A MAN UAL 
OF 
PRACTICAL NORMAL 
HISTOLOGY 
DR. M. L. TURNER 
Berwyn, McL 
Box 33 
BY 
T. MITCHELL PRUDDEN, M. D. 
DIRECTOR OF THE PHYSIOLOGICAL AND PATHOLOGICAL LABORATORY OF THE ALUMNI 
ASSOCIATION OF THE COLLEGE OF PHYSICIANS AND SURGEONS, N. Y. ; 
LECTURER ON NORMAL HISTOLOGY IN YALE COLLEGE ; PATHOLOGIST 
TO THE MANHATTAN EYE AND EAR HOSPITAL. 
SECOND EDITION. 
Revised, with an Appendix. 
NEW YORK & LONDON 
G. P. PUTNAM’S SONS 
fiaiclurbockcr |jrjsa 
1887 COPYRIGHT 
G. P. PUTNAM’S SONS 
1881. 
Press of 
G. P. Putnam’s Sons 
New York PREFACE TO THE SECOND EDITION. 
The advances in Normal Histology since the first 
edition of this book was written have been largely in the 
direction of improved technical procedures. These im- 
provements have been embodied in this edition, for the 
most part in an appendix, to which references are made 
in the text by foot-notes. 
T. M. P. 
New York, July, 1884. PREFACE. 
This book has been prepared for the use of those 
students and practitioners of medicine, who with a 
limited amount of time at their disposal, wish to 
acquaint themselves in a practical way with Normal 
Histology. It is especially designed for those who 
study the science in classes, with an instructor 
in a laboratory ; but the technical procedures are 
described with sufficient fulness for the needs of 
those who are obliged to pursue the study by them- 
selves. 
The method adopted is to give a brief description 
of the tissues and organs in appropriate sequence, 
following each description with an account of the 
way in which the structures described may be dem- 
onstrated. The descriptions were written for the 
most part at the microscrope table, with the prepar- 
ations made by the methods recommended, under 
the eye of the writer, so that it is believed that the 
student will have no difficulty in verifying them. 
Too much stress cannot be laid upon the neces- 
sity of each student making outline sketches of all VI 
PREFACE. 
but the more complicated structures examined, and 
for this provision has been made in the book. It is 
not to be expected that epitomized descriptions of 
structures as elaborate as are many of those with 
which we have to deal in Human Histology, will be 
in all cases perfectly clear and intelligible without 
the aid of plates ; but the specimens which the stu- 
dent prepares, and the sketches from them which 
he makes, will make good, it is hoped, the lack of 
illustration in the text. Indeed, the more critical 
examination which accurate sketching requires, as 
well as the facility which this exercise cultivates, 
will enlarge the achievements of such a course of 
study beyond the acquirement of a knowledge of 
this theme alone, so as to embrace a valuable train- 
ing of the eye and hand. 
This book is not designed to take the place ot 
more elaborate treatises on this subject; nor is it 
written with the design of fostering the deplorably 
wide-spread tendency among medical students, to 
be content with the barest smattering of those 
branches which are not in the most evident manner 
“ practical.” On the contrary, where time permits, 
collateral reading and additional practical work are 
most urgently recommended. But the necessity for 
improvement in medical education, which is expres- 
sing itself in the medical colleges of this country, 
especially in the establishment of laboratories and 
practical courses of instruction, is, unfortunately, PREFACE. 
VII 
not yet sufficiently deeply felt as to have led to the 
general lengthening of the period of undergraduate 
study; so that very little time is usually at the dis- 
posal of medical students for collateral reading, or 
for the pursuit of elaborate practical investigations. 
It is desirable, moreover, since the laboratory time 
itself is usually limited, to occupy as little of it as 
may be, in oral descriptions of tissues and methods. 
It is these considerations which seem to justify the 
addition of another to the long list of elementary 
text-books. 
There are many points in this, as in every develop- 
ing science, which are still unsettled—opinion in re- 
gard to them changing or being modified as new 
facts and investigations are recorded. These have 
been treated, for the most part, very briefly in the 
text, it being left for the supplementary oral instruc- 
tion to enlarge upon and explain them, as the light 
thrown upon each by new researches may seem to 
require. 
In the simpler form of “Notes on the Practical 
Course in Normal Histology” the substance of this 
book has been in use for two years in the laboratory 
of the Alumni Association of the College of Phy- 
sicians and Surgeons, and it has been found that 
with some preliminary preparation of tissues by the 
instructor, the subject essentially as presented here, 
can be embraced in a course of forty lessons of about 
two hours each. VIII 
PREFACE. 
The writer wishes, in conclusion, to express his 
sincere thanks to Prof. Francis Delafield, to whose 
wise counsel and unwearied assistance in many mat- 
ters requiring a wider experience than his own, he 
is greatly indebted. T. M. P. 
Laboratory of the Alumni Associa- 
tion of the College of Physicians 
and Surgeons. 
New York, May, xBBi. CONTENTS. 
INTRODUCTION I 
I THE CELL IN GENERAL - , 17 
II—CONNECTIVE TISSUE - - 2? 
111 EMBRYONAL AND MUCOUS TISSUE—FAT TIS- 
SUE RETICULAR CONNECTIVE TISSUE 48 
IV CARTILAGE BONE TEETH - - 56 
V BLOOD AND LYMPH - - 80 
VI—MUSCULAR TISSUE * - • 91 
VII NERVE-TISSUE - 103 
VIII—BLOOD-VESSELS—LYMPHATIC VESSELS - 119 
IX—LYMPH-NODES—SPLEEN - - - 129 
X—THE GASTRO-INTESTINAL CANAL - 143 
XI—SUBMAXILLARY GLAND—LIVER - - 155 
XII SUPRA-RENAL CAPSULES —THYROID GLAND 164 
XIII THE RESPIRATORY APPARATUS - - 168 
XIV THE KIDNEY .... 178 
XV THE GENERATIVE ORGANS - 188 
XVI—THE CENTRAL NERVOUS SYSTEM - 211 
XVII THE SKIN AND ITS ADNEXA - - 220 
XVIII—THE EYE - - - - 232 
APPENDIX --- - . 2<l 
PAGE INTRODUCTION. 
GENERAL METHODS FOR PRESERVING TISSUES AND PRE- 
PARING THEM FOR STUDY, 
Animal tissues must conform to certain physical 
conditions before they can be subjected to a satis- 
factory microscopical examination. Portions of 
them subjected to study must be sufficiently thin 
to allow the light to pass readily through them, and 
transparent enough to permit the determination of 
the form, character, and relations of their structural 
elements. At the same time the refractive power 
of the different elements should not be too nearly 
alike, since upon differences in this respect, the 
form and characters which microscopical objects 
present to the eye are largely dependent; or, in 
case they are so, the different elements must be 
rendered visible by staining them with coloring 
agents. 
Certain tissues naturally undergo rapid changes 
of structure after death ; these are to be prevented 
by the use of preservative agents. Some are too 
soft to permit the preparation of thin sections, and 
must be hardened ; others are too hard and must be 
softened. In some specimens one, in others another, 2 
NORMAL HISTOLOGY. 
structural feature is to be brought into prominence. 
All of these indications in the histological technique 
are to be met in such a way as to leave the struc- 
tures under investigation in as natural a form as 
possible. Finally, specimens suitably prepared for 
examination, are in many cases, to be rendered per- 
manent for future reference and study. 
We will now consider briefly some of the methods 
by which these indications may be fulfilled. Most 
histological specimens are laid in some enclosing 
fluid medium, on a glass plate and covered with a 
thin slip of glass, before being brought upon the 
microscope. One of the simplest methods of study- 
ing tissues is to place them, when quite fresh and 
after they are reduced to a condition of suitable 
tenuity, on a slide with some fluid which alters their 
physical condition but little or not at all, or at least 
very slowly, and examine them at once. Such a 
fluid is called an indifferent fluid, and for most pur- 
poses a dilute solution of common salt, one-half to 
three-quarters per cent., answers very well. 
The examination of fresh tissues is very important, 
not only because it enables us to study the vital 
phenomena in certain elements, but because we are 
thus enabled by comparison to determine the 
amount of change which tissues undergo when pre- 
pared by more elaborate methods. Still it is in 
many respects unsatisfactory. In the first place, it 
is not always easy to procure fresh tissues for every IN TROD UCTION. 
3 
observation, and even in an indifferent fluid, tissues 
sooner or later undergo considerable alterations, so 
that they cannot be permanently preserved. A 
still more important deficiency in this method is the 
lack of distinctness in structural details which it in- 
volves. Most of the fresh animal tissues are nearly 
transparent in thin pieces, and their structural ele- 
ments have so nearly the same refractive power, 
that we see through them, but do not see them ; or, 
if we do see them, it is not with that definiteness 
which our purposes demand. Now these difficulties 
are usually met by the use of agents which harden 
and preserve the tissues and at the same time ren- 
der the details of their structure visible, by changing 
the refractive power of one or other of their ele- 
ments ; or, we employ certain coloring agents, 
which, being taken up with different degrees of 
avidity by different parts, assist in the recognition 
of details by differences in color; or, such agents are 
used as both harden and stain at once ; or, finally 
which is the most common method, we employ two 
or more of the different classes of agents, one after 
the other. We shall consider here only some of the 
most common and useful of these agents. 
HARDENING AND PRESERVATIVE AGENTS. 
Alcohol is one of the most valuable of these. It 
causes a considerable shrinkage of most tissues, 
partly by the withdrawal of water from them, and. 4 
NORMAL HISTOLOGY, 
like many of these fluids, precipitates certain of 
their albuminoid constituents, thus diminishing 
their transparency. It is in general to be used at 
first diluted with one-third water, and after the tis- 
sues have lain for 24 hours in this, they are trans- 
ferred to strong alcohol in which they may be pre- 
served indefinitely. Bits of tissue to be preserved 
in alcohol, as in other hardening agents, should be 
quite small, not larger, as a rule, than 1 or 2 cms. on 
a side, and the quantity of fluid should be abun- 
dant. Certain structures are best preserved by 
plunging them at once into strong alcohol. 
Aqueous solutions of chromic acid and of potas- 
sium and ammonium bichromate and of the neutral 
chromate of ammonium are much used to preserve 
and harden tissues, and many structures are more 
perfectly preserved in these fluids than in alcohol. 
The hardening proceeds more slowly than in alco- 
hol, and the structures do not shrink as much. It 
is a common practice to commence the hardening 
with one of the chromic fluids and complete it with 
alcohol, the former being thoroughly washed out 
before immersion in the latter. Specimens should 
not remain too long in chromic fluids since they are 
apt to become brittle. An immersion of from 2-3 
weeks usually suffices, especially if alcohol is to be 
used afterward.* Chromic acid may be used in solu- 
tions of from £ to £ per cent, potassium and am- 
monium bichromate in 2 per cent., and the neutral 
ammonium chromate in 5-per-cent, solution. 
* See Appendix, p. 2 INTRODUCTION. * 
5 
A very useful preservative solution is Muller s 
Fluid, consisting of 
Sodium sulphate, i 
Potassium bichromate, 2 
Water, 100 
Chromic acid renders the lime salts in bone soluble, 
and is often used to soften them in preparation for 
section-cutting. 
Picric Acid.—This agent while hardening, pre- 
serves the structure of many tissues very perfectly, 
and at the same time stains them yellow. It is usu- 
ally necessary to complete the hardening with alco- 
hol. For the decalcification of bone it is one of the 
best of agents, although it acts very slowly. It is 
used in saturated aqueous solution. 
Osmic Acid.—This substance has the power of 
fixing and hardening the tissue elements in a nearly 
normal form, and is one of the most valuable of this 
class of agents. It gives tissues a gray or brown ap- 
pearance, and stains fat and certain allied substances 
deep black. It is used in one-per-cent, aqueous 
solution. The tissue should be quite fresh when 
immersed in it, and, as a rule, should remain for 
twenty-four hours. Specimens hardened in osmic 
acid commonly become quite granular and dark 
after a time. 
Preservative fluids are sometimes brought into 
more direct contact with the tissues, by injecting 6 
NORMAL HISTOLOGY. 
them into the blood-vessels of the part before cut- 
ting it in pieces; or they may be driven directly 
into the interstices of the tissue, by means of a 
small syringe with a sharp-pointed canula; this is 
called interstitial injection. 
Indications as to which of these agents are best 
adapted for the preservation of different tissues, and 
the more exact details of the methods of employing 
them, will be given as we proceed with our practical 
study. 
STAINING AGENTS. 
Hcematoxylin is one of the most generally useful 
of the staining agents. It has the power of coloring 
certain parts, as the nuclei of cells, deeply, while 
other parts are stained much less, or not at all. 
The following is Prof. Delafield’s method of prepar- 
ing the solution : To make six hundred c. c. of the 
solution, take four hundred c. c. of saturated solu- 
tion of ammonia alum, with an excess of the alum 
crystals, and add to this four grms. of hsematoxylin 
(Merck’s is preferable, the crude extract will not 
answer), dissolved in twenty-five c. c. strong com- 
mercial alcohol. This, at first, produces a light 
violet, or sometimes a dirty-red color, but on ex- 
posure to the light, in an unstoppered bottle, the 
color deepens; after standing for three or four days 
exposed to the air and light, the solution is filtered, 
and one hundred c. c. each, of glycerin and Hast- IN TROD UCTION. 
7 
ings’ wood naphtha (pyroxylic spirit) are added. 
The solution is now allowed to stand for a day of 
two, and is then filtered again, and this filtration is 
repeated, after standing, until a dark sediment is 
no longer formed. The color is now usually very 
deep, and the solution should be kept in a tightly- 
stoppered bottle. 
Such a solution is usually to be diluted with water 
before using, the exact degree of dilution depending 
upon the rapidity with which we wish the specimen 
to be stained. As a rule, slow staining with a dilute 
solution gives the best result, and is less likely to 
cause shrinkage of the specimen. In staining, bits 
of tissue are placed in a small dish of the solution, 
so that they are bathed on all sides by it, and al- 
lowed to remain until sufficiently colored. The 
time required will depend on the strength of the 
solution, and also, to a considerable degree, upon 
the character and previous preparation of the tissue. 
The excess of coloring fluid is to be thoroughly 
washed out of the specimen by water before further 
manipulation. 
Carmine.—This is a red stain, and is employed in 
the same manner as haematoxylin, and is useful 
where we do not wish as great body of color in the 
specimen as the haematoxylin imparts. It may be 
prepared by dissolving two grms. of commercial 
carmine in a few drops of strong ammonia, and 
adding one hundred c. c. of water. It should be NORMAL HISTOLOGY. 
allowed to stand in an open vessel until the excess 
of ammonia evaporates. As a rule, old carmine so- 
lutions stain better than those recently prepared. 
Picro-carminate of Ammonia, or Picro-carmine,— 
With this substance we can obtain at once a yellow 
color from the picric acid in certain elements, while 
others are stained red by the carmine. It is pre- 
pared by adding to a saturated solution of picric 
acid, a strong, ammoniacal solution of carmine to 
saturation ; evaporating the mixture to one-fifth its 
bulk; allowing to cool; filtering from the deposit, 
and evaporating the filtrate to dryness over a water 
bath. The picro-carmine is left in the form of an 
ochre-red powder, which, for use, may be dissolved 
in water in the proportion of one to one hundred. 
Eosin.—This substance stains tissues more uni- 
formly than many other dyes, and is especially 
valuable when used in connection with other color- 
ing agents, such as haematoxylin, which stains the 
cell nuclei more deeply, since by this method of 
double staining we have certain elements exhibiting 
one color, others another. Eosin may be conveni- 
ently used either in aqueous or alcoholic solutions 
of one to one hundred. 
METHODS OF PREPARING SPECIMENS FOR STUDY. 
Certain fluid tissues, such as blood, lymph, etc., 
are fitted for study, either fresh, or after suitable 
preservation, when a drop is placed on a slide, and INTRODUCTION. 
9 
covered. Certain tissues occur in the form of mem- 
branes, of sufficient thinness to admit of study with- 
out other manipulation than spreading them out 
smoothly on a slide. In other cases we have re- 
course to the dissociation of tissues by needles, 
called teasing. 
Section Cutting.—ln many cases we wish to study 
the structural elements of a tissue in their normal 
relations to one another, and in parts which are too 
thick to permit a direct observation. In such cases 
we have recourse to thin sections, cut from the 
tissue by a sharp knife or razor, the tissue, if not 
sufficiently hard naturally, being hardened by one 
or other of the above-described methods. The razor 
employed for this purpose should have a thin blade, 
perfectly flat on the lower side, and somewhat con- 
cave on the upper side, so that a small quantity of 
fluid will lie upon it. A flat, shallow dish is partly 
filled with alcohol, with which the surface of the 
specimen to be cut, as well as the razor blade, 
should be constantly covered, the blade being 
dipped into the alcohol, and as much taken up as 
will lie upon it. The bit of tissue being held firmly 
in one hand, and the razor firmly but lightly in the 
other, the sections are made by long, slow, diagonal 
sweeps of the razor, the blade being drawn from 
heel to tip along the tissue, and not crowded di- 
rectly forward. Much practice is required for mak- 
ing large, thin, and even sections, and the endeavor NORMAL HISTOLOGY. 
at first should be to get thin and even sections, no 
matter how small they may be. The razor should 
never be allowed to get dull, its edge being fre- 
quently freshened by a few light passes along a 
leathern strop.* 
INJECTIONS. 
It is often desirable in studying the distribution 
of the blood- or lymph-vessels to fill them by injec- 
tion with some colored substance by means of 
which their ramifications may be readily recognized. 
One of the most commonly employed injecting 
materials is a solution of gelatin colored with 
Prussian blue. This may be prepared as follows : 
Dissolve 4 grms. of gelatin in 60 c. c. of water on a 
water bath ; divide the solution into two portions ; 
to one portion add 4 c. c. of a saturated solution of 
sulphate of iron (green vitriol), stirring constantly ;f 
to the other add first 8 c. c. saturated sol. of fer- 
rocyanide of potassium, and then 8 c. c. saturated 
sol. of oxalic acid ; these two portions are now to 
be slowly mixed with constant stirring, and then 
heated up to about the boiling point of water. 
The solution is now filtered hot through flannel, 
and is ready for use. An animal or organ injected 
with this mixture should be kept warm during the 
injection, as should all the utensils employed, so 
f Should the iron cause a pasty precipitate in the gelatin, this 
portion should be allowed to cool, when on warming again, with 
stirring, it will dissolve. 
* See Appendix, p. 251. INTRODUCTION. 
that the gelatin may not harden prematurely and 
stop the vessels. The injection may be made 
with a syringe, or better with some form of appa- 
ratus furnishing a constant pressure of variable de- 
gree. 
EMBEDDING. 
It often occurs that a bit of tissue from which we 
wish to prepare a section is too small or delicate to 
be held in the fingers; in such cases the object may 
be placed between two bits of hardened tissue, 
such as liver, tied round with a thread, and thus held 
while the sections are made. Or, such a specimen 
may be embedded in a mixture of equal parts of 
white wax and paraffin melted together, with ad 
dition of a sufficient quantity of olive oil to giv 
the mass the proper consistence for cutting wh? i 
cold. 
Certain tissues are very friable, so that thin sec- 
tions fall apart as soon as they are made ; or they 
may contain cavities so that they do not afford suf- 
ficient resistance to the razor. In such cases the 
interstices may be filled with some fluid material 
which can afterward be rendered solid and resis- 
tant, so that the whole forms a firm mass ; after the 
sections are cut the impregnating material may be 
dissolved out, so as not to interfere with study. 
The details of such impregnating processes will be 
found on p.i 15.* 
* See also the celloidin method, Appendix, p. 252; 12 
NORMAL HISTOLOGY. 
MOUNTING. 
Sections, bits of dissociated tissue, membranes, 
etc., having been duly prepared, they are to be 
mounted on a slide for study. The choice of a 
a fluid for this purpose will depend upon the nature 
of the specimen, the mode of preparation to which 
it has been subjected, and the structural features 
which we wish especially to demonstrate. One of 
the fluids most frequently employed for this pur- 
pose is glycerin. Many of the hardening agents, 
such as alcohol, precipitates, as above remarked, 
certain albuminoid substances in the tissues, in the 
form of minute strongly refractive particles, thus 
rendering them more or less opaque, or at least 
translucent. Now glycerin has the power of pen- 
etrating many such tissues ; and since, as a rule, its 
index of refraction is much more nearly like that 
of the albuminous particles, than is the refractive 
index of the substance lying between them, when 
the tissue becomes soaked with glycerin the light 
passes more directly through, and the tissue is 
more transparent. Many specimens, furthermore, 
preserve their structural features very perfectly for 
a long time in glycerin. 
The stained specimens are either soaked until 
they become transparent in a small dish of glycer- 
in, and then transferred to a slide and mounted in 
the same; or they may be mounted at once, with- IN TROD UCTION. 
13 
out the preliminary soaking. Eosin is soluble in 
glycerin, so that if a tissue stained in it is mounted 
in pure glycerin it gradually fades. To prevent 
this the glycerin used for mounting should be 
slightly tinged beforehand with eosin. 
The strong refractive power of glycerin, although 
of value in rendering tissues transparent, is, how- 
ever, in some cases prejudicial to our aims, because 
it makes them too transparent; its refractive power 
being so nearly like that of the tissue elements 
themselves that their more minute structure is con- 
cealed. For we find, within certain limits, that the 
greater the difference between the refractive power 
of an object and that of the fluid in which it lies, 
the more distinct will be the outlines of the object. 
We have then in using glycerin as a mounting 
medium which renders tissues transparent, to guard 
against its too excessive action ; and this may be 
done by mixing with it, in varying proportions, 
some less refractive substance, such as water. For 
permanent preservation, however, most tissues are 
to be put into pure or neariy pure glycerin. 
Canada balsam is for many tissues a most excel- 
lent mounting medium. It possesses to a still 
greater degree than glycerin the power of render- 
ing them transparent, obscuring proportionately, in 
the manner above described, certain of their min- 
ute structural features. This difficulty can, how- 
ever, be to a considerable extent obviated with bal- 14 
NORMAL HISTOLOGY. 
Sam as with glycerin, by the judicious use of col- 
oring agents. Thus, for example, suppose we have an 
object containing cells, the exact outlines of which 
we wish to bring clearly into view ; if we stain with 
hasmatoxylin alone, and then mount the object in 
balsam, the nuclei will be distinctly seen, because 
they have a violet color ; but the cell body will in 
many cases be well nigh invisible, because it has al- 
most the same refractive power as the balsam 
which surrounds it. If, however, before mounting 
in balsam we stain with eosin, which colors the cell 
body, this will be distinctly visible under any cir- 
cumstances. We shall stain most specimens which 
are to be mounted in balsam first with haematoxy- 
lin and then with eosin, and throughout this man- 
ual, when the direction is given to “ stain a speci- 
men double,” this use of haematoxylin and eosin is 
to be understood. 
The most convenient way of using Canada bal- 
sam is in solution in chloroform. The commercial 
balsam is thinned with chloroform until it drops 
readily from the end of a glass rod. The mode of 
procedure in Canada balsam mounting is the follow- 
ing; The specimen having been suitably prepared 
and stained, it is freed as completely as possible 
from water by touching its edges with a bit of fil- 
ter paper, and then placed in a small wide-mouthed 
bottle containing a few cubic centimetres of common 
strong alcohol; after from ten to fifteen minutes it is INTRODUCTION. 
15 
transferred to absolute alcohol, where it remains fif- 
teen minutes. It is then taken out, the superfluous al- 
cohol removed by filter paper, and laid in oil of cloves. 
As soon as it becomes transparent, when it usually 
sinks to the bottom of the dish, it is spread on a 
slide, the excess of oil removed, a drop of balsam 
put upon it, and covered by thin glass. This pro- 
cess, which seems at first somewhat complicated, is 
readily understood, if we remember that neither 
the water in which the specimen usually lies when 
the staining is completed, nor the alcohol, which, be- 
ing hygroscopic, removes the water, are miscible 
with balsam ; and further, that alcohol is micsible 
with oil of cloves, and oil of cloves with balsam. 
Care must be taken in these manipulations not to 
breathe on the specimen, nor to allow any moisture 
to come in contact with it, since even a small 
amount of moisture produces a precipitate in the 
balsam which greatly diminishes the clearness of 
the preparation. Canada balsam is, as a rule, best 
adapted for mounting those specimens in which we 
wish to study the general structure of a tissue 
rather than its more minute characters. Prepara- 
tions in which the blood or lymph vessels are in- 
jected with some colored material, usually show 
best when mounted in balsam. 
To make the double staining with hasmatoxylin 
and eosin, as mentioned above, we may first stain in 
the usual way with an aqueous solution of hsema- NORMAL HISTOLOGY. 
toxylin, and then accomplish the eosin staining by 
adding a few drops of a saturated solution of eosin 
in absolute alcohol to the absolute alcohol used for 
the final dehydration of the specimen, before laying 
it in oil of cloves. We thus complete the dehydra- 
tion and stain with eosin at one operation. 
Acetic acid is sometimes used to render tissues 
transparent. This it does by causing the albumi- 
noid materials and particles within them to swell and 
become actually more transparent, differing in this 
from glycerin and balsam. It produces, however, 
very considerable changes in the form and character 
of many tissue elements, so that although very val- 
uable for special purposes, as will presently be seen, 
it is now much less frequently employed than for- 
merly. 
The chemical agents which the histologist uses, 
and the manipulative devices to which he has re- 
course in the study of the tissues, are very numer- 
ous, and we have considered here only a few of the 
more important and typical. The preparation of 
each tissue presents to the worker in histology a 
separate problem, and in few departments of science 
is careful attention to technical minutiae of more im- 
portance than in that which is now to engage us. CHAPTER I. 
THE CELL IN GENERAL. 
In all animal bodies are found certain tiny struc- 
tural elements called cells. These are parts which 
at one time or another are alive ; and all the varied 
activities of the body are the result of the single or 
combined activities of the cells which are within it. 
It is very desirable, owing to their great significance, 
that before commencing the systematic study of the 
tissues we should acquire a definite conception of 
the nature of these elementary organisms. We may 
consider ceils from a morphological and from \ 
physiological standpoint, asking first, what is their 
structure ? and second, what do they do ? 
First, then, what is the structure of cells ? We 
find in this a great diversity, some being extremely 
simple, others quite complex. The most common, 
and usually the most prominent structural feature 
of the cell, that portion which gives to it form and 
consistence, is called the cell-body. This usually con- 
sists of an albuminoid material, sometimes transpar- 
ent and apparently structureless, sometimes finely 
or coarsely granular, and not infrequently present- 
17 NORMAL HISTOLOGY. 
ing, at least after death, a reticulated appearance; 
this material is called protoplasm in its typical active 
form, and may be then very soft and viscid, like thin 
jelly, or it may become so modified as to be hard 
and even horny like the nail. The cell-body pre- 
sents a great variety of forms ; it may be spherical, 
cuboidal, cylindrical, fusiform, ovoid, pear-shaped, 
discoidal, or scale-like ; it often sends off processes 
like branches or wings, and sometimes assumes the 
most irregular bizarre forms. We not infrequently 
find imbedded in the cell-body, pigment granules, 
droplets of fat, and various kinds of crystals. The 
form of the cell-body seems usually to depend large- 
ly upon the pressure to which it is or has been 
subjected by adjacent structures. 
Within the cell-body and making up a part of the 
protoplasm, we usually find one or more spherical, 
ovoidal, or irregular-shaped bodies, called nuclei 
(singular, nucleus). The nucleus usually presents a 
sharply defined contour, is frequently coarsely gran- 
ular, and sometimes a coarse or filiform network is 
seen suspended within or stretching from side to 
side. The nucleus may be very small in proportion 
to the size of the cell-body, or may make up nearly 
the entire bulk of the cell. In the processes of de- 
generation and decomposition, and under the action 
of certain chemical agents, the nucleus is more re- 
sistent than the cell-body, and on treatment of the 
cell with certain coloring agents, such as hsematoxy- THE CELL IN GENERAL. 
lin, the nucleus is more deeply stained than the cell- 
body. Within the nucleus, again, we frequently 
find one or more small spherical or irregular-shaped 
bodies, looking like vesicles or shining granules, 
which are called nucleoli. They would seem, in 
some cases at least, to be connected with the above- 
mentioned intra-nuclear network. Of the exact 
nature and significance of the nucleus and nucleolus, 
we have at present little definite knowledge, but the 
nucleus, at least, seems to be a very important part 
of the cell. 
Finally, a small proportion of animal cells are 
enclosed by an envelope—the cell-membrane, which 
may be thick or thin, now presenting well-defined 
structural peculiarities, and again quite homo- 
geneous and structureless. In many cases the cell- 
membrane would seem to be simply a peripheral 
hardened layer of the cell-body. 
It will thus be seen that we may have, in an animal 
cell, four distinct structural elements: the body, the 
nucleus, the nucleolus, and the membrane. It is only 
in a few varieties of cells, however, that all of these 
elements are present. The cell-membrane is the 
least commonly present of all, and there are certain 
cells which consist of a cell-body alone. 
Regarding cells now from a physiological point of 
view, we find the expression of their vitality in four 
distinct ways; they nourish themselves ; they grow; 
they perform certain functions for their own good and 20 
NORMAL HISTOLOGY. 
for the benefit of the organism of which they form a 
part; and, finally, under certain circumstances, they 
are capable of reproducing their like. Or, in more 
concise language, we say the cell expresses its 
vitality in nutrition, growth, function, and reproduc 
tion. Not all of these expressions of vitality, how- 
ever, can be subjected to direct microscopical 
observation. Nutrition, being as we believe, essen 
tially a chemical process, cannot, with our present 
facilities, become to any considerable extent the ob- 
ject of direct microscopical study. The growth of 
cells, too, is for the most part so gradual, that we 
cannot directly follow it, but are obliged to study it 
in different phases of its progress. 
The functional activity of cells can be indirectly 
subjected to microscopical investigation when it is 
associated with demonstrable changes in the mor- 
phological characters of the cell, or directly observed 
when it expresses itself in motion ; thus, we can 
readily detect the difference between a condition of 
functional activity and rest in the peptic cells of 
the stomach, and the observation of ciliary and 
amoeboid movements in certain cells is among the 
most fascinating of histological studies. 
Finally, regarding the reproduction of cells, in a 
few instances the act has been directly observed 
under the microscope, but in the majority of cases 
our knowledge is derived from the study of a suc- 
cession of consecutive stages in the process. Every THE CELL IN GENERAL. 
21 
new cell which appears in the animal body, during 
and subsequently to its development, is derived 
from a pre-existing cell, and all the cells are deriva- 
tives of a single original cell, the ovum. New cells 
are produced by a process of division in older cells. 
Cell-division seems to occur in a variety of ways, 
usually commencing in the nucleus. Of the details 
of the process we have at present but little satisfac- 
tory classified knowledge, and although interesting 
and valuable facts are rapidly accumulating, we can- 
not tarry long upon the subject here. 
In one of the apparently simplest modes of cell- 
division, one or more constrictions appear around 
the cell-body, after certain changes in the nucleus* 
have led to its partial or entire division ; these con- 
strictions grow deeper and deeper, until finally the 
parts separate and become individual cells, each fur- 
nished with a nucleus. This form of cell-division is 
called reproduction by fission. Or, the cell-body 
may send off from some part a bud-like process, 
which, becoming nucleated, is, by a constriction of 
its pedicle, at length set free as an independent 
cell; this is called cell-reproduction by budding or 
* These preliminary changes in the nuclei of proliferating cells, 
which consist m a readjustment and perhaps new formation of fibres 
of the intra-nuclear network, and the development of bizarre and 
often symmetrical figures within the nucleus, are at present engaging 
the attention of many eminent histologists. The results of their re- 
searches, while now affording much, and promising far deeper, insight 
into the nature of cell-life, are not yet sufficiently classified, and are 
far too intricate to come within the scope of this manual. 22 
NORMAL HISTOLOGY. 
gemmation, A mode of division, called endogenous 
cell-reproduction, is described, in which the division 
is said to occur entirely within the membrane of a 
cell, called the parent cell, so that the new organ- 
isms—the daughter cells—are not at once set free. 
This mode of cell-division is, however, doubtful, or 
at least extremely infrequent. These modes of cell- 
reproduction seem to be different, and yet there is 
much reason for believing that they are really only 
modifications of one process; but in the present 
condition of our knowledge on the subject, all 
general statements should be very cautiously made ; 
and such classifications as the above are to be re- 
garded merely as for convenience of study, and not 
as expressing any absolute and fully established 
truth. 
Cells are variously classified according to their 
nature and relations to adjacent parts: thus we have 
epithelial cells, which cover the skin and mucous 
membranes, and occur in certain parts of the glan- 
dular organs; connective-tissue cells, which lie scat- 
tered throughout the substance of the structures, 
presently to be described as connective tissue, and 
in certain parts undergoing modification of form 
and relation to neighboring parts, and called endo- 
thelial cells ; gland cells are those which, possessing 
peculiar functional or morphological characters, 
make up the parenchyma of certain glands and or- 
gans. The special characters of these classes of THE CELL IN GENERAL. 
23 
cells, together with those of other classes not here 
mentioned, will be considered in our systematic 
study of the tissues. 
PRACTICAL STUDY. 
Many of the above-described general characters of 
cells may be seen by studying the epithelial cells of the 
bladder, the pigmented cells of the retina, and the living 
ciliated cells from the mucous membrane of the frog’s 
mouth. 
/ Epithelial Cells from the Rabbit's Bladder.—A small piece, 
including the mucous membrane, is cut from the wall of 
the bladder of a recently-killed rabbit and immersed for 
24 hours in a 5-per-cent, solution of neutral chromate of 
ammonium. It is then soaked for an hour in water to 
remove the chromate solution, and the now loosened cells 
are scraped from the surface of the mucous membrane 
and placed in a few cubic centimetres of the picro-car- 
mine solution, where they remain until they have acquired 
a distinct red color. A small fragment of the cell mass is 
now transferred to a slide, covered with a drop of gly- 
cerin, teased apart with needles, and carefully covered 
with thin glass so as to exclude all bubbles of air. The 
cover-glass should be allowed to close down upon the 
specimen by its own weight alone, since much pressure 
upon these delicate cells distorts and breaks them. This, 
like nearly all specimens, should be examined first with a 
low and then with a high power. The cells will be found 
to have a great variety of forms, some of them evidently 
determined by the pressure of adjacent cells. They have NORMAL HISTOLOGY. 
a finely granular body, with more coarsely granular nuclei, 
and nucleoli. In many cases, instead of appearing 
coarsely granular, the nucleus is seen to contain a distinct 
reticulum (intra-nuclear net-worh) of strongly refractive 
material, the thickened nodal points of which may be re- 
garded as nucleoli. To preserve this, and all specimens 
mounted in glycerin, a narrow rim of asphalt varnish is 
painted around the cover-glass, lapping over the edges of 
the latter and extending for a short distance on to the 
slide. 
Pigmented Cells cf the Retina.—An eye from the ox or 
sheep, which has lain for a few days in Muller’s fluid, is 
opened by an equatorial section, and the vitreous body 
and the retina removed from the posterior half. If the 
remaining portion, including the sclera, choroid, and a 
portion of the pigmented epithelium of the retina, be put 
under water in a shallow dish, and brushed gently over 
the surface with a fine camel’s-hair pencil, delicate pig- 
mented flakes will float off in the water. These are the 
desired cells. One or two bits should be put into a drop 
of glycerin on a slide. Another bit is put on to another 
slide with a large drop of hsematoxylin solution, and after 
about ten minutes the coloring fluid carefully washed off 
with water, and the stained fragments placed with the 
other in the glycerin on the other slide. They are now 
covered and examined. 
These cells appear hexagonal* and are joined together 
* These cells have really a very complicated structure, see page 241, 
but it is not necessary to study this in detail here, since they are only 
studied now for the purpose of demonstrating the occurrence of pig- 
ment in the bodies of certain cells. THE CELL IN GENERAL. 
25 
edge to edge, giving a pavemented appearance to the frag' 
ments. Most of the cell bodies are closely crowded with 
elongated brown or black pigment granules. Sometimes 
such are seen as have but few granules within them, and 
occasionally they are entirely free. When the cell bodies 
are crowded with pigment the nucleus appear as a rounded, 
indefinitely outlined structure, containing no pigment anu 
looking like a hole in the cell. When the pigment is 
present in small quantity or entirely absent, the nucleus 
is much less sharply outlined. In the cells which have 
been stained with haematoxylin, however, the nuclei all 
present well-defined outlines, and are stained of a violet 
color. 
Ciliary Movement in Living Ciliated Cells from the Frog's 
Mouth.—The mucous membrane of the roof of the mouth 
of a living frog is gently scraped with a scalpel, and the 
slimy mass thus procured is transferred to a large drop 
of one-half-per-cent, salt solution on a slide, and thor- 
oughly teased apart. The specimen is now covered, a bit 
of hair being placed beforehand beside it to prevent pres- 
sure from the cover-glass. The cells are mostly sphe- 
roidal, and will be seen isolated or in clusters the cilia, 
in the form of rows of delicate hair-like processes, spring- 
ing from one side of the cells. A considerable number 
of non-ciliated cells will also be observed. The form of 
the cilia will be most readily seen in cells in which the 
movement is becoming languid, which occurs gradually in 
all, and finally ceases altogether. The movement, when 
vigorous, often causes cells and masses of cells to revolve 
and move about in the fluid, and frequently produces 26 
NORMAL HISTOLOGY. 
currents in the latter, into which floating particles are 
drawn and then driven onward with considerable velocity. 
If it be desired to preserve specimens of ciliated cells, 
a fragment of the palate of the frog, or, better, of the 
trachea of the rabbit—since the cells here are much more 
like those in the air-passages of man,—should be excised 
and treated in the manner above described for the prepa- 
ration of the epithelial ceils of the bladder. CHAPTER 11. 
CONNECTIVE TISSUE. 
OUR knowledge of the animal tissues is not yet 
extensive and exact enough to enable us to make a 
satisfactory classification of them, but for conven- 
ience of study we may regard the body as composed 
of simple tissues and of organs As examples of 
the first we have connective tissue, muscular tissue, 
nerve-tissue, etc.; of the second, the liver, the 
lungs, the skin, mucous membranes, etc. 
Among the simple tissues there is a large and im- 
portant group, called connective tissues, the members 
of which, though presenting many marked differ- 
ences, yet seem so closely allied, both in structure 
and life history, as to justify their grouping under 
the above common name. The members of this 
group of tissues may be tabulated as follows : * 
i. Fibrillar connective tissue. 
* In addition to these varieties, we find in certain parts of the body 
membranous layers or sheaths—sometimes structureless, sometimes 
having well-marked structural features—which differ in many re- 
spects from the above-mentioned varieties of connective tissue, but 
which cannot be separately described here. They will be briefly 
considered as we meet with them in our systematic study of the parts 
of the body in which they occur. 
27 28 
NORMAL HISTOLOGY. 
2. Embryonal and mucous tissue. 
3. Fat tissue. 
4. Reticular connective tissue. 
5. Cartilage. 
6. Bone and teeth. 
Aside from many striking points of similarity in 
their structure, which we can better appreciate after 
having made a practical study of the group, three 
considerations may be briefly noticed here as of 
weight in determining this classification. At an 
early period of embryonic life, when the animal is 
composed almost exclusively of cells, it is found 
that one of the first definite arrangements or group- 
ings of these cells consists in the formation of three 
distinct layers: an outer, a middle, and an inner 
layer. Now it is found that the cells in these dif- 
ferent layers have an entirely distinct capacity in 
their power of producing the tissues which are found 
in the adult animal. From the cells in the outer 
layer are produced the skin with its adnexa, certain 
organs of sense, and the central nervous system ; 
from the inner layer are formed the intestinal epi- 
thelium and glands, and certain of the large organs 
of the body; while from the middle layer are de- 
veloped the muscles, the vascular systems, and, 
which especially concerns us here, the tissues tabu- 
lated above as members of the connective-tissue 
group. Besides the relationship given to them by 
this common origin, these tissues show their close CONNECTIVE TISSUE. 
29 
alliance by the fact that during the process of devel- 
opment one is sometimes formed from another. 
Finally, certain frequently observed pathological 
conditions seem to consist chiefly in the transforma- 
tion of one of these forms of tissue into another of 
the same group. 
With fibrillar connective tissue or connective tissue 
proper, or simply connective tissue, as it is often 
called, we commence our systematic study. This 
tissue is most widely distributed in the human body, 
occurring in the greatest diversity of forms, and an 
exact knowledge of its structure and arrangement is 
absolutely essential to a correct understanding of 
most other tissues and the organs, since it occurs in 
one form or another in nearly all of them. Fibrillar 
connective tissue, under the name of tendons and 
ligaments, forms bands and cords which bind the 
muscles to the bones, and bind the bones together. 
It is spread out in thin layers in the fasciae and 
aponeuroses ; it surrounds the bones and cartilage 
as periosteum and perichondrium. It divides and 
encloses muscular bundles and the nerves ; it sup- 
ports the blood and lymphatic vessels, and forms 
the limiting membrane of the serous cavities. It 
forms an encasing membrane for many organs, and, 
extending into their interior, serves, under the 
name of interstitial tissue, to support their paren- 
chyma. 
Fibrillar connective tissue is composed of two dis- 30 
NORMAL HISTOLOGY. 
tinct classes of structures : a. cells, and b. a substance 
lying between the cells, the intercellular or basement 
substance. We shall consider the latter, first. 
b. INTERCELLULAR SUBSTANCE. 
The intercellular substance consists chiefly of t-vyo 
distinct kinds of fibres : fibrillated fibres and elastic 
fibres. , 
The fibrillated fibres are tiny, grayish, translucent 
cords, which, sometimes singly, sometimes in straight 
or wavy bundles, lie nearly parallel to one another, 
and again cross each other at all conceivable angles, 
forming complicated net-works. When examined 
fresh, with high-magnifying powers, the individual 
fibres are seen to be moderately refractive ; they 
have a delicate longitudinal striation—this striation 
being, as we shall presently see, the expression of 
the fact that each fibre is made up of a number of 
still finer fibrillae. 
On boiling for a considerable time in water they 
are converted into gelatin, and when treated with 
acetic acid or dilute alkalies, they swell up, lose 
their longitudinal striations, become very trans- 
parent, and finally almost invisible. 
The second variety of fibres which occurs in con- 
nective tissue—the elastic fibres—are much more 
strongly refractive than the first, hence presenting 
more sharply-marked contours ; they are not longi- 
tudinally striated, and often branch and form anas- CONNECTIVE TISSUE. 
31 
tomoses with one another, sometimes joining at 
frequent intervals to form a narrow-meshed net, and 
again stretching away'for long distances to form a 
broadly-spaced reticulum. Sometimes the fibres 
are broad and band-like, sometimes extremely fine ; 
on being boiled in water they are not converted 
into gelatin, and they are unchanged by acetic acid 
and dilute alkalies. These fibres, as their name in- 
dicates, possess elasticity, and as a consequence of 
this property we often find, when the fibres have 
been severed by teasing or other modes of prepara- 
tion, that the free ends curl over in the act of re- 
traction, forming very characteristic curves or 
spirals. The elastic substance sometimes occurs in 
the form of granules instead of fibres, or as nearly 
homogeneous membranes. 
The relative number of the fibrillar and elastic 
fibres in connective tissue varies greatly in different 
parts of the body ; in some we find but few elastic 
fibres, others contain little else. The interstices of 
the interlacing fibres—both fibrillated and elastic— 
are filled with the nutritive fluids of the body ; or 
in some cases, a small amount of a more consistent 
homogeneous material cements them together. 
The marked difference in general appearance 
which is seen in different parts composed of con- 
nective tissue, is largely due to differences in the 
arrangement of the fibres and bundles, and in the 
relative proportion of the fibrillated and elastic 
fibres. 32 
NORMAL HISTOLOGY. 
a.—CELLS. 
We consider next the cellular elements of fibril- 
lar connective tissue. These are of two distinct 
classes. First, those which are essential components 
of it, preserving a fixed and definite relation to the 
basement substance, and which are quite constant 
in the different varieties of tissue, in form, size, 
and number ; these are called fixed connective-tissue 
cells. Second, small spheroidal cells, the white 
blood-cells, which, escaping in varying number 
from the blood-vessels, move about through the in- 
terstices of the tissues, and are called wandering 
cells. These will be studied with the blood. 
Among the fixed connective-tissue. cells, by far 
the greater proportion are more or less flattened, 
presenting to the eye, when seen from the edge or 
in cross-section, the appearance of slender spindles. 
The cell-bodies are for the most part quite trans- 
parent, often very thin and scale-like, frequently so 
delicate as to be difficult of recognition, and some- 
times the protoplasm in the vicinity of the nucleus 
is distinctly granular. These fixed connective- 
tissue cells present a great variety of forms, being 
round, ovoid, oblong, fusiform, or irregularly rec- 
tangular, often sending off branches which seem 
to be connected with the branches of neighboring 
cells. Sometimes the thin cell-body sends off one 
or more delicate wing-like processes at varying 
angles. These cells may have one or more nuclei; CONNECTIVE TISSUE. 
33 
they lie in the interstices of the fibres, which they 
often enwrap with their delicate bodies. The form 
which they assume in the different varieties of con- 
nective tissue would seem to be largely dependent 
upon the varying conditions of pressure to which 
they are subjected by the adjacent fibres. These 
flattened connective-tissue cells in many parts of 
the body may, and in certain parts constantly do, 
contain pigment granules. 
In certain parts of the body the connective tissue 
presents free surfaces, lining more or less well-de- 
fined closed spaces or cavities, or free surfaces 
which are movable over one another, as in the great 
serous cavities, in the blood- and lymph-channels, 
tendon-sheaths, etc. In these cases the flat con- 
nective-tissue cells usually undergo some modifica- 
tion in their form, character, and relations to one 
another, and are called endothelial cells or endothe- 
lium. 
Finally, in certain parts of the body, usually in 
the vicinity of blood-vessels, are found irregular- 
shaped granular cells, not usually flat, and of vary- 
ing size and form, called plasma cells, which resem- 
ble in many respects cells found in the embryo. 
PRACTICAL STUDY. 
b.—INTERCELLULAR SUBSTANCE. 
Fibres of Subcutaneous Connective Tissue.—To study 
these, the skin should be reflected back trom the abdomi- 34 
FORMAL HISTOLOGY. 
nal wall of a recently killed animal (mammal), and choos- 
ing a part which is free from fat, a bit of the loose, so- 
called areolar tissue is seized with the forceps and 
snipped off with scissors. The bit of tissue, which will 
contract to a little lump around the point of the forceps, 
is to be spread out very thin on a slide and covered with 
a |--per-cent. salt solution. The specimen will be seen to 
consist largely of fibrillated fibres crossing one another 
in all directions, with a few delicate elastic fibres. After 
studying in salt solution, a drop of 2-per-cent, sol. of 
acetic acid should be allowed to run under one edge of 
the cover-glass, the salt solution being drawn off by a bit 
of filter paper placed at the opposite edge, and the effect 
carefully observed. This preparation is not to be pre- 
served. 
Fibrillce in Tail Tendon of Mouse.—lt is not easy in 
studying fresh tissues to convince one’s self that the longi- 
tudinal striations on the fibres are really the expression 
of their fibrillar structure, since any attempt to pick the 
fibres apart with needles is of little avail, because the 
fibrillse are bound together by a small amount of cement 
substance. If, however, the tissue be placed for a few 
hours in some fluid which dissolves this cement substance, 
as osmic acid, the ultimate elements, the fibrillse, may be 
readily separated. A bit of the tail tendon of a mouse, 
or a small tendon from any mammal, should be soaked 
for a few days in a i-per-cent. sol. of osmic acid, washed 
and teased apart on a slide and mounted in glycerin. 
Elastic Fibres from the Ligamentum Nuchce.—A small 
fragment of this structure—conveniently obtained from 
the ox—is preserved in strong alcohol. A tiny bit is CONNECTIVE TISSUE. 
35 
teased thoroughly and mounted in glycerin. It will be 
seen to consist of a dense net-work of broad, closely-an- 
astamosing elastic fibres which curl over at the free 
ends. 
a.—CELLS. 
k 
'■ Cells in the Subcutaneous Connective Tissue.—The 
fixed connective-tissue cells, which occur in this form 
of tissue, may be studied in any mammal They 
vary somewhat in size, shape, and number in differ- 
ent animals, but those in the rabbit are sufficiently 
typical. In the study of these cells, whose bodies are, 
for the most part, so thin and transparent as to be 
almost invisible when fresh, and very liable to shrink and 
become distorted by contact with the usual hardening 
agents, we have to fulfil two important indications in our 
technical procedure ; we must treat the tissue with some 
agent which will render the cells visible, and, at the same 
time, not greatly alter the form of the delicate cell- 
body. 
These ends are best attained by the method suggested 
by Dr. W. H. Welch. The skin being reflected back 
from the abdominal wall of a freshly-killed rabbit, with 
a hypodermic syringe, inject beneath the loose adherent 
tissue a few cubic centimetres of a solution of analine 
red (Fuchsine), prepared by adding one part of saturated 
alcoholic sol. of the powder to forty parts of water. After 
the red fluid has remained for two or three hours in con- 
tact with the tissues, a small fragment is snipped off from 
the colored oedematous portion, spread very thin on a slide, 
covered with the same fluid, and enclosed at once with 36 
NORMAL HISTOLOGY. 
asphalt varnish. The cells in this tissue are, for the 
most part, extremely thin, and of various, often quite 
irregular forms, sometimes sending off narrow branching 
processes, by which they join neighboring cells, and 
sometimes furnished with wing-like projections. In ad- 
dition to these cells, and the intercellular fibres, nerves 
and capillary blood-vessels are sometimes seen in the 
specimens, and, occasionally, in the vicinity of the ves- 
sels are found the above-mentioned plasma cells. The 
cells prepared by this method preserve their form for a 
considerable time, but finally shrink, and lose their 
color. 
Pigmented Connective-tissue Cells of the Choroid.—These 
may be taken from the eye of any mammal (except al- 
binos) which has been hardened in Muller’s fluid and 
alcohol. A shred of the outer layers of the choroid 
should be torn off, stained with hsematoxylin, and 
mounted in glycerin. Irregular-shaped, often branched 
and flattened cells are seen lying embedded in a mem- 
branous nucleated basement substance, containing deli- 
cate elastic fibrils, the cells being more or less crowded, 
except in the part occupied by the nucleus, with a multi- 
tude of minute brown or black granules. 
Cells in Teased Tendon.—Tendons are composed essen- 
tially of parallel bundles of fibrillated connective-tissue 
fibres, with thin irregular-shaped cells between them. 
The complicated forms which tendon cells present can 
be most easily understood when they are studied in their 
natural relation to the fibres. 
Owing to their extreme tenuity, and the consequent 
possibility of studying them with but little manipulation, CONNECTIVE TISSUE. 
37 
the tail tendons of the mouse or rat are well suited for 
this purpose. If the skin of the tail of a recently-killed 
mouse or rat be torn across transversely, by slight twist- 
ing, or pressure with the edge of the nail, and gentle 
traction be exerted at both sides of the rupture, the 
caudal vertebrae will readily separate, and, as the trac- 
tion continues, a multitude of extremely fine tendon- 
bundles will be seen stretching across the break. When 
the tendons, by this natural and simple dissection, have 
been freed for one or two centimetres of their length, 
they are laid, still under slight tension, on a bit of glass, 
of suitable size, the ends cemented to the glass with a bit 
of soft wax or paraffin, and the remainder of the tail cut 
off. The fastening of the ends is to prevent the tendon 
from shrinking when immersed in the preservative fluid. 
The bit of glass, with its tendon-bundles, is now immersed 
for twenty-four hours in a one-per-cent, solution of osmic 
acid, then washed in water. 
One or two of the tiny bundles is now to be partially 
teased apart, lightly stained with hsematoxylin, and then 
with picro-carmine ; then still further very finely teased 
on a slide, and mounted in glycerin. The individual 
fibrillated fibres will now be readily seen, and arranged in 
rows along them, edge to edge, with more or less irregu- 
lar contours, the flattened tendon cells will be seen to 
lie. Their nuclei, stained violet by the hsematoxylin, 
when seen from the side appear oval or rectangular, and 
are often arranged in couples along the fibres ; when 
seen edgewise they look like short, thick lines. The 
cell-bodies, when seen sidewise, look like faintly-colored, 
often indefinitely-outlined, very thin plates, stretching 38 
NORMAL HISTOLOGY. 
out from the nuclei, and partially enwrapping the tendon- 
fibres. When the cell-body is placed with its edge toward 
the observer and in close apposition with the fibre, it is 
not to be distinguished, owing to its extreme thinness, 
from the line which marks the border of the fibre; if, 
however, it has been separated, in part or entirely, from 
the fibre by the previous manipulations, it will appear as 
a faint line, at some part of which is seen the elongated 
nucleus. Examining the specimen still further, one sees 
in the side view of the cells, sometimes along a single 
cell, sometimes along a row of them, one or more fine 
lines or striae, and on looking carefully at the cells placed 
edgewise, he can convince himself that thin, narrow 
wings are given off from the cell-body, and that it is the 
edges of these wings which cause the striae in the cells 
seen on the flat. In teased specimens of tendon one oc- 
casionally finds irregular-shaped branching cells. 
We have then in tendon parallel bundles of fibrilla'ted 
fibres, arranged along and in the interstices between 
which lie flattened cells whose thin bodies partially en- 
wrap certain fibres, and send off between other and 
neighboring fibres branches and thin narrow wings. The 
interstices between the bundles, in which the tendon- 
cells lie, are lymph-channels. 
Cells in Transverse Sections of Tendon.-—A very clear 
view of the relations between the cells and fibres of 
tendon, as well as the relation of the wings to the cell- 
bodies, may be obtained by making a transverse section 
of a hardened and stained tendon. Any small tendon 
from a recently killed animal will answer the purpose. 
It should be freed from surrounding tissues, and irame- CONNECTIVE TISSUE 
39 
diately immersed in a small quantity of a half per cent, 
solution of gold chloride. Here it remains for half an 
hour, when it is removed, washed with pure water, and 
put into a few cubic centimetre of the following mixture, 
known as the reducing fluid : 
Amyl Alcohol, .... I 
Formic Acid, . . i 
Water, ..... 100 
After remaining for twenty-four hours in the reducing 
fluid, the specimen will probably have assumed a rich 
violet color ; if not, it should be kept for twenty-four 
hours longer in a fresh portion of the fluid. When the 
requisite color has been obtained, the specimen is hard- 
ened for a day in alcohol, embedded in hardened liver 
or wax, and thin cross-sections made from it. The sec- 
tions are now stained lightly with hsematoxylin, and 
mounted in glycerin. They should be kept as much as 
possible from the light, which, after a time, destroys gold 
preparations. This method of staining with gold is known 
as Pritchard's method 
* The older method of gold staining, known as Conheim's method, 
differs from that just given, in that, after soaking in the gold solu- 
tion, the specimen is exposed to the light until it has assumed the 
violet color. It is then mounted and preserved as before. This 
method is less certain in its results than Pritchard’s, being less apt to 
give clear pictures. In both methods the staining action consists in 
the precipitation of the gold in metallic form in a state of extreme 
comminution in the tissue. In one case this precipitation is effected 
by the acid mixture, in the other by the light. This deposition of 
gold in the tissues occurs, for the most part, in the protoplasm of the 
cells, bringing them into sharp contrast with surrounding parts, and 
fixing their form. There is one source of error, however, in the in- 
terpretation of gold specimens, which should never be forgotten. 
The gold is apparently sometimes deposited, and the characteristic 40 
NORMAL HISTOLOGY. 
\ 
Transverse Sections of the Cornea.—Cells seen from the 
edge.—We shall employ for our study here the cornea of 
the frog, because of the ease with which it can be ob- 
tained, and, because, on account of its thinness, it is well 
suited to the various manipulations to which we shall 
subject it. A frog’s eye should be enucleated directly after 
death, and placed entire in Muller’s fluid, where it should 
remain for ten days. It is then washed, and put, for a 
few hours, into dilute alcohol (alcohol one, water two), 
then transferred to, and left, for forty-eight hours, in 
strong alcohol. The cornea is now excised, just within 
the sclero-corneal junction, and, two or three short 
radial incisions having been made at the edge, so that 
it will lie flat, it is embedded between two bits of hard- 
ened liver,* and thin transverse sections cut from it. 
These are stained double, and mounted in glycerin, 
slightly tinged red with eosin. 
If the sections are made so as to include the entire 
thickness of the cornea, both the anterior and posterior 
edges of the section will be seen to be covered with epi- 
thelial cells. Between these two layers of cells lies the 
connective tissue substance of the cornea, which alone 
concerns us here. This consists of delicate fibrillated 
fibres, closely bound together by a small amount of ce- 
menting substance, and arranged in lamellae. Between 
these lamellae are seen the corneal cells, which, in this 
color produced, outside of the cell protoplasm, and especially in spaces 
in the tissues which are filled with albuminoid materials, so that the 
utmost caution is required in determining whether a given area of 
gold deposit and staining really indicates the presence of cell proto- 
plasm, And, in fact, it is in some cases impossible, at present, to 
decide this question. 
* Better in celloidin. See Appendix, p. 252. CONNECTIVE TISSUE. 
41 
view, seem to have the form of slender elongated spin- 
dles, part of them being closely surrounded by the in- 
ter-cellular substance, part lying in small elongated cavi- 
ties. 
Lamina of Cornea.—the Cells seen on the Flat.—In order 
to determine the exact shape of the cells, which in the 
former preparation are seen only from the edge, it is 
necessary to look at the cornea from the side. For this 
purpose a fresh cornea should be very carefully excised, 
all pulling or stretching of the part being avoided, since 
this distorts the cells. It is now stained with gold 
chloride by Pritchard’s method, and then laid on a slide 
in glycerin. The epithelium on both the anterior and 
posterior surfaces is now scraped off, and with a little 
care the part may be divided into several thin layers by 
means of fine forceps. These layers are lightly stained 
with hsematoxylin and mounted in glycerin. 
In a specimen thus prepared, the basement substance 
looks homogeneous or delicately striated ; fine nerve- 
fibres are seen stretching across the specimen in various 
directions. The corneal cells, which are the most promi- 
nent objects in the specimen, are seen thickly scattered 
over the field, stained of a reddish violet color. They 
have flat, irregular-shaped bodies which send off a vari- 
able number of longer and shorter processes ; the nuclei 
are large, ovoidal, or irregular-shaped, and usually con- 
tain nucleoli. Fine irregular-branching, almost linear 
structures are seen in good preparations thickly scattered 
over the specimen, and very frequently lying nearly at 
right angles to one another. A part at least of these are 
continuous with the cell-bodies whose processes they are; 42 
NORMAL HISTOLOGY. 
whether or not they are all cell processes is not yet defi- 
nitely known. 
It will be seen from the above studies, that the connec- 
tive-tissue cells of the cornea are flattened and branched 
cells, and that certain of them, at least, lie in spaces 
between the fibres of the intercellular substance. We 
have now to study more carefully the nature of these 
spaces and their relation to the cells. 
. Cornea treated with Silver.—Relation of the Cells to 
the Basement Substance.—Strong solutions of nitrate of 
silver have the power of staining the intercellular sub- 
stance of connective tissue light brown, while the cells 
are left uncolored. In order to stain the cornea of the 
frog with silver, the following process should be employed: 
the spinal cord of the animal having been broken up with 
a needle, a finger is introduced into the mouth so as to 
press the eyeball forward and bring the cornea into 
prominence ; the membrana nictitans is drawn away with 
the thumb or a pair of fine forceps, so as to leave the an- 
terior surface of the cornea quite free. The eye is now 
held for an instant over a jet of steam, when the epithel- 
ium will become white or milky in appearance, and can 
be readily scraped off by passing the blade of a scalpel 
lightly over the surface. It is necessary to remove the 
epithelium in order that the silver solution may have 
ready access to the connective-tissue substance of the 
cornea ; and the advantage of steaming is, that it can be 
scraped off without the use of much force, which would 
disturb the relations of the parts beneath. The epithe- 
lium being thus removed, a five-per-cent, solution of 
silver nitrate is allowed to flow over the cornea and re- CONNECTIVE TISSUE. 
43 
main for two or three minutes in contact with it. By 
this treatment the whole cornea becomes opaque and 
stiff. The silver is now neutralized and its further action 
prevented, by washing the cornea with a one-per-cent, 
salt solution. It is now carefully excised and placed in a 
dish containing a mixture of alcohol and water, one to 
two, and exposed to direct sunlight, or bright daylight, 
for from a few minutes to half an hour, depending upon 
the intensity of the light. When it has become brown it 
is to be laid in glycerin and stripped into thin layers, as 
directed above, for the gold cornea; the layers are 
mounted in glycerin. 
If the preparation is successful, clear, branching, com- 
municating spaces are seen on a yellowish or brown 
ground. These spaces, although larger, evidently corre- 
spond in position and in a general way, in shape, to the 
cells in the cornea, as seen after treatment with chloride 
of gold ; and if a specimen thus prepared be stained with 
hsematoxylin, the corneal cells will be seen lying within 
them. 
It is difficult to determine with certainty whether or 
not the cells send processes into all of the channels which 
radiate from the spaces in which they lie ; it is probable 
that some of the narrow branching bodies or lines noticed 
above in the gold cornea are nothing more than these 
branching and communicating spaces in which an albu- 
minous fluid accumulates, which is stained by the gold 
very much as cell protoplasm itself is. 
We thus see that the cornea is permeated by numerous 
branching and intercommunicating spaces, and that in 
these spaces the flat, branching connective-tissue cells lie. 44 
NORMAL HISTOLOG Y. 
These spaces are called lymph-spaces, and what we have 
been able to demonstrate in regard to the relation of cells 
to the lymph-spaces in the cornea, by these various modes 
of preparation, seems to be true, with certain modifica- 
tions, of the cells in most of the varieties of .connective 
tissue. These cells lie in spaces, sometimes completely, 
sometimes only partially filling them. These spaces com- 
municate with one another, and communicate also, on the 
one hand, with the blood-vessels, and, on the other, with 
the lymphatics. Through them lymph-currents pass, 
bathing the cells and supplying them with nutritive ma- 
terial. 
It is extremely probable that it is through these lymph 
spaces exclusively that the white blood-cells travel, in 
their perigrinations through the tissues. We study them 
in the cornea alone, because the scope of this manual is 
too limited to admit of such a detailed study of all vari- 
eties of connective tissue, and because here the relation 
of the cells to the spaces is clearly defined. 
Endothelium of the Serous Membranes.—The serous 
membranes are formed by layers of fibrillar connective 
tissue fibres mingled with a varying number of elastic 
fibres, and containing ordinary flattened connective-tissue 
cells. They are more or less abundantly furnished with 
blood and lymphatic vessels. On the free surface of 
these membranes rests a continuous layer of flattened 
cells, differing in many respects from the ordinary con- 
nective-tissue cells, and called endothelial cells or endothel- 
ium. These cells are usually transparent, irregularly 
polygonal in form, and frequently much elongated ; they 
possess one or more ovoidal nuclei, which often project CONNECTIVE TISSUE. 
45 
above the general level of the free surface of the cell- 
body ; they are placed edge to edge, like the stones in a 
mosaic, and seem to be joined together by a minimal 
amount of an albuminoid cement substance.* 
Endothelium covering the Mesentery.—ln order to bring 
the outlines of the cells clearly into view, the membrane 
should be first treated with a solution of nitrate of silver. 
This substance in dilute solutions forms with the cement 
substance between the endothelium an albuminate of sil- 
ver, which, on exposure to light, becomes brown or black, 
thus clearly defining the outline of the cells. 
The mode of proceeding is as follows : A portion of 
the mesentery of the recently killed dog or rabbit should 
be carefully removed and laid over the rim of a shallow 
dish so that it rests loosely over the opening. All stretch- 
ing and pulling of the membrane should be avoided, be- 
cause this would destroy the natural relations of the cells 
to one another. The membrane must be allowed to sag 
a little into the dish, so that it may be bathed on both 
sides by the silver solution. It is now to be carefully 
washed with water to remove any albuminous substance 
or blood—which would cause a granular precipitate of 
silver albuminate on the surface—and the dish then filled 
with an aqueous solution of nitrate of silver, i to 500. 
The dish should be gently shaken at frequent intervals, 
so as to bring fresh portions of the solution into con- 
tact with the membrane, and after from twenty minutes 
* There is reason for believing that the cement substance between 
the endothelium, as well as between many kinds of epithelial cells is 
permeable to fluids, and, under certain conditions, to solid particles 
also, and thus forms an avenue of communication between adjacent 
but separated cavities or lymph spaces. 46 
NORMAL HISTOLOGY. 
to half an hour the tissue will be seen to have become 
cloudy or milky. 
The silver is now poured off, and the membrane care- 
fully washed with water. The cells will have been fixed 
by the silver, so that the membrane may be removed 
without further danger of disturbing the relation of the 
cells, and laid in a dish containing water to which one- 
third its bulk of alcohol has been added. It is now ex- 
posed to the sunlight, and after from a few minutes to 
half an hour—sometimes longer, depending upon the in- 
tensity of the light—the tissue will be seen to have as- 
sumed a brown color. 
A small piece from the thinner portion should now be 
lightly stained with haematoxylin and mounted in glyc- 
erin. 
These portions of the mesentery consist of a thin mem- 
brane of fibrillar connective tissue containing a delicate 
network of elastic fibres and a few small blood-vessels ; 
the whole being covered on both sides by the delicate 
mosaic of endothelial cells. The outlines of these cells 
on both sides, may be brought successively into view by 
careful focussing. 
Endothelium of the Omentum.—A portion of the omen- 
tum of the dog should be treated with silver in the way 
just directed for the mesentery, and also stained with hse- 
matoxylin and mounted in glycerin. The omentum of 
the dog, as of man, consists of an irregular meshed net, 
whose trabeculae are made up of fascicles of fibrillar 
connective tissue of varying thickness, the broader con- 
taining blood- and lymph-vessels and fat-cells, the nar- 
rower consisting of single bundles of fibrillae—all being CONNECTIVE TISSUE. 
47 
alike covered with a single layer of endothelium. In 
many parts the endothelial cells are seen in profile, when 
their nuclei appear lenticular in form, usually projecting 
above the general level of the cell-body, which is itself 
in most cases thicker in the vicinity of the nucleus than 
at the points of junction with adjoining cells. The speci- 
mens of both omentum and mesentery may be preserved 
in the usual way ; but silver preparations, like the gold, 
do not preserve their first clearness very long, unless care- 
fully kept from the light. CHAPTER 111. 
EMBRYONAL AND MUCOUS TISSUE.—FAT TISSUE.— 
RETICULAR CONNECTIVE TISSUE. 
EMBRYONAL AND MUCOUS TISSUE. 
At a certain period of embryonic life, those parts 
of the body which are destined finally to become 
fibrillar connective tissue, consist almost entirely of 
small spheroidal cells—the intercellular substance 
being absent, or consisting only of a very small 
quantity of fluid lying between and bathing the 
cells. As the process of development goes on, some 
of the cells retain their original spheroidal form, 
while others change their character, becoming elon- 
gated and fusiform, often terminating at their ex- 
tremities in delicate single or branching processes; 
others become flattened and assume irregular 
shapes, sending off branching processes by which 
they are joined to one another. Hand in hand with 
this change in the cells there occurs an accumula- 
tion of intercellular material, which is at first fluid, 
and later presents the appearance of a homogene- 
ous gelatinoid substance. Then within the gelati- 
noid intercellular substance appear fine fibrillae, 
which become more and more abundant, arranging 
themselves now in bundles, and again to form irregu* 
48 EMBRYONAL AND MUCOUS TISSUE. 
49 
lar networks. The cells approach more and more 
closely to the type of the adult connective-tissue 
cells, as development goes on ; the intercellular sub- 
stance loses its soft gelatinoid character, and is 
finally replaced by the fibrillated and elastic fibres 
with which we are already familiar. 
The process of development is a very gradual 
one, and although the younger forms of embryonal 
connective tissue and the adult connective tissue 
are distinct enough, we are yet unable to separate 
them sharply, since they merge so gradually into 
one another. In general, however, simply as a mat- 
ter of convenience, we call connective tissue which 
is almost entirely made up of spheroidal, spindle- 
shaped, or flattened cells, in which little accumula- 
tion and little differentiation of the intercellular 
substance has occurred, embryonal tissue; while to 
that older form, which consists of variously shaped, 
spheroidal, flat, branching and anastomosing cells, 
with a gelatinoid, homogeneous, or partially fibri- 
lated intercellular substance, the term mucous tissue 
is usually applied. The name mucous tissue was 
given to this form of young tissue, because the soft 
gelatinoid intercellular substance was found to con- 
tain a certain amount of mucin, which may be 
thrown down in the form of a whitish, often stringy 
precipitate, by the addition of acetic acid. At 
present, however, tissues presenting the above 
mentioned morphological characters are usually 50 
NORMAL HISTOLOGY. 
called mucous tissues, whether the intercellular sub- 
stance contains mucin or not. Mucous tissue is not 
found in the healthy human adult, but frequently 
occurs under pathological conditions. 
PRACTICAL STUDY. 
Subcutaneous Tissue of Embryo.—Embryonal connec- 
tive tissue may be studied in any young mammalian em- 
bryo, preserved in Muller’s fluid and alcohol. Bits of the 
subcutaneous tissue are torn off from the abdominal wall, 
stained double, finely teased, and mounted in glycerin. 
Mucous Tissue from the Umbilical Cord.—In the um- 
bilical cord of a nearly mature foetus we find typical mu- 
cous tissue. A bit of the cord of any mammalian foetus, 
as the pig, is hardened in Muller’s fluid and alcohol, then 
embedded in liver and transverse sections made. These 
are stained double and mounted in glycerin or balsam. 
The surface of the cord is seen to be covered with lami- 
nated epithelium, and the three large blood-vessels are 
seen to be cut across. The amount of fibrillation present in 
the intercellular substance depends upon the age of the 
foetus. 
FAT TISSUE. 
Fat-tissue is a modified form of connective tissue, 
in which the intercellular substance is present in 
proportionally small amount, and a large part of the 
protoplasm of the cells is replaced by fat, which 
crowds the remaining part, together with the nu- 
cleus, to the side of the cell, nearly or entirely con- FAT TISSUE. 
51 
cealingboth. The fat-cells thus formed are arranged 
in clusters or lobules, enclosed by fibrillar connective 
tissue, which sends into the lobules and between 
the cells broader and narrower bundles, which serve 
to support the cells and carry the blood and lym- 
phatic vessels, etc. Owing to the pressure to which 
the fat-cells are subjected, they usually assume, in 
the adult animal, a polyhedral form. 
Sometimes the fat appears within the cell in the 
form of clusters of radiating needle-like crystals. 
In order to understand clearly the nature of adult 
fat-tissue, it is necessary to study it during the pro- 
cess of development. At an early period of life, 
those parts of the body which are finally to become 
fat-tissue, possess the character of mucous tissue 
with a more or less fibrillated intercellular substance. 
The first change which we notice in the cells as the 
transformation into fat-tissue commences, is the ap- 
pearance in the cell-body of small shining particles. 
These particles, of which there may be many, be- 
come gradually larger, until they present the form 
and character of distinct droplets of fat. As these 
droplets increase in size, they coalesce, forming one 
or more drops, which presently become large enough 
to crowd the nucleus to one side. The growing 
drops finally unite into one large drop, which at 
length becomes so large as to occupy nearly the 
whole of the cell, leaving only a thin crescent of pro 
toplasm and a squeezed and distorted nucleus 52 
NORMAL HISTOLOGY. 
crowded up against the cell-membrane. At last we 
can no longer see, without special modes of prepara- 
tion, any trace of cell protoplasm—although a small 
amount of this really persists as a thin shell within 
the membrane—and only the deformed remnant of 
the nucleus. This process is called fatty infiltra- 
tion. 
In those parts of the body where the fat is invari- 
ably found, this change in the cells occurs in the 
vicinity of little tufts of capillary blood-vessels, so 
that at one period, the forming fat is seen lying in 
scattered clusters in the meshes of distinct groups 
of blood-capillaries. It is these clusters of fat-cells, 
with their accompanying blood-vessels, which deter- 
mine, when the fat is fully formed, the lobular char- 
acter of this tissue. 
In many parts of the body and under varying 
conditions—sometimes physiological, sometimes 
pathological—there is an accumulation of fat in the 
protoplasm of cells; but it is, under normal condi- 
tions for the most part, temporary, and the fat- 
cells have no definite grouping in lobules and about 
the blood-vessels in the way above described for the 
permanent fat. 
PRACTICAL STUDY 
Fresh Fat, teased.—A bit of fresh subcutaneous fat 
should be teased and covered in salt solution, without 
staining. In such a specimen little else is seen than a FAT TISSUE. 
congeries of more or less globular or polyhedral masses 
of fat-cells, with larger and smaller free fat droplets. The 
fat is characterized by its great refractive power ; by the 
dark contour of its globules by transmitted, and their yel- 
lowish silvery lustre by reflected, light; by its solubility in 
alcohol and ether, and by the deep black color which it 
acquires on treatment with osmic acid. The connective 
tissue which encloses the lobules is seen in broken masses 
and shreds, scattered through the preparation. 
Section of Adult Fat 7'issue.—A small piece of subcuta- 
neous fat from man should be hardened in alcohol, by 
which the fat will be for the most part dissolved out of 
the cells. Thin sections are made, stained double, and 
mounted in balsam. This preparation shows the relation 
of the cells to one another, and the lobular structure of 
the tissue. If the blood-vessels of the part from which 
the tissue is taken have been previously injected with the 
blue gelatin mixture, the relations of the vessels to the 
lobules and cells will be well shown. 
Developing Fat from Young Animals.—To study this in 
its early stages, some of the fresh mucous tissue from the 
axilla or groin of a foetal animal, such as a pig, 5 inches 
long, should be immersed for 24 hours in i-per-cent, osmic 
acid ; then washed and teased, and mounted in glycerin 
slightly tinged with eosin. The larger and smaller fat 
droplets within the cells will be black, and numerous cells 
will be seen in which the fatty infiltration has not com- 
menced. 
To study the fat cells at a later period of development, 
thin sections may be made from the subcutaneous fat of 
the human foetus, at from 6 to 8 months, or from any 54 
NORMAL HISTOLOGY. 
mammal of corresponding age. These are stained double 
and mounted in balsam. At this period, while the fat 
droplet in many parts occupies the greater part of the 
cell, a distinct crescentic’mass of protoolasm is still seen 
at one side, enclosing the nucleus. 
RETICULAR CONNECTIVE TISSUE. 
This tissue forms a large part of the supporting 
framework of the lymphatic glands, and is found, in 
somewhat modified form, in other parts of the body. 
It consists of delicate fibres, of varying diameter, 
which cross and join one another at frequent inter- 
vals, forming a fine meshed network. This net- 
work of fibres is not flattened to form a membrane, 
but extends in all directions, like the trabeculae of a 
sponge. Irregularly scattered over the fibres are 
flattened nucleated cells, having the character of 
endothelium, which sometimes lie at the points of 
intersection of the fibres, sometimes along their 
sides, enwrapping them with their transparent 
bodies. When these cells are in situ upon the fibres, 
the whole presents the appearance of a mass of an- 
astomosing, branched, or spindle-shaped cells; and, 
as such, the reticular connective tissue has until re- 
cently been regarded,—erroneously, however, as is 
shown by the fact that by appropriate manipulation 
the flat cells can be entirely freed from the underly- 
ing fibre-net, leaving the latter intact. The meshes 
of the reticular tissue are loosely filled, in the lym- RETICULAR CONNECTIVE TISSUE. 
55 
phatic glands, with small spheroidal cells—lymph 
cells—which, however, seem to have no direct con- 
nection with the tissue we are studying, and may be 
easily removed. 
Section of the Lymphatic Gland of Dog, Treated with Osmic 
Acid.—One of the mesenteric or cervical glands is re- 
moved from a recently-killed dog, and a hypodermic 
syringe being partially filled with i-per-cent. solution of 
osmic acid, the canula is thrust well into the gland, and 
the acid slowly injected until the organ becomes quite 
tense ; the canula is then withdrawn, and the gland placed 
in strong alcohol. After a few days it will be hard 
enough to make sections from.* The sections, which must 
be very thin, should be carefully shaken in a test-tube, 
one-third filled with water, to remove the lymph cells 
which lie in the meshes of the reticular tissue and conceal 
it. As these cells are shaken out, the sections look thin- 
ner, and when the operation is completed they are stained 
with hsematoxylin and mounted in glycerin. 
PRACTICAL STUDY. 
* It should be embedded in celloidin. CHAPTER IV. 
CARTILAGE—BONE—TEETH. 
CARTILAGE consists, like other members of the 
connective-tissue group, of cells and intercellular 
substance. There is nothing characteristic, how- 
ever, in the form of the cartilage-cells. It is in the 
peculiar nature of the intercellular substance and 
the relations which the cells bear to it, that we find 
the distinctive features of this form of connective 
tissue. The cartilage-cells are spheroidal, flattened, 
or angular in form ; the cell-body is finely granular 
and often contains tiny droplets of fat, and some- 
times pigment-granules. The cells have one, or 
sometimes two, sharply defined nuclei, which are 
coarsely granular and often contain an irregular 
network of a more strongly refractive substance. 
Around each cartilage-cell, in the adult animal, and 
closely enclosing it, is a homogeneous envelope 
called the capside. The substance forming this cap- 
sule is identical with the intercellular substance of 
hyaline cartilage, presently to be described. 
CARTILAGE. 
The cartilage-cells very readily lose their normal 
form and relation to the capsule by the application 
56 CARTILAGE. 
57 
of a great variety of substances, and even by slight 
exposure to the air. The most common change 
which is noticed in them is a rapid shrinkage, such 
as occurs when cartilage is exposed to the air or 
treated with strong salt solutions, or any substance 
which extracts water from the tissues. Under 
these circumstances the cell becomes more coarsely 
granular, it shrinks away from the capsule at certain 
points, giving the edge of the cell a festooned ap- 
pearance ; sometimes large, clear spheroidal spaces, 
called vacuoles, appear in the cell-body, and finally 
the cell shrinks to a shapeless mass in the centre or 
at one side of the cavity, or retains its connection 
with the capsule by one or more narrow irregular 
projections from the shrunken mass. 
The basement or intercellular substance is not 
the same in all cartilages, and, according to the dif- 
ferences in its nature, cartilage is divided into hya- 
aline cartilage, jibro-cartilage, fibro-elastic cartilage. 
In hyaline cartilage the intercellular substance is 
homogeneous and transparent in thin layers, some- 
what opalescent in thicker masses; it is of firm 
consistence, and contains at tolerably regular inter- 
vals variously shaped cavities in which the cells lie, 
exactly filling them. The layer of basement sub- 
stance which immediately surrounds the cells pos- 
sesses slightly different refractive power, and it is 
this layer which constitutes the capsule above men- 
mentioned. NORMAL HISTOLOGY. 
The cell-spaces or cavities in hyaline cartilage do 
not by the ordinary modes of preparation appear 
to be connected by lymph-channels, as are the 
cell-spaces in other varieties of connective tissue, 
yet the rapid passage of fluids through the tissue 
under certain circumstances, together with some 
recent microscopical observations, renders it ex- 
tremely probable that such communications do 
exist, though we are not at present able to demon- 
strate them with certainty. Although by the ordi- 
nary modes of preparation the basement substance 
of hyaline cartilage appears quite homogeneous, 
certain changes which it undergoes under patholog- 
ical conditions, or by the use of certain macerating 
or digesting fluids, lead us to believe that it really 
contains a groundwork of delicate fibrillae. 
The basement substance of hyaline cartilage dif- 
fers chemically from the basement substance of 
other members of the connective-tissue group, yet 
recent researches have thrown serious doubt upon 
the view formerly held, i. e., that cartilage gave, on 
boiling, a peculiar and characteristic substance 
called chondrin, it having been shown that the so- 
called chondrin is not a pure chemical substance, 
but a mixture of gelatin, mucin, and certain salts. 
Hyaline cartilage is found, in the adult, covering 
the ends of the bones in the joints; and most of the 
laryngeal and the tracheal, bronchial, costal and nasal 
cartilages are of this variety. CARTILAGE. 
59 
Fibro-cartilage differs from hyaline cartilage in 
having a distinctly fibrillated intercellular substance. 
This form of cartilage is found in the intervertebral 
cartilages, in the meniscuses of certain joints, and 
at certain points where the ligaments are inserted 
into the cartilaginous extremities of bones. 
In certain other cartilages—-such as the epiglottis, 
some of the small cartilages of the larynx, and the 
cartilage of the pinna of the ear—the intercellular 
substance contains, in addition to a few fibrillated 
fibres, elastic tissue, either in the form of fibres or 
in fine granules. Such cartilage is called fibro-elastic 
cartilage. In both fibre- and fibro-elastic cartilage 
the cells are identical in character with those of 
hyaline cartilage. 
Except at the free surfaces, which it presents in 
the joints, cartilage is surrounded by a layer of 
fibrillated connective tissue of varying'thickness, 
called the perichondrium, in which are found the 
blood-vessels which supply nutritive material to the 
non-vascular cartilage within. At the surface of 
many cartilaginous masses the cells are very much 
crowded together, and flattened in a plane parallel 
to the surface. 
PRACTICA.L STUDY. 
Hyaline Cartilage from Femur of Frog.—The head of 
a femur of a recently killed animal being exposed, a thin 
slice of cartilage is shaved off with a razor so as to leave NORMAL HISTOLOGY. 
a flat surface from which a thin section should be cut, 
and immersed in a drop of saturated solution of picric 
acid on a slide, and covered and surrounded at once by 
a rim of asphalt varnish, before the acid solution com- 
mences to evaporate. 
In such thin sections, cavities are seen here and there 
from which the cells have fallen out ; these may be filled 
with the preservative fluid, or with bubbles of air. Picric 
acid is one of the best agents for preserving the normal 
characters of cartilage cells, but even in this they shrink 
somewhat, and after a time become coarsely granular. 
Shrinkage of Cartilage Cells by Strong Salt Solution.— 
Since in most of the specimens containing cartilage, 
which we shall study later, the cells will have been con- 
siderably shrunken by the preservative fluids, it is desira- 
ble for us to acquaint ourselves here with the process of 
shrinkage, so that we may understand the various dis- 
torted forms which such cells present. To do this, we 
have simply to prepare a thin section of hyaline cartilage, 
as above, and mount it at once in half-per-cent, salt solu- 
tion. When a good field for observation has been se- 
lected, a drop of ten-per-cent, salt solution (alcohol will 
do as well) is run in at one edge of the cover glass, the 
agent being drawn through by filter paper at the other. 
In this way the process of shrinkage and formation of 
vacuoles may be readily observed. 
j Fibro-cartilage may be studied in thin sections from 
the intervertebral cartilages of man or any of the domes- 
tic animals ; or from the head of the femur, through the 
insertion of the ligamenturn teres, parallel with the course 
of its fibres. The tissues should be laid for a few days in BONE. 
alcohol before cutting. The sections are stained with 
picro-carmine, and mounted in glycerin. 
Fibro-elastic Cartilage.—This is best studied in the 
epiglottis of man or the lower animals, which has been 
preserved in alcohol. Thin sections are stained with 
picro-carmine, which colors the cells red, and the elastic 
granules and fibres yellow. They are mounted and pre- 
served in glycerin. The cells in both fibro- and fibro- 
elastic cartilage are, by the above modes of preparation, 
more or less shrunken and deformed. 
BONE. 
In studying bone we have to consider: I, the 
hard substance, or bone-tissue proper; 2, the connec- 
tive tissue envelope which surrounds the bone—the 
periosteum; and, 3, the marrow contained in the 
central cavities or spaces within. 
1. The most striking feature of bone-tissue proper 
is its firmness and hardness, which is due to the 
presence of certain inorganic salts of lime. Various 
acids dissolve these lime salts, and when they are 
removed a substance is left behind which retains, 
for the most part, both in general form and minute 
structure, all the essential features of the original 
bone. There is a basement substance, presenting 
many of the optical characters of hyaline cartilage; 
and lying in tiny, branching spaces, in the basement 
substance, are flat, nucleated cells. The lime salts 
are deposited in the intercellular substance in such 62 
NORMAL HISTOLOGY. 
an extremely minute state of division as to be in- 
visible, even with high powers of the microscope. 
The elongated and flattened cell-spaces of bone are 
frequently called lacuna, and the numerous fine, 
branching, intercommunicating channels which pass 
off from them in all directions, and open into the 
marrow cavities, or into the passages for the blood- 
vessels, are called canaliculi. 
The bone-cells, or bone-curpuscles, as they were for- 
merly called, are, in adults, thin, flat cells, with sphe- 
roidal or oval projecting nuclei. It was formerly be- 
lieved that they sent fine branching process-es off into 
the ramifications of the canaliculi. Recent investiga- 
tions, however, have thrown great doubt upon the 
existence of at least such numerous processes as 
were formerly believed to exist—it having been 
shown that some, at least, if not all, of the sup- 
posed processes are really portions of the intercel- 
lular substance lining the lacunae and canaliculi. 
In young bone the cells are not flat, but spherical 
or ovoidal. 
We distinguish two kinds of bone-tissue, spongy 
and compact. 
In spongy bone-tissue, which is found in abundance 
in the epiphyses of the long bones, the hard sub- 
stance, or bone proper, is arranged in the form of 
thin plates, which are grouped together so as to 
enclose tiny, irregular-shaped cavities, filled with 
marrow-tissue. In these thin plates of spongy BONE. 
63 
bone the cells lie irregularly scattered through the 
intercellular substance, which is homogeneous. 
In compact bone, such as is found in the diaphyses 
of the long bones, the intercellular substance is ar- 
ranged in layers, or lamellae, in and between which 
lie the cells. The lamellar arrangement is best seen 
in transverse sections from the diaphyses of the long 
bones. If we look at a thin cross-section of such a 
bone with a low magnifying power, we notice nu- 
merous round or ovoid, or irregular-shaped open- 
ings, of varying size, and around these are grouped 
several thin concentric layers of basement substance, 
in and between which lie the cells, flattened in the 
plane of the lamellae. 
These sets of concentric lamellae are called special 
or Haversian systems of lame lice. Sometimes these 
Haversian systems of lamellae lie closely crowded 
together, and again they lie at varying distances 
from one another. In the latter case the interven- 
ing space is filled up by other and irregular sets of 
lamellae which do not correspond with the Haversian 
lamellae, but pass off obliquely in various directions. 
These are called, from their position relative to the 
Haversian system, intermediate lamellce. Finally, at 
the surface of the bone beneath the periosteum, and 
sometimes at the inner surface adjacent to the me- 
dullary cavity, are seen a series of lamellae which lie 
parallel to the surfaces of the bone, and are called 
general or circumferential lamellce. If we make a 64 
NORMAL HISTOLOGY. 
longitudinal section of a long bone, we find that it 
is traversed by a number of more or less longi- 
tudinally arranged, branching and communicating 
canals, of varying size, in which lie the blood- and 
lymph-vessels. It is around these canals, called 
Haversian canals, that the Haversian lamellae are 
grouped, and the variously shaped openings which 
are seen in the transverse sections, are transverse 
sections of these vascular or Haversian canals. 
Within the Haversian canals, when they are not en- 
tirely filled with the blood-vessels, we find the latter 
enclosed in a tissue identical with that filling the 
medullary cavity, and presently to be described as 
marrow. In the flat and irregular-shaped bones 
essentially the same structural features are present, 
but the lamellar arrangement is much less regular. 
Although, for the most part, the intercellular sub- 
stance of bone is, by the ordinary modes of prepa- 
ration, apparently quite destitute of structure be- 
yond that indicated by its lamellation, we yet find 
in certain portions a well-defined system of fibres. 
If, in a decalcified bone, some of the external la- 
mellae are torn off, numerous fine, fibrillated, spicula- 
like projections are seen hanging on to the inner 
surface of the separated fragments. These are the 
so-called Sharpey s fibres, which, passing inward from 
the periosteum, pierce the bone either obliquely or 
at right angles. As we shall see when studying the 
development of bone, these Sharpey’s fibres are the BONE. 
65 
remains of fibrillated connective-tissue bundles, 
which originally occupied the situation now filled 
by bone. Recent investigations, moreover, have 
led to the belief that in bone, as in hyaline cartilage, 
the basement substance is everywhere delicately 
fibrillated, but we have not space in this manual to 
consider the methods by which this may be demon- 
strated. 
2. Periosteum.—The periosteum consists chiefly 
of fibrillated connective tissue, with a few elastic 
fibres, and we recognize in it two layers: an outer 
layer, composed chiefly of firm, dense connective 
tissue, which is continuous with the muscular apo- 
neuroses surrounding the bone ; and an inner layer, 
which is looser in texture, more vascular, and abun- 
dantly furnished with variously shaped cells. The 
periosteum is attached to the bone by connective- 
tissue fibres, which pass from the former into the 
substance of the latter, the attachment being firmer 
at some points than at others, as, for example, near 
the extremities of the long bones and at the points 
of insertion of the tendons and ligaments. Blood- 
vessels pass also from the periosteum into the 
bone. 
3. Marrow.—Marrow-tissue is found in the cen- 
tral or medullary cavity of bones, in the tiny cham- 
bers of spongy bone, and in the Haversian canals. 
Sometimes it has a yellowish color and is fatty, 
sometimes it presents itself in the form of a red- 66 
NORMAL HISTOLOGY. 
dish pulp. Red marrow is found in embryos and 
in young animals, and in adults in certain small 
bones and in vertebrae. In certain animals, such as 
the rabbit and guinea-pig, red marrow is found in 
most of the bones, even in adult life. In adult 
man, under normal conditions, the marrow—except 
in the vertebrae, ribs, and certain small bones—is yel- 
low. Yellow marrow differs from the red in that it 
contains a large amount of fat, sometimes consist- 
ing almost exclusively of fat-cells. 
We find in red marrow, which is best adapted for 
study, blood-vessels and spindle-shaped or branching 
cells, which constitute the supporting framework of 
the tissue. In the interstices of the latter lie sev- 
eral distinct kinds of cells: I. Fat-cells; 2. smaller 
and larger spheroidal cells, having essentially the 
same structure and character as the lymph-cells, and 
called, par excellence, marrow-cells; 3. cells some- 
what larger than the last mentioned, with, usually, a 
single very irregular-shaped and sharply defined nu- 
cleus ; 4. very large granular cells, which usually have 
several nuclei scattered through the cell-body, or 
grouped on one side, the so-called myeloplaxes or 
giant cells. It is not improbable that the two last 
varieties are only modified forms of the same kind 
of cells. In the marrow of developing bone are seen 
spheroidal, or irregularly cuboidal, large granular 
Cells, with commonly oval nuclei, usually situated 
at one side of the cell-body. These are the so-called BONE. 
67 
osteoblasts, with which we shall become better ac- 
quainted when we study the process of bone-de- 
velopment. 
In addition to the above cell-forms, red blood- 
cells, escaped from the blood-vessels, are usually 
seen in abundance. Not infrequently, when fresh 
marrow is studied, cells are seen which in many 
respects are like the true marrow-cells, but which, 
with a distinct nucleus, have a homogeneous cell- 
body resembling in its color the red blood-cells. 
These cells are the so-called nucleated red blood-cells, 
and are believed by some observers to be destined 
to lose their nuclei, and assume the character of the 
ordinary red blood-cells. Those who advocate this 
view regard the marrow of bones as one of the 
blood-producing tissues of the body. The trans- 
formation of these cells into red blood-cells has 
never been directly observed, and as the peculiar 
appearance which they present can be accounted for 
on other grounds, the formation of red blood-cells 
in the marrow, while not improbable, cannot yet be 
regarded as definitely demonstrated. 
PRACTICAL STUDY. 
Decalcified Bone.—To obtain a general view of the struc- 
ture of bone, we have recourse to transverse and longitudi- 
nal sections of one of the long bones (from man or the 
lower animals, such as the rabbit or dog), which has been 
freed from its lime salts by soaking in dilute acids, and 
rendered so soft as to be readily cut with a razor. 68 
NORMAL HISTOLOGY. 
Although various acids, such as nitric and hydro- 
chloric, effect the decalcification of bone, solutions of 
chromic or picric acids are preferable, because, while 
very perfectly removing the lime salts, they harden and 
I .reserve the soft structures in a most satisfactory manner. 
As the salts of lime, as they exist in bone, do not undergo 
rapid solution in these acids, the bits of bone which are 
to be decalcified should be small, or the process will be a 
very protracted one. They should not, at most, be larger 
than a cubic centimetre. The quantity of fluid should 
also be quite large (two hundred to three hundred cubic 
centimetres to a bit of bone of the above size). Picric 
acid, although slow in its action, is, on the whole, to be 
preferred, because the chromic acid often leaves the tis- 
sues in a granular or cloudy condition, which interferes 
with subsequent study. If chromic acid be employed, 
the bit of bone is put first into a weak aqueous solution of 
one in six hundred ; in a couple of days it is transferred 
to a fresh solution of one in four hundred, and again in a 
couple of days to another solution of one in two hun- 
dred. A stronger solution than this should not be used, 
but this should be renewed every few days, and the bottle 
frequently shaken. In two or three weeks the process 
will probably be completed ; this can be ascertained by 
passing a fine needle into the preparation. If it be de- 
sirable to hasten the process, after a week or ten days' 
soaking in chromic acid, as directed, a little nitric acid 
may be added to the solution (one c.c. to one hundred 
c.c.). The previous action of the chromic acid will pre- 
vent the swelling and partial destruction of the soft 
parts, which nitric acid alone causes. If picric acid be BONE. 
69 
employed, a saturated aqueous solution should be used, 
the preparation frequently shaken, and additional crys- 
tals of the acid occasionally added. 
When the bone has become sufficiently soft by either 
of these methods, it is allowed to soak for a day in 
water to remove the excess of acid, and then hardened 
and preserved in alcohol. Longitudinal and transverse 
sections should be made, and, if decalcified by chro- 
mic acid, are best stained double with hsematoxylin 
and eosin ; if by picric acid, the structure shows very 
well after staining with picro-carmine. Both may be 
mounted in glycerin. If the periosteum has not been 
removed, its structure and relation to the bone are well 
shown. 
Sections of Hard Bone.—In such preparations as the 
above, which are mounted in fluids, the canaliculi are 
for the most part invisible, because the fluids which fill 
them possess very nearly the same refractive power as 
the basement substance. The cell-spaces and canaliculi 
are best studied in thin sections of hard bone, which 
have been macerated for some time, so as to remove the 
medullary fat and other soft parts, and then dried. 
Transverse or longitudinal sections may be made, the 
latter being most easily prepared, because sections in 
this direction are less brittle. 
A small piece, as thin as possible, should be sawn from 
the bone (the diaphysis of a human long bone answers 
very well) in the proper direction; this is ground down 
very thin on a whetstone or grindstone, or on a plate of 
glass with emery powder, the section being held down 
with the ball of the finger or a bit of soft cork. When it NORMAL HISTOLOGY. 
has become quite thin, so as to be almost transparent, 
it is polished on a dry oil-stone free from grease, and 
then carefully washed and brushed under water with a 
fine pencil to remove particles of dirt. It is now al- 
lowed to dry, and is mounted in balsam. For this pur- 
pose the semi-fluid Canada balsam, such as is used for 
ordinary mounting, should not be employed, because it 
would run into the lacunas and canaliculi, and render 
them invisible. A bit of quite hard and solid balsam 
should be placed on a slide and heated until it melts ; 
just as it begins to fairly cool, but before it gets at all 
hard, the slip of bone is quickly immersed in the drop 
and covered. If the proper moment has been chosen, 
when the balsam is neither too hot nor too cold, the 
lacunae and canaliculi are clearly defined by reason of 
the air with which they are filled. Usually, however, in 
the most successful preparations, in the very thin parts or 
at the edges, part of the canaliculi have become filled 
with the balsam and rendered invisible. 
Marrow.—A long bone, from a rabbit or from a child, 
should be broken across and a little of the red marrow 
scooped out and laid for twenty-four hours in a mixture 
of alcohol and water (one to two). Fragments are then 
teased on a slide in glycerin which has been colored 
with eosin, and mounted in the same. By this process 
the red blood-cells are destroyed, and the characters of 
the so-called nucleated red blood-cells changed. For 
the study of the latter, fresh marrow should be teased on 
a slide in the indifferent salt solution. DEVELOPMENT OF BONE. 
71 
DEVELOPMENT OF BONE. 
At a certain period of embryonic life no bone-tis- 
sue is found in the body, the parts where it is finally 
to be, being occupied either by cartilage or fibrillar 
connective tissue. Out of these tissues the bone is 
developed by a process which, though presenting 
considerable differences in detail in various parts of 
the body, is yet, in its essential nature, the same in 
all. We recognize three ways in which bone is de- 
veloped : 1. In the substance of preexisting car- 
tilage—intra-cartilaginous; 2. beneath the perios- 
teum—sub-periosteal; 3. in the substance of preex- 
isting fibrillar connective-tissue membranes—intra- 
membranous. In all of these modes of bone-forma- 
tion the new bone seems to be deposited under the 
influence of certain large, granular, usually spheroidal 
or cuboidal cells, called osteoblasts. 
1. When bone is formed from cartilage, the latter 
bears a general resemblance in shape to the finished 
bone. The first change which we notice in such a 
cartilage which is about to undergo ossification, is 
that at a certain point—if it be a long bone, at 
about the middle of the diaphysis—the cartilage-cells 
begin to enlarge, the basement substance between 
them becoming partially absorbed, and what re- 
mains of the latter becoming infiltrated with fine 
granules of lime salts. Around this calcified por- 
tion we find the blood-vessels of the perichondrium 72 
NORMAL HISTOLOGY. 
accompanied by marrow-tisssue and the above- 
mentioned osteoblasts, growing into the calcified 
cartilage, absorbing the latter as they go, and form- 
ing irregular channels or cavities called medullary 
spaces. These channels are first separated from 
one another by narrow, irregular septa of the cartil- 
age basement substance which remains unabsorbed, 
and are lined by layers of osteoblasts, by whose 
agency the septa become covered with new bone, 
in a manner presently to be described. 
The region in which this new bone is first depos- 
ited is called the ossification zone. As the blood- 
vessels, accompanied by the osteoblasts and mar- 
row-tissue, proceed further and further into the car- 
tilage, channelling out the medullary spaces as they 
go, we always find—just in advance of the ends 
of the blood-vessels and the extremity of the 
spaces in which they lie—a zone of calcified cartil- 
age ; and beyond this, cartilage-tissue which appar- 
ently prepares the way for the advancing marrow- 
spaces and newly forming bone, by very character- 
istic modifications, chiefly in the form and arrange- 
ment of its cells. 
If we examine the cartilage at a considerable 
distance from the line of ossification, we find the or- 
dinary appearance of hyaline cartilage with more or 
less flattened cells. Approaching now the zone of 
ossification, we find that the cells are larger, are 
arranged in rows or groups of frequently four, eight, DEVELOPMENT OF BONE. 
73 
or sixteen, etc., the intercellular substance being less 
in amount, corresponding to the increase in size and 
number of the cells. Further inward, we find the 
cells still more plainly arranged in rows, very large, 
sometimes globular or flattened against one another, 
and the basement substance reduced to quite thin 
septa, enclosing spaces in which the rows of large 
cartilage-cells lie. Then comes a narrow zone, in 
which the septa of the basement substance are filled 
with fine granules of lime salts—calcification zone. 
Here the cartilage-cells have assumed a peculiar 
granular character. Finally, still nearer we find that 
the lime salts have disappeared from the septa, and 
that the spaces which contained the large granular 
cartilage-cells have become continuous with the 
advancing vascular, bone-walled marrow-cavities, 
above described. It is to be distinctly understood 
that the calcification zone is not bpne, but only cal- 
cified cartilage; the true bone being first formed 
after this lime has disappeared, on the surface of the 
septa in which it was temporarily deposited—for 
what purpose we do not know. 
Turning our attention now to the exact way in 
which the bone is formed under the influence of the 
osteoblasts, we find that just beneath these cells, as 
they lie along the walls of the new-formed medul- 
lary spaces, the basement substance of true bone 
begins to be deposited, at first in the form of a nar- 
row shell beneath each osteoblast. These deposits, 74 
NORMAL HISTOLOGY. 
which on cross-sections have a crescentic shape, be- 
come thicker and thicker, rising up around the cell, 
which they finally enclose—the enclosed osteoblast 
becoming, as it would seem, a bone-cell. This 
process going on around each osteoblast, the walls 
of the medullary cavities soon become covered with 
a layer of bone containing bone-cells. New osteo- 
blasts appear on the walls, and in turn become en- 
closed in a layer of bone, and thus the lamellar 
arrangement of bone-tissue is produced. The re- 
mains of cartilage basement substance between the 
medullary space thus covered by bone finally dis- 
appear in a manner unknown to us. 
2. Hand in hand with the formation of bone 
within the cartilage, new bone is formed on its sur- 
face beneath the perichondrium, which thus becomes 
periosteum. The process of sub-periosteal ossifica- 
tion, by which the bone increases in thickness, is 
dependent also upon the presence of osteoblasts. 
We find these arranging themselves along the blood- 
vessels which enter the bone, and along the inner 
layer of connective-tissue fibres of the periosteum, 
and bone is formed around them in the manner 
above described. New bone thus formed at the sur- 
face appears at first by no means in the form of 
smooth, continuous layers, for as the blood-vessels 
and connective-tissue bundles, along which the oste- 
oblasts lie, are arranged at varying angles with the 
surface of the bone and with each other, the effect DEVELOPMENT OF BONE. 
75 
is to produce irregular-branching cavities, upon 
whose walls the new layers of bone are deposited. 
When these branching cavities become filled, with 
the exception of the space occupied by the blood- 
vessels and marrow-tissue, by successive lamellae of 
bone, they constitute the structures with which we 
are already familiar under the name of Haversian 
canals and Haversian lamellae. Where the forma- 
tion of bone has taken place along the bundles Of 
connective tissue, these bundles sometimes persist 
for a long time, in a modified form, among the 
lamellae, and constitute the above-mentioned Shar- 
peys fibres. 
Thus, by the transformation of cartilage and ap- 
position at the surface, the long bones are formed. 
In these bones the ossification progresses toward the 
epiphyses, where independent centres of ossification 
are established. The lines of ossification approach 
each other, and finally, when the process of growth 
in the bone is complete, the band of cartilage which 
separated them disappears, and epiphysis and dia- 
physis join to form a single bone. As the bone 
grows by apposition beneath the periosteum, the 
osseous tissue which was first formed in the diaphy- 
sis is absorbed, and the medullary cavity is formed 
in the place which it originally occupied. 
3. When bone is formed in membranes of fibrillar 
connective tissue, as in the skull-cap, we notice, first, 
that some of the interlacing bundles which occupy 76 
NORMAL HISTOLOGY. 
the place of the future bone become infiltrated with 
lime salts; along these calcareous bundles cells be- 
come very abundant, osteoblasts appear and arrange 
themselves, and bone forms around them just as in 
the other varieties of bone-formation. Blood-vessels 
and marrow-tissue He between the new-formed layers 
of bone, so that at a certain period of embryonic life 
the bones of the skull-cap consist of a series of bony 
lamellae, arranged so as to enclose branching and 
communicating cavities, which are occupied by 
blood-vessels and marrow-tissue, and whose walls are 
lined with osteoblasts. A well-defined periosteum 
is finally formed, beneath which successive layers of 
new osseous tissue are deposited, and thus the bone 
increases in thickness and acquires its smooth sur- 
faces. 
The mode of origin of the osteoblasts is still very 
obscure. Many investigators believe that in the 
intra-cartilaginous ossification they are the large car- 
tilage-cells which we see at the calcification line, 
which in contact with the blood-vessels become so 
modified in form and function as to assume the role 
of bone-formers. Others assert that the large carti- 
lage-cells disintegrate and disappear, and that the 
osteoblasts are produced from cells which accom- 
pany the blood-vessels. Still others regard them as 
white blood-cells, modified and endowed with new 
functional powers. In the intra-membranous and 
sub-periosteal ossification, many suppose that they DE VELOPMENT OF BONE. 
77 
are formed from connective-tissue cells. So little is 
absolutely known, however, as to their genesis, that 
while recognizing their importance in bone-forma- 
tion, we can regard none of these various theories as 
to their origin as definitely established. 
PRACTICAL STUDY. 
Inira-cartilaginous and Sub-periosteal Ossification.—A 
long bone, from a nearly mature foetus or a young ani- 
mal, should be carefully removed without injuring the 
periosteum, and decalcified.* Thin longitudinal sections 
are made with a razor through the ossification zone, em- 
bracing the tissue for a considerable distance on either 
side of it. The sections are stained double and mounted 
in balsam. 
/ Intra-membranous Ossification.—To study the early 
stages of this process, a young embryo (if from the sheep 
or pig, four to six cms. long) should be soaked for a few 
days in Muller’s fluid, and a bit corresponding to the por- 
tion of one of the parietal bones cut out, and the skin, 
muscles, and dura mater torn away with forceps under 
water. The membrane in which ossification is occurring 
is now to be carefully brushed with a stiff pencil until 
it is thin enough to be examined with tolerably high 
powers. It is stained double and mounted in balsam. 
The irregular chambers, lined with osteoblasts and 
filled with blood-vessels and marrow, which are formed 
in the bones of the skull-cap at a later period, are well 
shown by transverse sections through the decalcified 
skull-bones of an older foetus (human, at about six or 
* Embed in celloidin. 78 
NORMAL HISTOLOGY. 
seven months, or from the beef or sheep, sixteen to 
twenty cms. long). These should be stained and mounted 
as above. 
TEETH. 
The teeth have many structural features in com- 
mon with bone. The chief bulk of the tooth is 
made up of homogeneous, brittle basement sub- 
stance much harder than bone, called dentine. The 
dentine contains lime salts, and is permeated by a 
multitude of fine branching channels which radiate 
from a central cavity, called the pulp cavity, which 
the dentine encloses. These delicate channels in 
the dentine are analogous with the canaliculi of 
bone. 
The pulp cavity is filled with a soft vascular 
tissue, called pulp, containing irregular-shaped, often 
branching cells, and nerves. Along the sides of the 
pulp cavity lie spheroidal or ovoid cells, which send 
off branches into the pulp and also into the above- 
mentioned delicate channels in the dentine. These 
cells are called odontoblasts or dentine cells, and arc 
usually considered to be the analogues of the bone- 
cells. The pulp cavity is open at the root of the 
tooth for the admission of vessels and nerves. Sur- 
rounding the root of the tooth is a thin layer of 
bone called cement. At the crown of the tooth the 
dentine is completely covered by a layer, of vary- 
ing thickness, of an extremely hard substance called TEETH. 
79 
enamel. The enamel consists of a series of closely 
packed, small, wavy or undulating prisms, placed 
edgewise upon the surface of the dentine, and cov- 
ered, over the free surface of the tooth, by a hard, 
tough, structureless membrane, called the enamel 
cuticle. 
PRACTICAL STUDY. 
Hard Teeth.—To study the hard parts of teeth, thin 
sections of a macerated and dried tooth should be ground 
down by the method described when we were studying 
hard bone, and mounted, with the same precautions, in 
hard Canada balsam. 
Decalcified Teeth.—The soft parts of teeth may be 
studied in sections from teeth which have been decalci- 
fied with picric acid. The tooth should be broken 
across, so as to expose the pulp cavity and hasten the 
action of the solvent. Sections are stained with hsema- 
toxylin and eosin, and mounted in glycerin. CHAPTER V. 
BLOOD AND LYMPH. 
BLOOD. 
ALTHOUGH strikingly different in physical char- 
acter from most animal tissues, we must yet regard 
blood and lymph as true tissues—tissues with a fluid 
intercellular substance. Let us first consider the 
blood. 
In normal human blood we find suspended in a 
colorless fluid, the plasma, three distinct kinds of 
formed elements: I. Colorless blood-cells; 2. red blood- 
cells ; 3. variously shaped free granules* 
1. Colorless or White Blood-cells or Leucocytes.—- 
These are small, usually spheroidal nucleated cells, 
without a membrane, the cell-body being finely, or 
sometimes coarsely, granular. The nuclei, of which 
there may be one or more, are not usually visible in 
the living cells on account of the granular character 
of the body which conceals them, and are of vary- 
ing form,— sometimes spheroidal or dumb-bell- 
shaped, sometimes having the form of a bent or 
twisted cylinder, and again entirely irregular. 
These cells possess the power, under favorable 
conditions, of spontaneous movement. They change 
* See Appendix, p, 253. BLOOD. 
their form and place. While, when in a state of 
rest, they assume in general the spheroidal form, as 
above stated, we find that when they become active 
they send out variously shaped processes, some fine 
and delicate, others broad and of very irregular 
shape. We often see, after a process has been 
thrown out, that it becomes gradually larger and 
larger, the cell-body becoming correspondingly 
smaller, until finally the whole cell seems to have 
passed over into the process, thus moving forward. 
Sometimes processes are thrown out and again with- 
drawn, and not infrequently the whole cell flattens 
out into an irregular-shaped mass, so thin as to be 
almost invisible. Not infrequently clear rounded 
spaces, called vacuoles, suddenly appear in the cell- 
body during its movements, and either remain for 
some time, or soon disappear as suddenly as they 
came. 
These movements are called amoeboid movements ; 
they are always very slow, and are greatly influenced 
by the temperature, density, and oxygen-content of 
the fluid in which they lie. By virtue of this loco- 
motive power the white blood-cells perform certain 
evolutions within the vessels; they escape through 
their walls, and sometimes singly, sometimes in vast 
numbers, move through the tissues in the larger and 
smaller lymph-spaces. This emigration of white 
blood-cells occurs apparently, to a slight extent, 
under normal conditions; but it is under patho- 
logical conditions that it is most active. 82 
NORMAL HISTOLOGY. 
The nuclei of these cells become visible on the 
application of a variety of agents which determine 
the death of the cells, such as acetic acid, dilute 
alcohol, and certain coloring agents. The cells vary 
greatly in size, but on the average are, in man, 
larger than the red cells. 
2. Red Blood-cells.—These cells, having in man the 
form of bi-concave discs, consist apparently, simply 
of a cell-body without membrane or nucleus. Al- 
though when crowded together in great numbers 
they give the blood a distinct red color, when seen 
singly they have a greenish-yellow tint. The cell- 
body is very soft and pliable, jelly-like, changing its 
shape on the slightest pressure. It is more deeply 
colored at the periphery, when seen from the side, 
because of its greater thickness at that part. Owing 
to the peculiar shape of the cell, it acts as a lens 
upon the light passing through it, and its central 
portion is either light or dark, depending upon 
whether the objective is approached to or with- 
drawn from it. When examined fresh in the plasma, 
many of the cells arrange themselves closely to- 
gether side by side, in longer and shorter rows. 
If water is mixed with blood, the red cells soon 
begin to swell and lose their color. Sometimes 
one side swells faster than the other and the cells 
become cup-shaped ; finally they become globular, 
are considerably larger than at first, and colorless. 
On being drawn from the vessels, if the plasma BLOOD. 
be allowed to evaporate, or if certain fluids—such as 
strong solutions of common salt or bichromate of 
potassium—be added, a part of the red blood-cells 
lose their regular shape, their edges become crenu- 
late and jagged, and they sometimes seem to be- 
come smaller; finally, they assume the form of ir- 
regular globular masses, beset with short, blunt 
spines. Various other irregular forms are produced 
under the same circumstances which it is not neces- 
sary to describe here. The addition of water causes 
the spines to disappear, and the cells swell up and 
assume a globular form. These changes in form, 
produced by chemical agents and by change in the 
density of the fluid in which the cells lie, should not 
be mistaken for an expression of vitality, or re- 
garded as analogous with the amoeboid movements 
of the white blood-cells. 
The red blood-cells are much more abundant than 
the white, there being in normal human blood about 
350 to 500 of the former to one of the latter. It is 
estimated that in man there are between four and 
five million red blood-cells in one cubic millimetre 
of blood. The diameter of the average cell it 
about Yrs-th a millimetre, or about 7.9 pi.1 Not 
infrequently in normal blood—very often under pa- 
thological conditions—-red blood-cells are seen which 
1 The Greek letter pi is frequently employed to represent the 
micro-millimetre, or the one-thousandth part of a millimetre, this 
having been widely adopted as the unit for microscopic measurement. 
In English measurement the average red blood-cell has a diameter of 
about of an inch. 84 
NORMAL HISTOLOGY. 
are much smaller than the above-described forms, 
and are often spheroidal in shape. 
The red blood-cells owe their color, as well as 
their capacity for performing certain important 
physiological functions, to the presence in them of 
a crystallizable substance called hcemoglobin. The 
exact relation existing between the haemoglobin and 
the substance of the cell is but little understood. 
They are but loosely combined, for the haemoglobin 
is .readily dissolved out by water, which itself be- 
comes colored, while the colorless and swollen cell 
or stroma is left behind. The shape of haemoglobin 
crystals obtained from the blood of different ani- 
mals is not always the same ; those from human 
blood have, in general, the form of rhombic prisms. 
3. Free Granules.—These are always found in 
greater or less number in human blood when drawn 
from the vessels. They are chiefly of two kinds; 
either small spherical bodies, somewhat resembling 
fat-droplets, or variously shaped, often angular 
masses, looking not unlike fragments of white blood- 
cells. They are sometimes seen singly, sometimes 
in clusters. Their nature is still undetermined. 
The above general description of the blood-cells 
of man applies, with few exceptions, to other mam- 
malia. The differences in size, however, which ex- 
ist between the red blood-cells of man and those of 
certain of the mammalia, are so considerable that 
they can be distinguished with certainty from one BLOOD. 
85 
another by microscopic measurements. It should, 
on the other hand, never be forgotten that the red 
blood-cells of certain other mammalia, e.g., the dog, 
have so nearly the same average diameter as those 
of man that they cannot be distinguished with ab- 
solute certainty by measurements. In other verte- 
brates the form and character of the red blood-cells 
differ greatly from those above described ; being for 
the most part oval, and having a distinct nucleus. 
The intercellular substance or plasma of freshly 
drawn blood is perfectly homogeneous ; but if we 
allow it to coagulate, we find, on subjecting it to 
microscopical examination, that in addition to the 
above-described elements, a multitude of delicate 
filaments lie among the cells, stretching in all direc- 
tions, and joining each other at frequent intervals, 
forming an irregular-meshed net. We find, more- 
over, if we examine a clot from which the red cells 
have been carefully removed or rendered invisible, 
that in many places the filaments are grouped around 
irregular-shaped granules, looking like those above 
described in normal blood ; and if the process of 
coagulation be carefully observed, they may be seen 
to actually shoot out from these granules, which 
thus seem to form starting-points for their forma- 
tion. The substance which thus separates from the 
plasma is called fibrin. 86 
NORMAL HISTOLOGY. 
LYMPH. 
In lymph, in addition to the plasma from which 
fibrin is formed on separation from the body, we 
find spheroidal cells identical in structure with the 
white blood-cells; sometimes a few red blood-cells; 
and variously shaped granules or minute globules, 
composed apparently of a combination of albu- 
minoid material, with fat. These globules, in that 
variety of lymph called chyle, are so abundant as to 
give the fluid a milky appearance. 
Origin of Blood-cells—Direct observation has 
shown that, in some animals at least, the white 
blood-cells can multiply by division. Whether the 
cells which supply the place of those which seem 
to be used up in the process of growth and repara- 
tion are produced in this way, and if so, whether 
the division occurs in the blood- or lymph-vessels, 
or in the cell-spaces of the connective tissue, or in 
certain special organs, or whether they are pro- 
duced in a manner entirely unknown to us—these 
are questions not only of theoretical but of practi- 
cal interest; but, in spite of much research, and the 
accumulation of many observations bearing on the 
matter, we are still unable to give them a definite 
answer. Still more obscure, if possible, is the origin 
of the red blood-cells. Although in the adult man they 
seem to possess no nucleus, yet in embryonic life 
they certainly are furnished with that structure* we L YMPH. 
87 
find nucleated red blood-cells. Now, it has been re- 
cently shown that in certain parts of the body, in 
adult life, cells occur which in many respects resem- 
ble the nucleated red blood-cells of the embryo; 
such cells are found, for example, in the spleen, in 
the red marrow of bones, etc. 
The most plausible theory in regard to the matter 
is, that in certain parts of the body—spleen, mar- 
row, lymph-glands, and liver—white blood-cells are 
produced, a part of which are changed into the red 
blood-cells. The so-called nucleated red blood-cells 
are supposed to be intermediate forms. It must be 
remembered, however, that this view is not estab- 
lished as yet, and many observers do not ascribe to 
the so-called nucleated red blood-cells the signifi- 
cance upon which the advocates of this theory 
insist. 
PRACTICAL STUDY. 
Fresh Human Blood.—This may be obtained by tying 
a cord tightly around the finger to cause congestion, and 
then pricking it sharply at the side of the nail with a 
bright, clean sewing needle. A small drop is received on 
a slide and covered at once, care being taken not to press 
upon the cover-glass. The film of blood should be 
very thin or the crowding of the cells will interfere with 
the observation. As the plasma evaporates, the changes 
in form due to shrinkage of the red blood-cells may be ob- 
served near the edges of the preparation. Finally, a 
drop of water should be allowed to run under the cover- 88 
NORMAL HISTOLOGY. 
glass and its action observed, first, in causing the dis- 
appearance of the crenulations on the shrunken cells and 
the swelling of all the red blood-cells, and second, in dis- 
solving the haemoglobin out of them. 
V Crystals of Hemoglobin from Rat's Blood.—Although 
readily separated by water from its combination with the 
stroma of the red blood-cells of man, the haemoglobin 
does not readily crystallize. But when separated from 
the red cells of certain animals, the rat for example, it 
commences to crystallize, under favorable conditions, al- 
most immediately. A small drop of rat’s blood is mixed 
on a slide with an equal quantity of water, covered and 
examined at once. The color begins to be discharged 
from the red cells very soon, and within a few moments, 
near the edges of the cover-glass, small crystals may be 
found in abundance. If the specimen is set aside and 
examined after a few hours, many very large and beauti- 
ful prismatic crystals may be seen. Haemoglobin crys- 
tals do not keep long enough for permanent preserva- 
tion. 
Demonstration of the Nuclei of the White Blood-cells. 
—ln order to see their outlines distinctly, the nuclei 
must be stained and the cell-body rendered transparent. 
This may be accomplished by mixing on a slide a small 
drop of blood from the finger with an equal quantity of 
the following fluid : 
Saturated alcoholic solution of Analine Red i part, 
Alcohol ....... 5 parts, 
Water 10 parts. 
After thoroughly mixing the blood with the fluid, and L YMPH. 
89 
covering, it will be found that while the red cells are par- 
tially decolorized and inconspicuous, the bodies of the 
white blood-cells have become transparent and their 
nuclei are stained deep red. 
Amoeboid Movements.—These are most conveniently 
studied in the blood or lymph from one of the cold- 
blooded animals, such as the frog, for they occur here at 
the ordinary temperatures of the air, while artificial heat 
must be resorted to if we would maintain the blood of 
warm-blooded animals at a proper temperature for their 
occurrence. 
The leg and toes of a frog having been carefully 
cleansed, the tip of one of the toes is snipped off, and on 
stripping the leg downward with the thumb and finger, 
a drop of mixed blood and lymph will presently exude 
from the toe. This is received on a slide, protected from 
pressure by a bit of hair, and covered. To prevent evap- 
oration of the plasma, a rim of oil is painted around the 
edge of the cover. On focussing now upon the specimen, 
white blood-cells will readily be found, and selecting one 
which, by its irregular shape, indicates its activity, the at- 
tention must be fixed upon this cell and sketches of its 
form made at short intervals—every two minutes. Al- 
though the movement is usually too slow to be actually 
detected by the eye, if the cell is fairly active, it will be 
sufficiently evident, after a few sketches, that it has 
changed its shape and perhaps its place also. 
If the temperature of the room be low, the movements 
may be tardy in commencing, and they can be hastened 
by holding the finger or any warm object for a moment 
near the cover. It should be borne in mind that in the 90 
NORMAL HISTOLOGY. 
frog’s blood the red cells are oval and nucleated, and that 
they are also larger than the colorless cells. 
Fibrin.—A small quantity of blood may be whipped and 
the cells washed from the clot by a stream of water, and a 
fragment of the remaining substance teased in water on a 
slide and studied ; but the objects thus obtained are not 
altogether satisfactory, since the relation of the fibrillse to 
one another is disturbed and no light is thrown on the 
way in which they are formed. For the accomplishment 
of these ends, the following method may be employed : a 
medium-sized drop of blood is received on a slide and 
immediately covered ; after a few moments, when coagu- 
lation has occurred, the cover-glass is gently raised with 
the forceps, and the blood-cells washed out of the clot by 
allowing drops of water to fall upon the inverted cover- 
glass from a pipette held a few inches above the prepara- 
tion. (If, in removing the cover-glass, the clot adheres 
to the slide, the water is, of course, to be applied here.) 
When no more color is seen in the clot, a drop of the above 
solution of Analine Red is placed upon it, and it is again 
covered. The fibrin will be seen in the form of minute 
inosculating filaments which often radiate from what ap- 
pear to be the above-described free granules. CHAPTER VI. 
MUSCULAR TISSUE. 
CERTAIN muscles are under the control of the 
will, and are called voluntary muscles; and as these 
have, as we shall see presently, a very characteristic 
transverse stnation of their structural elements, 
they are also called striated voluntary muscles. To 
this class belong, among others, the muscles of lo- 
comotion and the voluntary muscles of the trunk 
and head. Other muscles are not under control of 
the will, and are hence called involuntary. A cer- 
tain portion of these involuntary muscles possess 
the same striation of their elements as the volun- 
tary muscles, and hence are called involuntary 
striated muscles. These are found in the heart. In 
another kind of involuntary muscles, such as is found 
in the intestine and bladder, the elements do not 
possess the same kind of striations, and they are 
hence called smooth or non-striated involuntary mus- 
cles. ' 
We have thus to study three kinds of muscles: 
I a, smooth or non-striated, 
b, striated. 
i. Involuntary muscles 
2. Voluntary muscles (striated). 
91 92 
NORMAL HISTOLOGY. 
I. a.—SMOOTH MUSCULAR TISSUE. 
Smooth muscular tissue is made up of very much 
elongated, narrow, pointed, usually fusiform cells. 
These cells are commonly arranged in groups or bun- 
dles, enclosed in connective tissue and supplied with 
blood-vessels and nerves. The cell-body, although 
usually fusiform, is sometimes flattened and band- 
like, often divided at the ends into two pointed ex- 
tremities. Owing to pressure from adjacent parts, 
the fusiform cell-bodies are often more or less flat- 
tened at the sides, presenting on cross-section an 
irregular polygonal contour. The cell-jpody has an 
indistinct longitudinal striation, and frequently in the 
vicinity of the nucleus a few shining granules are 
seen. The nucleus is usually narrow and much 
elongated, rod-like, and commonly encloses one or 
more nucleoli. It usually lies near the middle of 
the cell, which is often thickened or bulging at 
that point. 
These cells lie side by side or lap over one 
another at the ends, and are joined together by a 
small amount of an albuminoid cement substance. 
These smooth muscle-cells are variously grouped in 
different parts of the body ; sometimes crowded 
together in solid bundles, which are arranged in 
layers and surrounded by connective tissue, as in 
the intestines ; sometimes arranged in narrow inter- 
lacing fascicles, as in the bladder, or scattered MUSCULAR TISSUE. 
93 
singly through certain tissues ; sometimes wound 
in single or double layers around the blood-vessels; 
and again running in various directions and associ- 
ated with bands of connective tissue, they form 
large compact masses, as in the uterus. 
The longitudinal striation—which, under favorable 
circumstances, is seen on the cell-body—is not a 
mere surface marking, but extends deep into the 
cell, as may be seen in transverse sections of suitably 
prepared cells where fine lines are observed passing 
inward from the periphery of the cell toward the 
nucleus. The blood-vessels supplying this tissue 
form for the most part elongated net-works through- 
out its substance. 
PRACTICAL STUDY. 
Isolated Cells.—These we obtain by teasing bits of the 
tissue, but as they are firmly bound together by the 
cementing substance, this must first be dissolved or 
softened. This can be conveniently accomplished by 
soaking a bit of the tissue—the wall of the intestine for 
example—for forty-eight hours in an aqueous solution of 
bichromate of potassium (i to 800). Shreds of the 
muscular layer are torn off, slightly stained with hsema- 
toxylin, washed, and then carefully teased in glycerin 
which has been colored by eosin. To prevent the shrink- 
age of the cells under the action of the bichromate, it is 
well to enclose a short segment of the intestine, dis- 
tended with the solution, between two ligatures, and im- 
merse it in a vessel of the same solution. 94 
NORMAL HISTOLOGY. 
The cells may be more perfectly separated by soaking 
a bit of the fresh tissue for a few minutes in forty«per- 
cent. solution of caustic potash and then teasing, but 
they cannot be stained or preserved. 
Transverse and Longitudinal Sections of the Cells.— 
The intestine of the cat is well adapted for this prepara- 
tion, since here the muscle-cells are unusually large. A seg- 
ment having been distended as above with Muller’s fluid,, 
it should be immersed for ten days in the same, then 
carefully washed and put for a day or two in strong al- 
cohol. A bit is then cut out, embedded between pieces 
of hardened liver,* and thin sections made in a direction 
exactly at right angles to the axis of the gut. The sec- 
tions are stained double and mounted in balsam or glyc- 
erin. In such a preparation two layers of muscle-cells 
are seen : in one the cells are seen in transverse, in the 
other in longitudinal, section. Since the cells lap over 
one another, in the transverse sections the forms which 
they present will obviously differ, depending upon 
whether they have been cut across at the level of the 
nucleus, or at a point nearer the extremity. In such a 
preparation, the cementing substance between these cells 
may be/Seen in the transverse sections ; and the serosa 
and mucous membrane are seen on opposite sides of the 
muscular layers. 
Muscle-cells of Frog's Bladder.—Elegant pictures of 
very much elongated, slender muscle-cells, lying singly or 
arranged in narrow interlacing fascicles, may be obtained 
from the frog’s bladder by the following method : the 
spinal cord of a frog being broken up, the abdominal 
cavity is largely opened by a crucial incision, and a 
* Better in celloidin. MUSCULAR TISSUE. 
95 
curved canula, attached to a small syringe filled with a 
saturated solution of bichromate of potassium, is passed 
into the cloaca and directed forward into the bladder. 
The fluid is now slowly injected, and when the bladder 
is partially distended a ligature is thrown around its 
base, and the injection continued till the organ is fully 
distended. The ligature is now drawn tight and the 
canula withdrawn. The bladder is cut out, still dis- 
tended, and put in the same bichromate solution, where 
it remains for three days, when it is washed and trans- 
ferred to alcohol. After twenty-four hours it may be 
opened, and a bit cut out, the epithelium carefully 
brushed from the inner surface, and stained double and 
mounted in glycerin. In addition to the muscle-cells, 
the nuclei of the endothelial cells covering the peritoneal 
surface will be seen, as well as connective-tissue cells and 
fibres in the wall of the bladder. 
2. STRIATED VOLUNTARY MUSCULAR TISSUE. 
As the involuntary striated or heart muscle oc- 
cupies, in structure, an intermediate position between 
the smooth and the voluntary striated muscle, we 
shall find it advantageous to postpone its study 
until we have considered the other varieties. 
Voluntary striated muscle, to which the greater 
part of the muscular tissue of the body belongs, is 
made up of narrow, cylindrical, cord-like elements, 
of varying length and thickness, called muscular 
fibres. These are grouped in variously shaped 
bundles or fascicles, surrounded by connective- 96 
NORMAL HISTOLOGY. 
tissue envelopes or sheaths, and abundantly sup 
plied with blood-vessels and nerves. Let us first 
study the structure of the individual fibres. They 
consist of three distinct elements: I, contractile 
substance, forming the centre and making up most 
of the bulk of the fibre ; 2, nuclei, which in man 
and most warm-blooded animals lie scattered upon 
the surface of the contractile substance ; 3, the 
sarcolemma, a thin homogeneous sheath or tube, 
which tightly encloses the other elements. 
I. If we examine a fresh muscle-fibre, or one 
which has been hardened under favorable condi- 
tions, with moderately high powers, we see that the 
contractile substance is indistinctly longitudinally 
striated ; and if we treat muscle with certain chem- 
ical agents, such as chromic acid or its salts, we 
find that by slightly teasing, the fibres break up 
along the longitudinal striae into a multitude of fine 
fibrillae, which are called primitive muscle-fibrillcE. 
Again, if we examine the fresh or hardened fibres 
still further, we find that in addition to the longi- 
tudinal striations, they are crossed by more promi- 
nent, narrow, alternating, dark and light bands or 
stripes, the relative width of the stripes varying ac- 
cording as the muscle is seen in a state of contrac- 
tion or relaxation. Still further, if we soak a fresh 
muscle for twenty-four hours in a half-per-cent, 
solution of hydrochloric acid, and then tease it, we 
find that the fibres, instead of breaking up longi- MUSCULAR TISSUE. 
97 
tudinally into fibrillae, break across transversely into 
thin discs. We thus see that, by breaking up in 
these two directions, we may conceive of the fibre 
as being resolvable into a multitude of tiny pris- 
matic structures, which are called sarcous elements. 
The central portion of each prism or sarcous ele- 
ment is occupied by a dark portion, while at each 
end is a lighter zone. The light and dark zones of 
the sarcous elements, when the latter are grouped 
together, form the alternating light and dark bands 
of the fibres. It is believed by many observers 
that the sarcous elements are definite and independ- 
ent structures, in which the dark portion is the 
contractile element, and that they are joined 
together side by side and end to end by peculiar 
cementing substances. 
In addition to these markings on the fibres, if 
high magnifying powers are used and the fibre is in 
a state of extension, a fine line is seen crossing the 
fibre through the centre of the light transverse 
band ; this corresponds with the dividing line 
between the ends of the sarcous elements, and is 
called Krause's line. Under favorable conditions 
the dark band is also seen to be crossed by a line 
called Hensens line, whose nature is as yet but 
imperfectly understood. 
All of the above-described structural features of 
the muscular fibres are much more distinct after 
treatment with chemical agents, and after the 98 
NORMAL HISTOLOGY. 
death of the tissue; the longitudinal striation is 
not visible during life, and the distinct separation 
of the primitive fibrillae and discs can only be 
accomplished by chemical means. We can see the 
various markings with sufficient clearness, on the 
fresh or living muscle, to convince ourselves that 
marked optical differences, at least, exist in different 
parts of the fibres; but that the living fibre is made 
up of distinct elements, having the structure which 
we see in the isolated or partially isolated sarcous 
elements, although probable, is by no means proven, 
since this isolation by chemical means may signify 
only a tendency to break up in certain directions, 
and not a definite, preexisting separate structure. 
2. The nuclei, which in the mammalia lie upon 
the surface of the fibres, and directly beneath the 
sarcolemma, in the amphibia, fishes, and certain 
birds, also embedded within the contractile substance, 
are usually large, flat, and ellipsoidal in shape, con- 
tain nucleoli, and lie with their long axes coinci- 
dent in direction with the axis of the fibres. They 
are irregularly scattered along the fibre, and a small 
amount of granular matter is usually seen in their 
immediate vicinity. 
3. The sarcolemma, a delicate, structureless, 
membranous sheath, is so thin, and so closely en- 
closes the contractile substance and nuclei, that we 
cannot usually see it, unless we separate it by 
artificial means from the underlying structures. MUSCULAR TISSUE. 
99 
Where the muscular fibres join tendons, the sarco- 
lemma ends in the form of a pointed or rounded 
blind sac, to which the tendon-fibres are attached. 
The muscular fibres lie closely packed together, 
their ends lapping over on to adjacent fibres, and 
forming bundles which are enclosed in sheaths of 
connective tissue. Such bundles are again grouped 
to form larger bundles, and thus the larger and 
smaller muscular bellies and bands are formed. 
Arteries enter the muscular bundles and break up 
into capillaries, which run along the fibres, forming 
a long and narrow-meshed net. Motor nerves also 
pass into the muscles, divide and subdivide, and 
terminate, at the surface of the individual fibres, in 
structures called motor end plates. 
PRACTICAL STUDY. 
Fresh Muscle.—A very small bit is dissected off, with 
as little stretching as possible, from one of the voluntary 
muscles of a recently-killed mammal, and carefully teased 
longitudinally in salt solution. In such a preparation the 
transverse bands and indistinct longitudinal striations will 
be seen, and here and there, where the needles have 
pressed on the fibres, the contractile substance may be 
seen to have been broken across and the broken ends to 
have retracted within the sarcolemma, leaving the latter 
as a clear and sometimes folded membrane stretching 
across the interval. At the cut ends of the fibres the 
contractile substance will often be seen swelling and ex- 
truding from the sarcolemma in the form of an obscurely NORMAL HISTOLOGY. 
striated fungiform mass. Here and there nuclei are seen ; 
but they maybe brought much more clearly into view by 
allowing a drop of two-per-cent, acetic acid to flow under 
the cover-glass ; then the contractile substance swells and 
becomes transparent, the striations becoming indistinct 
as the somewhat shrunken nuclei become more clearly 
defined. 
Muscular Fibres Hardened with Osmic Acid.— The 
above-described finer structural details of the muscle 
fibres are much more evident when they are in a state of 
extension than when contracted. We may render this 
condition permanent for study, by the following method : 
the skin is quickly removed from the leg of a freshly-killed 
animal (rabbit or dog), and one of the large muscles of 
the thigh is forcibly extended with the fingers ; the canula 
of a hypodermic syringe is then thrust into the muscle, 
and an interstitial injection is made of a mixture of equal 
parts of i-per-cent, solution of osmic acid and strong 
alcohol. This fluid, in three or four minutes, fixes the 
fibres in the extended condition. A small bit of that por- 
tion which has become brown is now snipped off and 
carefully teased and mounted in a mixture of equal parts 
of glycerin and water. In such a preparation some of the 
fibres frequently escape extension, in which case, the 
marked difference may be observed between the extended 
and non-extended condition of the fibres. 
Sections of Hardened Muscle.—The details of the struc- 
ture of muscular fibres, as well as their grouping and 
relation to the connective tissue, may be well studied in 
sections from hardened muscle. For this purpose the 
tongue of some animal—such as the dog—is well suited, MUSCULAR TISSUE. 
since here we have short muscular fibres running in vari- 
ous directions and attached to tendons, and we see in a 
single transverse section of the organ, at once, longitudi- 
nal and transverse sections of the fibres. The tongue of 
a dog is hardened in bichromate of potassium and 
alcohol, and transverse sections through the anterior half 
of the organ are stained double and mounted in glycerin. 
In muscular tissue thus hardened, the primitive fibrillse 
are loosened from one another, and in some parts of the 
specimen are usually more or less separated. The con- 
tractile substance, morever, usually shrinks away some- 
what from the sarcolemma, which then appears in the 
transverse section as a delicate ring around the fibre. 
Blood-vessels are seen in the above preparation, but 
they may be much better demonstrated in longitudinal 
sections of a muscle whose vessels have been injected. 
I. b. INVOLUNTARY STRIATED OR HEART-MUSCLE. 
In mammalia, the heart-muscle differs in several 
important structural features from the voluntary- 
muscle. 
The contractile substance has essentially the 
same structure as the latter, but, instead of being 
arranged in the form of elongated, unbranched cylin- 
ders or fibres, without distinct cell-structure, in the 
heart-muscle the fibres send off at frequent intervals 
short, narrow processes, which join neighboring 
fibres, forming a narrow- and long-meshed net. 
Further, the fibres which, owing to the numerous 
anastomoses, are very irregular in form, are made up 102 
NORMAL HISTOLOGY. 
of distinct segments or cells, each segment being 
cemented at the ends to its neighbors, and furnished 
with a flat, elongated, ovoidal, or often rectangular 
nucleus. In the vicinity of the nuclei we usually see 
a certain amount of granular material or pigment 
particles. The nuclei instead of lying, as in the 
voluntary muscles, at the surface of the contractile 
substance, are embedded within it. We are unable, 
in heart-muscle to demonstrate a sarcolemma. The 
fibres are grouped in bundles, which are enclosed in 
connective tissue and supplied with blood-vessels 
and nerves. 
Sections of Heart-muscle.—A bit of the heart of man, or 
any mammal, should be hardened in Muller’s fluid and 
alcohol. Longitudinal and transverse sections are stained 
double and mounted in glycerin. 
PRACTICAL STUDY. 
Teased Heart-muscle.—To demonstrate the segments 
or cells of which the heart-fibres are composed, a mod- 
erately thin bit of fresh heart-muscle is put for twenty- 
four hours into a dilute solution of chromic acid (i to 
5,000), then carefully washed with pure water and stained 
with picro-carmine. It is then teased on a slide and 
mounted in glycerin, to which a little formic acid has 
been added (1 to 100). The formic acid renders the tis- 
sue more transparent, and brings more clearly into view 
the narrow, jagged lines of strongly refractive substance 
which indicate the longitudinal boundaries of the muscle- 
cells. CHAPTER VII. 
NERVE-TISSUE. 
The primary structural element in nerve-tissue is 
the nerve-cell. Nerve-cells have the most diverse 
forms, and always possess one or more branching or 
unbranched processes. In certain cells the un- 
branched processes are extremely long, become as- 
sociated with other tissue elements, and constitute 
the nerve-fibres. Both nerve-cells and their processes, 
nerve-fibres, are enclosed and supported by pecu- 
liarly arranged connective tissue, and supplied with 
blood and lymphatic vessels. The nerve-fibres form, 
for the most part, the white matter of the nerve- 
centres and the peripheral nerves, while the cells 
enter largely into the composition of the gray mat- 
ter. In studying nerve-tissues, we have then to 
consider: 
I. Nerve-fibres, and the supporting connective- 
tissue structures, with their accessories. 
11. Nerve-cells. 
These are of two kinds: A, medullated, and B, 
non-medullated. This distinction corresponds with 
I. NERVE-FIBRES, ETC. 
103 104 
NORMAL HISTOLOGY. 
the physiological and anatomical classification of 
nerve-tissues into those of the cerebro-spinal and 
the sympathetic systems ; the medullated belonging 
to the former, the non-medullated to the latter. 
A. Medullated Nerve-fibres. 
If we disregard for the moment the structure of 
these nerves at their point of origin in the nerve- 
centres, and at their termination in the periphery, 
and study their structure as it is seen in the con- 
tinuity of any of the larger or smaller nerves, we 
find that the individual fibres present three distinct 
structural elements; I, the axis cylinder; 2, the 
medullary sheath; 3, the neurilemma. 
1. Running through the axis of the fibre is a 
cylindrical, with high powers, delicately longitudi- 
nally striated structure—the axis cylinder. This 
is believed to be the essential nerve-element of 
the fibre—the process of the nerve-cell, from which 
it passes without break of continuity to the periph- 
ery ; and it is probable that the longitudinal stri- 
ations are the expression of its composition from 
still finer primitive fibrils, which, as we shall see 
when we study the nerve-cells, seem to be continued 
on into the cell-body itself, within the nerve-cen- 
tres. 
2. Closely surrounding the axis cylinder is a tube 
or sheath of varying thickness—the medtUlary 
sheath—composed of a white, semi-fluid, translucent, 
strongly refractive substance, called myelin, which NERVE-TISSUE. 
105 
undergoes rapid changes after death, or on removal 
from the animal, and swells and assumes a multitude 
of bizarre forms on addition of water* it is soluble 
in alcohol, chloroform, and ether; and, like fat, is 
hardened and turned black under the action of osmic 
acid. The medullary sheath does not form a con- 
tinuous tube, but at tolerably regular intervals is 
separated into segments. 
3. The rieurilemma or sheath of Schwann is an 
extremely thin, structureless, membranous tube, 
which tightly encloses the medullary sheath, and, 
like the latter, is broken up into segments. At the 
ends of the segments is a constriction around the 
fibre, at the expense of the medullary sheath, and 
the ends of the neurilemma segments are joined 
together by a thin layer of cement substance, which 
extends inward to the axis cylinder. There is rea- 
son to believe that the neurilemma extends inward 
and between the medullary sheath and the axis 
cylinder, entirely enclosing the segments of the me- 
dullary sheath. 
Within each neurilemma segment, called inter annu- 
lar segment, and about midway between the constric- 
tions, lies a flattened, elongated, elliptical nncleus. 
We may regard the neurilemma segments, with 
their nuclei, as cylindrical cells cemented together, 
end to end, enclosing the segments of the medullary 
sheath and surrounding the axis cylinder, the latter 
passing uninterruptedly through the axis of the seg- NORMAL HISTOLOGY. 
ments. In addition to these structural features, we 
find, on examining with high powers, irregularly 
scattered along each interannular segment, delicate 
oblique lines or fissures, called the incisures of 
Schmidt, which seem to pass from the neurilemma 
at the surface inward to the axis cylinder, obliquely 
through the medullary sheath. Their significance 
is not, as yet, definitely determined. Medullated 
nerve-fibres vary greatly in diameter. 
Connective Tissue of the Nerves.—The nerve-fibres 
are bound together by connective tissue, to form 
larger and smaller nerve-fascicles, which, singly or in 
bundles, we usually call simply nerves. If we follow 
the nerves outward toward their peripheral termina- 
tions, we find that they divide and subdivide, be- 
coming, as they do so, smaller and smaller, until we 
finally come to nerves which consist of a single 
fibre. These single nerve-fibres do not lie free in 
the tissues, but are enclosed in a distinct sheath, 
called Henle's sheath, which is a tube formed of a 
single layer of endothelial cells, placed edge to edge, 
and cemented together. Between the sheath and 
the nerve-fibre is a narrow space, which, under nor- 
mal conditions, is filled with lymph. 
Having become acquainted with this simple struc- 
ture of the single terminal nerves, let us follow them 
backward. We find, as we do so, that as they be- 
come larger by the junction of several fibres a small 
amount of fibrillar connective tissue appears be- NERVE-TISSUE. 
107 
1 ween the fibres within Henle’s sheath, and that the 
latter becomes attached to the surrounding struc- 
tures by a layer of connective tissue. Finally, when 
we arrive at the larger nerve-trunks, we find that in 
each the connective tissue presents itself in three 
ways: 
1. It forms a distinct sheath, which, although the 
analogue of Henle’s sheath, has a much more com- 
plicated structure, and is called the lamellar sheath. 
This is composed of several concentric lamellae, each 
of which is formed of a fenestrated membrane of 
fibrillar connective tissue containing granules of 
elastic-tissue substance, and covered with endothe- 
lial cells. The lamellae are connected by oblique 
fibres, which pass from one to the other, binding 
them more or less firmly together. The whole forms 
a compact sheath, closely investing the fascicle of 
nerve-fibres. 
2. Outside of the lamellar sheath, and joining it 
to adjacent structures—to neighboring nerve-fasci- 
cles, if the nerve-trunk is composed of several of 
these, as is the case in many large nerves—we find 
loose fibrillar connective tissue with flattened, ir- 
regular-shaped cells—-like those found in the loose 
subcutaneous connective tissue-—reinforced by elas- 
tic fibres, and often containing fat-cells. The fibril 
lated and elastic fibres, especially in the immediate 
vicinity of the lamellar sheath, usually run in a di- 
rection approximately parallel with the axis of the NORMAL HISTOLOGY. 
nerve. This tissue is called the peri-fascicular connec- 
tive tissue. 
3. We find within the lamellar sheath and be- 
tween the nerve-fibres composing the fascicle, in the 
first place, prolongations inward of the tissue com- 
posing the lamellar sheath ; and, second, fine fibril- 
lated fibres and flattened cells which lie in the 
interstices between the nerves and fibres. This tis- 
sue is called the intra-fascicular connective tissue. 
Blood-vessels penetrate the lamellar sheath of the 
medium-sized and larger nerves, and a very long- 
meshed and abundant capillary net-work is formed 
in the intrafascicular connective tissue. Lymphatic 
channels and spaces are also abundant within the 
nerves, so that the fibres are bathed in nutritive 
fluids. 
Termination of Medullated Nerve-fibres 
1. In the Nerve-centres.—We find in the nerve- 
centres, nerves which have no neurilemma, and 
others in which both neurilemma and medullary 
sheath fail—the so-called naked axis-cylinders; we 
find, further, extremely delicate filiform structures 
which are believed to be the primitive nerve-fibrils. 
The axis-cylinders of the nerves being, as above 
stated, processes of nerve-cells, the nerve-fibres, as 
we trace them back into the centres, must sooner or 
later join cells. Their exact mode of connection 
with the cells is not in all cases sufficiently well un- NEK VE- TISSUE. 
derstood ; but it is believed that they either join 
the cells in the form of naked axis-cylinders, or, in 
other cases, that the axis-cylinders break up into 
their constituent primitive fibrils before entering the 
cells. 
2. In the Periphery.—The peripheral termination 
of nerves is a subject which presents extreme diffi- 
culties to the histologist, and with few exceptions 
the exact way in which this occurs is unknown. The 
motor nerves, which are distributed in the voluntary 
striated muscles, terminate in distinct, nucleated, 
finely granular structures on the surface of the 
fibres, called end plates; those which go to the 
smooth muscle tissue break up into fine plexuses, 
from which fibrils seem to pass either to the individ- 
ual muscle-cells or to the surface of cell-bundles. In 
the case of some of the nerves of special sense, we 
have elaborate nerve-structures such as the retina, 
auditory apparatus, etc. Again, we find the nerves 
ending in small, complex, isolated bodies, such as the 
so-called tactile corpuscles, etc. In some cases as 
the nerves approach their peripheral terminations, 
they lose the medullary sheath and neurilemma, and 
the axis-cylinder breaks up into very numerous, 
exceedingly delicate fibrils which sometimes form in- 
tricate plexuses; some of the fibrils appear to 
terminate by free extremities; others, it is probable, 
end in single cells of various kinds ; but the whole 
subject of peripheral nerve-endings is far too intrk NORMAL HISTOLOGY. 
cate and too little understood, to demand more than 
a passing mention in a course of study as elemen- 
tary as that which now engages us. 
b.—Non-medullated Nerve-fibres. 
These are also called fibres of Remak. Unlike 
the nerve-fibres which we have just been studying, 
they possess no medullary sheath and no neuri- 
lemma. They are simply grayish translucent cords 
of varying diameter ; they are indistinctly longitu- 
dinally striated, and are intimately connected with 
one another by frequent inosculations. The fibres 
seem to divide and send off oblique branches to join 
neighboring fibres. Flattened, elongated nuclei lie 
at frequent intervals upon the surface of the fibres. 
These fibres considerably resemble, in their general 
appearance, the fibrillated fibres of ordinary connec- 
tive tissue, but careful examination shows them to 
be entirely distinct structures. 
They are grouped in bundles to form nerves, 
sometimes alone, but very frequently in connection 
with medullated nerve-fibres. Thus, in the pneumo- 
gastric, we find a considerable part of the fibres to 
be non-medullated, and intimately bound in, by the 
intrafascicular connective tissue, with medullated 
fibres. The non-medullated fibres originate in 
nerve-cells of a peculiar structure, to be presently 
described ; but of their peripheral terminations we 
know almost nothing. NERVE-TISSUE. 
11. NERVE-CELLS. 
Nerve-cells, or ganglion-cells, as they are frequently 
called, although presenting the greatest diversity in 
form, have yet some quite distinctive characters in 
common. The cell-body is finely granular and 
delicately striated, often containing pigment-gran- 
ules. The nucleus is large, well-defined, vesicular in 
appearance, and usually contains a large shining 
nucleolus. They all have at least one process, most 
of them have more; and they are hence often 
classified as unipolar, bipolar, multipolar ganglion- 
cells. The above-mentioned striations in the cell- 
body are often seen to continue out into the 
processes, and are apparently continuous with the 
striations or fibrils of the axis-cylinder of the 
nerves. 
In many nerve-cells, especially in the spinal cord, 
we recognize two distinct kinds of processes: first, 
those which, soon after leaving the cell, divide and 
subdivide until they become extremely fine and 
delicate, and, in some cases, seem to join equally 
fine processes of other cells—such delicate cell- 
processes make up a considerable portion of the 
gray matter of the cord, and are called branching 
processes ; second, such as pass off from the cell, and, 
without dividing, presently are surrounded by a 
sheath of myelin, and become medullated nerve- 
fibres ; the latter are called axis-cylinder processes. NORMAL HIS TOLOGY. 
Nerve-cells vary greatly in size, and although the 
forms which they present are most diverse, we yet 
find that a considerable proportion of those found 
in different parts of the nerve-centres have certain 
broadly typical forms. Thus, among the cells in 
the gray matter of the spinal cord, we find larger 
and smaller fusiform or spheroidal branching cells, 
and, which are more characteristic, large, irregular- 
shaped cells, with several branching processes and a 
well-defined axis-cylinder process. In the cortex of 
the cerebrum, while we find variously shaped 
larger and smaller cells, we find also characteristic 
pyramidal cells of varying size, which give off 
processes from both the base and apex. In the 
cerebellum, we find just at the inner edge of the 
gray cortical matter, irregular globular or ovoidal 
cells, which, from the side toward the surface of the 
brain, send off one or two branching processes; on 
the opposite side we can usually demonstrate the 
commencement of a single delicate process, which 
is supposed to correspond to the axis-cylinder 
process, though, since it almost invariably breaks off 
near the cell in the attempt to isolate the latter, its 
nature is not yet definitely determined. These 
cells are called Purkinje s cells. 
The ganglion-cells of the sympathetic are usually 
globular or ovoidal, and are peculiar in that each 
cell is surrounded by a distinct capsule of connective 
tissue, lined with flattened cells, resembling endo- NER VE- TISSUE. 
113 
thelium. They have one or more processes which 
pierce the capsule and become non-medullated 
nerve-fibres. 
Fresh Nerve.—A bit of fresh nerve—the sciatic of the 
frog answers very well—should be carefully and rapidly 
teased apart longitudinally, in one-half-per-cent, salt so- 
lution—care being taken to pull apart the fibres from the 
ends, so as to break them as little as possible,—and cov- 
ered ; pressure from the cover-glass being avoided by 
placing a bit of paper or hair beside the specimen. The 
nerve-fibres present, if examined at once, in many parts, a 
sharp and regular double contour, which is their normal 
appearance, and along their course the constrictions and 
nuclei may here and there be seen. The axis-cylinder 
and neurilemma are for the most part invisible ; the for- 
mer owing to the lack of transparency in the medullary 
sheath, the latter because of its extreme thinness and 
close contact with the medullary sheath. Very soon, at 
once in some parts of the specimen, the contours of the 
fibres will be seen to become irregular, the myelin shrink- 
ing away at some parts from the neurilemma, and 
swelling out at others. At the severed ends of the fibres 
the myelin will be seen welling out from the neuri- 
lemma, and breaking off into the fluid in irregular glob- 
ular or contorted masses. 
PRACTICAL STUDY. 
After the swelling and irregular breaking up of the 
myelin has occurred—this may be hastened by allowing 
water to run under the cover-glass—the neurilemma may 
be seen here and there stretching across between the va- 114 
NORMAL HISTOLOGY. 
ricosities formed by the swollen myelin, and either at the 
broken ends of the fibres or along their course, the axis- 
cylinder may occasionally be seen. 
Nerve-fibres Treated with Osmic Acid.—The most 
complete demonstration of the nerve-fibre may be ob- 
tained by treatment with osmic acid. This agent fixes 
the myelin and other constituents of the fibre nearly in 
their normal form, staining the myelin black. In apply- 
ing this agent it is necessary to maintain the nerve in a 
state of gentle tension, because it is otherwise somewhat 
contracted and distorted. This is done by gently stretch- 
ing the nerve—the sciatic of the rabbit will answer—along 
a bit of wood which has been whittled away at one side, 
so that the nerve may lie free. It is fastened by the ends 
to the wood by threads. The nerve thus prepared is im- 
mersed for twenty-four hours in an aqueous solution of 
osmic acid (i to 100), then washed, and a small bit care- 
fully teased apart longitudinally in glycerin. In such a 
preparation nearly all the structures in the fibre can be 
readily seen : the constrictions and nuclei, the medullary 
sheath stained black, the incisures of Schmidt, and where, 
as will almost always occur in some parts of the specimen, 
the medullary sheath has been broken across, or the seg- 
ments pulled asunder, or the myelin has contracted at 
the constrictions, the neurilemma and axis-cylinder. Not 
infrequently, if the teasing has not been very carefully done, 
the segments of the medullary sheath are broken across 
in many places and separated, giving the fibre a beaded 
appearance. 
Transverse Sections of Nerves Stained with Osmic Acid. 
—A nerve treated as above with osmic acid is not firm NEK VE- TISS UE. 
115 
enough to permit the making of thin sections, and should 
be hardened by what is known as the gum embedding 
method,\ as follows : a bit of the nerve, after the osmic 
acid treatment, is immersed for twenty-four hours in al- 
cohol, soaked for a few moments in water, to remove the 
alcohol, and immersed for twenty-four hours in a syrupy 
solution of gum-arabic, then put again for twenty-four 
hours in alcohol. By this process the gum is precipitated 
by the alcohol in solid form in the interstices of the fibres, 
giving it sufficient consistence for cutting. The sections 
(which must be very thin), either stained with picro-car- 
mine or unstained, are mounted in glycerin. In such a 
preparation the uncolored axis-cylinder is seen sur- 
rounded by a black ring, the medullary sheath, and here 
and there the nuclei of the neurilemma are seen at the 
edge of the fibres. The connective tissue surrounding 
the fibres has a grayish color. The nerve-fibres will be 
seen to have varying diameters and to present marked 
differences in form, some of them depending upon artifi- 
cial changes, others upon the difference in level at which 
the fibres have been cut across. 
Transverse Sections of Nerves Preserved in Chro?nic 
Acid.—Bits of the sciatic nerve from the rabbit or any 
other mammal should be lightly stretched along a bit of 
wood and placed in a solution of chromic acid (i to 500); 
in two weeks it is washed and transferred to alcohol. It 
is now embedded in gum (see above),* and thin transverse 
sections made and stained double and mounted in balsam. 
In such preparations the general relation of connective 
tissue to the nerve-fibres is well seen. 
Nerve-fibres Treated with Nitrate of Silver,—By this 
* Better in ceiloidin. NORMAL HISTOLOGY. 
method we obtain hints concerning the structure of nerves 
which are of no little significance from a physiological 
point of view. A fresh nerve is slightly teased apart on 
a slide, a large drop of a one-half-per-cent, solution of 
nitrate of silver added and allowed to remain for four 
minutes ; this is washed off with one-half-per-cent, salt 
solution, the specimen transferred to a drop of glycerin 
on another slide, the fibres carefully teased apart, and 
covered. The preparation is now exposed to sunlight or 
diffuse daylight until it becomes brown. If now ex- 
amined, at tolerably regular intervals along the fibre, tiny 
brown or black crosses, called Ranviers crosses, will be 
seen ; the transverse arm of the cross being the stained 
cement substance between the neurilemma segments at 
the constrictions ; the longitudinal arm, which coincides 
with the axis of the fibre, and which is longer or shorter, 
depending upon the length of time to which the fibre was 
exposed to the action of the silver, is the axis-cylinder. 
If the specimen be allowed to remain longer than the 
above time in contact with the silver, the longitudinal arm 
of the cross will be longer. 
It is to be observed that the axis-cylinder is first stained 
at that part which passes through the constrictions, and 
not along the segments. Certain other soluble substances 
which stain the axis-cylinder comport themselves in the 
same way. We infer from this that at the constrictions 
certain substances in solution can pass into the fibre and 
come in contact with the axis-cylinder, or the nerve- 
element proper of the fibre. This inference is significant 
in connection with the nutrition of the nerves, since we 
are justified in assuming that nutritive substances in NE R VE- TISS UE. 
117 
solution may pass also to the axis-cylinder in the same 
way. 
It is not improbable that the constrictions serve yet an- 
other important purpose. The myelin of the medullary 
sheath being a semi-fluid substance—perhaps serving 
either to isolate the axis-cylinder or protect it from ex- 
ternal violence—it would inevitably tend to gravitate to 
the lower parts of the nerves, were it not that it is held in 
position by being enclosed, so to say, in cylindrical cases, 
i. e., the neurilemma-cells, between the constrictions. 
The non-7Jiedullated nerve-fibres may be demonstrated 
in connection with the sympathetic ganglion-cells ; see 
below. 
1. Nerve-cells : a. Spinal Cord.—Small bits of the gray 
matter from the spinal cord of man, or from the ox or 
sheep, should be put for ten days in a dilute solution of 
chromic acid (one to five hundred), and then carefully 
shaken in a test-tube with water colored lightly with car- 
mine ; when the bits have become thoroughly broken up 
into small particles, the tube is allowed to stand for a day 
or two, until the particles which have settled to the bot- 
tom are sufficiently stained. The supernatant fluid is 
then decanted, and with a glass tube a small drop of the 
disintegrated tissue is conveyed to a drop of glycerin on 
a slide and covered, pressure on the cells being avoided 
in the usual way. If the first preparation does not con- 
tain the required cells, others should be made. In this 
way, if the shaking be carefully done, the ganglion-cells 
are freed to a considerable degree from the surrounding 
parts, and such may be found as present numerous long 
branching processes, as well as the axis-cylinder process. 118 
NORMAL HISTOLOGY. 
In addition to the cells, such specimens present frag- 
ments of connective-tissue, bits of naked axis-cylinders, 
and medullated nerve-fibres, myelin-droplets, etc.* 
b. Brain.—In the way above described, cells should be 
prepared from the gray cortical portion of the cerebrum 
and cerebellum. 
c. Sympathetic.—For the demonstration of these cells, 
and the fibres connected with them, the frog answers 
very well. The animal having been killed by breaking 
up the medulla, the abdominal cavity is opened, and the 
intestines and liver carefully removed ; the aorta will 
then be seen lying along the vertebral column. The 
sympathetic ganglia and nerves lie along the walls of the 
aorta, and in the tissue surrounding the origin of the 
spinal nerves. The head and forelegs should now be 
cut off close behind the latter, and the hind legs severed 
close to the body ; the trunk is then laid in a small dish, 
and covered with equal parts of one-per-cent, solution of 
osmic acid, alcohol, and water. The dish is covered and 
set aside for twenty-four hours, when the aorta, together 
with the tissue surrounding the commencement of the 
spinal nerves, is dissected off in a single piece, spread on 
a slide, and examined with a low power. Groups of sym- 
pathetic nerve-cells are seen here and there in the speci- 
men, and are readily distinguished by the orange color of 
the cells : one or two of them are to be isolated and 
freed as much as possible from the enclosing tissue, care- 
fully teased apart on a slide, stained lightly with hsema- 
toxylin and then with eosin, and mounted in glycerin. 
Successful preparations will show not only the nerve- 
cells and non-medullated nerve-fibres, but also the con- 
nection of the tAvo within the capsule. 
* Neuroglia or “ spider cells ” may also be seen. See Appendix, 
p. 254- CHAPTER VIII. 
BLOOD-VESSELS—LYMPHATIC VESSELS. 
BLOOD-VESSELS. 
Blood-vessels are of three kinds: arteries, veins, 
and capillaries. Although merging without sharp 
demarcation into one another, these vessels, in their 
typical forms, present distinct differences in struc- 
ture. The capillaries being the simplest, it will be 
convenient to commence with them. 
If we examine a capillary vessel, either fresh or 
after it has been in preservative fluids, it presents 
the appearance of a narrow tube, with very thin, 
homogeneous walls, in which, at frequent intervals, 
elongated nuclei are embedded, their long axes 
being parallel with the axis of the tube. If, how- 
ever, we inject the vessels with a dilute solution of 
nitrate of silver, and expose them to the light, we 
find that the inside of the tube is divided by narrow 
black lines into elongated, irregular-shaped spaces; 
and if we then stain the specimen with haematoxy- 
lin, we find that a nucleus lies in each space. The 
walls of the capillaries are, then, not formed by a 
homogeneous membrane, but made up of cells having 
the character of endothelium. The capillaries are 
119 120 
NORMAL HISTOLOGY. 
endothelial tubes. This layer of endothelial cells, 
which alone forms the walls of the capillaries, is 
found lining all the other blood-channels, arteries 
and veins, as well as the heart. In the blood-vessels 
it is called the intima. 
If, now, we follow the capillaries in a direction 
toward the arteries, we find that the connective 
tissue in which they lie is arranged in the form of a 
thin layer along their walls. This layer, which is 
also present in all arteries and veins, is called the 
adventitia. Almost as soon as we find the adven- 
titia, we notice another layer between it and the 
intima, formed of a single row of smooth muscle- 
cells, or of scattered cells, wound transversely or 
obliquely around the vessel. This layer is called 
the media or musculosa, and a vessel having these 
three simple layers in its walls is called an arteriole. 
In these three layers, intima, media, and adventitia, 
we have the types of all the layers which occur in 
the walls of the largest and most complicated blood- 
vessels. The individual layers become, indeed, 
more complex in structure; but, with the exception 
of elastic elements, no new tissues appear. 
Turning now to a larger artery—the radial, for 
example—and examining the various layers in its 
walls, we find that the intima is no longer formed 
of a simple endothelial tube, but that outside of 
this a new layer has appeared, composed of ill- 
defined fibrillated and of elastic fibres, among which BLOOD- VESSELS. 
121 
lie large, flattened branching cells. This layer is 
called the intermediary layer of the intima, and is 
sharply separated from the media by a fenestrated, 
elastic membrane, called the membrana elastica in- 
timce, which in contracted vessels is usually folded. 
The media presents here quite a thick layer of 
smooth muscle-cells, passing transversely around 
the vessel, and among these we find a few elastic 
fibres, which are connected with the elastic elements 
in the intima and adventitia. The adventitia is 
thicker, and consists chiefly of fibrillar connective 
tissue with elastic fibres. 
In the larger arteries, such as the carotids, aorta, 
etc., we find that the individual layers are consid- 
erably less sharply defined. The three layers of the 
intima are much less distinct; in the media the 
elastic tissue is very abundant, taking the place, to 
a considerable extent, of the muscular elements; it 
is arranged in irregular lamellae and fibres, between 
which lie fibrillated fibres, and connective-tissue and 
smooth muscle-cells, the latter no longer all lying 
uniformly transversely to the axis of the vessel. In 
the adventitia also of the large vessels the elastic 
elements are very numerous, being most abundant 
in the vicinity of the media. In the adventitia of 
some of the large vessels, smooth muscle-cells occur, 
arranged usually with their long axes parallel with 
the axis of the vessel. 
The walls of the veins, like those of the arteries, 122 
NORMAL HISTOLOGY. 
consist of three layers, and these layers have in 
general an analogous structure; but they are 
neither as distinct, nor are their structural features 
as constant, as those of the arteries. Moreover, we 
find that veins of the same calibre present, in dif- 
ferent parts of the body, marked differences in 
structure, and, unlike the arteries, the thickness of 
their walls is not uniformly proportional to the 
calibre of the vessel. In general we may express 
the structural difference between veins and arteries 
by saying that in the walls of the former the elastic 
and muscular elements are much less, while the 
connective-tissue elements are more abundant, than 
in the walls of the latter. Now, since the muscular 
and elastic elements are the chief constituents of 
the media, and the fibrillar connective-tissue ele- 
ments, of the adventitia, we find, in general, that in 
the veins the media is less, while the adventitia is 
more developed. The intermediary layer of the 
intima is entirely absent in small veins; in many of 
medium size it appears, and is again absent in the 
largest vessels. In some veins, such as those of the 
bone, central nervous system, retina, etc., the mus- 
cular elements are almost or entirely absent. In 
certain other veins, on the contrary, such as the v. 
portarum, v. renalis, the adventitia contains a great 
abundance of muscular elements arranged parallel 
with the axis of the vessel. 
The walls of the larger arteries and veins contain 
blood and lymph-vessels, called vasa vasorum. BLOOD-VESSELS. 
123 
The valves of the veins consist of bundles of fibril- 
lar connective tissue arranged to form a membran- 
ous projection from the walls of the vessels—the 
bundles being arranged, in general, in a direction 
parallel with the free edge of the valve. They con- 
tain also a net-work of elastic fibres, which, at that 
surface of the valve which is exposed to the blood- 
current, form a dense layer like the intermediary 
layer of the vein-wall itself. The whole free surface 
is covered with endothelium like that lining the 
general surface of the vessel. 
ENDOCARDIUM AND VALVES OF THE HEART. 
The endocardium, which differs somewhat in thick- 
ness and structure in different parts of the heart, 
consists, in general, of a membranous expansion of 
fibrillar connective tissue, with elastic fibres and 
smooth muscle-elements, which lines the cavities of 
the heart, and is covered on its free surface with a 
layer of endothelial cells. 
If we examine sections made perpendicular to 
the surface of the endocardium, we find that just 
beneath the endothelium is a layer of fibrillar con- 
nective tissue, with flattened cells, reinforced by a 
net-work of elastic fibres, which become coarser and 
more abundant in that portion of the layer lying far- 
thest from the heart-cavities. In this layer are smooth 
muscle-cells running in various directions. Outside 
of this layer, and joining it to the muscular tissue 124 
NORMAL HISTOLOGY. 
proper of the heart, is a layer of loose fibrillar con- 
nective tissue, in which the blood, lymphatic ves- 
sels, and nerves lie embedded. 
The valves of the heart consist of fibrillar connec- 
tive tissue, arranged in membranes or fascicles, and 
associated with elastic tissue, the latter being most 
abundant at the free surfaces of the valves; and 
here it is present in the greatest quantity and 
density on the surface which is most directly ex- 
posed to the current of blood—that is, on the auric- 
ular surfaces of the tricuspid and mitral, and on 
the ventricular surfaces of the aortic and pulmonary 
valves. The elastic elements are also more abun- 
dant in the valves of the left than of the right side 
of the heart. The firmness and capacity for re- 
sistance of the elastic tissue being borne in mind, 
the significance of its distribution in the valves will 
be readily perceived; where they are the most ex- 
posed to the impact and pressure of the blood, 
there they are the most firm and dense. 
LYMPHATIC VESSELS. 
The larger lymphatic vessels have a structure 
quite similar to that of the veins, and like the latter 
they are supplied with valves. They approach the 
arterial type, however, in that the muscular fibres 
are quite abundant in proportion to the thickness 
of the walls, although the walls themselves are very 
thin in proportion to the size of the lumen. Fol- LYMPHATIC VESSELS. 
125 
lowing the larger lymphatics toward the periphery, 
we find that they pass over into irregular-branching 
and pouching channels, the walls of which consist 
of a single layer of endothelial cells, whose edges 
are very sinuous, dovetailing into one another like 
the pieces of a child’s puzzle-map. These channels 
are called lymphatic capillaries. Between these and 
certain spaces or lacunae in the tissues—those, for 
example, in which the connective-tissue cells lie (see 
page 44)—there seems to be a direct communica- 
tion, by means of which fluids, and probably formed 
elements, such as blood-cells, pass over from the 
blood into the lymphatic vessels. 
PRACTICAL STUDY. 
Capillaries.—The general appearance of the capillaries, 
as well as of the smaller arteries and veins, is best seen in 
those parts in which the vessels are surrounded by but 
little tissue, as in thin membranes such as the mesentery 
or pia mater. A slice about an inch thick should be 
made from the surface of the cerebrum and laid for 
twenty-four hours in Muller’s fluid.1 A small fragment 
from that part of the pia which dips into the sulci should 
now be carefully separated from the brain substance, 
stretched on a bit of thin cork, and fastened with pins. It 
is then laid for twenty-fours each, in dilute and strong 
alcohol, and finally stained in picro-carmine and mounted 
in glycerin ; or stained double and mounted in balsam. 
1 The normal relations of the parts are much better preserved by 
a preliminary hardening in this way before the pia is removed from 
the brain, than if it is removed while quite fresh. 126 
NORMAL HISTOLOGY. 
In such a preparation, although we see the elongated 
nuclei in the capillary wall, we cannot, as a rule, make 
out the outlines of the cells. To accomplish this we have 
recourse to the use of dilute solutions of nitrate of silver. 
This can be applied by immersing some thin membrane, 
such as the mesentery, for an hour in a solution of nitrate 
of silver (1-500), brushing off the endothelium from the 
surface, and exposing the specimen in water to the light, 
until it becomes brown. Or, what is better, the entire 
vascular system of a small animal, such as a frog, may be 
first rinsed out with water through a canula introduced 
into the aorta and attached to a syringe, and then injected 
with the above silver solution. Thin membranes, such as 
the mesentery or bladder, are removed from the animal, 
exposed to the light for a sufficient time, and then, either 
stained or unstained, mounted in glycerin.* 
Arteries and Veins.—Very small vessels can be studied 
entire, since by careful focussing we can bring one por- 
tion after another into view, obtaining thus what are 
called optical sections. 
The arterioles may be prepared by pulling out some of 
the arteries which enter the brain substance ; at the ends 
of these the arterioles into which they divide are seen. 
Some of the finer twigs are cut off, stained double, 
mounted in balsam, and studied entire. 
In larger vessels this simple method is no longer prac- 
ticable, and we have to resort to actual sections. Small- 
or medium-sized arteries and veins may be prepared by 
stretching them, when fresh, along a bit of wood, with 
pins, and allowing them to dry. The dried vessels are 
placed between two bits of soft cork or elder-pith, and 
* See Appendix, p. 254 LYMPHATIC VESSELS. 
127 
thin sections shaved of, in any desired direction, with a 
hard-tempered dry razor. The sections swell out on be- 
ing dropped into water ; they are then stained double 
and mounted in balsam. 
Larger vessels, such as the aorta, vena cava, etc., may 
be hardened in alcohol, embedded in liver, and the sec- 
tions stained and mounted as before.* 
Heart-valves and Endocardium.—These may be studied 
in thin sections made perpendicular to the surface of the 
valves, and the inner surface of pieces of the heart, which 
have been stretched on cork and hardened in alcohol. 
Lymphatic Vessels.—A general view of the relation be- 
tween the larger lymphatic trunks and the lymphatic 
capillaries, is best obtained by studying nitrate of silver 
prepartions of some part in which the latter are abundant. 
Such a structure we find in the tendinous portion of the 
diaphragm—so called central tendon—of the rabbit, which 
is very thin, covered on both sides with endothelium, and 
very richly supplied with lymphatic vessels. 
To prepare the central tendon, a rabbit should he 
killed by breaking up the medulla, and the thoracic and 
abdominal cavities freely opened by incisions above and 
below the anterior line of attachment of the diaphragm. 
Two ligatures are passed around the large vessels above 
the diaphragm, to prevent the escape of blood on to the 
part, the vessels cut across between them, and the heart 
and lungs removed from the chest. The suspensory lig- 
ament of the liver is now severed, and the diaphragm is 
left free, stretching across between the thoracic and ab- 
dominal cavities. Its upper surface is brushed with a 
soft pencil moistened with water, so as to remove the sur- 
* These structures may all be embedded in celloidin. 128 
NORMAL HISTOLOGY. 
face endothelium and allow the silver to penetrate readily 
into the lymphatics. The surface is now carefully washed, 
and a one-half-per cent, solution of nitrate of silver is al- 
lowed to run over it and remain for five minutes in con- 
tact with it. This is now washed off with water, the dia- 
phragm carefully cut out and pinned to a cork, so as to 
lie flat, and exposed to the light in dilute alcohol till it 
becomes brown. Small pieces are then cut out from the 
tendinous portion and mounted in glycerin. In such a 
specimen the large lymphatic channels will be readily 
recognized, lined with elongated endothelium like that of 
the blood-vessels, and furnished with valves, which appear 
here and there as curved lines crossing the vessel. The 
capillaries may be recognized by their irregular shape and 
sinuous endothelium. CHAPTER IX. 
LYMPH-NODES—SPLEEN. 
LYMPHATIC GLANDS OR LYMPH-NODES. 
If we follow the lymphatic vessels in their course 
from the periphery toward the thoracic duct, we 
find that, sooner or later, they are interrupted in 
their course by certain nodular masses, more 
abundant in some parts of the body than in others, 
and of variable size, commonly called lymphatic 
glands. They are not glands in the limited sense of 
the word, for, so far as we know, they furnish no 
specific secretion, they have no excretory ducts, and 
seem to have an entirely different structure and 
function from the glands proper. It would be 
better to call them lymph-nodes, for that would not 
be misleading, as the word gland is, in regard to 
their relations to other structures; but, as they are 
universally known as lymphatic glands, we shall at 
present use both terms. The lymph-nodes present 
a great diversity in form, being spherical, ovoid, 
discoidal, or irregularly prismatic; they always 
present at one side a hilus, at which the larger 
blood-vessels enter. 
If we make a section through a fresh gland, at 
129 130 
NORMAL HISTOLOGY. 
right angles i-o its long axis and through the hilus, 
we find it more or less distinctly divided into two 
zones : an outer, or cortical zone—the cortex—which 
is soft and grayish or reddish in color, and divided 
into ovoidal or irregular-shaped masses; and an 
inner, or medullary zone—the medulla—-adjacent to 
the hilus, which is firmer, and has a more uniform, 
or sometimes irregularly reticulated, grayish, or 
brownish-red surface. 
The nodes are surrounded by a firm, dense capstde 
of connective tissue, with a few elastic fibres and 
smooth muscle-cells. The capsule sends inward 
numerous partitions or trabecidce, which divide the 
cortex into a series of intercommunicating cham- 
bers, and the medulla into numerous irregular con- 
necting passages. These septa are formed of the 
same elements as the capsule, and at the hilus are 
continuous with a dense mass of connective tissue, 
through which the blood-vessels enter the organ. If 
we examine the spaces left between the septa, we 
find that in the cortex they are incompletely filled 
with ovoidal or globular bodies, which are continu- 
ous with cord-like anastomosing structures lying in 
the narrower and irregular spaces in the medulla ; 
the bodies in the cortex are called lymph-follicles, 
and the cord-like structures in the medulla, lymph- 
cords. 
If, now, we examine more minutely the structure 
of the lymph-follicles, we find that they consist, in L YMPH-NODES. 
131 
the first place, of a framework of reticular con- 
nective tissue, whose meshes are largest in the 
centre of the follicle, narrower and smaller in the 
periphery ; indeed, so closely crowded together are 
the trabeculae here, that they give to the follicle a 
tolerably well-defined outline. In the second place, 
the meshes of the reticulum are closely filled with 
small spheroidal cells, having, in general, the char- 
acters of lymph-cells ; in many of them, however, 
the nucleus is very large, occupying the greater 
part of the cell. The follicles do not entirely fill 
the cavities in which they lie, but are surrounded 
on all sides by a narrow space. 
If we examine the relation of the follicles to the 
walls of their investing spaces, we find that, from 
the walls of these spaces, delicate branching trabec- 
ulae pass inward to the surface of the follicle, 
where they become continuous with the reticular 
tissue of the latter. They are, in fact, themselves 
reticular connective tissue, similar to that of the 
follicle, except that the trabeculae are coarser and 
the meshes broader. Stretching across the space 
surrounding the follicles, they suspend the latter so 
that they hang free in the cavities. The space 
thus formed around the follicles is called the peri- 
follicular space, or, better, lymph-sinus, for reasons 
which will be presently given. 
If we now turn our attention to the lymph-cords 
of the medulla, which, it will -be remembered, are 132 
NORMAL HISTOLOGY. 
continuous with the follicles, we find that they have 
an exactly similar structure, and bear the same 
relation to the more irregularly arranged connective- 
tissue septa which bound the branching spaces in 
which they ramify, that the follicles do to the walls 
of their investing spaces, i. e., they are suspended 
in them by coarse trabeculae of reticular connective 
tissue, and surrounded on all sides by lymph- 
sinuses. These lymph-cords, ramifying and inoscu- 
lating in the medullary portion of the gland, form 
an intricate system of intercommunications between 
all the follicles of the gland. Injections of dilute 
solutions of nitrate of silver into the lymph-sinuses 
show that the surfaces of the follicles and lymph- 
cords, as well as the walls of their investing spaces, 
are covered with endothelium. 
If we study the relation of the lymph-vessels to 
the lymph-nodes, we find that the former, on arriv- 
ing at the surface of the node—afferent vessels— 
pierce the capsule and become continuous with the 
lymph-sinuses, into which they pour their contents; 
we find, further, that efferent vessels, still continuous 
with the sinuses, leave the organ at other points, 
frequently at the hilus. The lymph-glands, then, 
are structures interrupting the course of the lymph- 
atic vessels, in which the lymph is forced to pass 
through a series of irregular-branching spaces or 
sinuses, bathing in its course certain peculiar struc- 
tures—the follicles and lymph-cords—whose function L YMPH-N ODES. 
133 
we do not yet understand. The lymph-sinuses con- 
tain not only the fluid of the lymph, but numerous 
lymph-cells, and usually a certain number of red 
blood-cells. 
The principal blood-vessels enter the nodes at the 
hilus, and the arteries, sending off branches to the 
connective tissue there and to the septa, divide and 
subdivide, and soon enter the lymph-cords; they 
pass along in the axis of these, giving off a long- 
meshed capillary system ; then entering the follicles, 
they break up into a loose capillary net-work, from 
which the blood is collected into venous radicles, 
and poured into veins which pass out through the 
lymph-cords and out of the organ in connection with 
the arteries. Small blood-vessels usually enter the 
capsule at other points than the hilus, and are 
largely distributed to the capsule and the connective 
tissue of the septa. 
The number and arrangement of the follicles 
vary greatly in different lymphatic glands; in some 
there is but a single layer in the cortex; in others, 
several layers are superimposed and more or less 
crowded—thus giving to some glands a narrow, to 
others a broad and voluminous cortex. In many 
animals, as the ox, the reticular tissue of the me- 
dullary portion contains an abundance of brown 
pigment. 
There are, in many parts of the body, small dense 
masses of tissue, some of them sharply circumscribed, 134 
NORMAL HISTOLOGY. 
others diffuse and merging into adjacent tissues, 
which seem to be somewhat analogous to the lymph- 
nodes, although not, as a rule, forming well-defined 
organs. Thus we find in the intestines and stomach, 
either single or in clusters, circumscribed nodules of 
reticular connective tissue, whose meshes are filled 
with small spheroidal cells, and resembling in most 
respects the follicles in the cortex of the lymph- 
nodes. These, which will be more fully considered 
when we study the gastro-intestinal canal, are called 
the solitary follicles of the stomach and intestines, 
and Peyer’s patches.' Less well defined than these, 
we find scattered in various parts of the body, larger 
and smaller diffuse collections of small spheroidal 
cells, lying in a reticular stroma, and forming the so- 
called lymphoid tissue, which recent investigations 
have shown to be of no little importance under cer- 
tain pathological conditions, although of their rela- 
tions to the lymph-vessels or their physiological sig- 
nificance we know very little. These diffuse collec- 
tions of lymphoid tissue are found in the mucous 
membrane of the bronchi, beneath certain serous 
membranes, in the liver, kidneys, and elsewhere, and 
may be seen in the preparations of these parts pres- 
ently to be studied. 
PRACTICAL STUDY. 
Lymph-Sinuses Injected.—A general view of the lymph- 
sinuses and their relations to the follicles and cords is L YMPH-NODE S. 
135 
best obtained from sections of nodes whose lymph-channels 
have been filled with a colored solution of gelatin. A 
gland being exposed in a recently killed animal—one of 
the cervical glands of the dog answers well—a hypodermic 
syringe is warmed and filled with the warmed blue 
gelatin mixture ; the canula is now thrust through the 
capsule at any point, and the fluid injected. The node 
will become mottled with blue, and the mass will often be 
seen to flow into adjacent nodes. If it be not desired to 
inject more than one, a ligature should be passed around 
the vessels leading to the others. When a sufficient 
quantity of the fluid has been injected to render the gland 
firm and the capsule tense, the canula is withdrawn, and 
the node cooled by ice or cold water. When the gelatin 
has solidified, the gland is cut out, divided longitudinally, 
and put into strong alcohol. When it has become suffi- 
ciently hard, sections are made through the entire gland, 
stained, with picro-carmine or eosin, and mounted in 
balsam. 
Shaken Section of a Lymph-node.—The meshes of the 
follicles and cords, as well as the lymph-sinuses, are so 
closely crowded with cells, that the structure of the sup- 
porting tissue cannot be clearly made out, even in very 
thin sections, without removing some of the cells. This 
may be done by shaking in water, as in the preparation 
of reticular connective tissue p. 55). When the operation 
is completed—which will be determined by the extreme 
thinness which the section presents when most of the loose 
cells are removed—it is floated, without folds, on to a 
slide, stained double and mounted in glycerin. 
Blood-vessels.—To obtain an injection of the blood- 136 
NORMAL HISTOLOGY. 
vessels of the lymph-nodes, either a whole animal, such 
as the rabbit or dog, may be injected through the aorta, 
with the blue gelatin mixture ; or a single gland, such as 
the cervical or mesenteric, may be injected through its 
main artery. The glands should be hardened in alcohol, 
and the sections stained deeply with eosin and mounted 
in balsam. 
THE SPLEEN. 
The spleen, although differing in many important 
and probably most essential particulars from the 
lymphatic glands, yet presents many striking analo- 
gies with them. Like them, it presents, on cross- 
section, to the naked eye, a fibrous envelope—the 
capsule,—from which septa and trabeculae pass into 
the organ, enclosing irregular spaces. Here also we 
find the spaces between the septa filled ,with( a soft 
substance presenting two distinct modes of arrange- 
ment ; we find first, irregularly scattered through the 
organ, small grayish globular or elongated struc- 
tures, called Malpighian bodies, or follicles ; and, sec- 
ond, between these, filling up the remaining space 
between the trabeculae, a soft red tissue called the 
pidp. 
Finally, we find blood-vessels entering the organ 
at the hilus. We have, then, in studying the 
spleen, to consider the connective-tissue capsule and 
traheculce, the follicles, the pidp, and the blood- 
vessels. 
The capsule of the spleen consists of a dense en- THE SPLEEN. 
137 
velope of interlacing connective-tissue fibres with 
flattened cells, with a large number of fine elastic 
fibres and a few smooth muscle-cells. It is covered 
by a layer of endothelial cells similar to those of the 
general peritoneal surface. At the hilus it passes 
inward, forming a sheath for the large vessels, and 
joins a complicated system of septa and trabeculce, 
which, proceeding inward from all parts of the cap- 
sule, form a multitude of irregular communicating 
spaces in which the follicles and splenic pulp He. 
These trabeculae and septa are made up of the same 
elements as the capsule, and in size and abundance 
vary greatly in different animals, being in man only 
moderately developed. The follicles, or Malpighian 
bodies, have essentially the same structure as the fol- 
licles of the lymph-nodes—that is, they are formed 
by a small mass of supporting reticular connective- 
tissue, whose meshes are narrowest at the periphery, 
and closely filled throughout with small spheroidal 
cells, and supplied with a net-work of capillaries ; 
we usually find here, however, a small artery passing 
either through the centre or at one side of the fol- 
licle. 
But in order to fully understand the follicles of 
the spleen, it is necessary to study their relation to 
the arteries, in which respect they seem entirely to 
differ from their analogues in the lymph-nodes. 
The arteries and veins as they enter the hilus of the 
spleen are surrounded, as above mentioned, by a NORMAL HISTOLOGY. 
connective-tissue sheath ; after passing for a short 
distance inward, they separate, and the arteries, still 
accompanied by a certain amount of connective 
tissue, divide and subdivide, proceeding farther in- 
ward, until the small branches finally break up into 
brush-like bundles of delicate twigs. If, now, we 
carefully study the walls of the smaller arteries, we 
find that in certain parts they undergo a singular 
modification : at first the connective-tissue sheath 
and the adventitia become very loose in texture, and 
their meshes become filled with spheroidal cells re- 
sembling lymph-cells—this is called lymphoid infil- 
tration of the walls of the arteries ; then we find that 
at certain points this infiltration becomes quite ex- 
tensive, the intercellular substance assuming the 
character of reticular connective tissue ; and thus 
distinct spheroidal or much elongated swellings are 
formed either around or at one side of the arteries 
—these are the splenic follicles or Malpighian bodies. 
In some animals this infiltration is quite extensive 
and continues along the arteries for a considerable 
distance at either side of the follicles ; in others, as 
in man, it is not very marked except in the follicles, 
but may frequently be seen along the arteries ad- 
jacent to them, in the form of narrow cellular 
sheaths. The capillary net-work of the follicles is 
connected with arterial twigs which either penetrate 
from without, or are given off from the follicular 
artery as it passes through the body. THE SPLEEN. 
139 
Let us now turn to the pulp. This is composed, 
in the first place, of a multitude of irregular, fre- 
quently anastomosing cords—called pulp-cords— 
between which, and bounded closely by them, lie, in 
the second place, a series of branching channels—■ 
the cavernous veins. The pulp-cords—joined on the 
one hand to the follicles and infiltrated arterial 
sheaths, and on the other to the connective-tissue 
septa—consist of a framework of delicate reticular 
connective tissue, continuous with the sustaining 
tissue of the follicles, the meshes of which are in- 
completely filled with various kinds of cells. Among 
these cells we find spheroidal cells, like lymph-cells; 
larger colorless cells with one or more large nuclei; 
red blood-cells ; fragments of red blood-cells ; larger 
and smaller colorless cells containing pigment in 
various forms. Finally, there are sometimes found 
in varying number, cells which resemble the lymph- 
and larger colorless cells in form, but whose bodies, 
either homogeneous or granular, have a color sim- 
ilar to that of the red blood-cells. These latter 
cells, like certain similar cells already mentioned as 
occurring in the marrow of bones, are called nu- 
cleated red blood-cells, and are regarded by many 
observers as intermediate forms between the color- 
less and the red blood-cells. Although many re- 
cent observations would tend to confirm this idea, 
their nature is as yet by no means absolutely de- 
termined. 140 
NORMAL HISTOLOGY, 
We have still to consider the structure of 
the second constituent of the pulp—the cavernous 
veins. Following the splenic veins inward from 
the hilus, we find that they gradually lose 
their connective-tissue sheath, and then their 
outer coats, and then rapidly divide and sub- 
divide to form a multitude of intercommunica- 
ting thin-walled canals of tolerably uniform calibre, 
which occupy the irregular-branching spaces be- 
tween the pulp-cords. These ultimate venous trunks 
are called cavernous veins, and their walls consist of 
little else than a few widely separated, branching, 
circular and oblique fibres, upon which lie, at vary- 
ing intervals, elongated, curved, spindle-shaped, and 
flattened endothelial cells, which have their long 
axes parallel with the axis of the canal. These veins, 
whose walls, as will be seen, are not closed but fenes- 
trated, are in direct communication with the spaces 
which are still left in the meshes of the pulp-cords 
by the cells which incompletely fill them. 
Still another point remains to be considered, 
namely, the course of the blood after its exit from 
the above-described fine arterial twigs on which the 
Malpighian bodies are formed, until it enters the 
fenestrated cavernous veins of the pulp. The 
opinion of different observers on this point differs 
somewhat, owing to the extreme technical difficul- 
ties in the investigation ; but it seems probable that 
after passing out of the fine arterial twigs, through THE SPLEEN. 
the intervention of the capillaries it is poured direct- 
ly into the meshes of the pulp-cords, and that after 
circulating here around the cells, without distinctly 
walled channels, it finally finds its way through their 
fenestrated walls into the cavernous veins, whence 
it passes out of the organ through the large efferent 
veins at the hilus. 
PRACTICAL STUDY 
Sections of Uninjected Spleen, a. Cat.—A general 
view of the arrangement of the different structures of the 
spleen may be obtained from very thin sections of a cat’s 
spleen hardened in bichromate of potassium and alco- 
hol. They are stained double and mounted in bal- 
sam. b. Human.—Structural details may be studied in a 
section from a human spleen hardened as above. Before 
mounting, the sections should be placed in a shallow, flat- 
bottomed dish, and just covered with water ; with a fine 
camel’s hair pencil, held perpendicularly, the section is 
gently tapped until it appears thinner and more transpa- 
rent from the brushing out of the loose cells. It may 
then be stained double, and mounted in glycerin or bal- 
sam. 
Section of Spleen with Injected Cavernous Veins.—A 
spleen is injected, under low pressure, through the vein, 
with the blue gelatin mixture, hardened in alcohol, stained 
deeply with eosin, and mounted in balsam. 
Isolated Cells of the Spleen.—A bit of the fresh organ is 
teased on a slide in a half-per-cent, salt solution, and 
studied in the same. Should the red blood-cells, as is 142 
NORMAL HISTOLOGY. 
apt to be the case, be so numerous as to conceal the 
other forms, a drop or two of dilute alcohol (one to 
two) is allowed to run under the cover-glass, and after a 
few moments the red blood-cells will have become so 
transparent as not seriously to interfere with the observa- 
tion. If the nuclei are not sufficiently well defined, a 
drop of eosin may be added after the alcohol. In addi- 
tion to the above-described cells of the pulp-cords in 
teased specimens, narrow, elongated, often curved cells, 
with projecting nuclei, are frequently seen ; these are the 
above-described lining cells of the cavernous veins. CHAPTER X. 
THE GASTRO-INTESTINAL CANAL. 
THIS canal is a tube varying greatly in its calibre 
in different parts, and continuous at either end with 
the external surface of the body. In certain parts 
of its course it is intimately connected with adja- 
cent structures; but, for the most part, it is attached 
only at one side by a structure—the mesentery— 
which serves to convey to it its blood- and lym- 
phatic-vessels and nerves. The walls of the tube, 
although varying in structure in different sections, 
consist in general of a muscular layer, a mucous 
layer lining the tube, and, in those parts where 
it is suspended in the abdominal cavity, a serous 
layer covering it. 
Confining our attention to the stomach and in- 
testines, we find that these layers are not simple, 
but have each a composite structure ; thus, we find 
in the serosa, a layer consisting chiefly of dense 
fibrillar connective tissue, subserosa, covered with a 
layer of endothelium. The muscular tunic, or nms- 
culosa, consists of two layers of smooth muscular 
tissue: an external, in which the cells lie longitudi- 
143 144 
NORMAL HISTOLOGY. 
nally, and an internal in which they lie transversely 
to the axis of the canal. In certain parts of the 
stomach an indistinct third layer is found, in which 
the cells have an oblique course. Inside of the 
muscularis and joining it to the mucosa, is a layer of 
loose fibrillar connective tissue, called the submucosa, 
in which the blood and lymphatic vessels ramify. 
In the mucosa, finally, we have a delicate support- 
ing framework of connective tissue, varying some- 
what in its structure and abundance in different 
parts of the canal ; this is covered by epithelial 
cells and contains the glandular apparatus, while at 
the base of the glands and adjacent to the submu- 
cosa is a thin layer of smooth muscle-cells, lying in 
both transverse and oblique directions, called the 
muscularis mucosce, from which usually a few muscle- 
cells pass'ffp "Between the glands. 
The chief differences in minute structure between 
the stomach and intestines are in the mucous mem- 
brane, and since in this the glands are very impor- 
tant factors, a word should be said here about the 
structure of glands in general. 
Although the term gland is popularly applied to 
structures having the greatest diversity of form and 
function, and little in common but their name, we 
mean by it here, those organs whose physiological 
activity expresses itself, in part at least, by the 
elaboration of certain specific fluids, secretions, or 
excretions. All such glands have a somewhat analo- THE GASTRO-INTKSTINAL CANAL. 
gous structure, and present two distinct kinds of 
structural elements: 1. epithelial or gland-cells; 2. 
a connective-tissue framework, with blood- and 
iymphatic-vessels and nerves. The epithelial cells, 
usually large, differ in form in different and even in 
the same glands: in the latter case especially, when 
the gland is divided into a secreting and excretory- 
portion. They will be described when we study the 
glands in detail. The connective tissue, varying 
greatly in amount in different glands, is sometimes 
arranged in sheets and bundles so as to form 
variously shaped cavities which are lined with the 
gland-epithelium ; sometimes, in the form of simple 
or superimposed lamellae covered with flat cells like 
endothelium, it forms thin-walled tubes or chambers 
on whose sides the cells are placed ; in this form it 
is called the membra7ia propria of the gland cavities. 
The cavities and tubes thus formed and lined with 
gland-epithelium are variously arranged in different 
glands, but their different modes of arrangement 
may be reduced to three types: 
1. Tubular glands, which have the form of simple 
or occasionally branching, straight, curved, or vari- 
ously contorted tubes, terminating in blind extremi- 
ties. Such are the giands of the stomach. 
2. Racemose glands, in which the secreting portion 
in the form of vesicular or irregular-shaped cavities 
—alveoli—are grouped around simple or branching 
excretory ducts, into which they open; the whole 146 
NORMAL HISTOLOGY. 
structure has been not inaptly compared to a bunch 
of grapes, in which the fruit would correspond to 
the alveoli, the stem to the excretory ducts ; the 
analogy failing at this point, however, for in the 
gland the alveoli and ducts are bound together by 
connective tissue lying between them—called inter- 
stitial tissue—in which the vessels and nerves ramify. 
The alveoli which open into the same excretory 
duct are usually joined more closely to one another 
than to those opening into different ducts, and these 
clusters of alveoli are called the lobules or acini of 
the gland. Such are the mammary glands and cer- 
tain mucous glands of the bronchi. 
3. Vesicular Glands.—These consist of simple, 
spheroidal, or irregular-shaped closed alveoli, sur- 
rounded by a membrana propria, and lined with 
epithelium, the separate alveoli being embedded in 
interstitial connective tissue. Such glands are the 
thyroid and ovary. 
THE STOMACH. 
The muscularis of the stomach differs from that 
of the intestines, in that a certain number of the 
cells, especially in the cardiac extremity, do not 
have the typical transverse or longitudinal arrange- 
ment, but lie in an oblique direction. In the vicinity 
of the pylorus again, the inner circular layers are 
much thickened, forming the sphincter pylori. The 
mucosa is entirely made up of glands supported THE CASTRO-INTESTINAL CANAL. 
and held together by a small amount of delicate 
connective tissue, in which the blood and lymphatic 
vessels ramify. The glands are tubular, sometimes 
simple, sometimes divided, and often tortuous at 
the base. They have a membrana propria, and, de- 
pending upon differences in the epithelium which 
line them, they are classified as; I. mucous glands; 
2. peptic glands. 
The general surface of the stomach is covered 
with cylindrical epithelium. In the pyloric region, 
and here and there in other parts, the glands, or 
follicles, as they are often called, are lined through- 
out with cylindrical epithelium ; these are the mu- 
cous glands. 
The greater proportion of the glands, however, 
are lined only at their orifices with cylindrical epi- 
thelium ; deeper down in the gland we find usually 
two kinds of cells: a, spheroidal or polyhedral cells, 
with transparent or very finely granular bodies; 
and b, larger spheroidal, or somewhat flattened, very 
granular cells, which usually lie outside the others, 
between them and the membrana propria. These 
are the so-called peptic cells, and these glands are 
called peptic glands. The relative number of these 
different kinds of peptic cells varies, depending upon 
the degree of functional activity of the glands. 
When they are secreting rapidly, the granular cells 
are abundant ; when at rest they are few in number, 
the smaller transparent cells preponderating. 148 
NORMAL HISTOLOGY. 
The arteries pass obliquely through the serosa 
and musculosa, divide and subdivide in the loose 
tissue of the submucosa, from whence branches are 
sent in between the glands ; here, before reaching 
the surface, they break up into a close capillary net 
surrounding the follicles, and the blood is finally 
collected into narrow venous trunks directly be- 
neath the surface epithelium; from these it passes 
back into larger veins in the submucosa, where it 
collects in the efferent veins. The lymphatic ves- 
sels lie between the glands, form anastomosing 
channels in the submucosa, and pass out through 
the musculosa, receiving larger and smaller trunks 
from the latter. 
The nerve-trunks from the sympathetic and pneu- 
mogastric form a plexus, associated with minute 
ganglia, called Auerbach'splexus, between the layers 
of the musculosa; from this branches pass into the 
submucosa and form another similar plexus, called 
Meissner s plexus. 
Nodules of lymphoid tissue, varying greatly in 
size and number, are found in the mucosa of the 
stomach, at the base of the follicles, and sometimes 
extending up between them. These are sometimes 
visible to the naked eye as small grayish promi- 
nences on the surface of the mucous membrane, and 
have been called the lenticular glands or follicles of 
the stomach. THE GASTRO-INTESTINAL CANAL. 
The supporting connective-tissue framework of 
the mucosa in the small intestine is more abundant 
than in the stomach, and is richly infiltrated with 
small spheroidal and variously shaped cells. In it 
lie embedded tubular glands, not unlike the mucous 
glands of the stomach, but not crowded so closely 
together. These glands are often called the folli- 
cles of Lieberkiihn, and are lined with cylindrical 
epithelium. ■ Rising from the general surface of the 
mucous membrane, between the orifices of the 
glands, are very numerous short cylindrical or coni- 
cal projections called villi. These are formed by 
projections inward of the mucosa; they are covered 
by cylindrical epithelium, and contain an abundant 
vascular net-work, and the radicles of the lymph- or 
chyle-vessels. 
THE SMALL INTESTINE. 
The cylindrical epithelial cells are joined to- 
gether, side by side, by cement substance, and pos- 
sess a marked peculiarity in the structure of the 
free border, which is considerably thickened, and is 
crossed, in a direction corresponding with the long 
axis of the cell, by fine parallel, closely-set lines, 
which are usually interpreted as tiny pores or canals 
passing through the border. It was formerly taught 
that through these pores the chyle passed to enter 
the epithelium on its way to the lymph-vessels. 
More recently, however, the view has been ad- NORMAL HISTOLOGY. 
vanced that substances absorbed into the lymph- 
vessels from the intestines pass, not through the 
epithelial cells, but through the cement substance 
between them. 
Scattered here and there between the cylindrical 
epithelium, sometimes abundant, sometimes not, 
are transparent more or less ovoidal cells with a 
nucleus and a small amount of protoplasm in the 
vicinity of the narrow base ; they look as if the 
free border of the cell had fallen off and most of 
the cell-contents had disappeared. Not infre- 
quently a translucent structureless substance is seen 
protruding from the open end of the cell, as if in 
the act of passing out of it. These cells are called, 
from their form, goblet-cells. Their significance is 
not yet definitely determined in all cases : by some, 
they are regarded as cylindrical cells changed by 
artificial means ; but most observers believe them 
to be normal structures, and suppose that under 
certain circumstances the cell-contents undergo a 
mucous metamorphosis, swell up, burst out of the 
cell, leaving little but the membrane and nucleus 
behind, and that thus, under normal conditions, a 
certain amount of the mucus furnished by mucous 
membranes is produced. 
In addition to the tubular glands which are found 
throughout the whole extent of the small intestine 
—in the duodenum, especially in its upper por- 
tions—racemose, probably mucous glands, are THE CASTRO-INTESTINAL CANAL. 
151 
found, called Brunner s glands. They lie in the 
submucosa, and consist of variously shaped, but 
usually elongated alveoli, surrounded by a mem- 
brana propria and lined with cylindrical epithelium. 
The excretory ducts are also lined with cylindrical 
epithelium, and open on the surface of the mucous 
membrane. 
Smooth muscle-cells pass up from the muscularis 
mucosse into the villi. The central portion of the 
villi is occupied by one or more usually blind 
canals—the chyle-vessels—which pass outward to 
the bases of the villi, where they usually unite to 
form a net-work around the orifices of the tubular 
glands of Lieberkiihn and the lymph-follicles pres- 
ently to be described; they then pass into the 
submucosa, where they form larger anastomosing 
channels; from thence trunks pass through the 
musculosa, receiving vessels from its two layers, and 
from a well-developed net-work between them. 
The distribution of the nerves is essentially similar 
to that in the stomach. 
Closely connected with the lymphatic vessels, and 
apparently forming a part of the lymphatic appa- 
ratus of the intestines, are found certain structures 
called lymphatic follicles, and of these it is custom- 
ary to distinguish two kinds: I. Solitary follicles; 
and 2. Agminatcd follicles, or Peyers patches. 
1. Solitary Follicles.—These are irregularly scat, 
tered through the mucous membrane of both small 152 
NORMAL HISTOLOGY. 
and large intestines, in the form of small grayish 
nodules. They lie chiefly in the mucosa, often 
piercing the muscularis mucosce and descending into 
the submucosa; they are usually spheroidal or pear- 
shaped, and frequently project somewhat into the 
intestinal cavity. Where they lie, the tubular 
glands are crowded to one side, and the villi are 
absent over their surfaces. They may lie so near 
the surface as to be covered only by a single layer 
of cylindrical epithelium, or they may be more 
deeply placed, and covered, in addition, by a thin 
layer of the connective tissue of the mucosa. 
They consist of a nodule of reticular connective 
tissue, whose meshes are somewhat narrower at the 
periphery, where it becomes continuous with ad- 
jacent parts. The meshes are closely filled with 
small spheroidal cells, having the characters of 
lymph-cells. In their periphery the lymph-vessels 
of the mucous membrane form a closely anasto- 
mosing net-work. The blood-vessels also interlace 
in their periphery, and send an abundance of anas- 
tomosing capillary loops into their interior. 
2. Peyers Patches.—These are found chiefly in the 
small intestine, and here are most abundant in the 
lower portion of the jejunum and in the ileum ; 
they are round, or more frequently elongated 
usually slightly elevated structures, and are always 
situated at the side opposite the mesenteric attach- 
ment, with their long axes parallel with the axis of THE GASTROINTESTINAL CANAL. 
153 
the gut. They consist, essentially, of an aggrega- 
tion of a variable number of structures, having the 
characters of the solitary follicles; these are placed 
closely together, side by side, and supplied in essen- 
tially the same way as the solitary follicles with 
blood- and lymphatic-vessels. 
The mucosa of the large intestine is thickly set 
with tubular glands similar to Lieberkiihn’s glands 
in the small intestine, but is destitute of villi. 
Solitary lymphatic nodules are abundant, and are, 
as a rule, somewhat larger than those of the small 
intestine. The distribution of blood- and lymphatic- 
vessels resembles in most respects that described in 
the stomach and small intestine. 
THE LARGE INTESTINE. 
PRACTICAL STUDY. 
Sections of Stomach.—Bits of perfectly fresh rabbit’s or 
dog’s stomach, from the fundus and the pyloric region, 
should be stretched on a bit of cork to prevent shrink- 
age, and immersed in absolute alcohol. After twenty- 
four hours the fluid should be changed, and in three or 
four days the specimen will probably be hard enough to 
cut. After embedding in wax,* sections from both 
regions are made perpendicular to the surface, stained 
double and mounted in balsam. The nuclei of all the 
cells are stained violet by the hsematoxylin ; in the pep- 
tic glands the bodies of the granular peptic cells are 
stained a deep rose-red, while the others are but slightly 
♦ Better in celloidin. 154 
NORMAL HISTOLOGY. 
colored, or not at all. Sections perpendicular to the 
surface of a stomach, whose blood-vessels are filled with 
the mixture of Prussian-blue and gelatin, and stained 
with carmine, are very instructive. 
Sections of Intestine.—Bits of intestine from the upper 
portion of the duodenum, from the ileum, including one 
of Peyer’s patches, and from the large intestine, should 
be stretched on cork and immersed in a mixture of equal 
parts of half-per-cent, chromic acid sol. and alcohol ; 
after four days they are transferred to alcohol, in which, 
in a day or two, they will become hard enough to cut. 
Perpendicular sections from the various parts should be 
stained and mounted in the same way as the stomach. 
Sections from intestines, whose blood-vessels are injected 
with blue, are stained with eosin and mounted in balsam. CHAPTER XL 
SUBMAXILLARY GLAND—LIVER. 
SUBMAXILLARY GLAND. 
CONNECTED with the digestive tract are several 
racemose glands, which, although differing in impor- 
tant particulars, both in structure and function, yet 
have many features in common. These glands are 
the submaxillar is, the sublingual, the parotid, and 
the pancreas. Their details of structure are still in- 
sufficiently known, and within the limits of this 
manual we cannot consider at length even what is 
well understood. We will simply look at some of 
the more important features of one of the best 
known, the submaxillaris, considering this, in a gen- 
eral way only, as typical of the others. 
The submaxillary gland differs in structure in dif- 
ferent animals, its structure in the dog being per- 
haps best known, and quite closely resembling that 
in man. In the dog it consists, like other racemose 
glands, of alveoli and excretory ducts. The elon- 
gated alveoli are surrounded by a membrana propria, 
and grouped into lobules by more or less interstitial 
connective tissue, which is furnished with blood-and 
lymph-vessels and nerves. The alveoli, depending 
155 NORMAL HISTOLOGY. 
upon the gland-epithelium which lines them, present 
two distinct forms: in one form, the smaller of the 
two, we find the cavity of the alveoli nearly filled 
by cuboidal or polyhedral cells, whose bodies are 
cloudy or granular, and which have spheroidal or 
ellipsoidal nuclei. In the other form of alveoli— 
the larger—we find in the first place, surrounding 
the cavity of the alveoli, large, irregular-shaped, 
transparent cells, having a gelatinoid appearance, 
with an often flattened nucleus lying at the periphe- 
ral side ; these cells are not readily stained by eosin, 
and are called mucous cells. In the second place, in 
the periphery of the alveoli, between the cells just 
described and the membrana propria, lie large, in 
cross-section, crescentic, strongly granular masses, 
usually containing several nuclei; these are called 
the crescents of Gianuzzi. They are believed to be 
formed by a number of small angular cells closely 
crowded together; they are readily stained with 
eosin, and are apparently analogues of the granular 
peptic cells of the stomach. Like the latter, they 
are most abundant when the gland is in a condition 
of functional activity, and are believed to be des- 
tined to replace the inner layer of transparent cells 
as these are destroyed or changed in burnishing the 
specific secretion of the gland. 
. The excretory ducts differ in structure and in the 
diameter of the lumen, in different parts of the 
gland ; the difference depending chiefly upon differ- THE LIVER. 
157 
ences in the structure of the epithelial layer which 
lines them ; this, in the larger ducts, is columnar, 
and in the smaller, flattened. 
PRACTICAL STUDY. 
Section of Gland of Dog.—Small pieces of a perfectly 
fresh gland are hardened in absolute alcohol. Very thin 
sections are to be stained with hsematoxylin and eosin, 
and mounted in glycerin or balsam. One frequently 
finds in a gland taken from a dog shortly after eating, 
certain groups of alveoli with the cells in an active, others 
with the cells in a resting, condition. 
The liver presents three distinct elements of 
structure: I. The cellular elements, which in form, 
function, and arrangement, characterize the organ— 
the liver-cells or parenchyma. 2. The connective- 
tissue framework—the interstitial tissue, which sur- 
rounds the organ as a capsule, and in its interior 
supports the parenchyma and carries the larger 
vessels. 3. The blood-, lymph-, and gall-vessels. 
THE LIVER. 
The liver-cells are large, have the form of irregu- 
lar, often somewhat elongated polyhedra ; they have 
a granular body which frequently encloses granules 
of pigment and larger or smaller droplets of fat; 
they have one or more vesicular nuclei and nucleoli. 
When living, they are very soft, and the isolated 
cells often shc3w depressions on their sides caused 
by the pressure from adjacent blood-vessels. 158 
NORMAL HISTOLOGY. 
If we look at the cut surface of a fresh liver with 
the naked eye, we find that it presents, more or less 
distinctly, small polygonal or irregular-shaped 
figures, which are sections of certain groups of liver- 
cells, called acini or lobules. These lobules have, in 
general, the form of oblong polyhedra, and the dif- 
ference in shape presented by the sections is due to 
the fact that they lie crowded together, with their 
long axes lying in various directions. In order to 
understand the structure of these lobules, it is neces- 
sary to study them in connection with the blood- 
vessels of the liver, to which they bear a very 
constant and characteristic relation. 
The liver receives its blood from the portal vein 
and the hepatic artery ; it is conveyed away by the 
hepatic vein. If we follow the ramifications of the 
hepatic vein, we find that it divides and subdivides 
until it finally breaks up into short terminal radicles, 
around which as a centre the oblong liver-lobules 
are grouped. From its smaller branches also, before 
it breaks up into terminal radicles, small, short 
branchlets are given off, which form the centres of 
lobules. Veins bearing this relation to the lobules 
are called central veins, or vencc intralobulares. 
If now we follow the ramifications of the portal 
vein, on the other hand, we find that, dividing and 
subdividing, it, too, gives off small branchlets which, 
with the terminal branchlets into which it finally 
breaks up, pass to the surface of the lobules; there THE LIVER. 
159 
they pour their blood into a rich capillary net-work 
within the lobules, whence it passes directly into 
the radicles of the hepatic vein at the centre. The 
capillaries of the lobules radiate from the central 
vein, for the most part nearly at right angles to its 
axis, and take more or less direct, slightly divergent 
courses to the periphery, being connected with each 
other by frequent branches. A net-work is thus 
formed, in whose narrow and elongated meshes the 
liver-cells lie, sometimes ip a single row, sometimes 
in several rows, depending upon the breadth of the 
intercapillary spaces. The central vein does not 
usually extend quite to the extremity of the lobules, 
and here the capillaries are given off, brush-like, 
obliquely from its end. A liver-lobule, then, is a 
circumscribed portion of liver-tissue, having for its 
centre a branchlet of the hepatic vein—vena intralobu- 
laris,—and at its periphery the terminal branchlets of 
the portal vein—vence interlobulares,—while between 
these two sets of vessels, and joining them, is a rich 
capillary net-work, in whose elongated meshes lie rows 
of liver-cells. 
In certain animals, such as the pig, the lobules are 
very distinct, being surrounded by connective tissue 
which is directly continuous with the connective 
tissue surrounding the larger trunks of the portal 
vein, hepatic artery, etc., and called Glisson s capsule. 
In this connective tissue between the lobules are 
found, in addition to the branchlets of the portal NORMAL HISTOLOGY. 
vein, certain of the terminal branchlets of the 
hepatic artery and the capillaries connected with 
them, and the smaller gall-ducts. In the human 
liver, on the contrary, there is very little connective 
tissue between the lobules, only here and there small 
masses are seen surrounding the branches of the 
portal vein and its accompanying vessels, the lobules 
merging, for the most part, insensibly into one 
another. The hepatic artery sends its blood into 
capillaries which are distributed largely to the walls 
of the vessels and the connective tissue, and it 
finally passes, directly or indirectly, into the intra- 
lobular capillaries. 
We have finally to consider the gall-passages. The 
larger gall-ducts, lined with a well-developed mucous 
membrane, supplied with tubular and racemose 
mucous glands, and covered with cylindrical epithe- 
lium, enter the liver with the other large vessels, and, 
dividing and subdividing, accompany them in the 
capsule of Glisson. As they pass inward they 
become smaller and smaller, the mucous membrane 
loses its glands and becomes simpler in structure— 
the small ducts consisting of little more than a 
simple tube lined with low cylindrical or cuboidal 
cells. Finally, as the ducts arrive at the periphery 
of the lobules—interlobular gall-ducts—they are 
lined with flat, polygonal cells ; here they become 
continuous with the intralobular gall-passages or 
gall-capillaries. The gall-capillaries are extremely THE LIVERt 
narrow, and form a delicate net-work around the 
individual liver-cells; being arranged in such a way, 
however, that they never come into contact with 
the blood-capillaries, always being separated by at 
least a part of the diameter of a liver-cell from the 
latter. They do not seem to possess a distinct wall, 
but are rather, simple channels grooved in the walls 
of contiguous liver-cells. 
The connective tissue of the human liver is chiefly 
found in the capsule which surrounds the organ, and 
in the capsule of Glisson, which accompanies the 
larger vessels; but, in addition to this, we find it in 
very small quantity, not only in the vicinity of the 
hepatic vein, but also between the cells and along 
the capillaries within the lobules; in the latter situ- 
ation it occurs in the form of delicate fibres or 
membranes, with here and there fusiform or stellate 
cells. 
The lymphatic vessels of the liver form an abun- 
dant net-work in the capsule, and also accompany 
the larger vascular trunks in Glisson’s capsule and 
between the lobules, and are connected with minute 
intralobular lymph-spaces. Here and there in the 
interstitial tissue of the liver are found small irregu- 
lar nodules of lymphoid tissue, see page 134. 
PRACTICAL STUDY. 
Liver-cells.—A small fragment of fresh liver is teased 
in bait solution and studied in the same. It need not be 162 
NORMAL HISTOLOGY. 
preserved, as hardened cells will be seen in the following 
preparations. 
Sections of Pig s Liver.—A small piece of pig’s liver 
should be hardened in Muller’s fluid and alcohol, and 
very thin sections made near the surface, both parallel 
and at right angles to it, so as to cut the lobules, which 
are quite regularly arranged at the surface, in different 
directions. The sections are stained double and mounted 
in balsam. The lobules being here surrounded by toler- 
ably distinct layers of connective tissue, in which the in- 
terlobular vessels run, the lobular structure is quite evi- 
dent, and the pictures obtained by sections in different 
directions are easy of interpretation. 
Sections of Human Liver.—Sections are made from a 
bit of human liver hardened as above, stained double and 
mounted in balsam. Here the lobular structure is very 
ill-defined, because of the small amount of connective 
tissue between the lobules, and for the recognition of the 
different parts of the latter we are largely dependent 
upon the determination of the different kinds of blood- 
vessels, since these always bear a definite relation to the 
lobules. It is to be remembered that the branches of 
the portal vein lie only in the periphery of the lobules, 
that they are usually accompanied by other vessels be- 
sides capillaries, and are in most cases surrounded by a 
greater or less amount of connective tissue. The central 
vein, on the other hand, is usually unassociated with 
other dissimilar vessels, except capillaries, and sur- 
rounded only by a scarcely appreciable amount of con- 
nective tissue. 
Injected Liver.—The general arrangement of the blood- THE LIVER. 
163 
vessels is best studied in sections from a human or rab- 
bit’s liver, which has been injected through the portal 
vein with the blue gelatin mixture. The sections are 
stained with eosin and mounted in balsam. 
Injected Gall-capillaries.—By a careful injection of the 
blue gelatin mixture into the hepatic duct, the gall-capil- 
laries may be partially filled. Sections are stained with 
eosin and mounted in balsam. 
To show the relation between the blood- and gall-capil- 
laries, both may be simultaneously injected with gelatin 
of different colors, one forced into the hepatic duct, the 
other into the portal vein. CHAPTER XII. 
SUPRA-RENAL CAPSULES—THYROID GLAND. 
SUPRA-RENAL CAPSULES. 
In sections of the supra-renal capsules, through 
their thickest part, and at right angles to the long 
axis of the organ, we see with the naked eye two 
distinct layers ; a tolerably firm, yellowish, striated 
cortical layer of considerable thickness—the cortex, 
—and a narrower central, yellow or reddish portion 
—the medulla. Between the two, or rather at the 
inner side of the cortical portion, a more or less dis- 
tinct brown zone is seen. 
If we examine thin sections microscopically, we 
find that the organ is enclosed in a firm connective- 
tissue capsule, in which are numerous elastic fibres 
and smooth muscle-cells. From this capsule, deli- 
cate converging connective-tissue bands or septa, 
similar in structure to the capsule, pass inward, and 
being joined together by delicate transverse bands 
or trabeculae, divide the cortex into a multitude of 
variously shaped chambers. In the periphery, just 
beneath the capsule, the chambers are small and 
irregular in shape; then comes a broader zone, 
whose chambers are long and narrow; and again, at 
164 SUPRA-RENAL CAPSULES. 
the inner border of the cortex, they are small and 
irregular. In the medulla the supporting frame- 
work has the form of a delicate reticulum with small 
irregular meshes. The spaces thus formed are filled 
with cells—-parenchyma cells,—which differ in char- 
acter in the different parts; in the cortex they are, 
for the most part, large, polyhedral, and granular; 
less abundant are smaller cuboidal or cylindrical 
forms. Those in the elongated chambers are usually 
crowded with fat-droplets, and those lying in the 
inner zone usually contain an abundance of brown 
pigment, forming the above-mentioned brown zone. 
The meshes of the medulla are filled with large globu- 
lar or angular or branched, finely granular cells, 
which, in marked contrast to the cortical cells, are 
stained intensely brown by solutions of chromic acid 
or its salts. 
The blood-vessels are very abundant; many of 
them have very thin walls and lie in close contact 
with the cells of the parenchyma. The organ is 
abundantly supplied with nerves which, passing 
along the converging trabeculae, form a dense plexus 
in the medulla, in which, as well as in the capsule, 
considerable numbers of ganglion-cells are found. 
Lymphatic vessels and sinuses are also abundant. 
PRACTICAL STUDY. 
Sections.—A human supra-renal capsule, as fresh as 
possible—or, if this cannot be obtained, that of the 166 
NORMAL HISTOLOGY. 
guinea-pig or ox,—is cut transversely into two or three 
pieces and hardened in bichromate of potassium and 
alcohol. Transverse sections are stained double and 
mounted in glycerin or balsam. 
THE THYROID GLAND. 
The thyroid gland is composed of a congeries of 
larger and smaller spheroidal or irregular-shaped 
alveoli, enclosed in connective tissue and grouped 
together to form lobules. The alveoli are entirely 
separate from one another, and they have no excre- 
tory ducts. Each alveolus has a delicate membrana 
propria, and is lined with a single layer of cylindri- 
cal or cuboidal cells. The connective tissue between 
the alveoli contains numerous blood- and lymphatic- 
vessels. 
The entire gland, which consists of two lateral 
lobes, united at their lower extremities by a trans- 
verse commissure, is enclosed in a dense connective- 
tissue envelope. The alveoli are filled with a clear, 
homogeneous albuminous fluid, which in adult life 
is frequently transformed into or replaced by a 
translucent material, called colloid. Owing to the 
pressure which the accumulating colloid substance 
exerts on the epithelium lining the alveoli, they are 
often very much flattened, and not infrequently 
almost entirely disappear. The colloid material 
seems to be formed, in part at least, by a transforma- 
tion of the contents of the epithelial cells, and its THE THYROID GLAND. 
formation under pathological conditions gives rise 
to one of the forms of goitre. 
The thyroid of a child or adult—better the former—is 
cut into small pieces and hardened in alcohol. Sections 
are stained double and mounted in glycerin or balsam. 
PRACTICAL STUDY. CHAPTER XIII. 
THE RESPIRATORY APPARATUS. 
The respiratory apparatus consists of a multi- 
tude of small cavities or chambers, on whose walls 
the blood is brought into close contact with the air, 
and of a system of branching tubes through which 
the air is conducted to and from them. The con- 
ducting tubes are the larynx, the trachea, and the 
bronchi. We shall limit our study of the tubes to 
the two last. 
The walls of the trachea consist of several layers: 
commencing at the outside, we have first, a layer 
of firm connective tissue—the fibrous layer—in which 
lie embedded, incomplete cartilaginous rings, the 
space between whose free ends, at the posterior por- 
tion of the tube, is bridged over by transverse bands 
of smooth muscular tissue, which bind the ends to- 
gether. The cartilaginous rings are of the hyaline 
variety, and their perichondrium is continuous with 
the looser connective tissue of the layer in which 
they lie. This layer merges into the next, the sub- 
mucosa, which consists of loose, fibrillar connective 
tissue with elastic fibres, the latter running chiefly 
in a longitudinal direction. 
168 THE RESPIRA TOR V APPARA TUS. 
169 
Still farther inward, and not distinctly separated 
from the submucosa, lies the mucosa, composed of 
fibrillar connective tissue containing an abundance of 
variously shaped cells, and, for the most part, longi- 
tudinally arranged elastic fibres. In some parts of 
the mucosa the tissue resembles diffuse lymphoid 
tissue. The connective tissue of the mucosa, in 
some parts of the trachea, does not form an uniform 
layer, but is arranged in more or less well-defined 
longitudinal bundles, giving the surface a wavy or 
folded appearance. 
Internally, the mucosa is bordered by a thin, 
homogeneous membrane, the basal membrane, upon 
which the epithelial cells lining the trachea rest. 
The epithelial cells are usually arranged in about 
three layers. Lying upon the basal membrane are 
irregularly spheroidal, often somewhat elongated 
cells; upon these lie fusiform or pear-shaped cells, 
while the surface is formed by a layer of pyramidal 
or cylindrical ciliated cells. In the submucosa, and 
sometimes extending outward along and between 
the cartilaginous rings, lie racemose mucous glands, 
whose excretory ducts, lined with cylindrical epi- 
thelium, pass obliquely inward and terminate on the 
surface in expanded orifices. The alveoli of the 
glands are lined with a single layer of slightly granu- 
lar, polyhedral cells. When the glands are in a con- 
dition of functional activity, however, the cells 
become larger, the outlines indistinct, their nuclei NORMAL HISTOLOGY. 
are crowded to one side, and their contents are 
apparently transformed into a homogeneous mu- 
cous mass. Scattered here and there among the 
glands and between the cartilaginous rings, lie larger 
and smaller clusters of fat-cells. 
The blood-vessels, passing through the outer lay- 
ers, furnish an abundant capillary net-work to the 
mucous glands, and spread out in a rich capillary 
plexus beneath the basal membrane. 
Although the larger and medium-sized bronchi 
have the same general structure as the trachea, still 
we find, aside from a decrease in the thickness of 
the walls, certain noteworthy structural modifica- 
tions which chiefly concern the cartilaginous and 
muscular elements. The cartilage occurs in the 
form of regular, incomplete rings, only in the upper 
portion of the larger bronchi. As the tubes become 
smaller the cartilage occurs in the form of scattered, 
irregular-shaped, often angular plates, which become 
gradually smaller and thinner. Furthermore, a dis- 
tinct layer of smooth muscular tissue, in the form of 
transverse rings, connected with each other by in- 
terlacing cells, appears between the mucosa and the 
submucosa. We find, also, that the longitudinal 
bundles of fibrillar and elastic connective tissue in 
the mucosa are more strongly developed as the 
bronchi become smaller, so as to throw the mucous 
membrane into pronounced longitudinal folds. 
Following the bronchi now down toward their THE RESPIRA TOR V APPARA TUS. 
finer ramifications, we find that the outer connective- 
tissue layer becomes thinner, the cartilaginous plates 
become smaller and more infrequent, and finally 
altogether disappear; the mucous glands, too, after 
becoming smaller and simpler in structure, disap- 
pear with the cartilages. The muscular rings as- 
sume, gradually, the form of an uniform thin layer 
of transversely arranged muscle-cells, intermingled 
with elastic fibres, and are finally represented only 
by a few scattered transverse cells. The mucosa in 
the smaller tubes becomes gradually thinner, and 
finally merges into the fibrous layer, with the inter- 
vention only of a few scattered muscle-cells; the 
lower layers of epithelium gradually disappear, leav- 
a single row of ciliated cells upon the basal mem- 
brane. Finally, we have, in the smallest tubes, very 
thin connective-tissue walls, containing a few mus- 
cle-cells and elastic fibres, and lined with cuboidal, 
ciliated, and at last with flattened, non-ciliated cells. 
We are thus led to the respiratory cavities of the 
lungs—the air-chambers. If we look at the surface 
of a lung, we see that it is more or less distinctly 
divided, by narrow branching lines, into irregular 
polygonal spaces, each one of which corresponds to 
a pulmonary lobule. These lobules have, on the sur- 
face of the lung, where they are more uniform in 
shape than within, a pyramidal form, and are sepa- 
rated by narrow connective-tissue septa, and each 
lobule is, in fact, a group of air-vesicles, which are NORMAL HISTOLOGY. 
in communication with a single small bronchus and 
its terminal twigs. As the small bronchus enters 
the lobule, it divides into several terminal twigs; 
these open at the peripheral extremity into irregular 
tubular passages, called alveolar passages; on the 
sides of these alveolar passages still other irregular, 
sometimes branched elongated cavities, called in- 
fundibula, open out, and their walls, as well as the 
walls of the alveolar passages, are beset with tiny, 
irregular-shaped vesicles, called air vesicles or alveoli, 
which communicate with the cavities of the infun- 
dibula and alveolar passages by wide, irregular open- 
ings. All of these cavities are closely crowded to- 
gether, and their walls intimately joined. It is in the 
walls of the air-vesicles that that interchange of 
material between air and blood occurs, which is the 
essential factor in respiration. 
We have now to consider the structure of the 
walls of the alveolar passages, infundibula, and air- 
vesicles. The gradual thinning which we have ob- 
served in the walls of the bronchi as they approach 
their termination, is still more marked as we pass 
over into the alveolar passages and infundibula. 
Here, the walls consist of little else than a thin, 
delicately striated, membranous basement substance, 
in which numerous elastic fibres ramify, and a few 
connective-tissue and smooth muscle-cells are em- 
bedded, the whole being lined with flattened epithe- 
lium. At the opening of the infundibula and air- THE RESPIRA TOR Y APPARA PUS. 
vesicles the elastic fibres are grouped to form pro- 
jecting rings, which bound the opening. From these 
rings of elastic fibres which surround the openings 
into the alveoli, other elastic fibres are given off, 
which, dividing and subdividing, stretch over the 
walls of the air-vessels in the form of a wide-meshed 
net, the spaces between the fibres being occupied 
by an extremely thin, structureless membrane, in 
which lies an occasional oval nucleus. 
The alveoli, in the adult, are lined with a single 
layer of flattened, polygonal, epithelial cells. These 
are of two kinds: first, small granular, nucleated 
cells ; and, second, cells which are larger, more irreg- 
ular in form, very thin and transparent, and usually 
without nuclei. The relative proportion of these 
two kinds of cells is variable, and their outlines, 
especially those of the larger cells, it is difficult to 
see distinctly without resorting to silver-staining.* 
In the foetus the air-vesicles are lined at first with 
a distinct layer of cylindrical or cuboidal epithelial 
cells, which become gradually flattened, and when 
respiration is established assume the form of a layer 
of very thin polygonal cells ; these change their 
character as the animal matures, until in adult life 
we have the forms above described. 
Just beneath the epithelial cells, and separated 
by them alone from the air within the vesicles, lies 
the rich blood-capillary net-work, which, in bulk as 
in importance, is the most essential element in the 
* See Appendix, p. 254. 174 
NORMAL HISTOLOGY. 
walls of the vesicles. The lungs are supplied with 
blood through the pulmonary and the bronchial 
arteries. The blood from the latter is chiefly dis- 
tributed to the walls of the bronchi and larger 
blood-vessels, and to the connective tissue of the 
lungs. A large part of the blood from the bron- 
chial arteries, after passing through various sets of 
capillaries, returns through the bronchial veins; but 
a certain portion of it finds its way into the pulmon- 
ary veins; indeed, the two sets of vessels seem to 
be in communication in various parts of the lungs. 
The pulmonary artery, following the course of 
the bronchi, divides and subdivides, until on reach- 
ing the lobules the small trunks break up into 
smaller branchlets, which pass along the alveolar 
passages and in the interlobular connective tissue to 
the air-vesicles, where they break up into the rich 
capillary net-work which is spread over their walls. 
The capillaries wind over the free edges of the al- 
veolar walls, the vessels often projecting somewhat 
into their cavities. The net-work on the alveolar 
walls is quite dense, and the vessels are very broad, 
leaving only small oval or rounded spaces between 
them. A single net-work frequently supplies the 
walls of adjacent vesicles, which in such cases are 
merged into one. The blood passes from the vesi- 
cles into the pulmonary veins in the interlobular 
connective tissue, and then into larger trunks which, 
passing inward, follow the course of the other large 
vessels. THE RESFIRA TOR V AFFARA TCS. 
The surface of the lungs is invested with a thin 
layer of connective tissue,—thz pulmonary pleura,— 
which contains numerous blood- and lymph-vessels, 
and is covered with endothelium. Here and there, 
beneath the pleura, as well as elsewhere in the 
lungs, between the lobules and around the alveolar 
passages and small bronchi, are small irregular 
nodules of lymphoid tissue. 
The epithelial cells of the alveoli often contain 
brown or black pigment, and pigment deposits are 
of the most frequent occurrence, in the adult lung, 
in the interlobular connective tissue, and in the con- 
nective tissue and lymph nodes at the base of the 
lungs, as well as in the above-mentioned lymphoid 
nodules. The greater part of this pigment is prob- 
ably taken up from the respired air, and transported 
through the cells or lymph-channels to the parts in 
which it is found. 
PRACTICAL STUDY 
Trachea.—A portion of the human trachea is placed 
for ten days in solution of chromic acid, and 
the hardening completed with alcohol. A small bit is 
embedded in wax or hardened liver,* care being taken not 
to rub off the ciliated cells in the manipulation, and the 
longitudinal and transverse sections are stained double 
and mounted in balsam. 
Uninjected Lung.—The lungs from the human subject, 
or any small animal, such as the dog, rabbit, or cat, hav- 
ing been carefully removed, a canula is tied into the 
* Much better in celloidin. 176 
NORMAL HISTOLOGY. 
trachea (or one of the large bronchi, if one lung only is 
to be prepared), and the organ is distended by pouring a 
one-sixth-per-cent, solution of chromic acid into the 
canula, which, for this purpose, may be connected by a 
short rubber tube with a funnel. When the lung is filled 
and its surface tense, the trachea or bronchus is tied, and 
the entire organ immersed in the same fluid with which 
its alveoli are filled. After a couple of days the organ 
may be cut in pieces and put into a stronger solution of 
the chromic acid, one-fifth to one-fourth per cent. In 
three or four days they are washed and transferred at 
first to dilute, and then to strong, alcohol. Sections* may 
be stained double and mounted in glycerin. 
To demonstrate the elastic fibres in the walls of the air- 
vesicles, thin sections of an unstained human lung are 
mounted in glycerin to which strong acetic acid has been 
added in the proportion of i~ioo. 
Epithelium of the Air-vesicles.—The lung of a freshly- 
killed animal (a young cat is best) is filled with a solution 
of silver nitrate 1-500, in the manner just described, and 
after remaining for half an hour, the tube between the 
funnel and the lungs should be lengthened to about six 
or eight inches, so as to increase the pressure, and the 
funnel filled with a mixture of equal parts of alcohol and 
water. Under this increased pressure, the silver solution 
will be partially driven out through the pleura and re- 
placed by the dilute alcohol. When this replacement is 
partially accomplished, the lung is placed entire in alcohol 
of the same strength and exposed to the light. After a 
few hours it may be cut into pieces and preserved in 
strong alcohol. Sections are made * from the surfaces 
* After embedding in celloidin. THE REST IRA TOR Y APPARA TVS. 
which have become brown, and mounted in glycerin 
tinged with eosin. 
Injected Lung.—From bits of human lung whose blood- 
vessels have been injected with the blue gelatin mixture 
through the pulmonary artery, sections, which need not 
be very thin, are made, stained with eosin and mounted 
in balsam. CHAPTER XIV, 
THE KIDNEY. 
If a longitudinal section be made through the 
middle of a rabbit’s kidney, the cut surface will pre- 
sent a well-marked separation into an outer cortical 
and an inner medullary substance; between these 
two are seen sections of large blood-vessels. The 
medullary portion, called medullary pyramid or me- 
dulla, and occupying the central part of the organ, 
terminates in the pelvis in a single short, rounded 
prolongation, called the papilla, at the end of which, 
with a low magnifying power, several tiny openings 
may be seen. The cut surface of the papilla pre- 
sents an uniform grayish appearance, while the seg- 
ment of the medulla adjacent to the cortex presents 
distinct bands or striae, radiating from the papilla 
and extending, in the form of narrow, isolated 
tapering rays, into the cortex, almost to the surface 
of the organ ; these cortical rays are called medullary 
rays. 
The cortex, surrounding the medulla like a thick 
shell, and covered by a firm, dense layer of connec- 
tive tissue—the capsule—consists, besides the medul- 
178 THE KIDNE V. 
179 
lary rays, of a grayish substance lying in the form 
of elongated truncated pyramids between the rays, 
and in a thin irregular layer of the same appearance 
directly beneath the capsule. The grayish, pyra- 
midal portions of the cortex are called cortical 
pyramids, and the entire substance of the cortex, 
exclusive of the medullary rays, is sometimes called 
the labyrinth. If the blood-vessels of the kidney 
have been injected with some colored substance, or 
if the vessels are well filled with blood, tiny vessels 
can be seen passing off from the large trunks which 
lie beween the cortex and medulla; and extending 
radially toward the surface of the organ through the 
centre of the cortical pyramids, and at each side of 
these vessels, may be seen a row of minute globular 
structures, which are the Malpighian bodies or 
glomeruli. 
o 
The human kidney differs from that which we 
have jlist described, in that it consists of a number 
of just such structures crowded together to form a 
single organ. In embryonic life its composite nature 
is evident, because each renculus—as each portion 
corresponding to the rabbit’s kidney is called—is 
separated from its neighbors by a certain amount of 
connective tissue, giving the surface of the organ a 
lobulated appearance. As the individual matures, 
the renculi usually become merged into one another, 
so that we no longer see on the surface any trace of 
its composite character. This is betrayed, however, NORMA L HIS TO LOG Y. 
by the fact that the medullary pyramids of the 
primitive renculi persist as separate structures, and 
we thus have in the adult human kidney just as 
many medullary pyramids and papillae as there were 
original renculi. We find also, which is a striking 
feature in the adult human kidney, that the cortical 
substance is not confined to the cortex, but extends 
into the pelvis between the papillae, often as far as, 
and sometimes farther than the papillae themselves. 
Not very infrequently the divisions between the 
primitive renculi are not entirely obliterated in the 
process of development, and the surface of the kid- 
ney, even in the adult, is distinctly lobulated. 
Having thus acquainted ourselves with the general 
structure of the kidney, we have now to study the 
elements of which it is composed, and the way in 
which they are grouped to form the different parts 
above described. The kidney is a tubular gland; 
the innumerable tubes of which it is mainly com- 
posed are lined with epithelial cells, and run a very 
tortuous course from their origin in the cortex to 
their termination in the tiny openings, above men- 
tioned, at the apex of the papillae. They constitute, 
with the cells lining the walls of the glomeruli, in 
which they originate, the parenchyma of the kidney. 
In addition to the parenchyma we have, then, to 
study the connective tissue or interstitial tissue of 
the organ and the blood-vessels. 
The tubes of the kidney, called in general urin~ THE KIDNEY. 
181 
iferous tubules, consist of an apparently homogeneous 
membrana propria lined throughout with a single 
layer of epithelial cells, which differ greatly in char- 
acter and form in different parts of the tubules; the 
tubules have received special names in different 
parts of their course. 
Each tubule commences within a cortical pyramid, 
in a dilatation called the glomerulus, with whose 
capsule, presently to be described, its membrana 
propria is continuous; it is narrow as it leaves the 
glomerulus, but broadens out at once into a wide, 
convoluted canal—convoluted tubule—which winds 
about in the pyramid, finally approaching a medul- 
lary ray ; this it enters, and, suddenly becoming very 
narrow, descends more or less deeply into the 
medulla; here, widening somewhat, it turns sharply 
on itself and ascends into a medullary ray again. 
This portion of the tube, from the point at which it 
becomes narrow and begins to descend in the 
medullary ray, is called Henle's loop, and the arms of 
the loop are called, following the course which the 
description has taken, the descending or narrow, and 
the ascending or broad arms of Henle’s loop. The 
ascending arm of Henle’s loop, on arriving in the 
cortex, widens and enters a cortical pyramid, form- 
ing what is known as the intercalated tubide; this 
resembles the convoluted tubules, among which it 
winds in and out, and then passes over, entering a 
medullary ray, into a straight uriniferous tubule. 182 
NORMAL HISTOLOGY. 
This is again narrower than the convoluted tubules, 
and passes directly downward through the medulla, 
joining other similar tubules dichotomously and 
becoming larger as it does so, until at length it 
opens at the apex of a papilla. The uriniferous 
tubules run an entirely independent course until, as 
straight tubules, they join one another by twos, to 
form the outlet ducts. 
We have now to consider the epithelium which 
lines the tubules. Commencing at the straight 
tubules in the papillae, we find that in their lower 
portion they are lined by cylindrical cells with large 
nuclei and transparent bodies; further up the cells 
become more nearly cuboidal, and are often flattened 
in the medullary rays. The epithelium of the con- 
voluted and intercalated tubules is similar in charac- 
ter, and consists of large granular striated cells, 
whose outlines are not well defined, and which 
nearly fill the lumen of the tube. The ascending 
arm of Henle’s loop is lined with pyramidal or low 
cylindrical, granular cells; while the very narrow 
descending arm is lined with flat, transparent cells, 
whose nuclei usually project into the lumen of the 
tube. 
The glomeruli consist, in the first place, of a mem- 
branous, apparently structureless capsule, similar to 
and continuous with the membrana propria of the 
tubules. The epithelium of the convoluted tubules, 
as the latter join the glomeruli, becomes flattened THE KIDNEY. 
183 
and continuous with a layer of very thin transparent 
cells, which completely line the capsule. At one 
side of the glomerulus, usually opposite to the at- 
tachment of the tubule, a small artery—the vas 
afferens—pierces the capsule and immediately di- 
vides into a number of capillary loops, which wind 
about one another, forming a complicated vascular 
tuft; the blood from this tuft is collected into a 
vein—vas efferens—which is, as a rule, somewhat 
smaller than the afferent artery, and leaves the 
glomerulus near the point where the latter enters. 
The capillary tuft within the glomerulus is cov- 
ered also with a layer of flat cells like those lining 
the capsule. 
Let us now review the positions of the different 
parts of the tubules in the kidney. In the papillae 
are the termini of the straight tubules; in the 
medulla lie the straight tubules and portions of 
Henle’s loops ; in the medullary rays are the upper 
portions of the straight tubules, and of both arms 
of Henle’s loops ; in the labyrinth, including the 
cortical pyramids, are the convoluted tubules, inter- 
calated tubes, and the glomeruli. 
The distribution of the blood in the kidney yet 
remains to be considered. The larger branches of 
the renal arteries, accompanied by the veins, enter 
the organ at the bases of the medullary pyramids, 
and divide into large arching trunks which pass, in 
various directions, with their convexity toward the 184 
normal histology. 
cortex, along the irregular boundary line between 
the cortex and medulla. From the convex side of 
the arterial trunks spring numerous small branches, 
each of which enters at once the apex of a cortical 
pyramid, and proceeds directly toward the surface 
of the organ; these arteries are called interlobular 
arteries.* From these interlobular arteries lateral 
twigs are given off at frequent intervals, which, after 
passing a short distance, enter the glomeruli as the 
arteriae afferentes. On leaving the glomerulus, the 
efferent vein—which still carries arterial blood— 
breaks up into a capillary net-work, which lies 
among the adjacent convoluted tubules and in the 
neighboring medullary rays, the meshes in the for- 
mer region being rounded, in the latter, elongated, 
corresponding to the character of the tubules among 
which they lie. From these the blood is collected 
into small veins, which in turn pour it into interlob- 
ular veins, and these, following the course of the 
interlobular arteries, finally pour it into the large 
arched trunks between the cortex and medulla. In 
the superficial portions of the cortex there are no 
glomeruli, and here small venous trunks centre in 
1 If we consider a circumscribed portion of the cortex of the kid- 
ney, having for its centre a medullary ray, and extending on every 
side as far as to the nearest interlobular vessels, we see that in this 
limited area we have all of the essential structural elements of the 
cortex—a medullary ray surrounded by convoluted tubules and glomer- 
uli. Such groups of elements, although they have by no means a 
separate existence, and can be but indefinitely bounded, have been 
called iobuli; and, hence, the vessels passing between them are termed 
interlobular vessels. THE KIDNE V. 
185 
the commencement of an interlobular vein, forming 
the well-known stelhilcz Verheyenii. 
The medulla receives its blood in part from the 
vasa efferentes of the glomeruli, which lie near the 
boundary, between cortex and medulla; in greater 
quantity from the large arterial arches. Vessels 
from the latter sources descend in spreading tufts, 
called vasa recta, between the tubules, and break up 
into a long-meshed capillary net, the blood from 
which is collected in part into a round-meshed 
venous net-work in the papillae, and returned in 
straight veins along the tubules to the venous 
arches, and in part passes directly back to the 
arches without going down to the papillae. The 
capsule of the kidney receives its blood in part 
from the terminal twiglets of the interlobular ar- 
teries, in part from terminal branches of the phrenic, 
lumbar, and supra-renal arteries, and it passes into 
the stellate veins. 
The connective tissue of the kidney, aside from 
that which forms the capsule, lines the pelvis, and 
is distributed along the walls of the larger blood- 
vessels and around the glomeruli, is very small in 
amount. It may, however, be demonstrated here 
and there, and is most abundant in the vicinity of 
the papilla. 
PRACTICAL STUDY. 
Rabbit's Kidney—General View.—A rabbit’s kidney is 
cut transversely across the middle and hardened in two- 186 
NORMAL HISTOLOGY. 
per-cent, solution of bichromate of potassium and alco- 
cohol. Thin sections are made across the entire organ, 
including cortex, medulla, and papilla, stained double 
and mounted in balsam. 
Isolated Tubules.—A small fragment of fresh kidney, 
including both cortical and medullary portions, is placed 
in a mixture of equal parts of alcohol and strong hydro- 
chloric acid ; the acid partially dissolves the intertubular 
tissue, so that after a time the tubules can easily be pulled 
apart. This is usually effected in about twelve hours ; 
Dut the specimen should be examined from time to time 
after it has been in the acid for eight hours, and removed 
as soon as the object is accomplished. It is allowed to 
soak for a few hours in water to remove the acid, and 
then small bits are torn off, including cortical and medul- 
lary substance, and the tubules carefully separated on a 
slide. They are extremely brittle, and great care must 
be used in their isolation ; this may be done by needles, 
or better by allowing small drops of water to fall upon 
the specimen on a slide, from a pipette. When 
sociation is partially effected, the excess of water should 
be removed with filter paper, and a mixture of equal parts 
of saturated solution of picric acid and glycerin added, 
in which it is mounted and preserved. 
Sections of Uninjected Human Kidney.—A perfectly 
fresh human kidney is cut into small pieces and hardened 
in strong alcohol. Sections are made in a plane vertical 
to the surface of the organ, including both cortical and 
medullary portions, and also parallel to the surface, 
through the cortex. They are stained double and 
mounted in glycerin. THE KIDNEY. 
187 
Sections of Injected Kidney.—The kidney is injected, 
through both the renal artery and vein, with the blue 
gelatin mixture, and sections in different directions are 
stained with eosin and mounted in balsam. CHAPTER XV. 
THE GENERATIVE ORGANS. 
We shall confine our study of these organs to the 
testicle, prostate gland, and parts of the penis. 
MALE GENERATIVE ORGANS. 
THE TESTICLE SPERMATOZOA. 
This is a tubular gland, whose chief specific secre- 
tion is the spermatozoa; it is enclosed by a firm, 
dense connective-tissue capsule, called the albu- 
ginea, which sends inward several incomplete septa, 
which divide the organ into a number of communi- 
cating cavities, and unite at its posterior superior 
part in a dense, wedge-shaped mass of connective 
tissue, called the corpus Highmori. The more or 
less conical cavities between the septa contain wind- 
ing, anastomosing, and looped tubules, called semi- 
niferous tubules, which constitute the secreting por- 
tion of the organ. As the tubules approach the 
corpus Highmori, they become narrower and 
straighter—tubuli recti—and are lined with cylindri- 
cal epithelium, and, on entering that body, form a 
net-like series of intercommunicating channels lined 
188 THE GENERATIVE ORGANS. 
189 
with flattened cells, called the rete testis. The chan- 
nels of the rete testis are continuous with several 
tubules, which, passing upward and backward, be- 
come very much convoluted, and form a number of 
conical masses—coni vasculosi-z-which largely consti- 
tute the head of the epididymis. The tubules of 
the coni vasculosi gradually unite as they descend 
to form a single canal, which, with numerous wind- 
ings and contortions, constitutes the body and tail 
of the epididymis, and finally becomes continuous 
with a straight, thick-walled ascending tube—the 
vas deferens. 
The seminiferous tubules, which chiefly concern 
us here, lie embedded in loose, delicate, lamellated 
connective tissue, which is abundantly supplied with 
blood-vessels, and contains many cells ; among the 
ordinary connective-tissue cells of various forms, 
large granular, often pigmented cells are not infre- 
quently seen lying singly or in groups, and some- 
times in rows along the blood-vessels; their nature 
and significance are still doubtful. The tubules 
have a distinct membrana propria, and are lined 
with several layers of cells piled irregularly over 
one another, which differ in form under different 
circumstances, and sometimes in different parts of 
the same gland. 
In a tubule which is not producing spermatozoa, 
the outer row of cells—those lying upon the mem- 
brana propria—are large, granular, well-defined, nu- NORMAL HISTOLOGY. 
cleated cells; and upon these lie two or three irreg- 
ular layers of smaller nucleated cells with ill-defined 
cell-bodies. Between the cells of the inner layers 
a peculiar, irregular-branching net-work is seen, 
which, by some recent observers, is believed to be 
formed, for the most part, by branches of the outer 
row of cells; and it is supposed that it serves as a 
loose framework in which the inner cells are sup- 
ported. Others believe it to be only intercellular 
cement-substance. The lumen of these tubules 
may be filled with granular material or may con- 
tain spermatozoa. 
In tubules which are in full functional activity, 
the cavity is usually filled with more or less granular 
material and mature and immature spermatozoa, and 
on every side a multitude of clusters or bundles of 
developing spermatozoa are seen, with the heads 
embedded among the cells of the inner layers, which 
are similar to the lining cells above described, and 
the tails stretching brush-like into the cavity of the 
tube. 
According to some observers, the spermatozoa are 
formed from certain of the cells of the inner layers, 
which are called spermatoblasts. The process of de- 
velopment, according to this view, commences in the 
muclei of the spermatoblasts, which become con- 
verted into the head, while the tail is an outgrowth 
from the nucleus, or is produced by a transformation 
of a portion of the cell-protoplasm. Others believe THE GENERATIVE ORGANS. 
that the spermatozoa are formed by the growth in- 
ward, from the large outer cells, or from cells lying 
among these, of a long-stemmed bud-like process, 
whose dilated end divides into a number of longitud- 
inal segments, each of which finally becomes a sper- 
matozoon. That the latter is the mode of development 
in certain animals, e.g. the rat, would seem to be 
unquestionable. 
The mature spermatozoa differ in form in different 
animals; in man they consist of a flattened, pear- 
shaped portion, called the head, the small end of 
which is directed forward ; and a delicate, tapering, 
almost filiform portion, called the tail; while be- 
tween the head and tail is a short, narrow segment, 
called the middle piece. When living, and under 
favorable conditions, the spermatozoa are capable 
of performing rapid movements, the whole organism 
being driven hither and thither by wavy vibrations 
of the tail. 
Spermatozoa.—These may be obtained, from the sem- 
inal vessels of man, or from the sediment of urine in 
which they occur either normally, or under pathological 
conditions. They are well preserved by a mixture of 
equal parts of saturated sol. of picric acid, glycerin, and 
water, in which they may be mounted. 
PRACTICAL STUDY. 
Spermatozoa for comparative study may be readily ob- 
tained by making an incision into the head of the epi- 
didymis of a dog, rabbit, or guinea-pig, and receiving the 
milky fluid which exudes in the above picric acid fluid. NORMAL HISTOLOGY. 
The movements of the living spermatozoa may be 
studied by mixing some of the milky fluid from the epi- 
didymis of a freshly killed animal, on a warm slide, with 
salt solution, and protecting from pressure 
by a hair. 
The temperature of the slide should be kept at about 
the same elevation as that of the animal from which they 
are taken. The movement may be stopped by the ad- 
dition of water. 
Sections of Testicle.—Small pieces of the human tes- 
ticle, obtained as soon as possible after death, or, if this 
cannot be obtained, of the testicle of the cat, rabbit, dog, 
or rat, are hardened in 2-per-cent. sol. of potassium bichro- 
mate and alcohol. Sections from the different parts are 
stained double, and mounted in glycerin or balsam. The 
differences between the structure of the testicle in the 
lower animals and man cannot be described here. 
The prostate is a racemose gland, in which the 
alveoli, instead of being more or less spheroidal, as 
is usually the case in racemose glands, are often 
very much elongated and irregular in shape, and 
very frequently present high, narrow, irregular folds 
in their walls. The alveoli are lined for the most 
part with a single layer of cylindrical epithelium. 
The excretory ducts are lined, within the gland, with 
cylindrical, which pass over into flattened cells, as 
they approach the urethral orifice. The alveoli and 
ducts lie embedded in a dense mass of interlacing 
THE PROSTATE GLAND. THE GENERA TIVE ORGANS. 
bundles of smooth muscular tissue, intermingled 
with elastic fibres and a small amount of fibrillar 
connective tissue. In the periphery of the gland 
the muscular tissue forms a sort of capsule of vary- 
ing thickness, which, in turn, is enclosed in a fibrous 
tunic. 
Section of Gland.—A bit of that portion of the pros- 
tate gland of man which lies behind the urethra, is 
hardened in potassium bichromate and alcohol, and the 
sections are stained double and mounted in balsam. 
PRACTICAL STUDY. 
URETHRA AND CORPUS SPONGIOSUM. 
The tissues which form the penis are so various, 
and present such essential differences in their ar- 
rangement in different parts of the organ, that a de- 
tailed study of its structure does not lie within the 
scope of this manual. Inasmuch, however, as the 
urethra is so frequently the seat of surgical opera- 
tions, and as the corpus spongiosum, which sur- 
rounds a portion of it, presents an example of a 
variety of tissue which we shall have no opportunity 
to study elsewhere, it is desirable to briefly consider 
their structure here. 
The urethra, divided into three portions—a pros- 
tatic, a membranous, and a spongy,—consists of a 
mucous membrane which is surrounded by a muscu- 
lar sheath. The considerable differences in struc- 
ture which its different parts present are due chiefly 194 
NORMAL HISTOLOGY. 
to variations in the form of the epithelium and the 
character and arrangement of the muscular tissue 
The mucosa is composed, in all parts alike, of 
fibrillar connective tissue containing numerous elas- 
tic fibres and richly furnished with cells; upon the 
free surface of this rests the epithelium, which, at 
the meatus and in the fossa navicularis, is of the flat, 
laminated variety ; this passes over into a single 
row of cylindrical cells which line the spongy por- 
tion ; and this in turn merges into the spheroidal, 
pear-shaped, prismatic, and flattened ceils of the 
prostatic portion, which, lying in several layers, are 
quite similar in form and arrangement to the epithe- 
lium of the bladder. 
Outside of the mucosa, and but indistinctly sep- 
arated from it, is the submucosa, which consists of 
connective tissue with elastic fibres, and is especially 
characterized by a dense net-work of veins which re- 
ceive their blood from the rich capillary system lying 
in the mucosa beneath the epithelium. This venous 
net-work is so dense and the vessels so large as to 
lend to the submucosa, especially in the prostatic 
and membranous portions, the character of erectile 
tissue (see below). 
Here and there, in the spongy portion, larger and 
smaller irregular depressions, called lacunce Morgagni, 
are seen in the surface of the mucous membrane. 
Racemose glands, called Littre s glands, lie embed- 
ded in the mucous membrane, sometimes extending THE GENERATIVE ORGANS. 
into the muscular tunic ; their excretory ducts, 
sometimes short, sometimes long and tortuous, open 
on the surface of the mucous membrane. In the 
prostatic portion, the prostatic and ejaculatory ducts 
pierce the mucous membrane, as do the ducts of 
Cowper’s glands that of the posterior segment of the 
spongy portion. 
The muscular tunic of the urethra consists, in 
general, of an inner longitudinal and an outer circu- 
lar layer of smooth muscle-cells, but varies greatly 
in structure in the different portions. The outer 
layers of the posterior portion of the canal are 
formed, in part, of striated muscle. The musculosa 
of the spongy portion consists entirely of smooth 
muscle-cells, and forms a complete circular layer in 
the posterior region alone, while anteriorly only 
scattered, transversely and obliquely placed cells are 
found. 
When the urethra is closed the mucous membrane 
is thrown into irregular longitudinal folds. 
The urethra is enclosed through a part of its 
length in the corpus spongiosum, which is largely 
composed of a kind of tissue called erectile tissue; 
and before describing this body it will be well to 
consider for a moment the nature of this kind of 
tissue. 
Erectile tissue, in certain cases, consists simply of 
a somewhat circumscribed collection of larger and 
smaller veins, which under, certain circumstances, 196 
NORMAL HISTOLOGY. 
may become distended with blood, thus causing the 
part in which they lie to expand ; in other cases it 
consists of numerous larger and smaller irregular- 
communicating cavities, separated from one another 
by broad or narrow interlacing bundles of connective 
tissue and smooth muscular tissue, and in communi- 
cation with arterial trunks or capillary blood-vessels ; 
the cavities are lined with endothelium, and, while 
usually containing but a small amount of blood, and 
in this condition appearing simply as slits or narrow 
irregular spaces in the tissue, they may, under cer- 
tain conditions, become distended with blood, when 
they assume the character of spheroidal, or broad 
elongated cavities, and thus cause a considerable 
increase in volume of the part in which they are 
situated. The corpus spongiosum is composed 
largely of erectile tissue of the character last de- 
scribed. 
The corpus spongiosum is enclosed in a dense con- 
nective-tissue sheath which contains elastic fibres 
and a few smooth muscle-cells. From this a multi- 
tude of narrow trabeculae or septa, composed largely 
of smooth muscle-tissue, pass inward in variou 
directions, and dividing and subdividing, form an 
intricate series of spaces, which are the above-men- 
tioned blood-cavities. This system of trabeculae and 
septa is continuous, within, with the submucosa of 
the urethra. 
The erectile tissue is most abundant below the THE GENERATIVE ORGANS. 
urethra; above, the blood is collected into venous 
trunks, which, joining similar trunks from the cor- 
pora cavernosa above, convey the blood away from 
the part. The corpora cavernosa are similar in 
structure to the corpus spongiosum. 
PRACTICAL STUDY. 
Transverse Sections.—The corpus spongiosum and the 
posterior portions of the urethra are dissected from the 
remainder of the penis and hardened in potassium bichro- 
mate and alcohol. Transverse sections from the different 
regions are stained double and mounted in balsam. 
FEMALE GENERATIVE ORGANS. 
THE OVARY. 
The ovary is a gland whose vesicular alveoli have 
no excretory ducts, but discharge their contents by 
periodic rupture at the surface of the organ. These 
alveoli are called Graafian follicles, and the ovum 
may be regarded as their specific secretion. They 
lie embedded in a peculiar connective-tissue stroma, 
the interstitial tissue, and in the adult are confined 
to the peripheral zone. We have, then, in studying 
the ovary to consider the interstitial tissue, with its 
blood-vessels ; and the glandular tissue or Graafian 
follicles. 
On looking at a thin transverse section of the 
ovary, we see that it presents two indistinctly 
separated zones ; an inner or central zone, including 198 
NORMAL HISTOLOGY. 
the ramifications of the larger blood-vessels, and called 
the medullary portion ; and an outer, denser cortical 
zone, in which the follicles lie. The interstitial tissue 
consists, throughout the entire organ, of connective- 
tissue bundles, which in the medullary portion are 
somewhat loosely interwoven and associated with 
elastic fibres and smooth muscle-cells. In the corti- 
cal zone the muscular elements fail, the connective- 
tissue bundles are finer, and cross and interlace in 
all directions, surrounding the follicles, in whose 
vicinity they are modified so as to form a kind of 
capsule. Near the surface of the organ the connec- 
tive-tissue fibres arrange themselves in crossing lay- 
ers, to form a dense but not distinct sheath, called 
the albuginea. 
The connective tissue of the ovary, especially in 
the cortical zone, contains a great number, and in- 
deed in some parts seems almost entirely to consist 
of spindle-shaped, flattened, and irregular branch- 
ing cells, among which are not infrequently larger 
and smaller pigmented cells and polyhedral cells 
resembling epithelium. 
The surface of the organ is covered by a single 
layer of cylindrical epithelium, whose extreme sig- 
nificance we shall recognize when we study the de- 
velopment of the Graafian follicles. The ovary has 
no serous covering, the peritoneum being replaced 
by the epithelial cells. 
The interstitial tissue of the ovary is very vascu- THE GENERATIVE ORGANS. 
lar; the large arterial trunks, entering from the 
broad ligament, divide and subdivide in the medul- 
lary portion, and pass off in larger and smaller twigs 
into the cortex, from which an abundant capillary 
net-work is formed around the follicles. The ar- 
teries frequently run a very tortuous course, twist- 
ing and turning upon themselves, and are character- 
ized, moreover, by the great abundance of smooth 
muscle-cells in their walls. Lymphatic vessels are 
abundant. Concerning the distribution of nerves, 
our knowledge is still very meagre. 
We have now to consider the structure of the 
Graafian follicles, to which the parts just described 
are subservient. The Graafian follicles in the ovary 
of the adult female, at the child-bearing age, present 
by no means the same appearance ; some are large 
and readily visible to the naked eye ; others very 
minute, and presenting under the microscope an en- 
tirely different structure. These differences in 
structure are accounted for by the fact that certain 
of the follicles are mature or approaching maturity, 
while others are still undergoing development. 
We will first consider the structure of those which 
are mature, or nearly so. The interstitial tissue of 
the ovary arranges itself, in the immediate vicinity 
of the follicle, in the form of a tolerably well-defined 
wall, called the theca folliculi, consisting of an ex- 
ternal denser layer and an internal layer very richly 
supplied with cells, and containing an abundant 200 
NORMAL HISTOLOGY. 
capillary net-work. Within the theca folliculi is a 
layer, usually several cells deep, of larger and 
smaller spheroidal, or, in the periphery, cuboidal 
epithelium, called follicular epithelium, and consti- 
tuting the so-called membrana granulosa. At one 
or other side the follicular epithelium is heaped up 
into a larger or smaller mass, which projects into 
the cavity of the follicle and contains the ovum ; 
this accumulation of cells is called cumulus proligerus 
or germ-hill. The remainder of the follicular cav- 
ity is filled with a colorless fluid, in which not 
infrequently fine granules are suspended. This fluid 
increases in quantity as the follicle approaches ma- 
turity, and the pressure occasioned by its accumu- 
lation probably conduces in no slight degree to 
the final rupture of the follicle. The follicular 
epithelium immediately surrounding the ovum is 
cylindrical and arranged radially about it. 
In the ovum itself, which is a cell of the most 
highly developed type, we recognize four structural 
elements: I, a thick hyaline membrane, presenting, 
with high powers, a delicate radial striation, and 
called the zona pellucida; 2, within the zona pellu- 
cida is the cell-body, consisting of coarsely and 
finely granular protoplasm, and usually called the 
vitellus; 3, the vitellus encloses a comparatively 
large vesicular, transparent, and sharply-outlined 
nucleus, the germinal vesicle ; 4, the germinal vesicle, 
which is usually somewhat eccentrically placed, con- THE GENERATIVE ORGANS. 
201 
tains, in addition to a nearly transparent fluid, a 
small dark, often almost opaque nucleolus, the ger- 
minative spot. 
As the Graafian follicles mature, they approach the 
surface of the ovary, often projecting above it ; the 
walls become thinner and less vascular at the pro- 
jecting side, and finally burst at a menstrual period. 
The ovum, with the fluid and a portion of the follic- 
ular epithelium, is discharged, and through the 
hemorrhage which occurs from the capillaries in the 
follicular wall, the cavity becomes filled with blood. 
Changes now occur in the walls and cavity of the 
follicle, which result sooner or later in cicatrization 
and obliteration of the cavity. These changes vary 
considerably, depending upon whether or not the 
ovum is impregnated and develops; and the differ- 
ence expresses itself chiefly in a difference in size 
and persistence of the mass of tissue called the cor- 
pus luteum, which is produced by a growth of certain 
of the cells which remain after the rupture of the 
follicle. These differences cannot be considered 
here. The process of formation and disappearance 
of the corpus luteum, under all circumstances, is 
essentially the following: The blood which is poured 
out into the cavity passes through the same retro- 
gressive metamorphosis which extravasated blood 
in any part of the body may undergo : it coagulates, 
the serum is absorbed, the red cells disintegrate, and 
the coloring matter is in part taken up by surround- 202 
NORMAL HISTOLOGY. 
ing tissues, in part transformed into yellowish or red 
hematoidin (bilirubin) crystals, which in turn may 
change into a dark brown or black pigment, and be 
taken up by surrounding tissues, or remain for a long 
time unchanged. Hand in hand with these changes 
in the extravasated blood, go important changes in 
the follicular epithelium which is left behind, and in 
the cells of the theca folliculi. These cells prolifer* 
ate and form a soft, yellowish, very vascular tissue, 
resembling mucous tissue, which presently under- 
goes fatty degeneration. This yellow mass, sur- 
rounding and enclosing the remains of the extrava- 
sated blood, constitutes the corpus luteum ; and, as 
it disappears, its place is occupied by firm, dense 
connective tissue, which usually persists for a long 
time in the form of an irregular cicatrix, whose cells 
not infrequently still contain yellow or brown or 
black pigment. 
In order to understand all the forms which the 
immature Graafian follicles present, it will be neces- 
sary to study the way in which these structures 
originate. They are produced from the cylindrical 
epithelium which covers the ovary and is called 
germ-epithelium. At an early period of life the con- 
nective-tissue stroma of the ovary grows rapidly, and 
partially encloses groups of the germinal epithelial 
cells, which themselves proliferate, and dip down 
into the stroma of the organ in the form of elon- 
gated, solid or tubular masses. Presently these THE GENERATIVE ORGANS. 
203 
groups of cells become separated from the germinal 
epithelium at the surface, and appear then as irregu- 
lar masses of polyhedral or spheroidal cells, enclosed 
on all sides by connective tissue. A still further 
growth of the stroma separates these masses of cells 
into smaller groups, which gradually sink farther 
from the surface of the organ and become more 
widely separated from one another, while new 
masses of germ-epithelium are being enclosed at the 
surface. The cells which now lie in these separated 
cavities may at first all look alike, but later we 
usually find that one of them is larger than the 
others, is spheroidal, and occupies the centre of the 
cavity, while the rest are more or less cuboidal and 
arranged in a single layer around the wall, closely 
enclosing the central cell. This is the young 
Graafian follicle, and the central cell is the ovum ; 
but it presents as yet no zona pellucida. Gradually 
the follicular epithelium increases in quantity, form- 
ing several layers, and the ovum becomes eccentri- 
cally placed. There is still no cavity, but this soon 
appears, at first as a slit between the cells, and then 
grows wider and wider as fluid accumulates within 
it. Changes in the interstitial tissue lead to the for- 
mation of the theca folliculi, the epithelium directly 
about the ovum assumes a radial arrangement, the 
zona pellucida is formed, and we thus have the 
structure of the maturing follicle, with which we 
are already acquainted. 204 
NORMAL HISTOLOGY. 
Section of Adult Ovary.—The human ovary, or that of 
a recently killed dog or cat, should be divided 
great care being taken not to rub the surface, since the 
germ-epithelium easily comes off, and placed in a mixture 
of equal parts of one-quarter-per-cent, chromic acid so- 
lution and alcohol. After a week it is to be transferred 
to alcohol, in which in a few days it will become suffi- 
ciently hard. A half is embedded in wax,* the sections 
stained double and mounted in balsam. 
PRACTICAL STUDY. 
Section of Developing Ovary.—The ovary of a foetal or 
new-born animal is hardened and prepared as above. 
THE UTERUS. 
The walls of the uterus consist of crossing and 
interlacing bundles of smooth muscle-cells, with a 
small amount of connective tissue enclosing them 
and binding them together. The muscular tissue is 
arranged in three ill-defined layers, of which the 
middle is the thicker. It may be said, in general, 
that the bundles of the inner layer run transversely 
around the organ, those of the middle layer are 
longitudinal, while those of the outer layer are quite 
irregular; still in all the layers there is great lack of 
uniformity in the direction of the cells. A part of 
the external surface of the uterus is covered by the 
peritoneum, while its inner surface is lined with a 
mucous membrane. The latter consists of a frame- 
work formed of a delicate net-work of fibres, between 
* Better in celloidin. THE GENERATIVE ORGANS. 
which lie a great number of spheroidal, fusiform, and 
branched cells, and is covered on the free surface by 
cylindrical ciliated cells. In the mucosa the simple 
or branched tubular uterine glands are embedded; 
they are often tortuous, and, like the surface of the 
mucous membrane, are lined with cylindrical ciliated 
epithelium. * 
The surface of the mucous membrane of the body 
of the uterus is smooth, but in the cervix it presents 
regular folds, the so-called plicce palmatce; the con- 
nective-tissue framework of the cervical mucous 
membrane is, moreover, firmer in texture, contains 
fewer glands, and these, for the most part, are more 
or less globular and lined with short cylindrical or 
cuboidal epithelium. The ciliated epithelium of 
the body extends over on to the mucous membrane 
of the cervix, where it becomes continuous with the 
laminated epithelium covering the lower portion of 
the canal and the portio vaginalis. The uterus is a 
very vascular organ ; the mucous membrane is sup- 
plied with a rich capillary plexus, which passes inward 
close beneath the surface-epithelium. 
During menstruation the mucous membrane be- 
comes thickened—partly owing to the engorgement 
of its blood-vessels, and partly to the accumulation 
of fluid and lymph-cells in its interstices. The 
uterine glands are enlarged, and their epithelium, 
as well as that of the general surface of the cavity, 
is swollen. To what extent the blood, which, mixed 206 
NORMAL HISTOLOGY. 
with mucus and separated epithelium, is present 
in the cavity at the menstrual period, is due to 
the rupture of the engorged capillaries, and to 
what extent to diapedesis, is not yet definitely 
determined. 
PRACTICAL STUDY. 
Section of Human Uterus.—The uterus is cut into sev- 
eral pieces, and hardened in potassium bichromate and 
alcohol. The organ should be procured as soon as pos- 
sible after death, since the cilia of the lining epithelium 
are easily destroyed by the decomposition which com- 
mences very early in the uterine cavity. Sections per- 
pendicular to the surface of the mucous membrane are 
made from the cervix, and, in the body, from the lower 
portions or from the vicinity of the entrance of the Fal- 
lopian tubes, since here the uterine glands are more uni- 
formly arranged at right angles to the surface. They are 
stained double and mounted in balsam. 
THE VAGINA. 
In the walls of the vagina we recognize three lay- 
ers : an outer fibrous layer, a middle muscular layer, 
and a lining mucous membrane. 
The fibrous layer, by means of which the vagina 
is connected with adjacent parts, consists of connec- 
tive tissue with elastic fibres, and in texture is looser 
in its outer, denser in its inner, portions. The mus- 
cular layer consists of bundles of smooth muscle- 
cells, which present an indistinct grouping into an THE GENERATIVE ORGANS. 
207 
outer portion, formed of longitudinally arranged 
cells, and an inner, in which they have, in general, a 
transverse arrangement. 
The mucous vtembrane consists of delicate connec- 
tive tissue, loose in texture and containing coarser 
and finer elastic fibres ; it presents numerous trans- 
verse folds and elevations, and is covered by lami- 
nated epithelium, the cells in the lower layers being 
more or less spheroidal, but flat and scale-like at the 
surface. Numerous papillae project into the epi- 
thelium. Venous plexuses are formed within the 
deeper portions of the mucous membrane, which 
give to some parts of that structure the character of 
erectile tissue. 
PRACTICAL STUDY. 
Transverse Sections.—A bit of the vaginal wall should 
be stretched on cork and placed in a mixture of equal 
parts of one-fourth-per-cent, solution of chromic acid and 
alcohol, and after five days transferred to alcohol, in 
which the hardening is completed. Sections at right an- 
gles to the surface are stained double and mounted in 
glycerin. 
Isolated Surface-cells.—From a bit of vagina hardened 
as above, or simply in alcohol, the cells from the surface 
of the mucous membrane are scraped with a scalpel, 
stained on a slide with hsematoxylin, and mounted in glyc- 
erin. Familiarity with the appearance of these surface 
4tlls is of practical importance, since they are often found 
in urine. NORMAL HISTOLOGY. 
The mammary gland is a racemose, and when 
fully developed a lobulated, gland, whose spheroidal 
and elongated alveoli are formed by a membrana 
propria composed of flattened cells, and lined with 
cuboidal epithelium. The excretory ducts, which 
in each gland are fifteen to twenty in number, and 
open at the surface of the nipple, are lined with 
cylindrical epithelium. Fibrillar connective tissue 
with elastic fibres lies between the alveoli and 
lobules, and is abundantly furnished with blood- 
vessels. 
MAMMARY GLAND. 
The gland presents, both macroscopically and mi- 
croscopically, quite marked differences in appearance 
at different times, depending upon age, sex, and, in 
the adult female, upon whether or not the individ- 
ual is pregnant, and upon the period of pregnancy 
and the occurrence of lactation. 
In children, as in the adult male, the gland pre- 
sents, in general, a system of ramifying ducts, ter- 
minating in blind or in more or less pouched or 
dilated extremities; these lie embedded in connec- 
tive tissue, which makes up the greater part of the 
bulk of the gland. At puberty the gland of the fe- 
male undergoes considerable development; well- 
defined alveoli are found in the periphery of the 
gland connected with the excretory ducts, but the 
interstitial tissue is still more abundant than the THE GENERATIVE ORGANS. 
209 
gland-tissue proper. Essentially in this condition 
the gland usually remains until the climacteric 
period, if pregnancy does not occur. 
If, however, the individual becomes pregnant, the 
number and size of the alveoli rapidly increase ; the 
ducts, which in the virgin terminate only in dilated 
extremities, become connected with extensive groups 
of newly formed alveoli; the gland assumes a lobu- 
lated character, the connective tissue between the 
alveoli is very much less abundant in proportion to 
the gland-tissue, is looser in texture, and contains a 
great number of larger and smaller cells, and fre- 
quently fat-cells. During lactation the alveoli are 
very large, their epithelium contains fat-droplets in 
considerable number, and fat is found in greater or 
less quantity in the dilated cavities of the alveoli, 
and in the excretory ducts. When the secretory 
activity of the gland ceases, it undergoes involution, 
the alveoli become smaller, fat ceases to be produced 
by the cells, and the interstitial connective tissue 
becomes proportionally more abundant. 
With the decline of the reproductive power the 
mammary gland undergoes a marked and perma- 
nent involution: the terminal alveoli disappear, 
the smaller ducts are obliterated, and finally little 
is left of the organ excepting the deformed and 
collapsed larger ducts and a mass of connective 
tissue. 210 
NORMAL HISTOLOGY. 
Sections of Hardened Gland.—Portions of the gland 
from the human subject or from some of the lower mam- 
malia—if possible, both in a condition of rest and of func- 
tional activity—should be hardened in potassium bichro- 
mate and alcohol, and the sections stained double and 
mounted in glycerin or balsam. 
PRACTICAL STUDY. CHAPTER XVI. 
THE CENTRAL NERVOUS SYSTEM. 
THE SPINAL CORD. 
The spinal cord contains nerve-cells and nerve- 
fibres ; the former confined to the central, the latter 
most abundant in the peripheral, portions. These 
nerve-elements lie in the meshes of peculiarly 
arranged connective tissue in which blood-vessels 
ramify, and the whole is surrounded by a vascular 
connective-tissue membrane—the pia mater spinalis. 
On its anterior and posterior surfaces, narrow fis 
sures, reaching nearly to the centre, divide the cord 
into lateral halves ; into these fissures, called the 
anterior and posterior longitudinal fissures, the pi;; 
mater sends membranous prolongations. The 
anterior fissure is complete, the pia being found 01; 
both of its sides, which can be easily separated ; 
while in the posterior fissure the sides are bound 
together by the pia. 
In transverse sections of the cord a central gray 
portion is seen which is surrounded by an irregular 
white zone. The form which the gray matter as- 
sumes differs considerably in different parts of the 
cord, but has, in general, the form of an unsymmet- 212 
NORMA L HIS TO LOG V. 
rical H ; the cross-arm of the H is formed, in great 
part, by the nerve-substance which connects the 
lateral halves' of the cord, and is called the gray 
commissure; the uprights of the H lie completely 
embedded within the white matter of the lateral 
halves ; the anterior and broader ends being called 
the anterior cornua, the posterior and narrow ends 
the posterior cornua. Within the gray commissure, 
and separating it into an anterior and a posterior 
portion, a narrow canal, called the central canal, 
runs the entire length of the cord ; it is lined, in 
early life at least, with cylindrical ciliated cells, and 
is surrounded by delicate connective tissue. From 
the anterior and posterior cornua the spinal nerves 
pass off, dividing the white matter into three toler- 
ably distinct portions called the anterior, lateral, 
and posterior columns. 
In the white substance of the cord we find nerve- 
fibres, connective tissue, and blood- and lymph-ves- 
sels. The fibres are for the most part medullated, 
but have not, so far as we can determine with the 
technical facilities at present at our disposal, any 
neurilemma. They vary greatly in diameter, and 
although a large majority of them run longitudi- 
nally for the greater part of their course, we find 
in each transverse section a considerable number 
which run in an oblique or horizontal direction. 
Thus, we find in front of the anterior gray commis- 
sure, at the bottom of the anterior fissure, a band THE CENTRAL NERVOUS SYSTEM. 
213 
of horizontally arranged fibres running from one 
side to the other, called the white commissure. The 
fibres which pass out of the gray matter to form 
the roots of the spinal nerves, take also longitudi- 
nal and oblique courses. 
The connective tissue of the white substance is 
intimately connected at the periphery with the pia 
mater. The inner layers of the latter, consisting 
of delicate fibrillated and a few elastic fibres, send 
into the cord numerous branching septa, which 
divide the space occupied by the nerve-substance 
into smaller irregular spaces, in which the nerve- 
fibres run, these being surrounded by a delicate 
net-work of fibrillae, among which, here and there', 
variously shaped, for the most part flattened, some- 
times branching, connective-tissue cells are found.* 
This delicate supporting connective tissue is called 
ne2iroglia. In addition to the fibrillar and cellular 
elements above described, there seems to be a 
greater or less amount of soft homogeneous or 
finely granular material lying in the interstices of 
nerve- and connective-tissue fibres. The amount of 
connective tissue in the white substance of the cord, 
relative to the nerve-fibres, varies considerably in 
the different columns. 
In the gray matter of the cord, we have also 
nerve- and connective-tissue elements and blood- 
and lymph-vessels ; the first consisting of ganglion- 
cells and nerve-fibres. The nerve-fibres are in part 
* Neuroglia cells. See Appendix, p. 254. 214 
NORMAL HISTOLOGY. 
medullated, in part naked axis cylinders ; and be- 
sides these, a multitude of extremely delicate gray 
nerve-fibrils occur, which seem partly to come from 
the breaking up of axis cylinders, and partly to be the 
delicate branching processes of ganglion-cells. The 
nerve-cells of the gray matter are, for the most 
part, multipolar, and vary greatly in size, the largest 
being found, as a rule, in the anterior cornua. They 
are arranged in irregular groups in different parts 
of the cord. 
The connective-tissue elements of the gray mat- 
ter consist of a delicate neuroglia framework, simi- 
lar, in most respects, to that supporting the nerve- 
fibres between the coarser septa of the white 
substance. In the hinder portions of the posterior 
cornua there is a circumscribed area, which, in the 
fresh cord, has a peculiar gelatinous appearance, 
and is called the substantia gelatinosa of Rolando; 
in this we find comparatively few nerve-elements 
and much connective tissue. The limitations of 
this manual will not permit us to consider more in 
detail what is known of the course of the nerve- 
fibres through the cord, and the more exact rela- 
tions to the ganglion-cells. 
The blood-vessels enter the cord from the pia, 
along the septa which the latter sends into the 
organ, and ramify in its substance, the capillary 
plexuses being denser in the gray than in the white 
matter. THE CENTRAL NERVOUS SYSTEM. 
215 
In this organ also we have gray and white mat- 
ter ; but they are arranged in a much more compli- 
cated manner than in the spinal cord, the grouping 
being far too intricate for consideration here. The 
collections of gray matter are variously associated 
with one another by means of the nerve-fibres of the 
white substance. 
THE BRAIN. 
The white substance of both cerebrum and cere- 
bellum consists of coarser and finer, but all very 
small, nerve-fibres, running in various directions, and 
supported by a delicate connective-tissue frame- 
work, similar to the neuroglia of the cord. The 
gray matter consists here, as in the cord, of gang- 
lion-cells, and fine gray fibres supported by connec- 
tive tissue. In parts of the gray as of the white 
substance, certain cellular and fibrous elements oc- 
cur, of which it is at present impossible to say 
whether they are connective or nerve-tissue. In- 
deed, it is the difficulty of determining the nature of 
certain structures in the brain, together with their 
extreme delicacy, and the difficulty of isolating 
them, which renders the histology of the brain so 
difficult a theme, and explains the unsatisfactory 
state of our knowledge concerning it. 
We cannot do more in these lessons than to study 
briefly the structure of two of the best known and, 
at present, perhaps most interesting parts of the 216 
NORMAL HIS TO LOG V. 
brain—rnamely, the cortical portions of the cere- 
brum and cerebellum. 
a. Cortex of the Cerebrum.—The structure of this 
part of the brain differs somewhat in different re- 
gions, but that of one of the frontal lobes is suffi- 
ciently typical for our purpose. Here, in a section 
perpendicular to the surface, and extending through 
the entire depth of the gray matter, five zones or 
layers may be recognized, which, however, merge 
into one another. 
In the most superficial layer, the connective-tissue 
elements preponderate, and among them, delicate 
nerve-fibrils interlace, and a few small, scattered 
globular and elongated branching nerve-cells are 
found ; the second layer is characterized by a great 
number of small more or less pyramidal cells ; the 
third and broadest layer contains a proportionately 
smaller number of ganglion-cells than the second, 
but they are larger, and, for the most part, pyra- 
midal, or broad spindle-shaped, and multipolar, with 
their long axes perpendicular to the surface of the 
cortex ; in the fourth layer, which is much narrower 
than the last, are large numbers of small globular 
and irregular-shaped and branching cells; the fifth 
layer, finally, contains medium-sized spindle-shaped 
cells, with long tapering processes, together with a 
certain number of smaller irregular-shaped cells. In 
the third layer, certain of the delicate nerve-fibres 
begin to take a more regular course toward the THE CENTRAL NERVOUS SYSTEM. 
white matter; and in the fourth and fifth layers, 
they are readily seen in distinct bundles passing in- 
ward between the ganglion-cells. 
b. Cortex of the Cerebellum.—In sections through 
the cortex of the cerebellum perpendicular to the 
surface, three distinct layers are recognizable : the 
outer, sometimes called the molecular layer, consists, 
like the outer layer of the cerebral cortex, of a deli- 
cate connective-tissue framework, which supports 
fine nerve-fibres and small spindle-shaped and 
branching nerve-cells; the middle, cellular layer, is 
formed by an irregular row of large ganglion cells, 
Purkinje's cells, whose branching processes extend 
into and ramify in the outer layer, while the axis- 
cylinder process passes inward through the inner 
layer; the inner, granular layer, contains a great 
number of small spheroidal cells whose nature is un- 
determined. The granular layer merges gradually 
into the white substance and is thickest at the sum- 
mit of the convolutions, where also PurkinjVs cells 
are most abundant. 
The blood-vessels penetrate the cortex of both 
cerebrum and cerebellum, in the form of small arte- 
rial twigs from the pia, and form an abundant net- 
work in the gray substance, being somewhat differ- 
ently distributed in different paVts of the organ, and 
less abundant in the white .han in the gray matter. 
The Dura Mater of the brain is a dense connective- 
tissue membrane containing numerous elastic fibres 
and lined within by endothelial cells. Where it is 218 
NORMAL HISTOLOGY. 
attached to the bones of the skull, to whose inner 
surface it acts as periosteum, the tissue on the at- 
tached surface is looser in texture and abundantly 
supplied with blood-vessels. It contains the ordi- 
nary flattened connective-tissue cells, and usually a 
certain number of “ plasma ” cells. The dura mater 
of the cord does not form the periosteum of the 
bones forming the spinal canal, and hence in it the 
looser vascular layer is for the most part wanting. 
The Pia Mater of the brain is a thin connective- 
tissue membrane, covered on its outer surface with 
endothelium, and containing an exceedingly abun- 
dant net-work of blood- and lymph-vessels. Over 
the surface of the convolutions it forms a single mem- 
brane containing numerous small lymph-sinuses; 
but as it approaches the sulci it is partially separated 
into two indistinct layers, the outer bridging over 
the sulci, while the inner and more vascular layer 
dips down to the bottom of them. The space 
within the sulci, between the two layers, is occupied 
by numerous larger and smaller lymph-sinuses, 
which under normal conditions are little more than 
slits in the connective tissue, lined with endothelium; 
but they are capable of considerable dilatation when, 
for any reason, fluid accumulates in the meshes of 
the pia. These spaces are called sub-arachnoidal 
lymph-spaces; the outer layer of the pia having been 
formerly regarded as a distinct membrane, and called 
the arachnoid. These sub-arachnoidal lymph spaces, 
as well as the other numerous lymph-channels of the THE CENTRAL NERVOUS SYSTEM. 
219 
pia, are in communication with lymph-channels, 
called perivascular lymph-channels, which ensheath 
certain of the blood-vessels as they enter the brain- 
substance. 
PRACTICAL STUDY. 
Transverse Sections of Spinal Cord.—A perfectly fresh 
human cord should be freed from its dura mater, and short 
segments from different portions of it hardened in Muller’s 
fluid and alcohol.* Thin transverse sections are made 
through the entire cord in different portions, and may be 
stained first lightly with hsematoxylin and then deeply 
with eosin and mounted in balsam. A very excellent 
hardening agent for the nerve-centres is the bichromate 
of ammonium, 2-per-cent, solution, in which small frag- 
ments should lie for a week, and then, after careful wash- 
ing, the hardening completed with dilute and strong al- 
cohol. They may be stained and mounted as above.| 
Sections of Cortex of Cerebrum and Cerebellum.—These 
should be prepared in the same way as the spinal cord, 
pieces from the cortex of the frontal lobes being taken, 
and from the cortex of the cerebellum at any convenient 
part; they should not be larger than a cubic centimetre, 
and the chromic fluid well washed out before immersion 
in alcohol. 
Dura Mater.—A bit of this membrane should be 
stretched on a piece of cork with pins, hardened in alco- 
hol, embedded in hardened liver, and thin transverse 
sections made, stained double and mounted in glycerin 
or balsam. 
Pia Mater.—This may be prepared by the method 
given on page 125. 
* Embed in celloidin. 
f See new staining method, Appendix, p. 254. CHAPTER XVII. 
THE SKIN AND ITS ADNEXA. 
THE SKIN. 
We recognize in the skin three layers of tissue: 
I, an outer, epithelial layer, the epidermis; beneath 
this, 2, a layer of quite firm and dense connective 
tissue, the corium—true skin, cutis vera, or derma; 
3, a layer of looser connective tissue, the stibcu- 
taneous tissue, which, merging into the corium, 
serves to bind it to the underlying parts. The skin 
is variously modified in structure in different parts 
of the body, corresponding to the different condi- 
tions of exposure and wear to which it is subjected, 
and to form certain supplementary structures, such 
as the hair, nails, etc. ; and contains various sensory 
and secretory structures. 
In the epidermis we recognize two tolerably dis- 
tinct layers of cells: I, an outer'&r horny layer, con- 
sisting of very thin, transparent, tough, scale-like 
cells, which present, for the most part, no nuclei, 
and are packed closely together; 2, an inner layer, 
the so-called mucous or Malpighian layer, consisting 
of larger and smaller nucleated cells of varying 
shape and character; in the deeper portion, ad- 
220 THE SKIN AND ITS ADNEXA. 
joining the corium, the cells are more or less cyl- 
indrical ; above this they are spheroidal or polyhe- 
dral or elongated ; still nearer the surface they be- 
come flattened, and finally merge into the thin cells 
of the horny layer. In the middle zone the cells 
present a peculiar jagged outline, looking as if they 
were bordered by short delicate spines, by which 
the cells appear dove-tailed together. These spined 
cells—called prickle cells—are very characteristic of 
this part of the epidermis, and are also found in 
certain other parts of the body where stratified 
epithelium occurs, as in the vagina, mucous mem- 
brane of the mouth, etc. 
The relative thickness of the horny and Mal- 
pighian layers of the epidermis differs greatly in 
different parts of the body ; in some parts of the 
palms of the hands and soles of the feet the horny 
layer is very thick, and here we often find that the 
cells which lie between the horny and Malpighian 
layers form a distinct narrow, transparent zone, 
called the stratum lucidum. The deeper cells of the 
Malpighian layer contain, uniformly in the negro, 
and occasionally in circumscribed regions in white 
men, more or less brown or black pigment. 
The epidermis forms in but few regions of the 
body a layer of uniform thickness, since the corium 
sends up into it, at varying intervals, simple or 
branching, variously shaped papilla, the valleys be- 
tween which, as well as their summits, being cov- 222 
NORMAL HISTOLOGY. 
ered by the cells of the Malpighian layer. If we 
imagine a section made through the skin, parallel 
with its surface, and just deep enough to cut off the 
tops of the papillae, the cells of the Malpighian 
layer which lie between the latter, would appear, on 
looking at the cut surface, to be arranged in the 
form of a net-work, whose meshes are filled by the 
papillae of the corium. Hence it is that these col- 
lections of cells have received the name rete Mal- 
pighi. 
The corium is formed of interlacing bundles of 
connective tissue, which are coarser in the deeper, 
finer in the more superficial portions, where they 
extend into the epidermis, forming the papillae. 
Embedded in the papillae are capillary blood-vessels, 
nerves, and special terminal nerve-apparatuses. Elas- 
tic fibres are present in considerable number, and in 
the interstices of the fibres lie flattened, spindle- 
shaped, branching, and small spheroidal cells. In 
addition to these elements we sometimes find mus- 
cular tissue in the corium ; thus striated muscular 
fibres occur in certain parts of the skin of the face ; 
and smooth muscular tissue, aside from that belong- 
ing to the hair-follicle, is found about the sweat- 
glands, in the skin of the scrotum and penis, and in 
the nipple and its areola. 
The subcutaneous connective tissue we have al- 
ready studied when considering the connective tissue 
in detail. In some parts of the skin its texture is THE SKIN AND ITS ADNEXA. 
223 
so loose that the corium and epidermis can be 
readily moved to and fro upon the underlying parts 
or pinched up in folds; in others its fibres are short 
and tense, and bind the corium closely to the parts 
beneath. In the subcutaneous tissue of most parts 
of the body, greater or smaller deposits of fat occur, 
forming thpanniculus adiposus ; but in the subcu- 
taneous tissue of the scrotum, penis, eyelids, and the 
pinna of the ear, fat is not formed. 
Blood-vessels.—The arteries of the skin, which 
enter through the subcutaneous tissue, give off, in 
genera], three sets of branches, through which the 
blood is distributed to three principal sets of capil- 
laries: first, to those which supply the fat-tissue; 
second, to those which ramify in the sweat-glands ; 
third, to those which supply the hair-follicles, se- 
baceous glands, and the papillae of the corium. 
Each papilla is furnished with a capillary loop, ex- 
cept when it contains a tactile corpuscle, when the 
former may be absent. 
THE NAIL. 
We recognize in the hard substance of the nail, 
which corresponds to the horny layer of the epi- 
dermis, a body and a root; the former lies upon a por- 
tion of the somewhat modified corium, called the 
nail-bed, while the root is embedded in a shallow 
pocket of skin, the corium of which constitutes the 
matrix of the nail. The corium of the nail does 224 
NORMAL HISTOLOGY. 
not differ essentially from that of the skin in gen- 
eral; it is intimately connected with the periosteum 
of the phalanx, and presents longitudinal ridges, 
low in the matrix, higher in the nail-bed, which are 
covered with papillae. The latter are bent obliquely 
forward, and are more abundant in the nail-bed 
than in the matrix. Upon and between the pa- 
pillae several layers of variously shaped cells lie, 
corresponding to the Malpighian layer of the skin. 
In the body these cells pass quite abruptly into the 
flat, horny, nucleated cells of the hard substance of 
the nail; in the matrix, however, the transition is 
very gradual, and it is here that the growth of the 
nail occurs. The lunula is a portion of the nail in 
which the Malpighian layer is very thick, as it is in 
all parts of the root, and being evenly distributed 
over the surface of the papillae, does not permit the 
color of the blood in the capillaries of the papillae 
to be seen, as it is in the rest of the nail-bed, where 
the longitudinal ridges are higher, and covered by 
fewer cells. 
THE HAIR 
We distinguish in the hair; the shaft, which pro- 
jects above the surface of the skin ; the root, which 
is embedded in an oblique tubular depression, called 
the follicle; and the bulb, a dilated portion at the 
bottom of the follicle in which the hair ends. The 
follicle sometimes extends into the subcutaneous THE SKIN AND ITS ADNEXA. 
225 
tissue, sometimes only into the corium, and its walls 
are formed in the first place by a sheath of connec- 
tive tissue continuous with the corium, in which 
numerous blood-vessels ramify ; this sheath is lined 
by a thin transparent membrane, called the vitreous 
membrane. Within this follicular wall lies the root- 
sheath, which consists of two layers: an outer 
thicker layer, formed by the dipping down into the 
follicle of the cells of the rete Malpighi, and hence 
consisting of cylindrical, spheroidal; and somewhat 
flattened cells ; and an inner layer made up in turn 
of an external layer, called Henle's sheath, in which 
the cells resemble those of the horny layer of the 
epidermis, and are closely packed together to form 
a transparent mass ; and an internal layer, called 
Huxley s sheath, whose cells, belonging more prop- 
erly to the hair itself, are irregularly polygonal, 
somewhat flattened, and contain an elongated nu- 
cleus. 
Both at the opening of the follicle, and at its 
base, the layers of the root-sheath become indis- 
tinct, merging on the one hand into the cells of the 
epidermis, and on the other into those of the hair- 
bulb. At the bottom of the follicle is a projection 
from the connective tissue forming the wall of the 
follicle, in the form of a papilla, which corresponds 
to the papillse of the skin, and upon which the hair- 
bulb rests, surrounding it at the top and sides. 
The hair is produced by the growth of cells about 226 
NORMAL HISTOLOGY. 
the papillae; directly covering the latter are cylin- 
drical and cuboidal cells, corresponding to those of 
the rete Malpighi, which gradually become changed 
in shape, and more or less horny, and form the sub- 
stance of the hair-shaft. 
In the shaft we recognize three portions: I. A 
central or medullary portion, composed of cuboidal 
or more or less flattened cells, not infrequently en- 
closing between them tiny bubbles of air, which 
give the centre of the hair a dark appearance by 
transmitted light. Outside of this is 2, the cortical 
portion, making up the larger part of the bulk of 
the shaft, and composed of tough, horny, elongated, 
flattened cells closely packed together, and having 
within and between them, except in colorless hairs, 
granules of variously colored pigment. In that 
portion of the hair which lies within the follicle, 
and between the bulb and the free shaft, we find, 
while the hair is growing, that the cells of the cor- 
tical layer are larger, less flattened and horny, and, 
as above mentioned, merge into the large cylindrical 
and spheroidal cells of the bulb. Finally, the shaft 
is covered, 3, by the so-called cuticula, consisting of 
thin rectangular, non-nucleated, scale-like cells, 
which lap over one another, so that the lower 
cells, i. e., those nearest the root of the hair, cover 
a portion of the cells beyond, and these free edges 
often project slightly from the surface of the hair, 
giving it a finely serrated appearance. THE SKIN AND ITS ADNEXA. 
SEBACEOUS GLANDS, 
These are racemose glands, whose excretory ducts 
are lined with polyhedral and somewhat flattened 
cells. The alveoli, bounded by a membrana propria, 
are lined with granular polygonal epithelium, and 
the cavity is more or less filled with larger polyhed- 
ral cells, crowded with fat-droplets. The sebaceous 
glands, as a rule, either open into a hair-follicle near 
the surface of the skin, or their excretory ducts are 
pierced near the surface by the shaft of a hair. 
The hair-follicle, as above mentioned, is placed 
obliquely in the skin, and at the side at which it 
forms an oblique angle with the surface, a bundle 
of smooth muscle-cells is placed. This is attached 
to the connective-tissue sheath of the follicle in its 
lower third, and, passing obliquely upward, is in- 
serted into the upper portion of the corium at some 
distance from the opening of the follicle. A con- 
traction of the muscle thus placed will, of course, 
draw the hair-follicle, and with it the shaft, into a 
position more nearly perpendicular to the surface 
of the skin, and hence it is called the erector pilce. 
As a rule, the sebaceous follicle lies above the 
erector muscle in the angle which it forms with the 
upper portion of the hair-follicle, and is moved with 
the hair when the muscle contracts, and may even 
be pressed upon by it, when, as is frequently the 
case, it runs closely over the surface of the gland. 228 
NORMAL HISTOLOGY. 
This relation of the erector pilae muscle to the se- 
baceous gland is probably not without significance 
in connection with the discharge of the secretion of 
the latter. 
SWEAT-GLANDS. 
The sweat-glands, which are found in the skin of 
almost all parts of the body, although much more 
abundant in some than in others, are tubular glands, 
the tube consisting of a membrana propria, lined 
throughout with polyhedral and cuboidal epithelium. 
Its lower extremity, coiled into a ball, and held to- 
gether by loose connective tissue, lies sometimes in 
the corium, sometimes in the subcutaneous tissue. 
The upper portion of the tube, which serves as the 
excretory duct, passes to the surface of the skin, 
often taking a wavy course through the corium. 
It pierces the epidermis between two papillae, and 
here the walls of the duct cease, and it is bordered 
by epidermis-cells alone. If the epidermis-layer is 
thick, as in the palm-, etc., the course of the duct 
through it is a remarkably winding one. An abun- 
dant capillary net-work lies in the loose connective 
tissue of the gland-coil. 
NERVES. 
The nerves of the skin ramify in the subcutaneous 
tissue, and a certain number of them terminate here 
in the so-called Pacinian bodies; others pass into THE SKIN AND ITS ADNEXA. 
229 
the corium, where they form plexuses, varying in 
character in different parts of the body. From 
these, certain medullated nerves pass into the papillae 
and terminate in the tactile corpuscles (called Meiss- 
ner’s corpuscles); others pass to the hair-follicles 
and sebaceous glands; still other, non-medullated 
nerves enter the papillae or pass between the cells 
of the rete Malpighi, but their mode of termination 
is not yet definitely ascertained. The structure of 
the Pacinian bodies and Meissner’s corpuscles is too 
intricate, and the methods required for their com- 
plete demonstration too elaborate, to justify their 
further consideration here. 
PRACTICAL STUDY. 
Sections of Injected Skin.—A piece of skin is removed 
from an injected leg or arm, care being taken to include 
the subcutaneous tissue to a considerable depth ; it is 
stretched flat on a bit of cork, and placed in a mixture of 
equal parts of one-half-per-cent. chromic acid solution 
and alcohol ; after ten days it is transferred to strong al- 
cohol. When sufficiently hard it is embedded in wax or 
liver,* and sections made perpendicular to the surface ; 
these are stained lightly with haematoxylin, then with 
eosin, and mounted in balsam. 
Sections of Skin of Negro.—The skin is hardened in the 
chromic acid and alcohol mixture, the sections stained 
with picro-carmine, and mounted in glycerin. 
Sections of the Nail.—A nail should be separated from 
a finger which has been hardened in alcohol, together 
* Better in celloidin. 230 
NORMAL HISTOLOGY. 
with as much as possible of the connective tissue which 
binds it to the bone. In order to render the soft parts 
more consistent and more nearly like the body of the nail, 
so that uniformly thin sections can be made, the whole 
should be hardened by the gum method; see page 115. 
Longitudinal and transverse sections are made through 
the entire nail, and stained double and mounted in 
balsam. 
Sections of Hairs from Skin of Scalp.—A piece of skin 
from the scalp of an adult is stretched on cork and hard- 
ened in the above chromic acid mixture. Sections* are 
made as nearly as possible in the direction of the hair- 
follicles, so as to include the- entire root and bulb, and 
also at right angles to them. They may be stained double 
and mounted in balsam ; or instead of first staining with 
hsematoxylin they may be laid for twenty-four hours in a 
strong aqueous solution of analin green and then dehy- 
drated in the usual way in the eosin alcohol. By the 
latter method a very brilliant differentiation in color in 
the layers of the inner root-sheath may be obtained. 
Cells of the Cuticula of the Hair.—These are readily 
seen by placing a hair on a slide in a drop of strong sul- 
phuric acid, and covering; in a short time the cells will 
have become so much loosened that if the cover be lightly 
tapped upon, a certain number of them will float off into 
the acid, or may be seen bristling out from all sides of 
the shaft. 
Section of Skin from the Finger-tips.—This is prepared 
like the injected skin, and will show the thick layer of 
epidermis-cells with the stratum lucidum, the tortuous 
course of the sweat-gland ducts through the epidermis. 
* After embedding in celloidin. THE SKIN AND ITS ADNEXA. 
231 
In this preparation the ovoidal tactile corpuscles may be 
seen lying in some of the papillae, and if the subcutaneous 
tissue has been included in the section to a considerable 
depth, transverse or longitudinal sections of a Pacinian 
body may be found. CHAPTER XYIII. 
THE EYE. 
The organ of sight is composed of the eyeball 
and various accessory structures, such as the eye- 
lids, lachrymal gland, muscles, etc. The eyeball is 
composed, in the first place, of a dense, firm, sphe- 
roidal connective-tissue envelope, whose anterior 
transparent portion, the cornea, is more convex than 
the posterior opaque segment, the sclerotic, and 
differs somewhat from it in structure; the sclerotic 
is pierced posteriorly by the optic nerve. Within 
the sclerotic lies a vascular tunic, the choroid, 
formed of several layers of tissue, and thrown an- 
teriorly, just behind the sclero-corneal junction, 
into numerous longitudinal folds, called the ciliary 
processes. An extension from the ciliary processes 
passes forward, constituting the iris, which is a 
perforated vascular connective-tissue and muscular 
curtain, suspended behind the cornea, and con- 
nected peripherally, near the sclero-corneal junction, 
with a connective-tissue structure called the liga- 
mentum pectinatum. 
Passing backward from the ligamentum pectina- 
232 THE E YE. 
233 
turn, between the ciliary processes and the sclera, 
and attached posteriorly to the choroid, is a muscle 
having the form of a flattened ring, thickest in front, 
called the ciliary muscle. The direction of the 
muscle-cells in the ciliary muscle, which are of the 
smooth variety, is in part meridional or oblique, in 
part circular. The ciliary processes and muscle 
form together the greater part of a structure known 
as the ciliary body. The retina, the innermost of 
the layers forming the wall of the eyeball, spreads 
out from the point of entrance of the optic nerve 
over the inner surface of the choroid. At about a 
third of the distance back from the front of the 
eye, the nerve-elements of the retina cease in a 
wavy line, called the ora serrata; certain cellular 
elements continue, however, over the ciliary pro- 
cesses, under the name of pars ciliaris retince. 
The crystalline lens is suspended close behind the 
iris by a firm, delicate, fibrillated membrane, called 
the suspensory ligament, which is attached, on the 
one hand, to a membrane covering the ciliary pro- 
cesses, and on the other to the capsule of the lens. 
The cavity of the eyeball is divided by the lens 
and its suspensory ligament into two chambers,* 
the anterior and smaller of which is filled with a 
homogeneous fluid the aqueous fluid; the posterior, 
* By the anterior and posterior chambers of the eye, ophthalmolo- 
gists at present mean the cavities in front of the lens, separated by 
the iris, and formerly regarded as constituting the anterior chamber 
alone, while that containing the vitreous was called the posterior. 234 
NORMAL HISTOLOGY. 
with a gelatinous substance, the vitreous body, which 
presents an ill-defined lamellar structure, and some- 
times contains a variable number of ill-defined 
more or less granular cells. The vitreous is sur- 
rounded by a delicate membrane, called the hyaloid 
membrane, which is closely connected posteriorly 
with the lining membrane of the retina, and is 
hardly to be differentiated from it. The hyaloid 
membrane is thickened and fibrillated over the 
ciliary processes, where it is called the zonula ciliaris, 
and a prolongation forward from this constitutes 
the suspensory ligament of the lens. 
Having thus briefly described the general struc- 
ture of the eye, it remains for us to consider some 
of its parts somewhat more in detail; the scope of 
this manual will not permit us, however, to make 
an extended study of all or even any of the struc- 
tures in the eye j we shall be obliged to confine 
ourselves to the. more marked structural features of 
the cornea and sclera, the posterior portions of the 
choroid and retina, the iris and crystalline lens. 
The sclera is composed of very closely interwoven 
connective-tissue fibres, with fine elastic fibres, the 
latter most abundant near the inner surface. Be- 
tween the fibres, which have little regularity in their 
arrangement, lie flat connective-tissue cells, a certain 
number of which frequently contain pigment-gran- 
THE SCLERA. THE EYE. 
235 
ules. On the external surface the sclera sends off 
delicate fibres anteriorly into the subconjunctival 
tissue, while posteriorly, behind the muscle tendons, 
they join to form the wall of a lymph-sac, called the 
capsule of Tenon. On the inner surface certain 
fibres pass directly over into the choroid; others 
form the outer wall of a lymph-sac between the 
sclera and choroid, and called, on account of its 
yellow color, the lamina fusca; it resembles in 
structure the outer layers of the choroid, presently 
to be described as the membrana supra-choroidea, of 
which it is indeed a part. In man and many animals, 
the opening in the posterior segment of the sclera, 
through which the optic nerve passes, is crossed 
by a net-work of connective-tissue fibres; these pass 
in from the sclera on all sides, and surround the 
delicate bundles of nerve-fibres of the opticus, form- 
ing the lamina cribrosa. 
THE CORNEA. 
The cornea is directly continuous at its periph- 
ery with the sclera, but differs from it in struc 
ture in many particulars, among the more promi- 
nent of which are, the more regular lamellar 
arrangement of its connective-tissue basement-sub- 
stance, the greater transparency of the latter, the 
peculiar form of its cellular elements, and the free 
surfaces covered with cells. 
In a thin section of the cornea, perpendicular to 236 
NORMAL HISTOLOGY. 
its surface, we recognize, passing from before back- 
ward, five layers: 1. A stratified layer of epithelial 
cells—the anterior corneal epithelium—consisting of 
cells resembling in general form and arrangement 
those of the epidermis; that is, we have in the 
deepest layer, cylindrical cells, passing over into 
polyhedral, and these into flattened cells at the 
surface; 2. The anterior epithelium rests on a 
dense transparent membrane, called the anterior 
basal membrane, or lamina elastica anterior, which 
is composed of closely packed fibrillae ; 3. The body 
of the cornea—substantia propria cornece—is com- 
posed of connective tissue whose characteristics we 
have already studied ; 4. Lying closely upon the 
posterior surface of the last layer, is a thin, appar- 
ently structureless membrane—the membrane of 
Descemet or lamina elastica posterior—upon which 
lies : 5. A single layer of flattened polyhedral cells, 
called the endothelium of Descemet. 
Except at its extreme periphery, the cornea 
contains no blood-vessels. Nerves, on the other 
hand, are very abundant. These, in larger and 
smaller trunks, enter the cornea at the periph- 
ery, and dividing and subdividing, break up into 
bundles of extremely delicate fibrils, some of 
which are distributed to the superficial, others to 
the deep, layers of the cornea. These fibrils form 
extraordinarily delicate and intricate plexuses, and 
are finally resolved into the ultimate nerve-fibrvls THE E YE. 
237 
which, often finely beaded, pass off to their termi- 
nations. The exact mode of termination of the 
nerve-fibrils in the cornea is not yet sufficiently 
definitely known ; certain of them, however, seem 
to pass between the anterior epithelial cells, and are 
believed by some investigators to end in free ex- 
tremities at the surface. 
THE CHOROID. 
In the posterior portion of the eye, the choroid 
presents four layers, which, although intimately 
connected, and presenting no sharp line of division, 
may yet be more or less completely separated by a 
careful dissection. Directly beneath the lamina 
fusca of the sclera, and forming the inner wall of 
the above-mentioned lymph-sac, is the outermost 
layer, called the lamina supra-choroidea; it is com- 
posed of a series of superimposed connective-tissue 
membranes containing delicate elastic fibres and 
numerous flattened, irregular-shaped, often branch- 
ing pigmented cells. The layers are covered with 
endothelium, and the spaces between them are 
lymph-spaces or sinuses. 
Within the lamina suprachoroidea lies a layer, 
containing the larger arteries and veins of the 
choroid, called the external vascular layer, or the 
layer of Haller. This layer is composed of a 
groundwork similar to the suprachoroidea, in which 
the vessels are embedded, the arteries being often 238 
NORMA L HIS TOL O G V. 
closely surrounded by dense masses of pigmented 
cells. 
The inner vascular layer, called the chorio-capil- 
laris, follows next, and consists almost entirely of a 
very dense net-work of broad capillary blood-ves- 
sels. Finally, the choroid is limited within, by an 
extremely delicate, finely striated membrane, called 
the lamina vitrea, or membrane of Bruch. 
THE IRIS. 
The iris is a thin connective-tissue membrane, 
pierced near the centre by an opening, the pupil, 
and joined at the periphery to the ligamentum 
pectinatum and the ciliary body. The bulk of the 
iris, the substantia propria, consists of delicate inter- 
lacing connective-tissue fibres, among which are 
numerous variously shaped, often branching pig- 
mented and unpigmented cells. 
It contains numerous blood-vessels which are 
characterized by an extraordinary thickness of the 
walls. Near the pupillary margin lies a circular 
band of smooth muscle-cells—sphincter pupillcz— 
while radiating bands of similar cells passing from 
the periphery toward the pupil—dilator pupillce— 
are found in certain animals, but not in man. The 
anterior surface is covered by a layer of endothe- 
lial cells, while the posterior surface is covered by 
an irregular thicker layer of polyhedral cells, which 
are densely crowded with pigment, and constitute 
the so-called live a THE EYE. 
239 
THE RETINA. 
Of all the animal structures the retina is one of 
the most delicate, complicated, and difficult of 
study, and we can do little more here than indicate 
briefly the general grouping of its elements. It 
consists of a connective-tissue framework by which 
the nerve-elements are supported, and with which 
they are most intimately associated; and in some 
cases it is as yet impossible to say to which variety 
of tissue a given element belongs. We distinguish, 
in typical parts, ten layers ; commencing from 
within, they may be enumerated as follows: 
1. Membrana limitans interna. 
2. Layer of nerve-fibres. 
3. Layer of ganglion-cells. 
4. Internal molecular layer. 
5. Internal nuclear layer, 
6. External molecular layer. 
7. External nuclear layer. 
8. Membrana limitans externa. 
9. Layer of rods and cones. 
10. Pigment layer. 
The limiting membranes, the outer of which is 
perforated by numerous openings, are very delicate 
and homogeneous, and belong to the connective- 
tissue framework. In the layer of nerve-fibres, 
which is thickest around the entrance of the optic 
nerve,—thus forming the papilla,—the fibres spread 240 
NORMAL HISTOLOGY. 
out, intricately interlacing, into a thir sheet, and 
then pass outward into the next layer to join the 
ganglion-cells. These, which have the general 
characters of branching nerve-cells, send numerous 
processes into the internal molecular layer, where 
they break up into an extremely delicate fibrillar 
net-work associated with the connective-tissue 
framework. Most of the nuclei in the internal nu- 
clear layer are believed to belong to small nerve- 
cells, while the larger ones belong to the connective- 
tissue framework. In the external molecular layer, 
again, we have a delicate net-work of nerve-fibrils 
intermingled with connective tissue. The nuclei of 
the external nuclear layer seem to belong exclusively 
to nerve-elements, and are directly connected, by 
processes which pass through the openings in the 
external limiting membrane, with the rods and 
cones. 
Of the rods and cones, which within the limits of 
this book cannot even in a general way be ade- 
quately described, the rods are the longer, are usu- 
ally somewhat pointed at the inner extremity where 
they join the nerve-elements of the outer nuclear 
layer ; the cones are shorter, are connected also with 
nerve-elements within, and terminate externally in 
pointed or rounded extremities. 
The connective-tissue elements of the retina con- 
sist, in certain layers, of broad, irregular radial fibres 
forming frequent inosculations, and, in the molecu- THEE YE. 
lar layers, of a delicate reticulum, within which the 
nerve fibrils ramify. 
The pigmented epithelium of the retina consists 
of large polyhedral cells set together side by side, 
and forming a continuous layer over the distal ends 
of the r jds. As seen from the side, as we have al- 
ready studied them, p. 24, they appear like flat 
pentagonal or hexagonal plates, but when seen in 
profile while in situ, it is evident that they send 
down long, slender pigmented processes between 
the rods. 
The outer portion of these cells, that next to the 
choroid, usually contains the nucleus and but little 
pigment, while the amount of pigment in the pro- 
cesses seems to depend upon whether the eye had 
been exposed to light or not immediately before 
death. For it has been recently shown that in some 
animals the pigment particles under the influence of 
light can move within the narrow cell-processes so 
as to be now collected within the inner portion of 
the cell-body, and again grouped in larger and 
smaller masses betwen the rods. In this movement 
the pigment particles are themselves passive, the 
change in position being due to active movements 
in the protoplasm, induced by light. 
The larger arteries and veins ramify beneath the 
internal limiting membrane in the layer of nerve- 
fibres, and from these blood is distributed outward 
to all the layers, as far as to the external nuclear 
layer, beyond which no blood-vessels are found. 242 
NORMAL HISTOLOGY. 
THE LENS. 
The lens is a transparent double convex body, of 
sufficient firmness to maintain its form when re- 
moved from the eye, and is enclosed in a homoge- 
neous elastic capsule which is thicker on the ante- 
rior than on the posterior surface. To the periphe- 
ral zone of the capsule, on both anterior and 
posterior surfaces, the suspensory ligament is firmly 
attached. The body of the lens, although perfectly 
transparent, is by no means structureless. Behind 
the anterior wall of the capsule lies a single layer of 
flattened polygonal cells, which at the equator 
gradually lengthen out to form very much elongated, 
band-like nucleated cells, or lens-fibres, which run- 
ning meridionally, and joined by interfibrillar ce- 
ment-substance make up the greater part of the 
body of the lens. The lens-fibres are slightly ridged 
upon the surface, and have, on transverse section, a 
flattened hexagonal form; they are so intimately 
joined to one another at their sides by the cement- 
substance, that under certain circumstances they 
may be peeled off in layers. 
The course of the fibres in the lens is somewhat 
complicated, but it may be said in general that they 
run meridionally from one-half of the lens, in broad 
sweeps, over into the other ; inasmuch, however, as 
the individual fibres are not long enough to reach 
the entire distance from one pole of the lens around THE EYE. 
243 
to the other, they commence along certain definite 
lines at varying distances from the poles; and the 
farther from one pole one end of the fibre is, the 
nearer to the other will its other end lie. In the 
young human lens, the lines from which the fibres 
start may be seen on the anterior and posterior sur- 
faces, under certain circumstances, in the form of a 
three-rayed star; in the adult, the rays usually part 
at the ends, giving rise to secondary rays. 
THE EYELIDS. 
These are formed in general by a plate of connec- 
tive tissue, which toward the free border is very 
dense and firm, and called the tarsal cartilage, or tar- 
sus ; they are covered on the outside by skin, on the 
inside by the conjunctival mucous membrane; 
between the tarsus and the skin lie the bun- 
dles of the musculus orbicularis. The tarsus, 
which is, in no sense, cartilage, is a plate 
of very dense and firm fibrillar connective tissue, 
containing ordinary flattened connective-tissue cells, 
and is closely connected within with the palpebral 
conjunctiva. Embedded within the tarsus lie the 
Meibomian glands, thirty to forty in number in each 
lid. They consist of numerous vesicular alveoli, 
lined with short cylindrical cells, arranged along and 
opening into long excretory ducts, which are lined 
with laminated epithelium, and open on the inner 
border of the edge of the lids. They are some^ 244 
NORMAL HISTOLOGY. 
what modified sebaceous glands, but, unlike most 
sebaceous glands are not connected with hair-fol- 
licles. 
The skin of the eyelids is somewhat thinner than 
that of the face, is beset with delicate hairs, and 
supplied with sweat-glands and sebaceous follicles. 
It passes over on to the edge of the lids, at the in- 
ner border of which it becomes continuous with the 
mucous membrane. The eyelashes are inserted 
obliquely into the edge of the lid, in from two to 
four rows ; and the follicles, which are quite deep, 
are furnished with sebaceous glands. 
The conjunctival mucous membrane of the lids 
consists of a basis substance of loose fibrillar connec- 
tive tissue containing a few elastic fibres and numer- 
ous small spheroidal and branching cells. The 
epithelium is laminated, consisting of a deep layer of 
polyhedral cells, then more superficially of more or 
less columnar cells. 
The epithelium of the bulbar conjunctiva ap- 
proaches more and more closely in structure that of 
the cornea, as we pass from the lid over toward the 
sclero-corneal junction. 
Small racemose glands, called accessory tear-glands, 
are often seen opening on the surface of the mucous 
membrane. In addition to the striated muscular 
bundles of the orbicularis, smooth muscle-cells, 
forming a membranous layer, occur beneath the con- 
junctiva on the orbital portion of the lids. THE E YE. 
245 
PRACTICAL STUDY. 
General Dissection of the Eye.—For this purpose a 
large eye, like that of the sheep or ox, is preferable ; it 
should be opened by a short incision through the scle- 
rotic, so that the fluid can readily come into contact with 
the parts within, and placed in Muller’s fluid ; after two 
weeks it is carefully washed and placed in alcohol for a 
week, when the dissection may be made. 
The eye should be divided with a sharp razor into 
lateral halves, the section passing through the optic 
nerve. The cut surface shows clearly the general rela- 
tions of the parts ; cornea, iris, lens, ciliary body, vitreous, 
retina, choroid.’ and sclera are seen in approximately nor- 
mal relations to one another. 
If the vitreous be now removed from one of the halves, 
the retina and ciliary body come more fully into view. 
As the zonula ciliaris approaches the edge of the lens, 
it divides into two layers, which pass, one to the anterior, 
the other to the posterior surface of the body, forming 
the suspensory ligament ; the slit-like opening between 
the layers is called the canal of Petit, which may be seen 
by pulling the lens slightly backward, when the layers will 
separate. 
Now seizing the half of the lens with forceps and care- 
fully drawing it downward and backward away from the 
iris, the zonula ciliaris, in the form of a folded fringe- 
like membrane, will be separated from the surface of the 
ciliary body. A portion of this, in connection with a 
fragment of the lens-capsule, is detached from the lens, 
stained deeply in eosin, and mounted in glycerin. After 246 
NORMAL HISTOLOGY. 
the removal of the lens, the form and attachment of 
the iris are readily seen. 
In the same half of the eye, the layers of the chotoid 
may be demonstrated. For this purpose the retina is 
pulled off, and the pigmented cells, which are apt to ad- 
here to the inner surface of the choroid, are brushed or 
scraped off. The eye is now firmly pinned with the flat 
side down to a flat bit of cork which has been attached 
to a piece of sheet-lead and sunk in a dish of water deep 
enough to cover the eye. A window about a centimetre 
square is now cut through the sclera, including the sclero- 
corneal junction, and the bit of sclera having been re- 
moved, care being taken not to disturb the ciliary body, 
the membrana suprachoroidea will be seen as a brown 
loose tissue floating at the surface of the choroid. Bits 
of this are pulled off with the forceps, stained with hse- 
matoxylin, floated smoothly on to a slide immersed in 
water, and mounted in glycerin. The floating shreds 
of the suprachoroidea which remain after suitable speci- 
mens have been obtained, should now be pulled from the 
eye, when the vascular layer of Haller will come into 
view. 
The separation of the three remaining layers is not 
easy under the most favorable conditions, and is espe- 
cially difficult in the eye of the ox and sheep, where the 
layers are rendered more complicated and difficult of 
separation by the presence of a mass of interlacing 
fibres. Haller’s layer, however, and the membrana 
chorio-capillaris may be, with care, stripped off in pieces 
sufficiently thin for demonstration ; sometimes a frag- 
ment will be obtained, which, especially at the edges, THE EYE. 
247 
will show both of the vascular layers at once. They are 
stained double and mounted hr glycerin or balsam. 
Cornea and Sclera.—A fresh eye from the rabbit or dog 
is hardened in Muller’s fluid and alcohol. The cornea 
should now be excised close to the sclero-corneal junc- 
tion, embedded in wax or liver, and thin sections made 
perpendicular to the surface, including the entire thick- 
ness. They may be stained double and mounted in 
glycerin. 
A transverse section may be made from a bit of the 
sclera from the same eye ; stained double and mounted 
in balsam. 
Sclero-corneal Junction, and Iris.—The cornea and 
sclera, in their relations to one another, and the ciliary 
bodies, and iris, may be examined in a specimen pre- 
pared as follows : An eye—that of the pig is best, if a 
fresh human eye cannot be procured—is placed, after 
making a short incision in the sclera, in Muller’s fluid, 
where it remains for two weeks, the fluid being changed 
once or twice ; it is then soaked for an hour or two in 
water, and the hardening completed in dilute and strong 
alcohol. A bit is excised, including the sclero-corneal 
junction and adjacent parts, and embedded in cacao 
butter by the following method * 
This cacao-butter method of embedding is of great 
use in making sections of delicate parts where the tis- 
sues enclose spaces, or are not close enough together or 
firm enough to afford a sufficient resistance to the razor. 
The piece of tissue is transferred from alcohol to a small 
dish of oil of cloves, which in a short time will pene- 
trate the tissue and render it transparent. It is then 
*lt is better to use celloidin, See Appendix, p. 252. 248 
NORMAL HISTOLOGY. 
placed in melted cacao butter, whose temperature is 
kept just above its melting point, on a water-bath, for a 
couple of hours. It is now placed in a little box made 
from writing paper, in such a position that sections can be 
made in a suitable direction at the proper time, and the 
box filled with the melted cacao butter or with the wax 
mixture described on page II When the wax is cold 
the whole forms a solid mass of suitable consistence for 
cutting, and the wax serves to hold the delicate parts 
together while the section is being made. Sections are 
made at right angles to the ciliary body. 
The wax and the cacao butter must now be dissolved 
out by oil of cloves, the latter replaced by alcohol, and 
this by water ; the sections are then stained double and 
mounted in balsam. This method seems long and com- 
plicated, but the excellence of the sections of delicate 
parts obtained by its use will well repay the worker for 
his pains. 
Lens Fibres by Teasing.—A short incision is made 
through the sclera of a fresh eye which is soaked for 
three or four days in a mixture of alcohol and water, 1 
to 2. The lens will be found on removal to be white 
and soft, and readily breaks up into layers ; a bit of one 
of these is teased on a slide in eosin-glycerin and 
mounted in the same. 
Sections of the Lens.—The eye of a rabbit or pig 
should be kept for a fortnight in Muller’s fluid ; the 
lens is then removed, care being taken not to rupture 
the capsule, and placed for a day or two in dilute and 
then in strong alcohol. It is embedded in wax,* and thin 
sections, made in an antero-posterior direction through 
* Or celloidin. THE £ YE. 
249 
the centre, are stained double and mounted in glycerin 
or balsam. 
Transverse Sections of the Retina.—In a perfectly fresh 
human or pig’s eye, one or two small openings are made 
through the sclera and it is placed in Muller’s fluid ; 
after a week the eye may be cut across just behind the 
sclero-corneal junction, and the posterior segment placed 
in fresh Muller’s fluid. After another week it is trans- 
ferred for twenty-four hours to dilute, and then put for 
two or three days in strong alcohol. A small piece is 
now cut from the retina at a little distance from the 
optic-nerve entrance and embedded in cacao butter (see 
above).* Thin transverse sections are made, the cacao 
butter dissolved out in the usual way, and stained double 
and mounted in balsam. By this method the general 
arrangement of the layers is well shown, but many of 
the finer details of structure are obscure. 
* Celloidin is much better for embedding the retina. APPENDIX. 
Page io, Section-Cutting with the Microtome.—Although it is 
very important for every worker in normal Histology to be able to 
cut thin sections with the free hand, it is desirable in many cases to 
make use of an instrument called the Microtome for this purpose ; 
since, when many sections are to be cut, much time is thereby saved, 
and sections can be made much thinner and smoother. One of the 
best instruments is that devised by Prof. R. Thoma, of Heidelberg, 
and known as Thoma's Microtome. This instrument is made of 
three sizes, and the intermediate or largest size is most useful. This 
can be imported from the maker, Rudolph Jung, of Heidelberg, 
Germany ; or it can be obtained from the Prang Educational Co., 7 
Park Street, Boston, Mass., or of Meyrowitz Bros., corner of Fourth 
Ave. and Twenty-third St., N. Y. The method of using the instru- 
ment need not be described here, since with the instrument at hand 
any worker will readily make out for himself the necessary pro- 
cedure. 
The instrument and mode of using are described in Jour. Royal 
Microscopical Soc., vol. iii., p. 298, 1883. 
The Freezing Microtome.—For many purposes it is desirable to 
study thin sections of fresh tissues which have not been subjected to 
the action of hardening agents. Such sections are best prepared 
with a so-called freezing microtome, by means of which, by the action 
usually of a spray of ether or rhigolene, small pieces of tissue may in a 
few seconds be made hard and easily cut off in thin slices. The 
251 252 
APPENDIX. 
freezing microtome of Thoma is one of the simplest and cheapest, 
and can be obtained as above. A thin bit of the fresh tissue, not 
more than 2-3 mm. thick, is placed on the metal plate, and a spray of 
ether from an ordinary two-bulbed atomizer being directed against the 
lower side of the plate, the tissue will soon become solid, and sections 
may be shaved off by passing the knife—held a little obliquely on the 
edge, like the knife of a plane—over the glass plate. These sections 
may be studied unstained, or be stained with a one-per-cent, aqueous 
solution of analin green. This method is very useful when it is de- 
sirable to determine the nature of a tissue without waiting for the 
action of hardening agents, as well as for seeing it in a nearly natural 
condition. 
Page xi. Embedding in Celloidin.—Although the methods of em- 
bedding given on pages 11, 115, and 247, in wax and paraffin, gum 
and cacao butter, are useful for some purposes and were formerly uni- 
versally employed, celloidin, which has been recently suggested for 
this purpose, is much better in almost all cases, and has largely super- 
seded them. 
Celloidin is a purified form of collodion, which is non-explosive, 
and comes in the market in the form of dense glue-like sheets or 
shavings. It may be obtained in a pure form from Bachrach and 
Brother, corner Eutaw and Lexington streets, Baltimore, Md. It is 
prepared for use by making a saturated solution in equal parts of com- 
mon sulphuric ether and alcohol. The solution should be of about 
the consistence of moderately thick mucilage. The specimen to be 
embedded should have been previously soaked in alcohol. It is placed 
for a few hours in a mixture of equal parts of alcohol and ether, and 
then transferred to the celloidin solution and left until it is thoroughly 
penetrated by the latter. If the specimen is small this will usually 
be accomplished in from twelve to twenty-four hours. A small square 
box is now made of filter paper, and the specimen being placed in a 
proper position in this, the celloidin solution is poured around it so 
as to fill up the box. The box should be make considerably larger 
than the specimen, as the celloidin shrinks considerably in hardening. 
If the microtome is to be used for cutting the section, or if the bits of 
tissue are small, it is well to make the box by rolling the paper around APPENDIX. 
253 
one end of a straight cork of the proper size, so that it will project 
from the end, and tying it with a thread. The cork is now set upon 
end with the cylindrical box uppermost, and the specimen placed in 
this, and the celloidin poured in as before. In this way the celloidin 
with the specimen will harden on to the cork which can be readily 
clamped in the microtome. In many cases, if the specimen is small, it 
will suffice, after it is permeated with the celloidin, to place it directly 
on the end of a cork, and pour a little celloidin—as much as will lie 
on the end of the cork—directly over it. 
After enclosing the specimen in any of these ways in the semifluid 
celloidin, the latter is hardened by allowing the preparation to stand 
in the air or under a bell jar until some of the ether has evaporated, and 
the celloidin becomes partially hardened on the outside, and then 
placing it in a mixture of equal parts of alcohol and water. In this, 
after a longer or shorter time, the celloidin will acquire the proper 
consistency for cutting, shrinking considerably as it does so. By a 
little practice, the worker will soon learn just how thick to make the 
celloidin solution, and how long to leave it exposed to the air, and in 
the dilute alcohol for hardening. 
When the sections are cut they may be stained in the usual way, 
and mounted in glycerin or balsam. It is not necessary to remove 
the celloidin from the section, since it is transparent, and for most pur- 
poses interferes but little with the subsequent study, and it greatly 
facilitates the handling of delicate specimens, holding as it does very 
fragile or friable tissues perfectly in place In mounting in Canada 
balsam, if oil of cloves he used, the celloidin is dissolved by it, leav- 
ing the section free. The celloidin may be kept on the section by 
using for clearing up the specimen the white oil of thyme instead of 
oil of cloves. The uncut portion of the specimen may be preserved 
indefinitely, ready for cutting, in eighty per cent, alcohol. 
The So-called Third Corpuscle of the Blood.—Several observers have 
described the occurrence in the blood of numerous pale discoidal 
bodies considerably smaller than the red blood cells. They are apt, 
when the blood is withdrawn from the vessels, to become clustered in 
irregular masses. These are often called blood-plates. It is probable 
that many of the “ free granules ” described in the text are the struc- 254 
APPENDIX. 
tures described under this name. Too little is as yet known about 
their structure and function, or the conditions under which they occur, 
to make it necessary to describe them further here. 
Neuroglia.—The nerve elements of the central nervous system are 
supported and held in place in part by connective-tissue septa and 
prolongations which pass inward from the pia mater ; in part by a deli- 
cate net-work of a peculiar form of connective tissue called neu- 
roglia. The latter consists for the most part of fine fibrils, and of 
irregular-shaped flat-bodied cells, which frequently send off numerous 
exceedingly delicate branching processes. These cells are called 
neuroglia cells, and from their numerous and delicate process are 
very commonly known as “ spider cells." 
Silver Staining of Bladder.—As the injection of an entire frog is 
somewhat difficult without considerable practice, the following pro- 
cedure may be substituted for it : The bladder is exposed in a freshly- 
killed frog, and a canula being passed into it, the organ is moderately 
distended with air and ligated in this condition. It is then cut out, 
rinsed in water, and laid for twenty minutes in one-half-per-cent, 
solution of silver nitrate. It is then rinsed and exposed to the light, 
and treated as on page 126. The pictures are more distinct if the 
epithelium be scraped from the inner surface before mounting. 
Respiratory Epithelium.—These thin transparent cells which 
partially line the air-vesicles are sometimes called respiratory 
epithelium, and it was formerly supposed that such cells were con- 
fined to the terminal air-spaces. It has been recently shown, how- 
ever, chiefly by the researches of Kolliker, that the respiratory 
epithelium is abundant in the smaller bronchi as well, and these he 
accordingly calls respiratory bronchioles. The peculiar character and 
distribution of this epithelium, which seems so well fitted to facili- 
tate the interchange of material between air and blood in the lungs, 
would seem to indicate, therefore, that the actual respiratory surface 
in the lungs is greater than we have been wont to believe. 
Weigert’s Acict-Fuchsin Methodfor Staining Nerve- Tissue.—While 
for a standard method in studying the central nervous system, the 
double staining with hematoxylin and eosin answers a very good pur- 
pose, it fails to show the nerve-elements with sufficient distinctness, APPENDIX. 
255 
being best adapted to reveal the connective tissue. A method recently 
described by Weigert, on the contrary, when carefully followed, brings 
out the nerve fibres, even in their finest ramifications, with great dis- 
tinctness. It is called the acid-fuchsin method, because the stain em- 
ployed is one of the so-called acid anilines. It is rosanilin in which 
one atom of H is replaced by the radicle S 03H. It is a sulphate of 
rosanilin. It does not stain the nuclei of cells, but stains the tissues 
diffusely. It is found, however, that on treating the stained sections 
with caustic potash, the color is largely removed from every thing but 
the nerve fibres, which remain of a deep red color. The ganglion 
cells are not much colored by it. It-is necessary to use a particular 
preparation of acid-fuchsin for this purpose ; namely, one known as 
acid-fuchsin S. of the Baden anilin factory, which may be obtained 
in small quantities from Dr. Grlibler, 17 Dufour Strasse, Leipzig, 
Germany, or from Meyrowitz Bros., Fourth Ave. and Twenty-third 
Street, New York. 
The details of this method are as follows : The nerve tissues 
(brain or spinal cord) must be carefully hardened in Muller’s fluid. 
Alcohol may be used to complete the hardening, but should be used 
only at the end of the process. Sections are stained from one to 
twenty-four hours in a saturated aqueous solution of the fuchsin. 
The differentiation of the elements is accomplished by a saturated 
alcoholic solution of canstic potash, diluted with alcohol in the pro- 
portion of x-io. The sections are taken from the stain, rinsed in 
water, and placed in the alkaline bath. The exposure in the latter 
should be very brief, usually not more than five or six seconds, the 
section being moved to and fro. If left in the potash too long the 
color will be removed altogether, and this is consequently a delicate 
part of the operation. A little practice will enable the operator to 
determine how long an alkaline exposure to give the section. The 
latter is now transferred immediately to pure water, which should be 
changed once or twice to insure the complete removal of the potash. 
The section may now be dehydrated with alcohol in the usual way, 
cleared up with oil of cloves, and mounted in balsam. The nuclei 
of the cells may be brought out by staining lightly with hematoxylin 
before dehydrating. The color of the preparations is somewhat 256 
APPENDIX. 
deepened by dipping the section for an instant, after the removal of 
the alkali, into a solution of hydrochloric acid and water 1-5. 
In sections stained in this way, the connective-tissue elements have 
a gray or light violet color, the nuclei alone, if hematoxylin be used, 
being distinctly stained. Although not especially stained, the gangli- 
on cells may usually be seen with great distinctness. The nerve 
fibres on the other hand stand out, in successful preparations, with 
great distinctness, in light or deep red, and we are able to trace their 
courses and ramifications in a highly satisfactory manner. 
The hardening in chromic fluids—especially Muller’s fluid—may 
be greatly hastened by keeping the fluid in which the specimens are 
immersed at a slightly elevated temperature—350 C. In this way the 
hardening may be accomplished in about one third the time required 
at ordinary temperatures. The fluid should be frequently changed. 
A little gum camphor may be put into the fluid to retard the de- 
velopment of bacteria. INDEX 
PAGE 
Acetic Acid, action of, on tissues ..... rf 
Air-vesicles of lungs, demonstration of epithelium of 
structure of .... 173 
Albuginea, of ovary ....... Igg 
of testicle ....... 188 
Alcohol, as a hardening and preservative agent ... 3 
Alveolar passages of lungs, structure of ... i 7» 
Ammonium bichr., as a hardening agent .... 4 
Ammonium chromate (neutral), as a hardening agent . . 4 
Amoeboid movement, in white blood-cells, character of 81 
method of studying. . 89 
Aniline-red, as a staining agent ...... 35 
Arachnoid, of brain ....... alg 
Areolar tissue 
Arteries, structure of I 20) lai 
method of studying ...... 126 
Arterioles ..... 
• • • • • • ISO 
Asphalt varnish, for enclosing specimens .... 24 
Axis cylinder of nerve-fibres ...... 104 
Balsam, method of mounting in ..... IS 
Blo°d 80 
coagulation of 8s 
free granules in 84 
method of studying fresh ...... 87 
plasma of g5 
Blood-cells, red g2 
action of water on .... gs 
change of form in .... , 83 
coloring matter of .... 84 
difference in, in different animals ... 84 
nucleated, in marrow of bone ... 67 
in spleen ..... 139 
number of ..... 83 258 
INDEX. 
Blood -cells, red page 
number of, relative to white blood-cells , . 83 
origin of ...... . 86 
size of ...... 83 
stroma of ...... 84 
varieties in ..... 84 
white ........ 80 
amoeboid movements in . . . , 81,8g 
demonstration of nuclei in . . . 8 
origin of . . . . , . . 8 / 
Blood-crystals ........ 84,88 
Blood-vessels, adventitia of ..... 120 
arteries ....... 120,121 
capillaries ....... 119 
classification of ..... . rig 
intima of . . . . . . . 120 
musculosa of ..... 120 
method of preparing, for study . . . 125,126 
veins ....... 121 
Blue gelatine mixture for injecting, formula for prep, of 10 
Bone 61 
canaliculi of ....... 62 
cells ......... 62 
decalcified, method of preparing ..... 67 
developing, preparation of ..... 77 
development of, intra-cartilaginous .... 71 
sub-periosteal ..... 74 
intra-membranous .... 75 
hard, method of preparing sections of ... . 69 
Haversian canals of ...... . 64 
marrow of ....... . 65 
periosteum of ....... 65 
Bone-tissue, spongy ....... 62 
compact ....... 63 
Sharpey’s fibres in . . . . • . 64, 75 
Brain, arachnoid of . . . . . • • . 218 
blood-vessels of ...... . 217 
dura mater ........ 317 
general structure of ...... 215 
pia mater ........ 318 
preparation of sections of . . . . . . 219 
structure of cortex of cerebellum .... 217 
structure of cortex of cerebrum ..... ai6 
structure of white matter of .... . *l5 INDEX. 
259 
FACE 
Bronchi, large, structure of ..... 170 
small, structure of . .... , 171 
Bruch, membrane of, in choroid ...... 238 
Brunner, glands of, in duodenum ..... 150 
Budding, cell multiplication by 2I 
Cacao Butter, method of embedding in ... , 247 
Canada balsam, hard, for mounting bone .... 7o 
solution in chloroform for mounting , . 14 
Canaliculi of bone ........ 62 
Capillaries, structure of ...... llg 
method of studying ...... 125 
Capsule, of cartilage cells ....... 56 
supra-renal ,64 
Carmine, preparation and use of, as a staining agent . . 7 
Cartilage 5g 
cells of 56 
artificial shrinkage of ..... 60 
classification of ...... , 57 
fibro- •••• . . . , , , 
preparation of 59 
fibroblastic S9 
preparation of 6t 
hyaline, basement substance of ... . j7 
preparation of 6l 
Cells, body of 17 
bone 62 
ciliated, from frog’s mouth ..... 25 
classification of ...... a 2 
connective-tissue ...... 32 
corneal, seen on edge ...... 40 
seen on flat ...... 41 
relation of, to basement substance ... 42 
division of ....... si 
endothelial ........ 33 
epithelial, of small intestine ..... 149 
ganglion ttt 
general structure of ..... . >7 
goblet, in small intestine ...... 150 
liver IS7 
marrow # 
membrane of ....... tg 
nuclei of .« 260 
INDEX. 
PAGE 
Cells, nucleoli of . 10 
peptic ......... 147 
pigmented, in choroid ...... 36 
physiology of 19 
plasma ........ 33 
practical study of ...... , 23 
reproduction of ...... 20 
tendon ........ 36, 38 
Cell-spaces of connective tissue ...... 44 
Cement, in roots of teeth ....... 78 
Central nervous system ....... 211 
Central tendon, in diaphragm of rabbit .... 127 
Chondrin ......... 58 
Chromic acid as a hardening agent ..... 4 
Chyle vessels, in small intestine . . . . . 151 
Ciliary motion, in cells from frog’s mouth .... 25 
Coloring tissues (see staining) ...... 6 
Conheim’s method of gold staining . 39 
Coni vasculosi of testicle ....... 189 
Connective tissue, classification of .... 27 
distribution of, in body .... 27 
fibrillar ...... 29 
of nerves ...... 106 
origin of, in embryo .... a 8 
practical study of .... 33 
reticular ...... 54 
method of preparing ... 5S 
Corium of skin ........ 222 
Corpus Highmori of testicle ...... 188 
luteum in ovary ....... 201 
spongiosum of penis ...... 196 
preparation of .... 197 
Decalcification of bone ....... 67 
Delafield’s method of preparing hsematoxylin .... 6 
Dentine ......... 78 
Double-staining ........ 8 
in Canada balsam mounting .... 14 
Dura mater, structure of . . . . . , . 217 
preparation of ..... . 219 
Elastic Fibres in connective tissue ..... 30 
in ligamentum nuchse ..... 34 INDEX. 
261 
PACK 
Elastic granules in connective tissue ..... 31 
Embedding in cacao butter ...... 347 
in gum 115 
in liver „ 
in wax n 
Emigration of white blood-cells ...... 81 
Enamel cuticle ........ 79 
of teeth 7Q 
Endocardium, structure of ..... 123 
method of studying ..... 127 
Endogenous cell reproduction ...... 22 
Endothelial cells ........ 33 
Endothelium, of mesentery ...... 45 
of omentum ...... 46 
Eosin, mounting specimens stained with, in glycerin . . 13 
preparation and use of ..... , 8 
Epidermis 220 
Epithelial cells from rabbit’s bladder ..... 23 
Epithelium, renal ........ 182 
Erectile tissue, nature of 195 
Eye .......... 332 
aqueous fluid of ...... . 233 
canal of Petit ........ 245 
capsule of Tenon ....... 23c 
chambers of ....... 233 
choroid 237 
ciliary body 233 
cornea, structure of . . . . • . , 235 
preparation of ..... 247 
conjunctiva ........ 244 
dissection of ....... a 45 
general structure of . . . . . , . 232 
hyaloid membrane 234 
iris, structure of ...... , 238 
preparation of ...... , 247 
lamina fusca ........ 235 
lens, structure of ...... 242 
preparation of ...... 248 
ora serrata 233 
retina, structure of ...... 239 
• preparation of ...... 249 
sclera, structure of ...... 234 
sclero-corneal junction, preparation of . . . 247 262 
INDEX. 
Eye, suspensory ligament ...... 233 
uvea. ........ 238 
vitreous body ....... 034 
zonula ciliaris . ...... 234 
Eyelids 843 
Fat Cells, structure of ...... . 50 
development of ...... 51 
Fat tissue ......... 50 
fresh, preparation of ..... . 52 
method of studying, in adult ..... S3 
method of studying, in young animal ... 53 
Fatty infiltration ........ 52 
Fibres, elastic, in connective tissue ..... 30 
fibrillated, in connective tissue ..... 30 
nerve ........ 104 
muscle 9S 
Fibrillae in tail tendon of mouse ...... 34 
primitive muscle ....... 96 
Fibrillar connective tissue ...... 29 
Fibrin from blood, characters of ..... 85 
method of preparing .... 90 
Fibro-cartilage, structure of ..... 59 
Fibro-elastic cartilage ........ 59 
Fission, cell multiplication by ..... 21 
Fresh tissues, method of examining ..... 2 
Fuchsine (see aniline red) 35 
Ganglion Cells ........ 111 
Gastro-intestinal canal ....... 143 
Gelatin, for injecting ....... ro 
Gemmation, cell multiplication by .... . 22 
Generative organs, female ...... 197 
male ....... 188 
Germ epithelium of ovary ...... 202 
Giant cells, in marrow of bone ...... 66 
Gianuzzi, crescents of, in submaxillary gland .... 156 
Glands, Brunner’s ........ 150 
general characters of .... 144 
lymphatic *29 
mammary 208 
Meibomian ....... 243 
Peptic . 147 
PAGE 
Fresh tissues, method of examining INDEX, 
263 
Glands, prostate ........ *92 
racemose ........ >45 
sebaceous . • 227 
Sub maxillary .... • • 155 
sweat ........ 228 
thyroid ........ *66 
tubular ........ *45 
vesicular ........ 146 
Glisson’s capsule of liver ....... 159 
Glomeruli of kidney ....... r79, 182 
Glycerin as a mounting medium 12 
Goblet cells ......... 150 
Gold chloride as a staining agent ..... 59 
Graafian follicles, structure of ..... 199 
development of .... 202 
Htematoxylin, preparation and use of , . . . , 6 
Haemoglobin, characters of ..... 64 
preparation of crystals of . . . 88 
Hair, cells in cuticula of ...... , 230 
follicle, structure of . . . . , , , 225 
general structure and relations of .... 224 
papillae of ....... 225 
preparation of sections of . , , , , . 230 
shaft, structure of . , , , , , , 226 
Ha\ler’s layer of choroid ....... 337 
Hardening agents 3 
Haversian lamellae 63 
canals ....... , 64 
Heart, endocardium 123 
muscle of ........ 101 
valves of , . . , , . , 124 
Henle, sheath of , , . , , , . . 106 
Hensen’s line in muscle-fibre , . , . , . 97 
Highmori, corpus, in testicle ...... 188 
Hyaline cartilage, structure of . , , . . 57 
method of studying , . , . . S9 
Indifferent Fluids, use of ...... s 
Infundibula of lungs, structure of .... 172 
Injection, interstitial . . . . . . 6 
of blood-vessels . , * 10 
Intestine, large, structure of , , , ... 153 
FACE 264 
INDEX. 
Intestine, large, method of studying ..... 154 
small, >•***••• 149 
agminated glands of ..... 152 
Brunner’s glands ..... 150 
chyle vessels of ..... 151 
epithelial cells of . . , c 149 
follicles of Lieberkubn .... 149 
goblet cells of , .... . *5O 
lymph-vessels of ..... *5l 
muscularis mucosae of .... 151 
method of study of .... 154 
Peyer’s patches 152 
solitary follicles of .... . 151 
villi of ...... 149 
Kidney, capsule of ....... 178 
connective tissue of ..... . 185 
convoluted tubules of ...... 181 
cortex of . 178 
cortical pyramids of ..... , 179 
epithelium of . . . , • . 182 
general structure of ..... i7B 
glomeruli of . . . , , *79, 182 
Henle’s loops of ...... 181 
injected, preparation of .... , 187 
Intercalated tubules of ..... iBt 
labyrinth of . ...... 179 
medulla of ...... i7B 
medullary rays of . «... v i7B 
method of examining ...... 185 
papilla of ....... 178 
parenchyma of ...... . 180 
position of tubules in ..... . 183 
preparation of isolated tubules of , , . , 186 
rabbit’s, preparation of ...... 185 
straight tubules of ..... , 181 
uninjected, preparation of , , • . . 186 
uriniferous tubules of • . . . , 180 
Krause, line of, in muscle-fibres ..... 97 
Lactation, changes of mammary gland during ... SO9 
Lacunae, of bone ........ 6a 
Morgagni, in urethra. ...... 194 
PAGE INDEX, 
Lamellae, of bone 63 
Leucocytes . go 
Lieberkuhn, follicles of, in small intestine • , , , 149 
Ligamentum nuchae •••<.«. 34 
Littre, glands of, in urethra ..... Ig4 
Liver is? 
blood-vessels of ,s8 
cells of 157 
preparation of X6i 
connective tissue of ...... 161 
gall-vessels of j6o 
genera! structure of ..... . i5B 
Glisson’s capsule in ...... 159 
injection of blood-vessels of , , , , ,62 
gall-vessels of ..... 163 
lobules of 15Q 
lymphatic vessels of . .... . 161 
lymphoid tissue in ,6, 
pig’s, preparation of ,g2 
human, preparation of ...... *62 
Lungs, air vesicles of , 17a 
alveolar passages of ...... ,7a 
alveoli of ........ 17a 
blood-vessels of . ...... 174 
infundibula of ...... , xj2 
injected blood-vessels of ..... 177 
lobules of . ,7I 
method of examining ....... 175 
pigment in I7S 
uninjected, preparation of .... , 175 
Lymph . . . . . , , . 86 
follicles ........ i 34 
Lymphatic capillaries ....... 125 
glands 129 
spaces ........ 44 
vessels • 134 
Lymphoid tissue ........ 134 
Malpighian Bodies, of kidney . - . ... t 179 
of spleen • . c . . . 137 
Malpighian layer, of skin ...... aao 
Mammary gland, structure of , . . . . , aoB 
preparation of ..... azo 
PAGE 266 
INDEX. 
PAGE 
Marrow, of bone, structure of ..... , 65 
preparation of .... 70 
Medullary sheath, of nerve-fibres ..... 104 
Meibomian glands ....... 243 
Meissner’s corpuscles ....... 229 
Menstruation, changes of uterine mucous membrane in . . 205 
M esentery, endothelium of ..... 45 
Motor-end plates ........ 99 
Mounting, in glycerin ....... 12 
in Canada balsam ...... 14 
Mucin, in embryonal tissue ...... 49 
Mucous tissue ........ 48 
in umbilical cord, preparation of . . , 50 
Muller’s fluid, formula for ...... 5 
Muscle-cells, smooth ....... 92 
isolation of ..... 93 
preparation of, from frog’s bladder . . 94 
sections of, from intestine ... 94 
Muscle, erector pilze. ....... 227 
Muscle-fibres, general structure of .... 95 
Hensen’s line in ..... , 97 
Krause’s line in ..... 97 
nuclei of ...... 98 
preparation of fresh ..... 99 
by osmic acid . . . ' 100 
sections from tongue . . 100 
sarcolemma of ..... 98 
sarcous elements of .... , 97 
Muscle-fibrillse, primitive ...... 96 
Muscle-tissue, classification of ...... 91 
of heart . , • • , . . . 101 
preparation of .... . 102 
smooth ....... 92 
striated voluntary ..... 95 
Nail, structure of . . . . . . . , 223 
preparation of sections of ..... *29 
Nerves, connective tissue of ..... , 106 
Henle’s sheath of ..... 106 
intra-fascicular connective tissue of . , . . joB 
lamellar sheath of ..... 107 
peri-fascicular connective tissue of , , , , JO7 
preparation of sections of , , , , uj INDEX. 
267 
page 
Nerve-cells, classification of ..... m 
preparation of, from brain .... 118 
from spinal cord .... 117 
processes of ...... 111 
sympathetic, structure of . . . . . 112 
preparation of ... 118 
Nerve-fibres, axis-cylinder of . , , , . 104 
classification of ..... . 103 
fresh, study of ..... 113 
incisures of Schmidt in . . . . 106 
inter-annular segments of .... 105 
medullary sheath of .... . 104 
medullated ...... 104 
neurilemma of ... . 105 
non-medu Hated ...... no 
physiological significance of structure of . , 116 
preparation of, with osmic acid . . . 114 
with silver . 115 
transverse sections of . . 114 
Ranvier’s crosses on .... 115 
of Remak ....... no 
sympathetic, preparation of ... . 118 
termination of, in nerve-centres . . . 108 
in the periphery ... 109 
Nerve-tissue, classification of ..... 103 
Neuroglia, character of, in spinal cord ..... 813 
Nodes, lymph ........ 129 
Nucleated red blood-cells, in marrow ..... 67 
in spleen ..... 139 
Odontoblasts ........ 78 
Oil of cloves, use of, in Canada balsam mounting ... 15 
Omentum, endothelium of 46 
Optical sections ........ 126 
Osmic acid, action of, on tissues ..... 5 
Osteoblasts ......... 67,73 
origin of ....... 76 
Ovary, connective tissue of ..... . 198 
general structure of ..... , 197 
Graafian follicles of ..... . 199 
preparation of 204 
Ovum, structure of . . . , , . . , aoo 
Pacinian Bodies, in skin m 8 268 
INDEX. 
Panniculus adiposus . ~,,,, 923 
Papillae, of skin 932 
of hair . . ...... 225 
Periosteum ......... 65 
Peyer’s patches ........ 152 
Pia-mater, of brain ....... aiB 
preparation of ..... 919 
of cord ........ 2xl 
Pigmented cells, of retina . . . , ._ 24 
of choroid ...... 36 
Pleura, pulmonary, structure of ..... , 175 
Potassium bichromate ....... 4 
Preservative agents ....... 3 
Prickle-cells, in epidermis ...... 221 
Pritchard’s method for gold staining ..... 39 
Prostate gland, structure of ..... . 192 
preparation of . . , , , , ig3 
Protoplasm ......... 18 
Pulp, of spleen ........ 139 
of tooth ........ 78 
cords, in spleen ....... 139 
Purkinje’s cells, structure of ..... Ix 2 
position of, in cerebellum .... 917 
Ranvier, crosses of, on nerve-fibres . .... 116 
Remak, nerve-fibres of , 110 
Respiratory apparatus ....... 168 
Rolando, substantia gelatinosa of .... . 914 
Sarcolemma ........ 96 
Sarcous elements ........ 97 
Schmidt, incisures of, in nerve-fibres ..... 106 
Schwann, sheath of ....... 105 
Sebaceous glands ........ 227 
Section cutting ........ 9 
Seminiferous tubules ....... 158,189 
Serous membranes ....... 44 
Shaking, method of, in preparing tissues .... 55 
Sharpey, fibres of, in bone . . . . . . 64,75 
Silver nitrate, methods of staining with . . , . 42,45 
Skin, blood-vessels of ...... 223 
corium of ....... 223 
epidermis of ....... 990 
FACE INDEX. 
269 
PAGE 
Skin, from finger tip, preparation of , . . . 230 
general structure of ...... 220 
horny layer of 220 
injected, preparation of ..... 229 
mucous layer of ...... 220 
negro’s 229 
nerves of 228 
papillae of 222 
prickle-cells of ....... 221 
rete Malpighi ...*... 223 
stratum lucidum ....... 221 
Spermatoblasts ........ igo 
Spermatozoa, development of ..... 190 
movements of ..... 192 
preparation of ..... 191 
structure of ...... 191 
Spinal cord, arrangement of gray matter in . , . 211 
blood-vessels of ..... 214 
central canal of ..... 212 
columns of 212 
connective tissue of . . . , . . 213 
cornua of . - 212 
general structure of ..... 211 
gray commissures of ..... 212 
gray matter of, structure of ... 213 
neuroglia 213 
sections, preparation of .... 2lq 
substantia gelatinosa of Rolando ... 214 
white commissure ...... 213 
white matter, structure of . . . , . 212 
Spleen, cavernous venis of ...... I<o 
distribution of blood in . . . . , . 140 
follicles of ,37 
general structure of ..... 136 
preparation of 14, 
PulP °f 139 
Staining agents 6 
Stellulae Verheyenii ....... 185 
Stomach, blood-vessels of ...... 148 
general structure of ..... . 146 
lenticular glands of ..... 148 
mucous glands of 147 
nerves of 148 
white matter, structure of INDEX. 
Stomach, peptic glands of ...... 147 
preparation of sections of .... , 153 
Subcutaneous connective tissue, cells of ... 35 
fibres of ... 33 
Submaxillary gland, preparation of .... xS7 
relations and structure of . , IS3 
Suprarenal capsule, preparation of .... 164 
structure of ..... ifis 
Sweat-glands . 228 
Sympathetic, cells of ...... . 112 
fibres of xlo 
Thkth 78 
Tendon, cells of, demonstration of . . , . 36,38 
fi brillse of, demonstration of .... 34 
Testicle, preparation of ...... 192 
structure of xBB 
Thyroid gland, formation of colloid in . xgg 
general structure of .... 166 
preparation of ..... 
Trachea, blood-vessels of ...... 170 
mucous glands of zQg 
preparation of ...... i7S 
structure of 168 
Umbilical Cord, mucous tissue in .... 50 
Urethra, general structure of ..... i 93 
lacunse Morgagni of . . . . . . l 9+ 
Littre’s glands of ig4 
preparation of ....... 197 
Uriniferous tubules ....... 180 
Uterus, general structure of ..... 204 
mucous membrane of , . . . . 205 
preparation of ...... ao6 
Vagina, general structure of ..... 206 
mucous membrane of ..... 207 
preparation of ...... 207 
Vas deferens iB9 
Veins, preparation of 126 
structure of ........ I2i 
valves of . la 3 
PAGE INDEX. 
271 
PACK 
Wax-mass, for embedding ...... 11 
Welch’s method of demonstrating subcutaneous connective-tissue 
cells ......... 35 
Yellow elastic tissue ....... 30 
Zonula ciliaris ........ 234 
INDEX TO THE APPENDIX. 
Acid, chromic, mode of hastening action of .... 256 
hydrochloric, use of in fuchsin staining of nerves . . 256 
* 
Bladder, silver staining of blood-vessels of . . . 254 
Blood-plates . . . . . . . . . 253 
so-called third corpuscle of .... 253 
Bronchioles, respiratory of lungs ..... 254 
Camphor, use of in preventing the formation of bacteria in chromic 
fluids ......... 256 
Celloidin, use of as an embedding medium .... 252 
Cells, neuroglia . . . . ■ . . . 254 
spider .......... 254 
Chromic acid, method of hastening action of solutions of . . 256 
Epithelium, respiratory in lungs , . . . . 254 
Freezing Microtome, cutting fresh tissues with ... 251 
Fuchsin, acid, use of in staining nerve tissues . . . 254 
Green, anilin, use of in staining fresh tissues .... 252 
Microtome, freezing, for cutting fresh tissues .... 251 
section cutting with ...... 251 
Muller’s fluid, mode of hastening action of .... 256 
Nerve Tissue, Weigert’s method of staining with fuchsin . . 254 
Neuroglia cells ........ 254 272 
INDEX. 
PAGE 
Oil of Thyme, white, use of for clearing sections embedded in 
celloidin ......... 253 
Plates, blood ........ 253 
Potash caustic, use of in Weigert’s fuchsin nerve staining . . 255 
Respiratory Bronchioles . . . . . 254 
epithelium in lungs ..... 254 
Rosanalin, acid sulphate of, use of in nerve staining . . . 255 
Section-cutting, with microtome ..... 251 
Third Corpuscle of blood ...... 253 
Thoma, microtomes devised by . . . . . . 251 
Thyme, white oil of, use of in clearing sections embedded in 
celloidin ......... »S3 
Weigert’s add fuchsin, method of nerve staining . . . 254