic acid for at least four weeks. The chromic acid should be changed
several times during .this period. Then wash the tissue in running water
1 66 HISTOLOGY.
one or two hours and harden it in about 40 c.c. of gradually-strengthened
alcohols (p. 34). The sections should be cut with a very sharp razor ;
often the tendon is so brittle that it falls to pieces in cutting. The
sections need not be very thin. Mount them unstained in diluted
glycerol. Examined with the low power and reflected light (with the
mirror muffled) they yield beautiful pictures, better than the preparations
made like technic No. 69. With the high power they resemble Fig. 92
B. The black zigzag spaces are partly occupied by tendon-cells.
No. 71. — Tendon-cells. — From the tail of a rat or mouse cut pieces
of tendon from 0.5 to 1 cm. long and place them in 5 c.c. of alum-carmine.
The following day (or later) transfer the swollen pieces to a dry slide
and rapidly tease them (p. 29). It is not necessary to separate the
tendon into very small bundles, but care should be taken that the bundles
lie straight. Then cover the preparation with a drop of distilled water
and a cover-glass. With the low power the rows of cells appear for the
most part as dark streaks ; they are the cell-nuclei seen in profile. In
surface views the nuclei appear dull red. The body of the cells, the
protoplasm, can only be seen with the high power ; viewed laterally, it
appears as a sharp, dark streak (Fig. 93 A) ; from the surface, paler and
delicate (Fig. 93 B). Not infrequently the cells are folded, so that they
are visible partly from the edge and partly from the surface. The connec-
tive-tissue fibers may be occasionally distinguished as delicate parallel
lines ; the fine elastic fibers with their sharp contours are always distinct.
The focus should be changed by means of the micrometer-screw, and the
different planes of the section examined. If the cells are not distinct add
a drop of acetic acid (p. 51). To preserve, displace the water with
diluted glycerol.
No. 72. — Muscle and Tendon. — Remove the skin from the hind leg
of a frog just killed and with scissors cut off the leg above the knee-
joint, just above the origin of the gastrocnemius. Fix it in 50 c.c.
of Kleinenberg's picrosulfuric acid (p. 32). After twenty-four hours
transfer it directly to 50 c.c. of 70 per cent, alcohol for gradual
hardening. In about six days cut off the muscle with a piece of the
tendo-Achillis, and stain it in bulk in borax-carmine (p. 39). Then harden
again in 90 per cent, alcohol. Cut sagittal longitudinal sections, placing
the razor first on the tendon occurring on the posterior surface of the
muscle. Mount in damar (p. 48). Very often not a trace of the cross-
striation of the muscle-fibers is to be seen (Fig. 94).
THE CENTRAL NERVOUS SYSTEM. 1 67
IV. ORGANS OF THE NERVOUS SYSTEM.
1. THE CENTRAL NERVOUS SYSTEM.*
The Spinal Cord.
Topography. — The spinal cord consists of a white and a gray sub-
stance, distinguishable by the unaided eye. The arrangement and the
relation of these substances are best recognized in cross-sections of the
spinal cord.
The white substance encircles the gray substance and is partially
divided by a deep anterior cleft, the anterior median fissure, and a poste-
rior 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 column, 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 ivhite
commissure at the bottom of the anterior median fissure.
The gray substance in cross-section appears in the form of an H
and in its entirety consists of two lateral columns which are connected
by a horizontal lamella, the gray commissure. On each column a thick
a?iterior horn and a slender posterior horn may be distinguished. Ad-
joining the lateral portions of the anterior horns, in the same frontal
plane with the central canal, are the lateral liorns, which are especially
well developed in the upper thoracic region. From the front boundary
of the anterior cornua the anterior roots of the spinal nerves emerge in
several bundles, while the posterior roots enter at the postero-median side
of the posterior cornua. Laterally, at the base of each posterior horn,
a net-like mass of gray substance, the reticular process (formatio reticu-
laris) is found ; at the median side of each posterior horn, near the gray
commissure, lies the column of Clarke (dorsal nucleus), well defined in
the whole length of the thoracic and in the upper part of the lumbar
* I shall confine myself here to a brief account of the topography arid 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 nervosen
Centralorgane," Barker's " Nervous System and its Constituent Neurones," and Van Gehuch-
ten's " Anatomie du systeme nerveux de l'homme " are recommended.
1(38 HISTOLOGY.
region of the cord. At the summit of the posterior horns a glistening,
jelly-like mass, macroscopically easily perceptible, the substantia gelatinosa
(Rolando), may be distinguished. Posteriorly to this is the small zona
spongiosa, at the dorsal edge of which is found the border-zone, zona
terminate, an area of cross-sectioned thin nerve-fibers. In the gray
commissure lies the cross-section of the central canal, which extends
through the whole length of the spinal cord and is surrounded by th
substantia grisea centralis. The central canal 'is fr -om 0.5 to 1 mm. in
diameter; not infrequently it is obliterated. The portions of the gray
Posterior column.
Posterior * >
median Funiculus Funiculus
" Hornspougiosa." septum. gracilis, cu neat us.
e
Medial
Zona ;: '* : T'-#^ '" C' ■ : ?:'■,* ' . • ,)'::■<. ' '\fk^ / l-'^' 1 ^ 1
Portion of
posterior
root.
term
■ ," Entrance ot
?'s'$-f:'$f\'J*'*M '.i-f^f'''^' 7 '^."' posterior
2ona tf--—^"^. -:-_:__. .'.'\" J ,,, l ' '' . "'('. ".-' ' y '"'N,d } ■' : V'^ ^- root-fibers,
spongiosa. ; ■ ■■■, ';..•,"■.■,..■ ' ■ r„- r - '{ - }''J -■ " ■ x ' ... '. f-
Substantia - - -.'/.;_;,._„..._ :^'\ ; • '","•!■ ' «&''■' ^ J ' ' ' r " - - .'■'
gelatinosa. .-'.'■'-"' ,■ ' , ■". " f . ' : -':U /',-'■."' -'--:-'-■- ■' >_^„. Posterior
Processus " I "\~ : T. ~ ~~ 1 ' — 1 ~ '~^f~ — ■ "''■, //* ■' . //' ■ :! ■' v,wl' -*~:;~~'/ " "\ ■'■■'" - .> : ■
1 ci I' n l.ii is. / ;.~ : . ■•■;. .' . ."',. -;;,-' / ■'. f .' ■ ','V . '.'■.■■■ ' ■. ,'' ,■ ^^'V-v 1 . .■ : ,' , ■ f(.-"\.. p " -^ .. '^ ;;: ^j,
■ ..'.■.■..,,-,. ■■■■■■_- ■■■ v ; ■■■■..■■ ■-;■, . ■ I r\- ' ■ 1 ■ ...■■■.-
■■ ■""-■•'■'■'■' J ' '- ' '',-"'-'.'''■ i' ,"-'r . ' " -J~ ' "" _:)\ y'-' - ^-^ J : ' .. •"'■" '.^"'J^'v .. Lateral
1 ■■•■■> r"' 1 ^''. '.'-''*"-- .--.*-'-'- ; ■> „. _ _.- _■_—_■- ,."■; "..'■ ^ -. v, -■". " . .' •. , . . . column.
~ - / " ■ , ■~ : \"-^" ■ '"'-.: W '/'' ')■ "-.- "■ A, -'-'V-;'
'^.jJ^V'^:l"'.- : :v'/'' '.' .--' ", ■■■* !' V ">' :'- 1 ^'v ' "— +£ -* — £''- — Lcw^i, Anterior
Lateral posterior, - - L " -3-^^.fv^^,.-- ,'':.'■'" - \
' Anterior Anterior ,,.,'■ Grav commissure within
Medial anterior median column. White com- w f,ich is the central
fissure. m.ssure.
Gioups of nerve-cells.
canal.
Fig. 95. — Cross-skction of the Cervical Enlargement of the Human Spinal Cord. '■ 7.
Technic Xo. 73.
commissure in front of and behind the central canal are respectively named
anterior and posterior gray commissure. In man the latter is the smaller.
From the entire periphery of the gray substance coarser or finer pro-
cesses, the septula medullaria, radiate into the white substance. In the
cervical and lumbar enlargements of the spinal cord the gray matter is
more powerfully developed than in the thoracic region ; there is a corre-
sponding variation in the form of the H. The end of the conns mednl-
laris consists almost wholly of gray substance.
Minute Structure. — The gray substance will be first considered, a
knowledge of its composition being essential to the comprehension of
THE CENTRAL NERVOUS SYSTEM. 1 69
the structure of the white substance. The gray substance consists of
multipolar nerve- (ganglion) cells, that with their dendrites and nerve-
processes form a dense nervous tangle, the " nerve -felt " (iieuropilem).
This felt is penetrated by nerve-fibers, proceeding partly from the white
columns, partly from the posterior roots ; the whole is supported by a
framework of neuroglia.
We have to consider first the nerve-cells, then the nerve-fibers ; the
neuroglia, which also occurs in the white substance, will be described at
the conclusion of the entire recital.
The nerve-cells, in accordance with the relations and distribution of
their nerve-process, are divided into (i) motor cells, (2) column-cells,
and (3) internal cells.*
The motor nerve-cells {rhizoneurons') lie in two groups f in the ante-
rior horn. They possess a large cell-body (67 to 135 p.) and long den-
drites, extending far into the surrounding substance (Fig. 96) ; the nerve-
process emerges from the summit of the anterior cornu, makes an ob-
lique descent through the white substance, at the same time receives a
medullary sheath and becomes the axis-cylinder of a medullated nerve-
fiber. Occasionally the axis-cylinder process gives off a few insignificant
lateral twigs (collaterals) before leaving the gray matter. It leaves as a
constituent part of an anterior (ventral) root-fiber bundle* of the spinal
cord. All anterior root-fibers arise from the motor cells of the anterior
horn, from those of the same, not the opposite side.
* Editor's remark : A classification and nomenclature based upon the behavior and
distribution of the axis-cylinder have recently been suggested in America, that in many respects,
appear to me to be appropriate and natural, and they have been widely accepted. According to
this two chief groups are distinguished, namely : I, axoneurons, and, II, ganglioneurons.
I. The axoneurons embrace all those neurons the cell-body (nerve-cell) of which lies
in the interior of the spinal cord or the brain. Corresponding to the different behavior of the
nerve-process, they are further divided into two subordinate groups, namely:
[a) Rhizoneurons, the nerve-process of which leaves the spinal cord through the anterior
root (they comprise the motor nerve-cells), and —
(b) Endaxoneurons , the nerve-process of which does not leave the spinal cord. Among
these we may distinguish (1) those the nerve-process of which enters the different columns of
the white substance {column-cells), and (2) those the nerve-process of which within the gray
substance rapidly breaks up into its terminal ramifications [internal cells).
II. The ganglioneurons represent those neurons the cell-body of which lies within the
spinal ganglia or the cerebral ganglia and that stand in connection with the central nervous sys-
tem only by means of their central process.
f A medial-anterior and a lateral-posterior group, separate in the cervical and lumbar en-
largements, but in the uppermost cervical and in the thoracic regions united in a single cluster
(Fig. 95). In longitudinal sections it may be seen (conspicuously in amphibians) that the cell
groups, governed by the origin of the single roots, have a correspondingly typical segmental
arrangement.
lyo
HISTOLOGY.
The column-cells {Strangzellen, endaxoneurons) constitute the chief
mass of the nerve-cells of the gray substance and lie everywhere in -it
(except in the places occupied by the motor nerve-cells), partly scattered,
partly in groups in the lateral horn and in the dorsal nucleus. The
majority are smaller than the motor nerve-cells and possess few, little-
branched, but far-reaching dendrites. Their nerve-process, after sending
off numerous collaterals in the gray substance, enters the white substance
— in the anterior or lateral column, very rarely the posterior column —
either on the same or on the opposite side. Cells of the latter kind are
sometimes termed commissure-cells* because the nerve-process passes
Fig. 96.— Two Forms ok Motor Nerve-cells from the Anterior Horn of the Spinal Cord
of a Rabbit, w. Nerve-process. X 60. Techuic No. 76. (Schaper.)
through the anterior gray commissure before entering the white sub-
stance. Having arrived in the white substance the nerve-process of the
majority of the column-cells \ divides into a vertical ascending and de-
* The commissure-cells occupy an area which, arch-like, embraces the central canal on
the ventral side ; there they are of conspicuous size, approaching that of the motor cells of the
anterior horns. Also farther back, in the median division of the gray substance, scattered com-
missure-cells occur, but they are wanting in the posterior horns.
f The nerve-processes coming from the vesicular column of Clarke do not divide in the
white substance, but turn cranialward and proceed to the cerebellum. The nerve-processes of
still other column-cells enter the white substance and there, without dividing, turn upward or
downward. Under the name of " plurifunicular cells " column-cells have been described, the
nerve-process of which divides in the gray substance into two or three branches and continues
in as many fibers in different columns.
THE CENTRAL NERVOUS SYSTEM.
171
scending " stem-fiber," that in its course parallel to the longitudinal axis
of the spinal cord sends off lateral twigs (collateral fibers), which return
to the gray substance, where they terminate in tufts of free fibrils ; the
stem-fibers themselves finally terminate like the collateral fibers. The
collateral fibers that enter from the anterior columns penetrate the ante-
rior cornua singly or in bundles, where they weave a net around the
large motor cells ; they are especially numerous in the antero-lateral
curve of the anterior horn ; not less numerous are the collateral fibers
coming from the lateral columns. The spindle-shaped "marginal cells "
lying in the zona spongiosa also belong to the column-cells. In the
adult the nerve -processes of all the column-cells are enveloped in a
medullary sheath.
Posterior root
Lateral column-cell
with
Nerve-process.
Gray matter. -
White matter.'
Central canal.
i Motor cell of the lateral
posterior group.
Commissure-cell
Nerve-processes.
Fig. 97.— Cross-section of the Stinal Cord of a Seven-day-old Embryo Chick. X 80.
white matter is but slightly developed, the central canal is still very large. Technic No. 76.
The
The cells so far described are characterized by their long nerve-
process ; they belong to the nerve-cells of the first type (Deiters's).
There is another kind of cell, the nerve-process of which rapidly divides
and remains within the gray substance. Because they do not pass beyond
the gray substance these elements are named internal cells ; they occur
in the posterior columns (Fig. 98), where their terminal ramification
spreads out either on the same or on the opposite half of the spinal cord.
They are nerve-cells of the second type (Golgi's).
The nerve-fibers that enter from the anterior and lateral columns
partly arise from the medullated collaterals and terminals of the nerve-
processes of the column-cells, partly from the nerve-processes (likewise
invested by a medullary sheath) that come from the brain.* In addition
* For an account of the exact course of these fibers the student is referred to special
text-books.
iy 2 HISTOLOGY.
there are medullated nerve-fibers of the posterior (dorsal) roots which
originate in the centripetal processes of the cells of the spinal ganglia.
These posterior root-fibers enter the spinal cord in two groups, a lateral,
which runs in the zona terminalis, and a larger median, which runs in
the posterior column. These fibers do not directly enter the gray sub-
stance, but each divides Y-shape into an ascending and descending stem-
fiber (Fig. 99), from which numerous collateral fibers diverge at right
Motor cell.
Commissure-cell.
Column-cell.
. — Ascending fiber.
Internal cell.
Collaterals.
Spinal ganglion-cell.
Descending fiber.
Fig. 98. — Scheme showing the Location and Ramification of the Nerve-cells and of the
Posterior Nerve-roots of the Spinal Cord.
angles (Fig. 98). These now enter the gray substance * and with their
tufts of terminal fibrils distribute themselves over nearly every point of
the same. One set terminates principally in the summit of the posterior
horn ; these take their origin in the lateral root-fiber group and form a
* An exception occurs in the case of some fiber-bundles which directly enter into the
gelatinous substance and partly in this or ventral thereto (in the territory of the posterior horn)
divide into ascending and descending stem-fibers.
THE CENTRAL NERVOUS SYSTEM.
173
very fine-fibered dense plexus, that also partly lies in the substantia gela-
tinosa (Fig. 100, c) ; a second set terminates in the dorsal nucleus (Fig.
100, a) ; * these originate in the median root-fiber group, as also a third
set, which penetrating the middle of the substantia gelatinosa passes ven-
tralward into the anterior horn and there radiating fan-shape surrounds
the motor nerve-cells (Fig. 100, b) ; these latter very robust collaterals
(" reflex collaterals ") arise from the portion of the stem-fibers close to the
point of bifurcation and form the reflex bundle. f A fourth, smaller set of
collaterals passes through the posterior gray commissure to the posterior
horn of the opposite side. A fifth, likewise lesser, set crosses through the
base of the posterior columns to the lateral column. The stem-fibers,
probably only after a long course, sometimes extending into the oblon-
gata, turn into the gray substance,
where they terminate like the col-
laterals.
The peculiarities of the substantia
grisea centralis and substantia gela-
tinosa, which belong to the gray sub-
stance, are dependent upon the abun-
dance of neuroglia and will be de-
scribed with this.
The white substance consists only
of medullated nerve-fibers that do not
possess a neurilemma. The fibers
differ greatly in thickness ; the thick-
est are found in the anterior columns
and in the lateral parts of the poste-
rior columns, the thinnest in the
median part of the posterior columns and in the lateral columns where
the white touches the gray substance. In the remaining portions thick
and thin fibers are intermingled. The majority of the nerve-fibers run
parallel with the long axis of the spinal cord, hence in cross-sections are
cut transversely. In addition there are fibers that take an oblique direc-
tion ; these are found in large numbers in front of the gray commissure,
where they cross at acute angles and form the white commissure (Fig. 95).
An attempt to classify the nerve-fibers according to their origin will
result as follows : 1, fibers which are continuations of the posterior root ;
Ascending stem-
fiber.
Descending slem-
fiber.
Nerve-fibers of
posterior root.
Fig. 99. — From a Longitudinal Section of
the Spinal Cord of a Nf.wborn Rat. X
no. The section shows two posterior nerve-
roots. The collateral fibers are not visible.
Technic No. 76.
* Here the medullary sheaths extend farthest — that is, to the last terminal ramifications.
f The reflex bundle and the collateral fibers of Clarke's column sink into the gray sub-
stance in a curve with the concavity lateralward and form a considerable mass easily perceived.
The place at which they enter the gray substance has been named " root-entrance zone."
174
HISTOLOGY.
the entire posterior column consists of posterior root-fibers, because the
latter (or their stem-fibers), entering in the lumbar region, are pushed
toward the median line by the fibers entering at higher levels ; 2, fibers
which are continuations of the column-cells ; 3, fibers which are continua-
tions of the ganglion-cells of the brain. The latter two occupy the
anterior and lateral columns and are united in compact bundles (funiculi).
The supporting framework of the spinal cord is constructed of two
genetically distinct formations : 1 , connective-tissue extensions of the pia,
which penetrate the white substance as sheaths for the blood-vessels ;
WRm
Anterior
01 11.
Bl'iod-vessels.
Collateral fiber of a column-cell.
Fig. ico.— Cross-section of the Spinai Curd of a Newborn R \t showing Collateral Fibers.
■ 75. In the right half unl> one representative ol each clah.s has been sketched. Technic No. 76.
this mesenchymal framework steadily grows thinner as it approaches the
gray substance, into which it does not extend ; 2, the fieuroglia (" nerve-
cement"), which is derived from the same embryonic anlage as the cen-
tral nervous system. The neuroglia principally consists of nucleated
elements, the glia-cells (Fig. 101 ), and possibly of a small amount ot
homogeneous ground-substance. There are two kinds of glia-cells, epen-
dymal cells and astrocytes. The ependymal cells in a single layer line the
lumen of the central canal. In youth they are beset with cilia, their
cylindrical bodies are prolonged in an extended process that in the embrvo
reaches to the surface of the spinal cord, where it terminates in a simple
THE CENTRAL NERVOUS SYSTEM.
i/5
or branched end (Fig. 101). The cells of the ependyma are phylogeneti-
cally the older ; they arise also ontogenetically first, but in the further
course of development undergo regression in different degrees; the long
processes in particular are involved, which retain their original length to
the surface of the spinal cord only in the region of the posterior median
septum '' and opposite, to the base of the anterior median fissure. In the
course of development one division of the ependymal cells wanders per-
ipheryward and becomes transformed into astrocytes. Not infrequently
the central canal is completely obliterated. The astrocytes (Deiters's cells),
in the beginning of their development lie in the gray substance ; later
From the substantia gelatinosa of a newborn rat.
Glia-cell.
Ependymal cells. •'''
Concentrically-arranged glia-cells Glia-ce 11 of gray matter of the base of the
from a six-week-old cat. posterior hoin ol a human embryo.
Fig tot. — Glia-cells from the Spinal Cord. X 280. Technic No. 76.
they retreat into the white substance and then are very differently shaped.
Of the numerous processes of the astrocytes one, the "chief process ''
(Fig. 10 1 ), frequently originates earliest, the others, partly finer and partly
coarser "secondary" processes, arise later. Many of these cells, with
much-branched processes, reach to the surface of the spinal cord, where
they terminate in expanded ends \ and form a conspicuous border, the
-" The posterior median septum consists for the greater part of processes of ependymal cells.
"("These expanded ends stand close beside one another and form a " membrana limitans
meningea," which is not an independent membrane any more than the internal limiting mem-
brane of the retina (see The Visual Organ).
176 HISTOLOGY.
superficial glia-zone ("gelatinous cortical layer" or " hornspongiosa ").
Two varieties of the developed cells, united by many transitional forms,
may be distinguished : the mossy-cells and the spider-cells. The mossy-
cells possess shorter, very richly-branched processes, that not infrequently
are applied to the blood-vessels ; the)' chiefly occur in the gray sub-
stance. The spider-cells, the more usual form, have a small cell-body
from which besides short, also man}' longer, rigid, less-branched pro-
cesses radiate (Fig. 106) ; these chiefly occur in the white substance
and are not apt to be confused with the ganglion-cells. By the inter-
lacing of the numerous fine processes of neighboring glia-cells (they
do not anastomose) a close web is
constructed which envelops each
individual nerve-fiber.*
In the substantia grisea cen-
jS" doss -sections tralis and substantia gelatinosa the
ol inednllated b
neuroglia assumes a totally different
White matter. Hornsponeaosa.
consisting
appearance. In the former the
~; Axis-cylinder , , -,, ,, . i
astrocytes with their here very
"\ long, stiff, unbranched processes
'. "Medullary . r
sheath. , are concentrically arranged in a
fiber- wreath (Fig. 10 1). These
-— --^Giia-cdis. and the cells of the ependyma are
together called " central ependyma
filaments." The substantia eela-
- ■ -.... -^;;-v~^co,,,Kctive tine
very small ganglion-cells, the
'.:-';,'.;.:.. '--. —i-yJ^*. connective tinosa consists of a small number
^~v"; J Blood-vessels.
' ^jj ** nerve-processes 01 which turn into
Fig 102.— From a Cross-section of thf. Human the zona terminalis, of a plexus of
Spinal Cord in the Region of the Lateral
Column. iSo. Techmc No 75. delicate nerve-fibrils, and of nerve-
fibers (collaterals) passing through ;
there is besides a granular substance present which has arisen by a
transformation of numerous and very delicate processes of the astro-
cytes occurring there (Fig. 101).
The Brain.
The brain, like the spinal cord, is composed of a white and a gray
substance, which in their minute structure agree on the whole with the
* In accordance with this statement the neuroglia consists of cells ami their processes
only ; whether also free fiber., occur, that have become detached from the cell-body, has not
THE CENTRAL NERVOUS SYSTEM. 1 77
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 :
(«) As the cerebral cortex, an expansion covering the entire surface
of the cerebral hemispheres.
(U) In the form of discrete masses, which are situated in the cerebral
ganglia, — the corpora striata, the optic thalami, the corpora quadrigemina.
(c) As the lining of the ventricles, which is the direct continuation
of the gray substance of the spinal cord.
(d) As the cerebellar cortex, an expansion 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.
THE CEREBRAL CORTEX.
In vertical sections of the cerebral cortex four zones, not sharply
defined from one another, may be distinguished.
1. The molecidar zone (neuroglia layer), the most superficial, in
ordinary preparations appears finely granular or reticulated and contains,
besides many glia-cells, an interlacement of medullated nerve- fibers run-
ning horizontally, the tangential fibers (Fig. 103). By means of Golgi's
method, it may be seen that the reticulum is partly formed by the den-
drites of the pyramidal cells of the second and third zones and partly
by the processes of glia-cells. Besides the latter, the cells of Cajal occur
in the molecular zone ; they possess an irregularly-shaped cell-body that
sends out very long processes running parallel to the surface, from one
portion of which vertically to the surface ascending lateral twigs arise *
(Fig. 104, 1).
2. The zone of the small pyramidal cells (Fig. 103, Fig. 104) is char-
acterized by ganglion-cells from 10 to 1 2 /j. in size and of a pyramidal form ;
the apex of the pyramidal cell is prolonged into a long ramifying proto-
plasmic process (dendrites), f that after giving off minute lateral twigs
yet with certainty been distinguished. In favor of the latter conception is the fact that a por-
tion of the delicate processes are differentiated by their chemical nature from the usual cell-
processes.
* In animals four and even more " nerve-processes " of Cajal's cells have been described.
In the forms described as Cajal's cells in man a true nerve-process has not been distinguished ;
it is probable that these latter elements are glia-cells.
f For this reason it is difficult to determine the size of the pyramidal cells ; the consid-
erable differences in the estimated size may be referred to this gradual passage of the cell-body
into the apical process.
12
Tangential
fibers.
• i,
I
Molecular
layer.
'-' vl
■ ' ■ f ■ :''
< I '< < ' < $'u/\ ,
. ' ' . i _ i .1 4 Layer of
U TV J I .' ,< \ > small pyr-
( ,/ '-V i . ,1', ! i amidal
Superradial
reticulum.
ripes nf J
St
Genu
..iiiV li. ,
- . *• ■ ." . ■ .,■ ...
r j fir - - ■■•' 'i
Layer o(
large pyr-
amidal
cells.
Interradia
reticulun
Radial
bundles.
" | t&
II
3 ' jP4i
§:*?
aptfti 3
'i. ! . ;> - i
Layer of
polymor-
phous
nerve-cells.
Fie. 103. — Vertical Srction of Human Chreijral
Coktkx, • 60. Teebnic No. 77.
Fig. 104. — Scheme of Cerebral Cortex, sketched from
specimens prepared according to Technic No. 79 b- *•
Cell of Cfljal. 2, 2'. Small pyramidal cells. 3- Lar f e
pyramidal cell, 4 Polymorphous cell. 5,5'. Cells of the
second type. 6. Nerve-fiber ending: >" llie superficial
zone; a, mossy-cell, b, spider-cell (glia-cells). The epeii-
dymal cells are not represented.
173
THE CENTRAL NERVOUS SYSTEM.
179
enters the molecular zone, where it terminates in numerous, often serru-
late, branches (Fig. 104, 2); smaller dendrites spring from the lateral
surfaces and from the inferior surface of the cell. The nerve -process
always arises from the base and after giving off branched collateral
fibers, as a rule, passes toward the white substance, there to become
the axis-cylinder of one or, by division, of two nerve-fibers ; occasionally
it turns and runs to the molecular layer, where it divides and enters the
web formed by the tangential fibers (Fig. 104, 2'). The nerve-process
and the collaterals are enveloped in a medullated sheath.
3. The zone of the large pyramidal cells is distinguished from the
preceding zone by the greater size of its elements (from 20 to 30 /A the
extremely robust nerve-process, after giving off
in the gray substance several collaterals, always
goes to the white substance (Fig. 104, 3).
4. In the zone of the polymorphous nerve-
cells the majority of the elements are oval or
polygonal ; an apical dendrite is wanting ; the
delicate nerve-process, after sending off a number
of collaterals, enters the white substance, where
it passes into one or, dividing into T-branches,
into two nerve-fibers (Fig. 104, 4).
In the last three zones ganglion-cells of the
second type also are found. Their branched
nerve-process sometimes is confined to the gray
matter in the vicinity of the cell, sometimes
extends to the molecular zone, where richly
branched it terminates (Fig. 104, 5, 5').
The last two zones contain numerous med-
ullated nerve-fibers. They are partly arranged
in thick "radiating" bundles, which resolve
into single fibers near the zone of the small pyramidal cells (Fig. 103).
These bundles are formed by the descending medullated nerve-processes
of the large and the small pyramidal cells, by thick medullated nerve-fibers
of unknown origin that ascend from the white substance toward the
cortex (Fig. 104, 6), where they repeatedly divide and form the " super-
radial " and the tangential plexus (Fig. 104), and finally end in free
branches. Another set of medullated nerve-fibers runs transversely to
the radiating bundles and forms the interradial reticulum ; this, is some-
what condensed toward the " superradial " reticulum and thus represents
the stripes of Gennari or Baillarger (Fig. 103). This and the interradial
Nerve-process.
Fig. 105.— Pyramidal Cell
from a Perpendicular
Section of the Cerebral
Cortex of Adult Man.
X 120. The terminal
branches of the dendrites
runningtoward the molecu-
lar layer are not visible.
Technic No. 79 b.
i8o
HISTOLOGY.
reticulum are composed of the medullated collateral fibers of the nerve-
processes of the pyramidal cells.
The structure of the cerebral cortex is modified in certain localities.
In the hippocampal and the uncinate convolutions the tangential fibers
are present in larger numbers and form an expanded net-like white layer,
the substantia reticularis 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 localities, which render a classification according to the foregoing
description much more difficult.
Finally, extensions of the pia, that penetrate in company with the
Blood-vessel
Mossy-cell. Spider-cell.
Fig. 106. — From Sections of the Brain of Adult Man. X 280. Technic No. 79 b.
blood-vessels, and neuroglia participate in the construction of the cerebral
cortex.
■Neuroglia. — This like that of the spinal cord consists of ependymal
cells and of astrocytes. In the embryo the peripheral processes of the
former extend to the free surface. Of the latter two varieties are dis-
tinguished. The one variety are characterized by their small cell-body
and long, rigid, little-branched processes, of which the most delicate rest
like a short turf on the cell-body ; they are called spidcr-cclls (Fig. 106),
and chiefly occur in the white substance. The other variety, the mossy-
cells (Fig. 106), have short, gnarled, richly-branched processes and are
mainly found in the gray substance, where they are in intimate relation
* Regarding the minute structure of the cortex of the cornu ammonis and the bulbus
olfactorius, the reader is referred to special text-books.
THE CENTRAL NERVOUS SYSTEM. 1 8 I
with the blood-vessels, to the walls of which they are often attached by
one thicker process (Fig. 106). On the surface of the cerebral cortex
there is a glia-zone formed by the ends of the thitherward extending
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.
The macroscopic variations in color depend on the different proportions
in which the ganglion -cells and the nerve-fibers are mingled : wealth of
ganglion-cells is rendered perceptible by a dark red-brown color, pro-
fusion of nerve -fibers by a pale yellow-gray color.
THE GRAY SUBSTANCE OF THE VENTRICLES.
The gray substance of the ventricles extends from the floor of the
fourth ventricle through the cerebral aqueduct (Sylvii) into the third
ventricle, to the tuber cinereum and the infundibulum. 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 distinguished by their size
(in the nucleus of the hypoglossal nerve), or by their peculiar form (the
spherical ganglion-cells in the upper pair of the corpora quadrigemina).
An extension of the neuroglia and the cylinder cells lining the
central canal of the spinal cord lines its continuation as the floor of the
fourth ventricle, the cerebral aqueduct, the inner surface of the third
and the lateral ventricles. The cylindric or cubical cells of the epen-
dyma of the ventricles in the newborn, and in part also in the adult,
possess cilia.
The Cerebellar Cortex.
The cerebellar cortex consists of three well-defined strata of gray
substance, 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 ganglionic layer, and the molecular
layer.
The granule layer, the innermost, is characterized by its rust color
and consists of numerous strata of small cells, that by the ordinary
methods exhibit a proportionately large nucleus and a very small amount
of protoplasm. By the aid of Golgi's method it becomes apparent that,
apart from the glia-cells, two varieties of ganglion-cells are present :
182
HISTOLOGY.
Cortex,
small granule-cells and large granule-cells. The former (Fig. 108 and Fig.
ill, i), are multipolar ganglion-cells with short dendrites with claw-
like endings and a delicate nonmed-
ullated nerve -process, that passes
vertically into the molecular layer
and there divides into two T-
branches that run parallel to the
surface and to the axis of the con-
volution and terminate in free un-
branched ends. The small granule-
cells form the chief mass of the
cellular elements of the granule-
layer. Less numerous are the large
granule-cells (Fig. 109 and Fig.
ill, 2), multipolar ganglion-cells
more than twice the size of the smaller elements, the ramifying dendrites
of which extend into the outermost gray layer, the nerve -process of
Fig. 107. — From
Perpendicular Section
through the cortex of the cerebellum
of Adult Man. X 50. Technic No. 78.
r
M-
D
Fig. 108. — Small Granule-
cell with a Piece of the
Nerve-process, N, and
Short Dendrites, D.
From a section through the
cortex of the cerebellum of
a six-week-old cat. X 400.
Technic No. 80.
i-j
- Nerve-
process.
Nerve-plexus.
Fig. 109.— Large Granulk-cell from a Section through the
Cortex of the Cerkbellum of a Six-week-old Cat. X 200.
Technic No. 80.
THE CENTRAL NERVOUS SYSTEM.
I8 3
which, running in the opposite direction, rapidly divides and terminates
in a rich ramification penetrating the entire granule-layer.
A dense plexus of medullated nerve-fibers occurs in the granule-
layer (Fig. ill, 3) ; the greater part of the fibers come from the white
substance of the cerebellum and at the boundary between the granule
and the ganglionic layer form a horizontal bundle (3') running transverse
to the longitudinal axis of the convolution, from which fibers ascend into
Dendrites
Cell-body
Nerve-process.
Fig. no.— Nerve-cell (Cell of Purkinje) from a Section through the Human Cerebellar
Cortex. X 180. Technic No. 80.
the molecular layer (3"). A small portion of this plexus is formed by
the medullated nerve-processes of the cells of Purkinje.
The middle ganglionic stratum of the cerebellar cortex consists of a
simple layer of very large multipolar ganglion-cells, the cells of Purkinje
(Fig. 1 10 and Fig. 111,4). Their somewhat pear-shaped bodies send two
robust dendrites into the molecular layer, where they terminate in an
uncommonly rich arborization extending to the free surface (Fig. ill,
4). The ramification does not extend in all directions, but only in planes
1 84
HISTOLOGY.
transverse to the long axis of the convolution, therefore the entire rami-
fication can be seen only in transverse sections of the convolution.
From the opposite pole of the cell the nerve-process arises, that soon
acquires a medullary sheath and passing through the granule-layer
enters the white substance of the cerebellum ; while still within the
granule-layer it sends off collaterals that branch there and some of which
run back between the cells of Purkinje (Fig. m).
Molecular layer.
Granule-layer. Medulla.
Fig. hi. — Scheme of the Cerebellar Cortex, sketched from specimens prepared according to
technic No. 80. i, Small granule-cell; 2, large granule-cell; 3, plexus of nerve-fibers; 3', hori-
zontal bundle ; 3", fibers of the molecular layer ; 4, cell of Purkinje ; 5, basket-cell ; 6, small cortical
cell, a, Glia-cell of the molecular layer ; b, mossy-cell resembling a glia-cell ; c, spider-cell.
The outermost gray or molecular layer is distinguished by its gray
color and contains multipolar ganglion-cells the dendrites of which
mainly extend toward the surface. Their long nerve-process runs hori-
zontally in the transverse axis of the convolution, sends toward the sur-
face a few collaterals, toward the interior gives off at successive intervals
delicate branches the terminal ramifications of which form a basket-like
network — fiber-basket — around the bodies of Purkinje's cells (Fig. Ill,
THE CENTRAL NERVOUS SYSTEM.
I8 5
5, and Fig. 112). The "basket" often also embraces the beginning of
the axis-cylinder process of Purkinje's cell. These cells are called
basket-cells*
The medullated nerve-fibers in the molecular layer are extensions
of the reticulum of the granule-layer and in part pass toward the surface,
where after losing their medullary sheath they terminate in free branches
between the arborizations of the protoplasmic processes of the cells of
Purkinje, in part run horizontally between the bodies of these cells, par-
allel to the axis of the convolution.
The neuroglia of the cerebellum consists of two kinds of cells : (1) The
one kind lie at the outer boundary of the granule-layer ; they have a
Embryonal su- ^--— rc~"o~
perficial gran- f o ?■>■" .?cV
ule-Iayer.
Part of the
granule-layer.^
Dendrites. Nerve-process.
Cells of Purkinje.
Fig. 112. — Basket-cell from a Section through the Cerebellar Cortex of a Six-week-old
Cat. X 240. The five cells of Purkinje were not blackened but were plainly visible ; only the out-
lines of their bodies are sketched. Technic No. 80.
small cell-body that sends a few short processes to the interior, but
many long processes in a straight course toward the free surface, where
they terminate in a triangular expansion (Fig. 114, left). In this way a
relatively thick peripheral glia-layer is formed. (2) The other kind are
stellate cells resembling the mossy-cells of the cerebral cortex (Fig. 1 14,
right) ; they occur in all the strata. In the white substance typical
spider-cells are found.
So long as the cerebellar cortex is not fully developed it is charac-
terized by a series of peculiarities that are wanting in the adult. In
*The so-called small cortical cells (Fig. Ill, 6, and Fig. 113) are also basket-cells, the
processes of which have " blackened " only a short distance.
1 86
HISTOLOGY.
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 "mossy-fibers" are develop-
mental forms of medullated nerve-fibers ; of like significance are the
"climbing plexuses," which are 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 only by contact, not by direct connection.
Small cortical /-
cells. K"
f**^ Ascending
> nerve-fiber.
Small granule-cells.
Glia-cell.
Fig. 113.— From a Section of the Cerebellar Cortex of Adult
Man. X 24°- The transverse lines are nerve-processes of basket-
cells. The cell of Purkinje and the glia-cell were sketched in out-
line from another part of the specimen for the purpose of demon-
strating the difference in size. Technic No. 80.
Fig. 1 14. — Two Glia-cells
from a Section through
the Cerebellar Cortex
of Adult Man. x 90.
On the right the body,
P, and the dendrites, P\
of a cell of Purkinje are
sketched in outline to dem-
onstrate the difference be-
tween this element and
the glia-cells. Technic No.
80.
The -white substance, the medulla, of the cerebrum and of the
cerebellum, apart from the elements of the supporting framework
(connective tissue and neuroglia), consists throughout of medullated
nerve-fibers without a neurilemma and varying in thickness from 2.5
to 7 fJ.
The hypophysis cerebri (pituitary body) is composed of two genetic-
THE CENTRAL NERVOUS SYSTEM.
I8 7
ally different parts : (1) a posterior small lobe that belongs to the brain
and is a continuation of the infundibulum ; it contains delicate, much-
branched nerve-fibers, that form a very compact plexus, connective
tissue, many blood-vessels, and cells that closely resemble bipolar or
Anterior lobe.
Blood-vessel con-
taining blood
corpuscles.
Posterior lobe.
Colloid " sub-
stance.
Multipolar cell.
Connective-tissue
fibers.
Fig. 115. — Portion of a Horizontal Section of a Human Pituitary Body, showing the boundary
line between the anterior and the posterior lobe. Two gland-tubules on the left contain each a gran-
ular epithelial cell. X 220. Technic No. 81.
multipolar ganglion-cells, but the nature of which is still uncertain ; (2)
an anterior larger lobe derived from a diverticulum of the embryonal oral
cavity ; it contains gland follicles embedded in loose vascular connective
l<0
Fig. 116. — Acervulus Cerebri from the Pineal
Body of a Woman Seventy Years Old. x 50.
Technic No. 82.
; l.(°V
Fig. 1 17.— From a Teased Preparation of Gray
Substance from the Wall of a Ventricle
of the Human Brain. X 240. a, Corpuscula
amylacea ; A , myelin drops ; c, red blood-corpus-
cles ; d, ependymal cells; e, medullated nerve-
fibers ; f, ganglion-cell. Technic No. 83.
tissue, the majority of which are solid and filled with clear or granular
cubical epithelial cells (Fig. 115). Only a few of the follicles toward the
border of the smaller lobe are hollow and occasionally contain a mass
resembling the colloid substance of the thyroid body.
1 88 HISTOLOGY.
The pineal body (epiphysis, corpus piueale) is derived from a fold of
the wall 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 organ. Almost
invariably " brain-sand " (acervidus cerebri) is found in the epiphysis,
rounded concretions from 5 p. to 1 mm. in size, with an uneven, mulberry-
like surface (Fig. 116). They are composed of an organic basis and
calcium carbonate with magnesium phosphate.
Not infrequently (especially in advanced life) there occur in the
brain-substance round or discoid bodie.s exhibiting distinct concentric
stratifiation, which stain violet on treatment with iodin and sulfuric acid,
therefore are related to amylum (Fig. 117, a). These corpuscula amy-
lacea, almost constant within the walls of the ventricles of the brain, are
present in many other localities, as well in the gray as in the white
substance.
The Membranes of the Central Nervous System.
Two connective-tissue membranes envelop the brain and the spinal
cord : the dura and the pia.
The dura of the spinal cord (dura mater spinalis*) consists of compact
fibrous connective tissue and numerous elastic fibers, flat connective-tissue
cells and plasma-cells (p. 83 and Fig. 122). The inner surface is covered
by a simple layer of flat epithelial cells (endothelium). It is poor in
nerves and blood-vessels.
The dura of the brain {dura mater cerebralis) is at the same time
the periosteum of the inner surface of the cranium and consists of two
lamellae : (1) an inner, which corresponds to the dura of the cord and is
of like structure, and (2) an outer, which corresponds to the periosteum
of the vertebral canal. The latter is composed of the same elements as
the inner lamella, but the outer fiber-bundles are disposed in a different
direction ; anteriorly and laterally they extend posteriorly and median-
ward, while the inner fibers run from the anterior median region pos-
teriorly and lateralward. The outer lamella is rich in blood-vessels,
which pass from it into the cranial bones. The dura is rich in nerves, of
which two kinds may be distinguished, vessel nerves and nervi proprii.
The pia of the brain and the 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 (the " pia ") closely invests the surface of the
brain and the spinal cord and sends vascular processes into their substance.
The arachnoid and the pia are joined together by numerous lamellae and
THE CENTRAL NERVOUS SYSTEM. 1 89
trabecular 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 longi-
tudinal sinus, which pushing the attenuated dura before them project
into the venous sinus. These are the so-called arachnoidal granulations
[Pacchioni), which were long regarded as pathologic. The pia is com-
posed of delicate connective-tissue bundles and plate-like cells, which
cover the inner surface of the arachnoid, the lamellae and the trabecular.
The telce chorioidece and plexus chorioidei consist of connective tissue
and numerous blood-vessels, the fine ramifications of which are united
into lobules that are suspended within the ventricles. They are covered
by a simple layer of cubical epithelial cells, ciliated in the newborn, which
enclose pigment-granules or oil-globules.
Blood-vessels. x Epithelium.
Fig. 118. — Portion of the Plexus Chorioideus of Adult Man. X 80. x, Blood-vessel in optical
cross-section. The dots in the epithelium are not nuclei, but pigment and fat-granules. Technic
No. 84 b.
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, which are everywhere connected with each other. The
capillaries of the cerebral cortex open into veins that do not take their
origin in the cortex, but beneath in the white substance and from there
traverse the cortex and go to the veins lying in the pia. Therefore the
blood in the capillaries must traverse the entire cortex before it empties
into the veins. All the blood-vessels possess a second so-called adven-
titial sheath, which often consists of only a simple stratum of epithelial
cells. The walls of the intradural venous sinuses are formed by a simple
epithelial membrane.
The Lymph-channels. — Between the dura and the arachnoid there
is a deep capillary cleft or fissure, the subdural space, which communi-
190
HISTOLOGY.
cates 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 subarachnoid space, that between the two layers of the pia
(or arachnoid and pia), communicates with the lymph channels of the
peripheral nerves, with the lymph-vessels of the nasal mucous mem-
brane, with 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 spaces occurring within the adventitial sheath of the blood-
vessels can be injected from the subarachnoid space. They are called
adventitial lymph-spaces.
The spaces filled only by injecting the brain-substance itself cannot
be included in the system of lymphatic channels. These spaces occur as
pericelhdar spaces surrounding the larger ganglion-cells of the cerebral
cortex, also many glia-cells ; as perivascidar spaces of the blood-vessels,
that formed by the adventitial sheath excepted ; and between the pia and
the cerebrum, as the epiccrebral space. These may be regarded as an
independent juice-canal system.
II. THE PERIPHERAL NERVOUS SYSTEM.
The Nerves.
The cerebrospinal nerves chiefly consist of medullated nerve-fibers
varying in thickness and of only a few gray nerve -fibers ; therefore by
reflected light they 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. It is called the epincuriwn (Fig.
119). Extensions of the epineurium in the interior of the nerve sur-
round the (so-called secondary) nerve-fiber bundles (funiculi), of which
each is enveloped by the concentrically lamellated connective-tissue
perineurium. From the latter connective-tissue septa extend into the
interior of the secondary nerve-fiber bundles ; they constitute the endo-
neurium. Finally, delicate lamellae from the endoneurium, the fiber
sheaths, corresponding to the perimysium of the single muscle-fiber,
surround each individual nerve-fiber. These sheaths are in direct con-
THE PERIPHERAL NERVOUS SYSTEM.
I 9 I
nection with processes of the dura and the pia. Perineurium and
endoneurium consist not only of connective-tissue bundles, but. also of
elastic fibers and of a variable number of concentric lamellae ; each lam-
ella is formed by a simple layer of flattened connective-tissue cells, the
Fat-cells.
Aitery in transverse
section.
Cross-section of bun-
dles of nerve-fibers.
Epineurium.
Perineurium.
Endoneurium.
Fig. 119.— Portion of a Cross-section of the Human Median Nerve. X 20. Technic No. 85.
outlines of which can be demonstrated by silver staining. The fiber-
sheaths, in addition to delicate connective-tissue bundles, also consist of
plate -like cells. Divisions (namely collaterals) of peripheral nerve-fibers
do not occur during their course, but at the periphery ; on the other
Perineu-
rium.
Endoneu-
rium.
Medullary
Fiber sheath.
sheath
Fig. 120. — Portion of a Cross-section of the Human Median Nerve. X 220. Technic No. 85.
hand, not infrequently a variable, large number of nerve-fibers branch
from one bundle of nerve-fibers to join another bundle. The result of
which is an acute-angled plexus of fiber-bundles.
The sympathetic nerves are partly whiter and partly grayer in color,
i 9 -'
HISTOLOGY.
depending upon the greater or lesser number of fine medullated nerve-
fibers present ; for example, the splanchnic nerves contain many medul-
lated nerve-fibers, while the gray branches of the abdominal and pelvic
plexuses contain only a very few of the thinnest medullated and, on the
other hand, numerous nonmedullated nerve-fibers. One portion of the
medullated nerve-fibers are continuations of the spinal nerves, another
portion are nerve-processes of sympathetic nerve-cells ; long dendrites
of sympathetic nerve-cells occasionally occur in the course of the sympa-
thetic nerves (cf. p. 196). The nerve-fibers are held together and
grouped into bundles by connective tissue.
Nerve-cells.
r^ -.^— ^ny^^j- f »"V. r ^» k Ji j »iJ ac T ^ _ j-.'^ - ^— .<-^ 9 xs.-'
Nerve-fiber bundle
Fig. 121
Longitudinal Section of a Spinal Ganglion of a Calf
Technic No. 86.
Connective tissue.
X20.
(Schaper.)
The blood-vessels run lengthwise within the epineurium and form
capillary networks with elongated meshes that are supported by the
perineurium and the endoneurium.
The lymph-channels occur in the capillary clefts between the lamellae
of the perineurium and between the individual nerve-fibers, so that each
nerve-fiber is bathed in lymph. They are in communication with the
subdural and the subarachnoid space, but not with the lymph-vessels
accompanying the nerve-trunk.
The Ganglia.
Ganglia are groups of nerve-cells intercalated in the course of the
peripheral nerves. Usually they are macroscopically visible. All gan-
glia consist of small bundles of nerve-fibers between which lie ganglion-
THE PERIPHERAL NERVOUS SYSTEM.
193
cells partly arranged in rounded groups, partly in longitudinal rows
(Fig. 121). A connective -tissue capsule, an extension of the perineu-
rium, covers the outer surface of the ganglion and sends into the interior
delicate processes for the support of the nerve-fibers and the ganglion-
cells. The ganglia are very rich in blood-vessels, the capillaries of which
surround the individual cells. Respecting the minute structure, differ-
ences exist between the spinal ganglia and the sympathetic ganglia.
The spinal ganglia possess large, spherical, often pigmented cells,
the vesicular nucleus of which encloses a large nucleolus. Each cell is
enveloped in a "nucleus-containing capsule" (Fig. 122), which consists
Protoplasm
Nucleated sheath.
Nucleus.
-'>'• -,
'dp
o.s|-«g^- *,
%%
Bundles of cross-sec-
tioned nerve-fibers.
Dura.
Nucleated sheath seen
from the surface.
Plasma-cells.
Fig. 122. — From a Cross-section of the Gasserian Ganglion of Man. X 240. The cell-processes
cannot be seen in cross-sections. At X the protoplasm of the ganglion-cell has retracted and simu-
lates a process. In the axis of the transversely cut nerve-fibers the axis-cylinders are seen in
section. Technic No. 86.
of flat, concentrically stratified connective-tissue cells and is prolonged
on to the process of the ganglion-cell as the fiber-sheath. In embryonal
life the majority of the nerve-cells of the spinal ganglia are bipolar, the
processes springing from opposite poles of the cell. In the course of
development the portion of the cell-body from which the processes arise
becomes attenuated, stalkwise, to one fiber — one process — from which
the primordial two processes proceed ; thus the cell becomes unipolar.*
Recent investigations made on domesticated mammals, by the
methylene-blue method (p. 40), teach us that we must distinguish
different cell -types :
* Isolated bipolar cells also occur in the adult ; they may be regarded as elements ar-
rested in their development.
13
194
HISTOLOGY.
Type I. i. Large round nerve-cells; their nerve-process, spirally
wound in its initial portion, arises from a conical eminence of the
protoplasm and near to its exit from the cell receives a medullary
sheath and a neurilemma ; after sending off several delicate collateral
fibers, it divides at shorter or longer intervals, uniformly at the niveau
Dorsal root
Spinal ganglion.
Blood-
vessel.
Dorsal
ramus.
Visceral ramus
Cell ot a sympathetic gangl
Fig. 123.— Scheme of the Nkrvous Elements of a Spinal Ganglion, Projected from Prepa-
rations Produced after Technic No. 186 b. The sensory fibers are represented bv continuous
lines, the sympathetic fibers by dotted lines, the motor fibers bv a linear series of clashes. The
medullary sheaths of the motor fibers of the ventral root have not been drawn.
of a node of Ranvier, T- or Y-shape (p. 104) in two (Fig. 123, 1) or
three (Fig. 123, 3) branches.* One of these, the cellulipetal branch,
*Each of the two branches may divide once again; of the twigs proceeding from the
peripheral branch, the one runs in the ventral, the other in the dorsal ramus of the spinal
nerves (Fig. 123, 2).-
THE PERIPHERAL NERVOUS SYSTEM. 1 95
passes as the axis-cylinder of a sensory fiber to the periphery of the
body ; the other, the cellulifugal, usually slighter branch runs as a
constituent of a posterior nerve-root to the spinal cord, in the gray
substance of which it terminates in a free ramification (p. 172). Thus in
a measure each spinal ganglion-cell, by its yet undivided process, is
intercalated in the course of a sensory nerve-fiber.
2. Small round nerve-cells (Fig. 123, 4), that are distinguished
from the large cells only by their delicate nerve-process, that receives
no medullary sheath or only scattered traces of such a cover.
Type II. Spherical unipolar cells, the process of which, after re-
ceiving a medullary sheath and a neurilemma, repeatedly divides into a
large number of medullated nerves (Fig. 123, 6). These, after losing
their medullary sheath, approach the cells of the first type and form a
pericapsular plexus lying upon the nucleated capsule of these cells ;
from this arise delicate branches which pierce the capsule and resolve
into a pericellular plexus. Each cell of the first type is enveloped in
the plexuses of several cells of the second type (Fig. 123, 3). The
number of the cells of the second type is relatively insignificant.
Possibly to be regarded as modifications of the second type are
multipolar nerve-cells that besides short dendrites possess a centrally
and a peripherally running nerve -process (Fig. 123, 7). These processes
appear to become medullated nerves, that however do not pass beyond
the territory of the ganglion. The multipolar cells are present only in
very limited number.
The cells of the second type, possibly also of the first type, are
wrapped in varicose pericapsular and pericellular networks of fibers,
which are the nonmedullated endings of medullated nerve-fibers coming
from a few sympathetic nerve-cells of the sympathetic ganglia. Branches
of these fibers also go to the blood-vessels (Fig. 123). Thus the cells
of the second type achieve the approach of a small number of entering
sympathetic fibers into close relation with the large number of cells of
the first type.
The fact ascertained by careful enumeration, that in a spinal gan-
glion there are many more ganglion-cells than there are cross-sections
of medullated nerve-fibers in the posterior nerve-root, early permitted
the conjecture that further complications are still involved in the spinal
ganglion. That this conjecture was correct is testified by the brilliant
discovery of ganglion-cells of the second type, the nerve-process of
which does not pass out of the ganglion ; but their small number is not
sufficient to explain the discrepancy, — of six ganglion-cells to one
medullated nerve-fiber — even if to them we add the few multipolar
ganglion-cells regarding the course of the nerves of which yet little is
196
HISTOLOGY.
known. Into this breach leaps the new fact that the nerve-processes of
the small ganglion-cells of the first type are chiefly nonmedullated (Fig.
123, 4). Whether there are nerve-fibers that pass through the spinal
ganglion without entering into relation with its cells is uncertain. In
young chick embryos such fibers, coming from cells of the anterior
horns, have been demonstrated ; but they have not been found in any
mammal.
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 latter is said to be in part a sympathetic
ganglion. The ganglia of the auditory nerve (ganglia nervi cochleae et
nervi vestibuli) contain bipolar cells.
The sympathetic ganglia consist of nerve-fibers and of small, often
Artery in transverse
section.
Ganglion-cell.
Nucleated sheath.
Nucleated sheath
(from the surface).
Non-
medul-
lated
Nerve-
fibers in
cross-sec-
tion.
Fig. 124.— Portion of a Section of the Superior Cervical Ganglion of Man. X 24°-
Technic No. 87.
pigmented cells, likewise surrounded by a nucleated connective-tissue
capsule, that possess one or two nuclei (two in the rabbit and the guinea-
pig). The cells are multipolar ; * their branched dendrites press between
the neighboring nerve-cells through to the periphery of the ganglion,
where they form a " universal f peripheral plexus "; other dendrites even
extend into the neighboring ganglia, where they terminate in like manner.
Their nerve-process passes directly into a delicate nerve-fiber, that either
becomes medullated in varying length or remains nonmedullated. These
fibers are for the greater part motor and terminate — often after running
an extended course — on smooth muscle-fibers (p. 203) ; one portion ter-
* The nerve-cells of the sympathetic ganglia of fishes are bipolar ; in amphibians, per-
haps also in mammals, ganglion-cells occur of which the single process with "]"-branches is
embraced by a " spiral fiber," that surrounds the ganglion-cell in a ramification of free branches,
similar to the plexus of fibrils enveloping the cells of the spinal ganglia.
f The expression " universal " is used in contradistinction to the statement of R. y Cajal ,
according to which each individual nerve-cell is embraced in a basket formed of dendrites.
THE PERIPHERAL NERVOUS SYSTEM.
197
minate in free endings in the mucous membrane ; the terminal ramifica-
tions of another portion surround the nerve-cells. The dense terminal
ramifications of the medullated nerve-fibers coming from the motor spinal
nerves form plexuses which in part lie between the nerve-cells and in part
pierce their connective-tissue capsules and surround the cells themselves.
To the sympathetic ganglia belong the ciliary, sphenopalatine, otic,
and submaxillary ganglia.
<^'** m * f **~ '
Stratum corneum.
| : ; Stratum lucidum.
Stratum germinati-
vum.
- Epide
Fig. 125.— Vertical Section of the Skin of the Great Toe of a Man Twenty-five Years of
Age. X 200. The cell-nuclei of the stratum germinativum are distinct only in the deepest layer.
/, Cells of Langerhans ; w, intra-epithelial nerve-fibers. P t P l , two papillge of the corium ; Peon-
tains a capillary loop, c, of which only one limb is visible ; P l contains a tactile corpuscle, r, with
two approaching medullated nerve-fibers, m. Both papillae contain nonmedullated nerve-fibers.
Technic No. 88.
The Peripheral Nerve-endings.
terminations of sensory nerves.
The peripheral terminal branches of the sensory nerves either are
distributed naked, as free endings, or they are enclosed by epithelial or
connective-tissue cells with which they form special endings (terminal
corpuscles, end-organs). *
The free nerve-endings occur in this manner. The nerve-fiber
loses its medullated sheath, divides repeatedly, and forms a plexus of
primitive fibrils that terminate in pointed or club-shaped ends. These
* The nerve-endings of the neuro-epithelial cells are described in the chapters on the
special-sense organs.
I98 HISTOLOGY.
endings chiefly occur in stratified epithelium. They have been demon-
strated with certainty in the cornea, in the oral mucous membrane (see
The Taste-buds), and in the deeper strata of the epidermis. In the latter,
cells provided with long, branched processes, the cells of Langerhans
(Fig. 125), occur ; these were formerly regarded as migrated wandering
cells from the corium and it is possible that a few of them may have
such an origin ; but the majority are derived from ordinary degenerat-
ing epithelial cells ; all the transitional forms, from the typical epithelial
cells to the stellate bodies in question, may be found.
Sensory nerves have been found also in the muscles. The nerve-
fibers lose their medullary sheath and invested only by the neurilemma
divide dichotomously into numerous delicate fibrillas that extend length-
wise between the muscle-fibers and terminate in free endings (Fig. 131).
Epidermis.
Tactile ce
Tactile meniscus.
Nerve-fiber
Connective-tissue sheath
Fig. 126. — From a Vertical Section of the Skin of the Great Toe of a Man Twenty-five
Years Old. X 240. The outlines of the cells and the nuclei of the epidermis can only be indistinctly
seen. x. Tactile cells in the corium, resting upon the ramifications of a delicate nerve-fiber.
Technic No. 88.
The terminal corpuscles or 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 CELLS.
The tactile cells may be either simple or compound. The simple tac-
tile cells are oval nucleated bodies measuring from 6 to 12 11 (Fig. 126),
which occur in the deepest strata of the epidermis and in the outer root-
sheath of the hairs or in the adjacent portions of the corium. The tactile
cells rest on the tactile meniscus, a crescentic expansion of a nonmedul-
lated nerve-fiber.
The compotind tactile cells (Grandry's and Merkel's corpuscles) con-
sist of two or more somewhat flattened cells, each larger than a simple
tactile cell (15 p. deep and 50 p. wide) that contain a vesicular nucleus.
A medullated nerve-fiber approaches the compound tactile cells (Fig.
THE PERIPHERAL NERVOUS SYSTEM.
199
1 27) and the forks of the divided axis-cylinder clasp a flat disk, the tactile
disk (ts), that lies between two flattened cells (7.;). The nerve-fiber
loses its medullated sheath at the point of entrance and the neurilemma
becomes fused with the connective tissue of the capsule (/z) enveloping
the tactile cells. The compound forms consisting of two tactile cells
are named twin tactile cells (B 2), those containing three or four tactile
cells, "simple tactile corpuscles." The compound tactile cells have
only been found in the epidermis of the beak and in the tongue of birds,
especially in web-footed birds ; they are almost exclusively situated in
the uppermost stratum of the corium.
>£>/>
Fig. 127.— From Vertical Sections of the Skin of the Beak of a Goose. X 240. A. Com-
pound tactile cell (simple tactile corpuscle), cut parallel to the course of the entering nerve-fiber:
w, medullated nerve-fiber only, partially met by the section; a, axis-cylinder : its division here, in
profilers invisible; ts, tactile disk cut vertically; h, connective-tissue sheath; tz, tactile cells.
B. Two compound tactile cells cut transversely to the plane of the entering; nerve-fiber. 1. " Simple
tactile corpuscle," consisting of four tactile cells; 2, twin tactile cells; ts, tactile disks; a, axis-
cylinders in transverse section, before [dividing ; n, medullated nerve-fibers; c, corium. Technic
No. 89.
END-BULBS.
The end-bulbs are spherical or oval bodies in the interior of which
nerve-fibers terminate, sometimes in a simple, sometimes in a branched
ending. There are various forms of end-bulbs.
The so-called cylindrical end-bulbs, the simplest form (Fig. 128),
chiefly consist 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 composed of flattened connective-tissue cells, the con-
tinuation of the fiber-sheath. The inner bulb is a finely-granular mass
which exhibits concentric stratification and a few nuclei at the periphery.
The nerve-fiber loses its medullary sheath on entering the inner bulb, in
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 example, in the
scleral conjunctiva of mammals and in the oral mucous membrane.
The lamellar corpuscles (Vater, Pacini) are transparent, elliptical
200
HISTOLOGY.
structures, from 2 to 3 mm. long and 1 to 2 mm. thick, and like the
cylindrical end-bulbs consist of a capsule, an inner bulb, and an axis-
cylinder (Fig. 1 29). The latter two possess the same structure as in the
end-bulbs,* but the capsule is differently formed. It consists of a large
number of concentric capsules, or lamellae, each lined by a simple layer
of plate-like connective-tissue cells and separated from neighboring lam-
ellae by a serous fluid. Each lamella consists of an outer transverse and an
inner longitudinal layer of connective-tissue fibers. As the capsule of the
end-bulbs, so also these capsules originate from the connective-tissue
sheath of the entering nerve-fiber. They are the smaller the nearer they
lie to the inner bulb. Along the course by which the entering nerve
Medullated
nerve-fiber.
Fig. 128. — Cylindrical End-bulb from the Con-
junctiva of a Calf. X 240. Technic No. 90.
Axis-cylinder.
Inner bulb.
Fig. 129. — Small Lamellar Corpuscle from
the Mesentery of a Cat. X 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 bulb. Technic
No. 91.
passes to the inner bulb the lamellae are not infrequently united by a
longitudinal strand of tissue, the interlamellar ligament. A small artery
accompanies the nerve-fiber into the interior of the corpuscle, which
breaks up into a capillary network lying between the peripheral lamellae.
The lamellar corpuscles partly occur in superficial situations, abun-
dantly in the subcutaneous connective tissue of the palm of the hand and
the sole of the foot, more sparingly in other areas of the skin, in the
nipples, in the territory of the pudendal nerve, partly in deeper situations,
in the vicinity of the joints, on the nerves of the periosteum and the
bones, in the neighborhood of the pancreas, and in the mesentery.
* In the lamellar corpuscles the axis-cylinder not infrequently is forked at its extremity
or it breaks up into several twisted interlacing twigs.
THE PERIPHERAL NERVOUS SYSTEM.
201
The corpuscles of Herbst and Key-Retzius, occurring in birds,
are also lamellar corpuscles ; they only differ in being much smaller and
in possessing a double row of longitudinally-disposed nuclei in the inner
bulb.
The genital nerve-corpuscles of the lower mammals and of man are
spherical or oval forms (from 0.06 mm. to 0.4 mm. long), and consist oi
a finely-granular, nonnucleated inner bulb enveloped in a connective-
tissue capsule containing cells rich in protoplasm. The approaching
medullated nerve-fibers make several turns around the corpuscle, lose
their medulla and divide, while fiber-sheath and neurilemma pass into the
capsule ; the naked axis-cylinders penetrate the inner bulb at different
points, undergo rapid division and form a dense
plexus of fibrils ' with varicose enlargements.
In imperfect staining the varicosities simulate
club-shaped endings. Each plexus is connected
by delicate nerve filaments with plexuses ol
neighbor corpuscles.
The genital corpuscles lie in the depths of
the corium at various distances from the papil-
lary stratum ; in the papillae only smaller cor-
puscles, resembling the " spherical end-bulbs,"
are found. The largest number, from one to
four to the square millimeter, occurs in the
glans penis and in the clitoris. The so-called
spherical end-bulbs (they are sometimes round,
sometimes oval) have a similar structure ; they
are found in the conjunctiva and in the ad-
joining portions of the cornea of man, and possess a greatest diameter
of 0.02 to 0.1 mm. The articular nerve-corpuscles belong to the same
category.
The tactile corpuscles (Wagner's and Meissner's corpuscles) are ellip-
tical structures, from 40 to 100 p. long and 30 to 60 p. broad, which are
characterized by cross-markings (Fig. 130). They possess a connective-
tissue capsule (Fig. 130, h) with flattened cells, the boundaries of which,
as well as their transversely-placed nuclei, produce the cross-striations
just mentioned. One or two medullated nerve-fibers approach each tac-
tile corpuscle (Fig. 130, n), make transverse tours encircling the lower
pole of the corpuscle, part with their neurilemma and fiber-sheath, which
blend with the tissue of the capsule, then lose their medullary sheath,
and as naked axis-cylinders enter into a granular substance corresponding
to an inner bulb ; there they form a complicated plexus beset with vari-
Fig. 130. — Tactile Corpuscle
from a Perpendicular
Section of the Great
Toe of a Man Twenty-
five Years Old. X 560.
«, Medullated nerve-fibers ;
e, varicosities ; h, connec-
tive-tissue sheath. The nu-
clei are invisible. Technic
No. 88
202
HISTOLOGY.
cosities (e). * These tactile corpuscles lie in the papillae of the corium and
are most numerous (twenty-three to one square millimeter) on the palm
of the hand, on the finger-tips, and on the sole of the foot.
Sensory nerve
fibers.
Muscle-fibers.
Medullated
nerve-fibers.
Nerve-fiber
bundles.
Fig. 131. — Motor Nerve-endings of Intercostal Muscle-fibers of a Rabbit. X 15°-
Technic No. 92 a.
A' -if
a i-i
Vi
K-^-0,
TERMINATIONS OF THE MOTOR NERVES.
The small nerve-trunks supplying striated muscle divide into
branches, these subdivide into twigs (nerve-fiber bundles) that anasto-
mose with one another and form a plexus, the
intermuscular plexus. In the compass of this
plexus the medullated nerve-fibers undergo nu-
merous divisions, so that the number of nerve-
fibers is considerably increased. From the small
bundles of the plexus single delicate nerve-fibers
spring, each one of which finally connects with
a muscle-fiber. At the point where the nerve-
fiber comes into contact with the muscle-fiber
it loses its medullated sheath, the axis-cylinder
breaks up into a number of slightly-tortuous ter-
minal branches with bulbous, swollen extremities,
which form the so-called motor end-plate and rest upon a rounded, finely-
granular disk {sole-plate) containing numerous vesicular nuclei (Fig. 132).
Each muscle-fiber possesses at least one motor end-plate ; whether it lies
upon or under the sarcolemma is not yet definitely determined.
Fig. 132.— Motor Nkrvk-end-
ing in a Fiber of an
Ocular Muscle of a Rab-
bit. X 240. N. Medullated
nerve-fiber; K, nuclei of
the disk. The transverse
striae are distinct only in
the lower half of the mus-
cle-fiber. Technic No. 92 b.
* In imperfect staining the varicosities simulate club-shaped endings.
THE PERIPHERAL NERVOUS SYSTEM.
203
The nerves supplying the smooth muscles form a plexus from
which bundles of nonmedullated nerve-fibers arise ; the latter divide
repeatedly and form several networks, from which spring the most deli-
cate nerve-fibers. They apply themselves to the smooth muscle-fibers
and often are slightly thickened at the point of contact.
The Suprarenal Body.
The description of the suprarenal body with the organs of the
nervous system is warranted by the profusion of its nervous elements,
Zona glomerulosa.
Zona fasciculata
Zona reticularis
Cords of cells of the
medulla.
Nerve in transverse
section. #0*55;.,
. ..?*.«««&*
Ganglion-cells.
Buiultesof smooth mus- --— j-^7 - ^ - ".
cle-fibers in transverse %®£7-^t^*-aQ
section.
Veins in cross-section.
Cortex. Medulla. Vein.
A
Fig. 133. — A. Section of the Suprarenal Body of a Child. X 15. Technic No. 93. B. Section of
a Human Suprarenal Body. X 50. Technic No. 95.
Medulla.
by its relations to the central nervous system, as established by experi-
ment, as well as by the facts of comparative anatomy.
Each suprarenal body consists of a cellular parenchyma and a
connective-tissue capsule, which sends delicate processes into the interior
of the organ. The parenchyma consists of an outer stratum, the cortex,
which surrounds an inner mass, the medulla, on all sides (Fig. 133 A).
The cortex is of friable texture, of a yellow color when fresh, and is com-
posed of groups of cells about 1 5 /1 in size, rounded in shape, that possess
a coarsely-granular protoplasm, sometimes containing fat particles, and a
204
HISTOLOGY.
clear nucleus. In the outer zone of the cortex the cells are grouped
in oval masses, in the middle zone they are arranged in cylindric
columns, while in the innermost zone the anastomosing cords of cells lie
' Capsule.
Zona glomerulosa.
Zona fasciculata.
Zona reticularis.
> Medulla.
Fig. 134.— Section through Cortex and Medulla of the Suprarenal Body of Adult Man.
X 200. (Schaper.)
THE PERIPHERAL NERVOUS SYSTEM. 205
irregularly scattered in a reticulum of connective tissue ; the cells of the
innermost zone are characterized by their pigmentation. According
to the described arrangement the cortex is divided as follows : i , the
zona glomerulosa ; 2, the zona fascicidata ; 3, the zona reticularis (Fig.
133 B and Fig. 134). The medulla in the fresh state is sometimes
lighter, sometimes darker than the cortex ; it consists of polygonal cells
possessing a finely-granular protoplasm and a clear nucleus. They are
arranged in spherical groups or oval cords joined in an irregular net-
work.*
The arteries divide in the connective-tissue capsule into numerous
small branches that penetrate the cortex and there form a long-meshed
capillary network, which passes into the medullary substance where the
meshes are round. From the latter the veins proceed, of which the
larger are accompanied by longitudinal strands of smooth muscle-fibers.
While still within the medulla the veins unite and form the chief vein,
the suprarenal vein.
The numerous, chiefly nonmedullated nerves (in man about 33 small
trunks) come principally from the celiac plexus and pass with the arteries
through capsule and cortex to the interior of the medulla. During their
course they give off a few twigs to the capsule, that form a plexus there ;
from this delicate branches descend into the cortex between the cell-
groups of the zona glomerulosa and the zona fasciculata, which terminate
on the surface of the cell-clusters, without penetrating between the indi-
vidual cells. Richer is the nerve-plexus of the zona reticularis, which
originates by the branching of fibers that descend straight through the
cortex ; it also surrounds only cell-groups. In the medullary substance
the nerve -plexus is extraordinarily dense ; each individual cell is sur-
rounded by nerve-fibers. In the medulla, seldom in the cortex, groups
of sympathetic ganglion-cells occur. Some of the nerves terminate in
the walls of the blood-vessels.
* Recent researches indicate that only the cortex of the adrenals of mammals corresponds-
to these organs in other vertebrates ; the elements of the cortex are epithelial cells, the cells of
the medulla are peculiar elements belonging to the sympathetic nervous system, which until
recently were unrecognized in mammals ; therefore the cells of the medulla are not to be
regarded as specific constituents of the suprarenal bodies. If this statement proves correct, the
description of these organs in the chapter on the nervous system is no longer authorized.
2o6 HISTOLOGY.
TECHNIC.
No. 73. — The Spinal Cord. — For the study of the distribution of
the white and the gray substance the spinal cord of a child should be
fixed in toto in about one liter of Miiller's fluid, that should be fre-
quently changed ; after four or five months thick cross-sections of the
cervical, thoracic, and lumbar regions may be cut, and without further
treatment mounted in dilute glycerol (p. 23), or after the customary
preliminary treatment they may be mounted in damar.
No. J^.—Tlie Spinal Cord ; Staining of Medullated Fibers, after Pal.
— The success of the preparation depends especially on the state of
preservation of the organ. The fresher the tissue when it is put into the
fixing fluid, the better will be the result. The entire spinal cord should
be placed in a large quantity of Miiller's fluid, that must be changed
daily during the first week and frequently thereafter. If it is desired to
investigate only portions of the spinal cord, then place pieces of the fresh
cord about 2 cm. long, taken from the lower cervical, the middle thoracic,
and the lumbar region, in 200 to 500 c.c. of Miiller's fluid or, better, sus-
pend them in it. In four or six weeks, during which time the fluid must
be frequently changed, the tissue is to be transferred directly, without
previous washing, to 1 50 c.c. of 70 per cent, alcohol and on the follow-
ing day to the same quantity of 90 per cent, alcohol. The bottle con-
taining the tissue must be placed in the dark (p. 34), and the alcohol be
frequently changed during the first eight days. Sections may then be
cut. The sections are to be placed in a capsule containing 20 c.c. of 70
per cent, alcohol and as soon as possible transferred from this to 30 c.c.
of Weigert's hematoxylin to which 1 c.c. of lithium carbonate solution
has been added (p. 24). In five or six hours the now very dark, un-
transparent sections should be transferred to 50 c.c. of distilled water
plus 1 c.c. of lithium carbonate solution. In a half-hour, during which
time the fluid must be changed several times, the sections will give off
no more color and are then to be placed in 30 c.c. of potassium perman-
ganate solution for differentiation (p. 24). In from one-half to three
minutes the sections are to be washed for one minute in distilled water
and then transferred to 20 c.c. of the acid mixture (p. 24). The capsule
containing the acid mixture should be covered. The decolorization
occurs in from ten to fifty seconds ; the gray substance becomes light
yellow, almost white, the white substance (the medullated nerve-fibers)
appears very dark. Now transfer the sections to a capsule containing
30 c.c. of distilled water and in five minutes to a second capsule contain-
ing the same quantity of fresh distilled water. After ten minutes place
them in 10 c.c. of alum-carmine, in which they may remain from three
to fifteen hours. Mount in damar. The alum-carmine staining may be
omitted.
The foregoing directions are intended for thin, well-fixed prepara-
tions. If the sections are thick, if the tissue has lain a long time in
alcohol, more time will be required for staining and reduction. Should
THE PERIPHERAL NERVOUS SYSTEM. 2Q"]
the staining be unsuccessful, place unstained sections in Miiller's fluid
for twenty-four hours, wash one minute in distilled water, then stain,
and satisfactory results may be obtained. Should the decolorization be
insufficient, if the gray substance does not become yellowish-white, the
procedure may be repeated ; that is, the sections are to be again placed
in distilled water one minute, then in potassium permanganate one or
three minutes, then in distilled water one minute, and finally in the acid
mixture. The given quantities of the permanganate solution and of the
acid mixture are sufficient for only about 20 sections. If it is desired to
treat more sections larger quantities of these fluids must be used.
No. 75- — The Spinal Cord ; Staining of Axis-cylinders and of Cells.
— Place pieces at the most 2 cm. long in 200 c.c. of Miiller's fluid, that
must be changed daily during the first week and once a week thereafter.
In four weeks transfer the tissue directly from Miiller's fluid to about
50 c.c. of sodium carminate (1 per cent, aqueous solution), in which it
should remain for three days. During this time the bottle containing the
tissue must be frequently shaken. The stained pieces are to be washed for
twenty-four hours in running water, then placed in 1 50 c.c. of 70 per
cent, alcohol, and after five hours transferred to the same quantity of 95
per cent, alcohol. Mount the cross-sections in damar (Fig. 102).
No. 76. — Spinal Cord, after Golgi.* — Remove the spinal cord along
with the (still cartilaginous) vertebral column of newborn rats or mice
and treat them according to the. method described on page 43. The
length of time the objects should remain in the Golgi mixture depends
upon the elements it is desired to impregnate. f It requires frorn
Two to three days for neuroglia cells,
Three to five days for nerve-cells,
Five to seven days for nerve-fibers (collaterals).
Since the pieces must be used as soon as they are taken out of the
silver solution, only one piece at a time should be transferred to the
absolute alcohol. Cut the sections through spinal cord and vertebral
column.
The spina! cord of a three- or seven-day-old embryo chick furnishes
still better results, but it is necessary to embed the tissue in celloidin
(see Microtome Technic). The spinal cord of kittens as well as that ol
human embryos 20 to 40 cm. long yields very useful results.
No. 77. — The Brain; Staining of Medidlated Nerve-fibers. — Apply
the method given in No. 74. If an entire human brain is to be placed
* Editor's renlark : The application of the Cox- Golgi mixture, in the manner described
on p. 43, foot-note, is also highly recommended. Since it can be applied with good results to
the central nervous system of adult animals it offers, in the manipulation of the material and
the preparation of the sections, valuable advantages, particularly to the beginner. After the
treatment with alcohol the larger pieces, without being embedded, can be easily cut freehand,
when thick sections are desired.
t If the action of the mixture is too brief the central portions of the sections appear un-
transparent and are penetrated by abundant precipitates ; if the action of the mixture is too pro-
longed the resulting impregnation of the elements will be unsatisfactory.
208
HISTOLOGY.
Fig. 135.— Portion of a Section of
Human Cerebral Cortex. X
240. p, Small pyramidal cells ; a
the nerve-process of a pyramidal
cell.
in Muller's fluid, many deep incisions should be made in it and about 3
liters of the fixing fluid should be used.
No. 78. — The Brain ; Cells. — Treat pieces 1 or 2 cm. square of the
cerebral cortex (paracentral convolution) and of the cerebellar cortex like
No. 75. In the cerebral cortex, in ad-
dition to the cell-forms described, an ex-
tremely variable number of vesicular spaces
containing remnants of cells (protoplasm
and nucleus) may be seen (Fig. 135,-8);
they are probably pericellular lymph-spaces,
which by post-mortem alteration and the
influence of the fixation medium have be-
come abnormally enlarged. The sections
through the cerebellar cortex must be
made transverse to the long axis of the
convolutions, since the ramifications of the
cells of Purkinje extend only in planes
transverse to the convolution. Only a
few cells of Purkinje lie in the depressions between the convolutions.
No. 79. — The Brain ; Golgi Staining* — a. For a topographic view,
treat the brain of a newborn rat or mouse in the unopened cranium
according to the method given in No. 76. The cranium may be sec-
tioned with the brain-substance.
b. For specimens of the cortex the brain of a mouse from eight to
thirty days old is most suitable, treated with the Golgi mixture for from
two to three days, or of a one- to fifteen-day-old rabbit or a kitten under
six weeks old, treated with the Golgi mixture for five days. Pieces of
the brain of adults must remain in the Golgi mixture for from eight to
fifteen days. Further treatment like No. 76.
No. 80. — The Cortex of the Cerebellum ; Golgi Staining* — Remove
the cerebellum from the cranium of a newborn guinea-pig (or a kitten
less than six weeks old) and treat it according to the method given
in No. 76. The staining of the elements of the cerebellum is more
difficult to accomplish than of those of the cerebrum and the spinal cord.
Failures are frequent. The sections should be principally made vertically
to the axis of the convolutions. (For embedding, see Microtome
Technic.)
No. 81. — Hypophysis Cerebri. — Treat like No. 86.
No. 82.— Brain-sand, Acervulus Cerebri. — Tease the epiphysis in a
drop 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. Examine with the low power, without a cover-glass (Fig.
1 16) ; the granules are not always round, but often oval and dentated ;
occasionally the irregularity of the surface is indistinct, because they are
* For the application of the Cox-Golgi mixture see p. 43 and p. 207, remark *.
THE PERIPHERAL NERVOUS SYSTEM. 20O,
enveloped in concentrically arranged connective-tissue fibers. Push aside
the larger granules with a needle, cover a few of the smaller ones with a
cover-glass and treat with 2 or 3 drops of hydrochloric acid (p. 51).
Bubbles of gas develop and the sharp outlines of the granules disappear.
No. 83. — Corpuscula Amylacea. — Select the brains of elderly indi-
viduals. With a scalpel scrape the mesial surface — that directed toward
the third ventricle — of the optic thalamus 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. 117, a). They must not be confused
with drops of extruded myelin ($), which are always clear and have a
double contour. In addition there are found in such preparations
numerous red blood corpuscles, ependymal cells id), medullated nerve-
fibers varying in thickness, and ganglion-cells ; the latter are very pale
and often can be detected only by their pigmentation (/). Human
brains, even though not absolutely fresh, are still useful.
No. 84. — a. Spread out a piece 1 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.
b. Very pretty permanent preparations may be obtained as follows :
Carefully spread out a little piece of the plexus in salt solution ; if good
fields are visible with the low power, let the salt solution flow off and add
a few drops of Zenker's fluid (p. 21); then apply a cover-glass, at the
edge of which place a little more of the Zenker's fluid. After thirty
minutes displace this fluid by distilled water, and after another thirty
minutes the water by 50 per cent, alcohol to which a few drops of tinc-
ture of iodin have been added. In fifteen minutes take off the cover-
glass and transfer the now fixed preparation to a watch-glass with fresh
50 per cent, iodin-alcohol, to which, in case it becomes rapidly decolor-
ized, tincture of iodin is to be added. In from fifteen to thirty minutes
transfer the object to pure 70 per cent, alcohol, and after about twelve
hours stain it with hematoxylin and eosin (p. 38, 3 b) and mount in damar
(p. 48).
No. 85. — Transverse Sections of Nerve-fiber Bimdles. — Treat a piece
of nerve, if possible the sciatic of man, that possesses a well-developed
endoneurium, according to the method given in No., 35. Place it for six
days in a o. 1 per cent, solution of chromic acid, then wash it for from
three to four hours in running water, and harden it in gradually-
strengthened alcohols. When the hardening is completed, cut thin sec-
tions with a sharp razor. It is advisable to embed the tissue in liver,
better still, in elder-pith or in the pith of the sunflower. For this pur-
pose make a hole in the dry elder-pith 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 glycerol. The length of time required for staining
varies greatly. The sections must be very carefully handled and pressure
with the cover-glass must be scrupulously avoided, lest the sections of
14
2IO
HISTOLOGY.
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, sur-
rounded by the yellow medulla, which is enclosed by the reddish neuri-
lemma. The cross-section of the nerve-fiber has been compared to a
picture of the sun [Sonnenbildehenfigur) (Fig. 136).
No. 86.- — -Spinal Ganglia. — These are very inaccessible. Therefore
remove the Gasserian ganglion from the depression in which it is lodged,
on the anterior surface of the petrous portion of the temporal bone, and
place it in about 100 c.c. of Miiller's fluid for fixation.* After four weeks
wash it for three hours in running water and harden it in 50 c.c. of grad-
ually-strengthened alcohols (p. 34). Cut the thinnest possible transverse
and longitudinal sections ; stain them thirty seconds in hematoxylin,
then from two to five minutes in eosin (p. 38, 3 b), and mount in damar.
Epineurium.
Perineurium.
Eudoneurium.
Fig. 136. — From a Transverse Section of a Peripheral {Spinal) Nerve of a Rabbit, x 50. In
the lower funiculus, on the right, some of the liansyerse sections of nei ve-fibers have fallen out,
others are lying on one side, as a consequence of pressure. In the rabbit the eudoneurium is only
slightly developed.
The ganglion-cells are pale red ; the axis-cylinder deep red ; the med-
ullary sheath brownish; the nuclei blue (Fig. 121 and Fig. 122). If
the section is not sufficiently thin, the large number of deeply-stained
nuclei will render it difficult to see the other structures. For this reason
it is better to stain thick sections in picrocarmine, two or three 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 (Fig. 122, x), that may easily lead the be-
ginner to confuse it with a multipolar ganglion-cell.
T-shaped branches may be seen in preparations of the spinal cord
treated after No. 76. In young embryo chicks the spinal ganglion-
cells are still bipolar ; unipolar cells are found in embryo chicks about
seventeen days old. Transition forms occur in chick embrvos between
* Fixation in Kleinenberg's picrosulfuiic acid also gives very good results.
THE PERIPHERAL NERVOUS SYSTEM. 2 I I
the ninth and fourteenth days and in embryo rabbits from 5 to 1 2 cm.
long. Staining with methylene blue (p. 40) is strongly recommended.
No. 87. — Sympathetic Ganglia. — Fix' and harden the large superior
cervical ganglion of the sympathetic nerve like No. 86. Here, too, on
account of the abundance of nuclei, nuclear staining is applicable only to
very thin sections. Treated according to the method given in No. 86, the
processes of the multipolar ganglion-cells are not rendered distinct. For
this purpose place the thinnest possible sections for twenty-four hours in
5 c.c. of nigrosin solution (prepared like the methyl-violet solution,
p. 25), then transfer them to 5 c.c. of absolute alcohol for five minutes,
and preserve in damar. The characteristic bundles of nonmedullated
nerve-fibers, cut obliquely and transversely, can' be recognized with the
low power ; also the ganglion-cells ; but to see their processes high
magnification and careful scrutiny are necessary (Fig. 124). In many
sections the processes of the ganglion-cells cannot be seen ; the latter
may be best exhibited according to the method given in No. 76, and a
suitable object is the cervical portion of a ten- or fifteen-day-old embryo
chick.
No. 88. — Simple Tactile -Cells ; Intra-epithelial Nerve-fibers ; Cells of
Langerhans ; Tactile Corpuscles. — Prepare a mixture of gold chlorid and
formic acid (p. 45), boil it and let it cool ; then cut from the volar side
of a freshly-amputated finger or toe (with scissors applied flatwise) sev-
eral small pieces of the epidermis and uppermost layers of the corium
about 5 mm. long and 1 mm. broad. Carefully remove any fat attached
to the under surface of the corium and place the pieces in the gold and
formic acid mixture for one hour, in 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 (p. 45), and
expose the whole to daylight (sunlight is unnecessary). In from twenty-
four to forty-eight hours the tissue becomes dark violet. It is now to be
hardened in 30 c.c. of gradually-strengthened alcohols. In eight days
the pieces may be embedded in liver and sectioned ; mount in damar.
The epidermis 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 excretory ducts of the coil-glands, and the nerves are dark
violet to black. For tactile cells the thinnest possible sections are neces-
sary. They may often be found near the excretory ducts of the coil-
glands. Care must be taken not to confuse them with nuclei of shrunken
epithelial cells (Fig. 126).
The intra-epithelial nerve-fibers appear as delicate filaments ; their
connection 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. 125).
The cells of Langerhans and the tactile corpuscles may be easily seen ;
in thick sections the tactile corpuscles are black (Fig. 125), in thin sec-
tions red-violet (Fig. 130).
N _ 89. — Compound Tactile Cells. — Cut the yellowish wax -like skin,
2 I 2 HISTOLOGY.
or cere, from the lateral edges of the upper beak of a duck or goose and
treat pieces I or 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 from eighteen to twenty-four hours ; then wash the pieces for one
hour in running water and transfer them to 20 c.c. of 90 per cent, alcohol.
In six hours the objects may be 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 can be readily seen, but the entrance of the
nerve-fiber is difficult to find (Fig. 1 27). In addition, Herbst's corpuscles
occur in the sections. If it is desired to stain the sections, use a nuclear
staining solution (p. 37).
No. 90. — Cylindrical End-bulbs. — With scissors and forceps cut out
pieces 1 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 few drops of the vitreous humor obtained
from the eye of the calf; 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 if 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 difficulty. The slide with the preparation is next to be placed in
a glass jar containing 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 epithelium ; it may be loosened without much
trouble and floats off in fine white shreds. If this is not done cautiously
the end-bulbs lying cjose beneath the epithelium may be torn off with it.
The more thoroughly the epithelium is removed the better. After the
pieces have lain four or five 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 are 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 many 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 (Fig. 128). Only the prac-
* In the calf some of the nerve-fibers are nonmedullated ; these are not recommended
for the investigation.
THE PERIPHERAL NERVOUS SYSTEM. 21 3
tised microscopist will have much success in finding them. Beginners
are advised not to attempt this preparation.
No. 91. — Lamellar Corpuscles. — These are best obtained from the
mesentery 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 tissue 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 corpus-
cles have been sufficiently isolated. Cover them with another drop oi
salt solution and a cover-glass. Pressure must be carefully avoided.
The corpuscle represented in figure 129 was of very small size.
With the high power one can distinctly see the nuclei of the cells
lining the capsules ; the oval nuclei of the inner bulb are often indistinct
and pale. If it is desired to preserve the preparation, treat it under the
cover-glass with 1 or 2 drops of 1 per cent, osmic acid and after the
medulla is blackened and the inner bulb has become brown displace the
acid with very dilute glycerol. Methylene-blue staining (p. 40) is rec-
ommended.
No. 92. — Motor Nerve-endings. — a. Terminal Ramifications. — Pre-
pare a mixture of 24 c.c. of 1 per cent, gold chlorid solution plus 6 c.c.
of formic acid, boil it and let it cool ; cut out small pieces 3 or 4 cm.
long of the intercostal muscles of a rabbit and treat them like No. 82 ;
after the dark-violet pieces have lain from three to six days in 70 per
cent, alcohol tease a muscle-bundle about 5 mm. broad in a drop of
dilute glycerol 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. 131). The addition of another drop of acetic or
formic acid often renders the elements more distinct.
b. Nuclei 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 six 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 magnification (50 diameters), the anastomoses of the nerve-
bundles, as well as the blood-vessels, that are easily recognized by the
transversely placed nuclei of their smooth muscle-fibers, can be seen. On
account of the large number of sharply contoured nuclei belonging to
the muscles and the intramuscular connective 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 ceases abruptly and loses itself in a
group of nuclei ; these are the nuclei of the motor plate, the other
214 HISTOLOGY.
details of which are not distinctly visible. The cross-striation ot the
muscle-fibers, which are very. pale, is often indistinct (Fig. 132).
No. gi.—The Suprarenal Bodies; Topographic View. — Fix the
entire suprarenal body of a child in 200 c.c. of o. 1 per cent, chromic
acid for eight days and harden it in 150 c.c. of gradually-strengthened
alcohols ; mount unstained sections in dilute glycerol (Fig. 133 A).
No. 94. — Elements of the Suprarenal Body. — Tea?e portions of the
fresh organ in a drop of salt solution. The elements are very delicate
and therefore injured cells are of frequent occurrence.
No. 95 — For the study of the minute structure of the suprarenal
bodies, place 2 cm. cubes of the fresh organ in 100 c.c. of picrosulfu'ric
acid and after from twelve to twenty-four hours harden in an equal quan-
tity of gradually-strengthened alcohols ; cut thin sections, stain them
in Hansen's hematoxylin, and mount in damar (Fig. 133 B and Fig.
134). For the exhibition of the nerves, treatment with the Golgi mix-
ture for from six to eight days and with the 0.75 per cent, silver solution
for from two to three days, or several repetitions of this procedure, is
recommended.
VI. THE DIGESTIVE ORGANS.
Mucous Membranes.
The inner surface of the alimentary tract, of the respiratory organs,
of certain parts of the genito-urinary system, and of some of the organs
of special sense are covered by a soft, moist membrane, the mucous mem-
brane or tunica mucosa. It is composed of a soft epithelium and of
connective-tissue. The latter, immediately under the epithelium, is
usually specialized and condensed to form a structureless membrane,
the membrana propria or basement membrane ; beneath this follows the
tunica propria, which passes by a gradual transition into the subjacent,
loose-textured tunica submucosa, that in turn connects the mucous mem-
brane with the underlying structures, for example, muscles or bones.
The epithelium of the glands is derived directly from the epithelial ele-
ments of the mucous membrane (see p. 86).
A. HEADGUT.
the oral cavity.
The Mucous Membrane of the Oral Cavity.
The mucous membrane of the mouth consists of three parts : (1)
the epithelium, (2) the tunica propria, and (3) the submucosa (Fig. 137).
The epithelium is typical stratified squamous epithelium. The tunica
THE DIGESTIVE ORGANS.
215
propria is formed of interlacing connective-tissue bundles richly inter-
spersed with elastic fibers. The bundles of the uppermost strata are
very slender and form a compact, apparently almost homogeneous felt-
work. The surface of the tunica propria is beset with numerous usually
simple papillae (Fig. 137, 1), the height of which varies greatly in the
separate regions of the oral cavity. The highest papillae (0.5 mm.)
occur at the edge of the lips and on the gums. The tunica propria
passes without sharp limits into the subniucosa, which consists of some-
what thicker bundles of connective tissue, among which the elastic fibers
are not numerous. The submucosa is in general loosely attached to the
Ep
§ J Tunica propria.
'" M*lW
£%s
Muscles.
Fig 137 —Vertical Section through the Mucous Membrane of the Lip of Adult Man. X 3°-
1 Papilla- 2 excretory duct; the lumen is cut at only one point; 3, accessory gland ; 4, a branch of
the excretory duct in transverse section ; 5, gland-follicles grouped into lobules by connective tissue ;
6, a gland-tubule in transverse section. Technic No. 97.
walls of the oral cavity ; only on the gums and on the hard palate is it
firmer and here intimately united to the periosteum. It contains the
glands of the mucous membrane ; these are, with the exception of the
sebaceous glands occasionally found at the edges of the lips, branched
tubular mucous glands from I to 5 mm. in size. The main excretory
duct (Fig. 137, 2) is somewhat expanded at its lower end and in the
greater part of its length is lined with stratified scaly epithelium ; the
branches and twigs into which it divides and subdivides are lined with
stratified and simple columnar epithelium respectively. Not infrequently
the main excretory duct receives the excretory tubes of small accessory
2l6 HISTOLOGY.
mucous glands (Fig. 137, 2, 3). The minute structure of the gland-
tubules is the same as that of the submaxillary gland. The numerous
blood-vessels of the oral mucous membrane are arranged in two networks,
situated in two horizontal planes, of which the coarser lies in the submu-
cosa, the other finer in the tunica propria. From the latter terminal
capillary loops ascend into the papillae. The lymph-vessels similarly 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 submu-
cosa, from which many ramifying fibers ascend to the tunica propria.
Here they terminate in end-bulbs or they lose their medullary sheath
and as nonmedullated nerve-fibers penetrate into the epithelium and
after repeated division terminate in free endings.
The Teeth.
The teeth of man and the higher animals are solid structures, which
enclose in their interior a cavity, the pulp-cavity , filled with a soft mass,
the dentinal pulp. The portion of the tooth within the alveolus or socket
is called the fang, the exposed portion 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, (1) the dentine,
(2) the enamel with the enamel cuticle, and (3) the cementum. The dis-
position of these parts is as follows : the dentine, which contributes the
chief bulk of the tooth and determines its form, encloses the pulp-
cavity except at the apex of the fang where a narrow nutrient canal
admits the nerves and the 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. 138).
The dentine or ivory (substantia eburnea) is a white, opaque mass,
harder than bone. It consists of an apparently homogeneous ground-
substance containing very fine fibrillar, which is pierced by numerous
minute channels, the dentinal tubules. The latter begin with a diameter
of about 2.5 //at the inner surface of the dentine, describe an S-shaped
curve and then, steadily decreasing in caliber, proceed in a slightly
wavy course, radially directed toward the outer surface of the dentine ;
there they either terminate at the juncture of the dentine and enamel in
tapering ends or they form a loop and turn into a neighboring tubule.
During their entire course they send off numerous lateral branches, which
establish communication with neighboring canaliculi. The matrix imme-
diately surrounding the dentinal tubules is especially dense and forms
the so-called dentinal sheaths. The lumen of the dentinal tubules is
THE DIGESTIVE ORGANS.
217
occupied by the dentinal fibers. At the peripheral parts of the dentine
are the interglobular spaces, irregular spaces varying in size and filled
with a soft mass ; into these spaces the dentine juts in the form of usually
hemispherical protuberances, the dentinal globules (Fig. 139 and Fig.
140). At the neck and in the fang are many very small interglobular
spaces ; they form the so-called granule stratum lying immediately
beneath the cementum.
Enamel.
Pulp-cavity.
Fig. 138.— Longitudinal Section of a Human Tooth. X 4. Technic No. 98.
The enamel (substantia adamantina) is even harder than the dentine.
It is exclusively composed of long, hexagonal, homogeneous fibers,*
from 3 to 6 p. in thickness, the enamel prisms (Fig. 141), which are
firmly united with one another by a scanty amount of irriguous cement-
substance. They extend radially, with many undulations, from the sur-
* The transverse bands do not appear until after treatment with reagents.
211
HISTOLOGY.
face of the dentine to the free surface of the enarnei, which is covered by
a very thin but very resistant membrane, the enamel cuticle.
The cementiim (substantia ossea) coincides in its structure with that
of bone. It contains many Sharpey's fibers. Haversian canals are
found only in the cementum of older individuals ; stratification in lamel-
lae is seldom well defined. Bone corpuscles are absent near the neck.
Enamel prisms.
Dentine.
Enamel.
Fig. 139.— From a Longitudinal Section' of thk Lat-
eral Part of the Crown of a Human Molar
Tooth. X 240. 1, Dentinal tubules, extending for a
short distance into the enamel ; 2, dentinal globules
projecting into, 3, the interglobular spaces. Technic
No. 98.
Dentine
Cementum.
Fig. 140. — From a Longitudinal Sec-
tion of the Fang of a Human
Molar Tooth. X 240. 1, Dentinal
tubules interrupted by a granular stra-
tum, with many, 2, small interglobular
spaces; 3, bone corpuscles with many
processes. Technic No. 98.
/ >j
'')■'' '•■'?
%
Enamel prisms, Enamel prisms in trans-
isolated, verse section.
Fig. 141.— Enamel Prisms from the
Tooth of an Infant. Technic No. 100.
Fig. 142.— Six Odontoblasts with Dentinal
Fibers, /,- p, pulp processes. From the pulp of
an infant. X 240. Technic No. 99.
The space between the fang and the alveolus is occupied by the
richly innervated periosteum, which is firmly united to the cementum
by Sharpey^s fibers, which penetrate from the inferior maxilla through
the periosteum into the cementum. The uppermost portion of the peri-
osteum is called the circular dentinal ligament.
THE DIGESTIVE ORGANS.
219
The dentinal pulp is formed of a soft connective tissue containing
delicate fibers not united in bundles, the cellular elements of which, on
the surface toward the dentine, form a layer of elongated nucleated cells,
the odontoblasts ; these send out short processes, pulp processes (Fig.
142), that are connected with other elements in the pulp, and long pro-
cesses that extend into the dentinal tubules as the above-mentioned
dentinal fibers (Fig. 142,/"). Blood-vessels and nerves are limited to the
pulp of the tooth.
DEVELOPMENT OF THE TEETH.
The development of the teeth in man begins toward the close of the
second month of fetal life * and is first indicated by a linear proliferation
of the primitive epithelium of the oral cavity, which in the form of a con-
tinuous projection grows obliquely into the subjacent connective tissue.
Epithelium of the margin
of thejaw.
Dental bulbs. Dental furrow
Dental ridge.
A Papillae
Enamel organs. C
Fig. 143.— Schematic Representation of the Initial Processes in the Development of the
Teeth, showing the formation of three teeth. The anlage ol each anterior tooth is seen in section ;
the cut surface is stippled, k, Free edge of the dental ridge.
This projection, the dental ridge ("enamel germ") (Fig. 143 A), de-
velops on its lateral (labial) surface knob-like protuberances, the dental
bulbs (B), corresponding in number to the temporary teeth, while coin-
cidently in the surrounding mesoderm as many conical aggregations of
closely packed connective-tissue cells arise, the young dental papilla
(B) (tenth week). The latter advance obliquely from the labial side out
of the depths to the lingual side toward the surface, and are embraced
by the dental bulbs in such a manner that these form an epithelial cap
for the dental papilla?. Thus each bulb becomes an enamel organ.
Meanwhile the dental ridge has assumed a more nearly vertical posi-
tion (C). At about this time, too, a longitudinal groove on the margin
of the jaw is visible, the dental furrow, which exteriorly marks the
*That which at an earlier period (fortieth day) has been described as the anlage, is not
this alone, but includes the anlage of the labial furrow.
120
HISTOLOGY.
region from which the dental ridge grew into the depths. The time of
the appearance of the dental furrow varies ; frequently it is present in
the initial stages. It disappears later. The original broad attachment
Cartilaginous
" nasal septum.
Dental ridge
of upperjaw.
Epithelium of -
the oral cav-
ft ■- - i .O
V£- I-
Dental ridge
of lower jaw.
e
v>-.'flr v.
O
O
' Nasal cavity.
Anlage of the
upperjaw.
Oral cavity
Anlage of the
lower jaw.
Fig 144. — Frontal Section of the Head of an Embryo Sheet, 4 cm. lung. 15. Techuic No. 101.
' .-too
&-
-;'/
Epithelium \
' of oral mu-
cous mem-
fS
propria
lis :■„' J
v
raLEr
'.'.'■'-'
O
Papilla.
— Osseous trahecukv
ol lower ia\\ .
Lower lip, Orbicularis oris muscle in
transverse section.
Fig. 145.— Cross-section oe the Lower Jaw of a Human Embryo Four Months Old. X 42.
Techuic No. 101.
between the dental ridge and the enamel organ becomes diminished by
partial constriction and finally is reduced to a slender cord, the isthmus
(Fig. 143 D). Meanwhile the papilla and the enamel organ grow fur-
THE DIGESTIVE ORGANS. 22 1
ther into the depths, so that the free edge of the dental ridge does not
extend even to half the length of the enamel organ (Fig. 145 and Fig.
146).
At the same time the elements of the enamel organ undergo differ-
entiation. The inner layer ol cells, resting upon the papilla, develop
into tall columnar elements, the inner enamel cells (Fig". 146) ; their inner
surface is provided with a cuticular border. The peripheral cells (Fig.
146), steadily decrease in height (Fig. 147), until finally they are reduced
Thickened
epithelium
of the oral
mucous
membrane.
Outer enamel cells.
Enamel pulp.
Inner enamel cells.
"Vh
"Isthmus ofthe
bulb.
"Free edge of th
dental ridge.
-Papi
Fig. 146.— From a Cross-section of the Upper Jaw of a Human 1 Embryo Five Months Old.
X 42. Technic No. 101.
to thin plates, the outer enamel cells ; the cells between the inner and the
outer enamel cells, by an abundant increase of the intercellular substance,
become transformed into stellate, anastomosing elements and constitute
the enamel pulp (Fig. 146 and Fig. 147). At the point where the inner
enamel cells bend over into the layer of outer enamel cells, the enamel
oro-an prows further into the depths until it has reached the lowest ex-
trcmity of the anlage of the tooth. Thus, in a measure, the enamel organ
forms the matrix in which the tooth develops. The determination of the
[I ISTOLI IGY.
shape of the future tooth is the first function of the enamel organ ; the
second is the production of the enamel, which takes place only in that
portion of the layer of inner enamel cells enveloping the crown of the
Dental sack.
Outer layer. Inner la
Outer enamel cells.
Odontoblasts
Dental papilla ( fuLure
l>ulp)
Bloo%!
!# .''-. ! ©
1 ' • >'© Kj'K
(; > <-" ./ -.
: ®®®@j
c>
'69.''
1 /.Strife;:
Adenoid tissue ,-
of the tunica \
propria. '
Fig. 152.— From a Thin Section of a Lingual Follicle of Man. X 42°. On the left the epithelium
is free from leucocytes, on the right many leucocytes are wandering through. In this way the epithe-
lium is undermined and smaller or larger fragments of it are seen lying between the broad passages
made by the leucocytes. Technic No. 102.
The gland-cells of the one kind produce a mucigenous secretion (mucin) ;
they 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 ; they are called serous glands.
The mucous glands occur along the edges and in larger numbers at
the root of the tongue, where not infrequently their excretory ducts open
228
HISTOLOGY.
into the crypts of the lymph-follicles. The ducts are lined by columnar
epithelium, which occasionally is ciliated. The walls of the tubules consist
of a structureless membrana propria and of gland-
cells ; the latter are columnar elements possessing a
firm cell-membrane and vary in appearance with
their periodic functional state. The exhausted cell
is smaller, the transverse-oval-nucleus near the base
of the cell (Fig. 154, /, b) ; the cell loaded with se-
cretion is broader, the nucleus is pressed flat against
the cell-wall (Fig. 154, /, c, and II). Generally the
same mucous gland, often the same tubule, exhibits
different phases of secretion ; however, demilunes
are not formed here, because the rigid membrane
of the gland-cells resists the pressure exerted by
neighboring cells.* The anterior lingual gland
{glandula lingualis anterior) (Nuhn) occurring in
the tip of the tongue also is a mucous gland.
The serous glands are limited to the vicinity of the papillae vallatse
and foliatae ; the excretory ducts open into the furrows between the
papilla and the wall (Fig. 1 50), and are lined by simple or stratified,
not infrequently ciliated, columnar epithelium. The small tubules con-
sist of a delicate membrana propria and short cylindrical or conical cells,
Fig. 153. — From a Section
through the root of
the Tongue of a
Mouse. X90. A serous
gland ; the tubular sys-
tem silvered by Golgi's
"black reaction"; the
tubular structure is eas-
ily recognized. Technic
No. 125.
Rabbit.
It.
T r,|
- /
^ / \
w
~:.-f*
Mucous glands. Serous glands.
Fig. 154. — From Sections of Lingual Glands. /. Tubule in ci'oss-secuon with, b, gland-cells empt-
or secretion; c, gland-cells filled with secretion ; d, lumen. //. Tubule in cross-section, in which all
the cells are replete with secretion. ///. Cross-section of a mucous gland-tubule. IV. Several
tubules of a serous gland ; at d the very small lumen. /'. Tubules with d', a larger, and d, a smaller
lumen. All the sections are magnified 240 limes. Technic No, 102.
destitute of a membrane, that in man and the sheep exhibit two zones, an
inner dark zone beset with fine granules and an outer clear zone that
encloses the spherical nucleus f (Fig. 154, IV and V). The lumen of
the tubules, especially in animals, is very narrow.
*Only the lingual mucous glands of the cat exhibit demilunes.
-j- These differences can be demonstrated only by special methods and with high magnifica-
tion. They are not shown in figure 154. In the horse, pig, and cat the two zones are gener-
ally indistinct and in the rabbit are not present. Occasionally, between the serous tubules,
single mucous tubules with demilunes occur (p. 78).
THE DIGESTIVE ORGANS. 229
The blood-vessels of the mucous membrane of the tongue form net-
works disposed parallel to the surface, from which twigs ascend to all the
papillae up into the secondary papillae. 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 capillary networks around the gland-
tubules.
The lymph-vessels of the tongue are arranged in two sets ; a deep
set consisting 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 richly developed ; they form networks encircling the
lymph-nodules.
The nerves of the mucous membrane of the tongue, the glosso-
pharyngeal and the lingual branch of the fifth are furnished with small
groups of ganglion-cells along their course ; their endings behave partly
as in other portions of the oral mucous membrane, partly they enter into
intimate relation with the taste-buds.
THE SOFT PALATE AND THE PHARYNX.
The soft palate, on its anterior surface, is covered with a stratified
squamous epithelium ; the tunica propria is furnished with tall papillae
and separated by a continuous layer of thick elastic fibers from the sub-
mucosa. In the latter are found adipose tissue, cross-striped muscles,
and a powerful, well-guarded stratum of mucous glands, the bodies
of which often extend far into the muscles, while their long excretory
ducts are directed obliquely downward. The posterior surface of the
soft palate, upward for a distance from the free border, is clothed with
a mucous membrane containing no adipose tissue, but otherwise of
the same structure ; at a level varying individually this changes into
typical respiratory nasal mucous membrane with mixed glands (see
The Olfactory Organ) ; the latter occasionally may be traced to the
uvula.
The wall of the pharynx consists of three coats : a mucous, a mus-
cular, and a fibrous coat. The mucous membrane, consisting of stratified
squamous epithelium and a tunica propria with papillae, is sharply sepa-
rated from the muscular coat by a powerful layer of longitudinally-
disposed elastic fibers; this " elastic border-stratum " sends extensions
into the muscular coat that embrace the individual muscle-fibers and
downward toward the beginning of the esophagus it disappears ; up-
ward, too, the border-stratum diminishes in thickness, but where the
musculature is wanting it forms a dividing layer between the tunica pro-
23O HISTOLOGY.
pria and the submucosa * of the mucous membrane. Numerous tubular
branched simple glands, mucous glands of the structure of the lingual
mucous glands, lie beneath the elastic border-stratum ; their excretory
ducts are often surrounded by heaps of leucocytes. In the pharynx also
atrophic mucous glands occur. In the upper division of the pharynx
(pars nasalis) the epithelium changes into the stratified, ciliated columnar
variety, the lower limit of which is subject to considerable variation ; the
glands occurring here lie above the border-stratum and in structure coin-
cide with the glands of the respiratory nasal mucous membrane. Very
richly developed is the adenoid tissue. Between the pillars of the fauces
it forms conspicuous accumulations, one on each side, known as the pala-
tine tonsils (tonsilla palatind), which in respect to their structure in man
and many animals correspond to an aggregation of large lymph-nodules
like those of the root of the tongue (p. 226). 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. Many
mucous glands lie in the neighborhood of the tonsils. 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 structure with the palatine tonsils, excepting that the
lymphoid tissue is less sharply circumscribed. Here, too, many leuco-
cytes 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 domain of
macroscopic anatomy. The. fibrous tunic is a stout membrane composed
of a dense feltwork of fibro-elastic tissue. Blood-vessels, lymph-vessels,
and nerves are distributed in the same manner as in the oral mucous
membrane.
B. RUMPGUT.
the foregut.
The Esophagus.
The wall of the esophagus comprises a mucous, a muscular, and a
fibrous coat. The mucous coat is composed of a stratified squamous
epithelium, of a tunica propria beset with papilla, following this of a
* Passing upward the submucosa becomes greatly strengthened and as the basilar-pharyn-
geal fascia is attached to the base of the cranium.
THE DIGESTIVE ORGANS.
23I
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 contains small mucous
glands of the structure of the lingual mucous glands. Their excretory
duct; before its passage through the muscularis mucosa?, often is widened
ampulla-wise ; attached to it within the compass of the tunica propria is
a lymph-nodule. Their number fluctuates greatly individually ; as a rule
they are more numerous in the upper half of the esophagus. Not seldom
these glands, too, exhibit atrophying lobules, the tubules of which have
a wide lumen and low gland-cells. In the extreme lower end of the
esophagus, in a zone from one to four millimeters broad, the tunica pro-
pria contains branched tubular simple glands, with the excretory duct
often widened ampulla-shape. These " cardiac glands," in their micro-
Mucous coat.
Muscular coat.
Fibrous coat.
Fig. 155. — From a Cross-section of the Middle Third of the Human Esophagus. X 10. 1. Stratified
squamous epithelium. 2. Tunica propria. 3. Muscularis mucosas. 4. Submucosa. 5. Circular
muscles. 6. Longitudinal muscles, g, Blood-vessel. Technic No. 104.
scopic structure, resemble true gastric glands but are distinguished from
them by their profuse branching, as well as by the individual variation in
the presence or absence of the parietal cells. Groups of just such glands
lie laterally in the initial portion of the esophagus at the level between
the cricoid cartilage and the fifth tracheal ring ; their number, as that of
the cardiac glands, is subject -to great individual variation.
The muscular, tunic in the cervical portion of the esophagus con-
sists 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, in which the arrangement of the muscle-fibers is not everywhere
exactly transverse, and an outer longitudinal not continuous layer. The
fibrous coat consists of compact connective-tissue bundles interspersed
232
HISTOLOGY.
with numerous elastic fibers. The distribution of the blood-vessels,
lymph-vessels, and nerves is the same as in the pharynx. Between the
circular and longitudinal layers of the muscular coat the nerves form a
plexus, at the nodal points of which minute groups of ganglion-cells
occur (see plexus myentericus, p. 248).
The Stomach.
The wall of the stomach is from 2 to 3 mm. thick and comprises
three coats : a mucous, a muscular, and a serous or fibrous tunic.
The mucous coat, sharply contrasted with the white esophageal
mucous membrane by its
Epithelium, 'prftn,,^
il///// / /;r!M;Iii ,:| ;V,'fc,
fcfetelH
Wmw- iJwmM'lit
/Tunica propria.
Muscularis
mucosae.
Subn
/ Inner circular
I layer of muscle.
Muscularis.
reddish-gray color, consists
of an epithelium, a tunica
propria, a muscularis mu-
cosae, and a submucosa
(Fig. 156).
The epithelium is a
simple columnar epithe-
lium, the elements of which
produce a mucoid secretion.
Two zones can usually be
distinguished, an upper mu-
coid (Fig. 16, c), and a
lower protoplasmic (Fig.
16, p); the latter contains
the oval, round, or flattened
nucleus. The extent of the
mucoid zone varies consid-
erably with the functional
phase (cf. Fig. 16). The
epithelial elements often
very closely resemble gob-
let-cells. The tunica propria is composed of a mixture of fibrillar and re-
ticular connective tissue and of an extremely variable number of leuco-
cytes, 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 farther apart, the tunica propria is
conspicuously developed and not infrequently elevated in filamentous or
leaf-like villi.
[Outer longitud-
1 inal layer of
\ muscle.
Serosa. ""*--
Fig. 156.— Transverse Section of a Human Stomach. X 15-
The tunica propria contains glands standing so close to-
gether that its tissue is visible only at the base of the glands
toward the muscularis mucosae. Technic No. 105.
THE DIGESTIVE ORGANS. 233
Two kinds of gastric glands are recognized : fundus glands * (glan-
Epithelium of the surface.
x'v.
Tunica propria.
-«. |t :,i 4*/
Parietal-cells.
Chief-cells.
Leucocytes.
- Gastric pit.
Neck.
p^ mi, mi
Smooth muscle-fibers.
if. 1
W . ' V ^
Parietal-cell.
Fundus.
./>
//0
Fig. 157. — Vertical Section of the Mucous Membrane of the Cardiac End of a Human
Stomach. X 220. Technic No. 108.
*In the earlier text-books the fundus glands were called peptic glands, a. name based
upon a function of the glands now called into question.
9 3 I
HISTOLOGY.
dulae gastricae proprise), chiefly situated in the middle and cardiac thirds of
the stomach, and pyloric glands, confined to the small pyloric region. Both
are simple tubular glands, often branched, especially in the pyloric
Portion ofa parietal-cell.
Chief-cell.
Parietal-cell adjoining a latera
branch of the lumen.
Fig. 158.— Transverse Section of a Human Fundus Gland. X 240. Technic No. roS.
region, which open singly or in groups into minute, pit-like depressions,
the gastric pits (foveolse gastric^), in the mucous membrane of the free
" Tunica propria,
with glands.
I Muscularis
I niucoste.
Fig. 159,— Cross-section through the Mucous Membrane of the Fundus of the Stomach oi ; a
Mouse (during Digestion). 234. hi the gland on the right the entire system of canaliculi, in
the other two only a portion of the same, is silvered. The "baskets" formed by the secretory
capillaries can be distinguished. Technic No. 125,
surface. The portion of the gland adjoining these depressions is called
the neck, the following portion the body } and the blind end the fmidus
THE DIGESTIVE ORGANS. 235
(Fig. 157). Each gland consists of a membrana propria and of gland-
cells.
The fundus glands contain two kinds of cells, chief- or central-cells
and parietal- or acid-cells* The former are clear, cubical, or short col-
umnar cells, with a granular protoplasm surrounding a spherical nucleus.
The chief-cells are very unstable. The parietal-cells are usually con-
siderably larger, darker, and of a rounded or triangular form ; their
finely granular protoplasm envelops a round nucleus. The parietal-cells
are marked by their affinity for anilin dyes, with which they react in-
tensely. The two kinds of cells are not equally distributed ; the chief-
cells form the principal portion of the gland-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 extending between the chief-cells from the lumen to the
parietal-cells (Fig. 158). This lateral canal is the only one of the system
of minute canaliculi belonging to the parietal-cells (but not to the chief-
cells) that can be seen in ordinary preparations. By the aid of Golgi's
reaction, which also " blackens" secretion, it may be seen that passing
from the axial or chief lumen of the fundus glands are transverse canaliculi,
that divide and either terminate in free branches or anastomose with one
another and form a narrow-meshed network of "secretory capillaries,"
that surrounds each parietal-cell like a basket or spreads out within the
cell itself. (Fig. 20 and Fig. 159.) The secretion discharged from all
sides of the cell passes into the secretory capillaries, then into one or
more short lateral canals, and finally into the lumen of the gland.
The pyloric glands are furnished almost throughout with columnar
cells f containing a spherical nucleus situated near the base of the cell,
which in the intermediate zone, that is, the border zone between the
pyloric and the fundus mucous membrane, very closely resemble the
chief-cells, to which they have been compared.
The foregoing description applies to the stomach as it appears when
fasting ; during digestion the parietal-cells are larger, the chief-cells, as
*The assertion upheld on various sides that the chief- and the parietal-cells are different
functional appearances of one kind of cells and 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.
fin man isolated parietal-cells are found ; in animals, e. g., the dog, a few dark conical
cells occur, that owe their appearance to the compression exerted by neighboring cells.
?36
HISTOLOGY.
well as the cells of the pyloric glands, are darker, the nuclei of the latter
are pushed nearer to the middle of the cell, and the secretory capillaries
expanded with increased contents are wider than in the fasting organ.
Gastric pits.
'H
ii-* 1
:.$
Epithelium of the
surface cut ob-
liquely, so that it
appears to be
stratified.
Tunica propria.
Pyloric gland.
Portions of pyloric
glands.
m
Solitary follicle.
vs.
- Muscnlaris
mucosas.
Fig. 160.— Vertical Section of the Human Pyloric Mucin's Membrane. X 9<>- Technic No. 10S b.
The muscidaris mucosic consists of smooth muscle-fibers arranged in
two or three layers superposed in different directions, from which single
strands branch off and ascend vertically between the gland-tubules (Fig.
i 57)-
THE DIGESTIVE ORGANS. 237
The submucosa is composed of loosely united connective-tissue
bundles and elastic fibers and occasionally contains small clusters of
fat-cells.
The muscular coat : it is only in the pyloric region that two sepa-
rate layers of smooth muscle-fibers can be distinguished, 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 complicated
owing to the extension of the muscular strata of the esophagus to the
stomach, as well as to the curving of the organ that ensues in the course
of development ; sections exhibit bundles of fibers extending in every
possible direction (Fig. I 56).
The serous coat will be described with the peritoneum.
For the vessels and nerves see p. 245 and p. 247.
the midgut.
The Duodenum and the Small Intestine.
The wall of the midgut, like that of the stomach, is composed of
three tunics, a mucous, a muscular, and a serous.
The mucosa is thrown into circular folds, the plica circulares, or
valvulae conniventes (Kerkring), well marked in the upper part of the
small intestine, the object of which is to increase 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 the minute elevations and
depressions of the mucous membrane. The former, the villi, are present
only in the duodenum and the small intestine, in the large intestine of
man they are wanting ; they are processes about one mm. high, in the
duodenum of leaf-like, in the remainder of the small intestine of cylindri-
cal form.* The depressions begin at the pylorus and are found through-
out the whole length of the intestine. They exist in their most primitive
form in fishes and originate in longitudinal parallel folds of the mucous
membrane connected by small transverse folds. In vertical sections these
shallow depressions appear as short, wide sacks, and are called crypts.
In mammals the crypts are deeper, their lumen narrower, and 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
"""Toward the lower extremity of the small intestine the villi gradually diminish in height
and bulk, at the end of the ileum they are low, stand at greater intervals, and finally on the sur-
face of the ileo-cecal valve directed toward the large intestine they entirely disappear.
238 HISTOLOGY.
lining them produced a specific secretion, which is not the case.*
Nevertheless, the name intestinal glands (Lieberkiihn) has been retained.
The glands of the duodenum and the small intestine are from o. 1 to 0.3
mm. long.
The mucous membrane consists of an epithelium, a tunica propria, a
muscularis mucosae, and a submucosa. The epithelium, which clothes
the entire free surface, envelops the villi and lines the crypts, is a simple
columnar epithelium, the elements of which in their mature condition
Epilhe-
ium.
Wl'( Af
Circular muscular •—.
layer. ___
Longitudinal mus-
cular la\ 1 r r~
Si 1 osa. pt- — '
Fig. 161. — Longitudinal Skciion of the Jejunum of Adult Man. ■; 16. The circular fold (plica
circularis) on the right supports two small solitary nodules, that do not extend into the submucosa
and of winch the left exhibits a germinal center, X. The epithelium is slightly loosened from
the comiective-tissue core of many of the villi, so that a clear space, XX, exists between the two.
The isolated bodies lying near the villi (more numerous to the left of the plicae circulares) are
partial sections of villi that were bent, therefore not cut through their entire length. Technic No. in,
consist of a granular protoplasm containing numerous resorbed fat-
particles, a usually oval nucleus, and a cell-membrane (?) On the free sur-
face of the cells there is a sometimes homogeneous, sometimes finely-
striated cuticular border characteristic of the intestinal epithelium (cf.
p. 69).
""-The granular cells occurring in the depth of the crypts are young goblet-cells; the
.nannies are the precursors of the mucin (cf. p. 72).
THE DIGESTIVE ORGAN'S.
239
The regeneration of the epithelium takes place only in the intestinal
crypts, 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 epithelial 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 ;
the)' possess an elliptical, not infrequently a chalice-like form ; the upper
Tangential sections t Artifacts.
of villi. , ■
&T
l-l "%
§ 3
Epithelium.
Tunica
propria. " £3
Muscularis
mucosas.
Submucosa.
Intestinal glands.
Oblique sections of intestinal glands.
Fig. 162. — Section of the Mucous Memriunh of the Jejunum of Adult Man So The empty
space, a, between the tunica propria and the epithelium of the villi is an artificial product, the result
of the shrinking 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, b, at its apex. The goblet-cells have been drawn on one side of the
villus to the right. Technic No. 1 1 1 .
portion, that directed toward the surface of the intestine, undergoes
different degrees of distention as the protoplasm is transformed into
mucus, the nucleus with the remainder of the unaltered protoplasm lies
at the base of the cell ; a cuticular border is wanting, in place of which
a sharply-defined circular orifice is found, through which the mucus is
poured out on the surface (Fig. 163 A). The goblet-cells are derived
from the ordinary epithelial cells of the intestine. In proper conditions
240
HISTOLOGY.
each young intestinal epithelial cell may assume the functions of a goblet-
cell * and produce mucin.
The separate phases of secretion appear in regular sequence and so
that the final phases are always to be seen on the apices of the villi or
r^
5^1
t)
T i
B
Fig. 163.— Intkstinal Epithelium. X 560. A. Isolated goblet-cells of a rabbit, x. Escaping mucus*
Technic No. 110 b. B. From a section of the mucous membrane of the human intestine, b, A goblet-
cell between columnar cells. Technic No. in.
Epithelium.
Tunica propria.
Portion-of a capillary
blood-vessel.
Top-plate.
Nucleus of a wandering
leucocyte.
Tangential section of a
goblet-cell.
Mucoid zone of a gob-
let-cell.
Nucleus of a smooth muscle-fiber. Lacteal or central space.
Fig. 164.— Longitudinal Section through the Apex of the Villus ok a Dog. '< 360. The goblet-
cells contain the less mucus the nearer they lit: to the summit of the villus. Technic No. 112.
near the upper surface of the mucous membrane, the initial phases in the
intestinal crypts (Fig. 164).
*In regard to the mode in which the goblet-cells produce and discharge secretion, see p. 73.
THE DIGESTIVE ORGANS.
241
Between the epithelial cells migratory leucocytes from the underly-
ing tunica propria are found in varying number.
The tunica propria forms the bodies of the villi and fills the spaces
between the intestinal glands, at the blind end of which it is arranged in
a thin stratum. It consists chiefly of reticular and fibrillar connective
tissue intermingled with elastic fibers, and contains a widely varying
quantity of leucocytes (see The Peripheral Lymph-nodules, page 130).
The muscularis imicosce consists of an inner circular and an outer
longitudinal layer of smooth muscle-fibers. Fibers' derived from the
muscularis mucosae extend within each villus nearly to its apex. Their
contraction effects a shortening of the villus (cf. Technic No. 1 10).
Villi.
*7
Intestinal crypts
Duodenal glands. "
: [ j \^ Epithelium.
Tunica propria.
,' lint iA) 7lg K
Mm
(':
Ganglion-cells of the plexus — ;
myentericus.
f
LmJ
■ Muscularis mucosae.
Submucosa.
Circular muscular
layer.
Longitudinal mus-
cular layer.
■ Mucosa.
Muscularis.
Fig. 165.— Longitudinal Section through the Duodenum of a Cat. x 30. The epithelium has
become loosened from the connective tissue of the villus on the extreme left. The two villi at the
extreme right are cut obliquely. The epithelium has fallen from the middle villus, so that the con-
nective-tissue core lies exposed. The serosa is represented by a line beneath the longitudinal layer
of the muscular coat. Technic No. 109.
The submucosa consists of loose fibrous connective tissue with elastic
fibers and in the upper half of the duodenum contains branched simple
tubular glands, the duodenal glands (Brunner), from 0.2 to 3.4 mm. in
size. The excretory ducts of these glands are clothed with columnar
cells, pierce the muscularis mucosas, and run in the tunica propria
parallel with the intestinal crypts. The walls of the tubules are formed
of columnar gland-cells and a structureless membrana propria.
The muscular layer of the intestine consists of an inner robust circu-
lar and an outer thinner longitudinal stratum of smooth muscle-fibers.
For the structure of the serosa see "The Peritoneum," page 264.
16
2 A~-
HISTOLOGY.
ENDGUT.
The Large Intestine.
The wall of the large intestine likewise consists of a mucous, a
muscular, and a serous coat.
The mucous coat is smooth, villi are wanting, and the glands are
twice as long (0.4 to 0.6 mm.) as those of the small intestine. The
epithelium, tunica propria, and muscularis mucosa? are the same as those
Glands.
' S '%r\ J£L— Epithe-
'&"v.'S&r ilum -
Tunica
pro-
pria.
Fat-cells.
Solitary nodule with germinal center.
Fig. 166.— Vertical Section of the Mucous Membrane of the Descending Colon qf Man.
X80. Compare the length of the glands with those of the small intestine (Fig. i6z), that are from
the same individual and drawn under the same magnification. Technic No. 114.
of the small intestine, with which they also agree in their microscopic
structure and in the regeneration of the epithelium. The glands contain
a relatively large number of goblet-cells.*
* The reason for this lies in the fact that the young epithelial cells originating in the
glands of the small intestine move more rapidly to the surface ; for the superficies x>{ the small
intestine, so greatly augmented by the villi, requires a larger reparative supply to' replace the
cells perishing there ; the elaboration of mucus often does not take place within the crypts, but
first begins in the cells on the villi. In the large intestine, where the villi are absent, the transit
to the surface takes place slowly and the cells have time to produce secretion during their
sojourn in the crypts. It was this that gave rise to the erroneous impression that the small intes-
tine yielded a serous fluid, while the large intestine yielded mucus.
THE DIGESTIVE ORGANS. 243
The muscular coat of the large intestine consists of an inner annu-
lar and an outer longitudinal layer of muscle ; the latter is well-devel-
oped only within the compass of the taenia or bands, being extremely
thin in the intervals. The serosa agrees in its minute structure with that
of the small intestine.
The vermiform process of man, characterized by a large number of
round, in old persons flat, lymph-nodules (see below), is in many cases
— 25 percent. — partially obliterated, and this although' with advanced
age, in 50' per cent, of persons over 60 years, it augments in bulk. The
obliteration is not the result of pathologic processes, but the effect of
also elsewhere familiar involution or kataplasia. Epithelium and glands
perish, lymph-nodules disappear, and the tunica propria is transformed
into an axial connective-tissue strand, that is enclosed in the unaltered
submucosa and muscularis. These post-embryonal processes must not
be confused with the kataplastic changes in the intestinal glands occurring
from the 5th to the 6th embryonal month, which so far have been ob-
served only in man.
The Rectum.
In arrangement and structure the rectum in general agrees with the
large intestine, but is distinguished by its longer glands (0.7 mm.). At
the upper end of the columnar rectales begins the transition of the mucous
membrane into the skin ; instead of the simple cylindrical epithelium, a
thick stratified squamous epithelium appears, which covers a tunica pro-
pria with papillae containing blood-vessels. The intestinal glands may
be traced for a short distance into the territory of the stratified squamous
epithelium, but farther on they are wholly wanting. The columnar rectales
contain smooth muscle-fibers.
The Lymph-nodules of the Stomach and the Intestines'.
It has been previously mentioned that the tunica propria of the
mucous membrane contains leucocytes or lymph cells in variable num-
bers, occurring either as diffuse adenoid tissue or as circumscribed
masses from 0.5 to 2 mm. in size. The latter are lymph-nodules, which
occur either singly as the solitary nodules or in groups as the agminated
nodules.
The solitary nodules (" solitary follicles ") vary greatly in number
in the gastric mucous membrane, they are more numerous in the intes-
tines. They usually possess an oval form and in the beginning of their
development always lie in the tunica propria,* close under the epithelium,
*This is also their usual seat in the human small intestine, while in the large intestine
they extend into the submucosa (cf. Fig. 161 with Fig. 166).
244
HISTOLOGY.
with their base directed toward the muscularis mucosae. With advancing
growth (in cats at birth) they break through the muscularis mucosae
and expand in the submucosa, where the loose tissue offers but little-
resistance. The part of the nodule lying in the submucosa has a
Intestinal glands.
Submucosa.
W//jk*
Muscularis
mucosa.
- 2»Fv
Lymph-1
Longitudinal
'a.-\ er
Fig. 167. — Transverse Section of a Patch of Peyer of the Small Intestine of a Cat. The
crests of four nodules were not within the plane of the section. io. Technic No. 113.
Epitheliun
w
I uuica propi la.
Fig, 168. — From a Section of the Small Intestine of a Seven-day-old Kitten. \ 250. Crest
of a solitary follicle. The epithelium on the left contains many wandering leucocytes. The epithe-
lium on the right contains but three leucocytes. Technic No. in.
spherical outline and soon becomes considerably larger than that within
the tunica propria. Therefore the completed solitary nodules are in
general pyriform, with the small end turned toward the epithelium.
Where the nodules are situated the villi are wanting and the crypts are
THE DIGESTIVE ORGANS. 245
pushed aside. The solitary nodules are composed of adenoid tissue and
usually contain a germinal center. The young leucocytes formed in
them in part pass into the neighboring lymph-vessels and in part
wander through the epithelium into the intestine. The columnar
epithelium covering the apex of the nodules contains wandering leuco-
cytes (Fig. 168).
The agminated nodules (patches of Peyer) are groups of from ten to
sixty nodules that lie side by side, never over one another, each of which
has the structure of a solitary nodule. Occasionally the outline of an
individual nodule is altered by the pressure of adjacent nodules (Fig.
167). They principally occur in the lower portion of the small intestine,
either isolated from one another or transformed into a mass of diffuse
adenoid tissue, in which case only the germinal centers can be distin-
guished. This is not infrequently the case in the vermiform process of
man.
The Blood-vessels of the Stomach and of the Intestines.
The blood-vessels of the stomach and of 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 in the large intestine the
entering arteries first give off small branches to the serosa, then pierce
the muscularis, which they supply, and then in the submucosa form a
network extending parallel to the surface. From this small twigs ascend
through the muscularis mucosas and in the tunica propria at the base of
the glands form another network parallel to the surface. Fine capillaries
(from 4.5 to 9 [i wide) arise from the latter, which form plexuses around
the glands and pass into wider capillaries (from 9 to 18 /-*), which latter
form a subepithelial plexus, that wreath-like lies about the mouths of the
glands. Venules take their origin from the wide capillaries, pass verti-
cally down between the gland-tubules and open into a venous plexus
lying parallel to the surface in the tunica propria ; in their further course
the veins run alongside the arteries. The veins arising from the venous
plexus in the submucosa are furnished with valves to the point where
they open into the collecting veins approaching the intestine along par-
allel paths. The remaining branches and the trunk of the portal vein are
without valves.
In the small intestine only the arteries supplying the crypts are dis-
tributed in the same manner as in the large intestine. The villi are
provided with one artery (several when the villi are broad), which lies
opposite the vein ; from the former capillaries arise that lie close under
the epithelium and, obliquely or vertically to the long axis of the villus,
246
HISTOLOGY.
pass into the veins.* The further course of the veins is the same as in
the large intestine.
The duodenal glands 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
penetrate to the center, which is then without blood-vessels (Fig. 169).
Villi.
Lymph-follicle.
Tunica propria.
Submucosa.
Circular muscles.
Longitudinal mus-
cles.
Vein.
Artery.
Fig. 169. — From a Cross-section of the Injected Small Intestine of a Rabbit. X 50. The lymph-
nodule is sectioned so that in the upper half the superficial capillary network is visible, in the lower
half the capillary loops occurring within the interior of the nodule. The section is thick and un-
stained, and the intestinal crypts cannot be distinguished. 1. The network of blood-vessels within
the muscularis; 2, within the submucosa; 3, within the tunica propria. Technic No. 116.
The Lymph -vessels of the Stomach and of the Intestines.
The lymph- (chyle) vessels of the stomach and of 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-vessels begin in the axes of the villi ; in cylin-
drical villi they are simple, in leaf-shaped villi multiple canals (from 27
to 36 /j. wide) closed at their upper ends, and represent the lacteal or
* The distribution is the same in the dog, but in the rabbit and the guinea-pig the arteries
going to the villi break up into fine branches that run to the base of the villus and then form a
capillary network that lies close under the epithelium (Fig. 169, a). At the summit of the
villus the capillaries open into a small venous trunk that in the course of its vertical descent
takes up the capillaries surrounding the mouths of the glands (Fig. 169, ?•).
THE DIGESTIVE ORGANS.
247
"central space " of the villus (Fig. 164). 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 horizontal plexus in the submucosa ;
the lymph-vessels proceeding from this network arc provided with
valves ; they penetrate 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
numerous lymph capillaries of both muscular layers. The vessels then
run beneath the serosa to the mesentery and pass onward between
its folds.
In certain localities the course of the lymph-vessels in the mucosa
is modified. The nodules of the patches of Peyer never contain lymph-
vessels. The}' 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-sinuses of the rabbit (p. 130, remark) are
nothing else than such immensely widened, flattened capillaries.
The Nerves of the Stomach and of the Intestines.
The numerous nerves, mainly consisting of gray fibers, form a plexus
Fig. 170.— A. Surface View of the Plexus Myentericus of an Infant. 50. g, Groups of gan-
glion-cells ; y, layer of circular muscle-fibers, recognized by their rod-shaped nuclei. Technic No.
117 a.
B. Surface View of the Plexus Submucosus of the Same Infant. X 50. jr, Groups of ganglion-
cells ; 6, blood-vessel shimmering through the overlying tissue. Technic No. 117 b.
beneath the serosa, then pierce the longitudinal layer of the muscular
tunic and between this and the circular layer are arranged in a conspicu-
248
HISTOLOGY.
ous network, the intramuscular ganglionic plexus {plexus my enter i ens')
(Auerbach) ; numerous groups * of multipolar ganglion-cells are found
along the course of the nerves, usually at the nodal points of the net-
work, the meshes of which are angular or elliptical. From this network
bundles of gray fibers are given off usually at right angles, part of which
supply the longitudinal and circular strata of the muscular tunic, part
of which pierce the latter tunic and enter the submucosa. In the
muscular 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 plexus, the plexus
submucosus (Meissner), the meshes of which are narrower and groups of
ganglion-cells smaller. From this spring numerous fibers which enter
the tunica propria and in part weave a nervous net about the glands,
in part enter the villi, where they terminate free in the parenchyma or
close beneath the epithelium, without connection with the epithelial cells. f
A network corresponding to the intramuscular ganglionic plexus
also occurs between the layers of the muscular coat of the esophagus.
Excretory duct.
The Salivary Glands.
The salivary glands are the submaxillary, sublingual, and parotid
glands, and the pancreas. They are com-
pound tubular glands, which elaborate either
a mucous or a richly albuminous serous
fluid, or both the mucous and the serous
secretion. Accordingly we distinguish :
(i) mucous salivary glands (sublingual in
man, the rabbit, dog, and cat ; submaxillary
in the dog and cat) ; (2) serous salivary
glands (the parotid in man, the rabbit, dog,
and cat ; submaxillary in the rabbit, and the
pancreas) ; (3) mixed salivary glands (sub-
maxillary in man, the ape and mouse).
The Sublingual Gland. — The tubular
system consists of an excretory duct, the
branches of which continue as very short
Traces of mu-
cous tubules.
Fig. 171. — Scheme of the Human
Sublingual Gland.
* The groups — small ganglia— behave like the sympathetic ganglia in general.
f Spindle-shaped or stellate elements have been described as nerve-cells of the intestinal
plexuses, the processes of which form a plexus surrounding the blood- and lymph-vessels.
They do not stand in any relation to the above-described plexuses, nor can any nerve-procesies
be distinguished on them, therefore their nature is still uncertain.
THE DIGESTIVE ORGANS.
249
mucous tubes ; these pass directly into convoluted terminal pieces, which
are characterized by their varying caliber. They are often evaginated
A demilune consisting
of eight empty cells.
Part of an excretory duct
Cross-section
of cells filled
with secre-
tion.
Connective
tissue.
Excretory duct.
Fig. 172. — Thin Section of the Sublingual Gland of Man. X 252. Technic No. 118.
(Fig. 171). Intercalated tubes are wanting (see p. 79). The excretory
duct, called the sublingual duct (Bartholini), and its larger branches are
constructed of a two-layered columnar
epithelium and fibro-elastic tissue. The
smaller branches, 0.05 mm. in thickness,
possess a simple columnar epithelium ;
they continue into the mucous tubules,
the low columnar epithelium of which
only in a few places exhibits the char-
acteristic striation. The terminal pieces
consist of a membrana propria and of
mucous cells. The membrana propria is
composed of stellate connective-tissue
cells (see p. 86) ; the empty mucous
cells occur in groups (Fig. 172), there-
fore the "demilunes" (see p. 78) are
very large. The connective tissue lying
between the tubules and the lobules is
rich in leucocytes.
The Submaxillary Gland.-
Secretory
tubules.
Fig. 173.-
-SCHEME OF THE HUMAN SUB-
MAXILLARY Gland.
-The tubular system is more differen-
:$o
HISTOLOGY.
tiated than that of the sublingual gland, since distinct mucous tubes
and intercalated ducts are present. The convoluted terminal pieces
Serous gland-cells.
Intercalated piece.
Mucous
gland-cells.
Salivary tube.
Fig. 174.— Section of the Submaxillary Gland of Adult Man. X 252. Technic No. 118.
are of two kinds ; wide and narrow pieces may be distinguished (Fig.
173). The excretory duct, called the submaxillary duct (Whartoni),
and its branches exhibit the same epithelium
as the sublingual gland, but differ in having
a layer of connective tissue rich in cells and
external to this a thin stratum of longitud-
inally-disposed muscle-fibers, which form a
special peculiarity of the submaxillary duct ;
the epithelial cells of the mucous salivary
tubes are distinguished by the characteristic
basal striation (Fig. 174) and contain a yellow
pigment. The intercalated tubes are clothed
with cubical cells and lead into terminal pieces
that are built either of serous gland-cells or
of mucous gland-cells with demilunes (Fig.
174).
The Parotid Gland. — The tubular system
is the most highly differentiated of all the
oral salivary glands ; the branches of the excretory duct pass into well-
Intercalated
-a Terminal
pieces.
Fig. 175.— Scheme of the Human
Parotid Gland.
THE DIGESTIVE ORGANS.
251
Fat-cells.
developed salivary tubes, that continue as long, narrow, intercalated
parts. The latter lead into narrow, convoluted end-pieces. The ex-
cretory duct, called the
parotid duct (Stenoni),
is distinguished by its
broad membrana propria
lying close beneath the
epithelium, but other-
wise is like that of the
•sublingual gland. The
tall columnar epithelial
cells of the salivary tubes
have distinct lengthwise
striations on their base,
the intercalated tubules
(Fig. 176) are clothed
with elongated, often
spindle-shaped, cells.
Finally, the terminal
pieces consist of a deli-
cate membrana propria
with stellate connective-
tissue cells and of cubical serous gland-cells ; in the empty state these
cells are small and dimly granular, in
the replete or loaded state larger and
somewhat clearer (cf. p. 73).
The Pancreas. — The tubular system
of the pancreas consists of an excretory
duct, the ramifications of which do not
lead into salivary or mucous tubes, —
these are wanting here — but directly
into very' long intercalated tubes, that
pass into convoluted terminal pieces.
The excretory ducts, the pancreatic duct
(Wirsungi) and the accessory pancreatic
duct (Santorini), are composed of a sim-
ple columnar epithelium and of connec-
tive tissue, which latter is denser be-
neath the epithelium, looser toward the
periphery. The main excretory duct
and its larger branches carry small mucous glands in their walls. The
Intercal-
ated
piece.
Fig. 176. — Section of the Parotid Gland of Adult Man.
X252. The very narrow lumina are entirely invisible in this
preparation. Technic No. 118.
Intercalated
pieces.
End-pieces.
Fig. 177. — Scheme of the Hu-
man Pancreas.
2 c ~>
HISTOLOGY.
columnar epithelial cells of the smaller branches steadily decrease in
height and finally become transformed into the flat cells,* disposed
parallel to the long axis, of the intercalated tubules.
Terminal piece (tan-
gential section).
Intercalated tubule(lon-
gitudinal section).
End-piece (halved ).
Intercalated tubule
(transverse section).
End-piece (halved).
Intercalated tubule.
Fig. 178. — A. Gi.and-Cki.ls from the Pancrf;as of a Cat. X 560. Above, groups of cells as they
usualy appear; below, two isolated cells. />' From a Cross-section of the Pancreas of an
Infant. > 240. Techuic No. 1 19.
The epithelium of the terminal pieces consists of short columnar
or conical cells, that in the zone directed toward the lumen contain
numerous highly refracting granules, " zymogen granules." They are
visible even in fresh preparations, with
relatively low magnification (Fig. i /S A);
the clearer peripheral zone of the cell
contains the round nucleus. The gran-
ular and clear divisions vary in extent
according to the functional state of the
cell. In the beginning of digestion the
granules vanish, while the clear zone
of the cell becomes larger. Subse-
quently, the granular division augments
to such a degree that it occupies nearly
the entire cell. In the fasting state the
two divisions are of equal size (cf. p.
72).
In glands treated by the method
of Golgi, the elaborated secretion often stains and entire stretches of
the tubular system appear blackened. The secretory capillaries going
Fig. 179 —Transverse Section of a
Gland-tubule of the Pancreas of
Necturus; showing zymogen gran-
ules. X400. — (Schaper.)
* Continuations of the epithelium of the intercalated tubules into the interior of the ter-
minal pieces form the so-called " centroacinal cells," which as squamous elements lie upon the
inner surface of the epithelial cells of the end-pieces.
THE DIGESTIVE ORGANS.
253
from the central lumen of the terminal pieces may then be seen
(Fig. 180 and Fig. 181) running between the gland-cells, not quite to
the membrana propria, and without anastomoses terminating in free
branches.* Their terminal ends possibly lie within the gland-cells (cf.
P- 78).
The blood-vessels of the salivary glands are very conspicuously
developed. The arterial stems, as a rule, run alongside the main excre-
tory duct, where they divide into numerous branches which pass between
the lobules and finally penetrate within the latter, break up into capillaries
and form close networks around the tubules. The capillaries lie in
Intercellular
secretory .
capillary.
P'ig. 180. — From a Section of the Pancreas of
Adult Man. X 320. Technic No. 125.
-.7 Central lumen.
Intercellular
secretory
capillary.
Crescent.
Fig. 181. — From a Section of the Submaxil-
lary Gland of a Dog. X 320. Technic
No. 125.
immediate proximity to the gland-cells (see also p. yy). The larger
veins follow the course of the arteries.
With regard to the lymph-vessels little is known with certainty.
Clefts between the lobules and the tubules have been described as
lymph-channels.
The salivary glands are profusely supplied with plexuses of medul-
lated and nonmedullated nerves, along the course of which microscopic
groups of ganglion-cells occur. The fine nonmedullated nerve-fibers
partly ramify in the walls of the blood-vessels, partly form an " epilem-
mal " plexus lying immediately upon the membrana propria of the
gland-tubules ; from this delicate filaments arise which pierce the mem-
brana propria and as " hypolemmal " fibers terminate in short, varicose,
simple or branched ends, which lie upon the gland-cells.
*Such secretory capillaries occur in the serous glands, therefore in the parotid, in the
pancreas, and in the serous portion of the submaxillary; further, in similar form in the demi-
lunes of the mucous glands and upon this basis rests the conception of the serous nature of
the cells of the demilunes (cf. p. 78).
^54
HISTOLOGY.
Tin-: Liver.
The tubular system of the liver consists of an excretory duct (the
hepatic duct) the ramifications of which pass into terminal pieces.
Separate divisions corresponding to the salivary tubes or to the interca-
lated pieces of the excretory system will not here be considered. The
liver is a compound tubular gland * ; that this structure is only with
difficult}' recognized rests upon the following peculiarities :
i. In the other glands f the terminal pieces are convoluted (Fig.
I 82), in the liver the}- are nearly straight (Fig. 183).
2. In the other glands the terminal pieces course in every possible
Terminal pieces
FIG. lS2. — SCHEME OF AN ORDINARY COMPOUND
Tubular Gland. In lohule 3 only the ramifi-
cations of the excretory duct, and not the end-
pieces, are sketched.
Capillaries.
Vein.
Fig. 183. — Schemk of the Liver. In lobule 1 only
the direction, in 2 only the branching, of the
terminal pieces is sketched ; in 3 only the ex-
cretory ducts are drawn.
direction and surround on all sides the ramifications of the excretory
duct ; hence the latter lie in the interior of the gland-lobules (p. 74).
In the liver the terminal pieces run in a definite direction, toward
the axis of the lobule ; all branches of the excretory duct lie external
to the gland-lobules (cf. Fig. 182 with Fig. 18}).
3. In the other glands the end-pieces terminate blindly, without
anastomosing (the testicle excepted), in the liver the end-pieces are freely
* In this form the organ persists apparently only in one vertebrate (myxine) ; in other
vertebrates it changes during embryonal life to a net like gland, by the union of its branched
tubules.
|- In the entire ensuing comparison, the compound tubular glands are meant.
THE DIGESTIVE ORGANS.
255
connected with one another and form a net (Fig. 183, 2). Hence the
term "end-piece" (as also the phrase "terminal piece" used syn-
onymously) is inadequate, for blind ends have not yet been with cer-
tainty established in the liver; instead of the name "end-piece," the
phrase "trabecular of hepatic cells" or "hepatic trabecular " will be
adopted in the description of the liver.
4. In other glands the arteries and veins together proceed with the
ramifications of the excretory duct and like these lie in part within the
lobule (Fig. 182, 3). In the liver the portal vein, which corresponds
to the artery of other glands, follows the branches of the excretory duct
and like these lies external to the lobule. But the veins course inde-
pendently of the portal vein ; even their origin lies in the interior of the
lobule (Fig. 183).
Gland-lumen (bile-
' capillary).
Gland-lumen. —
Blood-
vessels.
Fig. 184. — Scheme of a Segment of a Ter-
minal Piece of an Ordinary Tubular
Gland.
Blood-vessels.
Fig. 1.85. — Scheme of a Segment of a Ter-
minal Piece (Hepatic Trabecula) of the
Liver.
In addition to these relatively gross distinctions there are minute
differences.
5. In other glands the axiallumen of the terminal piece in cross-
section is surrounded by many gland-cells — six or more (Fig. 184);
in the liver by only two gland-cells (Fig. 185). This difference is con-
ditionated by the relative size of the gland-cells (hepatic cells), on the
one hand, and by the significant narrowness of the gland-lumen of the
liver, on the other hand ; two hepatic gland-cells are exactly enough to
circumscribe the lumen.
6. In other glands each gland-cell attains to contact with a blood-
vessel only on one side ; in the liver each hepatic cell has several sides
256
HISTOLOGY.
touching blood-vessels (Fig. 184 and Fig. 185), a circumstance likewise
brought about by the size of the hepatic cells.
All these peculiarities would not so greatly obscure the tubular
gland character of the liver were it not for the existence of a still greater
difference :
7. In other glands the cells of the terminal pieces are not in direct
contact with the cells of neighbor terminal pieces, they are always sepa-
rated by connective tissue, the membrana propria and so forth (cf. e. g.,
Fig. 19) ; in the liver the cells of neighboring hepatic trabecular come
into immediate contact on several sides and these contiguous surfaces
likewise embrace a gland-lumen ; which figure 186 may serve to eluci-
date. Cross-sections of four trabecular of liver cells are drawn. The
first, consisting of cells 1 and 2,
touches directly on the second,
that consists of the cells a and b.
1 and 2 enclose a gland-lumen
(I), likewise a and b. Between
the contiguous surfaces of 1 and
a there is also a lumen (II).
Thus the gland-cells of the liver,
not only on one surface but on
several surfaces, touch on lu-
mina ; these lumina may be
united with one another by lat-
eral branches that run between
the gland-cells and thereby form
actual meshes. The right half
of the figure shows such a
mesh ; it embraces the cross-section of a blood-vessel and may there-
fore be named vasozonal mesh, in contradistinction to meshes that girdle
a single liver cell and are called cytozonal meshes. The arrangement
by which the gland-cells of the liver are embraced by gland-lumina
proceeding from different sides also occurs with other gland- cells, for
example, the parietal cells of the gastric glands, that are surrounded by
an entire basket of secretory capillaries (Fig. 20) ; the gland-lumina of
the liver may be directly compared with the secretory capillaries of other
glands and named bile capillaries. But while in other glands the secre-
tory capillaries open into a larger axial chief lumen, such axial lumina
are wanting in the domain of the hepatic lobule ; the bile capillaries open
at the periphery of the lobule directly into the interlobular bile-ducts.
The microscopic structure of the liver. The main excretory duct, the
Blood capillaries.
Fig. 186.— Sect ion of a Rabbit's Liver. X 570. The
outlines were made with a camera lucida. The
dark nuclei of the blood capillaries and the different
shading of the cells of the hepatic trabeculse are
schematic. The section passes through the hepatic
trabeculsei/2 and a/b in such wise that the gland-
cells are halved; through the trabeculae 3/4 and
c/d exactly between two gland-cells. The cells
3, 4 and c, d exhibit their surface to the observer.
THE DIGESTIVE ORGANS.
257
,• Trabecule of
hepatic cells.
„^ Central vein.
hepatic duct, and its larger branches consist of a single stratum of colum-
nar epithelium, occasionally containing goblet-cells, and of fibrous con-
nective tissue separated into tunica propria and submucosa. The tunica
propria is the carrier of the glands of the bile-duct, chiefly short, pear-
shaped follicles lined with mucous gland-cells, and of isolated longitudi-
nally- and transversely-disposed plain muscle-fibers. The cystic duct,
the ductus clwledochus, and the gall-bladder exhibit the same structure ;
the tunica propria is elevated in minute anastomosing rugae and there is
a thin continuous layer of interlacing smooth muscle-fibers. The col-
umnar epithelial cells of the gall-bladder are distinguished by their
height (0.05 mm.) from those of the ductus choledochus (0.024 mm.).*
The branches arising from the further
division of the hepatic duct, the inter-
lobular bile-ducts, with decrease in
caliber exhibit diminishing thickness
of the wall ; the larger consist of
simple columnar epithelium and fibro-
elastic tissue, the smallest possess
only a structureless membrana pro-
pria and a simple layer of low epithe-
lial cells provided with a cuticular
border, which as they approach the
lobule annex themselves directly to
the true gland-cells. This transition
is very difficult to see and can be dis-
tinctly perceived only in sections in
which the bile-ducts have been in-,
jected or have been blackened by
Golgi's silver method.
The lobules of the liver (hepatic
lobules, also erroneously named acini)
can be seen with the unaided eye, on examining the outer surface or
a cut surface of the organ, as irregular polygonal areas, that sometimes
are distinct, as in the hog, sometimes ill-defined, as in man and the
majority of mammals. Their true form is somewhat like that of a prism
rounded above, transversely blunted below, having a height of 2 mm.
and a breadth of 1 mm. (Fig. 187). Close under the capsule of the
Interlobular vein. Hepatic duct.
Fig. 187. — Scheme of an Hepatic Lobule,
represented in transverse section below and,
by partial leveling, in longitudinal section
above. In the left half the blood-vessels are
drawn, in the right half only the cords of
hepatic cells. X 20.
* The vasa aberrantia are blind-ending bile-ducts running outside of the parenchyma of
the liver. They are chiefly found at the left border of the liver, at the portal fissure, and in the
vicinity of the vena cava. They represent the last remnants of liver tissue occurring at these
places in embryonal life.
17
■58
HISTOLOGY.
liver the lobules often are arranged with their apex looking toward the
surface and a section made parallel to the surface will pass through
the lobules transversely (Fig. 188) ; but in the interior of the liver the
lobules stand in various directions. Each lobule consists of hepatic
trabecular and blood-vessels and is separated from its neighbors by the
interlobular connective tissue, which supports the branches of the excre-
tory duct (the hepatic duct), the branches of the portal vein and the
hepatic artery, of the lymph-vessels and the nerves. The demarcation
of the lobules depends on the development of the interlobular connec-
tive tissue.
On examining a cross-section of a lobule of the liver with low
Central vei
bile-duct.
ar connective
ssue.
Central vein.
Fig. 188.— From a Horizontal Section of Human Liver. X 40. Three central veins, cut trans-
versely, represent each a center of as many hepatic lobules, that at the periphery are but slightly de-
fined from their neighbors. Below and to the right of the section the lobules are cut obliquely and
their boundaries cannot be distinguished. Technic No. 122.
magnification, the trabecular of hepatic cells may be recognized as cords
and small blades that extend from a small vein, the central vein, situated
in the axis of the lobule, spread radially toward the periphery, and by
means of lateral branches connect with neighbor trabecular (Fig. 187 and
Fig. 188). By the usual methods the gland lumina in these trabecular can-
not be seen ; only by injection of the tubular system through the hepatic
duct or by the method of Golgi, which blackens the bile, can they be
successfully demonstrated. It is evident that the lumen of the smallest
interlobular bile-duct continues directly into the hepatic lobule and
there lies in the axis of the hepatic trabecula. In longitudinal section
it is seen that the lumen runs zigzag and is beset with small lateral
True meshes.
THE DIGESTIVE ORGANS.
Lateral branch.
259
®~;*®"''
Blood capillaries.
Portion of a central vein.
Fig. 189. — From a Cross-section of a Human Hepatic Lobule. X 300. The boundaries of the cells
could not be seen in the preparation. The black dots are foreign matter due to precipitation of the
silver. Technic No. 125.
branches* which, where several trabeculse of liver cells are in direct
* These intercellular lateral branches
must not be confused with short lateral
twigs of the bile capillaries that terminate
in a minute knob - shape enlargement.
The knob corresponds to a small vacuole
occurring in the liver cell, which by means
of a delicate canal (the lateral twig) com-
municates with the bile capillary. Un-
doubtedly these knobs are transient forma-
tions, only occurring in connection with a
certain functional cycle, are drops of secre-
tion that pass from the hepatic cell into the
Bile capillaries
without knobs.
Bile capillaries
with knobs.
Fig. 190.— From a Section of the Liver of a Dog.
X 490. Technic No. 125.
260
HISTOLOGY.
contact, by union with other lateral branches may form true meshes *
(Fig. 189). All the lumina lying in the interior of the lobule are named
bile capillaries. The entire system of bile capillaries is freely united, not
only through the meshes, but also through anastomoses brought about
by the union of neighbor hepatic trabecular, and in thick sections appears
profusely branched and entirely independent of the trabecular. But thin
sections show that in the main point the bile capillaries behave exactly
as other gland lumina, namely that gland lumen (bile capillary) and
blood-vessel do not come into contact, f but between them is intercalated
a gland-cell or a portion of such a cell (see p. 77). This is most clearly
recognized in thin sections in which the vascular capillaries are cut trans-
versely (Fig. 191); in those it may also be plainly seen that the bile
capillaries run along the
surfaces, the vascular capil-
laries along the edges of
the hepatic cells ; still this
is not an invariable rule,
for bile capillaries are found
that also follow the corners
of the cells (Fig. 191, x),
a relation occurring notably
in man.
The gland-cells of the
liver, the liver cells, hepatic
cells, are irregular, polyhe-
dral structures, which con-
sist of a granular proto-
plasm and one or more nuclei ; a cell-membrane is wanting. % The pro-
Hepatic cell.
Bile
capillary.
Fig. 191. — Thin Section of the Liver of a Rabbit, with
Injected Bil"e capillaries. X 560- (The drawing is not
schematic.) Two of the hepatic cells are in contact wilh
four blood capillaries (1, 2, 3, 4). X. Bile capillary at the
edge of an hepatic cell.
capillary; the proof of this I detect herein, that entire areas of the canalicular system maybe
free from knobs, while in immediate proximity each canaliculus is beset with them (Fig. 190).
It is probable that the formations resembling the secretory capillaries of the parietal cells
found in the liver cells in obstruction of the biliary passages belong to this category.
*The number of meshes is by no means so large as one might infer from the examina-
tion of not very thin sections. Very frequently meshes are simulated, by the canaliculi with
their lateral branches running a very zigzag course and crossing at different planes (Fig. 192).
One may survey entire sections, in particular such as pass transversely through an hepatic
lobule, without finding a single true mesh.
f Whether this is invariably the case appears to me latterly doubtful ; in very thin in-
jected sections of rabbit's liver I have, in isolated places, seen bile canaliculi close beside
blood capillaries.
% Where the liver cells bound the bile canaliculi their exoplasm (p. 59) is somewhat modi-
fied and is related to the cuticular border of the epithelium of the interlobular bile-ducts (p. 257).
THE DIGESTIVE ORGANS.
26l
toplasm contains pigment granules and oil globules, of various sizes, which
latter are invariably found in mammalian animals and well-nourished per-
sons. The cells have a size of from 18 to 26^. Optical functional differ-
Branch of portal
vein.
Small interlobu-
lar bile-duct,
continuing; into
bile capillaries.
Large interlobu-
lar bile-duct.
Branch of hepat-
ic artery.
Bile capillaries. "
Boundary, toward the central vein.
Fig. 192. — Transverse Section of the Liver of a Dog. X 240. Bile capillaries blackened accord-
ing- to the method of Golg;i. Technic No. 125.
■ ^:- //
Fig. 193. — Liver Cells of Man. X 560. A. Isolated liver cells containing smaller and larger fat-drops./;
b, imprint from contact with a blood-vessel. Technic No. 120.
B. From a section ; 1, exhausted cells ; 2, active-cells, filled with secretion. Technic No. 122.
ences also exist in the liver cells (Fig. 1 93 B). They are either small, dull,
and indistinctly contoured, — such conditions occur principally in the
This modified stratum has been improperly described as a special wall of the bile capillary.
With equal authority a special wall other than that formed by the gland-cells could be imputed
to all gland-lumina.
202
HISTOLOGY'.
fasting state — or larger, clear in the center, at the periphery provided
with a coarsely granular zone, — appearances that occur chiefly during
digestion. In man the two states often are met in the same liver.
( )f the blood-vessels of the liver the portal vein assumes the role
that falls to the artery in other glands, while to the hepatic artery is
assigned the subordinate part of the maintenance of the interlobular
branches of the bile-ducts, of the portal vein, and of the hepatic veins.
From the branches of the portal vein, that because they run in the
interlobular connective tissue are called interlobular veins, spring numer-
ous capillaries, which possess the conspicuous width of from 10 to 14 '->-.
Venae interlobulares.
Venae intralobulares (centrales)
Vena interlobularis.
Fig. 194.— Horizontal Section of thl Liver of
a Rabbit. Injected through the portal vein.
40. Three hepatic lobules are represented.
The injection mass filled only the branches of
the portal vein (interlobular veins) ; in the up-
per lobule it penetrated to the central vein.
Technic No. 124.
Fig. 195. — Horizontal Section of the Liver of
a Cat. Injected through the vena cava inferior.
-.40. Four hepatic lobules are shown The
injection mass filled the central vein and the
capillaries emptying into it, but did not pene-
trate to the interlobular veins. Technic No. 124.
They penetrate within the lobule, where they lie between the hepatic
trabecular (Kg. 196); during their course they repeatedly anastomose
with one another and finally empty in a small vein lying in the axis of
the lobule, the central vein, or intralobular vein, the transverse and longi-
tudinal section of which is apparent even in sections of the uninjected liver
(Fig. 188). The central veins represent the radicles of the hepatic veins
and empty into the snblobular veins, which run along the slightly flattened
side, the so-called base, of the hepatic lobules (Fig. 187).
The branches of the hepatic artery follow those of the portal vein
THE DIGESTIVE ORGANS.
263
and ramify only in the interlobular tissue, where the)' form capillary net-
works about the larger bile-ducts and the branches of the portal and
hepatic veins. The capillaries proceeding from the artery open into
the portal interlobular veins or into the portal capillaries at the margin
Blood capillaries.
Bile capillaries.
Hepatic cells.
Fig. iy6.— From a Section of the Liver of a Rabbit. X 240. The portal capillaries were injected
with a red mass, the bile capillaries with a blue mass. The hepatic cells are in contact with blood
capillaries on both sides. At a few points the red mass has retracted and given rise to a space (/),
between the hepatic cells and the portal capillaries. The bile capillaries are nowhere in contact with
portal capillaries, but are always separated from them by half the breadth of a cell. The dark spots
on the portal capillaries are optical cross-sections of blood capillaries which run vertically to the
plane of the section.
Hepatic lobules.
Interlobular connective
tissue.
Central (intralobular)
veins.
Sublobular vein,
Fig. 197. — From a Vertical Section of the Liver of a Cat. Injected through the vena cava in-
ferior. A sublobular vein cut longitudinally ; it takes up the central veins. The greater part of the
injection mass has fallen out of the wide blood-vessels. X 15. Technic No. 124.
of the lobules. In the capsule of the liver the hepatic artery forms a
wide-meshed capillar) 7 plexus.
The course of the blood-vessels therefore is as follows : the portal
vein enters at the transverse fissure, repeatedly divides into branches that
steadily decrease in size and run in the connective tissue between the
264
HISTOLOGY.
lobules as the interlobular veins. From these capillaries arise, which
pass toward the axis of the lobule and terminate in the central vein.
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 liver is provided with a capsule consisting of fibro-elastic tissue,
capsula fibrosa (Glisson), which is especially well developed at the trans-
verse fissure and in the form of special sheaths for the different chan-
nels * penetrates into the interior of the liver, where it is usually found
in such small amount between the lobules that the boundaries of the
latter are very imperfectly defined. Deli-
cate fibers ("lattice fibers") derived from
the interlobular connective tissue penetrate
into the interior of the lobules, where for
the most part they are arranged in the form
of a delicate, radially placed latticework.
The lymph-vessels accompany the
branches of the portal vein, which netlike
they embrace ; with the portal capillaries
they enter the interior of the hepatic lobules
which, having arrived at the central vein,
they then abandon. These deep lymphatics
communicate with a superficial narrow-
meshed network of lymph-vessels which
occurs in the capsule of the liver.
The nerves chiefly consist of nonmed-
ullated nerve-fibers, with which only a few medullated nerve-fibers are
mingled ; they enter the interior of the liver in company with the hepatic
artery and follow its ramifications ; their termination is unknown. Gan-
glion-cells occur along the course of the nerves.
The secretion of the liver, the bile, frequently contains drops of fat,
also granular masses of bile-pigment. Columnar cells from the bile-ducts
are to be regarded as incidental admixtures.
Fig. 198
-From a Shaken Section
of a Human Liver. X 240. c t
Blood capillaries, at x still con-
taining blood corpuscles, b. Intra-
lobular connective tissue. On the
right are five hepatic cells ; the
others have fallen out of the
meshes of the capillary network.
Technic No. 123.
The Peritoneum.
The peritoneum principally consists of bundles of fibrous connective
tissue and numerous elastic networks ; the free surface is covered with a
simple layer of flat, polygonal epithelial (endothelial) cells ; the size of
* The walls of the veins are firmly attached to the liver substance by the interlobular con-
nective tissue ; for this reason the veins do not collapse when cut.
THE DIGESTIVE ORGANS.
265
these cells varies according to the stretching to which they are subjected.
The connection with subjacent parts (the parietes, the viscera, etc.) is
effected by loose (subserous) connective tissue ; in the peritoneum re-
flected over the small intestine the epithelial cells send delicate processes
into the subserous tissue, that extend into the muscularis.
The connective-tissue bundles are arranged in thinner (in the visceral
peritoneum) or thicker (in the parietal peritoneum, in the mesentery)
layers, chiefly arranged 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 also are covered
with flat epithelial cells (Fig. 199).
Epithelial (endo-
thelial) cells.
Nuclei of connective-
tissue cells.
Fig. 199. — From the Greater Omentum of a Rabbit. X 240. The network is formed by large and
small bundles of connective tissue. The wavy striation of the bundles can only be indistinctly seen,
because the preparation is mounted in damar. At X the epithelial cells of the opposite surface can
be seen shimmering through. Technic No. 126.
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 all 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 peri-
toneum is easily shifted over the underlying parts, but on the liver and
the intestine 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.
266 HISTOLOGY.
Blood-vessels and nerves are scantily represented ; the latter partly
terminate in lamellar corpuscles.
Lymph-vessels occur in the superficial and the deeper layers of the
peritoneum.
TECHN1C.
No. 96. — Isolated Squamous Cells from the Oral Cavity. — With a
scalpel gently scrape the upper surface of the tongue and mix the scrap-
ings on a slide with a drop of salt solution ; apply a cover-glass ; in ad-
dition to isolated, pale, squamous epithelial cells, leucocytes ("salivary
corpuscles ") may be found, also, with more vigorous scraping, the tips
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 glycerol, pro-
vided too many air-bubbles do not make the preservation of the prepara-
tion impossible (Fig. 7, 1).
No. 97. — Mucous Glands of the Lips. — These are millet-sized nod-
ules perceptible to touch and accessible for macroscopic preparations.
For microscopic preparations cut from the mucous membrane of a human
lower lip (not the margin of the lip) 1 cm. cubes ; fix them in 50 c.c. of
Kleinenberg's picrosulfuric acid and in twenty-four hours harden in 50
c.c. of gradually-strengthened alcohols. In three days the tissue may be
sectioned. Cut many sections, not too thin, and stain them with hema-
toxylin ; 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. 137).
No. 98. — Dried Ground Tooth. — To prepare dried ground sections
of teeth they should be obtained immediately after they are extracted,
sawed into transverse disks 2 mm. thick, glued with sealing-wax upon
cork and treated like No. 61. If longitudinal sections are desired the
entire tooth should be glued to the cork. Longitudinal sections are to
be preferred, since they show all parts of the tooth in a single preparation.
If it is desired to decalcify the teeth of an adult, proceed as with No. 63.
The enamel consisting of earthy salts and only from 3 to 5 per cent, of
organic substances dissolves completely, hence only the dentine and
cementum remain (Fig. 138, 139, 140).
No. 99. — Odontoblasts. — Remove the teeth from the jaws of a new-
born child ; place them in 60 c.c. of Miiller's fluid ; after six 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 len-
til and tease a little the tolerably tenacious tissue in a drop of Miiller's
fluid ; apply a cover-glass, press lightly upon it, and. examine with the
high power. At the edges of the preparation the long processes of the
odontoblasts standing out like hairs will be seen ; also scattered, com-
THE DIGESTIVE ORGANS. 267
pletely isolated odontoblasts (Fig. 142). In order to preserve, treat
under the cover-glass with distilled water for two minutes, then with pic-
rocarmine ; when the staining is completed, add dilute acidulated glycerol.
No. 100. — Enamel Prisms. — These are obtained by teasing portions
of the lateral surface of the teeth of No. 99 in a drop of Muller's fluid.
Examine with a high power. The enamel prisms will be found in groups
of three and more ; they are distinguished by their dark outlines and
usually indistinct cross-striation (Fig. 141). Mount in glycerol. The
prismatic form of the enamel prisms 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, only true cross-sections of the prisms
(Fig. 141). The enamel of young teeth may be sectioned without pre-
vious decalcification.
No. 101. — Development of Teeth. — For the study of the early stages
select pig and sheep embryos ; these are the most easily obtained at the
slaughter houses ; for the first stage (Fig. 144) the pig embryos should
have a size of about 6 cm., for the second stage (Fig. 147) a size of about
10 or 11 cm. For later stages the inferior maxilla of newborn dogs or
cats is very suitable. Place the heads (or the lower jaws) in 100 c.c. of
Kleinenberg's picrosulfuric acid for from twelve to twenty-four hours and
harden in from 80 to 120 c.c. of gradually-strengthened alcohols. After
the heads have lain six or eight days in 90 per cent, alcohol, they are to
be decalcified in 100 c.c. of distilled water plus 1 or 2 c.c. of nitric acid.
When the decalcification is completed, in from three to eight days, harden
again in alcohol. In five or six days cut off the lower jaw and divide it
in front in the middle (larger jaws should be cut vertically into pieces 1
or 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 several 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. Mount in damar.
Not infrequently in sectioning the enamel organ is lifted from the papilla,
so that a free space exists between the two. The dentine is often stained
in different tones of red ; this is due to the different ages of the calcified
and uncalcified strata of the dentine. The objects may also be fixed in
Muller's or in Zenker'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. 102. — Papilla Filiformes, Fungiformes, Vallata , 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 attached to its lower surface ; for fungiform papillae cut the
piece from the tip of the tongue ; for filiform, from the middle of the
dorsum of the tongue ; for vallate, from the root of the tongue, and
for follicles (the punctiform openings of which can be seen with the
naked eye) from the root of the tongue, and place them in 100 or 200
268 HISTOLOGY.
c.c. of Miiller's fluid. The fluid must be changed several times ; after
two weeks wash the tissue and harden it in 50 c.c. of gradually-strength-
ened alcohols. For filiform papillae cut thick saggital sections of the
tongue and do not stain them ; stain the other sections in Hansen's
hematoxylin and mount in damar (Fig. 148, 149, 150). For the prepa-
rations represented in Fig. 151 and Fig. 154 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. 103. — The Tonsils. — The tonsils of adult man do not furnish
instructive preparations. They should be treated according to technic
No. 102. The tonsils of the rabbit and the cat are recommended ; to
find them proceed as follows :
Dissect the skin from the anterior surface of the neck and remove
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 forceps 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, 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 down-
ward, 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 deli-
cate 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 pharynx. They may be fixed in 60 c.c. of Kleinenberg's
picrosulfuric acid (p. 21), and hardened in 50 c.c. of gradually-strength-
ened alcohols (p. 34), stained with hematoxylin (p. 37) or with eosin and
hematoxylin (p. 38), and mounted in damar.
No. 104.- — -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 (p. 32) and in two weeks hardened
in 50 c.c. of gradually-strengthened alcohols (p. 34) ; stain with Hansen's
hematoxylin ; mount in damar (Fig. 155).
No. 105. — The Coats of the Stomach. — For topographic prepara-
tions place pieces from 2 to 5 cm. square for six hours in 100 c.c. of 3
per cent, nitric acid (p. 32). Remove the gastric contents adhering to the
mucous membrane by moving it slowly to and fro in the acid. In a half
THE DIGESTIVE ORGANS. 269
hour renew the acid ; harden in 60 c.c. of gradually-strengthened alcohols
(p. 34). Mount thick unstained sections in damar (Fig. 156).
No. 106. — 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 mem-
brane. Grasp the latter with forceps 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 per
cent, salt solution. The body and fundus of the
fundus glands can be satisfactorily isolated without
much trouble. The protoplasm of the parietal cells
can be distinctly seen (Fig. 200, B), the chief cells
are invisible. The nuclei may be stained with
picrocarmine and the preparation mounted in dilute
glycerol. The isolation of the pyloric glands can
be accomplished only by very careful teasing.
No. 107. — Isolated Gastric Epithelium. — Place
pieces 1 cm. square of gastric mucous membrane
for about five hours in 30 c.c. of Ranvier's alcohol fig. 200.— lower half of
, _ , \ t 1 r 1 n AN Isolated Fundus-
(see iurtner p. 2Q). In the maionty 01 the cells gland of a rabbit.
;, 1 _. / ■ , ,- ■ ■ , ;■; 240. B, Parietal cell ;
the mucous portion occupies a large division and m, membraim propria,
they have the appearance of those pictured in
Fig. 16, c. The preparation may be stained under the cover-glass with
picrocarmine and mounted in diluted acidulated glycerol.
No. 108. — Gastric Glands. — The stomach of a cat or dog that if
possible has been fasting for one or two days is especially 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 mus-
cular coat and place pieces of the former about 1 cm. square in about 10
c.c. of absolute alcohol. In about a half-hour transfer them to 20 c.c. of
fresh alcohol. The outlines of the glands can be recognized in moder-
ately 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 difficulty in a less degree. For
the study of the minute structure of the glands and of the superficial
epithelium embed the tissue in liver and cut the thinnest possible
sections.
a. For fundus glands , chief and parietal cells, cut vertical or, better,
horizontal sections of the mucous membrane and stain them with Hansen's
hematoxylin for two or four 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 0.03 per cent,
solution of Congo red (p. 25), for from three to six minutes, wash two
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
27O HISTOLOGY.
chief cells ; examine the thinnest parts of the sections, especially the
fundi of the glands, where the parietal cells are not so exceedingly pro-
fuse. The parietal cells can be recognized with the low power as isolated
red spots on a rose-red ground. With the 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 (sections parallel to the surface of
the mucosa). The lateral twigs of the chief lumen can only be perceived
in very favorable sections (Fig. 158). Figure 157 is a combination of
several thin longitudinal sections.
b. For pyloric glands, stain vertical and horizontal sections of the
mucosa with Hansen's hematoxylin and mount in damar. The lumen of
the pyloric glands is wider (Fig. 160). Owing to the extreme sinuosity
of the glands, thin sections contain but few glands cut in their entire
length, mostly only parts of them.
No. 109. — Duodenal Glands. — Cut out the stomach and duodenum
of a cat about one hour after death. Open both along their length,
remove the contents 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, in all a piece 5 or 6 cm. long, for six hours in 100 c.c. of
3 per cent, nitric acid. Further treatment like No. 105. Cut longitudinal
sections, which simultaneously pass through pylorus and duodenum.
Stain with Hansen's hematoxylin. Mount in glycerol or in damar
(Fig. 165). 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. 1 10. — Epithelium and Villi of the Small Intestine. — From the
middle portion of the small intestine of a rabbit just
killed cut a piece one cm. long, open it along its
length and remove the contents by carefully pouring
over it 0.7 per cent, salt solution. Then grasp the
piece at the left edge with the forceps, with fine scis-
sors 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
from the edge of the preparation. Examine the prep-
fig. 201.— intestinal aration without a cover-glass, with the low power.
Villus of a Rab- rp, ........ ° r
bit. X70. lne villi will be seen partly extended, partly con-
tracted ; the latter condition may be recognized by
transverse folds running across the villi (Fig. 201). Details cannot be
detected. Apply a cover-glass ; the villi thus become flattened and ap-
pear 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 some columnar cells are found inflated and of a spherical
THE DIGESTIVE ORGANS. 2"J I
form. The top-plate 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 second investigation an hour later,
when the epithelium will be sufficiently macerated to be brushed off.
b. For permanent preparations place pieces (i cm. square) of the
intestine in 30 c.c. of Miiller's fluid. In three or five 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 glycerol ; cover-glass ; high power (Fig.
163 A).
No. ill . — Sections of the Small Intestine. — Place pieces from 2 to
4 cm. long of the intestine of a rabbit, better of a puppy or a kitten, in
100 or 200 c.c. of 3 per cent, nitric acid. After six hours the pieces
are to be hardened in 100 c.c. of gradually-strengthened alcohols. Sec-
tions can be made through the entire intestinal tube ; in most cases, only
fragments of the villi are thus obtained ; to obtain entire villi, with a razor
cut open the hardened intestine along its length, pin it with needles on a
cork plate, with the mucosa uppermost. The villi can then be seen with
the unaided eye. Cut thick cross-sections, stain them for one minute
with Hansen's hematoxylin and mount in damar. Goblet-cells are very
frequently found in the epithelium (Fig. 163 B). Staining in bulk with
borax-carmine is strongly advised.
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 connective-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 state of the cell.
For the latter purpose the following is recommended : —
No. 112. — Triple Staining of the Intestine. — Small pieces of tissue
are to be fixed in Flemming's mixture (p. 33), hardened in gradually-
strengthened alcohols, and subsequently treated according to the method
given on page 41, 11.
No. 113. — Agminated Nodules {Patches of Peyer). — These can be
seen shimmering through the uninjured fresh intestinal wall of the rab-
bit, but in the dog and in the cat (on account of the thickness of the mus-
cular coat) often they are not perceptible. In the latter animals patches
are constant at the point 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. in. In the
cat take the lowermost portion of the ileum (about 2 cm. long) with a
272
HISTOLOGY.
piece of the cecum of the same length ; slit them open lengthwise and
span them out on a cork plate, with the mucosa uppermost. Usually
the mucosa is covered with a tenacious excrement, difficult to remove by
washing, which glues the villi together, so that only oblique sections of
the villi can be obtained. Further treatment like No. m.
Closely placed nodules are found in the blind half of the vermiform
process of the rabbit, which encroach upon the mucosa and compress it
to such narrow areas that cross-sections exhibit very complicated pic-
tures, scarcely intelligible to the beginner.
Fixation in o. 1 per cent, chromic acid, with hardening in gradually-
strengthened alcohols, renders the germinal centers very distinct, but is
not so good for the remaining elements as the nitric acid.
No. 114. — The Large Intestine. — Treat empty pieces like No. 11 1
or No. 1 12 (compare with Fig. 17, p. 74). Pieces filled with feces must
be cut open, washed, and spanned on cork.
No. 1 1 5. — Fresh Crypts of the Large Intestine of the Rabbit. — Cut a
piece 1 cm. long from the lowermost portion of the large intestine (be-
tween two spherical 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 0.7 per
cent, salt solution, grasp the piece with forceps at the
left edge and with fine scissors cut off an extremely
thin strip. Transfer this with a drop of the salt solu-
tion to another slide ; with needles separate the mus-
cularis from the mucosa and tease the latter a very
little ; apply a cover-glass with slight pressure. With
a low power the crypts can be readily seen, but it is
difficult to detect their orifices (Fie. 202). The epi-
FlG. 202. — t, Epithe- ,1.1,1 r 1-1 • 1
Hum; /.crypts. x8o. thehal cells are often granular in the portion border-
ing the lumen. With the high power the superficial
epithelium can be very well seen from the side and from the surface.
The contents of the goblet-cells often are not clear, as in sections, but
dark and granular.
No. 116. — Blood-vessels of the Stomach and the Intestines. — A
stomach and intestine injected from the descending aorta are to be fixed
in from 50 to 200 c.c. of Miiller's fluid and hardened in gradually-
strengthened alcohols. One portion should be cut into thick (up to 1
mm.) sections, stained, and mounted in damar (Fig. 169), 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 1 cm. square may be transferred from absolute alcohol to
5 c.c. of turpentine for clearing and mounted in damar. It is also easy
to strip the muscularis from the mucosa and to mount the separate coats
in damar.
No. 117. — AnerbacKs and Mcissncr's Plexuses. — For this purpose
intestines with a thin muscular coat are preferable, therefore the intestine
of the rabbit and guinea-pig (not of the cat) are especially suitable. It is
THE DIGESTIVE ORGANS. 273
not necessary that the object be absolutely fresh ; the small intestines of
children 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 (from 10 to 30 cm. long) ot
the small intestine from the mesentery. Cut it off and with the finger
lightly press out the contents ; tie the lower end of the intestine and fill
it from the upper end with the dilute acetic acid ; tie it above and place
the whole piece in the remainder of the acetic acid. In one hour change
the fluid. In twenty-four hours transfer the intestine to distilled water,
with scissors open it along one side of the line of attachment 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 attachment of the mesentery.
a. Plexus My enter icus. — 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 muscu-
laris, about 1 cm. square, in a drop of the dilute acetic acid to a slide ;
examined with the low power it furnishes a very pretty picture (Fig.
170 A). If it is desired to preserve the preparation, place the tissue for
one hour in 30 c.c. of distilled water, which must be changed several
times, and then for from eight to sixteen hours in 5 or 10 c.c. of a 1 per
cent, osmicacid solution, in the dark ; wash the piece quickly in distilled
water and mount in diluted glycerol. The osmium preparations are not
so 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 abso-
lutely fresh on being filled with the dilute acid) ; the plexus remains
attached to one stratum. Pieces of this should be placed for one hour in
distilled water, then treated with gold chlorid (p. 45), and mounted in
damar. The gold-chlorid treatment is less adapted to human intestines,
since both the muscular layers are likewise stained red and partially con-
ceal the plexus. The firm union of the muscular strata in the human
organ may be due to the age of the object.
b. Plexus Submucosus. — With a scalpel scrape the epithelium from
the isolated mucosa ; place a piece about 1 cm. square on a slide ; apply
a cover-glass, press upon it slightly, and examine with the low power
(Fig. 170 B). To preserve the preparation, proceed as in No. 117, a ;
but it is advisable to span the pieces on cork and before transferring them
from the ninety-five per cent, 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 trans-
versely placed nuclei of the muscle-fibers.
No. 118. — The Parotid, Submaxillary, and Sublingual Glands. —
From human glands (in winter useful after three or four days) cut a num-
ber of pieces from 0.5 to 1 cm. square and place them in 30 c.c. of Zen-
ker's fluid (for further treatment, see p. 32). Stain one piece in bulk in
borax-carmine. Embed another in liver and cut the thinnest possible
18
274 HISTOLOGY.
sections ; small fragments about 2 mm. long can be used ; stain them in
Hansen's hematoxylin, two or three 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 (No. 3 b, p. 38), and mount in damar.
(Very thin sections should be examined in water after the staining in hema-
toxylin is completed, since the cell boundaries are then very much more
distinct.) If the staining is successful, the salivary tubules and the cres-
cents are red. In the sublingual gland and on the mucous cells of the
submaxillary the membrana propria also stains red ; it must not be con-
fused 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. 174) ; the portion which stains is a retic-
ulum which occurs in 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 (Fig. 176)
(also in that of the rabbit). Of the end-pieces only 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.
No. 1 19. — The Pancreas. — The human pancreas as a rule cannot be
used. The treatment is the same as for the parotid gland, No. 118.
The characteristic granular zone of the gland-cells bordering the lumen
is not to be seen by this method (Fig. 178 B). Tease a pinhead-sized
piece of the fresh pancreas of a cat in a drop of 0.75 per cent, salt solu-
tion. With the low power the end-pieces appear spotted ; this is due to
the partly clear and partly granular divisions of the cell. With high
magnification the tissue appears like Fig. 178 A.
No. 120. — Liver Cells. — Make an incision in a fresh liver and with
the blade of a scalpel obliquely placed scrape the cut surface. The
brown liver tissue adhering 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. 193 A). In addition to the
liver cells, the preparation contains numerous colored and colorless
blood corpuscles.
No. 121. — Hepatic Lobules. — Place small pieces (about 2 cm. cubes)
of a pig's liver in from 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 three days sections can be made ; stain them with Hansen's hema-
toxylin. The division into lobules can be well seen with the low power,
but the hepatic cells as well as the bile-ducts are less satisfactory for
study. Better for this purpose is the following.
No. 122. — Human Liver. — Place pieces about 2 cm. square, as fresh
as possible, for four weeks in 200 c.c. of Miiller's fluid for fixation and
THE DIGESTIVE ORGANS. 275
then in ioo c.c. of gradually-strengthened alcohols for hardening. Ex-
amine unstained sections (cut parallel and also vertical to the surface) and
stain others with Hansen's hematoxylin and eosin ; mount in damar.
The demarcation 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 in-
tralobular veins ; while groups of such sections represent branches of the
portal vein, of the hepatic artery, and of the bile-duct. Exact trans-
verse sections of central veins may also be recognized by the trabecular
of hepatic cells radiating from them (Fig. 188). 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.
No. 123. — To demonstrate the capillaries and the intralobular con-
nective tissue, which in ordinary preparations are scarcely visible, shake
a number of thin double-stained sections of human liver (No. 122) for
from two to three 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. 198). This preparation can be
mounted in damar, but the more delicate connective-tissue fibers disap-
pear therein.
No. 1 24. — Blood- Vessels of the Liver.
a. Chloroform a rabbit and quickly place a 2 cm. cube of liver
(without allowing much blood to flow from it) in 50 c.c. of absolute alco-
hol. In two days the natural injection can be seen on the surface ; it is
indicated by brown spots within the center of the lobules. Cut thick
sections parallel to the surface and mount them unstained in damar.
Examine with a low power. Very frequently only the superficial strata
of the liver contain filled blood-vessels.
b. Of all injections that of the liver is most easily accomplished.
Inject Berlin blue (p. 46), either through the portal 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 the latter, and to insert
the canula through the right auricle into the inferior cava. The injected
liver is to be placed in toto in about 500 c.c. of Miiller's fluid ; after six
days pieces about 2 cm. square of the portions best injected are to be cut
out, again placed for two or three weeks in about 1 50 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. 194, 195,
197)-
No. 125. — Exhibition of Gland Lumina by Golgi's "Black Reaction."
— Place small pieces of the root of the tongue, of the stomach, of the
salivary glands, and of the liver for three days in the osmio-bichromate
mixture (in winter, in the warm chamber), and for the same length of
276 HISTOLOGY.
time in the silver solution. For further treatment see page 43. Very
often the staining does not succeed until after the procedure has been
repeated once or twice. After-staining (p. 45) is advised. In the liver
the "lattice-fibers" occasionally stain.
No. 126. — Epithelium of the Peritoneum. — Proceed as in No. 41, p.
135, but instead of taking the mesentery, which also yields instructive
pictures, use the greater omentum. The pieces may be stained in Han-
sen's hematoxylin and mounted in damar (Fig. 199).
VI. THE RESPIRATORY ORGANS.
The Larynx.
The mucous membrane of the larynx is a continuation of the pharyn-
geal mucous membrane and like this is composed of an epithelium, a
tunica propria, and a submucosa, which latter connects the mucous
membrane with underlying parts. The mucous membrane over nearly
the whole of the organ is covered with a stratified ciliated columnar epi-
thelium ; the ciliary wave is directed toward the cavity of the pharynx.
On the true vocal cords, on the anterior surface of the arytenoid cartilages
and on the laryngeal surface of the epiglottis the epithelium is of the
stratified scaly variety. The tunica propria consists of numerous elastic
fibers and of fibrillar connective tissue, which in the lower animals is
condensed 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 (p. 130) are found in the mucous membrane
of the ventricle of the larynx (Morgagni). Papillae mainly occur in the
mucous membrane clothed with stratified squamous epithelium ; on the
free border and on the lower surface of the vocal cords the papillae are
merged in longitudinal ridges. The submucosa contains branched tubu-
lar mucous glands from 0.2 to 1 mm. in size.
The cartilages of the larynx principally consist of the hyaline
variety, which in a measure exhibits the peculiarities of the costal car-
tilage. The hyaline cartilages are the thyroid, the cricoid, the (greater
portion of the) arytenoids, and often the triticeous cartilages. The epiglot-
tis, the cuneiform cartilages (Wrisbergi), the cornicular cartilages (San-
torini), the median portion of the thyroid, and the apex and vocal process
of the arytenoid cartilages are of the yellow elastic variety. Occasion-
ally the triticeous cartilages are composed of fibro-cartilage. Between
THE RESPIRATORS ORGANS. 277
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 nerves. The
blood-vessels form two or three networks extending in planes parallel
to the surface and a close subepithelial capillary plexus.
The lymph-vessels form two communicating networks also extending
in horizontal planes, of which the superficial consists of narrower chan-
nels and lies beneath the vascular capillary network.
The nerves in their course include microscopic ganglia and form a
deep and a superficial plexus. The nonmedullated nerves end partly as
little subepithelial terminal trees, the branches of which are provided
with enlargements, or in end-bulbs, and partly intraepithelial in the same
manner as on and in the tastebuds (see The Gustatory Organ). Below the
vocal cords subepithelial nerve-endings and buds are wanting ; but many
intraepithelial nerve-fibers are present, that spin networks about the
individual gustatory cells.
The Trachea.
The ciliated mucous membrane * of the trachea possesses a structure
like that in the larynx, excepting only that the elastic fibers form a close
network in which the fibers pursuing a longitudinal direction predomi-
nate. This network lies immediately beneath the epithelium and above
the glands. The cartilages are of the hyaline variety. The posterior wall
of the trachea is composed of a layer of transversely arranged smooth
muscle-fibers, that usually is covered by a stratum of muscle-fibers
extending longitudinally. The mucous glands of the posterior wall are
distinguished by their size (2 mm.) ; they not infrequently penetrate the
muscular layer, so that they 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 nerve-fibers ending on the smooth muscle-fibers
of the trachea are nonmedullated and arise from the nerve-cells of the
-small (sympathetic) ganglia; the sensory nerve-fibers are medullated and
of cerebro-spinal origin.
The Bronchi and the Lungs.
The lungs may be regarded as compound alveolar glands, in which,
as in all glands, excretory and secretory (in this case respiratory) por-
* The mucous membrane which covers the posterior wall of the trachea appears to vary ;
at least I have found there, in the mucous membrane of a healthy man, stratified squamous
epithelium and a tunica propria with papillae.
278 HISTOLOGY.
tions maybe 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,
by direct giving off of small lateral twigs, by branching at acute angles,
and by gradual decrease in the caliber of the large branches ; in this
way each bronchus breaks up into minute twigs, that nowhere anasto-
mose with one another and that retain the characteristics of the excre-
tory duct to a diameter of 0.5 mm.
At this point the respiratory division begins. Small, isolated, hemi-
spherical 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 bronchioles only in the larger number of alveoli in their
walls. The alveolar ducts divide at right or acute angles and pass with-
out sharp demarcation into the slightly expanded blind terminal vesicles
(less correctly, infundibula), the walls of which are thickly beset with
alveoli. Each alveolus is open, not only toward the terminal vesicle, —
this broad opening is termed base — but also is in direct communication
with neighboring alveoli by means of minute canals, the so-called pores.
The entire respiratory division is separated by areolar tissue into
lobules from 0.3 to 3 sq. cm. in size. All the branches of the excretory
division down to a diameter of from 1.5 to 1 mm. lie between the lobules,
are "interlobular ducts."
The minute structure of the bronchi in the largest branches does not
differ from that of the trachea. Gradually modifications appear, which
first involve the cartilages and the musculature. The C-shaped ring car-
tilages are replaced by irregular plates lying on all sides of the bronchial
wall. They diminish in size and thickness with the decrease in the diam-
eter of the bronchi and disappear in bronchioles 1 mm. in diameter.
The smootli 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. They are wanting in the terminal vesicles.
The mucous membrane is thrown into longitudinal folds and con-
sists of a stratified ciliated epithelium containing goblet-cells, that in the
smaller bronchi becomes gradually reduced to a single stratum, and ol
a connective -tissue tunica propria. The latter contains numerous longi-
tudinal networks of elastic fibers and leucocytes in greatly varying num-
ber. Occasionally the latter form solitary nodules, from the crest of
which leucocytes wander through the epithelium into the bronchial tube.
THE RESPIRATORY ORGANS.
279
Branched tubular mucous glands occur as far as the cartilages ex-
tend ; they are situated outside of the muscular layer (Fig. 203). They
are numerous and do not disappear until at the beginning of the respira-
tory bronchioles.
External to the cartilages is a fibro-elastic tunic, which envelops the
entire bronchus including the accompanying vessels and nerves.
The minute structure of the respiratory division, after the gradual dis-
Epithelium
Alveoli.
Excretory duct
of gland.
Fig. 203. — Cross-section of a Bronchus. Two Millimeters Thick, of a Child. X 30.
Technic No. 128.
appearance of cartilages and glands, is distinguished in particular by the
nature of the epithelium.
The respiratory bronchioles succeeding the smallest excretory bronchi
at their beginning still contain a single layer of ciliated columnar epithe-
lium ; as they proceed the cilia are lost, the cells become cubical, and
between these another kind of epithelial cell appears, in the form of
thin nonnucleated plates of different sizes. These plates and isolated
28o
HISTOLOGY.
or small groups of cubical cells form an epithelium called respiratory
epithelium. The transition of the cubical epithelium into the respiratory
epithelium is not abrupt, 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
Terminal Bronchiole.
Alveoli
33
f\ ?-.■■''■ i? JO
Alveolar duct.
Fig. 204.— From a Section of Lung of Adult Man. > 50- The terminal bronchiole divides into
two branches (011 the right). A portion of the wall of the bronchiole fell within the plane of the
section; here the entrance to the alveoli is seen from above; in the lower branch the alveoli are
viewed from the side. The epithelium of the bronchiole is mixed. The epithelial lining of the
alveoli is only partially visible with this magnification, Technic No. 129.
Cubical and flat epithelial cells.
Cubical and flat epithelial cells
"—:. '•■/,:'■■' .'--■- ■■* ,; ■■ ■
Fig. 205. — From Sections of Human Lung (A and B), and (C), of Lung of a Kitten Ninf. Days
Old. X 240. A. Mixed epithelium of terminal bronchiole. B and C. Alveoli drawn with change
of focus. The margin of the alveolus is shaded • it can be seen that the epithelium covering it is
like that in the depth of the alveolus (tire light portion) ; the nuclei ol the cells are not visible.
Technic No. 12Q.
epithelium and the reverse. [fence the respiratory bronchioles contain
a mixed epithelium (Fig. 204 and Fig. 205 A\ Since the respiratory
epithelium steadily gains in extent and the groups of cubical cells be-
come steadily less frequent, the epithelium of the bronchioles changes
into that of the alveolar ducts.
The epithelium of the alveolar ducts and of the alveoli is the same
as the respiratory epithelium of the bronchioles. The developmental
THE RESPIRATORY ORGANS.
28l
history teaches that the smaller nonnucleated plates originate from
cubical epithelial cells that become flattened by inspiration, that is, by
the inflation of the alveoli and the stretching of the alveolar wall. The
larger plates are formed by the subsequent blending of several smaller
ones. The alveoli of old embryos and of stillborn children contain only
cubical cells. The walls of the alveolar ducts and of the alveoli, in ad-
dition to the previously mentioned muscle-fibers in the former, are com-
posed of a delicate fibrous framework and many elastic fibers. The lat-
ter are circularly arranged in the alveolar ducts ; at the entrance to the
alveolus (the base) the elastic fibers form a thick annular band or ring,
Elastic rings.
Sinuous fibers.
Alveolar duct. Alveoli. Alveolar septa.
06. — Section of the Lung of A Rabbit. X 220. Stained elastic fibers. Technic No. 130 b.
while delicate convoluted fibers occur in the entire wall of the alveolus
(Fig. 206). The elastic rings of neighboring alveoli grow together at
the points of contact and then form the alveolar septa.
The interlobular connective tissue occurring between the lobules ot
the lungs, besides fine elastic fibers and a few connective-tissue cells, in
the adult contains black pigment-granules and minutest particles of car-
bon that have come there by inhalation. In children the interlobular
connective tissue is more richly developed and therefore the demarcation
of the lobules is more distinct.
Capillaries.
282 HISTOLOGY.
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 with a simple stratum of flat polygonal epithelial
(endothelial) cells. The parietal pleura has the same structure, but con-
tains 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, the bronchioles,
the alveolar ducts, and between
Vein. the terminal vesicles, where they
break up into a very narrow-
meshed capillary network, that
Artery. ; s situated immediately beneath
the respiratory epithelium of the
terminal bronchioles, of the alve-
FiG.207— From a Section of the Lung of a Child, 1 Hurts anH of the alveoli
Injected through the Pulmonary Artery. L > ld -i uucis, dim ui liic divcun.
X So. Of the five alveoli drawn the upper three T i ■ „„.* „ t, „+. j.u«
are fully injected. Technic No. 131. 1 he veins arise each at the
bottom of an alveolus (Fig. 207),
and unite in small trunks that follow the bronchi and the arteries. The
walls of the bronchi are supplied by special blood-vessels, the bronchial
arteries, which furnish a deep capillary plexus for the muscles and the
glands, a superficial 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 (see
also p. 127).
The numerous nerves of the lungs, derived from the sympathetic
and the vagus, contain medullated and nonmedullated nerve-fibers and
small groups of ganglion-cells. The nerve-endings stand chiefly in rela-
tion to the walls of the blood-vessels.
The Thyroid Gland.
The thyroid body in its anlage is a compound tubular retiform gland ;
its excretory canal, the thyro-glossal duct, opening at the foramen cecum
of the tongue, with the exception of a few atrophic remains was oblit-
erated in an early embryonic period ; the network of gland-tubules, that
at first are not hollow, becomes constricted at intervals and resolves itself
into short pieces, the "follicles," which become bound together into
THE RESPIRATORY ORGANS.
28 3
lobules by loose connective tissue. In the adult the tubules are oval
sacs blind at both ends, that differ greatly in diameter (from 40 u to
1 20 /i) and are lined with a simple layer of cubical epithelial cells. Their
contents consist of a characteristic, homogeneous, viscid mass, the colloid
substance, which also is found in the lymph-vessels of the organ. The
blood-vessels are exceptionally numerous and break up into capillaries
that form a network around the tubules, lying close beneath the epithe-
lium. The lymphatics, likewise profuse, form a network lying between
the tubules. The nerves follow the ramifications of the blood-vessels
and form plexuses chiefly distributed to the vascular walls, some of
which also surround the gland-tubules. The penetration of terminal
twigs into the epithelium has not been observed.
Colloid substance
Epithelium
Tangential section
of tubule ; the epi-
thelium viewed
from the surface.
Tubule in trans-
verse section.
Connective tissue.
Fig. 208. — A Lobule from a Thin Skction of the Thyroid Gland of Adult Man. X 220.
The tubules vary in diameter. Technic No. 132.
In the neighborhood of the thyroid body several " outer and inner
epithelial corpuscles," about two millimeters in size, are found ; they con-
sist of cords of epithelial cells, capillary blood-vessels, and connective
tissue, and probably are detached particles of the lateral anlage of the
thyroid body, arrested in a certain stage of development, which in circum-
stances can become transformed into the genuine thyroid tissue with col-
loid substance. In different mammalian animals, embryos and adults,
there has been found in each lateral lobule of the thyroid gland a duct
clothed with epithelium varying from flat to ciliate cylindrical, the central
canal of the thyroid gland, that is in communication with the surround-
ing lobules and the inner epithelial corpuscles.
284 HISTOLOGY.
The Thymus Body.
The thymus body, in its first anlage an epithelial organ, retains this
character only during a very brief embryonal epoch, since with the
„,,
Cortex. -I 4 _rf" I
< r ■ : ~4$-'-&-:^ ■■' ■ ■ ■■'■Sv-.-.i
Medulla.
.#-'<$
;•-' i^>
.*
^#^',.^ ; -
- - - 1
7*
/
•ft- c ; " ■,
c;; f ^
Connective tissue.
/
/
Blood-
/
■vessels.
v<-
Fig 209 —Section of Secondary Lobules of the Thymus Body of a Seven-Day-Old Rabbit.
X50. The lower lobules are sectioned tangentially, so that chiefly the cortex is visible. Technic
No. 133.
exception of very small remnants the epithelium immediately undergoes
degeneration, and in its place adenoid tissue appears.* The thymus in
childhood consists of lobes from 4 to 1 1 sq. mm. large, which are envel-
oped in fibrillar connective-tissue mixed
N th c eh i afcen e s epi \._ @ @ , i m @ ^ with fine elastic fibers. This connective
tissue sends septa into each lobe, by
which a subdivision into smaller (second-
ary) lobules 1 mm. in size is effected.
Leucocytes. '*% T'^n^' * ^ • Each of these lobules consists entirely
®J^&^%^ __ of adenoid tissue, which is more densely
Concentric x ^ ©e ® ia developed at the periphery than in the
corpuscle. ^ . . .
F,c 2 io.-coNCENTR,c Corpuscle from center, so that a darker cortical zone can
a" S°D are indicated by dotted lines. These lobules have
no relation whatever to the lobules of the kidney during fetal life.
f Consequently each glomerulus is an arterial rete mirabile (p. 127, remark). In dogs
and cats retia mirabilia occur in the kidneys that do not stand in any relation to uriniferous
tubules, that is, they are not enveloped in a capsule.
THE URINARY ORGANS.
293
interlobulares), which lie close beside the interlobular arteries, in their
further course continue alongside the arteries, and open into the vena^
arciformes ; the latter also take up small veins that arise from the con-
fluence of capillaries situated in the deeper portions of the cortex. The
vessels of the peripheral zone of the cortex converge to points where
they unite in radicles arranged in a stellate form, the vence stellatcE, which
are connected with the interlobular veins (Fig. 211, 5, and Fig. 219).
The foregoing account of the distribution of the blood-vessels applies
only to the cortex and to the medullary rays.
The medulla receives its blood supply from (1) the arteriole recta,
which arise from the arterial arches at the juncture of the medulla and
the cortex, from the efferent vessels of the most deeply situated glomeruli,
and direct from centrally running branches of the interlobular arteries or
,H^'f*?^ Renal corpuscle.
Nerve plexus of an interlobular artery.
Silvered uriniferous tubule.
Fig. 220. — Section of the Kidney of a Mouse. X 180. Technic No. 139.
of the arciform arteries ; and (2) from offshoots of the cortical capillaries
(Fig. 211, x, xx). The veins of the medulla take their origin from the
wide-meshed capillary network surrounding the papillary ducts and join
the venous arches at the juncture of the medulla and the cortex. The
renal vein and its branches have no valves. Direct communication
between the arteries and the veins occurs both in the capsule and in
the interior of the kidney.
The lymph-vessels run in part superficially, in the capsule, and in part
accompany the arteries in the parenchyma of the organ. The nerves
form plexuses which envelop the arteries as far as the renal corpuscles
(Fig. 220). The convoluted uriniferous tubules are said to be surrounded
by nerve-fibers, extremely delicate branches of which pierce the mem-
brana propria and terminate in free endings between the epithelial cells.
294
HISTOLOGY.
THE URETERS.
The ureters, the calices, and the pelvis of the kidney are composed
of three coats, (i) the mucous coat, which lies innermost, (2) the muscular
coat, and (3) surrounding this the outer fibrous coat (Fig. 221).
Fibrous coat.
Muscular coat.
Mucous coat.
Fig. 221. — Transverse Section of the Lower Half of a Human Ureter. X 15- ^. Epithelium;
t t tunica propria; j, submucosa; /, inner longitudinal muscle-bundles; r, circular layer of muscle-
bundles ; /1, accessory outer longitudinal muscle-bundles. Technic No. 140.
The tunica propria of the mucous membrane consists of delicate
connective-tissue fibers, which, richly interspersed with cellular elements,
Columnar cells.
£
V ,f %.v>!v V V tivity -
erstitial con- — ^'r^ .^' i ''Jli', , 'i'° ' is =' a ° °a"V CT°f "^ i r '** , K t0^s"°°» 8 a * **** . '
nective tis- .^7 ^''""?fi :> ■ "^ °" *Yftf?-\ ^^:?V°« ?/;£&> V*
— Epithelium in a
state of rest.
Fig. 224.— From a Cross-section of the Testicle of an Ox. X50. In the process of fixing and of
hardening the epithelium has become somewhat shrunken, so that spaces occur between it and the
interstitial connective tissue. Technic No. 146.
The wall of the convoluted tubules from without inward consists of
(1) several layers of flattened connective-tissue cells, (2) a thin mem-
brana propria, and (3) a stratified epithelium, the character of which
THE REPRODUCTIVE ORGANS.
3d
varies greatly in the several divisions of the tubule. When the gland
is in a state of rest several strata of spherical cells, the nuclei of which
stain more or less intensely, may be seen lining the tubules (Fig. 224).
In a state of activity the epithelium exhibits a cycle of phenomena relat-
ing to spermatogenesis. The naked epithelial cells lying next to the base-
ment membrane, the parietal stratum, are of two kinds, the cells of Ser-
toli, which take no direct part in the production of the seminal filaments,
and the spermatogonia (ancestral cells), the real producers of the semen
Spermatids
Sertoli's cell.
Spermatogenic eel
Blood -vessel with
blood corpuscles.
Spermatids
Sertoli's cells.
Spermatogenic cells, above
each a large mother-cell.
Sertoli's cells.
Fig. 225. — Cross-section of Seminiferous Tubules of a Mouse. X 360. Observe that the nuclei
of the spermatids (below on the left) at first round, become oval (above) and are transformed (below
on the right) into the heads of the seminal filaments. Technic No. 147.
(Fig. 225). They multiply by indirect division and grow to be large
cells, that occupy the next layer within. These are the spermatocytes
(mother-cells), which divide twice, each giving rise to four spermatids ,
semen-cells (daughter-cells), lying in a zone still nearer to the center of
the tubule. The latter now become spermatosomes (seminal filaments),
by the nucleus developing into the head, a small portion of the proto-
plasm forming the caudal filament, while the axial-fiber (p. 302) grows
out of the centrosome lying beneath the surface of the cell. Until recently
302 HISTOLOGY.
the role of the cells of Sertoli was generally assumed to be sustentative ;
it was supposed that during the processes just described a large number
of spermatids attached themselves to a cell of Sertoli,* that meanwhile
had grown in length centrad, and that through this " copulation" they
in all probability received nutritive material. Much keener is the recently
advanced, well-verified theory, that the cells of Sertoli likewise are
descendants of the spermatogonia, but instead of developing they perish ;
their protoplasm gradually passes into the intercellular substance occur-
ring between the groups of cells and there dissolves ; their nucleus dis-
appears. The tuft-like arrangement of the seminal filaments is the result
of the pressure exerted by the ancestral cells lying about the cells of
Sertoli.
The wall of the tubuli recti consists of a membrana propria and
within this of a simple layer of low columnar cells.
The canals of the rete testis are lined with a stratum of simple cub-
ical or flat epithelial cells.
The arteries of the testicles are branches of the spermatic artery,
which proceed in part from the mediastinum and in part from the tunica
vasculosa to the intertubular septa, and there break up into capillary net-
works which surround the seminiferous tubules. The veins arising from
these networks follow the course of the arteries. The lymph-vessels form
a plexus beneath the tunica albuginea, which is in connection with the
network of lymph capillaries enveloping the seminiferous tubules. The
nerves form networks about the blood-vessels ; whether single fibers
branch off from these networks, pierce the membrana propria, and
terminate in club-shaped endings between the epithelial cells is not yet
definitely established.
The Semen.
The secretion of the testicles, the semen (sperm), almost exclusively
consists of spermatozoa, pin-shaped structures in which a head and a tail
are distinguished (Fig. 226). In man the head is from 3 to 5 p. long and
from 2 to 3 n broad, flattened, viewed from the side pyriform in shape, with
the tapering end directed forward, seen from surface oval, with the ante-
rior end rounded and containing a clear portion (Fig. 226, 1). The tail
when very highly magnified exhibits a filament extending from end to
end, the axial fiber, which is composed of delicate fibrils. Three divi-
sions are recognized in the tail : the round middle-piece, lying next to the
head, 6 p. long and scarce 1 p. broad ; following this the main-piece, from
* Whence the "spermatoblast" of authors, see Technic No. 148.
THE REPRODUCTIVE ORGANS.
303
40 to 60 \i long, gradually diminishing in thickness posteriorly ; the tip
of the tail, the end-piece, is about 10 p. long and consists of the project-
ing axial fiber.*
The spermatozoa are distinguished by their extraordinary stability
(probably due to the calcareous substances which they contain).
The sinuous movements of the sper-
matozoa are executed by the cilium alone,
which propels the head before it ; they
seldom occur in the concentrated secretion
of the testicle and begin only after dilu-
tion normally effected by admixture of the
fluids of the ampullar, of the seminal vesi-
cles, of the prostate gland, and of the
bulbo-urethral glands. In this mixture of
fluids the motions may continue for from
twenty-four to forty-eight hours after death
and for a still longer period in the secre-
tions of the female genitalia. Water para-
lyzes the movement, which, however, may
be restored by the addition of normal animal fluids of alkaline reaction
and moderate concentration ; normal fluids in general, also a one per
cent, salt solution, exert a favorable influence on the vibrations of the
spermatozoa, while acids and metallic salts suspend them. In motion-
less spermatozoa the caudal filament is frequently looped (Fig. 226, 3).
Fig. 226. — i, 2, 3. Human Spermato-
zoa. X 360. 1. Viewed from the
surface. 2 Viewed in profile. 3.
Coiled seminal filament. 4. Sperma-
tozoon of an ox ; a, head ; 6, middle-
piece; c, main-piece. The end-piece
and the demarcation of these parts
cannot be perceived with this mag-
nification. Technic No. 149.
The Excretory Ducts of the Testicle.
The excretory ducts of the testicle include the epididymis, the ductus
deferens, the seminal vesicles, and the ejaculatory duct. (The tubuli
recti and rete testis belong to the excretory ducts, but were described
with the gland because they are enclosed within it.) From the upper
end of the rete testis about fifteen ducluli efferentes testis emerge, which
by their progressively increasing convolutions form as many conical
lobules, the lobidi epididymidis. The aggregate of the lobuli constitutes
the so-called head of the epididymis. By the union of the ductidi effer-
entes the ductus epididymidis arises, which with its complex convolutions
forms the body and the tail of the epididymis and then continues as
the ductus deferens.
*The forms of spermatozoa in different animals cannot be described here. In birds and
tailed amphibians a spiral fiber, united to the axial fiber by a hyaline membrane, has been dis-
covered ; it has been found in the rat and other mammals and appears also to occur in man.
304
HISTOLOGY.
The ductuli efferentes are lined by an epithelium consisting of totally-
dissimilar varieties ; groups of simple ciliated cylindric elements alter-
nate with clusters of cubical cells without cilia ; consequently the latter
have the appearance of simple saccular glands, that, however, do not
produce evaginations of the membrana propria (Fig. 227). A fibrous
membrana propria and a tunic of nonstriped muscle consisting of several
circular strata complete the wall of the ductuli efferentes.
The ductus epididymidis possesses a stratified ciliated epithelium ; its
convolutions are supported and held together by a loose, vascular con-
nective tissue ; toward the ductus deferens the circular strata of muscle-
fibers increase in thickness (Fig. 227).
The ductus deferens consists either of a two-layered columnar
epithelium or of a transitional epithelium, a layer of connective tissue
divided into a tunica propria and a submucosa, an inner circular and an
Cubical cells. Columnar cells.
T\f-A.
$£M& W,
Smooth muscle-fibers.
Connective tissue.
Fig. 227.— Transverse Section of an Adult Human Ductulus Efferens Testis. The right-hand
end of the illustration is schematic. No cilia could be seen, although those of the epithelium of the
epididymis were well preserved. Technic No. 152.
outer longitudinal stratum of smooth muscle-fibers, and a fibro-elastic
adventitia (Fig. 229). The latter, notably in the division lying between
the testicle and the ejaculatory duct, contains longitudinally-disposed
bundles of smooth muscle-fibers.* In the initial portion of the ductus
deferens there also is a thin layer of longitudinal nonstriped muscle-
fibers in the submucosa. The terminal portion expands forming the
ampulla, the walls of which are thinner, but otherwise exhibit a similar
structure. In the mucous membrane of the ampulla there are branched
gland-follicles ; the columnar cells of the epithelium contain numerous
pigment-granules. The seminal vesicles have the same structure. The
ejaadatory duct consists of a simple columnar epithelium and thin inner
* They really belong to the tunica vaginalis of the spermatic cord (funiculus spermaticus),
and are known as the musculus cremaster internus.
THE REPRODUCTIVE ORGANS.
305
circular and outer longitudinal strata of smooth muscle-fibers, as well as
of an adventitia containing dense venous plexuses.
In addition to the networks around the blood-vessels, the nerves form
an intricate plexus provided with sympathetic ganglia, the plexus myo-
spermaticus, situated in the muscuiaris of the epididymis and in that
0m \ ■
Stratified ciliated epithelium.
Membrana propria.
Circular muscle-fibers.
Loose connective tissue.
Fig. 228. — Transverse Section of a Human Ductus Epididymidis. X 80. Technic No. 152.
of the ductus deferens, where it is even more dense, from which delicate
fibers continue into the mucous membrane.
The paradidymis (Giraldes), lying between the convolutions of the
epididymis and the ductidus aberrans (Haller) are atrophic remains of
the embryonal mesonephros. Both consist of tubules lined with ciliated
cubical or cylindric epithelium and enveloped in a vascular connective
— Columnar epitbelium.
Tunica propria.
Submucosa.
Circular muscle.
Longitudinal muscle.
Fig. 229.— Transverse Section of the Initial Portion of a Human Ductus Deferens. X 240.
The transversely cut longitudinal muscle-fibers of the submucosa appear as minute circles and dots.
Technic No. 152.
tissue. The appendix testis or hydatid of Morgagni is a solid lobule com-
posed of a highly vascular connective tissue and covered with a ciliated
columnar epithelium ; it possesses a short pedicle, which contains a duct
lined with ciliated columnar epithelium. The inconstant appendix epidid-
ymidis is a vesicle lined with cubical epithelial cells and contains a clear
306 HISTOLOGY.
fluid. The meaning of these appendices has not yet been fully explained ;
it is uncertain whether they are remains of the anterior end of the
embryonal Mullerian duct, that in the female becomes the oviduct, or
remnants of the primitive kidney.
The Prostate Body.
The prostate body consists for the lesser part of glandular tissue,
for the greater part of nonstriped muscle-fibers. The glandular portion
is composed of from thirty to fifty simple branched tubular serous
glands, which are characterized by their loose structure, that is, by the
wide intervals between the tubules. The tubules open by two large and
a number of smaller ducts into the urethra. The gland-cells are low
columnar elements, which in a simple layer line the tubules. In the
larger ducts the epithelium is of the transitional variety, like that in the
prostatic portion of the urethra. In elderly persons the so-called prostatic
crystals — round stratified masses of secretion up to 0.7 mm. in size —
occur in the gland-tubules. The involuntary muscle-fibers, found in
large quantities everywhere between the gland-lobules, are augmented
toward the urethra and form a robust circular layer (the internal vesical
sphincter muscle) ; numerous involuntary muscle-fibers are also found on
the external surface of the prostate body, where they are contiguous to
the bundles of striated muscle-fibers of the musculus sphincter urethrse
membranaceE. * The prostate gland and the colliculus seminalis are
provided with many blood-vessels. The numerous nerves form wide-
meshed networks containing nerve-cells ; of the nonmedullated fibers
arising therefrom some approach the smooth muscle -fibers, some end in
free ramifications, some (in dogs and cats) terminate in special end-
apparatus (p. 201), that are found in the capsule and in the interior of
the organ.
The glanduliE bulbo-urethralcs (Cowper) are compound tubular
glands, the wide tubules of which are clothed with a simple layer of
clear columnar cells, the excretory duct of which is lined with two or
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.
* Both sphincters are now designated musculus prostaticus.
THE REPRODUCTIVE ORGANS.
307
Each corpus cavernosum is composed of a fibrous sheath, the tunica
albuginea, and of erectile tissue. The tunica albuginea is a stout con-
nective-tissue membrane, possessing an average thickness of 1 mm.,
intermingled with many elastic fibers, in which an outer longitudinal and
an inner circular layer may be distinguished.
The erectile tissue is constructed of lamellae and trabecular of con-
nective tissue containing bundles of smooth muscle-fibers, that by means
of numerous anastomoses form a network. The spaces of the net are
lined with a simple stratum of flat epithelial cells and are filled with
venous blood. The thick-walled arteries in part pass into capillaries, in
part open directly into the deep cortical plexus. The capillaries form a
f^n-lLt^i-Jifn •Sll'.ii} Mucosa
I- ----- -' .■ . ■..'*?■ '''is
W&^Oiz
i v
Submucosa.
3_-
.^-jV-.-V-" 1 ?-^--- -;'\ f ~:~ ■ Cavernous tissue.
Tunica albuginea.
Fig. 230.— From a Transverse Section of the Cavernous Portion of the Human Urethra.
X 20. /, Urethral glands; the lowermost line indicates the fundus of the gland, the upper lines, por-
tions of the excretory duct ; g, blood-vessels ; m, transverse section of longitudinally-disposed muscle-
fibers ; r, superficial cortical capillary network. Technic No. 153.
network beneath the tunica albuginea, the superficial {fine) cortical
plexus, which is connected with a many-layered net of wider venous chan-
nels, the deep {coarse) cortical plexus. The latter lies in the superficial
strata of the erectile tissue and gradually passes into the venous spaces
of the same. The so-called helicine arteries are small branches lying
within slender strands of connective-tissue, which in the collapsed organ
protrude as loops in the cavernous spaces and in an imperfect injection
appear to terminate in blind ends. The veins (venae emissaria?) which
return the blood from the corpora cavernosa partly arise from the deep
cortical plexus, partly from the deeper portions of the erectile tissue.
They penetrate the tunica albuginea and empty into the dorsal vein of
the penis.
308 HISTOLOGY.
The corpus spongiosum consists of two different divisions ; the cen-
tral portion is formed by a reticulum of the conspicuously developed
veins of the submucosa of the urethra (p. 296) ; 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, that are held
together by a conspicuously well-developed connective tissue, the carrier
of the arterioles and of the capillaries.
In the tunica albuginea of the corpora cavernosa, in the glans, and
also in the prepuce peculiar terminal organs of nerves are found (p. 201).
THE FEMALE REPRODUCTIVE ORGANS.
The Ovaries.
The ovaries consist of connective tissue and of gland substance.
The compact connective tissue, the ovarian stroma, is arranged in several
v3ft.
-^i •■■-^- ■-;■■•■•
Fig. 231.— Transverse Section of the Ovary of a Child Eight Years Old. X 10. i. Germinal
epithelium ; 2, tunica albuginea, as yet but slightly developed ; 3, outermost zone of the cortex con-
taining numerous minute follicles; 4, larger follicle; 5 inner division of cortex; 6, medulla wilh
numerous tortuous arteries; 7, follicle cut at the periphery; 8, large follicle, the cumulus oophorus
not within the plane of the section ; 9, hilus, containing wide veins. Technic No. 154.
strata ; outermost lies (i) the tunica albuginea, a structure composed of
two or more intersecting lamellae of connective tissue, which pass by
imperceptible gradations into the stroma of (2) the cortex ; the latter
encloses the gland substance and is continuous with (3) the medulla,
which contains numerous convoluted blood-vessels accompanied by
strands of smooth muscle-fibers. The gland substance is formed by a
THE REPRODUCTIVE ORGANS.
3°9
Germinal
Egg-ball. epithelium.
Primordial
ovum.
c =
Germinal spot
Germinal vesicle, -t — (:
Vitellus.
Follicular
epithelium.
Fig. 232. — From a Vertical Section of the Ovary of an In-
fant Four Weeks Old. X240. The primordial ovum has
a large nucleus with a nucleolus. The egg-ball contains three
ova, surrounded by cylindrical cells. Technic No. 154.
profusion of spherical epithelial sacs, the egg-follicles, each of which con-
tains an egg-cell (ovum). In the human ovary there are about 36,000
follicles. The majority of the follicles are microscopic in size (40 fi)
and in the outermost strata of the cortex form an arched zone embracing
the entire organ except at the hilus, the place where the vessels enter.
The larger follicles occu-
py the deeper portions of
the cortex. The largest,
those follicles readily
perceptible by the un-
aided eye, when fully de-
veloped extend from the
medulla to the tunica al-
buginea. The surface of
the ovary is covered with
a simple layer of very small, mostly short cylindrical cells, the germinal
epithelium (Fig. 231).
Only the 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 all its phases
in every functionally active ovary. During the fetal period many cells
of the germinal epithelium divide into two cells lying one above the
other, of which the lower en-
Germinal epithelium. -
larges and becomes the prim-
ordial ovum with its conspicu-
ous nucleus and nucleolus,
while the upper cell and also
its neighbor-cells become flat-
tened and apply themselves
shell-like around the ovum.
Such conditions are still found
after birth (Fig. 232).
The ovum, which under
circumstances may divide
again, surrounded by its in-
different neighbor-cells, moves down into the ovarian stroma, .while
above in the germinal epithelium new primordial ova arise in the same
way, that likewise move into the depths. Thus originate entire com-
plexes of egg-cells and indifferent cells of the germinal epithelium,
complexes which are named egg-balls (egg-pouches, egg-nests). Each
ovum subsequently becomes separated from its neighbor by the rapid mul-
Tunica albuginea.
Primitive follicle.
Follicle with a simple stratum
of cylindric epithelium.
Follicular epithelium.
Zona pellucida.
-
Vitellus.
Germinal vesicle
with germinal
spot.
:■■<%■'.%,
9
*f
Theca folliculi.
Fig. 233. — From a Section of the Cortex of the
Ovary of a Rabbit. X90. Technic No. 154.
3i°
HISTOLOGY.
tiplication of the indifferent epithelial cells, as well as by proliferation of
the connective tissue, and is then an isolated, spherical body, the primitive
follicle, that consists of the ovum and the epithelial cells enclosing it, the
so-called follicular epithelium, and of a connective-tissue sheath. So far
the processes are chiefly fetal. The cells of the follicular epithelium now
grow taller (Fig. 233), then become stratified, the ovum grows larger,
takes up an eccentric position within the follicle, and acquires a delicate,
radially striated border-zone that gradually increases in thickness,
the zona pellucida (oolemma). With the enlargement of the ovum a
differentiation of its protoplasm is also completed ; the greater portion
rt :d f Tunica externa.
U 3
*""£ I Tunica interna.
Stratum granulosum.
(Follicular epithe-
lium.)
Cumulus oophorus.
Ovum with zona pellu-
cida, germinal vesicle,
and germinal spot.
Fig. 234. — Section of a Large Vesicular Follicle of a Child Eight Years Old. X 90. The
clear space within the follicle contains the liquor folliculi. Technic No. 154.
\ ^^trVVC^*^ .- ; ' i :'''ii>jiiij£••'' .; ,'<
vw :
of it is transformed into a crummy mass, the deutoplasm ; of the original
protoplasm, the egg-protoplasm, there remains only a zone around the
eccentrically situated nucleus and a thin stratum covering the surface of
the ovum. The deutoplasm and the egg-protoplasm are together named
vitellus ; the nucleus is called the germinal vesicle (vesicula germinativa),
which contains the germinal spot (macula germinativa). Ameboid move-
ments have been observed in the latter.
The follicle now develops further ; during continual multiplication
of the cells of the follicular epithelium a cleft appears in their midst that
becomes filled with an aqueous fluid, the liquor folliculi. This liquid is
THE REPRODUCTIVE ORGANS. 3 I I
partly a transudate from the blood-vessels surrounding the follicle, and is
partly derived from the liquefaction of some of the cells of the follicular
epithelium ; it progressively increases in quantity and consequently the
follicle expands to a vesicle, the vesicular follicle (Graaf ), having a diameter
of from 0.5 to 12 mm. Around the larger follicles the connective tissue of
the stroma is arranged in circular strands forming a sheath called the
theca folliculi in which an outer fibrous layer, the tunica externa, and
an inner vascular layer rich in cells, the tunica interna, may be distin-
guished (Fig. 234). The stratified follicular epithelium (Fig. 234), which
in teasing fresh follicles becomes detached in large shreds, has long been
known as the stratum (membrand) granulosum ; at one point it presents
a thickening, the cumulus oophorus, which encloses the ovum. The cells
Zona pellucida.
Vitellus.
Zona pellucida. - -fiK^.V& £ > % "4-^ ,
Germinal spot.
Corona radiata
rus.
\ '' t 'W^'0SHVXT'*y-'P (cells of th
f\ '" '^£&tld3 :- Mucosa.
liiil
Fig. 238. — Mucous Membrane of the Resting Uterus of a Young Woman. X 35-
(After B'ohm and von Davidoff.)
The nucleus (not infrequently two or more are present in one cell) is usually
oval and lies embedded in a granular substance.
The mucosa is sharply defined from the muscularis. It is the coat
which in the different functional states of the uterus undergoes the pro-
foundest and physiologically the most important changes. Therefore a
description of the histologic structure of the mucosa of the uterus can
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 : —
I. The mucosa of the virgin resting organ.
3 16 HISTOLOGY.
2. The mucosa of the menstruating uterus.
3. The mucosa of the gravid uterus.
The mucosa of the virgin resting uterus (Fig. 238), after the advent
of puberty, has a thickness of from 1 to 2 mm. and bears on its surface
a layer of simple ciliated columnar epithelium, 30 p. 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 consists of elongated cells furnished with oval nuclei,
which send out in all directions branched processes that unite with those
of neighboring cells and form a cellular network, the meshes of which
are occupied by lymph and by numerous leucocytes.
The turiica propria supports many simple or forked gland-tubules, of
which the upper part pursues a more or less straight course, while the
lower part takes a serpentine course (Fig. 237). The glands extend
close 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 super-
ficial epithelium and likewise consist of a simple layer of ciliated epithe-
lium resting upon a delicate basement membrane composed of anasto-
mosing connective-tissue cells.
The blood-vessels run in a winding manner from the muscularis to
the surface of the mucosa and the arteries in particular are character-
ized by their extremely convoluted, corkscrew-like course. At the sur-
face they break up into capillaries and form a close network. A similar
network surrounds the gland-tubules. The veins proceeding from the capil-
laries form a plexus in the deeper strata of the mucosa, that is especially
well developed in the cervix and particularly around the external orifice.
In the cervix the mucous membrane is thicker and in its upper two-
thirds is clothed with a single layer of tall ciliated cells (60 (i high in the
middle portion),* while toward the external orifice papillae covered with a
stratified squamous epithelium appear. In addition to a few scattered
tubular glands, mucous follicles, the so-called mucous crypts, occur ; they
are 1 mm. wide, possess many evaginations, and by retention of their
secretion are converted into cysts, the ovula Nabotlii.
During the period of menstruation a number of progressive and
regressive changes take place in the mucosa of the uterus, which may
be grouped in three phases : —
(a) Thickening of the mucosa, accompanied by changes in its
histologic structure.
* Transformation of these cells into goblet-cells occurs.
THE REPRODUCTIVE ORGANS.
317
{p) Menstruation proper.
if) Regeneration.
The initial phase is characterized by a considerable increase in the
thickness of the mucosa (up to 6 mm.), in consequence of which the
surface becomes irregular and the orifices of the glands open in deep
depressions. The thickening of the mucosa depends in a measure on
Superficial epithelium.
Excretory duct.
ds.
pri.
Excretory duct.
Gland-tubule.
Blood-vessel.
Blood
Fig. 239. — Mucous Membrane of a Virgin Uterus During the First Day of Menstruation.
ds. Disintegrating surface ; pd, pit-like depression of the mucous membrane; gl, gland-lumen very
much enlarged. X30.—{Schafier,)
an actual increase of the tissue produced by proliferation of the connec-
tive-tissue cells and the 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 capil-
laries, undergo enormous distention, whereby the blood-supply of the
3i8
HISTOLOGY.
organ is extraordinarily augmented. In this condition the mucosa is
designated decidna menstrualis.
These changes are followed by a partial disintegration of the super-
ficial strata of the mucosa, accompanied by an infiltration of blood into
the subepithelial tissues. The molecular disintegration (associated with
fatty degeneration) of the surface advances rapidly, the greatly dilated
superficial blood-vessels become exposed, rupture, and cause hemor-
rhages within the uterine cavity, which flow into the vagina and give rise
to the external phenomena of menstruation. After this discharge of
blood the mucosa is rapidly reduced in thickness. The surface is now
%•- Excretory duct.
Compact layer. '
Cavernous layer.
Gland-tubules.
Fig. 240.— Vertical Section through the Mucous Membrane of a Human Uterus One Month
Pregnant ; it shows the outlines of the glands and the division of the mucosa into an upper com-
pact and a lower cavernous layer. — {After Minot.)
entirely devoid of epithelium and consists of connective tissue and
exposed blood-vessels. This condition is immediately succeeded by the
stage of regeneration. The hyperemia rapidly disappears, the extrava-
sated 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
capillaries are formed.
The histology of the mucosa of the uterus during pregnancy
(decidua graviditatis) (Fig. 240 and Fig. 241) is, on the whole, like that
of the decidua menstrualis, with the alterations more pronounced. It,
THE REPRODUCTIVE ORGANS.
319
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 development three essentially different parts of
the mucosa may be distinguished : —
(«) The (/tricf/td serotina (decidua basalis), the area of the mucosa
to which the ovum is attached (placenta uterina).
(/') The decidua vera, which comprises .ill 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 projects into the cavity of the uterus and encapsules the
ovum.
fw 'lU^xmasKTramrrn
lT 1 *.*"V^ p .'v
Compact layer.
'*&3&-'' SUP
-;^t^^^
■ iiT aft ©'-i. «,7.^V.-,.,- '-o&'i^-^ A '< ^-— w^^r^^s,
Cavernous layer. <
&.— Vein
Fig. 241.— Vertical Section through the Wall of a Uterus about Seven Months Pregnant,
with the Fetal Membranes in Situ. Between amnion and chorion are threads of the inter-
mediate gelatinous connective tissue. X 30. — (Schaper.)
The decidua serotina and the decidua vera undergo progressive de-
velopment during the entire course of pregnancy and persist until its
close; the decidua reflexa becomes gradually attenuated and disappears
in the course of the fifth month.
A section of the greatly thickened mucosa (decidua vera and
decidua 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,
320
IIISTOLOOY.
distention of the blood-vessels and glands) attain much greater propor-
tions. A superficial compact zone and a deep spongy zone can always be
distinguished (Fig'. 240). 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. 241.) Between
the glands are numerous blood-vessels, spindle-cells, and multinucleated
giant-cells. The epithelium of the glands early begins 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 super-
ficial 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 the veins open on the surface of the mucosa (Fig. 243 and
Fig. 244), so that here the maternal blood circulates between the chor-
ionic villi of the placenta (see page 326). In the decidua vera the
blood-vessels, toward the end of pregnane)', are less conspicuous.
Of especial interest are peculiar, typical cells, decidual cells, that
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 0.1 mm.), that
111 the latter half of pregnane}' assume a
characteristic brown color. They usually
possess but one nucleus, though occasion-
all}' two, three, or more are present, and in
rare cases as man}- as thirty or fort}- The
decidual cells are most numerous and most
densely aggregated in the upper compact
zone of the serotina (Fig. 241), which owes
its typical character anil 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,
therefore may be regarded as a modified
embryonal or so-called anastomosing connective tissue.
In a cross-section of the decidua vera in the latter half of preg-
Fig. 242.— Decidual Cells from the
Mi tors Membrane of a Human
Uterus about Seven Months
PregNAN r. He low a " giant-cell,"
above to the right n cell with ri kary-
okinelic figure, > 250.— (Schaper.)
THE REPRODUCTIVE ORGANS. 32 I
nancy, it will be seen that the surface of the mucosa is covered by two
distinct membranes, — fetal membranes — the chorion and the amnion (Fig.
241). The chorion 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 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 the 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 lymph-vessels of the uterus form in the mucosa a wide-meshed
network provided with blind branches. From this small stems proceed
through the muscularis and communicate with a close subserous network
of larger channels.
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 plexus in this and
in the mucosa. From the latter delicate fibrils may be traced between
the epithelial cells.
The Placenta.*
The placenta is an organ which from a morphologic standpoint is
composed of two heterogeneous parts, of which the one is produced by
the mother (placenta uterina), the other by the embryo (placenta fetalis).
It is the result of the intimate union of a circumscribed area of the
chorion (chorion frondosum) with that portion of the mucosa of the
uterus known as the decidua serotina. The placenta serves the purpose
of bringing the fetal and the maternal blood into the closest proximity,
to render possible the interchange of materials between them. To sub-
serve this function the organ possesses a peculiar histologic construction,
in which the blood-vessels, especially in their arrangement and structure,
take a prominent 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 pre-
viously mentioned fact that the finished organ is the product of two origi-
nally heterogeneous structures, the chorion on the one side, the decidua
serotina on the other, and that their union is substantially effected in that
*This chapter is an entirely new addition by the editor.
Am.
|
VI.
vi
l ; { -
D"
Fig. 243. — Section through a Normal Human Pi.acen rA ok alout Seven Months, in Situ.
Am., Amnion; Cho., Chorion; Vi, Linnk of a villus; vi , sections of villi in (he substance of the
placenta; D, decidua basalis; Mc, rnuscularis ; I)', compact layer of decidua; Ve, uterine artery
opening into the placenta, The fetal blood-vessels are drawn back; the maternal blood-spaces are
left white; the chorionic tissue is stippled except the canalized fibrin, which is shaded by lines; the
remnants of the gland-cavities in D" are stippled dark. — {After Minot.)
THE REPRODUCTIVE ORGANS.
323
the chorion, by means of numerous villous-like proliferations, penetrates
the underlying serotina, the surface of which is peculiarly modified and
further 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. The accompanying illustration
Compact
layer.
Cavernous ,
layer.
Chorionic villi.
Intervillous spaces.
Floating; villus.
Attached villi.
Vein.
Spiral artery.
Gland.
Fig. 244. — Diagram of the Human Placenta at the Close of Pregnancy. Ct. Fig. 243.
— (Schaper.)
(Fig. 243) shows their relations under low magnification, which will be
elucidated by referring to the schematic representation in figure 244.
The surface of the placenta directed toward the cavity of the uterus
is covered by a compact stratum, the membrana chorii, which is chiefly
composed of fibrillar connective tissue, 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 connect-
ive-tissue layer and is attached to the chorion by means of embryonic
connective tissue. The other surface of the membrana chorii, that
directed toward the wall of the uterus, is closely beset with innumerable
3^4
HISTOLOGY.
villous-like structures, large and small, which in the upper part of the
placenta form a dense tangle, the terminal ramifications of which 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 inter-
villous spaces, between the chorion and the serotina. Dependent upon
these relations the branches of the chorionic villi are divided into roots
of attachment, or main stems, and free processes, or floating villi. From the
chorion a branch of the umbilical artery enters each main stalk and
Protoplasmic coat.
Epithelial nucleus.
Capillaries.
Cell-patch (Zellknoten)
S m a„arter y ...-^&V^
Cell-patch (Zellknoten)
.Cell-patch (Zellknoten j in
process of formation.
Protoplasmic coat
(syncytium).
Small vein.
Capillary.
Fig. 245. — Cross-section through a Smaller (A) and a Lakger (B) Chorionic Villus of a
Human Placenta at the End of Pregnancy. X 250. — {Schaprr.)
within the terminal ramifications of the villus breaks up into a dense
capillary network from which the umbilical veins take their origin and
carry back the blood from the chorion through the umbilical cord to the
fetus. Accordingly, the blood-vessel system of the fetal placenta is entirely
closed. Nowhere does a direct intermingling of the maternal and the fetal
blood occur.
A cross-section of one of the smaller chorionic villi, highly magni-
fied, shows that it is chiefly composed of mesenchymal tissue (mucous
tissue), in which the blood-vessels are embedded (big. -45). This
central supporting substance is covered by an irregular and not every-
where continuous stratum of epithelium. In the earlier months of
THE REPRODUCTIVE ORGANS. 325
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 preg-
nancy, however, the epithelium of the villi undergoes great alteration,
as appears in the illustration (Fig. 245). On the larger villi a true epithe-
lial 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 frequently is covered only by a
thin, homogeneous stratum, or in some cases (especially 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 origi-
nated in the primitive inner stratum of the epithelium of the villi.* In
many places the syncytium is transformed into a peculiar hyaline sub-
stance permeated by fissures, which often lies upon the chorion in dense
strata and is called canalized fibrin.
The histologic structure of the maternal portion of the placenta —
placenta ulerina — in its essential features has been described in connec-
tion with the decidua in the preceding chapter. But certain peculiarities,
as well as the union of maternal and fetal placenta in a functional whole,
require a brief consideration.
The placental portion of the decidua (Fig. 243), that forming the
lower stratum of the placenta (basal plate), is greatly thinned (from 0.5
to 1 mm.), but as in the extraplacental 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. A honey-
combed 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
*It has not been yet determined with certainty whether the epithelium of the villi of the
human placenta is entirely derived from the epithelium of the chorion, or whether the epi-
thelium of the serotina participates in its composition. However, recent investigations as well
as comparative anatomical facts indicate that only the inner epithelial stratum of the villi
comes from the chorionic epithelium, while the syncytium is derived directly from the mucosa
of the uterus, the epithelium of which, on the ingrowth of the chorial villi, becomes closely
applied to, and blends with, the epithelium of the latter.
326 HISTOLOGY.
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 subchorialis. On the margin of the placenta the serotina
gradually increases in thickness and passes 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 the 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 sur-
rounds 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. 243 and Fig. 244). Numerous arteries from the
muscularis of the uterus penetrate the serotina, in which they make cork-
screw-like tours during the course of which they lose their muscular coat
and continue as wide tubes consisting alone of the lining endothelium.
Near the surface of the decidua they usually bend sharply at right angles
and then open directly into the intervillous spaces of the placenta.*
Nowhere do the arteries break up into capillaries. The veins (likewise
endothelial tubes, though wider than the arteries) also are in direct com-
munication with the placental spaces ; they enter the decidua usually
under a very narrow angle, run more or less parallel to the surface, and
unite in the deeper strata in a wide venous plexus. In accordance with
the description of these conditions of the vessels, the arteries and the
veins within the serotina can no longer be recognized by the histologic
structure of their walls, but can be distinguished only by their width and
* In regard to the relation of the decidual blood-vessels to the intervillous spaces there are
two conflicting theories. According to the one the intervillous spaces are independent clefts
without proper walls, that are formed in the course of development between the fetal and
maternal portions of the placenta, with which the blood-vessels opening on the surface of
the decidua are in direct communication. Accordingly the villi of the chorion are in direct
contact with the maternal blood circulating in these spaces. The opposite view regards the
blood-spaces of the placenta as the enormously widened capillaries of the decidua, which, dur-
ing the mutual process of intergrowth between the placenta uterina and the placenta fetalis, the
developing villi of the chorion have invaginated. According to this the blood-vessel system of
the decidua is closed and the arteries and the veins communicate through a system of capillary
lacunse (the intervillous spaces). Further, the chorial villi are not directly bathed in the
maternal blood, but are separated from it by a thin stratum of cells, the capillary endothelium,
which lies directly upon them. Recent investigations of Keibel apparently support the latter
view, since in a human placenta in an early stage of development he succeeded in tracing the
endothelium of the decidual blood-vessels into the intervillous spaces and demonstrating it as a
continuous stratum on the surface of the chorionic villi. It is possible that in the further de-
velopment of the placenta this endothelial covering undergoes regressive change, so that in later
stages it cannot as a rule be demonstrated.
THE REPRODUCTIVE ORGANS. 327
their course. In addition the arteries usually are characterized by a
thin, homogeneous, enveloping stratum that stains intensely with carmine,
in which a few scattered nuclei are found. This peculiar layer is prob-
ably a product of the degenerated muscular coat.
The Vagina and the External Genitalia.
The vagina is formed by a mucous membrane, a muscular tunic,
and a fibrous tunic.
The mucous membrane is composed of a stratified scaly epithelium
and a tunica propria beset with papillae and built up of small, inter-
lacing bundles of connective tissue ; it contains a few elastic fibers and
a varying quantity of leucocytes. The latter occasionally exist in the
form of solitary nodules ; in this case numerous migrating leucocytes are
found in the epithelium in these localities. The mucosa rests on a sub-
mucosa, which is composed of loosely united connective-tissue bundles
and robust elastic fibers. Glands are absent within the vaginal mucous
membrane.
The muscular coat comprises an inner circular and an outer longi-
tudinal layer of smooth muscle-fibers.
The outer fibrous tunic is a dense connective -tissue structure, rich in
elastic fibers.
The blood- and lymph-vessels are arranged in parallel horizontal net-
works in the submucosa and in the tunica propria. Between the bundles
of the muscular tunic lies a close network of wide venous channels.
The nerves form a plexus in the outer fibrous tunic, beset with many
small ganglia.
The mucous membrane of the external genitalia in the vicinity of the
clitoris and the urethral orifice differs from the vaginal mucosa in the
possession of numerous mucous glands, from 0.5 to 3 mm. in size, and
on the labia minora in the presence of sebaceous glands (without hair-
follicles) from 0.2 to 2 mm. in size. The clitoris repeats on a diminutive
scale the structure of the penis ; end-bulbs and genital nerve corpuscles
occur in the glans clitoridis.
The large glands of the vestibule (Bartholin) are the homologues of
the bulbo-urethral glands in the male.
The labia majora are folds of the skin and possess the same struc-
ture.
The acid vaginal secretion contains desquamated scaly epithelial
cells and leucocytes, and not infrequently an infusorium, trichomonas
vaginalis.
328 HISTOLOGY.
TECHNIC.
No. 145. — For a general view of the testicle make a transverse
ncision * through the testicle and the epididymis of a newborn child ; fix
the pieces in about 50 c.c. of Kleinenberg's picrosulfuric acid (p. 21)
and harden in 30 c.c. of gradually-strengthened alcohols (p. 34). Stain
thick transverse sections of the entire organ in dilute carmine (p. 38), and
in Hansen's hematoxylin (p. 37), and mount in damar. Examine with very
low magnification (Fig. 223). In the testicle of the rabbit, cat, and dog
the corpus Highmori is not at the margin but in the center of the organ.
No. 146. — Minute Structure of the Seminiferous Tubules. — Place
small pieces (2 cm. cubes) of the fresh testicle of an ox in 200 c.c. of
Zenker's fluid (p. 32), and harden them in 50 c.c. of gradually -strength-
ened alcohols (p. 34). Cut sections as thin as possible, stain them in
Hansen's hematoxylin (p. 38), and mount in damar (p. 48). Even with
the low power tubules in a condition of activity can be distinguished from
resting tubules ; the former may be recognized by the intensely blue
heads of the young spermatozoa (Fig. 224).
No. 147. — Still better preparations are obtained by placing the entire
testicle of a mouse in 10 c.c. of the platinum-acetic-osmic acid mixture
(p. 34) for twenty-four hours for fixation, then washing it for several hours
in running water and placing it in 20 c.c. of gradually-strengthened alco-
hols for hardening. Mount the unstained sections in damar (Fig. 225).
The platinum-acetic-osmium mixture does not pene-
trate sufficiently into the testicles of larger animals,
which therefore are not suitable.
No. 148. — Elements of the Testicle. — Place pieces
about 1 cm. in size of the fresh testicle of an ox in
20 c.c. of one-third alcohol (p. 20) and in five or six
hours tease the tubules in a drop of the same alcohol.
Stain under the cover-glass with picrocarmine and
mount in dilute glycerol. Several preparations from
different parts of the organ should be completed and
Fig. 246. — I S O L A T E D
Elements of the
testicle of an then not infrequently the cells of Sertoli with attached
Ox. X 240. a, c, x J
Mother - ceils ; *, spermatocytes, or the seminal filaments produced by
''spermatoblast." . .... , , . / . , x J
d, immature sem- them, will be obtained (Fig. 246, 0), structures that
ture se^a^'fiia- formerly were described as " spermatoblasts."
merit.
No. 149. — Elements of the Semen. — Make an in-
cision into a fresh epididymis f and place one drop of the milk-white fluid
that exudes from the cut surface on a clean slide ; add one drop of salt
solution, apply a cover-glass, and examine with the high power. After a
* If no incision is made into the organ it does not harden sufficiently, because the dense
tunica albuginea retards the penetration of the fluids.
f For a view of the spiral fiber mentioned above (p. 303, remark), that can be seen only
with very powerful immersion lenses, I recommend the seminal filaments of the rat ; they are
to be examined in water.
THE REPRODUCTIVE ORGANS. 329
time let one drop of distilled water flow under the cover-glass ; the move-
ments of the spermatozoa soon cease ; the heads of the majority of the
seminal filaments then present their broad surface and the tail curves and
forms a loop (Fig. 226, 3). Remnants of protoplasm still adhere to sem-
inal filaments not fully matured. The spermatozoa may be preserved by
allowing the semen diluted with water to dry on the slide ; then apply a
cover-glass and secure it with cement (p. 47). In examining such prepa-
rations, too much illumination gives rise to troublesome reflections.
No. 150. — The stability of the seminal filaments has led to investiga-
tions for forensic purposes. For example, it may be a question as to
whether spots occurring on a linen garment were produced by semen.
Cut strips from 5 to 10 mm. long from the suspected spots, soak them
for from five to ten minutes in a watch-glass containing distilled water, and
tease a few fibers. With the high power (500 : 1) chiefly examine the
edges of the isolated linen fibers, to which the seminal filaments if present
are attached. Not infrequently the heads are broken off; they are recog-
nized by their peculiar luster, their shape, and their (in man small) size.
No. 1 51. — Seminal Filaments of the Frog. — The male frog is recog-
nized by a well-developed wart on the ball of the thumbs. Open the
abdominal cavity ; the testicles are a pair of oval bodies (similar to the
kidneys of mammals) lying to either side of the vertebral column. Divide
the organ by a transverse incision ; dilute a drop of the fluid with a drop
of salt solution. The seminal filaments are large, the head thin and
elongated, the tail so delicate that at the first glance it may be overlooked.
Immature filaments lie grouped in tufts.
No. 152. — Epididymis, Ductus Deferens, and Seminal Vesicles. —
Pieces from 1 to 2 cm. in size are to be fixed in about 100 c.c. of Zenker's
fluid and hardened in 60 c.c. of gradually-strengthened alcohols. Stain
the sections with Hansen's hematoxylin and mount in damar (Fig. 227,
228, 229).
No. 153. — The prostate and the different divisions of the male
urethra are to be prepared in 2 or 3 cm. cubes like No. 152 (Fig. 230).
No. 154. — The Ovary. — The ovaries of small animals may be fixed
in toto and those of larger animals with several incisions transverse to
the long axis in 100 or 200 c.c. of Zenker's fluid (p. 32) and hardened
in 100 c.c. of gradually-strengthened alcohols (p. 34). For a topo-
graphic view (Fig. 231) it is advisable to cut thick sections, because
otherwise the contents of the follicles easily fall out. Not every section
includes large follicles ; it is often necessary to cut many sections, in order
to strike a favorable place. Stain the sections with Hansen's hematoxylin
(p. 37), or in bulk with borax-carmine (p. 39). Mount in damar (p. 48).
No. 155. — Fresh ova may be obtained as follows. Procure the
fresh ovaries of a cow. The large Graafian follicles are transparent, pea-
sized vesicles, which with the scissors may be easily shelled out in toto.
Transfer the isolated follicle to a slide and prick it with a needle. The
needle must be carefully thrust in on the side of the follicle lying against
the slide, otherwise the liquor will spurt out and carry the ovum with it.
330 HISTOLOGY.
With the low power, and without placing a cover-glass on the prepara-
tion, search for the ovum, which surrounded by the cells of the cumulus
oophorus will be found in the escaping liquor folliculi (Fig. 235 A).
Place two narrow strips of paper on either side of the ovum, carefully
apply a cover-glass, and examine with the high power.
The beginner will sacrifice many a follicle before he succeeds in
finding an ovum. Often the ovum does not escape when the follicle is
pricked ; it may then be found by teasing the follicle.
No. 156. — Ova of the Frog. — Place a small piece of the fresh ovary
of a frog on a slide and prick all the large pigmented eggs, so that their
contents escape. Place that which remains in a watch-glass with dis-
tilled water and wash it by moving it to and fro with needles. Place the
watch-glass on a black background ; the smaller, still unpigmented folli-
cles can then be seen. Transfer the washed object to a clean slide, apply
a cover-glass, and examine it. The ova have very large germinal vesi-
cles ; the germinal spot disappears early and usually is not to be seen.
On the other hand, a dark spot occurs in the vitellus, the "nucleus of
the vitellus,'' which probably corresponds to the astrosphere (p. 63).
Surrounding the ovum is a finely striated membrane, the inner surface of
which is covered with flat cells ; this is the theca folliculi with the simple
follicular epithelium.
No. 157. — The Oviducts. — Pieces 1 or 2 cm. long are to be fixed in
50 c.c. of 3 per cent, nitric acid and after five hours hardened in 60 c.c.
of gradually-strengthened alcohols. Stain with Hansen's hematoxylin
and mount in damar.
No. 158. — For topographic preparations of the human uterus the
uteri of young individuals are suitable. According to its size, fix the
whole uterus or pieces of it 2 cm. square in about 100 c.c. of Zenker's
fluid (p. 32) and harden in 100 c.c. of gradually-strengthened alcohols
(p. 34). Stain in Hansen's hematoxylin and in eosin (p. 38) and mount
in damar (p. 48). (Fig. 237.) In such preparations the gland follicles
are often very indistinct.* In the two-horned uteri of many animals
the often greatly convoluted gland-tubules can be more readily distin-
guished ; the arrangement of the muscular strata is different, more
regular than in the human organ.
No. 159. — For preparations of the human uterine mucosa, cut out
pieces 1 cm. square and treat them after No. 158. Owing to the extreme
tortuousness of the glands, sections contain only fragments of the folli-
cles. The cilia can seldom be seen in fixed preparations.
No. 160. — The placenta is to be treated according to No. 1 59.J
Before cutting sections the pieces must be embedded in celloidin or
paraffin ; in the latter case the sections must be fastened to the slide (see
Microtome Technic), in order that the innumerable branches of the villi,
cut in every plane, do not fall out. The study of preparations of this
kind is one of the most difficult tasks of the microscopist.
* Figure 237 was sketched from an unstained preparation. The glands were not so distinct
as they appear in the illustration.
I Fixation in absolute alcohol often yields very good results.
THE SKIN AND ITS APPENDAGES. 33 1
IX. THE SKIN AND ITS APPENDAGES.
The skin (integumentum commune, cutis) is principally composed of
connective tissue, which however is nowhere exposed, but is protected
by a continuous epithelial coat. The connective-tissue portion of the
skin is called corium, derma, or true skin, the epithelial portion, epidermis
or cuticle. The appendages of the skin, the nails and the hairs, as well
as the glands and the hair-follicles embedded within the corium, are
products of the epidermis.
The Skin.
The Corium. — The surface of the corium is marked by many fine
furrows, which intersect and enclose rectangular or lozenge-shaped areas
or run parallel between minute ridges. The lozenge-shaped areas may
be seen on the surface of the greater part of the body, while the ridges
are confined to the volar surface of the hand and the plantar surface of
the foot. These areas and ridges are beset with numerous conical eleva-
tions, the papillce, the number and size of which vary greatly in different
regions of the body. The largest (up to 0.2 mm. high) and most nu-
merous papillae occur on the palm of the hand and on the sole of the
foot ; they are very slightly developed in the skin of the face.
The corium chiefly consists of interlacing connective-tissue bundles,
mingled with elastic fibers, cells, and smooth muscle-fibers. In the super-
ficial strata of the corium the connective-tissue bundles are delicate and
are united in a closely interwoven texture ; in the deeper strata they are
larger and intersecting at sharp angles form a coarse-meshed network.
These differences have led to the recognition of two strata in the corium,
a superficial stratum beset with papillae, stratum papillare, and a deep
stratum, stratum reticulare. There is no sharp demarcation between the
two strata, the one gradually blending with the other (Fig. 249). The
stratum reticulare is connected with an underlying network of loosely
united bundles of connective tissue, the wide meshes of which contain
clusters of fat -cells ; this is the stratum subcutaneum. The storing of much
adipose tissue in the interfascicular spaces of this stratum leads to the
formation of the panniculus adiposus. The tissue of the subcutaneous
stratum is firmly or loosely connected with the sheaths of the muscles
(the fasciae) or of the bones (the periosteum). The elastic fibers, which
are thin in the stratum papillare and thicker in the stratum reticulare,
form networks uniformly distributed throughout the corium. The
easily displaceable skin over the subcutaneous tissue is relatively
poor in elastic fibers ; particularly rich in these is the skin of the face and
332
HISTOLOGY.
of the vicinity of the joints. The cells include spindle-shaped and plate-
like connective-tissue elements, leucocytes, and fat-cells. The number
( Stratum corneum.
Epi :
dermis. J Stratum lucidum.
l_Stfatum germinativum.
r Stratum papillare.
„ I Excretory duct.
Corium. ~\
- Stratum reticulare.
Coil-gland.
Stratum subcutaneum.
Fig. 247.— Vertical Section of the Skin of the Finger of Adult Man. X 25. With this mag-
nification the stratum granulosum is not visible. Technic No. 161.
ot the cellular elements is extremely variable. The muscle-fibers almost
exclusively belong to the nonstriped variety and the majority are
Depressions in which
the papillae were in-
serted.
Furrow corresponding
to a ridge of the
corium.
-■«■ -•\j : -'-''"~-' r, "'' ; **r-.'-'"'" : ':' <*■
Portion of the duct of a
coil-gland.
Fig. 24.8. — Epidermis from the Skin of the Dorsum of the Human Foot, seen from the Lower
Surface. X 120. The preparation is so to speak the cast, while the surface of the corium beset
with papillae represents the matrix. Technic No. 162.
attached to the hair-follicles ; only in a few situations in the body do
they occur as membranes in the skin (tunica dartos, nipple). Striated
THE SKIN AND ITS APPENDAGES. 333
muscle-fibers occur in the skin of the face, where they radiate from the
mimetic muscles.
The Epidermis. — The epidermis consists of a stratified squamous
epithelium, in which at least two sharply defined zones may be distin-
guished : a deep zone, the stratum germinativum (Malpighi), which fills
the depressions occurring between the papillae of the corium, and a super-
ficial, firmer zone, the stratum corneum. Both strata consist entirely
of epithelial cells, which exhibit different appearances in the separate
layers. In the deepest layer of the stratum germinativum the cells are
cylindrical and possess oblong nuclei ; these are followed by several
layers of spherical cells that are beset with numerous minute thorns, the
prickle-cells. The thorns are delicate thread-like processes, which pen-
etrate the small amount of intercellular cement-substance and serve
the purpose of connecting neighboring cells to one another. Therefore
they are called intercellular bridges (Fig. 14). In the stratum germi-
nativum new cells are continually being formed by indirect division.
The stratum corneum is not everywhere of the same structure and
two types may be distinguished : (1) In localities where the epidermis is
well developed, as on the palm of the hand and the sole of the foot, a
stratum of cells characterized by highly refracting granules * (keratohyalin
granules) lies next to the stratum germinativum. Perhaps these granules
are a transformation product of the achromatin constituents of the nuclei (?).
This zone is named stratum granulosum. In the next layer the granules
dissolve, blend with the parts of the protoplasm not yet transformed into
horny substance, and form a uniformly clear zone, the stratum lucidum.
This is covered by the broad stratum corneum proper. In this stratum
all the noncornified parts of the cell under the influence of the atmos-
phere are desiccated ; so it happens that each cell contains a delicate,
horny mesh-work and — since the intercellular bridges also become
cornified — is enveloped in a horny membrane. The nucleus desiccates ;
the space which it occupied persists for a long period. These partly
cornified, partly desiccated cells are only slightly flattened. (2) In situ-
ations where the epidermis is thinner, all the remaining surface of the
skin, the stratum granulosum is narrow and interrupted. The stratum
lucidum is absent. The horny cells of the stratum corneum are extremely
flattened and are united in lamellae. The last trace of the nucleus is
lost.
The surface of the horny stratum undergoes a continual physiologic
* These granules dissolve in a solution of potassium hydroxid and therefore are not
composed of keratin, which is insoluble in this reagent.
334
HISTOLOGY.
desquamation ; the resulting loss is compensated by the pushing upward
of the growing elements of the germinal stratum.
The color of the skin is due to the deposition of fine granules of
pigment between and within the cells of the deeper layers of the epider-
mis ; only in certain localities, for example, in the vicinity of the anus,
are pigmented connective-tissue cells found in the adjacent corium.
With regard to the source of the pigment of the epidermis there are
two theories, of which the one attributes its origin to the connective
tissue, the other to the epithelium. According to the first, hitherto
:,X_
■r -0,_
-— Part of the stratum
corneum.
— Stratum lucidum.
Stratum granulosum.
Stratum germinativum.
m,
■ ^&mLmk++ 9m £& ' layerof
e papillary
the corium.
■<*&$■:
Fig. 249.— From a Section through the Skin of the Sole of the Foot of Adult Man.
X 360. Technic No. 161.
frequently accepted opinion, the so-called "transportation" theory,
the pigment is carried to the epithelium by pigmented connective-tissue
cells, that wander from the corium into the epidermis and there dis-
integrate. In the human hair-bulb' pigmented forms presenting great
diversity in outline are found between the epithelial elements ; some of
these figures are cells, but it has not been demonstrated with certainty
that they are connective-tissue cells, others are not cells, but intercellular
clefts filled with pigment. The second theory is supported by the
developmental history, which teaches that the pigment originates in the
epithelium of the hair without the intervention of connective-tissue cells.
The pigment of the retina also is certainly and exclusively of epithelial
origin.
THE SKIN AND ITS APPENDAGES.
335
The Nails.
The nails are horny laminse, which rest upon a special modification
of the skin, the nail-bed. The nail-bed is bounded laterally by the nail-
walls, a pair of sloping folds with the descent forward. The nail-bed
and the nail-wall embrace a furrow, the nail-groove, in which the lateral
border of the nail is inserted (Fig. 250). The posterior border of the
nail, the nail-root, rests in a similar but deeper groove, the matrix* in
which the principal growth of the nail takes place. The anterior free
border of the nail projects over the nail-ridge, a small seam-like prom-
inence at the distal end of the nail -bed.
The nail-bed consists of corium and of epidermis. The fibro-elastic
f Corium.
Nail-]
bed - Epithe-
i. Hum.
Eponychium.
Fig. 250. — Dorsal Half of a Cross-section of the Third Phalanx of a Child. X 15- The
ridges of the nail-bed in cross-section appear like papillae. Technic No. 163.
bundles of the corium partly are disposed parallel to the long axis of the
finger, partly run vertically from the periosteum of the phalanx to the
surface. The surface of the corium does not possess papillae, but minute
longitudinal ridges. They begin low at the matrix, increase in height
toward the anterior border 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 germinal stratum of
the epidermis. It covers the ridges of the nail-bed, fills up the furrows
between them, and is sharply defined from the substance of the nail.
The matrix likewise consists of corium and of epidermis ; the corium is
distinguished by its tall papilla?, the stratified scaly epithelium is very
thick and is not sharply defined from the nail-substance, but gradually
blends with it. This is the place where by continual division of the
epithelial cells the material for the growth of the nail is furnished. On
* Some authors name the whole nail-bed matrix, which is in a measure justified by the
growth in the thickness of the nail that occurs here.
336 HISTOLOGY.
this account the epithelium is called the germ-layer of the nail. The
extent of the matrix is indicated by the lunula, a white, anteriorly convex
area, visible to the unaided eye ; it is produced by
the thick, uniformly extended germ-layer. The nail-
wall exhibits the usual structure of the skin. The
germinal stratum of the nail-wall gradually blends
with the epithelium of the nail-bed ; the horny stratum
extends into the nail-groove and as " eponychium "
covers a small portion of the border of the nail, but
Fi of a'human "nT" soon diminishes in thickness and disappears (Fig.
X 240- Technic No. ---A
164. 2 S°S-
The nail itself consists of horny epithelial scales,
that are very firmly united with one another and are distinguished from
the horny cells of the stratum corneum of the epidermis by the posses-
sion of a nucleus (Fig. 251).*
The Hairs and the Hair-follicles.
' 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 projects
beyond the free surface of the skin is called the shaft (scapus) ; the por-
tion obliquely embedded within the integument, the root {radix fill) ;
this at its lower extremity is expanded to a hollow knob, the hair-bulb
(bulbus pill), which is occupied by a formation of the corium, the hair
papilla (Fig. 252).
Each hair-root is inserted in the hair-follicle, a modification of the
skin in the formation of which corium and epidermis participate ; the
parts furnished by the latter are named the epithelial root-sheatlis, the
portion originating from the corium, the dermal or connective-tissue sheath.
From two to five glands, the sebaceous glands, open laterally into the
upper part of the follicle. Bundles of smooth muscle-fibers provided
with elastic end-tendons, the arrectores pilorum, pass obliquely from the
upper surface of the corium and attach themselves beneath a sebaceous
gland to the fibrous sheath of the hair-follicle ; the point of insertion of
these fibers is always on the side toward which the hair inclines and
forms an acute angle with the free surface of the skin ; consequently
when they contract the follicle and the shaft become erect.
* The new anatomic nomenclature reckons the epithelium of the nail-bed to the nail, that
according to this representation consists of stratum corneum and stratum germinativum.
THE SKIN AND ITS APPENDAGES.
337
The hair consists entirely of epithelial cells, which are arranged in
three well-defined strata : (i) the cuticle, which covers the surface of the
hair ; (2) the cortical substance, which forms the chief bulk of the hair ;
(3) the medulla, which occupies the axis of the hair.
The cuticle consists 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 very intimately united
with one another ; on the root the cells become the softer and rounder,
their nucleus correspondingly the more spherical, the nearer they lie to
the hair-bulb.
The medulla is absent in many hairs ; when it is present (in the
Hair-shaft.
Hair-root.
Sebaceous gland.
Arrector pili muscle.
Root-sheaths.
Connective-tissue hair-
follicle.
Hair-bulb.
Hair-papilla.
Fat-cells.
Fig. 252. — From a Thick Cross-section of a Human Scalp. X 20. Technic No. 168.
thicker hairs) it does not extend through the entire length of the hair.
It consists of cubical, finely granular epithelial cells, which contain a
rudimentary nucleus and are usually disposed in twofold rows.
The colored hairs contain pigment, diffused, and in the form of
granules, which partly occur between and partly within the cells of the
cortical substance.* In every hair which has attained its full develop-
ment extremely minute air-vesicles occur; they are found in the cortical
substance as well as in the medulla, and also in the intercellular clefts.
* As to the source of the pigment, see page 334.
338 HISTOLOGY.
The follicle of finer (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 longitudinal stratum formed of loosely united, longitudinally
disposed bundles of connective tissue, mingled with elastic fibers and
richly supplied with blood-vessels and nerves ; next follows a middle
circidar stratum, thicker, consisting of small fibrous bundles circularly
arranged, which is contiguous to an inner clear, homogeneous belt, the
glassy or hyaline membrane, resembling in character the elastic membranes.
Elastic fibers do not occur in the middle layer nor in the papilla. These
Cortical sub-
stance.
Medullary sub-
stance.
/ 2 ,."/
mm
^ mlPM
0\ &
Vv,
'" i'. i'im' 1 /i/v V,'.'
'«j.(4'f
Fig. 253.— Elements of a Human Hair and Hair-Follicle. X 240. 1. White hair ; 2, scales of the
cuticle ; 3, cells of the cortical substance of the shaft ; 4, cells of Huxley's layer; 5, cells of Henle's
layer having the appearance of a fenestrated membrane ; 6, cells of the cortical substance of the root.
Technic No. 166 and No. 167.
three strata are derived from the corium and together are named the
dermal or connective -tissue hair-follicle. Within the hyaline membrane
lies the outer root-sheath, which as a continuation of the germ-layer of
the epidermis consists of stratified scaly epithelium ; inward to this lie
continuations of the stratum granulosum and stratum corneum, which
extend about to the point where the ducts of the sebaceous glands open
into the follicle ; immediately below (toward the papilla) the inner root-
sheath begins abruptly, which in the lower portion of the follicle is
differentiated into two sharply defined layers. The outer of these two,
Henle's layer, consists of a single or double row of epithelial cells
THE SKIN AND ITS APPENDAGES.
339
without nuclei (here and there an atrophic nucleus is present), while the
inner, Huxley's layer, is formed of a simple stratum of nucleated cells.
The inner surface of this layer is lined with a delicate membrane, the
cuticle of the root-sheath, which exhibits the same structure as the cuticle
of the hair. Toward the base of the follicle the outer root-sbeath
diminishes in thickness and disappears ; the elements of the inner root-
Connective-
tissue
hair-follicle.
Inner root-
sheath.
Hair.
Longitudinal fibrous
layer.
Circular fibrous layer
Glassy membrane.
Outer root sheath
r Henle's layer.
i Huxley's layer.
Sheath and hair-cuticle
Cortical substance.
Medullary substance.
Fig. 254. — From a Horizontal Section of Human Scalp. X 240. Cross-section oi a hair and hair-
follicle in the lower half of the root. Technic No. 168.
sheath, as well as those of the cuticulae, all become nucleated cells, that
can be distinguished as separate layers until near the neck of the papilla ;
there they lose their sharp demarcation and gradually coalesce with one
another, but nevertheless can be distinguished from the cells of the hair-
bulb by the pigmentation of the latter.*
DEVELOPMENT OF THE HAIR.
The first anlage of the hair and of the bair-follicle appears at the
end of the third embryonal month, in the form of a local thickening of
the epidermis, which is chiefly effected by elongation of the (columnar)
cells of the deepest layer of the germinal stratum. This thickening
grows in length down into the corium (Fig. 255 A) and forms a solid
epidermal peg, the hair-germ (Fig. 255 A, E), that at its lower end
* Already at the level of the papilla keratohyalin granules appear in the cells of Henle's
layer, at a somewhat higher level also in those of Huxley's layer, that a little farther up
disappear ; from this upward the elements of the inner root-sheath are corneous.
340
HISTOLOGY.
becomes expanded and club-shaped (Fig. 255 C). Meanwhile the
papilla {C,p) and the dermal portion of the hair-follicle (C, hb) develop
by differentiation of the connective tissue of the surrounding corium.
The hair-germ separates into an outer stratum and into an inner axial
cord (D, s). The former becomes the outer root-sheath (aw), the
A a
.Viii l| ''ȣ
v
Fig. 255 — From a Vertical Section ( A ) of the Skin of the Cheek of a Four Months' Human
Embryo and (i?, C, Z>) of the Skin of the Forehead of a Human Embryo Five and a
Half Months Old. X 80. E, Epidermis, consisting throughout of nucleated epithelial cells ;
C, corium ; x, thickening; hk, hair-germ ; A A , connective-tissue hair-follicle; fi, papilla; aw, outer
root-sheath ; j, axial portion, in which in the upper division the separation into (iw) inner root-sheath
and (A) hair is visible ; t t anlage of the sebaceous glands. Technic No. 169.
peripheral portion of the axial strand becomes the inner root-sheath
(iw), the central part, the hair (It). The sebaceous glands arise as local
outgrowths of the outer root-sheath (t).
The development of hairs in the manner desciibed may occur after
birth and until late in life.
GROWTH OF THE HAIR AND OF THE ROOT-SHEATHS.
The growth of the hair, of the cuticular sheaths, and of the inner
root-sheath takes place by continual mitotic division of the epithelial
elements around the papilla, that becoming horny annex themselves
from below to previously cornified cells. Therefore the tip is the oldest,
the portion lying immediately above the hair-bulb the youngest, part of
the hair. The outer root-sheath, on the other hand, grows in a radial
direction from the inner surface of the glassy membrane towards the axis
of the hair.
SHEDDING AND REPLACEMENT OF HAIR.
After birth all the hairs are shed and replaced by new ones. In the
adult a constant, but not periodic, replacement of the dead hairs of the
THE SKIN AND ITS APPENDAGES.
341
scalp and beard occurs.* With regard to the shedding and renewal of
the other hairs nothing is definitely known.
The details of the process are as follows : the hair-bulb becomes
horny and frayed, like a brush ; the now dead hair pushes upward
from the papilla,f the empty root-sheaths collapse, while at their
inferior extremity lies the papilla, atrophied and altered in form (Fig.
256). After a (often long) period the epithelial elements of the empty
Dead hair.
Empty root-sheath.
Hair-papilla.
Sebaceous gland.
Dead hair.
Empty root-sheath.
Hair-papilla.
Fig. 256. — From a Vertical Section of the Hairy Scalp of Adult Man. X 40. Technic No. 170.
root-sheaths begin to grow and form a new hair-germ, from which the
new hair develops by the same processes as the embryonal hair. The
new hair thus formed pushes itself upward under and beside the effete
hair, while the latter after a shorter or longer period falls out.
The Glands of the Skin.
The sebaceous glands (glandulse sebaceae) are either unbranched or
branched simple saccular glands. Each gland consists of a short
excretory duct (Fig. 257 A, a) and of a variable number of little gland-
* The duration of life of a scalp hair is said to be 1600 days.
f Further growth of the cornified hair does not occur ; the ascent is passive and de-
pendent on the multiplication of the noncornified epithelial cells lying under the dead hair.
342
HISTOLOGY.
sacs (J), The duct is lined by stratified scaly epithelium, an extension of
the outer root-sheath, which by a gradual decrease in the number of its
layers passes into the epithelial lining of the gland-sacs. This at the
beginning consists of low cuboidal cells (Fig. 257 B, /), that toward the
interior are followed by spherical or polyhedral elements varying in size,
which fill the entire gland-sac and exhibit all the transitional phases in
the process by which the cell is converted into the secretory product of
the gland (Fig. 257, 2, 3, 4). The secretion, the sebum, during life is a
semifluid substance that consists of fat and disintegrated cells. While
the sebaceous glands occur as appendages of the hair-follicles of the
coarser hairs (Fig. 252), in the case of the lanugo hairs reversed relations
prevail, since the follicles of the latter appear as the appendages of the
Epidermis. J. ' ~ ;^~g> ? > . fef i
"~<^--'T:i
C™.
\
4 Cell with shrunken
nucleus.
.? Cell with well-de-
veloped drops of
secretion.
.-, Cell with develop-
ing drops of se-
cretion.
/ Cubical cells.
Fig. 257.— A. From a Vertical Section through the Ala Nasi of a Child. X 40. C. Stratum
corneum ; M, stratum germinalivuni ; r, sebaceous gland consisting of four follicles, a, duct of the
same; w, lanugo hair, about to be shed, h, hair-follicle of the same, at the base of which a new hair,
x, is forming.
£. From a Vertical Section of the Skin of the Ala Nasi of an Infant, x 240. Follicles of
a sebaceous gland containing gland-cells in various stages of secretion. Technic No. 171.
powerfully developed sebaceous glands (Fig. 257 A). The sebaceous
glands are distributed with the hairs over the entire body and are wanting
only where they are absent, on the palm of the hand and on the sole of
the foot. There also are sebaceous glands that are not associated with
hair-follicles ; for example, on the red edge of the lips, on the labia
minora, on the glans, on the prepuce of the penis ; in the latter situation
they are known as glandulce praputiales (Tyson). The sebaceous glands
are always situated in the superficial layers of the corium, in the stratum
papillare. Their size varies from 0.2 to 2.2 mm. ; the latter are found
in the integument of the nose, where their excretory ducts are visible to
the unaided eye.
The coil-glands {glandulce sudoriparm) are long, unbranched tubules,
THE SKIN AND ITS APPENDAGES. 343
that at their lower end are rolled into a spherical coil having a diameter
of 0.3 to 7 mm. (of the latter size in the axilla). Two parts are dis-
tinguished, the excretory duct and the coil (Fig. 247). The duct runs a
straight or sinuous course through the corium, enters the epidermis
between two papillae, through the stratum corneum of which it is spir-
ally twisted, and opens on the surface of the skin by a rounded orifice,
the sweat-pore, just visible to the naked eye. The walls of the duct
consist of longitudinally disposed bundles of connective tissue, lined
within by several layers of cubical epithelial cells. The coil is a greatly-
convoluted simple * canal, the walls of which are formed of a single layer
of cubical cells, containing granules of pigment and of fat, surrounded
by a delicate membrana propria. In well-developed glands longitudinally
disposed smooth muscle-fibers occur between the membrana propria and
the gland-cells.
The secretion usually is an oily fluid substance, for the purpose of
lubricating the skin; only under the influence of disturbed innervation
do the coil-glands discharge the watery liquid called sweat. The coil-
glands are distributed over the entire surface of the skin and are absent
only on the glans and on the inner surface of the prepuce. They are
most numerous in the skin of the palm of the hand and of the sole of
the foot.
The Blood-vessels, Lymph-vessels, and Nerves of the Skin.
The arteries of the skin originate in a network lying above the fasciae
and branch as they pass toward the surface of the skin. These branches
anastomose with one another and with those of neighboring arteries
and in the lower stratum of the corium form a horizontally disposed
reticulum, the cutaneous network. The arteries supplying the skin are
therefore not end-arteries. f
From this network two capillary territories are supplied ; the deeper
is intended for the adipose tissue (Fig. 258, a'), the more superficial
appears in the form of basket-like plexuses surrounding the coil-glands
{a"). From the cutaneous network twigs ascend that anastomose and
form a second horizontal network in the upper third of the corium, the
subpapillary plexus ; from this very small twigs arise, which run for a
short distance along the rows of papillae and send little branches into
* Branched tubules have been observed only in the axillary and circumanal glands.
f "End-arteries" are those small arteries which do not anastomose with neighboring
arteries, but independently supply capillary circuits of varying extent. When they become
obstructed the part of the organ which they supply dies.
344
HISTOLOGY.
them (Fig. 258, a'"). These smallest twigs do not anastomose with one
another, hence are end-arteries. The branches for the hair-follicles and
the sebaceous glands also arise from the subpapillary plexus.
The blood returning from the capillaries of the papillae, the hair-
follicles, and the sebaceous glands is taken up by veins that form a dense
horizontal plexus lying beneath the papilla? and that occasionally are
united with a second horizontal plexus lying close below the first. From
this plexus small venous trunks descend beside the arteries and lead to
a third network lying in the lower half of the corium, which is not so
, s £ I Epidermis.
Corium.
Stratum subcutaneum.
Fig. 258. — From a Vertical Section of the Skin of the Sole of a Human Foot. X 50. sc,
Stratum corneum ; sg, stratum germinativum ; a, artery; v, vein ; a' v', branches to the panniculus
adiposus ; a" v", branches to the coil-glands ; k, duct of the same ; vx, vein accompanying the duct.
Technic No. 172.
evenly spread out as those preceding. This plexus takes up the veins
coming from the coil-glands and then those proceeding from the lobules
of adipose tissue. It should further be noted that a branch of the veins
of the coil-glands passes along the excretory duct to the venous plexus
of the stratum papillare (Fig. 258, v x) and that the hair-papilla receives
an independent arterial branch. From the third venous network larger
veins lead to the lower boundary of the skin, where a fourth horizontally
disposed, "subcutaneous" venous network occurs, from which still
THE SKIN AND ITS APPENDAGES. 345
larger trunks turn into the subcutaneous tissue and then unite with the
large subcutaneous veins, some of which are provided with names. The
lymph-vessels form two horizontal capillary networks, of which that con-
sisting of smaller tubules and narrower meshes lies in the papillary-
stratum of the corium beneath the vascular network ; the other, wider-
meshed, is situated in the subcutaneous tissue. Special networks of
lymph-capillaries surround the hair-follicles, the sebaceous and the
coil-glands.
The nerves of the integument (numerous in the palm of the hand
and the sole of the foot) partly terminate in the subcutaneous tissue in
lamellar corpuscles ; partly they end in tactile-corpuscles, in tactile-cells,
and as intra-epithelial fibrils (Fig. 125). The hairs are also supplied with
medullated nerve-fibers, which run up to the point where the sebaceous
glands open into hair-follicles ; here they divide, lose their medullary
sheath, and as naked axis-cylinders, usually running longitudinally, ter-
minate in a spoon-shaped expansion o?i the glassy membrane (epilemmal
nerve-ending) ; in the tactile-hairs (sensory hairs) of animals delicate
twigs arise from these nerves, which pass through the hyaline membrane
of the hair-follicle into the outer root-sheath and there end in tactile-
disks. The hair-papilla does not possess nerves. The nerves of the
coil-glands behave similarly to those of the salivary glands, see page 253.
The Mammary Gland.
The mammary gland, a convoluted compound tubular gland, in
children of both sexes consists chiefly of connective tissue, which en-
closes the branched excretory gland-ducts. These ducts have a bulbous
enlargement at their extremities. Terminal pieces are wanting. The
mammary gland of the adult male exhibits the same structure.
In the adult female the mammary gland up to the occurrence of
pregnancy is a disk-shaped body, that consists preponderately of con-
nective tissue and of the excretory gland-ducts. Terminal pieces are
present only in limited number at the ends of the smallest branches of
the excretory ducts.
At the time of pregnancy and of lactation the mammary gland con-
sists of from fifteen to twenty compound tubular glands, which are held
together and united in a common body by loose connective tissue con-
taining fat-cells. Each of these glands has its own excretory duct open-
ing on the nipple, that shortly before its termination is provided with a
conspicuous spindle-shaped expansion, the ampulla or sinus lactiferus,
and by means of dichotomous ramifications is connected with the terminal
346 HISTOLOGY.
pieces. The latter, lying close beside one another and bound together
by connective tissue, form small lobules.
Touching the microscopic structure, the excretory ducts consist of
a columnar epithelium (that in the larger branches not infrequently is re-
placed by a stratified scaly epithelium), surrounded by a membrana pro-
pria and external to this by connective-tissue bundles in the main circu-
larly disposed. The terminal pieces differ in structure during the period
of pregnancy and during the period of lactation. According to late
researches the end-pieces in the guinea-pig during the term of gestation
are clothed with a simple cubical or slightly flattened epithelium ; their
lumen contains leucocytes, that have wandered in from the subjacent
interstitial connective tissue through the epithelium. Some of these
leucocytes perish (their nucleus is ragged, often divided into several
pieces), the others take up oil-drops furnished by the gland-cells and
grow to be conspicuous bodies, the colostrum corpuscles (Fig. 261). A
membrana propria formed of cells (p. 86) separates the end-pieces from
the interstitial connective tissue, which is not only rich in uninuclear
leucocytes, but also contains many oxyphile cells (p. 124).
After parturition the gland-cells are
larger, filled with stainable granules (precur-
sors of the secretion ? ) and with oil-drops,
which latter lie on the side of the cell directed
toward the gland-lumen and often exceed in
size the nucleus of the cell (Fig. 259).
When lactation has been established
for a couple of days, some of the gland-cells
fig. 259. - from a thin Cross- appear flat (empty of secretion), some as tall
SECTION OF THE MAMMARY L l v r J '*
' ^TrA^nX^nd-ceiil; cylinders, that with a ragged top extend to
No n 'i e 74 lb ' ra " a propria ' Techni<; the lumen ; both forms are united with each
other by transitional phases and contain (the
tall cells more often) two nuclei. Both forms contain oil-drops ; these
are not as in the sebaceous glands the product of a fatty degeneration of
the cell, but the product of an act of secretion, that the cell repeats many
times and of which it does not perish. Besides the oil-drops ("milk-
globules"), the gland-lumen contains a large number of free nuclei, that
appear to be extruded from the gland-cells. These nuclei perish by dis-
solving (p. 66) and regulate the nuclein constituent of the milk.* Colos-
trum corpuscles and leucocytes are now wanting, even the greatly dimin-
* Nuclear divisions by mitosis do not occur in the functionating mammary gland ; it is
assumed that the nuclei here are produced by amitosis (p. 63, remark J ).
THE SKIN AND ITS APPENDAGES.
347
Fig. 260. — From a Thick Section of the Mammary
Gland of a Woman Last Pregnant Two Years
Before. X 50. 1. Large excretory duct; 2, small
excretory duct; 3, gland-lobules, separated from
one another by connective tissue. Technic No. 173.
ished interstitial fibrous tissue contains extremely few leucocytes and
eosinophile cells.
When lactation is ended a gradual regressive metamorphosis takes
place, that is soon manifested by abundant development of the interlob-
ular fibrous tissue * (Fig. 260).
The lobules become smaller, the
terminal pieces begin to atrophy.
In elderly persons all the ter-
minal pieces and the lobules
have disappeared and only the
excretory ducts remain.
The integument of the nip-
ple and of the areola is charac-
terized by deep pigmentation,
by tall papillae, and by the pres-
ence of smooth muscle-fibers,
which latter partly are circu-
larly arranged around the ori-
fices of the galactophorous
ducts, partly vertically to the apex of the nipple. The pigmentation is
due to the presence of pigment granules in the deepest layers of the epi-
dermis. In the integument of the areola accessory mammary glands, the
areolar glands (Montgomery), occur during pregnancy and lactation.
The blood-vessels approach the mammae from all sides and form
capillary networks embracing the gland-
tubules. The lympli-vessels form capil-
lary plexuses lying within and between
the gland-lobules. Lymphatic networks
also occur in the vicinity of the ampullae
and the areolae.
The nerves are in part distributed
to the blood-vessels, in part behave like
those of the salivary glands (p. 253).
Microscopically milk consists of a
clear fluid, the milk plasma, in which
milk-globides, from 2 to 5 fi in size, are
suspended. In addition, isolated cells
enclosing oil-globules (leucocytes) are found in milk.
° o
0:0
Fig. 261.— ,4. Milk-Globules from Hu-
man Milk. X560. Technic No 175.
B. Elements of the Colostrum of
a Pregnant Woman. X560. 1. Ceil
containing uncolored fat-globules ; 2,
cell containing minute colored fat-
globules; 3, leucocyte; 4, milk-glob-
ules. Technic No. 176.
* Leucocytes also reappear, that behave in exactly the same manner as during the period
of gestation and become colostrum corpuscles, etc. Therefore the leucocytes invariably are
present when the secretion of milk begins.
348 HISTOLOGY.
The elements of milk secreted before and in the first few days after
parturition appear somewhat different. Beside the milk-globules the
colostrum corpuscles occur, leucocytes enclosing a spherical nucleus,
some of which contain small yellowish and larger uncolored oil-globules,
others only uncolored oil-drops.
TECHN1C.
■ No. 161. — Strata of the Skin ; Coil-glands. — Cut from the pad of
the finger, the palm of the hand, or the sole of the foot pieces of skin,
as fresh as possible, from i to 2 cm. square, together with a thin stratum
of the 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 three to four 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 children, on the sole of the foot,
because the still short ducts of the coil-glands here run vertically (Fig.
247). Stain with alum carmine, ten minutes (p. 38) ; the red coils can
be seen with the unaided eye ; mount in damar. Examine with the low
power. In thick sections the papillae often are indistinct, because they
are encircled by the red-colored stratum germinativum ; the screw-like
twisted ends of the excretory ducts may be most distinctly see'n when
the object is faintly illuminated or with oblique illumination (see p. 53,
remark *).
To render the stratum granulosum visible, bulk-staining with borax-
carmine for two or three days (p. 39) is to be recommended. The
granules of this stratum are then stained an intense red (Fig. 249).
No. 162. — Pretty preparations of the under surface of the epidermis
are obtained by fixation of shreds of the epidermis of the dorsum of the
foot, that can often be detached from injected cadavers, in 30 c.c. of
absolute alcohol. Stain for two minutes in Hansen's hematoxylin and
mount in damar (Fig. 248).
No. 163. — For preparations of the nails fix the distal phalanx of a
child from eight to twelve years of age (in adults, that of the little finger,
if possible of women), two or four weeks in 100 or 200 c.c. of Miiller's fluid
and harden in about 100 c.c. of gradually-strengthened alcohols ; decalcify
(p. 35) ; harden again and stain thick cross-sections ten minutes in alum-
carmine (p. 38). (Fig. 250.) 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 differently colored strata. In the nails of old
cadavers the epithelium often becomes loosened from the. ridges.
No. 164. — Elements of the Nails. — Place pieces of nail 1 or 2 mm.
THE SKIN AND ITS APPENDAGES. 349
broad in a test-tube containing 5 c.c. of concentrated potash-lye and
heat it 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. 251. 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. 165. — 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 imbri-
cation 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. 166. — For the demonstration of the elements of the Jiairs, place
a piece of hair 1 or 2 cm. long in a drop of pure sulfuric acid on a slide
and apply a cover-glass ; press lightly on the cover-glass with a needle
and the cortical substance will split into fibers, which consist of adherent
cortical cells. 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 (Fig. 253).
No. 167. — 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 dis-
tilled water). In two days the individual hairs with their sheaths can be
easily withdrawn and their elements separated by teasing in a drop of
distilled water (Fig. 253). The cells of Henle's sheath float in small
complexes in the preparation and closely resemble fenestrated membranes
(Fig. 253, 5). The fenestra are spaces normally occurring between
Henle's cells, through which processes of the cells of Huxley's stratum
extend to the outer root-sheath. Not infrequently a hair-follicle is
obtained at the base of which a new hair is developing (similar to Fig.
257)-
No. 168. — For the study of hairs and hair-follicles place pieces 2 or
3 cm. square of the fresh skin of the scalp in about 200 c.c. of a 2.5
per cent, solution of potassium bichromate (p. 20, 9) for from four to
eight weeks ; wash them from one to three 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. 252 thick
sections, unstained, are to be mounted in glycerol. Thin sections usu-
ally 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 hairs and hair-
350 HISTOLOGY.
follicles ; such sections are to be stained in dilute carmine (p. 38), and
Hansen's hematoxylin, or better, first with hematoxylin and then with
picrocarmine (p. 39) ten minutes, and mounted in damar. Especially
instructive are the sections through the hair-follicle close to the hair -bulb
(Fig. 254).
No. 169. — For the development of hair cut pieces about 2 cm. square
of the skin of the forehead (not of the hairy scalp) of a five- or six-
months'-old human embryo ; span them out (see No. 161) ; place them
for fourteen days in 100 or 200 c.c. of Muller's fluid and harden in about
100 c.c. of gradually-strengthened alcohols. Stain the tissue in bulk in
borax-carmine (p. 39). The sections may also be stained in Hansen's
hematoxylin (p. 37). Embed the tissue in liver ; endeavor to cut sec-
tions 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. 255). The epithelial
thickenings are only to be seen in well-preserved epidermis, which in
embryos is often somewhat macerated. They are more easily found in
embryos of the lower animals.
No. 170. — Shedding and Replacement of Hair. — The eyelids of
newborn children are most suitable. Treat like No. 191. Cut sagittal
sections. Vertical sections of the hairy scalp often yield good results
(Fig. 256).
No. 171. — The Sebaceous Glands. — Fix and harden the alae nasi of
newborn children in 100 c.c. of a 2.5 per cent, solution of potassium
bichromate (like No. 168). Cut thick and thin sections ; stain them with
dilute carmine (p. 38), and with Hansen's hematoxylin (p. 37), and mount
in damar. Sections lengthwise to the dorsum of the nose often show
sebaceous glands and hair-follicles, but they must be exactly vertical (Fig.
257). The alse 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 sebaceous glands with hair-follicles can
be seen with the unaided eye in stripping off the macerated epidermis of
old cadavers.
No. 172. — Blood-vessels of the 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 from 1 to 2 liters of Muller's fluid ;
after several days cut pieces 2 or 3 cm. square of the palm of the hand
or of the sole of the foot, place them (two or four weeks) in 100 or
200 c.c. of Muller's fluid and harden them in 100 c.c. of gradually
strengthened alcohols. Cut thick sections and mount them unstained in
damar (Fig. 258). The papillae in such sections can only be recog-
nized by the capillary loops. To the beginner it appears as if the loops
extend into the stratum germinativum.
No. 173. — For a general view of the mammary gland place the
nipple and a portion of the gland (3 or 4 cm. square) in 60 or 100 c.c.
of absolute alcohol. If possible, obtain the glands of an individual that
THE ORGAN OF VISION. 3 5 I
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 Hansen's hematoxylin ; mount
in damar (Fig. 260).
No. 1 74. — For the minute structure of the mammary glands place
the warm living tissue (3 or 5 mm. cubes) of a pregnant mammal in 5
c.c. of Flemming's mixture (p. 33), and harden after one or two days in
30 c.c. of gradually-strengthened alcohols. Cut very thin sections, stain
them with safranin (p. 38), and mount in damar (Fig. 259). The struct-
ure is often difficult to understand on account of the small size of the
gland-cells (in the rabbit).
No. 175. — Elements 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 plac-
ing the cover-glass upon the nipple and then pressing out a drop. Ex-
amine with a high power (Fig. 261 A).
No. 1 76. — Elements of Colostrum. — Obtain the colostrum shortly
before parturition. Proceed as in No. 175. Be careful to avoid pressure
on the 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 (Fig. 261 B).
X. THE ORGAN OF VISION.
The organ of vision consists of the eyeball (bulbus oculi), the optic
nerve, the eyelids, and the lacrymal glands.
THE EYEBALL.
The eyeball is a hollow globe, which encloses partly formed, partly
fluid contents. The wall of the globe is composed of three coats :
(1) the tunica externa, a fibrous membrane in which an anterior transpa-
rent division, the cornea, may be distinguished from the remaining opaque
portion, the sclera; (2) the tunica media, rich in blood-vessels, which
includes three divisions, the choroid, the ciliary body, and the iris ; (3) the
tunica interna, the retina, which contains the specialized terminal appa-
ratus of the optic nerve. The formed contents within the eyeball are the
lens and the vitreous body.
The Tunica Externa.
The cornea consists of five strata, which enumerated from before
backward are the following : —
352
HISTOLOGY.
i. The corneal epithelium.
2. The anterior elastic lamina.
3. The substance proper.
4. The posterior elastic lamina.
5. The corneal "endothelium."
The corneal epithelium is a stratified scaly epithelium and consists of
a lowermost layer of sharply contoured columnar cells, which is followed
by three or four (more in animals) layers of spherical cells, that in turn
are covered by several strata of flattened elements still possessing nuclei.
Corneal epithelium.
Lamina elastica ante-
rior.
Substantia propria. .
Lamina elastica poste-
rior.
Corneal endothelium. - S:Ww.-,w^>-
Fig. 262. — Vertical Section of a Human Cornea. X 100. Technic No. 177 b±
The thickness of the epithelium in man is 0.03 mm. At the rim of the
cornea the epithelium is continuous with that of the conjunctival sclera.
The anterior elastic lamina (Bowman's membrane, anterior basal
membrane) in man is a distinctly visible stratum, about 0.01 mm. thick,
and almost homogeneous in appearance. The surface is provided with
minute serrations and ridges for the attachment of the columnar cells of
the corneal epithelium. Posteriorly it gradually passes into the sub-
stantia propria of the cornea, of which it is a special modification.
The substance proper (substantia propria cornese) constitutes the chief
THE ORGAN OF VISION.
IS-
bulk of the cornea. It consists of delicate parallel fibrillae, which are
united by an interfibrillar cement-substance into bundles of nearly
uniform thickness ; the bundles in turn are united by an interfascicular
cement-substance into flat lamellae, which lie in many superposed strata
and are held together by an interlamellar cement-substance. The
lamellae are arranged parallel to the surface of the cornea and run in
meridional curves one above the other, so that a vertical section through
the center of the cornea shows alternate longitudinal and transverse
bundles. A number of bundles running obliquely, the so-called arcuate-
fibers, unite each lamella with its neighbor above or below ; especially
well-developed arcuate fibers occur in the anterior strata of the substantia
propria.
Embedded in the cement-substance is an intercommunicating sys-
Corneal canaliculi
paces.
Fig. 263. — Horizontal Section of the Cornea
of AN Ox. Silver-preparation ; negative pic-
ture;, the canalicular system is light upon a
dark ground. < about 240. Technic No. 182.
t
if
-J
- j
7 \:
Corneal corpuscles.
Fig. 264. — Horizontal Section of the Cornea
of A Rabbit. Positive picture of the corneal
canaliculi. X about 240. Technic No. 1S4.
tern of much-branched canaliculi, the conical canaliculi, lymph canaliculi,
which at many places are expanded to broad oval lacunae, the corneal
spaces, lymph-spaces (Fig. 263). The latter lie between the lamella?,
while the canaliculi also penetrate between the bundles. The lacuna;
and canaliculi contain a serous fluid and cells, " fixed " corneal corpuscles
and wandering cells. The corneal corpuscles are flattened connective-
tissue cells possessing large nuclei (Fig. 264) ; they lie against the wall
of the lacuna.
The posterior elastic lamina (membrane of Descemet, posterior basal
membrane) is a transparent elastic layer, only 0.006 mm. thick. In
adult man the posterior surface, at the periphery of the cornea, is beset
with hemispherical protuberances.
354
HISTOLOGY.
The corneal endothelium is composed of a single layer of flat, polyg-
onal cells, often having slightly projecting nuclei.
The sclera principally consists of interlacing bundles of connective
tissue, extending for the most part in meridional and equatorial direc-
tions. In addition, delicate elastic fibers arranged in networks and flat-
tened connective-tissue cells are present; the latter, like the corneal
Cross and longitudinal
sections of bundles of
scleral fibers.
Lamina suprachorioidea.
Lamina vasculosa.
Boundary zone.
— Choriocapillaris.
Basal membrane.
Pigment layer of the retina.
Fig. 265. — Vertical Section through a Part of the Human Sclera and the Entire Choroid.
X 100. g. Larger vessels; /, pigment cells; c, cross-sections of capillaries. Technic No. 177 c.
corpuscles, lie in lacunar, that differ from the corneal spaces only in
having more irregular outlines. Between the sclera and the choroid is a
layer of loose, highly elastic tissue containing branched pigmented cells
and flattened elements free from pigment (" endothelial " cells), which on
separating the two coats adheres partly to the former and partly to the
latter ; the portion on the sclera is called the lamina fusca sclera, that on
the choroid, lamina suprachorioidea.
The sclera is thickest posteriorly (one millimeter) and becomes
gradually thinner toward the cornea.
The Tunica Media.
The choroid is characterized by the great abundance of its blood-
vessels, which are arranged in two layers. The superficial layer, adjoining
the inner side of the lamina suprachorioidea, the lamina vasculosa {layer of
larger blood-vessels), contains the ramifications of the arterial and venous
channels, that are embedded in a supporting tissue, the stroma, consist-
THE ORGAN OF VISION.
355
ing of networks of fine elastic fibers and numerous branched pigment-
cells. In addition, the stroma contains the tissues accompanying the
larger arteries ; namely, fibrillar connective tissue, smooth muscle-fibers,
Fig. 266.-^4. From a Teased Preparation of a Human Choroid. X 240. p. Pigment cells; e, elastic
fibers; k t nucleus of a flat nonpigmented cell ; the cell-body is invisible.
B. Portion of Human Choriocapii.laris and the adherent Hyaloid Membrane. X 240. c. Wide
capillaries, some of which contain (b) blood corpuscles; e, hyaline membrane, snowing a fine
" lattice-work." Technic No. 178 a.
and nonpigmented plate-like cells that are united in delicate " endothe-
lial " membranes. The deeper layer, the lamina choriocapillaris, or layer
of capillary networks, is composed of a narrow-meshed net of capillaries,
Fig. 267.— Meridional Section through the Right Irido-Corneal Angle of Man. X 30. J. Epi-
thelium, 2, conneclive tissue of the conjunctiva. 3, Sclera. 4, 5, 6, 7, and 8. Ciliary body ; 4, meridi-
onal, 5, radial, 6, circular fibers of ciliary muscle; 7, ciliary process; 8, ciliary portion of retina.
9. Iridal portion of retina. 10. Stroma of the iris. 11. 12, and 13. Cornea; 11, posterior elastic
lamina; 12, substantia propria; 13, epithelium. 14. Venous sinus of sclera. 13. Angle of iris.
Technic No. 177 a.
between which no formed elements are found. Between the two laminae
of blood-vessels lies the boundary zone, a portion of the stroma consisting
of networks of fine elastic fibers and almost devoid of pigment. In
ruminants and horses this zone consists of wavy bundles of connective
356
HISTOLOGY.
tissue, to which is due the metallic reflex seen in the eyes of these
animals. This shining membrane is known as the tapetum fibrosiim.
The similar iridescent tapetum cdlulosum of carnivora is composed of
several strata of plate-like cells containing numerous minute crystals.
Attached to the lamina choriocapillaris is the lamina basalts or
vitreous lamina, a structureless lamella about 2 p. thick, which on its
outer surface is provided with delicate lattice-like markings. The
polygonal areas noticeable on its inner surface are imprints of retinal
pigment. The vitreous membrane approaches in character the elastic
membranes.
The ciliary body is formed by the ciliary processes and the muscular
ring lying upon them, the ciliary muscle. The ciliary processes are seventy
or eighty meridionally placed folds, which begin low at the ora serrata,
Endothelial nuclei.
*.. Anterior boundary
layer.
3. Vascular layer.
«$|K. Qsg^-1— V 1 "/ -y---- . ' 4. Posterior boundary
layer.
5. Pigment layer.
Fig. 268.— Vertical Section of the Pupillary Portion of a Human Iris. X ioo. About one-fifth
of the entire width of the iris is shown, g. Blood-vessel, with thick connective-tissue sheath ; m,
sphincter pupilla^ muscle cut transversely; p, pupillary border of the iris. Technic No. 178 c.
gradually attain a height of one millimeter, and terminate with an abrupt
descent near the edge of the lens. Each ciliary process consists of fibrillar
connective tissue containing numerous blood-vessels and inwards is limited
by a continuation of the vitreous membrane, that here is distinguished by
minute intersecting folds. The blood-vessels of the ciliary processes
supply the intraocular fluid. The ciliary muscle is an annular band about
3 mm. broad, anteriorly 0.8 mm. thick, arising from the inner wall of the
venous sinus of the sclera. The nonstriped elements of which it is com-
posed extend in three different directions. We distinguish (a) meridional
fibers (Fig. 267, 4), numerous fasciculi lying next to the sclera, which reach
to the smooth portion of the choroid and are known as the tensor cho-
rioideje ; (b) radial fibers, lying next to the meridional bundles, which from
without inward progressively assume a more radial disposition (oriented
THE ORGAN OF VISION. 357
to the center of the bulbus oculi) and posteriorly, still in the region of
the ciliary body, turn and follow a circular course (5) ; (c) circular
(equatorial) fibers, the so-called ring-muscle of Midler (6) .
The iris consists of a stroma divided in three layers, covered anteriorly
by a continuation of the posterior endothelium of the cornea and pos-
teriorly by a modified extension of the retina. Accordingly five layers
may be distinguished : —
1. The anterior "endothelium."
2. The anterior boundary layer.
3. The vascular layer.
4. The posterior boundary layer.
5. The pigment layer.
The anterior endothelium covers the anterior surface of the iris and,
like that on the posterior surface of the cornea, consists of a single layer
of flattened polygonal cells.
The anterior boundary layer (reticular layer) comprises three or four
strata of networks, which are formed by stellate connective-tissue cells ;
it resembles the reticulum of adenoid tissue. The posterior stratum
gradually passes into the adjoining vascular stroma.
The vascular layer of the iris contains numerous radially disposed
(to the pupil) blood-vessels embedded in a stroma consisting of slender,
loosely united bundles of connective tissue. The blood-vessels and
nerves are provided with conspicuously thick connective -tissue sheaths.
There are smooth muscle-fibers in the vascular stroma, arranged in two
sets, (1) as annular bundles encircling the pupillary margin of the iris in a
zone about one millimeter in width, constituting the sphincter of the pupil,
and (2) as a few radially disposed bundles, which do not form a contin-
uous layer, the dilator of the pupil. In the anterior boundary layer and
in the vascular stroma pigmented cells occur in greatly varying num-
bers ; in blue eyes they are absent.
The posterior boundary layer is a clear, glassy, homogeneous mem-
brane, elastic in its nature.
The pigment layer of the iris (pars iridica retinse) comprises two
layers, of which the anterior contains spindle-shaped, the posterior
polygonal pigment-cells. Both layers are so crowded with pigment-
granules that recognition of the individual elements is almost impossible.
The pigment is wanting only in albinos. The posterior surface of the
pigment layer is covered by an exceedingly delicate membrane, the mem-
brana limitans iridis, a continuation of the membrana limitans interna
retinse.
The Irido-comeal Angle. — The junction of the sclera and the
358 HISTOLOGY.
cornea is of especial interest, since here the iris, the cornea, and the
ciliary body meet. The transition of the sclera into the cornea is abso-
lutely direct ; the more wavy bundles of the sclera without interruption
in continuity pass over into the straight bundles of the cornea, the sys-
tem of canaliculi of the sclera communicates with that of the cornea.
The line of transition is oblique and microscopically not sharply defined,
because the transformation of the sclera into the tissues of the cornea
takes place sooner in the posterior than in the anterior strata of the
tunica externa. At the periphery of the cornea the posterior elastic
lamina and the hindermost laminae of the substance proper meet the
ciliary border of the iris and form the irido-corneal angle (Fig. 267, 1 5).
Here the iris sends toward the posterior surface of the posterior elastic
lamina connective-tissue processes, the iridal processes, that, well devel-
oped in animals (cattle, horses), constitute the so-called ligamentum iridis
pectinatum. In man these processes are inconspicuous. At the per-
iphery of the cornea the posterior elastic lamina splits into fibers which,
strengthened by contributions from the intramuscular connective tissue
of the ciliary muscle and from the elastic tendons, also with accessions
in a lesser degree from the sclera, blend with the iridal processes. The
tissues participating in the formation of the loose mass of fibers occupy-
ing the angle of the iris are derived from the structures that meet one
another at the irido-corneal angle : cornea, sclera, iris, and ciliary muscle.
The posterior endothelium of the cornea continued on to the surface of
the iris forms a sheath for these fibers. The spaces between them, that
stand in open connection with the anterior chamber of the eye and con-
tain the same fluid, are called the spaces of Fontana. In man they are
scarcely developed.
The Tunica Interna.
The retina extends from the entrance of the optic nerve to the
pupillary margin of the iris and in this tract three zones may be distin-
guished : (1) the pars optica retina, the entire expanse of the optic nerve ;
(2) the pars ciliaris retina, extending from the ora serrata to the ciliary
margin of the iris ; (3) the pars iridica retime, which covers the posterior
surface of the iris from the ciliary to the pupillary margin.
The pars optica retime, the portion of the retina alone sensitive to
light, lines the entire posterior segment of the eyeball and extends to
within a short distance of the ciliary body, where it terminates in a sharp,
macroscopically perceptible, serrated line, the ora serrata. It falls into
two divisions, an outer 11 euro-epithelial lamina and an inner cerebral lamina.
In each of these divisions several layers may be distinguished, four in the
THE ORGAN OF VISION.
359
neuro-epithelial lamina, five in the cerebral lamina ; if the pigment layer
(pigment-epithelium) lying close beneath the choroid, that genetically
belongs to the retina, is added, there are ten layers, that from without
inward are arranged in the following order : —
i. The pigment layer.
2. The layer of rods and cones. \
3. The external limiting membrane. V Neuro-epithelial layer.
4. The outer granule layer. j
5. The fiber-layer of Henle.
6. The outer reticular layer.
7. The inner granule layer.
8. The inner reticular layer.
9. The ganglion-cell layer.
10. The nerve-fiber layer.*
} Cerebral layer.
Capillary
Pyramidal expansion of a radial-fiber.
—1. Pigment layer
(not shown).
-2. Layer of rods
and cones.
-3. Membranalim-
itans externa.
-4. Outer granule
layer.
-5. Fiber-layer of
Henle.
-6. Outer reticular '
layer.
-7. Inner granule
layer.
— S. Inner reticular
layer.
— 9. Ganglion - cell
layer.
— 10. Nerve-fiber
layer.
Neuro-
epithelial
layer.
Cerebral
layer.
Fig. 269.— Vertical Section of a Human Retina, from the Posterior Portion of the Eyeball.
X 400. — {After Sckaper.)
The elements of the preceding layers are only in part nervous or
epithelial in their nature ; the other part is formed- of supporting sub-
stance, that however is not of the nature of connective tissue (p. 174).
The most conspicuous elements of the supporting tissue are the radial-
fibers (Muller), elongated cells which extend from the inner surface of
*To these the membrana limitans interna is sometimes added as an eleventh layer, but
it does not represent an independent membrane.
360 HISTOLOGY.
the retina through all the layers to the rods and cones. The inner end
of the fibers is characterized by a conical foot, the radial-fiber pyramid ;
the expanded bases of these pyramids are so closely placed beside one
another that they apparently pro-
Pigment epithelium. - s^gs duce a continuous membrane on
Rods and cones. 'v/.v/ ';''' - r r ,. ,,
External limiting membrane. l - ^ rmmF the inner surface of the retina, the
so-called membrana limitans in-
terna. From the apex of the pyra-
mids the radial-fibers, with progres-
sive decrease in thickness, proceed
inner reticular layer, j 111 j through the inner reticular layer to
Gangiion-ceii layer. - tejL-J the inner granule layer, where they
Nerve-fiber layer. ~--dTf&°X' ■=■
Outer granule layer.
Outer reticular layer.
Inner granule layer.
are provided with a nucleus ; from
Fig. 270. — Vertical Section of the Retina of r
a Rabbit. X 240. k. Expanded base of radial hprp thev naw rhrnncrri trip nnfpr
fibers; n, nucleated portion of the same; /, nCYC Uley P dbb ulruu 5 u ule ouuer
^membrana limitans interna." Technic No. reticu l ar and outer g ran ule layers
to the external limiting membrane,
with which they unite. Throughout their entire course the radial-fibers
give off lateral processes for the support of the nervous elements. In
addition to these radial supporting cells, concentric supporting cells are
found in the outer reticular layer ; they extend parallel to the surface,
are provided with long processes, are partly nucleated, partly nonnucle-
ated. Glia-cells occur in the vicinity of the optic entrance. From the
surface of the membrana limitans externa delicate processes extend to
the rods and cones, the bases of which they embrace as the so-called
fiber-crates (Fig. 271). A portion of both the reticular layers belongs
to the supporting substance, as also the small quantity of cement-sub-
stance in the ganglion-cell layer.
In the more detailed description of the individual layers of the
retina the series will be taken up in the reverse order, from within out-
ward.
THE CEREBRAL LAYER.
The nerve-fiber layer consists of naked axis-cylinders which, ar-
ranged in bundles, are united in a sort of plexus. From the entrance
of the optic nerve, where the fiber-layer is thickest, the fibers expand in a
radial direction to the ora serrata. The radial arrangement of the fibers
is disturbed in the region of the macula lutea. The majority of the axis-
cylinders are centripetal fibers, which originate in the ganglion-cells of
the retina ; the smaller portion are the axis-cylinder processes of cerebral
ganglion-cells, centrifugal fibers, which ramify in the inner granule layer
and terminate in free endings.
The ganglion-cell layer (" ganglion nervi optici ") consists of a single
THE ORGAN OF VISION.
361
row of large multipolar ganglion-cells,* which send one unbranched axis-
cylinder process (nerve-process) centralward, toward the nerve-fiber
layer, one or more branched protoplasmic processes (dendrites) periph-
eryward, toward the inner reticular layer ; there they divide and are
arranged in delicate networks lying parallel to the surface, which with
the processes from other ganglion-cells form a dense nervous tangle
(Fig. 271).
The inner reticular layer (" neurospongium ") consists of an exceed-
ingly delicate network of supporting tissue, which sustains a dense fiber-
Fiber-crate.
Concentric
sustentac-
ular cell
(nucleated)
Concentric
sustentac
ular eel
(nonnucle-
ated).
Radial-fiber
Limiting
mem-
brane.
Outer
reticular
layer.
Fig. 271.-
Inner re-
ticular
layer .
-Scheme of the Elements of the Retina'; the figure on the left represents the supporting
elements, that on the right the nervous and epithelial elements.
maze in the formation of which processes of all the ganglion-cells of the
retina participate.
The inner granule layer includes elements that differ greatly in their
nature. The innermost stratum consists of large ganglion-cells, f which
*A few of these cells are marked by their large size ; such giant ganglion-cells occur at
tolerably regular intervals.
t These cells were formerly called spongioblasts, because they were erroneously regarded
as the producers of the " neurospongium " ; they are elements of the ganglion of the optic nerve
which, unlike the other elements, have not wandered through the inner reticular layer.
362 HISTOLOGY.
send branched processes into the inner reticular layer. From many of
these cells — but not all — a nerve-process passes to the optic-fiber layer
(Fig. 271). The remaining strata, for the greater part, are composed of
small bipolar ganglion-cells (ganglion retinae), the central process of
which extends into the inner reticular layer and there breaks up into
delicate varicose branches, while the peripheral process passes to the'
outer reticular layer ; there it divides into forks, spreads out parallel to
the surface and resolves into extremely minute nbrillae which pass into
a subepithelial tangle formed by the felting of processes of neighboring
ganglion-cells. All bipolar ganglion-cells send up one process between
the visual cells, that near the membrana limitans terminates in a minute
knob (Fig. 271). Finally, the nuclei of the radial-fibers occur in this
layer.
At the border of this zone, next to the outer reticular layer, lie
small and large stellate cells ; they send many processes to participate
in the formation of the subepithelial network ; one process runs to the
inner reticular layer, where it terminates in minute branches, and another
— the nerve-process — after a long horizontal course, bends and passes
in a vertical direction to the nerve-fiber layer.*
The outer reticular layer (subepithelial layer) likewise is a delicate
network of sustentacular tissue, which supports the nervous tangle just
described. The cellular elements of this layer include the concentric
sustentacular cells and the " subepithelial ganglion-cells " ; the latter are
dislocated elements of the ganglion retinas, that differ from the bipolar
ganglion-cells only in their rounded form, entirely agreeing with the
latter in regard to their terminal ramifications (Fig. 271).
THE NEURO-EPITHELIAL LAYER.
The neuro-epithelial layer consists of two kinds of elements, the
rod-visual cells and the cone-visual cells, that are characterized by
the situation of the nucleus in the lower half of the cell and the sharp
demarcation of the upper nonnucleated division from the lower portion
by the perforated membrana limitans externa. This gives rise to the
appearance of different layers, the inner nucleated portion of the visual
cells being known as the outer granule layer, the outer nonnucleated
division as the layer of rods and cones. Between these two lies the
limiting membrane.
The Rod-visual Cells. — The outer halves of these elements are the
* According to other authors this process ends in the outer reticular layer, where its rami-
fications surround the base of the visual cells.
THE ORGAN OF VISION. 363
rods, slender cylinders (60 ;i long, 2 }jl thick), which consist of a homo-
geneous outer segment and a finely granular inner segment. The outer
segment is the exclusive seat of the visual purple. The inner segment
possesses in its outer end an ellipsoidal, fibrillated body, the fiber-body.
The inner halves of the rod-visual cells are named rod-fibers ; they are
exceedingly delicate filaments which are provided with nucleated expan-
sions, the rod-granules. The nuclei are marked by from one to three
clear transverse bands. The basal end of the cell is prolonged as a
minute process terminating in a free, club-shaped expansion (Fig. 269
and Fig. 271).
The Cone-visual Cells. — The outer halves of these cells, the cones,
likewise consist of an outer segment and an inner segment. The outer
segments are conical and shorter than those of the rods. The inner
S
iVO
xy
i-'r-
t
V
Fig. 272. — Isolated Elements of the Retina of an Ape. x 240. 1. Mutilated ganglion-cell of the
ganglion of the optic nerve. 2. Elements of the inner granule layer. 3. Rod-visual cells and frag-
ments of the same ; below, two outer segments, one of which exhibits transverse striation, the begin-
ning of a disintegration into transverse platelets ; above are two rods, the outer segment of the lower
one falling apart. The uppermost figure shows more complete rod-cells; a, outer segment ; ?', inner
segment ; k, nucleus of rod ; x, fiber-body. 4. Cone-visual cells : a, outer segment ; z, inner segment ;
k, nucleus of cone ; f, cone-fiber, torn at lower end ; x, fiber-body. 5. Radial-fiber ; k, nucleus of the
same ; r, pyramidal base of radial-fiber. Technic No. 181.
segments are thick and expanded ; therefore the cone as a whole is flask-
shaped. The inner segment of the cones also contains a fiber-body.
The inner halves of the cone- visual cells are the cone-fibers; these are
broad and rest with an expanded pyramidal foot on the outer reticular
layer (Fig. 269). The nucleated enlargement, the cone -granule, usually
lies immediately to the inner side of the membrana limitans.
The number of the rods is much greater than that of the cones.
The latter occur at regular intervals, so that three or four rods always lie
between two cones (Fig. 271).
The basal portion of the visual cells resting upon the outer reticular
layer usually is plainly to be recognized as a special radially striated
layer (Fig. 269), Henle's fiber-layer ; in the region of the macula lutea
this fiber-layer is particularly broad and gradually diminishes — often very
unsymmetrically — toward the ora serrata.
564
HISTOLOGY.
"Wl
:.
•%i3
'■ ■: .
■ , *»*•*
;,*:-'. . .
: •" If** 8
■ -- - ^ c "
- Kb®®
r — »( , r ■
.'■■■■
" ■'.-- ■;■..,
' :
,'-
- -
Z 1/3 _
w ~
0S.2
5::
-< CJ >
C_ in
= ^-
(/IjD -
j«c 5
h > rt
z 1- 3
ogi
" U u
X' B
1 10 u
"x.=
n 1
-a *s
£ c
THE ORGAN OF VISION. 365
The pigmented epithelium consists of a simple layer of hexagonal
cells, which on their outer surface, toward the choroid, where the nucleus
lies are free from pigment, while their inner division contains numerous
rod-shaped pigment-granules, from i to 5 /j long. From the inner divi-
sion numerous delicate processes extend between the rods and cones. In
albinos and on the tapetum the epithelium is free from pigment.
In the region of the macula lutea and fovea centralis, also of the ora
serrata, the structure of the retina above described presents modifications
calling for special consideration.
The Macula Lutea and Fovea Centralis (Fig. 273).— In the region of
the macula the layers of the retina exhibit the following variations. Deli-
cate fibers of the optic nerve run direct from the optic entrance to the adja-
cent median portion of the macula ; above and below these fibers, thicker
nerve-fibers run from the optic entrance convexly upward and downward
and unite at the lateral margin of the macula. The ganglion-cell layer is
greatly increased in thickness, owing to the development of the layer of
bipolar ganglion-cells, which instead of a single row are arranged in many
(up to nine) rows ; also the inner granule layer by multiplication of its
elements is almost twice as broad. The inner and outer reticular layers
suffer no essential change. The neuro-epithelial layer is here repre-
sented by the somewhat smaller cone-visual cells alone. Already at the
margin of the macula the rod-visual cells diminish in number and within
the macula they are wanting altogether ; as a result the cone-fibers are
visible in a wide extent ; here they alone form the fiber-layer of Henle.
The cone-granules, on account of their large number, lie in several rows
one above the other. The radial-fibers no longer stand vertically to the
thickness of the retina, but obliquely toward the fovea.
Toward the fovea centralis situated in the center of the macula the
layers of the retina become gradually thinner and are in part totally sus-
pended. With the exception of a few fibers, the nerve-fiber layer first
disappears ; then the cerebral layers fuse with one another and in the
center of the fovea with the cone-granules, forming a thin layer in which
the boundaries of the individual strata can no longer be recognized. In
the center of the fovea (fundus fovese) the neuro-epithelial layer (cone-
cells) almost alone is present.
A diffuse yellow pigment permeates the cerebral layer, but is absent
in the neuro-epithelial layer ; therefore the fundus fovea? is colorless.
In the region of the ora serrata a rapid diminution in the retinal
layers takes place. Optic-fibers and ganglion-cells disappear before
reaching the ora serrata. Of the visual cells the rod-visual cells are the
first to vanish ; the cone-visual cells are still preserved, but appear to be
jS 6
' Vacuole."
Radial-fibers of Miiller.
^
Pars ciliaiis retinae.
•1
274. — Meridional Section of the Ora Skrrata and the adjacent portion of the Pars
Ciliaris Retinae of a Man Thirty-seven Years of Age. X 1S0— {Schapei .)
THE ORGAN OF VISION. 367
deprived of their outer segment. Then the outer reticular layer is lost,
so that the outer and inner granule layers become confluent, and finally
the inner reticular layer ceases. The radial-fibers of Muller, on the con-
trary, persist and are highly developed. [Within the region of the ora
serrata commonly smaller or larger clefts or even rather voluminous
spaces occur, which are called vacuoles (Fig. 274). They are either
confined to the neuro-epithelial layer or extend centrally into the inner
reticular layer. They are probably filled with a lymphatic fluid. The
meaning of these spaces is unknown, but they are certainly not to
be regarded as pathological or senile changes, because they are rather
common in the perfectly normal retinae of young individuals. — Editor.]
The pars ciliaris retina consists of a simple layer of slender colum-
nar cells, which gradually originate in the blended inner and outer
granule layers (Fig. 274). These cells are covered on their centrally
directed surface by a cuticular membrane, a true membrana limitans
interna, which is not present in the pars optica retinae ; their peripheral
surface is joined to pigmented cells, a continuation of the pigmented
epithelium.
The pars iridica retince, the pigment layer of the iris, has been
described (p. 357).
With regard to the connections of the nervous elements of the retina,
according to the foregoing description the nerve-processes of the ganglion-
cells of the ganglion of the optic nerve and of the stellate cells of the
inner granule layer are the centripetal optic-fibers, while the centrifugal
nerve-fibers terminate in free endings in the inner granule layer. The
ganglion-cells of the ganglion retinae apparently do not possess a nerve-
process ; their union with the other nervous elements is effected by means
of the nervous tangles in the two reticular layers, and not only as else-
where by contact in the customary manner (p. 106), but also by direct-
connection by means of true anastomoses.*
The connection with the visual cells is effected by means of the
intraepithelial processes of the cells of the ganglion retinae, that ter-
minate between (not within) the visual elements. Physiologic researches
make it highly probable that the visual cells constitute the essential
percipient part of the retina.
The Optic Nerve.
The optic nerve in its entire intraorbital course is enveloped in
sheaths which are processes of the cerebral membranes. Outermost is
*Not shown in Fig. 271.
368 HISTOLOGY.
the compact dural sheath, consisting of longitudinally disposed bundles
of connective tissue (Fig. 275); following within this is the exceedingly
delicate arachnoidal sheath, which sends numerous relatively thick con-
nective-tissue trabecule inward to the pial sheath, while the union with the
dural sheath is represented by a few delicate fibers. Innermost lies the
pial sheath, which closely invests the optic nerve and sends numerous
septa between the individual nerve-fiber bundles. These septa are con-
nected with one another by transverse trabeculse, the resultant structure
being a transverse lattice-work.
The tissue of the pial sheath does not penetrate within the nerve-
fiber bundles, but only forms an outer envelope for them. The nerve-
fiber bundles consist of medullated fibers without a neurilemma ; they
Central artery.
Fibers of the lamina cribrosa. | Central vein.
Hyaloid membrane
loosened.
Bundles of optic nerve
Pial sheath
Arachnoidal sheath
Dural sheath.
Fig. 275. — Longitudinal Section of the Optic Entrance of a 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 longitudinally, but above at several points transversely, Technic No. 177 d.
are held together by many neuroglia cells (spider cells). At the entrance
of the optic-nerve into the eyeball the dural sheath passes into the sclera,
the arachnoidal sheath at its anterior border resolves into fibers, so
that the subdural space lying on its outer side communicates with the
subarachnoid space on its inner side. The pial sheath blends with the
sclera, which here is pierced with numerous apertures for the nerve-fibers
passing through it ; this portion of these sheaths is called lamina cribrosa.
The choroid also participates, though in a slight degree, in the forma-
tion of the lamina cribrosa. The nerve-fibers lose their medullary sheath
at the point of entrance and consequently the nerve is considerably
reduced in size.
THE ORGAN OF VISION.
369
The central artery and vein of the retina lie in the axis of the
distal half of the optic nerve ; the connective tissue investing these
vessels is connected at many points with the pial sheath, as well as with
the lamina cribrosa.
The Lens.
The lens consists of a substantia lentis, that on its anterior surface is
covered by the epithelium of the lens ; the whole is enveloped in the lens-
capsule. In the substantia lentis a soft cortical substance and a firm core
may be distinguished ; it consists throughout of colossal, greatly elongated
epithelial cells, the lens-fibers. They have the form of six-sided pris-
matic bands, that are thickened at their posterior extremities. The
Fig. 276. — Lens-Fibers of an Infant.
A. Isolated lens-fibers, three with
smooth, one with dentated borders.
X 240. Technic No. 187. B. Human
lens-fibers cut transversely; c, section
through club-shaped ends. X 560.
Technic No. 188.
Fig. 277. — Capsule and Epithelium of an Adult
Human Lens. C. Inner aspect. X 240. Technic
No. 189 a. D. Lateral aspect, from a meridional
section through the equator of the lens ; j, cap-
sule ; 2, epithelium ; j>, lens-fibers. X 240. Tech-
nic No. 189 b.
lens-fibers of the cortical substance have smooth borders and in the
vicinity of the equator an oval nucleus. The lens-fibers of the central
portion of the lens have dentated borders and are nonnucleated. All
the fibers are united with one another by a small amount of cement-
substance, that is accumulated in larger quantities at the anterior and
posterior poles of the lens and gives rise to the so-called anterior and
posterior lens-stars, stellate forms seen in macerated preparations. 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.
The lens-epithelium consists of a simple layer of cubical cells, which
24
370 HISTOLOGY.
covers the anterior surface of the lens and extends as far as the equator;
here the epithelium, with gradual elongation of its elements, is trans-
formed into the lens-fibers (Fig. 277 £>).
The lens-capsule is a transparent, elastic membrane ; the anterior
capsule, the portion covering the anterior surface of the lens, is from 1 1 to
1 5 /j. thick, the corresponding posterior portion, the posterior capsule, only
5 to 7 ft. The lens-capsule comprises two genetically distinct parts ; the
one is a cuticular formation, a product of the epithelium of the lens, the
other, partly of the nature of connective tissue, is a transformation
product of the embryonal connective-tissue sheaths.
The Vitreous Body.
The vitreous body consists of a fluid substance, the vitreous substance,
and of fibers, which extend in all directions through the former. The
surface of the vitreous body is covered by a firmer membrane, the hyaloid
membrane, and in certain localities contains a limited number of fibrillar
and a few cells ; of the latter two forms may be distinguished, (1) round
elements, resembling leucocytes, and (2) stellate and fusiform cells. Cells
containing clear vacuoles probably are degenerating forms.
Regarding the hyaloid canal {canalis hyaloideus), see pp. 371 and
374-
The Suspensory Ligament.
The suspensory ligament (zonula ciliaris, zone of Zinn), consists of
delicate homogeneous fibers which extend from the surface of the hyaloid
membrane, in the vicinity of the ora serrata, in a meridional direction
toward the lens. They are attached to the inner surface of the
ciliary processes and proceed from the tips 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 any-
where form a continuous membrane, but are radially plicated extensions
of the hyaloid membrane that find attachment on and afford support to
the lens. The annular cleft between the zonula ciliaris behind and the
vitreous body in front is designated canal of Petit (spatia zonularia).
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 organ of vision. 37 1
The Blood-vessels of the Eyeball.
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.
I. Territory of the Vasa Centralia Retina (Fig. 278). — The central
artery of the retina, at a distance of from 1 5 to 20 millimeters from the
eyeball, enters the axis of the optic nerve (a) 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 downward, each of
which subdividing supplies the entire pars optica retinae to the ora
serrata. During its course in the optic nerve the artery gives off numer-
ous small branches, which run within the processes of the pial sheath
between the nerve-fiber bundles and anastomose with small arteries (£)
that have entered the sheaths of the nerve from the surrounding adipose
tissue and also with twigs of the short ciliary arteries (at c). 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 foveae the cerebral 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
retince enclosed within the axis of the optic nerve (Fig. 269, «').
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.
II. Territory of the Vasa Ciliaria. — This region is characterized by
the complementary veins taking a course entirely different from that of
the arteries.
Of the arteries, the short ciliary arteries (Fig. 278, Roman numerals)
supply the smooth portion of the choroid, while the long ciliary arteries
(Fig. 278, Arabic numerals) and the anterior ciliary arteries (Fig. 278,
Greek letters) are primarily destined for the ciliary body and the iris.
The branches, about twenty, of the short ciliary arteries (arteriae
ciliares posticse breves) penetrate the sclera in the vicinity of the
optic entrance (I) ; after giving off twigs (II) which supply the
posterior half of the surface of the sclera, the arteries break up
into a narrow-meshed capillary network, the choriocapillaris (III). At
the optic entrance the arteries anastomose with branches of the arteria
centralis retinae (Fig. 278, c) and in this way form the circular artery of
372
HISTOLOGY.
the optic nerve ; at the ora serrata they anastomose with recurrent twigs
of the long ciliary and of the anterior ciliary arteries (for the latter
anastomosis see Fig. 278, y).
Cornea,
x '4jf if x
Fig. 278.— Scheme of the Vessels of the Eye, according to Leber. External tunic stippled,
middle tunic white, internal 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;
&, anastomosis with vessels of the sheath ; c, anastomosis with branches of the posterior short ciliary
arteries; rf, anastomosis with choroidal vessels. Region of the vessels of the sheath Charge Italic
letters) : A, inner, £, outer vessels of the sheath. Region of the posterior short ciliary vessels
(Italic numerals) : /, arteries, /', veins (short posterior ciliary) ; II, episcleral arterial, II', epi-
scleral venous branches of the same ; III, capillaries of the choriocapillaris. Region of the posterior
long ciliary vessels (Arabic numerals) : 1, posterior long ciliary artery : 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) ; ^ ) connection with the circulus iridis
major ; y, connection with the choriocapillaris ; 5, arterial, £', venous episcleral branches; e, arterial,
«', venous branches to the scleral conjunctiva ; ?j, arterial, V, venous branches to the corneal limbus ;
V, vena vorticosa ; S, cross-section of the venous sinus of the sclera.
The two long ciliary arteries (arterise ciliares anticae longae) (i) like-
wise penetrate the sclera at the optic entrance ; the one artery passes to
THE ORGAN OF VISION. 373
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 these branches of the two long ciliary arteries a
vascular ring (2) is formed, the larger arterial circle of the iris (circulus
iridis major) from which numerous twigs arise for the ciliary body and
ciliary processes (3) and for the iris (4). Near the pupillary margin of
the iris the arteries form an incomplete ring, the smaller arterial circle
(circulus iridis minor).
The a?iterior ciliary arteries (arteriae ciliares anticse) 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 (ft) supply the ciliary muscle, and send recurrent branches to unite
with the choriocapillaris (V). Before the anterior ciliary arteries penetrate
the sclera, they give off twigs toward the back for the anterior half of
the sclera (S), toward the front to the conjunctival sclera (?) and to the
corneal limbus (y). The cornea itself is without blood-vessels ; only at
the margin, in the anterior lamellae of the substantia propria, is there a
circumferential network of capillary loops.
All the veins run toward the equator, where they converge to four
(more rarely five or six) small stems, the whorl veins or vena vorticosce,
which forthwith pierce the sclera (Fig. 278) and empty into one of the
ophthalmic veins. In addition to these there are small complemental
veins that run parallel to the short ciliary arteries and to the anterior
ciliary arteries, the short ciliary veins (Fig. 278, V) and the anterior
ciliary veins (a') ; the anterior ciliary veins receive twigs from the ciliary
muscle, from the episcleral vascular network (Fig. 278, #'), from the
conjunctival sclera (e'), and from the circumferential capillary loops of
the cornea (1/). The episcleral veins also communicate with the venae
vorticosae at the equator (at V). The anterior ciliary veins finally com-
municate with the sinus venosus sclerce (Schlemm) (S). This is a venous
wreath encircling the cornea, that, lying within the sclera, still possesses
completely closed walls.* It takes up small veins from the capillary
network of the ciliary muscle.
The Lymph-channels of the Eyeball.
The eye possesses no proper lymph-vessels, but a series of inter-
* The communication with the anterior chamber of the eye formerly described is facti-
tious ; the assertion that such communication existed was based on the fact that colored fluids
injected into the anterior chamber pass over into the venous wreath by filtration.
374 HISTOLOGY.
communicating lymph-spaces. Two complexes of such spaces may
be distinguished, an anterior and a posterior. The anterior complex
comprises : —
1. The lymph canaliculi of the cornea and the sclera.
2. The anterior chamber of the eye, which, by means of the capil-
lary cleft between the iris and the lens, communicates with —
3. The posterior chamber of the eye. The latter is in open connec-
tion with —
4. The spatia zonularia.
The last three spaces stand in close relation to one another and may
be injected from the anterior chamber.
The posterior complex includes : —
1. The hyaloid canal (canalis hyaloideus).
2. The lymph-clefts between the sheaths of the optic nerve, the sub-
dural and the subarachnoid space, the narrow cleft between the choroid
and the sclera, the perichoroidal space, and the spatium interfasciale
(Tenon), which extends from the dural sheath of the optic nerve to the
optic foramen. These spaces may be filled from the subarachnoid space
of the brain. The content 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 the interfascial space, normally is
exceedingly scanty. Both these spaces serve to facilitate the movements
of the choroid and of the eyeball and may be regarded as synovial spaces.
The Nerves of the Eyeball.
The nerves of the eyeball penetrate the sclera in the circumference
of the entrance of the optic nerve and run forward between the outer
tunic and the choroid ; after giving to the choroid bundles provided
with ganglion-cells, they form an annular plexus intermingled with
ganglion-cells lying upon the ciliary body, the ciliary ganglionic plexus
(plexus gangliosus ciliaris), from which branches arise for the ciliary
body, the iris, and the cornea. The nerves of the ciliary body terminate
in delicate, pointed ends in the blood-vessels and in the ciliary muscle,
partly between the muscle-bundles in the form of branched terminal
twigs, which perhaps subserve the muscular sense, partly on the scleral
surface of the ciliary body in the form of a delicate plexus. The medullated
nerves of the iris form networks and lose their medullary sheath as they
pass to the pupillary margin ; their terminal ramifications are in part dis-
tributed to the smooth muscle-fibers and to the blood-vessel walls, while
another portion form a dense sensory plexus lying close beneath the an-
THE ORGAN OF VISION. 375
terior iridal surface. The nerves of the cornea first enter the sclera and form a
circular plexus, the plexus annularis, surrounding the corneal margin, from
which branches arise for the conjunctiva and for the cornea. In man the
twigs in the conjunctiva 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 one to two millimeters 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 axis-cylinders penetrate
the entire structure. They form networks, which according to the
plane they occupy are described as the stroma-plexus, which lies in
the deeper strata of the cornea ; the sub-basal plexus, which is situated
Epithelium.
Anterior elastic lamina. *. " ' XfaV&s.J&Jfa
Portion of substantia propria. (
Fig. 279. — From a Vertical Section through the Human Cornea. X 240. n. A dividing nerve
penetrating the anterior basal membrane; j, subepithelial plexus beneath the cylindrical cells; a,
fibers of the intraepithelial plexus ascending between the epithelial cells. Technic No. 186.
beneath the anterior elastic lamina ; the subepithelial plexus, which lies
close under the epithelium. From the latter plexus exquisitely delicate
nerve-fibrillse ascend into the epithelium between its elements and form
the exceedingly fine intraepithelial plexus, the ramifications of which ter-
minate in free ends between the epithelial cells (Fig. 279). Nerve-end-
ings also occur in the sclera.
The Eyelids.
The eyelids, palpebra, are folds of the integument, which enclose
muscles, loose and compact connective tissue, and glands. The outer
fold of the eyelid retains the usual character of the skin ; the inner fold,
that toward the eyeball, is considerably modified and is called the palpe-
bral conjunctiva. The skin on the external surface of the eyelid extends
over the anterior free margin of the lid and does not pass into the palpe-
bral conjunctiva until it reaches the posterior border, the palpebral
border.
The eyelid is best studied in a sagittal section (Fig. 280) in which,
counting from before backward, the following strata are found :
1. The integument is thin and beset with fine lanugo-hairs, the folli-
376 HISTOLOGY.
cles of which it encloses ; in the corium small coil-glands are found, also
pigmented connective-tissue cells, that are of rare occurrence in the corium
elsewhere. The subcutaneous tissue is very loose, rich in fine elastic
fibers, poor in fat-cells, that may be entirely wanting. Near the border
of the lid the corium is more compact and beset with more conspicuous
papillae. In the anterior edge of the margin of the lid two or three rows
of robust hairs, the cilia, are obliquely implanted, the follicles of which
extend far into the corium. The cilia undergo rapid shedding ; their
length of life is said to be about from one hundred to one hundred and
fifty days ; consequently hairs in all stages of development are frequently
found among the eyelashes. The hair-follicles of the cilia are provided
with small sebaceous glands, in addition to which they take up the
excretory ducts of the ciliary glands (Moll), which in their minute
structure resemble coil-glands, from which they differ only in having
their lower end less convoluted.
2. Posterior to the subcutaneous tissue lie the transverse bundles of
cross-striated muscle-fibers of the orbicularis palpebrarum muscle; the
portion of the muscle lying behind the cilia (McR) is named the tarsal
muscle (Riolan).
3. Behind the muscle the fibrous extensions of the tendon of the
levator palpebrse muscle are met, which are partly lost in the areolar
tissue present, the so-called fascia palpebralis, and partly attached to the
upper margin of the tarsus ; the latter portion contains smooth muscle-
fibers (?nps) the superior palpebral muscle (Miiller). In the lower eyelid
the expansion of the tendon of the inferior rectus muscle also contains
bundles of nonstriped muscle-fibers, the inferior palpebral muscle.
4. The tarsus is a plate of dense fibrous tissue, which gives firmness
and support to the eyelid. It lies immediately in front of the conjunctiva,
to which it belongs, and occupies the lower two-thirds of the height of
the entire eyelid. In its substance the tarsal glands (Meibom) (in) are
embedded, elongated bodies which consist of a wide excretory duct
opening on the palpebral border and of little follicles with short stalks,
that empty into it on all sides. In their histology the tarsal glands agree
with the sebaceous glands. At the upper end of the tarsus, partly
enclosed by its substance, lie branched tubular glands which in their
minute structure coincide with the tear-glands and therefore are called
accessory tear-glands (Fig. 280, a t) ; they principally occur in the inner
(nasal) half of the eyelid.
Behind the tarsus lies the conjunctiva proper, which consists of an
epithelium (e) and a tunica propria (tp). The former is a stratified
columnar epithelium, with several rows of spherical cells in the depths
THE ORGAN OF VISION.
377
and a row of mainly short cylindrical cells on the surface. The latter
possess a narrow hyaline cuticular border. Goblet-cells also occur in
varying number. At the posterior palpebral border the epithelium
gradually passes into the stratified scaly variety, that occasionally extends
far over on the conjunctiva. The lower portion of the palpebral con-
junctiva is smooth. In the upper portion, on the contrary, the epithe-
lium forms irregular pocket-like depressions, the " conjunctival recesses,"
McR W"E] h
Fig. 280.— Sagittal Section of the Upper Eyelid of a Child Six months old. X 10. 1. Integu-
ment: E, epidermis; C, corium ; Sc, subcutaneous tissue ; Hb, hair-follicles of lanugo hairs; X, coil-
gland ; IV. eyelash, with the anlage of a new hair (Eh) ; W, W", portions of follicles of eyelashes ;
M. portion of a ciliary gland. 2. Region of the orbicularis palpebrarum muscle : O, bundles of this
muscle cut transversely ; McR, tarsal muscle. 3. Expanded tendon of the levator palpebrarum supe-
rior; mps, superior palpebrarum muscle. 4- Conjunctival portion: e, conjunctival epithelium; tp,
tunica propria ; at, accessory tear-gland ; t, tarsus ; m, tarsal glands, the mouth of the excretory duct
is not shown ; a, transverse section of the arcus tarseus ; a', transverse section of the arcus tarseus
externus. 5. Margin of the eyelid. Technic No. 191.
that differ greatly in individual development and in sections, when highly
developed, may resemble glands. The tunica propria of the conjunctiva
consists of connective tissue, of plasma-cells in varying number, and of
lymph cells, the number of which likewise varies greatly. In animals,
especially in ruminants, the latter form true nodules, the so-called
trachoma glands, from the summit of which the leucocytes wander
378 HISTOLOGY.
through the epithelium to the surface ; in man the migration of the
leucocytes occurs in a slighter degree. In the region of the conjunctival
recesses, the tunica propria is divided into papillae by the depressions of
the epithelium, hence the name "papillary body."
The palpebral conjunctiva passes from the eyelids to the eyeball, the
anterior surface of which it covers. At the point of transit, the fornix
conjunctiva, a loose sub-conjunctival tissue consisting of connective-
tissue bundles occurs under the tunica propria. The epithelium is the
same as that on the palpebral conjunctiva ; the tunica propria contains
fewer leucocytes, but also in man normally possesses about twenty small
lymph-nodules and a few mucous glands. The scleral conjunctiva is
modified in so far that the stratified columnar epithelium within a certain
distance of the cornea is transformed into the stratified scaly variety,
which continues in that of the cornea (see also Fig. 267).
The rudimentary third eyelid (plica semilunaris) consists of connective
tissue and stratified squamous epithelium. The caruncula lacrimalis
resembles the skin in structure, only the stratum corneum is absent, and
contains fine hairs, sebaceous and accessory tear-glands.
The blood-vessels of the eyelids proceed from branches that ap-
proaching from the outer and inner angles of the eye form an arch,
the circus tarseus (Fig. 280, a), at the margin of the lid and a second arch,
the arcus tarseus externus (a'), at the upper end of the tarsus. Branches
from these arches ramify in the skin, surround the tarsal glands, and
penetrate the tarsus to supply a capillary network lying beneath the
conjunctival epithelium ; they also supply the fornix conjunctivae, the
scleral conjunctiva, and anastomose with the anterior ciliary arteries.
The lymph-vessels form a close-meshed network in the tarsal conjunc-
tiva, a very open-meshed network on the anterior surface of the tarsus.
According to some authors the lymph channels of the scleral conjunctiva
are closed at the corneal limbus ; according to others they send minute
canaliculi into the tissue of the cornea and are in communication with
the system of lymph-spaces and canaliculi in the latter.
The nerves form a very dense plexus in the tarsus and in the palpe-
bral conjunctiva, which is characterized by a peculiar, coil-like, twisted
arrangement of its fibers. One portion of the tarsal plexus surrounds
the tarsal glands * and here consists of many nonmedullated and few
medullated nerve-fibers ; another portion terminates in the walls of the
blood-vessels. From the " conjunctival " plexus medullated nerve-fibers
* Whether nerve-fibers penetrate between the gland-cells has not yet been distinguished
with certainty; probably the nerves of the tarsal glands behave like those of the salivary glands
(page 253)-
THE ORGAN OF VISION. 370
arise, that run obliquely toward the margin of the lid and the palpebral
conjunctiva, lose their medullary sheath, in part penetrate directly into
the epithelium, where they branch and terminate in free endings, in part
terminate in end-bulbs lying close under the epithelium. These end-
bulbs are found in large numbers not only in the papillae of the margin
of the lid and in the palpebral conjunctiva, but also in the ocular conjunc-
tiva and in the margin of the cornea (see also Fig. 267).
The Lacrymal Organ.
The lacrymal glands are compound tubular glands, provided with
several excretory ducts. The latter are clothed with a two-layered
cylindrical epithelium and pass into long, narrow, intercalated tubules
clothed with low epithelial cells. These pass into the gland-tubules, which
are lined with serous gland-cells.
>W0 fifr' 1 -
b
Kaf-'
Fig. 281. — From a Thin Section of a Human Lacrymal Gland. X 240. A. Gland; a, tubule cut
transversely ; a', group of tubules, mostly cut obliquely, the lumen of only one tubule visible, below ;
s, intercalated tubule with cubical (above to the right) and flat (below to the left), epithelial cells;
y, intercalated tubule in cross-section, lined with moderately high cylindrical cells; b, connective
tissue. B. Cross-section of the duct; e, double layer of cylindrical epithelium ; b, connective tissue.
Technic No. 192.
The walls of the lacrymal canaliculi consist of stratified scaly epi-
thelium, of a tunica propria rich in elastic fibers, beneath the epithelium
also rich in cellular elements, and of cross-striped muscle-fibers, for the
greater part running longitudinally.
The lacrymal sac and the naso-lacrymal duct consist of a two-lay-
ered columnar epithelium and of a tunica propria which is chiefly adenoid
in character and separated from the underlying periosteum by a dense
plexus of veins.
TECHNIC.
No. 177. — Carefully cut the fresh eyeball out of the optic cavity
and secure as much as possible of the optic nerve ; then with the scis-
sors remove the attached fat and muscle and with a sharp razor make an
380 HISTOLOGY.
incision at the equator, about 1 cm. long, through all the coats of the
eye. Place the eyeball in 150 c.c. of 0.05 per cent, chromic acid solu-
tion (p. 31) ; after from twelve to twenty hours, beginning at the incision
already made, divide the eyeball with the scissors completely into an
anterior and a posterior half and change the fluid. After another twelve
or twenty hours wash the pieces and harden them in 100 c.c. of gradu-
ally strengthened alcohols (p. 34).
a. Carefully remove the lens from the anterior half of the eyeball
and treat it further like No. 188 ; then cut out a quadrant and with the
attached ciliary body and iris embed it in liver and cut sections through
the irido-corneal angle. The thick sections are to be stained with Hansen's
hematoxylin and mounted in damar (Fig. 267).
b. From the remaining three-fourths of the anterior half of the
eyeball cut out a piece of the cornea, 5 or 10 mm. square, embed it in
liver and make sections through the layers of the cornea (Fig. 262).
The alternating lamellae of the substantia propria can only be well seen
in unstained sections mounted in dilute glycerol.
c. From the posterior half of the eyeball cut pieces including the
three coats, 5 or 10 mm. square, and cut sections, not too thin, for the
study of the strata of the sclera and choroid (Fig. 265). Stain them with
Hansen's hematoxylin (p. 37) and mount in damar (p. 48). In section-
ing, the retina usually becomes loosened.
d. For preparations 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 the coats of the eye ; embed this portion with about
one centimeter 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. 38) and with Hansen's hematoxylin (p. 37), and
mount in damar. Examine with very low magnification (Fig. 275).
No. 178. — Remove a fresh eyeball according to the method given
in No. 177, make an incision at the equator and place it in from 100
to 200 c.c. of Muller's fluid. In from twelve to twenty hours divide it
with the scissors into an anterior and a posterior half. In two or three
weeks carefully wash both halves in slowly running water for from one
to two hours. Then cut pieces including all the coats about 8 mm. long
and use for them the following preparations : —
a. Teased Preparation of the Choroid. — Tease and mount a fragment
in a drop of dilute glycerol ; it exhibits large blood-vessels, the capil-
laries of the choriocapillaris, branched pigment-cells, elastic fibers, some-
times also the glassy membrane; the "lattice-work" of the latter is
only partially distinct. The isolated membranes may be stained with
Hansen's hematoxylin and mounted in damar, but the more delicate
structures are thus rendered indistinct (Fig. 266).
b. Elements of the Retina. — Carefully tease a small piece of the
retina in a drop of Muller's fluid. 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
THE ORGAN OF VISION. 38 1
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.
In order to see beautiful cone -visual cells, examine according to the
method just given the eyes of fishes. (See further, No. 180 and
181).
c. The remaining parts of the eyeball are to be transferred from
the water to 80 c.c. of gradually-strengthened alcohols (p. 34) for hard-
ening ; when the hardening is completed cut out the iris, embed it in
liver, and make meridional sections ; stain them in Hansen's hematoxylin
(p. 37) and mount in damar (p. 48) (Fig. 268).
d. Cut out a portion 1 cm. long of the retina, including the ora ser-
rata, which is macroscopically visible as a wavy line, embed it in liver,
and make meridional sections ; stain them in hematoxylin (p. 37) and
mount in damar (Fig. 274).
e. Treat in the same manner a piece of the retina taken from the
posterior portion of the eye where the optic-fiber stratum is thickest.
The radial-fibers of Muller can be seen in their entire length only in
accurate vertical sections (Fig. 270 and Fig. 274).
f. In the same manner treat meridional sections through the macula
and 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
mammals only the ape possesses a yellow macula and a central fovea ;
but the majority — insectivora and certain rodents excepted — have an
" area centralis," without yellow pigmentation, 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. 179. — Retina, after Golgi. — For this purpose thick retinae are
most suitable, therefore select the eyes of large animals. Divide the
eye into an anterior and a posterior half, remove the vitreous body, and
with forceps and scissors carefully dissect a piece of the retina from the
choroid. Cautiously roll this piece into a cylindrical or spherical mass,
and dip it for one second in thin celloidin-solution ; expose it for a few
seconds to the air, until the envelope of celloidin is somewhat stiffened,
and then place the piece in the Golgi mixture (p. 43). (The object of
this envelope is to prevent the formation of precipitates on the surface.)
Let the object remain in the Golgi mixture for from twelve to seventy-
two hours, then transfer it for twenty-four hours to the silver-solution
(p. 44). Then repeat the procedure (p. 45). The impregnation occurs
first, after twelve hours, in the rods and cones ; after another twelve
hours in the bipolar cells and the "spongioblasts" (p. 361, remark f),
later in the cells of the ganglion nervi optici and in the nerve-fibers, last
in the sustentacular cells.
382 HISTOLOGY.
No. 180. — Fresh Elements of the Retina. — Select the warm eyes of
animals just killed. Divide the eyeball 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. 50), 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 former 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 very unstable and soon lose their sharp
contours ; molecular motion of the pigment-granules may be very fre-
quently observed.
No. 181. — The best method for isolating the elements of the return
is the following : Place the eye unopened, but freed from fat and muscle,
in 1 per cent, osmium solution. In twenty-four hours cut the eye open
at the equator and for maceration place it for two or three days in dis-
tilled water ; then with scissors cut out a piece of the retina about 2 mm.
long and tease it in a drop of water ; the preparation may be stained
under the cover-glass with picrocarmine (p. 51) and mounted in dilute
glycerol. With the high power, in addition to many fragments the
source of which is not always to be determined with certainty, elements
like those pictured in Fig. 272 may be found.
It is advisable to select the eyes of small animals — e. g., a small
water salamander — in which the sclera is thin and allows the osmium
solution to penetrate easily. For such an eye 1 or 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. 182. — Corneal Spaces and Canalicnli. — Select an eye as fresh
as possible ; 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 surface with distilled water ; cut through the eye 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 for-
ceps and scalpel remove the ciliary body, the lens, and the iris, so that only
the anterior portion of the sclera and the cornea remains, which is to be
placed in 40 c.c. of a 1 per cent, solution of silver nitrate. The whole is then
placed in the dark for from three to six hours and then transferred to 50
c.c. of distilled water and exposed to sunlight (see further, p. 42). Harden
the objects in 50 c.c. of gradually-strengthened alcohols and cut horizontal
sections, which are most easily obtained 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 Hansen's hematoxylin and mounted in
THE ORGAN OF VISION. 383
damar. The pictures are negative, the spaces and canaliculi white
on a brown or brown-yellow surface (Fig. 263). Carefully examine
the usually somewhat thinner margins of the section ; in sections stained
in hematoxylin the nuclei of the fixed corneal corpuscles are a dull blue ;
the contours of the cells can seldom be perceived.
No. 183. — Fixed Corneal Corpuscles by tlie Gold Method. — The
method described on page 45 is to be somewhat modified, as follows :
Express the juice from a fresh lemon ; filter it through flannel. Kill the
animal,* cut out the corriea and place it for five minutes in the lemon-juice,
in which it becomes transparent ; then wash it in 5 c.c. of distilled water for
one minute ; transfer it to 10 c.c. ofgold-chlorid (p. 22) solution and place
it in the dark for fifteen minutes. With glass rods transfer the cornea to
10 c.c. of distilled water for one minute, then to 50 c.c. of distilled water
to which 2 drops of acetic acid have been added, and expose it to day-
light ; in from twenty-four to forty-eight hours the reduction is com-
pleted. 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 separate the thin lamellae
from the posterior surface ; with a little attention this can be successfully
done without much trouble. Mount the lamellae in damar.
No. 184. — Very good preparations of the corneal canaliculi are
obtained by the method of Drasch. The objects are not to be taken from
the animal recently killed, but twelve or twenty-four 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-chlorid solution plus 5 c.c. of distilled water, and stood in
the dark for one hour ; during this time frequently stir the fluid with a
glass rod. With glass rods transfer the pieces to 30 c.c. of distilled
water, in which they should remain (in the dark) for from eight to six-
teen 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. 45) the dark-violet pieces are to be hardened in gradually
strengthened alcohols and in about six days thin sections parallel to the
surface can be cut and mounted in damar (Fig. 264).
No. 185. — Nerves and Blood-vessels of the fresh Cornea. — Select the
eye of an ox and cut out the cornea and the adjoining portion of the
sclera extending from the limbus to the attachment of the ocular muscles ;
with scalpel and forceps remove the ciliary body, iris, and lens, immedi-
ately 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 power.
When the surface of the cornea is in focus the loop-shaped blood-vessels
can be seen at the scleral margin ; the majority still contain blood
corpuscles. Medullated nerve-fibers are found here, as well as in the
* Frogs are especially recommended ; their corneal canaliculi are very regular and their
posterior lamina is easily detached.
384 HISTOLOGY.
deeper strata ; they are arranged in bundles and within the cornea can
be traced only 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 distri-
bution of the nerves.
No. 186. — Nerves of the Cornea. — a. Gold Method. — Cut out the
cornea twelve or twenty-four hours after death, remove the ciliary body
and iris, and treat it according to the method given in No. 183. When
the hardening is completed cut horizontal sections, which contain the
epithelium and the uppermost lamella? of the cornea, and vertical sections
through the thickness of the cornea. Mount in damar (Fig. 279).
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 ; thus the vitreous
humor escapes into the watch-glass. Then with scissors separate from
the point of incision the entire cornea, place it on a slide with the con-
cave surface upward and with the handle of the scalpel scrape off the
ciliary body, iris, and lens, which is easily done ; transfer the cornea
thus cleansed to a second watch-glass containing from 3 to 10 drops of
the vitreous humor and from 3 to 4 drops of a 0.06 per cent, methylene
blue solution (p. 40).. The concave surface of the cornea should be
uppermost and covered by the staining fluid.
The time required for staining cannot be given with certainty ; there-
fore it is 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 ten minutes.
So soon as the nerves can be distinctly seen the cornea is to be
transferred for from eighteen to twenty hours to 20 c.c. of the ammonia
solution (p. 40) ; then cut out a quadrant and mount it in dilute glycerol,
to which a drop of the ammonia-solution has been added ; after being
kept in the dark for twenty-four hours the preparation is sufficiently
transparent and can be investigated with the high power.
No. 187. — Lens-fibers. — Cut the eyeball 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. 20). In about two hours thrust needles into the anterior and
the posterior surface of the lens and strip the capsule 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 for from ten to forty hours. At 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. 19). Apply a cover-glass, taking care to avoid
pressure ; if it is desired to preserve the fibers, stain with picrocarmine
THE ORGAN OF VISION. 385
(staining usually occurs in a few minutes), and mount in dilute acidulated
glycerol (Fig. 276 A).
No. 188. — 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 from
twenty-four to forty-eight hours with a needle break the lens into shell-
like pieces, transfer them after ten or fifteen hours to 30 c.c. of 70 per
cent, alcohol, which is to be replaced on the following 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 sec-
tion will pass through the zone lying next to the equator. If the section,
which need not be very thin, has passed through the fibers transversely
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 length-
wise. The sections are to be transferred directly from the blade to the
slide and mounted in dilute glycerol (Fig. 276 B).
No. 189. — The Lens Capsule and the Lens Epithelium. — Place the
eyeball, free from muscle and fat, in 100 or 200 c.c. of Muller's fluid.
Treat it further as follows :
a. Surface view of the Lens Capsule and Epithelium. — After two or
three days cut the eye open, remove the lens, and with forceps strip off
a piece of the anterior lens capsule ; place it for about five minutes in a
watch-glass with distilled water, which is to be changed once, then stain
it in Hansen's hematoxylin ; mount in damar. The capsule is stained a
homogeneous light blue ; the nuclei and contours of the epithelial cells
are very sharp (Fig. 277 C). If it is desired to obtain the lens capsule
alone strip off a portion of the posterior lens capsule.
b. Sections of the Capsule and Epithelium. — Let the eyeball remain
in Muller's fluid for two weeks ; remove the lens, wash it for one hour in
running water and harden it in 50 c.c. of gradually-strengthened alcohols
(p. 34) ; cut meridional sections through the anterior surface and the
equator of the lens ; stain them with Hansen's hematoxylin (p. 37) and
mount in damar (Fig. 277 D).
No. 190. — The Blood-vessels of the Eye. — For this purpose surface
preparations are especially suitable. Open a fresh eye at the equator.
The course of the central artery of the retina is macroscopically percep-
tible. 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, beginning at the equator, 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 content to remove only
one quadrant of the sclera.) All the firmer points of attachment between
the sclera and the choroid (the venae vorticosae) must be cut through.
25
386 HISTOLOGY.
Then by careful brushing with a sable pencil moistened in water remove
the attached portions of the lamina suprachorioidea from the choroid ;
by this manipulation the course of the larger blood-vessels is brought
to view. So far the investigation may be pursued on the uninjected eye
(compare with No. 178 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 the ciliary body may be easily stripped from the sclera ; re-
move the lens and then mount in damar. Examine at first with the low
power.
No. 191. — Place the upper eyelid of a child in 100 c.c. of 0.5 chromic
acid for from one to three days, wash it two hours in running water, and
harden in 50 c.c. of gradually-strengthened alcohols. For a general view
cut thick (Fig. 280), for the finer details thin sections (Fig. 27 C). Stain-
ing with Hansen's hematoxylin is at first difficult, but more readily ac-
complished after the object has lain in alcohol several months (compare
p. 37, remark *). Mount in damar.
No. 192. — The Lacrymal Glands. — The lower tear-gland in man
can be easily removed, without visible external injury, from the fornix of
the conjunctiva. In the rabbit this gland is very small and when fresh
resembles pale muscle tissue. It must not be confused with Harder's
gland lying in the median angle of the eye. Treat like No. 118.
Small pieces 1 mm. square can be used. The excretory duct and the
tubules are easily seen ; difficult, on the other hand, it is to see the inter-
calated tubules, the epithelium of which varies greatly in height and
occasionally is so low that care must be taken not to confuse them with
blood-vessels (Fig. 281).
XI. THE ORGAN OF HEARING.
The organ of hearing consists of three divisions ; the innermost, the
internal ear, encloses the end-apparatus of the auditory nerve ; the other
divisions, the middle ear and the external ear, are only accessory appa-
ratus.
The Internal Ear.
The internal ear consists of two membranous saccules lying within
the bony vestibule (vestibulum), that communicate with each other by
means of a minute canal, the ductus utriculo-saccidaris. The one saccule,
the utricle, is in connection with membranous tubules, the semicirctdar
canals (ductus semicirculares), each of which at the point where it opens
in the utricle possesses a dilatation, the ampulla. The other saccule,
the sacculus, connects by means of the ductus reuniens with a long
spirally wound membranous sack, the cochlea (ductus cochlearis).
THE ORGAN OF HEARING. 387
The sacculus and the utriculus, the semicircular canals and the cochlea
are called the membranous labyrinth. This is enclosed within the petrous
bone in a space having similar outlines, the bony labyrinth, which it does
not completely fill. The unfilled space is occupied by a watery fluid, the
perilymph. A similar fluid, the endolymph, is contained within the interior
of the membranous labyrinth.
The saccules and the semicircular canals exhibit the same struc-
ture, but the cochlea is so essentially different that it requires a separate
description.
THE SACCULE, THE UTRICLE, AND THE SEMICIRCULAR CANALS.
The walls of these canals comprise three layers. The outermost is
a connective- tissue layer rich in elastic fibers ; this is followed within by
a delicate basal membrane beset with minute excrescences, which on its
inner surface is covered by a simple squamous epithelium. This simple
structure undergoes alteration at the positions where the filaments of the
auditory nerve are distributed, the maculce of the saccule and the utricle,
the crista acusticcs on the ampullae of the semicircular canals. The con-
nective tissue and basal membrane here become thicker ; the squamous
epithelium already in the vicinity of the maculae and cristas becomes
transformed into a columnar epithelium with a cuticular border, and this
passes into the neuro-epithelium of the maculae and cristas. The neuro-
epithelium likewise is a simple layer and consists of two kinds of cells :
(1) fiber-cells, elongated elements occupying the entire depth of the epi-
thelium, slightly expanded at the upper as well as at the lower end, and
containing an oval nucleus ; they are the sustentacular elements ; (2)
hair-cells, cylindrical elements occupying only the upper half of the epi-
thelium, which in their lower rounded division contain a large spherical
nucleus and on their free surface bear a bundle of long, delicate, agglu-
tinated filaments, the "auditory hairs." The hair-cells are the terminal
apparatus of the auditory nerve. The nerve-fibers of the ramus ves-
tibularis nervi acustici are in connection with the hair-cells in this
way. On entering the epithelium the nerve-fibers lose their medullary
sheath, divide, and as naked axis-cylinders ascend to the base of the
hair-cells ; there each fiber divides into three or four varicose twigs, that
run beneath 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
*The horizontal branches interlace and form a small but dense " lattice- work," that also
by other methods than that of Golgi appears to consist of a special layer of strongly refracting
granules. The granules are the varicosities and the optical cross-sections of the horizontal
fibers. ,
e?
"Q
cs>
^0
* #
Fig. 282.-
-Otoliths
FROM
the Saccu-
lus of an Infant.
X560.
, Technic No.
193.
388 HISTOLOGY.
they send upward a few twigs, that in the same manner end in contact
with the hair-cells. These ends do not reach to the surface of the epi-
thelium. The free surface of the neuro-epithelium is covered by a con-
tinuation of the cuticular zone, a "limitans,"' which is
perforated by the auditory hairs. The maculae acus-
ticse are covered by a soft substance (a cuticula ?), in
which innumerable prismatic crystals of calcium car-
bonate, the otoliths, from 1 to 1 5 fx in size, are em-
bedded ; they form the " otoconia," the auditory sand.
On the cristse acusticae the so-called cupula occurs, in
fresh preparations an invisible substance, that on the
application of fixation fluids coagulates and thus be-
comes visible.
By means of strands of connective tissue the saccules and the semi-
circular canals are secured to the bony labyrinth, the inner surface of
which is covered by a thin periosteum and flattened connective-tissue
cells.
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 (Fig. 283) ; the upper or vestibular
wall, the vestibular membrane (Reissner), bounds the scala vestibuli ; the
lower or tympanic wall, the membranous 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 connective tissue of the ductus cochlearis are espe-
cially well developed and form a prominence, the limbus spiralis, which
rests with a broad surface on the bony spiral lamina, slopes upward
and terminates in a sharp edge. This edge is called the labium vestibu-
lar, the free margin of the bony spiral lamina is called the labium
tympanicum, between the two runs the sulcus spiralis (Fig. 289). 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 the scala tympani, are covered by a delicate continuation of
the periosteum which clothes both scalse. On the outer wall of the cochlea
the periosteum becomes greatly thickened and in cross-section appears
as a crescentic mass, the ligamenium spirale, that extends above and
below the attached surface of the ductus cochlearis (Fig. 283).
* I here follow 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.
THE ORGAN OF HEARING.
389
The minute 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 (the periosteum) ; this passes into a loose connective tissue which
contributes the chief bulk of the spiral ligament. The epithelium con-
sists 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, and at its lower end is limited by a vein that projects
farther into the lumen of the cochlea, the prominentia spiralis (vas promi-
Limbus spiralis.
Mernbrana
vestibularis. Ductus cochlearis.
Organ of Corti (organon
spirale).
6} _L — Outer bony wall of the
r\ ■ cochlea.
Vas prominens.
Ligamentum spirale.
Bony axis of the cochlea
(modiolus).
Ganglion spirale.
Lamina spiralis mem-
branacea.
Lamina spiralis ossea.
Fig. 283.— Section through the Second Turn oi* the Cochlea of an Infant. X 25- The modiolus
contains longitudinal canals cut obliquely. J. Bony wall between the second and third (half) turns
of the cochlea. The mernbrana vestibularis is torn through, the upper fragment being turned up-
ward. The mernbrana tectoria can not be seen. Technic No. 195.
nens) (Fig. 283). The capillaries of the stria vascularis lie close beneath
the epithelium ; they are the source of the endolymph.
The vestibular wall, mernbrana vestibularis (Reissner) (Fig. 283),
consists of a process of the periosteum of the scala vestibuli, that is, of
delicate fibrous connective 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, (1) the limbus, with the
free margin of the bony spiral lamina, and (2) the lamina spiralis mem-
branacea.
The limbus consists of compact connective tissue, containing an
abundance of spindle-shaped cells, which below is continuous with the
39°
HISTOLOGY.
tissue of the periosteum, on its free surface is beset with peculiarly
shaped papillae. They have the form of an irregular hemisphere ; -
toward the labium vestibulare they develop into small, elongated plates,
the so-called auditory teeth (Fig. 284 and Fig. 287), that lie in a single
row beside one another. The surface of the limbus is covered by a
Labium tympanicum.
■ — 3?s^__. ,, Foramina nervina.
Lab i U mve St i b uia r e.j|||(:^aJ *"»-*—■
Auditory teeth.
Papillae.
Fig. 284.— A Surface View of the Lamina Spiralis of a Cat. x 240. The vestibular lamina is seen
from above; between the auditory teeth two nuclei of the epithelial cells are seen. On the left of the
picture the plane of the auditory teeth is in focus, on the right, the plane of the zona perforata.
Technic No. 194.
simple layer of flattened epithelial cells, which at the edge of the
labium vestibulare passes into the cubical epithelium of the sulcus
spiralis (Fig. 287, A).
The upper surface of the free margin of the osseous spiral lamina is
perforated by a single row of slit-like openings, the foramina nervina
(Fig. 284), through which the nerves enclosed within the bony lamina
emerge, to penetrate within the epithelium of the lamina spiralis mem-
branacea. This portion of the osseous spiral lamina
is called zona perforata.
The membranous spiral lamina (lamina spiralis
membranacea) consists of (1) the membrana basil-
ars, an extension of the limbus and of the perios-
teum of the osseous spiral lamina, (2) the tympanic
lamella, a process of the periosteum of the scala
tympani which clothes the lower surface of the
basilar membrane, and (3) the epithelium of the
ductus cochlearis, which rests upon the upper sur-
face of the basilar membrane.
The membrana basilaris consists of a struc-
tureless substance which contains rigid, perfectly
straight fibers, extending from the labium tym-
panicum to the spiral ligament, and oblong nuclei.
The membrane has a finely striated appearance (Fig. 285,/).
The tympanic lamella consists of a delicate connective tissue contain-
ing spindle-cells, the fibers of which are disposed vertically to the
elements of the basilar membrane (Fig. 285, b).
The epithelium of that half of the membranous spiral lamina toward
Fig. 285. — Surface View
of the Lamina Spir-
alis Membranacea of
a Cat. X 240. Strata
of the zona pectinata
drawn with change of
focus. e. Indifferent'
epithelium (cells of
Claudius) of the ductus
cochlearis in focus ; y,
the fibers of the mem-
brana basilaris in focus;
6, the nuclei of the tym-
panic lamella in focus.
Technic No. 194.
THE ORGAN OF HEARING.
391
the axis of the cochlea is differentiated as the highly specialized neuro-
epithelium of the spiral organ (organ of Corti), while that occupying the
outer half, toward the spiral ligament, consists of indifferent epithelial
elements. Therefore the spiral lamina is 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, peculiarly shaped, for the greater part rigid forms, arranged in two
rows the entire length of the cochlea. The inner row of pillar-cells
form the inner pillars, the outer row, the outer pillars (Fig. 287). The
two rows of pillars are obliquely inclined toward one another and form
an arch, the arcus spiralis, which spans a triangular space, the tunnel, the
Cells ol Claudius.
Fibers.
Outer hair-cells. — i
Pillar-cells.
Inner hair-cells.
Zona pectinata.
Im.
Zona tectoria.
W> — Labium tympanicum.
Labium vestibulare.
Ganglion spirale. — iuiWiim
Fig. 286. — Lamina Spiralis of a Cat, seen from the Vestibular Surface. The membrana tectoria
has been removed. X 50. lo. Lamina spiralis ossea, inner half cracked and broken at several
points; at the posterior border of the same cells of the spiral ganglion project forth. Im. Lamina
spiralis membranacea. The cells of Claudius have partly fallen off, so that the fibers of the mem-
brana basilaris are seen as a delicate striation. Technic No. 194.
base of which is directed toward the basilar membrane. The tunnel is
nothing more than a very large intercellular space, that is filled with
a soft mass, the intercellular substance. 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 expanded foot, a slender
body, and a concave head, with the concavity directed outward, may be
distinguished. The head is furnished with a thin process, the " head-
plate " (Fig. 287). The body and foot of the cell are surrounded by a
scant amount of protoplasm, that only to the outer side of the foot in
the vicinity of the nucleus is present in somewhat larger amount. The
outer pillar-cells exhibit the same details, excepting that the portion con-
taining the nucleus lies to the inner side of the foot ; the rounded
articular head rests in the concave facet of the head of the inner pillar-
392
HISTOLOGY.
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 forty stiff hairs on their free surface. To the inner side of the
inner hair-cells lies the cubical epithelium of the sulcus spiralis. On the
outer side of the outer pillars lie the outer hair-cells ; they resemble the
inner hair-cells, but possess hairs that are one-third shorter and are char-
Fig. 287. — Scheme of the Structure of the Tympanic Wall of the Duct of the Cochlea.
A. Seen from the side. B. Seen from the surface. In the latter the free surface is in focus. It is
evident that the epithelium of the sulcus spiralis, lying in another plane, as well as the cells of
Claudius, can only be distinctly shown by depressing the tube. The membrana tectoria is not drawn.
The spiral nerve-bundles are indicated by dots.
acterized 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 filament and
at their upper end support a cuticidar top-plate, which has the form of a
* In the scheme (Fig. 287, A) this body is indicated by a dark speck close beneath the
auditory hairs.
THE ORGAN OF HEARING.
393
digital phalanx. The free spaces between the " phalanges '' are occupied
by the upper ends of the outer hair-cells * (Fig. 288). The cells of
Deiters are sustentacular elements, that exhibit much in common with
the pillar-cells ; like these they consist of a rigid filament and a proto-
>/{>>
tyvV'^r^L-- ??
Fig. 288. — Surface View cf the Lamina Spiralis Membranacea of a Cat. X 24°- ^- 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; kip, 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, ip, of the inner pillar-cells. Technic No. 194.
plasmic 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 in the cells of Deiters. The phalanges are
Labium Pillar-cells. ' — v — '
tympanicum. Tympanic lamella.
Lamina spiralis ossea.
Organ of Corti.
Fig. 289.— Vertical Radial Section through the Peripheral Half of the Lamina Spiralis
Ossea and through the Lamina Spiralis Membranacea of an Infant. X 80. The membrana
tectoria has been torn from its point of attachment on the labium vestibulare. Technic No. 195.
joined to one another and form a beautiful netted membrane, the mem-
brana reticularis.
The outer hair-cells do not extend to the basilar membrane, but
* The inner hair-cells are kept apart from one another by short processes of the inner
pillar-cells. These processes are not shown in Fig. 287 B.
394 HISTOLOGY.
occupy only the upper half of the spaces between the cells of Deiters ;
the lower divisions of these spaces remain unoccupied, and are called
Nuel's spaces or, since they communicate with one another, the space of
Nuel (Fig. 287 A). The latter also has the significance of an intercel-
lular space and is connected with the tunnel.
External to the last' row of Deiters's cells lie the cells of Hensen,
elongated cylinders, that gradually decrease in height and pass into the
indifferent epithelium of the cochlear duct, the elements of which, so far
as they cover the basilar membrane, are called the cells of Claudius.
A soft, elastic cuticular formation, the membrana tectoria, lies above
the sulcus spiralis and the spiral organ (Fig. 289). It is attached to the
vestibular lip of the sulcus and extends to the outermost row of hair-
cells.
The cochlear branch of the auditory nerve penetrates into the axis of
the cochlea and in its spiral uninterrupted ascent gives off branches
which pass to the root of the osseous spiral lamina ; here each medul-
lated nerve-fiber loses its medullated sheath and passes into a nerve-cell
that like those of the spinal ganglia possesses a connective-tissue capsule ;
these nerve -cells collectively form the ganglion sfiirale* which winds
along the entire periphery of the axis of the cochlea (Fig. 283) ; from
the opposite pole of each cell springs a second nerve-fiber, that soon
acquires a medullated sheath and unites with neighboring fibers in a
wide-meshed plexus enclosed within the osseous spiral lamina ; this
plexus extends near to the labium tympanicum, where the fibers lose
their medullated sheath, escape through the foramina nervina and end
in the epithelium. This occurs in such a manner that they bend in the
direction of the circumvolution of the cochlea and run in spiral bundles,
of which the first passes to the inner side of the inner pillar -cells (Fig.
287 A), the second into the tunnel, the third between the outer 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. — The auditory artery gives only a
small twig to the membranous labyrinth and another small twig to the
bony labyrinth ; the majority of its branches pass to the roots of the fifth,
seventh, eighth, ninth, and tenth cranial nerves and to the under surface
of the cerebellum. The artery for the membranous labyrinth divides
into two branches : 1. The arteria vestibularis (Fig. 290) sends twigs to
* 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
ganglion vestibulare in the interior of the cochlea also possesses bipolar ganglion-cells.
THE ORGAN OF HEARING.
395
the vestibular nerve and to the lateral-upper half of the sacculus and
of the utriculus, as well as to the corresponding portions of the upper and
lateral semicircular canals, which supply a capillary plexus that in general
is wide-meshed, but at the terminal points of the vestibular nerve, the
crista; and maculae, is narrow-meshed. 2. The arteria cochlearis com-
munis divides in two branches. The one branch, the arteria vestibule-
Arterise
labyrinth, j . . , ,
3 I Arteria cochlearis com mm
/
Arteria vestibularis
Ductus semicircularis
superior.
Ampulla lateralis.
Vena aquseductus
vestibuli.
/ Ductus semicircularis
lateralis.
Arteria cochlear
propria.
Arteria vestibulo-cochlearis. Vena spiralis.
Arteria cochlearis
Vena vestibularis.
Posterior Ampulla
posterior.
Ductus semicircularis
posterior.
comrnuii is.
Vena aquaeductus cochleae.
Fig. 290. — Scheme. Blood-vessels of the Right Human Labyrinth. Median and Posterior
Aspect. D.c. Ductus cochlearis. .S. Sacculus. U. Utriculus. 1. Ductus reuniens. 2. Ductus
utriculo-saccularis. The saccus endolymphaticus is cut oft'.
cochlearis, supplies one twig to the median-posterior half of the sacculus,
utriculus, and semicircular canals and in its minute ramifications behaves
like the vestibular artery ; another twig ramifies in the initial third of the
first turn of the cochlea. The other branch, the arteria cochlearis pro-
pria, supplies the remaining extent of the cochlea ; on entering the axis
of the cochlea it divides into three or four branches, which in their
59 6
HISTOLOGY.
spiral ascent form the tractus arteriosus spiralis. From this about
30 or 35 radial twigs arise, which supply three separate capillary terri-
tories : (I) the canal in which the ganglion spirale is enclosed, (2)
the lamina spiralis, (3) the intermediate and outer walls of the seals
(Fig. 291, 1, 2, 3).
The veins of the labyrinth follow three separate paths :
1. The vena aquceductus vestibuli runs through the aquaeductus
vestibuli ; it collects the blood from the semicircular canals and from
Scala tympani. Scala vestibuli.
Cross-section of an artery of the
tractus spiralis.
Vena lamina spiralis
Ganglion spirale.
Vena spiralis supei ior.
Cross-section of an artery of the
tractus spiralis.
- Vena lamina spiralis.
Anastomosis.
Vena spiralis inferior.
Fig. 291. — Scheme. Vertical Section of the Right Hale of the First (Basal) and Second
Turns of the Cochlea, a. Vas prominens. b. Vas spirale.
one portion of the utriculus ; it opens in the sinus petrosus superior
(Fig. 290).
2. The vena aquceductus cochlece runs through the aquseductus
cochleae ; it collects the blood from one portion of the utriculus, from
the sacculus and from the cochlea. The venous radicles in the cochlea
behave in the following manner : The veins collecting at the vas prom-
inens and at the vas spirale (Fig. 291, a, />) pass in the wall of the scala
tympani to the spirally running vena spiralis, King below the spiral
THE ORGAN OF HEARING. 397
ganglion ; this originates from the confluence of two veins, of which the
lower receives the blood from the first (basal) and a portion of the second
turn of the cochlea, while the upper spiral vein collects the blood from
the remaining cochlear turns. The spiral vein also takes up one set of
the capillaries in the canal of the spiral ganglion and is united by anas-
tomosis with a vein lying above this canal, the vena lamina spiralis
(Fig. 291). This receives the blood from the other set of capillaries of
the spiral ganglion, as well as from the lamina spiralis,* and opens in
the central vein of the cochlea.
3. The central vein of the cochlea is the main radicle of the internal
auditory vein. The latter takes up veins from the auditory nerve and
from the bone, and in all probability opens in the vena spinalis anterior.
The Lymph-channels. — The endolymph in the interior of the mem-
branous labyrinth is connected with the subdural lymph-spaces by means
of minute canals passing from the ductus endolymphaticus. The peri-
lymphatic spaces (see p. 190) are in connection with the subarachnoid
space by means of a lymph-vessel running through the aquseductus
cochlea?, the " ductus perilymphaticus." Blood-vessels and' nerves are
surrounded by conspicuous perivascular and perineural lymph-spaces, that
probably also are connected with the subarachnoid space.
The Middle Ear.
The mucous membrane of the tympanic cavity is intimately united
with the underlying periosteum. It consists of thin connective tissue and
a single stratum of cubical epithelial cells, that sometimes on the floor,
occasionally also in larger areas of the tympanic cavity, are ciliated.
Glands (short, o. 1 mm. long follicles) occur sparingly in the anterior half
of the tympanic cavity. The mucosa of the eustachian tube consists ot
a fibrillar connective tissue (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 (cf. p. 88) ;
in the anterfor portion the matrix of the cartilage is penetrated by dense
networks of elastic fibers. The blood-vessels in the mucosa of the tym-
* The vestibular membrane is nonvascular in the adult. The arrangement of the blood-
vessels in the cochlea is such that the scala vestibuli is chiefly encircled by arteries, the scali
tympani mainly by veins. The portion of the scala tympani adjacent to the lamina spiralis
membranacea is thus removed from the influence of arterial pulsation.
398
HISTOLOGY.
panic cavity form a wide -meshed, in the mucosa of the eustachian tube a
narrow-meshed superficial 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.
The External Ear.
The tympanum consists of a lamina of connective tissue, lamina
propria, in which the fibrous bundles on the outer side are radially
arranged and connected with the periosteum of the sulcus tympanicus,
while cm the inner side, toward the tympanic cavity, the fibrous bun-
Epidermis.
Hair-follicle.
Corium.
Excretory duct.
Young hair.
Cuil of cerumiuous
gland.
Fig. 292. — From a Ykrtical Section
through the slcin of the external
Auditory Meatus of an Infant.
X 50, The excretory duct opens into the
hair-follicle. Technic No. 19S.
Membrana propria.
Nuclei of smooth muscle-fibers.
Secretion.
Gland-cells.
Secretion.
-Cuticular border.
-^ Gland-cells.
lp!oTo^'-V o r u ' !ȣ__ Nuclei of smooth muscle-
fibers.
Membrana propria.
Fig. 293. — A. Cross-section of a Coil-Tubule
of the Skin of the External Auditory
Meatus of an Infant. B. Longitudinal
Section of a Coil-tubule from the Ex-
ternal Auditory Meatus of a Twelve-
year-old Boy. X 2^0. Technic No. 198.
dies are circularly arranged. On its inner surface the tympanum is cov-
ered by the mucous membrane of the tympanic cavity, on its outer sur-
face by the integument of the external auditory canal. Both investments
are very firmly attached to the lamina propria, are smooth, ami are with-
out papillae. Where the malleus lies against the tympanum, the latter is
provided with a superficial stratum of hyaline cartilage.
The external auditory canal, so tar as it is cartilaginous and on the
whole length of its upper wall, is clothed with an extension of the skin,
which is characterized by its thickness and by a great abundance of pecu-
liar coil-glands, the ceriuninoiis glands (Fig, 292). In some respects these
THE ORGAN OF HEARING. 399
glands correspond with the ordinary larger coil-glands (sweat-glands) of
the skin ; like these, they possess an excretory duct lined by several
layers of epithelial cells, and the tubules of the coil contain a simple layer
of cubical gland-cells, which rest on smooth muscle-fibers and a conspicu-
ous basement membrane (Fig. 293) ; they are distinguished from the
sweat-glands by the very wide lumen of the coiled tubule, that particu-
larly 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 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 of the hair-follicles. In the (remaining) region of the
bony external auditory meatus, the integument is thin and without ceru-
minous glands.
The cartilage of the external auditory canal and of the pinna is of
the elastic variety.
The blood-vessels and nerves are distributed as elsewhere in the skin ;
only on the tympanum do they exhibit peculiarities. Close behind the
handle of the malleus an artery descends, which breaks up into radially
disposed branches ; the blood is returned by two paths : (1) by a venous
plexus extending along the handle of the malleus and (2) by a venous
plexus lying on the margin of the tympanum.
These vessels lie in the integumentary covering of the tympanum.
The mucous membrane of the tympanum is provided with a dense capil-
lary network, which anastomoses with the integumentary vascular net-
work by means of perforating branches at the margin of the tympanum.
The lymph-vessels are principally found in the cutaneous stratum of
the tympanum.
The nerves form delicate networks lying beneath the mucous and
the cutaneous covers.
TECHNIC.
A fundamental condition is an exact knowledge of the macroscopic
anatomy 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. 193. — 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 is placed in water, the white spots
400 HISTOLOGY.
(maculae) in the sacculus and utriculus can be detected. With delicate
forceps lift out the saccules and spread out a small piece in diluted gly-
cerol 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 glycerol must not be too thick, or it will
render the otoliths completely invisible (Fig. 282).
In taking out the saccules portions of the semicircular canals are
not infrequently also removed ; stain these with picrocarmine and mount
them in dilute glycerol. Only the epithelium and here and there in
optical section the delicate glassy membrane can be seen. The connec-
tive tissue is scanty.
No. 194. — Surface Preparations of the Membranous Cochlea. — The
base of the cochlea lies in the bottom of the internal auditory meatus,
the apex is directed toward the eustachian tube, therefore the axis
of the cochlea is horizontal and transverse to the long axis of the petrous
bone.
Open the free portion of the cochlea, that is, remove the promon-
tory close to the fenestra rotunda, open the apex of the cochlea and
having removed the superfluous osseous mass as far as practicable place
the preparation in 20 c.c. of 0.5 per cent, osmic acid (5 c.c. of 2 per cent,
osmic acid to 1 5 c.c. of distilled water). In from twelve to twenty hours
wash the preparation for about one hour and then place it in 200 c.c. of
Miiller's fluid. In from three to twenty days (or later) open 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 glycerol on a slide, It is advisable to break off
the axial portion 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 surface must be directed upward ; it may be recog-
nized by the auditory teeth, which are visible when the upper surface is
in focus (Fig. 284), 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. 286, labium vestibulare) ; the papillae 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. 287 B, the membranous spiral
lamina is drawn schematically, as seen with the upper surface in focus,
therefore only the free surface 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 likewise disappears and can
be seen only when the tube is elevated. The preparation may be stained
with picrocarmine and preserved in dilute glycerol. The foregoing direc-
THE ORGAN OF HEARING. 4OI
tions are intended to apply to the human ear and that of the cat. The
labyrinths of children are recommended.
No. 195. — Sections of the Bony and Membranous Cochlea. — Remove
the cochlea of a child from the labyrinth. The compact osseous sub-
stance of the cochlea is surrounded by spongy bone so soft that the latter
may be removed with a stout penknife. Having done this, 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 the cochlea in 15 c.c. of distilled water plus 5 c.c. of 2 per cent,
osmic acid. After twenty-four 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 alcohols. When the hardening is completed de-
calcify the cochlea in the following mixture : 1 c.c. of a 1 per cent,
aqueous solution of palladium chlorid, 10 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 frequently changed. When the decalcification is com-
pleted the object should be again hardened, embedded in liver, and sec-
tioned. 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 mem-
brane is usually torn, so that the ductus cochlearis and scala vestibuli
appear as a common space (Fig. 283). The spiral organ leaves most to
be desired ; only very thin sections which pass through the organ verti-
cally furnish intelligible pictures ; usually a section contains several inner
and outer pillar-cells, in part only fragments of them ; the cells of Hen-
sen appear pale and swollen (Fig. 289), so that orientation presents many
difficulties to the beginner.
Among animals, the cochlea of the guinea-pig and of the bat are
recommended ; it is not embedded in spongy bone and does not need to
be chiseled out and punctured, but can at once be placed in the fixing fluid.
No. 196. — The Nerves of the Macula, Crista, and Cochlea. — For
this purpose the ear of the newborn mouse is recommended, treated ac-
cording to the method given on page 43. The base of the cranium, after
removal of the vertex, brain, and lower jaw, is to be placed for from
three to four days in the osmio-bichromate mixture and for two days in
the silver solution. As a rule it is necessary to employ the double method
(p. 45). Cut horizontal and frontal sections through the cranium without
decalcifying it. The former are the more readily made.
No. jgy. — The Eustachian Tube. — To obtain transverse sections (in-
cluding cartilage and mucosa) the oblique direction of the tube down-,
ward, forward, and inward must be ascertained. Cut out the pharyngeal
division of the tube together with the surrounding muscles and fix it in
200 or 300 c.c. of Miiller's fluid (p. 32). In from three to six weeks
wash it in running water and harden it in 100 c.c. of gradually-strength-
ened alcohols (p. 34). The sections may be stained in Hansen's hema-
toxylin (p. 37) and mounted in damar (p. 48). For a general view,
examine with the low power.
26
402 HISTOLOGY.
No. 198. — The Ceruminous Glands. — Cut out the ear and the car-
tilaginous auditory passage close to the bony auditory passage. From
the cartilaginous portion cut a piece 1 cm. square and place 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 Hansen's hema-
toxylin (p. 37) may be employed (Fig. 292). Examine thin unstained
sections in diluted glycerol ; in these the fat-globules and the pigment-
granules can be seen. The organs of newborn 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. 293).
XII. THE OLFACTORY ORGAN.
In this chapter the entire nasal mucous membrane will be described.
The olfactory mucous membrane proper in man is confined to the middle
of the superior turbinal bone and to the corresponding portions of the
nasal septum ; the remaining portions of the nasal fossa? (the accessory
nasal spaces included) are covered with respiratory mucous membrane.
In addition there is another division in the region of the movable nose
(vestibulum nasi) which is clothed by a continuation of the skin. Accord-
ingly three different divisions of the nasal mucous membrane are to be
distinguished.
The Vestibular Region.
The mucous membrane of the vestibular region consists of a strati-
fied squamous epithelium and a tunica propria supporting papillae.
Numerous sebaceous glands and the hair-follicles of the stiff nasal hairs
(vibrissae) are embedded in the tunica propria.
The Respiratory Region.
The respiratory portion of the nasal mucous membrane consists of
a stratified ciliated columnar epithelium (Fig. 11), that sometimes con-
tains many, sometimes few goblet-cells, and of a conspicuous tunica
propria, up to four millimeters thick on the inferior turbinal bone, which
is built of fibrillar connective tissue, of a large, variable number of leu-
cocytes, and toward the epithelial border is condensed to a homogeneous
membrana propria provided with minute apertures. These leucocytes are
THE OLFACTORY ORGAN. 403
occasionally balled together in solitary nodules and often wander in large
numbers through the epithelium into the nasal fossae (cf. p. 227).
The tunica propria in man contains branched tubular glands, which
produce partly mucous and partly serous secretion, therefore are mixed
glands. Not infrequently they open in funnel-shaped depressions (Fig.
Epithelium.
Glands.
Artery. - >J" " _ - , 3bj^.._ '^^ffg^f /" 1
Tunica propria.
rf.f^y Periosteum of the vomer.
Fig. 294. — Thick Vertical Section of the Respiratory Mucous Membrane of the Human
Nasal Septum. X 20. The excretory ducts of two glands are visible, t. Funnel-shaped depres-
sion ; v, vein. Technic No. 200.
294, t), which are lined by an extension of the superficial epithelium and
on the inferior turbinal are perceptible to the unaided eye. In the acces-
sory nasal spaces the epithelium and tunica propria are considerably
thinner ( — 0.02 mm.), but otherwise of the same structure; the glands
are small and few in number.
The Olfactory Region.
The mucous membrane of this region by its yellowish-brown color
can be macroscopically distinguished from the rosy m.ucosa of the res-
piratory division. It consists of an epithelium, the olfactory epithelium,
and of a tunica propria. In the olfactory epithelium two forms of cells
occur. The one form (Fig. 295, st) is cylindrical in its upper half and
here contains a yellowish pigment and minute granules, often arranged
in longitudinal rows. The lower half is slenderer, the edge is serrated
and indented, the inferior end is forked and is said to unite with the sim-
ilar ends of neighboring cells to form a protoplasmic network. These
elements are called sustentacula cells. Their usually oval nuclei lie at
the same level and in vertical sections occupy a narrow belt, the zone
of the oval nuclei (Fig. 297). The second form (Fig. 295, 7' and Fig. 296)
possesses a spherical nucleus and only in the vicinity of the latter an
appreciable amount of protoplasm ; from this a slender ciliated cylin-
drical process extends upward, while from the opposite pole a very deli-
cate process continues directly into the axis-cylinder of a nerve-fiber.
404
HISTOLOGY.
/"
r -
,. , ,,
■
<>■:
These cells, the olfactory cells, are ganglion-cells and their lower process
a centripetal nerve-fiber. Their round nucleolated nuclei lie at different
levels and occupy a broad belt, the none
of the round nuclei ( Fig. 297, sr). Occa-
sionally, in the nonnucleated epithelial
territory, round nuclei in varying num-
ber are found above the zone of the oval
nuclei ; they either belong to dislocated
olfactory cells or are the nuclei of wan-
dering, often pigmented, leucocytes. In
addition to these two kinds of cells there
are intermediate forms, that sometimes
resemble the olfactory elements, some-
times the sustentacula!" cells. At the
border of the epithelium, toward the con-
nective tissue, there is a protoplasmic
network furnished with nuclei, the so-called basal cells (Fig. 298, /?).
The surface of the epithelium is covered with an extremely delicate homo-
geneous membrane, the membrana liinitans olfactoria , it is pierced by
the ciliated extremities of the olfactory cells and is itselt covered with a
peculiar substance, regarded by some authors as a cuticular formation
similar to that of the intestinal epithelium, by others as delicate cilia, by
b
Fig. 295. — Isolated Cells of the Ol-
factory Mucosa of a Rabbit. 5<><>.
St. Sustenlacular cells ; s, extruded
mucus resembling- cilia; r, olfactory
cells, at ?-Mlie lower process has been
torn off; f, ciliated cells ; b, cells of ol-
factory glands. Technic No. 199.
Epithelium.
Bundles of fibers of the olfactory nerve. Centripetal process ot an olfactory cell.
Fig. 296.— Ykrtical Section through the Olfactory Region of a Young Rat. ;< 4S0.
Technic No. 202.
still others interpreted as minute particles ot discharged mucus (Fig.
295, s).
The tunica propria consists of a loose feltwork of rigid connective-
tissue fibers intermingled with delicate elastic fibers, which in some
animals (for example, in the cat) toward the epithelium is condensed
THE OLFACTORY ORGAN.
40S
to a structureless membrane. Numerous glands, the so-called olfactory
glands (Bowman) are embedded in the tunica propria ; they are either
simple or (for example, in man) branched follicles, in which an excretory
duct situated in the epithelium, a body, and a fundus may be distin-
guished (Fig. 297, a). The cells of the body of the glands are pigmented.
The olfactory glands (also those of man) until recently were regarded as
serous glands, but latterly they have been pronounced mucous glands.
The olfactory glands frequently 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 throughout of non-
medullated fibers, that readily separate into their component fibrillae ; the
fibers grouped into bundles are the inferior processes ot the olfactory
Fig. 297. — Vertical Section of the Olfactory Mucosa of a Rabbit, x 50. zo, Zone of oval, zt'
zone of round nuclei, dr, Olfactory glands ; a, excretory duct, k, body, g, fundus, n, Branches of
olfactory nerve cut transversely ; v, veins ; ar, arteries ; b, bundles of connective tissue in cross-
section. Technic No. 201.
cells, which pass in horizontal arches from the epithelium and descend
into the tunica propria and by union with neighboring bundles form the
branches of the olfactory nerve. The terminal ramifications of the fifth
nerve lie within the tunica propria ; delicate fibers that ascend to the
epithelium and there terminate in free ends possibly belong to the fifth
nerve.*
Of the blood-vessels of the nasal mucosa the arterial stems run in the
deeper strata of the tunica propria (Fig. 294, Fig. 297) ; they supply a
capillary network that reaches close beneath the epithelium. The veins
are remarkable for their size (Fig. 294) and over the posterior end of the
* Different authors have described structures in the nasal mucous membrane resembling
the taste-buds. However, it is not certain but that folds of the nasal mucous membrane have
been mistaken for these " olfactory-buds."
406
HISTOLOGY.
inferior turbinal bone form so dense a network that the tunica propria
resembles cavernous tissue.
The lymph-vessels form a coarse-meshed net lying in the deeper
strata of the tunica propria. The lymph-vessels of the olfactory mucosa
Epithelium.
Tunica propria.
Fig. 298. — Vertical Section through the Olfactory Mucosa of a Rabbit. X 560. s, Cuticular
border; zo, zone of oval, zr, zone of round nuclei; b, basal cells; dr, portions ot olfactory glands,
on the right the lower portion of the excretory duct is shown ; n, branch of the olfactory nerve.
Technic No. 201.
may be injected from the subarachnoid space, through the perineural
sheaths of the branches of the olfactory nerve acquired from the cere-
bral membranes on passing through the cribriform plate.
Medullated twigs of the fifth nerve may be found in the respiratory
as well as in the olfactory mucosa.
TECHNIC.
No. 199. — 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 of the mucosa, about 5
mm. long, together with the corresponding portion of the turbinal bone,
and place it in 20 c.c. of one-third alcohol (p. 20). In five or seven hours
transfer the same to 5 c.c. of picrocarmine and on the following day to
10 c.c. of distilled water. In about ten minutes remove the piece and
lightly strike it against a slide on which a drop of diluted glycerol 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-
THE GUSTATORY ORGAN. 407
preserved sustentacular elements may be obtained. Very frequently the
delicate central process of the olfactory cells is wanting (Fig. 295).
No. 200. — The Mucous Membrane of the Respiratory Region. — Cut
out a piece about 5 or 10 mm. long from the lower half of the nasal
septum ; strip off the mucosa and fix and harden it in about 20 c.c. of
absolute alcohol (p. 31). Use the nasal mucous membrane of the rab-
bit's head (No. 199) for thin sections; embed the pieces in liver and
stain sections with Hansen's hematoxylin ; mount in damar. For gen-
eral 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 glycerol (Fig. 294).
No. 201. — -The Mucous Membrane of the Olfactory Region. — Remove
pieces from 3 to 6 mm. long of the brown mucosa from the upper por-
tion of the nasal septum of a rabbit (No. 199), and place them for three
hours in 20 c.c. of Ranvier's alcohol, which somewhat loosens the ele-
ments 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 fifteen to twenty-four 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 from twenty to thirty seconds in Han-
sen's hematoxylin ; mount them in damar.
In order to obtain good views of 1 the glands make thick sections
transverse to the course of the nerve-fibers (Fig. 297). For the exhibi-
tion of the nerve-fibers and the epithelium thin sections parallel to the
course of the fibers are suitable (Fig. 298).
No. 202. — The nerve-processes of the olfactory cells may be obtained
in preparations made according to No. 179. In these the duct system
of the olfactory glands often is blackened.
XIII. THE GUSTATORY ORGAN.
The gustatory organs, the taste-buds, are oval bodies, about 80 /j.
long and 40 ft 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 here ex-
hibits a funnel-shaped depression, the taste-pore. Each taste-bud con-
sists of two kinds of elongated epithelial cells ; the one either is every-
where of the same diameter or tapers at the basal end, which occasion-
ally is forked, while the upper end is prolonged to a fine point ; the
protoplasm is clear. These cells constitute the bulk of the taste -bud,
408
HISTOLOGY.
are principally situated at the periphery of the bud, and are called teg-
mental 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 thickened where the nucleus is situated ; the
/ JK'\ ■•jJa- /?■ Ks 1 I If f?\ EpiLhelium
/i;^-": ■ ;?\v
£4-ff|
I Tunica propria.
Fig. 299. — Vertical Section of Two Ridges of the Papilla Foliata of a Rabbit. X 80. Each
ridge, I, bears secondary ridges, /'; g, taste-buds; m, medullated nerves ; rf, serous gland ; a, portion
of an excretory duct of a serous gland ; M t muscle-fibers of the tongue. Technic No. 204.
latter is sometimes nearer the lower end, sometimes in the middle,
rarely at the upper 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. 300) ; the lower
Taste-pore. ~^z
Epithelium.
> Tunica propria.
Fig. 300.— From a Vertical Section of the Papilla Foliata of a Rabbit. X 560. Technic No. 204.
division is sometimes slender, sometimes thick, and terminates in a
blunted end or in a triangular foot, without however extending into
the connective tissue of the mucosa. Their protoplasm is granular.
Not infrequently leucocytes — often in large quantities — are found in the
interior of the taste-bud.
The taste-buds chiefly occur in the lateral walls of the vallate
THE GUSTATORY ORGAN.
4O9
papillae and on the ridges of the papillae foliatae, in smaller number on
the fungiform papilla;, on the soft palate, and on the posterior surface of
the epiglottis.
The conjecture that the terminal ramifications of the glossopharyn-
geal nerve have the same anatomic 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 (sym-
7 [ntragemmal fibers.
Secondary ridge.
Connective tissue.
Secondary ridge.
Epithelium
Fig. 301. — From a Vkrtical Section of the Foliate Papilla of a Rabbit. X 220. At x the inter
gemmal fibers lie upon a taste-bud, F'or orientation compare with Fig. 299. Technic No. 205.
pathetic) ganglia,* which form a dense plexus in the tunica propria,
from which numerous branches arise. Some of the latter perhaps termi-
nate in the connective tissue in end-bulbs, but the majority of the gray
fibers penetrate into the epithelium. Here two kinds of fibers maybe
distinguished. The one kind, the " intragemmal " fibers, enter the taste-
buds, divide, and form a plexus beset with numerous conspicuous vari-
cosities that extends up to the taste-pore ; these fibers do not anastomose
* Whether the so-called " taste-granules " beneath the epithelium of the papilla: foliatae
are multipolar nerve-cells is very questionable ; a nerve-process has not as yet been demonstrated.
4IO HISTOLOGY.
with one another, nor do they connect with the gustatory cells, but all
terminate in free ends. The other kind, the smoother " intergemmal "
fibers, penetrate the epithelial areas between the taste-buds and, usually
without dividing, extend to the uppermost strata of the epithelium.
TECHNIC
No. 203. — For orientation regarding the number and position of the
taste-buds proceed according to the method in No. 102. Suitable objects
are the vallate papillae of any animal and the papillae foliatae 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 mod-
erately thin sections vertical to the long axis of the folds, with the low
power, the taste-buds may be recognized as clear spots.
No. 204. — The Minute Structure of the Taste-buds. — Dissect off with
scissors a papilla foliata of a rabbit, with as little as possible of the sub-
jacent muscle substance. Pin the piece with spines on a cork stopper,
the muscle side toward the cork, and expose it for one hour to the vapor
of osmic acid (see further p. 33, 7). Thin sections of the hardened
preparation embedded in liver are to be stained thirty seconds in Han-
sen's hematoxylin and mounted in damar (Fig. 299).
No. 205. — Exhibition of the Nerves. — Place the papillae foliatae of a
rabbit for three days in the osmio-bichromate mixture, for two days in
the silver solution (p. 43). The double method is recommended. The
intergemmal fibers are more numerous and more readily blackened than
the intragemmal fibers, which are exceedingly delicate (Fig. 301). Fre-
quently, single tegmental and gustatory cells become blackened.
APPENDIX.
MICROTOME TECHNIC.
The Microtome.
The most useful microtomes are constructed according to two dif-
ferent principles.
The principle of the one kind consists therein, that the object to be
sectioned 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.
Both kinds are excellent instruments.*
All parts of the microtome should be kept as clean as possible.
When not in use it should be protected from dust by covering it with a
light wooden case. The slideway in which the knife moves must be kept
scrupulously clean. It should be occasionally cleansed with a cloth
moistened in benzin and should then be freely lubricated with vaselin, 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 easily pass through a
thin hair held at one end between the fingers.
* The workmanship of the 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, by G. Miehe in Hildesheim, are also to be highly recommended, and very
good are those of A. Becker in Gottingen.
Editor 1 s rei?iark : The automatic microtome of Minot is widely used, particularly in
American laboratories. This instrument is distinguished from those above described by the
great rapidity with which it can be worked. Therefore it is to be highly recommended, espe-
cially for the preparation of long series of paraffin-sections attached one to the other in the form
of a ribbon ("ribbon-cutting"). In exactness of action it is hardly surpassed by the German
models, from which it altogether differs in construction. The object is moved by the rotation
of a wheel in a vertical direction up and down across the edge of a knife and previous to every
cut is advanced toward the knife a certain distance, which is regulated by an automatic microm-
eter-screw.
It is difficult to recommend in particular any one of the microtomes mentioned. Each has
its advantages and disadvantages, and to be successfully used demands a certain amount of ex-
perience and practice, which determines the individual preference for a certain instrument.
The Minot-microtome is made by E. Zimmermann, Leipzig, Germany, and in the United
States by the Bausch & Lomb Optical Co., New York and Rochester, N. Y. The latter also
make a very satisfactory sliding microtome, on the principle of the Schanze-microtome.
411
412 histology.
Embedding,
the paraffin method.
The following materials and apparatus are required : —
1. 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 be-
cause 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 * answers for most purposes.
2. Chloroform. 20c.c.
3. Paraffin-chloroform : a saturated solution (5 grams of the paraffin
mixture and 25 c.c. of chloroform). This solution is liquid at room-
temperature.
4. An embedding oven of block-tin with double walls, between which
is a space to be filled with water. f A small gas-burner is to be placed
beneath the oven. On top there are three openings ; two lead into the
space between the walls, into one a Reichert thermo-regulator % is to be
inserted, into the other a thermometer ; the third opening leads into the
air-space or oven and into this a second 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,
1 5 cm. high, and 1 5 cm. deep. The embedding oven with its acces-
sories is indispensable if much embedding in paraffin is to be done ; but
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
~| this way.
Instead of this frame little paper trays made of stiff paper or cardboard
can be used.
The objects to be embedded must be absolutely free from water
and to this end should have lain three days in absolute alcohol which
has been changed several times ; they are then to be transferred to a
bottle containing 20 c.c. of chloroform, in which they should remain
* To be obtained of Dr. Griibler, of Leipzig.
t Made by R. Jung, Heidelberg, Germany, and in the United States by the Bausch &
Lomb Optical Co. , New York.
% To be obtained of the Bausch & Lomb Optical Co., New York.
MICROTOME TECHNIC. 4I3
until the following day. From this the objects should be carried to the
solution of paraffin in chloroform and in from two to eight hours, accord-
ing 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 one to five hours. f The paraffin should not be
heated more than two or three degrees above its melting point ; for the
mixture advised the air in the oven should have a temperature of 50
Celsius.
When the objects have been in the paraffin bath the required length
of time, place a slide in a broad dish and on this the embedding frame,
into which paraffin and object now are 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 at once
begin to harden, whereupon more water may be added until the entire
frame is submerged. By this manipulation the paraffin hardens into a
homogeneous mass, whereas otherwise it is apt to crystallize and is then
difficult to cut and also has an injurious influence on the structure of the
embedded tissues. In about ten minutes the metal frames may be re-
moved ; 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.
THE CELLOIDIN METHOD.
Two solutions are required : —
a. A thin solution of about 30 grams of celloidin cut into cubes
dissolved in 60 c.c. of a mixture of equal parts of absolute alcohol and
ether.
b. 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
solution has the consistence of a thick syrup.
Both solutions should be kept in wide-mouthed bottles. If they
become too thick they may be thinned by the addition of some of the
alcohol-ether mixture. 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 one or two days in absolute alcohol which has been
changed several times. From this the objects should be transferred to
the thin and on the following day to the thick celloidin solution. In the
latter, the objects may remain for an indefinite length of time. Usually
* If the paraffin has been melted on a water-bath, place the flame at such a distance that
the surface of the paraffin remains covered by a thin film.
f This is sufficient for all cases ; for small objects from one to two hours will be enough.
414 HISTOLOGY.
they are sufficiently permeated after twenty-four hours, but large objects
enclosing many spaces must remain in the thick solution about eight
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 stratum of celloidin one or two millimeters thick between the cork
and the object* Now the whole is to be placed under a bell-glass to
slowly dry ; 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 four 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 purpose transfer the objects embedded in celloidin from the 80 per
cent, alcohol for two days or longer into an alcohol-glycerol mixture
(80 per cent, alcohol one part, pure concentrated glycerol from six to
ten parts). The larger the proportion of glycerol to alcohol, the harder
the celloidin becomes. This mixture may be differently prepared ; an
extreme limit is one part of alcohol to 30 parts of glycerol. Still greater
difference in the proportions produces strong curling of the sections. In
order to prevent the yielding of the elastic celloidin block, dry it carefully
with filter-paper when it is removed from the alcohol-glycerol 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-
glycerol mixture.
Preparations fixed by Golgi's method require special treatment, since
the absolute alcohol has an injurious influence if the object remains in it
beyond one hour. When the tissue is taken from the silver solution it
is to be placed in 30 c.c. of 95 per cent, alcohol, fifteen or twenty
minutes, then hardened in absolute alcohol for fifteen minutes, then
placed in the thin celloidin solution for five minutes. Meanwhile, in the
previously smoothed lateral surface of a broad piece of elder-pith make
an excavation just large enough to take in the whole preparation ; insert
it, cover it with celloidin solution, fit a second piece of elder-pith on the
first, pour on more celloidin, and place the whole for five minutes under
a bell-glass to dry ; then transfer it to 80 per cent, alcohol for five
minutes, and cut sections with a knife flooded with 80 per cent, alcohol.
The microtome is altogether unnecessary ; satisfactory sections can
easily be cut free-hand. If the microtome be used, the thickness of the
sections should vary from 40 to 120 p.. The elder-pith should be
trimmed off so that only a small border (1 mm.) surrounds the celloidin.
* 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 TECHNIC. 41 5
Sectioning.
PARAFFIN OBJECTS.
With the Knife Placed Obliquely. — The paraffin block containing the
tissue is to be secured in a hollow cylinder coated with hard paraffin (in
the Thoma microtome) or (in the microtome bf 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 cylinder and by means of a heated needle inserted between them
establish a firm union. In order quickly to cool the paraffin place the
cylinder or the plate for five minutes in cold water. The projecting por-
tion of the paraffin block containing the object should then be trimmed
to a four-sided column, the base of which is a right-angled parallelogram.
The column must not be taller than one centimeter, and the object
should be covered by a layer of paraffin not over one or two millimeters
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 Obliquely. — 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 so stand that the knife strikes it first on one corner of the
column. The knife should be moved slowly in the slideway and pres-
sure upon it should be carefully avoided.
Sectioning with the Knife Placed Transversely. — Screw the knife
down perpendicular to the long axis of the microtome, turn the paraffin
block so that the blade will strike it first on a flat surface. The knife
should be rapidly moved with a planing 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 smoothly 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 deli-
cate sable brush and led back to the right position. Ribbon-cutting is
most successful when the sections have a thickness of o.oi of a milli-
meter; thicker sections easily curl and do not readily adhere to one
another at their edges.
OBSTACLES IN SECTIONING AND THEIR REMEDY.
Every 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
41 6 HISTOLOGY.
it ; in the latter case remove the knife and with a cloth wetted with tur-
pentine carefully cleanse it. Knives with thin backs buckle if the distal
end of the blade is used ; thus it happens that when the knife is obliquely
placed the blade cuts the tissue only at the edge where it first touches
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 thor-
oughly dehydrated, in which case it exhibits opaque spots or it still con-
tains 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 sections as they are cut.*
The cause of this curling lies in the hardness of the paraffin, which is
also responsible for —
3. The sections break. The usefulness 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 frequently
placing the block in cold water or by cutting the sections in a cold room
(in summer, in the morning hours).
CELLOIDIN OBJECTS.
The embedded object is to be trimmed so that it is surrounded by
a stratum of celloidin only one or two millimeters thick ; clamp the
knife obliquely, so that it makes a very acute angle with the long axis
of the microtome. The knife must be moistened with 70 per cent.
alcohol by means of a sable brush ; this must be done after every second
or third section is cut. The sections should, be removed with a sable
brush and transferred to a dish containing 70 per cent, alcohol. Very
thin sections (less than 0.02 mm.) cannot be cut unless the celloidin has
been hardened.
*A " section-smoother" for 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 TECHNIC. 417
Preservation of 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 sections, if the tissue has been stained in bulk, are carried to a slide
and mounted according to the directions given on page 46. If the sec-
tions are unstained, transfer them from turpentine to 5 c.c. of ninety-five
per cent, alcohol, which is to be changed in five minutes. In another
two 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 portion of the
" ribbon "), and at the edge of the same place a drop of distilled water
by means of a delicate sable brush. Another section (or portion of the
ribbon) is now placed 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 for from one to three 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 pour
turpentine 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 placed in ninety-five per cent, alcohol. f After
five minutes take the slide from the alcohol, which is to be quickly wiped
off around the sections, breathed upon, 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 glycerol (p. 47), or
with the customary preliminary treatment with ninety-five per cent,
alcohol and oil of bergamot (p. 48), mount it in damar.
CELLOIDIN OBJECTS.
Place the sections in a dish containing 20 c.c. of ninety per cent,
alcohol. If the tissue has not been previously stained in bulk, staining
in bulk to be preferred, the sections may be subsequently stained ; but
* The paraffin must not be allowed to melt ; the resulting mixture of melted paraffin and
water is not soluble in turpentine.
fThe turpentine, also the alcohol, must be quickly wiped off, because the sections are
rendered 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 section may also be fastened to the cover-glass and this
method permits the use of smaller quantities of the staining solution, alcohol, and other
reagents.
27
41 8 HISTOLOGY.
anilin colors cannot be used, since they also stain the celloidin ; even hema-
toxylin imparts a light-blue tint to the celloidin. The sections must not
be placed in stronger alcohol, since this dissolves the celloidin ; they are
to be taken from the ninety per cent, alcohol and placed in chemically
pure amyl alcohol and then transferred to xylol ; when the clearing is
completed mount them in xylol-balsam.
Serial sections of celloidin objects are used only for special purposes,
for example, for the central nervous system. See the articles by Wei-
gert in the " Zeitschrift fur wissenschaftliche Mikroskopie," Bd. ii.,
p. 490, Bd. iii., p. 480, Bd. iv., p. 209, and by Obregia, " Neurologisches
Centralblatt," Leipzig, Jahrg. 9, 1890, p. 195. The negative varnish
recommended by the former is to be obtained of Dr. Grubler.
BOOKS RECOMMENDED FOR COLLATERAL STUDY.
GENERAL WORKS.
Kolliker, A. — Handbuch der Gewebelehre des Menschen. 6. Auflage. Leipzig (Engelmann),
1896.
Schafer, E. A. — Histology and Microscopical Anatomy, — in Quain's Elements of Anatomy,
Tenth Edition, London and New York (Longmans, Green & Co.), 1896.
SPECIAL WORKS.
The Cell.
Bergh, R. S. — Vorlesungen iiber die Zelle und die einfachen Gewebe. Wiesbaden, 1894.
Henneguy, L. F. — Lecons sur la cellule. Paris (Carre), 1896.
Hertwig, O. — Die Z,e\\e und die Gewebe. I. Buch : Allgemeine Anatoraie und Physiologie
der Zelle. Jena (Fischer), 1892. Translation published by Macmillan, London and
New York, 1895.
Wilson, E. B. — The Cell in Development and Inheritance. New York and London (Mac-
millan), 1896.
The Tissues.
Bergh, R. S. — Vorlesungen iiber die Zelle und die einfachen Gewebe. Wiesbaden, 1894.
Hertwig, O. — Die Zelle und die Gewebe. H. Buch : Allgemeine Anatomie und Physiologie
der Gewebe. Jena (Fischer), 1898.
The Blood.
Cabot, R. C. — A Guide to the Clinical Examination of the Blood for Diagnostic Purposes.
New York (Wood & Co.), 1897.
The Nervous System.
Barker, L. F. — The Nervous System and its Constituent Neurones. New York (Appleton &
Co.), 1899.
Dejerine, J. — Anatomie des centres nerveux. Tome I. Paris (Rueff et Cie), 1895.
Edinger, L. — Vorlesungen iiber den Bau der nervosen Centralorgane. 5. Aufiage. Leip-
zig, 1897.
Gehuchten, A. van. — Anatomie du systeme nerveux de l'homme. 2 Edition. Louvain,
1897.
Golgi, C. — Untersuchungen iiber den feineren Bau des centralen und peripheren Nervensys-
tems. Jena, 1894.
Lenhossek, M. von. — Der feinere Bau des Nervensystems im Lichte neuester Forschungen.
2. Aufiage. Berlin (Fischer), 1895.
Ramon y Cajal, S. — Neue Darstellung vom histologischen Bau des Centralnervensystems.
(Arch. Anat. und Physiol., Anat. Abth., 1893).
Les nouvelles idees sur la structure du systeme nerveux chez l'homme et chez les
vertebres. Paris (Reinwald & Co.), 1894.
419
420 histology.
The Intestines.
Oppel, A. — Lehrbuch der vergleichenden mikroskopischen Anatomie der Wirbelthiere. I. Der
Magen, II. Schlund und Darm. Jena (Fischer), 1896-1897.
The Sensory Organs.
Pollitzer, A. — Die anatomische und histologische Zergliederung des menschlichen Gehor-
organs im normalen und kranken Zustande. Stuttgart (Enke), 1889.
Ramon y Cajal, S.— La retine des vertebres. (La Cellule, ix, 1893.)
Schwalbe, G. — Lehrbuch der Anatomie der Sinnesorgane. Erlangen, 1887.
Technic.
Apathy, S. — Die Mikrotechnik der thierischen Morphologic I. Abtheilung. Braunschweig
(Bruhn), 1896.
Behrens, W., Kossel, A., und Schiefferdecker, P. — Das Mikroskop und die Methoden der
mikroskopischen Untersuchung. Braunschweig (Bruhn), 1889.
Bohm, A., und Oppel, A. — Taschenbuch der mikroskopischen Technik. 3. Auflage. Miin-
chen (Oldenbourg), 1896.
Lee, A. B. — The Microtomist's Vade-mecum. A Handbook of the Methods of Microscopic
Anatomy. Third Edition. Philadelphia (Blakiston), 1900.
INDEX.
Acervulus cerebri, 188, 208
Acetic acid, 20
Achromatin, 60
Acid alcohol, 25
" mixture, 24
Adenoid tissue, 86, 128, 130
of the intestines, 243
of the lymph-glands, 127
of the pharynx, 230
of the stomach, 243
of the tongue, 226
Adipose tissue, 84, 93
Agminated nodules, 243
Alcohol, 19, 20
acid, 25
one-third, 20
Alcohol-ether mixture, 413
Alcohol-glycerol mixture, 414
Alum-carmine, 25, 38
Alveolar ducts, 278
Ameboid movement, 62
Ammonium picrate, 26
Amphypy renin, 60
Anaphase, 65
Anisotropic substance, 97
Appendix epididymidis, 305
testis, 305
vermiformis, 243
Arachnoid, 188
granulations of, 189
Arcuate fibers, 353
Arcus tarseus, 376
" " externus, 376
Areolar tissue, 85
Arrectores pilorum, 336
Arteries, 115
classification of, 115
Astrocyte, 175
Astrosphere, 63
Attraction-sphere, 63
Auditory sand, 388
Auerbach's plexus, 248
Axis-cylinder, 102
Axon, 104
Axoneurons, 169
B.
Baillarger's stripes, 179
Basement membrane, 77,
86
Bergamot oil, 23
Berlin blue, 46
Bile, 264
Bile-capillaries, 256
Bioplasts, 60
Blood, 122
cells of, 123
crystals of, 125
development of the cells of, 125
elementary granules, 124
examination of, for legal purposes, 138
fibrin, 124
hemoglobin of, 125
permanent preparation of, 137
plasma, 122
-platelets, 1 24
Blood-vessel system, 113
arteries, 115
blood- vessels of, 121
capillaries, 120
heart, 113
lymph-spaces of, 122
nerves of, 122
technic, 134
veins, 119
Bones, 142
articulation of, 147
blood-vessels of, 147
development of, 150
endochondral formation, 152
endosteum, 145
growth of, 156
haversian canals, 142
haversian systems, 143
Howship's lacunae, 157
lamellae of, 143
lymph-vessels of, 147
marrow of, 144
neoplastic formation, 155
nerves of, 147
osteoblasts, 154
osteoclasts, 157
perichondral formation, 155
periosteum, 146
primary, 151, IS 2
resorption of, 157
secondary, 151, 156
Sharpey's fibers, 147
technic, 157
Volkmann's canals, 143
Books, for collateral study, 419
421
422
INDEX.
Bowman's capsule, 288
" glands, 405
" membrane, 352
Brain, 176
cerebellar cortex, 181
cerebral cortex, 177
ganglia of, 181
Golgi staining of, 208
gray substance of, 177
hypophysis cerebri, 186
pineal body, 188
technic, 208
ventricles of, 177
white substance of, 186
Brain-sand, 188, 208
Bronchi, 277, 285
blood-vessels of, 282
cartilages of, 278
glands of, 279
mucosa of, 278
muscle-fibers of, 278
technic, 285
Brunner's glands, 241
Brushborder, 69, 280
Budding, 65
Bundle of Vicq d'Azyr, 180
Bursas, 164
C.
Cajal's cell, 177
Calcification, center of, 152
Canada balsam, 23
Canalized fibrin, 325
Capillary blood-vessels, 120
development of, 121, 136
Capsule of the glomerulus, 288
Cardiac muscle, 99
Carmine, alum-, 25, 38
borax-, 25, 39
neutral solution of, 24
Carotid gland, 122
Cartilage, 86, 94
capsule, 87
cells, 88
elastic, 89
fibrous, 89
hyaline, 87
varieties of, 87
Cartilages, 150
articular, 1 50
bronchial, 278
costal, 150
epiphyseal, 156
perichondrium, 150
Caruncula lacrymalis, 378
Cells, 59
acid, 235
basket, 185
blood, 122
bone, 90
Cajal's, 177
cartilage, 88
central, 235
chief, 235
Claudius's, 394
Cells, column, 170
commissure, 170
concentric, 360
cone-visual, 363
connective-tissue, 83
decidual, 320
Deiters's, 175, 392
e gg". 3°9
enamel, 221
endothelial, 70
ependymal, 174
epithelial, 68
fat, 84
fat, serous, 84
fiber, 387
fixed, 85
forms of, 61
ganglion, 102
giant, 145, 157
gland, 72
glia, 174
goblet, 73, 239, 242^316, 377
granule, 83. 182
growth of, 66
gustatory, 408
hair, 387, 392
Hensen's, 394
hepatic, 260
internal, 171
interstitial, 299
Langerhans's, 198
length of life of, 68
liver, 260
lutein, 312
marrow, 144, 159
mast-, 83
mossy, 176
motion of, 62
multiplication of, 63
muscle-, 95
nerve-, 102
olfactory, 404
parietal, 235
pigment, 68, 83
pillar, 391
plasma, 83, 377
plurifunicular, 170
polymorphous, 179
prickle, 71
Purkinje's, 183
pyramidal, 178, 1 79
reproduction of, 63
rod-visual, 362
secretory activity of, 73
secretory products of, 66
semen, 301
Sertoli's, 301
size of, 62
spider, 176
structure of, 59
sustentacular, 359, 360, 391, 403, 407
tactile, 198
tegmental, 407
tendon, 163
undifferentiated, 58
vasoformative, 136
INDEX.
423
Cells, vital properties of, 64
wandering, 85
Cell-division, 63
duration of, 65
Cell-membrane, 61
Cell-patch, 325
Cement-substance, 67
Central-spindle, 64
Centrosome, 61
Cerebellar cortex, 181
basket cells of, 185
cells of Purkinje, 183
Golgi staining of, 208
granule layer of, 181
molecular layer of, 184
neuroglia of, 185
Cerebral cortex, 177
bundle of Vicq d'Azyr, 180
cells of Cajal, 177
interradial reticulum, 179
molecular zone, 177
neuroglia of, 180
radiating bundles of, 179
staining of, 208
stripes of Gennari, 179
substantia reticularis alba, 1 80
superradial reticulum, 179
tangential fibers, 177
zone of large pyramidal cells, 179
zone of polymorphous cells, 179
zone of small pyramidal cells, 177
ganglia, 181
Cerumen, 399
Ceruminous glands, 398
Chondrin, 88
Choriocapillaris, 355
Choroid, 354
boundary zone of, 355
lamina basalis, 356
" choriocapillaris, 355
" vasculosa, 354
stroma of, 354
tapetum cellulosum, 356
" fibrosum, 356
Chromatin, 60
Chromic-acetic acid, 22
Chromic-acetic-osmic acid, 22, 33
Chromic acid, 20
Chromosomes, 64
Ciliary body, 356
" muscle, 356
" processes, 356
Ciliated epithelium, 70
Clearing, 48
Close-skein, 64
Coccygeal gland, 122
Cochlea, 388
Cohnheim's fields, 98
Coil-glands, 342
distribution of, 343
secretion of, 343
Collateral fibers, 102, 171
Colored blood corpuscles, 123
development of, 125
hemoglobin, 123
stroma of, 123
Colorless blood corpuscles, 123
development of, 125
granules of, 124
varieties of, 123
Colostrum corpuscles, 346
Congo red, 25
Conjunctiva, palpebral, 375
" scleral, 378
Conjunctival recesses, 377
Connective tissue, 80, 91
arrangement of, 85
bundles, 82
cells of, 83
elastic, 83
fibrillar, 81
fixed cells of, 85
intercellular substance of, 80
lymph-spaces of, 90
mucous, 8i
nerves of, 90
reticular, 86
wandering cells of, 85
Conus medullaris, 168
Cornea,35i
anterior elastic lamina of, 352
arcuate fibers of, 353
blood-vessels of, 373
canaliculi of, 353
corpuscles of, 353
endothelium of, 354
epithelium of, 352
nerves of, 375
posterior elastic lamina of, 355
spaces of, 353
substance proper, 352
technic, 382, 383
Corona radiata, 31 1
Corpora quadrigemina, 177
" striata, 177
Corpuscula amylacea, 188, 209
Corpus Highmori, 299
" luteum, 311
" pineale, 188
Corpuscles, articular, 201
concentric, 284
corneal, 353
genital, 201
Grandry's, 198
HassalFs, 284
Herbst and Key-Retzius's, 201
lamellar, 199
Malpighian, 132, 288
Merkel's, 198
mucous, 227
Pacinian, 199
renal, 288
salivary, 227
tactile, 199
Vater's, 199
Wagner and Meissner's, 201
Cover-glass cement, 23, 47
Cover- glasses, 18
Cox-Golgi method, 43
" " mixture, 21
Crescents of Giannuzzi, 78
Crusta, 61
424
INDEX.
Cumulus oophorus, 311
Cupula, 388
Cuticula, 61
Cystic duct, 257
Cytoblastema, 63
Cytogenous tissue, 86
D.
Dahlia, alum-carmine, 26
Damar-vamish, 23
Daughter-stars, 65
Decalcifying, 35
Decidua graviditatis, 318
" menstrualis, 318
" placentalis subchorialis, 326
" reflexa, 319
" serotina, 319
" vera, 319
Decidual cells, 320
Demilunes, 78, 249
Dendrites, 102
Dentine, 90
Descemet's membrane, 353
Deutoplasm, 310
Diarthroses, 148
Diaster, 65
Direct cell-division, 63
Dissection, 28
Drawing, 55
Ductus choledochus, 257
Duodenum, 237
glands of, 241
Dura, 188
Ear, 386
arcus spiralis, 391
arteries of, 394
auditory hairs, 387
auditory sand, 388
auditory teeth, 390
bony labyrinth, 387
cells of Claudius, 392, 394
cells of Deiters, 393
cells of Hensen, 394
ceruminous glands, 398
cochlea, 388
cristse acusticae, 387
cupula, 388
ductus cochlearis, 386, 388
ductus endolymphaticus, 397
ductus perilymphaticus, 397
ductus reuniens, 386
ductus semicirculares, 386
ductus utriculo-saccularis, 386
endolymph, 387, 397
fiber-cells, 387
foramina nervina, 390
ganglion spirale, 394
hair-cells, 387, 392
labium tympanicum, 388
labium vestibulare, 388
lamina spiralis membranacea, 388,
ligamentum spirale, 388
limbus spirale, 388, 389
390
Ear, lymph-channels of, 397
maculae, 387
membrana basilaris, 390
membrana reticularis, 393
membrana vestibularis, 388, 389
membranous labyrinth, 387
mucosa of eustachian tube, 397
mucosa of tympanic cavity, 397
nerves of, 394
Nuel's space, 394
otoconia, 388
otoliths, 388
perilymph, 387
pillar-cells, 391
prominentia spiralis, 389
Reissner's membrane, 389
saccule, 387
semicircular canals, 387
spiral body, 392
spiral organ, 391
striae vascularis, 389
sulcus spiralis, 388
technic, 399
tunnel, 391
tympanum, 398
utricle, 387
veins of, 396
vestibular membrane, 388
zona pectinata, 391
zona perforata, 390
zona tecta, 390
Egg-protoplasm, 310
Ehrlich's dry method, 137
Elastic tissue, 83
Elementary granules, 124
" organism, 59
Embedding, 412
in celloidin,4l3
in liver, 36
in paraffin, 412
Enamel prisms, 217
Endaxoneurons, 169
End-bulbs, 199
Endogenous cell-formation, 65
Endothelium, 70
Eosin, 25
Ependyma of the ventricles, 181
Epicerebral space, 190
Epididymis, 303
Epiglottis, 276
Epiphysis, 188
Epithelium, 68
brushborder of, 69
cells of, 69
ciliated, 70
columnar, 68
cuticular zone of, 69
cylindrical, 70
distribution of, 69, 70
germinal, of ovary, 309
gland-cells, 72
glandular, 74
goblet cells of, 73
isolation of, 29
neuro-, 69
of lens, 369
INDEX.
425
Epithelium of mucous membranes, 214
pavement, 69
pigmented, 68
prickle-cells of, 71
respiratory, 280
secretory activity of, 72
squamous, 68
terminal bars of, 7 1
top-plate of, 69
transitional, 294
varieties of, 69, 70
Eponychium, 336
Epoophoron, 313
Erythroblasts, 125, 146
Esophagus, 230
Eustachian tube, 397
Exoplasm, 59
Eyeball, 351
blood-vessels of, 371
canal of Petit, 370
canal of Schlemm, 373
choroid, 354
ciliary body, 356
coats of, 351
contents of, 351
cornea, 351
hyaloid canal, 370, 374
hyaloid membrane, 370
irido-corneal angle, 357
iris, 357
lacrymal organ, 379
lamina fusca sclera?, 354
lamina suprachorioidea, 354
lens, 369
lymph-channels, 373
nerves of, 376, 377
optic nerve, 367
retina, 358
sclera, 540
spaces of Fontana, 356
suspensory ligament, 370
technic, 379
venae vorticosae, 373
vitreous body, 370
Eyelashes, 376
Eyelids, 375
blood-vessels of, 378
caruncula lacrymalis, 378
cilia. 376
glands of, 376, 377
lymph-vessels of, 378
muscles of, 376
nerves of, 378
ocular conjunctiva, 378
palpebral conjunctiva, 376
plica semilunaris, 376
tarsus, 376
technic, 386
Fallopian tube, 313
Fasciee, 164
Fenestrated membranes, 82
Fibers, arcuate, 353
cone-, 363
Fibers, lattice-, 264
lens-, 369
mossy-, 186
rod-, 363
stem-, 171
tangential, 177
Fiber-body, 363
Fiber-cell, 387
Fiber-crate, 360
Fixation of tissues, 31
Flemming's mixture, 22, 33
Formic acid, 22
Fresh objects, examination of, 5°
Frommann's lines, 1 10
G.
Gall-bladder, 257
Ganglia, 192
cerebral, 181
spinal, 193
sympathetic, 196
Ganglion-cells, 102
apolar, 104
bipolar, 103
multipolar, 103
unipolar, 103
Ganglioneurons, 169
Gastric glands, 233
" pits, 234
Gemmation, 65
Generatio aequivoca, 63
Genitalia, external, 227
Gennari's stripes, 179
Germinal center, 128, 133, 226, 245
Germ-layers, 58
Glacial acetic acid, 20
Glands, 74
accessory tear-, 376
alveolar, 75
areolar, 347
Bartholin's, 327
Bowman's, 405
Brunner's, 241
bulbourethral, 306
ceruminous, 398
ciliary, 376
classification of, 75
coil, 342
Cowper's, 306
dehiscent, 77
duodenal, 241
fundus, 235
gastric, 233
Harder's, 386
intestinal, 238
lacrymal, 379
Lieberkiihn's, 238
lingual, 277
Litri's, 296
lymph, 127
mammary, 345
Meibomian, 376
Moll's, 376
Montgomery's, 347
mucous, 227, 248
426
INDEX.
Glands, Nuhn's, 228
olfactory, 405
periurethral, 296
preputial, 342
pyloric, 235
salivary, 248
sebaceous, 342
serous, 227, 248
structure of, 76
sudoriparous, 342
sweat-, 342
tarsal, 376
tear, 379
trachoma, 377
tubular, 75
Tyson's, 342
urethral, 296
Glomus caroticum, 122
" coccygeum, 122
Glutin, 82
Glycerol, 22, 47
Goblet-cells, 73
Gold chlorid, 22
Golgi's method, 43
" mixture, 21
Graafian follicle, 311
Granula, 60, 73
Ground-substance, 67
Gustatory organ, 407
H.
Hairs, 336, 349
color of, 337
development of, 330
distribution of, 336
elements of, 337
follicle of, 326
growth of, 340
parts of, 336
renewal of, 340
shedding of, 340
Hair-follicles, 336
dermal sheath, 338
hyaline membrane, 338
inner sheath, 338
outer sheath, 338
Hardening of tissues, 34
Heart, 113
annuli fibrosi, 1 14
blood-vessels of, 114
endocardium, 113
epicardium, 1 14
lymphatics of, 115
myocardium, 113
nerves of, 115
pericardium, 115
valves of, 114
Heidenhain's method, 42
Hematoblasts, 125, 146
Hematoidin crystals, 125, 139
Hematoxylin —
Delafield's, 24, 41
Hansen's, 23, 37
Mallory's, 24, 41
Weigert's, 24, 41
Hemin crystals, 125, 139
Hemoglobin, 125
Howship's lacuna?, 157
Hyaloid canal, 370
" membrane, 6, 370
Hyaloplasm, 60
Hydatid of Morgagni, 305
Hydrochloric acid, 20
Hydroquinone developer, 21
Hypophysis cerebri, 186
I.
Illumination, central, 53
" lateral or oblique, 53
Injecting, 46
Instruments, 18
care of, 29
Intercellular bridges, 71
" substance, 66
Interstitial cells, 299
" granules, 98
" tissue, 86
Intervillous spaces, 324
Intestines, 237, 242
blood-vessels of, 245
crypts of large, 242
goblet-cells 0^239, 242
intestinal glands, 238
Lieberkiihn's glands, 238
lymph-nodules of, 243
lymph -vessels of, 246
nerves of, 243
plicae circulares, 237
regeneration of epithelium, 239
technic, 270
tunics, 237, 242
valvulsE conniventes, 237
villi, 237, 270
Involuntary muscle, 95
Irido-corneal angle, 357
Iris, 357
Iron-hematoxylin, 42
Iron solution, 21
Isolating, 29
Isotropic substance, 97
K.
Karyokinesis, 63
Karyomitosis, 63
Karyosomes, 60
Keratohyalin granules, 333
Kidney, 287
blood-vessels of, 290
brushborder, 290
capsule of the glomerulus, 288
connective tissue of, 290
cortex of, 287
glomerulus, 288
Henle'sloop, 287
lymph-vessels of, 293
medulla of, 287
medullary rays, 287
nerves of, 293
INDEX.
427
Kidney, papilla; of, 287
papillary duct, 287
renal corpuscle, 287, 288
technic, 296
tunica albuginea of, 290
uriniferous tubules, 287, 289, 290
Kleinenberg's solution, 21, 32
Lacrymal canaliculi, 379
" duct, naso-, 379
" glands, 379,386
" sac, 379
Lamellar corpuscles, 199
Lamina basalis, 356
" choriocapillaris, 355
" cribrosa, 368
" fusca sclera:, 354
" suprachorioidea, 354
" vasculosa, 354
Lanterman's notches, 109
Lanugo hairs, 342
Larynx, 276
blood-vessels of, 277
cartilages of, 276
glands of, 276
lymph-vessels of, 277
nerves of, 277
solitary nodules of, 276
technic, 285
vocal cords, 276
Lens, 369, 384
epithelium of, 369
Lens-capsule, 370
Lens-fibers, 369
Lens-stars, 369
Leucocytes, 123
classification of, 123
development of, 125
granules of, 124
Lieberkilhn's glands, 238
Ligamentum iridis pectinatum, 358
Ligamentum spirale, 388
Linin, 60
Lithium carbonate, solution of, 24
Litri's glands, 296
Liver, 255
bile-capillaries, 256, 260
blood-vessels of, 260
capsule of, 264
cells of, 260
hepatic duct, 257
hepatic trabeculae, 255
interlobular bile-ducts, 257
interlobular connective tissue, 258
lobules of, 257
lymphatics of, 264
nerves of, 264
relation of bile-capillaries to cells of, 256
secretion of, 264
technic, 274, 275
tubular structure of, 254
vasa aberrantia, 257
Lungs, 277
Lungs, alveolar ducts, 278, 280
alveoli, 278, 280
blood-vessels of, 282
elastic fibers of, 281
infundibula of, 278
interlobular tissue of, 281
lobules of, 278
lymph-vessels of, 282
nerves of, 282
pigmentation of, 281
pleura, 282
respiratory bronchioles, 279
respiratory epithelium, 280
technic, 285
terminal bronchioles, 278
terminal vesicles, 278
Lunula of nail, 336
Lymph, 90, 136
" capillaries, 126
" corpuscles, 130
" spaces, 90
Lymphatic tissue, 130
Lymph-follicles of the tongue, 226
Lymph-glands, 127
blood-vessels of, 129
distribution of, 127
germinal center, 128
nerves of, 129
structure of, 127
technic, 140
Lymph-nodules, peripheral, 130
Lymphocyte, 144
Lymph-sinus, 128
Lymph-spaces, adventitial, 122, 190
perivascular, 122, 190
Lymph-vessels, 126
origin of, 1 26
stomata, 127
M.
Macula lutea, 365
Malpighian corpuscle of kidney, 287
" " of spleen, 132
Mammary gland, 345
areolar glands, 347
during lactation, 346
during pregnancy, 346
secretion of, 347
sinus lactiferus, 345
technic, 351
Margarin crystals, 85
Marrow, 144
elements of, 144, 146, 159
gelatinous, 144
red, 144
yellow, 146
Mast-cells, 83, 92
Material, 27
Measurement, 56
Medullary rays, 287
Meissner's plexus, 248
Membrana chorii, 323
" granulosum, 311
■' limitans iridis, 357
" limitans olfactoria, 404
428
INDEX.
Membrana propria, 86
Nerve-endings, tactile-cells, 198
" reticularis, 393
tactile corpuscles, 199, 200, 201
" tectoria, 394
technic, 211
" vestibularis, 388
Nerve-felt, 169
Metakinesis, 65
Nerve-fibers, 107
Metaphase, 65
axis-cylinder, 108
Methyl-violet, B, 25
internode, 109
Methylene-blue, 25, 40
medullary sheath of, 109
Microscope, care of, 17
medullated, 107
management of, 53
myelin, 109
Microsomes, 59
neurilemma, no
Microtome, 41 1
nodes of, 109
Mikron, 62
nonmedullated, 107
Milk, human, 347
technic, no
Mitotic cell-division, 63
Nerve-process, 102
in the intestines, 239
Nerves, 190
in the lymph-glands, 128
blood-vessels of, 192
Moist chamber, 51
cerebrospinal, 190
Molecular motion, 63
endoneurium, 190
Monaster, 65
epineurium, 190
Mother-star, 65
fiber sheath, 190
Mounting, 46
Nerve-trunks, lymphatics of, 192
Mucous glands, 77, 215,227, 248
perineurium, 190
Mucous membranes, structure of, 214
sympathetic, 191
Miiller's fluid, 21, 32
technic, 209
Muscle, 162
Net-knots, 60
perimysium, 162
Neuroblasts, 102
technic, 165
Neurodendron, 102
Muscle-columns, 98
Neuro-epithelium, 69
Muscle-fibers, 95
of ear, 387, 391
branched, 96
of nose, 402
cardiac, 99
of retina, 362
Cohnheim's fields, 98
of taste-buds, 407
fibriUs of, 97, 100
Neuroglia, no
nuclei of, 95, 98, 100
Neuron, 102
pale, 99
Neuropilem, 169
red, 98
Neuroplasm, 109
sarcolemma, 93
Nitric acid, 20, 32
smooth, 95
Nodes of Ranvier, 109
striated, 96
Normal salt solution, 19
technic, 100, 101
Nuclear fluid, 60
Myelin, 109
" spindle, 65
Myelocytes, 144
Nuclein, 60
Myeloplaxes, 145
Nucleolus, 60
Nucleus, 60
N.
Nails, 335
Nuhn's glands, 228
O.
elements of, 336
eponychium, 336
Ocular-micrometer, 56
growth of, 335
Odontoblasts, 90, 219, 223
lunula, 336
Olfactory glands, 405
matrix of, 335
membrana limitans olfactoria, 4c
technic, 348
organ, 402
Nerve-cells, 102
cells of, 403, 404
of the first type, 106
mucous membrane of, 402,
of the second type, 106
nerves of, 405
processes of, 103
olfactory region, 403
technic, no
respiratory region, 402
Nerve-endings, 197
vestibular region, 402
end-bulbs, 199
Omentum, 265
in epithelium, 198
Optic nerve, 367
in smooth muscle, 203
lamina cribrosa, 368
in striated muscle, 202
Ora serrata, 365
motor, 202
Oral cavity, 214
sensory, 199
mucous membrane of, 214
INDEX.
429
Orcein, 26, 41
Organ of Corti, 391
Organ of Giraldes, 305
Osmic acid, 22, 33
Osmio-bichromate mixture, 21, 43
Osseous tissue, 89
Osteoblasts, 154
Osteoclasts, 157
Otoconia, 388
Otoliths, 388
Ovary, 308
blood-vessels of, 312
corpus luteum, 311
germinal epithelium, 309
lymph-vessels of, 313
nerves of, 313
primitive follicles, 309
stroma of, 308
technic, 329
tunica albuginea of, 308
vesicular follicles, 311
Oviduct, 313
Ovula Nabothi, 316
Ovum, 309
corona radiata, 311
dentoplasm, 310
germinal spot, 310
germinal vesicle, 310
vitellus, 310
zona pellucida, 310
P.
Pacchionian bodies, 189
Pacinian corpuscles, 199
Palate, soft, 229
Palatine tonsils, 230
Pal's mixture, 24
Pancreas, 251
technic, 274
zymogen granules, 252
Panniculus adiposus, 331
Papillae, filiform, 224
foliate, 226
fungiform, 226
vallate, 226
Papillary body, 378
Paradidymis, 305
Paraffin-chloroform mixture, 412
Paranuclein, 60
Paranucleus, 61
Paraxon, 106
Paroophoron, 313
Parotid gland, 250
Pellicula, 61
Pelvis of kidney, 284
Penis, 306 *
arteries of, 307
corpora cavernosa, 307
corpus spongiosum, 308
erectile tissue of, 307
helicine arteries, 307
tunica albuginea of, 307
veins of, 307
Perforating vessels, 143
Perichondrium, 150
Perichoroidal space, 374
Perilymph, 387
Periosteum, 146
Peritoneum, 264
Perivascular spaces, 122, 190
Permanent preparations, storing of, 51
Peyer's patches, 130, 245
Pharyngeal tonsil, 230
Pharynx, 229
Pia, 188
Picric acid, 21
Picrocarmine, 24, 39
Picrosulfuric acid, 21, 32
Pigmentation of the skin, 334.
theories of, 334
Pineal body, 188
Pituitary body, 1 86
Placenta, 321
blood-vessel system of, 326
canalized fibrin, 325
cell-patches, 325
decidua placentalis subchorialis, 326
fcetalis, 321
intervillous spaces, 324
membrana chorii, 323
septa of, 325
syncytium, 325
technic, 330
uterina, 321, 325
villi, 324
Plasma-cells, 83
Plastin, 59
Platinum-acetic-osmic mixture, 22, 34.
Platinum chlorid, 22
Pleura, 282
Plexus chorioidei, 189
" climbing, 186
" epilemmal, 253
" myentericus, 248
" myospermaticus, 305
" submucosus, 248
Plica circularis, 239
Plica semilunaris, 379
Polar field, 64
radiation, 65
Potash lye, 22
Potassium bichromate, 20
" permanganate, 24
Prickle-cells, 71
Prophase, 63
Prostate body, 306
Prostatic crystals, 306
Protoplasm, 59
Pyramids of Ferrein, 287
Pyrenin, 60
R.
Radial-fibers of M Uller, 359
Reagents, 19
Rectum, 243
Reissner's membrane, 389
Remak's fibers, 107
Renal corpuscle, 288
Retia mirabilia, 127
430
INDEX.
Retina, 358
cerebral layer, 360
cone-visual cells, 363
elements of, 371
fovea, 365
macula, 365
neuro-epithelial layer, 362
ora serrata, 365
pigment layer, 367
rod-visual cells, 362
technic, 380, 381
visual purple, 363
Rhizoneurons, 169
Ribbon-cutting, 415
Rod-fibers, 363
• Rod-granules, 363
Safranin, 25
Salivary corpuscles, 227
glands, 248
blood-vessels of, 253
demilunes, 249
lymph-vessels of, 253
mixed, 248
mucous, 248
nerves of, 253
serous, 248
technic, 273
Salt solution, normal, 19
Sarcolemma, 98
Sarcoplasm, 98
Sarcostyles, 98
Sarcous elements, 97
Schlussleisten, 71
Sebaceous glands, 215, 341
distribution of, 342
secretion of, 342
Sebum, 342
Secretory capillaries, 78, 235, 252, 256
Sectioning, 35, 415
celloidin objects, 416
obstacles in, and their remedy, 415
paraffin objects, 415
Sections, preservation of, 417
Semen, 302
Seminiferous tubules, 299
Sharpey's fibers, 89, 147
Silver nitrate, 22
Silver staining, 42
Sinus lactiferus, 345
Skin, 331
arrector pili, 336
blood-vessels of, 343
coil-glands, 342
color of, 334
corium, 331
epidermis, 333
hair-follicles, 336
hairs, 336
keratohyalin granules, 333
lymph-vessels of, 342
nails, 335
nerves of, 342
panniculus adiposus, 331
Skin, papillse of, 331
pigment of, 334
sebaceous glands, 342
stratum corneum, 333
stratum' germinativum, 333
stratum granulosum, 333
stratum lucidum, 333
stratum papillare, 331
stratum reticulare, 331
stratum subcutaneum, 331
striated muscle-fibers of, 333
technic, 348
Slides, 18
Smooth muscle, 95
Sodium carmmate, 25
" hyposulfite, 21
Solitary follicles, 130, 243
Spaces of Fontana, 358
of Nuel, 384
Spatia zonularia, 370
Spatium interfasciale, 374
Spermatids, 301
Spermatogenesis, 301
Spermatogonia, 301
Spermatosomes, 301
Spermatozoa, 302
Spinal cord, 167
anterior column, 167
anterior cornu, 167
anterior gray commissure, 168
anterior median fissure, 167
anterior roots of nerves, 167
astrocytes, 175
central canal, 168
collateral fibers, 172
column-cells, 170
column of Burdach, 167
column of Clark, 167
column of Goll, 167
commissure-cells, 170
conus medullaris, 168
Deiters's cells, 175
dorsal nucleus, 167
ependymal cells, 174
funiculus cuneatus, 167
funiculus gracilis, 167
gelatinous cortical layer, 176
glia-cells, 174
Golgi's method of staining, 207
gray substance of, 167, 108
hornspongiosa, 176
internal cells, 171
lateral column, 167
lateral cormia, 167
marginal cells. 171
motor cells, 169
nerve-fibers of, 171, 173
neuroglia, 174, 176
plurifunicular cells, 170
posterior column, 167
posterior cornu, 167
posterior gray commissure, 168
posterior roots of nerves, 167
posterior septum, 167
,., reticular process, 167
septula medullaria, 168
•INDEX.
431
Spinal cord, stem-fibers, 171
substantia gelatinosa, 168, 176
substantia grisea centralis, 168,
176
technic, 206
white commissure, 167, 173
white substance of 167, 173
zona spongiosa, 168
zona terminalis, 168
Spiral organ, 391
Spleen, 131
blood-vessels of, 133
capsule of, 131
follicles of, 132
intermediate lacuna, 134
lymphatics of, 134
nerves of, 134
pulp of, 133
trabecular of, 131
Spleen-follicle, 132
Spongioplasm, 59
Stage-micrometer, 56
Staining, 37
bulk, 39
connective-tissue fibrils, 41
diffuse, 38
double, 39
elastic fibers, 41
- gold, 45
mucus, 41
nuclear, 37, 38, 39
silver, 42
triple, 41
under the cover-glass, 51
Stomach, 232, 268
blood-vessels of, 245
coats of, 232, 237
epithelium of, 232
glands of, 233
lymph-vessels of, 246
nerves of, 247, 273
Striated muscle, 96
Subarachnoid space, 190
Subdural space, 189
Sublimate-salt solution, 22
Sublingual gland, 248
Submaxillary gland, 249
Substantia adamantina, 217
" compacta, 142
" eburnea, 216
" gelatinosa, 168
" grisea centralis, 168
" lentis, 369
" reticularis alba, 180
' ' spongiosa, 142
Sudoriparous glands, 342
Supporting tissues, 80
Suprarenal body, 203, 2,14
blood-vessels of, 205
cortex of, 203
medulla of, 205
nerves of, 205
Sutures, 148
Sweat-glands, 342
Syncytium, 325
Synovia, 150
Synovial membranes, 150
villi of, 150
Tactile cells, 199
" corpuscles, 201
Tapetum cellulosum, 356
" fibrosum, 356
Tarsus, 376
Taste-buds, 407, 410
gustatory cells, 408
nerves of, 409
orientation of, 410
taste-pore, 407
tegmental cells, 408
Tear-glands, 379
accessory, 376
Teasing, 29
Teeth, 216, 266
cementum, 218
crown, 216
dentinal fibers, 217, 219
dentinal globules, 217
dentinal ligament, 218
dentinal pulp, 216
dentinal sheaths, 216
dentinal tubules, 216
dentine, 216
development of, 219
enamel, 217
enamel cuticle, 216
enamel organ, 219
enamel prisms, 217
fang, 216
interglobular spaces, 217
neck, 216
odontoblasts, 219, 223
technic, 267
Tela; chorioidea;, 189
Tendon, 163
Tendon-sheath, 164
Tendon-spindle, 165
Tenon's space, 374
Terminal bars, 71
" bronchioles, 278
" vesicles, 278
Testicle, 299, 328
blood-vessels of, 302
ducts of, 303
elements of, 301, 328
lymph-vessels of, 302
mediastinum, 299
nerves of, 302
rete testis, 299
secretion of, 302
seminiferous tubules, 299
technic, 328
tunica albuginea of, 299
tunica vasculosa of, 299
Thymus body, 284
corpuscles of, 284
Thyro-glossal duct, 282
Thyroid gland, 282
colloid substance of, 283
corpuscles of, 283
432
INDEX.
Thyroid gland, duct of, 283
Tissues, 58
animal, 59
vegetative, 59
Tongue, 224, 267
blood-vessels of, 229
glands of, 227
lymph-follicles of, 226
lymph-vessels of, 229
mucosa of, 224
muscles of, 224
nerves of, 229
papillae of, 224
technic, 267
Tonsils, 230,268
Top-plate, 69, 392
Trachea, 277
Trachoma glands, 377
Transitional epithelium, 294
Triacid solution, 138
Tympanum, 399
U.
Ureters, 294
Urethra, 295
Urinary bladder, 295
Urogenital sinus, 296
Uterus, 314
blood-vessels of, 316
cervix, 316
glands of, 316
lymph-vessels of, 321
mucosa of gravid, 318
mucosa of menstruating, 316
mucosa of virgin resting, 3 1 6
mucous crypts, 316
nerves of, 321
ovula Nabothi, 316
technic, 330
Vagina, 227
Valvulse conniventes, 239
Vasa aberrantia, 257
Vasa vasorum, 121
Vasoformative cells, 136
Vater's corpuscles, 199
Veins, 119
valves of, 120
Ventricle of Morgagni, 276
Vermiform process, 243
Vesicular follicle, 311
cumulus oophorus, 311
liquor folliculi, 3 10
stratum granulosum, 311
theca folliculi, 31 1
Vesuvin, 25
Villi of placenta, 324
of small intestine, 237
synovial, ijo
Visual purple, 363
Vitellus, 310
Vitreous body, 371
Vocal cords, 276
Volkmann's canals, 143
Voluntary muscle, 96
W.
Wagner and Meissner's corpuscles, 201
Wandering cells, 85
hematogenetic, 85
histogenetic, 85
Westpbal's alum-carmine dahlia, 26
Xylol, 23
Xylol-balsam, 23
Z.
Zellknoten, 325
Zenker's fluid, 21, 32
Zona pectinata, 382
" pellucida, 311
" perforata, 381
" tecta, 382
Zone of Zinn, 371
Zonula ciliaris, 371
Zymogen granules, 252