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FORM NO. 609; 9,20,38: 1O0M.

COMPENDIUM OF HISTOLOGY.

TWENTY-FOUR LECTURES

HEINRICH FREY,

PROFESSOR.

TRANSLATED FROM THE GERMAN, BY PERMISSION OF THE AUTHOR,

GEORGE R. CUTTER, M.D.,

9
ASSISTANT SURGEON NEW YORK EYE AND EAR INFIRMARY ; OPHTHALMIC AND AURAL SURGEON

N. Y. DISPENSARY, ETC., ETC.

ILLUSTRATED BY 208 ENGRAVINGS ON WOOD.

NEW YORK:
G . P. PUTNAM'S SONS,

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COPYKIGHTED BY

G. P. PUTNAM'S SONS,
1876.

TRANSLATOR'S PREFACE.

The science of Histology has made rapid advances of late
years, and many new facts have been acquired in this depart-
ment. This will be readily appreciated by those who are
familiar with the excellent and exhaustive text-books of
Frey and Strieker. But many are intimidated by the very
copiousness of such works.

Even in Germany, where thoroughness is the great excel-
lence, there is a demand for a compendium. That Professor
Frey's little book meets this want, is proved by its enormous
sale and the favorable notices of the press.

I hope that this translation may meet with the same kind
reception as did that of our Author's work on Microscopic
Technology.

GEORGE R. CUTTER, M.D.,

No. 228 East Twelfth Street, New York.
August, 1876.

AUTHOR'S PREFACE.

HISTOLOGY has, in the course of a few decades, triumphantly
won its field ; it has become an integral part of medical
studies. The hand-books have necessarily become constantly
more voluminous, in consequence of the immense wealth of
materials.

A short compend of the most essential facts is desirable for
students and practicing physicians. I have often heard this
wish expressed.

May the attempt, which I herewith venture, be, therefore,
indulgently received. The defects of this little book are very
well known to the author.

H. FREY.

Zurich, July lot/i, 1875.

CONTENTS.

PAGE

Translator's Preface iii

Author's Preface v

FIRST LECTURE.
General : the protoplasma, the cell, and its derivatives I

SECOND LECTURE.
Classification of the tissues. — Blood, lymph, chyle 20

THIRD LECTURE.
The epidermis, or the epithelium 28

FOURTH LECTURE.

The connective-substance group. — Cartilage, gelatinous tissue, reti-
cular connective tissue, fat 41

FIFTH LECTURE.
Connective tissue 51

SIXTH LECTURE.
Bone tissue 60

SEVENTH LECTURE.
Dentine, enamel, lens tissue 72

EIGHTH LECTURE.
Muscular tissue ' 79

NINTH LECTURE.
The blood-vessels 89

TENTH LECTURE.
The lymphatics and the lymphatic glands 102

ELEVENTH LECTURE.

The remaining lymphoid organs, with the spleen. — The so-called

blood-vascular glands , 112

viii CONTENTS.

PAGE

TWELFTH LECTURE.
Gland tissue 128

THIRTEENTH LECTURE.
The digestive apparatus, with its glands 139

FOURTEENTH LECTURE.
Pancreas and liver 1 50

FIFTEENTH LECTURE.
The lungs 157

SIXTEENTH LECTURE.
The kidney, with the urinary passages 163

SEVENTEENTH LECTURE.
The female generative glands, the ovary with the efferent apparatus. . . 173

EIGHTEENTH LECTURE.
The male generative glands, the testicles with the efferent apparatus. 183

NINETEENTH LECTURE.
Nerve tissue 192

TWENTIETH LECTURE.
The arrangement and termination of the nerve fibres 202

TWENTY-FIRST LECTURE.

The central organs of the nervous system, the ganglia, and the

spinal cord 215

TWENTY-SECOND LECTURE.

The central organs of the nervous system, continued — the medulla

oblongata, and the brain 224

TWENTY-THIRD LECTURE.

The organs of sense — skin, gustatory, olfactory, and auditory ap-
paratus 234

TWENTY-FOURTH LECTURE.
The organs of sense, continued — the eye 246

Index , 265

Compendium of Histology.

FIRST LECTURE.

GENERAL : THE PROTOPLASMA, THE CELL, AND ITS

DERIVATIVES.

A DEEP abyss separates the inorganic from the organic,
the inanimate from the animate. The rock-crystal on the
one side — vegetable and animal on the other ; how infinitely
different the image !

Is it, then, many will inquire, possible to bridge over
this gulf? We answer, not at the present time. It is, perhaps,
reserved for future generations of men to fill up this yawning
chasm, by the aid of a more thorough knowledge of nature,
and to comprehend the sphere of the material world as a
unit.

What, we ask further, is the primary beginning of the
organic ?

An admirable English
naturalist, Huxley, suc-
ceeded, in the year 1868,
in making a marvelous dis-
covery.

The bottom of our seas,
at the most considerable
depths, is covered over
large tracts with a strange
shiny substance. When
this thing, called the ba-

thybius, is drawn up by the

I

Fig. 1. — Bathybius.

FIRST LECTURE.

dredge, and placed under the microscope — under that instru-
ment which has conquered the mighty world of minuteness
for natural science — a very peculiar image is presented to the
astonished eye.

We perceive a transparent jelly, with diminutive granules,
in its interior. We also frequently meet with small cor-
puscles, surrounded by this, consisting of carbonate of lime.
They look like our modern sleeve buttons.

And this mass lives ! It changes from one shape to another
in slow metamorphosis, exhibiting a constant, though sluggish
restlessness. Separated portions present the same slow mu-
tability, the same life.

The mass formed by this bathybius is a nitrogenous carbon
compound, distended in water, and of an extremely compli-
cated chemical structure. It belongs to the group of albumin-
ous bodies, and is called protoplasma. It coagulates in death,
and also at a relatively slight elevation of temperature. The
granules it encloses consist partly of coagulated albuminous
substances, partly of fat ; mineral substances are also not
wanting.

Leaving the dark deep, and turning to the sunny surface
of the seas, we here meet with numerous small lumps of

protoplasma, which
show the same vital
transformations ,
shooting out process-
es, sometimes short,
sometimes longer, and
drawing the m i n

such is the

protamceba of our

Fig. 2. These are the

simplest organisms or forms of life. They increase by division.

One of our most distinguished investigators, Haeckel, has

called such a lowest being a cytode.

We meet with similar organisms intermingled with these
cytodes in the water ; as, for example, the amoeba (Fig. '3),

again ;

Fig- 2. — Protamoeba. A, undivided : I?, commencing,
and C, completed division.

THE PROTOPLASMA AND THE CELL.

Fig. 3. — Amoeba ; a, nucleus ; !', vacuoli ; r, alimentary
bodies taken in.

though in the interior of
this constantly change-
able protoplasma, to-
gether with excavations
(/>), and small foreign
bodies (c), accidentally
taken up from the neigh-
borhood, a roundish
structure with small
punctiform contents (a),

is found. The contained body bears the name of the kernel
or nucleus ; the small bodies enclosed within the latter are
called nucleoli. The entire creature has the significance of a
simple naked cell. What service the nucleus renders the
amoeba we are, at present, unable to say. We now leave
these lowest creatures, and pass, at a bound, to the highest
animal form — to examine the human body. Its parts have
been called organs since the primitive days of medicine. They
correspond to the separate pieces of one of our machines. It
was also long since known that certain substances of our
bodies, such as bone, cartilage, muscle, and nerves, were re-
peated in all portions of the organism and, slightly or not at
all changed, enter into the structure of the most different parts
of the body. These substances, which maybe compared to
the different materials of which the machine is formed, were
early known to be composed of still smaller parts. They were
compared to the products of the loom, and designated as
tissues. This name has been retained, and that branch of
anatomical science which treats of these homogeneous parts,
is called the science of tissues, or Histology.

On attempting, with the aid of the knife and scissors, to
separate such tissues, we, at first, succeed very readily ; the
fragments permit of a new division, and this may, perhaps, be
repeated on those thus obtained. But at last — sometimes
sooner, sometimes later— a period arrives when even the finest
and sharpest tools become unserviceable ; they are too blunt,
too coarse.

4 FIRST LECTURE.

Here, where the mechanical analysis terminates, the optical
begins, by means of the microscope. The latter is an extra-
ordinarily delicate one ; the fragment, which the anatomist's
scissors are unable further to divide, now proves to be infi-
nitely compounded ; it may still consist of thousands of the
smallest elements.

These elements are again, in their turn, cells or their
derivatives.

Thus, this structure, which forms in an independent manner
the body of an amoeba, now constitutes our tissues, although
in a very conditional independence. The cell has, therefore,
entered into the service of a mighty unity ; it has to sub-
ordinate and conform itself; nevertheless, the thing remains
a living individual, comparable to the officer of a modern
state department. As he fulfils his individual duty in the
service and as a member of a great whole, so, also, does the
small cell labor unremittingly until its death.

It appears of interest that these very small living foundation-
stones in the body of the higher animals always form cells, and
that the cytodes of Haeckel have disappeared.

We have just said that the cells of the human organism

were very small. Their diameter varies, in fact,

a & from 0.076, 0.0375, 0.0228 down to 0.0057 mm.

Thus it becomes possible that a small particle

of the substance of the body, about a cubic milli-
metre, may contain an extraordinary multitude
of them. It has been computed that such a

\{°]
*•-«.

particle of space of the human blood is capable
of containing five million red cells, though it is
true they only measure 0.0077 mm.
e '-^\^ 1 The cells present very considerable variations.

The latter are gained subsequently with the devel-
^0P _ opment of the body. In the earliest period of
^!9 embryonic life they were all still very similar.
ceUs'^vftiTnucl'eus The primitive form of a cell is that of a globe
andprotopiasma. or of a body approximating a sphere. Thus ap-
pear the cells d, e, g, b of our Fig. 4. The cell, also, from

THE P ROTO PLASMA AND THE CELL.

5

which in a momentous manner the bodies of all the higher
animals have proceeded, the ovum (Fig. 5),
presents itself as an elegant spheroidal
structure.

From this primitive form two other
forms, resulting from compression and
adaptation, may be readily traced ; the
tall, slender, or, as we say, cylindrical cell
(Fig. 6, b), and the flattened. The latter
finally assumes the form of a lamella or
scale (Fig. 7).

The bodies of other cells grow in two
opposite directions, like processes. We
thus obtain the spindle-shaped cell (Fig.
4, c, f). When such processes are numer-
ous and are also branched, a singular thing
appears, the stellate cell (Fig. 8).

Fig. 5. — Young ova,
from the ovarium of a
rabbit.

Fig. 6. — Cylindrical cell-, from the human small
intestine; 6, ordinary elements ; a, so-calkd
Kecher-cells.

Fig. 7. — Epithelial scales from the
human mouth.

The quantity of the cell protoplasma, and hence
the magnitude of the body of the cell, is subject
to great variation (Fig. 4).

While protoplasma occurs originally in every cell,
it may subsequently be replaced by other materials.
Thus, in the cells of our Fig. 7, a harder, more water-
less substance — keratine — has been substituted.
Other cells obtain a lodgment of dark, black pig- a,an'dvmpha
ment granules of great chemical resistance (Fig. 9).
These dark molecules are called melanin. One of the
most widely diffused structures of the human body is the

Fig. 8.— Stel-
late cell from
lie

FIRST LECTURE.

colorless globular lymphoid cell. It also occurs in the blood
(Fig. io, d), and is at last transformed into a disc-shaped

Fig. 9. — Pigmented connective-
tissue corpuscle (stellate pigment
cell from the mammalial eye).

a

jpJm*

a

Fig. 10. — Disc-shaped cells
of human blood, a, a, a. At b,
half from the side ; at r, seen
entirely from the side ; d, lym-
phoid cell.

structure {a,b, c), whose cell body contains a homogeneous red
substance, of an extremely complicated chemical constitution,
haemoglobin. Other cells subsequently become reservoirs
of fatty matters, often in a high degree.

We now pass to the kernel or nucleus. Its medium
diameter may be assumed to be from 0.007 to 0.005 mm- It is
originally a vesicle (Figs. 4 and 5), that is, a structure en-
veloped by a delicate covering. Nucleoli occur singly, double,
or in greater number (Auerbach). Attention has very recently
been directed to a circle of small molecules deposited between
the nucleolus and the wall of the nucleus, and called the
granule-sphere.

The nucleus may subsequently lose this vesicular character
and assume a different arrangement. Thus it not unfrequently
changes, later, into a firmer, more homogeneous structure
(Fig. 7), or becomes granular. Should the growing cell be-
come considerably lengthened, the nucleus also frequently
assumes a more elongated form.

As a rule, the nucleus remains a definite, tolerably con-
servative constituent of the cell. Nevertheless, we meet with
others of the latter which have lost by age the nucleus of an
earlier period of life. Such non-nucleated cells form the most

THE PROTOPLASMA AND THE CELL. 7

external layers of the epidermis covering our skin (Fig. 11).
Other. -cells (Fig. 12) contain, in complete contrast, double
nuclei. Their signification will occupy us later. Very singu-
lar structures, of irregular form, and, in part, of extraordinary

Fig. 11. — Non-nucleated cells

of the epidermis.

Fig. 12. — Cells with double nuclei :
a, from the liver, b from the choroid
of the eye, and c, from a ganglion.

m

Fio. 13. — Multi-nuclear giant
cell from the bone marrow of the
new-born.

dimensions, occur in the bone marrow, and also in many ab-
normal tumors. They have been called myeloplaxes and
giant cells (Fig. 13). Their larger specimens may contain a
multitude of nuclei.

In these two things, the protoplasm and the nucleus, we
have become acquainted with the essential constituents of

the cell.

The youthful cell shows nothing further.

Later, it may become different. The surface of the cell
body hardens, or from this vicinity is formed a firmer envel-
oping layer. Thus we have, when this remains very thin,
what is called a cell membrane, while to a thicker covering is
given the name of the cell capsule.

We just said, " this may occur ; " but it need not. At the
present time we occupy a standpoint different from that of

8 FIRST LECTURE.

our predecessors. Towards 1840, Schwann, the founder of
modern histology, erroneously ascribed the cell membrane as
a third essential constituent to every cell, so that the cell
would have two concentric envelopes, that of the vesicular
nucleus and the external one of the cell body. The still fre-
quently used name of "cell contents" is derived from that
period.

It is impossible for any one to demonstrate where such a
membrane really begins ; that the surface of a cell protoplasm
in contact with the surrounding objects may, and, in fact, often
does become more solid, would not be denied by any one ac-
quainted with the great changeability of protoplasm. We
may only speak of a cell membrane when we are able to iso-
late the thing, and thus place it with certainty before the mi-
croscopist's eye. A smooth, sharp, dark line of demarcation
on a possibly strongly changed cell corpse gives us neverthe-
less no proof of a membrane. We shall find later, it is true, that

the isolation of an envelope on a fat
cell, for instance, is very easy. Tak-
ing, by way of example, our Fig. 14,
the lateral surfaces of the cylindrical
structure a are provided with a cover-

FiG. 14. — Cylindrical epithelium • i • i • ■ i i_ i

from the small intestine of tne "ig which is certainly recognizable.

rabbit; a. Side view of the cells A , .11 1 •. • ^1

with the thickened and somewhat AbOVe, at the broad part, it IS Other-
elevated seam, which is permeated . TT t. , , ,

by p.,rous canals; b, view of the wise. Here the cell membrane is

cells from above, whereby the ap- . , . . ,

enures of the porous canals appear wanting ; and a thicker covering piece,

as small points. , . . . . . ...

permeated by very delicate longitudi-
nal canals, overlays the protoplasm. We perceive a cell cap-
sule on the mammalial ovum (Fig. 5, 2), while a more youthful
ovulum (1) still appears membraneless. In cartilage tissue-
cell capsules are quite ordinary occurrences ; we shall there
be more intimately occupied with them.

We proceed further; we inquire after the life of the cell.
A life we have already ascribed to it, although a limited one
in the service of the whole.

Can this, however, be demonstrated ? This question is
asked by many. We answer, yes. We recall to mind that

THE PROTOPLASMA AND THE CELL.

which we remarked above concerning the bathybius and
protamoeba, that constant mutability, that vital power of
contraction of the protoplasm. Numerous cells of our body,
as, for instance, the lymphoid cells (Fig. io, d), show the
same, and possess an " amoeboid" change of shape.

When, by an artificial experiment, we produce an inflam-
mation of the eyeball of a frog, instead of the clear aqueous
of the normal condition, the contents of the anterior chamber
soon appear more cloudy. In this less transparent fluid, we
now meet with innumerable lymphoid cells which, in this case,
are called pus corpuscles.
If we subject these cells in a
conservative manner to micro-
scopical examination, we rec-
ognize the vital metamor-
phosis, already familiar to us,
of the protoplasm. Every
shape which our Fig. 15 pre-
sents— and innumerable oth-
ers also — may, one after the
other, be assumed by one and
the same cell, till finally, in
death, it comes to rest as a
spherical body (/). Formerly
only these corpses were
known.

Still other remarkable things are connected with these pe-
culiarities of the protoplasm.

If to this cloudy aqueous of the eye we add inoffensive col-
oring matters in a condition of the finest division, indigo or
carmine, for instance, we see that the always restless proto-
plasm gradually takes up into the cell body one colored gran-
ule after the other (b). Even larger structures may be thus
introduced. Fragments and even whole red blood corpuscles
may thus enter into the lymphoid cells of the spleen. The
amoeba (Fig. 3), received its small alimentary corpuscles in
exactly the same way. This introduction may take place, in

Fig. 15. — Pus cells fiom the inflamed eye of
the frog ; a, to A\ the changes in the form of the
living cell ; /, dead cell.

*

10

FIRST LECTURE.

both cases, at any portion of the outer surface ; the latter is,
indeed, similar throughout.

By means of this vital transformation, our lymphoid cell is
able, like an amoeba, to shove itself over whatever it rests
on ; and thus, very slowly and sluggishly, it is true, wander
about. This may be observed in the pus cell in the cloudy
aqueous mentioned. In the magnificently transparent cornea
of the normal eye of a frog, the lymphoid cells may be seen
to wander through the corneal canals in the most distinct
manner, so that they gradually pass over the entire micro-
scopic field.

This has been rather drastically expressed by the words,
" the cells devour and march."

Such amoeboid cells may wander into other cell forms
which have come to rest. The surfaces of the body have cell
layers which are called epidermis or epithelium. This tis-
sue participates actively in the catarrhal irritations of the
mucous membranes. Lymphoid cells then wander from the
deeper layers of the latter into the bodies of these epithelial
cells (Fig. 16). These strange cells had already been ob-
served before the vitality of the
protoplasma was conjectured.
The process was then naturally
not understood. It was then
imagined that the lymphoid cells
were produced within those of
the epithelium.

A form of cell has long been
known, a species of epithelium,
which presents the most strik-
ing vital phenomena. This is
the ciliary cell (/). Very small
and thin cilia, which cover the
free surface of the cell body,
are constantly occupied in a
to and fro motion. These vibrations are repeated with such
extraordinary rapidity that the human eye is unable to dis-

Fig. 16. — Pus corpuscles in the interior of
epithelial cells from the human and rnam-
malial body ; a. Simple cylinder cell of the
human biliary canal ; b, one with two pus
cells ; r, with four, and d, with many of
these contained cells ; e, the latter isolated ;
f, a ciliated cell from the human respiratory
apparatus with one, and g, a flattened epi-
thelial cell from the human urinary bladder,
with numerous pus corpuscles.

THE PRO TO PLASMA AND THE CELL. \\

tinguish the individual ones. It is only on the death of the
ciliated cell, when these oscillations are retarded, that they
can be counted. We now know that these fine ciliae are pro-
toplasma threads, and that their movements fall within the
vital sphere of that remarkable substance. The rapid work
of these small hairs and the sluggishness of ordinary proto-
plasm, it is true, present a difference which is still inexplicable.

Where there is motion in the domain of animal life, there
is also sensation. Have the cells, the vitalized, minimal cor-
ner-stones of our bodies, the latter capacity ? We may affirm
this unreservedly.

When these changeable figures, as they were represented
in our Fig. 15, are subjected to a weak electrical irritation,
they rapidly return to the spherical form, to subsequently
recommence the old play of forming processes.

Every organism, even the smallest and most simple, has a
transmutability ; that is, it gives off altered unserviceable par-
ticles of matter, it receives into itself new matter, and trans-
forms it into the constituents of its own body. The mass of
the organism then increases, it grows.

All this happens, likewise, to the cell. The perception of
these vital actions is rendered difficult by the smallness and
the obscure existence of our structures. That the cells grow
may be abundantly shown and with the greatest certainty, as,
for example, in the fat and cartilage tissues. That they take
up and transmute matter ; that is, make it something chemi-
cally different, may also be perceived without trouble. Melanin,
, the black pigment we mentioned above, is wanting in the
blood. It is formed by the cell (Fig. 9). Choleic acid salts
and biliary pigment, the former, at least, certainly not present
in the blood, are productions of the living hepatic cell. The
latter presents us, furthermore, with a striking example of the
exchange of matter. Both the substances just mentioned
appear later as ingredients of the bile. We could readily cite
many such occurrences, but these few remarks may suffice ;
they show, at least, the coming and going of the materials.

The law of destruction adheres like a curse to the heels of

12 FIRST LECTURE.

the Organic, from the infusoria, whose life is counted by-
hours, to the oak, whose existence lasts centuries, throughout
this limited duration of life. Concerning the human organ-
ism, this highest cell-complex, there is a very ancient, well-
known saying that it lives seventy years, and at the furthest
eighty.

We now encounter the question : Are the cells, those vital
corner-stones of our body, once for all present, to remain
with us permanently as faithful companions to the day of
death ? Or does our body-cell, that delicate little thing, pos-
sess a more limited and, perhaps, compared with human life,
only a very short existence ?

We answer unreservedly in the latter acceptation.

The life of the body is long, under fortunate circumstances;
that of our cells is short. We can present but a very defec-
tive proof of this, however, at the present time.

We again present a few examples. We have said above
that the outer surface of our body is covered by layers of cells.
The superficial layers are in loose connection ; they are cells
in old age. The friction of our clothing daily removes im-
mense numbers of them. A cleanly person, who uses sponge
and towel energetically every day, rubs off still greater quan-
tities.

This takes place very actively in our mouth every day.
We swallow ; our tongue acts in speaking ; drink and food
pass this entrance of the digestive apparatus. Every one
knows this. The mucous membrane of the mouth is, again,
covered with a thick layer of epithelial cells. Here, also,
many thousand senile cells are rubbed off daily. That which
began at the entrance is continued throughout the entire di-
gestive apparatus. An excess of cells is thus lost daily.

To show the duration of life of a cell variety, let us turn to
the human nail. The latter, growing from a fold of skin, is
a cell-complex. In the depth of the furrow, youth prevails ;
at the upper border — which we trim — old age. The deceased
physiologist of Gottingen, Berthold, proved that a nail cell
lives four mont'is in summer and five in winter. A person,

THE PROTOPLASMA AND THE CELL.

13

dying in his eightieth year, has changed his nail two hundred
times, at least — and the nail appeared such an inanimate, ap-
parently unalterable thing !

We consider the nail cell a relatively long-lived constituent
of the body. We believe that most of the cells of our body
have a very much shorter existence. We repeat, however,
that it is a matter of belief, for no one can prove it, at pres-
ent ; but everything compels the view that, for example, the
red blood corpuscles, of whose multitude we spoke above,
have a much shorter existence than the elements of the
nails, and they are certainly resembled by many other cell-
varieties.

Most cells being destined to an early death, how do they
die ?

Science can give to this, at present, but an insufficient
answer. Certain cells, those of the outer surface of the body
and of many mucous membranes, dry up in their old age ;
the connection with the vicinity dissolves, the thing falls from
its bed. The red blood cells die by being dissolved in the
blood plasma. Others stick fast in the complicated tissue of
the spleen, and are likewise children of death ; for the blood
corpuscle lives only in the perpetual motion of the current ;
rest stamps it with the impress of death.

Other cells show in their old age granules of lime salts.
They mummify. In this condition they may, as cell corpses,
possibly remain for a still longer time constituents of the
body. Generally, however, they soon afterwards become
dissolved.

A very disseminated form of death of ani-
mal cells, in healthy as in unhealthy life, is
the so-called fat degeneration. In the place

r . . ... Fig 17 — Fatty degen-

01 the protoplasma, we perceive, in increas- crated cells from theGraa-

• . fian follicles of the ovary.

ing quantity, molecules of fatty matter

(Fig. 17). They finally destroy the cell life and cell body.

The human body daily loses, therefore, immense numbers
of its living corner-stones. How does it replace this loss ?

We here enter a very interesting department of our science.

14

FIRST LECTURE.

Schwann, the founder of modern histology, taught : " What
the crystal is in regard to the inorganic, so is the cell in the
sphere of life." As the former shoots forth from the mother-
lye, so also, in a suitable animal fluid, are developed the
constituents of the cell, nucleolus, nucleus, covering, and
cell contents.

This view was embraced during many years. It explained
everything so conveniently !

This was, however, over-hasty. Two highly endowed in-
vestigators, Remak and Virchow, exposed the error ; the
former for the embryonic, the latter for the diseased human
body.

The organic kingdom forms a continuity from the Bathybius
to man. We do not hesitate an instant to acknowledge that
this is also our conviction.

There is an old well-known saying : " Omne vivum ex
ovo," and in imitation of this sentence : " Omnis cellula e
cellula." The cell arises from the cell ; a spontaneous origin,
in the sense of Schivaun, does not occur.

We know but one certain method of increase of the cells
of our body.

The protamceba, Haeckel's non-nuclear cytode (Fig. 2),
divides itself into two beings by constriction. Each portion

grows, by a predominant reception of
material, to a new protamoeba. This is
also the method of propagation of the
nucleated cell of the human body.
Nucleus and protoplasm divide ; from
one structure are formed two, and so
forth. Our figure (Fig. 18) shows this
multiplying process of embryonic blood
corpuscles. When, however, the cell
has once become surrounded by an
a young deer embryo fat a, the envelope or a capsule, when the proto-

most globular cells ; b to J, their 1 l l

process of division. plasma is imprisoned, then (Fig. 19) the

contrast of the active and the passive is strikingly presented.
The capsule remains stiff and quiet, the cell in prison

Fig. 18. -Klood corpuscles of

THE PROTOPLASMA AND THE CELL.

15

maintains the old life. This multiplying process was, in
old times, badly z

enough designated
" endogenous cell for-
mation." Mother and
daughter cells were
spoken of. The so-
called mother cell is
nothing but the cell
capsule.

Does the process of
division of the human
cell take place slowly
or rapidly ? We be-
lieve the latter ; al-

Fig. 19. — Diagram of dividing mcapsulated bone cells ;
tllOUcrll a proof Can *■ ce" body; <S capsule; c, nucleus; d, endogenous
fc> " cells ; e, supplementary capsule formation.

scarcely be presented

here. In the lower animal groups, at all events, processes

of division occur which are completed with great rapidity.

We cannot yet leave the process of division, for we now
encounter the question : Which constituent of the cell,
nucleus, or protoplasm, here assumes the chief role f That a
non-nucleated lump of protoplasma is capable of dividing, is
shown by the protamceba. It is poss'ble that the nucleus is
only passively simultaneously con-
stricted, an opinion to which we are
inclined. Meanwhile cells which, in
the undivided body, present two sep-
arated nuclei (Figs. 12, 18, 19), and the
multi-nuclear myeloplaxes (Fig. 13),
constitute a certain objection. Once
more, therefore, uncertainty.

The blood, lymph, and chyle consist
of cells suspended in a large quantity of fluid ; in the blood,
as we already know, these bodies are present in enor-
mous numbers. Something similar is presented by a
pathological product — pus. Should one speak here of tis-

Fig. 2c. — Simple flattened epi-
thelium ; «, of a serous mem-
brane ; b, of the vessels.

i6

FIRST LECTURE.

sues? According to our opinion it is permissible; still,
we readily admit, the opposite view may be defended.
Other tissues, such as the epithelium or the epidermis (Fig.
20), present the cellular elements in close conjunction. At
the same time, even the first examination teaches us that our
cells are not loosely crowded together ; they are intimately
united ; they are plastered or cemented together. This

Fig. 21. — Capillary vessel from
the mesenlerium of the Guinea-
pig, after the action of the ni-
trate of silver solution ; a. vascu-
lar cells : l>, their nuclei.

Fig. 22. — Cells of the enam-
el organ of a four months' hu-
man embryo.

substance, which is of very frequent occurrence in a minimal
thin layer, is called either the tissue cement or the intercellu-
lar substance. If a portion of such tissue is placed for a short
time in a very dilute solution of nitrate of silver and then
exposed to the light, the tissue cement becomes black.
This excellent accessory is nowadays very frequently used.
In this manner we years ago recognized that the finest blood-

THE PROTOPLASM A AND THE CELL.

17

vessels, the capillaries, were formed of cemented, elongated
cell lamellae which become curved and joined together as a
tube (Fig. 21).

Stellate cells (Fig. 22), may blend together through their
processes, and form a very delicate net-work. The meshes
may be filled up with homogeneous gelatinous matter, and
also with a multitude of lymphoid cells. In the former case
we again have a variety of intercellular substance.

The latter acquires a considerable thickness in many tissues,
as in cartilage. At first (Fig. 23), this intermediate substance
is homogeneous throughout. This condition is either main-

Fig. 2 j. — Cartilage of a
young sheep toetus.

Fig. 74. — Cartilage from the auricle of a calf's
ear ; a, cells , b, intercellular substances ; c,
elastic fibres of the latter.

tained, or else fibres subsequently shoot out from the inter
cellular substance. Frequently (Fig. 24), we
meet with them crossed in a felt-like or reticu-
lated manner. They present an obstinate
power of resistance to reagents. Such fibres
are called elastic. Therefore— we repeat it—
the elastic fibre is the result of a subsequent
metamorphosis of an originally homogeneous
substance.

Connective tissue is infinitely diffused
through the human body. A small piece of
this, taken from the embryonic body, shows us,
together with cells, bundles of very fine
fibrillae, the connective-tissue fibres (Fig. 25).
They have a quite similar origin. Subsequently, the con-

FlG. 25. — From the
tendon of a hog's em-
bryo ; <i, the cell ; /',
connective tissue fi-
brillae.

i8

FIRST LECTURE.

nective tissue has also formed those elastic fibres, which we
have just met with in cartilage.

From whence, however, does the tissue cement and the
intercellular substance come ? Have they been inserted from
the neighborhood between the cells, or have the cells them-
selves produced these substances ?

The latter is the case. These substances were once con-
stituents of the cell body, at one time represented protoplasm.
The formation of these substances was sometimes compared
more to a secretive act of the cell, at others, more to a meta-
morphosis of the outer portion of the cell body. We think
both occur, and the difference between these views is, in fact,
of little importance.

A deposition may also take place from without upon a
single cell or a cell-complex and enter into a closer union
with it. The mammalial ovum (Fig. 5), shows a capsule.
It is the elaboration of the small cells (a) covering the ovu-
lum.

The capsule of the cartilage cells appears very similar to
the ovum capsule. Its origin, however, is entirely different.

The cartilage cells have
themselves formed the car-
tilage capsule. We shall
return to this subject later.
The glands (Fig. 26), con-
sist of secretory cell-com-
plexes surrounded by a
hyaloid covering, the so-
called membrana propria.
This is not a secretory pro-
duct of the cell-aggrega-
tion, as was formerly assum-
ed. The membrane is trans-
formed from the connective tissue adjacent to the glandular
cell-aggregation. It may remain structureless, but extremely
flat stellate cells may also enter into its structure. They then
appear as delicate, rib-like thickenings of this membrane.

Fir;. 26. — Tubular glands from the large intes-
tine of the Guinea-pig. At a, a gland with the
membrana propria showing in places ; at />, escape
of the contents through a rent in the latter.

THE PROTOPLASMA AXD THE CELL.

19

We will add one more example of a
widelv diffused cell transformation ; wc
allude to the transversely striated volun-
tary muscle.

This, a thick, cylindrical fibre, not
unfrequently of considerable length,
consists of a contractile, longitudinal
and transversely striated substance. In
the outer portions of the latter lie
numerous nuclei with adherent proto-
plasma remains. It is surrounded by
a hyaloid sheath. The whole, how-
ever, arises from a single cell (Fig. 27).
This (a), with a continual increase of the
nuclei, grows into a thread ; the proto-
plasma is transformed into the longitudi-
nally and transversely marked substance
(V) ; only a scanty remnant surrounds the
nucleus, forming it into a rudimentary
cell, and the homogeneous covering of
the thing is derived from a transforma-
tion of the adjacent connective tissue.

The examples presented may suffice.
They show, at least, how the most het-
erogeneous may result from what was
originally similar, through subsequent
cell metamorphosis, and they attest the
high signification of the cell in the structure of the organism.

FlG. 27. — Development of
the transversely striated mus-
cular fibre (sheep embryo).

SECOND LECTURE.

CLASSIFICATION OF THE TISSUES. — BLOOD, LYMPH, CHYLE.

A CLASSIFICATION of the tissues was, in the course of time,
often attempted ; but it is, and remains, a very difficult thing.
A scientifically adequate arrangement can be founded only
on the course of development of the elements. The latter is
unfortunately not yet accurately established throughout.
One might nevertheless proceed with strictness, by the aid of
the history of development ; the three well-known germinal
plates from which the embryo arises might be employed as a
basis of the arrangement. Still the representation of the tis-
sues thus arranged would be attended with not inconsiderable
difficulties.

We will, therefore, employ a preponderating artificial
classification, which, with all its defectiveness, possesses, at
least, the advantage of presenting the material in a more
convenient form to the learner.

We distinguish :

A. Tissues of simple cells with fluid intermediate sub-
stance : I. Blood; 2. Lymph; 3. Chyle.

B. Tissues of simple cells with scanty, firm, structureless
intermediate substance : 4. Epithelium; 5. Nails; 6. Hair.

C. Tissues of simple or metamorphosed cells, with partly
still homogeneous, partly fibrous, and, not rarely, more firm
intermediate substances (connective-tissue group) : 7- Carti-
lage ; 8. Gelatinous tissue and reticular connective substance ;
9. Fat tissue; 10. Connective tissue; 11. Bone tissue; 12.
Dentinal tissue.

D. Tissues of metamorphosed, as a rule, unfused, cells, with
scanty structureless intermediate substance: 13. Enamel tis-
sue ; 14. Lens tissue ; 15. Muscular tissue.

CLASSIFICATION OF THE TISSUES.

21

E. Compound tissues : 16. Vessels; 17. Glandular tissue ;
and 18. Nerve tissue.

We shall, therefore, proceed in this manner, and turn first
to the blood.

" Blood is quite a peculiar sort of juice," Goethe lets his
Mephistopheles say. Modern science, after nearly a hundred
years, endorses the apothegm completely.

If a little drop of this fluid, which appears homogeneous to
the naked eye, is spread out in a thin layer under the micro-
scope, we are surprised by a peculiar image. The homoge-
neous red has disappeared ; we perceive innumerable yellow-
colored cells in a colorless fluid. The fluid is called plasma,
the cells bear the name of the colored or red blood corpuscles
(Fig. 10, a, b, c). Among the colored companions, still
another, though not abundant, colorless structure may be
noticed by closer examination. This is the lymphoid cell of
the blood, the so-called white blood corpuscle id).

The human red blood cells are diminutive structures ; they
measure only 0.0088 to 0.0054 mm. Their smallness and their
innumerable quantity renders it possible that a small space —
a cubic millimetre of blood — may contain five millions of
them.

Their form, as Fig. 10
showed, is spherical, the
periphery appears yellow,
the centre bright and
nearly colorless. When
the blood corpuscle rolls
over the microscopical
glass slide, the side view
presents the appearance
of c. Our cell, conse-
quently, represents a cir-
cular disc, with excavated
central portions of both
broad surfaces.

Fig. 28. — Red blood corpuscles of man
with water ; b, in evaporating plasma ;

a, treated
dried ; it,

after coagulation ; e, rouleaux-like arrangement.

The red blood corpuscle is, besides, a very changeable

22

SECOND LECTURE.

thing. In evaporating blood it becomes indented (Fig.
28, b). Rapidly dried, it presents the appearance of c. On
the addicioii of water, the cell becomes globular and loses its
color. The coloring material, an extremely complicated sub-
stance, called haemoglobin, has now become dissolved.
Something similar is also seen in previously frozen blood.
The colorless residue is called stroma.

A series of reagents, which have been applied to our
structures during many years, act similarly, some distending,
others shrinking ; but by no treatment does a nucleus make
its appearance. The human red blood corpuscle is, therefore,
a non-nucleated cell.

Has the thing a membrane — does it possess a covering ?
we ask further. We answer negatively. An interesting ex-
periment is here, according to our opinion, decisive. When
living blood cells are warmed to 520 C, they commence a
marvelous transformation. Indentations of the border rapidly

Fig. 29. — Colored blood cells ; i, from man ; 2, camel ; 3, pigeon ; 4, proteus ; 5, water salaman-
der ; 6, frog ; 7, cobitis ; 8, ammoccetes. At a, surface view ; b, profile (mostly after Wagner).

occur, and partial constrictions of the cell body rapidly follow,
which either immediately break off or remain in connection

CLASSIFICATION OF THE TISSUES. 23

with the main portion by means of a thin, pedicle-like bridge.
The strangest appearances are hereby presented to the eye.
It is plain that only a membraneless cell body can present
such constrictions.

The cells, these living corner-stones of our body, are other-
wise quite similar in the various vertebrate animals ; it is not
so, however, with the blood. The differences in most of the
mammalia are certainly slight. The form remains ; only the
diameters vary somewhat. A few ruminants, the camel, al-
paca, and llama, have oval cells (Fig. 29, 2).

The blood corpuscles of birds (3), amphibia, and most
fishes (3), appear elliptic ; but in the middle of both broad
surfaces we meet with an elevation. The diameter changes
in an interesting manner. In birds, it is 0.0184 to 0.0150 mm.;
in the squamigerous amphibia, 0.0182 to 0.0150; in osseous
fishes <7j, 0.0182 to 0.01 14. Our cells reach prodigious dimen-
sions in the ray and shark, 0.0285 to 0.0226 mm.; then among
the batrachia, the frog (6) and the toad have blood corpuscles
of 0.0226; the triton (5), up to 0.0325 mm.; and the salamander
has still larger. The group of the pisciform amphibia have the
largest of all. In the proteus they measure 0.057 mm. The
cyclostomen, a low group of fishes, have, strangely, again,
spherical bi-concave discs measuring 0.0113 mm. (8).

All these blood corpuscles behave, with reagents, similar
to those of man and the mammalia. But in them all, on the
contrary, there is a nucleus. Even in the dying cell it is
visible. Many reagents — for example, water, very dilute
acetic acid — let it show out from the now discolored cell as a
granular structure (Fig. 30, a, b).

The second element of the blood, the
lymphoid cell, is much more homogeneous.
The form is, throughout, spherical ; the size
is, in man (Fig. 10, d ; Fig. 31, 1 to 4), rarely FlG. 30._Kio?d

„ „ n j_ __,__ , „„„ i-i cells of the fro^ with

0.005, generally 0.0077 to 0.012 mm. I he granular nuclei,
most of our structures, according to this,
exceed the dimensions of the colored corpuscles. It is the
same in the mammalia. In the remaining classes of the

24 SECOND LECTURE.

vertebrates, however, the lymphoid cell is smaller than the
colored element.

7 j They show a molecular proto-

© © ^^ plasma, with a granular contour.
s , s A few lymphoid cells harbor, in

®[0J ^p W^j addition, fat molecules (4). If water
s~\> sj\ s-^f ^e a^owe<^ to act on them, the
t>, v_y ^ty (~ ) nucleus immediately begins to de-
« /2 tach itself (5). After this we have

JSyr^'ft'SdiS anVO nuclear forms> s«ch as the cells 6, 7,
9aprhTnuc.ts^!n:\6o%^:,11kewi^ and 8 possess. Other cells show a
£i»"^7«^fc£d£ reniform (9), or triplicate nucleus
substance- (10, ID. This artificial production

may finally break up into a number of small fragments (12).

The lymphoid cells adhere readily, they are of a somewhat
sticky nature. Their specific weight is less than that of the
red blood corpuscles. During life we meet with the already
described amoeboid change of form, as well as a locomotion
thereby induced ; this takes place most actively in diluted
plasma (Thoma). The cells can also be made to take up
small foreign particles.

There are one, two to three colorless blood cells to 1,000 red
ones in man. The number increases after a plentiful meal, after
the loss of blood, and also under conditions which indicate a
more active blood formation. An interesting phenomenon is
presented by the spleen. The blood flowing into it shows the
usual small number of lymphoid cells, while in the blood of
the splenic vein 5,7, 12, 15, and more of them occur. In the
lower groups of vertebrate animals, the number of the color-
less cells is more considerable ; in the frog, the proportion of
lymphoid cells to red blood corpuscles is I : 4-10.

The web of the frog and the tail of its larvae are adapted to
examinations of the circulation. The wonderful spectacle
(Fig. 32), shows how the colored blood corpuscles readily and
rapidly pass along and among each other, while the viscous
lymphoid cells move much less rapidly, and not unfrequently
adhere for a time to the inner surface of the vessel.

CLASSIFICATION OF THE TISSUES.

25

cells originate ? First,
is, from the lymphatic

Fig. 32. — The blood current in tSe web of
the frog ; a, the vessel ; b, the epithelial cells
of the lissue.

But whence do our lymphoid
from the lymph and chyle, that
glands, then from the spleen
and bone marrow. They are
carried away from both the
latter parts by the blood cur-
rent.

What becomes of our cells
in the veins ?

They become, in part, grad-
ually transformed into red
blood corpuscles, and cover
the loss of the latter. Whether,
however, a greater or only a
lesser portion undergoes this
metamorphosis, we are not
yet able to say ; for this, we

must first learn more accurately the duration of the life of the
red blood corpuscles.

The manner of this metamorphosis we can state in some
degree. The globular form changes to the specific one of the
red blood cell, and the protoplasma is replaced by a homo-
geneous colored substance. In mammalia and man, finally,
there is also a loss of the nucleus.

Isolated examples of such intermediate forms have been
recognized in the blood for years, especially in that of the
spleen, the mammary ducts and the bone medulla.

The bright red color of the arterial, and the dark of the
venous blood is caused by a combination of oxygen with the
haemoglobin, or a reduction of the latter. Prolonged changes
in the form of the blood corpuscles likewise exert a modifying
effect on the color. Distended, they lend a darker color to
our fluid ; shriveled, a brighter one.

When a drop of blood is left to itself, it coagulates. The
filiform separation of the fibrine is shown in our Fig. 28, d.

When blood is beaten, that is, the fibrine caused to coagu-
late, the cells sink, the red ones more rapidly, the colorless,

26 SECOND LECTURE.

lighter ones more slowly, the former arranging themselves
in rolls (e).

We come, finally, to the blood formation of the embryo.
The fiat germinal layer, from which the human body arises,
consists of three membranous cell layers lying one over the
other, the horn layer (Hornblatt), the middle germinal layer,
and the intestinal gland layer (Darmdriisenblatt) (Remak).
The heart, vessels, and blood proceed from this middle layer,
from which, besides, many parts of the body originate.

The first blood appears very early, and consists only of
colorless cells, formed of protoplasma and a vesicular nucleus.
The homogeneous yellow substance gradually replaces the
molecular protoplasma. We have now before us, nucleated
colored blood corpuscles (Fig. 18, a), of 0.0056 to 0.016 mm.

At this period an increase also takes place by the way of
division (a to_/). Later, this procedure becomes extinct, and
the cells assume more and more the specific form, the nucleus
at the same time disappearing.

Let us now proceed to the lymph and chyle.

The fluid of the living blood, the plasma, constantly passes
through the thin capillary walls into the adjacent tissues. It
brings to the latter the nutrient materials, to the one these ;
to the second, again, others. The fluid becomes impregnated,
however, with the products of decomposition of the tissues.
The latter are again different.

The tissue fluids, which are in consequence so variable in
their chemical constitution, finally collect in the fissures and
spaces of the body. Thin-walled vessels are gradually de-
veloped from these ; and then, uniting in larger trunks, they
finally enter the blood passages. These are the lymphatic
vessels; and the fluid contents, whose nature we have just de-
scribed, are called lymph.

The walls of the intestines also have their lymph districts.
Towards the close of active digestion they contain tempora-
rily another cloudy or white fluid, which is very rich in albu-
men and fat. This is the lacteal juice or chyle. The canals
bear the name of the chyliferous system of vessels.

CLASSIFICATION OF THE TISSUES.

27

The lymph appears colorless and clear as water. Taken
from the smallest vessels, it may be without cells. It con-
tains large quantities of them when drawn from the larger
vessels, especially just after the passage of the latter through
lymphatic glands or allied structures. Nevertheless, it is infi-
nitely less rich in cells than the blood. They are the same
lymphoid cells we became acquainted with in the blood (Fig.
31) ; further description is therefore unnecessary.

The lymph presents nothing further. In the chyle, on the
contrary — and they cause the cloudy or whitish appearance
of the fluid — we meet with innumerable infinitely fine dust-
like molecules. With a strong magnifying power they show a
peculiar, dancing, driving about, the so-called Brunonian
molecular movement. But there is nothing strange in this.
It is natural to all very small bodies suspended in water,
small particles of fat, the smallest crystals, carmine granules,
and the like. These dust-like particles consist of fat, sur-
rounded by a very thin albuminous covering.

Red blood corpuscles may be met with in the lymph and
chyle as incidental constituents, and occasionally as transition
forms. I have seen the latter in the thoracic duct of the
rabbit.

Red blood cells, pressed out from the blood-vessels, may
also finally reach the lymphatics. There is no doubt that the
actively emigrated colorless blood cells often penetrate these
passages, and thus again commence the journey back into the
blood.

THIRD LECTURE.

THE EPIDERMIS, OR THE EPITHELIUM.

Under epithelium we understand closely-arranged cell lay-
ers, held together by a minimal quantity of cement (p. 16); it
covers the surface of the body, the external as well as the
internal.

All three plates of the germinal layer (p. 26), participate in
the production of the tissue under examination. The horn layer
supplies the covering of the corium, the so-called epidermis.
The lower germinal plate forms the epithelium of the diges-
tive apparatus and the organs arising from the latter. Not
less important is the role of the middle cell layer. Manifold
cavities originate in it; the passages of the vascular system,
the so-called serous sacs, the articular cavities, down to innu-
merable small and diminutive tissue spaces. All these again
have their epithelial cell covering. The latter is now called
endothelium. The principle is correct ; but the boundaries
cannot yet be sharply drawn throughout.

Epithelium consists either of a simple cell layer, or the
cells are stratified more or less manifoldly over each other.
We distinguish, therefore, unstratified and stratified epithe-
lium. The latter originates in the horn layer. The former
is due to the intestinal gland, as well as the middle germinal,
plate.

The form of the cell varies. Many kinds of epithelium
present only thin, flat, scale-like cells (Figs. 7 and 20). We
speak now of flattened or pavement epithelium. In other
varieties the cell is tall and slender. This is called cylindrical
epithelium (Figs. 6 and i<p. When the surface of the cylin-
drical cells has vibratory ciliae (Fig. 33) we have the vibratile
or ciliated epithelium.

THE EPIDERMIS.

29

Fig. 33. — Various forms of
ciliated epithelium.

The simplest unstratified pavement epithelium belongs in
most, but perhaps not all its occurrences, to the endothelium.
We find it in this way on the surface of
the serous sacs, on the posterior wall of
the cornea of the eye, over the lateral
surfaces of the synovial capsules of the
joints. The same endothelia are met
.with on the inner surface of the cardiac
cavities and the vessels.

These cells, very thin lamellae, appear
sometimes broad and short (Fig. 20, a),
on the serous membranes, again very narrow and long (5) on
the inner surface of the arteries. The endothelium of the veins
has a median character.

A larger blood-vessel is a complicated thing. In proportion
as we descend to the smaller and still smaller branches, one
outer layer after the other disappears from this complicated
structure, and at last only the inner-
most endothelial layer remains. Large
cells with lapped edges, and — induced
by the position of the vascular tube
— now much more strongly incurvated
and in close connection, constitute the
walls of the capillary (Fig. 21). The
lymphatic vessels are also formed in
the same manner, though their finest
canals — and they occur in immense
numbers throughout the body — show
the outer surfaces of these endothelial
cells grown into an intimate connection

with the neighboring tissue, so that one might here speak of
lacunae.

The terminal respiratory portions of the lungs, the air vesi-
cles or alveoli, have a layer of simple flattened epithelium
which does not belong to the endothelium.

We pass over the others at present.

An interesting variety is found at the outer surface of the

Fig. 34. — Endothelial cells after
treatment with nitrate of silver.

30 THIRD LECTURE.

retina. They were formerly called polyhedral pigment cells
(Fig- 35)- Their surface presents a delicate mosaic, as a rule,
of a hexagonal form, of 0.0135 to 0.0204 mm. The quantity

of the pigment granules embedded in the
soft, homogeneous substance of the cell
body varies, so that the nucleus is some-
times visible, at others concealed. The
outer portion of the cell remains free
fig 35 -rigment epkhe- fr°m these melanine molecules, which
IS,? .fort&jlJS appear to form small crystals (Frisch).
^nalone!1 ",alargerocta" The profile view shows, however, that

our cell, far from constituting a flat struc-
ture, possesses, rather, a certain, sometimes a considerable,
height, which, at least, equals the diameter. It is thus in the
lower vertebrate animals ; here their body sends downwards
a number of filamentous and spiny processes. The latter,
at first, still contain pigment molecules, and surround in a
sheath-like manner the rods and cones, the marvellous termi-
nal apparatus of the retina. This is less frequent in mam-
malial animals. These pigmented cells extend beyond the
limits of the specially nervous portion of the retina, over the
so-called ora serrata, where they become smaller, more rich
in pigment, and are in thin layers. In this manner they then
cover the ciliary processes and the posterior surface of the
iris.

Certain of the mammalia (the carnivora and ruminantia)
have a bright, glistening place in the interior of the eye,
called the tapetum. Our retinal epithelium is here unpig-
mented. In albinos this is the case throughout, and the
cells present the appearance of a delicate pavement epithe-
lium, as, for instance, in the white rabbit.

Many mucous membranes present material, and sometimes
very considerable, layers of pavement epithelium. Among
these are the conjunctiva of the eye, the mucous membrane
of the nostrils and of the anus, the mouth and pharynx, the
oesophagus, the urinary passages, and the vagina.

In the most superficial layers of the conjunctiva (Fig. 36, a)

THE EPIDERMIS.

31

we meet with flattened, not inconsiderable cells. In the
middle layers these elements become smaller, but taller, more
round, and, in the deepest layer {/?), at last, cylindrical.

Fig. 36. — The cornea of the rabbit in vertical transverse section, after treatment with chloride
of gold ; a, the oldar, /', the young epithelial cells of the anterior surface ; c, corneal ti-sue : </, a
nerve branch ; e, finest nerve fibres or primitive hbriUae ; /, their distribution, and termination in
the epithelium.

With a greater increase of the epithelial stratification, the
number of the upper and middle cell layers is much more
considerable.

All the cells have a nucleus. The lowermost have a soft
protoplasma body ; the superficial (Fig. 7) have become more
solid and harder; they consist of corneous matter, or kera-
tine, a derivative of the albuminous group. These cornified
cells absorb weak alkaline solutions with avidity, becoming,
at the same time, distended to a globular form.

A vertical transverse section, after the manner of our draw-
ing, favors the supposition that our cells have a pretty regu-
lar form.

When, however, the cell cement has been dissolved by a
suitable macerating medium, an entirely different appearance
is presented. The stratified pavement epithelium now ap-
pears very much more like extremely polymorphous cells.
They lock into each other with their pointed and leaf-like
processes ; the convex surface of one cell is in contact with
the concave surface of its neighbor ; the surface is rough and

32 THIRD LECTURE.

sometimes indented (Lott, Langerhans). This was first seen
in the epithelium of the urinary bladder. When the epithe-
lial stratification is more developed, the cells of the lower
and middle layers lock into each other with their enormous
spines and ridges, like two brushes pressed together (Fig. 37).

These "spinous and dentate cells"

J$^&J$i£% (Schultze) lead to an intimate clinching.

a t'M$^:fi$% This connection is, however, again dis-

^*§6§'£0^iii$ solved upwards, and their deciduousness

d^^ip-fT^v-'i is thus promoted.

^^"^''•# The most dense formation of flattened

epithelium covers the human corium. It
b v^'^;''-*.!t^ nas l°ng been known under the name of

the epidermis.

This corium projects in small papillae of

various shapes. They are called the sensi-
JE? %*£?*?££ tive or tactile papillae. The epidermis
mf"\°ceiihuf™m a'p'S" forms a smoother covering over the whole ;
'tongue™0" °f ** human its deeper cell layers must, therefore, fill

up the valleys between these papillae.
These younger cell layers, which have a not inconsiderable
thickness between the papillae, while they are but slightly
developed over their apices, present all the characteristics of
a stratified epithelial mucous membrane. Collectively, it is
called the Malpighian rete mucosum, or rete Malpighii.
The layers of old cornified cells make their appearance by an
abrupt transition. They bear the name of the epidermis in
the strict sense of the word. Its thickness varies considera-
bly ; it may exceed a Paris line. The number of layers
varies, in consequence, extraordinarily. The latter are the
same scales as those on the surface of the mucous membranes,
though the cells in contact with the atmospheric air have be-
come dryer and harder. The nucleus, which these cells for-
merly possessed, has likewise been lost by the old, effete
epidermis scale. They measure 0.0285 to °-045° mm.; in the
mucous epithelium of the mouth, 0.0425 to 0.075 mm.

We will speak of the color of the human skin. If we

THE EPIDERMIS. 33

cover a red cloth with a piece of milk-glass, we have the flesh
color presented to our eyes, and the thicker the piece of glass
selected, the lighter the tone will be. It is thus with the
complexions of Europeans. The corium during life appears
red, in consequence of its extreme richness in blood ; the
epidermis is semi-transparent, whitish or whitish- yellow.
The thinner the latter, the redder the color (lips, cheeks) ;
the thicker the cell covering (the foot-sole, frequently the palm
of the hand also), the paler the surface of the body.

In the skin of the dark human races, that of the negro, the
nuclei in the deeper layers of the epidermis are diffuse
brown ; the cell bodies are also somewhat darker, and may
also contain pigment molecules. In the darker portions of the
bodies of the light races (the nipple and its areola) the same
condition prevails. The coloring matter here conceals the
red of the cutis.

All stratified epithelia. as we already know from what has
preceded, are of a perishable nature. Millions of the super-
ficial cells fall off daily, from rubbing, pressure, etc. The
new formation takes place at the deepest layer, by a process
of division. Between the latter cell layers, finally, immi-
grated lymphoid cells may also be met with.

The second form of epithelial tissue, the cylindrical, be-
longs to the digestive apparatus, from the entrance to the
stomach to near the anus, likewise to the ducts of the liver
and pancreas, the ducts of the lacteal and lachrymal glands,
and also some portions of the sexual apparatus.

We there (Fig. 6, b, 14, a) meet, as a rule, with a single row of
narrow, vertically elongated cells, with a sometimes super-
ficially, sometimes more deeply lying nucleus, which contains
a nucleolus. A thin layer of cement substance unites our
cells, which, seen from above (Fig. 14, b) present a fine mosaic.
Their height and breadth vary. In the human small intes-
tine, the former is 0.0182 to 0.027, the latter 0.0057 to 0.009 mm-
The lateral walls show an envelope ; the free base may present
naked protoplasma, as in the stomach ; it may, also, how-
ever, show a different character. This is the case in the
2*

34 THIRD LECTURE.

small intestine (Fig. 14, a). There occurs here an already
mentioned covering piece, 0.0017 to 0.0025 mm. high, formed
of a firmer, very changeable substance, and permeated by
very fine canals, the so-called porous canals. We shall have
to mention the latter later in alluding to the absorption of
the chyme.

That the cylindrical epithelial cells, many of them at least,
are destroyed by a mucous metamorphosis of their interior
(" Becher cells ") we have shown in Fig. 6, a. The reparation
remains unclear. It is not accurately determined that there
is a deeper, younger layer of cells destined to this purpose.

Vibratory or ciliary epithelium (Fig. 29) is formed of modi-
fied cylinder cells. The same cell bodies, with similar varia-
tions in height and diameter, present themselves. Only the
free surface, which has the cilice, those most restless proto-
plasma filaments (p. 10), causes the peculiarity.

Ciliary epithelium lines the human respiratory apparatus.
Commencing at the base of the epiglottis, it covers the
larynx, with the exception of the lower vocal cords, which
have stratified pavement epithelium; also the trachea and the
bronchi, as far as their finest ramifications, but not the respi-
ratory vesicles of the lungs (p. 29). We meet with it, fur-
ther, in the olfactory organ, with the exception of limited
places. The oviducts and uterus of the female, the vascula
efferentia, the coni vasculosi, and the canal of the epididymis,
as well as the upper half of the vas deferens, have this
variety of epithelium. Finally, to pass over its more limited
occurrence, the cavernous system of the spinal cord and
brain " vibrates " in the embryo and neonatus.

The ciliae are often of considerable size in the lower ani-
mals ; in the higher, they become smaller and smaller. They
appear exceptionally long, measuring 0.0226 to 0.034 mm., on
the large epithelial cells of the canal of the epididymis, and
very short, 0.0056 to 0.0038 mm. , in the respiratory apparatus.
A high degree of perishableness is impressed, as a character-
istic sign, upon them all. Whether compensatory cells occur
in ciliated epithelium is, perhaps, not yet accurately deter-

THE EPIDERMIS. 35

mined. They have, at all events, been frequently admitted.
Mucous metamorphosis, as in the cylinder cells, is also fre-
quently met with here.

Lymphoid cells may also occur between the cylinder and
the ciliated cells ; indeed, they may even penetrate to the in-
terior of the cell body (comp. Fig. 16).

Let us here devote a few words to the remarkable ciliary
motion.

Discovered in olden times, subsequently, especially of late
days, frequently investigated, it has not yet been satisfactorily
explained. Its occurrence in the animal kingdom is quite
variable. Sometimes this part vibrates, at others that,
sometimes nearly all the surfaces ; at others, as in the arthro-
poda, not at all. What purpose does this work of the cilia?
serve ?

If we fold a suitable detached piece of mucous membrane and
examine the edge of the fold, we have the appearance of an
undulating border, of a flickering candle-flame. If we look
from above downwards on to it, it suggests the comparison to
a field of grain agitated by the wind.

Small bodies suspended in the fluid medium, color granules,
blood cells, sweep past the folded border, when we examine
with a high magnifying power. When we use very weak
lenses, the excursion proceeds more slowly; a cell will require
several minutes to make its course.

When the ciliary motion is still in full vital energy, and
several vibrations then take place in a second, the human eye
is powerless. It is only when the action becomes retarded
that we perceive the separate motions — the regular, syn-
chronous, and homogeneous vibrations of the ciliae. At-
tempts have been made to distinguish several varieties of
these vibrations ; as for example, a hook-like and an oscilla-
tory.

We pass over this ; but we must here mention an apparently
strange condition. In the ciliary movement, we see the cilia?
vibrate towards one side, and the small passing bodies take
the opposite direction !

36 THIRD LECTURE.

The matter is readily explained. We first recognize the
slower, less energetic direction of the vibration ; the other,
more rapid and powerful, we do not yet perceive. In which
direction, however, will the current be driven ? Manifestly,
in the latter. Engelmann explains the more sluggish move-
merit as a vital act of the protoplasma ; the more rapid, as the
effect of elasticity. We agree with him.

Later, as death approaches, both movements become dis-
tinct. The current finally ceases, only a to and fro fluctuation
still remains.

The ciliary movement has nothing to do with the blood
current, or with nerve life. It perishes rapidly in warm-
blooded animals, often very slowly in the lower cold-blooded
creatures. An elevation of the temperature to 440 and 450 C.
kills them, likewise increasing cold. Everything which exerts
a chemical influence likewise produces a destructive effect, occa-
sionally with a temporary increase of the vibration — water,
for example. It is an interesting observation, that dilute
solutions of potash and soda may temporarily excite the
paralyzed vibratory phenomenon to renewed energy (Virchow).

The true epithelium — that is, so far as it originates in the
corneous and intestinal gland layers — is developed very early.
Even in the human embryo of five weeks, according to
Koelliker, the surface of the body is covered by a double
layer of cells, a deeper one consisting of smaller rounded
structures, and an upper one of larger, flatter, indented bodies.
The former represents the primary rudiments of the rete
Malpighii, the latter, the horny layer.

Closely related to the epidermis, and arising from it in the
third month of fcetal life, are the human nails. These obtuse
quadrangular plates are arched outwards, and lie posteriorly,
with the so called nail roots, embraced within a deep furrow
of the skin. At the sides, the furrow becomes from behind
forwards more and more shallow. The anterior border of the
nail remains free. The portion of the cutis covered by the
nail bears the name of the nail-bed. The latter shows lon-
gitudinal rows of cutaneous papillae.

THE EPIDERMIS.

37

Fig. 38.— Cells of the
horny layer of the nail ;

a, a, view from above ;

b, b, seen from the side.

The nail consists of two strongly demarcated layers, a deep
and a superficial. The former is the ordinary
Malpighian mucous reticulum, such as is
shown by any other part of the skin. The
superficial layer, corresponding to the horny
layer of the epidermis, has gone through the
process of hornification in a much higher
degree than occurs elsewhere. At the first
consideration, we perceive only a brittle,
homogeneous substance. The power of refrac-
tion of all its constituents has
become equal. Reagents, and
above all, solutions of the alka-
lies, are here of inestimable
value. With them we dissolve
the cement substance and re-
store a recognizable appear-
ance to the cell. The latter, an
originally flat thing, measures
0.0375 to 0.0425 mm., but, dif-
fering from the ordinary epider-
mis cell, contains a lens-shaped
granular nucleus, as may be
readily recognized from Fig. 38,
a and b.

Concerning the duration of the
life of the nail cell, see p. 12.

The highest variety of epider-
moidal tissue is represented in
man, by the hair.

An extreme complication of
structure welcomes us here, all
at once.

The hair (Fig. 39), lies in an
obliquely directed sac, an invo-
lution of the corium, and fre-
quently likewise of the subcutaneous cellular tissue

Fig. 39. — Human hair ; <?, the sac : /', its
hyaline inner layer ; r, the external, d, the
inner root-sheath ; e, transition of the outer
sheath to the hair-bulb ; /, epidermis of the
hair (at_/, in the form of transverse fibres) ;
g, lower portion of the same ; //. cells of the
hair-bulb ; /, the hair papilla; ; k, cells of the
medulla ; /, cortical layer ; m, medulla con-
taining air ; n. transverse section of the lat-
ter ; o, the cortex.

The

33

THIRD LECTURE.

sac shows externally (Fig. 39, a ; 40, i) longitudinally, then
transversely arranged connective tissue (40, //), and, finally,
internally (39, b ; 40, g), a hyaline boundary layer. At the
bottom it juts forward as a vascular papilla (Fig. 39, i). It
is the formative and nutritive organ of the whole.

On the hair itself we distinguish the hair-bulb (Fig. 39, h),
resting on the papilla and the shaft (/). Only a slight portion

of the latter is surrounded by the sac ;
the larger, often very long, remaining
portion, projects freely from the skin,
as, for instance, the hair on women's
heads. As the corium is involuted,
so also does the epidermis with its
two layers, the rete Malpighii and the
horny layer, dip down into the sac.
These depressions are very appropri-
ately named root-sheaths ; and the in-
sinuated rete Malpighii is distinguish-
ed as the external root-sheath (Fig.
39, c, 40, e), the horny layer of the
sac as the internal (Fig. 39, d). The
former requires no further description,
it presents nothing special ; but the
latter acquires a modified structure.
It consists of two layers of hyaline
cells, an external layer of vertically
arranged non-nucleated elements, of
0.0377 to 0.0451 mm. (Fig. 40, d),
between which longitudinal clefts may
; c, inner, and rf, outer layer be perceived, and an inner layer of

: inner root-sheath ; c. outer *■ J

root-sheath ■/, its peripheral layer radially arranged cells with nuclei (c).

of elongated cells : g, hyaline jo \ /

membrane of the hair sac ; a, its Downwards, in the depth of the sac, the

middle, and i, external layer. r

external root-sheath becomes single.

The substance of the hair bulb (Fig. 39, //) shows the same

cells as the external root-sheath, with colorless or pigmented

molecules. Upwards the appearance changes ; it then

comes, or at least very frequently, to a differentiation into

Fig 40. — Transverse section
through a human hair and its fol-
licle ; a, hair; b, epidermis uf the
same
of the

THE EPIDERMIS. 39

cortex (k), and medulla (/). In the former we see the cells
becoming longer and flatter, until finally they are quite dry,
irregular, elongated cortical plates of 0.075 1 mm., and fre-
quently non-nucleated, in close union, forming the outer por-
tion of the hair shaft. A diffuse coloring matter, light in
blondes, deeper in dark-haired individuals, permeates the
whole. Pigment granules and the finest air vesicles may ap-
pear in the spores and clefts.

The medullary substance does not, by any means, occur in
every hair, since in all lanugo hairs and also in many of those
of the head it may be entirely or partially wanting. At first
(Fig. 39, k), the cells of the

hair bulb are perceived to be a'""M "^e^^ ^^"5^5

transformed into larger polyne- 7?ff

dral elements of 0.015 1 to 0.0226
mm. Further above follows m-^-h

the drying and shrinking of the ^MJP^ ~" *

elements, which have in the

m

mean time become non-nucleat- „, „ ,. ,-..,.

Fig. 41. — Rudiments of the hair of a rul-
ed. Very Small air Vesicles man embryo of .6 weeks : a 6, epidermal
J layer; m. m, cells ot the rudiments of the
dlter the innumerable Small hlLlir: *> structureless membrane covering

them .

spaces. A white hair thus re-
ceives its appearance, while in colored hairs the serrated sub-
stance glistens through the coloring of the cortex, as if
tinged.

We have still one structure remaining, the epidermis or
cuticle of the hair (Fig 39,/, 40, b). A double layer of hy-
aline obliquely standing cells covers the hair, as long as it is
surrounded by the sac. With the latter terminates the outer
cell layer, but not so the inner one. This covers the free
hair, as a system of quite obliquely arranged, flat, non-nu-
cleated lamellae, covering each other in a tile-like manner, like
a scaly coat of mail. Not unfrequently, after pressure and
maltreatment, the lamellae present the appearance of regular
transverse fibres (Fig 39, /*).

Hairs are found over nearly the whole body, as so-called
lanugo hairs, and in limited places as thicker, coarse hairs.

40 THIRD LECTURE.

Its smooth or frizzled condition depends on the cross section
In the former hair it is round, in the latter oval or reniform.
The growth of the hair takes place by a cell increase from the
lower portion of the hair bulb. So long as the sac with its
papilla remains uninjured, it regenerates the lost hairs ; that is,
such as are stunted in their hair bulbs and are separated from
the papillae. This power of reproduction is tolerably ener-
getic, for the physiological loss of hair is not inconsiderable.
The origin of the embryonic hair commences at the end of
the third or the beginning of the fourth month (Fig. 41).
The epidermis forms with its deeper cells (b) a knobby down-
ward growth. A structureless boundary layer, furnished by
the impressed corium (/), leads to the formation of the hair
sac. From the cell aggregations (m, m), are developed both
the root-sheaths and the entire true hair with its cuticula.
The hairs, like the nails, are, therefore, secondary epidermoi-
dal structures.

FOURTH LECTURE.

THE CONNECTIVE-SUBSTANCE GROUP. — CARTILAGE, GELA-
TINOUS TISSUE, RETICULAR CONNECTIVE TISSUE, FAT.

CONNECTIVE TISSUE, fat tissue, cartilage, bone, dentine, are
well known constituents of the body. Their finer structure
proved extremely heterogeneous at the commencement
period of modern microscopy. It was in the year 1845 tnat:
Reichert recognized all these things as members of a natural
unity. Science is indebted to him for the exposition of a
" connective-substance group." Here Virchow accomplished
further progress in the domain of pathology ; and, indeed,
also committed errors. Much labor has subsequently been
bestowed upon this group ; we have made further progress,
but are still far enough removed from a conclusion.

All these tissues mentioned — and to these are to be added,
as new acquisitions, gelatinous tissue and the reticular con-
nective substance — arise from the middle germinal layer (p.
26). They are originally similar, but then, pressing on to-
wards maturity, they assume quite variable forms. Connect-
ing intermediate forms, however, remain. No one can, for
example, draw a sharp boundary between gelatinous and
ordinary connective tissue, or between the latter and carti-
lage. We meet in places, therefore, with a continuous tran-
sition of one connective substance form into another. Truly
different tissues never do this. We meet, furthermore, in
the animal kingdom, very frequently a substitution of one
tissue of our group by another. That, for example, which
in one creature is connective tissue is in another gelatinous
tissue, or even bone. A temporary substitution also occurs.
The parts of our skeleton were, for the most part, formerly
cartilage. In morbid growths we meet with extraordinary
frequency with such substitutions of the one for the other.

42

FOURTH LECTURE.

The connective-substance group, occurring throughout,
forms a large part of our body, the general frame-work, in
which the other tissues are embedded. They have rightly
been called the scaffold and supporting substance of the
body.

Let us now examine their individual varieties.
Cartilage tissue makes its appearance very early in the con-
struction of the body, though frequently to disappear after a
short duration of life. Most cartilage, accordingly, does not
become old. Even at the hour of birth a considerable por-
tion of the cartilage has fallen a sacrifice to a new secondary
tissue, the osteoid or bone tissue. A portion of the cartilage
lasts, however, till the death of the person, and may thus
reach a great age.

The texture is distinguished, according to several varieties
of the mature tissue, into : a, the hyaline ; b, the elastic ; c,
a rather uncertain variety, the connective-tissue cartilage, an
intermediate thing between cartilage and connective tissue.

In its first embryonic appearance, the progressing cartilage
presents small spherical protoplasmic formative cells with
vesicular nuclei and rather scanty homogeneous intermediate
substance. The latter is still soft, and consists of albuminous
matter. Soon, however, the cells increase in size ; the inter-
mediate substance is augmented, and becomes more firm (Fig.

23). A chemical change also takes
place gradually ; it becomes a gelat-
inous tissue ; on boiling, it yields
chondrine.

When the intercellular substance
retains its original homogeneous
character, it forms hyaline cartilage.
Thin sections appear transparent like
glass. The cells (Fig. 42) have also,
in the mean time, assumed quite a
variation in their appearance.

They appear larger, round, oval,
wedge-shaped. A portion of them show capsules, and not

Fig. 42. — Diagram of a perfectly
mature hyaline curtilage, with quite
a variety of cells.

THE CONNE CTI VE-S UBS TA NCE GR O UP.

43

unfrequcntly the latter envelop so-called daughter cells (comp.

Fig.

19)-

WW

Fig. 43.— Thyroid cartilage
of the hog The basis sub-
stance is divided into cell-
districts.

fShki

How have these capsules and the intermediate substance
been formed ? Concerning this there has
been much discussion. Nowadays we
must say that both are cell products, are
substances yielded by the cell, and were
formerly a part of the cell body itself. In
the ensiform process of the sternum of the
rabbit, it is easy to recognize, without re-
agents, that the intercellular substance is
formed only of the cemented capsules of
the cartilage cells (Remak). By the aid
of macerating media this can also, with greater difficulty, it is
true, be demonstrated in other
mammalial and human cartilage
(Fig. 43). Here, also, the appar-
ently homogeneous intermediate
substance becomes divided into a
system of concentric capsule lay-
ers, which embrace within them
the cell or the cell group. The
individual capsular systems are
cemented to each other and like-
wise the external capsules of ad-
joining cells. From the similarity
of the power of refraction is caused
the phantasm of homogeneous-
ness ; the cartilage cell lies in a
chasm. When the innermost,
last-formed capsule has preserved
an additional, peculiar exponent
of refraction, we perceive this
(Figs. 42, 44) as something dif-
ferent from the remaining intermediate substance.

This division of the cells within their cavities, or, which
amounts to the same, within their capsules, gains consider-

Fig. 44. — From the costal cartilage of
an old man.

44

FOURTH LECTURE.

able dimensions in many mature cartilages (Fig. 44, a), so
that we may meet with enormous capsules of O. I to 0.2 mm.
with whole troops of contained cells. Not unfrequently, how-
ever, this exuberant increase foretells the approaching disap-
pearance of the tissue.

Depositions of fat in the cell body, especially in the vicinity
of the nucleus, then form very common transformations.
They may begin very early. Later, the nucleus frequently
becomes invested by a coherent spherical shell of fat (Fig.

44).

A subsequent metamorphosis of the apparently homoge-
neous intercellular substance into firm, delicate fibrillae, which
resist acetic acid, is frequently observed ; this is especially
constant in the interior of old costal cartilage (Fig. 44).

Calcification is, finally, a quite frequent occurrence in car-
tilage undergoing retrogression. Dark granules or crumbs

of lime salts surround the cells or cell
groups, at first in an areolated man-
ner. They increase in quantity ; the
whole intermediate substance acquires
a dark, granular appearance ; the cap-
sules also become implicated in the
deposition, and finally all is black and
opaque ; only the cells glisten through
as bright gaps. The older investi-
gators could not master this. Now-
adays we readily succeed by the aid of decalcification
with chromic or lactic acids.

This calcified cartilage is, however, far from being or from
becoming bone. We shall hereafter return to this subject.

Hyaline cartilage substance constituted originally almost
our entire skeleton, with the exception of the portions form-
ing the vault of the cranium and the bones of the face. This
is the transitory cartilage. Remains of the same form the
articular and costal cartilages and others. Other masses of
cartilage have nothing to do with the skeleton. To these
belong the larger cartilages of the larynx, and the cartilage

Fig. 45. — Commencing calcifi
cation ot hyaline cartilage.

THE CONNECTIVE-SUBSTANCE GROUP. 45

of the trachea and bronchia. The cartilage of the nose also
appears to be hyaline.

The young, healthy, hyaline cartilage, but not that which
is growing old, is without vessels.

An interstitial growth is evident ; the increasing size of the
cartilage cells, the expansion of the capsules, and the increase
of the intermediate substance remove every doubt. Is there,
besides, an increase of substance by apposition ? This is not
known. The nutrition takes place either from the blood-
vessels of a connective-tissue covering, the perichondrium,
or, when the cartilage envelopes the bone, from the adjacent
vessels of the latter.

Elastic or reticular cartilages arise from a supplementary
metamorphosis, which commences during the embryonic pe-
riod. Their number is not large. Among these are the epi-
glottis, the Santorinian and Wrisbergian cartilages of the
larynx, the Eustachian tube, and the cartilage of the ear.
The arytenoid cartilages of the larynx and the symphyses of
the vertebras present the same peculiarity only partially.

In reticular cartilage (Fig. 24) we generally meet with more
abundant cartilage cells, surrounded by a homogeneous area,
and the remaining intermediate substance permeated by a
close net-work of fine elastic fibres. Considerable variations
occur, however, in the different varieties of animals (Hertwig).

By connective-tissue cartilage is denoted a substance which
presents small cartilage cells, surrounded by bundles of a con-
nective tissue which becomes homogeneous in acetic acid.
This variety is met with, for example, in the cartilaginous
lips of the joints, and locally in the vertebral symphyses ;
other parts of the latter present hyaline cartilage ; still others,
only ordinary connective tissue. In the so-called cartilages
of the eyelids only connective tissue can be recognized.

We pass to the gelatinous tissue and reticular connective
tissue.

Cartilage presented the quality of solidity ; gelatinous tis-
sue shows the character of softness in the highest degree.
Its most simple variety, the vitreus of the eye, is the richest

46 FOURTH LECTURE.

in water of all the tissues of the body ; it contains only 1. 5
per cent, of solid constituents, of which a part must still be
referred to a delicate pellicle surrounding and permeating the
whole. And yet the origin of the cartilage and corpus vit-
reum are similar. We again meet with rounded, indifferent
cells with a homogeneous, intercellular substance. In car-
tilage (Fig. 23) the latter early solidifies ; in the vitreus it
becomes watery and swells up, so that in a human embryo

of four months (Fig. 46) the
protoplasmatic cells, meas-
uring 0.0104 to 0.0182 mm.,
are separated by considera-
ble intermediate gelatinous
tissue. The latter gives the
reaction of mucous sub-

man^A^Ti5SUe °f ^ vltre°US b°dy °f 3 hU" stance or mucin, that sub-
stance with which we have

already become acquainted (p. 36), as a product of the meta-
morphosis of the epithelial cells. For this reason our tissue
has already been given the name of mucous tissue.

In the vitreus of the mammalia after birth, the formative
cells become arrested, and, widely separated by the interven-
ing gelatinous tissue, are only with difficulty recognized.

A higher development of the gelatinous tissue is consti-
tuted by the so-called enamel organ of the progressing tooth.
The teeth, as is known, are formed and concealed in the jaws ;
the crown is first formed and the root last. The former is
covered, at its commencement period, by a cap or bell-shaped
structure, from the concave under surface of which the for-
mation of the enamel takes place. Hence the name.

Here (Fig. 22) we meet with a net-work of delicate, nucle-
ated stellate cells with a varying number of processes. Some-
thing like a cell division ib) is occasionally seen. The meshes
are filled with a homogeneous gelatinous tissue containing
mucus.

The same condition prevails, at an early period, in the
Whartonian jelly of the umbilical cord. Later, we meet, in

THE COXXECTIVE-SUBSTANCE GROUP.

47

ddli^

addition, with connective-tissue bundles which lie externally
to the now flattened cells. The system of spaces is again
rilled with gelatinous substance.

This is a tissue, therefore, which
early disappears.

Under reticular connective tissue
(Fig. 47) we understand a cellular
tissue, in the meshes of which lie
innumerable lymphoid cells. His
has called this adenoid tissue. It
appears to be frequently a second-
ary formation, proceeding from
metamorphosed common connect-
ive tissue of the fcetal body.

Reticular connective tissue pre-
sents, in addition, many changes,
according to age and locality. As
its element (Fig. 8), we meet with a
delicate, stellate cell with a nucleus
of 0.0059 t° 0.0075 mm- and a

moderate-sized protoplasma body. The latter sends out
numerous processes, which repeatedly divide and thereby
become constantly finer. By the conjunction of such adja-
cent branches, which have often arisen under a right angle,
smaller nodal points are frequently formed, in which a nucleus
is naturally wanting.

The delicate, mostly polyhedral meshes are usually rounded,
but may also assume an elongated form. They are smaller
in the new-born than in the adult. In the latter, during the
period of health, the nucleus and cell body are usually
shrunken, so that they may be overlooked. In irritated con-
ditions, however, the former tense condition is rapidly re-
established in the swelling tissue.

Such reticular connective tissue is met with in the lymph
glands, as well as in a series of allied parts of the body, which
we will combine as lymphoid organs, such as the tonsils,
thymus gland, and Peyer's follicles. The Malpighian cor-

Fig. 47. — From a lymphoid follicle
of the vermiform appendix of the rab-
bit. Fig. 1. reticular tssue with the
meshes, b, and the rema'nder of the
lymph cells, a ; most of the latter h ve
been artificially removed. Fig. 2.
more superficial.

43

FOURTH LECTURE.

puscles of the spleen also belong here. The tissue of the
spleen pulp is still more strongly modified.

The mucous membrane of the small intestine also contains
our tissue ; although the number of lymphoid cells is here much
less, and the cell processes not unfrequently appear broader,
lamelliform. In the large intestine, finally, something inter-
mediate between our tissue formation and ordinary con-
nective tissue is met with.

We now turn to the adipose tissue.

True connective tissue, to the consideration of which we
shall soon arrive, appears partly as a firm, partly as a loose
texture. In the latter case^ as under the corium, under

mucous and serous membranes, etc., it
encloses irregular communicating spaces.
These are frequently occupied by groups
of peculiar cells, overladen with fat.
This is fat tissue (Fig. 48, a).

The cells appear large, measuring
0.076 to 0.13 mm., with nuclei of 0.076
to 0.009 mm. A thin covering closely en-
velops a single large drop of fat. The
latter, from its strong refractive power,
conceals the nucleus and the outlines of
the envelope.

An appearance is thus caused as if
there were free drops of fat, with a dark
periphery by transmitted light, yellow-
ish, silvery and bright by incident illumination. Still, the
always considerable diameter, a slight polyhedral flattening
of the elements which are closely pressed together, avert the
mistake. Free fat forms spherical drops of every possible
size (b).

The envelope, after its rupture and the escape of the con-
tents, may be demonstrated as a thin, collapsed sac (c), like-
wise in an intact condition, after drawing out the fatty con-
tents with alcohol or ether. The nucleus, lying quite excen-
trically, is readily recognized after tingeing with carmine.

FlG. 48. — a, human fat cells,
lying together in groups ; b,
free glabules of fat ; c, empty
envelopes.

THE CONNECTIVE-SUBSTANCE CROUP.

49

The fat of the human body is a mixture of an oleaginous
substance, triolein, which contains in solution certain quanti-
ties of more solid matter, tripalmitin and tristearin. When
the latter increase, there are, on the cooling of the body at
first, depositions of tuberculated forms, and finally of crys-
talline. We now perceive irregular needles, at one time tuft-
shaped and stellate, radiating from a central point, again in
crowded aggregations filling the whole cell. On warming
they again disappear.

Adipose tissue takes a very active part in the material
changes of the body ; it is likewise a very vascular substance.

As a result of prolonged starvation, in exhausting diseases,
a portion of the fatty contents disappear from the cell
(Fig. 49). The fat drop (d)
is at first but slightly re-
moved from the membrane.
A spherical cortex of gela-
tinous, finely granular sub-
stance (protoplasma?), sur-
rounds the former ; the nu-
cleus nOW becomes Visible. FlG- 49— Impoverished fat cells from ^the sub-

cutaneous cellular tissue ol a human cadaver.

The progressing deprivation

of fat is shown by the cells a to/ and h. Finally {g), only a
{cw fat globules remain ; the entire cavity is now occupied by
the gelatinous matter. Such examples have been designated,
not especially happily, as fat cells " containing serum."

If the body outlasts this condition of emaciation, and sub-
sequently, by a more abundant nourishment, resumes the old
full appearance, the cells have again become filled with the
fatty contents.

The massiveness of the adipose tissue varies considerably.
It is greater in children and women than in men ; more con-
siderable in the blooming period of life than in senility.
Here, above all, individuality asserts itself very powerfully.
In high degrees of obesity, fat cells frequently occur in places
where they do not belong, as, for example, between the mus-
cular fibres. In far advanced emaciation, the panniculus adi-

50

FOURTH LECTURE.

posus disappears ; though certain parts, like the orbital cavity
and the medulla of the central portion of the hollow bones,
still obstinately retain the fatty contents
within their cells.

Adipose tissue is of a secondary nature.
It is entirely wanting in the earlier embryo-
nic life. The fat cell arises from a metamor-
phosis of the cells of the connective tissue.
The ordinary flat, lapped and pointed ele-
ments of the latter (Fig. 50, a) take up fat
drops in increasing quantity (b) ; these flow
together, the cell becomes rounder, losing
its processes (c), and finally assumes the
well-known appearance (d). There is also
another coarsely granular connective-tissue
cell, to which more attention has only re-
cently been called, and which may possibly
be transformed into a fat cell. We regard the so called cell
membrane as a boundary layer formed from the adjacent
connective tissue.

Fig. 50. — Transfor-
mation of the connect-
ive tissue corpuscles
into fat cells, from a
human muscle, serving
at the same time as a
diagram of the embryo-
nic origin.

FIFTH LECTURE.

CONNECTIVE TISSUE.

TRUE connective tissue, the " cellular tissue " of the older
anatomists, is very extensively diffused throughout the body.
As a member of the whole tissue group, it also consists of
cells and intercellular substance. The latter, on boiling, does
not yield the chondrin of cartilage (p. 42), however, but
ordinary glue or glutin. The intercellular substance here
shows a further metamorphosis in a double direction ; firstly,
into the so-called connective tissue bundles and ffbrillae ; and
secondly, into the multiform elastic elements. The latter
form fibres, reticular fibres, perforated membranes, limiting
layers around connective-
tissue bundles, and also
around spaces which con-
tain cells.

The longest known is the
gelatine yielding fibrilla,
the constituent which im-
mediately attracts the eye.
It appears in the form of a
very fine, hyaline, un-
branched filament, 0.0007
mm. in diameter, often
very extensible, and at the
same time possessing elas-
ticity (Fig. 51, to the left).
These very readily isolat-

able fibrillae very commonly unite into sometimes thinner,
sometimes thicker bundles (in the figure to the right). Their
elasticity very frequently produces an undulated or curly

52

FIFTH LECTURE

appearance in separated portions of the tissue. The inter-
weaving of the fibres varies considerably. When loosely in-
terwoven, the bundles running in one plane are united by
homogeneous, membranous intermediate substance.

Acetic acid, an important reagent, causes the bundles to
swell up rapidly and the fibrous appearance to disappear. By
washing out, or neutralizing that reagent, the former ap-
pearance is restored.

Previously, the excess of connective-tissue fibrilla very fre-
quently concealed the intermingled elastic elements. Now,
in the acid preparation, the latter make their appearance

Fig. 52. — Human elastic fibres.

(Fig. 52). We perceive, firstly, the finest, frequently corru-
gated fibrillae without ramifications (a). They remind one of
the connective-tissue fibrillae ; but the darker appearance,
and the power of resisting acetic acid, permit of no mis-
take. Other elastic fibres are larger.

Very frequently there are ramifications, and by the com-
munication of the branches an elastic net-work is formed.
We perceive such an one at b, with large meshes, and fibres
which measure only 0.0014 to 0.0025 mm. in thickness.

CONNECTIVE TISSUE.

53

fibres are embedded as ledge-like thickenings
occur homogeneous

\

If we search further, we meet with transitions to broader
and thicker ramified fibres (c), which, in contradistinction to
the extensible finer ones, gradually assume a considerable
inflexibility and brittleness. Their diameter may increase to
0.0056 to 0.0065 mm.

In other places, the walls of the larger arteries, we find co-
herent elastic membranes, in which fine fibrillar and reticular

There also
layers of elastic sub-
stances which are perforated with little holes
(Fig- 53) !)- Between these and a small-
meshed reticulum of very broad, flat elastic
fibres (2) it is, indeed, often
impossible to make a demar-
cation.

These changing elastic ele-
ments are met with in still
another condition. They
form a structureless sheath
around many connective-tis-
sue bundles. As surely as
an innumerable quantity of
these bundles are without
envelopes, and exhibit only
a fibrillated cord, even so
little can the presence of a
sheath around others be
doubted ; as on those which
pass from the arachnoid, at
the base of the brain, to the
larger blood-vessels, on the
fasciculi of the tendons, on
much of the subcutaneous cellular tissue,
agents which produce considerable swelling
strange appearance is caused (Fig. 54). The sheath is torn
into transverse portions, and these rapidly contract between
the protruding portions of the connective-tissue bundle to

Fig. 53.— Elastic net-
work fi\,m the aorta ; I,
of the ox ; 2, of the
horse.

Fig. 54. — Acon-
nective-:issue bun-
dle, from the base
of the humanbrain,
treated with acetic
acid.

If we apply re-
as acetic acid, a

54

FIFTH LECTURE.

very delicate rings, which have a striking resemblance to an
elastic fibre. Cotton fibres undergo a very similar change on
the addition of ammoniac copper ; only, everything is here
more massive and easier to observe.

The most difficult part in the investigation of the connective
tissue is formed by the cellular elements, the connective-tis-
sue corpuscles of an earlier period. After manifold strayings,
a greater light has only of late years been disseminated.
Since the cells were, as a rule, usually concealed by the
substance of the fasciculi, acetic acid was formerly generally
used for the recognition of the former. This, and even
water, immediately distorts the cells into caricatures. The
latter have been almost universally known and described for
tens of years ; and capital has been made of them !

The cellular elements are distinguished into non-essential
migratory, and essential fixed. The former are lymphoid
cells, which, having escaped from the blood and lymphatic
vessels, slowly wander through the channels of our tissue.

The ordinary fixed connective-tissue cell appears as a
simple or complicated lamellar structure. An oval nucleus
is surrounded by some protoplasma. The thin structure
becomes extremely pale and veil-like at the periphery,
and runs out into points or fibrillar. Very frequently, how-
ever, there is also a vary-
ing number of lateral plates
resting at different angles
over the middle of these
chief plates (Fig. 55, a), so
that .a certain resemblance
to an irregular, crumpled
shovel edge is produced
(Ranvier, Waldeyer). Such
cells lie in the firm connec-
tive tissue, in the spaces
between the fasciculi, and have, according to our views, as-
sumed the described forms subsequent to the growth in thick-
ness of those fasciculi. The procedure may be illustrated by

Fig. 55. — Cells of human connective tissue : a,
flat and shovel-shaped elements ; 6, coarse granu-
lar cells.

CONNECTIVE TISSUE.

55

placing a lump of warm, soft wax between the points of
three fingers and pressing them together.

There is still another cell formation met with in connective-
tissue structures ; they are often very rare ; in places, how-
ever, quite numerous. They are larger, coarse granular
structures, with a nucleus and an either rounded or spindle-
shaped body, without that system of lamellae and processes
of the previous form (b). They have been met with in the
vicinity of vessels, especially arteries, and have received the
name of plasma cells (Waldeyer).

Fat cells may proceed from both varieties of cells, the flat
and the coarse granular (p. 49).

Connective-tissue cells also assume an extremely peculiar
appearance from receiving melanine granules into their body
(Fig- 9). This is the "stellate pigment cell" of the earlier
histolomsts. The coal or brown- black molecules are smaller
than in the pigmented epithelium (p. 30). In man such cells
are limited almost exclusively to the eye. In the lower ver-
tebrates, such as many of the amphibia, this process of pig-
ment embedding is enormously diffused, so that in every little
piece of connective tissue the strangest cells are met with,
occurring in every possible stellate form.

The fiat connective-tissue cells and their colored associates
(Fig. 56), show a slow,
but unmistakable vital
contractile power. This
is not yet recognized in
the plasma cell.

Connective tissue, whose
immense diffusion in the
human body we have al-
ready mentioned, by the
arrangement and interlac-
ing of its bundles, by its
very dissimilar proportion of elastic elements, the extremely
variable vascularity, and, finally, by the commingling of insol-
uble elements, forms substances which appear to the naked

Fig. 56. — Gradual change of form of a pigmented
connective-tissue corpuscle from a water newt, during
45 minutes.

56 FIFTH LECTURE.

eye as quite dissimilar things, and which in reality are very
nearly related.

The usual system of anatomy recognizes primary bundles,
that is, simple fibrous cords. A portion of these, held
together by loose connective tissue, constitute secondary
bundles, and from these latter tertiary are formed.

We have, firstly, as a badly selected name runs, "form-
less " connective tissue. Soft and extensible, it forms the
general filling up substance of the organism. Membraniform
connective-tissue bundles with homogeneous interstitial sub-
stance (Fig. 51), form thin lamellae, which superimposed on each
other at various angles, incompletely limit cavities. These
are the so-called " cells" of the older anatomists, who gave
our tissue the name of cellular tissue. The lamellae are often
nearly in contact with each other, but the space enclosed by
them may also be completely filled by collections of fat cells.
Where structureless connective tissue occurs in greater quan-
tity it has received special names. Thus, one speaks of sub-
cutaneous, submucous and subserous connective tissue.
Elastic elements are here met with, sometimes scanty, some-
times more profuse, but never in excess.

We now come to the formed connective tissue, with its nu-
merous varieties. This constantly arises from the formless
variety without any sharp demarcation, so that this division
of the anatomists is entirely artificial.

We enumerate here : 1. The corneal tissue. The cornea
has on its anterior surface stratified pavement epithelium, on
its posterior a simple cell covering. Under both epithelial
coverings there is a hyaline layer. The anterior is called the
lamina elastica anterior, the posterior the Descemet's or De-
mours' membrane. The hyaline corneal tissue consists of a
net-work of decussating bundles, which may be divided into
fibrillae of extreme delicacy. The whole is permeated by a
system of passages which have a sort of parietal layer. In
these lie the " corneal capsules," which are flattened cells,
comparable to a paddle-wheel. Wandering lymphoid cells
are also not wanting.

CONNECTIVE TISSUE.

57

2. Tendinous tissue. Longitudinal bundles of a fibrillary
connective tissue with an elastic boundary layer arranged in
a compact manner are met with. Between them one recog-
nizes in transverse sections a system of indented and stellate
spaces. In these lie, arching over the connective-tissue
bundles, ordinary lamelliform and shovel-shaped connective-
tissue cells, and also isolated lymphoid corpuscles. Only
scanty, fine, elastic fibres occur in this extremely bloodless
tissue.

3. The ligaments are, with the exception of the elastic,
formed like the tendons.

4. The connective-tissue cartilage (see p. 45).

5. The so-called fibrous membranes. Firmly woven, non-
vascular structures with a varying intermixture of elastic ele-
ments. Among these are the dura mater of the brain and
spinal cord, the sclerotic of the eye ; the firm envelopes of
many organs, for example, of the kidneys, testicles, and
spleen ; furthermore, the fasciae of the muscles, the coverings
of the nerve trunks (the perineurium or neurilemma), the
covering of the cartilage and bone (the perichondrium and
periosteum). The latter is permeated by numerous blood-
vessels, but which serve principally for the nutrition of the
invested bone.

6. The serous membranes, which formerly were erroneously
considered as entirely closed sacs, consist of a but slightly
vascular net-work of connective-tissue bundles, occasionally
with a considerable contingent of elastic-reticular fibres. The
free surface is covered by endothelium. To this variety be-
long the pleura, pericardium, peritoneum and tunica vaginalis
propria of the testicle. As more incomplete structures, we
mention the arachnoid membrane of the brain and spinal
cord, the synovial capsules (having a serous membrane only
at the sides, and here covered by a simple layer of epithelial
cells), and also the mucous pouches and the sheaths of the
tendons. The serous cavities, like the passages between the
connective-tissue bundles, must be regarded as belonging to
the lymphatic apparatus, as we shall perceive hereafter.

3*

58 FIFTH LECTURE.

7. The corium. More firmly interwoven, decussating con-
nective-tissue bundles with numerous elastic fibres. The
closely interwoven, very vascular tissue projects towards the
surface in small papillae of varying shape, in the form of the
tactile bodies. It is continuous below, without any sharp
demarcation, with the subcutaneous cellular tissue. Other
foreign constituents consist of hairs, involuntary muscles,
glands, nerves. As a covering, we are already familiar with
the epidermis, the thickest pavement epithelium of the body

(P- 32).

8. The mucous membranes. Also extremely vascular, but
less compactly arranged, and with fewer elastic elements.
In places it is enormously rich in glands. Smooth muscles
form a widely diffused constituent. The surface frequently
projects in papillae. The ordinary connective tissue of the
mucous membranes may, however, be replaced by reticular
connective tissue (p. 47). We already know that the epithe-
lial covering differs exceedingly (pp. 30, 33, and 34).

9. The vascular membranes of the central nervous organs
and of the eye ; that is, the pia mater, choroidal plexus and
choroid. A thin, soft connective tissue, in the choroid a
reticulum of pigmented cells, here shows throughout an enor-
mous wealth of blood-vessels.

10. In the structure of the vascular zualls connective tissue
plays an important role. Nevertheless, the elastic element
often increases to such an extent, that the connective-tissue
bundles and cells recede. One speaks then of "elastic"
tissue.

11. This predominance of the elastic elements is also pre-
sented by the ligaments and membranes of the respiratory
organs, and likewise by the tissue of the lungs. The same is
also seen in the outer layer of the oesophagus, the yellow
ligaments of the vertebral column, and the ligamentum
nuchae of mammalial animals. Many of the latter structures
have lost all connective-tissue bundles.

Connective tissue possesses but slight vital dignity ; it
comes into consideration in the structure of the organism, in

CONNECTIVE TISSUE.

59

consequence of its physical properties. Only the more vas-
cular connective-tissue structures take a more active part in
the normal material changes.

During abnormal conditions, however, our tissue assumes
a new and more vigorous life. From the cells other tissue
elements may be formed. To determine the magnitude of
this participation more accurate studies .
are indeed necessary, for the wandering
lymphoid cells also play their part, and, in
our opinion, in a very important manner.

We also mention the origin of the con-
nective tissue. The terminations are
again similar to those of cartilage. Mem-
braneless protoplasmatic stellate and
spindle cells are noticed at an early peri-
od, held together by a scanty intercellular
substance, which is at first homogeneous.
A transformation soon takes place in the
latter and in the cells, the processes of
the latter dividing into groups of fine
connective-tissue fibrillar (Fig. 25, /;).
These bundles of fibrillar gradually ap-
proach the cell nucleus. The original
cell protoplasma also becomes changed
into bundles of fibrillar ; new protoplas-
ma, taking the place of the old, surrounds
the nucleus, to subsequently pass through
the same process of metamorphosis (Fig.
57, A), till at last the cells lie outside of
their children, that is, the bundles formed from them, in the
shape of lamellae, with notched margins, or irregular, paddle-
wheel-like structures (see above).

In this intercellular substance, the genesis of which we
now understand, the formation of elastic fibres and reticular
fibres also takes place subsequently (B). How far the cellu-
lar elements participate in this requires still more accurate
investigation.

Fig. 57. — From the liga-
mentum nuchae of a hog's
embryo. A. side view ; a.
spindle cells in a fibrous ba-
sis substance, b ; B, the
elastic fibres c, brought out
by boiling in a solution of
potash (alcohol preparation).

SIXTH LECTURE.

BONE TISSUE.

We now turn to the most complicated variety of connective
substance : we refer to the osteoid or bone tissue.

It is distinguished for its considerable hardness and firm-
ness. In man, this member of our tissue group is, with the
exception of a covering to the tooth root, limited exclusively
to the bones.

The anatomists divide the latter into long or cylindrical,
broad or flat, and, finally, short or irregular bones.

Let us begin with the middle portion or diaphysis of the

former, taking a radial longi-
tudinal section sawn out from
the dry femur (Fig. 58).

A very peculiar appear-
ance is presented. The thin
lamella is permeated by a
system of longitudinal ca'nals,
connected, in a reticular man-
ner, with a medium width of
O.i 128 to 0.0149 mm. (a).
The transverse branches open
out onto the surface of the
bone, as well as inwards into
the medullary canals, and re-
ceive the nutrient vessels
from both sides. They bear
the name of the medullary
or Haversian canaliculi.
Tr; nsverse sections (Fig. 59) naturally present an entirely
different appearance. The rounded and oblique spaces (c)

-«H«' \--ii

mmmhl

mum

Fig. 58. — Vertical section through the human
femur; a, medullary canals ; b, bone corpuscles.

BONE TISSUE.

6r

M .*- v,_s <*>^ *

----.. >> -_.

Fig. 59- — Transverse section of a human
metacarpal bone ; a, outer surface ; c. medul-
lary canals with the special lamellae ; d, inter-
nal general lamellae ; e, bone corpuscles.

are transversely or obliquely opened longitudinal canals.
Communicating horizontal canals are now also seen opened
in a longitudinal direction or
obliquely.

The bone substance pre-
sents, as is shown by the
transverse section, a lamel-
lated structure.

There is a double system of
layers, however. Firstly, we
meet with plates which pass
through the entire thickness
of the bone, in contact ex-
ternally with the periosteum
and internally limiting the
great medullary canals. They
are called general or funda-
mental lamellae {a, d). An-
other uncommonly abundant

system of lamellae surround the individual medullary canals
with a varying number of layers. These are the special or
Haversian lamellae (around c). The thickness of both varieties
of lamellae varies from 0.0065 to 0.0156 mm., and the ar-
rangement is often far removed from making any claim to
regularity. This stratification may also be recognized in
longitudinal sections as a system of lines, though with less
distinctness.

A plate of dry bone, let it be taken from where we will,
always presents a further extremely peculiar structural con-
dition ; it appears black by transmitted and white by incident
light, and consists of a marvellously complicated very fine
canal-work with indented and radiated nodal points. The
former passages are badly enough named calcareous canali-
culi : the dilatations bear the name of the bone corpuscles cr
lacunae (Figs. 58, 59).

The form of the lacunae (Fig. 60, a) may be illustrated by
calling them lens-shaped, or by comparing them to the figure

62

SIXTH LECTURE.

Fig. 60. — Lacunas (</, a) with their
numerous offshoots, opening into the
transversely divided Haversian canal
{V-

produced by two human hands when their volar surfaces rest
over each other. The length is 0. 1805 to 0.0541, the breadth

O.0068 to 0.0135, tne thickness
0.0045 to 0.009 mm. The offshoots
of this system of cavities, very nar-
row canals of O.OO14 to 0.0018 mm.
diameter, permeate the entire tissue
in innumerable multitudes, ramifying
irregularly in a radial direction.
They open (1) in the Haversian
canals {b), (2) on the surface of the
bone, and (3) in the large medullary
cavity in the interior. Transverse
and longitudinal sections (the tan-
gential must also be added) teach
this most distinctly.
In the dried bone, the marvellously complicated system of
canaliculi has become filled with air in a condition of the
finest division. An earlier epoch erroneously assumed the
contents to be inorganic hardening material, to be the finest
molecules of the so-called bone earths. Hence the name of the
" calcareous canaliculi." If we place the small thin plate in
turpentine oil, the thousands upon thousands of finest canali-
culi rapidly fill with the fluid through capillary attraction.
The bone corpuscle now presents the appearance of a cavity;
the fine canaliculi disappear more or less in the basis sub-
^=^ stance.

But what does this remarkable canal work
contain during life ?

We answer to this, there is in the lacunae a
protoplasmatic membraneless cell (Fig. 61, b).
Whether this bone cell, the equivalent of the
connective-tissue corpuscle, sends off capillary
offshoots into the lacunae, which is very prob-
able, we do not yet know. The latter canalic-
ular system is certainly filled with transuded blood plasma.
This fluid must, besides, be rather stagnant, for the frictional

Fig. 61. — From
the fresh ethmoid
bone of the mouse;
a. basis substance;
t, the bone cell.

BONE TISSUE. 63

resistance here imposes a veto to the circulation which is with
difficulty removed.

Are the lacunae and calcareous canals only cavernous sys-
tems excavated in the hard, solid basis substance, or have
they a special parietes ? After energetic macerating media,
the previously decalcified bone presents a thin resistant
boundary layer around the lacunae and canaliculi. It appears
to be a decalcified elastic substance. It was formerly errone-
ously considered to be a cell membrane.

Having become familiar with the most essential portion of
the structure in the diaphysis, let us now turn to a very short
discussion of the other parts of the skeleton. The beauti-
ful regularity here disappears, sometimes to a less, sometimes
to a greater degree. Even in the epiphyses of the cylindrical
bones, in consequence of the thinness of the osteoid plates,
the systems of lamellae are present in a far less developed
condition around the Haversian canals, and the inner funda-
mental lamellae are absent. In spongy' bone tissue the
laminar arrangement may still be distinctly recognized in the
thick trabeculae and plates, while it disappears more and
more with the decrease in size. In the cortical layers of flat
bones, the medullary canals run parallel to the surface, gene-
rally starting from a point and assuming a radiate direction.
In the short bones the course generally preponderates in one
direction. Funnel-shaped apertures of the Haversian canali-
culi may join together and form small medullary cavities, the
prefigurations of the larger, etc.

The bones contain but little water, the compact having 3 to
7, the spongy 12 to 30 per cent. The organic, form-deter-
mining basis, amounting from 30 to 45 per cent, in the dry
bone, is transformed by boiling into glutin, that is, the ordi-
nary glue of the connective tissue. This is diffusely hardened
by the embedded bone earths. By this is understood a mix-
ture, amounting from 51 to 60 per cent., of lime salts with a
slight admixture of magnesia salts. The bone earths yield
about 86 per cent, of phosphoric acid, 9 of carbonate of lime,
3.5 of fluoride of calcium, and 2 of phosphate of magnesia.

64 SIXTH LECTURE.

When the bone is carefully decalcified its texture remains
as of old. It is easy to cut the mass, which has now become
semi-transparent. It is badly enough named the bone car-
tilage.

In the mechanical construction of the body, the bones
come into consideration by reason of their solidity. They
serve as a protection to softer organs, and form systems of
levers moved by muscles. The less the proportion of bone
earths contained, the greater the flexibility and cohesion. A
preponderance of these mineral substances, on the contrary,
renders the bone inflexible and brittle. The mutability of its
materials is very considerable. In harmony with this is the
double system of canals for the blood-vessels and lacunae.

The larger cavities of the bone become filled with so-called
bone marrow. This occurs in a double form, though with
transitions. In the central portion of the long bones it appears
as a yellow marrow, that is, as fat cells contained in loose
connective tissue (p. 50). In the epiphyses, on the contrary,
as well as in flat and short bones, we find a softer reddish or
red substance containing, together with scanty connective
tissue and isolated fat cells, very numerous lymphoid cells of
O.009 to 0.0113 mm. The latter elements, according to Neu-
mann and Bizzozero (p. 25), present transitions into red
blood corpuscles. Finally, we meet in the bone marrow,
especially towards the surface, the myeloplaxes, which have
become familiar to us in Fig. 13. The veins are without
endothelium ; they consist only of an adventitia (Hoyer).
Altogether, the vessels of the medulla promise still further
interesting conclusions.

We now turn to the theory of the origin of the bone tissue,
osteogenesis. It forms a very difficult and complicated sec-
tion of histology.

With the exception of a number of the bones of the cranium
and face, as we have already said, all portions of the skeleton
are preformed in cartilage. They afterwards present bone
substance.

During a long period the direct metamorphosis of the

BONE TISSUE. 6$

former tissue into the latter was unhesitatingly accepted.
Sharpey, Bruch, H. Mueller, first demonstrated the erro-
neousness of this hypothesis.

Disregarding rare exceptions, the facts run, nowadays, in
this way : The calcified cartilage does not become osteoid
tissue, but rather melts down, and in the system of cavities
thus obtained, the bone substance produced by the peri-
osteum is established as a new tissue.

If we take a cartilage which is destined to end in this man-
ner, two different processes are presented :

i. A local softening of the cartilage tissue (of the cells as
well as of the intercellular substance) has taken place from the
surface in an inward direction. Very irregular, manifoldly
ramified passages have thus been formed. Vessels have
grown into the latter from the perichondrium, accompanied
by lymphoid and unripe connective-tissue cells. This sub-
stance has been not badly named the cartilage marrow.
Until recently, it was erroneously assumed that the so-called
cartilage marrow cells represented derivatives from cartilage
cells which had penetrated the softened portion.

2. In the centre of such a cartilage, a calcification of the
intercellular substance (p. 44) and very generally, also, an
energetic forma-
tion of so-called „ * /"/^©^C-o©^^ rx

|«l :mmjr m

occurs (Fig. 62). .^3«SPr

This place has KM WW

been called the IW^^^^M

point of ossifi- (ftMtes«-«#*M«eHM

rn h'nn K o A 1 ir ¥ig. 62. — Dorsal vertebra of a human foetus of ten weeks in vertical

Cciuuil UdUiy section, a, calcified ; b, soft cartilage.

enough, we add.

For, although a further melting down of the calcified tissue
occurs here forthwith, and, in the spaces thus formed, the first
deposition of osteoid tissue commences immediately after-
wards, this calcified cartilage has nothing whatever to do with
the latter.

The two metamorphoses just mentioned proceed rapidly

66

SIXTH LECTURE.

side by side and against each other. The calcification of the
cartilage spreads peripherically ; the liquefaction and re-forma-
tion of the cartilage canals is constantly increasing in extent,
and likewise in the domain of the calcified cartilage.

Fig. 63. — Ossifying border of a phalangeal epiphysis of the calf, in vertical section. At the uppei
part, the cartilage, with its irregularly disposed capsules, containing daughter cells ; a, smaller
medullary spaces, appearing in part as though closed, drawn" empty ; £>, the same with narrow cells ;
c, remains of the calcified cartilage ; d, larger medullary spaces, on the walls of which are depo-
sitions of thinner or thicker bone tissue, and in the latter case stratified; e, developing bone cell ;
/, an opened cartilage capsule, with an embedded bone cell ; g; a partially filled cavityv covered
externally with bone substance and containing a narrow cell; //, apparently closed cartilage capsules
containing bone cells.

The latter must naturally first become physiologically
decalcified before undergoing solution. This removal of a but
just deposited lime salt is, up to the present time indeed,
somewhat enigmatical.

Let us look at Fig. 63. At the upper part, the cartilage

BONE TISSUE.

67

still presents the old soft appearance. The cartilage cells lie
here, in an epiphysis, irregularly. In a diaphysis they would
be seen pressed together in longitudinal rows, or " ranked,"
as it has been expressed. Below, however, we meet with a
cavernous tissue, the spaces of which, as a result of the prepa-
ration, in places no longer lodge the cartilage marrow con-
tents (a), while it still remains preserved in others (&, d).
Cloudy, dark trabeculae of the most irregular form constitute
the last remains of the liquefying decalcified cartilage (c).
Even these trabecular remains are deprived of further re-
pose.

Fig. 64. — Transverse section from the femur of a human embryo of about eleven weeks ; a, a
transverse, and l>, a longitudinally divided medullary canal ; c, osteoblasts ; d, the more trans-
parent, younger, e, the older bone substance ; f, lacunae with the cells ; g, cells still limited
to the Osteoblast.

If the contents of these cavernous passages are attentively
examined at this period, their peripheral cells are found to
have assumed an anomalous shape. They resemble, with
their cubical bodies (Fig. 64, c), an irregular, badly developed
cylinder epithelium. Gegenbaur, their discoverer, has

68 SIXTH LECTURE.

called them osteoblasts— and rightly, for they form the osteoid
tissue.

As in a line of inordinately crowded soldiers, one or
another will be pressed out in front, so does it happen to cer-
tain of these osteoblasts (g). They now assume indented or
stellate shapes ; homogeneous, but very soon diffusely calci-
fied intercellular substance then appears around them. The
latter as a thin layer — we might say, covering the irregular
surfaces of the still remaining calcified cartilage trabecular like
a wax impression — is the first lamella of the osteoid sub-
stance ; the indented osteoblasts form the first bone cells,
however. Our Fig. 6$ shows this at its upper portion
(a, a, a), also at the left, half way up (c, d).

Concerning the conception of the intercellular substance,
whether it arises from a secretion ot the cells or from the
metamorphosed cell bodies, the same uncertainty of opinion
prevails as with other members of the connective substance
group.

We have here still more peculiar illusive appearances to
consider. It is comprehended that by the continual lique-
faction of the cartilaginous trabecular the cavities of the tissue
become opened, and must then serve for the deposition ot
bone cells and homogeneous basis substance. When the
conditions are as zXf of our Fig. 63, the matter is at once
clear, the places is also, in a measure, appreciable. When,
however, the cavities are ruptured from below or above, this
does not fall within the plane of the section, and we have the
deceptive appearance of closed cartilage cavities with endo-
genous bone cells.

This, which thus occurred for the first time, is repeated
in rapid sequence manifoldly after each other. Lamella
upon lamella with enclosed bone cells result (Fig. 63 in
the lower half). We obtain in this way a stratified
osteoid tissue. The remains of the cartilaginous tabecular
disappear more and more with the continuing process of
liquefaction.

But this thing, in its wild, confused irregularity is very dif-

BONE TISSUE. 69

ferent from the bone tissue which appears in such elegant
regularity at a later day.*

Now, how does the latter arise from the former ?

Two different opinions exist on this subject. According to
the first, and we adhere to this for the most part, the osteoid
tissue, which is formed at the expense of, and within the fcetal
cartilage, the so-called endochondral bone, has not a happy
life. It yields to an early death, a speedy process of lique-
faction, in order to permit the formation of the large medul-
lary canals. On its surface is deposited, by the periosteum,
into which the perichondrium has now become changed, and
with the aid of a deeper osteoblastic layer, new bone tissue
which, with a supplementary loss of its inner layers, persists
in the outer portions and causes the regular, beautiful struc-
ture of the bone. This may be denoted as the apposition
theory of osteogenesis. Koelliker has recently re-entered the
lists for this with great energy.

Another view rejects the resorption of the endochondral
osteoid tissue absolutely, and explains the transformation of
the irregular cavernous bone of the commencement period
into the regular of the later period of life, by interstitial
growth alone. An industrious Russian investigator, Strelzoff,
supported by German predecessors, has recently endeavored
to substantiate this with greater accuracy.

We cannot enter further into this actually burning contro-
versy. The truth, according to our views, lies more towards
the former side. Nevertheless, the young bone certainly has
an interstitial growth, which Koelliker also, naturally,
acknowledges ; but to what degree this occurs no one can, at
the present time, state with accuracy. A resorption is surely,
also, not wanting in the normal bone. This is proved by the
Haversian spaces of healthy bone, if we disregard the long
known abnormal resorption processes. Those who deny the
demonstrative force of such facts are, in our opinion, not
to be reasoned with further.

* The central portion of the cylindrical bone has also once had the same cav-
ernous structure that is presented by the epiphysis.

7o

SIXTH LECTURE.

Let us then investigate these Haversian spaces.

Our figure (Fig. 65), shows us three Haversian lamellar
systems. The two hatched ones (a, a), present inter-
nally an indented resorption line {b> b). New bone lamellae,
maintaining the outline, have been deposited on this. To
the right (c), a second liquefaction has overtaken the latter,
for which a new lamellar formation endeavors to compen-
sate.

Fig. 65. — A human metacarpal bone in transverse section ; a*, a Haversian lamella system of
the ordinary variety ; a, a, two others which have undergone absorption internally (6, />), and thus
form Haversian spaces, which are rilled up by new lamellae ; c, supplementary absorption in one of
these with deposit of new bone substance ; d, irregular, and c, ordinary intermediate lamellae.

Koelliker has ascribed to the multi-nuclear giant cells (Fig.
13), the property of dissolving the bone substance, and called
them osteoclasts. We do not share in this view. Between
the bone-producing osteoblasts of Gegenbaur and the bone-
destroying elements of the first mentioned investigator, transi-
tion forms exist.

We hold fast to the absorption of the endochondral bone,
therefore, and now inquire into the particulars of the peri-
pherical reparation. This is produced by the periosteal bone ;
that is, the osteoid tissue, which is subsequently furnished
from the inner surface of the periosteum.

An. eminent French observer, Oilier, informs us that the
detached living periosteum, whether it be retained in the body

BONE TISSUE.

n

of its owner, or whether it be transplanted into that of another
animal; again produces new bone tissue, only the deepest
layer must be uninjured.

If we examine this deepest layer with the help of the
microscope, we discover our old friends, the osteoblasts. This
cell layer then grows downwards in a conical form into a re-
trogressing, indifferent cell substance.

With the bone-producing force of the osteoblasts we are
already familiar. Therefore the osteoblast-cones {sit venia
verba) produce the Haversian lamellae, while the general
lamellae are produced by the flat osteoblast layer, which is
immediately beneath the periosteum. In this manner is also
explained the regular structure of the diaphysis and its increase
in thickness. Concerning the latter, further remarks are
scarcely necessary.

We may, therefore, say : The endochondral bone dis-
appears as an embryonic structure, the periosteal remains
during the subsequent life.

As we have already learned above, a number of cranial and
face bones never were cartilage.

They arise from a soft, foetal connective substance, and have
been badly named the "secondary" bones. Here, also,
when there is to be a production of osteoid tissue, we
meet with osteoblasts and the same process of origin of the
bone tissue as when formed from the periosteum. The
development of the bone substance commences centrically
in certain places, and advances from these peripherically.
These are, therefore, true points of ossification, in contra-
distinction to the false, or the calcifying centres of endo-
chondral bone.

That connective-tissue fragments are frequently hardened
with the periosteal and secondary bones, we readily under-
stand. These things — they sometimes appear like a board
with nails driven in — have received the name of Sharpey's
fibres.

Many modern investigations also favor an immediate trans-
formation of one or another cartilage into osteoid substance,

72 SIXTH LECTURE.

and likewise of a connective-tissue structure. Still, a calcified
connective tissue has not thus become bone.

The proliferous formative life of bone is met with more
frequently in the abnormal than in the normal processes. Un-
fortunately, we cannot here enter into this subject.

SEVENTH LECTURE.

DENTINE. — ENAMEL.— LENS TISSUE.

The tooth as a whole is known to everybody. We distin-
guish, (a) the crown, the free part, {b) then a middle portion
surrounded by the gum, the neck, and, finally (c), the simple
or multiple fang wedged into the alveolus of the jaw.
Through the centre of the tooth
passes a canal which has a caecal
termination above and below,
corresponding to the fang ; it is
simple or multiple in form, and
has a free opening at the apex
of the root. This is filled with
a soft connective tissue, rich in
vessels and nerves, the pulp.

The chief mass of the tooth,
which is limited internally by
the cavity, and is covered exter-
nally by a thin cortical layer,
consists of the so-called tooth-
bone or dentine, a modified
osteoid tissue. The crown is
invested by the enamel, the
fang by the cementum ; both
substances meet at the neck.

Let us first of all examine
the dentine (Fig. 66, d). It

contains in a collagenous matrix a still greater quantity of
lime salts than the osteoid substance. It is permeated by
extraordinarily numerous, very fine canaliculi, O.oon to 0.0023
mm. broad, the so-called dentinal canals (e, e). Their course,
4

Fig. 66. — Human tooth-fang d, with ce-
ment covering a. At b the granular or
Tomes' layer with interglobular spaces ; at
c and e the dentinal canals.

74

SEVENTH LECTURE.

disregarding the most acute-angled ramifications and looped
communications, is on the whole regular. They are, in gen-
eral, perpendicular to the surface of the pulp cavity and
therefore vertical on the vertex of the crown, oblique on its
marginal portions, horizontal over the neck and fang, and at
the apex of the latter reassuming an obliquely descending
direction. A transverse section shows them radially
arranged. By more careful examination, however, we
meet with a number of smaller interesting variations (Koll-
man).

Filled with air they appear dark, saturated with fluid as
transparent, readily disappearing canals. The condition
of the lacunae of bone is, therefore, repeated here. An
elastic, calcified parietal layer, like that of the bone, is
also not wanting in the dentinal canals. They are now-
much more easily recognized with the greater diameter of the
tubuli.

Our dentinal canals open internally into the central cavity.
The latter may be very well compared to a Haversian canal
of the bone.

The fang is covered by cement, as we have already
remarked. This (a), is a thin layer of bone substance,
increasing downwards towards the apex of the root, gen-
erally without lamellar structure, but with delicate bone cor-
puscles.

A portion of the lacunae of the latter communicate with the
dentinal tubuli which have entered the cement or — more cor-
rectly said — pass over into the latter. At the margin of the
bone covering and the dentine, numerous spaces occur, the
so-called interglobular spaces (b), which may be mistaken for
bone corpuscles.

Let us leave the enamel covering of the crown for the
present, and turn to the contents of the dental cavity, the
pulp.

In the progressing bone, as the previous lecture taught, the
ruptured cavities were filled with unripe tissue, on the surface
of which the osteoblasts appeared. Now the tooth pulp pos-

DENTINE.— ENAMEL.— LENS TISSUE.

75

Fig. 67. — Two dentinal cell-., b,
which pass with their processes
through a portion of the dentinal
canals at a. and protrude from
the fragment of dentine at c ; af-
ter Beale.

sesses — and at a later stage as well — a similar cell covering.
These (Fig. 67 , b), are the dentinal cells or, as they have been
characteristically named (Waldeyer),
the odontoblasts, the sculptors of the
tooth bone. Our cells, oblong,
measuring 0.02 to 0.03 mm., are stra-
tified. One or more of their fine,
thread-like processes penetrate the
dentinal tubuli peripherically. An
able English investigator, Tomes, first
saw such " soft fibres " here.

The crown is covered with enamel,
the hardest substance of the body. The organic form-deter
mining basis amounts to only a slight per
cent. (3.5 to 6), against a prodigious excess
of bone earths.

The enamel (Fig. 68), a petrified epithe-
lial production, consists of long, closely
crowded polyhedral cylinders, the enamel
prisms or enamel columns {b). They fre-
quently appear to pass through the entire
thickness of the enamel covering ; their di-
ameter is 0.0034 to 0.0045 mm.

Transverse polished sections of the enamel
show a delicate hexagonal mosaic (Fig. 69).

A peculiar transversely striated appearance may be recog-
nized in the isolated enamel prisms.

The surface of the enamel, finally, is cov-
ered by an uncommonly tough membrane.
This is the cuticle of the enamel (Fig. 68, a).

Beneath the enamel the dentinal tubules
form loop-like and reticular transitions (Fig.
68, d). In the hard brittle substance of
the former, there has been a formation of
numerous clefts (c), which may communicate with the canals
of the dentine.

With the tolerably simple structure of the teeth, which has

y.

Fig. 68. — Peripheral
portion of the dentine d,
from the crown; with
enamel covering,/': a,
enamel membrane ; c, the
cavities filled with air.

Fig. 69. — Transverse
section of the human
enamel prisms.

76

SEVENTH LECTURE.

been described, is connected a very complicated history of
their origin. We here mention only the chief points.

That the teeth are formed in the maxillary bones, that in
the infant the eruption first takes place after months and
years, that the first teeth are for the greater part replaced by
permanent ones, is known to all.

Two of the three germinal plates participate in the produc-
tion of our structures, the corneous layer and the middle ger-
minal layer. The former produces the enamel, the latter the
pulp, dentine and cement.

On the free borders of
the embryonic jaw ap-
pears at first a mound-
like thickening of the

pavement
(Fig. 70, a).

epithelium
It presses

Fig. 70. — Tooth formation of a
hog's embryo ; a, epithelial
mound ; b, younger cell layer ; c,
the lowermost ; e, enamel organ ;
f, tooth germ ; g, inner, and h,
outer layer of the progressing
tooth sac.

Fig. 71. — Tooth sac of an older human embryo, partly
diagramatic ; a, connective-tissue parietes nf the
tooth sac. with the outer layer at a1 and the inner at
a'1 ; b, enamel organ, with its external, c, and inferior
cells, d ; e, dentine cells ; f. dentine with the capillary
vessels,^; i, transition of the connective tissue of the
parietes into the tissue of the dentine germ.

downwards into the soft substance of the maxillary tissue as a
vertical elongated ridge. The former has been named the
tooth papilla, the latter the enamel germ.

From place to place, springing up from the depths of the
tissue of the jaw, convex papillar structures, the so-called
tooth germs (/), grow towards the enamel germ. Here and
there, increasing in diameter, they press in the under surface

DENTINE.— ENAMEL.— LENS TISSUE.

77

of the enamel germ, and thus give this locally the form of a
cap or bell. The latter is called the enamel organ (e).

Leaving the intermediate forms aside, let us pass at a
bound to a later period. Here (Fig. 71) the enamel organ
(I?) has long since become separated by constriction from its
point of origin, the epithelium of the jaw, and also thrown
off the lateral bridge connecting it with the ridge of the enamel
germ. It is covered on the upper convex and inferior concave
surfaces with cylindrical epithelial cells (c, d). In the interior
(/?) we find gelatinous tissue (Fig. 22). Below (Fig. 71, f)
we perceive the thick tooth germ, the progressing tooth crown.
Both are enclosed within a connective-tissue capsule (a), the
so-called tooth sac, with external (a1) and internal (a2) layers.
The sac and tooth germ finally become continuous with each
other below.

The tooth germ bears on its surface the layer of odonto-
blasts [e). From them is produced the first thin cortical layer
of the dentine. Layer on layer are subsequently formed
over the longitudinally growing tooth germ. By this growth
it finally obtains the neck and fang ;
its soft, vascular tissue remains more
and more retarded in its further
development, and becomes the pulp.
From the epithelium at the concave
surface of the enamel organ, occurs
the formation of the enamel prisms
(below d), whether these represent
calcified portions of the cell body or
secreted cell substances. The tooth,
growing up, kills the enamel organ
at last, and makes its eruption. Its
cement may originate from the lower
portion of the tooth sac. This per-
sists, for the most part, as the peri-
osteum of the alveolus.

For the permanent teeth, a secondary enamel germ appears
to branch off from the original one at a very early period.

Fig. 72. — Crystalline lens ; a, cap-
sule ; b, epithelium of the anterior
half; c, lens fihres, with the anterior,
d, and posterior ends, e ; _/, nuclear
zone.

78 SEVENTH LECTURE.

To close with the epithelial productions, we here notice
briefly the tissue of the crystalline lens of the eye. This
(Fig. 72), arising from an ingrowth of the corneal plate of the
foetus, is invested by a structureless capsule {a, a), which is
thicker anteriorly and thinner posteriorly. The inner surface
of the anterior segment of the capsule has an unstratified,
low, cubical pavement epithelium (b).

The marginal zone of the latter, advancing towards the
equator, undergoes a gradual transition into elongated nuclear
elements, the so-called lens fibres (c). These are
pale, hyaline elements, in the external portion55
of the organ, 0.009 to 0.0113 mm. ; in the inter-
nal, where they appear more firm, only 0.0056
mm. broad. The lens fibre, surrounded by a
fibres in trans- sort 0f envelope, has the value of a full-grown

verse section. * ' °

cell. The nuclei (f) lie adjacent to the equatorial
zone. The arrangement is, in general, meridional. Trans-
verse sections of the lens fibres present an elegant band of
elongated hexagons (Fig. 73).

Fig. 73.— Lens
ibres in tr;
verse section

EIGHTH LECTURE.

MUSCULAR TISSUE.

We now return to the mid-
dle germinal layer of the em-
bryonic germ, and discuss one
of its most important and
extensive productions ; we
refer to the -muscular tissue.

This presents, in man and
the higher animals, two quite
different appearances. In the
one we recognize as elements
elongated, spindle-shaped cells
of a homogeneous appear-
ance (Fig. 74) ; in the other
we meet with a longer, larger,
striated fibre (Fig. 75, a).

One speaks, accordingly, of
smooth and transversely stri-
ated muscles. Do not believe,
however, that we have here to
do with two entirely different
things ! In the first place, we
meet with quite a number of
intermediate varieties in the
great multiform animal world ;
and then the two different
representatives of the mus-
cular tissue originate from ex-
tremely similar initial struc-
tures. The smooth element

Fig. 74. — Smooth muscular tissue of man
and the mammalia , a, a developing cell from
the gastric region of a two-inch long hog's em-
bryo ; 6, a more advanced cell ; c to g, various
forms of the human contractile fibre cell ; h,
one with fat granules ; i, a bundle of smooth
muscular fibres ; k, transverse section through
such a one from the aorta of the ox, with
many nuclei in the plane of the section.

stops at a lower stage ; the

So

EIGHTH LECTURE.

transversely striated has become further developed. The
latter contracts rapidly and energetically, the former slow-
ly and sluggishly ; the latter constitutes the voluntary mus-
cle, the former the involuntary acting. The heart, with
transversely striated involuntary fibres, makes, it is true, an
exception.

Pale, nucleated bands were formerly assumed to be the
elements of the smooth muscles (Fig. 74, i).
In the year 1847 Koelliker reduced the
band into a series of cellular elements, lin-
early arranged behind each other, his con-
tractile fibre cells. At that time this was
an important discovery, a proof of the dis-
tinguished observer's sharp-sightedness.

We perceive these contractile fibre cells
at a to h. They are sometimes short, some-
times longer, not infrequently immensely
long, spindle-shaped structures, 0.0282 to
0.2256 mm. and more in length, and of
moderate diameter, 0.0074 to 0.0151 mm.
The appearance of the membraneless cell
body is, as a rule, entirely homogeneous,
except when a deposition of fat (It) has
taken place within it. An elongated nu-
cleus (it is called rod-like) is readily seen.
fig. 75.— Two trans- Jt contains one or more nucleoli. Occa-

versely striated muscular

nbriite («), with the con- sionallvwe find the nucleus double or in

nective-tissue bundles [l>). J

even greater number.
Smooth muscles are widely diffused throughout the human
body. From the oesophagus till near the end of the rectum
they form the long known thick muscular layer, and, besides,
a still finer one — the muscularis mucosae — in the tissue of the
mucous membrane. Smooth muscles are met with, further-
more, in the respiratory apparatus, as in the posterior walls of
the trachea, in the circular fibrous membrane of the bronchi
and their ramifications. According to many, our tissue is
not wanting even in the respiratory vesicles of the lungs,

MUSCULAR TISSUE. 8 1

although we never could convince ourselves of this. The
middle layer of the vessels, especially of the arteries, contains
smooth muscle. Small bundles of the same occur in the co-
rium ; thus, in the hair-sacs, arrectores pilorum, furthermore,
from the surface of the corium to the subcutaneous cellular
tissue (J. Neumann), then, more connectedly, on the nipple
and the areola, and especially in the so-called tunica dartos
of the testicle. The walls of the gall-bladder are also muscu-
lar. In the urinary apparatus, in the calices, and pelvis of
the kidneys, the ureters, and the bladder our tissue acquires
a greater development. The male generative apparatus is
likewise abundantly provided with smooth muscular sub-
stance ; still more so that of the female. Even the ovary,
according to our view, harbors this tissue. It forms con-
nected layers in the oviducts. Altogether the most massive
collection of the tissue is met with in the womb. During
pregnancy it acquires a still greater increase. The lymphatic
glands, the eye (sphincter and dilator pupillae, choroid, the
ciliary, orbital, and palpebral muscles) also have smooth
muscles.

We meet with transversely striated tissue in all the muscles
of the head, trunk, and limbs, the auricle, the external mus-
cles of the eye, in the tongue, the pharynx, the upper por-
tions of the oesophagus, the genitals, the termination of the
rectum. Our tissue likewise forms the diaphragm and, modi-
fied, the heart.

As element (Fig. 75, a) we recognize in man at once a long,
unramified, cylindrical, filamentous element of O.oi 13, 0.0187
to 0.0563 mm., transverse diameter. This is the muscular
filament, the muscular fibre, or, as is badly said, the primi-
tive bundle.

Here, however, we at once notice a peculiarly complicated
texture.

We meet with an envelope and contractile contents ; the

sarcolemma and sarcous element. The former, closely applied

to the living muscular filament as a constant companion, may,

in death, become elevated in a vesicular manner by the

4*

82

EIGHTH LECTURE.

Fig. 76. — Muscu-
lar fibnlla torn
across ; b, b, sarcous
portion ; a, sarco-
lemma.

Fig. 77. — A muscular fasciculus of
the frog by 800-fold enlargement ; a,
dark zones, with sarcous elements ; /',
bright zones; c, nuclei; d. interstitial
granules (alcohol preparation).

absorption of water. When the sarcous por-
tion has been torn by traction, the sarcolemma,
or primitive sheath (Fig. j6, a), appears most
distinctly. It is a hyaline, aggregated, elastic
membrane.

Directly superimposed on this envelope, one
meets with numerous oval nuclei (Fig. JJ, c),
measuring 0.0074 to o. 01 13 mm. The lateral
surfaces, and the pole of the latter, are sur-
rounded by a small quantity of a protoplas-
matic substance (d). This, a cell rudiment,
has been called a muscle corpuscle (M.
Schultze). This is the condition of the human
muscle. In the lower animals, however, the
nucleus also lies in the interior, and the same
is the case in our heart muscle.
All this is readily understood.
Extraordinary difficulties are, on
the contrary, presented by the sub-
stance surrounded by the sarcolem-
ma, the sarcous elements. It is, in
the first place, very changeable,
and, with its infinitely delicate
structure, we soon arrive at the
limits of the microscopic solution
possible at present.

In many cases, and regularly
after the use of certain reagents,
the sarcous elements appear as a
bundle of fine, transversely striated,
elongated fibrillae, measuring o.ooi I
to 0.0022 mm. It would appear,
therefore (after the manner of the
connective tissue), to be a primi-
tive bundle.

With other methods of treatment,
and also in the living muscle, we

MUSCULAR TISSUE.

83

see little or nothing of these fibrillae. The filament permits
the recognition of transverse lines only. It now appears,
comparable to a Volta's pile, to consist of discs piled upon
each other.

The fibrillar, as well as the transverse discs, were both re-
garded as normal, pre-existing structures, and in this, accord-
ing to our view, a double error was committed. In the living
muscle there are neither fibrillae or discs.

The first who here trod the correct path, a generation since,
was the Englishman, Bowman. It is true that, with the opti-
cal aids of that period, he was unable to exhaust the subject ;
but we are also unable to do so at the present time, although
we have at our disposal much more perfect microscopes.

According to the view of this distinguished investigator,
the muscular filament consists essentially of an aggregation
of small bodies, the sarcous
prisms or sarcous elements
which, united and holding to-
gether in the transverse direc-
tion, afford the appearance of
a disc or a thin plate {disc
according to Bowman) (Fig.
yy, a) while, disposed in the
longitudinal direction, they pre-
sent that of the fibrillae (Fig. 78,
I, a, b). Accordingly, neither
fibrillae or discs pre-exist. There
is merely a disposition present
in the muscular filament to become divided, sometimes in the
transverse, sometimes in the longitudinal direction. The
cohesion in the latter direction is certainly the strongest ; for
the fibrillae in the dead element are met with more fre-
quently than transverse plates.

Let us next examine the muscular filament somewhat more
closely, with the aid of the highest magnifying powers.

The transverse lines are readily resolved into dark trans-
verse zones, separated by more transparent ones (2, a, b).

Fir.. 78. — Two muscular fibrillae, from
the proteus. i, and the hog, 2, magnified
1 odo times ; a, sarcous prisms ; i, bright
longitudinal connecting medium. At a*
the sarcous elements are further apart, and
the transverse connecting medium is visi-
ble ; c, nucleus.

84

EIGHTH LECTURE.

The former consist of sarcous elements (a*) placed nearer each
other. This may also be recognized without trouble by the
aid of good and strong magnifying powers. They are elon-
gated prismatic bodies, measuring 0.0017 nim. in the proteus,
0.0013 m the frog, o.ooii to 0.0012 mm. in the mammalia and
man.

The sarcous elements must, naturally, be joined one to the
other.

If we split off one of the finest longitudinal filaments, that
is a so-called muscular fibrilla (1), the longitudinal series of
sarcous elements (a) are held together by the transparent
longitudinal connecting medium (b). If we examine a mus-
cular filament split up into transverse plates, the dark and
light transverse zones are found to be connected by a trans-
verse connecting substance, which extends over the outer
surface from a and b of our Fig. 78, 2. Here the longitudinal
connection is naturally, completely dissolved.

Up to about ten years ago, we thought the matter
might thus be passably explained ; but newer observa-
tions have been added and further
doubts have arisen.

In the year 1863, the Englishman,
Martyn, had already seen a dark trans-
verse line in the transparent longitu-
dinal connecting medium. These ob-
servations were afterwards corroborat-
ed and extended by Krause (Fig. 79).
Let us name this thing (a), therefore,
Krause's transverse line or disc.

But with this we have still not
reached the end. At the same time
another competent investigator, Hen-
sen, found the dark transverse zone, the
transverse series of sarcous elements,
divided by a transparent transverse
This is the Hensen's middle disc. Granules which

Fig. 79. — Krause's transverse
discs ; a, a, i, a muscular fibrilla
without; 2, one with strong longi-
tudinal traction, both very strong-
ly enlarged (Martyn) ; 3, muscu-
lar filament of the dog imme-
diately after death.

line.

were contiguous above and below to Krause's transverse line

MUSCULAR TISSUE.

85

F11, 80.— Piece ' f a
dead muscular til 1-
ment from the fly, after
Engelmann ; a, trans-
verse discs ; />, acces-
sory discs.

were subsequently designated by Engelmann as accessory
discs (Fig. 80 b).

From these singular observations, which
touch and, perhaps, in part, exceed the limits
of microscopic analysis, we are at present un-
able to derive an anyways reliable conclusion.

An old observation of Bruecke's is also in-
teresting. The Bowman's sarcous elements
refract the light double, the longitudinal con-
necting medium refracts simply.

We pass, finally, to some more simple structural conditions
of the transversely striated muscle.

Among these are the so-called interstitial granules, small
fat molecules (Fig. JJ, d), which, commencing at the nuclear
poles of the muscular corpuscles, permeate the filament in a
linear longitudinal direction over shorter or longer distances.

The preparation of transverse sections
through the frozen muscle (Fig. 81) was taught
by Cohnheim. Groups of sarcous elements
{a) are here recognized as a mosaic of small
areas of transverse to hexagonal shape.
Enclosing these are noticed a system of
transparent, glistening lines (c) which must
belong to the transverse connecting medium.

A modification of the transversely striated
muscles is met with in the tongue and heart
of the mammalia and man. These are rami-
fied and reticularly connected filaments. In
the former organ are noticed frequently sarcous elements : c,

0 *■ J transparent trans-

repeated divisions at aCUte angles. verse connecting me-

r ° dium ; 0, nucleus.

In the heart (Fig. 82), a narrow-meshed
net-work is constituted by the abundant formation of anasto-
moses. A sarcolemma is probably wanting in these dimin-
ished filaments. The latter, furthermore, show strongly pro-
nounced transverse and longitudinal markings. It is an
interesting circumstance, finally, that this muscular reticulum
consists of cemented cells (Fig. 82, to the right).

Fig. 81.— Trans-
verse section through
a frozen muscle of
the frog ; a, groups of

86

EIGHTH LECTURE.

^^:

Fig. 82. — Muscular filaments of the
heart. To the right appear transparent
boundaries and nuclei.

The remaining transversely striated muscles show the fila-
ments arranged parallel, slightly prismatically flattened against

each other (Fig. 83, a), and in
man containing the muscular cor-
puscles \e) in their periphery.
Between them occurs a scanty
amount of connective tissue, the
highway for vessels {d) and nerves.
With rich living this may develop
fat cells (Fig. 50).

A varying number of muscu-
lar fibres unite into bundles,
measuring 0.5 to 1 mm., which are
separated from the neighborhood
by abundant connective tissue.
Such primary bundles then unite
into secondary ones. The con-
nective tissue covering of the
muscle bears the name of peri-
mysium externum, in contradistinction to the perimysium
internum of the inner connecting substance between the fila-
ments and bundles.

Smooth muscles also show a
bundle-like grouping.

We come, finally, to the con-
nection with the tendons. The
latter tissue has already been de-
scribed above, page 57.

With a rectilinear insertion
(Fig. 75) the sarcous substance (a)
appeared to pass immediately
over into the tendinous bundle
[b) ; not so, however, with an
oblique insertion, where an inter-
rupted muscular end becomes ap-
parent.
Weismann first obtained convincing appearances here by

Fig. 83. — Transverse section through
the human biceps brachii ; «, the muscu-
lar fibres ; />, section of a larger vessel ;
c, a fat cell lying in a large connective-
tissue interstice; d, capillaries cut across
in the thin connective-tissue layer be-
tween the several fibres; e, the nuclei
(muskelkorperchen) of the latter lying
on the sarcolemma.

/

MUSCULAR TISSUE.

87

means of potash solutions (Fig-. 84). The end of the filament,

sometimes rounded, at others pointed, and again irregularly

shaped, is always covered by sarcolemma

(/' 1. The tendinous bundle is attached

by a corresponding excavation (c, d).

During life the whole is united in the

firmest manner by means of a cement

substance.

The muscular filaments are of various
lengths, but according to Krause do not
exceed four centimetres. Thev termin-
ate, therefore, repeatedly far from the
end of the entire muscle, in its interior
and in the form of points.

The muscular filament consists of vari-
ous albuminous bodies. The sarcous
elements, transverse and longitudinal
connecting medium, are formed of modi-
fied members of this so little understood
group of substances. The proportion of
water present is considerable, corresponding to the softness
of the tissue.

We turn to the embryonic development of our tissue.

The elements of the smooth muscles present nothing but
cells grown into a spindle shape (Fig. 74). The rounded or
oval developing cells (a, b) simply exchange their protoplasma
with the homogeneous sarcous substance, the nuclei assume
the rod form, and an envelope is altogether wanting.

We have already (Fig. 27) briefly mentioned the origin of
the transversely striated fibre. After the example of Schwann,
they were formerly considered to arise from the fusion and
metamorphosis of formative cells arranged in rows. In the
heart muscles, as we have already seen, something of the
kind does, in fact, take place ; but not so in the remaining
voluntary muscles. Here the element is a single cell, which,
it is true, undergoes a much more extended development than
the contractile fibre cell of the smooth tissue.

Fig. 84.— Two muscular
fibrillas (a, b) after treatment
with solution of potash, the
one still in connection with
the tendon (r), the other
separated from the same {d).

88

EIGHTH LECTURE.

In small embryos one obtains thin (0x045 to 0.0068 mm.),
but long (0.28 to 0.38 mm.) spindle cells, with one or
two vesicular nuclei, and in the centre commencing for-
mations of transverse lines, that is with a transformation
into sarcous elements. With an increase in nuclei, the
structure increases not only in length but also in breadth.
The transverse striation advances towards the ends, but leaves
the axial portion still free. We still meet here with the old
protoplasm. Later, however, after the longitudinal markings
have also appeared, this protoplasma has disappeared, with
the exception of a slight residue, which surrounds the nucleus
and thus forms the muscle corpuscle. We find the latter, at
last, in mammalia and man, displaced towards the periphery.
We have already above (p. 82), declared the sarcolemma
of the transversely striated filament to be a homogeneous
boundary layer furnished by the adjacent connective tissue.
All investigators do not, however, coincide with our view.

The muscular filaments of the new born are still much finer
than those of the adult. The subsequent increase in thick-
ness explains in great part the growth of the
muscle in transverse diameter. New fibres
are also subsequently developed (Budge).
This has, it is true, been recently disputed.
Weismann observed that the muscles of
the frog divide in a longitudinal direction,
with a prodigious increase in their nuclei.
One then sees regular columns of nuclei de-
scending near each other. The filament di-
vides, one becomes two, which subsequently
acquire the normal diameter by a growth in
thickness. The two products of division
may afterwards repeat the same cleaving pro-
cess. A single muscular filament may in this
way finally become a whole group of filaments.
Among the forms of retrogression of
our tissue, fatty degeneration is the most frequent (Fig. 85).

Fig. 85.— Fatty degen-
erated human muscular
fibre ; a, slighter ; /;,
increased ; c, highest
degree.

NINTH LECTURE.

THE BLOOD-VESSELS.

ONE cannot really speak of a vascular tissue. Only the
innermost layer consists of a simple layer of closely cemented
endothelial cells. This is the original stratum ; it forms the
simplest, finest vascular tube.

All the remaining layers, on the contrary, which by their
further aggregation reinforce the walls of the vessel — and
they commence very soon — belong to tissues which we have
already discussed ; they consist of connective tissue and elastic
substances, as well as layers of smooth muscles.

The blood is conducted from the heart, as is known,
by immensely ramified systems of arteries. Its return is
consigned to the not less ramified veins. Between them
is intercalated, but without any sharp demarcation, the
district of the capillaries. They maintain the nutrition
of the organs and tissues, as well as the secretion of the
glands.

The finest capillaries — they do not by any means occur in
all parts of the body, however — have a calibre which just
suffices to permit the passage of the blood cells, one after the
other, though often with a certain lateral compression. Their
lumen may, therefore, be assumed to be for man 0.0045 to
0.0068 mm. In other parts of the body, however, the finest
capillaries present double this diameter.

Without being treated with a suitable reagent, their struc-
ture appears extraordinarily simple. A hyaline, structure-
less, extensible and elastic membrane contains embedded,
from place to place, rounded or elongated oval nuclei of
0.0056 to 0.0074 mm., with nucleoli. In the finest capil-
laries the nuclei lie in the simplest manner behind each

90

NINTH LECTURE.

other ; in somewhat larger ones an alternating position begins
to take place.

If, however, we force a stream of dilute nitrate of silver
solution through our capillary, it then appears to be com-
posed of the plates and curved, nucleated, endothelial or vas-
cular cells represented in Fig. 21. With stronger magni-
fying powers (Fig. 87), one recognizes in places, between the

Fig. 86. — 1, capillary with a thin wall, and the
nuclei a and b ; 2, capillary with double contoured
walls ; 3, small artery, with the endothelial layer a,
and the middle layer b.

Fig. 87. — Capillary from the mes-
entery of th< frog \t a and b, small
apertures, '"Stomata."

endo" elia, larger and smaller, mostly rounded, dark cor-
puscles (a, a) or light circular markings (b). There are small
openings here, through which the lymphoid cells, by their
vital migration (p. 10), probably make an active exit, and the
colored elements of the blood are passively forced out (p. 27).
The former marvellous emigration has been known for years
(A. Waller, Cohnheim).

In other capillaries (Fig. 86, 2) the walls are circumscribed
by a double line. Here, there already appears to be the pri-
mary rudiments of a so-called tunica interna or serosa.

THE BLOOD-VESSELS.

91

More frequently, there are capillaries where the endothelial
tube is surrounded by a connective-tissue layer, a so-called
adventitia capillaris. The latter is,
for a certainty, the primary rudi-
ment of the layer, which with in-
creasing complexity occurs in all the
larger vessels as the most external
layer or adventitia. We here meet
at first with either ordinary connec-
tive tissue, which has indeed re-
mained at an earlier stage, with lon-
gitudinally arranged nuclei or cell
remains (Fig. 89, d), or, when capil-
laries of lymphoid organs are con-
cerned (Fig. 88, b), the reticular con-
nective substance has become spread
over the endothelial tube in an ele-
gant manner, and the capillary is
kept distended by this cellular reticu-
lum, like the embroidery in a frame.

Passing, now, to somewhat larger trunks, numerous
variations of the structure occur. They coincide in part
with the nature of the vessel, whether arterial or venous
branches ; they are also, in part, of a more individual or local
nature.

Frequently, when we follow the capillaries towards the
arterial tubes, we perceive branches where a layer, striking
the eye by its transversely arranged nuclei (Fig. 86, 3, b), is
met with around the endothelial tube (a). The former con-
stitutes the very commencement of the muscular middle layer
or tunica media of the vessels. An equally large venous
branch usually has in the place of the latter layer a con-
nective-tissue adventitia. Still, it often enough occurs in
the finer arterial branches also, spread out over the muscular
layer.

Let us take a small arterial trunk, after the manner of our
Fig. 89. The endothelial tube is not drawn here. Lying on

Fig. 88. — Capillary vessels and fine
branches of the mammalia ; a, capil-
lary vessel from the brain ; />, from a
lymphatic gland : c, a somewhat
larger branch with a lymph-sheath
from the small intestine ; and d, a
transverse section of a small artery
of a lymphatic gland.

92

NINTH LECTURE.

this, and consequently as the innermost layer of the figure,
we recognize at b a homogeneous, longitudinally striated,

elastic membrane, the tu-
nica serosa of the older
anatomy. The same is
surrounded by a layer of
transversely running con-
tractile fibre cells at c.
The connective-tissue laver
d, with longitudinally ar-
ranged cells, forms the last.
Under certain circumstan-
ces, it may be very much
thicker than in our figure.

Other small arterial
trunks show the muscular
layer to be constituted by
several layers of fibre cells,

Fig. 89.— A small arterial trunk. At f>, the homo- lying Over One another, aS
geneous, nun-nucleated inner layer; c, the middle

la\e-, consi>ting of contractile fibre cells ; d. thecon- \x\ Figr 88 d where tile
nsctive tissue external layer. ° '

adventitia is again formed
of reticular connective tissue.

Larger trunks, finally, can no longer be surveyed in their
totality, under the microscope. One must, therefore, exam-
ine singly the separately prepared layers, or make longi-
tudinal and transverse sections through the hardened walls.

The further transformations, from those immediately fol-
lowing up to the most remote of the largest blood-vessels,
consist in the following : The endothelial tube always
remains a single layer; the connective-tissue adventitia does
the same, but it increases in thickness; the connective-tissue
bundles become more distinct, and elastic fibre reticula are
more and more frequent, especially in the arteries. Both the
middle layers, the serosa and media, begin on the contrary
to become stratified ; each of them consists of an increasing
number of layers lying over each other. On this depends
the growing thickness of the vascular walls. The inner

THE BLOOD-VESSELS. 93

group of layers essentially preserve in their membranous
layers the nature of the elastic tissue, and present the most
heterogeneous varieties of the same with a longitudinal
arrangement. The middlemost group changes into a system
of alternating layers of elastic tissue and smooth muscles,
both with a transverse direction, or also of connective tissue.
The tunica media remains much thinner in veins than in
arteries of similar size, and the result is that the walls of the
former vessels are thinner. The endothelial cells of the
arteries appear as narrow, lancet-shaped lamellae ; those of the
veins are shorter and broader (p. 29).

Taking a small vein of about 0.25 mm. in calibre, we find
succeeding the epithelium a serosa with fine, elastic, longi-
tudinal reticula. The middle layer consists of several mus-
cular layers, which have between them elastic reticula and
connective-tissue layers. The adventitia shows longitudinally
running connective tissue and a contingent of elastic fibres.

The appearance is different in middle-sized veins. The
serosa has here become a group of layers. We now meet
with homogeneous or striped layers with longitudinally
arranged spindle cells, elastic membranes or elongated reti-
cula. Indeed, even the elements of the smooth muscles may
be continued in these inner groups of layers. The middle
layers consist of connective tissue running transversely, with
elastic reticula arranged in the same manner, and smooth
muscles. Nevertheless, isolated elastic layers with longitu-
dinal fibres also occur here. The adventitia is as usual ; still
it may also harbor contractile fibre cells.

The largest veins possess a similar serosa, though without
the smooth muscles, while the media remains undeveloped
and may he entirely absent. It shows scanty muscular
elements, permeated by transverse connective tissue. Elastic
longitudinal fibro-reticula have likewise maintained their posi-
tion here. In the thick adventitia of many veins, one meets
toward the interior with thick longitudinal muscles, as, for
instance, that of the pregnant uterus, while the sinuses of the
dura mater arj entirely without muscles.

94

NINTH LECTURE.

In the smaller arteries, the serosa and adventitia remain toler-
ably unchanged. Still, there frequently occur in the former
reticular perforated elastic layers, so-called " fenestrated mem-
branes," or free elastic longitudinal reticula; the media pre-
sents several layers of transversely directed muscles, lying over
each other, and an elastic net-work is also developed in the
fihrillated outer layer.

In the larger branches, the stratification of the inner and
middle layers increases. In the latter, elastic plates with
transverse fibres, are now interpolated between the muscular
layers, and the elastic reticulum of the adventitia becomes
thicker.

The largest arteries (Fig. 90') show under the endothelium
(a), strongly stratified, the group of the inner vascular mem-
brane (b). The several lamel-
lae, in varying texture, present
the entire multifariousness of
the elastic tissue. Inwards,
towards the endothelial cover-
ing, one may, indeed, meet
with more homogeneous, or
more striated layers with cellu-
lar reticula imbedded over each
other (Langhans, von Ebnen.
In the more middle group
of layers the membranous
character of the elastic fibrous
net-work (d) becomes more
and more prominent. Their
fibres may be thinner or thick-
er; the membranous connect-
ing substance may appear
whole or perforated. The num-
ber of these elastic layers may
increase to 30, 40, 50, and
more. The muscles of the
middle layer (e) appear unequally developed ; frequently not

e m

Fig. 90. — Transverse section through the
walls of a large artery : a, endothelium ; /.
sa ; c. outer layer of the same ; d. elastic, e, mus-
cular layers of the media : g, adventitia ;/, their
elastic fibro-reticula.

THE BLOOD-VESSELS.

95

to a high degree. The direction of the fibres is by no means
exclusively transverse. In the outer portions of the media,
fibrillated connective tissue occurs (Schultze, von Ebner). In
the adventitia {g), finally, the elastic fibro-reticulum (/)
acquires in an inward direction, in large mammalia, a very
prodigious development.

The valves of the vessels consist of connective tissue with
elastic intermixtures, and the endothelial covering.

Vasa vasorum is the name given to the capillary vessels

which occur in the middle and outer layers of the larger trunks,

and supply the nutritive materials to the walls of the vessel.

The vascular nerves terminate at the muscles of the

media.

We pass to the arrangement of the
capillary vessels in the human body.

It is known that they do not occur
everywhere. Thus, the epithelial struc-
tures, with the crystalline lens, the cornea
of the eye, and the permanent cartilages
are non-vascular.

A peculiarity of the capillary division

Fig. 91. — Vascular net-
work of a transversely stri-
ated muscle ; a, arterial,
6, venous vessel; c, d,
the capillary net-work.

Fig. 92. — A pulmonary alveolus of the calf ;
a, larger blood-vessels, which run in the pari-
etes of the alveoli ; b, capil ary net-work ; c,
epithelial cells.

consists in this, that the tubes by giving off branches do
not become narrowed to a noticeable degree, and that by

g6 ninth lecture.

the conjunction of the branches there are formed reticula
of more regular, and frequently of extremely characteristic
form.

The diameter of the capillaries (see above) is by no means
the same in the different portions of the human body. The
brain and retina present the finest of 0. 0068 to 0.0065 mm.,
and less. The muscles have somewhat larger ones of 0.0074
mm. The calibre is again increased, somewhat, in those of
the connective tissue, the external integument, and the mu-
cous membranes. The lumen is greater in the capillaries of
most of the glands, such as the liver, the kidneys, and the
lungs. Here we have a diameter of 0.0099 to 0.0135 mm.
The most considerable ones, finally, of 0.0226 mm., are seen
in the bone medulla. That, with the larger blood corpuscles,
even the finest capillaries of animals have a more considerable
calibre, it is hardly necessary to remark.

The capillaries are sometimes more profuse, sometimes more
scanty, in a part of the body. The size of the portion of the
tissue comprised within their net-work is, accordingly, quite
variable ; it is small in the vascular, large in the non-vascular
parts. The former have an energetic, the latter a sluggish
assimilation. The lungs (Fig. 92) appear uncommonly vas-
cular. Their capillary net- work,- serving for respiration, is the
most compact of the organism. The other glands approxi-
mate. The fibrous membranes, the tendons, the neurilemma
are quite non-vascular.

The form of the capillary net-work is determined by the
shape of the parts to be circumvoluted, the nature of the
several elements, or of their arrangement.

We have, firstly, the straight, capillary net-work. A trans-
versely striated muscle (Fig. 91) may represent this. The
several filaments are surrounded by the uncommonly elongated
meshes (c). The involuntary, smooth muscles also possess
the same capillary net-work. Here, however, from the thin-
ness of the elements, a bundle of fibres takes the place of
the transversely striated filament.

Other parts with elongated elements — for example, the gas-

THE BLOOD-VESSELS.

97

Fig. 93. — Vessels of the fat cells. The arterial (a),
venous branches (6-), with the rounded capillary net-
work of a fat lobule.

trie mucus membrane, with its long, thin, tubular glands —
show a similar straight net-work.

We are familiar, from Fig. 48, with the fat cells, large,
rounded structures. Their
capillary reticulum, in
correspondence with this,
forms rounded meshes
(Fig. 93). The small, ar-
terial branch (a), and the
small, venous branch (/;)
of an aggregation of these
fat cells appear very dis-
tinct.

We shall later, at the
glands, become acquaint-
ed with very extended
organs of a racemose
structure. A rounded or

elongated saccule (acinus) surrounds an aggregation of smaller
parenchyma cells. The acini are likewise circumvoluted by
a complete, quite

similar, round net-
work, like the indi-
vidual fat cells.

A handsome, very
characteristic ar-
.rangement is pre-
sented by the capil-
laries of the liver
(Fig. 94). The liver
— we shall return to
it in greater detail
subsequently — is di-
vided into so-called
lobules, into collections of radially arranged cells. The ex-
tensively developed capillary system maintains the same
arrangement— a rounded, stellate one.
5

Fig. 94. — The capillary net work of the rabbit's liver, crossed
by a branch of the portal vein.

98

NINTH LECTURE.

The human corium projects in microscopically small papil-
lae, which the thick epithelium (p. 32) surrounds with a
smooth surface. The greater part of these papillae contains

a capillary vessel, which ascends on one
side, bends over the top of the papilla,
and descends on the other side. This is
the capillary loop.

Larger papillae occur on many of the
mucous membranes ; thus, on the dorsum
of the tongue, as the so-called gustatory
papillae, the whole small intestine, as intes-
tinal villi, to omit others. The simple
capillary loops are here no longer suffi-
cient (Fig. 95). Between them are inter-
posed communicating capillaries and capil-
lary net-works. Thus arises the looped
net-work.

A quite peculiar formation is presented
by the cortical layer of the kidney, in the
so-called glomerulus or vascular coil (Fig.
96).

A microscopic arterial branch (to the
right) divides, and each branch forms a
convolution of closely crowded capillaries.
These portions, with educting canals, reunite, at last, into a

single abducting vascular tube.
We here speak, therefore, of a
centripetal (vas afferens) and a
centrifugal vessel (vas efferens).
From the" latter arises, further
below, a new capillary reticulum.
To study the capillaries, they
must be injected from the larger
trunks with transparent, colored
(with carmine, Prussian blue) gel-
atine, at an elevated temperature. Opaque, granular masses
(cinnabar, white lead, chrome yellow) were the more imper-

Fig. 95. — An intestinal vil-
lus ; a, the cylindrical epi-
thelium with its thickened
seam : b, the capillary net-
work ; c. longitudinal layers
of smooth, muscular fibres ;
li, central chyle vessel.

Fig. 96.
ney.

-Glomerulus of the hog's kid-

THE BLOOD-VESSELS.

99

feet accessories of an earlier epoch. They are rarely used
at present. Other vehicles for the coloring material, resin-
ous, waxy masses, or etherial oils, are, at the most, only here
and there employed for very special purposes.

The embryonic origin of the vessels is still attended with
many obscurities.

The heart, a production of the middle germinal layer, is
formed very early, and enters soon afterwards into activity.
It is hollow from the commencement, and the large, adjacent
blood-vessels likewise appear to possess the same charac-
teristic.

With regard to the more particular details of this process,
we must state that our present knowledge is little satisfactory.

According to Klein, the first large vessels of the hen's em-
bryo are formed from cells of the middle germinal layer.
The contents of the latter soon liquefy. A protoplasma shell
now invests the enlarged and macerated cell-body with the
original nucleus. From such cells are derived the first vascu-
lar wall, or endothelial tube, as well as the first blood corpus-
cles. The cell is said to swell, and the nuclei increase, and,
as during this increase the nuclei assume a regular position,
the protoplasma mantle finally divides into flat, endothelial
cells. From these endothelial walls the first blood corpuscles
are also said to take their origin by a process of constriction.
They are said, however, to have another origin, also.

The first vascular walls and the first blood corpuscles,
therefore, derive their origin from the same cells.

We add to this the important fact that it is only subse-
quently to the use of nitrate of silver solution that the pri-
mary vascular wall is resolved into the familiar endothelial
cells.

A process of aggregation then leads, in a secondary man-
ner, to the formation of the additional external vascular
layers, a serosa, media, and adventitia. There is here, also,
a great want of accurate observations.

Capillaries — we assume, at first, a homogeneous, nucleated
protoplasma tube — are present at an early period.

100

NINTH LECTURE.

They soon present further metamorphoses. These may-
be beautifully recognized in the transparent tail of the tad-
pole (Fig. 97). It is a sort of budding process.

Fig. 97. — Development of finer capillaries in the tail of the tadpole ; /, p, protoplasma buds
and cords.

From the parieties of already mature neighboring capilla-
ries is supplied a protoplasma, capable of further independent
development, in the form of pointed cones (Fig. 97, I, 2,
p, p). By their confluence (2) the latter are, at first, trans-
formed into solid cords. If, then, the axial portion of the
meanwhile enlarged cord melts down, we have the proto-
plasma tube (3,P). By a further metamorphosis of the lat-

THE BLOOD-VESSELS. IOi

ter, the formation of new nuclei appears to take place. The
endothelial tube is finally established by the protoplasma
walls and the young nuclear formation.

1 The abnormal new formation of vessels in later life likewise
follows the old embryonic law.

TENTH LECTURE.

THE LYMPHATICS AND THE LYMPHATIC GLANDS.

WHAT is understood by lymph we have already mentioned
in our second lecture (p. 27). It was the blood plasma which
had passed out through the capillary walls, and which gave
off the dissolved nutritive constituents to the tissues, and took
up in exchange the products of the decomposition of the lat-
ter. We even then mentioned that this fluid, which is unin •
terruptedly supplied from the blood current, must necessarily
be removed. The arrangement serving this purpose must
now be discussed.

Our present course will, however, be the reverse of that
followed in the previous lecture ; for the large and medium
lymphatic discharge tubes are more accurately known, while
numerous uncertainties still prevail concerning the knowledge
of the finer and finest elements.

Let us commence with the ductus thoracicus, the terminal
large discharge tube of the lymphatics. We here meet with
a condition corresponding to the walls of the veins.

The endothelium is surrounded as a serosa by several layers
of a striated substance, and then by a net-work of longitudi-
nal elastic fibres. As a middle layer, we have next, longitu-
dinally running connective tissue, and then transverse mus-
cles. The adventitia also shows remains of the latter tissue.
Valves are not wanting here, nor afterwards in the finer
lymphatics.

Descending to the latter, the stratification, as in the veins,
becomes more simple ; but more accurate studies are here
still necessary. In small trunks of 0.2 to 0.3 mm., the four
characteristic vascular layers have been found still present.

The adventitia, media and serosa gradually disappear, and

THE LYMPHATICS AND LYMPHATIC GLANDS.

103

we have remaining only the endothelial tube with cells simi-
lar to those of the blood-vessels. Here also we still meet
with valves and isolated nodal or ampulla-like enlargements.
Such vessels remain distinctly demarcated from the immedi-
ate neighborhood. The relation of these passages to the
blood-vessels varies greatly. For the most part, both vessels
simply run alongside of each other. Not unfrequently an
arterial branch is accompanied by a pair of lymphatic canals.
One may then readily commit an error, namely, the assump-
tion that the blood current is invested by a lymphatic. The
latter condition does, indeed, actually take place (Fig. 88, c),
although rarely, as many assert.

At last, however, the appearance of the lymphatics changes ;
the outer surface of our vascular cells has now grown firmly
together with the surrounding tissues ;
thus there arises at the first examination
the impression of a cavity and cleft. For-
merly this was generally considered to be
the true interpretation, until the employ-
ment of the dilute solution of nitrate of
silver opened our eyes (Fig. 98, a).

For the examination of the finest termi-
nal lymphatics, artificial injections are nat-
urally again requisite ; and, indeed, to a
higher degree than in the capillaries of the
blood passages, where under favorable
conditions the colored cells permit the fine
tubes to stand out. The lymph, a colorless fluid, poor in
cells, does not do this, as is known, and only the chyle ves-
sels, overladen with fat, become at times distinctly prominent
without any further assistance.

But, as is known, the lymphatics have no affluent tube
comparable to an artery ; they show merely a capillary divi-
sion and effluent canals, comparable to the veins. Filling
the latter downwards is, almost without exception, prevented
by the resistance of the valves. A highly celebrated modern
anatomist, Hyrtl, rendered the service of discovering a very

Fig. 98. --Lymphatic ca-
nal from the large intestine
oi the Guinea-pig; a, vas-
cular cells ; 6, spaces be-
tween the same.

104

TENTH LECTURE.

simple and at the same time extremely effective method of
injection. We allude to his " puncturing method."

The point of a fine canule is carefully forced into a tissue
which is thought to contain lymphatics, and an attempt is
made to carefully and slowly inject a wounded lymphatic.
Many of the attempts are, it is true, thoroughly unsuccessful,
still practice makes the master, and with patience and perse-
verance the object is finally accomplished. Teichmann's ele-
gant work on the lymphatics, not to mention others, has
shown this.

Let us commence first with the chyliferous vessels which,
at the termination of an abundant digestion, by their fatty
contents stand out as dark canals.

In the intestinal villus (Fig. 95), there lies, occupying the
axis, a caecal canal (d), surrounded by a looped reticulum of
capillaries (b, b\. Its transverse diameter is 0.0187 to 0.0282
mm. At the first cursory examination it is a lacuna; with
more accurate investigation one recognizes here, as elsewhere,
the thin walls formed of plates of cemented endothelial cells.
The condition just mentioned also characterizes the re-
maining portion of the lymphatics. The canals of the latter

are more irregular, angular
and wider, and situated nearer
the interior. They are again
surrounded by the external,
much finer and more regular
capillary net-work of the
blood current.

Let us now pass from the
intestinal villi, further down-
wards, and examine the infe-
rior flatter portion of the
mucous membrane of the
small intestine in which these
caecal lacteals from the intes-
tinal villi bury themselves.
Let us look at Fig. 99. Here, in connective tissue con-

Fig. 99. — Transverse section through the mu-
cous membrane of the small intestine of the
rabbit (near the surface); ay the reticular con-
nective tissue containing lymph cells; b, lymph
canal ; c, transverse section of a Lieberkuhn's
gland ; the same with the cells ; e, f, g, blood-
vessels.

THE L YMPHA TICS AND L YMPHA TIC GLANDS.

105

taining lymphoid cells (a), we discover the sections of blood-
vessels (e, f, g) and of glands (d and c). Our attention is
then attracted by an oblong cleft (b). It is a lymphatic canal
consisting of endothelium.

Our three drawings, Figs. 100, 101 and 102, contain

further representations of such

lymphatic passages.

The caecal commencements are

quite perceptible in the first two

figures.

Fig. 100. — A colon papilla of the rabbit,
in perpendicular section ; a, arterial ; b,
venous trunk of the submucous tissue ;
c, capillary net-work ; d. descending
venous branch ; e, horizontal lymphatic Fig. 101. — Trachoma gland from the conjunctiva of

(sheathing an artery) ; /, lymph canals of the ox, with injected lymphatics, in vertical section ;
the axial portion ; g; their caecal com- a, submucous lymphatic vessel ; c, its distribution to
mencements. the passages of the follicle b.

Thus far all is clear and intelligible. But we now come
to an uncertain and much disputed territory.

Fig. 102. — From the testicle of the calf. Seminiferous canals seen in more oblique, a, and
more transverse sections, b ; c, blood-vessels ; d, lymphatics.

The connective tissue, this substance which is so infinitely

5*

io6

TENTH LECTURE.

diffused throughout the human body, is permeated by-
millions of clefts and spaces. They receive nutritious plas-
matic or lymphatic fluids, and contain wandering lymphoid
cells. In the serous cavities and sacs we meet with an im-
mense lymphatic lacunar system ; nevertheless, the quantity
of fluid is small.

Now, do these latter lymphatic passages, lined with endothe-
lium, pass over continuously into these connective-tissue canals,
and do the former open into the system of serous caverns ?

It is just these questions which we are now to answer.
Let us tarry for an instant at the latter relations.

A communication of the lym-
phatics with the cavity of the
serous sac has, for several years,
been recognized with certainty.
The names of Recklinghausen,
Ludwig, Dybkowsky, Schweig-
ger-Seidel and Dogiel deserve
mention here.

Recklinghausen discovered at
the under surface of the centrum
tendineum of the rabbit (Fig. 103,
i), between the epithelium, aper-
tures (a) of not inconsiderable size,
or at least greater than the diame-
ter of a red blood corpuscle. He
saw how the milk and color gran-
ules entered here and reached the
lymphatics of the diaphragm.
Other short lateral passages of the
lymphatics were then found to
open into these apertures (2, b).
No further doubt can, therefore,
exist here.

The question assumes a different shape, however, concern-
ing the relation of the above mentioned connective-tissue
chasm to the vascular system.

Fig. 103. — 1. Epithelium of the under
surface of the centrum tendineum of the
rabbit ; a, apertures or stomata ; 2. sec-
tion through the pleura of the dog ; b,
free opening, short, lateral passage of the
lymphatic canal ; 3, epithelium of the me-
diastinum of the latter animal ; a, pores.

THE L YMPHA TICS AND L YMPHA TIC GLANDS. \ 07

According to Recklinghausen, these passages are directly
connected with the lymphatics. He has given them the name
of the "juice canals," a denomination which Waldeyer sub-
sequently changed into "juice clefts."

I regret to be obliged to contradict the former investigator.
The conservative injection teaches nothing of the kind. I
dare to assert this after numerous personal studies, and I ap-
peal, besides, to the testimony of distinguished investigators
in this department of the technology of injection. I mention
the names of Hyrtl, Teichmann, His and Langer. By immod-
erate pressure (in normal life it should never be attained), it
is true, these chasms or stomata become filled with the colored
mass. For an illustration, we refer to the small spaces be-
tween the vascular cells of the lymphatics (Fig. 98, b). We
have distended them inordinately or, perhaps, forced out a
soft substance filling the spaces.

The normal blood-vessels act in a similar manner. Here,
by careful injection, no one fills the "juice clefts" of the
connective tissue. No one could show a direct transition of
the vessel into these passages.

Under abnormal conditions of the living body, however,
with a vascular tube over-filled with blood, the stomata even
here become permeable. If, now, the cadaver be artificially
injected, the colored substance penetrates these juice passages
(von Winiwarter, Arnold).

Thus we regard the matter at present.

Important constituents of the lymphatic apparatus of the
mammalia are represented by the lymph-nodes or, as they
were earlier less happily named, the lymphatic glands. They
interrupt the course of the vessels simply or manifoldly.
They are to be denoted as one of the chief forming places of
the lymphoid cells. Within them takes place, furthermore,
a lively reciprocative action between the lymph and the
blood.

A lymphatic gland may appear globular, oval, or bean-shaped
(Fig. 104). In the latter case it presents a so-called hilus
most distinctly. When the former has reached a certain size,

io8

TENTH LECTURE.

induction lymphatic vessels, vasa afferentia, penetrate, for the
most part manifoldly, into its convex surface (f,f). The
educting vessel at the hilus (A) remains, at the same time,
frequently single.

Fig. 104. — Section through one of the smaller lymphatic glands, with the current of the
lymph — half diagramatic figure ; a, the capsule; 6, septa between the follicles of the cortex
(d) ; c, system of septa of the medullary substance as far as the hilus of the organ ; e, lymph
tubes of the medulla ; f, lymphatic passages, which surround the follicles and flow through
the spaces of the medulla ; g, union of the latter into an afferent vessel (/i) at the hilus.

It is surrounded by a connective -tissue sheath (Fig. 104, *,
T05, f) with a muscular admixture. This capsule continues
inwards in a similarly constituted but perforated septum (Fig.
104, b, c, 105, g, k), which finally unites towards the hilus in a
thicker connective tissue mass (" hilus-stroma " of His). In
the lymphatic glands of large animals this " septum system "
is immensely developed ; in small creatures it is often uncom-
monly slight.

We distinguish in the lymphatic glands a cortical and a
medullary layer. The former consists of rounded or irregular
bodies of 0.5 to 2 mm. and more, the follicles (d), which in the
smaller organs are placed in single, and in larger glands in
double or manifold rows.

The medullary substance is composed of reticularly united
strands, which spring from the inner side of the follicle, pass
through the septum, and thus constitute a connection be-
tween these structures of the cortical layer (Fig. 104,^,105,
d, e). The transverse diameter of the strands varies extraor-
dinarily, from 0.04 too. 13 mm. and more.

THE L YMPHA TICS AND L YMPHA TIC GLANDS. \ 09

The follicles and medullary strands are never closely applied
to the sheath and septa (Figs. 104, 105 ) ; a system of clefts is
always left. We shall soon learn their signification.

The follicle (Fig. 105) consists of reticular connective tissue

Fig. 105. — Follicle from a lymphatic gland of the dog, in vertical section ; a, reticular frame-
work of the more external, ^, of the internal portion ; c, fine reticulum of the surface of the follicle ;
ei, origin of a larger, and e of a finer lymph tube ; f, capsule : g; septa ; k, division of the one ; i, in-
vestment space and its tenter-fibres ; k, vas afferens ; /, attachment of the lymph tubes to the septa.

(Fig. 105, b and a), containing an excessive number of lym-
phoid cells. At the surface the meshes of the connective
tissue reticulum become much more narrow (c).

From it arise fibres which, attached to the inner side of the
capsule and the outer surface of the septa, keep the follicle
stretched, as the frame does embroidery. I once named them
" tenter-fibres," and the cup-like spaces permeated by them,
the "investment spaces" of the follicle (?'). The follicles
themselves are held together in numbers, side by side, by
connecting bridges of their own tissue.

The same tissue, containing lymphoid cells, and having
either its own vessel in its axis (Fig. 105, d, e, 106, a) or an
entire rectilinear capillary reticulum (Fig. 107, a), forms the

no

TENTH LECTURE.

strands and reticulum of strands of the medullary substance.
These "lymphatic tubes" are again, according to my dem-
onstration, attached by similar tenter-fibres (b) to the septa
(Figs. 105, /, and 107, £),and
also connected together by a
connective-tissue cellular net-
work.

Kig. 106. — Lymph tube
from a mesenteric gland of
the dog : a, capillary vessel ;
b, reticular connective tissue,
forming the tube.

Fig. 107.- — From the medullary sub-
stance of an inguinal lymphatic gland
of the ox ; a, lymph tube with the com-
plicated system of vessels ', c, piece of
another: d, septa; 6, connecting
fibres between the tube and septum.

The lacuna system between the lymphatic tubes we call
the lymphafics of the medullary substance. That this arises
from the investment spaces of the follicle is taught by the Fig-
ures 104, e, and 105, i, I.

The blood-vessels attain the interior of the organ, for the
most part, from the hilus. The arterial affluent, and venous
effluent tubes are contained in isolated lymphatic tubes. In
the follicles they form a broad-meshed, rounded, capillary net-
work.

Besides these, other smaller vascular branches, surrounded
by tenter-fibres, may enter our organ from the capsule.

What purpose is served by these spaces or canal -work be-
tween the capsule and septum system, on the one hand, and
the follicles and lymph tubes on the other ?

We have already answered this. It is the path of the
lymph in the interior of the organ.

On perforating the capsule, the vasa afferentia lose their
walls (Fig. 105, h)\ they become lacunar passages, but are, it

THE L YMPHA TICS AND L YMPHA TIC GLANDS. \ \ \

is true, still lined with the familiar endothelium in the cortex.
In the medullary substance the latter cells are absent. The
vas efferens, with its independent parietes, is again formed
towards the hilus by the conjunction of the medullary canals.
The formation of the vas efferens is not easy to examine, as
I, the discoverer of this condition, know from former studies.
Fig. 104,/,^, k, represents this current.

Under natural conditions, there are also lying in the cav-
ernous passages of our organ, numerous lymphoid cells.

Whence come the latter ? They have simply, we remark,
emigrated actively and passively through the narrow-meshed,
reticular surfaces of the follicles and lymphatic tubes. We
thus comprehend that a vas afferens may present merely a
few lymphoid cells, while the vas efferens may subsequently
appear relatively rich in these cellular elements.

I do not need to remark that the current of fluid through
the lymphatic gland can only be determined by the aid of
troublesome artificial injections, as His and I can affirm. My
studies were, at that time, the first.

ELEVENTH LECTURE.

THE REMAINING LYMPHOID ORGANS WITH THE SPLEEN.
THE SO-CALLED BLOOD-VASCULAR GLANDS.

STRUCTURES, which are identical with the follicles of a lym-
phatic node, and appear partly single, partly grouped, but
are always without the medullary substance of the former,
are met with manifoldly in the human and mammalial body.
In older times they were given the erroneous name of
"glands."

Among these are included, as isolated occurrences, the
so-called lenticular glands of the gastric mucous membrane;
furthermore, the follicles in the mucous membrane of the
small and large intestine, to which has been assigned the
name of the solitary glands. Groups of lymphoid follicles
form the amygdale or tonsils, then the Peyer's glands of the
intestinal canal, as well as the so-called trachoma glands or
lymphoid follicles of the conjunctiva. A large allied organ
of the earlier period of life is presented in the thoracic gland
or thymus. Finally, the spleen, with a similar although con-
siderably modified structure, terminates this series.

We comprehend all these, including the lymphatic nodes,
under the denomination of the " lymphoid " organs.

Commencing with a so-called solitary gland of the gastric
or intestinal mucous membrane, we find it to be an ordinary
lymphoid follicle surrounded by a cup-like cavity. The
latter is again permeated by connective-tissue fibres which,
passing to the tissue of the adjacent mucous membrane, con-
stitute the connection with the neighborhood. The so-called
solitary glands of the small intestine — as I ascertained years
ago by injection — are again washed by the lymph. In
regard to the "lenticular glands" of the stomach, the authen-

LYMPHOID ORGANS.

i'3

tication has not yet been furnished, but the facts are undoubt-
edly the same.

Let us now pass from the simple to the complicated.

Let us take the amygdale or tonsils (Fig. 108). These,
subjected to many changes in the mammalia, show in the

Fig. ioS. — Tonsil of the adult (after Schmidt); a, larger excretory duct ; b, more simple one ;
c, lymphoid parietal layer, with follicles ; d, lobule, reminding one of a lingual follicle ; e, superficial ;
f, deeper mucous follicle.

human body a complicated system of fossse in the surface of the
mucous membrane. The passages of these depressions open
in part conjointly (a), in part separately (b). At the peri-
phery of the follicular aggregation, there are often still smaller
and shallower fossae (c). The cavities are lined with the
pavement epithelium of the mouth. A thick, lymphoid
parietal layer (c), surrounded externally by a connective-
tissue capsule, invests the entire system of fossae. In this
lymphoid tissue occur rounded bodies of a large-meshed
structure and a brighter appearance. These are the follicles.
In the narrow-meshed connecting tissue, one recognizes
reticular passages which circumvallate these bodies. They
form the paths for the lymph, as the injection shows.

Simplified formations are presented by the lingual follicles
on the posterior portion of the dorsum of the tongue. Their
structure reminds one of the place d of our Fig. 108.

The so-called trachoma glands have a similar structure, but
spread out flatter, and are without fossae (Fig. ioi). They
likewise present brighter follicles (b), as well as a narrower-
meshed and therefore, again, more opaque connecting layer.
In the latter runs a more developed lymphatic canal-work (c),

U4

ELEVENTH LECTURE.

which surrounds the follicle with a reticular passage, and com
mences in a caecal manner just beneath the epithelium.

Let us also discuss the Peyerian glandular plates. They
belong to the lower portions of the human small intestine,
and consist, according to their extent, of a very unequal
number of aggregated lymphoid follicles. In mammals, where
however great mutability prevails, they may also be met
with in the large intestine. The human processus vermi-
formis, and in still higher development that of the rabbit,
forms an enormously developed continuous Peyer's plate.

The shape of our follicle changes according to the species
of animal. They are rounded in man (Fig. 109) and in the
Guinea-pig, and strawberry-shaped in the small intestine of
the rabbit, while in the vermiform process of the latter animal

Fig. 109. — Vertical section through a human Peyer's patch : a, intestinal villi; h, Lieberlciihn-
ian glands ; c, muscular layer of the mucous membrane ; d, apex of the follicle ; f, basis portion ;
g; lymph-passages around the follicle ; i, at the base of the same ; k, lymphatics of the sub-mucous
tissue ; /, lymphoid tissue of the latter.

an elongated thing, reminding one of the sole of a shoe, is
met with. A similar appearance is presented by the Peyerian
follicles in the ileum of the ox.

Let us now pass to a closer analysis of our structure.

LYMPHOID ORGANS.

115

In the follicle (Fig. 109), we distinguish three parts, the
apex (d), covered only by epithelium, and projecting between
adjacent villi (a) into the lumen of the intestine, then a middle
zone (at the elevation of c), and, finally, a basis portion (/).
The middle zone and basis portion are buried in the sub-mu-
cous cellular tissue. Here — and we are reminded of the tonsils
and trachoma follicles — the middle and lower portions are
united by a more narrow-meshed lymphoid tissue. The sur-
faces of both these parts are again surrounded by a lymphatic
canal-work in a reticular form. Not so in the follicles in the
small intestine of the ox, and in the processus vermiformis of
the rabbit. In these the basis portion is surrounded, similar
to the follicles of a lymphatic gland, by a connected cup-like

JU

Fig. iio. — Transverse section, through the equatorial plane of three Peyerian follicles of the
rabbit ; a, the capillary net-work ; b, the larger annular-shaped vessels.

lymphatic investment space, while in the middle zone, it is
true, the reticular passages are still retained.

The lymphatic injection shows interesting conditions, re-
minding us of those of the lymphatic glands, and the discover-

1 1 6 ELE VEN TH LECTURE.

ies made in the tonsils and trachoma follicles confirm what
follows.

The chyle vessels of the intestinal villi (a), are the vasa
afferentia (p. 108). Passing further down, they form the
lymphatic net-work {g, i), which surrounds the follicle, as the
thread does the toy ball of the child. From these arise, at
the base of the follicle, the efferent lymphatics (/<;), compar-
able to the vas efferens of the lymphatic gland.

The capillary net-work of the Peyer's plates appears extra-
ordinarily developed. Fine capillaries permeate the follicle
in a radial direction (Fig. no, a) ; additional tubes (b) form
a no less elegant interfollicular net-work.

The thymus consists of lobular groups of a reticular con-
nective tissue containing lymphoid cells. The interior of the
lobule is hollow, connected on all sides with a convoluted
main canal. Here we also meet with an elegant capillary retic-
ulum, which differs in man and the calf in the arterial and
venous arrangement. The lymphatic passages require more
accurate investigation. The retrogression of the enigmatical
organ begins before and with puberty. Fat cells in great
quantity are developed at the expense of the lymphoid tissue.

The spleen constitutes the most difficult organ of the lym-
phoid group. It has been the object of many researches in old
and modern times. We have, indeed, progressed further than
our predecessors, but much still remains a matter of contro-
versy. I here give only what I, after numerous personal
studies, regard as correct.

Similar to a lymphatic gland, our organ is surrounded by a
fibrous envelope containing sometimes more, sometimes less
smooth muscular tissue. This sends off again, in an inward
direction, an interrupted system of septa. The latter, also
called the trabecular system of the spleen, is extensively de-
veloped in large mammals, while in small creatures (marmot,
rabbit, Guinea-pig, rat and mouse) only scanty rudiments of
it are met with. We are, therefore, once more reminded of
the lymphatic glands (p. 108).

It is best to commence the investigation with one of the latter

L YMPHOID OR GA NS.

117

creatures, a rabbit (Fig. in), for instance. In the larger
mammals, this system of septa considerably impedes our com-
prehension of the relations, which is already difficult.

The soft spleen tissue proper consists of two substances.
In the first place, we find, scattered throughout the entire
thickness of the organ, rounded, oblong or irregular structures

Fig. nr. — Rabbit's spleen ; a, Malpighian corpuscles ; b, reticular frame-work of the pulp.

of a whitish color. Sometimes they stand out sharply, at
others they can only be recognized with difficulty. In many
species of animals they are observed crowded, in others more
scanty. Their size slowly decreases in the smaller mammalia.
These are the Malpighian corpuscles of the spleen or — let us
say at once — the lymphoid follicles of our organ (a).

Between them appears a very soft, and in consequence of
its immense wealth of blood, dark red mass, the so-called
spleen-pulp. The microscopic analysis of the same shows a
system of reticularly connected canals (&), which connect
adjacent Malpighian corpuscles with each other, and leave a
likewise retiform space — 01 cavernous system between them.
The pulp is, therefore, suggestive of the medullary substance
of the lymphatic glands, as are the Malpighian corpuscles of
the follicles of the latter.

n8

ELEVENTH LECTURE.

Both portions of the spleen tissue are, however, shoved
through each other ; it is, therefore, impossible to speak here
of a special, cortical, or medullary layer.

We next examine the lymphoid follicle ; and here we again
meet with the old familiar reticular connective tissue, filled
with an excess of lymphoid cells, forming in the interior a
larger meshed, on the surface a more narrow meshed reticu-
lum. The capillaries of the interior are also readily recog-
nized.

The tissue — we repeat — of the pulp strands (Fig. 112,0)

112. —From the pulp of the human spleen brushed preparation (combination); a, pulp
with the delicate reticular frame-work ; b, transverse section of the caverni ; c, longitudinal

Fig.

Strand Wltll UlC LlCIIUdlU ICUtUlitl UdUlCV^UlK . t/, L! J 1 1.1 V^i SC 3CULIU11 KJl LIIC L4VCHI1 , L I ' ' I I ^ 1 I i 1 ' 1 1 1 I . I

section of such a one; d, capillary vessel in a pulp tube dividing up at e ; f, epithelium of the
venous canal; g, side view of the latter ; h, its transverse section.

arising from the surfaces of the Malpighian corpuscles pre-
sents, on the contrary, a considerable modification of the
reticular connective substance, of extremely fine delicate tex-
ture and with very small meshes, so that only one or a few
lymphoid cells find room in the latter. The surface of this
pulp tube preserves the same reticular character. If we
adjust the focus to the fundus of the caverni invested by them,
we find numerous transversely arranged fibres (c). These pas-
sages are lined with flat, spindle-shaped cells (/), which,
indeed, as the transverse section {b) teaches, have globular
nuclei. We have once more before us a vascular endothelium ;

LYMPHOID ORGANS.

119

only its cell borders are, by way of exception, not cemented
to each other. If we also add to this that capillaries run in
the axis of the pulp strands, and that in the narrow reticulum
of its tissue regular red blood corpuscles are met with, some-
times fresh and unchanged, sometimes shrivelled and in va-
rious stages of disintegration, we have then described the
most essential portion of the structure of the tissue of the
spleen.

In order, however, to gain a further insight, we must now
turn to the vascular arrangement of this strange organ.

This is very complicated and quite peculiar, and it is just
here that the views of investigators are diametrically opposed
to each other.

The arteria lienalis buries itself, in the ruminantia unrami-
fied, otherwise, as a rule, with several branches, directly into
the so-called hilus. The latter become further divided in the
interior, and finally break up, at an acute angle, into a number
of fine terminal branches. These, called penicilli, and pecu-
liarly formed, resemble the branches of a willow stripped of
its foliage. On these branches (but no longer on the penicil-
lus) sit the familiar Malpighian corpuscles, like the berries on
the stem of the grape.

The arteries and the veins are still invested by a connec-
tive-tissue sheath, which is continuous with the septum sys-
tem of the organ. This sheath, like the entire vascular
expansion, is very different in the several varieties of animals;
it is slight and rudimentary in the small, complicated and
thick in the large mammalia.

Pausing now, however, at that of man, we find the arteries
and veins, already divided into 4 to 6 branches, passing in and
out of the organ. Up to trunks of 0.2 mm. they are invest-
ed in common by a connective-tissue sheath. The latter has
at first a parietal thickness of about 0.25 mm., diminishing
to O.i mm., whereby arteries of 0.2 and veins of 0.4 mm.
are still invested in common. There is now a gradual sepa-
ration of the venous from the arterial branches. The sheath
in its original condition is continuous for a less distance over

120 ELEVENTH LECTURE.

the arteries ; it is gradually changed into a reticular connec-
tive tissue containing lymphoid cells, a metamorphosis in
which the adventitia soon participates. The sheath struc-
ture is extended somewhat further over the venous branch ;
at last its fibres begin to separate, and it is also lost in the sep-
tum or trabecular system of our organ.

From this lymphoid metamorphosis of the artery arise the
already familiar Malpighian corpuscles of the spleen. They
lie in part on the point of ramification of arterial branches,
in part laterally on the unramified vascular tube. Finally —
and it is a frequent occurrence — the arterial branch passes
through the centre of the follicle. If we examine more
closely, we find that no line of demarcation can be drawn
between the separate follicles and this elongated lymphoid
covering of the arterial branch. Every Guinea-pig's spleen
teaches us this.

In the follicle, we never meet with a venous branch, but,
rather, a capillary reticulum with rounded meshes, sometimes
scantily and poorly developed, sometimes more abundantly.
The source of supply varies ; sometimes it is branches of the
follicular artery, sometimes it is through the adjacent pulp-
tubes.

We have now to follow the further course of the arterial
offshoots, the so called penicilli of the spleen. They enter
the pulp-tubes of our organ, to pass through their axis and
to become capillaries. The capillary reticulum of the Mal-
pighian corpuscle also, at last, sends its offshoots down into
the adjacent pulp-tubes (Fig. 113, e).

Now, these capillaries of the pulp-tubes are quite peculiar.

We follow them by the greatest attention for a certain dis-
tance (on an uninjected spleen or in a good injected prepara-
tion), then the capillaries (Fig. 112, d) commence to be
uncertain and indistinct [e). Separated cell-demarcations
may still be recognized ; but soon even these disappear. We
are in the presence of a lacuna — a finest blood current with-
out walls (Fig. 113, e).

Let us recall to mind that the tissue of the pulp-tube pre-

L ] 'MP HOW OR GA NS.

121

sents a reticulum with very narrow meshes, in the interspaces
of which one, or, at the most, a few lymphoid cells find
place; and let us not forget that the pulp-tubes possess, su-
perficially, the same reticular character, covered by an en-
dothelium consisting of separate, uncemented cells.

Fig. 113. — From the spleen of the hedgehog ; a, pulp, with the intermediate currents ; h, fol-
licle ; c, boundary layer of the same : g, its capillaries ; e, transition of the same into the interme-
diate pulp-current ; f, transverse section of an arterial branch, at the border of the Malpighian
corpuscles.

If we adhere to this previously described textural condi-
tion, the lacunar capillary blood current, which arises after
the loss of the capillary walls, will present no further con-
siderable difficulty. As the failing branch of a drying brook
wanders at last between the pebbles of its bed, slender and
scanty, so is it with these finest blood currents. The lym-
phoid cells resemble the pebbles.

Still, the blood current contains cellular elements and the
red blood corpuscles in excess. A portion of the latter
slip through with their pliable, smooth surface ; others stick
fast.

For our colored elements, however, as we have already
learned, movement is life, rest is death. Thus are explained
those numerous corpses and fragments of the colored blood
cells in the spleen, which we mentioned above (p. 119).

Something additional is also satisfactorily explained by
this. The closely crowded amoeboid lymph cells are capable
of taking up into themselves the imprisoned blood corpuscle
6

122

ELEVENTH LECTURE.

or the fragments of its corpse (p. 9). These are the blood-
corpuscle-containing cells of the spleen, occurrences which,
many years ago, caused so much racking of the brains, and
yet are, at present, so easy to interpret. Let us remember
the amoeba of our Fig. 3.

We have remembered the dead : let us now return to the
living. What becomes of these finest blood currents after they
have successfully passed through the narrow mesh-work of
the pulp-tubes ?

If our description has thus far been altogether comprehen-
sible, the answer follows of itself. These currents enter the
system of caverni, which Fig. 1 12 shows between the pulp-
tubes b and c.

Let us pause for a moment. If we inject a rabbit's and a
Guinea-pig's spleen, or the organ of a new-born child, from

the vena lienalis, it is a mere child's
play to instantly fill these reticular
spaces between the pulp-tubes
(Fig. 114, c).

Thus — we return to the inverted
course once more — the lacunar
pulp current passes over into these
spaces of the pulp, into the " cav-
ernous veins " of Billroth. From
the latter, presenting many di-
versities, it is true, according to
the variety of animal, arise two
veins {d), enclosed in continuous
although very thin walls.
We said previously (p. 121) the spleen was a burying- place
of the red blood corpuscles. This requires no further discus-
sion now. On the other hand, however, the spleen forms a
generating focus of these elements, since it contributes lym-
phoid cells, the substitutes of those colored elements, to the
blood current. This also requires no further discussion ; cer-
tainly not, when we recall to mind the reticular surfaces of
the Malpighian corpuscles, and of the pulp-tubes, and when

— d

Fig. 114. — From the sheep's spleen
(double injection) ; a, reticular frame-
work of the pulp ; i, intermediate pulp
current ; c, its continuation into the ve-
nous roots, with incomplete walls ; d,
venous branch.

LYMPHOID ORGANS. 1 23

we think that milliards of lymphoid cells are here surrounded
by perforated surfaces.

When our organ becomes enlarged in its pulp, the contact
surfaces between the blood current and the lymphoid tissue
increase materially. The latter now sends off more con-
siderable quantities of its cells into the former. The number
of the colorless blood corpuscles is thus necessarily increased.
This is the lienal leucaemia, as it is called by the doctors, a
disturbance of the equilibrium between the blood and spleen
tissue, with the saddest consequences.

Lymphatic passages occur with certainty in the capsular
and trabecular systems of the spleen. As to what is thought
to have been met with in the true lymphoid tissue, it stands
on a weak foundation.

In the embarrassment of our knowledge we here include
several parts of the body which a former epoch has, like the
lymphoid organs described, also called "glands," and for
which their successors found the likewise very unsatisfactory
name of the "blood-vascular glands."

We speak of the thyroid gland, the suprarenal capsule and
the apophysis cerebri, structures which to the present time
mock all physiological explanation, and once more confirm
the old saying, that even the trees do not grow up into
heaven.

The thyroid gland, the glandula thyroidea of the anatomist,
lies, as is known, in front of the respiratory passage leading
to the lungs. Every one in the Canton of Zurich knows
that it forms the goitre, that national decoration. We physi-
ologists are, unfortunately, scarcely able to say more con-
cerning it than the people.

Let us, then, examine the strange organ somewhat more
closely.

In a connective tissue frame-work we meet, closely ap-
proached to each other, rounded, oblong or even more irreg-
ular cavities of 0.05 to o. 1 mm. The inner wall is beset
with a single layer of low cylindrical cells, 0. 02 mm. high and
O.oi wide. The cavity is filled at an early period with a

I2/|

ELEVENTH LECTURE.

Fig. 115. — Colloid metamor-
phosis of the thyroid gland ;
a, gland-vesicle of the rabbit ; b,
commencing colloid metamor-
phosis of the calf.

homogeneous firm mass, an obscure derivative of the albu-
minous bodies, the so-called colloid. In the interstitial con-
nective tissue we meet with a developed,
round-meshed reticulum of blood capil-
laries 0.02 to 0.023 mm- broad ; together
with these there is a widely extended
lymphatic canal-work. How far it
stretches, whether it finally circumvo-
lutes each cavity in a cap-like manner,
as Boechat recently asserted, requires
more accurate investigation. Previous
injection studies by myself and Pere-
meschko showed nothing of the kind.

At a later period of life — and the
thyroid gland appears to grow old
early — this colloid substance seems to
increase more and more. The cavities
become distended, the small parietal
cells are more and more compressed, and with them the in-
terstitial connective tissue. In the further progress, these
cavities flow together, forming larger ones.

It is assumed of the thyroid gland, like the apophysis cere-
bri and the suprarenal capsule entirely hypothetically, that
it removes matters from the blood which, when the same are
further metamorphosed, either indirectly or directly, are
afterwards restored to the central fluid of the organism.
Hence the denomination of the " blood-vascular glands," a
proof of our ignorance at that time.

Just as obscure are the suprarenal capsules, glandular suc-
centuriales, structures which once at an earlier foetal period
possessed an immense size, and subsequently remained more
and more behind.

Here, also, we meet with a double mass, a cortical and a
medullary layer. The former appears to have a radiated dis-
position, brownish, reddish or yellowish. The latter, much
softer, is usually more transparent, grayish, red or yellowish.
The least resistance is possessed by a border zone which in

LYMPHOID ORGANS.

125

i— J

man is clouded and narrow. It liquefies very readily after
death.

A connective-tissue envelope, permeated by elastic ele-
ments, surrounds the organ. Inwards it
forms a frame-work (Fig. 116, b); in
the spaces of the latter lie soft cells.
The superficial cavities are, as a rule,
short ; further inwards they acquire a
radial elongation (a). Transverse sec-
tions of these spaces, which are con-
nected at acute angles, frequently present
oblong and bean-shaped formations. In-
wards, towards the medullary border,
the spaces again become smaller, more
rounded, and the frame-work substance
delicate and reticular, forming a sort of
reticular connective tissue (Joesten).

The contents consist of coarse, granu-
lar, membraneless cells, closely pressed
against each other, and containing mole-
cules of albumen and fat. The cells
measure 0.0135 to 0.0174 mm., with
nuclei of 0.0056 to 0.0090 mm. In the
boundary zone, towards the medullary
substance, our cells lodge abundant brownish pigment mole-
cules. A delicate connective tissue fibro-reticulum also per-
meates these cavities, which have no membrana propria.

It is likewise not easy to investigate the soft medullary
substance.

The connective-tissue frame-work having again become
somewhat more resistent, and at last fused with the connec-
tive tissue surrounding the veins, forms large oval cavities.
They are larger than the peripheral ones of the cortical layer,
without the radiated disposition of the latter. They turn
their broad side, on the contrary, towards the surface of the
organ. The medullary cavities are, however, rounder and
smaller in man.

Fig. 116. — Cortex of the hu-
man suprarenal gland ; d,
gland cylinder ; 6, interstitial
connective tissue.

126 ELEVENTH LECTURE.

In them occur, closely crowded, delicate granular cells,
measuring 0.018 to 0.035 mm., with fine vesicular nuclei.
The cells appear, in contradistinction to the cortical elements,
very poor in fat molecules. The behavior of these medul-
lary cells with chromate of potash is very remarkable, as
Henle discovered. They become deeply browned, while the
cortical cells are very slightly changed.

The vascularity is great, and the arrangement of the ves-
sels peculiar in the suprarenal capsules. Numerous small
arterial branches arising from various sources form a capillary
reticulum in the cortex, with elongated meshes. These capil-
laries first combine in the medulla into considerable, but very
thin-walled venous canals. The latter, having likewise a ra-
diated direction, unite at acute angles, and thus largely devel-
oped occupy a considerable portion of the medulla. The
latter large trunks finally open into the very wide veins situ-
ated in the centre of the organ.

The lymphatics are still little known.

In many mammals the medullary mass appears very rich
in nerves, which may form considerable microscopic plexuses.
There was, therefore, an inclination to consider it as related
to the sympathetic.

The pituitary gland, the hypophysis cerebri, is smaller in
the higher vertebrates than in the lower, and consists of two
lobes ; a small posterior one, of a nervous texture, and a
larger anterior one, with the structure of a blood-vascular
gland. Through the latter passes a canal lined sometimes
with flattened epithelium (mammals), sometimes with ciliated
cells, and which sinks into the infundibulum (Peremeschko).
Rounded and oval, 0.0496 to 0.0699 mm. large gland spaces
are enclosed by a connective tissue, rich in capillaries. In its
interstices lie cells measuring 0.014 mm., with a consider-
able finely granular body. Colloid metamorphosis may be
noticed.

The name of the coccygeal gland, glandula coccygea, has
been bestowed on a small thing situated at the apex of the
coccyx. It consists of a system of diverticulated arterial

LYMPHOID ORGANS.

127

branches of capillaries and veins, invested externally by gran-
ular cells.

The so-called ganglion intercaroticum also has a nearly
related structure.

The granulated cells, such as we are familiar with in the
suprarenal capsule, apophysis cerebri, and the two last named
organs, belong to the form of coarsely granular connective-
tissue cells that are so often met with in the neighborhood of
the vessels (Fig. 55, b).

TWELFTH LECTURE.

GLAND TISSUE.

In olden times they were very liberal in their conception
of the glands. We have already learned this in the lym-
phoid organs, as well as the thyroid gland, suprarenal capsule
and apophysis cerebri, which preceding generations of anato-
mists erroneously regarded as glands. A rounded, limited
form, and a considerable vascularity was at that time suffi-
cient to stamp a thing as a gland. We thus obtained the
lymphatic, Peyerian, and thyroid glands, etc. Later, the
physiological importance came more into the foreground.
The true glands take materials from the blood, not alone or
only principally in the interest of an egotistical nutrition, but
rather in the service of the whole, whether it be to simply
free the blood from decomposed substances, or to restore the
latter, more or less metamorphosed, and serving for other pur-
poses. On this rests the old distinction of excretion and
secretion.

The gland requires an efferent canal system to remove its
contents. We must lay great weight on this canal in connec-
tion with the gland ; still the former may, under certain cir-
cumstances, be wanting, or may remain separate from the
organ. This is shown by the human ovary. Here the wall
of the glandular cavity is ruptured. The contents of the lat-
ter now escape through a rent. It does not thereby cease
to be a gland, for we know of ovaria- enough in lower ani-
mals which contain quite common glandular formations, pro-
vided with continuous canals.

No doubt can therefore prevail here.

How weak the matter is, however, with the so-called
blood-vascular glands has already been taught by the previ-
ous lecture.

GLAND TISSUE.

129

In modern times, however, the so advanced microscopic
analysis has furnished characteristics which, in our opinion,
permit of the certain recognition of a gland.

Each of our organs (Fig. 117) consists of
two elements: 1st, of an, as a rule, hyaline
and thin membrane, the so-called gland
membrane, membrana propria id) ; and 2d,
of cellular contents (b) enclosed within the
latter.

Without a blood supply, however, secretion
does not take place. A non-vascular gland
would be a nonentity. We therefore meet
with a vascular net-work (c), circumvoluting
the membrana propria, as a third integral
constituent.

As further constituents, we have lymphatic
vessels, muscular elements and nerves.

Let us now pass to the individual analysis.

The gland membrane appears, at the first
examination, homogeneous, and, as a rule,
very delicate. Exceptionally, however, it
may acquire a thickness of 0. 001 to 0.002 mm.
It may also be replaced by undeveloped con-
nective tissue (sebaceous glands of the
skin). Finally, ordinary connective tis-
sue or a muscular layer may form a re-
inforcing stratum around this limiting
membrane.

In more recent times, a manifold sys-
tem of quite flat stellate cells (Fig. 118)
has been met with which, embedded in
or resting on the homogeneous mem-
brana propria, form rib-like thickenings
of the latter, as for example, in the sub-
maxillary and lachrymal glands.

Firm, extensible, and formed of a very unchangeable mate-
rial, probably related to the elastic substance, the membrana
6*

Fig. 117. — A mam-
malian I.ieberkiihniun
gland ; <?, membrana
propria ; /', cells : r
capillaries ; d, gland
aperture.

Fig. 118. — Plexus of star-
shaped, flat, connective-tissue
cells, from the membrana pro-
pria, isolated by maceration.
From the submaxillary gland
of the dog.

130

TWELFTH LECTURE.

propria serves for the transudation and filtration of the blood

plasma.

. . . *

Its origin takes place in the nature of a boundary layer,

formed from the adjacent connective tissue.

The form of the gland or of its constituents
is determined by the membrana propria, or the
connective tissue, by which it is frequently re-
placed. For the organ may, with microscopic
dimensions, remain very simple, while, on the
Other hand (think of the liver and kidney),
with an increased size, it may assume the most
complicated structure.

We distinguish :

I. The tubular glands (Fig. 117). Here,
the membrana propria forms a caecal tube,
generally of considerable length and of rela-
tively slight diameter. Several such ceecal
tubes, invisible to the naked eye, may come
together in a common terminal portion, so
that there is always a more distinct excretory
duct.

Extraordinarily long reticular and caecal Cle-
ric 119. — Aeon- J °

voimcd gland from ments, w^ith many peculiarities, united in im-

the conjunctiva of •? *

lhe calf- mense numbers, constitute the testicle and

kidney. We speak now of the tubular glands.

Another modification is formed by the so-called convo-
luted glands (Fig. 119). The terminal portion of this small
organ presents a peculiar convolution like the coil of a pack
thread.

2. Another uncommonly diffused form is the racemose
gland (Fig. 120). The membrana propria here appears as a
microscopically small, rounded, elongated or irregularly
formed saccule." These " gland vesicles " are united at their
openings in groups, and in this manner a lobule or acinus is

* It has been proposed to include the small racemose structures of the mucous
membrane among the ;< tubular" glands, on account of their elongated saccules.

GLAND TISSUE.

131

Fig. 120. — Human racemose pala-
tine glands.

formed. It may acquire an excretory duct, and then the race-
mose gland, in its smallest and most simple form, is complete.
But these most elementary structures
are rare. As a rule (Fig. 120), several
acini form the still small gland body.
In larger and large organs the num-
ber of the gland lobules becomes
very great.

It is scarcely necessary to remark
that transitions occur between the
tubular and racemose glands.

3. Finally, we have another gland
with closed rounded gland capsules,
which latter are contained in abun-
dant connective tissue. This is the ovary. These rounded
.structures, which are constituted by a connective-tissue wall,
are called the Graafian follicles. Among the cells it con-
tains, one is noted for its size. This is the ovum (Fig. 5).

That the latter becomes free by the rupture of the follicular
wall, we have mentioned above. Let us also add that the
ruptured follicle is incapable of further repair, but rather goes
to ruin by a process of cicatrization. The conditions are,
therefore, in contradistinction to those presented by other
glands, peculiar and anomalous enough. a

The second and much more important constituent of our
organ is presented by the gland cells. We shall subsequently
see that they are nearly all derivatives of Remak's corneous
and intestinal-gland layer. Even in subsequent life, this epi-
thelial character is not renounced.

The inner surfaces of the membrana propria are thus lined,
sometimes simply, sometimes in strata. In the excretory
portion of the gland, an ordinary epithelium subsequently
makes its appearance. The gland cell may be called a micro-
scopically small chemical laboratory. With its body it forms
the secretion, or changes the formative material received
from the blood into the latter.

For this purpose our cells require

a certain magnitude.

132

TWELFTH LECTURE.

We shall, therefore, comprehend that those cells, flattened
into the thinnest plates, such as we previously met with in the
pavement epithelium, are absent.

The gland cell is a membraneless, cubical thing, occasion-
ally somewhat flattened from above downwards, in other
cases rendered cylindrical by lateral compression. The for-
mer shape is represented by the cells of the liver, with a size
of 0.018 to 0.226 mm. (Fig. 121). The cells (Fig. 122, b) of the
" gastric mucous glands " of the dog are taller and more slen-
der. The elements of the Lieberkiihnian
glandular tubes of the small intestine have
likewise assumed the cylindrical form, as our
Fig. 117, b (representing a longitudinal sec-
tion of this tube) teaches.

Gland cells covered with ciliae are verv
rarely met with in man. They are only
known in the uterine tubes.

Many gland cells — we here allude chiefly
to those of the liver and kidney — appear
to constitute tolerably permanent structures.
In others the cellular elements retain the
great perishability of the epithelium, and
perish in the formation of the secretion.

Let us take, for example, a sebaceous
gland of the external integument, a small
clustered structure. An acinus is shown in
Fig. 123, A.

It is covered by several cell layers. In
the cavity (/;) we meet with a fatty mass,
which subsequently becomes free as sebum
cutaneum.

How has the latter been formed ?
In the peripherical cells, those lying im-
mediately against the wall of the gland
vesicle, one already notices an increasing deposit of fat
molecules. This is, therefore, the fatty degeneration which
we have already mentioned at page 13. It causes the

Fie;. 121. — Human
liver cells.

Fig. 122. — From a gas-
tric mucous gland of the
dog ; a, lower portion of
the excretory duct ; />,
commencement of the
glandular canal.

GLAND TISSUE.

133

retrogression of the tissue elements in a normal wav here,
as by a pathological process elsewhere. The gland cell
swells with the increasing embedment of fat, and finally falls
from its matrix. Suspended in the cavity of the acinus, it
has now become a corpse. We meet, accordingly, in the

Fig. 123. — A, the vesicle of a sebaceous gland; a, the gland-cells resting on the wall; b.
those which have been cast off, containing fat and filling the cavity ; B, the cells more highly mag-
nified ; a, smaller ones, poorer in fat and belonging to the wall ; ^.larger ones, more abundantly
filled with fat; c, a cell with larger fat drops joined together, and d one with a single drop of fat;
e,f, cells whose fat has partially escaped.

sebum with these cells fatty degenerated to a high degree,
with their fragments, their nuclei which have become free, and
fat molecules with an albuminous connecting substance. This
is the origin of the sebum cutaneum, a relatively unimpor-
tant secretion.

The lacteal gland consists of a group of enlarged sebaceous
glands, destined for a higher performance.
Even before the final period of pregnancy,
the human organ forms the so-called colos-
trum. We meet in the latter with globular
cellular elements ofo.0151 to 0.0563 mm. in
size (Fig. 124, b).

These " colostrum corpuscles " are simi-
lar to the detached, highly fatty, sebaceous
follicle cells. Subsequently, soon after the
delivery, the milk contains millions of the so-
called milk globules (a). They are drops of
fat which have become free, and are surrounded by a very
thin shell of a coagulated albuminous body, which is usually

o

9 O

0

,0

,0

Fig. 124. — Elemen-
tary forms of human
milk ; a, milk globule ;
b, colostrum corpuscle.

134

TWELFTH LECTURE.

called caseine. Their size varies between 0.003 to 0.009 mm.
The gland cells should now, with a far more energetic secre-
tion in the acinus, have been early destroyed. A different
view might, however, be entertained. The membraneless
cells may have thrown out the elaborated secretion, as the
crater of the volcano does the lava — -only the cells, like the
volcano, may persist. I regard this as indeed very plausible.
We have just spoken of probably the most perishable gland
elements, immediately after the discussion of more permanent
elements. Let us now return to the latter for an instant,
taking up the liver cells. One meets in them, from time to
time, with brownish molecules and drops of fat. Both ap-
pear subsequently in the bile ; the former is the " biliary
coloring matter " (to repeat a crude expression of former
days), the latter becomes " cholesterine." Therefore, even
here, the gland cell once enclosed in its body the secretory
substance which subsequently becomes free. Here the com-
ing and going of the latter through the permanent cell body
is not to be doubted.

A still further confirmation of the persistence of many
gland cells has been more recently obtained. Extraordinarily
fine permanent canaliculi, "the gland capillaries" (first found

in the liver), occur between the gland cells
as the terminal offshoots of the excretory
ducts. Our Fig. 125 represents such from
the pancreas. We shall, later, refer to
the matter more in detail.

With the membrana propria and the
secretory cells we are, therefore, finished.
Let us now refer to the capillary reticu-
lum, the art and manner in which the in-
dispensable blood current reaches the
surface of the secreting organ.

We repeat what we said at page 96.
The form of the tissue elements deter-
mines the arrangement of the capillaries.

With thin and long glandular tubes, such as stand close to

tn. e

Fig. 125. — From the pan-
creas of the rabbit ; a, larger
excretory duct ; £, finer one
of an acinus ; c, finest secre-
tory canal.

GLAND TISSUE.

135

each other in the gastric-mucous membrane, the individual
tubes occupy about the position of the transversely-
striated muscular filament (Fig.
91). The reticulum (Fig. 126)
becomes similarly elongated ;
only the rings around the
gland apertures, together with
anomalous arterial and venous
branches, produce a considera-
ble difference in the thing.

Turning

to

Fig. 126 — The vascular r.et-work of the mu-
cous membrane of the human stomach— semi-
di.uramatic. The (finer) arterial trunk di-
vides into the elongated, capillary net-work,
which passes over into the rounded reticulum
of the gland apertures, from which the vein
(the wider, darker vessel J arises.

the racemose
glands, with the generally
rounded form of the element,
the small acinus, the capillary
net-work must, as we have
already remarked, correspond
to the form of a fat lobule (Fig.
93). Our Fig. 127 represents
the capillary arrangement of a
larger lobular group of the
pancreas. The figure might,
with equal propriety, be used
for the vascular arrangement
of a conglomeration of the lobules of fat cells.

The immense assimilation of glandular organs renders a
considerable wealth of lymphatic passages, which are to re-
store the superfluous transudation to the blood passage, very
appreciable. A portion of these lymphatic passages have
been discovered very recently. Smooth muscular fibres,
which either invest the gland body or occur in the parieties
of the excretory ducts, scarcely require a further physiologi-
cal explanation. They are of great importance for the ex-
pulsion ot the secretion.

Concerning the gland nerves, this most obscure portion of
the structure of the organ in question, we shall speak later.

The last which remains for discussion is the excretory duct.
If we take a simple gland tube (Fig. 128), such as are con-

136

TWELFTH LECTURE.

j Jm.

tained in infinite numbers in the gastric mucous membrane,
and examine a so-called " peptic-gastric gland " (it may also,
it is true, be somewhat more complicated),
we readily recognize from d to b the secre-
tory cells. Over b we meet with a cylindri-
cal epithelium, the same which covers the
surface of the gastric mucous membrane.
A further explanation is, therefore, super-
fluous.

Let us, furthermore, cast a glance back to
our Fig. 122. The drawing represents a so-
called "gastric-mucous gland." A long,

a

m

Fig. 127. — The vascular net work of the rabbit's pancreas.

Fig. 128. — A lateral
view ol a gastric glnnd
of the cat ; a. stomach
cells : b, inner ; r, ex-
ternal inierca'ary por-
tion ; d, the g an<l tube,
with both varieties of
cells.

excretory duct bears the same cylinder cells (a). It then
divides into two caecal tubes. These (b) contain lower
cubical elements, the suppliers of a tolerably unknown secre-
tion.

Let us examine a still earlier figure — our Fig. 120 — the
small racemose glands. No doubt can prevail here concern-

GLAND TISSUE. 1 37

ing the excretory duct. Its cell covering is not rarely different
from that of the acini.

The walLof the excretory canal is here of a connective-tis-
sue nature. In larger, and the largest glands of a similar
structure, the omitted duct acquires an increasing complica-
tion. We shall later return to the particulars.

Let us now take a cursory survey of the different glands
of the human body.

a. To the tubular group belong : the Bowman's glands in
the regio olfactoria of the organ of smell ; the tubes of the
mucous membrane of the stomach, small and large intestine,
which bear the names of the gastric juice glands, or peptic-
gastric glands, or gastric-mucous and Lieberkuhnian tubes ;
finally, the uterine glands. Then, as modified structures, as
so-called convoluted glands, we have, finally, to mention the
smaller and larger sudoriparous glands, together with the ce-
ruminous glands of the ear.

Very complicated tubular organs are, as we previously
mentioned, the kindey and testicle.

b. Among the racemose glands are included a host of our
organs from the smallest to the largest dimensions. First
belong here all the small glands of the mucous membranes
of the body, then the so-called Brunner's glands of the duo-
denum, the sebaceous glands of the skin, and the Meibomian
of the eyelids. As larger and largest, the group includes :
the lachrymal gland, the various salivary glands, the pancreas,
the lacteal glands, then the Cowper's and Bartholinian glands
of the sexual system ; and, furthermore, the prostate.
Finally, according to their manner of origin, the lungs
should also be included here. We shall subsequently have
to refer more particularly to them, as well as to their prede-
cessors.

c. The closed gland capsules. We scarcely need to repeat
that the ovarium forms the only gland of this kind in the hu-
man body.

Our organs, with slight exceptions (the primitive kidney
and the generative glands), originate, in their cellular portions,

138

TWELFTH LECTURE.

either from the upper or lower germinal layer, from the cor-
neous and intestinal gland layer of Remak. The membrana

propria and capillary reticulum are
aggregated productions of the middle
layer, which produces so much.

A previous figure, 41, the primary
rudiment of a hair germ, passes as
well for the glands of the external in-
tegument as for those of the mucous
membrane. When, by a continuous
increase of the cells, lateral buds
branch off from the cellular cone as
it grows downwards, there is formed
at first a solid, slightly berry-shaped
mass (Fig. 129). It finally becomes a
complicated racemose system, which
at last becomes hollow (a), and
thereby constitutes the completed
gland.
With this we leave the glandular organs in general.
The subsequent lectures will, however, carry us back to
certain of them.

Fig. 129. — Developing racemose
gland ; <?, excretory duct, already
permeable ; b, solid gland bud ; c,
membrana propria ; rf, surrounding
connective tissue.

THIRTEENTH LECTURE.

THE DIGESTIVE APPARATUS WITH ITS GLANDS.

The digestive apparatus, in its connective-tissue external
layers and the muscular middle layers, is certainly of a rela-
tively simple nature. The mucous membrane, however, with
the immediately adjacent loose connective tissue, and with all
which is connected with it, presents an abundance of the
most diversified structural relations.

Let us therefore briefly examine the long canal work, with
the varying constituents in its interior.

The oral cavity contains the already described teeth (p. 73),
as well as the tongue. In it open the salivary glands, large
racemose organs, and, together with these, a number of
smaller associates, the so-called mucous glands.

From the vascular mucous membrane of the mouth project
closely crowded papillae. It is covered by the stratified pave-
ment epithelium spoken of at
page 30. The latter may here
acquire a thickness of 0.45 mm.
The submucous connective tissue
appears sometimes dense (gums),
sometimes loose and extensible
(the floor of the mouth). In
it lie the bodies of the numer-
ous small racemose glands. The

secretion is mucus ; the cells

Fig. 130. — Gland vesicles of the palatine
gland of the rabbit ; a, rounded, b, an elon-
gated acinus.

form a layer of pale, cubical or
low cylindrical elements (Fig.
130). They occur as labial, buc-
cal, palatine and lingual glands.

Among the salivary glands the submaxillary has recently
undergone an accurate investigation (Pfliiger, Gianuzzi, Hei-

HO

THIRTEENTH LECTURE.

denhain). Its cells differ in the several animals. The former
are granular in the rabbit. In the dog and cat, on the con-
trary, we find a mucous gland.

The cells (Fig. 131) here consist of two different structures.
Firstly (a), we meet with large rounded elements, which are

filled with a homogeneous
mucous substance. Be-
sides these, quite granular,
smaller cells occur in the
periphery of the gland
vesicle (c). Pressed closely
together, and indistinctly
separated from each other,
they form a sort of cres-
cent (Gianuzzi). They
subsequently change into
those large mucous cells.
The finest secretory capil-
laries, after the manner of
our Fig. 125, likewise
make their appearance
here, as also do the flat
stellate cells of the membrana propria (see Fig. 118). The
excretory ducts show cylinder cells (Fig. 131, d), with longi-
tudinal striations beneath the nucleus. We have, finally, to
mention a rounded capillary reticulum, and abundant lym-
phatics around and between the lobules and lobes.

The sublingual appears to be nearly related to the sub-
maxillary gland.

We cannot, however, yet leave the latter. As experimen-
tal physiology teaches, the irritation of the chorda tympani
produces a profuse watery secretion ; that of the sympa-
thetic, on the contrary, a scanty quantity of a thick fluid
substance.

The continued irritation of the nerves, as Heidenhain ascer-
tained, produces an important change in the contents of the
acini (Fig. 132). Nearly all the large round cells (a) have,

Fig. 131. — The submaxillary g'and of the dog ;
a, mucous cells ; 6, protoplasma cells ; c, crescent :
d, transverse section of an excretory duct, with the
peculiar cylindrical epithelium.

THE DIGESTIVE APPARATUS. 141

in the mean time, given off their mucine as a secretion. A

granular protoplasmatic substance now fills the altered cell
body.

m&

Fig. 132. — Submaxillary gland of the dog, with its contained cells ; a, changed by the strong
irritation of the chorda ; I', those remaining unchanged (after Heidenhain).

This was altogether the first difference which a quies-
cent and active gland presented to the eye of the micros-
copist.

The parotid gland contains in its acinus (measuring 0.034
to 0.052 mm.), granular cubical cells (of 0.014 to 0.018 mm.),
without any mucous metamorphosis. Fine secretory tubes
have been met with between the latter. Here, again, the ex-
cretory duct has ordinary cylinder cells.

The tongue is an essentially muscular organ, with transverse-
ly striated filaments crossing each other. The dorsum of the
tongue has innumerable different papillae. Three forms have
been distinguished here : the filiform (papillae filiformes, s.
conicae), the fungiform (p. fungiformes, s. clavatae), and, finally,
the circumvallated (p. circumvallatae). To the latter have also
been added the so-called papillae foliatae, which were early
discovered, then forgotten, and recently more accurately in-
vestigated. Both the latter organs contain the terminations
of the gustatory nerves.

Our organ is rich in racemose glands. We meet principally
with mucous glands, with the contents rendered familiar to us
by Fig. 130. In the vicinity of the p. circumvallata and the

1 42

THIRTEENTH LECTURE.

Fig. 133. — Acini (a, round, 6, ob-
long) of a serous gland from the
vicinity of a circumvoluted papilla of
the cat.

p. foliata, quite similarly shaped glands appear, it is true, but
they have different anomalous contents, with granular cloudy

cells (Fig. 133). The same organs
have been met with in great numbers
in the nasal mucous membrane, and
they have received the name of the
" serous glands" (Heidenhain).

The tissue of the mucous mem-
brane commences at the posterior
fourth of the tongue to undergo a
lymphoid metamorphosis, in which
the pharynx may also participate.
We thus have demarcated lymphoid
organs, the lingual follicles, the ton-
sils, and the pharyngeal tonsils, discovered by Koelliker
(compare p. 1 13).

The pharynx, with its transversely striated muscles, has the
same covering of stratified pavement epithelium as the oral
cavity. The tough mucous membrane acquires papillae below.
The upper portion is rich in mucous glands.

The oesophagus also retains the old epithelial covering.
The muscular coating consists of a thicker longitudinal ex-
ternal layer and a thinner internal transverse layer, and, as it
descends, shows a replacement of the voluntary transversely
striated fibrous formation by the involuntary smooth tissue.
The mucous membrane projects in longitudinal folds, and
contains racemose mucous glands.

We may touch upon these only cursorily.
The stomach or ventriculus, on the contrary, requires a
more careful discussion. Its serous covering, it is true, pre-
sents nothing worthy of remark, neither do its smooth muscles,
which consist of layers running in longitudinal, transverse,
and oblique directions. But the mucous membrane, which is
lined with cylinder cells 0.0226 to 0.0323 mm. high and 0.0045
to 0.0056 mm. broad, shows, on the contrary, an abundance
of interesting and important things.

Its surface is not smooth, but uneven. Either lower or

THE DIGESTIVE APPARATUS.

143

higher isolated prominences (Fig. 134, a), are met with
there, or projecting folds, which are united in crossing each
other.

The glands open only in the valleys, and never on a hill
or a fold. Numerous differences of the gastric surfaces
occur according to the variety of animal. In general, the
cardial half of the stomach presents a thinner and more
even mucous membrane than the pyloric portion. The
mucous membrane may here, at last, acquire an elevation
of 2 mm.

An enormous quantity of tubular
glands (Fig. 134, b) permeate the
mucous membrane. The massiveness
of the latter is, therefore, in compar-
ison to this embedment, but slight.
We find an ordinary soft connective
tissue (Fig. 135, a). Lymphoid meta-
morphosis of the latter may, however,
take place.

The glandular tubes of the stomach
have been divided into two differ-
ent forms ; the so-called peptic-
gastric glands and the gastric- mucous
gland.

The former constitute the more dis-
seminated and more important
glandular formations (Fig. 134).
They open in part singly (Fig.
128), in part by the conjunction
of several tubes into a common
excretory duct (Fig. 136, 1).

In both cases the aperture
appears in the transverse sec-
tion to be rounded (a), and
lined with the ordinary slender,
high cylindrical epithelium of the gastric mucous membrane
(Fig. 128, a, 136, a).

Fro. 1 34. — Vertical section of
the human gastric mucous mem-
brane ; a, surface papillae ; b,
glands.

Fig. 13s. — Transverse section through the
gastric mucous membrane of the rabbit; a,
tissue of the mucous membrane : b, trans-
verse sections of empty and injected blood-
vessels, c ; <i, spaces for the glands.

144

THIRTEENTH LECTURE.

The gland body itself appears as a sometimes smooth bor-
dered, sometimes sinuous tube. The membrana propria

shows the familiar flattened stellate
cells.

Passing, now, from the outlet of
the gland in a downward direction,
we meet at b with a new metamor-
phosed cell formation, broader,
lower and more granular. Further
below, at c, we have two large gland
cells (peptic cells). The latter are,
however, first met with at d in their
highest development. Here, lying
on an uninterrupted series of smaller
gland cells are isolated larger, gran-
ular elements (Fig. 128, d), lodged
in niche-like sinuosities of the mem-
brana propria. The latter struc-
tures are the " overlying cells " of
Heidenhain, in contradistinction to
his " chief cells."

We have already learned how dif-
ferent is the appearance presented
by the quiescent and overworked
submaxillary gland of the dog. Something similar — and we
are again indebted to Heidenhain for the interesting fact — is
shown by the peptic-gastric glands. In the fasting animal
they appear smooth bordered, somewhat shrunken, and their
chief cells are transparent. A few hours after a plentiful meal
an essentially different appearance is met with. The peptic-
gastric glands are now swollen, their walls are sinuous, their
chief cells enlarged, granular and cloudy. At a later period
they again shrink ; the chief cells, however, remain per-
ceptibly clouded.

Now which of the two varieties of cells supply the gastric
juice, we do not yet know. We are inclined to conjecture
that it is the peptic-gastric glands.

Fig. 1^6. — 1, a compound peptic-
gastric gland of the dog; «, the
wide aperture (stomach cell) with the
cylinder epithelium ; l>, the division ;
c. the isolated tubes lined with pep-
tic cells ; d, the escaping contents ; 2,
the aperture a in transverse section ;
3. transverse section through the in-
dividual glands.

THE DIGESTIVE APPARATUS. 145

The second glandular formation, the gastric mucous
glands, were long since discovered in the hog. In the dog,
cat, rabbit and Guinea-pig they occupy a large extent of the
pyloric region ; in man, on the contrary, but a small zone
here. They are, again, in part ramified, in part unramified
tubes. One may also recognize here in the excretory duct
(and it may acquire a very considerable length) the ordinary
cylindrical epithelium of the gastric mucous membrane (Fig.
122, a). The lower true portion of the gland shows, on the
contrary, lower cubical cells (b) richer in fine granules. They
become cloudy in acetic acid, and call to mind the " chief
cells " of the peptic-gastric glands.

Small racemose glandules appear in the human pyloric re-
gion. Isolated lymphoid follicles form the lenticular glan-
dules, familiar to us from p. 112.

At the border of the mucous membrane, towards the sub-
mucous tissue, there is a net- work of smooth muscular fibres,
the muscularis mucosae (p. 80). Thin strips pass up between
the gland tubes.

The arrangement of the vessels in the gastric mucous mem-
brane (Fig. 126) is elegant and characteristic. Thin and slen-
der arterial branches, rising up through the submucous tissue,,
terminate in a long-meshed capillary net-work, circumvolut-
ing the gland tubes, and forming rings around the apertures
of the latter. The transition into venous roots takes place
on the surface only, and these rapidly unite into large de-
scending veins. The latter form a broad-meshed reticulum
of wider tubes beneath the mucous membrane.

The lymphatic passages were recently discovered by an
eminent Swedish investigator, Loven. Large net-works,
situated in the submucous tissue, send upwards considerable
caecal canals, which pass between the glands and reach nearly
to the gastric surface.

The gastric juice, an acid fluid, contains a peculiar fermen-
tative body, pepsine. The granules in the covering cells (and
possibly in the chief cells) are this substance, which has been
formed by the gland cells. The power of the secretion to
7

146

THIRTEENTH LECTURE.

digest albumen must be left for discussion in another lec-
ture.

Let us pass to the small intestine.

Its serous covering and the smooth muscles, forming a double
layer, we here omit. The mucous membrane, on the con-
trary, requires an accurate description, for its structure is
more complicated than in the stomach.

In the first place, we meet with innumerable large crescen-
tic folds (increasing downwards in height), the valvulae con-
niventes Iverkringii. The surface of the small intestine, be-
sides, projects in millions of complicated papillae, the intes-
tinal villi. In the mucous membrane we meet, furthermore,
with an infinite number of small glandular tubes, the Lieber-
kuhnian glands; and in the duodenum, with small racemose
organs, the Brunonian glands. Finally, the small intestine
contains solitary and aggregate (Peyerian) lymph follicles.

The tissue of the mucous membrane of the small intestine
also shows a muscularis mucosae, but it is thinner than in the

stomach, and then a reticu-
lar connective substance
containing numerous lym-
phoid cells (Fig. 47, a).
The villi (Fig. 137) — we
have already mentioned
them in a previous lecture
— also consist of a similar
tissuu. Even the surface
is distinctly fenestrated,
although with narrower
meshes. In the axis we
find the chyle vessel (Fig.
95, d), single or multiple,
in the latter case sometimes connected in an arched and
bridge-like manner, covered by thin slips of smooth muscle
{c) derived from the muscularis mucosae, and finally circum-
voluted by a looped net-work of capillaries (b . We are
already familiar with this from what has preceded.

U~o

Fig. 137. — Lieberkiihnian glands (a) of the cat,
with the intestinal villi [b) situated over them.

THE DIGESTIVE APPARATUS.

H7

That the whole intestinal canal is lined with cylindrical epi-
thelium, was mentioned in the second lecture. We also de-
scribed the peculiarity which the cylinder cells of the small
intestines presented, the thickened seam, permeated by
porous canals, of the free broad surface.

We now turn to the glands. By far the more important
formations are the Lieberkuhnian tubular glands (Fig. 137, a).
They are infinitely numerous, and occupy not only the mu-
cous membrane of the small, but also that of the large intes-
tine. We are thus reminded of the gastric glands ; the
capillary net-work is also the same.

The Lieberkuhnian glands are smaller, however ; they are
only 0.38 to 0.45 mm. long, and 0.056 to 0.09 mm. broad.
Their membrana propria also appears more delicate ; the
tube remains undivided, and is lined by a simple layer of cyl-
indrical gland cells (Fig. 117, b). The opening occurs regu-
larly in the narrow vales which are enclosed by the adjacent
villi. They secrete the intestinal juice.

The racemose or Brunonian glands (Fig. 138) of the small
intestine are of far more subordinate importance. They com-

Fig. 138. — A human Brunner's gland.

mence, in man, just beyond the stomach, and form, in a
crowded sequence, a regular glandular cushion embedded in
the submucous tissue. They thus extend to about the en-

143

THIRTEENTH LECTURE.

trance of the biliary duct, becoming more scanty further
downwards. The mammalia show numerous variations.

The size varies in man from 0.25 to 2 mm. The acini ap-
pear rounded, elongated, sometimes regularly tube-like (0.56
too. 14 mm.) The duct and gland body have the same cover-
ing of low cylindrical, pale and irregular cells. If I am not
mistaken, the Brunonian gland stands in the middle, between
the ordinary racemose mucous gland, the gastric-mucous
gland and the serous gland. Concerning the secretion we
know very little.

Isolated lymphoid follicles (solitary glands) may occur
throughout the entire small intestine. These, as well as the
aggregated lymphoid follicles (the Peyer's plates) have already
been mentioned in the eleventh lecture.

We have already mentioned that the Lieberkuhnian tubu-
lar glands have an elongated net-work of blood-vessels. From
it arise, and to it return, the afferent and efferent vessels of
the intestinal villi, which form the looped net-work (Fig. 95, b).
The lymph or chyle vessels of the intestinal villi, having

descended into the mucous
membrane, likewise form a net-
work, very much more incom-
plete it is true, of wider tubes.
Our Fig. 109 (a, b, c, k, to the
left) may represent this toler-
ably. During the resorption
of the chyme, its fat, in a con-
dition of the finest division,
penetrates first the body of
the cylindrical epithelium ; it
then enters a wall-less passage
through the reticular connective
substance of the villi, and, at
last, the csecal chyle canal (Fig.
1 39) occupying the axis of the latter. ■ ' Preformed passages "
for this process of wandering have frequently been searched
for, it is true, and they have often been thought to be found,

Fig. 139. — The very slender intestinal
villus of a kid, killed during digestion, with-
out epithelium, and with the lymphatic ves-
sel tilled with chlye, in the axis.

THE DIGESTIVE APPARATUS.

149

Fig. 140. — Glands of the large intes-
tine of the rabbit. One tube with cells ;
the others drawn without cells.

but subsequently nothing of all this was confirmed. These
were simply microscopic observations such as should not be
made, instituted for the purpose of filling up a gap in the
present physiological knowledge at any price.

The Lieberkiihnian tubes continue throughout the mu-
cous membrane of the whole large intestine, but now receive,
most superfluously, a new name,
that of the glands of the large intes-
tine (Fig. 140). They have not be-
come changed in the least.

The reticular connective sub-
stance of the mucous membrane of
the small intestine has, however,
been further transformed into an
ordinary connective tissue ; the
reticular character is less pronounc-
ed, and the number of lymphoid
cells contained in the tissue has de-
creased enormously. The intesti-
nal villi of the small intestine have finally entirely disappeared.
If the mucous membrane, as in the upper part of the
rabbit's colon, still projects as papillae, the latter appear
broader and as prominences of the ordinary mucous mem-
brane permeated by tubular glands (Fig. 100).

The colon presents isolated lymphoid follicles. In the
vermiform process of man and the rabbit, on the contrary,
there is an enormous Peyerian plate, as we remarked at page

114.

The blood-vessels of the large intestine correspond with
those of the stomach (Fig. 126) for an interchange. Lym-
phatics have also been subsequently met with in the carni-
vora and herbivora. Those of the upper colon of the rabbit
are represented by our Fig. 100, g, f, e.

In the anus the simple cylinder epithelium is sharply de-
marcated from the modified epidermis. At the lower end
of the intestine, the smooth and transversely striated muscles
become intermixed, reminding us of the oesophagus.

FOURTEENTH LECTURE.

PANCREAS AND LIVER.

We have still left the two largest glandular organs of the
digestive apparatus, the pancreas and liver. We shall soon
finish the pancreas ; the liver, on the contrary, requires a more
accurate discussion, in consequence of its peculiarities.

The pancreas is an enormous racemose structure. It re-
minds one of the salivary glands. The rounded acini meas-
ure 0.06 to O.09 mm. The membrana propria is likewise
said to have flat stellate cells. The rounded vascular net-
work was represented in our Fig. 127. The lymphatics re-
quire still more accurate investigation.

The gland vesicles are lined with indistinctly separated, very-
granular cubical cells. In the adult rabbit the latter show
fatty molecules in their interior, that is in the parts turned to-
wards the lumen. The middle and external portions remain
transparent. Between them appears the net work of finest
secretory tubes, already familiar to us from Fig. 125 (Sa-
viotti).

The thin-walled excretory duct of the human pancreas
contains no muscular elements. Below, it presents mucous
glandules.

It is covered by a low cylindrical epithelium. If followed,
in animals, into the gland, these cells are found to become
more and more flat in the branches. Finally, in the gland
vesicles themselves, we meet with thoroughly flattened ele-
ments, reminding us of the endothelia of the vessels. These
are the so-called " centro-acinary " cells (Langerhans), which
are found widely extended, not only in the pancreas, but also
in the parotid.

The character of the gland cells in a quiescent and active
condition requires further investigation.

PANCREAS AND LIVER.

151

Let us now turn to the liver.

The liver — as its natural external surface, or that of an arti-
ficial section teaches — consists of individual, crowded areae,
the so-called hepatic islets or hepatic lobules. In many crea-
tures, as the pig, the demarcation of the lobules is very dis-
tinct. The borders of the lobules appear tolerably distinct
in the human organ during the infantile period of life, but

very indistinct, on the
contrary, in the adult.
Our liver islets are as-
sumed to measure, as a

mean, 2.2 mm.

A hepatic lobule (Fig.
141), however, consists
essentially of innumera-
ble gland cells and, cross-
ing them, an uncommon-
ly complicated capillary
net-work. The latter
unite at the central point
of the lobule to form

Fig. 141. -Hepatic lobule of a boy ten years old, S11 initlal branch of the
Wiethe transverse section of the central hepatic vein hepatic Vein J the limits

are shown externally
by the branches of the portal vein and the fine biliary
branches.

The liver cells have already been noticed at Fig. 121.
These thick, obtuse-angled structures, whose mean measure-
ment is 0.018 to 0.023 nim., contain nuclei of 0.006 to 0.007
mm., with nucleoli. The soft, granular cell body remains
membraneless and endowed with a slow contractility (Leuc-
kart). The brown molecules of the biliary coloring matter
in the cell body, as well as the fatty embedments, we have
already mentioned. The latter occur in the suckling infant,
in adults whose diet is rich, and also in fattened animals.
They form the so-called fatty liver (Fig. 142). The cell sup-
ports such an overloading with fat (c, d) relatively well.

152

FOURTEENTH LECTURE.

Fig. 142.— Cells of the fat-
ty liver ; a, t>. with smaller
fat molecules and drops ; c,
rf, with large drops.

abundantly (pig).

With an altered manner of life, the unusual contents soon
disappear again.

In the lobule (Fig. 141) the cells lie crowded together in

a radiated manner, forming simple rows.
Reticular combinations gradually become
more frequent externally. These are the
so-called cellular trabecular and cellulo-
trabecular reticula of our organ.

Between the lobules we meet with in-
terstitial connective tissue, sometimes
only slightly developed (man), sometimes
This connective tissue derives its origin,
in part, from the investing membrane of the liver ; it is, in
part, the continuation of a connective-tissue sheath which sur-
rounds the blood-vessels and biliary passages entering the
porta hepatis (Glisson's capsule).

The liver receives its blood from two unequally developed
supply tubes, the wide portal vein and the narrow hepatic
artery. The first forms, around the lobules, partly shorter or
longer branches (Fig. 94), sometimes, however, nearly and
actually assuming a ring-shaped arrangement (pig). These
branches rapidly divide into the compact capillary net-work
of 0.009 to 0.0126 mm. wide tubes. They approach the cen-
tre of the lobule in a radial manner to bury themselves in the
commencing portion of the hepatic vein, which is situated at
this point. The latter, like its larger trunks, has uncom-
monly thin walls, and has coalesced externally with the
parenchyma of the liver.

The branches of the hepatic artery, running along with the
portal vein and biliary ducts, form, in the first place, nu-
tritious vessels for both the last mentioned parts, and then
capsular capillaries ; finally, they penetrate the lobule itself.
They either bury themselves here in the branches of the por-
tal vein, or pass over into the peripheral portion of the capil-
lary net-work.

Both varieties of net-work, that of the hepatic cell tra-
becular and that of the blood-vessels, are most intimately

PANCREAS AND LIVER.

153

zfeOYJ

interwoven with each other, so that every space of the one
meshwork is occupied by portions of the other.

After suitable treatment,
as Beale and Wagner found,
thin sections of the hard-
ened hepatic tissue show an
uncommonly elegant reticu-
lar tissue of a right delicate,
homogeneous, nucleated,
connective substance (Fig.

143, a).

In the last period of fcetal
life, or in the new-born (Fig.
143), this consists distinctly,
in places, of a double mem-
brane. The one layer corresponds to the capillary walls (and
shows here and there a combination of the flat, vascular cells
— Eberth) ; the other, investing the hepatic cell-trabeculse,
represents a finest membrana propria.

Fig. 143. — Frame-work substance from the rab-
bit's liver ; <7, homogeneous membrane with nu-
clei : 6, thread-like strands of the latter ; e, sev-
eral hepatic cells still retained.

Fig. 144. — Biliary capillaries of the rabbit's liver. 1. A part of the lobule ; <7, vena hepatica :
b. branch of the portal vein ; c, biliary ducts ; d, capillaries. 2. The biliary capillaries (i) in their
relation to the capillary blood-vessels (a). 3. The relation of the biliary capillaries to the hepatic
cells ; a, capillaries ; b, hepatic cells ; c, biliary ducts ; d, capillary blood-vessels.

Great difficulty was encountered, during a long period, in
the investigation of the finest biliary passages (Fig. 144). A

n*

154 FOURTEENTH LECTURE.

reliable result was at last secured here by means of trouble-
some injections* (Gerlach, Budge, Andrejevic, MacGillavry).

The finer ramified system of the biliary passages may, it is
true, be still readily recognized (Fig. 144, 1). They run with
the branches of the portal vein (b\ in the intervening spaces
of adjacent hepatic lobules. From them arise fine branches
which circumvolute the branch of the portal vein (V).

They are continuous inwards with a marvelously delicate
net-work of finest canals, the so-called biliary capillaries (d).
The diameter of the latter is 0.0025 to 0.0018 mm. (rabbit).
They surround the individual liver cells (3, b) with elegant
cubical meshes (a), so that the cellular element comes into
contact at one point or another of its surface with these finest
tubules. We thus have, in addition to the two coarse net-
works of the cellular trabecular and capillary vessels, this
third, finest one, of the biliary capillaries.

They are also not wanting in the other classes of vertebrate
animals. There is, nevertheless, considerable variation (Her-
ing, Eberth).

We now encounter the question : do the biliary capillaries
possess a proper wall, or are they only the finest lacunar
canals? Furthermore, what is their more exact relation to
the hepatic cells ?

I have not doubted that there was a special, although
extremely thin wall, from the instant that I began to study
the biliary capillaries of the rabbit. One sees here, not only
the artificially injected, but also the adjacent empty tubules
(often to a considerable extent), regularly demarcated by
sharp, straight lines. A lacunar system between contractile
cells would otherwise scarcely present the regularity of the
biliary net-work. We therefore coincide with Eberth and
Koelliker in the assumption of a wall. The same is also
shown bv the cat's liver.

* These may be made from the biliary passages in the fresh animal cadaver.
This was the earlier procedure. An injection may also be made into the vein of
the living animal of indigo sulphate of soda, which is soon (as in the kidney)
secreted by the liver (Chrzonszczewsky).

■AJ

A1*^ ^ . .a. rau

PANCREAS AND LIVER,

155

Fig. 145. — Finest biliary passages of the rabbit's
liver ; <r, blood-vessels ; i, hepatic cells ; c, biliary
capillaries.

Years ago, Andrejevic had already correctly asserted that
the blood and biliary capillaries never touched each other,
but rather that the body of a hepatic cell always lies between
them as a separating structure.

The livers of the amphibia and reptiles, and even of birds,
show this most distinctly. Nevertheless, the more compli-
cated relations of the mam-
malial liver yield the same
result (Fig. 145), although
with more trouble, to the
attentive observer. We
see the blood-vessels (a)
in part transversely, in
part longitudinally. The
biliary capillaries (c) are
in repeated contact with
the hepatic cells {b) ; but

portions of the cell body always remain as intervening parts
between these and the capillary vessels of the passage.

Our figure teaches, furthermore, that biliary capillaries
occur only at the contiguous surfaces of two cells. We shall,
therefore, have to regard the extremely thin walls of the
capillaries as the product of adjacent cells which has become
hardened.

The lymphatics run in the capsule of Glisson in the same
manner as the portal vein, hepatic artery, and biliary ducts.
Having entered the lobule, they invest the capillary blood-
vessels (MacGillavry, Frey, Biesiadecky and Asp). The deli-
cate external wall of these " perivascular " lymph passages is
without doubt the thin membrana propria of the hepatic cell
trabeculae.

Let us, finally, look after the efferent biliary canals.

These canals also show between the lobules a membrana
propria covered with low cylinder cells. Later, the walls
become connective tissue, the cells are higher and have a
seam which is permeated by porous canals (p. 8).

In the largest canals passing out from the hepatic paren-

156 FOURTEENTH LECTURE.

chyma, there is an external fibrous membrane and an internal
mucous membrane. In the gall bladder there are, in addition,
smooth muscular fibres.

The largest biliary canals have numerous excavations
(probably reservoirs for bile), as well as racemose glandules.

FIFTEENTH LECTURE.

THE LUNGS.

THE lungs originate in the same manner as the racemose
glands, but acquire an essentially different texture. Their
efferent canal system requires an especial preliminary dis-
cussion, on account of its peculiarity and complication.

The cartilages of the larynx are hyaline, as the thyroid and
cricoid cartilages. In certain parts of the arytenoid cartilages
there is an elastic metamorphosis. The Wrisbergian and
Santorinian cartilages, with the epiglottis, are pure reticular
cartilage. The triticeaen cartilages are formed of hyaline or
connective-tissue cartilaginous substance. The ligaments of
the larynx present a considerable wealth of elastic tissue.
The lower true vocal cords are purely elastic. The muscles
are transversely striated. The mucous membrane, rather
compact and likewise not poor in elastic elements, shows
embedments of lymphoid cells. It contains racemose, true
mucous glands.

Strongly stratified pavement epithelium covers the anterior
surface of the epiglottis ; there are not so many layers in that
covering the posterior surface as far as the base ; the same is
also true of the lower vocal cords. Otherwise, we meet with
slightly stratified ciliated epithelium, which descends far down
into the lungs.

The wind-pipe or trachea, with its system of branches, the
bronchi, presents a fibrous tube, in the anterior wall of which
are embedded half rings of hyaline cartilage (annuli carti-
laginei). A deeper layer of transverse smooth muscles con-
nects the terminal portions of the half rings posteriorly. In
the mucous membrane we again meet with numerous mucous
glandules.

I$8 FIFTEENTH LECTURE.

In the lungs themselves the bronchi divide dichotomously
again and again, and thus become finer and finer passages.
The cartilaginous half rings disappear, simple lamellae appear-
ing in their place. Their last remains are still seen in canals
of 0.23 mm. The thin parietes have a simple ciliated epithe-
lium of 0.0135 mm- m height. Mucous glandules continue
far down, as also do the smooth muscles, which form regular

rings round the bronchial ramifi-
cations, and possibly till near the
so-called pulmonary vesicles.

At the end of the terminal bron-
chial branches (Fig. 146, a) we
now arrive at the true respiratory
portion of our organ.

We have, first, thin-walled (0.4
to 0.2 mm. wide) canaliculi, the

Fig. 146.— A portion of the lung of an a1v~nlar mccTcr^c f^rli 11I7M
ape {cercof>itii,cus\ injected with quick- cUV CUldl pUbbd^Cb ^OCIlLUZe^.
silver; a, endxif a bronchial twig ; c, al- npi • i i ■/» ,•

veoiar canal ; %, infundibuia. I heir acute-angled ramifications

(c) are familiar. Communicating
with them laterally and also terminally are short, conical hol-
low structures (b), the primary pulmonary lobules or, as they
are commonly called, the infundibuia.

As the gland lobule consists of the gland saccules or acini,
so does the just mentioned infundibulum consist of similar
structures, the pulmonary vesicles, pulmonary cells or alveoli.
They are less isolated from each other, however, and to a
certain extent present more diverticulations of their walls,
which meet in common cavities. At a later period, indeed,
there is not unfrequently an absorption of individual portions
of the walls. Such expansions of the wall of the alveolar
passage into pulmonary vesicles (c) are met with every-
where.

On making a section through the lung tissue, we meet
with the alveoli in the form of rounded and oval spaces (Fig.
147, b, b). Their diameter varies from o. 1128 to 0.3760 mm.,
and increases with the age.

The hermetic enclosure of the respiratory organs in the

THE LUNGS.

159

thoracic cavity compels the pulmonary alveoli to maintain a
certain expansion permanently. In consequence of their
great distensibility, the lungs follow the expansion of the
thorax. By means of their elastic power, and assisted by
the muscles of their canals, they contract at each expiration,

Fig. 147. — Transverse section through the pulmonary substance of a child of nine months. A
number of pulmonary cells, b, surrounded by the elastic fibrous net-work, which bound them in a
trabecula-like manner, and, with the thin structureless membrane, forming their walls {11) ; d, por-
tions of the capillary net-work with their vessels curved in a tendril-like manner, projecting into
the cavities of the pulmonary cells ; c, remains of the epithelium.

as far as the thoracic walls permit. It is only when the tho-
racic cavity is opened that the lungs with their alveoli com-
pletely collapse.

The parietes of the pulmonary vesicles, a continuation of the
terminal canal system, is a very thin connective-tissue mem-
brane. It is surrounded by elastic fibres, finer and coarser,
sometimes single, sometimes aggregated in groups. The latter
are met with in the interalveolar septa. The fundus of the
pulmonary alveolus shows only the finest elements, measur-
ing 0.0011 mm., in part more isolated, in part connected in a
reticular manner.

l6o FIFTEENTH LECTURE.

The primary pulmonary lobules of the new-born — later the
nature of the arrangement becomes more indistinct — united
by connective-tissue intermediate substance, form larger or
secondary lobules. The latter appear on the surface of the
organ in the human adult as areae. measuring I to 2 mm. and
more, demarcated by a black substance, and often appearing
quite distinct. They form, at last, the large lobes. Their
delineation belongs to descriptive anatomy.

We have just mentioned the black substance in the inter-
lobular connective tissue ; it may occur between and in the
walls of the pulmonary vesicles, and even in the bodies of
their epithelial cells, as we shall mention hereafter. This is
the so-called black lung pigment.

We have just used the epithet "so-called." In fact these
substances are not melanine, the complicated, dark ferrugi-
nous coloring matter of the organism. They have rather an
extraneous origin ; they are carbon, breathed in in a finely
divided condition, which is induced by our artificial life in
enclosed place's.

Mammals living wild show nothing of this, but it is seen
in their kin when domesticated by man. In human beings
constantly surrounded by smoke and soot, or in laborers in
coal mines, the lungs may at last become quite black. If we
shut a dog up in a place in which there is a constant genera-
tion of soot, a similar change of the respiratory organs takes
place with relative rapidity.

In a condition of the finest division, these particles of car-
bon penetrate the epithelial cells, and from them enter the
pulmonary tissue. A great portion of them here become
permanently quiet. Others enter the lymphatics, and pass
from these into the lymphoid bronchial glands. They also
become fixed in the latter organs. This is the so-called mela-
nosis of these structures.

Let us now examine the vascular arrangement.

By the continual division of the pulmonary artery, there
arises a system of fine blood-vessels, which encircle the in-
dividual pulmonary vesicles, and frequently combine into

THE LUNGS.

161

Fig. 148. — A pulmonary alveolus of the calf;
a, larger blood-vessels, which run in the alve-
olar septa ; b, capillary net-work ; c, epithe-
lial cells.

incomplete or more complete rings (Fig. 148, a). From them
arises an uncommonly close capillary net-work of tubes
0.0056 to 0.0113 mm. wide,
which are scarcely separated
from the atmospheric air by the
thin membrane of the alveolar
walls (b). The respiratory in-
terchange of gases takes place
here. These capillaries appear
elongated when the lung vesi-
cles are strongly expanded.
When less expanded they pro-
ject, in a tendril-like manner,
into the cavity, reminding us
of a relative condition in the
muscles. The pulmonary veins

commence with small branches in the interalveolar septa.
Gradually combining into larger trunks, they accompany the
ramifications of the bronchia and the divisions of the pulmo-
nary arteries.

The bronchial arteries are regarded as the nutritive vessels
of the respiratory organ, but there is no very sharp demar-
cation between them and the respiratory pulmonary arteries.

The former supply the walls of the larger blood-vessels, the
adjacent lymphatic glands, the connective tissue between the
pulmonary lobules and beneath the pleura. Finally, they
form the capillary net-works of the various parietal layers of
the efferent bronchial system ; but the most superficial net-
work of the mucous membrane arises, in a peculiar manner,
from the respiratory system of vessels.

The bronchial veins appear to be quite peculiar. They are
conjectured to be only the reflux vessels of the arterial
branches from the larger bronchial ramifications, from the
lymphatic glands and from the pleura nearest the hilus of the
lungs. The venous roots from the walls of the finer bronchi
pass, on the contrary, into the respiratory pulmonary veins.

The lungs are rich in lymphatics, beneath the pleura as well

l62

FIFTEENTH LECTURE.

as in the bronchial system. Lymphatic lacuni also occur in
the pulmonary vesicles, and their efferent vessels subsequently
invest the blood-vessels (Wywodzoff).

We have, finally, to mention the epithelial lining of the
alveoli. This has occasioned much discussion. In the mam-
malial and human embryo there is a continuous covering of
flat, protoplasmatic, nucleated cells. A change occurs after
birth, however, with the commencement of aerial respiration.

FlG. 149. — The epithelium from the basis portion of an infundibulum. situated just
beneath the pleura of the developed cat ; treated with nitrate of silver.

Only a small contingent of our cells now retain their old
characteristics (Fig. 149). The epithelial element, over the
incurvations of the pulmonary vessels, and over all the other
prominences, has become a much more considerable proto-
plasmless and non-nucleated scale.

SIXTEENTH LECTURE.

THE KIDNEY, WITH THE URINARY PASSAGES.

The structure of the mammalial kidney is extremely com-
plicated. This bean-shaped organ is covered by a not very
thick, but resistent, connective-tissue envelope. The blood-
vessels and lymphatics pass in and out at the hilus, and the
efferent canal, the ureter, also has its exit at this point.

The kidney (Fig. 150), consists of two
different layers, a cortical, and a medul-
lary substance. The former (above, /),
appears to the naked eye dark and homo-
geneous ; the latter (a, b), paler, displays
a radiated fibrous arrangement. In most
mammals it projects in a single point into
the pelvis of the kidney (a). In man the
medullary substance is divided into a num-
ber of conical portions, with their bases
turned towards the cortex and their points
towards the hilus.

These are the Malpighian or medullary
pyramids. The columnae Bertini are de-
pressions of the cortical substance between
the latter portions of these cones.

The cortex and medulla are, further-
more, permeated by a connective-tissue
frame-work.

The elements of the cortex, as well as
of the medulla, are long, glandular tubes,
the so-called uriniferous canals or Bellinian
tubes.

In the medulla they divide frequently,
and run in a radial direction (b). They continue through the

Fig. 150. — Diagram of
the mammalial kidney :
a, papilla; b, straight
uriniferous canals of the
medulla ; c, so-called
medullary rays of the
cortex ; d, outermost
cortical layer ; e, cortical
pyramids, with the arte-
ries connected with the
glomeruli ; f, border
layer.

1 64

SIXTEENTH LECTURE.

d —

cortex from point to point, in the form of straight bundles (c).
They are here called medullary rays. Between them, al-
though incompletely demarcated, remain considerable portions
of the cortical substance (e), comparable to a truncated pyra-
mid. These are the so-called cortical

(| P pyramids. In them run the glandular

1 I 11 • 1 , -r , ,

tubules, with the most manifold turnings,

which finally encompass, with their knob-
like dilatations, the Malpighian vascular
coil or glomerulus (Fig. 96). The latter
structures occur in this portion of the
organ only.

Let us now commence the discussion
of the particulars with the most internal
division, with the apices of the medul-
lary pyramids, the renal papillae. Here,
alone, in the form of 10 to 15 apertures,
the efferent canal-work of this organ,
which is so complicated in its structure,
opens as a system of short canals (Fig.
151, a). Very soon afterwards they
break up, by acute-angled ramifications,
into branches of the first and second
order [b, c), and this is repeated several
times more. The whole thus acquires a
brush-like appearance. The canals be-
come narrowed, in consequence of this
continual subdivision, from 0.3 and 0.2
to 0.05 mmv About 4 to 5 mm. from
the apex of the papilla the process oi
division ceases, however ; the straight
canals now maintain their diameter un-
changed for a long distance.

Between them — and this was dis-
covered by Henle — occurs an additional
system of much finer loop-shaped canals (d). In order to
facilitate a further insight, let us give to that particular part

Fig. 151. — Vertical section
through the medullary pyra-
mids of the pig's kidney (semi-
diagramatic) ; a, trunk of a
uriniferous canal, opening at
the apex of the pyramid ; b
and c, its system of' branches ;
d, loop-shaped uriniferous ca-
nals ; e, vascular loop, andyj
ramification of the vasa recta.

THE KIDNEY AND URINARY PASSAGES.

165

of the tube which descends from the convoluted cortical por-
tion, and the side of the loop which passes off from this, the
name of the descending, and that portion which returns
towards the surface of the organ the name of the ascending
side. The former usually has the least, and the latter the
greatest diameter. The number of the looped canals in-
creases in proportion as we examine the cortical layer further
upwards towards the medullary layer.

The terminal trunk of the efferent canal-work is invested
by the connective-tissue frame-work of the papillary apices,
and is without a membrana propria. The latter gradually
makes its appearance at the system of branches, and is more
distinct as well as more compact at the looped canals. Low
cylinder cells of 0.03 to 0.02
mm. border the transverse
section of the efferent canal
system (Fig. \$2,a). In the
further system of branches
the lining cells are still lower
(down to 0.016 mm.)

Let us now, for an instant,
leave the efferent apparatus
and examine the secretory
portion of the kidney.

We will now turn to the
cortical layer of our organ
and, first of all, examine more
closely the so-called cortical

pyramids (Fig. 150, e). In their axis is seen a branch of the
renal artery, to which the glomeruli are attached by lateral
branches, like the berries on the stem of the grape (Fig.
150, e\ Fig. 155).

A cortical pyramid, however — we repeat what was pre-
viously said — consists, for the rest, entirely of convoluted
uriniferous canals. They take their origin with a balloon-
shaped portion which surrounds the glomerules, as a bag does
a sponge. This is the Miiller's or Bowman's capsule. Its con-

Fig. 152. — Transverse section through a re-
nal pyramid of the new-born child ; a, collec-
tive tubes with cylindrical epithelium ; b, de-
scending side of the looped canal with flat
cells ; c, returning side of the loop with granu-
lar celU ; d, transverse sections of vessels ; e,
connective-tissue frame-work substance.

1 66

SIXTEENTH LECTURE.

tracted transition into the uriniferous canals (the so-called
neck) was discovered at a relatively recent period.

Only the most external cortical portion of our organ (Hyrtl
named it the cortex corticis) is without this peculiar vascular
coil (Fig. 150, d\ Fig. 155, d).

The inner surface of this capsule has a lining of large, fiat,
endothelial cells.

The external surface of the glomerulus presents an invest-
ment of smaller cells which are not so flat. I found them
thus, formerly. According to Heidenhain, however, the lat-
ter elements are likewise quite flat.

In the convoluted uriniferous canals we meet with a clouded,
granular, cubical epithelium, and the lumen is quite narrow.
Following this glandular tubule downwards, we find it as-
suming a straight and direct course. At first it still remains

wide, and the gland cells are
unchanged. Then, having en-
tered the medullary substance,
it diminishes in width, exceed-
ingly, and now becomes the
narrow descending side of
Henle's looped canal. A re-
markable transformation of the
epithelial lining has taken
place at the same time ; quite
thin, flat scales, appearing like
vascular endothelium, now
line the canal (Fig. 152, #.)
Following the loop further,
we arrive at the ascending
wider side. Its epithelium is
again the old, clouded, glandular variety of the convoluted
uriniferous canals, as we must maintain in contradistinction
to Ludwig.

The returning side finally passes over in the cortex — some-
times deeper, sometimes quite near the surface — into an
expanded, gut-like convoluted structure, the so-called " inter-

I ig. 153. — From the kidney of the pig (scmi-
diagramatic) ; «, arterial branch : b. afferent
vessels of the glomerulus, c ; d, vas efferens ;
e, breaking up of the same into the straight
capillary plexus of the medullary ray ; _/,
rounded plexus of the convoluted canals ; /', ,f,
commencement of the venous branch.

THE KIDNEY AND URINARY PASSAGES.

167

calary piece." Several of these intercalary pieces open into
a collective tube, and the latter combine into larger canals.
We have thus presented the whole connection of the kidney.
Heidenhain has quite

recently made an interest-
ing discovery concerning
the epithelium of the con-
voluted uriniferous canals,
of the returning side of
the loop, and of the inter-
calary piece. Its proto-
plasm is in great part
metamorphosed into a con-
siderable number of very
fine cylinders or rods.

Around the nucleus,
which these "rod cells"
invest, as well as between
the rods, there remains a
residue of unchanged pro-
toplasm. These rods, with
which the gland cells rest
on the membrana, give the
transverse section of these
uriniferous canals a radio-
striated appearance.

The medullary rays pene-
trate the cortex, like groups
of pegs driven close to-
gether into a board. They
consist of two different
elements. In the first

Fig. 154. — Diagram of the uriniferous canals in a
vertical section of the kidney; R, cortex: M,
medulla ; *. border : a, efferent canal-work, with the
system of branches b ; c. transition canal (or inter-
calary pieced in the ascending or returning side d\
e. descending ; /, convoluted uriniferous canal of
the cortex ; g, capsule with the glomerulus.

place we have the cortical branches of the efferent canal-work
of the medullary substance pushing forwards to near the sur-
face of the kidney ; these are accompanied by the upper
portions of the ascending looped canals, which have a smaller
diameter.

1 68 SIXTEENTH LECTURE.

I cannot presume that the highly complicated structure of
the mammalial and human kidney is hereby rendered appre-
ciable to every one ; let us, therefore, make a brief repeti-
tion. From the glomerulus (Fig. 154, g) and convoluted
cortical canals (/) the secretion reaches the descending (nar-
rower) side (<?), and from this into the ascending (d). From
the latter, the secretion passes through the intercalary piece
(c) into the efferent canal system (b and a). Our urine, there-
fore, passes through this long course.

The frame-work substance consists, in the cortex, of a
scanty scaffolding of a connected, undeveloped connective
tissue. The latter is somewhat thicker in the medullary sub-
stance, especially below (Fig. 152, e). Cells are not wanting.

We have the blood-vessels and lymphatics still remaining.

The arrangement of the former vessels (Fig. 155) is the
most complicated, and, therefore, certain differences of opinion
still prevail in regard to it.

In man the arterial and venous branches enter at the hilus
and pass into the interior, becoming more and more ramified.
After giving off branches to the capsule, the)' perforate the
latter external to the calyx of the kidney, an arterial branch
being accompanied, as a rule, by a venous branch. They
thus pass between the medullary pyramids to the bases of
the latter (a, h). They here assume an arched arrangement,
which is less complete in the arteries than in the veins.

From the arteries now arise the coil-bearing branches (b),
which, keeping in the axis of the cortical pyramids, continue
as far as the surface, and give off laterally the vasa afferentia
of the glomeruli (c). In the lower animals, such as the frog
and the adder, the latter forms a single coil-shaped convolu-
tion. In man and the mammalia (Fig. 196), on the contrary,
we meet within the latter with the already mentioned (p. 98)
acute-angled divisions, which subsequently unite into the sin-
gle vas efferens.

This (Fig. 153, d '; Fig. 155) is now resolved in a peculiar
manner into a capillary net-work (Key), forming at first an
elongated reticulum in the medullary rays (Fig. 153, e; Fig.

THE KIDNEY AND URINARY PASSAGES.

169

155, e). Fromtheperiphery
of the latter a rounded net-
work of somewhat wider
vessels extends to the con-
voluted uriniferous canals
of the cortical pyramids

(Fig. 153,/; Fig. I55,£-)-
The most external cor-
tical layer, Hyrtl's cortex
corticis, receives its blood
from the efferent vessels
of the uppermost glome-
ruli and the terminal
branches of the coil-bear-
ing arteries (Fig. 155, d).
Let us pass to the veins
of the cortex. Stellate
venous rootlets, the so-
called stellulae Verheyenii
{e), appear quite superfi-
cially. Connected with
these stars, there is then
formed in the cortical
pyramids a long venous
trunk (/{), which lies in
close apposition to the
coil-bearing artery. Into
its regular lateral branches
open the rounded capil-
lary net-work of the cor-
tical pyramids. The vein,
itself, sinks at the margin
between the cortex and
medulla, into the venous
arched vessel which we
mentioned above.

Thus far all is settled.
8

Fig. 155. — The vascular arrangement of the kidney in
vertical section; (7,arterial branch at the margin between
the cortex and medulla ; i>, coil-bearing artery ; c, vasa
afferentia of the glomeruli ; d, capillary reticulum of the
external cortical layer ; c, vein of this p;irt ; f, elongated
capillary net-work of the medullary rays ; g, rounded
net-work around the convoluted uriniferous canals of the
cortical pyramids ; h, venous branch of the cortex ; z,
efferent vessels of the deepest glomeruli ; /■. their capil-
lary net-work ; /, venous tubes of the medulla ; «',
capillary net-work of the papilla.

170 SIXTEENTH LECTURE.

A variety of views prevail, however, concerning the vascular
relations of the medulla. Elongated vascular tufts, which
appear in the upper portion of the medullary substance, the
so-called boundary layer (Fig. 150,/), are called vasa recta
(Fig. 151, f\ 155, k and /). They pass, sometimes further
upwards, sometimes further downwards, in a looped or
noose-like manner, into each other, and may be mistaken
for the looped canals of the urinary passages (Fig. 151, e).
Our vasa recta then form an elegant net-work (Fig. 155, m)
around the apertures of the uriniferous canals at the apex of
the medullary pyramids.

These vasa recta have frequently, if not predominantly, a
venous character (/) ; they are continuations of the capillary
net-work of the cortical pyramids.

Then — and we regard this source of supply as the more
important — the medullary vessels arise from the breaking
up of the vasa efferentia of the deepest glomeruli (Fig.

155,0-

Quite isolated arterial branches, which have left the coil-
bearing arteries before the giving off of the glomerulus
branches, are, according to our views, of little consequence,
though many investigators have considered these so-called
arteriolae rectae to be of great importance.

The combination of the vasa recta into venous roots (/)
presents a similar condition. They frequently have a tuft-
like character. Their affluent tubes are the returning sides
of the looped vessels and the effluent canals of the papillary
apices. These venous roots empty in part into the lower
terminal portion of the cortical veins, in part into the arched
communications at the margin between the cortex and the
medulla.

We are familiar with the lymphatics of the dog's kidney
(Ludwig and Zawarykin). They occupy the interstices of a
connective tissue full of clefts, which is situated beneath the
capsule, and from here are in communication with the capsu-
lar passages, and then form in the cortical pyramids finer,
deeper canals between the uriniferous canals, capsules of the

THE KIDXE Y AXD URINAR Y PASS A GES. \ 7 r

glomeruli and blood-vessels. Later, in making the injection,
the narrower passages of the medullary rays become filled, and
at last the lymphatics of the medullary substance itself. The
whole reminds us of the arrangement in the testicle (see be-
low). True lymphatics with valves first appear, however, at
the hilus.

The question now arises, which of the two systems of ves-
sels, that of the glomerulus or the net-work circumvoluting
the uriniferous canals, secretes the urine ? This role has been
assigned to the glomerulus, and only the signification of an
absorbing arrangement ascribed to the capillary net-work of
the uriniferous canals (Ludwig). According to another view
(Bowman), however, the glomeruli secrete the water chiefly,
and the cells of the uriniferous canals, as true gland cells, fur-
nish the characteristic solid constituents of the urine, which
are washed out by the water flowing past. A new, and as I
can say correct, observation of Heidenhain's is of signifi-
cance for this theory of Bowman's. Indigo sulphate of soda
injected into the veins of a living mammal is not excreted by
the glomeruli, but through the convoluted glandular canals
of the cortical pyramids.

Let us finally take a hasty glance at the passages which
convey away the urine.

The calices and pelvis of the kidney present a connective-
tissue outer layer, a middle layer of crossed smooth muscles
(especially in the pelvis of the kidney), then a mucous mem-
brane with the pavement epithelium mentioned at p. 30.
Mucous glands may also occur.

The muscular coating is thicker in the ureter. An external
layer shows longitudinal, and an inner layer transverse fibres.
Further downwards, a third, innermost, longitudinal layer is
added. The urinary bladder has a relative structure. The
muscular layer, considerably thickened, consists of oblique
and transverse reticularly connected bundles of fibres. The
sphincter vesicae appears at the neck of the bladder as a
thicker annular layer. The longitudinal layers of the detru-
sor urinoe run over the vertex and anterior wall of the organ.

172

SIXTEENTH LECTURE.

The mucous membrane and epithelium remain the same.
Simple mucous glandules are likewise met with.

The female urinary canal, the urethra, presents a longitu-
dinally folded mucous membrane with papillae. The mucous
membrane is very vascular, and has numerous mucous gland-
ules, the largest of which bear the name of Littre's glands.
A strongly developed muscular layer consists of longitudi-
nally and transversely arranged fibres. The epithelium is of
the stratified flattened variety.

SEVENTEENTH LECTURE.

THE FEMALE GENERATIVE GLANDS. — THE OVARY WITH
THE EFFERENT APPARATUS.

The ovary, a peculiarly constructed organ, forms the most
important portion of the female sexual apparatus. It has a
flattened oval, occasionally bean-shaped form, and therefore
has a hilus through which considerable blood-vessels and
lymphatics enter and leave the organ.

We may distinguish in the ovary a sort of medullary sub-
stance, that is, a connective tissue, uncommonly vascular sub-
stance or the vascular zone of Waldeyer ; and then an invest-
ing glandular layer, the parenchyma zone.

The medullary substance begins at the hilus. Its large
vascular canals remind us of the later-to-be-mentioned cav-
ernous tissue of the urinary and sexual passages. It radi-
ates outwards into a frame-work permeating the glandular
cortical layer. At the surface of the organ the frame-work
reunites into a more solid continuous substance (Fig. 156, b).
The entire ovary is covered by a simple layer of low cylin-
drical cells (a). This was formerly erroneously called a serous
membrane, but now bears the name of the germinal epithe-
lium, a designation the correctness of which we shall learn
later.

We have next to describe the glandular constituents of the
ovary, which are by far the most important.

Beneath the firmer connective-tissue border layer we meet
with an almost non-vascular layer of youngest ovules, the
cortical or primordial follicle zone (Fig. 156, c).

We here discover the young ova, already represented in
Fig. 5. They are small globular elements (0.0587 mm. large),
with an elegant globular and vesicular nucleus (0.0226 mm.).

174

SEVENTEENTH LECTURE.

The cell body is constituted by a membraneless protoplasma
containing fat granules. Each of these ovules is surrounded
by a corona of small nucleated cells. The whole is finally
enveloped in connective tissue. These are the so-called pri-
mordial follicles which, often occurring quite crowded here,
present an enormous excess of egg-germs.

Other primordial follicles (Fig. 5, 2) become larger ; the
ovule, which has meanwhile also increased somewhat in size,
appears to be surrounded by a thicker hyaline rind. The
small investing cells now form a double row (a).

In the further development, however, both the cell layers

@;

■\

•"-*

FlG. 156.— Ovary of the rabbit ; a, germinal epithelium (serosa) : b, cortical or external fibrous
layer; c, youngest follicles ; <i, a somewhat more developed older one.

are separated from each other ; there is thus formed a smaller
cavity (Fig. 156, d) filled with a clear albuminous fluid.

In the growing follicle, this cavity becomes larger and
larger. The small cells increase and gradually form a strati-
fied epithelium. The ovum lies at one point crowded against
the wall, and surrounded and held by a heap of these cells.
A developed vascular net-work has, in the meanwhile, also
been formed in the follicular walls.

THE E EM ALE G EXE NATIVE APT A RATES.

175

The normal ovarium contains besides a small number of
ripest gland capsules (12 to 20). These are the Graafian fol-
licles (Fig. 157), discovered long ago by De Graaf. Their size
is determined, in a measure, by the dimensions of the mam-
malial ovum. In women they finally attain to 6 to 9 mm.

Fig. 157. — Mature follicle ; a, ovum : epithelial stratum covering the same, i, and lining the
cavity, c ; d, connective-tissue wall ; t», outer surface of the follicle.

The parietes consist of a double layer, an inner one with a
close capillary net-work, and an outer one with the ramifica-
tion of the larger blood-vessels. The wall itself (e, d) is unde-
veloped connective tissue. We here again meet with the
granular connective-tissue cells mentioned at page 54. They
may surround the vessel like a mantle. The small epithelial
cells of the follicles measure 0.0074 to 0.OT13 mm. (c).

At one point, mostly at the bottom of the follicle (Schro'n,
His), but occasionally also at the surface that is turned to-
wards the germinal epithelium (Waldeyer), we meet with the
mature ovum (a) surrounded by a thicker epithelial stratifica-
tion (8).

In the mammalial animal it remains uncommonly small, 0.2
to 0.3 mm. in diameter. This explains why its discovery was

176

SEVENTEENTH LECTURE.

C-

a~

'^r^SWIp

J

b —

o .,

first made in 1827, by an investigator of great merit, K. E.
von Baer. It appears scarcely conceivable to us ; for a sharp
eye sees the ovule, removed from the ruptured follicle, as a
white point, without a magnifying glass. The successor,
however, stands on the shoulders of the predecessor.

Let us tarry for an instant at this most important of all
cells (Fig. 158), without which there would be no higher ani-
mal world. Let us remove from
its surface the cells, which have
now become cylindrical, of the
epithelial investment, and our at-
tention will be first of all attracted
by the thick (0.009 to °-01 1 3 mm.),
resistant hyaline capsule, the so-
called zona pellucida or chorion (a).
Fig. 158.— Mature ovum of the rabbit; It is an inwardly deposited pro-

ti, zona pellucida : /'. yolk : c, germinal

vesicle ; ei, germinal spot. dlict of tllC SUl'l'OUnding Smaller

cells, and, seen with higher magnifying powers, is permeated
by the finest radial passages, the so-called porous canals.

The cell-body is a thick, fluid, more or less cloudy mass.
We perceive in it granules of albuminous matter, as well as
small drops of fat. In many mammalial animals, the quanti-
ty of the latter may become great, and the substance darker
and darker. This cell body is call the yolk or vitellus.

The cell nucleus (V) attracts our attention by its elegant
globular form, bordered by the finest lines. It now lies con-
centrically; its diameter is 0.0377 to 0.0451 mm. It has
received the name of the germinal, or Purkinje's vesicle.

In it, and almost always single, we finally notice the nu-
cleolus {d), a fat-like, glistening granule 0.0046 to 0.0068
mm. in size. It bears the name of the germinal, or Wagner's
spot, the macula germinativa. *

* We have just become familiar with quite ordinary things provided with special
names. This nomenclature originated in a former epoch of embryology. Further-
more, the follicular walls are called theca; their epithelial lining has been denomi-
nated the formatio or membrana granulosa, and the cellular substance surrounding
the ovum the cumulus proligerus.

THE FEMALE GENERA TIVE APPARA TUS.

177

The blood-vessels of the ovary pass, as we mentioned above,
from the hilus into the medullary substance. They at once
acquire such a development that the connective tissue forms
a relatively scanty connecting substance. The outer surfaces
of the veins coalesce with the latter tissue. The spindle cells
of the connective tissue must be muscular, for the ovary is
contractile (His, Frey). From the medulla numerous and
elegant vascular expansions pass between the follicles of the
cortex, circumvoluting them with the already described net-
work. The cortical zone, alone, is very poor in blood-vessels,
as we already know.

A considerable wealth of lymphatics is also met with in the
medullary substance. A net-work of the same also circum-
volutes the follicles.

The parovarium represents the remains of the embryonic
primitive kidney or the Wolffian body. It consists of con-
nective-tissue passages, lined with ciliated cells.

The ovary also originated from this primitive kidney, and
the permanent ordinary kidney from the efferent canal of the

e & .7

Fig. 159. — The ovary of a human fetus of 32 weeks, in perpendicular section ; a, germinal epi-
thelium ; b, youngest ova cells (primordial ova) lying in this ; c, a growing connective-tissue trabe-
cula ; d, epithelial cells becoming buried ; e, youngest follicles ; /, ovum — and germinal epithelial
cells in groups : g, lymphoid cells.

latter gland. Unfortunately, we cannot enter further into this

subject. We merely mention that, according to Waldeyer,

in the embryonic chicken, at an early period, at the inner side
8*

178

SEVENTEENTH LECTURE.

of the primitive kidney, an epithelial thickening appears, into
which the connective tissue of this organ sprouts in a hill-like
form. The latter becomes the frame-work substance ; from
the former originate the germinative epithelium, the epithelial
cells of the Graafian follicle, and, as the favored daughters of
the latter, the ova.

This section of the development is represented by our Fig.
159, a copy from Waldeyer's excellent monograph. The first
embryonic ovula, the "primitive ova," are, therefore, of epi-
thelial origin.

Pfliiger had, even before Waldeyer, acquired interesting

conclusions concerning the ovaries of the creature after birth.

From time to time, soon after birth, and then towards the

period of parturition, in the adult mammalial animal, the

old embryonic affinity reasserts
itself. The germinal epithelium
again proliferates downwards
in a conical form, and is at last
separated from the point of
origin. Thus arise irregular,
occasionally cord-like, and cy-
lindrical masses. These are
Pfliiger's follicular chains. I
have called them the egg strands
(Fig. 160). In their axis we
meet with certain of the epithe-
lial cells which have grown to
be ova. By constriction (2, a),
new Graafian vesicles are
formed.

What becomes of the follicles
of the ovary ?

Before sexual maturity they
appear to be frequently de-
stroyed by fatty degeneration
and also by colloid metamor-
phosis (Slayjansky, Frey). During the period of propagation,

Fig. 160. — Follicular chains from the ovary
of the calf; i, with ova forming ; 2 at a,
showing constriction into Graafian vesicles.

THE FEMALE GENERATIVE APPARATUS. 179

also, a similar destruction takes place in a portion of the
follicles.

Others, on the contrary, meet with a different fate. The
ripest follicles, which have reached the surface of the ovary,
become ruptured, naturally at the place of the least resist-
ance, and, therefore, towards the surface. The follicular fluid
with the ovule leaves the organ through the ruptured outlet.
The ruptured follicle is transformed into the so-called cor-
pus luteum, that is — to express ourselves more intelligibly
- — it returns, at last, by a complicated process of cicatriza-
tion, to a connective-tissue frame-work substance, leaving no
trace.

In the human female, the follicle normally ruptures at the
menstrual period ; in mammalial animals at the period of
rutting.

The ovule, liberated from the ovary and received into the
oviduct, there undergoes the familiar segmentation of the en-
capsulated cell (p. 15). Without impregnation, however, this
multiplying action is soon paralyzed. If the former takes
place, the old life is merrily and energetically continued. The
encapsulated ovum at last becomes an aggregation of numer-
ous small cells. From these living building stones is con-
structed the new animal body, somewhat as the architect
builds his house with stones. But the latter, the lifeless ones,
are brought from all directions, the former are the primitive
offspring of a single cell, members of a living family. It is the
difference between the living and the lifeless.

The oviducts, Fallopian tubes, have, beneath the serous
covering, longitudinal and transversely arranged smooth
muscles. The mucous membrane is glandless,* and projects
in a highly developed system of papillae and folds. The in-
ner surface is covered by ciliated epithelium.

During menstruation and pregnancy the womb or uterus
undergoes extremely important anatomical transformations.
There is scarcely any organ, except the ovary, perhaps, on

* All attempts to discover nerves here have, thus far, been unsuccessful.

1 80 SE V EN TEEN TH LECTURE.

which is so thoroughly impressed the stamp of a proliferating
formative life as the uterus.

Its fleshy substance is formed of longitudinal, transverse
and oblique muscles. Developed in an annular form, it at
last constitutes the sphincter uteri.

The mucous membrane — its tissue reminds one of lymphoid
connective substance — is lined with ciliated epithelium. Be-
low, in the neck, commences the stratified flattened epithe-
lium of the vagina. The surface of the mucous membrane is
sometimes smooth (fundus and body), sometimes with trans-
verse folds (upper portion of the cervix), sometimes projecting
in papillae (terminal portion of the cervix).

Tubular, frequently spiral uterine glands, which are sub-
ject to considerable variation, occur in the fundus and body
of the uterus. They have a lining of ciliated cylinder cells
(Lott). Our glands disappear below.

The uterus has a highly developed system of blood-ves-
sels. The wide veins coalesce with the tissue of the latter,
and gape in transverse sections.

The lymphatic apparatus also acquires a great develop-
ment, especially in the loose connective tissue of the mucous
membrane, then in the muscular layer, and finally, in the
subserous layer (Leopold). This is also in beautiful harmony
with this proliferating formative life.

The immense enlargement of the pregnant uterus consists
in the first line, in an increase of the muscular tissue. The
old mucous membrane is hereby disposed about the ovum as
a so-called transient membrane, the decidua, while a new
mucous membrane, destined to be a substitute, is meanwhile
formed beneath. Still, much is here obscure, and, in certain
groups of mammalial animals, we meet with great variations.

In the vagina we find external annular, and internal lonm-
tudinal muscles. The mucous membrane shows numerous
rugosities and folds, columnae rugarum. It has no glands,
and is covered by stratified, flattened epithelium.

The hymen is a vascular duplicature of the mucous mem-
brane.

THE FEMALE GENERATIVE APPARATUS. 181

The clitoris has a prepuce of mucous membrane tissue ;
the female glans is also covered by such a membrane with
numerous papillae. The corpora cavernosa and bulbi vesti-
buli remind us of the same tissue in the male.

The labia minora, nymphae, are folds of mucous mem-
brane, containing no fat, but numerous papillae and sebaceous
follicles.

The labia majora are rich in fat, and have internally the
characteristics of the mucous tissues, externally those of the
corium.

In the vestibulum and the ostium vaginae, numerous
mucous glands occur. The glands of Duverney or Bartho-
lini are larger organs of this kind.

The lacteal glands are primarily of similar formation in the
male and female body ; they do not become developed in the
former, and in the latter only after a prolonged period of
quiescence, and even then only when pregnancy commences.

We recognize in the mammary gland an aggregation of in-
dividual racemose glands, which open into numerous (18, 20
and more) canals, the so-called "lactiferous ducts."

Examined in the earlier period of life, our organ consists
merely of a ramified canal-work. It is hollow above ; below
in its knob-like terminal portion, it is completely plugged by
closely compressed cellular masses. The special gland-vesi-
cles or acini destined for secreting are still wanting. This is
the condition, during the days of childhood, of the male and
female lacteal gland, though the latter gradually advances
somewhat in its development.

The entrance of puberty exerts no influence oh the male
organ, but a great one on that of the female. There is here
a bud-like production of numerous terminal vesicles. As-
sisted by a development of fat cells, they produce the curved
elevation of the maturing female breast. In this manner the
female gland is prepared for a possibly coming activity ; but
it is only with pregnancy, and towards the end of the same,
that the lacteal secreting apparatus acquires its complete de-
velopment.

182

SEVENTEENTH LECTURE.

Let us now examine the organ at the height of its activity

in the body of the nursing woman
(Fig. 161).

The gland vesicles, rounded or
elongated (o. 1 128 to o. 1872 mm.),
are formed by a membrana propria
with fiat stellate cells. They have
a simple lining of low cylinder cells
(of 0. 01 13 mm.). Those finest se-
cretory canals between the cells,
which we have already mentioned
at p. 134, have also been demon-
strated here by means of injections.
The excretory canal-work also
has a cylindrical epithelium. How
far the fatty secretion of our organ,
the milk, depends upon the destruc-
tion of the gland cell, or whether the latter structure does not
simply express the produced or received fat substance from
the membraneless, contractile cell-body — are questions which
require more accurate investigation.

In advanced life, the female mammary gland loses its
secretory apparatus. It becomes reduced to the old canal-
system of a long passed period of childhood (Langer).

The colostrum (already mentioned at Fig. 124) contains, in
addition to albuminous fat vesicles surrounded by a very thin
envelope, gland cells and cell fragments, 0.01 5 1 to 0.0564 mm.
in size. The ordinary milk of a later period contains only
the former elements, the so-called milk globules. The size of
the latter varies from about 0.0023 to 0.009 mm-

Fig. 161. — Gland-vesicles of a nurs-
ing woman, with cells and capillaries.

EIGHTEENTH LECTURE.

THE MALE GENERATIVE GLANDS, THE TESTICLES WITH
THE EFFERENT APPARATUS.

THE seminal gland or testicle represents in the male organ-
ism that which the ovary does in the female body. We leave
its coarser structure, for the greater part, to descriptive
anatomy.

A firm connective-tissue envelope, called the albuginea,
invests our organ. Numerous and incomplete septa radiate
from it into the interior, where they finally unite above into
a thickened wedge-shaped mass, the corpus Highmori. The
interior is thereby divided into conical lobules whose apices
are turned towards the corpus Highmori.

A testicle-lobule consists of an aggregation of uncommonly
long convoluted canals or tubes. They present divisions and
communications, and finally pass over into each other in the
form of a loop, but never terminate in a cul-de-sac (Mihal-
kovics). These tubules are called seminiferous canals.

At the apex of the lobule, the seminiferous canal becomes
united into a straight excretory duct (tubulus rectus) which,
passing into the corpus Highmori, unites with others in a
reticular manner and forms a further tubular system, the rete
testis. From the latter continue nine to seventeen larger
canals, the so-called vascula efferentia. They at first pursue
a direct course, and thus perforate the albuginea ; then,
becoming narrow, they form with numerous convolutions
several conical lobes, the so-called coni vasculosi ; the latter
form the caput epididymis. The terminal canals gradually
come together into a single one 0.3767 to 0.45 mm. in
diameter. It forms, with numerous convolutions, the cauda
epididymis.

1 84

EIGHTEENTH LECTURE.

Further below, the efferent canal becomes straighter, and
its diameter increases to 2 mm. It is now called the vas
deferens. Not infrequently, a lateral caecal branch, the vas

aberrans Halleri, has previously entered
it. This is the coarser structure.

Having become familiar with this compli-
cated arrangement, let us investigate the
histological texture.

The seminiferous canals* (Fig. 162) have
about the same diameter throughout their
entire length. Their diameter is, in most
mammals, 0. 1 to 0.25 mm. They are re-
markably large in the rat (0.4 mm.). In
small animals the walls consist of a single
layer of firmly cemented endothelial cells.
In larger creatures, this inner layer is sur-
rounded by others which show the same
construction of flat nucleated scales, but
are fenestrated (Mihalkovics). As we shall
subsequently return to the parenchyma
cells, we merely remark here that the
efferent ductuli recti, deviating from these,
have a different epithelial lining, namely,
cylinder cells. In the rete testis there is

no gland membrane ;
the cells are pavement
shaped. Towards the
end of the rete, how-
ever, commences the
cylinder epithelium of
the epididymis.

The quiescent semi-
niferous canal is either
entirely (Fig. 163, a,
b), or, up to a narrow

Fig. 163. — From the testicle of the calf; a, seminiferous Himetl, ullea Willi

canals seen in more oblique, b, in more transverse sections ; j j 1 i

r, blood-vessels ; d, lymphatics. T O U 11 d e d polygonal

Fig. 162. — Human semi-
niferous canal; a, parietes,
b, cells.

WL

I

THE MALE GENERATIVE GLANDS. 185

cells, measuring 0. 01 13 to 0.0142 mm. The peripheral ones
present a radiated appearance. In man, their cell bodies
may contain a yellowish pigment. A coagulated, originally
thick fluid, albuminous substance between the spermatic cells
has been erroneously regarded as a second cell-work.

The connective-tissue frame-work substance of the organ is,
as we have previously said, developed from the inner surface
of the albuginea and the system of septa.

In many creatures (man, dog, rabbit) fibrillated connective
tissue prevails ; in others (rat, male cat, boar) it is much less
developed. In the rabbit the connective-tissue bundles are
invested by the first mentioned (Fig. 55, a) forms of cells
(the thin, nucleated plates, with protoplasma in the centre,
and a hyaline, cortical portion) ; there may even be regular,
endothelial cell membranes spread out over the seminiferous
canals and the blood-vessels. In the just mentioned second
group of animals we find the granular connective-tissue cells
(Fig. 55, b) in immense numbers, while in the first division
they are more scanty, or are scarcely met with.

These granular cells (generally rounded or polygonal, rarely
having processes, rich in protoplasm, fat, and brownish pig-
ment) remind one of the hepatic cell (Fig. 121). They have
a strand or column-like arrangement. Very frequently the
blood-vessels are here regularly ensheathed by such cell
layers, as we have described them (p. 55) in connection with
the vicinity of the vessels.

The blood-vessels (Fig. 163, c) circumvolute the convoluted
seminiferous canals in close apposition, with a long-meshed,
tolerably wide capillary net-work. We find this net-work
more strongly developed and rounded in the epididymis.
The latter part, also, probably has a secretory glandular ac-
tivity (Mihalkovics).

Let us consider, finally, the lymph passages (d) ; for the
gland tissue is entirely without lymphatic vessels. It was
Ludwig and Tomsa who founded our knowledge of this sub-
ject. Subsequent investigations, also a trifle of mine, have
been added.

1 86 EIGHTEENTH LECTURE.

The lymph passages keep in the spaces of the connective
tissue, bounded by the membranous but fenestrated combina-
tions of the flat connective-tissue cells.

They form a copious reticular canal-work. In transverse
sections of the seminiferous canals they form regular rings
around the latter, with large expansions at the nodal points.
A continued injection finally drives the mass through the
spaces of the flattened cells, as far as the outer layers of the
walls of the seminiferous canals. The solid inner layer of
the latter alone prevents the further advance of the mass
(Mihalkovics). Here and there a blood-vessel becomes en-
sheathed by the lymph current, but this is not the rule.

Larger lymph passages penetrate from the glandular por-
tion into the septal system and from here, coalescing, pass
beneath the albuginea. Having entered the latter, they be-
come valved vessels, which unite with those of the epididy-
mis. The final removal of the lymph takes place through
the spermatic cord.

The testicle arises, similar to the ovary, at the inner side of
the Wolffian body. From its canal-work arises the epididy-
mis (equivalent to the parovarium) ; the efferent canal of the
primitive kidney, disappearing in the female, persists in the
male generative apparatus, and becomes the vas deferens.
The remainder must be left to the history of development.

We have thus far considered only the quiescent gland.
Let us now, however, examine the same at the height of its
activity.

Let us commence with its product, the semen, or sperm.
It is by no means exclusively the product of the convoluted
glandular canals of the testicle, but its fluid portions are cer-
tainly also derived from the epididymis and the accessory
glands, although its most important and characteristic ele-
ments originate from the former source.

The whitish, thickened fluid, spread out in a thin layer on
the microscopic glass slide, presents a remarkable appearance,
which has been stared at for two hundred years, and was
formerly very curiously explained.

/

THE MALE GENERATIVE GLANDS. 187

Innumerable, lively moving, thread-like elements, the so-
called seminal filaments, seminal animalculae, spermatozoa
(Fig. 164) are here met with, suspended in a hyaline fluid.
Their movement was, at an earlier epoch,
credulously accepted as a proof of an inde-
pendent animal life. The name of the seminal
animalculae, spermatozoa, reminds one of that
period.

Nowadays we know that the motility of
the seminal filaments is very nearly related to
the ciliary motion (p. 35) ; we likewise know
that the so-called " seminal animalculae " rep-
resent tissue elements, cell derivatives. We
are now no less familiar with the motley di- Fis- l64 — Sper-

J matozoaof the

versity of forms which these filaments present sh.e?v : <?> head ; b

J * middle piece; c, tail.

in the animal kingdom.

Let us confine ourselves to the class of mammalia.

The filamentous, diminutive thing here shows a so-called
head (a), then a somewhat thicker, thread-like, middle ap-
pendage, the middle piece {b), and finally, extraordinarily
thin, and becoming finer, the terminal piece or tail (c).
There was formerly no distinction made between these fila-
mentous portions.

Whether this remarkable structure also has an internal
complication is not determined, but is improbable.

The head of the human seminal element appears as an oval
disk, somewhat widened backwards, 0.0045 mm. long and
about half as much in breadth, and not more than 0.0013 to
0.0018 mm. thick. The entire filament may have a length
of 0.0451 mm. ; but its terminal end is infinitely thin and dif-
ficult to recognize.

In the fruitful copulation, the seminal filaments penetrate
the zona pellucida of the ovum, conducted through the very
fine porous canals of this envelope (Fig, 158, a), and pass
into the yolk, that is, into the true ovum cell. They here
finally disintegrate by fatty degeneration.

The process of division which we have already mentioned

i88

EIGHTEENTH LECTURE.

at p. 14 may, indeed, commence without spermatozoa, and
even in the mammalial animal ; but it soon ceases. When,
however, the seminal elements have mingled their expiring
body with the yolk, then (in an enigmatical manner, it is
true), the multiplying process of the segmentation of the vi-
tellus is continued, until at last innumerable building stones
have been acquired, of which we have already spoken (p. 179).
Whence comes the seminal filament ?

For more than one generation this question has been very
correctly answered : from the convoluted canals of the testi-
cle. But the hozv has called forth the most diversified an-
swers among the older investigators, their successors, as well
as the present generation of histologists. The incipient,
crude and bad methods of examination certainly led the pio-
neers to the grossest delusions.

That we at present understand the whole, I certainly doubt
very much ; still we have made some progress.

Let us listen, therefore, to the results of the most recent
studies (Neumann, von Ebner, Mihalkovics).

We have already mentioned (p. 185) that the most external
gland-cell layer of the quiescent seminiferous canal presents

a prismatic radiated form. This
cell is the spermatozoa-producing
structure. All the numerous inner
cells of this glandular canal appear
to have no future ; they form merely
an indifferent redundant substance.
When the seminal gland becomes
active — in mammals this is only pe-
riodically the case, generally once
a year, in man in uninterrupted se-
quence throughout the entire pro-
creative epoch — when, therefore,
the testicle is active, a remarkable
metamorphosis occurs in these pris-
matic parietal cells (Fig. 165, b).
The epithelial cell-body grows inwards, that is towards the

Fig. 165. — From the seminiferous
canals of the rat ; «, parietes with the
cell nuclei ; parietal cells and sperma-
toblasts , c, the latter with small nar-
row nuclear corpuscles ; d, inner cell
layer.

THE MALE GENERA TIVE GLANDS.

189

axis of the glandular canal, into a pedicle or neck-like proto-
plasma process. It might remind one of a rude and clumsy-
candelabrum — but the comparison is a lame one.

These modifications of our peripherical cell layer have been
appropriately named spermatoblasts (von Ebner).

In each club-like projection there is formed a nucleus (c) —
how, we do not know. It becomes the head of the seminal
element. The protoplasma, further inwards, is changed into
the filament or tail. Thus each of our spermatoblasts pro-
duces a number (8 to 12) of seminal filaments. At last the
latter are set free, and lie in the lumen of the convoluted
canals of the testicle, the caudal end in the axis of the canal,
and directed downwards (Fig. 166, 1, b, c, 2).

Ova and spermatozoa are, there-
fore, according to their origin, quite
different things. The former repre-
sent very highly developed cells ;
the latter proceed from portions of a
more simple cell body.

Let us finally turn to the efferent
apparatus.

The vas deferens presents an exter-
nal connective-tissue layer, a middle
layer consisting of three strata of
muscles, and, finally, a mucous mem-
brane covered with cylinder cells.
The latter acquires below a greater
development.

The seminal vesicles and ejacula-
tory duct have a similar structure.

The prostate presents a system
of small racemose glands embedded
in an abundance of connective tis-
sue, which first acquire their com-
plete development at the period of puberty. The epithelium
has a double layer (Langerhans).

The Cowper's glands likewise belong to the racemose for-

Fig. 166. — Development of the
rat's spermatozua. i. Spermato-
blast a, with head b, and filament
c. 2. Nearly mature seminal fila-
ment with adherent protoplasma re-
mains.

190

EIGHTEENTH LECTURE.

mation. Their cells are cylindrical, but become lower in the
efferent canal-work.

The male urethra presents a pars prostatica, a consecutive
membranous middle portion (pars membranacea), and a
terminal division running through the penis (pars cavernosa).
The latter portion is surrounded by a cavernous tissue (corpus
spongiosum urethrce), which takes the shape of the glans an-
teriorly. Two similar cavernous structures, the corpora cav-
ernosa penis, are added.

The mucous membrane of the urethra has at first flattened,
and further downwards cylindrical cells. It is surrounded
by loose connective tissue, which might be called cavernous in
consequence of its great vascularity, and over this there are
smooth muscles. Racemose glandules occur in the prostatic
portion, as well as in the colliculus seminalis. The mucous
membrane presents folds. In the middle and lower portions
the muscular coating diminishes more and more. The mucous
membrane of the lower portion contains excavations (lacunae
Morgagnii) and small, undeveloped Littre's mucous glandules.
Towards the orifice of the urethra stratified flattened epithe-
lium again commences.

The skin of the penis, thin and flaccid, has a loose subcuta-
neous cellular tissue, free from fat, and permeated by smooth
muscular fibres. An extensible connective tissue, free from
fat, unites the two plates of the prepuce ; it also contains mus-
cular elements.

The thin skin of the glans has numerous papillae, which dis-
appear in the epithelial covering ; the inner, mucous-mem-
brane-like surface of the prepuce also shows such papillae.

The Tyson's glands occur on the inner surface of the pre-
puce, occasionally also on the glans, especially on the frenu-
lum. They participate in a very subordinate manner in the
formation of the fatty smegma praeputii.

Let us also mention, in conclusion, the structure of tile
corpora cavernosa. These structures are surrounded by a
firmer, elastic element, which is however poor in muscular
elements, a so-called albuginea. It sends off innumerable

THE MALE GENERATIVE GLANDS. 191

processes in an inward direction, which are sometimes larger
sometimes smaller, in the form of trabeculae and plates. Con-
nective tissue, elastic fibres and smooth muscular substance
combined form the latter.

This incomplete system of septa, as we must call it, is
divided and interconnected in the most multifarious manner.

We have, therefore, a system of spaces and cavities, remind-
ing one of a bathing sponge, lined with vascular cells, des-
tined to receive venous blood. Herein consists just the pecu-
liarity of the so-called cavernous tissue.

The various " cavernous bodies " present small subordinate
structural peculiarities. We pass over these minutiae.

Constantly filled with blood, they become periodically over-
charged with the same, and cause the erection of the male or-
gan.

The cavernous bodies receive their blood supply to a slight
extent from the arteria dorsalis penis, essentially from the
arteria profundae. These arterial branches, enclosed in the
tissue of the septum, pass into the cavernous spaces, partly
through a capillary net- work, partly with an intermediate
opening (Langer). Corkscrew-like, crooked arterial branches,
the so-called arteriae helicinae of J. Miiller, constitute artefacts
(Bouget, Langer).

The various venae emissariae serve for the removal of the
blood from the caverni.

Abundant lymphatic net-works are not wanting in the male
urethra and the organ of copulation (Teichmann, Belajeff).

The theory of the erection we leave to physiology.

NINETEENTH LECTURE.

NERVE TISSUE.

We turn to the final and highest histological formation of
the animal body : we refer to the nerve tissue.

This has been included among the so-called " compound
tissues," that is those which possess more than one element.
And, in fact, we here meet with two such, namely, fibres and
cells. The former bear the name of the nerve fibres, nerve
tubes or primitive fibres ; the latter are called nerve cells or
ganglion bodies.

The human nerve fibres appear either as dark contoured

medullated elements (Fig. 167) or as
pale non-medullated ones (Fig. 172, b).
Since the former constitute by far
the most widely extended and impor-
tant peripheral elements, let us begin
our discussion with them.

They are, like the non-medullated,
for long distances unramified fila-
ments, but of very unequal diameter,
from 0.0226 to 0.0018 mm. and less.
We distinguish, accordingly, broad or
coarse nerve fibres (Fig. 167, a) and
fine or narrow ones {c, d, c). Inter-
mediately between these appear the
ill \lj nerve tubes of medium width (b).

V \ II I"' (\ Let us commence our investigations

of the structure with the coarse, medul-
lated elements.

Fresh and living, it appears like a
thread of a homogeneous milk-glass-like substance. We
recognize in it no further composition.

a

Fig. 167.— Human nerve
fibres : a, broad ; 6, medium
breadth ; c, d, e, fine.

NERVE TISSUE.

193

The nerve tube is, however, a marvelously changeable
thing. Under our eyes, and against the will of the observer,
it changes its original appearance most rapidly into a second,
third cadaveric image.

It is at present established that every broad nerve tube con-
sists of three elements.

It is invested by a, as a rule, very fine homogeneous con-
nective-tissue envelope, the neurilemma, the Schwann's or
primitive sheath (Fig. 169, b, 171, e). The latter contains, from
point to point, an elongated nucleus. Occasionally the neu-
rilemma appears considerably thickened (Fig. 171, c).

In the axis, occupying a fifth to a fourth of the entire
diameter, we recognize a pale cylindrical filament, formed of

Fig. 168. — Human nerve
fibres in various stages of
coagulation.

Fig. 160. — Various nerve fibres ;
a, after treatment with absolute
alcohol : £, with collodion ; c,
fibres of the lamprey ; d, from the
olfactory nerve of the calf; e and
y", from the human brain.

an albuminous substance. This is the axis cylinder, the sole
essential portion of the nerve tube (Fig. 169, a, b, c, e, 171, e).
It is surrounded by the so-called nerve medulla or medullary
sheath, a peculiar and very delicate combination of albumin-
9

194 NINETEENTH LECTURE.

ous bodies, as well as lecithin and cerebrin. This investment
originally conceals the axis cylinder.

As soon as we isolate broad nerve tubes, we encounter the
cadaveric form of the medullary sheath (Fig. 168). "They
are now coagulated," is a customary expression of the histolo-
gists. We meet with the most varying stages of coagulation,
often close to each other, and even in the course of one and
the same primitive tube.

As a commencing stage, we discover on both sides a
double contour, a sharp but dark external, and a closely
applied finer border (Fig. 167, a, b, 168, b, above).

Later, the double contours no longer run parallel with each
other, and the inner one appears frequently interrupted (Fig.
168, b, below). The latter becomes constantly more and
more irregular, and in the previously homogeneous axis por-
tion, dark bordered, lumpy substances are formed (a, b).
The process of coagulation may, it is true, be arrested at an
earlier stage. The cortex then forms to a certain extent, a
protective mantle around the axis portion. In other cases,
the latter also does not escape its final destiny ; together
with the cortex it is completely disintegrated into clots (c).

It was a long time before the just described structure of
the nerve tubes could be agreed upon. The existence of the
axis cylinder, especially, gave rise to heated debates. It is
to-day a child's play to recognize the latter in any transverse
section of a hardened peripheral nerve or — which amounts to
the same — each primitive tube in a white column of the spinal
cord (Fig. 170).

The nerve tubes of medium size have a
similar constitution.

A similar structure— envelope, axis cylin-
der and medullary sheath — is also perceived
in the fine filaments of the nerve trunks.

Fig. 170. — Trans-

verseiy divided nerve The medullary sheath ( Fig. 167, c,d) remains

fibres from the postern ir '

column of the human clear, and simply demarcated, even with

spinal cord. l J

advanced post-mortem changes. Osmic
acid, which rapidly blackens the medulla of the broad nerve

NERVE TISSUE.

195

fibres, as it does other fatty substances, here acts much less
thoroughly and more slowly ; there must certainly, therefore,
be a difference in the constitution of these two different
fibrous substances.

Our fine nerve tubes present an additional peculiarity.
Every mistreatment, pressure, pulling or reagent to which it
is subjected causes a certain displace-
ment of the medulla, so that unnaturally
thinned spaces interchange with rounded
bulgings (e). The latter have been desig-
nated as varicosities, and varicose nerve
fibres are spoken of. Nothing of the
kind exists during life.

We here touch upon another unsettled
question. Ranvier, at present the first
histologist of France, called attention to
a familiar phenomenon, to constrictions
which occur in the course of broad
medullated (peripheral, but not central)
fibres. Formerly, however, these con-
strictions were always regarded as a
product of the methods of preparation.
Now, these constricted places (Fig. 171)
are pretty regularly situated, and be-
tween every two, very nearly at half
the distance, one meets with a nucleus
of the sheath of Svvann (a). It is thus
in mammals, birds, and amphibia ; but
in fishes the number of nuclei is greater
between every two of these constric-
tions.

These Ranvier's " constriction rings,"
as the Germans have christened them,
deserve — although we are at present far removed from an
accurate knowledge of them — every consideration. The
medullary sheath certainly isolates the axis cylinder ; but
this medullary space permits the penetration of nutrient

Fig. 171. — Nerve fibres of
the frog; a, after treatment
with picro carmine : b, c, d, with
osmic acid ; e, with nitrate of
silver.

196

NINETEENTH LECTURE.

constituents and the giving off of the products of decomposi-
tion.

Let us now pass to the pale non-medullated nerve fibres.
Originally, in the foetal period, all the primitive tubes of
the entire nervous system were thus constituted. If we take
one of the lowest fishes, the lamprey (petromyzon), we meet
with this condition throughout its entire life (Fig. 169, c). A
nucleated sheath invests the axis cylinder. Medullated nerve
fibres are here entirely wanting.

Let us turn, at a bound, to the highest animal being, to
man.

In us, the olfactory nerve, alone, consists throughout of
pale, non-medullated fibres, as does in great
part the sympathetic with its ramifications.
These pale structures have been called
Remak's fibres. They appear as delicate
0.0038 to 0.0068 mm. wide, nucleated fila-
ments (Fig. 172, b).

Does what has been mentioned above,
however, contain the entire structure of the
nerve fibre ? We now encounter this diffi-
cult question.

It does not appear so ; nevertheless, we
are once more at the limits of the microscopy
of the present day.

The axis cylinder, the best portion of the
nerve tube, most probably consists of a
bundle of extremely fine filaments.

They (Fig. 173) appear to be embedded in
a delicate granular substance. They have
been called axis fibrillae (Waldeyer) or primitive fibrillae
(Schultze). Here, also, the incitation was furnished by a bril-
liant investigator, who has by no means been honored by his
cotemporaries in proportion to his merits, Remak, the
founder of the modern history of development. Many years
ago he saw this combination in the nerve fibres of the river-
crab.

Fig. 172. — A sympa-
thetic nerve branch of
a mammalial animal ;
two dark bordered
nerve fibres, a, with an
excess of the Remak's
formation, b.

NERVE TISSUE.

1 97

Diagnostic weight has subsequently been laid on the finest
varicosities of these primitive fibrillar (M. Schultze).

We shall subsequently return to this.

We are now, so far as it is at present
possible, familiar with the fibres. Let us
turn to the cellular elements. They belong
solely to the gray substance of the nervous
system (the peripheral, as well as the cen-
tral) ; the white substance consists through-
out solely of nerve tubes.

SI

: .

;

;
■

Fig. 173. — Fibrillated
arrangement of the
axis cylinder ; a, a
thick axis cylinder from
the spinal cord of the
ox ; b, nerve fibre from
the brain of the torpedo.

Fig. 174. — Ganglion cells of the mamma-
lia ; a, cells with connective-tissue envelopes,
which are continued in fibres, d, d ; a, a cell
without a nucleus ; b, two single nucleated
ones ; and c, one with two nuclei ; b, a gan-
glion body without an envelope.

We frequently encounter, in a very characteristic form,
those cellular elements, the ganglion bodies (Fig. 174, B). It
is one of the handsomest cell-forms which the organism pos-
sesses. The dimensions of most of the globular, ovoid or
pear-shaped elements lies between 0.0992 to 0.0451 and
0.0226 mm. In a very delicate granular, thickly gelatinous,
generally colorless, occasionally brown or black pigmented
mass, we meet with a globular, delicate walled nuclear vesicle,
0.0180 to 0.009 mm- in diameter. In it occurs, as a rule
single, a dull glistening granule, the nucleolus, 0.0029 to
0.0045 mm- m size-

198

NINETEENTH LECTURE.

Our structure is surrounded by an envelope. It appears
thick, a sort of nucleated connective tissue at the first glance ;
however, the nuclei may have another signification, for, on
the inner surface of the capsule, a lining of endothelial cells
has subsequently been noticed.

This envelope appears more simple and thinner around the
ganglion cells of the lower vertebrates, fishes (Fig. 175) and
amphibia.

At the first, most cursory examination — and the older his-
tologists, with their bad methods of investigation, arrived no
further — all the peripheral ganglion cells appear to have no
processes or, as a scholastic expression runs, are apolar. We
have subsequently adopted an entirely different view ; apolar
ganglion cells either do not occur at all, or only exceptionally

as embryonic, arrested in
their development, and
possibly futureless ele-
ments.

About 1845, Koelliker,
one of the most cele-
brated histologists, dis-
covered in the sympa-
thetic of the vertebrates
ganglion bodies which
sent off from one of their
ends a pale filament, which
after a sometimes shorter,
sometimes longer course,
was enveloped in a me-
dullary sheath, and be-
came a nerve fibre (Fig.

175,4

In vertebrate creatures

something of the kind
has, it is true, been previously seen. These are the so-called
unipolar ganglion cells.

Soon after this, R. Wagner, Robin and Bidder, with Rei-

Fig. 175. — From the peripheral nerve ganglion of a
fish, godus lota ; a, b, bipolar ganglion 'cells ; c, uni-
polar ; d, e, abnormal forms.

NERVE TISSUE.

1 99

chert, met with other conditions. They discovered the bi-
polar cells.

The spinal nerves arise by a double root ; an anterior,
which passes over the spinal ganglion, and a posterior, which
passes through the ganglion.

Frc. 176. — Multipolar ganglion cell from the anterior horn of the spinal cord of the ox, with the
axis cylinder process [it), and the branched protoplasma process, from which, at b, the finest
filamenis arise.

As has been known since the days of Charles Bell, the
former consists of motory, the latter of sensory filaments.

200 NINETEENTH LECTURE. ■

On teasing out the spinal ganglion of a fish (the ray is most
to be recommended) we recognize (Fig. 175) that each nerve
fibre penetrates a ganglion cell, to again pass out at the other
pole (a, b). Broad fibres connect with larger cells, narrow
nerve tubes with smaller ones.

The latter nerve fibres are probably sensory constituents
of the sympathetic. Numerous individual, otherwise consti-
tuted combinations occur, in addition to these, perhaps as
anomalous products of development {d, e).

Both varieties of ganglion cells show distinctly that their
envelope passes over into the primitive sheath of the nerve
fibre connected with them.

As a third form, we have to mention the multipolar gan-
glion cells. They were seen for the first time in the year 1838
(Purkinje). They are met with in man in the sympathetic
ganglia, in the retina of the eye, and in the gray substance
of the brain and spinal cord.

In the so-called anterior cornu of the latter is found the
elegant form of our Fig. 176.

A membraneless cell body sends off a varying, often quite
considerable number of delicate granular processes (b), which
undergo repeated divisions and continual ramifications, until
they at last disappear from view in the form of the finest fila-
ments. The finest lateral filaments were regarded as primi-
tive fibrillar of the axis cylinders (Deiters), but hardly with
accuracy, for all is here obscure.

Together with this system of processes — they have been
called protoplasma processes — we also meet with a long pro-
cess, which is always single, and usually arises from the cell
body, more rarely from the origin of another thick offshoot.
It never ramifies, and is conspicuous from its sharper, homo-
geneous appearance. This is the axis-cylinder process (a).
Later it is invested by the medullary sheath, and becomes a
nerve' fibre. This has also, however, been recently doubted
(Golgi).

In the sympathetic of the frog Beale and Arnold met with
an interesting, although not yet accurately determined struc-

NERVE TISSUE.

201

ture of the cells (Fig. 177). From the interior of its rounded,
or pear and kidney-shaped body passes a straight axis-cylin-
der process (c), which subse-
quently acquires a medullary
sheath.

From the surface of the cell
arises, singly or doubly, with
close spiral convolutions, an-
other filament, which surrounds
the straight axis cylinder with
wider turns ; it may also run
alongside of the latter (d), and
subsequently leave it (/), pass-
ing further in a straight form.
Whether these spiral fibres are
elastic or — which we regard as
more probable — are actually of
a nervous nature, is still unde-
cided. Subsequent German in-
vestigations have, unfortunately,
not determined this.

Finally, the fine, fibrillated
formations, such as are pre-
sented by the axis cylinder (p.
196), have also been most re-
cently observed, continuing into the interior of the cell body,
and more especially in the cortical portion of the latter. The
finest fibrillae which stream in from the protoplasma, as well
as the axis-cylinder process, run sometimes divergently, some-
times crossing each other.

Fig. 177. — Ganglion cell from the sym-
pathetic of the hyla or green tree-frog ; a,
cell body ; b, sheath ; c, straight nerve
fibre : and d, spiral fibre ; continuation of
the former, e ; and of the latter, f.

TWENTIETH LECTURE.

THE ARRANGEMENT AND TERMINATION OF THE NERVE

FIBRES.

The spinal nerves and those of the brain appear white
through the medullary sheaths of their tubular constituents ;
the trunks of the sympathetic appear gray from the excess
of non-medullated fibres.

The former, at their exit from the central organ, become
invested in a delicate connective-tissue envelope ; they are
subsequently surrounded by an additional reinforcement of
connective tissue, furnished by the dura mater. This affords
together the nerve sheath, perineurium or neurilemma. This
connective tissue penetrates, in a lamellar or sheath-like man-
ner, between the bundles of nerve fibres, becoming, at the
same time, looser and softer. Its modified boundary layer
forms at last the primitive sheath of the nerve tube. A
scanty, straight net- work of finest capillary vessels permeates
the whole. Injections made from the lymph spaces likewise
penetrate beneath the perineurium and between the nerve
bundles (Key and Retzius).

The primitive fibres run alongside of each other in the
nerve trunk, undivided and indifferent. The nerve trunks
usually send off their branches at an acute angle, the bundles
of fibres bending away from the main path to the lateral.

When anastomoses take place, groups of fibres pass, at the
point of communication, from the one nerve to the other, or
we have a double interchange of fibres.

The perineurium becomes finer and finer in proportion as
we proceed from the larger trunks to the finest systems of
branches. Finally, it appears as a striated or more homo-
geneous connective substance with rather stunted cells.

ARRANGEMENT OF THE NERVE FIBRES. 203

The investigation of the peripheral termination of the
nerve tubes — in the crude, incipient period they were erro-
neously regarded as a noose or loop-shaped connection be-
tween each two fibres — cost the histologists much trouble and
labor, and even at the present day we are still far removed
from a satisfactory scientific possession. We present only
the most important facts, and leave numerous, in part very
uncertain, minutiae to the more comprehensive text-books on
this subject.

Let us commence with the termination of the motory nerve
fibres in the transversely striated muscle.

If we follow the small nerve branches which have entered
the latter, in suitable objects, for example, many quite thin
membranous muscles of the frog, we meet with a few broad,
double contoured nerve fibres, subsequently surrounded by a
hyaline sheath. If the branch divides again, we not infre-
quently perceive that something new comes over the nerve
tube ; it becomes narrower, forming a Ranvier's constriction
ring (p. 195), and, at the same time, divides into branches,
two as a rule. With the continued division of these smallest
nerve trunks, this diminution of the nerve branches is con-
tinued ; they divide into branches of a new order, and so on.
The latter hereby become finer, but still retain the double
contours for a distance; at last they are bordered by a simple
boundary line.

In the lower vertebrates this ramification of the primitive
tubes is very extensive. In fishes, the latter may finally
divide into fifty and even one hundred branches. Reichert,
many years ago, examined the so-called thoracic cutaneous
muscle of the frog. It contains from 160 to 180 muscular
filaments, but only from 7 to 10 nerve tubes pass in for their
supply.

While, therefore, in the lower vertebrates a motory primi-
tive fibre supplies with its system of branches quite a number
of transversely striated muscular filaments, the arrangement
is different and higher in mammals (and even in reptiles and
birds). The primitive fibre is much less divided ; the mis-

204

TWENTIETH LECTURE.

proportion between the number of the nerve and muscular
filaments is accordingly very much less.

In regard to the termination, the lower vertebrates present
a different condition from that of the higher. The termina-
tion takes place regularly, however, in the interior of the
muscular filament, beneath its sarcolemma. We consider
only the mammalial muscle (Fig. 178).

<r

Fig. 178. — Two muscular filaments from the psoas of the Guinea-pig, with the nerve terminations ;
a, b, the primitive fibres and their continuation into the two terminal plates c./\ c, neurilemma
with nuclei, d, d, and passing over into the sarcolemma, g, g\ k, muscular nuclei.

The nerve fibre {a, b), surrounded by an expanding nucle-
ated primitive sheath (c, d), here passes to the muscular fila-
ment. Its neurilemma becomes the sarcolemma (g). Beneath
the latter, at the place of entrance, appears a nucleated, deli-
cate molecular substance, a rounded or oval bent plate with
nuclei (e,f), concave within, convex without. This (occur-
ring only single in the mammalial muscle, and more towards
the middle) is the terminal plate of Krause, Rouget and Engel-
mann, or the nerve-mound of Kuehne. At f, we have the

ARRANGEMENT OF THE NERVE FIBRES.

205

profile view ; at e, we see the structure from its broad
external surface. Its size varies between 0.0399 to 0.0602
mm. ; the number of the nuclei from 4 to 20.

The great delicacy and changeableness of the motory ter-
minal plate impedes its further study considerably. Does the
axis cylinder actually cease on spreading out into the former?
Or, does the termination of the axis cylinder first occur in the
interior of the terminal plate, so that the signification of some-
thing like a cushion is to be ascribed to the latter?

In the muscular filament of the lizard (Fig. 179) we obtain,
under certain circumstances, a peculiar interesting appearance.
In penetrating the terminal plate, the axis cylinder of the nerve
fibre {b, c) divides and, rapidly
losing its medulla, passes over by a
continual ramification into a pale,
obtusely branched, antler-like fig-
ure (d,d). The molecular nucleated
substance is just beneath this ex-
pansion. We are indebted to
Kuehne for this observation. I
have seen something similar by
reexamination ; but we are once
more at the limits of the present
microscopy. Kuehne named this
antler-like formation the true ter-
minal plate.

This is, according to our expe-
rience, the present state of the

matter. Others maintain deviating views, as most recently
Arndt and Gehrlach. It is impossible for us to enter here
into a polemic, the more so as this lies at the limits of the
present microscopic perception.

Concerning the nerve termination in the muscles of the
heart, only hypotheses exist at present.

We have also no very satisfactory knowledge of the nerves
of the smooth muscles.

Many years ago various observers (Beale, Arnold, His,

Fig. 179. — Muscular filament (a) of
the lizard ; b, nerve fibre ; c, its branches
with the peculiar terminal figure, d.

206

TWENTIETH LECTURE.

Klebs and others) had met in this tissue formation with
plexuses or net- works of pale, fine nerve fibres with nuclei in
the nodal points. This net-work was regarded as terminal.
Others have, however, proceeded further, whether correctly
we certainly doubt.

Arnold, who has investigated these things most accurately,
gives us the following information concerning them :

The nerve trunks of the smooth muscular tissue (Fig 180)
consist in part of medullated, in part of non-medullated fi-
bres. The latter diminish
into nucleated filaments mea-
suring 0.0018 to 0.0023 mm.
Even externally in the con-
nective tissue surrounding
the muscular substance, there
occurs a wide-meshed plexus,
having ganglion cells in
places, Arnold's so - called
basis plexus. From the lat-
ter pass nucleated fibres,
which become pale, longitu-
dinally striated, nucleated fil-
aments, 0.0041 to 0.005 mm-
in diameter. The latter grad-
ually diminish to 0.0018 to
0.0023 mm.

From these — though pale
and, therefore, non-medullated fibres also enter it from the
basis plexus — there is formed a second and likewise tolerably
wide-meshed reticulum, which also has nuclei at the nodal
points. This is Arnold's intermediate plexus. It is either
closely applied to the smooth muscles, or lies in the connec-
tive tissue between the several layers of the first-mentioned
tissue.

From this second plexus pass off fine fibres, which are at
first still nucleated. They rapidly become finer, and pass be-
tween the contractile fibre cells. Finally, after repeated divi-

Fig. 180. — The termination of the nerves in the
smooth muscles of a frog's artery.

ARRANGEMENT OF THE NERVE FIBRES. 207

sions, they have diminished to fibrillae of only 0.0005 to
0.0003 mm. They arc said to form a new, but now very
narrow-meshed reticulum of the third order, the intramuscu-
lar plexus, between the spindle ceils of the tissue.

From the latter proceed extremely fine filaments, 0.0002
mm. in size, and therefore primitive fibrillae, into the fibre
cells. Their discoverer, Frankenhaeuser, asserts that they
terminate in the nucleoli, but Arnold is already doubtful on
this point.

A few years ago, as I examined the muscular vascular walls
of the frog, by the aid of the best customary methods, I saw
only nerve plexuses. Klein also went no further. I suspect
that the predecessors — in this most difficult department — have
also deceived themselves.

The nerves of the cornea of the eye have been the object
of very extensive researches for years. We here meet with a
twofold manner of termination ; one in the proper corneal
tissue, and another in the epithelial stratum of the free an-
terior surface The latter is certainly sensory, the former
most probably of a motory nature.

The corneal nerves enter at the periphery as a bundle of
fine, at first medullated fibres. The medullary sheath is soon
lost ; we have pale filaments to which must here, as in the
smooth muscles, be at first ascribed the signification of the
axis cylinder, and subsequently of the primitive fibrillae (p.
196). In the cornea we also meet, from behind forwards,
with a series of nerve plexuses, lying one over the other, with
evident divisions of the fibres.

A considerable contingent of the latter terminate in the cor-
neal tissue. How, is unknown. A former statement of
Kuehne's, according to which the primitive fibrillae were said
to finally unite with the corneal cells (p. 56), could not be
confirmed.

Cohnheim, after the example of Hoyer.has shown that from
the most superficial nerve plexus of the cornea the finest nerve
filaments (primitive fibrillae or fasciculi of the latter) pass into
the stratified, flattened epithelium of the above mentioned

208 TWENTIETH LECTURE.

conjunctiva corneas. Ascending perpendicularly, and rami-
fying once more, they finally disappear in the most superfi-
cial layers of flattened cells (Fig 36, d, e,f).

We have no certain knowledge concerning the termination
of the nerves of glandular organs. That the secretion of
the submaxillary gland is very dependent on nervous influ-
ence (p. 140J, is an old physiological experience. What
Pflueger has communicated concerning the salivary glands
and the liver has not been confirmed. Other statements of
Krause's must likewise be more accurately tested.

Passing now to the sensory nerves, we meet with three dif-
ferent conditions :

a. A portion of the same run out into considerable, and
in part, right complicated larger or large structures.

b. Others have their termination in the small corpuscles of
the epithelium.

c. The higher nerves of sense, finally, pass into quite pecu-
liar specific cellular elements, so-called " sensory cells."

We discuss directly the first two terminations. The third
and last we shall have to mention at the organs of sense, at
the close of these lectures.

The larger terminal apparatuses of the sensory nerves
are :

1. Krause's terminal bulbs. 2. The Pacinian corpuscles.
3. The Wagner-Meissner's tactile bodies.

Let us commence with the first. The terminal bulbs, dis-
covered by Krause, are of isolated occurrence, and are not
easy to find in the unpropitious tissue of the mucous mem-
brane ; they are by no means favorites of the histologists.
For years, only Koelliker and myself maintained their exist-
ence, which was at that time doubted even by Arnold. Wal-
deyer, an excellent investigator, recently declared to us that
he had also been unable to find them. I have seen them
in the calf, but have not had a sufficiency of human autop-
sies.

According to Krause, the terminal bulbs occur in the con-
junctiva bulbi, in the mucous membrane of the floor of the

ARRANGEMENT OF THE NERVE FIBRES.

209

mouth, in the papillae fungiformes and circumvallatae of the
tongue, in the glans penis and clitoridis. The discoverer
also found them in not inconsiderable extension in mam-
mals.

Let us take the sclerotic conjunctiva of a calf's eye (Fig.
181), and follow the course of the nerve
through the separated mucous membrane.
After a long interval, we meet in the first
place (*) with a dichotomous division of
the double contoured nerve fibre (c).
Then, after following the branch for a
shorter or longer distance, we arrive at a
striking appearance (a). It is an elongated
oval, occasionally slightly bent body,
measuring 0.075 1 to o. 1409 mm. in its
greatest diameter, and about one-third as
much in its transverse. In man and the
ape, the structure has a globular form, ac-
cording to Krause.

Let us return to the calf. We here
meet with a dull, nucleated, moderately
thick envelope, with an enclosed hyaline,
homogeneous, rather thick fluid contents.

The primitive sheath of the nerve trunk
gives off its neurilemma to this mem-
brane, or, to express ourselves more intelli-
gibly perhaps, it increases in thickness
and becomes the parietes of the terminal
bulb.

At the first cursory examination, one might suppose that
the nerve fibre had thus terminated. One would, however,
be very much deceived ; for, after losing its medullary
sheath, the most important constituent of the nerve fibre,
the axis cylinder, passes through the structure to end at
the opposite pole, occasionally with the slightest intumes-
cence.

This is the terminal bulb, so far as I am familiar with it.

Fig. 181. — Terminal bulb
from the conjunctiva bulbi
of the calf; «, terminal bulb;
c, nerve fibre, branching at*;
i, axis cylinder.

210

TWENTIETH LECTURE.

Concerning the Pacinian capsules (Fig. 182) we have abun-
dant and no longer to be doubted material.

These structures have had a
peculiar history.

They have been known for
more than one hundred and thirty
years.

They were described in 1741,
in the doctor's dissertation of a
certain Lehmann, having already
been discovered by a professor
Vater of that period. They were
forgotten for nearly three genera-
tions.

They were rediscovered soon
after 1 830, without any presenti-
ment of a predecessor, by Pacini
of Pistoja and, almost simultane-
ously, on the occasion of an ana-
tomical concourse, by Parisian
physicians. The attention of
the German investigators was
especially directed to our structure by the monographs of
Henle and Koelliker, in the year 1844. As a student at
that time in Gcettingen, I had already found them in the
abdominal cavity of the cat, and had seen the entering
nerve.

Let us leave these historical reminiscenes, however, and
pass to matters of fact.

The Pacinian bodies appear as elliptic structures, measur-
ing 1 to 2 mm. and more, sometimes more elongated, some-
times more developed in width. Without the microscope,
we perceive them to be tense, tolerably firm, semi-transpar-
ent, and with white axial striations.

They are regularly met with in the human body on the
nerves of the palm of the hand and the sole of the foot,
especially of the fingers and toes. Their total number varies

FlG. 182. — Pacinian body from the mes-
entery of the cat ; a, nerve fibre with its
envelope, forming the stem ; b, the cap-
sular system ; c, the axis canal or inner
bulb, in which the nerve tube ends.

ARRANGEMENT OF THE NER VE FIBRES. 2 1 1

here between 600 and 1,400 examples. They may occur
manifold or isolated.

In mammals we meet with them in the sole of the foot.
An admirable locality is the mesentery of the cat. Many of
the latter animals contain them in innumerable quantities ; in
others, on the contrary, one may bother and fret one's self and
find only 6 to 12 altogether.

The capsular system of the Pacinian corpuscle {b) is much
more complicated in its structure than the simple envelope
of the terminal bulb.

It consists of a considerable number of thin, connective-
tissue membranes, embedded over each other, and kept tense
by a fluid intermediate substance. They formerly appeared
to contain nuclei in their parietes. According to the investi-
gation of Hoyer, however, their inner surfaces are lined by
a thin covering of nucleated endothelial cells. The outer
capsular systems are further removed from each other, follow-
ing the curvature of the entire structure ; the inner ones are
more nearly approached to each other, their lateral curvature
is lessened, and they finally surround an axial canal. This,
the so-called inner bulb (c), may be compared to the Krause's
corpuscle. It is filled by a homogeneous, tolerably resistant
substance.

The capsular systems unite below, and form a thicker con-
nective-tissue tube (a). Through it passes a broad or medium
sized, but always double contoured nerve fibre. Having
entered the inner bulb, it loses (at c, below) the medullary
sheath ; it becomes an axis cylinder, and terminates towards
the upper closed pole, for the most part undivided, occasion-
ally (and then varying in its details) divided (c, above). This
axis cylinder is the most beautiful known. It shows a longi-
tudinally striated structure, and consists of primitive fibrillae.

Let us turn, finally, to the so-called tactile bodies of the
human integument (Fig. 183). They belong — no doubt can
prevail concerning this — to the related series of the terminal
bulbs and Pacinian structures ; but the nerve termination is
not yet known.

212

TWENTIETH LECTURE.

In a preceding lecture (p. 58), we remarked that the human
corium developed papilla-like projections, which were some-
times higher, sometimes
lower. In the volar sur-
face of the fingers and
toes, the hollow of the
hand, and the sole of
the foot, and, finally,
the heel, we meet with
papillae of a double na-
ture. One portion con-
tains a vascular loop {b) ;
others, non-vascular,
contain the nerve ter-
mination (above, i).
The number of these
nerve papillae is great-
est at the volar surface
of the finger point ;
from here they con-
stantly decrease. The
toes are less favored ;
but here, also, the same
law prevails of the diminu-
tion towards the sole of
the foot. Without going
further into this subject,
we merely remark here
that only the ape, our
nearest corporeal relation,
presents tactile bodies.
They are wanting in the
other mammals.

A tactile body (Fig.
184) is either oval or,

Fig. 184.— Two human nervous papillse from the ,,,,>1, cmallpr rlimptisinns

skm of the volar surface of the index finger. In the W1U1 Smaild aimeilSlOIlb,

interior of the papilla is the tactile body, into the ~r\t\nAc*A Tfc rlinmptpr

tissue of which the nerve fibres enter. rOUnaea. IIS UlclIIlCLCr

Fig. 183. — Human skin in perpendicular section; a,
superficial layers of the epidermis ; b, Malpighian rete-
mucosum. Beneath the latter is the corium, forming the
papillae above at c, and terminating below in the subcu-
taneous connective tissue, in which at A, aggregations of
fat cells appear ; g, sudoriparous glands, with their excre-
tory ducts e andy"; ti, vessels ; c, nerves.

ARRANGEMENT OF THE NERVE FIBRES.

213

varies between 0.0133 and 0.0037 mm- It l'cs in the axis por-
tion of the papilla, and consists of homogeneous connective
substance, with transverse and obliquely disposed nuclei.
The whole thing acquires thereby a peculiar appearance,
which reminds one of a fir cone. The nerve fibres (with their
trunks passing from below upwards) arrive at our structure
singly, doubly, or three or four together. Their neurilemma
passes over into the capsule. They themselves, after previous
curved excursions or- looped windings, enter the tactile bodies
manifoldly. Having become pale and transformed into axis
cylinders, they soon disappear from the eye.

We have thus become familiar with this most peculiar man-
ner of termination of the sensory nerves.

How do the millions of other simple sensory nerve fila-
ments terminate ? We now raise this question.

Unfortunately, we know but little concerning this at the
present time. Much has been stated concerning the terminal
plexuses of the finest nerve fibres, in the frog as well as in
mammals.

It is, furthermore, settled that occasionally the terminal
filaments of the sensory nerves pass into the epithelium and
end in it. We have already become familiar above (p. 207)
with the most beautiful example of this kind, in the cornea of
the eye (Fig. 36). The primitive fibrillar here run out between
the epithelial cells.

Others speak of a penetration of these filaments into the
cells, and of a termination in the nucleolus ; thus Hensen
concerning the skin of the frog, Lipmann concerning the
posterior corneal epithelium of the same animal.

Other cutaneous nerves appear finally in the form of fine
non-medullated filaments, which terminate in small cells,
0.0088 to 0.0033 mni. in size, embedded in the human
rete Malpighii ; a portion of them may also pass further
downwards. They have been called Langerhans' corpus-
cles.

Something similar has been subsequently observed in quite
different mucous membranes, where these Langerhans' struc-

214 TWENTIETH LECTURE.

tures have sometimes been met with, and sometimes also not
found.

The dental nerves appear to be peculiarly constituted (Boll).
We have long been familiar with medullated nerve tubes,
0.0067 to 0.0038 mm. in diameter, situated in the parietes of
the dental sac. They form below an elongated nerve plexus.

From the dichotomous separation of these nerve tubes
arise innumerable very fine primitive fibrillar. They press
through the covering of the odontoblasts (p. 75), reach the
inner surface of the dentine, and probably penetrate the den-
tinal tubules. The latter have, according to this, a double
variety of contents, one part being the filamentous processes
of the odontoblasts, and then the remains of these nervous
filaments. The sensitiveness of the dentine has also been
long known by the dentists.

TWENTY-FIRST LECTURE.

THE CENTRAL ORGANS OF THE NERVOUS SYSTEM.
GANGLIA AND THE SPINAL CORD.

-THE

WHEREVER the ganglion cells accumulate, the formation of
a central nerve organ commences. Therefore, from these
smallest cells, only to be discovered by means of the micro-
scope, up to the brain and spinal cord, with their immense,
frequently combined, gray substances, proceeds a continuous
series of developments. Our knowledge concerning the latter
is at present, however, very insufficient ; methods for manag-
ing such complicated structures are wanting.

Let us discuss, first, the peripheral ganglia or nerve nodules
(Fig. 185). A connective-tissue envelope, a modified peri-
neurium, surrounds the organ. It sends into the interior,
fenestrated, leaf-like processes, the bearers of a tolerably de-
veloped capillary net-work.
The irregular and also con-
nected cavities are filled with
ganglion cells (d, e,f), placed
close to each other, and in-
vested by connective tissue.

Between them run isolated
nerve fibres or bundles of the
same. At an earlier period
it was believed that both these
elements, the cellular and the
fibrous, merely lay alongside
of each other. At that time
they distinguished penetrat-
ing primitive fibres, which
passed for the most part in
bundles and straight through
the nodules, and circumgyrating, which passed singly, with

Fig. 185. — A sympathetic ganglion of the
mammalial animal (diagramatic) ; a, S, c, the
nerve trunks ; d, multipolar cells ; d*, one
with a dividing nerve fibre ; e, unipolar ; /,
apolar.

2i6 TWENTY-FIRST LECTURE.

manifold turnings, through the narrow spaces between the
ganglion bodies, to subsequently reassociate themselves with
the out- coming (single or multiple) nerve trunks.

This arrangement does in reality (combined, it is true,
with transitions) occur. We already know that the ganglion
cell enters into communication with the nerve fibre (Fig. 1 75)-
In the ganglia of fishes and amphibia, the connective tissue
is weakly developed ; the elements are, therefore, more
readily isolated, still we have by no means any satisfactory
results to report. The ganglia of higher animals are, how-
ever, permeated by an exuberant fulness of firm connective
tissue ; picking them apart yields us, unfortunately, only the
fragments of the nervous contents.

The requirements of the physiologist, who desires an in-
sight, cannot at present suffice here for the microscopist, and,
indeed, should not. For he would have to combine an im-
perfect perception with hypotheses into an abstract image.
For the coming races of men, the light of a better intelli-
gence will be kindled at some future day. We grope about
in the dark.

Let us take a spinal ganglion of the fish, with its ganglion
bodies. The greater portion of the latter are certainly bi-
polar, that is, the cell is interpolated into the course of a
broad sensory fibre of the spinal cord (Fig. 175, a).

Since the elements of the sympathetic in fishes exhibit
narrow medullated nerve fibres, we should accordingly de-
clare the nerve fibres connected with ganglion bodies to be
sensory elements of this division of the nervous system {U).

One meets in our ganglia, furthermore, with smaller uni-
polar cells (c). Their narrow, sympathetic nerve fibre passes
downwards and spreads out peripherically. The ganglion
might, with these latter constituents, be one of the many
centres of the sympathetic, like all the remaining ganglia of
the fish's body.

Even in the frog, however, the matter becomes much more
difficult. The presence of bipolar ganglion cells, interpo-
lated into the course of a sensory fibre of the spinal cord,

CENTRAL ORGANS OF NERVOUS SYSTEM. 217

is not determined with certainty ; neither is that of sympa-
thetic bipolar ganglion cells. We are only familiar here with
the unipolar cells with the descending, narrow, sympathetic
nerve fibres.

We know next to nothing, at present, about the similar
nerve ganglia of the mammalial animal.

Let us now pass to the sympathetic in the sense of the
older anatomy. In the frog we can, at least, demonstrate
unipolar ganglion cells. Others give us the impression of
the apolar, whether rightly or not we leave undecided.

Sixteen years ago, by the aid of Remak's investigations, I
drew the diagramatic figure 185, as a sympathetic ganglion.
I repeat the figure here ; not because I regard it as complete
(I am far removed from this), but because I am unable to
present any better substitute in a more reliable manner. So
slight has been the advance made during this long epoch !
Remak, that excellent observer, here met with multipolar
ganglion cells. He attributed to them 3 to 12 processes,
which might be increased two or threefold by further ramifi-
cations. They are said to at last become nerve tubes. Ac-
cording to what we have learned above (Fig. 176) concerning
the protoplasma and axis-cylinder processes of the ganglion
cells, this cannot very well be correct. Repeated, more accu-
rate investigations appear, in consequence, to be urgently
necessary ; but who will make them ?

With the larger sympathetic ganglia are associated a num-
ber of smaller and smallest ones. This is the case in the
ciliary muscle and in the choroid of the eye, in the expan-
sions of the glosso-pharyngeal nerve passing to the oesopha-
gus, in the lingual branches of the ramus lingualis of the
fifth nerve. We also meet with similar small ganglionic en-
largements in the walls of the larynx, and of the bronchi,
in the interior of the lungs, and in the heart muscles.

In the walls of the digestive apparatus there is a developed
plexus of ganglia belonging, in the first place, to the sub-
mucous tissue ; then there occurs in the muscles, between

the longitudinal and annular layers of fibres, the plexus my-
10

218

TWENTY-FIRST LECTURE.

entericus, discovered by Auerbach, with its manifoldly mul-
tipolar cells (L. Gerlach). The former plexus appears to be
of a motory and sensory constitution ; the latter possesses
predominantly the former nature. Such small ganglia are
also encountered in the urinary and generative organs, as
well as in glandular structures. Our Fig. 186, a ganglion

Fig. 186. — Ganglion from the submucous plexus of the small intestine of an infant ; a. ganglion
with the ganglion cells ; b, c, nerve trunk, with the pale, nucleated fibres ; 2, a nerve trunk from a
boy five years old.

from the submucous plexus, may represent this. At a, we
perceive the ganglion with the non-medullated, nucleated
fibres ; at 2, a similar nerve trunk is isolated.

Let us now turn to the cerebro-spinal system, to the spinal
cord and brain.

The spinal cord (Fig. 187) presents a cylindrical cord, con-
sisting of an inner gray and an outer white substance. Both
form connected layers of substance throughout the entire
length of the spinal cord. The gray substance forms an
irregular Latin H, in transverse sections. One distinguishes
accordingly, anterior (d) and posterior (e) horns. The latter
are then invested by Rolando's " gelatinous " substance. In
the centre of the whole we perceive, lined with cylinder cells,
the axis canal (a), the last remains of a much wider cavity
in the earlier foetal period. Two deep furrows, the fissura
anterior (b) and posterior (c), cut nearly into the centre. In

CENTRAL ORGANS OF NERVOUS SYSTEM.

219

front of this exists a crossing of nervous fibres, the commis-
sura anterior (f) ; behind the axis canal we meet with a pre-
dominantly connective-tissue mass, the so-called commissura
posterior (h). The white investing substance presents the

Fig. 187. — Transverse section through the lower half of the human spinal cord : a, central
canal ; 6, fissura anterior : c, fissura posterior ; d, anterior horn, with the considerable ganglion
cells ; e, posterior horn, with the smaller ones ; f, anterior white commissure ; g, frame-work sub-
stance around the central canal; k, posterior gray commissure; i, bundles of the anterior, and k,
posterior spinal roots ; /, anterior, vi, lateral, and «, posterior column.

anterior column (/), the lateral (in), and the posterior (n),
consisting essentially of longitudinally arranged medullated
nerve fibres. At the margin of the anterior and lateral col-
umns, the motory roots of the spinal nerves pass through to
the gray substance (i) ; between the middle and posterior
systems of columns we perceive, shining through, the poste-
rior sensory roots of these nerves (k).

A delicate connective tissue permeates the whole organ as
a supporting and frame-work substance. It is the bearer of
the nutritive system of blood-vessels.

Let us first discuss this connective-tissue substratum.

220 TWENTY-FIRST LECTURE.

Our supporting substance comes forward most purely in
the vicinity of the axis canal ; externally, toward the periph-
ery of the gray substance, it becomes profusely permeated
by nervous elements. It has been given the name of the
neuroglia (Virchow).

As we here naturally pass over the subordinate varieties,
we will characterize this supporting tissue as a very delicate

and extremely decomposable, fine reti-
cular substance, with nuclei at the
nodal points, so that cell-bodies must
be present here (Fig. 188). The fine
clefts are permeated by a chaotic maze
of the finest nerve fibrillar ; in the larger

Fig. 188.— Neuroglia from the SpaceS are ganglion Cells,
gray substance of the human cen- l o o

trai nervous system (cerebellum), Proceeding; further towards the peri-

with embedded nuclei. <-> '■

phery of the spinal cord, we arrive at
the white columnar systems, and here the connective-tissue
substratum has become more compact and firmer. Some-
times appearing more homogeneous, sometimes more striated,
and again containing nuclei in individual nodal points, it
forms a system of septa, an incomplete one it is true, which
surrounds the descending nerve fibres as a fenestrated system
of sheaths (Fig. 170). Thicker, connective-tissue vascular
lamellae radiate out to the pia mater which, as is known, sur-
rounds the surface of the spinal cord. This envelope finally
sends folds with considerable blood-vessels into the anterior
and posterior longitudinal clefts of the organ.

The vascular net- works of the white substance, which main-
tain a radial arrangement, are scanty and large-meshed. The
capillary net-work of the gray substance is compact and
narrow-meshed ; the latter is very vascular.

Let us now consider the nervous contents of the connective-
tissue frame-work.

The white cortical substance consists essentially of vertically
arranged nerve tubes of 0.0029 up to 0.009 nim. diameter.
The thickest fibres are presented by the anterior columns ;
the finest by the posterior, especially towards the fissura pos-

CENTRAL ORGANS OF NERVOUS SYSTEM. 221

terior. The latter here forms the wedge-shaped or Goll's
column. The inner nerve fibres, that is, those which are
adjacent to the gray cornua, are also usually finer than their
external associates.

These longitudinally arranged fibrous masses are permeated
by the bundles of the transversely and obliquely departing
and entering roots of the spinal cord.

The anterior or motory roots of the latter reach the anterior
cornu (Fig. 187, i), and radiate into the latter in every direc-
tion in a brush-like form.

Let us now examine this gray substance of the anterior
cornu.

Here (d) lie groups of large multipolar ganglion cells, after
the manner of our Fig. 176. The so-called axis-cylinder pro-
cess (a) is the commencement of the motory nerve fibre, its
axis cylinder. This is settled, according to my experience,
although it has recently been doubted (Golgi). It is certainly
not easy to observe, but it is and remains the best portion of
our present knowledge concerning the origin of nervous ele-
ments in this so infinitely complicated organ.

If we turn further backwards towards the posterior cornu,
we meet with, for the most part, smaller, not rarely spindle-
shaped cells (/), with the same duplicity of systems of pro-
cesses. At the base of the posterior cornu, further inwards,
there is also a group of smaller rounded ganglion cells.
These are the Clarke's columns.

The cellular elements of the posterior cornu have generally
been considered as sensory, and brought into relation with
the origin of the fibres of the posterior roots ; still this cannot
be demonstrated.

We now encounter the question : What becomes of the
second system of processes (Fig. 176), the so-called proto-
plasma processes ?

Their lateral finest filaments (b), like the terminal radiations
of the branch itself, were considered by Deiters, as we already
know, to be primitive nerve fibrillar. From them — and they
might arise from different cells — an axis cylinder was said to

222 TWENTY-FIRST LECTURE.

be at last composed. Gerlach subsequently came to a dif-
ferent conclusion. According to him, the terminal ramifi-
cations of this system of processes unite into a narrow, fine
net-work, from which the nerve fibres arise by the combi-
nation of the thinnest filaments. The last-mentioned investi-
gator absolutely denies that the proper cells of the posterior
cornu have axis-cylinder processes. A fundamental ana-
tomical difference is, therefore, maintained for the motory and
sensory cells. I trust neither the statements of Deiters or
Gerlach. With the present accessories we can, unfortunately,
obtain no certain result. Everything remains a conjecture.
The manner of arrangement of the bundles of the posterior
sensory root is, unfortunately, still more complicated than
that of the anterior, and the fibres become considerably nar-
rower on their entrance into the gray substance. Our knowl-
edge is, accordingly, here still incomplete.

The greater portion of the bundles of fibres appear to main-
tain a chaotic course through the posterior columns, to later
pas^ from the side into the convex part, or portion turned
inwards, of the posterior cornu (k). The substantia gelatinosa
Rolandi is here seen to be permeated by the finest nerve
fibres. The latter are said to pass in part to the base of the
posterior cornu, part of them reaching the Clarke's columns.
Furthermore, still other bundles of fibres pass over the latter,
more in front. Bundles of sensory fibres may even enter
both commissures.

We now come to the question, what do the white longitu-
dinally disposed systems of columns signify ?

That they do not represent the bent fibrous masses of the
roots of the spinal cord which pass to the brain, as was as-
serted at an earlier epoch, requires no further discussion
after what we have learned concerning these roots.

According to the views of Deiters, these vertical bundles
of white fibres come from one transverse plane of the gray
substance to subsequently sink into another. The roots of
the spinal cord terminated, therefore, in the ganglion cells,
and the latter sent off, as a simplified continuation, these ver-

CENTRAL ORGANS OF NERVOUS SYSTEM. 223

tical fibres of the white columnar system. These cell groups
were accordingly a provisory centre.

The further communications of the ganglion bodies, of the
equivalent between each other, as well as of the motory with
the sensory cells, are up to the present time veiled in the
deepest obscurity.

Let us mention, finally, in the uncertainty of our knowl-
edge, the transverse commissures of the spinal cord. The
anterior shows true nerve fibres in the most distinct manner.
The bundles of the same arise from the gray substance of the
one half (without our knowledge of the manner of their ori-
gin), to ascend and descend and gain the fibrous mass of the
anterior column at the other side. An endeavor has been
made to deduce from this a total decussation of the motory
tract of our organ.

The posterior commissure also contains, together with con-
nective-tissue constituents, bundles of fine nerve fibres.

TWENTY-SECOND LECTURE.

THE CENTRAL ORGANS OF THE NERVOUS SYSTEM, CON-
TINUED.— THE MEDULLA OBLONGATA AND THE BRAIN.

THE spinal cord, as we learned, cannot be mastered with
the present methods of investigation.

It appears still more dubious with regard to the far more
complicated medulla oblongata. As with the subsequently
to be mentioned brain, it is scarcely possible to here condense
the existing, in part contradictory material, into a short sum-
mary view. We limit ourselves, therefore, to a fragmentary
discussion.

The most recent investigations of this central structure
were made by Deiters, of Bonn, and Meynert, of Vienna.

The axis canal of the spinal cord opens in the medulla ob-
longata, in a dorsal direction, into the sinus rhomboideus or
calamus scriptorius, to continue forward as the fourth ventri-
cle. By this means changes of position occur in the white
columns, as well as the gray substance of the spinal cord.
The anterior longitudinal fissure finally closes as the raphe.

Large portions form anteriorly and inwardly, with their de-
cussations, the pyramids, externally from these the (lower)
corpora olivaria. Then follow externally the lateral columns
and the corpus restiforme, that is, the wedge-shaped and del-
icate columns (the latter is a continuation of Goll's column,
p. 221).

In the direction of the brain, the pons Varolii rests upon the
organ. As a connection with the cerebellum we have the
crura cerebelli (with their two portions, the crura cerebelli ad
medullam oblongatam and ad pontem). The connection with
the cerebrum takes place through the peduncles of the brain.
Finally, ten cerebral nerves arise from the medulla oblongata.

The homogeneous connected gray substance here changes,

THE MEDULLA OBLONGATA AND BRAIN. 22$

becoming permeated by bands of nerve fibres. This arrange-
ment, the so-called formatio reticularis, gradually extends
over nearly the whole medulla oblongata.

Connected masses of gray substance form what has been
called " nuclei." A portion of these are the centres of escap-
ing nerves ; in others, systems of fibres of the medulla ob-
longata acquire a provisory termination, to become modified
at these places, and subsequently pass further on with their
derivatives. Among the latter, the so-called "specific nuclei,"
are included the superior and inferior olivary bodies, the
Deiters' nucleus, the pyramidal nucleus, the ganglia post
pyramidalia, the gray substances of the pons Varolii, and in
further extension also, the corpus dentatum cerebelli, the
gray masses of the crura cerebelli, and the greater portion of
the eminentia quadrigeminae (Deiters).

There is besides a transverse, arched and circular system
of fibres, Arnold's stratum zonale.

In the formatio reticularis, as well as in the nuclei, we meet
with ganglion cells of the most varied form, and in part of
considerable size, with axis cylinder and protoplasma pro-
cesses. In consequence of the penetration of the gray sub-
stance into the funiculus gracilis, the floor of the fourth ventri-
cle is almost exclusively formed of gray substance. The
neuroglia which surrounded the axis canal of the spinal cord
also undergoes a proliferous increase to subsequently form a
considerable share of the walls of the aqueductus Sylvii, the
third ventricle and the infundibulum.

Now, how do the cerebral nerves arise from the medulla
oblongata ?

Deiters found here not only an anterior and a posterior
centre of origin, as in the spinal cord, but also a third lateral
one. The latter begins in this organ, at the anterior horn,
and gradually acquires a mixed character.

From it arise the accessorius, vagus, glosso-pharyngeus,
facialis, acusticus and anterior trigeminus root.

The sensory portion of the trigeminus is said to be derived

from the posterior system of origin.
10*

226 TWENTY-SECOND LECTURE.

To the anterior roots of the spinal cord correspond, together
with the hypoglossus, the nerves of the muscles of the eye ;
the abducens, trochlearis and oculo-motorius.

We cannot here enter further into the nerve nuclei. The
centres of the hypoglossus and accessorius, with large multi-
polar cells, are located furthest below.

What becomes of the columns of the spinal cord within the
medulla oblongata ?

As we have already remarked, there can here be only a
simplified continuation of the same.

The anterior columns, passing to the side of the raphe, and
displaced by the pyramids, may be followed far under the
pons ; they are perforated by zonal fibres and gray substance,
and finally, after the intercalation of ganglion cells, are still
finely fibrillated. They appear to pass towards the cerebrum
and cerebellum.

The lateral columns, forming the funiculus lateralis, reach,
in part, the cerebrum. Their fibres are interrupted and dis-
placed by the formatio reticularis, the Deiter's nucleus, the
inferior, accessory and superior olivary bodies.

The posterior columns of the spinal cord do not, as we
formerly conjectured, continue as the crura cerebelli ad
medullam oblongatam directly into the cerebellum. Their
processes in the medulla oblongata, the funiculus gracilis
and cuneatus, are interrupted by intruded gray substance,
the so-called ganglia post pyramidalia, and here cease as
white fibrous masses. The gray continuations pass in
part into these crura, in part (crossed and uncrossed) to
the corpora olivia, and, finally, increased in size, to the pyra-
mids.

The pyramids commence with fine nerve fibres from the for-
matio reticularis. With them are associated nerve fibres
from the lateral and posterior columns. After the decussa-
tion they pass in the pedunculi cerebri to the cerebrum,
to probably reach the corpora striata, the nucleus lenticularis,
and even the cortex of the hemispheres.

The inferior corpora olivaria, in man, contain in their gray

THE MEDULLA OBLONGATA AND BRAIN. 227

substance a peculiarly folded leaf (corpus dcntatum) which
encloses white substance.

The former substance contains small yellowish pigmented
ganglion cells. A system of fibres arising from the olivary
bodies is said to pass in part to the cerebellum, in part to the
cerebrum.

The crura cerebelli ad medullam oblongatam form in part
processes of the medulla oblongata into the cerebellum ; they
probably also send motory fibres from the latter in a down-
ward direction to the medulla oblongata (Meynert).

The crura cerebelli ad pontem are of an essentially different
nature. They form in the first place a transverse commissure
system between both the cerebellar hemispheres ; then they
conduct fibrous masses, arising from the cerebellum, up to the
cerebrum.

The cerebellum can, however, absorb only a portion of the
fibrous masses which ascend from below, and subsequently,
after the passage of gray substances, sends them off trans-
formed to the cerebrum. It is merely — as we must at present
assume — an accessory conducting apparatus ; for the other
fibrous masses ascend directly through the pedunculi cerebri.

The blood-vessels of the medulla oblongata remind us of
those of the spinal cord.

We know very little indeed concerning the cerebellum. We
have already mentioned two of its crura ; a third commissure,
the crura cerebelli ad corpora quadrigemina, connects the
organ with the cerebrum.

The cerebellum consists essentially of aggregations of white
nerve substance, with fibres 0.0029 to 0.0902 mm. broad.
Gray substance occurs in the roof of the fourth ventricle, in
the corpus dentatum, in Stilling's so-called roof nucleus, and
as the external covering layer of the convolutions.

In the folded gray plate of the corpus dentatum lie ganglion
cells in a threefold stratum. We pass over the entirely un-
certain course of the fibres.

The structure of the cortical layer is interesting. It presents
an internal rust-brown, and an external gray stratum.

228

TWENTY-SECOND LECTURE.

The former, I to 0.5 mm. thick, has crowded and stratified
granules, that is nucleus like structures or, more properly
said, small cells ofo.0067 mm. They remind one of the sub-
sequently to be described elements of the retina of the eye,
and, like the latter, give off the finest filaments from both
poles (Fig. 189, below).

Whether these granules of the cerebellum are of a nervous
or connective-tissue nature is still undecided.

The gray stratum contains a simple layer of large remark-
able ganglion cells. Purkinje described them forty years ago.

They send downwards an axis-
cylinder process id), and up-
wards or outwards a system
of antler-like ramified proto-
plasma processes (c). The
finest terminal branches of the
latter (Hadlich) are said to
bend over (a) in a loop-like
manner at the surface, and
return to the rust-colored
layer.

Connective-tissue support-
ing fibres (r) form a special
boundary layer at the surface.
The pedunculi cerebri re-
ceive ascending masses of
fibres from the medulla ob-
longata and cerebellum ; they
also receive others which de-
scend, from the cerebrum to
the medulla oblongata. Their

Fig. 189. — The cortex of the human cerebellum
in perpendicular section. Two Purkinje's cells, SlipeiTOr TOUnded DOl'tlOn

beneath them a portion of the granular layer ; d, _

the lower, c. .the upoer process of the former. At (cap) is Separated from tile
r, supporting fibres ; at a, the loop-shaped V * ' *■

bends of the finest cell processes; c, tangential inferior Semilunar (basis) pOr-
thmnest nerve fibres. ' A

tion by a dark substance.
Black pigmented multipolar ganglion cells occur here.

The so-called cerebral ganglia consist of the corpora

-C

THE MEDULLA OBLONGATA AND BRAIN. 229

quadrigemina, the thalamus opticus, the corpus striatum, and
the nucleus dentatus. They are only imperfectly known.

The crura cerebelli ad corpora quadrigemina simply pass
oft" beneath the corpora quadrigemina. They pass to the
hemispheres of the cerebrum ; they are in truth the crura
cerebelli ad cerebrum. The histological acquisitions in this
department remain, up to the present time, scarcely worth
mentioning. Small cells, larger multipolar, and spindle-
shaped ganglion bodies have been met with here.

The thalamus opticus has likewise yielded nothing further
in a histological direction. A portion of the optic nerve
radiates into it, as well as into the anterior corpora quadri-
gemina. The cap of the crus cerebri is intimately connected
with the thalamus (Meynert).

Fibrous masses of the basal portions of the cerebral
peduncles are said to terminate in the corpus striatum and
nucleus dentatus. Their finer structure likewise requires more
accurate investigation.

The so-called rod corona fibres, in their great development
in man, are probably connected with his mental abilities.

They consist in the first place of fibrous masses which,
without having been in contact with the cerebral ganglia, are
conducted upwards through the peduncle of the brain, and
secondly of the radiations of the ganglionic substances.

The trabeculae and anterior commissure are probably true
simple commissures, which have nothing to do with either
the crura cerebri or these rod-corona fibres.

The white substance of the hemispheres consists essentially
of medullated nerve fibers, measuring 0.0026 to 0.0067 mm.

The gray cortical stratum of the hemispheres may be
reduced to a number of single layers. They may be assumed
to be six in number.

Smaller cells occur in the more superficial layers. In the
fourth layer one meets with considerable many rayed gan-
glion bodies, measuring 0.025 to 0.040 mm. One of their
processes is usually directed towrards the surface, and three
others inwards. The central one of these three basal pro-

230 TWENTY-SECOND LECTURE.

longations is an axis-cylinder process. Then two other cell
layers follow. This is all that we know at present.

Here, also, Gerlach assumes the presence of a very fine
problematical nerve reticulum, such as we have already
mentioned at page 222, in connection with the gray substance
of the spinal cord.

At the apex of the occipital portion, in the vicinity of the
so-called sulcus hippocampi, the cortical stratum becomes
still more complicated. The cornu ammonis also has its
peculiarities.

A remarkable, although in man considerably stunted por-
tion, of the cerebral substance is the bulbus olfactorius. The
cavity, which is lined with ciliated epithelium, presents pa-
rietes consisting of internal white, and external gray substance.

The former contains the root bundles, which are two in
number, a thicker external one, coming in part from the
anterior inferior cerebral convolution, in part from the corpus
callosum, and a thinner internal one, which is thought to be
derived from the corpus striatum, the chiasma nervorum opti-
corum and the pedunculus cerebri.

In a strongly developed neuroglia, we meet, in an inward
direction, with the longitudinally arranged medullated root
fibers, and then, connected with these, a nerve plexus of very
fine tubes. We finally meet with granules and multipolar
ganglion cells.

Below, or rather externally, the gray substance becomes
strongly altered. One here meets with globular balls of a
granular substance with nuclei (glomeruli nervi olfactorii, ac-
cording to Meynert).

From these lumps are developed the pale nucleated fibres
of the special olfactory nerves.

The apophysis cerebri has already been discussed, so far as
its anterior portion is concerned, in connection with the blood-
vascular glands (page 126) ; the posterior consists of gray
cerebral substance.

The so-called Pineal gland, conarium, has long been remark-
able on account of its calcareous concretions. In its connec-

THE MEDULLA OBLONGATA AND BRAIN. 231

tive-tissue substratum it presents rounded cavities which are
sometimes more and sometimes less complete. We here
meet with two kinds of cells ; large stellate ones, forming a
net-work, and smaller ones. In the adult, the latter have pro-
cesses, in the new-born child, however, they were at one time
without these (Bizzozero).

The blood-vessels of the brain, similar to those of the spinal
cord, form very compact vascular net-works in the gray sub-
stance ; in the white substance the meshes are much wider.

The arrangement in the individual portions of the brain is
often, however, very characteristic and elegant, as for ex-
ample in the olfactory lobules, the corpus striatum and the
cortex of the cerebellum. We cannot here enter into details.

We have finally to mention the membranes of the cerebro-
spinal system.

The dura mater (page 57) of the brain is intimately con-
nected with the periosteum of the cranial cavity. Around
the spinal cord, on the contrary, with the exception of the
anterior side, it forms a freely suspended tube. The spaces
of the vertebral canal are filled by connective tissue with fat
cells. The vascularity is very moderate in the cerebral por-
tion, and very slight in the spinal portion. The lymphatics of
the dura mater are very abundant. The dura mater of the
brain presents nerves of unknown termination.

The dura mater and arachnoid leave a system of cavities,
the subdural space (Key and Retzius), between them.

The latter membrane, the arachnoid, is very poor in blood-
vessels, is thin, delicate and fenestrated in a reticular manner.

Over the spinal cord it is separated from the lowermost
tunic of the pia mater, with the exception of connecting fila-
ments of connective tissue. There is thus formed a consider-
able subarachnoidal space. Over the brain, on the contrary,
the arachnoid and pia mater are for the greater part coalesced
with each other, and spaces occur only in those places where
the former membrane stretches over the furrows of the sur-
face in a bridge-like manner, while the pia mater descends to
the bottom. The considerable subarachnoidal space of the

232 TWENTY-SECOND LECTURE.

spinal cord is therefore broken up into numerous smaller
spaces.

The connective-tissue bundles of the arachnoid are invested
in a sheath-like manner by the familiar flat stellate endothe-
lial cells (Key and Retzius). The latter also fill the connec-
tive-tissue spaces, and after treatment with nitrate of silver,
show the familiar areolations.

The connected cavities contain a very watery fluid, the
cerebro-spinal fluid.

The pia mater likewise appears thin and delicate, with
similar fiat connective-tissue cells. It is characterized, how-
ever, by its immense wealth of blood-vessels ; it is, also, by
no means poor in lymphatics. Its numerous nerves are
probably desigrred (at least principally) for the vascular
walls.

Our pia mater covers, in close apposition, the nervous
masses of the central organ. His, it is true, formerly as-
sumed that there was here an epispinal and epicerebral cavity.
This does not exist, however ; it is an artefact. More recent
observations teach that the blood-vessels entering the ner-
vous substance have connective-tissue adventitia, only loosely
spread over their so-called tunica media, and that they thus
open into the subarachnoidal space with funnel-shaped dila-
tations of the outer layers. They may be artificially injected
from the subarachnoidal space far into the interior of the
brain.

The nerve trunks and ganglia have, according to Key and
Retzius, the same external dural and internal arachnoidal
sheath, as well as subarachnoidal spaces. The injection also
succeeds here. All this, like the serous sacs, belongs to the
lymphatic apparatus.

The name of the Pacchionian "glands" or granulations
has been given to small rounded connective-tissue masses
which occur especially at the upper longitudinal venous si-
nuses of the brain.

According to the two frequently mentioned Swedish in-
vestigators, the just mentioned structures form transition

THE MEDULLA OBLONGATA AND BRAIN.

233

portcs of these lymphatic spaces into the venous blood cur-
rent. This naturally requires further confirmation.

The venous plexus, the plexus choroidei, contains an im-
mense vascular convolution in undeveloped connective tissue.
Its covering is formed by a low cubical epithelium, which runs
downwards into numerous points.

TWENTY-THIRD LECTURE.

THE ORGANS OF SENSE.— THE SKIN; THE GUSTATORY, OL-
FACTORY AND AUDITORY APPARATUS.

THE human external integument presents the apparatus of
feeling and touch. The tongue alone takes a further share
in the function of this sense.

The course of our lectures required that we should discuss
the individual portions of the general protecting organ in
different places. We mentioned the epidermis at p. 32, the
corium at p. 58, the subcutaneous cellular tissue at p. 56, the
nails and hair at pp. 36 and 37. The tactile nerves were
alluded to at p. 211, the simple sensory cutaneous nerves at
p. 212. Additional information may also be obtained from
our Fig. 183.

We will also add something here. The corium is thin-
nest over the eyelids, the prepuce, the glans penis and inner
surface of the labia majora ; it is thickest over the back,
the palm of the hand, the buttocks and sole of the foot,
which are the seat of the greatest pressure. The thickness
of the epidermis (p. 32J varies still more. We have already
mentioned that the color of the skin of Europeans is deter-
mined by the latter.

That the corium is uncommonly vascular is known to
everybody. In it occurs a highly developed net-work of ca-
pillary vessels, 0.0074 to O.Oi [3 mm. broad, which send loops
into by far the greater proportion of the cutaneous papillae.
We meet with more independent portions of the vascular
system around the flat lobules of the panniculus adiposus,
the hair follicles and the bodies of the sudoriparous glands
(Tomsa).

Lymphatics, which are said to possess independent parietes,
are abundant in the corium (Teichmann and J. Neumann),

THE ORGANS OF SENSE.

235

forming a double flat net-work. They penetrate the papillae
as culs-de-sac and loops, so that one is reminded of relative
conditions of the intestinal villi (p. 98). Great variations
prevail, however, in the individual portions of the skin.

We have, finally, to discuss the glands of the skin, which
have thus far been only cursorily mentioned.

The more important ones are the convoluted, sudoriparous
glands (Fig. 183,^, 190, a, b). They remain small, with the
exception of those of the axilla, where they acquire enor-
mous dimensions and
more fatty contents.
Their convoluted
gland body is more
rarely situated in the
depths of the corium,
but, as a rule, in the
subcutaneous cellular
tissue. The excre-
tory duct (e, f) , some-
times shorter, some-
times longer, accord-
ing to the thickness
of the part, is slightly
spiral, and terminates
in the palm of the
hand and sole of the
foot, by way of ex-
ception, with funnel-shaped dilatations. It has a double
layer of epithelium. The walls of the convoluted gland
body present smooth muscles, which apparently increase with
the size of the gland body.

The gland cells form a simple layer of low, cubical elements.
An elegant wicker-work of capillary vessels (V) surrounds the
secretory portion.

The human skin contains these sudoriparous glands, with
few exceptions, but they are quite variable as to number and
position. The older Krause — he was a thorough observer—

Fig. 190. — A human sudoriparous gland ; a, the coil, sur-
rounded by the commencement of venous vessels ; b, the
excretory canal ; c, the basket-like capillary plexus, with the
arterial trunk.

236

TWENTY- THIRD LE CTURE.

once computed that our body contains nearly two and a half
millions of these convoluted glands.

Considerable sudoriparous glands also surround the anus
(Gay).

In the external auditory canal, these convoluted glands ac-
quire a shorter excretory duct, which is no longer convoluted,
and their secretion is fatty and brownish-yellow. These are
the glandulae ceruminosae.

Let us now investigate the submucous follicles, the glandu-
lae sebaceae of the older anatomists. Their secretion, an es-
sentially fatty, thickish substance, we have already become
familiar with in a preceding lecture (p. 132).

They form racemose organs (Fig. 191), which are some-
times smaller and more simple, sometimes more voluminous
and complicated in their structure. They are situated in the

corium, and are, for the most part,
but by no means unexceptionally,
confined to the vicinity oT the hair,
into the sac of which (p. 37) they ex-
crete the tough, fat substance. We
also meet with smaller examples of
our organ connected with thick hairs,
and larger glands with lanugo hairs.
At last these open freely externally,
without the intermediation of a hair
sac. Their size varies considerably,
from 0.2 to 1 mm. and more. The
vesicles differ considerably in dimen-
sions and form. Young, striated
connective tissue here replaces the so-called membrana pro-
pria.

Passing now to the gustatory organ, we have again to com-
bine what has been previously mentioned. Even at that
time (p. 141) we remarked that the posterior portion of the
tongue, upwards in the long known papillae circumvallatae,
and laterally in the subsequently rediscovered papillae foliatae,
contained terminal fibres of the glosso-pharyngeus serving as

Fig. 191. — A sebaceous follicle ;
a, the gland vesicle ; b, the excre-
tory duct ; c, the sac of a lanugo
hair ; d, the shaft of the latter.

THE ORGANS OF SENSE.

237

Fig. 192. — Vertical section through the so-called papilla
foliata of the rabbit.

nerves of taste. Both systems of papillae occur in man,
though the foliatae are subject to many individual variations.
The change is great in mammalial animals. Cats have no
papillae foliatae ; Guinea-pigs have no circumvallatae.

We have now to examine the above nerve terminations
more closely. They are more recent histological acquisitions
(Loven, Schwalbe, and others). Complicated cup or bud-
shaped organs, the so-called gustatory buds, have been met
w i t h here. Large
numbers of them oc-
cur, as is distinctly
represented in our
Fig. 192, in the lateral
walls of the papillae
themselves, and in the
inner surface of the surrounding
mounds of mucous membrane.
The gustatory bud (about 0.08
mm. high in man) is an epithelial
structure. It (Fig. 193) permeates
the entire thickness of this layer,
and its points lie free.

We meet, in the first place,
with flattened, lancet-shaped,
pointed parietal cells (a). They
stand like the staves of a barrel.
Above, possibly running out into
the finest ciliae, they surround a
small opening.

These supporting or cover cells
(2 a) ensheath an inner cell forma-
tion, belonging to the axis portion
of the gustatory bud, the rod cell,
or, as it has also (hypothetically,
it is true) been called, the gusta-
tory cell (2 b).

Above, there is a sort of styliform or rod-shaped process

ze

Fig. 193. — 1. Gustatory bud of the
rabbit ; 2 a, cover cells ; 2 b, rod cells ;
2 c, a rod cell with a fine terminal fila-
ment.

238 TWENTY-THIRD LECTURE.

(of irregular form, it is true) ; below, there is a filamentous
process. It is conjectured that the latter passes over as an
axis cylinder or primitive fibrilla (?) into the gustatory nerve
fibres, which run beneath the gustatory bud, and, there-
fore, that the gustatory cells may be terminal nerve structures.
No one has yet seen this, however. We shall first appreciate
the consequences subsequently, at the olfactory, auditory, and
optic nerves. The circumstance is interesting that so-called
mucous glandules (p. 141) occur in both varieties of papillse
(von Exner).

Accurate facts are wanting concerning the nerve termina-
tions in the other papillae of the tongue.

The human olfactory apparatus consists of a relatively
small part, which contains the termination of the specific nerve
of sense. This is the soft parts over the upper portion of the
septum, the upper and a portion of the middle turbinated
bone. The mucous membrane, which is here yellowish or
brownish, bears the appropriate name of the regio olfactoria.
All the remainder, the lower divisions of both main cavities,
as well as the three adjacent cavities, are unimportant acces-
sory parts, as has also been long since taught by compara-
tive anatomy.

The latter division is lined by a very vascular mucous
membrane having ciliated cells (the Schneiderian membrane).
It contains an immense wealth of serous racemose glands
(p. 142). The mucous membrane is thinner in the accessory
cavities, and the glands begin to disappear.

We have no intimate knowledge of the terminations of the
sensory nerves of the latter parts.

Let us now return to the most essential parts, and exam-
ine more closely the structure of the regio olfactoria (Fig.
194).

The region bordering on the Schneiderian mucous mem-
brane, which therefore is unprovided with olfactory fibres,
presents the old ciliated covering and the old serous glands.
Here, however, it is different. Bowman's gland tubes appear
in the mucous membrane, with yellowish cells. A thickened

THE ORGANS OF SENSE.

239

(as a rule) non-ciliated epithelial mass finally covers the
olfactory region.

Let us first examine this epi-
thelium.

We here meet with two differ-
ent elements. Firstly (a), long
cylindrical cells (2 a). Their body
contains yellowish granules and,
in connection with the Bowman's
glands, causes the mentioned
color of our locality. The lank
non-ciliated cylinder sends down-
wards a thin process which
becomes divided. By the union
of such systems of processes a
regular horizontal net-work is
formed in the connective tissue
of the mucous membrane.

The cells just described have
nothing at all to do with the
nerve termination. They are a
modified, but indifferent epithe-
lium.

Between them, however, there
appears a second cell formation,
the terminal structure of the olfac-
tory nerve, the olfactory cell (b) ;
thus called, and with probability.
times more deeply situated, we meet with a spindle-shaped
cell body (1, 2, b). Below (1,2, d) the latter gives off an
exceedingly thin filamentous process. It presents, with cer-
tain treatment, small varicosities, like a primitive fibrilla of
the nerve fibre (p. 196). At the upper pole, our spindle
cell sends off a broader, smooth rod (1, 2, c), 0.0018 to
0.0009 mm- wide. Ascending between the epithelial cylin-
ders, it reaches the surface of the parts.

In many animals, the terminal surface of the rod has

Fir;. 194. — 1. Cells of the regio olfac-
toria of the frog ; a, an epithelial cell,
terminating below in a ramified process ;
b, olfactory cells with the descending fila-
ment ; d, the peripheral rod, c, and the
long vibratile cilia;, e ; ?, cells from the
same region of man. The references the
same, only sh'.rt projections, e, occur
(as artefacts I on the rods : 3, fibres of
the olfactory nerve from the dog ; at a
dividing into n.,i_ fibrillae.

at least, it is at present
Sometimes higher, some-

140

TWENTY-THIRD LECTURE.

single or multiple long ciliae, as for example in the frog

b —

The olfactory nerve — we are already
familiar with its pale primitive fibres (Fig.

194, 3, Fig- 195,/) from p. 196— gives off
branches as it ascends to the cell layer of
the regio olfactoria. The axis cylinder (Fig.

195, e) proves to be finely striated. At last,
after losing their sheath, the primitive or
axis-cylinder fibrillar radiate upwards in a
brush-like manner, as exceedingly thin vari-
cose filaments (d). It is assumed that they
are connected with the descending, similarly
constituted finest processes of the " olfac-
tory cells " (c).

This theory proceeded from M. Schultze.
The eminent investigator — he has, unfortu-
nately, been prematurely torn from us — could
not, however, bring forward a forcible proof
here, any more than with regard to the other
nerves of sense, after years of arduous hon-
est labor. One cannot avoid certain con-
clusions, therefore, that by the aid of im-
proved methods, the matter may subse-
quently become quite different. However,
this is my subjective view.

Exner has more recently denied the differ-
ence between the epithelial and olfactory
cells. In contradistinction to him, Von
Brunn has subsequently subscribed to the
older view of Schultze. Brunn found Over the regio olfac-
toria a homogeneous boundary layer after the manner of
the retina (see below). It has pores for the olfactory cells
only.

Let us now pass to the termination of the nervus acusticus,
and thus enter the most difficult department of modern his-
tology.

C

Fig. 195. — Probable
termination of the olfac-
tory nerve in the pike ; a,
olfactory cells : b, rods ;
r. lower varicose fila-
ments ; r, axis fibrillar in
the sheath f; d, spread-
ing out of these ; at —
wanting connection wiih
the same fibrillse, c.

THE ORGANS OF SENSE. 24 1

Let us fiist make a cursory sketch of the unessential acces-
sory parts.

The external ear presents the auricle and the external au-
ditory canal. The former consists of elastic cartilage covered
with rarefied corium. Its muscles are transversely striated.

The ceruminous glands of the external auditory canal have
been previously mentioned (p. 137).

The drum membrane, or membrana tympani, a fibrous
diaphragm, is clothed externally by a rarefied cuticular cover-
ing, internally by the delicate mucous membrane of the tym-
panic cavity with simple pavement epithelium. The vascular
net-work of this membrane is complicated (Gerlach). Lym-
phatics and nerves are likewise abundant. The termination
of the latter is for the most part unknown.

The entire "middle ear" is lined with a thin, vascular mu-
cous membrane. The vascular net-work shows a considera-
ble development of the venous portion. The nervus tym-
panicus presents ganglia. The auditory ossicles consist of
true compact bone substance ; their muscles are transversely
striated. The Eustachian tubes have stratified ciliated epithe-
lium and true mucous glandules. Their nerves show small
ganglia.

The internal ear, as is known, consists of the vestibule,
the semi-circular canals and the cochlea. Vesicles filled with
watery lymphatic fluid occupy the cavities. The auditory
nerve terminates in the ampulla and in the saccules of the
vestibule, and then on the spiral plate of the cochlea (ramus
vestibuli and ramus cochleae).

The vestibule and the inner surfaces of the semicircular
canals are lined with periosteum. The fluid contained in
their interior is called the perilymph. The periosteum and
the tissue of the mucous membrane of the tympanic cavity
combined, form the so-called membrana tympani secundaria.
The parietes of the saccules of the vestibule (sacculus hemi-
ellipticus and rotundus) and the membranous semicircular
canals, together with their ampullae, present externally unde-
veloped connective tissue, internally a hyaline nucleated layer
11

242 TWENTY-THIRD LECTURE.

(in the latter, canals with papilla-like incurvations), as well as

a flattened epithelium. A second watery fluid, the endo-

lymph, fills this system of cavities.

The otoliths are enclosed within a special saccule, and form

columnar-shaped crystals, measuring 0.009 to 0.002 mm.

They consist of carbonate of
lime, though they are said to
have an organic basis.

Let us pass to the expan-
sion of the auditory nerve.
The ampullae and sacculus
hemi-ellipticus are supplied by
the vestibular branch, the sac-
culus rotundus, on the con-
trary, by a branch of the
cochlear nerve. It terminates

Fig. 196. — Otoliths, consisting of carbonate .1 1 1 • . r .1

0f lime. in the duphcatures 01 the pa-

rietes, that is at the entering
angle of the same, the crista acustica.

In fishes (rays), M. Schultze, many years ago, observed
simple cylinder epithelium and rod cells intermingled with
them, reminding one of the probable terminal structures of
the olfactory nerves (p. 239). F. E. Schulze subsequently
met with a shock of uncommonly long stiff ciliae in osseous
fishes and tritons. The otolith sacs of fishes also presented
a similar condition.

In man the salient points of the vestibular saccules are less
developed (maculae acusticae of Henle), but are more dif-
fused. Here, also, fine non-medullated nerve fibres penetrate
the epithelium. Two kinds of cells and cilia-like processes
have also been noticed.

We now come to the cochlea.

This convoluted structure contains two nerveless winding
canals, the two so-called scala of the older anatomists, the
scala vestibuli and the scala tympani (Fig. 197, V, T), sepa-
rated by an internally osseous, and externally soft membranous
spiral plate. Reissner has discovered, in addition, a third cen-

THE ORGANS OF SENSE.

243

tral spiral canal, forming on transverse section an irregular
triangle, with its apex directed towards the axis of the cochlea.
This is Reissner's cochlear canal, canalis cochlearis (Cj, the

f\J K I <t ]

r

Fig. 197. — Perpendicular transverse section through the canal of the cochlea and neighborhood, in
an older embryonic calf ; V, scala vestibuli ; T, scala tympani ; C, canal of the cochlea ; />,
Reissner's membrane with -its insertion (a) into a projection at the so-called habenula sulcata (c) ;
b. connective tissue stratum with a vas spirale at the under surface of the membrana basilaris ; c> ',
teeth of the first series ; d, sulcus spiralis, with thickened epithelium, which extends as far as the
developing Cortian organ, f; e, habenula perforata ; C »i, Corti's membrane (1. inner thinner, 2,
middle thicker portion of the same, 3. its outer end) ; g, zona pectinata ; //, habenula tecta ; k,
epithelium of the zona pectinata ; k'. of the outer wall of the canal of the cochlea ; k", of the
habenula sulcata ; /, ligamentum spirale (?', transparent connecting portion of the same with the
zona pectinata) ; «?, entering projection ; «, cartilaginous plate ; 0, stria vascularis ; /, periosteum
of the zona ossea ; ^, transparent outer layer of the same ; q< bundle of the cochlear nerve ; j,
place of termination of the medullated nerve fibres ; /, place of the axis cylinder in the canalicula
of the habenula perforata ; r, tympanic periosteum of the zona ossea.

proper cochlea of the lower groups of amphibia. Here alone,
at the bottom, terminates the nervus cochlearis.

It is impossible for us to describe here the infinitely com-
plicated structure of the fundamental portion of this true
cochlea, the more so as, unfortunately, in addition to all the

244

TWENTY-THIRD LECTURE.

uncertainty, an extremely complicated nomenclature has also
been developed.*

The osseous portion of the spiral plate contains the expan-
sion of the cochlear nerve. At its peripheral exit its bundles
of fibres meet the so-called organ of Corti (Fig. 198, //).

7>9 *

mkmSSiW^i

Fig. 198. — The Corti's organ of the dog in perpendicular section : a, b, homogeneous stratum of the
membrana basilaris ; u, vesicular stratum : 7', tympanic stratum with nuclei and protoplasma ;
a, labium lympanicum of the crista spiralis : a, continuation of the tympanic periosteum of the
lamina spiralis ossea ; c, thickened commencing portion of the membrana basilaris, together with
the place of section, //, of the nerve d, and e blood-vessels ; _/, the nerve: g, epithelium of the
sulcus spiralis externus ; i, inner hair cell with the basal process, k, surrounded by nuclei and pro-
toplasma (of the " granule stratum "), into which the nerve fibres radiate : », base or foot of the inner
pillar of the Corti's organ; m, its "head piece," connected with the same part of the outer pillar,
the lower part of which is wanting, while the next following pillar o, presents the middle part
and the base : /, q, r, the three outer hair cells ; z, a so-called supporting cell of Hensen ; L, lamina
reticularis ; w, nerve fibre terminating at the first of the outer hair cells.

In a transverse section it forms a conical elevation of the
membranous base of the cochlear canal. It is hollow in its
interior, and forms collectively, by the cochlear convolutions, a
spiral tunnel. Its structure is infinitely complicated.

We here meet with a double row of convergent ascending
"pillars" {n, mf o) which meet each other at the top of the Cor-
tian organ. There are two of the " external pillars " (o) to
three of these internal elements (/i, ni). At their base we
meet with cell rudiments.

A further diversity is induced by the epithelial cells of the
cochlear canals. They become from within outwards (that is
from the axis of the cochlea towards its convex external arch)

* The cochlear canal has been the object of extraordinarily extensive labors on
the part of Reissner, Claudius, Boettcher, Schultze, Deiteis, Hensen, Waldeyer,
Gottstein and others.

THE ORGANS OF SENSE. 245

higher and higher (^). To the inner side of the inner pillar
of the Cortian organ is applied a long cylinder cell, which is
covered at the free upper border with short hairs it). This
is the " inner hair cell " of Deiters. The " outer hair cells "
{p, q, r), which are also obliquely directed, adhere in three or
fourfold rows to the outer pillars of this Cortian tunnel. Fur-
ther outwards occur spindle-shaped elements, " supporting
cells " of Hensen (s), and then, gradually becoming flattened,
lower cubical epithelial cells.

The supports of the inner and outer pillars lock into each
other in a quite peculiar form. From this point is developed
an extremely remarkable horizontally extended membrane,
the lamina velamentosa of Deiters (/, /). It is impossible to
describe here the marvelous reticular structure.

Where do the primitive fibrillae of the cochlear nerves end ?
Freed at last from the confinement of the lamina spiralis ossea,
it passes between the inner pillars in the tunnel of the Cortian
organ. They are said to have previously become partially
lost in the inner hair cells. They now terminate in the outer
hair cells (zv). Notwithstanding the infinite pains and labor
bestowed on this subject, it still stands on a weak foundation.

TWENTY-FOURTH LECTURE.

THE ORGANS OF SENSE, CONTINUED. — THE EYE.

We have still to mention the termination of the optic
nerve. In doing this we must of course draw into the circle
of our discussion the entire eye, that magnificent and won-
derful organ which is so important for the physician. Never-
theless, in consequence of its extremely complicated structure,
we can only present a cursory incomplete description.

The eyeball (Fig. 199) presents first an external capsular

Fig. 199. — Transverse section of the eye ; a, sclerotica ; b, cornea ; c, conjunctiva ; d, circulus
venosus iridis ; e, choroid, with the pigment layer of the retina ; f, ciliary muscle ; g, ciliary process ;
It. iris : z, optic nerve ; i', colliculus opticus ; k, ora serrata retinae ; /. crystalline lens ; m, tunica
Descemetii ; «, membrana limitans interna of the retina ; o, membrana hyaloidea ; j>, canalis
Petiti ; q, macula lutea.

system ; the posterior, opaque, greater portion is formed by
the sclerotic {a), while the anterior, smaller, transparent seg-

THE EYE. 247

ment (6) is constituted by the cornea. These membranes
enclose a black stratum, the so-called uvea. It consists of the
choroid (e) with the ciliary processes (g) and, applied exter-
nally to the latter, the ciliary muscle (_/") and, finally, a more
anterior ring-shaped disk, the iris (//).

The contents of the hollow ball are formed by the various
light-refracting media. Even the cornea {b) participates in
this action. Next to it comes the so-called humor aqueus,
that is, the watery contents of the anterior and posterior
chambers of the eye (in front of /). Then follows a firmer
structure, the most important refracting body, the crystalline
lens (/). The completion is formed by a large globular mass,
having a concave impression in front, the vitreous body or
humor vitreus (behind /).

The greater portion of the latter is covered by the cup-
shaped expansion of the optic nerve, the retina (/). It termi-
nates anteriorly, according to the usual impression, in the
region of the origin of the ciliary processes, with an undulated
border, the so-called ora serrata (k).

A very complicated system of vessels, springing almost
exclusively from the arteria ophthalmica, supplies our organ
with blood. Lymphatics are, naturally, also not wanting.

The cornea, with its two homogeneous boundary layers, was
mentioned at p. 56; the stratified pavement epithelium of the
anterior surface at p. 31 ; the simple cell layer of the posterior
at p. 29 ; the nerves at p. 207.

We mentioned at that time the system of passages of the
cornea, and ascribed to them a sort of parietes. Differences
of opinion prevail concerning this, however. The passages
of this system of juice-clefts (Fig. 200) may be artificially filled
by the puncturing method, in successful cases, with the pres-
ervation of their old shapes, in numerous others, however,
distorted, with the appearance of wide misshapen canals.
They have been not badly termed "rupture spaces." The
circumstance is interesting that a successful injection of the
juice-spaces finally leads to the lymphatics of the conjunctiva.

The cellular contents of the canal-work has caused endless

248 TWENTY-FO UR TH LECTURE.

controversies ; not the lymph corpuscles wandering through
them, but rather the "fixed" corneal cells (Fig. 200, to the
left and below). They are stellate and water-wheel-like cells,
the nucleus of which is always invested by some protoplasm,
while the peripheral portions are metamorphosed into homo-

Fig. 200. — The human cornea impregnated with silver. The corneal corpuscles, that is, the system
of juice-spaces, colorless. To the left, below, four metamorphosed parenchyma cells.

geneous veil-like plates. The cells probably have a limited
contractility. Their processes do not, according to our views,
form any connected net-work. Hence, a portion of the juice-
canals remain filled with fluid. All this is disputed by others,
however. No one should here leave the decision with confi-
dence to one reagent, such as gold, for instance.

The sclerotica (p. 57) is a firm connective-tissue membrane,
and consists of bundles arranged meridionally, with others
crossing them in an equatorial direction. In front they pass
continuously over into the modified hyaline connective tissue
of the cornea. It also contains regular passages with lymph
corpuscles and in part colorless, in part pigmented connective-
tissue cells (Waldeyer). It appears to have nerves only at
the corneal border.

At the margin of both membranes, although belonging to
the inner surface of the sclerotica, we meet with a complicated
ring-shaped reservoir. This is the sinus Schlemmii (Fig.
199, d). It has been declared to be a venous reservoir

THE EYE.

249

(Leber). Others regard it as a lymphatic passage (Schwalbe,
Waldeyer).

Posteriorly, the sclerotica passes over into the external
sheath of the optic nerve, derived from the dura mater. This
membrane is finally strengthened by the insertions of the ten-
dinous bundles of the ocular muscles.

The system of the uvea, with the exception of its most
anterior portion, the iris, is characterized by very considerably
developed vessels.

The entire inner surface (and the posterior surface of the
iris) is covered by the pigmented outer epithelium of the
retina (p. 30). During a portion of the fcetal period, the
latter extended much further forwards than it does at a more
mature period.

The greater portion of the uvea is formed by the posterior
segment, the choroid. The thin membrane consists of sev-
eral, not sharply demarcated, connective-tissue layers.

We recognize a, an inner hyaline boundary layer, 0.0006 to
O.OO08 mm. in thickness, thicker and more uneven in front ; b,
a thin homogeneous layer, with extraordinarily developed
stellate capillary net-works (choroidea >capillaris) ; c, the
choroid proper of the histologists, with stellate, very generally
pigmented connective-tissue cells, and a great wealth of arte-
rial, as well as venous vessels ; and, finally, d, a loose pig-
mented connective tissue, which forms the connection with
the inner surface of the sclerotica. It is called the lamina
fusca, and also the supra-choroidea ; it forms a lymphatic
space.

The vascular net-work in the ciliary body, and in the ciliary
processes which project inwards from the latter, is greatly
developed. The substratum remains similar to that of the
choroid, though the pigmented connective-tissue cells dis-
appear.

Externally to these processes we meet with a peculiar
smooth muscular mass, the tensor choroideae, musculus ciliaris,
or ligamentum ciliare of an older epoch (Fig. 199, /).

The human ciliary muscle arises from the inner side of the
11*

250

TWENTY-FOURTH LECTURE.

boundary region of the cornea and sclerotica. Meridional
bundles of the former radiate in a posterior direction into the
ciliary body. Below and inwards occur interwoven filaments,
and still further inwards, circular bundles (Mueller's ring
muscle).

We meet with colorless connective-tissue cells in the con-
nective-tissue substratum of the iris of light eyes, and pig-
mented cells in that of dark ones. Besides these, smooth
muscular elements occur. Annular bundles (Fig. 201, a)

Fig. 201. — Surface of the human iris ; a, the sphincter ; b, the dilator of the pupil.

form the constrictor or sphincter of the pupil. From it pro-
ceeds the dilator pupillse, an object of controversy of later
years.

Muscular bundles, which are at first separated, form more
peripherically a connected radial layer of fibres (b). At the
ciliary, that is the outer border, we finally meet with an an-
nular muscular layer.

This external or ciliary border of the iris gives rise at its
anterior surface to another peculiar tissue, the ligamentum
pectinatum iridis (Huek).

We have already learned (p. 56) that the posterior surface
of the cornea is covered by a hyaline membrane, the mem-
brana Descemetica or Demoursii. At its periphery, this
posterior covering layer passes over into a peculiar reticular
tissue (probably, in man, most intimately connected with the
elastic tissue), which passes through the outer margin of the

THE EYE. 251

anterior chamber of the eye. This is the ligamentum pcctina-
tum, which has just been mentioned. Its trabecular are
covered with epithelial cells. The anterior surface of the iris
also has such a layer. An incompletely closed, ring-shaped
canal, which is bounded by the trabecular of this ligamentum,
has been called the canalis Fontanae.

Small ganglia of the ciliary nerves occur in the choroid.
The ciliary muscle and the iris are more plentifully supplied
with nerve fibres, but their manner of termination we do not
yet know.

Concerning the crystalline lens and the vitreous body in
general, we refer to pages 78 and 45. There is one circum-
stance which requires more special mention here. According
to a widely disseminated acceptation, the hyaloid membrane
(Fig. 199 in the vicinity of k), separates into two leaves, a
posterior and an anterior, the so-called zonula Zinnii, which
is impressed in a ruffle-like manner by the ciliary processes.
Both continue on to the crystalline lens at its equatorial zone.
The zonula Zinnii presents a peculiar pale and resistant sys-
tem of fibres. A three-cornered annular sinus, bounded by
both lamellae, bears the name of the canalis Petiti. Much is
still obscure here, and the space is, after all, only an artefact
(Merkel, Mihalcovics).

Let us now turn to the expansion of the optic nerve into the
retina. Our membrane has its greatest thickness (0.38 to
0.23 mm.) at the place of the entrance of the optic nerve. It
becomes thinner (to about the half) towards the periphery.
Passing beyond the equator (thinned to 0.09 mm.) it termi-
nates as the so-called ora serrata (Fig. 199, k). Externally
from the place of entrance of the optic nerve (z1), about 3 to 4
mm. removed from it, is the macula lutea, the seat of the most
distinct vision (g). In its centre there is an excavation, the
so-called fovea centralis.

The retina, provided with numerous other elements, appears
to be an extraordinarily complicated structure, and, at the
same time, of extreme delicacy and variability. It has been
the object of infinite research in older and more recent times ;

252

TWENTY-FOURTH LECTURE.

but, notwithstanding the labors of H. Mueller and M. Schultze,
we are still exceedingly distant from a conclusion, as Schwal-
be's most recent studies show.

The retina (Fig. 202) is invested externally by the simple
pigmented epithelial layer already familiar to us (p. 30).

Then (1) we have the stratum of
rods and cones ; thereupon follows
the so-called external limiting mem-
brane, the membrana limitans ex-
terna (the transverse line between I
and 2). Next comes the external
granular la}Ter (2), then the inter-
granular layer (3). Thereupon fol-
lows the inner granular layer (4),
then the molecular stratum (5).
Further inwards we meet with the
stratum of the ganglion cells (6),
thereupon the radial expansion of
the optic nerve fibres (7). The
termination is formed by the inter-
nal limiting membrane, the mem-
brana limitans interna (10). The
layer of rods and cones, as well as
the external granular layer, is called
by Schwalbe the neuro-epithelial
stratum, all the rest the cerebral
stratum.

In the structure of this thin
and wonderfully complicated mem-
brane we must, however, distinguish two different elements,
connective tissue and nervous.

Let us first take the former into account (Fig. 203, A), and
commence at the inner surface.

The membrana limitans interna (/), an apparently hyaline,
o.oon mm. thick layer, deserves mention as the first connec-
tive-tissue boundary layer. In an inward direction (to-
wards the vitreous body), smoothly demarcated, it passes over

Fig. 202. — The human retina in ver-
. tical section ; i, layer of the rods
cones, demarcated below by the mem-
brana limitans externa ; 2, the exter-
nal granular layer ; 3, intergranular
layer; 4, internal granular layer:
5, tine granular layer ; 6, layer of gan-
glion cells ; 7. expansion of the optic
nerve fibres ; 8, Mueller's supporting
fibres ; 9, their transformation into the
inner limiting. membrane ; 10, the mem-
brana limitans interna.

THE EYE.

253

externally (towards the choroid), commencing with a triangu-
lar expansion, and then diminishing into a connective-tissue
radial fibre system (e), which is wanting only in the macula
lutea.

'Wt

Fig. 203. — Diagramatic representation of the retina ; A, connective-tissue frame-work : a, mern-
brana limitans externa ; c, radial or Muellerian supporting fibres with their nuclei, e' ; d, frame-
work substance of the intergranular, and g, of the molecular layer ; /, membrana limitans in-
terna ; B, nervous elements ; 6, rods with outer and inner members ; c, cones with outer member
and body ; i\ rod, and c\ cone granule ; rf, expansion of the cone fibre into the finest fibrillae in
the intergranular layer ; f, granules of the inner granular layer ; g, confused mass of finest fibres in
the molecular layer ; h, ganglion cells ; k\ their axis-cylinder processes ; i, layer of nerve fibres.

These are the Mueller's supporting fibres (e). They in-
ciease more and more towards the anterior terminal portion.

254 TWENTY-FO UR TH LECTURE.

Lateral branches of the latter lead to manifold communica-
tions. In the molecular (gf) and the intergranular layer (d)
there is thus formed a very fine reticular frame-work, such as
we are already familiar with in the gray substance of the cere-
brospinal system (p. 220).

Nuclei or cell equivalents occur occasionally in the system
of supporting fibres, as in the external granular layer (<?').

The supporting substance certainly extends as far as the
base of the rod and cone layer (a). There is scarcely
any doubt, however, that it extends still further as a delicate,
homogeneous connecting substance. At the former locality
it forms, as the membrana limitans externa, a fenestrated
boundary layer, further outwards a connecting medium of
the rods and cones.

Having thus become familiar with the connective-tissue sub-
stratum— it should by no means be genetically confounded
with the ordinary connective tissue — let us pass to the ner-
vous elements of the retina (B). Let us here select the re-
versed course, and commence with the outer layer.

This stratum is formed by the rods and cones. The whole
layer is called the rod-layer, stratum bacillosum. They are
terminal nerve cells, similar to those which we previously met
with at the higher nerves of sense. Those of the retina,
however, possess many peculiarities, and we have a more ac-
curate knowledge of them than of their relatives. The cir-
cumstance is also interesting that the rods and cones vary
according to animal groups. Their dimensions are propor-
tionate to that of the red blood cells.

The rods, bacilli (B, b), are slender cylindrical structures.
They consist (Mueller, Braun, Krause) regularly of two parts,
an apparently homogeneous narrower so:called " outer mem-
ber," which refracts the light more strongly, and a shorter
" inner member." The latter appears paler, somewhat granu-
lar, and of considerable diameter. In the lower vertebrate
animals the retinal pigment forms regular sheaths around the
outer member of the rods and cones. In mammals and man
the pigment sheath is less developed.

THE EYE.

255

The rods acquire their greatest length, 0.06 mm. and more,
at the bottom of the retina. Further forwards they become
shorter, towards the ora serrata they are only 0.0399 mm.
high. Their diameter may be estimated at 0.0016 to
0.0018 mm.

Downwards or inwards, beneath the membrana limitans
externa, the rod becomes pointed, and runs out into an ex-
traordinarily fine filament, a primitive
nerve fibrilla (Fig. 203, B, Fig. 204, 1,
4, Fig. 205, 1, .3). The latter passes
through the outer granular layer verti-
cally (and also radially). A small cell,
the so-called " rod granule" (Fig. 203,
B, b\ Fig. 204, 1, 2, 3, Fig. 205, 3) is
embedded in its course, sometimes
higher up, sometimes further down-
wards. This granule forms the single
element of the outer granular layer.

Still more complicated textural con-
ditions have been observed in the rods
(Fig. 204). At the border of the in-
ner member towards the outer mem-
ber, embedded in the former, a plano-
convex body has been found with its
plane base directed upwards (1, a, 2).
" rod-ellipsoid " of Krause.

Furthermore, as has been long known, the outer member
breaks up into transverse plates (3). These discs may have
a thickness of 0.0003 to 0.0004 mm. in man (Schultze).

The outer member shows a longitudinal striation, caused
by longitudinal, channel-like depressions, with longitudinal
elevations springing up between them, like a fluted column
(Fig. 204, i, 2, and Fig. 205, I a). Longitudinal striations
have also been subsequently discovered on the inner members
(Fig. 205, 1, and 3 b). In the axis of the rod a very fine
filament, a primitive nerve fibrilla, is also said to have been
noticed (Ritter).

Fig. 204. — Final structure of
the rods ; I, from the chicken
with the outer and inner mem-
ber, as well as the cone-ellip-
soid ; 2, from the frog ; 3, the
outer member of the rod of a
frog dividing into transverse
discs ; 4. rod with granule
from the Guinea-pig.

This is the so-called

256

TWENTY-FOURTH LECTURE.

Our present knowledge concerning the cones (Fig. 203, B,

Fig. 205 2), is uncertain.

In man, they have the form of a slen-
der bottle. Their base rests on the
membrana limitans externa. Upwards,
the cone passes into a shorter, conical,
infinitely changeable structure, the so-
called cone rod (Fig. 203, B, above c,
Fig. 205, 2 a). It is the equivalent of
the external member of the rod, charac-
terized by its great tendency to break
up into transverse discs. The inner
member, or the cone body <Iig. 205, 2
b), also shows the longitudinal striation,
similar to the equivalent portion of the
rod.

At the base of the rod, immediately
beneath the limitans externa, we meet

with a cell-like
body, the so-
call ed cone
granule (Fig.
203, B, C, Fig.
205, 2, below d).
A broad cone
filament (up to
0.0029 mm- m
thickness) finally
runs downward,
passing through
the outer granular layer (Fig. 203, below c'). It is a fascicu-
lus of primitive fibrillar.

Interesting local variations (Fig. 206) in regard to the num-
ber of cones and rods occur in the human eye.

In the macula lutea, the seat of the most distinct vision,
we meet with cones alone, which have become extremely fine
(1). In the vicinity the latter are still quite crowded, and are

Fig. 205. — Fibrillated cover-
ing of the rods and cones ; i,
rods ; 2, cones of man ; a,
outer ; 6, inner member ; c,
rod-filament ; d, limitans ex-
terna ; 3, rod of the sheep.
The fibrillie project beyond the
inner member ; the outer mem-
ber is wanting.

Fig. 206. — The rod layer
seen from without ; a, cones ;
b, cone rods ; c, ordinary
rods ; 1, from the macula lu-
tea : 2, at the margin of the
same ; 3, from the centre of
the retina.

THE EYE. 257

surrounded by a single circle of rods (2). The further out-
wards we proceed, the further we find the cones removed
from each other, and the greater the number of rods situated
between them (3).

Apes, andv the most of our domestic animals, present an
analogous condition. Nocturnal animals, such as the cat,
have only stunted cones ; bats, hedgehogs, moles, are entirely
deprived of the latter elements. Birds, on the contrary,
generally have an abundance of cones. In the chameleon
and lizard there are no rods at all ; we find only cones, as
in the human macula lutea. The rod appears to be the ter-
minal apparatus, serving for the objective colorless vision, as
the cone does for the color perception of the outer world
(Schultze).

The membrana limitans externa, the sieve-like fenestrated
boundary structure, we are already familiar with. The rod
apices pass downwards through small spaces, the cone gran-
ules through larger ones. Finally, this membrane sends out-
wards the already mentioned delicate homogeneous connect-
ing substance between the rods and cones.

The external granular layer, stratum granulosum externum,
is already familiar to us so far as its connective-tissue frame-
work is concerned. It (Fig. 203, B) consists of layers of
small cells stratified over each other, a minimal body closely
surrounding the nucleus. We distinguish here the larger
higher cone granules (c'), measuring 0.009 to O.012 mm., and
the smaller rod granules, measuring 0.0045 to 0.0079 mm.,
situated more deeply. The latter alone present a peculiar,
perhaps normal transverse striation (Fig. 204, 4).

Thus far the connection of the retinal elements is clear.
Now, however, on coming to the so-called intergranular
layer, the stratum intergranulosum, this clearness is lost.
There exists here a grievous defect of knowledge.

Schultze, the excellent investigator whom we have thus far
followed, asserted that the finest rod-fibrillai, having arrived
at the intergranular stratum, formed very fine terminal knobs
(Fig. 203, B, above d). This is decidedly not the case. The

258 TWENTY-FO UR TH LECTURE.

filament simply bends into another plane, suddenly and at
a considerable angle. I have convinced myself of this with
certainty.

The broad cone fibres divide at the same place into three
very fine processes (above d).

In the most delicate connective-tissue frame-work of the
intergranular layer we meet with a confused mass of fine
horizontally and obliquely disposed filaments (d), the con-
tinuations of the rod and cone fibrillar.

The inner granular layer — the stratum granulosum inter-
num— contains, in the first place, as we already know (A, e'),
connective-tissue nuclei or cellules of oval shape. Together
with these appear layers of sharply demarcated, globular, nu-
cleated cells (B,f), into the upper pole of which sinks a
rather fine nervous filament, to again pass out at the lower
pole, very much finer, and continuing further in a perpen-
dicular direction. These nervous granules do not show any
transverse striation.

The molecular or fine granular layer, stratum moleculare
(B, g), repeats, although with greater thickness, the fine con-
nective-tissue spongy structure of the stratum intergranulo-
sum. We again discover in it a confused mass of primitive
fibrillar. Ascending fibres from the more deeply situated
cells of the intergranular layer, having entered this confused
mass, may be observed here and there ; following their course
is not to be thought of. We have here, therefore, a new de-
fect in our knowledge of the retina.

We now arrive at the layer of the ganglion bodies, the
stratum cellulosum (B, Ji), These occur stratified (in IO to 6
layers) at the bottom of the retina, to gradually appear to-
wards the periphery as a single layer, and with an increasing
distance from each other. With the exception of the macula
lutea, where the ganglion bodies are bipolar, they form fine
multipolar cells of not inconsiderable size (up to 0.0377 nim.).
Their protoplasma processes turn outwards, and finally disap-
pear with their terminal branches in the maze of fibres of the
molecular stratum ; their axis-cylinder process is directed in-

THE EYE. 259

wards (/*'). It passes over into a nerve fibre of the optic
nerve-fibre layer, the stratum fibrillosum (i).

In order to comprehend the latter we must commence with
the contents of the optic nerve. It has medullated nerve
fibres, 0.0045 t° 1. 0014 mm. thick. Having entered the ball
of the eye, their medullary sheath is lost, and they become
pale axis cylinders.*

Having advanced into the retina, our optic nerve fibres di-
vide and reunite at acute angles into bundles, forming a nerve
plexus. In proportion as we follow their further course for-
wards, the fibre bundles become thinner and thinner, and the
distance between them is constantly increased. At last we
meet with only isolated axis cylinders.

We have grounds for assuming that each optic-nerve fibre
penetrates the body of a ganglion cell as an axis-cylinder
process ; still we cannot prove this at the present time.

The membrana limitans interna, of a connective-tissue na-
ture, has been previously mentioned.

The best portion of the retina, the yellow spot or macula
lutea, requires a short mention.

The connective-tissue frame-work substance, with the ex-
ception of the limitans interna, is undeveloped. The nerve-
fibre layer likewise disappears ; the layer of the ganglion
cells, still largely developed at the periphery, also disappears
completely in the centre of the fovea. The molecular and
inner granular layers also suffer the same fate. There re-
mains, therefore, only the (exclusively occurring) cones with
the stratum granulosum externum.

The latter (Fig. 207) are no longer as of old. Their body
has at last become narrowed to 0.0028 to 0.0033 mm.
(Schultze) ; it has diminished to nearly the thinness of the
rod, and the cone rod too.ooi to 0.0009 mm. The cone fibre
appears to have participated but little in this thinning. The

* It is remarkable that in individual human retinas the medullary sheath of the
nerve tubes is preserved. In the dog the same not unfrerruently occurs ; in rab-
bits and hares it is even the rule.

26o

TWENTY- FOURTH LECTURE.

cone granule lies sometimes higher, sometimes deeper (a) ;
we might say from necessity.

We meet with still another
condition. In the peripheral
layers of the retina the cone
fibre passes through our mem-
brane in an ascending perpen-
dicular direction. The latter
now leaves this direction more
and more, to pass obliquely out-
wards and downwards (a). This
induces beneath the outer gran-
ular layer (that is the cone gran-
ules), a quite peculiar appear-
ance.

Forwards, towards the ora
serrata, the retina increases in
thinness, and the nervous ele-
ments diminish ; the connective
tissue frame-work acquires the
upper hand more and more ;
finally all the nervous elements
have disappeared.

By the ciliary portion of the
retina is designated a system
of cylindrical cells which lie on
the zonula Zinnii beyond the
ora serrata, and run as far as
the iris, according to many even to the pupillary border of
the latter.

The blood-vessels of the retina, springing from the arteria
centralis, form an elegant wide-meshed reticulum of very fine
tubes. They occupy the inner portion of the retina, but pass
outwards to the inner granular layer, and perhaps still fur-
ther. The adventitia of the same surrounds the inner layer
but loosely, leaving a lymphatic space.

It is impossible for us to enter into the exceedingly com-

Fig. 207. — Cones from the macula lutea and
fovea centralis of man ; a, with decomposed
outer membrane ; l>, with the lamellar decom-
position of the same.

THE EYE.

261

plicated arrangement of the blood vessels of the eyeball.
We must leave this to more special works.

We would add, however, a few words concerning the
lymphatics of. the eyeball
(Fig. 208), basing them on
Schwalbe's admirable work.

We may assume with this
investigator an anterior and
a posterior system of lym-
phatics.

The former, arising from
the iris and ciliary processes,
has its central reservoir in
the anterior chamber of the
eye. To this division be-
long also the lymphatics
of the cornea and conjunc-
tiva.

All that lies behind the
ciliary processes forms the
posterior lymphatic system.
The sclerotic and the cho-
roid are perhaps without
definite lymphatic canals.

The cup-like space between both membranes, with which
we are already familiar as the lamina fusca, has, on the
contrary, the signification of a lymph reservoir. This is
Schwalbe's perichoroideal space (p). From it (at the eleva-
tion of m r of our figure) occurs the transition of the lym-
phatic fluid into the so-called Tenon's space (/), that is the
interval between the outer surface of the sclera and the Te-
non's capsule of the eyeball. The connecting lymph canals
surround the vasa vorticosa of the choroid in a sheath-like
manner. Posteriorly the Tenon's reservoir continues into
the supravaginal space (s p v), a cylindrical sheath membrane
of the optic nerve.-

Key and Retzius, the two able investigators mentioned in

Fig. 208. — The posterior lymphatics of the hog's
eye : c, conjunctiva ; m r, the recti muscles :
111 retr., retractor bulbi ; a, layer of fat: 7>, the
outer sheath of the optic nerve ; t, the '"Tenon's"
space, passing backwards into the "supravaginal,"
s />7' : .? 6 v, " subvaginal " space between the in-
ner and outer sheath of the optic nerve ; /. "per-
ichoroideal" space connected with the Tenon's
space by oblique passages.

262 TWENTY-FO UR TH LECTURE.

connection with the lymphatics of the nervous central organs,
injected from the subdural space of the brain (p. 231) an
intermediate space located between the external and internal
sheath of the optic nerve, the subvaginal space of Schwalbe
(s b v), and from this they drove the injection mass into the
perichoroideal space of Schwalbe. Schwalbe does not, how-
ever, accept the latter communication.

Injection masses maybe forced beneath the inner sheath of
the optic nerve, between the bundles of optic-nerve fibres,
and this may be done from the subarachnoidal space of the
brain (p. 231).

The lymphatics of the retina invest its capillaries and veins,
therefore, in a sheath-like manner.

We return to the chambers of the eye, the central reservoir
of the lymph of the anterior portion of the globe. What is
the relation of its affluent passages ?

In the first place a cleft system leads from the canal of
Petit into the posterior, and thus into the anterior chamber
of the eye. Wider and more important introductory passages
open from the Fontana's space in the ligamentum pectinatum
iridis, probably for the lymph of the iris and ciliary pro-
cesses.

Injection masses pass from the periphery of the membrane
of Descemet into the canal of Schlemm (p. 248).

Can a communication between the lymphatic and venous
passages actually exist here, similar to that which Key and
Retzius admitted, by the aid of the Pacchionian granulations
for the membranes of the brain (p. 232) ? Leber, an observer
who has rendered great service to the anatomy of the eye,
has, it is true, disputed this, and he may be right.

We have still to mention, briefly, the external, less import-
ant appendices of the eyeball.

The eyelids contain, embedded in the firm connective tis-
sue of the tarsal cartilage, the so-called Meibomian glands,
short sinuous tubes with fatty parenchyma cells, but without
a membrana propria or muscular tissue in the excretory duct.
Its secretion is the sebum palpebrale.

THE EYE. 263

The conjunctiva presents a complete mucous membrane
over the posterior surface of the eyelids and the anterior sur-
face of the sclera ; only the stratified pavement epithelium
remains over the cornea, the mucous membrane having
become metamorphosed into corneal tissue.

The conjunctival glands are of manifold species. In man
and in certain mammals we meet with small mucous glandules,
though the cells contain fat granules. Convoluted glands
(Fig. 119) occur at the periphery of the cornea in ruminating
animals (Meissner). Simple culs-de-sac have been recognized
in the hog, externally to the corneal periphery, towards the
outer canthus of the eye (Manz). In the tarsal border of the
human eye we meet with modified sudoriparous glands
(Waldeyer).

Concerning the trachoma glands, we have already commu-
nicated all that was necessary (p. 113). In man there are
probably no true lymphoid follicles (Waldeyer). The ter-
minal bulbs of the conjunctiva have been mentioned at p.
209.

The tear-gland, glandula lacrymalis, consists of an aggre-
gation of single racemose glands. We are not yet familiar
with the nerve terminations here. The efferent apparatus
presents differences of structure in its different portions.
We leave the description of them, like that of so many other
things, to more comprehensive text-books.

INDEX

Acinus of the glands, 130.

Adventitia of the capillaries, see Vessels.

Air cells, see Lungs.

Alveoli of the lungs, 158.

Amoeboid changes of form of the cells, 9.

Anthracosis of the lungs, 160; of the
bronchial glands, 160.

AquulaCotunnii (perilymph) of the audi-
tory organs, see Auditory apparatus.

Aquula vitrea auditiva (endolymph), see
Auditory apparatus.

Arachnoid, see Nerve centres.

Arrectores pilorum, 81.

Arteriae helicinae, 191.

Arteries, 94.

Arteriolar recta? of the kidney, 170.

Articular cartilage, 44.

Assimilation by the cell, II.

Auditory organ, 240 ; external ear, 241 ;
membrana tympani, 241 ; auditory
ossicles, 241 ; Eustachian tube, 241 ;
internal ear, 241 ; vestibule and semi-
circular canals, 241 ; otoliths, 242 ;
cochlea, 242 ; its structure, 242 ;
Reissner's, or the cochlear canal,
Corti's organ, termination of the coch-
lear nerves, etc., 243.

Auditory ossicles, see Auditory organ.

Auerbach's plexus myentericus, 218.

Axis canal of the spinal cord, 224.

Axis cylinder, 193.

Axis-cylinder process of the ganglion
cells, 200.

Axis fibrillar of the nerves, 196.

Bacilli of the retina, see the Eye.

Bartholinian glands, 181.

Bathybius, 1.

Becher cells, 5.

Bellini's tubes, see Kidney.

Biliary capillaries, see Liver.

Biliary passages, see Liver.

Bladder, see Urinary apparatus.

Blood, 21 ; cells and plasma, 21 ; red
blood corpuscles and lymphoid cells,
21 ; nature of the former, 22; differ-
12

ences of the same according to the
groups of vertebrate animals, 23 ;
lymphoid cells of the blood, 23 ; rela-
tive number, 24; circulation of the
blood, 24 ; fate of the lymphoid cells ;
25 ; genesis of the blood in the em-
bryo, 26.

Blood- vascular glands, 123 ; thyroid
gland, 123; structure, 123; colloid
formation. 124 ; suprarenal capsules,
124; cortical and medullary layer,
124; structure, 125; vessels and
nerves, 126 ; apophysis cerebri, 126 ;
coccygeal gland, 126; ganglion inter-
caroticum, 127.

Blood-vessels, see Vascular system.

Bone tissue, 60; kinds of bone, 60;
medullary or Haversian canal, 60 ;
Haversian and general lamellae, 61 ;
canaliculi, 61 ; bone corpuscles or
lacunas, 62 ; bone cells, 62 ; composi-
tion of bone, 63; bone cartilage, 64;
bone medulla, 64 ; osteogenesis, 64 ;
cartilage marrow, 65 ; ossification
points, 65 ; formation of bone at the
expense of the cartilage tissue, 65 ;
osteoblasts, 68; endochondral bones,
69 ; theory of apposition and expan-
sion, 69; Haversian spaces, 70; os-
teoclasts, 70; periosteal bone forma-
tion, 70; Sharpey's fibres, 71.

Bowman's glands of the olfactory region,
see Olfactory organ.

Brain, cerebrum and cerebellum, see
Nerve centres.

Bronchia, see Lungs.

Bruch's trachoma follicles, 113, 263.

Brunner's glands, 147.

Buccal glandules, see Digestive appa-
ratus.

Bulbus olfactorious, see Olfactory appa-
ratus.

Canaliculi, see Bone tissue.
Canalis cochlearis, see Auditory appara-
tus.

266

INDEX.

Canalis Fontanse, see Eye.

Canalis Petiti, see Eye.

Canalis Schlemmii, see Eye.

Canalis semi-circular of the ear, see
Auditory apparatus.

Capillaries, see Vessels.

Carotid gland, 126.

Cartilage, 42 ; hyaline, elastic (reticular)
and connective-tissue cartilage, 42 ;
cartilage cavities and cartilage cells,
43 ; cartilage capsules, 43 ; intercel-
lular substance, 43 ; metamorphosis
of fibres and calcification, 44 ; occur-
rence of hyaline cartilage, 44 ; reticu-
lar cartilage, 45 ; connective tissue, 45.

Cartilage capsules, see Cartilage.

Cartilage cell, see Cartilage.

Cartilage medulla, see Bone.

Cavernous bodies, see Sexual apparatus
of the male.

Cavernous passages of the lymphatic
glands, see Lymphatic glands.

Cells, 3 ; naked cells, 3 ; cell doctrine,
3 ; cell and cytode, 4 ; cell forms, 4,
5 ; globular, flattened and cylindrical
forms, 5 ; spindle cells, 5 ; proto-
plasma, 5 ; transformation of the
same, 5 ; nucleus, 6 ; nucleolus, 6 ;
non-nuclear cells, 6 ; multinuclear cells
(myeloplaxes), 7 ; cell envelope and
capsule, 7 ; porous canals, 8 ; vital
(amoeboid) changes in form of the cell,
9 ; pus corpuscles, 9 ; nutrition and
locomotion, 9 ; penetration of cells
into cells, 10 ; ciliated or vibratory
cells, 10; sensibility of cells, 11;
assimilation, 11 ; duration of life, 12;
kinds of death of the cell, 13 ; spon-
taneous genesis, 14 ; processes of divi-
sion, 14 ; endogenous cell formation,
with mother and daughter cells, 15 ;
intercellular substance, or tissue
cement, 16; metamorphosis of the
cells, and production of tissues, 17 ;
metamorphosis of the intercellular sub-
stance, 17 ; elastic fibres, 17 ; glands,
18; transversely striated muscular fila-
ments, 19.

Cerebellum, see Nerve centres.

Cerebral ganglia, see Nerve centres.

Cerebrin, 194.

Cerebrum, see Nerve centres.

Cerumen, see Auditory apparatus.

Ceruminous glands, see Auditory appa-
ratus.

Chorio-capillaris, see Eye.

Chorion of the ovum, 176.

Choroid, see Eye.

Chyle, 26.

Chyle vessels, 103, 116.

Ciliary cells, see Epithelium.

Ciliary motion, see Epithelium.

Ciliary muscles, see Eye.

Circulatory apparatus, see Vessels.

Clitoris, see Sexual system of the female.

Coagulation of the blood, 25.

Coagulation of the nerve medulla, 194.

Coccygeal gland, 126.

Cochlea, see Auditory apparatus.

Cochlear canal, see Auditory apparatus.

Colloid, 124.

Colloid metamorphosis of the thyroid

cavities, 124; of the apophysis cere-
bri, 126.
Colostrum, see Sexual system of the

female.
Columnar Bertini, see Kidneys.
Columns of the spinal cord, see Nerve

centres.
Commissura anterior and posterior of the

spinal cord, see Nerve centres.
Commissures of the spinal cord, see

Nerve centres.
Conarium of the brain, see Nerve centres.
Coni of the retina, see Eye.
Coni vasculosi, see Sexual apparatus of

the male.
Conjunctiva, see Eye.
Connective substance, 41.
Connective substance, lymphoid and

reticular, 45.
Connective tissues, 51; fibrillse, bundles,

elastic elements, 51 ; elastic sheaths,

53 ; cells of two different forms, 54 ;

formless connective tissue, 56 ; formed,

56 ; cornea, 56 ; tendons, 57 ; liga-
ments, 57 ; connective-tissue cartilage,

57 ; fibrous membranes, 57 ; serous,
5 7 ; corium, 58 ; mucous membranes,

58 ; vascular membranes (pia mater,
plexus choroides, and choroid), 58;
connective tissue vascular walls, 58 ;
elastic structures, 58 ; pathological,

59 ; embryonic conditions of the tissue,

59- . •

Constituents of the body, 3.

Contour, double, of the nerves, see Nerve

tissue.

Contractility of the living cell, 9.

Convoluted glands, 130.

Cornea, 56, 207, and see Eye.

Corneal cells, 56, 248.

Corneal corpuscles, 56, 248.

Corneal nerves, 207.

Corneal tubes, see Eye.

Corneous layer of the epidermis, 32.

INDEX.

267

Cornification of the pavement epithelium,

see Epithelium.
Cornu ammonis of the brain, see Nerve

centres.
Corpora cavernosa, 190.
Corpora quadrigemina of the brain, see

Nerve centres.
Corpus callosum, see Nerve centres
Corpus ciliare, see Eye.
Corpus epididymis, see Sexual apparatus

of the male.
Corpus Highmori, see Sexual apparatus

of the male.
Corpus luteum, see Sexual apparatus of

the female.
Corpus striatum of the brain, see Nerve

centres.
Corpus vitreum, see Eye.
Cortex corticis of the kidney, see Kidney.
Corti's cells, see Auditory apparatus.
Corti's fibres, see Auditory apparatus.
Corti's organ, see Auditory apparatus.
Cowper's glands, see Sexual apparatus of

the male.
Crura cerebri and cerebelli of the brain,

see Nerve centres.
Cuticula of the hair, see Epithelium.
Cytode, 2. 1

Daughter cells, 15.

Dehiscence of the ovarian follicles, see
Sexual system of the female.

Deiter's cells of the cochlea, see Auditory
apparatus.

Dental nerves, 214.

Dentinal cells, 75.

Dentinal tubes, etc., see Tooth tissue.

Dentine, 73.

Desquamation of the cells, 12.

Digestive apparatus, 139 ; oral cavity,
139; mucous glands, 139; salivary
glands, submaxillary and sublingual,
139 ; change of the gland cells, 140 ;
parotid, 141 ; tongue with its various
papillae, 141 ; serous glands of the
tongue, 142; pharynx, 142; oesophagus,

142 ; stomach, 142 ; tubular glands

143 ; frame-work of the mucous mem-
brane, 143 ; peptic and gastric-mucous
glands, 143 ; blood-vessels, 145 ;
lymphatics, 145 ; small intestines. 146;
intestinal villi and Lieberkiihnian
glands, 146 ; Brunner's glands, 146 ;
lymph or chyle passages, 14S ; absorp-
tion of fat, 14S ; large intestine and
its tubular glands, 149 ; lymphoid
follicles of the intestines, 149 ; blood-
vessels, 149; anus, 149.

Dilator pupillse, see Eye.
Discs of the transversely striated mus-
cles, see Muscles.
Division of the cells, 14.
Ductus ejaculatorii of the testicle, 189.
Dura mater, 57 and 231.
Duverney's glands, 18 1.

Ear, see Auditory apparatus.

Egg germ, see Sexual organs of the fe-
male.

Egg-strands, see Sexual organs of the
female.

Elastic tissue, 52.

Emigration of colored blood-cells through
the walls of the vessels, 90 ; of lym-
phoid cells, 90.

Emigration of red and colorless blood-
cells, 90.

Enamel germ, 76.

Enamel of the teeth, 75 ; enamel prisms,
75 ; enamel cuticle, 75 ; transverse sec-
tion, 75 ; genesis, 76.

Enamel organ, 46, 76.

Enamel prisms, etc., see Enamel.

Endogenous cell formation, 15.

Endothelium, 28.

Engelmann's accessory discs of the trans-
versely striated muscle, 85.

Envelopes of the finer nerve trunks, 57,
202. '

Enveloping structures of the central
nervous system, 231.

Blpidermis, see Epithelium.

Epididymis, see Sexual apparatus of the
male.

Epithelium, 28; endothelium, 2S ; pave-
ment, cylinder and ciliated epithelium,
2S ; cement substance, 31; pigment-
ed epithelium, 30 ; stratified, 30 ;
stachel and riff cells. 32 ; epidermis,
32 ; ciliary movement, 35 ; nail tis-
sue, 36 ; nail cells, 37 ; hairs, 38 ;
hair shaft and root, 38 : root sheath,
3S ; cortex and medulla of the hair,
39 ; epidermis, 39 ; appearance of the
hairs, lanugo hairs, 40.

Erection, 191.

Eustachian tubes, see Auditory appara-
tus.

Eye, 246; parts of the eyeball, 247;
cornea, 247 ; sclerotic, 248 ; canalis
Schlemmii, 249 ; choroid, 249 ; parts
of the same, 249 ; ciliary body, 249 ;
ciliary processes, 249 ; ciliary muscle,
249 ; iris, 250; sphincter and dilator of
the pupil, 250; ligamentum pectina-
tum iridis, 250 ; nerves of the iris, etc.,

268

INDEX.

251; crystalline lens, 251; vitreous;
body, 251 ; zonula Zinnii, 251 ; cana-
lis Pfliti, 251 ; retina, 251 ; arrange-
ment, 252 ; macula lutea, 252 ; layers,
252 ; frame-work substance, 252 ;
membrana limitans interna, 252 ;
Mueller's fibres, 253 ; membrana
limitans externa, 254 ; rods and cones,
254 ; external granular layer, 257 ;
intergranular layer, 257 ; inner gran-
ular layer, 25S ; molecular stratum,
258; layer of ganglion cells, 258; of
nerve fibres, 259 ; macula lutea, 259 ;
pars ciliaris, 260 ; lymphatics of the
eye, 261 ; eyelids, 262 ; glands of the
conjunctiva, 262 ; lachrymal glands,
263.
Eyeball, see Eye.

Fallopian tube, see Sexual organs of the

female.
Fat tissue, 48 ; fat cells, 48 ; fat drops,

48 ; chemical constitution of the tat

of the body, 49 ; cells losing their fat,

49 ; occurrence of fat tissue, 50 ; gen-
esis, 50.
Fatty degeneration, 13, 88.
Fiore cell, contractile, see Muscular

tissue.
Fibro-cartilage, see Cartilage tissue.
Fibro-reticular cartilage, see Cartilage

tissue.
Follicles, Graafian, of the ovary, see j

Sexual organs of the female.
Follicles, Malpighian, of the spleen, see '

the latter.
Follicles of the lymphatic glands, see the

latter.
Follicular chains of the ovary, see Sexual

organs of the female
Follicular rudiments of the ovary, see

Sexual organs of the female,
forked cells, see Gustatory apparatus.
Formatio granulosa of the ovary, see

Sexual organs of the female.
Fovea centralis of the retina, see Eye.

Gall-bladder, see Liver.

Ganglia, see Nerve centres.

Ganglion body, see Nerve tissue.

Ganglion cell layer of the retina, see
Eye.

Ganglion cells, see Nerve tissue.

Gastric glands, see Digestive apparatus.

Gastric-mucous glands, see Digestive ap-
paratus.

Gastric-mucous membrane, see Digestive
apparatus.

Gegenbaur's osteoblasts, see Bone tis-
sue.

Gelatinous tissue and reticular connec-
tive substance, 45 ; vitreous body, 46;
reticular connective substance, 47 ;
lymphoid celis and modifications of the
tissue, 47.

General lamellae, see Bone tissue.

Germinal plates, 28, etc.

Germinal spot, see Ovum.

Germinal vesicle, see Ovum.

Giant cells, see Myeloplaxes.

Gland capillaries, 134.

Gland nerves, 208.

Gland tissue, 128; definition, 128; con-
stituents of the glands, 129 ; various
forms of glands, 130; gland cells, 131 ;
secretions, 132; vessels, 134 ; lymphat-
lcsi 135; nerves, 135; excretory
ducts, 135 ; individual glands of the
body, 137 ; genesis, 138.

Glands, mucous, 139.

Glands, serous, 142.

Glomerulus of the kidney, 9S, 164.

Goll's column of the spinal cord, see
Nerve centres.

Graafian follicles of the ovary, see
Sexual organs of the female.

Granular layer of the retina, see Eye.

Growth of the cells, 11.

Gustatory apparatus, 236 ; the various
papilla;, 236 ; papilhe circumvallatae
and foliatte, 236 : gustatory buds, 237 ;
nerve termination, 238 ; gustatory
cells, 238.

Gustatory buds, see Gustatory appar-
atus.

Gustatory organ (tongue), see Gustatory
apparatus.

Gustatory papillae of the tongue, see
Gustatory apparatus.

Habenuke of the cochlea, see Auditory
apparatus.

Haemoglobin, 22.

Hair bulb, see Epithelium.

Hair sac, see Epithelium.

Hair, see Epithelium.

Haversian canals, see Bone tissue.

Haversian lamellae, see Bone tissue.

Haversian spaces, see Bone tissue.

Heart muscles, 86.

Hemispheres of the cerebrum and cere-
bellum, see Nerve centres.

Henle's loops of the uriniferous canals,
see Urinary apparatus.

Hensen's middle discs of the transversely
striated muscles, 84.

INDEX.

269

Hepatic lobules, see Liver.
Hepatic vessels, see Liver.
Hilus-stroma of the lymphatic glands,

10S.
1 [istology, 3.
Horn laser, 28.

Horn layer of the epidermis, 32.
Humor aqueus of the eye, see Eye.
Humor vitreus of the eye, see Eye.
Hymen, see Sexual apparatus of the

female.
Hypophysis cerebri. 126.

Infundibula of the lungs, see Lungs.

Interglobular spaces of the dentinal tissue,
see Teeth.

Intestinal glands, see Glands, and Diges-
tive organs.

Intestinal villi, 104; and Digestive or-
gans.

Iris, see Eye.

Iris nerves, see Eye.

Keratine, 5.

Kidney, 16 j ; cortex and medulla, 163 ;
Malpighian or medullary pyramids,
163 ; columnse Bertini, 163 ; uriniferous
canals or Bellini's tubes, 163 ; medul-
lary rays, 164; cortical pyramids, 164;
glomerulus, 164; papillae renales,
164; looped canals, 164; excretory
passages and secretory portion of the
kidney, 165; vascular arrangement of
the cortical pyramids, 165 ; Mueller's
or Bowman's capsule, 165 ; epithelial
relations, 166; intercalary piece, 167;
frame-work substance of the kidney,
16S ; blood and lymph vessels, 168 ;
blood passages, 168 ; lymph passages,
170; urinary passages, 171 ; renal
calices and pelvis, 171 ; ureter, 171 ;
bladder, 171 ; female uretha, 172.

Krause's transverse line of the muscles,
see Muscular tissue.

Labia, see Sexual organs of the female.

Lachrymal gland, etc., see Eye.

Lacunae, see Bone tissue.

Lamellae of the bones, see Bone tissue.

Lamina elastica of the cornea, see Eye.

Lamina fusca of the choroid, see Eye.

Lamina recticularis (velamentosa), see
Auditory apparatus.

Lamina spiralis of the cochlea, see Audi-
tory apparatus.

Large intestine, see Digestive organs.

Larynx, see Lungs.

Lens tissue, 7S ; lens capsule, 7S ; lens
fibres, 78.

Lentiform gastric glands, see Lymphoid
organs.

Leucaemia, 123.

Lieberk tinman glands, see Digestive
apparatus.

Ligaments, see Connective tissue.

Ligaments, elastic, see Connective tis-
sue.

Ligamentum ciliare, see Eye.

Ligamentum pectinatum iridis, see Eye.

Ligamentum spirale of the cochlea, see
Auditory apparatus.

Lingual papillae, 141.

Liquor folliculi, see Sexual apparatus of
the female.

Liver, 150; hepatic lobules, 151 ; hepa-
tic cells, 151 ; fatty liver, 151 ; hepa-
tic cell trabecule, 152; vessels, 152;
frame-work, 153 ; biliary passages and
biliary capillaries, 154 ; lymphatics,

155-

Lungs, 157 ; larynx, 157 ; trachea, 157 ;
lungs, 158; alveolar passages and pul-
monic lobules, 158 ; pulmonary vesi-
cles, p. cells, alveoli, 158; structure,
159; black lung pigment, 160; ar-
rangement of vessels, 160 ; pulmo-
nary epithelium, 162.

Lymph, 27.

Lymph corpuscles, see Lymphoid cells.

Lymph passages, 102 ; ductus thoraci-
cus, 102 ; lymphatics, 103 ; injection
of the lymphatics, 103 ; arrangement
of the same, 104 ; clefts, 106 ; juice
canals or juice clefts, 107 ; lymphatic
glands, 107 ; envelope, cortex and
medulla, hilus-stroma, 108 ; follicles,
108 ; septa and tenter-fibres, 109 ; in-
vestment spaces, 109 ; lymph canals,
no; blood-vessels, no.

Lymph sheaths of the blood-vessels, see
Vessels.

Lymph vessels, see Lymph passages.

Lymphatic glands, see Lymph passages.

Lymphoid cells. 5, 9, 23, etc.

Lymphoid follicles, see Lymphoid or-
gans,
j Lymphoid organs, 112; lens-shaped
glandules, solitary and Peyerian fol-
licles, tonsils and trachoma glands,
112; structure of the tonsils, 113;
trachoma glands in particular, 113;
structure of the Peyerian plaques, 114;
spleen, 116; Malpighian corpuscles,
and pulp, 1 17; vessels, 119; cells
containing blood corpuscles, 122 :

270

INDEX.

leucaemia, 123 ; lymphatics, 123 ;
blood -vascular glands, 123.

Macula lutea of the retina, see Eye.

Malpighian bodies of the spleen, see
Lymphoid organs.

Malpighian glomerulus, see Kidney.

Malpighian pyramids of the kidney, see
Kidney.

Malpighian rete mucosum, see Epider-
mis.

Medulla, see Spinal cord and medulla
oblongata.

Medulla oblongata, see Nerve centres.

Medulla of the nerves, see Nerve tissue.

Medullary canals of the bones, see Bone
tissue.

Medullary substance of the lymphatic
glands, kidney, etc., see the organs in
question.

Meibomian glands, see Eye.

Melanin, 5, 30.

Membrana Descemetica (Demourisiana),
see Eye.

Membrana hyaloidea, see Eye.

Membrana limitans of the retina, see
Eye.

Membrana propria of the glands, see
Glands.

Membrana tympani, see Auditory ap-
paratus.

Membranes, fibrous, serous, etc., see
Connective tissue.

Middle germinal layer, 28.

Milk, see Sexual organs of the female.

Milk glands, see Sexual organs of the
female.

Milk globules, see Sexual organs of the
female.

Molecular movement (Brunonian), 27.

Mother cells, 15.

Mucous corpuscles, see Lymphoid cells.

Mucous membrane, see Connective
tissue.

Mucous tissue, 46.

Mueller's capsule of the kidney, see Kid-
ney.

Mueller's supporting fibres of the retina,
see Eye.

Muscle nerves, 203.

Muscles, see Muscular tissue.

Muscular filaments, etc., see Muscular
tissue.

Muscular tissue, 79 ; smooth and trans-
versely striated, 79 ; smooth muscles,
contractile fibre cells. 80 ; their occur-
rence, 80; transversely striated, 81;
muscular filaments (fibres), 8i ; sar-

colemma an.d sarcous elements, 81 ;
fibrillas and discs, 83 ; transverse discs,
84 ; accessary discs, 85 ; interstitial
granules, 85 ; heart muscle, 86 ;
transverse section of the muscle, 86 ;
connection with the tendons, 86 ;
embryonic development, 87 ; increase,
88 ; fatty degeneration, 88.
Myeloplaxes, 7.

Nail tissue, 37.

Nails, 36.

Nasal cavities, see Olfactory apparatus.

Nerve centres, 215; ganglia, 215; their
structure, 215; sympathetic, 217;
sympathetic ganglia, submucous and
plexus myentericus, etc., 217, 218;
spinal cord, 218 ; neuroglia, 220 ; nerve
roots of spinal cord, 221 ; white
substance of spinal cord, 222 ; medulla
oblongata, 224 ; its several parts, 224;
cerebellum, 227 ; its several parts, with
the cortex, 227 ; cerebrum, 229 ; its
several parts, 229 ; blood and lymph
vessels, 231.

Nerve fibres, etc., see Nerve tissue.

Nerve plexuses, etc., see Nerves, ar-
rangement of.

Nerve sheath, 202.

Nerve tissue, 192; nerve fibres and
ganglion cells, 192 ; medullated and
non-medullated nerve fibres, 192;
broad and narrow medullated fibres,
192 ; primitive sheaths, 193 ; axis
cylinders, 193 ; nerve medulla (med-
ullary sheath), 193 ; coagulation of
the medulla, 194; transverse section,
194; varicosities, 195; Ranvier's
constriction rings, 195 ; pale (Re-
mak's), nerve fibres, 196; axis or
primitive fibrillas, 196 ; ganglion cells,
197 ; apolar ganglion cells,. 198 ;
origin of nerve fibres, 198 ; uni- and
bipolar ganglion cells, 19S, 199 ; mul-
tipolar ganglia, 200; protoplasma and
axis-cylinder processes, 200.

Nerve tubes, see Nerve tissue.

Nerves, arrangement and termination of,
202 ; nerve sheath (neurilemma), 193,
202 ; nerve termination, 203 ; ter-
minal plates of voluntary muscles,
204 ; nerves of the smooth muscles,
206 ; nerve termination in the cornea,
207; gland nerves, 208; terminal
bulbs, 208 ; Pacinian corpuscles, 210 ;
tactile bodies, 211 ; other nerve ter-
minations, 213; Langerhans' cor-
puscles, 213.

INDEX.

271

Nerves, see Nerve tissue.

Neurilemma 1 nerve sheath), 202.

Neuroglia, see Nerve centres.

Nipple, see Sexual apparatus of the fe-
male.

Nucleus dentatus cerebelli, see Cerebel-
lum.

Nucleus of the cell, 6.

Nymphse, see Sexual organs of the fe-
male.

Odontoblasts, see Dentine.

CEsophagus. see Digestive apparatus.

Olfactory hairs, etc., see Olfactory ap-
paratus.

Olfactory nerve, see Olfactory organ.

Olfactory organ, 23S ; regio olfactoria,
238 ; its structure, 238 ; olfactory
cells, 239 ; termination of the same,
240.

Optic nerve, see Eye.

Ora serrata retinae, see Eye.

Oral cavity, see Digestive apparatus.

Ossification process, see Bone tissue.

Osteoblasts, etc., see Bone tissue.

Otoliths, see Auditory organ.

Ovarian follicles, see Sexual organs of the
female.

Ovary, see Sexual organs of the female.

Oviduct, see Sexual organs of the female.

Ovulum, see Sexual organs of the female.

Ovum, 5, 175.

Ovum, primordial, see Sexual organs of
the female.

Pacchionian granulations, see Nerve cen-
tres.

Pacinian corpuscles, see Nerve termina-
tions.

Palatine glands, see Digestive appara-
tus.

Palpebral, see Eye.

Pancreas, 150; contents, 150; centro-
acinary cells, 150.

Panniculus adiposus, 49.

Papilla foliata of the tongue, see Gusta-
tory apparatus.

Papilla spiralis (Corti's organ) of the
cochlea, see Auditory apparatus.

Papillae circumvallatse of the tongue, see
Gustatory apparatus.

Papillae filiformes of the tongue, see Gus-
tatory apparatus.

Papillae fungiformes, see Gustatory ap-
paratus.

Papillae of the corium, 5S, 212.

Papillae renales, see Kidney.

Parotid, see Digestive apparatus,

Parovarium, see Sexual apparatus of the
female.

Pavement epithelium, see Epithelium.

Pedunculi cerebri, see Nerve centres.

Penicilli of the splenic arteries, see
Spleen.

Penis, see Sexual apparatus of the male.

Peptic-gastric glands, see Stomach.

Peptic-renic cells, see Stomach.

Pericardium, see Connective tissue.

Perichondrium, see Connective tissue.

Perilymph (aqua Cotunnii), see Auditory
apparatus.

Perimysium, see Muscular tissue.

Perineurijm (nerve sheath), 202.

Periosteum, see Connective tissue and
Bones.

Petit's canal, see Eye.

Peyer's glands (follicles), see Lymphoid
organs.

Pharynx, see Digestive apparatus.

Pia mater, see Connective tissue and
Nerve centres.

Pigment cells, see Epithelium and Con-
nective tissue.

Pigment epithelium of the retina, see
Epithelium.

Pineal gland of the brain, 230.

Pleura, see Connective tissue.

Plexus choroidei of the brain, see Nerve
centres.

Plexus myentericus, see Nerve tissue.

Plexus of the nerves, see Nerve arrange-
ment.

Plica semilunaris, see Eye.

Pons Varolii, see Nerve centres.

Porous canals of the cells, 8.

Primitive fibnllae of the connective tis-
sue, muscles, and nerves, see these tis-
sues.

Primitive sheaths of muscles and nerves,
see these tissues.

Primordial kidney, see Kidney.

Primordial ova, see Sexual organs of the
female.

Processus ciliaris of the eye, see Eye.

Processus vermiformis, 114.

Prostate, see Sexual organs of the male.

Prolamceba, 2.

Protoplasma, 2, etc.

Pulp of the spleen, see Lymphoid or-
gans.

Pulpa dentis (tooth germ), 74.

Purkinje's ganglion cells, see Central
nervous system ; germinal vesicle of
the ovum, see Sexual organs of the
female.

Pus corpuscles (lymphoid cells), 9.

272

INDEX.

Pyramids of the kidney, see Kidney.
Pyramids of the medulla oblongata, see
Nerve centres.

Regio olfaetoria, see Olfactory apparatus.
Reissner's membrane of the cochlea, see

Auditory apparatus.
Remak's nerve fibres, see Nerve tissue.
Remak's studies on cell formation, 14.
Renal papillae, etc., see Kidney.
Respiratory organs, see Lungs.
Rete Malpighii, see Epithelium.
Rete testis, see Sexual organs of the

male.
Reticular cartilage, see Cartilage.
Retina, see Eye.
Retinal vessels, see Eye.
Riff cells (stachel cells), see Epithelium.
Rod corona fibres, see Nerve centres.
Rods of the retina, see Eye.

Salivary glands, see Digestive apparatus.

Sarcolemma, see Muscular tissue.

Sarcous element, see Muscular tissue.

Scala media of the cochlea, see Auditory
apparatus.

Schlemm's canal, see Eye.

Schneiderian membrane, see Olfactory
apparatus.

Schwann's cell doctrine, 14; Schwann's
nerve sheath, see Nerve tissue.

Sclerotic, see Eye.

Sebaceous follicles, 236.

Sebum cutaneum, 132, 236.

Sebum formation of the glands of the
skin, 132.

Sebum palpebros, see Eye.

Segmentation of the yolk, 179.

Semen, see Sexual organs of the male.

Seminal filaments, etc., see Sexual or-
gans of the male.

Sexual organs of the female ; ovary,
173 ; cortical and medullary substance
of the same, 173 ; germinal epitheli-
um, 173 ; cortical or zone of the pri-
mordial follicle, 173; ripe Graafian
follicle, 175 ; ovum with the chorion,
yolk, germinal vesicle, and germinal
spot, 176; blood and lymph vessels,
177 ; parovarium, 177 ; genesis, 178 ;
follicle chains or ovum strands, 178 ;
corpus luteum, 179 ; segmentation of
the ovule, 179 ; oviduct, 179 ; uterus,
179; uterine glands, 180; blood ami
lymph passages of the uterus, 180 ;
pregnancy, 180 ; vagina, 180 ; hymen,
clitoris, nymphs, and labia majora,
181 ; vestibule, entrance to the vagina,

181 ; lacteal glands, 1S1 ; colostrum
and milk, 182.

Sexual organs of the male ; testicle, 1S3 ;
corpus Highmori and seminal canals,
183; epididymis, etc., 183; vas defe-
rens. 1S4 ; vas aberrans Halleri, 184 ;
structure of the seminal canals, 184 ;
blood and lymph vessels, 185 ; genesis,
1S6; seminal filaments, 187; copula-
tion,, 187; genesis, 188; spermato-
blasts, 189 ; structure of the vas defe-
rens, 189; seminal vesicles, ejaculatory
ducts, prostate, other glands, 189 ;
urethra, 190 ; corpora cavernosa,
glans 190; colliculus seminalis, 190;
Littre's and Tyson's glands, 190;
structure of the cavernous tissue, 190;
erection, 191 ; vessels, 191.

Sharpey's fibres of the bone, see Bone
tissue.

Sheath of the nerve fibres, see Nerve
tissue.

Skin, see Connective tissue, 58, and or-
gans of sense, 234 ; tactile papilla;,
234 ; blood-vessels and lymphatics,
234 ; glands, 235.

Small intestine, see Digestive apparatus.

Solitary glands of the intestinal canal,
see Lymphoid organs.

Sperm (semen), see Sexual organs of the
male.

Spermatozoa, see Sexual organs of the
male.

Sphincter pupillse, see E\e.

Spinal cord, see Nerve centres.

Spinal ganglia, see Nerve centres.

Spiral fibres of the ganglion cells, see
Nerve tissue.

Spiral leaf of the cochlea, see Auditory
apparatus.

Spleen, see Lymphoid tissue.

Splenic follicles, see Lymphoid organs.

Splenic vessels, see Lymphoid organs.

Spot, yellow, of the retina, see Visual
apparatus.

Stachel cells (riff cells), see Epithelium.

Stelluke Verheyenii of the kidney, see
Kidney.

Stomach, see Digestive apparatus.

Stomata of the vessels, see Blood and
lymph vessels.

Subarachnoidal spaces, see Nerve cen-
tres.

Subdural space, see Nerve centres.

Sublingual glands, see Digestive appara-
tus.

Submaxillary gland, see Digestive ap-
paratus.

INDEX.

273

Submucous ganglion plexuses of the di-
gestive organs, see Nerve centres.

Suprarenal capsule, see Blood-vascular
giands.

Suc.it glands, see Gland tissue.

Sympathetic nerve, see Nerve arrange-
ment.

Tactile bodies, see Nerve terminations.

Tactile organs, 234.

Teeth, 73.

Tendons, see Connective tissue.

Tensor choroidife, see Eye.

Terminal bulbs of the nervous system,

208.
Terminal plates of the muscular nerves,

see Nerve terminations.
Terminal structures of the nerves, see

Nerve terminations.
Testicles, see Sexual apparatus of the

male.
Thalamus opticus, see Nerve centres.
Theca of the ovary follicles, see Sexual

organs of the female.
Thymus, see Blood-vascular glands.
Thyroid, see Blood-vascular giands.
Tissue, 3 ; simple, 20; compound, 21.
Tissue cement, 16.
Tissue elements, 4.
Tissues, division of the, 20.
Tonsds, see Lymphoid organs.
Tooth tissue, 73 ; dentine, 73 ; enamel

and cement, 73 ; dentinal tubes, 73 ;

cement, 74 ; interglobular spaces, 74 ;

dentinal cells or odontoblasts, 75 ;

genesis of the teeth, 76 ; tooth mound,

enamel germ, tooth germ, 76 ; enamel

organ, tooth sac, 77.
Trachea, see Lungs.
Trachoma glands, see Lymphoid organs

and Eye.
Tubae Eallopii, see Sexual organs of the

female.
Tunica vasculosa of the eye, see Eye.
Tympanum, etc., see Auditory appar-
atus.
Tyson's glands, see Sexual organs of the

male.

Ureter, see Kidney.

Urethra, 172, 190.

Urethra, female, see Urinary apparatus ;

urethra, male, see Sexual organs of the

male.
Urinary apparatus, 163 ; kidneys, 163 ;

cortex and medulla, 163 ; medullary

pyramids, 163; columns; Bertini, 163;

uriniferous canals (Bellini's tubes),

163 ; cortical pyramids and glomerulus,
164; papillae renales, 164; looped
canals, 164; their two sides, 165;
Mueller's or Bowman's capsule of the
glomerulus, 165 ; course of the urini-
ferous canals, intercalary portion, etc.,
166 ; vascular arrangement, 168 ;
cortex corticis, 169; vasa recta, 170;
lymphatics, 170 ; theory of the urinary
secretion according to Ludwig, Bow-
man, 171 ; urinary canals, renal cali-
ces and pelvis, 171 ; ureter, 171 ; urin-
ary bladder, 171 ; female urethra,
172.

Uterine glands, see Sexual organs of the
female.

Uterus, see Sexual organs of the female.

Uvea of the eye,' see Eye.

Vagina, see Sexual organs of the fe-
male.

Varicosities of the nerves, see Nerve tis-
sue.

Vas aberrans Halleri of the testicle, see
Sexual organs of the male.

Vas afferens and efferens of the lymph-
atic glands, see Lymphatics.

Vasa recta of the kidney, see Kidney.

Vascula efferentia of the testicle, see
Sexual organs of the male.

Vascular membranes, see Vessels and
Connective tissue.

Vascular tissue, see Vessels.

Veins, see Vessels.

Venae, inter, and intralobulares of the
liver, see Liver.

Venae vorticosoe of the eye, see Eye.

Venous plexus (plexus choroides), of the
brain, see Central organ of the nervous
system.

Vesiculae seminales, see Sexual organs of
the male.

Vessels, blood, 16 ; arteries, veins and
capillaries, 89 ; capillaries, 89 ; vascu-
lar cells, 90; adventitia capillaris,
91 ; lymph sheath, 91 ; structure of
the large arterial and venous trunks,
91 ; structure of the veins, 93 ; of the
arteries, 94 ; valves, 95 ; capillary
system, 95 ; capillary net-work, 96 ;
various forms of the same, 96 ; genesis
in the embryo, 99.

Vessels, lymphatic, 102; intestinal villi,
104 ; other localities, 105 ; lymphatic
apertures, 106 ; juice canals and clefts,
107 ; lymphatic glands, 107 ; their
structure, 10S ; cortex, medulla, fol-
licles, medullary strands, septum sys-

2/4

INDEX.

tern, investment space, 108, 109 ;
lymphatics of the medulla, no; ves-
sels, no; lymph current, in.

Vestibule of the ear, see Auditory ap-
paratus.

Visual apparatus, 246.

Vitreous body, 45, and the Eye.

Wandering of the cells. 10.
Wolffian body, 177, 186.

Yolk, see Ovum.

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