HISTOLOGY

AND

HISTOCHEMISTRY OF MAN

4J2*x

«\

PKEFACE.

IF only in the* eyes of those valued friends whose kindly interest
in my work has ofttimes been -as great a stimulus to sustained
exertion in the laborious task of translation as it has been a solace
in the usual and varied delays and disappointments of publishing,
I feel that perhaps some justification of myself is necessary for the
late appearance of this volume ; so much later than either they or
I had anticipated. The delay has in a great measure been due to
my being obliged to recast a large portion of my first manuscript, in
order to bring it down to a new and much enlarged and altered
Fourth Edition of the original ; commenced just as I had concluded
my translation more than a year ago, and the " Proofs " of which
I received as they were pressed off, and revised by the Author.
The task accomplished, however, I now feel my regret at the delay
lightened to a great extent by the consideration, that through it the
value of the work is considerably enhanced, and that the latter now
contains the most recently gathered matter from many important
fields of investigation ; passing, as it does, through the printer's
hands, at the same time, with the last edition of the original.

As regards the work which I now present to my medical brethren
in an English dress, and which has already been translated into
French, any lengthy personal testimony to its value is unnecessary.
The fact that it now appears for the fourth time in a new edition is
a sufficient proof of the favour with which it is regarded as a hand-
book in Germany, where it was recommended to myself, when a
student in that country, as the best work of its kind, by one of the
fathers of Histology, my late valued and lamented teacher and
friend, Professor Max Schultze. But I am aware this translation

vi PREFACE.

leaves much to be desired ; and yet to those critics thoroughly
familiar with German literature, I feel but little apprehension in
submitting it, confident that fully conversant with the varied diffi-
culties of rendering German into English, they will be lenient to
its faults and careful of censure. In undertaking the work I have
been actuated by the desire to render accessible to my fellow-
students, young and old, a good standard work, which has been
a great aid to myself in dealing with a subject as yet but little
studied in English-speaking countries, and especially in my own,
and upon which we possess but few native manuals. I have been
prompted, moreover, by the feeling that we all need to enter more
fully into the spirit of other men's researches before we can deal
fairly with their theories, or deduce any practical conclusions from
their investigations. And I cannot but think that a greater effort
should be made by all medical men who love progress, to vindi-
cate the dignity of Pathological Histology as a science in this
country, and to raise it above the complacent smiles of a large class
appropriating to themselves the title of " the thoroughly practical,"
who, for the most part, ignorant of its most elementary principles,
appear to regard it as merely the pet hobby of a few vague theorisers
and entirely unprofitable. General profit will only accrue to the
practical surgeon or physician when, after patient toil, all are able
to view the subject closely and from its many aspects. If my
humble efforts to render this easier, by giving <the English reader
access to a compendium of the views of the greatest histologists
arranged in a system, conduce, in however small a degree, to this
desirable end, I shall deem my labour well bestowed.

In conclusion, I have to express my cordial thanks to Professor
Emerson Reynolds for some valuable suggestions in regard to
chemical terms in the first part of this work, the " Proofs " of which
he was kind enough to read over.

A. R J. B.

2 HUME STREET,

October 1874.

CONTENTS,

Introduction, §§ 1-6, 1

L THE ELEMENTS OF COMPOSITION AND OF STRUCTURE

OF THE BODY, §§ 7-64, 11-64

1. ELEMENTS OF COMPOSITION, .11

A. Albuminous or Protein Compounds, §§ 8-14, . . .12

Albumen, § 10, 14

Fibrin, Fibrinogen, and Fibrinoplastin, § 11, . . . . 15

Myosin, Muscle-Fibrin, or Syntonin, § 12, . . . . 16

Casein, ...... 17

Globulin, Crystallin, 17

Peptones, 17

Ferments, 18

B. Hsemoglobulin.

Haemoglobulin, Hsematoglobulin, Hsematocrystallin, § 13, . 18

C. Histogenic Derivatives of the Albuminous Substances

or Albuminoids, 21

Keratin, Mucin, Colloid, § 14, 21

Substances yielding Glutin, § 15, 21

Collagen and Glutin, 22

Chondrigen and Chondrin, 22

Elastic Material, Elastin, .23

D. The Fatty Acids and Fats, § 16, 23

Glycerin, 23

Formic Acid, . . . . . . .24

Acetic Acid, 24

Butyric Acid, 24

Capronic, Caprylic, Caprinic Acids, ..... 25

Palmitic Acid, Tripalmatin, 25

Stearic Acid, Tristearin, . 25

Oleic (Elaidic) Acid, Triolein, 25

Cerebral Matters, Cerebrin, and Lecithin, § 20, . . . 28

Cholestearin, § 21, 30

E. The Carbohydrates, § 22, 30

Glycogen, 31

Dextrin . . .32

Grape Sugar, .32

Inosite or Muscle Sugar, ........ 33

Sugar of Milk, ... 33

Vlll CONTENTS.

Page

F. Non-Nitrogenous Acids, § 23 34

Lactic Acid, Paralactic Acid, 34

Oxalic Acid, Oxalate of Calcium, 35

Succinio Acid, _» . . 35

Carbolic Acid or Phenol, . . . . . . .36

Taurylic Acid or Taurol, '36

G. Nitrogenous Acids, § 25, . 36

Inosinic and Hydrotinic Acids, . . . . .36

Uric Acid, Acid Urate of Sodium and of Ammonium, . . 37

Hippuric Acid, § 26, 38

Glycocholic Acid, Glycocholate of Sodium, § 27, . .39
Taurocholic Acid, Taurocholate of Sodium 40

H, Amides, Amido Acids, and Organic Bases, ... 40

Urea or Carbamide, . . 40

Guanin, Hypoxanthin (Sarkin) Xanthin, § 29, . . .43

Allantoin, 43

Kreatin, Kreatinin, § 30, 44

Leucin, § 31, 45

Tyrosin, § 32, . . 47

Glycin, § 33, 48

Cholin (Neurin), 48

Taurin, § 34, 48

Cystin, 50

I. Animal Colouring Matters, § 35, 50

Haematin, • . . . .50

Hydrochlorate of Hsematin, Hsemin, 50

Hsematoidin, .51

Uroerethrin or Urohsematin, § 36, 52

Black Pigment or Melanin, 52

Biliary Pigments, Bilirubiu, Biliverdin, Bilifucsin, Biliprasin, 53

K Cyanogen Compounds, § 38, 54

Sulpho-cyanogen (Rhodan), Sulphocyanide of Potassium, . 54

L. Mineral Constituents, § 39, . 55

Oxygen, . . . ... . . .56

Nitrogen, . 56

Carbonic Acid or Carbonic Dioxide, 56

Water, § 40, . . . . 56

Hydrochloric Acid, .57

Silicic Acid 57

Calcium Compounds, § 41 — Phosphate, Carbonate, Chloride,

and Fluoride, 58

Magnesium Compounds — Phosphate, Carbonate, Chloride, . 58
Sodium Compounds, § 43 — Chloride, Carbonate, Phosphate, . 59

Sulphate, 61

Potash Compounds, § 44 — Chloride, Carbonate, Phosphate, . 61

Sulphate, . . 62

Salts of Ammonium, Chloride, Carbonate, . . .62

Iron and its Salts, Protochloride, Phosphate, 62

Manganese, 62

Copper, . 62

CONTENTS. IX

Paj?e
2. ELEMENTS OF STRUCTURE, 63

A. The Cell, §§ 45-58, 95

B. The Origin of the Remaining Elements of Tissue, §§ 59-64, 95

II. THE TISSUES OF THE BODY 103

A. Tissues composed of Simple Cells with Fluid Inter-

mediate Substance, §§ 65-85, 105

1. The Blood, .105

2. The Lymph and Chyle, § 82 131

B. Tissues composed of Simple Cells, with a small amount

of Solid Intermediate Substance, §§ 86-100, . . .137

3. Epithelium, § 86, 137

4. Nail, § 99, 160

C. Tissues belonging to the Connective Substance Group,

§§ 101-155, 164

5. Cartilage, § 103, 166

6. 7. Gelatinous and Reticular Connective Substance, §§ 113-

119, 187

8. Fatty Tissue, §§ 120-124, . . . - . . . 198

9. Connective Tissue, §§ 125-139, . . . . .205

10. Tissue of Bone, §§ 140-149, 238

11. Dentine, §§ 150-155, 260

D. Tissues composed of Transformed, and as a rule Coher-

ing Cells, with homogeneous, scanty, and more or
less Solid Intermediate Substance, §§ 156-173, . . 273

12. Enamel Tissue, §§ 156-158, 273

13. Lens Tissue, §§ 159-161, 276

14. Muscle Tissue, §§ 162-173, 280

E. Composite Tissues, §§ 174-218, 305

15. Nerve Tissue, §§ 174-192, 305

16. Glandular Tissue, §§ 192-200, 344

] 7. The Vessels, §§201-211, 362

18. The Hair, §§ 212-218, . . . . . . .388

19. Combination of the Tissues, § 219, 298

III. THE ORGANS OF THE BODY, 401

A. Organs of the Vegetative Type, §§ 220-287, . . .403

1. Circulatory Apparatus, §§ 220-238, .... 403

2. Respiratory Apparatus, §§ 239-243, 448

3. The Digestive Apparatus, §§ 244-268, . . . .458

4. The Urinary Apparatus, §§ 269-276, . . . .514

5. The Generative Apparatus, §§ 277-287, . . . .536

B. Organs of the Animal Group, 570

6. Bony Apparatus, §§ 288-289, 570

7. Muscular Apparatus, § 290, 573

8. Nervous Apparatus, §§ 291-300, 574

9. Sensory Apparatus, §§ 301-326, 603

INDEX. 665

MANUAL

OF THE

HISTOLOGY AND HISTOCHEMISTRY OF MAN.

INTEODUCTION

THROUGH the industry and perseverance of many talented investigators,
human anatomy, as a science, had already reached an advanced stage of
development so early as the close of the last century. As far as the
dissecting knife could open up the structure of parts, these had been
investigated in a manner sufficiently detailed for the requirements of the
practical physician. And let us here offer the easy tribute of remem-
brance to the name of Sdmm&rri-ng, which will ever be connected with
this particular branch of study. That progress in development to be
observed in all branches of natural science as a consequence of one of
the nobler characteristics of human intellect, had also become manifest in
anatomy. Out of a multitude of isolated facts general principles had
been established. Anatomists had begun to recognise the significance of
the occurrence over and over again, in the most dissimilar parts of the
body, of certain definite structures, such as bone, cartilage, muscle, and
nerves, but slightly or not at all modified in each, though taking a most
important part in their formation. Here then, we have the origin of
" GENERAL ANATOMY," the study of the structure of the body.

But again, bones, cartilages, muscles, and nerves were observed each
to be made up of smaller parts, and it became necessary to resolve them
into those ultimate elements of form of which they are composed, in such
a manner as to be able to recognise the latter in various situations.
Thus .the conception of an "animal tissue" originated, and with it the
consideration of tissues, or " HISTOLOGY," as a special branch of anatomical
study. This, although the most important part, constitutes by no means
the whole of general anatomy.

By tissues we understand organic masses, in so far as they are made
up of more minute parts, and receive from these their physical, chemical,
anatomical, and physiological characters.

The various arrangement and nature of these minute parts gives rise
to the difference in what is termed the "texture" of the mass; they
themselves , are known as " tissue elements." But these constituents of
form, these particles composing the tissues, are, in the marvellous con-

2 MANUAL OF HISTOLOGY.

struct/ion of the animal body, of such minuteness that the usual instru-
ments of anatomical dissection are insufficient for their discovery and
recognition, and we are therefore obliged to look around us for other
assistance. On the other hand, a tissue, as such, may be investigated to
a, certain extent with the means at the disposal of an earlier epoch,
when there is no question as to its further resolution or insight into its
ultimate composition. Indeed, we see the rudiments of histology in the
first discoveries of a period long gone by. 13ut as these could only be
of historic interest when we consider the vast strides that science has
since made, we shall pass them over without further comment.

Fortunately for us, the science of general anatomy at the close of the
eighteenth century numbered amongst its students a highly gifted man,
through whose genius it underwent an amount of development greatly to
be wondered at. when we consider the scanty aids to investigation of
that period.

This man was M. F. X. Bicliat, who died at Paris in the year 1802,
at the early age of thirty-one, thus terminating a career memorable in
the annals of medicine. Child of a stirring time, urged on by the great
and celebrated philosophers of his day, and, we might add, inspired by
that spirit of accurate investigation of which science of the present
day is so proud, he founded a system of histology by the help of the.
anatomical knife, chemical analysis, and of pathological and physiological
research, which his immediate successors were unable to improve upon to
any considerable extent for lack of newer methods of examination.

With Bicliat there commenced and reached its zenith an epoch in
histological research which may be designated as that of investigation
without the microscope — as that in which the tissue-elements still remained
veiled in obscurity.

REMARKS. — Bichafs essays are to be found in a large work entitled Anatomic
gineraU applique a la physiologic ct a la medicine, which appeared in Paris in the
year 1801, and was frequently reproduced afterwards.

§2.

The second epoch of histology may be termed that of microscopical
research; as that of penetration down to the elements of the tissues. From
this period our science took the name of Microscopical Anatomy, however
inappropriate this term may be. Its first crude beginnings are lost in
the clouds of a period far remote, in that age of reformative activity to
which we owe the vigour of our modern intellectuality. In its scientific
development it is the offspring of a maturer age, and the founders of the
science of modern histology are many of them still alive.

Three nationalities contend for the honor of having been the first to
discover the microscope — this instrument which has enabled us to pene-
trate into the regions of "The Minute." These are the English, Dutch,
and Italians. There can be but little doubt, however, that the first
instrument of the kind was constructed by a Dutch optician of the name
of Z. Janssen, about the year 1590 ; and that Drebbel, Galilei, and
Fontana, are incorrectly stated to be the discoverers. This much, how-
ever, is incoiitestably proved, that many microscopes had been manu-
factured before the middle of the seventeenth century, and soon after
came into use in scientific research.

Mar cello Malpighi (1628-1694), and Anton van Leeuwenlwek (1632-

INTRODUCTION. 3

1723), are generally looked upon as the fathers of microscopical anatomy.
The first of these made observations on the circulation of the blood, on
the glands and lungs ; the second, endowed with indefatigable industry,
saw for the first time many of the constituents of the organs of the body,
with tolerable distinctness too, although aided by very imperfect instru-
ments. But the additions which Leeuwenhoek made to science, in keeping
with the curiosity-loving spirit of the time, partook less of the nature of
discoveries according to a definite principle, than of mere detection of
strange and wonderful things, where the unaided eye had previously seen
nothing. The infancy of microscopical anatomy is in fact represented in
him. Indeed, the exertions of the Dutch seem just devoid of that which
so characterised the investigations of the Frenchman Bichat,* namely,
that effort to combine units to a scientific whole. If we now associate with
these fc\vo names those also of Swammerdam (1637-1685), and Ruysch
(1638—1734), as the discoverers and developers of our present mode of
injection, we shall have reached the close of the first epoch of histological
study defined by the discovery of the microscope.

The instruments of that day were, however, most imperfect, so that
Leeuwenhoek used simple lenses only. Hence, it is not surprising that in
the hands of his successors, these microscopes, so difficult to manipulate,
and so liable to deceive, became a frequent source of error. This explains
the fact that Bichat preferred laying the foundations of his general
anatomy without their aid.

After this there followed a long period of inactivity in histological
research, reaching far into the nineteenth century, when the science
received fresh impetus from the brilliant discoveries of our own schools.

REMARKS. — Marcello Malpighii. Opera omnia. Lond. 1686 ; and Opera posthuma.
Lond. 1697-.. .2. The works of Leeuwenhoek may be found in the Philosoph. Transact.,
and in his Opera omnia. Lugd. Bat. 1722. Arcana naturae detccta. Delph. 1695.
Continuatio arcanorum naturce detectorum. Liigd. Bat. 1722, &c.

§3.

A new era in histological research was now ushered in by the discovery
of achromatism in the middle of the last century, and by the construction
of achromatic object-glasses for the microscope. The first of these are
said to have been made by a Dutchman named van Deyl, and a German
optician of the name of Fraunhafer, in the years 1807 and 1811. Thus
the microscope was transformed from the clumsy and deceptive imple-
ment of the last century into the elegant and accurate instrument of the
present day.

And now, in all the enthusiasm of novelty, the improved microscope
became the means of adding discovery to discovery in the hands of many
excellent German observers, so that an insight into the essential nature
of the tissue-elements, and of their combination to form the various
tissues, was gained in an inconceivably short time. It may suffice here,
in speaking of the founding of modern histology, to mention the names
of JZhrenbe.rg, Mutter, Purkinje, R. Wagner, Valentin, and Henle. Be-
sides these, many others might be added, of younger observers, who have
since distinguished themselves as developers and furtherers of the science.

Histology without the microscope had had a Bichat among its students ;
but the newer science was fortunate enough at its very outset to undergo,
at the hands of Th. Schwann, the most searching and energetic elabora-

4 MANUAL OF HISTOLOGY.

tion. By him the cell was proved to be the starting-point of all animal
structures. He also indicated the mode of origin of the various tissues
from the cell. It may be said that many points in relation to this fact
were known before Sclnuanris time, and that he came to false conclusions
in many things : but though this be true, the merit, nevertheless, remains
with him of having been the first to make prominent this fundamental
principle — the greatest discovery of histology — by an overwhelming mul-
titude of facts in detail. Schwann may therefore be hailed as the founder
of the science of " HISTOGENESIS," or the study of the origin of tissues — one
of the most important subjects which can come under our consideration,
and one which has more recently undergone very extensive elaboration at
the hands of Reicliert, Koelliker, Remak, and others.

Another branch of histology, again, has gradually become distinct from
the study of the nature of the textures in the normal state. This, which
deeply aifects pathology, is the consideration of the modifications which
tissues undergo in diseased conditions. J. Miiller may be looked upon
as the originator of this particular line of study, known as " PATHO-
LOGICAL HISTOLOGY," while more recently Virchow has become famous
for his great efforts in the same direction. To these two may be added
the well-known names of some of the disciples of the latter, as, for in-
stance, those of Recklingliausen, Rindfleisch, and Colmheim.

Like pathological, so is also "COMPARATIVE HISTOLOGY " indispensable for
a scientific knowledge of the finer structure of the animal frame ; and yet,
in spite of numerous individual efforts, and the most ingenious researches,
this branch is still in its infancy, owing to the immense amount of matter
to be dealt with. To this particular field of investigation Mutter, Siebold,
Koelttker,Leydig,,a.i\d. others, have devoted their great talents with the
happiest results.

REMARKS. — The microscope, its construction, way to work with it, &c., has become
lately the theme of many literary effusions. We will only mention here one of the
more important essaj's on the subject — C. Robin, Du Microscope et des injections, 2d
fd., Paris, 1871. Queckctt, "A Practical Treatise on the Use of the Microscope,"
Loncl., 1848. W. Carpenter, "The Microscope," 3d ed., London, 1862. //.
Schacht, "Das Mikroscop," 3 Auf., Berlin, 1862. L. Beetle, " How to work with
the Microscope," 4th ed. ; and "The Microscope in Medicine," just published.
//. Frey, " Das Mikroskop und die mikroskopische Technik," American Transl.- - (2.)
Schwann's works are to be found in an attractive little book, "Mikroskopische
Untcrsuchungen liber die Ueberemstimnmng in der Struktur und dem Wachstum
tier Thiere und Pflanzen," Berlin, 1839.— (3.) As to the rich literature of Histology,
which is in its origin chiefly German (as this whole branch of anatomy is essentially
the production of German industry), we shall only mention a few handbooks and
other similar aids, and even these only sparingly. Among the older works which
deserve mention are, A. Koelliker, "Handbuch der Gewebelehre des Menschen,"
Leipzig, 1852. 5 Auf., 1857; and besides German works, Todd and Bowman,
"Anatomy and Physiology of Man," Lond., 1856. 2 vols. L. Bcale, "The
Structure of the Simple Tissues," Last ed. A. Eckcr's copper -plates in Wagner 's
Icones pliijswlogicce., may also be recommended.

§4-

In an' earlier section we have seen that the study of the anatomical
characters of tissues is the offspring of a comparatively late era of natural and
medical science. But the chemistry of the -tissues, or " HISTOCHEMISTRY,"
is of more recent origin still. And in that an acquaintance with the com-
position of the different structures of the body can only be gained by the
application to them of the facts of organic chemistry, so is histochemistry

INTRODUCTION. 5

in its progress dependent on tho latter: in fact, it is only a special
branch of the same.

Although in the infancy of chemical study a certain amount of notice
had been taken of organic bodies, nevertheless, owing to the nature of the
matter to be considered, they could only be dealt with (scientifically
speaking) subsequently to the establishment of laws relative to inorganic
substances and their combinations. And only after the latter, as the
simpler had been studied, and that the more important laws of inorganic
chemistry had been laid down, did it become possible to invade the more
obscure field of organic chemistry with success.

It must be admitted, however, that important discoveries had been
made by Sclieele (1742-1786) in the latter subject. Thus a number of
vegetable acids, glycerin, uric acid, and cyanic acid, had all been brought
to light. But these were only details, whose worth from a scientific point
of view it remained for a later day to demonstrate. It was only with
the introduction of quantitative analysis by Lavoisier (1743-1794), and
after that his contemporary, Priestley (1733-1804), had: discovered oxy-
gen, that a new era in chemical science began to dawn — an epoch of exact
research supervening upon the overthrow of phlogistic theory. From
this point on it became possible to gain an insight into chemical com-
bination by means of the balance — to recognise the elements of organic
bodies, to place upon a sound basis the rules of equivalent and atomic
weight, and establish a foundation for a system of stochiometry.

And as in microscopical anatomy the improvement of instruments led
within a short space of time to a more extended acquaintance with the
subject, so do we see here in the province of chemistry the dawn of an era
under the sun of Lavoisier's genius, in which, by a rapid succession of
discoveries, the new science attained, within a short space of time, a
wonderful degree of development and cxtensiveness.

It would be impossible, in the scope of such a work as the present, to
bring in review the details of this progress in development, and we shall
only mention a few points in regard to it of special interest.

The first impulse was given to the study of organic substances through
the works of Vauquetin (1763-1829) and Foucroy (1755-1809). Much
profit accrued also to zoochemistry through their labours in the investiga-
tion of the constituents of the urine, which were also ably handled by
Proust (1755-1826). In the year 1815 Gay-Lussac (1788-1852) dis-
covered cyanogen, an organic compound which conducts itself in com-
bination much in the same way as an organic element. Thus he paved
the way for the theory of organic radicals, to be further developed at the
hands of future observers. Many other discoveries, both in organic and
animal chemistry, were made about the same time by Thenard (1777-1857),
and in 1823 Clievreul published his celebrated treatise on animal fats.
Modern elementary analysis (brought to such a degree of perfection at a
later date) was first opened up by Gay-Lussac and Thenard, and from
that time on a knowledge of organic bodies, from a quantitative point of
view, was rendered possible.

But under Berzelius (1779-1848), the greatest chemist of his time, the
whole science now made the most brilliant advance, especially in the
direction of organic analysis, which was pursued by him with all the
accuracy of the present day. He was, in fact, the founder of the stochi-
ometry of organic bodies, and of the definite systematised zoochemistry wo
at present possess. Then the name of Mitscherlich (born 1796) must be

6 MANUAL OF HISTOLOGY.

remembered as the discoverer of isomorphism. Among those who have
lived in our own day, LieUg (1803-1873) may be said to have taken the
place of the last-named Swedish philosopher. By his labours in the field
of organic combination he has made himself celebrated, and has obtained,
also in a wider circle than any other, a recognition of his genius by his
imperishable popular essays on the science. He may be looked upon as
the founder of the physiological chemistry and elementary analysis of the
present day. Another important step towards an insight into the origin
of organic substances in the body was made in 1823 by Wohler, Liebig's
talented coadjutor, through his well-known discovery of the composition
of urea,

§5.

Study of the nature of the substances occurring in the animal economy,
— their properties, constitution, transformations, &c. — constitutes what is
termed " ZOOCHEMISTRY." The application of zoochemical facts to the elu-
cidation of processes taking place in the system, the contemplation of the
chemical features of life and significance which the elements of composition
have in the same, includes, if not all, yet the chief objects of "PHYSIOLOGICAL
CHEMISTRY." That both these branches of study could only be carried on
subsequent to the arrival at a certain degree of maturity of chemical science,
is perfectly obvious, as has been already remarked, and requires no farther
comment.

Again, the special application of the facts of physiological and zoochemis-
try to the tissues composing our frame, constitutes what is termed " HISTO-
CHEMISTRY." Its sphere lies in the consideration of the chemical con-
stitution of the "structural elements," and consequently also of the tissues.
It is engaged with the substances occurring in the latter, their introduction,
origin, and the significance they possess in the life of the/orw and tissue-
elements ; it traces their metamorphosis, decomposition, and elimination.

At present we can only boast of a very rudimentary histochemistry.
In fact, we are met at all points by the most discouraging difficulties in
this branch of study, owing to the nature of the subject to be dealt with.
Compared with the extraordinary accuracy of anatomical analysis, through
the aid of the microscope of the present day, the means at the disposal of
the chemist for the separation of the unstable constituents of the tissues
appear coarse and rude. While the histologist is able, for instance, to dis-
tinguish with ease, in the most ordinary form-element the cell, envelope,
contents, nucleus, and nucleolus, the chemist is still unable to bring these
several parts within the grasp of his analysis. Further, it is a rare thing
with him to succeed in the analysis even of similar structural elements for
themselves, even setting aside their ultimate composition ; for, owing to
the complex nature of most tissues, he has to deal with a mixture of several
kinds of form-elements, which cannot be separated by chemical means.

After what we have just seen, too much must not be expected from the
histochemistry of the present day. And yet we need not forget, in the
contemplation of its necessary deficiencies, how much this special branch
of science has produced. We must remember, farther, that without a
knowledge of composition, true scientific study of histology is impossible,
and the latter is in danger of degenerating into a mere toying with details
of form. And as histochemistry, on the one hand, can only be based on
a clear insight into the minute anatomical relations of the tissues, so does
it form, on the other hand, the indispensable complement to histology.

INTRODUCTION. 7

Among those who have specially distinguished themselves in connection
with this subject, we may mention the names of Mulder, Danders, C.
Schmidt^ Lehmann, Schlossberger, Hoppe, and Kuhne. Schlossberger is
the author of the first hand-book on histochemistry which scientific litera-
ture can produce.

§6.

In conclusion, we have only to give a brief sketch of the plan we shall
pursue in the following pages. Histology and histochemistry combined,
or the study of the finer structure and chemical composition of parts, con-
stitutes the most important foundation for physiology and scientific path-
ology. The whole subject may be arranged, according to our views, into
three great natural divisions.

In the first will be considered the matters of which the human and
animal body generally is composed, with their histological and (as far as
inseparable from these, and that a knowledge of them is indispensable
for a proper comprehension of the whole) their physiological characters.
Again, in another section of the same, the organised units of the body,
the " structural or tissue-elements" will be brought in review, with their
shape and composition, purposes and origin, ultimate destiny and origin,
one from another. This constitutes "GENERAL HISTOLOGY AND HISTO-
CHEMISTRY."

In the second division — histology in the more restricted and real mean-
ing of the word — the various tissues, in their anatomical relations and
composition, will be brought under notice. Here also we shall consider
the mode in which the form or structural elements of the first division
are employed in the building up of certain masses. It stands to reason
that here also the physiological characters of the tissues and their
origin must still be frequently referred to.

A third division, finally, will be devoted to the consideration of the
more minute structure of the organs and systems of our body, or the man-
ner in which they are put together out of different tissues. This may be
termed " TOPOGRAPHICAL HISTOLOGY."

THE

ELEMENTS OF COMPOSITION

AND OF

STEUCTUEE OF THE BODY.

I. ELEMENTS OF COMPOSITION.

CHEMICAL investigation has gradually brought under our notice a number
of bodies, some organic and some inorganic, which enter into the
formation of the human frame as elements of composition. Owing to
the rapid progress of science the tale of these increases year by year.

But these bodies are by no means laid down once for all in the
organism to belong to the latter for the whole term of its existence, and
to form permanent constituents of its fluid and solid portions. On the
contrary, the material of which the animal body is composed is subject
to continuous change, to constant transformations, or, in other words, is
incessantly coming and going.

The substances of which our body is made up — those, namely, entering
into the formation of tissues — consist, together with water and other
mineral matters, of certain groups of organic principles. These are the
albuminous, or, as they are called, the "protein substances," and the nearer
derivatives of the same, especially the glutin-yielding and elastic materials,
with fatty matters and pigments. Thus we observe that the number of
chemical compounds of which our frame is made up is primarily but
small.

But owing to the fact that these do not continue long in their original
condition, but undergo decay and metamorphosis, and must in conse-
quence be changed, we have an extensive series of chemical mutations
bound up with the exitus of matter. We need not be surprised, then,
if, out of this limited number of histogenic substances, a whole host of
mutation or decomposition products takes its rise. The introduction
also of new material to make up for waste likewise introduces many
chemical metamorphoses.

In considering, then, the elements of composition, all these points
must be borne in mind. It belongs to the province of histochemistry
to show .by what processes alimentary matters are ultimately converted
into the constituents of organs and tissues, or, in other words, to follow
up the formation of histogenic substances. Again, it must deal as far as
possible with the question as to the nature of the numerous products of
decomposition. It should demonstrate also how and by what chemical
processes the latter spring from histogenic substances ; what is the rela-
tion of one to the other; how one mutation product takes its origin
from another; and what part each plays in the occurrences of the
economy, until it is finally cast out of the system. In this way only
could we acquire a satisfactory knowledge of the chemical constitution
and decay of our body.

But, unfortunately, the state of science at the present day does not
admit of all these requirements being satisfied in the remotest degree.

12 MANUAL OF HISTOLOGY.

We are, to be sure, tolerably well acquainted with the general inter-
change of matter which takes place in the system, but not so that in the
individual organs. We are, indeed, justified in concluding that this in-
terchange of material in the latter possesses varying degrees of intensity ;
that it increases during the action of the part, and decreases during rest ;
but we are possessed of almost no facts which would enable us to de-
monstrate with desirable accuracy the amount of this traffic, as it were,
which goes on, even in a single tissue.

If in this way the destiny of many constituents of our body is veiled
in obscurity, how much more so, then, their real chemical relations.
Although of many substances we are able to say, " They are products
of decomposition, residues, relics of broken down tissue, their sojourn in
the body has no other significance," still, in dealing with others, great
difficulties arise when it is to be decided to what side of metamorphosis
they belong — to the formative or to the retrogressive. Of the sources of
many products of decomposition we know nothing certain ; and even
the changes effected by chemical action are either but very unsatisfac-
torily understood, or not at all. Superfluous alimentary matter, so often
present in the system, may possibly be hardly distinguishable in its
derivatives from the matters resulting from metamorphosis of some con-
stituents of the body itself. Finally, we are uncertain still in regard to
many mineral substances, whether they are essential integral components
of our body, or are only casually present in the latter.

Now it is, properly speaking, the theme of physiology to follow up
this behaviour of material in detail, and to interpret its full significance
for animal life ; but histochemistry will be frequently obliged to enter
upon physiologico-chemical research, for only in this way can a know-
ledge of the precise nature of the substances of which tissues and organs
are composed be acquired..

Commencing with the axiom, that the physiological characters of a
matter are in the first place dependent on its chemical constitution, we
choose as an introduction to the elements of composition of the human
body a section principally chemical.

A. Albuminous or Protein Compounds.

Absent from no organism, and taking part in the construction of all
tissues, these matters, which constitute the most important materials of
nutrition, appear of the highest significance in animal life ; indeed, they
may be regarded with all propriety as the chemical substrata of the
latter. Their histogenic qualities come even more prominently before us
in the embryonic body than in the mature ; for in the latter, many parts
consist of other than albuminous substances : for instance, of collagen,
chondrigen, elastic matter, and fats ; whereas, in the earliest periods of
existence, protein compounds are everywhere present. Those matters
just named, however, must also be looked upon as derivatives of the
latter, produced by metamorphosis of albuminous principles.

The great instability and tendency to decomposition of all the members
of this group cause the appearance of a considerable number of substances
in the system, which in some cases participate still, though in a minor
degree, in the formation of tissues, and are in others (having undergone some

ELEMENTS OF COMPOSITION. 13

further modifications) to be looked upon as effete, and no longer service-
able for any of the functions of life. As such, they may either circulate
in the various juices of the body until eventually excreted, or may
remain behind in the tissues in the character of dregs or sediment as it
were.

All protein substances are of exceedingly complex composition. They
contain, beside carbon, hydrogen, and oxygen, a large amount of nitro-
gen, and invariably sulphur. Phosphorus was also formerly supposed,
though erroneously, to be present. Their true constitution is still quite
obscure.

They all become swollen and puffy when placed in water, and enter
into combinations with acids and bases, but whether in regular propor-
tion is not yet known. They dissolve in alkalies, but probably with meta-
morphosis or decomposition, and may be thrown down from such solu-
tions by the mineral acdds. They likewise form combinations with acids,
from which they may be again precipitated by means of the alkalies.
The action of nitric acid causes them to assume a yellow hue, from the
generation of an acid known as xantlioproteinic. Millon's reagent also,
a solution of nitrate of mercury, containing nitrous acid, communicates a
red colour to them, while iodine tinges them yellowish-brown. In con-
centrated hydrochloric acid they are dissolved, assuming at the same
time a violet tint. The action of sugar and concentrated sulphuric acid upon
the protein substances gives rise to a change of colour in them, at first to
purple, and subsequently to more of a violet-hue (Schultze) — a reaction
which they share with the acids of the bile and with elain. In watery
solutions they bend a ray of polarised light to the left. Oxidizing agents,
as well as dry distillation and putrefaction, develope in albuminous
bodies a number of decomposition-products, such as formic, acetic, and
benzoic acids, oil of bitter almonds, and also crystalline matters, as
leucin and tyrosin. (See below.)

Most of the protein substances appear in the body under two isomeric
modifications — firstly, in solution, or gelatinised, as in the greater number
of fluids and tissues of the system ; and — secondly, in a coagulated or in-
soluble state. They pass from the former into the latter condition in
various ways, partly by boiling, partly by the action of strong acids, and
finally, as the saying is, spontaneously. In the first modification the
protein substances may be far more easily distinguished, one from the
other by certain definite reactions, than when in the coagulated con-
dition.

§9-

The complex composition of the principles under consideration, their
indifferent nature, and great instability, account for the fact that, up to
the present, their true constitution has remained utterly unknown.
Indeed, we find a most discouraging obscurity resting over this most
important of all groups of animal substances. So far is this the case
that, in fact, we are not even able to enumerate the various albuminous
principles with anything like certainty.

Again, the great instability of the protein substances gives rise to the
appearance in the organism of a considerable number of decomposition-
products, to whose nature and mode of origin we are still in most cases
almost complete strangers. Among these may be reckoned, as far as we
know at present, urea, uric, hippuric, and gallic acids; taurin, glycin,

14 MANUAL OF HISTOLOGY.

leucin, tyrosin, sarkin, kreatin, kreatinin, glycogen, grape and milk
sugar, inosit, and others besides. From a knowledge of these matters, it is
not possible at present to arrive at any definite conclusions in regard to the
constitution of the protein substances themselves ; we may, however, set
it down as being very complex. Owing to their great liability to under-
go decomposition, farther, the protein compounds appear to be peculi-
arly fitted to act in the economy as ferments, i.e., to effect a metamor-
phosis in other substances without at the same time acting through their
chemical affinities. We shall refer again to these properties in § 12.

Turning now to the peculiarities of the protein compounds and their
formative derivatives, especially important in histogenesis, we must bear
the following points in mind : —

1. The fact that the substances in question are not crystallizable, but
belong to the colloid group in the ordinary sense, as stated by Graham,
This seems to constitute them peculiarly well fitted to assume the specific
forms of tissue elements, and to preserve the same.

2. Their readiness to imbibe water, and to swelL up in the latter
into gelatinous masses, seems to render them suited for the formation
of the watery, soft, and semi-solid matters of many tissues. Their capa-
city for gelatinisation appears greatest in slightly alkaline or acid water ;
in solutions of neutral salts less than in pure water.

3. The remarkable readiness manifested among the protein bodies to
change from one modification to another, as well as from the liquid to the
gelatinous or coagulated state, and vice versa, renders them capable of
becoming deposited from the animal juices in the solid form, or, when
previously so laid down, of undergoing re-solution and easy transport to
other localities.

4. While gelatinised protein substances admit of the passage through
them of crystallizable matters, they oppose the most determined resist-
ance to the diffusion of colloid materials.

5. Albuminoous principles manifest a readiness to intermix with other
bodies, e.g., fats, and phosphate of lime, and to retain these with obstinacy.
They may therefore be regarded as the bearers of these substances.

6. On the other hand, true albuminous substances appear unfavourably
constituted to form for any length of time unchanged the elements
of composition of a tissue, owing to their great unstableness. They seem
to impart to the textures into whose- structure they enter, a certain
aptness to undergo physical change, as may be strikingly seen in many
instances. This is not the case, however, with many of their derivatives,
whose liability to alteration appears to be far more limited — as, for
instance, keratin, chondrigen, and elastic material. These being pecu-
liarly suited for permanent tissues, serve for the formation of indifferent
membranes, allowing the transudation of animal fluids, or including the
same.

§10.
Albumen.

This most important of all the protein substances in the system,
coagulates between 55° and 75° C. from its solutions in the form of flakes,
and not spontaneously like fibrin. From very dilute solutions it can
only be separated by a much more elevated temperature.

Like other protein matters it has two forms, a soluble and coagulated.

ELEMENTS OF COMPOSITION. 15

Of the first there are many varieties ; but all these differences are probably
dependent upon the admixture of other matters, such as alkalies or acids.

Soluble albumen is precipitated by alcohol, mineral acids, tannic acid,
and the salts of most metals. A larger or smaller quantity is also thrown
down by the passage through it of a stream of carbonic acid.

It becomes converted. into the insoluble modification as already men-
tioned by boiling; further, by the action of most acids, without, however,
being always precipitated. The alkalies likewise transform albumen into
a very insoluble substance, but do not throw it down.

Albumen is not present in the animal juices in a pure state, but com-
bined with a certain proportion of soda, saline water being the solvent.
Such albumen has a weakly alkaline reaction, coagulates more in gelatin-
ous masses than in flakes, and is, on the whole, more soluble than in the
pure condition. A larger proportion still of soda may modify the coagu-
lation of albumen by heat in many ways.

Coagulated albumen partakes of the same nature as the remaining pro-
tein substances in the same state.

Entering the body with the protein substances of the food, ^ appears
as a constituent of blood, chyle, and lymph, and also of the fluids saturat-
ing various organs. Combined with some peculiar substances, it appears
to form the medulla of nerves. To what extent it exists in the system
in the coagulated form is a question difficult to answer in the present state
of science. It can hardly be doubted, however, that it does so occur, and
the finely granular contents of many animal cells are probably entirely or
partially composed of it.

"VVe are likewise at fault when asked to indicate the histogenic signi-
ficance of albumen more in detail. It can hardly be doubted, however,
that it is of very great importance, in that it is the first protein substance
from which many of the others in the organism take their origin.

§n.

Fibrin, Fibrinogen, and Fibrinoplastin.

Fibrin has always been described as a substance which does not coagu-
late at boiling point, but, as the saying is, spontaneously, a short time after
the animal fluids in which it is dissolved during life are poured out of
the body.

It coagulates more rapidly at a moderately high than at a low tem-
perature. The oxygen of the atmosphere has probably no accelerating
effect upon the process, for in the interior of the body it is observed to
take place in fluids which have come to a state of rest in closed cavities.
The process may be retarded by the presence in the fluid of carbonic
acid, or the addition of various alkaline salts, such as Glauber salt, for
instance.

Coagulated fibrin can never be obtained pure, however ; for, in the
act of congelation, the numerous cellular constituents of the fluids in
which it is contained become entangled in it. It offers, besides, many
varieties for our consideration. In water acidulated with hydrochloric
acid, it swells up, without, however, dissolving (Lielig) • in contrast to
syntonin obtained from muscle tissue (see below). Coagulated fibrin
is dissolved in solutions of various alkaline salts — for instance, in nitrate
and carbonate of potash, when the temperature is somewhat elevated —
forming a substance similar to albumen. According to Thenard, further,

16 MANUAL OF HISTOLOGY.

superoxide of hydrogen is rapidly decomposed by fibrin. Fibrin may be
obtained from blood, chyle, and lymph, in small but variable quantity,
also from serous transudations.

Let us now consider for a few moments the phenomena of coagulation
of fibrin. Fluids in which this substance is contained become of a
thickish or even jelly-like consistence soon after coming to a state of
rest. Later, in consequence of progressive contraction of the fibrin, a
certain quantity of the entangled fluid is squeezed out, and the coagu-
lum becomes more or less solid as it decreases gradually in size. Under
the microscope a homogeneous jelly is at first perceived ; later on a tangle
of usually very delicate threads or fibres (rarely broad), by which the
cellular corpuscles of the fluid are caught. By many these fibres are re-
garded as the optical expression of folds or rugae on fine membranous masses.

In regard to the origin of fibrin, it was for a long time generally sup-
posed that it took its rise from albumen. And from the fact that its
analysis showed a larger proportion of oxygen than is found in the latter,
the hypothesis was advanced that fibrin is formed by a process of oxida-
tion or putrefaction from albuminous substances.

Some years ago an interesting discovery was published by A. Schmidt,
which completely upset all earlier theories as to the constitution of the
material in question.

According to this observer, there exists no fluid fibrin at all in the
animal fluids as long as in motion. It is first generated in the blood and
other liquids by the chemical combination of two nearly related com-,
pounds, which have been named by the author "fbrinogen" and " fibrino-
plastin" The first of these (also called metaglobulin) is dissolved in the
plasma of the blood; the second (or paraglobulin), which, combining
with fibrinogen, converts it into fibrin, exists, on the contrary, according
to Schmidt, in the bodies of the coloured blood-cells, passing from these
into the plasma. It is exceedingly similar to the globulin of these cells,
(§ 12), or perhaps identical, and probably corresponded with the so-
called "serum casein," (A. Schmidf). Lymph, chyle, pus, and many
tissues containing cells (but not cartilage and tendon), and also fluids
into which these cell-contents have passed, — as, for instance, the serum of
the blood, synovia, humours of the eye, and saliva, — are all fibrinoplastic.
Fibrinogen also, which is very like fibrinoplastin in its reactions — both
may be precipitated from dilute solutions by conducting through them a
stream of carbonic acid — appears widely distributed throughout the sys-
tem, and is contained in almost all serous fluids, as well as those saturat-
ing connective tissue and muscle. The rapid mutation of matter which
takes place in the moving juices of the -body is supposed to be the
obstacle to the formation of fibrin during life. Schmidt believes himself
also justified in the conclusion that, on the chemical combination of these
two " mother substances " to form coagulated fibrin, the alkalies, which
previously held them in solution, are set free.

§ 12.
Myosin. Muscle-Fibrin, or Syntonin.

The contractile structures of the organism, the protoplasm of which
the bodies of young cells are formed, with striped and smooth muscle-
fibres, all consist of a series of albuminous substances remarkable for

ELEMENTS OF COMPOSITION. 17

peculiar reactions, as well as in almost all cases for the property of coagu-
lating at comparatively low temperatures, ranging from 35° to 50° C.

One of these substances, the myosin of Kuhne, coagulates after death,
and is thus the cause of rigor mortis. Coagulated myosin is not soluble in
pure water, but is readily so in such containing as little as ten per cent, of
chloride of sodium. It may likewise be dissolved in dilute acids and
alkalies. It has the same action upon superoxide of hydrogen as fibrin.

Beside myosin, the fluids with which muscle is saturated contain three
other soluble albuminous matters, namely, an albuminate of potash, and
two substances which coagulate, — one at 45° C., and another at 75° C.

From dead muscle, but also from other albuminous materials, a muta-
tion product has been extracted by very dilute acids, to which the name
of mmde fibrin or syntonin has been given by Lehmann. In contradis-
tinction to the fibrin of blood, it is soluble in water containing 0*1 per cent,
of hydrochloric acid, but not so in solutions of nitrate and carbonate of
potash. It has no effect, moreover, upon superoxide of hydrogen.

Casein.

This protein substance, which is probably an albuminate of potash, does
not pass from the soluble to the insoluble form spontaneously, like fibrin,
but on coming into contact with the mucous membrane of the stomach.
On being heated, liquids in which it is contained become covered with a
thin pellicle, consisting of casein modified by the oxygen of the air.
Casein is precipitated by acids in flakes, and in contradistinction to
albumen by acetic acid. According to Lehmann it is not thrown down
from milk by a stream of carbonic acid.

This substance forms the chief constituent of the milk of man and the
mammalia, and the most important aliment for the infant. How far it is
besides distributed through the system is still uncertain ; its presence in
alkaline fluids, however, is very probable. It is said to exist in the
middle coats of arteries by M. Schultze.

Globulin. Crystallin.

By these names are known certain albuminous substances coagulating
like albumen when heated. They require, however, a higher temperature,
and then separate either in the form of a globular mass or milky coagulum.
A solution of globulin, acidulated with acetic acid, is said to be pre-
cipitated by careful neutralisation with ammonia, and an ammoniacal
solution by acetic acid. Globulin is entirely thrown down in fluids by a
stream of carbonic acid.

Many things have in course of time received the name of globulin.

It is found in the lens, in blood-cells (?), in the plasma of the blood, as
fibrinogen and fibrinoplastin (§ 11), and in exudations.

Peptones.

The albuminoids entering into the composition of tissues, as we have
just seen, do not possess the power, when in watery solution, of passing
through animal membranes. They are colloids in Graham's sense of the
word (p. 14).

These, on being received into the body, partly from the animal and
partly from the vegetable kingdom, are all converted by the processes of

18 MANUAL OF HISTOLOGY.

digestion into what are termed peptones — i.e., easily diffusible substances
of very similar or identical constitution. These peptones are by no
means so easily precipitated by reagents as the colloid albuminates.
Thus, in contradistinction to the latter, they are not thrown down by
boiling, by dilute mineral acids, or by acetic acid. On being precipi-
tated by alcohol, they may be again dissolved by watery spirits of wine.
A polarised ray of light is deflected by them strongly to the left.

Matters containing collagen and chondrigen, and also mucus, the con-
sideration of which will soon occupy us, yield with greater or less certainty
corresponding peptones.

Ferments.

It has been already noticed above (p. 1 4), that the instability of the
albuminates permits of their ready conversion into what are termed
ferments. By the action of such substances, — we believe them at present
to spring in all probability from this source ; the albuminous matters are
converted into peptones. The ferments appear combined with water as
constituents of the gastric, intestinal, and pancreatic secretions. Others
of them, from the mouth and salivary glands, transform amylon, dextrin,
and glycogen into grape sugar. A ferment in the pancreatic juice splits up
the neutral fats into fatty acids and glycerin. Decomposing albuminous
substances convert urea into carbonic acid and ammonia, &c. Thus the
mutation of the most important substances in the body introduces a
great chemical action in the same, and leads even to the assimilation of
new albuminoids in the most extraordinary manner.

B. Hsemoglobulin.

§13.
Hsemoglobulin, Haematoglobulin, Hsematocrystallin.

We have been recently made acquainted with a remarkable substance
of still more complex constitution than the albuminates, which may very
easily be resolved into an albuminous matter resembling globulin and
into hcematin.

From the red blood-cells of man and the vertebrates generally, a
coloured crystalline substance may be obtained, namely, after destruction
of the cells, containing iron, and of the greatest instability. Of this the
blood-crystals so long known are composed (fig. 1). From the investiga-
tions of the Germans Funke, Lehmann, Kunde, Teiclimann, Bojanoicsky,
Rolletl, Hoppe, Bottcher, and others, we learn that the substance which
thus crystallizes is by no means the same in all classes of vertebrates, but
offers many differences for our consideration as regards solubility and
crystalline form. The difficulties of dealing with it chemically are greatly
enhanced by its liability to decomposition, and its admixture with other
matters.

It may be obtained with greater or less ease in various ways : by first
conducting a stream of oxygen through a mixture of blood and water,
and then carbonic acid ; then by evaporation of diluted blood, to which
alcohol and ether have been added upon the glass slide of the microscope.
Its separation is favoured by the presence of light according to • the
general opinion. Crystals may likewise be obtained by the freezing and

ELEMENTS OF COMPOSITION.

19

subsequent thawing of blood ; by elevation of temperature to 60° C. ; by
electric discharges and the continuous current ; by pumping out the gases
of the blood; by the addition to the latter of various salts, such as
sulphate of soda and those of the bile ; and by the action of chloroform
with free access of air. The blood of different animals crystallizes with
varying degrees of readiness. In that of the guinea pig crystals are
formed particularly rapidly. The blood of the splenic vein is also remark-
able above that of all other
localities for the freedom with
which crystals are formed in it.

There appear to be further
several kinds of haemoglobin
in the animal kingdom.

In the reddish blood of many
of the invertebrate animals
haemoglobin has also been
found.

The colouring matter of
muscle is identical, according
to Kiihne, with that of the
blood-corpuscles.

Blood-crystals are met with
under various forms — such as
prisms, tetrahedrons, hexagonal
tables, andrhombohedrons. The
first is by far the most univer-
sally encountered, appearing in
man and the greater number of
mammals (tig. 1, c), in which
rhombic tables may also occur f^^

(b). The haemoglobin of the f\^J
mouse and guinea pig assumes ^-^

(&

Fig. 1.— Crystals from the blood of man and some mam-
mals, a, blood-crystals from human venous blood;
6, from the splenic vein; c, crystals from the blood of
a cat's heart ; d, from the jugular vein of a guinea
j>ig; e, from the hamster; and/, from the jugular vein
of the squirrcL

f ^ >

the form of tetrahedrons (d).

Hexagonal plates have up to

the present been found in the

blood of the squirrel only (/).

In the hamster or German

marmot we find rhombohedrons

(e). In fact, almost all blood-crystals belong to the rhombic system,

with the exception of those of the squirrel, which. belong to the hexagonal

(Rollet, von Lang).

Haemoglobin, crystals are double-refracting and pleochromatic ; observed
in one aspect they are bluish-red, in another, scarlet.

They are insoluble in ether and alcohol, but dissolve in water, com-
municating to it a blood-red tint.

"Watery solutions of haemoglobin coagulate on being heated, owing to
the production of an albuminous substance globulin, and haematin to be
mentioned below. The same separation is brought about by the action
of acids and alkalies.

Haemoglobin combines with many gases, e.g., oxygen, carbonic oxide,
and nitrous oxide. Crystals obtained under free access of air con-
tain oxygen in loose chemical combination, which is parted with in a
vacuum, or when the former are heated. This is the oxylieemoglobin

20

MANUAL OF HISTOLOGY.

of Hoppe, to which the statements made above in respect to blood-
crystals refer.

A dilute solution of oxyhaemoglobin shows, as was discovered by Hoppe,
two broad bands of absorption between the lines D and E of the solar
spectrum (fig. 2, a) in the yellow and green part. Solutions of reduced

Fig. 2. — Appearances of solutions of haemoglobin in the spectroscope, a, oxyhoemoglobin and nitroxy-
haemoglobin ; 6, carbonic oxide haemoglobin ; c, reduced haemoglobin ; d, haematin in acid solution ;
e, haematin in alkaline solution ;/, reduced haematiu. Solar spectrum with Frauenhofer's lines.

haemoglobin, on the other hand, have only one absorption band between
D and E (e), (Stokes).

Reduction of oxyhaemoglobin takes place easily. It may be brought
about by the action of carbonic acid also.

Reduced haemoglobin may also form crystals. They are of a deep
purple colour, and far more soluble than those of oxyhsemoglobin.

The latter substance, in contact with carbonic oxide gas, parts with its
oxygen, and absorbs the last named compound. In this way a crystalline
compound of carbonicoxide with haemoglobin is produced (Hoppe).

ELEMENTS OF COMPOSITION. 21

The combination of haemoglobin with nitrous oxide (Hermann) conducts
itself in a manner similar to its combination with oxygen.

C. Histogenic Derivatives of the Albuminous Substances
or Albuminoids.

Keratin. Mucin. Colloid.

We come now to certain matters which receive in general but little
attention. They are related to the protein compounds, and take their
origin apparently from the latter within the body. They also are colloids.
Their decomposition products are, in many respects, very similar to those
of the albuminous substances.

In the older cells of horny tissue, of epithelium, of nails and hair, as
well as in the analogous structures of animals, there exists a mixture or
compound difficult to isolate in a pure state, and insoluble in water. It
may contain up to five per cent, of sulphur, and is partially soluble in
alkalies. Its. decomposition products, among which leucin and a large
quantity of tyrosin are found, indicate a close relationship with the pro-
tein substances. To this compound the name keratin has been given.

Under the name of mucin is known a substance, sometimes gelatinous,
sometim'es dissolved, which occurs in the secretions of the mucous mem-
branes, in synovia and the vitreous humour of the eye, in the gelatin of
WJiarton of the umbilical cord, in several connective-tissue structures, and
finally, in certain pathological products (mucous tissue). This substance
does not coagulate on being heated. It is thrown down in flakes by acetic
acid, and is not redissolved by an excess of the same. Alcohol produces
a species of stringy coagulum in solutions containing mucin, but this
dissolves again in warm water. In many other respects mucin resembles
the protein compounds ; its reaction with sugar and sulphuric acid is also
the same. It appears to contain no sulphur, but is, on the other hand,
rich in phosphate of lime (Scherer). Mucin, which is not diffusible,
manifests fermenting properties. It appears to form a kind of peptone
(Eichwald).

Colloid matter may also be mentioned here : a usually homogenous
substance of some consistence, insoluble in acetic acid, but not, like
mucin, precipitated by the latter. It is soluble, on the other hand, in
alkalies. It is generally met with as a pathological product of the
transformation of tissues (colloid degeneration), but also normally at cer-
tain periods of life, particularly in the thyroid gland of man.

§15.
Substances yielding Glutin.

From experience, we know that the important group of glut in-yield-
ing materials takes its origin from protein compounds. These principles
only occur in animal organisms, and constitute a large part of our body,
in the form of interstitial matter in structures composed of connective
tissue, of bone, and of cartilage. We understand by glutin-yielding
materials, compounds containing nitrogen and sulphur, completely in-
soluble in cold water, but which may be gendered soluble by prolonged

22 MANUAL OF HISTOLOGY.

boiling in the same — yielding then a principle which becomes gelatinous
on cooling, known as glue. It is supposed that in these processes the
composition of the materials under consideration is not essentially altered.
Our knowledge of the chemistry of the formation of glue is not, how-
ever, at all satisfactory at present.

From allied protein substances these materials differ in their solubility
in boiling water and subsequent gelatinisation. With the sugar and
sulphuric acid test, likewise, they do not become red, but yellowish-
brown. With nitric acid they assume a yellow colour, like albuminous
materials.

All efforts to convert albuminous matters into glutin-yielding sub-
stances artificially, as well as the latter into one another, have up to the
present proved futile.

Collagen and Glutin.

Collagen, or the substance converted into ordinary glue or glutin by
boiling, has received but little attention, while glutin has been made the
object of extensive investigation as regards its reactions. A solution of
glue is not affected by mineral or acetic acids, or by alkalies ; tannic acid
alone gives a copious precipitate. Among the earthy and metallic salts,
the chlorides of mercury and platinum, and basic sulphate of iron, pre-
cipitate glutin, but not acetate of lead. A polarised ray of light is bent
to the left by a watery solution of the matter in question. With man-
ganese and sulphuric acid it yields the decomposition products of albumen;
with acids and alkalies, ammonia, leucin, glycin, and other compounds.

From glutin is formed the extensive group of connective-tissue struc-
tures, the organic substratum of bones and ossified cartilage. Conse-
quently collagen is found widely throughout the body, entering into the
composition of tissues of low physiological dignity. From the fact that,
with one exception, that of leucaemic blood (Scherer), no glutin has as
yet been found in the fluids of the body, we infer that collagen must
spring from the protein substances. Connective tissue likewise, at an
early embryonic period, yields no glutin, but appears to consist of a
protein compound (Scliwann). As to the mode in which the necessary
changes here take place, the present state of zoochemistry does not admit
of an answer being given.

Chondrigen and Chondrin.

Chondrin, or cartilage-glue — obtained from the cornea, from per-
manent cartilage, from bone cartilage before the commencement of
ossification, and likewise from a pathological growth, enchondroma — is
allied to glutin. Most acids, however, produce precipitates in a solution
of chondrin, which are again dissolved by an excess of the reagent. The
precipitate, however, caused by acetic acid does not redissolve. Watery
solutions of chondrin possess greater power of left-sided polarisation than
those of ghitin. Heavy precipitates are also seen here on the addition of
alum, sulphates of the protoxide and sesquioxide of iron, sulphate of
copper, neutral and basic acetate of lead, nitrate of silver, and nitrate of
mercury. Boiled with hydrochloric acid, or digested in gastric juice,
chondrin yields, besides numerous other products, a sugar (cartilage
sugar), as far as we know, non-cry stallizable, but capable of fermentation.
If this last statement be correct, chondrin may be regarded as a nitro-

ELEMENTS OF COMPOSITION.

23

genous glycosid, giving some indication as to the constitution of the
albuminates. With sulpnuric acid chondrin only yields leucin appa-
rently. Of cliondrigen but little is known.

As to the origin of chondrin from the protein substances, the same
may be said as of glutin. In regard, however, to a transformation of
chondrin into glutin during the process of ossification, spoken of by some,
but rather improbable, the present state of chemistry permits of no
definite conclusions being drawn.

It would appear that other matters nearly related to these two better
known glue-yielding substances may also cccur in the body.

Elastic Material, Elastin.

In numerous tissues of the body a substance destitute of sulphur is
met with, which, unlike the glutin-yielding materials, is remarkable for
its great insolubility and unchangeableness.

This elastic substance, even on prolonged boiling, yields no glutin, if
completely free from connective tissue. It is likewise unaffected by
acetic acid, whether warm or cold. It may be dissolved, however, by a
boiling concentrated solution of caustic potash, and by cold sulphuric
acid; also gradually, by saturated nitric acid with the formation of xantho-
proteinic acid. Elastin is not coloured red by the test of sulphuric acid
and sugar. As decomposition products under the action of the last-named
acid, we find leucin, but neither tyrosin nor glycin.

Elastin, the definition of which presents many difficulties also to the
microscopist, enters into the formation of fibres, plates, and limiting
layers in connective tissue. It forms also in various organs possibly,
both follicles and tubes, and capsules around animal cells, without being a
constituent of the true cell-body itself.

The great unchangeableness of this substance, with its chemical inert-
ness, seem to render it peculiarly fitted to include the fluids of the system,
and to act at times as a filter for the same. Its great elasticity also
serves many purposes.

Its source is not as yet known with any degree of certainty. There
can be hardly any doubt however that it has its origin from the protein
compounds of the body.

D. The Fatty Acids and Fats.

Fatty acids appear in our body either free or combined with an
inorganic base (fat-soap), or as a mixture of glycerin-ethers (neutral fats).
Let us glance for a moment at the latter : —

c*

(OH

Glycerin, C3H803 or C3H5 j OH
i OH

( OH,

Glycerin, a triatomic alcohol, with the radicle glyceryl = C3H5, is met
with as a colourless, non-crystallizable syrup, miscible with water in all
proportions.

Before going further, let us consider for a, moment glycerophosphoric
3

2*4 MANUAL OF HISTOLOGY.

acid, having the empyrical formula C3H9P06. It is a bibasic ether-acid
of glycerin.

(OH

C3HJOH
(P04H2.

Glycerophosphoric acid is to be found combined with various matters
— in the yelk of the ovum, in cerebral substance, and in the bile.
(Comp. § 20, Lecithin.)

The neutral fats, however — those glycerin ethers already mentioned
above — are the compounds of most ordinary occurrence and greatest
importance in the system.

From the fact that in our £n'-atomic alcohol, 1, 2, or 3 atoms of H of
the hydroxyl may be replaced by the acid radical, we have derived three
series of fats known as monoglycerides, diglycerides, and triglycerides .

The neutral fats occurring naturally belong only to the last group —
the triglycerides of many acids.

Glycerin finds its way into the body with the neutral fats of the
food. It becomes free upon the saponification of these, and must again
re-combine with the fatty acids on the formation of fats in the tissues,
occurrences in regard to which we are still in the dark. The physio-
logical decomposition products of glycerin are also still obscure.

§17.

The fatty acids of the system belong to two natural series, of which
one is arranged after the formula, CnH2n02 ; the other CnH2n_202.

Among the numerous monobasic acids of the first group, some of the
lower or fluid fatty acids do not possess the characters of tissue elements,
but rather those of decomposition products.

Formic Acid, CH202 .

Has been met with by Scherer and Miiller in the fluids with which
muscle, the brain, and the spleen are saturated ; also in the thymus gland
(Gorup-Besanez), in sweat in considerable quantity (Lehmann), and the
blood of dogs after a prolonged sugary diet (Boucliardat and Sandras).
It is also found pathologically in blood. Many of these statements ap-
pear, however, questionable.

Acetic Acid, C2H4Oa .

Is a constituent of the juices of muscle and the spleen (Scherer}. Further,
it is to be met with in the thymus gland, and has been observed in the
perspiration. Acetic acid is also known as one of the ingredients of the
gastric juice ; it occurs probably also in the fluids of the brain. Finally,
it appears as an occasional constituent of the blood after brandy pota-
tions.

Butyric Acid, C4H8O2 .

Appears in flesh and the juices of the spleen {Scherer) ; also in the milk,
sweat, and secretions of the sebaceous follicles of many parts of the body,
as, for instance, on the genitals : in the urine also (?). Its presence in
blood seems doubtful (Lehmann). It is found also in the contents of the

ELEMENTS OF COMPOSITION. 25

stomach and intestines, as a product of the fermentation of hydro-
carbons.

( 0 . C4H.O
With glycerin as tributyrin, = C3H5 \ 0 . C.H-0 it is a constituent

( o.cXo

of neutral butter fat.
Capronic, C6H1202 . Caprylic, C8H1602. Caprinic, C10HSOO, . Acids.

These are met with, in a free state, with glycerin, as constituents of
butter, and possibly also of sweat.

Among the higher members of the group with which we are engaged,
there occur several of these acids (usually solid at the ordinary tempera-
ture of the body) as constituents of the neutral fats, and consequently
as histogenic compounds. They are introduced into the system with
the flits of the alimentary matters as a rule. Their physiological decom-
position probably results in the production of carbonic acid and water by
oxidation, at the same time that the series is split up into lower members.

Palmitic Acid, C16H8203 .

Palmitic acid is an element in almost all fats of the vegetable and ani-
mal kingdom. Its melting point is about 62° C. It crystallizes in glit-
tering pearly scales.

This acid forms with glycerin a compound occurring naturally and
abundantly in human fat, as

Tripalmitin,

(O.C16H810
C,H5 O.C16H310.
(O.CMHnO.

Stearic Acid, C^H^O, .

This is also a widely-spread constituent of the animal neutral fats, and
is present in the human body. Here, however, it is exceeded in quan-
tity by palmitic acid ; but it preponderates, on the other hand, in more
solid suety fats, as those of cows and sheep. Its melting point is higher
than that of the preceding acids, being about 69° C. It crystallises in
white silvery needles or scales.

Its neutral combination with glycerin is known as

O.C,«HaK0

I8"35V

Tristearin, C3H5 O . C, ^H,SO

Among the acids of the second group there is only one of any import-
ance in the human economy, namely —

Oleic Acid (Elaidic Acid), C,8H840S.

Pure oleic acid is met with as a fluid which stiffens into leaves at a
temperature of - 4° C. It is scentless and tasteless, and cannot be volati-
lised without decomposition. Its salts are not crystallizable.

Elaidic acid is found as a most important constituent of the neutral
fats of the body, combined with glycerin, namely, as

26 MANUAL OF HISTOLOGY

( 0 . C18H830

Triolein, C3H5 \ 0 . C18H330
( 0 . C18H330

and also saponified with alkalies.

It is introduced into the body with the neutral fats of the food. Its
physiological decompositions are probably manifold.

REMARKS. — It was formerly believed that margaric acid was the most widely-dis-
tributed of all animal fats. From the fact, however, that a mixture of equal parts of
palmitic and stearic acids has naturally the same composition as margaric acid,
C17H3202 , some have denied the existence of the latter altogether, but incorrectly,
for it has been produced artificially (Becker, Heintz). It is still a matter of doubt,
however, whether it and trimargarin are constituents of the ordinary fats of the body.

§18.

In the foregoing section the constitution of the neutral fats which occur
naturally, have been brought before our notice ; we have also alluded to
the different fatty acids of these compounds. It is not possible to separate
one from the other, with any degree of accuracy, the individual neutral
fatty combinations which occur here, so that our acquaintance with the
latter is very unsatisfactory. They receive their peculiarities from the
fatty acids of the combination.

Neutral fats, when pure, are colourless, without odour, and tasteless.
Their reaction is neutral, they are lighter than water, and bad conductors
of electricity. They are insoluble in water, but soluble in warm alcohol
and in ether. They give rise to fatty stains upon paper, burn with bril-
liant flame, and cannot be volatilised without decomposition.

By the action of steam, heated up to 220° C., the neutral fats are split
up into acids and glycerin. The same effect is produced through the
agency of ferments, as, for instance, putrefying protein compounds. Ex-
posed to the air they greedily absorb oxygen, and with this and the com-
bined action of ferments, become rancid, water being absorbed and glycerin
and fatty acids set free. Further, by the action of alkalies in the presence
of water, they are decomposed and converted into soapy compounds, in
which process glycerin is set free, while the acid combines with the inor-
ganic base.

It has been already remarked above, that the separation of the several
neutral fats from the natural fats of the human body is not possible.
Hence the questions in regard to their nature have been answered in various
ways. Berth clot, following up Pelouze, has recently composed the neutral
fats by artificial means out of glycerin and the fatty acids, and has thus
opened up a new way for the recognition of the fatty matters occurring
in the system. From the correspondence between their properties and
those of the natural fats, many of these compounded neutral fats have
been recognised as constituents of the body.

They are, therefore, all of them, combinations, in which the three atoms
of H of the hydro xy Is of the glycerin are replaced by the corresponding
radicals of those fatty acids. Thus we have a compound corresponding
with elaidic acid, triolein, a fluid at ordinary temperatures, and then hold-
ing two other solid crystalline neutral fats in solution, namely, tripalmitin
and tristearin* It is still doubtful whether we have here all -the con-
stituents of the mixture of neutral fats occurring in the system. In butter
* To these may be added probably trimargarin.

ELEMENTS OF COMPOSITION. 27

there exists a combination of butyric, caprinic, caprylic, and capronic
acids, with glycerin.

According to the quantity of solid neutral fat dissolved in the triolein,
are the animal adipose tissues soft, or hard and suety after death. During
life, however, owing to the natural warmth of the body, they all remain
soft, and more or less fluid. In one and the same animal, moreover, the
adipose matter of many parts of the body may contain variable quantities
of solid fats.

The neutral combinations of the latter occur widely distributed through-
out the body. They are to be met with in nearly all fluids and tissues
accompanying all the protein compounds and histogenic substances.
Their amount is very variable. They appear in enormous quantities in
the cells of fatty tissue, under the skin, in the orbit ; around the heart and
kidneys, and in bone; likewise in medullary nervous matter, together
with some special compounds, now better known than formerly. Its
constant presence in the tissues leaves no doubt as to the histogenic nature
of fat. On the other hand, other tissues
are frequently destroyed with fatty infil-
tration or generation, both physiological
and pathological (fatty degeneration). The
histogenic significance of the fats appears
greatly heightened when we remember the
fact that the hard crystalline combinations
forfeit their crystallizability on becoming
dissolved in triolein.

Under certain circumstances, solid fat
separates from the natural fatty matters of
the body on the cooling of the latter after
death, in the form of needle-shaped crys-
tals Or groups Of the Same (fig. 3). These Fig. 3.— Crystals of margarin. a, single

are known to the microscopist as margarin

crystals. a fat-cell quite free of them.

REMARKS. — The percentage of fats in different tissues is — in lymph, 0'05 ; in chyle,
0-2 ; blood, 0'4; cartilage, 1'3 ; bone, 1-4 ; lens, 2'0 ; liver, 2'4 ; muscle, 3'3 ; brain,
8'0; nerves, 221; spinal cord, 23 '6; fatty tissue, 827; yellow marrow of bones,
96-0.

§19.

In considering the objects for which fat is designed in the human
system, the following points may be borne in mind : —

1. The fats appear important, owing to their soft, fluid consistence
at the ordinary temperature of the living body, as distributors of pres-
sure, as pads and filling-up matters in various positions.

2. Large collections of neutral fats, as bad conductors, prevent to a
certain extent loss of heat to the system.

3. They possess the somewhat subordinate property of rendering
many hard tissues, such as epidermis and hair, pliant and soft, by satu-
rating them. For this purpose the secretions of the sebaceous glands
appear particularly designed.

4. Their want of affinity for water seems to render them peculiarly
suited to separate from watery fluids in the form of granules and drops,
and so give origin to the formation of elementary molecules and vesicles.

28 MANUAL OF HISTOLOGY.

5. Owing to a certain chemical inertness in fat, the latter appears
fitted for the formation of tissues which take but little active part in the
chemical processes of the economy.

6. By the fermenting action of the protein compounds, but more by
contact with the oxygen of the atmosphere, the fats become decomposed,
and the fatty acids formed into other combinations, the final result of
which is the production of carbonic acid and water. The heat which
is evolved in this process constitutes them of the highest importance.

7. According to Lehmann, the fats possess the nature of ferments, in
that with the protein compounds they lead to the generation of lactic
acid in fluids containing sugar and starch. The energy of pepsin in the
gastric juice is also said to be increased by the presence of fats.

8. Though the neutral fats are not soluble in the watery fluids of the
body, their soapy combinations are, and are consequently of great im-
portance for the distribution of fatty acids through the system.

The neutral fats are received into the body with food, although the
possibility of their production also in the human organism from hydro-
carbons must also be granted. That this takes place in many animals has
been proved, as is well known, by Liebig. Their origin from protein
compounds can likewise be no longer really doubted.

§20.
Cerebral Matters, Cerebrin and Lecithin.

Among the substances of which the brain and spinal cord ar.e made up
("but also in other parts of the animal body) there occur several peculiar,
unstable compounds, difficult of analysis. They are remarkable for the
property of swelling tip in hot water into a substance like starch, for
their solubility in warm alcohol and ether, and for their occasionally
containing phosphorus. They were formerly erroneously designated as
phosphorous fatty matters.

Cerebrin, C,7H3S]Sr08 .

Cerebrin, originally described by Fremy as cerebric acid, and after-
wards investigated by Gobley and Miiller, is a white powder, seen under
the microscope to be composed of roundish globules. It can only be dis-
solved in warm alcohol and ether, and is decomposed by boiling hydro-
chloric and nitric acids. It is insoluble in ammonia, caustic potash,
and baryta water, and also in cold water ; while in hot, as already men-
tioned, it swells up into a substance resembling boiled starch.

On being boiled with acids, cerebrin yields a species of sugar, and is
therefore a glucoside. Its precise nature remains for further investiga-
tion.

Lecithin, C42H84NP09 .

This substance, first discovered by Gobley, is indistinctly crystalline.
It resembles wax, may be easily melted, and is soluble in hot alcohol
and ether. It enters into combination with acids and salts. In warm
water it gelatinizes like cerebrin.

Lecithin is a substance easily decomposed. By prolonged boiling in
spirits of wine, or better still, in acids or bases, as baryta water, it

ELEMENTS OF COMPOSITION.

29

C2H

OTT

\/n TT \ QTT

palmitic and

may be split up into neurin, (cholin) =

oleic acid, and glycerophosphoric acid.

Lecithin may be derived from glycerophosphoric acid, in which the
two hydroxyl hydrogens of the glycerin are replaced by the radicals of
palmitic and elaidic acids, at the same time that the neurin (half alcohol
and half base) forms with the glycerophosphoric acid an ether-acid. Its
formula is therefore

C^ TT (~\

O.PO

OH
O.C2H4(CH3)3^.OH.

This substance, besides being found in nervous tissue, is also found in
the yelk of the eggs of hens, in the blood-corpuscles, in bile, semen, and
pus. There appear to be various kinds of lecithin in nature.

Protagon, a substance described some years ago by Liebreich, is simply
a mixture of cerebrin and lecithin.

By myelin, as described by Virchow, we understand a substance of
peculiar microscopic appearances occurring in different parts of the body,
especially in those undergoing decomposition. It has a characteristic
dull lustre (fig. 4), and is usually met with in masses of roundish, oval,
filiform, looped, or lobulated figure, with double outline. Myelin is
tinged slightly brown by iodine, while in concentrated sulphuric acid it
becomes of a red, or at times violet, colour. It resembles cerebrin and
lecithin in its property of absorbing hot water, and
swelling up into a gelatinous mass, and also in its rela-
tions of solubility to alcohol and ether. Myelin drops,
however, may be obtained from compounds of quite a
different nature, as, for instance, from oleic acid and
ammonia (Neubauer). Myelin is therefore chemically
untenable as a special combination.

Another allied substance, known as amyloid, may be
also mentioned here. This appears in peculiar homo-
geneous masses of dull lustre, and is probably a mixed Fig. 4
degeneration product of many, especially glandular por-
tions of the body (waxy or lardy degeneration). Amyloid matter is
coloured of a peculiar reddish-brown or brownish-
violet with a solution of iodine, which turns to violet
usually on the subsequent addition of concentrated
sulphuric acid, or, more rarely, to blue.

We turn finally to the corpuscula cimylacea,
round or bilobular structures of very variable size,
which bear a strong resemblance to granules of
starch, whence the name. They are sometimes
laminated, sometimes not, and vary in their re-
actions, becoming violet under the action of iodine
and sulphuric acid, but frequently blue or bluish
with iodine alone. Thus they resemble amylum in
one respect, and cellulose in another, although we are not justified in re-
ferring them to either of these substances.

The corpora amyiacea are to be found in the nervous centres of putre-
fying corpses, and, moreover, in quantity increasing with the advance of

Different forms

/*\

\|y

.— Corpnscuia amyiacea

from the human brain.

30 MANUAL OF HISTOLOGY.

decomposition. Besides, however, they may occur pathologically in the
living body, e.g., in the organs just mentioned, the brain and spinal cord,
whose sustentacular connective tissue may contain them in abundance.
They are met with also in the prostate of considerable size.
KEMABKS.— Sfrw&er in the Zeitschr, fur Chemie, 1868, S. 437.

§ 21.
Cholestearin, C26H.4 0 + H20 .

Sensible of the difficulty of appropriately grouping animal substances,
for the present we insert here monatomic alcohol, with the distinct charac-
ters of a decomposition product.

This compound (fig. 6) has a very characteristic crystalline form ; it is
found, namely, in extremely thin, rhombic tables, whose obtuse angle is
100° 30', and acute, 79° 30', according to C. Schmidt. These are
usually arranged overlapping each other, and are frequently broken at
the corners.

Cholestearin is completely insoluble in water, but perfectly soluble in

boiling alcohol, ether, and chloroform. It is
dissolved in fats and ethereal oils ; in the
two combinations with soda of the biliary
acids and in soap-water — important proper-
ties in regard to the occurrence in the
human body of this otherwise insoluble
substance.

Treated with sulphuric acid, crystals of
cholestearin become of a rusty or purple
colour, beginning at the edges. In concen-
trated acid, on the other hand, they dis-

Fig. 6.-Crystai77"choiestearin. solve gradually, forming coloured globules.
The addition of iodine to these reagents
produces more lively colours still.

Cholestearin, which has been recently met with widely distributed
throughout the vegetable kingdom (Beneke, Kol~be), has no histogenic pro-
perties, its crystallizability seeming to render it but little fitted to enter
into the structure of tissues. It possesses entirely the nature of a mutation
product — whether of the fats or of azotised histogenic substances is still
undecided. It is extensively distributed throughout the system, but is
only excreted in minute quantities, so that some further decomposition
still quite unknown to us may be inferred.

It is found in the blood, but in small amount, and in most of the
animal fluids, especially in bile, but not in the urine. It is also met
with in the substance of the brain, as a constituent of myelin, in patholo-
gical fluids and tumors, and in biliary calculi. Passing off with the
bile, it is found in the excrements.

E. The Carbhydrates.

§ 22.

These substances bear this not very happily chosen name on account
of their containing oxygen and hydrogen in the same proportions as in

ELEMENTS OF COMPOSITION. 31

water; they have therefore been regarded as hydrates of carbon. Al]
have at least six atoms of the latter. Should they contain more, they
are still complete multiples of six. They may be looked upon as deriva-
tives of the six-atomed alcohols, and are divided according to their com-
position into three groups.

I. The grape-sugar group (C6H1206). These may be regarded from the
way in which they conduct themselves as aldehydes of the six-atomed
alcohols.

II. The cane-sugar group (C12H22On), may be looked upon as made up
of anhydrites or ethers, formed of two molecules of the last, with the loss
of one molecule of H20.

III. Cellulose group (C6H1005). The molecular proportions of these
compounds are not yet ascertained. Most of them appear to possess a
higher molecular weight than the last. They are likewise anhydritic
derivatives.

All hydrocarbons are of neutral constitution; none are volatile;
some are crystalline ; some are insoluble ; others easily soluble in water.
The latter appear in the system usually in watery solution, or possibly
entering into the composition of other substances as so-called glucosides.

The various hydrocarbons pass easily one into another, and in these
processes many of the albuminous matters of the body play an impor-
tant part as ferments. On being digested in dilute mineral acids, most
of them are converted into grape sugar. The relation, further, of the
hydrocarbons to the organic acids is of importance, many of them
possessing the same empyrical composition, and a part springing easily
from the latter, as in the case of acetic and other fatty acids, and lactic
acid. Their relations to alcohols must also be remembered.

The importance of the hydrocarbons in the vegetable kingdom is very
great, produced as they are, with some exceptions (as, for instance, sugar
of milk), by the plant ; some of them are likewise of great histogeriic
worth here, especially cellulose. The case is quite otherwise in the ani-
mal organism, particularly in the bodies of the higher animals and man.
The few hydrocarbons which here appear do not manifest tissue-forming
qualities in the remotest degree, and are dissolved in the juices; on the
contrary, they seem to be decomposition products of other materials,
such as the protein compounds, or their source is the food taken into
the body. By their physiological decomposition they yield, according to
the commonly received theory, carbonic acid and water. It is still an
undecided question how far they can pass into the higher members of
the fatty acids, thus playing a part in the formation of fat, but that some
of the hydrocarbons do so is certain.

In this group are included among several other substances three kinds
of sugar, namely, grape sugar, inosite, and sugar of milk, as constituents
of our body.

The sugars are generally sweet to the taste, soluble in water, and
almost all crystalline. They undergo vinous fermentation with greater
or less readiness quickly in the case of grape sugar ; slowly, as in. that
of sugar of milk ; or not at all, as in that of inosite.

Glycogen, C^H1005.

This compound, standing between amylum and dextrin, was dis-
covered by Bernard. It is met with as an amorphous substance, which

32 MANUAL OF HISTOLOGY.

swells up in cold water, and is dissolved in warm, forming an opalescent
fluid, manifesting strong right-handed polarisation. Glycogen becomes
of a wine-red colour on the addition of iodine, or also brown and violet.
It occurs in the tissue of the liver, and also temporarily in different
embryonic tissues, as well as in the muscles of phytophagous animals.
It may be converted in various ways into grape sugar, as, for instance,
by boiling with dilute acids, by admixture with diastase, saliva, pan-
creatic juice, or blood. Glycogen is of great importance in the formation
of hepatic sugar through the action of a ferment. Its hypothetic origin
may be referred to the decomposition of some albuminous substance.

Dextrin, C6H1005 .

This compound is soluble in water, and viscous when in concentrated
solution. A polarised ray is deflected strongly to the right by its watery
solution, which is coloured reddish- violet by the addition to it of iodine
dissolved in iodide of potassium. It is converted readily into grape
sugar by the action of dilute sulphuric acid, diastase, and saliva.

It is found in the contents of the intestine after starchy food, in the
blood of phytophagous animals, in the liver of horses after feeding on
oats, as well as in the muscles of the latter (Limpricht).

Grape Sugar, C6H1206 + H20 .

Grape sugar (fig. 7) usually crystallizes indistinctly in crumb-like or
warty masses ; rarely in tables, which probably belong to the clinorhom-
bic system. It is soluble in water, and in this form polarises light tc
the right. Grape sugar reduces sulphate of copper with a solution of
potash, .and, on being heated slightly, to the condition of suboxide, and
forms a combination with chloride of sodium, which crystallizes in
large four or six-sided pyramids. In the presence of other nitrogenous
substances, as albumen and casein, and also of bases, it undergoes lactic,
and later, butyric acid fermentation.

Grape sugar occurring in the animal kingdom, and springing from
other carbohydrates in various ways, is formed from the latter, more par-
ticularly from arnylum, by the fermenting action of many glandular
secretions, particularly those of the mouth, pancreas, and intestines

within the body. It is absorbed in the
digestive tract, and appears in the chyle and
blood. It is generally supposed, from the
fact of its disappearing rapidly in the latter,
that it undergoes combustion with the for-
mation of carbonic acid and water ; but the
intermediate products are unknown.

Besides this, the grape sugar found in
dead hepatic tissue has a second significance

O already alluded to in speaking of glycogen.

Normal human urine is probably not en-
tirely free from grape sugar ; but the latter

FIR. 7.— Tabular crystals of crape sugar may be made to appear in considerable
obtained from honey. quantities in the urine of animals, by irri-

tation of the medulla elongata (Bernard) : irritation of other portions
of the nervous centres, however, produces the same remarkable pheno-
menon. This substance occurs pathologically, and often in considerable

ELEMENTS OF COMPOSITION.

33

quantity, in a peculiar disease known as diabetes mellitus. In this
affection it is found in the urine and most opposite fluids of the body.

Inosite or Muscle Sugar, C6H1206 + 2H20 .

This substance, discovered by Scherer, is identical with the phaseoman-
nite first found in beans by Vohl, and subsequently, extensively distri-
buted through the animal kingdom.

Inosite (fig. 8.) forms clinorectangular prisms, which lose at 100° C.
two molecules of water of crystallization, efflorescing in the air. From
its solution in boiling alcohol it separates in brilliant scales. It is easily
dissolved in water, and undergoes fermentation with cheesy substances,
generating so lactic and butyric acids.

The plane of polarisation is not affected by it, nor does it reduce sul-
phate of copper. On the other hand,
when evaporated almost to dryuess
with nitric acid, and then treated with
ammonia, it becomes of a lively rose-
red colour on being again evaporated,
especially when chloride of calcium is
present.

Inosite is widely distributed through-
out the body. It is met with in the
juices of the muscle of the heart, in
the muscles of dogs, in the pancreas
and thymus (Scherer}. It has been
also found by Cloetta in the lungs,
kidneys, spleen, and liver, and finally,
by Mutter in the substance of the brain,
and by Holm in the suprarenal capsules
of the ox. Inosite may also pass off by
the urine, as in diabetes and Bright s disease (Cloetta, Neukomm)^

It is, without doubt, a decomposition product of histogenic substances.

Sugar of Milk, ClaHM011+ HaO.

This compound is distinguished from that just mentioned by its che-
mical composition, as well as its crystallization in oblique four-sided prisms
(tig. 9), and lower degree of solubility in water. It polarises a ray of light
also to the right, and reduces oxide of copper
like grape-sugar. Sugar of milk, like inosite, is
converted by cheesy and other ferments into
lactic and butyric acids.

Milk-sugar is not found in the vegetable
kingdom, but is a constituent of mammalian
and human milk. Its quantity in this fluid
stands in proportion to the amount of carbo-
hydrates introduced into the system, and yet
it is not absent in the milk of the carnivora
after an exclusively fleshy diet, as Bensch has
shown in confutation of Dumas' statements.

It has not yet been demonstrated in the blood of mammals with cer-
tainty, and appears not to exist there.

Sugar of milk, therefore, is probably generated by the (fermenting1?)

Fig. 8.— Inosite, from the muscle of the human

Fig. 9 — Sugar of milk.

34

MANUAL OF HISTOLOGY.

action of the mammary gland. There seern strong grounds for believing,
farther, that grape-sugar is the substance from which it is formed in this
process.

F. Non-Nitrogenous Acids.

§ 23.

In considering the fats (§ 17), we have already been obliged to refer to
two homologous series of acids, partly possessing histogenic properties.
We now add here another series, having decidedly the nature of decom-
position products.

In the first place may be mentioned two acids of the lactic-acid group,
isomeric combinations, but differing in their constitution — the first being
derived from aldehyd, the second from ethyl compounds.

Lactic Acid, C3H603, or

CH8

CH.OH'

C02H.

This acid, which is easily formed from amylum or sugary fluids by fer-
mentation, gr also from inosite, is found in the gastric
juice; further, in the contents of the intestinal
canal, as a decomposition product of ingested carbo-
hydrates, and also in the brain, and various gland-
fluids of the body (?). With bases it forms salts
under certain circumstances.

Among these we have lactate of calcium (C:JH503).2Ca
+ 5H20 (fig. 10), which crystallizes in brush-like
groups of very fine needles.

Another salt, lactate of zinc, is of considerable
diagnostic worth in the recognition of lactic acid.
Its formula is (C3H503),Zn + 3H20, and it crys-
tallizes in four-sided obliquely-truncated prisms,
which present a characteristic clubbed appearance
while in process of formation.

In regard to the source of lactic acid in the body,

in groups of flue needles. ^here can ^e no doubt that, where it is not a pro-
duct of fermentation, it is derived from the decomposition of histogenic
substances.

CH2OH
Paralactic Acid, C3H603, or \ CH2

C02H.

This acid, so similar to ordinary lactic acid, differs from it in its salts,
which vary in their solubility and amount of water of combination.

Paralactate of calcium, (CaH503)2Ca + 4H20 , has the same crystalline
form, but is less soluble than the corresponding salt of ordinary lactic
acid.

Paralactate of zinc, (CgH/X^Zn + 2H20 , is the same as the crystalline
form, but easier of solution in water and alcohol than lactate of zinc.

Paralactic acid is to be found in muscle, on the death of which it
becomes free, giving to its juices their acid reaction. It is also present
in bile (Strecker).

Fig. 10. — Lactate of lime

ELEMENTS OF COMPOSITION. 35

§24.

Two other acids, from another series occurring in the human body
must now be considered, namely, oxalic and succinic.

Oxalic Acid, C202 (OH)2 .

This acid is found widely throughout the vegetable kingdom, and ap-
pears as an end product in the oxidation of most animal and vegetable
substances. Oxalic acid forms with one atom of Ca neutral oxalate of
calcium, almost the only one of its salts found in the human body.

Oxalate of Calcium, C204Ca + 3H20 .

This compound is insoluble in water and acetic acid, but soluble in
hydrochloric and nitric acids. On being roasted it is converted into car-
bonate of calcium. It crystallises in blunt, and at times also pointed, square
octahedrons, which look like envelopes under low micro-
scopic power (fig. 11).

Oxalate of calcium, a large amount of which is never met with
in the body, is probably, in very minute quantity, a normal
constituent of the urine. After a vegetable diet, and drinks
containing a large amount of carbonic acid, this salt has been
most frequently observed. It likewise appears in conjunc-
tion with disturbance of the respiratory functions, and may
give rise to the formation of mulberry calculi. It is, further,
met with in the gall-bladder and in uterine mucus (G.

Schmidt). ofcalcium.

The sources of oxalic acid may be manifold, as is indicated by its occur-
rence and origin. In the first place, it may spring from vegetable food,
and, in the second, from the decomposition of various animal matters. In
the latter respect its formation from the oxidation of uric acid must be
mentioned ( Wohler and Liebig) ; also the fact that, on the injection of
mates into the blood, the amount of urea and oxalic acid is increased in
the urine ( Wohler and Frerichs).

Succinic Acid, C4H604.

This compound, which originates in the oxidation of the fatty acids,
as well as from the fermentation of different organic acids, crystallizes in
colourless monoclinometric prisms (fig. 12),
and is soluble in water and alcohol.

It was formerly supposed to occur, as has
been already mentioned, only as a patholo-
gical constituent of the body, in encysted
tumours and dropsical fluids, until demon-
strated by Gomp-Besanez in a number of
gland-juices, namely, those of the spleen,
thymus, and thyroid. It has been, like-
wise, met with by Me'tssner and Shepard in Fig' 12-Cr>'stais of succinic add.
the blood of phytophagous mammals, in human urine, and that of both
carnivora and vegetable feeders, after fatty diet or the reception into the
system of malic acid (Meissner, Koch).

36 MANUAL OF HISTOLOGY.

Carbolic Acid or Phenol, C6H50 .

The sources of this compound are manifold, as, for instance, the distil-
lation of many organic substances and the oxidation of glue, also, which
produces it in traces only. It possesses poisonous properties for the
human body. It has been obtained from human and mammalian urine
(Staedeler), and met with also, in the same after reception into the
stomach of benzol (Schulzen and Naunyn).

Taurylic Acid or Taurol, C7H80 .

This second compound, allied to the last, has been obtained from the
same fluids, but not as yet in a pure state (Staedeler). It is, perhaps,
identical with kressol discovered later.

G. Nitrogenous Animal Acids.

§25.

Although from organic chemistry we have learned how to produce a
whole series of nitrogenous acids artificially, in a manner reminding us of
the alkaloids, the number of such compounds occurring naturally in the
Human body is very limited, and none of them have up to the present
been composed by art. They are not found in the vegetable kingdom at all.
None of these substances possess histogenic properties ; all are — and in
this respect they resemble animal bases — mutation products of histogenic
matters or plastic alimentary materials. Owing to their complex constitu-
tion they give rise, under certain circumstances, to chemically interesting
mutations. If we except two less- known acids which are met with in

muscle and sweat, they are either constituents
of the urine or the bile, forming essential
elements of these secretions.

Inosinic Acid, C,0H14N4On.

This is a non-cry stallizable acid, met with
in the form of a syrupy fluid, whose constitu-
tion is not yet quite certain. It is a constituent
of muscle-juice, and as such probably a muta-
tion product of the fleshy fibre.

Hydrotinic Acid.

This is likewise a syrupy acid, recognised
by Favre as a constituent of human sweat.

Uric Acid, C5H4N4O8 .

Fip.13. — Uric acid in its various crys- _. . , .. . ,

taiune forms, a, a, a, crystals such Inis Dibasic acid, a derivative ot ammonia,

as are met with on the decomposi- Qrir| nf 11T1Vnnwn pnnofifntirm annoara fr» fh»
tion of urates ; 6, crystalline forms and Ol Unknown Constitution, appears to tne

from human urine; c, dumb-beii unaided eye as a white powdery or scaly
substance. Under the microscope the greatest

variety in crystalline form, may be seen in uric acid. By the splitting up
of the salts of uric acid we obtain rhombic tables, or six-sided plates
(fig. 13, a, a, «) resembling cystin. Precipitated very slowly, uric acid
forms elongated right-angled tables, or parallelopipedic figures, or even
right-angled, four-sided prisms with straight ends. The latter are often

ELEMENTS OF COMPOSITION. 37

grouped together in knots. Pyramidal or barrel-shaped pieces may
also be found among other figures (Schmidt, Lehmann).

Uric acid, which has become deposited in urine (fig. 13, I), is dis-
coloured by the pigmentary matters of this fluid, its crystals appearing
yellow or brownish. The latter are met with as a rule either in the so-
called " whetstone form," i.e., as though they were transverse sections of
strongly biconvex lenses, or in rhombic tables with blunt or rounded
angles. Another very remarkable crystalline form
is that known as the " dumb-bell" (c). This may be
met with as a natural product, or may be produced
artificially by the decomposition of urate of potas-
sium (Funke).

Uric acid, whose acid properties are very feeble,
requires about 14,000 parts of cold and 1800
parts of boiling water for its solution. With
bases it forms salts, seldom neutral, and as a rule
acid. Those of the first kind, wrhich contain two
atoms of base, are readily converted into the latter
kind by the action of carbonic acid. They are,
moreover, easier of solution than the acid salts, in gated ? 6 &, spheroidal
which only one atom of base exists. Among the
latter two of the most important alone need be mentioned, which are
very difficult of solution in cold water.

ACID URATE OF SODIUM, C5H3NaN403.

•This salt forms short hexagonal prisms, or thick six-sided tables. It
is usually found under the microscope in the form of rounded bunches
of crystals (fig. 14). It also appears at times in strange spheroidal
masses with beaded processes (b, ft).

ACID URATE OP AMMONIUM, C5H3(KH4)N403.

A compound crystallizing in fine needles, usually combined to form
rounded tufts, in which the individual crystals are generally supposed to
be smaller than in the preceding salt (fig. 15).

Both salts, as well as the acid itself, on being evaporated at a moderate
heat with nitric acid, leave behind a reddish residue, which assumes a
beauteous rose-red colour on the addition of ammonia,
and on the subsequent addition of caustic potash an
exquisite violet tint. This test, known as the mur-
exide test, accurate for the detection of uric acid.

From its numerous decomposition products we are
as yet unable to gain any sure insight into the true
constitution of uric acid ; its being the source, how- R»- is.— Acid urate of
ever, of urea, allantoin, and oxalic acid, and, according
to Strecker, of glycin, renders it of great interest, and shows its import-
ance.

Uric acid, as its name denotes, is a constant constituent of human urine.
It is present, in the latter, however, in far smaller quantity than urea,
amounting only to about one per thousand, and combined with soda more-
over. It is also met with, though in smaller proportion still, in the
urine of carnivorous mammals. Traces only of it are found in the urine
of phytophagous animals. Its amount in human urine appears to vary

38

MANUAL OF HISTOLOGY.

but little according to the nature of the food taken, but much in certain
morbid conditions. Uric acid is besides a constituent of blood (Strahlt
Lieberkukn, and Garrod). It is also found in the fluids with which
many organs are saturated; as, for instance, that of the brain (Muller), of
the kidneys and lungs in the ox (Cloetta); and in man, of the spleen
(Scherer and Gorup-Besanez).

Uric acid is a mutation product of azotised tissue-constituents, and as
such is widely distributed throughout the animal kingdom. As to its mode
of origin, we are unable to point it out, owing to our ignorance of the nature
of the matter itself. The fact, already mentioned, that the injection into
the body of this acid increases the amount of urea in the urine ( Woliler and
Frericlis), seems to point it out as the source of the latter in the system :
and the purely chemical decompositions of uric acid, also, which so fre-
quently lead to the formation of urea, appear likewise to confirm this view.

§ 26.

Hippuric Acid, C9H9N08.
Hippuric acid is a glycin (see below), i.e., an amido-acetic acid =

or H V N,
|CH2 j
1 CO,H

in which one atom of the hydrogen is replaced by benzoyl (the radicle of
benzoic acid), CJELCO, thus—

H

V CH.2

This acid, which takes its name from its occurrence in the urine of

horses, has the primary crystalline form
of a vertical rhombic prism, and sepa-
rates from hot solutions in small
spangles, or large obliquely streaked
four- sided pillars, which have two end
surfaces (fig. 1 6). By slow evaporation
from dilute solutions, crystals (b) may
be obtained resembling in many respects
those of phosphate of magnesium and

0" I I ^* ' II "\^ ammonium, to be described presently.

\ 1 1 Hippuric, which has much stronger

II V acid properties than uric acid, may be

\ dissolved in 400 parts of cold and easily

& \V in hot water. It is also soluble in

alcohol, but only slightly so in ether.
It forms with alkalies and alkaline
earths crystalline salts soluble in water.
As to the numerous decomposition
products of the acid with which we are engaged, the most characteristic is
the transformation which it undergoes on being heated with acids and
alkalies : it is split up, namely, into benzoic acid and glycin after taking
up water (Dessaignes).

'Fig. 16. — Crystalline forms of hippurlc acid.
«, a, prisms; 6, crystals formed by slow
evaporation, and resembling those of phos-
phate of magnesia and ammonium.

ELEMENTS OF COMPOSITION.

39

Fig. 17.— Crystals of benzoic acid.

The same effect is produced by animal ferments in the presence of
alkalies (Buchner).

Like the acids we have just been considering, hippuric is nowhere
found in the vegetable kingdom. It is doubtful whether it exists in the
blood of vegetable-feeding mammals and that of man (Robin and Verdeil).
It appears in human urine in about the
same quantity as uric acid, though in
larger amount in certain diseased states
of the system. The proportion of hip-
puric acid in the urine of phytophagous
animals is greater, as, for instance, in
that of the horse. Up to the present
this acid has not been met with in the
juices of the organism ; it has, however,
been found in the scales of a skin disease
known as ichthyosis.

It is a fact of great interest, that ben-
zoic, kinic, and cinnamic acids, oil of
bitter almonds, and of tolu, introduced into the stomach, are excreted as
hippuric acid through the kidneys.

Hippuric acid possesses the nature of a decomposition product of
azotised substances of the body. The fact that on the oxidation of pro-
tein substances by permanganate of potash, a great quantity of benzoic
acid is developed, is in favour of this view.

§27.
Glycocholic Acid, C.,6H48N06 .

This, which belongs to the bile, is of analogous constitution to hippuric
acid, splitting up like the latter into glycin and a non-nitrogenous acid,
known as cholic acid.

Let us consider this latter in the first place : —

Cholic, or cholalic acid of Strecker, C24H4005, crystallizes from ether
with two equivalents of water of crystallization in rhombic tables ; from
alcohol with five molecules of water in tetrahedrons : or more rarely, in
square octahedrons, which effloresce when exposed to the air. This acid
is insoluble in water, but very soluble in alcohol and ether. "With
sulphuric acid and sugar it becomes of a purple-violet colour. The con-
stitution and origin of cholic acid has not
been fixed as yet.

Let us now return to glycocholic acid.
This crystallizes in very fine needles, which
maybe heated to 130° C. without under-
going change. It is tolerably soluble in
water, very easily so in alcohol and alkalies,
but insoluble in ether. It may also be
dissolved cold, and without decomposition,
in many mineral acids, as, for instance, Fig. m— Crystals of cholic acid,
sulphuric and hydrochloric, but also in acetic acid. With sugar and
sulphuric acid it gives the reactions of cholic acid. It is , monobasic,
and forms partly crystalline, partly amorphous salts, soluble in spirits
of wine.

On being boiled with potash ley or baryta water it is split up with

40 MANUAL OF HISTOLOGY.

absorption of water into cholic acid and glycin. Boiled with dilute
mineral acids, on the other hand, it yields choloidinic acid, C24H3804, and

glycin.

Among its salts one in particular must
be borne in mind, namely,

GLYCOCHOLATE OF SODIUM, C26H42IS"aN06.

(Fig. 19) a compound easily soluble in
water, which, precipitated from its solution
in alcohol by means of ether, crystallizes
in large, brilliant white stellate groups of
acicular crystals.

This acid forms an essential constituent

19,-Crystais of giycochoiate of human, as well as most mammalian
of sodium. biie> j^ js combined with sodium, even

among the vegetable feeders.

Taurocholic Acid, C26H44NS07 .

This second acid is related very nearly, as regards its chemical consti-
tution, with the foregoing. It splits up, however, into cholic acid;
and (instead of glycin) taurin, an indifferent substance, containing sulphur,
and no longer basic. This is the amide of isethionic acid or sulfethylenic

Taurocholic acid, which is very easily decomposed, is non-crystallizable,
but exceeds the last acid in its solubility in water and stronger acid
properties. It dissolves fats, fatty acids, and cholestearin with great
readiness. With sugar and sulphuric acid it gives the same reactions
as glycoholic acid. Its combinations with alkalies are very soluble in
alcohol and water, but insoluble in ether. Retained for a long period in
contact with ether, they crystallize. They burn with a brilliant flame.

As regards the decomposition products of this acid, they are, as has
been already mentioned, analogous to those of the foregoing. On being
boiled with alkalies taurocholic acid splits up, on the absorption of water,
into cholic acid and taurin ; while, with the mineral acids, choloidinic
acid besides taurin is produced, analogously to the previous case.

Combined with sodium taurocholic acid forms the second chief con-
stituent of the bile of man and numerous mammals, namely, tauro-
cholate of sodium, C26H4;JNaNS07.

H. Amides, Amido-Acids, and Organic Bases.

Under these names we have now to consider a series of further decom-
position products.

Urea or Carbamide, CH4N20, or CO j ^2

Carbamide, which, like all the rest of the substances under considera-
tion here, is absent in the vegetable kingdom, but which forms, on
the other hand, the chief constituent of the urine of the human body,
is of perfectly neutral reaction — corresponding in this respect with
kreatin, glycin, and leucin — to be referred to presently. It crystal-
lises in long four-sided pillars, terminating at either end in two
facets (fig. 20). It is quite soluble in water and alcohol, but not so
in ether.

ELEMENTS OF COMPOSITION.

.41

Urea combines with oxygen acids, forming salt-like combinations,
in which, one molecule of water is
•always present ; thus it is with nitric
and oxalic acid.

These two combinations are of par-
ticular importance in the recognition
of urea, owing to their characteristic
crystalline form.

Nitrate of urea, CO^H^H^O,
(fig. 21, a a), crystallizes in pearly
scales or glittering white leaves, which
appear under the microscope in the
form of rhombic or hexagonal tables.

Oxcdate of urea, 2CO(NH2),,
H.2C.204 + 2H20 (fig. 21,6 6,) appears

to the naked eye in the form of long 20_Crystals of urea. „ four.8ide; pillars;
thin leaves or prisms, found under
the microscope to be made up of

hexagonal tables as a rule, but also of four-sided prisms,
belong to the monoclinic system.

Urea combines also with metallic oxides and salts, as, for instance,
with chloride of sodium.

6, indefinite crystals, such as are usually
formed in alcoholic solutions.

Both salts

Fig. 21. — Crystals of combinations of urea with nitric and oxalic acid.
a a, nitrate of urea ; b 6, oxalate of the same.

As regards its decomposition, urea may be artificially split up on
absorbing water into carbonic acid and ammonia.

The same change is brought about by contact with animal matters
undergoing putrefaction, such as protein compounds, or mucus, &c. It
is owing to this fermentation that urine becomes after a time alkaline
on being exposed to the air.

Urea may be obtained from other alkaloids, such as kreatin and
allantoin, by treatment of the latter with alkalies ; further, by subjecting
uric acid to the action of oxidising acids and caustic potash. Urea may
be produced artificially in many ways besides.

Carbamide appears in human urine as the most important of all its solid
constituents. It amounts to from about two and a half to three per cent.

MANUAL OF HISTOLOGY.

of the fluid excreted, and is carried out of the body daily in con-
siderable quantity. It is found likewise in the blood in very minute
quantity (Strahl and Lieberkuhn, LeJimann, Verdeil, and Dollfuss), and
in the chyle and lymph of mammals (Wurtz). It is also stated, but
with uncertainty, by Millou, to be present in the aqueous humour of
the eye. Further, it has been met with in the brain of the dog (Staedeler),
and in normal sweat, according to Favre, Picard, and Funlte. Under
certain diseased conditions it may appear very widely distributed through-
out the system.

Urea, like all allied substances, a decomposition product, and unfit,
owing to its solubility, to take part in the formation of tissues — springs,
as we know by experience, from the protein compounds of the system ;
from those albuminous substances entering into the constitution of
tissues, as well as those received into the blood from the food, and super-
fluous there. Thus the amount of urea in the body is increased by
muscular exertion and abundant fleshy diet ; the introduction of many
alkaloids into the stomach has the same effect, as, for instance, thein,
glycin, alloxantin, and guanin. Finally, the injection of uric acid into
the circulation causes an augmentation in the amount of urea excreted
with the urine ( Wohler and Frerichs).

In regard to detail, we are still in the dark as to the formation of urea
in the body. We do know that it is a decomposition product of the
protein compounds, and also that almost all the nitrogen which leaves
the system passes out in this way ; and yet, on the other hand, as to the
chemical mutation series whose end factor is urea, we are in possession of
but few facts. Two points, however, may be alluded to as throwing
some light upon the origin of the substance in question, namely, that
kreatin, a mutation product of the protein compounds, splits up into
sarkosin and urea under the action of alkalies ; and again, urea may be
obtained from guanin, among other substances, by treatment with oxidiz-
ing reagents (Strecker). But in this respect the presence of uric acid
is probably of greater importance as a source of urea in the system — urea
being one of the usual decomposition products of the same, derived from
its oxidation.

§29. ,

We turn now to three substances closely allied one to the other, to

be regarded as members of a mutation
series of histogenic matters, and which
possibly lead to the formation of uric
acid in their further physiological
transformation.

They are compounds very insoluble
in water, but which dissolve readily
in alkalies and acids, forming with
the latter crystalline salts which are
partly decomposed by water. All
three evaporated with nitric acid,
form yellow substances which, on
the addition of potash without heat,
assume a red colour, turning to a
lively purple on the temperature

Fig. 22.— Crystals of chlorate of guanin. being raised.

ELEMENTS OF COMPOSITION.

43

Guanin, CSH5N60 .

Guanin, discovered by Unger in guano, forms with hydrochloric acid
a crystalline salt, met with in obliquely pointed needles or parallopipedic
tables, belonging in general to the clinorhombic system (fig. 22). Some
years ago Strecker obtained xanthin from the transformation of guanin.
Guanin is not a constituent of urine, but is found in the pancreas.

Hypoxanthin (Sarkin), C5H4N40 .

Hypoxanthin of Scherer, which is identical with sarkin, investigated
subsequently by Strecker,
is seen, by comparison of
their respective formula,
to be nearly related to
guanin, as well as to the
substance we are about tc
allude to, namely, xanthin.
The crystalline forms of
their nitric and hydrochlo-
ric acid salts (fig. 23) are
characteristic, especially the
first. Nitrate of sarkin,
on rapid separation, forms
rhomboidal plates ; slowly
deposited, it is met with in
tufts of obliquely pointed
flat prisms or rhomboidal
crystals. Evaporated quiet-
ly, large darkly striped
bodies like rock crystal are
formed, besides smaller
cucumber-shaped crystals.
The chlorate crystallizes
partly in bunches of four-sided bent prisms with curved surfaces, and
partly in coarser, irregular, and darker
prisms, groupe^ in pairs (Lehmann).

It has been found in human blood
in the disease known as leucaemia,
(Scherer) ; in the blood of the ox and
horse; in muscle, in the heart, in the
liver, spleen, thymus, and thyroid
glands (Scherer, Strecker, Gorup-Bes-
anez), and, finally, in the kidney and
urine.

Xanthin, CSII,N402.

Xanthin, which differs from hypo-
xanthin in having one more, and from
uric acid one less, atom of oxygen,
forms a salt with nitric acid, which
crystallizes in bunches of rhombic tables
and prisms. Chlorate of xanthin oc-
curs in glittering, six-sided tables (fig. 24).

Xanthin was formerly only known as a constituent of very rare urinary

Fig. 23. — Crystals of nitrate of sarkin (upper half), and of
chlorate (lower half).

Fig. 24.— Crystals of nitrate of xanthin
(above), and chlorate (below).

44 MANUAL OF HISTOLOGY.

calculi ; it has, however, been since found to occur very extensively, but
in small quantities, in many different organs — in the brain, in glands and
muscles, and in the urine.

Allantoin, C4H6N403.

This compound crystallises in glittering, colourless prisms, of rhombic
fundamental form (fig. 25). It is difficult of solution in cold, but more
soluble in warm water ; not at all so in ether, on the contrary. Allantoin
appears neutral, but combines with metallic oxides. Through the agency

of yeast-cells it may be split up
into ammoniacal salts and urea.

Allantoin may be obtained with
urea artificially on the oxidation
of uric acid, by boiling with super-
oxide of lead.

It is a constituent of the allan-

urine of young calves. According
to Frericlis and Staedeler, it ap-
pears in the urine of mammals,
coincident with disturbance of
their respiratory functions, but

Fie. 25.— Crystals of allantoin ,-, • •

whether in man under similar
circumstances has not yet been decided.

It must be regarded, like the bases with which it is physiologically
related, as a decomposition product of azotised substances in the body.

§ 30-

Kreatin, C4H9N3Oa + H2O .

This compound, known even before its constitution was accurately
ascertained by Liebig, is of neutral reaction. It is soluble, in a minor
degree, in cold, more so in hot water, arid quite insoluble in pure alcohol
and ether. It crystallizes in transparent rhombic prisms ^fig. 26), loses

its water of crystallization at 100° C., and at
a higher temperature melts with decomposi-
tion. With acids kreatin forms salts of acid
reaction.

Some of the decomposition products of
kreatin are also of importance. Dissolved in
acid and heated, it is transformed, with the
loss of one molecule of water, into a closely-
related substance, which also occurs naturally
in the body; this is known as kreatinin,
C,H.KO. Boiled with baryta water, kreatin

Fig. 26.— Crystals of kreatin. 4 7 3. , «i-r' -KT /^ /!' i_«

passes into urea, CH4N2O (taking up a mole-
cule of water), and another base, not yet met with naturally, known as
sarkosin (methylglycocoll), C2H4(CH3)JST02 .

Kreatin springs, according to Volkard, from sarkosin and cyanamid =

This is looked upon as methyluramido-acetic acid (methylguanidiii-
acetic acid).

ELEMENTS OF COMPOSITION.

45

Kreatin is found (but only in small amount) in the juices of the muscles
of man, and the vertebrates generally ; also in the fluid saturating the
brain (in the dog, according to Staedeler, together with urea), in the
testes (?), and in the blood ( Verdeil and Marcet Voigt). In the urine it
is said by Heinz not to exist primarily, but to be formed secondarily
from kreatinin.

Kreatin may be looked upon us a decomposition product of muscle and
the substance of the brain, leaving the body through the kidneys. Per-
haps the greater part of the kreatin Avhich is formed in the body under-
goes immediate decomposition, and is one of the sources of urea. This
seems probable when we remember the mode in which it is split up by
boiling with baryta water.

Kreatinin, C4H7N30 .

This substance, nearly allied to kreatin, crystallizes in colourless oblique
rhombic pillars belonging to the monoklinic system (fig. 27). In contra-
distinction to the compound last men-
tioned, kreatinin possesses strongly basic
properties, and is readily soluble in water.
With acids it combines to form crystal-
line and usually soluble salts.

Kreatinin may be obtained by treat-
ing kreatin with acids. A watery solu-
tion of kreatinin, on the contrary, be-
comes again transformed into kreatin.

Boiled with baryta water, it splits up
into ammonia and methylhydantoin,
C4H6N202. It is now looked upon as
glykolylmethylguanidin.

Kreatinin is.a constituent of the juices
of muscle, and appears in the urine;
here it is present in large quantities,
and becomes transformed, as already
remarked, into kreatin. Verdeil and Marcet state that they have found
it, like the latter, in the blood:

§31.
Leucin, C8Hn(NH2)O2.

Leucin, or amidocapronic acid, is produced by the artificial decomposi-
tion of the protein compounds, glutin-yielding matters and elastin, by
means of acids or alkalies. It is, likewise, met with as a product of the
putrefaction of albuminous substances, like tyrosin, to be alluded to pre-
sently, and as such it was discovered many years ago by Proust.

Through the investigations of Frerichs and Staedeler, who showed it to
be a physiological decomposition product widely distributed throughout
the body, it has become of much interest. Contributions on the same
point have also been made by Clo'etta and Virchow. Many of these
statements, moreover, are confirmed by Gorup-Besanez and Radziejewsky,

Leucin is met with as a crystalline substance, partly (but only rarely
and when very pure) in delicate kliriorhombic plates, partly in spheroidal
lumps possessing a very characteristic appearance. They are either small
globules (a), or hemispheres (b b), or aggregations of rounded masses (c c d),

Fig. 27.— Crystals of kreatiniu.

46

MANUAL OF HISTOLOGY.

and not rarely a number of segments of small spheres rest with their flat
side upon a larger globe (d ef).

Leucin globules may be either unmarked (in which ease they slightly
resemble fat-globules), or they may present a concentrically laminated
appearance (g g g g). They are frequently met with also with rough
surfaces, as though eroded.

Leucin has no action upon vegetable colours, is quite soluble in water,
hydrochloric acid, and alkalies, and slightly so in cold alcohol, while in
ether it is insoluble. It may be volatilised by a cautious elevation of
temperature. Rapidly heated, it fuses with decomposition. From its
solutions it is not precipitated by most of the usual reagents.

In regard to the occurrence and significance of this substance in the
human system, we must distinguish between leucin produced by the
putrefaction of histogenic substances, and that formed physiologically in
the living body.

The latter appears often, but not invariably, accompanied by tyrosin
as a constituent of many organic fluids and gland juices, in greater or
less quantity. Under diseased conditions it is often unusually abundant

in organs in which traces
alone are to be found during
health, as for instance in the
liver.

It is present in the spleen,
the pancreas, and its secre-
tions, the salivary glands and
saliva; in the lymphatic glands,
the thymus and thyroid glands,
and in the fluid saturating
pulmonary tissue. In the
healthy liver it is not to be
found, or only so in traces, as
is also the case with the
brain. Muscle appears like-
wise to be destitute of leucin,
though in the heart it may
not unfrequently be found as a
pathological product. It is at
times present in large amount
in the kidneys, and may pass
into the urine (Staedeler).
These facts are of some physiological worth, in that they pr.ove the
existence in different organs of distinct series of mutations among their
histogenic substances. Thus, leucin is no mutation product of muscle,
but of many glandular structures. There can be no doubt, further, that
as artificially, so also in the system naturally, does leucin spring from
protein compounds, gelatin-yielding substances and elastin ; its physio-
logical origin from albuminates by the action of one of the ferments
existing in the pancreatic juice has also been proved (Kuhne).

Leucin is partially excreted with the glandular secretions, and appears
in the intestinal canal, and probably undergoes further decomposition
also in the body. It is a fact worthy of notice, that in the lymphatic and
blood-vascular glands, there occurs besides leucin ammonia also, allowing
of the hypothesis that leucin may be resolved there into ammonia and

Fig. 28. — Spheroidal crystalline masses of leucin. a, a very
minute simple spherule; b, hemispheroidal masses; c c,
aggregates of small globules; d, a large globule sup-
porting two halves; e /, a large spheroid of leucin
richly studded with minute segments ', g g g g, lamin-
ated globules of leucin, some with smooth, some with
rough surface, and of very various sizes.

ELEMENTS OF COMPOSITION.

47

volatile fatty acids (Frerichs and Staedeler) — a change which certainly
takes place in the lower part of the intestinal canal.

§32.

Tyrosin, C9HnN03.

This substance is also an amido-acid, whose constitution, however, has
not yet been fully ascertained. It possesses weak basic properties, and
may be obtained like the foregoing, but in much smaller amount, from
the artificial decomposition of protein matters. Not, however, like leucin,
from that of elastin and gelatin-yielding substances. It is also produced
by the putrefaction of protein compounds, and in especially large quan-
tity from the decomposition of silk-fibrin and glue. Keratin and animal
mucus also yield more tyrosin by far in their decomposition than the
original protein matters. Thus we see it to be associated chemically with
leucin, and it has been recently proved to be a physiological companion
of the same as a constituent both of the normal and diseased body
(Frerichs and Staedeler). Tyrosin, nevertheless, is not so extensively
met with as leucin. It crystallizes in white silky needles (fig. 29, a)
which are frequently arranged in very delicate, small, or large groups
(b b). While leucin is very soluble in water, tyrosin is but little so,
besides which it is insoluble in the pure state in alcohol and ether. It
fuses with decomposition when heated, and combines in regular propor-
tions with acids and bases. Warmed with concentrated sulphuric acid,
there is found in it, beside other acids, a compound named tyrosin-sulphuric
add, which, like its salts, when mixed with chloride of iron assumes a
beautiful violet colour (Piria's test).

This reaction with chloride of iron just mentioned resembles that of
the salicylecompounds, although
its nature has not yet been as-
certained.

Without taking into account
the tyrosin developed in the
processes of putrefaction in the
body, we find that it has similar
physiological sources to the fore-
going base. It is missed in the
healthy liver like leucin, pro-
bably because it undergoes there
rapid transformation into other
compounds. In disease, how-
ever, it appears in this organ.
Tyrosin which, as has been
already mentioned, springs in
smaller quantities from albu-
minous substances than leucin,
and lacks besides the physiologi-
cal sources of the latter from
gelatin and elastin, as well as its

SOlubilitV, is frequently missed Fig. 29.— Acicular crystals of tyrosin. a, single crystals
• ' i . b b. smaller and larger groups of the same.

where leucin occurs.

Thus it has been found alone in no inconsiderable amount in the

48 MANUAL OF HISTOLOGY.

spleen and tissue of the pancreas, as also in the digest of albumen in
pancreatic juice.

The physiological significance of tyrosin is probably in general allied to
that of leucin.

§33.
Glycin, C2H3(NH2)02.

Gtycin or glycocott, or also glut in sugar, which is in reality amido-acetic
acid, has not as yet been met with free in the system. It appears, how-
ever, on the splitting up of several animal acids, as hippuric and uric, and
one of the biliary acids, namely glycocholic. It is also of interest as an
artificial decomposition product of glutin and chondrin. It is obtained
in greatest abundance by the decomposition of silk-fibrin (fibroin), in
which it is present together with leucin and tyrosin. It may be artificially
produced from chloracetic acid by the action of ammonia.

Glycin crystallizes in colourless rhombic pillars belonging to the mono-
klinometric system (fig. 30). These crystals bear a heat of 100° C. with-
out losing any water, but at 178° C. they fuse, and are decomposed.
Glycin is sweet to the taste, without alkaline reaction, soluble in water,

but almost insoluble in alcohol and ether. It
forms acid salts with acids, and can combine
with bases or even salts themselves. There
must be some substance nearly related to glycin
formed in the body, in all probability from
glutinous matters (although at present we are
unacquainted with it), which in combination
with cholic acid constitutes glycocholic acid,
and with benzoic, hippuric acid. This sub-
stance then becomes free in the form of glycin
upon the absorption of water, and splitting up
of the two acids.

_ Glycin leaves the body partly with hippuric

Fig. so.-crvstais of tfycin of acid through the kidneys, and is partly reab-
different forms. sorbed into the blood as a component of glyco-

cholic acid as (shown by Bidder and Schmidt) in order to undergo there
further alterations with which we are unacquainted.

SOFT
N(CH,)tOH.

Some years ago a new base known as cholin was met with by Strecker
(in but small quantities, however) in the bile of oxen and swine. "We
know that by boiling lecithin with baryta water neurin is obtained (§ 20),
a base of strong alkaline reaction. The identity of this substance with
cholin has recently been established in a very interesting way. Neurin is
now regarded as hydrated oxide of trimethyl-oxethyl-ammonium (Baeyer).
Finally, Wurtz succeeded in producing hydrochlorate of neurin from
hydrochlorate of glycol and trimethylamin.

§34.

rso3, o

This substance, containing as much as 25 '7 per cent, of sulphur, was

Taurin, C2H7NS03, or CSH4 j

ELEMENTS OF COMPOSITION.

49

discovered long ago as a constituent of the bile. It crystallizes with the
fundamental form of a right rhombic prism (whose lateral angles are
respectively 111° and 68° 16'), in colourless six-sided prisms, with four
and six facets on their extre-
mities (fig. 31, a}. From im-
pure solutions it separates in
irregular sheaf-like masses (&).

Taurin has no eifect upon
vegetable colours; it is toler-
ably soluble in water, but insol-
uble in alcohol and ether. The
great stability of the substance
is remarkable : even boiling in
mineral acids in which it dis-
solves does not decompose it.
Taurin is not precipitated from
its solutions by tannic acid and

the metallic salts. The sulphur n* 31-Cr>'stals of tanrin-
it contains was for a long time
overlooked ; .it is contained in it in a different combination to that
which exists in cystin.

Taurin has recently been produced artificially. It is related to

{OTT
SO H

Isethionate of ammonium, when heated up to 200° C., according to
8trecJcer, yields taurin, with the loss of one molecule of water.

a, well-formed six-sided
priMns; b, irregular sheaf-like masses from an im-
pure solution.

S03NH4

NH«
SO,H

Thus taurin is an amido-sulfethylenic acid.

Kolbe obtained it also by the action of ammonia upon chlorethyl-
sulphuric acid.

Taurin may be obtained by the splitting up of one of the two biliary
acids, and contains all the sulphur of the bile. It also becomes free
on the decomposition (commencing in the body) of this acid known as
taurocholic, and appears- thus in abnormal as well as putrid bile, and in
the lower portion of the intestinal canal (Frerichs). Tt has been also
met with by Cloetta in the juices of renal and pulmonary tissue.
As obtained from the latter source, it was formerly described by Verdeil
as pulmonic acid. The suprarenal capsule contains it also (Holm), though
the blood does not.

At present we are uncertain as to the origin of taurin ; but it has all
the nature of a decomposition product, and there can be hardly any
doubt (from the fact of its containing sulphur) that it is derived from
albuminous matters, a considerable quantity of the sulphur of the latter
being present in it.

In regard to its farther changes, an observation has been made by
Buchner of great physiological interest. Taurin, otherwise so stable, splits
up by the action of a ferment (namely, the mucus of the gall-bladder)
in the presence of alkalies, into carbonate of ammonium, sulphurous,
and acetic acids. The latter acid, combined with an alkali, is changed
into a carbonate, and the sulphurous acid in combination with sodium
becomes later converted by oxidation into sulphuric acid, so that in

50 MANUAL OF HISTOLOGY.

putrefying bile we meet with Na2S04. The circumstance that most
of the bile poured out into the intestine is reabsorbed, as observed by
Bidder and Schmidt, thus explains, at least partially, the origin of the
sulphates, which eventually leave the body with the urine.

Cystin, C3H7NS02.

This substance is remarkable for the large quantity of sulphur which
it contains, amounting to over 26*5 per cent.

« Cystin crystallizes in colourless hexagonal tables

II or prisms (fig. 32), and is insoluble in water,
alcohol, and carbonate of ammonium. It is, on
1JJ the other hand, readily soluble in mineral acids

r ->. and in alkalies, from which it may be precipitated

rxv by organic acids, as, for instance, by acetic acid.

/ — v T 1 ^c-^V. Cystin enters into combination with both acids
\-/ VS^3 and alkalies. Its mutation products and consti-
^^ tution have not as yet been ascertained, nor do
32,-Crystais of cystm. we ^QW in ^^ form gulphur is contained in it.

Cystin is of rare occurrence ; it forms certain kinds of urinary calculi,
and may also appear as an abnormal constituent of urine.

It was once met with in the liver (Sclierer) ; likewise in the tissue of
the kidneys of oxen by Cloetta, but not invariably. The physiological
relations of the substance are still quite obscure.

I. Animal Colouring-Matters.

§35.

The animal colouring-matters, which are not found in the vegetable
kingdom, have their origin for the most part from the natural pigment of
the blood, haemoglobin (§ 13). They are met with either as artificial
decomposition products, or occur in the living body.
Haematin, C34H34N4Fe05 (Hoppe).

This substance, as already mentioned, may be obtained from the red
blood-corpuscles or hsemoglobulin, but only in a coagulated form.

According to Hoppe, haematin usually presents itself as an amorphous
blue-black substance, which becomes of a reddish-brown on being triturated.
It is insoluble in water and alcohol, but soluble in the latter if there be
added to it a certain small amount of sulphuric or nitric acid. It may
likewise be dissolved in a watery or spirituous solution of ammonia ;
and also in caustic alkalies in dilute watery or alcoholic solution. Such
a fluid containing hsematin is frequently changed to a greenish colour
by the action of a large amount of potash — especially if it be boiled.
Haematin, suspended in water, is decolorised by the action of chlorine
with the formation of chloride of iron ; the dried powder also becomes
green by contact with chlorine gas. Dichroism is seen in alkaline, but
not acid solutions of haematin ; in a thin layer they appear olive-green,
in a thick stratum red (Lfrucke).

With the aid of concentrated sulphuric acid, the iron it contains
may be extracted from haematin, water taking its place in the com-
bination (Hoppe).

Hydrochlorate of Haematin, Hsexnin, C34H34N4Fe05 . HC1 (Hoppe).
We are indebted to Teiclimann for our acquaintance with this peculiar

ELEMENTS OF COMPOSITION. 51

crystalline element of the blood. Dried blood, treated with warm acetic
acid, even when putrefaction has already set in, deposits regularly innu-
merable crystals of brown, dark-brown, or almost black colour, which
appear either in the form of rhombic pillars (when they resemble
hrematoidm), or in needles, single or arranged in stellate groups (fig. 33.)
The presence of chlorides of the alkalies
is, as Teichmann very properly remarks,
indispensable for the occurrence of this
crystallization. Ha3min crystals are
tolerably stable, do not decompose in
the air, and are neither soluble in water,
alcohol, ether, nor in acetic acid. They
may be dissolved, however, in boiling
nitric acid. Sulphuric acid likewise
reduces them readily to solution, as also
ammonia and weak potash. The latter,
when concentrated, changes the colour

Of hsemin Crystals to black, Causing Fig. SS.-Crystals of hamiin.

them at the same time to swell up. These crystals are of the greatest
importance in a forensic point of view, as a means of proving the presence
of small quantities of blood. Klihne obtained them from the colouring
matter of muscle.

Until a few years ago, the chemical constitution of haemin was but
very imperfectly known. We are indebted to Hoppe for the first accu-
rate investigations of the subject. By him it was produced from pfce
haemoglobin (see above), besides which he demonstrated that it might be
again reconverted into ordinary hsematin.

Hsematoidin, C17H18U,08, or C34H36^T406 (?)

Blood which has left the vessels, and is stagnating in the tissues,
undergoes gradually farther changes, by which a crystalline colour-
ing-matter is formed, nearly allied to hsematin, but destitute of iron.
This, which is known as hcematoidin, crys-
tallizes in rhombic prisms (fig. 34), but
also in acicular crystals (Robin). tinder
the microscope these appear red with trans-
mitted light ; with reflected, of a canthara-
dine green colour. Hsematoidin is very
soluble in chloroform, to which it communi-
cates a golden yellow tint, and also in sul-
phide of carbon, which acquires from its
presence a flame colour. Its crystals are
likewise dissolved by absolute ether, but not
by either absolute alcohol, water, ammonia,
solution of soda, or dilute acetic acid : in
concentrated acetic acid, however, they dis- Fi* 34-H*matoidin «r*"ta.
solve when warmed, communicating to the fluid a golden-yellow colour
(Holm).

Staedeler obtained unusually large crystals of this pigment, measuring
as much as 0'45nim. from the ovary of the cow, by treatment with chloro-
form or sulphide of carbon (fig. 35). They appear under the micro-
scope, in the first place, in the form of acute-angled triangular tables with
one convex side, a. This curved border, however, may be replaced by

52

MANUAL OF HISTOLOGY.

two right lines, giving rise to deltoid tables (b). Again, two such

tables very frequently become fused
together by their convex sides, or
overlap each other (be). We then
have the rhombic tables usually
ascribed to hsematoidin (fig. 34) ;
still showing indentations in most
cases at the blunt angle of the rhombs,
which gradually become obliterated
(dd). It not unfrequently happens
that two other crystals become asso-
ciated with the two first, so that a
four- rayed star is produced (e). These
then give origin to four-sided tables
on the filling up of the indentations
at their corners, and each sometimes

wig. ss.-very lar^e crystals of hemauddin assumes eventually the appearance of

from the ovary of a cow, obtained by treat- an oblique dice, from its having

gradually become thickened (fg.)

§36.
Uro'erythrin, or Uroheematin.

-jln the urine a very small quantity of a red colouring matter is to be
found, which gives to the fluid its yellow tint, and may colour the
sediment of the same of a lively red. This substance is very unstable,
and only obtainable with great difficulty, whence our imperfect acquaint-
ance with its nature. The colouring matters of urine were first investigated
by Scherer, and more recently by Harley. The latter obtained a red
pigment almost insoluble in water, but freely so in warm fresh urine,
giving to the latter a yellow tint, and to ether and alcohol, in which it is
also dissolved, a beauteous red colour. Harley found this pigment to be
ferruginous, and regards it as a species of modified hsematin. Besides
this, some other pigmentary matters were also met with by him.

A red pigment has been recently discovered by Jaffe in the urine,
possessed of some spectroscopic peculiarities : it has been named by him
urobilin, from the fact of its also occurring in bile and the excrements.

Blue and violet colouring matters, which may occasionally be met with
in human urine, appear in but very small quantity. Under certain
circumstances indigo has been observed here without having been taken
up from without (Sich&rer), while indikan, C26H31N017, or chromogen of
indigo is, according to Hoppe, constantly present.

Black Pigment, or Melanin.

Black pigment is found in normal tissues in the form of very minute
granules or molecules. It is a substance remarkable for its insolubility
and unchangeableness. Melanin . is not soluble either in water, alcohol,
ether, dilute mineral acids, or concentrated acetic acid. It is dissolved in
warm potash solutions, but only after some considerable time. The same
takes place in concentrated nitric acid, by which the melanin is decom-
pounded, however. Its ash contains iron.

The investigations in regard to the constitution of melanin which have

ELEMENTS OF COMPOSITION.

53

hitherto been made, must be received with reserve, for the substance is
only to be obtained pure with the greatest difficulty.

Melanin, which with hsematin is the only pigment in the body to
which a certain amount of histogenic significance cannot be denied,
appears, as a rule, forming the contents of polygonal or stellate cells. It
is met with in greatest abundance in the interior of the eye. The large
amount also in which it is met with in some of the lower vertebrate animals,
as for instance in the frog, is remarkable.

As a pathological product, it (or something nearly allied to it) is frequently
met with in great abundance in different organs, tumours, &c.

The source of melanin is usually, and probably correctly, supposed to
be the colouring matter of the blood. This view is borne out by the
nature of pathological black pigments, whose origin from hsematin may
in many cases be accurately traced.

We must be on our guard, however, not to confound the ordinary black
pigment found in the human lungs with melanin. This consists of
particles of carbon, charcoal, dust, or lamp-black, suspended in the air
which is inspired. It is not met with in the lungs of infants or of wild
mammalian animals.

§37.
Biliary Figments.

Until very recently but little has been known of the colouring matter
of the bile. It is characterised by its reactions with nitric acid. The
latter, if it contain nitrous acid, or if concentrated sulphuric acid be
added to it, produces in bile a peculiar play of colours, — green, blue, violet,
red, yellow, following rapidly one upon the other.

Two kinds of pigment may be usually distinguished in bile : a brown,
known as cholepyrrhin or bitiphcein, and a green or biliverdin.

According to Staedeler's recent investigations, a whole series of probably
characteristic pigments may be obtained from bile, although it is still a
question whether they all exist in the latter when perfectly fresh.

BILIRUBIN, C16H18N203 (or C9H9ISr02?)

A red substance allied to haamatin and haematoidin (but not identical
with the latter), which may be obtained from its solutions in chloro-
form, sulphide of carbon, and benzol, in beautiful
ruby -red crystals. These (fig. 36), when crystal-
lized from sulphide of carbon, appear in clino-
rhombic prisms, with a basal surface, whose
foremost angle is very sharply curved, and prism
surface convex, so that a view of the basal
surface presents an elliptical figure. Lying upon
their convex surface these crystals have a rhombic
form.

Bilirubin is insoluble in water, and nearly so
in ether. It is soluble, on the other hand, in
alkalies arid in chloroform, communicating to
the latter a pure yellow or orange-red colour;
also in sulphide of carbon, which is tinged
golden yellow by it. It possesses, further, the
properties of a weak acid, and shows the play of
colours just mentioned with nitric acid containing nitrous acid in the most

bon«

54 MANUAL OF HISTOLOGY.

marked degree. It is the most essential colouring matter of human
bile and biliary calculi, and is probably derived from haematin ; it is
also found in the urine of persons suffering from jaundice (Schwanda).

BILIVERDIN, CI6H20N20., or (C6H9N02?)

This is a green colouring matter, which may, under certain circumstances,
be obtained in a crystalline form. Its presence in fresh bile is still
questionable, for it is probable that it absorbs water and passes into
biliprasin, a coloring matter, to be presently alluded to. The relation-
ship to bilirubin will be easily understood from the following formula : —

CWH18N A + HS0 + 0 = CJ3JS.O.
Bilirubin. Biliverdin.

BILIFUSCIN, C16H20]S"204 .

A non-crystallizable compound, soluble in water, containing soda or
ammonia, communicating to it a brown colour. It is, to all appearances,
of subordinate importance, and differs from bilirubin only in having one
more molecule of H20 .

BILIPRASIN, C16H22N206 .

A green amorphous pigment, soluble in alkalies with a brown colour,
in contradistinction to biliverdin, which, with the former, produces a green
solution. The formula of this pigment corresponds to that of biliverdin
-f one molecule of H20. It occurs in biliary calculi and jaundiced
urine.

BILIHUMIN, finally, is a name given by Staedeler to a dark earthy-looking
substance, which, however, has not yet been obtained perfectly pure, so
that its formula is not known. It may be obtained as the ultimate
decomposition product of all the four biliary pigments like melanin.

REMARKS. — It may be well at this juncture to bestow a few words upon the
extractive matters. Under this name we understand in zoochemistry, a set of sub-
stances which are partly present in the body naturally, and are partly the results of
chemical manipulation. They manifest no characteristic peculiarities by which they
may be recognised ; they do not crystallize, nor combine in regular proportions with
other matters, nor do they volatilise at definite temperatures. From this may be
perceived the difficulty of dealing with these substances, either chemically or physio-
logically. Our chemical acquaintance with them is therefore very incomplete.
Physiologically they are held to be decomposed materials, intermediate products in
imitative processes, although in reality there is but little proof that this is the case.
Several bases, acids, &c., already alluded to, have recently been separated from these
compounds.

K. Cyanogen Compounds.

§38.

As a supplement to the consideration of the azotised decomposition
products of the system, cyanogen, CN, and its combinations may be
appended here.

Sulplwcyanogen (rhodan), CNS. This ternary radical, whose com-
pounds are remarkable for the beautiful red colour which they produce
with salts of iron, forms with H what is known as hydrosulphocyanic

ON )

acid TT [ S. Unlike other compounds of cyanogen, this is generated in

the human body, and possesses but slight poisonous properties. It occurs
in combination with potassium.

ELEMENTS OF COMPOSITION. 55

p"M- \

Sulphocyanide of potassium (rhodanide of potassium), -r/ > S , is the

only cyanogen compound met with in the human economy, and that in
extremely small quantity. It is a constituent of saliva, in which it was
discovered "by Treviranus ; its occurrence here, however, is not without
exception.

The origin and relations of this compound are still entirely unknown.

Sulphocyauide of potassium gains in interest, moreover, when we remem-
ber that in the physiological mutation series no other cyanogen combina-
tions make their appearance.

L. Mineral Constituents.

§39.

The number of mineral substances and inorganic compounds occurring
in the human body is not inconsiderable. Our knowledge of these, how-
ever, is unfortunately far less perfect at present than the nature of the
substances in question might lead us to expect. In respect to the com-
bination of inorganic matters, we are — so far as the question turns upon
their pre-existence in the various parts of the body, or to what extent
they must be regarded as only produced by chemical manipulation itself
— by no means as clear as might be desired. But greater obscurity still
prevails in regard to the physiological relations of some of these substances.
Granting, for instance, that no doubt can exist that in water we have
before us the chief solvent and agent in saturation and gelatinization of
the system, and that phosphate of calcium constitutes the most important
hardening medium of the same, and so on, there remains still a consider-
able number of substances whose purposes in the body we are unable to
ascertain with anything like certainty. It is likewise beyond our power
at present to distinguish with precision between those inorganic com-
pounds which occur as decomposition products in the economy, and those
which possess histogenic properties. Finally, there are in all probability
many mineral matters in the system which are only casual constituents of
the same, introduced with the food.

It would lead us too far to detail here all the differences in' amount
between the ash constituents of the several tissues and organs of the
body. The variation in this respect, according to age, is of such great
interest, however, that a few points may be noticed in regard to it.

While, in the earlier periods of foetal life, the ash only amounts to 1
per cent, of the whole weight of the body, it rises later on to 2, and reaches
in mature mammals so high as 3*5, 4, or even 7 per cent. In advanced age
it is probable that this is still further increased (Bezold and Schlossberger).

Among the inorganic matters and compounds found in the body, the
following must be specially borne in mind : —

(a.) Gases — oxygen, nitrogen, and carbonic acid.

(b.) A cidsr- carbonic, phosphoric, sulphuric, hydrochloric, hydrofluoric,
and silicic. These, with the exception of the carbonic acid, diffused through
fluids, and hydrochloric acid, found free as a constituent of the gastric
juice, hardly ever occur in a free state in the body, but almost invariably
combined with bases.

(c.) Bases — potash, soda ammonia, lime, magnesia, oxides of iron, man-
ganese (and copper). These usually appear as salts, and yet we have free
5

56 MANUAL OF HISTOLOGY.

alkalies, especially soda, combined with protein compounds, and also iron,
in many animal substances, as, for instance, in hsemoglobulin and me-
lanin.

In regard to the gases just mentioned, they are found either in the cavi-
ties of the body, or diffused, or chemically combined in its various fluids.

Oxygen, 0.

Oxygen occurs in the organic matters of the animal body in combina-
tion. It appears, however, also as an element in all the air cavities of the
system. Finally, it is met with in all the fluids of the economy. In the
blood oxygen is dissolved in very minute quantity, while the greater por-
tion appears combined (though loosely) with the other constituents of the
fluid. We need hardly remark that this element, from its strong tendency
to combine with other substances, plays a most important part in the
chemical and physiological life of the organism.

Nitrogen Gas, ET2 .

Nitrogen, as is well known, occurs in combination in many organic
matters in the body : it is also met with, however, in the air cavities of
the latter, and in very small quantities dissolved in its various fluids.

Carbonic Acid, or Carbonic Dioxide, C02 .

Carbonic acid appears partly in combination (especially with inorganic
bases), partly free, either as a gas, or dissolved in the fluids of the body.
As a gas, carbonic acid is present in considerable quantity in the gases
expired from the lungs, and in various cavities containing air. Dissolved,
it is a constituent (though in variable amount) of all animal fluids. It
appears in abundance in the blood, moreover, partly free and partly com-
bined. Carbonic acid, which is introduced into the economy in but small
amount from without, is the most important end-product of many chemical
mutation series in the body. It leaves the latter in large quantities
through the lungs, and to a small extent with the exhalations of the skin.

§40.
Water, H30 .

No inorganic compound is of such great importance for the existence
of the organism, or occurs throughout all its parts in such abundance, as
water : without it life is impossible. Setting aside that which occurs in
hydrates and in crystals, water is necessary to the organism, in the first
place, as a solvent for many of its constituents. By virtue of this property
it renders an interchange of material possible. Dissolved in water, the
alimentary matters are absorbed into blood and tissues, and by it effete
substances are carried out of the body. In the preceding section we have
already alluded to its power of absorbing gases.

The proportion of water to the whole weight of the body is in general
very considerable ; in the higher animals at a period of maturity it is, on
an average, about 70 per cent., while in embryos it is still larger, ranging
from 87 to 90 per cent. In the infant and in younger animals its amount
gradually sinks, while that of solid organic and mineral matters undergoes
constant increase (Schlossberger, Bezold). That the proportion of water
in different parts of the body varies to an enormous extent is quite evident,

ELEMENTS OF COMPOSITION. 57

and will be alluded to later on more in detail. For the present it need
only be remarked that, as water, on the one hand, renders possible all
the chemical occurrences of the body by virtue of its solvent power, so,
on the other hand, does it communicate to each tissue its individual
stamp, from a physical or physiological point of view, as an imbibed mat-
ter. Its amount in the soft, semi-solid portions of our body appears dis-
proportionally large, but even in the harder structures, such as bone, it
is not inconsiderable.

Besides that which is generated within the body by oxydation from
the H of organic substances, water is introduced into the body with food,
both solid and liquid.

Hydrochloric Acid, C1H .

This acid is only found free in the gastric juice.

Silicic Acid or Silicon Dioxide, SiO, .

Very small quantities of silicic acid, either free or combined in salts,
have been met with in human blood (Millori), saliva, urine, bile, and
excrement, as well as in biliary and urinary calculi, bones, and teeth.
But of all the tissues of the human body, the hairs, according to Gorup-
Besanez, contain most of it.

Silicic acid is taken into the body with the food and drinking water,
and passes out of the same, for the most part, immediately through the
intestinal canal, while a portion of it is absorbed into the blood, and
appears later in the secretions of the various glands.

The physiological or anatomical significance of silica in the human
system is not known.

§11.

Calcium Compounds.

Lime, CaO, which next to soda is the most important inorganic base
of the body, presents itself in many different combinations.

PHOSPHATE OF CALCIUM.

Phosphoric acid occurs, as is well known, under various modifications,
of which, however, only the ordinary or tribasic acid appears in the
system. The following are its calcium salts : (a), Acid phosphate of
calcium, as it is called, CaH4P208; (b), Neutral phosphate, CaHP04; and
(c), Basic phosphate, Ca;iP208 .

Basic, Ca3P208, and neutral CaHP04, phosphates of calcium.

The first of these is almost insoluble in water, but to a certain extent
soluble in that containing carbonic or organic acids, as also in solutions
of ammonium salts, chloride of sodium, and of animal gelatin. It is, as we
have seen, the particular salt of calcium which occurs in the bones and
teeth, and probably exists besides widely distributed throughout the
animal body, while the acid salt is present in human urine.

Phosphate of calcium, which has its origin in general from the alimentary
matters, appears in very variable amount in all the solid arid fluid portions
of the system. Wherever it is present in large quantities it is the most
important hardening agent of the latter. Its deposits are almost always
amorphous.

Phosphate of calcium has been shown to exist in the blood, urine, gastric

58 MANUAL OF HISTOLOGY.

juice, saliva, semen, and milk, as well as in the juices of organs. Again,
it invariably accompanies histogenic substances, as has been already men-
tioned, and appears with the same in the tissues and fluids of our body.
It is present in bone in large quantities as the chief constituent of the
hard material of this tissue known as bone earth. But in the enamel of
the teeth, the hardest substance in the whole body, it exists in still
greater quantity.

Phosphate of calcium must be regarded as an indispensable element of the
tissues of the body ; we must, therefore, ascribe to it histogenic properties.

CARBONATE OF CALCIUM, CaC03 .

This, like the preceding salt, occurs in the amorphous condition as
hardening material in bones and teeth, but only in small amount. Be-
sides this, it is met with in some of the animal fluids, as, for instance,
the saliva, and in alkaline urine. It is also found in a crystalline form
in the internal ear of man, constituting what are known as otoliths. It
is met with more frequently still, however, in this state, in the bodies of
the lower vertebrates, as, for instance, in frogs, deposited upon the mem-
branes of the brain and spinal cord, and also on the anterior aspect of
the spinal column, about the place of exit of the spinal nerves.

Otoliths (fig. 37) are small crystals of short, thick, columnar form, com-
binations of rhombohedrons and hexagonal prisms in their fundamental
figure ; among them may also be found pure rhombohedrons, or scaleno-
hedrons.

The question as to what it is that retains carbonate of calcium in solution
in the fluids of the body, has not yet been answered satisfactorily. It
seems probable, however, that the carbonic acid diffused through the latter
is the real solvent for the salt. Any other physiological purpose besides

that of a hardening medium of the
second class, has not as yet been
recognised for carbonate of calcium as
it appears in the bodies of the higher
animals.

Carbonate of calcium is partly taken
up as such from without, and is partly
formed in the body by the develop-
ment of carbonic acid as a decom-
position product (see above).
^f^ar * ^HX

CHLORIDE OF CALCIUM, CaCl2 .

Is of but subordinate significance,

Fig. 37. — Otolithsconsistingofcarbonateof calcium, n^^ has as Vet been met with in

the gastric juice only (Braconnot).

FLUORIDE OF CALCIUM, CaFL2.

This salt is found in the enamel of the teeth and in small quantities in
bone also ; traces of it are also met with in the blood, milk, and urine,
saliva, and bile, and in the hairs (Nickles). Fluoride of calcium is
taken up from without as such.

§42.

Magnesium Compounds.
Magnesium appears under similar circumstances, combined with phos-

^

ELEMENTS OF COMPOSITION. 59

phoric acid, like calcium, mentioned in the preceding section. Its amount,
however, is everywhere smaller than that of calcium.

PHOSPHATE OF MAGNESIUM, Mg3P208 + 5H20, or MgHP04 + 7H20 .

We are not yet able to state which of these two salts it is which occurs
in the body. — Like phosphate of calcium, the corresponding combination of
magnesium is met with in all the fluids and solid portions of the body. — It
is one of the hardening constituents of bones and the teeth, but only in
a minor degree. The preponderance of phosphate of magnesium over the
corresponding salt of calcium in muscle and the thymus gland (Liehig) is of
interest. It is taken up as such from without, and is offered to the body
in superabundance by a vegetable diet, so that the greater part of all that
is received into the body passes through the intestinal canal unabsorbed.

PHOSPHATE OF MAGNESIUM and AMMONIUM, MgNH4P04 + 6H20.

During putrefactive decomposition, or indeed with every generation
of ammonia in the system, the latter combines with phosphate of mag-
nesium to form a crystalline salt known as phosphate of magnesium and
ammonium. This salt (fig. 38) is found in crystals of rhomboid funda-
mental form, and appears most generally
in three-sided prisms bevelled at both
ends on one of their edges ; this form is
known as the "coffin-lid crystal." Further
varieties are produced by the bevelling of
two polar opposed angles, or finally of the
two remaining ones.

Crystals of phosphate of magnesium and Fig. 38.— Crystals of phosphate of mag-

• , v /» j • n i ,, nesium and ammonium.

ammonium are to be found in isecal matter,
alkaline urine, and all putrefying animal substances.

CARBONATE OF MAGNESIUM

Is of very minor importance in animal life. It is met with in the urine

2CO )
of the vegetable feeders, probably as a bicarbonate M TT > 04 also, per-

M811a )

haps, in bones. It is very difficult, namely, to determine whether it is
the carbonate or phosphate of magnesium that exists in the latter, however.

CHLORIDE OF MAGNESIUM, MgCl2 .
This salt is said to be present in the gastric juice.

§43.
Sodium Compounds.

While the lime compounds appear, as a class, to possess in part the
characters of hardening materials for the animal body, those of soda seem
entirely devoid of these qualities as far as we know. On the other hand,
however, they appear to play an important part in the chemical occur-
rences of the economy, although as yet we have not arrived at satisfactory
conclusions in regard to all their purposes. It has been mentioned before
(pp. 15-17) that soda is combined with the protein substances of the system,
and retains the latter in solution ; also that, combined with the two biliary
acids, it forms the most important constituents of the bile (pp. 40 and 41).

60

MANUAL OF HISTOLOGY.

CHLORIDE OF SODIUM,

This salt, which is soluble in water, never meets with an opportunity
for crystallization within the body, but may be found in crystals upon the
surface of the latter under certain circumstances. These crystals (fig. 39)
assume the form of dice, frequently marked with step-like depressions on
their surfaces, or may be met with in the form of square prisms. Mixed
with urea this salt crystallizes in the form of octahedrons, or, according
to G. Schmidt, in tetrahedrons also.

Chloride of sodium, or common salt, is to be found in all animal fluids,
and in all the solid parts of the body. Its amount in the juices is variable,
but seldom exceeds 0'5 per cent. The fluid which saturates muscle is
poorer than any in chloride of sodium. We see also, on the other hand,
that though the animal juices may be at one time supplied with a larger
quantity of the salt than at another, still the proportion in each fluid is
tolerably constant, the surplus passing rapidly out of the body with the
urine. The quantity of the substance in question is not less variable in the

solid portions of the system ; the blood-
cells are extremely poor, while cartilage
is rich in it. An extremely interesting
fact has been pointed out by Bidder and
Schmidt, namely, that starving animals
very soon cease to void chloride of sodium
in their urine, — an indication that it is
retained by the tissues and juices in the
most determined manner as an indispens-

O»^ | __l able ingredient in their composition.

jjv Some of the discoveries of pathology,

also, bear out this conclusion, showing,
as they do, that during the rapid forma-
tion of cells in exudations, the excretion
of salt with the urine almost ceases, and
that an extraordinary amount of chloride
of sodium is required for the plastic process (Heller, Redtenbacher). The
experiences we have gathered from observation of domestic animals may
also be alluded to here. In them the effect of a greater admixture of the
salt in question with their food may be seen in the way it favours the
whole process of assimilation (Boussingault).

All these facts seem to point to the conclusion, that chloride of sodium
must be regarded as possessing the nature not only of an aliment, but also
of a histogenic ingredient of animal tissue. But as to all the purposes
in detail for which it exists in the body, we still possess but a scanty
knowledge of them.

CARBONATE OP SODIUM, Na2C03, and NaHC03 .

Carbonate of sodium (the simple as well as the bicarbonate) appears very
often in the products of the incineration of animal matters. It cannot
be regarded as anything more than a calcination product in this case.

It is, however, present in several alkaline fluids, as, for instance, in
blood, lymph, and the urine of vegetable feeders. In the blood it is the
bearer of carbonic acid, and elsewhere the solvent for different protein
substances.

Fig. 39,

-Different crystalline forms of
chloride of sodium.

ELEMENTS OF COMPOSITION. 61

PHOSPHATE OF SODIUM, Na2HP04, and NaHJPO4.

Like potassium, to be alluded to presently, sodium forms three combina-
tions with phosphoric acid, namely, basic phosphate of sodium, Na3P04 ;
neutral phosphate of sodium, with two atoms of base, Na.2HP04; and an
acid salt with one atom of base NaH2P04. The first of these probably
does not occur in the system, so that we have only to deal with the two
last. Of these the neutral salt is the most common.

Phosphate of sodium is widely met with throughout the body. It has
been found in the blood, the milk, the bile, the urine, and in the tissues.
It is, perhaps, the bearer of the carbonic acid of respiration, and is, pro-
bably, the solvent for many matters, as, for instance, casein and uric acid.
It probably plays an important part, also, in the formation of tissues,
which is not yet fully understood.

SULPHATE OP SODIUM, ETaaS04 .

Like the sulphates of the alkalies generally, this salt is found in animal
fluids, especially in urine, and in* the excrements. In some of the most
important secretions, however, it is not met with, as, for instance, in the
gastric juice, the bile, and the milk. Like other sulphates, it cannot be
said to possess any histogenic properties, but rather those of a decomposi-
tion product, the sulphur of the protein compounds and allied substances,
forming sulphuric acid by oxidation, and displacing the carbonic acid of
the soda salt.

In confirmation of what we have just stated, the facts may be adduced —
first, that sulphates introduced into the body are rapidly excreted, and
on the other hand, that after an abundant fleshy diet their amount in the
urine increases (Lehmann) ; secondly, that the sulphur of taurin, as
already mentioned (see above, p. 49), is set free under the action of.
ferments in the form of sulphurous acid which becomes subsequently con-
verted into sulphuric acid by oxidation (Buchner).

§44.
Potassium Compounds.

These are of subordinate importance in the human economy, which
fact may to a certain extent depend upon the nature of our food. Among
the vegetable feeders, however, the serum of the blood still shows a pre-
ponderance of soda salts, and soda is also the base in their bile. But in
many other portions of the system we find the most remarkable prepon-
derance of potassium salts over those of sodium.

CHLORIDE OP POTASSIUM, KC1 .

This compound is found together with common salt in animal fluids; in
smaller quantity in man than in phytophagous animals. Its amount in
the blood cells is however large (C. Schmidt], and in the juice of muscle
it replaces chloride of sodium (Liebig). ,

CARBONATE OF POTASSIUM, K2C03.

Probably occurs with carbonate of sodium in some of the animal fluids,
and in the urine of vegetable feeders in all probability as bicarbonate,
KHC03.

PHOSPHATE OF POTASSIUM, KH2P04, or K,HP04 .

It is not yet decided in what form of combination with potassium ordi-

62 MANUAL OF HISTOLOGY.

nary phosphoric acid occurs in the body, whether as an acid salt with one
atom of base and two molecules of water, or a neutral as it is called, in
which two atoms of base go to one molecule of water. The salt is met
with in the juice of muscle (Liebig).

SULPHATE OF POTASSIUM, K2S04.

Appears in the body, probably, with the corresponding salt of sodium
and under similar circumstances.

Ammonium Salts.

The physiological processes of the body are attended by but a compara-
tively small development of ammonia, so that in this respect they may be
said to offer a contrast to putrefactive decomposition. The combinations
of ammonium in the body are probably of various kinds ] for the present,
however, we are unable to enter into them very fully.

CHLORIDE OF AMMONIUM, KH4C1 .

It is still an undecided question how far this or the carbonate appear
in the economy.

CARBONATE OF AMMONIUM.

Is found in expired air, in decomposed urine, in blood, in the lymphatic
glands and blood-vascular glands. The combinations which are here met

2CO )
with are the sesquicarbonate /-M-TT \ TT > 04, and bicarbonate NH4.HC03.

Iron, Fe, and its Salts.

This metal is extensively distributed throughout the body, and occurs
probably in all its parts. It is met with in various forms also, being sup-
plied to the system in great abundance with the food.

In some way not very fully understood at present, iron enters into the
composition of the most important of all animal colouring matters, haemo-
globin (p. 18). Uroerythrin and melanin also contain iron (p. 52).

PROTOCHLORIDE OF IRON, FeCl2 .

This salt is said by Braconnot to be present in the gastric juice of
dogs.

PHOSPHATE OF IRON, Fe2P208 .

Another compound of iron generally accepted, though perhaps on in-
sufficient grounds, as occurring in the living body.

In regard to the presence of iron one thing is certain, namely, that all
portions of the body supplied with blood must contain it. It has also
been found in chyle, lymph, urine, sweat, bile, and milk, and finally in
hair, cartilage, and other solid tissues.

Manganese, Mn.

This metal is introduced into the system in company with iron, and is
met with here in minute quantity. It seems to be merely an accidental
constituent. It is found in hair, and in biliary and urinary calculi.

Copper, Cu.

Copper has been noticed in the blood, bile, and biliary calculi of man.
It is excreted by the liver.

2. ELEMENTS OF STRUCTURE,

A. The Cell.

§45.

THOSE anatomists of recent times who seek with the assistance of our
improved microscopes an insight into the minute structure of the human
and animal body, have all arrived at this conclusion, however widely
their other scientific views may differ, that " the cell," cellula, is the most
important of all the structural or form-elements of the system. This fact,
although surmised by earlier observers, who recognised the structure in
question under the name of "vesicle," was first firmly established by
Schwann. Following up Schleideris discoveries in vegetable anatomy, he
showed the cell to be the starting-point, in the broadest meaning of the
term, of the animal body (see above, p. 4). This is the greatest discovery
ever made by the aid of the microscope.

Present-day investigation tends more and more to confirm the correct-
ness of this proposition of Schwann, that the cell alone, and by itself,
must be regarded as the primordial structural element of our frame, and
that all the various other elementary parts to be found in the mature body
are originally derived from the cell.

The first point, then, to be attended to here is, to obtain a correct im-
pression of what is meant' by a " cell," and what by a " structural
element."

By " form constituents," " form elements," " elementary parts," or
" structural elements," we do not by any means understand (as might be
incorrectly inferred from the terms) the smallest particles of the body re-
cognisable by the microscope in the shape of granules, vesicles, or crystals.
A form-element is rather the last, or— contemplating the subject from
another point of view, the first — anatomical unit : a combination of the
most minute particles to form the smallest organic apparatus. Struc-
tural elements are the first representatives
of organic activity; they are, consequently,
physiological as well as anatomical units ;
they are "LIVING THINGS."

But what is the cell? This question
cannot be answered in a word, but re-
quires to be met with a somewhat detailed
description.

The cell (fig. 40) is a microscopically
small, primarily spheroidal body, which
often assumes, however, other forms, and which consists of a soft mass

c—

Fig. 40. — Two cells of round or oval form.
a a, border of the cell ; 6 6, cell body ;
c c, nuclei with nucleoli, d d.

64 MANUAL OF HISTOLOGY.

including within it a peculiar structure. These parts require special
names. The soft substance mentioned is known as the cell-substance or
cell-body (b b), the central structure enclosed within it as the nucleus
(c c), and a minute dot-like particle situated within the latter again as the
nucleolus (d d).

The external boundary of the cell (a a) is in certain cases formed by
the soft mass alluded to, or more frequently by a somewhat hardened
stratum, the enveloping or cortical layer, or, finally, by a distinct indepen-
dent pellicle separable from the cell-body, and known as the cell-mem-
brane.

In regard to the latter, the views entertained respecting the animal cell
have latterly undergone considerable change through the results of recent
investigation. The presence of a special membrane was formerly con-
sidered necessary (Schwann) to the conception of a true cell; but the
frequent absence of this envelope and its relatively small physiological
significance has been since recognised (Schultze, Briicke, Beale).

]3ut although its anatomical characters offer us the first and most
important points in the definition of the cell, its physiological properties
cannot be overlooked. By these the cell is constituted a living structure,
endowed with special energies and the peculiarities of active vitality; with
the power of absorption of matter, of transforming the same, and of excre-
tion ; with the capability of growth, of change of form, and of cohesion or
fusion with similar organisms. The cell possesses further, undeniably —
although there may be a variety of opinion as regards the extent of these
powers in individual cases — the capability of vital motion, as well as of
proliferation, or the generation of a progeny. The cell, we repeat it, is
the earliest physiological unit, the first physiological apparatus : it has
been called an "elementary organism" with propriety.

One of the most important facts established by recent scientific
investigation is, that that mass from which the bodies of all the higher
animals take their origin, namely, the ovum, has entirely the nature of a
cell, so that, consequently, each such animal body, be it ever so complex
in constitution, once consisted of one single cell. While in this respect
the- latter must be regarded as the starting-point of animal life, naturalists
again have brought to light creatures of such simple organisation that
their whole body is formed of nothing more than one independent cell, and
whose whole existence is included within the narrow circle of cell-activity.
Among such may be reckoned those animals known as gregarines.
Finally, single-celled plants have been discovered by botanists, as single-
celled animals by anatomists : and even still more rudimentary organisms
have been met with.

REMARKS. — Compare the work of this author, " Mikroscopische Untersuchungen
iiber die Ubereinstimmung in der Struktur and dem Wachsthum der Thiere und
Pflanzen ;" also L. Beale, "The Structure of the Simple Tissues of the Human Body,"
Lond. 1861. But is the cell the simplest "elementary organism,'' i.e., the simplest
structure which can meet all the requirements of the lowest grade of life ? This
question may be negatived. An excellent observer, E. HdcTcel (Generelle Morphologic,
Band 1, s. 269, Berlin, 1866 ; and Biologische Studien, Heit 1, s. 77, Leipzig,
1870), has shown that a particle of protoplasm, or "cytode," as he terms it, suffices
for this. It is only subsequently, after the generation of a nucleus that the whole
becomes a cell. It is, nevertheless, a deeply significant fact, that the building
stones of the bodies of higher animals are never represented by "cytodes," but
always by cells.

ELEMENTS OF STEUCTURE. 65

§46.

Turning now to the more detailed analysis of cells, the first point to be
borne in mind is, that the latter, in the earlier portions of their existence,
manifest a certain amount of uniformity, whether as the cells of young
embryos or those of later life. Again, that in the course of further
development they may assume, as mature and senescent structures, the
most diverse shapes, as well as acquire an entirely different body, so that
they not unfrequently take on an appearance which may remove them
very far, nay, even so far as to be unrecognisable from the plan of a cell,
given in the foregoing section.

1. Directing our attention, then, in the first place, to the size of cells, we
find them, in the human body as well as almost everywhere in the animal
kingdom, to be within microscopic measurement. The smallest, such as
we find, for instance, among the blood-corpuscles, have a diameter of only
0 '006-0 '007 mm. (millimeters), while the largest typical cell of our body,
namely, the ovum, may attain a breadth of more than 0'23 mm. Between
these extremes the greater number of cells range in diameter from O'Ol 1
to 0 '02 3 mm. Those of 0-07-0-115 mm., such as occur, for instance, in fat
and nerve tissue, must be looked upon as very large. Thus we observe
that the most important structural element of our body is of remarkable
minuteness, as usually met with.

2. If we next turn to the shape of the cell, we are struck likewise with
its extreme variability. The fundamental form (fig. 40) is, however,
spherical or spheroidal.

From this primary form two others, easily derived, are produced by
compression and flattening in two opposite directions ; these are the
flattened and the tall narrow cell.

Flattened cells springing from the spherical primary form by compres-
sion are met with, in the first place (fig. 41), as disks, such as may be
seen in human and mammalian blood-corpuscles ; or they may become,
by a further increase of superficial extent, flat or scaly structures (fig. 42)
such as those, for instance, of the epithelium of many parts of the body.

c

Fip. 41 — Diskoid cells of human Fig. 42.— Flattened scaly epithelium cells
blood, a, a, a. At 6, half side ' from the human mouth,

view ; close by at d, colourless
corpuscle.

That there may exist every gradation between flattened cells and the
spheroidal species appears self-evident, and needs no farther comment.

If the elements in question undergo, on the other hand, lateral com-
pression, the resulting form may be either more or less cylindrical or
conical, and the tall narrow cell is produced (fig. -43). We shall see later
on, in our consideration of the several tissues, that many modifications of

66

MANUAL OF HISTOLOGY.

this figure may appear. The fusiform cell may be regarded as one of
these; besides being narrowed, it is fined off" at either end to a point
(fig. 44).

The fusiform cell usually gives off at either end a thread-like process ;
but such filaments may occur in greater number in many animal cells,
and on their part undergo further ramification. It is in this way that
the stellate cell (fig. 45) is produced — one of the most remarkable forms
in which the structure in question can meet the .eye.

Fig. 43.— Tall, narrow
cells, as found in
what is known as
cylinder or columnar
epithelium.

Fig. 44.— Fusiform cells
from immature con-
nective tissue.

r. 45.— Stellate cell
from a lymphatic
gland.

3. But far more important than either shape or size is the substance of
the cell-body : in this the greatest variety is observed.

Let us, take in the first place, young cells (fig. 46) : here we perceive
that the body is made up of a more or less soft, usually viscid and slimy
mass, containing in a transparent cementing medium a variable amount
of albuminous and fatty granules (a-g). This primordial cell-substance
is known at the present day by the name protoplasm (Remak and
Schvltze) borrowed from botany. It has also received from Beale,
Koelliker, and Dnjardin respectively, the names bioplasm, cytoplasm,
and sarcode. The chemical peculiarities of this proto-
plasm have been already referred to in § 1 2, and we
shall be obliged presently to enter somewhat minutely
upon the consideration of its vital properties. It will
suffice to remark here, that it consists of an extremely
unstable albuminous compound, insoluble in water, but
which becomes gelatinous (or in some instances shrinks)
on imbibition of the latter : it coagulates further at a
low temperature and at death, so that only by the most
careful manipulation can it be examined in a normal
condition under the microscope.

The amount of this protoplasm with which the nucleus
is enveloped is very variable, and consequently the size
and general appearance of cells. Our woodcut repre-
sents from a to d elements with a medium amount of
this substance; e, a larger proportion. Other cells are
observed to possess but a very small quantity of pro-
toplasm, as / and g, without having lost the capability,
however, of increasing in substance and subsequently
fulfilling all the purposes for which cells in general are
designed. As far as we know at present, a cell can never again be
formed from a nucleus which has quite lost its protoplasm.

But if we turn now to mature or senescent cells, we frequently find
that the protoplasm of an earlier period of existence is replaced by

Fig. 46. — Different
kinds of cells with
nuclei and proto-
plasm ; lialf dia-
grammatic.

ELEMENTS OF STRUCTUKE.

67

matters of completely different characters; thus the body of the blood-
corpuscle is found to be made up of a transparent yellow gelatinous sub-
stance (fig. 47); in old scaly cells also, such as are met with on the
surface of many mucous membranes (fig. 48), the protoplasm is replaced

Fig. 47. — Human blood-corpusclea.

Fig. 48.— Old epithelium cells from the
human mouth.

by a hard substance, poor in water, and almost destitute of granular matter,
— a metamorphosed albuminous material, to which the name of keratin
has been given.

Such cells, however, as those in both instances cited, are no longer
capable of supporting a prolonged existence, they have lost their active
vitality with their protoplasm.

Again, there are cells still more fre-
quently met with which contain other
substances as formed deposits in their pro-
toplasm (fig. 49).

Setting aside for the present those cells
into whose bodies foreign matters, such as
granules of carmine (a), or blood-corpuscles
and fragments of the same (&), have pene-
trated from without (remarkable objects Fig> 49._Cel]s ^deposits of foreign
which will be considered at greater length
presently), we frequently meet with globules
and drops of neutral fats laid down in the
original cell-mass (d), which may gradually
coalesce, supplanting the protoplasm until
but a small remainder of it is left. Besides
such fatty matters, molecules of brown
biliary pigment are to be seen in other cells, as, for instance, in those
of the liver (c).

Cells also which have become the receptacles of 9 melanin granules
(p. 52) present the most peculiar appearance. This pigment may be pre-
sent in such abundance that the whole body of the cell becomes black
throughout (fig. 50). The occurrence of crystals in the interior of animal
cells is less frequent. They are, however, to be met with as acicular for-
mations, already alluded to (p. 27), and appear in the interior of fat cells
on the post mortem cooling of corpses, within the membranes of the
former (fig. 51). But while the appearance of these is by no means rare,
there are other crystalline deposits which are only encountered in minute
quantity, and under abnormal pathological conditions. Matters which
assume the crystalline form in such watery solutions as exist in the animal
economy, must be regarded generally as unfitted to take part in the con-

matter in their protoplasm (half dia-
grammatic), a, a lymph corpuscle with
granules of carmine imbedded in it;
6, another of the same, with included
blood-cells and fragments of the latter
c, an hepatic cell, containing fat globules
and granules of biliary pigments; rf,
a cell with fat globules and distinct
membrane; e, another, with granulesof
melanin.

68 MANUAL OF HISTOLOGY.

struction of tissues. The rarity of crystals as cell-contents is thus
explained by this law, as it may be called, to which, with all the varie-

Rg. 50.— Stellate cells containing black Fig. 51.— a b. Crystals of margarin; c,

pigment. the same contained within fat cells;

of, a cell from adipose tissue destitute
of crystals.

ties of cells in the different groups of the animal kingdom, there are but
few exceptions.

§47.

Among the further characteristics of the animal cell there now only
remains for our consideration the envelope and nucleus.

4. The envelope. It has been already remarked that the protoplasm
at the surface of the cell rarely remains so soft as in the interior. In
general terms it may be stated that a hardening of the non-granular or
free periphery of the cell usually takes place by contact with surrounding
media (enveloping or cortical layer of protoplasm). This hardening is
certainly, in numbers of cases, exceedingly slight, so that it is only to be
recognised by the sharper outline of the cell: it can also be easily overcome,
and softening again brought about by the very brief action of external
agencies. In other cases, however, it is greater ; the transparent, tough
layer increases in thickness, and may be brought into view as distinctly
separable from the richly granular protoplasm of the interior, by the action
of water and other reagents.

It is such appearances that have been over and over again accepted as
proofs of the existence of cell-membranes, especially when, through a rent
in the cortical layer, the contents have been observed to protrude. And
in fact, this hardened peripheral layer of protoplasm does lead us on to
the cell-membrane as it becomes gradually more and more independent,
and assumes different chemical properties.

But no one is able to define where this cortical layer of protoplasm
ends, and where the membrane of the cell begins — a point essayed on all
sides in the case of animal cells at an earlier period of histological study.

Occasionally, at some distance from the shrunken cell-body such a
covering with double contour may be recognised (fig. 49, d). But its
presence cannot be doubted for an instant, when, either mechanically,
as, for instance, by rupture and squeezing out of the contents, or by
chemical reagents which dissolve the latter, the membrane is successfully
isolated. Those fat-cells already mentioned (fig. 51, a) allow of the fluid
fat (b) being pressed out in drops, when such a membrane (c) becomes
recognisable. The same may be seen when the contents have been

ELEMENTS OF STRUCTURE.

G9

Fig. 5-J.

extracted by alcohol. These membranes exist in many cellular formations
of the body beyond question. Their purposes appear
chiefly anatomical, in that the consistence requisite for
many animal tissues is, as we know by experience, greater
than could be yielded by the soft protoplasm of the cell-
body alone.

Where, however, the individual cells are widely
separated by considerable quantities of solid intermedi-
ate substance, or where just the reverse is the case,
and they are suspended in a liquid, forming a fluid-
tissue, this membrane is probably absent as a rule,
Such cells are those of dentine tissue and of bone, as
also the cellular elements of the blood, the lymph, and
the liver (fig. 52).

The membranes of cells are usually transparent, and, as far as we can
see with our present optical instruments, structureless and without open-
ings or pores. Attention has, however, been lately directed to certain cells
in which pores may be distinguished by means of the microscope — a cir-
cumstance into which we shall have to examine more closely further on.

It is probable, also, that in isolated cases this cortical layer or envelope
covers only certain portions of the body of the cell.

As a rule, we find the demarcation of a cell such that a smooth contour
encloses the figure ; but it may happen that the
granular contents produce a rugged appearance on
the surface, which leads us involuntarily to the dis-
tinction between smooth edged and granulated cells
(fig. 53, a d). Both of these differences are, how
ever, of minor importance. Again, owing to a par-
tial exit of the matter contained within, the cell,
which had been up to that time perfectly smooth,

. *, , , ..r

may assume a wrinkled appearance ; while, on the

other hand, the reverse may take place with a

granulated cell through the imbibition of water ; it may swell out and

become a smooth rounded object.

Attention has lately been directed by M. Schultze
to a remarkable appearance in the borders of young
cells, and especially those of flat epithelium ; their
surface, namely, is completely covered with points,
ridges, and prickles, as they might be named (fig.
54), which fit in among those of the neighbouring
cells "like the bristles of two brushes which have
been pressed against one another." The appropriate
name of " spinous and furrowed " cells has been
given to these.

5. If we now turn to the analyses of the nucleus,
with its adjuncts, we meet with a certain vari-
ability in it likewise. First, the difference in size
of the various animal cells brings with it very con-
siderable fluctuation in the diameter of the nucleus ;
proportionately less, of course, than that of the
cell itself. We may accept O'OOl 1-0-075 mm. as
a medium diameter for the nuclei of animal cells ;
but at the same time, it must be borne in mind that some may be found

t 6 c, Smooth-eaged
diskoid blood - corpuscles,
with one granulated white
cell (d) whose nucleus is ob-
scured.

Fig. 54.— Spinous or far-
rowed cells, o, from the
undermost layers of the
human epidermis; b. a
cell from a papillary
tumour of the human
tongue (copied from
Schultze.)

70

MANUAL OF HISTOLOGY.

much smaller, even down to 0'006 mm., and less, whilsb other cells again

possess nuclei whose diameter may reach
0-023-0-045 mm. The position of this
nucleus in the animal cell is at one time
central, at another excentric.

The fundamental form of the object
under consideration, as it is met with in
the earliest formative cells of embryonic
tissue, and frequently enough in those
of more mature parts of the body, appears

nucleus'atd'^Th'e nuclei themselves"lie to be that of a Vesicular body approach-
excentricintnebodyof thecell,*. ing ^ spherical figure (fig> ^ ^ ^

more or less fluid, and, it may be added, homogeneous, transparent con-
tents and strong cortex, which latter shows, under the strongest micro-
scopes of the present day, a double contour as optical
expression of its thickness. Thus we see that the nucleus
possesses an analogous structure to the cell, which is
endowed with a membrane, and one of whose components
it is.

In the interior of this hollow nucleus, or, as it has been
named, nuclear utricle, or vesicle, may be discovered, single
or double, a roundish formation, almost a mere speck on
account of its minuteness: this is the nucleolus already
mentioned (d d).

This fundamental form, however, of the nucleus is fre-
quently enough exchanged subsequently for another, alter-
Fig.56.— TWO ceils ing thus its original appearauce, although the variations
muscieTi?"!the of tne nucleus may be stated as a rule to be less in propor-
rod-iike homoge- tion than those of the cell itself. We find, for instance,
cleL in turning to the consideration of some of these changes
of figure, that it may become elongated, as in those cells which enter into
the composition of unstriped muscle (fig. 56, It), or diskoid, as seen in the
tissue of nail (fig. 57). Ramifications of nuclei have also been met with
in certain cells of lower organism, but not as yet in those of the human
body.

Fig. 57.— Cells of nail
tissue, a a, view from
above, with the granu-
lar nucleus; b b, side
view of the cell, with
the flattened levelled
nucleus.

Fig. 58.— Flat epithelial cells, with
completely homogeneous smooth-
edged nuclei.

On the other hand, the nucleus may exchange the original vesicular
condition of an earlier period for solid contents, as is the case, for instance,
in the superficial epithelial cells of the mouth (fig. 58), or for perfect
homogeneity, so that even the envelope of the nucleus is no longer to be

ELEMENTS OF STKUCTUEE.

71

Fig. 59.— Two blood-
cells of the frog,
a 6, with granular
nuclei, as they pre-
sent themselves af-
ter treatment with
water.

distinguished. This latter form is seen in the cells of involuntary muscle
just mentioned (fig. 56, Z>). In such cases the nucleoli
are frequently invisible.

It often occurs also that elementary granules are laid
down in the nucleus, giving to it, when in large quanti-
ties, a rugged appearance, and precluding the possibility,
further, of the nucleolus being distinguished. It is thus
that the so-called granular nuclei have their origin.
Again, there are cells whose nuclei may be obscured by
an enveloping drop of oil. The former may be seen on
treating the blood-corpuscles of the lower vertebrates with
water (fig. 59), while the latter are of frequent occurrence among certain
cartilage cells.

It is not always that we are able to make out the object in question in
the interior of animal cells : it is often hidden from view, as for instance,
in the living cell. We have already men-
tioned in a previous section that a rich de-
posit of elementary granules also, or pig-
ment molecules, may obscure the nucleus
(fig. 60). The same may be the case if the
cell-body be occupied by a quantity of fatty
matter; but very close scrutiny will always
reveal the nucleus to the observer after
a time. On the other hand, there are cells
in which such a covering up of the
nucleus cannot be thought of, in which
the contents appear perfectly clear, and
yet in which we can by no means in our
power render the nucleus visible. The
coloured blood-corpuscles of mature mammalia and human beings belong
to "this category (fig. 61); likewise the cells of the more superficial layers
of the epidermis which clothes the external sur-
face of the human body (fig. 62). But of both
these we know that they possesssed nuclei at an
earlier embryonic period. There are, consequently,
certain cells in our system whose nuclei disap-
pear usually at some period of their existence.
We may also remark here and there in tissues
whose cells are as a rule destined to retain their
nuclei for the whole life of the animal to whose
body they belong, an isolated cell without a nucleus among its complete
companions; but it must be looked upon as a rare anomaly. All such
non-nucleated cells are moreover incapable of
existing for any length of time, and are simply
on their way to dissolution as far as we know
at present.

In contrast to the kind of cell just men-
tioned, we meet with others in which two or
even a greater number of nuclei exist. The
first case (fig. 63) is seen with comparative
frequency, and in very dissimilar tissues:
cells with many nuclei are rare, and found principally in the medulla
of bones, where they may contain ten, twenty, or even forty nuclei, and

Fig. 60.— Stellate cells filled with black
pigment. In two of the same we can
recognise the nucleus, but in the third
the latter is hidden by the quantity of
melanin granules contained in the cell-
body.

Fig. 61. — Coloured human
blood-corpuscles, a be.

Fig. 62.

-Epidermis cells without
nuclei.

72

MANUAL OF HISTOLOGY.

Fig. 63.— Cells with
double nuclei, a,
from the liver; 6,
from the choroidea
of the eye ; c, from
a ganglion.

at times attain enormous proportions (fig. 64). Such conditions are in-
variably coincident with a process of proliferation in
the cell, and will be treated of more minutely when
discussing the latter. We must distinguish this truly
double or multiple nucleus from another deceptive ap-
pearance of two or several more in one animal cell.
There are, namely, cellular formations in various fluids
of the system, as in the blood (the white or colourless
blood-corpuscles) lymph, chyle, mucus, pus, &c. — we
will call them lymplioid cells — which contain originally
a simple nucleus ; which when mature may often, under
the action of reagents, such as dilute acids, for instance,
be made to break up into several pieces, so that the ob-
server is deceived into the belief that he has before him
cells with several nuclei.

The question as to whether the body and nucleus of

the cell possess any further finer texture, cannot at present be answered

with certainty.

§48.

Turning now to the chemical constitution of the animal cell, we find
ourselves entering upon a field of histochemical inquiry of which little is
known : here more than elsewhere does microscopical
research in the investigation of the elements of form
appear to be far in advance of chemical analysis.
In order to follow up this line of inquiry with any
hope of success, we should be able to separate the
cell from its surroundings, i.e., from elements of
tissue; to take it asunder, or resolve it into its
various parts, i.e., inucleus, cell-body, membrane,
and subject these separately to chemical analysis.
Unfortunately this is for the present impossible,
and thus the existence of a great gap in our know-
ledge is more than sufficiently explained.

We are in general only able to state so much;
that the still very obscure group of protein com-
pounds or albuminous principles, with its numerous
members and modifications, with certain of the his-
togenic descendants of the latter, play the chief
part in the constitution of the animal ce41.

Besides these, as in all other parts of the system,
we find as further constituents, water, and moreover
usually in considerable amount; also certain mineral
matters, and probably also everywhere fats.

But though, after what has just been remarked, we
may look on the protein matters, and their immediate derivatives, as those
substances from which the materials for the production of the animal
cell are derived, chemical investigation teaches, on the other hand, that the
various parts of the latter must be composed of modifications of these, in
that nucleus, cell-body, and membrane (when the latter is present) gener-
ally display different reactions. Not unfrequently we are obliged to oivn
our knowledge of the composition of animal cells as comprehended in
these few and general propositions only. In some other cases, however,

Fig. 64. — Multinuclear
" giant-cells " from the
medulla of the new-born
infant

ELEMENTS OF STRUCTUltE. 73

and under favourable circumstances, it is possible to penetrate somewhat
more deeply into the chemical constitu-
tion of these most important of the ele-
ments of form.

Let us first, then, inquire into the
constitution of the cell-body. We have
already seen in one of the preceding sec-
tions that this is originally formed of
protoplasm. In speaking of the latter *'

we described it as a tough, viscid, or **

. , , , ' , • /• i« Fi£- 65. — Lymphoid cells, 1-4, nn-

niUCOld Substance, consisting OI a peculiar changed; 5, the nucleus and mem-

albuminous compound, which coagulates ^^SB** S&F*l VB

at death, and also when heated up to a cer- and ii; 12, it has broken up into six.
tain point; which becomes further swollen pieces; 13) fre
up or gelatinised by the action of water, but not dissolved. This is
about all we know, at present of this important compound protoplasm.
The granules which lie embedded in the homogeneous substances of the
latter in greater or less quantity, consist partly of coagulated albuminous
matters, partly of neutral parts, and more rarely of pigments, especially
melanin. That mineral constituents are also present need hardly be
remarked.

In many cells the protoplasm is transformed gradually into various
other modifications of the protein compounds. Thus, instead of it the
mature blood-corpuscle is composed of watery haemoglobin, the formative
cell of the fibres of the lens likewise of an albuminoid known as globulin.
Other cells again contain mucin or allied substances, as for instance colloid,
and it often occurs that the original cell-body is converted by a loss
of water into one of the more solid modifications of the albuminoid
group, for instance into keratin, found in the older cells of epidermis
and nail tissue, &c. However imperfect our knowledge at present may
be, it must still be considered of importance to know for certain that
those more remote descendants of the albuminoids, as we meet them, for
instance, in glutin and elastin (§ 15)., never form the proper body of an
animal cell.

Ferments, also, are probably of frequent occurrence in the bodies of cells.
Thus we find minute molecules of pepsin e in the protoplasm of the glan-
dular cells of the stomach, and allied matters in the elements of the in-
testinal glands.

We have also hydrocarbons presented to us in hepatic cells in the form
of granules of glycogen (§ 16).

Deposits of neutral fats are likewise of extremely common occurrence
here. Granules and globules appear at first in the various kinds of cell-
substance, gradually forming in seme cases large drops, which may eventu-
all}r displace almost the whole of the latter. And although it cannot be
doubted that most of these fatty compounds are taken up into the body of
the cell from without, it must still be regarded as extremely probable that
a formation of fat can be brought about in the cell itself by the splitting
up of its proper albuminous body.

With the exception of the salts of lime, formed deposits of inorganic
substances do not occur in the bodies of cells.

In turning now to the consideration of the chemical constitution of the
surface of the cell, we must remember that very generally the enveloping
layer of protoplasm has been hardened, now more, now less, through con-

74 MANUAL OF HISTOLOGY.

tact with surrounding substances. As to the composition of this layer, as
to its difference as compared to the softer protoplasm within, we know at
present nothing. Its power of resisting the action of reagents, such as
acids and alkalies, is for the most part very limited.

Further metamorphosis of this superficial layer leads on through in-
termediate stages to the formation of the proper " cell wall." This
appears to possess a far greater power of resistance, in that the albu-
minous matter of the cortical layer has been converted into a substance,
which in its whole demeanour as regards various reagents, and in its im-
mutability, manifests a strong resemblance to, if not accordance with,
elastin. Even years ago it was asserted by Donders, that the membranes
of all animal cells consisted of elastin ; and although this expression of
that most excellent observer may be somewhat exaggerated, nevertheless
the capability of changing into a cell membrane possessed by the cortical
layer of protoplasm, gives support to the proposition that elastic matter
(elastin) may take its rise from the protein substances, although the
minutiae of the process of transition are not yet known.

Passing on, finally, to the constitution of the nucleus, we have to dis-
tinguish between the envelope and contents of this originally vesicular
body. The contents, formed of a pellucid fluid, appear to be composed of
some soluble modification of protein matter ; for we can frequently pro-
duce a precipitate of small granules in it, by the action of alcohol, acids,
&c., as, for instance, in the nuclei of ganglion cells, and that of the
ovum. The envelope consists comparatively seldom of matter which
does not resist the action of acetic and other allied acids, as, for instance,
in the nuclei of the cells just mentioned. Usually — and this is the
means for the recognition and distinguishing of the nucleus, long in use
empirically among histologists — the envelope of the latter and the
remaining substance is not acted on by such acids. JSTow, although the
substances in question correspond in the last respect with the elastic
material of many cell-membranes, they yet differ from them most dis-
tinctly in their greater or less degree of solubility in alkalies. This has
been very properly pointed out by Kpllilter to be a distinguishing feature
between the nucleus and membrane of the cell.

The chemical transformations which the nucleus undergoes during the
life of the cell are manifold, as, for instance, when it becomes solid, or
exchanges its vesicular nature for a granular one. The tendency, further,
of certain nuclei to deposit fats round about themselves is very striking,
a process which can go so far that, as is the case in certain cartilage
cells, finally, instead of a nucleus, nothing but a drop of oil can
be distinguished. It is also remarkable that pigments are seldom
seen in the nuclei of cells. Those of the epidermis of dark parts of
the skin, however, appear to be tinged by some brown colouring
matter.

The nudeolus, owing to its minuteness, has almost completely escaped
chemical investigation hitherto. It is supposed, from its refracting pro-
perties, to consist of fat.

Great uncertainty still prevails as to how far the products of the
decomposition of histogenic matters (already discussed in a former
section), which are found in the fluids saturating cellular tissue, are
originally constituents of the cell-body. It is also impossible to state,
even in the most favourable cases of simple cellular tissue, what products
of decomposition belong to the different parts of the cell, what to the

ELEMENTS OF STRUCTURE.

75

body, and what to the nucleus, as in the case of the hepatic and con-
tractile fibre-cells.

If, as would appear from all this, our knowledge of the composition of
the cell is very unsatisfactory from a qualitative point of view, how
much more so when we glance at it from the quantitative side of
chemistry ! In fact, we are unable to give the quantitative analysis of
any single form of cell in the body.

§49.

In regard to phenomena of vitality observed in cells, they would
appear, in the first place, to be of the vegetative type — consisting in
processes of absorption of matter, transformation and execretion of the
same, growth and proliferation. Again, the vitality of the cell is mani-
fested in the most striking manner by the extraordinary phenomena of
contractility which have recently been met with among the corpuscular
elements of the animal body.

Contractile cells have long been known — one might say as curiosi-
ties— in the bodies of lower animals. Comparatively recently they ha\e
been recognised also as existing very widely distributed among the
same, and some animals are known of such simple structure that almost
the whole mass of the body consists of them. But we have also
gradually become acquainted with an ever-increasing number of the same
kind of cells in the bodies of the higher animals, likewise endowed with
the power of vital contractility. Besides this, such a property could no
longer be doubted after the recognition of the fact that a widely-spread
species of muscular tissue, known as unstriped, as also the heart (at
least at an earlier period of embryonic life), had Consisted of such cells
entirely. Taking with all this the fact that, up to the present, this
vital contractility has been observed in the cells of all but a few tissues,
such as, for instance, those of the nervous system, we are almost war-
ranted in concluding that, at an earlier period of their existence,, all
cells are endowed with this power of contraction; that is to say, as long
as they consist of protoplasm alone,
and before they are enclosed in a
distinct cell-membrane, and that this
power is dependent probably on some
property inherent in the latter sub-
stance.

Let us take a somewhat nearer
glance at this wonderful phenomenon
of cell-life in individual cases.

If we take a frog in whose eye
inflammation has been produced by
the action of nitrate of silver applied
to the cornea, we find after a few
days that the aqueous humour be-
comes milky. A drop of this fluid,
placed with extreme care under the Fig. 66.— Contractile lymph -ceils from the

microscope, Will often show US the A«wwr a?i*t« of an inflamed eye of a frog.

cells sketched in fig. 66 (pus-corpuscles). These seldom or never appear
of simple spheroidal figure, but almost always under a variety of jagged
shapes, whose points and angles are engaged in an incessant change OJL form,
usually very sluggish, but at times somewhat energetic. We are able to

76 MANUAL OF HISTOLOGY.

recognise also, that certain thin, thread-like processes, consisting of a clear
structureless substance, extend themselves rapidly from the main mass
(a), while others much broader (b df) commence an extensive ramifica-
tion (g li k). Should the branches of neighbouring processes come into
contact with one another, they coalesce at the point of contact, forming
net-like figures or broad flat meshes, which gradually assume the
dark appearance of the rest of the body of the cell. Other prolongations
of the protoplasm, on the contrary, have in the meanwhile receded and
disappeared in the body of the cell. At times the most extraordinary
intermediate forms of the cell result from these changes (?' e). All this
time a slow circulation of the granules lying in the protoplasm may be
observed, the nucleus moving about passively with them. It is only
on the death of the cell that this extraordinary movement ceases, and
that the former assumes the round shape (/), formerly supposed to be the
only one in which the pus-corpuscle ever appeared.

The species of cell just mentioned, our " Jymphoid cell" (p. 72), is found
widely distributed throughout the bodies of vertebrate animals, and has
received different names, according to the region in which it is met with,
as, for instance, the " white blood-corpuscle," the " lymph and chyle
corpuscle," the " mucous corpuscle," &c..

Does it undergo the same changes of form in the human and mam-
malian body generally 1

This question may be answered in the affirmative ; but, owing to the
much smaller size of the cell in the latter, and the rapid cooling of the

preparation, the demonstration of vital
contractility is attended with more diffi-
culty. The series of changes sketched
in fig. 67 may be followed (a, 1-10) on
the white corpuscles of the blood; but
the energy of the movement is greatly
increased if the natural warmth of the
fluid be kept up artificially.

Another instance of change of figure
is depicted in fig. 68, which represents
a small portion of living connective
Fig. e? .-white contractile corpuscles of tissue from the body of the frog. The

human blood, a, 1-10, changes of shape cells known as COimective-tlSSUe COr-
succeeding one another in a cell, within a , , /» n i i i

period of forty minutes' duration; b, & puscles put torth here Very long and

stellate ceil. thin fiiiform processes (a b c), but the

sequence of change is of the slowest kind. These processes meeting
together with others like them from neighbouring cells, fuse into one
another temporarily. But all such connective-tissue corpuscles do not
appear to possess the same power of motion, for at d and e the form
is not altered. The stellate cells of corneal tissue are said, however,
to afford a much more beautiful example of vital change of form.

The appearance and disappearance of these protoplasm processes, and
their irregular development, resemble in the most striking manner those
wondrous variations in figure observed to take place in the body of one
of the naked rhizopods, the amceba, which consists entirely of protoplasm ;
and we may, therefore, with perfect propriety, adopt the name " amoeboid
motion" for the phenomena under consideration.

It is very easy to convince one's self, with the aid of the microscope,
that the amoeba is able to take up solid particles into its body from the

ELEMENTS OF STRUCTURE.

77

Fig. 68.— Living connective tissue from the frog's leg. ale
d e, various forms of connective-tissue corpuscles ; (o-c,
contractile) ;/, fibres, and g, bundles of the same ; A, elastic
network.

surrounding medium in which" it floats. The mode in which the little
animalcule slowly effects a change of position in the field by means of its
contractility may also be recognised. It is observed, namely, to put out
a process in one direction, into which the rest of the body gradually
streams, as it were, until
finally this process has be-
come the body of the organ-
ism. The interesting disco-
very also was made a few
years ago, that these two pro-
perties are not exclusively
confined to the elementary
organisms just mentioned,
but exist in the less inde-
pendent amoeboid cells of
the bodies of higher animals.
Thus we see that tiny mole-
cules of pigmentary matters,
such as cinnabar, carmine,
indigo, and aniline, or the
oil-globules of milk, are taken
up into the bodies of the
amoeboid cells of blood, of
lymph, and of pus, — some
of them while lying at rest
being reached and embraced,
as it were, by processes of the protoplasm, and so received into the body
of the cell (fig. 69, a). But what is thus brought about artificially with
comparative difficulty, takes place readily
and extensively in the living body.
Closely-packed in the narrow interstices
of organs, amoeboid cells receive into
their substance even larger formed masses ;
these may, however, be forced into the
soft protoplasm from without. In the
interior of such cells we find at times
conglomerations of animal colouring mat-
ters, fragments, or even perfect examples
of blood-corpuscles, which have left the general circulation (b), objects
which were regarded as enigmatical in former times, when the cell was
supposed to possess an imperforate membrane.

With the power of receiving matters into its body there coexists in the
cell another of expelling the same. After a certain time the contractile
protoplasm works the granules, or fatty molecules as the case may be,
towards its surface, and finally discharges them from the body of the cell
completely.

This wandering of amoeboid cells through the interstices of living parts
was discovered years ago by ReeklingTiausen. The readiest mode of
studying the phenomenon for ourselves is by taking a drop of some fluid
containing cells from the body. In the tissues of the system the cells
wander on with a continual change of shape through fine narrow inter-
stices (usually compressed somewhat into elongated figures), and traverse
thus in a short space of time comparatively large distances.

Fig. 69.— a.

78

MANUAL OF HISTOLOGY.

Both of these — the reception of matters into their interior, and the
locomotive propensities of cells — furnish us with an insight into a new
world of liliputian life. Owing to these properties, the amoeboid cells of
such animal fluids as lymph, mucous and serous exudations, may wander
out from deep or remote organs in any direction. Cohnheim has fur-
nished us lately with some extraordinary results of his observations on
these points in regard to inflammation, but we will defer the considera-
tion of them until we can enter into it at greater length in another part
of our work. We learn, however, from these — and the possibility cannot
be denied — that small, formed particles of zymotic and infecting sub-
stances can be taken up by amoeboid cells, and
transported by the latter to distant localities in
the body, to the imminent danger of, and with at
times the greatest inj.ury to the system.

It seems to us, further, as though a comparison
may be instituted between this contractility of
the bodies of cells, and another kind of motion
observed in certain appendages of the latter. We
refer to the small, hair-like formations attached to
the surface of various epithelial elements, to which the name cilia has
been given, the latter on which they are placed being termed on this
account ciliary epithelia (fig. 70). As long as life
clings to the part so long are these delicate hairs
engaged in a constant and rapid undulating movement.
But we will consider this " ciliary motion " more fully
further on.

The nucleus, also, or parts formed from it may,
although exceptionally, become contractile in animal
cells. But up to the present we are acquainted with
really contractile nuclei only among the inverte-
-Human sper- brata. The spermatozoa of vertebrates, however (fig.
matozoa. 7]^ with their wonderful power of rapid progression,

afford an example of bodies which have their origin perhaps in the
nucleus. These will be discussed more at length presently.

ijf. 70.— Ciliated cells of the
mammal, a-d, body of the
cell with cilia.

. 7i

§50.

Let us now contemplate among the vegetative phenomena of cell-life
the growth of this element.

Like all other organic structures the animal cell possesses the capa-
bility of growth, of increase in size, by means of the introduction of new
particles among those already composing its body, or, as it is the custom
to say, by " intussusception." And in that the most extended use is made
of this property throughout the system, we see .consequently that in size,
newly formed cells are much smaller than those already arrived at maturity.
The enlargement of cells, however, takes place very unequally in the
several tissues; in some they usually increase but moderately in size, as,
for instance, in certain epithelia, while in others, as in the elements of un-
striped muscle, they may undergo an enormous augmentation in volume.
These latter are the contractile fibre cells already so frequently referred
to. Certain cells, also, as, for instance, those of fatty tissue and cartilage,
are often much more minute in the advanced embryo, or infant, than
in the same tissue in the adult human body, — a fact established many

ELEMENTS OF STRUCTURE. 79

years ago by the Dutch investigator Harting with the aid of the micro-
meter.

A satisfactory physical analysis of cell-growth is not possible in >the
present state of science, and \ve can only here and there at most seize on
certain items of the process.

If its surroundings afford the growing cell sufficient room for opera-
tion, and if those elements lying next to it are separated from it by con-
siderable intervals of soft, yielding matter, it increases uniformly in all
directions, and preserves its primary spherical form. But if, on tLe other
hand, growing cells are crowded closely together, owing to this increase
in size the various members of the crowd must come into contact
eventually, and consequently a mutual flattening of each individual
element ensue on account of their softness. It then depends, of course
merely upon mechanical moments, whether they will assume the flat-
tened sbape, and become squamous, or take on the elongated form.

We meet, however, often enough with cells increasing in size, in tissues
of soft consistence, which are difficulties in the way of such an explana-
tion as that just given of the law of growth of cells, where the deposi-
tion of new molecules does not progress with uniformity, and in conse-
quence the cell becomes fusiform or pyriform, losing its original figure
altogether. If these additions to the substance of the cell take place
only at very limited points, they give rise not unfrequently to the forma-
tion of long processes in varying number.

We cannot, however, hope to have attained much by this mode of
explanation of the shapes assumed by cells; for, just as the many species
of plants and animals possess each one its own special stamp, so do the
various kinds of cells of our body possess their own peculiar specific
characters whose origin mocks every kind of analysis we can apply.

But not alone does the body of the cell grow, but the nucleus and
nucleolus also undergo an addition to their bulk, though in a minor
degree. The nucleus, on account of its similarity in nature to the cell,
may be supposed to increase in the same manner; and, in fact, we often
remark, besides the general enlargement, an irregular growth through
which me spheroidal body may become flat, elongated, and narrow, or
columnar, &c. The increase in size of the nucleolus is probably least of
all, although it can be distinguished in ganglion cells, and many others,
as, for instance, in the primitive ovum.

In contrast to these cells there exist others in which, on account of the
growth or senescence of the body, the nucleus previously present disap-
pears— is, in fact, dissolved.

Thus the nuclei of the most superficial, or, in other words, the oldest
and largest cells of the epidermis vanish; and again the formative white
blood-corpuscle is endowed with a nucleus, which is absent in the red cell
later on, at least among human beings and mammals.

Should the cell have developed around itself a more or less sharply
defined cortical layer of protoplasm, or an independent wall, this may
become increased in superficial extent by the deposit in it of new mole-
cules produced in the body of the cell.

The envelopes, also, of growing cells frequently become thickened,
besides by a constant deposit of solid matter on their internal surfaces.
We shall have to take all these points into consideration below when con-
sidering cartilage cells.

Other phenomena of growth which lead to a relinquishing of the

80 MANUAL OF HISTOLOGY.

cellular nature and individuality of the cell will come under our notice
lower down.

§ 51.

All structures of the body — the tissue elements, and, in the case in
point, the cells — show a transmutation of the matters of which they are
composed (p. 11) ; they present for our consideration an "interchange of
material" in connection with them.

Simple microscopic investigation even affords us many proofs of this,
by showing that, beside the growth of the cell, its contents may become
eventually of a different nature from an optical point of view. Thus we
see, in glancing at embryonic processes in the first place, that the forma-
tive cell of tissues exchanges its previously homogeneous or finely granular
contents for more specific materials, in that, instead of the granules of the
yelk, fat globules, pigmentary matters, and blood-pigments, &c., may make
their appearance in its body. The same interchange of matter is also seen
in the mature animal system ; the white formative blood-corpuscles are
transformed into- red cells. The neutral fats, which, enveloped in a thin
layer of protoplasm, form the contents of the so-called fat-cells, may dis-
appear from the body of the latter in consequence of prolonged fasting or
exhausting disease, and be replaced by watery protoplasm, or, as it was
formerly expressed, by a "serous fluid." Again, in the interior of the
epithelial cells of the small intestine, certain fat globules may be ob-
served after every meal, which, in the course of a few hours, have regu-
larly disappeared again. And/ indeed, we might bring forward many
other examples.

One more example of cellular transmutation may be mentioned here as
a recent discovery.

In the inactive submaxillary gland are to be found cells which contain,
besides a small amount of protoplasm expanded peripherally and a nucleus,
a large drop of mucus. By the action of a continued electric stimulus,
these gland-cells may be made artificially to discharge the mucin, and on
doing so, are found to be granular throughout, and, freed of the gelatinous
substance, smaller. In a few hours the whole cell-body is observecl to be
formed entirely of protoplasm.

Now, although we are in this way able to see, one might almost say,
with the naked eye, the transmutation of matter in the cell, nevertheless
great difficulties arise so soon as the question turns upon a more detailed
analysis of the same ; and this it is which causes the advance to appear
so inconsiderable which has been hitherto made in a field of inquiry so
important for general physiology. The very knowledge of the fact, also
(first observed by Graham), that crystalloids, but not colloids, can pass
through the envelopes and body of the cell, which consists of colloid mat-
ter, renders it difficult to comprehend how the nourishment and growth
of the latter take place, although it may explain, on the other hand, the
mode of excretion of the products of decomposition.

When we are questioned as to the vigour with which this interchange
of matter takes place in the animal cell, we are only able to offer conjec-
tures. In the first place, different parts of the cell may be endowed with
different degrees of transformative energy. The membrane, for instance (if
the cell have acquired one), appears to be endowed with less than the other
portions, and to be the most stable of the whole, especially when it con-
sists of tough and indifferent elastic matter. On the other hand, everything

ELEMENTS OF STRUCTURE. 81

points to the conclusion that, as in the growth of the cell, so also in its
transmutative functions, the body takes the most prominent part, for in
it the most important alterations are observed to take place. The nucleus
seems to stand between the inert membrane and active body of the cell
in point of energy in the metamorphosis of matter.

Of the amount of transmutation in large groups of cells of particular
tissues we know just as little. There are physiological facts, however,
which would lead us to the conclusion that those tissues to which we
ascribe the highest physiological dignity — as, for instance, those of the
muscular and nervous systems— possess this power to a very considerable
extent ; so that we may look on the cells of unstriped muscle and of gan-
glia as structures possessing the capability of rapid renovation of their
substance. But the coming and going of material must be still more rapid
in those numerous cells which clothe the interior of the glands of our
body, from all we know of the processes of secretion. On the other hand,
we find certain kinds of cells whose transformative abilities are probably
very inconsiderable, as, for instance, those of old laminated epithelia and
of nail- tissue (so closely related to that of the epidermis), and the cells
of cartilage. In respect to many other cellular structures, we are not
even able to form likely conjectures.

The consideration of the means employed by nature to bring about this
transmutation of matter in the animal cell, is likewise bound up with
many difficulties.

Among these agencies, however, may be reckoned, in the first place, the
property of imbibition inherent in histogeuic materials; and, secondly,
great stress must be laid upon the processes of endosmosis always accom-
panying cell-life. And in that chemical processes are incessantly at work
in the interior of the cell, and aro often of considerable energy ; in that
constant series of transmutations follow one upon another here, and that
the contents of the element change their nature very frequently; in that
fluids of different constitution pass over the surface of the cell finally, the
phenomena of diffusion must be very various.

Looking somewhat more closely into the vital actions of the cell-sub-
stance, we find them to be of two kinds : "egotistical," or occurring in the
interests of the proper nutrition of the latter ; and again of another
nature, for the attainment of greater ends no longer confined to the narrow
purposes of cell-life. The latter are to be observed in gland cells.

The mode of action of these is two-fold, with transitions from one
to the other. Certain cells only receive into their bodies substances
which existed previously in the blood, and which pass through them
without undergoing change, into the ducts of the gland, to form the pecu-
liar secretion of the latter. Thus, in the case of the gland-cells of the
kidney, for instance, we find them simply allowing of the passage through
them of certain constituents of the blood, namely, urea, uric and hippuric
acids, and several salts. It is probable, also, that the cells with which
serous sacs are lined admit of the transudation, in a similar manner, of
the fluids with which they are moistened and lubricated. On the other
hand — to return to the gland-cells — we find a considerable number of
glandular organs which do not constitute simple apparatuses for the fil-
tration of constituents of the blood, but which receive, on the contrary,
certain matters into their interior in order to transform them — to cause
them to enter into new combinations, or to split them up into new com-
pounds, and so on. The tendency to refer all this chemical change to the

82 MANUAL OF HISTOLOGY.

action of fermenting matters in the cell-body, or to some properties inhe-
rent in the nucleus, seems natural. Thus, \ve see that the action of the
hepatic cell gives rise to the formation of the bile acids and glycogen. In
the gland-cells of the functionating mamma sugar of milk must be pro-
duced from some of the hydrocarbons it receives, or from albuminous
matters. In the cells of the salivary glands of the gastric and intestinal
follicles and of the pancreas, ferments are generated which do not exist
as such in the blood, and which impart to the secretions of the organs in
question their peculiar physiological properties.

Now, these operations engaged in by the gland-elements are repeated
again in the proper or egotistical nutrition of individual animal cells. It
seems probable that in many cases constituents of the blood simply enter
animal cells in order — perhaps after undergoing very slight modification —
to become constituents of the latter. This is borne out by the fact that
the cells are principally built up, as it were, of albuminous compounds.
On the other hand, we frequently observe considerable transmutation to
take place, by means of which matters received acquire another nature.
Thus the protein compounds of laminated epithelium are converted gradu-
ally into keratin, the albuminous substances of other cells are transformed
into mucin, and again the fatty soaps of the blood assume the form of
neutral fats on entering the cells of adipose tissue — a metamorphosis of
which but little farther is known.

But the metamorphosis of matter taken up into the cell becomes espe-
cially striking in the case of the formation of pigments. Here we behold
the white blood-cell generating in its interior a colouring matter and be-
coming a red corpuscle ; in the same way granules of black pigment or
melanin are developed in the bodies of many originally colourless cells,
when they are known as pigment cells.

The question as to what matters are generated by the cell itself, and
what are received into it from without already formed, is in many cases
difficult, and frequently impossible, to answer.

Now, as to the retrograde metamorphosis of the components of the cell,
as to the liquefaction and discharge of the products of decomposition, we
know at present but very little. The most purely cellular tissues usually
exist in too small quantity to admit of chemical investigation. But occa-
sionally, under favourable circumstances, a few conclusions may be drawn
on these points. Thus the products of decomposition of striped muscle
may most probabty be regarded as similar to those of involuntary fibre,
judging from their chemical and morphological relationship ; and in the
contractile fibre-cell of the latter we suppose the albumen to be transformed
into kreatin, kreatinin, hypoxanthine, inosinic acid, inosite, and the
paralactic acid.

In concluding this section, it may be remarked that Schwann has
designated those phenomena connected with the chemical transmutations
of the cell as " metabolic occurrences," and speaks of a " metabolic force"
inherent in cells.

§52.

The interchange of material going on among animal cells, as a study,
(however scanty our knowledge of it may be), has made us acquainted with
the elaboration of amorphous matter, and with the excretion of fluids
containing the products of decomposition or the earlier substance of
cells in solution. It has also brought under notice a number of formations

ELEMENTS OF STRUCTURE.

83

m

of much deeper import in histology, in which material supplied by the
cell-body solidifies and assumes definite forms, a process of the greatest
importance in histogenesis, and upon which great stress vas laid many
years ago, especially by Koelliker.

The formations to which we refer may be regarded at one time as pro-
duced by secretions from the surface of the protoplasm ; at another by
metamorphosis of peripheral layers of the latter. In fact, both these
processes are merged into one another so frequently that no great stress
need be laid on their separation.

These solid formed structures, although of greater significance in the
bodies of the lower animals than in the human, appear nevertheless to play
no unimportant part in our organisation, although the distinctions between
the processes by which they are formed are still obscure.

In one of the foregoing sections the cortical layer of the protoplasm of
cells was described, as also the cell-wall, which was recognised as an
envelope differing chemically from the rest of the element.

When such membranes attain a certain degree of thickness and inde-
pendence as regards the body of the cell, "they are known as cell-capsules.

The best examples of such capsular membranes are to be found among
the elements of a very widely spread tissue, cartilage (fig. 72).

The cartilage cell proper (b), consists of a nucleus (a) imbedded
transparent contractile protoplasm. On
the surface of the latter a chemically
different layer is gradually formed, which
is at first thin and delicate, but eventu-
ally attains considerable thickness (c)
by the deposit on its internal surface of
laminae of new matter. Not unfrequently
a distinctly concentric marking may be
observed in the capsule, as optical ex-
pression of this successive formation
within it of lamina?. Again, much may
be learned from the action of water upon
the body of the cell, under which the latter shrivels up and becomes
widely separated from the capsule (3).

It is probable that the thick tough envelope known as the chorion (fig.
73), which invests the primitive ovum cell, is
of analogous nature to the cartilage capsule.
This has recently been discovered to possess
a very peculiar structure ; it is marked, namely,
by very delicate radiating lines, which are the
optical expression of extremely fine passages
or canaliculi, known as the "pore-canals" of
Leydig. These which are also present in
vegetable cells are undoubtedly of the deepest
significance in cell-life.

As related to these capsular structures
enveloping whole cells, other formations may
be mentioned which are only partial, occurring
on the free surface of epithelial cells. They are to be found, for instance,
among the columnar epithelial cells of the mammalian intestine, with their
delicate pore-canals, discovered many years ago almost simultaneously
and independently of one another, by Funke and Koelliker.

Fig. 72. — Diagram of three cartilage cells
M-ith capsules, a, nucleus; 6, cell-body
c, capsules.

Fig. 73. — Ovum of the mole (copied
from Leydig). a. nucleus ; 6,
cell-body; r, thickened capsule
traversed by pores.

84

MANUAL OF HISTOLOGY.

Fig. 74. — Columnar cells from the
small intestine of the rabbit, a,
side view of cells with thickened
raised lids traversed by pores ; 6,
view from above, in which the
orifices of the pores appear like
dots.

SO.

It had long been known that the free surfaces of the columnar cells in
question were covered with transparent borders.
These, however, were held to be the optical
expression of thickened cell -membranes. We
now know, however, beyond doubt, that each
cell is topped by a kind of lid as it were. In
this fine streaks or pore-canals may, as a rule,
be distinctly recognised (figs. 74 a, 75 b) • seen
from above, also, the cells are observed to be
finely dotted (fig. 74 b). At times, however,
the markings on the borders of the cells are
not distinguishable, or only very indistinctly

This transparent lid may be loosened from the surface of the cells

by the action of water or
pressure ; either in the
form of one continuous band
(figs. 74 a, 75 a), or, only
specially attached to each
cell (figs. 75 c-/). Then
again, the delicate sub-
stance of the lid, composed
of some unstable albumin-
ous matter, splits up fre-
quently on imbibing water,
or under slight pressure,
into a number of rod-
like pieces, which may
give to the columnar epi-
thelial cells in question

Fig. 75. — The same cells. At o, the border is loosened by
water and slight pressure; 6, natural condition; c, a portion
of the lid destroyed; d e /, the latter is resolved into a
number of rod-like or prismatic pieces, by maceration in
water.

very much the appearance of ciliated elements.

§53.

The nature of this cell-border on the free surface of the columnar
epithelia just mentioned, leaves no room to doubt that the layer is
produced by the cell itself, and not deposited on its membrane from with-
out in some way or other.

But many other formations leave us less cer-
tain as to their origin. These may occur lying
beneath cells, or again, on the exterior of large
collections of the latter, in which case they re-
present continuous layers, capsules, sacs, blind
follicles, tubes, &c., formations which all cor-
respond in their structureless transparent appear-
ance, and usually in their insolubility, and in
consisting of some material allied to, if not iden-
tical with el as tin.

Thus; underneath the coatings of epithelial
cells which, cover different mucous membranes of the body, a transparent
layer may frequently be observed with varying degrees of distinctness
(fig. 76 c c). This is the so-called intermediate membrane of Henle or
basement membrane of the English investigators, Todd and Bowman.
There appear in like manner transparent Iamina3 underneath the epithe-
lium, clothing the anterior and posterior surfaces of the cornea.

Fig. 76. — Diagram of a mucous
membrane covered with
columnar epithelium, a, the
cells ; 6 ft, interstitial sub-
stance between their lower
ends^ cc, transparent, layer ;
d, fibrous tissue of the
mucous membrane.

ELEMENTS OF STRUCTURE.

85

In our opinion, the latter glass-like subepithelial strata have nothing to
do with the cells of this tissue, they are more probably modified limiting
layers of the connective tissue of cornea and mucosa.

Fig. 77. — Glands from the large intestine
of the rabbit; one follicle with cells
and four glands, of .which only the
Membrana propria has remained com-
pletely stripped of cells.

Fig. 78.— Follicle from the large intestine of the
guinea-pig. Gland at a, with Membrana pro~
pria partially visible ; at 6, the contents have
escaped through a slit in the latter membrane.

As we have just remarked, there occur, enveloping certain groups of
cells, homogeneous layers, constituting, especially among the glandular
structures, what is known as the
Membrana propria, i.e., a trans-
parent tunic investing the gland
und determining its shape, us
well as that of its several parts,
and on this account of much im-
portance. Of these membranes
are formed the vast multitude
of follicular glands, having the
shape of long narrow pouches
(figs. 77, 78 «), whilst in the no
less widely distributed group of
racemose glands the latter are
replaced by numbers of flask-
shaped saccules packed closely
together (fig. 79).

But also around aggregations
of embryonic cells, destined
later on to become definite
structures, similar transparent
envelopes are to be found, as,
for instance, around the rudi-
mentary human hair, as pointed out by Koelliker (fig. 80).

Such homogenous membranes have been regarded by some as produced
by the solidification of a secretion from the cells themselves, — a theory
which is not tit all weakened by the fact of the separation of the trans-
parent envelope from the cells by which it is formed, nor that it outlasts
the elements from which it has had its origin. It is, however, difficult to
explain why in an aggregation of cells identically the same, only those
situated externally should possess the power of generating such a secre-
tion.

Fig. 79. — A human racemose gland (Brawler's) with
saccules of the Membrana propria.

86

MANUAL OF HISTOLOGY.

Fig. 80. — Rudiments of a hair from a human
embryo sixteen weeks old. a 6, cuticular
layers ; m m, cells of the rudimentary hair ;
6, transparent layer enveloping the latter.

In fact, close observation teaches here also that the structures in ques-
tion are merely modified, limiting layers
of the fibrous tissue of the cutis. And
although, in most glandular organs this
may arrive at such a degree of indepen-
dence as allows of its isolation, still there
are other glands destitute of such a mem-
brana propria, and in which the groups
of cells are simply embedded in a pit in
the mucous tissue, bounded by homo-
geneous transparent connective sub-
stance.

The consideration of these points in-
troduces us to a doctrine in histology originating with Schwann, which
for a long time exercised great influence over the progress of development
of the science, arid regulated the views regarding the formation of cells.
We refer to his theories respecting "cytoblas-
tema," or the " ground-substance " of tissues,
which, when occurring between cellular ele-
ments is known as "intercellular substance."

If we direct our attention to portions of the
body consisting mainly of cells, we frequently
find the latter so closely crowded together that
they come into immediate contact one with the
other, so that at first nothing is to be seen of the
matter lying between them which holds them
together, and to which the name of tissue-cement
This is the case, for instance, in some of the epithelia,
such as the flattened species, which line the in-
ternal surfaces of serous cavities and blood-vessels
(fig. 81).

Again, layers of cells are to be found in which
a connecting medium is apparent between the
several elements of the tissue, though perhaps only
in small quantity, as, for instance, in columnar
epithelium already mentioned (fig. 82).

When the cells of a simple tissue become more widely separated on the
other hand, the intercellular substance in-
creases more and more in amount, and com-
mences to determine the consistence of the
whole tissue. Cartilage supplies us with per-
haps the best example of this (fig. 83).

This intercellular substance is of many
kinds, both as to appearance and composition.
Thus we meet with it, for instance, perfectly
transparent — its most usual form — without
granules, &c., as between the cells of epithe-
lium. In many species of cartilage it is milky
white; in others finely streaked to a greater
or less extent.

Another kind of cartilage, known as the " elastic " or " yellow." presents
a most peculiar appearance : in it the intercellular matter is made up of a
tangle of irregularly interlacing bands and fibres (fig. 84).

Fig. 81. — Simple flattened epithe-
lium: a, from a serous mem-
brane; 6, from the lining of
blood-vessels.

may be given.

Fig. 82. — Columnar cells with
intercellular substance, 6 b.

83.— Cartilage cells of various
forms with homogeneous intercel-
lular substance (diagrammatic).

ELEMENTS OF STRUCTURE.

87

Fig. 84.— Fibro-reticular cartilage
from the human epiglottis.

Chemically, intercellular substance may either appear as a fluid con-
taining albuminous matters in solution (blood, lymph), or as a jelly com-
posed of gelatinised protein compounds (many
fcetal tissues), or as coagulated metamorphosed
albuminous substances (epidermis, nails), or as
glutin-yielding tissue, such as chondrin (in per-
manent cartilage), or finally as elastic material
(in elastic or yellow cartilage).

Now, by ScJiwann this intercellular substance
was regarded as the primary structure in which
he supposed the cells subsequently to take their
origin, — a view which was favoured for a very
long time by the greater number of histologists.
The fact, however, that in the earlier periods of foetal life no intercellular
substance is found between the cells of growing tissue, seems to point to
another conclusion (especially when viewed in the light of present-day
science), namely, that the matrix is a product of the secretion of the cell
itself, or a metamorphosed peripheral portion of the cell-body, the con-
tribution of each element fusing, of course, into the common mass.

And, indeed, there are appearances in cartilage which admit of no other
explanation. Thus, we not unfrequently remark that the peripheral
capsular layers surrounding the cells like a halo, blend into the adjacent
intercellular substance without any sharp line of demarcation. But the
appearances presented by sections of cartilage which
have been treated with certain reagents are of far
greater importance even (fig. 85). Here the ap-
parently homogenous matrix of fig. 83, for instance,
is resolved into systems of thick capsules, which en-
circle the various cartilage cells, or groups of the
latter touching each other at their circumference.
We shall refer to this again further on.

But if blood, lymph, and chyle be numbered
among the tissues of the body — which may be rea-
sonably done — their fluid intercellular substance is
certainly of other origin, i.e, not produced by the
corpuscles. The cellular elements of lymph have rather wandered
actively out of the lymphatic glands in part, and have been partly carried
out with the currents of the fluid, just as a stream may sweep away por-
tions of its banks, and transport them to a greater or less distance.

§54.

In a former section we have already considered the question, how far
the growth of parts depends upon a simple enlargement of cells already
present, and how far upon an increase in the number of the cellular
elements of which the part is composed. "We have seen that the last-
named mode of growth is the rule: cellular structures increasing in
volume, usually show a multiplication of their elements. The cell, like
all organic formations, is a transient structure, and in all probability
invariably endowed with a term of existence far shorter than that of the
body generally, and which may be named in many cases exceedingly
brief when compared with the latter. It stands to reason, then, that it
must either possess the capability of proliferation, — of reproducing similar
structures to itself, of generating a progeny, — or whole families of co'ls
7

Fig. 85. — Thyroid cartilage
of the pig treated with
bichromate of potash and
nitric acid.

88

MANUAL OF HISTOLOGY.

must be produced independently of those originally present "by a species
of spontaneous generation in the tissues themselves.

That animal cells really possess the property in question, is indicated
by the processes of segmentation which have been long known to take
place in them, to which attention was directed many years ago by Remtik,
and which have since then been observed over and over again.

Division of cells appears invariably to depend upon the vital contrac-
tility of their protoplasm, and to be an impossibility so soon as the cell-
body becomes transformed into other substances. It is, therefore, essenti-
ally a vital property of young cells. The process of segmentation may
either take place in cells destitute of membranes, or in those contained
within capsules. Owing to this the occurrence is variously modified.
When the division takes place in membraneless elements, the whole
structure is constricted until separation into two halves occurs; while in
those which possess an envelope or capsule, the latter remains unaffected
by the process which divides the cell within it. The last variety is
known as " endogenous multiplication or cell growth."

1. Division of naked cells, or, as it may be called, free segmentation,
can be observed accurately in the white corpuscles of the blood of young
mammalian animals and embryonic birds. In
the first (fig. 86) we usually find a round nucleus
(a) in a spheroidal cell. When segmentation is
about to take place, the former becomes some-
what elongated, and is shortly after observed to
be marked by a slight transverse constriction,
the whole cell assuming at the same time an
oval form (&). This transverse furrow on the
nucleus then deepens more and more until the
latter is finally divided into two pieces (c),
Avhich at first lie very close together, indicating
their origin, but soon begin to separate from
one another (c?). On this the body of the cell
undergoes the same constriction (commencing
either at one side, or regularly all round), which
causes the cell to assume a form likened at times
to a double loaf (e). Later on there only exists a narrow band of con-
nection between the two portions of the body (/), which is finally com-
pletely severed, giving rise to the formation of two cells. By subsequent
growth these rapidly attain the typical dimensions of such elements. In
the embryonic chick, an easily obtainable object, the nucleoli may be
first seen to undergo the process of division within the
nucleus. This fact has been improperly denied by some
in connection with embryonic blood (Bittroth).

But the process of segmentation does not always occur
with the regularity of the example just cited. Thus, in
the frog division is described by Remak as occurring in
such a manner as to produce from a single corpuscle
three, four, or six cells. In other respects, however, and
as regards nucleus and body, the process is similar to that of simple cleaving
(fig- 87).

Those very remarkable formations known as "giant cells" (Kiesenzel-
len) (fig. 64, p. 72) are produced by multiplication of the nuclei with-
out corresponding segmentations of the body.

Fig. 86. — Blood-corpuscles from a
young deer embryo, a a a,
spheroidal cells ; b-f, segmenta-
tion of the same.

Fig. 87.— A cell from
the frog undergo-
ing segmentation
into three portions
(after Remak),

ELEMENTS OF STRUCTURE.

89

§55.

2. Passing on now to the consideration of segmentation in cells
endowed with a wall or capsule, we find perhaps the best example in
the cellular elements of cartilage. Endogenous growth in the cells in
question does not take place with the same simplicity as in the process
just referred to, and is a phenomenon the details of which are not yet
fully known; so that in the following description much that is hypothe-
tical must be advanced to supply points upon which we possess no certain
information yet (fig. 88).

The nuclei of naked cells enveloped in secondary capsules (b) are found
at first to possess a single nucleolus (1). On the commencement of the
process of division this becomes double (2); upon which a transverse
furrow may be recognised in the nucleus (3) ; by the deepening of this
furrow the latter is eventually divided into two segments (4); which
then recede from one another, thus initiating the constriction of the cell-
body (5) ; on the completion of the latter act (6), two perfectly distinct
cells (7) are found within the capsule, which has remained throughout
entirely passive. These new elements are known as " daughter cells,"
while the original cell, or, more correctly speaking, the capsular membrane
of the same, has received the inappropriate name of " mother cell," or
parent cell.

Now, if this sketch be correct, the only difference existing between the
simple division described afc (1), and the latter, consists in the presence
of a capsule, so that in a blood-corpuscle of a mammalian embryo, if we
imagine it endowed with an envelope, we have precisely the same plan of
segmentation as that of cartilage cells.

But the division of the latter does not by any means always stop here ;
in both daughter cells the
same process of segmentation
may be repeated until the
capsule includes four of them
(8), around which capsular
formations are eventually de-
veloped (e). So by a repe-
tition over and over again of
the same acts, whole genera-
tions of new cells may be
produced within a common
capsule (9).

On the fusion of this
envelope of the parent cell
with the surrounding in-
tercellular substance, the
daughter cells may eventually
appear to lie free in the
matrix. Part of the cartil-
age cells which have multi-
plied on the above plan assume an apparently free condition in this
way. Others again remain permanently enclosed in the parent capsule.

The ovum, after fertilisation has taken place, presents to us a similar
process of cell-division, of the utmost anatomical and physiological moment,
known as yelk-segmentation (fig. 89). The mode in which this takes

Fig. 88.— Plan of dividing cartilage cells, a, oody of cells;
6, capsules ; c, nuclei ; d, endogenous cells ; e, subsequent
formation of capsules around the latter.

90

MANUAL OF HISTOLOGY.

Fig. 89. — Segmentation of the mammalian ovum (half-
diagrammatic). 1, Yelk cleft in two ; 2, further subdivided
into four spherules (cells; with nuclei ; 3, a large number
of nucleated cells; 4, a b, separate -corpuscles.

place in the mammalia is, unfortunately, not yet conclusively ascer-
tained. The primordial nucleus of the ovum, however, known as the

" germinal vesicle, seems first
to disappear ; after this two
transparent spots are seen,
two new nuclei, and around
each, half of the cell-body or
yelk, by which name the latter
is known here (1). By further
subdivision, four cells are
formed from these two seg-
ments (2) ; and from these
again eight, and so on, until
finally, in consequence of re-
peated segmentation, the cap-
sule of the ovum contains a
multitude of small nucleated
cells (3, 4). From the latter
the first rudiments of the
embryonic body are formed :
from them spring all normal
and pathological form-ele-
ments ; they are the most
important and highly destined
cells in the whole system.
Throughout the whole animal kingdom this segmentation of cells is
observed in the ovum. Those cases are particularly instructive in which
the original nucleus of the egg (germinal vesicle) (seen among some low
groups of animals) is found to remain, and in which the phenomena of
segmentation may then be followed up with the greatest ease on the
nuclei with distinct nucleoli, which have taken their origin from it. It
is to be hoped that further research may lead to the same results in regard
to the mammalian egg, and thus rid the theories of yelk-segmentation of
many contradictions and difficulties which at present offer such unpleasant
obstacles to true progress.

As regards the mechanism of the process of segmentation, science is not
yet able to give any satisfactory explanation. There can be no doubt,
however, that the vital contractility of the cell-body plays an important
part in it ; for only in young elements, i.e., containing protoplasm, do we
observe the process of multiplication to take place. "Were it the case that
both cell and nucleus were always similarly affected by the act, we might
suppose the latter to be simply divided passively by the constriction of
the protoplasm. But this is contraindicated by the occurrence of two
nucleoli in a still simple nucleus, as also of two nuclei widely separated
from one another in a cell-body which has as yet undergone no change
(fig. 86 c).

One fact, adduced from extended observation, is of great importance,
namely, that the whole process of division may be, and usually is, corn-
completed very rapidly, probably within the space of a few minutes. This
enables us to comprehend the enormous proliferation of cells which we not
unfrequently meet with in pathological processes. It also explains the
fact that cells engaged in the act of segmentation are comparatively rarely
met with, even where the liveliest plastic processes are going on in an organ.

ELEMENTS OF STRUCTURE.

91

§56.

The question now arises, whether in the two processes of segmentation
of animal cells just described, the entire act of
multiplication of the elementary parts in question
is contained, or whether the cell may not produce
similar elements in other ways.

A kind of gemmation has been observed on the
nuclei of both normal and pathological cells. This
was found years ago, by Koelliker, to take place in the
large colourless cells of the spleen of young mammals
(fig. 90). In these, from three to five or more nuclei may be recognised
clinging together, displaying a peculiar modification of the process of

4. 3 2

Fig. 90. — Colourless blood-
cells from the spleen of a
kitten.

Fig. 91.— Supposed formation of pus-cor-
puscles in the interior of epithelial cells,
from the human and mammalian body.
a, simple columnar cell from the
human biliary duct; 6, another with
two pus-corpuscles; c, with 4, and J,
with many of the latter; &, the latter
isolated; /, a ciliated cell from the
human respiratory apparatus, contain-
ing one pus-corpuscle ; and (g), a flat-
tened epithelial cell from the human
bladder, with a large number of the
same.

Fig. 92. — Psorospermia in the interior
of epithelial cells from the small intes-
tine of the rabbit. 1, Simple epithelial
cell ; 2 and 3, nuclear multiplication ;
4 and 5, columnar elements with single
psorospermia cells ; 6, with two ; 7,
with a large contained body ; 8, with
two, without the cell nucleus ; 9, divi-
sion of contained body; 10 and 11,
cells with perfect psorospermia (the
latter are marked by 6, the cell nuclei
by a).

division in the nucleus. I have myself observed something similar in
modified columnar epithelium from the small intestine of the rabbit
(fig. 92, 3).

Gemmation, as a mode of multiplication of whole cells, has not yet been
met with in the human body or that of the higher animals.

Of late years another remarkable process, apparently of cell formation,
has been observed, in which the proto-plasm of the original cell becomes
transformed into one or more new cells, possessing completely different
characters from the cell-body from which theyhave had their origin.

It is thus that pus-corpuscles are supposed to be produced in the interior
of different epithelial cells of the human body under inflammatory condi-
tions (Remalc, Buhl, Eberth, and others).

Fig. 91 will give some idea of the case in point. Here we have ordi-
nary columnar cells (a) containing two (b) or four (c) pus-corpuscles, the
regular nuclei remaining visible. Such cells may also be encountered in-

92 MANUAL OF HISTOLOGY.

eluding a still larger number of pus-corpuscles, and altered in their shape
on. that account (d).

On being liberated from the cells in which they have been contained,
these structures display all the characters of pus-corpuscles (e). But even
in ciliated cells, such as are to be met with in the mucous membrane of the
respiratory organs, these pus-cells may be found (/), as also in the flattened
epithelium of the bladder (g). Such things are, however, capable of
another explanation. Pus-corpuscles, elements whose vital contractility
is beyond a doubt (§ 49), may have wandered into the epithelial cells
from without. Such an immigration of strange elements has been proved
to take place recently into the cells of some morbid growths (Steudener).

The same appearances are presented farther by psorospermia, peculiarly
puzzling single-celled structures, which are frequently to be found, in the
bile-ducts and intestinal canal of rabbits, and which are looked upon as
parasitic organisms (fig. 92).

§57.

Of the various modes of reproduction or proliferation of animal cells,
that which goes by the name of endogenous growth has been long known,
although its details have been variously interpreted. But it is only com-
paratively recently that segmentation has been generally recognised, and
mainly so through the numerous proofs adduced by two observers, Remak
and Virchow — the first from the wide field of embryology, the latter from
pathology. From them emanated a contradiction of a doctrine put forward
by Schwann, which influenced for a long time all our views in regard to
histogenesis ; and the opposition soon became so widely supported as com-
pletely to throw Schwann' s theory into the shade.

According to the latter, animal cells are formed free, that is, indepen-
dently of any previously existing. " There is," says he, " either in those
cells already present or between them, a structureless substance, the cell-
contents or intercellular substance ; this matter (cytoblastema) possesses in
itself, to a greater or less extent, according to its chemical constitution and
degree of vitality, the power of giving rise to new cells. The genesis
of cells represents in organic nature what crystallization does in inorganic."

In the first place, says Schwann, there springs up in this cyto-
blastema a minute corpuscle, namely, the nucleolus, and owing to the
attraction of this body for surrounding molecules of matter, layers of these
are precipitated, as it were, around it, giving rise to the nucleus. By a
repetition of the process, a second layer is deposited upon the latter,
which, though differing from the surrounding medium, is not yet sharply
defined, but becomes so later. This deposit, hardening externally, forms
the substance and wall of the cell. At the commencement the newly
formed envelope lies closely round the nucleus — the cavity of the cell,
and with it the entire structure, being still small, but the wall increases
subsequently in size, and the whole obtains finally its specific contents.

To this was added later another theory, according to which the nucleus
of certain cells is enclosed, in the first instance, by the future specific
contents, and then only, around this mass, containing in its interior
the nucleus (the so-called "enveloping sphere"), is formed a wall by
solidification of part of the deposit, which brings the whole structure to
completion.

For many years these two modes of origin of the animal cell appeared
to be proved beyond all doubt, and the sole differences of opinion which

ELEMENTS OF STRUCTURE. 93

existed were as to the prevalence of one or other of them. The occurrence
of free nuclei was taken as conclusive evidence of the pre-existence of
these structures, although all were obliged to admit that they might have
been liberated by destruction of the body of the cell. And, indeed, the
occurrence of cells in such fluids as lymph, mucus, and pus, appeared to
be capable of most plausible explanation by means of this theory of free
origin; and proliferation of already existing cells, which could not rightly
be denied, was yet regarded as exceptional. Tis true that this spontaneous
generation (Urzeugung) of animal as compared with vegetable cells, which
spring from others already in existence, presents a strange contrast be-
tween the construction of the animal and vegetable systems. But, on the
other hand, the rapid development of pathological histology based on
Schicann's work, seemed to give weight to the theoretical views of this
talented man in this department also. The organisation of exudations,
the formation of tumours, &c., were interpreted in this manner, to the
support of the theory of spontaneous origin.

On Remak'sr demonstrating in a most elaborate manner that no sponta-
neous formation of cells takes place in the embryos of mammalia, but that
all new elements have their origin solely from division of previously exist-
ing ones, this theory of the generatio cequivoca of animal cells became
untenable, as regards the construction of the embryonic body at least.
Great exertions were also made by Virchow to prove that for the growth
of pathological tissues also (a far more difficult and obscure subject),
spontaneous generation of the cell need not exist; and giving up all earlier
theoretical conclusions, he conducted his case with the happiest results.
A review, likewise, of the earlier investigations touching the cellular
tissues of the healthy mature body, showed likewise a scarcity of free
nuclei at those points where cells were being formed anew, and led to
another easy interpretation, also, of the existence of cells without mem-
branes. And now that earnest search began to be made for those already
mentioned examples of cell multiplication which had been up till then so
rarely met with, they were found to exist in far greater number than was
at first supposed.

This, then, may be regarded a turning-point in histological science.
Histologists, as a rule, have now abandoned the theory of the origin of
cells without parents, accepting in its stead that of formation alone from
others previously existing, — though, indeed, still to a certain extent in the
light of an article of scientific faith, it must be confessed. The proof,
namely, that spontaneous generation of cells in the system does not
exist, is not even in the present day capable of being established by
facts. And, indeed, it is probable that we never shall be able to adduce
proof that such spontaneous generation does not take place in the midst
of some of the more inaccessible tissues of the living body.

And now at the present moment, remembering the former state of
science, and how for decades these theories of Schwann were clung to
generally, and with an amount even of wantonness, we would inculcate
caution. And though everything now seems to point to the conclusion
that spontaneous generation of animal cells does not take place, neverthe-
less, it seems desirable, for many reasons, that the old view should still
have its defenders as well as the new its opponents. Thus will science
be compelled to put forth all her energies for the accumulation of that so
indispensable material " facts," in order to set her dogmas upon a firm
foundation, and histology can only gain by it.

94

MANUAL OF HISTOLOGY

Fig. 93.— Detached cells of epider-
mis from the human skin.

§58.

Now, as to the decay of animal cells, \ve find their destinies to be very
various.

Firstly, the existence of a cell may terminate purely mechanically; it
may be rubbed or peeled off from its bed. Thus we see the superficial
scale-like cells of the epidermis becoming dry and hard, and losing their
nuclei; at the same time that their previously secure connections, by means
of a cementing substance, become loosened, allowing of their easy separa-
tion. The same is the case, also, with the nucleated surface cells of
certain laminated epithelia of mucous membranes, as, for instance, of
those of the mouth. Such a separation also takes place from some of the
more simple or even single-layered epithelial coatings, although not to
the same extent as was formerly supposed. Thus mucus carries off some
of the cells of the locality in which it is produced.

This mode of destruction, however, is the most rare, the cell passing on
more frequently through changes in its con-
sistence and composition to decay.

The most usual way, probably, in which
cells are destroyed, is that of solution of their
bodies, and in the case of those possessing
membranes, rupture of the latter, with escape
of the contents, and eventual liquefaction of
the nucleus, if such have been present. Jn
this manner it is that blood-corpuscles are
supposed to disappear, as also the cells which clothe the cavities of
glands, and those in which spermatozoa are developed. Digested in
the slightly alkaline fluids of the system, the matter of which the
dying cell is composed is often transformed into a substance resembling
if not identical with mucus. These occurrences, taking place in the
gradual decay of the cell, are of interest from another point of view,

namely, from the fact of their having
been misinterpreted by the adherents of
the older theorists, who reversed the order
of things to the support of their own pecu-
liar view.

We occasionally meet among the more
delicate epithelia with both modes of de-
cay side by side. Thus, of those cells of
the'intestine covered by a thickened border,
some are cast off, whilst others first undergo
decomposition with solution of the upper
part of the membrane of the cell and escape of the contents (fig. 94, a).

Another change to which the body of the cell is liable, is into colloid
matter, a much more stable substance than mucin, which, in contra-
distinction to the latter, is not precipitated by acetic acid. The connective
tissue cells of the plexus choroidei, and the cellular elements of the thy-
roid gland, are specially subject to this degeneration.

But, again, through far different chemical transformations, so to speak,
can the cell meet the destiny of all organic things, its dissolution being
at the same time hastened. There are usually two kinds of deposits of
foreign matter to be found in the bodies of cells, which may make the latter
incapable of further existence, and, curiously enough, of substances widely

Fig. 94.— Cylinder epithelium from the
human intestinal villi (after Schuhze).
6, normal cell ; a, another in process of
transformation into inucus.

ELEMENTS OF STRUCTURE.

95

distributed throughout the system, and which constitute the normal
contents of the cells of other tissues. These are (1), neutral fats, deposits
of which, for instance, cause the destruction of nume-
rous cells of the Graafian follicle during the forma-
tion of the corpus luteum in the ovary (fig. 95. a).
The same effect is produced by these fats on the
gland cells of the mamma during secretion; (2), by salts
of calcium (phosphates and carbonates) in the process
which is termed calcification. We meet the latter very
frequently in the cells of many cartilages. Inhaled
molecules of charcoal may also accelerate the decay
of the epithelial cells of the lungs.

It belongs to the province of pathological histo-
logy to show that the same modes of decay are largely
met with in the pathological processes of the system,
namely, those of mucous and colloid metamorphosis, of fatty and cal-
careous degeneration; likewise that forms of degeneration appear in
diseased states of the tissues which do not exist in the normal ; as, for
instance, the amyloid (§ 21), and the peculiar withering of cells in tuber-
culisation.

Fig. 95.— Modes of de-
generation of animal
cells, a, cells of the
Graafian follicle filled
with fat; 6, epithelial
elements of pulmonary
alveoli, replete with
pigment.

B. The Origin of the Remaining Elements of Tissue.

§ 59.

Now, it is from these cells of which we have been speaking, and the
substance to be found between them, that the remaining elementary parts
of the animal body take their rise.

But, first of all, let it be borne in mind that it is by no means possible
everywhere to define sharply between cells and many other elementary
parts. Though we have seen, in the preceding pages, that
a large number of the various cells preserve their cell-
nature unchanged, or with but slight modifications, from the
commencement to the end of their existence, still we have
also become acquainted with some very striking transfor-
mations in their bodies, owing to which they may assume
the most anomalous forms. To these may be reckoned
the fibre-cells which make up the unstriped muscle of the
human body and of all vertebrates. H,ere the cell has be-
come a fusiform fibre owing to its nnsymmetrical growth,
and the nucleus also, though to a minor extent, has taken
part in the process of elongation. While in this example
of increase in the length of the cell the nucleus has also
become elongated, still, in other similar enlargements, it
may preserve its originally oval shape. This is the case
in those long transparent cylinders consisting of globuline, which form the
fibres of the crystalline lens.

On the other hand, in some structures multiplication of the nucleus may
accompany excessive elongation of animal cells to form tissue elements.
This may be observed in a very abundant tissue of the body, namely,
in striped muscle.

The elements of the latter are long cylindrical fibres (fig. 97, 1), of vary-
ing thickness, which possess certain contents (2, a) enclosed within a

Fiir. 96. — Contrac-
tile fibre-cells.

96

MANUAL OF HISTOLOGY.

structureless sheath. This contained substance is seen, with varying de-
grees of distinctness in different cases, to be marked by fine longitudinal
lines combined with transverse striation, and to be studded with nuclei
(d d) at short intervals; these nuclei are surrounded each with a small
amount of protoplasm.

r ,

Fig. 97. — 1. Fibre of striped muscle split up into
primitive ftbiillae, a; more distinctly striped
at b; longitudinal lines more visible at c;
nuclei, d d. 2. A fibre, 6 b; torn through, with
empty sheath partially separated, a. (Copied
from Bowman).

Fig. 98. — Stages of development in the for-
mative cell of the striped muscle fibre of
the frog. (After Remak.)

Leberts and Remak's, as well as more recent investigations, have shown
that each of these fibres has its origin in a single cell.

In the formative cells of frog's muscle (fig. 98), (the usual nucleated
elements, with granular protoplasm, of which the body of the embryo is
formed), segmentation may be recognised as elsewhere (a). By the growth
of the cell and multiplication of the nucleus by division, the whole struc-
ture assumes the appearance sketched in fig. 98, 6. Later on the dark
granules disappear from the elongated cell, and the characteristic trans-
verse streaking commences (c d e). Finally, by continuous elongation
and constant multiplication of the nuclei, the cells take on the form in-
dicated by/, where the longitudinal lines are commencing, and the muscle-
fibre has almost reached its full development. ' The origin of the nuclei
in fig. 97 (1), is thus cleared up. But it must not be supposed, as was
formerly the case, that the structureless sheath (&) corresponds to the cell-
membrane ; it is rather a matter deposited externally on the fibre.

§60

From what we have seen of the mode of development of striped muscle-
fibres in the preceding section, it is clear that many cells may undergo
considerable transformation without in the least forfeiting their indivi-
duality.

ELEMENTS OF STRUCTURE.

But it is otherwise in the construction of some tissues, in which the
various cells commence to cohere
and fuse more and more into one
another, losing eventually, in many
instances, their independence com-
pletely. By such series of meta-
morphoses (and they occur widely
throughout the animal system, and
are therefore of the greatest impor-
tance) networks of cells, tubes, fibres,
and such like, may be formed. The
changes in question are of the most
various kind, but cannot be de-
scribed in all cases with desirable
accuracy. It will suffice, however,
to take a few of the better known
as examples.

The finest tubes in the circulatory
system, namely, the capillaries (fig.
99, A, a b, and B, a), are found by
ordinary examination to be made
up of a delicate transparent mem-
brane, in which nuclei are imbedded
at intervals. Until a few years ago,
this was generally thought to be the
entire structure of the capillary
tubes, whose development was ex-
plained in the following manner.
Formative cells were supposed to fuse
together, the cavities of the cells to
become the lumen of the tube by
opening into one another, and the
walls of the cells with their nuclei
to supply the delicate transparent
nucleated membrane of the vessel.

From the German investigators — Hoyer, Auerbach, Eberth, and Aeby —
we have recently learned, however, the true
structure of the capillaries, and the incor-
rectness of the former views entertained
with regard to them.

By treatment with a solution of nitrate
of silver, namely, this fine membrane may
frequently be resolved into extremely thin
nucleated formative cells of considerable
size, terminating in laps and processes (fig.
100), by which the cells adhere to one an-
other at their edges, and, taking the hol-
lowed form of the lumen, thus produce the
vessel. — It is the action of light on the
silver at the junction of the elements
which makes their boundaries visible. —
Thus we see that the lumen has not had its
origin in the cavities of coalescing cells, but is rather an intercellular space.

Fig. 99. — Small blood-vessels from tlie pia mater
of the human brain. A, & twig, c, terminates
above in two delicate capillaries, a b; B, & simi-
lar vessel, with capillaries, a; (7, a stronger twig,
with longitudinal and transverse nuclei.

Fig. 100.— Capillary vessel from the lung
of a frog, after treatment with dilute
solution of nitrate of silver, a, nuclei;
b, boundaries of the cells.

98 MANUAL OF HISTOLOGY.

§ 61.

As we have just seen, the intercellular matter between the formative
cells of the capillaries appears in the most minute quantity, reminding us
of the allied tissue epithelium (fig. 81).

But it is otherwise in certain textures which, though appearing under
great variety of changeable forms, are yet connected by intermediate links,
and merge at times from one variety into another. These must be regarded,
consequently, as members of one natural group, and are known as the con-
nective substances. Cartilage, the consideration of which occupied us in
a former section (§ 53), is one of these ; further, colloid, reticular, and
ordinary connective tissue, fatty, bony, and — nearly related to the latter
— dentine tissue, must be also reckoned as belonging to them.

In all those various forms in which the members of this widely-spread
group of connective substances appear, we meet with cells imbedded

in more or less abundant intercellu-
lar substance. The cells, however,
display very different characters in
different instances, and no less so
the intercellular substance, which
may be found either in the form
of mucoid jelly, fibrous, and more
solid substance, or of hard stony

Fig. 101. — Tissue of the vitreous humor of a hu- matter

The' vitreous humor of the foetal

eye affords a beautiful example of an extremely simple texture (fig. 101).
Simple nucleated cells lie here in a watery jelly. If we can imagine
the latter replaced by a solid mass of chrondin, we have the well-known
appearance of cartilage (fig. 83).

It is seldom, however, that in the group of tissues under consideration
the cells remain in an abundant intercellular substance, so slightly
matured, as in cartilage. Crowded together, they may perhaps increase
in size, and, retaining their spherical shape, become rilled with neutral
fats, as is the case with fat-cells which have this origin,
as far as is known at present. But, as a rule, the forma-
tive cells of the connective-tissue group abandon the
spheroidal form, and grow irregularly.

At one time they become fusiform by extension in
Fipr. 102.— stellate ceils two opposite directions, as we have seen in a similar
suc- case, though on a far larger scale, among the elements
of involuntary muscle (comp. tig. 96, p. 95) ; at another they assume
more or less of a stellate form (fig. 102).

And, just as certain connective-tissue cells may become fat-cells, so at
this stage of development many pigments may be laid down in their
bodies, terminating their transformations. It is in this way that the
structures known as stellate pigment-cells are formed (fig. 50, p. 68).

In their further progress in development, connective-tissue cells mani-
fest, besides a tendency to continuous elongation, an inclination to fuse
with one another. In this way, by the cohesion of the processes of
adjoining cells, extremely delicate cellular networks are formed (fig. 103),
whose meshes are occupied by a mucoid jelly. But this latter may again
disappear, and be replaced by totally different matters, as, for instance, by
lymph-corpuscles. As they grow older, also, connective-tissue cells, tense
and full when young, may shrink and decrease very considerably in volume.
But, as already mentioned, the variety which the intercellular substance

ELEMENTS OF STKUCTUKE.

99

of connective tissue presents for our consideration is not less consider-
able than that existing among the cells themselves.
Consisting originally of albuminous matters (con-
sistently with its origin from the protoplasm of
the cells), it commences later on, as its solidity
increases, to contain glutin, or more properly,
collagen. In bone again, and in dentine, it
attains a high degree of hardness and firmness by
the reception into its' composition of large quan-
tities of the salts of lime.

It is not, however, changes alone of this kind
in consistence and composition which are to be
met with in the intercellular substance of the
connective-tissue group. Even if it escape solidi-
fications of the species just described, it still
manifests a great tendency to become streaky or
banded, or finally to break up into fibrillae.
Again, between all these varieties no very distinct
boundaries exist; and in the neighbourhood of
banded or fibrillated portions, we may encounter
more or less of a residue, as it were, of unchanged
homogenous intercellular substance. The fibrillse
alluded to are sometimes found in the form of
extremely fine isolated threads, but are usually
Arranged in bundles. They are known as con-
nective or cellular-tissue fibrillse.

Fig. 104 is designed to represent the latter.
In the preparation, which is from a structure four months,
intermediate between true cartilaginous and connective tissue, we find
simple cartilage cells scattered among bundles of fibres. In fig. 105
also we have these fibres (/), (grouped
in bundles at (g] ), between stellate con-
nective-tissue cells (a-e).

But this metamorphosis of the for-
merly homogenous intercellular mass
into collagenic fibres is not the only
one met with in connective tissue.
Another kind of thread-like element,
consisting of a material with far greater
power of resistance to reagents (comp.
§ 15), is formed by the transformation
of intercellular matter, and is known as

the elastic fibre (fig. 105, h). It also Fig. 104.- Fibrous cartilaginous substance
.. , , ° , , ' ' , from a ligamentum intervertebrale of man

is liable to vary much, both as regards

strength and the occurrence or absence of branches (fig. 106),

However, this appearance of elastic matter in the form of fibres is not
the only one it makes in connective tissue. The intercellular matter
may be transformed, at the boundaries of the tissues in question, towards
the cells and cellular networks, and likewise at their surfaces, &c. (but
still retaining its homogenous appearance), into limiting layers of divers
kinds, formed of a substance identical with, or optically and chemically
the same as elastin. These have frequently been erroneously taken for
cell-membranes and other peculiar envelopes.

Thus in the course of development of connective substance, a whole

100

MANUAL OF HISTOLOGY.

series of the most striking transformations takes place in an originally

purely cellular tissue.

§62.

Another series of metamorphoses which may be mentioned here leads,

it is supposed by a process
of fusion, to the formation
of many of the final ramifi-
cations of nerve-fibres.

But the mode of origin of
the unbranched nerve-fibres
situated in the middle of
nervous trunks (fig. 107, 1)
is still, it must be granted,
a most obscure point.

Nerve-fibres are usually
observed to divide in binary
order when near their ter-
mination (fig. 108). At
such points (at least appar-
ently) are situated stellate
cells, with usually three
processes (fig. 107, 2 a1,
bl. tr), one of which is

Fig. 105. — Connective tissue from between the muscles of the .. , ' , /» . .,, .-,

leg of a frog, a-e, connective-tissue cells ;/, flbrill£e ; and United by lUSlOU Wltll the
<7, bundles of the same ; A, network of elastic fibres. upper unbranched portion of

the fibre, thus preparing the way for ramification of the latter.

The neurilemma, or primitive sheath, a structureless tube which

envelopes the mature nerve-
fibre (fig. 108), is probably, as
in the case of the sarcolemma
of muscle elements, laid down
from adjoining structures.

§ 63.

The physiological relations
of the remaining tissue ele-
ments originating in the meta-
morphosis of cells, dealt with
in the second division, are so
very various that they must,
for the most part, be reserved
for future consideration. In
muscle-fibres and nerve-tubes
we have tissues of the highest
physiological dignity, while
the great group of connective
substances takes but a low
rank as investing or support-
ing tissues for the system.
The capabilities of transmuta-
tion are very various in the different tissues derived from the cell; but
at present our knowledge of the details of this subject is very imperfect.
Muscles and nerves, we are aware, are remarkable for the energetic

Fig. 106.— Elastic fibres from the human body. or. simple
and of the finer kind; c, a thick one, branching; 6,
fibrous network.

ELEMENTS OF STRUCTURE.

101

transformation of material which goes on in them, although the nature
of the processes is only known
as regards the striped fibre. In
contrast to this, many connective-
tissue parts are remarkable for
the great permanence of the sub-
stances of which they are consti-
tuted, especially when they are
only scantily supplied with blood-
vessels, and possess numerous
elastic fibres. In other struc-
tures of the same kind a very
rapid transmutation of material
may take place, when a large
amount of blood passes through
them, or when they are finely
canalised, as for instance, in the
case of bone. On the other hand,
all connective-tissue structures
display an enormous degree of
energy 111 a formative direction
under conditions of pathological
irritation, and are thus of great
worth in the plastic processes of
the diseased body, considerations
which will occupy us again in a

subsequent section. Fiff 107.— Development of nerve-fibres in the frog.

In regard to the products of transmutation much has been already said.
We refer the reader to pp. 21,
22 for the glutin-yielding sub-
stances ; to pp. 40-50 for the
alkaloids. The voluntary or
striped muscles, consisting of
albuminates, yield as decom-
position products, kreatin, krea-
tinin, hypoxanthin, inosinicand
lactic acids, and inosite.

Of the physiological decay
of the form-elements, and the
regeneration and length of exis-
tence of the same, we know
very little, excepting in the
case perhaps of striped muscle-
tissue. The duration of many
of them, as for instance, of
elastic fibres and allied struc-
tures, is probably long, for in
their case we have only remain-
ing the processes of solution
and degeneration, mechanical

attrition beino- excluded (comp. FiS- 108-~ Sma11 branching nerve-fibres, a and 6, from the

. ° 1-1 /> mesentery of the frog, surrounded by thick envelopes

p. 94). Ihe three Kinds OI studded with nuclei; 7, the trunk; 2 and 3, the branches.

transformation, by pigmentation, deposit of fat (fig. 109), and of cal-

102

MANUAL OF HISTOLOGY.

Fig. 109. — Human mus-
cle-fibre undergoing
fatty degeneration.

careous matters in cells, may at least be partially regarded as physiological
processes, but belong probably, in the elementary parts with which we are
now engaged (like many other modes of degeneration),
in a great measure to the pathological changes of the
system. Later on we shall be obliged to enter more
fully into the consideration of this subject.

§ 64.

Now, by the combination of structural- elements
of similar or dissimilar kinds, and in larger or smaller
quantity, the various tissues of the human and animal
body generally are formed. These are naturally regu-
lated as regards their anatomical texture, chemical
constitution, and physiological properties, by the ele-
mentary parts of which they are composed.

A classification of tissues that shall have any
scientific value is still a matter of the greatest dif-
ficulty— nay, we might almost say, of impossibility.
Such a classification, namely, can be founded only on
a knowledge of the mode of developmen^ of the
structural elements. But histogenesis, unfortunately, although com-
manding a considerable amount of material in many branches of our
science, is yet but very imperfect in others. The history of the origin
of tissues is, as a whole, not far enough advanced to enable us accu-
rately, and without being obliged to resort to many hypotheses, to
trace the outlines of a scientific classification of the various tissues. Even
that apparently easy and accurate division into simple and composite
textures cannot be strictly adhered to, and the question whether we
have before us a composite tissue or not must, in many cases, be decided
according to individual opinion, as to whether certain metamorphosed
portions of the ground-substances are to be considered as structural
elements or no.

The following classification, therefore, is only to be accepted as pro-
visional, being designed (as is usually the case in artificial systems) more
to bring in review in a certain order the materials to be considered,
than always rigidly to associate together parts probably related to one
another in their mode of development. The practical objects aimed at
in this work will render it necessary, besides, to consider many things
together, which logically should be dealt with separately. The following
is our division : —

A. Tissues composed of simple cells with fluid intercellular sub-

stance.

1. Blood.

2. Lymph and Chyle.

B. Tissues composed of simple cells with a small amount of solid

intercellular substance.

3. Epithelium.

4. Nail.

ELEMENTS OF STRUCTURE. 103

C. Tissues composed of simple or transformed cells (in some cases

cohering), situated sometimes in homogeneous, sometimes
fibrous, and, as a rule, more or less solid intermediate
substance (Connective-tissue Group).

5. Cartilage tissue.

6. Colloid do.

7. Reticular connective-substance.

8. Adipose tissue.

9. Connective do.

10. Bone do.

11. Dentine do.

D. Tissues composed of transformed and, as a rule, non-cohering

cells, with scanty homogeneous and more or less solid inter-
mediate substance.

12. Enamel tissue.

13. Lens do.

14. Muscle do.

E. Composite Tissues.

15. Nerve tissue.

16. Gland do.

17. Vessels.

18. Hairs.

8

n.

THE

TISSUES OF THE BODY.

II. THE TISSUES OF THE BODY.

A. Tissues composed of Simple Cells with Fluid
Intermediate Substance.

1. The Blood.

§65.

In the blood-vessels of our body, a closed system (except in the case of
the spleen) of intercommunicating canals, into which, however, the lym-
phatic and lacteals discharge their contents, there exists an extremely com-
plex fluid, " the blood," which is constantly in motion during life. And
just as on the one hand no pause takes place in its continuous circulation
while life remains, so on the other hand is this fluid unceasingly engaged
in a lively interchange of matter. The walls of the blood-vessels being
formed of membranes permeable to endosmotic currents, and processes of
nitration further occurring in glands, the blood is constantly being robbed
by the organs and tissues of certain of its constituents in the form of
watery solutions, while other substances similarly dissolved are rendered
back to it again. It receives also bulky additions of other complex fluids
in the shape of lymph and chyle poured into it.

Notwithstanding this coming and going of material which constitutes
the blood the centre of the vegetative processes of life, the fluid in ques-
tion is always singularly unvarying, both in regard to chemical and ana-
tomical composition, any deviations from the normal standard being
rapidly compensated.

Human blood is a thickish, opaque fluid with a peculiar faint odour,
alkaline reaction, temperature of about 38° C., and a red colour, — light
cherry-red in the arteries, but somewhat deeper in the veins. The amount
of blood contained in any one body cannot be estimated at present with
anything like accuracy, and we find statements on this point very various
as regards the human system. It appears probable that the weight of
the blood averages in man about a twelfth or thirteenth of that of the
whole body.

REMAKKS.^-Compare Nasse's article "Blut" in the Hundwb'rterbuch der Physiol.,
Bd. i.p. 75, and Milne Edwards, Lemons sur Tanat. et laphysiol. comparee, Paris, 1857,
tome i. p. 36 ; as also the various handbooks of histology.

§66.

If we examine the anatomical composition of the blood with the aid
of a high microscopic power, we find it to be made up of a transparent

108 MANUAL OF HISTOLOGY.

colourless fluid, the plasma, or liquor sanguinis, in which two kinds of

cells are suspended, namely, the " red blood-cells " and the " colourless," or

"lymph-corpuscles" of the blood (lymphoid-cells) (fig. 110). The first occur

^-v x-^-y^v in grea* preponderance, and are the cause of the

(§EJ > re(^ c°l°ur °f the blood, while the latter generally

' represent but a small fraction of the number of

•0 jj $@b~d ce^s contained in the whole mass of the fluid in

. Jj /->. question. Besides these, we also meet in human

(ff)a blood with conglomerationsof minute pale granules,

Fig. no.-Human Wood-ceils, measuring 0-001 1-0-0022 mm. (Schultze).

From above, a a; half side The coloured Uood-cells discovered long ago by

view, b; seen completely •*• » . t • ji-ii • ,1 • j

from the side, c; lymph- Malpigtii, and which have since then received very
corpuscles, d. difi?erent names, such as " blood-granules," " blood

globules," " blood-disks," "blood-corpuscles," and " blood-vesicles," appear
in human blood as circular formations, with a yellowish tint, and sharp
and delicate contour. They display among themselves but little variety
either in size or otherwise. Their number in a drop of blood is enormous;
it may be accepted as being about five millions to the cubic millimeter.
C. Schmidt estimates their specific gravity at 1-088-1-089, Welcker at
1*105. The diameter of the cell in the blood of the male averages
0-0077 mm., with extremes of from 0-0039 to 0-0024 mm.

With very accurate focus the living blood-corpuscles lying in the plasma
present in their centre a clear colourless space, and also at a spot in their
interior a slight shading of more or less semicircular outline, situated at
that side of their border opposite to that from which the light is thrown
on the field (fig. Ill, a).

The reason of this appearance becomes clear so soon as the cells are set
in motion. Far from preserving their circular form, in rolling over the
glass plate of the microscope, they appear when standing on their edge
(c c) like thin biscuit-shaped rods, with thickened bevelled ends, and con-
striction in the middle. In thickness they are about O'OOIS mm.

From what we have just seen, there can be hardly any doubt that the
form of the cell is in reality that of a biconcave disk with bevelled,
swollen edges. The volume of the human blood-corpuscle has been
estimated by Welcker to be 0*000000072 cub. millim, the weight 0-00008
milligram, and the superficial extent 0-000128 square millim. Its body is
composed of a completely homogeneous substance of a yellowish colour
by transmitted light ; this deepens to a rather reddish tint at points where
any two cells overlap one another. Should they commence to form
larger aggregations, they then begin to show the red colour of the blood
itself.

§67.

In order to make ourselves better acquainted with the further nature
of the blood-corpuscle, it is necessary to observe the effects of certain
external agencies upon it. If we expose a drop of blood on the glass
plate of the microscope for a short time uncovered, and allow it to evapor-
ate, the form of the cell changes (fig. Ill, b). With a decrease in size
down to from 0*0059 to 0-0052 mm., it becomes irregularly angular,
lumpy, and frequently stellate, the pointed portions coming out as dark
dots in the object. We have here to deal with a shrinking together of
the body of the cell depending on a loss of water, a process the interpreta-
tion of which in human blood presents many difficulties owing to the

TISSUES OF THE BODY.

109

Fig. 111. — Human blood-cells; a, after the action of water;
6, in evaporating blood ; c, dried up ; d, in coagulated
blood; e, arranged one over another in rouleaux.

minuteness of the object. If the blood dry up rapidly in very thin layers,
the corpuscles have usually a round smooth outline, with a distinct pro-
jecting central portion (fig. Ill, c).

If water be added to a drop of human blood, a completely different
picture is presented to the eye
of the observer. Far from be-
coming knobbed and jagged, the
cell preserves its circular smooth-
edged aspect, but the clear cen-
tral portion is no longer recognis-
able, and the yellowish border
stands out no more in relief
(fig. Ill, a). Close observation
teaches that the swelling up of
the cell commences at the border,
and that the encroachment of
the swollen portion it is which
causes eventually the two de-
pressions in the centre of the
blood -corpuscle to disappear.
As soon as a cell so treated
begins to roll, the important
difference caused by the loss of
its biconcave discoid figure becomes evident. We find the corpuscle
from every point of view spherical; it has swollen out into a globule
with diminution in diameter, down to 0'0061-0057 mm. Under the con-
tinued action of water this globule grows paler and paler (a to the right)
whilst the surrounding fluid acquires a yellowish tinge. Some cells are
very rapidly decolorised, others resist the action of the water for a longer
period. At last the corpuscle becomes so perfectly decolorised that it
can only be recognised by high magnifying power and in a shaded field ;
it is there seen as a very delicate, completely smooth-edged structure of
extreme paleness. During the whole procedure no nuclei make their
appearance.

The employment of many watery solutions, such as those of sugar, gum
arabic, common salt, &c., produces an effect on the cells similar to that of
evaporation. But if these reagents be gradually diluted a degree of con-
centration is at length reached, at which no further change of form in the
cell can be observed. If the solutions be still further diluted, we observe
eventually the same effects produced as those of pure water, namely, a
puffing out and bleaching of the cell until it becomes invisible. It is
most interesting to mark on one and the same cell the changes produced
by the alternate addition of various fluids one after the other, — changes
from the stellate wrinkled to the spherical tense form, and back again,
or rice versa.

All observations which have been made up to the present teach the
absence of nuclei, and present to us the blood-corpuscle as a structure
whose substance rapidly absorbs and parts with water, in the first instance
swelling up and acquiring greater volume, and in the second shrinking to-
gether. We see, further, that the colouring matter of the cell-body is soluble
in water. Now, if we apply the results thus obtained to the corpuscle as it
circulates in the blood, we have in it an element which must, indeed,
engage in a lively interchange of matter with the fluid of the plasma, but

110 MANUAL OF HISTOLOGY.

which, at the same time, undergoes neither a considerable variation in
volume nor loss of its colouring matter. It may he roughly stated to he
composed of a soft gelatinous substance which swells up in an excess of
water.

Besides these matters which act on the cell in the manner just
described, we are acquainted with a number of others in which the
protein matters of the blood-cell are dissolved, and with them the whole
structure. To these belong many of the mineral acids, and the salts which
the alkalies form with the bile acids. The action of another series of
reagents consists in coagulating the albuminous matters of the blood-cor-
puscles ; alcohol, tannic, and chromic acid, kreasote, and certain metallic
salts, may be mentioned among these.

Now, as to the effect of gases on the shape of the blood-cell, oxygen is
said to have the same power of diminishing its size possessed by saturated
solutions, while carbonic acid gas has the contrary effect.

An elevated temperature is also said to diminish the bulk of blood-
corpuscles. But besides these changes already long known, we have come
to the knowledge of many others of great interest within the last few years.
If the blood-corpuscles be left to themselves in defibrinated blood, they
pass gradually, in losing their vitality, from the disk-shaped to the
spherical figure. At a low temperature many days may elapse before
this transition is completed.

An electric discharge causes the cells to assume a rugged appearance,
coarsely granular at first, but finer later on. Soon after the corpuscle
takes on again the form of a smooth spheroid, and finally loses its colour
(Rollett).

If a living blood-cell be warmed up to about 52° C., a wonderful change
comes over it (fig. 112); it becomes rapidly marked by a varying number
of deep indentations ; shortly after this the formation of a series of bud-
like processes takes place, which either separate at once, or remain for a
time in connection with the rest of the cell-body by means of slender
filiform styles (a).

Owing to this, the most singular appearance of beaded rods is produced ;
globules are found with caudal appendages, &c.,
while the portions which have become free imme-
diately engage in the most lively molecular motion
(Bvale, Schultze).

By none of these modes of treatment are we
enabled conclusively to demonstrate the presence
of a membrane on the blood-cell of adult human
beings ; besides which, the changes just mentioned,
produced on them by an elevation of temperature,
can hardly be reconciled with the supposition of
such a structure. We are likewise never able to

Fig. ii2.-Hu?an blood- recognise any of those phenomena of vital cpn-
corpuscies heated up to 52° tractility in the mature blood-corpuscle, which

appear in so many other cells of the system.

Attention has bee a rather recently directed to some interesting dif-
ferences between the blood-cells of different regions of the circulatory
system. According to Lehmann's discoveries, the blood of the vena
porta contains the ordinary so mutable corpuscles, whilst in that of
the hepatic vein cells of anomalous constitution are to be found ; these
are smaller, more swollen, approaching the spheroid form, and having

TISSUES OF THE BODY.

Ill

nothing of the usual central depressions ; they resist for a comparatively
long space of time also the action of water. Similar cells also make their
appearance in the spleen (FunJce). They are looked upon by some as
young newly-formed blood-corpuscles.

REMARKS. — Beale in the "Quarterly Journal of Microscop. Science," 1864.
Transact, p. 32.

§68.

The study of the coloured cells of the blood of other vertebrates, as a means
of controlling the results obtained in the investigation of those of human
blood, is of great interest, and a chapter of comparative histology which
cannot, therefore, be completely passed over here.

The blood-corpuscles of mammalia present almost unexceptionally the
form of biconcave disks (fig. 113, 1), and the only slight variations in
them are those of size. Thus the cells of the elephant, which are the
largest, attain a diameter of about 0*0095 mm., those of apes correspond
with the human cells, and in many other mammals they are smaller than
our own, as, for instance, in the horse, 0'0056 mm., and rabbit, 0*0080 mm.
The blood-cells, however, of some of the ruminants, as of the lama, alpaca,
and camel, show striking deviations, being oval disks of O'OOSl mm. Of
nuclei, we see just as little in the coloured elements of mature mammal
blood as in those of our own.

Such elliptical blood-cells, however, become the prevailing form in the
succeeding classes of vertebrates, manifesting, moreover, striking varia-
tions in size; and the nucleus, which we have missed up to this, now
takes its place as a regu-
lar constituent of the
cell. It is only in a low
order of fishes, the cyc-
lostomata, that the cir-
cular figure of the mam-
mal cell is found again ;
and the lowest of all ver-
tebrates, the extraor-
dinary Amphyoxus lan-
ceolatm, possesses com-
pletely anomalous blood,
no longer red in colour,
and reminding us of that
of invertebrates : it need
detain us no longer here.

The corpuscles of
birds have an average
length of 0-0184-
0*0150 mm., and trans-
verse diameter amount-
ing to the half of this
(a a) (fig. 113, 3).

Seen from the side, instead of the biconcave disk, they present a bulging
out in the central portion of each surface. The nucleus, which in uninj ured
cells is either not at all visible, or only so as a slight clouding, appears on
proper manipulation, e.g., desiccation, or the action of water, &c., as
a dark structure with rough contour, elongated figure, and diameter of

Fig. 113. — Coloured blood-corpuscles. 1, From the human being ;
2, camel; 3, dove; 4, proteus; 5, water salamander; 6, frog;
7, cobitis ; 8, ammocoetus. At a, views in profile ; &, from the
edge (mostly after Wagner).

112 MANUAL OF HISTOLOGY.

0-0050-0-0043 mm. (in the hen). The nucleus usually occupies the
middle portion of the cell, but lies occasionally excentric.

Again, we find the blood-cells of scaly amphibia, of tortoises, lizards,
and snakes, also oval, but somewhat broader and longer than those of
birds. In length they range from 0-0182 to 0*0150 mm. ; but the central
boss is somewhat less prominent. The cells of the osseous fishes also are
small, and bat slightly oval (fig. 113, 7, a a 5), measuring O'0182-O'OIH.
In the naked amphibia and fishes with transverse mouth, the oval or
elliptical blood-corpuscles show the most astounding dimensions. The
length of those of rays and sharks is 0-0285-0-0226 mm. ; of toads and
frogs (fig. 113, 6, a a &), on an average 0*0226 mm.; of tritons
(fig. 113, 5, a a &), 0 '0325-0 -02 25 mm. ; and of salamanders,
0-0445-0-0375 mm. The diameters of the cells of the ichthyoida (Fisch-
lurche) are even considerably larger, so that a powerful eye can just recog-
nise them, without a microscope, as minute dots ; as, for instance, in
the cryptobranchus, in which their length is 0'0510 mm., and proteus
(fig. 113, 4), where they are 0*0570 mm.

.Finally, the cyclostomata (fig. 113, 8) possess, as we have already
remarked, red cells, having the form of small round
biconcave disks (b) with a diameter of about 0-013 mm.
All these cells conduct themselves towards reagents
in a similar manner to those of man ; but many of the
FI in— TWO bio< effects produced on them are naturally clearer and
ceils from the fro^. sharper owing to their larger proportions. In this
nudeiwasththlyacome respect the corpuscles of the frog may be particularly
to view under the noticed as objects easily procurable for first observa-
tions ; in them the nucleus can be rendered visible
in a moment by the addition of water (fig. 114).

The bodies of these cells may possibly contain a certain amount of
protoplasm, but a membrane is certainly not present on the greater
number of the corpuscles of frog's blood, as the spherical segmentation
observed among them seems to indicate : Rolletfs discovery also, that two
cells may coalesce to form one spheroidal mass, on being subjected to a dis-
charge of electricity, would lead to the same conclusions. Some isolated
cells, however, of frog's blood (possibly senescent) do possess a distinct
membrane.

REMARKS. — 1. Comp. Besides R. Wagner's works, which opened the way to farther
discoveries (Beitrage zur vergleichenden Physiologic des Blutes, Leipzig, 1833 ; und
Nachtrage, Leipzig, 1836. Gulliver (Proceedings of Zool. Society, 152, 1842).
2. The Amphiuma tridactylum has, according to Riddel, the largest of all blood-cells,
exceeding those of the proteus by a third. (New Orleans, Med. and Surg. Journ.,
1859. January). 3. Comp. Robert's in. ihe Quart. Journ. of Microscop. Science, 1863,
Journ. p. 170.

§69.

Whilst the coloured blood-corpuscles present in beings of the same
kind the greatest uniformity and correspondence (with the exception of
those extraordinary typical deviations in the vertebrates), and must be
looked upon as the fully developed and completed cells of the blood,
which undergo no further kind of perfecting in the system, but rather
decay at a later period by rupture and solution, the nature of the second
cellular element of this fluid, namely, the colourless blood-cell or so-called
lymph-corpuscle (lymphoi-d cell), is completely different. We have here

TISSUES OF THE BODY.

113

Fig. 115i — Coloured blood-cor-
puscles from the human
being, a toe; rf, a colourless
cell or so-called lymph-cor-
puscle.

to deal with cells engaged in the process of formation, with all the differ-
ences incident to their various stages of development. We have pos-
sibly also to deal with others engaged in retrograde metamorphoses. We
meet, therefore, in one and the same body several kinds of these cells.
But let us look to their characters.

The colourless cells of human blood appear when at rest, or in a life-
less condition, of spheroidal form, and varying considerably as to size.
Small examples measure on an average only about 0'0022, while those of
larger dimensions may be of the same size as the red corpuscles. They
usually, however, exceed the latter in magnitude, ranging from 0'0077 to
0'0120 mm. As the result of measurements made on those of my own
blood, I have found their usual diameter to be 0-0091 mm.

The appearance of these cells is finely granular, but the granules show
usually no molecular motion. Under high mag-
nifying power, however, this may be seen as in
other lymphoid cells. Their contour is also more or
less rugged. In most cases the molecules of pro-
toplasma are very small and delicate, but in some
isolated specimens we find considerably larger,
dark particles, consisting of fat, imbedded in the
interior. These have been probably taken up
from without (fig. 116, 4). The nucleus, enve-
loped in the smaller cells by a thin layer only of
protoplasm, is in many cases not to be seen with-
out the aid of reagents.

In some it may be rendered visible by the simple addition of water :
this, however, causes a change in its appearance, and the cell is at the
same time puffed out to a certain extent, and acquires a smoother and
more delicate contour. The action of acetic acid, also, brings it rapidly
into view. Thus treated, the nucleus is not unfrequently smooth (fig.
116, 6), but it is usually more or less rugged (7, 8), containing in its
interior a nucleus. In form it is roundish m ^

or elongated, and frequently irregular, espe-
cially after the prolonged action of acetic
acid. The diameter of the nucleus is
mostly about 0-0077-0-0052 mm. It may
frequently appear reniform (9), and in other
cases consists of two or three portions lying
in contact with one another (10, 11). In
consequence of the prolonged action of the
reagent just mentioned, these three portions
may become separated from one another by
considerable intervals. Finally, we meet
with cells whose nuclei have in this manner
been split up into four, five, six (12), or
even seven fragments. In addition to all
this, it must be borne in mind that some isolated lymph-corpuscles are
destitute of nuclei, so that the variety met with in the colourless blood-
cell is not inconsiderable.

Compared with coloured cells, the white are somewhat less sensitive
towards reagents. Observation of floating blood-cells teaches likewise that
the colourless corpuscles roll about with less ease, adhere more frequently,
and in general change their position with more sluggishness than the

i*> ©••

.(£)'© ef

Fig. 116. — Human colourless blood-
corpuscles. From 1 to 3, ordinary
unchanged cells; 4, one rich in fat
granules; 5, commencement of the
action of water; appearance of the
nucleus from 8 to 11 ; 12, the nucleus
divided by the action of acetic acid
into six pieces ; 13, free nuclei

114 MANUAL OF HISTOLOGY.

others, which has been set down to a certain clamminess of their surface.
Again, they are specifically lighter than their red companions. In a
drop of blood copiously diluted with water they gradually collect on the
surface. We will refer again, lower down, to their position in whipped
as well as coagulated blood, as the best proof of their lower specific
gravity.

REMARKS.— 1. It is now many years since Wharton Jones first demonstrated finely
and coarsely granular lymph-corpuscles in the blood of the most different vertebrates.
(Philosoph. Transact. 1846, Part II. p. 63. ) 2. Whilst the red blood-cell of the human
being is incapable, owing to its characteristic peculiarities, of being confounded in
any way with other cells of the body, it is quite another matter with the colourless
corpuscles. In many fluids of the system, containing protein matters in solution,
we meet with very similar, or more correctly, identical cells ;— in chyle, in lymph,
mucus, pus, and saliva; to distinguish these from the others is impossible. There
can be hardly any doubt, also, that the deviations from the typical form mentioned
above, may be partly owing to differences in age ; but to determine which are old
cells and which young is hardly possible. These colourless elements exist also in the
blood of animals, but subject to less variation as to size than the coloured. Accord-
ing to the dimensions of the latter, they may be the largest or smallest of the two
species.

§70.

In fresh blood the red cells give no signs of an active change of form,
and are only remarkable for their elasticity and extensibility. The white

corpuscles, on the other hand, belong,
in almost every case, to the class of con-
tractile cells already mentioned (§ 49) ;
and can retain this power of motion for
many days in blood which is preserved
cool. In cooled preparations, however,
these changes of figure can only be re-
cognised with difficulty, and take place
but slowly (fig. 117). But the whole
scene is changed if the normal tempera-
ture of the body be artificially main-
tained during examination (fig. 118).
We can then distinguish a lively de-
velopment of frequently very long pro-
cesses, and wonderful configurations of the lymph-corpuscle. The latter
creeps at the sa"me time hither and thither over the glass plate, and takes
up small particles of any matter in the neighbour-
hood into its interior, such as cinnabar, carmine,
or milk-globules, &c. But for this it is requisite
that the lymph-corpuscle have attained a certain
magnitude ; smaller ones put forth but inconsider-
able processes, and do not alter their position, while
the most minute, measuring perhaps G'0050 mm.,
do not even possess the power of varying their
shape.

These changes of form and locality of the lymph-
corpuscle may be also very easily seen in the blood
of cold-blooded animals : the frog and salamander
them contain particles of afford excellent examples.

The number of white blood-cells compared with

the coloured is always inconsiderable, and in the human being as a rule
very small; to a thousand of the latter we find at most two or three

TISSUES OF THE BODY. 115

colourless corpuscles. Their number is smallest during the hours of fast-
ing, when it may fall to about from 2 or 3 per thousand to 1000:0*5.

Old age, also, is usually accompanied by a decrease in the comparative
number of lymph-corpuscles. On the other hand, their quantity increases
on the introduction of food into the system, and especially after an abun-
dant meal of animal substances. Finally, we are told that during preg-
nancy, and at an early age, as well as after severe haemorrhages, the
number of these cells is greater than usual, — facts which all indicate a
lively formation of blood going on at those particular periods.

We find, also, that the proportions of both species of cell are not the
same in the various parts of the circulatory system. It is especially
worthy of note, that the streams of blood flowing from the liver and
spleen are uncommonly rich in colourless cells, so that of these we may
reckon 5, 7, 12, 15, and more, to each thousand of red. Under certain
pathological conditions, also, the relative proportions of both forms may
vary very much. In that strange disease, more nearly investigated by
Virchow, which is known by the name of leucaemia, the white corpuscles
may make their appearance in such multitudes as nearly to equal the red
in number, so that we may sometimes count to every five or three red, one
white cell. Indeed, it appears that the lymph-corpuscles may in some
cases attain a numerical preponderance over the coloured elements.

It is a very interesting study to watch the passage of both species of
blood-cell through the vessels of a
living animal. For this purpose the
thin web of a frog's foot (fig. 119), or
tail of a tadpole, may be chosen. Here
we see the red corpuscles hurrying
on swiftly and easily, and often pass-
ing one another in the race, while
the white cells advance with far less
rapidity, owing to their adhesiveness,
and not unfrequently remain cling-
ing to some point on the internal
surface of the vessel. Here, again,
we may convince ourselves of the
elasticity and extensibility of the
red corpuscle, which appears at one
moment diminished in breadth, for Fig 119_A 8tream 07blood in the web of a

instance, or indented at the point frog's foot, a, the vessel ; 6, epithelial cells

where it squeezes past a neighbour,

the next taking on its old form on again arriving in the unimpeded

stream.

But these passive variations in shape are met with to a far greater
extent in the red corpuscles of circulating mammalian blood, which pre-
sent to our view all kinds of forced changes of form so long as the fluid
is in motion, immediately returning, however, to the well-known disk-
shaped figure at the moment it attains a state of rest (Rollett).

§71.

If we now inquire into the origin of the colourless cells of the blood,
there can be but little doubt as to that of a certain number of them at
least. They are simply the cells of the chyle and lymph-systems, and, as

116 MANUAL OF HISTOLOGY.

we shall presently see, have been partly washed passively out of the
glands of the latter, partly have migrated actively from the same. They
may come likewise from the tissue of the spleen and medulla of bones, car-
ried off from these organs by the stream of venous blood flowing from them.

And touching their further significance, they have been for many years
regarded, and we may now say rightly so, as cells which are destined to
pass into red corpuscles, and thus to cover the loss of the latter according
to the rate of their decay. The colourless cells serve to replace the red
therefore.

This conjecture has, moreover, been confirmed by a remarkable discovery
of Von Recklinghausen, that frog's blood, collected in a vessel and kept
from evaporation, while the air about it is renewed several times daily,
will show, in from eleven to twenty-one days, a transformation of the
colourless corpuscles into the characteristic red cells of that animal. How
many or how few of the uncoloured cells undergo this change in the living
body is a question, however, which cannot at present be met by scientific
facts. The statements made on this point must necessarily vary greatly,
depending as they do on the hypothesis as to the amount of chyle and
lymph streaming daily into the blood, as well as on the still completely
unknown length of existence of the coloured blood-cells. It seems highly
probable, however, that a large number of these colourless elements never
attain this state, and pass to decay without being transformed into red cells.

But we are also still in the dark as to how this change exactly takes
place. We only know so much that the white corpuscle is transformed
(usually diminishing in bulk) into a circular flat plate, and generates
within itself a yellow material at the same time that it loses its nucleus
and protoplasm. Among the groups of vertebrates in whose coloured
cells a nucleus occurs, the latter structure is permanent.

Nor are we better enlightened as to the region in which this change
takes place. In some cases it appears to be over the whole circulatory
tract ; for we may remark in the blood of the three lower classes of ver-
tebrates, rare intermediate forms — that is, besides the usual nucleated,
red corpuscles — others of a much paler colour, with round or oval figure
(pale blood-corpuscles). These may be readily recognised, especially in
the large-celled blood of the frog and salamander (2). Then, again, very
similar cells may be found in the blood of the human and mammalian
spleen, of which it is difficult to say whether they still belong to the
lymph-corpuscles, or are already red blood-cells. Finally, similar inter-
mediate cells are met with, according to Bizzozero and Neumann, in the
medulla of bones, especially in the red species of medulla.

REMARKS. — 1. See Von RecTclinghausen in the Archiv. fur mikrosk. Anatomic, Bd.
ii. § 137. 2. Comp. Wharton Janes' work.

§72.

Though, from an anatomical point of view, blood may appear a toler-
ably simple tissue, with fluid intercellular substance, physiologically it is
a fluid of very complex constitution. In it we have the very focus of
vegetative activity, the stream upon which all the traffic of the system
takes place as it were. In it we must expect to find matters which serve
as well for the formation of tissues as for nutrition. These, however, may
still exist in several varieties of combination not met with in the tissues.
The most diverse products of metamorphosis also pass through the blood
on their way to excretion. We can hardly be surprised, then, that almost

TISSUES OF THE BODY. 117

all the most important substances in the system, with which we were
made acquainted in a former part of the work, are represented in the
blood. Many gaps, however, still exist in our knowledge on this parti-
cular branch of physiology, owing to the difficulty of the subject.

The matters which may at present be looked upon with more or less
certainty as constituents of the blood are the following : — 1. From the
albuminous group — haemoglobin, albumen, the two constituents of fibrin,
namely, fibrinogen and fibrinoplastin, near to which we place globulin,
obtained by the splitting up of the latter. Casein is not found, nor are
the glutinous substances or elastic matters. — 2. Of the solid fatty acids
(usually saponified, more rarely as neutral fats), stearic, palmitic (and
margaric ?) acids, to which oleic may be added. Of the volatile fatty acids,
we find butyric, with lecithin and cerebrin from the brain. — 3. Of the
carbohydrates, grape sugar, whilst sugar of milk and inosite are missed.
— 4. Of non- nitrogenous and nitrogenous acids, we find lactic and suc-
cinic (?), whilst others, as, for instance, oxalic, benzoic, and gallic acids,
are absent. — 5. Of amides, amido acids, and bases, urea, kreatin (?), krea-
tinin (?), hypoxanthin (?), and xanthin (?) ; whilst, on the other hand,
other allied matters, as leucin, tyrosin, glycin, taurin, are not contained in
it. — 6. Of extractives ; and finally, — 7, numerous mineral constituents,
among which we find, beside water — of bases, lime, magnesia, potash,
soda; and of metals, iron, copper, manganese (?) ; of acids, carbonic, phos-
phoric, sulphuric, hydrochloric, and silicic ; and finally, of gases, carbonic
acid, oxygen, and nitrogen.

A chemical analysis of this kind of the whole mass of the blood, is of
but little worth, however ; at most it only adds a few facts to chemical
statistics. Such an enumeration of its constituents only renders evident
that in it are contained the most important alimentary matters, as well as
many of the products of transmutation of our body.

Owing to the abundance Of elements of composition which it contains,
the first and most important point to be made out is — 1. What substances
enter into the composition of the red corpuscles, and in what proportions
do they exist there 1 2. Of what are the colourless cells composed 1 3.
Of what materials does the intercellular matter of the blood, the so-called
plasma, consist? 4. Since we must expect that some of the ingredients
of the blood exist in the cellular elements as well as in the fluid, we ought
to determine in what relative proportions they appear in the cells and in
the plasma.

In this way alone could we gain anything like a satisfactory insight
into the chemical constitution and physiological properties of the blood,
or ascertain what the blood-cell chemically is, and of what nature the
fluid is in which it is suspended, and with which it is constantly engaged
in interchange of material.

Do we now ask how far the requirements just stated are to be looked
upon as met by the present state of science, we must bear the following
points in mind. : — Firstly, all efforts to isolate the white from the red cor-
puscles of the blood have been hitherto unsuccessful. We are completely
in the dark, therefore, as to the composition of the former, and can never,
on the other hand, obtain the red perfectly free from the presence of
the colourless elements, — a source of error which is, however, but incon-
siderable in analysing human blood, owing to the small number of the
latter contained in it. Then, again, it is only occasionally possible to
make an analysis, which is then but approximate, of the blood-cells in

118 MANUAL OF HISTOLOGY.

a fresh, state as they exist in the blood, namely, loaded with water. This
is an evil which renders all earlier analyses useless, from the fact that
chemists were compelled to reckon the whole amount of water contained
in the blood to the plasma alone, which was quite incorrect, as, instead
of that, it should have been distributed, of course, between the latter and
cells. ?The plasma, according to this mode of calculation, appeared to
have a naturally large proportion of water, while wide play was given to
the theories in regard to the constitution of moist, moving blood-cells.

§ 73.

Some years ago the proportion, of moist cells in the blood was

ascertained by Hoppe. It is necessary to have for this analysis blood

which coagulates unusually slowly, so that the sinking cells may have

already disappeared at the time of operation from the uppermost layer of

the fluid. If we now ascertain the proportion of fibrin contained in a

certain quantity of this plasma freed from cells, and likewise in a given

quantity of blood, it is easy to find the amount of blood-plasma by a simple

calculation, and likewise by subtraction that of the moist corpuscles.

The following is the composition of horses' blood according to Hoppe: —

1000 parts contain —

Plasma, . 673'8

Moist corpuscles, ...... 326*2

1000 parts of blood-corpuscles contain —

Water, 565

Solid constituents, . . . . . . 435

1000 parts of plasma contain —

Water, . " 9084

Solid constituents, . . . . . . 9T6

Fibrin, . lO'l

Albumen, .' 77'6

Fats,

Extractives, 4'0

Soluble salts, 6 '4

Insoluble do., . ... . 1'7

From the foregoing analysis we see that the proportion of water in the
cells is not quite Jths, while in the plasma it is -j^*nsJ with which
the differences in specific gravity agree (cells = 1-105 plasma = 1-027-28
in the human being). We shall presently find that the solid constituents of
the blood-corpuscle consist principally of haemoglobin, a matter which
is entirely absent from the plasma, whilst fibrin and albumin are sub-
stances belonging particularly to the latter.

§74.

If we now turn to the consideration of the composition of the blood-
cells, that of the colourless elements must be passed over, in that they can-
not be isolated as already remarked. The little which might be said of
them, besides, can be more appropriately brought forward when we are
discussing lymph and chyle.

Red cells, as they appear in human and all mammalian blood, are
structures destitute of a nucleus, consisting of a homogenous yellow gela-
tinous substance, in which a lively interchange of matter may be recog-
nised. All substances, accordingly, which are contained in the blood-cell,
must be so in a state of gelatinisation or solution, if we deny the presence

TISSUES OF THE BODY.

119

Fig. 120. — Crystals of haemoglobin, from the
inea pig (above); from the horse flower

guine!
half).

of a membrane on the cell. The elements of composition belonging to
the red corpuscle are numerous.

In the first place, the cell-body consists of haemoglobin (§ 13), as was
already mentioned, divisible into two substances — an albuminous and
pigmentary, known respectively as globulin (§ 12) and hsematin (§ 35).
The first of these, however, has only been obtained in an impure state,
as both bodies defy perfect separa-
tion from one another. It appears in
the cell in far larger proportion than
the colouring matter ; for instance,
1000 parts of blood-corpuscles from
the horse contain 3 60 '4 of solid con-
stituents, of which 19 -9 consist of
hsematin and 321-1 of globulin.

Blood-ci'ystals, which were dis-
covered first by Funke in the blood
of the splenic vein, have already been
discussed (§ 13).

The crystallizing substances of
blood-cells are not by any means
always identical, a fact which is indi-
cated by the greater or less readiness
with which crystallization commences
in the blood of various species of
animals, and which is further corroborated by the varieties in the cry-
stalline form (figs. 120, 121).

The colouring matter of blood is, on account of its composition, into
which iron enters, one of the
most remarkable substances
of our body. Not being met
with either in the plasma
or the fluids compensating
the blood for loss, namely,
lymph and chyle/ it must
be formed by the chemical
activity of the blood-cell by
a process still unknown to
us. It is not always con-
tained in the same amount
in the corpuscles, which we
might at once infer from the
variation in intensity of the
tint of isolated cells, which
ai-e at one time yellow, an-
other of a paler hue. The
dilference in the colouring
properties of certain kinds of
blood when mixed with water
points to the same conclusion.

Fibrino plastic matter (Schmidt) has also been met with in the blood-
cell, and, it appears, in no inconsiderable quantity; besides which,
lecithin, cerebrin, and cholestearin (§ 21) (Hoppe, Hermann) have been
met with here. A proposition first made by Berzelius, that the " fatty

Fig. 121.— Haemoglobin trom the squirrel, crystallizing in
the hexagonal system.

120 MANUAL OF HISTOLOGY.

matters containing phosphorus" found in the blood might possibly
belong to the cell, was subsequently shown by Lehmann to be quite cor-
rect. The cells of venous blood, moreover, appear to be richer in these
cerebral substances than those of arterial blood.

Of the products of decomposition of the blood-corpuscle but little is
as yet known, except that hsematoidin (§ 35) may be regarded as a trans-
formation product of blood-cells breaking down in the living body; as
also bilirubin (§ 37), and in all probability cholestearin.

As far as these matters generated by the trans mutative power in the
cell do not rapidly leave the latter, or undergo further metamorphosis
immediately, they appear in the uninteresting form of the so-called extrac-
tive matters (p. 54, remarks).

Finally, the nature of the mineral constituents, proper to the cell in
contradistinction to those of the plasma, is of great interest, — an aspect of
blood analysis first brought under notice by C. Schmidt. Among the salts
of the blood-cell there appear some which are soluble in water, but in
smaller quantity than if the cell were simply saturated with plasma.
Further, the cell appears to be poorer in chlorine, but richer in phosphoric
acid than the plasma; it likewise shows a much larger proportion of
potash, and on the other hand a considerably smaller one of soda than
the latter fluid. Thus, we find in it principally the phosphates of the
alkalies, together with chloride of potassium, whilst chloride of sodium
preponderates in the liquor sanguinis. The latter is, moreover, richer in
phosphatic earths than the cell.

Now, since iron is not met with in the intercellular fluid (C. Schmidt),
all of this metal which exists in the blood must be contained in the cells.
Copper, also, and manganese (whose presence in. the blood, however, must
be still regarded as doubtful), ought also, according to analogy, to belong
to the contents of these elements.

Finally, the red corpuscles possess of gases almost all the oxygen of
the whole fluid, which gas is retained in loose chemical combination
with the haemoglobin, — a fact which may be looked upon as the greatest
in physiological significance of any yet adduced in connection with the
little structure in question. Besides this, the corpuscles contain a con-
siderable amount of carbonic acid (A. Schmidt).

What the nuclei of the blood-corpuscles of the lower vertebrate animals
consist of is not yet known with certainty; it is generally supposed to be
of some albuminous substance like fibrin, although a recent observer,
Brunton, believes them to be composed of mucin.

§75.

The number of substances held in solution by the intercellular fluid of
the blood is still more considerable than those contained in the cell.

First of all, we meet in the plasma with several matters belonging to
the albuminous group.

In the first place, the two constituents of fibrin, namely, fibrinogen
and tibrinoplastin, the latter finding its way into this fluid from the
blood-cells (§ 11). Coagulated fibrin formed from these appears in the
proportion of about 4 in 1000 parts of liquor sanguinis, but is liable to
vary considerably as to quantity, even in the healthy subject.

Albumen (serum albumen), which, as previous analyses have shown, is
contained in far larger proportion in liquor sanguinis than fibrin, is very
probably held in solution by salts.

TISSUES OF THE BOD!. 121

Besides this, another matter belonging to the albuminoid group is
generally present, namely, the "serum-casein" of Panum; yet, as
we have already seen (§ 11), it is probably nothing else than Schmidt's
fibrinoplastin.

As to the fats contained in serum, very little is at present known.
They occur for the greater part in the state of soap, and dissolved; more
rarely suspended in the form of fine molecules. Should they become
unusually abundant in the latter form, a cloudy opalescent appearance may
be communicated to the blood, although this is more frequently the effect of
a molecular precipitation of some albuminate. Moreover, it appears to
be the ordinary fatty acids which enter into the composition of the
serous fats, and we are warranted in accepting the presence of oleic,
palmitic, stearic (and margaric T) acids here (§ 17). Further a peculiar
substance, cholestearin, already mentioned (§ 21), is to be found in small
quantity in the plasma.

Turning now to the remaining and better known constituents of plasma,
which may be regarded for the most part as products of decomposition,
we find their number very considerable, owing to the nature of the fluid.
The following notes may be said to contain almost all that is at present
known about them.

Among the organic acids the existence of lactic acid in healthy blood
is not yet entirely beyond doubt, but it has been found in the latter under
abnormal conditions. Blood may also contain formic acid from the group
of fluid fatty acids. Acetic acid has been remarked after indulgence in
alcohol (§ 16), and succinic in the blood of phytophagous mammals (§ 24).

The non-existence of taurocholic and glycocholic acid in the plasma is
again of the highest physiological importance, whilst, on the other hand,
uric acid is met with ; the existence of hippuric remains doubtful (§ 26).
Among the organic bases we must accept urea, kreatin, kreatinin (?);
hypoxanthin, and probably' also xanthin, as being many of them present
in the fluid under normal conditions, a series which will probably be
enlarged in the next few years. Leucin and tyrosin only appear patho-
logically ; they may occur in the blood during diseases of the liver. In
addition to these substances we have grape sugar also (belonging to the
group of hydrocarbons) as a constituent of plasma (Bernard and C.
Schmidt) : it is partly introduced as such into the system, and partly
formed in the liver. This substance, as Lehmann and Bernard have
shown, is not to be found at all, or only in traces, in the blood of the
vena porta, whilst that of the hepatic vein is rich in it. Milk sugar, on
the contrary, is probably absent ; inosite has not been observed.

Finally, there exists an unknown colouring matter in the liquor
sanguinis, which gives rise to its pale yellow tint. The pigmentary
matters of the bile are absent here, on the other hand, in its normal
condition (at least usually). As to the extractives, their amount in the
plasma is greater than in the cells.

Ko\v, when we come to consider the mineral matters of the plasma, we
find them essentially different in quantity from those of the blood-
corpuscles. The proportion of chlorine is more considerable here than in
the cell, but that of phosphoric acid, on the other hand, smaller ; and
whilst the amount of potash exceeded that of soda in the cell, the case is
completely reversed in plasma, the quantity of soda salts, and more
especially of chloride of sodium, preponderating in the latter.

Further, the liquor sanguinis contains bicarbonate of soda, a small

122 MANUAL OF HISTOLOGY.

quantity of silicic acid, and probably also traces of fluoride of calcium.
Salts of ammonia are also present, in all probability, in healthy living
blood, though in very small amount. Iron, as was already mentioned, is
missing in the plasma.

In conclusion, the plasma, like all animal fluids, contains absorbed
gases, — small quantities of 0 and N, and a larger amount of C02 ;
besides this, carbonic acid appears in double chemical combination;
loosely combined, it represents the second acid atom of bicarbonate of
sodium, and is besides united in a subordinate manner with the phosphate
of the latter (§ 43). In fixed combination it is supposed to constitute the
first acid atom of carbonate of sodium.

REMARKS. — Volatile fatty acids belonging to the higher members of the series
appear to be not entirely absent ; witness the peculiar odour of fresh blood. This
odour may be due to the presence of butyric acid, although the latter has not yet
been proved to exist in the blood.

§76.

In the foregoing section we have had an example of the mean com-
position of the blood. But it stands to reason that the latter must be
subject to great variation in the proportions of its constituents, according
to age, sex, and other circumstances — according to the species of food,
and state of the secretions, even in our healthiest days. However, these
considerations belong more to physiology than to histochemistry. The
blood of men is generally supposed to be richer in cells than that of
women. The amount of corpuscles decreases also with increasing age,
and is in the earlier periods of life smaller than in the adult body. The
proportion of cells, further, sinks with bad nourishment, and also in conse-
quence of great loss of blood. Of the solid constituents of the intercellular
fluid, we know that the fibrin is subject to greater variation as to quantity
than the albumen. The latter, however> occurs in far greater proportion
than fibrin, and must, in fact, be looked upon as the most important con-
stituent of the plasma for the support and formation of the tissues.

But the difference in the various kinds of blood of one and the same
body is a subject of much more importance. Blood being the general
nutritive fluid, enters everywhere into an interchange of matter with the
tissues ; it gives up certain substances, and receives others back again.
And in that the chemical constitution of the several tissues and organs is
different, and also their series of transmutations, the composition of the
blood must be considerably modified in the various regions of the circu-
latory system. For instance, we will find blood flowing from the secreting
breast of a woman of a different nature from that which returns from
supplying the substance of the brain. But these deviations are still more
remarkable in the glands and lungs. The blood which enters the kidney
must be richer in urea, uric and hippuric acids, and certain mineral con-
stituents, than that which leaves it by the renal vein. Blood which flows
from the lung has given off carbonic acid and water, and, on the other
hand, received oxygen ; and so on.

Owing to the crude state of blood-analysis, this productive field of
inquiry has up to the present day yielded but little. We are even now
hardly able to ascertain anything accurately ; thus the difference between
arterial and venous blood, and that also between the blood of the vena
porta and hepatic vein : again, in what respect the fluid contents of the
splenic artery differ from that of the corresponding vein.

TISSUES OF THE BODY. 123

1. Arterial and venous Hood. The usual manner of examining these
is to compare blood taken from a vein of the skin with that from an
artery, consequently only one kind of venous blood. It is generally sup-
posed that arterial blood coagulates more rapidly on the whole, and is
richer in tibrin, extractives, water, and salts, than the venous, but does
not come up to the latter in its amount of albumen and fats. However,
we must not give too much weight to this. According to Lehmann, the
smaller veins contain more fibrin and water, but less cells, than the arte-
ries. The same observer found that the corpuscles of arterial blood have
more hseniatin and salts, but far less fats, than those of the venous fluid.
Again, arterial blood possesses, in comparison to the remaining gases, more
oxygen, while venous is richer in carbonic acid : the corpuscles of the first
of these appear red, those of the latter more or less greenish. Venous
blood is dichroic, when in thick layers it is dark red, and in thinner green
(JBrucke). A solution of reduced haemoglobin manifests the same dichroic
properties, whilst oxyhaemoglobin is monochromatic.

2. Blood from the vena porta and hepatic vein. It has been already
remarked above (§ 70) that fewer colourless cells appear in the vena porta
than in the hepatic vein. The cells, likewise, of the latter seem to differ
from those of the remaining kinds of blood, and especially from those of
the V. portai (§ 67). Finally, no fibrin separates from the blood of the
hepatic vein, according to Lehmann (a statement which is, however, ques-
tioned), while the vena porta does yield ordinary fibrin. This investigator
directed his chemical inquiry towards the blood of horses and dogs, and
obtained as a result a much greater richness in cells in the fluid of the
hepatic vein, together with a considerable decrease in the quantity of
water, consequent on the secretion of the bile. Further, the amount of
albumen here is said to be smaller than in the vena porta. In conclusion
(according to Lehmann), the blood of the hepatic vein is poorer in salts
and fats, richer, on the contrary, in extractive matters, and especially so
in grape sugar. The coloured cells of the hepatic vein are, besides,
remarkable chemically for their abundance of solid constituents, but the
amount of fat, salts, and iron in them has at the same time undergone
diminution.

3. Blood from the splenic artery and vein. We have already referred
to the blood of the splenic vein as that which, anatomically speaking,
deviates most from the usual standard of this fluid, in that it possesses a very
large contingent of colourless corpuscles (§ 70), and contains intermediate
forms between the two species of cells. It is, further, remarkable for the
more spherical figure of its cells, and the readiness with which crystalliza-
tion takes place in it, as we have seen in section 13. Fiuike directed
attention also to a somewhat modified form of lymph-corpuscle in this blood;
it is of larger size, and filled with fine dark granules. The only real
chemical difference, however, which could be distinguished by this observer
between this peculiar kind of blood and the ordinary kind of the splenic
vein, was a decrease in the amount of fibrin.

4. Menstrual blood. This blood, which is poured out from the turgid,
and probably lacerate'd, vessels of the uterine mucous membrane of women,
at intervals of four weeks, during the whole time they are capable of bear-
ing, is remarkable, at least frequently, for a deficiency of fibrin. It is sup-
posed that the latter has either coagulated already within the uterus, or is
prevented from undergoing this change by the admixture of mucus when
passing through the internal genital parts. But we are still in want here

124 MANUAL OF HISTOLOGY.

of a satisfactory chemical analysis. Microscopical examination shows the
fluid to be contaminated with the form-elements of mucus.

REMARKS. 1. Gray "On the Structure and Use of the Spleen" London, 1854, pp. 144

and 147. Here we find the abundance of colourless elements corroborated. Atten-
tion is also directed to the constant occurrence of dark pigment granules, or small
elongated crystalline formations, which are occasionally contained in cells. 2. Ac-
cording to Gray, loc. cit. p. 152, the blood of the spleen is poorer in cells, but, on the
other hand, richer in water, fibrin, albumin, and fat, than other blood. We shall
have to discuss, later on, the occurrence in it of other peculiar matters, in consider-
ing the organ in question.

§77.

This is probably the most suitable place to consider more closely
the varieties in colour in arterial and venous blood, already men-
tioned.

The colour of the blood (a body-colour) is produced, as we have already
seen, by the presence of multitudes of coloured cells suspended in the
usually colourless intercellular fluid. Without taking the subordinate
differences into account, the tint of arterial blood is a light or cherry red,
while that of the veins is of a darker or bluish red tinge (modena).

The. following is all that is known at present of the cause of these vari-
ations in colour.

It has long been known that certain gases produce a change in the
colour of blood. From time immemorial the light tint of the arterial
fluid has been ascribed to the action of oxygen, and the darker shade of
veins to that of carbonic acid. The correctness of this theory is easily
proved by conducting a stream of these gases separately into a quantity
of blood. A stream of oxygen causes the latter to become of a light cherry
red, and carbonic acid makes it dark. Besides this, blood which has stood
for a long time exposed to the air is always much lighter in colour on the
surface than deeper down.

A solution of haemoglobin is similarly affected by a stream of either of
these gases.

But this solution, freed, from formed elements, is transparent; it has
the appearance of a " lac colour."

If we allow blood to freeze, it displays, on being again cautiously thawed,
the same transparent colour. The microscope discloses the bodies of the
cells, but decolorised. The hemoglobin has passed from them in solu-
tion into the plasma. Such lac-coloured blood conducts itself in respect
to its colouring properties very similarly to the artificial haemoglobin solu-
tion of the chemist, and is exactly the same as the latter after complete
destruction of the cells. Its transparency is much greater than that of
normal blood with its coloured cells, and it appears with reflected light
darker than the latter.

The more red cells, then, the blood contains, the darker and more opaque
is it ; the less it possesses of such elements, the lighter and more trans-
parent does it become, seen by transmitted light.

The form, also, of the cells has a very great influence on the tint of the
blood. All agents which cause the red corpuscle^ to shrivel, as, for
instance, a concentrated solution of common salt, also render the blood paler
in appearance, as seen by reflected light, whilst all reagents which produce
an expansion of the cell, such as water, give rise to a darkening of the
whole fluid. Such blood increases also in transparency, as might be
expected.

TISSUES OF THE BODY.

125

It has been maintained by Nasse and Harless that a change of form is
produced in the red cells by the action of carbonic acid and oxygen gas,
the latter decreasing its size, the former causing it to swell out. This has
been doubted by others, but has again received support from recent
observers.

Many other things may also act on the colour of the blood, modifying
it; for instance, an abnormal preponderance of colourless elements may
produce a lighter tint in the fluid. Thus leucasmic blood often appears
strikingly changed.

§ 78.

Sinking of the Hood-cells. — The coloured blood-corpuscles possess, as
has been already mentioned, a considerably greater specific gravity than the
intercellular fluid — about as 1*105 : 1 -028 in man. They would always,
therefore, sink rapidly to the bottom in a vessel containing blood, or
indeed in any quantity of the same in a state of rest, in obedience to the
laws of gravity, were it not that the rapid coagulation of the fibrin ren-
ders this in most cases impossible. This gravitation, however, of the cells
does to a certain extent take place in blood coagulating slowly. But the
process may be distinctly followed up in blood deprived of the power of
coagulation, by being beaten up or mixed with other reagents. Here we
may perceive, after a considerable time, the commencement of a separation
of the whole mass of blood into two portions — a superficial, almost colour-
less, transparent layer of fluid, and a red mass of coloured cells, occupying
the floor of the vessel. Microscopical examination shows that the second
element of form, the lymphoid cell, has taken no part in this gravitation,
being a lighter body. Comparison of examples shows, also, that this sink-
ing of the red cells commences sometimes rapidly, and often after some
little time.

The position which the blood-corpuscles of human beings and mam-
malia (but not those of the other classes of vertebrata) take up in this state
is peculiar. Instead of floating about singly in the fluid, as was the case
during life, they now lie together

with their broad surfaces in con-
tact with one another, forming
aggregations (fig. 122, e) like
rouleaux of coins. If we follow
up this formation of rolls, which
begins even in a drop of blood
freshly taken from a vessel, and
observe it from its commencement
on under the microscope, the pro-
cess is seen to be initiated by the
coming together of pairs of cells,
which then cohere by their broad
surfaces. From this on, the rouleau
grows rapidly by the addition of
new members, and it frequently
comes to pass that other little
columns, or rouleaux, range them- F*- 122^Human^°edaS" s; '' formatlon of
selves with the first -formed at

various angles, giving rise to the formation of dendroid, and often almost
net-like figures. The addition of water at this stage of the process dis-

126 MANUAL OF HISTOLOGY.

members the rouleaux, in that the several cells swell out and assume the
spherical form, and thus again separate from one another. On this account
the roundish corpuscles of the blood of the hepatic and splenic vein show
no such columnar grouping.

The cause of this formation of columns is still unknown. The explana-
tion of the phenomenon through the adhesiveness of the intercellular
fluid or surfaces of the cells does not suffice.

At all events, it favours the descent of the coloured cells essentially,
for the little structures thus united must be able to overcome better than
when isolated the resistance offered to their gravitation by the fluid.
If rouleaux have once been formed, the same settling down makes itself
again rapidly evident in blood which has been re -agitated.

REMARKS. — It is a striking fact that, on the addition of anything which renders
the intercellular substance more dense, as, for instance, of concentrated solution of
sugar, the settling down of the blood-cells is accelerated, although just the contrary
might be expected.

§79.

Coagulation of the Hood. — The consistence of the blood begins very
rapidly to change a few minutes after it has been obtained from the
vessels — it coagulates, namely. This process commences much more
slowly within the vessels of the corpse, or in sanguineous effusions in
the interior of the living body. The latter may preserve their original
consistence for many weeks.

Now, as regards the phenomenon itself — first of all, we remark the com-
mencement of this change in blood taken from the living body in from
two to five minutes. The first step in the process is the formation of a
thin pellicle of the greatest delicacy on the surface of the fluid, which
soon acquires greater thickness and solidity, so that it may be at length
lifted off with- the point of a needle.

Commencing thus on the surface of the fluid, this formation of mem-
brane extends itself gradually along the sides and down to the bottom of
the vessel — in fact, at every point at which our sample of blood comes in
contact with the latter. The consistence of the blood so enclosed then
begins to change ; it becomes firstly somewhat thickish, like a half-cooled
solution of glue, attaining not long after the consistence of stiff jelly, or
of a saturated cold solution of glue. Then, at the end of from seven to
fourteen minutes the blood has lost all its fluidity, and has been trans-
formed into a thoroughly solid mass, whose form is determined by that
of the vessel in which it is contained.

This is, however, by no means the end of the process. The solid jelly,
overcoming the adhesion to the walls of the vessel, contracts subsequently
more and more, pressing out a part of the fluid which has been entangled
in it by the coagulation. The commencement of this contraction takes
place tolerably early, but it only reaches its termination after a compara-
tively long period, ranging from twelve to forty-eight hours. At first
there appear on the surface of the coagulum a few drops of a transparent
fluid ; the number of these soon increases, upon which they coalesce, form-
ing larger drops, and at last run together into a layer of fluid which covers
the surface of the coagulated mass. Whilst the coagulum thus pro-
gressively contracts to a smaller volume, similar layers of fluid to that
on the surface collect under the latter, as well as along the edges and
floor of the vessel, until the mass which at first adhered closely to the

TISSUES OF THE BODY.

327

cup; so that the latter could "be turned upside-down without its falling
out, commences to float in the expressed liquid.

From this on, the process only undergoes a quantitative alteration — that
is, a continuous contraction of the lump causes it to decrease more and
more in size, at the same time that an ever-increasing quantity of fluid
is being pressed out of its interstices. When the whole process is at an
end, we have a larger or smaller coagulum, sometimes soft and sometimes
hard, floating in a varying amount of transparent fluid, which has, like
the plasma, a slight yellowish tint. The coagulated mass having con-
tracted uniformly, preserves the figure of the vessel, and forms a diminu-
tive cast of the same, appearing in an ordinary porcelain basin plano-
convex, and in a test-tube cylindrical. Its colour is that of the blood, —
of a darker red, however, at the lower and internal portions than on the
surface, where it is light.

This red lump has received the name of the crassamentum or placenta
sanguinis, while the fluid in which it swims is known as the serum, or
serum sanguinis.

Now, how are these two portions of the coagulated blood related to
that which circulates in the living body, to its cells and intercellular
substance ?

We must remember, in the first place, that the latter is a fluid con-
taining the two constituents of fibrin in solution. And as in other cases,
so also after withdrawal of the blood from the system, these combine to
form coagulating fibrin, by which, in that the fibrinogen is. sufficient,
the whole fluid, together with its
cells, is entangled by the solidify-
ing mass ; just as a solution of
glue retains, on cooling, any par-
ticles which may have been sus-
pended in it — to make use again
of this ordinary simile. By the
progressive contraction of the
gelatinous mass, a part of this now
defibrinated intercellular fluid is
expressed in ever-increasing pro-
portion from its meshes, whilst the
blood-cells remain behind en-
tangled. From this we see that the
liquor sanguinis consists of inter-
cellular fluid deprived of its fibrin,
or is, in other words, defibrinated

plasma. The crassamentum must Fig. 123.— Human blood-cells ; coagulated fibrin at <?,

consequently be formed of the with included corpuscles,

blood-corpuscles entangled in coagulated fibrin. And, in fact, microscopical
examination of thin sections of the placenta sanguinis shows us the
unchanged cells embedded in a homogenous, fibrinous, or plaited sub-
stance (fig. 123,cZ).

Of course a more or less considerable quantity of the intercellular fluid
must still remain entangled in the cake of blood.

According to what has just been remarked, serum shares with the
plasma its transparency, light yellowish colour, and chemical characters.
Its specific gravity must, however, be somewhat lower, and may be
stated at between 1-026 and T029. It not unfrequently happens that a

128 MANUAL OF HISTOLOGY.

certain number of the red corpuscles escape being entangled in the
coagulum, appearing as a kind of reddish sediment in the lower strata
of the serum.

"When a quantity of blood is beaten and whipped up, the fibrin
deposits around the instrument used, and the former remains fluid. In
such defibrinated blood the sinking of the red corpuscles mentioned in § 78
may be best observed.

§80.

The process of coagulation of blood, moreover, displays much variety.
The consideration of each several point connected with it in detail, how-
ever, would lead us too far here ; we will only, therefore, touch on some
of the most important matters of interest.

As regards the rate at which the changes take place, we find that they
may be hastened or retarded. Retardation is easiest produced, as a rule.
The coagulation of blood is accelerated by setting the fluid in rapid motion,
as, for instance, by means of whipping or beating. The blood of men is
said to coagulate in general, more slowly than that of women. Further,
arterial blood solidifies more rapidly than venous, whose greater amount
of carbonic acid exercises a retarding influence on the process.

Again, atmospheric air accelerates the clotting Of blood, which explains
the fact that, the finer the stream of blood flowing from the orifice of a
vessel, or the flatter the dish in which it is caught, the more rapidly does
it become solid. Hewson's experiences, also, are in harmony with this,
who found that air injected into the vessels of a living animal frequently
furthered coagulation. However, we may prevent the access of air to the
blood of a dead animal with all caution, without being able to preserve it
in a fluid state. Thus we see that it may coagulate without the influence
of the oxygen of the air, as it does also in an atmosphere of carbonic
acid, hydrogen, or nitrogen gases.

As to the influence of temperature, we find that warmth favours the
process in general, while cold retards it. Coagulation may take place at
any point above freezing, and if we subject fluid blood to the action of
great cold it may be frozen before coagulation sets in, subsequently under-
going this change on being cautiously thawed.

How far changes in the composition of the blood may influence the
rate of coagulation has not yet been sufficiently accurately ascertained.
One important item in the process appears to be the nature of the fibrin
itself. Thus the blood of certain animals, as, for instance, of the horse,
solidifies slowly, whilst that of the sheep does so more rapidly. The
annals of medicine also record extraordinary cases of extremely late coagu-
lation, which are probably only to be explained likewise by some modifica-
tion in the constitution of the fibrin.

The character, also, of the crassamentum is liable to vary greatly; some-
times it is uncommonly small and hard, sometimes large, soft, and fragile.
Poorness in corpuscles may cause the first of these states, an increase in
the latter the second, in that a superabundance of cells — other things
being equal — must be looked on as a hindrance to the contraction of the
fibrin, whilst in an opposite state but slight resistance to it is offered.
A larger proportion than usual of water in the blood gives rise also to
a softer coagulum.

Beside all this, there occur also very incomplete cases of coagulation
where the process remains stationary in one of its earlier stages; indeed,

TISSUES OF THE BODY. 129

we see that very soft fragile clots may subsequently become again fluid.
Finally, in some portions of the system the blood does not undergo this
change at all, as, for instance, in the hepatic vein, and also possibly the
menstrual blood of the female (p. 121). The blood of persons struck by
lightning, and of those dead of asphyxia, has been found fluid in toto.

If in the moment of coagulation the coloured cells have already disap-
peared from the uppermost layers of the fluid, the coagulum does not
present the usual red colour, but is yellowish white in its superior por-
tion, then known as the crusta phlogistica s., wflammatoria. Micro-
scopic examination of the latter shows the absence of red corpuscles in the
coagulated fibrin, and, on the other hand, the lymph-corpuscles which are
specifically lighter imbedded in the lower part of this light coloured
stratum. And in that a quantity of cells usually hinders the contraction
of the fibrin, the latter shrinks with much more energy in this uppermost
layer, which is poor in the former, than in the parts of the cake which
are of a deeper red. This explains the fact, that the crusta phlogistica
generally forms a concave disk depressed in the centre, and smaller than
the red part of the placenta lying underneath it.

This buffed portion then is produced, on the one hand, by the more than
usually rapid gravitation of the red cells, or on the other by delay in the
coagulation of the fibrin. Thus we meet it as a normal appearance in the
blood of horses. It is met with frequently, likewise, in the human being
as a pathological phenomenon, and especially during inflammatory dis-
eases of the respiratory apparatus; but also under more normal conditions,
as, for instance, in the blood of pregnant women.

Owing to our ignorance in regard to the protein substances, this pheno-
menon of coagulation cannot be at present explained. Since the earliest
days of medicine, however, there has been naturally no lack of efforts to
do so. The cooling of the mass of blood, its coming to a state of rest,
or the action of oxygen on it, have all been looked upon as the causes of
the process. Eecently Briiclte has entered the lists in defence of an old
theory formerly held by A. Cooper and Thackrah, namely, that the blood
is retained in a fluid state by contact with the internal surface of the
living heart and blood-vessels. A. Schmidt also ascribes to these surfaces
the property of retarding coagulation.

This is the present (but let us hope temporary) state of our knowledge
on this point.

§81.

If we now ask, at the conclusion of this long inquiry into the nature of
the blood, How much is known at the present day of the conditions
during life of its two species of cells? we must allow that the results of
all research so far are but very unsatisfactory.

The red cells are the vehicles for the oxygen of respiration, and appear
to generate haemoglobin within them, and to contain fibrinoplastic matter.

The physiological destruction of these cells takes place, firstly, in the
blood passing through the vessels of the liver, taking a part there in
the production of the bile, as is indicated by the solvent power of the
alkaline salts of the biliary acids (p. 108), as also the near relationship
between haemotoidin (§ 35) and bilirubine (§ 37).

Again, we meet with another species of decay of the blood-cells in the
more quiescent blood of the spleen, where they form small aggregations,
which are transformed gradually into dark pigmentary masses. Forced

130

MANUAL OF HISTOLOGY.

into the amoeboid lymph-cells of the splenic tissue, the corpuscles and
their fragments may give rise to the formation of those cells containing
blood-corpuscles observed in the spleen. The same may also take place
possibly in the medulla of bones.

We may mention here another circumstance for the discovery of which
we are indebted to Strieker, namely, that by impeded circulation and
increased pressure the red cells of the blood are forced through the unin-
jured walls of small vessels (capillaries and veins). Thus partly unin-
jured, partly divided into small beads, in consequence of being obliged
to squeeze through, they reach the exterior, and are found in the neigh-
bouring tissues and adjacent lymphatic passages according to Herirtg.
In the first position they probably decay very rapidly, while their occur-
rence in the latter explains, at least partially, the presence of red blood-
corpuscles in the lymph, already long known.

It is only seldom that under normal conditions blood escapes into the
tissue of any living organ from lacerated vessels; but we have one case,
that of the ruptured Graaffian vesicle. Such extravasations, however, are
not of unfrequent occurrence pathologically. In both these cases we meet

Fig 124.— Blood-vessels of the frog's mensentery, eight hours after irritation Had "been set up, showing
emigration of lymphoid cells. A, a large capillary, shows at a, the mode of escape of cells, at 6, some
already escaped. B, a vein ; o, the lymphoid cells closely applied to the walls, and making their way
through; 6, external to the vessel; c, coloured blood-corpuscles.

with destruction of the coloured elements after coagulation, and production
from them of haematoidin crystals. In such effusions of blood, also, we
may again meet with those cells already mentioned containing blood-
corpuscles.

The colourless cells derived from the medulla of bones, the spleen, and
lymphatic glands, are now looked upon, and indeed rightly, as serving
to replace the loss of the red corpuscles (§ 71).

But in what proportion these undergo transformation into the latter is
not yet ascertained, and is dependent upon the length of existence of the
red cells, still completely unknown. However, we cannot doubt that such
a metamorphosis of white corpuscles into red does take place very exten-
sively after severe losses of blood, where a rapid reparation occurs.

But these lymph-corpuscles have yet another destiny.

TISSUES OF THE BODY. 131

Like the red cells, they also (but by virtue of their vital contractility)
pass through the uninjured walls of the vessels (fig. 124) in the healthy
as well as the diseased body ; in some cases re-entering the lymphatic cir-
culation, in others penetrating into various tissues (§ 49). Now it is
probable that partly, at least, from this source the wandering lymphoid
cells of connective tissue have their origin. These we will make the sub-
ject of later consideration. Under conditions of inflammatory irritation
such an exit from the blood-vessels in the vicinity of the affected part
takes place on a large scale (A. Waller, Cohnheim), and the pus-corpus-
cles appearing at this spot are, in part, nothing but the lymphoid cells of
the blood which have emigrated.

Finally, touching the origin of the blood in the embryo, we may pre-
mise by stating that we are but partially acquainted with this chapter of
histogenesis.

But in order properly to comprehend the process, we must first render
ourselves familiar with the broader and more important outlines of
embryology generally.

By the processes of segmentation in the impregnated ovum a cellular
material is formed which represents the germ, i.e., that spot at which the
body of the coming being is to be built up. It is first disposed in the
form of a membrane which, according to Remaps admirable investigations
(recently questioned, however), may be distinguished as made up of three
layers of cells arranged one over the other, from each of which certain
distinct tissues and organs have their origin. Thus we have a key to a
scientific classification of the tissues of the body.

For the present it need only be borne in mind that the upper stratum
bears the name of the " corneous" the lowermost that of the "intestinal
gland " layer (Darmdriisenblatt). The derivatives of each of these will be
met with presently. From the intermediate leaf known as the "middle ger-
minal" layer very many structures take their origin; thus, the whole of the
large connective-substance group, the voluntary and unstriped muscles,
the vascular and lymphatic systems with their accessory organs and con-
tents, including the tissue under present consideration, the " blood"

The first formation of blood then takes place at a very early period
in foetal life. But the primary blood-cells are not related in any way to
the characteristic corpuscles of later times, they are nothing but what
are known as the ordinary formative or embryonic cells of which originally
the most widely different structures of the body may consist. .

The first appearance of the primary blood-cells corresponds with that
of the heart and larger vessels immediately adjoining it. Both of the
latter are said not to be originally hollow, but solid aggregations of cylin-
drical form, consisting of cells. Now the destiny of these cells entering
into the formation of the cylinders is various ; the peripheral become ad-
herent to one another, or unite more closely still to represent the primitive
walls of the heart and vessels, while between the most internal, bordering
on the axis, fluid gradually accumulates in such quantity as eventually to
immerse the cells completely.

From this moment on we may with propriety speak of blood in the
embryo, in that the fluid in the rudimentary heart and vessels represents a
scanty plasma, and the cells suspended in it the primitive blood-corpuscles.

At first the latter appear, as has been already mentioned, in the form
of plain spherical cells, with finely granular protoplasm, vital contractility,
and frequently vesicular nuclei, within which nucleoli may be seen. They

132 MANUAL OF HISTOLOGY.

ire still destitute of haemoglobin, which gives them their characteristic
peculiarities at a later period of their existence. Their size is also very
•various, exceeding frequently that of the cells of fully developed blood.
Their average diameter in the embryo of fowl is, according to my obser-
vations, about 0*0128 mm.

Little by little the cell becomes clearer, and the characteristic yellow
tinging with haemoglobulin commences, this substance being deve-
loped by the body, of the former. Such coloured nucleated cells range
in their diameter in the human being and in mammals, from 0'0056 to
0-0160 mm. (Paget, Koiliker).

Whilst this transformation of embryonic cells into blood-corpuscles is
proceeding with the further development of the circulatory system, the
blood must of course contain, at the same time, both kinds of cells,
the coloured as well as the more advanced, besides immature colourless
ones.

During the earlier periods of foetal life, however, rapid multiplica-
tion of the red cells by means of division takes place, as was first observed
by Remak. This may easily be followed in the embryonic chick.

The process begins here with division of the nucleolus, then follows
that of the nucleus, which generally splits into two portions, and only
very, seldom, according to Remak, into three or four. Sometimes such
a nucleus will divide anew, but it requires a very close search to discover
in the chick cells engaged in more than the usual binary division. Finally,
the contractile body of the cell is seen to undergo constriction in the
middle until the two portions part company. The extreme delicacy of
these blood-cells frequently gives rise to artificial appearances, for
instance, of cells which are furrowed in the .middle, and only contain a
nucleus in one-half, or others whose two portions containing nuclei are
held together by a long, thin, connecting thread. In the foetal chick it
is just in these periods of formative life in which the liveliest increase of
blood takes place, that this process of division (which may, as it appears,
pass over very rapidly) can be best observed. Later on, at a more
advanced stage of development, it ceases altogether, according to Remaks
and our own observations.

We owe much to Koiliker for his profound in-
vestigations in regard to the blood of the mam-
malia. Of the correctness of his views I con-
vinced myself years ago in embryonic deer (fig.
125), as well as later on in rabbits and the human
embryo. Here also the same process of division
may be recognised. According to Remak, multi-
nuclear cells occur also frequently. To me the
nuclei always appear granular. Moreover, the act
of division is liable to temporary variations, it ap-
pears. Thus in rabbit embryos of 9 mm. long I
have only remarked a very small number of cells
fig. 125. -Biood-ceiis from the engaged in division, while the process could be

early embryo of the deer. The often recognised in much lamer Ones. The fur-
more spherical cells at a a a; ,, , ,.° p ,,

multiplication of the same from ther destiny of these in general st ill larger cells
(though they may vary considerably as to dimen-
sions), consists in this, that they take on more and more the spherical form,
lose their inequality as to size, and assume the typical shape ; the nucleus
disappears at the same time in mammals. Even at a very early period

TISSUES OF THE BODY. 1 33

isolated examples of such fully formed, yet extremely delicate ceils may
be observed among the spherical and nucleated of a still earlier stage
of development. Thus the embryos of the rabbits which I have examined,
of about 9 mm. long, showed £th to ^th of the whole number already with-
out a nucleus, and presenting the characteristic form of the blood-cell.
Kolliker found in sheep embryos of 8 -6 mm. long no such mature blood-
corpuscles, and Paget missed them also completely in a human foetus 9 mm.
in length. According to the first of these investigators, they are still
uncommonly rare in foetal sheep of 20 mm., while they constitute by far
the largest proportion of the cells in the young of the same animal measur-
ing 29 mm. In human embryos of the third month they only amount to
about from £th to ^th of the whole mass of the blood. Sheep embryos,
on the other hand, of 11 to 29 mm. show a fall in the number of nucleated
cells to a very small fraction.

The continued multiplication of red cells, which goes on naturally after
the process of division has ceased, appears to be carried forward in the
foetus, as in the adult, by the lymphatic glands, the medulla of bones, and
by the spleen. Very early the characteristic lymph-corpuscles, derived
from the latter sources, may be seen among the other coloured cells. That
the liver takes part in the formation of blood, as has been supposed,
appears very doubtful.

REMARKS. — Much has been adduced within the last few years in regard to the exit
through the walls of vessels of the cellular elements — an occurrence of the highest
significance in pathological and physiological questions, and especially in inflamma-
tion.

2. Lymph, and Chyle.
§82.

While describing the foregoing tissue we mentioned that certain of the
constituents of the blood are constantly passing from the capillary vessels
into the surrounding tissues in the form of watery solutions.

This escape of fluid is indispensable for the nutrition of the various
parts of the body, the organs as well as tissues, in that in these solu-
tions various alimentary materials are contained. Now the latter, we
know, are different in the several' tissues; they are specially adapted, for
instance, to the wants of bone, of the brain, of muscle, and so on. Then
the fluids of the tissues become gradually quite different as to chemical
composition by the loss of various materials of nutrition in particular
parts of the body.

But to these fluids are also added the results of the interchange of
matter going on in the tissues; the products of their decomposition; and
these are also, as has already been remarked in the chapter on general
chemistry, again different in the several organs. Here, then, we have a
new source of variety in constitution of the several tissue-juices of the
body.

Now for the carrying off of the latter, as far as they do not immedi-
ately return to the stream of the blood by processes of diffusion ; the body
is supplied with a special system of fine canals which communicate by
means of their main outlets (already long known) with the circulatory
apparatus. Their mode of commencement is only partially understood at
present.

This system of canals is known as the lymphatic or absorbent system.

134 MANUAL OF HISTOLOGY.

and the colourless fluid found in its vessels which has been strained
off from the blood -capillaries, as " lymph"

Now the latter, although it may appear pretty much the same to the
observer's eye in the various regions of the body, cannot possibly have
identically the same composition everywhere from what we have just seen
above. On the contrary, it will always be found to differ according to
the nature of the tissue or organ from which it flows, and to be, there-
fore, a fluid of more variable constitution than the streams of blood
belonging to the several regions of the circulatory system.

There is, however, in our body one portion of the lymphatic system which
serves other purposes, at least, at certain times. The lymphatic canals
namely, of the intestinal mucous membrane contain in the fasting state a
fluid possessing all the usual characteristics of lymph. During digestion,
however, there enters by the radicals of this system of canals a mixture of
albuminous substances and fats taken up from the alimentary matters. We
now find the passages charged with a whitish, opaque, and frequently milky
fluid, to which, owing to its appearance, the name "milk-juice" or "chyle"
has been given. These particular vessels are then spoken of as lacteals.

§83.

Both these juices contain, suspended in a plasma or fluid intercellular
substance, a considerable number of cells all possessing the same nature
(lymphoid cells) ; these are known, from the mode of their occurrence, as
lymph and chyle corpuscles. They were first discovered by Leeuwenhoek
and Mascagni.

In all essential particulars they correspond with the colourless cells of
the blood, already discussed at (§ 69) ; nay more, they are identical with
them. The cells of the lymph and chyle, namely, pass into the blood,
and circulate there as white corpuscles. Besides these, there are other
immeasurably small molecules to be seen, especially in the chyle, as also
larger elementary granules, while in some particular regions, especially of
the lymphatic system, isolated red blood-cells may be observed.

The ceils in both fluids display much variety as to size and other
relations, and no regular law seems to govern their distribution, although
one or other form of cell may at times gain the ascendancy in this or

that region. It is a fact of great interest,
farther, and one which may be especially
clearly recognised in the chyle absorbents,
that either none at all, or very few of these
corpuscles are to be seen in the finest

\~ ^~ , radicals, when on the point of leaving the

/>) (K) (^f wall of the intestine; but that they be-
V 0s— ' ^< \^J come all at once very numerous in the
fluid after the passage of the latter through
and° the mesenteric glands. The same may be

idae: °bSei>Ved in °tlier P<dI>tS °f the ^P^
as also at 10 and 11 ; at 12 it has sepa- System.

i?be?at±u8cfeipieces; at 13 we have Now as to the cells themselves, more

particularly, they may be said to have been

already considered when speaking of the blood. They are the same for-
mations, namely, with like diversity as to size, as to the body of the cell
and its contents, with the same kind of nuclei and endowed with the
like vital contractility as the colourless corpuscles of that fluid.

TISSUES OF THE BODY. 135

But while the cells of lymph and chyle are everywhere alike, the con-
trary is the case with the remaining elementary particles of these fluids.

On microscopical examination the chyle of mammiferous animals dis-
plays a certain amount of turbidity — the cause of its white colour to the
eye — produced by innumerable minute dust-like particles suspended in it,
and not by small globules of fat with which this fluid was formerly sup-
posed to be so richly filled. These particles (as is usually the case with
substances in a minute state of division suspended in fluid), are engaged
in a peculiar tremulous or restless movement, termed the molecular motion
of Brown. The more opaque and milky the chyle appears, the more nume-
rous are these molecules found to be. They decrease in number again
in the larger passages of the lymphatic system, and are completely absent
in the clear lymph of fasting animals. Eventually these particles flow
from the absorbents into the blood through the ductus tkoracicus, and
may form in it transient constituents of the plasma. As to ascertaining
their magnitude, with any approach to accuracy, we must confess our
utter inability to do so, owing to their extreme minuteness.

These dust-like molecules consist, we are told by H. Muller, of neutral
fats enclosed in a wondrously delicate layer of a coagulated protein
substance (albumen). Owing to this they do not coalesce, as free fat
globules would do, nor do they on the addition of water. But if chyle
be evaporated to dryness, the particles do unite on the subsequent addi-
tion of water, as also when acetic acid is mixed with the fluid. They are
dissolved by ether, to the action of which the albuminous envelope seems
to present no obstacle. We will see further on that these fatty particles
represent the fats of the food absorbed from the intestinal tract.

Besides these, larger and less clearly defined elementary granules of
0'0002 - O'OOll mm. in size are to be found in the chyle, partly scattered
and partly in groups. They appear to be the wreck of lymph corpuscles,
and probably occur in the blood also (§ 64) (Hensen, H. Muller).

Finally, we have blood corpuscles again brought before us in both
lymph and chyle. Some of these, doubtless, gain access to our prepara-
tions from wounded blood-vessels, and the admixture may be completely
avoided by careful dissection. On the other hand, such red cells may be
found almost always in the ductus thoracicus of many animals, as, for
instance, in that of the dog. The lymph of the spleen further appears to
be very rich in red cells (Thomsa), as also that of the liver (Hering}.
From this there would appear to be but little doubt that in isolated cases
lymph-corpuscles may undergo transformation into red cells before enter-
ing the* circulation. For my own part, I believe, I have observed inter-
mediate forms in the thoracic duct of the rabbit, between the two species
of cells; they are also to be seen in the blood of the splenic vein (§ 76),
and in the medulla of bones. On the other hand, the possibility of a
migration of red cells from the blood-vessels into the lymphatics through
the walls of the former (§ 81), Hering, must be allowed.

§84.

!Nrow, the question as to the source of these lymph and chyle cells, is
one of the utmost importance for the histology of the present day.

And since their spontaneous generation in both fluids could not any

longer be allowed, and that they were found to be either entirely absent, or

only to occur with extreme rarity in the commencement of the absorbents,

while immediately after the passage of the fluid through the lymphatic

10

136 MANUAL OF HISTOLOGY.

glands they were met with, the possibility of their origin in these so-
called glands was recognised even years ago. This view received sup-
port, also, from, the discovery that the contents of the latter is the same
as that of the lymphatic vessels. In the mucous membrane of the
digestive tract there occur also small lymphatic glands, known as "Peyefs
patches," and hence the origin of the few isolated lymph-corpuscles found
in the smaller branches of the chyle vessels, leaving the intestinal
tube.

And, in fact, the cells of lymph and chyle are the corpuscles of these
organs which have penetrated into the hollow interstices of the lymph-
nodes, and have been carried off by the stream of fluids. These points if
borne in mind will render the description of the lymphatic glands more
easy of comprehension, in discussing which we shall have to consider the
origin of the cells in question in the latter organs.

How far these cells are capable of undergoing multiplication in the
lymph and chyle streams, is also a matter worthy of our consideration.
At present we are in possession of no reliable facts bearing upon this
point.

§85.

However important it might be to determine the amount of these fluids
in the body, even approximately, science possesses at present no certain
data to go upon in regard to- their quantitative analysis. We can only,
so far, conjecture that the amount of both must be very considerable, and
that, as through the lacteal system, so also through that of the lymphatics,
an extensive intermediate circulation exists.

If we now turn to the chemical constitution of these two fluids, we
have at present but very insufficient analyses to go upon. Hitherto it
has not been possible to investigate chyle and lymph in a manner
adequate to the requirements of histology. We cannot yet even accurately
determine the composition of the moist lymph-cell. All the rough analyses,
too, which have hitherto been made, display enormous differences, owing
to the difficulty of obtaining large quantities of lymph and chyle in a
pure state, and to the changeable nature of both liquids.

As to the cells, they consist of various modifications of albuminous
compounds, the enveloping layer showing different reactions to those of
the nucleus and protoplasm of the body of the cell, which encloses
molecules of a coagulated albuminoid, and of fats : it is soluble, namely,
in dilute acids, while the nucleus is not.

Lymph is a more or less clear, alkaline, watery liquid, whose specific
gravity is not yet known. In it may be found, again, those protein sub-
stances which are likewise present in the plasma of the blood namely,
the two constituents of fibrin, with albumen and its modifications. The
former give rise here, also, to the coagulation of the fluid when collected
in a vessel. And yet a difference exists between the fibrin of lymph
and that of blood in the manner in which it solidifies. Lymph, namely,
does not usually coagulate in the corpse, but subsequently on being
drawn off, and only after frequently very long continued exposure to the
oxygen of the atmosphere. As far as is known at present, from ten to
twenty minutes appear necessary ; but even an hour may pass over before
it takes place (Nasse). The lymph-clot retains also, as was the case with
that of the blood, the form of the vessel in which it solidifies, but is
naturally much smaller on account of the much smaller number of cells

TISSUES OF THE BODY.

137

which it contains. Another peculiarity frequently observed, and which
I myself am in a position to verify, is also very striking ; the coagulum,
namely, may become red on exposure to the air, a change of colour
probably depending upon the generation of the pigmentary principles of
the blood through the action of the atmospheric oxygen.

The amount of fibrin seems, moreover, to be liable to considerable
variation.

The albumen of lymph exists, like that of the plasma of the blood, in
combination with soda as albuminate of sodium. Casein is missed, as in
the blood also.

The fatty matters, individually but slightly known, appear partly as
neutral fats and partly saponified with soda. Their amount, like that of
albumen, seems to vary considerably. Besides these, lymph contains
also grape sugar and urea. As to the extractives which are here met
with in no small amount, their nature has not been investigated.

Chloride of sodium is very strongly represented among its mineral
constituents, as well as the carbonates of the alkalies; besides which, the
usual combinations of phosphorus and sulphuric acid of the system all
occur in lymph. Finally, iron also makes its appearance here.

Although the proportion of water in this fluid always remains larger than
that in the liquor sanguinis, it is still subject to very considerable variation.

Lymph contains no oxygen, or only traces of it; it does, however,
possess nitrogen in small amount, and carbonic acid seems to be present
in great abundance. A portion of the latter is held in loose combination,
another portion can only be displaced by acids.

On the whole, it would seem that lymph possesses a composition
allied to that of the plasma of the blood, both of them apparently con-
taining exactly the same proportion of salts (Nasse). But in general
it may be stated to be richer in water and extractives, but poorer in
albumen, fats, and salts than the liquor sanguinis.

Not long since analyses were undertaken by C. Schmidt, in which, for
the first time, the coagulum and serum of lymph were separately treated.

The lymph to be analysed was obtained from the neck of a foal, which
had been previously well fed with hay : it showed the following com-
position : —

1000 parts of lymph contain
• Serum, . . . " . .955-2
Coagulum, . . . 44 '8

1000 parts of serum contain : —
Water, . . . 957'6
Albumen, . . 32 "0

Fats and fatty acids, . 1*2
Other organic .matters, 1'8
Salts, . . . .74

1000 parts of coagulum contain: —
Water, . . . 907'3
Fibrin, . . . 48 '7
Albumen, . . \

Fats and fatty acids, V 34'3
Other organic matters, |
Salts, . . .'9-7

In regard to the mineral constituents, Schmidt observed a similar,
though less marked, contrast between cells and plasma, as in the blood
(comp. § 75).

Now, as to the chemical constitution of the chyle, we find it slightly
alkaline. Owing to its greater richness in fatty matters also it is more cloudy
or milky than the fluid last mentioned, and in general richer in solid
constituents, so that its specific gravity lies between 1'012 and 1'022.

138 MANUAL 01 HISTOLOGY.

It partakes of the same peculiarity as lymph, in coagulating some con-
siderable time after it has been collected from the body; it does so, how-
ever, with much greater rapidity on the addition of a certain amount of
blood (A. Schmidt). We have already mentioned (§ 11) that the fibrino-
gen of the latter fluid has its origin in the red blood-corpuscles. The
coagulum of chyle may also subsequently become red on exposure to the
air. Its fibrin generally contracts much less, and remains more gelatinous,
at the same time that it possesses greater solubility.

Albumen, an important constituent, as we would be led to expect from
the nature of chyle, appears in considerable, but, according to the kind of
food, variable quantity. We have already mentioned its partly forming
the envelopes on the minute molecules of this fluid; but another portion
of it is present in the form of solution in water.

The amount of fats, also, in chyle, though necessarily subject to great
rise and fall, is far larger than in lymph. Primarily, whilst in the finest
vessels all of them are found as neutral compounds suspended in a state
of the most, minute division, later on saponified fats make their appear-
ance, as observation with the microscope teaches us, by means of which
we see the formation of fat-globules in a clear fluid on the addition of
an acid (H. Muller).

Again, we find that grape sugar and urea are contained in this fluid.
It may also have lactic acids in its composition, according to Lehmann.

Chyle contains, also, a by no means inconsiderable proportion of ex-
tractive matters and the ordinary mineral compounds, such as the alkaline
salts, with chloride of sodium in large quantity. Further, minute
quantities of the earthy salts and iron have been found in it.

A rather old analysis of Rees (1) may serve as a clue to the com-
position of the chyle, beside which we give one of lymph by the same
author.

Chyle obtained from the ductus thoracicus of a^-onng donkey -. .. «mltlw. nf

seven hours after having been fed on peas and beans (after Se wme wiTmaT

Water, .... 902-37 965'36

Fibrin, *$ . . . 3'70 1-20

Albumen, . . .- . 35 -16 12-00

Watery extract, . . 12-33 13-19

Alcoholic do., ... 3 -32 '2-40

Fats, 36-01 Traces

Salts, . . . . 7-11 5-85

Strangely enough, the most recent experimenter on chyle, C. Schmidt,
arrived at completely different results in his analysis of that from the
thoracic duct of the foal. According to this observer, the composition
of both fluids, of lymph and chyle is exceedingly similar, except that
the latter showed a somewhat larger proportion of iron, whilst the
amount of fat found in it was extremely small.

The following is the composition of the chyle obtained from the
thoracic duct of a healthy foal, which had been fed three hours before
with meal-pap and hay : —

1000 parts contained

Serum, 967'4

Coagulum . . . 32 -G

TISSUES OF THE BODY.

ISO

In 1000 of coagulum of the chyle : —
Water, . . . 887 '6
Fibrin, . . .39'0
Free fat, . . . 1*5
Fatty acids of the soaps, 0'3
Albumen . . . ")
Sugar and other organic >• 66*0

matters, . . )

Haematin, . . 2'1

Mineral constituents )

without iron, . j

5-5

In 1000 of serum of ditto : —
Water, . . . 958*5
Fibrin,

Free fat, . . . 0'5

Fatty acids of the soaps,
Albumen,
Sugar and other organic )

matters, . . j
Hsernatin,
Mineral constituents

without iron, .

0-3
30-9

2-3

7-5

As yet we know but little as to the first appearance of lymph-cells in
the embryo. But from the fact alone, that lymph-corpuscles may be
observed in foetal blood at an early period, we may infer that they occur
also largely in the lymph.

REMARKS. — London, Edinburgh, and Dublii
Comp. also Nasse's article "Chyle," p. 235.

Philosophical Magazine, Feb. 1841.

B. Tissues composed of simple cells, with a small amount
of solid intermediate substance.

3. Epithelium.
§86.

By epithelium we understand a tissue formed of closely associated
cells, which clothes, in layers of greater or less thickness, the external and
internal surface of the body, canals of exit and even numerous com-
pletely closed cavities of the system. It is only through the nearer
acquaintance with the history of its development that we have been
enlightened as to its true nature. And for this we are indebted to the
searching investigations of Remak, from which we learn Jihat at an early
period of development the flat rudimentary embryo is bounded above
and below by two strata of cells, the corneous and intestinal glandular
layers. From the first of these the epithelium of the external surface
takes its origin, and from the second that of the digestive tract. But the
cells of these two layers play a further part in the construction of
numerous' other organs.

Thus we find that it is not alone the outer clothing of the body, the
skin, with its manifold reduplications, which bears these epithelial layers
of cells, but the mucous membrane also with which it is continuous,
the glands of the intestinal tube, the internal surfaces of the respiratory
and generative apparatus, and even parts which have completely ceased
to communicate with these primordial epithelial layers ; as, for instance,
the cavities in the brain, the spaces and bounding surfaces in the eye
and auditory, organs: these all possess this characteristic covering. Owing
to the fact that the secreting gland-cells having the same origin as
the epithelia, we frequently find transitions from one kind of cell into the
other in the interior of those organs.

The epithelium extends, however, still further throughout the body.
The strata of cells enclosed between the corneous and intestinal glandular
layers, namely, the so-called middle or intermediate layer, becomes, with

140

MANUAL OF HISTOLOGY.

advancing development, the seat of various cavities which acquire subse-
quently on their inner surface a clothing of epithelium. It is in this
exceptional manner that the epithelia of serous cavities and lining mem-
branes of the heart, with the blood and lymphatic vessels, have had their
origin.

The elements of epithelium are pale, transparent cells, with distinct
nuclei, only absent in the older cells of many kinds of tissues. The
size of these cells is liable to vary greatly; it lies between 0*0074 and
0'056 mm. ; that of the nucleus is less so, whose diameter may be stated
on an average to be from 0'0045 to 0'0091 mm. The appearance of the
latter may be vesicular, homogenous, or granular.

It has already been remarked that the surfaces of the body are clothed
with layers of epithelium of varying thickness. The depth of the tissue,
in fact, changes to a most extraordinary extent in the several localities of
the system. Whilst some strata of epithelial cells may attain a height of
2 mm. and upwards upon the external skin of
the human body, so that they were recognisable
to earlier generations of anatomists without the
aid of the microscope, they may yet decrease
in thickness in other places, forming thin coat-
ings of only a few layers of cells, invisible to
the unaided eye. Finally (and this is the case
over by far the greatest portion of the sur-
face of the body), this tissue may consist
Fig. 127,-Fiat epithelium cells from of one single extremely delicate layer of cells.

the human mouth. The most important feature which this so

widely-distributed tissue presents for our consideration is the variety
of form which it displays, which has led to the recog-
nition of several distinct species of epithelium. It is
comparatively seldom-^-and in the human body over
very limited areas — that epithelial cells preserve the
original typical form of the cell, namely, the sphe-
roidal. We generally find either one or other of the
changes affecting the spherical body already considered
(§ 46), i. e., flattening or lateral compression, so that
it usually appears, with modifications in particular instances, either
as a flattened, squamous, or narrow cylindrical cell.

We must therefore distinguish between 1, the flattened or .pavement
epithelium (fig. 127) and 2, cylinder or columnar
epithelium (fig. 128).

Other modifications of this tissue may arise from
the free surface of the cells bearing minute hair-like
appendages, as we have already mentioned. Thus
a third special form is produced, the ciliary epi-
thelium, fig. 129. In man and the higher animals
it is almost exclusively upon the cylindrical cells
that these supplemental structures occur.

Again, in certain regions of the body the cell is
found to possess peculiar contents, namely, granules
of black pigment or melanin, with which its body may be charged.

In human beings and mammalia it is only the more flattened cells of
the epidermis which have these exceptional contents. They represent
what used to be described by histologists as polyhedral pigment cells

Fig. 128.— Cylinder ojr
columnar epithelium

tine of the rabbit.

Fig. 129.— Various forms of
ciliary cells from verte-
brata.

TISSUES OF THE BODY.

141

(fig. 130). According to our way of thinking they should be called
pigmentary epithelia.

The extremely variable depth of this tissue just mentioned leads to
further variety. Besides epithelium, in which many layers are placed
one over the other, forming a heavy coating
(fig. 131), we find others made up of but one
single stratum of cells (fig. 132) ; and between
the densely laminated and non-laminated species
there exist many intermediate forms, in which
only a few strata are to be seen, disposed one over
the other. It must be borne in mind, from this Fig. iso.— Pigmentary flattened
on, that it is only the flattened epithelia which are hSnS
capable of becoming laminated to any remarkable 8heeP-
extent ; but that they need not necessarily everywhere take on this form.

§87.

The most widely distributed variety of the tissue under consideration
is the flattened or pavement epithelium.
Overlooking its more limited occurrence
in certain regions, it is met with on the
external skin, on many mucous mem-
branes, in serous sacs (true and false),
as well as on the internal surfaces of the
vessels of the circulatory system. Its
thickness is subject to the greatest varia-
tion, so that, at one time strongly lamin
ated, it represents the strongest of all
epithelia; at another it displays merely
a delicate coating of cells of the simplest
kind.

Simple pavement epithelium (1), in
the first place, forms the internal coating
of the cavities of the heart, as also of
the blood and lymphatic vessels. (2.)
It makes its appearance, further, in the
true serous sacs on synovial membranes
(bursse, sheaths, and capsules for the
joints). (3.) Again, within the eye, on
the posterior surface of the cornea and
anterior of the iris ; on the internal surface of the anterior segment of the
capsule of the lens ; within the auditory apparatus,
namely, on the periosteum of the internal ear, the
inner surface of the semicircular canals and vesti-
bule. To what extent gland ducts possess such a
lining need not for the present be discussed. We
find sometimes a simple and sometimes slightly
laminated pavement epithelium in the canals of Fig. 132.— simple coating of
exit of the sweat and ceruminous glands. The nTuc^me^bran^Fibrou*
infundibuli of the lung are likewise lined by the tissue of mucous membrane
same species of cell. (4.) Finally, the greater part

of the ventricles of the brain in the adult is covered with a species of
pavement epithelium instead of the ciliated cells of early life.

Fig. 131 —Vertical section of the skin of a
negro. Thick laminated epithelium lying
on the elongated papillae of the dermal
tissue (a), with younger cells at b and c,
older at d.

142

MANUAL OF HISTOLOGY.

Fig. 133.— Simple pavement epi-
thelia. Serous membrane at, a ;
from a vessel at b with lateral
view.

The elements of this tissue consist of pale flat cells (fig. 133) placed
closely together, and without any apparent intercellular matter. They are
frequently destitute of granular contents, but display at times very minute
dust-like molecules. Such is the indistinctness of limitation in the cells, in
certain instances, that their outlines may not be
apparent, or they may seem to fuse into one an-
other. Their boundaries usually become visible,
however, in the form of dark lines, on treat-
ment with a dilute solution of nitrate of silver.

These cells possess distinct nuclei, sometimes
granular, sometimes smooth-edged, in the in-
terior of which one or more nucleoli are usually
visible. Their form is twofold; in one instance
they may be broad, with a polyhedral outline
(d) and diameter of 0'0226-0'0090 mm., while
the round nucleus is 0'0075-0'0057 mm. ; in another their shape is more
or less lanceolate, and length — 0 '0226-0 '0455 mm. — with a similarly nar-
rowed nucleus (b). In side view such cells may present a very peculiar
appearance (&); they then seem to possess the form of short fibres, thickened
considerably in the middle, where the nucleus is situated. The first of
these species of cells is found lining serous sacs, the latter clothing the
internal surface of blood-vessels and lymphatics ; but here again there
exists much variety (Legros). In the arteries we find long and narrow
cells, while the endothelium of veins is made up of shorter and broader
elements.

The thickness of these structures, and with it that of the whole covering,
must, as we have already mentioned, present much variety. Where
but a small amount of flattening has taken place, the depth of the cell
and thickness of the whole layer is generally about 0'0055 mm. and
upwards, whilst strata which have undergone more compression may
sink in depth to only 0 -0037-0 -0032 mm.

Those tall cells, again, which occur in the hollows of the brain also

deserve special notice as peculiar elements ;
also those of the choroid plexus. The latter
(fig. 134) are likewise thicker and rounder,
giving off one or more pointed processes,
and containing, besides the nucleus, as a
rule, one or several granules of a dark brown
substance, which is, moreover, absent in
the younger cells.

Pavement epithelia are very delicate
structures which undergo rapid decay in the
dead body. In the living subject, on the other hand, they probably con-
stitute more durable tissues, with but little power of rapid regeneration
however. The epithelia of the lung are perhaps an exception in this
respect. The mode of their regeneration is not yet known.

REMARKS.—!. See ffcnle's Allg. Anat. p. 226, &c. Luschka, Die Structur der serdsen
Haute. Tubingen, 1851. 2. We refer our readers to the special chapter on the vas-
cular system for the rest. 3. Those views which were formerly entertained on this
point, and which taught of the existence of a laminated pavement epithelium on the
surface of connective tissue, were based on deceptive appearances. However, at an
early embryonic period the surfaces of cartilages do seem to be clothed with a layer
of cells similar to those of epithelium. We will refer to this again. 4. Comp. the
paragraph on the respiratory apparatus for the epithelium in question.

Fig. 134.— Epithelial cells from the hu-
man choroid plexus, a, cells from
above; 6 and c, side views of the same.

TISSUES OF THE BODY.

143

Fig. — 135. — A papilla from the gum of a child,
showing the vascular net-work and lamination
of the epithelium.

§88.

The simple pavement epithelia just referred to pass, without any
sharp line of demarcation, into the more or less strongly laminated
species, through certain intermediate
forms. Thus, on the internal surface ,
of the tympanum and dura mater,
and external surface of soft skin,
we find an epithelium formed of
several layers, but still thin; of
these the more superficial are recog-
nised as formed of larger and flatter
cells.

The anterior surface of the cornea
of mammals affords an interesting
example of a moderately laminated
epithelium. Here we find from
seven to nine layers of cells laid one
over the other. The counting of
them, however, is not in all cases
easy. In some of the strata we
observe flattened cells, and in others
call bodies, generally of round figure,
but often assuming other forms
under the influence of lateral pressure. The undermost layer consists
of naked elements, greater in height than in breadth, and having each
a full, plump nucleus (perpendicularly elongated cells).

The lining of the urinary apparatus is still less markedly laminated.
The uppermost layer is formed of a single stratum
of cells of different sizes, with vesicular nuclei.
Their under surface displays a varying number
of grooves with ridges and prominences situated
between them. Applied to these depressions,
we find the rounded ends of columnar cells belonging
to a second layer. Then follows a third stratum
of more irregularly shaped elements, at one time
cylindrical, at another, more or less fusiform, next
to which, finally, a fourth and terminating* layer of
^mall polygonal cells may be recognised (Linck,
Henle).

The pavement epithelium of many mucous mem-
branes of the body often displays much stronger and
even very considerable lamination, as for instance,
that of the conjunctiva of the eye, the entrance to
the naves, the cavity of the mouth and pharynx,
as well as the oesophagus down to its connection
with the stomach, the vocal cords, and finally, the mucosa of the female
genitals, as far up as the uterus.

For a closer examination of these typical formations, the mouth may be
recommended as peculiarly adapted (tig. 135). In the deepest layers,
seated immediately upon the fibrous tissue of the mucous membrane, we
meet with strata of soft small cells of roundish, or at times more oval
figure, with a diameter of only about 0*0075 or 0'0114 mm., and vesicular

Fig. 136. — The so-called
spinous or furrowed cells.
At a, from the undermost
layers of the human epi-
dermis ; at 6, from a pa-
pillary tumour of the
human tongue.

144 MANUAL OF HISTOLOGY.

nuclei of 0-0056 mm. in size, or less. All these cells display under high
microscopic powers a very peculiar structure (fig. 1 36). Their whole surface
namely is covered with prominent ridges and spines (a), by mean of which
neighbouring cells are attached to one another, " like two brushes whose
bristles are pressed in among one another " (SclmUze).

In the outer layers, finally, the epithelial cells (fig. 136) appear as thin
scaly structures, without either grooves or pro-
minences, and of considerable size (0-0425-
0-0750 mm.), with more or less oval and
homogeneous nuclei of from 0'0090 to
0-0114 mm. Here the body of the cell con-
tains a few granules usually in the vicinity
of the nucleus.

But the cell has also changed in its
physical condition. Instead of the softness
of former days, it now manifests a greater

Fig. 137.— Epithelial cells from the , • « « , n , . ,°

uppermost layers of the human or less degree ol hardness and brittleness ;

moufch- it has become horny, as the saying is : it is

also destitute of soft protoplasm.

Apart from the differences in thickness which the whole bed may
show (being, according to Henle, 0-2 mm. on the palate, and on the gums,
behind the teeth, between the papillae, 0'4 mm.), the cells of the locality
just mentioned seem to differ but slightly.

The persistence of epithelium, already considered in speaking of the
simplest pavement cells of closed cavities, appears to be the same in the
urinary apparatus ; in the thickly laminated coatings of other mucosse it
is well known not to obtain. Here we have to do with a tissue under-
going rapid repair, in that a certain quantity of the most superficial cells
is rubbed off continually, forming a regular constituent of the mucus of
the part, whilst the deeper cells advance to the surface, and a process of
cell-formation takes place in the undermost strata in order to cover the
loss of the desquamating cells of the surface. The multinuclear epithelial
cells which may be observed, by no means unfrequently, in deep parts
of the strata, are evidence in favour of such a process of cell-formation,
That the obliteration of the spines and ridges in senescent cells prepares
them for separation, is very probable.

REMARKS.— -M. Schultze in yirchow's Archiv, bd. 30, s. 260.

§ 89.

A modification of the pavement epithelia we have just been discussing
is found in the eye, in the so-called "polyhedral pigment cells" of the uvea.
These are epithelial cells, partly laminated to a small extent, and partly
not, and moderately flattened, which occur in the eye in the form of a
delicate mosaic. They have peculiar contents as a rule, made up of
numerous elementary granules of the black colouring matter, melanin,
already described (p. 52).

These cells are met with on the internal surface of the choroidea in an
unbroken but single layer, "which becomes suddenly laminated in the
vicinity of the ora serrata of the retina, at the same time that the
individual elements decrease in size. Thus arranged, they are found
covering the ciliary processes, and in the human eye the posterior surface
of the iris as far as the edge of the pupil.

The granules of black pigment are sometimes elongated, sometimes

TISSUES OF THE BODY.

145

rounded, and usually appear darker the smaller they are, in any one
individual. They are probably crystalline. The tint of the mole-
cules is by no means exactly the same in different mammals. In man,
where the granules are small, it is seen to be brownish black, but in
many of our mammalia, as in the pig and calf, it is jet black. The
size of these particles remains always considerably below 0-0023 mm.
Answering to their minuteness, they show, on becoming free in water, the
liveliest molecular motion, a phenomenon which may, however, be
remarked in the substance of uninjured cells when strongly swollen
under the action of imbibed water.

The pigmentary epithelium itself (fig. 138) appears on the choroid as a
simple bed of closely crowded cells, of a beautiful polyhedral, usually
hexagonal figure, running at times through whole groups (a) with the
greatest regularity. Ar»d yet they may be found indefinitely angular ; and
some unusually large cells are frequently octagonal (b). The diameter of
most of these cells is on an average O'OOl 4— 0*0204 mm., and their thick-
ness 0-0090 mm.

The quantity of molecules of melanin contained in the transparent thick
and tenacious contents of the cell is by no means everywhere the
same. We meet some cells (and they are the
most suitable for examination) in which
the amount of black elementary particles
is but small, so that the nuclei and mem-
branes, always very delicate, may easily
be distinguished. In such specimens the
nucleus is found to be 0-0055-0-0075 mm.
in size, either round or more or less oval, and
always smooth-edged. It has usually one or
more nucleoli. But much oftener the amount of molecules in the pig-
ment cells is far more considerable, so that the nucleus only glistens
through as a clear speck. Should the particles remain somewhat distant
from the external surface of the cell-body, such groups of cells appear at
first sight as though separated by narrow intervals of transparent inter-
cellular substance. Finally, cells are encountered,
in which, such is their richness in pigmentary par-
ticles, the nucleus is completely hidden.

A side view of these pigment cells (easily
obtainable, owing to the small amount of flatten-
ing present in the structure) shows that only in
one-half of them, namely, that directed towards
the retina, do these melanin granules occur, a
transparent contents occupying the other half.
The nucleus is situated in the latter, or at the
junction of the clear and dark portions (fig.
139, b).

In conclusion, we may remark that cells with
two nuclei are also encountered here, but are of
rare occurrence.

At the boundaries of the choroid, near the processus ciliares, the lami-
nated cells are smaller and less clearly polygonal, while they have become
"far richer in pigment, so that the nucleus can only be rendered visible in
general by squeezing the cell-body. The lining of the back of the iris is
of precisely similar nature.

Fig. 138. — So-called pigment cells
from the choroidea of sheep.
At a, a mosaic of hexagonal cells ;
at b, & larger octagonal

Fig.139.— Cells from the choroid
of the calf, a, cell with two
nuclei; b, a side view of ordi-
nary cells, moderately filled
with pigment ; c, some which
are only supplied with but a
scanty amount of pigment
particles; from the neighbour-
hood of the tapetum.

146 MANUAL OF HISTOLOGY.

With those mammals in which the choroidea forms a tapetum, the
epithelial cells of the same undergo an interesting modification, being
here destitute of the pigment molecules of the contents. On the bound-
aries may be found certain intermediate forms, with very scanty colouring
matter (fig. 139, cd}', besides which some isolated black cells are encoun-
tered among the colourless ones of the tapetum. In albinos, where the
pigment fails completely in the eye, all these cells with which we are now
engaged are completely bleached, appearing in the form of a very delicate
pavement epithelium. This interesting fact may be verified on any white
rabbit. The more markedly laminated epithelia have no pigment cells in
man, but such may make their appearance in other mammals, as, for
instance, in the conjunctivas of the horse (Bruch).

KEMARKS.— 1. This layer of cells belongs, however, as we learn from the history
of development, not to the Uvea, but to the Retina.

§ 90.

The region in which pavement epithelium is most strongly laminated,
though indeed with certain modifications, is the external surface of the
body.

The surface of the cutis, which appears quite smooth to the unaided
eye, is covered, nevertheless, by a number of minute prominences known
as the papillae tactic (fig. 140, a, a, a). These, together with the depres-
sions between them, are covered with very numerous layers of cells lying
one over another (b c d). Of course, the latter naturally possess a far
greater depth in the intervals between the papillae than on the apices of
the latter, in that the surface of all the strata collectively, or the epidermis,
is tolerably even.

But apart from, these inequalities, produced by the ridges of the cutis,
the thickness of the whole clothing of cells is very different .in the various
parts of the body. It may range from 0*04-3 mm. and upwards, the
more superficial layers of flattened cells being subject to the greatest
change, the deeper, smaller, and rounder, to least of all (C. Krause).
The unequal pressure which the various portions of the skin experience,
differences of occupation, and consequent use of certain parts of the body,
especially of the hands and feet, account, at least in a great measure,
for this. And yet it has long been known that the epidermis on the
sole of the foot,, even in .the foetus, is much thicker than that of any
other region of the body.

The cuticle of human beings and other mammalia may be divided into
two groups of strata, into a superficial and a deep, which are continuous
with one another, at one time gradually, at another with a tolerably sharp
line of demarcation. The first (d) is usually termed the epidermis in the
more precise meaning of the word, while the second has received the
name of the Malpigliian layer, or rete mucosum (b, c). By a certain
amount of maceration, these may be separated from one another.
From the fact that the deeper strata fill up the intervals between the
papillas, they must naturally possess here quite a different depth from that
the points of the latter, as already mentioned. Hence their appearance
is rendered more or less sieve-like or reticulated, which has given rise to
the name generally employed by the older anatomists.

In these deepest layers we encounter not free nuclei, but small cells of
about 0-0075-0-0090 mm. in size, of roundish or oval form, in which case

TISSUES OF THE BODY.

147

Fig. 140.— Skin from a negro's leg. At a,
the papillae of the cutis, upon which the
cells of the epidermal layers may be
observed ; ef, older, and b and c younger,
strata.

their diameter is greater, and may rise to 0-0114 mm. The outlines of
these cells are very delicate and difficult to distinguish ; they contain a
more or less granular, and frequently
yellow nucleus, 0-0045-0-0075 mm. in
diameter, whose shape is either roundish
or oval. Then there follow a consider-
able number of strata of cells lying one
over the other, in which, however, the
latter become gradually larger, ranging
from 0-0181 to 0'0280 mm. A poly-
hedral flattening is apparent at the same
time, and the cells seem to increase in
superficial extent, their nuclei becoming
paler and assuming more of a lenticular
form. All these layers of the rete Mal-
pighiicontainthe same spinous and ridged
cells already described as occurring in
strongly laminated mucous epithelium
(fig. 141 a). But besides these younger
epithelial elements, lymphoid cells which
have wandered out of the blood-vessels
are encountered in varying frequency (§
81). They may be distinguished by their
brilliant border, irregular outlines, and
very small size. Finally, we come to the smooth-edged cells of the horny
or outermost layers, or epidermis in the more restricted meaning of the
word, whose diameter is 0-0285-0 -0450 mm. From below upwards they
become more and more like flattened scales, formed of a transparent and
solid substance, without any immediately recognisable membrane (fig. 142).
Though in this respect they resemble the most superficial cells of lami-
nated mucous epithelia, they still differ from these in possessing no nuclei.

This absence of a nucleus is, however, immaterial, for in young embryos
all, even the most superficial scales, are nucleated,
as also those on the adult body, at spots where the
skin is of a soft texture, and naturally moist.

Now, as the layers of the epidermis lying one over
the other present a dull white or brownish appear-
ance, they must, more or less, damp the deep red
colour, due to its great vascularity, of the cutis lying
underneath, and, moreover, in a degree proportionate
to their thickness.

We are taught this also by experience. In
those localities, namely, where the tint of the skin
is reddest, the epidermis is very thin, as on the lips
and cheeks. It attains, on the contrary, in the
sole of the foot and, with many individuals, in the
palm of the hand, a great thickness, combined with
a progressive decrease in the red flesh colour, until
at last at those points where the cuticle is thickest
nothing but the tinge of the epidermal layers is
apparent. This is also seen in weals.

It is well known that the skin of Europeans presents at certain points
a brownish tint, lighter in blonde individuals than in brunettes. Among

Fig. 141.— So-called spinous
or ridged cells, a, from
the deeper layers of hu-
man epidermis; b, cells
from a papillary tnmoui
of the human tuiiguu.

148 MANUAL OF HISTOLOGY.

these points may be reckoned the nipple and areola of the breast, the
scrotum, the labia, and the vicinity of the anus, as well as the more indi-
vidual cases of freckles and moles. Now, this
colouring, which is only found in isolated
portions of the bodies of those belonging to
the white human races, appears most exten-
sively in the multifarious shades of skin of
the remaining varieties of our species, down
to the deep black of many tribes of negroes.

As *** as has hitherto been ascertained, these
with a eiobuie of fat lying upon darker tints (in which the fibrous tissue of
it; c, another in half profile. the cutis •„ \^ affected) are dependent

on three conditions, which are combined in the specially marked cases :
namely, on a tinging of the nucleus with a usually diffuse pigment ;
secondly, on a similar but much slighter colouring of the whole con-
tents of the cell ; and finally, on the deposit in the body of the cell of
a granular pigmentary matter. It is principally the deeper layers of the
cuticle which take part in these changes (fig. 138 b c).

Like the mucous membranes, epidermis suffers considerable loss by
desquamation, owing to friction, washing, the pressure of clothes, &c., so
that it may be looked upon as a rather transient tissue.

REMARKS.— When these tints of the skin are less intense, we usually find that it is
merely the deepest and most recently formed layers of cells which contain nuclei of a
slightly brownish colour. But if the hue of the skin deepens, that of the nuclei be-
comes intensiiied to a chestnut brown or brown black. The contents, however, of the
cell are now no longer free, but slightly tinged with brown. Finally, in the undermost
layers of the cuticle we find cells with granular colouring matter also, which vary in
shade from yellow to brown, or even from this to the black of melanin. Here, then,
we have epidermal cells containing melanin also in the human subject.

§91.

We now turn to another form of the tissue we are engaged in consider-
ing, known as cylinder or columnar epithelium, occurring in the human
body on its mucous membranes. This is the epithelium of the digestive tract,
whose internal surface is clothed by it from the cardiac end of the stomach
to the anus in uninterrupted course, where it terminates with a sharp line of
demarcation against the epidermis. Further, it is found in the larger excre-
tory ducts of those glands pouring their secretions into the intestinal tube,
as, for instance, those of the pancreas of the liver and gall-bladder. The
passages of exit likewise, from the mamma and lachrymal glands, as well as
certain portions of the generative system, are lined with the same cells.
Further, a modified cylinder-epithelium is found on isolated portions of the
organs of sense, as, for instance, on the regio olfactoria of the nose, and on
the broad papilla of the frog's tongue. We shall have to refer to this again.
This species of epithelium consists of a single layer or
coating of tall narrow cells, set up perpendicularly on their
ends, which either possess the same breadth through-
out, or are broadest at their free extremities (fig. 143),
while at the opposite end they are narrowed down more
or less to a point. In many of these cells the nucleus
lies aboufc in the middle, in others it is situated lower
the. rabbit; in pro- down. Externally, we find here also a polyhedral
accommodation where the cells come into contact, so
that cylinder epithelium, observed from above, often presents the appear-

TISSUES OF THE BODY.

149

Fig. 144.— Cylinder cells of a
mucous membrane, arranged
perpendicularly (diagram-
matic), o, the cells; 6, the
intermediate matter; c, base-
ment layer; rf, the fibrous
tissue of the mucous mem-
brane.

ance of an extremely delicate mosaic, similar to that of pavement epithe-
lium. But the fields are smaller, and the nuclei lie deeper than the edges
of the cell.

Below, the pointed portions of the cell, separate ,at times from one
another (fig. 144), in which case the transparent intercellular-substance
becomes visible with considerable distinctness (&).

But where the cells remain broad below, or serve to clothe strongly
curved surfaces (fig. 145), they lie in contact with one another throughout
their whole length.

The nuclei of cylinder cells are roundish and
smooth, supplied also with nucleoli. The body
of the cell is seldom quite transparent, but usually
delicately granular and slightly clouded. The
membrane is generally very thin and fine laterally,
and is probably absent on certain portions of the
free base of the cell, or rather replaced by a soft
boundary layer ; at times, however, it is met with
apparently thickened by a transparent layer of
the cell-contents lying beneath it, containing no
ganules (fig. 143).

Both as to size and form, our cells are subject to numerous variations.
Many appear tolerably short, while others are
long, and ab times also run out into long pro-
cesses below. Many of them again are broad,
so that the nucleus may be seen surrounded by
the membrane at no inconsiderable distance (fig.
143), whilst others remain much narrower. In
the latter case the envelope surrounds the
nucleus closely, or appears bulged out by the
latter. Finally, we meet with cells which con-
tain double nuclei.

The relation of length to breadth in the cells
of the human small intestine, is as 0'0182-
0-0270 mm. to 0-0057-0-0090 mm. at its upper
end, while at the openings of the biliary and
pancreatic ducts the cells are narrower, with
the same length. Henle has seen unusually
slender ones in the human stomach.

§92.

As has already been remarked in the general
section (§ 50), cylinder-cells may display strange
deviations from the characters just mentioned,
especially those in the small intestine of man and
other mammals.

The thickness of the border pierced with
minute pores (fig. 146 a, 147) is, in the rabbit, from 0'0017 to 0-0025
mm,, and the number of lines crossing it from 10 to 15.

This secretion of the cell consists, as we have already mentioned, of a
coagulated protein substance, differing from the membrane, and offer-
ing but small resistance to the action of water, on the application of
which transparent drops rapidly well from it. Whether these pores

Figr. 145. — An intestinal villus
clothed with cylinder cells.
a, cylinder epithelium with
border; 6, vascular network;
c, longitudinal bundles of
muscular fibres; rf, chyle
vessel in the centre.

150

MANUAL OF HISTOLOGY.

really pass through, a regular cell-membrane or no has not yet been
ascertained. Cells which have puffed out under the action of water show
clearly the presence of a lateral membrane at least.

However, it is nob alone the cylinder cells of the small intestine, but
also those of the gall-bladder and larger biliary
ducts, which possess these thickened lids per-
forated by canaliculi (Virchow, Friedreicli); the
same structures are said to have been encoun-

Fig. 146. — Cylinder - epithelium
from the small intestine of the
rabbit, a,, the cells in profile,
with the thickened border some-
. what elevated and traversed by
pores; 6, view of the same from
above, in which the orifices of the
little canals appear as dots.

tered in the large intestine and other localities.
Columnar cells containing melanin have
neither been met with in man nor any other
mammal.

Cylinder epithelium appears to undergo
in general but moderate physiological reno-
vation. The older views, according to which a
frequently repeated stripping of larger surfaces took place, have long since
been recognised as erroneous.

Among these cylinder cells, but also between the elements of ciliary
epithelia and the soft slimy epidermis of the lower vertebrates, are to be
found certain peculiar elements which have been named "goblet-cells "

(Becherzellen) (fig. 148 a).
They are sometimes dis-
posed without order, but at
other times possess a certain
regularity of arrangement.
They have usually the form
either of a plump, or more
or less slender flask or
wide-mouthed goblet, and
are destitute, of membrane
on their free surface. The
nucleus and protoplasm of
these elements is displaced
towards the lower pointed
extremity, while the other
half is occupied by a slimy

mfflratt

Fig. 147.— The same cells. At a, the border has been
loosened by the action of water and slight pressure ; 6, view
of the cells in the normal condition; c, a part of the
thickened border is destroyed; d e f, the latter resolves
itself into separate columnar or prismatic pieces.

substance, granular when in a fresh condition, but transparent in speci-
mens subjected to maceration. We look upon them as decaying cells
engaged in a process of slimy metamorphosis.

REMARKS. — The goblet-cells in question, known many years a^o to various
observers, have become lately the object of general attention, and have evoked, one
might almost say, a superabundance of treatises. This is no place to enter upon
a criticism of those works, but it may be observed that they regard the matter from
three different points of view : 1. Goblet-cells are epithelial elements en<m"ed in
Slimy metamorphosis. 2. They are independent formations, not derived from the
Drdinary epithelial cells. 3. They do not exist in the living body, and are purely

artificial productions

§ 93.

We turn now to the last modification of this clothing tissue represented
in ciliated epithelium. We understand by ciliated epithelium, a coating of
cells, sometimes single, sometimes laminated, which bear on their free ends a
varying number of small hair-like bodies endowed with a power of motion ;
these are the cilia. The fully developed cell is usually presented to us

TISSUES OF THE BODY.

151

Fig. 148.— Gob let-cells from the epi-
thelium of an intestinal villus from
the hnman subject,' treated with
Mailer's fluid (Schutze). a, goblet-
cells; &, cylinder-cells.

in the form of a cylinder, less frequently as a more rounded or flattened
body. The undeveloped elements, lying deeper down in the tissue spoken
of as laminated ciliary epithelium, are
rounder, and destitute naturally of the char-
acteristic cilia.

The columnar cells of ciliated epithelium
(fig. 149) manifest the same diversity of
form, and the same difference of length, as
those of the simple tissue. The free edge of
the cell sometimes presents a darker con-
tour than the side Avails. Its substance is
at one time transparent, at another, finely
granular, but always tolerably pale. The
number of cilia, as we have already mentioned, is liable to vary, and ranges,
probably, between ten and thirty. In mammalian animals and man
the cilia appear somewhat flattened, and terminate above slightly blunted,
although some observers speak of their being pointed. The size of these
minute hairs is subject to variation among the higher animals. In the
first place, those attached to any one cell are not
necessarily all of the same length ; and again they
are met with of larger or smaller proportions in
different localities. The gigantic magnitude which
they attain in many of the lower groups of animals
is never seen here. The largest cilia, of from
0-0226 to 0-0340 mm., are found in the human
subject upon very large -sized cylinders, mea-
suring 0 '0445-0 -0560 mm., which clothe the
upper part of the passage of the epididymis
(Kolliker).

In other situations the cilia are smaller, as for
instance in the com vasculosi of the testicle (0'0114 mm.), but their length
is still less in the epithelial cells of the respiratory organs, namely,
0-0056-0-0038 mm. The length of the cells themselves ranges in the
human body from 0-0285 to 0"0570 mm. The cilia are of a delicate and
perishable nature, and consequently decay rapidly a few hours after
death. At times, however, they remain exceptionally in a very perfect
condition even for days in the bodies of the warm-blooded animals.

Ciliated epithelium is found in the following parts of the human
body : —

It clothes the mucous membrane of the respiratory tract, commencing
at the base of the epiglottis, after which it covers the whole larynx, with
the exception of the vocal chords. Here it is slightly laminated, forming
a bed of from 0*0056 to 0*0992 mm. in depth. It likewise extends over
the trachea and bronchi with decreasing lamination, until at last the
very smallest tubes are covered with a single layer of minute elongated
ciliated cells, 0-0135 mm. high (Koelliker).

The organs of smell also possess a laminated ciliated epithelium, com-
mencing about at that point at which the cartilaginous nose terminates.
It is from 0*0451 to 0-0992 mm. in thickness. The regio olfadoria alone,
in the more restricted application of the term, is an exception to this
with its epithelium, which will be considered more at length in discussing
the apparatus. Moreover, it is not only the main cavities which are lined
with these cells, but the adjacent ones also connected with the organ.
11

V

#. 149.— Ciliated cells from
the mammal, a b, simple
forms; c, narrow elongated
cell; d, one still more so,
with double nucleus.

152 MANUAL OF HISTOLOGY.

Simple ciliated cells are also met with covering the mucous membrane
of the female generative apparatus from about the middle of the neck of
the uterus up to the free edge of the fimbria.

Again, in the male, the vasa e/erentia, coni vasculosi, and the passage of
the epididymis, down to about its middle, are clothed with similar cells,
which become larger and support longer cilia as we advance downward
(Becker, KolUker).

In the new-born child it would appear the cavities of the brain and
spinal cord still possess throughout a lining of ciliated cells. This is only
partially the case, however, in the adult. Thus, we find these cells in the
central canal of the cord, at the posterior end of the fourth ventricle, in
the aquceductus Silvii, and in the lateral ventricles. The remaining parts
of these regions are lined by simple pavement epithelium of more or less
rounded cells, in the adult individual. The plexus clwroidei and telce
choroidcee are covered by that modified rounded pavement epithelium men-
tioned already in an earlier section (§ 88), though in the embryo they are
clothed with ciliated cells.

In conclusion, we find a stratum of flattened epithelium cells, arranged
simply or in layers, and covered with cilia, in the Eustacldan tube and
cavity of the tympanum, which gives way on the surface of the latter,
however, to a niultilaminar pavement epithelium.

Pigmentary ciliated cells are unknown. Ciliated epithelium appears
to possess a limited physiological power of renovation. " Goblet-cells "
are frequently met with among them (Schulze).

§94

Any chemical examination of epithelium to meet adequately the require-
ments of present day histology would have to undertake the analysis of
cells and intercellular substance, as well as that of the nucleus, body, and
envelope of the latter, should it be present. It would have to show also
what the changes in chemical constitution are which the young cell
passes through in laminated epithelium, while undergoing transformation
into the scale-like formations of the older and more superficial layers.

But these theoretical requirements cannot be responded to, in that we
possess no means of isolating the several portions of epithelial tissue from
one another, and can only subject the whole mass in the form of a mix-
ture to analysis. In spite of all this, however, so much is certain, that
epithelium is a tissue which, in its simpler forms and younger layers, is
made up of cell-bodies, consisting frequently of protoplasm, while in
epithelia of greater thickness the superficial layers undergo chemical
transformation to a considerable degree, owing to which they become
hard, dried, and more consistent, i.e., become converted into corneous
matter or keratin (§ 14), or. as the saying is, become horny.

Many non-laminated pavement epithelia, together with cylinder and
ciliated cells, display the ordinary characters of elements formed of unstable
protoplasm, the action of water even causing changes in the cell, such as
puffing, expulsion of spherical drops, and bursting of the envelope. On
the other hand, numbers of simple pavement epithelia resist the action
of both cold and hot water, and are affected only by acids and alkalies,
earlier or later, after which the protoplasm is changed, though a portion
of it may remain unaltered around the nucleus. The latter usually offers
a determined resistance to the action of acetic acid.

The bearing of the deeper or younger cells of laminated epithelia agrees

TISSUES OF THE BODY.

153

with the description just given, while the more superficial scale-like forma-
tions, at one time nucleated, at another not so, give the reactions of keratin.

This represents, naturally, a mixture of substances; it forms the nucleus,
contents, envelope of these elements, and the scanty intercellular matter;
the residue after treatment with water, alcohol, and ether.

This mixture is then insoluble in cold as well as boiling water, and (if
not contaminated with other elements of connective tissue) yields no glutin
on boiling ; nor is it acted on by acetic acid. Even to sulphuric acid, in
which it becomes puffy, it offers a certain amount of resistance. With
hydrochloric and sulphuric acid it gives the reactions of the protein sub-
stances.

Its conduct toward alkalies is, however, of the greatest importance:
with them keratin enters into combination, at the same time that it puffs
out or becomes gelatinous, and is subsequently dissolved on the addition
of water. If to such a solution of keratin acetic acid be added, certain
products of the decomposition of the albuminoid group are precipitated.

The swelling up of this tissue before solution, as it occurs both in cold
and heat, has much interest for the anatomist (fig. 150). In order to
produce this appearance, we treat the epidermis either with a very strong
caustic solution, and then with water, or we employ from the commence-
ment more dilute reagents. On this the older cells become puffed out
into spheroids (1 b-f, 2 b, c), lose their flattened figure, and again assume,
in the most striking manner, their original cellular character, the contents
beginning to dissolve in the imbibed fluid, and the envelope to become
sharply defined. At the same time, also, the stratification of the epithelial
beds becomes distinctly visible, so that in this respect likewise alkalies
may be of the greatest service to microscopists. Later on the nucleus is
attacked (1 b-d), and
then the intercellular
matter. Finally the
envelope is dissolved,
but only if the cell be
not one of those which
have been completely
converted into horny
matter. Very old squam-
ous elements possess, on
the other hand, a mem-
brane which reminds us
in its great capacity for
resistance to alkalies, of
the substance of the elas-
tic tissues. The addi-
tion of acetic acid pro-
duces in the cell which
has gelatinised in the
manner described, a
precipitate of decom-
posed protein substances
already mentioned (1 #,
2 d\ "

After what has just
been remarked, there can be hardly any doubt that keratin partakes of

Fig. 150.— 1. Epithelial cells. At cr, an unchanged flat cell from
the mouth ; from 6 to /, the same kinds of cells after treat-
ment with caustic soda, some containing nuclei (6 c d) and some
not; g, on the addition of acetic acid, after treatment with caustic
soda. 2. Epidermal cells, a, unchanged; b, commencing action
of the soda; at c, after prolonged action of the same; d, on the
addition of acetic acid.

154 MANUAL OF HISTOLOGY.

the nature of a mixture, so that its present analyses are almost worthless.
We may take, for instance, those quantitative ones of Mulder and Schererj
which apply to the epidermis of the sole of the human foot.

(Scherer.) (Mulder.)

C 51-036 50752 C 50-28

H 6-801 6-761 H 6*76

X 17-225 17-225 X 17*21

o) 04.000 25.9fi9 o 25-01

S |24938 S 0-74

The amount of sulphur (0'74 per cent.) in Mulder's analysis appears
strikingly small, while it is found to rise to between 2 and 5 per cent, in
the keratin of other tissues. As to the form in which it is contained in
the latter we know nothing. It is, however, only loosely combined. The
proportion of ash rises to about from 1 to 1 -5 per cent. The salts obtain-
able are chlorides of sodium and potassium, sulphate and phosphate of
calcium, phosphates of magnesium and of iron, besides which silicates are
also contained in the epidermis.

The pigmentary cells possess the same characters as all the other
epithelial formations. Those of the eye correspond in their delicate con-
stitution with the non -laminated epithelia. In regard to the melanin
with which they are charged, comp. § 37. Finally, we are still quite
ignorant as to what the matter is with which the nuclei of epidermal
cells, of dark spots of the skin, are coloured.

§95.

The elements of epithelium stand in very close genetic relationship to
the gland-cells. Remak has shown that both tissues have their origin
from those two layers of cells continuous with one another, which clothe
the internal and external surfaces of the embryonic body. There like-
wise exists frequently between the epidermal elements and gland-cells of
the mature body a gradual transition : many glands, namely, are lined
with cells which can hardly be distinguished from those of the epithelia.
On the other hand, as a feature in epithelial life, the formation of
mucus has much in common with the destiny of certain gland ele-
ments; and those goblet-cells mentioned above (§ 92) may be named
single-celled glands. Finally, the tendency which they both display to
excrete amorphous matter, as for instance, the thickened cell-border or
that which hardens into the membrana propria or basement membrane,
may perhaps be regarded as another feature common to the gland and
epidermal cells. The genesis of these two structures, however, must be
more fully ascertained before we can unreservedly adduce it as additional
proof of this relationship between the two.

Now, when the question arises as to the purposes which epithelium
serves in the body, and why all the surfaces of the latter are clothed
with such a continuous cellular coating, we must confess ourselves in
a difficulty in ascribing to each species its particular properties.

If we look for a physiological significance jn our tissue, it may be
said to have its basis in all probability in the relation of the latter to the
processes of transudation, diffusion, and absorption of the economy ; and

TISSUES OF THE BODY.

155

we may perhaps regard epithelium as the regulator of these processes
spread over the parts where they take place.

As a purely cellular tissue untraversed by blood-vessels, epithelium
presents to us many sides of cell-life in the most beautiful manner, such,
as multiplication, growth, and change of form. That the whole vegetation
of the epithelial cells is dependent upon the vessels of their connective-
tissue substrata is easy to conceive, though we meet with epithclia on
non-vascular portions of the body, as for instance on the cornea and
capsule of the lens. But of the direction of the interchange of matter
in our tissue we know nothing, either of that in ordinary epithelium, or
the modified forms of it, where in the interior of the cells a formation
of melanin and other pigments takes place. That this alteration of
material in laminated epithelium is only undertaken with any degree ol
energy by the younger cells which still possess soft contents, is more-
over not difficult to understand. It is also probable, on the other hand,
that this interchange of material has ceased entirely in the more superfi-
cial scales of laminated epithelia which have undergone horny metamor-
phosis : in these also decomposition commences very late.

Then the cylinder epithelial cells of the small intestine are made the
media for much transfer of matter, and moreover, not in their own
egotistical interest, and for their own special support : through them,
namely, the absorption of fats with the other constituents of the chyle
takes place. Here again we are reminded of many kinds of gland-
cells.

Attention has likewise been directed within the last few years to the
penetration into the interior of epithelial cells of minute coloured par-
ticles, which had been introduced into the circulation of the lymph
and blood, and, indeed, of red blood-corpuscles also (1). These we may
observe in the goblet-cells of the small intestine and in ciliated cells.

We are obliged for the present to explain the fact of the occurrence of
mucous and pus corpuscles, as well as of contractile elements, in the
interior of cylinder and pavement epithelium (fig. 151) in the same manner
(§ 56). It is manifest that a penetration of small bodies into open
goblet-cells might take place without
difficulty. But, besides, we find these
lymphoid- cells within the epithelial
stratum, between the columnar ele-
ments of the intestine, engaged in mi-
grating from the connective-tissue of
the mucous membrane into the lumen
of the tube.

Epithelium may, in general, be set
down as a tissue capable of under-
going no further development. No
doubt from the earliest rudiments, from
the cells of the corneous and intestinal
glandular la}ver, many other tissues,
and some of them of high dignity,
take their origin in the construction
of the embryonic body, as we shall see in some of the succeeding chapters.
But not so in the mature body : its epithelial cells are only able to
reproduce similar structures, and not other elements, such as, for instance,
fat-cells or connective-tissue corpuscles.

Fig. 151. — Occurrence of mucous and pus-
coipuscles in the interior of epithelial
cells, a-d, cylinder cells of a biliary
duct; e, free pus-corpuscles; /, ciliary cehs
of the respiratory tract; g, flat ceiis from
the urinary passages.

156 MANUAL OF HISTOLOGY.

The destruction of epithelial cells is brought about, first, by solution,
nextly, by mechanical attrition. This naturally deprives the system
daily of a certain quantity of albuminoid matters, though in an altered
condition.

REMAEKS. — The question as to a connection between epithelial cells and the ele-
ments of connective substances and of nerve-tissue, must be discussed in a future
section. — 1. I have convinced myself of the presence of granules of cinnabar in the
cylinder cells of a frog's intestine, three days after their injection into the circula-
tion.

§96.

Owing to their composition decaying epithelia are of the greatest im-
portance in the formation of mucus. The consideration of these tissues
must, therefore, extend itself over fluids likewise.

We understand by mucus a coating of a rather thick semifluid sub-
stance, more or less stringy and tenacious, which covers the surfaces of
all mucous membranes in varying quantity, and endows the latter with
their usual moistness and smoothness. It must also be regarded, owing
to its consistence, as well fitted to form a protecting medium against
chemical action, and it is probably not indifferent, besides, to the inter-
change of gases.

Mucus is without odour and tasteless, and variable in its reactions. It
is found sometimes transparent, sometimes more opaque, white or yellowish.
Microscopical examination discloses to us in it the cast off epithelial and
gland-cells of the locality in which it is formed, but in variable number ;
and besides these a small cell, the so-called mucus-corpuscle, whose appear-
ance, size, and bearing repeats the colourless blood-cell completely, as well
as the elements of chyle and lymph, and whose origin, as far as is at pre-
sent known, may be very various. It may spring not only from epithelial
cells, but also from those of connective tissue and lymphatic organs. To
these are added the cells of the glandular formation of the part from
which the liquid is obtained. Again, owing to its viscidity, mucus
entangles usually a number of very minute air-bubbles. From all this it
would appear that mucus is a most variable substance. From an ana-
tomical point of view it is only a mixture of many dissimilar matters, and
amongst others of various gland juices, which endow it further with
chemical differences, as an expression of which we recognise the multi-
farious fermenting properties of the several kinds of mucus.

Chemical anaylsis discloses as a solid constituent a peculiar substance
already mentioned (§ 14) known as mucin. Besides this we find extrac-
tive matters, fats, and mineral constituents.

Among the latter chlorine, phosphoric, sulphuric, and carbonic acid,
silicates, lime, and soda are said to exist in mucus. The following
table from Nasse may be taken as an example of its quantitative composi-
tion. By subjecting human mucus, which had been coughed up, to
analysis, he obtained the following results : —

Water, 955 '52

Solid constituents, . . . . . 44*48

Mucin (and a trace of albumen), . . 23'75

Extractive matters, 9 '8 2

Fats, . 2-89

Mineral constituents, . . . . 8 -02

TISSUES OF THE BODY. 157

Of all these components inucin alone requires further consideration.
It appears in mucus under two forms : as an insoluble substance, merely
gelatinising in water, and which remains behind on a filter } and as a
soluble matter which may be filtered, Now, in that the reactions of both
are the same, we are warranted in supposing that mucin in a pure state
is insoluble, and has probably acquired its solubility by admixture with
other compounds, especially alkalies, — an hypothesis which appears to
receive further support from its parallelism with many protein matters in
this respect.

Synovia also reminds us of mucus (FrericJis). We meet it as a clear,
colourless, or straw-coloured fluid of slimy consistence and alkaline re-
action, in which the microscope reveals to us the epithelial cells of the
capsule of the joint, which have been shed, as well as lymphoid cor-
puscles. The use of this liquid is, as is well known, to retain the parts
entering into the formation of the joint in a moist and slippery
condition.

Synovia, strangely enough, has farther the same constituents as mucus,
in addition to which albumen is also present. Of salts we find, chloride
of sodium, basic phosphates of the alkalies, sulphates of the alkalies, phos-
phatic earths, and carbonate of calcium.

The two following analyses of Frericlis may serve as an example of its
composition per cent. The first applies to the synovia of an ox fed in
the stall, while the second is that of one in pasture : —

II.

Water, 969-90 948-54

Solid constituents, . . . 30' 10 51*46

Mucus with epithelium, . . 2 -40 5 -60

Albumen and extractives, ... 15 '76 35 '12

Fats, 0-62 0-76

Salts, .... 11-32 9-98

According to this, it would appear as though the friction of the surfaces
of the joints induced by exercise .were of importance in the formation of
synovia, for we find it during inactivity, watery, less viscid, and poorer in
mucin. At the same time, however, its quantity is far more consider-
able. Again, on energetic bodily exertion the quantity of this fluid
decreases considerably, and the amount of mucin increases, with its
oiliness or thickness. The contents of bursae and the sheaths of ten-
dons appear, also, according to Virchow, to be allied to synovia in com-
position.

Now, as to the formation of mucus and the origin of mucin parti-
cularly, the older views, which referred both exclusively to the secretion
of special glandular organs, the so-called mucous glands, can no longer
obtain, in that the proportion of the fluid stands in no relation to the
frequency or rarity of those glands ; and in that synovial capsules, which
have none of the latter, nevertheless secrete mucus. Epithelial cells,
however, appear to stand in close relation to the origin of mucin, beside
which the elements of the glands themselves, without doubt, play a part
in the formation of mucus. There seems, indeed, much probability in
the supposition, that an alkaline fluid transuding through the capillaries
of mucous membranes macerates the cast-off cells3 aided by the natural

158 MANUAL OF HISTOLOGY.

warmth of the body, and thus transforms their contents into nnicin
(Simon, Frerichs). If this mode of explaining its origin be correct, mucin
must represent in numerous cases a physiological transformation product
of epithelial tissue.

§97.

To what extent epithelial cells are endowed with the property of vital
contractility, when young and still soft, we are for the present unable to
state. But a most remarkable movement is met with on the other hand
in ciliated epithelia, which has been named ciliary motion (Motus vibra-
to ius). This phenomenon, known from the earliest epochs of microscopic
research, has been recently very closely studied, but unfortunately with
but small results. For although its wide distribution throughout the
animal kingdom has been recognised, and ciliary motion not long since
observed in low vegetable organisms, we are still completely in the dark
as to its mechanism and object. The elucidation of points of this kind
regarding it are rendered thus difficult by the fact, that the phenomenon
of ciliary motion is met with in very varied extent throughout the animal
kingdom, parts which are ciliated in one class being no longer so in,
another group ; thus, for instance, none of these cells can be found among
any of the arthropoda.

Ciliary motion, a simultaneous and regular swinging of all the minute
hairs, appears, as seen on the edge of a fold of membrane, somewhat
like to the undulation of a shaken cloth, or the flickering of a candle
flame. Seen from above it frequently reminds us of the waving of a
tield of corn moved by the wind, or when it takes place in a tube of
extreme fineness, of the current of a brook in the sun light. All these
comparisons, however, are perhaps hardly adequate to express the pecu-
liarity of the appearance.

Small particles suspended in water — as, for instance, blood-corpuscles
and pigmentary granules — are driven along by the movements of the cilia
at the edge of a membrane possessing them in one definite direction, and
apparently with great rapidity when the action is energetic, and the
magnifying power great. In reality, however, this rapidity is much less
than it seems, but still by no means inconsiderable, for an interval of an
inch may be traversed by one of these particles in a few minutes. Even
a shred of a ciliated stratum of cells may be driven along by the motion of
its own particular cilia, if it be not altogether too large, while a smaller
piece, or single detached cell, may whirl itself through the water in
a lively manner, simulating in a most deceptive way the motions of the
infusoria.

However, in a fresh state, and when the cilia are endued with great
vital energy, the motions of the hairs follow so rapidly in succession, that
the latter are not seen, nor can the phenomenon be recognised as a rule.
Several vibrations are usually observed to take place in the course of a
single second.

For the closer examination of the phenomenon that moment is most
suitable at which the movement of the cilia has become slower and
weaker, owing to the approaching death of the cells, and when each
individual little hair may be observed for itself. The mode in which it
is carried out is not always the same, so that the motion has been classified
into four varieties (Purkinje and Valentin), namely, into (1), the hook-
like (hakenformige), in which each cilium makes the movement of a

TISSUES OF THE BODY. 159

finger \vhich is alternately bent and extended ; (2), the funncl-sliaped
(trichterformige), in which the upper portion of the hair describes a circle
in swinging, and the whole a cone, whose apex is formed by the firmly
attached base of the cilium ; (3), the oscillating, in which the whole hair
sways more like a pendulum from side to side ; and (4), the undulating.
In this the hair executes a movement like the lash of a whip moderately
wielded, or the tail of a spermatozoon. Of all these forms of ciliary
motion the first appears to be by far the most frequent (2).

This movement appears quite independent of the circulatory and
nervous systems. Destruction of the latter or interruption of the stream
of blood causes no cessation of its activity. The cilia, also, of detached
cells persist in their oscillation still, as we have already remarked.
Should they, however, become separated from their cells they cease to
manifest vitality, and soon disappear completely in the water surrounding
them. Ciliary motion, farther, is of longer duration than the life of the
animal, but with extraordinary differences. Sometimes it only lasts a
short time, especially among birds, and also mammals, where it continues
about until the cooling of the corpse, whilst among cold-blooded animals
it may be observed for days (3).

Elevation of temperature increases the energy of this movement, until
finally at from 44° to 45° C. coagulation commences. On the other hand,
cold has a retarding and finally destructive influence, while agents which
do not act chemically do not disturb it in the least. Thus it continues
unimpeded in serum, milk, and also in urine. Water accelerates ciliary
motion at first, but subsequently puts an end to it rapidly, owing to its
action on the very delicate cell. The addition of bile produces an injurious
effect on it also, while that of alkalies, acids, alcohol, and such like, put
an end to it for ever. A very interesting discovery was made not long
since by Virchow, that ciliary motion which has come to a state of
rest under normal conditions may be again excited by the application
of dilute solutions of soda and potash (4). The influence of gases on
the phenomenon has also been lately investigated by Kuhne. It appears
that like protoplasmic contractility, to which they are akin, the motions of
the cilia require oxygen for their support, and that 'hydrogen causes them
to cease. They may be again set agoing by the introduction of a stream
of oxygen into the medium in which the cells are immersed. Acidulation
also with carbonic acid has a retarding influence on the ciliary motion,
counteracted again by alkaline vapours. The retarding effects of alkaline
vapours can also be met by acid ones.

There seems to be an inclination to bring this ciliary motion physiolo-
gically to bear upon the transport of small bodies, and to ascribe to it, for
instance, the power of forwarding mucus from the nose and lungs, and
the ovum from the ovary into the uterus. But these are surely only
incidental objects of ciliary motion, which receive their just value when
we take into consideration the fact that coatings of ciliary cells occur in
completely closed cavities. That the little hair-like appendages may
effect a change of locality of the whole body, however, of lower organisms,
or induce a motion in the water in contact with the surface of the latter,
or, finally, a rotation of alimentary matters in their digestive tract, &c.,
is beyond doubt.

REMARKS. — 1. The discovery of ciliary motion appears to have been made Ly
A. de Heyde, in the year 1683*; and the Dutch Coryphsei of former days were also
acquainted with it. But the most accurate studies, dating from 1830, in which this

160 MANUAL OF HISTOLOGY.

subject was first treated with, effect, were made by PurkinJQ and Valentin, comp.
Dephcenomeno generali et fundamentali motus vibratorii continui in membranis cum
externis turn internis animalium plurimorum et superiorum et inferiorum ordinum
obvii comment, phys. Vratislavice, 1835.— 2. According to Englemann's varying
observations, this swinging of the cilia depends upon two motions of unequal length, —
upon a longer one produced by the contractility of the protoplasm, and a shorter one
caused by elastic resistance. Currents of fluid passing over ciliated surfaces do so in
the direction of the last of these, in which also the cilia stiffen after death.— 3.
Under certain circumstances, difficult to explain, the ciliary motion may persist for one
or .two clays after the death of a mammalian animal. — 4. As Koelliker has demonstrated,
the same peculiarity is displayed by the spermatozoa.

§,98.

Now, as to the origin of epithelium in the embryo, we must enter here
at somewhat greater length upon the consideration of the relations of
parts briefly touched on already at § 86, in order to obtain a clear con-
ception of its development.

As we have already seen, the rudimentary embryonic body according
to Remak (1.) consists of three layers of cells, of the so-called leaves or
germinal plates. These are known as the superior or the corneous, the in-
termediate or middle germinal, and the inferior or intestinal glandular
leaf or plate. From these the various tissues and organs of the body take
their rise.

The corneous plate produces, first of all, the epithelium, with the nails
and hair which are closely allied to it, and beside these the crystalline
lens, a decidedly epithelial organ. The cellular elements, likewise, of the
various glands of the skin, together with those of the mammary and
lachrymal organs, take their origin from the same layer. Finally, the
axial portion of the corneous plate enters into the construction of the
nervous centres (brain and spinal cord) as well as the internal portions of
the higher organs of sense. That the peripheral nerves also originate in
the axial part of the corneous plate primarily, is at least probable. (2.)
The significance, consequently, of the corneous plate is very great, physio-
logically the highest in the body.

Thus a large part of the epithelium described in former sections, the
epidermis, including those layers of cells which clothe the openings of the
larger passages of the body, takes origin from this source, and appears as
laminated epithelium, with a horny substance devoid of vitality. The
pigmentary pavement epithelium also, of the eye, together with the
internal coating of the cavities of the nervous system, are also derived
from this superior plate.

The second, or intestinal-glandular plate, supplies the epithelia of the
digestive apparatus, as well as the cellular constituents of all the glands
in connection with the latter, including the lungs, liver, and pancreas.
Its epithelial formations appear principally in the form of the cylinder-
cell, either naked or ciliated.

We must now finally devote a few moments to the middle germinal
plate, and inquire after its contributions to the epithelia. This middle
stratum of the rudimentary embryos supplies material for a great many
structures. First of all, for the formation of all the tissues of support in
the system, the whole group of connective* substances; for the building up
of muscle ; for the blood and lymph, together with the so complicated
system of vessels which contains both ; and finally, for the so-called
lymph or blood-generating glands (including the spleen). The cutis

TISSUES OF THE BODY.

161

vera containing the vessels of the dermis, with the connective tissues
of mucous membrane and true glands, take their rise from this source.

It is evident that the changes must be very great in the middle layer
which produce from it such structures.

To many of these changes we shall have to refer again in subsequent
pages, but for the present our attention must be principally directed to
the formation of numerous cavities in the middle plate appearing in the
course of its development. Thus it is that the serous sacs originate, as also
the bursae and sheaths of tendons. Thus is formed the most intricate
of all systems of canals, namely, that of the blood and lymphatics.
Together with this formation of cavities, also, we must expect besides
to find a whole series of epithelial coatings springing up.

The latter have much about them that is peculiar. If we except the
more circumscribed laminations as they appear in synovial membranes,
they almost always consist of a single layer of thin flat scales (§ 87) with-
out the transient nature of the two other forms of epithelium. Further, as
observation of the circulatory system teaches, such an epithelial tunic
may acquire sufficient strength by cohesion of its cells, as to fit it to form
the chief part of the finer and more minute canals of the former. But
these epithelia of the intermediate germinal plate do not possess the power
of yielding in continuous transition the secreting cells of glands, nor are
they able to develope any physiological function similar to glandular
activity. On the other hand, they are remarkable for the great ease with
which the fluids of the blood transude through them, which is far from

Fig. 152.— Skin, withru<1iments of a hair, in
a human embryo of sixteen weeks old. a,
the superficial layers of cells of the epi-
dermis; b, the deeper; m m, cells of the
rudimentary hair; »', transparent mem-
brane clothing them.

itf. 153 — Epidermis from the neighbourhood of
the head of a sheep-embryo of 4 in. in length.

1, epidermal cells, of the most STtperficial layer ;

2, from deeper lamina; 3, vertical section of
the same; 4, cuticle from the free edge of the
eyelid.

being the case with the epithelial structures of the corneous layer. If we
are asked for another contrast, it is to be found in the nonvascularity
of the subjacent tissue, of this last species of epithelium compared to
the great vascular! ty of the other two kinds.

This intermediate species has been termed false epithelium, or endo-
thelium, by His.

As regards the epithelium of the corneous layer, Koellilter found the
epidermis in the human embryo of five weeks old to consist already
of two laminae of nucleated cells : a superficial, made up of delicately-
edged polyhedral elements of 0'0275-0'0451 mm., with round nuclei,
measuring 0'0090-0'0136 mm.; and a deeper layer, in which the cells

162 MANUAL OF HISTOLOGY.

were smaller, about 0 '0068-0 -0090 mm. in diameter, with nuclei of only
0 '003 4—0' 0045 mm. From this we see that the epidermis, properly so
called, and the rete Malpighii, are each formed originally of one layer
of cells. Later on in the fourth month these are slightly laminated,
the whole epidermis consisting of three or four strata (fig. 152, a b).
From this on the lamination becomes stronger by degrees. Let us take,
for example, the epidermis of a foetal sheep 4 inches long (fig. 153).
This consists of six or seven layers of cells (fig. 153), of which the
most superior (a) are transparent, and measure 0'0156-0'0206 mm., with
nuclei 0'0052-0'0066 mm., whilst the deeper (b) are only 0'0104-0'0124,
the nuclei preserving the same dimensions as in the more superficial
laminre. In the superficial strata are found scattered cells with a double
nucleus (fig. 153, 1), and division of the latter may be remarked at times
in those lying deeper (2). The epithelium on the free edge of the eye-
lid shows in this embryo but two layers of cells (4). I have found the
epithelium of the cornea also in a human foetus four months old 0'0205
mm. thick, and consisting of two upper and two lower layers of
cells.

With the further growth of the foetal body, the thickness of the epi-
dermis and the number of its laminae increase more and more, and the
most superficial of the latter already resemble the scaly non-nucleated
structures of later years, before the close of the second half of intra-
uterine life.

Desquamation of the cuticle commencing in embryonic life, produces
upon the body of the child a coating of a greasy whitish substance,
intermingled with fat, known as the vernix caseosa, in which the micro-
scope reveals to us the scale-like epidermal cells.

The epithelia, also, of the intestinal glandular plate likewise evince at
an early period a disposition to assume their characteristic forms. The
increase of the superficial extent of these coverings necessitates likewise
multiplication of the cells by division.

That the endothelia also make an early appearance has been already
observed above, where we have also considered the cells from which they
take their rise.

REMARKS. — 1. Conip. the work on embryology of this investigator. — 2. In a re-
cent work His points out that from a superior germinal plate the nervous system,
animal muscles, Wolflian bodies (the kidneys and sexual glands), take their rise
together with the epidermal structures and cells of external glands. A subse-
quently formed inferior plate gives origin to the sympathetic system, unstriped
muscles, epithelia, and glands of the mucous membranes. These two plates con-
stitute liis " archiblast. " Between them the "parablast " is then inserted, from
which connective tissue and blood are formed. For the present we prefer adhering
to Remak's views.

4. Nail.
§99.

Like the epidermis and the hair, to be considered farther on, the nails
have long been placed by anatomists among the horny tissues. And,
indeed, they represent nothing more than a peculiarly modified cuticle
for the part of the skin lying underneath. But the transformation
proves to be less on microscopic investigation than we might have
expected from the physical constitution of the tissue.

The nail is a hard, flat and arched body of rounded quadrangular

TISSUES OF THE BODY.

1G3

shape. It is more strongly doubled down at the sides than in the
middle; and at the anterior free edge is thicker than posteriorly.

Fig. 154. — Noil and matrix in transverse section, a, the matrix with the
ridges of the cutis; 6, side portion of the same, forming the groove of
the nail ; c, rete Malpighii ; e, homy layer; d, rete Malpighii of the nail,
dipping in between the papillae of the matrix ; /, the homy substance of
the nail.

Of the edges only the anterior is exposed, while the lateral ones are
concealed in a fold of the skin (fig. 154, b) which commences at the
point of the finger as a flat groove, and becomes deeper and deeper
behind. The posterior portion of the nail finally disappears in a very
deep furrow of about 4'5 mm, in depth (fig. 154, a left), in which, a con-
siderable proportion of the whole nail is contained, known as the " root "
(fig. 155, Z), while the lateral grooves have received the name of "the
fold,"and the portion of skin concealed by the nail, that of "the matrix"
(fig. 154, a; 155, a).

Fig. 155. — Nail and matrix divided vertically and longitudinally, cr, the matrix, forming at the left
hand side the deep fold for the root, /; k, the horny part of nail; in, its anterior free edge; /, epi-
dermal layer on the point of the finger; g, its termination towards the rail; 6, rete Malpighii of the
same, which becomes that of the nail at c, and of the fold of the nail and root at d ; while at e, it is
continuous with that of the dorsum of the finger; A, epidennal layer on the d«i>,nm of the latter; »',
termination of the same towards the nail.

The nail, which determines, roughly taken, the form of the matrix in
conjunction with the lateral fold, is so closely adherent to the first of
these that, like the rete Malpighii on other parts of the fibrous tissue of
the cutis, it can only be separated from it by maceration or boiling.

If we examine the surface of a matrix so exposed, we find it marked
by a number of longitudinal ridges. These, as Henle has demon-
strated, commence at, the posterior border of the matrix as from
one pole, and, in the middle portions, pass directly forwards to the
anterior edge, while at the sides they maintain a course convex exter-
nally. On these ridges are' situated, more or less isolated, the papillse of
the cutis. Fig. 154, d, represents the former, of which from 50 to 90
may be reckoned on one matrix. They are arranged much closer to-
gether under the root of the nail than elsewhere, but are, at the same
time, much less elevated there. Both parts of the matrix are usually

164

MANUAL OF HISTOLOGY.

sharply defined one against the other by a curved line, which is visible
through the nail as the edge of the so-called lunula.

Now, as we have already remarked, the rete Malpigliii dips down with
jagged projections into the intervals between the ridges of the cutis; it
conducts itself consequently just as at any other part of the skin (fig.
154, d). The young cells of which it is composed correspond also in
their histological constitution with those of the external skin (fig. 156,/).
In size they range between 0*0090 and 0*0160 mm., and their nuclei
between 0*0065 and 0-0075 mrn. The only difference appears to be, that
in 'the deepest layers the cells of the younger lamime are apparently
more or less oval. According to C. Krause, the nuclei of such nail cells
contain, in negroes, the same dark brown pigment as the skin itself

(§ 90) ; a fact of much interest. Cells
with a double nucleus are not unfre-
quently met with here also (g). That
the rete Malpigliii of the nail is conti-
nuous with the younger cells of the
epidermis in the furrow, and at the
point of the finger, hardly requires to
be mentioned, and may be seen in fig.
154, c, and 155, b.

Now, while the cells of the deeper
layers have but little about them that
is striking, the reverse is the case with
those of the superficial laminse or true
horny substance of the nail. Generally
speaking, we have only to remember
that the under surface of the horny layer
clings, by means of slight indentations,
to the rete Malpicjliii (fig. 154, /), and that on the root of the nail it is con-
siderably thinner and softer than the free uncovered portion. Finally,
the epidermis of the skin passes forwards a certain distance on the surface
of the nail from the inferior fold (fig. 155, i\ while that of the tip of the
finger is lost under the free edge of the same (fig. 155, /).

Sections of this horny substance give no clue to its texture with-
out further treatment ; for we have to deal with a brittle, hard, and
tolerably transparent mass, which appears, to a certain extent, split up
and torn by the edge of the knife. If we subject such a section, how-
ever, to the action of sulphuric acid, or, still better, to that of caustic
soda or potash, the whole of it swells up in a very remarkable manner
(especially when warmed) into the most beautiful epithelial tissue (fig.
156, a-e). At first the cells are marked off one against the other, as flat-
tened polyhedra (d) ; but eventually they separate from one another,
under the continued action of the reagent. Their size is usually
0-0375-0-0425 mm.

But though they correspond so far with epidermis cells, the elements of
nail-tissue possess one distinguishing characteristic (if the chemical action
of the reagents have not gone too far), in the form of a rounded granular
nucleus, a delicate lenticular structure, seen in fig. 156, &, c, d, e, from
above, as compared with the side view at a. Its diameter lies between
0-007o and 0'0090 mm.

Fig. 156. — Tissues of the human nail, mostly
after treatment with caustic soda, a, cells
of the superficial layer in profile ; 6, one seen
from above ; c, halt profile ; d, a number of
cells, of polyhedral outline, in contact with
one another; e, a cell whose nucleus is about
to disappear; /, cells from the undermost
part of the rete Malpighii; g, one of the same
kind, with double nucleus.

TISSUES OF THE BODY. 165

§100.

The nails of the human being differ from the epidermis in their greater
hardness and solidity, but correspond very essentially with the latter in
their chemical relations. Like the scales of the cuticle, they yield on
treatment with alkalies keratin, already mentioned (§ 94).

Analyses of the substance of human nail-tissue have been frequently
made ; of those available we will only quote the following, from Scherer
and Mulder : —

Scherer. Mulder.

C, . . 51-09 51-00

H, . . 6-82 6-94

N, . . 16-90 17-51

( 2-80

S, \
0,J

25'19 ) 21-75

According to these, the proportion of sulphur in the keratin of nail-
tissue appears more considerable than that of the epidermis, in which it
only amounts to 0'74 per cent. (p. 152). The proportion of mineral con-
stituents was found to be 1 per cent.

The tissue of nail, like that of the cuticle, is nourished by the blood-
ve'ssels of the matrix and furrow, and shows, in our condition of culture,
a constant and tolerably lively growth, exceeding by far the loss of sub-
stance induced by the ceaseless wear and tear going on at the free edge.
It appears, however, that with those who do not pare their nails, as, for
instance, the Chinese, the growth of the former reaches a limit eventually,
for those talon-shaped nails, of about two inches in length, sometimes met
with, do not increase any more, according to Hamilton. According to E.
H. Weber > the free edge is cast off at times in children in the form of a
crescentic strip. Some interesting experiments were made by JBerthold
in regard to the amount of growth of the nail, or, what is the same thing,
into the length of existence of a horny cell of the latter. Eegeneration
takes place, according to this observer, more rapidly in infancy than at
an advanced age, and in summer than in. winter; a nail, which requires
during the warm part of the year 116 days for its complete renovation,
consuming 152 days in the latter process during the winter. The nails
also of different fingers, as well as those of corresponding members on the
right and left hands, are said to be dissimilar in growth also.

The mode in which they grow is as follows : — The deeper cells of the rete
Malpighii preserve their position, whilst the horny lamina is pushed for-
ward over the softer layer of cells covered by it, by the constant production
of new elements at the posterior border of the root, which become trans-
formed into scales. That the nail anteriorly is considerably thicker than
behind is explained by ther fact that the more superficial cells of the rete
mucosum are also transformed on the surface of the matrix into horny
laminae, which unite with the under surface of the completed corneous
portion of the nail, strengthening the latter, and naturally pressed for-
ward with it.

Now, just as there is a normal physiological renovation of the nail, so
do we find that the latter may be completely regenerated after having been
lost in an abnormal manner, provided that the matrix have preserved its
integrity. If the latter have suffered, an ill-formed nail is produced.

And further, in that the nail is dependent for its growth on the vessels
of the matrix, it is easy to conceive how many affections combined with

166 MANUAL OF HISTOLOGY.

disturbances in the circulation of the latter may lead to its malforma-
tion. The nails, likewise, are shed from the extremities among rabbits,
as Steinruck's well-known experiments have shown, after division of the
sciatic nerve. The fact also observed by Koelliker is very interesting,
namely, that in those cases in which we find thickening and malforma-
tion oif the nails of elderly individuals, the capillaries of the anterior por-
tion of the matrix may be impervious, owing to a deposit in them of fatty
granules

Finally, as to the first appearance of the nail in the embryo, we find
its rudiments in the third month of inter-uterine existence in the form of
a fold in the usual situation, which is clothed with the ordinary cells of the
embryonic skin. Then in the fourth month, under the embryonic epider-
mis, and above the rete Malpighii of the matrix, a layer of new cells
is seen, destined to become the horny cells of the future nail. Later
on, more of the same kind of strata are deposited on these, so that the
corneous layer, although still soft, acquires considerable thickness. At
the end of the fifth month the coating of simple epidermal scales has dis-
appeared from over the nail, and the latter lies freely exposed. In the
nail of the new-born child we may still recognise its cellular nature with-
out the aid of reagents, but after the first year the cells are of the same
constitution as in the adult body.

C. Tissues belonging to the Connective-
Substance Group.

§ 101.

Having discussed the epithelia, we now <turn to the consideration of
another natural group of textures, namely, the connective-substance group,
one of the most important, but at the same time most difficult chapters of
histology.

This name has been given by the greater number of investigators of
our day to a series of tissues, all of which probably take their origin from
the so-called middle embryonic plate, and start from the same rudiments.
They usually, however, in the course of their farther development in
various directions, become separated further and further from one another,
taking on the most diverse forms, as well from a chemical as anatomical
point of view. Thus, in the mature organism, there occur in the connec-
tive-substance group masses which appear at the first glance to be sepa-
rated by a very wide gap. Among these may be reckoned cartilage,
mucoid or gelatinous tissues, recticular connective-substances, ordinary con-
nective tissue, fatty t'issue, bone, and the substance composing teeth or
dentine.

The near relationship, however, of all these different tissues is not to
be denied.

In the first place, we often see, — though the typically marked varieties
of these several tissues may differ widely from one another, — intermediate
forms, as, for instance, between gelatinous and ordinary connective tissue,
and between the latter and cartilage; so that a sharp line of demarcation
cannot possibly be drawn between the various members of the series.

Again, in many regions of the body, these several tissues merge one into
another, as, for instance, in the case of those just mentioned.

Further, a substitution or replacement of one tissue by another equi-
valent one has been remarked, and moreover of threefold nature.

TISSUES OF THE BODY. 167

In the first place, comparative histology teaches that the different forms
which belong to this group of connective tissues replace each other
frequently enough. What is in one animal, for instance, ordinary con-
nective tissue appears in another 'in the form of reticular substance,
cartilage, or bone. The cartilage of some organs in one being is replaced
in the same parts of another by bone, or bony tissue by dentine, and
so on.

But in one and the same organism also typical development brings
with it a substitution of one member of the connective-substance group
for another. There, for instance, where in the embryonic state gelatinous
tissue existed, the latter is found transformed into connective tissue or
fat at a later epoch; cartilage with its derivatives takes on the form of
bony substance.

Finally, we encounter every kind of this substitution in the richest
abundance in pathological research, brought about by formative activity
of a system modified by disease. Almost every member of the group of
connective tissues may be replaced by very nearly any other, firstly by
immediate metamorphosis, then again more particularly by reconstruction
from the offspring of the original tissue.

Now, while we thus have sufficient examples of relationship on anatomi-
cal territory, all the tissues of this group are also found to correspond in
another respect, namely, from a physiological point of view. Their signifi-
cance in the actions of the healthy body is of a more subordinate kind,
although they make up an enormous proportion of it. They represent, as
is usually said, tissues of lower vital dignity, certain connecting, enclosing,
or supporting matters in our system, or a kind of widely distributed
framework, in whose interspaces other tissues, as, for instance, muscles,
nerves, vessels, and gland-cells, lie imbedded. The name, therefore, " con-
nective-substance," formed after that of " connective-tissue " proposed by
Miiller, appears in many respects a suitable one. The term " sustenta-
cular tissue " applied to it by KoUiker might also be recommended.

However, though connective-substance takes but little part in the phy-
siological occurrences of the mature and healthy body, as we have just
said, it loses this character of quiescence and indifference in the
numerous transformations and luxuriant growths of the diseased body,
and becomes on the contrary the most active tissue of the whole system.
We are indebted to Virchow for having brought out, by an extensive
series of observations, that it is principally from the tissues of the con-
nective-substance group that most of the pathological new formations
take their rise, " so that the connective-tissue with its equivalents may
be regarded as the common germ-bed of the body."

REMARKS.— Science has to thank Reichert for having in the year 1845 placed our
views as regards connective-tissue on a firm basis.

§ 102.

Now, although it is comparatively easy to sketch the first outlines of
the connective:substance group, definition in individual cases, and the
arrangement of the various forms of tissue by means of the history of
their development, is attended at present with the greatest difficulty.

Indeed, the requirements of histology on these points can be only but
very imperfectly satisfied in the present state of science. In the first
place, there still exist great gaps, and then the earlier and more extensive
12

168 MANUAL OF HISTOLOGY.

memoirs on the subject — as, for instance, those of Virchow, Donders, and
others — are no longer serviceable in the present condition of histology.
And, finally, owing to the difficulty of investigation, and a certain amount
of weariness produced by unprofitable discussions, the connective-tissues
have recently been somewhat neglected by microscopists.

The following are about all the features we can pronounce as histologi-
cally characteristic of the group of connective substances : —

The embryonic rudiments of all the tissues in question consist origi-
nally of aggregations of more or less spheroidal formative cells, without any
membrane, and enclosing vesicular nuclei. Between these a soft, homo-
geneous intercellular substance, consisting of albuminous matter, begins
to be formed, be it as a product of the cells, or as a transformed portion
of the cell-bodies. This appears later on in considerable though varying
abundance. Subsequently the cells as well as the intercellular matter
commence to take on other forms. As a rule, the ground-substance or
matrix undergoes more or less a division into fibrous or stringy masses or
a transformation into fibrillae, while the cells become stunted, or on the
other hand develop into spindle-shaped or stellate elements, which again
may unite to form a cellular net-work. Calcification likewise of the
intercellular substance is a typical occurrence in some of the tissues under
consideration.

And with these anatomical changes we find besides corresponding
chemical metamorphoses. As we have just said, the ground-work of con-
nective-substance consists originally of protein matter or near deriva-
tives of the same. A substance nearly allied to, or identical with,
mucin (p. 21), also makes its appearance here very frequently. Almost
everywhere the chemical constitution of earlier days is missed, more
remote descendants of the protein group appearing, namely, the glu-
tinous substances (p. 22), and amongst them usually glutin or more rarely
chondrin : local transformation of the ground-substance into elastic mate-
rial (p. 23) may also take place. In the cell-body also the original proto-
plasm may be replaced by other matters, such as pigments, fats, &c.

Now, as we have already remarked, a classification of the tissues be-
longing to this group must be looked upon as a doubtful matter, owing
to the intermediate forms and transitions which are constantly en-
countered. We will, however, distinguish between — 1. cartilaginous;
2. gelatinous and reticular connective-substance ; 3. fatty tissues ; \. ordi-
nary connective tissue; 5. bony tissue; and, 6. dentine.

5. Cartilage.
§ 103.

By cartilage we understand a compact tissue (appearing very early in
the embryo, often rapidly maturing and as often rapidly decaying), which
is widely distributed throughout the body, and formed of cells situated in
an originally homogeneous intercellular substance. The specific gravity of
cartilage in keeping with its solidity is considerable, amounting, according
to W. Krause and Fischer, to 1'095 and 1'097 for that of the joints
and the ear. The flexibility and elasticity of cartilage is by no means
inconsiderable when in thin pieces or plates; but thicker pieces are brittle,
and snap easily.

According to the regions in which they occur, anatomists have
divided cartilages into articular, or such as clothe the extremities of

TISSUES OF THE BODY.

169

bones entering into the formation of joints, and membranous, or such as
serve for the formation of cavities, in that they strengthen and solidify
the walls of the latter.

Another classification based on the length of existence of the tissue
might be said to be natural. We meet, namely, early in intra-uterine
life and very widely distributed, a cartilaginous skeleton, the greater
part of which disappears in the normal process of development at an
early period, being destined to give place by decay to another tissue,
namely, bone, whilst only a small portion is retained throughout the
whole of life. The first of these is temporary, the second permanent car-
tilage (!)._

There is, however, a third and more rational classification, which is
based on the histolcgical texture of the cartilage or that of its inter-
cellular substance.

The latter appears originally in all cartilages, homogeneous, transpa-
rent, or slightly clouded. This transparent constitution may last the
whole life through, when such cartilages are known as hyaline, and
represent the typical form of the tissue (fig. 157). These may be re-
cognised by the unaided eye, from their appearing in thin slices, trans-
parent as water, while in larger or thicker masses they present a bluish-
white or at times milky appearance.

Fig. 157.— Hyaline cartilage.

Fig. 158.— Rcticuiar cartilage,
from the human epiglottis.

Cartilaginous tissue is, however, liable to undergo in the course of
time many kinds of anatomical metamorphoses even of the inter-
cellular substance, which in some cases
commence very early, in others how-
ever delay a long time in making their
appearance. At one time again, they
affect but small portions of a cartil-
age, and at another extend themselves
over the whole of the latter. If they
appear early and spread throughout
whole cartilages, they produce special
modifications of the latter and are speci-
ally named.

Thus intercellullar substance may

undergo a coarsely granular clouding, Fig- 159.

or become streaky and banded, or be transformed into fibres of various
kinds. At one time we perceive a partial change into parallel bands and
fibres unacted on by acetic acid ; at another, meet with an interlacing of
dark elastic fibres, or remark in the matrix the characteristic, delicate

170 MANUAL OF HISTOLOGY.

fibrillce of connective tissue paling under the action of this reagent. The
two last-named varieties have given rise to the distinction between the
elastic or reticular cartilages (fig. 158), and the connective tissue or fibro
cartilage (fig. 159). Parts which have undergone metamorphoses of the
intercellular substance of this kind lose the bluish-white appearance of
hyaline cartilage, and become opaque and either yellow or white.

REMARKS. — Correctly speaking, this division is not good, in that we are unable
to draw any distinct line between permanent and temporary cartilage, and the ques-
tion is only as to differences of degree. Comparative anatomy teaches likewise that
the temporary cartilages of one group of animals may be permanent in another, and
vice versa. Finally, it is very frequently the case that late in life bony growths are
formed at the expense of the so-called permanent cartilage.

§ 104.

The cells of cartilage manifest no less an inclination to change than
the intercellular substance. And though in very young tissue these
elements present nothing very striking in their appearance, yet they
may become very characteristic structures through subsequent transfor-
mation.

In its rudimentary condition growing cartilage presents itself as a simple
aggregation of nucleated formative cells (flattened somewhat where they
are in contact with one another), between which close scrutiny enables us
to detect thin streaks of a homogeneous glistening substance. This con-
dition remains throughout life among the cartilages of lower animals.
Soon after this these streaks become broader, and within a short time
the interstitial matter may attain proportions as great as represented in
fig. 160.

The cartilage cells now appear round, oval, or more or less crescentic in
form, and frequently very strongly flattened. Their dimensions, exclusive
of extreme cases, may be stated at 0'0182-0'0275 mm. The body of the
cell consists frequently of a homogeneous or delicately granular proto-
plasm without a membrane, and in it we almost
always find a simple vesicular nucleus, measuring
from 0-0075 to OO144. According to Rollett, this
protoplasm becomes clouded in a peculiar manner
on being heated up to 73-75° C.

Under the action of reagents, and even of water,
the body of the cells of many cartilages may be
seen to assume jagged or stellate forms. Violent
Fij?. 160.— Ceils of an em- electric discharges also cause the cells in question
Sage? rommtherpig. car to take on the same forms, with a simultaneous de-
crease in size (Heidenhain, Rollett). They are also
probably endowed with vital contractility ; but this has not yet been
proved beyond doubt.

The further changes to which the cell (fig. 161) is liable apply less to
the shape (which generally remains one of those mentioned) than to the
size, which increases, and at times to a very great extent. The nuclei
also frequently lose their vesicular nature, becoming solid while they re-
main smooth, or else assuming a granular appearance. Deposition of fats
in the body of the cell may also commence early.

Another appearance, which is remarked not unfrequently in many
mature cartilages, though to a variable extent, is also of great significance.
Halos or rings of a sometimes homogeneous, sometimes laminated, sub-

TISSUES OF THE BODY.

171

Fijr. 161. — Diagram of well-deve-
loped old hyaline cartilage, with
various kinds of cells.

stance, surround isolated cells or groups of the same, at one time very
distinct, at another blending in their periphe-
ral portions into the matrix (fig. 161). These
are the long-known cartilage-capsule's, which
we have already considered in a former part
of our work (p. 87).

We are here met by the important ques-
tions: how have these capsules originated?
what is their relation to the cell and inter-
cellular substance ] and what is the source of
the latter]

The opinions of histologists on the points
in question have varied from the earliest days
of microscopy in the most marked way. It
was long ago supposed, under the belief in the
spontaneous generation of cells and the doctrine of blastema, that the
intermediate substance was gradually insinuated between the cells (§ 102),
and that the cartilage-capsule was formed of a modified layer of the latter
around the cell : consequently, that the capsule was deposited externally
upon the cell-body. On the other hand, some, while they allowed the
origin of the apparently homogeneous intercellular substance to be that
just stated, still looked upon the cartilage capsule as a product of secre-
tion from the cell, fusing at its periphery with the matrix. According to
a third view (1), the capsule, as well as the intercellular substance, is a
material supplied by the cartilage cells. But it is still a subject of con-
troversy whether the capsule and groundmass are to be looked upon as a
secretion of the cells, which has become solid, or a part of the body of the
la'tter, which has undergone metamorphosis; or, again, whether, as a rule,
this intercellular matter is to be considered structureless or the reverse.
The last of these three views is, in our opinion, the only one tenable at
the present day (2).

We are able, indeed, by means of certain reagents, to demonstrate with
complete certainty that the so-called intercellular substance of many car-
tilages is only apparently structureless (fig. 162).
This is seen to be the case in the frog, while it is
less distinctly evident and more difficult of demon-
stration among mammals. It is, in fact, by a
process of repeated formation of capsules that the
matrix is produced and increased in quantity. The
whole ground-work of cartilage consists of nothing
but a number of large systems of capsules, which
have become fused into one another. Each car-
tilage cell, therefore, takes a part in this process.
In many cases these concentric laminae in the cap-
sule appear in section of exactly the same refrac-
tive power, and consequently it was formerly sup-
posed that the intercellular substance of cartilage
was homogeneous and structureless. But if, on the other hand, the
youngest layers in the system presents different optical bearings (which
occurs, as we know, not unfrequently), the term cartilage - capsule is
usually applied to them.

But although so much is, in our opinion, certain, yet the problem as
to whether these capsules are the products of secretion of the cell-body

Fip. 162. — Thyroid cartilage
from the pig, after treat-
ment win chlorate of pot-
ash and nitric acid, showing
the intermediate substance
resolved into the portions
belonging to each cell.

172

MANUAL OF HISTOLOGY

or are the transformed outer portion of the latter, is not yet capable of
solution, in the present state of our knowledge. "We are inclined, how-
ever, with others, to give the preference to the latter view.

REMARKS.— 1. There are, besides, instances in which this origin of the intercellular
matter may be recognised without any trouble. As Remak has very correctly shown,
the xiphoid process of the rabbit affords a suitable object. Here the cells may be
seen surrounded by broad halos. — 2. Remak may, to a certain extent, be numbered
among these. The observations oiHeidenhain also are of importance. He succeeded,
with the help of warm, water, and the action of potash with nitric acid, in resolving
the structure of the apparently homogeneous intercellular substance of frog's cartil-
age. I myself have arrived at the same result on repeating the experiment.

§105.

The segmentation of its cells, or, as the usual expression is, endogeneous
cell-formation (fig. 163), is no less characteristic of cartilage. This pro-
cess has already been described in § 55 : we refer the reader to what
was there stated. We mentioned there also that all the phases of this
process of segmentation had not yet been placed beyond doubt by obser-
vation. Thus we still require satisfactory proofs of stages 2, 3, 5, and 6,
which have not yet been observed, owing perhaps to the rapidity of the
process.

As we have already seen, two (7), four (8), or indeed whole generations
of so-called daughter-cells (9), may lie in the interior of a capsule. In the

costal cartilages of elderly indi-
viduals, we have the best oppor-
tunity of observing these latter
very much enlarged, and con-
stituting the so-called mother
or parent 'cells : they may at-
tain a diameter of from 0!113
to 0-226 mm. These again
may enclose whole swarms of
daughter -eel Is. The forma-
tion of laminated envelopes
may then take place subse-
quently on the daughter-cells
which have sprung up within
the original capsule (8, 9), and
these may appear in course of
time to lie free- in the tissue,
(after that the parent capsule
has become fused with the
ground-substance) undergoing
probably later on the same
process of segmentation over
again. Thus the cartilage be-
comes very rich in cells, showing the important part endogenous multipli-
cation plays in the formation of the latter tissue.

This explains the tact that growing cartilages, in which no kind of
regeneration of cells can be discovered, nevertheless acquire gradually a great
number of cartilage elements. And, in fact, on searching through cartilage
tissue, we frequently meet with spots where the cells still appear as
though jammed against one another, and flattened at the point of contact

Fijr. 163. — Cartilage-cells engaged in the act of segmenta-
tion (so-called endogenous multiplication), a, body of
the cell; b, capsule; c. nucleus; d, endogenous cells ; e,
subsequent formation of capsules on the exterior of the
latter; g, external portion of the capsule, which fuses
Avith ground-substance of the cartilage. Diagrammatic.

TISSUES OF THE BODY.

173

(fig. 161), arid whose partial origin in the manner just mentioned is at
least very probable.

In many cartilages besides, which are on their way to dissolution,
and where a lively change of tissue is commencing again, there often
occurs a very extensive segmentation of cells. This is especially the
case where in the foetus the production of bone begins at the expense
of, and together with, softening of the cartilages. It was formerly sup-
posed that other tissue elements (medullary cartilage cells), allied to lym-
phoid corpuscles, could spring from the daughter-cells. These were then
believed to take part in the formation of other tissues, such as the bony,
fatty, and connective. We shall refer again to this in dealing with osteo-
genesis.

§ 106.

The nature of cartilage, as that of a very early formed and rapidly
senescent tissue, explains the fact that, in examining, not alone the
mature or aged body, but also the foetal in part, we encounter a series of
changes in the tissue in question, which, occurring more rarely in other,
parts, are usually looked upon there as pathological occurrences, but which
may here be set down for the greater part as normal processes, and must,
therefore, be discussed here.

The transformations which may affect the cell and ground-substance in
various ways are more especially three— -fatty infiltration, calcification,
and softening. They occur principally, but not exclusively, in hyaline
cartilage.

Fatty deposit may commence, as, for instance, in the human costal cartil-
ages, even in infancy (fig. 164 a, b). We first remark very small isolated
globules of oil, which either lie separately in the body of the cell or
grouped around the nucleus. On their becoming more numerous, they
coalesce, forming drops of
greater magnitude, which
either lie in the cavity of
the cell, without order, or,
more frequently still, they
so envelope the nucleus that
it cannot be recognised with-
out the aid of reagents. Thus
it was that that view, held by
earlier authors, originated,
namely, that the nucleus
could itself be transformed
into an oil-globule. Should
the process advance very far,
almost the whole cavity of
the cell may eventually be
occupied by one large drop
of oil, or a swarm of globules.
Calcification of cartilagi-
nous tissue is essentially
different from true ossifica-
tion, that is, from the for-
mation of genuine bony sub-
stance containing peculiar cells, although both processes were formeily
confounded with one another.

Fig. 164.— Costal cartilage of an infant, transversely cut.
a, a portion from the circumference ; b, from the interior.

174

MANUAL OF HISTOLOGY.

We now know that cartilage hardly ever becomes bony tissue, but on
being calcined, it has rather attained the end of its course, and neither
grows nor is further developed in any other manner. In this form it may
exist for a longer or shorter period, and, in many of the lower animals, the
whole life through, or, more frequently still, it may undergo a rapid re-solu-
tion, in order to make way for the formation of true osseous tissue.

We are indebted to Bruch, but more even to H. Mutter, for having
first enlightened us as to the right way of viewing these processes.

In some rare cases it is
the cells (a-e) which are
first affected by calcifica-
tion (fig. 165), but more
commonly the ground-
mass (/). Later on, we
see both parts equally at-
tacked by it, or perhaps
the process may con-
fine itself principally to
the intercellular sub-
stance. This process
consists in the deposit
of either finely granular,
or, what is more rare, of
coarser crumbs and mole-
cules of the salts of lime.
The tissuebecomes, owing
to this, more and more
opaque, until, finally, it is
so in an extreme degree.
Touching the cartilage-
cells, those whose cap-
sules are apparent, still as
well as those where the latter have been merged into the ground-sub-
stance, may become the seat of the deposition of lime-salts. Thinly cap-
suled cells show us the molecules more on the interior of the enve-
lope, or perhaps in its cavity also (e). If the capsule be stronger (a, &, c\
it is impregnated with calcareous salts, while the real cell usually remains
soft. When daughter-cells are present (g, above), we frequently remark,
beside the calcification of the parent-capsule, a deposit of salts in the
layers of the secondary envelopes.

If the deposition take place regularly in the ground-substance, the
granules of lime are (especially at first) arranged in groups around the
cells (fig. 165, g, below, and 166, a). Later on their amount increases
more and more in the rest of the matrix (fig. 166, bt c, d) until at last
they may appear heaped up, molecule on molecule, in the closest contact
with one another (fig. 165, /).

This calcification of cartilaginous tissue occurs in the first place to a
very great extent in the embyronic and earlier periods of life, appearing
there in the falsely-called ossification of cartilage. Cartilage of this
kind soon becomes dissolved.

On the other hand, this same process appears subsequently as an ordi-
nary occurrence in the so-called permanent cartilage of later life ; for in-
stance in that of the ribs and larynx. Calcified masses of the last kind

Fig. 165. — Diagrammatic sketch of calcified cartilage, a, A cap-
su'e with thick walls and shrivelled contents; 6, another, wirh
daughter-cells; c. with very thick walls ; d, very markedly calci-
fied ; e, cell with a thin memhrane undergoing calcification; /.
a piece of cartilage with molecules of lime between and around
the cells; g. another, in which the granules surround the cell
more completely.

TISSUES OF THE BODY.

175

may again undergo solution at certain points, and show a new formation

of bone in the spaces which have

thus been formed. But they may

also (and this is most frequently

the case) remain in this same

condition to the end of life.

It is not alone in hyaline and
streaky cartilage that calcifica-
tion is met with; it appears also,
though less frequently, in the
reticulated species.

Softening, the last of these
transformative processes, may
affect either calcified or the soft
and still unchanged tissue.

In the latter it occurs in the
first place very extensively in
the temporary cartilaginous por-
tions of the skeleton, during
fcetal life, or in early infancy,
but may appear likewise in older
permanent cartilage, though not
as a regular occurrence. The
first step of the process is a kind
of colloid softening of portions
of the matrix, taking place at iso-
lated points in the intercellular
substance, attacking the walls of
the capsules situated here in its
further progress, and forming
cavities into which the cartilage cells or their descendants find entrance.
In consequence of this process of liquefaction, a system of canals may be
formed, which may either open externally towards the perichondriura, or
enter into communication with the passages of a neighbouring portion of
bone containing vessels, which soon make their way into the interior of
the cartilage, and may be recognised there. In the mass which fills
up these sinuses in the cartilage, we have the before-mentioned medullary
cells (p. 171).

The process of liquefaction of a portion of already calcified cartilage-
tissue is of a precisely similar kind.

§ 107.

In inquiring now into the mode of occurrence of the several varieties
of cartilage, the following facts as regards the human body may be remem-
bered.

Hyaline cartilaginous matter (partially fibrous, softened, or calcified,
however, after a certain age) forms the rudimentary skeleton in the foatus,
that is, the several portions of the vertebral column, of the thorax (not ex-
cepting the clavicle), of the shoulders, of the pelvic bones, and in addition,
many of those of the head. In the adult this hyaline texture remains in the
cartilages, clothing the ends of the bones entering into the formation of arti-
culations (with the single exception of the maxillary). It remains in the car-
tilages of the nose, and the larger ones of the larynx, namely, the thyroid

Fig. 166. — Cartilage from symphysis of a woman
one hundred years of age, undergoing calcification.
a, cartilage-cells surrounded with scattered mole-
cules of lime-salts ; 6, c, d, more copious deposit in
the intercellular substance, and around the cells ; e,
true bony tissue.

176 MANUAL OF HISTOLOGY.

and cricoid, but only partly in the c. arytenoidea. Again, in the half rings
of the trachea and bronchi, as well as in the costal cartilages, and ensi-
form process of the sternum. Finally, in the symphyses, and equivalent
Ugamenta intervertebralia. a thin layer immediately in contact with the
bone is to be found, which consists of genuine cartilaginous matter with
homogenous intercellular substance.

Of the numerous parts formed of this tissue some deserve special notice.

The rudimentary cartilaginous skeleton of the foetus presents at first
small roundish simple cells, closely crowded together, with vesicular
nuclei, and situated in a scanty soft ground-substance. Should such
a cartilage have reached an age at which it is about to fall a prey to
advancing ossification, the intercellular matter is seen to have consider-
ably increased. The cells have also increased in size, especially towards
the line of commencing ossification, at the same time that their capsules
cannot be said to have become thickened. Endogenous multiplication
has produced here a large increase also in their number. The daughter
cells so formed are now, as the saying is, free, in that the capsule of the
parent-cell is merged into the ground-substance, which is either homo-
geneous, fibrous, or streaky. They now lie either in long rows one
after another, frequently compressed into an obliquely oval form, as in the
middle portion of a growing hollow bone (in the so-called "direction" of
cartilage-cells), or they appear in irregular groups, as in the epiphyses
and short bones. The cartilage has now become vascular besides.

Articular cartilages are thin coverings for the ends of bones entering
into the formation of joints. When firmly united to the bone at their
under surface, they represent the remainder of the original rudimentary car-
tilage, which has not given way to the encroachments of ossification. Their
superficial portions, lying free in the cavity of the joint, contain small but
strongly flattened cartilage cells measuring O'Ol 13-0*01 78 mm., crowded
one over the other, in a way that reminds ITS (when seen in vertical sec-
tion) somewhat of laminated epithelium. Further down, or at a greater
depth, we see the cells in the growing substance separated somewhat
more widely from one another. They lose at the same time the flat-
tened appearance, becoming taller and larger, increasing to 0-0156-
0-0282 mm. and upwards, with nuclei of from 0'0065-0'0090 mm. At
first they are piled without arrangement in heaps over one another; but
deeper in the vicinity of the bone, they group themselves into long rows,
perpendicular to the surface of the latter. The remainder is made up of
beds of calcified matter. In the large cells of articular cartilage, daughter- •
cells are frequently present, while fatty globules are occasionally, but
rarely met with.

The costal cartilages have been frequently described by histologists as the
best examples of hyaline structure, but incorrectly so on account of their
various transformations. In the new-born infant there appear in a com-
pletely homogeneous ground-substance (fig. 167) beds (a] of small cells
(parallel with the surface) like rents in the matrix, which have a delicate
outline, and which contain nuclei of about 0-0056 mm. in diameter. The
length of these cells is 0'0095-0'0150 mm.

Their contents are either quite transparent or dotted with a few very
minute oil-globules of about 0*0018 mm., or even less in diameter. More
internally we encounter a number of generally narrow oval cells, some-
times reniform or wedge-shaped, placed in every position as regards one
another, while in the deepest portions of the costal cartilages, the largest and

TISSUES OF THE BODY.

177

same cartilage
or

Fig. 167. — Costal cartilage from ,ihe infant in transverse
section, a. external portion lying next the perichondrinm ;
ft, internal portion.

broadest cells (I) are to be found, some of oval or spherical form, and

diameter of 0'0169-0'0282

mm. Capsules are either

not at all visible, or only so

in. the form of delicate

halos, and within the latter

we find at most one pair of

so-called daughter-cells.

If we now examine the
in an adult
older individual (iig.
1 68), we remark, particularly
in the internal portions,
isolated whitish or white
spots, where the tissue pre-
sents a silky gloss or appear-
ance like asbestos, in the
midst of the more trans-
parent ordinary ground-sub-
stance (a). Under the micro-
scope we find the tissue to be
here fibrous (c), and indeed
most regularly so; we see
stiff, crowded bundles of
fibres running parallel with one another, and becoming lost in the neigh-
bouring ground-mass. These do not pale on treatment with acetic acid.
Again, in many localities the intercellular substance appears granular and
clouded, in others cleft or further split up into bundles (&).

Here also, in transverse sections, we meet with small flattened cartilage
cells, close under the surface, arranged in several layers, and without any
capsules or so-called daughter-cells. They lie in the usual manner with
their long axis parallel to the edge of the cartilage. Deeper down the
cells, which are still in general of but small dimensions, take up an irre-
gular position, becoming gradually broader and larger. We may meet
with some towards the centre, measuring 0'0750-(H150 mm. At the
same time, the position of the elements either remains irregular, or they may
be more or less arranged in radiating lines. Here we find the daughter-
cells also more numerous (d, e, /).

The cells found in the portions which have become fibrous may be
enormously large, attaining in some cases a diameter of 0'1423-0*2256
mm. They are of roundish, oval, or elongated form, with whole swarms
of endogenous cells, 20, 25, or 30, or even 60, as Donde.rs once saw.

Capsules are of very ordinary occurrence around the cells in the more
internal portions of the costal cartilages. They are of varying but gene-
rally considerable thickness (/), and appear at one time distinctly marked
off externally, at another blending into the surrounding ground-substance.
In other cartilage cells this capsule system cannot be distinguished opti-
cally from the surrounding matrix (d), or has developed into fibres (e).

The large amount of fat which (commencing at birth) has been gradu-
ally accumulated here, is also very remarkable. Here may be seen
larger or smaller globules, which coalescing — especially in the neighbour-
hood of the nucleus — may frequently envelope the latter, so that we have
apparently to do with a drop of oil in its place.

178

MANUAL OF HISTOLOGY.

Again, processes of liquefaction and calcification, as well as incipient
ossification, are of common occurrence in the costal cartilages of elderly
individuals.

Now, concerning the hyaline cartilages of the larynx, we observe in
the larger ones, namely, in the thyroid and cricoid, many layers of small
>and narrow flattened cells, immediately beneath the perichondrium, lying
in a homogeneous, or occasionally streaky intercellular substance, accord-
ing to the direction of the cells.

The innermost layers, containing daughter-cells, on the other hand,
present large and distinct cartilage cells with thickened walls. In older

Fig. 168. — Transverse section of the costal cartilage of an old man. a, homogeneous ground-sub-
stance, which has become striated at 6, and has broken into fibres at c ; cartilage-cells may also be
seen, possessing for the most part thickened capsules. At d and e, two large parent-cells with nume-
rous offspring; another at/, with well-developed laminae in the capsule.

subjects the intermediate matter may be fibrous or banded ; deposit of
fats in the cells is also of frequent occurrence here. Between these two
portions, again, is situated a thin layer of larger cells, whose intermediate
substance appears granularly clouded (Rheiner). Calcified portions, with
finely granular calcareous matter, are also very commonly met with in
older individuals ; and true ossification is also seen. The half rings of the
trachea correspond with these two cartilages in all essential particulars of
texture.

The texture of the arytenoid cartilages is of great interest, constitut-
ing as it does an intermediate form between that just mentioned and

TISSUES OF THE BODY. 179

elastic cartilage. In some parts, namely, these are homogeneous, and
then in others again the intercellular substance is traversed by elastic
fibres. The latter may be seen in the processus vocalis, and at times in
the tips.

§ 108.

Elastic, reticular or fibro-reticular cartilages (fig. 169), which are
remarkable for their rather yellowish tint and great opacity, spring
from the hyaline cartilage of the foetal body. The development of their
elastic fibrillation reminds us thus of the formation of the chondrin-
yielding fibres of hyaline cartilage. It must be remembered, however,
that it is a process which belongs to the earlier periods of life, whilst the
appearance of fibres containing chondrin is an occurrence of a later time.
In young bodies the originally homogeneous constitution of the cartilage
may remain at particular points, especially in the vicinity of some of

,.,„ _ .. . Fie:. 170. — Fibro-reticular carti-
r. 169. — Reticular cartilage from the ear of !„„.„ trrirn *hp human puio-int

the calf, a, cells; 6, intercellular substance ;
c, elastic fibres of the latter.

the cartilage cells. The fibres are at one time thin and delicate, at
another dark and irregularly bordered, with a very intricate course, reti-
culated or tangled like the fibres of felt. Wherever this fibrillation
is very strongly pronounced, the cells may be concealed to a great extent,
as, for instance, in the epiglottis (fig. 170), and pinna of the human ear.
The proportion of intercellular substance to the cells is also subject to
great variation, to such an extent at times that the latter may in one
instance be separated from one another only by narrow belts, or, on the
other hand, by a large quantity of interposed matter. The fibres are those
belonging to the elastic series, with the characteristic power of resisting
the action of reagents. They take their rise through an immediate meta-
morphosis of the homogeneous blastema without the intervention of
cells, as is indicated by the fact that in the human arytenoid cartilages
the homogeneous ground-substance is immediately continuous with the
fibrous.

The cells of reticular cartilage, which vary greatly as to form and size,
are easier of isolation than those of the hyaline tissue. They are usually
scattered without any definite arrangement, although we may find in the
peripheral portions of the epiglottis small narrow elements, as in perma-
nent hyaline cartilage. The cells of reticular cartilage, farther, are often
remarkable for possessing less definite capsules and a less marked ten-
dency to the production of daughter-cells. The nuclei, which are either
smooth (in which case they contain a nucleolus), or granular, occur there-
fore single as a rule, or more rarely in pairs. In the body of the cell or
round about the nucleus fat may also be met with here.

180 MANUAL OF HISTOLOGY.

Among the cartilages of the human body which have a thoroughly
solid reticular intercellular substance, may be numbered certain portions
of the respiratory apparatus, namely, the epiglottis, the cartilages of
Wrisb&rg and Santorini, the Eustachian tube and pinna of the ear.
Further, as having a partially fibrous blastema, the arytenoid cartilages
and intervertebral ligaments.

§ 109.

We have now to enter on the consideration of a third species of this
tissue, namely, of the connective-tissue cartilage, or, as it has been less
happily termed, fibro-cartilage (fig. 171). This may be looked upon
as a hyaline cartilage whose abundant matrix has developed into fasci-
culi of connective-tissue, or as a solid species of the latter, through
which cartilage cells are scattered. The fact is that it is usually a
mixture of connective-tissue and cartilage. Like connective-tissue, it
contains elastic fibres as well as the cells of this tissue, known as con-
nective-tissue corpuscles. Between the latter and many cartilage cells
there occur intermediate forms, so that fibro-cartilage may pass into
ordinary connective-tissue without any line of demarcation, especially at
those points at which it becomes poor in cells.

^n ^ie ot^er hand, its bearing as a
cartilage, with connective-tissue matrix,
appears clearly in the intervertebral liga-
ments, where we find close to portions
which are hyaline in texture other points
where the matrix is obscurely fibrous, and
continuous with a substance which is evi-
dently connective-tissue.

Fibro-cartilage, which is brought espe-
cially into use in the construction ^of
joints, appears to the unaided eye of
whitish or slightly yellow colour, and to
possess a texture sometimes solid and
sometimes rather soft. It is more exten-
s^le> furtner, than ordinary cartilage.

Under the microscope we find, instead
of the homogeneous matrix of hyaline cartilage, connective-tissue with
fibres sometimes more indistinct than at other times, when they may
be very sharply defined. The bundles are usually crossed in all direc-
tions confusedly. They may, however, preserve some definite direction on
the other hand, while their optical and chemical bearing is quite that of
ordinary connective-tissue (see below). As to the cartilage cells, their
proportion is in general but small, and frequently, indeed, very incon-
siderable, so that they require to be searched for. The size, further,
of the ^ cells is also small, and their whole constitution simple, the out-
line being usually very delicate, and the nucleus, as a rule, single. Cells
with two nuclei are rare, and those containing daughter-cells apparently
do not occur at all. Fatty infiltration likewise, which is so common in
other species of cartilage, is here of rare occurrence. The position of
the cells is also liable to variation. They are either without arrange-
ment or crowded together in small groups, or again, arranged one after
another in rows. The latter position corresponds with the direction of
the fibres of the tissue.

TISSUES OF THE BODY.

181

Connective-tissue cartilages possess vessels, "but only in small num-
ber ; but as to the presence of nerves, we are as yet unable to state any-
thing certain.

Among them the cartilages of the eye-lids may be reckoned, of which
the upper appears to be richer in cells than
the lower, which has but few of the latter
( Gerlach) ; further, the c. triticece of the
larynx, which may, however, consist of hya-
line substance (Rheiner) ; then the c. inter-
articulares, as well as the so-called labra
cartilaginea of certain joints, with the car-
tilaginous knots found in tendons. As a
rule, it seems to be part of the composite
character of the tibro-cartilages, that struc-
tures formed of pure connective-tissue may
be transformed at points into the varieties
of the tissue in question by the imbedding of cartilage cells,
is the case in the terminal portions of tendons where they are inserted
into bone, as well as many parts of their sheaths (Kolliker).

Finally, fibro-cartilage, springing, moreover, continuously from the
hyaline, appears in the symphyses and so-called half-joints, which have
their origin in the liquefaction of the central portion of solid masses con-
necting bones (Luschka).

Among the latter, those most worthy of consideration are the sym-

6

Fig. 172.— Diagram of a vertebral
symphysis divided vertically. At
o, the pulpy centre ; at 6, tlie
fibrous ring; at c, the cartilagin-
ous covering of the body of the
vertebra ; d, the periosteum.

This

, Fig. 173. — Vertical section through the bodies, the last dorsal and first lumbar

vertebra of a human embryo at ten weeks. Body with calcified carti-
laginous tissue, a ; and unchanged, b ; at c the fibrous ring developing, con-
sisting of elongated cells (?), and with a cavity containing transparent
cells at d, which becomes the pulpy nucleus of the infant

physes of the vertebra, so frequently the subject of investigation, the so-
called ligamenta intervertebralia, about which Luschka has imparted to
us such valuable information.

They present themselves as solid connecting plates between the bodies
of the vertebra (fig. 172), taking their rise continuously (at least at their
circumference) from a layer of hyaline cartilage which clothes the surfaces
of the bone (c). They each consist of a fibrous ring externally (&),

182

MANUAL OF HISTOLOGY.

that is, of concentric portions of fibrous tissue crossing each other per-
pendicularly and obliquely. This ring has sometimes the character of
simple connective-tissue, sometimes that of an elastic or fibro-cartilage.
The central portion is soft, and often possesses a cavity containing a jelly-
like mass, the so-called gelatinous or pulp nucleus (a). This is made up
in the adult of ragged processes of the peripheral fibrous cartilage, which
lie closely crowded together, leaving in their midst a cavity filled with
gelatinous matter.

While the pulp nucleus resembles more arid more the fibrous ring as
its solidity increases at an advanced period of life, it shows a very dif-
ferent bearing in the infant and foetus. Here (fig. 173), at an earlier
embryonic epoch, the origin of the nucleus is quite manifest. It takes
its rise, namely, from the exuberant growth of the residue of a rudimentary
foetal structure, the chorda dorsalis (Luschka). This latter, which per-
sists among the lowest animals for a part of, or the whole of, life, pre-
sents itself as a cylindrical rod blunted before and fining off to a point
posteriorly. It passes from the base of the skull down to the lower end
of the vertebral column in the place of the bodies of the bones making
up the latter.

It consists of a tissue which may be perhaps classed among the
cartilages, formed of transparent cells crowded close together, and
enclosed in a homogenous envelope. The chorda dorsalis disappears
almost entirely with the formation of the cartilaginous base of the skull
and vertebral column. However, in the intervertebral ligaments there

remains a space filled with the
characteristic cells of the notochord
(d), which may even extend into
the body of the vertebra themselves.
Thus we see it in the embryo of
ten weeks old.

In the foetus in the fifth month
(fig. 174) we find here again very
similar cells, with a single vesicular
nucleus, and about 0 '01 36-0 '01 80
mm. in diameter. From these (1, a)
there are gradations up to some of
0*0413 mm! and upwards, in which
we encounter double and quad-
rupled nuclei, or even still more(&&),
or the same number of endogenous
cells (c, d). Beside these, spring-
ing from the further growth of such
parent-cells very large bodies are
met with, measuring up to 0-1128
mm., of tough constitution and
transparent appearance. They are
partly filled with distinct daughter-
cells, but principally with extreme-
ly numerous transparent globules
of a metamorphosed albuminous
substance.

In the still infantile body we meet with the same structures with a
tough envelope (the thickened parent capsule), which may attain a

Fig. 174.— Descendants of the cells of the chorda
dorsalis in a foetus of five months old, and in an
infant. 1, Cells from the foetus of five months;
2, single cell from the infant; 3, another, with
daughter-cells; 4 and 5, a structure which has
taken its rise from a very much enlarged parent-
cell, with nucleated cells and many transparent
globules of albuminous nature.

TISSUES OF THE BODY. 183

diametor of 0*0226 mm. (4.5). Other smaller bodies of this kind (3) still
bear clearly the characters of large parent-cells.

These gelatinous collections of cells exist throughout the first year
after birth, and then appear to fall a prey to the centrifugal growth of
the fibrous ring encroaching on them.

§ no.

In the chemical investigation of cartilage, the variations corresponding
to the different forms in which the tissue makes its appearance should be
taken into account. It ought to be ascertained (a) of what substances
the cartilage cell, with its several parts, consists ; (&), what matters enter
into the composition of the system of capsules and the substance cementing
them together ; (e), how far the youngest layers immediately surround-
ing the cells differ from the older ones, which form the apparently
structureless matrix ; (d), how far the composition of the latter changes
according as it remains homogeneous or becomes granular, and like-
wise on the appearance of elastic fibres in it. In chemical examina-
tion we should be able to follow up (e) the changes which the composi-
tion of cartilage undergoes in the physiological metamorphoses of the
tissue ; and, finally, the fluid saturating the latter should come within
the range of inquiry, and we should look in it for the products of
the transformations going on in the tissue. Unfortunately, however,
these requirements cannot be met by any means in the present state of
science.

If cartilage be treated microchemically, we immediately recognise the
fact that it belongs to the tissues which are not very mutable. In cold
water it shows but little sensibility, with the exception of the bodies of
the cells, which rapidly shrink up (§ 104). Acetic acid has the same
action upon the latter, but, like other weak acids, has no effect on the
whole. Even sulphuric acid and strong solutions of potash are resisted
for a remarkably long time by the cells of cartilage (Donders and Mulder}.
The latter may be obtained in an isolated condition by maceration in
hydrochloric acid ( Virchoii). With sugar and sulphuric acid the cells
assume a red colour, while the intermediate substance of hyaline cartil-
age becomes yellowish red (Schultze). The nuclei also appear difficult of
solution as a rule. It is otherwise, however, with the intermediate sub-
stance. This may be dissolved by long-continued boiling in water, after
from twelve to forty-eight hours, and yields chondrin : it consists, there-
fore, of what is known as chondrigen. The microscopic examination of
the dissolving tissue during this process is a matter of some interest.
The cells resist the solvent action in the most determined manner, and
are, therefore, not formed of chondrigen or any of the other glutinous
compounds. It is no proof to the contrary that they are subsequently
dissolved. Again, the laminae of the capsules immediately adjacent to
the cells resist the action of boiling water longer than ths rest of the
ground-substance. They do not, therefore, possess the same composition,
though they may be said to yield chondrin.

The same difference also is manifest in the granules of chondrigenous
cartilage.

The granular clouding of the ground-substance does not disappear on
treatment with acetic acid or ether, but does so in a warm solution of
potash, and on heating in dilute, hydrochloric, and sulphuric acids.
13

184 MANUAL OF HISTOLOGY.

These granules especially are coloured red when heated with Millon's
reagent (Rkeiner). The fibres of hyaline cartilaginous tissue yield
chondrin likewise, as far as we can gather from investigations which have
been made up Jo the present.

From all this we learn that hyaline cartilage is a tissue yielding
chondrigen with cells of a different constitution, with which we are not
more nearly acquainted.

§ HI.

Now, concerning elastic or reticular cartilage, we may obtain from it,
that is, from the residue of hyaline matter which it still contains, a small
quantity of chondrin, but only after long-con tinued*boiling. The elastic
fibres, which must take their rise from a metamorphosis of the chondrigen,
manifest here the same characteristic insolubility as elsewhere. It is only
after digestion in potash of many days' duration that they become jelly-
like and break down into granules, which are dissolved on the addition
of water. Whether the cells of reticular cartilage are more soluble than
those of the hyaline species, as has been stated, but without sufficient
foundation, requires more accurate investigation.

Passing on then to fibro-cartilage, we find that its ground-substance
gives the same reactions as connective-tissue, and is transformed like-
wise into glutin by boiling. The latter is not, however, chondrin, but
the ordinary glutin of connective-tissue (p. 22). The semi-lunar cartilages
of the knee-joint are said to be most difficult of solution.

At present we know nothing of the fluid with which cartilaginous
tissue is saturated. But the so variable proportion of mineral matters
which are found in the latter seem to point to a variation also in its
composition. Leucin, glycin, and cartilage-sugar may probably be re-
garded as physiological products of the transformation of the tissue in
question. Comp. §§31, 33, and 22.

The percentage of water in this tissue is reckoned at 54-70 per cent,
and the fats, which are entirely absent in no cartilaginous structures
from the very earliest periods, are found to vary naturally very con-
siderably. Their proportion, according to most observers, is about from
2 to 5 per cent., but which of their varieties occurs in the tissue of car-
tilage has not yet been ascertained.

There now only remain for consideration the mineral constituents.
The proportions of these are very differently stated, which is, most pro-
bably, dependent on the imperfect methods of calcining which have been
resorted to. Phosphate of calcium and magnesium, with chloride of
sodium, carbonate of sodium, and sulphates of the alkalies, have been
mentioned as occurring here.

We may set down a few results here which have been obtained in one
and the same animal as examples of the relative proportions of mineral
constituents. Schlossberger found that the ashes yielded by the nasal
cartilages of an old rabbit amounted to 3 '51 per cent., those of the ear
to 2*30 per cent., while those of the ribs rose to 22-80 per cent. Hoppe
again obtained from the costal cartilage of a suicide aged 22, 2 '20 per
cent., and from that of the knee-joint, 1*54 per cent, of ash.

The observations which have been made on the costal cartilages of
the human being teach that the proportion of inorganic constituents is
increased in one and the same cartilage by age. The following analysis,
with the exception of the fifth, have been all made by Bibra : —

TISSUES OF THE BODY. 185

A child of six months, . . .2-24 per cent, of ash.

A child of three years, . . .3*00 „

A girl of nineteen years, . . .7*29 „

A woman of twenty- five years, . . 3 '92 f,

A man of twenty years, . . .3-40 „

A man of forty years, . . .600 „

§ 112.

The cartilages of the adult body may he regarded as the residue of
a tissue very widely distributed through the system at an early period
of intra-uterine existence, which has for the greater part given way to the
subsequent formation of bone (§ 103). In many structures, therefore,
this tissue manifests a remarkable degree of transitoriness. And even
those cartilages which persist in the body up to its maturity show a
certain inclination to undergo anatomical metamorphosis, that of softening,
of fibrillation, of calcification, and even of ossification ; in other words, to
pass through subsequent processes which in the so-called temporary
cartilages had taken place at an earlier epoch (§ 106),

For the rest, cartilaginous tissue, which is, as a rule, non-vascular,
possesses but a small amount of transformative power over the matters
whicli it receives ; and such as it is, its bearings are unfortunately still
very obscure. The nutrition of the tissue occurs in two ways. Some
cartilages are clothed with a fibrous membrane, the perichondrium, whose
vessels supply the nutritive materials. For all tins it is a strange fact
that, in the interior of the cartilage, the tissue appears most highly deve-
loped— thus at the point most remote from the blood-vessels. How far,
and whether indeed the tissue can further grow at all from the perichon-
drium, has not yet been ascertained. Other portions of the tissue in
question, which enter into the structure of joints, possess no perichon-
drium, and depend on the vessels of the adjacent bone for their nutriment.

According to all this, we have in cartilage to deal with an aggregation
of simple cells, whose intercellular substance is its only essential peculi-
arity; on which also the physical properties of the tissue, its solidity,
hardness, and pliancy, depend. It is owing specially to this latter quality
that cartilage is of such importance to the system; it adapts to form sup-
ports for other parts, to strengthen the walls of membranous canals, &c.,
to clothe the ends of bone, forming a layer peculiarly suitable for articula-
tions through its hardness, smoothness, and small liability to wear and
tear. Finally, it presents itself as a very strong connecting matter for
joining bones together.

Although non-vascular, cartilages may undergo the same changes as
other vascular portions of the body, under conditions of inflammatory
irritation. Energetic segmentation of its cells has been remarked, as well
as increase in size of the capsule and deposit of fats in the body of the
cells. The intercellular substance may also split up into fibres and fasci-
culi, or break down altogether. Calcification or transformation of the
whole into a substance more or less like connective-tissue may also occur
(Ned fern, Virchow}. These changes are, in many cases, brought about by
but a repetition of the process described in § 106.

The substance of cartilage is not regenerated, however, so that two
fractured portions of the latter can only be united again by a connective-
tissue cicatrix. But an accidental new formation of cartilage is by no means
of rare occurrence. In the first place, it may start from cartilage already

186 MANUAL OF HISTOLOGY.

present (ekchondrosis), or a cartilaginous tumour may spring up in places
where cartilage does not normally appear, as, for instance, in bone or
glandular structures (enchondroma). In the latter, and not unfrequently
in the same tumour, we meet with the several varieties of cartilage as
regards its cells and interstitial substance ; islands of the true tissue are
sometimes separated from one another by fasciculi of connective- tissue.

It now remains for us to consider the first appearance of cartilage in
the embryo, and the changes which take place in it subsequently. On
this point much valuable information has been contributed by Schwann,
Kolliker, Bmch, Heidenhain, and others.

The histological development of cartilage takes place at a very early
period of intra-uterine life, as is indicated by the original simplicity of the
tissue, and its similarity to the first cellular rudiments of the organs and
various other parts of the system, namely, the embryonic cells. The first
anatomical rudiments of cartilage, that is, of the temporary tissue, appear at
the commencement whitish and clouded, without differing in texture from
the neighbouring structures. Its characteristic features begin, however,
to be developed very early.

Originally these primitive cartilage cells lie closely crowded together,
and there is hardly the slightest trace of intermediate matter. The latter,
however, soon makes its appearance somewhat more distinctly.

Thus, in the embryos of sheep, of 6-7 mm. in length, Kolliker found car-
tilage cells measuring 0 -01 35-0 '0226 mm., and the intercellular substance
still very scanty. In larger embryos even, as those of the pig, of 2
inches long and upwards, the ground-substance is still much less in quan-
tity than the cells, in which latter the production of daughter-cells is be-
ginning. Fig. 175 represents this process. In other foetuses of the same
animal, measuring 3|- inches long, the intercellular substance amounts to
only about one-fourth of the whole volume, according to Schwann. At
the same time, the tissue is so soft that, on the slightest pressure, the
cells separate from one another, and float about in the surrounding fluid.
Later on, the proportion of the intercellular substance increases more and
more, while the cells enlarge, and endogenous multiplication reaches
in many cartilages a high degree of activity. But
during the growth of a cartilage, the number also of
the cells it contains increases by segmentation of those
previously existing. The stronger capsules, present-
ing different optical characters from the surrounding
medium, are only found at a later period of develop-
ment. Deposition of fats also (at least in the cartil-
ages of many new-born infants) may also be found
. 175.— Carriage cells commencing (comp. fig. 165). The formation of

from the body of aver- , , * " -L (i • ui. -n ,

tebra of a foetal pig, of bands and appearance of chondrm fibrillation occurs
at a much later period.

Great interest attaches to the discovery made by Schwann, and after-
wards confirmed by Hoppe, that the ground-substance of fcotal cartilage
does not consist originally of a matter yielding chondrin, or indeed of any
material which stiffens, like glutin, on cooling.

All the statements just made refer, in the first place, to hyaline carti-
lage : the primary form of reticular and of fibro -cartilage, however, is also
included. The latter consist originally also of a homogeneous ground-
substance, in which the metamorphosis into fibres commences sooner or
later, and continues in some parts even after birth.

TISSUES OF THE BODY.

187

6 and 7. Gelatinous and Reticular Connective-Substance.
§113.

Under the name of gelatinous or mucoid tissue and reticular connec-
tive-substance combined, we shall now consider a second series of tissues,
liable to great variation, and belonging to the group of connective-sub-
stances. This classification, however, can only be said to have a provi-
sional value : it remains for more accurate histogenic investigation to
show, at some future time, whether the mode of development of the
different tissues placed together here justifies or modifies our method of
arrangement.

Gelatinous and reticular connective-substance appear at the first glance
separated by a wide gap from car-
tilage. Whilst in the latter we
have to deal with a tissue made
up of round cells held together
by a solid glutinous intermediate
matter, the plan of the tissues
with which we are now engaged
is completely different. They are

all of them more Or less Soft, partly T\K. 176.— Gelatinous tissue with roundish cells

swollen up into a glutinous condi- from the vitreous humour of a human foetal eye-
tion, or in other rarer cases even present themselves in the liquid form.

Only in exceptional cases do their cells preserve their spherical form : they
present themselves, as a rule, in most character-
istic figures, radiated and stellate, and united with
each other by means of simple or branched pro-
cesses, forming networks of cells (figs. 177 and
178).

The system of meshes so formed varies as to
its contents very considerably, apart from the
differences in the size of its meshes.

In a certain number of the tissues which
may be reckoned in this category, the net'
work formed by these elements is occupied by a
structureless, watery jelly, containing mucin or
some allied substance, when we term it a gelatinous
or mucoid tissue (fig. 177).

A second and more extensive group shows
us these interstices, instead of being occupied
by a mucoid mass, filled rather with innumerable
granular cells, which correspond exactly with
the elements of lymph. We have thus pre-
sented to us the most widely distributed species
of reticular connective-substance (fig. 178). It
has been named " cytogenous connective-sub-
stance " by Kolliker, and by His " adenoid sub-
stance."

Another series of connective matters belonging
also to this group in our opinion, encloses, in a Fig. 177.— Gelatinous tissue with

,, A , , iii- 11 i i stellate cells, from tlie enamel-

USUally narrow-meshed and delicate cellular net- organ of ti«e human embryo.

work, another kind of contents, e.g. chiefly, ner-
vous elements (fig. 179), or also, though much more rarely, masses of

a,

188

MANUAL OF HISTOLOGY.

fat. This may be designated for the present as sustentacular nervous
matter, and is a species which has, up to the present, been investigated
least of all.

The fibrous character of most of the tissues enumerated here is by no

Fig. 178.— Reticular connective-substance with lymph corpuscles from
Peyer's follicle of the adult rabbit, a, capillaries ; 6, reticular frame-
work; c, lymph cells (most of the latter have been removed by
brushing).

means lost, however; for we frequently see, whether in the course of
physiological development or as a pathological occurrence, many of these
tissues, the mucoid as well as the reticular, becoming
transformed into ordinary fibrous tissue, in that the
cellular network obtains coatings of filaments while
the gelatinous intercellular matters, or as the case
may be, lymphoid corpuscles, decrease and finally dis-
appear.

Then, again, we recognise that other substitu-
tion already mentioned section 101, in different
groups of animals. Thus, for instance, the reti-
cular connective-substance in one organ of certain
animals is replaced by ordinary fibrillated connective-tissue in other
species, and so on. Finally, it seems probable that any of the other
tissues belonging to this so wide)y distributed connective-substance group
are all capable more or less of reproducing from their cellular offspring
either mucoid or reticular tissue.

Fig. 179.— Sustentacular
tissue from the poste-
rior column .of the
human spinal cord.

o

We have just seen that by gelatinous or mucoid tissue is understood a
cellular structure, characterised by possessing a very soft and watery
intercellular substance, containing either mucin or some matter very

TISSUES OF THE BODY. 189

similar to it, and which is thus distinguished from glutin-yielding car-
tilage and regular connective-tissue. The amount of this interstitial
substance is usually considerable, so that all the physical properties of
the tissue are determined by it. In this respect cartilage and gelatinous
tissue resemble each other, though, on. the other hand, they may differ
widely as regards consistence.

The cells in a soft interstitial substance of this kind are originally
of spheroidal figure, and when imbedded in a completely homogeneous
mass may be regarded as the simplest form of gelatinous tissue — one
which is, however, but extremely rarely permanent, and which is
destined to undergo, as a rule, further transformation, fhe cells, in
such cases, are metamorphosed into fusiform and stellate structures,
displaying a strong inclination to unite with one another, and in the
intercellular substance there commences to make its appearance a streaki-
ness and fibrillation.

In general, mucoid tissue may be said to be a species of connective-
substance standing low in the group, and as such it enters into the com-
position of temporary embryonic structures under normal conditions,
which do not attain in this form a state of maturity. In fact, we have
to do with foetal tissues. The cells further, while still in their simplest
form, may be so compressed by the superabundant interstitial matter
that they cease to exist, the latter only remaining over. It is, how-
ever, more usual to meet with an ascending metamorphosis in other of
these textures, by which they are developed into ordinary soft connec-
tive-tissue. The points of distinction, consequently, between the two
cannot be very definitely laid down.

The parts of the human body which are looked upon at the present
day as belonging to this group of tissues are the following : — the vit-
reous humour of the eye ; the gelatin of Wharton of an early period of
life \ certain substances filling up the interior of the rudimentary ear ;
the enamel organ of the rudimentary teeth ; and the soft, formless con-
nective-tissue of intra-uterme life, which has not yet developed collagen.
But in animals gelatinous tissue is more permanent. Thus the sinus
rhomboidalis in the spinal cord of birds is formed of it, and the form-
less connective -matter of fishes. It appears also widely distributed among
the lower animals. The bodies of the acalephse are chiefly made up of it
(Virchow and Schultze).

Whilst in the mature body no gelatinous tissue is to be found, with
the exception of that small quantity known as the vitreous humour, it
may be produced anew under abnormal conditions by development from,
another member of the group of connective-tissues, as, for instance, from
fatty tissue in cases of emaciation. Tumours formed of mucoid tissue
are known as myxomas ( Virchow).

§115.

The simplest form of this gelatinous tissue to be found is in the corpus
vitreum of the eyes of embryos and very young individuals.

The surface of the latter is originally covered with a vascular net-
work, which is obliterated, however, very early. If we examine the
structure in a fcetus at about the end of the fourth month (fig. 180),
we find it to consist of an abundant and completely colourless, homo-
geneous, and somewhat viscid ground-substance, which becomes stringy
on the addition of acetic acid. In this are imbedded, at tolerably

190 MANUAL OF HISTOLOGY.

regular intervals, a rather scanty proportion of cells, either quite spherical
or spheroidal, which may take on other distorted forms, however, owing
to their soft consistence and the semi-fluid nature of the surrounding
medium. They resemble enlarged colourless lymph oid cells, &c., and
are granular, either coarsely or finely so, but usually to no great extent,
so that they are not very opaque. Their membrane opposes a certain
amount of resistance to the action of acetic acid, and the nucleus appears
more or less granular, showing in its interior a nucleolus. We also meet
with round, oval, reniform, and double nuclei, which have always their
special nucleoli, indicating probably a multiplication of cells here.

The size ofthese cells is 0-0104, 0-0156-0-0182 mm., while the simple

nuclei have an average diameter of
0-0052 mm.

Fusiform and stellate cells are
not entirely absent in the true
corpus vitreum, but are found
principally in the membrana hya-
loidea in connection with the for-
mation of the vessels of that part,

Fig. 180.— Structure of vitreous humour in a four as Kolliker j UStlv observes.

The same is found to be the struc-
ture of the vitreous humour of the infant, while, according to the general
opinion, the cells undergo decay in the first years of childhood, so that
in adults the corpus vitreum is composed of the intercellular substance
alone; a view which is opposed by 0. Weber. According to this
observer, namely, the cells of the mucoid substance remain in all cases,
though more scanty towards the centre than at the periphery.

Examined chemically by JBerzelius, Lohmei/er, and Virchow, the corpus
vitreum was found to contain more than 98*5 per cent, of water, and
among the solid constituents an abundance of inorganic matter, chiefly
made up of chloride of sodium. Among the organic matters we find
traces of albumen. According to Virchow a substance allied to mucus is
also to be found here, to which the semi-fluid gelatinous nature of the
structure is due. The vitreous humour is now regarded as composed of
a certain quantity of mucin gelatinised in a large amount of saline fluid.
The following analysis by Lohmeyer is given for the purpose of showing
more clearly the composition of the substance in question.

1000 parts of vitreous humour contain : —

Water, ._.'.' 986 "400

Membranes, . . . . . . . 0'210

Albuminate of sodium (and mucin ?) . . 1*360

Fats, . -. ".; . ' . . . . 0-016

Extractives, 3*208

Chloride of sodium, ..... 7 -757

Chloride of potassium, ..... 0'605

Sulphate of potassium, . . . . . 0'148

Phosphate of calcium, . . . . . O'lOl

Phosphate of magnesium, .... 0'032

Phosphate of iron, 0'026

Lime earths, 0-133

Mucin was not looked for, but urea was found by Millon and Wolder,
but not by Lohmeyer.

TISSUES OF THE BODY.

191

The vitreous humour is the most posterior of the refracting media of
the eye. Its refractive index is (taking water to be 1'3358) 1'3506 in
the human being (Krause). If destroyed it is not regenerated.

REMARKS. — Besides the German literature, comp. Bowman, Lectures on the Parts,
<fcc., of the Eye, London, 1849, p. 100.

§ H6.

Again we find gelatinous tissue presented to us in a higher state of
development (setting aside the tissues of the membranes of the ovuin), in
the first place in the enamel organ, then in the gelatin of Wharton, and
finally in the formless connective-substances of embryos.

Here we find universally, in a transparent gelatinous substance, fusi-

Fig. 181.— Cells from the
enamel organ of a foetus
four months old. At a, small;
at 6, larger and more highly
developed stellate cells.

Fig. 182.— Tissue of the gelatin of Wharton in trans-
verse section ; from the cord of an embryo of four
months, o, a net-work of branching cells ; b, conden-
sation of the ground-substance forming bands ; c, un-
changed, roundish, formative cell.

form and stellate cells, known since the days of Sclmann. These form
with their processes a cellular net- work, and lie at first somewhat closely
together, but after a while separate more widely one from another, a deposit
of the condensed intercellular substance forming around them. Thus we
have a system of reticulated bands within which the cellular net-work
still exists. ' The meshes enclose a soft and gelatinous mass in which
may be distinguished isolated unchanged formative cells.

The substance, however, of which the enveloping bands are composed
commences early to present the appearance of being longitudinally
streaked. This gradually becomes more evident until the whole assumes a
fibrous condition, on which the mass is transformed into ordinary connec-

192

MANUAL OF HISTOLOGY.

tive-tissue fibrillse. Elastic fibres make their appearance also by the trans-
formation of the same substance (see below, with connective-tissue). The
cells again frequently take on a more elongated, narrowed form. If the
whole series of transformations passes over them to its conclusion, which
is by no means always the case, what is known as formless connective-
tissue is formed.

After this general description, let us subject the enamel organ and
umbilical cord to nearer examination. The first of these covers the germ
of the rudimentary tooth during intra-uterine life and the earliest years
of infancy.

Its tissue (fig. 181) consists of delicate stellate cells with distinct nuclei.
The latter are vesicular in the embryo of four months, measuring 0-0066-
0-0090 mm., whilst the cell with its processes shows an extent of 0-0260-
0-0385 mm. The number of these latter is at times only four (a), but
often far greater (a, b). There occur also cells with double nuclei, and at
times a species of segmentation is observed (6, below).

The interstices between the cells so united to one another attain a

• breadth amounting to
0-0204-0-0320 mm. and
upwards, and are filled
with a homogeneous gela-
tinous mass, which gives
to the whole enamel organ
the same consistence vary-
ing in density according
to its amount.

That we have here to do
with a transient tissue re-
quires no farther comment
after what has been just
stated. It ceases to exist
when the enamel of the
tooth attains maturity.

In themucoid substance
again which enters into
the composition of the
umbilical cord (fig. 182),
namely, the gelatin of
Wharton, cells exactly
similar to those encoun-
tered in the enamel-organ
are to be found.

But this cellular net-
work (fig. 182, a) becomes
enveloped at a very early
period by a clear and deli-
cately streaked intermediate substance (b), and in the continuous system of
meshes still remaining, we meet with the same structureless mucoid jelly.
Here may be found also spherical cells (c) as they appear in the same
stage of development of structureless connective-substance. They are
contractile, and migrate (Koester). The bands of condensed ground-
matter enveloping the cellular net-work (fig. 183, a, b) are subsequently
transformed into fibrillse of connective-tissue, and between these there

Fig. 183.— Tissue of the umbilical cord a short time before birth,
with well -developed connective-tissue fibrillation, a, b.
bands of the latter with their corpuscles in the axis : c, d, e
isolated cells.

TISSUES OF THE BODY. 193

appear elastic fibres (at least in animals). The network also shows
increase of the distance between individual cells, a development of long
filiform processes, and the bodies of the former, in which, however, a
nucleus is still apparent, become smaller as the processes are extended
(c, d, e).

For the rest this cellular network displays at a later period much
variety ( Weismanri). In its power of resistance towards reagents it re-
minds us of elastic matter, whilst, on the other hand, it is rapidly acted on
by alkalies in contradistinction to the latter.

"We have before us here, then, a connective-tissue transformation which
is far advanced when at birth the death of the tissue takes place.

The soft, structureless connective-tissue of early life has just the same
nature. In its meshes likewise, as Schwann has shown, the same rounded
cells are to be found, which possibly become fat-cells eventually. The
banded portions of both these tissues yield originally no glutin on being
boiled.

REMARKS. — The origin of the enamel organ appears indeed to be peculiar, in that
it takes place from epithelium (comp. chapter on the teeth). Of the truth of this
statement we are assured by KoUiJcer, after due examination of the development of
the teeth. Further investigation of the matter is desirable, however, considering
the great histological interest which attaches to the subject, and the difficulty of such
embryological research.

§117.

Having now concluded the consideration of gelatinous tissue, we turn
to another member of the so very varied group of connective-substances,
namely, to the reticular — the adenoid of His, or cytogenic of Kolliker.

Here we encounter similar networks of radiated connective-tissue cells
(subject, however, in individual cases to much variation), which are meta-
morphosed into fibres or fasciculi of more or less extensive course, and
may receive also coatings of a streaky or fibrillated intermediate substance.
The spaces, however, incompletely enclosed by them, are not filled with
mucoid jelly, but by structural elements, by innumerable lymphoid cells,
such as are found in lymph, chyle, &c.

A considerable number of organs possess a tissue of this kind. For
instance, the framework of the lymphatic glands is composed of it, as well
as that of those lymphoid organs so nearly related to the latter, namely,
the tonsils, thymus gland, and follicles which are met with, isolated or in
groups, imbedded in the intestinal tube and conjunctiva. The Malpighian
corpuscles also of the spleen consist of reticular connective-substance.
The latter again, although presenting many varieties, forms, among the
higher animals, the mucous membrane of the small, and partly of the
large intestine ; and, finally, it is met with, strongly modified, in the
pulp of the spleen.

Here also we encounter again certain peculiarities, already frequently
mentioned. In the first place, we see in such organs the peripheral por-
tions undergoing further changes in their reticular connective-substance,
through which the latter may eventually become converted into ordinary
fibrous tissue. Further (and this is the case, for instance, in the intestines
of the lower animals), the reticular substance may be replaced by the latter.
Finally, it may spring from ordinary connective-tissue under pathological
conditions, on the other hand, or become transformed into the latter.

As elements we meet with stellate cells (fig. 184), whose nuclei have
smooth borders and a nucleolus, and measure, on an average,

194

MANUAL OF HISTOLOGY.

Fig. 184.- A cell
from the reti-
cular connec-
tive - substance
of a lymphatic
gland, strongly
ramified.

0*005 9- -0-0075 mm. They may, however, be met with more or less
granular. They are enclosed in a thin layer of a clear sub-
stance, forming the body of the cell, which is spread out
peripherally into a varying number of pale radiating pro-
cesses. These are primarily about 0*0023 mm. in diameter,
becoming, after a short course, three or four times as fine.
A secondary formation of branches is observed on these
processes rather frequently, which pass off usually more or
less at right angles. Further, there are generally formed,
by the union of such processes of adjacent cells, small
knots, in which naturally no nuclei are to be seen. The
meshes thus formed are usually of roundish or delicate
polyhedral figure (fig. 185), with a breadth of 0*0114-
0'0226 mm. The latter may, however, be much less, or,
on the other hand, more considerable; and meshes are found in certain
parts of far greater length and extent still.

The whole of this delicate network, in
the fresh state, is very soft and fragile, and
only to be rendered perfectly visible on that
account by hardening treatment of the tis-
sue and removal of the lymph-corpuscles.
The connective-tissue cells withstand boil-
ing, but are, on the other hand, rapidly acted
on by alkalies and acetic acid.

The genesis of this network of cells, and
of the lymph corpuscles enclosed in it, still
requires further investigation.

§ US.

The description of the cellular network of
reticular connective-substance just given, ap-
plies to its usual appearance in the system
at an early age. But we frequently encounter
in more mature bodies a certain change in
the tissue — a shrivelling-up of the body of
the cell and nucleus — so that these chief
central knots are only evident as slight
swellings at the corresponding points in the network. The appearance of
such portions has given origin to the mistake of confounding this cellular
network with which we are engaged with an interlacement of elastic fibres.
Fig. 186 gives a good idea of the structure of such a portion of tissue.
In it we may recognise also the characteristic relations of the reticular
connective-substance to the blood-vessels. Such a network, namely, is
always traversed by blood-vessels, in contradistinction to gelatinous tissue,
which is either very poor in the latter or entirely non- vascular. Eound
these vessels there is woven a secondary investing tunic, a microscopic
adventitia (a), formed by the union of neighbouring cells with their pro-
cesses and membranous expansion of the latter.

This shrinking together of nucleus and cell-body may, moreover, give
place, under conditions of irritation, to a speedy increase in size again,
when we find, after a short period, the former plump appearance of both
restored.

In other modifications of the cellular network a strong expansion

Fig. 185.— From a lymphoid follicle of
tne vermiform appendix of the rab-
bit ). Reticular tissue, with the
system of im-shes, b, and remains of
the lymph cells, a. Most of the latter
have been removed artificially.

TISSUES OF THE BODY. 195

of the ramifications of the processes may he ohserved, by which the latter
become, not unfrequently, membraniform. We likewise ohtain views of
isolated, more or less fusiform cells, joining to form fibres, which might be
mistaken for elastic were they not acted on by alkalies. Finally, we some-
times see — and in this the bearing of gelatinous tissue is repeated — the
cellular network enveloped in thin layers of an intermediate substance,
sometimes more or less streaky, and sometimes fibrillated, which may be
continuous with ordinary connective-tissue. The matter so deposited is,
without doubt, a product of the cells themselves, and may be regarded in
the same light possibly as that laid down in cartilage (§ 104).

The mucous membrane of the small intestine supplies a very good

a-

Fig. 186.— Reticular connective-substance with lymph-cells, from a Peyer's
patch of the full-grown rabbit a, capillaries ; 6, reticular sustentacular
tissue ; c, lymph-cells. Most of the latter removed by brushing.

example of the changeable character of reticular connective-substance,
as well as its gradual transition into ordinary fibrous tissue. If we
examine the tissue, for instance, in the sheep, from the immediate neigh-
bourhood of a lymphoid follicle (fig. 187, 1), it still presents its customary
reticulated appearance (&), but even at a short distance the banded network
may be met with very much thickened and irregular (2).

Very usually, however, we find, especially around glandular cavities, a
more homogeneous and nucleated connective-substance (3, d), which may
nevertheless assume the old reticular nature at points (3, b).

In the .large intestine we find an intermediate form between reticular
connective-substance and ordinary fibrous tissue, with a usually small
proportion of lymphoid cells.

We have now to enter on the consideration of the finest and most deli-
cate species of this tissue, that of the so-called pulp of the spleen, which
takes its rise continuously from the ordinary net-like sustentacular matter
of the Mdlpigliian corpuscles of this organ.

196

MANUAL OF HISTOLOGY.

In hardened preparations it consists of a fine network of pale, delicately-
contoured, and very slight fibrillje, which may be, however, partially ex-
panded into membranous processes at points. Here and there we meet
with pale oval nuclei in these. The meshes of this framework, measuring
0-0226-0-0068 mm., are occupied, in the first place, by lymphoid cells,
but also by coloured blood-corpuscles.

Fig. 187. — Reticular connective-substance from the intestinal mucous membrane of the
sheep; strongly magnified. 1. Taken from the immediate neighbourhood of a fol-
licle, a, transverse section of a follicle of Lieberkiilm ; 6, network; c, lymph-cells.
2. Somewhat more remote, a, rounded; 6, elongated, nuclei. 3. At a still greater
distance from the follicle, a, tissue of indefinite character; 6, reticular; c, nuclei;
d, lymph-corpuscles; «, vacant space where a gland had been.

In pathological processes this kind of reticular substance, also contain-
ing lymphoid cells, plays no unimportant part.

Apart from enlargement of the organs consisting of it, as the lymphatic
glands, the tonsils, Payer's patches, and the spleen, we also recognise
new growths of the tissue in question in other parts, at the expense of
the framework of fibrous tissue, as, for instance, in the liver, kidney, and
stomach.

§119.

We turn now to a formation about which far less is known than of
ordinary reticular connective-tissue, namely, the delicate sustcntacular sub-
stance of the nervous centres and the retina. That it originates from the
middle germinal plate, the source of the other members of this series, appears,
besides, doubtful, so that its position among the connective-tissues may re-
quire to be altered in consequence. Although long ago the presence of
such a framework in the substance of the brain and spinal cord was here
and there allowed, it was a long time, nevertheless, before the present views
regarding it were generally recognised. Moreover, we are met by the
impossibility of drawing any very sharp line between the tissue in
question and the nervous form-elements of grey matter. We cannot
wonder, then, that Bidder and his pupils suppose this substratum of con-

TISSUES OF THE BODY.

197

Fig. 188. — Connective-
tissue sustentacular
matter from the pos-
terior pillars of the hu-
man spinal cord, sur-
rounding sections of
the nerve-libres.

nective-tissue to exist in large quantity in the nervous centres, while
other investigators deny almost completely the presence of any other than
nervous form-elements in those organs.

Wherever the connective-tissue framework is well developed, and to a
certain extent pure, as is the case in the " ependyma"
(so named by VircJiow) of the ventricles of the brain,
and in the matter lining the central canal of the
cord, it occurs as a more or less homogeneous or
streaky or fibrillated mass, in which ordinary radiated
or fusiform cells are seen to be imbedded.
• This substance, whose connective-tissue character
cannot conveniently be doubted, is continuous then
with the sustentacular substance of the white and
grey mass, — a far more difficult subject for investiga-
tion— namely, with the so-called " nerve-cement " or
" neuroglia " of Vircliow.

If we examine a portion of the white substance of the brain which has
been hardened artificially, we see how the fibres are separated from one
another by bands of such a substance.

This may be either homogeneous or streaky; and in it are situated,
at intervals, round or oval nuclei, smooth in contour, and measuring
0*0093-0'0075 mm. We learn also, from side views, that these septa,
seen in the transverse section, are continued further between the nervous
cylinders as membraniform prolongations, so that in this way a regular
system of tubular compartments is formed. The elements of form, of
which the latter is composed appear to be cells with radiating processes,
spreading out into membraniform prolongations and investing masses.

But the sustentacular tissue of the grey
matter of the nervous centres, though much
more abundant, is far more fragile and difficult
to elucidate. In fresh preparations it is found
usually as a rather granular complementary
matter, filling up the interstices between the
nervous fibres and cells. It sometimes con-
tains but a few, sometimes, however, very
many, nuclei with smooth contour, and measur-
ing 0 -0090- 0-0075 mm. In successfully-treated
preparations (fig. 189) we recognise, with the
aid of extremely powerful lenses, a wondrously fine and dense network of the
most delicate fibrillae, which take their rise from knots, in each of which
one of these nuclei lies imbedded, not unfrequently enveloped in a thin
layer of pro topi asma. Here again we may have before us a network of
stellate cells in this porous spongy tissue. But the pre-existence of such
a network, though very probable, is not yet capable of proof, and the
possibility of the tissue before us being an artificial fabric must be
admitted.

This porous supporting substance, with its cellular equivalents, is,
moreover, traversed at points by definite fibres of connective- tissue.

The connective-matter of the retina appears precisely the same, the
supporting fibres of which are known under the name of Mutter's fibrillas.

In that extraordinary fatty organ, the so-called thymus gland of hiber-
nating animals, which occurs in many of the Mammalia, we meet with a
similar dense network of the finest fibres in hardened preparations.

Fig. 189. — Spongy tissue from the
grey substance of the human
cerebellum, obtained by treat-
ment with very dilute chromic
acid.

198

MANUAL OF HISTOLOGY.

Fig. 190. — a, Human fat-cells com-
pletely filled with oil, lying in
groups together. 6, free drops ;
c, empty envelopes.

The sustentacular connective-tissue of the nervous centres is reproduced
in a number of pathological growths. These have been named " glioma "
by Virdwiu.

8. Fatty Tissue.

§ 120.

Fatty tissue, with a specific gravity of 0*924 (W. Krause and L.
Fischer), consists of large roundish cells
measuring 0'0340-0'1300 mm., and nuclei of
0-0076-0*0090 mm., whose thin envelope is
usually completely occupied by one single oil
globule. These fat-cells usually lie heaped
together in considerable groups (fig. 190), and
occur in parts formed of connective-tissue of
loose texture, the so-called formless species.
They generally constitute the complementary
substance of the cavities in the latter, which
diminishes frequently in quantity between the
individual cells of such a group.

The thin membrane is completely obscured
by the dark outlines of the fatty contents, so
that cells of this tissue display much similarity
to free drops of fat. They show sharply
defined dark edges with transmitted light ; but
when reflected, their silvery border appears whitish or yellowish white.
But, on the other hand, the close crowding to which they are subjected
frequently leads to a flattening of adjacent cells at the points of contact,
so that they assume a polyhedral form, which does not take place with

free drops of oil (fig. 190, b), which coa-
lesce when pressed one against the other,
like those drops of grease seen floating on
the surface of soup.

Careful examination directly of com-
pletely filled fat-cells may lead to the
conclusion that they possess a membrane,
but does not enable us to discover it.
For this certain treatment is required.
Thus, by increasing pressure, we may cause
the very tense membrane to rupture, on
which the flaccid empty envelopes of large
cells are seen as thin structureless saccules
(fig. 190, c). We may likewise extract
the contents from the uninjured envelope
chemically, by treatment with alcohol and
ether. In such cells artificial colouring is
necessary before the nuclei can be seen.

But the fat-cells may deviate more or less from the fundamental form
just described. Their contents consist of a mixture of oily and solid
neutral fats, always, however, of one which is fluid and soft at the ordinary
temperature of the living body. In warm-blooded Vertebrates the
cooling of the corpse brings about, not unfrequently, in such as are rich
in solid fats, a congelation of the contents. The fat-cells lose, in such a
case, their round plump figure and delicate outline, and become rough,

Fig. 191.— Human fat-cells occupied ty
crystals, a, Single needles; 6, larger
groups; c, cells with groups of the
latter in the interior; rf, an ordinary
fat-cell without crystals.

TISSUES OF THE BODY.

199

angular, and knotty. On being warmed, they assume, however, their
former smooth appearance once more.

Again, we meet with peculiar appearances in those cells in which a part
of the solid fat of the contents has become crystalline (tig. 191, c). In
such, groups of needle-shaped crystals, either single, double, or in greater
number, are to be found. These were declared formerly, quite arbitrarily,
by microscopists, to be composed of inargarin or margaric acid. Such cells
have long been known. Eventually, the whole contents may be converted
into such a crystalline mass (K'6llik.er).

Such cells are the result of the cooling' of the corpse, and are not found
in the warm living body.

REMARKS. — 1. Todd and Bovmianris Physiol. Anat., vol. i. p. 80. 2. Fat-cells
mounted in glycerin usually show these crystallisations.

§ 121.

These normal cells just described — i.e.) those surcharged with fat — have
little instructive about them. There
can be but little doubt that here
also the oil globule is enveloped in
a thin coating of protoplasm with
a peripheral nucleus. This will be
easily understood after examination
of those cells, poor or almost entirely
deprived of fatty contents, the serum
cells of early observers (fig. 192,
2, b), small structures found in
emaciated subjects. Here we find
an abundant, probably watery, proto-
plasm in the place of the fat. Let
us examine such cells somewhat more
minutely.

Instances are met with, in the
first place, in which a considerable
fat globule is separated from the
delicate outline of the envelope by
a thin interposed layer of fluid (1,
a, 6), in which the nucleus (c, d),
situated at the circumference, may
be discovered. The latter is smooth
in outline, and at times vesicular.
In such cases we not unfrequently
observe a darker yellowish tint than
usual in the fatty contents, which inten-
sifies the more the latter decreases in
quantity; so that adipose tissue which
has undergone this change strikes
even the unaided eye on account
of its yellowish-red appearance. When such fat-cells are crowded
together, they frequently give rise to an uncommonly delicate structure
resembling hyaline cartilage surcharged with fatty globules.

Owing to the progressive disappearance of fat from these cells, we
not unfrequently find an oil globule decreasing more and more in
size (/). In others, this decreasing globule may become divided into

192.— Cells incompletely filled with fats.

From the subcutaneous cellular tissue of
a lean human subject, in which the amount
of fatty contents is on the decrease, a, with
a large, 6, with a smaller oil globule ; c and
rf, the nuclei visible ; e, a cell with separate
globules : /, with a single small drop ; g.
almost free of fat ; and h, without fat and
with a globule of an albuminous substance
in the interior. 2. Cells of fatty tissue
from tlie neighbourhood of the kidney of
a sheep embryo, measuring 10 inches.
They are becoming filled more and more
with fat; a and 6, isolated cells without
the latter; r, a collection of the same; d-h,
cells with increasing deposit of fatty con-
tents.

200

MANUAL OF HISTOLOGY.

several drops of different sizes, and frequently very diminutive (e, g).
Finally, we meet with cells from which (A) all the fatty glomerules
of the contents have vanished, and in which the whole cavity is occupied
by a homogeneous liquid.

With the decrease of the fat the nuclei become more apparent as
essential constituents of the cells. If the envelope, in other respects,
preserve its original thinness, the whole structure is very delicate in
contour and easy to examine. Sometimes the disappearance of the fat
is accompanied by another process — namely, segmentation of the nuclei of
the different elements, until the old envelope is filled with several nuclei
and cells (Flemming). The same is seen in inflammation of adipose
tissue.

REMAJIKS.— The fact that the nucleus always reappears in cells which thus lose
their fats, allows of no other explanation than that in the completely-filled cells of
ordinary fatty tissue it is likewise present. Portions of this tissue prepared with
carmine, and mounted in Canada balsam after their water has been extracted, reveal
the presence of a nucleus also.

§ 122.

As we have already seen, fat-cells are found accompanying formless,

soft connective-tissue, whose in-
terstices and cavities they oc-
cupy. Here they form closely
crowded pellets of fatty tissue,
which are traversed by a very
.complex network of capillaries
(fig. 193, A), in each mesh of
which a single cell is situated
(B}. The energetic interchange
of matter which takes place at
times among these cells is thus
easily accounted for by the great
vascularity of the structure.

Fatty tissue, which forms a
large proportion of any well-
nourished body, is found, first
of all, in subcutaneous connec-
tive-tissue, constituting here the
panniculus adiposus, and in
numerous other smaller and ir-
regular collections chiefly along
the course of the blood-vessels.
Its amount varies, however,
according to the region of
tho body. Thus large collec-
tions of cells are to be found
under the skin of tho foot, of

the palm of the hand, of the buttocks, of the female mammary gland,
&c., while the eyelid is quite destitute of fat. Further, we meet with
an abundance of adipose tissue around the synovial capsules of joints
very frequently, as well as in the orbit, where it is never absent, even
in cases of the greatest emaciation. Again, in the medullary canal of
compact bones, where it constitutes the yellow marrow of the part.
We may mention also, among the points in the interior of the body

Fig. 193.—^. Capillary network of a pellet of fat.
a, the arterial; 6, the venous branch. B. Three
fat-cells enclosed in the meshes of the capillary net-

TISSUES OF THE BODY.

201

whose connective-tissue is usually occupied by rich assemblages of fat-
cells, the neighbourhood of the kidney, the omentum, and the surface of
the heart.

Again, the quantity of these collections of fat-cells, which, as a mode-
rately developed panniculus adiposus, imparts to the body its usual
plump, smooth appearance, is subject to great variation. It is usually
larger in proportion in the bodies of women and children than in men,
and during childhood than at an advanced age. We know also how
great the differences in. the amount of fats are in well-fed and lean
individuals. A body in good condition may part with all its adipose
tissue in consequence of continued fasting, wast-
ing disease, or a dropsical infiltration of the con-
nective-tissue, and regain it all again rapidly with
the return of health. The fact that we fre-
quently find in very lean corpses a preservation
of the cells, although their contents have dis-
appeared, seems to point to the conclusion that the
latter are more or less permanent structures, in
which, on subsequent return to embonpoint, the
fluid contents can be expelled by the deposit of
fat.

In exaggerated degrees of obesity, such as may
be produced in domestic animals by cramming, we
meet 'with fat-cells in situations in which they
do not otherwise occur; for instance, in the soft
connective-tissue between the fibres of voluntary
muscles (fig. 194), where it may, to a certain
extent, impair the functions of the organ. The
same is the case in muscular parts which have
not been used for a long time. But we must
discriminate between such fatty infiltration of

muscle and fatty degeneration, in which the structure is destroyed by a
deposit of the substance in question in the interior of the fibre.

By fatty tumours or lipomas we understand new formations of con-
nective-tissue loaded with oil globules.

Adipose tissue is to be found in the bodies of all vertebrate animals,
but in very varying quantity and with different anatomical distribution.

REMARKS.— Collections of adipose tissue on the exterior of synovial capsules force
the latter inwards at times in folds, producing thus the glandules vmicilaginosce of
Havers.

§123.

In the fat-cells we have the receptacles for the physiological deposit
of the neutral fats of the body. Their repletion with the latter must
be looked upon, further, as the normal state at a certain period of life,
while poverty in this respect must be designated as an abnormal con-
dition. Why these cells above all others possess the power of taking up
fat is a question we are still unable to answer.

We have already considered (pp. 26-28) the neutral fats of the human
body, and referred to the unsatisfactory state of our acquaintance with
them at present : it would be superfluous, therefore, to enter again on
the subject at this place.

As we have seen there, the fatty substances of the system consist of

Fig. 194.— Muscle with fatty
infiltration. o, three
muscle fibres; 6, fat-cells
in the interstitial connec-
tive-tissue.

202 MANUAL OF HISTOLOGY.

tripalmitin and tristearin, held in solution by another oily neutral fat,
triolein. The more of the solid fats there are contained in the latter,
the higher stands the liquefying point of the compound, and the easier
does it congeal after death into a hard suety mass. In keeping with
this there exist also differences between the various portions of the
body. The consistence of the fats of various groups of animals differs
likewise. In this respect the adipose tissue of the Carnivora and Pachy-
derms corresponds most nearly to that of the human being, whilst that
of the Ruminants and Rodentia appears to be much more solid. The
fatty tissue of Cetaceans and fishes is, on the other hand, of an oily
nature, a necessary condition on account of their living in water. Com-
bined with its fatty contents there exists, besides, a still unknown colour-
ing matter in the cell occasioning its yellowish tint. It is retained with
considerable tenacity by the residue which still occupies the envelope after
the greater part of the fat has left the latter, and communicates to it a
reddish yellow tinge, as already remarked (§ 121).

Now, as to the chemical constitution of the cells which contain these
fats, the following is all that is at present known on the subject. After
extraction of the oily contents by means of ether and hot alcohol, the
empty cell remains behind in a flaccid condition. Its membrane is not
affected by acetic acid, but treatment with the latter causes the exit of
globules of oil from it, an effect produced likewise by the action of sul-
phuric acid, and also by an elevation of temperature. Further, the
envelope offers a more or less determined resistance to the action of
caustic potash, and probably consists of a material allied to elastin.

The physiological significance of adipose tissue corresponds partly to
that of the animal fats in general. It is well adapted, through the
contents of its cells (fluid at the normal temperature of the body), for
the distribution of pressure and for acting as padding. Further, it
is suitable for the filling up of certain interstices between portions of
the body which require a yielding material of the kind. Again, owing
to its bad conducting powers, it must restrain the giving out of heat,
and consequent cooling of the body. The fatty contents, besides, of
these cells, like other fats, undergo decomposition through the atmo-
spheric oxygen, especially when they leave the cavity of the cell and
return to the blood, the ultimate results of which process (after many
intermediate products have been formed) are the -generation of carbonic
acid and water, accompanied by the evolution of heat.

The neutral fats of the tissue we are considering have their origin in
the oily constituents or matters adapted to fatty metamorphosis of our
food. This seems indicated by the rapid deposition of fats which takes
place under good nourishment. But an important physiological question
here arises. The fats of the alimentary matters enter the radicals of
the lacteals in a neutral form, are met with saponified in the blood,
and again as a neutral combination in the interior of the cell. What
now becomes of the glycerin which is set free in the animal juices by this
saponification, and whence comes the same organic body on subsequent
resolution of this soapy compound 1 In regard to these points we pos-
sess at present but few facts (§ 18). That the protoplasm of the cell-
bodies plays an important part in the processes cannot, therefore, be
maintained without question. Just as little is known also about the.
series of changes produced in the elaboration of fats from albuminous
substances and hydro carbons.

TISSUES OF THE BODY.

203

195. — Tissue of the gelatin of Wharton, serving at
the same time to explain the development of form-
less connective -tissue, a, connective -tissue cor-
puscles; 6, fasciculi of connective-tissue; c, spheri-
cal formative cells, possibly passing into fat-cells.

§ 124.

The development of fat-cells in the embryo, and the nature of the
tissue at an early age, is partially understood. The former takes place
along the course of the blood-
vessels (early or late according
to the locality) (Flemming,
Toldt), possibly by the meta-
morphosis of roundish cells
bearing more of an embryonic
character (Virchow, Frey, Rol-
lett), or from connective-tissue
cells (F lemming}. There is
no doubt, however, that later
in life a formation of fat-cells
does take place frequently in
connective-tissue by metamor-
phosis of its cells.

Reserving the consideration
of its development in the hol-
lows of rudimentary bone, we
will here discuss the formation
of fat-cells in formless connec-
tive-tissue.

This takes place possibly
from the spheroidal cells which occupy the interstices of rudimentary
formless connective-tissue (fig. 195, c, c). By the segmentation of
the former, groups spring up, which fill up these spaces at a later
period.

According to Valentin's statements, which, however, neither Gerlach nor
myself have been able to verify, there
may be seen isolated adipose cells,
but still destitute of fat, in the sole
of the foot and palm of the hand of
very young human embryos — e.g., of
fourteen weeks old.

At a later period (fig. 196, 2), the
fatty tissue presents very peculiar
appearances. Spheroidal cells (a, b)
of considerable size, containing vesi-
cular nuclei, and finely granular
contents, lie crowded together in
the usual characteristic manner (c),
squeezed into polyhedra, and en-
closed in the well-known vascular
network. As yet, however, they
contain no oil globules. The cells
of a 10-inch sheep's embryo are
about half as large as those in
the full-grown animal, while the
nuclei are on an average 0'0066
mm. Now commences (apparently) the very interesting and gradual pro-
cess by which the cell is filled with fatty matters, which may be ob-

Elg. 196.

204

MANUAL OF HISTOLOGY.

served in a number of cases at various stages in its progress. It
repeats in fact, inversely, the appearances presented in the mature body
by the cells whose fatty contents are diminishing (§ 122). We first
see isolated globules of oil appearing (d), which become more nume-

Fig. 197. — Adipose tissue from a young rabbit. In the middle may be seen contiec-
tive-tissi\e cells; to the right, similar structures tilled with fat. Fat-cells to the
left (Fiemming).

rous (</), and subsequently run into one another, forming larger drops
(<?> /, h), while the original finely granular contents of the cell decrease
more and more. This deposit of fat, moreover, commences sometimes
early, sometimes late, in the different classes of Mammals. These
appearances, however, are explained in a completely different manner
by Flemming, the most recent observer of note.
He looks upon these cells also as elements partly
deprived of fat, and supposes that in embryos and
young animals which have been richly fed (fig. 197),
fat-cells are always formed subsequently from the cell-
ular elements of connective-tissue. The final decision
upon these points must remain for future investigation.
The . fat-cells of an early period of life are, as we
have known since RaspaiVs day, and as our ex-
ample shows, much smaller than in the mature body.
According to Hart ing's very careful measurements,
those of the orbit in the infant are about half, those
of the palm of the hand, about a third as large as the
same in the adult. Harting concludes from this, that
with the increase in volume of an organ only a cor-
responding increase in the size of the cells takes place.
It would be well if the interesting question proposed
by him could be accurately answered, namely, whether
the fat-cells of a lean body are generally smaller than
those of a well-fed and plump one.

This near relationship existing between the cells
of fatty and connective tissue is confirmed by further
As Virchow, Wittich, and Forster state, atrophied organs

Fig. 198.— Conn ective-
tissue corpuscles
from a human mus-
cle infiltrated with
fat, undergoing

transformation into
fat-cells, a, almost
unchanged; b, cells
tilling with fat; c,
others whose pro-
cesses are diminish-
ing in size; d, fully
developed adipose
tissue cdls.

observation.

TISSUES OF THE BODY. 205

are often enveloped in and traversed by tracts of fatty tissue. We
have already alluded to the same kind of transformation between the
elements of muscle (fig. 194). Here (fig. 198) may be seen all the
transitions from connective-tissue corpuscles to fat-cells in the loose
connective- tissue situated in fleshy substance. We see the first of
these (a) becoming gradually filled with small and large globules (I).
which commence to fuse with one another. Owing to this, cells origi-
nally fusiform become expanded gradually (c) into the spherical form
of the fat-cell. Here, then, we have fat-cells springing from connective-
tissue corpuscles, an occurrence which has also been observed by Furster
in the formation of lipomas.

The question also as to whether fat-cells may again undergo retrograde
development into ordinary fusiform and stellate connective-tissue cells,
may be answered in the affirmative. Thus Kolliker observed, after
disappearance of the fatty matter of the subcutaneous cellular tissue,
the so-called serous fat-cells (§ 121) become transformed into such con-
nective-tissue corpuscles. The same may be seen under similar circum-
stances around the hilus of the kidney and under the pericardium, where
the fatty tissue is transformed into a regular mucoid tissue (VircJiow).

9. Connective-Tissue.
§125.

Under the name of connective-tissue is understood a substance widely
distributed throughout the body, consisting, like those structures already
considered, of cells or their rudiments and intercellular matter. The
latter, however, is here glutin-yielding, and indeed affords almost always
collagen, except in rare and exceptional cases, such as the cornea, where
chondrin is obtained from it. It is likewise characterised by its ten-
dency to break up into fibres, which latter process has already taken
place, more or less, in every well-developed connective-tissue, giving rise to
connective-tissue fibrillas and fasciculi in a structureless substance. Again,
there appear in this tissue elastic elements besides, which have originated
in the metamorphosis of the intercellular matter. They enter into the
formation of fibres, networks of the latter, fenestrated membranes, ter-
minal layers around fasciculi of connective-tissue and interspaces, which
may harbour cells.

Now, although it is thus possible to characterise in a few words the
peculiarities of most parts of the body consisting of connective-tissue,
and though, from this point of view, the latter may be looked upon, in
many cases, as only a higher stage of development of that substance,
described in a previous section as gelatinous tissue, still we must remember
that many parts formed of this tissue differ more or less from this plan
which we have just given, and may deviate even so far as to be beyond
being recognised as belonging to it. Connective-tissue appears indeed
in such a variety of forms that its limits arc rather difficult to define, and
every histologist of the present day gives the name connective-tissue to
tilings which are frequently very remote from what was considered such
at an earlier microscopic epoch.

If we now inquire, in order to obtain a clue through the difficulties of
the coming description, what these modifications are, the following points
may be noticed.

206 MANUAL OF HISTOLOGY.

We have, in the first place, one species of this tissue which is charac
terised by the scanty development of its interstitial matter, while the
greater part of it consists of abundant fully-developed connective- tissue
corpuscles, either in the form of simple cells or of cellular networks.
In this there is no sign of fibrillation, as a rule. The cells may retain
their ordinary homogeneous contents, or may become filled with granules
of melanin, thus giving rise to the so-called stellate pigment cells. As
long as the corpuscles are assembled together without order, the homoge-
neous intermediate substance shows no tendency to divide in any definite
direction ; but where, in other parts composed of this tissue, the cells are
arranged in rows, one after another, the intercellular substance undergoes
a change, and becomes scissile in the direction indicated by the position
of the cells : it divides into bands and leaves.

Both arrangements of the cells now lead gradually on to fully-developed
connective-tissue, in that the intercellular matter becomes cleft, shreddy,
and finally fibrillated. At the same time (and we are here introduced to
a new variety of the tissue), the corpuscles either preserve their original
cellular character, or are diminished down to their nucleus merely. ISTo
less liable to variation is the proportion of these cells and their residue in
the different structures formed of connective-tissue. Finally, the elastic
elements, whose multifariousness has already been referred to above, dis-
play the greatest diversity of form, and in the relative frequency with
which they occur.

The present state of our acquaintance with the nature of connective-
tissue, however, leaves much still to be desired. In the first place, we
are unaware here and there of the limits of the tissue; and then again
the mode of development of parts consisting of it requires a more thorough
investigation in many cases than it has yet received. Finally, the nature
of the tissue opposes many obstacles to investigation ; for instance, the so-
called fibrillse of connective-tissue obscure, as a rule, all the other elements,
so that the latter can only be recognised after treatment of the whole with
strong chemical reagents. But these give rise to great changes, especially
in the cells, and the distorted structures seen by their aid are very differ-
ent things from the normal living connective-tissue cells. In regard to
the latter our knowledge is still very insufficient.

REMARKS. — In the earlier days of modern histology, connective-tissue was de-
scribed as a substance composed of fine transparent fibres, crossing one an other partly,
and in part collected together in bundles, but having no farther and especial cellular
elementary parts. The latter were first noticed much later.

§126.

We now turn to the consideration of the elements of typical connective-
tissue, and shall, in the first place, describe that part of it which has been
longest known and is most characteristic — namely, the glutin-yielding
fibre. The latter is met with in the form of a very delicate, extensible,
and, at the same time, elastic thread, transparent, and having a thickness
of about 0-0007 mm., and without branches.

These primitive fibrillce of connective -tissue (fig. 199) are at times
grouped in very varying number, in strands and bundles of extremely dis-
similar strength, but may be separated from one another either by simple
mechanical dissection or by the action of chemical agents (Rollett),
and this with tolerable ease and in considerable length. The elasti-

TISSUES OF THE BODY.

207

city of the fi'bre often gives rise to a peculiar delicately wavy or undulating

course in the fasciculi of the tissue, which gives to many parts the appear-

ance, recognisable even without the microscope, of being made up of bands,

or transversely ribbed. The interlacement of the bundles is besides

liable to variation. They frequentl}7 pass through the same plane along-

side of one another, in which case there usually appears a considerable

amount of homogeneous residual interstitial matter, as a pale thin lamella,

through which the several fasciculi

are connected with one another.

In other cases, again, the bundles

are arranged parallel to one an-

other, and at the same time rather

densely, so that the residue of un-

changed intercellular substance is

greatly diminished, as, for instance,

in a tendon. Finally, the bundles

may be woven together more con-

fusedly, though at times also with

a certain amount of regularity and

rectangular arrangement, but so

that no particular direction in their

course appears to be the predomi-

nant one — as, for instance, in the

sclerotic coat of the eye. From

this we see that parts formed of

Connective-tissue may differ most

,. 1-, . .

essentially in appearance, consist-
ence, &c.

Connective-tissue bundles possess, according to the number of fibril.s
contained in them, a greater or lesser diameter. And as these may again
be associated to form thicker cords, they can be distinguished as primary,
secondary, and tertiary fasciculi.

An important question now arises, namely, whether these aggregations
of fibrillae are naked and without any envelope, or whether the whole
strand is not encased in a homogeneous sheath of condensed substance.
The first of these may be looked upon in general as the most probable
state of the two. And yet we may distinguish in many places bundles
which arc enclosed in an envelope, sometimes thick, and sometimes of
great delicacy. These occur especially where the connective-tissue is
loosely arranged, as, for instance, in subcutaneous cellular tissue, or, more
distinctly still, at the base of the brain. The membranes so formed,
moreover, may have preserved the ordinary glutin-yielding nature, or have
undergone subsequently a metamorphosis into elastic matter (see below1).

Acetic acid has come greatly into use as an important reagent in the
investigation of the tissue in question. The fasciculi of connective-tissue,
namely, which, owing to their nature as collagenic structures, are to a
certain extent remarkable for their insolubility, lose very rapidly their
fibrous appearance under the action of the acid, and become clear and
transparent, swelling up at the same time very considerably. In tissue
rendered clear in this manner, which is not unfrequently marked by a
transverse striping together with the puffing out of the bundles, the
elastic fibres and networks now make their appearance in the most beauti-
ful way, beside which we are also able to recognise the changed connective-

g- 199.— Bundles of connective-tissue lyinp in an
abundant interstitial matter. To the left are seen

a few isolated flbriiise.

208 MANUAL OF HISTOLOGY.

tissue corpuscles. The relative proportions also of elastic parts may be
estimated by the aid of this reagent, and without the microscope ; for a
connective-tissue which has a great abundance of the former as compo-
nents is rendered but little clearer by this treatment.

That no solution of the fasciculi takes place is easy of demonstration ;
for on carefully washing out a small portion of tissue which has been
acted on by the acid, the fibrillae again become visible.

REMARKS. — 1. From the fact that the fibrillse of connective-tissue are so extremely
fine, and only appear associated in bundles, it is not strange that at a time not long
past their existence as natural structures should have been completely denied. This
has happened with Reiehert, in his otherwise so important and stimulating work.
According to his view, the ground-mass of parts composed of connective-tissue con-
sists of homogeneous, structureless matter, which has a tendency to shrink together,
forming folds, which convey to the eye the impression of fibrillse. It has also a
tendency to split up in the same direction. Now, although, in former times, the
structure of connective-tissue was looked upon to too great an extent as uniform, and
the residues of intercellular substance had been frequently overlooked, still every unpre-
judiced inquirer into the true state of the case may satisfy himself of the untenableness
of Reichert's theory. A portion of living tissue even shows the fibrillse, and examina-
tion with the polarisation apparatus teaches their presence also. On transverse sections
of tendons, for instance, we may also remark a finely-punctated appearance, which has
been regarded by many observers as due to the ends of divided fibrillre. 2. After
that Henle had shown that fibres could be isolated by alternate treatment with differ-
ent reagents, producing shrinking or swelling, as, for instance, with dilute and con-
centrated nitric or hydrochloric acid, Rollett found that steeping in lime-water (or,
much more rapidly, baryta) dissolved the cementing substance, so that the fibres could
be spread out." According to this observer, connective-tissue resolves itself, on being
treated with the reagents in question, either immediately into fibrillee or into bundles,
which only divide into the latter on prolonged maceration. Based on these facts,
Rollett proposes to distinguish two forms of fibrillation in connective-tissue. For
the first of these, tendon affords an example. In the same category he reckons also
the bundles of the sclerotica of the aponeuroses, the fibrous ligaments of joints, the
dura mater, and the inter-articular ligaments.

Among the tissues which show the second form of resolution are the cutis, con-
junctiva, subcutaneous cellular tissue, submucosa of the intestines, and tunica ad-
veiriitia of vessels. In our opinion, the question here only turns upon quantitative
differences.

§ 127.

By means of the reagents mentioned in the previous section we are
enabled also to recognise the elastic elements imbedded in the connec-
tive-tissue, which is rendered clear by the former. These are all alike
in their power of resisting not only the -action of acids, but also that of
potash ley, however much the form in which they appear may vary.
The latter is the most important agent for their recognition.

Elastic fibres are of the commonest occurrence. They are* met with at
one time fine, at another of no inconsiderable thickness; sometimes simple,
sometimes branched.

The most delicate elastic fibres (fig. 200, a) were formerly known by
the name of nucleus fibres (Gerber and Henle), being erroneously sup-
posed to arise from the fusion of fusiform elongated nuclei. They
are frequently met with as constituents of connective-tissue in many parts
of the body, as, for instance, in that of loose texture lying under the skin.
Their diameter may be the same as that of the connective-tissue fibril, but
their dark contour and far more tortuous course, their irregularly-twisted,
cork-screw-like or hooked appearance, renders their recognition easy.
Their peculiar appearance is the result of their elasticity, as well as of the
manner in which they have been cut, combined with the swelling up of

TISSUES OF THE BODY.

209

the connective-tissue under the action of the acetic acid. Whether these
finest fibres are all solid or
may not be hollow in part,
we are not yet able to state.

By the occurrence of
branches on such very fine
fibres, and their ever-increas-
ing ramification (the diameter
of the tubes reaching at times
0-0014-0-0022 mm.), an elas-
tic network is at length
formed (b). This again varies
considerably as regards the
breadth of its meshes. It
usually maintains with its
principal fibres the same
direction as the bundles of
the connective-tissue.

From these elastic threads
we now find transitions to
even broader and thicker
forms (c), which are decidedly
solid, and which, contrasted
with the so extensible fibrils
of lesser magnitude, display often a considerable degree of brittleness, so

Fig. 200. — Elastic fibres from the human beinpr. «. un-
branchcd, fine, and finest; 6, a network of tne elastic
fibrils; c, a thicker one with branches.

Fig. 201.— From the middle
coat of the carotid artery
of an ox. a, a mem-
brane with a network of
the finest elastic fibres;
6, a similar membrane
feiu-strated at intervals.

Fig. 202. — From the middle and ex-
ternal coat of the aorta. 1. An
clastic membrane (from the ox)
fenestrated to a great extent (a),
and with thick bauds between the
various holes, 6, c. 2. A network
of broad elastic fibres from the
whale, which are partly pierced
with minute foramina.

that, in many instances, we can only obtain by dissection short fragments-
of the formations in question.

210

MANUAL OF HISTOLOGY.

Tims the yellow ligaments of the vertebral column are uncommonly
rich in elastic fibres of 0-0056-O0065 mm., which are usually met with
bent or arched, and giving off a tolerable number of branches, which are
also hooked or like tendrils, and frequently attain a remarkable degree of
fineness. In the infant such fibres have still but a small diameter, and
it is not before a certain amount of maturity of the mammal body has
been attained that the formation of these broader fibres takes place.
Smaller individuals only show the finer examples.

The amount of fibrillated connective-tissue found amongst these is
subject to great variation. Though in many localities tolerably abundant,
it becomes in others rather scanty, and often excessively diminished in
amount. It was in such cases as this that earlier investigators were
accustomed to speak of elastic tissue.

There could hardly be a more suitable object for the study of an elastic
tissue of this kind in all its peculiarities, than the
walls of the larger arteries, especially those of the
larger mammals.

Here we meet with thin elastic membranes (fig.
201, a), in which is seen a network of very fine
elastic fibres embedded in homogeneous intermediate
matter; or this membranous ground-substance may
bo pierced with holes of various kinds (fig. 201, &),
(the fenestrated tunic of Henle}. We likewise
encounter very simple elastic tunics without em-
bedded fibres (fig. 202, 1), which are also studded
with apertures (a), the whole of the substance
presenting the appearance of bands and broad irre-
gular fibres (b, c). Between such and a dense in-
terlacement of broad elastic fibres (fig. 202, 2), it is
often difficult to distinguish with certainty. Those
dense networks which have a homogeneous inter-
stitial substance, as in fig. 203, afford still better
objects.

In those localities where the elastic fibres are very
broad, their edges may be here' and there jagged like a saw. Again they
are frequently pierced with very minute holes. This is seen very gene-
rally in the external coat of the aorta of the whale, where the fibres may
measure 0-0056 or even 0 '00.75-0 -0088 mm.

§ 128.

Having now made ourselves acquainted with the ordinary bearings of
elastic fibres and nets, we must turn to the consideration of the limiting

Fig. 203.— A. very dense
network of broad elas-
tic fibres from the mid-
dle coat of the aorta of
an ox. The fibres are
connected by a homo-
geneous intermediate
substance of a mem-
branous structure.

FIR. 204.-A connective-tissue bundle from the base of the human brain, treated with acetic acid.

layers of many connective-tissue bundles, which have spruncr from
metainorphosis mto elastic substance of some matter situated arold

TISSUES OF THE BODY.

211

The bundles of connective-tissue which pass from the arachnoid to the

larger vessels on the base of

the brain (fig. 204), with other

isolated fasciculi in the loose

cellular tissue under the cutis

and certain serous membranes,

and that of tendons even, show

us a very interesting example

of the artificial production of

figures extremely like annular

or spiral elastic fibres, and

which have even been taken

for them. To demonstrate

this, acetic acid is employed

or prolonged maceration in

water.

In the first place we meet

with fasciculi in which the elas-
tic envelope is puffed out and
stretched by the action of the
reagent, but remains unin-
jured, the consequence of
which may be twofold as to
appearance. Firstly, the gela-
tinised substance of the con-
nective tissue may be puffed
out at intervals into globules,
so that annular or at times
spiral indentations arise (fig.
205, 1, 2, c), or the puffing
may be more one-sided, in
which case the furrows appear
clearer and more distinctly
spiral (4). All these furrow-
ings are characterised by their
delicate outline, which is never
double. Further, we may be-
sides recognise the presence of
the envelope on the cut end of
a bundle (2 d), or when it has
become separated from the
contents, in consequence of the

penetration of fluid (la) f!& 205.— Bundles of connective-tissue from the base of

r T, f ,, v ' , the human brain, after treatment with acetic acid.

It trequently OCCUrS, nOW- Some of them have more or less developed elastic

fibres in their interior. 1. A bundle whose envelope is
not torn, but obliquely M-rinkled; a small portion of
the latter is separated for a short distance at a. "2. A
bundle with annular shrunken porti< ns of the sheath
at a, a more strongly pronounced puffing of the sub-
stance of the connective-tissue at fc, and a longer por-

ever, that a number of trans-
verse rents are produced in
this elastic envelope, in conse-
quence of which the substance
of the connective-tissue may
swell out in globules, while
each portion of the envelope be-
comes more and more shortened
by the pressure, a contraction ensuing, which is rapidly increased by the

tion of the wrinkled envelope at c, c, from the cut end
of which, at d, the contents are protruding. 3. A bundle
with annular fragments of the envelope at a, and
a larger portion of the latter at 6, more strongly
wrinkled. 4. A smaller bundle with uninjured varicose
sheath.

212

MANUAL OF HISTOLOGY.

elasticity of the membrane. Thus we remark at first the fragment of the
sheath still long and transversely ribbed (3 /;), but soon, and especially when
from both ends of the torn sheath the contents swelling out press upon the
latter, that portion of the envelope contracts into a fine narrow ring with a
dark contour (2 a, 3 a) ; more rarely, in consequence of
a spiral rent, it shrinks into a filiform structure passing
round the mass with a spiral course. Did we not know
their origin, we might look on these shrunken fragments
of the envelope as fibres of a coarser kind, encircling
either as rings or spirals the bundle of connective-
tissue. It is an interesting fact that fibres of cotton
undergo the same changes, under the action of am-
monio-oxide of copper, which may here be observed
in all their phases with the most perfect ease.

It seems, therefore, beyond doubt that elastic mem-
branes may shrink into filiform structures in conse-
quence of being completely rent.

We are here met by the question, whether something
similar to this, which we have found as an artificial
production, may not also occur as a normal process in
many of the elastic membranes of the body, — whether,
by a partial reabsorption or rending of its substance,
a membrane of this kind may not be converted into a
network of elastic bands and fibres, at the same time
that its substance so fenestrated diminishes greatly in
extent owing to elasticity.

There seems, indeed, to be no doubt that networks
of elastic fibres or flat bands, as we meet with them in
the middle coat of the greater arteries in large mammals (fig. 206), have
frequently had their origin in the manner just described. It is probable
also that, by the thickening of elastic membranes at particular points in
folds and bands, a network of elastic tissue may be formed (fig. 203).

§ 129.

We turn now to the most difficult point in this subject, to the cellular
constituents, or, as they were formerly called, connective-tissue corpuscles.
In them we have the most important physiological elements of the tissue
under consideration. As we have already remarked, these cells are usually
obscured by the fibrillse around them, and only come into view after the
use of acetic acid and other strong reagents, amid the gelatinised ground-
substance. But where it is possible to obtain a view of the still living
and unchanged connective-tissue corpuscle, it is very far removed in
appearance from those which have been acted on by reagents.

Besides the true connective-tissue cells, all the structures we are en-
gaged in considering appear to contain a second element, the lymphoid
cell, which has migrated from the blood-vessels. The "cells of connective-
tissue might, therefore, be classed with propriety into fixed and wan-
dering.

Let us turn now to the living tissue.

An excellent spot for obtaining living connective-tissue was pointed
out not long ago by Kilhm : this is in those thin transparent lamellae
which occur between the muscles of the leg of the- frog.

In one of these (tig. 207), we may see in the extremely soft ground-

20C.— Elastic nets
from the aorta. 1.
An elastic fenestrated
membrane from the
ox; 2. A distinct net-
work of broad fibres
from the whale.

TISSUES OF THE BODY.

213

substance, which is gelatinous and transparent, first of all the fibrillse and
fasciculi of the connective-tissue (/, g)t as well as a network of extremely
delicate elastic fibres (h). Then the expected cells (a-e) are observed,
though not so close together as in our plate, but at rather greater inter-
vals. ^All of them are naked, and appear in several varieties. The
most usual form in which they are met with is that of a delicate proto-
plasmic structure in which no nucleus can be discerned, but in its place a
darker spot (a). The cells in question send off several processes which may
attain considerable length, and come into contact with those of neigh-
bouring cells (b). By very strong magnifying power there may be seen,
beside these longer processes, a large number of shorter and paler ones,

Fig. 207. — A portion of living connective-tissue, cut out from
between the muscles of the frog's thigh (strongly magni-
fied). «, a pale contracted cell with a dark lump in the in-
terior; 6, ramified corpuscles; c, a similar corpuscle with
vesicular nucleus; d and e, motionless, coarsely granular
cells; /, fibrillae; <;, bundles of connective-tissue; A, elastic
fibrous network.

giving to the contour of the structure a regularly jagged appearance.
Other connective-tissue corpuscles preserve generally a more even outline,
and contain a vesicular nucleus (b above, c). By their processes, few in
number, they are connected with one another, as well as with the cells
belonging to the first variety. Finally, there appear other cells of a third
form, remarkable for the opacity of their protoplasm. They are usually
fusiform (d, e), and contain a vesicular nucleus.

With the exception of the last mentioned and more coarsely granular
cells, connective-tissue corpuscles are endowed with the power of very
slow but unmistakable vital contractility, their form changes, processes
commence to make their appearance, elongate and unite with those of
neighbouring cells, and become again disunited. Nothing can be seen of
pre-formed paths for these processes ; the almost mucoid consistence of the
intercellular substance allows of free play to their motion in all directions.

In other organs also, and in the bodies of many different animals, the
same contractile corpuscles of connective-tissue have been observed, so

214

MANUAL OF HISTOLOGY.

that we are probably dealing with a peculiar property inherent universally
in these elements.

Let us now return for a moment to the connective-tissue corpuscles
we were observing in the frog. It is only necessary to add a drop of
water to the preparation to produce a great change in the nucleus, and
greater in the protoplasm, which contracts around the latter to 'a kind
of fine network. Acetic acid has even a more lasting effect. It causes
the nucleus to appear darkly and clearly in the shrunken protoplasm,
and gives rise to a distinctly marked halo around the cell. This boundary
line encircling the corpuscle formed of altered intermediate substance
may simulate a membrane upon it.

§ 130.

After what has just been remarked, it Will be seen that for the present
we must abandon all hope, in studying human connective-tissue, of meet-
ing these cells in an unchanged condition. When most fortunate, we can
only obtain them just dead, and as yet but slightly altered. Acetic acid,
which was formerly much used in studying the connective-tissue cells,
exercises a strong gelatinising influence upon the intermediate substance,

Fig. 208.— -Tail tendon of a young rabbit. A, the tendon
stretched, magnified 200 times. B, a. less tense tendon en-
larged 300 diameters; a, cells of the tendon filled with fat
at 6 ; c, fine elastic fibres.

by which the cellular elements are distorted and assume the most extra-
ordinary forms. This reagent has been the cause of numerous errors, and
has regulated for many years our views in regard to connective-tissue.
• -Now, what is known at the present day of these elements ?
We must confess not much. Something we have, however, gained
from more accurate investigation. The connective-tissue cells of the
mature body are frequently (though not invariably) flattened structures,
nucleated plates displaying still some protoplasm in the neighbour-
hood of the nucleus as a rule, but so thin at their borders as to require

TISSUES OF THE BODY.

215

the closest scrutiny in order to make out their boundaries at all. The
recognition of them is rendered, moreover, difficult by their not lying
all in the same plane as a rule, but at very variable intervals, and
their being bent and squeezed into the greatest variety of shapes besides
by their position.

Many years ago Henle had remarked peculiar flattened nucleated
cells (like epithelial elements) lying in rows between the bundles of which
tendons are made up. Mttnvier, an excellent French observer, has directed
attention to the same in the tail tendons of the rodents, falling into the
error, however, of taking them for tubular elements curled on them-
selves.

Fig. 208 will give an idea of the nature of the parts.

But how variable is this system of bent cells investing imperfectly
the surface of the tendon bundle ! Immoderate tension converts them,
into extremely delicate long nucleated bodies like fibres, while, on the
part relaxing, the flat cells may curl and warp anew.

It is not the tendons alone, however, which display these flat cells:
their presence in the cornea also
was maintained by an excellent
observer, Schweiyger-Seidel, whose
early death is to be lamented.
They have been accurately described
by F lemming as occurring in soft
formless connective-tissue in their
usual strange, jagged, crumpled
shape. His drawings, our fig. 209,
are very faithful.

In spite of every effort, however,
we are still as regards the connective-
tissue cell but very imperfectly
enlightened. Let us not forget this
fact.

In order to convey a clear idea
of what we have just stated, we
repeat fig. 210 in illustration as
we close the section. In this we
have connective-tissue corpuscles as
they are seen altered by the ac-
tion of acetic acid. At a, b, ft,
and c, d, d, we perceive tolerably
simple cells from foetal connective-
tissue : i-e, on the other hand,

are purely artificial productions, dis- Fi* 209.-Cells from the formles9 connective-
J r ,« tissue of a young rabbit just born (a), and ot

tortions Which have more than a mature Guinea-pig (6).

once played a part in the history

of both normal and pathological histology.

Thus it was formerly maintained that the formation of elastic fibres
took place from those narrow elongated structures, connected with one
another by long thin processes. But although the appearance of the
latter under the microscope, as well as their bearing under treatment
with strong mineral acids, is the same, still they differ from elastic fibrous
networks in being destroyed by strong alkaline leys, while the latter
resist the action of the same (Koelliker),
15

216

MANUAL OF HISTOLOGY.

Ill many structures formed of connective-tissue it is probable that

the protoplasm becomes more
and more expended in the
production of the inter-
mediate substance, until the
latter, either fibrillated or
streaky, appears as though
i only nuclei alone instead of
cells were left in existence.

The total disappearance
also in many parts of the
connective-tissue cells pre-
sent in the embryo, may be
bound up with the develop-
ment there of numerous
elastic elements. This has
been remarked in the liga-
mentum nuchae of mammals
(Koelliker).

§ 131.

We now turn to the mode
of occurrence of connective-
tissue.

The numerous portions of
our body consisting of this
tissue offer for our considera-
tion fibrous and generally
fibrillated intermediate sub-
stance, cellular elements, the
connective-tissue corpuscles,
and wandering lymphoid
cells, and also the various
species of elastic fibres and networks. In some structures a few only of the
latter constituents occur amid a large quantity of fibrillated intermediate
substance ; but they are met with more abundantly in other parts, and
may eventually appear here and there in such excess that the glutin-
yielding fibres and cells begin to be obscured or actually cease to be
present. Thus, in some cases, we find elastic membranes and fibrous
networks alone, the latter being held together by a membranous inter-
stitial matter neither fibrous nor glutinous. They may also make their
appearance naked and without such a cementing medium. In that
numerous intermediate forms exist, however, between them, the latter
cannot be classed as a tissue distinct from the true connective-tissue.

Associated with these essential form-elements of connective-tissue we
sometimes find other incidental constituents, such as cartilage -cells
(§ 109), fat-cells (§ 122), smooth muscle fibres (in which the Tunica
darios of the scrotum is very rich), blood and lymph vessels, nerve
fibres, &c. Here, then, we have, in consequence of these additions which
differ exceedingly from one another, a new ground for variableness in parts
formed of connective-tissue.

These latter appear either as yielding substances, filling out the
spaces between organs or portions of organs, as loose enveloping masses,

fig, 210. — Different forms and stapes of development of
the so-called connective-tissue corpuscles, after treat-
ment with acetic acid.

TISSUES OF THE BODY. 217

and paths for vessels and nerves, or they may constitute formed struc-
tures, membranes, cords, or solid envelopes. Accordingly, we distinguish
two kinds of this tissue, the formed and the formless, — a division which
is, generally speaking, well based, although it must not be forgotten
that there are in many places transitions from the formed to the form-
less, and vice versa, and that, therefore, nature has drawn no sharp
bounding line between the two species. As a rule (which is not with-
out exceptions, however), the first of these is a soft slimy matter, the
latter a more solid substance.

Formless connective-tissue, or, as it has been named when occurring
in large quantities, loose or areolar tissue, possesses besides a homo-
geneous, gelatinous, and almost mucoid ground-substance, connective-

Fig. 211.— Formless or areolar connective-tissue from the large omentum of man.
a, a, a capillary vessel.

tissue fasciculi, elastic fibres and cells, but in. very varying propor-
tions. The interlacing of these fasciculi (in general rather loose, so
that the whole remains on that account yielding and extensible) is
either retiform, or several of the bundles lie longitudinally together,
embedded in and held together by the soft formless substance. By
the heaping up of fat-cells within this loose tissue it is opened up,
and a number of communicating spaces are produced with septa between
them. These are the cells of older anatomists, which procured for
the tissue the, designation cellular, a name which has given way to the
histological nomenclature of the present clay. We may also succeed
mechanically, as for instance by inflation with air, in producing a
more or less artificial separation of this substance, which is saturated
during life with small quantities of a watery transudation similar to
synovia, § 96. These " cells " or loculi appear also pathologically on
the accumulation of large quantities of fluid or the entrance of air.

218 MANUAL OF HISTOLOGY.

In all this we see a resemblance between the structure in question
and gelatinous tissue. And, indeed, the greater part of this areolar tissue
existed at an earlier embryonic period in the form of a reticular mucoid
substance. The elastic fibres also are no less subject to variation, for we
meet both with fine and medium-sized specimens ; their amount, how-
ever, is but moderate. The connective-tissue cells proper are situated
either between the fasciculi in the form of fusiform or stellate elements,
or in the softer interstitial mass. Here also we encounter lymphoid
corpuscles, which may wander through the mucoid substance by virtue
of their vital contractility ; and yet we are unable to recognise any pre-
formed paths for them.

According to its occurrence in more considerable amount in several
localities, this tissue has received corresponding names, such as sub-
cutaneous, submucous, and subserous areolar tissue.

This, and indeed formless connective-tissue generally, is continuous at
its bounding portions through one of its bundles of fibres with some
structures made up of formed connective-tissue, e.g., the sheaths of nerves,
the fibres of fasciae, the subcutaneous and dense tissue of the cutis, &c.

But this formless connective-tissue presents itself under other condi-
tions, namely, as the supporting or sustentacular substance of many organs
(Stutzmasse). Thus we meet with it in the larger glands. Here we
encounter either a fibrillated mass with fusiform or ramifying connective-
tissue cells, or the intercellular substance only appears streaky, while
the cellular elements may merely be evident as very much stunted
nuclear formations. Fibrillated tissue is to be found, for instance, in
the testicle and thyroid gland; streaky sustentacular substance in the
kidney (where we may isolate stellate cells from the medullary por-
tion in the young subject). The supporting tissue in the interior of
muscles and nerves frequently appears striped or streaky, but is at times
fibrillated.

§132.

But the diversity of the so-called formed connective-tissue is far more
considerable, not only in respect to the manner in which its fasciculi and
elastic constituents are interlaced and interwoven, but also in regard to
its texture. And though, as a rule, we have to do with a well-marked
typically developed connective-tissue, yet there occur not unfrequently
very peculiar varieties. A few of these may here be mentioned.

We have, first of all, certain connective-tissue structures, in which the
cells are exceedingly stunted, and seen as though only the nucleus had
been left over, and in which the intermediate substance is either homoge-
neous or streaky, but not fibrillated. Radiated corpuscles and elastic
fibres are absent, either totally, or only give very slight indications of their
presence.

The tissue of the dental pulp apparently belongs to this class. And
yet we may have to do with a species of gelatinous or mucoid tissue here,
in that the interstitial matter does not become clear on the addition of
acetic acid.

Again, the sheath or pcrineurium of the smaller nerves consists of a trans--
parent substance, through which are scattered long oval and apparently naked
nuclei, measuring about O'0075-O'OIH mm. If we pass on from these
to somewhat more considerable branches, we find the ground-substance of
the envelope becoming stringy and fibrillated, while, instead of nuclei, we

TISSUES OF THE BODY.

219

o

Fig. 212. — A portion of a human sympathetic
ganglion. A, four ganglion cells surrounded
by homogeneous nucleated connective-tis-
j«ue; a, without a nucleus; c, containing
two of the latter. This tissue, b 6, passes off
into the fibres d d. It, & cell without an
envelope.

find connective-tissue corpuscles, until, finally, in tlie larger nervous trunks,

the perineurium assumes an exquisitely fibrillated character, and discloses

a rich network of elastic fibres.

Further, a similar homogeneous nucleated tissue encloses, as an external

capsule, the nerve-cells in the ganglia (fig. 212, A}. Not unfrequently we

have opportunity of remarking how, from

this connective-tissue acting thus as an

envelope to the cells, flat bands pass off

(d d). There is a pressing necessity here.

however, for closer investigation.

Later on we shall have to inquire into

the nature of the so-called fibres of

Remalc, in considering the nervous

system, pale nucleated threads of mixed

nature. Some structures described as

such appear to belong to the connective-
tissues, and to be a species of the latter

similar to that of the envelopes of the
ganglion cells just mentioned.

We meet with very peculiar masses of
connective-substance in certain tissues of
the body of vertebrate animals, in which
(like many of the flat epithelia, § 89)
the cells are filled with granules of black
or the nearly allied broicn pigment.
The particles of this melanin, however, are smaller than those in the epithe-
lial cells.

Connective-tissue corpuscles of this kind, the stellate pigment cells of
an earlier epoch (fig. 213), are found in the human body almost ex-
clusively confined to the eye. Among the
lower vertebrates, however, they may attain
an enormously wide distribution through-
out the body, so that we encounter them in
all parts formed of connective-tissue, for
instance, in the frog.

In these vital contractility has been
observed, and the power of wandering from
one situation to another. Thus they may
penetrate from the connective-tissue be-
tween the cells of the epidermis, by virtue Fig 213
of this power.

Fig. 214 represents the changes of form
in one of these migrating cells.

In the human eye, the number of melanin cells of this kind is either
very considerable, while the proportion of intermediate matter is mode-
rate (the latter being at the same time homogeneous more or less), or the
cells occur more isolated amid fibrous typical connective-tissue.

A case of the first kind is to be found in the choroid. In it we encounter
a dense network of these cells, of stellate or fusiform figure, with oval
nuclei, and a varying number of processes, which elongate themselves
frequently into extremely thin filaments, appearing at times tangled :
through these the cells are connected with one another. The size of the
latter is about 0 '0226-0 '0452 mm. Altogether this reminds us of the

-Pigmentary connective-tissue
corpuscles (so-called stellate pigment
cells), from the lamina fusca of the
mammal eye.

220 MANUAL OF HISTOLOGY.

cellular networks of many of the colourless connective-tissue corpuscles,

with which indeed it most com-
pletely corresponds in the body
of the infant, where the body of
the cells have not yet become
filled with granules of melanin.

This uncoloured state of the
choroid cells only persists in cer-
tain exceptional cases, until late
in life, through absence of pig-
ment. Thus among albinos, of

. which we have always a §ood

the toe of a water-salamander. The observation example in white rabbits. As ;l

SSd °Ver " SPaC6< 5minutes-tAfter^ rule,, it will be found that, soon

afterbirth, the deposit of granules

takes place in these cells, especially in their body and thicker part of
the processes. This pigmentation spreads likewise from the choroidea to
the cells of the lamina fusca, which is situated between the latter and
the sclerotic.

A part also of the connective-tissue cells, of the iris, of dark but not
blue-eyed individuals, is likewise effected by it. But the colouring matter
appears here to be, as a rule, lighter, and of a clearer brown.

If we examine the pigmentary connective-tissue cells of adult animals
or human beings (tig. 213), we are struck "by their irregularity of form,
which may be explained by the hindrance to their further development
through the deposit of melanin. For the same reason, the nucleus remains
here broad and oval, whereas in better-developed cells it usually becomes
long and narrow.

Ifc is a point of special interest in viewing the stellate pigmentary cells
as modified connective-tissue corpuscles, that there exist gradations between
parts formed of them and purely fibrous structures. This is the case in
the lamina fusca, whose pigmentary cells are continuous towards the sclera
with ordinary colourless connective-tissue corpuscles. Pigmentary con-
nective-tissue cells are usually found also in the pia mater of the medulla
oblongata, and the adjacent portions of the cord, in adults. Their colour
is brown or blackish, and their quantity and distribution, moreover, liable
to variation.

In diseased states of the tissues we may likewise find transitions of this
kind, and an abundant development of pigmentary cells.

§133.

Many widely different parts are reckoned among the formed connective-
tissues. 1. We commence with the cornea. No connective-tissue structure
has so frequently been the subject of research as it.

The cornea (fig. 215) presents for our consideration on its anterior
aspect, the laminated epithelium of the conjunctiva (d), while the posterior
surface is clothed with a layer of simple pavement cells (e), a so-called
endothelium. "Under each of these layers we come next upon a trans-
parent structureless membrane or lamella, of which that on the anterior
surface is. not easy of isolation, whilst that on the posterior aspect appears
stronger and easier to separate, as has long been known.

The first of these, the lamina elastica anterior of Bowman (which is,
however, said to have an extremely dense fibrillated texture, by Rollc.tt

TISSUES OF THE BODY.

221

and Engelmanri) (1), has a thickness of from 0'0068-0'0090 mm. in man.
It is soluble in boiling water. It is, however, by no means sharply de-
lined against the tissue of the,
cornea lying underneath. The
second layer (c), which bears
the name of the membrane of
Demours and Descemet, and is
0-006-0-008 mm. in the cen-
tral portions, and 0 '01-0 '01 2
at the border (H. Muller), is
separable in various ways from
the cornea. It has a consider-
able amount of elasticity, so that
it rolls up upon itself on loosen-
ing. At its circumference it is
lost on the anterior aspect of the
iris, as the ligamentum petiin-

atum iridis. £Tow, between

a

these two transparent mem-
branes is found the true tissue
of the cornea (a), which has
been the subject of such ex-
tended research, and whose
structure is still far from being
satisfactorily elucidated. It
is formed of intercellular mat-
ter and a system of canals con-
taining cells. The first is con-
tinuous peripherally with the
fibrillated connective-tissue of
the conjunctiva, but also, and to
a greater extent, with that of
the sclerotic.

This ground-mass of the cor-
nea presents transparent, flat
bands of 0'0282-0'0090 in
breadth, and 0'0045-0'0090
mm. in thickness, which are,
for the most part, so arranged

in respect to the surface, that a regularly laminated structure is the result,
though, at the same time, a crossing of the bands may be remarked
frequently enough, especially on the anterior surface and periphery of the
cornea. Owing to the fact that those can be demonstrated either as
hanging together in lamella? or separable one from the other, the cornea
has been declared at one time to be laminated, at another to be fibrous,
or both at once, as a combination of both views. As far as we know at
present, the cornea may be likened to a compressed network of ilat bands,
matted in layers, a view which is farther borne out by its double refracting
properties with polarised light (His}. Reagents, as, for instance, perman-
ganate of potash, employed by JRollett, or a 10 per cent, solution of com-
mon salt, by Schweigger -Seidel, show it to be made up of the finest fibrilla;
however, held together by a homogeneous intermediate substance, which
mav also be recognised on fresh corneal tissue, and, better still, in that

Fig. 215. — The cornea of the infant in vertical section,
but much shortened, a, corneal tissue; b, anterior; c,
posterior transparent htyer; d, laminated scaly epithe-
lium ; e single layer of epithelial cells.

222

MANUAL OF HISTOLOGY.

which is shrivelled. Swelling up of the tissue, on the other hand, renders
these delicate fibres invisible in a moment. The system of canals (fig.
216, a) has been erroneously taken by many to be a system of retiform
cells, the corneal corpuscles, and indeed it is deceptively like something
of the kind when treated with dilute acids. It always occupies with its
accessories the spaces between the bands of the ground-substance, and
appears as a ramifying system of tubes, capable of isolation by means of

Fip. 216. — Cornpal corpuscles, a. from the ox, as seen from the surface; 6, from
an infant (surface) ; c. side view of the same from a child four months old ; c?, from
small embryos of the human being and ox.

boiling and maceration in strong mineral acids. That it is in reality
hollow is indicated by the fact that morbid growth and deposits of fat and
pigment take place in it. Artificial injection of the cornea by puncture
(Bouman, Recklinghausen, Leber, C. F. Mullcr, Schweigger-Seidel\
generally gives rise to a rupture of the tissue (Rollett), and produces
various appearances in it. The canal-work of the so-called corneal
corpuscles appears also to be capable of being filled however (Boddaert).
This system of canals, which possesses probably a modified parietal layer
(extremely extensible, and certainly not everywhere continuous), has far
wider meshes in the adult than in the infant or foetus.

Seen from the surface, its characters are those of a network possessing
widened radiating nodal points of considerable magnitude (fig. 216), while,
in profile, it presents longitudinal and usually fusiform enlargements,
running parallel with the bounding lines of the cornea. The former
stand in communication with one another by means of fine passages, and
at times also with those of the deeper or more superficial series, through
ascending or descending lines. These stellate enlargements are, therefore,
flattened in a direction perpendicular to the surface of the cornea.

As to the size of these points or of the corneal corpuscles, their
length is stated at 0-0135-0-0180 mm., and breadth at 0-0102-0'0124
mm. Their processes have a diameter of about 0-0023-0-0007 mm.

TISSUES OF THE BODY 223

The average distance of the corneal corpuscles from one another is
0-0226-0-0452 mm.

After the customary treatment of the cornea with dilute acetic acid,
we may recognise in these nodal points nuclei of O'0090-O'Ollo mm.
in size (fig. 216, c). And in that, as a rule, the substance of the body
of the cell reaches as far as the limiting lines of the space, we have
the appearance of a stellate cell clothed with a membrane. The use
also of a dilute solution of nitrate of silver for obtaining the like views
has been recommended (Recklinghaiisen).

But we are obliged to turn to the cornea in a condition as far as
possible unchanged, in order to gain a correct view of the state of
things. Here we see the tissue studded with membraneless stellate
cells extending their processes in all directions, and frequently forming
a cellular network through union of the latter. This network, in our
opinion, lies within the system of canals already mentioned. Very
elegant objects illustrating the nature of this cellular network may be
prepared with chloride of gold.

The contractile lymphoid wandering cells of connective-tissue parts
(already mentioned, p. 77), were discovered several years ago by
Recklingliausen in the cornea of frogs and mammalia also, travelling,
as he supposed, through the passages of this structure. This discovery,
confirmed on all sides, has led to a multitude of other observations
and experiments, which have unveiled most interesting features in cell-
life of the widest significance. If we place the excised cornea of one
frog in the lymph-sac of another, we may demonstrate this immigration
of lymph corpuscles into the corneal tissue (Recklinghatisen). We have
already considered the power these cells possess of taking up molecules
of colouring matter into their protoplasm. This may easily be brought
about by injecting granules of pigmentary substances either into the
circulation or into a lymph-sac in a frog. The same injection produces
similar occurrences among mammals. Fed in this way, the lymph cor-
puscles leaving the blood pass into the corneal tissue, in small numbers
indeed, into that which is healthy, but in great quantities, on the other
hand, in a cornea which has been inflamed through an irritant (Cohn-
heim). But all of these cells, which now go by the name of pus cor-
puscles, have not the same source, i.e., from the circulation. There
must be a new formation in the interior of the corneal tissue itself
(Hoffmann and Hecklinghausen, Norris and Strieker), about which, how-
ever, we have but insufficient information at present.

We will add but one word more on the structure of the cornea at an
early period of life.

In the embryo (fig. 216, rt), the so-called corneal corpuscles show but
few processes, and the nuclei enclosed in them appear vesicular. Divi-
sion may also be observed among them. The network formed of these
is extremely dense as it is first seen (b), and the intermediate substance,
originally very scanty, increases in proportion later .on. It is still com-
pletely homogeneous and without any cleavage. Double refraction is
also absent. The formation of the two transparent limiting membranes
also takes place very early.

REMARKS. — The literature to which investigations of the cornea have given rise
is very extensive, and frequently very contradictory in its statements. Among the
newer works we may mention, beside those of the Germans, Toynbee, Philosophical
Transactions for the year 1841, Part 2, p. 179; W. Bcwman, Lectures on the Parts

224

MANUAL OF HISTOLOGY.

Fig. 217.— Transverse section of the tendon of the tail of
a young rat.

concerned in the Operation on the Eye and on the Structure oftJie Eetina and Vitreous
Humour, Lond. 1840.

§ 134.

The following, parts are further reckoned among the formed connective-
tissues.

2. The tendons. They consist (with a sp. gr. of I'll 7, Krause and

Fischer) of a solid and but
slightly elastic tissue formed
of longitudinally arranged
cylindrical connective- tissue
bundles of a distinctly fibrous
nature. These are combined
to form stronger cords, and
are separated from similar
bundles by layers of loose
connective -tissue, in which
the few blood-vessels of the
structure are situated. The
tendons contain also longi-
tudinal rows of connective-
tissue cells. Portions of
them may possess cartila-
ginous deposits. They are
connected with the neighbouring structures by means of ordinary form-
less connective- tissue, or the latter
may bo condensed around them into
a kind of vaginal envelope, the sy-
novial sheath of the tendon. We
have already considered the mucoid
fluid which collects in the latter
when speaking of synovia (p. 155).

The more minute structure of these
parts is by no means easy to make
out, and has given rise to much con-
troversy.

If we examine a transverse section
of an infant's tendon which has been
previously dried and subsequently
softened, we remark a number of an-
gular and jagged figures connected
with one another by means of from
r , two to four processes, presenting thus

/», transverse section (spirit of wine pre- t-\ p n i , i

paration). the appearance of a cellular network

(fig. 217).

Side-views of the tendons display under proper treatment longitudinal
rows of Henle's or Ranvier's flat cells (fig. 208). These are not, how-
ever, rolled up into* tubes, as the French" investigator erroneously sup-
posed, but only lightly curved, enclosing the connective-tissue bundles
incompletely.

Turning again to the transverse sections, we may discern in each of
the apparently cellular interspaces (Henle) these transversely divided
cellular elements, at least faintly. They are, moreover, frequently
curved and crumpled.

Fig. 218.— From thctendo Aehillis of a foetal
pig 8" in length, A, the fusiform cells
and flbrous intermediate matter in profile;

TISSUES OF THE BODY. 225

If we turn to a still earlier or embryonic period (fig. 218), wo find
in side views (^4) narrow, fusiform, connective-tissue corpuscles without
membranes, and with elongated nuclei 0 '01 88-0 '002 3 mm. in length,
and O0038 mm. in breadth. These are arranged in longitudinal rows,
and are divided from those beside them by narrow deposits of fibrillated
intercellular substance measuring about 0-0068-O0045 mm. Transverse
sections (B) show, on the other hand, the outlines of the cells contained
in irregular roundish or jagged interstices. Thus both views correspond.

In the adult we find a strongly marked increase in the connective-
tissue fibrous matter. The jagged interstices in transverse sections are
separated from one another by intervals of 0'0668-0'0£90 mm. (2). In
longitudinal view of the stretched tendon the rows of cells are seen
as extremely thin rod-like structures, displaying the greatest diiferences
according to the tensity of the tendon (Ranvier). If 'we examine, on
the other hand, a tendon in vertical section, no longer on the stretch,
but gelatinised and constricted at points by the action of acetic acid
(as was formerly done as a rule), we then see narrow twisted structures
measuring 0*0451 mm., and reminding us at the first glance of nuclei.
These appear to extend themselves into long thin elastic fibres.

These deceptive appearances were formerly often seen and described.

But that all tendons contain those flattened cellular elements I doubt
very- much from recent investigations.

REMARKS. — 1. The so-called sesamoid cartilages imbedded in certain tendons belong
to these. Here we meet with aggregations of cartilage cells generally simple, lying
in a ground substance of connective-tissue. 2. If we destroy the interstitial matter
formed of connective-tissue by means of concentrated mineral acids, we have
remaining a figure corresponding to the cellular network in question. This appears
to be the contents of the system of interspaces enclosed in such a modified bounding
lamina. For further particulars on this point we must refer to the headings cornea,
bone, and dentine. Transverse sections of dried tendons present a very peculiar
appearance during the action of acetic acid on them. A number of sinuous band-like
figures, namely, appear with fusiform connective-tissue corpuscles and fragments of the
most delicate elastic fibres. These are the edges which have turned over on account
of the swelling up of the mass, therefore the side view of the sections of the bundles.

§ 135.

3. The ligaments have a similar structure to that of tendons, with the
exception of those which are elastic.

4. Fibro- or connective-tissue cartilage^ which might be treated of here
with an equal right as when considering cartilage, owing to the nature of
its intermediate substance, has been described already with the latter
tissue (§ 109.)

5. The large group of fibrous membranes. These are remarkable for
the close interweaving of their frequently very strong bundles of connec-
tive-tissue, which cross and recross each other. Their elastic elements
may correspond to those of the tendons, but are frequently moro
numerous, and display a greater breadth of fibre. The proportion of
blood-vessels in their composition is but small. • Among the fibrous
tissues we generally reckon —

a. Such closely-woven whitish envelopes as occur frequently in the
form of external coverings to the internal organs of the body. Thus the
sclerotica of the eye, with its densely interlacing connective-tissue bundles;
the dura mater of the brain and spinal cord, with its numerous elastic
fibres ; the fibrous part of the pericardium. Then, again, other fibrous

226 MANUAL OF HISTOLOGY.

envelopes, as those of the testicle, the kidneys, the spleen, the penis, and
clitoris. There is generally a considerable richness in elastic fibrillse here
also. This tissue may, besides, be continuous internally towards the
organ, with a banded or plaited network, in which smooth muscular
fibres appear sometimes as farther form-elements. This arrangement may
be seen in the cavernous portions of the urino-genital apparatus in the
lymphatic glands and spleen.

b. The fasciae, which run externally into formless connective-tissue, and
likewise penetrate between the muscle fibres internally, in the form of
thin plates. At one time they have more the texture of tendon; at
another the elastic fibres gain the preponderance, to such an extent, in
certain cases, that abundant networks of the broadest fibres may occur.

c. The perineurium, or, as it is usually called, the neurilemma, likewise
continuous externally with formless connective-tissue, and passing
inwards between the nervous fibres in a more homogeneous form. It
consists, on the larger nervous trunks, of regular bundles of connective-
tissue lying side by side, parallel with the course of the nerve. The
undulating arrangement of these it is which gives to the structure its
glistening plaited appearance. Beside these we find numerous elastic
fibres. The structure of the sheath continues thus down to the smaller
nervous branches, only decreasing in quantity ; here its substance loses
more and more the fibrillated character, and fusiform connective-tissue
corpuscles make their appearance at considerable intervals, until finally,
in the smallest ramifications, we find only a transparent homogeneous
membrane with single nuclei imbedded in it. There is, therefore, a
gradual transition here from a fully-developed connective or fibrous tissue
into a very plain connective-tissue substance.

d. Periosteum and perichondrium. The first of these is a strong mem-
brane clothing the outer surface of bone, which, on account of its supplying
the bone with nutrition, is traversed by a multitude of blood-vessels.
Its external layers show a large proportion of connective-tissue, and its
internal, or those lying nearer the bone, more of the fine elastic fibrous
networks considered already. Its connection with the bone is effected by
means of the blood-vessels sinking from it into the latter, while,
externally, it merges into formless connective-tissue. Whenever processes
of mucous membrane extend over the surfaces of bony cavities, it is the
custom to speak of a coalescence of the former with the periosteum,
although this cannot be demonstrated. Perichondrium, except that it is
the enveloping membrane of cartilage, is similar in structure. It is rich
in blood-vessels, which are destined for the supply of the former (§ 112).
In reticular cartilage we may remark the elastic fibres of its intermediate
substance passing continuously into similar elements of this connective-
tissue tunic.

6. The serous membranes. In these, bundles of connective-tissue are
discovered intersecting each other in all directions, but they may appear as
though converted on the free surface into a more homogeneous layer.
Besides these, we encounter also, in tolerable abundance, and at times
even in large quantity, networks of fine elastic fibres in them. Here the
amount of blood-vessels is inconsiderable. Underneath, towards the
organ enclosed, this structure passes into a loose formless connective-tissue,
the so-called sub-serous, whilst the free surface is clothed with flattened
epithelium springing from the middle germinal plate (§ 98). Theoretically,
the serous membranes were formerly held to be completely closed sacs,

TISSUES OF THE BODY.

227

which had been doubled in by the organs which they invest. But this
is by no means always the case, and only so at most in those which have
received the names of true serous sacs, among which may be reckoned the
pericardium, pleura, peritoneum, and tunica vafjinalis propria of the
testicle. The arachnoidea,
which has also been numbered
among these, has no parietal
layer.

The synovial capsules of
joints only possess also the re-
quisites of a serous membrane
on theirlateral portions, namely,
a layer of connective - tissue
clothed by epithelium, while
the floor and roof of the cavity
are formed of the naked articu-
lar cartilage.

But some other cavities, ar-
ranged also in this category,
are even more imperfectly de-
fined, namely, the synovial
bursse and sheaths of tendons.
Here we have frequently to
deal, not with a regular wall, but
with an extremely soft connec-
tive-tissue, saturated with fluid,
gradually becoming more solid
externally, instead of a distinct
cavity. But in those situations
where the sheaths and bursaB
in question are more sharply defined, we may encounter at points a simple
flattened epithelium on the con-
nective-tissue forming the walls of
the cavity.

The formation of these " true "
and "false" serous sacs is explained
by the occurrence of those cavities
in connective-tissue mentioned at
§ 98. By the formation in the
middle germinal plate of larger
hollows of this kind, which become
more and more defined, we pass
gradually from the mucoid sheath
to the true serous sac. The sub-
arachnoid spaces may be looked
upon to a certain extent as inter-
mediate forms.

The same serous exudation which
saturates formless connective-tissue
retains the surfaces of these cavities
moist and slippery. Its amount is
normally but very smalL We have already met with this fluid in greater
abundance in the form of synovia (p. 155).

Fig. 219. — Human skin in vertical section, a, super-
ficial layers of the epidermis ; b, rete Idalpighii. Un-
derneath the latter is the cerium, forming papillae at r,
and passing below into the subcutaneous connective-
tissue, in which collections of fat-cells may be seen us
A ; ff, sweat glands with their ducts, e and /; rf, vessels;
t, nerves.

Fig. 220.— Two tactile papillae of the skin freed of
epithelium. Here may be seen the connective-
tissue entering into their composition, with the
tactile corpuscles in the interior and the nerves
ending in the latter.

228

MANUAL OF HISTOLOGY.

Fig. 221. — Diagram of a mucous
membrane clothed with col-
umnar cells, a, the cells;
6, 6, the intermediate sub-
stance between their lower
extremities; c, transparent
layer or basement membrane ;
d, mucous membrane tissue
formed of fibrous connective-
substance.

§ 136.

7. Whilst the serous membranes are poor in blood-vessels, as we have

just seen, we have to deal, in considering the
cutis (fig. 219), with a structure very different
from them in this respect. The1 latter consists of
a very vascular tissue, made up of densely
interwoven fibrillated bundles of connective-
tissue, accompanied by very numerous elastic
fibres. It possesses connective-tissue and emi-
grated lymphoid corpuscles also. In the papillae
alone (fig. 220) and on the surface does its
fibrous character become less strongly marked,
giving place to a more homogeneous appear-
ance on account of the interweaving of the
filaments becoming so intimate as to get rid of
all interstices (Rollett). Here, then, we may accept the presence of a
structureless limiting layer, the so-called intermediate membrane of
Henle, or basement membrane of Todd and Bowman (comp. p. 84).
The cutis is covered by the strongest bed of epithelium in the body,
namely, by the epidermis. Further, it is rich in nerves, contains many
small bundles of smooth muscular fibres, possesses lymphatic canals,
and is traversed by the hairs and their follicles as well as the ducts of
numerous glands. Below it is continuous with the soft fatty subcutaneous
connective-tissue (fig. 219, h).

8. The tissue of the mucous membranes, which is also very vascular,
has a similar structure to that of the corium, if it do not consist, as in,
the small intestine especially, of reticular connective-substance containing
lymphoid cells. We have already considered (at § 88, 91, 93) the various
kinds of epithelium which may be found clothing it, all having their
origin from the lower or intestinal glandular plate of the embryo. The
true mucous membrane (fig. 221, d) consists of interlacing bundles of con-
nective-tissue of softer constitution and looser texture, however, than those

in the cutis. The proportion of elastic
matter here is liable to variation, but
is smaller than in the skin. Super-
ficially, as well as in the various
prominences of the tissue, e.g., in the
villi, papillae, and folds, the fibrous
character becomes fainter, so that we
not unfrequently have here, as in the
cutis, a transparent layer (c). But the
mucous membrane tissue in different
organs varies to a certain extent. In
those parts, for instance, where it is
less abundant, owing to the presence of a large number of glands lying
close together, it usually appears as a more or less streaky or slightly
fibrillated substance containing nuclei (fig. 222). On its deep aspect
it is continuous with the submucous connective-tissue, which is remark-
able in many parts, and more especially in the digestive tract, for
.s ^strong texture and white appearance, and which constitutes the
tunica nervea of older anatomists. The mucous membranes, which are in
general very vascular, possess a varying number of lymphatics and nerves.

Fig. 222.— Transverse section through the mu-
cous membrane of a rabbit's stomach. CT,
tissue of the mucous membrane ; 6, sections
of empty vessels ; c, the latter injected ; d
spaces for tiie peptic glands..

TISSUES OF THE BODY.

229

At certain points they contain no glands, but in most cases the latter
occur in such quantities that the groundwork of connective-tissue is
completely thrown into the background owing to their amount, as has
been already remarked. As an instance of such extreme richness in
glands, we may take the mucous membrane of the stomach (figs.
222 and 223). Attention has been recently directed to the occurrence
of smooth muscle fibres in many of these membranes, to which we
must ascribe considerable physiological importance. We shall refer to
this again.

9. The so-called vascular membranes of the brain and eye, the pia
mater and plexus chorioidea, and choroid, also

belong to the connective-tissues. In all these
we find a multitude of blood-vessels supported
by soft connective-tissue. The latter appears
under different forms. One of these, that of
the choroid of the eye, has been already de-
scribed (p. 219). The plexus chorioidei show
in the infant a completely homogeneous sub-
stance, in which round non-ramified cells are
imbedded. In the adult also the whole bears
in general the character of an undeveloped
streaky connective- tissue (Hdckel). In the^'a
mater, on the other hand, we have the fibrillated
form of the latter.

10. Finally, connective-tissue tunics are
found widely distributed throughout the vascu-
lar system. The. endocardium may be reckoned

among these, also the external coat of the vessels, or so-called tunica adven-
titia, and most of the middle and internal layers of the arteries, veins, and
lymphatics. Great variety is met with here, however. Together with
structures of fibrillated connective-tissue, with a larger or smaller propor-
tion of elastic fibres, are found, especially in arteries, membranes which,
without having any bundles of the former, present in a homogeneous
ground substance elastic networks alone, of either fine or coarse, or some-
times very thick fibres. They may also occur homogeneous without fibres.
Thus we find a gradual transition from connective-tissue membranes to
purely elastic ones.

11. In other parts also we encounter a preponderance of elastic
elements, with a sometimes slight, sometimes great, decrease, and at other
times almost complete disappearance of the fibrillated interstitial connec-
tive-tissue. This is the case in the various ligaments and membranes of
the larynx, the trachea, the bronchi, and tissues of the lungs. Externally
also, around the oesophagus, is found a principally elastic layer, and
connecting the latter with the tubes of the respiratory apparatus. Beside
other more limited occurrences, we may reckon also to this category the
ligamenta flava of the spinal column and ligamentum nuchce of some
mammalian animals.

§137.

All connective-tissues of the living body are, as has been already
remarked, saturated by small quantities of an animal fluid, in which we
may suppose the matters of nutrition and decomposition to be contained.
This, arriving by the blood-vessels and exuding from them, gives up its

Fig. 223.— Vertical section of the
mucous membrane of the hu-
man stomach, a, papillae of the
surface ; b, peptic glands.

230 MANUAL OF HISTOLOGY.

surplus to the radicals of the absorbents contained in the tissue (§ 82).
Unfortunately, the amount of this fluid is too small to allow of oui
obtaining it for chemical analysis, so that its composition still remains
unknown. Conclusions as to the constitution of the normal fluid drawn
from analysis of those abnormal collections met with in formless connec-
tive-tissue in oedema, appear to us inadmissible.

In the serous t=acs and cavities likewise we meet with a very similar
fluid, in varying but usually small quantity, which might be named a
watery exudation from the intercellular fluid of the blood, containing, on
analysis, albumen, extractive matters, salts, and at times also fibrin (1).
Up to the present, the only fluid contents of any of the true serous
sacs that have been examined, under completely normal conditions, are
those of the pericardium in the case of executed criminals (Gorup-
Besanez and Lehmann). The results varied. The first of these investi-
gators obtained in two cases a fluid of weak alkaline reaction and yellowish
colour.

1000 parts of pericardial fluid consist of —

1. 2.

Water, . .. .' . . 962'83 955-13

Solid constituents, . -.,< . 37'17 44-87

Albumen, . ;.. • i • 21 '62 24'68

Fibrin, . ....,;.,';. 0-81

Extractive matters, . . . 8'21 12-69

Salts, . • \i . ,.. ; .,, 7-34 6-69

Lehmann, on the other hand, only obtained 8'79 of albumen, 0'93 of
other organic matters, and 0'89 of mineral constituents, per thousand.
For synovia (comp. p. 155). The intercellular matter of connective-
tissue, together with the fasciculi of the latter, consists of a glu tin-yield-
ing material. The composition of the cells is, on the other hand, still
enveloped in obscurity, while in the elastic elements we may recognise
elastin. The intermediate substance of the cornea alone is an exception,
in that it yields chondrin. This short notice includes all that was for-
merly, and is to a great extent at present known of the composition of
connective-tissue.

In the embryonic state this tissue possesses, according to Schwann's
investigations, repeated subsequently by Schlossberger, a ground mass,
from which no glutin can be obtained on boiling, and which appears to
belong rather to the protein group. This corresponds also with investiga-
tions made on the constitution of pathologically formed immature con-
nective-tissue, so that we see a parallel between recently formed con-
nective-tissue and undeveloped cartilage (§11 2). But in that the fully
developed tissue, after it has been chemically cleansed, may be converted
to a greater or less extent into glutin by boiling, there must take place
between the embryonic period and that of maturity some transformation
of the albuminoid intermediate substance into a collagenic one. Of the
intermediate steps we know nothing, and as to the manner also in which
this change takes place we have at present but hypotheses to offer; for
we have not as yet been able, as is well known, to effect an artificial trans-
formation of the protein substances into glutin or glutinous matters. The
chemical constitution likewise of those undeveloped and not yet fibril-
lated portions of connective-tissue already mentioned has, with the excep-

TISSUES OF THE BODY. 231

tion of the cornea, remained undiscovered : the latter also in the foetus,
it appears, yields no chondrin.

The ground substance of connective-tissue remains unchanged in cold
water, alcohol, and ether, and swells up into a jelly-like mass under the
action of acetic acid, which only dissolves it to a certain extent when
warm, and after a considerable lapse of time. Potash, on the other hand,
commences to dissolve it even when cold. By boiling in water this inter-
cellular matter is converted into glutin (§ 15), but whether in toto is still
an unsettled question. The time necessary for this is liable to variation,
according to the quality of the connective-tissue on which we are work-
ing. As to the process also by which the collagenic tissue is trans-
formed into glutin, we are as much in the dark here as elsewhere. And
if in the analysis of portions of connective-tissue the same results per
cent, have been obtained as in the case of the glue prepared from the
latter by boiling, it only speaks for the imperfection of the chemical
manipulation. It is, in fact, impossible to elucidate with any degree of
accuracy the constitution of this intercellular matter, in that we possess
no means of separating it from the numerous form elements entangled in
its substance, namely, connective-tissue corpuscles, elastic fibres, &c.,
without even taking into account other accidental and unessential tissue
elements, such as blood-vessels, fat cells, &c. The substance cementing
the fibrillae together is soluble in permanganate of potash (Rollttt),
10 per cent, solutions of common salt and in baryta and lime water; these
take up from tendinous tissue an albuminous substance giving the reactions
of mucin (Rollett).

The composition also of connective-tissue corpuscles is but to a small
extent known, on account of our being obliged to base almost all our con-
clusions on microchemical reactions. Their nuclei show the usual resist-
ance to acetic acid, and the protoplasm — it appears in the tendon-cells of
the mature body to be reduced to a minimum — though it may become
greatly changed by the action of water alone, still offers to that of acids
considerable opposition. Jt holds out against concentrated mineral acids
for a period in which the connective intermediate substance is softened
into a pulp or dissolved (2). Hot solutions of potash, on the contrary, dis-
solve the whole cell rapidly, and are thus of importance in the demonstra-
tion and diagnosis of elastic elements. The latter only admit of nearer
investigation in those parts in which they are met with in great prepon-
derance, as in the ligamentum nuchse, and to this is due the slight
acquaintance we possess with elastic matter in general (§ 15).

Those homogeneous elastic membranes of large vessels already discussed
(§ 127), as well as the structureless intermediate substance of many elastic
fibrous networks, resemble in their microchemical bearing ordinary elastic
fibrous tissue. The homogeneous envelopes of certain of the connective-
tissue bundles appear still to consist of glutinous substance, in that they
give way to the action of caustic alkaline solutions, while in other
instances they are decidedly composed of elastic material (comp. § 128).
The transparent limiting layers of connective-tissue membranes likewise
are liable to the same variation in composition. Descemefs membrane ori
the cornea is elastic, while the anterior transparent lamina of the latter
and the basement membranes are of glutinous nature.

These facts just stated are, however, of interest in another way. They
show that elastic matter represents a product of the subsequent transfor-
mation of glutin-yielding intermediate substance, and, moreover, of that

16
•

232 MANUAL OF HISTOLOGY.

form from which collagen as well as chondrigen is produced : comp. what
has been already stated in regard to elastic cartilage (§ 108).

Analysis of organs wholly formed of connective-tissue has been
undertaken comparatively rarely up to the present. The proportion of
water in the tendons amounts according to Chevreul to 62 '03, in the
cornea to 73-94-77*82 per cent. (His). The latter has, therefore, 26*06-
22 '18 of solid matters, of which in one case 20*38 were converted into
glutin 011 boiling, and 2*84 was found to be made up of organic non-
glutinous substance. The latter may be referred to the corneal cells and
their processes, as well as the membrane of Descemet. Together with
these were found besides 0*95 per cent, of mineral constituents, of which
0*84 were soluble in water.

REMARKS. — 1. According to A. Schmidt "fibrinogen" is almost always one of the
components of such exudations. 2. We can thus isolate connective-tissue passages
with their terminal layers, and remains of cells in the interior, by means of sulphuric,
hydrochloric, or nitric acids. Prolonged boiling also in alcohol acidulated with
hydrochloric acid, and subsequent maceration in water, leaves the protoplasm of
the cells still remaining, while the interstitial substance undergoes solution, and the
elastic fibres crumble up.

§ 138.

Connective-tissue forms a large part of the ordinary investing and sus-
tentacular substances of the body. It connects organs with one another,
envelopes them, and fills out interstices between them and between their
divisions : it fixes parts against one another, forms passages for vessels
and nerves, and cavities for collections of fat cells, &c. This so widely-
distributed tissue, then, comes under our consideration, as regards its
physical properties, mainly for the building up of our body. Loosely
interlaced as regards its fasciculi, connective-tissue presents itself in the
form of a yielding extensible substance. But, on the other hand, we usually
encounter a more dense and intimate interweaving of its fibres, especially
in formed connective-tissue; so that a greater or less degree of solidity is
attained, as opposed to the extensibility of that formless species. The
plentiful occurrence in it of elastic elements has also a great influence on
the physical qualities of the tissue.

On the other hand, we encounter structures formed of connective-tissue
which play a part in the chemical processes of the system, owing to their
great vascularity or abundant exudatory activity, as, for instance, the
skin and mucous membranes. This depends, however, properly speaking,
upon the contained blood-vessels.

It is usually supposed, though without sufficient data for proof, that
the transformative capacities of connective-tissue in regard to the matters
passing through it are in general but small. We are led to infer this by
the passive part which the tissue takes in the assimilative revolutions of
the body, or its slight inclination to decay, and by the poorness in vessels
of many parts formed of it.

This interchange of matter, however, be it great or small, is still
completely veiled in obscurity as regards its nature. The fact that
glycin and leucin (§ 35 and 31) are products of the artificial decomposi-
tion of glutin, while elastic material yields the last of these only, may
give us some slight point to hold by in the present helpless state in
which we find ourselves.

Some years ago, from the connective-tissue theory of Bonders and
Virchow, an idea sprung up that the cellular networks of its cor-

TISSUES OF THE BODY. 233

puscles, supposed to be supplied with, membranes, constituted a hollow
system of canals, like that to be met with in bone, for the con-
ducting of certain definite nutritive fluids through the tissue, forming
thus a,plasm,atic circulation. Eased on this view, the name of sap canali-
culi was given by Koelliker to these passages. But there was no phy-
siological necessity for supposing that this must be the case in connective-
tissue, in that it does not occur in cartilage. Besides, the system of
interstices in parts formed of connective-tissue would appear but little
suited for the fulfilment of such an object, frequently stopped as they
are by cells, and compressed by the intermediate substance. Communica-
tions between these interspaces and the vascular systems do not occur,
either with the blood-vessels or lymphatics, although this erroneous doc-
trine still permeates histology.

The question now arises, which of the elements of form are to be
looked upon as physiologically the most active and important in con-
nective-tissue masses 1 Here also as anatomically the decision must be in
favour of the cells, so long as the latter possess even a small remnant
of their body. On the other hand, connective-tissue structures, in which
the cellular elements no longer exist, and where alone dense networks of
elastic fibres remain, must be looked upon as tissues endowed with a
minimum amount of life ; for instance, the ligamentum nuchae.

Among the transformations of senescent connective-tissue we must now
bestow a few words on calcification, occurring in a similar manner to that in
cartilage, and by no means rarely. Bony tissue may likewise take the
place of the former, but much more seldom by direct transition of one
tissue into the other as by a neoplastic process, corresponding to that
which takes place in the embryo, where the newly-produced bony mass
takes up the place of the vanishing connective- tissue. We shall be
obliged to refer again to this question in considering osseous tissue.

We are now met by another difficult question, namely, how far con-
nective-tissue cells may become transformed into the elements of other
tissues not belonging to this group. It appears plain that, with their
power of vital contractility, no great distinction can be made between
them and the cellular elements of unstriped muscle. And yet there
have been long and indeterminable controversies as to what are muscle
and what connective-tissue cells in certain organs, e.g., the lymph glands
and the ovary. We have already stated (§ 98) that the so-called endo-
thelia must take rise from the cellular elements of connective-tissue. On
the other hand, there appears to be no transition into the cells and
offspring of the corneous and intestinal glandular plates, and there seems
further (if we except the neuroglia and many portions of the higher
organs of sense) to be no true connection between these tissues. It
is true that such intercommunication has been frequently asserted to
take place, as, for instance, in the intestinal villi by Heidenhain. Here
long processes of the cylinder-epithelial cells are stated to be united
with those of the connective-tissue corpuscles of the sustentacular sub-
stance of the villus. These statements have not, however, been corrobo-
rated.

The contractile and wandering lymphoid cells of connective-tissue have
been already dealt with in a former section. That they generally take
their rise from the derivatives of the middle germinal plate in enormous
numbers there can be no doubt.

It is a striking fact, ascertained by Virclww, that connective-tissue,

234

MANUAL OF HISTOLOGY.

Fig. 224. — Pus corpuscles in the
interstices of tendinous tissue;
from the tendo Achillis of the
rabbit.

which usually appears so quiescent and indifferent in the adult body,
displays during pathological processes a new and mighty vigour of

growth.

Simple inflammatory irritation alone gives rise to a rapid swellmg-up
of the cells contained in the interstices of the tissue. In the dull proto-
plasm of these we may remark division of the nuclei also, in non-vascu-
lar parts like the cornea, as well as in vascular structures (Strieker and

NorrisY

We have already seen (p. 129) that pus corpuscles (lymphoid cells)
may frequently accumulate in the passages and
interstices of connective-tissue (fig. 224) in
great quantities, owing to such irritation, arriv-
ing there partly from the circulation. But others
originate in the tissue itself; and it has been
by some maintained now for many years, with
the utmost certainty, that the parents of these
are the connective-tissue corpuscles.

But the mode of this origin requires nearer
investigation than it has as yet received. It is
possible that the membraneless connective-
tissue cell may divide into these lymphoid ele-
ments by simple or double nuclear segmenta-
tion.

Owing to its wide distribution throughout the
body, connective- tissue plays the most important
part in pathological neoplastic processes. Loss of substance in the organs
of the middle germinal plate is replaced by it (cicatricial tissue) just as it
may take the place physiologically of degenerated organs. Luxuriant
growth of this structure causes an increase in quantity of the sustenta-
cular substance of glands and other parts, as well as thickening of mem-
branes, and so on. Numerous new formations, in the form of tumours,
from the simple wart up to the supporting tissue of the most dangerous
cancerous growths, consist of it. Tumours consisting of pure connective-
tissue, with a more or less dense texture, have been given the name
of fibromas. The starting-point of these is in most cases ordinary or
physiological connective-tissue, with an undoubted participation of
lymphoid cells.

The appearance of such a pathological connective-tissue is very vari-
able. Beside the most fully developed texture, such as only formed con-
nective-tissue can show, we meet with structures of a softer species allied
to the so-called formless kind. We encounter also appearances such as
are presented by the young embryonic tissue. Thus, wherever a rapid
development of the tissue is taking place, soft fusiform and stellate cells
in close juxtaposition are observed, or there may be merely round and
very primitive elements with scanty intermediate matter to be seen. It
appears, also, that nucleated formative cells without a membrane may
coalesce owing to their abundant protoplasma, forming more or less homo-
geneous multi-nuclear masses. This must have been the origin of the
many alleged exudations with spontaneous generation of nuclei spoken
of in former days. We leave the rest to the hand-books of pathology,
and pass on in the next section to the origin of the tissue.

TISSUES OF THE BODY.

235

§ 139.

The first indication of the formation of connective-tissue is the
appearance at an early foatal period of delicate embryonic cells (fig. 44,
p. 66), crowded together, without any membrane, and
containing vesicular nuclei. These are held together by
a small amount of an albuminous intercellular substance,
so that connective-tissue and cartilage commence both of
them with extremely similar primary forms. This first con-
dition of rudimentary connective-tissue, however, is only
very transient.

The further transformations take place with equal
rapidity, and are of different kinds in the various connec-
tive-tissue structures. If these remain poor in blood, as,
for instance, the tendons, the cells preserve their original crowded position,
but become fusiform (fig. 225). If, on the other hand,
they become vascular, as is the case with subcutaneous
cellular tissue, an outpouring of a plasmatic fluid
containing albumen and mucin takes place : the
formative cells separate from one another, and assume
frequently stellate figures (fig. 226).

But even already all these cells have undergone
metamorphosis. Their processes have broken up into
a number of the most delicate fibrillse, which are at first straight, and
contain abundant granules of protoplasm between them. Later on the
latter withdraw more towards the middle of the cell, and the original cell-

Pig. 225.— Fusi-
form cell s from
embryonic con-
nective-tissue.

Fig. 226.— Stellate cells
from the same.

Fig. 227. — Soft connective-
trssue from the neigh-
bourhood of the tendo
Achillis of a human em-
bryo of two months old.

Fig. 228. — From the tendo Achillis of a pig
embryo 8" long. A, the fusiform cells
and their fibrous intermediate matter in
profile; B, transverse section (spirit of
wine preparation).

body diminishes to a corresponding degree in volume. The fibrillae
then assume gradually a more and more wavy character, and are con-
verted into an ordinary bundle of connective-tissue fibrillse (the interstitial
molecules disappearing at the same time) (Breslauer and Boll), or into
single fibril (Kutznetzoff and Obersteiner). From personal observation we

236

MANUAL OF HISTOLOGY.

are inclined to accept this as the correct view, although Rollett supposes
the connective-tissue fibres to have their origin independently of the cell.

The fasciculi, according to this, spring from the metamorphosis of the
original cell-body, or, if we prefer an expression of M. Schultzds, are pro-
duced by "the formative agency of the protoplasm."

We refer the student to figs. 227, 228, 229, and 230, almost all of
which apply to the development of solid connective-tissue masses poor in
blood-vessels and intermediate fluid.

Such appearances were known long ago to Schwann, who interpreted
them quite correctly. Later on the connective-tissue fibrillse were sup-
posed to be formed by a metamorphosis of the intercellular substance, — a
theory for which at last even Koelliker declared himself.

At the present day, when the absence of an envelope on the connective-
tissue cells is looked upon as certain, and the intercellular substance is
regarded as at least in many cases a metamorphosed external part of the
cell-body, as in cartilage (p. 167), the relationship of the cell-body to the
fibrillae appears again such as indicated by Schwann.

From the length of mature connective-tissue bundles, it may be inferred
that the fibrillae of adjacent cells unite in a longitudinal direction in their
formation (Boll).

"We turn now to the inquiry, what is the further destiny of the so
much impoverished formative cell of connective-tissue 1

It appears to vary in different ways.

In some cases this cell persists, separates from its product the fasciculus,
and is transformed into that frequently flattened, sometimes smooth-edged,

Fig. 229.— a, Fusiform,
apparently forma-
tive cells of connec-
tive-tissue fasciculi ;
ft, cell-body and
flbrillar substance
still distinguishable.

Fig. 230.— A fusiform
cell from the tendon
of an embryonic pig
8 inches long, a, a
cell with protoplasm ;
b, connective - tissue
fibrillse (spirit of wine
preparation).

sometimes jagged element with which we have become acquainted through
the investigations of Kuhne, Ranvier, Flemming, and JBoll, as the cell of
mature connective-tissue (comp. § 129).

Again, the nucleus remains behind with a small (fig. 230) or frequently
almost imperceptible residue of protoplasm. This is the case in those
connective-tissue structures we have already considered, in which appa-
rently naked nuclei are met with in the fibrous mass (§ 132, for instance.)

Thirdly, the nucleus seems, in some cases, to disappear early with its
scanty remainder of protoplasm, by commencing fatty degeneration (Boll),

TISSUES OF THE BODY.

237

so that we may only meet with fasciculi intermixed with elastic elements,
but without a trace of the original formative cell (comp. fig. 201-203).

We must still leave it an open question, whether lymphoid cells which
have wandered out of the foetal blood-vessels may not be transformed
into formative cells of connective-tissue. It seems, however, probable.

The mode in which elastic fibres have their origin, though compara-
tively easy to observe, has been long a subject of controversy. And
although the manner of their separation from the interstitial substance
remains up to the present completely unexplained, still there can be no
doubt that they originate independently of the connective-tissue cells.

In § 136 we spoke of the ligainentum nuchse of the adult mammal as a
mass abounding in elastic fibrous networks, and in which no corpuscles
are to be found. Now, it was from this tissue in question that Muller,
and subsequently Henle and Reichert, obtained proof of this.

If we examine the ligamentum nuchae of very small foetuses, we observe
the same to consist of numerous spindle-shaped cells arranged longi-
tudinally, and of an intermediate substance with-
out any elastic elements. Later on (fig. 231, A),
we recognise exactly similar fusiform cells, with
considerable sized nuclei and short pointed ex-
tremities (a). Between these there appears an
indistinctly fibrous matter (ft). Even here
nothing is seen of the elastic elements until
the whole has been treated with boiling potash
(B), when the cells are destroyed, and a net-
work of extremely fine elastic fibres becomes
visible.

If we continue our research on older embryos,
we find these fusiform cells becoming thinner and
longer until they gradually disappear. In the
new-born animal only traces of the latter are to
be seen. The elastic networks increase in density
in the same proportion, and their fibres in
strength. The bundles of connective-tissue also
become more apparent in the ligamentum nuchae
(Koelliker).

The above sketch of the development of con-
nective-tissue will, no doubt, receive, through
continued research, many additions, the more so
as our acquaintance with the subject must be
looked upon as being merely in its commencement.
If we inquire into the mode of appearance of
connective-tissue in the body, we find that it
may be classed into a primary and secondary.
The primary is from a metamorphosis of the cells
of the middle germinal layer. The secondary,

also from the same embryonic layer (never from the corneous and'
intestinal glandular leaf), takes place usually from other members of
the connective-tissue group, most probably from lymphoid corpuscles.
As an instance of secondary formation of connective-tissue, we may
cite the process of the production of bone to be described in the
following section.

In pathological novogenesis, also, the formation of the tissue takes

B

Fig. 231. — From the ligamec-
tum nuehse of an embryonic
pig 8 inches long. A,- la-
teral aspect; a, fusiform
cells in fibrillated ground
substance, 6; 5, elastic
fibres, c, rendered visible by
boiling in potash. (Spirit of
wine preparation.)

238 MANUAL OF HISTOLOGY.

place in the same manner as has been described above for the normal
structure. But that many subordinate peculiarities may make themselves
evident here must be granted.

REMARKS.— We should be obliged to overstep the bounds of a work of this kind
by a great deal did we enter more minutely, or in a manner which could be regarded
to any extent as exhaustive, upon this still unsettled question as to the origin of
connective-tissue. In the year 1839, its mode of origin was held by Schwann to be
the following : — Cells, originally spheroidal, took on the fusiform figure, and, becoming
further elongated, underwent a splitting up of their substance into fibrillse, com-
mencing at their extremities, thus giving rise on the metamorphosis of the latter
into the so-called bundles of connective-tissue. As to the destiny of the nuclei of
these formative cells, it remained unexplained, and the development of elastic fibres
from other cells was looked upon as probable. Henle, however, appeared soon after
as propounder of a new theory of origin, in consequence of renewed investigation.
According to his view, connective-tissue consists of an originally nucleated blastema,
in which the nuclei are arranged with regularity, and the ground substance splits up
into bands following their direction. By a fibrillar metamorphosis of the latter, the
ordinary fasciculi are produced. At the same time, the nuclei are supposed to become
elongated into fusiform bodies, which may subsequently unite, forming fine elastic
fibres (Kernfasern). No personal investigations have been published by him as to
the formation of the larger elastic filaments. In 1845, Reichert brought out a very
important work for the history of connective-substance. In this he taught that between
the original cells of embryonic connective-tissue an intercellular matter gradually
makes its appearance, the former coalescing with this to form a homogeneous mass,
so that in that the nuclei are still recognisable ; we have arrived at about the same
starting-point as that maintained by Henle. Later on, the nuclei were supposed by
him to disappear in part, while the occurrence of fusiform cells was denied, and the
objects which had been held to be such, were declared to be (together with the fibrillse
of connective-tissue) artificial products, as already mentioned. Elastic fibres were
regarded as transformations of the ground substance. In the year 1851, however,
there came a turning-point, through the works of Virchow and Danders. These
investigators demonstrated, with the scanty aids to research of the time, in the first
place, the persistence of nucleated cells, and laid, with perfect justice, the chief stress
on these elements of the tissue. They fell, however, into a dangerous error in regard
to the origin of elastic fibres, in that they supposed the latter to take their origin
i'rom a change in these cells. According to both observers, the latter never take the
form of connective-tissue bundles, but enter into the construction of stellate and
fusiform corpuscles, which may unite to form elastic tubes and fibres. The latter, as
a rule, have origin only from such cells (a point long defended by Koellikcr). True
connective-tissue is intercellular substance. This view, supported by Virchow and
Donders, was at once attacked by Henle in the most determined manner ; the stellate
cells were declared to be the transverse sections of interstices between the bundles of
connective-tissue, and the whole to be an optical illusion. Now, although Henle, we
must confess, has in many respects gone too far, still he is entitled to praise for
having directed attention to errors in the theory just mentioned as that of Virchow
and Donders. On the other hand, this new theory, sometimes unchanged, and some-
times with greater or less modification, was received (and further developed by
observation of the normal as well as diseased tissues) by a number of new adherents of
the two men just named. The formation of bundles of connective-tissue from cells,
in the sense in which Schwann spoke of it, has only been supported (among men of
any note) by Koelliker, up to the year 1861, when he too gave it up ; all others
have regarded the fasciculi and fibrillse as metamorphosed intercellular substance.
Again, a new era was initiated by a paper by M. Schultze in Reichert and Du Bois-
Jtcymond's Archiv. 1861, p. 13. In this he proclaimed the formative cell of connec-
tive-tissue to be membraneless, like other young cells.

•

10. The Tissue of Bone.

§140.

Bony or osseous tissue is a member of the group of ' connective-
substances, by no means springing in the first instance and immediately
trom the cells of the middle germinal plate. It is rather formed

TISSUES OF THE BODY.

239

d

secondarily from metamorphosed descendants of cartilage or connective-
tissue cells, and may therefore be regarded as the most complex
structure of this group. It consists of a network of stellate ramifying
spaces containing cells, and an abundant intermediate substance of homo-
geneous nature. The latter is remarkable for its extreme hardness and
solidity, and renders the whole the most resistent of all the more widely
spread tissues. Its specific gravity in the compact substance of hollow
bones is 1-930; in the spongy, 1-243 (Krause and Fischer). As the
name expresses, the occurrence of this tissue is in the human body normally
confined to the bones, if
we except a thin coating
on the roots of the teeth.
Its distribution, however,
among the vertebrates, pre-
sents considerable variety.

As is well known, bones
are divided by anatomists
according to their form, —
into the long or cylin-
drical, the flat or tabular,
the short or irregular.
Again, in accordance with
their texture, — into the
compact (in which the
tissue has the appearance
of a solid continuous
mass), and the spongy or
cancellated, in which the
osseous substance, occur-
ring in the form of bands
and plates, encloses a sys-
tem of cellular intercom-
municating cavities. The
cylindrical bones display
a compact texture, except
in their terminal portions
or epiphyses, whilst those
belonging to the short or
irregular class are formed
of spongy tissue, with the
exception of their super-
ficial layers. In tabular
bones we encounter
spongy substance or dip-
Ibe clothed externally by
laminse of a very hard
tissue known as vitreous
layers (Glastafeln).

The great hardness of osseous tissue does not admit of the usual
methods of examination being applied to it, and we are obliged either to
have resource to plates which have been sawed out and ground thin, or
we must extract from the tissue its solid mineral constituents, after which
the decalcified remainder (bone-cartilage, as it has been inappropriately

f

Fig. 232. — Perpendicular section through a human phalanx.
At a and 6, two medullary canals with branches, c and d; «,
the orifices of canaliculi appearing as dots; /, osseous cells
filled with air.

240

MANUAL OF HISTOLOGY.

named) or ossein permits of being cut up owing to its cartilaginous
consistence.

In vertically cut plates of compact substance from long bones (fig.

227) we may recognise the following
points. The whole is traversed by a
system of canals formed of longitudinal
passages connected in a reticular man-
ner with one another (a, b, c. d\ and
having an average diameter of 0*1 1 28-
0*0149 ram., with extremes on both
sides. These run more or less parallel
with one another, separated by in-
tervals of about 0-1128-0-2802 mm.
At certain intervals also connecting
tubes are seen passing between these at
one time directly transverse, at another
rather more obliquely. If the section
include the whole thickness of the
bone, some of these canals may be
observed • to open freely into the
medullary cavity internally, as well as
externally towards the periosteum,
widening as they do so into funnel-
shaped orifices.

Towards the ends of the long bones,
in the neighbourhood of their articular
cartilages, certain bends in the course of
the medullary canals may be observed.
This system of passages is destined for
the adm ission into the bone of the blood-
vessels necessary for its nutrition. The
passages themselves are known by the
nameofHaversian or medullary canals.
Transverse sections, as fig. 233, have
of course quite a different appearance.
Here we see, at corresponding dis-
tances, the severed ends of the longi-
tudinal canals in the form of rounded
apertures (c, c} ; or should the section
have been made somewhat obliquely,

of more or less oval deficiencies of substance. Again, if the cut have
fallen in the plane of one of the transverse intercommunications between
two such canals, the latter appear as round holes connected by an open
slit. Intermediate forms occur also as a matter of course.

This beautiful regularity, however, presented by the central portion of
a long bone, is more or less at an end in other than compact osseous
tissue. In the external crust of tabular bones, the Haver sian canals
generally run in a direction parallel with the surface; in most cases also
radiating from a central point. In the short bones also there is usually
one preponderating direction in their course.

In the bands and septa of spongy osseous tissue, this system of
medullary canals is far less strongly developed, the latter frequently
opening into the cancellous spaces with funnel-shaped enlargements.

Fig. 233.— A portion of a human metacarpal
bone in transverse section, a, external, 6,
internal, surface with their respective gene-
ral lamellae ; c, transverse sections of Haver-
rian canals surrounded by their special
lamellae; d, intermediate lamellae; e, bone
corpuscles with their ramifications.

TISSUES OF THE BODY. 241

Several Haversian canals may often be seen also uniting with their enlarged
ends to form a small medullary cavity, between which and the larger
kind many intermediate forms exist.

REMARKS. — Beside the German works on the subject, compare Tome's article,
" Osseous Tissue," in the Cyclopedia of Anatomy and Physiology, as well as the
excellent treatise of Tomes and De Morgan in the Phil. Transact, for the year 1853,
part i. p. 109.

§141.

The hard homogeneous osseous tissue between these Haversian canals
has a laminated structure, explained by the mode of origin and formation
of the mass in successive portions. These lamellae are united in the most
intimate manner with one another, but may be separated in macerated
bone which has been deprived of its mineral constituents.

The systems of laminae, however, are of two classes. In one of
these the leaves affect the whole thickness of the bone, in the other
they are arranged round the individual Haversian canals. We may
designate the first as general or fundamental, the others as special or
Haversian lamellae.

Nowhere can this be better seen than in a transverse section of the
middle portion of a hollow bone, such as we have in fig. 233. The
general lamellae are here distinguishable as a system of concentric layers
traversing the whole thickness of the piece : commencing internally (b)
around the central medullary canal of the bone, whose walls they form
(medullary lamellae) ; then usually less distinct in the middle portion (d),
with numerous interruptions (intermediate lamellae), and on the other
hand appearing in the most distinct manner again externally towards the
periosteum (d) (periosteal lamellae). Of course these stratifications belong
to one and the same system of lamellae. The number and the thickness
of the individual leaves is subject to variation. The latter amounts to
0'0077-0'0156 mm. and upwards. The special lamellae surround the
Haversian canals in varying number — from 6-18, with extremes in both
directions (c). Their thickness is, on an average, 0'0065-0'0127 mm.,
and their arrangement is, as a rule, more or less concentric, the most
internal of them constituting the walls of the Haversian canals. The
latter are not unfrequently situated eccentrically in their systems of
lamellae. Should this be the case to any great extent, the latter may be
incomplete towards one side, and it occasionally happens also that the
systems of two Haversian canals are enclosed again in secondary lamellae
(Tomes and De Morgan). The strength of these systems further round
the canals is very variable. Those of the latter, which have a medium
calibre, usually possess the strongest. In the heavier cylindrical bones
of the human skeleton, the Haversian canals usually lie so close
together that their concentric lamellae almost entirely obscure the inter-
mediated ones ; not so, however, in the smaller bones of the metacarpus
and fingers, where the distance between them remains greater, as is the
case generally among other mammals.

If we prepare a longitudinal section of the compact substance of a long
bone, the extended network of the Haversian canals will be seen sur-
rounded by lines running parallel with their contour, and at the same
distance from one another as those concentric ones of the transverse
section. Thus the lamellae appear to be a system of tubes of consider-
able length, disposed one within the other, and placed, as a rule, per-

242 MANUAL OF HISTOLOGY.

pendicularly, only that the horizontal passages of communication are
enveloped by corresponding lamellae. The latter may be best seen,
though seldom, in the horizontal canals occurring in transverse sections,
cut through in their length.

In other parts of the skeleton this beautiful regularity is less marked.
Thus we see, even in the epiphyses of the cylindrical bones, that these
systems of lamellae are much less developed, that the medullary canals
are enclosed within an inconsiderable number of the latter, while the
more internal general lamellae are entirely missing. In spongy osseous
tissue the laminated texture is rather more apparent in thick bands and
plates, while it disappears more and more as the latter diminish in volume.
In the outer layers of flat bones the general lamellae, as well as the Haver-
sian canals with theirs, run parallel to the surface. The same may be
remarked with both systems in the compact layer covering the short bones.
The great energy of the formative process in young bone often effects a
re-solution of already perfect tissue, commencing in one of the Haversian
canal-systems (fig. 234, a). This produces irregularly-bounded cavities of
varying size, with eroded edges, and lamellae appearing as though gnawed
away at points. Tomes and De Morgan, who first directed attention to
this, have given to these the name of "Haversian spaces-."

S: £7 Transjers« section of a human phalanx. «*, 7/aversian system of the ordinary kind
a a two others which have undergone re-absorption in the interior (b b) thus giving rise to Ha
Persian spaces, which are filled anew with lamella; c, another such system in *vhich re absoS

Such a cavity may be subsequently filled up by a new system of special
lamellae, its characteristic outline nevertheless betraying its origin (b b}
Indeed, as I myself saw, some years ago, in a human phalanx, one of these
systems ^occupymg an Haversian space may undergo re-absorption for the
second time from the centre, with a tertiary formation of concentric lamellae
n its interior (c). Haversian spaces of this kind are of no very rare occur-
rence When present in large number, they may impart to the bone con-
siderable irregularity of texture.

§142.

Osseous substance, which may be numbered among the double refract-
in- tissues, as the polarisation microscope teaches, has a rather homoge-

TISSUES OF THE BODY. 243

neous, but by no means very transparent appearance : it is, on the con-
trary, tolerably dull and opaque. If we -employ very strong magnifying
powers, we remark at times, with tolerable clearness, a finely-dotted ap-
pearance in the mass. Owing to this, many histologists (Todd and Sow-
man, Toiiies and Koelliker) look upon the texture of the tissue as being
granular, which is denied by others (Henle and Gerlacti). It appears
more than probable, however, that the transverse sections of the finest
of the canaliculi, though they do not entirely produce this appearance,
do play some part in it.

In transverse sections, likewise, we may distinguish on every Haversian
lamella, with more or less distinctness, an external and more deeply shaded,
and an internal and much lighter part — a difference the significance of
which is doubtful.

Attention has been directed rather recently to a peculiar system of fibres
in the ground-mass of osseous tissue, namely, to the perforating fibres of
Sharpey (fig. 235), (Sharpey, H. Muller, Koelliker (2), Gegenbaur). They
are to be found in human bone and that of other mammals, but more
frequently still in that of amphibia and fishes, appearing with a certain
irregularity and variableness.

Those systems of lamellae which are formed by the periosteum, namely,

the general lamina), as well as
the more superficial of the Ha-
versian system, are pierced by
the fibres in question, sinking
into them from the perios-
teum " like the leaves of a
book by a nail which has been
driven through them." They
are frequently enlarged at one

Fig. 23-5.— Sharpens fibres (6) of a penosteal lamella, from prifl into a fimnpl <*har»p "hut
the human tibia, a c, osseous cell-cavities. nnel snaPe> Dut

may also be pointed or branched ,

&c. In certain localities they enter into the construction of a network, some-
times wide and sometimes narrow, in its meshes. In the hollow bones of
amphibia and mammals (fig. 236) this system of fibres consists of longitu-
dinal columns (b b), from which radiating systems of branches (cc) pass off,
piercing the lamella in the direction of the periosteum, as well as towards
the Haver sian canals.

In the substance of these fibres, but especially in their nodal points, we
may encounter osseous corpuscles. Sharpens fibres are connected with
the periosteum; they are the residue of connective-substance, i.e., of
bundles of connective-tissue dating from the period of the formation of
those lamellaB. The cells contained in their cavities have the significance
of connective-tissue corpuscles also (Gegenbaur}. The chemical bearing
also of these mostly calcified fibres agrees likewise with this view. In
keeping with their origin from the periosteum, they must be absent in the
systems of leaves, filling up the Haversian spaces (fig. 234).

The most important elements of osseous tissue, however, are the cells
of the latter, imbedded in it in the greatest abundance, and situated in
the enlarged and radiating nodal points of a highly-developed system of
canaliculi traversing the hard osseous substance.

With these, therefore, we must occupy ourselves before passing on to
anything else.

This system of canals, whose finer branches are called canaliculi (Kalk-

244

MANUAL OF HISTOLOGY.

kanalchen), while the wider spots or nodal points bear the name of lacunae
(Knochenhohlen), was formerly held to be the source of deposit of the bony
earths — an erroneous view, which has perpetuated itself in one of the
names just mentioned.

The lacuTwe (fig. 237) appear in fresh moist bone as oval lenticular

Fig. 236.— Transverse section of the metatarsus of an ox (after
Gegenbaur). a, Haversian canals; 6, transversely cut columns of
Sharpens system of fibres, whose branches, c, are partly in con-
nection with osseous corpuscles.

cavities, sometimes short and at others more or less elongated, lying with
one broad surface towards an Haversian canal. They have a transparent

Fig. 237.— Transverse section of a human bone, a 6, two divided Haversian
canals, surrounded by special lamelhe c d; #,/, the general lamellae.

appearance, and vary considerably in figure. In length they range from
0-0181 toO-OSHmm, in breadth from 0-0068 to 0-0135 mm., and in

TISSUES OF THE BODY. 245

thickness from. O0045 to Q'0090 mm. In transverse sections they usually
lie in the middle of the lamellae, at times also between the same, with
their long axis parallel to the limiting edge of the lamella. General and
special lamellas display but little difference in this respect. The processes
of the lacunas, fine tubules of 0 '00 14-0 '00 18 mm. in diameter, can only
be followed up for a short distance, when they disappear in the ground-
substance.

But we gain a far more perfect insight into the arrangement of
these lacunas and canaliculi from sections of dried bone, in which the
former are filled with air, and are brought out with great sharpness,
appearing dark or black with transmitted and white with rejected
light, and constituting now the most striking form-elements in micro-
scopical investigation of the tissue, catching every eye (figs. 232,
233, 234, 237). From these jagged lacunte the canaliculi take their
rise in enormous numbers; traversing the ground-substance in an
irregular radiating course, and with many ramifications, and inosculat-
ing in great numbers with the processes of neighbouring lacunas. The
canaliculi likewise of one system of lamellae may pass over into another
adjacent to it.

If we follow up these fine passages in a transverse section (fig. 238, «),
we see them in the first place converging
towards an Haversian canal, and opening into
the latter (&). Again, we can easily make out,
in the internal general lamellae bounding the
great medullary canal, the orifices of other
canaliculi, and also in the peripheral periostea!
leaves a third mode of exit externally under
the periosteum.

In longitudinal section (fig. 232), we see
the lacunae surrounding the medullary canals
and some of their processes opening into the
latter in a more or less horizontal direction.
Those spots are specially instructive at which ^v ''

thp wall nf an 'RmiPrtinrt panal i«s pYnnQprl Fi&- 238.— Lacunas (a, a) with their
01 an Uaverbian Canai IS exposed numerous ramifications opening

Which has been Opened longitudinally. Here ™tO a transversely-cut Haver$ian

the numerous orifices of the canaliculi may be

observed, giving to the surface a dotted appearance (fig. 232, e). The other
bones also show the same relations as those just described, with very many
modifications of course as to number and position.

A glance at this so highly developed system of lacunas and canaliculi,
with its multitude of free openings, explains the fact that a thin section
of bone rapidly fills with air on drying, and on being subsequently
placed in oil or very liquid Canada balsam, that the air is again dis-
placed by the latter. It is an object well worthy of microscopical
examination this gradual expulsion of the air by the advancing oil. In
microscopical preparations put up in Canada balsam, we have not
unfrequently an opportunity of observing both conditions of the lacunae
and canaliculi. At one point we see the air retained, at another it has
been replaced by the Canada balsam. The whole may be injected
likewise with coloured liquids (Gferlach).

The question as to whether the walls of this complicated system of
canals are formed of a substance differing from the remaining ground-
mass, or whether the system merely represents a series of lacunae

24G

MANUAL OF HISTOLOGY.

possessing no regular internal layers, is one which has been frequently
discussed^ but not yet conclusively answered.

A method of isolating from the ground-mass by means of alkalies or
concentrated mineral acids, a something corresponding to these lacunae
and canaliculi, has been known for many years past. The structures so
laid bare have been looked upon by some as being a soft cellular net-
work, by others as made up of the lining layers just mentioned of the
system of canals.

And not alone from fresh bone do we succeed in isolating the reticular

mass in question, but also from that in which all the softer tissue must

have been destroyed by maceration ; even in bony masses which have

been made use of for turning, it may be

/ separated, as Neumann has shown ; so that

w^ ••* ^A^J^ ^or our own Par^ we mus^ Declare ourselves

K*V on the side of those who maintain the exist-

jf[ yfmjr-l> ence °f an independent calcified wall.

\ We have now taken a survey of the canali-

sation of bony tissue, but have not yet become
acquainted with the cellular elements imbedded
in the lacunae. These " bone-cells," as they are
called, were for a long time overlooked, owing
to the practice so much in vogue amongst
former anatomists of examining principally
macerated osseous structures. But after some
earlier observers had given it as their opinion
that nuclei were to be seen here and there in
the lacunae, general attention was directed to
the cells of osseous tissue by Vircliow.
And, indeed, it is a matter of slight difficulty to obtain bodies re-
sembling cells from structures belonging to this class. For this purpose
we make use of fresh bone (fig. 239), which has been either simply
macerated in hydrochloric acid or subsequently boiled ;
or, better still, which has been boiled for a short time
in a solution of soda after having been previously treated
with the acid just mentioned. In the now soft and
almost liquid intercellular substance (6) we see struc-
tures similar in form to the figures of the pre-existing
lacunae, with shorter or longer processes, definite walls,
and each with an oval or elongated and more or less
sharply defined nucleus, and measuring on an average
0*0074 mm. The most striking objects are to be
obtained by cautiously squeezing and moving the
glasses between which the tissue is placed, when some of the cells may
be freed from the intercellular matter clinging to them (a-d).

These " isolation products " were regarded by some as stellate cells with
remarkably resistent envelopes, in that the persistence of cell-body
invested with an ordinary membrane, or even completely naked, was out
of the question after boiling in caustic soda.

But careful observation of fresh bone will lead to other conclusions.
Under cautious treatment, aided by carmine tinction, we may recognise in
the lacunae (fig. 240, a) small, membraneless, indistinctly oval cells (b),
with small projections, at times very short, which are directed towards
the openings of the canaliculi. They are possessed also of elongated

Fig. 239. — Figures resembling cells
from the diaphysis of the femur,
with nuclei at a and c ; 6, with a
portion of the softened inter-
cellular substance: d, another
whose nucleus has broken up
into granules.

Fig. 240.— Bone -cell
from the fresh
ethmoid bone of the
mouse ; tinged with
carmine.

TISSUES OF THE BODY. 247

nuclei. How far this structure (corresponding to the connective-tissue
corpuscle) resembles in this condition the cell of the living tissue,
remains for future investigation, — whether the contractile protoplasm
does not protrude filiform processes into the canaliculi. In fig. 239,
then, we have the walls of the lacunae isolated, together with the cell-
body.

In what has just been described we may trace a very important
parallel between the " bone-cell " with its " wall-system," and the con-
nective-tissue corpuscle with its bounding layer, as also with the cell and
capsule of cartilage.

REMARKS. — 1. Tomes (1. c. p. 848) obtained extremely fine granules on crushing
calcined bone. Koelliker goes so far as to suppose the ground-substance of bone to
be made up of an intimate intermixture of organic and inorganic compounds in the
form of closely-united fine granules. 2. The fibres in question were discovered
by Sharpey in the year 1856 (see 6th ed. of Quain's Elements of Anatomy : edited by
Sharpey and Ellis, Lond.). Their nature and occurrence were then investigated,
especially among the higher animals and human beings, by H. Miiller, and among the
lower classes of Vertebrata by Koelliker. A calculation made by Harting, from which
it appears that a square millimetre contains about 910, gives some idea of the vast
number of bone-corpuscles in osseous tissue.

§ 143.

Turning now to the composition of bone, we must bear in mind that
the medullary receptacles, whose multifarious contents cannot be removed,
must be taken with the proper substance of the former, namely, cells and
ground-mass.

Fresh bones from human beings and the higher classes of Yertebrata
have a rather small proportion of water, especially their compact tissue,
in which it amounts to 3—7 per cent., whilst in spongy tissue it may rise
to from 12 to 30 per cent. (Stark). Young bone is richer in water than
the mature tissue.

Dry osseous tissue consists of about from 30 to 45 per cent, and
upwards of glutinous material, rendered hard by a large amount of the
so-called bony earths, a mixture of inorganic salts. Beside this, there
is present a small but varying amount of matters not convertible into
glutin, which may be set down as derived from the bone-cells, the
systems of walls belonging to the lacunae and canaliculi, as well as
from the contents of the medullary cavities which have not been
removed.

The glue obtained by boiling, from bone deprived of its salts (which,
as has been mentioned, appears soft and cartilaginous on the loss
of its earths, and is called in that state ossein or bone-cartilage), is
glutin (p. 22), as is also the case with connective-tissue.

The occurrence of small quantities of chondrin is of great interest also,
as indicating residual traces of the original cartilage (Miiller, Simon,
fiibm). Secondarily formed bone springing from the periosteum is
probably entirely free from chondrin (see below).

Bony earths are a mixture of various salts, whose bases are lime and
(in a subordinate degree) magnesia, combined with phosphoric and
carbonic acids, and a small amount of fluorin.

Basic phosphate of calcium (p. 57) appears in by far the greatest quantity,

although subject to great variation, according to age, the nature of the

food, and the part of the skeleton we examine. It is still a question

whether this is the only combination occurring in bone. The carbonate

17

248 MANUAL OF HISTOLOGY.

is found taking a far more subordinate position, and the amount of
fluoride of calcium is still less. The admixture, finally, of magnesia
appears quite inconsiderable in comparison to the abundant occurrence of
the lime salts ; it is supposed generally, and rightly, to occur in the form
of a phosphate.

Besides these, we meet with alkaline salts, with phosphoric acid, in
fresh bone ; also chlorine (sulphuric acid ?), iron, manganese, and silica,
which may be set down as belonging to the nutritive fluid saturating the
tissue.

By means of calcining, the organic substratum may be removed from
bone without destroying its form. But when thus treated, the tissue loses
all cohesion, and breaks up into a white powdery mass on being handled.
If we accept it as a fact that no equivalent combination of phosphate of
calcium with glutin exists, that the proportion of bony earths in the several
bones varies considerably, and that the mineral constituents may be ex-
tracted from osseous tissue without the slightest injury to its texture, we
must see that the combination of bony earths with the so-called bone-
cartilage is probably only mechanical. And yet the granular deposit of
lime-salts in cartilage undergoing calcification, compared with the diffuse
deposit in true osteogenic tissue from the very commencement, ia some-
what puzzling.

The following are the results of two analyses, by Heintz, of the compact
tissue of a female tibia : —

1. 2.

Phosphate of calcium, . 85'62 85 -83

Carbonate of calcium, -ir; 9'06 9*19

Fluoride of calcium, .' 3 '57 3-24

Phosphate of magnesium, . T75 1-74

As is usually admitted, the bony earths vary, first of all, according to
the portion of the skeleton in one and the same body subjected to analysis.
Thus Rees obtained as a maximum 63'50 from the temporal, and the
smallest amount from the scapula, namely, 54*51 per cent. (2). Bibra
found the highest figures in the femur, and the lowest in the sternum, the
numbers being respectively 69 and 51 per cent. Compact osseous tissue
is in general richer in bony earths than the spongy kind, probably
because the latter can be but imperfectly freed of the soft parts enclosed
in it.

Further, the same portion of bone is said to change with age ; for at
an early period it appears to be richer in organic material than at a
later. Thus Bibra found in the femur of a foetus seven months
old, 59-62 per cent, of bony earths ; in that of an infant of nine months,
56.43 ; in that of a child at five years, 67'80 ; in a man of twenty-five
years old, 68-97; in a woman of sixty-two, 69 -82; and in another of
seventy-two years of age, 66*81.

It is an interesting and not yet satisfactorily explained fact, that fossil
bones are very rich in fluoride of calcium. The latter may rise as high as
10 or even 16 per cent, of the ash in quantity.

REMARKS.— 1. The theory of the transformation of chondrigen into collagen duriner
the process of ossification (p. 22), which formerly occupied the attention of chemists
ami physiologists to a great extent, has almost lost all worth since the investigations
of Bruch and //. Muller on the subject. We now know that cartilage is not metamor-
phosed into bone, but is dissolved, so making room for the development of osseous

TISSUES OF THE BODY. 249

tissue. The particles of chondrigenous substance are probably decomposed and ab-
sorbed, while new albuminous material is separated from the circulation and trans-
formed into collagen just as in connective-tissue. 2. Jtees (London and Edinburgh Phil.
Mag. 1838) arranged the following series in relation to the matter in question (but
possibly based on insufficient research) — temporal bone, humerus, femur, radius, ulna,
fibula, tibia, ilium clavicle, ribs, vertebrae, metatarsus, sternum, and scapula. Bibra
found, however, a different sequence.

§ 144.

Owing to their hardness and solidity, the bones are peculiarly well
adapted for the mechanical construction of the body, excelling by a great
deal cartilage in this respect. They serve to protect internal organs, and
form systems of levers to be worked by the muscles.

By the deposit of bony earths the flexible bone cartilage is rendered
hard, in order to bear the weight of the body without bending. There
remains at the same time, however, a certain amount of elasticity and
cohesion, which enables osseous tissues to withstand very strong blows,
&c., without any breach of continuity. An increase in the proportion of
mineral constituents gradually imparts to bone a greater brittleness and
fragility. This may be very clearly seen in the difference between the
bone of infants and that of very old individuals in a normal state, while
in pathological conditions it may be more strongly marked.

The bones take part also, to a great extent, in the chemical occurrences
of the organism, owing to the lively interchange of matter going on in
them. And though this is as yet but imperfectly known, both as to its
amount and direction, still most physiological facts compel us to regard
it as by no means inconsiderable, though subject to great rise and fall.
Among these facts relative to the energy of the processes going on in
bony tissue may be mentioned the whole vegetative life of the same, the
frequent regeneration of its substance, the healing of fractures, &c. The
well-known experiment of placing a metal ring round a bone in a young
animal, which is found at a later period to be imbedded in the interior,
teaches us also the great transformations going on in bony tissue, for which,
however, the best proof is to be found in the mode of development of the
latter. Moreover, there is not necessarily any destruction of tissue bound up
with this interchange of material. The rapid coming and going of matter
may be also demonstrated chemically. It is easy to conceive that where
there is such abundance of phosphate of calcium, a deficiency in the supply
of this salt will result in an inadequate hardening of the bone (Chossat).
On the other hand, the well-known experiments of feeding with madder
have lost in recent times in scientific significance ; for only the new osseous
tissue formed during the absorption of the red colouring matter (i.e.,
the most external ground lamella under the periosteum, as well as the
internal layer of the medullary canals) become coloured (Lieberkuhn,
Kodliker}.

The so wondrously complicated system of canaliculi and lacunae has
been looked upon by some as a physiological apparatus presiding over
this energetic interchange of material, as a system of vessels for the plasma,
which receives with its minute openings nutritive fluids from the exuda-
tions of the blood-vessels of the medullary canals and surfaces of the
bone, conducting them through the whole tissue, so that every smallest
part of the ground-substance participates in the transmission of nutritive
matter, organic as well as inorganic (Goodsir, Lessing, Virchow). The
circulation, however, of a nutritive fluid through this system of canals, so
frequently interrupted by the bone-cells, appears questionable, at the same

250 MANUAL OF HISTOLOGY.

time that we do not wish to deny its significance in the processes of nutri-
tion taking place in bone.

REMARKS —1 On this experiment, performed in the last century by Duhamcl,
comp. Flourens (Annal. de Scien. Nat., 2 serie, tome 13, p. 97). 2. Goodsir (Anatomi-
cal aiid Pathological Researches, Edinburgh, 1845, p. 66).

Osseous tissue, as has been already mentioned, is not one of the primary
formations ; it belongs rather to those appearing late in the human body,
and is missing at a period in which the development of most of the
remaining tissues is far advanced.

Its nature is consequently quite different from that of cartilage, whose
place it is destined to take to a great extent. For the rest, this tissue is
developed within very different spaces of time in the various localities of
the body.

Its origin, or the theory of the process of ossification, is one of the
most difficult chapters of histology, and one in regard to which there is
the greatest variety of opinion at the present day.

Now, in that all the bones of the skeleton are moulded first in cartilage,
with the exception of some of those of the head, and that this substance
appears to the unaided eye to be transformed into osseous tissue, nothing
could be more natural than the idea that this actually took place, — that
bony masses were developed by a transformation of cartilage, — a view which
was held by microscopic histologists even until comparatively recently.

But the investigations of Sharpey, Bruch, Baur, and H. Mutter, soon
made it clear that this older theory is incorrect, — that the carti-
laginous mass may undergo calcification, but does not generally become
bony tissue, dissolving rather, and so making room, for the advancing
formation of bone (p. 172). The latter always comes about in a simple
way. New generations of stellate cells make their appearance in a
ground-substance, at first soft, and soon becoming diffusely calcified,
representing thus osseous tissue.

REMARKS. — For a very long time endeavours were made to elucidate, by means of
the microscope, the manner in which this metamorphosis of the non- vascular non-
laminated cartilage, containing round cells, could take place into laminated bone
with its stellate cells, and especially the mode of transition of the latter elements of
cartilage into those of bone. In the history of this branch of science we find three
different views as regards the last point, springing up one after another, and taking
the field against each other. According to one of these, the nucleus of a cartilage
cavity spreads out and becomes stellate, forming thus a bone corpuscle. From the
second theory we gather that the whole cartilage cell undergoes this transformation.
A third view, which appeared for a time to reign supreme, originated with Schwann
and Herilc. According to it, the bone-corpuscle is formed by an uneven thickening
of the wall of the capsule of the cartilage cell. Indeed, the appearance of stellate,
shrunken, true cartilage cells within their capsules, as well as the cellular nature of
the bone-corpuscle by Virchow, seemed to give weight to this theory. Koellikers
discoveries also of the nature of rachitic bone supported it likewise. But in the
year 1846, Sharpey (Quain's Anatomy, fifth edit., by Quain and Sharpey, part 2,
p. 146, Lond., 1846), and shortly after him Koelliker, declared that true bone takes
its origin in the human being and vertebrates also from connective-tissue substrata
of a membranous nature, explaining first of all the growth of bone from the
periosteum, and next that of a number of osseous structures not previously laid down
in cartilage, the so-called secondary formations. Thus it was that two modes of
origin of osseous tissue were supposed to exist by many, — first, by a transformation of
cartilage already present ; and again, by the metamorphosis of a substratum of con-
nective-tissue, although Sharpey maintained the latter mode of origin to be exclusively
that also of the bones even previously moulded in cartilage. The following is an

TISSUES OF THE BODY.

251

outline of the view which formerly obtained in regard to the supposed metamorphosis
of cartilage : — During the process of ossification, bony earths are deposited in the car-
tilage ; the cells of the latter change, according to the third theory mentioned above,
into bone corpuscles ; while their secondary envelopes fuse into the intercellular sub-
stance, forming thus the ground-mass of the bone. The origin of the medullary
cavities and canals was set down to a process of absorption and resolution in the
tissue undergoing this change. The formation of the lamellae remained more or less
unexplained, and that of the canaliculi was but unsatisfactorily touched on. We owe
much to Bruch, Baur, and more than all, to H. Mullcr (Zeitschrift fur wissensch.
Zoologie, Vol. 9, p. 147), for having shown this view of the supposed transformation
of cartilage into bone to be erroneous, working on Sharpey's premises.

§ 146.

Now, although from the foregoing section we must perceive that bone
is not formed by an immediate trans-
formation of cartilage, nevertheless, in
order to comprehend rightly the pro-
cess of ossification in portions of the
skeleton preformed in the latter, a
knowledge of the texture prevailing in
the same is indispensable. Eeference
has already been made (§§ 106 and
107) to the calcification and softening,
as well as to the arrangement and
nature of the cells of cartilage. The
various groupings of the latter are
represented in fig. 241, g, and 242
(above).

Cartilage shows further, previous
to the commencement of ossification,
blood-vessels, which spring up at an
early period of foetal life, and are of
course of importance in the changes
about to take place. They grow from
the perichondrium in tufts into the
softening tissue. Around them a soft
immature connective- tissue is formed,
and thus canals are produced. This
is the so-called cartilage medulla, whose
cellular constituents were formerly
looked upon as descendants of the car-
tilage cells (although no one had ever
seen the transition). The boundary
of the medullary canals in the cartilage
is always sharply and suddenly defined
against the cells of the latter (fig. 241).

Those broad irregular vessels just
mentioned require further examination,
both as regards their course and the
structure of their walls.

In the condition just described, car-
tilage is prepared for calcification and
the formation of bone, closely follow-
ing on it. The latter commences, as
is well known, at certain definite spots, the points of ossification, or

Fig. 241. — Vertical section from the edge of
the ossifying portion of the diaphysis of a
metatarsus, from a f ostal calf 2' long ; after
Millier. a, ground-mass of the cartilage;
6, of the bone; c, newly-formed bone-cells
in profile, more or less imbedded in inter-
cellular substance; d, medullary canal in
process of formation with vessels and medul-
lary cells; e, /, bone-cells on their broad
HRpect; g, cartilage capsules arranged in
rows, and partly with shrunken cell-bodies.

252

MANUAL OF HISTOLOGY.

(more correctly speaking) of calcification in this case. Several of these
points, or bony nuclei as they have also been named, may occur in
one bone, without, however, necessarily springing up simultaneously. In
tubular bones the point of ossification of the diaphysis is mostly situated
in the interior of the middle ; and in double, flat, and short bones, in the
centre. Single bones have two or more such bony nuclei. From the
circumference of the latter the process of ossification now advances by

degrees farther and far-
ther into the cartilage.
The latter, therefore, dis-
plays a difference of tex-
ture according to its
proximity to the bone
nucleus.

In the examination of
such portions of cartilage
from the neighbourhood
of one of the latter, much
difficulty was formerly
experienced owing to an
opacity very difficult to
be overcome due to the
granules of lime. This
it is which has rendered
it so difficult to acquire
a correct knowledge oi
osteogenesis. We have,
however, rather recently
learned from H. Midler
a mode of overcoming this
obstacle by the employ-
ment of chromic acid, in
which the preparations
are placed.

The deposition of the
calcium salts, further, dis-
plays much variety. In

Rg. 242.— Edge of ossification in a phalangfal cpiphvsis from a those places where the
calf, m vertical section; after If fitter. Above, the cartilage with
irregularly scattered cartilage capsules com aininglarge daughter
ells, a, sm.ill medullary spaces, appearing in some cases as
though closed, they are sketched empty ; 6, some of the latter
with medullary cells; c, residue of calcified cartilaginous
tissue; rf, larger medullary spaces, with thinner or thicker
osseous deposits on their walls, in the latter case it is laminated •

•J

cartilage cells lie close to-
gether, in small groups
or singly (fig. 237), they
are more completely

tithT°hein^p^ enclosed in the lime

T!L*>ne-ce" d^P°81ted..'n «•? * a cavity partly filled up. „„!„„ ,i_

n

^i^n^^w^ia^t^^i^oi^^^^^ granules than when ar-
ceuTKlTnt^ ranged in rows as

bridges of the ground-substance often remain soft.°

§ 147.
li uef6 Calclfied .cartilaSe commences now to undergo a rapid process of

it is now traversed. This gives rise to the formation^of8 nunLoL
medullary spaces. As a matter of course, the so much softer capsuTes are

TISSUES OF THE BODY.

253

ilie first to fall a prey to this re-solution. If we still keep to the
diaphysis of the cylindrical bones, we see the walls of the capsules of one
row, as well as the small amount of intercellular matter between them,
becoming dissolved, by which long narrow cavities with wavy contour
are produced (fig. 241, d). Then again, owing to the fact that other
neighbouring parts of the ground-mass of the cartilage become a prey to
advancing liquifaction, numerous communications are formed between
adjacent sinuses (d, above). If we now turn to an epiphysis (fig. 242)
or a short bone, we are struck by the fact that the re-solution takes
place irregularly in all directions, starting from the bone already formed.
The consequence of this is, that the medullary sinuses form a system* of
irregular tortuous cavities, the tracing of which is a matter of difficulty,
and whose arms not unfrequently simulate closed medullary spaces, when
the entrance has come away in making the preparation (fig; 242, a [to the
right and above], &.)

The contents of the cavities formed in this manner are of great import-
ance, supplying the substratum for future processes, or, as we might express
it generally, constituting the foetal medulla.

The latter (fig. 244), a soft reddish substance, shows moderately small

Fig. 243. — Tranvci se section from the upper portion of
the femur of a human embryo of eleven weeks old.
o, residue of cartilage ; 6, coating of osseous tissue.

Fig. 244.— Medullary cells of cartilage, a,
from the humerus of a human foetus of
five months old ; 6, from the same bone
of an infant; c, fusiform cells; rf, for-
mation of the fat cells of the nedulla;
e, a cell filled with fat globules.

roundish cells, measuring 0*0129-0*0257 mm. (a), of a very primitive ap-
pearance, reminding one of embryonic elements or lymphoid cells. They
possess more or less granular contents and a single or double nucleus.
These are held by some to be either immediate or more remote descend-
ants of the cartilage cells, which have found their way into the cavities,
commencing with the absorption of the capsules, there undergoing
segmentation, and thus producing new generations. However, though
we do not wish to deny the possibility of such an origin, the greater part
of these (perhaps contractile) cells of the cartilage medulla has certainly
another source. They are young formative-cells, entering the cartilage
cavities with the advancing blood-vessels of the internal layers of the
perichondriurn and periosteum (Gegenbaur, fret/, Rottett, Stieda). They
may be regarded as emigrated lymphoid cells of the blood.

The further destiny of these cells is very various. Some of them become
fusiform (c c), and form very early. scattered connective-tissue fibres, which
traverse the tissue, which probably contains mucin. Other cells preserve
the old lymphoid form. In the red medulla the latter are to be seen the

254

MANUAL OF HISTOLOGY.

whole life through. Others again, it is supposed, become filled with
neutral fats after increasing in size, thus constituting the fat-cells of the
yellow medulla eventually (e). This last view, however, requires con-
firmation.

But other of these cells have a higher destiny : they become the gene-
rators of the osseous tissue. H. Miiller supposed this to take place imme-
diately, the roundish lymphoid cell becoming transformed into a bone-
cell; but Gegenbaur recognised an intermediate form, a modification of
the medullary cell, to which he gave the name "osteoblast" (figs. 245, 246).
There is but little difficulty in recognising that the irregular medullary
cavities are lined by these cells in a manner similar to the arrangement of

epithelium (fig. 245, c).
Crowded together (fig. 246,
I, 6), round, polygonal, or
more or less cylindrical in
form, with single or mul-
tiple nucleus, and consider-
able variation as to size,
these osteoblasts secrete
externally a thin layer of
a homogeneous opalescent
matter, which covers the
internal surface of the un-
dulating walls of the cavity
(fig. 245, d), or a part of
their membraneless body
may be continuous with
this substance. Both these
views have found defend-
ers. For the last Waldeyer
has entered the lists, fol-
lowed byRottettand Stieda;
and for the first, Gegenbaur,
Landois, Koelliker. We
must declare ourselves in-
clined to look on Gegen-
baur's interpretation of the
appearances presented as
the more correct, although

245.— Transverse section from the femur of a human
embryo of about eleven weeks old. a, a medullary sinus
cut transversely, and 6 another longitudinally; c, osteoblasts;
a, newly-formed osseous substance of a lighter colour; e that
«C greater age;/, lacunae with their cells; a, a cell still
united to an osteoblast.

.. . .

we do not regard the difierence of views as anything essential.

But this layer of osteoblasts supplies not only the material for the
ground-substance of the osseous tissue, but the cells of the latter like-
wise. Advancing from the ranks of these osteoblasts, either single and
entire cells or parts of the same sink themselves into the newly-formed
lamella (fig. 245, g,f, fig. 246, c), where they may be recognised in everv
stage of growth up to the stellate form, on assuming which they are not
untrequently connected by means of their processes with contiguous cells.

Hey are, however, larger and poorer in ramifying processes than the
structures of a later period.

These processes are repeated over and over again. On the completion
ol the first homogeneous lamella with its contained cells, there follows

tt0£ Y?^ with new Cell3> and so on> and the

thicker and thicker, assuming a laminated appearance i

n conse-

TISSUES OF THE BODY.

255

quence of its deposition in successive portions. This is the beginning of
the laminated formation of bony tissue.

We are still in uncertainty as to the mode of formation of the canali-
culi during these processes.

The characteristic peculiarity
of osseous substance soon makes
its appearance now, — namely,
its calcification ; not in granules
moreover, but by a more dif-
fused deposit of bone earths,
communicating to the whole to
a certain extent a translucent
appearance. The organic sub-
stratum of these layers is pro-
bably from the very commence-
ment collagenous matter.

Naturally enough, the irregu-
lar form of the medullary sinuses, Fig. 246.— Osteoblasts from the parietal bone of n
and Continuous re-Solution of human embryo thirteen weeks old (after Gegenbatir).

„ «. bony septa, with the cells of the lacunas; b, layers
the Still remaining portions OI of osteoblasts; c, the latter in transition to bone cor-

cartilage, give rise to very dif- P"sclcs-

ferent appearances in the osseous tissue first formed, as we may see in

fig. 241, or more strongly marked still in fig. 242.

A transverse section, also, through the middle portion of the femur,
discloses the same irregular struc-
ture, the bone consisting principally
of longitudinal septa connected by
means of transverse bridges (fig.
243).

Here, then, we have a contrast
to the regular texture of completed
bone.

Those points are of special in-
terest, as explaining the former
error of supposing a direct transi-
tion of cartilage cells' into bone
corpuscles, where the ruptured
cavity of a cartilage cell has been
made use of as a receptacle for the
deposit of one or more bone cor-
puscles with the accompanying
ground-substance. Here one, two,
or three of the latter elements may
appear to be contained in the in-
terior of a closed capsule, owing
to the ease with which the open-
ing of the latter may be over-
looked (fig. 242, h,f; fig. 241, e.)

But sometimes almost all the
septa of a preparation of osseous tissue have this same extraordinary
appearance, so difficult of description, which may be better understood
by a glance at fig. 242 (to the left, below).

By the gradual liquifaction of the remaining portions of cartilaginous

Fig. 947. — Section of the frontal protuberance of
the calf (after Gegenbaur). a, hyaline, and 6, calci-
fied cartilage; c, bone corpuscles.

256 MANUAL OF HISTOLOGY.

substance, and the consequent acquisition of new spaces for the growing
bony tissue, which lays down additional layers of progressively increas-
ing thickness, at the same time that the canaliculi are being more and
more developed, the new osseous substance takes the place of the pre-
existing cartilage very extensively. That a residue of the original calci-
ned tissue may persist in the interior of fully-matured bone appears
certain, although at present we know nothing definite as to the extent
to which it may do so (Tomes and de Morgan, Mutter}.

That a rapid and extensive re-absorption takes place in the formed bone
will be seen later on. But apart from this re-solution of calcified osteoid
tissue on a large scale, there is besides another hidden process in osseous
tissue, by which older portions of the latter are dissolved, and new masses
laid down in their place. This is first of all borne witness to by the
nature of the medullary cells in old spongy bone, as compared to those of
the same parts in younger individuals. And that there is an incessant
disappearance of material of the same kind at a late period has been
seen when discussing at § 141, fig. 234, the formation of the Haversian
spaces, and their being re-lined subsequently by new lamella of bony sub-
stanoe.

A direct transformation, however, of cartilage into osseous tissue does
likewise occur, though as a rare exception. In such cases we remark
certain jagged cartilage lacunae in the calcified tissue (fig. 247, Z>), which
have arisen from a peculiar mode of thickening of layers on the internal
surface of the capsules. Later on the granular calcification becomes
diffuse (c), the jagged processes of adjacent cells unite to form passages;
in short, bone corpuscles and canaliculi (c) are produced. In these the
cells lie in twos or threes. The frontal protuberance of calves and
tracheal rings of birds afford the best examples of transformations of this
kind (Gegenbaur). In rachitic bone, also, as has long been known,
isolated spots of this kind are to be found with the same transitions
going on in them. In the antlers of deer undergoing ossification similar
changes probably take place to a more marked extent.

§ 148.

There still remains for our consideration the formation of osseous
tissue in parts of the body where cartilage is not previously laid down,
to be again dissolved in order to make way for the former. Under this
head we shall have to discuss, first, the origin of bone /row the periosteum,
and again the ossification of the so-called secondary bones.

The first of these, a process very extensively met with, and in its
beginnings frequently preceding the ossification which takes place in
cartilage, is the source of the increase in thickness of bones.

Holding still to the example of the cylindrical bones, we know by ex-
perience that the latter increase with the growth of the body, not only
in length, but also considerably in thickness. The increase in length,
we may here mention, is -a continuation of the process treated of in the
foregoing section : it takes place, namely, at the expense of the epiphysis
and articular cartilages, whose deeper portions become calcified and then
dissolved to make room for the advance of osseous substance. During
this time the cartilage also grows upwards by division of its cells and
accumulation of its ground substance. The increase in thickness takes
place in the following way : — New layers of bone are formed under the
clothing periosteum, which envelope the mass within in a series of tubes.

TISSUES OF THE BODY.

257

It is hardly necessary to add that eacli newly formed ring must be
larger than the older one formed before it. And the growing bone also
becoming lengthened, each of these osseous tubes is likewise longer than
the preceding.

The importance of the periosteum in the formation of bone has been
further proved by Oilier through a series of remarkable experiments.
Detached portions of this membrane, whether still in connection with
the remainder of the structure or completely separated from it, have the
power of generating again a complete bone; and not only in this case,
but even when transplanted to other parts of the body, or from one
animal to a second of the same species. But the deeper layer of the
periosteum must be carefully preserved in doing this, — a precaution which
we will presently understand.

If we now turn to the histology of the process (fig. 248), we must first recall
to mind the structure of the
fibrous periosteum (p. 226),
which is more vascular at an
early period than later on.
The latter consists internally
(Blasteme sous- -periosi 'ale of
Oilier) of a mass of young
connective-tissue, not fibrous,
but formed of fusiform and
stellate ceils ( b). Under this
appears the stratum, of Gegen-
baur's osteoblasts (c), which
generate the osseous tissue
here, as in the interior of cal-
cified cartilage, and in the
same manner. Both pro-
cesses, the intracartilaginous
as well as the periostea!, are
therefore identical. The
newly-formed bone (tig. 248,
c) is irregular, and jagged
towards the still soft external
layers, and is traversed in
the interior by sinuses, giving
it a spongy texture. These
are filled with medullary
cells, and covering the latter
with osteoblasts, and become
eventually Haversian canals.
Thus the osteoblasts, as in
the intracartilaginous formation of bone, give rise also to the production
of the special lamellae of the Haversian passages (a). Bundles of connec
tive-tissue which penetrate this new layer of bone ossify immediately,
and are known later as Sharpens fibres (§ 142).

During all this, however, the secondary formation of the great medul
lary cavity introduces new changes into the young osseous tissue. When
we remember the large dimensions of the former, it is easy to conceive the
great quantity of the latter which must undergo re-solution in its produc-
tion.

Fig. 248.— Formation of secondary bone. Longitudinal
section of the femur of a well-grown foetal sheep. »,
the internal layer of the periosteum, consisting of con-
nective-tissue; 6, younger stratum, or Oilier 's layer of
the periosteum ; c, layer of osteoblasts ; d, newly-formed
osseous tissue; e, lacunae and cells.

258 MANUAL OF HISTOLOGY.

If we remember, also, that the cavity in question of a fully grown
bone occupies more space than is taken up by the entire bone at an
earlier period of life, we see that the whole of the primitive osseous
tissue must have fallen a prey again to absorption, and the mature bone
consist of osseous substance formed only from the periosteum. The
Bayers supplied by the latter are the general lamellae, as is easy of com-
prehension, and as may be seen in every section (fig. 233). Of course,
from what has just been stated, it will be remarked that the oldest of
them that are present become eventually medullary lamellae, bounding
the great medullary cavity.

In regard to the details of this process of re-solution, to which we
have been obliged to allude so frequently, but little was known until very
lately. From Koelliker's very extensive investigations, it would appear
that modified multinuclear cells spring from Gegenbaur's osteoblasts,
attaining considerable dimensions in some cases : these are closely applied
to the undulating eroded borders of the " lacunae of Hmoship" of the
dissolving bony tissue.

These multinuclear " giant cells " (discovered, to be sure, years ago)
have been named "ostoklast" by Koelliker, who ascribes to them a
power of dissolving the bone. I have not the faintest belief in their
possessing this latter property.

It is improbable that, at the same time that this takes place, the bone-
corpuscles formerly enclosed in ground-substance are set free, and, becom-
ing medullary cells by retrograde metamorphosis, provide for the necessary
increase in the bulk of the marrow.

In short and flat bones, on the other hand, a certain amount of the
original bony tissue, sometimes greater, sometimes less, remains, — of that,
namely, which wTas formed at the expense of the cartilage.

REMARKS. — The investigations of L. Oilier are to be found in the Journ. de la
vhysiologie, Tome ii. p. 1, 170, 468, and T. iii. p. 88, as well as in the Gazette me~di-
cale, 1859, Nr. 37, and 1860, Nr. 12. A resume of these works, with new experi-
ments, appears in a new two- volume work of the same author, Traitl experimental et
clinique de la rfytntration des os et de la production artificielle du tissue osseux.
Paris, 1867.

§ 1^9.

We now come to the origin of secondary bones, or, better expressed,
of those not previously moulded in cartilage. To these belong, as is
usually received, the flat cranial bones, with the exception of the under
part of the occipital, which is modelled first in cartilage ; further, the
upper and lower jaw, the nasal, lachrymal, and palate bones, the vomer,
zygoma, and, finally, the inner leaf of the wings of the sphenoid and
Cornua splienoidalia (Koelliker). These spring up outside of the primor-
dial skull from circumscribed spots, which spread out subsequentlv.
gaining rapidly in superficial extent. Here we first meet with a (true)
osseous nucleus, which grows out in all directions, forming a network of
bony bands and needles (Kalkbalkchen and Kalknadelri), which are lost
in the adjacent soft tissue. It is easy to recognise here, also, the simi-
larity of the osteogenetic process to that in other parts of the system, and
to see that these bony bands are covered by a layer of osteoblasts
(fig. 246).

Much difference of opinion still prevails as to the nature of this original
tissue, as also of that of the corresponding subperiosteal stratum ; one
party regarding it as an undeveloped connective-tissue substance, and not

TISSUES OF THE BODY. 259

cartilage (Koettiker), and another as a kind of fibro-cartilage (Reicliert).
The latter view is decidedly incorrect : we have before us most unmis
takably a young and undeveloped connective-tissue, with fusiform and
stellate cells.

The diffuse calcification now advances superficially, as has just been
remarked, accompanied by a border of osteogenic tissue, so that the full
size and ultimate form of such, a secondary bone is only attained gradually,
in contradistinction to the cartilaginous preformations of the first kind.

In order now that the bone may increase in thickness, a deposit of
osseous substance takes place from the periosteum on both surfaces, and
so the compact external layers are formed, which present at first all the
porous characters of newly-formed periosteal bony tissue. The deposit
of osteogenic matter from the medullary spaces resembles the process as it
occurs in bones previously modelled in cartilage.

These observations tend to show what energy exists in the growth of
osseous tissue, an energy in which may be manifested afresh in fully
developed bone, especially under abnormal conditions.

But though these processes, as we see them in the development of
cylindrical bones, are so far clear, we must not think that a solution
internally and a deposit externally alone takes place : there is some-
thing moro, namely, an interstitial and expansive growth ("a growth
by intussusception"), such as is to be observed in almost all tissues.
(R. Volkmann).

But highly developed connective-tissue may also, under certain circum-
stances, be transformed directly into bony substance. The flat cranial bones
of embryonic birds (fig. 249) present to us most unmistakably, according
to Gegenbaur, a process of this kind. Here a network of connective-tissue
bundles is seen (c), in part still soft and fibrillated and in part granularly
calcified (d). Later on these bands of hardened tissue become broader,
are now diffusely calcified, while the cells enclosed in them remind one
of bone-corpuscles. A layer of osteoblasts (&, e) is also demonstrable here,
which deposits that stratum of bone clothing the connective-tissue frame-
work. That we have to do here with an occurrence which, taken gene-
rally, has been already discussed in referring to the formation of Sharpens
fibres, is quite apparent.

The conversion of tendons into osseous tissue is well known to take
place largely as a physiological occurrence in mature birds. Here we
encounter, at first, a simple calcification of the connective-tissue, so that,
on depriving the part of its bony earth, the tendinous texture is again
presented to us unchanged. Later on, however, true osseous substance
makes its appearance, with a small number of lacunae, lamellae, and
Haversian canals. It was formerly supposed that here a direct transfor-
mation took place from tendinous into osseous tissue (Lieberlculm), but
this is an error. There appear, rather, in the calcified tendon, spaces
containing vessels which correspond to the medullary sinuses of cartilage,
and are filled with a soft mass. From these cavities the deposit of a solid
substance takes place, which becomes calcified at once, " resembling true
bone more or less" (H.Muller). Eemnants of calcified connective-tissue
are left, however, in these ossified tendons.

Regeneration of osseous tissue occurs pathologically, with great fre-
quency, on the fracture of various bones, — for the repair of breaches of
continuity and replacement of lost substance, whether it have been
thrown off by a pathological process or removed by surgical instruments ;

260

MANUAL OF HISTOLOGY.

further, in uninjured bones a luxuriant growth may occur, in the form of
hypertrophies, exostosis, and osseous tumours. In most of these cases

the production 01 the new tissue
takes place from the periosteum
in the manner described. "With-
out this, however, we may be
satisfied of the great importance
of the membrane in the produc-
tion of bone from Oilier 's experi-
ments (p. 257). But while the me-
dullary tissue remains inactive
in the normal formation of bone,
as was ascertained by the inves-
tigator just mentioned, it may,
under abnormal conditions, be-
come transformed into a more
or less solid connective -tissue
on its exterior — into a species of
endosteum, and generate bone-
like matter. The latter is rarely
developed in soft parts remote
from bone. The formation of
true osseous tissue independent
of bone is very circumscribed. It
takes place, however, far on in
life in cartilage, and at its ex-
pense, when the processes of
foetal ossification are repeated ;
likewise in parts formed of con-
nective-tissue, when a growth
similar to that from periosteal
osteogenic substance is the start-
ing-point. Masses of bone formed pathologically have frequently a porous
character at first, resembling the normal tissue, but may also be com-
pact, and endowed with a high degree of solidity.

The occurrence of re-solution of normal osseous tissue is by no means
rare in disease. It takes place with previous decalcification, in the same
way as physiological absorption in growing bone.

REMARKS. — From the fact that bones not previously modelled in cartilage are in
many cases developed before those others become ossified which are thus pre-formed,
\ve may perceive that the designation "secondary" has not been very happily
applied" to them. An attempt has been made, therefore, to replace ic by the names
" tegumentary or overlaying bone" (Deck-or Belegeknochen). The whole thing has
lost considerably in histological worth, however, according to the latest observations
in osteogenesis.

11. Dentine.
§ 150.

Before entering upon the description of dentine (1), it will be necessary
first to devote a few words to the consideration of the teeth, the greater
part of which it forms.

A tooth may be divided into three distinct parts, — into the crown,
which lies exposed ; the neck, enclosed in the gum ; and the root, buried

Fig. 249.— From the edge of the frontal bone of a
chick undergoing ossification (from Gegenbaur). a,
network of osseous bands ; d, granularly calcified,
and c, soft connective-tissue ; 6, e, osteoblasts.

TISSUES OF THE BODY.

261

in the alveolus. It is hollow internally, traversed by a canal which,
commencing above in the crown, terminates below at the point of the
root by a free opening. In the incisor and canine teeth this cavity is
single, and is divided in the others according to the number of their roots.
It is filled with a peculiar connective-tissue, very vascular, and largely
supplied with nerves, which is called the pulp. The nutrition of the whole
organ takes place from this as from the Haversian canals of bone.

From a histologies! point of view the tooth may be regarded as made
up of three kinds of tissue (fig. 250), — of a coating on the root, called the
cement, i.e., a bony substance ; then of a layer covering the crown,
known as the enamel (see next section) ; and
finally, of a mass situated internally, the proper
tissue of the tooth surrounding the cavity just
mentioned. This has received the names of the
" ivory" "dentine"

The latter possesses a hardness exceeding that of
bone, and must be looked upon as a species of the
latter without bone-corpuscles, and with a more regular
course in its canaliculi. It appears white, in thin
sections, with a satiny lustre frequently, as long as
the system of canals is filled with air and is not
occupied by a fluid.

These passages or dental canaliculi appear, in dried
sections containing air, as extremely numerous and fine
dark tubes of from O'OOH-0'0023 mm. and upwards.
They maintain a tolerably parallel course, side by
side, perpendicular to the surface of the cavity of
the tooth. This is consequently vertical in the
middle of the crown (fig. 250), oblique at the
sides of the latter, becoming horizontal below towards
the root (2). In transverse section the middle and
under portions of a tooth display a radiating arrange-
ment of the canaliculi. f~

If the latter become filled with fluid, they blend
into the ground-substance and are rendered partly or
altogether invisible, reminding us of what takes place
in bone under similar circumstances.

They correspond farther with the canaliculi of bone in having a
special lining layer, which is, however, thicker than in the latter. In
macerated dentine this layer appears on sections in
the form of tubes projecting beyond the surface.
The latter may be easily isolated by the softening
action of acids, as well as boiling of the tooth-cartilage
or treatment with alkalies, on which they are pre-
sented to us as intercommunicating structures (Koelliker,
Hoppe, Neumann, Frey, Waldeyer).

In suitable sections of dentine we may likewise see
the canals transversely opened (fig. 251).

If we now examine into the more minute arrangement
of the canaliculi in thin leaves of dentine containing
air, we find their number to be greater in that portion of
tissue surrounding the central cavity, and in the crown,
than in the root. We remark also in the whole course of one of these tuben,

Fig. 250.— A human in-
cisor, with the cavity
in the axis surrounded
by dentine, which lat-
ter is covered ahove by
enamel, below by ce-
ment.

251. — Softened
dentine, with trans-
versely cut canali-
culi.

262

MANUAL OF HISTOLOGY.

from within outwards, usually three, or sometimes only two, undulating
curves (known as the lines of Schreger), and within these again a number
of very small jagged or spiral bends, of which about two hundred may
be seen in the length of a line (Retzim).

Like the canaliculi of bone, those of
dentine (fig. 252, e) are observed to
divide over and over again, and to com-
municate through their branches ; though
in other respects they differ, owing to
their more regular course.

In the internal portions of the dental
tissue a number of divisions take place
at acute angles, and in rapid succession,
with decrease in the size of the branches.
This becomes more rare externally, gain-
ing again in frequency in the most super-
ficial portions. Thus from one canal a
whole system may be produced.

We encounter further, in many cases,
intercommunications between adjacent
canaliculi by means of oblique branches
(c). This may lead eventually to
the formation of a regular network in
the external portion of the tissue (fig.
253). Here some of the canaliculi join
in loops (fig. 252, c), whilst others sink
down into the cavities of a granular layer
situated at that part (&), and a third set
advances beyond the limits of the den-
tine into the cement (fig. 252, a), or
perhaps (1) into the enamel (fig. 253, c). We will meet with these
again. Internally, this system of canals terminates by free openings in
the cavity of the tooth.

The ground-substance of dentine, finally, is a
homogeneous substance which may be split into
bands artificially after maceration. The direction in
which this cleavage takes place is determined by
the course of the canals.

In addition to these elementary and essential
features of the tissue in question may be added some
of minor significance. For instance, a certain system
of irregular cavities, of extremely variable size, named
by Czermak " interglobular spaces" (fig. 152, b),
exists normally in this tissue, the interstices between
the projections of a number of more or less spheroidal
masses aggregated in the ground-substance, known
as " dentine globules." The cavities in question are
found, very numerous and small, principally under the cement covering,
or crusta petrosa, of the root. They here enter into the construction of
the so-called granular layer of Tomes, and may be confounded with
lacunae, more especially as they receive into them the terminations of
canaliculi. These interstices, however, contain no air during life but
a soft organic mass.

Fig. 252. — External portion of human den-
tine d, with coating of cement a; at b, the
granular or Tomes' layer of the first of
these, with interglobular spaces; c and e,
canaliculi

Fig. 253.— External por-
tion of dentine, rf, from
the crown of a tooth,
with its layer of enamel
fr. a, enamel cuticle; c,
interstices filled with air.

TISSUES OF THE BODY.

2G3

Larger globules of dentine may make their appearance internally on the
boundary wall of the cen-
tral cavity of the tooth,
communicating to it here,
as has been very well said,
a "stalactitic" appearance.
In the crown we may fre-
quently recognise concen-
tric tracings running more
or less parallel to the sur-
face, probably pointing to
a kind of lamination
which may hereafter find
its explanation in histo-
genesis. These are the
so-called " contour-lines "
of Oioen.

We have already re-
marked that dentine may
be regarded as a species of
bone. Comparative his-
tology also teaches us that
the osseous tissue of many
bony fishes supplies inter-
mediate forms bet ween bone
and dentine, and that in
no inconsiderable number
of these the latter appears
in the place of osseous
tissue (Koelliker) (3).

REMARKS. — 1. Beside the
German works of Henle, Ger-
lach, and Koelliker, com p. Todd
and Bowman (Vol. 2). Fur-
ther, E. Owen — Odontography,
etc. Vol. 1 ; Loud. 1840-45.
J. Tomes — A Course of Lectures
on Dental Physiology and Sur-
gery. Lond. 1848; andPhilos.
Transact, for the year 1856,
p. 515. Beale. The struc-
ture of the simple tissues. 2.
In the many-pointed crowns of tho back teeth the direction of the canaliculi is the
same as if every knob were the crown of a simple tooth. Between the many roots on
the so-called alveolar surface, as Purkinje has very happily named this part, the
perpendicular course of the middle portion of the crown is again re-established. 3.
Subsequently to Queckett's having directed attention to this in certain fishes
(Catalogue of Surgeons of England, Vol. 2), the above-mentioned German investigator
proved the frequent and extensive occurrence of this interesting relation.

Fig. 254.— Premolar tooth of the cat (after Waldeyer). 1,
enamel with cross and parallel streaks; 2, dentine with
so-called lines of Schreger; 3, cement; 4, periosteum of
alveolus; 5, bony tissue of the lower jaw.

The pulpa dentis is the unossified remainder of the papilla existing in
the embryonic tooth (see below). It is a kind of undeveloped soft con-
nective-tissue, possibly belonging to the mucous or gelatinous species,
containing numerous cellular elements of elongated or round form. The
intermediate substance, which is not rendered clear by acetic acid, is
18

204 MANUAL OF HISTOLOGY.

indistinctly fibrous, and devoid of elastic elements. ^ The pulp is further
rich in nerves and very vascular, almost presenting in transverse section
the appearance of a cavernous tissue. The small arterial stem which pene-
trates into its substance splits up into several branches, which advance
through the latter, forming in the crown of the tooth numerous capillary
loops° through which transitions to veins having a similar course back
a<*ain' takes place. The nutrition of the tooth is presided over by these
vessels. The nerves will be referred to in a subsequent section. To
them is due the great sensitiveness of the tooth, which, as is well known,
may increase to intense painfulness at times. The external surface of
the pulp is covered by a laminated stratum of narrow cylindrical cells,
0-0452-0-0902 mm. in depth, resembling epithelium. These elements,
0-020-0*030 mm. in length, contain an elongated nucleus. They
are connected in the first place with one another by means of their
ramifications, and in the next with the deeper-lying cellular ele-
ments : finally, they send off soft delicate processes, single or multiple,
externally.

The "dentine cells," or, as they have been more recently and better
named, the " odontoblasts " (Waldeyer) (fig. 255, I), have been long
known ; but attention has only been directed gradually to their relations
to the dental tissue.

It used to be thought that the system of canaliculi was nothing but
a series of canals possessing no formed con-
tents, and only filled with a nutritive fluid
(Leasing). Indeed, dentine appeared to pre-
sent one of the 'most beautiful examples of a
system of vessels for plasma in the whole
group of connective-substances.

But Tomes' discoveries, confirmed by the
observations of Beale, Koelliker, Neumann,
Frey, Waldeyer, Hertz, and Soil, showed the
Fig. 255.— TWO dentine ceils, 6, errorieousness of this older view.

traversing with their processes ^TT ... , ,

a portion of the canaliculi at a, We may easily convince ourselves, namely,

that the odontoblasts protrude those of their
processes already mentioned as directed out-
wards into the so-called canaliculi of the tooth
(fig. 255, «), probably traversing the latter with their ramifications in
their whole length ; at least, they may be still seen in the crown of the
adult tooth. It would appear also as though these fibres of Tomes, or
" dental fibres," filled up the whole lumen of the passages.

It has been supposed that the structures resembling canaliculi, isolated
by means of maceration, are nothing but these ramifications of the den-
tine cells. This, however, is not correct ; for even after processes which
must have destroyed all the softer parts of the tooth, after the most
active decomposition, canaliculi endowed with a special wall may be laid
bare (Neumann).

This wall can just as little be looked upon as the calcified membrane
of dentine cells and their processes as in the corresponding elements of
bone. It is here also, as in bone, a modified bounding layer of the
ground-substance, so that we are correct in speaking of " dental sheaths "
(Neumann, Waldeyer, Boll).

Tomes' view of the matter is of great interest : he refers the great
sensitiveness of the dentine to the soft fibres of these cells. We shall

TISSUES OF THE BODY. 265

have to discuss this point at greater length in a future section, when con-
sidering the termination of the nerves of the pulp.

In passing, it will be convenient to touch here on the nature of the
cement, or crusta petrosa, of the teeth. This commences at the
termination of the enamel as a thin layer clothing the root (figs. 250
and 254), increasing in thickness below until it attains its greatest thick-
ness at the point of the latter. It is, however, nothing but simple
osseous tissue (fig. 252, a), and, like this tissue, generally greatly
inferior in hardness to dentine and still more so to enamel. It is not
always sharply defined against the ivory of the tooth. Its ground-
substance is sometimes homogeneous and sometimes streaked : when very
thick it may also appear faintly laminated, but it rarely comes to the
formation of Haoersian canals. No bone-cells at all are found in the
cement around the neck of the tooth, and they only become numerous
towards the point of the root. Their size and shape, and the number of
their ramifications, which is often considerable, are more liable to varia-
tion than those of ordinary bony tissue. Some of these ramifications
are united with the canaliculi of the tooth which have penetrated as far
as the cement ; others form anastomoses with adjacent cells (fig. 252,
in the middle of a).

These lacunse must not be confounded with clefts which are frequently
to be met with in the cement of old teeth in the form of irregular, branch-
ing interstices.

§ 152.

Dentine, whose specific gravity is 2 '080 according to G. Krause, con-
tains, notwithstanding its hardness, several per cent, of water : some
analyses give 10 per cent. It consists, like bone, of a glutin-yielding
substratum, rendered hard by a considerable excess of calcium and also
magnesium salts.

The organic substratum, determining the form of the structure, is
collagenic matter without any admixture of chondrin. An interesting
observation has been made in regard to the walls of the canaliculi,
namely, that though they may be isolated by means of the stronger
acids and alkalies, they remain for a time undissolved in a Papwts
digester, in which the ground-substance is transformed into glutin
(Hoppe). showing that these canals are not formed of glutin-yielding
matters. We have thus a similar condition of things as in the
lacunse of bone and their ramifications. The dentine globules also are
not convertible into glutin,' and their substance offers even a more
determined resistance to the action of acids than the other portions of
the tissue.

The bony earths of dental tissue consist of a considerable proportion
of phosphate of calcium, with a smaller quantity of carbonate, and also —
taking a more subordinate place — fluoride of calcium and phosphate of
magnesium. , The carbonate of calcium appears to be subject here to more
variation in amount than in bone. Fluoride of calcium was originally
determined by Berzelius, and Bibra made the interesting discovery that
the dentine of many mammals is comparatively very rich in phosphate
of magnesium.

Beside these, many other salts and mineral constituents are met with
in the teeth, and also a small proportion of fat.

The bony earths, taken quantitatively, amount in human dentine from

266

MANUAL OF HISTOLOGY

27-61
0-40

6672
3-36
1-08
0-83

20-42
0-58

67-54
7-97
2-49
1-00

71 to 78 per cent., while the collagenic substratum of the tissue (the so-
called tooth cartilage) ranges about from 20 to 29 per cent.

The following two analyses of Bibra may be taken as an example.
They refer to the dried dentine of human molar teeth. The first of these
was from an adult male ; the latter from a woman twenty-five years of age.

Organic collagenic substratum,

Fat, . •

Phosph. and fluoride of calcium.

Garb, of calcium, .

Phosph. of magnesium, ..

Other salts, .

As to the softer crusta petrosa, any distinction from dentine is doubt-
ful. The investigations which have taken place up to the present show
somewhat more organic substratum yielding glutin. Its nature is other-
wise similar to that of dentine. Bibra obtained from that of the human
teeth, 29-42 (inclusive of some fat) of organic substance, and 70*58 of
mineral constituents.

§ 153.

The development of the teeth (1), as productions of mucous membrane,
is, even in its coarser outlines, a most difficult chapter in embryology.

From the fourth month on of
intra-uterine life, we remark in
the human embryo preparation
for the formation of the future
milk-teeth. This takes place on
the edges of the jaws, by the
formation of closed follicles, from
the floor of which a papilla pro-
jects into the cavity, destined to
produce the dentine of the struc-
ture, and, moreover, in the first
place, that of the crown, while
the remainder enters into the
formation of the pulp. These
papillary structures, which re-
semble in form the crown of
the future tooth, are called the
" ' tooth' or ' dental ' germs."

In fig. 256 we have a sketch
of one of these follicles from a
tolerably mature embryo, with
its but ill-defined wall of con-
nective-tissue (a) and dental
germ (/) containing numerous
capillaries (g). The latter is
covered by a peculiar structure,
in the form of a cap, hanging down over its sides (b). This has been
named the " enamel-organ," on account of its presiding over the produc-
tion of the enamel, as we shall see presently. Its concave inferior surface
is lined by a layer of narrow cylindrical cells (d) covering the dental

Fig. 256. — Dental sac of a human embryo at an ad
vanced stage of development, partly diagrammatic.
a, -wall of the latter, formed of connective-tissue, and
with its outer stratum a1, and inner a2; 6, enamel
organ with its papillary and parietal layers of cells c;
d, the enamel membrane and enamel prisms; e,
dentine cells; /, dental germ, and capillaries g;
i, transition of the connective-tissue of the wall of
the follicle into the tissue of the dental germ.

TISSUES OF THE BODY.

267

germ, while its convex external aspect is covered by a similar coating of
smaller cells (c).

But though all is so far tolerably clear, we are now met by the difficult
question, so variously answered at different times, as to how these several
structures take their origin.

.Recent investigations, and the researches of Tiersch and KoettiJier,
supported at a later date by those of Waldeyer (with which my own subse-
quent observations correspond), seem to point to the following conclusions.

The parts which are contained in the dental sac are of various origin.
The dental germ corresponds to a papilla of the mucous membrane, which
becomes enclosed in the
parietal portion of the fol-
licle as with a sheath of the
latter. Both these struc-
tures have their origin from
the proper tissue of the
mucous membrane of the
foetal jaw.

The enamel organ, on the
other hand, is a produc-
tion, by reduplication, of
the mucous epithelium,
which covers the dental
germ, just as a papilla of
the mucous membrane is
covered by cuticular tissue.
But the mass which has
grown down into the gum
has (in the phase in which
we see it in fig. 256) be-
come completely separated,
by the closing in above,
from its original source
of origin.

In order really to under-
stand these relations, we
must look back to a much
earlier period of foetal ex-
istence.

Originally, before any
trace of either dental germ
or tooth sac is to be seen,
the edges of the jaws,
which are marked with a
slight groove known as
the " dental groove," are
covered by a thick ridge of epithelium, just over the spots where the
future structures are to be formed. This latter has been named the
" dental ridge" (2) by Koelliker (see fig. 257, 1 a, 2 a).

The epithelium soon after commences to grow down from the dental
groove into the substance of the mucous membrane, in the form of a
leaf-shaped process, which becomes curved downwards and inwards,
appearing sickle- shaped, in vertical transverse sections. To this the

7

Fig. 257.— Developmentof the teeth from Thiersch's preparations
of embryonic pigs (vertical transverse sections of the upper
jaw). 1, 2. From a small embryo : the right and left halves of
the maxilla, a, dental ridge ; 6, younger layer of epithelium ;
c, the deepest ; d, enamel germ ; *, enamel organ ; /, dental
germ ; g, inner, and A, outer layer of the growing tooth sac.
3. From an older embryo : d, the style of the enamel organ ;
f, blood-vessel severed; £, bony substance. The remaining
letters as in 1 and 2.

268 MANUAL OF HISTOLOGY.

name of " enamel germ" has been given (1 d). Its walls are formed of
narrow cells arranged perpendicularly, and its interior is taken up by
small round cells.

Later on may be seen how various parts of this enamel germ (3) increase
in breadth at their deepest half, at those spots where the development of
the several dental papillae is to take place, thus preparing the way for the
formation of the individual enamel organs (2 d). It is the small round
cells of the interior just mentioned which principally occasion this enlarge-
ment, in that they gradually become transformed into the already well-
known non- vascular gelatinous tissue (fig. 181) with stellate elements (2 e).

After this the formation of the dental germ or tooth papilla (2 / ) takes
place. This grows, upwards against the under surface of the enamel organ
belonging to it, and soon transforms the shape of the latter into that of a
thick cap covering it over.

The parietes of the follicle are now laid down from the adjacent tissue
of the mucous membrane, but gradually and but ill-defined, and soon we
may recognise an external and more closely interwoven stratum (2 A), and
a thick internal layer of softer and looser texture (2 g),

In fig. 257 (3) we have represented the stage of development in
question. At / is seen the dental germ projecting upwards, beneath
which the lumen of a considerable vessel appears which has been cut
across (i), and the commencing bony portion of the upper jaw-bone (&).
This germ passes continuously into the substance of the still unfinished
walls of the tooth follicle, whose external layer is to be seen at h, and
internal at g.

But we recognise also, at the same time, that the style (d) of the
enamel organ (e) has become strongly narrowed, owing to the growth
upwards of the walls of the sac, — a process which is destined to effect a
separation of the enamel organ from the mouth.

But before this the formation of an organ of the future takes place from
the style, namely, of the secondary enamel germ. This plays the same
part in the rudiments of the permanent teeth as its predecessor did in the
formation of the milk-teeth (Koelliker).

A leaf of epithelium is seen to spring from this style, and to sink down
into the tissue of the mucous membrane in a manner similar to that
described as occurring in the formation of the first enamel organ. This
leaf lies beside the latter in a central position. From this it would
appear that the permanent teeth have for their formation 'a new dental
germ, but the old enamel organ (4).

When the further progress of this striking and interesting series of
changes leads to the obliteration of the stalk-like connecting bands of
epithelium between the summit of the enamel organ and the epithelium
of the jaw, we arrive at the phase of development presented to us in
fig. 256 : the parietal portions of the tooth sac have closed over the
enamel organ, covering it in.

REMARKS.— 1. Literature is very rich in essays on the development of the teeth.
Compare (beside the older and more recent German writings) Goodsir, in the Edin-
burgh Med. and Surg. Journ., 1838, No. xxxi. 1 ; Huxley, in the Quart. Journ. of
Microsc. Science, vol. iii. p. 149, vol. x. p. 127, and vol. xix. p. 166; Magtiot,
Atudes sur le dfveloppement et la structure des dents humains, Paris, 1856 ; and also
Comptesrendus, I860, p. 424 ; Guillot in the Annal. des scienc. nat.., 2 Sgrie, Tame
ix. p. 22 1 ; Jolly in the same, 3 Serie, Tome ii. p. 151 ; Robin et Magitot in the
Journ. de la physiologic, Tome iii. p. 1, 300, 663, and Tome iv. p. 60 ; as also in
the Gaz. mfd. de Paris, 1860-61, in many places. 2. For a long time Goodsir*

TISSUES OF THE BODY.

269

description was held to be correct. According to him, the first item in the develop-
ment is the formation of a groove in the edges of the jaws, taking place in the human
embryo during the sixth week. In this the twenty-teeth germs of first dentition take
their rise. He supposed hollows to be formed around these by the subsequent develop-
ment of septa between the several dental germs, and that these underwent later on a
closure above. This theory of Goodsir was attacked most vigorously, at a later date,
in the works of French histologists, — Ghiillot, Magitot, and Robin. According to the
latter, the tooth sacs, dental germs, and remaining parts, are developed, in the first
instance, within the sub-mucous connective-tissue, quite independent of epithelium
and mucosa. 3. Huxley was the first to declare the whole enamel organ to be of
epithelial origin. 4. In the fifth month of intra-uterine life there may already be
seen new follicles, situated above the germs of the milk-teeth in an oblique position.
They become, however, more vertical later on, and lie behind and beneath the milk-
teeth. Their ossification is spread over the earlier years of infancy. Since the histo-
genic occurrences in both cases are similar, it will suffice if we confine ourselves in
the text to the consideration of the milk-teeth.

§154.

The connective-tissue envelope of the tooth sac (fig. 258, a) consists
(as we have already seen in the previous section), at an early period, of
two layers, an external (a1) and an internal (#2). The first of these pre-
sents a great denseness in its fibrous text-are ; the latter, rich in cellular
elements, preserves a softer and more gelatinous character. The inner
surface of the dental sac assumes a more or less homogeneous aspect, and
to such an extent sometimes that a hyaline terminal layer has been
spoken of.

The occurrence of villous projections of this inner layer, which are
directed towards the surface of
the enamel organ, is of great
interest. They appear to be
equivalent to the ordinary
vascular papillte of a mucous
membrane (1). A complex vas-
cular network, which receives its
blood from the vessels of the
jaws and gums, traverses the
whole parietal portion of the
dental sac, and may be seen
forming loops in the projections
just mentioned.

The enamel organ presents for
our consideration, upon its con-
cave under surface, a coating of
epithelial cells already long
known. The latter are narrow,
cylindrical, and nucleated ; in
length 0-0226-0-0338 mm.,
and in breadth 0'0451 mm. The
whole of this layer was formerly
called the enamel membrane.

The epithelium, on the other
hand, which clothes the external
convex surface of the enamel organ (b), was only generally recognised at a
later date. It consists of low cells, measuring in man 0'0113 mm. (2).

The last-named coating, however, does not by any means everywhere
possess the same thickness : it forms, rather, numerous small bud-like

Fip. 258.— Dental sac of a tolerably mature humtin
foetus, partly diagrammatic, a, fibrous wall of the
sac with its external stratum a1, and internal a2;
6. enamel organ, with its papillary and parietal cells c;
d, enamel membrane and enamel prisms; /, dental
germ with its capillaries g; continuation of the con-
nective-tissue of the parietes into that of the dental
germ.

270 MANUAL OF HISTOLOGY.

growths towards the follicle, especially at that portion covered by the gum.
These interdigitate with the vascular tufts just referred to.

We have already considered, in § 116, the gelatinous non-vascular tissue
enclosed in the cellular tunic of the enamel organ, so that we refer the
reader again to what was there remarked.

The dental germ ( f) appears to be formed of an undeveloped .connective-
tissue, of a finely granular dull mass, containing a multitude of roundish
nuclei and cells of like shape, or more or less fusiform. It is, moreover,
highly vascular, the capillaries being recognisable at a short distance from
its surface, forming numerous terminal loops (g, and fig. 258). Numerous
nerves are also formed in it subsequently, whose origin calls for more
accurate investigation, as also the question as to the occurrence of
lymphatic vessels.

The dental germ is covered by delicate cells arranged in strata, now
more or less cylindrical, now of irregular figure (fig. 258, e ; 259). These
are the dentine cells or odontoblasts, whose nature and position in the per-
fect tooth has already been treated of in § 151. They correspond to the
osteoblasts of Gegenbaur, which we have seen in the bony tissue (§ 147).
These cells, taken as a whole, have been described as the "ivory or
dentine membrane."

REMARKS. — 1. These villous projections were first seen by English investigators
(Huxley, Cfoodsir, Todd, and Bowman, II. cc.), and then more accurately described
at a later date, principally by Robin and Magitot. 2. The epithelium on the outer
surface of the enamel organ was also first recognised by English observers (Nasmyth,
ffuxley) ; but the French have made it an object of closer study ; comp. Guillot, I. c.,
Robin and Magitot (Journ. de la physiol., Tome 4, p. 71).

§ 155.

The dental germ is now destined, with the odontoblasts, to produce
dentine. To this end the elements in question send out long filiform

of a lmman molar tooth wi«i incipient
; * 8°-

processes externally, which constitute the soft dental fibres of Tomes,

already known to us from § 151. Between them a homogeneous

stance then makes its appearance, whose origin must be accepted as

>emg similar to that of the intercellular matters of the connective-tissue

TISSUES OF THE BODY.

271

group. This is converted into dentine by a diffuse calcification similar
to that of the so nearly allied osseous tissue ; while the walls of the
canaliculi of the teeth are
formed by the bounding / j

laminae of the mass sur-
rounding the fibres of
Tomes.

The following sketch
may be accepted as toler
ably faithful as far as we
are acquainted with the
course of development, so
difficult to follow.

Young dentine cells (fig.
259, b; fig. 260) present
themselves as membrane-
less nucleated structures
closely crowded together,
and of irregular jagged
form, and united one
with another by means
of short processes. Exter-
nally, they send off single
or multiple prolongations,
which form interlacements
by means of side branches
with the processes of adja-
cent cells. The odonto-
blasts eventually become
longer and narrower, and the more peripheral portions of their processes
attain a considerable length. Thus are formed the soft fibres of Tomes.

The calcification already mentioned commences at the apex of the
dental germ, in the tissue just described, in the form of a single, or
frequently, at first, of several separate thin plates. This plate has been
named the "dental cup" (Zahnscherbchen) (fig. 259, c). On the further
superficial extension of this structure the calcified layer spreads down
over the sides of the dental germ, in which, with the commencement
of calcification, the vascular network has already reached its fullest
development.

But, owing to the continued production of the fibres of Tomes, of
the canaliculi and the ground-substance, through the agency of the
still soft ivory cells below the dental cup, and the progressive calcifica-
tion of the ground-substance, the thickness of the dental germ decreases
more and more, although it has grown considerably in length.

This increase in length leads eventually to the formation of the root,
which is changed into ivory exactly in the same way as the crown, and
becomes calcified externally.

The production of the cement commences before the passage of the
teeth through the gums, as soon as the root is developed. But the bony
mass in this case arises, it is supposed, from a growth of the inferior
portion of the dental sac, the latter becoming converted into osteogenic
substance, as in the growth of the periosteum, and undergoing diffuse
calcification. Osteoblasts and bundles of connective-tissue are also to be

itf. 260.— Dentine cells after Lent. At a and 6, simple filiform
processes, which become converted into canaliculi: c, d,
specimens of the latter with branches; e, fusiform cell; and
/, one of the latter undergoing division.

272 MANUAL OF HISTOLOGY.

seen here, the latter reminding us of Sharpey's fibres (§ 142) in the
way in which they ossify. According to this description, both parts
have a similar or identical nature to that of osseous tissue. Dentine
represents a modified bony substance, and the cement is deposited upon
it in the same manner as a younger periosteal layer upon an older, while
the communications between the canaliculi of the tooth and those of the
bone occur in a way analogous to that taking place in concentric growth
of bone.

Just as the cement is formed around the root, so is the enamel laid
down upon the crown as a coating closely adherent to the subjacent
mass. The elongated tooth then presses gradually against the enamel
organ and roof of the dental sac until these disappear with the super-
imposed gum. Thus the eruption of the twenty milk teeth comes to pass,
which begins in the sixth or seventh month of an infant's life, terminating
at about the commencement of the second, or sometimes in the middle
of the third year. The residue of the dental follicle persists as the
periosteum of the alveolus. Around the milk teeth, which have been
already protruded, it forms a system of obliquely ascending fibres passing
from the edge of the alveolus to the neck of the tooth (ligamentum
circulare dentis of Koelliker).

The external epithelium of the enamel organ may, perhaps, persist also
in the form of the " enamel cuticle."

The subsequent falling out of the milk teeth is preceded by re-absorp-
tion of their roots.

The successive eruption of the thirty-two permanent teeth commences
in the seventh year, lasting until the end of the second decade, when the
wisdom teeth make their appearance.

The cause of the falling out of the teeth at an advanced age has not
yet been sufficiently cleared up. It is probable, however, that a narrow-
ing of the canaliculi, and degeneration of Tomes' fibres, prepares the way
for the decay of the organs.

The origin of dental caries requires also further investigation. In it
we remark in succession, softening and destruction of the enamel mem-
brane and enamel, of the dentine in its ground -substance, and of the
dental sheaths and fibres. In this process vibriones and filiform fungi
make their appearance.

The so-called tartar of the teeth consists of albuminates and allied
matters from the fluid of the mouth, together with a large proportion of
phosphates. The former amount, according to Berzelius, to 21, the latter
to 79 per cent.

Hypertrophies of various external portions of the teeth are of fre-
quent occurrence : they generally affect the cement or dentine, or both
together.

There likewise occurs frequently enough a new formation of dentine on
the internal surface of the tooth and an ossification of the pulp. To
compensate for the wear and tear of the crown also, produced by chewing,
and also of loss of substance on the external surface through disease,
there are new layers of dentine laid down by the pulp on the interior of
the central cavity.

Teeth which have been drawn may again become attached, and healed
in their alveoli on being replaced.

The formation of teeth in strange localities occurs also as a rarity,
especially in the ovary, but occasionally in other situations.

TISSUES OF THE BODY. 273

REMARKS. — 1. Here we meet with two different views, as in considering hone and
connective-tissue. According to one of these, dentine arises from the odontoblasts in
the form of an intercellular substance produced by the latter; according to another, a
direct calcification of these cells takes place. The latter theory has been defended
recently, principally by Waldeyer : — " The formation of dentine consists in a trans-
formation of part of the protoplasm of the ivory cells into a glutinous substance,
which becomes subsequently calcified, after which the other unchanged part of the
body of the cell remains over in the hardened mass in the form of soft fibres." 2.
Besides diffuse calcification, the laying down of the dentine globules takes place at
this period. These are small spheroidal calcified bodies, which are supposed to be
partly permanent (p. 262), and partly to disappear subsequently. Hoppe maintains
that they are not simple concretions of the bony earths with an organic collagenic
substratum, as has been already mentioned. He was unable to convert their organic
substratum into glutin by boiling. He is rather of the opinion of Hannover, that
their nature is cellular. In the interstices incompletely calcified appearing between
them, again we have the " interglobular spaces" touched on in section 150. 3.
See Trans. oftheLorulon Pathol. Society, vol. vii., p. 185. Earlier numbers also of
this periodical contain other important works of the same author on the diseased
states of the teeth.

D. Tissues composed of Transformed and as a rule Co-
hering Cells, with homogenous, scanty, and more or
less solid Intermediate Substance.

12. Enamel Tissue.
§ 156.

Enamel, which in the human subject is confined to the teeth, as also
among the higher animals, and which is, as we shall find further on, a
decidedly epithelial production, presents a glistening white appearance like
porcelain, "but may also be met with of a more or less yellow or bluish
tint. Its surface appears at first quite smooth, but by the help of a lens
\ve may usually discover a number of delicate grooves encircling the
crown, of which Retzius counted 24 to the 1 mm., and which become
more frequent down below near the edge of the. cement. Like the
osseous coating of the dentine, the enamel is thinnest at the neck of the
tooth, where it is sharply defined against the cement.
From this point upwards it becomes stronger, at-
taining its greatest thickness in the middle of the
crown (comp. fig. 250, p. 261). Examined with
polarised light, enamel displays much more double re-
fracting power than either dentine or cement (Hoppe,
Valentin).

From the examination of finely ground sections, or
of small portions of enamel macerated in acid, we
gather, that the tissue (fig. 261) consists of long
polyhedral fibres or pillars, closely crowded together,

r ,J , , , ., , . i? Fig. 261.— Vertical sco-

and held thus by a scanty amount ol some cement- tson of enamel, with sub-

ing substance. K&XSL'SSi:

These are called "enamel columns or prisms. o, enamel cuticle; &,

They generally extend through the whole thickness Sees bet'we'en'these

of the enamel layer, resting with one end on the den- latter; d, dentine with

T -i ! , i ' i • t- • . T. _j? c its tubes.

tine, while the other assists in forming the surface ol
the former. It is possible, however, that shorter prisms also occur,
which terminate at a greater or less distance from the dental tissue.
Their transverse diameter lies between 0*0034 and 0*0045 mm., and

274

MANUAL OF HISTOLOGY.

Fig. 262. — Transverse
section of human
enamel prisms.

their direction roughly taken corresponds to that of the canaliculi of the

tooth.

If a transverse section of the enamel layer be made, the cut prisms
appear like a delicate tesselated pavement of four or
six sided plates, reminding one of epithelium (fig.
262).

Finally, the enamel is coated and protected by an
extremely hard and resistent homogeneous membrane
discovered by Nasmyth (fig. 261, a). This is the
so-called " enamel cuticle" or cuticula dentis (Koel-
liker). Its thickness is about 0 '00 1-0 '00 13 mm.

§ 157.

Nearer inspection discloses to us many peculiari-
ties in the texture of enamel.

Owing to the fact that certain groups of the prisms project deeper
into the surface of the dentine than others, the latter becomes rough and
uneven. Further, a question arises whether the prisms do not increase in
breadth externally, since the internal surface of the layer appears to be
less extensive than superficial, and since no considerable interstitial sub-
stance can be detected; or whether a certain number of the prisms,
shorter than the others, may not terminate at some distance from the
surface of the subjacent dentine. The occurrence of such short pillars
has been supposed by many, although it is hardly possible to decide the
question owing to their unsteady course. Czermak
states, however, that he has often observed a widen-
ing of the columns externally.

The latter (fig. 263) display as a rule, in vary-
ing clearness and distance, a transverse linear mark-
ing, which may be partly dependent perhaps upon
the progressive laminar calcification of the struc-
ture (Hannover, Hertz}.

Finally, as to the direction of the individual
prisms, we find it very variable; owing to their
undulations and different bends, whole groups of
them may intersect others. Thus in longitu-
dinal sections, the prisms are cut through, in part
longitudinally, in part transversely and obliquely,
and so communicate a streaky appearance to the surface.

Enamel possesses no special nutritive canals. But a system of acci-
dental cavities is met with in it (fig. 261, c), which vary greatly in magni-
tude, and are sometimes simple, sometimes branched, mostly elongated
in a direction parallel to that of the prisms : they may, however, run
obliquely also. They are usually situated in that portion of the enamel
tissue nearest to the cement. But rents and cracks resulting from the
grinding of sections may give rise to the same appearances. Finally, it
seems probable that some of Tomes' fibres penetrate with their canaliculi
from the dentine into the substance of the enamel, as already mentioned,
and run here for a short distance between the prisms, either sinking into
the cavities or coming to an end among the prisms.

REMARK.— Comp. Tomes' work (Phil. Transact.), p. 522.

Fig. 263. — Pieces of human
enamel prisms.

TISSUES OF THE BODY.

275

§ 158.

This substance enamel, now under consideration, is the hardest and
densest in the body, and admirably suited for the protection of the sub-
jacent dentine. In this respect, however, the prisms are excelled by the
enamel cuticle.

As far as we know of the chemical constitution of this tissue, it is the
poorest in water of any in the system, and most rich at the same time in
inorganic constituents. For every 2, 4, or 6 per cent, of organic matter
which retains the form of the prisms after treatment with acids, but which
yields no glutin on boiling (Hoppe), we find 81-90 per cent, of phosphate,
4-9 of carbonate, and more than 3 per cent, of fluoride of calcium
(according to Berzelius}} also 1*5-25 of phosphate of magnesium. We
shall take as examples the two following analyses of Bibra, of which
the first refers to the enamel from the molar tooth of an adult man, and
t he latter to that from a woman of twenty-five years of age : —

1. 2.

Organic substratum, .... 3'39 (?) 5.97

Fat, 0-20 ' traces

Phosphate and fluoride of calcium, . . 89 '82 81'63

Carbonate of calcium, . . . . 4' 3 7 8-88

Phosphate of magnesium. . . . 1'34 2 -55

Other salts, ..'.... 0'88 0'97

Partially developed enamel is naturally far richer in organic constituents.
The substratum of organic matter found in the enamel cuticle is remark-

Fig. 264.

able for its power of resisting acids and alkalies. It yields, moreover, no
glutin (Koelliker).

The development of enamel takes place, as has long been known, from
the cells clothing the concave surface of the enamel organ (fig. 258, c),
and in such a way that each future prism corresponds to a cell. The
process is, however, still a matter of controversy, although everything
seems to point to the conclusion that a calcification of the bodies of the
cells takes place.

As we are already aware, the latter at first appear in the form of cylin-
drical structures, with vesicular nuclei and very delicately granular con-
tents, and of about the same breadth as the prisms. Later on, as the

276

MANUAL OF HISTOLOGY.

calcification of the dentine is commencing, we may remark the surface o*
the latter covered with already hardened but still short prisms (fig. 264, d}.
Not' seldom we encounter appearances as if over these prisms there were
superimposed a special cuticle, the so-called membrana prceformativa
(fig. 264, e). Such a membrane does not in reality exist however, and
the whole is only a deceptive appearance produced by the youngest layer
of enamel which is undergoing development, and which may often be
raised off in the form of a membrane (after the decalcification of the whole)
from the fully formed tissue beneath.

13. Lens Tissue.
§ 159.

The crystalline lens (1) consists of a capsule enclosing a tissue formed
of extremely fine transparent fibres or tubules. The latter have had their
origin from the cells of the corneous embryonic plate, and the whole
structure bears a decidedly epithelial character.

The capsula lentis (fig. 265, a) is a perfectly transparent membrane,
apparently structureless, and only under very high magnifying power
finely streaked. It is much thicker anteriorly than posteriorly (about
0-0135-0-0068 mm.). The inner surface of the anterior half of the
capsule is lined with flattened epithelium of simple nucleated cells, already
mentioned § 87. These measure from 0*0169 to 0-0226 mm. in diameter
(fig. 265, b, and 269, d).

In the neighbourhood of the zonula Zinnii this epithelium passes at its
external border into a zone of young cells with multiple nuclei and but
little cell body ; here also the thickening of the capsule ceases.

Nearer still to the circumference we encounter (springing from these

formative cells) roundish nucleated ele-
ments, destined to be transformed into
the fibres of the lens (Becker).

The fibres of the lens or "lens tubes"
(Linsenrohren) (fig. 266, a, b) are pale and
transparent, without any further structure
in their interior. In the most external
layers of the lens they are especially trans-
parent, and measure in breadth 0-0902-
0-0113 mm., while in the central portion
of the organ they are finer (0-0056 mm.),
but more distinctly bounded and clearer.

The fibres at the periphery (d) possess
a viscid homogeneous contents, probably
enclosed in a very delicate envelope, and
deserve, therefore, rather the name of
tubes.

Those of the interior (b), on the other
hand, have become more solid, and not
unfrequently present a serrated appearance
along their border, a condition of great
significance, for the adhesion of the several
tubes one with another, especially among fishes, where these edges are
regularly toothed.

As may be seen even from side views, the fibres of the lens are not

Fig, 265.— Diagrammatic sketch of the
human lens, a, the capsule; e, the
fibres of the lens, with widened ends,
4 applitd to the anterior layer of
epithelium b, and abutting behind
against the capsule e ; /, the so-called
nucleus zone.

TISSUES OF THE BODY.

277

Fig. 266.— Fibres of the hu-
man lens, a, from the cir-
cumference; and b, from
the more central part.

cylindrical, but more or less flattened (fig. 266, a). This is, however,
most evident when we take the transverse section of a dried lens (fig. 267)
for our object. Here we find the several tubes most delicately marked
out as compressed hexagonal figures, measuring
0-0113-0-0056 mm. in breadth.

Looking now to the arrangement of the fibres
(fig. 265), we find them placed meridionally, pass-
ing from the middle portion of the anterior half
of the capsule over the equator of the organ to a
corresponding point on the posterior half. Their
broad surfaces are always directed outwards, and
their borders are closely applied to those of ad-
jacent fibres. Owing to the latter union being the
stronger of the two, whole layers of fibres can be
peeled off from the lens in the form of delicate
concentric lamellae, which follow at the surface of
the organ the greater curves of the latter, while
within they are more circular.

In perpendicular sections of hardened lenses the fibres (fig. 265, c) are
seen to spring up with a broad extremity (d) under the epithelial coat-
ing (b) of the anterior wall, and then, pursuing their curved course, to
end in a similar manner by insertion into the posterior half of the capsule
(e), which is devoid of cells (2). In following up this course of the fibres, we
remark in the neighbourhood of the equator of the organ, in each, a beau-
tiful rounded vesicular nucleus (/), about 0-0074-0-0129 mm. in diameter.

A glance through the transparent tissue down upon this arrangement
of the nuclei, the " nucleus zone," of H. Meyer, is one
which well repays the observer for the trouble of
preparation. The statement, however, that each fibre
of the lens possesses only one nucleus is not correct
in all cases (see below) : in a foetus of eight months
old I myself have seen them with two or three, most
distinctly visible (fig. 270).

We must not, however, picture this nucleus zone to ourselves as a
diaphragm occupying the equatorial plane ; it resembles far more a leaf
attached at the periphery, which is continued inwards in an undulating
course, at regular distances from the rays of the "lens star," to be referred
to immediately (von Becker.}

The cloudy organ of the infant (fig. 268) presents for our consideration
a very peculiar arrangement in its structure
in the relations of the so-called '• lens
stars." In the centre of the anterior sur-
face (a), namely, we perceive three bands
meeting together at an angle of 120°,
forming a three-rayed star or inverted Y.
On the posterior wall, either a similar
figure reversed is met with or that of a
four-rayed star (b). In the first case the
arms of the posterior Y occupy a position in relation to the anterior
as though turned on their axis to the amount of 60°. Later on in life
each of these rays subdivides at acute angles into regular series of
branches, giving rise to complicated stellate figures.

The microscope teaches us that within such a ray and its system of

Fig. 267. — Transverse sec-
tion of the fibres of a
dried lens.

oo

Fig. 268. — Lens from an infant, a, the
anterior ; 6, the posterior surface.

278 MANUAL OF HISTOLOGY.

branches there exists no lens fibres, their place being occupied by a tena-
cious homogeneous mass. Thus we see that the organ in question is
divided by a system of partitions, springing with its layers from a central
space in the lens ; in that this substance can be followed through the
latter in the form of septa.

The libres, therefore, form in each half of the lens some three or four
wedge-shaped pieces.

This arrangement naturally determines the course of the fibres, and
makes it impossible that any one of them should actually reach both
poles.

REMAKKS. — 1. Beside German handbooks on histology and monographs, comp.
Bovman, Lectures on the parts concerned in the operations of the eye, etc., London,
1849 ; Th. Nunnely in the Journ. of Microsc. Science, 1858, p. 136. 2. These
broadened ends of the fibres of the lens may simulate when in transverse section a
flattened epithelium, without nuclei however. It was formerly supposed that there
existed between the lens and capsule a small quantity of a clear thick fluid, the
humor Morgagnii. This is not, however, present in the living eye, and is the result
of a post-mortem change, produced by the decomposition of the so delicately con-
stituted peripheral fibres and epithelium. The latter swells up before bursting into a
number of spherical globules (fig. 269, e).

§160.

Turning now to the composition of the tissue of the lens, that of the
capsule, in the first place, is at present but insufficiently known. Th«
latter gelatinises in acetic acid and solutions of the alkalies, without, how-
ever, becoming clouded or dissolved. Even after two days' boiling, also,
it is not converted into glutin. It offers prolonged resistance to the
action of alkalies, but is, on the other hand, gradually dissolved in the
mineral acids (Mensonides). Thus we have the reactions, to a certain
extent, of most of the transparent elastic membranes. On the other
hand, according to Strahl's statements, each capsule may be dissolved by
boiling for several hours in water, yielding a substance which does not
give, however, the reactions of glutin.

The composition of the nuclei and walls of the lens fibres is not as
yet known. In their interior is contained a concentrated solution of a
peculiar and very unstable protein substance known as crystallin (§ 12,
p. 1 7). Qwing to its close relationship to albumen, all reagents which cause
the latter to coagulate produce clouding in the tissue of the lens, and when
suitably employed may render the structure of the latter more distinct.
In this respect chromic acid has gained great repute. Besides this, the
lens contains a not inconsiderable proportion of fats, and, according to
older analyses, of extractive matters also. For the human lens Berzelius
obtained the following percentage, of

Water, . . . . 58*0

Protein matter, . •*• . . . . 35 '9

Walls of the fibres, &c., remaining on the filter, . 2*4

Extractive matters, . . . . . . 3*7

The proportion of fats in the human lens was found to be 2 '06 per
cent. (Husson) ; among them cholestearin is present (Lolnneyer). The
amount of mineral constituents met with is only 0*35 per cent. The
clouding of the lens after death depends upon some change in composition
not yet understood.

The specific gravity of this organ in the human being is, according to
Chenevix, 1*076 in the external layers, while that of the more denso

TISSUES OF THE BODY.

279

nucleus may reach 1'194. The index of refraction amounts, in the
external strata, to 1-4071 according to Krause; in the middle to 1-4319,
and in the central to 1'4564.

§ 161.

The lens is developed from a doubling-in of the superficial layer of cells
coating the embryonic body or the corneous layer, which has been already
discussed in considering the epidermis.

But even at a very early period it appears as a structure completely sepa-
rated from the layer just mentioned. It is hollow in the interior, and
has very thick walls, which are bounded by a transparent membrane.
These walls are formed of several strata of elongated cells. From them,
possibly, the excretion of the homogeneous substance has taken place,
which subsequently solidifies into a capsule for the whole organ. In our

Fig. 269. — er-e, Cells from the lens of a
foetal pig two inches long, a, original
cells; 6, other elongated specimens;
c, some more so still, passing into the
form of tubes; d, epithelium of the
lens of a human embryo at eight
months; e, cells from the so-called
humor Morgagnii.

Fig. 270. — Fibres from the lens of a human
foatus at eight months, a, fibies with
one nucleus; 6, another, which still
shows its cellular character; c, flattened
form, as seen from the side; d, fibres
with two or three nuclei.

opinion, however, the capsule is a modified deposit from the adjacent
connective-tissue. These cells gradually fill up, it is supposed, with their
descendants, the central cavity, and become developed in most cases into
lens tubes or fibres, while a certain remainder only, preserving their
original characters, constitute the epithelium of the capsule seen on its
anterior internal surface.

In young embryos we have an opportunity of studying the fibres of
the lens in process of development (fig. 269, a-e).

In more advanced foetuses, as for instance in the human towards the
19

280

MANUAL OF HISTOLOGY.

last months, the fibres are quite similar to what are found in the adult
(fig. 270, a, c), at times, however, still preserving the cellular character
(5). Not very unfrequently we encounter also lens fibres with double or
even triple nucleus (d). The further production of these tubes probably
takes place by a process of segmentation of the immature cells in the
zone situated at the border of the epithelium of the capsule (§ 159), the
new elements being laid down over the older ones. That the process and
the growth of the lens extend far beyond the period of intra-uterine life
is almost a matter of certainty.

At an early period the capsule of the lens is enclosed in a vascular
membrane, which forms a part of the well known system of envelopes of
the organ under the name of the membrana capsulo-pupillaris.

After birth the number of the fibres of the lens is multiplied with the
growth of the body, but their diameter is not increased.

They take their rise from the epithelial cells of the capsule, and, in
keeping with the character of epithelial structures, can be regenerated
provided the capsule and layer of cells be preserved. It is not difficult
to conceive that a lens formed after the capsule has once been opened never
attains the same regularity of form as the first structure, seeing its figure
is quite dependent on that of the capsule. The amount and nature of the
interchange of matter going on in this organ is not yet known. The
former is probably not entirely insignificant.

14. Muscle Tissue.

§162.
The muscles, springing from the middle embryonic plate, are made up

d

Fig. 271.— Striped muscle-fibres.

Fig. 272.— Elements of
smooth muscle, from
the rabbit.

of a soft reddish fibrillated tissue, which is remarkable for the property it
possesses of contracting when its motor nerves are excited. This pecu-
liarity is characterised by the term irritability. As we are taught by

TISSUES OF THE BODY. 281

physiology, the contraction of muscular tissue is of two kinds, voluntary
and involuntary.

Viewed from a histological point of view, muscles may be divided into
those which are made up of long transversely striated fibres as elementary
structures (fig. 271), and those built up of smooth or unstriped fusiform
elongated cells (fig. 272). Dependent on these differences we speak of
striped and smooth muscle.

This anatomical difference, however, seems at first sight much greater
than it is in reality.

In the first place, we encounter many intermediate forms between these
two species of muscular tissue in the animal world ; and, secondly, the
history of development has recently shown that both elements have an
origin extremely similar, namely, each form a single cell (§ 59). The
element of the unstriped tissue preserves this character throughout life,
the striped fibre forsakes its original nature in the greater complication
of its development.

In conclusion, we need only remark that the voluntary muscles of our
body consist of striated fibres (the heart, however, also, among those organs
which are involuntary), whilst those muscles withdrawn from the influence
of the will are composed of smooth fibres. The expressions, therefore, of
"smooth" and "involuntary," or "striped" and "voluntary," do not
correspond exactly in the human body. The specific gravity of the first
of these was settled by Krause and Fischer to be 1'058, that of the latter
1-041.

§163.

The elements of unstriped muscular tissue (fig. 273) were formerly held
to be long, pale, band-like fibres (i)t displaying at intervals several like-
wise elongated nuclei. It remained for Koelliker's quickness of perception
to recognise in these fibres a series of elongated cells arranged linearly one
after the other, and in the year 1847 to introduce to the notice of his-
tologists the " contractile fibre-cell" (c-7*), — a great step towards a proper
comprehension of the structure of this tissue, so difficult of investigation.

We usually meet with the smooth muscle-cell in the form of a long
(d-f) band, which may at times possess extremely great length (g), and
which generally runs off to a point at both ends. It is often short however
(c). Its medium length is about 0 0451-0'0902 mm., short cells measuring
often 0'0282 mm., and very long specimens 0'2256 mm. and upwards.
Its breadth lies between 0'0074 and 0'0151 mm.

Further, it appears pale and homogeneous, either completely colourless
or tinged slightly yellow, and without recognisable difference between
the envelope and contents. Not unfrequently we may remark a row of
granules, the residue of the earlier protoplasm, extending from each pole
of the nucleus into the body of the cell (fig. 272, er) ; small dust-like
molecules of the same may also cloud the otherwise clear substance of the
cell. Finally, as a sign of retrograde metamorphosis, we find fat granules
in varying quantity and size (fig. 273, h).

The contractile fibre-cell may present a very characteristic appearance,
principally due to its nucleus, which appears under the action of strong
acid as a tolerably pale, long, cylindrical rod, more or less rounded at both
ends. Again, this nucleus is met with quite homogeneous, without any
difference of contents and envelope, and apparently without any nucleus.
Its medium length is 0-0226 mm., and breadth 0'0023-0'0029 mm. Its

282

MANUAL OF HISTOLOGY.

situation is generally at an equal distance from both ends and in the axis
of the cell, as may be best seen in transverse sections of previously dried
muscle (*) ; from which, also, we may convince ourselves of the cylin-
drical form of most of the fibres. In
most cases the nucleus is only single ;
but two, three, or even four, may
occur in one cell (Remdk, Koelliker,
G. Schwalbe), — a circumstance of great
importance in tracing the relationship
, , - nx of these to striated muscle fibres.

F 111 llVWV It is only very lately that, by the

i III l\ tX\\\\%. aid of more advanced technical know-

ledge, we have been enabled to render
visible in many nuclei, single or mul-
tiple (1-4), granules of round form and
glittering appearance, which have pro-
bably the significance of nucleoli.
Their diameter is 0-0009-0-0002 mm.
(Hessling, Frankerihauser, Arnold,
Schwalbe}.

Under the polarising microscope
the contractile fibre-cell is found to
\* \\ i re1 ¥1^P&~ ^e doukle refracting and positive to

\ \ f » a flB^ the axis (Valmtin)-

^ \\ " )' * But though this cell appear thus

singular in a state of maturity, it
bears in the embryonic body a less
striking character; the nucleus is then
round and vesicular (a, &). Whether
this original constitution may not per-
sist in many parts of the body is a
question incapable at present of being
answered. Besides this, it is impossible
to indicate any very certain features of
distinction between the fusiform cells
of connective-tissue, which are like-
wise endowed with vital contractility,
and the elements of smooth muscle.
The many controversies which have
taken place in the last few years as to
whether we are to admit the presence
of contractile muscle cells in this part and that, or no, must be judged
accordingly.

On the other hand, the singly nucleated contractile fibre-cells may
acquire striated contents, and thus approach nearer to the elements of
voluntary muscle.

Among such may be reckoned the elements of the muscle of the heart
of lower vertebrates ( Weismann), of the bulbus aortae of the salamander
and proteus (Leydig)-, but probably not the fibres situated under the
endocardium of the ruminants, of pigs and horses, bearing the name of
the fibres of Purkinje.

Smooth unstriped muscle is to be found throughout the whole diges-
tive tract, from the inferior end of the oesophagus down nearly to the

Fig. 273.— Smooth muscle fibres from the
human being and other mammals, a, a for-
mative cell from the neighbourhood of the
stomach of a foetal pig ten inches long ; ft,
another more developed ; c-g, various forms
of contractile cells from the human body ;
A, one of the latter, containing fat granules ;
<, a bundle of smooth muscle fibres;*, a
transverse section through one of these
from the aorta of the ox, with several nuclei
In the plane of the cut.

TISSUES OF THE BODY. 283

termination of the rectum; it is met with also in the mucous membrane
itself, as the so-called muscularis mucosce, in the form of thin layers and
small bundles. The organs of respiration are likewise supplied with this
tissue : thus, it is seen in the posterior wall of the trachea, in the circular
fibres of the bronchi and their branches, and perhaps also in the pul-
monary vesicles. The walls of blood-vessels possess it also, especially in
the middle layer of their coats. These contractile cells make their appear-
ance too in the cutis: firstly, in the form of small groups, as in the
hair follicles, the sebaceous and sudoriferous glands; and then again
forming more or less continuous layers, as in the tunica dartos of the
scrotum, the mamma, and areola. The human biliary apparatus only
shows tissue in the walls of the gall bladder (Henle, Eberth}. Further,
the tissue is distributed throughout the urinary apparatus. It occurs in
the calyces of the kidneys in the form of continuous strata, and also in
the pelvis of the latter organ, in the ureters and vesica. Again, in the
form of scattered elements along the urethra and over the surface of the
kidney. In the male organs of generation also it is extensively met
with : thus, in the tunica dartos, between the tunica vaginalis communis
andpropria of the cord, epididymis, vas deferens, seminal vesicles, prostate,
Cowper's glands, and corpora cavernosa. Also in the female : thus, in the
ovaries, in the Fallopian tubes, and uterus, which latter organ presents to
us during pregnancy the greatest accumulation of the tissue in question
which exists in the bo.dy. Again, in the round (Koelliker] and broad
ligaments (Luschka), and in the corpora cavernosa. Further, smooth
muscular fibres are supposed to exist in the envelope and in the septa within
the spleen and lymphatic glands of mammals. Finally, they occur in the
organs of vision as sphincters and dilators of the pupil ; also in the choroid,
in the ciliary and orbital, as well as eyelid muscles (H. Miiller).

§ 164.

The second species of muscular tissue, namely, the sftiped or
striated,, is to be found in all the muscles of the trunk and extremities,
— those of the ear and external parts of the eye, with the exception of
the muscles mentioned in the preceding section. It enters further into the
construction of many internal organs, as the tongue, pharynx, upper portion
of oesophagus, larynx, genitals, termination of the rectum, and diaphragm.
Finally, it presents itself, modified to a certain extent, in the heart.

As elements, we here meet with long cylindrical and strongly flattened
fibres (fig. 274, 1), which do not, as a rule, give off branches. They
have a thickness of from 0'0113 and 0*0187 mm. up to 0'0563 mm. in
the human body. To these the name of " muscle fibres " or " primitive
bundles " has been given. The human primitive bundle, which is, owing
to its greater thickness, of a yellower tint than the smooth element, dis-
plays, in 'contrast to the latter, a most striking and characteristic texture
under high magnifying power.

It consists of an envelope and contractile contents. The first of these,
called usually the " sarkolemma " or " primitive sheath," is a transparent,
homogeneous membrane, which, on account of its high degree of elasticity,
always remains closely adherent to the included mass in all the changes
of form which take place in the latter (fig. 274, 1). The primitive
sheath may be demonstrated apart from chemical aid by simply break-
ing the continuity of the contents (2 a), or also, as is strongly recom-
mended, by treatment of the living fibre with water, on which the

284

MANUAL OF HISTOLOGY.

membrane becomes raised up 'in blebs by endosmosis. Preparations
also of the muscles of naked amphibia which have lain in spirit frequently
afford very good objects, in which the envelope is observed widely sepa-
rated from the included mass.

On the internal surface of the sarkolemma are situated a series of
roundish or oval nuclei (1 d) 0'0074-0'0113 mm. in length. More
minute examination of the muscle fibres of naked amphibia (fig. 275)
with very high magnifying powers shows the nuclei (c) to be vesicular,
with tolerably thick, and therefore doubly contoured walls, and to contain
one or two nucleoli. In fresh tissue the nucleus lies closely enveloped
in a fusiform cleft. The apices of the latter are occupied by a homo-
geneous clear substance. This is the remainder of the original proto-
plasm, which has not been consumed in the formation of the fleshy
matter of the fibre. This, taken as a whole, has been named the " muscle

Fig. 274.— 1. Striated muscle fibre with a
breaking up into primitive fibrillae a; more
distinct striat ion at 6, and longitudinal lines
at c; d, nuclei. 2. A fibre, 6, torn through
at a. with the sheath partially empty and
visible.

Fig. 275.— A muscle fibre from the frog,
magnified 800 times, a, dark zones with
sarcons elements; b, lighter zones; c,
nuclei ; d, interstitial granules. (Alcohol
preparation).

corpuscle " (M. Schultze, Welcker), and is looked upon as equivalent to a
cell.

In fig. 275 we may remark filiform streaks springing from these muscle
corpuscles, and dotted with fat granules throughout, as also is the
degenerated body of the cell. These we shall have again to take into
consideration below.

The number of these nuclei or muscle corpuscles is not inconsiderable ;
their position is sometimes without arrangement, sometimes alternating.
In the fibres of the heart alone do there exist, beside the circumferential
nuclear formations, others which occupy the axis. But among the lower

TISSUES OF THE BODY. 285

animals, as for instance in the frog, the nuclei lie at every depth in the
fibre.

The contents enclosed in the sarkolemma, or the fleshy substance of the
muscle (fig. 274, 1), is of extremely complex and delicate texture. It
presents, but in varying degrees of distinctness, a longitudinal (c) and
transverse striation (d), affecting the whole thickness of the fibre.

In many dead muscles the longitudinal marking may be observed with
the greatest clearness in many fibres, appearing in the form of very
delicate but distinct parallel lines, traversing the whole length of the
element.

The distance of these from one another varies between O'OOl 1-0*0022
mm. In many cases the lines run continuously for a considerable dis-
tance, but more frequently only make their appearance at intervals in the
fleshy mass, and, after running a short course, disappear again.

On transverse sections of a fibre we may frequently observe the sub-
stance of the contents projecting in the form of fine fibrilla3 or bands
(1, a), bounded by the linear marking.

The objects, however, which we obtain by the action of certain reagents
on the muscle fibres are extremely peculiar,— a method of treatment much
in use. Those which have been macerated in cold or boiled in hot water,
such also as have been subjected to the prolonged action of alcohol,
bichloride of mercury, chromic acid, and, more than all, of bichromate of
potash, are often seen split up
in the most beautiful way into
long fine fibres of O'OOl 1-
0-0022 mm. in breadth (fig.
276).

Owing to this circumstance,

it has been Supposed by many Fig. 276.— A muscle fibre after the continued action of
., . ,, nr •» 1 bichromate of potash for twenty-four hours, showing

that the fibres 01 mUSCle are its partial resolution into fibrilhe.

made up of fine elementary

threads or " muscle fibrillse," as they have been named ; the muscle fibres

are also known, on this account, as " primitive bundles."

The theory in question has had among its defenders a number of men
whose opinions should have great weight. Among these we may mention
Schwann, Valentin, Henle, Gerlach, Koelliker, Leydig, WelcJccr, Schon.

REMARKS. — Comp. beside HenWs work, Bowman in the Phil. Transact. 1840,
Part 2, p. 69, and 1841, Part 1, p. 457 ; also the two articles by the same, " Muscle"
and "Muscular Motion," in the Cyclopaedia, vol. iii. p. 506 and 519 ; and in the
work edited in conjunction with Todd, vol. i. p. 150.

§165.

The transverse striation of muscle is also subject to much variation,
and it is a matter of great difficulty to gain a proper conception of it,
owing to the minuteness of the object and the obstacles in the way of
correct focus. In the first place, we meet with dark, sharply defined, and
continuous .lines, running parallel to one another, whether in a straight or
undulating course. Their distance from one another likewise lies between
O'OOl 1 and 0'0023 mm. Again, these transverse strisB may be inter-
rupted, ceasing for a certain distance. The contour of the whole fibre is at
the same time quite smooth. In other muscle fibres, markings not so dark,
but much broader, are seen, regular cross-bands, so that the whole appears
to consist of a double system of dark and light transverse zones. Finally,

286 MANUAL OF HISTOLOGY.

though seldom, the transverse lines may become separated from one
another, the lateral outlines of the fibre becoming indented ; so that the
whole conveys to us the impression that it is about to break up into a
number of plates. Coincident with the more distinct appearance of trans-
verse striation, the longitudinal marking usually decreases in clearness. •

When treated with certain reagents the peculiarities of the tissue in
this case also are forcibly brought before us. Thus, acetic acid causes
the longitudinal lines to vanish, while the transverse remain a certain
time still visible. In very dilute hydrochloric acid, and also in the acid
gastric juice, the muscle fibre is resolved into a number of thin disks, while
at the same time that it swells up, and commencing solution sets in, the
longitudinal markings becoming completely destroyed. These disks often
separate from one another in the most regular manner imaginable (fig.
277, 4, 5). Carbonate of sodium has a similar action, but does not produce
swelling of the tissue ; chloride of calcium also, which, however, gives rise
to a shrinking and transverse wrinkling in the fibre, and not unfrequently
causes the appearance in its interior of transverse rents. Now, as in the
former cases, we believed ourselves warranted in accepting with certainty
the fibrillated composition of the muscle fibre, so ought we now, seeing
these effects produced by the chemical reagents just named, to look upon
the latter as made up of a number of disks or plates arranged one over
another (1).

The theories broached by histologists as to this peculiar double mark-
ing of the muscle fibre are naturally enough very various, owing to the
obscurity of the subject.

If we except a multitude of manifestly incorrect efforts at explanation,
there remained for many years only two modes of viewing the matter, by
which the nature of the texture could be interpreted, at least in its most
important features. Hence both of the views in question found assailants
and defenders.

According to the first of these theories, already mentioned in the pie-
ceding section, the fibrillae are the pre-existing essential elements of the
fleshy mass, and remarkable for their jointed structure (fig. 277, 2).
Owing to the fact that the transverse markings of all the fibrillse occur at
the same intervals and lie one beside the other, a striped appearance is
communicated to the whole fibre (1). It is not difficult to see that the
appearances presented may be thus tolerably well explained, and why it
is that we sometimes remark a longitudinal and sometimes transverse
striation to preponderate. On the other hand, the occurrence of disks,
with absence of the longitudinal lines, is difficult of interpretation.

The second theory, which has gained for itself in recent times a consi-
derable circle of adherents, and which we believed also, with certain modi-
fications, to be correct, originated with that excellent English investigator
Bowman. Among those who supported it, with greater or less modifi-
cation, the names of Harting, HaecM, Leydig, Keferstein, Margo, may
be mentioned.

According to this theory, the muscle fibre consists essentially of an
aggregate of small particles (Fleischprismen, Fleischtheilchen), or sarcous
elements, which, united in a transverse direction and clinging together,
give the appearance of a disk or thin plate (Bowman's Disk, fig. 277, 3,
4, 5), and, arranged longitudinally, that of a fibril (1, 2). Both, how-
ever, fibrils as well as disks, it was held, are not the optical expression
of a pre-existing composition of the kind, which is entirely absent in the

TISSUES OF THE BODY.

287

fresh, living muscle fibre; they rather indicate a tendency, on the part of
the muscular element, to split up in one of these two directions (2). It
must be allowed, however,
that the tendency to break
up into fibrillse in a longi-
tudinal direction is greater
than in the transverse into
disks, the latter being of
rarer occurrence than the
primitive fibrillae.

The supposition of the
existence of these sarcous
elements, connected longi-
tudinally and transversely
with one another, neces-
sitates of course the pre-
sence of a uniting medium
between them. And when
we remember the com-
pletely opposite effect of
the two reagents already
mentioned, that, for in-
stance, very dilute hydro-
chloric acid resolves the
muscle fibre into plates,
while alcohol and bichro-
mate of potassium convert it
into fibrillse, we must look
for two kinds of cement-
ing substance, — one for
the agglutination forming
longitudinal fibrillaB, and
another different one unit-
ing the flesh prisms in a transverse direction and forming disks. The
quantity of transverse cement (probably more or less gelatinous) -is far
smaller than that of the probably fluid longitudinal. The latter is remark-
able for its great capacity for contraction and swelling out. In con-
formity with this, we sometimes find the dark transverse zones placed far
closer to each other than at other times.

Here arose the very important question, how the closer relation of
the sarcous elements to the transverse lines of the fibre was to be repre-
sented.

We frequently remark (and especially regularly after slight treatment with
acetic acid) the transverse striation to be made up of dark zones, refract-
ing the light very strongly, alternating with clearer belts of less refracting
power. The latter are the layers of the longitudinal cement, swollen up
and rendered clear ; while the darker zones represent the sarcous elements,
united together by an agglutinating medium, and forming disks. Accurate
study of the effect of water acidulated with hydrochloric acid showed
how the clear transverse zones become more distinct with the rapidly-
commencing swelling up of the longitudinal cementing medium preceding
solution ; that a muscle fibre might then break up into disks, each of the
latter consisting (like a voltaic element with its zinc and copper plate) of

tig. '277.— 1. A muscle fibre with primitive fibrillae and trans-
verse striation strongly marked, taken as the fundamental
form. 2. Isolated fibrillae strongly magnified. 3. Sarcous
elements united, forming a disk (diagrammatic). 4. Plates
of human muscle after treatment with hydrochloric acid.
5. A human fibre after prolonged treatment with hydrochloric
acid, with dark (c) and light (d) zones and nuclei (a, b). 6.
Two pointed fibres from the human biceps brachii. From one
of them the interstitial connective-tissue is prolonged over
the end.

288

MANUAL OF HISTOLOGY.

a darker and clearer portion (fig. 277, 5, c, d) (3) ; it showed further, that
the clear part underwent solution by degrees, while the dark zone remain-
in^ over occasionally presented to view the sarcous elements of a disk, as
though in the act of separation from one another.

The improved and greatly increased magnifying power of our new
microscopes has since rendered it no longer difficult to obtain a view
of the fleshy prisms and of the fibrous structure of many muscles (fig.
278). The lamprey, and, better still, the lower amphibia (Proteus, Siredon),
afford very good objects, owing to the large size' of their sarcous elements.
However, the same may be recognised in the smaller particles of the
muscles of frogs, mammals, and human beings (4).

The prisms appear now as cylindrical or hexagonal prismatic particles,
of greater height than breadth. Their length in the proteus (fig. 278, 1, a)
is 0.0017 mm., in the frog (fig. 280) 0-0013 mm., in the pig (fig. 278, 2, a)
and in man O'OOl 1-0*0012 mm. Standing one beside the other, they
form the dark transverse zones, and are almost in actual contact with one
another as a rufe, owing to the scanty amount of interposed cement
(fig. 278, 2, a; fig. 279, a).

Those spots are particularly instructive where the sarcous elements of a

Fig. 1.

Fig 2.

Fig. 278.— Two muscle fibres from the proteus,
1, and fig. 2, magnified 1000 times. (The first
was an alcohol preparation, the latter treated
with acetic acid of 1-01 per cent.), a, sarcous
elements; 6, clear longitudinal cement. At a,
the sarcous elements are more separated from
one another, and the transverse cement is visible,
c, nucleus.

Fig. 279.— Kravse's transverse
disks, a, a. 1, a muscle fibre
without, 2, one under strong ex-
tension; both highly magni-
fied (Martyri); 3, a fibre from
the dog immediately after
death.

transverse row appear somewhat distant from one another (fig. 278, 1
below, 2, a*).

In our description so far of the structure of the muscle fibre, we have
intentionally followed up the historic course of the opinions held regarding
it, in order to facilitate the comprehension of the most recent investiga-
tions by the reader.

From the newest researches we learn that our earlier views were incom-
plete. But still the field of inquiry is so exceedingly wide, the matters
to be dealt with lie so near the verge of invisibleness, and the composition
of the fleshy mass is so very unstable, that the views of present-day
observers differ widely.

In the first place, the transparent transverse zone is traversed by a very
fine dark line. This was referred to by the English observer " Martyn
with others, and the second edition of this hand-book, in the year 1862.

TISSUES OF THE BODY.

289

Later on, its nature was made the subject of more extended research by
Krause, so that we may name it the " transverse plate of the transparent
zone" of Krause. This cross-line (fig. 279, a) maybe recognised without
great difficulty in the living muscles of mammals and the naked amphibia.
It is to be seen very distinctly in the muscle fibres of insects, after pre-
vious stretching, attaining a thickness at times of 0*0008 mm. After
the action of very weak acetic acid it is the source (at least very fre-
quently) of the transversely striated marking of the muscle fibre of the
vertebrates.

Krause holds a very peculiar view in respect to the structure of muscle
(fig. 280). He regards the dark cross-line just mentioned as the optical
expression of a delicate transverse parti-
tion springing from the sarcolemma.
which divides the interior of the muscle
fibre into a number of diskoid compart-
ments built up one over the other. The
contents of such a compartment, then,
would consist from below upwards of
(1) half of a transparent transverse
zone ; (2), of a dark zone occupying the
middle (i.e., of a transverse disk of sar-
cous elements); and (3), of another half
of a transparent cross zone (see fig. 280).
Krause believes also in the existence
of a delicate lateral membrane, invest-
ing closely the sides of the sarcous
elements and ends of its transparent
appendages, and uniting with the trans-
verse membrane. In this way he sup-
poses the elementary structures of the
striped fibres to be formed — the so-
called " muscle caskets." In longitudinal rows they constitute the fibrillse.
This author also believes the clear longitudinal and transverse cementing
medium to be liquid, and that during contraction the layers of fluid flow
from the end surfaces to the sides.

Almost at the same time, however, Hensen observed the dark transverse
zone to be divided in its middle by another transparent
cross-line of weaker refracting power (fig. 281, a). This
is now known by the name of the " middle-disk" of
Hensen. The views regarding its nature are very
various. By some (Krause^ Heppner) it is regarded as
an optical illusion, while others (MerJcel. Engelmamn)
maintain its presence in the living fibre. The last
view, of course, does away with the pre-existence of
the sarcous elements. They would have to consist
either of three portions, — two dark terminal, and -a
central transparent, — or could only be products of coagu-
lation, assuming a homogeneous constitution after death,
composed of the dark matter of the transverse zone and
middle disk.

Finally, minute granules have been remarked, arranged
in rows, at each side of Krause 's transverse lines (Flonel, MerJcel).
These rows have been named " accessory disks" (Engelmann) (fig. 282).

Fig. 280.— "Muscle caskets," a; &, flbrillae
forming transverse disks at c; c, sarcc-
lemraa.

Fig. 281— Muscle-fibre
of the lancelet (am-
fhioxus). a, the
" middle disk " of
Hensen; b, transpa-
rent transverse zone
(alcohol prepara-
tion).

290

MANUAL OF HISTOLOGY.

Fig 282.— Portion of
dead muscle fibre,
after Englemann. a,
transverse disks; 6,
accessory disks.

This does not appear to be the place for entering more deeply into the

subject.

The structure of striped muscle fibres will probably remain a matter of
controversy for many years to come. We look, however,
upon the cross-lines of Krause as fully substantiated.
But as to the existence of lateral membranes, and the
theory of the u muscle caskets" dependent on it, we do
not believe in it any more than in the fluidity of
the cementing medium. As regards the middle disks,
we have not yet come to any definite conclusion. We
look upon the sarcous elements as pre-existing in some
form or other, and not as products of coagulation
(Engelmanri). In our opinion the longitudinal fibrillae
are artificial productions.

Unexpected results were obtained some years ago by a method of treat-
ment practised by CoJmheim, namely, the preparation of transverse sections
of frozen muscle. In these may be recognised groups
of sarcous elements, like a mosaic of small par-
ticles of from three to six-sided figures. Between and
bounding these is a trellis-work of transparent glit-
tering lines, which become broader only at irregular
intervals. These belong to the transverse cementing
medium.

It is still a matter of uncertainty whether the ele-
ments of unstriped muscle possess sarcous elements or
not.

Bruclte made a very interesting discovery long ago,
namely, that Bowman's sarcous elements, together
with the cross-lines of Krause and middle disk, are
double refracting, and are positively monaxial, while
the cement deposited between them is single refracting.
The first are " anisotropic," the latter " isotropic."
The correctness, however, of Bi-iicke's statement has
been since questioned by Rouget and Valentin.

REMARKS. — 1. The slight inclination of the fibrillae to separate from one another
(when no reagents are made use of) seems also to point to this conclusion. 2. " The
muscle fibre is therefore just as little a bundle of fibrillfe as a pillar built up of disks
arranged one over the other. Should a total separation in both directions really take
place, the result would necessarily be a breaking up into fleshy prisms." " And if we
tear off a fibril from a muscle fibre we take away from every disk a sarcous element,
and vice versa" (Xowman). 3. Dobie (Annal. of Nat, Hist., Feb. 1848) also discri-
minated m the same manner long ago between the darker sarcous elements of Bow-
man and a second system of clearer portions situated between them. Muscle fibres,
when stretched, show, according to Martyn (Scale's Archives, Vol. iii. p. 227), another
transverse line passing through the centre of each clear zone. The same was pre-
viously observed by Amici, Koelliker, and others. I myself have remarked it
frequently too. 4. They may assume very large proportions, also, in the crawfish.
> they were found by Hakel to vary from 0'0020 to 0'0099 mm. in height ; and
ic was able to isolate them in a gelatinous condition as long as 0' 0114 mm. He looks
upon them as hexagonal prisms. Amici s observations are also of great interest.
According- to him, the elongated prismatic elements ot the muscle of the common
s-ny, separated by a distinct cement or clear zone from one another, assume
during contraction a marked obliquity of position. This I can corroborate myself,
lurther, according to Schonn, there is a dark spot visible in each sarcous element.

Fig. 283. — Transverse
section of a frozen
frog's muscle. o,
groups of sarcous ele-
ments ; 6, a nucleus ;
c, clear cement.

TISSUES OF THE BODY.

291

§ 166.

The occurrence in its substance of certain foreign molecules, partly con-
sisting of fat, is another peculiarity of the muscle fibre. These are known
as the " interstitial granules of Koelliker" although described long ago
by Henle.

They are not always distinct in human muscle, but when present are
encountered in rows parallel to the direction of the fleshy fibres.

In the muscle of the frog they appear with greater distinctness (rig.
284, d), and are often uncommonly numerous also, resisting, further, the

Fig. 284.

Fig. 285.— Muscle fibre from the leg of a
frog, after prolonged treatment with
dilute hydrochloric acid. From the
cut surface very fine fibres are seen
projecting, a; with granules, b; the
latter are distributed along the whole
fibre.

action of water acidulated with hydrochloric acid entirely. Here they
commence at the poles of the nuclei, and appear as though situated in a
system of canal-like interstices, occupied by nuclei, granules, and fat
molecules (Koelliker), which, under ordinary circumstances, are filled up
with the well-known protoplasm. When coagulated, these masses may
form a series of extremely delicate fibres (0*0006 mm. thick) and project from
the cut end of a muscle fibre which has been treated with water contain-
ing a trace of hydrochloric acid (fig. 285). The fibres contain fat mole-
cules, partly externally, and partly in the interior. Leydig, JBottcher, and 0.
Weber, erroneously regard these structures, together with the nuclei of the
muscle, as a network of stellate connective-tissue cells with tubular pro-
cesses traversing the substance of the muscle-fibres.

On transverse sections of muscles which have been dried and subse-
quently moistened (fig. 286, a), we see these rows of fat granules as
a number of dark dots, as long as the molecules remain in the section,

292

MANUAL OF HISTOLOGY.

Fig. 286. — Transverse section of the hu-
man biceps brachii. «, muscle fibres;
6, section of a large vessel; c, a fat-cell
in a considerable connective-tissue in-
terstice ; d, section of a capillary vessel
in the thin septum of connective-tissue
between two muscle fibres ; e, nuclei of
the latter lying close to the sarcolemma.

but as small round openings on their falling out. But, besides these,

the sarcous elements appear, under low
magnifying power, more or less distinctly,
-••* in the form of extremely fine pale dots.

§ 167.

We now come to a special modifica-
tion of striped muscular tissue, namely,
that formed of branching or reticulated
fibres. These are of frequent occurrence
in the lower animals, but are, as far as
we know, at present confined to but
limited portions of the human and mam-
malian body.

For many years past the occurrence of
muscle fibres of this kind has been recog-
nised in the tongue of the frog. Here
they are seen dividing and subdividing at
acute angles. In the same organ of man they have since been found
by Biesiadecky and Herzig, as also by Rippmann, having been previously
observed in some of the mammalia. In the lips and snouts of many of
these animals the same variety of the tissue appears.

On the other hand, the muscle of the human heart, and that of other

vertebrates, shows with the greatest fre-
quency division of the fibres with anasto-
moses; thus the formation of regular
muscular networks.

The muscle fibres of this organ (fig.
287) are smaller than elsewhere, and richer
likewise in fat molecules. Envelopes are
less apparent than on other striped fibres,
or are entirely absent. Finally, the trans-
verse striae appear with greater distinct-
ness, and the tendency to break up into
fibrillse is here considerable.

The union of adjoining fibres (a, b)
is effected as a rule by short (c) and usually
slender branches, which leave the stem
now obliquely, now more transversely, so
that a regular network is produced, very
important in the mechanism of the
motions of the heart.

According to Kodliker's statements,
each ramifying muscular element of the
heart corresponds to a stellate cell, and
the whole to a cellular network. Weismann, however, declares that his
investigations have led him to other conclusions. According to him, the
muscle bands consist (and it is easy to convince ourselves of the fact), in
fishes and amphibia, of simple elongated fusiform and sometimes branch-
ing cells, associated together. The same is the case in the embryos
of the higher vertebrates.

In the latter, however, they become, later on, more closely united to
form the common mass of the band. But even here it is possible to

Fig. 287.— Muscle fibres from the heart,
after Schweigger-Seidcl. To the right
the boundaries of the cells and the
nuclei are to be seen.

TISSUES OF THE BODY.

293

Fig. 288.

render visible the boundaries of the individual cells artificially (Aeby,
Ebertli , Sch weigger-Seidel) .

In the other transversely striped muscles of the body it is the exception
to find branching fibres.

REMARKS. — The retiform connections of striped muscle fibres were described by
Leuckart and myself many years ago, and probably for the first time, as occurring
in arthropods, and noted later as of frequent occurrence among invertebrate animals.
In the year 1849 they were again brought to light by Koelliker, having been pre-
viously seen by Leeuwenhock.

§ 168.

The fibres of striped muscle are arranged parallel to one another (with
exception of those of the heart), and ^

appear prismatic, owing to their mutual
contact (fig. 288, a). Their direction is
that of the long axis of the muscle. Be-
tween them is situated a very small quan-
tity of interstitial connective- tissue, in
which the nutrient capillaries (d) and
nerves of the part are contained.

Several of these muscle fibres are usually
united to form a bundle varying in thick-
ness from 0'5 to 1 mm., and separated
from the surrounding bundles by a
stronger layer of connective- tissue. Such
primary fasciculi are then combined to form secondary, which present
themselves in very varying thickness.

The connective-tissue envelope and uniting substance of muscle is
known under the name of " perimysium," two
kinds of which are recognised, namely, an external,
enveloping the whole structure, the perimysium
externum, and a continuation of the latter between
the fibres, the perimysium internum.

Fat-cells (c) may also be met with in the connec-
tive-tissue of muscle, becoming more numerous in
obese bodies, or in muscles which have remained
long unused. Seen from the side, they are ar-
ranged in rows one after the other (fig. 289, b).
They may eventually interfere with the ability of
the fibres to perform their work.

Bands of smooth muscle also, although they
seldom form such bulky muscles in the human
body as the first formation, are nevertheless put
together in a similar manner in bundles, wherever
they are crowded and collected in large numbers
together. On the other hand, contractile fibre-
cells appear frequently enough in the body in very
small aggregations, hidden and obscured by an excess of connective-tissue,
so that they can only be discovered amid the latter with difficulty. Con-
sequently, we may distinguish between pure and mixed unstriped muscle
(Koelliker).

The vascularity of muscle is very considerable, and the arrangement of
its vessels characteristic (fig. 290). The arterial stems entering the

Fig. 289. — Human muscle
showing fat-cells, o, mus-
cular fibre; 6, rows of fat-
cells.

294

MANUAL OF HISTOLOGY.

muscle (a), send off to the fibrilke short transverse branches, which
are then broken up into a delicate capillary network
(c, d), whose longitudinal tubes pass between the
muscular fibres, and communicate with one an-
other at long intervals by means of short cross twigs.
Thus, a long-meshed capillary network is formed
within which the muscle fibre is situated. The
proper fleshy substance of the latter receives none
of these capillaries. As to the venous vessels,
their course corresponds precisely to that of the
arterial.

The nerves met with here will be considered in
the next chapter.

§ 169.

As is well known, muscles are united very closely
with their tendons, and in such a manner that
the latter, in their course, appear to be either the
immediate prolongation of the muscle fibres, or, the
insertion of the latter into the substance of the ten-
don takes place at an oblique angle.

The arrangement of the tissues is, however, essen-
tially alike in both cases. Yet for all this it was a
long time before conclusive results could be arrived
at here, owing to the want of suitable modes of
manipulation.

With a rectilinear insertion of the tendon, there
appears to be no sharp boundary between the fleshy
substance and that of the connective-tissue, so that
a casual observer would be warranted in supposing
an immediate transition of one tissue into the other (fig. 291). On the
other hand, a completely different appearance is presented, where the
insertion of the fleshy fibres is oblique, namely, a sudden termination of
the latter, so that simple agglutination of two tissues was supposed to
exist here by Koelliker.

Weismann, on the other hand, succeeded in demonstrating in every
case, with the help of strong solutions of potash, the sharp termination
of muscle fibres against the tendinous tissue. He showed them to be
covered also here with sarcolemma (fig. 292, .&), and to end rounded
(a, b), pointed, or obliquely truncated, and so on. They are merely
cemented to the tendinous bundle (c, d) >at this point, although most
securely. Other macerating fluids may be made use of with similar results,
and even immersion in glycerine may produce the desired effect (Biesiadecky
and Herzig).

We are now met by the important question as to the length of the
contractile fibres of muscles.

Do they traverse the latter in their whole extent, or do they terminate
before they have done so 1

It was formerly supposed that each muscle fibre was of the same
length as the muscle to which it belonged. More recently, however, the
interesting discovery was made by Rollett, that many of the fibres are not
obliged to pass through the whole extent of the muscle in order to end in
a tendinous bundle, but that the termination of the strongly pointed fibre

Fig. 290. —Capillary net-
work of a striped muscle,
o, arterial veHsel; 6,
venous; c and d, the
network of capillaries.

TISSUES OF THE BODY.

295

may take place rather in the middle of the muscle (fig. 277, b). Continuous
with its end, and playing the part of a tendon to a certain extent, we find
interstitial connective-tissue. These statements were then subsequently
corroborated by E. H. Weber, Biesiadecky, and Herzig, Aeby, and Krause,
who met with rounded and pointed forms of termination besides.

291.— Two muscle
fibres (a), with apparent
transition into the con-
nective-tissue bundles
of the tendon (6).

Fig. 292.— Two muscle fibres (a, b) after treat-
ment with solution of potash. One of them is
still connected with a tendinous bundle (c),
the other loosened from its attachment to
one of the latter (d).

We can also convince ourselves that the opposite end of the fibres
may terminate in like manner. Krause is of opinion that no muscle
fibre exceeds 4 c. m. in length, and that those which are apparently longer
consist of two fusiform elements adhering together (2). Further investi-
gation appears desirable here. In short muscles the fibres probably tra-
verse, as a rule, the whole length of the muscle. In the longer muscles
of the frog, also, we may convince ourselves that this does in reality take
place (Koelliker, Weismann, Kiilme).

EEMARKS. — The views which were formerly most widely held may be arranged
under two heads. According to the first of these, the fleshy mass was directly con-
tinuous with the tendinous bundles ; to the second, that the muscle fibre, terminating
abruptly, was embraced externally at its end by the fibres of the tendon, in the same
way that the finger of one hand may be grasped by the tips of those, of the other.

§ 170.

In examining muscular tissue chemically, we should be able to
separate its essential constituents, such as the striped fibres and con-
tractile cells, from those which are mere accessories, namely, connective-
tissue, vessels, and nerves. Further, we should be able to determine
what organic and what inorganic substances enter into the composition of
fibre and cell, and how they are distributed over nucleus, envelope, and
20

296 MANUAL OF HISTOLOGY.

contents. Finally, we should analyse the fluid saturating muscles, with
its nutritive matters and products of decomposition resulting from the
energetic transformative processes going on in the tissue.

Zoochemistry, however, of the present day is unable to meet these
requirements of physiology; and yet, muscle is one of those tissues
which has received most attention to this end. In the year 1847,
Liebig presented us with his elaborate treatise, and, more recently, Kuhne
has essentially furthered our acquaintance with the subject by his elegant
experiments on the muscles of frogs.

From the already mentioned microchemical bearing, we gather that the
substance of the sarcous elements, of the longitudinal and of the transverse
cement, is to be recognised as three distinct materials with separate
reactions. We have still, then, the nucleus, insoluble in acetic acid,
dark transverse disk of Krause (also of resistent nature), and the sarco-
lemma, with its reactions so similar to elastic tissue (but greater solubility
in alkalies); so that, taken in all, there is very considerable complexity to
be coped with.

The specific gravity of striated muscle is stated to lie between 1'055
(G. Krause) and 1'041 (W. Krause and Fischer), while the proportion of
water contained in it ranges from 78 to 72 per cent. (1). This water belongs
first of all to the tissue of the fibres, then to the other structural con-
stituents scattered among the latter, and finally, to the fluids with which
the whole mass is saturated, the amount of which, however, is not yet
known. This latter has been named the "muscle plasma," Like the
plasmatic fluid of the blood, it loses, on the death of the muscle and con-
sequent "spontaneous" coagulation as it is called, an albuminous substance,
and becomes " muscle-serum " (Kuhne).

The juice of living muscle has a distinctly alkaline reaction (Du Bois-
Reymond) ; that of the dead tissue, or that affected by rigor mortis, is acid
(Liebig).

From the solid constituents of muscular tissue, which amount to some-
where about 20 per cent., we have first a varying quantity of glutin'ous
matter to deduct, which belongs to the commingled connective-tissue.
About from 0-6 to 2 per cent, of glutin may be obtained from fresh muscle.

The fresh tissue then contains, to the amount of 15-18 per cent., a series
of albuminous matters, partly soluble and partly insoluble, witli which
we are still but imperfectly acquainted. These are in the first place con-
stituents of the juices of the tissue, then again of the fleshy fibres of the
latter. The soluble members of the group are for the most part remark-
able for their coagulation at a low temperature (35-50° C.), a property
which is to be met with only in those of the contractile substances of the
system.

Kuhne has obtained the spontaneously coagulating albuminous sub-
stance of the plasma from the muscles of frogs, and has named it myosin
(§ 12). It is the congelation of the latter which communicates to the
fibre of muscle its cloudy appearance on rigor mortis setting in. The
coagulum of myosin is insoluble in water, but soluble in solutions of
common salt, which contain less than 10 per cent of CINa, likewise in
dilute acids and alkalies.

Three other albuminous substances, besides, may be obtained, according
•to the same observer, from muscle serum, namely, the so-called albuminate
of potash, a second material, coagulating at 45° C., and a third, which
requires 75° C., before the latter process takes place in it.

TISSUES OF THE BODY. 297

If, on the other hand, muscle be treated with a very dilute solution of
hydrochloric acid (1 : 1000), another modification of the albuminate group
is obtained, from the members of the latter contained in it, namely,
syntonin,. This body was formerly named " muscle fibrin," until Liebig
prove its difference from fibrin. It may be obtained, moreover, by a
similar process, from other albuminous matters, and is probably also
formed physiologically by the action of the acid gastric juice during
digestion.

The quantity of syntonin varies very much in the muscles of different
animals (Liebig), and we are taught further, by the microscopic control of
the fibre engaged in solution, that we have here to deal, not with a simple,
but with a compound matter, consisting of three substances,- — first, the
longitudinal cementing medium, which falls the first prey to the solvent
action of hydrochloric acid, and then the sarcous elements and transverse
cementing substance, which are probably not simultaneous in their
solution. Besides these, there remains over in the sarcolemma a slimy
granular residue with fatty molecules.

Neither nucleus nor sarcolemma yield any of this syntonin. The first
affords no glutin (Scherer, Koelliker), but consists of a substance nearly
allied to elastin, but differing from it in its smaller power of resistance to
reagents ; the latter resists the action of dilute hydrochloric acid for days
in the most determined manner (fig. 277, 5, a, b), but gives way on the
other hand to strong alkaline solutions.

Like all other tissues, muscle contains fat, but in most variable
quantity. A certain proportion of it may be set down to the cells of the
nerves and fat-cells of the fleshy mass, but a certain amount belongs to
the fibres themselves.

By means of washing and expression, about G per cent, of constituents,
soluble in cold water, may be extracted from the dead muscles of the
mammalia. They are of very various nature and great physiological
interest. In the liquid so obtained, which is of reddish colour, opaque,
and of strongly acid reaction, we encounter, in the first place, a not incon-
siderable proportion of soluble albuminoids, amounting in the fresh tissue
to 2-3 per cent.

We obtain in the first place, then, the red colouring matter of the
muscular fibres in solution, which is identical with that of the blood
(Kuhne), and with which the tissue is saturated during life. The tint of
striped muscular tissue is more intense than that of unstriped fibres, and
is, as a rule, only present, with any degree of markedness, among the
higher vertebrates, whilst the flesh of the lower members of this group
appears in general but slightly reddened, or even quite pale.

Besides this, the juice of muscle contains, as shown by Liebig, a series
of important products of decomposition, which were known to earlier
investigators as " extractives." Among these there appear, in the first
place, several azotised substances. The first of these is kreatin (p. 44),
whose amount is usually small, existing, it is generally supposed, in largest
quantity in the heart. It varies also in different species of animals,
and is more abundant in lean than in fat bodies, and likewise after
muscular exertion. A hundred parts of fresh human muscle contain,
according to Schlossberger, O'OG of kreatin (in the horse. 0'07. according
to Liebig), while the heart yields 0'14 per cent. The next of the series
is Jcrealinin (p. 45) (nearly allied to the last), which appears to occur in
smaller quantity than the last. Its occurrence, however, appears doubtful

298 MANUAL OF HISTOLOGY.

from Neubaur's investigations. Then we find hypoxanfhin (p. 43).
Strecker states the amount of the last of these to be only 0'022 per
cent, in the fresh flesh of oxen. In addition to these, a fourth substance,
xanthin (p. 43) is supposed by Scherer and Staedeler to exist in the flesh
of mammals. A new substance, discovered by Weidel in Liebig's extract,
may also be mentioned here, to which the name of carnin has been given.
Urea is not usually present in human muscle ; tyrosin and leucin are also
absent (2). The muscles of embryonic pigs of two inches long, however,
contain, besides kreatin, a moderate amount of leucin.

In muscular tissue also there is a peculiar species of spurious sugar,
which has been named inosite (p. 33), and which has up to the present
only been met with in the substance of the heart. According to Valen-
tiner, it appears to be a normal constituent of the muscles of drunkards (3).
Staedeler met with it also in the muscles of dogs. Meissner has likewise
demonstrated the presence of a kind of sugar, " muscle sugar," peculiar to
muscle, in the flesh of the five classes of vertebrata, although as yet no one
has succeeded in obtaining it in a pure state. It is a matter of some
interest, further, that the embryonic muscle fibre, as well as the contractile
fibre-cell, both contain glycogen (Rouget, Bernard, and Kuhne) ; but it
appears also to be regularly present at a later period (0. Nasse).

In that the muscles of phytophagous mammals contain dextrin, the
occurrence of this muscle sugar is easily explained.

The series of organic acids is no less considerable. In the first place, we
have G'6-0'7 per cent, vfparalac&ic acid (p. 34) — the source, apparently,
of the acid reaction of dead muscle. It was formerly supposed with
Licbig that it was a component of every living muscle also, but Du Bois-
Reymond showed later that the plasma of quiescent or moderately active
muscle has a neutral or weakly alkaline reaction, and only becomes acid
when the structure has been called on for immoderate exertion. On the
other hand, after the death of the muscle, which is ushered in by rigor
mortis, the fluid of its parenchyma becomes rapidly acid by virtue of the
presence of free lactic acid. As to the particular constituent of the
muscle from which this acid has its origin, we are at present unable to
answer anything with certainty.

Besides this, we meet with inosinic acid (p. 36), according to Liebig,
about which but little is known, and which appears also in very small
quantity. Schlossberger, however, was unable to discover it in human
flesh. Further, muscle juice contains of the volatile fatty acid group
bvtyric, acetic, and formic acids. Uric acid was only once met with by
Liebig.

Finally, the mineral constituents of muscle (of the tissue as well as con-
tained fluid) are very peculiar. The same compounds as those occurring
in the plasma of blood are certainly met with, but in completely different
proportions. While in the latter the combinations of soda preponderate,
muscle tissue shows the greatest poverty in soda, and an excess of potash.
In contrast also to the plasma of blood, the phosphatic salts exceed in
muscle the combinations of chlorine by a large amount, the greater part
of the phosphoric acid being united with potash, and the proportion
of chloride of sodium appearing but very inconsiderable. In conclusion,
among the combinations of phosphoric acid with earths, we find the
magnesian phosphate exceeding in amount the corresponding salt of
calcium. Iron is also contained in flesh in a small quantity. The absence
of sulphates is rather remarkable.

TISSUES OF THE BODY. 299

When the question is started, Where are we to suppose these mineral
constituents to exist, whether in the fibre or its nutritive fluid 1 the fol-
lowing fact may be borne in mind, that the proportion of salts soluble in
water which are present in flesh is very considerable. The former amount,
according to Clievreul, to 81, and to Keller, to 82 '2 per cent of the whole
ash, while the quantity of phosphate of calcium is stated to be 5-77,
and that of magnesian phosphate 12 '2 3 per cent. Of course a
larger proportion of potash compounds must occur in the fluid of
muscle than in the fibre itself, whereas the latter is richer in phosphatic
earths.

Living muscle contains, further, carbonic acid and oxygen gases. The
latter is absorbed by it so long as its vitality exists, while carbonic acid
is generated within it as a product of decomposition, whether blood be
conveyed through it or no. The amount, moreover, of the latter increases
with the use of the muscle, which appears to be one of the most import-
ant sources of this ultimate product of mutation in the body.

Smooth muscles, with the contractile substance of their cell body and
their nuclei, manifest less complication than those formed of striated
fibres, but appear on account of their smaller bulk less suitable objects
for chemical investigation. Their composition appears, moreover, to
be the same as that of the striped tissue. Syntonin has naturally
been obtained from them also (Lehmann). Further, in their juices
albuminous substances have been found — kreatin, hypoxanthin, lactic,
acetic, formic, and butyric acids. Here also the potash combinations
predominate.

REMARKS. — 1. Bibra states the proportion of water in the human muscle to be
only 72-74 percent, as opposed to the usual figures, 77-78. 2. Among the fishes
we find the muscular tissue of the plagiostoma to contain enormous quantities of urea
(Staedeler and Frerichs in Erdvianris Journal, Bd. 73, p. 48, and Bd. 76. p. 58). 3.
The same observers found, further, a substance very similar to inosite in the muscles of
the plagiostoma ; this is named ",

§ 171.

In regard to the many physiological and physical properties of the
tissue, a few points only heed be touched on here.

Quiescent living muscle displays a high degree of extensibility, return-
ing almost completely to its original length as soon as the extending
force is suspended ; it has slight, but very perfect elasticity. The active
fibre is still more extensible, i.e., its elasticity has undergone diminution.
The dead muscle fibre possesses much less capability for being extended,
and return to its original length does not take place.

The living structure possesses electromotor properties, and presents
the so-called " muscular stream," in the study of which Du Bois-
Reymond has lately done so much. We cannot here enter upon its
differences during quiescence and activity of the muscle. The latter
ceases to possess electromotor properties so soon as its vitality is at an
end.

The most important property, however, of the living muscle fibre
(striped and smooth) is, that it contracts on stimulation of the motor
nerves terminating in it, decreasing in length, and enlarging it in a trans-
verse direction. The nature of this peculiar property inherent in muscle —
whether it be itself capable of being excited, or only through the medium
of the nerves which end in it — has been now for many years the subject
of physiological controversy.

300 MANUAL OF HISTOLOGY.

•

The kind of contraction, again, varies according to the histological
elements with which we are engaged. In striped fibres we observed it to
commence almost simultaneously with the application of the excitant to
the nerves of the part, ceasing very rapidly again on cessation of the
stimulus, and giving way to relaxation. The reverse may be observed in
smooth muscle. Here an appreciable interval of time is remarked be-
tween the application of the stimulus and contraction, while the latter
outlasts the action of the excitant for some moments; the fibre reassum-
ing gradually a condition of quiescence. This is evident in the motions
of whole groups of animals, and also in those of individual organs, as in
the iris of birds, made up of striped fibres in contrast to that of human
beings and mammals generally, in which the former are smooth. With
us it is the striated fibres alone which obey the influence of the will
in their rapid and precise action.

In the rectilinear muscle, with the aid of the microscope, we see during
contraction the longitudinal stria? become less distinct, and eventually
disappearing, while the transverse markings become clearer and clearer.
It would naturally be a great point achieved could we ascertain precisely
how the elementary particles of the active fibre are affected by this, and
especially how the dark zones behave in relation to the clear. It appears,
however, as though the former approached each other, while the clear zones
decreased in height. These points are, however, still too doubtful for us
to be able to draw any great conclusions from them. We regard it as not
improbable, however, that the sarcous elements may be relatively immut-
able, as compared with the particularly contractile longitudinal cement-
ing medium. According to Amicfs observations on the muscles of the
common fly, the elongated fleshy particles appear to assume an oblique
position at the moment of contraction. This we have ourselves seen.

According to the most recent observer, W. Engelmann, the seat of the
contracting force is exclusively the dark (anisotropic) layer. The trans-
parent (isotropic) transverse zone is either contractile in a minor degree, or
only elastic probably, like the dark transverse disk of Krause. While
the volume of the muscle casket enclosed between two of the latter does
not become appreciably lessened, the dark transverse zone at the moment
of contraction increases in bulk, the clear becomes less voluminous ; the
first swells, the last shrinks, so that an overflow of fluid takes place.
Besides this the first becomes clearer and softer, the latter darker and
more solid.

The sarcolemma, owing to its elasticity, follows the changes of form in
the fibre, tightly investing the latter throughout. That the transverse
striai are not produced by wrinkles across its substance was recognised
long ago. The motor nerves will be referred to in a future chapter.

It is a matter of far greater difficulty to obtain a view of the contractile
fibre-cell, or unstriped fibre, in the moment of contraction. According
to Heidenhain, each element (at least among invertebrate animals) be-
comes likewise simultaneously and evenly thicker in all its parts, with a
corresponding decrease in length.

As to the rigor mortis connected with the death of muscle, on which
an albuminous substance contained in the latter undergoes coagulation,
while its reaction becomes acid, the microscope has added but little to
our knowledge. The dead fibre appears more rigid and dull, and less
transparent than during life.

TISSUES OF THE BODY. 301

§ 172.

Turning now to the development of the tissue, we find smooth muscle to
take its rise from the simple transformation of round formative cells with
spheroidal vesicular nuclei of the middle germinal plate. These elements
change into contractile fibre-cells by growth in two opposite directions,
during which the nucleus assumes its before-mentioned elongated con-
figuration (p. 281). Fig. 273 (a, b) represents two such embryonic cells
from the wall of the stomach of a foetal pig two inches long.

Touching now the striated structures, it was for a long time supposed,
in accordance with Schwann's view, that the fibre was always produced by
a fusion of formative cells arranged in rows, whose united membranes
went to form the sarcolemma, while the nuclei persisted, and the com-
bined contents of the cells took on the characteristic form of fleshy matter
through further metamorphosis.

But this view is, as we now know for certain, quite erroneous. The
muscular fibre, far from being a result of the fusion of a series of cells, is
nothing more than a single elongated filiform cell, in which the nucleus
has undergone division and multiplication, and the contents metamor-
phosis, and which has attained gigantic dimensions in proportion to the
length of the striped muscle. We have already referred to this mode of
development (for the discovery of which we are indebted to Lcbert and
Remak] in discussing the growth of the tadpole (p. 96).

In the mammalia and human beings the same is to be observed. Here
we may follow up, in young embryos, the steps in development of the
tissue, which are essentially similar.

Thus in the human foetus, at about the sixth or eighth week, very
narrow membraneless and fusiform cells, often only 0 '0025-0*0036 mm.
in breadth, are met with as elements of the rudimentary muscle of the
hands and feet. They are formed of very delicate protoplasm, with a
single or double vesicular nucleus, and attain a length of 0'14— 0*18 mm.
(Koelliker, Frey).

The same is to be seen in mammalian embryos at corresponding stages
of development. In those of the sheep, measuring 27—9 mm. in length
(fig. 293), we may obtain from the diaphragm and abdominal muscles
fusiform cells 0'28-0'38 mm. long, and 0'0045-0'068 mm. in breadth.
These show a vesicular nucleus 0'0077-0'0104 mm. in diameter, and
incipient transverse striation in the central portion (a, b). These nuclei
range in number from two to four, but other cells further advanced
possess many more of the latter (c), and increase in transverse diameter to
double or even more (d). As a rule, their axis remains unaffected by the
transverse striation, and in it we see the original protoplasm. In some-
what older animals the muscular fibre is 0 "01 29-0 '01 56 mm. in thickness,
and so long that it can no longer be isolated in its entire length, although
the pointing of one end (e). or blunt rounding off of the same (/), may
be easily found. The number of nuclei now becomes greater and
greater, arid the process of division is observed as an ordinary occurrence
(e,fy g). Sometimes the position of the former is central (/, g, i) and
sometimes peripheral (//). The axis of the fibre generally remains free
from transverse marking (/, h, g), while at its circumference the longitu-
dinal cleavage commences to manifest itself. The tendency among muscles
of this kind to break up into thick discs under the action of water (i) is
a point of much interest.

302

MANUAL OF HISTOLOGY.

Foetal muscle, as already remarked, contains glycogen, but at first, before
the embryonic cells have begun to undergo their characteristic transfor-
mation into fibres, this substance is entirely absent, according to the

interesting investigations of Ber-
nard and Kuhne. In smooth
nucleated fibres it presents itself
as a granular matter deposited
around the nucleus. Rouget, how-
ever, asserts that it only occurs
diffusely. Later on, with the de-
velopment of the transverse striae
and appearance of the characteristic
muscular structure, the fibre is in-
filtrated with glycogen, which per-
sists until birth, disappearing
rapidly on the commencement of
respiration.

As yet we have not said one word
as to the origin of the structure-
less envelope, the sarcolemma. In
earlier years, supposing the for-
mative cell to be endowed with
an envelope, this sarcolemma was
looked upon very generally as be-
ing the metamorphosed cell-mem-
brane of the former. But now
that we have convinced ourselves
that no such envelope exists upon
the formative cell, such a view can
no longer be entertained. At the
present we find two theories very
generally held in regard to this
point. According to one, the sar-
colemma is a hardened secretion
from the cell, of the same nature
as the so-called cuticular forma-
tions ; according to the other (and
we are inclined to favour this

View) this Structureless sheath is

a connective-tissue formation laid

down On the muscle fibre from
. . , i • i i j

Without, which may be Compared

fn f^p PlaC;fip linn n diner lavPTN of

many connective-tissue structures.
That the end of the muscle fibre can be separated with its envelope
from the tendon, as we have seen at p. 294, appears to us to be no very
weighty objection to this view. Do we not also see elastic fibres sepa-
rating themselves from connective-tissue bundles] and yet they have both
the same origin.

The branching muscular elements of the heart correspond, we are assured
by Koelliker, each to a metamorphosed stellate cell, and the whole to a
cellular network. Weismann, however, is opposed to this theory from his
own observations. In his opinion the muscular bands consist (and of

Fis: 29.').— Development of striped muscle fibres

tion; c, d, portion of a somewhat more mature
fibre, with numerous nuclei and considerable dia-
meter; «,/,?, fibres still further developed, with
nuclei in the axis ; h. nuclei beneath the enve-
lope; t, a fibre breaking up into thick discs.

TISSUES OF THE BODY. 303

this we may convince ourselves very easily), in fishes and amphibia, of
aggregations of simple elongated fusiform and at times branching cells.
The same is the case in the embryos of the higher vertebrates. In the
latter, however, these cells unite more intimately at a subsequent period
to form the common substance of the band. But we may still render
the boundaries of the various cells visible here also by artificial means
(Eberth).

§173.

Let us now turn to the growth of muscle.

Embryonic muscular fibres, as we have already mentioned in the
previous section, are considerably finer than those of the infant, and their
diameter in the latter is far less than in the adult.

According to Hart ing's accurate measurements, the muscle fibres of the
adult appear about five times as thick as at the time of birth. This
increase in length and breadth is brought about by the reception of new
particles between those already present in the fleshy substance, or, as it is
the custom to say, by intussusception.

But the fibres of growing muscle become not only larger, but their
number also increases, as was demonstrated beyond gainsaying by
Budge, by experiments on the sural muscles of a frog's leg. We are
indebted to Weismann also for further interesting information on the
same point. According to the last-named observer, the growth of the
muscles of frogs takes place only in part through increase in thickness of
the fibres originally present ; there occurs, besides, a considerable augmen-
tation of the number of the latter by a process of longitudinal division.
This process is ushered in by an active proliferation of the nuclei or
muscle corpuscles (Muskelkbrperchen) in the old fibre, so that we soon
meet with regular columns of the former arranged one over the other,
while the fibre itself becomes flattened and widened. Subsequently to
this the fibre splits into two threads, in each of which the process just
described is repeated, so that out of one old muscle element a whole
group of new ones eventually takes its rise. Each of the new fibres
then attains its typical diameter through that growth from within, which
has already been referred to.

In full-grown frogs, also, during their winter torpidity, we may see a
lively regeneration, with fatty degeneration of the previously existing
muscle fibres (Witticli). In this case, likewise, the same process of multi-
plication was observed by Weismann.

Great interest attaches further to a discovery made by Lenker, that an
extensive -destruction of human muscle fibres takes place during typhus
fever, combined with rapid multiplication of the muscle corpuscles and
connective- tissue cells. This is due to a peculiar degeneration, and is fol-
lowed by energetic regeneration of the elements on recovery. The pro-
cess is probably the same as that observed in the hibernating frog.

This luxuriant growth of the muscle corpuscles takes place, besides, in
other states of irritation of the tissue.

From these facts, few though they be, we may infer that muscle
fibres are by no means so persistent structures as was formerly tacitly
agreed to.

The uterus of pregnant women offers us a good opportunity of setting
on foot interesting investigations as to the nature of the growth of the
elements of unstriped muscle. As is well known, the organ in question

304

MANUAL OF HISTOLOGY.

Fig. 294. — Human muscle
studded with fat-cells, a,
muscular fibre ; 6, rows of
fat-cells.

increases enormously in volume at certain times, a fact which depends
chiefly on changes in its muscular tissue. The contractile fibre-cells
become enlarged°to 7-1 1 times their original length, and to 2-5 of their
breadth (KoeUiker). Besides this, there takes place, according to the
same observer, a reproduction of cells also.

After parturition a decrease in the size of the contractile cell begins to
be apparent, with which it returns in about three
weeks to its original dimensions. Fatty infiltra-
tion of the substance of the latter during this
period is of frequent occurrence, and we may also
accept as a certainty the resolution of a certain
number of the muscular elements also.

That there really may be such a thing as a phy-
siological hypertrophy of the striped fibres can
hardly be doubted any longer since Auerbach's dis-
coveries.

In hypertrophied hearts it was stated by Hepp
long ago that thickening up to four times their
original size took place in the fibres. It would
appear, however, that there is really only a multi-
plication of the fibres here (perhaps by longitudinal
division).

Pathological hypertrophies, however, of un-
striped muscle, amounting even to the formation of
tumours, are of frequent occurrence. They affect
parts which are richly supplied with this tissue,
such as the oesophagus, stomach, and uterus. Their genesis requires to be
made the subject of more accurate investigation than has as yet been the
case. That a transformation of connective-tissue cells into contractile
elements takes place is at least probable (Aeby, Arnold, Koclliker).

Finally, we meet with an atrophy of muscle fibres or disappearance of the
same. In the first place, this is encountered as a more or less normal pheno-
menon in old age. Then, again, it appears more fre-
quently under pathological conditions as a diminu-
tion in the diameter of the fibre (as in paralysis of
various members), combined, to a certain extent, with
fatty degeneration of the fibre or development of in-
terstitial fat-cells. The latter (fig. 294) have been
already discussed (§§ 122 and 169). If this latter pro-
cess proceed to too great length, it may possibly inter-
fere at last with the functions of certain portions of
muscle through pressure, as, for instance, in the heart.
The deposit of small molecules of fat in the interior of
fibres is of frequent and normal occurrence when the
quantity of the former does not become too great.
Thus we meet with it in the muscle of the heart, and
in the frog in the muscles of the extremities (§ 166).
In a greater degree it must be looked upon as a pheno-
menon of retrograde development (fig. 295), of patho-
logical significance. But, on carefully searching
through healthy muscles, we will always encounter
certain fibres containing a considerable amount of fat granules of this
kind, and not unfrequently also a diminution in thickness, so that it is

Fig. 295. — Fatty de-
generation of human
muscle fibres. «, low
degree; 6, a higher; c,
the highest degree.

TISSUES OF THE BODY.

305

probable that a physiological decay with fatty degeneration also takes
place to a limited extent.

Calcification of this tissue is rarely seen.

Neoplasis of striped muscle, at points where it did not previously
exist, is of very unt'requent occurrence. A certain number of those few
cases which have been up to the present recorded have reference, strange
to say, to the testicle and ovary. Here there can hardly be any doubt of
the development of muscle fibres from connective-tissue cells, however we
may suppose their source to be from the muscle corpuscles in the intra-
muscular new formation.

Though it was formerly believed that wounds of muscles could be
repaired by connective-tissue alone, numerous recent observations have
proved the power of regeneration inherent in the tissue. The mode
of this new formation of muscle is a matter, however, about which much
difference of opinion still exi.sts.

E. Composite Tissues.

15. Nerve Tissue.
§ 174.

The form-elements of the nervous system (1) are structures of two
different kinds, namely fibres and cells, imbedded in a ground-work of con-
nective-tissue. The first of these, known under
the several names of "nerve fibres," "nerve
tubes," and " primitive fibres " of the nervous
system, make up almost exclusively the white
substance of the neural apparatus. The last, to
which the names of " nerve or ganglion cells "
have been given [also " ganglion corpuscles "
(" Ganglienkbrper ")], are found mixed up with
the first described elements, in the grey matter.

The " groundwork " of connective-tissue pre-
sents itself in the first place in the form of a
highly developed fibrillated structure, more fre-
quently, however, as a more or less homogeneous
connecting substance (perineurium), or, finally,
as an extremely delicate tissue containing cells
and nuclei, as in the nervous centres.

Nerve-fibres (fig. 296) are met with either as
dark-bordered threads, the medullated, or pale,
the non-medullated. They are simple un-
branched fibrils, except at their origin and
termination, and vary to an extraordinary extent
in thickness, measuring from 0'0225 down to
0*0018 mm. and less. Owing to their appear-
ance not being the same in all cases, we dis-
tinguish between broad or coarse fibres (a and b) of 0'0226 mm. (more
usually of O'Ol 13-0.0056 mm.), and. fine or narrow fibres, whose diameter
may fall to 0 '0045-0 0018 mm. (c, d, e).

Dark-edged nerve fibres consist of three parts, — namely, of a very deli-
cate envelope of connective-tissue, the " neurilemma " or " primitive
sheath ;" of an albuminous portion extending down the centre, the so-

Fig. 296.— Nerve fibres from the
human being, a, a coarse speci-
men; 6, medium-sized fibre;
c, rf, e, finer still.

306

MANUAL OF HISTOLOGY.

called "axis cylinder;" and of another portion situated between the
envelope and the latter, a mixture of albuminous substances, cerebral
matters, and (?) fats, the "medullary sheath" or neural medulla"
(Nervenmark). Of these three, which cannot be demonstrated on the
perfectly fresh fibre, but only by round-about modes' of treatment, the
axis cylinder must be looked upon as the most essential and only indis-
pensable structural constituent.

The appearance of broad nerve fibres in a recent state is that of threads

formed of some completely homo-
geneous transparent or milky mass.
It is rare, however, that we obtain a
view of them in this state, owing to
the exceedingly rapid changes which
take place in the contained matter.
All the more customary modes of
preparation (if we desire to isolate
the fibres) bring the latter before us
in a form which has already under-
gone change, or has " coagulated," as
the saying is. This congelation,
however, is met with in various stages
of completeness (fig. 296, a, b ; fig.
297).

When isolated with as great rapidity
and care as possible, the nerve fibre
presents to our view a dark border,
and closely applied to this internally
a second and finer bounding line
(fig. 296, a, b-} fig. 297, 6, above).

Later on, these two lines or
"double contours" are not quite par-
allel, and the internal one is no longer
continuous throughout. The thin
layer interposed between the two
lines on each side of the fibre appears
homogeneous (fig. 296, a, ft) or granular.
At this stage of transformation the nervous fibre may remain stationary,
the outer coagulated layer acting to a certain extent as a protecting
covering for the portion situated more internally, or, the congelation may
advance further at points, and the nerve fibre may frequently present a com-
pletely different appearance at various parts of its course (fig. 297, b).

After this the internal line becomes separated more and more from
the outer one, while between the two, and also in the central part of
the fibre, lumpy, granular, or globular masses are formed (a, b), until
eventually the whole appears transformed into a sometimes coarse and
sometimes finely granular substance (c), and the entire nerve tube has
become dark (2).

REMARKS.— 1. Literature is very rich in information on this subject. 2. Neural
medulla which has escaped from its sheath displays precisely the same changes
("Myelin"ofVirchow.)

§ 175.
The existence of an envelope on the nervous tube is easily inferred

Fig. 297.— Human nerve fibres at an advanced
stage of coagulation.

TISSUES OF THE BODY.

307

from the fact that the latter can be isolated in a considerable part of its
length, in spite of the soft nature of its contents. This neurilemma may
be seen not ^infrequently as a short empty tube, at points where the
included mass has been displaced (fig. 297, c). It may likewise be
demonstrated by means of chemical reagents, which completely or par-
tially dissolve the substance contained within it (fig. 298, a, c).
JNTeurilemma consists either of elastin or some material nearly allied to it,
and is usually encountered among the higher vertebrates and in the
human body as a completely homogeneous and very delicate membrane,
either with or without nuclei. Among the lower orders of vertebrates,
and on the peripheral ramifications of human nerves, it may be found
thickened and supplied with numerous nuclei.

To what extent this sheath exists among the elements of the nervous
system is a more difficult question, and one
which cannot at present be answered with
certainty. Thus, in the branches of many
of the cranial nerves it is absent; and
in the terminal peripheral ramifications
not unfrequently. Its demonstration,
moreover, on very fine medullated nervous
tubes is a matter attended with some dif-
ficulty. Finally, the fibres of the brain and
spinal cord are destitute of this sheath.

The axis cylinder of Purkinje, or
primitive band of RemaJc, cannot be
recognised in the fresh nervous tube on
account of its delicacy and soft consist-
ence. It is frequently missed also in
many simply coagulated fibres, owing to
the fact that it also has undergone a
granular metamorphosis.

It appears, however (and upon this we
would lay greatest stress), at the point of
origin (fig. 298, g), as well as at the
terminations of the nerve tubes, where
the medullary sheath fails. It is likewise
to be seen in many nerve fibres, coagula-
ting in the ordinary manner, as a pale
homogeneous band -like structure, about
a fourth or third of the breadth of the
former, projecting from its cut end (fig.
297, «, above).

Certain chemical reagents again may be
employed for its demonstration to great
purpose. Among these are several sub-
stances, in the first place, which are well known to render the protein
bodies hard, without dissolving or producing any particular effect on the
fats; these are, for instance, chromic acid, chromate of potash, and chloride
of mercury (fig. 298, 5). Again, there are reagents which are employed
for the same ends on account of their power of dissolving the fats, but not
the alburninates ; of these we may mention alcohol and boiling ether (a).
Sometimes we obtain specimens in which the axis cylinder projects from
the cut end " like the wick from a candle." One of the best aids, however,

Fig. 298.— Nervous fibres of various kinds,
a, a broader one from the frog after
Treatment with absolute alcohol, show-
in g the axis cylinder and "neurilemma ; b,
another, with axis cylinder, after treat-
ment with bichromate of potash ; c, a
fibre from the same animal, treated with
collodium, showing the axis cylinder
and neurilemma ; d, a non-medullated
fibre from the petromyzcm with the axis
cylinder and nucleated envelope; e, a
non-medullated fibre from the olfactory
of the calf; /, gr, A, fine fibres from the
human brain -with axis cylinders; the
fibre d (copied from R. Wagner) unites
above with the process of a ganglion
cell.

308 MANUAL OF HISTOLOGY.

in. the demonstration of the structure in question, is collodium, recom-
mended by Pfliiger. Under its action the axis cylinder makes its appear-
ance almost instantaneously throughout the whole length of every fibre, fre-
quently bent over strongly to one side (c). Tinction with carmine may
also be employed, and aniline (Frey) or chloroform ( Waldeyer).

Very instructive objects, as regards the nature of the structure just
described, may be prepared from transverse sections of nervous trunks
previously artificially hardened (Reissner}. In these we recognise the
envelope of each tube, its axis cylinder as a small central formation,
and between the two the medullary sheath. In the latter may be seen
an irregular concentric marking, first observed by Lister and Turner^
which is probably the optical expression of lamination in the medullary
substance. Transverse sections also, through the white substance of the
spinal cord, present the same views of the axis cylinder, and medullary
matter.
REMARK. — Quart. Journ. of Microsc. Science, 1860, p. 29, pi. 2.

§ 176.

Turning now to ike fine dar/c-edged nerve fibres (fig. 296, c, d, e), we find
it possible here also to demonstrate in many cases the presence of the
primitive sheath, although with greater difficulty. We recognise at the
same time the axis cylinder, especially in the fibres of the brain and
spinal cord (fig. 298, /, g, h), where the primitive sheath is no longer present.

It is a striking fact that, in these fine nervous tubes, we do not remark
the same inclination to lumpy or granular coagulation as is seen to such
an extent in the broader ones; we find them rather preserving their
transparency, whether their contour appear double, as in larger speci-
mens (fig. 298, /), or single, as in the more minute (fig. 296, c, d, e).

In a degree proportionate to their thinness, these fine nerve tubes are
remarkable for being subject to a displacement, and the formation into
globules of their medullary substance under the action of water, or from
pressure, twisting, &c., in consequence of which they often present a
knotted appearance (fig. 296, c, d, e, and 298, h). These swellings are
known as " varicosities," and are nothing, we repeat it, but artificial
productions, which do not exist in the living body.

Next in succession to these dark-edged medullated fibres, we come now
to a second species, namely, to the pale or non-medullated.

This is the primary form of all the fibrous neural elements in the
embryos of man and the vertebrates.

In the family of the petromyzon, a lowly organised fish, this non-
medullated pale appearance of the fibre, presenting simply an axis
cylinder, persists throughout life (fig. 298, d). But even in the bodies oi
the higher vertebrates, and human beings also, the nerve tubes may still
preserve this original embryonic condition in various positions ; thus, in
the nervus olfactorius, as soon as it enters the nose.

While there can be but little doubt as regards the nature of the
fibre-elements in the olfactory nerves, it is quite a different matter in
the course and distribution of the sympathetic. Here we encounter in
the human body and among the higher vertebrates, together with medul-
lated tubes, the so-called fibres of Remak (ganglionic nerve fibres), which
may even preponderate. These are transparent sometimes ; flat bands of
about 0-0038-0-0068 mm. in breadth and 0*0018 mm. in thickness (fig.
299, 300, &). Their appearance is usually homogeneous, while at intervals

TISSUES OF THE BODY.

309

an elongated oval or fusiform nucleus may be remarked, measuring about
0'0068-0'0113 mm. in length. At times, also, these flat fibres are split
up, though imperfectly, into fibrillrc (fig. 299, b).

As to the nature of these fibres of Remak, whether they are composed
of connective-tissue, or are (as was supposed by their discoverer, and with
him by J. Mullcr) nervous elements, are points which, in the annals of
histology, have been the subjects of controversy for years past. The
existence of similar pale nerve elements among the lower animals and in
the petromyzon, and among the embryonic and olfactory fibres of the
higher animals, seems to point to the conclusion that they are of nervous
nature, and, indeed, the general opinion grows stronger from year to year
that this is the case. They are just nerve-fibres destitute of medullary
sheath, and in which the axis cylinder is enclosed within a nucleated

Fig. 299.— Remaps fibres from the calf
a, simple flat nucleated bands; 6, a
fibre split above into fibrilL*.

Fig. ^00. — A small nervous
branch from the sympathetic
of a mammal. Two dark-
bordered nerve tubes, a,
among a number of Remak's
fibres, 6.

neurilemma. On the other hand, it must be granted that young imma-
ture connective-tissue may present precisely the same appearance. The
nucleated envelope of many ganglion cells is also a difficult point for ns,
which will be discussed in the next chapter.

In some small trunks of the sympathetic system (fig. 300), the propor-
tion of these pale fibres (/;) is so large, and the number of the medullated
tubes is so small, that it is difficult to conceive what would be the object
of such an enormous amount of enveloping connective-tissue for so few
nervous fibres.

In the nerves of the spleen of fully developed mammals twigs have been
found of 0'45 mm. in thickness, which contain nothing but Remains fibres.

The question whether this variety in the appearance of the nerve-fibres
corresponds to a difference in their functions ox energies must be generally
negatived. The nerves of voluntary muscle and those of the skin have,
for instance, the same kind of fibres. The preponderance, however, of
narrow dark tubes in the sympathetic is certainly remarkable, but the
same occur in great abundance in the brain and spinal cord. Transitions
from broad to narrow fibres are also numerous, and in the sympathetic

310

MANUAL OF HISTOLOGY.

system as well as in the olfactory nerves, as has just been mentioned,
pale, non-medullated, nucleated fibres are to be found

But our position is far more difficult when we are
asked for an answer to the question, whether, in
what has been just described as the texture of the
nerve tubes, their whole structure has been given, or
whether they possess a further and more complex
constitution.

For many years past there has been no lack of
efforts (and some very daring) to prove the latter to
be the case. Only one point, however, of any great
importance has been ascertained, through the im-
proved optical auxiliaries to our investigations,
namely, that the axis cylinder is made up of ex-
tremely delicate fibrillce, imbedded in a finely granular
substance. This fact was first recognised in the
pale nervous tubes of many invertebrate animals, and
in the olfactory nerve and fibres of Remak of the
vertebrates. It is also true for the axis cylinders of
the nervous centres (fig. 301), according to Schultze.
These extremely fine fibres, on which delicate vari-
cosities may be remarked after treatment with certain
reagents, have been named " axis fibrillas" by Wal-
det/er, and by Schultze " primitive fibrilla3."

The axis cylinders of the stronger nerve tubes ap-
pearing thus as bundles of the most delicate fibres of
immeasurable fineness, those of less diameter must be
looked on as collections of smaller members of the
same, until eventually, in the most minute axis
cylinders, the number is reduced to one single pri-
mitive fibril (1).

Later on we shall see that the primitive fibrilla (which call, however,
for closer observation as to their nature) make their appearance naked,
and separated one from the other in the termination of numerous fibres,
and also constitute important fibrous elements in the nervous centres.

REMARKS. — 1. The importance of the facts but briefly mentioned in the text entitles
them to more extended consideration. It was Itemak who first pointed out, years
ago, this remarkable complication in regard to the axis cylinder of the craw-fish.
In the garigliated cord of the latter are to be found, besides others, unusually thick
nerve fibres, whose axis cylinders consist of bundles of above a hundred of the finest
fibrillae, only 0'0004 mm. in diameter. This was subsequently corroborated \)y HaJcel,
Leydig, G. Walter, and Waldeyer, with discoveries of similar composition in the
nerves of other invertebrate animals. M. Schultze observed the same structure in the
axis cylinders of the olfactorius and nervous centres of vertebrates. As to the further
points of interest in regard to the structure of the nervous tubes, we have already
referred (p. 308) to the concentric markings to be seen in the medullary substance
on transverse section of the latter. It seems to depend on lamination, but this view
has been opposed by Frommann. According to JClebs, the axis cylinder is imme-
diately surrounded by a fluid substance, — the "periaxial fluid." Years ago Stilling
also described as very complicated, the structure of the nerve fibre, working with very
high microscopic powers, and preparations made in chromic acid. Compare Lockhart
Clarke in the Quart. Journ. of M icrosc. Science, 1860, p. 165. More recently still
Frommann and Grandry have described a transverse striation on the axis cylinder
after treatment with nitrate of silver. RoudanowsTcy informs us further that the axis
cylinder is knotted, and gives off branches at right angles which anastomose with
those of neighbouring fibres.

Fig. 301. — Fibrillated
structure of the axis cy-
linder (after Schultze).
a, a strong axis cylinder
from the spinal cord of
the ox ; 6, a nerve fibre
from the brain of the
electric ray.

TISSUES OF THE BODY.

311

§ 177.

We now turn to the cellular elements or the ganglion corpuscles, whose
appearance is very characteristic, with the exception of many in the brain
and spinal cord, where their boundaries are difficult to define. They
may be divided into those without processes (fig. 302) and those with
processes (fig. 303). To the first-mentioned species the term " apolar "
has been applied, and to the latter " unipolar," " bipolar," or " multipolar,"
according to the number of their ramifications.

In every variety of size, from 0*0992 mm. down to 0-0451-0-0226-
0-0018 mm. and even less, we meet with these cellular bodies of spherical,
oval, pear-shaped, or renal form. In these are situated spheroidal vesicular
nuclei of 0'0180-0'1090 mm., with a round slightly lustrous nucleolus of
0'0029-0'0045 mm. Another round point, frequently visible in the
interior of the latter — either granular or clear — has been given by
Mauthner the name of nucleolulus (fig. 308). Not unfrequently the
nucleolus is double, but the nucleus is seldom so. The latter, unlike
most nuclear formations, gives way comparatively rapidly to the action of
concentrated acetic acid.

The contents of these cells, probably a species of protoplasm, appears
as a tough doughy mass, with numerous minute granules of a protein
substance, and in addition to these, fat molecules, soluble in alcohol and

Fig. 302.— Ganglion cells from a mammal. A, Cells Fig 303.— Multipolar ganglion
with connective-tissue envelope, from which Re- cells with protoplasm pro-
raaA's tibres take origin, d, d; a, anon-nucleated cesses, from the grey sub-
cell ; 6, two cells with single nuclei; and c, one stance of the human brain
with two of the latter structures. B, A ganglion
cell destitute of envelope.

ether, and, not at all unfrequently, particles of yellow, brown (fig. 303).
or black pigment (fig. 305, 4). The latter substances offer a most
determined resistance to the action of alkalies.

All these ganglion cells, the central as well as the peripheral, are
destitute of distinct membranes. In the grey matter of the nervous
centres they are imbedded in that fibrillated sustentacular substance
already mentioned at p. 197. In the peripheral ganglia, on the other
hand, of man and the vertebrates, they are usually enclosed in envelopes
21

312 MANUAL OF HISTOLOGY.

of a non-fibrillated nucleated tissue (fig. 302, A), from which they may
be isolated in the form of membraneless corpuscles (B).

According to recent investigations, the internal surface of each of these
corpuscles Fs lined in man and the vertebrate animals with delicate
flattened epithelium or endothelium, resembling that of the blood-vessels
(Frdntzel, Koelliker, Schwalbe) (1).

What is the nature of this enveloping nucleated tissue?

Here we meet with a great variety of opinions. It was formerly set
down as being in toto a connective-tissue structure, but Beale and Eemak
ascribe to it a nervous character. Be this as it may, the distinct origin
of Rematis fibres from these systems of capsules is very remarkable.

REMARKS.— 1. This was noticed years ago by Robin and R. Wagner in the case of
the ganglion cells of the electric ray. Heutak too was aware of the presence of this
cellular lining.

§ 178.

The processes and ramifications of the ganglion cells serve, in the first
place, possibly as connections between neighbouring cells (commissural
fibres), and, in the next place, they certainly go to form the axis cylinders
of different nerve fibres. For the investigation of these very difficult points
the lower orders of vertebrates, and especially fishes, are to be recom-
mended, in which the dissection is rendered easy by the small amount of
enveloping connective- tissue (1). The following points may be noticed
in the nervous knots of the burbot \_Gadus lota (2) ] (fig. 304).

Some of the ganglion cells appear apolar (i, &), no trace even of
ruptured processes being discoverable, the appearance of the capsule
conveying the impression rather of its being closed. These represent
possibly only the earlier stages of development of ramifying cells (Beale).

Others, and they are of a smaller kind, are unipolar, giving off at one
end a process which assumes, after having run for a certain distance, a
darker and more medullated appearance, becoming eventually a narrow
nerve fibre (/). On some ganglion cells, though apparently unipolar (e),
another ruptured portion of fibre may be recognised on the mutilated
envelope. Unipolar cells, continuous through their processes with broad
nerve tubes, are not met with.

Bipolar ganglion cells are of frequent occurrence. The smaller are in
communication with narrow, the larger with broad, nerve fibres. The
first (d) frequently show us pale fibres of considerable length, which,
in the case of the unipolar cell, become transformed into nerve tubes.
The latter (a, b, c) present to us the fibre as a dark medullated tube,
extending as far as the extremity of the cell (a). Here the medullary
matter spreads out in a thin layer, investing the body of the latter (3)
and may persist in that situation even after the rest *of it has escaped
from the cut end of the nervous tube (5, c).

Such bipolar origins as at h are of rare occurrence, as also the appear-
ance of two ganglion cells on one and the same nervous tube, as at g.

Our diagrams show also that the enveloping neurilemma or capsule of
the ganglion cell is continuous with the connective-tissue primitive sheath
of the nerve tube. In the peripheral ganglia of fishes, multipolar cells
do not occur. Even those with three processes, are very rare (Stannius).

The recognition of corresponding structural relations in the human
being and among the mammalia is of much greater difficulty, owing to
the larger proportion of interstitial connective- tissue, and mutilated

TISSUES OF THE BODY.

313

ganglion cells are also of frequent occurrence here. Nor dare we form
conclusions in regard to the mammal body from what is found in the fish.

The existence, however, of apolar, unipolar, and bipolar ganglion cells,
cannot be denied in this case
also after candid consideration,
although we are still in the dark
as to the relative frequency of the
various forms.

Multipolar cells must be looked
upon as peculiar to many peripheral
ganglionic masses, as also to the
terminal expansion of the optic
nerve in the retina. They were
discovered by Remak in the sym-
pathetic.

The same species of, and pos-
sibly also exclusively, multipolar
ganglion cells, occur likewise in
the grey matter of the brain and
spinal cord (fig. 305); those apolar
specimens which are found here,
or such as have only one or two
processes, being probably mutilated
cells ( Wagner, Schroder van der
Kolk). These cells, which contain
either a pale substance alone (2),
or, besides this, brown and black
pigmentary particles (4), possess a
very variable number of ramifica-
tions, ranging from 4 to 20 and
upwards (1-4). The latter appear,
under high magnifying power,
partly as broad or narrow processes
of the finely granular cell body
(2, c), and partly homogeneous
(1, a). Some of these ramifica-
tions split up eventually, with
repeated subdivision (4), into fibres
D£ extreme fineness. Others, acting
is commissures (2, c; 3, b), are sup-
posed to combine the ganglion
cells to a physiological unit (4).
Finally, axis cylinders are seen
arising from them (fig. 305, 1, a,
b; 3, c; and 298, </*).

It is at present impossible to trace any connection between the variation
in the ganglion cells just described, and a difference in function in each or
any.

REMARKS. — 1. In older historical works of the year 40, apolar ganglion cells
alone were recognised. Purkinje, it is true, had seen the processes of ganglion cells in
1 838, but had not recognised their significance. Subsequently toHelmholtzs and Will's
discovery of the one-sided origin of fibres among the invertebrate animals, Koelliker,
was the first to demonstrate its occurrence among the vertebrates. Great progress was
next rn^de in this direction in the year 1847, through the discovery, by Wagner and

Fig. 304. — Xerve cells from the peripheral ganglia
of Gaduslota. a, b, c, Bipolar connected with
broad nerve fibres ; d, similar cell produced into
a narrow fibre ; e, another of the same kind, from
which a nerve fibre has been torn off; /, an uni-
polar cell with narrow tube; g, two bipolar (g-l,
g-2) peculiarly united to fine nerve tubes; h, an-
other bipolar cell ; t, k, two apolar ganglion cells.

314

MANUAL OF HISTOLOGY.

Robin of bipolar cells in the ganglia of fishes. 2. Phil. Transfer the year 1863, vol.
eliii. part "• P- 543- 3- In llis excellent treatise (Observationes de retince structura
penitori) M. 'Schultze divides ganglion cells into four classes, and, as far as our own
observation goes, they may be so classed with propriety, though intermediate forms
also exist. The four are as follows : (a) those that have neither neurilemma nor
medullary sheath, as in the brain, cord, and retina ; (b) such as have neurilemma, but

Fig. 305.— Multipolar ganglion cells from the human brain. 1, a cell, one of whose
processes (a) becomes the axis cylinder of a nerve fibre (&) ; 2, a cell (a) connected
with another (b) by means of a commissure (c) ; 3, diagram of three cells (a) con-
nected by means of commissures (6), and running into fibres (c) ; 4, a multipolar cell
containing black pigment.

no medullary envelope, as in the sympathetic and other peripheral ganglia with
multipolar elements ; (c) ganglion cells with medullary envelope, but no neurilemma,
of which we see isolated examples in the N. acusticus ; and, finally, those which
possess both medullary sheath and neurilemma, as in the bipolar cells of spinal
ganglia. Corresponding to these we have four species of nerve fibres, namely, (a)
naked axis cylinders ; (b) axis cylinders with neurilemma, but without a medullary
sheath, as in the olfactory nerve and Remalcs fibres ; (c) axis cylinders without a
primitive sheath, but supplied with an envelope of medullary substance, as for
instance in the white matter of the nervous centres ; and finally, (d) axis cylinders
surrounded by both medulla and primitive sheath, the usual form. 4. Strange to
say, the existence of commissural fibres between the central ganglion cells is stoutly
denied byDeiters. I myself have seen them most certainly many years ago, and believe
in them still.

§ 179-

Here also, as in the consideration of the nerve tubes, the question
arises, Does the description of the ganglion cell just terminated give us
its complete structure, or does it possess a finer texture?

At present the extremely various views on the subject supply us with

. but very inadequate materials for replying to this query conclusively.

Thus the nerve fibre, i.e., the axis cylinder, has been stated to spring from

the nucleus or nucleolus. Among the various observations made on this

TISSUES OF THE BODY.

315

point tliere are doubtless some few which are correct (always excluding
those based on optical illusions), but they are probably the exception (1).

One discovery made by Beale some years ago, on the other hand, we do
look upon as correct, having satisfied ourselves further by personal observa-
tion. It applies to the ganglion cell of
the tree frog (fig. 306). Here may be
seen, namely, making its exit from the
interior of the pear-shaped or round
structure, at its pointed end, a straight
fibre, in which a nucleus (c, e) is not un-
frequently visible. This is surrounded
by the coils of one or more spiral fibres,
which also contain nuclei. These spring
from the surface of the cell-body in
close spiral turns (d, d), which increase
in girth as they proceed on their way
round the straight fibre, until they
eventually attain a straight course them-
selves, and pass on as spinal fibres with
their own special sheath (/). The first
mentioned fibre, which, as has been
already mentioned, springs from the in-
terior of the cell-body (whether from the
nucleus or no we are unable to say with
certainty), is of nervous structure. Beale
maintains also that the spiral have the
same character, though they appear to
us to be, as a rule, of elastic nature.
But we are far from denying the pos-
sibility that, when two fibres spring
from the one pole of a ganglion cell,
one of them may encircle the other
spirally. /. Arnold maintains that
these cells possess a much more highly
complicated structure.

Deiters mentions having found a double mode of arrangement in the
ramifications of the cells of the nervous centres (fig. 307). The greater
number of the processes is formed, namely, by prolongations in various
directions of the protoplasm composing the body of the cell. These
"protoplasm processes" then undergo repeated subdivision, giving off
branches in all directions, until they finally dip into the sustentacular
matter in the form of the most extremely delicate fibrillaa.

From these protoplasm ramifications we can distinguish at a glance one
peculiarly long process (a), which springs either from the cell itself or
from one of the first and broadest prolongations of its body. This pro-
cess never gives off branches, and becomes clothed later on with a
medullary sheath ; it is known as the " axis cylinder process" Of the
correctness of this we may easily convince ourselves.

Beside these just mentioned, other very fine fibres may be recognised
(b, 5), leaving the protoplasm ramifications at right angles. In these
Deiters supposes (without, however, giving any reason for his opinion),
that we have before us a second system of extremely fine axis
cylinders.

Fig. 306. — Ganglion cells from the sympa-
thetic of the tree frog (from Beale). a,
cell-body; 6, envelope; c, straight nervous
fibre; d, spiral fibres; e, continuation of
the former; and /, of the latter.

316

MANUAL OF HISTOLOGY.

According to Schnitzels recent investigations, both forms of processes
of these central ganglion cells (fig. 30-8) possess a fibrillated texture, more
apparent in the axis cylinder processes (a) than in the protoplasm ramifi-
cations (6), in which latter a granular interstitial substance is present iu
considerable quantity. All these primitive fibrillse may be followed up

Fig. 307.— Multipolar ganglion cell from the anterior cornu of the spinal cord
of the ox, with an axis cylinder process (a), and other protoplasm processss
with their ramifications, from which the finest fibres take origin (after
Deittrs).

into the body of the ganglion cell, and may be easily recognised there,
especially in the external portions, imbedded in a finely molecular
mass. Their course is a complicated one, sometimes diverging on
entry, and sometimes giving rise to an interlacement of crossing and
re-crossing fibrillre. Connection with the nucleus or nucleolus does
not take place. Whether we have here the true origin of the primi-
tive fibrillse, or whether the latter merely undergo a re-arrangement
here, — that is, that, arriving from remote localities through the various

TISSUES OF THE BODY.

317

protoplasm processes and penetrating the body of a cell, they are collected
together in the latter, and pass out as an axis cylinder, — are questions
still undecided.

Fig. 308.— Ganglion cell from the anterior conra of the spinal cord of the
ox (after Schultze). «, axis cylinder; 6, processes sent off by the cell.

REMARKS. — See Beale's treatise in the Phil. Trails, for the year 1863, part ii.
p. 543. Many other German observers agree with us in our view of the probably
elastic nature of the spiral fibres.

§ 180.

Having become acquainted with the two kinds of form-elements of the
nervous system, let us now turn to the consideration of their general
arrangement in the peripheral nervous apparatus.

The nerves of the brain and spinal cord, differing in their white colour
from those of the sympathetic system, which are usually grey or greyish
red, become clothed with a delicate envelope at their exit from the
nervous centres. This covering receives another addition from the dura
mater of connective-tissue bundles in its passage through the latter, and,
thus strengthened, constitutes what was formerly known as "neurilemma,"
but which we will designate from henceforth " perineurium " (1).

318 MANUAL OF HISTOLOGY.

Internally this perineurium extends between the bundles of nerve-fibres,
which, as in muscle, may be divided into primary and secondary, and in
which the tubes are already arranged in the series in which they even-
tually leave the trunk. In some cases the connective-tissue preserves its
fibrous character, especially when it binds together larger collections of
nervous tubes than usual, while around the primary fasciculi it appears
rather as a homogeneous nucleated substance. Again, having become
modified to a homogeneous material, it enters into the formation of the
primitive sheaths around the medullary portion of the nerve-tubes con-
tained in the trunk. Finally, the latter is traversed by a scanty network
of capillaries, consisting of fine tubes measuring about 0'0056 mm.

From the fact that the primitive fibres run along side by side unchanged
in the nerve, without giving any indications as to their functions by their
appearance, all branchings, anastomoses, and formations of plexuses, may
be regarded by the physiologist with tolerable indifference.

As is well known, there occurs a progressive splitting up of the nervous
trunks at very acute angles in their course towards the periphery. Thus,
the primitive tubes leave the stem or common path in bundles, and, bend-
ing off sideways, pursue their way separately towards the organs they
supply. The actions of the various nerves is, however, by no means
determined by this arrangement ; but in one made up of sensitive and
motor fibres, this formation of branches may bring about a separation of
the latter.

Anastomoses, for the interchange of different kinds of fibres for anato-
mical ends, are connections between neighbouring nerves or branches of
the latter. We may distinguish between simple and double anastomoses
also. In the first, a number of nerve-tubes pass through a connecting
branch into another trunk, pursuing in this their further course ; in the
second, both nerves exchange fibres with one another.

This interchange of fibres between adjacent nerves, when it takes place
to any great extent, gives rise to the so-called plexus.

These branchings, anastomoses, and formations of plexuses, are con-
tinued down to nerves of microscopic minuteness, and even in the
organs within which the latter are to terminate. In them especially the
formation of plexuses is a very general occurrence just before the final
radiation of the fibrillae, and has been alike described in earlier and more
recent times. In the larger and more massive plexuses an interchange of
single primitive fibres alone is to be observed ; while in the finer, or, as
they have been called, the terminal plexuses, repeated divisions of the
nervous tubes arid retiform intercommunications between their branches
have been met with.

In its whole course, from its central origin until towards its peripheral
distribution, the nerve fibre does not change its character in the least, and
its diameter but to a slight degree.

With the progressive division of the nervous trunk, however, certain
modifications of the connective-tissue sheathing make their appearance,
This latter, namely, decreases in amount from the stem towards the
branches, and appears no longer fibrillated on the finer twigs, but only
streaky, until, finally, in the terminal filaments, we find nothing but a
homogeneous nucleated mass. This simplest form of perineurium may be
seen on little twigs which only contain a few primitive fibres. Even
single nervous tubes may course through a tissue for a considerable dis-
tance in a clothing of this kind, until they terminate finally with loss of

TISSUES OF THE BODY. 319

the latter. In such cases the connective-tissue envelope is perineurium
and neurilemraa at the same time. These facts, however, are variously
viewed, some regarding this simplified perineurium as a thick primitive
sheath.

The trunks and branches of the sympathetic system are essentially the
same in structure as those just described, except that in them Remak's
fibres (already mentioned at § 176) make their appearance in great
numbers.

REMARKS. — This name was first applied by Robin to the envelopes composed of
simple connective-tissue of the finest twigs.

§ 181.

From time immemorial anatomists and physiologists have been occu-
pied with the question, how the nervous fibres terminate peripherally.
In older times, of course, before the introduction of microscopic analysis,
conjecture alone could be formed on this point. It was supposed that
the nervous twigs broke up into finer and finer fibrils, which became
fused finally with the tissue of the organ they supplied.

With the aid of the microscope, about the thirtieth year of this
century, it was already a matter of no difficulty to follow the progressive
sub-division of the smaller branches down to their finest twigs, and to
recognise here and there the course of the latter through the tissue, as
well as the formation of the plexuses and minutest anastomoses already
mentioned (§ 180).

At that time many observers maintained that they had found a
looped termination, and, moreover, in the most different organs. They
supposed that two neighbouring fibres were always united at the peri-
phery in the form of a wider or narrower loop, or, what is but another
mode of expressing the same thing, that each nerve tube, on arriving at
the periphery, became doubled on itself, and took its course back again to
the nervous centre, from whence it came. This theory of terminal loops,
which held good for motor and sensitive fibres alike, led however to great
physiological difficulties.

We now know, from a series of newer and more accurate investigations,
that these loops are of frequent occurrence among the peripheral ramifica-
tions of nerves, but that they possess no terminal significance, since the
nerve fibre in this curved course has not yet arrived at its final destina-
tion. This theory of the looped termination of nerves has, therefore,
disappeared from histology.

As far as we know at present (though our knowledge on the subject
is still in a most unsatisfactory condition), nervous fibres terminate without
any medullary substance — first of all in the form of simple or ramifying
axis cylinders, and, in the next place, in the form of primitive fibrillce.
The final disappearance of the fibre, moreover, is frequently seen to take
place in special "terminal structures" or "end corpuscles." These are
either complex or single-celled.

§182.

It was for some time supposed that an insight of the mode of termina-
tion of the motor nerves in striped muscle (fig. 309) had been gained with
tolerable correctness through the labours of R. Wagner and Reichert (1).
It was believed that the motor nerve tube ceased on the striped fibre after
repeated sub-division in the form of pale terminal filaments. On account

320 MANUAL OF HISTOLOGY.

of this repeated splitting-up of the primitive fibres further, a considerable
number of terminal filaments could be formed from a few of the latter (2).
So far the difficulty of following up the nerves is but small, if we take,
for instance, the platysma of the frog.

But experience teaches that this repeated division of motor nerve fibres
is peculiar to the lower orders of vertebrate animals. In fishes also it. may
give rise to the formation of more than one hundred terminal filaments
from one such ; and primitive fibres are by no means rare, which supply
upwards of fifty muscular fibres.

Among the higher orders of vertebrata, on the contrary, this splitting
up becomes less and less frequent, so that its occurrence is only excep-
tional among the mammalia. The number of muscle and nerve fibres
becomes almost the same, — a fact of great physiological importance.

If we examine one of the thin transparent muscles of a frog, we find
without any difficulty the small trunks of the nerves, which have entered
the substance of the latter, lying sometimes obliquely, sometimes parallel
to its fibres, and giving off numerous branches and anastomotic twigs.
In human and mammalian muscle likewise a plexiform interchange of
fibres between adjacent twigs may be observed.

At the points of division of the latter, and especially when they have
attained a considerable degree of fineness, and contain but few primitive
fibres, we not un frequently perceive the manner in which a nerve-fibre
suddenly breaks up into two or more branches, with a contraction generally
at the point where the latter part from one another. These branches
possess the same medullated appearance as the parent stem, and pass
onwards, according to the character of the whole nerve, more or less
divergent. Deceptive appearances, however, are matters of possibility here.
At those points, however, where, in the further course of their ramifica-
tions, the nerve fibres come to lie either singly or in extremely small
number together, traversing thus the muscle in a usually oblique direction
(309, a), their further subdivision may be most distinctly observed.

This most frequently occurs by division into two threads, more rarely
into three or four. The latter may either correspond to one another in
breadth, or are unlike in that respect (a below and in the centre). Con-
tractions at the points of division may not be present, or if so, only
slightly marked ; or again, they may be very strongly pronounced. But
complete solution of continuity, to such an extent that the empty primitive
sheath alone remains, is always an artificial production. The axis
cylinder, on the other hand, divested entirely of medullary sheath, appears
frequently as a natural formation.

The division of this axis cylinder is for the rest hardly anything more,
than the separation of the original primitive fibrillse" into two new
fasciculi of smaller diameter.

In consequence of this repeated division, the nerve fibres (which
possessed at the outset a medium diameter of 0-0142-0-.0113 mm. and a
double contour) become gradually reduced in calibre down to 0*0056 mm.,
and lose their double outline (6).

Finally, however, we observe the terminal twigs of 0'0045-0'0038 mm.
in breadth approaching the single muscle fibres in the form of free axis
cylinders having lost their dark medullated appearance, and apparently
ending here in two short branches.

It was formerly believed that we had here in these pale fibres the trco
termination of the nerves, while it still remained a matter of uncertainty,

TISSUES OF THE BODY.

321

owing to the difficulty of investigation, whether this took place externally
on the sarkolemma, or after perforating the latter in the interior of the
fleshy substance.

Fig. 309. — Distribution of nerves in a voluntary muscle from the frog. a. a nerve
fibre destitute of neurilemma, showing repeated subdivision down to apparent!}
terminal filaments 6, b; c, an undivided nerve fibre with a thick envelope.

From a whole series of recent investigations, among which those alone
of Beale, Kuhne, Margo, Koellilter, Krausc, Rouget, Engelmann (3;. need
here be mentioned, the conclusion has been arrived at that this early
view is likewise untenable, and that the true ending of the fibres takes
place far beyond these apparently terminal twigs.

But in what form and where this final cessation of the fibre is situated,
whether within or external to the sarkolemma, is a point about which
considerable difference of opinion still prevails.

Beale, Krause, and Koelliker believe the fibre to terminate externally,
while the other observers are of the opinion that it perforates the sarko-
lemma ; and we believe rightly.

In fact, we may see, on examination of the muscular fibres of verle-

322

MANUAL OF HISTOLOGY.

brates (fig. 310), that the dark-edged primitive fibre (a, b) approaches the
muscle fibre (g, left), enclosed within a loose nucleated sheath (c, d), and
pierces the sarkolemma, while the neurilemma becomes continuous with
the latter (e, left). Beneath the sheath of the muscle the terminal
filament swells up into a finely granular mass of a flattened form containing
nuclei (/, left). This merges at its edges (e, e}, and concave under
surface, into the fleshy substance of the fibre (4).

To this structure in which the fibre ends, and which occurs only singly
in mammalian muscle fibres, has been given the very appropriate name

of " terminal plate " by
Krause, Rouget, Engelmann,
and others ; while Kuhne
calls it the "neural emin-
ence " (NervenliugeT).

In the mammalian body,
in which these terminal
plates are well developed,
and occupy a not incon-
siderable portion of the sur-
face of the muscle fibre,
their diameter ranges from
0-0399 to 0-0602 mm., while
in thickness they vary.

Their nuclei are smooth,
clear, oval, and contain one
or two nucleoli, thereby dif-
fering from the more opaque
formations of the neuri-
lemma, and likewise from
those of the muscular fibres.
In diameter they range from
0-0049 to 0-0099 mm.
Their number is liable to
variation ; from four to
twenty being found in one
plate.

Terminal plates of the same kind are to be met with in birds and
reptiles.

But a number of questions relative to the nature of these neural
eminences must for the present be left unanswered, and perhaps for a
long time still ; for instance : Do we see in them the whole of the ultimate
distribution of the fibre? Does the finely granular substance of which
they are composed take its origin from a transformation of the axis
cylinder, or does the latter end within them, and, if so, in what form1? On
these points there is no lack of variety of opinion.

According to Jfrause, we may recognise a pale, single, double, or triple
fibre (axis cylinder) within the terminal plate, ending with a swelling or
knob upon it. A very fine and somewhat tortuous fibre was also
remarked in the same situation by Sclwnn. But from Killings researches,
which from our own observations we are inclined to regard as correct, we
learn that the structure is far more complicated. On its entrance into
the^ terminal apparatus (fig. 311), the axis cylinder of the nerve fibre
divides, and spreads out with further ramification into a peculiar pale

Fig. 310. — Two muscular fibres from tlie psoas of the Guinea
pig, showing terminations of nerves, a, 6, the primitive
fibres with their transition into the terminal plates e,/; c,
neurilemma with nuclei d, d, continuous with the sarko-
lemma g, g\ A, muscle nuclei.

TISSUES OF THE BODY.

323

Fig. 311. — A muscle fibre from the
lizard, a; b, nerve fibre; c, dichoto-
mous division in the terminal plate,
with transition into the true terminal
structure of Kiihne.

formation, bounded by undulating lines and truncated processes. This is
the " true terminal plate" The nuclei and
finely granular substance of the "neural
eminence " are situated beneath this struc-
ture, adjacent to the fleshy mass of the
fibre (5). Engelmann also speaks of an ar-
borescent arrangement of branches of the
axis cylinder lying in the granular sub-
stance of the neural eminence.

Now if, as would appear to be the case,
the distribution of the nerve fibre be
confined to the immediate mass of the
terminal plate, the extremities of the
muscle fibre must remain without nervous
supply, in that the former is set into the
latter at about its middle. But the fleshy
matter manifests contractility at the ex-
tremities also !

The bearing of the terminal portions
of the nerves supplying the muscles of
the lower orders of vertebrates, of naked
amphibia and fishes, present new difficulties in this so uncertain, but phy-
siologically so important subject. Here we find that those complex mul-
tinuclear terminal plates are no longer present. In the frog, the nerve
tube, on arriving at the fibre, not unfrequently breaks up into a multitude
of dark-edged fibrils, forming thus the " terminal tuft " of Kiilme. These
having pierced the sarkolemma, course along within the muscle fibre as
intra-muscular axis cylinders with isolated nuclei, and eventually become
merged, to all appearance, in the fleshy mass. Whether we have to deal
here with simple uninuclear terminal plates (Krause, Waldeyer) (of which,
in that case, several would seem to be present in one muscle fibre), or
whether this system of intramuscular axis cylinders may not represent in
the frog the true terminal plate of Krause, mentioned above, are questions
which must be determined by future research.

According to Krause, these terminal plates are to be found also in the
heart of the rabbit.

Taken from, other sources, the results which have been obtained on
inquiry into the nature of the final terminations of nerve fibres are
essentially different.

REMARKS. — 1. /. Mullcr and Briickc appear to have been the first who observed
division in the nerve fibres supplying muscle, in the year 1844. 2. Thus Reichert
counted 7-10 afferent nervous fibres in the thin platysma of the frog, containing
about 160-180 muscular fibres. These split up, eventually, with progressive rami-
fication, into 290-340 terminal filaments. 3. With regard to the final distribution of
nerves, modern literature is very rich. Compare, besides the works of Continental
investigators— of Kiihne, Rouget, KoelliTcer, Engelmann, and others — Beale (Proceed-
ings of the Royal Soc., vol x. p. 519 ; Phil. Transact, for the year 1861, p. 611 ;
and 1862, Pt 2, p. 889 ; also his Archives ofMed., No. 11, p. 257 ; and in the Quart.
Journ. of Micros. Science, 1863, p. 97 ; Proceedings, p. 302 ; and lastly (1864),
Transact., p. 94. 4. This is most beautifully seen in the group of small spider-like
animals, the tardigrades. Here, where many years ago the terminations of the
nerves, i.e., the neural eminence or terminal plate, had been recognised by Doyere,
the naked nerve fibre applies itself to the likewise membraneless muscle fibre, and
both masses become fused one into the other at the point of contact. If we now
suppose both nerve and muscle fibre enclosed in their sheaths, we obtain the same
relation of parts as in the mammal body. 5. According to Rouget, the neural

324 MANUAL OF HISTOLOGY.

eminence is not the true terminal structure. The nerve fibre, he says, becomes
forked (amon» the arthropods) at the summit of the eminence, giving off two fibrils.
These latter then travel the substance of the terminal plate, and breaking up into
numerous filaments, end in the fleshy mass of the muscular element. 6. According
to Scale, there is situated on the exterior of the sarkolemma a very fine nucleated
network'of nervous elements, to which formation this English investigator ascribes
just as little terminal significance as elsewhere in the body, in that the nerves are
only spread out peripherally in loops. A similar view of the subject had been pre-
viously taken by Schafhausen. The statements of such a man as £eale, however,
and the peculiar methods of investigation made use of by him, deserve more con-
sideration than has as yet been given them. Koellikcr's views, as regards the termina-
tion externally upon the sarkolemma, correspond with those of Beale. On the other
hand, he only recognises pale terminal fibres in the frog, which he regards as con-
tinuations of the axis cylinder and primitive sheath, and which probably end, as a
rule, naked. He encountered, however, some isolated cases, which seemed to indicate
a termination in a very fine dense network. Margos views, on the other hand, are
completely different. According to him, the nerve pierces the sarkolemma, sinks
into the fleshy matter, and is in communication here with a peculiar terminal
apparatus. The latter he looks upon as formed of the greater part of the muscle
nuclei and the network of the so-called interstitial granular threads (§ 166).

§ 183.

Turning now to unstriped muscular tissue, we find it far more difficult
to recognise in it the final distribution of the nerve fibres than in the tissue
we have just been considering. Division occurs here also, as has been seen,
for instance, in the stomach of the frog and rabbit by Ecker ; in the heart
of amphibia and nerves supplying the uterus of rodentia by Kilian.

In the mesentery of the frog (fig. 312), moderately treated with acetic
acid, we may observe in the narrow medullated nerve fibres enclosed in
a thickened envelope several repeated dichotomous divisions, until at
last the branches penetrate the walls of the part and are removed from
further observation. These fibres are enclosed, as was before indicated,
in a thick nucleated envelope.

But what becomes of these nervous elements on arrival in the unstriped
muscular tissue ?

This is a question which for a long time remained without any satis-
factory answer. It is true that years ago plexuses or networks of pale
delicate filaments had been met with, with nuclear structures at the
expanded nodal points, and that this network was held by many to be a
terminal structure, which view seemed strengthened by the fact of the
occurrence of a similar nervous end-formation in the electric organs of the
ray.

But not long ago an important discovery apparently was made by
Frankenhduser, subsequently confirmed by Lindgren, and more recently
still through the most comprehensive researches by Arnold. This was
that the nerve fibres of smooth muscle penetrate to the nucleus of the
contractile cell in the form of a fine terminal filament, the primitive
fibrilla, and end probably in the nucleolus.

From Arnold's experiences it would appear that the nervous twigs sup-
plying unstriped muscle consist partly of medullated and partly of non-
medullated fibres, in varying proportion. We encounter the latter as
fine or broad threads, measuring in diameter 0'0018-0'002 mm., and
showing at intervals small nuclei. Externally, in the connective-tissue
covering the muscle, these nerves are arranged in the form of a wide-
meshed network, in which, as Scale has pointed ou*-, ganglion cells are
to be found at certain points in the muscles of the vascular system. To
this the name "ground plexus" lias been given (1).

TISSUES OF THE BODY.

325

Fig. 312. — Two narrow branching nerve fibres (a, b) from
the mesentery of the frog, surrounded with a thick
nucleated envelope. At 1, the trunks; at 2 and 3, the
branches.

From this plexus are given off, in the first place, medullated nervous*
fibres, which assume, after a
longer or shorter course, the
form of pale longitudinally
striated bands of 0'0041-
0'0050 mm. in diameter, con-
taining at intervals nuclei of
the same dimensions. These
bands become gradually nar-
rowed down until we meet
them as the nucleated fibres,
0-0018-0-0023 mm. in dia-
meter, which have been already
mentioned.

From these, again, is formed
a second network with toler-
ably broad rhomboidal or
elongated meshes, whose no-
dal points show nuclei with
distinct nucleoli. Pale fibres,
however, are also given off
directly from the "ground-
plexus" to the muscle cells.
This the "intermediate net-
work" (fig. 313) lies imme-
diately upon the layers of mus-
cular tissue, or between the latter. From it there pass off small fibres which
penetrate between the muscle fibres. These are only supplied with nuclei
at the commencement, and become
rapidly smaller, so that after repeated
subdivision they are reduced to
threads of 0 '0005-0 -0003 mm. in
thickness. On the latter, as well at
their point of division as- elsewhere,
there occur elliptical, round, or other-
wise shaped swellings or granules.

The last-mentioned fine fibres unite
once again to form a new, but this
time very close-meshed network, the
"intramuscular," whose varicose fib-
rillae occupy the narrow passages be-
tween the contractile cells.

Finally, leaving this intramus-
cular interlacement, dark straight
fibres of extreme fineness pass off,
which are at the very most 0*0002
mm. in thickness. These penetrate
into the contractile cells, and ad-
vancing to the nucleus, terminate,
according to Frankzriliauser, in the
nucleolus. The number of terminal filaments which enter any one muscle
cell corresponds with the number of granules occurring in the nucleus
(§ 163).

Fig. 313. — Ramification of nerves and termina-
tion in the muscular tunic of a small artery of
a frog; from Arnold.

326 MANUAL OF HISTOLOGY.

Arnold believes, however, that in very many cases these fibrill?e leave
the nucleoli again in an opposite direction, and after having traversed
the nucleus and body of the cell, unite once more with the intramuscular
network. According to this, the nucleolus would appear to be not the
terminal point, but only a knot on the ultimate filament.

Later on we shall have to discuss the reticulum of the corneal nerves.

We must now turn to the consideration of the nerves supplying glands,
which were discovered by Krause. Here, besides dark-edged fibres which
occur in the salivary and lachrymal glands of mammals, and come to an
end in peculiar terminal structures, to be referred to again ; besides these,
pale nucleated nerve fibres, only about O0020 mm. in diameter, may be
remarked between the glandular follicles, and applied, with dual division,
to the so-called membrana propria of the gland element. These fibres just
described take their origin from dense networks of medullated tubes
situated around the excretory ducts of the lobules.

Finally, it is stated by Pfliiger that in the salivary glands the delicate
end filaments of the nerve fibres terminate in the gland-cells after piercing
the membrana propria. He has also seen the processes of multipolar
structures, lying external to the follicles, coming to an end in the same.
These he supposes to be ganglion cells. The same observer states that
a similar arrangement of parts is to be seen in the pancreas. In the liver
also he has found a connection between the nerve fibres and gland cells.
Between the cells likewise of the lacrymal gland, a radiation of fine
terminal fibres has been described by Boll. We regret being obliged to
express our incredulity as regards the correctness of all these statements ;
in our opinion, the termination of the nerve filaments in glands is still
unknown.

REMARKS. — Philos. Trans, far the year 1863, part ii. p. 562.

§184.

The final destination of the sensory nerve fibre, to which we now turn,
is found to be in the first place a special terminal structure — the
extremely abstruse and much-disputed question of their bearing in most
of the organs of special sense we leave out of the question — in the next
place, it seems probable that the fibre may end with free ramifica-
tions. .

The best known anatomical recipients of the sensitive nerves are — (1)
the Pacinian bodies ; (2) the tactile corpuscles of Wagner and Meissner ;
and (3) the terminal bulbs of Krause. The first of these, the oldest
discovery, present the greatest complexity of structure; the last or
newest, the least.

The terminal bulbs of Krause (fig. 314) are found in the human being
on the sensitive nerves of the mucous membrane and in the skin. They
are met with again in the conjunctiva bulbi, in the mucous membrane at
the base of the tongue, in the fusiform and circumvallate papillae of the
latter, and in the soft palate, glans penis and clitoris. In the mam-
malian body they are also widely distributed. They have been also
met with in the external skin, as, for instance, in that of the mouse, and
they occur on the volar aspect of the Guinea-pig's toes. Their nature,
moreover, is the same in the mammalia as in our own frame.

The form of these structures in the mammal is egg-shaped (1, a),
0-0751-0-1409 mm. in length, and (2 a) about one-fourth as broad. In
man and the monkey they are more rounded, their diameter being from

TISSUES OF THE BODY.

327

0'0322 to 0'0751 mm. Some isolated bulbs may attain, however,
much greater dimensions, and twisted or indented forms are also met
with.

The terminal bulb of Krause consists of a transparent nucleated envelope,
containing a soft, homogeneous, slightly lustrous substance.

The nerves connected with it (c) undergo subdivision into branches
more or less frequently repeated (1*, 2). Thus from one primitive fibre
from 6 to ] 0 terminal corpuscles may be
supplied. On entering the latter, the pri-
mitive fibres of medium size until there
(about 0'0046-0'0075 mm.) become imme-
ately still finer, constituting then the pale,
non-medullated end filament or axis cylin-
der (1 b). The latter is 0-0039-0-0029
mm. in thickness, passes through the axis
of the structure, and ends towards its upper
pole with a slight button -like swelling
about O0046 mm. across.

The terminal bulbs of the human con-
junctiva (2) frequently present sinuosities
and twists on the primitive tube as it
is about to enter or has already entered the
former. These may be present to such an
extent as to form a regular convolution,
especially in the interior of the corpuscle.
Within the latter itself, or before its en-
trance, a splitting of the nerve tube may
take place ; beside which many varieties
are to be seen as regards its bearing.

The number of these formations also
seems to vary considerably. In 1 Q/7/ of
the conjunctiva of the calf Krause noticed
1 3 terminal bulbs.

Structures allied to the latter were also
met with by Krause in the glans clitoridis,
and in smaller number in the penis.
These " genital nerve-corpuscles " lie in the tissue of the mucosa at the
bases of the papillae of the mucous membrane. In size and form they
vary, some of them attaining a diameter (H439, or even 0*2001 mm. As
a characteristic of these genital nerve-corpuscles, constrictions may be
mentioned which occur in varying number on the surface, and com-
municate to the whole a mulberry-like appearance. They appear to be
the recipients of sexual sensation, for which reason finger proposes giving
them the name of " sensual corpuscles " (Wollustkbrperchen).

The same observer has described another kind of structure similar
to the end-bulbs, as present in the racemose glands of mammalia. These,
the " end capsules of the gland nerves,1' have a somewhat elliptical form,
and consist of a number of concentrically laminated membranes, from
four to eight of which may be observed in each, and which are studded
with numerous nuclei. In the interior is to be seen the minute cylin-
drical end-bulb, which is not unfrequently of sigmoid figure, and whose
axis is occupied by an almost immeasurably fine lustrous terminal fibre.
The latter springs from a dark-edged nerve tube.
22

Fig. 314.— Terminal bulb. 1. From the
conjunctiva of a calf. 2. From that
of a human being, a, Bulb ; c, nerve
fibre ending in (1) an axis cylinder (b).

328 MANUAL OF HISTOLOGY.

§ 185.

Another modification, to a certain extent, of these end bulbs of Krause
is presented to us in the tactile or touch corpuscles of the skin (fig. 315).

The nervous network supplying the latter give off primitive fibres
towards the bases of the so-called tactile papillae (p. 234), which pass

Fig. 315. — Vertical section of three groups of tactile papillae of the human index finger,
occupied partly by vascular loops, and partly by tactile corpuscles.

forward either isolated or lying together in small fasciculi of microscopic
fineness. Here division of the nervous tubes, at acute angles, occurs
with great frequency.

These touch-corpuscles may be found on the volar aspect of the fingers
and toes, and on the palm of the hand and sole of the foot. Their number
is greatest on the aspect of flexion of the last joints of the fingers, and
decreases then from the second to the first. In the palm of the hand
they are still fewer in number. Thus in the Q'" to 400 papillae, 108
tactile corpuscles were found by Meissner on the last joint of the finger,
while in the second joint the latter only amounted to 40, on the first to
15, and in the palm of the hand to 8. Their amount is also most con-
siderable on the last joint of the toes. Here, however, the proportion, as
compared to the hand, is very small. On the back of the hand, the
dorsum of the foot, and volar surface of the forearm, we may also en-
counter a few of these tactile corpuscles. Krause has found them,
besides, in the conjunctiva. Finally, they are to be met with in the
nipple and skin of the lips, though in but moderate number. In the
latter regions intermediate forms between them and the terminal bulbs
have been described. Among the mammals they have only been recog-
nised in the ape, in the palm of the hand, sole of the foot, and skin of the
lips (Meissner, Krause}.

Size and form are liable to considerable variation. In the vola manus
they measure upwards of 0-1115 mm. with a breadth of 0-0451-0-0563
mm. Smaller specimens may only reach 0-0451-0-0377 mm. Those of
greater dimensions are usually oval ; those of smaller, mostly of rounder
figure.

These structures are situated in the axis and apex of the tactile papillae,
but excentrically in those which are in any degree complex. Only the
latter are exceptionally supplied also with vascular loops (fig. 315 ; in the
middle a double papilla). Otherwise those which contain tactile cor-
puscles are non-vascular.

The touch corpuscle consists of a capsule formed of a homogeneous
substance enclosing a finely granular soft matter best seen in transverse
section.

In the capsule, further we may remark numerous elongated bodies
arranged transversely or obliquely. We shall refer to these again pre-

TISSUES OF THE BODY.

329

Fie. 316— Two human tactile papillae from the
velar surface of the index finger. In the interior
we have the tactile corpuscles, into whose tissue
the nervous fibres may be seen entering.

sently. They communicate to the whole structure a characteristic trans-
versely striated appearance.

The nerve fibres (fig. 316) pass out towards these bodies either singly,
or, as is more frequently the
case, double : at times, also,
they are trebled or quadrupled.
They are enveloped in simple neu-
rilemma (fig. 316), which is con-
tinuous with the capsule. They
are dark-edged, 0'0045 mm. and
less in breadth, and enter the base
of the touch-corpuscle, or at times
also its side.

The mode in which they end,
however, is difficult to determine.
At limes a peculiar twining of the
nerve tubes around the tactile cor-
puscle may be remarked, or they
may be seen to run for a greater or
less distance straight along the
latter. They all finally pass into the
interior of the corpuscle, however,
but in what manner they end there
is still unascertained. In all probability they spread out in the form of pale
non-medullated fibres or axis cylinders, like those of the terminal bulb.
That the transversely arranged nuclear bodies, already mentioned, are con-
nected with the termination of the fibrillse appears extremely improbable.

§186.

We turn now, in conclusion, to the Pacinian bodies, which may be
likened to a terminal bulb enveloped in numerous concentric capsules of
connective-tissue.

As they come under our notice they are elliptical structures, sometimes
more elongated than at others, and measuring from 1 to 2 mm. in length.
To the unaided eye they appear translucent, and marked towards the
axis with a streak. In man they occur regularly on the nerves supplying
the palm of the hand and sole of the foot, but with especial frequency on
those passing to the tops of the fingers and toes. Their total number, in
these parts taken together, has been estimated at from 600 to 1400.
According to Rauber, they are met with also, but with less frequency and
constancy, at many other points in the body : thus on the dorsum of the
foot and back of the hand, beneath the skin of the arm, forearm, and
neck ; on the intercostal nerves, and all the articular nerves of the extre-
mities. They are likewise to be found on many nerves supplying bone,
and in the interior of the muscles of the hand and foot ; further, in the
nerves of the parts of generation, and finally on the plexuses of the sym-
pathetic system, round about the abdominal aorta. Again, they are
encountered among the mammalia; especially on the sole of the foot, and
with exquisite distinctness, and in greater or less number, in the mesentery
of the cat. Pacinian bodies are also found in birds as well as in mammals,
although modified to a certain extent.

The laminae of the capsules are looked upon as formed of connective-
tissue, consisting of an either homogeneous or somewhat fibrillated

330

MANUAL OF HISTOLOGY.

Fig. 317. — Pacinian bodies from the mesen-
tery of a cat. a, a nerve with its peri-
neurium forming the stalk ; 6, the system
of capsules; c, axial canal or internal
bulb, within which the nerve tube ends
forked.

ground substance, in which elongated nuclei or cells are imbedded.
On the internal surface of these membranes a mosaic marking, like

epithelium, has been recently remarked
by Hoyer after treatment with nitrate of
silver. These systems of capsules, fur-
ther, are traversed by a scanty vascular
network. The individual laminae of which
they are composed follow the contour of
the whole corpuscle, and are not so thick
outwardly as within, where they appear
more condensed, and where they sur-
round in shorter curves the canal or in-
ternal bulb occupying the axis. The
latter consists of a soft nucleated connec-
tive substance.

The internal bulb (c) is rounded off at
its termination. Its walls, like those of
the capsules, are continued at the oppo-
site extremity into a stalk (a), by which
the Pacinian body is attached like a berry
to the nerve.

This style consists of ordinary longitu-
dinally marked connective-tissue, and is
formed by the perineurium of the afferent
nervous fibre.

The diameter of the latter is 0-0142-
0*0113 mm. and less. It presents the usual medullated appearance, and
so reaches the corpuscle, at whose inferior pole it makes its entry into
the central canal, occupying the axis of the latter. On entering the
central passage the fibre loses its dark border, as is the case in the ter-
minal bulb of Krause; it then becomes considerably diminished in size,
and comes to an end as a pale terminal filament or axis cylinder of dis-
tinctly fibrillated constitution. The latter traverses thus the whole
internal bulb, and ends at the roof of the latter (c, above) with a slight
button-like swelling.

Division of the nerve fibre before its entry may occur ; and not unfre-
quently do we see, too, the pale terminal fibre splitting into two or three
branches, divisions in which the axial canal may also participate.

Very rarely two nerve fibres are seen to enter the same corpuscle,
and terminate singly or doubly in a single internal bulb (Koel-
liker).

Many other variations besides those mentioned here must be passed
over.

That these Pacinian bodies are connected with the sensory-nervous
apparatus can hardly be a matter of earnest doubt any longer, since the
discoveries of Wagner, Meissner, and Krause.

REMARKS. — These wondrous structures were known even long ago, but they
received but little attention. The old German anatomist Vatcr observed, more than
a century ago, that the nerves of the skin of the palm of the hand and sole of the
foot were studded not unfrequently with small oval swellings, to which he gave the
name of papillce nervce. Later on, in the year '30, after having been completely
forgotten for some time, they were again discovered by Pacini of Pistoja, and noticed
also at the same time in France. They were, however, specially brought into notice
through a monograph by Henle and Koelliker, which appeared in the year 1844.

TISSUES OF THE BODY. 331

These two observers gave the corpuscles the name of Pacinian bodies, without any
idea of their previous discovery by Vater. This name has been retained by some,
while by others the structures are designated as Vater- Pacinian corpuscles.

§187.

Having finished the consideration of these terminal bodies, let us now
turn to the question as to how the remaining wholly sensible nerves end,
one of the most obscure subjects in minute nervous anatomy, and one
about which much uncertainty still prevails.

It is quite obvious that centripetal nerves must occur in voluntary
muscle as recipients of muscular sensation. Our acquaintance, however,
with them, is still very slight.

With a view to throwing some light on this point, the platysma of the
frog was subjected by Kodliker to minute investigation, being peculiarly
well suited for this purpose. Here there is to be seen — possibly springing
from the division of a single broad nerve tube — a slight nervous ramifica-
tion, confining itself almost entirely to the anterior surface of the muscle.
The narrow nervous twigs of the same are, at their commencement, still
dark-edged, but become paler as the branching progresses, and are seen
later on as fibrils clothed with a loose neurilemma studded with nuclei.
Eventually they terminate, after the loss of this envelope, in the form of
extremely fine still branching filaments. The latter measure less than
0'0023 mm. in diameter. At intervals in their course, as well as at the
nodal points of their division, small structures like nuclei are to be
observed. Eetiform connections among the fibres appear to occur only
as exceptions.

In connection with other nerves, however, to which a sensory nature
may be ascribed with greater or less probability, terminal networks of
various kinds, formed of pale fibres, have been described. Arnold the
younger, for instance, mentions such an one on the surface of the con-
junctival mucous membrane, and Billroth another on the mucous
membrane of the pharynx of the water salamander. Again, Koelliker
speaks of one in the mucous membrane of the small intestine of the frog,
and confirms Billrotli's statements as regards the pharynx of the last-
mentioned animal.

Similar terminal networks of pale fibres have also been described by
Axmann and Ciaccio as occurring in the cutis of the frog, and, many
years ago, as existing in the tail of the tadpole. Klein has also met with
the same networks, and described them as occurring very widely
throughout the body of the same animal.

For many years past we have known of certain isolated instances of
their occurrence in the skin of mammals, and ScJicll has recently demon-
strated their presence here in great abundance.

There can be no longer any doubt that the most superficial termina-
tions of sensible nerves frequently penetrate into the epithelial layers of
their organs.

But their ultimate arrangement is still very variously explained. The
fact is, that at the present time our modes of investigation are still too
imperfect to admit of our settling the matter conclusively.

Some suppose them to end in a terminal plexus, so that we would only
have an intermixture simply of epithelial cells and nerve fibres. Others,
again, state that the latter penetrate into the cells and end in the nucleoli.
Thirdly, many support the view that there exist certain peculiar

332

MANUAL OF HISTOLOGY.

structures imbedded in the epithelium, in which the nerve fibres ter-
minate. These are known as Langerhans' cells. A few more points may
be mentioned in regard to these views.

A few years ago an excellent observer, Hensen, stated that in the tail
of the tadpole the terminal filaments penetrated into the nucleoli of the
epithelial cells. His observations gained greatly in interest through the
further investigations of Frarikenhauser and Arnold (§ 183). But these
statements have not since been confirmed, and must now be declared
incorrect : this we maintain against Lipmann, who asserts that very
delicate nerve fibrillse may be seen to terminate in the nucleoli of the
posterior epithelial cells -of the cornea.

We must also confess our disbelief in Joseph's theories with regard
to a similar ending of the nerves in the cells of bone, and to Lavdowskijs
with respect to those of the cornea.

But, on the other hand, we have since learned from the beautiful inves-
tigations of Hoyer and Cohnheim, that very fine nerve-fibres or primitive
fibrillse do terminate in the epithelium of the corneal conjunctiva. Of this
there can be no doubt.

The cornea possesses several distinct plexuses of these nerve fibres.
From the most superficial, which lies close under the lamina elastica
anterior (fig. 318), and which consists of bundles of delicate primitive

fibrilloe, there arise at inter-
vals isolated twigs (e), which
perforate this anterior boun-
dary layer of the cornea per-
pendicularly. Arrived at the
external surface of the latter,
they break up into a tassel of
primitive fibrillse, and form
a " sub-epithelial plexus " of
the most delicate threads
(6, below), with elongated
meshes radiating from the
centre of the cornea (Guinea

Pig);

From this horizontal end-
plexus a number of primi-
tive fibrillse are given off as
side branches, which ascend
vertically in the epithelium, sending out twigs in various directions, and
terminating as such in the superficial epithelial layers. The same arrange-
ment almost is to be seen in the human cornea.

According to Klein, two very dense webs of the most delicate nerve
fibres are to be found in the epithelium, a deep and a terminal, which is
very superficial, only covered by about two layers of cells.

In the year 1868 Langerhans pointed out fine non-medullated nerve
fibres passing in between the cells of the rete Malpighii, partly uniting here
with elongated oval cells measuring 0-0088-0-0033 mm,, and partly pass-
ing on farther upwards with subdivision. This arrangement was con-
firmed as existing in the cornea of the rabbit by Podcopaew.

A similar arrangement of terminal nerve filaments had, however, been
found before this in the mucous membrane of the tongue by Freyfeldl-
Szabadfrtdy ; and Luschka made the same discovery in regard to the lining

Fig. 318.— The cornea cf a rabbit in vertical section after
treatment with chloride of gold, o, the older; ft, the
younger epithelial cells of the anterior surface ; r, corneal
tissue; d, a nerve twig; (, finest filaments or primitive
fibrillae; /, their splitting up and termination in the epi-
thelium.

TISSUES OF THE BODY. 333

membrane of the human larynx. Kisselcff appears to have seen similar
things in the mucous membrane of the frog's bladder, and recent investiga-
tions by Morano, Klein, Elin, and Chrschtschonovitsch, show that the same
arrangement of non-medullated filaments exists in the epithelium of the
conjunctiva, mouth, and of the vagina, sometimes with, sometimes with-
out the corpuscles of Langerhans.

The mode of termination of the nerves in the pulp of the teeth (already
mentioned, p. 269), has also been recently followed up.

Nervous twigs have long been known to exist in the walls of this struc-
ture. They may be easily seen here, and consist of dark-bordered fibres
whose diameter is 0'0038-0'0067 mm. These run upwards parallel to
each other, and then form an elongated nervous network by the branching
of their fasciculi.

By the binary subdivision of these nervous twigs immense numbers of
very delicate silky primitive fibrillse are formed, according to Boll, which
resemble elastic fibres in some degree, but which are never seen to join in
a reticulated manner. These pass in between the odontoblasts (p. 270) to
reach the inner surface of the dentine, where they probably sink into the
dental canaliculi. Thus the latter contain a double system of fibres,
composed partly of Tomes' dental fibres (p. 270), and" partly of these
nerve fibres. The well-known sensitiveness of the tooth depends upon
the latter.

§188.

We now turn to one of the most difficult subjects in nervous histology,
and one which is still the theme of much controversy — namely, the struc-
ture of the ganglia.

In regard to the relation of the nerve fibres to the cells even in the bodies
of fishes, where research is attended with least difficulty, considerable differ-
ence of opinion still exists. But this is the case to a far greater extent in
man and the higher vertebrates, where the difficulty of obtaining good
and serviceable objects is very great. Besides, it would be hardly prudent
to make use here of analogy to too great an extent, and to apply those
discoveries, which have been made in the body of the fish, to the human
organisation without due caution, — in that we are not able to estimate,
with any certainty, the whole physiological connection between nerve
fibres and cells in general. On the other hand, it is no less dangerous to
take isolated observations, which have been with difficulty made on the
human and mammal body, and, generalising from these, to dash off with
bold strokes plans of the organisation of the nervous knots, which dazzle
us for a time by an apparent physiological consistency, it is true, but
which may be subsequently recognised as entirely incorrect.

At first sight we recognise investing the nervous ganglia an envelope of
connective-tissue of varying thickness, a modified perineurium, consisting
partly of fibrillated connective-tissue alone, and partly of the latter inter-
mixed with Remaps fibres. This fibrous mass, in which the blood-vessels of
the ganglion are situated, extends also into the interior of the organ, which
is, however, 'chiefly made up of ganglion cells packed closely together.

The nervous trunk or trunks entering the knot (fig. 319, b) are divided
in the latter into fasciculi, which conduct themselves in various ways.
Some of them, namely, traverse the structure directly, or with but little
deviation from the straight line (k), while others are resolved into primi-
tive fibrillse (/), which continue their course through the ganglion, twist-

334

MANUAL OF HISTOLOGY.

ing and winding in every possible direction between the cells of the latter.
Eventually, however, they become again united into bundles, which asso-
ciate themselves with those which passed through in a straight line. In
this way are formed the stem or stems which leave the ganglion (d, e).

The nerve fibres entering the knots have, on this account, been classed
into " direct" and " tortuous," terms which will still be found appropriate.
There exist, however, as might be supposed, many intermediate forms
between the two modes of arrangement.

It used formerly to be believed that the relation of the fibres to the
cells within the ganglion was only that simply of close proximity. This
view, however, was found to satisfy the requirements of the physiologist
just as little as that which held that the nerve-fibres ended in loops, and
was finally abandoned on the discovery of the origin of the fibres.

Confining ourselves for the present to the spinal ganglia (fig. 319), we

find that a number of investigators have
observed an extraordinary arrangement in
these structures in the fish, namely, that
all the nervous fibres of the posterior root
of the ganglion are interrupted in their
course within the latter by a cell, — the
broader fibres usually by a larger, the
finer by a smaller element.

The corresponding ganglia of mam-
mals and man, however, present but
rarely such bipolar cells (7i). Here
some of the processes may take an op-
posite course, as in the fish, or both pass
out below towards the periphery (a). As
a rule, we meet with nerve cells here which
only give off one process towards the cir-
cumference (/), which may subsequent-
ly divide into two fibres, according to
Remain Finally (and it is in the spinal
ganglia of the smaller mammalian animals
that we obtain the most characteristic
objects), isolated apolar cells are to be
found (t), probably but undeveloped forms
of the first kinds. It appears, neverthe-
less, undeniable that a certain number of
the nerve-tubes entering the spinal gan-
glia may pass through the latter without
being connected in the least with its
cells. How many do so is not yet deter-
mined.

The ganglion cells found in the sympathetic knots (fig. 320, d, «,/)
appear to be somewhat smaller as a rule, but not so much so that we
should feel ourselves justified in placing a distinction between sympathetic
cells and cerebro-spinal on this account.

tn^YT^8 fib£eS are S°me of them broad> but for the most part fine
es (a, b C). Besides these, there may be seen in the sympathetic
ganglia, and sometimes in considerable quantity those formations known
as Ucmaks fibres

Finally, turning to the relation of the two kinds of structural elements

Fig. 319.— A spinal ganglion from the
mammal c (diagrammatic), a, anterior
or motor, 6, posterior or sensitive root ;
«, «, efferent nervous trunk; *, direct
and I, tortuous fibres; / unipolar, g
and A, bipolar, and t, apolar ganglion
ceils.

TISSUES OF THE BODY.

335

Fig. 320.— Sketch of a mammalian sympathetic
ganglion, a, 6, c, nervous trunks^ d, multi-
polar cells; rf*, some of the latter with a divid-
ing nerve fibre; e, unipolar, and/, apolar cells.

to one another, — in the first place, apolar ganglion cells (/) are to be met
with, but whether their number is a large one or no, we are unable to
determine. Secondly, unipolar cells
(e) are encountered, giving off a deli-
cate nerve fibre, which is distributed
peripherally. Again, we meet with
bipolar ganglion corpuscles, whose
two nerve tubes take a course at
one time opposed to each other, at
another in the same direction. It
is one of the many things also for
which we are indebted to Remak,
that he has pointed out besides, the
existence in the sympathetic of a
fourth form among these elements,
namely, the multipolar cell. Taking
their rise from the latter (d), we see
from three to twelve processes which,
by rapid ramification, may soon in-
crease threefold (d*). The amount
of these is dependent on the number
of nervous trunks in connection
with the sympathetic knot, and into
which the processes are continued in
the form of nerve tubes : thus it is greater in the solar plexus than in the
ganglia of other parts of the cord.

According to the observer just mentioned, the processes of unipolar and
bipolar cells of sympathetic ganglia undergo division likewise.

§189.

Beside these larger ganglia just described, we have to consider a multi-
tude of smaller, and also most minute nervous knots, which have only
recently been recognised, owing to their frequently microscopical dimen-
sions. We find them, on the one hand, containing numerous ganglion
corpuscles, or, again, with but few of the latter. Their number is quite
surprising throughout the body. They seem to belong, more or less, to
the sympathetic system, supplying principally the smooth and involuntary
muscles with their fibres.

Among these may be numbered groups of ganglion cells, which are
found in the ciliary muscle of the eye, on the branches of the circular
plexus to be found in the same (C. Krause, H. Muller). Several small twigs
from the ciliary nerves, likewise penetrating into the choroid coat, form
there, in the deeper portions of the latter, a delicate plexus, in which
scattered ganglion cells and small aggregations of the same have been
remarked (H. Muller and Schweigger, Samish).

Other small nervous knots were discovered also, many years ago, by
Remak on the branches of the N. glossopharyngeus, distributed to the
pharnyx and tongue ; but those on the twigs of the Lingualis, supplying
the last-named organ, are still more minute. The nervous twigs, likewise
distributed to the walls of the larynx and bronchi, as well as the interior
of the lungs, bear also similar ganglia upon them.

Another series of extraordinary ganglia is to be met with in the muscle
of the heart, presenting itself in man and the mammalia imbedded in the sub-

336

MANUAL OF HISTOLOGY.

stance of both ventricles and auricles (Remdk). The most carefully studied
have been those of the frog, where they are situated in the septum between

the auricles, and at the union
of the latter with the ven-
tricles. They are said only
to contain unipolar cells.

These ganglionic plexuses
are also encountered in great
abundance in the walls of the
alimentary canal. Here at-
tention was first directed to
them by a discovery ofMeiss-
ner's, which initiated a series
of further investigations.

The first of these gangli-
onic and nervous plexuses
extends in the human
and mammalian intestine
from the stomach downwards
through the submucosa. Its
peripheral branches probably
contain, for the most part,
motor elements for the mus-
cularis mucosce and some few
sensible fibres for the mucous membrane.

This submucous ganglion plexus, as seen in the infant (figs. 326 and
322, 1), has narrow meshes, but in the adult broader and more irregular
ones. The number of twigs given off from it is variable (fig. 321, t>\

and the ganglia differ also
greatly as to size and
shape (fig. 321, a; 322,
1, a}. The smaller cells
of the latter are entangled
in the meshes of a nuc-
leated perineurium which
clothes (fig. 321, &/ 322,
c) likewise the efferent
trunks and commissures,
consisting of fine pale
nerve fibres (322, 2).
These cells are said to be
unipolar, apolar, and bipo-
lar : multipolar do not

Fig. 322. -1. A large ganglion from the small intestine of a aPPear to exist here,
suckling ten days old. a, ganglion with its cells; 6, c. efferent
nervous trunks with pale nucleated fibres in a fresh state. 2.
Small nervous twig of the same nature from a boy five years of
age, showing three primitive fibres. After treatment with

Fig. 321. — A ganglion from the submucosa of the smalt
intestine of a suckling ten days old. «, ganglion; 6,
nervous »twigs given off by the latter; e, injected capil-
lary network. This preparation had been macerated for
a very long period in pyroligneous acid.

pyroligneous acid.

Internally, this gang-
lion plexus gives off twigs
to the muscular coat of
the alimentary canal.

Here, between the circular and longitudinal layers of the latter, a second
nervous apparatus, no less remarkable, is to be found— namely, the so-
called plexus myentericus (fig. 323), for the discovery of which we are
indebted to Auerbach.

Reaching from the pylorus to the rectum, it is seen as a regular and

TISSUES OF THE BODY. 337

delicate interlacement of nerves, woven, as it were, round the intestinal
tube (a), and having polyhedral meshes.

At each nodal point in these there is always situated an aggregation of
ganglion cells (b), sometimes large, sometimes small, but usually causing
but a moderate thickening of the cord. Two adjacent ganglia, also, may
be connected by means of a band formed of cells, beside which form the
most characteristic examples of annular ganglia and commissures are also
to be met with. Though liable to variation to a certain extent, according to
the different species of animals, the whole formation is usually very much
flattened everywhere. Here again we also meet with smaller ganglionic
bodies, pale and very fine nerve fibres, and a nucleated perineurium,
beside which apolar cells are to be observed, with others giving off two or
three processes.

From this plexus in question innumerable delicate nervous twigs are
sent off to the circular and longitudinal muscular fibres of the alimentary
canal, presiding over the peristaltic action of the latter.

The genito-urinary apparatus, also, is no exception in the occurrence of
such small nervous knots. Thus they have been seen by Remak in the

Fig. 323. — From the small intestine of the Guinea pip (after Auerbach). a, nervous inter-
lacement ; 6, ganglia ; c, lymphatic vessels.

bladder of the pig, and in other mammals by Meissner. In the same
organ of the frog they may be recognised with great ease also (Manz, Klels.}

In the corpora cavernosa of the male organ of generation these knots
were found between the years 1830 and 1840 by /. Mutter. They are
also present in the nerves of the human and mammalian uterus, and in
the connective-tissue around the vagina, as well as in the submucosa of
the latter.

Remak and Manz mention ganglionic plexuses around the muscular
gland-ducts of birds also.

In the lachrymal and salivary glands of mammals, finally, — therefore,
in organs which elaborate large quantities of secretion under nervous
stimulus, very complicated nervous networks of dark-edged fibres, richly
studded with ganglia, have been met with by Krause.

338 MANUAL OF HISTOLOGY.

§ 190.

Of the chemistry of nervous tissue, but little is known on account of its
anatomical peculiarities; for, in the first place, the most massive nervous
apparatus, namely, the cerebro-spinal, which is on account of its bulk
most frequently the object of chemical research, has a very complex struc-
ture, and in it together with a ground-work of connective-tissue, we have
to deal with nerve tubes and ganglion cells which cannot be separated.
On the other hand, but little has been done to elucidate the nature of the
albuminous substances of the neural apparatus, and much obscurity still
hangs over the so-called cerebral matters (§ 20).

The living nerve displays, while at rest, a neutral reaction which be-
comes acid at death. The same change is produced, also, according to
Funke, by over excitement of the fibre. This is but a repetition of what
takes place in muscle under similar circumstances (§ 170).

From the anatomical study of the various parts of ganglion cells, we
know that the latter are made up of albuminous compounds, in which
fatty molecules and granules of pigment may be present (§ 178).

We have seen likewise (p. 307) that the sheaths of nerve fibres consist
of a substance resembling elastin, but more soluble than the latter in
alkalies, whilst the axis cylinder is composed essentially of several matters
belonging to the protein group, and the medullary sheath principally of
cerebrin.

All that is known of the chemical composition of nervous tissue has
been learnt almost exclusively from examination of the substance of the
brain.

The specific gravity of nervous trunks is 1-031, according to the obser-
vations of Krause and Fischer ; that of the white matter of the cerebel-
lum 1-032, of the cerebrum 1O36, and of the spinal cord 1-023, whilst
for the grey substance of both cerebrum and cerebellum we find 1-031,
ai\d for that of the cord 1-038. From several experiments which have
been made, it would appear that cerebral substance possesses in a high
degree the power of absorbing water.

The amount of the latter in nervous tissue is subject to much variation.
In some cases it is but moderate, and in others it may become very con-
siderable. The proportion of water, for instance, in the peripheral nerves
is estimated by Schlossberger at 70-78, or even 80 per cent., that in the
white substance of the brain at between 69-64-70-68, and in the grey
matter 84-84-86-64, showing that the latter is richer in aqueous consti-
tuents. In the infant the brain is still poorer in solids. In the spinal
cord the percentage of water is lower, being, according to Bibra, 66 per
cent. Of course this water is distributed over both the tissue and the
nutritive fluids saturating the latter.

As already mentioned, nervous matter consists of several albuminous
bodies of cerebral substances (lecithin and cerebrin), together with mineral
constituents. Finally, it contains certain decomposition products.

Touching the albuminous matters, we are here more than elsewhere in
the dark as regards their nature. Our slight unacquaintance with the
chemical constitution of nerve cells only permits of our accepting the
presence of one or more members of the group in general, but gives no
indication as to what substance or substances occur specially.

Tho reactions of the axis cylinder are those of an albuminoid substance
in a coagulated condition. But how far other albuminous matters may

TISSUES OF THE BODY. 339

occur in nervous tissue, apart from a small amount of it in a soluble form,
is still uncertain. Quantitively it is impossible to analyse them on
account of being obliged to include the primitive sheath, and other tissue
elements. The amount, besides, of residue insoluble in ether varies
considerably, from 9 to 14 per cent.

As soluble in ether, we obtain further the so-called cerebral substances
lecithin and cerebrin (§ 20), and likewise cholesfearin in considerable
quantity (§ 21). The amount of these matters, further, has been found
to be far greater in the white substance of the brain than in the grey,
and they may, therefore, be regarded as essentially constituents of the
nervous medulla, although we do not possess any satisfactory explana-
tion of the manner in which they occur here being insoluble in water.

From the fact that lecithin (which exists in great quantity in the brain),
yields, besides neurin (§ 33), and glycerophosphoric acid (§ 16), palmi-
tinic and oleic acid also, we may infer that the fatty acids and fats, upon
which such stress used formerly to be laid, were possibly only products
of the decomposition of the former.

Clwlestearin, which occurs in cerebral tissue in large quantities (amount-
ing, according to Von Bibra, to a third of the matters soluble in ether), has
the nature likewise of a decomposition product.

Turning now to the quantity of these matters soluble in ether, we find
their proportion in the grey substance, in which much water is contained,
to be 5-7 per cent. ; in the white tissue, which is poorer in the latter, on
the other hand, it is 15-17 per cent., and rises still higher in the spinal
cord. Considerable difference may be observed, also, between the various
parts of the same brain. In the infant the amount of these matters is
very small, there being, besides, no difference in this respect between the
white and grey tissue. In the foetus they are present in still smaller
quantity.

Among the products of transformative processes going on in nervous
tissue, may be reckoned formic and lactic acid (found in the brain), and
possibly also acetic acid, also inosit, Jcreatin, leucin (in the ox), xantliin
and hypoxanthin (Scherer), urea (in the dog), and uric acid.

The ash of cerebral substance amounts, according to Breed, to 0*027
per cent, of the fresh tissue. In a hundred parts of the former he found : —

Free phosphoric acid, . . . . . 9 '15

Phosphate of potassium, . . . . . 55 '24

„ of sodium, 22 -93

„ of iron, 1-23

„ of calcium, 1'62

„ of magnesium, . . . . 3 '40

Chloride of sodium, ..... 4*74

Sulphate of potassium, . . . . . 1'64

Silica, 0-42

The preponderance of potash and magnesia over soda and lime recalls
to mind the state of things in muscle.

§191.

Turning now to the application to neural physiology of the points
regarding the structure of the nervous apparatus, which have just been
described, w© see in the first place, in the two kinds of structural elements,
a contrast between merely conducting fibres and cells which are endowed

340 MANUAL OF HISTOLOGY.

with higher functions, with those of perception, and of directing voluntary
and reflected motion. Thus we find the latter structures in the grey
matter of the brain, spinal cord, and ganglia, to which we have long been
compelled by experience to ascribe reflex functions. They are met with,
also, at some other points where their significance is not yet quite appa-
rent, as, for instance, among the terminal ramifications of some of the
higher nerves of sense.

With regard to the nerve tubes, we have learned from the last section
that their varieties of form and thickness do not go hand and hand with
functional differences. Thus the sensitive roots of the spinal nerves con-
tain fibres which differ in no respect from those of the motor roots. In
the sympathetic system we meet with Remakes fibres, whose nervous
nature would seem to be almost beyond doubt, and to these the most
analogous formations are the nerve tubes of the olfactory nerve. The
fine medullated nervous fibres can with as little right be looked upon as
a special sympathetic form, presiding over peculiar functions, as was
formerly ' maintained by Volkmann and Bidder; for numbers of inter-
mediate grades between coarse and fine tubes are met with at points
where there can be no suspicion of sympathetic influence. In this
respect the accurate microscopical analyses of recent times has greatly
modified the sanguine expectations of an earlier epoch.

On the other hand, some important aids to physiology have been
acquired through the knowledge of the finer anatomy of the nerve fibre.
All observers concur in regarding the continuity of the nerve tube as
certain, — a point necessarily accepted as indispensable by the physiolo-
gist, likewise in respect to the isolated course of the latter. Thus we see
everywhere the same state of things ; the nerve fibre taking an unin-
terrupted course through the long interval between the nervous centre
and the place of its final termination, although this course may be modified
somewhat by the insertion of a ganglion cell. The question as to what
part of the nerve tube is to be looked upon as the realty active, i.e.,
conducting medium, may perhaps be answered in favour of the axis
cylinder, in that it is frequently the only portion present at the origin of
the nerve fibre, and probably always at its ultimate termination, whilst
the medullary and primitive sheath enclosing it are here absent. At
those contracted portions of the fibre, also, which are seen at points
where branches are given off, the axis cylinder may present itself for a
short distance divested of its usual medullary envelope. The theory of
the termination of the nerves in loops having been shown to be incorrect,
has given further support anatomically to the theory of isolated conduc-
tion. The separate termination of the nerve fibre, whether single or with
many ramifications, is also consistent with the views of the physiologists
of the present day. The splitting up «by which, as we have seen in the
nerves supplying muscle, a primitive fibre may become resolved into a
multitude of branches, must be looked upon as an ingenious provision of
nature for obtaining as highly nervous a periphery as possible, both sensi-
tive and motor, with comparatively thin nervous trunks. This arrange-
ment seems certainly to have the character of something belonging to a
lower order of creation, for the higher we ascend in the animal kingdom,
the more do the numbers of tubes and muscle fibres become alike, as we
have already remarked above. An acquaintance with the terminal appa-
ratus of motor nerves is, also, another important advance recently made.
Regarded from a physiological aspect, Krause's and Kuhne's discovery of

TISSUES OF THE BODY. 341

muscular substance, excitable though free of nerves, has done much towards
the adjustment of that very old controversy in regard to whether there
be such a thing as muscular irritability. The termination of sensory
nerves in special anatomical structures, such as the Pacinian bodies, or
Krause's tactile corpuscles, is also of great interest.

To return to the ganglion cells : there seems to be among them just as
little coincidence between their anatomical variety and physiological
difference as among the nerve tubes. The physiological significance,
further, of the apolar nervous cells, is still unknown to us ; even the fact
of their existence has in it something strange to the physiologist. The
unipolar cell, also, which is looked upon as the starting-point of the fibre
proceeding from it, should be connected with the cells adjacent to it by
commissures. The physiological purpose for which bipolar cells exist is
likewise veiled in obscurity. The most comprehensible are the multi-
polar elements with their efferent nervous fibres.

But, although we are at present unable to understand many things in
the texture of the ganglion, nevertheless, important points in relation to
the motions of organs have been gained by an acquaintance with the
smaller ganglionic plexuses discovered in such surprising numbers. We
refer to the submucous ganglionic networks, and plexus myentericus of
the digestive apparatus.

Living nervous substance, further, has, like muscle, electromotor pro-
perties.

As to the amount of interchange of matter which goes on in the
nervous elements, we are still in the dark. That it is probably consider-
able, is indicated by the fact that a fatigued nerve regains, after a certain
period of rest, its original power of functionating, and also that ligature
of the arteries of a part brings about a rapid paralysis of the motor and
sensible nerves supplying the same. The scanty notes of the preceding
section likewise contain all that is at present known of the nature of this
interchange of matter.

As to the question, further, how far an anatomical change goes hand in
hand with the chemical, or, in other words, how far the nerve tubes and
cells may be regarded as persistent structures, or, on the other hand, only
destined for a short existence as transitory formations, we are unable to
give any answer. The corpuscles and fibres present themselves in far too
great variety of form in the adult body for us to be able to separate
young, mature, and older elements from one another.

§ 192.

The mode of development of nervous tissue in the embryo is one of
the most obscure chapters of modern histology.

That the brain and spinal cord, together with the internal portions of
the higher organs of sense, formed from the first of these, are productions
of the so-called corneous layer of Remak, is an ascertained fact. They
take their rise, in other words, from the cells of the upper cellular layer
nearest the embryonic axis.

On the other hand, the point of origin of the ganglia and peripheral
nerves is still unknown to us. We are still unable to determine whether,
as is very probable, these parts are productions of the corneous embryonic
leaf, or whether, according to one view which is held, they have not
originated independently in the middle germinal plate, and only become
subsequently connected with the nervous centres. The connection of

342

MANUAL OF HISTOLOGY.

the ends of nerves with tissues at the periphery, such as the muscle
fibres which, as far as we know at present, have had their origin from the
middle germinal plate, is a great theoretical difficulty.

The usual but unsatisfactory view which is held regarding ganglion
corpuscles is that they are metamorphosed formative cells.

By the enlargement of these, and their subsequent acquisition of a
characteristic finely granular contents, the ganglion cell is arrived at.
When their further growth takes place regularly we have the apolar
element, and the structure with processes when the former is unequal.
Through these latter adjacent cells may be connected, and from them
nerve fibres are given off. It is possible that multiplication by segmen-
tation may take place in already formed nerve cells in the foetal body,
but the subject requires closer investigation.

The formation of nerve fibres, which has been already touched on in
the general part of our work (p. 100), was formerly supposed generally to
be brought about by the fusion of cells in such a way that (in the case of
the non-ramifying nerve tube) connection took place between the indivi-
duals of a series of fusiform or cylindrical elements.

The nervous trunks of man and the mammalia have not that white
appearance in early foatal life which characterises them at a later date ;

they are on the contrary grey
and translucent, the more so the
younger the embryo. At first
we only remark on teazing them
out the individual formative
cells of fusiform, or simply elon-
gated figure, and with vesicular
nuclei. Later on we may suc-
ceed in splitting off rows of these
from the main structure in the
form of pale fine nucleated
"bands. These are the first nerve
fibres whose pale non-medul-
lated appearance reminds us of
Remak's elements ; their me-
dium breadth is 0 '002 9-0 '005 6
mm.

In the older nerves we may
perceive the specific contents of
the primitive tubes, advancing
gradually from the central to-
wards the peripheral portions,
the axis cylinder arising in all
probability first, and the fatty
medullary mass being deposited
subsequently between it, and
the primitive sheath formed of
the membranes of the cells.

These, then, are the usual
views on the subject based upon
Schwann's outlines, which have

Fig. 324. —Development of nerve fibres; from the tail
of a tadpole. 1. A pale siill non-medullated fibre
flii ^ *T K "UCleL 2' More adva»ced tubes partly
filled with medullary matter, a, a fibre, with which
* stellate formative cell (ai) is connected at its side,
while lower down, where the fatty contents gradually
give way to a paler (a*), Its division into two branches

(pMa?Ma4)A2 * fibre wllich i8 united to two 8tellate
-ells (6i and 6»). 3. A nerve tube srill more developed,
at a, the stem at 6, and c, the branches.

been received into histology.

The formation of branches on nerve fibres was supposed to take place

TISSUES OF THE BODY. 343

by the fusion of stellate formative cells (provided usually with three
processes), with the terminating portion of the already formed fibres, the
latter growing by the addition at their periphery of ne\v cells. The tail
of the tadpole and electric organ of the torpedo were put forward as
suitable objects for the recognition of these points. And, indeed, here we
have the best opportunity at this great distance from the central organs
of coming upon younger and younger specimens of nervous branches.

In the tail of the tadpole (fig. 324) we encounter isolated nerve tubes,
which bear all the characters of Remaps fibres, showing nuclei situated
one behind the other (1). Others (2 b) without any thickened envelope
appear dark and medullated in the upper part, while below they become
finer, and are continuous with the peripheral formative cells (bl ft2),
which radiate with their pointed processes in the. surrounding tissues.
Again Ave may meet, and by no means unfrequently, with nerve fibres
possessing thickened envelopes (2 a) and dark medulla, which is con-
tinued below into a progressively paling fibre (2 a3 and a4) resembling an
axis cylinder.

Now, although we do not yet possess a satisfactory knowledge on these
points, nevertheless we have acquired enough material to demonstrate the
untenableness of these earlier views.

Bidder and Kupffer, in their inquiries into the origin of the spinal
cord, found that the formation of nerve tubes from one row of cells occurs
neither in the white substance of the organ, nor in the roots of the spinal
nerves. In place of these fibrillse only are observed, without nuclei and
cells. These, the axis cylinders of the future, according to the authors in
question, grow simply outwards towards the periphery. The envelopes
appear to be formed for themselves subsequently, from new tissue elements
appearing between these fibrillae.

The late excellent observer Remak also maintained, many years ago,
quite a different mode of origin for the ramifications of nerves in the tail
of the tadpole from that described in the text. According to him, the
branching rudiments of the cutaneous nerves appear everywhere to be
prolongations from the spinal ganglion.

According to Hensen, also, the nervous ramifications in this well-
trodden locality are present from the commencement all the way down to
the periphery, in the form of fine, lustrous forked fibres (axis cylinders) with-
out a sign of nuclei. It is only subsequently that the mode in which they
become sheathed in thin, pale, and extremely elongated cells, can be recog-
nised, until eventually the axis cylinder lies in the interior of a nucleated
envelope, the stellate cells spoken of taking no part in the process.

Besides a great instability in their contents, owing to which the latter
may assume the appearance of a chain of separate drops, the newly-formed
nerve tubes are remarkable for their great fineness as contrasted with
corresponding elements in the mature body. The increase in thickness of
the whole nervous trunk is sufficiently explained by the augmentation in
the diameter of the individual primitive fibres. According to Harting,
their thickness, in the median nerve of a foetus at four months is only
0-0024 rnm., while in the infant and adult they measure respectively, on
an average, O'OIOS and 0'0164 mm. The number of primitive tubes, at
these three periods, were estimated by him at 21-432, 20-906, 22-560.

It is a well-known fact that nerves, on being severed, cease to fulfil
their functions, but after a certain time has elapsed regain their powers.
The separated ends, namely, heal rapidly ; yes, and even after a tolerably
23

344

MANUAL OF HISTOLOGY.

long piece has been cut out from a nervous trunk, connection is again
restored by means of new tissue.

According to the early observations of Waller, which have been since con-
firmed by others, that part of the nerve situated at the distal side of the
cut degenerates down to its ultimate ramifications, with coagulation and
subsequent absorption, until eventually the neurilemma a]one remains,
which also disappears completely after a certain time, according to the
same investigator. Prom this we infer that a new formation of nervous
fibres must take place in order to effect connection with the central por-
tion. This last view is opposed by Lent, who asserts that a new filling-in
of medullary matter into the primitive sheath supervenes upon the union
of the two cut ends. According to Ujelt, finally the severed nerve fibres
only degenerate in pa/t completely, being replaced by neoplasis, whilst
other primitive tubes are capable of a regeneration subsequent to their
reunion. Lent, again, has observed a very interesting multiplication of
nuclei in the primitive sheath. But the whole question, as regards the
origin of the newly-formed interposed tissue, is worthy of being made the
subject of renewed research in the present state of histology.

Whether regeneration of ganglion cells takes place is still uncertain.
Pathological new formation of nervous elements in other neoplasms is of
rare occurrence, as are also nervous tumours or neuromas. The latter may
consist of tubes or grey matter

In atrophied nerves a decrease in the thickness of the primitive tubes
is manifest, and, instead of a continuous medulla, a number of fat globules
and granules are presented to us.

16. Glandular-Tissue.
§193.

The definition of what we understand by a gland was, until compara-
tively recently, a matter of considerable difficulty, so that a talented
anatomist, more than thirty years ago, was fully justified in expressing

...Of

Fig. 325. — Glands from the large
intestine of the rabbit. A fol-
licle filled with gland cells;
four others without cells, show-
ing the membrana propria.

Fig. 326. — A racemose so-called
mucous gland from the rab-
bit's ossophagus. a, the duct ;
6, the follicles; c, the invest-
ing connective tissue.

himself thus: — "That class of structures called glands is one of those
careless productions of an infant science, to define which, set it upon a
firm basis, and support it there, requires all the care and pains which the
latter can bestow in its present state of maturity."

TISSUES OF THE BOD Y.

345

In the earlier days of anatomical study a round form, soft consistence,
and great vascularity, sufficed to gain for an organ the name of " gland."
Later on, however, the physiological requisites for the proper conception
of a gland became more prominent. And first of all, that the latter
abstract from the blood matters which are not to be made use of for its
own nutrition, but which tend to benefit the whole system, either by
being cast out of the body as decomposed material to be gotten rid of, or
turned to account in the economy as specially prepared by the gland.
Thus, the latter came to be looked upon as a secreting organ, great stress
being laid, consequently, on its efferent duct. Finally, it was recognised
that there are many completely closed organs from which no secretion is
ever given off, and to which, nevertheless, we cannot deny the right to be
called glandular structures. This was subsequent to comparative anatomy
having shown the comparatively small
weight to be given to the duct as the
distinguishing mark of glands.

Recent microscopical analysis has
supplied us with characteristic signs by
which, in general, a gland may be diag-
nosed, although there remain certain
points relating to structure about which
doubt still exists.

The history of development like-
wise has also afforded most important
information here. From it we learn
that the physiologically important parts
of true glands, namely, their secreting
cells, all take origin either from the
corneous or intestino-glandular em-
bryonic leaves. JS"o truly glandular organs spring from the middle
germinal plate.

Finally, owing to our extended knowledge of the nature of the lym-
phatic apparatus, we are now
enabled to class with the latter
as lymphoid organs a series
of parts springing from the
middle embryonic leaf, which
used formerly to be reckoned
among the glands.

Let us now return to the
histogical characters of glands.
These organs consist of two
kinds of structural elements
(figs. 325 and 326) (1) of a fine
structureless transparent mem-
brane, known as the membrana
propria, which determines the
form of the organ as well as
that of its sub-divisions, and
(2) of the contents of the
latter, the so-called gland cells

(figs. 325, 327. and 328). As a third indispensable factor, we find on
the external surface of the homogeneous membrane a vascular network (fig.

Fig. 327. — Gastric glands from the dog, filled
•with cells, and interlaced by a vascular net-
work.

Fig. 328.— Lobule from the liver of a boy ten years old.

346 MANUAL OF HISTOLOGY.

327), from the contents of which the materials of the secretion of our
or^an are abstracted.

°0f the three requisites of a gland the blood-vessels and cells are never
absent, and the homogeneous membrane only rarely so.

Besides these, we have to take into account the nerves distributed to
the or<*an the lymphatics, connective-tissue, and at times also muscular
envelopes'; and, finally, as a frequent occurrence, a special and often toler-
ably complicated excretory duct.

§ 194.

The membrana propria, when such a structure exists, presents itself in
the form of a homogeneous envelope, at one time immeasurably thin, at
another thickened frequently up to O'OOll, or more rarely 0-0023 mm.
It is often mixed with or enveloped in an extra layer of connective-tissue
until a tunic of 0 '0045-0 '0090 mm. results. As an
exception, we may perceive between these two strata
a layer of unstriped muscle, as in the large sweat
glands of the axilla. At times, also, as, for instance,
in the sebaceous glands, we find the membrana pro-
pria replaced by an undeveloped connective-tissue.
In other cases there appears (fig. 329) imbedded in
it a web of flattened connective-tissue cells contain-
ing nuclei (parotid, submaxillary, and lachrymal
gland).

The structureless membrana propria manifests
further a considerable amount of distensibility and
strength, and likewise of power of resistance to the
Fig. 329.— Web of flat action of weak alkaline solutions and acids, so that

stellate connective-tis- . , , ,. . , j &• ± v •*.

sue cells isolated by these may be made use of with good etiect lor its
membrma ^opria. demonstration. At present we are not acquainted
From the submaxiiiary with its chemical constitution; it is probably formed

gland c dog, aft ^ many ^^ Qf ^^ 8ubstance closely allied to

elastin.

From an anatomical point of view, this covering may be regarded as
determining the form of the organ as already mentioned, physiologically
it serves for the filtration and transudation of the plasma. In respect to
the histology of the structure, it has been supposed to be a substratum
secreted by the first aggregations of rudimentary gland cells on their
exterior, and hardened in that situation. This process was looked upon
as having taken place at an early period in existence, the membrane out-
living many generations of gland cells. But another recent view appears
to us far more worthy of acceptation, namely, that the gland-membrane is
only the transformed, and more or less independent limiting layer of the
surrounding connective-tissue, and represents therefore a contiguous por-
tion of the middle germinal plate. This theory offers an easy explana-
tion for the presence or absence of the membrana propria. It seems,
moreover, to be a characteristic of the gland cells, in contradistinction to
other cellular elements of the body, that they do not generate externally
definite formed products.

The shapes under which the membrana propria or limiting layer of con-
nective-tissue presents itself to us, are, as has been already remarked,
very various. Three varieties may be generally recognised, and corres-

TISSUES OF THE BODY. 347

ponding to these, three forms of glands, which are, however, liere and

Fig. 330. —Simple tubular
glands from the mucous
membrane of the human
stomach.

Fig. 331.— A convoluted
gland from the con-
junctiva of the calf.

Fig. 332. — The vesicles of
a racemose gland (Brun-
ner't) from the human
being.

there blended one into another, and also make their appearance at one
time as simple, at another as very complex apparatuses.

(1.) In the first form (fig. 330) the envelope
presents itself as a narrow passage of very variable
length, almost always closed at one end and open
at the other, discharging itself either indepen-
dently or in connection with other structures of
the like nature in the form of a very complex
apparatus. An envelope of this kind is known
as a gland tubule, and such glands are named"*
tubular. Of these two kinds are recognised,
namely, the simple, where the whole organ con-
sists entirely of one microscopically small sac ;
and the complex, where several or very many of
these tubuli are combined to form a new anato-
mical unit, or if we prefer another view, where
the tubules are sub-divided. They may even form
a retiform combination of tubes. If the latter
attain great length, as is the case in two com-
pound glands of the human body, the testicle and
the kidney, they may be regarded as a special
variety under the name of gland tubes (fig. 333, a-e).

Fig. 333. — Branching urni-
ferous tube from the kidney
of a kitten, a-e, progressive
subdivision at acute angles.

348

MANUAL OF HISTOLOGY.

Fig. 334. — One of Rrunner's racemose glands from the human
being.

Another peculiar species of tubular glands is presented in those in

which the upper and
usually undivided blind
end is twisted into a con-
volution like a coil of
rope (fig. 331). To these
the suitable name of
" convoluted glands " has
been given (Knauel-
drusen of Meissner}.

(2.) In a second group
of glandular organs we
meet the membrana pro-
pria under the elementary
form of the so-called open
gland vesicle, that is of a
short wide blind sac of
microscopic dimensions
(fig. 332). This struc-
ture may frequently be
very aptly compared to a short-necked flask with a wide body, whilst in
other cases it is more like a spheroidal berry or short blind gut.

In this case the most characteristic points are the grouping of these
vesicles together. Such a group (which frequently attains considerable
dimensions) may form a complex gland still of microscopical minuteness,
or may be associated with other aggregations as a sub-division of an
organ (figs. 326 and 334),

^ These aggregations are known under the names of lobuli or acini (1).
From these open vesicles a multitude of glands is built up, as, for instance,

the so-called racemose, which,
with all their variety of general
figure and difference of size are
really under the microscope,
comparatively speaking, very
uniform as to structure.

No very sharp line, however,
can be drawn between these
last described and the tubular
species. If the walls of the
latter be not smooth, namely,
and the membrana propria
bulges outwards in the form
of spheroidal projections, and
that a certain division of the
sac is combined with this, we
have as a consequence inter-
mediate forms which may witli
equal right be said to belong
to either species of gland.

(3.) In a third species of glands we find a bounding layer of connective-
tissue in the form of a roundish capsule, closed on all sides, and fre-
quently of considerable size (fig. 335). Capsules of this kind get rid of
their contents either by rupture of their walls, known as dehiecence, by

Fig. 335.— Glandular capsules from the thyroid of a child,
a, ground-work of connective-tissue; b. the capsule
itself; c, gland cells of the latter.

TISSUES OF THE BODY.

349

which they are, without exception, destroyed, or the cavity remains
closed during the whole of life, the contents exuding through the
parietes. To the first of these species the glandular elements of the
ovaries belong; to the second, those of the thyroid body. In man,
however, we never meet with a whole gland formed of one closed capsule
by itself, as is the case with the tubular follicles. The few organs in our
body which may be numbered with the last species, are composed of a
multitude of elements of this kind imbedded in a connective-tissue ground-
work.

REMARKS. — The word "acinus " is also made use of to designate the gland-vesicle,
so that it is as well, perhaps, to avoid the term entirely.

§ 195.

The second, and more important elementary structures of the organs
with which we are now engaged, are the gland cells. These are derived
from the corneous and intestinal glandular embryonic leaves, and in
keeping with their origin, never completely lose their epithelial characters.

In the bodies of many of the lower animals the significance of these
gland cells appears in the most striking way. The interesting discovery,
namely, has been made, that in them there exist glandular organs which
consist of but one single cell only.

Within the cavities of glandular organs these cells are either packed
closely together without order, filling out the former, or they clothe their
internal surfaces like epithelium. Not ^infrequently, when so arranged,
their -figure is polyhedral. They may also occur either arranged in one
single layer, or forming a double lamina.

At the outlets of glands these cells are continuous with those of the
neighbouring epithelial formations, and frequently without any sharp line
of demarcation, so that the latter may be looked upon as having become
gradually transformed into glandular elements. Indeed, wo meet with

Fig. 336. — Cells from the peptic glands of
man. a, cell without a membrane;
6, a nucleus enveloped in a residue of
the body of the cell ; c, a cell with two
nuclei; d-g, cells with sharper contour
and decrease in the number of granules
usually contained in such.

Fig. 337. — Human hepa-
tic cells, a, one with
a single nucleus; ft,
another with two of
the latter.

many glandular organs whose cells are but little different, at least anato-
mically, from those of the epithelia.

The different species of cells which are met with in the latter have their

350

MANUAL OF HISTOLOGY.

Fig. 338.— Transverse section through the mu-
cous membrane of the small intestine of a
rabbit (near the surface), a, reticular con-
nective substance containing lymph cells; 5,
lymph canal ; c, transverse section of a follicle
of Lieberkuhn; d, another of the latter with
its cells in situ; e, /, g, blood-vessels.

counterparts again ariong those lining glands. On account of the physio-
logical calls made on them, however, they require greater volume than

simple epithelial elements. For this
reason we miss among them the ex-
tremely flattened scales of many
pavement epithelia, and meet, on
the other hand, as a rule, more cubi-
cal forms, which display, however,
considerable diversity to the manner
in which they are fitted in among
their neighbours. Ciliated gland cells
are never met within thehumanbody,
if we except those of the gland -fol-
licles of the uterus, and are but of
rare occurrence elsewhere. Deposits
of melanin likewise are never seen
here, although granules of yellow
and brown pigment are not so rare.
Small spheroidal or completely
spherical cells, first of all are to be
found for instance in the ovary, clothing its capsules and larger ones in the
sebaceous glands of the skin and meibomian of the eyelids. The gland

cell may frequently re-
semble very closely, when
seen from above, one of
the elements of flattened
epithelium, its body having
become widened out. It
is in this form that the
cells lining the peptic
glands of the stomach are
presented to us (fig. 336),
and also those of the liver
(fig. 337), with many
others. Another species is
the more or less cylindrical
cell. This is to be seen
in the uterine glands, the
so-called tubular mucous
glands of the stomach, and
racemose glands of mucous
membranes (Schlemmer,
Puky Akos, ScJiwalbe),
and in Lieberkuhn's fol-
licles of the small intestine
(fig. 338, d). In the latter,
according to Schuhe, the
most exquisite examples of

Fig. 339.— Gland capillaries from the pancreas of a rabbit, filled
with Berlin blue (after Saviotti). 1 and 2, a large excretory
duct; 6, that of an acinus; c, finest capillary passages; 3,

'beaker cells" are to be
seen between the ordinary
columnar elements.

We have recently been
made acquainted with the fact that in certain glands there exist two

an acinus with cells, and gland capillaries only partially

TISSUES OF THE BODY. 351

kinds of cellular elements, as, for instance, in the submaxillary and peptic
glands of many mammals. "We shall refer to these again.

Differences in gland cells have also been remarked corresponding to
their conditions of activity and rest, e.g., in the glands of the stomach and
submaxillary of niaiiy mammals, &c.

Finally (en passant), between the hepatic elements, and later still
between those of several racemose glands, a system of the most delicate
canals has been met with, to which the name of " gland capillaries " has
been given. Fig. 339 will give some idea of the nature of these.

Turning now to the size and further composition of the gland cell, we
observe great diversity, especially in the former. Those elements, for
instance, clothing the internal surface of the ovarian vesicles, possess a
diameter of only 0'0074-0'0090 mm., while the roundish polyhedral cells
of the racemose mucous glands measure G'0068-0'0113 mm., those of the
peptic glands 0 -0226-0*0326 mm., and those of the liver almost as much,
&c. In these cells are to be found single, or not unfrequently double,
nuclei of from 0'0056 to 0*0090, at one time vesicular, and at another more
homogeneous. At a later period, in the more mature cell, these may, how-
ever, become dissolved. The contour of such elements is usually very deli-
cate, and their contents are of various kinds ; this we shall again refer to.

§196.

The delicate constitution of the cells in question, together with the
lively interchange of matter which is carried on through their agency,
tends to render the existence of a certain number of them very transitory,
showing again another parallel with many epithelial elements. But while
we are able to demonstrate the briefness of the existence of many cells
with all the certainty desirable, we have no facts to support us in other
cases, nay, we even have observations which point to the very opposite
conclusions as regards them. Thus the hepatic (fig. 337) and renal cells
are known to be comparatively permanent elements.

Here again, as among the epithelia, mechanical wear and tear takes
place also, the stream of fluid which flows towards the outlet of the
gland carrying off with it greater or smaller quantities of the cellular
lining. If we observe, for instance, the stratum of mucus which covers
the coats of the stomach while digestion is going on, especially among
phytophagous animals, we may frequently discover extraordinary numbers
of peptic cells swept away in the gastric juice which wells up from below.
The sebaceous secretions of the skin contain likewise cellular elements
derived from the glands, from whence they emanate. In other organs,
however, such as the kidney, lachrymal, and sweat glands, the cells appear
to be washed away to a smaller extent, and in the bile hepatic cells are
never to be found.

The transient nature of these elements is manifested again in another
way. They are destroyed, namely, to form the secretion of the gland to
which they belong. Without taking into account such peculiar changes
as lead to the, origin of spermatozoa within the cells of the seminal
tubules, we find the most ordinary mode of decay to be in physiological
fatty degeneration, as it may be expressed, of the elements of glands.
Here the cells are observed to be destroyed by the generation within
them of fatty contents, undergoing subsequently a process of solution
by which the latter are liberated, and appear as constituents of the
glandular secretion. This is found to take place in the sebaceous glands

352

MANUAL OF HISTOLOGY.

of the skin, in the mamma during lactation, in the Meibomian and
ceruminous glands, as well as many of the sudoriferous organs.

Thus we see the saccules of sebaceous glands (fig. 340, A) clothed on
their internal surface with cells (a), which
may be regarded as a modified prolonga-
tion of the Malpighian layer of the skin,
but which differ from the latter in being to
a certain extent rich in fatty granules (23, a).
By a further deposit of fat within the cell
the latter is increased in size (B, b-f), and
becomes detached from the membranapropria
(A, b), so that in the cavities of the organ
cells of 0-0377-0-0563 mm. are met with—
elements in which the amount of fat is very
considerable. The latter presents itself
either in the form of innumerable granules
(B, b), or several globules of oil (c) enclosed
within the membrane of the cell, or, one
large drop communicates to the latter the
appearance of an ordinary fat cell (d). The
nuclei of these elements are gradually de-
stroyed, apparently, as also their envelopes,
at least frequently. Thus the secretion of
sebaceous glands contains, in the first place,
free fatty globules, and in the next place,
those cells loaded with oily matters just
described.

A process precisely similar to this takes
place in the mamma of the nursing woman.
Here we see in the so-called colostrum (a
milk which is secreted during the later
period of pregnancy) round bodies of
0-0151-0-0563 mm. in diameter (fig. 341,
b), know as colostrum corpuscles, which are
simply aggregations of fatty particles of
varying size, held together by some agglutinating matter. At one time
they are seen to possess envelopes and nuclei, at another to be without
^ 0 n either. There can be no doubt that in these structures

are presented to us the gland cells which have been
shed, and having undergone fatty degeneration, are
now in process of solution.

Soon after delivery the milk contains innumerable
milk globules as they are called (a), that is, small
drops of oil enclosed in a delicate film of coagulated
casein. These bodies are of very different diameters,
measuring from 0'0029 to 0-0090 mm. In this case
the increased energy of secretion has led to rupture
of the gland cells while still within the organ.
In those situations where the gland cell possesses a finely granular
body consisting of albuminoid matters, we find it a matter of greater
difficulty to convince ourselves of the destruction of the former in the
formation of the secretion. "We usually meet, however, in the mucous
and peptic glands of the stomach with a certain number of liberated

Fig. 340.— Saccule of a sebaceous
gland, a, gland cells clothing the
walls ; 6, those which have heen cast
off, filled with oil globules, and occu-
pying the lumen of the sac; /?, the
cells under higher magnifying
power; a, smaller specimens belong-
ing to the parietal layer, and poor in
fat; b, larger, with abundance of the
latter; c, a cell in which several oil
globules have coalesced to form
larger drops ; and d, one with a
single fat globule ; e, /, cells whose
fat has partially escaped.

k«0

341. — Form ele-
ments of human milk.
a, milk globules; 6,
colostrum corpuscles.

TISSUES OF THE BODY.

353

molecules, as well as naked nuclei, and even broken down cells, so that
the destruction of numerous cellular masses cannot well be denied. Such
cellular debris has long been known ; at an earlier epoch, however, by
reversing the order of things, a view of its nature was taken which
favoured the theory of the spontaneous origin of cells.

Another, and it appears equally widely-spread destructive process, is met
with in the metamorphosis by which mucin is formed. Ordinary albumi-
nous cells made up of the usual protoplasm occupy the parietal portion of
the glandular sac, while larger elements containing mucus, and which have
had their rise in the first form, are situated in the more central part. By
the solution of the latter the mucus of the gland is produced. This is
found to take place, for instance, in numerous small mucous glands, such
as the labial of man and the rabbit, those of the larynx of the latter
animal and the dog, in the submaxillaris of many mammalia, beginning
with the dog and cat, and finally, in the sublingual of the dog.

We shall have to consider these points at greater length among other
things in the third part of our work, in referring to the salivary glands.

The reverse of all this takes place in other glandular organs, as, for
instance, in the kidney, where the cells allow the secreted matters to pass
through their membrane, repeating again what occurs among the epithelia.

The question as to how gland cells are regenerated calls for renewed
investigation. There can be but little doubt, however, that a process of
segmentation takes place
among them, for in many
organs the occurrence of
cells with two nuclei is
of great frequency (fig.
336, c ; and 337, 6).

§ 197.

The vascularisaticm of
glands in keeping with
their extreme vegetative
energy is very perfect.
The form of the vascular
networks is liable, how-
ever, to great variation,
being determined by the
shape of the glandular
elements. Thus race-
mose glands are found
to possess around their
spheroidal vesicles cor-
responding bag- shaped
capillary networks (fig.
342), like those of fat
lobules. On the other hand, tubular or follicular glands are supplied
with a system of capillaries arranged in more elongated meshes or loops
along their walls (fig. 327 and 343), not dissimilar at times to the mode
of arrangement of the minute vessels in striated muscle. Around the
outlets alone when crowded together do the meshes again assume a cir-
cular form (fig. 343 above, and 344 c). The vascular network of the

Fig. 342. — Capillary network from a racemose gland (the
pancreas).

354

MANUAL OF HISTOLOGY.

Fig. 343. — Network of blood-vessels from
peptic gland of the human stomach.

liver (fig. 345), is extremely dense surrounding the cells (comp. fig. 328),
partly with roundish and partly with more or less radiating loops.

With the exception of the latter anomalous organ, we never find the

capillary networks situated actually
among the groups of cells them-
selves, but external to the mem-
brana propria or envelope of connec-
tive-tissue.

In those cases in which the vessels
penetrate into the interior through
the enveloping structures, as in
Peyer's glands and lymphatic knots,
the part is improperly termed a
secreting organ, and belongs rather
to the lymphatic formations.

The energetic transformation of
material which takes place in glands,
appears as a rule to necessitate the
presence in them of lymphatics, an
acquaintance with the nature of
which has recently been gained with
greater accuracy than was previously
possible. The testicle and thyroid
gland (fig. 344, d, and 346, d-f) may
be mentioned as examples.

With the consideration of the
nervous supply of glands, we come to one of the most obscure points in
histology. The nerves here met with consist partly of Remaps fibres,
and partly of medullary elements. Their distribution is in the first
place to the blood-vessels of the organ, then to the excretory ducts and
secreting elements of the latter. As a rule, but few and scattered nerves

can be recognised in glands,
but that several of the latter,
as, for instance, the lach-
rymal and salivary, are richly
supplied with them has
v already been mentioned in
a previous section (§ 189).

Unstriped muscle may also
be an important element in
the structure of glands.
Thus, without taking into
consideration the muscular
structures around the effe-
rent ducts, we may see in
the first place narrow
bundles, ascending between the individual glands, as, for instance, in the
mucosa of the stomach, or the same may be observed in the connective-
tissue enveloping the several sub-divisions of the organ, as in the prostate
and Cowper's glands (Koelliker). The wall of the organ again may be
muscular, as best seen in the large sweat glands of the axilla.

The excretory passages of glandular organs must now be specially de-
scribed. We have already seen that these are not indispensable to the

rig. 344.— From the testicle of the calf. At (a) the seminal
tubules are seen somewhat from the side; at (6) trans-
versely; c, blood-vessels; rf, lymphatic passages.

TISSUES OF THE BODY.

355

proper conception of a gland, and even in cases in which the latter pos-
sesses an outlet, there may be as yet no trace of a special canal for the
carrying oft' of the secretion of the part.

All simple follicular glands belong to the latter order, in which the
form of cell changes just before
the outlet is reached, but the ter-
mination of the follicle itself is not
clearly defined. In those cases
only in which several of the latter
are united in one common, short,
and widened terminal portion,
can we speak of such a canal,
as in those peptic glands of the
stomach, in which the portion
common to the several tubules
(Stomach cell of Todd and Bmv-
man) is marked by the difference
of its columnar cells (fig. 347, a).
The straight portion of the tubules
of convoluted glands may be
looked upon as an excretory duct,
as it passes from the convolu-
tion toAvards the outlet, although
neither the structure of the wall
nor the cellular lining is altered in the least ; the diameter, however,
decreases at first. On the other hand, among complex tubular glands,

Fig. 345.— Network of vessels in the rabbit's liver.

Fig. 346.— From the thyroid of the infant, a, crypt of
gland filled with cells alone ; b, incipient colloid meta-
morphosis of the contents; c, the latter far advanced ;
d and/, large lymphatics; «, small lymphatics.

Fig. 347.— A compound peptic gland
from the dog. a, wide orifice of exit
(stomach celt) clothed with columnar
epithelium; 6, point of division; c,
single follicles lined with peptic cells;
rf, contents passing out. 2. The orifice
(a) in transverse section. 3. Section
through the several glands.

such as the kidney, we find an elaborate system of excretory ducts lined

356

MANUAL OF HISTOLOGY.

—e

with clear, low, cylindrical cells, traversing the whole organ (fig. 348,

a-d). We shall refer to this again.

The ducts, or systems of ducts of racemose glands, however, are recog-
nised by all. The most simple forms in which
these may be seen are to be found in the small
glands of mucous membranes (fig. 349). Here
we see the vesicles making up a lobule, continued
into a shorter or longer passage of small diameter,
whose wall is formed by a prolongation of the mem-
brana propria. Among very small glands of this
nature the junction of two tubes, such as that just
described, may constitute the whole duct of the
organ (fig. 326). But in others the matter is not
so simple, and in the larger mucous glands the
common canal of exit from a group of lobules
formed by the confluence of their ducts is but a
branch of the true common passage, In the
latter, or even in a branch of the first order of
any considerable gland, we no longer find the
simple homogeneous structure of the membrana
propria ; the walls are here composed of longi-
tudinally arranged connective-tissue fibres, in
addition to which an external stratum of looser
texture may be remarked. They are lined, like-
wise, within with a layer of epithelium cells.
The length and breadth of these passages is sub-
ject to much variation.

What has just been described may serve as a
key to the mode of formation of the larger arfd
even largest glands. The subdivision and rami-
fication of the passages in the latter has only
advanced further, and the groups of lobules
may be said to correspond to a certain extent to
the individual mucous glands.

The further diversity of form of organs of this
kind depends, also, in a great measure on the
peculiar course of these passages. Thus, 'in the
pancreas we see the principal duct passing almost

directly through the axis of the gland towards its apex. Many other

organs, also, as, for instance, the lachrymal and mammary glands, are pos-

Fig. 348.— Fvom the kidney of
the Guinea-pig, in vertical
section, a-d, excretory ; and
e-h, secreting poi-tion of the
canal.

Fig. 349. — Small mucous glands, some of whose ducts unite in a
common outlet.

sessed of several outlets : the union of the final twigs to form one common
canal may be said in this case not to have taken place.

In regard to the texture, in these instances we have presented to us in

TISSUES OF THE BODY. 357

the finer ramifications the state of things already seen in the smaller
mucous glands. The more considerable and terminal passages, however,
acquire a tougher internal tunic, rich in elastic -elements, which is
enveloped in the external coat. Between these two layers there is inter-
posed, further, in one class of glands a muscular sheath, consisting, when
only slightly developed, of longitudinally arranged unstriped fibre-cells, as
in the mamma and Cowper's glands. When more highly developed it is
made up of an external longitudinal and internal transverse layer, to
which may be added another still more internal of longitudinal fibres (vas
deferens). The tunic situated internal to these, formed of connective-
tissue, is gradually converted into a mucous membrane clothed with
cylinder cells, and in it again minute mucous glands may appear (biliary
and pancreatic ducts).

§ 198.

Turning now to the individual glands, the following points may be
borne in mind : —

1. Among the tubular glands of the human body may be reckoned
Bowman's of the regio olfactoria, Lieberkuhn's of the small intestine, the
so-called follicles of the large intestine, the peptic and mucous glands of
the stomach, and the glands of the uterus. These all consist of follicles
of varying length, formed of a simple membrana propria. Their length,
which depends on the thickness of the mucous membrane, ranges from
0-2256 to 2-2558 mm. and upwards. In breadth they differ consider-
ably; in Bowman's glands the diameter being 0 -032 3-0 '05 6 4 mm., in
LieberJcuhn's 0*0564 mm., the large intestine 0-0564-0-1128 mm., and
those secreting the gastric juice 0'0323-0'0457 mm.

The number of these glands is often very considerable, so that they may
cover the whole surface of the mucous membrane when crowded together,
— as, for instance, the follicles of Lielerkuhn of the cat (fig. 350.) The
tubes usually remain undivided, but in many glands, as those of the
stomach and uterus, each may be
split into two or three branches.
The cells contained within them
are partly flattened and round,
partly cylindrical.

Among the convoluted glands
we have the smaller and larger
sudoriferous organs, the cerumi-
nous glands of the ear, and the
tubules occurring in the conjunc-
tiva at the edge of the cornea
in many mammals. It is seldom
that, as in the latter situation,
they possess a simple membrana

propria. • In most the Wall is Fig. 350.— Lieberkuhn's glands from the cat (a), sur-

stronger, this membrane being > mounted by intestinal vim (6).

again enclosed within a layer of connective- tissue, between which struc-
tures muscular elements may be interposed as a middle tunic, e.g., the
large sweat glands of the axilla. In this manner. the walls may attain a
thickness of 0'0045-0'0094, or even 0'0135 mm. The breadth of the
very long tubules of a convolution varies from 0'0451 to 0'0992, or even
0-1505 mm., and that of the whole of the latter from 0'2 to 6 '7 mm.

358

MANUAL OF HISTOLOGY.

Fig. 351. — Brunner's glands from the human duodenum, o,
villi; 6, bodies of the glands situated in the submucous
tissue, which empty themselves through their ducts between
the bases of the villi.

The efferent, duct is at first narrow, later on expanded somewhat, and
loses its walls on penetrating the strata of the epithelium. The cells

lining these glands are
usually roundish and flat-
tened, and possess a more
or less fatty contents.

The complex tubular
glands present either a
homogeneous membrane,
as in the kidney, or this
is replaced by connective-
tissue, as in the testicle.
The seminal tubules of the
latter have a diameter of
about (HI 28 mm., and the
uriniferous tubes of the
former range from 0'2 and
1-2 to 0-0377 mm. and
upwards. These cells are
polyhedral, calling to mind
the appearance of flattened
epithelium.

The physiological pur-
poses served by the several
kinds of tubular glands are
exceedingly various.
2. The racemose glands constitute a very large group of organs, varying
greatly both as to size, the character of the secretion yielded by each,
and their physiological significance. To these belong the many small glands

of the mucous membranes of the
body. They occur with very dif-
ferent degrees of frequency ; often
as, for instance, in the mouth and
in the duodenum, they are very
densely crowded together (fig.
351).

In different situations they
are known under special names,
as in the last case, where they
have obtained that of Brunner's
glands. The sebaceous glands of
the skin, likewise, with those
modified forms of them known
as the Meibomian of the eye-
lids, belong to this same cate-
gory. At the commencement

Fig. 352.— From the thyroid of the infant. of their development the first

«-c, glandular spaces. Qf ^^ ^^ themselves ag

simple flask-shaped follicles, which are subsequently converted by saccu-
lation of their walls into smaller or larger racemose organs.

Among the larger glands of this group may be reckoned the lachrymal,
the various salivary glands, the pancreas, the mammary, Cowper's and
Bartholini's glands in the organs of generation, as well as that aggregation

d

TISSUES OF THE BODY. 359

of these structures known as the prostrate. The lungs might also be added
here on account of their structure and development. The gland vesicles,
almost always formed of a delicate membrana propria, vary in size from
(H128 to O0451 mm., with extremes in both directions. The contents
consists either of rounded, or more or less cubical cells. Some of them are
filled with a fatty secretion. We have already considered their efferent
ducts in the foregoing section.

3. Turning, finally, to those glands consisting of entirely dosed roundish
cavities, the thyroid (fig. 352) may be taken as the type. . Here we
find a number of short glandular spaces of roundish form in a ground-
work of connective-tissue, having a diameter of 0'1128-0'0564 mm. and
less, and consisting of a fibrous wall (without any distinct membrana pro-
2)ria) with a coating of small round cells. In the Graafian vesicle of the
ovary, which is opened by rupture, and destroyed after expulsion of the
ovum and remaining contents, we have another more complicated cap-
sule, also imbedded in abundant, dense fibrous tissue. The interior is
lined by minute, round, nucleated cells, in the midst of which lies the
primitive ovum.

§ 199.

As to the composition of glandular-tissue, to which we will now devote
a few lines, it is one of the most neglected subjects in histology. Even
of the nature of the membrana propria we know but little : its substance,
however, is no albuminous one. It consists rather of some material
difficult of solution, and offering a tolerably prolonged resistance to the
action of weak acids and alkalies, reminding us of the bearing of the
transparent membranes of the eye. Its power of resisting concentrated
alkalies is sometimes also considerable, in which cases this gland-enve-
lope may consist of elastin, an important point when we take into
account its indifferent nature and stability, and the great secretory energy
of the organ. In other cases this membrane is not so durable, and we have
not the slightest clue as to its composition. It need hardly be remarked
that at those points where, instead of a transparent homogeneous mem-
brane, a layer of connective-tissue presents itself, bounding the sub-
divisions of the organ, we have to deal with a glutin-yielding substance.

The gland cells, the most important parts of the organ in question, —
those, in fact, which constitute them, glands, — have but little remarkable
about them excepting the contents of their bodies. Their membranes
consist, for the most part, of a matter which gives way even to the weaker
acids, but sometimes of a material possessing much greater power of resist-
ance, thus reminding us of many of the so closely allied epithelia. The
nuclei present the same peculiarities here as elsewhere.

The matters, however, contained in these gland cells vary with the
species of secretion to be produced. Thus, for instance, we meet with
materials in the cells of the liver which are subsequently found free in
the bile, — such as fats, pigments, and glycogen, which leads to the forma-
tion of sugar, and is carried off with the blood of the hepatic vein. In
the cells of the mammary gland, further, we have the butter fats of the
milk ; in those of the sebaceous glands, the fatty matters observed on the
skin ', in the gastric cells, the pepsin found in the juices of the stomach,
and so on. Muciri also is contained, together with other substances, in
those cells held to be the generators of mucus.

Now, although the components of the secretions present themselves
24

360 MANUAL OF HISTOLOGY.

first as constituents of the gland cells, \ve find, nevertheless, that they
differ among themselves in two particulars.

In the first place we remark, that in a certain number of the organs in
question these substances are only abstracted from the blood to sojourn
simply in the body of the cell for a longer or shorter space of time. This
is the case, for instance, with the constituents of the sweat glands and
kidneys, in which we are unable to demonstrate any notable chemical
metamorphosis through the agency of the cell. The latter may, however,
be evident, though in a minor degree, in other glands, for instance in the
female breast, in which an albuminous substance is transformed into
casein, and, we suppose, grape sugar into sugar of milk. Such instances
are connecting links between the first case and another, in which the cell
produces, by the disintegration and rearrangement of the matters it
receives, completely new and peculiar substances, as may be seen in the
liver, in the production of the bile acids.

Another difference concerns the cell itself, as we know already. This
may either be cast off after the generation of its specific contents, setting
free the latter (sebaceous, milk, and peptic cells), or the contents may
escape from its uninjured body, while it itself remains as a permanent
structure (renal and hepatic cells).

Finally, the "egotistical" mutation of matter of glandular tissue, i.e.,
that which takes place in the interest of its own proper nutrition, must
give rise to the generation of the more general decomposition products
of the system. Thus, according to Staedeler and Frerichs, leucin has
been found in exceedingly small quantity as a very general transforma-
tion product in glands, seldom in larger amount, as in the pancreas.
Other bases, such as tyrosin, taurin, cystin, hypoxanthin, xanthin, and
guanin, appear more rarely. Iriosit and lactic acid may also be met with,
and uric acid, though with less frequency. These matters are partly dis-
charged with the secretions of the glands, and partly taken up again into
the circulation.

Later on, in considering the salivary glands, we shall see the control
which the nervous system possesses over the chemical action of these organs

§ 200.

Turning now to the development of glands, it will be remembered that
the epithelial nature of these structures has already been touched on.
The mode of origin is the best proof of this. It is well known that a
whole series of glandular organs is derived from the external cellular
layer of the foetal body from the so-called corneous leaf. They commence
in the form of nodulated prolongations downwards of the epithelial cells,
ill which at first no trace exists of either central cavity or gland-mem-
brane. This latter is subsequently formed on the exterior of the aggrega-
tion of cells as a deposit. The size of this mass is increased by division of
the cells of which it is composed, while the connective-tissue surrounding
it becomes eventually the envelope of the gland. Among the structures
so formed may be mentioned the sweat, mammary, and lachrymal glands.

The sweat glands (fig. 353, a) are developed, according to Koelliker,
after the fifth month of intra-uterine life. Commencing as small flask-
shaped growths formed of the rete Malpujldi cells, .they advance deeper
downwards through the skin in the following months, becoming eventu-
ally curved, in a gradual manner, at their lower end. Then a trace of
the central passage and external outlet becomes apparent. The sebaceous

TISSUES OF THE BODY.

361

(jlands also, the first rudiments of which may be observed somewhat
earlier than in the preceding case, are likewise solid lateral growths of
the undermost cells constituting the rudiments of the embryonic hair
follicle, and possess the same flask-like form. The cells in their interior
begin very early to undergo that so characteristic fatty infiltration with
which we are already acquainted, at the same time increasing in volume.
Then by continuous growth they gradually form those vesicular lobules
met with in the fully matured structure,?. The mammary glands, again,
are developed in a manner precisely similar, from the fourth and fifth
month on. Around the several aggregations of cells (fig. 354) an
external connective-tissue envelope may be seen, a doubling in of the skin.
But it is only at the period of puberty and pregnancy that the organ
attains a state of perfect development.

Fig. 353.— Sweat glands of a foetus Fig. 354.— The mammary gland from a toler-

at five months, a, superficial, 6, ably mature embryo, after Longer, a, the

deeper layer of the epidermis; the middle nodulated portion with shorter excre-

rudiments of the gland are formed scences; 6, and longer,
by the exuberant growth down-
wards of the latter.

As to the germ-producing glands, the ovaries and testicles, as far as
concerns their cellular elements, we are still, unfortunately, in the dark
in spite of numerous investigations.

Besides those just mentioned, there are a great number of organs of
the same nature, whose development takes place on a precisely similar
plan, from the so-called intestinal glandular embryonic plate. Among
these may be reckoned the glands of the digestive apparatus and the
larger organs connected with the latter, e.g., the liver, pancreas, and lungs.
Here, instead of the cells of the corneous layer, we have before us the
elements of the glandular leaf arranged over the surface of the tube as
intestinal epithelium. The mode of formation of these, however, is but
imperfectly known, as, for instance, that of the peptic glands and follicles
of the large intestine. The follicles of Licberkuhn appear, on the other
hand, to consist, from the very commencement, of hollow duplicatures.
The first rudiments of Brunner's glands, however, as well as those of the
remaining racemose mucous glands, are formed of solid masses of cells.
The salivary glands seem to be formed on an analogous plan of develop-
ment, except that a far more extensive proliferation of the cells takes
place, producing roundish aggregations of the form of the vesicles of the
organ. The pancreas commences also in a hollow duplicating whose
clothing of cells gives rise by a similar process to the various lobules and

362

MANUAL OF HISTOLOGY.

vesicles of the organ.
similar plan.

The formation of the lungs is carried out on a

17. The Vessels.
§201.

Of a special vascular tissue, or tissue peculiar to vessels, we can only
speak in a very limited sense. The most internal layer alone consists
everywhere of a series of flattened cells of a peculiar kind, cemented
together at their edges, and resembling very closely epithelium. The
walls of the finest and most simple tubes are composed solely of these
cells. All the remaining coats, on the other hand, which strengthen the
walls by being laid down around them (and they are seen very early) are
formed of muscular and elastic tissue, of structures, therefore, to which
we have already given our consideration. But in that the fine tubes with
their simple texture are continuous K through the most gradual transitions
with those of wider gauge and more complex structure, a general glance
at the blood-vessels and lymphatics will be found useful.

It is well known that the canals
of the vascular system are classified
into those which convey the stream of
blood from the heart, called arteries,
those which collect and bring back
the same known as veins, and those
which are interposed between these
two, forming a system of fine hair-
like tubes, to which the name of
capillaries has been applied. The
latter, compared with the merely con-
ducting veins and arteries, constitute
the most important part, physiologi-
cally, of the whole, in that through
their delicate walls the interchange
of matter between the blood and
organic fluids, as well as secretion,
takes place.

The capillary vessels present for
our consideration, as a rule, a wall
quite distinct from the neighbour-
ing structures. For those so con-
stituted we would retain the name
of capillaries. In other and rarer
instances, this tube containing the
blood is fused with the adjacent
tissues, the fluid, as it were, flowing
through grooved passages, in which
case we have the capillary canal.
Finally, recent observations seem to
teach that in the pulp of the spleen
the finest streams of blood actually
flow through membraneless inter-
stices. These latter are known as
capillary lacunae.
Capillaries of the smallest calibre, which do not, however, occur in all

Fig. 355.— Fine blood-vessels from the pia mater
of the human brain. A, a small branch,
which divides above into two delicate capil-
laries, o, 6, and which consists below (d), of two
tunics; £, a similar tube, with branches; C, a
vessel of greater calibre, with a double mem-
brane, the internal (a) snowing longitudinally
arranged, and the external (6), as well as
intermediate, transverse nuclei.

TISSUES OF THE BODY.

363

parts of the body, are tubes just sufficiently large to permit the passage
through them of a single blood corpuscle, which can even be compressed in
its course. The diameter of the lumen may be stated consequently at
0 -0045-0 '0068 mm., whilst other and more considerable tubes attain a
breadth of 0'0113 mm. and upwards.

These canals (355, A, B) were supposed, until very recently, to have
an extremely simple texture. As a rule, their walls are perfectly trans-
parent and structureless, and endowed with remarkable elasticity and
extensibility. Chemically, they resemble the sarcolemma of muscle
fibres and primitive sheath of nerves, displaying a considerable power
of resisting the action of many strong reagents. In the walls of these
tubes rounded or oval nuclei are to be seen, 0'0056--0'0074 mm. in
diameter, in which nucleoli may be remarked. These are arranged
irregularly one behind the other at considerable intervals (A, a, b, J3, a),
but at times at more regular distances (A, a, B, b). In larger branches,
measuring perhaps 0'0113 mm. and upwards, the latter arrangement is
the rule; otherwise the structure remains the same, except that such
tubes may attain considerable thickness, amounting to 0'0018 mm. The
long axis of the nuclei corresponds to that of the vessel ; they are conse-
quently said to be longitudinally oval in figure.

§202.

This view just mentioned of the nature of the walls of capillaries was
held for many years with unquestioning tenacity, no expedient having as
yet been hit upon by which the structure of the trans-
parent nucleated membrane of which they consist could
be farther resolved.

However, all at once the analysis of structure was
accomplished through the discoveries of Auerbach,
Eberth, and Aeby following in the footsteps of Hoyer.
From them we learned the usefulness of very dilute
solutions of nitrate of silver in rendering visible, in
the most exquisite manner, the delicate contour of
cells (whether those of epithelium or smooth muscle)
in the form of dark lines. The transpare^ nucleated
membrane in question is formed of flat cells, often
peculiarly bordered, and having a single nucleus (figs.
356 and 357); they are united closely with one
another at their edges, and curved towards the lumen
of the vessel. The tube thus formed is endowed,
moreover, with vital contractility (Strieker}.

These cells, further, extend continuously into the
more considerable and even the largest trunks, though
to a certain extent modified. This may easily be re-
cognised. Here they were known even to the earlier
histologists, their contour being plainly visible without
any further treatment. They were described as the
epithelia of the arteries, veins, and cardiac cavities
(§ 87), and we may add, with perfect correctness, for
these lining cells of the vascular system are members
of the epithelium group of the middle germinal layer (pp. 158, 159), the
endothelia of His. Another name has been proposed for them also by
Auerbach, namely, perithelium. It may be found more convenient, how-

Fig. 356. — Capillaries
from the mesentery
of a Guinea-pig after
treatment with solu-
tion of nitrate of sil-
ver, a, cells; 6, nu-
clei of the same.

364

MANUAL OF HISTOLOGY.

ever, if, for the future, we make use of the term primary vascular mem-
brane in referring to this cellular tube.

In regard to the cells themselves, they are presented to us according to

the breadth of the tube, either under a
more or less fusiform or polygonal form.
The first variety (fig. 356), bounded by
delicate serrated or undulating lines, have
a length of 0-0756-0'0977 mm., and
breadth of 0 -009 9-0 -050 mm. Such ele-
ments are to be found forming the walls
of the finest capillaries, arranged either
parallel to the axis of the vessel, or more
rarely obliquely, as regards the latter. In
transverse sections of the vessels two or
three, or less frequently four of them, may
be remarked.

•In many of the finest vessels portions
of the tube are formed of one single cell
alone, its two edges meeting around the
lumen. Such cases may be found among the capillaries of the brain, the
retina, the muscles, and the skin.

Capillaries of larger calibre are made up of cells of the second variety.
We encounter here either regular polygons, as, for instance, in the
clwrio-capillaris of the cat and iris of the bird's eye, or more irregular

Fig. 357.— Capillary network from tlie
lung of the frog treated with solution
of nitrate of silver. 6, vascular cells;
a, nuclei of the same.

Fig. 358. — Capillary ves-
sel from the mesen-
tery of the frog treated
with nitrate of silver.
Between the vascular
cells at a, a and 6, the
"stomala" are to be
seen.

Fig. 359.— Capillaries and finer trunks
from a mammal, a, capillary from
the brain ; 6, from a lymphatic gland;
c, a somewhat stronger branch, with
a lymphatic sheath, from the small
intestine; and d, transverse section
of a small artery of a lymphatic
gland.

plates (fig. 357), in many instances giving off long processes. In the
transverse section of the vessel we may have two or four of these. In
size they are naturally subject to great variation, and may attain a diameter
at certain points of 0'0749-0'01737 mm.

The interdigitation of their

TISSUES OF THE BODY. 365

processes presents a most peculiar appearance under the microscope. Be-
tween these cells, however, may be observed a greater or smaller number
of roundish marks of varying size, sometimes in the form of a dark spot
(fig. 358, a, a), sometimes in that of a ring (b).

These have been hitherto held by many to be preformed openings or
"stomata," and to account for the exit of white and coloured blood cor-
puscles (p. 128).

The recent investigations of Arnold also have confirmed the correctness
of this view.

£Tow, whilst we believe that in many parts of the body the whole of the
capillary vessel is represented in this cellular tube just mentioned, there
are some localities in which the latter is enveloped in a delicate homo-
geneous membrane, probably the first indication of the tunica intima.
There are again places in which the surrounding connective-tissue forms
an external envelope for all capillaries, even the most minute, — in fact,
an adventitia capillcms, which may be regarded as equivalent to the
tunica cellulosa of larger trunks. Thus we find the capillaries of the
brain (fig. 359, a) enclosed in a homogeneous nucleated membrane, and
those of lymphoid organs (I) closely invested in reticular connective
substances. Again, other more considerable, but still capillary vessels,
may be enveloped loosely in a layer of connective-tissue (c), and the space
thus left between the latter and the vessel may serve the purpose of a
lymphatic passage. We shall refer again to these lymph sheaths, and
only stop to remark here, that every adventitial tissue of a blood-vessel
containing lymphoid cells, must not be regarded as one of the latter.
Another circumstance also may frequently give rise to the deceptive appear-
ance of such a sheathing, namely, that a blood-vessel is often bounded
on each side by lymphatic canals ; this is most commonly seen in
uninjected preparations.

Now, although in those cases just described the capillary wall is easy
of recognition in it own individuality, there are others in which the cells
of the tube become so intimately united with the adjacent tissues, that
they are either totally inseparable from the latter, or only so with the
help of the stronger reagents at our disposal, although treatment with
nitrate of silver naturally renders them visible. This is the texture of
the capillary canal as found, for instance, in the membrana pupillaris of
the fcetal eye, the skin, and other strong fibrous structures.

§ 203.

Passing on now from these finer forms to the larger trunks, we meet
again with those layers already known to us, namely, the epithelial, and
the intima enveloping it, and finally the external fibrous coat. The latter
appears in the form of longitudinally striated connective-tissue, with
vertically arranged nuclei or connective-tissue corpuscles.

Very soon, however, even in extremely fine trunks, especially as we
pass towards the artery, between the two internal membranes and. the
external coat, a thin layer of transversely arranged contractile fibre cells
may be observed, whose nuclei we may easily detect. The latter are
spoken of as transversely oval. There can be now no doubt but that in
this we have before us the first rudiments of the middle or muscular coat
of the larger trunks.

Once more to recapitulate : \re see first (a) the layer of flattened cells,
then (b) the longitudinally streaked internal coat, then (c) the transverse

366

MANUAL OF HISTOLOGY.

muscular elements as middle coat, and finally (d) the external envelope
of connective- tissue.

Vessels of this kind can by no means be called any longer capillaries ;

d-

Fig. 360.— Two considerable vessels from the pia mater of the human brain.
1. A small arterial twig. 2. A venous twig; a, 6, internal; c. middle;
and d, external layer.

they bear from henceforth far more the character of fine arterial and

venous branches. According to
their nature in this respect, they
offer certain differences for our
consideration, and besides, a series
of others of a more local or indi-
vidual kind.

Taking vessels of about 0'0282-
0-04512mm.indiameter(fig.360),
only two membranes are to be dis-
tinguished in a venous branch (2)
of this kind. In the first place an
inner (a, b), in the form of a toler-
ably resistant elastic tunic, re-
markable for its tendency to form
smaller or larger longitudinal
folds, and studded with numerous
nuclei. The latter on treatment
with silver are seen to be the
nuclear formations of the vascular
cells, which are smaller here than
in the capillaries, presenting also
a broader and more rhomboidal
figure. It is still a matter of

uncertainty whether these are again clothed in a thin longitudinally marked

Fig. 361.— An artenal branch. At (ft) the homo-
geneous internal layer destitute of nuclei; (c) mid-
dle tunic formed of contractile fibre cells; d, the
external connective-tissue tunic.

TISSUES OF THE BODY. 367

coat or not. The second layer (d) presents itself in the form of a streaky
fibrous tissue envelope with elongated nuclei and connective-tissue cor-
puscles.

If we compare with this an arterial branch (1), we find again the
two coats (b and d) just described ; but between the inner membrane
and outer tunic of connective-tissue there now appears a layer of trans-
versely arranged contractile fibre cells lying side by side (c), whose elongated
nuclei present themselves in transverse sections of the vessel as encircling
the latter. This tunic is of varying strength. In other arterial twigs it
may appear with greater distinctness, either as a single or multiple layer.
Fig. 361 represents this in a side view, and fig. 359, d, the transverse
section of a small artery with laminated muscular coat, and an adventitia
consisting of reticular connective-tissue. The epithelium cells are narrower
here than in the veins, hut much more elongated in the direction of the
vessel, and fusiform.

§204.

Thus far is it possible to subject the blood-vessel as a whole to micro
scopical analysis. Larger tubes must be examined in their various parts,
either by rending the walls, peeling off layers with a forceps, the vessel
having been slit up, or by preparing sections of the previously dried or
hardened wall.

The further changes from the next in order to those occurring in the
formation of the largest vessels, consist in this, that all the layers, with
the exception of that formed of endothelial cells, which remains single,
commence to become more and more laminated, especially the internal
and middle, thus collectively bringing about an increase in the whole
thickness of the vessels. The internal strata preserve in their systems of
membranes arranged in laminae one over the other their elastic character,
presenting every variety of elastic tissue in longitudinal arrangement.
The middle coat is transformed into a system of laminae of smooth muscle
fibres, connective and elastic tissue, with a transverse direction. The
external tunic, finally, becomes thicker and thicker in its connective sub-
stance with an ever increasing development of elastic networks. Tig.
362 represents at (1) the umbilical artery of a foetus of eight months old
in transverse section, and at (2) a large artery from the adult similarly
cut, and gives us for the present an idea of the arrangement of parts in
question. The distinction between the different coats becomes, however,
less and less apparent at the same time. We must, however, bear in
mind that the coats of veins are thinner than those of arteries of corre-
sponding calibre, a circumstance which depends upon the minor develop-
ment in them of the middle tunic. The endothelial cells of venous
vessels preserve everywhere the same short broad figure already men-
tioned in the foregoing §.

Small veins, merely higher grades of development of such a vessel as
that represented in fig. 360 (2), commence much later to acquire a muscular
layer than arteries of the same magnitude. A venous vessel, for instance,
of 0'23 mm. in diameter offers for our consideration an internal membrane
in which may be observed elastic longitudinal interlacements, a few
laminae of muscle-fibres in the middle coat, intermixed with elastic net-
works and layers of connective-tissue, and, finally, an external thicker
coat, formed of fibrillated connective-tissue and elastic fibres.

In medium-sized veins the internal coat consists of either one or several

368

MANUAL OF HISTOLOGY.

laminae, longitudinally streaked and studded with nuclei and fusiform
cells, and a stratum of elastic membranes and fibrous networks arranged
longitudinally, between which the elements of smooth muscle may even
be insinuated. The middle tunic is formed of obliquely-crossed fibrous

tissue, with elastic networks,
whose fibres take the same direc-
tion, and also of unstriped muscle
cells. Between these there ap-
pear, however, elastic membranes,
whose fibres maintain a longitu-
dinal course. The middle layer
of vessels of this kind is, as a
rule, much weaker than that of
arteries, but is rich in muscular
elements. The strong external
coat is formed of connective-tissue
with elastic interlacements. Un-
striped muscle may, however, also
occur.

The largest veins of all, finally,
present a similar arrangement of
their internal laminae, except
that the latter have no unstriped
muscle fibres, while the middle
layer remains comparatively un-
developed, or may in rare cases
be entirely absent. The muscle
elements of the latter when pre-
sent are scanty, and accompanied
by abundant connective -tissue,
whose fibres are obliquely ar-
ranged. Elastic fibrous networks
of longitudinal direction are also
present still. A strange pecu-
liarity has been remarked here
in the usually strongly developed
external layer of many veins,
namely, the occurrence of a large
amount of longitudinally arranged
muscle, which generally occupies
the internal portion of the former
in varying strength : it is mixed
with fibres of connective- tissue
taking an oblique course. There
are certain veins, indeed, which
show an excessive development
of these muscular elements, as,
for instance, those of the preg-
nant uterus ; in others they are
entirely absent, as in the sinuses of the dura mater.

The valves of veins, which are covered with endothelium, consist mainly
of connective-tissue interspersed with elastic fibres.

In small arteries the internal and external layers remain comparatively

Fig. 362.— Transverse sections of arteries. 1. The
umbilical of a human foetus eight months old. a,
epithelium; 6, layers of the internal coat; c, the
muscular layers of the middle coat without any
intermixture of elastic elements; d, external cover-
ing, made up of colloid tissue. 2. A large artery
from the adult ; a and 6, as in fig. 1 ; c, the line of
demarcation between the inner and middle coats;
rf, elastic, and e, muscular laminae of the middle
coat; g, the external tunic traversed by elastic
networks; at/, below, the latter are highly deve-
loped.

TISSUES OF THE BODY. 369

/

unchanged. The former, however, may frequently acquire the characters of
a reticular elastic tunic, owing to incipient absorption at certain points ;
this is the so-called fenestrated membrane (§ 127). Condensation may
also lead to the formation of an elastic network stretched in the direction
of the axis of the vessel. The middle layer consists of several strata
of transverse un striped muscle-fibres, laid one over the other. In the
outer, finally, the connective-tissue becomes fibrillated, and the corpuscles
of the latter unite to form fine elastic fibrous networks.

We must be permitted here to refer, in a few words, to the umbilical
arteries (fig. 362, 1). These are remarkable for the extraordinary
development of their muscular middle coat (c). As tunica adventitia wo
find (d) a reticular connective substance, already seen in the gelatin of
Wharton (p. 191). The arteries of the ovaries likewise have very strong
muscular tunics. The latter may attain an enormous pitch of develop-
ment in the branches supplying the so-called corpus luteum.

Trunks of more considerable magnitude, of about 2 mm. in diameter, for
instance, show in their internal coat an increase of elastic tissue, in addition
to which longitudinally striated layers may occur. There are likewise inter-
posed between the greatly thickened laminae of muscle fibres imperfectly
developed membranes of elastic nature, with webs of elastic fibres holding
an oblique course ; the latter attain also, in the outer tunic, a high pitch of
development. In vessels of larger diameter still these elastic networks are
developed more and more, especially internally, towards the tunica media.

Turning now, finally, to the largest arterial trunks of the body (fig.
362, 2), we find, in the first place, that the internal layer (b) has increased
in thickness by multiplication of its elastic laminae. These latter present
themselves, in keeping with the variability of elastic tissue, either in the
form of membranes or of membranous networks stretched in the long
axis of the vessel, or again as fenestrated coats. More internally, close to
the epithelial layer, may be seen laminse, either homogeneous or longitu-
dinally striated, in which, as for instance in the ascending aorta, networks
of stellate cells exist, lying one over the other, as was discovered by
Langhans and confirmed by Ebner. In the middle coat (d, e) the mem-
branous character of the obliquely running elastic webs becomes more and
more marked. The latter may be very thick, or, again, fine and delicate,
and the whole present a fenestrated appearance, owing to absorption of
the interstitial connecting substance. As a rule, these membranous elastic
layers, whose number may amount to from thirty to fifty and upwards,
are interleaved with tolerable regularity with the lamina of the muscular
substance (e). The latter presents itself in varying degrees of perfectness,
and is frequently but slightly developed, which may depend upon the high
degree of development of the elastic intermediate layers : its direction, like-
wise, is by no means always the same. In the outer portions of the middle
tunic fibrillated connective-tissue is also to be found (Schultze, von Ebner\
In the most external coat (g) the elastic networks are frequently more and
more strongly marked at its inner portion (/), so that among the larger
mammals, as, for instance,. in the whale, they furnish one of the strongest
examples of elastic tissue that can be met with. As an exception, smooth
muscle may also make its appearance in the internal coat of human
arteries. Corresponding muscle elements to those we have described as
occurring in the external layers of the veins appear to be entirely absent
in the arteries of the human body.

Commencing even in the smaller twigs, the blood-vessels are supplied

370

MANUAL OF HISTOLOGY.

with arteries for the nutrition of their walls. These are known as the
vasa vasorum, and are distributed, for the most part, to the middle and
external coats, and especially to the latter, in which they are tolerably
numerous. They are here arranged like those of formless connective-
tissue, except that they form narrower meshes. Later on they appear in
the middle layer, where they have been seen in
arteries to form vascular networks of fine tubes,
with elongated oblique meshes (Gerlach).

The nerves of arteries derived from the sympa-
thetic and cerebro-spinal system are distributed in
the larger trunks to the middle and external tunics.
As a rule, the arteries seem to be richer in nerves,
on account of their thicker middle layer, than the
veins, but the greatest variety exists in this respect.
All that is necessary has already been remarked in
respect to the termination of the nerves of vessels
in § 183.

Fig. 363.— Vessels of striped
muscle, a, artery; 6, vein;
c and d, extended capil-
lary network.

§205.

"We mus now turn to the more careful considera-
tion of the capillaries as to the most important
subdivision of the vascular system.

We have already seen that no sharp boundary
can be drawn between these vessels and the arteries
and veins, in that the most imperceptible transition
exists from one to the other. But one thing is char-
acteristic in the capillaries, namely, that their* tubes
no longer decrease in calibre from the giving off of
branches, and that they form among themselves, in
the various organs supplied by them, networks of
tolerably regular size and shape (fig. 363, c, d).
The diameter of the vessels so connected is, how-
ever, by no means the same in the various organs,
and the finest are not presented to us in every locality. The brain and
retina possess the most delicate. Their transverse diameter in these organs

may be stated at 0'0068-0'0065 mm.,
or, in some cases, even so low as
0*0056 mm. In muscle they appear
to be somewhat larger, measuring
0'0074 mm. Those of the connec-
tive-tissue of the skin and mucous
membranes, again, are still larger. In
most glands, as, for instance, the liver,
kidneys, and lungs, the diameter of
the capillaries lies between 0'0091
and 0-0135 mm. The largest of all
vessels of this kind are to be found
in bony tissue, where they measure as
high as 0-0226 mm. It must be
borne in mind, however, that, owing
to the elasticity of the capillary tube,
and its variation in diameter according to the amount of blood contained
in it, these measurements can only be regarded as approximate.

Fig. 364. — A pulmonary^alveolus from the calf.
a, large blood-vessel •" 6, capillary network;
c, epithelium cells.

TISSUES OF THE BODY.

371

Fig. 365. — Vessels from the human retina, a, arterial
6, capillary network ; c, venous twig.

It is easy to conceive that,

In other vertebrates, likewise, the size of the capillaries must be greater
to correspond with the larger dia-
meter of the blood corpuscles.

Touching now the distances
between the tubes, and the
greater or less vascularity of a
part depending thereon, the
most remarkable variety pre-
vails. The lungs, the glands, the
mucous membranes, and the skin
are the most vascular of all struc-
tures ; whilst other parts, such
as the serous and fibrous mem-
branes and the nervous trunks,
are very poor in vessels. The
vascular networks of the lungs
(fig. 364) and of the retina
(fig. 365) afford examples,
although the latter membrane
cannot be reckoned among
those poorest in blood in the
body.

Finally, we know of tissues
which contain no blood-vessels,
such as the cornea, the lens
cartilage, the epithelial structures, and nails,
owing to the minuteness of the
elements of form, only consider-
able groups of the latter can be
surrounded by the capillary net-
works in organs with a small
amount of vascularity. But even
in those parts most abundantly
supplied with blood the capillary
tube always lies external to the
elementary structure, and never
penetrates into the interior; at
the very most, is each individual
form element surrounded with a
single loop, as in the case of
the fat cell (§ 122) and muscle
fibre (§ 168). The forms under
which capillary networks pre-
sent themselves are very nume-
rous, and at the same time fre-
quently so characteristic of the
various parts to which they be-
long, that the practised eye can
often recognise an organ from a

c;pr>rirm nf it* sn'hstanpp wViiVVi Fig. 366.— Vessels from about fat cells. A, an arterial

twig at a, and venous at 6, with round capillary
has been injected. network of a fat globule. B, the capillaries of three

These forms are chiefly deter- free cells of the latter'
mined by the texture of the part and the grouping of its structural elements,

372

MANUAL OF HISTOLOGY.

as well as the shape of the latter (fig. 366, A, B). Thus, around certain

globular structures, such as fat
cells and the terminal vesicles of
racemose glands, we find bag-like
nets of vessels, and also about the
outlets of follicular mucous mem-
branes a circular interlacement of
the latter.

The cells of an hepatic lobule,
which have a radiating arrange-
ment, as depicted in fig. 328, p.
345, produce also a radiating
course in the capillaries of the net-
work of the part, which is pri-
marily bag-like (fig. 367). Again,
in those parts whose structural ele-
ments are elongated and regularly
grouped, we find the meshes of
the vascular web likewise much
drawn out, as it were, and verv

Hg. 367.— Capillary network from a rabbit's liver. £ • • /

narrow, as, lor instance, in muscle

(fig. 363, c, d\ in nerves, in follicular qr tubular glands, such as those of
the stomach (fig. 343, p. 354).

Fig. 368.— Capillary loops from the sensitive papillae of human skin.

Fijr. 369.— The vascular loop network of an intestinal villnsL
a, arterial twig; 6, capillary net with its circular arrange-
ment around the outlet of the Liebcrkuhns follicle at d;
r, venous branch.

the twig supplying the convolution ; c, glo-

TISSUES OF THE BODY. 373

It is easy to conceive also that eacli form of network may make its
appearance with ever so many different modifications.

On account, for instance, of the narrowness of the space in such conical
protuberances as the sensitive papillae of the skin and papillae of the mucous
membranes, regular capillary loops, as they are called, may be formed
(fig. 368). Again, if these cones attain much greater dimensions, as in
the villi of the small intestines, an arrangement of capillaries is brought
about which is known under the name of the loop network, a further
complication of the former. Tn this
case we see, passing between the two
or more principal vessels of the sling,
a finer set of tubes holding a trans-
verse course (fig. 369, b).

Finally, in this sketch may be in-
cluded the glomerulus, as it is called,
of the kidney, an arrangement of
vessels peculiar to, and characteristic
of, that organ (fig. 370). Here we find
a minute arterial twig (6), micro-
scopically small indeed, suddenly
curled upon itself in a manner
similar to the inferior portion of a
sweat gland (c). . Within the con-

VOlutlOll it may divide into branches

to a certain extent, as in man and the

mammalia, or remain single, after »fc ff; H urinary tubules.

which an efferent vessel makes its appearance (d\ which, at a short

distance from the glomerulus is resolved into a capillary network (ef).

§206.

The lymphatic system is an appendage of the circulatory, designed to
bear back into the blood those nutritive fluids, impregnated with the pro-
ducts of decomposition of the tissues, which have transuded into the inter-
stices of organs from the capillaries. It likewise takes up, during the
period of digestion, by means of its radials terminating in the mucous
membrane of the small intestine, that fluid known as chyle, which has
been already referred to (p. 131). Owing to the fact, therefore, that the
lymphatic system is only destined for the conveyance of these matters
into the circulation, it is entirely wanting in vessels corresponding to the
arteries. It consists rather of a set of vessels corresponding to the
capillary part of the circulation, and of drainage tubes taking their rise
from those which may be compared to the veins.

Lymphatic vessels are widely distributed throughout the body, but
occur most abundantly in vascular parts. They have, however, been
missed, up to the present in certain portions of the body well supplied with
blood. They are not found in such non-vascular tissues as the epidermis,
nails, and cartilages.

The mode of origin of lymphatics was for a long time veiled in the
deepest obscurity, owing to the fact that the numerous valves of the
larger trunks offered the most determined resistance to injection, and thai
the colourless nature of the contents of the finer tubes rendered their
immediate recognition almost impossible. Further, it is only certain
specially transparent parts that allow of the latter being seen at all. That

374

MANUAL OF HISTOLOGY.

Fig. 371.— Villus from the intestine of a kid,
after treatment with acetic acid.

portion of the system presiding over the absorption of the chyle is, how-
ever, on account of its dark fatty contents during digestion, more favour-
able for observation, and was in fact
the only point, a few years ago, at
which the relations of the vessels in
question could be studied with any
success.

In the first place, then, let us take
a glance at the lacteals.

If we choose for examination the
intestinal villi of a mammal which
has been fed some hours before with
rich fatty food, such as that of a young
sucking animal. (fig. 371), which best
answers our purpose, we shall see, in
the central portion of eachvillus travers-
ing its axis, a passage filled with
minute fatty molecules, and dark on
that account. This duct frequently
terminates in a rounded enlargement or bulb, and is usually single in
slender villi, although in instances in which the latter are broader it
has been seen to be double, treble, or quadruple.

Minutely examined, this vessel (fig. 372, d), which has a diameter of
0'0187-0*982 mm., is seen to possess a thin
homogeneous, but distinct wall. Above, it ter-
minates blind, without the interposition of any
finer system of canals, and may be expanded at
its end to a diameter of O'OSOO mm. in some
cases. This axial vessel has been supposed by
some to be merely a deficiency in the connective-
tissue substance of the villus, but this is incor-
rect. Years ago I had frequently met with the
villus half torn through, and the uninjured wall
of the axial canal thus isolated. The results of
artificial injection (§ 208) have since corrobo-
rated this explanation of its nature. Around
this chyle radicle the capillaries of the loop net-
work (b), mentioned in section 205, are coiled
with a thin layer of unstriped muscle-cells inter-
posed : a fact of great interest.

Lymphatic radicles were observed also, many
years ago, by Koettiker in the tail of the tadpole.
Their appearance as they occur here is very
variable. They most usually present themselves,
however, in the form of tubes much finer than
in the preceding case, measuring in diameter
0'0045-0'0113 mm., and consisting of a thin
homogeneous wall, which is nucleated and stud-

372.— Intestinal villus. o,
the thick border of the cylin-
der epithelium; 6, capillary
network ; c, longitudinally ar-
ranged smooth muscle fibres;
rf, chyle radicle in the axis.

ded with a multitude of minute saccules.

They are arranged as a whole in the form of a tree, with branches passing
off at acute angles, and do not present the reticulated appearance of the blood
capillaries. The terminal tubules seem to end in delicate filiform processes,
directed towards similar ramifications belonging to stellate formative cells.

TISSUES OF THE BODY.

375

Fig. 373. — Vertical section through the mucous mem-
brane of the conjunctiva of the ox, from the lower
lid. a, large lymphatic vessel ; b, follicle ; c, super-
ficial lymphatic canals.

d

§207.

That difficulty of filling the peripheral portions of lymphatics owing to
their valves, already mentioned in the preceding section, we have recently
learned to overcome. The fol-
lowing is the method usually
employed, known as Hijrtl's
method of puncture : — A fine
cannula is passed into such parts
as are supposed to contain lym-
phatics, and through this the
injection fluid is gently forced.
The extensive researches of
Teichmann have greatly in-
creased our knowledge as re-
gards this branch of study, be-
side which other contributions
have been made by Ludioig and
his pupils, Tomsa, Zawaryltin,
and MacGillavry, as well as by His, Frey, Langer.

As far as is known at present, the radicals of absorbents, the peripheral
lymphatic canals, occupy the in-
terstitial connective-tissue of the
various organs, or are at least
always situated in its course.

They are seen here either in
the form of networks, reminding
us of the peripheral portions of
the circulation, or they begin in
blind passages which are sub-
sequently united in a reticular
manner.

The first form is met with, in
general, where the surface of an
organ is smooth, or in the in-
terior of the latter (figs. 373,
374, 375, 377) ; the second in
parts of the body where the sur-
face is covered by round or
tufted appendages (figs. 371,
376).

The arrangement of the canals, however, in the various regions of the
body is variable enough, and we miss everywhere that beautiful regularity
to be seen among the capillaries of the blood-vessels.

The diameter of lymphatic canals is in general much more considerable
than that, of the capillaries, ranging from 0'0113 to 0-0451. Only for
short distances, however, do they preserve anything like the same diameter
of lumen. As a rule, these vessels present strong dilatations and sudden
constrictions, down to about 0'0027 mm. and less ; and so on. The
whole may present frequently a jagged or knotted appearance, diffi-
cult of description (fig. 373, 374), but which to a practised eye is unmis-
takable.

The amount of lymphatic vessels varies in the different organs, and
25

Fig. 374.— Prom the thyroid gland of the Infant, a, c,
glandular spaces ; d, /, larger and terminal lym-
phatics.

376

MANUAL OF HISTOLOGY.

indeed frequently, to a considerable extent, in regard to the various parts
of the same.

As to their relation to the blood-vessels one thing is certain, that a

Fig. 375. — Surface of the vermiform ap-
pendix of the rabbit, a, a depression ;
6, outlets of the follicles of lAeberkiihn ;
c, lymphatic network; d, descending
canals.

Fig. 376. — Papilla from the colon of the
rabbit, a, arterial; b, venous twig; c,
capillary network ; d, descending vein of
the papilla; e, lymphatic vessel; /, lymph
canals of the papilla; g, blind termina-
tion of the latter.

transition of one into the other takes place nowhere, neither directly nor

with the interposition of fine tubules.

In many instances we may
see lymph canals surrounded
externally by capillaries (fig.
372, 376). In other cases
tubes of both kinds run, with
greater or less regularity, side
by side (fig. 377).

Finally, a stream of lymph
may be taken up by the ad-
ventitia of a blood-vessel, en-
veloping the latter as with
a sheath (fig. 376, <?). Thus
we see that the arrangement

f ,1 , , ,•

01 the Structures in question

is Very various.

A few moments must now be devoted to the consideration of that
ensheathing of blood-vessels in lymph streams which has just, been men-
tioned.

It has been the custom to speak of this as of frequent occurrence
among the lower orders of vertebrates, such as reptiles. It has been
denied, however, that it takes place at all in the frog by Langer, who has
given the matter his.closest attention. In the higher animals and in man
it may appear, without, however, being anything but an accidental
occurrence, except, perhaps, in particular portions of the body.

We have recently learned from His that the blood-vessels of the
nervous centres, the brain and spinal cord, are loosely enveloped in a
sheath of streaked connective-tissue in a vast number of cases. This
arrangement of parts is seen among arteries, veins, and capillaries alike,

Fig. 377. — From the testicle of the calf, a, seminal tubules
in side view; 6, more obliquely seen; c, blood vessels ; d,

lymphatic canals.

TISSUES OF THE BODY.

377

and has been named by His the perivascular canal system. This observer
is inclined to regard it as belonging to the lymphatic system, in which
he is perhaps right. The merit of having first discovered this rests,
however, with Robin, who, several years previously, had maintained the
presence of lymph sheaths around the capillaries of the parts in question.

§ 208.

Having discussed the disposal of the lymphatics, let us now turn to
the consideration of the nature of their peripheral portions, a point of
great importance.

Are they, in the first place, vessels, — that is, endowed with a special
wall like that of blood capillaries ?

This has recently been declared to be the case by Teichmann (1), after
the most extensive researches, aided
by injections, and also by Koelliker,
who investigated the matter in the
tail of the tadpole (§ 206).

Another view, which has found
numerous defenders within the last
few years, is, however, directly op-
posed to this. According to it, the
peripheral circulation is only lacunal,
i.e., takes place within the interstices
of connective -tissue (2) (BriicJce,
Leydig, His, Ludwig). For my own
part, I have for many years looked
upon the lymphatics as bounded alone
by connective-tissue, which is, how-
ever, condensed and membranous,
and encloses the space completely,
playing the part of a sheath. Indeed, it was impossible, until very recently,
to make out anything but a homogeneous boundary layer around the
lymphatic passage (fig. 378, b).

By means of the new reagent, however, dilute solution of nitrate of
silver, this apparently homogeneous limiting layer of connective-tissue has
been resolved into a series of united, smooth,
and nucleated cells or endothelia, allied to
those of the blood-vessels (fig. 379).

But while in the blood capillaries this wall
maintains its independence in regard to the
adjacent tissue, it fuses here with the latter,
so that only as an exception, and where the
surrounding substance is of loose texture, can
it be isolated.

The peripheral tymphatics, whose structure
is represented in fig. 380, are, according to
this, in contrast to the blood-vessels, by no
means regular vessels, but canals (p. 372).
In the last-mentioned woodcut, also, we see
that here, as in the blood-vessels, gaps or
sto'inata occur between the cells.

A communication between the lymphatic system and the cavities of
serous sacs, namely, of the peritoneum and pleurae, by means of orifices

Fig. 378. — From the small intestine of the rab-
bit, a, reticular connective substance with
lymph cells ; 6. lymph cavity ; c. space for a
follicle of Lieberkulm ; d, one of the latter
with its cells: «, /, capillary in transverse
section ; gr, thicker trunk.

Fig. 379.— Cells from a lymphatic
passage, a, elongated plates; 6,
broader specimens.

378

MANUAL OF HISTOLOGY.

Fig 380.— A lymphatic canal
from the large intestine of
the Guinea-pig, a, cells of
the vessel; b, stomata or
gaps between the latter.

opening into the .former, has been recognised within the last few years by
Recldinghausen, Ludivig, DyWcowsky, Schweigger-
Seidel, and Dogiel, corroborating the suppositions
of the older observers, as, for instance, those of
Mascagni.

Recklinghausen was the first to point out that
the centrum tendineum of the rabbit's diaphragm,
is studded with openings whose diameter exceeds
that of the red blood-cells, and through which
formed particles, such as milk globules and granules
of cinnabar, can make their entry, passing into
the lymphatics of the diaphragm. This interesting
discovery has been confirmed by Schweigger-Seidel
andLudwig, in respect to the locality mentioned, and
DyHkowsky observed the orifices in question in the
intercostal pleura of the dog, and Schweigger-Seidel
and Dogiel in the peritoneum of the frog. The fact was also recognised
that the lymphatic vessels of serous membranes give off short lateral
processes in the direction of the surface (fig. 381, 2, &), which are seen

to open into the cavities, spoken of by
orifices, situated between the epithelial
cells [fig. 381, 1 and 3, a, a (3)].

Turning now from these finest lymph-
atic passages to the larger canals, we
observe that the latter have at the com-
mencement a precisely similar texture,
while their arrangement varies to a great
extent, being frequently retiform (fig.
382). Here also the walls are formed
of nucleated cells alone. The occurrence
of scattered nodal and ampullar enlarge-
ments is the first striking feature in
regard to these canals while still of
medium size. In larger trunks the
former are more frequently to be seen,
in addition to which valves similar to
those of veins also present themselves.

It is only trunks of this kind that
can with perfect correctness be called
lymphatic vessels. In them at times
(however, in smaller branches also), the
walls commence to become more and
more independent, and to appear distinct,
from the surrounding tissues. Here also
the relation to the blood-vessels is very
different. As a rule, to be sure, lymphatic
and blood-vessels run along side by side,
but not very rarely we encounter larger
lymphatics accompanying a great arterial branch in pairs. They event-
ually may lead to an ensheathing of the blood-vessel in a lymph stream,
but the latter is of less frequent occurrence than is usually supposed.

The appearance of new external layers in addition to the cellular tube is
a point requiring closer investigation.

Fig. 381. — 1. Epithelium from the under sur-
face of the centrum lendineum of the rabbit,
a, pores; 2, epithelium of the mediastinum
of the dog; a, pores; 3, section through
the pleura of the latter animal ; 6, free
orifices of short lateral passages of the
lymph canals (copied from Ludwig,
Schweigger-Seidel, and Dybkowsfy).

TISSUES OF THE BODY. 379

Koelliker tells us that twigs of only 0*2256-2609 mm. may be pos-
sessed of three tunics. Around the cellular coat a longitudinally fibril-
lated elastic membrane is to be found, as serosa, then a media consisting
of contractile fibre cells and elastic fibres, which is covered by an
adventitia of longitudinal fibrous tissue.

Fig. 382. — Lymphatics from between the longitudinal and transverse layers of muscle in the
small intestine of the Guinea-pig, c, fine, and d, larger canals; ab, plexus myentericus of
Auerbach.

In still larger absorbent vessels the structure is similar. They corre-
spond in this respect with the veins, as is well known.

In the thoracic duct the epithelium presents itself enclosed in several
layers of fibrous membranes, upon which an elastic network is laid down,
its elongated meshes arranged in the long axis of the vessel. The next
or middle coat consists of connective-tissue, coursing with its fibres
in the direction of the tube, after which we come upon transverse
muscular fibres. The adventitia presents for our consideration, besides
ordinary connective-tissue, scattered bundles of unstriped muscle arranged
in a reticular manner. According to Koelliker. the serosa has a thickness
of hardly 0-0135-0-0226, and the media of 0-0564 mm.

The relations of these canals to the lymphatic glands, on their arrival
in the latter, we reserve for the third part of our work.

REMAKKS. — (1.) Teichmann was of opinion that the foundation of the whole lym-
phatic system consisted of structures resembling stellate cells (Saugaderzellen). He
regarded them as metamorphosed cells which had preserved their envelope, and
which, united through their processes, thus formed the "lymphatic capillaries." (2.)
Among the views in question great variety may be observed. Many have simply
accepted the membraneless interstices of interstitial or other connective tissue as the
commencement of the absorbent system. The extensibility of this tissue was sup-
posed to lead to the formation of clefts or openings into the neighbouring parts on
increased pressure, artificial or natural (Briicke and Ludwig). Recklinghausen, in his
article "Die Lymphgefasse und ihre Beziehung zum Bindegewebe," Berlin, 1862,
appears to have arrived at peculiar results in his investigations. According to him
(and the merit of the discovery rests with him), all lymphatic radicles are clothed
with that epithelium already mentioned. They are, however, says he, related to
those formations of connective-tissue so well known from Virchow's works as con-

380 MANUAL OF HISTOLOGY.

nective-tissue corpuscles. Eecklinghausen does not mean, however, that a system of
hollow cells is formed of these, but rather a series of fine clefts as it were (Saftka-
nalchen) traversing the tissue, in which elementary spheroidal (connective-tissue)
cells are lodged. This view, however, has met with the greatest opposition, and is,
we are convinced, incorrect. In order to account for the transition of these "sap-
canals " into the larger lymphatic radicals, which are lined with cells, Eeckling-
hausen points to the stomata already mentioned in the text. Many of these small
figures, however, may possibly have another significance. They may, namely, be
nothing more than separated processes of some of the vascular cells, possibly designed
to provide for the increase in size of the vessel. Klein and Burdon- Sanderson both
speak of another set of openings on the serous sacs besides those of the lymphatics
just mentioned ; these are the terminations of the sap carialiculi on the free surface
of the membrane, and have been named by them " jpseudo-stomata ." (3.) In the
fluid of serous sacs Eecklinghausen has found lymph corpuscles, from which fact it
might be imagined that the formation of such lymphoid elements could take place
from the epithelial cells of these cavities. Ludwig and Schweigger-Seidel allow that
such a multiplication and transformation of the epithelium cells on the centrum
tendineum of the rabbit may take place. Kodliker informs us also that on the
human peritoneum, and especially in that part, namely, forming the great omentum,
there occur a number of aggregations of epithelial cells in the form of nodulated
excrescences filled with lymphoid cells. An explanation of this phenomenon has,
however, since been offered by the discovery of the migration of lymphoid cells.

§ 209.

As to the physiological relations of the vessels, we will only discuss, in
as few words as possible, a few of their leading features. We have
already seen that the thicker wall of the arteries chiefly depends upon
the well-developed middle coat; that it displays greater richness in
transverse layers of unstriped muscle, interleaved with elastic plates,
while veins of the same calibre have thin walls, owing chiefly to thinness
in the tunica media, while the tunica adventitia is strongly developed.
"We have likewise seen that in the smaller veins the muscular elements
soon disappear completely, whilst in the very smallest arteries, even down
to their termination in the capillaries, these contractile fibre-cells are
distinctly visible. The capillaries themselves are entirely destitute
of muscular tissue, but possess, according to Strieker, vital contractility
(§ 202). >

The circulation of the blood takes place, as is well known, with pulsa-
tions through the arterial vessels, and evenly through the veins and
capillaries. The pressure of the blood upon the walls of the arteries is
very considerable, exceeding at least tenfold that upon the internal sur-
face of veins, and increasing, besides, more and more with the ramifications
of the former.

The walls of the larger vessels, in keeping with their texture, possess a
slight but very perfect elasticity, that is, they can be stretched by a small
amount of force, returning subsequently to their original form. It must
be borne in mind, too, that the vascular tubes are always largely dis-
tended with blood, so that the elasticity of their walls also exercises a
certain amount of pressure on the columns of fluid enclosed by them. If
we consider this centred in the arteries, whose expansion under increas-
ing pressure is much less than that of the veins, we have in them a
system of elastic tubes charged with blood, into which, at every contrac-
tion of the heart, a new quantum of the latter is forced. The pulsation
of arteries is an undulation produced in the walls of the latter by this
pumping in of fresh quantities of fluid, and is gradually destroyed as it
advances toward the periphery by the resistance of the vessels, which are
undergoing an ever-increasing ramification. Owing to this the capillaries

TISSUES OF THE BODY. 381

are not reached by it. This undulating motion of the artery does not
constitute the propulsive force of the circulation; its only effect is to
accelerate the course of the stream of blood. The advance of the latter is
occasioned rather by the difference of pressure prevailing in arteries and
veins, each contraction of the heart forcing a new mass of blood into the
distended arterial tube, and each diastole abstracting a certain quantity
from the venous trunks, and receiving it into the auricle.

The course of the circulation is in general very rapid, the time con-
sumed in the completion of its circuit amounting on an average to about
half & minute. The rapidity is greatest in the arteries, equalling in the
carotid of the horse 400 millimetres in the second, while in the veins it
is considerably less, being only 250 mm. in the second, as seen in the
jugular of the same animal. In the following section we shall see that
the flow of blood through the capillaries is very slow, the length of the
latter being also very considerable. This sluggishness depends probably
upon the narrowness of the arterial canals, compared with the much
greater extent of surface in the capillaries, and the consequent increase of
friction to the column of blood. The subsequent decrease in the super-
ficial extent of the bed of the stream, consequent on the confluence of the
capillaries to form veins, explains the comparative acceleration which
again becomes evident in the latter in the flow of the blood, which still
remains, however, as has been already remarked, far more tardy than
that in the arteries.

The question now arises, What have (together with the elastic materials)
the muscular elements of vessels to say to the motion of the streams in
the vascular system ?

We know that the arterial walls, which are rich in these, contract con-
siderably under electric and mechanical irritation, as well as under the
action of cold and many chemical reagents. Consequently, we cannot
deny the presence of vital contractility in the arteries, and, from their
allied structure, in the veins also. The general opinion is, that the muscu-
lar tissue of the vascular system is perpetually in a state during life of
slight tonic contraction, which supports the elastic action of the remain-
ing elements, entering into the composition of the wall. In that here,
also, as everywhere else, the action of the muscles is under the influence
of the nervous system, we must expect to find certain vessels narrowed
by the increased contraction of their muscles, and expanded on relaxation
of the latter. The regulating action, then, of vascular muscles on the
amount of blood contained in certain parts cannot be denied. Experi-
mental nervous physiology has shown, besides, that section of the nerves
supplying the vascular system gives rise to expansion of the arteries
(Bernard and others). We have to thank this observer for our acquaint-
ance with the striking fact that irritation of the sympathetic nerves
supplying the arteries of the submaxillary gland causes decrease in their
calibre, so that the blood passing through the organ is found to be dark,
while only a small amount of viscid saliva is secreted. Stimulation, on
the other hand, of the cranial nerve which enters the gland, namely, the
chorda tympani, produces a completely opposite effect, bright red blood
streaming rapidly through the part, and a copious watery secretion being
poured out. Other organs also, such as the parotid, kidney, and stomach,
manifest the same antagonism in the actions of expanding and contract-
ing nerves. In them, likewise, we observe that the enlarged vascular
territory contains during the process of secretion bright red blood.

382 MANUAL OF HISTOLOGY.

Finally, the capillaries, supplied likewise, it would appear, with nerves,
constitute the most important part of the whole vascular system. Through
the membranes of which they are formed takes place the interchange of
matter between the plasma of the blood and the organic juices : from them
are exuded those fluids which .appear afterwards as glandular secretions.
We have already learned (§ 205) that upon the richness in capillaries of
any organ or tissue depends the energy of its transformative power.
The variety in the matters given out from and received into the several
portions of the capillary system, may partly depend upon a different
molecular constitution of the walls of the vessels ; partly on difference in
composition of the blood of various regions of the vascular system, as well
as the changeable nature of the organic fluids. The form of the afferent
and efferent vessels of capillary networks is also certainly of importance.
It will suffice here to point to the retarding effect of the glomerulus of
the kidney (fig. 370) on the stream of blood traversing the organ. The
different amount of pressure in the several parts of the capillary system
produced by this is, however, probably the most important moment in
the processes taking place here.

We have already referred (§ 81) to an occurrence of great vital import-
ance, which has only been recognised very recently, namely, — the passage
of colourless as well as red blood corpuscles through the uninjured walls
of vessels, — the contractility of the vascular cells appearing to provide for
the closure of each successively formed aperture.

We turn now to the question, so frequently discussed, as to the existence
of the so-called vasa serosa, or plasmatic vessels. Are there in the system
capillaries of such small calibre that they do not admit, in the normal
state, of the passage of blood-cells through them, and consequently only
serve for the transmission of the liquor sanguinis ? Such vessels do not
exist, although it was formerly supposed that such was the case, and that
a non-vascular organ could rapidly acquire capillaries when in a state of
irritation by the enlargement of these to such an extent as to allow of the
passage of blood-cells. Long ago attention was directed by Henle to the
presence in the substance of the brain of fine filiform tubes communi-
cating with ordinary capillaries. These were afterwards discovered to be
merely fine vessels which had been unnaturally stretched, and thus
narrowed ( Welcker). Here and there efforts have, indeed, been made to
maintain the transition of capillaries into plasmatic passages or " sap-
canals" (Coccius, Eckard, Heidenhain), but without success. However
the hypothesis of such an intermediate system of vessels between capil-
laries and lymphatic radicles may recommend itself on account of its con-
venience, observation does not support anything of the kind.

§210.

The circulation of the blood in the living body is one of the most
beautiful spectacles which the microscope can reveal. The readiest mode
of seeing this is to examine the transparent parts of cold-blooded verte-
brates, such as the web of the frog's foot or the tail of the tadpole. The
embryos of fishes and birds, the wing of the bat, the mesentery of pre-
viously narcotised small mammals, &c., will serve the same purpose.

Taking, for instance, the first-named portion of the frog's body (fig. 3S3-),
we see in the larger arterial and venous branches of the web the blood
streams coursing in opposite directions, with a rapidity magnified natu-

TISSUES OF THE BODY. 383

rally in proportion to the strength of the lens employed. In the minute
arteries the characteristic pulsation may be recognised, while in the capil-
laries a sluggish and more even flow is observed. The blood in the veins
is seen also to move along steadily, but again slightly increased in pace.
In the large tubes the oval blood-cells are driven along end foremost,
sometimes side by side, or one over
the other, and in the more consider-
able arterial twigs are frequently
seen twisting and whirling in rapid
motion. The internal surface, how-
ever, of such a vessel, of some what con-
siderable calibre (a), is not touched
by the rapidly- moving red cor-
puscles. In contact with it we ob-
serve a clear colourless layer, in
which, in the case of veins scattered,
white corpuscles may be discovered,
which advance much more slowly
and lazily than their hurrying com-
panions, and sometimes even adhere

to the Wall of the Vessel for a COn- Fig 383 —Stream of blood in the web of a frog's

siderable time. In the arteries, on the ^£%™ff£ J^^SSt *> the epi'
other hand, this colourless stratum

of fluid consists, according to Conheim, of liquor sanguinis, almost entirely
free of cells. Thus, a distinction may be drawn between a rapid axial and
lazy parietal stream. In the finest vessels and capillaries this peripheral
layer disappears on account of the narrowness of the tube, and instead of
the helter-skelter which goes on in the arteries, a more quiet, measured pro-
gression commences. At last the coloured and colourless blood-corpuscles
glide along singly one after the other, sometimes closely packed, sometimes
separated by considerable intervals. The former, which are smooth and
pliant, as well as endowed with a high degree of elasticity and extensibility,
are driven through the finer canals with greater ease than the latter, which
are not unfrequently arrested in their progress owing to their roughness
and adhesiveness. As soon, then, as the compression exercised upon it is
removed, the red corpuscle returns to its primary form again. In certain
cases some of the capillaries appear completely devoid of cells for the
time being, and transmit plasma alone. It seems almost superfluous to
remark here that, in the normal condition, a continuous transition of the
arteries into the veins takes place through the capillaries. In this exqui-
site spectacle a great number of subordinate variations may be observed
beside those already mentioned. But the moving coloured cells of the
mammal are liable to even greater changes, according to Rolletfs interest-
ing observations. They assume continually (of course passively) the most
diverse fprms, and only appear exceptionally in their normal shape. This
they assume again on the blood coming to a state of rest.

The rapidity of the capillary circulation can only be estimated approxi-
mately. The red cell of the frog traverses about the fourth or fifth of a
line in a second, while the lymph-corpuscle requires for the same distance
about ten or fifteen times as long. It is only the great shortness of the
capillaries, of which we have already spoken, which renders possible the
rapid circulation of the whole mass of the blood through the body.

384 MANUAL OF HISTOLOGY.

§211.

As to the development of the vascular system, we know that it takes
place from the middle embryonic plate. According to an old and wide-
spread theory, the heart and the earliest trunks which appear in the
rudiments of the embryo, namely, the arch of the aorta and primitive
veins, are met with at first in the form of solid cylinders composed of
cells, without any distinction between the axis and peripheral portion.
The latter, through the close union of its cells, becomes the primary wall
of the vessel, while the cellular elements in the axis constitute, on the
liquifaction of the intercellular substance, the first blood corpuscles (§ 81).
More recent investigation, however, has shown that the heart is developed
from the very commencement as a hollow organ (Sclienck, Hensen, Klein).
In the embryonic chick, Remak states that he has recognised the first blood-
vessels in the form of solid cylinders 0'0282-0'0451 mm. in breadth; in
the transverse section of which, as a rule, from three to eight formative
cells may be seen, but at times only two. At a more advanced stage of
development these cylinders are observed to be hollow and tubular, their
walls consisting of a single layer of formative cells projecting far into the
interior, and constituting, in all probability, the endothelium of a later
period. Subsequently great stress was laid here also upon the hollow
rudiment.

The vessels of a later period were long supposed to be developed after
another fashion, namely, from the fusion of simple rows of cells with sub-
sequent investment in other cells.

This is almost identical with the mode of development which, since
the days of Schwann, has been regarded as that of the capillaries.

The latter, as the older theory goes, are formed by the melting down
of the central portion of formative cells, which, arranged in rows one after
the other, and united in this position, are converted into a tube by open-
ing into one another. In this case the membrane of the cell becomes the
wall of the vessel, and the nucleus remains with it, as is always seen.

The formation of non-branching capillary tubes was believed to occur
in the following manner : — It was supposed that fusiform cells, arranged
one after the other, became united by means of their processes, the differ-
ence in the diameter of the cell, and its ramifications, gradually disappear-
ing later. The cellular tubes so formed were then supposed to receive
their blood by becoming connected with the previously existing vessels.

But owing to the fact that such unbranched tubes but seldom occur in any
length, and that a retiform arangement of tubules is the rule, the stellate
cell was regarded as playing an important part in the production of ramifica-
tions among rudimentary capillaries. This also has since been shown to
be incorrect. The lumen of the capillary vessel is an intercellular space.

Seeing, then, that these older views are no longer tenable, let us inquire
what have recent observations done towards showing the true mode of
development of the blood-vessels.

Let us take first that of the earliest rudimentary vessel in the foetus,
which is of considerable size, as is well known.

The first-formed vessels in the chick spring, according to Klein, from
cells of the middle germinal layer, whose contents become fluid until the
enlarged and watery cell-body is contained within a cortex of protoplasm
supplied with a nucleus. From such cells the primary wall of the vessel
takes its origin with the endothelium tube and first blood-corpuscles.

TISSUES OF THE BODY.

385

A cell of this kind, then, swells up into a vesicle, while at the same
time its nucleus undergoes segmentation. Some of these nuclei presenting
great regularity of arrangement throughout the protoplasm cortex (endo-
thelium vesicle of Klein), the latter may be regarded as made up of not yet
separated endothelial cells. These are to be seen later more distinctly.

From the endothelial wall further yellow-coloured and white cells spring,
by a process of gemmation,
— the first blood corpuscles.
The genesis of these cells,
therefore, appears now un-
der a new light (§81).

In other of these forma-
tive cells the inner portion
of the protoplasm is said to
assume a red colour, and to
divide itself over the new
nuclei formed by segmen-
tation to form blood-cor-
puscles. Finally, coarsely
granular cells are said to
undergo a precisely similar
process of transformation.

Thus, we see that both
the walls of the vessels and
the first blood corpuscles
take their origin from the
same cells, "the brood-
cells" (Brutzellen) of Klein.

But how is the vascular
tube formed from these sepa-
rate endothelial vesicles'?

The first of the vesicles
become elongated and sac-
culated. They may, how-
ever, only at first send out
laterally solid buds of proto-
plasm which subsequently
become hollowed. Now,
by the union of all these,
one with another, the first vascular tubes are formed.

Even the largest vessels and the heart itself appear to have a similar origin.

We have before us, then, protoplasm tubes which gradually divide into
endothelial cells by a process of segmentation of the nuclei. This agrees
very perfectly with an old-established fact, namely, that only from a
certain stage of development on, does the nitrate of silver solution pro-
duce the well-known mosaic appearance in the walls of capillaries.

Very early it may be remarked in the chick that the growing arteries
receive a clothing of flat stellate cells forming an embryonic adventitia.

The further development of vessels, but more especially of new capil-
laries from those already present, agrees most beautifully with all this.
On this point we have lately had some very excellent observations by
Arnold, with some not quite so recent.

An object formerly much studied has recently received much attention.

Fig. 384.— Development of fine capillaries in the tail of the
tadpole. />, p, protoplasm sprouts and cords.

386

MANUAL OF HISTOLOGY.

also, namely, the tail of the tadpole. Here (fig. 384) a rapid formation of
capillaries, from some already present, may be observed to take place, as
has long been known, by a species of budding.

Fig. 385. — From the vitreus humour of the foetal calf. Two vessels connected by a " cord " of proto-
plasm, and clothed with an adventitia. a, insertion of this cord into the primary wall of the vessels.

From the walls of already formed capillaries protoplasm is supplied
capable of further independent development (p, p). By the growth of

this those sprouts and threads
are produced to which we
have just alluded. These,
again, are converted into cords
by fusion one with another,
and the axial portion of each

,OW \\ Mb >§h-<3M thread becoming fluid subse-

quently, tubes of protoplasm
are formed.

But with this further trans-
formation of the walls a for-
mation of new nuclei goes
hand in hand. The latter
are at first small and not
sharply defined, but become
larger and more distinct later
on. From these two consti-
tuents, then, nuclei and pro-
toplasm, the vascular or en-
dothelium cells already men-
tioned are formed by a species
of segmentation (Arnold).

In fig. 385 we have repre-
sented something similar in
the formation of vessels in
the corpus vitreum of the
foetal calf. Here, however, numerous adventitial cells are also present.

The next woodcut also (fig. 386), which appeared in the first edition of
this work, represents the same thing.

Fig. 38(5. — Vessels from the tnembrana capsulo-pupillaris of
an embryonic pig, 2£ inches long, overlaid with round
adventitial cells. 1, a fine vessel with a single one of
the latter; 2, with numbers of the same; 3, three vessels.
a, 6, connected by a transverse thread; 4, clothing of
cells only on the undermost portion; 5, a vessel with
rounded cells 6, connected by a transverse branch a
(which acquires to the right at c, a new clothing of cells)
with another tube d, which shows the adventitial cells in
profile.

TISSUES OF THE BODY. 387

The vessels frequently undergo, subsequently, further development, both
in regard to form, size, and texture. Those of the gravid uterus present
a peculiar periodical increase in size. Others, as, for instance, those of the
cornea towards the close of foetal life and after birth, suifer extensive
obliteration. During this process His observed the formation of stellate
bodies resembling ramifying pigment cells.

Pathological neoplasis of vessels is of frequent occurrence. It was for-
merly supposed, however, that they were formed independently of the
normal vessels already present, the pathological tubes becoming subse-
quently united to those physiologically formed. But there can be no doubt
that the pathological have the same mode of origin as the normal.

Thus, in the regeneration of a tadpole's tail we may remark (fig. 387,
a, &, c, d) the same long known protoplasm sprouts and threads again If

Fig. 387.— Development of capillaries in the regenerating tail of a tad-
pole after Arnold, a, b, c, d, sprouts and cords of protoplasm.

we look at the same vascular region twenty-four hours later, it presents
the appearance figured in fig. 388. The protoplasm thread, d, has become
converted into a pervious capillary tube ; a, b, and c have become wide
protoplasm cords.

It appears, however, that a new formation of vessels may take place in
another manner. According to Thiersch, if a wound be made in the
tongue of mammals, a number of wall-less passages are observed between
the arteries and veins at a certain stage of the healing process, which carry
the blood. Some of these lacunar passages become later on converted
into true vessels, the neighbourhood probably supplying vascular cells, while
the greater number are destroyed. Hereafter, in speaking of the spleen,
we shall have to consider similar lacunar blood streams as existing in it.

Vascular tumours, known as angiomas, present a different structure. "We
refer the student to the handbooks of pathological anatomy.

As to the development of the lymphatic vessels we possess very little
information at present. There can be but little doubt, however, that the

388

MANUAL OF HISTOLOGY.

fine canals in the tadpole's tail have a similar origin to the blood capil-
laries.

The pathological new formation of lympatic vessels has been remarked,

Fig. 388. — The same region after the lapse of twenty-four hours.

however, as, for instance, in pseudo-membranes and adhesions, by Schroder
van der Kolk, E. Wagner, and Teichmann. W. Krause was the first to
demonstrate their presence in tumours by injection.

18. The Hair.
§212.

The hairs are productions of the corneous embryonic plate. They are
filiform appendages, composed of a modified epithelial tissue, and are of
rather complex structure. In hairs we have to distinguish between the
shaft (fig. 389, Z), which projects beyond the skin in the greater parb of
its length, and terminates above in a point, the root or lower portion
which is concealed in the skin, and ends in a flask-shaped duplicature of
the latter, called the hair follicle (a), and the bulb, which is the thickened
and rounded terminal portion (/?). The latter, hollowed out below, is
seated on a papilla (i) rising from the floor of the follicle. Between the
follicle and the proper hair is found a complex encasing sheath, which is
divided into an external (c) and internal portion (d).

It may be found most convenient if we commence our observations
with the most deeply seated portions of the structures in question, for in
them we have the source from whence the latter spring, and can observe
the earliest forms under which the tissue makes an appearance. In this
way we shall be best enabled to comprehend the further transformations
which take place until eventually the texture of the shaft is arrived at.

The hair follicle (a) is a reduplication of the cutis vera of variable
length and oblique direction. In some cases, when the hairs are long,

TISSUES OF THE BODY.

389

it may project downwards into the subcutaneous cellular tissue. Its
form is in general cylindrical ; not seldom, however, it is narrowed at its
lower end. It consists, like the corium, of fibrous connective-tissue, in
which several layers may be observed. To this one or several bundles of
unstriped muscle are attached externally, the arectores pili of Eylandt.
The outermost layer of the follicle, which may be extremely thin when
the surrounding tissue is densely interwoven, is seen to be made up of
longitudinally arranged connective-tissue bundles with fusiform nuclei
lying in the same direction. The thick-
ness of this layer usually ranges be-
tween 0-0036 and 0-0070 mm. In it a
complicated network of capillaries is to
be seen, and nerves have been in some
instances also observed.

The middle layer of the hair follicle
is in general somewhat thicker, mea-
suring from 0-0149 to 0'0233 mm. It
consists of undeveloped connective-
tissue, whose fibres have a transverse
direction, with several layers of elon-
gated nuclei, whose appearance brings
to our recollection that of the well-
known nuclei of involuntary muscle
fibres (Koelliker), although no such
elements can be clearly demonstrated
here. A capillary network is also to be
seen here, whose meshes have a direction
chiefly transverse. This middle layer
commences at the bottom of the fol-
licle, but terminates above on arriving
at about the neighbourhood of the seba-
ceous glands. The human hair follicle,
further, is surrounded by lymphatic
vessels.

Finally, the whole induplication is
enclosed in a transparent structureless
membrane (fig. 389, b-} fig. 390, g)
finely striated internally, which may
be looked upon as a modified limiting
membrane or hyaline coat. Like many
structures of the same nature, it mani-
fests great power of resisting the action
of acids and alkalies. Between this
layer and the middle, in the large tactile
hairs of some mammals, there is situated, according to Leydig and Odenius,
a highlyTdeveloped cavernous vascular plexus, which terminates above in
a circular venous sinus (Dietl and School).

According to the more recent investigations of Wei'theim, however, the
hair follicle is not, as has been up to the present generally supposed,
rounded off at its termination in the manner represented in our fig. 389.
It is continued down through its external and middle layers into a cord
of connective-tissue, which becomes at first enlarged " like a cup," and
then narrowed into a kind of " stalk." Preserving the direction of the

Fig. 389. — Human hair and follicle, o,
fibrous follicle; 6, transparent internal
layer of the latter; c, the external, and rf,
the internal root-sheath ; e, transition of
the external sheath into the hair bulb ; /,
nair-cuticle, seen at /* in the form of
transverse fibres ; g, the lower portion of
this structure; h, cells of the hair-bulb;
f, hair papilla; *, cells of the medullary
part ; /, cortical portion ; m, medulla con-
taining air; n, transverse section of the
latter; o, cortex.

390

MANUAL OF HISTOLOGY.

follicle, or bending off more at right angles, this cord pursues a downward
course to a greater or less distance, and eventually becomes continuous,
together with other of its companions, with a strong bundle of connective-
tissue down below.

Rising from the fundus of this follicle, we next see the papilla of the
hair (i), consisting of a species of undeveloped nucleated connective-tissue
with a slight intermixture of fibres. This structure may be regarded as a
modified tactile papilla of the skin. Its shape is either conical or more
or less ovoid, the length from above downwards always exceeding the
breadth ; thus the former, foi instance, may amount to 0*2256 mm., and
the latter to 0*1128 mm. In. its interior is contained a fine capillary net-
work. This papilla is the point from which the hair is developed, and

that also from whence the latter receives its
nutritive supply.

a jgp^ ^e Presence of nerves, on the other hand,

\ ^3 s^Z& lias not been remarked in the papillae of hair,
7 • /*jj%tfZ%/^^Eajffl although in man the external layer of the
^ *** follicle contains isolated fibres, which are

seen hero and there to undergo division.
According to recent observations, these latter
appear to be connected with peculiar terminal
cells situated in the external root-sheath,
which, as we have seen before (§ 187), are
also to be found in the rete Malpighii of
the skin (Langerhans).

§213.

The hair follicle being a portion of the
skin which has been folded in, as it were,
the external root-sheath (fig. 389, c; and
390, e,f) represents the undermost layer of
the rete Malpighii. As to the precise nature
of the internal root-sheath (fig. 389, d; and

390, c, d), on the other hand, there still
exists considerable difference of opinion.

If the entrance of the follicle be closely
examined, the deeper layers of cells of the
adjacent skin are seen descending as ex-
ternal root-sheath into the sac, and lining its
walls. The number of layers of these small
rounded and nucleated cells varies with the
strength of the hair (fig. 389, c; 390, e; and

391, c). The cells themselves are about
0-0074-0 -01 13 mm. in diameter. Those of
the most internal stratum are more or less
flattened, while those situated more ex-
ternally appear to be elongated in a radial direction, recalling to mind
the state of things seen in the Malpighian layer of the skin. Just as
this outer root-sheath is continuous above with the rete mucosum, so is
it continued on reaching the fundus of the follicle (fig. 389, e) into the
cellular mass of the hair-bulb (h). In some cases, however, it does not
extend so far.

The internal root-sheath is distinguished from the duller mass of the

5

Fig. 390. — Transverse section of a
human hair from the head, with
its follicle, a, the hair; 6, cuticle of
the same; c, the inner, and d, the
outer layer of the so-called internal
root-sheath; «, the external root-
sheath:; /, its peripheral portion
formed of elongated cells; g, hya-
line -membrane of the follicle ; h,
middle layer ; and t, external layer
of the latter.

TISSUES OF THE BODY.

391

£. 391.— Cells of the root-sheaths. In-
ternal root-sheath, with Henk"s layer,
a; and Huxley's, b; c, cells from the
external sheath.

outer by its lighter and more transparent appearance : it is, "besides,
thicker (fig. 389, d; 390, c, d). Two strata of large cells may be
remarked in it. The external (fig. 390, d; 391, a) (the root-sheath of
Herile) consists of transparent ovoid cells without nuclei, between 0*0377
and 0'0451 mm. in diameter. Between
these may be observed small narrow clefts,
which can be rapidly increased in size
by pressure, &c., owing to the brittle
nature of the whole mass. Within this,
again, there appears either a single or
double layer of cells first seen by Huxley
(fig. 390, c; and 391, b). These elements
are likewise transparent and polyhedral,
owing to pressure one against another.
Their axis parallel to that of the hair
is short, while their radial diameter
exceeds that of the elements compos-
ing Hentts layer (fig. 390, c, d). The
most important point of distinction be-
tween them, however, js that the cells of
Huxley's layer possess small narrow nuclei,
bringing to our recollection the appear-
ance of nail-cells seen from the side (p.
162, fig. 156).

Below, towards the fundus of the hair follicle, the internal sheath con-
sists of only one layer of nucleated cells, which may be continuous with
the peripheral elements of the hair-bulb. Above, towards the outlet of
the follicle in the neighbourhood of the sebaceous glands, it ends, how-
ever, with a sharp, jagged border.

§ 214.

We come now to the proper hair, into the bulb of which, as it rests on
and overlays the papillae, the cellular strata of the external and internal
root-sheaths are continued.

In the hair-bulb (fig. 392, h), throughout its whole substance, with
the exception of a thin coating, the same small, round, and densely-
crowded cells are to be seen as those which form the external root-sheath
(fig. 393, a). Their contents are either colourless molecules, or there
appear in them (at one time in small quantity, at another in larger propor-
tion) granules of pigment varying in tint with the colour of the hair.

Above, however, the nature of these cells is changed, and in many
hairs a contrast is distinctly seen, owing to the metamorphosis, between
the axial and peripheral portion ; we then speak of the medullary mass
(fig. 392, k) and cortical substance (I).

In the ;first place, the cells of the latter become ovoid, while the
nucleus still preserves its original spherical form. Higher up we find
these cells transformed, through flattening, into a plate of 0'0451 mm.
and upwards in length, whose nucleus has become likewise long, narrow,
and rod-like (fig. 393, b). Higher still, where the stem has attained the
hard horny consistence of the shaft, the cells acquire the nature of thin
and flat oval plates, with irregular outline (c, d), with an increase in
length to about 0'0751 mm., the transverse diameter sometimes falling to
0'0045 mm. Their nuclei are either changed into very thin filiform
26

392 MANUAL OF HISTOLOGY.

spindles, or finally disappear completely. The union, however, of these

Fig. 393.— a. Cells of the hair bulb;
6, from the first part of the shaft;
c, cortical substance treated with
sulphuric acid, resolved into sepa-
rate plates at d; e and/ are cells
f rora the hair cuticle.

Fig. 392.

hair-scales, forming the cortical portion, is so intimate that not the slightest
indication of their existence appears in the fresh hair (fig. 392, I). Even
by mechanical means we can only split off rows of them in the form of
rough splinters. Chemically, however, — namely, by the aid of sulphuric
acid, — we are enabled quickly and easily to render visible the elements of
•the structure by the solution of the matter cementing them together.

Looking upon the cortical mass as a whole, we find it saturated
with a colouring matter varying according to the tint of the hair. Together
with this the latter is marked with definite longitudinal streaks, which
either represent the borders of adjacent hair-scales, or depend upon the dis-
position in rows of the pigmentary molecules, which in darker hairs may
make their appearance in large and broad groups.

Finally, the hard dry consistence of the shaft of the hair favours
the entrance of air-bubbles, which frequently occupy small elongated
cavities in the interior of the hair-plates. We shall meet again with
a far larger accumulation of air in the medullary mass.

§ 215.

In the preceding section the presence, from the lower part of the root
up, of a peculiar thin enveloping layer, was noticed. This, as it ascends,
is known as the cuticle of the hair. Close observation of the bulb at its
base (fig. 392) shows us that, from that point on, at which its cells cease
to be continued into the external root-sheath, the structure becomes

TISSUES OF THE BODY.

393

Fig. 394.— Cuticle from the shaft ol the
human hair. One specimen shows the
medullary mass, the other not.

clothed with a double layer of small pale nucleated cells (g). Taking the
hair higher up, we see the peripheral layer of these cells assuming more a
short thick figure, even after they have lost their nuclei. They extend
as far as the upper part of the follicle, where they terminate. From the
fact that they are frequently met with loosened from the hair and
clinging to the internal root-sheath, they have been regarded by some as
representing the cuticle of the latter.

But the cells of the internal layer, which are not lost as we ascend, are
of greater importance. These remain fixed to the shaft throughout its
whole length, and communicate to it a peculiar transversely striated
appearance. The cells assume, at the upper portion of the bulb, a more
elongated form and a position more and more oblique as regards the
surface of the latter. Losing their nuclei and becoming more and more
flattened (fig. 392, /), they are gradually transformed into a series of
obliquely-placed thin and transparent scales (fig. 39 3, e,f) of 0 -03 7 7-0 '0451
in diameter, which overlap each other like roofing tiles, the lower lying
with their free edges upon those above.
Thus originates that series of delicate
irregularly undulating or jagged lines
which are seen passing across the sur-
face of the fresh hair (fig. 394; and
392,/*/), connected in a reticular man-
ner with one another by means of other
obliquely coursing lines (1). We some-
times succeed in detecting these cells,
on the outline of the hair, owing to their
upper free edge projecting from the shaft
in the form of small ridges. To show them properly, we have recourse to
the action on the tissue of solutions of soda, or, better still, of sulphuric
acid.

There still remains for consideration the axial or medullary mass of
the hair (2). This is, however, no essential constituent of the structure
in question, in that it is not to be found as a rule in downy hairs, and
is frequently absent in part or entirely in those of the head. It presents
itself in the form of a streak in the centre of the stem, occupying about a
fourth of the thickness of the latter (fig. 392, m, n; 394).

Whilst at the boundary between the bulb and commencement of the
shaft the external cells become elongated, and the transformation into
the characteristic hair-plates commences, those situated internally assume
a more or less angular form as they become arranged in several layers and
increased in size until they may measure 0'0151-0'0226 mm. These
soon lose their nuclei and dry up (fig. 392, Tc). On the other hand, small
cavities are found in great number and most extensively in the contents
of the cells, which become filled with corresponding bubbles of air, pre-
senting, owing to their tiny proportion, the appearance of fatty or
pigmentary molecules (fig. 392), which they were long supposed to be.
They communicate to the medullary substance of white hair a silvery
appearance with reflected light, whilst in coloured hair, whatever be its
tint, the white axial portion shines through. By suitable treatment we
are able to expel the air from the medulla in the same manner as from a
thin section of bone, when, on subsequent drying, it rapidly fills again.

REMARKS. — On the upper edges of the cuticular cells becoming more everted the
transverse lines appear with greater distinctness. Hairs which have been torn out

394 MANUAL OF HISTOLOGY.

frequently display an extensive folding back of the cells towards the bulb, giving rise
to the appearance of encircling fibres. 2. The medullary portion of the hair is the only
part about which there exists at present any considerable difference of opinion. The
presence in it of air was first pointed out by Griffith in the Loud. Med. Gazette, 1848, p.
844. On this point no doubt can be entertained. Steinlin held the medullary mass to
be a process of the papilla of the hair, consisting of cells, and extending into the shaft.
The lower part is, according to him, vascular, and made up of soft cells, while above,
the vessels become obliterated, and the cells shrink, making room for the accommo-
dation of air, so that the medulla might be said to be formed from the dried papilla.
Reichert supposes the dried remainder of the papilla to occupy the interior of the
medulla in the form of a delicate axial thread, and likens it to the "pith of a feather."
In some of the mammalia such an extension of the papilla into the shaft of the hair
does take place, and even far up into the latter, but in man it is doubtful that this
occurs. The representation given in the text is that most generally received, and
probably the simplest expression of observation. It is likely also that many com-
munications exist between the residual cells, which explain the rapid readmission of
air.

§ 216.

The hairs, like cuticle and the nails, are numbered among the so-called.
horny tissue*, in that from them all, by treatment with alkalies, that mixture
of metamorphosed albuminous matters can be obtained, to which the name
of keratin (p. 21) has been given. The complex structure of the hair,
however, renders this analysis of less value than that of the two other
more simple tissues.

Microchemical reaction shows that, in the hair and its envelopes, the
young recently-formed cells are still composed of ordinary albuminous
materials, so that even the more feeble attacks made by acetic acid and
dilute solution of the alkalies are capable of destroying their membranes,
and, soon after, the nuclei in the case of the latter reagents. This is the
case with the rete mucosum of the hair follicle, the external root-sheath,
and also the root of the hair. On the other hand, we are met by a most
striking insensibility to the action of chemicals in the cellular layers of
the internal root-sheath and cuticle of the hair, with the exception of
the most internal portion of both tissues bordering on the bulb. We
find that even concentrated sulphuric acid and alkaline solutions have no
action on the cells, even when the latter are treated for a considerable
time with these fluids. The latter do not even produce any amount of
swelling up in the elements, so that we have at all events peculiar kinds
of combination before us in these tissues.

The action of sulphuric acid on those dry and horny cellular plates
which form the cortical portion of the hair, causes them to separate
readily from one another, while alkalies produce a swelling up of the
cortical mass, and solution of the whole when dilute and at an elevated
temperature.

The cells likewise of the medullary mass can be recalled from the
shrunken condition in which we find them in the mature hair to their
original tense round form by these reagents.

The transparent internal layer of the follicle, finally, manifests, as has
been already mentioned, all the insensibility of the elastic hyaline
membranes.

The solubility of hair in solutions of soda and potash, with previous
swelling up, repeats, as we have already stated, what takes place with
epidermis and nail tissue under similar treatment. The products of the
combustion of hair also are similar to those of the latter. An analysis of
Van Laer's will serve as an example : —

TISSUES OF THE BODY. 395

C . . 50-65 per cent

H . . . 6-36

N . . . 17-14

0 . 20-85
S 5-00

The amount of sulphur, 4-5 per cent., seems considerable.

But little is known at present of the nature of that diffused colouring
matter which saturates the cortical tissue of the hair, or of the granular
pigment of the structure. Those fatty matters which may be extracted
in varying amount from hairs appear to contain the ordinary neutral
combinations found in other parts of the system. They probably have
their origin, for the most part, in the sebaceous glands.

The ashes of hair amount to from 0*54 to 1*85 per cent. They consist
of salts soluble in water, together with phosphate and sulphate of calcium,
silicates and oxide of iron (0'058-0'390 per cent.) Manganese, although
formerly stated by Vauquelin to exist in the hairs, has not been found
by chemists of a later period. That the presence of iron has anything to
say to the tint of the latter is very improbable.

§217.

Hairs are to be found on almost every part of the human body. They
are missed, however, on the upper eyelid, the lips, the palm of the hand
and sole of the foot, the last joints of the fingers and toes, the inner
surface of the prepuce, and on the glans penis. Their size, further, is
liable to considerable variation, as we may see from the range in their
diameter from 0'15 mm. and upwards down to even 0'0153 mm. A distinc-
tion is always made between the very pliant downy hairs (lanugo) and
those which are stronger, sometimes pliant and sometimes stiff. No
sharp distinction, however, can be drawn between them. The thickest
are those of the beard and pubis. The length of the free portion also
varies extremely, ranging from 1-2'" among the smaller downy hairs, to
4—5', as on the heads of women. Many hairs, notwithstanding their
thickness, remain exceedingly short ; this is the case in the eyebrows
(supercilia), eyelashes (cilia), and bristles at the entrance to the anterior
nares (vibrissce). The straightness or curliness of hairs depends upon
the form of their shaft. In the first instance, the transverse section of
the latter is round ; in the second, oval, or even reniform.

Hairs are found either singly, in pairs, or small groups. The oblique
direction of the follicles also brings with it great variety of position in
the various localities (Eschricht). In the several parts ol the body the
number of hairs likewise is found to vary considerably, so that, while
on the scalp 293 have been counted to the square inch, the same super-
ficial extent of the chin has only shown 39, and on the anterior aspect of
the leg, 13 (Withof). It is hardly necessary to remark that, together
with this variation, many individual differences present themselves.

The structures we are engaged in considering are remarkable for their
great strength and elasticity. They will support a considerable weight
without breaking, and return almost to their original length again on
removal of the extending force, if the latter have not been altogether too
great. Owing to their dry and horny composition, they belong to the
most durable of all the tissues of the body ; witness the hairs of mummies.
They absorb moisture greedily from without — in the first place, aqueous

396 MANUAL OF HISTOLOGY.

vapour from the atmosphere ; and again, through the bulb, from the fluids
of the neighbourhood. It is upon this property that the interchange of
matters which takes place in hairs is dependent. The latter appears to
be by no means inconsiderable, as we may infer from the rapidity with
which hairs in some instances turn grey. The appearance of air within
the medulla follows upon a process of drying up which takes place there.
The shaft of the hair, however, is also saturated with the oil of the
sebaceous secretions. As Henle very properly remarks, we may recognise
the physiological condition of the skin from the state of the hairs ; their
brittleness on the one hand, and softness, pliancy, and glossy appearance
on the other.

The growth and the nutrition of these structures takes place in a
manner exactly similar to that of the nails (p. 164). Multiplication of
cells takes place by segmentation at the lowest and softest part of the
bulb, kept up by supply of material through the blood-vessels of the
follicle, and more directly through those of the papilla?. And just as the
growth of nails can be accelerated by paring the free edge, so does cut-
ting of the ends of the structures in question favour tbeir rapid produc-
tion, as is seen in the beard after frequent shaving. On the other hand,
when both these tissues are left in the natural state, uncut, they seem
eventually to reach a point at which they cease to grow. We have
already seen that the nail may be completely reproduced so long as its
bed remains uninjured. The same is the case with the hair if its follicle
remain intact. This regeneration is called into play extensively during
the earlier periods of life ; and even later on, renewal takes place, to supply
the loss of large numbers of hairs which is sustained by the healthiest
body yearly, owing to disappearance of their roots. The hair destined
to be cast off is seen to be swollen at its lower end, and to be destitute of
the earlier excavation for the papilla. This is the "hair-knob" (Haar-
kolben) of Henle. Later on, loosening from the papilla, the whole hair
splits, and breaks up into a number of shreds, and becomes like a brush.
Pincus estimated the average daily loss of hairs from the heads of young
men to be, under normal conditions, from 38 to 108.

The phenomena of growth observed accurately by Berthold in relation
to the nails have also been studied as regards the hairs. The latter grow
more rapidly at night than during the day, and in the warmer than in
the cold seasons of the year. They are also produced more quickly when
frequently cut. Thus the hairs of the beard when shaved every twelve
hours, show a growth in the year of 12"; when cut every twenty-four
hours, only 7 J" ; and when shaved every thirty-six hours, only 6f ".

§218.

From the extensive researches of Valentin first, and then Koelliker, we
learn that the first rudiments of the hairs are formed in the human
embryo at the end of the third and beginning of the fourth month, appear-
ing first on the forehead and eyebrows (fig. 39.5). Here we find nodulated
or mamillated aggregations of cells (m) 0-0451 mm. in length, belonging
to the rete mucosum (b\ which sink gradually into the cutis by a process
of proliferation, pushing the adjacent part of the latter before them.
These cells increase rapidly in number, so that the collection soon becomes
larger and more flask-shaped. Around the latter there may now be
remarked a thin homogeneous transparent membrane (i), probably the
hyaline internal layer of the future follicle, about which the corium is

TISSUES OF THE BODY. 3.97

gradually transformed into the peripheral portion of the follicle. Up to
this stage the development of sweat glands and hairs is identical (§ 200).
Although at the commencement the whole aggregation of cells appears
solid, and of the same nature throughout, a distinction soon, makes itself
evident between an axial and peripheral
portion. From the first is formed the
hair and its internal root-sheath, from the
second the external sheath. The cells
of the last-named stratum are elongated
transversely, while those of the axial
portion of the rudimentary hair in-
crease in a longitudinal direction. This
is the state of the parts in the eighteenth

wpplr nf infra iiforiiio lifa af wViinV> fimp Fi£- 395.— First rudiments of a hair from the

week ol mtra-uterme lite, at wnicn time human embryo at 8ixteen weeks> 0> 6i

the agglomeration of Cells has attained layers of the cuticle; m, m, cella of the
a length of 0'226-0'0451 mm. rudimentary hair; < hyaline envelope.

Soon after, a new division in this internally somewhat club-shaped mass,
— broad below, and more or less pointed above, — commences ; the outer
layer, namely, with its cells, is transformed into the clear transparent
internal root-sheath, whilst the axial part, which becomes the bulb and
shaft of the hair, remains dark. At this period, also, the papilla may
be clearly seen.

The true hair thus commenced is at first short, and surrounded by a
very strong internal root-sheath, but without any recognisable medullary
substance. 'It then gradually increases in length, passes between the
undermost cells of the epidermis, and perforates the latter either immedi-
ately or after turning on itself, and taking an oblique course for a certain
distance.

The other hairs are developed in a manner exactly similar, but later.
At the end of the sixth or commencement of the seventh month, most of
them have made their appearance through the epidermis. The hairs, so
appearing by perforation of the cuticle, are thin and light-coloured.

In regard to the regeneration of hairs it must be remembered that
many of the downy ones are cast off during intra-uterine life, and become
mixed up with the waters of the ovum. After birth, however, this
change of hairs increases in amount, the new appearing in the place of the
old. Even at an advanced age this regeneration does not cease in man.
Among the mammals, as is well known, a very extensive renewal of hair
takes place periodically. In regard, however, to these processes there
still exists considerable difference of opinion.

It was Koelliker who first observed the regeneration of hairs in the
eyelids of the infant (fig. 396). From his statements it will be seen, in
the first place, that the bulb of the old hair separates from its papilla,
from which the rudiments of a new structure are produced in the form of
a conical mass (A, m).

Above' this, consequently, lies the loosened hair (de), horny down to
the very bulb. This rudimentary structure (B) is transformed into hair
bulb (/) and shaft (bh), with inner root-sheath (g), in a manner pre-
cisely similar to that we have already seen in the formation of hair in the
embryo. The inner root-sheath of the old hair disappears from the com-
mencement, and the new-comer drives its point by the side of the first,
which is displaced, through the outlet of the follicle occupying the whole
of the latter as soon as its former occupant falls out. Koelliker has also

398

MANUAL OF HISTOLOGY.

stated that with this process there takes place, farther, a growth downwards

of the follicle into the cutis, but this view is combated by other observers.

This mode of explaining the regeneration of the hair from the old

papilla, from what we and others
have seen, is, we consider, quite
correct. Whether it includes all
that occurs at the time of change,
is another question.

According to Stiedas state-
ments, on the other hand, the
papillse of those hairs which are
..ft about to be cast off degenerate.
A residue of those indifferent
formative cells, however, from
which, as we have seen, the
specific tissue of the hair is formed
(§ 214), remains behind in the
fundus of the follicle, commences
then to grow downwards into the
cutis, and becomes cupped by
pressing down upon a new papilla
rising and formed from the latter.
From this cellular mass covering
the papilla the new hair takes its
origin.

That the whole structure — fol-
licle, outer root-sheath, and hair —
may be newly formed under
normal conditions, at a later
period of life, appears probable ;
indeed, Wertheim believes such an occurrence to be the rule in the
change of hair in the human being. This requires, however, more care-
ful investigation.

Pathological neoplasis of hairs and follicles, on the other hand, does
occur without doubt under the most extraordinary circumstances. Hairs
are met with on mucous membranes, but only extremely rarely ; again,
on the internal surface of follicular tumours or cysts in the skin and
ovaries, in which case the wall of the cyst has been found to have
assumed a similar constitution to the outer skin, and to contain not
only hair and sebaceous glands, but also sweat glands. Transplantation
of hairs, together with their follicles, succeeds likewise.

Search among the follicles often brings us into contact with hairs
destined to fall out. These have parted from the papilla upon which
young cells and pigmentary matters are to be seen. The appearance of
their roots is also altered; they seem as though broken up into fibres
resembling in figure the end of a broom, and are, like the whole hair,
paler and free of pigment. Beneath these the root-sheaths and follicles
are narrowed for a greater or less distance, and in the latter small newly-
formed hairs may be met with,

§219.

The tissues we have been engaged in describing up to the present, are
combined in various ways, and under great variety of outward form, to

Fig. 396.— From the eyelid of a child of a year old,
showing new formation of hairs at the bottom of the
sacs. A, early, £, later stage of development, a,
external, g, internal root-sheath; d, bulb, and «,
shaft of the old hair; i, sebaceous follicles; k,
ducts of sweat-glands; c, funnel-shaped pit at
base of the new rudimentary hair which is
seen at m, fig. A, to be still quite homogeneous;
whilst in fig. B the bulb /, stem 6, and point h,
may be recognised.

TISSUES OF THE BODY. 399

produce the several organs and apparatuses of the body. These organs,
whose performances are dependent on the individual qualities of the
various tissues of which they are composed, present far greater difficulties,
as regards their classification, than the tissues themselves (§ 64), — the
more so, as we are unable accurately to define what is precisely meant
by an organ. If we compare the many apparatuses of the body, we find
the greatest differences existing as regards their construction. Some of
them are formed in the simplest manner of one single tissue, as, for
instance, the nails, the lens, the vitreous humour. Their performances,
in such cases, may also agree with the physiological energy of the tissue.
Other organs, however, are combinations of several, of many, nay, even of
most, of the tissues of the body. It will suffice to point, by way of
example, to the organs of vision. Thus, here, as in the classification of
tissues, the systematic worth of the terms simple and compound seem to
recommend them for use. This principle of division, however, can be by
no means so strictly adhered to here, owing to the multitude of organs, as
was the case in dealing with the tissues.

It is a common mode of classification among anatomists to group
the organs of the body in particular systems. By this we understand
the arrangements of parts together, which are found to be identical or
similar as regards the finer composition of their tissues. Thus the
present divisions into nerves, muscles, osseous, and vascular systems have
been arrived at. We also speak, however, of a digestive and generative
system, where this similarity of texture in the various parts making up
the whole by no means exists. Thus in the many manuals which treat
of these subjects the greatest differences as regards classification may be
observed.

It may be found most expedient, then, if we base the third section
of this work upon the principle of physiological classification, and make
use of the old division of organs, into those which take part in the
vegetative occurrences of the body, and those belonging to the animal
side of life. It cannot be denied, however, that this classification will
not everywhere hold good; for in the wonderful linking of parts one
with another there occur many intermediate forms. Thus nerves and
muscles make their appearance in apparatuses belonging to the vege-
tative sphere, blood and lymphatic vessels, and glands in animal organs,
and so on.

Starting from this point, then, we come to another mode of grouping parts,
namely into apparatuses, that is, a combination of a number of organs for
the carrying out of some one physiological purpose. A system and
apparatus may correspond, as in bony, muscular, and nervous portions of
the body, but do not necessarily. Thus from one point of view there is
such a thing as a digestive and respiratory apparatus, but not a diges-
tive and respiratory system. 'The following is our classification of
organs :—

A. Belonging to the Vegetative Group.

1. Circulatory apparatus.

2. Respiratory apparatus.

3. Digestive apparatus.

4. Urinary apparatus.

5. Generative apparatus.

400 MANUAL OF HISTOLOGY.

B. Belonging to the Animal Group.

6. Bony apparatus or system.

7. Muscular apparatus or system.

8. Nervous apparatus or system.

9. Sensory apparatus.

Having been obliged, in speaking of the different tissues, to refer fre-
quently to their arrangement in the formation of various organs, or their
constitution within composite apparatuses, the discussion of this third part,
or Topographical Histology, will be very irregular as regards. the several
parts. The chief object to be kept in view will be the description of the
finer structure of organs, with reference to that, in the microscopical
relations of the same which could not before be brought under notice.

m.

THE

OEGANS OF THE BODY.

III. THE ORGANS OF THE BODY.

A. Organs of the Vegetative Group.

1. Circulatory Apparatus.
§220.

As we have already considered the blood and lymphatic vessels in the
second part of our work (§§ 201-211), we shall here be engaged merely
with gleanings from what has been previously referred to. Thus we have
to describe the heart, the lymphatio glands and lymphatic, organs, with
the spleen, as well as the remainder of the so-called blood-vascular glands.

The heart — the muscular central organ of the circulatory system —
consists of the pericardium, a serons sac (which has been previously
referred to, p. 226) of muscle, and of the so-called endocardium. The
latter is analogous to the T. intima of larger vessels (§ 204), while the fleshy
mass of the organ corresponds to the mus-
cular layers of the latter. Many modifi-
cations, however, are apparent.

The pericardium corresponds in its
texture to many of the true serous sacs.
It presents for consideration a thick pari-
etal and thin visceral portion. The latter
is connected with the fleshy mass of the
organ by means of that connective-tissue
known as subserous, and shows espe-
cially in the grooves of the heart, but at
times also over nearly its whole surface,
collections of fat cells (p. 198).

The vessels of this structure have
nothing special about them, and the nerves
of the parietal layer are supplied, accord-
to Luschka, by the right vagus (ramus
recurrens) and phrenic. The epithelium
has beeri already dealt with at p. 139,
and the fluid contents of the sac at p.
230.

We have likewise considered the stri-
ated muscle of this involuntarily acting organ while speaking of muscle
generally at p. 292.

The connection of the reticularly united muscular fibres one with
another (fig. 397) is very peculiar. They are not, as in other striped

y p'Tjipj Moggr^

Fig. 397.— Muscle-fibres from the heart,
after Schweigger Seidel. To the right the
boundaries of the cells and the nuclei
are to be seen.

404 MANUAL OF HISTOLOGY.

muscle, collected into bundles, excepting the trabeculce. carneoe, in.pectinati
and papillares. The single fibres lie rather closely crowded side by side,
held together by a small quantity of connective-tissue.

As is well known, the strength of the fleshy mass varies much in the
different divisions of the heart. It is most massive in the left ventricle,
thin in the two auricles, and weakest in the right of these. The course
which the fibres take is also very complicated, for which reason we shall
confine ourselves to only a few of the chief points of interest as regards it.

The course of the fibres of the heart, which is different in the auricles
and ventricles, may be divided into longitudinal and circular. This
distinction, however, can only be made with accuracy as regards the
auricles, and not the ventricles. It is a remarkable fact, further, that
some of the muscular fibres are common to the two auricles, and another
to the two ventricles, while each of these four parts possesses also its
special fibres.

The starting-points of the fibres of the heart are usually held to be
the two annular masses of fibres which encircle the ostia venosa of the
ventricles, known as the annuli fibro-cartilaginei. They consist of very
strong connective-tissue, with very delicate elastic fibres. Sometimes
their tissue assumes a similar appearance to that of the perichondrium at
its transition into true cartilaginous tissue.

From these rings the fibres take their origin, and return, after travelling
round the cavities of the organ, to be inserted into them again, thus
forming loops. In consequence of this, both auricles and ventricles must
contract towards these points, the Bases of the ventricles, during systole
of the organ.

In the auricles we encounter in the first place, as most internal layer,
bundles of fibres springing from tbe ostium venosum, and forming a series
of loops, which arch over the cavity, producing a kind of dome. From
their peculiar development in the right auricle they give rise to the m.
pectinati. This layer is enveloped by another stronger one, formed of
circular fibres, which is in the first place distinct for each of the auricles,
and then specially developed on the anterior aspect of the organ, it
includes both of them in common. Finally, surrounding the openings
of the veins we find circular fibres, continued to a certain distance over
the wafts of these vessels.

The arrangement of the fibres of the ventricles, however, is more
complex. In the first place, it may be remarked that the left ventricle
possesses a special set of fibres. The right has likewise its own, which
are, however, so arranged as to strengthen the muscular mass of the left,
being produced into it. Finally, fleshy fibres are to be seen, which,
starting from the left ventricle and returning to the same, surround in
their course the right cavity in loops.

It may be remarked, namely, that from the fibrous ring of the left side,
and from the aorta also, in the whole circumference of the ventricle, a
number of longitudinal fleshy fibres take their origin, which descend on
the one wall in its outer portion, and bending round at the apex of the
heart, return in the inner surface of the opposite wall to the annulus fibro-
cartilagineus. Owing to the oblique course of these fibres, they cross
each other at the apex of the left ventricle, forming there the so-called
vortex of the heart. In the right ventricle, likewise, we meet with an
origin of fibres from the annulus fibro-cartilagineus. There one limb of the
loop pursues a course in a similar manner down to the apex of the right

ORGANS OF THE BODY. 405

cavity, but passes then, not into the opposite wall of the same, but into
the wall of the left ventricle, arriving eventually at the left fibrous ring,
where it terminates.

Besides this peculiar arrangement of the fibres, which is, however, on
the whole a longitudinal one, there is also a circular set. This takes its
rise from the left annulus, and surrounds the wall of the left ventricle in
figures of eight, while other fleshy bundles arising in the same region
envelope the right chamber in simple loops. These different masses of
fibres lie between the longitudinal. From the right annulus also, though
in much smaller number, similar fibres take their rise, encircling the wall
of the left ventricle in the same kind of simple loops. Finally, we have
another set of circular fibres, which, springing from the right annulus,
return to be inserted into the same, encircling in their course the conus
arteriosus.

The musculse papillares are formed both from, the longitudinal and trans-
verse fibres.

In conclusion, we must devote a few lines to those peculiar structures,
discovered in the year 1845 in the hearts of horses, cows, sheep, and
pigs, which have been named, in honour of the discoverer, the fibres of
Purkinje.

These present themselves as flat grey jelly-like threads, spread out in a
reticular manner, immediately under the endocardium, on the internal
surface of the ventricles. They penetrate further into the muscular
papillares, and stretch across various depressions in the walls of the heart.

Purkirtje's fibres (which were subsequently found to exist in the hearts
of deer and goats) are structures whose significance is far from being
understood as yet. We may see that they consist of rows of round or
polygonal nucleated bodies, ranged side by side, or one over the other,
which have received the name of " the granules." Between these is
noticed a plexiform or reticulated arrangement of the so-called "interstitial
substance." The latter consists of thinner or thicker fibres of striped
muscle, which can be followed into the substance of the heart. Those
cell-like bodies which lie in the interstices also frequently present a
transverse and longitudinal striation, and may unite finally with the
surrounding striped network to form stronger muscular fibres.

For our own part we look upon the whole as a strange complicated
interlacement of cardial or endocardial muscle fibres, which have remained
stationary at an embryonic stage of development. We refer the reader
to the genesis of the latter (§ 172).

§221.

All the cavities of the heart, with their inequalities and projections, are
clothed with an endocardium of varying thickness. This structure is
thinnest in the ventricles, where it is presented to us in the form of a
delicate membrane, and thickest in the atrium sinistrum, where it forms
a tough lining.

It consists of several layers. As a substratum may be recognised an
elastic lamina with abundant elastic fibrous networks, and corresponding
poorness in connective-tissue. Internally appears a specially dense lamella
of an elastic network supporting a coating of simple endothelium (p. 139).

The external layer contains, besides, in the ventricles, smooth and
transverse muscle fibres ; but in the auricles only a few scattered contractile
fibre-cells are to be found (Schweigger-Seidel).

406 MANUAL OF HISTOLOGY.

The valves betAveen the auricles and ventricles (valvulce tricuspidales
and mitrales) are duplicatures of endocardium, Avith a strong middle layer
of fibrous tissue, derived principally from the fibres of the annulus fibro-
cartilagineus, and expansions of the tendons of the musculi papillares.

On one aspect they are clothed with the strong endocardium of the
auricle, on the other by the thinner of the ventricle.

Under the first of these endocardia muscular bands are prolonged into
the valves from the muscular substance of the auricle penetrating to
various depths (Gussenbaur).

Finally, the whole is covered with simple endothelium. The semi-
lunar valves also of the arteries have a similar structure, except that the
middle layer is thinner.

The blood-vessels of the heart present in its muscular substance the
most typical form of the elongated mesh-work (p. 370). Several capil-
laries pass immediately and together into one strong venous root. The
ready outflowing of the blood is thus better provided for than elsewhere.
The endocardium is only provided with vessels in its undermost connec-
tive-tissue layer. A few may also be seen in the auriculo-ventricular
valves, but none in the semilunar (Gerlach).

The heart is supplied with lymphatic, vessels in considerable number, and
according to Ebertli, Belajeff, Wedl. The two leaves of the pericardium,
as well as the endocardium, contain dense networks of coarser or finer
trunks. In the interior of the auricles they appear more scanty than in
the ventricles. In the chordae tendinese, on the other hand, they are not to
be found, and in the semilunar and auriculo-ventricular valves are only
present in small number. The fleshy substance of the heart does not
appear to be so richly supplied with them as was formerly supposed by
Luschka.

The nerves of the heart have their origin from the cardiac plexus, which
is itself made up of branches from the vagus and sympathetic.

The course of the numerous nervous stems is alongside of the blood-
vessels until they spread out in the auricles and ventricles. The auricles
are poorer in nerves than the ventricles, of which the left is the most
richly supplied. The nerves of the heart appear more or less grey, and
consist of fine medullated tubes with an intermixture of Eemak's fibres.
They terminate for the greater part in the muscle, while some of them
may be traced into the endocardium. All efforts to elucidate the mode
of ultimate termination here have hitherto proved futile in man and the
mammalia generally. The occurrence of numerous microscopically small
ganglia is also peculiar. The latter appear on the nerves imbedded in
the substance of the heart, especially in the neighbourhood of the trans-
verse groove and septum ventriculorum.

Physiology, as is well known, has brought to light the interesting fact
that these two kinds of fibre elements are entirely different in function.
Whilst the sympathetic, namely, preside over the contraction of the
muscle, having their chief centres of energy in the ganglia just referred
to, so that the heart continues to pulsate after removal ; the vagus fila-
ments exercises a completely opposite influence, causing, when stimulated,
an interruption to the motor power of the sympathetic elements, and to such
an extent also that the heart comes to a standstill in a condition of diastole
(E. Weber). It is possible that the fibres of the vagus may terminate in
the cardiac ganglia, i.e., in their cells.

Regarding the composition of the muscle of the heart, vide chemistry of

ORGANS OF THE BODY.

407

muscular tissue (§ 170, p. 295). The occurrence in it alone of inosite is
a fact of great interest.

The structure of the arteries and veins has been already discussed in
§§ 203 and 204, that of the capillaries in §§ 201 and 202.

§ 222.

We now turn to the consideration of those peculiar bean-shaped and
very vascular organs, the lymphatic glands or lymph-nudes, which occur
in the bodies of the higher vertebrates, interrupting the course of the
larger absorbent vessels. They are met with in greatest number on the
lymphatic trunks of the intestines, and at those points where superficial
and deeper sets of vessels join. It not unfrequently comes to pass that
one single vessel is in this way interrupted over and over again by sucli
nodes, and it is probable that every trunk in its course from the peri-
phery to the ductus thoracicus has at least one such. In those lymph-
nodes, which are not very minute (fig. 380, a), we usually find several
lymphatic twigs penetrating into their interior from the convex border.
These are the vasa afferentia (/, /). From the other side either one or
more vessels (in the first case of greater calibre), make their exit, known
as the vasa efferent ia (h). This takes place as a rule at a point where a kind
of depression may be observed, and where the larger blood-vessels enter
the organ. This spot, when the depression is present, is named the bilus
(h). It is entirely absent, however, in many glands.

The internal arrangement of the lymph-nodes is a point most difficult
to determine, and it is only very recently that any satisfactory insight has
been gained into their
minute structure. We
learn, besides, from recent
observations, that the organs
in. question display consi-
derable variety, both as re-
gards volume, compared
with the size of the mam-
mal body, and also their
locality ; so that the struc-
ture, for instance, of a
large lymph-node from an
ox, and a small one from
a rabbit or Guinea-pig,
exhibits great difference.
Were this axiom allowed
its due weight, we should
be spared many unprofit-
able controversies.

In those lymph -nodes
which are riot altogether too small we can distinguish a reddish grey cor-
tical portion, consisting of round bodies, the follicles (d), and a darker
spongy medullary portion, composed of the tubes and reticular prolonga-
tions (e) of these follicles.

Each lymphatic gland is enclosed in a thicker or thinner fibrous enve-
lope (a), moderately vascular, and consisting of ordinary connective-tissue
cells, fibrillated interstitial substance, and elastic elements. A continuous
layer of muscular tissue does not occur in this envelope. The outer
27

Fig. 398. — Section of a small lymphatic gland, half diagram-
matically given, with the course of the lymph, a, the enve-
lope ; 6, septa between the follicles or alveoli of the cortical
portion; c, system of septa of the medullary portion, down
to the bilus of the organ; e, lymph-tubes of the medullary
mass; /, different lymphatic streams which surround the
follicles, and flow through the interstices of the medullary
portion ; gr, confluence ot these passing through the efferent
vessel; 7i, at the bilus of the organ.

408

MANUAL OF HISTOLOGY.

portion of the tissue in question merges into a formless connective-tissue
mass, not unfrequently very rich in fat-cells.

Internally the capsule gives off a very extensive system of either simple
or extremely complicated septa (b, b, c), which divide the interior of the
organ into a number of intercommunicating cavities by splitting up and
again becoming united. These spaces are occupied by the proper lym-
phoid tissue.

The septa correspond in structure with the tissue of the capsule.
They consist of fibrous connective-tissue, intermixed with smooth mus-
cular fibres. These latter are found in certain cases in large number,
as in the inguinal, axillary, and mesenteric glands of the ox (His).
According to Schwartz, the muscular fibres at the line of junction of the
medullary and cortical portions have a principally radiating arrangement.
The partitions of which we are speaking usually spring from the interior
of the capsule, with broad bases, between the rounded ends of the follicles,
descend perpendicularly between the latter, and undergo a change below,
where, as we shall soon see, the lymphoid tissue presents likewise a differ-
ent arrangement. At the transition from cortical to medullary substance
a general splitting up and subdivision of these connective-tissue plates
take place, the latter decreasing greatly in thickness. But no follicle is
completely ensheathed at its under surface in this system of septa. On
the contrary, either one or several gaps, or even wide deficiencies, are left,
through which the follicular tissue comes into immediate contact with

the medullary substance.

s> i i i ••••• PI n

the

In the same way
partitions passing in-
wards between adjacent
follicles may be inter-
rupted by massive bridges,
as it were, of lymphoid
tissue, by which these
are connected one with
another.

§223.

By means of this ar-
rangement of partitions
just mentioned, the corti-
cal portion of each lymph-
node is divided into a
smaller or larger num-
ber of usually roundish
bodies (fig. 399, b, c)
known as the follicles.
These, however (figs. 398,
d, and 399), do not come
into contact with the sur-
face of the septum ; there
remains rather a remark-
able interspace, of greater or less breadth, between the two, called usually
the investing space of the follicle (fig. 399, i).

The follicles themselves may be either closely crowded together or moro
or less widely separated, and are arranged sometimes in a single layer, and

Fig. 399. — Follicle from the lymphatic gland of a dog in vertical
section, a, reticular sustentacular substance of the more
external portion; 6, of the more internal, and c, of the most
external and finely webbed part on the surface of the follicle;
d, origin of a tliick lymph-tube ; e, the same of a thinner one ;
/, capsule; g, septa; AT, division of one of tbe latter; i, invest-
ing space of the follicle with its retinacula; A, vas afferens;
//, attachment of the lymph-tubes to the septa.

OEGANS OF THE BODY. 409

sometimes bedded in several rows one over the other. Owing to this, the
depth of the whole cortical portion in the different lymphatic glands is
liable to great variation.

Further, the diameter of the follicles varies according to the species of
animal, and also the region of the body. It may range from 0'3760 to
1*1279, or even 2 -25 5 8 mm., and upwards.

The form of these constituents of the organ is generally roundish,
bulging greatly towards the circumference of the gland. Exceptions,
however, are frequently met with here also. When closely crowded, the
follicles of the cortical portion exhibit usually a certain amount of
accommodation towards each other, leading to a more or less definite
polyhedral flattening of each. Besides this, the fact that the follicles are
pointed at their internal portion, which is directed towards the centre,

Fig. 400. — Reticular connective substance from a Peyer's follicle of an old
rabbit, which may also be made use of as exemplifying the structure of
the follicles of lymph-nodes, a, the capillaries; 6, reticulated susten-
tacular matter of connective-tissue with shrunken cell-bodies ; c, lymph-
cells.

is quite apparent in most cases, so that the whole presents a somewhat
pear-shaped form (fig. 398). More distinctly pronounced variations may
be met with when in the cortical portion of a lymph-gland several rows
of follicles are crowded one over the other.

With the tissue of the follicles (fig. 400) we have already been made
acquainted (§ 117, p. 195). It consists of reticular connective-tissue,
formed of the well-known cellular network, in all directions continuous,
with roundish polyhedral or irregularly shaped meshes. It is, however,
liable to vary greatly, both as to the bodies of the cells, the number and
strength of their processes, and the breadth of the meshes formed by the
interlacement of the latter. These differences depend upon the age and
turgescence of the lymph-gland, and also upon its state as regards health
and disease.

410 MANUAL OF HISTOLOGY.

If a lymphatic gland from a new-born child be examined closely, it
will be seen that in some part of each nodal point in this network there
is a distinct cell-body, with a plump nucleus measuring 0'0045-0'0056
mm. in diameter. The breadth of the meshes is 0'0097 and 0'0160 mm.,
but may rise to 0.0139-0.0226 mm. The cellular nature of the network,
however, may at other times be far less evident.

In the adult we most usually meet with either a rudimentary shrunken
nucleus, or indeed none at all, in the but slightly thickened nodal points.
The openings of the meshes may be stated on an average to be O'OllS-
0'0194 mm. The septa may be fine or coarse, and vary in many respects.

In the mammalian body the same appearances are presented in the
sustentacular matter, and similar varieties of the latter.

]S"ow, though the structural relations just mentioned are easy of recog-
nition, the question as to the peripheral demarcation of the follicle
involves us in much difficulty. One thing is certain, namely, that they
.have no investing membrane. We may see, on the contrary, that the
cellular network, whose meshes are largest in the centre of the follicle
(fig. 399, b), becomes more dense towards the periphery (a), the meshes
which have been so far of roundish figure assuming the form of longi-
tudinal slits of considerable minuteness. The cellular nature of the net-
work is also more and more lost here, bands with numerous ramifications
being most abundant. Finally, on the surface of the follicle these fibres,
arranged like an elastic network of great denseness, envelope the former,
following all its curves (c). The small slits bounded by them usually
measure in their greatest diameter only 0-0081-0*0065 mm. Through
these small openings the passage of fluid, of fat molecules, and also of a
certain number of lymph-corpuscles may take place with great ease.

As to the investing space spoken of above, it resembles, as we shall see
later on, that of many of Peyer's follicles. It may be observed surround-
ing every normally constituted follicle of the lymphatic glands, though
it disappears under many structural changes induced in these organs by
disease. It invests the whole follicle in the form of a perfectly continuous
transparent line, of by no means equal thickness, however, at all points
(fig. 398 ; and 399, i). Its breadth is usually about 0'0194-0'0303 mm.
and upwards.

Within this space a varying number of lymphoid cells are to be seen.
If these be removed by brushing, a second tissue element then presents
itself, occupying the investing space, namely, a system of solid fibres (i),
which, springing from the internal surface of the capsule and sides of the
partitions, take a radial course towards the surface of the follicle, to be
inserted into the narrow meshed cellular network situated here. Thus,
taking their rise from the capsule and the surfaces of the septa, they hold
the follicle stretched and tense, as embroidery is fastened within a frame.
In consequence of this, collapse of the delicate follicular network is pre-
vented, and the fine slits in the surface of the latter are retained in an
open condition, — provisions of importance as regards the lymph-stream and
the whole life of the organ. The retinacula in question present themselves
either in the form of non-nucleated, coarse or fine fibres, or bands, usually
giving off branches at an acute angle ; or there may occur in the nodal
points of the former nuclei showing that we have to do with a system of
cells. Here again we have presented to us the various forms of that so
varied group, the reticular connective-tissues.

ORGANS OF THE BODY.

411

§224.

We now turn to the medullary portion of the lymphatic glands.
This may be looked upon in its complex nature as a continuation of
the cortical septa and the substance of the follicles with their investing
spaces and retinacula.

Under microscopical analysis many varieties are observed to exist in
the nature of this portion of the gland, according to the age of the animal
from which the latter has been taken. Thus it is more fully developed
m younger, as a rule, than in older bodies, in which it appears more
or less degenerated. It is observed to differ also, to a certain extent
according to the species of
animal examined. Finally,
the medullary substance of
the lymph-nodes belonging
to the interior of the body,
and especially to the diges-
tive tract, as a rule, displays
a higher degree of develop-
ment than those situated
more superficially, as the
inguinal and axillary glands.

Let us commence with
the septal system, formed of
connective-tissue. This (fig.
401, c), supposing it to be

moderately developed, is the continuation of the interfollicular partitions,
and consists of fine, but dense, connective-tissue plates and bands,
uniting with one another at acute angles at intervals, or dividing in
the same way one from another. Eventually, in the neighbourhood of
the bilus, i.e., of that point at which the efferent
vessels leave the organ (b), the connective-tissue
septa converge and unite to form a common fibrous
mass. The latter again exhibits in its amount the
greatest variety imaginable. Whilst in many of
the internal lymph-nodes it is extremely insignifi-
cant, or even almost entirely absent, it may attain
enormous thickness in others, especially those lying
less deeply, encroaching upon the lymphoid tissue
of the medullary substance.

To this massive fibrous structure, arising from
the union of the septa, the name of the connective-
tissue nucleus (Frey), or hilus-stroma (His) has been
given.

Turning to the essential, i.e., lymphoid portion
of the medullary mass (e), we find it to be made up of cylindrical tubular
elements, which, connected with one another in a reticulated manner, give
rise to a peculiar spongy tissue, whose interstices correspond to prolonga-
tions inwards of the cortical investing spaces. We shall speak of these
cylindrical elements for the future as the lymph-tubes ("medullary tubes "
of His) and of the system of lacunae between these, under the name of
lymph passages of the medullary substance (cavernous passages).

Let us now glance, in the first place, at the lymph-tubes (figs. 402,

Fig. 402.— Lymph tube f run
the mesenteric glands cf a
dog. a, capillary, 6, re-
ticular connective sub-
stance forming the tube.

412

MANUAL OF HISTOLOGY.

403, 404). These vary extremely in thickness, besides which one and

the same tube may exhibit
at different parts of its
course very different dia-
meters. Fine lymph tubes
may measure 0'0361 mm.,
or even considerably less,
across, whilst others show
a thickness two or three
times as great. Even in the
smaller mammals some may
be met with of 0-0902-
0'1263 mm. in diameter.
In the large lymph-nodes of
the ox tubular elements of
the medullary substance
may be encountered present-
ing a still greater diameter.
If we now pass on to
the structure of the lymph-
tubes, we have the most
striking picture presented
to us on rilling the blood-
vessels artificially; all the
lymph-tubes, namely, are
traversed by blood-vessels,
so that they appear like
lymph-sheaths around the
latter. According to their
strength, we find the axis
occupied by either an arterial twig, a capillary (figs. 402, a ; 403), or

a small venous branch. If, as is the case
in larger animals, the lymph tubes are of
considerable thickness, their vascular system
is more complicated, as is seen in fig. 404,
a. Here also an arterial or venous twig
passes through the axis, while the peripheral
portion is traversed by interlacing capil-
laries belonging to the axial vessel and
forming elongated meshes.

The tissue of the lymph-tubes is again
reticular connective substance ; a cellular
or banded network (fig. 402, £>), which
surrounds the blood-vessels and takes the
place of an adventitia.

In thick lymph-tubes also the reticular
character may be recognised in their in-
terior. The surface likewise is often ob-
served with the greatest distinctness to
have mesh-like slits. In finer tubes, as
also in those of the smaller animals, such

Fig. 403.— Lymph tubes (a, a) from the medullary portion of
the pancreas Asellii of the rabbit, with simple vessels and
their branches, 6, b. Between them is to be seen a strongly
stretched cellular network c.

Fig. 404. — From the medullary substance
of the inguinal gland of the ox (after
His), a, Lymph-tube with its com-
plicated system of vessels ; c, portion
of another; d, septa; b, retmacula
stretched between the tube and the
septa.

as the rabbit (fig. 403, a, £>), the external surface may become more or
less membraneous and homogeneous, resembling a hyaline glandular

ORGANS OF THE BODY.

413

tube to a certain ex'.ent. This variety, in the demarcation of the forma-
tions in question, is explained by the changeable nature of reticular
connective substance.

We are now met by the questions, whence come these lymph tubes ?
what is their origin, and what becomes of them ?

It is comparatively easy to recognise the origin of the lymph-tubes
from the follicles (fig.

405). They spring from ^ ^^ ^^.^^ • %

the under surface of the
latter (d, e), and it ap-
pears always several of
them together. The sus-
tentacular matter of the
follicle becomes the band-
ed network of the lymph-
tube, and the blood-vessel
of the latter enters the
follicle at this point. At
this under surface the
septal system is very fre-
quently extremely imper-
fect ; com p. fig. 401.

Passing on now to the
consideration of the se-
cond question, namely,
What becomes of the
lymph, tubes 1 nothing
would seem more natural
— bearing in mind the parallelism of the latter with the blood-vessels —
than that they should converge towards the hilus of the organ, forming
eventually by their confluence, and on separating from the latter, the
vas efferens ; and, indeed, this utterly incorrect view of the state of parts
has been put forward by some. More accu-
rate observation, however, of the medullary
portion of the gland convinces us that no
such thing takes place, but that the net-
work of the tubes, just as it took its rise
on the one hand from follicles, so is it on
the other hand continuous (subject to many
variations certainly) with other follicles
(fig. 401). Consequently, in this highly
developed reticular arrangement of the
lymph tubes of the medullary substance,
we have nothing but a very complicated
system of intercommunications between the
follicles of the lymphatic nodes.

Recognising now the medullary mass as
a network of lymph-tubes, we must, of
course, expect to meet with a correspond-
ing system of interstices. Throughout these lacunse (sometimes in the
greater part of them (fig. 388, b), sometimes only in some few) the system
of connective-tissue septa with which we have been already made ac-
quainted extends. But, as was before observed, in regard to the parti

Fig 405.

Fig. 406.

414

MANUAL OF HISTOLOGY.

tions in the cortical portion, the septa do not come into contact with the
lymphoid .substance here either. On the contrary, we find, — as in the
first case, so here also, — the lymph-tubes and septa, or, where the latter
are absent, the lymph-tubes alone, separated from one another by a nar-
rower or broader interval analogous to the investing space of the follicle.

There now remains for consideration the contents of these reticulated
passages of the medullary substance. Here, as in the investing space of
" the follicles, a certain number of lymph-corpuscles are to be found, which
may be removed with a brush. Besides these, we observe that a con-
nective-tissue network, with a varying amount of nodal points, nuclei, and
processes, occupies the passages with wide straggling meshes (fig. 406, b;
405, I). Springing on the one hand, from the septa of the gland, its fibres
sink on the other into the reticular tissue of the lymph-tube, or, where
there are no septa, connect one lymph-tube with another.

Not unfrequently in the mesenteric glands, as for instance in the
pancreas Asellii of the rabbit, some very interesting points in regard to
the cellular network occupying the interstices of the medullary substance

may be observed (fig. 407,
c). The bodies of the cells
appear tense and swollen :
they have, moreover, no
membrane. Their processes
or ramifications are like-
wise thickened and broad.
Within both the bodies
and their processes, be-
sides soft -looking nuclei,
isolated lymph corpuscles
are to be seen ( W. Muller,
Frey\ which may have
come there either by im-
migration or possibly by
generation on the spot.
The possibility of this
latter alternative remains,
however, still a matter of
uncertainty.

If we follow up the rebi-
cular interstices of the
medullary substance to the
boundary of the latter, we
have no difficulty in re-
cognising the fact (especi-
ally if we carry our eye
along one of the partitions)
that they lead into the investing spaces of the follicles (fig. 405).

From all this we learn that the lymph-nodes are formed of a system of
cavities (imperfectly bounded by septa) which are occupied by lymphoid
matter — in the cortical portion by the follicles, and in the medullary by
the lymph-tubes — but always so arranged that the lymphoid substance
does not come into contact with the fibrous septal system. Thus we
have both a series of spaces, encasing, as it were, the follicles, (investing
spaces), and a system of intercommunicating passages enveloping the

Fig. 407.

ORGANS OF THE BODY. 415

lymph-tubes (the lymph-passages of the medullary portion. Throughout
this extremely complicated cavity in the larger lymph-glands, then, a net-
work of fibrous bands and cells extends, springing from the lymphoid
substance on the one hand, and is attached to the septa on the other,
holding the whole lymphoid sustentacular matter in a tense condition.

We must now turn to the more active portions of our organ, namely,
the blood and lymph streams.

§ 225.

Artificial injection of the blood-vessels of lymph-nodes is a matter of
but slight difficulty. It shows us that the organs in question receive
their supply of blood from two different sources of unequal importance.
The larger arterial twigs in the first place pass into the septa and glandular
tissue through the hilus without exception, while the smaller branches
penetrate through the capsule into the interior. The last mode of supply,
however, is probably not always present, though others are wrong who
assert that it does not exist at all.

Passing through the hilus in the first place then, one or several
small arterial trunks are seen which give off their first branches while
within the connective-tissue situated here. With the connective-tissue
a small number of these branches pass into the system of septa within,
ramifying with further division towards the periphery. Most of the
arterial twigs, however, penetrate into the lymph-tubes of the medullary
substance, and pursue their way within the offsets of the latter. Among
the smaller lyniph-tubes, such as those of the pancreas Asettii of the
rabbit and Guinea pig, as well as the mesenteric glands of man, each of the
former contains, as a rule, but one single axial vessel, either a small artery
vein or capillary. In lymph-tubes of greater diameter several of these
may be met with, or, as is the case in the inguinal glands of man and
lymph-nodes of the ox, these elements of the medullary substance contain
within them a thick arterial or venous axial vessel, and a long-meshed
capillary network around it (fig. 406), whose tubules have a medium
diameter of Q'0046-0'0090 mm., and form a most delicate interlacement
about the central vessel. Passing from the more external lymph-tubes,
these twigs, together with their capillaries, enter the follicles, and occupy
a considerable portion of its space, terminating eventually in a very loose
and rather irregular capjllary network. The latter exhibits at the periphery
of the follicle where it is most highly developed as a rule, numbers of
loops on the tubes from the union of which the venous radicals take
their origin, which lie more internally. These, on leaving the follicles,
penetrate into the lymph-tubes, and return (imitating the arrangement of
the arteries) through these to the hilus.

The second source of supply of blood is the capsule of the lymph-node
which is traversed by arterial venous and capillary vessels. The first of
these appear in the bases of the interfollicular partitions as horizontal
twigs, which divide finally into finer branches encircling the various
follicles. The veins of the capsular tissue have a similar course.

Internally the greater number of these capsular vessels sink into the
septa, communicating there with others coming from the hilus.

Other twigs (rarely arterial or venous, but usually capillary) enter
the follicular tissue itself, taking a course through the stronger retinacula
of the investing space or through the partitions.

We shall find later on that other organs, such as the spleen, liver, and

416 ' MANUAL OF HISTOLOGY.

kidneys, exhibit a similar connection between the vessels of the paren-
chyma and capsule.

For the recognition of the course of the lymph, also, we require the aid
of artificial injection. This may be successfully performed through the vas
afferens, though not easily. On the other hand, it may be very easily
effected by Hyrtl's method of puncture beneath the capsule. The true
course of the lymph through the gland was, however, first ascertained by
myself in the year 1860, and shortly afterwards by His.

The afferent lymphatic, vessels (fig. 408, /, /) enter the organ either
singly or, as is the case with larger nodes, in greater number. Their walls
are thin, and they exhibit considerable variety of diameter and richness
in valves. There may also be one or several efferent vessels leaving the
glands. They have a similar structure to the last.

Their point of exit may be a depression like the hilus, although not
necessarily, so that the distinguishing of afferent and efferent vessels from
one another is not always an easy matter.

If we cautiously force in some injecting fluid through one of the vessels
leading into the organ, the first portion to nil is a series of spaces under
the capsule, closely communicating with one another, and surrounding
the follicle : this is effected with great ease. Perpendicular sections show
that the fluid penetrates also into the interior by keeping along the sides
of the follicles, and in the middle of the stream the banded network of
the interfollicular septa is seen distinctly.

What is here produced artificially is effected by nature also. A few
hours after a meal of fatty food, the cortical portion of the mesenteric
glands is filled by white chyle in a manner precisely similar.

It requires but a slight acquaintance with the lymph-nodes to convince
one's self that the injection fluid, in fact, on first entering the organ,
finds its way into the investing spaces of the follicle, and, filling these,
occupies those circular networks on the surface of the latter which have
been already mentioned above as being 0'0162-0>0323-0104S3 mm. in
breadth.

Close inspection shows farther that the afferent lymphatic vessel,
from that point at which it enters the capsule, loses its independent

wall by the fusion of the
outer layers of the latter
with the connective-tissue
of the capsule. In this way
it opens into the investing
space, either in the form of
a simple or branched pas-
sage. Thus the effects of
injection are easily ex-
plained.

It may be mentioned, as
a modification of this ar-
rangement, that the afferent

Fig 408 lymphatic tubes sometimes

first pass for a certain dis-
tance through the interfollicular partitions before opening into the lym-
phatic spaces of the gland.

Let us bear in mind farther that the investing spaces of the organ
are immediately continuous with the network of interstices of the medul-

ORGANS OF THE BODY.

417

lary substance (§ 224), eo that there can be no f doubt as to the farther
course of the injection fluid: it fills namely this network of lymph pas-
sages also, while the lymph tubes of the medullary substance remain
colourless so long as only slight pressure is used.

From the mode of termination of the injection we perceive that the
vas efferens must take its rise from the passages of the medullary portion
of the gland, in that it is at last filled by the fluid employed. It is also
possible at times to drive the liquid back through the vas efferens into the
lymph node by overcoming the opposition of the valves. Retrograde
injections of this kind impel the matter used first into the reticulated
passages between the lymph-tubes of the medulla, and from thence further
on into the investing spaces of the follicles.

The confluence of these medullary lymph streams, however, to form a
branch of the vas efferens is a point very difficult of detection (fig. 409).

The latter vessel which leads into the connective-tissue at the hilus
undergoes there further division into branches, as has been already
remarked. These may vary greatly according to the size of the gland,
and the greater or less development of
the fibrous nucleus of the latter. En-
closed within the partitions of the
medulla, the last branches of the vas
efferens (e) are observed to course along
in the form of tubes of various calibre,
whose walls are, as a rule, fused with
the surrounding connective-tissue (/).

Finally, on penetrating further into
the gland we observe that the partitions
which contain such ramifications of
the vas efferens become subdivided more
and more, forming series of diverging
bands, so that the lymph stream is no
longer enclosed within an envelope,
and exhibits all the reticular characters
and irregular limitations (d) charac-
teristic of the hollow cavities of the
medulla. In fact, there can be no
doubt that we have before us the origin
of the vas efferens from the cavernous
portion of the medulla of the gland.

It may be remarked, further, that the vasa efl'erentia on their exit from
the lymph nodes present much variety of appearance, depending upon the
size of the organ and the development of the connective-tissue nucleus in
the neighbourhood of the hilus. Thus in the hilus of the large mesenteric
glands of the ox a regular plexus of peculiar, very tortuous, and knotted
vessels has been seen by Koelliker, and Teichmann also gives drawings of
exceedingly complicated vasa efferentia.

From the foregoing description, then, the following conclusions may be
drawn. The vessel leading into the gland pierces its capsule in the form
of a canal, and opens into the investing spaces of the follicle. These
lead then into the lymph passages of the medullary portion, from the
confluence of which the radicals of the vasa efferentia enclosed within the
substance of the converging partitions are formed.

From this we see that really independent lymphatic vessels do not

Fig. 409. — From the medullary substance ot
an inguinal gland of a large dog. a,
lymph tubes; 6, empty reticulated passages
of the medulla; c, the same filled ; d, tran-
sition into the commencement of a twig of
the vas efferens; e, the latter coursing along
within a fibrous septum //.

418

MANUAL OF HISTOLOGY.

exist in the glands in question, and that the views entertained to the '
opposite effect are incorrect, as those of Teichmann* for instance.

On the other hand, that older and so widely held view to which we our-
selves subscribed for many years can no longer
be supported in its integrity, namely, that only
lacunar circulation takes place within the
lymph, nodes. The lymphatic canals, namely,
traversing the capsule are, as we may easily
convince ourselves, lined with peculiar flat
epithelium-like cells (fig. 410), already dealt
with in considering the vascular system
(§ 208). The investing spaces are likewise
lined in the same manner, not only on the
surfaces of the septa and the retinacula con-
nected with them, but those of the follicles
themselves (His). It is still a matter of uncer-
Fig. 410. tainty whether the lymph passages of the

medulla possess a similar lining or no. This

matter calls, at all events, for more accurate investigation ; for we find —
not alone after artificial injection, but also from the stream of lymph pass-
ing through — that small granules of colouring matters or fats penetrate
from the periphery towards the centre of the follicles, and also into the
lymph tubes. They are also seen in the cellular network passing across
the interstices of the medullary portion of the gland. We know, farther,
that the lymph of the afferent vessels is not unfrequently poorer in cells
than that which leaves the organ. From this fact we may infer that
from the substance of the gland lymph corpuscles are yielded to the
passing fluid. The lively change of shape of the cells of the latter, and
consequent power of change of locality (§ 40), as well as the trellis-like
surface of both follicle and lymph tube — the fact, finally, which has been
already considered in a previous section, that cellular networks containing
lymph corpuscles are observed in the passages of the medulla, — all these
point to the probability of such an addition being here made to the fluid.
Our knowledge of the nervous supply of the lymph glands is at present
extremely scanty. Some fine nervous twigs have been observed by Koel-
Wcer, in the larger nodes of the human body, to pass in with the arteries
into the medullary portion ; beside which Remains pale nerve fibres have
also been observed in the glands of the ox.

REMARKS. — 1. No doubt can any longer prevail as to the perviousness of the
lymph glands to small solid granules. And although, after tatooing, molecules of
pigmentary matter are laid down in these organs, the fact can be explained in a
manner quite reconcilable to this view. Every one who has ever injected lymph nodes
with any granular matter, and afterwards essayed to brush it out, knows very well
with what tenacity the granules cling to parts of the surface of the investing space.
That lymphoid cells possess the power of taking up molecules of pigmentary matter
into their bodies has already been remarked at p. 77. Why it is that Virchow still
doubts the possibility of the passage of pus cells, or even granules of cinnabar, through
lymph glands, is to me somewhat incomprehensible.

§226.

It has been long supposed, and rightly so, from physiological experi-
ences, that a lively interchange of matter takes place in the lymph nodes
between the blood and the lymph. The same is taught us by the changes
produced in the glands in question in morbid states of the juices of the

ORGANS OF THE BODY. 419

body, manifested by inflammatory appearances and swellings of these
organs.

Thus we see that the lymphatic glands of man are liable to vary much
in structural appearance, which must be partly attributable, no doubt, to
the metamorphoses accompanying increasing age.

Among the latter may be reckoned the partial transformation of the
connective-tissue framework into fat cells, and degeneration of the reticular
connective substance into ordinary fibrous tissue, with consequent gradual
obliteration of the whole organ.

A third change observable in lymph nodes is true pigmentation. This
affects principally the bronchial glands, and is almost invariably to be
met with after a certain age, though with varying degrees of intensity.
It may be due to the irritation of inflammation in the pectoral organs.
Small granules of melanin (p. 52) are formed by the gradual metamor-
phosis of the colouring matter of the blood. But though this may be
accepted as one source of black pigmentary molecules, the latter have a
very different origin, most probably, in many other cases. They are,
namely, particles of carbon in a state of the most minute division, given
off as soot from lamps, &c., and inspired and conveyed from the lungs
into the lymphatic glands (Knavff). But between these two kinds of
molecules we are at present unable to distinguish with any certainty.
They lie utterly without order, partly within the lymph corpuscles, and
in peculiar lumpy masses, and partly in the ground-work of the septa and
walls of the vessels. In some instances the follicles appear to be the
parts most affected, in others the lymph tubes of the medulla. A slight
amount of this "melanosis" communicates to the bronchial glands a
mottled appearance, while strongly marked it may cause the whole organ
to appear uniformly black.

The effect on the lymphatic glands of inflammation of neighbouring
parts is most evident. The meshes become narrower in the framework ;
the bodies of the cells of the same become plump, their nuclei undergo
division, while great distension of the capillaries is also observed, — in
fact, the whole gland acquires more or less the appearance it presented at
an earlier age. Later on the reticular framework may grow luxuriantly,
the distinction between medulla and cortex ceases to be apparent, the
lymphatic system of canals disappears, and the whole organ becomes in-
capable of functionating.

The derelopment of the lymphatic glands in the embryo, as well as
their nature, was until quite recently entirely unknown. That their
origin, together with the whole vascular system, was from the middle
germinal plate, is all that was known about them. This had been demon-
strated years ago by Remak. The labours of Sertoli and Orth, however,
have recently thrown some light upon the subject as regards these points.
According to the interesting, but by no means exhaustive treatise of the
first of these observers, there may be seen in the mesenteric glands of the
ox, in the first place, a system of lymphatic canals at that spot where
the connective-tissue nucleus or hilus-stroma of His is to be found.
Around this system a quantity of connective-tissue, rich in lymph cor-
puscles, is gradually developed, from which the cortical substance, in the
first place, takes its rise, and then the lymph tubes of the medulla. The
investing spaces and cavernous passages of the medulla make their
appearance subsequently, as well as the capsule, septa, and reticulated
tissue connected with the latter.

420

MANUAL OF HISTOLOGY.

As to the composition of the lymph glands but little is known. They
contain a certain amount of leucin as a product of decomposition, according
to Stadeler, and may also, it appears, contain uric acid, tyrosinC?), and
xanthin (?) Krause and Fischer state the specific gravity of the organs
in question to be 1*014 in the human being.

§ 227.

N early related to the organs we have just been considering, we find
others which consist partly of single follicles, and partly of a number of
the latter crowded together closely, and held thus by a peculiar connect-
ing substance. These are mostly situated in the mucous membranes or
submucous tissue. Among these may be reckoned, as occurring in the
human being and mammalia, the so-called trachoma glands or lymphoid
follicles of the conjunctiva, the lingual follicular glands, and tonsils, cer-
tain irregularly occurring follicles of the gastric mucous membrane (lenti-

Fig. 411.— Vertical section of a Peyerian gland Fig. 412.— Reticular sustentacular

from the small intestine of the rabbit, a, tissue between the follicles of the

villi ; 6, c, follicles. vermiform appendix of the rab-

bit, 1. Deeper portion in hori-
zontal section, a, framework;
6, lymph canals. 2. Superficial
portion ; a, 6, as in 1 ; c, depres-
sion in the mucous membrane
lined with cylinder epithelium.

cular glands), and the solitary and agminated glands of the intestine, 01
PC-yen's patches (fig. 411).

That large massive organ, the thymus, may also be mentioned as pre-
senting a similar structure.

This whole group, including the lymphatic glands themselves, may be
named with propriety the group of lymphoid organs. In addition to them
we have, finally, the spleen, though no doubt a modified form.

In all those .organs first mentioned, which belong to the mucous mem-
branes, we find the follicle as the essential structure. It corresponds in
its structure to the analogous elements of the lymphatic glands, and con-
sists of a reticular substance enclosing lymph corpuscles (comp. fig. 400
and 412). This presents not unfrequently in its interior a loose and open-
meshed appearance, whilst more superficially the network becomes denser,
and further outwards still, on the surface, exceedingly close, just as we

ORGANS OF THE BODY.

421

have seen it in the lymph-nodes (§ 223). The vascularity of these mucous
follicles is liable to vary to a considerable extent. In some of them, such
as those of the conjunctiva,
the capillaries only occur
sparsely, in the form of
very open interlacements ;
while in other cases we ob-
serve an extremely com-
plex and delicate network,
the tubes having, to a cer-
tain extent, a radiating
arrangement when viewed
in transverse section. Fig.
412, sketched from such
a preparation of one of
Payer's patches from the
rabbit, will serve as an
example of the latter form.
These rounded follicles,
sometimes spherical and at
others vertically elongated,
are situated either in the
tissue of the mucous mem-
brane itself, or when of
considerable length, they
project down into the sub

mucosa. Their upper por-

Fip. 413. — Transverse section through the equator of three
Payer's patches of the same animal, a, the capillary net-
work ; 6, of the larger circular vessels.

tion [the cupola (fig. 414, d)] may be covered by a thin layer of mucous
tissue [conjunctival follicle (fig. 415)], but may also advance so far for-
wards as to be covered merely by an epithelial coating lying directly
on the reticulated sustentacular tissue [tonsil Peyer's follicles (fig.
413)].

In the middle equatorial region [" mesial or equatorial zone" (fig. 414, e)]
the follicle is connected to a greater or less extent with the adjacent parts ;
sometimes with the neighbouring mucous tissue, which in that case pre-
sents, for a certain distance, the same reticular character, containing also
lymph corpuscles, and at other points with abutting follicles. Thus we
see, for instance, in the vermiform appendix of the rabbit — a portion of
the intestine consisting entirely of crowded oval follicles — that the latter
are regularly united in the neighbourhood of their equator by bands of
lymphoid tissue (fig. 412), whilst the whole lower half of the follicle (the
base) exhibits the same continuous investing space as in the lymph nodes.
The analogy, however, is even more perfect than might be inferred at
first sight, for careful observation teaches that here also a system of
fibrous septa exists, which, springing from the submucosa, passes under
the follicles, and sends up partitions perpendicularly between them.
These spaces are even lined by the same characteristic endothelial cells,
as those seen in the lymph nodes, according to His.

Should these extensive investing spaces be absent, the follicles of each
group are usually united to one another by means of reticular lymphoid
tissue. The latter, in contradistinction to that of which the follicle itself
is composed, exhibits a much closer texture, so that under the microscope
it appears as a dense and non-transparent layer, within which the more

422

MANUAL OF HISTOLOGY.

loosely woven follicles are observed to lie. This condition of parts may
be seen in the tonsils and conjunctival follicles.

i.

Fig. 414.— Vertical section of one of Peyer's patches from the human being, injected through the
lymphatics, a. villi with their absorbent radicles; b, glands of Lieberkiihn; c, muscular coat of
the mucous membrane; d, cupola of follicle; e, mesial zone; /, base; g, passage of the chyle-radicles
of the villi into the true mucous membrane; h, reticulated arrangement of the absorbents about the
mesial zone; i, course of the latter at the bases of the follicles; and k, their confluence to form the
lymphatics of the submucosa; I, follicular tissue of the latter.

When this arrangement prevails the investing spaces cannot be said to
be entirely wanting, they are rather converted into a system of narrow
passages, which interlace upon the surface of the follicle " like the net
upon the surface of a child's toy Indian rubber ball."

The view that holds these passages around the follicle to be lymphatic
canals is shown to be correct by injection (fig. 415). We observe that,
from the surface of the mucous membrane, and mostly from the neigh-
bourhood of the follicle generally, e.g., in many of Pei/er's patches, from
the adjacent villi ffig. 414, «) ; and in the case of the conjunctival

follicles from the mucous mem-
brane, especially on the surface
of the band of union (fig. 415, c) ;
that lymphatic vessels which
take the place of the vas afferens
of the nodes are conducted to
the surface of the follicle, either
simply (fig. 415), or with a certain
amount of complex interlacement
(fig. 414, (J). Arrived here, they
open into either the investing
space or its retiform equivalent
(fig. 414, A, i; 415, c).

Those submucous lymphatic
vessels, which take on such a
variety of forms (fig. 414, k; 415, a), are the conduits corresponding to
the vasa efferentia of the lymph nodes; in short, the parallel between these

Fig. 415. — Trachoma gland from the ox in vertical
section and with injected lymphatic canals, a, sub-
mucous lymphatic vessel ; c, distribution of the
same to the passages of the follicle b.

ORGANS OF THE BODY.

423

latter and the follicles of the mucous membrane is almost complete. The
latter may be regarded as small lymphatic glands occurring in mucous
membranes, with which view the simi-
larity of the pathological changes occur-
ring in them to those observed in lym-
phatic glands, is in perfect accordance. /

§ 228.

The thymus gland, a double organ
whose function is unknown, and which
is, as far as we are at present aware,
similar to a lymph node in structure,
exists in full development only during
the earlier periods of life, falling, later
on, more and more a prey to fatty de-
generation. Thus it is only exceptionally
to be recognised in the bodies of older
individuals.

The first point which we observe in
the structure of the organ is that, besides
being exquisitely lobulated, it possesses
a very vascular fibrous envelope. Owing
to the fact that the latter invests the
internal mass but very loosely, the glan-
dular tissue of each half of the organ
may, after severance of the blood-vessels,
be disentangled from it in the form of a
band-like skein. The latter consists
everywhere of a venous and arterial twig
of accompanying lymphatic vessels, and
a peculiar gland-duct, known as the central canal, upon which are situated,
externally, the lobes and lobuli of the gland. When dissected out, the
whole is of considerable
length (fig. 416, 1). The
central canal, which, accord-
ing to His, has in the calf
a diameter of only 0-7444
mm., is twisted up into a
kind of spiral in the natural
state, and the lobes are in
close contact with one an-
other.

If we proceed with our
analysis, we find that each
lobe is made up of a num-
ber of smaller lobuli, and
the latter, enclosed within
a vascular envelope of con-
nective-tissue, are again

composed of Smaller poly he- Fig. 417.— Portion of the thymus of a calf (after His), showing
, ,r a 4.4. A the arterial, a, and venous rings, &; the capillary network,

dral Structures, flattened c; and the cavities of the acini, d

one against the other, whose

diameter is 0-5640-M128 mm., or, in the calf, 1-1128-2-2256 mm.
28

Fl£. 416. — 1. Upper portion of the thyimis
of a foetal pig of 2" in length, showing
the bud-like lobuli ar.d glandular ele-
ments. 2. Cells of the tliymus, mostly
from man ; a, free nuclei ; b, small cells ;
c, larger; d, larger, with oil globules,
from the ox; «,/, cells completely filled
with fat at /, without a nucleus ; g, h,
concentric bodies ; g, an encapsuled nu-
cleated cell; A, a composite structure of
a similar nature.

424 MANUAL OF HISTOLOGY.

These are the elements of the gland, the so-called granules or acini of the
thymus. At first sight they remind us forcibly of lymphoid follicles.
Under closer observation, however, important differences manifest them-
selves. Externally, these acini of the thymus are separated from one
another by deep indentations, whereas, internally, they become united,
as many as fifty of them together, to form, a medium-sized lobe — recall-
ing to mind the state of things observed in the racemose glands. Then —
and great stress must be laid upon this point — the thymus element appears
hollow in its interior, and the cavities of the thick-walled acini of each
lobe unite, as in the racemose glands, to form its common passage. This
then joins with similar canals belonging to other lobes, until, by a repeti-
tion of the occurrence, the spiral central canal of each half of the organ is
produced.

Even in the walls of this common duct, bulgings or attached acini, or
groups of the same, may be remarked, so that its thickness varies at
different points.

As to the texture of the acinus, we find that the central cavity, occu-
pying about J-J- of the whole diameter, is bounded by a layer of soft
tissue. This consists of an exceedingly dense network of stellate cells of
reticular connective-tissue. The narrow meshes of this structure are occu-
pied here,. as in the lymphoid follicles, by an immense number of lymph
corpuscles. A very delicate membrane, richly supplied with blood-vessels,
covers its surface. The blood-vessels, farther, which traverse the follicular
tissue, are also very numerous, and possess the well-known adventitia
(§ 202). With the exception of a few stronger twigs, these are for the
most part capillaries of 0'0063-0-0068 mm. in diameter. Injection of
these brings out their arrangement in the most instructive manner.

From the larger vessels of the central band smaller twigs are given off
to the lobuli. Here they eventually form (in the calf) delicate circular
and arched groups of arterial and. venous branches (fig. 417, a, b) around
the individual acini. Springing from these the capillaries are seen inter-
nally (c) taking a convergent course, and forming a most exquisite net-
work amid the lymphoid substance. Close to the central cavity they
double on themselves (d) according to His.

In the thymus of the infant, though the arrangement of the capil-
laries is the same, an exception is so far to be seen to this arrangement
of parts, that while the vein courses along at the periphery of the acinus as
in the calf, the artery and its system of finer tubes occupies the interior of
the glandular tissue near the central cavity in a manner wholly different.

In the small meshes of the reticulum it has been asserted that numbers
of free nuclei may be seen (fig. 416, a) suspended in an acid, viscid,
albuminous fluid. The essential element is, however, beyond doubt a
small nucleated lymphoid cell (b) measuring 0'0074 mm. in diameter.
More rarely we meet with large cells of from 0*0046 to 0'0023 mm.,
containing several nuclei, from 2 to 8. Ecker mentions further, as a
phenomenon of retrograde development, that a deposit of fat globules
takes place (d) in many cells, which, as soon as the organ is on the
decline, run together to form one large drop, filling the whole body of the
elements in question (e,f). He states, besides, that in older cells he has
not unfrequently observed an absence of nuclei (/).

But there are other structures to be met with here which are by no
means connected with the involution of the thymus ; these are the so-
called concentric bodies.

ORGANS OF THE BODY. 425

Around certain single cells, namely, which appear not unfrequently to
be undergoing fatty metamorphosis, or again, about a group of the latter,
we notice the formation of dense concentric layers, which may be seen on
closer examination to be composed of flat nucleated cells, like pavement
epithelia (Ecker, Paulitzky], reminding us of the formations in epithelial
cancer, so well known to pathologists.

The smaller examples of these bodies (g) are formed of a group of cells,
sometimes filled with granules, sometimes with fatty matter, and in some
cases still possessing nuclei ; which is surrounded by the thick laminated
rind alluded to ; they may attain a diameter of 0 -01 69-0-0208 mm. The
larger structures of this kind (h), measuring 0-0593 mm., are formed by a
repetition of the process enclosing several of these smaller corpuscles.

As regards the lymphatics of the thymus, we are still comparatively
ignorant. That the chief stems accompany the arteries and veins through
the central band, has been already remarked above ; but besides these
there are finer lymphatic vessels to be seen. These are found in the
interstitial connective- tissue of the lobes, according to His, in the form of
delicately walled tubes, only coursing round the latter. They are even
stated by that observer to open into passages about 0'0226 mm. in
breadth, filled with lymphoid cells, which spring from the centre of the
acinus. Through these tubes a communication exists, according to His,
between the central cavity and the lymphatic vessels, by means of which
the cellular elements can pass into the latter.

From the fact, however, that up to the present no one has succeeded,
by puncture, in filling lymphatic vessels around the acini of the thymus,
(and my own numerous experiments also teach me that it cannot be done) ;
and as the discoveries of more recent date, relating to lymphoid organs,
do not seem favourable to the supposition of such an arrangement of parts
as His describes, the matter would seem to call for closer investigation.

The final distribution of nerves in this organ is still enveloped in
obscurity.

As to the composition of the thymus (whose specific gravity is stated
at 1 '046 by Krause and Fischer), analyses have been made by Simon and
Friedleben. The former of these obtained from the organ of a calf three
months old, about 77 per cent, of water, circa 4 of an albuminous sub-
stance, traces of fat and 2 per cent, of salts.

The thymus ef the calf is further stated by Gorup, Frerichs, Staedeler,
and Scherer, to contain large quantities of leucin, also hypoxanthin and
xanthin, volatile fatty acids, such as acetic and formic ; also succinic and
lactic acids. The mineral constituents consist principally of phosphates
and chlorides of the alkalies, with a preponderance of phosphoric acid and
soda. The proportion likewise of the magnesian exceeds that of the lime
salts. Sulphuric acid is only present in small traces. The presence of
salts of ammonia is a fact of some interest (Frerichs arid Staedeler). On
the whole, its composition has some resemblance to that of muscle.

The development of the thymus was first explained by Simon, whose
statements were subsequently corroborated by Ecker.

In the mammal, as far as has up to the present been ascertained, it
appears first in the form of an elongated and closed sac lying in front of
the carotids, which is filled with cells and granular contents. By a
bulging of the walls of this, numerous rounded prominences are formed,
in which we have the first indication of the future lobes. By a repetition
of the process the capsule of the glands is eventually formed. A subse-

426 MANUAL OF HISTOLOGY.

quent liquefaction of the central portion gives rise eventually to the
formation of the central cavities. From fig. 416, 1, representing the
gland of a foetal pig two inches long, in course of development, we may
obtain some idea of the process, and understand better the structure of
the gland at the period of maturity.

The retrograde development of the gland takes place with decrease of
volume by the formation, as has been already remarked, of fat cells at
the expense of the tissue, by which we are reminded of a similar meta-
morphosis in the lymph nodes (§ 226). That fatty degeneration of the
gland cells also occurs, has been asserted, as we have already said, by Ecker.
The time at which the retrograde process begins appears to vary; it
lies between the eighth and twenty -fifth years.

§ 229.

We have still to consider in conclusion one other organ belonging to
the lymphoid series, namely, the spleen.

Owing to the great difficulties attendant on the study of this organ, it
remained until a comparatively recent date the subject of but brief and
unsatisfactory research. But, lately, through the labours, especially, of
Gray, Billroth, Schweigger-Seidel, but more than all of W. Mutter, we
have been made acquainted with the leading peculiarities of its structure.
In the latter it resembles a lymph node, even more strongly than the
thymus. In fact, the spleen may be regarded, as I myself expressed it
many years ago, after careful consideration of the subject, as a lymph
gland in which the system of lymphatic passages is replaced by the blood-
vessels ; it might be named, perhaps, with propriety a blood lymph gland.

The organ presents, in accordance with this view beside, a. fibrous enve-
lope with a system of trabeculce or septa, and a sheath-like formation of
connective-tissue around the vessels, a soft glandular parenchyma. The
latter is of two kinds ; it presents itself, in the first place, in the form of
lymphoid follicles, and in the next as a brownish red friable mass, known
as the pulp of the spleen. The first of these correspond to the elements
of the same name found in the lymph nodes ; the latter is more or less a
modified species of the medullary substance.

Beneath the serous covering, which may be isolated from the organ in
the ruminant body, the fibrous envelope or capsule of the spleen appears.
In man, on the contrary, this tunic is closely adherent to the investing
peritoneum. It is seen, under the microscope, to be made up of a dense
interlacement of connective-tissue fibrillse, with a preponderance of fine
elastic fibres, and contains also unstriped muscular elements. The latter
are present in large numbers in many of the mammalia, as, for instance,
in the sheep, dog, pig, horse, and hedgehog, especially in the deeper por-
tions of the envelope. In other animals of this class they do not make
their appearance in such quantities, as, for example, in the ox ; while in
man the contractile fibre cells are present in but small proportion.

The capsule which invests the whole spleen is folded in at the point of
entry of the vessels and nerves, — the so-called hilus, — and is continued
further inwards in the form of sheaths to the various vessels. It accom-
panies the ramifications of the latter (more strongly developed and massive
around the arteries than the veins) down to their finest twigs. It
exhibits, however, considerable variety in the various species of animals,
a point to which we shall be obliged to refer again further on.

Besides the sheaths of the vessels, and continuous with them, we meet

ORGANS OF THE BODY. 427

with another prolongation of the fibrous envelope of the spleen directed
inwards in the form of a system of septa. In the nature of the latter, as
regards the spleen of the several mammalian animals, extraordinary
variety has been observed. Just as was the case in the lymph nodes, it
is but very slightly developed in the spleen of smaller mammals, as, for
instance, in that of the mouse, the squirrel, the Guinea pig and rabbit,
while in larger animals, as in horses, pigs, sheep, and oxen, it attains a
high pitch of development. In man, and in the dog and cat, on the other
hand, it is but moderately marked, reminding us of the lymph nodes
again. The more numerous the trabeculse in any spleen the harder is the
organ found to be.

From the whole internal surface of the fibrous envelope there spring a
multitude of fibrous cords and bands, varying as to their distance from
one another, and as to the angle at which they are given off. Their
diameter is about 0-1128-0-1279, or even 2*2556 mm. These trabeculoe of
the spleen traverse the organ in all directions, uniting and again branch-
ing in the most irregular manner. They form, when in a state of perfect
development, a very complicated sustentacular tissue. On the other side
they are connected with the sheaths of the vessels, or continuous with
the latter, especially the veins (Tomsa).

Within the innumerable irregular spaces, — formed by the intercom-
munication of these trabeculse, — the glandular tissue of the spleen is con-
tained. When the system of septa is fully developed, therefore, the
spleen of the larger animals acquires necessarily a complexity of structure,
rendering the recognition of its nature of great difficulty. On this
account the spleen of smaller animals is the most suitable object for
investigation, as was also the case with the lymph nodes.

In its more minute structure the tissue of the trabeculae resembles that
of the capsule. Here we find, again, a closely woven whitish connective-
tissue, with nuclei and elastic iibres ; in addition to these, also, longi-
tudinally arranged muscular elements. The latter present themselves,
either in all the septa, as in the case in the spleen of pigs, dogs, and cats
(Koelliker, Gray), or, as is stated by many, only in the smaller trabeculae.
Thus it is in the ox and sheep (Koelliker, Ecker, Billroth). In man the
number of muscle fibres is small.

§230.

Now, in the cavities aiready described in the preceding section, amid
this system of trabeculae, the glandular or lymphoid portion of the gland
is contained. This consists, as we have already remarked, of a network
of cords or bands, the pulp tubes analogous to, but not identical with, the
lymph tubes of the medullary portion of the true lymphatic glands. In
this, and connected with it, a number of lymphoid follicles are imbedded,
discovered some centuries ago by Malpiglii, and named in honour of him
Malpighian corpuscles (Milzkorperchen, Milzblascheri).

In many respects these are exceedingly like the follicles of lymphatic
glands. They are not, however, grouped peripherally to form, as in the
latter, a cortical portion, but occur scattered throughout the whole of the
pulp. Their relation and connection to the arterial part of the vascular
system is very peculiar, calling for a few moments' consideration.

It is only rarely that, as among the ruminants, the splenic artery makes
its entry into the spleen as one single trunk: it generally divides into
several branches before doing so. Each of the latter then preserves in

428

MANUAL OF HISTOLOGY.

Fig. 418.— From the spleen of a pig. a, an arterial twig
invested with its sheath, showing its twigs, 6, and
attached Malpighian corpuscles, c.

the interior of the organ its own individuality as regards its ramifications.
Soon after there commences a most extensive division and subdivision of

the vessels, until, finally, the
latter, greatly diminished in
size, form a series of terminal
groups, which have been long
compared to the hairs of a paint-
brush. But a more appropriate
comparison has been made be-
tween these " Penicilli " and
the branches of a willow tree
divested of its leaves. Fig.
418 gives a tolerable represen-
tation of the arrangement re-
ferred to.

Drawing such a branch out
of the tissue of the spleen, we
may recognise on it the follicles
of which we have been speak-
ing. They are of a whitish
colour, and hang on the fine
arterial twigs like grapes on
their stalk. They are either
attached by their border to the
artery, or the latter traverse
their interior; or, finally, the
angles of division of such a series of branches may be surrounded by
numbers of them for a considerable distance. In form they are some-
times spheroidal, sometimes more or less elongated.

Such spleen corpuscles are to be found in all the mammalia, although
presenting much variety. In the human organ, however, they are less
distinct as a rule than elsewhere; and in bodies which have suffered from
protracted illnesses they were formerly supposed not to exist, while in
those in which death had occurred suddenly they were said to be always
recognisable, even without the microscope ; as also in youthful corpses
(von Hessling). For this reason they were looked upon even years ago
as integrant portions of the human spleen.

If we follow' up the disposal of the vessels commencing at the
hilus, we soon remark that it is liable to vary greatly in different animals.
The sheaths of these tubes also are no less subject to variation. Though
very imperfectly developed in the Guinea pig, rabbit, squirrel, and mar-
mot, they attain a high degree of development in other animals, as, for
instance, in the dog and cat. There the arteries enter the spleen in
several branches, each of the latter accompanied by a vein and one or
two nerves. Both artery and vein while passing in receive a sheath, but
not in the same way. Around the artery the latter is loose, and only
runs for a short distance unchanged, undergoing rapidiy a peculiar
lymphoid transformation. The vein, on the contrary, is accompanied for
a much greater distance by a tight investment, closely united to its walls.
On the smaller venous twigs the latter resolves itself into a few bands of
connective-tissue, which sink into the septa of the spleen. Deviations
from this general plan are to be seen in the ruminants and the pig.

In man the arteries and veins arrive in the spleen, already divided into

ORGANS OF THE BODY.

429

from four to six branches. Down to twigs cf about 0*2030 mm. they
are contained in a common sheath, possessing a thickness of about 0-2256
mm. at its commencement. This investing formation then becomes
gradually finer and finer, until reduced to a thickness of 0-1128 mm.,
enveloping in this state arteries having a diameter of 0"2256 mm., and
veins of 0-4512 mm.

The arterial twigs with their sheaths then separate by degrees from the
accompanying veins, and ramify independently. But about the venous
tube the simple sheath extends somewhat farther still, becoming even-
tually split up into fibres, continuous with the trabeculae of the organ
(W. Muller).

These sheaths exhibit the same minute structure, farther, as the trabeculse.

At those points, however, at which the arterial separates from the
venous twig, the structure of the tunic of the former changes its nature.
Its fibrous tissue is transformed into reticular lymphoid connective sub-
stance, together with which a decrease in its amount goes hand in hand.
The advancing metamorphosis also, commencing externally, attacks even-
tually the proper tunic of the artery. Progressing still, this trans-
formation, this construction of " lymph sheaths " gradually leads to more
or less circumscribed swellings of different shapes, and these finally
to the Malpighian corpuscles of the spleen (fig. 419, a). In fact, the
latter, with their varied configuration sometimes roundish, in other
instances elongated more or less, and possessing a diameter of 0-2256-
0'7444, or on an average 0'3609 mm., take their origin from the infil-
trated sheaths of the arteries, from which they can be by no means
sharply defined.

Arterial twigs of 0-1579 and 0-0993 mm. in diameter, clown to those
of only 0'0203, are usually seen to possess this metamorphosed sheath,
and may all acquire a great increase of size by its formation.

Owing, however, to the fact that the position of the artery is by no means
always the same as regards
this infiltrated sheath, fur-
ther variety may be noticed.
The former, namely, may
pass either through the axis
of these elongated masses or
more laterally. In those
parts, also, converted into
follicles, we meet, at one
time, with an eccentric
course in the arterial twig, at
another with a more central
one.

This position, further, has
an effect on the texture of
the various parts of the
sheath. In the lower degrees
of transformation we usually
meet with an ordinary
loosely woven connective-
tissue with lymph cells in
its interstices. The same is
the case with the sheaths of the arterial twigs passing along the borders

Fig. 419. — Section of the spleen of a rabbit a, Malpighian
corpuscle; 6, su.stcntacular niatter of the pulp, with the
interspaces filled with venous blood.

430 MANUAL OF HISTOLOGY.

of follicles. When, however, these take a course through a swollen
point, or even excentrically, or through a Malpighian corpuscle, the trans-
formation usually goes farther, leading to the formation of a tissue nearly
allied to lymphoid tissue. Whilst in the lower degree of lymphoid
infiltration the sheath alone is affected, and not the proper adventitia, in
the more advanced stages of the same the latter is drawn more and more
within the circle of lymphoid metamorphosis.

Turning now to the follicle, we find the sustentacular tissue framework
denser and more resistent peripherally, while within it possesses wider
meshes, and is more delicate. At times the internal is marked off from
the more cortical portion by a circular line, as in the rabbit, Guinea pig,
and marmot. This arrangement, however, calls for closer investigation.

Here also, as in the lymph nodes, we may distinguish in some of the
expanded nodal points distinct nuclei. The external demarcation of a
Malpighian follicle is never produced by a homogeneous membrane
enclosing it, but always by reticular connective-tissue, even at those
points where by its denser texture its surface is sharply defined against
the adjacent structures. In other cases the follicle is continuous, as to
its delicate framework, with the surrounding tissue of the pulp, without
any sharp line of limitation existing between them.

Entangled within the meshes of all these different portions, there
appear, beside free (?) nuclei (Muller), a host of ordinary lymph cells, pos-
sessing as a rule but a single nucleus. Some of them, however, are
multinuelear when very large. Beside these there occur, although in no
great number, elements formed of colourless granular matter, or again
containing molecules of a deep yellow or brown pigment.

As regards the vessels of those portions which have become infiltrated,
and converted into follicles, there are also capillaries to be considered,
besides those arterial twigs already referred to. Veins, on the other
hand, are entirely absent. In parts but slightly infiltrated, is to be
found a slightly developed long-meshed capillary network, whereas those
portions greatly swelled exhibit, as a rule, a far more highly developed
mesh work of capillaries derived from a special and rather variable arterial
twig. This latter either springs from the artery of the follicle itself, or
approaches the Malpighian corpuscle from without. The capillary net-
work itself varies also ; in the first place, in different follicles of the
same organ, and in the second place, in different animals. It is some-
times met with presenting a more or less regular radiating arrangement of
its capillaries with arched anastomoses, the tubes having a diameter of
0-0029-0-0081 mm. But far more frequently the disposal of these
minute vessels is irregular both as to anastomosis, division, and diameter.

Observing the texture of the capillaries more closely, we recognise
beside those presenting the ordinary appearance, with an adventitia, such
as are seen, for instance, in reticular connective substance (§ 202), others
whose walls are exceedingly delicate wanting the double contour, but
which may on the other hand exhibit great richness in nuclei. In speak-
ing of the pulp we shall refer again to this point, which is of great im-
portance as regards the arrangements for the circulation in the spleen.

In man the nature of the lymphoid infiltration, and the mode of for-
mation of follicles, is similar to that just described, although the trans-
formed arterial sheaths, and their local thickenings, may display con-
siderable variety. We must not forget, however, that we are obliged to
undertake our researches into the nature of the human spleen under

ORGANS OF THE BODY. 431

much more unfavourable circumstances than when dealing with animals,
namely, long after the death of the individual, and not unfrequently in
cases where death has been produced by protracted illness. Neverthe-
less, we may easily satisfy ourselves as to the infiltration of the arterial
sheaths, the local thickenings giving rise to follicular masses, and the
analogous arrangement of the finer blood-vessels.

§ 231.

On passing beyond the lymphoid infiltrated investments, and also the
follicles, the arterial twigs continue their course for a certain distance
ramifying in the manner already described, but without any intercom-
munication among their branches.

Finally, they are resolved into a multitude of straight capillaries which
anastomose only to a very small extent with one another. These are of
rather fine calibre, and are not unfrequently very tortuous also. They
pass on, — taken as a whole, — eventually into the finest vascular passages
of the pulp.

Among the various mammals, however, the minute structure of these
capillaries differs considerably. In the pig, the dog, the cat, and the
hedgehog, most of them are (according to Schweigger-Seidel, Muller)
enveloped in elliptical swellings of the adventitia. These "capillary
husks" as they have been named by Schweigger-Seidel, which are of
great frequency among the capillaries of the spleens of birds (Muller) con-
sist of a pale, soft, and very finely granular mass, in which numerous
delicate nuclei are imbedded. Their dimensions in the dog, cat, and
hedgehog, are 0'0451-0'OGOO mm. in breadth, and 0-0902-0-1489 mm.
in length. The capillaries, enclosed either singly or in greater number
in these husks, present the same two-fold constitution of their walls,
already described in the foregoing section. Other capillaries of the same
animals just mentioned do not, however, show these husks, and corre-
spond thus with capillaries of man and the rest of the mammalia.

The latter present for the most part a strong wall, as far as their transi-
tion into the vascular passages of the pulp, while some of them are seen
to be more delicate, more richly nucleated, or as though formed of single
apparently distinct vascular cells.

Great variety, however, is seen among the lymphoid adventitise of such
capillaries. They may appear to be made up of a delicate mass of con-
nective substance, with round or elongated nuclei in the nodal points or
interstices, but may also become thicker, obtaining a more or less ribril-
lated coat of connective-tissue externally, with a more loosely reticular
portion internal to it, in whose interstices lymphoid and fusiform cells are
situated; thus reminding us of the "capillary husks" between which
and these there are intermediate forms.

In possession of these points regarding the structure of the capillaries,
we may now at last turn to the consideration of the pulp. This is found
to be a very soft red mass, occupying all the interstices of the organ
between the partitions, vascular sheaths, follicles, and those other consti-
tuents already described. Its coarser and more minute structure is only
recognisable after artificial hardening.

The pulp is made up of a nehcork of irregularly formed cords and
bands of a medium diameter of 0'0677-0'0226 mm. (fig. 420, &), which
bound a system of spaces and cavities varying again according to the
species of animal, but in every case designed for the reception of the

432

MANUAL OF HISTOLOGY.

venous blood. The former or pulp tubes, like the lymph tubes of the
lymphatic nodes, spring, in the first place, in great number, and with

gradual transitions from the
surface of the follicles. Here,
as in the rabbit, Guinea-pig,
hedgehog, and marmot, they
may be, for the most part,
concentrically arranged, the
interspaces bounded by them
naturally corresponding in
direction. A similar origin
of the pulp cords from the
lyrnphoid infiltrated arterial
sheaths as well as from the
adventitise of the last rami-
fications of the arteries,
may also be recognised.
Eventually they are inserted
into the fibrous trabeculae of
the interior.

The tissue of the pulp
tubes or pulp curds is a
Flg'420' modification of the reticular

connective species, and is of very delicate texture (fig. 421). It presents
everywhere a reticulum usually of extremely fine fibres, but also of some-
what more expanded bands. In some of the nodal points nuclei appear

to be imbedded, al-
though, owing to the

J- „ great delicacy of the

tissue, doubt still-

bedded, or only ad-
herent externally. If
we now follow up the
connections of this
network towards the
follicles or thickened
points of the arteries,
we recognise the fact
that the reticulated
tissue of the pulp is
continuous with the
coarser and tougher
sustentacular matter
of these parts ; inter-
mediate forms exist-
ing between the two kinds. If we now examine with special care the
numerous venous passages, and the limitations of the pulp cords towards
them, we soon convince ourselves here also of the reticular character of
the tissue in question. If successful in obtaining a view of the floor of
one of these venous passages, as at c, we will soon come to the conclu-
sion— and to this Henle was the first to direct attention — that the tissue

Fig 421. — From the pulp of trie human spleen. The preparation has
been brushed out (combination), a, pulp cords with delicate re-
ticulated sustentaculiir substance: 6, transverse section of hollow
venous canals: c, longitudinal section of the same; d, capillary in a
pulp tube, dividing at e; f, epithelium of venous canals; g, side
view of the same; and h, transverse section.

ORGANS OF THE BODY.

433

of these pulp elements is composed of a network of fine circular fibres anasto-
mosing at acute angles, which constitutes the boundary of the blood stream.
These venous passages are clothed with a peculiar species of vascular
cells. The latter are, as regards form, fusiform elements (fig. 42 I,/, g,
h), and present in man round and projecting nuclei. They lie in the long
axis of the venous path, crossing, consequently, at right angles the meshes
of the cellular network. They are non-adherent to one another — a pecu-
liarity of the utmost importance — and on this account may easily present
clefts between them if the venous passage be subjected to a more than
ordinary distending force. Here, then, the distinctly impervious walls of
other venous canals do not exist. The vascular cells in question have
long been known, from the fact of their extending back into the larger
venous trunks, but they were only recognised a few years since in the
venous pulp passages by Billroth. They are to be seen with great dis-
tinctness in the human spleen.

In the small meshes of the network of the pulp cords are entangled the
same lymphoid cellular elements in pairs or singly, which we have already
mentioned when speaking of the follicles and metamorphosed sheaths of
the vessels. Pigmentary cells, and even free aggregations of pigment
granules, golden yellow, brownish, or black, occur with such frequency in
many spleens, that even to the unaided eye the colour of the pulp
presents great variety.

In addition to these elements a certain number of coloured blood
corpuscles are regularly met with, at one time unchanged, at another
twisted, distorted, and altered. In preparations which have been carefully
managed, moreover, the important fact may be
noticed with comparative ease, namely, that
these corpuscles are situated in the meshes of
the tissue of the pulp perfectly free, that is.
unenclosed by any capillary walls.

On leaving the bloodstream they, undergo,

in fact, changes of various kinds ; they shrink,

they become fissured, and are thus converted

into those pigmentary molecules of different

kinds already alluded to.

But the most remarkable feature in this

decay of .the red elements, is the production of

those cells of the spleen containing coloured

corpuscles, known now for many years. These

structures, which were a puzzle to the observers

of early times, and to which have been given

consequently the most various signification, have

been already considered at pp. 77, 78. Here,

as in other organs, the vital contractility of the

membraneless bodies of the lymphoid cells

enables them to take up into their interior, not

indeed the whole blood corpuscle, perhaps, but

fragments of its substance. That the lymphoid

cells of the spleen possess this power of contracting, I saw myself very

clearly some years ago in water salamanders and frogs.

Later still the phenomenon was observed most extensively among

mammals also, by Cohnheim, and in the embryos of the latter animals

by Peremeschko. In conclusion, we would point out that, owing to the

Fig. 422.— Cells from the spleeii
of man, the ox, and horse.
a-d, from m;m; a, free nu-
clei; b, ordinary cell (lymphoid
corpuscle) ; c, nucleated cell
•with a blood corpuscle (?) in
the interior; d, with two such;
e, the same from the ox with
several; /, a cell from the
latter animal with fat-like
granules; g-h, from the horse ;
g, a cell containing several
fresh blood corpuscles and
granules, as in the last figure ;
h, cell with an agglomeration
of granules; i, the same, free;
*, a cell containing small
colourless molecules.

434 MANUAL OF HISTOLOGY.

incomplete nature of the walls of the venous passages, these cells, con-
taining blood corpuscles in every stage of development, may make their
way into the stream occupying these passages, and thus become elements of
the splenic blood.

Besides these. Funke and Koelliker mention, as farther elements of the
splenic pulp in young and sucking animals, other small yellowish nucleated
cells, which they hold to be young blood corpuscles in process of develop-
ment. Our own experience does not enable us to offer any remarks on
this point.

§ 232.

We have still to consider the course of the blood-vessels and of the
lymphatics in the organ with which we are engaged, and to glance at the
arrangement of its nerves.

Commencing with the veins, we find them liable to vary greatly in
different mammals. They are remarkable for their large calibre and great
distensibility, even when the distending force is but very small, a
peculiarity which explains the rapid physiological' and morbid congestions
with which this organ is affected.

Among the ruminants, — as, for instance, in the sheep and ox, — the vena
lienalis enters the organ as a single trunk, parting with its aduentitia,
and soon after its media, to the surrounding connective-tissue sheath, and
then divides into wide branches, which send off a number of lateral twigs,
whose walls consist above of a very thin, membrane, so that these appear
on section as interstices in the parenchyma of the spleen. In their
further ramification, these vessels present an arborescent appearance, the
branches springing from them at right and acute angles, and no anasto-
mosis taking place among them. Thus the whole arrangement assumes a
peculiar character, from the fact that these venous ramifications (whose
calibre is remarkably great), breaking up rapidly into finer twigs, are
directed towards the numerous Malplgldan follicles in greater or less
number. All these venous tubules are possessed of walls of extreme
tenuity, but which are usually entire nevertheless. They consist, as a
rule, of a layer of fusiform cells, 0-0029-0'0079 mm. in breadth, and
0'0201-0'0501 mm. in length, whose elongated nuclei project to a small
extent above the surface of the cell. Externally the finer twigs are
enveloped in the reticular tissue of the pulp already mentioned.-

Venous branches of this kind have been named by Billroth " capillary
veins," or " cavernous splenic veins." They are met with in all the
mammalia, though presenting much diversity as regards arrangement, by
which again the form of the pulp-cords is also modified.

Whilst among the ruminants these cavernous veins pursue their
course with acute angled division, and without anastomosis, they break
up into branches among other animals, more or less, at right angles, in the
primary dendroid ramifications, and communication amongst the twigs of
the latter takes place, GO that eventually, and by degrees, a regular network
of like:sized venous canals, or more or less expanded passages, is formed.
This reticular arrangement is seen, for instance, in the spleen of the
rabbit, the Guinea-pig, the marmot, and likewise in man. In certain
cases the spleen of the infant displays with peculiar beauty this retiform
intercommunication of venous canals, and in such instances the lateral
twigs springing from ensheathed trunks assume almost immediately a
net-like character. I myselt was the first to establish, in the year 1860,

ORGANS OF THE BODY. 435

their venous nature by means of injections, and it was from my prepara-
tions that Billroth became acquainted with them. Their diameter is, on
an average, 0'0169-0'022G mm., with extremes of 0-0113 and 0'02S2
mm., and their structure precisely the same as in the sheep. A spleen of
this kind, on the whole, presents, in regard to its pulp, great similarity to
the medullary mass and medullary passages of lymphatic glands.

Here too, as in the sheep and all other mammals, the walls gradually
assume a more and more interrupted character, by separation of their
vascular cells, and thinning down of their cribriform substratum, so that
clefts leading into the bounding pulp-cords are formed. Finally, diminished
to 0'015S-0'0099, all the cavernous veins conduct the blood everywhere
into the venous radicles with their fissured Avails and defective vascular
cell-lining.

§233.

Having now followed the cavernous venous passages down to their
finest subdivisions, the lacunar venous radicles, bounded only by the
tissue of the pulp, we next come to the important question so much dis-
cussed within the last few years, namely, How does the blood from the
ultimate ramifications of the arterial system find its way into the radicles
of the venous ?

Many observers, among whom Gray, Billroth, and Koelliker may be
mentioned, believe that fine terminal capillaries open immediately into
the cavernous veins without having formed previously any true network.
Schiveigger-Seidel supposes the transition to take place through peculiar
vessels formed of fusiform cells alone. The views, however, of Key and
Stieda are quite different. According to them, there exists between the
capillary ramifications of the arterial system and the cavernous veins an
exfremely dense network of most delicate capillary vessels with distinct
walls, in whose tiny meshes the lymph oid cells are entangled, and which,
in broad terms, constitute the pulp.

Many of these views are based upon the appearances produced by
incomplete injection or improper interpretation of preparations good
enough in themselves.

Thus it not unfrequently happens that we believe we see direct open-
ings of capillaries into veins, which prove, on closer inspection, to be in
almost all cases optical illusions.

We do not wish,, however, to characterise these immediate transitions
as impossible. We have, indeed, ourselves, during a long study of the
subject, met with appearances hardly capable of any other interpretation ;
but their number was extremely small, so that the conclusion that they
were only exceptional was forced upon us. Our own studies, therefore,
compel us to dissent from the opinion of Gray, Billroth, and Kodliker on
this point.

Key and Stieda, on the contrary, have determined the true mode of
transition, but have mistaken an extremely dense reticulum of very delicate
lacunar passages for a network of capillaries possessed of distinct Avails.

The fact is, that the passage of the arterial blood of the spleen into
the veins of the latter takes place in man and the mammalia generally in
small streams, having no special bounding walls. The blood traverses
the network of the pulp and interstices of the lymphoid cells contained in
the latter in the same manner — if we may be allowed the comparison —
as the water of a swelling river finds its Avay through the pebbles of its

436 MANUAL OF HISTOLOGY.

bed. These interstices have been named the intermediate pulp-pas-

We have to thank W. Miiller for being the first to place the existence
of these lacunae beyond doubt, although such an arrangement of parts
had been already pointed out here and there. Our own observations on
the spleens of the sheep, rabbit, Guinea-pig, mouse, mole, and human
being, have led us to the same conclusions on the subject as those arrived
at by the gentleman just mentioned.

To understand correctly, however, the nature of these pulp-passages, it
will be necessary to return for a moment to those ultimate ramifications
of the arteria lienalis already dealt with in section 230. There we con-
sidered fully the capillaries of the simply infiltrated arterial sheaths of
the lymphoid swellings on the latter and of the Malpigliian corpuscles.
In all these parts, either the usual structure of the capillary tube was
presented to us, or a modified and much thinner wall indicative of its
approaching transformation.

But all these capillaries to which we referred make their way into the
pulp of the spleen, becoming merged, after a shorter or longer course, in
the wall-less passages of the tissue, either single or branching. We not
unfrequently meet with spleens whose pulp must be said to be rich in

/*:r-a Tat^acf \¥ttwyr&wsKiim*^e£?>-

-

Fig. 423.— From the spleen of the hedgehog (after W. Mutter). «, pulp
with its intermediate streams; 6, follicle; c, bounding layer of the
same; g, its capillaries; e, transition of the same into the intermediate
interstitial pulp-streams ; /, transverse section of an artery at the border
of the Afalpighian corpuscle.

long capillaries, which occupy the axes of the pulp-cords in a way
reminding us of the lymph tubes.

As to the mode now in which these capillaries run out, the following
points may be recognised (fig. 423). The walls of the little vessels become,
as they are about to run out, finer and thinner without exception, besides
which they appear delicately granular, as well as richly studded, with
nuclei imbedded in their substance. Subsequently we notice a regular
fibrillation commencing in the tissue of the wall, the nuclei, with the
portion of tissue adjacent, developing into separate bands and fibres, pale
in colour, which are inserted continuously into the reticulum of the
pulp. We are often uncertain, indeed, for some distance, whether we
have still before us the passage of a capillary on the eve of termination,
or a canal-like interstice of the pulp. Naturally, at these points, the
matters injected into the capillaries find their way into the adjacent por-
tions-of the pulp.

OKGANS OF THE BODY.

437

Now, the latter, as the reader is already aware, is formed of a very
narrow-meshed retiform sustentacular substance, whose interstices are
occupied by lymphoid cells. Between these latter, and along the fine
bands of the reticulum, we find that the injection (a) passes further into
the pulp. If glue have been employed, the mass hardens subsequently
in the form of thin but irregularly defined shell-like fragments around the
lymp corpuscles of the pulp, broader at one spot than another. The
diameter of each stream varies from about 0'0032 to O'OOOO mm., and is
of course affected by the amount of force exercised in injection. The
great distensibility of the spleen observed during both health and disease,
and which is sufficiently known to every one who has devoted any time to
its artificial injection, is in a great measure owing to this capacity for
dilatation of the intermediate pulp-passages.

It was the contemplation of such appearances under the microscope
which led to the view supported by many recent observers, that there
exists in the pulp an intermediate network of very delicate capillaries,
bounded by special walls. At the same time, the reticulum of the pulp
was erroneously held to be formed of the collapsed canals of this net.

It is quite obvious that a slowly increasing pressure will fill a larger
and larger portion of this system of interstices in the pulp. Thus we see
the Malpighian corpuscles encircled by rings of the reticulated passages ;
and eventually the matter employed for injection may advance into the
more superficial portions of the same, and give rise there to the same
appearance of retiform interlacement.

But, finally, the injection (b) advances from the pulp (fig. 424, a) into
the radicals of the veins (c) already known to us from the preceding
section. To its progress there
are no obstacles, from the fact
that the radicles of the veins are
nothing else than interstices
found in the tissue of the pulp ;
and, therefore, enclosed by the
same reticulated tissue which
had been filled through the
capillaries.

If, for the control of these
artificial injections, other natur-
ally filled spleens be carefully
examined, in which the red blood-
cells have been preserved by
certain modes of treatment, and
the whole hardened, we will observe that at the terminal portions of
the capillaries these coloured elements are prolonged in wall-less pas-
sages between the lymph corpuscles, and at other points arranged together
in similar rows and groups, which coalesce to form the wail-less radicles
of the vein's.

Thus seeing that both artificial and natural injection point to the same
conclusions, we may venture to sum up as follows : the blood from the
arterial capillaries is emptied into a system of intermediate passages,
which are directly bounded by the cells and fibres of the network of the
pulp, and from which the smallest venous radicles with their cribriform
walls take origin.

termediate pulp-passages; c, their transition into
Je venous mdicles with their imperfec

438 MANUAL OF HISTOLOGY.

§234.

As regards the lymphatics of the spleen, it was for some time believed,
from the results of injection, that it only possessed such vessels on its
surface. These are situated underneath the serosa, and are arranged in a
very complex network, in the ox, sheep, and pig, formed of valved
vessels of considerable size (Teichmann, Billroth, Frey). In the first
animals mentioned these vessels may be easily injected, and are seen then
to present a number of bead- like dilatations at various points.

From the fact that during injection of the external vessels the matters
employed for that purpose could not be forced into any deeper lymph
passages in the parenchyma of the spleen, and that it had been already
ascertained that the Malpigliian corpuscle is not possessed of anything
corresponding to the investing space of the lymph follicle, the spleen came
to be regarded as an organ analogous to the lymph nodes, but in which the
internal lymphatic passages are replaced by venous canals. The well-
known participation of the organ in the life of the blood, the entrance of
lymphatic cells into the venous stream, and the very probable destruction
of multitudes of red corpuscles within the organ, all seem to justify its
being declared a blood lymph gland (Frey).

Of course, the denial just mentioned of the existence of internal
lymphatics led to contradictions of the older views, based upon the
stated entrance of absorbent tubes at the hilus of the organ, together with
the arteries and veins (Ecker, Koelliker, and others). While the super-
ficial lymphatics, namely, were found to contain a pellucid fluid, those of
the interior were stated to be filled with a coloured liquid reddened by
the presence of blood-cells.

A few years* ago, however, TJiomsa demonstrated lymphatic vessels in
the horse's spleen, and moreover in communication with those of the
surface of the organ. They traverse partly the banded sustentacular
matter, following the ramifications of the veins, and partly the connec-
tive-tissue of the sheaths of the vessels, together with the stronger arterial
twigs, whose finer ramifications they completely ensheath eventually.

Now, the statements of this talented observer have not the slightest
trace of inconsistency about them. Here, as elsewhere, we find muscular
and connective-tissue structures traversed by lymphatic passages, and,
owing to the lymphoid transformation which comes over these sheaths
continuous on the other hand with ordinary connective-tissue, the lymph
cells may be supplied to the fluid from such localities.

But when Thomsa states, further, that the final ramifications of the
internal absorbents conduct eventually into the follicles and pulp, and
there clothe the individual lymph corpuscles and agglomerations of blood-
cells with ring-like passages, we cannot rid ourselves of the greatest doubt
upon the point, nor avoid regarding what he has observed as probably
the result of extravasation into a tissue we know to be so fragile. We
can hardly conceive it possible, that beside the almost ubiquitous blood
stream, unconfined by a definite wall, a similar lymph stream could have
room to exist, and such an extensive peripheral mixture of lymph and
blood would be without any analogy in all that has as yet been observed
in the body in the two systems.

But whichever view, is correct, the significance of the spleen as a
blood lymph gland is by no means shaken.

The ueroes of the spleen having their origin from the phxits lienalis of

ORGANS OF THE BODY. 439

the sympathetic, consist principally, and not uiifrequently almost exclu-
sively of pale elements already known under the name of Remaps fibres.
They enter at the hilus, and pursue the same course as the ramifications
of the arteries. The number of nerves supplying the organ is very con-
siderable as a rule, but their mode of termination, judging from Koel-
liker and BillroiKs observations in the sheep and ox, is still uncertain.
Division of their trunks was observed by Koelliker, and Ecker probably
saw terminal resolution. According to W. Muller, finally, there occur at
certain points of the splenic nerves groups of cells like ganglion cor-
puscles : once only did he succeed in tracing a fibre into a capillary
sheath in the spleen of a pig. We are tempted to ascribe to the struc-
tures in question a similar significance as the end capsules of Kruuse on
the gland nerves (p. 327).

§ 235.

The spleen, whose sp. gr. is 1*058 (Krause and Fiaclier), contains 18-
30 per cent, of organic matter, and an average of O'5-l per cent, of
mineral constituents (Oidimann).

That organic fluid of acid reaction, which saturates the tissue of the
spleen, contains, according to Scherer, Frerichs, Staedeler, Cloetta, and
Gorup, a large number of interesting substances.

Among these may be named inosite, volatile fatty acids, — e.g., formic,
acetic, and butyric, also succinic, lactic, and uric acids. Among the
bases we find, in the normal human spleen, considerable quantities of
leucin, and a moderate, that is comparatively large amount of tyrosin
(Frerichs and. Staedeler). Xanthin and hypoxanthin are also encountered in
the organ. Beside these, Sclierer succeeded in obtaining non-carbonaceous
pigments, a very interesting albuminous substance rich in iron, and much
iron combined, it appears, with acetic and lactic acids. The peculiar con-
stitution of the veins must provide for tho passage of these matters into
'Jie circulation, but up to the present no analysis of the blood of the
splenic vein has come upon them there (comp. p. 121).

Special attention has been bestowed by Oidtmann upon the mineraJ con-
stituents, and among them he has found chlorine, phosphoric, sulphuric,
and silicic acids, potash and soda (the latter preponderating), lime,
magnesia, iron, manganese, and copper.

Turning, then, to the physiological significance of the spleen, so fre-
quently a subject of debate, it is supposed to play an important part in
the economy of the blood. It is believed to be concerned, namely, in the
destruction of the blood-cells on the one hand ; on the other, in the repro-
duction of the same. The first of these views may be defended, but not
incontrovertibly proved in the present state of science ; for although, in
many spleens, the blood-cells are certainly very extensively destroyed,
still a doubt exists whether this is anything more than an accidental
occurrence. , The second theory appears, however, more capable of proof.
According to it the spleen may be regarded as analogous in function to
the lymphatic nodes, producing the colourless cells of the pulp, which, on
finding their wayinto the blood, are known there as white blood corpuscles,
and which possibly, in part at least, undergo ere they leave the cavernous*
portions of the tissue of the spleen a transformation into coloured cells.
The amount of blood in the organ, further, is influenced in various ways by
its fibrous and muscular elements. The elasticity of the former opposes
to every expansion an amount of resistance varying with the volume of
29

440 MANUAL OF HISTOLOGY.

the contained blood, while the periodical activity of the muscular elements
presided over by their nervous systems leads to the expulsion of the
fluid contents of the spleen towards the point of least resistance, namely,
the veins and lymphatic vessels, and so to a decrease of volume in the
organ.

In support of the theory that the spleen is a species of accessory or
modified lymphatic gland, providing for the reproduction of colourless
blood-cells, we have, in the first place, the parallelism which exists in the
changes taking place in both these organs in certain diseases, then the
greater richness of the blood of the splenic vein in white elements (§ 70),
and, finally, the analogous structure of the spleen and lymph nodes. This
latter point, namely, that of similarity of structure between the spleen and
lymphatic glands, is most easily demonstrable in the lizard and snake, in
which a definitely enclosed stream of blood is seen to flow between certain
follicular masses (W. Muller}.

Gray's view is that the spleen serves the purpose of a reservoir for a
certain quantity of the blood. Schiff, on the other hand, regards the
organ as an auxiliary to the digestive apparatus, yielding to the pancreas
its power of digesting albuminous matters.

The origin of the spleen, as far as at present known, is from a special
aggregation of cells belonging to the middle germinal plate, and quite
unconnected with the digestive organs. These cells are subsequently
metamorphosed into the various tissues of which the organ is composed.
The first rudiments*are remarked at the end of the second month. Accord-
ing to Remak, the appearance of the Malpighian corpuscles is very early,
but Koelliker believes, on the contrary, that it is only towards the end of
intra-uterine life that they are formed.

Other conclusions, however, on these points have recently been arrived
at by Peremeschko. According to him the spleen is developed as an off-
shoot of the pancreas. The envelope and trabeculse, as well as the fine
reticulated tissue of the pulp, is first formed ; then the lymphoid cells,
with numerous red blood corpuscles, make their appearance, at first in
but small number ; then, from the rapid increase in number of the lym-
phoid elements, numerous collections of the latter are formed in the
sheaths of the arteries, giving rise, at a very early embryonic period, to
the Malpighian corpuscles.

The numerous morbid changes in structure taking place in this organ
require more careful attention than has up to the present been accorded
to them, owing to insufficient acquaintance with the minute structure of
the part. Among these a great increase of volume in the organ, asso-
ciated with an excess of white corpuscles or leucaemia, has awakened
much interest

§236.

Pending a more satisfactory classification, impossible in the present
state of histology, we shall for the present associate with the lymphoid
parts a series of other organs whose functions are still a problem, and as
to whose structure much doubt still exists on many points. These are
the thyroid gland, the supra-renal body, and the pituitary body. For the
present we may retain for them the old name of blood-vascular glands. In
many cases they have already reached or passed their full development,
as met with in the adult body, and are engaged in retrogression or pro-
cesses of decay.

ORGANS OF THE BODY.

441

The thyroid gland is found to "be made up of closed vesicles of roundish
form embedded in vascular connective -tissue (fig. 425, a, b). These
appear, at first sight, like closely grouped granules of 0'5641-1'1279 mm.
in diameter, rounded or flat, and of a reddish-yellow colour. They are

Fig. 425. — Two lobules from the thyroid of a a infant.
a, small glandular vesicles and their cells; 6, the
same with incipient colloid metamorphosis more
strongly marked at c; d, coarse lymph canals; and
e, fine radicals of the same ; /, an efferent vessel of
considerable size.

Fig. 426. — Colloid metamorphosis.
a, glandular vesicle from the
rabbit; if incipient colloid me-
tamorphosis from the calf.

again arranged in small lobules, and these in larger lobes, the considera-
tion of which we leave for descriptive anatomy.

The stroma is made up of ordinary fibrillated connective-tissue of toler-
ably loose texture, mixed with elastic elements. The gland vesicles,
0'0501-0'1026 mm. in diameter, possess a limiting membrane formed of
rather delicate homogeneous connective-tissue, which is enveloped exter-
nally in a dense round network of capillaries. The latter of a diameter of
about 0-0072-0-0115 mm. in the dog, and 0'0088-0'0115 and 0-0114 mm.
in the calf, are arranged in meshes of an average breadth of 0-0201-0-0226
mm. Their internal surface (fig. 426, a, b) is clothed with low cylin-
drical cells about 0-0196 mm. in height and 0*0113 mm. in breadth.
These resemble epithelium, and contain nuclei of about 0*0086 in diameter
(Peremeschko). The cells separate very easily from the walls in conse-
quence of decomposition, and on their solution the nuclei become free.
In the embryo the cavity of the round gland capsule is represented at
first by a finely granular substance, in which cells and nuclei are
embedded. Later on the growing cavity is usually seen to contain a
homogeneous, transparent, and almost fluid substance, known as colloid
matter (p. 21). By it the whole interior of the gland capsule is com-
pletely filled in the fully developed animal.

The recent researches of Frey and Peremescliko have made us
acquainted with the lymphatic vessels of the part. The whole envelope
of the organ is covered by knotted trunks, which take their origin from
a network of very complicated canals, situated in a deeper layer of the
former. This latter network is formed around the secondary lobules
of the gland by the reticular intercommunications of these canals (fig.
425. /).

442 MANUAL OF HISTOLOGY.

From the peripheral network formed of canals burrowing through the
connecbive-t issue of the capsule, lateral ramifications are given off, which
penetrate into the interior, and gradually enclose the primary lobes in
complete rings, or more or less perfect arches (d, d). From these a few
fine terminal passages with blind ends (e) are seen sinking in between the
different vesicles.

The nerves supplying this organ do not spring from the vagus or hypo-
glossus, but from the sympathetic, entering with the vessels of the part.
They consist for the most part of non-medullated fibres, forming trunks
with numerous branches, which ramify amid the connective -tissue
between the lobes and lobules. Among them may be seen ganglion cells,
partly isolated, and partly arranged in groups of from 2 to 5. Their
mode of termination is as yet unknown, except so far that fine terminal
filaments are lost in the connective-tissue bounding the vesicles. Con-
trary to the general opinion, the thyroid gland cannot be said to be poor
in nerves, nay, in the calf it appears even to be richly supplied with the
latter (Peremeschko).

The structure, as it has just been described, undergoes, however, a rapid
change, even at an early period, so that in the infant, even, we may meet
over a considerable area with modified glandular tissue, in such quanti-
ties sometimes as to render the recognition of its original structure of
some difficulty. The glandular cavities now become more and more
filled with a homogeneous transparent and semifluid substance (fig. 425,
5, c), a product of ?he transformation of the gland cells to which the name
colloid matter has been given (fig. 426). Later on in life the cavities
just described undergo in the human being a great increase in volume
through increase of the colloid matters, and most unmistakably at the
expense of the interstitial connective- tissue, which suffers compression.
An extreme degree of colloid accumulation leads not unfrequently in man
to a considerable enlargement of the whole organ, constituting that con-
dition known as goitre, the glandular struma of Ecker.

This progressive colloid metamorphosis, in which small whitish semi-
transparent points may be seen even with the naked eye, gives rise to
compression of the interstitial connective-tissue, and with it of the
lymphatic canals embedded in it. In consequence of this the absorbent
apparatus decreases more and more in efficiency, while the blood-vessels,
which remain pervious for a longer time, continue to supply material for
a continuation of the colloid metamorphosis. Further accumulation of
this substance leads to obliteration of the gland vesicles, the connective-
tissue disappearing, and the cavities opening into one another. If we
now examine a portion of the gland in which the process has advanced
to this stage, each lobe appears as a pale yellow coloured jelly-like mass,
enveloped in a network formed of the dwindling and half-macerated con-
nective-tissue bundles. Finally, it may come to pass that a whole lobe is
metamorphosed into a pellet of colloid matter. Hand and hand with these
changes anatomical transformations take place in the gland cells, the
latter becoming filled with the same substance, and finally undergo
solution.

The views regarding the functions of the thyroid gland are still only
hypothetical. The fluid which may be pressed out of its substance con-
tains leucin, hypoxanthin, as well as volatile fatty acid, and lactic and
succinic acids. The specific gravity of the organ has been set down by
Krause and Fischer at 1 '045.

ORGANS OF THE BODY. 443

From Remak's investigations as to its origin, it would appear that the
thyroid springs in the form of a saccule from the middle line of the anterior
wall of the pharynx, and is formed consequently in the same manner
primarily as the glands of the intestine. Soon after, however, it becomes
completely separated from the pharynx, and out of the single vesicle two
sacs are formed by division, which assume a lobulated appearance from
indentations and constrictions which are eventually developed on them.
In the thickened walls of these sacs solid aggregations of cells are subse-
quently formed, which are developed later on into the gland vesicles of
the organ, becoming invested with an envelope of connective-tissue, within
which a certain amount of fluid collects among the elements. The large
main vesicle on each side appears, likewise, to give origin to glandular
elements, by undergoing constriction at various points, and seems thus to
work its own obliteration. According to Peremescliko, we not unfre-
quently encounter division of the gland capsules as phenomena of growth.
The thyroid gland is probably at its greatest pitch of development in
the new-born infant, and becomes very sluggish in growth a few weeks
after birth.

§237.

The suprarenal ladies (glandulce suprarenalcs) have, on the other hand,
a different origin from the last, namely, from the middle germinal plate.
These are double organs, in regard to whose functions we are totally in
the dark. Enclosed in a capsule they present considerable variety of sub-
stance, both from an anatomical and physiological point of view, and we
may distinguish a cortical and medullary portion. The cortical .sub-
stance is marked with radiating streaks in different animals, varying in
colour from a brown or reddish, down to a whitish yellow, and is of a
tolerably firm consistence. Contrasted with this the lighter greyish red
or whitish medullary portion is less resistent. In man a dark narrow
boundary zone may be observed between these two portions, usually
yellowish brown, but at times greenish or blackish brown. After death
this breaks down rapidly, and becoming fluid, causes the loosening of the
medullary part of the organ from the rest.

The envelope (fig. 427, c) consists of connective- tissue with elastic
elements. Externally it merges into formless areolar tissue, containing
fat cells. Internally it gives off those numerous fibrous processes which
traverse the organ, and in their ultimate arrangement form a framework
within which the cells are enclosed.

Let us now glance at the cortical substance of the suprarenal bodies.

Those band-like processes just mentioned are tolerably strong, and take
a slightly convergent course inwards, giving to the cortex, which in man
is about 0'6767-(H279 in thickness, a fibrous appearance, distinctly
visible even to the unaided eye. From these numerous bundles of
connective-tissue coming off, laterally intercommunicate with others also
given off from the internal surface of the envelope, giving rise to a large
number of glandular cavities. Near the surface of the organ these latter
are generally short, but soon attain considerable length as they follow the
course of the septa, assuming a columnar figure (fig. 427, «, b; 428, a).
In transverse section, however, these rows of cells do not always appear
round, but not unfrequently present to our view oblong, reniform, and
crescentic configurations. Again, in profile, we may easily make out that
such gland cylinders divide and give off branches at' acute angles.

444

MANUAL OF HISTOLOGY.

Fig. 427.— Cortical portion of the
human suprarenal body in ver-
tical section, a, small, and b,
larger gland cylinders; c, cap-
sule.

Further inwards still the cavities of the cortical portion "become shorter
and shorter, assuming, consequently, a more
rounded form. From this point on there
commences, in the strong and but slightly
altered septa of connective-tissue, a rapid
fibrillation, the fibres converging so that the
further we advance towards the cen'tre of the
organ, the smaller do the interstices become.
In the nodal points of this network we find
nuclei, the general arrangement of parts re-
sembling in many respects what we have
already met with in lymphoid reticular con-
nective substance (Joesten).

The interstices in the cortex just alluded
to contain a dark viscid mass, which is found,
on closer inspection, to be made up of naked
cells containing albuminous granules, and. not
unfrequently, numerous fatty molecules also
(fig. 428, a ; 429, d). Within the soft bodies
of the former, whose diameter is about 0-0135
or 0*0174 mm., large nuclei may be observed;
measuring from 0-0090 to 0*0056 mm. The
cells situated within the dark boundary zone
already alluded to, contain large quantities of brown pigmentary granules.
While the more internal and smaller meshes
enclose but a few cells, the elongated and radiating
compartments contain multitudes of them (fig.
428). The latter cavities are, besides, traversed
by minute fibrous bands, forming a reticulum.

As to a membrana propria, eacb agglomera-
tion of cells was formerly supposed to be en-
veloped in one, in the same manner as a glandular
crypt (Eclcer) ; but this covering certainly does
not exist in our opinion.

Elucidation of the structure of the delicate
medullai^y substance is attended with great
difficulties.

We see, however, that at the inner border of
the cortical portion the fine fibres of the frame-
work, though very closely arranged, approach
each other still more, and are inserted eventually
into processes of a mass of tough connective-
tissue, which occupies the centre of the organ en-
veloping the stronger blood-vessels, and especially
the large veins.

Enclosed within this fine sustentacular sub-
stance of the medullary portion of the organ,
a number of large oval cavities are to be seen.
These exceed in size those of the cortex, but
do not possess the same radiating arrangement ;
they lie rather with their broad surfaces towards the centre and surface
of the organ. In man these medullary cavities appear to be generally
smaller and rounder than in other animals.

Fig. 4?8.— Cortical portion of
human suprarenal body un-
der high magnifying powei.
a, gland cylinders; 6, inter-
stitial connective-tissue.

ORGANS OF THE BODY.

445

Fig. 429.— Transverse section through the
cortical substance of the human supra-
renal body, a, framework of connec-
tive-tissue ; b, capillaries ; c, nuclei ; rf,
gland cells.

These interstices are likewise occupied by naked cells, with beautiful
vesicular nuclei and finely granular bodies.
Fatty molecules are present, however, in
this case in but small quantity. The
dimensions of the cells (0-0180-0-0350
mm.) exceed those of the cortical elements.
Owing to their softness, also, they accom-
modate themselves one to another. Frpm
the fact of their form being somewhat
that of a thick angular plate, they recall
to mind, when seen from the side, the
appearance of columnar epithelium. It
is a point worthy of note that, while the
cells of the cortical portions of the organ
are but slightly affected by the action of
bichromate of potash, the bodies of these
which are now under consideration ac-
quire a deep tinge of brown from immer-
sion in a solution of this salt (Henle).

The blood-vessels of the suprarenal body
offer many peculiarities for our consideration. They are very abundant
in this organ. Multitudes of small arterial twigs, partly from the aorta
and partly from the phrenic, cseliac, lumbar, and renal trunks, penetrate
into the interior of the suprarenal body with numerous ramifications,
and break up there into a network of capillaries, whose elongated
meshes are arranged in the direction of the radiating bands of tissue
within the organ. These small tubes have a diameter of about 0*0059-
0-0074 mm., and follow the course of the connective-tissue processes
which traverse the cortical substance. The meshes formed by them,
measuring about 0-0451-O0564 mm. in length, and 0'0293-0'0201
mm. in breadth, invest eventually the many agglomerations of cells already
alluded to. The medullary portion appears to have no true capillaries, and
the cortex is certainly destitute of venous twigs.

On entering the medulla the arterial capillaries become larger, and
form, by anastomosis, a number of vessels of considerable calibre. These,
then, continue to join one with another at acute angles, maintaining, as a
rule, the direction of the capillaries of the cortex. Thus the whole of
the medulla becomes occupied, to a great .extent, by an uncommonly
highly developed venous network of tubes, measuring 0 '0200-0 '02 9 3
mm. and upwards, with interspaces between them of 0'0200-0'0345 mm.
The union of these vessels produces larger, which empty themselves into
the usually single large venous trunk, situated in the centre of the organ.
Thus we find the cortical portion traversed by a delicate arterial interlace-
ment, and the medulla occupied by a coarse venous network.

As regards the lymphatics of the organ, we possess at present no
reliable information.

The chief interest, however, which attaches to the medulla is owing to
its great richness in nerves (Bergmann) which are arranged here in many
mammals in a highly intricate plexus of microscopic minuteness, in which,
according to Holm, ganglion cells may be recognised, Owing to this it
has been surmised that the suprarenal body has some connection with the
nervous system. The final termination of the nerves is still unknown.
The cortical portion often appears to be utterly devoid of nerve fibres.

446 MANUAL OF HISTOLOGY.

As regards the composition of the suprarenal body, we only possess a
few notes at present. Its specific gravity is, according to Krause and
Fischer, 1*054. It contains leucin and myeliri in large quantities
(Virchow). Holm has also met with inosite and taurin in the ox.
Among the graminivora, hippuric and taurocholic acids are also stated by
Gloez and Vulpian to be present in the organ in question (?) Another
matter was also discovered in the medulla by Vulpian, and its presence
confirmed by Virclww, which became red on exposure to the air and on
the addition of iodine in solution, and blackish blue under the action of
chloride of iron.

We are still entirely in the dark as to the physiological significance of
the suprarenal bodies. They are, however, liable to undergo many
morbid changes, which have recently become the subject* of much con-
sideration in their relation to the so-called Morbus Addisonii. This
manifests itself in very emaciated subjects as a very deep discoloration
of the skin, together with disorganisation of the suprarenal bodies. The
tingeing of the skin is produced by the presence in the deeper layers
of cells of the rete mucosum of either a diffuse or very finely molecular
pigment of a yellowish or yellowish brown colour. That peculiar colouring
matter in the boundary zone between the medullary and cortical portion of
the organ which we have already considered above, is very possibly con-
nected with this very obscure and enigmatical phenomenon.

The suprarenal body is developed at the same time as the kidney, but
independent of it, from an aggregation of cells in the middle germinal
plate. It is a curious fact, that during the earlier portion of intra-uterine
existence these bodies at first exceed in magnitude the urine-secreting
organs. At about the twelfth week in the human subject they are about
equal the latter in size, and from that on they remain more or less
stationary. The histogenesis of these organs, however, is not yet quite
settled.

§ 238.

The pituitary body, or hypophysis cerebri, was formerly supposed to be
a glandular structure, but was subsequently classed among the nervous
organs.

Present in all five classes of vertebrata, but smallest in man arid the
mammalia, it consists in the latter of two portions or lobes. In the
smaller posterior part, which is greyish in colour, we meet in a connective-
tissue substratum with fine isolated nerve tubes, cells resembling ganglion
corpuscles, a quantity of sustentacular connective-tissue, with fusiform
cells and blood-vessels, but no glandular elements.

The anterior lobe, much larger and redder, has by no means the same
structure. It is traversed by a canal according to Peremeschko, and, as
was found many years ago by Ecker, it possesses great similarity with the
so-called blood-vascular glands. Here we encounter, within a connective-
tissue framework very richly supplied with blood-vessels, roundish or oval
glandular cavities, measuring in man and among the mammalia 004:96-
0'0699 mm. These are occupied by cells of about 0'0140 mm. in
diameter, with tolerably large and finely granular bodies. Here also we
find, according to Ecker and Peremeschko, a colloid metamorphosis of the
cells, like that which takes place in the thyroid gland. The canal, whose
form is very various in different animals, is lined among the latter with
flattened cells, which in man are ciliated. It is continuous with the

ORGANS OF THE BODY.

447

cavity of the infundibulum. Behind the canal the glandular tissue
assumes a somewhat different character. Here we remark, besides, a
finely granular mass and free nuclei, cells, whose bodies seem poor in
granular substance. Colloid vesicles are also to be found here ; the frame-
work is formed of a somewhat more highly developed connective-tissue
than elsewhere.

The pituitary body is richly supplied with interlacing capillaries,
0'0050 mm. in diameter, the anterior portion being most vascular
(Peremeschko).

Some years ago an extraordinary little organ, of roundish figure, and
about 2 mm. in diameter, was discovered by Luechka, which, owing to
its position on the tip of the
coccyx, he named coccygeal
gland. The structure of this
body, as described by the dis-
coverer, resembles, if we except
several peculiarities, in general
that of the blood -vascular
glands, namely, the hypophysis
cerebri and suprarenal capsules.
The subsequent researches of
Henle, Krause, and KoeUiker,
have not shown any essential
inaccuracies in his description.

Like the pituitary body, the
coccygeal gland is placed at
one extremity of the sympa-
thetic chain ; and, like the
suprarenal capsule, it is rich in
nervous elements. As gland-
ular elements, it is stated to
contain round vesicles and
simple and branching follicles,
imbedded in a tolerably solid
connective-tissue interspersed
with numerous elongated nuclei.

The coccygeal gland, which
is very vascular, receives its
blood from a branch of the sacralis media.

The accuracy of this description has, however, been recently questioned
by /. Arnold, in toto. According to him, the organ does not contain
glandular elements, but belongs rather to the vascular system, being
composed of a multitude of saccules communicating with the arterial
twigs of the part (fig. 430, b, c). When strongly marked these may
form a system of convoluted diverticula, recalling to our minds the
glomeruli of the kidney, and possessing always^the same structure as the
walls of arteries, with a strongly developed external layer of longitudinal
muscle fibres (h, i). Groups of these saccules may open immediately into
the arterial twigs (a), and are like them filled with blood ; they may,
however, owing to the fineness of the afferent and efferent blood-vessels
(d, e,f), appear to be completely closed on all sides. These statements
have, however, been again questioned. The glandular structure of the
organ has once more been insisted on, the cells supposed by Arnold to be

Fig. 430. — Vascular diverticulurn, 6, c, of the coccygeal
gland lined with endotlielium ; a, afferent, d, efferent
arterial twig; e. /, brandies which break up into a
capillary netwoik; h, t, muscular tissue; g, envelope
(alter Arnold).

448 MANUAL OF HISTOLOGY.

endothelium, are regarded now as covering vessels situated in its in-
terior.

The so-called ganglion inter car oticum, which was found by Lusdika to
be very similar, as regards its microscopical appearance, to the coccygeal
gland, has also been declared by Arnold to have the same peculiar vascular
structure as the latter.

2. Respiratory Apparatus.

§239.

The respiratory apparatus is made up of a system of branching canals
for the entrance and exit of air, and a proper respiratory part. The first
of these is represented by the larynx trachea and its ramifications, the
latter by the lungs. The whole may be compared to a racemose gland.
It presents important peculiarities as well physiologically as anatomically,
and especially in the high development of its elastic tissue.

The larynx consists, we know from descriptive anatomy, of several
cartilages, the ligaments connecting these one with another, the muscles
by which they are moved, and a lining of mucous membrane.

In describing cartilaginous tissue we have already referred to the
various cartilages of the larynx. These afford examples of the different
species of this tissue. The thyroid, crycoid, and arytenoid are formed of
hyaline substance. At certain points in the latter, however, namely, in
the processus vocalis and apex, a change into elastic cartilaginous tissue
has already commenced (§ 107, p. 176). The cartilages of Wrisberg and
Santorini, and the epiglottis, are entirely formed of the latter tissue (§ 108,
p. 180), while the c. triticea appear to be principally composed of iibrous
tissue (§ 109, p. 181).

The ligaments of the larynx are either almost entirely composed of
elastic fibres, or are at least very rich in them (p. 229). Those in which
the essentially elastic nature is best marked are the vocal cords, the
ligamenta tltyreo-arytcenoidea inferiora.

The muscles of the larynx belong to the striped class (§ 164, p. 103).

The epiglottis is in the human subject covered on its anterior surface
with a strongly laminated epithelium 0-2 or 0'3 mm. in depth, and on
its posterior aspect with a much thinner bed, only 0-06 or O'l mm. The
lower part of the latter is lined with laminated ciliary epithelium 0'15
mm. or even more in thickness.

The mucous membrane, which, especially in its deeper portions, is rich
in elastic tissue, presents as a rule a smooth surface and tough texture.

At certain points, however, it presents larger or smaller papillae, as on
the true vocal cords. Its most superficial layer contains lymph cor-
puscles embedded in it close under the epithelium. These may be pre-
sent in such number as to give rise to regular lymphoid follicles, single or
grouped.

Finally, it is studded with numerous racemose mucous glands, either
scattered or crowded together in certain situations. The bodies of these
glands may lie embedded in depressions in the subjacent cartilage. It is
by these organs that the mucus of the larynx is secreted. Their excretory
canal appears thick-walled, and the acini are frequently elongated and
clothed with low columnar cells.

From the base of the epiglottis and false vocal cords the epithelium
(with the exception of that clothing the true cords, which is of the

ORGANS OF THE BODY. 449

laminated flattened species) consists of a slightly laminated layer of cili-
ated cells (1) (p. 149). Among these are scattered a certain number of
beaker cells, which are also present in the trachea and its ramifications,
according to Gegenbavr and Knauff.

The nerves supplying the larynx are branches of the vagus, namely,
the Laryngeus superior, composed of fine medullated fibres principally
sensitive, and the /. inferior, formed of broad filaments, and essentially
motor. Their ramifications have in many cases microscopically small
ganglia connected with them. They are distributed to the muscles, the
perichondrium, and the mucous membrane. Their terminal plexuses
may be recognised in the latter, but not the ultimate ending of their
primitive fibrillse.

Nothing unusual is to be seen in regard to the blood-vessels. The
lymphatics are numerous, and are arranged in the mueosa and sub-
mucous layer in a superficial and deep network, which are not, however,
sharply defined against one another in all cases (Teichmann).

§ 240.

The trachea, with its branches the bronchi, may be described as a
ramifying tube, consisting of a strong fibrous tissue, in whose anterior
wall lie embedded the annuli cartilaginei. Thus the fibrous tube pre-
sents in the first place perichondrium, and then the ligamenta interan-
nularia connecting the half rings of the trachea one with the other, and
finally closing the cartilaginous canal behind the membrana transversa.
The latter is strengthened internally under the mucous membrane by a
thick layer of muscular bundles, running for the greater part transversely.

The fibrous tissue of which the canal is principally formed possesses
besides an abundance of elastic fibres (p. 229).

The tracheal cartilages belong to the hyaline species (§ 107), and have
nothing remarkable about them.

The muscular substance of the wind-pipe is made up of smooth fibres
(§ 163). It is about 0 '8-1 -2 mm. thick. The great abundance of elastic
tissue present throughout the whole respiratory apparatus, allows also of
the formation of beautiful elastic tendons, through which these muscles are
attached to the perichondrium on the extremities of the annuli cartila-
ginei. External to these transverse muscular, fibres there are frequently,
though not invariably, found a number of scattered longitudinal bundles
which take their rise from the fibrous wall of the canal (Koelliker).

The mucous membrane of the trachea, 0'13 or 0*15 mm. in thickness,
contains a multitude of racemose mucous glands, in some instances small
and simple, in others large and complex, in which case the body of the
organ reaches deeper into the wall of the tube. The larger glands are
situated partly between the rings of the trachea, and partly in the pos-
terior wall, in which a regular layer of them presents itself.

The surface of the mucous membrane is clothed with ciliated epithelial
cells, of 0*0594 mm. in height, interspersed with beaker cells.

The trachea is also richly supplied with blood-vessels and lymphatics.
The latter are arranged in a superficial layer of minute canals, measuring
in diameter 0'0678 mm., lying in the mucosa, and taking principally a
longitudinal direction, and a deeper set of much larger tubes 0'0941 mm.
in diameter. The course of these stronger trunks is, at least, partly
transverse (Teichmann). The nerves of the part which are supplied by
the sympathetic and inferior laryngeal require closer study.

450

MANUAL OF HISTOLOGY.

§ 241.

We turn now to the consideration of the lungs.

These organs may, as regards form, be compared to racemose glands. This
resemblance is also seen in their mode of development. The excretory
canals are represented by the bronchial ramifications, and the acini by
the air- vesicles. Besides these numerous blood-vessels, lymphatics, nerves,
and connective-tissue structures enter into their composition.

The two bronchi, which, as is well known, divide again into two before
their entry into the roots of the lungs, continue to sub-divide with the
factor two, and at acute angles, on entry into the organ, so that a multitude
of ever decreasing canals is soon formed. The cartilaginous supports lose
from this on the character of rings, and assume rather the form of irregular
plates and scales, which are no longer confined to the anterior wall, but
for the rest, as far as their texture is concerned, differ in no respect from
those of the trachea. The last traces of cartilaginous plates are only lost

in bronchial twigs of extreme fineness,
Gerlacli having found them in those of
only 0*23 mm. diameter. The walls of
these tubules present, but in decreasing
strength, of course, the same fibrous layer
that we have already seen in the trachea,
and a mucous membrane with ciliated
cells, which loses gradually its laminated
structure, until there only remains at last
but one single layer, 0*0135 mm. in height,
of dwarfed cells (p. 149). Racemose
mucous glands, likewise, present them-
selves here until we pass into canals of
extreme fineness. The smooth muscular
layer which, as we have seen in the foregoing section, exists in the
trachea, forms around the bronchial passages a continuous tunic. It may be

followed here, likewise, down to the
very finest tubes, and is present possibly
even in the neighbourhood of the air-
vesicles, but is certainly not to be found
on the latter. In the very finest tubes
the mucous membrane and external
fibrous layer become eventually fused
into one single thin coat, made up of
a homogeneous membrane surrounded
externally by elastic fibres.

Owing to this progressive sub-divi-
sion, together with which small lateral
twigs are given off from the larger
bronchi, a very complex system of
branching passages is produced.

At the end of the last bronchial twigs
(fig. 431, a), tubes of 0'3-0'2 mm. in
diameter, we come upon the true re-
spiratory part of the organ. This con-
sists, in the first place, of thin-walled
round canals of 0'4-0'2 mm. across. To these the name pf alveolar

Fig. 431. — A portion of the lung of an
ape (Cercopithesus) filled with quick-
silver (after F. E. Schulze). a, end of a
bronchial twig ; c, alveolar passage ; b,
infundibula.

Fig 432. — Two primary pulmonary lobuli
or infundibuli (a) with the air-vesicles,
6; and terminal bronchial tubes, c; which
also bear some of the pulmonary ve-
sicles, 6.

ORGANS OF THE BODY. 451

passages has been given by Sclmlze (fig 431, It; 432, c). They are sub-
divided again at acute angles, and end finally in peculiar dilatations (431,
b; 432, a). These are the so-called primary pulmonary lobules. They
are of short conical figure, and have received from Rossiynol the name of
infundibula.

These primary lobuli correspond, to a certain extent, with the primary
lobules of the racemose glands, and are like them made up of terminal
vesicles, as a rule roundish, but polyhedral when strongly distended.
They are always met with on the surface of the organ in this form.

There is, however, a difference between the two. While the saccules,
namely, of every genuine racemose gland remain more or less distinct
from one another, the analogous parts of the respiratory organs, to which
the names air cells, pulmonary vesicles, alveoli, or Malpighian cells, have
been given, are far less isolated. They appear to be rather saccular
dilatations in the walls of the primary lobules, in which no further
canals are to be discovered, all the alveoli, on the contrary, opening

Fig. 433.— Transverse section through the substance of the ]ung of a child of nine months
(after Ecker). 6, a number of air vesicles enveloped in elastic fibrous networks winch,
together with a thin structureless membrane, form the walls of the same; d, a portion
of the capillary network of the part, with its tendril-like tubes projecting into the
cavities of the alveoli; c, remains of epithelium.

directly into a common cavity. In the adult body, moreover, absorption
of the walls between the several air cells of an infundibulum may take
place (Adriani).

The side walls of the alveolar passages are also thickly covered with
numbers of similar pulmonary vesicles (fig. 431, c, c).

In sections of pulmonary tissue (fig. 433) the more or less round or
oval form of the vesicles may be recognised in the open spaces of varying
size brought into view (b}, agreeable to the description just given.

The diameter of the alveoli is generally stated as ranging between
0-1128 and 0'3760 mm. Their great elasticity admits, of course, during
life, of their dilatation to a great degree, so that, as we would expect, the
vesicles are, at the end of inspiration, much larger than during expiration.

452 MANUAL OF HISTOLOGY.

Complete collapse or distension of the air cells, however, never takes
place under normal conditions in the lung. The possibility of this is pre-
cluded by the situation of the organ. This, namely, is hermetically sealed
up within the cavity of the chest. On account of its distensibility, there-
fore, it follows all the motions of the thorax in inspiration, most accurately
lying in contact with every part of the internal surface of the latter.
Then, on account of its elastic nature, and aided by the muscles of its
air passages, it contracts with every expiration as much as is admitted of
by the walls of the chest. It never, however, goes so far as entire collapse,
which is only reached naturally when the cavity of the thorax is laid
open, on which it at once takes place.

If we now inquire into the texture of this elastic alveolus, which is
constantly expanding and contracting during life, we will find a few
points elucidated by fig. 433. The walls of the air vesicles, as continua-
tions of the finest bronchial ramifications, present for our consideration,
in the first place, an extremely delicate membrane of connective-tissue,
measuring about 0*0023 mm., and less, in thickness. At the right side
of the plate a portion of this may be seen in the large central alveolus.
This very fine membrane serves to connect the crowded capillaries of the
walls, and probably clothes the surfaces of the latter. We require, llow-
ever, further research on this point before it can be established.

This membrane of the air cells is then covered externally by a greater
or smaller number of elastic fibres, varying greatly as to thickness. They
present themselves either scattered or in groups. The strongest fibres are
to be seen in the interalveolar septa, especially between adjacent vesicles,
closely packed together. The remaining portions of the alveolus are
poorer in them than the entrance, and especially the fundus. Here are
to be seen, scattered at wide intervals, the most delicate elastic elements,
measuring perhaps 0*0011 mm., and appearing like reticular connections
between the air vesicles. The limiting membrane, on the other hand,
does not appear to possess many nuclei, most of those which are to be
seen probably belonging to the capillaries or epithelia.

These primary lobules of the lung, best studied in the infant, the
structural relations often becoming very indistinct in the adult, enter
again into the formation of the secondary lobuli, connected together
through the medium of connective-tissue. The diameter of these latter
may be roughly estimated at 1 or 2 mm. They are more distinctly seen
in the adult than in the infant, in the form, of polygonal fields on the
surface of the organ, marked out by the deposit between them of black
pigment.

By the aggregation of these lobuli the larger lobes are gradually formed,
the consideration of which belongs to descriptive anatomy.

It is a curious feature in the existence of the interstitial connective-
tissue of the lung, that there is usually a certain amount (frequently very
large) of black pigment deposited in it. The walls of the air vesicles, also,
may likewise be affected in the same way; besides which, molecules of
this substance are met with in the protoplasmic bodies of the smaller
epithelial cells of the respiratory tubes, and in certain rounded corpuscles
connected with the mucus of the part. We have already referred to the
pigmentation of the bronchial glands (p. 418).

It was for a long time supposed that this pigmentation resulted from a
deposit here of true melanin. But from the fact of its not being present
in the lungs of wild animals, while in man, living in an atmosphere of

ORGANS OF THE BODY.

453

smoke, and loaded with soot, it is found in large quantities, it was
inferred that the true origin of the pigmentation must lie in the inspira-
tion of particles of carbonaceous matter. This view seems to be confirmed,
farther, by observations made on the organs of those engaged in occupa-
tions which necessitate their breathing an air charged with supended dust
of various kinds, as, for instance, those of coal miners, whose lungs may
be found to be perfectly black. It was also discovered that large frag-
ments of wood charcoal often make their way into the air vesicles, and
that the lungs of animals, when confined in sooty chambers, become quite
black (Knauff}. That a deposit of genuine melanin, however, does
also take place in the lungs and air passages, as well as in the bronchial
glands, is beyond doubt, but we are unfortunately unable as yet to dis-
tinguish between the two kinds of particles.

REMARKS. — A distinction between " anthrakosis " and "mclanosis" of the respira-
tory organs may be made. The cells which we have given in fig. 95, frequent con-
stituents of the sputa, are in many instances genuine melanin cells ; "but in other
cases which may be set down as more the rule, the contractile body of the cell has
taken up fine carbonaceous particles from without. We nmst confess, however, that
the deposit of these matters in the interstitial connective-tissue of the lung and
parenchyma of the bronchial glands is still a subject of great obscurity.

§242.

There now remain for our consideration but a few more structural
relations in dealing with the lung. There are the arrangement of its
blood and lymphatic vessels, epithelium of the air vesicles, nerves, and
serous covering.

The blood-vessels of the organ receive their blood, as is well known,
from two sources: firstly, from the bronchial; secondly, from the pul-
monary arteries. The first of these serve the subordinate purpose of yield-
ing nourishment to the tissue of the organ ; the second are set apart for the
requirements of respiration. The distinc-
tion between the two, however, is by no
means sharp.

The arteria pulmonalis divides and sub-
divides, following the ramifications of the
bronchi, and arrives thus with its twigs
between the lobuli. Here a further split-
ting up occurs until very fine tubes are
formed, which penetrate into the elastic
band-work between the pulmonary vesicles
(fig. 434), often sub-dividing still further in
their course here. At the same time, the
most extensive anastomosis takes place, so
that imperfect or even complete rings are
formed (b). From these a multitude of
capillary tubes is given off to form the
respiratory capillary network, which clothes
the walls of the air-vesicles, only separated
from the atmospheric air by the most deli-
cate membrane.

This network (a) is remarkable for the great regularity and small size
of its meshes. It may be reckoned among the densest, as also the most
regular occurring in the body. The peculiar form of its wide capillaries
is also striking. The diameter of the latter is about 0-0056-0-0113 mm..

Fig. 434. — The respiratory capillary net-
work of a horse's lung, injected
after GerlacKs method. 6, the end
branches of the arteria pulmonalis
encircling more or less the several
pulmonary vesicles; a, the capillary
system.

454 MANUAL OF HISTOLOGY.

being sufficient to allow of the easy passage of the blood-cells. When
the pulmonary vesicle is contracted, or but very slightly distended, they
appear too long for the extent of surface to be covered by them, and pro-
ject in the form of loops and tendril-like convolutions, pushing before them
a portion of the delicate lining membrane of the alveolus (fig. 433, d).

But when the air-cells are strongly distended, these capillaries assume
a much straighter direction, while the loops and projections into the
vesicles disappear in a corresponding degree.

In muscle, also, which is constantly undergoing change in length, we
find the same provision of nature. When contracted the longitudinal
tubes of its capillary network assume a spiral course ; when relaxed, on
the other hand, they appear straight.

As to the walls of the capillaries, there is nothing remarkable about
them. They are usually nucleated, and may easily be resolved into the
well-known vascular cells (fig. 356, p. 363).

The meshes bounded by these tubes are very close, even in lungs

which have been previously inflated
(figs. 433, 434, 435). They may be
more or less round or angular. They
have a diameter of from 0P0393 to
0-0293 mm. That in the uninflated
organ the meshes will be found much
smaller than in the inflated, owing
to their shrinking together, is quite
evident.

The capillaries, further, of adjacent
alveoli intercommunicate very exten-
sively.

But the fine twigs of the pulmonary
artery also, curious to say, form in

Fig. 435.— Pulmonary vesicle from the calf, a, .f ., ,. .-, r J M

large blood-vessels traversing the septa of the another situation a wide-meshed capil-

alveoli; 6, capillary network; c, epithelial }ary network, namely, Under the

pleura. Here they communicate with
the terminal tubes of the bronchial arteries.

The pulmonar y veins take their origin from ths capillary networks just
described, with scattered twigs in the interalveolar septa. The con-
fluence of these produqes larger trunks, which accompany the bronchi
and ramifications of the pulmonary artery back to the root of the organ.

The bronchial arteries, giving off as a rule a single branch to each of
the air passages, supply numerous twigs in the root of the lung to the
larger vascular trunks, the lymphatic glands of that neighbourhood, and
the connective-tissue between the lobuli and under the pleura. In the
walls of the bronchi and their ramifications they are resolved into an
external loose network of capillaries for the muscular tissue of the part,
and- an internal and much denser for the mucous membrane. In the
latter, however, there is, besides, another coarser and more superficial
capillary network, which does not appear to communicate in any way
with that of the bronchial arteries. It belongs to the respiratory system
proper, and may be injected easily from the vena pulmonalis, with diffi-
culty from the arteria pulmonalis, and not at all from the bronchial arte-
ries. From this we may infer that its radicals spring from the respiratory
capillary network (Herile).

The arrangement of the bronchial veins, further, is peculiar. These pro-

ORGANS OF THE BODY.

455

bably only receive the blood returning from the thick walls of the larger
bronchi, and from the lymphatic glands and pleura around the root of
the organ. The finer and internal venous radicals, on the other hand,
coming from the smaller divisions of the air passages, and which corre-
spond to the distribution of the bronchial arteries, empty themselves into
the branches of the pulmonary veins.

Lymphatics, as has long been known, are present in the lungs in con-
siderable number. They may be divided into two classes : into super-
ficial (arranged in retiform interlacements immediately under the serous
covering of the organ) ; and into deep, which may be traced outwards
along the air passages into the bronchial glands. Both of these sets of
vessels communicate freely, however, with one another.

Not long since Wywodzoff was fortunate enough to succeed in injecting
the radicals of the lymphatics in the walls of the alveoli in the lungs of
the dog and horse, and Solwrsky also in the first named animal and in
the cat. In these walls are found lacunse, which are enlarged opposite
the meshes of the capillaries. They
cross the capillaries, without, how-
ever, forming sheaths of any kind
around them. Soon after, however,
the lymphatic canals as they pass
away commence to occupy the adven-
titia of the blood-vessels.

We now come to the considera-
tion of the epithelium of the air-
cells — still a subject of controversy,
and which, has been recently the
object of the most earnest investiga-
tion.

Turning then, in the first place, to
the lung of the frog, we find the
arrangement of parts of the simplest

kind (fig. 436). The whole respiratory portion of the organ is lined
with a single continuous layer of flattened nucleated epithelial cells.

But the lungs of the mammalia and man present greater difficulties.

Here we must first study the structure of the parts at an early period
of existence, if we would understand
it in the adult body.

In the mammal foetus we likewise
find a continuous epithelium lining
both pulmonary vesicles and alveolar
passages, and entirely the same in
both. Its elements are flat polyhed-
ral cells, with nucleus and protoplasm.

After birth, however, several
changes become rapidly apparent,
consequent upon the commencement
of respiration. Only a small portion
of the epithelium preserves its former
character. Over the projections of
the capillaries, and all other promin-
ences, we can find much larger pale cells without protoplasm or nucleus
in many cases.

30

Fig. 436. — A portion of an air-cell from the
lung of a frog.

Fig. 437.

456 MANUAL OF HISTOLOGY.

Fig. 437, after an old drawing, represents the original cells in the
meshes of the capillary network of a young animal.

The condition of parts, on the other hand, in the mature mammal, is
given in hg. 438. Here large non-nucleated plates are seen, with remnants
of the original small cells, and a trace of the protoplasm and nucleus with
them, at their points of contact and corners (Schulze).

The nerves of the organs of respiration spring from the anterior
and posterior pulmonary plexus. They are derived partly from the sym-
pathetic and partly from the vagus, and take the same course, to a great
extent, as the ramifications of the bronchi or the pulmonary arteries.

Fig. 438.— Epithelium from the base of an infundibulum situated immediately under
the pleura. From a fully-grown cat ; treated with nitrate of silver.

The pulmonary veins and bronchial arteries are not accompanied to the
same extent by nervous twigs. On the external surface of the bronchi
there are to be found, in connection with the latter, numerous small ganglia
(Remak). The same are seen on the finer ramifications of the nerves in
the tissue of the lung (ScJiiff). These nervous filaments appear to ter-
minate in many cases in the mucous membrane of the bronchi.

The pleural covering of the lung and thorax presents, as far as epithe-
lium and connective-tissue substances are concerned, the ordinary texture
of all serous membranes. The nerves of the structure are derived from
the phrenic, vagus, and sympathetic (plexus pulmonalis). Those distri-
buted to the pulmonary pleura are stated by Koelliker to have scattered
ganglion cells among them. The vascularity of the membrane is low,
the capillaries being very fine, and forming wide meshes. The pulmonary
pleura receives its vessels, as has been already mentioned, from the pul-
monary and bronchial arteries.

The lymphatics of this membrane are to some extent well known, espe-
cially from the recent studies of Dyblcowsky. In the dog they are only
evident in the movable portions of the parietal layer, i.e., in the inter-
costal spaces, and upon the sterna costalis muscles, but not upon the ribs.
On the mediastinal portion they are only seen at those spots where col-
lections of fat-cells exist.

ORGANS OF THE BODY.

457

The lymphatic network is very dense, and may be divided into two
layers separated from one another by fibrous tissue. The superficial
canals traverse the interstices of a reticulated layer of connective-tissue,
the substratum of the serosa. Here their walls, composed of vascular
cells, are covered solely by the epithelium of the membrane between
whose cells those orifices already described in section 208, fig. 381, 2, 3,
are situated.

Absorption from the cavity of the pleura is effected through the
agency of the respiratory movements in the intercostal spaces, and the
varying amount of tension to which the connective-tissue in which these
canals are situated is subjected thereby. The contents of the networks
formed by the latter are received by valved vessels running along tho
ribs towards the vertebral column and by the mammary twigs.

§243.

Turning now to the composition of the pulmonary tissue, we find that
only of the products of decomposition occurring in the fluids with which
it is saturated is anything reallv known. Cloetta obtained inosite,
taurin, and leucin from the
lung of the ox. The human
lungs, also, were found to con-
tain leucin in considerable
quantity. In the foetus the
organ yields glycogen (Ber-
nard, Rouget).

The development of tho
lungs (fig. 439, 1) takes place
very early in the same way as
the large glands connected
with the intestinal tube,
namely, in the form of two
hollow processes (c) attached
by one stalk (a) to the anterior
wall of the pharynx. This
body is hollow from the very
commencement. Both the
internal and middle germinal
plate are here represented, the
former in the cellular layer
(c), the latter in the fibrous
wall of the part (&). From
the cellular layer the epithe-
lium of the respiratory tract
is derived, while in the ex-
ternal investing mass we
have the rudiments of all the
fibrous and cartilaginous por-
tions of the air- passages,

bronchi, and lungs. From these blind tubes of the glandular plate an
ever-increasing number of new sacculi (d) are now given off into the
surrounding substance by means of cell-multiplication, so that the arbores-
cent arrangement of the respiratory canals becomes more and more marked,
as the enveloping layer decreases progressively in proportion. At the

Fig. 439. — Development of the lungs. 1. Plan of the for-
mation of the whole organ, o, common canal (the future
trachea) dividing into (c) the two bronchi, with their
incipient bud-like saccules, (<f); 6, the surrounding
fibrous mass. 2. Ramifications farther advanced, from
the lung of a human faetus about four months old. a,
the tube; 6, lobulated dilatations lined with cylinder
epithelium, from which the infundibulaare formed appa-

rently 3. The same strongly magnified, a, cylinder
epithelium; c, cavit
remainder of &, fig.

epithelium; c, cavity; 6, the investing fibrous layer, the
1.

458

MANUAL OF HISTOLOGY.

ends of the branches (2, a) there then appear round vesicular dilatations
(6), lined with cylindrical cells (3, a), which by a process of gemmation
are resolved into a number of finer loculi, from which then the infundi-
bula or primary lobules are derived, and in all probability also their air-
vesicles by a further sacculation of their walls.

The pulmonary tissue is subject to many changes. One senile meta-
morphosis consists in the disappearance of parts of the alveolar walls, and
confluence of the air vesicles to form larger cavities, with consequent
destruction of the capillaries contained in the interalveolar septa.

The occurrence, of new growths here is an obscure subject, especially
as regards their point of origin. This may probably be the nuclei of
the vascular cells, or the epithelium of the lung.

3. The Digestive Apparatus.
§244.

The digestive apparatus consists of the mouth with its teeth, already
described^ 150 and 156, the tongue, and attached salivary glands, then
of the pharynx, oesophagus, stomach, large and small intestine, the large

glands emptying their secretions
into the upper portion of the last
of these, namely, the pancreas and
liver. Almost every variety of
tissue takes part in the formation
of this extensive group of organs, in
which the glandular elements espe-
cially are pre-eminently important,
and are found from the upper to
the lower aperture of the alimentary
canal forming a mucous covering
for the whole internal surface.

The cavity of the mouth is lined
by a mucous membrane of the texture
roughly described already (§ 136),
which is marked on its free surface
by a multitude of closely crowded
conical and filiform papillae (fig.
440). The thickness of this mem-
brane varies, its maximum being
sometimes 0'45 mm. The papillae likewise differ greatly in length, rang-
ing from 0*23 mm. to 0-45 mm. The strongly laminated epithelial layer
consists of flattened cells (fig. 444), which we have already considered at
greater length at p. 141. At the opening of the mouth they are con-
tinuous with the cells of the epidermis.

This mucous membrane itself is rich in elastic fibres, and presents a
network of connective-tissue bundles. It is denser towards the surface,
upon which a homogeneous transparent limiting layer may be seen. In
the papillae here, as in those of the external skin, and still more in the
villi of the intestine, the connective-tissue loses its fibrous character more
or less, and presents itself in a rather undeveloped form.

Below, the mucous membrane gradually merges into submucous tissue.
The latter is in some localities a solid fibrous mass, as in the case of the
gum, and in others soft and elastic, with loose texture, as on the floor of

Fig. 440. — A papilla from the gum of an infant,
with its vascular network and epithelial cover-
ing.

ORGANS OF THE BODY. 459

the mouth. In this substance are to be found globular groups of fat
cells and the bodies of mucous glands.

The last named organs (fig. 442) present themselves in large numbers
in the mucous membrane of the mouth. They measure in diameter from
4-5 and 2'3 down to 0*5640 mm., or even lower, and are usually situated
in a row underneath the true mucosa, where they may be so closely

Fig. 441.— Epithelial cells from Ftg. 442.— Racemose mucous glands

the most superficial layers of from man (so-called palatal glands),

the mucous membrane of the
human mouth.

crowded as to form a regular special glandular stratum. From this their
short and more or less straight ducts penetrate the mucous membrane,
and open on the surface. Their structure is as elsewhere : for which
see sections 198 and 197.

In certain localities these little glands, which play an important part
in the production of the mucus of the mouth, are particularly numerous,
and then receive special names. Such are the labial, buccal, and palatal.
The first of these, which are very numerous, form, at some little distance
from the red margin of the lip, a regular group. They are most
numerous in the under lip (Klein). Their cells usually present them-
selves in the form of numerous low, clear, columnar elements, but slightly
coloured by carmine, as was very correctly described by Puky Akos.
According to Heidenhain, however, there occur also (in man and the rab-
bit) other smaller elements, richer in protoplasm, from the transformation
of which the first take their rise. The little palatal glands, likewise, are
arranged in a thick pad under the mucous membrane of the soft palate.

The vascularity of the mucous membrane of the mouth is very great,
the capillaries forming a close network. In the papillae we encounter
either a single loop or congeries of vessels (fig. 440). We are still to a
great extent in the dark as to the lymphatics. So much is known, how-
ever, that they interlace along the lips, the inner surface of the cheeks
and the tongue, and covering the glands of the mouth, form interlace-
ments, which communicate with the vessels of adjacent parts (Teichmann).
The final distribution of the nerves of the mouth is a point on which
even less is known. Krause observed end-bulbs upon them (§ 184), in
the furrows of the mucous membrane on the floor of the mouth, near the
tongue, in the soft palate, and in the tissue of the membrane, at the edge
of the red margin of the lips, but not always in the papillae. Elin states,
on the other hand, that both in the hard and soft palate of the rabbit,
fine nerve filaments penetrate into the epithelium, and (§ 245) terminate
in ramifying cellular bodies (§ 187).

460

MANUAL OF HISTOLOGY.

§245.

Until very recently, the salivary glands received but little attention from
a histological point of view, but a step in the right direction has lately
been made in the interesting studies ofPftiiger, Gianuzzi, and Heidenliain,
followed by a number of other observers.

These organs may from their form be regarded, to a certain extent, as
highly developed and complex mucous glands.

The submaxillary gland presents in various mammals, according to its
cellular contents, considerable and important physiological differences.
Its vesicles in the rabbit are occupied by closely crowded naked cells,
consisting of soft protoplasm. The organ in other animals — as, for
instance, the dog (fig. 443), the cat, and in a minor degree, the sheep —
departing from this form, have all the characters of a mucous gland.
Here the greater part of the vesicle is filled with large, clear, non-granular
cells, with a nucleus which is usually situated near the circumference («).
Besides these, we may see in the greater number of vesicles, close to the
border of the latter, a peculiar element usually of semicircular form, and
either single or double, the "crescent" of Gianuzzi (c). At first this appears
to be a granular mass of protoplasm with imbedded nuclei, but after being
subjected to a particular kind of treatment, it may be recognised to be a
collection of small highly compressed cells. Other saccules contain
protoplasm cells alone (b). These crescents reach the highest stage of
development in the submaxillary of the cat.

The first of these elements — we shall give them the name of mucous
veils — present, after maceration, the most remarkable irregularity of

outline. They may, however,
discharge their mucous con-
tents, as we shall see later on,
and then present protoplasm

only-
Intermediate forms teach us
that these mucous cells are not
specifically different from those
of the crescent, or border cells,
but only so on account of their
having become altered and un-
dergone mucous metamorphosis.
In newly born animals they
are not yet to be found. The
submaxillary glands of man, like-
wise (specific gravity of 1*041,
accord in g to Krause and Fisch er),
contain the same mucous cells,
which require, however, closer
investigation.

For a long time it was main-
tained that the submaxillary
pland possessed, most unquestionably, a structureless membrana propria.
More recent investigations, however, have shown that the boundary
layer is only formed of greatly flattened cells of stellate figure, which
probably belong to the connective- tissue group (Heidenhain, Koclliker),
§ 194.

i(?. 443. — Submaxillary gland from the dog. a, mu-
cous cells; 6, protoplasm cells; c, "crescent" of
Qicmuzzi; d, transverse section of an excretory duct
with its special columnar epithelium.

ORGANS OF THE BODY.

461

We have already referred (p. 350, fig. 339) to a network of fine
secreting tubules or canaliculi, which have been met with in the acini of
many racemose glands. These are also to be found in the submaxil-
lary glands (Pfluger, Ewald, and others). Even uninjected, they can
be recognised as a network of clear, somewhat lustrous, streaks of
0-002-0-003 mm. in diameter.

How far a recently observed connective-tissue reticulum (Boll), which
traverses the acinus, has anything to say to these secretion tubules, or is
connected with the wall cells of the membrana propria, are points which
require closer investigation.

The walls of the excretory duct are made up of connective-tissue. A
thin layer of muscular cells, difficult of . recognition, has been stated by
Koelliker to occur here ; these have not, however, been found by others
(Eberth, Henle). The epithelial lining consists of a single layer of
cylinder cells (d), in whose bodies we may recognise distinct and per-
sistent longitudinal markings (Pfluger) underneath the nucleus.

The vascular networks are, as in most racemose glands, round. The
capillaries lie loosely about the glandular vesicles, while their tubes of
supply and overflow accompany the ramifications of the ducts.

The recent investigations of Gianuzzi have made us acquainted with
the lymphatics of the salivary glands of the dog. Here they appear as
clefts in the interstitial connective-tissue between the lobuli and vesicles,
as well as around the lobes of the organ. They are stated, also, to

Tiff. 444— Mode of termination of the nerves in the snbm axillary gland of the rabbit, after
Pfliigtr. In I. and IT. the nerves penetrate into the gland vesicles, and end between the cells
of the latter. In III. the termination of a nerve fibre in the nucleus of a gland cell is
observed. ' IV. the same, with a "ganglion cell."

ensheath the venous and arterial twigs before becoming developed into
regular lymphatic vessels.

The mode of termination of the nerves of the submaxillary gland is
very remarkable and important, though not, perhaps, in some cases
ascertained beyond all doubt. After some earlier studies by Krause,
Reich, and Schluter, the point was taken up and pursued with much
vigour by that excellent observer, Pfluger, taking the rabbit as subject

462 MANUAL OF HISTOLOGY.

(see § 183). The following are the conclusions drawn from his investiga-
tions. In the first place, medullated nerve fibres make their way as far
as the gland vesicles, then pierce the membrana propria of the latter
(fig. 444, I.), and so get between the cells of the gland. The terminal
filaments, however, advance still further (II.), penetrating into the very
body of the cells, arid end in the nuclei of the latter (III.)

The nerve fibres, further, are connected with multipolar cells declared
by Pfliiger to be ganglion corpuscles. These are situated on the external
aspect of the membrana propria (IV.), sending their processes from thence
into the protoplasm of the gland cells.

Pfliiger describes, finally, another set of fibres which become resolved
into pencils of the most delicate primitive fibrillae, which become fused
eventually with the bodies of the epithelial cells lining the ducts. These
it is which produce that longitudinal striation beneath the nucleus already
spoken of.

For the present we defer giving any opinion as to these statements, but
must just remark that we have never been able to find anything of the kind,
and have already described the ganglion corpuscles alone as connective-
tissue cells, entering into the structure of the walls of the gland vesicles.

But little attention has, up to the present, been given to the texture of
the suMingual glands. From Heidenhain we learn that in the dog they
appear to be very similar in structure to the submaxillary, and to have
likewise two kinds of cellular contents, mucous elements surrounded by
border cells. The groups of the latter, however, are usually larger than
in the submaxillary gland, and in many instances extend around the
whole circumference of the gland vesicles. Sometimes even the latter are
entirely devoid of mucous cells. The interstitial connective-tissue of this
gland, farther, is remarkable for the great abundance of lymphoid cells
Avhich it contains.

The ducts of Bartliolini and Rivin are completely destitute of muscular
fibres.

Comparatively little is known also about the structure of the parotid
gland. In its wall we find the same flattened multipolar elements already
mentioned in speaking of the submaxillary organ. The diameter of the
gland-vesicles is 0'0338-0'0519 mm., and the granular cells contained in
them O'135-O'OISO mm. Mucous metamorphosis of the latter is never
met with, however, either in man or the lower animals. Their excretory
ducts are lined with ordinary epithelium, none of that fibrillation of the
lower half of the cells being seen here which is to be found in the sub-
maxillary gland. In the interior of the parotid, and several other race-
mose glands, possibly also in the submaxillary of many mammals, the
commencement of the excretory canals is formed of a different species of
cells, the so-called " centro acinal " cells first discovered by Langerhans
in the pancreas (see below). These are flat elements resembling vascular
epithelium usually of spindle or more rarely stellate figure. They bound
an axial canal of the acinus more or less perfectly. According to Pfliiger
the termination of the nerves is the same, as in the submaxillary gland of
the rabbit.

The development of the salivary glands is on the same plan as the race-
mose. They commence to be formed in the human embryo in the latter
half of the second month. They are then seen as solid aggregations of
cells from which they are developed by gemmation. At the third month
they are already pretty well marked.

ORGANS OF THE BODY. 463

§246.

The saliva, as found in the human mouth, is a very complex mixture
of the secretions of different organs connected with that cavity. In the
first place of the matters produced by the numerous little mucous glands
already described § 244, then of those secreted by the parotid submaxillary
and sublingual glands. Under certain circumstances, also, the secretions
of the mucous membranes of the nose and lachrymal gland are likewise
mixed with it. We shall first enter upon the consideration of the variety
of composition of this fluid as a whole, and then turn to what has up to
the present been ascertained in regard to the individual secretions from a
physiological and chemical point of view.

The saliva, taken as a whole, is a colourless, slightly clouded, and some-
what viscid fluid without either odour or taste. Its reaction is generally
alkaline or neutral, more rarely acid. Its sp. gr. ranges between T004
and 1-009.

Under the microscope this fluid is found to contain cast-off epithelium,
and at times gland cells which have been washed out of their original
position. As a third and never absent element, we meet with great
numbers of what have been named salivary corpuscles (mucous corpuscles).
The latter present the same appearances as lymph cells which have
become swollen in water. Within their bodies, as long as they are
uninjured, a lively movement of small molecules may be perceived. This
motion was always regarded as of the ordinary molecular species, until
lately, when Briicke came forward to oppose the theory.

Turning to the chemical analysis of the secretion, we find that it con-
tains between five and ten parts per 1000 of solid constituents. Among
the organic matters the most important is a ferment combined with alka-
lies or lime, called by Berzelius ptyalin insoluble in alcohol, slightly so
in water. It has not yet, however, been obtained in a pure state.
Besides this, leucin is probably present (?) also mucin, extractive matters,
fats, and combinations of the fatty acids with the alkalies. Urea has also
been found as an abnormal or pathological constituent. The inorganic
compounds are chlorides of the alkalies, small quantities of phosphates of
the alkalies and earths, carbonates, some oxide of iron, and besides, — at
least in man, — sulphocyanide of potassium (comp. § 38). We insert here
an analysis by Frericlis, as a specimen of its quantitative composition.
The saliva of a healthy man contains : —

Water, 994-10

Solid constituents, ..... 5 '90

Epithelium and mucus. . . . . 2 '13

Fat, . . 0-07

Mucin and traces of alcoholic extract, . . 1'41

Sulphocyanide of potassium, .... O'lO
Chloride of sodium, chloride of potassium, phos- \

phates of the alkalies, and earths, and oxide > 2 '19
of iron, ...... |

The saliva contains of gases small quantities of nitrogen and oxygen
(the latter in far greater quantities than other secretions), and abundance
of carbonic acid.

The amount of saliva secreted is, of course, liable to variation. Bidder

46-4 MANUAL OF HISTOLOGY.

and Schmidt have estimated it at 1500 grammes in man, but also at a
lower figure.

Its action and use are, in the first place, the same as water ; further, as
a slimy fluid it lubricates the various matters taken into the mouth,
causing them to pass the more easily into the oesophagus; and then again
its action on starch (C6H1005) is chemical, transforming the latter into
dextrine (C6H1005) and grape sugar (C6H1206). It is the ptyalin alone
which here acts as a ferment.

Let us now turn to each of the secretions in succession of which the
saliva is composed, taking first the mucus of the mouth. The amount of
this is inconsiderable, if we are to judge from experiments on animals.
It was found by Bidder and Schmidt to contain water to the amount of
99 per cent. In the mucus of the mouth we find, likewise, an abundance
of form elements, flattened epithelium cells, and salivary corpuscles.

Of all these secretions, that with which we are best acquainted is the
saliva obtained from the submaxillary gland of the dog. As was shown
many years ago by Ludivig, the secretion of this fluid is presided over by
the nervous system. From a whole series of experimental studies, partly
undertaken by Ludwig and his pupils, partly by Koelliker and Muller,
Czermak, Bernard, Eckhard, Adrian, and Heidenhain, we have become
acquainted with, the following points of interest. The submaxillary
gland receives, first of all, branches from the facial nerve, mixed with a
small contingent of the trigeminus : this is the continuation of the chorda
tympani. In the second place, a number of filaments of the sympathetic
enter the organ with the arteries. Finally, it receives nervous offsets
from the submaxillary ganglion, which run with the chorda through the
organ, and are excited by reflex action from the tongue through the
lingualis.

Irritation of the chorda tympani gives rise to the secretion of a large
quantity of a strongly alkaline and non-viscid fluid, whose proportion of
water is about 99 per cent. Together with this the gland becomes filled
with a larger quantity of blood than usual ; the pressure in the veins is
increased, and the whole mass of the blood, leaving the organ, presents a
bright red colour (Bernard), while the temperature of the latter rises
about 1° C. (Ludwig and Spiess). That this secretion is independent of
the increased influx of blood is clear from the fact, that after interruption
of the flow through the carotid, as well as in a head severed from the
body, it may be induced by stimulation of these nerves.

Stimulation of. the sympathetic salivary nerves, on the other hand, has
quite a different effect (Czermak, Eckhard). Here the circulation is con-
siderably retarded, and the venous blood leaving the organ is of a dark
red colour. A small quantity only of a very viscid, cloudy, and strongly
alkaline secretion issues from the excretory duct, containing solid con-
stituents in the proportion of from 1'6 to 2 '8 per cent.

In the saliva given off after stimulation of the chorda, mucin has been
found with various albuminous substances. After irritation of the sym-
pathetic it is also very rich in mucin. As far as we know, neither of these
secretions of the submaxillary gland have any action on the food, with
the exception of a slight power of producing sugar manifested by the
sympathetic saliva of the dog.

The form elements appearing in these two kinds of saliva of the sub-
maxillary are of great interest. Many years ago numerous pellets of
colloid matter were noticed by Eckhard in the sympathetic secretion of

ORGANS OF THE BODY. 465

the dog. These are entirely absent, it is stated, in the chorda
saliva.

The fluid excreted by the submaxillary gland contains farther, as was
observed by Heidenhain, in the first place, cast-off mucous cells ; either
those of the gland vesicles intact, or changed by maceration and swollen
up, the result of which is the production of a multitude of peculiar round
and very pale masses, like drops of some viscid substance. Besides
these, saliva corpuscles are present in the secretion, i.e., small lymphoid
cells in various stages of development, and which have wandered out with
the fluid.

When one of the two secretory nerves of the submaxillary gland is
irritated uninterruptedly for a considerable period, the number of these
salivary corpuscles be-
comes naturally in-
creased. Another effect
of this proceeding is
further seen, as was
pointed out by Heid-
enhain, in an extraor-
dinary transformation
of the interior of the
gland (fig. 445). In
the greater number of
the vesicles the mucous
cells are found to have

entirely disappeared, Fiff- 445._Submaxillary gland of the dog with its contents, a, niodi-

granular ^e<^ by strongly stimulating the chorda tympani; 6, unchanged
? residue : after Heidenhain.

nucleated elements,

smaller than the original cells, occupying their place. The explanation is
simply this, that these cells have parted with their mucus, and have
again become filled with protoplasm (Ewald, Rheiner).

In man the saliva of the submaxillary gland contains a large quantity
of mucin dissolved in an alkaline fluid, together with a sugar-forming
ferment and sulphocyanogen (§ 38), which latter is also found in the sub-
lingual and parotid secretions. In the saliva of the lower animals, on
the other hand, this compound is not to be found.

The secretion of the sublingual gland has, up to the present, excited
but little attention. According to Heidenhain, the organ is presided
over by the same nerves as the submaxillary gland in the dog, namely,
the facial and sympathetic. Stimulation of the chorda tympani causes
here also an increased flow of the secretion.

The saliva of the sublingual gland is an extremely tenacious and
completely transparent substance, which can hardly be called a fluid. Its
reaction is alkaline, and its percentage of solid constituents about 275.

The product of the parotid finally may be increased by irritation of one
of the cranial nerves, namely, the lesser superficial petrosal, a branch of
the facial (Ludwig, Bernard). Stimulation of the sympathetic also has
the same effect (Eckhard, von Wittich, Nawrocki). The fluid thus
obtained has a much less alkaline reaction than that of the submaxillary
gland. It is always thin, and never in the least viscid. The secretion
of the parotid, further, has no reaction on mucin, and contains from five
to six per cent, of solid constituents (Ordenstem) ; also albumen, and,
as already mentioned in the human subject, sulphocyanogen combined with

466 MANUAL OF HISTOLOGY.

potash or soda. According to Ordenstein, the sugar-forming ferments
appear in the corresponding fluid obtained from the dog (Bidder and
Schmidt, Bernard).

§ 247.

The tongue is an organ essentially muscular, but covered by a mucous
membrane which, over the greater portion of the anterior part of the
dorsum, is studded with a multitude of highly developed papillae supplied
with nerves, the gustatory pqpillce, which constitute the whole an organ
of sense.

Leaving the greater portion of the description of its striped fibres,
which have a partly perpendicular, partly longitudinal, and partly oblique
direction, to general anatomy, we shall merely touch here on one or two
points of special interest.

That portion of the tongue known as its fibro-cartilage, which occupies
the middle line of the organ in the form of a thin vertical septum, cannot
be numbered among the cartilaginous structures, seeing it merely consists
of densely interwoven bundles of connective-tissue. At either side of this
band the two genioglossi pass up into the substance of the tongue, inter-
mixed, as their fibres diverge, with the fibres of the transversus linguae,
which cross the former more or less at right angles. The greater part of
the substance of the organ is formed by these two muscles. The hyoglossus,
with its two portions, the first of the muscles entering into the formation
of the border of the tongue, passes to tne lateral portion of the organ in
manner similar to the genioglossus, and likewise crossed by the external
fibres of the transversus on each side. The styloglossus sends its weaker
internal division between the genioglossus and hyoglossus and as far as
the fibro-cartilage. Its longer external band passes forwards on the
external surface of the hyoglossus, intermixing behind the frsenum and
anterior to the foremost extremity of the sublingual gland, with the fibres
of its fellow of the opposite side. Besides these there are longitudinal
bundles of muscular fibres coursing from the root to the tip of the tongue,
partly on the dorsum and in part near its inferior surface. The latter are
the most numerous, and go by the name of the lingualis muscle. They
are strengthened anteriorly by fibres from the external division of the
styloglossus. Their course is between the genio- and hyoglossus muscles
towards the tip of the tongue, where their fibres diverge, some passing
upwards and others still forwards. The superficial layer of bundles
(lingualis superior) is spread out over the whole dorsum of the organ
under the mucous membrane. Those muscle bundles which are lost in
the mucous membrane, such as the ascending fibres of the genioglossus
in the middle line, and of the hyoglossus in the lateral portions of the
organ, may be seen to bifurcate at acute angles, and terminate in the
connective-tissue in conical points.

The most important part, however, of the tongue is the mucous mem-
brane itself. This is covered over with the flattened epithelium of the
mouth (§ 90), and is, with the exception of having papillae, in no essential
feature different from other mucous membranes. Its connective-tissue
substratum is tolerably strong, and interspersed with numerous elastic
fibres. It is also extremely vascular.

In the gustatory portions there is no submucous tissue, its place being
taken by a closely woven layer of fibrous tissue, the undermost portion of
the substance of the mucous membrane.

ORGANS OF THE BODV.

4G7

§248.

While the mucous membrane on the under surface of the tongue is
quite smooth and destitute of papillae, the dorsum of the organ is covered
from the foramen caecum to the tip with innumerable gustatory papillce.
Of these, as is well known, there are three species, although between each
kind there exist a number of intermediate forms. These three species
are named respectively the filiform, fvngiform, and circumvallate.

The papillce filiformes, s. conicce (fig. 446), are found in by. far the
greatest number of all. They consist of a conical base bearing on its
apex a number of thin pointed papillae, the whole presenting a tufted
appearance. The number of the latter varies from 5 to 15 and upwards.
The point most worthy of note here is the high degree of development to
which the epithelial layer may attain. Very horny in texture, it presents
itself in long filiform and frequently bifid shreds on the end of the
papillae, causing the latter to appear considerably increased in length.
Together with these, examples of the same kind of papillae are met with
whose epithelial covering is very delicate.

The vascular supply consists
of single capillary loops for
each of the conical papillae,
with one arterial and one
venous twig for each group.
The mode of termination of
the nerves is not yet ascer-
tained. The papillae are most
strongly developed along the
middle of the dorsum of the
tongue, decreasing in size near
the edes and tip. In these
situations they are in many in-
stances arranged in rows, en-
veloped in a common sheath
of epithelium.

The second form, the pa-
pillce fangi formes, s, clavatce
(fig. 447), are found scattered
over the whole surface of
the tongue among the latter
variety, but most numerous
towards the tip. They are
remarkable for their thick coni-
cal form and smooth surface,
and absence of tufts, together
with diminution in the thick-
ness of their epithelial coat.
They are elevated above the
surface of the tongue with a
somewhat constricted neck, and
terminate above in round and
blunted bulbs. The whole surface of the latter (A) is studded with
numerous conical accessory papillae (p), which are covered again by
the epithelial coating of the tongue (^4, e, B, e). In this species the

Fig. 446. — Two filiform papillae from man, the one (p,
left) with, the other (p. right) without epithelium, e,
epithelial covering, ending above in lonsr tufted pro-
cesses, /; vascular portion of the papilla, with its
arterial twig a, and vein v. Copied from Todd and

468

MANUAL OF HISTOLOGY.

vascular loops are far more numerous than in the first form. The nerves
enter the papillae as tolerably strong twigs : the mode of their ultimate

termination, however, is still undecided.
According to Krause, terminal bulbs may
be found here (§ 184).

In the third form, finally, the papillce
vallatce, s. circumvallatce (fig. 448), we
have the largest of all these organs, and
probably also the most important, as far
as the sense of taste is concerned. In
man and the mammalia generally they
present many varieties. Their number
is small but variable, amounting to from
10 to 15. They are arranged at the root
of the tongue in a V-shaped figure. Each
of the projections (^4) is surrounded by a
circular ridge of epithelium (B), into
which racemose glands empty themselves
(Schwalbe), and supports on its broad
surface a multitude of conical accessory
papillae (c) overlaid with a smooth stratum
of epithelium (a). That eminence which
forms the apex of the V-springs fro in the
bottom of a deep groove known as the
foramen caecum linguis.

These little organs are abundantly
supplied with nerves (b b). The latter
form delicate interlacements, from which
the primitive tubes are given off whose
ultimate distribution will be referred to
presently. The annular folds also encir-
cling the papillae are likewise richly supplied with nerves (B, b).

The sources of the nervous supply of these parts are the trigemini and
glossopharyngei, the ninth or hypoglossus being simply a motor nerve of
the tongue. The anterior part of the dorsum of the organ is innervated
by the ramas lingualis from the lower division of the fifth nerve, and by

the chorda tympani, while
the posterior portion is sup-
plied by the lingual branch
of the glossopharyngeus,
which sends its ramifica-
tions into the circumval-
late papillae. On both of
these nerves small ganglia
are to be seen. It seems
hardly probable that the
filiform papillae, clothed as

they are with a large

amount of horny epithelium, should be the recipients of the sense of taste
(Todd and Bowman). The two other forms seem to preside over the
latter as well as the sense of touch.

The lymphatics of the tongue have been carefully studied by Teicli-
mann and Sappey. According to the former, the mucous membrane, and

Fig. 447.— Fimgiform papilla, from tlie
human tongue. A, a papilla covered
to the left with epithelium, «, and
over its whole surface with conical
smaller papillae, p. B, another, less
strongly magnified, with its epi-
thelial envelope c, its capillary loops
d, artery a, and vein v; e, vascular
loops in the adjacent simple papillae
of the mucous membrane. Copied
from Todd and Bowman.

Fig. 448. — A circumvallate papilla from the human tongue
A, with accessory papillae c, its epithelium a, and nervous,
twigs 6. B, the ridge running round the papilla, with its
nerves b. Copied from Todd and Bowman.

ORGANS OF THE BODY. 469

still more so the submucous tissue, is very abundantly supplied with
absorbent canals, while the muscular substance is only traversed by
regular vessels. In the roots also of the filiform papillae is to be found a
capillary network, from which caecal prolongations are sent off into the
papillae themselves.

The development of the tongue in the embryo commences as early as
the sixth week of intrauterine life, in the form of a thick ridge, which
seems subsequently to become stationary as regards its growth. The
papillae are said to be rudimentarily formed in the third month.

REMARKS. — 1. Compare Todd and Bowman, vol. i. p. 437-2. Much variety is to
be seen in the form of the filiform papillae. It is not uncommon also to meet with a
thread-like fungus, the leptothrix buccalis, in great quantity among and upon these
papillae.

§249.

Behind tho foramen caecum the mucous membrane presents to the
unaided eye a more or less smooth appearance. Here the laminated
epithelial stratum merely covers a series of small simple papillae, each
supplied by a single vascular loop.

In this locality a number of different varieties of secreting organs make
their appearance. In the first place, even anterior to the foramen caecum,
small scattered mucous glands present themselves, which form more
posteriorly under the circumvallate papillae, and towards the root of the
tongue a thick continuous glandular layer.

On the under surface of the tongue also, near its tip, are to be found
two other racemose glandular masses of considerable magnitude. These
empty themselves by several ducts at either side of the fraenum (Blandin,
Nukn). Their functions are, however, still unknown.

From the posterior fourth of the tongue on, finally, the tissue of the
mucous membrane, commences to undergo at points a lymplioid metamor-
phosis. This may be absent in many mammals, but attains in others,
on the other hand, as for instance in the pig, a high degree of develop-
ment. In the latter animal this process may advance to the formation of
follicles in the larger papillae imbedded in a densely reticulated connec-
tive substance (Schmidt).

This metamorphosis of the mucous tissue (by which the pharynx also
may be affected) leads, as it advances, to the formation of larger and more
sharply defined lymphoid organs, varying greatly as regards distribution
and structure. They are largely met with among the mammals, and are
not absent in man.

Among these may be numbered the lingual follicles ov follicular glands
of the mouth, the tonsils, and, at the top of the pharynx, the pharyngeal
tonsils, structures discovered some years ago by Koelliker.

The lingual follicles (fig. 449) occur in man sometimes scattered, some-
times crowded, upon the posterior portion of the dorsum of the tongue,
from the cirjcumvallate papillae down to the root of the epiglottis, and
from one tonsil across to the other. They consist of a depression of
a greater or less depth (3 '5 mm. and upwards), implicating the whole of
the mucous membrane, so that, beside flattened epithelium, accessory
papillae may also exist within the reduplicated portion.

Each crypt or depression is enveloped in a thick stratum of reticular
connective substance, entangled in which innumerable lymphoid cells are
to be found. This stratum extends to immediately beneath the epithelial
tunic. In it, and distinguished by their looser and wide meshed frame-

470 MANUAL OF HISTOLOGY.

work, and consequently lighter shade, a number of small lymphoid
follicles may be observed, measuring in diameter from 0'28 to 0'56 mm.
These are sometimes sharply denned, sometimes less distinctly so. Other
of these crypts, however, are quite destitute of these follicles. Most
usually we find these lingual crypts encased in a strong fibrous capsule.
This, however, is also often absent in less distinctly defined . examples.
Among and beneath these lingual follicles are
generally scattered a great number of racemose
glands, whose ducts open partly in the immediate
neighbourhood of the crypt (but on the surface of
the mucous membrane), and partly within its
cavity. In many mammals these lingual follicles
are entirely absent, as in the tongue of the
rabbit, sheep, and dog. In others they are formed
upon the same plan as in man, for instance,
in the horse, pig, and ox.

Fig. 449.— Plan of a lingual rr, , , * ° ' , 7 , , . „ , ,

follicle, a, hollow redupH- Ihe blood-vessels and lymphatics are ol the same
suerithfitspapiii*C-06SiymI description as those in the tonsil, to which we
phoid portion of the 'walls refer the reader for minutiae.

The tonsils or amygdala*, the largest lymphoid

organs of the mouth, are to be found in man and most of the mammalia,
presenting, however, considerable variety of structure in the latter. In
some of these, moreover, as in the Guinea-pig, the rat, and the mouse,
they are entirely absent. The form of the organ, as it appears in the
rabbit and hare, is from its simplicity very instructive. Here we find
a simple depression surrounded by a thick stratum of lymphoid structures
containing small lymph-follicles. The boundary of the organ, externally,
is a fibrous capsule. Numerous minute racemose mucous glands lying
adjacent, send off their ducts, partly external to the depression, and partly
through the lymphoid mass, to empty themselves into the latter. In this
case, therefore, these organs show all the characters of a lingual follicle.

As a rule, however, the tonsils present^ far more complicated structure.
They are generally made up of groups of such bodies as those we have
just described as representing the tonsils in the hare. These are collected
together in greater or less number, their follicular ducts opening either
singly on the surface or converging like the corresponding portions of a
racemose gland to form passages of greater magnitude. These latter may
then discharge their contents, either independently of one another, or,
pursuing the same system of confluence, may eventually, as in the tonsil
of the ox, give origin to one large excretory duct. Between these two
extremes many intermediate forms are met with.

Each pit is enveloped in a thick lymphoid layer external to the
flattened epithelial lining and mucous membrane papillaB often present.
This layer, enveloped in dense fibrous tissue, extends as far as the
epithelium or its immediate vicinity. As a rule, but not invariably, it
contains within a loose tissue a number of follicles.

The latter present, both as to number and distinctness of demarcation
against tne denser interstitial tissue around, considerable variety. Their
diameter, in most mammals, is on an average about 0'28 or 0*51 mm.
In the dog they may even attain greater magnitude, reaching 0'9-1*4 mm.
The large tonsils of the pig, further, are unusually rich in follicles.

Here also are to be met with, as might be expected, numerous racemose
mucous glands, playing an important part in the construction of the

ORGANS OF THE BODY.

471

1-

Fig. 450.— Tonsil of an adult (after Schmidt), a, large excretory
passage; 6, a simple one; c, lymphoid parietal stratum with
follicles; d, a lobule strongly resembling a lingual crypt ; e, a
superficial, /, a deeper mucous gland.

tonsils, and as varied in the arrangement of their excretory ducts as those
of the lingual follicles. They discharge their contents, namely, either
into the caecal depression of the organ or free on the surface of the tonsil.

The frequent inflammatory affections to which the amygdalae are subject
in adult human beings, render them rather dubious objects of research,
for which reason specimens obtained from young children should be
preferred. The ordinary arrangement of the openings in the adult was
found by Schmidt to be either a separate duct for each pit (fig. 450, b) or a
collection of the latter to form one large canal (a). The surface of the
organ presented the usual mucous membrane papillae, but the depression
only showed traces of them. He frequently encountered, also in the
immediate neighbour-
hood of the tonsils, a few
scattered crypts with lym-
phoid walls, in which
follicles were imbedded,
resembling greatly the
blind follicles of the
tongue (d).

This extension, just
mentioned, of lymphoid
tissue from the fundus of
the crypt up to the under
surface of the epithelial
covering, may be readily seen in the tonsils and lingual follicles of the
calf. In some spots even this covering appears not to be completely
continuous throughout. Taking this arrangement of parts into con-
sideration, it does not seem unwarrantable to suppose that from out the
meshes of this superficial reticular tissue, lymph cells may be set
free, constituting, when surrounded by
the watery secretion of the mouth,
those saliva corpuscles so enigmatical as
to their origin. This view may be the
more safely accepted now that we are
acquainted with the amoeboid powers of
motion of the lymph cells (§ 49).

If the mucus welling from the orifices
on the tonsils of a newly killed calf be
examined, the abundance of saliva cor-
puscles to be met with there (Frey] will
strike every eye.

The Hood-vessels (remarkable for the
number of highly developed veins among
them) form, with their ramifications, a
dense network of coarse and fine tubes,
which becomes more delicate as it ap-
proaches the surface, where it sends off loops into any papillae which may
be present. As soon as follicles commence to make their appearance in
this lymphoid layer, the vascular network is restricted to the smaller
space of the interfollicular connective-tissue, so that it becomes more
dense still. In the follicle itself, however, a very delicate network of
radially arranged capillaries is now to be seen, very similar to that already
encountered in the follicles of Peyer's patches.
31 *

Fig. 451. — Froin the tonsil of the pig. a,
depression in the mucous membrane;
6, lymphoid tissue; c, follicle; d, lym-
phatic vessel.

472 MANUAL OF HISTOLOGY.

Passing on to the lymphatic canals of the tonsils (fig. 451) (Frey, Th.
Schmidt) we find in the neighbourhood of the capsule and in the latter
itself, considerable vessels, with valves and knotty dilatations. From
these branches are" given off, internally, some of which encircle, at
considerable distance, the bodies of the racemose mucous glands, and
some reach the base and external surface of the different divisions
of the tonsils. Here they enter into the formation of a network of
canals, with greatly dilated nodal points, and some of them penetrate
upwards into the tissue connecting the follicles (b). In the latter situa-
tion they are remarkable for their extreme fineness and arrangement in
dense but irregular networks. Around the follicles themselves (c), these
lymphatic canals form circular networks, their calibre being rather
small. The interfollicular lymphatics penetrate, to a greater or less
distance, towards the surface of the depression which occupies the axial
portion of each division of the tonsil, and end here eventually, blind.

The lymphatics of the lingual crypts possess in all salient points the
same arrangement as these just mentioned.

On account of their near relationship, we will here append a few
remarks on the lymphoid organs of the pharynx. The latter, in many
mammals, is found to present a very extensive lymphoid infiltration of
the mucous membrane. In man, the arch of the pharynx is possessed of
follicular glands and a pharyngeal tonsil, composed of a number of the
latter. This is situated at the point at which the mucous membrane
comes into contact with the base of the skull. It is a mass several lines
in thickness, which extends from the opening of one Eustachian tube to
the other. In structure it resembles the tonsils.

The same organ is to be found among the mammalia, as in the pig,
sheep, ox, and dog. Other animals, however, are not possessed of it, as,
for instance, the hare (Schmidt).

According to Koelliker, the first rudiments of the tonsils may be seen
in the fourth month of intra-uterine life, in the form of a simple depres-
sion in the mucous membrane of the mouth. A month later, several
other additional little pits are evident, and the lymphoid infiltrated walls
are of considerable thickness. The follicles appear subsequently in the
substance of the latter. In the new-born child they may be already
present, but in many instances this is not the case.

The mode of development of the lingual crypts is in its broad outlines
the same.

§250.

The muscles of the pharynx are made up of striped fibres (§ 164).
The tough mucous membrane of the lower portion is covered with simple
papillae clothed with laminated flattened epithelium. The upper part
(furnix), on the other hand, is quite destitute of these, and is covered in
the infant with ciliated epithelium, while in the adult body the latter is
replaced by the flattened species. This portion of the pharynx, farther,
is that most abundantly supplied with glands. These are, in the first
place, of the racemose mucous species, and then lymphoid organs men-
tioned in the preceding section. The mucous membrane of the pharynx
is very vascular, besides being abundantly supplied with lymphatic
canals. Interlacements of delicate nerve-fibres have also been seen in it
(Billrolh, Kodliker).

We now turn to the oesophagus, which, n its strong external longitu-

ORGANS OF THE BODY.

473

dinal layer of muscular fibres, as well as its fine internal transverse tunic,
shows a gradual substitution of contractile fibre cells for the striped tissue,
of which the upper portion of the tube is composed. In the superior
third of the latter the first species of muscle alone is to be found. Then,
on the entry of the oesophagus into the thorax, contractile fibre cells begin
to make their appearance, either scattered or in groups, first among the
transverse bundles, and later, in the longitudinal tunic. After this they
become more and more numerous, so that from about the middle of the
tube on the muscle tissue usually appears to be made up entirely of the
smooth variety of cells (Welcker and Schweigger-Seidel) remaining so
throughout the whole of the digestive tract.

The mucous membrane loosely adherent to the muscular tunic beneath
is thrown into a multitude of rugae, and contains numerous simple papilla?
covered by strongly laminated epithelium. In the upper part of the
oesophagus large numbers of isolated bundles of vertically arranged con-
tractile fibre cells are scattered through it, and lower down a continuous
longitudinal Muscularis mucosce presents itself, occupying the deeper

Fig. 452. — (Esophageal glands from the human subject.

portion of the membrane (Koettiker, Henle, Klein). The latter (at least in
the new-born child) is formed of distinct lymphoid tissue (Klein).

The glands of the oesophagus (fig. 452 and 453) occurring, it would
appear, in varying numbers, sometimes scanty, sometimes abundant, are
of the small racemose species, two or three of their excretory ducts
frequently joining to form one common canal. At the extreme end of
the human oesophagus, about the cardiac opening, are to be found small
structures, extending not quite down to the sub-
mucosa ; these are the cardial glands of Cobelli.
Here they form an elevated ring about 2 mm. in
height.

The blood-vessels are arranged in a moderately
loose network of capillaries, and the lymphatics
also in a retiform interlacement with small meshes,
the tubes measuring about 0-0200 or 0-0699 mm.
in diameter, and lying for the most part parallel
with the axis of the oesophagus. These latter are
situated in the deeper strata of the mucosa, and in
the submucous 'connective-tissue. The arrangement
of the nerves here appears to be similar to that in the pharynx.

§ 251.

"VVe now come to the description of the stomach (ventricvlus), which,
on account of the physiological importance of the organ, must necessarily
be more minute than that of the last mentioned parts, its mucous mem-
brane calling for our special attention.

The serous covering of the viscus presents the ordinary structure of

Fig. 453. — A small racemose
cesophageal gland from
the rabbit.

474 MANUAL OF HISTOLOGY.

membranes of this kind (p. 226) ; the muscular substance, consisting of
longitudinal, transverse, and oblique fibres, belongs to the involuntary
species (§163).

The mucous membrane of the stomach is clothed from the cardiac
orifice on (where the flattened epithelium of the oesophagus terminates
with an irregular boundary line) with columnar epithelium (§ 91), which
is continuous from that point on throughout the whole extent of the intes-
tinal tube. The cells are of the long and narrow species (about 0-6323-
0-6226 mm. in length and 0-0045-0-0056 in breadth). In profile they
are seen to possess a cell-membrane, of which the free base of many of
them is probably quite destitute during life (Schulze). Younger and
smaller epithelial elements may also be seen between the undermost
pointed extremities of these cylinders.

The surface of the gastric mucous membrane is by no means smooth,
but on the contrary very uneven, with prominences varying in height from
0-0751 to 0-1128 and 0'2 mm. The latter possess either a tuft-like form
or that of intersecting folds, bounding a multitude of smaller or larger
depressions into which the peptic glands discharge their contents.
Orifices at the summits of these eminences, on the other hand, never
occur. There is much variety, as regards these points, both in different
animals and localities.

Still more considerable eminences of this kind are to be found at the
pyloric end of the stomach, where, as a rule, the mucous membrane attains
its greatest thickness, measuring up to 2 mm. in depth. Towards the
cardiac end, on the other hand, where the surface is smoother, the
membrane decreases greatly in depth, falling down to from 1-1128 to
0-5640 mm.

The proper tissue of the mucous membrane is, owing to the enormous

number of glands imbedded in it,
but very scanty. As a rule, it pre-
sents itself in the form of a soft
nucleated connective-tissue of loose
texture (fig. 454). It varies, how-
ever, considerably in different classes
of animals. Beneath the glandular
layer is situated a stratum about
0-0564 or 0-1128 mm. in thickness,

Fig. 454.— Transverse section through the gas- Consisting of fibrOUS Connective-tissue
trie mucous membrane of the rabbit. «, an(J intersecting muscle fibres. Ill
tissue of the mucous membrane; 6, transverse . i

sections of empty and injected biood-vesseis ; this two layers may be recognised — an

d.openingswherepepticglandsweresituated. internalj formed principallv Of trailS-

verse fibres, and an external or longitudinal coat. The relative thickness
of these two layers varies greatly in different portions of the stomach
(Schwartz). Then from this laminated muscular substance there ascend
email bundles of contractile fibre-cells between the glandular follicles.
These musculares mucosce, whose beginnings we have already seen in the
oesophagus, persist now from this on, with certain variation of arrange-
ment as might be supposed, and form integral elements of the digestive
mucous membrane.

This constitution, however, of the mucous membrane may give
way to another. There may appear, namely, between the bands of
connective -tissue a greater or smaller number of lymph -corpuscles,
pointing to an intermediate form of tissue between that of the gastric

ORGANS OF THE BODY.

475

Fig. 455. — Vertical section of the
human gastric mucous membrane,
a, ridges ; 6, peptic glands.

mucous membrane, and the reticular lymphoid substance of the mucosa
of the small intestine.

The almost innumerable glands of the stomach are of two kinds, not
always easy to distinguish from one another,
however. These are the peptic and gastric
mucous glands.

The first of these are those blind tubules,
already mentioned in section 198, which are
closely crowded together, and occupy the
whole thickness of the gastric mucous mem-
brane in vast numbers (fig. 455, b). The
fact that in the neighbourhood of the pylorus
in the rabbit about 1894 may be counted
upon 1 Q mm. of surface, will give some
idea of their abundance. Their length, which
corresponds to the depth of the mucosa, is on
an average about 1'13 mm., but may fall to
the half of this, as well as exceed it by more
than double. Their transverse diameter ranges
from 0-0564 to 0'0451 mm. In children the
tube is shorter and of smaller calibre.

The openings of these tubuli, which may be either grouped together
or parted by regular intervals from one another, are roundish orifices
considerably decreased in size by the columnar epithelium cells with
which they are lined, and which are arranged in a radiating manner
(fig. 456).

Both chemically and mechanically there may be easily demonstrated a
membrana propria on all the tubuli, formed by
a condensation of the soft loose connective-
tissue of the mucosa in which flat stellate cells
have been met with. In the human subject
this is only slightly wavy in outline (fig. 457),
but in many animals it is on the contrary
markedly sacculated, as, for instance, in the
dog. The blind end of the tube, which is usually
more or less bulbous, is that at which it attains
its greatest calibre, while towards its opening it
is generally somewhat contracted. Double
tubuli, although of rare occurrence, may fre-
quently be simulated by the crossing of the
extremities of adjacent tubuli. Treatment with alkali will generally,
however, bring out the true arrangement of parts.

Only on very limited portions of the human stomach are deviations
from the arrangement of the peptic cells just described to be met with.
Thus a very narrow band of compound tubules is to be found around the
cardiac extremity, of which fig. 460, 1, taken from the same region of the
dog's stomach, will give an idea. From a common excretory duct of
greater or less length (a) 4, 5, 6, or 7 gland tubules spring.

Such compound peptic follicles appear to exist in much greater abund-
ance among the mammalia.

As regards the contents of these peptic glands the earlier views
may be summed up as follows. Columnar epithelium lines the depres-
sions to a greater or less distance (fig. 460, b). Intermediate cellular

Fig. 456.— Surface of the stom-
achal mucous membrane, with
scattered openings of the
peptic glands, showing also
the cylinder epithelium lining
the latter.

476

MANUAL OF HISTOLOGY.

elements then make their appearance, and after them the specific gland or
peptic cells (fig. 457). The form of these when isolated is more or
less cubical (fig. 459). They are of considerable size, and almost completely
fill the gland tubule.

In man they had only been met with in a more or less decomposed

Fig. 457. —Three stomach
glands from the human
being, partly filled with
peptic cells.

Fig. 458. — Peptic glands from the
human stomach after treat-
ment with alkalies.

condition (&). In suitable objects (a, c-g) they appear roundish or inde-
finitely angular, 0'0323-0'0.187 mm. in diameter. They present a delicate
boundary layer (e, /, g), or are quite membraneless (a, c), and are com-
posed of protoplasm which becomes clear in
acetic acid, surrounding a nucleus 0 0074 mm.
in diameter, within which a nucleolus may
be recognised.

Of late years, however, this older view of
their nature has been shown to be quite incom-
plete. Recent investigations by Heidenliain
and Rollett have adduced much that is new,
but the extreme difficulty of the subject has
prevented definite conclusions being drawn on
all points.

The conclusions drawn from our own personal
observations are as follows : — The peptic gland consists of several parts :
with Rollett we distinguish four.

Fig. 459. — Different forms of
peptic cells from man.

OEGANS OF THE BODY.

477

(1.) The first is the entrance portion ; sometimes deep, sometimes
shallow, in one instance wide, another very narrow. This is the
" stomach cell " of English writers, the " Magengriibchen " of the Germans.
This depression is lined with the ordinary slender columnar epithelium
of the surface of the stomach. The nucleus lies far down in the cells,
and is of elongated oval figure (fig. 461, a).

(2.) The second is the undermost portion of the stomach cell, or, if we
prefer a term made use of by fiollett, the " inner intermediate portion
of the peptic gland." Here (b) the cells, without departing from their

Fig. 460. — A compound peptic gland from the
dog. a, wide entrance ("'stomach cell") lined
with columnar epithelium; ft, division; c, the
several tubules lined with peptic cells; d, pro-
trusion of the contents of the peptic follicle. 2.
The opening, a, in the transverse section. 3.
Transverse section through the several glands.

Fig. 461.— A peptic gland from
the cat in side view, a,
"stomach cell;" 6, inner; c,
outer intermediate portion;
d, the gland tubule with its
two kinds of cells.

epithelial character, are broader, lower, and more granular. The nucleus,
a round structure, takes up about half the height of the cell. The lumen
of this part is usually strikingly narrowed.

(3.) The third part now is the "outer intermediate portion" of
Rolktt (c). It consists of a continuous layer of peptic cells. Exter-
nally these are in contact with the membrana propria, and internally
they bound the axial canal. We have not been able to find any

478

MANUAL OF HISTOLOGY.

other kinds of cells here, although others are stated by Heiderihain to

exist. "We are supported in this by
Rollett.

(4.) Finally, we come upon the true
gland tubule (d). Here the picture
is entirely changed. The lumen is
bounded by a continuous layer of a
special kind of cell, which in many
places comes in contact with the mem-
brana propria. External to this layer,
and as if imbedded in it, we find our old
friends the peptic cells, sometimes few,
sometimes in large number. The inner-
most cells have been named by Heiden-
liain " chief cells," and by Rollett ade-
The peptic elements, on the other hand, are spoken of

Fig. 462. — Transverse section through the
peptic gland of a cat. a, peptic cells ; 6,
internal cellular elements ; c, transverse
section of the caDilJaries.

lomorphous cells.

Fig. 463. — Peptic glands from the dog,
after Heidenhain; the peptic cells
darkened with aniline blue. 1. From
a fasting animal. 2. A portion
swollen up in the first period of
iligestion. 3. Transverse and oblique
section of the same. 4. Gland fol-
licle at the end of the period of
digestion.

by the first observer as " overlaying cells,"
and by the latter as " delomorphous "
cells.

These two kinds of cellular elements in
the true peptic gland tube may be easily
seen in the dog and cat. Transverse sec-
tions also show them (fig. 462). In other
mammals also essentially similar relations
are likewise to be seen (Heidenhain^
Rollett).

Heidenhairi s observations in regard to
the differences to be observed in the ap-
pearance of the peptic glands in the states of
rest and activity are of great interest further.

In a fasting dog (fig. 463, 1) the gland
tubules appear shrunken, and usually regu-
lar in their outline, while their " adelo-
morphous" cells are transparent. Some
hours after receiving food quite a different
appearance presents itself (2, 3). The
peptic glands appear swollen, and their
walls bulged out at points, the adelomor-
phous cells are enlarged and clouded with
a finely granular contents. Later on all
this swelling up has disappeared (4). The
adelomorphous cells are much diminished
in volume, but still very rich -in granular
matter.

Which kind of cell now produces the
gastric juice, the peptic or adelomorphous?
or does one species of cell yield the pepsin
and the other the acid 1

These questions cannot at present be
answered. We are inclined to ascribe the
greatest importance to the peptic cells,
and with Rollett to regard them as con-
tractile elements.

ORGANS OF THE BODY.

479

§ 252.

There is beside those just mentioned another species of gastric glands,
discovered many years ago in the pig by Wasmann. Here we have tubes
with blind endings and hollow down to the
latter, which are clothed internally not by
peptic cells, but columnar elements like those
of epithelium. The tube itself becomes
opaque on treatment with acetic acid. These
(tig. 464) are the gastric mucous glands
(Koelliker}. They have since been recog-
nised as occurring very widely in the
stomachs of the mammalia, and may be met
with either simple (fig. 464, 1) or compound
(2). In the dog, cat, rabbit, and Guinea-pig
they are met with near the pylorus in large
numbers. They are arranged in a narrow
zone in the neighbourhood of the pylorus
in man also, but in the form of compound
glands (Koelliker).

Very accurate observations have lately
been made by Ebstein on the stomach of the
dog. Here the ordinary columnar epithe-
lium of the surface of the stomach is con-
tinued down to a considerable depth into
the sometimes simple, sometimes compound
tube (fig. 465, a). The under portion or
blind end presents, on the other hand, lower
cellular elements rich in fine granules and
clouded (b, b). These resemble in many
respects the adelomorphous cells of the peptic glands. They also mani-
fest the same differences iu the fasting and digesting animal, which were
pointed out by Heidenliain (previous §) in the latter.

As regards the composition of the two kinds of
stomachal gland cells some observations were made some
years ago by Frerichs. They are composed of an albu-
minous substance, and a finely granular matter, pepsin
(see below), which may be dissolved out with water.
Besides this they contain a certain amount of fats,
and among them cholestearin. The ashes, amount-
ing to 3-3 '5 per cent., consist of earthy phosphates,
traces of phosphates of the alkalies, and sulphate of
calcium.

That their contents have anything to do with the
formation of gastric juice has not yet been proved,
although some suppose them to have.

The existence, in the human stomach, of those
ordinary racemose glands which are of such frequent
occurrence in most mucous membranes, is denied,
and as a rule with justice. They are, however,
constant in the pylorus, in the form of minute organs imbedded in the
mucosa itself. In man they are grouped together in longitudinal bands
of from 5 to 7 (Cobelli).

Fig. 464.— Stomachal mucous glands.
1. A single gland tube, from the
cardial end of !lie pig's stomach,
lined with columnar cells, a. the
cells; 6, the axial passage. 1*,
isolated cells. 2. A compound
gland from the pylorus of the dog.

Fig. 465. — From a stom-
achal mucous gland of
the dog. a, undermost
portion of the canal of
exit ; 6, conuaeacecient
of the trae gland tube.

480

MANUAL OF HISTOLOGY.

The lymplioid follicles of the gastric mucous membrane have long been
known under the name of the lenticular glands. They are not always to

be found in man, but are of rather
exceptional occurrence, varying greatly
in number, also, wherever they are
present.

The vascular system of the stomachal
mucous membrane (tig. 466), upon
which the secretion of the gastric
juice and absorption of the fluid con-
tents of the stomach is dependent, is
very characteristic (§ 197). The arte-
ries undergo division immediately on
arriving in the submucosa, so that
they arrive at the under surface of
the true mucous membrane in the
form of very fine twigs having an
oblique course (figs. 466 and 467, c).
Here, with but slightly diminished
calibre, they are finally resolved into
a delicate network of capillaries (fig.
467, d), whose tubes of 0-0070-
0-0038 mm. are woven around the pep-
tic glands forming elongated meshes
(figs. 466and 468). Thus they advance
as far as the surface of the mucosa,
where the orifices of the glands are sur-
rounded in a circular mesh-work, and
loops are prolonged into any papillae
that may be present (fig. 466, above). It is from this last portion of
the vascular apparatus alone that the transition of arterial into venous
blood takes place. The radicals of the veins are more or less scattered,
so that a certain amount of resistance is offered to the flow of blood into

them. These venous twigs, then,
become very rapidly developed into
trunks of considerable calibre, which
traverse the mucous membrane per-
pendicularly downwards to empty
themselves eventually into a wide-
meshed network lying horizontally
underneath the latter (figs. 466 and
467, b, a). This arrangement per-
sists, as a rule, throughout the vari-
ous species of mammals, with slight
modifications, affecting principally
the surface of the mucous membrane.
In the long-meshed network of
capillaries we have before us that
. 467 -From the stomach of the dog. a a portion of the vascular system pre-

vem ; 6, its branches ; r, an arterial twig break- L . . . , . i . .

ing up into a capillary network (d) for the Siding OV6r the Secretion OI the organ,

and in the round meshed network

with the venous radicals, that part formerly erroneously supposed to be
devoted to absorption.

Fig. 466. — Vascular network of the human
gastric mucous membrane (half diagramma-
tic). A fine arterial twig breaks up into a
long-meslied capillary network, which passes
again into a round-meshed around the open-
ings of the glands. From this latter the vein
(the large dark vessel) takes its origin.

OKGANS OF THK BODY.

481

As regards the lymphatics of the stomach, only the deeper were known
until quite recently.

According to Teichmann — with
whose views my own observations are
in perfect harmony — there exists be-
neath the peptic glands a network of
lymphatic canals, about 0 '0305-0-0501
mm. in diameter, which communicate
with a deeper wide meshed network of
passages of larger calibre, measuring
transversely, from 0-1805 to 0'2030!
From these latter the true, valved
lymphatic vessels are then developed,
which gradually perforate the muscular
tunic to follow subsequently the two
curvatures of the stomach.

For many years this was supposed to be the true arrangement of parts,
and numerous efforts were made to prove that the superficial veins of
the stomachal mucous membrane presided over the absorption of the
organ.

Fig. 468.— Undermost half of peptic glands
from the dog, with their long meshed
capillary networks.

Fig. 469,

-Lymphatic vessels in a vertical section of the mncous membrane of the stomach of an adult
man (original drawing by Loven).

But quite recently this difficulty has been got over at the hands of an
excellent Swedish observer, Loven, whose dexterity we may thank for
the injection of these passages, and that of the highly developed lym-
phatic, apparatus, whose radicals ascend almost to the surface of the
mucous membrane. The arrangement of these will be easily understood
from fig. 469, and no further explanation need be given.

The nerves of the stomach, derived from the vagus and sympathetic,
are arranged in the submucous tissue in a plexus studded with numerous
minute ganglia (Remak, Meissner). The greatest obscurity, however, still
remains as to the ultimate termination of the fibres.

482 MANUAL OF HISTOLOGY.

The development of the stomach is a subject in the history of develop-
ment to which great interest attaches. We will, however, occupy our-
selves only with its accessory organs. These, the tubular glands, commence
in the form of pointed processes, springing downwards from the intestinal
glandular germinal plate, which become gradually hollow, beginning at
the openings. It is a point worthy of notice, that these glands are for
a long time entirely unconnected with the subjacent loose fibrous intestinal
layer ; and it is not until the fifth month of intrauterine life that the
latter sends up tufted processes between the gastric tubuli to form the
mucosa of the part (Koelliker).

§253.

The mucous membrane of the non-functioning stomach is pale in
colour, and more or less completely covered by a quantity of either
slightly acid or alkaline slimy mattter of considerable viscidity. This is
the secretion elaborated by the gastric mucous glands. In it may be seen,
under the microscope, beside cast-off columnar epithelium, numerous
peptic cells escaped from the peptic tubuli, and frequently, also, a
number of more or less broken down structures of the same nature, naked
cells, and free nuclei surrounded by particles of the original cell contents.

According to Brucke and Bernard, it is only the surface of the mucosa
which is acid in the living animal, the deeper portions having an alkaline
reaction. After death the whole becomes rapidly acid owing to diffusion.

On the introduction of food into the stomach, or under the influence
of other chemical or mechanical excitants of the gastric mucous mem-
brane, the condition of things is immediately changed. Owing, probably,
to some reflex action not yet understood, although indicated in many
ways, an increased influx of blood into the intricate vascular interlacements
of the mucosa takes place. The veins become distended, and contain
brighter blood, and the whole surface appears to the unaided eye of a more
or less rose-red colour, in addition to which phenomena the temperature
rises. Coincident with these changes the gastric juice commences to
well up from the tubules, bearing with it numerous peptic cells from the
lining of the latter.

This juice is a transparent fluid of strongly acid reaction, either perfectly
colourless or of a pale straw tint. It takes up certain constituents of the
mucous coating of the stomach, and extracts subsequently various fer-
menting substances from the granular contents of the peptic cells, a
process which commences while the juice is still within the tubuli in
which the peptic cells are contained. It is likewise mixed with
whatever saliva may have been swallowed. It cannot then be a matter
of surprise that the gastric juice possesses a specific gravity of I'OOl,
1-005, and 1-010.

The proportion of solid constituents in this secretion is, as a rule,
small but variable. Thus, in the sheep, it contains, according to Bidder
and Schmidt, 1'385, and in the dog, 2'690 per cent., while, according to
the last named observer, that of the human female only contains 0-559
per cent. The nature of the fluid also would lead us to expect consider-
able variety also in one and the same individual.

The two most important of these constituents are a free acid and
peculiar fermenting substance, which possesses in the presence of the
former, and only then, a great amount of energy.

The add in question has given rise to much debate regarding its

ORGANS OF THE BODY. 483

nature. It has been held at different times to be either lactic or hydro-
chloric, without taking into account a number of other ill-founded
theories. The matter has been at last set at rest, however, by C. Schmidt,
in favour of the latter view. Lactic, acetic, and butyric acids may,
however, be present as decomposition products, the first being indeed
a very frequent constituent of gastric juice. Og02 per cent, of hydro-
chloric acid was discovered by Schmidt in the gastric juice of a female,
and 0'305 per cent, by Bidder in that of the dog.

The ferment found in the gastric juice is known as pepsin. It was
many years ago made the object of very extended investigation by
Schwann and Wasman, and since then by many other observers, but can
hardly be said to have ever been obtained completely pure. Its propor-
tion generally amounts to about, on an average, 1 per cent. Bidder and
Schmidt's analyses give 1'75 for the dog. 0'42 for the sheep, and for man
only 0'319 per cent. At present but little is known of pepsin as about
all the other fermenting substances of the animal economy. "We are
aware, indeed, that it occurs in a soluble form, is precipitated by alcohol
without losing its digestive power on subsequent re-solution in water,
whilst elevation of temperature above 60° C. destroys this for ever. This
pepsin, as has been shown by Frericlis, is the granular matter seen m
the contents of the peptic glands. It appears to possess almost unlimited
digestive properties in the presence of an adequate amount of dilute acid,
so that there seems to be an inexhaustible store of it in the mucous
membrane of the stomach.

The mineral constituents of the gastric juice are, chlorides of the
alkalies, phosphatic earths, and phosphate of iron (Bidder and Schmidt).
Among the first we find a great preponderance of common salt, and
besides chlorides of potassium, of calcium, and of ammonium also. We
shall take an analysis by the two last named observers as an example of
the proportions of the various salts. The percentage in the gastric juice
of the dog was as follows : Chloride of sodium, 0'251 ; of calcium, 0'062 ;
of potassium, 0'113; of ammonium, 0*047; phosphate of magnesium,
0-023 ; of calcium, 0'173 ; of iron, O'OOS.

Just as the peptic cell is able to produce pepsin from an albuminous
substance, so also does it yield hydrochloric acid by the splitting up
possibly of the chlorides. This process, however, is probably carried on
only at the undermost portion of the gland tubule, i.e., near the orifice
(Brilcke), the source of the watery fluid with its salts being the long-
meshed capillary network of the peptic glands.

The amount of gastric juice poured out is naturally very variable,
owing to the periodical nature of the functions of the stomach, and
therefore necessarily difficult to determine. It is stated by Bidder and
Schmidt to be at all events very considerable. A dog of about a
kilogramme weight produces, in the course of a day, about 100 grammes,
with extremes in both directions. Schmidt estimated the amount
secreted hourly in the body of a woman at the enormously high figure
of 580 grammes.

The use of this fluid is to dissolve the albuminous matters taken into
the stomach, and to convert them into peptones, i.e., modifications of
these substances which neither coagulate at boiling point or under the
action of mineral acids, nor combine with metallic salts to form insoluble
compounds (Lehmann). They transude, on the other hand, with great
readiness through animal membranes, a property of the utmost import-

484

MANUAL OF HISTOLOGY.

ance, which undigested albumen does not possess. In contradistinction
to the latter, then, these peptones might be designated as albuminates
capable of being absorbed. Owing, however, to the extreme difficulty of
the subject, there still exists up to this very hour a great difference of
opinion among physiologists as to the nature of peptone, in spite of the
exertions of very excellent observers (Brucke, Meissner).

§ 254.

The small intestine, with its serosa and well-known double layer of
muscle fibres, presents, as regards its mucous membrane, a far more

Fig. 470.— From the small intestine of the vab- Fig. 471. — Vertical section of the mucous mem-
bit, a, tissue of the mucous membrane; 6, brane of the small intestine of a cat. a, the
lymphatic canal; c, an empty transverse sec- glands of Lieberkuhn; b. villi.
tion of a gland of Lieberkuhn; d, another of
the same occupied by cells.

complicated structure than that of the stomach. This membrane, in the
first place, is thrown out into a multitude of crescentic duplicatures,
known as valvulce conniventes Kerkringii, and is covered in the next by
innumerable small conical processes, the villi intestinales. By this
arrangement of valves and tufts, an enormous increase of surface is
obtained. We find, further, in the tissue of the mucosa, two forms of
glands, namely, the racemose mucous glands of Brunner, and the tubular
of Lieberkuhn, to which may be added the lymphoid follicles, either
single or in groups, known as the solitary and agminated glands of
Peyer.

But the tissue of the mucous membrane itself (fig. 470), is also different
in texture from that of the stomach. Thinner, and supplied with the
muscularis mucosce, it no longer presents the character of ordinary fibrous
tissue, as does that of the stomach as a rule. It consists rather of
reticular connective-tissue, containing, entangled in its interstices and
meshes, an abundance of lymphoid cells, and only assuming a more or
less homogeneous membranous structure towards the gland cavities and
towards its free surface, whilst at other points, as, for instance, near the
surface of large vessels, it appears to be made up of longitudinal fibres.
This tissue of the mucous membrane varies also to a certain extent,
according to the different species of animals.

The villi commence on the intestinal aspect of the pylorus, flat and
low at first, and increasing gradually in height until they assume a
conical or pyramidal form, which merges step by step, as we progress
downwards, into a slender tongue-like figure. They stand tightly packed

ORGANS OF THE BODY.

485

one against the other (fig. 471, &), so that, according to Krauze's
estimate, about from 50 to 90 spring from 1 Q mm. in the jejunum, and
duodenum, and in the ileum from 40 to 70, giving
for the whole extent of the small intestine, accord-
ing to his calculation, 4,000,000. Their height
varies from 0*23 to 1'13 mm. and upwards.
Their breadth also differs, naturally, according to
their form. Transverse sections show them to be
either cylindrical or leaf-shaped.

All these villi are clothed with peculiar col-
umnar epithelial cells, already referred to (p. 147),
which present on their free surfaces a thickened
border, perforated by pores or fine canaliculi (fig.
472, a).

Between these cells (fig. 473, b) may be ob-
served— not unfrequently distributed with toler-
able regularity — those "goblet cells" which have
been already brought before our notice (§ 93).
In number they vary with the species and the
individual.

We also encounter here, as in the stomach,
small roundish structures lying between the in-
ternal extremities of the columnar epithelium
cells. These may be regarded as destined to
replace the latter as they successively perish.

Under the epithelial layer we next come upon
the framework of the structure in the form of
reticular connective - substance with entangled
lymphoid corpuscles and nuclei in some of the
nodal points of its not unfrequently long meshed network.

The recognition of the true nature of the surface of the villus is
attended with considerable difficulty. Nevertheless, we may see that
here also it preserves the same retiform character, although the bands
may in many instances become broader and flatter, and the interspaces
between them decrease in size until they
become merely small apertures, so that the
effect almost of a homogeneous mem-
branous limiting layer may be given.

This tissue of the villi is traversed in
the first place by a vascular network (?;),
next by a lymphatic canal (d), occupying
the axis of the structure, and lastly, by
delicate longitudinal bundles of unstriped
muscular fibres (c). For the discovery of
the latter we are indebted to Briiclke, although anterior to his researches
on tlie subject, distinct contractility had been recognised in the intestinal
villi in the living or recently killed animal, producing numerous wrinkles
on the surface of the process .(Lacauchie, Gniby, and Delafond). These
bundles of muscle fibres may be traced down through the mucous mem-
brane into the muscularis of the latter.

The vascular netivorks of the intestinal villi (figs. 474, 475) occupy
invariably the peripheral portions of the latter, and are supplied in the
smaller mammalia each by a small arterial twig or pair of the same (a),

Fig. 472,— An intestinal villus
(after Leydig) . a, columnar
epithelium with thickened
border or cuticular mem-
brane ; b, capillary network ;
c, longitudinal muscular
bundles; d, axial chyle
radicle.

Fig. 473. — Epithelial cells from a human
intestinal villus (after Schulze). a,
goblet cells; 6, ordinary elements.

486

MANUAL OF HISTOLOGY.

which ascend at one side, bend over at the apex, and follow the opposite
wall in returning, as venous vessels (c). Between these afferent and

efferent vessels a capillary net-
work exists, sometimes exceed-
ingly complex, sometimes very
simple in its arrangement (&).
It not unfrequently happens
that a system of capillaries is
first given off by the arterial
twig to supply the glands of
Lieberkulm (d), opening at the
base (fig. 474, a to the right)
of the villus, which system is
simply continuous with that of
the latter (b to the right).

The diameter of the arterial
vessel may rise to 0-226-0-0282
mm., that of the vein to 0*0451
mm. In calibre the capillaries
measure on an average 0*0074
mm., and their arrangement
is usually in elongated meshes.
The disposal in loops of the
arteries in their transition into
veins may be absent, a capillary network being interposed between the
two vessels at the summit of the villus.

We have already alluded (p. 374) to the
coecal chyle canal of the intestinal villus.
"When the latter is more than usually broad
there may be two or even several of these
blind tubes, but when small and slender
they are only single. The chyle canal occu-
pies the axis of the villus, and presents itself,
under ordinary treatment (fig. 472, d), in cer-
tain cases quite distinctly as a tube formed
of a homogeneous non-nucleated membrane,
on an average 0*023 mm. in diameter. On
treatment with a solution of nitrate of silver,
however, this tube is easily shown to be
composed of a layer of those jagged-edged
vascular cells already so frequently alluded
to. It may be seen with great clearness when
injected artificially, and also in the villi of
animals killed while engaged in digesting an
abundance of fatty food (fig. 476).

Fig. 474. — Vascular system of an intestinal villus in the
rabbit, a, the arteries (shaded), breaking up first
into a capillary network around the glands of Lieber-
kiihn (d) ; 6, network of capillaries in the villus; c,
venous vessels (unshaded).

§ 255.

Turning now to the glandular elements of
the small intestine, we shall commence with
the least important, namely, with the race-
mose mucous glands (fig. 477, &), known com-
monly as Brunner's. They are confined to the duodenum, and begin close
to the stomach, closely crowded together into a regular adenous layer

Fig. 475. — Vascular network from
the intestinal villus of a hare, with
its arterial branch 6, capillaries c,
and venous branch a.

ORGANS OF THE BODY.

487

seated immediately under the mucosa. Thus they extend as far as the
orifice of the ductus clwledochus, and from that point on appear more
rarely. Among the mammalia much variety is observed as regards thuoe
organs. When only slightly developed, as is frequently the case, they are
confined to the neighbourhood of the
pylorus, forming a complete zone just
behind it. The diameter of these
glands ranges from 0 -2 3 to 2 mm. The
branches of the excretory ducts present
a complicated series of twists unlike
other glands of the same kind
(Schivalbe). The aoini are round,
elongated, or even tubular, and measure
from 0-0564 to 0'1421 mm. The ex-
cretory canals of these glands, con-
siderable in calibre (fig. 477), ascend
obliquely upwards, slightly bent, dis-
charging their contents at the base of
the villi (fig. 477, c).

Both excretory duct and gland
vesicle are, strange to say, lined by
the same species of cells. These are
low columnar elements, whose nucleus is situated low down in the body,
and which are but very slightly coloured by carmine. They are unlike
the contents of the follicles of Lieberkuhn soon to be described.

Fig. 476. — Very slender villus from the intestine
of a kid, killed while engaged in digestion ;
without epithelium, and showing the absorb-
ent vessel in the centre filled with chyle.

Fig. 477. — Brunner's glands from the duodenum, a, villi ; b, bodies of glands ;
c, excretory canals opening between the villi.

That same network of extremely delicate gland canaliculi we have

already spoken of as occurring in many racemose organs (§ 195), as well

as in the salivary glands (§ 245), is to be found also in the glands of

Brviwer, according to Sehwalbe. The membrana propria, which is here

32

488

MANUAL OF HISTOLOGY.

completely closed, and contains imbedded nuclei, sends no processes into
the interior of the gland vesicles.

Fig. 478. — One of Brunner's glands from the human being.

These organs appear to be richly supplied with lymphatic vessels of
large size, which penetrate between their vesicles and lobules.

The secretion of these glands appears to be peculiar. According to
Schwalbe, the contents manifest considerable similarity to those of the
stomachal mucous glands already alluded to (§ 251). Heidenhain tells
us that in the dog, at least, the cellular elements
of Brunner's glands present the same changes in
the fasting and digesting condition that were
observed by EbsUin, in those of the stomachal
mucous membrane.

According to Budge and Krolow, the contents
of these organs convert (in the pig) starch into
dextrin and grape sugar, and dissolve fibrin at 35°
C., but have no effect, on the other hand, on either
coagulated albumen or fat. In the dog and horse
the secretion is rather viscid, and contains a
considerable amount of mucus (Costa).

The crypts of Lielerkuhn, on the other hand,
are glands of far greater importance. They are
to a certain extent a modified extension of the
mucous glands, as they are called, of the stomach.
The whole of the mucous membrane of the
small intestine, like that of the stomach, is beset
with an enormous number of these crypts crowded
closely together perpendicular to the surface of the membrane (fig. 479).
The arrangement of their vascular supply is similar to that of the peptic
glands.

The length of these crypts is less than that of the gastric tubuli, ranging
from 0-3767 to 0-4512 mm., with a breadth of 0'0564-0'0902. mm.
Their membrana propria is hardly distinguishable from the surrounding
connective-tissue. It is delicate, and the outline of the tube is conse-
quently smooth. At its blind end we may either find a dilatation or
decrease in calibre.

Fig. 479. — Lieberkuhn' s glands
from the cat, with broken
down cellular contents.

ORGANS OF THE BODY.

489

Fig. 480. — Openings of the glaiids
of Lieberkiihn in the mouse. At
(a) an empty opening, in the
other cases each is tilled with
columnar cells, placed with
their long axis towards the
centre.

The contents of these crypts, unlike those ofBruHnei** glands, consist of
delicate columnar nucleated cells, with widened
base, which rest on the membrana propria.
These, together with the open axial canal, may
be seen in every transverse section (fig. 470,
(I). According to Schulze, between these cells
other goblet cells may present themselves, a
point worthy of note.

In suitable preparations (fig. 480) the orifices
of the glands are to be seen at varying dis-
tances from one another, lined with columnar
epithelium, which passes in through the en-
trance of the tube. At those points at which
the villi are very crowded, the orifices of these
glands of Liebekuhn surround their basesin ring?.

§ 256.

We now turn, finally, to the lymphoid follicles of the small intestine.
These occur with greater frequency here than in the stomach, which fact
is explained by the greater similarity of their
tissue to that of the mucosa of the small in-
testine. As has been already mentioned,
they are in the first place met with scattered
over the whole length of the small intestine
as glandulcu solitaries. These are roundish,
opaque, white bodies of very unequal size,
ranging from 0'2 to 0*4 and 2'2 mm. In
some subjects they are very scantily repre-
sented, or even entirely absent, while in other cases they appear in mul-
titudes. In situation and structure they correspond with the agminated
glands into which they may merge without any sharp boundary. At parts
of their periphery they are continuous with tl e circumjacent connective-
tissue.

By the agmination of these follicles it is that Peyer's patches or plaques
are formed (figs. 481, 482), _^ A

which occur in man, as in
all mammalia, in the greatest
abundance, but in very
various degrees of develop-
ment. In some cases they
are made up of from 3 to 7
follicles only, but more fre-
quently of from 20 to 30.
Again, when large, they may
contain up t,o 50 or 60 of
the latter.

Peyer's patches are found
principally in the small
intestines, and always at the
free side, or that opposite to the mesenteric attachment of the viscus. They
appear, as a rule, first at the end of the jejunum, and become more
frequent in the ileum.

But although this is the usual mode of distribution, it is not without

Fig. 481.— One of Peyer's glands from
the rabbit.

Fig. 482. — Vertical section through one of Fryer's glands
from the rnbbit. «, villi: ft, bodies of gla.ids rounded off
above ; c, others, apparently open above.

490

MANUAL OF HISTOLOGY.

exceptions, especially in the occurrence of isolated Peyer's glands in the
colon.

The vermiform appendix of man, and to a greater extent also that of
the rabbit, may likewise be said to be one large Peyer's gland, composed
of crowded follicles (Teichmann, His, Frey).

The number of these agminated glands to be found in the human small
intestine varies from 1 5 to 50 and upwards. The diameter of such a group
cannot, offcourse, be definitely laid down, varying, as it does, from 7 mm.
to several centimetres. The form they assume is usually oval, their long
axis corresponding with that of the intestine.

Subjecting the glandulce agminatce to close inspection, we find in
longitudinal sections that, although the form of the follicles may be
similar in one and the same group, nevertheless it is liable to vary to a
large extent, both in different animals, and according to the locality in
the intestine we choose for examination.

Beside spheroidal follicles, namely (fig. 483), we meet with others more
or less elongated, presenting somewhat the figure of strawberries. But in
other instances the follicles maybe so increased in vertical diameter as to
present on section an outline resembling that of the sole of a shoe. In

Fig. 483.— Vertical section of one of Peyer's plaques from man, injected through its lymphatic canals
a, villi, with their chyle passages; b. follicles of Lieberkuhn; c, muscularis of the mucous membrane;
d, cupola or apex of follicles; e, mesial zone of follicles; /, base of follicles; g, points of exit of the
chyle passages from the villi, and entrance into the true mucous membrane; ft, retiform arrange-
ment of the lymphatics in the mesial zone ; i, course of the latter at the base of the follicles ; k.
confluence of the lymphatics opening into the vessels of the submucous tissue; I, follicular tissue of
the latter.

man they are usually of the spheroidal kind ; in the small intestine of
the rabbit strawberry shaped. Those very much elongated examples just
mentioned are to be found chiefly in the under portion of the ileum of
the ox and vermiform appendix of the rabbit.

The follicle, however, may be of what shape it will, we can always
distinguish three portions in it, namely, the summit or cupola, the mesial
zone, and the base. The cupola (d) projects into the intestinal tube ;
the base (/) descends to a greater or less depth into the submucous
connective-tissue ; and the mesial zone (e) serves to connect together all

ORGANS OF THE BODY.

491

Fig. 484,— From the surface of the pro-
cessus vermiformis of the rabbit, a,
narrowed entry to the cupola of a fol-
licle ; 6, mouths of crypts in the broad
ridge of mucous membrane; c, hori-
zontal lymphatic network ; d, descend-
ing lymph canals.

the follicles of one gland by means of a tissue entirely iRmilar to their
own. It is also continuous, without any line of demarcation, with the
adjacent infiltrated retiform tissue. It is at its level that we usually find
the muscularis mucosce (c) which opens in each case to allow room for
the follicles (Frey).

We must now turn to the nearer consideration of the cupolse. These
are surrounded by annular ridges of mu-
cous membrane, containing follicles of Lie-
berkuhn (b), and are continuous down-
wards into the mesial zones, supporting on
their free surface, either ordinary or, what
is more frequently the case, somewhat
modified irregular villi (a). The actual
summits of the follicles, however, are quite
destitute of villi. They are, in fact, so
freely exposed that each lymph follicle
appears to the naked eye as a little pit
on the surface of the plaque.

The ridges around the follicles may,
however, as in the plaques of the colon,
be quite bare of villi. In the processes
vermiformis of the rabbit, also, the surfaces of the rings may be increased
greatly in breadth (fig. 484, 5), so that only a narrow entrance (a) to the
follicles is left.

If we turn now to the finer structure of the elements of Peyer's patches,
we find it to be exactly
that of other lymphoid
follicles. Their sustenta-
cular tissue is a species of
retiform connective sub-
stance, traversed by capil-
laries in which innumer-
able lymph cells are
entangled (pp. 195 and
420). Many of the nodal
points in this network
contain in young indivi-
duals full-bodied nuclei,
met with in adults, on the
other hand, in a shrunken
condition. At the mesial
zone this reticular tissue
is continuous with the similarly constituted connecting lymphoid layer,
and through this with the closely related tissue of the mucous membrane.

The sustentacular matter in the interior of the follicles is very loosely
interwoven, while externally it assumes a denser texture.

At two spots it becomes exceedingly densely reticulated and distinct ;
in the first place on the surface of the cupola, which is, like the villi,
covered immediately by columnar epithelium, and then at the peripheral
portion of the base. This latter in some of Peyer's glands is surrounded
by a continuous investing space, which corresponds to the investing
spaces of the lymphatic glands (§ 223). In many animals the resem-
blance is increased by the interposition o/ perpendicular fibrous septa

Pig. 485.— Vertical section through an injected Payer's follicle
of the rabbit, showing the capillary network of the same; the
large lateral vessels, 6, and those of the villi, c.

492

MANUAL OF HISTOLOGY.

between adjacdftt investing spaces, which are lost at the level of the

mesial zone.

In other plaques, instead of these continuous investing spaces, the

surface of the base is covered by numerous fine lymphatic canals, like a

child's toy ball with a net.
In the connecting layer,
between th& mesial zones, a
network of similar passages
may likewise be recog-
nised.

The walls of these pas-
sages, then, are made up of
very small -meshed lym-
phoid reticular substance.

In the actual follicles
themselves, however, no
such passages exist.

We have only to add, that
the superficial lymphatic
canals of the mucous mem-
brane, of the smooth as
well as villous annular
ridges, all sink down to
empty themselves into these
lymph passages of the con-
necting layer already men-

Fig. 486.— Transverse section through the equatorial plane of
three of Peyer's follicles from the rabbit, a, capillary net-
work ; 6, large circular vessels.

tioned ; also that, at least,

a part of the investing
spaces around the follicles
is clothed with the characteristic vascular epithelium of the lymphatic
system (p. 377).

The vascular supply of each follicle is composed (as was demonstrated
many years ago by myself) of an exceedingly complex network of delicate
capillaries, from about 0*0056 to 0'0074 mm. in diameter. This network
(fig. 485, a) stands in close connection with the large arterial and venous
vessels (&), which course up and down between the follicles supplying the
villi (e) of the intestine, as may be seen in vertical sections. In trans-
verse sections the arrangement of the capillaries in the interior of the
follicles is seen to be in lines converging towards the centre (a), starting
from circular vessels externally — an object of extreme beauty under the
microscope.

§257.

The nervous apparatus of the small intestine is exceedingly compli-
cated, deriving its roots from the ventral divisions of the vagus and
sympathetic. It consists of a double plexus of microscopic ganglia con-
nected above with the nerves interlacing in the walls of the stomach.

In the submucosa we first meet with the plexus1 of Remalt and Meissner,
remarkable for its highly developed knots. Prom this pale nucleated
fibres are given off, principally to the muscularis of the mucous mem-
brane, and muscular bundles in the villi, and to a minor extent to the
surface of the membrane as sensory elements. We are still lacking in
observations on these points, however.

ORGANS OF THE BODY.

403

Externally this submucous plexus is connected with the remarkable
and no less developed plexus myentericus of Auerbach. The latter, with
its regularly flattened ramifications, but more minute ganglia, is situated
between the internal transverse and external longitudinal muscular tunic
of the gut. These it supplies
with its numerous twigs,
forming first a secondary
plexus of threads, O'OOl-
0-005 mm. in thickness, each
of which possesses from 3
to 6 of the finest nervous
filaments (L. Gerlach), leav-
ing no doubt as to the motor
nature of the latter, although
we are still in the dark as to
the ultimate termination of
the fibres.

We may form some esti-
mate of the extent to which
the nervous system of the in-
testines is developed, from the
fact that about 100 ganglia,
belonging to the submucous,
and over 2000 to the my en-
teric plexus, are to be found
in 1 Q" of the intestine of the rabbit.

The following is the general arrangement of the vessels of the intestine.

On arriving in the walls of the latter, a few small twigs are given off

Fig. 487. — A ganglion from the submncous tissue of a
human infant, a, nervous knot; b, radiating twigs; c,
capillary network.

Fig. 488. — From the small intestine of the Guinea-pig, a, plfows n>yentericv&, with its
ganglia ; b, c, fine, and ef, larger lymphatic vessels.

to the serous covering of the part, after which the vessels break up in the
muscular tunics into the usual well-known capillary network with elongated

494 MANUAL OF HISTOLOGY.

meshes, whose long axes correspond with that of the contractile elements.
The submucosa is from this supplied further with another network of
capillary tubes of somewhat greater calibre than the first (Frey).

The chief supply, however, is to the mucous membrane itself. Here
arterial twigs arriving at the bases of the crypts of Lieberkuhn gradually
break up into networks of capillaries of medium calibre, with oblong
meshes, similar to those of the peptic glands. These are disposed, in the
first place, around the mouths of the glands in delicate rings, and then
continued into the mesh-work of the villi. The veins arising in the
latter, with which we are already acquainted, descend directly downwards
through the mucous membrane, receiving but few lateral twigs, and
empty themselves into the submucous venous network.

The presence of racemose glands and lymphoid follicles necessitates, in
many parts of the intestinal tract, a modification of this vascular arrange-
ment. The well-known round-meshed network, for instance, is met with
around Brunner's glands in the duodenum. Then Peyer's patches require
a more highly developed vascular system. Here little arteries ascend,
either in the septa, or the connecting or junction layer of the follicles,
after sending off twigs for the fundus of each of the latter, as well as for
their sides. Thus they reach and break up into the terminal capillary
network of the ridges and intestinal villi. From thence the blood is
taken up by lateral branches of the veins arising here, which descend by
the side of the arteries, receiving also an addition from the follicles.

§ 258.

Through the exertions of Teichmann, His, Frey, and Auerbach, we
have recently become accurately acquainted with the nature of the
lymphatic apparatus of the small intestine. This is from many points
of view of great interest.

Its roots have two sources : in the first place, the mucous membrane
with its villi, and then the muscular coats of the intestine. The last
source was only lately discovered by Auerbach, while the first has long
been known, owing to the fact of the vessels here being so distinctly
visible when full of chyle.

A few hours after the reception of fatty food into the stomach, the
matters found in the small intestine are found to contain neutral fats in
a condition of the most minute division, a physical change brought about
by the admixture with tbem of the bile and secretions of the pancreas
and mucous membrane of the intestinal tubes. The fats are now in a
condition capable of being absorbed, and they are soon taken up in large
quantities. In this last process the villi are especially active, if not
exclusively so, and principally their apices.

The commencement of the process is as follows : The fatty globules
in the form of extremely minute particles of from 0'0045 to O'OOll mm.
in diameter, after passing through the thickened porous border on the
epitheliad cells, arrive within the bodies of the latter. At first only a
few cells are seen to be filled in this manner, the fatty granules occupy-
ing principally that portion of the cell between the nucleus and the free
end. The number of cells, however, presenting this fatty infiltration
soon becomes greater and greater, and the fat-molecules penetrate past
the nucleus into the pointed and attached half of the columnar elements.
In the further progress of this process the granules of fat pass through
the apices of the cells into the tissue of the mucous membrane beneath,

ORGANS OF THE BODY. 495

either filling the whole apex of the villus in such myriads as to give it
the appearance of being diffusely infiltrated, or else ranging themselves in
long streaks, which may be mistaken for fine canals charged with fatty
globules, as they course along between the lymph cells and connective-
tissue fibres. In the third stage of the process we remark that the
minute fatty molecules have penetrated through the walls of the chyle
radical into its lumen, entirely filling the latter, so that this element of the
intestinal villus, at other times so difficult of detection, becomes dis-
tinctly visible, as has been already mentioned. The concluding phase of
the whole act is especially instructive ; here we see the columnar epithe-
lial cells and tissue of the mucous membrane again freed of fat, while the
chyle vessel is still full (fig. 476, p. 487).

That this is the true course of the process may be confirmed by artificial
injection of the lymphatic canals in the mucous membrane of the small
intestine.

The radicles of the chyle or lacteal system (fig. 489) are easily recog-
nised in the villi of the gut as blind canals, which in our opinion (in
which we are supported by Teichmann and His), are not continuous with
the actual tissue of the villus. According to the form of the latter, they
present themselves either single (a) or double (b), or even in greater
number (c). In the last case we either find a looped communication
between them in the apices of the villi, or the vessels end separately.
Towards the roots of the villi we not unfrequently encounter transverse
connecting branches.

On arriving in the mucous membrane after leaving the villi, the lacteal
vessels descend through the former between the follicles of Lieb&rkuhn,
either directly or subsequent to the formation of a superficial horizontal

CL--

Fig. 489. — Vertical section of the human ileum. a, villas, with one chyle canal ; 6, another
with two; c, another with three; d, absorbent canals in the mucous membrane.

network, which lies at the bases of the villi, and encircles with its meshes
the mouths of these glands of Lieberkuhn.

At the boundary between the mucosa and submucosa, and in the
latter, a network (d) is formed by the intercommunication of these chyle
canals. These latter may be of considerable calibre, as in the sheep and
rabbit, or small, as in man and the calf. They accompany the network
of blood-vessels also here, and in some cases form sheaths around the
latter. As a whole, moreover, much variety is met with among them,
depending on the thickness of the mucous membrane and species of animal
chosen for observation.

496

MANUAL OF HISTOLOGY.

The arrangement of the lacteals is modified wherever Peyer's plaques
occur (fig. 490). Those lymphatic passages («), returning from the
modified villi of the circular ridges of these localities, form around
the tubular glands (b) of the villous ridges a network (#), which is
continuous with another system of intercommunicating passages (h)
formed in the reticular substance encircling the mesial zones of the
follicles. The latter open either into simple investing spaces enveloping
the basal portions of the follicles, and precisely similar to those of the
follicles in a lymph gland (in the rabbit, sheep, and calf for instance), or
(the case in man, the dog, and cat) these spaces are replaced by a system
of separate canals (i), interlacing around the bases of the follicles like
those we have already considered in § 227.

From this set of passages, or from the simple investing space, as the
case may be, the efferent lymph vessels finally take their rise.

Returning now to the system of canals of the submucous tissue, we

Fig. 490.

find springing from it a certain number of regular knotted lymphatic
vessels, which empty themselves, after piercing the walls of the intestine,
into the subserous lymphatic trunks. These latter are arranged in a
narrow band following the mesenteric attachment of the gut (Auerbacli).

The submucous lacteal network communicates, moreover, by means of
another set of passages with a second plexus of lymphatic vessels lying
between the longitudinal and transverse layers of muscle of the part.
This (fig. 488, p. 493), to which the name interlaminar network has been
given by Auerbach, accompanies the plexus myentericus situated here
also, with which we are already acquainted. It collects all the lymph
from the muscular substance of the intestinal tube, from a series of very
densely reticulated lymph canals of exceedingly small calibre, which are
found singly in the longitudinal tunic, but bedded one over the other in
the transverse layer. This interlaminar lymph net is connected finally
with the subserous trunks by efferent vessels.

In this complex arrangement there is most undoubtedly a double pro-

ORGANS OF THE BODY.

497

vision made for the escape of the chyle, as Auerbach very correctly
remarks, and during the peristaltic action of the bowel, also, the latter fluid
is able on this account to give way to the pressure in many directions.

In conclusion, we have only to state, as regards the development of the
small intestine, that in man the villi make their appearance in the third
month of intra-uterine life. They are then apparent as wart-like excres-
cences. Further, we would point to the fact, that the crypts of Lieberkuhn,
unlike the gastric tubuli, are present from the commencement as pits in
the mucosa, and that the follicular structure of Peyer's glands is apparent
.in the seventh mouth. The cells of the intestinal mucous membrane,
and of Lieberkiihn's follicles, contain glycogen in the fetus (Rouget).

§ 259.

The mucous membrane of the colon corresponds in most essential
particulars with that of the small bowel, except that it is quite destitute

Fig. 491. — Tubular glands from the
rabbit's colon. One tube filled with
cells, the others sketched without
them.

Fig. 492. — Tubular gland from the colon of a Guinen-
pig. At a, a tube is seen with membrana propria
apparent at certain points; at fe, the contents are
escaping through a rent in the latter.

of those important appendages the villi. Its substratum, also, is far poorer
in lymph cells than that of the smaH intestine,
and approaches more in character to ordinary
fibrous connective-tissue.

The epithelium cons'ists of columnar cells
similar to those of the ileurn, but lacking pores
in the but slightly thickened border. Goblet
cells are also met with here (Schulze).

Its muscular tunic resembles that of the
mucosa of the stomach (§ 251), and exhibits
the same variety in the relative development of
its two layers (Schwartz, Lipsky). Imbedded
in it we find a great number of tubular glands,
the tubuli of the colon, and a variable number
of lymphoid follicles like those already met
with in the small intestine.

The tubuli of the colon (fig. 491) are merely
modifications of the follicles of Lieberkuhn from
which they are gradually developed.

They present themselves in the form of
simple undivided tubes with tolerably smooth and even walls, and a

Fiir. 493.— Tubuli from the colon
of the rabbit, treated with
caustic soda.

498

MANUAL OF HISTOLOGY.

Fig. 494.— Mouths of tubuiar
glands from the colon of the
rabbit, with radiating ar-
rangement of columnar cells.

length which varies between 0*4512 and 0'5640 mm. and upwards,
the transverse diameter lying between 0-0902 and 0'1505 mm. More-
over, they are just as crowded as the gastric and jejunal tubuli, and are
found in every part of the large intestine, including the processus vermi-
form is.

They contain a viscid, and at times somewhat fatty mass (fig. 491 and
492, b), consisting of nucleated gland cells (measuring 0-0151-0-0226 mm.)
made up of granular protoplasm. These present the appearance when seen
on the surface of flattened epithelium, from the fact of their being accommo-
dated to one another, but are found on section of the gland to be columnar.
Here also goblet cells may be encountered
(Schuhe). The mouths of these glands are of the
ordinary kind, lined with columnar epithelial
cells converging towards the lumen (fig. 494).

The lymphoid follicles are, as a rule, larger
than those of the small intestine. Their cupola;
project from depressions in the mucous mem-
brane.

We have already remarked that their being
crowded together, in the vermiform appendix
of the human being, lends to the latter organ a most peculiar appearance
(§ 255).

The vascular apparatus of the mucous membrane of the colon presents
the same arrangement as that of the gastric mucosa, so that we may refer
the reader to fig. 466.

The lymphatics of the mucous membrane of the colon were until very

recently quite unknown, although the
well-known network of the submucosa
had been discovered long before. We
are now certain of their existence in the
mucous membrane of phytophagous and
carnivorous animals, and it is highly
probable thai they are not absent in
man.

Though the surface of the colon is, as
a rule, quite smooth, we find its upper
fourth in the rabbit thickly studded with
broad projections comparable to the in-
testinal villi.

These papillae, however (fig. 495), in
contradistinction to the villi of the small
intestine, are just as densely crowded
with tubular glands as the other por-
tions of the mucous membrane of the
colon. '

In the axial portion of these pro-
minences one or more blind lymphatic
radicles are to be seen (/, g\ precisely similar to those of the small intes-
tine. Descending perpendicularly, and twined about by a vascular net-
work (a-d), they pass into the loose mesh-work of the submucous
lymphatic vessels. In other animals the smooth mucous membrane of
the colon is traversed partly by perpendicular caecal canals, and partly by
a wide-meshed net-work. These lymphatic vessels, which do not by any

Fig 495.— Papilla from the colon of a rabbit,
in vertical section, a, arterial; 6, venous
twig of the submucosa; c, capillary net-
work ; d, descending venous twig ; e, hori-
zontal lymphatic vessel ensheathing an
artery ; /, lymph canal in the axis ; g,
caecal extremity of the same.

ORGANS OF THE BODY. 499

moans attain the same degree of development as those of the small intes-
tine, have been traced down into the rectum.

The lymphatic apparatus, on the other hand, attains in the vermiform
appendix of man the most remarkable degree of perfection, as was first
shown by Teichmann. The external ramifications of the absorbent
vessels in the walls of the colon presents the same arrangement as in the
small intestines, and the same complicated distribution is evident as in
the muscular tunic of the latter.

The nervous supply of the large intestine is derived from a wide-
meshed submucous plexus beset with ganglia. The plexus myentericus
presents the same peculiarities here as in the jejunum and ileum.

No further reference need be made to the muscular and serous coats
of the large intestine.

At the anus the columnar epithelium suddenly ceases, where the
epidermial cells commence, with a sharply defined line of separation.

Close to the termination of the gut below, a certain admixture of
voluntary or striped muscle fibres presents itself among the unstriated
elements like what is seen in the oesophagus.

The mode of development of the mucous membrane of the colon is the
same as that of the mucosa of the stomach (Koelliker).

§ 260.

The physiological significance of the crypts of LieferkGhn, and tubular
glands of the large intestine, is still a point of considerable obscurity.

They are, however, supposed to secrete what goes under the name of
the intestinal juice (succus entericus), — a fluid in the production of which
the glands of Brunner, in the upper portion of the small intestine, must
also take a part. The secretion requires further examination before we
can pronounce upon its composition with any certainty.

By a very ingenious mode of procedure, we have recently learned how
to obtain pure intestinal juice from the small intestine of dogs (Thiry).
This is then found to be a thin, strongly alkaline secretion of a light wine
colour, and sp. gr. of 1-0125. It possesses about 2'5 per cent, of solid
constituents, of which nearly 2P5 per cent, is albumen, and 0'3 per cent,
carbonate of sodium. It dissolves fibrin as long as alkaline, but neither
raw flesh nor boiled albumen are acted on by it. Moreover, it is said
neither to convert starch into grape sugar, nor to decompose the neutral
fats. This, however, is denied by Eichhorst, as regards the secretion of
the small intestine. The amount of this fluid poured out appears to be
very great.

The secretion of the tubular glands of the large intestine has also an
alkaline reaction. The vermiform appendix is nothing but one large
absorbent apparatus.

§261.

The pancreas, to which we now turn, exhibits, as regards its structure,
many points of similarity to the salivary glands. Its vesicles are roundish,
measuring 0'0564-0'0902 in diameter. The membrana propria is studded
over at certain points with nuclei, showing that here also, as in other
kinds of racemose glands, the construction, probably, out. of flat stellate
cells.

The investing vascular network (tig. 496) is of the ordinary round form
of the whole of this group of organs.

500 MANUAL OF HISTOLOGY.

The numerous lymphatics require closer attention than has, up to the
present, been bestowed upon them.

The gland vesicles of the pancreas are clothed with cubical cells. In
the full-grown rabbit these present in their inner half, or that next the
lumen of the gland, fatty particles, while the middle portion in which the
nucleus lies, and external to the latter, is clear.

The excretory canals possess rather thin walls without muscular ele-
ments, in which are embedded, at the lower portion, a number of small
racemose mucous glands seated in the mucosa.

If we examine closely in animals the clothing of columnar cells, we
find that from the beginning they are not particularly high. But in the
branches they decrease more and more in length, until, finally, in the
gland vesicles we meet with flattened epithelium, reminding us, in many
respects, of vascular endothelium. These are the centro-acinal cells of
which we have already spoken in considering the salivary glands (§ 245).
They were first seen here by Langerhans.

By careful injection of the excretory canal- work, the same system
of extremely fine secreting tubules may be brought to view in the
pancreas (fig. 297), as that to which we have already so frequently alluded
(Langerhans, Saviotti).

As regards the nerves nothing certain is known. According to Pfliiger
their mode of termination is the same as in the salivary glands.

The development of the
pancreas takes place very
early from the posterior
wall of the duodenum in
the form of a small sac-
cule or bud.

As far as the composi-
tion of the alkaline react-
ing tissue of the gland
is concerned, nothing is
known. Its sp. gr. is,
according to Krauxe and
Fischer, 1 '047. A series
of very interesting decom-
position products, how-
ever, have been met with
in the fluid saturating the
gland ; in the first place
leucin in large quanti-
ties, and a considerable
amount, comparatively, of
tyrosin ( Virchow, Stae-
delcr, and Frerichs) : fur-

Fig. 49«.-Va8cular network of the pancreas from the rabbit.

(Scherer), sarkin or hypoxanthin (Gorup), lactic acid, (and in the ox)
inosite (Buedelcer and Cooper Lane). Among these leucin (and tyrosin?)
have been remarked in the secretion of the gland, with which they find
their way into the intestinal canal.

In a state of rest, or, more properly speaking, of slow secretion, the'
gland in question appears pale. When, on the other hand, it is actively
functionating, from about the fifth to the ninth hour after the reception of

ORGANS OF THE BODY.

501

food into the stomach, it is of a deep red colour. In this condition bright
scarlet blood flows from the veins of the organ, while in the inactive state
the capillaries contain a dark fluid.

The secretion of the gland or pancreatic juice (succus pancreatics) has
been obtained from the living animal. So obtained, it is a strongly
alkaline viscid fluid (Bernard), while that collected from a permanent
pancreatic fistula is a very
thin liquid (Ludwig and
Weinmann}. In thefirst al-
bumen was digested (Ber-
nard, Corvisart], starch.
was transformed into grape
sugar, the neutral fats
(after first forming an
emulsion) were split up
into glycerine and free
fatty acids. In the latter
form the first of these pro-
perties was absent. The
thick liquid, whose per-
centage of water is about
90, is secreted by the
gland when the latter is
of a deep red colour from
increased vascularity ; the
thinner liquid containing
about 95-98 per cent, of
water wlien it is pale.

The amount of fluid
secreted is greatest within
the hours before mentioned

, ,. T Fi£. 497.— Gland tubules from the pancreas of the rabbit, after

during digestion. It Varies, Sattotti. a, strong excretory canal ; 6, the same of an acinus

however, to a great extent «• delicate ^P^T Pass«*es between the cells-

at other times, so that calculations as to the amount produced daily are

found to differ considerably.

The most essential constituents of the fluid consist, in the first place,
of an albuminoid substance, which separates, in a gelatinous form on cool-
ing below freezing point, from the thicker kind of pancreatic juice, but
not from the thinner fluid ; then, again, of a ferment occurring in both
forms of the fluid, which converts starch very rapidly into grape sugar.
Further, as Corvisart has pointed out, there is present in the first modifi-
cation of the fluid another ferment which digests albumen, and whose
action does not cease on neutralisation, or even weak acidulation of the
secretion (Kuhne). Finally, there is a third fermenting substance, which
effects that peculiar decomposition of the fats already mentioned. The
change also alluded to produced in the albuminates is of great interest,
namely, a process of disintegration, with the formation of an albumen
peptone, as well as considerable quantities of leucin and tyrosin (Kulmc).
A gelatin petone has also been so obtained (ScJiwcder).

The constituents of pancreatic juice obtained by incineration, and
amounting to 0'2-0'75 and 0*9 per cent., are lime, earths, magnesia and
soda, chlorides of sodium and calcium, phosphates of sodium, calcium, and
magnesium, sulphates of the alkalies, and traces of iron combined with

502 MANUAL OF HISTOLOGY.

phosphoric acid (Bernard, Frerichs, Bidder, and Schmidt). Sulphocyanide
of potassium is not present in the secretion of the pancreas.

§ 262.

We come now to the liver, the largest of all the glands connected with
the digestive tract in man and the mammalia. Underneath its fibrous
investment it presents, even to the unaided eye, a most peculiar appear-
ance, owing to its texture. A finer analysis of the latter shows it still
more distinctly to be alone among the glands of the body.

If we carefully examine either the surface or a section of the liver,
we notice markings which divide the former into regular fields. This
is seen in many mammals very distinctly, but especially so in the pig
and also the polar bear. The portions included in these markings are
known as the hepatic lobules. They are separated from one another by
narrow bands of lighter coloured substance, and are at one time of a
dark reddish brown in the central portion, and of a lighter hue nearer
their circumference, and at another quite the reverse, appearing light
internally and dark externally. These differences depend entirely upon
the state of the circulation in the organ. In man this marking is toler-
ably easy of recognition in the infant's liver, but is, on the other hand,
very indistinct in the adult. The diameter of the lobules may be roughly
estimated, on an average, at 9 mm., and about a third more in larger indi-
viduals, while, in some cases, they may only measure I'l mm.

Each of these lobules consists essentially of innumerable gland cells,
and an exceedingly complex network of vessels passing among them, and
tending all towards one central point, where their confluence forms the
commencement or radicle of an hepatic twig, while externally they are
bounded by branches of the portal vein and biliary canals.

The hepatic elements are distinct from one another (fig. 498), and pre-
sent great similarity to peptic cells. Their form is more or less irregularly
polygonal, owing to their mutual accommodation. In
diameter they are, on an average, about 0'0226-
O'OISO mm., with extremes up to 0*0282 mm. and
down to 0'0113 mm. Their nuclei, which are oval,
and contain nucleoli, have a diameter of 0'0056-
0-0074 mm. Each cell usually contains one of them
(«), but may in some cases be possessed of two (b).
The substance of which the hepatic cells are composed
is of viscid consistence, and presents a greater or less
number of fine elementary granules embedded in it.
The cells are entirely destitute of membranous cover-
ing, and the whole structure, when isolated, is seen to
?iof ma;THa?wttChCone be possessed of the power of amoeboid motion, very
nucleus; 6, a ceil with distinct, though slow (Leuckarf).

two of the latter. -,-, . , ,, ° . , v ,. i ,1 ,, p

Besides these just mentioned, other matters are fre-
quently met with in the contents of the hepatic cells, which, when pre-
sent in small quantities, may be regarded as normal constituents, while
their appearance in greater amount denotes a morbid condition of the
cell. These are, in the first place, molecules of a brown or yellowish-
brown pigment (biliary colouring matter), and, secondly, fatty globules
of varying sizes (fig. 500). The latter, chiefly in the form of very fine
fatty molecules, are found normally in sucking animals and children, and

OEGANS OF THE BODY.

503

may be called into being artificially by the administration of very rich fatty
food to an animal. In very well marked specimens considerable masses of
fat are to be seen filling the whole of the cell, and completely obscuring its
nucleus. The cells in such cases are often increased in size. Amongst
adults, and especially after habitual indulgence in rich food, such fatty
livers are of frequent occurrence.

But besides this fatty infiltration, as it may be called, of the hepatic
cells, which the latter are well able to tolerate, regaining their previously
normal condition as soon as freed
from the oily molecules, there is
also a true fatty degeneration, a
morbid change of the whole ele-
ment into lardy matter, which
leads to its entire destruction.

The arrangement of the cells
of the lobules is very remarkable.
They are placed in long rows
side by side and connected with
one another at points, without
by any means being fused to-
gether. This arrangement, in
elongated groups, may be fre-
quently recognised among hepatic
cells which have been scraped
off the cut surface of the liver
(fig. 498), but more clearly in
delicate sections of the lobules,
as in fig. 499, in which a radiat-
ing arrangement of the bands of elements is perfectly manifest, especially
in the more internal part, while externally this is more or less lost, the
cells being disposed with greater irregularity.

In the human and mammalian liver generally, the cells of such a band
are arranged in a single row, only doubled at certain points. Much variety
exists, however, in the mode of grouping.

These so-called lobules, which do not, however, like the well-known
divisions of racemose glands, open into an execretory duct, but are
placed on a twig of the hepatic vein, are separated
one from the other (at those points at which they
are seen sharply defined) by distinct septa of
connective-tissue, which may be isolated from
about the lobules in the form of regular capsules.
This mesh-work of connective-tissue is derived,
in the first place, from the so-called capsule of
Glisson, i.e., that sheath of cellular tissue which
clothes the blood-vessels and bile ducts, entering
the organ at the porta hepatis, and again from the
connective -tissue covering the whole organ. In the normal condition
of the human liver this septal connective -tissue, dividing lobule from
lobule, is very scanty, while, in a certain peculiar affection of the organ,
known as cirrhosis, it becomes hypertrophied.

§263.

In order to gain a farther insight into the structure of the organ, it will
33

499. — Hepatic lobule from a child ten years old
(copied from Ecker), with the central hepatic vein
in transverse section.

Fie. 500. — Cells from a fatty
liver, a, 6, filled with smal
oily particles and globules
c, c/, with larger drops.

504

MANUAL OF HISTOLOGY.

be necessary, in the first place, to consider the arrangement of its llood-

The vascular system of the liver possesses this peculiarity, that it receives
its blood from two sources, namely, from the hepatic artery and portal
vein. The last of these conveys a much larger proportion of blood to the
organ than the former, which takes part less in the elaboration of bile
than in the nutrition of the hepatic tissue. Its branches, accompanying
the divisions of the portal vessels and bile ducts, are distributed, in the
first place, as vasa nutrientia to the coats of both (rami vasculares) ; and,
secondly, to the serous covering of the liver, as far as which they pene-
trate (rami capsulares), forming there a wide-meshed capillary network.
The veins derived from these empty themselves into the ramifications of
the portal vessels, so that the latter may be injected from the hepatic
artery, and vice versa, if the canula be inserted into the portal vein the
injection may be driven into the hepatic artery. Finally, a few very
small twigs (rami lolmlares) sink into the peripheral portion of the capil-
lary network of the hepatic lobules. Through these the hepatic artery
takes some part, at least in the production of the bile.

The portal vein, with whose course we take it for granted the reader is
already acquainted from the study of general anatomy, forms, with its
terminal branches, the vence interlobulares of Kiernan, or vence periphericce
of Gerlach. These are fine tubes of 0'0338— 0*0451 mm. in diameter,
which surround the lobules either in the form of short (in man) or long
(rabbit) loops, or, as is pre-eminently the case in the pig, in the form of
regular rings, breaking up rapidly on all sides, either into finer branches
or immediately into capillaries. In fig. 501 we have a representation
of what takes place here : a twig of the portal vein is seen passing
through the middle, and giving off on either side the rami-interlobu-

lares, which terminate eventually
in a capillary network after en-
circling the lobules.

This network, the most highly
developed which exists in the body,
consists of vessels from 0-0090 to
0'0126 mm. in diameter, whose
delicate walls can only with diffi-
culty be demonstrated. The meshes
formed by these are very dense, mea-
suring only from 0'0226 to 0'0451
mm. They are either rounded,
square, or triangular in figure, and
lie, for the most part, with their
long axis, often rather indistinctly
directed, towards the centre of the
lobules.

In the interior of the latter the
capillaries either form, by their
rapid confluence, a single hepatic
venous radicle, or, what is more
frequently the case, two or more
such. These may, in some instances, be met with in much larger num-
bers. The hepatic twigs are situated in the centre of the lobules ; they
are from 0'5640 to 0'0677 mm. in diameter (Gerlach), and have been

Fig. 501.— RabbiWi liver injected, showing a portal
branch, the vence interlobulares, the capillary net-
work, and a vena intralobularis in the centre of
a lobule.

ORGANS OF THE BODY. 505

named by Kiernan, on account of their position, the vence intralobulares,
by Gerlach vence centrales. On their exit from the lobules these vessels
join together to form larger trunks. The latter are intimately connected
with the parenchyma of the organ, so that they remain gaping even
when emptied. From the fact that the veins of the liver do not possess
valves, the whole hepatic circulation may be just as easily injected from
them as from the portal vessels.

§ 264.

So far we have only discussed those points of structural arrangement of
the liver which are easily recognisable, and may be therefore regarded as
permanent additions to histological knowledge.

Far different is it now, however, when we come to deal with questions
as to the nature of the sustentacular substance of the interior of the
lobules, with the relations of the veins to the finest biliary ducts, as well
as the disposal of the radicles of the lymphatic system in the parenchyma
of the gland.

From the fact that the two networks — that formed by the intersection
of bands of hepatic cells and that of the circulation — are closely inter-
woven one with another, many suppose that the hepatic cells are simply
entangled in the meshes of the capillary network.

Nevertheless, if very fine sections of a properly hardened liver be care-
fully brushed with a camel's hair
pencil, there remains, after removal
of the hepatic cells, an exquisitely
delicate reticulated framework, com-
posed of homogeneous membranous
bands, which separate the rows of
gland cells and blood stream from
one another. In this network may
be seen, in the first place, the nuclei
of the capillaries, and then, small
Isolated nuclei, which present them-
selves in a shrunken condition in

t£.~ KAO\ Fi£- 502.— Sustentacular tissue from the liver of

(ng. OU^;. the infant. 0) homogeneous membrane with

In the liver of the infant. Or nuclei; 6, filiform folds in the former ; c, isolated
„ , • ,1 i , ,1 f , hepatic cells, remaining after brushing.

foetus, m the later months ot utero-

gestation, this fine transparent membranous structure may be seen at
certain points to be double. One of its layers corresponds to the walls of
the capillaries, and in some instances has been resolved into those vascular
cells so well known (p. 363) (Eberth). Its other lamina, on the other hand,
invests the bands of hepatic cells as they intersect each other.

From this it would appear to be beyond doubt that a thin homogeneous
layer of sustentacular connective-substance envelopes the various rows of
hepatic cells. This layer is often of the most extreme delicacy, but may
be seen with comparative ease to be continuous at the periphery of each
lobule with the interlobular connective-tissue.

Here then we hav« the long sought for membrana propria of the
hepatic cells presenting itself. To it belongs indubitably the second and
smaller series of nuclear formations, which appear at an early period in
greater abundance, as a system of connective-tissue corpuscles, frequently
exhibiting distinct cell bodies.

While at first these two membranes, namely, the sustentacular connec-

506 MANUAL OF HISTOLOGY.

tive-substance of the gland and the walls of the vessels, appear quite
distinct from one another, they assume the appearance, later on in older
animals, of being fused into one single lamina. That this, however, is
probably not the case, will be seen further on when we come to consider
the arrangement of the lymphatic streams.

For our acquaintance with these important points, in regard to the
structure of the liver, we are indebted for the most part to the exertions
of Beetle and E. Wagner.

§265.

The arrangement of the ultimate radicles of the bile ducts in the
interior of the lobules, and their relations to the secreting cells, is a subject
fraught with difficulty for the microscopic anatomist, and one which for
a long time baffled every attempt at elucidation, owing to the imperfection
of the earlier methods of treatment of the hepatic tissue. It is no
wonder, then, that here extensive use was made of hypothesis, and that
many theories as to the arrangement of parts sprung up only to be aban-
doned again. At last success attended the efforts of some to demonstrate
distinctly the finest bile ducts. The first successful observers in this
interesting field of discovery were Gerlach, Budge, Andrejevic, and
MacGillavry. The results of their investigations were all very similar,
and our own experiences, as well as those of Chrzonszczeivslcy (arrived at
by means of a peculiar method of treating the hepatic tissue), are in exact
accordance with them. Further progress in this direction was made again
through the elegant demonstrations of Hering, confirmed and amplified
later on by Eberth. Subsequently similar passages were discovered in the
various racemose glands, to which we have already frequently referred
(§§ 198, 245, 255, and 261).

The first point to be noticed, and one which has long been recognised
with ease, is that the ramifications of the bile ducts accompany the
branches of the portal vein between the hepatic lobules. From these,

Fig. 503.— Biliary capillaries from the rabbit's liver. 1. A part of a lobule ; o, vena
hepatica; b, portal twig; c, bile ducts; d, capillaries; e, biliary capillaries.
2. Biliary capillaries (6) in their relation to the capillaries of the vascular system
(a). 2. Biliary capillaries in their relation to the hepatic cells; a, capillaries; 6,
hepatic cells; c, bile ducts; d, capillaries of the blood-vessels.

then, another set of fine thin-walled biliary canals take their rise (fig.
503, 1), which invest the further ramifications of the vena portae (b) with
delicate networks (c) in their course between the lobules.

ORGANS OF THE BODY. 507

More internally still these tubules are continuous with an exquisitely
delicate mesh-work of the finest tubes, known as the biliary capillaries
(d). These are passages of extremely small calibre, measuring in the
rabbit only 0 '0025-0 '00 18 mm. Arranged in a dense network (3 a),
they pass between the hepatic cells (b) in such a way that the sur-
face of each of the latter conies in contact with them at various
points.

The meshes are cubical, so that the network presents the same appear-
ance from almost every point of view. The breadth of each mesh is, on
an average, G'0144-0'0201 mm. in the rabbit, and corresponds as a rule
with that of the gland cells. The whole is characterised by the wonder-
ful delicacy of arrangement, and the regular way in which this third and
finest network is interwoven with the two others formed by the blood
capillaries and bands of gland cells.

These biliary capillaries have been known for many years past to
exist in many mammals, among which the rabbit appears to be best
suited for their demonstration. They have recently, however, been dis-
covered in the other three classes of vertebrata also (Eberth, Hering).

The questions now arise — Do the biliary capillaries possess independent
walls, or are they simply lacunar passages ; and what relation do they
maintain to the hepatic cells *?

For our own part, we would with MacGillavry, as formerly, so still
answer the first question in the affirmative, having always held the
opinion that the biliary ducts do possess independent walls. Isolation of
the latter has, however, up to the present been impossible, but the signi-
ficance of this fact seems of minor importance when we consider the great
delicacy of all the component tissues of the part. Again (2), the
interlacement of the blood capillaries (a) is seen to take place in such a
peculiar manner through the network of the biliary capillaries (b), and in
many localities the latter present such regularity when injection has been
successfully accomplished, that the existence of a system of lacunae of this
kind between cells endowed with vital contractility seems highly impro-
bable. Further, we may at times encounter points, at the junction
of injected and uninjected portions of tissue, at which the amount of
granules of colouring matter of the former diminish in the latter in a way
that permits of our following on the network of biliary capillaries a little
farther by the thin lines of coloured fluid, until they appear eventually in
the tissue around the several hepatic cells quite destitute of coloured con-
tents. Under very high magnifying power, also, the empty network may
be seen clearly, presenting great regularity, the canals of the same calibre
throughout, with no enlargements at the nodal points, and sharply con-
toured. Sometimes we are even so fortunate as to obtain a section so
thin that it is almost entirely formed of a network of bands of hepatic
cells only one tier thick ; and here, along the middle of each band, some
of these biliary passages may take their course, maintaining the axis, and
lying quite free and uncovered by other rows of cells. An appearance of
this kind is easily explained, if we accept the presence of a special wall
to each canal, but is, on the other hand, difficult to account for if the pas-
sages be regarded as lacunar. The existence of these walls has been since
recognised by both Eberth and Koelliker.

The next question is : How are these biliary ducts related to the hepatic
cells?

On this point the opinions of histologists have until recently been very

508

MANUAL OF HISTOLOGY.

much divided owing to the obscurity of the subject. Many (as, for
instance, Andrejevic some years ago) supposed the bodies of the hepatic
cells to be always interposed between the blood and biliary capillaries,
so that these two could never come into contact one with another.
MacGillavry, on. the other hand, believed in the interlacement and
weaving together of both networks in such a way as to render this
possible.

The discoveries of Her ing and Eberth, however, have since given sup-
port to the first view, which, from our own researches, we are also led to
believe to be the correct one.

But in order to understand this fully, we must examine not only the
complex liver of the mammal, but the gland also in a simpler form, as it

presents itself in, other verte
brate animals, among which we
would reckon for the case before
us not only fishes and amphibia,
but also birds.

Let us take, then, first of all
the liver of the amphibia, which
is especially instructive. Here
we find — as, for instance, in the
common ringed snake — that the
bands of cells and networks of
these bands are made up (as is
shown in fig. 504, 1) of rouleaux
of gland cells, bounded exter-
nally by blood-vessels, and con-
vergent towards a line biliary
duct running through the axis
of each rouleau. One of the
latter is in transverse section
comparable to an ordinary tubu-
lar gland clothed with unlamin-
ated epithelium, and possessed
of a very narrow lumen, each
blood capillary being separated
from the bile ducts by the full
height of the hepatic cells (Her-
ing). The livers of the batrachia,
also, present a similar arrange-
ment of parts. A side-view (2)
discloses between each two rows
of hepatic cells a long bile-duct
holding the axis of the bands
formed by these rouleaux, while
external to the latter the blood-
capillaries are situated. Nearer
the circumference of the organ
biliary ducts of greater calibre
are to be found clothed with low
columnar epithelium which has taken the place of the hepatic cells.

Among the lower orders of vertebrate animals lateral branches on the
bile ducts are seen, but sparely, and the existence of blind terminations to

Vis. 504.— Ultimate radicles of biliary ducts in the
liver. 1. From the common snake (alter Hering). 2.
From the salamander (after Eberth). 3. From the
rabbit, a, blood-vessels; 6, hepatic cells ; c, biliary
capillaries.

ORGANS OF THE BODY. 509

these (although liable to be simulated by imperfectly injected canals), can-
not be denied in our opinion.

It is only when we ascend to birds, that we meet with a higher deve-
lopment of this system of lateral branches.

Among those mammals, on the other hand, which have been hitherto
made the subject of research, it is in many cases found in an extremely
high state of development in the form of that exceedingly complex network
of biliary capillaries, represented in fig. 503. Here the surface of each
hepatic cell comes in contact with one or more biliary ducts. But even
still, and though presenting complex and various modifications, the funda-
mental plan, as seen in fig. 504 (3), remains distinct. The biliary (c) and
blood-capillaries (a) never come into actual contact ; they are always sepa-
rated from one another by a whole or fraction of an hepatic cell (b). In
the lower vertebrates several hepatic cells combine to enclose the former,
while higher up the scale the contact of fewer, and at last of two, is suffi-
cient for their formation.

Finally, we are met by the inquiry, What is the nature of the delicate
wall of the biliary duct ?

The cuticular border of the epithelial cells in the terminal ramifications
of the bile ducts, is pointed out by Ebertlt, as its probable source. Just as
the cell secretion or cuticular formation becomes thickened and perforated
by pores towards the larger branches, as already mentioned (§ 92), so
does it, as we advance upon the biliary capillaries, acquire greater delicacy,
forming eventually the walls of the biliary capillaries at the points of con-
tact of the hepatic cells.

§266.

There are still left for our consideration the larger biliary ducts, the
lymphatics, and nerves of the organ.

Eesembling to a considerable extent the ramifications of the portal
system, in their course and mode of confluence, the bile ducts present for
our consideration a homogeneous membrane with a clothing of small low
cells from the ductus interlobularis, which has been already mentioned
in the preceding chapter. In the larger trunks, instead of homogeneous
walls, fibrous coats and long cylindrical epithelial cells make their appear-
ance, upon whose surface a porous cuticular border may be recognised
with increasing distinctness, as we advance from within outwards. In
those passages of large size, which have already left the parenchyma of
the liver, a mucous membrane and external fibrous layer are to be seen
composing their walls. It was formerly supposed that, besides these, a
series of longitudinal contractile fibre cells entered into the structure of
the tube : this has not, however, been since confirmed.

The coats of the gall bladder are formed, according to Henle, of layers
of connective-tissue alternating with muscular Iamina3, consisting of
unstriped fibres which cross each other in all directions. The mucous
membrane is marked by beautifully regular folds, and is covered by the
same coating of nucleated columnar cells met with in the small intestine.
These latter are also endowed with the same power of absorbing fats as
those of the intestine.

The bile ducts possess also numerous follicles and racemose glands.
The first are to be found in the larger canals, as in the ductus chole.docliu&
cysticns and hepatic duct with its larger branches : they are arranged
sometimes irregularly, sometimes in rows. The racemose mucous glands

510

MANUAL OF HISTOLOGY.

are but sparely found in the gall bladder and inferior portion of the
cystic duct, but make their appearance in the upper portion of the canal,
and ductus choledoclms and hepaticus (fig. 505, a). In the wider passages
of the latter, with a diameter of about 0 '7 mm., is to be found another series
of simple csecal formations, some of tubular, some of flask-like figure. In
that network of fine passages situated in the transverse fissure of the liver
they occur also (b) ; likewise in those ducts arranged around the larger

branches of the portal vein
within their sheaths, and
finally in the lateral twigs
given off from the branches
lying in the longitudinal
fissure of the organ. These
appendages have by some
been supposed to be im-
perfectly developed mucous
glands, but by the majority
of histologists they are re-
garded now as blind rami-
fications of the bile ducts
or receptacles for the bile
(Beale, Koelliker, Riess).
According to this last view
they would be numbered
among the vasa aberrantia
of E. H. Weber. We
understand under this
name, passages of 0 '02-0'7
mm. in diameter, which
leaving t-he substance of
the liver, undergo sub-divi-
sion into smaller branches'
in a connective - tissue
stroma. They are to be
found in the ligamenium triangulare sinistrum, and the fibrous bridge
across the inferior vena cava. They are partly disposed in a retiform
manner, and some of them terminate with bulbous dilatations.

The numerous lymphatics of the liver consist of a series of superficial
vessels, and another situated more deeply communicating with the first.

The first lying in the deepest layer of the peritoneal covering of the
organ, is made up of a complex unlaminated network of fine canals, whose
larger efferent vessels pass off in various directions. Those on the convex
surface of the liver take their course towards the ligaments of the organ,
and do not meet with lymphatic glands until their entrance into the
thorax. Those from the under surface of the viscus, on the other hand,
empty themselves into lymph nodes in the neighbourhood of the trans-
verse fissure and the gall-bladder.

The deeper lymphatic vessels enter with the portal veins, hepatic
arteries, and bile ducts, into the interior of the organ, enveloped in a
fibrous prolongation of Glisson's capsule, and follow all the ramifications
of the latter canals. In their course they invest the branches of both
ducts and blood-vessels with a delicate network of tubes, and arrive thus
at the periphery of the lobules, still in the form of distinct vessels. Here

Fig. 505. — a, bile-duct glands from the hepatic duct of the
human liver; 6, injected twig of the biliary plexus of the
fossa transversa (after Henle).

ORGANS OF THE BODY. 511

they merge, either as distinct vessels or interlobular lacunae, into a very
remarkable network of lymphatic passages, traversing the whole lobule in
every direction. Every blood capillary, namely, is ensheathed in a lymph
stream, whose external boundary is without doubt formed by the delicate
fibrous sustentacular membrane of the hepatic cell bands ; so that each
of the cells of such a band bounds, with a portion of its surface, the inter-
lobular lymph stream. We are indebted to MacGillairy for the discovery
of these perivascular lymphatic spaces (§ 207). These facts we have
confirmed by personal observations, and Biesiadecky has recently succeeded
in demonstrating that the same arrangement of parts prevails in the
human liver. Incautious injection of the biliary capillaries frequently
results in rupture of the latter, and communication between them and the
lymphatic interlacements, giving rise to appearances which have led at
least several observers into the error of regarding the latter as biliary
networks.

The nerves of the liver, springing for the most part from the plexus
cceliacus, and consisting of both Remains fibres and other dark, fine, or
broader filaments, spread themselves along the course of the bile-ducts,
along the hepatic arteries and its ramifications, as far as its interlobular
branches, along the portal and hepatic veins and serous covering of the
organ (Koelliker). The mode of their ultimate termination is still very
obscure.

§267.

Turning now to the composition of the liver, older and rougher analyses
of its tissue (whose sp. gr. is stated by Krause and Fischer at 1'057)
give, beside about 70 per cent, of water for man, soluble albumen,
coagulated protein matters, glutinous substances, fats, extractives, and
about 1 per cent, of mineral constituents.

In addition to these, a number of interesting mutation products have
been found in the liver. As far as we know at present, glycogen,
grape sugar, inosite (in the ox), lactic acid, uric acid, hypoxanthin,
xanthin, and urea have been met with here. Kreatin and kreatiniu,
on the other hand, have not been found, nor leucin and tyrosin, of which
the first is at the most only present in traces in the healthy liver (§ 31
and § 32). Cystin has also been found in the organ under morbid
conditions.

]STone of these matters are present in the bile, and must consequently
return into the circulation.

The mineral constituents are, in the first place, phosphates of the
alkalies, which appear in large quantities, the salts of potassium prepon-
derating, while phosphate of calcium and magnesium, chlorides of the
alkalies and sulphates are present in but small amount. Iron, manganese,
and copper (p. 62), with traces of silicates, have also been found.

Accurate observation has shown that the tissue of the liver, which is
of soft consistence during life, possesses also an alkaline reaction, while
in the dead animal it reacts acid.

The glandular elements, or hepatic cells, are composed of richly albu-
minous protoplasm, containing frequently glycogen. This latter coin-
pound vanishes from the cells of starving animals. Glycogen, which is
neither found in the vegetable kingdom nor in the blood, must be
regarded as a product of cell life. Through the agency of a ferment also
existing in the cell, this substance is converted first into dextrin, as an

512 MANUAL OF HISTOLOGY.

intermediate step, and then into grape sugar. Its amount in the living
cell is so small that we are unable actually to prove its presence there, but
immediately after death it increases considerably in quantity. Besides
this, fatty matters are encountered in the glandular elements, and frequently
also biliary pigment in the form of granules. The hepatic cell, however,
fabricates besides several other substances of great importance in the
formation of bile, as we shall see presently in considering this secretion.
It is not improbable that the formation of glycogen, and certain of the
constituents of bile, are only different portions of one and the same
mutative chemical process.

The fatty matters of hepatic tissue still await accurate analysis.

§ 268.

The l/ile, an exceedingly decomposable secretion, is, as it flows
immediately from the liver, a clear and rather thin fluid of alkaline
reaction. Its colour is sometimes reddish yellow, as in the carnivora,
and sometimes greenish, as in the case of the vegetable feeders. What-
ever its tint be at the outset, it always turns to green on exposure to
the air. To the taste it is sweetish bitter, leaving little aftertaste.
During its sojourn in the gall-bladder its characters become changed, its
alkalinity appears more marked, it receives an admixture of mucus, the
colour deepens to brown, and it becomes more concentrated. The sp. gr.
of human bile is usually accepted as 1 '026-1 '032.

The fluid is usually completely homogeneous, without either granules
or fat globules ; nor do hepatic cells make their appearance in it} owing
to the small calibre of the biliary capillaries.

The most important and essential constituents of bile are the com-
pounds of sodium with two peculiar acids, and the pigmentary substances.

These two acids, taurocholic and glycocholic, have been already
considered (§ 27). From the fact that they are absent from the blood,
we are forced to the conclusion that they are generated in the liver.
Their mode of origin, however, is still a matter of great obscurity.

For a long time the greatest uncertainty prevailed as to the nature of
the colouring matters of the bile. It was not until after Staedeler's
beautiful investigations were published that any progress was made in
this direction (p. 53). Fresh bile appears to
contain only two of those pigmentary matters
discovered by this chemist, namely, the more
essential bilirubin and biliverdin.

Bilirubin (fig. 506) may be obtained from

t/MF /Sk ^ ^ slightly acidulated bile by agitation with chloro-
MK Ml Rl & form. That it is nearly allied to hsematin, and
lias its origin in the destruction of the pigment of
the blood-cells in the parenchyma of the liver,
can hardly be doubted, although we were
obliged at p. 50 to negative the question of
identity of the two substances. The peculiar
crystalline form of this pigment is also against

Tig. 506.-crystais of bilirubin our *f epting .** as identical with heematin, its
obtained from its solution in crystals assuming a whetstone figure.

Very small crystalline bodies, made up of

bilirubin in irregular and sometimes stalk-like masses, may be met with
in the bodies of the hepatic cells at times.

ORGANS OF THE BODY. 513

The enormous colouring power possessed by this pigment is also a point
of great interest. Diluted to a million times its volume, it is still capable
of communicating a distinctly yellow tinge to a layer of fluid two inches
deep. Again, as is well known, a very small quantity in the blood
of jaundiced persons imparts a yellow colour to their skin and con-
junctiva.

The pigment of fresh green bile is probably biliverdin, nearly allied to
the last. It is also developed in the other species of bile on their
becoming green. Dissolved in alkalies, it gradually assumes a brown tint.

In decomposirg bile, another brown colouring matter is also to be
found, which, on the addition of acid, assumes a green colour. This is
probably biliprasin.

We have already referred, as far as necessary, to the mode of generation
of the various colouring matters (§ 37).

Another colouring matter, also present in the urine, has likewise been
recently discovered in this fluid, to which the name of urobilin (§ 53)
has been given (Jaffe).

Besides these constituents, neutral fats are also present in the bile,
also combinations of fatty acids with alkalies, lecithin, with its two
decomposition products, glycero phosphoric acid and neurin or cholin,
cholestearin (p. 30), and mineral matters. The latter consist principally
of chloride of sodium, some carbonate and phosphate of sodium, phosphate
of calcium and magnesium, as well as traces of iron, copper, manganese
(p. 62). Fresh bile contains no sulphates ; these are, however, produced
in it by incineration and by the processes of putrefaction, from taurin, which
contains sulphur (p. 49).

Of gases, the bile contains (dog) a small amount of oxygen, abundance
of carbonic acid, and some nitrogen (Pfluger).

The proportion of these matters in the bile is usually higher than in
the other digestive fluids, but varies greatly, according as the bile remains
for a longer or shorter time in the gall bladder, where it undergoes a loss
of water by absorption. The percentage of solid constituents in the
human bile is generally estimated at from 9 to 17 (Frerichs, Gorup).
That from the ox contains from 7 to 11 per cent., that obtained directly
from the livers of dogs, cats, sheep, only about 5 per cent. (Bidder and
Schmidt). The bile of the Guinea-pig is still richer in water. The
organic matters in man amount, according to Frerichs, to about 87, or,
according to Gorup, to 93 per cent, of the dried residue. Among these
the combinations of sodium, with the two biliary acids, appear to pre-
ponderate greatly, while the proportion of fats and of cholestearin is
much less considerable. The percentage of mineral constituents is stated
by Gorup to be about 6*14 of the whole solid residue.

The secretion of bile in the normal conditions of the system is con-
tinuous,'but liable to vary considerably. It depends, in the first place,
on the nature of the alimentary matters taken into the system, being
most abundant after a meal of flesh mixed with fat, while it decreases
niter purely fleshy food, and is still less after an exclusively fatty diet.
A draught of water also increases its amount, and after the introduction
of food into the system, the quantity elaborated becomes larger and larger
for several hours.

The quantity of bile produced in twenty-four hours varies in many
animals, and has besides been estimated differently by several observers
for one and the same animal. From 1000 to 1800 grammes is supposed

514 MANUAL OF HISTOLOGY.

generally to be about the average amount secreted by the adult human
being daily ; though we must admit that this statement is based upon
very uncertain data.

As to the use of bile in the processes of digestion, we know that it
possesses no fermenting power over the albuminates, but precipitates on
the contrary albuminous substances from their acid solutions whether
digested or undigested. It has the same effect on pepsin. It is still a
debated question, whether it possesses the power of transforming starch
into sugar. It saponifies the free fatty acids, and forms an emulsion with
fat, thus facilitating its absorption by the intestinal villi (Bidder and
Sch midt, Wistingli ausen) .

Besides this, as Bidder and Schmidt have shown, the greater part of the
bile, in fact almost all its water, as well as |ths of its solid constituents,
is again taken up into the circulation by absorption from the intestines ;
but nothing farther is known as to what changes its constituents undergo
there. In a changed state the pigmentary matters pass through the intes-
tine, together with a small quantity of cholestearin, and occasionally some
taurin. The products of the metamorphosis of choleic acid are also met
with, namely, choloidinic acid and dyslisin. Neurin also and glycero-
phosphoric acid also partake of the nature of decomposition products.

The development of the liver, although still a knotty point in his-
tology, has been cleared up to a great extent by the important dis-
coveries of Rernak. From these it would appear that the organ springs
very early from the cells of the so-called gland layer in the form of two
saccules, clothed externally by a fibrous envelope, derived from the walls
of the intestine, and which has been pushed before the growing saccules.
From the most internal cells of these primitive bile ducts, solid groups of
elements are produced by a process of division, the " hepatic cylinders,"
which advance in their farther growth into the external enveloping layer,
dividing in their progress, arid branching with the formation of networks.
Those cells of the originally external envelope, which have become as it
were entangled within the meshes of the network formed by the hepatic
cylinders, are gradually converted into fibrous or connective tissue, vessels
and nerves, while the secreting elements of the gland are to be found in
the cells of the hepatic cylinders. It is a fact of great interest, first
pointed out by Bernard, that at an early period of intra-uterine existence
the liver contains no glycogen, although this is to be found in the placenta,
the epidermal cells, and epithelium of the intestine, as well as in the
passages of the glands developed from the latter, and also in muscle
(§ 170). With the development of the liver the disappearance of glycogen
commences at one point early, at another later, continuing until birth.

4. The Urinary Apparatus.
§ 269.

The urinary apparatus consists, as is well known, of two glands : the
kidneys (designed to secrete the urine), and a system of excretory pas-
sages made up of the ureters, which terminate in a common reservoir, the
bladder, and the urethra, by which the fluid is eventually carried off from
the latter.

The kidney, Ren, a large bean-shaped organ with a smooth surface, is
covered by a thin but strong fibrous envelope, the tunica propria, which
is continued on to the external surface of the infundibula at the hilus,

ORGANS OF THE BODY.

515

where the ureter leaves the gland, and its nutrient blood-vessels
enter.

The substance of the kidney presents for consideration two portions,
namely, the cortical or external, which is of a brownish red colour, and in-
distinct structure to the naked eye, and an internal paler medullary portion
of fibrous appearance. The latter is marked by fine lines converging towards
the hilus, and consists in most mammals of a single conoid mass with the
apex towards the hilus, but in the case of the human being and pig this is
divided into from 10 to 15 sections, whose bases lie towards the cortical
part of the organ, their apices being directed towards the hilus. To these
the name Malpigliian or medullary pyramids has been given. Between
them the cortical substance is
prolonged inwards in the form of
septa, known as the columnce
Bertini, while both portions of
the organ contain interstitial
sustentacular connective-tissue.

Notwithstanding their want
of similarity in appearance, both
portions of the kidney consist of
glandular elements resembling
each other in many particulars.
These are long branching canals
or tubes, known as the urinifer-
ous tubes of Bellini. In the
medullary part of the organ,
however, they pursue a straight
course diverging slightly or run-
ning nearly parallel, and dividing
at very acute angles ; while on
their arrival in the cortex they
commence to turn and twist
upon themselves, and intertwin-
ing one with another (fig. 507,
e), terminate eventually in a
blind dilatation (d) which enve-
lopes a peculiar congeries of
vessels (c*, c1).

The difference of texture ob-
served in both portions of the
organ is thus explained.

This is all that was known

until recently about the structure of the kidney, and much difference of
opinion existed, besides, as regards the relations of the blood-vessels to
the several elements of the organ.

We owe much to Henle for having given a new impetus to the study
of the histology of this organ some years ago by his interesting dis-
coveries. He found, namely, that the medullary substance contains,
besides the well-known straight tubes, with acute-angled division, which
open into the pelvis of the "organ, a series of finer canals arranged in loops,
whose convexities are directed towards the apex of the medullary pyramids
and which on arrival at the limits of the latter are continued into the
cortex.

Fig. 507. — From the cortex of the human kidney, a,
arterial twig giving off branches; 6, to the con-
geries of vessels c*, c1 ; c, efferent vessel of the
latter; d, dilatations on the ends of convoluted
uriniferons tubes, e.

516

MANUAL OF HISTOLOGY.

But HeMs work on the subject, besides elucidating much that was
most useful, led to incorrect conclusions as to the structure of the cortex.
it served, however, a great purpose in provoking a series of farther inves-
tigations, and thus through individual exertions the views on the struc-
ture of the organ have undergone since a most salutary change.

REMARKS. — (1.) Among the older essays on the subject which may be said to
extend up to the year 1862, we shall only mention, beside the German works of Ger-
lack, Litdwig, and Koelliker, those of Bowman in the Phil, Trans. Act. for the year
1842, pt. i. p. 57, and Johnstons article "Ecu" in the Cyclopedia vol. iv. p. 231.

§ 270.

Turning now to the medullary pyramids, whose apices have received
the names of papillce renales, we find the latter studded with the open-
ings of the excretory canals. The number of these oval orifices for each
papilla is from 10 to 30. They correspond to a
similar number of trunks of the gland tubes (fig.
508, a). The latter are, however, very short, and
almost in the immediate neighbourhood of then-
mouths each begins to divide usually at very acute
angles into two or three branches. These again
split up into several more (b, c, d, e) until the
whole assumes the appearance of a bunch of twigs.
In the most peripheral groups in the human
kidney each tube presents to a certain extent the
appearance of a runner with somewhat knotted
branches creeping for a greater or less distance
along the ground (Henle).

With this rapid sub-division the canals become
considerably narrower. While the mouths and
primary trunks possess a calibre of 0 '3-0 '1985
mm., the diameter even of the first series of
branches sinks to O'l 985-0*0990 mm., and in the
next in order to 0'0510-0'501 mm. This is the
diameter of the uriniferous tubes at about two
lines from the apex of the papillae, and which
they continue to maintain throughout the rest of
their slightly divergent course through the medul-
lary substance. Further division is now no longer remarked, or if seen
is only exceptional.

The increase in bulk of the medullary pyramids towards the cortical por-
tion of the organ is partly explained by this division and subdivision of the
uriniferous tubes, but only partly so. Another factor in this enlargement
of the bases of the pyramids is the system of narrow, looped, uriniferous
tubes (Henle), which appear here in addition to those opening at the
papillae, and to which the name of canals of Henle has been given (Koelliker).
These, from 0'04, to OO2 mm. in diameter, pass in great numbers out of
the cortex into the medullary portion, and are here doubled back upon
themselves sooner or later (i.e., at a greater or less distance from the
papillae), forming regular loops. Thus they return to the cortex, becoming
wider in their course back again. In order now to prevent all misun-
derstanding in the rather complicated explanation of the arrangement of
parts about to follow, we shall apply to those limbs of the looped canals

Fig. 508.— A uriniferous tube
with its branches from the
medullary substance of a
new-born kitten's kidney
(prepared with hydro-
chloric acid), a-e, divisions
from the first to the fifth
order (original drawing
from Schujeigger-Seidel).

ORGANS OF THE BODY.

which leave the cortex of the kidney the term
curving back again that of recurrent tubes.

In fig. 509 we have a representation of these
looped canals (d) lying between the widely sepa-
rated tubes (b, c). It shows likewise the in-
equality in the distances from the papillae, at
which the smaller tubes turn on themselves.

It seems hardly necessary to remark that the
number of looped tubes increases the nearer
we approach the cortex of the organ. This is
shown by transverse sections of the medullary
pyramids taken at varying heights. Near the
apices of the papillae but few cross-sections of the
looped tubes of Henle are to be seen around the
wide openings of the straight canals. But nearer
the bases of the pyramids of Malpighi the
small lumina of the former become more and
more numerous. Again, while the open urini-
ferous tubes are at first arranged close to one
another, surrounded by circles of the orifices
of the looped canals, we meet them further out-
wards with larger intervals between them, which
are occupied by cross-sections of the tubes of
Henle in great numbers. But it is not only
a difference in diameter which distinguishes
these two systems of uriniferous tubes from one
another : the glandular epithelium in the open
canals is of a species entirely distinct from
that in the looped, and the so-called mem-
brana propria presents several points of dif-
ference, though of a less marked kind.

The short trunks of the open canals have
at their commencement no membrana propria ;
they are simply bounded by the fibrous frame-
work of the apex of the papillae. Further on
a delicate, transparent, limiting membrane be-
gins to be apparent. This remains throughout
the ramifications thin and fine, presenting always
a single outline under the microscope. The case,
however, is quite different with the looped
canals (fig. 510, a, b, c). Here the membrana
propria is stronger and thicker, and exhibits
under high magnifying power a double contour.

In the short primary trunks of the open canals
we find an epithelial lining continuous with
that covering the surfaces of the papillae.
But the cells here are clearer, and of the low
columnar type, with broad bases turned towards
the walls of the tube. A considerable lumen
is still left, however, for the height of the
cells is only 0'0300-0'0201 mm. They re-
main thus as far as the branches of the first
and second order (Henle). The last system of

descending, afid to those
J

Fip. 509. — Vertical section
through a medullary pyra-
mid of the pie's kidney (half
diagrammatic), a, trunk of
uriniferous tube opening on
the tip of a pyramid ; b and
r, branches of the same;
rf, looped tubes, or Henle $
canals ; e, vascular loops; and
j\ branches of the rasa recta.

branches which run, as

518

MANUAL OF HISTOLOGY.

we have seen, undivided for long distances towards the "bases of the
pyramids, possess a lining of gland cells only 0*0158 mm. high.

The gland cell of the looped canals is, on the other
hand, in the descending arms and curves, a very
flat pavement element, presenting great similarity
to the endotheliurn of the vascular system (§ 87).
Its nucleus also, as in the latter, projects slightly

#i jjjjf beyond the surface (fig. 511, d). The resemblance
m Jm| / ^0 these vascular cells is really very striking.
m JH The recurrent tubes, however, oiHenle's loops com-
mence sooner or later to enlarge, and from this on the
lining cells assume a different character. Instead
of clear, flattened elements, the ordinary cubical gland-
cells with distinct nuclei and granular protoplasm pre-
sent themselves, with not unfrequently ill-defined
boundaries between each one and its neighbour.
Hence the recurrent arm becomes cloudy or granular
in appearance, and its lumen decreases in diameter.

These points are very well seen in fig. 511, which
is taken from the kidney of the infant. Here may
be recognised, at a, the transverse sections of the
open canals ; at b, the clear, flat, epithelial cells of
the descending tubes ; and at c, the granular clouded
gland elements of the recurrent arm of the looped
uriniferous canals.

We must, of course, expect to find the number
of sections of tubes filled with dark gland-cells, increasing more and
more as the cortex is approached.

The clearest insight into the ar-
rangement of parts, just described, is
to be obtained from preparations in
which the open canals have been
injected from the ureter with one
colour, and the blood-vessels of the
medulla with another.

Above, at the termination of the
medullary substance and commence-
ment of the cortex, the distinctive
differences between the two species of
tubes disappear more and more, as far
as diameter and epithelial lining are
concerned. But even here injection
from the ureter exhibits the peculiari-
ties of the two systems ; for, though
the open canals are easily filled, the
urine-secreting looped tubes remain, as a rule (unless special modes of
treatment be adopted), completely devoid of the fluid injected. The
upper portion of the medullary substance assumes, on injection of the
blood-vessels, a deep red hue for a considerable depth. This is the
boundary layer of Henle. Its deeper colour is due to the presence of
numerous tufts of radiating vessels.

Fig. 510. — Looped canals
from the renal pyramid
of an infant, o, 6, the
two arms; c, another
tube ; c/, capillary blood-
vessel.

Fig. 511.— Transverse section through a renal
pyramid of an infant, a, collecting tube with
columnar epithelium; 6, descending arm of
a looped canal with flat cells; c, recurrent
arm with granular epithelial elements; d,
transverse section of a blood-vessel; e, fibrous
sustentacular tissue.

ORGANS OF THE BODY.

519

§271.

Turning now to the cortical substance of the kidney, we find just as
peculiar and complex an arrangement of parts as in that portion we have
been considering.

In vertical sections (fig. 512) we observe that it consists of tubes twist-

Fig. 512. — Vertical section through the cortical portion of the kidney
of the infant (half diagrammatic). A A, medullary processes; B,
true cortical substance; a, collecting tube of the medullary pro-
cess; 6, finer tubes of the latter; c, convoluted tubes of the cor-
tical substance; rf, peripheral layer of the latter; e, an arterial
twig; /, glomeruli; g, transition of uriniferous tube into one of
Bowman's capsules ; h, envelope of th« kidney with its lymphatic
interstices.

ing and intertwining in all directions (B} ; but that, besides these, it is
traversed from within outwards by cylindrical bundles (A) of about
0-2707-0*3158 mm. in diameter, at regular and short intervals. These
bundles or cords are made up of canals of different calibre, which, in
some instances, become narrowed in their course outwards, where they
are lost in convolutions immediately under the surface, forming there a
narrow stratum of convoluted tubes (d). This cortical stratum of convo-
luted elements, consequently, is interrupted at intervals by the bundles
of straight uriniferous tubes (fig. 512, A), in about the same way that a
board is pierced by groups of closely-standing nails driven through it.

These bundles, although discovered long ago, have only very recently
received particular attention. They have been given by Henle the name
of "pyramid processes" and by Ludwig that of " medullary radii''
34

520

MANUAL OF HISTOLOGY.

We shall presently take into consideration their significance and bearing

as regards the canals of the medullary substance.

We may, if we like, look
upon the mass of the con-
voluted tubes, taken as a
whole, as divided into a
multitude of pyramidal
blocks by these groups
of straight passages, — the
bases of the blocks being
directed towards the sur-
face of the organ. These
may be named, as Henle
has suggested, the " corti-
cal pyramids"

Such a division, how-
ever, is artificial, as a cut
parallel with the surface of
the kidney shows (fig. 5 1 3).

Fig. 513.— Section parallel with the surface of the cortical por-
tion of the kidney of an infant (half diagrammatic), a,
transverse section of the urinif erous canals of the medullary
processes or radii ; 6, convoluted tubes of the true cortical
substance ; c, glomeruli and capsules of Bowman.

Here we remark that the so-called cortical pyramids run into one another

with the greater, part of their
lateral surfaces (b).

Let us now turn to the con-
sideration of the convoluted tubes
of which the greater part of the
cortical mass is composed.

Those whose diameter is on an
average about 0'0451 mm., un-
dergo no farther division ; their
outline is also single, and the
membrana propria possesses con-
siderable thickness, their outline
being in almost every case
smooth.

The cells of the convoluted
tubes are also very characteristic
in appearance. Their bodies are
made up of granular cloudy pro-
toplasm, in which fatty molecules
are often imbedded, increasing
its opacity. In diameter they
range between 0'0099 and
0-0201 mm. (Scliweigg&r-SeideT).
Should the preparations have
been treated by the method most
generally in use at present,
namely, that of maceration in
hydrochloric acid, the convoluted
tubes will probably appear dark,
withoutany indication ofalumen,
and not unfrequently without
any distinct marking off of one gland cell from the other.

The mode of termination of the uriniferous tubes is a point in regard

Fig. 514. — From the cortical portion of the human
kidney, a, arterial twig giving off the afferent
blood-vessel (6) of the glomerulus (c*, c1) ; c, efferent
vessel of the latter; d, capsule of Bowman opening
into a convoluted uriniferous tube of the cortex e.

ORGANS OF THE BODY.

521

to which, at an earlier epoch, the most erroneous views were held. They
were supposed by some to end blind in the cortex, and by others to be
continuous one with another by means of loops (Huschke, J. Mutter).
It was, to be sure, remarked that a peculiar congeries of vessels, known
as the glomerulus of Malpiglii was enveloped in a capsule, but its con-
nection with the uriiiiferous tubes was denied in the most decided manner
by the discoverer, J. Muller.

In the year 1842, however, this connection was demonstrated by
Bowman, who seems thus to have advanced the histology of the organ
by several decades.

Let us now turn for a moment to the mode of termination of the tubes
in these capsules, known either in connection with Bowman's or /.
Mutter's names.

It is not unfrequently seen that, on arrival in the neighbourhood of
the capsules, the uriniferous tubes (tig. 514) execute a series of very rapid
undulations, more or less in one plane. Further, that immediately before
opening into the capsule (d) there occurs pretty commonly a constriction
on each tubule, more or less marked, and for a greater or less distance
(fig. 515, d), and that the limiting membrane of the latter runs continu-
ously into the apparently homogeneous tunio of the capsule. The latter
has, as a rule, a diameter of about G'1415-0'2256 mm., and spheroidal
figure. It may, however, present itself of an elliptical or laterally widened
form, or even heart-shaped.

In a very thin superficial layer of the cortical substance, the cortex
corticis of Hyrtl, neither capsules nor glomerules are to be found. They
are, however, very numerous in the cortex. Their number, as estimated
by Schweigger-Seidel, appears to be, in the kidney of the pig, about 6 to
every cubic millimetre, or 500,000 for the whole cortical portion of the
organ.

It is generally held by many observers, among whom Boicman,
Gerlach, and Koelliker may be mentioned, that
those capsules situated deeper in the kidney are
of greater magnitude than the others, and that
those nearest the boundary, between the cortex
and medulla, have the greatest diameter of all.

The most difficult point to determine in regard
to Bowman's capsules, is the relation to them of
the vascular glomerulus and the cellular lining of
the interior.

It was at one time supposed that the vessels
simply perforated the wall of the capsule, and
that the glomerulus lay naked within the cavity
of the latter. Other observers, as Koelliker, for
instance, supported the view as far as regarded
the perforation, but believed the glomerulus to be
covered over by the cells lining the capsule.
Another theory is, that the knot of vessels is re-
ceived into a depression in the capsule, somewhat
in the same way as the lungs are received into
the pleura. From my own investigations I am
inclined to accept the last view as correct, besides
which, it is easiest reconciled with the history of the development of the
part (Remak). It must, however, be admitted that the membrana

Fig. 515.— From the kidney of
the common snake (after
Ecker). a, vas afferens; c
glomerulus; b, vasefferens;
d, cessation of ciliated cells
at the point of exit of tlie
uriniferous tube e.

522

MANUAL OF HISTOLOGY.

propria of the capsule is excessively thin over the glomerulus, and
more like a homogeneous connective-substance or delicate boundary layer
of the whole.

Turning our attention now particularly to the epithelial lining, we at
once recognise the fact that the thick granular gland cells of the convo-
luted tubes become transformed, at
the entrance to the capsule, into deli-
cate pavement epithelial elements (fig.
515, e), which line the whole internal
surface of the capsule, and may be-
easily rendered visible by the aid of a
solution of nitrate of silver (fig. 516,
g}. Among the lower vertebrates a
number of ciliated cells are arranged
around the entrance of the capsule, a
most 'fragile species of ciliated epi-
thelium (fig. 515, d).

But the cellular layer said to exist
over the glomerulus, is far more dif-
ficult of recognition, and has not as
yet been satisfactorily demonstrated.
Nuclei are easily seen in this situation,
but the borders of cells are not to be
made out in the adult. From the fact
that distinct cells are seen upon the
glomerulus in the foetus, it has been
supposed that they may have become
fused together into one homogeneous
nucleated membrane (Scliweigger-
SeideT). Other observers, on the other
hand, have described here a complete covering of distinctly separate cells,
and have even put forward statements in regard to their size as com-
pared to the epithelial cells of the capsule. Our own experience inclines
us to the belief that they are correct in their views (fig. 516,/).

§ 272.

From the preceding section we have learned that the convoluted tube
is an important element of the cortex, and takes its origin from the
capsule of the glomerulus. Leaving the destination of its other end for
the present undecided, let us turn our attention in the meantime to those
other constituents of the cortical portion of the organ whose position
and coarser structure have been already touched on (§ 270) ; we allude to
the pyramid processes or medullary radii.

We may easily satisfy ourselves that, in these bundles of straight
canals we have before us some of the open tubes of the medullary
pyramids, which, after passing through the so-called boundary layer,
arrive either singly, or, more rarely, in twos, in each of the processes, and
traverse the latter from below upwards, nearly to the surface of the
kidney. These passages, remarkable for their considerable calibre (fig.
517, a), have received the appropriate name of collecting tul)es (Ludwig).
They are lined by transparent low columnar epithelium, which we have
already seen in the last branches of the open medullary canals ; this is,
however, less characteristic here than in the situation just alluded to.

Fig. 516. — A glomerulus from the rabbit, a,
vasafferens; 6, vasefferens; c, glomerulus;
d, undermost portion of capsule without epi-
thelium ; e, neck ; /, epithelium of the glo-
merulus ; and g, that of the internal surface
of the capsule alter treatment with nitrate of
silver.

ORGANS OF THE BODY.

523

Each of these collecting tubes is accompanied by a number of smaller
passages. These, as we shall see presently, are the descending and
recurrent arms of the looped tubes of Henle, which are consequently
elements of the cortex both before and after traversing the boundary
layer.

But what becomes of the collecting tubes on their arrival at the surface
of the kidney ?

Fig. 517.— Vertical section from the
kidney of the Guinea-pig (hydro-
chloric acid preparation), a, trunk
of a collecting tube; 6, branches
of the same; c, further subdivision;
d, convoluted canal (intercalated
portion); e, descending arm of a
loop tube; /, loop; g, recurrent
arm; and A, continuation as con-
voluted uriniferous tube of the
cortex.

Fig. 518.— The upper portion of a medul-
lary ray from the kidney of the pig; a
and d, so-called collecting tubes; 6, their
arched branches and continuation at c,
into the descending arms of the looped
canals.

Maceration in acid (fig. 517) enables us to convince ourselves that on
their arrival here they give off numerous branches, and eventually break
up into arching, and, not unfrequently coiled tubules (d). The latter
may present in smaller animals a rugged appearance, not seen in larger
creatures. These are the " intercalated portions " of Sclmeigger-Seidel or
" connecting canals " of Roth.

524 MANUAL OF HISTOLOGY.

The same result is obtained when the passages of the gland have been

Fig. 519.— Vertical section from the
kidney of the mole (hydrochlo-
ric acid preparation), c, terminal
branch of collecting tube ; d, por-
tion of a convoluted uriniferous
tube; c, descending arm of the
looped canal; /, loop; g. h, re-
current arm and continuation into
a convoluted tube at i; k, neck of
the latter ; Z, Bowman's capsule ;
m, glomerules.

i

Fig. 520. — Diagram representing the course of the
uriniferous tubes, based on the arrangement as
seen in the kidney of the pig. a, Bowman's cap-
sule; b, convoluted uriniferous tube; and c. "*e-
current arm of loop ; d, descending arm ; e, con-
voluted passages; /, collecting tubes joining to
form one large, open uriniferous- canal, g, which
communicates with another canal, h; i, main
trunk opening on the papilla.

artificially injected through the ureter with success, as may be well seen

ORGANS OF THE BODY. 525

in the dog and pig, for instance. In the latter animal the breaking up of
the collecting tubes into arching ramifications (b) is easily recognisable.

It appears, moreover, that loops of communication never occur between
the ramifications of one collecting tube and those of another, although we
might sometimes be easily led to believe otherwise in thick sections of
injected kidneys.

It was such deceptive appearances which tempted Henle, after he had
been successful in filling the renal tubuli so far, through the ureters, to
the conclusion that the terminations of the strait canals which open
at the apices of the papillae lay before him ; and farther, that a system of
tubes, distinct from these open passages, and in no way communicating
with them, is formed by the convoluted uriniferous canals, capsule of
glomerulus, and looped tubuli of the medulla.

Both modes of procedure mentioned above, namely, that of macera-
tion in acid, and that of complete artificial injection, show that series
of passages, of various forms, spring from the arches just mentioned, and
also earlier still from the collecting tube itself. These it is (fig. 518, c)
which, arriving in the medulla, somewhat decreased in size (fig. 517, /?, g),
form there the descending arms of the looped tubes of Henle (fig. 517,
519, *,/).

Here, then, we have the origin of the descending portion of the loops.

If we now follow it still farther — to repeat a former description — we
find it (fig. 519, e) advancing into the medullary substance for a greater or
less distance, and then curving round on itself (f), pursuing the same
course back again to the medullary process (g, li). At the same time its
diameter increases, as already stated, and its lining of cells changes in
character. Arrived here it turns off sideways, sooner or later, to become
a convoluted tube of the renal cortex (/), terminating eventually as such in
one of Bowman's capsules.

We now have the whole intricate course of the uriniferous tubes
before us.

In some few instances we may be fortunate enough to succeed in driv-
ing the injection fluid as far as the capsules.

It seems almost superfluous to add another diagram (fig. 520) for the
purpose of once more tracing the course which the secretion must take
from the glomerulus outwards,

From Bowman's capsule (a) the fluid escapes into the convoluted tube
(&), which, after numerous twists and curls in the cortex, arrives in the
medullary substance, where it pur-
sues a straight course (c). Lined by
its own peculiar epithelium, it tra-
verses the medullary pyramid in a
direction more or less directly down-
wards, then forms a loop (c), and re-
turns to the cortex (d). The recur-
rent arm so formed alters sooner or
later in character : it becomes wider
and more tortuous (e), and, together
with other similarly constituted tubes,
empties itself into the collecting f
canal (/), which uniting with adja-
cent passages of the same order at acute angles (g, h~), pours out the
urine finally at the apex of the papilla (i). Many efforts have been made

526

MANUAL OF HISTOLOGY.

to ascertain the length of this very tortuous passage through which the

urine must now. and, from the
calculations of Sclnceigger-Sei-
del, it would appear that, from
Bowman's capsule to the tip of
the papilla is about 26 mm. in
the Guinea pig, 35-40 in the
cat, and about 52 mm. in man.
Turning now to the susten-
tacular substance of these very
intricate glandular passages, we
find that it consists of a small
but by no means unvarying
amount of fibrous stroma
throughout the whole organ.
In the cortex it consists of par-
titions composed of connective-
tissue elements, with homoge-
neous or streaky intercellular
matter, which is somewhat more
abundant in the neighbour-
hood of the adventitial lamina
of the larger blood-vessels and
Bowman's capsules. At the
surface of the organ, also, this
stroma presents itself as loose
areolar tissue, and is continuous
here with the capsule of the
kidney. The sustentacular sub-
stance is somewhat firmer in
the medullary rays than else-
where. It appears to attain its
highest degree of development,
though this is always but of a
very low order, in the medul-
lary substance (fig. 521, e). It
may be well seen in sections of
kidneys hardened in alcohol or
chromic acid, the sections hav-
ing been well brushed out, and
by the aid of maceration in
hydrochloric acid the stellate
connective-tissue cells may be
isolated very clearly, as has
been shown by Schiceigger-
Seidd.

Fig. 522.— Plan of the circulation of the kidney (much
shortened). 1. External portion of cortex. 2. Cortex.
3. Boundary layer. 4. Medulla. 5. Apex of papilla,
a, arterial twig ; 6, vein ; c, vas afferens ; d, vas efferens ;
e, vas efferens and /, capillary network of the surface ;
g, the was efferens of a deeper-seated glomerulus; h,
arteriola recta ; t, venous radicle of the surface ; k, capil-
laries of the medullary process; I, of the convoluted
tubes; m, venul-ce rectos; n, medullary capillaries; o,
network around the openings of the uriniferous tubes.

§273.

We have now to consider
the blood-vessels of the organ,
which exhibit considerable
peculiarity of arrangement.
As a rule both arterial and veinous trunks enter the human kidney at

OEGANS OF THE BODY.

527

the hilus, having previously divided, after which their subdivision is con-
tinued immediately within the organ. Here, after giving twigs to the
fibrous envelope of the organ, they pierce the latter external to the infun-
dibulum, each arterial twig be-
ing usually accompanied by a
large venous branch.

In this way they advance be-
tween the several medullary pyra-
mids as far as the bases of the
latter. At this point both kinds
of vessels give off curving
branches, forming imperfect
arches among the arteries, but,
on the other hand, complete
anastomotic rings on the veins.

From these arterial arches
those branches spring which bear
upon them the glomeruli of the
cortical substance (fig. 522, a).
They pass in general through the
axial portion of those blocks of
cortical tissue, bounded on either
side by medullary processes (the
cortical pyramids of Henle), giv-
ing off towards the periphery the
afferent vessels of the glomeruli
(fig. 523, «, b- 512, e,f-, 522,
«, c).

Each of these vasa afferentia
subdivides at an acute angle
within the glomerules of man and
the mammalia (fig. 524, b, c1), and gives origin, after coiling and twist-
ing there, to the vas efferens, by the union of the small branches so

Fig. 523.

Fig. 524. — Gomerulus from the
pig's kidney.

Fig. 525.

formed (fig. 522, d; 526, d; 527). In the lower vertebrates, as for
instance in the adder (fig. 525), the vas afferens (a) commences to curl

528 MANUAL OF HISTOLOGY.

upon itself without undergoing division (c), leaving the capsule as an
efferent vessel (&).

In man and the mammalia this efferent vessel breaks up into a net-
work of fine capillaries, with elongated meshes surrounding the straight
uriniferous canals of the medullary radii (iig. 522, k; 526, e). From the
periphery of this network a multitude of somewhat wider tubes is given
off (fig. 522, 1; 526, /), which, encircle with their rounded meshes the

convoluted uriniferous tubes (?) of the
cortical substance proper (or cortical
pyramids (Stein, Key), and others).

The most external layer of the cor-
tex is destitute of MaJpighian glome-
ruii. It receives its capillaries (fig.
522, /) principally from the efferent

e a aim _***&? • y-y vessels of the superficial glorneruli

^ (e), and to a smaller extent, and un-
doubtedly in only some of the mam-
malia, from certain terminal twigs of
the arteries supplying the Malpighian
bodies, which pass forward directly to
this layer of the cortex.
Fig. 526.-From the kidney of the pig (half Immediately underneath the cap-

diagramieatic). a, arterial twig ; 6, afferent sule microscopic V6I10US radicals may

vessel of the glomerulus, c; d, vasefferens; , -, , ,N . ,-, ,. f , -,, ,

e, subdivision of the latter, forming the long- be recognised (t) in the I0rm 01 Stellate

meshed network of the medullary processes ; fjo-nrpq frfpJh/Jfp Vprhpiimih Othpr

/, round meshes of capillaries around the ngures (SteilUlO, V 61 lieyeUU). U1116

convoluted tubes f,- gr, radicle of a venous venous twigs take their origin deeper

in the cortical tissue (fig. 522, 6),

and both of these, joining usually to form larger trunks, empty themselves
at the boundary between cortex and medulla into the venous arches.

Those long bundles of vessels which appear in the medullary substance
at its boundary, between the uriniferous tubes, running from thence down-
wards, and either communicating with each other in loops, or forming a
delicate network around the mouths of the uriniferous canals, at the apex
of the papillae, are known by the name of the vasa recta (fig. 509, e, /,
and 522, h, g, m).

Between these, according to Ludwig and ZawaryJcin, there is inter-
posed another large meshed capillary network of finer tubes (n). This is
a continuation of the oval network which encircled the straight urini-
ferous tubes of the cortex. There still exists, however, great difference of
opinion as regards the origin of the vasa recta. In our opinion they
partake partly of the arterial, partly of the venous nature ; but in many,
though not the greater number of cases, more of the latter than of the
former springing from the capillary network of the cortical substance (fig.
527,/).

They are joined then by the vasa efferenfia of the deeply-seated glome-
ruli (fig. 522, g ; 527, e, /, &), which possibly constitute their most
important source of supply.

The number of arterial twigs, on the other hand, is quite inconsider-
able as far as we have ourselves observed, which are given off from the
branches bearing the glomerules, but before the latter are formed, and which
sink as arteriolae rectae into the vascular portion of the medulla (fig.
522, h; 528, /).

As we have already remarked, the subdivision of stronger trunks to

ORGANS OF THE BODY.

529

form these vasa recta gives rise in many instances to vascular tassels or
bundles.

The confluence of the returning, straight
venous vessels (fig. 522, ?w), takes place in a
manner precisely similar. They commence
partly as loops and partly as capillaries of the
medulla. Others, too, spring from a special
capillary network of larger tubes, situated at
the apices of the papillae (o). They empty
themselves finally into the arching veins,
already mentioned above, as lying at the
boundary between cortex and medulla.

All earlier efforts to inject the lymphatic*
of the kidnev, by the method of puncture,
were unattended with success, and it was not
until Ludwig and Zawarykin had invented
a peculiar mode of procedure that it was
effected. The kidney chosen to be operated
on was that of the dog.

The lymphatic canals of the parenchyma
occupy the interstices of that areolar tissue
which we know to exist immediately under
the capsule of the organ (fig. 512,^). Here
they communicate externally with other ves-
sels of the fibrous envelope, and penetrate
internally through interstices in the connec-
tive-tissue strom a, passing between the urini-
ferous tubes and around the capsules of Bow-
man and finer blood-vessels towards the
deeper portion of the organ. But though in-
tercommunication between the lymphatics of
the cortex exists very freely, the fine absorbent
vessels of the medullary processes can only
be filled with some difficulty, and still later
those of the medulla itself. The whole arrangement, indeed, resembles,
to a great extent, that of the lymphatics of
the male generative glands, the testes, to be
referred to again below. The canals collect-
ing the lymph in the cortex take precisely
the same course as the blood-vessels towards
the hilus. They only commence to present
valves in the vicinity of the latter, where
several very large trunks may be seen.

The nerves of the kidney belonging to the
sympathetic system, and springing from the
plexus rehalis, enter with the arteries of the
organ. Their course and mode of termina-
tion, as well as their relations to the pro-
cesses of secretion, are however entirely un-
known.

The development of the organs, as investi-
gated by Remak, takes place from the lowest part of the intestinal
tube, in the form of hollow buds, composed of a portion of the intes-

Fig. 527. — A deepiy-seated
rulus, TH, m, from the kidney of
the horse, a, arterial twig ; a /,
vas afferent; m, glomerulus; e f,
vas efferent ol the latter, dividing
at b into branches for the urini-
ferous tubuli of the medullary sub-
stance.

Fig. 528. — From the boundary layer
of the human kidney, a, arterial
twig; c, branches of the same
bearing at c and rf, as vasa affe-
rentia, two glomeruli ; /, another
branch (arteriola recta) breaking
up into long capillary meshes of
the medullary substance.

530 MANUAL OF HISTOLOGY.

tinal germinal plate, with an external fibrous layer, consequently in the
same manner as the lungs (§ 243). Subsequently the uriniferous tubes
are developed from this system of cavities, in the form of solid bands
of cells, which become hollow at a later stage of development, acquiring
at the same time a membrana propria. The results of Kupffers obser-
vations, however, would seem to point to different conclusions. According
to him the organs in question are first developed in the form of saccules,
on the passages of the primordial kidneys or Wolffian bodies.

§274.

From the investigations of Frerichs, it would appear that the kidney
(whose sp. gr. is placed by Krause and Fischer at 1*044 for the medulla
and 1*049 for the cortex) contains from 82 to 83 '70 per cent, of water.
Of the 18-16*30 per cent, of solid constituents, albumen seems to be the
largest in amount. The proportion of fatty matter is from 0*1 to 0*63
per cent. The tissue of the organ is alkaline here also during life, and
acid after death (Kuhne). As to the composition of the gland elements,
we know that the membrana propria partakes of the nature of the elastic
substances, while the contents and whole substance of the cells must be
looked upon as albuminous. The fatty molecules observed in the cell
bodies explain the amount of adipose matter found in the organ, which
varies considerably.

The decomposition products of the kidney found in its juices are of
some interest. Among them appear inosite, hypoxanthin, xanthiri, and
at times leucin in considerable abundance (Staedtler). Further, in the
dog kreatin is to be found (M. Hermann}, in the ox, cystin and taurin
(Clo'etta). Most of these matters probably pass off in the urine.

The urine is designed to carry off from the body the greater part of all
the water received into it, as well as the principal products of the decom-
position of histogenic substances, and also the excess of albuminous
matters received into the system as food. Finally, it eliminates all
mineral constituents set free in the interchange of material in the animal
economy, together with any excess of salts which may be present in the
alimentary matters. Taking all this into consideration, and especially
that its composition is materially influenced by the nature of the alimentary
matters, as far as quantity, wateriness, and chemical constituents are con-
cerned, we can easily conceive that it must be subject to considerable
variation even in normal states of the system, a variation which may
become even more strongly marked under pathological conditions, or the
influence of drugs which are partly eliminated through the kidneys.

Healthy urine, freshly secreted, is a light yellow fluid of acid reaction,
bitter taste, and peculiar odour. Its sp. gr. varies greatly, according to
the proportion of water contained in it, and may range from 1*005 to
1*030, but usually lies between 1*015 and 1*020. The amount of urine
secreted in the course of the day varies also. It usually exceeds some-
what 1000' grammes, and may rise and fall between 1200 and 1800.

On cooling a light cloud is generally found in animal urine, consisting
of mucus secreted by the urinary passages, especially the bladder, together
with the characteristic flattened epithelium of these parts, and a few
mucous corpuscles.

The acid reaction which human urine exhibits when just voided, de-
pends not upon the presence of one or more free acids, for such are not tc
be found in it, but upon acid salts, and especially on phosphate of sodium.

ORGANS OF THE BODY. 531

The following are the principal constituents of urine, as far as the pre-
sent state of science enables us to enumerate them with any certainty :
urea, kreatin, and kreatinin, xanthin, and hypoxanthin, uric, hippuric,
and oxalic acids, extractives, colouring matters, indican, and salts. Grape
sugar is probably also constantly present in the urine (Brucke)^ as well as
oxalic acid (combined with lime), phenol, and taurol (Stcedeler). The
whole amount of solid ingredients varies much in the course of the day,
ranging from 40 to 70 grammes.

Urea (§ 28) is found in the large proportion of from 2 '5 to 3 per cent,
in normal urine, or to the amount of from 25 to 40 grammes per diem.
This can, however, only be regarded as an approximate estimate. Its
quantity is not increased by muscular exertion ( Voit), contrary to an old
and widely-spread theory. But under a diet consisting largely of animal
food, it rises in amount ranging from 52 to 53 grammes, and after purely
vegetable food or complete abstinence, its quantity becomes considerably
diminished, and may only amount to about 15 grammes, or even less, per
diem (Lelimann}. Copious draughts of water and excretiqn of the latter
through the kidney also increases its amount. Urea is the most important
end product of the nitrogenous tissue elements, and consequently of the
albuminous substances introduced into the system with the food. It
appears in many cases to be derived from uric acid, a fact not only
supported by the nature of its chemical constitution, but also by the
observations of Wohler, Frerichs, and Zabelin, that the injection of uric
acid into the circulation increases the amount of urea excreted with the
urine. Kreatin, however, has also been regarded as one of its sources.
The introduction, also, of certain other bases into the body occasions
likewise, it is believed, a rise in the quantity of urea eliminated. These
are glycerin, guanin, and alloxantin.

Uric acid (§ 25) presents itself, on the other hand, in far scantier
amount than urea. In round numbers its proportion may be stated as
about O'l per cent., and its quantity for the whole day from 0*5 to 0'9
grammes, descending even so low as 0*2 grammes. Under similar con-
ditions to those alluded to in discussing urea, its amount rises and falls
analogously, though not, perhaps, to the same degree. It is contained in
large quantities in the urine of the lower order of mammals. It frequently
presents itself in very large quantities during fevers, accompanied by
great disturbance of the functions of respiration, a fact which lends
additional support to the theory already alluded to, that the formation of
uric acid is but a preliminary step to the formation of urea. As to where
it is generated, we know as little as of urea. The products of its physio-
logical decomposition are, besides urea, allantoin (§ 29), oxalic, and car-
bonic acids. Streaker's discovery, also, that the decomposition of uric
acid gives rise to glycin, promises farther light on this subject. Uric acid
is supposed to exist in the urine in combination with soda, held in solu-
tion by acid phosphoric acid. The sparing solubility of its salts is the
cause of those sediments in the urine observed so frequently on the cooling
of the latter in a saturated condition. The rose coloured or brick dust
precipitates so formed consist of urate of sodium.

The appearance, further, of one of the decomposition products of uri-
acid in the urine is of great interest ; this, oxalic acid occurs combined
with ammonia (Schunk, Neubauer).

Hippuric acid (§ 26) appears, under normal conditions, to occur in
but small quantities in human urine, and to have a double origin. In the

532 MANUAL OF HISTOLOGY.

first place, it possesses the nature of a decomposition product of the nitro-
genous constituents of the body, which is indicated by the production of ben-
zoic acid and oil of bitter almonds by the oxidation of albuminous matters.
This source, however, is not its greatest, for, after a purely fleshy diet, its
amount sinks to a minimum. In the next place, it takes its origin from
vegetable food, which yields the un nitrogenous constituent of the acid.
Consequently, its amount is much increased in man by a vegetable diet.
It is also very abundant in the urine of the herbivora, while again, that
of the calf is quite free from it so long as sucking (Wohler). It has been
already mentioned that benzoic acid, oil of bitter almonds, cinamic and
kinic acids, and oil of tolu, when taken into the stomach, are eliminated
by the kidneys as hippuric acid (§ 26).

The nitrogenous part of hippuric acid, which, on combination with
water, separates in the form of glycin (§ 33), is originally a product of
the decomposition* of the glutin-yielding tissues in all probability. We
are not yet sure, however, in what way its construction takes place, or,
in other words, how hippuric acid is generated. It was supposed, some
years ago, that the process was carried on in the circulation of the liver
(Kuhne and Hallwachs). It has been shown, on the other hand, more
recently by Meissner and Shepard, that the acid is probably formed in
the kidney itself exclusively.

Oxalate of calcium, as already stated, is possibly constantly present in
very small quantity in normal urine ; at all events, it appears very com-
monly there. The frequent appearance of oxalic acid, also, coincidently
with the decomposition of uric acid, is a point of some interest (p.
35). Kreatin may likewise play a part here. Of one point, however,
we are certain, that oxalic acid may take its origin from vegetable ali-
ment.

Carbolic and taurylic acids (p. 36) are also possibly constant con-
stituents of human urine (Staedeler).

We now come to two substances with all the characters of decomposi-
tion products of nitrogenous tissues, namely, of muscle and nervous
matter ; we allude to kreatin and kreatinin (§ 30). The latter is always
to be found in human urine (Neubauer, Munk), in which kreatin may
also be present. Both bases are almost invariably to be met with in the
urine of dogs (Voit, Meissner). In considering this subject, sufficient
weight must be given to the fact that kreatin is converted into kreatinin
by the action of acids, whilst the latter may be transformed into the
former by contact with alkaline solutions. Their presence, then, in acid
or alkaline urine must be judged accordingly. The amount of these two
substances increases greatly under an abundantly fleshy diet. Injected
also into the blood they are eliminated with the urine (Meissner). In
starving animals, likewise, in which combustion of their own muscular
tissue is going on, the quantity of both alkaloids is found to rise (Voit,
Meissner). Muscular exertion, on the contrary, produces no effect on their
generation. It is an interesting fact, that the urine of dogs whose ureters
have been ligatured, and which has consequently been secreted under
high pressure, contains no urea, but an abundance of kreatin (M .
Hermann).

Xantliin and Jiypoxanthin are likewise present in minute quantity in
human urine. The first is also to be found in the renal secretion of dogs
after moderate muscular exertion (Meissner}.

As regards the existence of grape sugar as a normal constituent of urine

ORGANS OF THE BODY. 533

which is maintained by Briicke and denied by others, no definite con-
clusions can be come to upon the point.

The extractive matters of the urine are partly -derived from the products
of nmtative processes in the tissues of the body, and partly from the
alimentary substances introduced into the latter. Their daily amount
varies from 8 to 20 grammes and upwards. Prom Lehmann's researches
it would appear that they are most abundant after vegetable food, and
appear in small amount under a meat diet.

We have already referred to the unsatisfactory state of our acquaint-
ance with the colouring matters of the urine (§ 36). It is a point of
interest, however, that indican and indigo-chroinogen have been proved
to exist here by Hoppe and Jaffe working on Schenck's and Carter's method
(§ 36). This explains the fact that blue crystals of indigo (uroglaucin)
may be obtained by treating urine with the mineral acids, and that these
crystals are found at times in the latter. Indigo- carmine has also been
met with here. From the circumstance that indican is not present in
the rest of the body according to Hoppe' s investigations, and that it is
found in the urine of the lower mammals as well, we may conclude that
it is generated by the kidney.

The mineral matters of the urine are, owing to the nature of the
fluid, very variable in their amount. The latter may be set down at from 10
to 25 grammes for the twenty-four hours. They consist of chlorides of
the alkalies, and indeed almost entirely of compounds of soda, especially
of chloride of sodium, which is present in from 1 to 1'5 per cent.,
amounting in the day, on an average, according to Bischoff, to 14'73
grammes, but falling sometimes as low as 8'64, or rising again as high as
2i'84 grammes. Chloride of sodium, which is introduced, as is well
known, into the system with the food, is a constant constituent of the
body. Both the perspiratory glands and kidneys take part in its
elimination. There are many points of interest attached to this process.

If the blood and tissues of the body be saturated with chloride of sodium,
all the absorbed salt is again excreted by the organs mentioned. If, on the
other hand, the body have previously suffered a deprivation of the salt
excretion does not follow upon its ingestion, until the system has recovered
its normal percentage of chloride of sodium. If, however, all supply of
the latter be cut off, as is the case in starvation or existence on food devoid*
of saline ingredients, it still continues to be eliminated, but in much smaller
and ever decreasing quantity ( Voit), until, after some days, albumen begins
to make its appearance in the urine ( Wundt) — a proof of incipient disin-
tegration of the blood.

The amount of chloride of potassium and ammonium in the urine is
small on the other hand.

Urine contains, farther, certain phosphatic salts, and especially acid
phosphate of sodium with phosphate of calcium and magnesium. As is
well known, the corresponding combination of potash (§ 170) is to be
found in muscle, while the phosphates of the earths are combined with
some of the histogenic substances, and especially albumen. The brain
likewise contains phosphorus as one of the ingredients of lecithin.
According to the nature of the alimentary matters, phosphoric acid
appears in greater or less abundance. It does not, however, fail to be
excreted when the system ceases to be supplied with it (Bischoff).

The amount daily eliminated by tbe kidneys has been estimated by
Breed at from 3'8 to 5 '2 grammes. Its rise and fall is to a certain extent

534 MANUAL OF HISTOLOGY.

proportional to that of urea, which likewise originates in the splitting up
.of some of the albuminates.

Among the urinary salts we also find sulphates of the alkalies, amount-
ing in the day to 2 '09 4 grammes (Vogel). These are augmented by
animal food, and diminished, on the other hand, by vegetable &\Q\>(Lehmann}.
From the fact that, as a rule, no sulphates are introduced into the body
with the food, those which appear in the urine must be looked upon as
developed in the decomposition of histogenic substances having sulphur
as an ingredient. This latter element is also cast out of the economy as
a component of taurin, as well as of those particles of horny tissue con-
stantly being shed from the surfaces of the body.

The secretion of the kidney possesses likewise traces of iron and
silicates, and small quantities of ammonia; further, nitrogen and
carbonic acid gas, both free and in combination, together with a trace of
oxygen.

Among the abnormal and occasional constituents of urine, we have
(without taking into account casual matters) albumen in many diseases
and disturbances of the circulation. Then again, haemoglobin, as, for
instance, after poisoning with phosphorus or injection of biliary acids into
the blood, causing destruction of the red corpuscles of the same. Grape
sugar is found in diabetes, and inosite likewise, as also in Briglifs
disease. Lactic acid, too, is frequently to be found in normal urine
and after acid fermentation. Besides these fatty matters, butyric,
succinic, benzoic, and biliary acids (§ 27), present themselves here ; also
the pigmentary matters of the bile (§ 37), cystin (partly in solution and
partly in crystalline concretions), leucin, and tyrosin (in various diseases).
Allantoin, likewise (§ 29), a product of the artificial decomposition of uric
acid, which occurs also in the liquor amnii of ruminants and urine of
sucking calves, was met with by Frerichs and Staedeler in the urine of
dogs suffering from obstructions to respiration. It was found also by
Meissner in abundance after fleshy food or injection into the circulation of
kreatin. Cats fed in the same way excrete it also.

According to an old and, we believe, correct view, urine, when exposed for
several days to the air, undergoes a process of acid fermentation, by which,
as has just been observed, lactic and acetic acids are produced, increasing
its acid reaction, and during which crystals of free uric acid, coloured by
the pigments of the urine, are deposited. This view, however, is stated
by some later observers to be incorrect. According to them, the acid
reaction of the urine becomes less marked the longer it stands, the acid
phosphate of sodium is converted into a neutral combination, and acid
urates and free uric acid are produced. The latter are then thrown down

(J 25).

Later on, another, an alkaline fermentation, is frequently observed, in
which urea is split into carbonic acid and ammonia (§ 28). Coincident
with this, the urine becomes somewhat decolorised, extremely foetid and
turbid, and deposits a whitish sediment, while a light pellicle forms upon
its surface. The former consists of crystals of ammoniaco-magnesian
phosphate (§ 42), and of urate of ammonium (§ 25). This process of
alkaline fermentation may take place, on the other hand, almost immediately
after the urine has been voided, or even during its sojourn in the bladder.

§275.
We now come to the question, how far the secretion of urine is to bo

OKGANS OF THE BODY. 535

regarded as merely consisting in an elimination of matters from the blood
which already existed there ?

From the fact that some of the most important and best known con-
stituents of the urine had been met with in this central fluid (§ 75), the
agent in so many of the exchanges of matter going on in the system, it
was for a long time supposed that the secretion of the fluid in question
was analogous to the process of filtration, and so essentially dissimilar to
the formation of bile in the liver. But though the statements of Zalesky.
that urea and uric acid are generated by the kidneys, have been shown to
be incorrect, still many circumstances point to caution as regards the
acceptance of this old view. Thus, for instance, the acid nature of the
urine, the transformation of benzoic into hippuric acid in the kidney itself
(Mdssner and Sltepard], and the fact that albumen does not transude
under ordinary circumstances. It seems extremely probable, indeed,
that the process of excretion of urine partakes both of the nature of
secretion and filtration.

When we consider the structure of the kidney, as described above,
the question also naturally presents itself — Which of the two vascular
apparatuses, the glomerulus or the network investing the uriniferous
tubes, presides over the excretion of the fluid1?

When we remember that the kidney and glomerulus go hand and hand
among the vertebrates, we must be inclined to ascribe to this portion of
the vascular system the greatest importance, even though the gland cells of
the convoluted tubes do possess the power of secretion, and represent
something more than a mere passive epithelial lining, which is hardly to
be doubted. It is only the straight canals running from the external
surface of the medullary rays to the points of the papillae, which present
the latter in our opinion.

If we bear in mind that in man and in the mammalia the vas afferens
breaks up into branches in the glomerulus, besides being arranged in con-
volutions, and that these branches combine again to form a smaller vas
efferens, — that a retardation of the blood must be brought about in the
convolutions of the glomerulus, owing to the greater area to be traversed
by it, will be clear ; and that this sluggishness must be succeeded by
rapid circulation in the narrow efferent vessel, giving way again to
a second and more clearly marked retardation in the capillary network
around the uriniferous tubes, is also plain. This narrowness of the vas
efferens produces, then, a greater or less degree of obstruction to the blood
in the glomerulus, and, consequently, to an increase of lateral pressure,
far exceeding that of the second capillary system ; it favours thus excre-
tion. The blood in the capillary network, on the other hand, investing the
uriniferous tube, flows certainly under smaller pressure, and appears partly
to possess the power of absorption, and to rob the urine as it passes of
some of its water again (Ludivir/}. The peculiar disposal, further, of the
derivatives of the vas efferens, first around the passages of the medullary
ray, and subsequently around the convoluted tubes of the cortex, seems
to indicate some physiological purpose beside all this.

The progress of the urine towards the openings on the papillae takes
place without any muscular aid, merely through the vis a tergo produced by
the continuous secretion behind pushing forward the columns of fluid in
the uriniferous tubes. Besides this, in the ureters the gravitation towards
the bladder comes in aided by the contraction of the muscular walls of
the ureter (Engelmanri). Owing to the well-known anatomical arrange-
35

536 MANUAL OF HISTOLOGY.

merit of parts below, a return of the urine from the bladder into the ureters
is just as difficult as from the latter into the papillae.

§276.

The urinary passages commence in the calyces renales at the pelvis of
the organ. In these parts we find an external fibrous tunic, a middle
layer of smooth muscular fibres crossing each other in various directions,
and but slightly developed in the calyces, and then an internal mucous
membrane with a smooth surface and laminated epithelium of peculiar
flattened cells, to which we have already referred (p. 141). Here we also
meet with either tubular or racemose mucous glands in man and the
larger mammals. They are not so frequently seen in man as in other
animals, as, for instance, in the horse.

The ureter presents the same structure, except that its muscular tunic
is stronger, consisting of an external longitudinal and internal circular
layer of fibres, to which is added, lower down, a third and most internal
layer of longitudinal elements. Under the epithelial lining the blood-
vessels are arranged in a dense network of delicate tubes. In the fibrous
covering of the ureter in the rabbit a nervous p]exus, almost destitute of
ganglion cells, is to be found. The mode of termination of the nerves
is not yet known.

As is well known, the ureters terminate in a round diverticulum known as
the bladder or vesica urinaria, piercing its walls obliquely. The structure
of the bladder is similar to that of the ureters. Its external surface is in
part covered by a serous membrane, the peritoneum. Its muscular coats,
however, attain a much greater degree of strength here than in the ureter,
and are no longer arranged with the same regularity, consisting for the
most part of obliquely running muscular bundles, interlacing in a retiform
manner. At the neck of the organ these fibres are disposed in a thick
circular fasciculus, the sphincter vesicce, besides which they form, externally,
on the anterior wall and summit, longitudinal masses, to which the term
detrusor urinw is applied. However, much variety is to be observed in the
arrangement of the muscular tissue. Within the organ the mucous mem-
brane presents a smooth surface and characteristic flattened epithelium.
A few scattered mucous glands of small size may be found in the fundus and
around the neck. Here also a complicated network of capillaries lies close
under the epithelium. The manner in which the nerves of the bladder ter-
minate is just as obscure as in the ureters.

The female urethra is lined by a mucous membrane thrown into heavy
longitudinal folds and covered with papillae. It is studded also, in the
neighbourhood of the bladder, with a number of mucous glands of either
simple or complex structure, the largest of which are known by the name
of glands of Littre. The muscular substance of the part, which is of con-
siderable thickness, consists of separate longitudinal and oblique bundles
of fibres ; the epithelium is of the flattened species. The vascularity of the
walls is very considerable, the vessels having a plexiform arrangement.

5. The Generative Apparatus.

§ 277.

The generative apparatus of the female consists of the ovaries, the
Fallopian tubes, opening into a diverticulum called the uterm, the vagina,
and external genital organs. Finally, the mammary gland is connected
•with the reproductive functions of the female.

OKGANS OF THE BODY.

537

The ovary (fig. 529), the most important part of the whole, is a very
remarkable organ.

It may be divided into two portions,, namely, into a kind of medullary
substance, i.e., non- glandular
and very vascular connective-
tissue, and into a glandular
parenchyma enveloping the
latter. The first has been named
the vascular, the external layer
theparenchymal zone by Wal-
deyer.

Taking the former of these
first, we find it commencing at
the so-called hilus of the organ
(the hilus stroma of His), at
which spot large blood and
lymphatic vessels enter and
leave the part. Traversed in

all rh'rppHnrxa "hv iTiTnTmpra"hlp Fig. 529.— The ovary, a, stroma ; 6, mature Gracyfan fol-

tons by innumerable licle; c< a larger one; d) a fresh corpus luleum with

blood-vessels, this fibrOUS nUC- thick lining*; e, an old corpus luteum ; g, veins with

leus presents itself as a spongy their first branches'/> within the °^an-
red mass, comparable to cavernous tissue.

From it a number of centrifugal bands of fibrous tissue are sent off into
the gland parenchyma, where they form septa, and coalesce again peri-
pherally, giving rise, by their close intermixture, to an external boundary
layer (fig. 530, b). It was formerly held that this last might be divided

Fig. 530.— Ovary of the rabbit a, germinal epithelium (supposed serosa) ; 6, cortical or external
fibrous layer; c, youngest follicles; d, a somewhat better developed and older one.

into an internal lamina of very dense texture, the albuginea, and an
external serous membrane covering the latter. This condition of parts
does not exist, however. The surface of the ovary uncovered by peri-
toneum is coated with a layer of low columnar cells (a) (Pfliiger, Wai-
To this the suitable name of germinal epithelium has been given.

538

MANUAL OF HISTOLOGY,

Having now dwelt for a moment on the general anatomy of the ovary,
let us commence a more particular consideration of its finer structure with
that of the glandular portion.

Immediately underneath the boundary layer just mentioned is situated
a remarkable stratum, almost quite destitute of vessels, which has only
recently been recognised. This, which is composed of glandular consti-
tuents in process of development, may be called the cortical zone or zone
of the primordial follicles.

Here the essential elements of the organ lie closely crowded in several
layers, namely, the young ova (c, d), — beautiful globular structures about
0*0587 mm. in diameter, consisting of naked granular protoplasm con-
taining fatty molecules and a spherical nucleus of about 0'0226 mm. in
diameter (fig. 531, 1).

Each egg-cell, further, is enveloped in a mantle of small nucleated ele-
ments. The narrow interposed septa which exist
here, forming the stroma of the ovary, are composed
of closely-packed fusiform connective-tissue cells,
and generally surround each ovum, including its
covering of small elements, with a species of special
tunic, bounded towards the ovum by a homoge-
neous limiting layer or membrana propria. This
then constitutes the so-called follicle of the ovary
in its earlier form. In this description we have
followed the appearances presented in the ovary of
the rabbit ; but in the organs of other animals, as,
for instance, the dog and cat, a more or less race-
mose grouping of the egg-cells is met with fre-
quently (fig. 536, c), (Waldei/er). In man and
the larger mammals the connective fibrous tissue
is more abundant, and the ova more distant one
from the other.

Turning now from this external stratum, with
its enormous number of germinal structures, to the
more internal portion of the ovary, we find the
follicles as we proceed more and more highly deve-
loped. Here we encounter some which may have even attained a diameter
of 0-0902 or 0'1805 mm. The ovum contained within them is also
increased in size, and is enveloped in a distinct membrane (2). The
minute cells, situated within the latter and around tire ovum, are also
present, but in several layers now, while a system of capillaries may also
be observed encircling the follicle with a small number of vessels. In
other larger follicles (fig. 530, d), the layers of the smaller elements just
mentioned begin to separate from one another, producing a narrow inter-
space between the two.

In the subsequent growth of the follicle this becomes larger and larger,
filling at the same time with a watery fluid.

A follicle at this stage may measure from about 0'3835 to 0'4512 mm.
in diameter. On the internal surface of its walls, now supplied by a well-
developed capillary network, may be noticed at some one point an enlarged
ovum increased to 0*1805 mm. transverse measurement, containing within
it a nuclear vesicle of 0'0609 mm. and nucleolus of 0'0135. The tough
capsule of the cell is also increased in thickness to 0-0063 mm., and the
whole ovum is enclosed within a mass of small cells arranged in layers

K. 531.— Early follicle from
the ovary of a rabbit. In
1, the ovum is seen with-
out the zona pellucidn, a ;
in 2, the latter begins to be
ay>parent.

ORGANS OF THE BODY. 539

which cover also, peripherally, the whole internal surface of the follicle as
an epithelial lining.

Finally, the ovarium (fig. 529) generally contains a limited number of
mature follicles, varying from 12 to 20, which, from the fact of their
having been discovered at the end of the seventeenth century by an ana-
tomist of the name of De Graaf, have received the name of the Graafian
follicles. These vary in diameter, according to the maturity and size of
the animal, from 1 to 8 mm. (b, c).

Fig. 532 represents such a follicle with its wall (d, e), its epithelial
lining (c), the ovum (a) embedded in the thick epithelial mass (b), and
enlarged cavity.

In the walls of the follicle, or, as it has been named, the tJieca or mem-
branafollicuJi, two Iamina3 may be distinguished, an internal and external.
Within the first of these the ramifications of the capillaries take place,
while the external contains the branches (e) of the larger vessels. The
outer layer is composed of the same elements as the remaining sustenta-
cular matter of the organ, namely, of fibres of connective-tissue and very
densely crowded fusiform cells.

Owing to the fact that the blood and lymphatic vessels of the tissue
form around the'external layer of the membrana folliculi a series of open
sinuous cavities, the follicle may be separated with ease, and in a perfectly
uninjured condition, from its surroundings. In the internal lamina of
the wall we then observe that the capillaries enter the latter in lines con-

Fig. 532. — Marure follicle, a, ovum ; 6, layer of epithelium enveloping the latter and lining
the cavity of the follicle c; rf, fibrous wall; e, external surface of the follicle.

verging towards the centre of the follicle, forming internally a very dense
network with circular meshes. Like embryonic tissue this layer is parti-
cularly rich in cells of different forms and dimensions. Besides smaller
ones resembling lymphoid elements, we find another kind of larger cells,
roundish or poly'gonal in figure, and measuring about O0226 mm. in
diameter. These are, in part, situated in the intervals between the vessels,

540 MANUAL OF HISTOLOGY.

and partly around the latter, enveloping them in a manner which reminds
one of the mode of formation of the walls of vessels already described
(§211), (His).

The Graafian follicle is distended by that fluid, the commencement of
whose formation we have already alluded to above. It is transparent,
alkaline in reaction, and contains albumen. It is known as the liquor
folliculi. The round nucleated cells covering the internal surface of the
cavity, in ill-defined layers, are known, taken as a whole, as the formatio
or membrana granulosa : the elements measure individually about from
0*0074 to O'OllS mm. The breaking down or solution of the latter may
account for the presence of albumen in the fluid. The point at which
this stratum attains its greatest depth, in order completely to surround the
egg (cumulus proligerus of embryologists, cumulus ovigerus of Koelliker),
was formerly supposed to be at that aspect of the follicle nearest to the
periphery of the organ. More accurate and recent observation has, how-
ever, shown this view to be erroneous, and that the ovule is attached
to that side of the follicular cavity, as a rule, which is most remote from
the surface of the ovary (Schron., His). It may, however, be found in th.e
first position ( Waldeyer).

The mature ovum (fig. 533, 1, 2) is still of great minuteness^ and
therefore not easy to find. In order the better to investigate its nature
we are obliged, in the first instance, to free it from the elongated cells of
the membrana granulosa, fixed upon it in a radiating manner (2, c). It
is then found to be a spherical structure from 0'28 to 0*1379 mm. in
diameter, or, in other words, a beautifully developed cell with a thickened
capsule. All these different parts have received names from the anato-
mists of former times.

The capsule, in the first place, is known as the zona peRucida or cliorion.
It presents itself as a soft, transparent, semi-solid substance, homogeneous
in appearance, in all probability pierced, nevertheless, by minute pores
(fig. 73, p. 83). It is now about 0-0090-0-0113 mm. in thickness. Its
origin is at present unknown. It may either be formed by the ovum
itself, or deposited upon the latter from without. The latter, in our
opinion, is the most plausible hypothesis.

Chemically it is a substance difficult of solution in alkalies, resembling
elastin in a great measure.

The cell body (&), possessing a hardened cortical layer, appears in man
and the mammalia as a more or less opaque mass, containing in a viscid
substratum molecules of coagulated albuminous matters, as well as granules
and globules of fatty substances. It is known as the vitellus.

The nucleus (1, c), generally known under the name of the vesicula
germinativa, or germinal vesicle of Purkinje, is situated in the mature
ovum excentrically. It is a very delicate and perfectly spherical vesicle
of 0'037-0'0451 mm. in diameter, quite transparent, and presents a
round and highly refracting nucleolus (d), from 0*0046 to 0*0068 mm. in
diameter. The latter has received the name of the macula germinativa,
or germinal spot of Wagner.

Let us now turn to the blood and lymphatic vessels of the ovary.

We have already been obliged to refer to the blood-vessels in the fore-
going description. They arrive at the hilus in the form of large arterial
and venous twigs, the former taking a very tortuous spiral course on
their way thither. Arrived in the stroma they break up into numerous
branches, so that the medullary substance of the latter is, in reality, a

ORGANS OF THE BODY.

541

mass of vessels. The interstitial tissue is extremely scanty, consisting
merely of intersecting bands of fusiform cells, which turn off from the
middle muscular tunic of the arteries. Intimately united to this interstitial
substance are to be found the venous walls which gape on being cut through.

For this reason the whole tissue of this so-called hilus stroma has been
regarded as composed of the modified walls of vessels, themselves traversed
again by smaller vessels (His), recalling to mind the structure of the
corpora cavernosa (Rouget). From this
it would appear that the spindle cells of
the medullary substance are muscular
elements (§ 163, p. 283), in keeping with
which view the fresh stroma of the ovary
has been observed to possess the power of
contractility by both His and myself.

Further, numerous pencils of vessels
are seen to penetrate from the periphery
of the stroma of the hilus between the
internal follicles towards the surface of
the organ. In this course they supply
follicles, as mentioned above, with a
dense network of vessels. Prolongations
of the latter, however, penetrate still
further towards the zone of cortical cells,
doubling on themselves, for the greater
part, before their arrival in the latter,
which remains almost entirely devoid of
vascularity.

But besides being very rich in blood-
vessels, the whole stroma of the hilus
possesses numerous lymphatics. In the
latter, which are similar in their arrange-
ment to the veins, the characteristic vas-
cular cells of these passages may be every-
where rendered visible by treatment with nitrate of silver.

Their relation to the follicles is of special interest, however. The latter
having attained a large size, and having pressed forwards towards the sur-
face, may be seen in this position to be surrounded by a dense network of
lymphatics, situated principally in the external lamina of the wall of the
follicle. According to His the apex of the latter is completely destitute
of lymphatics, as also of blood-vessels. Smaller follicles also, as soon as
their internal tunic has been developed, are found to present an investing
network of lymph canals, even long before they have reached the surface
of the organ.

The numerous nerves of the ovary springing, for the most part, from the
genital ganglia, as has been shown by Frankenliailser (§ 279), contain
medullated and non-medullated fibres, and enter the organ with the
arteries. Their ultimate distribution is still obscure.

Lying between the ovaries and Fallopian tubes a trace of the Wolffian
bodies may be seen on either side of the uterus, in the form of a few
small tortuous canals, situated in the ala ve-spertilionum. To this the
name of the parovarium has been given. The tubules are composed of
a fibrous wall, epithelial lining, and transparent contents.

The chemical composition of the ovary still awaits accurate investiga-

Fig. 533. — Egg of a mammal, 1, one in
which a rent lias been made in thezona
pellucida (a), allowing the escape (6*) of
a portion of the yelk, 6*; c, the pre-
germinal vesicle with germinal spot, d ;
'2, mature ovum covered with radiating
epithelial cells, c; with the chorion, a;
and yelk, b.

542

MANUAL OF HISTOLOGY.

tion. Its sp. gr. in the human female is, according to Krause and Fischer,
1 '045. Chemical analysis, on the other hand, of the ova of the mam-
malia is not practicable, owing to the minuteness of the objects to be
dealt with.

REMARKS. — See Waldeyers beautiful monograph, "Eierstock und Ei," Leipzig,
1870. The best work which has, up to the present, appeared on the subject.

§278.

Having in the foregoing section become acquainted with the structure
of the ovary, let us now take up the question, Whence are the follicles
with their cellular contents, and especially the ovum ? For an answer to
this query we shall be obliged to follow up the development of the
organ.

The following is the view which obtains most generally in regard to
the origin of the ovary.

The germ-preparing glands of the female spring from the sides of those
temporary urinary glands of the embryo known as the Wolffian bodies.

The epithelial covering of the Wolffian bodies is observed very early to
undergo a thickening at the spot in question in the embryonic chicken
(Waldeyer). At the same time a small cellular growth makes its appear-
ance here also, springing and projecting from the connective-tissue mass
of the organ.

Now, from the thickened epithelium covering this projection the rudi-
ments of the Graffian follicles and ova are formed, as well as the later
ovarial epithelium, while from the connective-tissue the vascular susten-
tacular substance of the organ takes its rise.

The epithelial clothing is soon observed to contain (not only in the
chick, but also in the mammal embryo) certain enlarged cells or primor-
dial ova.

The further changes consist in an intermixture of the fibrous and epi-
thelial constituents. Fig. 534 gives a representation of what now takes

Fig. 534. — Vertical section of the ovary of a human foetus 32 weeks old (after Waleteuer). a,
germinal epithelium; 6, younger egg-cells, the "primordial ova" contained in this; ^in-
growing band of fibrous connective-tissue; rf, epithelial cells in process of being folded
in; e, youngest follicles; /, ova and germinal epithelial cells in groups; g, lymphoid cells.

place. The connective-tissue processes increasing rapidly in length, the
aggregations of cells become smaller and smaller, and contain one or

ORGANS OF THE BODY.

543

several primordial ova. In this way. follicles are eventually formed in
their most rudimentary form.

On the external side of the Wolffi.an body this epithelium dips down to
form a groove. From this, again, a canal is formed subsequently, the
canal of Mutter ( Waldeyer\ and from it the Fallopian tube and uterus
are developed.

Several very important points have recently been brought forward by
Pfliiger in regard to the follicles,
which enable us the better to com-
prehend some statements made long
ago by Valentin and Billroth, which
had almost sunk into oblivion. These
have since been confirmed by many
other observers, among whom may
be named Borsenkorp and Spiegel-
berg, His, Letzerich, Langhanns,
Freij, Koelliker, and Waldeyer.

According to Pfluyer's investiga-
tions the Graafian follicles are
secondary formations. He asserts
that they take their origin from ob-
long or irregular aggregations of cells
by a process of constriction affect-
ing the latter at various points. To
these collections of cells the name
of primordial rudimentary follicles,
or, more briefly expressed, " ova
chains" (Eistrangen), has been given
(fig. 535). They contain besides
peripheral cells of small size and
pale colour (the elements of the
future membrana granulosa), the
primordial ova. These are situated
in the axis of the group, and may
be distinguished by their greater
magnitude and granular protoplasm.
Their existence, therefore, anterior
to the formation of the follicle, is a point about which there can be
but little doubt. These cell-gronpings are sometimes enclosed in a homor
geneous membrana propria, giving rise to regular tubular structures, as in
the cat. This may be absent in other cases, as in the calf. The arrange-
ment of newly-formed follicles which, instead of occurring singly, appear
still in groups, or ranged like beads on a string (Follikelketten), is thus
easily understood as regards the mode of their development. The primor-
dial ovum possesses farther vital contractility, and multiplies by segmen-
tation (Pfliiger).

It is only at certain points, however, that at this period we come upon
these " ova chains," which explains the fact of their having so long
remained undiscovered.

Pfliiger states that he has satisfied himself that in the kitten, four
weeks after birth, the period for finding these primordial tubes is already
passed. But towards the time of casting their young the formative
energy awakes afresh in the ovary of the mammal, and not only are

Fig. 535. — Chains of follicles from the ovary of a
calf. 1, containing ova in process of develop-
ment; and, 2. showing gemmation to form*
Graaffian follicles.

544 MANUAL OF HISTOLOGY.

there formed both ova and Graafian follicles, but the manner in which the
process is carried on is the same as before, — " ova chains" appear anew.

The origin of these remarkable structures is a question of great interest.
Pfluger was the first to point out that they were probably derived from
in-growth of the epithelium on the surface of the ovary, in the form of
tap-root like processes, and Waldeyer has since proved his supposition to
be correct.

In suitable preparations (fig. 536) it is a matter of no difficulty to dis-
tinguish the growth downwards into the connective-tissue susteritacular
tissue beneath of the germinal epithelium at certain points (b). In

Fig 536.

the middle of such cellular masses certain large elements or primordial
ova are to be seen (c). Then by constriction at the surface of the organ
the follicle chain, or ova chain, represented in fig. 535, is produced.

Thus, then, is the ovum formed.

But what becomes of the ova ? Their destiny is twofold, — one during
the period of immaturity of the animal, another all through the period of
generative activity.

In the first period it would appear that both follicle epithelium and
ovum are frequently destroyed by fatty degeneration (Slavjansky). In
very young and healthy mammals, moreover, I myself have not unfre-
quently observed an extensive colloid metamorphosis of the whole con-
tents of the follicles.

But the destiny of the ovum is quite different in the mature animal.
Here containing the material for the construction of a new individual, it
is destined to become free by bursting of the Graafian follicle.

It was formerly believed that the stimulus of connection with the male
was requisite, as a rule, to bring about this rupture. Hence those who
held this view regarded the Graafian vesicles as persistent structures, of
which only a certain limited number ever really did burst during the
reproductive period of female existence.

Recent investigation, however, has thrown quite a new light on this
subject. We now know that the expulsion of an ovum takes place with
every menstruation in the human female. It is, therefore, independent
of sexual intercourse, since this occurs in virgins as well as in married
women. Amongst the lower animals the period of heat, or rutting, is that
in which either one or more ova are liberated.

ORGANS OF THE BODY.

545

"When a Graafian vesicle arrives at this epoch of its existence it under-
goes a further increase in size, owing to continuous proliferation of the
cells of the internal membrane of the follicle and accumulation of fluid
within it. t It now gives rise to a prominence on the surface of the ovary,
from the fact of its being tense and swollen, and no longer situated in the
stroma of the organ, but merely covered by a thin layer of connective-
tissue.

Finally, there comes a moment at which the wall of the follicle becomes
so stretched and distended that it must succumb to the forces acting on
it, and it ruptures. The rent always takes place at the point of least resist-
ance, and consequently in the external surface of the ovary, which is
only covered by a thin fibrous envelope. For the reception of the ovum
at this time the ostium abdominale of the Fallopian tube is closely
applied to the surface of the ovary.

The ovum now commences its journey down the tube towards the
uterus, in which it arrives after some days. After it has escaped from
the Graafian follicle, the inherent energies of the encapsuled cell are
aroused by the penetration of spermatozoa into its yolk, and the process
of segmentation commences (fig. 537, 1), which has been already described.
This process continuing for
some time (2), a mulberry-
like aggregation of cells is
formed (3), which constitutes
the material for the con-
struction of the new indivi-
dual. This process was for-
merly very generally sup-
posed to be preceded by the
disappearance of the nucleus
of the ovum or so-called ger-
minal vesicle ; but from re-
cent observation it would
appear that this does not take
place, but that by its divi-
sion it is bound up with seg-
mentation of the cell in the
usual manner of endogenous
growth.

But when impregnation
does not take place, the ovum
is destroyed within the gene-
rative organs by a process of liquifaction or solution. This is what occurs
in by far the greater number of cases with the egg of the human female.
And if we take into consideration the number of menstruations which
occur during the whole time that a woman is capable of bearing, we shall
gain some idea of the number of follicles requisite to supply the ova.
This is, nevertheless, exceeded by far by the enormous production of
the latter.

We have now to consider the destiny of the ruptured and emptied
Graafian vesicle (fig. 538). The latter, soon after the fulfilment of. its
functions, is to be found filled up with cicatricial connective-tissue, con-
stituting what is known under the name of the corpus luteum, after which
it gradually disappears entirely in the stroma of the organ.

Fig. 537. — Division of the mammal ovum (half diagram-
matic). 1. The yolk divided into two globules (cells)
with nuclei. 2. Quadrupled. 3. A large number of
nucleated cells. 4. a, 6, isolated cells.

546 MANUAL OF HISTOLOGY.

If we examine a recently ruptured follicle very minutely, we notice in
many instances the internal tunic projecting into the cavity on either
side in folds (fig. 538, d*). These folds consist of young exuberant cell-
growths, and contain in their
axes fasciculi of hard ill-de-
veloped fibrous tissue. On
the coming in contact of the
apices of the folds a peculiar
system of septa is formed of
the latter, the cells constituting
the yellow substance of the
corpus luteum.

If, again, a completed corpus
luteum (of a cow, for instance,
His) be closely examined, it is
found to have a peculiar radi-
ating structure, produced by

Fi 6:jg filamentous bands passing out

from a central fibrous nucleus,

the so-formed interspaces being occupied by a soft yellow substance.
The whole is enclosed within the external membrane of the follicle to
which the septa are attached. The vascularity of the corpus luteum is
extremely great, and it contains, like the rest of the ovary, numerous
lymphatic vessels. In fact, this yellow mass may be numbered among
the most vascular parts of the whole body, so highly developed is its capil-
lary network.

Beside this vascular framework we find two forms of cells in the yellow
substance. In the first place, there are fusiform elements, 0'0338-0'0451
in length and O'OOSG-O'OOGS mm. in breadth, with oval elongated nuclei ;
and then, again, we meet with larger cells. 0'0226-0'0451 mrn. in diameter,
of various shapes, and containing yellow fatty granules within them
(iig. 95, a, p. 95). The former invest at all points the highly deve-
loped vascular network of the part like the cells of a rudimentary
adventitia. The latter, on the other hand, occupy the narrow meshes
between these. Thus the general structure of the mature corpus luteum
corresponds with that of the membrana internet, of a fully developed
Graqfian vesicle.

The yellow body, however, does not long remain in this condition of
exuberant growth. It soon begins to undergo a process of retrograde
development, diminishing at the same time in magnitude (fig. 538, e).
This change commences in all probability in a decay of the afferent
arterial tubes, which are now found to possess enormously thickened
walls (His). For some time we may still recognise, besides the vanishing
yellow mass, the remains of the fibrous septal system, and external follicle
membrane, distinguished by its dark brown pigments contained in cells.
This colouring matter is laid down along the course of the vessels, and is
possibly metamorphosed haemoglobin.

As soon as this pigment has been absorbed, the yellow substance,
formerly so abundant, melts gradually away with the adjacent ovarian
tissue, until it is no longer recognisable.

The time consumed in this retrogressive process varies considerably.
When pregnancy does not supervene upon menstruation, the changes
mentioned follow one another in rapid succession. But if gravidity takes

ORGANS OF THE BODY. 547

place, the process is carried on with greater tardiness : the yellow body
increases in magnitude, remains for some months at a high degree of
development, and only recedes after /our or five months. At the end
' of pregnancy it has not yet disappeared. These differences appear to be
occasioned by the continuous increase of vascularity in the organs of
generation in the latter case, compared with the more transitory excite-
ment in the first instance. The corpora lutea have been classified, owing
to this, into true and false.

§279.

We now turn to the consideration of the Fallopian tubes and
uterus.

The first of these may be divided into two portions, namely, an upper
and more or less tortuous half of greater diameter, known as the am/pulla,
of Henle; and an inferior and much narrower half, which leads into the
uterus, the isthmus of Barkow. They present an external layer of con-
nective-tissue belonging to the peritoneum, and beneath this a muscular
tunic, consisting of longitudinal involuntary fibres, on the outside, and
transverse fibres within. The cells of this coat, largely intermixed with con-
nective-tissue, are extremely difficult to isolate. During pregnancy this is
somewhat easier. The mucous membrane of the tubes is entirely destitute
of glands. In the isthmus it is covered with small longitudinal folds ;
in the ampulla with a series of very considerable ones, which are supplied,
as I find in the pig, with a very complex network of looped vessels, and
almost close the lumen completely. Its ciliated epithelium (p. 150),
which extends as far as the external surface of the firnbrise, moves in a
ciliary wave directed towards the uterus. As in the mucous membrane
of the uterus, so also here do we miss those goblet cells described by
Scliulze.

The uterus or womb, although it undergoes numerous changes during
the earlier periods of existence, owing to the processes of menstruation
and pregnancy, is nevertheless in many points similar in structure to the
tubce Fallopii. Its muscular tissue is, however, of greater strength, and
its mucous membrane contains glands.

The fleshy mass of the uterus consists of transverse, oblique, and longi-
tudinal bundles of smooth muscular fibres, interlacing in every conceiv-
able direction (p. 283). To a certain extent we may distinguish three
layers, of which the middle is the thickest. Around the neck of the
womb the fibres are arranged in transverse bundles, so as to form a regu-
lar sphincter uteri. In this neighbourhood the contractile fibre-cells
are particularly difficult to isolate if the organ is not in the gravid con-
dition.

In the mucous membrane of the uterus (which is closely adherent to the
muscular tissue, and exchanges with it many of its elements of form), we
find both in the body and cervix a network of stellate and fusiform
cells similar to those of the framework of lymphoid organs (Henle, Lind-
gren).

Those bands of smooth muscular fibres which extend into it appear to
terminate in its deeper strata. The mucous tissue of the vaginal portion
was found by Lindgren to be traversed by vertical bands of elastic fibres,
connected with one another in arches near the surface. The body and
parts of the neck also of the uterus present ciliated epithelial elements,
described at a very early period as simple columnar cells without cilia.

548 MANUAL OF HISTOLOGY.

But the lower portions of the cervix are lined by the same flattened
epithelium met with in the vagina (p. 141).

The surface of the mucous membrane varies also according to locality.
In the fundus and body it is smooth and destitute of papillae, while
numerous transverse folds of plica*, palmatce occur in the cervix, and many
mucous papillse in its lower portion, with vascular loops in their interior.
These are particularly abundant about the os, and are met with through-
out the vagina.

The same diversity is manifest in the occurrence of the glands. In the
fundus and body of the organ they are crowded together, subject to
variations, in this respect, in different individuals. These glandulce utri-
culares are found in the form of either branching or undivided tubes,
about 1-13 mm. in length, and 0 '045 1-0 -0751 mm. in breadth. They may,
however, exceed in both directions. They are lined internally by columnar
cells, and resemble in many respects the mucous glands of the sto-
mach (§ 252), or crypts of Lieberkuhn of the intestine, though frequently
convoluted at their inferior extremities. They are either entirely desti-
tute of a membrana propria, or the latter is only present towards the
mouth of the gland. In the pig the uterine glands are clothed
within by ciliated epithelium, as was pointed out many years ago by
Leydig. More recently the same species of epithelium has been found
by Lott in these glands, in various other mammals. In the cervix they
are no longer to be found (Herde), but are replaced by numerous depres-
sions in the mucous tissue, lined with columnar cells, which appear be-
tween its folds. These have been by some included among the glands of
the organ.

Both these structures, but especially the latter, preside over the secre-
tion of the alkaline mucus of the uterus. Not unfrequently the little
pits just mentioned become occluded, and in consequence distended with
mucus. They then present themselves in the form of small round
vesicles, known as the ovula Nabothi.

The large arterial tubes of the uterus, which is very vascular, are
chiefly situated in the external and middle muscular coats. The capil-
lary networks are to be found in the mucous membrane, the coarser
in the deeper portions of the latter, the more delicate near the surface :
they are rather irregular as to their arrangement, however. Both kinds
of vessels are possessed, in the mucosa of the body of the uterus, of very
delicate walls, while in that of the cervix the latter are extremely thick
(Henle). The radicles of the veins are wide, and the walls of the latter
are intimately connected with the tissue of the organ. They occur in the
form of a dense plexus, especially in the middle layer of the muscle sub-
stance, and are entirely without valves. The arrangement here, as in the
ovary, was pointed out by Rouget to be similar to that of the corpora
cavernosa.

Lymphatics were long ago observed in the gravid uterus, princi-
pally in the outer portions of its walls, but those of the mucosa re-
mained for a long while unknown. Here they were found, however,
by Lindgren, arranged (in the cervix) in retiform and arched passages,
ending under the surface of the mucous membrane, either blind or in
loops, and passing from thence into a deeper wide-meshed network of
larger canals. The portio vaginalis possesses just the same kind of
vessels. The mucous membrane of the body of the organ requires further
observation.

ORGANS OF THE BODY. 549

The nerves of the uterus have been very carefully investigated by Fran-
kenhduser. They are derived from the genital or spermatic ganglia, and
through these from the so-called plexus uterinus magnus and p. hypo-
gastrici, to which branches of the sacral nerves are given off.

On the posterior wall of the neck of the uterus is situated a ganglionic
mass of considerable size, the ganglion cervicale of Lee. From this most
of the nerves supplying the organ take their rise beside vaginal and
vesical twigs. Only a very small number come from ihep. hypogastricus.
The course of the nerves in the walls of the organ usually corresponds
with that of the blood-vessels ; it is, however, very hard to follow. In
regard to the ganglia found here, we refer to § 189. The termination
also of the filaments in the muscular substance has been likewise dealt
with in § 183.

In the ligamenta lata bundles of unstriped fibres are to be found
between their two layers. The round ligaments are, however, still more
richly supplied with these elements, besides which they contain volun-
tary fibres. On the other hand, the lig. ovarii are but slightly muscular.
During menstruation the uterus becomes looser in texture and increased
in volume owing to a great influx of blood into it at this time. At the
same time, the glands of the mucosa increase considerably both in
length and breadth. A discharge of blood takes place also from the
gorged capillaries of the mucous membrane, the walls of the latter being
either ruptured in the act, or, by the passage, as some believe, of red cor-
puscles through the uninjured walls. The blood of menstruation, which
is poured out at the external genitals (p. 121), is found besides to contain
a large admixture of cast-off uterine epithelium.

During pregnancy the uterus undergoes a considerable increase in
volume, affecting principally the muscular layers, and, as microscopical
analysis has shown, consisting in a remarkable growth of the contractile
fibre-cells (§ 173) (which may now be easily separated from one another)
as well as in a multiplication or neoplasis of the same, at least at the
commencement of the period.

Both the blood-vessels and lymphatics, as might be expected, partici-
pate also in this increase in size.

It is also an interesting fact, that the nerves of the uterus becomes
thicker and grayer at the same time through thickening of their peri-
neurium, while the individual fibrillee present a darker outline than
before, so that they can now be followed farther into the parenchyma
(Kilian). That the number of primitive fibrillse actually becomes larger
is a matter greatly to be doubted.

We must now bestow a few words on the most important of all the
changes which take place here, namely, the metamorphosis of the mucous
membrane. Already before the arrival of the ovum in the cavity of the
uterus this structure becomes thicker, softer, and more vascular. Further,
its fibrous elements gaining in number, and the uterine glands increasing to
'four or five times their original length, a separation takes place between it
and the inner surface of the uterus. Covering the ovum, now it is known
as the decidua. After parturition a new mucous membrane and new glands
are formed on the surface of the uterine cavity, a regeneration of which
neither of the two tissues are capable under normal circumstances. The
involuntary fibres of the womb undergo, about the same time, fatty
degeneration, retrograde development, and partial destruction.

550 MANUAL OF HISTOLOGY.

§280.

The vagina, an elastic tube, is to a certain extent a continuation, as far
as structure goes, of the generative organs situated higher up. In it we
find a layer of muscular fibres internal to a thick envelope of connective-
tissue, loose without and dense within, and containing numerous elastic
elements. This muscular coat consists of a layer of longitudinal fibres
internally, and another of circular fasciculi externally. The mucous
membrane of the part presents ridges and protuberances which go by the
name of columnar rugarum, besides which it is possessed of numerous
papillae, similar to those of the cervix uteri, lying underneath its flattened
epithelium. It appears to be quite destitute of mucous glands, and its secre-
tions have an acid reaction.

The hymen is nothing but a duplicature of mucous membrane rich in
nerves and vessels.

The vascular system of the vaginal wall has a different arrangement for
each of the three layers of the latter, and is remarkable for the high
degree of development of the venous networks. But little is known, on
the other hand, of the lymphatics of the part, but scattered lymphoid
follicles have been met with in the vaginal mucous membrane of both
man and the mammalia, and considerable patches have been observed to
present an infiltration with lymph-cells. The nerves by which it is sup-
plied are derived from the sympathetic and plexus pudendus. In man
their termination in papillae has not been recognised, although their fibres
are seen to divide ; but in the rabbit the vaginal tunics are supplied with
terminal bulbs and Pacinian bodies (Krause). See p. 333.

The external female genitals consist of the clitoris and lalia major a
and minora.

The clitoris is possessed of a prepuce or fold of mucous membrane
continuous with that covering the glans, in which situation it is supplied
with numerous papillae. Its corpora cavernosa and bulbi vestibuli are
analogous to the cavernous portions of the male organ (see below).

The labia minora, or nymphce, are also small duplicatures of mucous
membrane. They present numerous papillae and very vascular connective-
tissue without any fat cells. In them, as in the external parts of genera-
tion, numerous sebaceous glands, without hairs, are to be found.

The labia majora — folds of skin padded with fat — present on their
internal surface all the characters of a mucous membrane, while externally
their structure is that of the skin. On their outer surface they are
covered with hairs, into whose follicles numbers cf sebaceous glands pour
out their secretions.

The vestibulum and opening of the vagina contains many ordinary
racemose mucous glands, of which the largest, attaining a diameter of
15 mm. are known as the glands oiBartholin ofDuverney, which open with
tolerably long excretory ducts into the vestibule. They correspond to
Cowper's glands in the male generative apparatus. They are lined with
low columnar epithelial cells, and filled with a transparent mucoid secre-
tion of viscid consistence.

The Hood-vessels of the part, with the exception of those of the corpora
cavernosa have nothing remarkable about them. The lymphatics require
closer study, as also the nerves which spring from the plexus pudendus of
the sympathetic. The latter are stated by Koelliker to terminate in
certain papillae of the clitoris in a manner similar to their arrangement in

ORGANS OF THE BODY.

551

the tactile corpuscles. These observations have been since confirmed by
the discovery of the presence in this organ of end bulbs, as they are
called, and other mulberry-shaped terminal structures allied to them, the
genital bodies (Wollustkorperchen of Krause, Finger}, Pacinian cor-
puscles have also been found in the labia majora, where they merge into
the nymphse, and in the prseputium clitoridis (Schweigger-Seidel).

§ 281.

The mammary glands, which only attain their full development in the
female body and corresponding secretory power, belong to the great group
of racemose organs, as
has been already re-
marked (p. 358). They
are peculiar, however,
in that each organ does
not empty itself event-
ually into one single ex-
cretory duct. In either
breast the milk is poured
out by from eighteen to
twenty canals or galac-
topherous duds as they
are called, each of which
belongs to one of the
primary lobes, or, better
expressed, glands. Hav-
ing already frequently
referred to the nature
of racemose glands, we
need only, remark here,
that in this particular
instance the end vesicles
(formed of a homoge-
neous membrana pro-
pria) are more sharply
defined one from the
other, also that their
form is spherical or pear-
shaped, each having a
diameter of between

0'1128 and 01872 mm. Fig. 539.— The mammary gland; for the most part after Langer.
(fitr 539 1 2 O\ 1. A lobule, from the interior of the gland of a pregnant woman.

Their membrana propria
presents, as in other
allied glandular organs, a network of flattened stellate cells (Langer}. Both
the lobules and lobes are enveloped in fatty connective-tissue, which gives
to the breast its usual smooth rounded appearance. The former are
also invested in the characteristic vascular networks of racemose glands.
Of the lymphatics of the organ but little is known at present, and the
nerves of the interior have but rarely been the objects of research. The
influence of the latter on the process of secretion has likewise never been
demonstrated experimentally. The interior of the vesicles is lined finally
36

2. a, vesicle ; 6, gland-cells. 3. Ducts from an infant. 4. Galac-
tophorous duct from a boy 9 years old. 5. The same from a girl
of 15. 6. The same from a grown man.

552 MANUAL OF HISTOLOGY.

by ordinary cubical or polygonal cells about 0*0113 mm. in diameter (fig.

540).

It is an interesting fact, that here also that well-known network of very

delicate tubules already mentioned (§ 195) may be rendered visible by in-
jection, between the cells in the interior of
the acini (Gianuzzi and Falaschi). Accord-
ing to Langer, however, no fibrous network
can be discovered within the gland vesicles.
The excretory ducts terminate amid the
wrinkles of the mamilla with orifices about
0'7 mm. in diameter. Following them up
into the gland, we find them traversing
the mamilla in the form of tubes measuring
from 1-1 to 2-2 mm. across. At the base
of the nipple they become dilated into
what are known as the sacculi lactiferi,
diverticula of from 4 -5 to 6*8 mm. in trans-
verse measurement. After this they then
become narrowed again to 2 -2-4 '5, and con-
tinue their course with rapid ramification

F*. 540.-Gland vesicles from suckling d°Wn to the ultimate Vesicles.

woman, showing cells and capillary The excretory canals of the lactiferous

system present a lining of columnar cells.

Their walls are composed of connective-tissue and a layer of elastic
fibres lying internally, and possibly also a few muscular elements occur
here, as they are to be found around the lobules (Henle).

Both the nipple and areola, however, remarkable for their dark colour
and contractility, are possessed of these unstriped muscular fibres in
abundance. In the former are *to be found principally transverse bands
intersecting each other, while longitudinal bundles are of less frequency.
The arrangement of the bundles in the latter is chiefly circular, these
being again crossed by radiating bands (Henle). The mamilla contains
numerous papillae, and the areola sebaceous glands.

It may be well to turn now for a moment to the development of the
organ.

Like other glands connected with the skin (§ 200), the mamma takes
its origin from the corneal germinal plate in the form of a growth inwards
of the cells of the latter. In the fourth or fifth month of intra-uterine
life it may be found as a solid mass of flattened globular or knobbed
figure, enveloped in the fibrous layer of the skin, and consisting of cells of
the rete Malpighi (Koelliker, Langer). A few weeks later (fig. 541) we
remark that the knobbed process (a) has given off new solid buds (b, c)
through cell proliferation. These are the first rudiments of the ducts of
the primary lobes, and are distined to further gemmation (c). Up to the
time of birth (fig. 539, 3), however, the rudimentary vesicles have not
been formed. During all this time the border is always more highly
developed than the central portions, as we might infer from the diskoid
figure of the gland, and this continues to be its condition until the end
(Langer). The ducts of the mammary gland of the infant present fibrous
walls lined with small cells. At their ends we find solid aggregations of
cells of irregular shape, the formative material for farther ramification.

Even during childhood, and in girls (fig. 539, 4) as well as boys (5),
the development of terminal vesicles has not yet begun ; the canals con-

ORGANS OF THE BODY.

553

tinue to present the same structure as before. The female breast is, how-
ever, at this period in a more perfect state than the male.

At the commencement of puberty the formation of a considerable
number of gland-vesicles takes place in the female breast, and with tolerable
rapidity, causing the organ to assume its well-known shape. But even
still, and throughout the whole term of virginity, the gland does not attain

541. — The mammary gland from a
mature foetus, after Longer, a, central
knobbed mass with smaller internal I
and c, larger external buds.

Fig. 542. — Degenerated mammary gland
from woman 90 years of age.

anything like its full development, for which the supervention of the
first pregnancy is requisite. In this state of maturity it remains through-
out the whole period of fecundity, decreasing, however in size when at
rest, and losing some of its vesicles. Finally, with the decline of the
reproductive powers a retrograde development of the mammary gland
takes place, with gradual disappearance of all its terminal vesicles, and
destruction of the smaller ducts, until eventually nothing but fatty tissue
is to be found in its place. It is represented in this condition in fig.
542. Here the canals only are to be found; everything else has dis-
appeared. The interstitial connective-tissue appears rich in elastic fibres
(Langer).

The mammary gland of the male (fig. 539, 6), with very rare exceptions,
never attains the same degree of development as in the female. In it we
generally find nothing but a system of ducts, varying greatly in size, no
trace of terminal secreting vesicles being apparent (Langer).

§ 282.

Milk is an opaque bluish or yellowish -white fluid, without odour,
sweetish to the>taste, with a slightly alkaline reaction, and a sp. gr. usually
of about 1 -028-1 '034. When kept in a state of rest it separates into two
strata- — an upper, thick, fatty, and white (cream) ; and a lower of much
thinner consistence. Some considerable time after this a process is set up,
in which its alkaline reaction is changed for an acid by the conversion of
sugar of milk into lactic acid. ' As a consequence of this, the casein con-
tained in the fluid coagulates, a change which is also effected by contact
with the mucous membrane of the stomach (p. 17).

Anatomically, milk consists of a transparent fluid, in which innumer-
able fatty globules are suspended : it is therefore an emulsion.

554 MANUAL OF HISTOLOGY.

These globules (fig. 543, a), present the usual optical characters of oil drops,
and an average diameter of 0-0023-0-0090 mm. 'Under ordinary circum-
stances they do not coalesce, but do so readily on the addition of acetic acid,
showing that each particle possesses a very delicate
membrane of some protein substance, probably casein.
The microscopic appearance, however, of milk,
which is secreted in the last days of pregnancy, and
immediately after parturition, continuing sometimes,
even under abnormal conditions, for a longer period,
is quite different. This fluid is known as colostrum.
It is of strong alkaline reaction, rich in solid con-
stituents and salts, and contains, besides fatty globules,

°ther bodies to which the name °f Colostrum COT-

a, globules; 6, cuio- puscles has been given. These (b) are spherical struc-
tures of from 0-0151 to 0-0564 in diameter, consisting
of an agglomeration of oil globules, held together by some species of
cement. Sometimes a nucleus may be found in them, besides which
they are endowed with the power of contractility, sluggish no doubt, but
unmistakable (Strieker, Schwarz).

Taking milk chemically, we find in it, besides water, casein (p. 17),
neutral fats (p. 26), and a kind of sugar known as sugar of milk (p. 33);
further, extractives and mineral constituents, free carbonic acid, and
nitrogen, gases, and small quantities of oxygen (Hoppe). Even blood and
bile pigments may also be abnormally present.

Casern is generally supposed to occur partly in combination with soda,
dissolved in the watery portion of the milk, and partly, as we have already
remarked, coagulated in the form of delicate membranes around the milk-
globules. The amount of phosphate of calcium present in this fluid is
quite remarkable. Albumen also appears to exist in milk, but in colos-
trum it is undoubtedly present. The neutral fats of the milk consist
first of the ordinary fatty matters, and then of those which, on saponifi-
cation, set free butyric, capronic, caprylic, and capinic acids (p. 25).
We have already spoken of them in detail in an earlier section. The
sugar of milk is found in solution, as also the extractives and the majority
of the mineral ingredients. The latter consist of chlorides of sodium and
potasium, of combinations of phosphoric acid with the alkalies and earths,
and of soda and potash with casein ; iron is also present. The insoluble
salts usually preponderate.

The name "fairy's milk" (Hexenmilch) has been applied to a peculiar
milky secretion produced by the mammary glands of infants for some
days after birth.

In the quantitive analysis of human milk we must bear in mind that it
varies considerably according to age of the individual, and nature of food
indulged in by the latter. These variations are much more decidedly
marked in many of the mammalia. The following is an analysis of
Simon's : — •

1000 parts contain —

Water, 880-6

Casein, 37 -0

Sugar of milk, 45*4

Fatty matters, . . . . • . 34-0
Extractives and salts, . . . . 3'0

ORGANS OF THE BODY. 555

The proportion of casein in woman's milk is, according to Simon, about
3 '5 per cent, on an average ; that of fats, 2*5-4 per cent. ; of sugar of milk,
between 4 and 6 per cent. ; of salts (among which phosphatic earths pre-
dominate), 0-16-0-20 per cent.

The average amount of milk secreted daily by the human female,
during the period of lactation, is somewhat over 1000 grammes. About
50 or 60 grammes may be produced by one breast in two hours (Lam-
perierre).

The use of milk is, as is well known, for the aliment of the infant. It
is secreted at the expense of the nutritive material of the mother's blood,
and may be designated as the prototype of all aliment.

If we compare the ingredients of milk with those of the plasma of the
blood (p. 115), we find that the mineral constituents of the latter may
have simply transuded into the former, somewhat in the same manner as
that in which they find their way into the urine. But the three series of
organic substances are not to be found as such in the blood, or, if so,
only in small amount. To the first of these, casein and sugar of milk
belong, the sources of which may be regarded as albumen and grape sugar;
to the third the fatty matters. All this seems to indicate an inherent
power in the mammary gland of causing a species of fermentation, as also
of producing within its cells a part, at least, of the oily matters found in
the milk.

The mode in which the secretion of the mammary gland is produced in
the interior of the vesicles is similar to that in which the sebaceous
matter of the skin is formed. The gland-cells become enlarged by the
generation within them of oil globules (fig. 539, 2, b), and are in this way
physiologically destroyed, at least in many cases, although the membrane-
less body of the contractile gland-cell no doubt frequently enough
simply disgorges its fatty contents. During the less active formation of
the colostrum these cells, or fragments of them, are carried off in the
watery portion of the milk. The gland-cell of the suckling woman is
regarded by us as a very transitory structure.

§ 283.

The male generative apparatus consists of two testicles, enclosed in the
scrotum, and invested with their several tunics ; of the excretory $ucts,
emptying themselves into the urethra; of the copulative organ; and,
finally, of accessory structures. Among the latter we have the single
prostatic gland, a pair of glands known as Cowper's, and the ves-iculcR
seminales.

The testis, with its accessory epididymis, is a gland consisting of a
multitude of fine and very tortuous tubules, known as the tubuli semi-
niferi. The whole is covered by a fibrous investment, to which the name
of tunica albuginea, s. propria test'is (p. 227), has been given, — a tough,
whitish membrane of considerable thickness. It is again contained within
another sac, the tunica vaginalis propria, a serous investment, whose
internal portion (t. adnata) cannot be distinguished from the albuginea.
Finally, the testicle and spermatic cord are enveloped in the t. vaginalis
communis, a strong bag, composed of a serous and fibrous portion, which
contains, around its junction with the vaginalis propria and epididymis, a
number of contractile fibre-cells (Kodliker). Upon this coat the striped
fibres of the cremaster muscles are situated externally. This vaginalis
communis is connected without with the muscular tunic of the scrotum,

55G

MANUAL OF HISTOLOGY.

the dartos (p. 283), by formless connective-tissue. Finally, the whole is
covered by a thin layer of true skin quite destitute of fat.

If we seek to remove the albuginea, we observe that numerous but im-
perfect fibrous septa are given off by the latter, and penetrate into the
interior of the gland.

These partitions, which divide the parenchyma into lobules (fig. 544, 6)

Flgr. 544.— The human testicle, after Arnold, a, testicle
divided into lobuli b ; c, tubnli recti; d, rete vasculosum ;
e, vascula efferentia; /, coni vasculosi; g, epididymis;
h, vas rtef evens; f, vas aberrans of Nailer; in, branches of
the internal spermatic artery, with their arrangement in
the gland n; o, artery of the vas deferens, anastomos-
ing at^j with the last named vessel.

Fig. 545. —Seminiferous
tube from a human tes-
ticle, a, membrane; 6.
cells.

of conical form, whose apices are directed inwards and upwards, con-
verge in the superior part of the organ, to be inserted into a dense wedge-
shaped mass known as the corpus Highmori, whose base is attached to the
albuginea.

Each of these lobules is made up of several extremely long semini-
ferous tubules, about 0>1128-0'1421 mm. in diameter, folded on them-
selves several times. These may be seen to divide frequently, and anas-
tomose, and to terminate, not blind, but in the form of slings and loops.
At the apices of the lobules the seminiferous tubules, becoming rapidly
narrowed, open into a straight passage, which goes by the name of the
tubulus rectus (c), and which penetrates the corpus Highmori (lined with
low columnar cells), and forms what is called the rete testis (d), by inter-
communication with the vessels of the same kind. From this network
the larger tubes, or vascula efferentia (e), take their rise. Their number
is from 9 to 17, and their course at first straight until they pierce the
albuginea, after which they become again very tortuous, and are arranged
in a series of conical lobes, known as the coni vasculosi (/), which form
the caput epididymis.

ORGANS OF THE BODY.

Fig. 546. — From the testis of a calf. 1. Transverse
section of a seminiferous tubule, a, b, walls of the
latter; <-, capillary network; d, connective-tissue
framework; e, lymphatic canals. 2. Side view of
the wall of a seminiferous tube ; a and ft, wall

They then gradually combine to form one single wide canal (g, y)
0-3767-0*45 mm. in diameter; which turns and twists upon itself still
further in forming an elongated body known as the corpus and cauda
epididymis.

By degrees this tube, of which the epididymis is composed, becomes less
tortuous and of greater calibre, its diameter amounting on an average to
2 mm. It is now known as the vas deferens (h). Frequently before
this it receives the addition of a short coecal branch, the vas aberrans of
Haller (i).

Turning now to the structure of the seminal gland, we find in the first
place that it presents a sustentacular substance. This is found in the
form of fibres of connective-
tissue (fig. 546, 1, d), radiat- - ' ^^
ing from both septa and capsule
throughout the whole organ. In
this connective-tissue numerous
cells and nuclei are encountered
in young animals : its bands vary
in thickness ; in the calf from
0-0564 to 0-0113 mm.

These bundles of connective-
tissue (Mihalcowicz) are enve-
loped in those flat membraneous
cells of which we have already
spoken (§§ 130, 223), and to which we shall again have occasion to refer
in considering the arachnoid. These cells cover like a membrane both
seminal tubules and blood-vessels, leaving, however, chinks between them,
which serve a purpose in the lymphatic circulation.

In the human and mammalian testicle besides a number of peculiar cellu-
lar elements, undergoing pig-
mentary and fatty metamor-
phosis, the " interstitial
cells," are met with, at
times in great abundance.
They are usually arranged
in bands, their diameter be-
ing in the cat 0-014-0-020
mm. They may envelope
the vessels like a sheath.

The interstices of this sus-
tentacular substance are
occupied by the seminiferous
tubules (figs'. 545, 546, 1 a;
547, a, b) whose diameter
is on an average from
0-1 128 to 0-1421 mm. By the aid of the microscope we learn that the mem-
brana propria is represented by a coat (sharply defined from the interstitial
connective-tissue) of tough texture, and fibrous or banded structure, contain-
ing elongated nuclei (fig. 545, a; 546, 1 a, b, 2 a, b). Its thickness ranges
from 0-0046 to 0'048 mm. In man this wall is particularly well marked.

It consists, according to Mihalcowicz, of several layers of flattened cells
united with one another in the form of a membrane. The most internal
layer is quite impervious ; but the external is open and net-like.

Fig. 547. — From the testis of the calf, a, seminiferous
tubules in profile ; b, in transverse section ; c, blood-vessels ;
ef, lymphatics.

558 MANUAL OF HISTOLOGY.

The interior of these tubes is filled with cells, of which the most peri-
pheral may cover the membrana propria in a manner similar to epithe-
lium. They are usually roundish or polygonal, and from 0 '01 13-0 '01 42
mm. in transverse section. They are composed in young subjects of a
finely granular, rather pale substance (containing yellow pigment in man),
which becomes charged in the course of years with an ever-increasing
number of fatty granules. These cells of the testes have been observed
even in embryos to be endowed with contractility, and to possess the power
of amoeboid change of form (La Vedette St George).

Recently, however, a more complex structure has been ascribed to the
seminal tubes.

In man and the ox, for instance, a framework of flat stellate cells with
membraneous processes is stated to exist in their interior (Sertoli, M&rkd,
Boll). We regarded these, the " sustentacular cells " of Merkel. as the
same network to which we have already had such frequent occasion to
allude in dealing with the racemose glands. Milialkowicz, on the
other hand, in his excellent work, declares this appearance of sustentacular
cells to be an artificial production caused by the coagulation of an albumi-
nous material between the seminal cells.

Such is the structure of the seminiferous tubes as far as the rete testis,
in which for the time being their external fibrous tunic is fused into the
connective-tissue of the corpus Highmori. The tubes, which leave the
latter as they increase in size, obtain an additional layer of smooth muscular
fibres, which is further strengthened lower down in the body of the epidi-
dymis by two coats of longitudinal fibres, an external and an internal.
This arrangement we shall again meet with in the vas deferens.

We have already (p. 150) alluded to the peculiar ciliated epithelium of
the epididymis.

The blood-vessels of the testes are branches of the internal spermatic
artery. They penetrate into the interior of the organ-form without, and
from the corpus Highmori, and take their further course along the septa
dividing as they go. Finally, they break up into a long-meshed, rather
loose capillary network of somewhat contorted vessels, from 0 '0128 to
0-0056 mm. in diameter (fig. 546, 1, c; 547, c), which invests the semini-
ferous tubes. The vascularity of the epididymis, which is supplied by
the arteria vasis deferentis Cooj)eri, is no less considerable. The veins
present the same arrangement as the arteries.

The lymphatics of the parenchyma of the organ, lined by the special
cells of such vessels (Tommasi), occupy the soft interstitial connective-
tissue of the former, arranged in a close network of canals (fig. 546 1, c;
547, d). In transverse sections of the seminiferous tubes, it may be seen
that these lymphatic canals form regular rings around the latter, of pas-
sages from 0'0128 to 0'0292 mm. in diameter, and strongly dilated at the
points of junction with each other. Steady injection at last drives the
fluid employed through the external cellular layers of the Avails of the
seminiferous tubes. The most internal layer alone is entirely impervious
(Mihalkowicz). The blood-vessels, also, are here and there ensheathed
in lymph streams.

From the rings just mentioned other lymphatic canals are given off to
the numerous connective-tissue septa of the lobules. Under the albuginea,
also, they are arranged in a very complex network of wide canals, and
then penetrate the former in the form of wide-valved intercommunicating
passages, most highly developed on the dorsum of the organ. Finally,

OKGANS OF THE BODY. 559

they unite with the lymphatics of the epididymis and tunica vaginalis
to form several main trunks, which then take their course along the sper-
matic cord.

The nerves of the testis spring from the internal spermatic plexus ; as
to their ultimate mode of termination, however, nothing is at present
known.

In connection with the epididymis we have to consider several struc-
tures, and in the first place the so-called hydatids of Morgagni. These
present themselves under two forms, seen in some cases together. The
first kind is a petiolite vesicle seated upon the anterior surface of the
head of the epididymis. Its style is usually solid and fibrous, while the
vesicle contains a clear fluid, cells, and nuclei. But the second form is
far more frequently met with. In it we have a knobbed flattened struc-
ture with hardly any stalk, and either simple or divided into lobes. Its
position varies, and it sometimes communicates with the passage of the
epididymis.

Finally, at the posterior edge of the testicle, between the head of the
epididymis and the vas deferens, a small flattened structure presents itself,
composed of several loosely connected whitish nodules. Each of the latter
consists of the convolutions of a tube terminating at each end in a blind
dilatation. The interior of these is filled with a clear fluid, and lined
with pavement epithelium whose cells are in process of decay. This
body is known as the corps innomine of Giraldes, or organ of Giraldes
(Koelli'ker), or parepididymis (Henle). In the infant, and up to the age
of ten years, this structure is encountered in complete development; later
on, it degenerates.

Referring to the history of development, we find some light is thrown
upon the nature of these accessory structures.

The testis, like the ovary (§ 278), is developed at the inner side of the
Wolffian bodies. Here, however, the germinal epithelium never attains
that degree of perfection we have observed in the female embryo. The
genesis of the seminiferous tubules is not yet fully ascertained. Accord-
ing to Waldeyer, they are formed, not from the germinal epithelium
at all, but from the glandular passages themselves of the primordial
kidney.

From the canals of the Wolffian body, then, which are insignificant in
the female generative system (a mere trace remaining in the mature body
as the parovarium), the epididymis is formed, while the duct of the organ
is gradually converted into the vas deferens. The other remnants of the
Wolffian bodies, then, give rise to the organ of Giraldes, and the structure
known as the vas aberrans.

But beside the duct of the Wolffian body, we -find at a very early age
the rudiments of a second canal, that of Mutter, already alluded to in
speaking of the female generative system. This has, however, a different
destiny in each sex. While in the female it becomes converted into the
Fallopian tube and uterus — therefore into very important parts— in the
male generative system it degenerates almost completely. The last
trace of its upper portion alone is to be seen as the hydatid of Morgagni,
just referred to ; while its most inferior portions form by their junction
the so-called uterus masculinus, or vesicula prostatica of anatomists.

The composition of the tissue of the testicle, whose sp. gr. is 1'045
(Krause and Fischer), still awaits investigation. Glycogen was found by
Kuhne in the organ in the dog.

560 MANUAL OF HISTOLOGY.

§284.

In the foregoing section a microscopical analysis of the contents of the
seminiferous tubes in the state of rest, not of activity, has been presented
to us. During the whole period of virility in man, however, and in the
rutting season of animals, these glandular tubes generate another kind of
contents, namely, semen or spermd).

Human semen, as secreted by the testis, is a whitish slimy fluid desti-
tute of any odour, and of high sp. gr. Its reaction is either neutral
or alkaline. Semen, however, as discharged in coitu, has received addi-
tions from the accessory glands of the generative organs, and so undergone
considerable modification. It reacts strongly alkaline, and has a peculiar
odour, which has been aptly compared to that of freshly sawn bone.
Besides this, it is more fluid and transparent. Shortly after being ejected
it coagulates, forming a thick gelatinous mass, which becomes again liquid
after some time.

A glance at fresh human semen under the microscope shows innumer-
able thread-like form elements engaged in the most lively motion. To
these several names have been given, — such as seminal filaments, seminal
animalcules, and spermatozoa (fig. 548). Suspended in a homogeneous
fluid they are seen to consist of two portions, namely, an anterior wider
end known as the head ; and a long filiform process posteriorly, to which
the term tail has been applied.

The form of the head (a) is oval, or, more correctly speaking, pear-
shaped ; the broadest end being posterior, at the insertion of the tail. Its
length is, on an average, 0-0045 mm., and its breadth
about half as much. When the head is seen in
profile (&), we remark that, like the corpuscles of
the blood, it is greatly flattened. Seen from the
surface it appears broad, with sharp but not dark
outline, but viewed from the side it is narrow, and pre-
sents a broad dark border. Its thickness lies probably
somewhere about 0-0018-0-0013 mm. (Koelliker).
The hindermost division of the structure, the fili-
form process («, b) commences with a constricted
neck, succeeded by a somewhat thickened por-

ae

broad surface; 6, in pro- tion, gradually becoming thinner and finer, until at

last it attains such a pitch of tenuity as to baffle

microscopic analysis. It may be followed to a length of about 0'0451 mm.

For a long time it was supposed that the spermatozoa only consisted of
these two parts, and that they were quite homogeneous throughout,
without any distinction between envelope and contents, More recent
observations, with the aid of the stronger systems of lenses of the present
day, would seem to place this view in question. The reports, however,
of Valentin, Grohe and Schiveigger-Seidel on the subject do not yet
entirely agree.

From the able researches of the last-named observer it would appear
that the tail of the spermatozoon (fig. 549) may be divided into two por-
tions, often sharply defined one from the other, and different in diameter
and in chemical and optical characters : these are, first, the middle
portion (&), as it is called ; and, secondly, the delicate terminal filament
(c). In those instances in which the head of the human spermatozoon
possesses the length mentioned above, of 0-0045 mm., the middle portion

ORGANS OF THE BODY. 561

is 0-0061, and the terminal filament 0'0406. Both the head and middle
portion appear rigid, leaving the end fibre alone movable. That a differ-
ence exists between envelope and contents in the sper-
matozoa, as maintained by Grohe and Schweigger-Seidel, C3 a
we do not think has been yet clearly proved.

Throughout the whole animal kingdom semen is pos-
sessed of certain definite form -elements. But though
the prevailing shape of these spermatozoa is filiform in all
animals, nevertheless they present extremely interesting
and considerable varieties of appearance, reminding us of
the similar though much less markedly characteristic
peculiarities of the red blood-cells (§ 68). The narrow
limits of our work, unfortunately, do not permit us to
enter deeper into this very interesting subject ; but we
cannot relinquish it without pointing to the probable safe-
guard against hybrid impregnation which exists in these FimafozoaofPthe
strongly-marked peculiarities, — a kind of aid to the per- sheep, after
sistence of distinct species. Besides this, in many animals S^^head-
this motion has been missed, while in others a lazy amse- &» middle por-
boid change of form only could be observed.

From a chemical point of view the spermatozoa of the mammalia con-
sist of a resistent metamorphosed albuminous substance, rich in lime,
which approaches in quality to elastin. They withstand for a very long
time the process of putrefaction, and even oppose a determined resistance
to the action of the mineral acids, dissolving, on the other hand, but still
very slowly, in caustic alkalies (Koelliker). Owing to the large propor-
tion of mineral ingredients in the spermatozoa, they preserve their form,
although subjected to a red heat.

The composition of pure semen, — that is, the secretion of the testicle, —
was studied many years ago by French*, especially that of the carp, but
also of the cock and rabbit. In his observations he found the fluid
neutral, resembling a dilute solution of mucus, and containing a certain
amount of albumen. Chlorides of the alkalies, and small quantities of
phosphates and sulphates of the same, were present in its residual ash, as
also phosphate of magnesium.

The dry substance of the spermatozoa contained 4 -05 per cent, of a
yellow matter like butter, probably containing phosphorus, and, we may
now add (?), probably also cerebrin and lecithin. Besides this, 5 '21 per
cent, of ash constituents, among which lime and phosphoric acid pre-
sented themselves.

Pure semen from the horse has 18*06 of solid ingredients; that of the
bull 17 '94, of which the metamorphosed protein substance of the sper-
matic filaments amounts to 13'138 per cent, lecithin (?) to 2'165, and
mineral matters to 2 '637 per cent. (Koelliker).

Semen, as discharged from the urethra, is richer in water, from the addi-
tion of the secretions of the accessory glands : that of man was found by
Vauquelin to contain, on the whole, only 10 per cent, of solid matters.

The substance which causes semen to coagulate after emission, named
long ago by Vauquelin "spermatin," appears to be an albuminate of
sodium (Lehmann).

The development of the spermatozoa was formerly supposed to take place
from peculiar cells in the seminiferous tubules. But the process was first
accurately described by Koelliker. At the time when semen first begins

562

MANUAL OF HISTOLOGY.

to be formed (puberty in man, rutting season in animals), most of the
glandular epithelium cells of the seminal tubules undergo division, by
which act a multitude of delicate, pale, and transparent elements of
spherical form are produced, with vesicular nuclei of 0'0056-0-0079 mm.
in diameter, sometimes single, sometimes ranging from 10 to 20. These
cells vary in diameter between O'OllS and 0*0074.

From them the seminal filaments are supposed to be developed, and,
moreover, from the nuclei. At first it was thought that, in the interior
of each of these vesicular nuclei, a seminal element took its rise ; but
Koelliker asserted later that the whole nucleus becomes converted into a
spermatozoon. This he stated to take place by its becoming elongated
and flattened, and dividing into an interior dark and posterior lighter
portion, and sending out at one end a filament destined to increase more
and more in length, while the nucleus itself assumed gradually the char-
acteristic form of the head.

The spermatozoa so formed were supposed to lie eventually within the
cells, in number corresponding to the original number of nuclei. Their
arrangement there was stated to be regular when more than a few were
present, namely, with their heads close to one another and the tails like-
wise parallel, bent according to the amount of space left to contain them.
A small number of these formative cells were supposed to rupture before
leaving the testis, setting free the spermatozoa; but by far the largest
proportion of the latter to be liberated in the epididymis.

But these theories, the correctness of which was for some time believed
to be beyond doubt, have been since found to be untenable, and the
genesis of the spermatozoa is at the present day a point of great obscurity.
Henle was the first to point out, some years ago, another order of things
from that just mentioned. He found, namely, two kinds of cells in the
seminiferous tubuli, — one with coarsely and another with finely granular,
sharply-defined, nuclei. He supposed the head to take its origin from the
latter, which project beyond the surface of the cells ; further, that the
filamentous process does not spring from the interior of the cell. In the
last view he is supported by Schweigger-Seidel. This observer regards the
spermatozoon as a single ciliated element formed
by the metamorphosis of a whole cell. The nuc-
leus, he believes, is transformed into the head, and
the middle portion to be derived from the remainder of
the cell-body, while the terminal filament represents
a cilium. According to Henle, cells with rolled-up
filaments never occur as normal structures in the
seminiferous tubes, which is also denied by both
Schweigger-Seidel and La Valett-St George, with
whom we also entirely agree.

From our own, but, we must confess it, rather hasty,
observations (fig. 550), the process of the formation
of spermatozoa appears to be as follows : — The nucleus
of the primary seminal cell (a) advances to the peri-
phery (b). Then the formation of the caudal appen-
dage commences (c). The nucleus then passes beyond
the original boundary of the formative cell, clothed
in a thin layer of protoplasm (d). Later still, the nucleus, -with this cover-
ing of protoplasm, forms the head of the seminal element, while the
appendage of the cell-body grows out into a long thread (e). Finally (/),

Fig. 550.— Mode of forma-
tion of spermatozoa in
the mammal. 1, head ;
2, middle portion; 3,
terminal filament.

ORGANS OF THE BODY. 5G3

we have the head or nucleus (1), the middle portion or remainder of the
cell-body (2), and the filament, the elongated cilium (3).

§ 285.

The most striking and important peculiarity of the seminal elements,
and one recognised as such ever since their discovery, consists in their
movements. These, which were in olden times accepted as a proof of
their independent individual life (whence the name " spermatozoa")
appear to be very nearly allied to the phenomena of ciliary motion (§ 99),
and, like the latter, baffle at present all explanation.

If semen be taken from the seminal tubes of some freshly slaughtered
mammal, it will be found, as a rule, that the movements in question have not
yet commenced. But if a drop of the fluid, immediately after emission from
the urethra, be placed upon a glass slide under the microscope, innumerable
spermatozoa are observed moving in all directions in the utmost confusion.

Closer inspection shows us that the individual elements of the semen
execute a series of movements, consisting in alternate flexion and exten-
sion, and undulating motions like those of the lash of a whip, by means
of which the whole structure is propelled from place to place. Though
tempted for a moment to compare this with the independent hurrying to
and fro of a host of infusoria, we very soon observe the most marked
points of distinction. We miss, in the first place, the spontaneity of the
latter organisms, — that swimming in definite directions and avoidance of
obstacles which characterise their movements ; also that momentary
acceleration and slackening in pace. The rate of progression moreover of
the spermatozoa is by no means very great, several minutes being consumed
in advancing even the distance of an inch. Like the motions of the cilia,
those of the seminal filaments commence, after a time, to decrease in rapidity
and the structure dies. We remark the intensity of the whip-like undu-
lations of the fibre growing less and less, until at last the movements of
the latter cease to propel the spermatozoon any farther, and all evidences
of life become extinct.

Let us now consider the conditions of these movements. Their dura-
tion, in the interior of the male organs of generation or in emitted semen,
varies in these different classes of animals. In birds they cease most rapidly,
often within a quarter of an hour. Among the mammalia they persist
for a much longer period, at times almost for a whole day. Thus in
human semen, after pollution, the spermatozoa may be observed still to
retain the power of motion sixteen or twenty hours after emission.
Among the Amphibia they last much longer, and in fish longer than in
any other animals. Here they may be seen under favourable conditions
four days after the discharge of the semen (Wagner). We are thus
reminded again of ciliary motion. If the temperature be reduced to
below freezing-point, the movements of the spermatozoa cease ; but even
after remaining four days in a congealed state they may regain their power
of locomotion on being warmed. Cooled down to — 17 C., they die ; as
also on being heated up to + 50 C. (Mantegazza) .

As to the effects of the addition of other fluids to the semen, we find
that indifferent matters of a certain average concentration, — as, for instance,
solutions of sugar, urea, glycerine, and neutral salts of the alkalies and
earths, — may be added without arresting the motion of the spermatozoa,
while very dilute solutions cause their destruction. Very concentrated
fluids also prevent by their viscidity any play or motion in the filaments.

564 MANUAL OF HISTOLOGY.

The same mechanical obstacles to the motions of the spermatozoa are pre-
sented by matters which become simply gelatinous in water; such as
vegetable mucous. Those re-agents, also, which act chemically on either
the seminal filaments or fluid, — as, for instance, mineral acids, metallic
salts, acetic acid, tannic acids, ether, alcohol, and chloroform, — all bring
the lively movements of the former to an end. They may be best exa-
mined in serum, white of egg, and vitreous humour ; as also in the contents
of the vesiculse seminales, prostate, and Coioper's glands, as the natural
ingredients of the semen. In the secretions of the internal female organs
of generation their motions are for a long time preserved. Here they
may be observed, in the mammalia, wandering hither tand thither for
days, under the favouring influence of the animal heat of the parts.
The acid mucous of the vagina, as well as the transparent and viscid
secretion of the cervix, are said to put an end to the movements of the
spermatozoa. Urine,' when neutral or slightly alkaline, has no very great
effect upon the latter ; but when strongly acid or alkaline, its action is
very well marked. In alkaline milk or mucus the phenomenon of
motion is quite evident, while saliva has the same effect on it as water.
This is peculiar, bringing all movement rapidly to an end ; but it is pre-
ceded by increased activity for a short time, during which the sperma-
tozoa hurry about with great rapidity, striking and lashing with their
tails. Soon, however, they come to a state of complete rest, when the
under end of the filament is usually observed to be folded round the
upper portion, like the lash round the stock of a whip. It is an interest-
ing fact that such motionless spermatozoa may be again called into
activity by surrounding them with saturated solutions, such as those of
sugar, white of egg, and common salt, and also, when in too strong solu-
tions, by subsequent addition of water, — an indication of the important
part which endosmosis plays in the phenomenon.

We have already seen in an earlier section that the caustic alkalies have
a most stimulating action on the ciliary motions : the same has been
observed by Koelliker to be the case with the elements of semen.

Recent research has shown that the spermatozoa penetrate into the
interior of the ovum in order to impregnate it, moreover, — in the mammalia
in considerable number. This entrance appears here, as among all the
vertebrates, to be effected by the efforts of the spermatozoa, and carried
out by the movements of their thinner portion. A special opening
(micropyle), to admit them, has not yet been demonstrated in the zona
pellucida, but those radiating lines seen on the envelope of the ovum may
possibly represent, as pore-canals (§52), such passages for the spermatozoa
which may be enlarged by the latter. These, on penetrating into the
yelk, become motionless, and soon after break down and become fluid.

§ 286.

Turning now to the thick-walled vasa deferent-ia, it will be remembered
that they take their origin gradually from the passages of the epididymis,
and are therefore possessed of a similar structure to the latter. They
are made up of an external fibrous investment, then a muscular coat of
considerable thickness, composed of three laminae (already mentioned in
speaking of the epididymis), an external strong and internal weak layer
of longitudinal fibres, together with a middle tunic of circular bundles,
which is the strongest of the three. The mucous membrane with which
they are lined is covered by columnar cells, O'OSOl mm. in height. Near

ORGANS OF THE BODY. 565

the lower end of the vas deferens is a fusiform dilatation, the " ampulla "
of Henle, from which a number of blind diverticula, leaving the main
tube, pass at very acute angles upwards into its walls.

In this expanded portion of the canal the mucous membrane differs
from elsewhere : it is thicker and rugose, and presents a number of pits
and saccules. In the walls of the ampulla further vermiform glands pre-
sent themselves, filled with polyhedral cells, and containing molecules of
a yellow and brown pigment (Henle). The nerves of the vas deferens
possess* ganglion cells, and are medullated. Their mode of termination is
not yet known.

The thin-walled vesiculce seminales have also a similar structure. They
are, in fact, little else than highly-developed diverticula of the same stamp as
the ampulla of the vas deferens, but branching. They are partly designed
as receptacles for the semen as it is secreted, and partly as secreting organs
themselves. Their walls are supplied with scattered bundles of smooth
muscular fibres. Within them we find a transparent fluid which coagulates
into a gelatinous substance on exposure to the air, becoming subsequently
liquid again. This is manifestly the same matter as the semen dis-
charged from the uretha (§284). According to Gerlach, the rugose mucous
membrane with which they are lined contains numerous compound mucous
glands, which are stated by Henle to be of the tubular kind, and by Klein
to be only pits. Their structure is otherwise similar to that of the ampulla.

The ejaculatory ducts correspond also in structure with the last-named
organs.

Their calibre decreases greatly in their course through the prostate.
In the more dilated portions their mucous membrane presents similar
folds, tubular mucous glands, and yellow and brown pigment granules, as
the ampulla and vesiculse seminales. Within the prostate the muscular
layer of the ejaculatory duct gives place to cavernous tissue (Henle), and
the mucous membrane becomes thinner, smoother, and loses its glands.

The prostate, the largest of all the organs connected with the male
generative organs, is an aggregation of glands belonging to the racemose
type, but presents, besides, many peculiarities. With Henle we may con-
sider it as divided into three portions, namely, the two sphincters of the
bladder, the internal formed of unstriped fibres, and the external with an
increasing number of striped elements ; and finally, the body of the gland
just mentioned. Besides a fibrous tunic with an admixture of muscle
elements, the prostate is enveloped in a tough yellowish membrane, con-
sisting chiefly of smooth muscular fibres. This latter sends off into the
interior of the glandular mass a number of processes forming a massive
framework, and making up a considerable portion of the whole organ.
The separate elements of the gland, in number varying from 15 to 20,
appear to be of the racemose kind. In them we find pear-shaped vesicles
of 0 '12 54-0*2 3 mm. in diameter, lined with columnar epithelial cells.
The ducts of the gland are fine, surrounded by a muscular coat, and lined
with the same columnar epithelium : they empty themselves singly, in
the neighbourhood of the colliculus seminalis, into the urethra.

The vascularity of the organ is considerable, its vesiclers being enve-
loped in capillary networks. The lymphatics and mode of termination of
the nerves of the prostate which present ganglion cells are still unknown.

The secretion of the prostate is probably allied to that of the vesiculse
seminales. In both we find an albuminous matter freely soluble in acetic
acid.

566 , MANUAL OF HISTOLOGY.

Those concentrically laminated concretions known as prostatic calculi
are composed of this substance. In old men almost every prostate con-
tains some of these bodies, which are often seated in the excretory ducts.

The sinus prostatica or, as E. Weber has named it, the uterus masca-
linus, is a slender saccule, from 7 to 14 mm. in length, lying in the sub-
stance of the prostate. Like the coliculus seminalis it is lined with laminated
epithelial plates, has a fibrous wall intermixed with muscle elements, and
is enveloped in a thin layer of cavernous tissue. It opens at the summit of
the colliculus seminalis between the two orifices of the ejaculatory 'ducts.

Cowper's glands are small, round, and more or less lobulated bodies, a
few lines broad. They possess a fibrous envelope, containing some
isolated bundles of striped muscle, and present the usual structure of race-
mose glands. In their lobules, which are separated from one another by
connective-tissue mixed with contractile fibre-cells, we find small gland
vesicles lined with columnar cells. The somewhat wide ducts of the
lobes are clothed with flattened cells. In the interior of the organ they
unite to form a number of large passages, which give to a transverse
section of the organ an appearance as though sacculated. Subsequently,
however, they combine at acute angles to form one single trunk.

§287.

There still remain to be considered the urethra and copulative organ
of the male.

The first of these consists, as is well known, of three portions, — the pars
prostatica, passing through the prostate gland ; the p. membranacea, a
middle portion, made up of an independent membrane ; and a third com-
pound part, which is the longest of the three, and named p. cavernosa.
This latter belongs to the penis, in which it is enveloped in a spongy
body, the corpus cavernosum, s. spongiosum urethrce, which forms with its
anterior extremity the glans penis. Associated with this spongy mass are
two other structures of a similar nature, the corpora cavernosa penis,
which, together with an external covering of skin and several voluntary
muscles (m. m. ischiocavernosi and bulbo-cavernosi), make up the copulative
organ of the male.

The urethra of man presents for consideration, internally, a mucous
membrane, covered in the prostatic and membranous portion with flattened
or transition cells, but lower down with cylinder epithelium (§ 91).
This mucosa is invested, again, in a fibrous tunic, rich in elastic elements
and of looser texture, in whose interstices a cavernous tissue is formed
(Henle). External to this, again, is a layer of involuntary muscular tissue
formed of longitudinal fibres internally, and transverse externally.
The three portions must, however, be considered separately.
The first thing which strikes the observer in the prostatic portion is
the prominence of the colliculus seminalis, to which we have already
referred in speaking of the ejaculatory ducts and prostate. It is covered
by a longitudinally wrinkled mucous membrane, and consists of elastic
tissue (intermixed with bundles of contractile fibre-cells), which bears all
the characters of cavernous substance. This spongy tissue is near the
surface displaced at certain points by glands similar to those of the pros-
tate, situated partly in the mucosa and partly deeper (Henle). The
mucous membrane of the pars prostatica is seen to be arranged in fine
intersecting folds, chiefly, however, longitudinal : it contains glandules
identical with those just mentioned.

ORGANS OF THE BODY. 567

In the middle or membranous portion of the passage under the mucous
membrane a long-meshed cavernous tissue again presents itself. The
organic muscular layer, on the other hand, is weaker, and covered by
bundles of the musculus urethralis, which consists principally of trans-
versely arranged bundles of striped fibres.

But the unstriped muscular tissue of the pars cavernosa is even less
developed still. Here the mucous membrane is covered with cylinder
cells, which give place to a covering of flattened epithelium at a greater
or less distance from the mouth of the urethra.

The last-named portion of the urethra contains farther little depres-
sions or pits, the lacunce Morganii, which are not glandular in their
nature ; also isolated small and ill-developed racemose glandules, known
as glands of Littre, whose vesicles and ducts are lined with cylinder
epithelium. These do not appear to exist in the pars niembranacea (Henle).

Just a few words in regard to the skin of the penis. This is thin and
loose down to the free edge of the prepuce, and is possessed of fine downy
hairs, which decrease in length below, and into whose follicles sebaceous
glands empty themselves. Its very elastic subcutaneous areolar tissue
presents longitudinal bundles of involuntary muscle-fibres, prolongations of
the tunica dartos of the scrotum, and is quite devoid of fat-cells. This
subcutaneous tissue invests the whole organ 'down to the base of the
glans : it is known as the fascia penis. At the root of the member it is
condensed into an elastic band — the ligamentum suspensorium penis.

The connective-tissue binding the two laminae of the foreskin together
manifests the same distensibility, but is destikite of fat : it is intermixed
with muscular elements.

The surface of the glans is covered by a delicate membrane, closely
adherent to the cavernous tissue beneath. This membrane is possessed
of very numerous papillae arranged in rows converging towards the orifice
of the urethra, and obscured by the flattened epithelium covering of the
part. On the corona glandis we may frequently observe larger papillae,
measuring from, 0*9 to 0*5 mm., and appearing as white specks through
the membrane or bulging out the latter.

The internal leaf of the foreskin, smooth and without wrinkles, presents
all the characters of a mucous membrane. It is quite destitute of hair
and convoluted glands, but is supplied with numerous tufted papillae.

On the inner surface of the prepuce are situated a number of sebaceous
follicles, known as Tysoris or Littre's glands. These occur in varying
number and form, and are found at times also upon the surface of the glans,
especially in the vicinity of the fraenum. Their secretion mixes with the
epidermal scales of the part when shed, and so assists, though, in a very
minor degree, in producing that tallowy substance, known as the smegma
preputii, which collects sometimes underneath the foreskin.

Each of the corpora cavernosa is enveloped in a nbro-elastic tunic, con-
taining but few muscular elements, the tunica albuginea, v. fibrosa, from
which innumerable bands and septa are given ofi" internally, consisting of
ordinary and elastic connective-tissue fibres, with a number of muscular
elements. These bands, then, undergo repeated subdivision, and unite
in every conceivable way; so producing a system of cavities communicat-
ing with one another, like those of a sponge, and lined throughout with
vascular cells or endothelium. Thus a peculiar venous receptical is
formed for the blood.

The several cavernous bodies in man resemble each other, as a rule, in
37

568

MANUAL OF HISTOLOGY.

structure. The description just given, however, refers more particularly to
the corpp. cav. penis. These are separated from one another anteriorly by
an imperfect partition. But, besides these, there is another cavernous
body, the bulb of the urethra, quite distinct from them, and remarkable for
having a thinner envelope, more delicate trabeculse, smaller receptacula,
and a larger proportion of elastic fibres. The interstices in the spongy
tissue of the glam are even narrower still.

The reservoirs just mentioned are constantly filled with blood, but
become overcharged with the same at intervals, effecting that change in
the male organ known as erection.

In order to understand this phenomenon clearly, it will be necessary to
review first of all the whole arrangement of vessels and circulation of the
cavernous organs. In doing this we shall adhere to the description given
in a very excellent work by Langer.

The corpora cavernosa of the penis only receive a few inconsiderable
twigs from the dorsal artery ; they are chiefly supplied by the artericv
profundce which run close to the septum. These are enclosed in a sheath

connected with the cavernous
cellular network, and give off
gradually numerous anastomos-
ing twigs to the cavernous sub-
stance which run along within
the trabeculae, and take a tor-
tuous course in the quiescent
state of the organ.

The modes in which these
vessels merge into the cavities
of the venous spongy tissue are
several.

In the first place, they de-
crease rapidly in diameter
towards the surface of the
corpora cavernosa, and more
so still in the vicinity of the
septum. Here we find true
capillary networks of some-
what large-sized tubes at the
point of transition. These con-
stitute, as Langer expresses it,
the "superficial cortical net-
work," and (fig. 551, 1, a) com-
municate with a "deeper sys-
tem of wide venous canals"
(b), " the deep cortical net-
work."

An immediate transition of
fine arterial twigs (2, a) into
these latter is also to be seen, however, which explains the rapid occur-
rence of turgidity in the peripheral system of lacunae.

Direct communication of terminal arterial twigs takes place also with
the deeper venous receptacles of the interior, a remarkable funnel-shaped
opening being evident at the point of transition (" Zap/en ").

The trabeculae of the interior of the corpora cavernosa contain also

Fig. 551. — From the peripheral portion of the corpus
cavernosum penis, under low magnifying power. 1. a,
network, known as the superficial ; 6, the deep. 2. Con-
nection of arterial twigs (a) with the canals of the
deeper cortical network (copied after Langer).

ORGANS OF THE BODY. 569

wide-meshed capillary networks, which probably empty themselves like-
wise into the venous cavities of the part.

Finally, the coats of the arteria profunda are supplied with a meshwork
of capillary vessels. These gather themselves together to form venous
twigs, also to be seen here, which empty themselves into a network of
venous spaces surrounding the artery.

The so-called arterice helicince, brought into notice by /. Miiller, and
the subject of such frequent controversy, used to be supposed to terminate,
after many contortions and tendril-like convolutions, partly with blind sac-
cules in the cavernous spaces projecting into the latter. The appearances
which led to these conclusions were, however, artificial (Rouget, Langer),
produced in part by imperfect injection, partly by the constriction caused
by severed elastic trabecuke.

The conveyance of the blood out 'of this system of lacunae is effected,
in the first place, in the dorsal portion of the organ, by short venous
passages, which spring from the deeper cortical network, and empty them-
selves into the dorsal vein of the penis (so-called vence emissarice). Again,
by the vence emissarice inferiores, which come- from the interior of the
cavernous system, and make their exit near the urethral furrow ; lastly,
by the vence profundce of the crura of the corpora cavernosa.

In the spongy portion of the urethra we find a venous network inter-
nally around tl^e tube, consisting of long meshes connected with the
venous lacunae. In the bulb alone do we encounter a direct entrance of
arterial twigs into the lacunae : the transition in other localities takes
place through the medium of capillary networks, as seen, for instance, in
the mucous membrane of the urethra.

In the spongy part of the glans, where the lacunar system is more or
less replaced by genuine venous vessels, the connection between arteries
and veins is everywhere effected through the medium of capillary inter-
lacements (Langer).

The lymphatics of the male urethra, connected with those of the
bladder, are arranged in complicated networks, which, with longitudinally
arranged meshes, open directly into the lymphatic canals of the glans
penis. The latter are numerous, but thinner than those of the urethra
(Teichmann). They interlace in the uppermost layer of the skin in the
form of wide passages, seen in greatest numbers in the glans, and less
highly developed in the prepuce and other portions of the organ (Belajeff).
The larger trunks derived from these course along the dorsum of the penis,
and are received partly into the true pelvis, partly into the glands of the
groin.

The nerves of the penis are derived partly from the cerebro-spinal
system (n. pudendus), partly from the sympathetic (plexus cavernosus).
The latter are stated to supply the cavernous tissue alone ; the first the
skin, and mucosa besides. The skin of the glans is peculiarly rich in
nerves. Many years ago Krause discovered terminal bulbs in this situa-
tion, and since then genital nerve-corpuscles (p. 327) have been also
observed. Tomsa mentions also a second and more simple mode of ter-
mination of the nerves of the glans. Pacinian corpuscles also were found
by Schweigger-Seidel behind the glans, in the neighbourhood of the dorsal
artery of the penis.

In regard to the theory of erection of the penis, Koelliker endeavoured,
many years ago, to explain it as effected by a relaxation of the muscular
tissue of the corpora cavernosa under the influence of the nervous system.

570 MANUAL OF HISTOLOGY.

This would naturally allow of the distension with blood of the small
receptacles of the cavernous substance. Later Eckbart found in the dog
fibres running from the plexus ischiadicus to the hypogastricus, which lu>
showed to be the erection nerves. Loven found that during irritation of
these a bright red stream of blood spurted from a small arterial twig
suddenly on being opened ; the pressure of the blood, at the same time,
in the vessels of the penis continuing much less than in the carotid. Here,
then, we have before us a relaxation of the walls of the smaller arteries
brought about by stimulation of a nerve similar to that produced in the
heart by irritation of the vagus.

But, besides this, no doubt hindrance to the exit of the blood from the
organ increases the erection. This is possibly brought about by the
m. transversus perinoei (Herile) preventing the return through the roots of
the penis. Also by the position of the venae profundce in the corpora
cavernosa, and the fact that the veins of the plexus pudendalis possess
numerous projections of smooth muscles.

B. Organs of the Animal Group.

6. Bony Apparatus.

§288.

Although we have already referred at some length, in the second part
of our work, to the bony apparatus or osseous system in dealing with the
tissues of which bones are composed, there still remain some comple-
mentary considerations which must occupy us for a few moments. These
are, in the first place, the mode of connection of the various portions of
the skeleton with one another ; secondly, the vessels and nerves of bone ;
and thirdly, the substance with which the cavities of the latter filled up.

The ways in which bones are joined together are, as is well known, very
various. While in the embryo the connecting masses are, in all proba-
bility, almost universally solid, but a small number of them remains so at
a later period. In such instances they are known to anatomists as
examples of synarthrosis, a mode of connection represented in sutures and
symphyses. In other rudimentary masses of this kind a process of liqui-
f action in the interior gives rise to the formation of cavities, while the
peripheral cells of the mass are transformed into the tissue of a capsule,
with its epithelial cells, &c. This mode of connection is designated as
diarthrosis, or jointed union. If, as is often the case with symphyses,
the process of liquifaction should cease at an early period, we have what
has been called half joints (Luschka). The latter are usually somewhat
ill-defined, and are variable in nature : no synovial capsule is to be recog-
nised in their interior.

In regard now to the several media of articulation between bones, the
suture is united by what is incorrectly named suture-cartilage, which is
nothing less than a fine band of whitish fibrous connective-tissue. Sym-
physis is effected by hyaline, or fibrous cartilage and connective-tissue.
Here the ends of the bones are clothed with a layer of hyaline substance,
which, covered externally by connective-tissue, completes the union ; or
this cartilage passes gradually, more and more, into a fibrous mass, which
may at certain points give way to pure connective-tissue. We have already
referred to this texture, in speaking of fibrous cartilage, in § 109, where the
intervertebral disks were fully described. The symphysis pubis and
sacroiliaca are half joints, as also almost invariably the points of union of

ORGANS OF THE BODY. 571

the costal cartilages with the sternum from the "second to the seventh rib.
We not unfrequently meet in the symphyses with a layer of calcified car-
tilaginous tissue in the vicinity of the bone. The further consideration
of these parts must be left to works on descriptive anatomy.

As regards the joints, we have already considered their cartilages (§ 107),
and in § 109 their labra cartilaginea, sometimes present.

Under the cartilaginous coverings of bones forming joints we very
generally find a layer of peculiar undeveloped osseous tissue. It is, on
an average, 0'27 mm. in thickness (Koelliker), and consists of a yellowish
and usually fibrous solid mass, which presents, however, neither Haversian
canals nor bone corpuscles. Instead of these, we observe in thin sections
cartilage capsules filled with air.

A description of the tissue of the synovidl capsules will be found in
§ 135. The latter are very vascular, and are richly supplied, apparently,
with lymphatics (Teiclimann). They are strengthened externally by the
'addition of strong fibrous tissue. Their epithelial lining has been already
discussed, as far as it occurs, in § 88, and the synovia itself in § 97. For
a description of the inter-articular cartilages — those disks of connective-
tissue cartilage attached laterally to sy no vial capsules, and interposed
between the heads of bones forming joints — compare § 109. The liga-
ments of joints consist of connective or fibrous tissue (§ 135).

From the frequent deposit of fat-cells in the connective-tissue envelop-
ing synovial capsules, it is often found, as already alluded to in § 122,
that collections of the former are protruded into the cavity of the joint in
the form of duplicatures. These are most usually met with in the knee
and hip joints, and are known there as the glands of Havers. The appear-
ance, however, of very vascular fringed folds of synovial tissue is of far
more frequent occurrence, and encountered in almost all joints. These
are usually destitute of fat-cells, and present occasionally a few cartilage
elements intermixed with those of the connective-tissue. They have been
given the name of plicce vasculosae (1), and are represented also in the half
joints, according to Luschka, although devoid of vessels in those situations.

REMARKS (1). — The structures in question are frequently covered with smaller pro-
cesses, leaf-shaped or membraneous, and sometimes of the strangest shapes. From
these the loose cartilages found at times in the interior of joints are derived, though
not exclusively. They consist of more or less calcified cartilage, and occur most
frequently in the knee. Compare Virchow, " Die krankhaften Geschwiilste, " Bd. i. 5,
449.

§289.

As regards the blood-vessels of bone, we have to bear in mind, in the
first place, that the periosteum (§ 135) is very vascular. It is" supplied by
a number of large vessels, which pierce it, however, for the most part, only
on their way to supply the osseous tissue beneath. It is possessed,
further, of finer vessels proper to itself, which are arranged in rather com-
plex capillary networks.

In order the better to comprehend the arrangement of the vessels of
osseous tissue, let us first take one of the tubular bones as an example.
As we have seen above, numerous vessels from the periosteum are given
off to the openings of the Haversian canals (§ 140), and are there arranged
in a long- meshed network of tubes of considerable size, which often assume
characters different from those of true capillaries, and belonging rather to
the smaller veins and arteries. Beside this, we always meet with a large
single or double canal in the diaphysis of such a bone, the foramen nutrl-

572 MANUAL OF HISTOLOGY.

tium, into which an arterial twig is sent which makes its way eventually
into the central medullary canal as the arteria nutritia. The latter then
divides into an ascending and descending branch, which again break up
into a capillary network, including the fat-cells of the medulla in its
loops (see below), and giving off a series of vessels which enter the
internal opening of the Haversian canals to anastomose with those coining
from the periosteum. In the epiphyses, also, the supply of blood is
partly from without, through small vessels derived from the periosteum, or
larger twigs entering through the more numerous nutritious foramina of
these portions ; and partly from within, through close connection with the
vessels of the medullary canals of the diaphysis. These vessels, then, are
situated, in the first place, within the Haversian canals, and again distri-
buted through the medullary cavities.

The course of the veins is analogous to that of the arteries. One set of
venous vessels convey the blood out of the part through the larger and
smaller nutrient canals ; another set of branches return to the periosteum •
by the peripheral openings of the smaller medullary canals.

Turning now to the other kinds of bones — to the short and tabular,
namely, — we find that they present the same arrangement of vascular
supply as the epiphyses, with the exception of the flat bones of the head.
Through the many openings, namely, on their surfaces, small arteries and
veins make their entrance and exit : their terminal branches are found,
however, more in the medullary cavities than the scanty Haversian
canals. The flat bones of the cranium, on the other hand, are supplied
by numerous fine arterial twigs, which enter through holes in the two
vitreous plates, and break up in the cavities of the diploe into capillaries
interlacing amongst themselves. The veins, however, present themselves,
as was discovered by Breschet, in quickly-branching wide bony canals, in
the form of very thin-walled tubes traversing the diploe in various direc-
tions, and emptying themselves partly into the external veins of the
head, and partly into those of the dura mater. The cartilage covering
the ends of bones is quite destitute of vessels.

The existence of lymphatics in osseous substance has not been demon-
strated to. a certainty.

The nerves with which bones are supplied present the same arrange-
ment as the blood-vessels. The periosteum is very richly supplied with
them ; but the greater proportion simply pierce this membrane to reach
the osseous tissue beneath, — so that, in fact, but a' small number properly
belong to it itself. In this respect, however, the periosteum varies greatly,
according to locality : in some spots it appears to be quite without nerves,
while in others it is richly supplied. The nerves consist of broad and
medium-sked fibres which split up before their termination.

One set of nerves enter the bone with the blood-vessels which pass
through the periosteum, by means of the Haversian canals : these are
very fine. Other stronger twigs find their way into the interior through the
foramina nutritia. From thence they are distributed to the larger medul-
lary cavities. Their ultimate termination is still a matter of doubt. Many of
the short and flat bones are, according to Koelliker, very highly innervated.
Most of the nerves are derived from the cerebro-spinal system.

The capsules of the joints are also very rich in nervous supply, while
the ligaments are but scantily furnished with sentient elements.

The cavities of the bones are filled up with a substance known as the
marrow. This presents itself under two forms, with intermediate varie-

OKGANS OF THE BODY.

57;

ties. In the long bones it is met with as a yellow mass, found under
the microscope to be made up of scanty bundles of connective-tissue
interspersed with fat-cells (fig. 552, d, e). Chemical analysis shows it to
be composed of neutral fats to the amount of 96 per cent., according to
Berzelius (comp. §§122 and 147). In the epiphyses, on the contrary,
and in flat and short bones, the medulla is a reddish or red mass of
soft consistence, made up usually of bundles of connective-tissue similar
to those of the last variety (but in smaller quantity), with an ever-
decreasing number of fat-cells containing, on the other hand, numerous
small contractile lymphoid elements, with granular contents and distinct
nuclei. These latter, 0-0090-0-0113 mm. in diameter, are identical with
the cells figuring in plate 552, b, from the medulla of an infant. Like
them, they were formerly supposed to be
descendants of the cartilage medullarv
cells (§ 147).

On the surface also of the yellow variety
of medulla, cells of this kind are to be met
with here and there.

An interesting point, in regard to these
lymphoid cells of the medulla of bones,
has recently been noticed by Neuman and
Bizzozero in the osseous tissues of man and
other mammalia. This is the transfor-
mation of the former into red blood cor-
puscles, reminding us of the formation of
embryonic blood. The possibility of im-
migration of these into the vessels of the
medulla is suggested.

Another kind of element is also to be
found in the medulla of bones, and, more-
over, at all periods of life, namely, large isolated membraneless multi-
nuclear cells, known as myeloplaxes (p. 258). According to Berzelius, red
medullary substance from the diploe contains 75*5 per cent, of water,
traces 2 4 '5 of solid constituents, protein compounds, and salts, but merely
of fatty matters.

7. Muscular Apparatus.

§ 290.

The structures we are now about to consider briefly have been already
described in the second portion of our work in dealing with muscular tissue
(§§ 162-173). The structure of the tendons formed the subject of § 134,
belonging as they do to the connective-tissues, among which the fascias
also are included. In § 109 the fact was also mentioned, that at those
points where tendons are inserted into bone, deposits of cartilage cells are
not unfrequently met with between the bundles of fibres, of which the
structure is chiefly composed, thus giving rise to a kind of fibro-cartilage.
That the same cartilaginous tissue may be developed in the interior of
tendons was also remarked in the same place. Here, then, we have the
source of se.satnoid cartilages, whose place again may be taken by analogous
osseous formations known as sesamoid bones.

The blood-vessels of the tendons can be only found with great difficulty,
nay, further, small sinews are entirely destitute of them, and are supplied
entirely by a wide-meshed network contained in the connective-tissue in

Fig. 552.— Medullary cells of cartilage, a,
from the humerus of a human foetus at
five months; 6, from the same bone of
an infant shortly after birth ; c, stellate
and fusiform cells from the first; a",
formation of the fat-cella of the marrow;
e, a cell filled with oil

574

MANUAL OF HISTOLOGY.

\vhich they are enveloped. Large tendons contain in their superficial
layers isolated vessels ; while those of greatest magnitude are supplied
with blood-vessels as far as their internal Iamina3, while that portion
farthest from the surface remains non- vascular.

The mucous or synovial sheaths of the tendons, vagince synoviales have
been already described in speaking of the latter. The synovial sheaths of
•niiLsdes have also a similar structure, as likewise the biii'scr. mucosce. Most
of these are, however, by no means shut serous sacs, as was formerly sup-
posed : this is only in some measure the case here and there. The same
may be said of the epithelial lining of simple flattened cells (§ 87) : it is
only met with in portions of the capsules, in the walls of which, further,
a sprinkling of cartilage cells may be met with. The contents of all these
cavities have been already dealt with in considering the synovia (p. 155).

In § 168 the blood-vessels of the muscles are dealt with, and the
nerves of the latter in § 182, with the nervous system generally. The
lymphatics, as far as we may judge from the scanty observations which
have up to the present been made upon the subject, present themselves
in muscular tissue in but small number (Teichmann). They were found,
however, by Tomsa in the interstitial connective- tissue between the
fibres of these organs in the dog : another superficial set, also, is described
by His.

8. Nervous Apparatus.

§291.

The greater part of the nervous system has already come under con-
sideration in an earlier portion of our work (§ 174-192): there still

and spinal cord.

The medulla spinalis (1), a
cylindrical nervous cord, con-
sists of an internal grey or
greyish-red, and an external
white substance. The first,
prolonged throughout the
whole length of the cord, has,
on transverse section of the
latter (fig. 553), the shape
generally of the letter H;
that is, it may be said to con-
sist of a middle portion, two
anterior (d) and two posterior
cornua. The latter, further,
are enclosed within another
clear gelatinous layer, known
as the substantia gelatinosa of
Rolando (/). In the middle
of the grey substance a deli-
cate central canal (c) is ob-
served, the only trace left of
the rudimentary groove which

gradually closed in to form the foetal spinal cord. It is lined within by

ciliated epithelial cells (§ 93).

The circumferential white substance presents deep indentations both

V

Fig. 553.— Transverse section of the spinal cord of a calf
(after Ecker). a, anterior, 6, posterior median fissure;
c, central canal; d, anterior, e, posterior cornua; /, sub-
xtantia gelatinosa of Rolando; g, anterior column with
motor roots; A, lateral column with connective-tissue
partitions; t, posterior column with sensitive roots; k,
anterior, and Z, posterior transverse commissure.

ORGANS OF THE BODY. 575

before and behind, the anterior (a) and posterior medium fissures (b), so
that its two halves are only connected at the bottom of the anterior fissure
by a white band (&), the white commissure or commisura anterior. The
isthmus, however, contains besides a band of grey substance, known as
the posterior commissure (I). The white matter of the cord may be con-
sidered as consisting of three imperfectly defined symmetrical longitudinal
bands, — the anterior (g), lateral (h), K&& posterior (i) columns.

In the cervical portion of the spinal marrow the latter most internal
and posterior portion constitutes what is known as the band of Gott, to
which we will again refer in speaking of the medulla oblongata.

At the junction of lateral and anterior columns the motor roots of the
spinal nerves penetrate as far as the anterior cornu ; while the entrance
of the posterior sensory roots takes place in a similar manner at the point
of union of the middle and hinder columns.

Looking at it from a histological point of view, the whole spinal marrow
may be said to be supported interstitially by a lowly-organised vascular
connective-tissue, and to be composed of nervous fibres and ganglion cells
imbedded in this framework. In the white substance, however, we find
fibrous nerve-elements alone, but in the grey, besides these, ganglion
cells. There are, however, so many difficulties still connected with the
investigation of the more minute arrangement and combination of these
nerve-elements, that, with the brain, the spinal cord may be said to be one
of the most obscure and unsatisfactory fields of modern histological
research. One of the obstacles to advance in this direction is, that we
are unable here to draw any sharp line of distinction between nervous
and connective-tissue constituents (see § 119). One school of histologists
believe that connective-tissue constitutes a very large portion of the sub-
stance of the spinal cord, while quite the opposite view is held by another
party.

REMARKS. — (1.) Literature is very rich in treatises on the structure of the spinal
cord. Besides numerous Continental essays by Stilling and Wallach, Schroder van
der Kolk, Koelliker, Reissner, Deiters, Gcrlach, may be mentioned those of Lockhard,
Clarke, Philos. Transact. 1851, p. ii. p. 607, and p. iii. p. 347; and Beale's Archiv. of
Medic. 1858, p. iii. p. 200. Further, in the Proceed, of Roy. Soc. vol. viii. No. 27 ; and
Philos. Trans. 1858, p. i. p. 231, and 1859, p. i. p. 437. /. Dean's Microscopical
Anatomy of Lumbar Enlargement of the Spinal Cord, Cambridye (U.S.) 1861. W.
Hendry in Micros. Journ. 1863, p. 41.

§ 292.

We shall now consider the neuroglia or connective-tissue sustentacular
substance of the spinal cord, whose chief peculiarities have been already
touched on in a former section (§ 119).

In it we have a framework, as it were, for the medulla, in contact with
the pia mater externally, and continuous throughout the whole cord,
though of by no means of the same structure in the different divisions of
the latter.

We find it in its simplest form surrounding the central canal as a ring
merging imperceptibly at its periphery into the grey matter. To this
several names have been given, such as " central ependymal thread," " grey
central nucleus," "gelatinous central substance." It presents itself here
as a soft substance of homogeneous, streaky, or even at certain points
finely fibrous appearance. Filiform processes from the epithelial cells of
the axis canal project into it, as also connective-tissue ramifications of the
pia mater from both fissures of the cord. Cellular elements may also be

576

MANUAL OF HISTOLOGY.

mm
**»*

Fig. 554. — Sustentacular
connective-tissue from
the posterior column of
the human spinal cord,
showing the nerve-
fibres in transverse sec-
tion.

recognised as entering into the composition of this ependymal tissue.
They appear to have been formerly incorrectly described as nerve-cells, of
which, as well as of nerve-fibres, this tissue is entirely destitute.

The substantia gelatinosa ofJRolando, mentioned in the preceding section,
presents also purely connective-tissue characters. It is remarkable for its
richness in cellular elements. Some very few nervous constituents may
be observed in it in the form of scattered fibres.

But the sustentacular substance in the grey matter of the cord is far
less pure : it is mixed up with nerve-fibres, ganglion cells, with their
various processes, and blood-vessels. It forms here a finely porous spongy
tissue, referred to already at § 119, of the most delicate texture, with
numerous free nuclei or (if the latter still retain a thin layer of protoplasm)
with the equivalents of small cells.

The connective-tissue framework of the white substance, however,
attains a greater degree of massiveness. In trans-
verse section (fig. 554) it appears homogeneous or
streaky, dotted at its nodal points with nuclei, and
forming so a lace- work as it were, in whose meshes
the transverse sections of the nerve tubes are to be
seen ; while in longitudinal cuts a more or less regu-
larly tubulated appearance is presented by the slice,
which may also show oblong deficiencies of substance.
Larger collections of connective substance some-
times form radiating partitions around groups of
nerve-fibres, giving by their numerous intercommuni-
cations a net-like appearance to the whole (fig. 553, h).
Towards the periphery of the cord the sustentacular substance is
again much more highly organised, and is free from nerve-fibres (Bidder,
and Kupffer, Clarice, Koelliker, Frommann). Lastly, the pia mater

covers the surface of this grey cortical
layer.

Turning now to the Hood-vessels
of the cord (fig. 555), it may be
usually observed in trans verse sections
that from the branches of the art.
med. spin, anter. two twigs are given
off in the anterior fissure, which
pass into the substance of the spinal
marrow, and that a third twig, cor-
responding to them, lies in the poste-
rior fissure (b, c). Other finer arterial
tubes are conducted into the white
substance (/, g, h) by the radiating
bands of connective-tissue of the pia
mater. It is from these principally
that the capillary interlacements of
the white matter are supplied, which
are here particularly large meshed,
and composed of very delicate tubes.
The capillary network of the grey
substance is much more dense (d, e).

6 —

J

Fig. 555.— Transverse section in the dorsal region
of the medulla spinalis of the cat. a. Cen-
tral canal; 6, anterior, c, posterior fissure;
rf, anterior cornu; e, posterior cornu; /, y, h,
white columns, with their wide-meshed capil-
lary networks.

It is chiefly derived from the arteries of the fissures just named, but is con-
nected at all points of its periphery with the vessels of the white substance.

ORGANS OF THE BODY.

577

Of the veins, two are specially striking in the neighbourhood of the
central canal (Clarke, LenhosseK).

Some years ago the arrangement of the capillary network of the cord
was very minutely studied by Gull. The widest meshes were found by
him in the anterior columns, the finest in the lateral, while those of the
posterior columns lay between the two. But the densest capillary inter-
lacements of all are to be met with in the grey matter in those situations
where many ganglion cells are collected together. Finally, the restiform
bodies are remarkable for having meshes of capillaries as small as those
of the grey substance.

It has been already mentioned (§ 207) that throughout the whole spina]
cord and brain, all the blood-vessels, including arteries, veins, and capil-
laries, are invested with a loose sheath of connective-tissue. A watery fluid
found within tho latter has been regarded by some as lymph. The existence,
however, of this system of perivascular canals of His is not yet firmly
established, and has lately been the subject of very earnest controversy.

§293.

Having now discussed the connective-tissue groundwork of the cord,
let us turn to its nervous elements.

The white substance, as has been already remarked, consists entirely of
fibres. These present all the characters of central structures (fig. 556,/, g, h),
i.e., they are not supplied with the same primitive sheath as the peripheral
tubes, so that in many cases we are only able to obtain them in broken
fragments. In the finer specimens further there seems to be a tendency to
varicosity (§ 176), and we may easily recognise their axis cylinder. Their
diameter may be roughly estimated
at from 0'0029 to O0090 mm., show-
ing, that besides very fine elements,
broader ones also exist. It appears
beyond doubt, further, that these central
fibres divide, although we are confined to
conjecture at present as to the frequency
of the occurrence.

Passing on to the arrangement of the
nerve fibres in the white columns of the
cord (fig. 557), we have to discriminate
between bundles which hold a longitu-
dinal, a horizontal, and an oblique course.
The greater proportion of fibres belong to
the first of these classes (I, tn, n], and are
often unmixed with bundles having any
other direction. Their course in the
peripheral portions of the cord is regularly
parallel, while in the vicinity of the grey
matter they generally may be observed
to interlace, and to be collected in small
fasciculi.

Further, and in this we have probably
an important physiological fact, certain
regular differences in the diameter of those nerve fibres of the white
columns are manifest.

In the first place, the more internal, lying close to the grey matter,

Fig. 556. — Different kinds of nerve fibre,*,
f, g, h, central ; the fibre g, as axis cylin-
der, is continuous above, with the pro-
cess of a ganglion cell.

578

MANUAL OF HISTOLOGY.

are remarkable for their small diameter, as compared with their fellows
situated more externally. One spot in particular presents very fine fibres,
namely, close to the inner angle of the lateral column, where the anterior
and posterior cornua meet.

Very characteristic differences in diameter are also apparent, if we com-
pare the chief masses of fibres of the various columns. The anterior (/)
possess the broadest, and consist principally of such. Those bundles of the
lateral column in the vicinity of the grey matter are made up of very fine

elements. Further out to wards
the periphery a stronger series
is to be found occurring with
great regularity (m), and in-
termixed more externally still
with small fasciculi of finer
fi brillae. The fibres of the pos-
terior column, compared with
those of the anterior, are dis-
tinctly smaller in diameter.
But in the bands of Goll we
meet with the most delicate
filaments of all disposed with
the utmost regularity.

Let us now turn to the
transverse and oblique sys-
tems of fibres coursing through
the white columns.

These, without counting
the elements of the two com-
missures, consist of the root-
bundles of the spinal nerves
(i, k) emerging from the grey
cornua, and intersecting the
longitudinal bands of fibres
of the white substance. But
it is only the posterior sys-
tems of fasciculi that run
really horizontally, the motor root-bundles take an oblique course.

The anterior or motor roots pass through the white substance in several
fasciculi, and with a tolerably straight course, separating the anterior from
the lateral columns. In this way they arrive at the anterior cornu still
in the form of broad fibres, and then break up into delicate elements,
which radiate in all directions, and in various planes, forming at the same
time numerous loops. Many take their course along the surface of the cornu
inwards, in an arch towards the anterior longitudinal fissure. Others,
again, are directed outwards towards the boundary of the lateral column,
turning round again and running inwards. Other bundles, again, may be
followed directly backwards as far as the base of the posterior cornu.

In order the better to understand their further destiny, let us accom-
pany these nervous fasciculi into the anterior cornu, and in the very first
place inquire into the complicated structure of the grey matter. '

In the delicate spongy mass, of which its sustentacular tissue is com-
posed, we see, in the first place, an inextricable maze of fine and extremely
delicate nerve filaments. Then, in the anterior cornu large multipolar

Fig. 557. — Transverse section through the under half of the
human cord (after Deiters). a, central canal ; 6, anterior;
c, posterior fissure; d, anterior cornu, with large ganglion
cells; e, posterior cornu with smaller; /, anterior white
commissure; g, sustentacular substance around the cen-
tral canal; h, posterior grey commissure; i, bundles of
the anterior, and k, of the posterior spinal nerve roots;
I, anterior; m, lateral; n, posterior column.

ORGANS OF THE BODY. 579

ganglion cells (d) are ooserved, imbedded in the sustentacular substance
of the part. These are not unfrequently tinged with brown pigment,
and vary considerably both in shape and in the number of their pro-
cesses. They are specially numerous at the apex of the anterior cornu,
where they usually form several dense clusters as it were. Here they are
separated from one another by interposed broad nerve fibres. Other
scattered multipolar cells, however, are met with singly, and especially
towards the surface of the grey substance. In the most internal portions
of the cord also, near the axis, as also at the base of the posterior cornu,
we find them still presenting precisely the same essential characteristics,
though decreased in size. .

The numerous processes of these ganglion corpuscles spread them-
selves out in all directions, and, as a rule, are soon lost to view by dipping
into other planes. As observed by Deiters, whose statements we here
follow in regard to many points, these processes may penetrate into the
radiating septa of connective-tissue running through the white substance;
others, also, may be regularly looped around bundles of nerve fibres in
certain cases (Clarke, Deiters).

These groups of multipolar ganglion cells have been very commonly
described as connected with one another by means of some of their rami-
fications, and great stress has been laid upon the importance of the latter
as commissures. It cannot be denied, however, that a deplorable misuse
has been made of this supposed existence of connecting fibres (fig. 305, p.
314). and it is only extremely rarely that a perfectly unmistakable view can
be obtained of them. Thus, in the works of many authors it is openly con-
fessed that, with all their efforts, they were never successful in obtaining a
sight of anything of the kind (Goll, Koelliker). Others even deny the
existence of such commissures altogether (Deiters). Others, again, are
able to state that they have observed them, but in rare instances (Reissner).
Our own experience coincides with that of the latter. Even Dean, a very
sound observer, who is, notwithstanding, somewhat too profuse with such
commissural processes, only speaks of them as exceptions.

A second widely received axiom in the anatomy of the spinal cord, is
that other processes of the ganglion cells become the axis cylinders of the
nerve fibres of the anterior roots. This also is asserted on many sides
with great certaintj1- to be quite easy to see, whereas it is a matter of the
greatest difficulty in reality to obtain even one clear instance of it, some
observers honestly confessing their ill fortune in this respect (Goll). As
a rule, under favourable conditions, one such process may perhaps be
observed uniting with one of the motor root-bundles (Clarke, Dean, Ger-
lach, Frey}.

Deiters, a recent and very thorough investigator, has added much to
our stock of knowledge on this very abstruse subject of the relations of
the central ganglion cells. We have already referred to his important
and repeatedly confirmed discovery (§ 179), that the ramifications of the
ganglionic bodies are of two kinds (fig. 558). In the first place, wide
branching processes of protoplasm (b) present themselves, and then for
every cell another smooth undivided one (a), the axis cylinder process.
This observer, nevertheless, states that only in exceptional cases was he able
to follow up the latter for any distance in a section of the spinal cord.

As may be seen in our plate, there also spring (usually at right angles)
from the broad protoplasm processes of the cell, a number of other very
delicate fibrillae. These Deiters regards as a system of secondary axis

580

MANUAL OF HISTOLOGY.

cylinders for the most delicate nerve fibres, as we have already briefly
stated (p. 315). But probably the end filaments of all these tree-like
processes eventually acquire the same constitution.

The fact that both species of processes, namely, the branched proto-
plasm arid the axis cylinder, may be observed to be marked with fine
lines, indicating fibrillation (Schultze), has been already alluded to (p.
316, fig. 308).

The cells also situated close to the central canal, and those as far back

Fig. 558. — Multipolar ganglion cells from the anterior tornu of the spinal
cord of the ox. a, axis cylinder process ; 6, finest filaments springing
from the ramifying protoplaspi processes.

as the base of the posterior cornu, present the same remarkable structure
recognised by Deiters. The destiny of these " protoplasm processes."
however, is by no means settled as yet. According to Gerlacli they first
break up into a delicate, dense network of nervous nature, from which
the nerve fibres then spring, or (if we prefer the converse) into which
they sink after previous ramification.

Going further backwards still, regularly into the posterior cornu (fig.

ORGANS OF THE BODY. 581

557, Z), we encounter smaller cells, in many cases fusiform and of delicate
consistence. In them also one process becomes an ordinary, though thin
axis cylinder, beside which may be seen again ramifying protoplasm pro-
cesses with lateral derivation of the finer axis cylinders of the second
order. In size and shape these cells also vary considerably, larger
examples resembling in a great measure those of the anterior cornu.
These corpuscles of the posterior cornu have been set down as the source
of the fibres of the sensitive roots, and been designated as sensory elements,
although at present we are possessed of no really complete proof of the
correctness of this view: Gerlach reckons them, moreover, among the
motor ganglion corpuscles.

At the base of the posterior cornu, internally, almost throughout the
whole length of the cord, other small groups of cells are to be seen (the
pillars of Clarke, or nuclei of Stilling, according to Koellilcer). The
elements, collected here, are of medium size, round, and ramifying. Very
little is as yet known about them. According to Gerlach, further, they
are not possessed of an axis cylinder process. Their ramifications merely
sink into the dense neural network of the grey substance.

The proper ganglion cells of the posterior cornu possess, as a rule, in
the opinion of the last-named observer, processes only, which merge into
that nervous reticulutn just spoken of. From the latter, then, the sensory
fibres of the posterior roots arise.

from all this it would appear that the mode of origin of the motor and
sensory nerve fibres is entirely different.

The delicate neural net-work alluded to is only observed to be absent
in the immediate neighbourhood of the axial canal, and in the substantia
(jelatinosa of Roland. It may be easily distinguished from the elastic
reticulum of the neuroglia by certain reactions according to Gvrlach.

§ 294.

Turning now to the posterior roots of the cord (&), we find far greater
complication than among the motor bundles of the spinal nerves. Our
knowledge, therefore, of the nature of their arrangement is necessarily
more scanty than of the latter. The remarkable diminution, besides, in
diameter which the sensitive nerve fibres undergo on entering the grey
matter, renders the tracing of them very difficult.

It is stated by some (Koelliker) that the external portion of the pos-
terior root-bundles passes directly through the posterior column into the
grey substance. Another, and moreover larger part is said, on the other
hand, to pursue a rather devious curving course through the hinder
column, bending round subsequently in order to pierce from the side the
convex border of the posterior cornu, which is turned towards the middle
line. From this the fasciculi advance towards the anterior cornu, passing
partly into the anterior commissure, and partly in among the posterior
group of motor ganglion cells ; or, again, penetrating at times as far as the
anterior portion of the lateral column, where they are lost. The first-men-
tioned bundles are said to pass forwards, partly as separate longitudinal fasci-
culi, tending at the same time with radiation towards the centre, in order to
arrive at the pillars of darkens they are called, without becoming connected
with cells. Some of them reach the anterior cornua and commissure.

Commenting on these statements, Deiters showed later that it is
always the greater part of the posterior root which takes this curved
course through the posterior column, and enters the cornu from it. Here

582 MANUAL OF HISTOLOGY.

we see the substantia gelatinosa of Roland traversed in its whole circum-
ference by separate fasciculi of very delicate fibres, which advance later
into the base of the posterior cornu in part, or, taking another direction,
enter the pillars of Clarke. Other bands of fibres may be observed to
pass forwards through the latter, disappearing eventually in the grey
matter beyond. Others, again, are said to enter the posterior commis-
sure, and many, probably, the grey matter of the anterior.

So far, then, it appears at least possible, that all the fibres of the
posterior root penetrate into the grey matter. And in that they here
probably pass between sensory ganglion corpuscles, we might expect a
(direct or indirect) connection with the latter. An immediate turning in
of a portion of the posterior root into the posterior column in order to
pursue a course towards the brain (" sensory fibres" of Schroder van der
Kolk) appears for many reasons very unlikely.

According to Deiters the three white columns — mainly composed of
the conducting portions of the cord — may be regarded as springing from
the grey matter, and the system of the ganglion cells as interpolated
between them and the roots of the spinal nerves.

Accepting this as correct, the ganglionic cell system would appear to
possess the significance of a provisional central point, from which the
neural tract, altered in direction, and in all likelihood simplified, takes
its course onward to the cerebrum. It must, however, be designated as a
mere point of histological dogma if all the fibres of the roots be stated to
have such a connection with ganglionic corpuscles. Whether the very
fine protoplasm processes of the latter, discovered by Deiters, are commis-
sures between the ganglionic cells ; whether after further isolation, and
increase in breadth, they become the axis cylinders of the nerves of the
white column's ; whether for the formation of one of the latter axial
structures, several of these very delicate fibrillae first combine, or whether,
as Gerlach maintains, the latter form a network of filaments of the most
extreme tenuity, — are all questions to which science is unable at present to
give satisfactory answers/ The same want of facts is felt in regard to the
existence of a connection between motor and sensitive cells.

It is generally supposed that the anterior columns serve as conductors be-
tween the motor nerves and the brain, and the posterior between the latter
and the sensory nerves, while the lateral cords partake of the nature of both.

We shall now conclude this extremely unsatisfactory description with
a brief mention of the two transverse commissures of the spinal cord.

If we examine the most anterior of these bands (/) closely, we shall
soon convince ourselves that a number of genuine nerve fibres exist in it,
enclosed in sustentacular connective-tissue, and intersecting each other at
various angles. In the medulla spinalis of the calf and ox, in which the
relations of parts may be very clearly seen (Deiters), the transverse inter-
secting bundles advance even into the white substance of the anterior
column. They arise in the grey matter on one side, and after descending
and again ascending to a certain extent in their course, arrive in the
fibrous substance of the anterior column on the opposite side. No con-
nection with ganglion cells can be demonstrated with certainty. Many
have argued from this a total decussation of the motor nervous tracts in
the spinal cord ; but, perhaps, without sufficient grounds. At certain
points, also, in the grey portion of the anterior commissure, fine nerve fibres
may be observed to pass across from one side of the cord to the other.

In the posterior commissure (h), likewise, we have a connective-tissue

OKGANS OF THE BODY.

583

framework, intersected by a number of nervous bands, of great fineness
however. The latter, it is stated by some, may be seen to be connected
in part with the lateral columns, in part with the posterior or sensitive
nerve roots, and in part to be lost in the grey substance at the junction of
the anterior and posterior cornua.

§295.

"We. come now to the consideration of the medulla oblongata, whose
complicated structure involves us in far greater difficulty even than that
of the medulla spinalis. The earlier investigations of Stilling, Schroder
van der Kolk, Koelliker, Lenhossek, Clarke, and Dean, all led to different
conclusions. But considerable light has since been thrown upon the
subject by Deiter's observations, and later still by Meinert's studies. •

In order to recall to the mind of the reader the rough anatomy of the
medulla oblongata, it may be remarked, in the first place, that this con-
necting link between cord and cerebrum has one of its numerous pecu-
liarities impressed upon it through the central canal. The latter, namely,
opens out gradually into the sinus rhomboideus or calamus scriptorius, and
is continued as the fourth ventricle upwards. From this alone it is evident
that a most essential change in position of the various columns and collec-
tions of grey substance must take place ; parts situated close to the central
canal, at a lower point on the cord, must now be displaced laterally.

But while this spreading out takes place on the dorsal aspect of the
cord, the anterior fissure begins to close in to form the raphe (fig. 559, r).

Besides these changes
we now remark a num-
ber of different parts
visibly distinct from one
another even externally,
and known by special
names. At either side
of the anterior median
line the pyramids, with
their remarkable decus-
sation, are first seen.
Then external to them,
and bounded on both
edges by ascending
fibres, the (inferior) oli-
vary bodies appear. Ad-
joining these we next
observe the so-called la-
teral columns (funiculi
laterales), and behind
them (later on quite ex-
ternal) the corpus resti-
forme of each side, or
funiculus cuneatus, witli
the /. gracilis in the cervical portion of the cord, — a prolongation of the
band of Goll.

The medulla oblongata is covered above and anteriorly by the pans
Varolii, and at either side may be seen to be connected with the cerebellum
by means of thick cords known as the crura cerebelli. These may be
33

Fig. 559. — Transverse section of the medulla oblongata (after
Dean). R, raphe; 0, olivary bodies; //, hypoglossus; and V
vagus; r, posterior cornu; a, arched fibres; 12, hypoglossus
and 10, vagus nerves.

584 MANUAL OF HISTOLOGY.

divided into two portions, namely, the crura cerebflli ad mcdullam oblonga-
tnm and adpontem. The pedunculi cerebrii connect it with the cerebrum.
Finally, numerous nervous trunks spring from the medulla oblongata.

Turning now from this mere outline sketch to the structure as seen with
low magnifying powers, the full peculiarity of the medulla oblongata soon
strikes us.

The cornua of the central grey mass, as found in the medulla spinalis,
become rapidly changed here, the alteration of shape commencing at the
point, of junction of anterior and posterior cornu, and spreading from
thence further and further. Instead, namely, of the continuous grey sub-
stance of another part of the cord, the cineritious matter here assumes
the appearance of a series of bands or network, through which nerve
fibres take their course (formatio reticularis).

This metamorphosis then gradually extends, affecting eventually the
white columns also almost throughout the whole medulla oblongata.

Here and there, however, masses of grey matter still remain undis-
turbed, which are known as the nuclei of the medulla oblongata; these
give rise to further peculiarities.

Such nuclei are of two kinds. From one set of them the nerves
springing from the medulla oblongata seem to take their rise primarily :
these are the nerve nuclei of Stilling. A large number of them may be
recognised, as we shall see later on. They have nothing absolutely new
in them as compared with the spinal cord, and are equivalent to the
sources of origin of the spinal nerves.

But in addition to these, we meet with collections of ganglionic matter
presenting other characters. These have nothing to do with the origin of
peripheral nervous tracts ; they seem rather to be the points at which the
fibres and cords of the medulla oblongata end provisionally, previous to
their becoming changed both as to number of fibres and direction, and
making their way into the brain.

Among these specific nuclei, as we shall call them for shortness' sake,
may be numbered, in the first place, the inferior olives (olivary bodies, in
a word), with the accessory olives; then the superior olives, formerly
erroneously held to be an upper nucleus for the trigeminus by Stilling, and
a grey nucleus of considerable size imbedded in the lateral column, and
named by Schultze the nucleus of Deiters ; then, again, the pyramid nuclei
and so-called ganglia post-pyramidalia of Clarke, situated in the posterior
columns ; and further, the special grey masses of the pons Varolii. Taking
a still wider view with Deiters, we may include here the corpus dentatum
cerebelli, the grey collections in the interior of the crura cerebelli, as well
as those constituting the greater part of the corpora quadrigemina.

The bundles of white fibres, then, ascending from the medulla spinalis,
although they may be found again in the medulla oblongata, preserve no
longer their original uniformity of direction, but pursue, in many cases, a
totally different course.

Besides the latter fasciculi, there appears in the medulla oblongata
another very peculiar and complicated system of nerve tubes, — that of the
transverse, arched, and circular fibres (a, a). This was named, many
years ago, the zonal by Arnold. In the raphe a very complex group of
these intersecting fibres exists, but grey matter presents itself here also.

If, in addition to all this, we remember the root fibres of the afferent
and efferent nerves, we cannot but be struck with the truly labyrinthine
complexity of the medulla oblongata.

ORGANS OF THE BODY. 585

§ 296.

Let us now endeavour, as far as the scope of our manual will permit, to
clear up some of the difficulties connected with this most complicated
arrangement of parts in the medulla oblongata.

And first, as regards the grey substance.

In the upper portions of the spinal cord we may remark, in transverse
sections, that at the external angle of contact of the two cornua, at one
particular spot, the grey matter is prolonged outwards into a pointed
process. This has been named by Jacubowitsch the lateral accessory
cornti, and by Clarke and Dean the tractus intermedia -later alls. It
attains, in its passage into the medulla oblongata, a higher degree of
development, and assumes, at the same time, a decidedly retiform appear-
ance, bands of fibres from the lateral columns occupying its meshes. We
shall see later on what great importance this lateral region of the medulla
oblongata possesses, being, as it is, the origin of a special system of nerves
commencing with the spinal accessory.

This is the beginning of the fonaatio reticularis.

Advancing further through the medulla oblongata towards the brain,
we find this reticulated and banded mass encroaching more and more
upon the anterior and base of the posterior cornu. This change gradually
advances so far that the whole of the upper portion of the medulla may
be regarded as a mesh work of grey matter, traversed by bundles of white
nerve fibres. The grey substance is, in fact, spread out almost to the
periphery, and is connected with the grey nuclei situated there. From
the fact, however, that the most internal portions of grey matter, i.e.,
those originally surrounding the axis canal, remain for the most part
unchanged, they may present an appearance liable to deceive, namely, as
though they alone were the prolongations of the cornua of the spinal cord.

That in this very extensive band work of grey matter, as well as in the
nuclei, we should encounter ganglion cells of the greatest variety of form,
and in certain cases of remarkable size, with primary and secondary axis
cylinders, will excite no wonder. And that the tracts of this grey reti-
culum should also give origin to part of the cranial nerves might likewise
be expected.

The reader will also understand very easily, from the foregoing descrip-
tion, that the posterior cornu suffers the most displacement from the
opening out of the central canal, and that it must now lie much more to
the side than formerly.

We have already mentioned, in the preceding section, the separation of
the posterior band of Gall, and its transformation into ihefuniculnsgracilis.

In it likewise, and about it, the grey reticulated mass becomes more and
more expanded, pressing down the remainder of the posterior column. Thus
the fourth ventricle obtains a lining of grey matter almost over its entire
floor. The suste'ntacular substance, also formed more exclusively of connec-
tive-tissue, which surrounded the central canal, experiences here a great
increase in quantity likewise, and plays, later on, an important part in the
fromation of the aquceductus Silvii, the third ventricle, and infundibulum.

Leaving for the present the grey matter of the medulla oblongata, let
us now take a preliminary survey of another very important series of
parts, let us inquire into the origin of the ten cranial nerves.

A most important discovery was made in regard to these by Deiters.
Besides the two modes of origin, corresponding to the anterior and pos-

586 MANUAL OF HISTOLOGY.

terior roots of the spinal nerves, the medulla oblongata was found by him
to possess an additional one, namety, from a third lateral tract. This
commences so low down as the upper -part of the spinal cord (with the
farther development of the so-called lateral accessory cornu) as a narrow,
separate, nervous bundle.

To these three systems of roots all the nerves of the medulla oblongata
may be referred.

(a.) From the lateral system several nerves spring. The first of these is
the accessorius, which is soon followed by the vagus and glossopharyngeus.
This place of origin of the lateral system is originally nothing but a
special division of the anterior cornu for the accessory nerve. To this
there is soon added a portion of the posterior sensitive cornu (which may
be followed up as far as the pons), so that the nerves springing from this
lateral part may be of mixed nature.

The facialis and acusticus also, as well as the anterior root of the
trigeminus, take their origin likewise from this lateral tract of the
cineritious substance. This surprising relation, however, is explained
by the fact, that each of them again splits up into a sensitive portion
(acusticus), and a motor (anterior root of trigeminus and facialis).

(b.) The sensitive portion of the trigeminus, on the other hand, is
derived from the posterior root system. The fibres of the latter are like-
wise collected, from the first spinal nerves on, into longitudinal tracts,
which do not, however, leave the medulla oblongata as separate sensitive
bundles, as in the cord, but unite to form this root.

(c.) Besides the hypoglossus, the abducens, trochlearis, and oculomo-
torius, all correspond to the anterior spinal roots.

As to the nuclei, already mentioned, of the numerous nerves arising
here, those of the hypoglossus and accessory first appear most inferiorly,
appertaining to the deepest portion of the anterior cornu, and situated in
the neighbourhood of the central canal. These are collections of multi-
polar motor ganglion cells in the cineritious substance, which, as has been
already mentioned, is split up here and reticulated. Then there make
their appearance successively on the floor of the fourth ventricle and
around the aqueduct of Silvius, similar spots for the vagus, glossopharyn-
geus, abducens, trochlearis, and oculomotorius.

Let us turn again, for a few moments, to the nucleus for the hypo-
glossus. Its large multipolar ganglion cells present, like those of the
anterior cornu of the grey matter of the spinal cord, protoplasm ramifications
and an axis cylinder process, which probably becomes eventually a fibre
of the hypoglossus (Gerlach). It was at one time generally supposed that
a complete decussation of the hypoglossal fibres took place here. This
is, however, more probably only partial (Clarke, Dean, Deiters). The
arrangement, as found by Gerlach, is as follows : — In the first place, a set
of delicate fibres, lying posteriorly, passes across from one hypoglossal
nucleus to the other, and may be regarded as commissural between the
nuclei themselves. Other fasiculi, again, lying more anteriorly at the
bottom of the raphe, and of greater diameter, decussate, as proper roots of
the hypoglossal nerves, with the fibres of the opposite side, pursuing their
course in the trunk of the side opposite to that on which they took origin.

The external portion of the posterior cornu likewise remains almost
unchanged in its grey substance, and the connection between it and the
motor nucleus of the middle line is still continuous and diffuse. It gives
origin to the sensitive trigeminvs root and the accusticus, which does not,

ORGANS OF THE BODY. 587

as was formerly supposed, spring from a collection of large cells in the
crura cerelelli ad medullam oUongatam, but rather from small cells of the
posterior cornu and of the raphe (Deiters). It likewise gives origin to
the sensitive portion of the vagus and glossopharyngeus.

Finally, there still remain in the reticulated grey substance some
remote unbroken masses. Towards these the motor portion of the trige-
minus advances, a part of whose root constitutes what is known as the
" sounding-rod " (Klangstab) of Bergmann. (Stilling, Lenhossek, Deiters.}
Further, the facial nerve arises in this neighbourhood. Upon it a sudden
bend was discovered by Deiters at a spot corresponding to the emminentia
teres in the fourth ventricle. This observer does not regard the nucleus
of the last-named nerve as situated near the abducens, as his predecessors
believed it to be (Stilling, Clarke, Dean), but rather in the vicinity of
the motor nucleus of the trigeminus. Finally, the motor portion of the
vagus, discovered by Deiters, takes its origin here also.

§297.

Turning now to the question : What becomes of the continuation of
the three columns of the spinal cord on arrival at the medulla oblongata 1
the first point that appears quite evident is that a prolongation of all the
nerve fibres of the whole cord into the latter cannot take place. We
have to do here rather with a continuation of the fibres in question under
a simplified form, and in reduced number, — a modification which is most
probably effected through the interposition of ganglion cells in a manner
similar to that found in the spinal cord.

The decussating portions of the pyramids were formerly supposed by
Schroder van der Kolk to be derived from the anterior columns, but
erroneously, for the latter particularly, preserve for a considerable distance
into the medulla their original straight course and shape. It is true,
that in the lower portion of the latter they become displaced by the
extrusion of the decussating fibres of the pyramid; but when these cease
to pass across, they assume again their old position, and continue their
course augmented by fibres of the hypoglossus, and probably also of the
vagus, as longitudinal cords lying at either side of the raphe, and extend-
ing far under the pons.

But the anterior column becomes considerably modified during this
course. In the first place, it is traversed by circular fibres springing for
the most part from the posterior columns. Again the grey substance
commences even very early to make inroads into it. It is characterised
here, as in the spinal cord, by the great breadth of its nerve fibres.

Beneath the pons Varolii, however, fine and also very delicate fibres
begin to take the place of the latter. Here we observe an interpolation
of ganglion cells in the usual way, so that the apparent continuation of
the anterior column under the pons is in reality a second system of fila-
ments springing from these, and passing into the cerebrum, and partly
also into the cerebellum.

The lateral columns, which have likewise, though incorrectly, been
described as the source from whence the decussating fibres of the pyramids
spring (Koelliker, Lenhossek) form the funiculus lateralis of the medulla
oblongata, and extend, at least in part, probably as far as the cerebrum.
They, too, are affected by the general complication of the medulla oblongata.

The reader has not yet forgotten the formatio reticularis appearing in
the angle of junction of the two cornua of grey matter. A part of this is

588 MANUAL OF HISTOLOGY.

regarded by Deiters as derived from a change in the lateral column, that
is to say, some of the fibres of the latter terminate provisionally in the
cells of this formation. — The fibres passing off from these ganglionic
bodies centripetally we shall meet again in dealing with the formation of
the pyramids. — The remaining portion of the lateral column advances
now unchanged for a certain distance towards the brain. It begins, how-
ever, very soon to be encroached upon by the reticulated cineritious mass
already alluded to ; besides which, a special nucleus, named after Deiters,
is developed in the lateral column as mentioned before, containing some-
what small ganglion cells. Like the other so-called specific nuclei of the
medulla oblongata, this may be regarded as a central point for arrival of
one and departure of another system of fibres on its way to the brain.
The first of these belongs to the lateral column, while the latter forms a
zonal system of fibres, the stratum zonale Arnoldi, which pursues its
course into the cerebellum. Whether other efferent fibres preserve the
original direction of the lateral column towards the cerebrum is still an
undecided question.

Other collections of ganglionic substance in the neighbourhood of
the lateral columns, are the inferior olivary bodies, which also receive, in
all probability, some circular fibres from these. Again we meet with
cineritious substance in the accessory olive, and at the point of departure
of the cms cerebelli ad medullam ; also in the superior olivary bodies.
The latter appear, moreover, to be fed by fibres coming from the lateral
column, and to give off a zonal system of fibres which (lying in the lower
mammals anterior to, and in man within the pons) is known as the corpus
trapezoides.

As regards the posterior columns, they were for a long time supposed,
and again incorrectly, to pass directly into the cerebellum as the crura cere-
belli ad medullam. The direction of both these sets of fibres, it is true, is
the same, and this explains the mistake; but the fibres of the posterior
columns are in their farther course replaced by quite a different species.

From the posterior column of the spinal cord, as we have already seen,
its internal portion becomes distinct as the band of Goll, which then forms
the funiculus yracilis of the medulla, while its remaining portion is known
as the funiculus cuneatus in its further course.

Both these bands become mixed internally with grey matter (ganglia
postpyramidalia of Clarke], and increase consequently in size to a con-
siderable extent. Here also the white substance of the posterior column,
consisting of fine nerve tubes, diminishes in a corresponding degree more
and more, coming to an end provisionally in the grey matter just mentioned,
as well as in the adjacent parts of the posterior coniu. From this it
again starts in the form of a system of circular fibres. Thus it may be said
that the posterior column disappears entirely as regards its original position.

The fibres arising from it secondarily appear destined to augment in
part the pyramids (see below), but also to enter partly and gradually into
the formation of the crura ad medullam (seemingly a direct continuation
of the posterior columns). Again, some of them penetrate into the olivary
bodies, decussating to arrive at the opposite side, none passing straight
into the olive of their own half. These fibres thus constitute the chief
source of supply to these specific nuclei of the medulla oblongata.

The pyramids, remarkable for the fineness of their nervous tubes, are,
according to Deiters, no direct continuation of the white cords ; they
represent rather one of those numerous secondary systems of fibres which

ORGANS OF THE BODY. 589

spring from the cells of the forrnatio reticularis, wiiich receives fibres
both from the lateral and posterior cords. This explains the increase in
volume also supervening upon the formation of the pyramids. After
their decussation the latter advance into the brain through the crura cerebri,
strengthened by additional bundles of fibres, but augmented no farther
by grey matter. Here they are said to reach as far as the corpora striata,
nuclei dentati, and even the cortical portion of the hemispheres.

The olivary bodies (i.e., inferior) are, as is well known, very character-
istic organs of the medulla oblongata. Their grey substance forms in
man a peculiar corrugated capsule, the corpus dentatum olivce, which
encloses a white nucleus on all sides except internally. In the spongy
sustentacular tissue of this cineritious substance we find, according to
Clarke and Dean, small yellowish cells from 0*0156 to 0'0189 mm. in
diameter with rounded body, and the so often mentioned two species
of processes. .Between these small bundles of the most delicate nerve-
filaments take their course.

It has been supposed by many that there exists some relationship
between the olivary bodies and the hypoglossal nerves — that they are in
some way "auxiliary organs" for the latter; but this is not the case. It
is true that the roots of these motor nerves, so remarkable for the size of
their fibres, pass by the organs in question, a few even through them in
part, but no connection with their elements takes place.

Deiters' researches, which we here quote, have led him to the conclusion
that those very delicate fibres received into the olivary bodies, to termi-
nate provisionally in their cells, are derived, as has been already men-
tioned, in each case from the posterior columns, each olive obtaining, how-
ever, fibres from both sides of the cord. A new system of fibres then
springs from these cells, which passes partly into the brain, partly into the
cerebellum. Thus we see that the olivary bodies also belong to those
interpolations in the very complicated chain of the central organs, and are
related both to the cerebellum and pons. Besides, they are traversed by
numerous fibres of the circular and transverse systems. Further, they
are embraced round their external border by a set of zonal fibres springing
from the posterior columns. At the summit of the olivary bodies poste-
riorly, the so called accessory olivary nuclei of Stilling present themselves,
having a similar texture to the former, while higher still, above the abdu-
cens and facialis, and external to the first of these nerves, another body
of similar structure is to be found on each side, known as the superior
olive; this is not absent in man, but is buried in the pons. It likewise
possesses a zonal system of fibres. It was formerly supposed to be con-
nected with the facial or acoustic nerves of its own side.

Let us now turn our attention for a moment to the crura or connecting
bands of the medulla oblongata.

The crura cerebdli ad medidlam oUongatam are, without doubt, in part
processes of the latter continued into the little brain. Their fibres consist
for the most part of prolongations to the stratum zonale of Arnold, spring-
ing, in the first place, from the olivary bodies, and probably also from the
nucleus of Deiters in the lateral column, and from the corpus trapezoides.
Meinert, however, states that a sensory band from the funiculus gracilix
and cuneotus passes into the cerebellum, and a motor from the latter
downwards back into the cord again.

The fibre bundles of the crura cerebelli ad pontem possess quite a dif-
ferent significance. Apart from the fact that they connect similar portions

590 MANUAL OF HISTOLOGY.

of the two halves of the cerebellum as commissural systems, they conduct
no new fibres into the interior of the organ, but, on the contrary, convey
fasciculi of nerve fibrils springing from the cerebellum further upwards into
the cerebrum.

Now, it seems very improbable that the whole mass of fibres conveyed
through the first-named crura into the cerebellum, terminate provision-
ally there, to escape again through another set of processes by the last-
named crura. It is far more likely that only a portion of the mass
takes this circuitous route through the cerebellum, while the rest passes
directly into the cerebrum. Thus we have in the cerebellum a most com-
plicated accessory apparatus. Its abscision, moreover, in keeping with
this view, disturbs certain connections to a great extent, but does not
completely put an end to them.

The blood-vessels of the medulla oblongata have the same arrangement
as those of the spinal cord.

As elsewhere, the white substance found in the medulla oblongata is
traversed by an open network of capillaries, whose elongated meshes are
seen according to the direction of the fibres, either in profile, or in trans-
verse section. The collections of grey matter, on the other hand, are
much more vascular, and supplied by a denser interlacement of capillaries.
The very closely intercommunicating capillaries of the cineritious capsule
of the human olivary bodies present a peculiarly beautiful appearance ;
they are partly supplied by vessels from without, and partly by another
set of larger tubes, situated in the white nuclei. We shall speak of the
lymphatics further on (§ 300) in their proper place.

§298.

Turning from the medulla oblongata to the neighbouring parts of the
brain, we find that less and less is known of their structure the farther
we advance.

In the foregoing section we have had frequent occasion to touch upon
many points relating to the pons Varolii and cerebellum, so that they
may now be first described.

In regard to the pons Varolii we have already remarked, in the pre-
ceding section, that in it we have before us collections of grey matter
with the white cords of the medulla passing through it. Further, it con-
tains a series of well-marked transverse fibres.

The cerebellum consists essentially of collections of white nervous
tissue, cineritious matter only presenting itself on the roof of the fourth
ventricle, in the corpus dentatum, the so-called roof nucleus of Stilling,
and in the layer covering the surface of the convolutions.

Into and out of it, as we know, the crura cerebelli ad medullam conduct
bands of fibres of the medulla oblongata. In the same way further ele-
ments leave it through the (§297) crura cerebelli ad pontem. Finally, the
crura cerebelli ad corpora quadrigemina connect the organ with the brain.

The whole of the cerebellum presents, likewise, that very delicate sus-
tentacular connective-tissue alread}' mentioned (§ 119). It is especially
highly developed in the cortical layer.

The nerve fibres of the white substance of the cerebellum are stated to
present a similar arrangement and diameter at almost all points ; the
latter is, on an average, 0'0045, but may range from 0'0027 to 0'0902
mm. (Koelliker).

The cineritious substance is only to be found, in small amount, on the

ORGANS OF THE BODY. 591

roof of the fourth ventricle. Here we encounter ganglion cells of consider-
able size, varying from 0*045 to 0*067 in diameter, and of brownish tint,
disseminated through the white substance (substanfia ferruglnea superior
of Kuelliker).

The nucleus dentatus of the cerebellum is of great interest on account
of its relationship to the specific nucleus of the same name in the olivary
bodies. In its plicated capsule of grey matter numerous ganglionic cor-
puscles of medium size (0*018-0*036 mm.) are to be met with disposed
in three layers, — an external and an internal of fusiform cells, and middle
of multipolar elements. The bodies of these also are coloured, as a rule,
with pigment. Between them a maze of fibres is to be seen.

Our knowledge of the course of the fibres in the cerebellum is at pre-
sent exceedingly imperfect. Nervous bundles of the crura cerebelli ad
med. oblong, are said to advance as far as the crumpled plate of grey
matter of the corpus dentatum, and to terminate in its ganglion cells pro-
visionally. Then, again, efferent fibrous bands are stated to make their
way out of the organ, at that point where the corrugated capsule of grey
substance is imperfect, passing into the crura cerebelli ad, corpora guadri-
gemina (Rutkowsky). The fasciculi of the- last-named crura, however,
have also been described as radiating from the corpus dentatum towards
the surface of the cerebellum; they are said to .connect this cortical layer
with the so-called corona radiata fibres (Stabkranzfaserung) of the hemi-
spheres of the cerebrum (§ 299). But the bundles of fibres of the crura
cerebelli ad medullam ollongatarri are also described as entering the roof
nucleus of Stilling, and spreading from thence to the cortex. Some
speak also of a system of arching fibres here (similar to those we shall
have to consider presently in the hemispheres of the cerebrum), serving to
connect adjacent convolutions of the cortex with one another.

In short, the whole matter is still very obscure.

The cortical layer of the cerebellum has, to be sure, been recently made
the subject of very earnest study, and, to some extent, the older and newer
investigations have thrown a light on the subject.

And first, as regards its coarser structure, it presents two layers, — an
internal of a rusty brown colour, and an external grey. The first of these
is not so deep as the latter.

It was at one time supposed (Gerlach, Hess, Rutkowsky) that the nerves
of the white substance undergo repeated division, radiating at the same
time in a brush-like manner, and forming eventually, with further sub-
division, a retiform plexus of fibres of only 0*0023 mm. in thickness, in
whose course the numerous nuclear structures of the rust -brown layer are
interpolated (Gerlach). This view, however, has not since been confirmed.

The rmt-brown stratum, which has a thickness of from 1 to 0*5 mm.
(least at the bottom of the sulci), is by no means sharply defined against
the white matter beneath it. In it we find densely aggregated those
nuclear structures already mentioned, which also occur in the white
stratum (the "granules" of Gerlach). These are of rounded form and
diameter of about 0*0067 mm. on an average ; each presents also one or
two nucleoli (fig. 561, below). Whether we have before us cells or nuclei
here is a point very difficult of decision. One fact, however, in regard to
them can hardly escape even the superficial observer, namely, that they
possess considerable resemblance to certain elements of the retina, i.e., those
of the granular layers of the latter.

Many of these elements present very fine filiform processes, of which

592

MANUAL OF HISTOLOGY.

two are often exactly opposite one another. As a rule the latter are only
visible for a very short distance from their point of origin.

Two species of these elements are recognised by Schulze. In the first
place, smaller ones of O0067 mm. in diameter, and smooth edged, which,
on treatment with bichromate of potash, acquire great brilliancy of out-
line, and are seen to possess one or
two small nucleoli and the filaments
just mentioned; in the second place,
larger elements, 0'0090 mm. in dia-
meter, which have distinct nucleoli.
These show no polar filaments, but
have frequently attached to them
small shreds of the fibrous sustenta-
cular substance, to which latter they
probably belong, while the first
form of cell is, by this observer, set
down as nervous, and analogous to
the granules of the retina.

There is, however, great differ-
ence of opinion upon this point ;
and some very weighty authorities,
among whom Koelliker, Stieda, and
Deiters may be mentioned, look
upon the whole as part of the spongy
tissue of the sustentacular substance,
and deny any connection with nerve-
fibres ascending from below. This
view we ourselves also are inclined
to regard as the most correct.

A set of small ganglion cells has
been described by Koelliker and
Schulze as occurring at the border
of this stratum, which give off a
a number of ramifying processes ;
and Meinert speaks of a layer of
tangentially coursing nerve fibres,
with similarly arranged fusiform
cells here. We have already al-
luded to this above.

Turning now to the most external
of these two cortical strata, the grey
or cellular layer, as it is called, we
find its most striking elements to be
large ganglion cells (fig. 560), dis-
covered many years ago by Purkinje.
They lie chiefly in the inner portion
of the stratum, but are by no means abundant (fig. 561), and form but a
single row. Internally they give off one process only of a different appear-
ance from themselves (fig. 560, b). According to Gerlach this breaks up
into the fine network of the rusty-brown layer, already alluded to, with its
interpolated nuclei, which would be a very peculiar arrangement of the
nervous fibres. But although others have expressed their concurrence in
this view of Gerlach' s (Hess, RutUowslnj], it must, nevertheless, be declared

Fig. 560. — A ganglion cell of Purkinje, from the
human cerebellum, a. cell; 6, pointed pro-
cess; c, anller-like ramifications, with delicate
branches, /; d, axis cylinder; e, nerve fibre
(d and e, completed from the dog).

ORGANS OF THE BODY.

593

as incorrect. The process mentioned remains undivided (d), and, becom-
ing clothed with a layer of medullary substance (e), may be regarded as
the ordinary axis-cylinder process of the central ganglion cells (Deiters,
Koscliewnikoff, Hadlich, Boll).

Externally — that is, directed towards the surface of the cerebellum —
these large ganglion cells send off
several (generally two) character-
istic protoplasm processes through
the so-called "molecular layer of
Hess" These then gi^e origin to
regular systems of branches, thin
at first, and running down to the
most delicate terminal filaments
finally (c, c, /, /). Taken as a
whole, they present somewhat the
appearance of a stag's antlers. Com-
misstiral union of one cell with
another, by means of these pro-
cesses, does not occur. On the
contrary, the discovery of Hadlich
(if it be confirmed) is of great
interest (fig. 561), namely, that
these finest filaments of the arbo-
rescent system of ramifications (a)
bend over on arriving near the
surface of the cortex in shorter or
longer arches, and run inwards
again through the grey layer in the
direction of the granular layer of the
rust -brown stratum. Before they
reach this, however, they sink into
a very delicate filamentous network,
according to Boll, which is spread

Fig. 561. — Section through the cortex of the
human cerebellum (after Hadlich). Two gan-
glion cells of Purkinje; below them a part of
the granular layer. At r, sustentacular fibres;
a, the looped filaments of the delicate ramifica-
tions of the ganglion cells; c, finest tangential
nerve fibres.

through the whole of the grey
matter. This network would cor-
respond, then, to that described by
Gerlach in the interior of the spinal cord. From it then, in the granular
layer stronger nerve-fibres are said to arise.

The nerve fibres of the white internal portion of the cerebellar convo-
lutions pass outwards to the grey covering layer, interlacing at the same
time. They pass into the rust-brown layer, radiating like hairs of a paint-
brush. Here most observers state (we believe correctly) that they undergo
extensive subdivision, so that only very fine twigs reach the under surface
of the large, remarkably formed ganglion cells. They appear at last to
terminate in the fine neural network of Gerlach. The axis-cylinder
processes, on the other hand, of these strange ganglion corpuscles pass
inwards towards the white substance.

The nervous plexus of the rust-brown layer is continuous, with rapid
diminution in the thickness of its fibres through the internal third of the
molecular layer.

The framework of the grey layers is formed of ordinary spongy susten-
tacular tissue (Koellilcer, Rutkotpsky), with those scattered nuclear elements
of which, according to Schulze, two kinds may be distinguished.

594 MANUAL OF HISTOLOGY.

In the outer portion of the cineritious substance is to be be found
another very interesting textural arrangement, again reminding us of the
retina (see below). A homogeneous connective-tissue boundary layer,
lying underneath the pia mater, and corresponding to the grey peripheral
lamina of the spinal cord, gives off internally, converging sustentacular
fibres (fig. 561 r), which may not unfrequently be followed through more
than half the depth of the whole grey matter (Bergmann, Schulze).

§ 299.

There now remain for our consideration a few points in regard to the
histology of the cerebrum.

The pedunculi cerebri, or crura cerebri ad pontem, consist of masses of
nerve-fibres, which pass partly from the medulla oblongata and cerebellum
to the brain, and partly from the latter into the medulla possibly. In
transverse section each crus is observed to be divided into two portions
by a crescentic band of grey matter, the substantia nigra. The most
inferior of these (" the base ") is crescentic, and the upper (" the cap ")
round. According to Meyjiert, it is motor fibres from the corpus striatum
and lenticular nucleus, or nucleus dentatus, which pass through this lower
part of the peduncles serving the purposes of voluntary motion. Through
the " cap," or upper portion, on the other hand, other fibres, arising in
the optic thalamus and quadrigeminal body, descend, which preside over
the reflex motions. Under the microscope the white matter of the crura
presents the ordinary central nerve-tubes and grey ganglionic corpuscles,
with numerous processes, which ramify largely, and pigmentary mole-
cules in their interior (fig. 305, 4, p. 314).

Those structures which go by the name of the cerebral ganglia, namely,
the corpora quadrigemina, thalami optic?', nucleus dentatus, and corpora
striata, have up to the present received but little attention.

The corpora qadrigemina possess, like the thalami, a white layer over-
laid with a zonal stratum of nerve-fibres. Underneath them the crura
cerebelli ad corp. quad, simply pass on to reach the cerebral hemispheres.
They are therefore incorrectly so called, for they are much more crura
cerebelli ad cerebrum. Laterally, there enter the corp. quad from
below the two lemnisci springing from the motor part of the medulla
oblongata, and traceable back to the same. Each of the ganglia sends
off two cords, the quadrigeminal arms, which are said to pass into the
system of the corona radiata. In the anterior of the quadrigeminal bodies
a root of the optic nerve, coming from the corpus geniculatum internum,
is said to terminate. The achievements of histology in this field -are still
very insignificant. Small cells have been recognised in the internal grey
substance with larger multipolar and fusiform ganglion corpuscles. The
latter are to be found in the deeper layers of the anterior bodies about the
aqueduct of Sylvius (Meynert).

The optic thalami, we take it for granted, are already familiar to our
readers as regards form. Their posterior end has received the name of
the puluinar. Internally to it is situated the corpus geniculatum internum,
more posteriorly ; and externally the e.g. externum. Into the latter a
portion of the optic tract passes on its way to the pulvinar. The cap of
the crus cerebri is intimately connected with the thalamus. These are then
the newest views of Meynert ; but some years ago, J. Wagner came to
different conclusions in regard to the optic tract, and they will be probably
modified still by subsequent observations. An abundant corona radiata

ORGANS OF THE BODY. 595

of fibres further springs from the external border of the thalamus. As
to the histology of the part, we possess but very little satisfactory informa-
tion. Cells are to be found here which appear to differ from the large
multipolar elements, most of them being fusiform. The pulvinar presents
nothing remarkable about it. In the external geniculate body the cells
are frequently pigmented ; the internal contains fusiform elements.

We pass on now to the corpora atriata and nucleus dentatus.

Both these present a grey surface. In them terminate fibres from the
bases of the crura cerebri. Externally, both ganglia send fibres tp the corona
radiata (Stabkranz). The grey matter of both ganglia presents for the most
part great uniformity of structure. In it we meet with larger and smaller
multipolar ganglion cells and small elements, measuring 0 '005-0 '01 mm.
The neuroglia is similar here to that in the cortex of the cerebrum.

In respect to the nuclei amygdalce and claustrum we are in want of
trustworthy observations.

Turning now to the coronata radiata, we find that it consists in
the first place of fibres which, without having touched one of those
ganglia, ascend directly through the crura cerebri, and then of the radia-
tions of the ganglionic masses. These great masses of fibres are probably
connected with the intellectual functions.

The corpus callosum, on the other hand, has nothing to do either with
the peduncles of the brain or the corona radiata. ]t is a purely commis-
surai system of fibres, radiating extensively in the hemispheres of the
cerebrum, as also is the anterior commissure. Besides these, there are
well developed systems of fibres which connect various parts of the brain
on the same side, as, for instance, the fibres of the surface which unite
the gyri one with the other "associating fibres."

The white substance of the hemispheres consists of medullated fibres of
about 0'0026-0'0067 mm. in diameter. At the surface only of the larger
ganglionic masses, and towards the cortex is the non-medullated species
to be found.

The nerve-fibres are grouped together in bundles invested with a cover-
ing of connective-tissue cells (Gfolgi, Soil).

The cortex of the hemispheres may be divided into several layers, not
distinctly marked off, however, against one another at all points. Their
number, also, has been variously estimated by several observers, among
whom may be mentioned Koelliker, Stephany, Berlin, Arndt, Meynert,
Henle, and Stieda. This is easily conceivable, and it is probable that it
varies also in the different lower mammals.

We regard the cortex in man as divisible into six laminae, but would
mention that our material has been in the last few years very insufficient.
We were unable to procure brains fresh enough for our object.

(1.) The uppermost layer (Koelliker) consists of a series of horizontal
transverse and oblique fibres, probably of nervous nature.

(2.) The next — the first, of Meynert (fig. 562, ]), is among the mam-
mals deeper than in man, and is composed chiefly of neuroglia with a few
scattered nervous elements. Two forms of the latter have been described
— in the first place, namely, small cells of 0 '009-0 '010 mm. in diameter,
and of polygonal or pyramidal figure giving off processes ; and secondly,
networks of the most delicate nervous fibrillse of unknown nature.

(3.) A layer of crowded small multipolar nerve cells usually of pyra-
midal form (2).

(4.) A deep stratum in which much larger many-rayed ganglion cells,

596

MANUAL OF HISTOLOGY.

^ A ?,Lv? ^'^ITl I*.*

III

0-025-0-040 mm. in diameter,
are met with at wide intervals.
These present roundish or oval
nuclei. Usually from the apex
of the cell one process passes
outwards, and three others
from the broader part inwards.
They may be seen to be of fibril-
lated structure. The middle
one of these basal processes is
in contrast to the others, which
ramify, an "axis-cylinder pro-
cess" (Meynert, Koschewnilcoff),
and is prolonged into one of
the nerve-fibres of the corona
radiata. (3.) The smaller cells
of the third layer are also said
to present the same arrange-
ment likewise.

(5.) A layer of closely packed,
roundish, smaller cells 0*008-
0-010 mm. in diameter, with
hardly recognisable processes

(•i). "

(6.) A lamina, consisting of
fusiform cellular elements, mea-
suring O'OSO, from whose apices
filiform processes spring (5).

These last ramifications are
not supposed to have anything
to do with the corona radiata,
but are connected, in all pro-
bability, with " associating
fibres " of Meynert. The mul-
tipolar ganglion cells of the
fourth layer are stated by this
observer to be motor, the ele-
ments of the fifth resembling
the "granules of the retina"
(see below), possess sensitive
properties. This is all, in our
opinion, purely hypothetical.

A discovery has recently
been made by Gerlach which
seems important. The cortex
of the cerebrum presents,
namely, in the first place, a
wide-meshed network of medul-
lated fibres in whose inter-
stices ganglion cells are situ-
ated. Here we find, besides
that very delicate network of
extremely fine fibres already

ORGANS OF THE BODY. 597

met with in the grey matter of the spinal cord (§ 293). Nay, further,
the ramifying cellular processes are also seen here sinking into the latter.
But though the cortex presents this general plan of structure, there are
nevertheless local deviations from it.

In the first place, at the point of the posterior lobe, in the neighbour-
hood of the sulcus hippocampi (a spot investigated long ago by Clarice}, a
number of anomalous white streaks present themselves in the cortical por-
tion. Meynert regards this part as made up of eight layers. The first
two of these conform to Nos. 1 and 2 of our fig. 562. The third stratum
lacks the large pyramidal cells, but presents in their place granules.
Under these there appear, as fourth layer, those scattered pyramidal
cells already mentioned, but very sparsely and at great intervals from one
another. As a fifth layer, we find granules again, as in the third. The
sixth resembles the fourth in having again scattered pyramidal bodies.
On this there follows another granular layer. The eighth and last layer,
finally, consists of ordinary fusiform cells (fig. 562, 5).

The cornu ammonis presents the same difference of appearance. It
was first studied by C. Kupffer in the brain of the rabbit, and later by
Arndt and Meynert in the human being.

According to the first of these observers, the structure is complicated,
but allied to that of a cerebral convolution. The cornu ammonis presents
under its most superficial layer of nerve fibres another so-called molecular
stratum of grey matter, which contains in its deeper portions a series of
closely-packed ganglion cells, one set of whose ramifying processes is
directed towards the centre, thus constituting a deeper streaked grey
lamina. Under this we next come upon a reticulated, then a second mole-
cular, and finally a stratum formed of closely-crowded " granules."

According to Meynert, the grey cortical layer of the cornu ammonis in
man may be regarded as a thin covering layer without granules. At one
point alone — namely, at the apex of the fascia dentata — do these "granules"
appear in any great abundance.

We turn now to the Iwlbus olfactorins, a remarkable piece of cerebral
substance, but ill developed in man. In many mammals it is, as is well
known, quite hollow. Its walls consist, if we will, of two groups of
laminae, an inner white and an external grey. The latter becomes more
and more highly developed as we approach the ethmoidal cells.

Into the first the root bundles from the neighbouring parts of the brain
enter. Of these there are two — first a strong root coming from the exter-
nal side, of which one-half seems to be a continuation of the anterior
inferior convolution of the brain, while the other thinner portion can be
followed into the corpus callosum ( Walter) ;. second, an internal weaker
root of the bulb, consisting of three bundles of fibres, one from the corpus
striatum, another from the chiasma nervorum opticorum, and the last from
thp pedunculus cerebri. In many points, however, Clarke's views differ
essentially from this sketch.

If we now examine the walls from within outwards, the very complex
structure of the central organs presents itself to us here also.

The cavity is lined with delicate ciliated epithelial cells, whose filiform
root processes penetrate into the strongly developed neuroglia of the sub-
stratum, with its roundish cellular equivalents. This latter is traversed
again at a slight depth by a set of fine longitudinal but medullated nerve-
fibres, which are a continuation of those of the root-bundles. Next to, and
probably derived from them, is to be found a stratum of nervous elements

598 MANUAL OF HISTOLOGY.

arranged in a plexus (Clarke), presenting very fine tubes as a rule, and
nuclear elements of the sustentacular substance between the perpendi-
cularly descending nerve-fibres. The sustentacular tissue presents itself
here in a very pure state, but at the same time, of extreme delicacy. It
contains numerous nuclei, and among them some of considerable size,
which belong, according to Walter, to small bipolar ganglion cells.
Besides this, it presents a layer of large multipolar ganglionic corpuscles,
with widely branching protoplasm processes. The whole reminds- us con-
siderably of the cortical layer of the cerebellum (§ 298). Below, or, more
properly speaking, externally, the walls of the bulb acquire a very obscure
character from the transformation of the grey matter. Here we encounter,
namely, spheroidal pellets of a granular nucleated substance, lying in
spongy tissue, from which the peculiar pale peripheral olfactory fibres are
given off. These we have already alluded to, and shall consider again in
dealing with the organs of smell.

Thepineal gland, or conarium, is a very puzzling organ, which probably,
like cartilage, undergoes early changes. It has been by some supposed to
have some relationship to the lymphatic glands (Henle). It presents in
a connective-tissue framework, roundish, sometimes complete, sometimes
incomplete cavities. These are occupied by two kinds of cellular elements,
namely, larger, provided with long, thick, ramifying processes, forming a
delicate " reticulum," and smaller, which give off processes in the adult,
but not in the infant just born (Bizzozero).

Numerous peculiar concretions occur here also, known as the acervulus
cerebri, a full description of which we reserve for the following section,
where we shall consider them in connection with the choroid plexus.

The hypophysis cerebri has been already disposed of, with the other
members of that obscure group of "blood vascular glands" (§ 238) to which
it belongs.

In respect to the composition of the brain and spinal cord we have
already mentioned all that is necessary to be borne in mind, in the second
part of our work (§ 190). We have also alluded there to the extremely
imperfect state of our knowledge on the subject.

§ 300.

We now come finally to the membranes investing the brain and spinal
cord, of which there are three. In the first place, there is the dura mater
externally, a strong fibrous coat (p. 225) ; then in the middle the arach-
noidea, with all the characters of a serous membrane (p. 226) ; and
finally, tine pia mater, a delicate internal membrane, immediately in con-
tact with the nervous substance of the brain and cord (p. 229).

The dura mater has been already dealt with, as regards its structure
generally, in another chapter. It is rich in elastic fibres. Its relations
to the brain and spinal cord are somewhat different. The latter is con-
tained within it as in a tube, which hangs down in the spinal canal (lined
throughout with periosteum), loose at either side and behind, and only
attached anteriorly by a band of connective-tissue to the ligameiitum
longitudinale posterius. The matter which occupies the cavity so result-
ing is a soft colloid tissue, containing connective-tissue corpuscles and fat
cells. Without taking into account the well-known venous plexuses
traversing it, the latter is rich in small and extremely delicate blood-vessels.

Within the cranium, on the contrar}r, the dura mater is intimately con-
nected with the periosteum, or, more properly speaking, it plays the part

ORGANS OF THE BODY. 599

of the latter with its external portion, which is more vascular and of less
dense texture than the internal laminae. In the spinal cord it is very
scantily supplied with vessels. The dura mater is very rich in lymphatics.
Some of these run along side by side with the blood-vessels, while others
ensheath the latter. It appears very probable, further, that they open
into the cavity between the dura mater and arachnoid. The same seems
to occur also on the external surface of the first-named membrane
(Michel}. As yet no nerves have been found in the dura mater of the
cord, in contrast to that of the brain, which receives twigs from the sym-
pathetic and trigeminus, The mode of termination of these nervous
elements, which have been observed to undergo subdivision, has not yet
been sufficiently cleared up. They appear to end in the blood-vessels and
bones.

The dura mater is separated from the next membrane underneath it by
what is known as the " subdural space"

The second membrane, the arachnoidea, was formerly described as form-
ing a shut serous sac, but erroneously so ; the parietal leaf being usually
repcesented as fused together with the outer layer of the dura mater, since
it could not be demonstrated separately. It presents for our consideration a
very thin delicate membrane on the spinal cord, investing the pia mater
quite loosely, and only connected with the latter and with the nervous
roots by means of numerous bands of connective- tissue, varying according
to locality. Consequently there is left a considerable interspace between
it and the pia mater, known as the sub-arachnoid space,. But the relations
of this envelope on. the brain are different in some respects. Here we find
it for the greater part firmly adherent to the pia mater, the latter, however,
dipping in between the convolutions, while the arachnoid stretches across
the depressions between the same, and also those larger ones situated at
the base of the brain. In this way a great number also of smaller sub-
arachnoid spaces are produced. In regard to the connective-tissue of the
arachnoid Key and Retzius have recently made some admirable observa-
tions. The retiform fibrillated bundles are covered with flat connective-
tissue cells, similar to those we have already considered in speaking of
connective-tissue (§130), the lymphatics (§223), and the testes (§283).
These are united to each other to form a kind of membrane, and fill up
the interstices of the various layers. Under the action, further, of nitrate
of silver solution they present tha well-known mosaic appearance of the
" endolhelial cells" (§98, &c.)

"Within these spaces situated under the arachnoid of the brain and
cord, and communicating more or less with one another, as well as within
the ventricles of the brain, we find what is known as the cerebro-spinal
fluid. This contains, besides, about 99 per cent, of water, small quan-
tities of album 'mate of sodium, extractives, and the ordinary salts of the
body (C. Schmidt, Hoppe).

The number of capillaries encountered in the arachnoid is extremely
small. Nerves, on the other hand, are not uncommon, but whether they
actually end here is a point not yet decided. The outer surface of the
arachnoid and internal of the dura mater are covered with a slightly
laminated flattened epithelium (p. 141).

We come now, finally, to the third and last of the coverings, the pia
mater. In it we have before us a delicate connective-tissue tunic. Here
also we find those flat membranous cells just referred to, with connective-
tissue bundles and elastic fibres. The whole, however, is a continuous and
39

600 MANUAL OF HISTOLOGY.

unbroken envelope. The pia mater is completely closed (Key, Retzius).
It appears, moreover, much thinner on the brain than on the cord.

In it, as is well known, innumerable blood-vessels present themselves,
penetrating for the most part into the nervous matter. We have already
considered (§ 292) this point in speaking of the spinal cord. In the brain
their arrangement is analogous. The pia mater, further, is richly supplied
with well-developed lymphatic canals.

Between the pia mater and the brain, or spinal cord, there does not exist
any appreciable space. The "epispinal" and "epicerebral" spaces described
by His are artificial productions. After personal observation, we do not
hesitate for a moment to declare this statement of Key and Retzius as
entirely correct. Boll is also of the same opinion.

We now turn to a very interesting and important point, as bearing
upon the lymphatics of the central organs, namely, the nature and rela-
tions of the walls of the vessels entering the substance of the brain.

These are loosely invested in a sheath, which, lying next the tunica
media, opens out into the subarachnoid space with a kind of funnel-shaped
dilatation. Owing to this arrangement, the sheaths may be artificially
injected from the subarachnoid space far into the interior of the brain
and spinal cord. Injections, however, which penetrate under the pia
mater, or into the actual nervous tissue of brain or cord, are the result of
ruptures. There are no such things as " perivascular" spaces, i.e., passages
between the adventitial coat and the adjacent neuroglia ; if anything of
this kind present itself, it is an artificial production.

Another very interesting discovery has also been made by Key and
Retzius, viz., that nerve-trunks and ganglia are also invested with a
similar dural sheath and arachnoid envelope, and which can be artificially
filled in the same way. Here, again, then, we have the "subarachnoid"
space.

We glance now finally at the Pacchionian granulations, small round
masses of connective-tissue, met with as normal structures principally
along the course of the longitudinal sinus.

Key and Retzius have made some remarkable statements in regard to
these.

They say that if fluid be injected into either the subdural or subarach-
noid space, it makes its way easily into the venous sinuses and venous
ramifications of the dura mater. The entrance takes place through the
spongy tissue of these granulations. We naturally look for further obser-
vations on this point.

The two entrances to the cavities of the brain, the posterior and anterior

transverse fissures, are closed by the stretch-
ing across them of the pia mater (telce cho-
roidece). From their inner side, especially
in the anterior transverse fissure between
the cerebrum and cerebellum, a leaf-like
process with large vessels penetrates into
the ventricles of the brain, to form there

*Hr. 563.-EPit.hclial" cells from the *&* pleXU* choridei. This is nothing but a

human choroid plexus, a, the ceils network of vessels (§ 136) embedded in

from above; ft, the same in profile. homogeneOUS, COlbid, OF, later on, streaked

•connective-tissue containing cells. On its free surface, as far as this
exists, we find those peculiar rooted epithelial cells (fig. 563) already
described, § 87. The ventricles, however, receive no further covering of

ORGANS OF THE BODY.

601

pia mater than this : on their surface the ill-developed connective sub-
stance of the ependyma appears under the epithelial covering (§ 119).

This deepest membrane of brain and spinal cord is also the most highly
innervated of all. The nerves here form dense plexuses, not only in the
course of the vessels, but also in the connective-tissue itself. According
to Koelliker, they even penetrate, in part, into the substance of the brain
along with the liner arterial twigs. The nerves supplying the pia mater
spring, in the first place, from the posterior roots of the spinal cord
(Remak) ; and, secondly, in all probability, from the cranial nerves also,
as well as from the carotid and vertebral plexuses' of the sympathetic. It
would appear also that, from the surface of the brain and spinal cord,
delicate filaments may likewise be given off in the opposite direction to
the pia mater (Bochdalelt, Lerthossek). The choroid plexus is quite desti-
tute of nervous supply.

The blood-vessels of the cerebral substance have in so far an analogous
arrangement to those of the cord, that they form larger meshed networks
in the white matter than in the grey.

The mode in which they are disposed in the cortex of the cerebellum
was found by Gerlach to be different in the three layers,— the white, the
rust-coloured, and the grey. In the first is seen a loose network of vessels
with long meshes fitting closely to the fasciculi of the nerve-tubes. But
the densest capillary network is found in the rust-coloured layer. Its
meshes, roundish or polygonal, branch off inwards with greater rapidity,
but enclose, on the other hand, the larger ganglionic corpuscles of the
grey stratum externally. The meshes of the latter are less dense, and are
arranged in the direction of lines radiating from the centre of the cere-
bellum. The most external boundary lamina of the grey layer is quite
devoid of capillaries. The latter terminate here in the form of loops.
The larger vessels supplying the brain enter, for the most part, with the
processes of the pia mater, which dip in between the convolutions from
the surface. Here they give off regular twigs at right angles to their
course, which may be traced pretty far into the cortical grey matter, form-
ing there, by lateral subdivision, the capillary networks just mentioned.
Other larger branches ramify in the white substance.

Not less delicate, and rather similar in frontal section to that of the
cortical 'port ion of the cerebellum, is the
arrangement of vessels in the olfactory
bulb, as seen in the rabbit, for in-
stance.

Between the two olfactory lobes
runs a large vessel, sending off on either
side fine branches, with the greatest re-
gularity, into the grey matter, while
the outer aspect of the lobes is simi-
larly supplied by other twigs. From
these a dense network is formed in the
grey substance, with elongated meshes
externally, and very small round ones
internally. After this we then come
upon the large and long meshed capillary
net-work of the white internal layer.

We have still left for consideration
the sabulous matter of the brain (fig. 564), which is found in the choroid

Fig. 564. — Concretions from the human brain :
1. from the pineal gland, 2. from the
choroid plexus ; with their envelopes of
connective-tissue.

602 MANUAL OF HISTOLOGY.

plexus and pineal gland. It consists of very irregular granules, ranging
in diameter from 0'0113 to 0-5638 mm. of flattened or more generally
spheroidal, or at times most fantastic shape. These masses, formed of
concentrically arranged layers of carbonate of calcium, with phosphate of
calcium and magnesium combined with an organic substratum, are usually
imbedded in bundles of connective-tissue, in which they present a dark
outline. Their occurrence is almost entirely confined to the human brain,
and much doubt exists as to their histological significance.

Turning now to the origin of the central organs in the embryo, it will
be remembered that both brain and cord are developed from the so-called
corneous germinal plate, that is, from that portion of it bordering on the
middle long axis of the embryo, and named, accordingly, by Rema'k, the
medullary plate. Properly speaking, it is more the province of embryo-
logy than of histology to follow up the transformation of this portion ot
the germ into a groove, and the subsequent closure of the latter. This
much, however, may be mentioned here, that at an early period the still
wide central canal of the spinal cord is lined by a layer of grey substance
composed of small cells of round form. These elements gradually become
increased in number at the spot where the anterior cornu exists later on,
and from this point the nerve fibres of the anterior roots make their exit.
The white portions of the cord are developed later on, but their mode of
origin and relation to the grey substance requires further investigation.
The fibres of the sensitive roots are formed at the same time with the
development of the posterior column. Both the lining epithelium and
subjacent layer of sustentacular tissue are distinctly visible at an early
period : the former is originally thick, and made up of several layers.

At present we possess but a very fragmentary knowledge of the histo-
genesis of the brain and its appendages. The important question, like-
wise, as to the origin of the connective-tissue framework of the nervous
centres is especially difficult to answer.

Two species of cells were found by Boll, even at a very early period,
in the cortical layer in the embryonic chick,— one with vesicular nuclei
and sharply defined body, the other with bodies hardly distinguishable
from the surrounding protoplasm.

From the first species the ganglion corpuscles are developed ; from the
second the cellular elements of the sustentacular substance. From the
first a number of ramifications, with varicose fibres, may be seen to spring ;
the latter present, after a time, halo-like rings of the peculiarly consti-
tuted neuroglia around them.

In the early brain of birds the white substance presents bundles of
extremely fine fibrillse, separated by long rows of roundish, polygonal,
flattened, nucleated cells. From the first the sustentacular matter is
developed. The second, formed of spindle cells with two long varicose
fibres at the poles, attract around them, later on, a number of the granules
of the nervous medulla, and by the fusing together of the latter the
medullary sheath is produced.

The envelopes, blood-vessels, and lymphatics of the brain and cord are
developed from the middle germinal layer. The blood-vessels may be
beautifully seen, advancing into the substance of the brain and spinal
medulla, in the form of bud-like excrescences from the envelopes, and
spreading out and uniting in their interior (His).

ORGANS OF THE BODY.

COS

9. Sensory Apparatus.

§ 301.

The skin in man (fig. 565), the organ presiding over the sense of touch,
consists of the cutis vera (below, c), the cuticle (a, b), the subcutaneous
areolar tissue (h), nerves (&), vessels (d), sudorific (#, e, f), and sebaceous
glands, hairs and nails.

All these parts have been already separately considered in speaking of
the several tissues. For the cutis, see p. 228; the epidermis, p. 144;
the subcutaneous areolar tissue, and the collection of fat cells occurring in
it, §§ 120-123. The nerves, as far as their course and mode of termina-
tion is known, were discussed in §§ 185 and 187. The two species of
glands occurring in the skin have been already spoken of generally, at
§§ 198 and 196, in describing glandular tissue. Hair has been dealt with
in § 212, and the nails in § 99.

The thickness of the cutis varies in different parts of the body, ranging
from 0*45 to 3*38 mm. It is thinnest in the eyelids, the glans penis and
prepuce, and inner surface of the labia majora. In the face, the scrotum,
and areola of nipple it becomes thicker, varying from 0'68 to 1*13 mm.,
and on the forehead it is 1 '50 mm. Its average depth, on most parts of
the surface of the body lies between 1*69 and 2*26 mm. On the sole of
the foot, the nates and back, and often, likewise, in the palm of the hand,
it attains the greatest thickness. In males it is stronger than in females,
and in children under seven
years of age it is hardly half
as deep as in the adult (C.
Krause).

The epidermis also, already
considered at greater length in
another place, varies much in
different localities, and, more-
over, in a much higher degree
than the corium. This varia-
tion affects principally its cor-
neous layers ; while the soft
strata of cells underneath only
range from 0-1128 to 0-0347
mm. or so ; the horny portion
may vary from 0*0347 to 2 -26
mm. Its average thickness, in
most regions, was fixed by C.
Krause at 0-075 1-0 -1735 mm.
The epidermis attains the great-
est strength in the palm of the
hand and sole of the foot, [in
both of which situations, as has
been known from the earliest
days of histology, this inequa-
lity may be noticed even in the
embryo.

The tactile papillae of the skin have been already described in § 136.
They are to be found over the whole extent of the latter, but present con-

Fig. 565. — Vertical section of human skin, a, superficial
laminae of the epidermis; 6, rete Malphighii. Below
this the corium is seen forming papillae at c, and
merging into subcutaneous areolar tissue underneath ;
g, sweat glands, and their ducts e and/; d, vessels; »',
nerves.

604 MANUAL OF HISTOLOGY.

siderable variety among themselves as to position, size, and shape (fig.
565). In certain localities — as, for instance, in the palmar aspect of
the hand — they are frequently aggregated in small groups arranged along
the ridges of the corium.

At other spots the grouping is more irregular, and the papillae are some-
times found widely scattered, at others crowded together. Their size also
varies greatly. The longest, rising to 0-1505, or even 0'23 mm., are to
be found on the volar aspect of the hand, the sole of the foot, and nipple.
The most usual length of the papillae is 0'1128-0'0564: mm. ; but small
examples, such as those found, for instance, ill the face, may not measure
more than 0 '045 1-0 '037 7, or even less. The largest of them are conical or
tongue-shaped, but the smaller are truncated, or merely slight elevations.
Besides the simpler papillae, there exist also compound, that is, broader
excrescences, running into two or more, rarely three, points (fig. 566 in

Fig. 566.— Three groups of tactile papillae from the skin of the human index finger, in
vertical section. Some are supplied with vascular loops, some with tactile corpuscles.

the middle). We have before spoken of their apparently homogeneous
substratum, § 136. Their surface, further, is thrown into ridges and
furrows, giving to the whole a toothed appearance (Meissner).

"We have already said as much as necessary in regard to the muscular
elements of the skin § 163. Bands of these pass, as we have learned
recently from J. Neumann, from the upper part of the cutis into the
panniculus adiposus, dividing frequently in their course, and sending off
both vertical and horizontal bundles. There occur, besides, both above
and below the perspiratory glands, horizontal muscular branches, especi-
ally in the hairy part of the scalp : these probably belong to the arrectores
pili (§ 212). Finally, beneath the tactile corpuscles, especially those of
the scalp, and on the extensor aspect of the limbs, are to be found other
sets of bands of unstriped muscle. In different individuals, however,
considerable variety exists in this respect.

The vascular network of the skin commences in the subcutaneous
areolar tissue in the form of round meshes enclosing the fat cells, and
capillary interlacements around the hair follicles and convoluted ends of
the perspiratory ducts (fig. 567, c). In the corium itself, we encounter a
very complicated plexus of fine capillary tubes, 0'0074 to 0'113 mm. in
diameter. These spread out horizontally, and supply the greater part of
the papillae with loops on an average 0'0090 mm., except at those points
where some of the papillae contain tactile corpuscles, in which case they
are without vessels (§ 1.85).

The lymphatics of the skin, known to earlier observers as very dense
networks, have recently been closely studied by Teichmann, and more so
still by Neumann.

In the corium these present a system of tubes possessing independent
walls, and arranged in two different dense networks, a deeper, of coarser
canals with wider meshes ; and a more superficial, of finer passages with

OEGANS OF THE BODY. 605

closer meshes. The lymphatics of the cutis vera do not contain valves,
which first appear in the subcutaneous areolar tissue.

The arrangement of these vessels varies much in the different localities.
Here and there blind-ended offshoots of varying thickness are met with.
In the papillae of the skin the lymphatics present sometimes single tubes,
sometimes loops.

The several complementary structures of the skin, as the hairs with
their sebaceous follicles and the sweat glands, all possess their own special
lymphatic vessels; even the fat lobules are surrounded with looped
canals. The lymphatic vessels are very highly developed in the sub-
cutaneous areolar tissue.

The various parts of the body present considerable difference as to the
number of these vessels to be found. The parts which seem to be most
richly supplied with them are the scrotum, labia majora, palms of the
hands, and soles of the feet.

The arrangement of the nerves of the skin in plexuses, which constitute
the latter one of the apparatuses of special sense, has been before touched
on in the second part of our work. We refer to §§ 185 and 187 for a
description of the several modes of termination of the nerves, — in the
first place in the tactile corpuscles, and then at other points. In § 184
the scattered observations on the occurrence of the end bulbs of Krause
are mentioned.

The development of the epidermis in the embryo has been already
treated of at p. 159. The cutis still consists entirely, according to Koel-
liker, in the fourth and fifth month of human intra-uterine life, of collec-
tions of round and fusiform formative cells, and has a thickness of
O'Ol 35-0*0226 mm. In the third month the subcutaneous areolar tissue
may be distinguished, and both layers are of about the same depth.
Both together, including the cuticle, measure (H353 mm. A month
later the first lobules of fat may be remarked, and in the sixth month the
papillae make their appearance, the corium having attained a thickness
of 1*13 mm. and upwards. In the new-born infant the panniculus
adiposus is particularly strongly developed.

§ 302.

The glandular structures which lend to the skin the character of a
secretory organ are of two kinds, perspiratory and sebaceous.

The sweat glands (glandulce sudori/erm, figs. 565 and 567) have been
before dealt with, as far as relates to the differences of size and structure
observed among them (p. 357).

The convoluted portion with which they commence is situated either
in the deeper parts of the corium, or more generally in the subcutaneous
areolar tissue, deeper than the hair follicles, and surrounded by the fat-
cells of the panniculus adiposus. The excretory duct, long or short,
according to the thickness of the corium, perforates the latter, passing
between the papillaa into the epidermis. In this course it frequently
twists and turns spirally, especially in the cuticle. The mouths of these
ducts, on the surface of the skin, are of microscopical minuteness, with
the exception of those on the palm of the hand and sole of the foot,
which are wider and funnel-shaped. Here they appear as rows of small
dots upon the ridges of the skin, whereas in other localities they present
themselves in irregular groups. Internally the glands in question are
lined sometimes with a single, sometimes double layer of round or poly-

606

MANUAL OF HISTOLOGY.

Fig. 567. — Sudorific glflnd from the human being, a, con-
voluted portion surrounded by the radicals of venous
vessels; c, basket-like plexus of capillaries from around a
convolution, with arterial twigs; 6, excretory duct.

gonal gland-cells of rather small size, ranging from 0'0113 to 0-0157 mm.
in diameter, and containing in their interior, as a rule, molecules of a
brownish pigment and of neutral fats.

The space in the axis of the tube is filled either with a more or less

transparent fluid, destitute
of granular matter, or, as is
the case with the larger
convoluted glands, with a
thickish matter, rich in
molecules of fats and albu-
minous substances, which
has its source in a bursting
of the gland-cells, and in
some instances nearly re-
sembles the fatty secretions
of the allied ceruminous
glands of the ear or race-
mose sebaceous follicles.
The blood-vessels are dis-
posed around the convolu-
tions of these organs in
delicate basket-like capil-
lary networks, c, c. Apart
from a dense network of
nerves surrounding the
capillaries of the sudorific glands (Tomsa), no special secretory nerves are
known for the organ, although the agency of the nervous system in the
mechanism of absorption is very probable.

Sudorific glands occur over the whole surface of the human skin
whether covered with, hair or no, with the exception of a few limited
spots. They are liable, however, to vary considerably, both in regard to
grouping, size, and number, in different localities. On the ridges of skin
in the palm of the hand and sole of the foot they are arranged with
regularity in rows. It is most usual, however, to find them in small
irregular groups, separated from one another by small tracts of skin quite
free of glands. On the lip they extend as far as the red edge, and on
the nose to the entrance of the nostrils ; on the penis, again, as far as the
border of the external skin of the prepuce ; and on the pudenda to the
limits of the outer integument. Over the whole body almost, the smaller
species of glands alone present themselves, while the large tubules of
more complex constitution appear in the axilla only, crowded together
and forming a regular stratum. We are indebted to Krause for some
very interesting calculations in regard to the number of the sudorific
glands in different localities. Whilst on the back of the neck, back, and
nates, 417 on an average may be found in n"> the cheeks, for instance,
have 548 ; the inner surface of the thigh and leg, 576 ; the forearm
externally, 1093, internally, 1123; the breast and belly, 1136 ; the fore-
head, 1258; the dorsum of the hand, 1490; the palm, 2736; and the
sole of the foot, 2685. Thus, computing for the whole surface of the
body, this observer estimates the total number of these glands at
2,381,248. No doubt this is subject to great variation, according to the
individual. The mode of origin of the glandulae sudoriferae has been
referred to before at p. 360.

ORGANS OF THE BODY. 607

The thickish fatty nature of the secretion of the axillary glands hardly
•warrants the application to them of the term "sudorific" with any
degree of propriety ; they require some special name just as much as the
glands of the external ear.

Eeceritly a ring of very large sweat glands, lined with columnar epithe-
lium, has been described as surrounding the opening of the anus by A.
Gay, by whom they are named the ".circumanal glands"

The glandules ceruminosce, closely crowded together, are seated in
the cartilaginous portion of the external auditory meatus. They present
the same structure as the ordinary sweat glands, with convolutions of
G'23-1'69 mm. in diameter, but differ from them in possessing short,
almost straight and never spiral, excretory ducts. The gland-cells of the
convoluted portion contain granules and drops of fatty matters with
molecules of a brownish pigment, which communicate to the secretion its
well-known colour.

The cerumen auris, a yellowish, thick, and bitter substance, presents
under the microscope, beside epidermal scales, granules and globules of
an ordinary yellow fat, molecules of a brown pigment just mentioned
(either separate or aggregated), and large cells filled with oil globules,
which in the opinion of Koelliker may be derived from the sebaceous
glands of the neighbourhood.

According to an analysis of Berzelius, the cerumen of the ear contains,
besides epidermal scales, a soft fat, a yellowish substance soluble in
alcohol, and bitter to the taste, but which has nothing to do with the
constituents of bile (Lehmann), extractive matters, potash, and lime salts.
Petrequin found also a potash soap here. In fact, potash is almost the
only alkali present in the cerumen ; only traces of soda and lime are to be
found.

§ 303.

Part of the water contained in the skin is continually exuding through
the hard, dry, epidermal scales over the whole surface of the human
body. This process, which, although varying in intensity at times, may
nevertheless be regarded as a constant one, is known as perspiration.
The sources of this moisture are in the first place the blood-vessels of the
papillae, and the transuded tissue fluid of the latter, and then the aqueous
contents of the passages of the sweat glands, which also exhale fluid from
their surface. How much is to be set down to these sources respectively
is still a matter of doubt. According to C. Krause the largest proportion
by far is derived from the bodies of the papillae. We are indebted to
this observer for the discovery that horny epidermis is almost impervious
to water in such a condition that it will form drops, but permeable to all

In contrast to this constant and purely physical process of evaporation
of the water of the skin, there is another, which is only periodically active,
namely, the generation of sweat, the efflux of water in the condition of
drops from the innumerable orifices of the sudorific glands, in which the
small isolated globules form by confluence larger drops upon the greasy
surface of the skin. Both processes, however, are frequently merged into
one another.

The amount of water which the body loses through the skin varies
naturally at different periods. It may be estimated, according to Krause,
at from 8 to 9 hundred grammes per diem on an average, with extremes

608 MANUAL OF HISTOLOGY.

as high as 550 to 1 500. We see, then, that the excretion of water through
the kidneys (§ 274) exceeds that of the skin in general, and further, that
but a small amount of the products of decomposition escape through the
latter. The amount of moisture eliminated by the skin is, however, far
more than that exhaled from the surface of the lungs, which is only from
5 to 7 hundred grammes in twenty-four hours. Further details on this
subject may be left to physiologists..

The chemical analyses which have been hitherto made of the watery
secretions of the skin have been directed partly to the fluid exhaled over
the surface of the body, and condensed there in drops again ; partly to
the water welling from the perspiratory glands themselves in the form of
drops ; and lastly, towards both together. To this mixture, then, the term
sweat is generally applied.

The sweat (sudor) always contains an admixture of cast-off epithelial
scales and fatty molecules, which last are derived partly from the seba-
ceous matter of the skin, partly from the contents of the convoluted
glands. Otherwise the secretion is quite devoid of form elements of
every kind.

It is a clear, colourless fluid, normally of acid reaction when fresh, but
becoming, after some time, neutral or even alkaline. Its taste is usually
salty, and smell more or less intense, and dependent on the presence of
volatile fatty acids.

The proportion of solid constituents is small but variable, decreasing
relatively with the amount of water excreted : it may be stated at 0'5-2
per cent, of the latter. They consist of both organic and mineral matters.
To the first belong several members of the volatile fatty acid series (p.
24), and prominent among them formic, buttyric, and acetic acids. The
presence also of metaceton, capronic, caprylict and caprinic acids is at
least probable. But there can be no doubt that we have here to deal
with a very variable fluid, which is indicated, among other things, by the
different odour of the perspiration of various parts of the body, as well as
of different races of men, such as that of Europeans and negroes. Accord-
ing to Favre's observations, further, a peculiar acid may be demonstrated
in sweat, which he has named hydrotinic acid (p. 36).

Recent observation has shown also that sweat, even under normal
conditions, contains urea, to the presence of which substance the rapid
change in the reaction of the secretion, combined with the development of
ammonia, may be ascribed. In morbid conditions of the system also,
induced by impairment of the functions of the kidneys, this compound
may be excreted largely by the skin. Among the other widely diffused
animal bases none have been demonstrated here as yet.

Neutral fat is likewise a constant constituent, and cliolestearin has
also been met with (ScJwttin). Leube also met with a peculiar albu-
minous substance here.

Under abnormal conditions the biliary pigments may also appear in the
sweat.

The mineral matters found here consist, besides iron and phosphate of
calcium (derived from the epithelial cells), principally of chlorides of the
alkalies, and above all of sodium ; then, again, small quantities of phos-
phates and sulphates of the alkaline salts. Finally, free carbonic acid is
met with here, and salts of ammonia, due to decomposition.

ORGANS OF THE BODY.

609

Fig. 568.— A sebaceous gland, a
the gland vesicles; b, excretory
duct; c, the follicle of a downy
hair ; d, shaft of the latter.

§ 304.

The sebaceous glands (fig. 568), small structures included in the race-
mose class, are to be found likewise almost everywhere over the whole
surface of the skin, although less extensively
distributed than the sweat tubules.

Their secretion is essentially a fatty one
(fig. 569) ; its mode of origin has been already
treated of at § 196.

The sebaceous glands, always seated. in
the corium itself, and never in the subcu-
taneous areolar tissue, are, as a rule, asso-
ciated with the presence of the large and
small hairs of the body, into whose follicles
they empty themselves, either singly, doubly,
or in greater number. While in relation
to the larger, hair follicles they appear but
as lateral appendages to the same with the
downy hairs, the case is altered, the hair fol-
licles of the latter seeming but appendages
of the glandular organs. In addition to these
sebaceous glands connected ^with hairs, the "hair-follicle glands," there
exist others found only on bald parts of
the body, which pour out their secretion
directly on the surface. The naked parts of
the skin are almost, without exception, des-
titute of them, such as the palm of the
hand, sole of the foot, and last joints of
both fingers and toes. On the whole these
are not widely distributed, and only occur
in certain parts of the sexual organs, namely,
on the prepuce and glans penis (known
there as the glands of Tyson), and on the
labia minora of the female.

The structure of the sebaceous glands,
which range in diameter from 0'2 to 2'2
mm., is very different in different cases.
When small and simple their form is that
of a wide, shallow sac. Others, again, are
found at whose lower ends isolated buds
commence to present themselves, which be-
come more and more frequent, acquiring
eventually in some cases a flask-like form
(fig. 569, A), and in others a more globular
shape. These gland vesicles, whose length
is consequently very various, differ also con-
siderably in transverse measurement, ranging
from 0-0564 to 0*0751 mm., or even 0-2256
mm. The largest are observed on the nose,
scrotum, mons veneris, and labia majora.
The envelope of the vesicles and excretory
passage is not, as is the case with most
glands, a transparent structureless membrane, but consists of streaky con-

Fig. 569. — A, the vesicle or a seba-
ceous gland, a, the gland cells
next the wall; 6, cast-off elements
filling cavity of the vesicle, and con-
taining oily matters, £, the same
cells more strongly magnified. </,
small elements belonging to the
walls, and poor in fat; 6, larger
richly filled; c, a cell with large
confluent globules ; d, another with
a single drop of oil.

610 MANUAL OF HISTOLOGY.

nective-tissue. As a rule we find no blood-vessels about the body of the
gland. The process of secretion in the latter appears to be of a very low
order, but active enough to meet all the functional requirements of the
organ, which is designed to communicate to the hairs and surface of the
skin a certain slight degree of oiliness.

The secretion itself, sebum cutaneum, when fresh, is a thickish oily sub-
stance, which stiffens after some time like lard which has been heated.
Its form-elements (B), found together with cast-off epidermal scales in
variable amount, have been described at p. 352. Chemically the mass
consists — apart from slight differences dependent on locality — of a large
proportion of neutral fats in addition to soapy materials, cholestearin, and
a protein substance. Among its inorganic constituents the chlorides and
phosphates of the alkalies appear in small proportion, but the earthy
phosphates in considerable amount.

The development of the sebaceous follicles takes place from the external
cell-layer of the skin like the sudorific and mammary glands ; it is, how-
ever, usually linked with that of the first rudiments of the hairs, and
may be remarked in the fourth or fifth month of foetal existence.

At first these glands present themselves in the form of solid buds on
the rudimentary external root sheaths (p. 390), primarily of globular
figure, and subsequently flask -like. These buds are produced by prolifera-
tion of the formative cells of that sheath ju^t mentioned. As Koelliker
has pointed out, there very soon commences in the axis of this simply
formed sebaceous gland a fatty degeneration of its contents, so that the
little organ, even at this early period, already exhibits the characteristic
features of its secretory process.

The further changes destined to convert this simple flask-shaped sac
into a plain or complicated racemose gland begin, on the other hand, at a
comparatively late period, namely, in the later months of intrauterine
life. They depend upon a multiplication of the peripheral cells causing
new gemmation at the surface, — a process which is not completed at the
time of birth, and by the continuation of which the complicated lobulated
form' of many of the sebaceous glands is gradually perfected.

REMARKS. — (1.) Todd and Bowmann, vol. i. p. 424.

§ 305.

As regards the mode of termination of the (justatory nerves of the tongue
our knowledge is still scanty and unsatisfactory. The organ itself has
been considered at greater length in speaking of the digestive apparatus
(§§ 247, 248). Much advance, however, has been made of late years in
increasing our stock of facts relating to this question.

In the circumvallate papillae of the human and mammalian tongue,
peculiar terminal apparatuses were discovered almost at the same time,
and independently of one another, by Loven and Schwalbe, for which the
name of " gustatory buds" chosen by the first of these observers, recom-
mends itself most. The term " taste-cups" proposed by Schultze, appears
less suitable. Here, again, Engelmann and Wyss both found, indepen-
dently of each other, an analogous gustatory organ on the side of the root
of the tongue in the rabbit, a plicated body presenting similar " gustatory
buds'" represented in our woodcut. This is known as the " papilla
foliata."

These papillae foliatae also occur in the human tongue. They are seated
immediately before the bases of the pillars of the arcus glossopalatinus,

ORGANS OF THE BODY.

611

Fisr. 570. — From the lateral gustatory organ of the rabbit.
The gustatory ridges are represented in vertical transverse
section (.after Engelmann).

are several millimetres across, and present five longitudinal clefts, which
contain numerous gustatory buds (Krause).

The crown and side walls of the circumvallate papillae, with the
internal surface of the surrounding ridge of mucous membrane, are
clothed with a thin layer of the ordinary flattened epithelium of the
tongue. Now it is principally the side walls of the papillae (fig. 570), but
not unfrequently the inner
aspect likewise of the en-
circling ridge (the crown of
the papillae never), which
presents the terminal struc-
tures just mentioned. These
are pear-shaped or bud-like
organs which traverse the
whole thickness of the epi-
thelial covering, and present,
according to the animal examined, a plump, or slender figure. Their
number is, as a rule, considerable. In length they attain in the tongue
of the ox, 0-1717; in man, 0'0810-0'0769 ; in the deer, hare, and dog,
0*0729 mm.; in the rabbit, 0-0575 mm.

Their walls consist of flattened lanceolate cells (fig. 571, 2 a) arranged
side by side like the staves of a cask, or the sepals of a flower bud.
Above these supporting or encasing cells
converge ; below they are narrowed into
ribband-like processes, which sink into the
tissue of the mucosa, and are to all appear-
ance connected with the elements of the
same.

The apices of the gustatory buds (1)
perforate the epithelial covering, and lie
naked and free. Here we may observe
small round holes arranged with consider-
able regularity, and formed by the borders
of either several, or perhaps two, or even
of one single cuticular cell. Through
these openings delicate terminal filaments
may project (Sckwalbe).

A second species of cell (2 I) is now
found in the interior of the gustatory bud,
enclosed within the cortical lamina of
encasing cells. These elements appear in
the form of longitudinal bundles, and are
known as " gustatory cells" A fusiform
nucleated body becomes narrowed above
into a thin rod or spike, and is fined off
below into a thread-like process. The
ends of such rods project at times to a
greater or less extent from the openings
of the gustatory buds, while the end filaments below, on which varicosities
may be observed, penetrate into the tissue of the mucous membrane.

Underneath the gustatory buds the latter is seen to contain a plexus
of pale and medullated nerve fibres. Immediately under the epithelial
covering pale single or dividing terminal filaments present themselves.

Fig. 571. — 1. Gustatory bud from the
rabbiD. 2 a, encasing cells; 2 b, rod-
cells; 2 c, a rod-cell with fine terminal
thread.

612 MANUAL OF HISTOLOGY.

Their appearance is the same as that of the terminal filaments of the
gustatory cells. Fusion with the latter fibres has not been yet observed,
however. The hidden position of the gustatory buds within the narrow
grooves formed by the elevations of the papillae seems to have some signi-
ficance in regard to the persistence of after-taste sensations.

The mode of termination of the nerves of the papilla* fungiformes is
not so well known. Loven states that he has found a gustatory bud in the
centre of the crown of each in the rat. Krause also mentions the same.

A few years ago some points of interest in regard to what we now
know to be similar structural relations in the tongue of the frog were
put forward by Key.

The tongues of frogs, namely, present, besides a narrower form of papilla,
another broader species, reminding us of the p. fungiformes of mammals.
On these we can better study the structural arrangement of such parts.

The side walls of these broad papillae are clothed with columnar cells,
the edges of the crown with ciliated epithelia. The surface itself of the
crown, on the other hand, is covered by one of the other varieties of
epithelial elements destitute of cilia. In the first place, columnar cells
are to be seen giving off processes below, which anastomose with one
another, forming thus a kind of network in which here and there im-
bedded nuclei may be recognised.

But between these cylinder cells, and at different heights, smaller roundish
or elliptical elements present themselves, with relatively large nuclei.
Each of these gives off both above and below a process ; the first ascends
to the free surface between the columnar epithelial elements in the form
of a slender rod, while the process extending downwards into the mucous
membrane is but an extremely delicate filament, on which minute vari-
cosities may be recognised characteristic of the finest nerve fibrillae.

In the axis of each papilla is a nervous twig, consisting of a few broad
medullated tubes. At the end of the twig the latter axis cylinders split
up into very delicate filaments, likewise varicose. They resemble greatly
the end filaments of the last species of cell mentioned, and, according
to Key's statement, may be seen to be directly connected with the latter.

With some show of reason, this coating of the crown of the papillae of
the frog's tongue has been compared to a superficially unfolded gustatory
bud of the mammal. But more recent investigation by Englemann has
put the correctness of this comparison again in question, and has revealed
to us a greater amount of complexity in structure here than was at first
suspected. This observer notices, in addition to his "bowl-cells" (the
" cylinders"), the rod-bearing structures of Key, to which he gives the
name of " cylinder cells," and whose nervous nature he denies, as also that
of the bowl cells. Besides these, he speaks of another peculiar set of
elements, however, branching both above and below, which he calls
" forked cells," and which he regards as the terminal structures of the
gustatory nerves, with whose axis- cylinders the ultimate ramifications of
their inferior processes are continuous.

§ 306.

The organ of smell, to the consideration of which we now pass on,
consists, as is well known, of the two nasal fossce and accessory cavities
in connection with the latter. Besides being a sensory apparatus, this
organ also serves as a passage for the respiratory system, and a canal for
the reception of the tears.

ORGANS OF THE BODY. 613

i

But the whole of this organ does not participate in the perception of
odours. It is only the upper portions of the two greater cavities which
preside over the reception of this particular kind of impressions; the
other parts are either accessories in the process, or merely endowed with
ordinary sensation through twigs of the trigeminus nerve.

That portion of the organ designed for the perception of odours corre-
sponds to the distribution of the olfactory nerves. It consists generally
of the upper part of the septum, the superior, and portion of the middle
turbinated bones. It is remarkable for its yellow or brownish tint, better
seen in the mature than in the newly born animal, and but slightly pro-
nounced in man. It is further liable to vary in extent in different indi-
viduals, especially of the human species. To this tract the appropriate
name of regio olfactoria has been given (Todd and Bowman). The
older name of Schneiderian membrane may be retained for the remainder
of the mucous .surface not endowed with perceptive power.

The bony boundaries of the organ of smell need not be described, nor
its cartilages, which consist of hyaline tissue.

The external skin of the nose is thinly clothed with epidermis, and
contains, together with a few sweat glands, a large number of sebaceous
glands of considerable size (§ 198). In the anterior nares strong hairs are
to be found, known as vibrissce, designed to prevent, to a certain extent,
the entrance of foreign bodies. Internally, the coating of flattened
epithelial cells extends for a certain distance from the entrance, and
then gradually gives way to a slightly laminated ciliated species already
alluded to, which extends from thence throughout all the cavities of the
organ. Here, also, we find beaker-cells, except in the regio olfactoria
(Schultze).

The Schneiderian membrane, which is very vascular in the greater
cavities, differs much in structure in particular localities. In the acces-
sory cavities it is thinner, and so intimately connected with the surface
of the bone, that its submucous tissue plays the part of periosteum to the
latter. In the nasal fossae proper, the mucosa attains, on the contrary,
greater, and at certain points, very considerable thickness. Here it is
richly supplied with racemose mucous glands, which only occur very
sparely in the adjacent cells. It presents, also, in this region, a dense
plexiform arrangement of blood-vessels, especially of veins, to which
is due the great tendency of the nose to bleed. The mode of termina-
tion of the sentient nerves of the nose is still unknown.

REMARKS. — Compare Todd and. Bowman, I.e. vol. ii. p. 1, and Schultze. Unter-
suchungen iiber den Bau der Nasenschleimhaut, namentlich die Structur und
Endigungsweise der Geruchsnerven bei dem Menschen und den Wirbelthieren.
Halle, 1862.

§307.

The regio olfactoria (fig. 572, left) offers for our consideration a very
remarkable and extremely delicate tissue, whose constituents are peculiarly
liable to suffer early from decomposition. For our present acquaintance
with its nature we are particularly indebted to ScJiultze, and before him,
for many points, to Eckard and Ecker. Apart from difference of colour,
it may be distinguished from the surrounding membrane by its greater
thickness, and dissimilarity in the species of glands it contains, as well as
in not possessing ciliated epithelium.

The glands in question (D) have been named by Koelliker after their
discoverer Bowman (§ 189). They belong to the tubular species, and

614

MANUAL OF HISTOLOGY.

remind one of the follicles of Lieberkuhn. In the central portion of the
regio olfactoria they present themselves in great number, becoming more
scattered towards the edge, and finally disappearing. Their form is that
of an elongated tube, somewhat twisted below, and of varying calibre,
generally narrowing greatly at the mouth (d). Internally they are lined
with rather large gland-cells, containing usually a considerable quantity
of small yellow or brown pigment molecules, which fact explains, to a
certain extent, the peculiar tinge of the olfactory region. These glands
of JBoivman, whose existence was formerly erroneously denied, are to be
found in all the lower mammalia (2), and are not absent in man, although
they take the form here of a kind of transition to ordinary racemose
glands (Frey, Schultze). The secretion of Bowman 's glands, as regards its
composition and physiological significance, has not yet been made the
subject of investigation.

Thus, we find the olfactory region in the lower mammals and human
infant (Schultze). In the adult, also, spots quite destitute of cilia are to

Fig. 572.— The olfactory region of the fox in vertical section (after Ecker).
B, columnar epithelium ; a, line of nuclei ; 6, of olfactory cells ; c, of pig-
mentary layer. A, adjacent ordinary ciliated epithelium ; e, boundary
between the two. C, ordinary racemose mucous gland. Z>, glands of
Bowman, with excretory ducts, d. E, a branch of the olfactory nerve;
/, ascending twig ramifying at g.

be found, which vary, however, considerably in extent. But, under
certain circumstances,, the whole regio olfactoria has been observed to be
clothed with ciliated columnar cells (Geyenbaur, Leydig, and //. Mutter,
Welcker, Luschka, Henle, with Elilers).

When we take into consideration the varying acuteness of the sense of
smell in different individuals, and also that frequently recurring catarrh
may induce changes of structure, this need not surprise us.

At the border of the regio olfactoria the ordinary ciliated epithelium
gradually terminates (fig. 572 A), giving place to a no longer laminated
covering of long cylindrical cells (B). These (fig. 572, B ; 573, 1 a, 2 a)
dwindle down below .into thread-like processes, which descend into the
subjacent connective-tissue, where they become widened again, and under-
going division, unite by means of their branches with one another. In
this way a network of fibres, or rather of more or less homogeneous bands,

ORGANS OF THE BODY.

615

3

is formed. Between those cylindrical elements there remain naturally
interstices, which serve for the reception of another species of cell, to be
referred to again immediately. The occurrence of particles of yellowish
or brown pigment, either in the upper broader portion of the columnar
cells (fig. 573, 2 a), or deeper down below their nuclei (fig. 572, c), is
peculiar ; these granules may not unfrequently be seen also in the widened
portions of the processes (fig. 539, c). The former is the case in man
and many of the mammalia. Like the contents of the glands of Bowman,
these coloured particles communicate to the locality in which they are
situated a peculiar tint.

Between these decidedly epithelial elements (and moreover, in all verte-
brate animals) a second species of cell presents itself (fig. 573), different
in shape and composition, and of nervous nature. These cells consist of a
fusiform body (fig. 573, 1 b, 2 b), situated deeper down, however, than the
bodies of the first kind, containing a vesicular nucleus and finely granular
contents. From both poles of each of these nervous structures, as they are
held to be, these olfactory cells, a process is
given in opposite directions. The descend-
ing (fig. 573, Id, 2 d) is of extreme deli-
cacy, and liable to undergo early decom-
position. At intervals it is studded with
minute varicosities, recalling to mind those
of very fine nerve tubes (§ 176). The
ascending process (1 c, 2 c) is, on the
other hand, thicker and less knotted,
presenting a more or less smooth outline.
It has the form of a slender cylinder or
rod, 0-0018 or 0-0009 mm. in diameter,
reminding us of one of the elements of
the retina, to be referred to presently.

These rods mount up between ' the
columnar epithelial cells to the surface
of the mucous membrane, terminating
here in various ways. In the frog and
allied amphibians (in which they may
be easily seen), they are surmounted at
their free extremity (fig. 573, 1 e) by a set
of delicate hairs of considerable length, in
a certain number of which ciliary motion
has been observed, while others, gene-
rally the longest, remain quite stiff. These
two kinds of " olfactoi-y filaments" appear
to be linked together by intermediate
forms. In other amphibia and birds
very similar, and in certain cases, even
longer hairs are to be found, either in
large numbers or single (Schultze) • none
have been observed among the fishes,
mammalia also, we may seek in vain for these • paradoxical cilia. Here
we only remark small appendages, about from 0*0023 to 0-0045 mm. in
length, seated on the extremities of each rod (fig. 573, 2e), and projecting
beyond the ends of the columnar cells ; these, however, are only artificial
productions.

40

Fig. 573.— 1. Cells from the rcgio olfactoria
of the frog. a. an epithelium eel!
dwindling below into a ramifying pro-
cess; ft, olfactory cells, with descending
fbres rf, peripheral rods c, and long
cilia, e. 2. Cells from the same locality
in man. The letters and description are
the same here, only tliat little (artificial)
appendages appear at e, upon the tips of
the rods. 3. Nerve-fibres of the olfac-
torius from the dog, breaking up at a
into fine fibrillse.

In man, and the rest of the

616

MANUAL OF HISTOLOGY.

In order the better to understand the nature of these remarkable olfac-
tory cells, we must now make ourselves acquainted with the arrangement
of the branches of the first cerebral nerve.

In one of the foregoing sections (§ 299) we have already described the
olfactory lobes, and seen that the nerves of scent
take their origin from peculiar lumpy masses in the
lower surface of the latter, in the form of bundles of
pale fibres. A few dark-edged fibres, which have
been met with by Remak and Schultze in the olfac-
tory nerves, are probably derived from anastomosis
with the trigeininus.

The true olfactory fibres are pale elements, O0045-
0'0074 mm. in thickness, enclosed within a nucleated
sheath. The contents of the latter are not constituted
by a single axis cylinder, however, but, as was found
by Schultze, by a bundle of extremely delicate vari-
cose primitive fibrillae, 0 '002 3-0 -0002 mm. in dia-
meter, presenting a secondary nucleus formation
(comp. § 175). Similar fibres are to be found
in the grey matter of the bulbus olfactorius ( Walter,
Schultze).

In the mucous membrane of the regio olfactoria
several other bundles may be recognised (fig. 572,
E, f). These spring at acute angles from branches
of the olfactory twigs, and give origin in their further
course to the true (complex) nerve tubes. The latter
are for a short distance enclosed within their nu-.
cleated sheaths, until eventually the delicate varicose
fibrillas of the interior stream out free into the tissues
around (Schultze).

The mode in which these filaments ultimately ter-
minate is not yet fully ascertained. It seems, how-
ever, extremely probable that the varicose fibrillce
are continuous with the descending fibres of the olfac-
tory cells, so that these bodies, with their narrow rods,
may be looked upon as the terminal structures of the
nerves of smell.

In fig. 574 we have given a diagram of the pro-
bable arrangement of parts here, which appears very
nearly allied to the mode of final distribution of the
gustatory nerves in the tongue of the frog (§ 305).
The fact, however, cannot be concealed, thr.t the most recent observations
by Exner on the structure of these parts have pointed to other conclusions.
According to him there is no such very sharp line of distinction
between the two species of elements of the regio olfactoria, the olfactory
and columnar epithelial cell; they are, he says, connected by inter-
.mediate forms.

Further, underneath these cells there exists a ("subepithelial") band-
work of protoplasm, whose interstices are filled with nuclei. Into this
(in man) thin network the ramifications of both kinds of cells sink from
above, and become fused. From below, also, the olfactory fibres ascend
into it. Thus we have in it an intermediate nervous plate.

The course of development of the olfactory organs in the embryo,

Fig. 574 — Probable mode
of termination of the
olfactory nerves in the
pike (after Schultze). a,
olfactory cells ; 6, rods ;
c, deeper varicose
threads; e, axis fibrillae
in the sheath/; d, dis-
tribution of the latter.
At missing con-
nection with the corre-
sponding fibres, c.

ORGANS OF THE BODY. 617

although followed up in its "broader outlines, has not been minutely investi-
gated up to the present.

REMARKS. — (1.) In many of the mammalia we meet with peculiar structures, known
as the organs of Jacobson. These consist of tubes, with cartilaginous walls, and are
situated in the substance of the palate ; they open into the duct of Stenson. In these
is contained a branch of the olfactory nerves. In their texture they resemble much
the regio olfactoria (C. Balogh.}. — (2.) Bowman's glands may be made out with com-
parative ease. — (3.) Those delicate fibrillae which spring from the inferior end of the
olfactory cells, and those .which are derived from the spreading out of the olfactory
nerves, resemble each other in the most complete manner in every respect. But the
difficulties connected with investigation in this direction have hitherto rendered it
impossible to demonstrate a direct transition of one into the other. On this account
we have marked the gap between the two with a line.

§ 308.

The organ of sight is made up of the eyeballs and a series of other
accessory structures. These consist of membranous parts, as the eyelids,
of glands, especially the lachrymal, and of muscles.

The bulbus oculi (fig. 575) is formed almost entirely of a system of

Fig. 575.— Transverse section of the eye, after Helmholtz. a, the scle-
rotic ; 6, cornea ; c, conjunctiva ; d, circulus tenosvs iridis ; e, tunica
choroides and membrana pigmenti; f, ciliary muscle; g, processus
ciliaris; h, iris; f, optic nerve; i', colliculus options; k, ora serrata
retinae; I, lens; m, membrane of De^emft; n. membrana limitans
retinae; o, membrana hyaloidea; p, canal of Petit; q, macula lutea.

capsules. Its posterior and larger segment is constituted by the opaque
sclera (a), while the anterior and smaller division is made up by the
transparent cornea (b). Internally it is lined by a system of blackened
membranes — the uvea, consisting of the choroid (e), the ciliary processes
(g\ the ciliary muscle (/), and diaphragm, or iris (h). The cavity of this
hollow globe is filled with various refracting media. These, among which
the cornea may be numbered as the most anterior, are the fluid of the
chambers of the eye (anterior to I), the crystalline lens (I), and the vitreous
humour (behind Z). The greater part of the cup-shaped expansion of the
optic nerve, or retina (i), is covered by the latter.

(US MANUAL OF HISTOLOGY.

Besides these parts, we have in the eye a complicated vascular system,
derived almost exclusively from the ophthalmic artery. This may be con-
sidered as consisting of several divisions, with separate afferent and efferent
vessels, but communicating one with another. These are (a) the system
of the retina, (b) the ciliary system, and (c), as far as the globe of the eye
is covered by the conjunctiva, the conjunctival system.

REMARKS. — (1.) Compare Bowman, Lectures on the parts concerned in the opera-
tions of the eye, &c. London, 1840.

§ 309.

The sclerotic, the hard, or white tunic of the eyeball, belongs to the
large group of fibrous membranes. Like these it consists of a dense inter-
lacement of connective-tissue bundles, intermixed with numerous fine
elastic fibres, which appear in greatest number on the internal concave
surface. The mode in which these bundles are interwoven is peculiar —
one set anastomosing around the entrance of the optic nerve, and radiating
from thence meridionally towards the edge of the cornea, while another
set is arranged parallel to the equator of the eyeball. Thus the fasciculi
intersect each other at right angles (Loewig).

Close to the point of insertion of the cornea, the inner surface of the
sclerotic coat is traversed by a complicated circular sinus — a regular plexus
of venous twigs (fig. 575, d) — known as the canalis Schlemmii, to which
we shall be obliged to refer again in speaking of the vessels of the choroid.
Posteriorly, the outer portion of the sclera is connected directly by means
of its meridional fibres with the external covering of the optic nerve,
derived from the dura mater. The internal neurilemmatic substance of
the nerve, and the lamina cribrosa, and inner part of the sclerotic, also
merge one into the other. Anteriorly, the latter is strengthened by the
addition to its meridional layer of fibres of the tendons of the recti muscles,
while those of the obliqui unite with the equatorial fasciculi in the pos-
terior segment. As has been already mentioned, this hard membrane of
the eyeball is poor in vessels, its fine capillaries presenting rather large-
meshed networks (Briicke). These we shall be obliged to refer to again
in connection with the vascular system of the bulbus. Nerves are said
to have been met with in this structure in the rabbit (Rahm).

The cornea (fig. 576, a), with its two transparent limiting membranes
(b, c), has been already minutely described (§ 133). The laminated flat-
tened epithelium of its anterior surface (d), to which the name of con-
junctival layer of the cornea has been given, was also considered, and also
the simple cellular covering of the posterior surface (e), (§§ 87 and 88).

The peculiar chondrin-yielding tissue of the cornea becoming somewhat
changed towards the periphery, is continuous with the ordinary collagenic
connective-tissue of the sclerotic, more particularly with its meridional
fasciculi. At its edges the membrane of Descemet undergoes a peculiar
transformation into streaky membranous masses, which are then disposed
in various ways. The most external pass partly into the posterior wall
of the canal of Schlemm, and are in part lost in the ciliary muscle of
the choroidea ; the internal break up eventually into bands and cords,
which pass across the anterior chamber, disappearing in the tissue of
the iris. They thus constitute the ligamentum pectinatum of the latter
(see below).

In adults the cornea appears almost completely destitute of blood-
vessels. At the border alone a narrow row of them, from 1*1 to 2*3 mm.

ORGANS OF THE BOD?.

619

in diameter, may be observed, being the last trace of a more extensive
vascular covering of the anterior surface of an earlier period of existence.
Here we find either a single or double row of fine capillary loops, derived
from the anterior ciliary arteries. The calibre of the capillaries is from
0*0090 to 0*0045 mm. They reach as far inxvards as the fibrous portion
of the conjunctiva extends over the edge of the cornea. Among the lower
mammals they usually form a broader zone, in which case they are joined
by deeper, finer capillaries, springing from the vessels of the sclerotic.
The latter accompany the nervous twigs, supplying the part and end like-
wise in loops.

Whether the cornea is possessed of lymphatics or not is a question still
undecided, in spite of very ex-
tended research. We have
already seen, in § 133, that
this very peculiar tissue of the
cornea is traversed by a system
of passages containing contrac-
tile wandering cells, andremark-
able for their great dilatibility,
and which seem also to pos-
sess a species of modified lining
membrane. We have also
stated that this set of canals
is capable of being injected arti-
ficially, when, either strongly
distended " cornea! tubes" pre-
sent themselves, or finer pas-
sages (Bowman, Recklinghau-
sen, Leber, Schweigger-Seidel,
and Lavdowski). But the
fact that from them the lym-
phatics of the conjunctiva may
be eventually filled does not
seem a conclusive proof that
they are of lymphatic nature.

The nerves of the cornea, so
frequently the subject of study,
are derived almost exclusively
from the ciliary branches, and
have two modes of termina-
tion.— they end, namely, either

in the epithelium or in the

proper tissue of the cornea.

They spread from the border

of the latter into its substance

in considerable number, the

adult cornea presenting about

60 (of a diameter of 0 '02-0 '055 mm.), while that of the infant has only

from 30 to 34 (Sdmisch).

Close to the edge of the cornea these thicker or thinner twigs, as the

case may be, are observed to contain delicate, but clearly-defined primitive

fibrillae of from 0*0045 to 0*0023 mm. in diameter. Their perineurium

is rich in nuclei.

Fig. 576. — Vertical section of the cornea of an infant
(shortened considerably, however), a, corneal tissue ;
6, anterior; c, posterior transparent lamina; d, lami-
nated, flattened epithelium of the anterior; and e,
single layer of the posterior surface.

620

MANUAL OF HISTOLOGY.

Rapidly decreasing in size, the nerve fibres quickly lose their medullary
sheath, and are then suddenly found, at a greater or less distance from
the border of the cornea, in the form of filaments, reduced in diameter to
0'0009 mm., which, under the action of certain reagents, are seen to be
varicose. The bundles of fibres run in a direction towards the centre and
anterior surface of the cornea, and in their course divide and subdivide
over and over again, forming by intercommunication a nervous plexus at
the nodal points, of which nuclei may be observed. At the same time, an
increase of the number of the fine fibrillae unmistakably takes place,
while, on the other hand, the perineurium is no longer to be seen.

Of these nervous plexuses there are several, lying one over the other.
The most anterior, with its delicate bundles of fibres, was looked upon by

earlier observers (His) as a
terminal network of the
nerves. From it, however
(fig. 577), bundles of fibres
are again given off, which
pierce the anterior surface of
the cornea (Hoyer, Cdhn-
heim), and, splitting up into
tassels, form that sub-
epithelial interlacement al-
ready mentioned (§ 177),
whose perpendicularly as-
cending fibres terminate in
the epithelium (Cohnheim).

At its border this last in-
terlacement receives other
twigs, which enter the cornea
with the minute vessels of that part, and, ascending more or less abruptly,
takes part in the formation of the plexus, and extend also as far as the
anterior surface.

Besides these sensory nervous interlacements, the cornea possesses
deeper plexus-like ramifications of nerves. KuJme maintained, many
years ago, that in the frog the termination of the varicose end filaments
of these in the epithelial cells might be seen ; but this has not been since
confirmed (Koelliker, Engelmann, Hoyer). Here also the primitive fibrillse
probably terminate, in part at least, with free ends. They are to be found
but rarely in the posterior layers of the cornea, in larger numbers in the
middle, and tolerably abundant in the anterior portions. A plexus, seated
here under the lamina elasfica anterior, has been described by Hoyer.

§310.

We turn now to the uvea or tunica vascvlosa, with its various consti-
tuents, mentioned above, and find the arrangement of parts much more
complex than in the structures just dealt with.

The choroid is usually described as consisting of an external fibi'ous
coat, and an internal single layer of pigmentary flattened epithelium,
which latter belongs, properly speaking, to the retina, as we learn from
the history of its development. In fig. 578 we have the latter figured
again ; but it has been already described, at greater length, in § 150. As
we shall have to refer to these cells again in speaking of the retina, we
shall, for the present, say no more about them.

Fi£. 577.— Vertical section of the cornea of a rabbit, a, ft,
epithelium; d, a nervous twig; e. /, sub-epithelial distri-
bution of fine varicose nerve nbrillse ; /, distribution and
termination in epithelium.

ORGANS OF THE BODY.

621

Fig. 578. — Polyhedral pigment cells
from the choroid of the sheep, a,
mosaic of six-sided cells; 6, a
larger octagonal example.

Apart from this cellular coating, the uvea consists of several layers, not
in all cases, however, distinctly defined one against the other.

First, and most internally, we find a transparent limiting layer, smooth,
and only O'OOOG-O'OOOS mm. in the fundus of the eye-ball, but thicker,
and presenting a more uneven internal surface anteriorly.

The next stratum is the choriocapillaris, an extremely dense network
of nucleated capillaries (already spoken of in § 311), imbedded in a simple
connective-tissue. This stratum extends to the ora serrata.

The third layer, the proper choroid, consists of a network of ramifying
stellate, or irregularly jagged connective-tissue cells, with thread-like pro-
cesses of varying length. These cells are remarkable for the great avidity
with which they take up dark black pigmentary matters (fig. 579).
We have already considered them under the name of "stellate pigment
cells" in speaking of connective- tissue, p. 219. But what particularly
characterises this layer further is the great abundance of arterial and
venous vessels found in it. The first present a strongly developed mus-
cular tunic. Longitudinal bundles of invo-
luntary muscular fibres also occur in the pos-
terior segment of the choroid accompanying
these arterial vessels (H. Mutter), and lymph
cells likewise (G-. Haase).

Externally the choroidal tissue is con-
tinuous, in the form of a soft, brownish con-
nective substance with the sclerotic, and is
known here as the lamina fasca or supra-
choroidea.

Anteriorly, as is well known, the choroid is continuous with the
corpus ciliare and its numerous ciliary processes projecting inwards.
These structures are likewise clothed with the same flattened pigmentary
epithelium. Here, however, the latter has become laminated, or at least
double-layered (p. 143).

On and within the corpus ciliare, whose tissue resembles that of the
choroid (although pigmentary cells are
fewer in it), and which also possesses the
same delicate limiting membrane as the
latter, a peculiar involuntary muscle pre-
sents itself, the tensor cltoroidea, or
musculis ciliaris (fig. 573, /), for the dis-
covery of which we are indebted to Brucke
and Bowman, while many important
points, in regard to its nature, were sub-
sequently put forward by H. Midler.
This muscle, which has been so frequently
the subject of investigation, was formerly
held to be nothing but simple connective-
tissue, under the name of the ligamentum ciliare.

It springs (fig. 580), at the line of union between the cornea and sclerotic
coat, from the fibrous tissue which forms the internal wall of the canal of
Schlemm, and its distribution is to the tissue of the ciliary body. Its
fasciculi, closely crowded, maintain from this point of origin a radiating
or meridional course backwards, and are lost in the external portion of
the corpus ciliare. Here it is separated from the sclera by a thin prolon-
gation of the so-called suprachoroidea (Henle, Schulfze). Internally, that

i/ioouo leseuiuies i/iicib

<^V/<Q-*

Fig. 579.— Pigmentary connective-tissue
corpuscles (so-called stellate pigment
cells), from the lamina fusca of a mam-
malian eye.

622

MANUAL OF HISTOLOGY.

is to say, towards the ciliary processes, this tough muscular plate breaks up
into a long, fan-shaped, wide-meshed network of thin bands (I), in which,
at last, the direction of the fasciculi changes gradually from being meri-
dional externally to equatorial in its inner portions, forming so the circular

Fig. 580. — Section through the ciliary region of the human eye (after Iwanoff). a, radi-
ating bundles of the ciliary muscle; 6, deeper bundles; c, circular network; d, annular
bands of Mutter; e. tendon of ciliary muscle; /, muscles on the posterior side of the iris;
g, muscles on the ciliary border of same ; A, ligamentum pectinatum.

network. Finally, internally (d) the so-called " ring muscle" of Muller
makes its appearance. This is formed of tolerably strong fascicles, the
anterior quite independent, the posterior taking their rise from the mus-
cular structure just mentioned.

This, then, is the arrangement of the ciliary muscle of man, but among
the other mammalia it is thoroughly retiform (Flemming). It is strongest
amongst the beasts of prey, weaker among ruminants, and especially so
in the rodents. Although there still exists much difference of opinion
in regard to many minor points relating to the functions of this muscle,
it is commonly agreed that it plays an important part in the accom-
modation of the eye.

In the iris or diaphragm the connective-tissue cells of the whole uvea
present themselves again. In blue eyes, however, they are devoid of pig-
ment, while in those of other deeper tints they are more or less crowded

with either lighter or darker
yellowish, brownish, or even
black granules. Between
these cells the ground sub-
stance is no longer homo-
geneous, but streaky and
broken up into fibrillse, in
fact, it has become genuine
fibrous connective-tissue.

The muscular character
of the iris has been long
recognised. In the first
place, we encounter around
the central aperture, but
more towards its posterior aspect, a muscle known as the sphincter pupiU<&
This is composed of a system of circular bundles of smooth muscular
tissue, of about-0-8-1 mm. in breadth in man (fig. 581, a). From this
sphincter other separate bundles of contractile fibre cells take their rise (as

Fig. 581. — Surface view of the human iris (after Iwanoff"). or,
the sphincter; 6, dilator of the pupil.

ORGANS OF THE BODY. 623

may be seen in the eye of any white rabbit), which, seated likewise
in the back part of the iris, radiate outwards through the tissue of the
latter.

Not so, however, in man.

The dilator appears, to be sure, here also to be a continuation of those
circular fasciculi of the sphincter. At first, still in the neighbourhood of
the latter, we may recognise separate arched interwoven bundles partly in
the circular muscle, partly behind it. After passing beyond the limits
of the circular muscle, however, these radiating bands unite to form a
completely continuous muscular plate, with regular layers of fibres forming
the posterior wall of the iris (b). At the ciliary border, at last, a circular
layer is formed by the interweaving of thicker and thinner bundles spring-
ing from the muscular plate (Iwanoff, Jeropheeff, Merkefy. The muscular
substance of the iris, however, is not connected with the ciliary muscle.

The radiating fibres, then, just mentioned, constitute the dilatator
pupillce.

It is a fact of great interest, that the muscular tissue of the iris, which
in man and the mammalia is composed of involuntary fibres, consists in
birds and scaly amphibia of transversely striated fibres.

At its circumference the diaphragm of the eye receives another element
of tissue on its anterior surface, in the form of the so-called ligamentum
pectinatum iridis (Huek), (§ 309).

The fibres of the latter, originating in a transformation of the membrane
of Deseemet, as we have already seen, and covered at first with the normal
epithelium of this coat, commence near the border of the cornea as a fine
network, which is changed at the edge of the latter into a plexus of
stronger bands. These pass free across the peripheral portion of the an-
terior chamber, and so reach the anterior surface of the iris, in whose
tissue they are lost. The ligamentum pectinatum encloses a circular
space crossed, of course, by bands of fibres known as the " canal of
Fontana" (fig. 580, at h).

In regard to the nature of these fibrous masses much difference of
opinion still exists. Erom their chemical reactions they would appear in
man to be allied to the elastic tissues, without, however, possessing the
same power of resistance to reagents, while among the mammalia they
manifest rather the constitution of connective -tissue. In birds, again,
they give the reactions of elastic tissue.

In all probability there was originally a cellular network here.
On its posterior surface the iris is covered by a laminated coating of
pigmentary epithelium cells, and on its anterior aspect by a single layer
of colourless polyhedral and roundish elements. These latter are con-
tinued in single rows over the bands of the ligamentum pectinatum.

Reserving the arrangement of the vessels of the uvea for the next
section, let us turn now to the nerves of the same. These, the nervi
ciiiares, are distributed principally to the iris and ciliary muscle. Their
number is from 14 to 18, and they spring for the greater part from the
lenticular ganglion.

After piercing the sclera, these twigs advance through the external
layer of the vascular membrane of the eye to the ciliary muscle, giving
oil' in this course a few twigs to the choroid itself. The latter form super-
ficial and deep plexuses, whose fibres are found to be partly medullated,
partly pale, and among them small ganglia are formed by collections of
nerve cells (H. Muller, and C. Schweigger, Sdmich).

624 MANUAL OF HISTOLOGY.

But the nervous supply of the ciliary muscle is much more abundant.
Before their entrance into the latter the ciliary nerves have undergone
repeated subdivision. "Within the muscle they then form a ganglionic
annular plexus, the orbiculus gangliosus, in which, according to Krause
and //. Mutter's observations, ganglia are to be found.

This plexus supplies twigs to the tensor choroidece, besides those
branches to the cornea already mentioned, p. 619, the iris, likewise, is
innervated by it.

In the latter structure, twigs made up of medium-sized and fine dark-
edged fibres may be observed to course inwards from the whole periphery,
dividing as they go dichotomously. Converging while still in the peri-
pheral portion of the iris, they commence the formation of an extremely
complex nervous plexus, presenting rows of transversely anastomosing
twigs. From this, then, in the first place, recurrent branches are given
off towards the ciliary border, and then others directed more inwards.
These, again, form an irregular network of nerve fibres, — about 0'0045-
0*0023 mm. in diameter, at first medullated, but later on losing their
medulla, — which at many of the nodal points presents triangular expan-
sions. This plexus is then prolonged farther into an interlacement of the
finest species of filaments, only 0 -0020-0 "00 18 mm. in diameter. It is
still an unsettled point whether this is a terminal network or not.

While this nervous interlacement just- described belongs more parti-
cularly to the posterior wall of the iris, another is spread over its anterior
surface. Its broader elements are probably sensory.

Finally, a plexus is found traversing the substance of the sphincter,
whose fibres are at first still medullated, but later on pale in appearance.

(L) A very peculiar appearance is frequently to be found in the eyes of
some mammals. This proceeds from the tapctum lucidum, a colourless glittering spot
situated behind the choriocapillaris, between the most internal lamella of the choroid
containing its capillaries and the middle coat, in which the larger vessels are con-
tained. Among the ruminants, in the horse and elephant, &c., it consists of a deli-
cate and regularly undulating arrangement of connective-tissue bundles, which, from
the uniformity of their disposal in wavy lines, gives rise to a play of prismatic colours.
In the carnivora, and in seals also, it consists, on the contrary, of smooth, blunt-
angled nucleated cells. The cell-substance of these presents, according to Schultze,
a very remarkable structure. It consists, namely, of extremely fine-pointed double-
refracting crystals, arranged in groups within the cell. Each of these groups reflects
the light from a particular angle of incidence into another, producing colour. Over
the tapetum the epithelial cells are usually devoid of pigment molecules.

§311.

The vascular system of the uvea (fig. 582) has been the subject of much
study both in earlier and later times. It has been lately investigated in
the most thorough manner by Leber.

Owing to its extreme complication, it will require a very minutely
detailed description, during which, however, we shall have an opportunity
of referring again to the blood-vessels of the sclerotic and cornea already
noticed cursorily (§ 309).

The choroid, corpus ciliare, and iris, all receive their supply from the
ciliary arteries as they are called. Of the latter, those springing directly
from the ophthalmica are known as the posterior, those given off from the
arteries supplying the recti muscles as the anterior.

The first break up again into the short and long posterior ciliary
vessels.

1. The short posterior ciliary arteries (a, b), three or four in number,

OEGANS OF THE BODY.

625

advance to the back of the bulb and split up there into a large number, of
twigs. Besides the hinder part of the sclerotic coat and point of entrance
of the optic nerve (see below), they supply only the choroidea pro-
per, about 20 small
branches lying in the
outer layer of the lat-
ter. Moreover, these
are distributed chiefly
to the back part of the
choroid coat, and reach
neither the iris nor
ciliary processes. They
are, however, con-
nected at certain points
both with the long pos-
terior and the anterior
ciliary vessels. Their
end branches spreading
out internally, break
up finally into the
capillary network of
the choriocapillaris
(d, d).

This capillary net-
work, whose tubes mea-
sure from 0-0090 to
0-0113 mm. in dia-
meter, is one of the
most dense in the
body, especially at the
back of the eyeball,
whereas, anteriorly,
the meshes gradually
increase in size. Its
tubes (fig. 583) radiate
from numerous central
points, which are either
arterial or venous ter-
minal twigs. In the

Fig. 582. — Diagram of the ar-
rangement of the vessels of
the eye-ball (after Leber). a,
large, and 6, small twig from
a short posterior ciliary ar-
tery; c, long posterior; d,
choriocapillaris; e, arterial
collar around the optic nerve,
and branches of the same to
the latter; /, anterior ciliary artery; gr, large circlet of the iris; A, artery of the same; f, small
circlet of the iris; *, capillary network of the sphincter pupillce; I, artery of the ciliary process;
m, artery of the musculus ciliaris; n, recurrent branch to the choroidea; o, posterior conjunc-
tival vessel, and p, anterior; q, arterial branch to the border looped network; r, arteria centralis
retinae; s, artery to the internal sheath of the optic nerve; f, artery to the external sheath of the
same; u, twig from the short ciliary vessels to the sclerotic; v, twig from anterior ciliary artery to same ;
x, vein of one of the vortices; t/, posterior vena ciliaris; z, central vein of the retina; 1, vein of the
internal sheath of optic nerve; 2, of the outer sheath of same: 3, vein and artery of the choroid
which enter the optic nerve; 4, vein of the sclerotic opening into the trunk of a vortex; 5, anterior
ciliary vein; 6, its branches to the sclerotic; 7, vein to the border looped network; 8, anterior, and 9,
posterior conjunctival vein ; 10, venous ciliary plexus (canal of frhlemm); 11. connection of the same
with the anterior ciliary vein; 12, vein of the ciliary muscle running into the plexus ciliaris ; 13. vein
of the ciliary process; 14, vein of the iris; 15, vein of the ciliary muscle emptying into a vortex trunk.

626 MANUAL OF HISTOLOGY.

neighbourhood of the ora serrata this peculiar arrangement of vessels is
no longer preserved.

(2.) Turning now to the sources of blood for the anterior portions of
the choroidea, the processus ciliares and iris, we find besides the anterior
the long posterior ciliary arteries (c).

These two branches after piercing the sclerotic, and without giving off
any twigs, run for a considerable distance over the vascular coat of the
eye to the posterior edge of the ciliary muscle. Here each splits into
two branches, which penetrate into the ciliary muscle (m\ and parting
there from one another bend sideways into arches embracing a correspond-
ing portion of the eye-ball. Thus they take part in the construction of a
double vascular collar in common with the anterior ciliary arteries to which
we must now direct our attention.

(3.) The anterior ciliary arteries (/), five or six in number, piercing the
insertions of the rectic muscles, lie upon the sclera, and running along
the latter for a certain distance, eventually perforate it with many branches
in the neighbourhood of the ciliary muscle.

The two vascular circlets, already alluded to, which are derived from
both kinds of arteries, are — first an anterior,
known for a long time past, the circulus
arteriosus iridis major (g), which is com-
plete, and encircles the outer portion of the
iris, but for the most part within the ciliary
muscle ; and second, a posterior and external
circlet which is incomplete, and imbedded
Fig. Hi-Arrangement of the capit- likewise in the same muscle. This may be
laries of the choriocapiiiaris of the named the circulus arteriosus musculi cilidris

(Leber).

From these two vascular circlets, and partly also immediately from the
arterial tubes supplying them, a series of very important branches are
given off to different parts of the eye-ball, namely, to the choroid (a), the
ciliary muscle (b), the ciliary processes (c), and iris (d).

(a.) The choroidal twigs (n), variable both as to number and calibre,
are connected in the first place with the branches of the posterior short
ciliary arteries, and again take part in the formation of the chorio-capil-
laris : principally of its anterior portion.

(b.) The recurrent branches (??i), passing back into the ciliary musde,
are very numerous. They are arranged in a very fine network within the
latter, and their meshes are disposed according to the direction of its
fibres.

(c.) The arterial twigs to the processus ciliares (I) are very short tubes,
sharply curved backwards and inwards. They enter the structures,
springing from the circulus arteriosus iridis major, after traversing the
ciliary muscle. Each ciliary process then receives either one special twig,
or, as is more frequently the case, two or more are supplied to it by one
such rootlet. In each process itself the arterial vessels split up rapidly,
and subdivide into a considerable number of fine tubes, which form with
arches of anastomosis a beautiful and characteristic network. From the
latter then spring the venous radicles of the part.

(d.) The vessels supplying the iris (h) are all derived from the circulus
arteriosus iridis major, and extend beyond the outer border of the latter
in considerable number. Their direction is more or less towards the
anterior surface, and convergent towards the pupil. Giving off lateral

ORGANS OF THE BODY.

627

"branches they form a long and wide-meshed capillary network. Near the
opening of the iris a certain number of these tubules enter into the con-
struction of a new vascular circlet, the circulus arteriosus iridis minor (i),
but the greater proportion of them bend back in loops, and merge into
venous radicles after supplying the sphincter of the pupil.

§312.

The veins derived from this very complex arterial system do not cor-
respond to its vessels
(fig. 584).

The uvea is pos-
sessed of two sets of
venous canals ; of dif-
ferent degrees of
importance however.
The greater propor-
tion of blood from
this membrane is
taken up, namely, by
a moderate number of
large trunks, the vence
vorticosce (x) while the
anterior ciliary veins
(5) at the foremost
part of the choroid,
and especially in the
ciliary muscle, play
but a subordinate part
in draining these
parts. Veins, corres-
ponding to the pos-
terior ciliary arteries
do not exist.

Let us first, then,
direct our attention
to the vence vorticosce.

These are situated
in the external layer
of the choroid, and are
arranged in stellate
figures or vortices,
numerous wide venous
trunks converging to-
wards a central point.
Of these vascular stars
from four to six well-
developed ' examples
may be distinguished
in addition to some
others less perfect in
form and poorer in
radii. These several systems are connected together by transverse twigs.
The blood of the choriocapillaris is conducted into them by fine veins

Fig. 584.

628 MANUAL OF HISTOLOGY.

passing from behind from the fundus of the bulb, while that from the
foremost portion of the choroid, as well as the ciliary body and iris, is
also received into them.

In the iris and ciliary processes numerous frequently anastomosing
venous radicles take their rise. Crowded close together, they unite at
very acute angles to form larger branches, which reach the choroid after
further intercommunication, and diverging here in groups empty them-
selves into the adjacent vence vorticosce. Owing to their slender make
they may be easily mistaken for arteries.

The venous vessels of the iris (14) springing from the capillary net-
work, and the terminal loops at the edge of the pupil (&), maintain a
course similar to that of the arteries ; they lie, however, nearer to the
posterior surface than the latter, anastomosing also frequently with one
another.

In their further course back again they communicate either directly
with veins of the ciliary processes, or dip into the furrows between the
latter, receiving more blood from them, and from the ciliary muscle
(15). The processus ciliares are, moreover, drained by a regular venous
plexus formed of numerous transverse branches situated within their sub-
stance.

The axial veins, springing from the venae vorticosae of the choroid,
pierce the sclerotic at about the equator of the eye -ball to run external
to the latter.

Beside this system of vessels, there is, as has been already remarked, a
second venous drainage more anteriorly. The blood from some of the
structures lying in the fore part of the eye is carried off, namely, through
the anterior ciliary veins (5), and the canal of Schlemm (10) in connec-
tion with them, presenting an annular venous plexus (Rouget, Leber).
The arrangement of the latter is not, however, by any means the same in
all portions of the ring or in different eyes, and its retiform nature may
be very slightly marked. Small twigs from the inner part of the scle-
rotic, as well as from 12 to 14, somewhat stronger branches from the
ciliary muscles (12), open into this ring. The tubes, leaving the canal of
Schlemm, named by Leber the plexus venosus ciliaris, are very numerous.
They perforate the solera obliquely, opening upon its external surface into
a venous plexus, that of the " anterior ciliary veins."

Having described the vascular supply of the uvea, we shall have but
little difficulty with the vessels of the sclerotic. This tunic is fed by the
same branches of the ophthalmic artery as the vascular membrane, namely,
the art. cil. post, et ant. Their twigs to the sclerotic are seen at (u) and
(v). The veins of these two coats are likewise more or less common to
both. They empty themselves into the anterior ciliary veins and venae
vorticosae. Besides these, however, we have in the posterior part of the
sclerotic the small venae ciliares posticae, which, receiving no blood from
the choroid, constitute a peculiarity in the vascular arrangement of the
fibrous coat. All these vessels, and especially the veins, form a wide-
meshed network over the sclerotic. Corresponding to them we find also
a similar loose reticulum of capillaries.

The short posterior ciliary arteries (a, 6), whose distribution to the
choroid has been described in the foregoing section, have peculiar and
important relations in the neighbourhood of the entrance of the optic
nerve into the eye-ball. They are (e) connected, namely, with the
vascular supply of the retina (see below), which is otherwise a perfectly

ORGANS OF THE BODY.

629

distinct system of vessels. Two twigs from the posterior ciliary arteries
form a ring around the nerve, sending off one set of small branches in
between the fibres of the latter, and anothe.r externally to the choroid.
In this way provision is made for indirect communication between the
two circulations. In addition to this there is also a direct communication,
however, consisting in arterial and line venous twigs and capillaries, which
pass directly from the choroid into the optic nerve.

The conjunctiva of the sclerotic is supplied by the vessels of the lids
and lachrymal gland ; it is, therefore, also independently provided. Its
arteries are represented at (o) and (p). Near the border of the cornea
only are they connected with those of the sclerotic.

Here, namely, the end branches of the scleral vessel:? communicate
with one another in arches. From the latter, then, in the first place,
recurrent loops are seen to spring, which course back through the
conjunctiva, anastomosing with the proper vessels of that membrane.
Further, there arise partly from these loops, and partly also from the
terminal twigs of the anterior ciliary arteries themselves, the branches for
that capillary network already mentioned (§ 309) situated round the
border of the cornea. This is drained by the anterior ciliary veins to
which we now turn.

These (5) receive their blood from four different sources.

(1.) The radicles springing from the border network of the cornea,
which form a polygonal network encircling the latter, in the form of a
ring from 4 to 7 mm. in breadth, lying upon the sclera. This is known
as the episcleral venous network, and from it twigs of the ciliary veins
take their rise (7).

(2.) In its whole extent the venous network just mentioned is rein-
forced from the capillaries of the sclerotic itself (6).

(3.) Into the ciliary veins, also, the efferent vessels of the canal of
Schlemm (11), as well as those of the
ciliary muscle (12), empty themselves.

(4.) Finally, we have venous twigs spring-
ing up in the neighbouring portions of
the conjunctiva and corresponding to the
arterial connecting arches, which unite with
them.

§ 313.

The refracting media of the eye, situated
behind the cornea, consist of the aqueous
humour, the lens, and the vitreous humour.

Of these the lens (fig. 585), with its
capsule, have been already described in
speaking of the tissue of which it is com-
posed (p. 276). The vitreous humour was
also alluded to in connection with gelatin-
ous tissue (p. 190).

There remains then for our considera-
tion, in the first place, the aqueous humour.
With it both chambers of the eye are
filled. According to His it passes easily through the tissue of the cornea,
and we know that when evacuated it is very rapidly replaced. The
aqueous humour is an alkaline fiuid of a sp. gr. of 1 '003-1 "009. It

Fig. 585. — Diagram of the structure of
the lens, a, capsule ; 6, epithelium ;
c, lens fibres; d, anterior; and e, pos-
terior end ; /, nuclear zone.

630 MANUAL OF HISTOLOGY.

possesses no form elements, but is simply water containing 1-1-5 per
cent, of solid matter in solution , which is secreted, probably, by the
vessels of the ciliary processes and iris. The solids dissolved in the
humour aqueous are albumen in combination with soda, urea according
to Millon (p. 42), extractives, and mineral substances. Among the latter
chloride of sodium is the chief.

We avail ourselves here of an analysis of Lohmeyer's, in which he gives
the following average composition of the fluid, as found in the eye of the
calf:—

Water, 986-870

Albuminate of sodium, .... . 1-223

Extractives, 4*210

Chloride of sodium, 6 '890

Chloride of potassium, . . ; . . 0'113

Sulphate of potassium, ..... 0-221

Earthy phosphates, 0-214

Lime earths, . . . . . . . 0'259

The refracting index of the human aqueous humour stands, according
to Krause, at 1*3349. The exponents of refraction for the vitreous
humour, lens, and cornea, are all mentioned with their respective tissues.

The fact that puncture of the vitreous humour causes the escape of some
fluid, but not of all contained in it, seems to indicate (apart from its finer
texture), the presence of some structure within it of membranous or septal
nature. But this is still a matter of great obscurity. The existence of
a system of concentric lamellae, or of vertical partitions arranged like those
of an orange, radiating from a centre, has been supposed by many from
what they have observed in artificially hardened eyes. Neither of these
views, however, has been confirmed.

But the presence of an external envelope, of the membrana hyaloidea,
was for years admitted by all. This is an extremely delicate, structure-
less pellicle lying loose upon the retina, and only attached at the entrance
of the optic nerve to the latter, and anteriorly to the ciliary body.

In the neighbourhood of the ora serrata it was formerly supposed that
the membrana hyaloidea split into an interior delicate and posterior
thicker lamina. These, increasing gradually in distance from one another,
were held eventually to be inserted into the capsule of the lens and fused
into it. The posterior leaf was known as the true hyaloidea, and the anterior
the zonula Zinnii, while the passages enclosed within them, which encircles
the lens in its equator, received the name of the canal of Petit. The latter
is occupied either by a small amount of fluid during life (Koelliker), or
the two lamina come into contact (Herile).

This, however, has been denied, within the last few years, by the most
competent authorities (Merkel, Iwanoff).

According to their views there is no such thing as a special membrana
hyaloidea, but merely a limitans of the retina, while anteriorly the zonula
ciliaris becomes well marked as a special layer. Schwalbe, however,
opposes this view in favour of the old idea.

The zone of Zinn, closely united to the ciliary processes, is indented by
them, presenting somewhat the appearance of a ruff, inserted with its
wavy border into the capsule of the lens. Although to the naked eye it
appears formed of a strong transparent membrane, it presents under the
microscope a system of very pale, stiff fibres, holding a meridional dircx.

ORGANS OF THE BODY.

631

tion, best seen near the lens. These were discovered by Henle. They am
some of them very fine, some stronger, as though made up of bundles of
the first, and are often connected together in a retiform manner. In many
points this membrane resembles certain kinds of connective-tissue, although
we are unable to discover at the nodal parts the usual nucleus of the con-
nective-tissue corpuscle. The fibres resist also, with great obstinacy, the
action both of alkalies and acids.

§ 314.

The retina of the eye consists primarily of an expansion of the optic
nerve; but, besides this, it contains other form-elements of various kinds,
presenting a very complex structure. The extraordinary delicacy of this
membrane, combined with its liability to rapid decomposition, render it
one of the most difficult objects of histological investigation. For this
reason the controversies, in regard to its structure, are still far from being
set at rest, in spite of very extensive and thorough study, aided by the
discovery of the action of chromic, and later of osmic acids, on such
tissues.

Of the later observers who have largely added to our knowledge of the
structure of the retina, H. Mutter deserves to be first mentioned. More

Fig. 586. Fig. 587.

Vertical sections of the human retina. Fig. 586, half an inch from the entrance of the
optic nerve. Fig. 587, close to the latter. 1, layer of the rods and cones (columnar
layer), bounded underneath by the membrana limitans externa; 2, external granular
layer; 3, intergrannlar layer; 4, internal granular layer; 5, molecular layer ; 6. layer
of the ganglion cells; 7, expansion of optic fiores ; 8, sustentacular fibres of Muller;
9, their attachment to the membrana limitans inlerna ; 10, the latter.

recently still, the master-mind of Max Schultze has swept away many of the
difficulties which hung about this subject, on which he was justly regarded
as the highest authority at the time of his lamented death, which took
place on the 16th of January 1874.
41

632 MANUAL OF HISTOLOGY.

The depth of this nervous coat, at the point of entrance of the optic
nerve, where it is greatest, is from O38 to 0'23 mm. Anteriorly it thins
off to about half of this, and at its foremost edge it is still 0'09 mm. in
thickness. Here it ends with an undulating border, the ora serrata.
External to the point of entrance of the optic nerve, and about 3 '4 mm.
from the centre of the latter, a yellow spot, the macula lutea, may be
observed, an oval patch about 3'4 mm. long and 1*13 mm. in breadth,
tinged with diffuse yellow pigment. In its centre it presents fh&fovea cen-
t ralis, an irregular depression corresponding to a great decrease in thick-
ness of the retina. The macula lutea is the point at which sight is
clearest.

The retina (figs. 586 and 587) consists of the following layers, in suc-
cession from without inwards : (1) the layer of the rods and cones
(columnar layer, 1.1); (2) the membrana limitans externa (between 1
and 2) ; (3) external granular layer (2.2) ; (4) the wtergranular layer
(3.3) ; (5) the internal granular layer (4.4) ; (6) the so-called molecular
layer (5.5) ; (7) the ganglionic cell layer (6.6) ; (8) the expansion of the
optic nerve (7.7); (9) of the membrana limitans interna (10.10); we
add finally (10) of the pigmentary layer.

We have recently been brought to consider this chaos of textural
elements as consisting of two essentially different constituents, although
it is still difficult to draw everywhere a sharp line between them. The
retina possesses in the first place (and in this it resembles the central nerv-
ous system) a connective-tissue framework. This springs up in the outer
part of the retina, soon attaining, at the inner side of the rod and cone
layer, considerable development as the membrana limitans externa. From
this it spreads itself throughout all the retinal strata lying internal to
this, and terminates by forming the membrana limitans interna. Between
these two membranes are stretched a number of vertical sustentacular
septa, the radial fibres, or fibres of Muller. The remainder of the retina
— and in this is included a system of similarly radiating or oblique nervous
fibrillse — -'may probably be reckoned' to the nervous tissue.

REMARKS. — Literature is very rich in new essays upon the structure of the retina.
The last are those of H. Muller and M. Schullze.

§ 315.

We turn now, first of all, to the delicate sustentacular tissue of the
retina.

For our acquaintance with this we are especially indebted to M. Schnltze^
and any one who has thoroughly investigated the subject with an unbiassed
mind will be forced to concede the correctness of his views.

The point from which this framework of the retina starts (fig. 588,
A) is a modified bounding layer, about O'OOll mm. in thickness, the
transparent membrana limitans interna (I). Anteriorly it is stronger than
posteriorly. Its internal surface is smooth, but not so the external, from
which a series of sustentacular fibres (e) take origin, which traverse
almost the whole thickness of the retina, perpendicularly to its internal
surface. These are known as the radiating fibres of Muller. Absent in
the macula lutea, they increase in quantity anteriorly. They spring from
the msmbrana limitans interna with a delicate triangular flat or conical
pedicle, or with several extremely fine fibrils, which unite at very acute
angles (e, below). In their course they give off numerous branches, by which
thev are connected one with another in a retiform manner. In addition

ORGANS OF THE BODY.

633

to these stronger bands, and passing into them without any sharp line of

distinction, we find at certain points, but especially in the molecular

(g) and intergranular layer

(d), an extremely delicate

porous or spongy tissue (e),

like that already met with

in the grey matter of the

nervous centres. This (neu-

roglia) has been regarded by

some as an artificial product,

formed by the coagulating

action of the chromic acid

on some of the fluids of the

tissue (Henle).

The spongy substance in
question is so delicate in man
and many other mammals,
that with weak microscopic
power we are only able to
make out a dotted mass,
perhaps adherent to the fibres
of Mutter. Very strong
lenses, on the other hand,
reveal its reticulated struc-
ture and connection with the
sustentacular bands, whose
outline on that account is
by no means smooth. In
different portions of the
retina, however, this susten-
tacular matter presents much
variety. In some of the
nodal points nuclei are to be
seen, so that here again we
have the cellular equivalents
of the grey matter of brain
and spinal cord. In the in-
ternal granular layer the
fibres of Muller are observed
to be possessed invariably of
elongated nuclei (er).

The sustentacular matter we are considering extends as far as the
internal surface of the so-called rod-layer (columnar).

Here we find a repetition of the relations already seen at the internal
surface of the retina, although less marked, namely, a fusing together of
the fibres of Muller to form a cribriform limiting membrane. To this
(a, a), which u'sually presents itself in vertical section as a sharply
defined line, the name of membrana limitans externa has been given
(Schultze). But the name is unfortunately selected, for many of these
bands of Muller apparently terminate before reaching it, in the first place
— namely, in the intergranular layer, or even deeper still \ and then, again,
as very recent observations show, the connective-tissue sustentacular
matter does not cease at the membrana limitans externa. It extends

Fig. 588. — Diagram of the retina, after Schultze, with its
connective-tissue portion, a, Membrana limitans externa ;
e, radiating, or Miil/ers sustentacular fibres, with their
nuclei ef ; d, framework of the intergranular, and gr, of the
molecular layer ; I, membrana limilans interna.

634

MANUAL OF HISTOLOGY.

further outwards still as a system of delicate envelopes, the consideration
of which we must reserve for a future section.,

§ 316. '

We must now devote our attention more particularly to the several
strata of the retina in succession.

(1.) The columnar layer, stratum Ijaeillosum or membrana Jacobi, is
composed of two kinds of very remarkable elements — the rods and cones,
which are arranged perpendicularly side by side.

The rods, bacilli (fig. 589, b) are delicate cylinders extending through
the whole thickness of Jacob's membrane. They consist invariably of
two portions, as was shown by Braun and Krause, after Mutter, — of an
external member, slender, homogeneous, and transparent, and possessed
of high refracting power, and of an internal member. The latter is some-
what greater in diameter than the first, and paler in outline; it not unfre-
quently presents a granular appearance.

The internal joints of the rods become more deeply dyed by carmine
than the external, which, on the other hand, are
blackened by the action of osmic acid, while the
internal member remains for a long time quite
colourless in the same. The reagent just mention-
ed has come greatly into use since its application
by Schultze to the investigation of the structure
of the retina. According to this observer, the
external member is double refracting in the frog,
but not the internal. The length of the whole
rod in man, which is greatest in the posterior part
of the eye, is 0*0600 mm.; more anteriorly it is
O'OSOl mm., and at the ora serrata about 0-0399.
Its thickness may be stated at from 0'0016 to
0'0018 mm. (Milller). Eegarded from a chemical
point of view, these structures appear to con-
sist of an extremely perishable albuminoid sub-
stance. Owing to this, they present themselves
under the microscope in the greatest variety of
shapes.

The external truncated end of the column is
in contact with the pigmentary epithelium of the
choroid. In the three first classes of the verte-
brates the cells of the latter form around the
external members of the rods (and also of the
cones) complete pigmentary sheaths.

This may also be seen among the mammalia,
but slightly marked however. Prom the under
surface of these cells filiform prolongations of
their bodies extend downwards between the rods
(and cones), like pencils of very fine hairs.

The inner members of the rods extend some-
what beyond the limitans externa in the form of very fine points, easily
broken off, and which are prolonged into filaments of the most extreme
delicacy. Under careful treatment with certain reagents, the latter are
found to present varicosities, similar to those so characteristic of nervous
filaments. Each of these bacillary threads traverses the external granular

Fig. 589.— Rods and cones from
the equatorial portion of the
retina, after Schultze. a, Mem-
brana limituns fxterna; 6,
rods; c, cones; V, rod gra-
nule; c', cone granule; d, in-
tergranular layer.

ORGANS OF THE BODY.

635

layer perpendicularly, — or in other words, in a direction convergent
towards the centre of the eyeball Eventually it terminates in a body
known as its "granule" (&'). We shall be obliged to refer to it again.

The rods of the retina, like the cones, belong to those few tissue
elements of the animal body, which manifest characteristic differences
among the various classes of living creatures. In the eyes of naked
amphibians, such as frogs, toads, and salamanders, they are enormously
large.

The great tendency to change after death, manifested by the rods,
renders it a difficult point to decide how far many other structural pecu-
liarities recently described by numerous observers really exist in the living
retina.

The first point to be borne in mind is, that the internal member of the
column is not found to be homo-
geneous among all the mammalia. In
connection with the larger rods of the
batrachia (fig. 590, 2, 3), of fishes
(4), and even of birds (1), we meet —
namely, with remarkable lenticular
bodies of hemispherical or planopara-
bolic figure, whose flat sides are
applied to the bases of the external
members (a, a). These structures
are extremely rapid in decomposition
(Schultze). They have been named
" bacillary elipsoids" (Stabchen elip-
soide) by Krause.

It has been long known (but the
process has been recently more fully
investigated by Schultze) that the ex-
ternal halves of the rods may resolve
themselves (fig. 591, 5) into a number
of transverse plates, or if the process of
decomposition have progressed farther,
into thin disks, resembling slightly
those of the muscle fibres. The transverse markings are, in man and the
mammals, about 0*0003-0 "0004 mm. distant from one another (Schultze).

The external members of the rods present further, as has been known
for years (Hensen, Schultze), a peculiar longitudinal striation. Transverse
sections in the frog show that this is produced by a longitudinal grooving,
running to the extent of internal cleavage.

However — and here we tread upon very uncertain ground — the in-
ternal joints of the rods in man, and many mammals (fig. 591,1,3), present
superficial longitudinal striation too. This is, perhaps, directly continu-
ous with the longitudinal cleavage rifts of the external members. It
appears to correspond to a delicately grooved connective-tissue investing
lamina, which Would therefore represent an outward prolongation of the
membrana limitans externa. Quite recently this has been named by
Schultze. the "fibre-basket." According to this observer, however, the
internal joint of the rod presents, likewise, a fibrillated structure, and,
moreover, in the interior.

We shall now enter somewhat further into the consideration of the
various views entertained upon this very obscure subject.

Fig. 590.— Structure of the rods of the retina.
1, From the hen; 2, from the frog; 3, from
the salamander ; 4, from the pike, showing
external and internal members, and in the
latter the lenticular bodies referred to in the
text ; 5, resolution of the external portion of
a column into disks, from the frog (after
Schultze).

636

MANUAL OHF ISTOLOGY.

In the year 1860 a very fine fibre was said by Hitter to exist, running,
through the axis of the rod. This, lie alleged,
terminates externally with a slight swelling,
leaving the hollow rod internally in the form of
the bacillary thread, already referred to. This
statement has received confirmation from Manz,
Spiess, Hensen, and Hasse, but its correctness
has been questioned by Krause, Hulke, Steinlin,
and others. In fig. 592, 2, we have given a
representation of these "fibres of Ritter" after
/Schultze. Their existence in the recent retina
may be regarded as still undecided.

Turning now to the cones (fig. 588, B, c), we
find a still more remarkable structure than in the
last. In man these bodies present the shape of
slender flasks, whose bases are seated upon the
external limiting membrane. At their narrower
£nds they run into somewhat pointed rod-like
structures, of the most extreme delicacy, and very
prone to rapid decomposition. These are known
as the cone-styles (Zapfenstabchen). They cor-
respond to the outer halves of the so-nearly related
rods, and manifest a tendency to break up into
the same series of disks as the latter (fig. 591, 2 a ;
594, b). The inferior expanded portion (answer-
ing to the belly of the flask), the body of the cone,
is at one time stumpy and broad, at another, thin
and slender; from O0041 to 0'0067 mm. in
diameter. The cones of the macula lutea are
particularly slender; they will be referred to
again later on. Here also the same longitudinal
striation is presented to us (fig. 591, 2, b), which
we have seen in the analogous internal joint of the
rods. The interior is likewise observed to possess
a fibrillated structure. At their bases, immedi-
ately underneath the limitans (fig. 591, 2, d), is
situated the " cone granule" a slight constriction
intervening between the two. This body consists of a small oval or pyri-
form cell, possessing both nucleus and nucleolus, and belonging to the
external granular layer of the retina. The whole length of the cones is,
as a rule, somewhat less than that of the rods, and sometimes consider-
ably so, as in the retina of the pig (Schultze).

In regard to the proportion of rods and cones in the human retina,
much difference has been remarked according to locality. In the macula
lutea, where the sense of sight is most acute, cones alone are to be found,
as was discovered by Henle (fig. 593, 1). Around this spot the cones are
still crowded, so that they are only encircled by single rows of rods
(2). Further forwards and externally they occur more rarely, and are
surrounded by several rings of rods (3). The number of the latter,
therefore, in the whole retina, exceeds by far that of the cones.

The rods and cones of the ape tribe are similar in all points to those of
the human being.

In most of our domestic animals, likewise, such as the ox, sheep, pig,

Fig. 591.— Fibrillar coating of
rods and cones. 1. Rods.
2. Cones (of man), a, Ex-
ternal ; 6, internal joint ; c,
bacillary threads; d, limit-
ans externa. 3. Rods (from
the sheep). The fibrillag
here overtop the internal
joint. The external mem-
ber is missing (after
Schultze).

ORGANS OF THE BODY.

637

horse, and dog, the same variety in the distribution of both elements of
the retina may be observed.

Strange to say, however, the retina of the bat is, according to Scliultze,
quite destitute of cones (although this is indeed
denied by Krause). The same is the case with
the hedgehog, the mouse, the Guinea-pig, and
mole, as well as many nocturnal and burrowing
animals.

In the cat we find but ill-developed cones, while
in rabbit and rat traces merely of them exist
(Schultze). Whether, as appears probable, the
retina of the whale is quite without cones, is a
point which requires further investigation.

The eyes of bony fishes approach those of man in
many respects ; their cones are of considerable size.
In rays and sharks rods alone are to be found.

The case is quite different in birds and the naked
amphibia. In the first of these cones are present
in large numbers, reminding us of the yellow spot
in the human eye. In the lizard and chameleon,
on the other hand, rods are entirely absent ; perhaps
also in the snake.

The cones of the bird's retina are remarkable for
peculiar spheroidal structures at the junction of style
and body, more or less imbedded in the latter.
They are glittering in appearance, and occupy the
whole breadth of the cone, so that no ray of light
can pass them by. They are usually of a yellow or red tint, but rarely
colourless. In owls (nocturnal fowl, as every one knows) the long rods
become again so prominent, and the cones so few in number, that the
ordinary structure of the bird's retina is reversed. Red spheroids are never
found here, and those yellow present become paler near the ora serrata.

Globules similar to those just mentioned are to be met with also
among the scaly amphibia. In the cones of the
tortoise they are red, yellow, or colourless ; in
lizards yellow.

Among the naked amphibia we find a few
very small cones standing amid a host of colossal
rods.

The former present either colourless or pale
yellowish globules at the point of union of style
and body.

The " twin cones," as they are called, discovered
some time ago by Hannover, present to us an-
other remarkable modification of these structures.
These are united to each other by their lateral
surfaces, remaining on the other hand quite dis-
tinct as regards their styles and bodies. They are frequently met with
in bony fishes; but even in birds and amphibia may be found inter-
spersed with the simple cones (Schultze).

They, are probably the result of an uncompleted process of longitudinal
segmentation of the simple elements (Steinlin, Dobrowolsky).

Those peculiar. lenticular bodies already mentioned as occurring within

Fig. 592.— Structure of the
rods of the retina. 1.
From the Guinea-pig ; a.
with internal and exter-
nal member; 6, still in
connection with a trans-
versely striped granule.
2. Macerated rods from
MacacwCynomolgus,v(\\\\-
altered external and in-
ternal members, and the
"fibres of Bitter'' in the
axes of the latter (after
Schultze).

Fig. 593.— The stratum bacilio-
sum viewed from without, a,
cones; &, cone-styles; c, ordi-
nary rods. 1. From the yellow
spot; 2. from the border of
the same; 3. from the middle
of the retina.

C38

MANUAL OF HISTOLOGY.

the substance of the internal members of the rods, close to their junction
with the outer halves (ellipsoids of Krause), are of not very infrequent
occurrence in apes (fig. 594, b), frogs, and water
newts (Schultze). The human cones possess them
also (Dobrowolsky).

(2.) Having already devoted sufficient time to the
consideration of the membrana limitans externa in the
foregoing §, we shall now turn to the next stratum.

(3.) The external granular layer, stratum, granule-
sum externum consists of, besides the sustentacular
connective-tissue, several strata of small cells, whose
scanty body merely covers thinly their nuclei (fig.
595, A between a and d). The whole bed ranges in
thickness from 0*0501 to 0-0600 mm. over the greater
part of the retina, but decreases in depth both to-
wards the ora serrata and near the axis of the eye*
The cells of which this layer is made up are con-
nected both with the rods and cones, and have con-
sequently been classed into cone granules (fig. 589, b')
and rod granules (c'). The former are somewhat
pyriform or roundish oval in shape, and are remark-
able for their size (0-0090-0-0120 in length, 0-0041-
0-0061 mm. in breadth) : they also possess both a
large nucleus and nucleolus. They are never marked
by those dark transverse lines discovered recently by
Henle, which are only to be seen on the rod granules.
We have already described these bodies as applied
to the bases of the cones, so that nothing more need
be said here. The second species of granules are
smaller (0 '0045-0 '0079 mm.) oval, and generally
more numerous than the last. They are rarely applied
immediately to the bases of the rods, but are, as a
rule, connected with the latter by a shorter or longer
filament as the case may be. Those dark transverse
zones, already alluded to, which are observed on them (fig. 592, 1), are
still difficult to interpret. They are possibly post-mortem appearances.
They may, be single or multiple, but are usually double on each rod
granule (Henle, Hasse, Schultze).

There now remain for our consideration the nervous fibre elements of
the inter-granular layer.

As the fine fibres coming from the extremities of the rods enter the
corpuscles above, so do they leave the same at their opposite end, and
descending perpendicularly enter the inter-granular layer. Here they
appear to terminate with a fusiform or button-shaped swelling, exceeding
the ordinary varicosities in magnitude (fig. 595, B; fig. 589). But in
reality they have a longer course. Thus Hasse has in many cases seen a
delicate filament leaving this swelling, and losing itself in the inter-
granular layer. He looks, therefore, upon the little body as '•' an inter-
polated ganglion cell."

According to Schultze's observations, extremely delicate filaments may
be seen very distinctly to spring from these small swellings (at least in
birds and amphibia), and taking a horizontal course to become lost in the
tangle of the inter-granular layer.

Fij?. 594. — 0, human
cone with decomposed
external member, and
an apparently fibrous
internal half; 6, the
same from Macacus
ct/nomolgus, showing
division into plates of
the s'yle, and lenti-
cular structure in the
body.

ORGANS OF THE BODY.

639

cone granule

r

C

The fibres which descend perpendicularly from
through the external granu-
lar layer (tig. 589), differ
from the rod fibrillee in their
greater thickness (reaching
0-0029 ram.) though still of
great delicacy. They tra-
verse the layer just men- A
tioned in a straight course,
coming likewise to an end
at the outer surface of the
stratum intergranulosum in
a conical swelling. In this
course they present consider-
able resemblance to axis
cylinders, and give indica-
tions of being made up of
the most delicate axis-cylin-
der fibrillae (comp. § 176).
Schnltze states (the expan-
sion on the fibres having
been recognised, however,
before by Muller and Henle)
that in the stratum inter-
granulosum he has distinctly
seen a splitting up of those
cone fibres into extremely
delicate fibrillae, whose
course from that on is hori-
zontal (fig. 595, B, d).
Hasse, on the other hand,
never observed more than
three of these processes, one
single in the middle, and
one at either side. He re-
girds this expansion as tri-
angular and smooth. The
central process, he believes,
moreover, he has followed
up in a perpendicular course
into the inter-granular layer.

It seems almost super-
fluous to remark that the external granular layer is only composed of rod
corpuscles when the retina is destitute of cones.

Finally, this layer appears to possess no connective-tissue cells.

§317.

Passing on now to the consideration of the remaining layers of the
retina, we take the next in succession.

(4.) The stratum intergranulosum or intergranular layer (fig. 595, A,
By d, d) which is about O'OIO mm. thick, is crossed, as we know already,
by the radial fibres of Muller. The finely dotted substance of the
intergranular layer, which presents the appearance of being streaked

Fig. 595.— Diagram of the retina, after Schttltze. B, neural
constituents; 6, rods with external and internal members;
c, cones with style and body ; 6/, rod-granule, and c/, cone
granule; d, expansion of the cone fibre forming very
delicate fibrillae in the intergranular layer ; /, granules of
the internal granular layer; g, maze of very delicate fila-
ments in the molecular stratum; h, ganglion cells; A',
their axis-cylinder process ; t, nerve-fibre layer.

640 MANUAL OF HISTOLOGY.

perpendicularly by the fibres of Muller (when seen in vertical section)
is found to be composed mainly of a dense connective-tissue network.
It contains, as was found by Muller and Schultze in fishes, and as Koel-
liker recognised in the mammalia, a superficially expanded network (with
nuclei in the nodal points), formed by the union of flattened stellate
cells. This exists, according to Krause, as a single layer in all verte-
brates likewise, and has been named by him membrana fenestrata, and
declared to be an extremely important " boundary structure " for the
retina.

At present but little is known as to the arrangement of the nervous
fibre elements in the intergranular layer. According to Schultze, there
exists here an interlacement of the finest fibrill?e running horizontally and
obliquely (fig. 596, B, d), formed by the splitting up of the rod and cone
fibres already mentioned (§ 316). In the opinion of Hasse, however, the
two side processes only of the latter run a short distance in an oblique
direction, the other middle fibre sinking perpendicularly into the stratum
intergranulosum.

(5.) The stratum granulosum internum or internal granular layer is
usually (0'03-0'04 mm.) of less depth in man than the external. Its
" granules " are also somewhat larger, and more distinct in outline.

From the observations of Vintschgau, Muller, and Schultze, it would
appear that two kinds of elements may be distinguished here. In the
first place (fig. 596, B, /), we meet with roundish cells remarkable for
their distinct and brilliant outline, large nuclei with nucleoli, and small
amount of cell-body. They are usually spoken of as bipolar, i.e., giving
off a process at either end. These processes are extremely delicate, but
that directed outwards towards the intergranular layer is of considerably
greater diameter than that springing from the opposite pole (Schultze) —
in the second place, we find pale-edged oval nuclei with large nucleoli (A,ef).

The latter elements belong to the connective-tissue of the part. They
are not, however, as was formerly supposed, imbedded in the fibres of
Muller, but only firmly seated upon the latter, enveloped in masses of
delicate spongy tissue, and may be regarded as the central points of cell-
like bodies. In number they fall far short of the first species of granule.
For the rest, the connective-tissue framework of the internal granular
stratum presents the same constitution as that of the external.

Here also we are ignorant of the course of the nerve fibres. As in the
last layer treated of, so here strong fibres, corresponding to the axis
cylinders of the cones, are wanting in the stratum granulosum externum.
We can only expect to find here primitive fibrillae, or plexuses of the
same. The fine threads which spring from both poles of the " granules,"
giving to the latter the appearance of small bipolar ganglion-cells, are
probably fragments of such. After a short course, however, they are
lost to sight. In some instances such a thread, springing from a cell
situated high up, extends upwards into the inter-granular layer. Again,
springing from cells seated low down near the molecular layer, filiform
processes may be seen which sink into the latter.

(6.) The stratum moleculare, or finely granular layer (Bg), presents very
much the appearance of the delicate molecular matter already encountered
in the grey substance of the brain and spinal cord. Under high micro-
scopic power, it is found to be made up of fine spongy tissue. As has
been before mentioned (§ 315), this layer (in man 0'03-0'04 mm. thick)
is traversed vertically by the fibres of Muller. It appears to contain a

ORGANS OF THE BODY.

t>41

complete maze (B, g) of the most delicate nerve fibrillae (Schultze, Steinlin,
Hasse), which, there is every reason to believe, spring from the bipolar
cells of the internal granular layer and from the ganglion cells.

(7.) The stratum cellulosum, or layer of the ganglion corpuscles, is the
next in order. It lies next the inner surface of preceding layer, but is
indistinctly marked off against the latter. Its pale, delicate, membraneless
cells (fig. 586, 587, 6 ; 596, B, h) are of different sizes, and may measure,
when particularly large, 0-0377 mm. in diameter. They belong, partly at
least, to the multipolar class, like those of the brain and spinal cord, and
appear also to possess a fibrillated structure (§ 179, fig. 308). It is pro-
bable, also, that their ramifications have the same relations here as in the
nervous centres. One of them directed inwards, the axis-cylinder pro-
cess (fig. 596, B, h') appears to be continuous with one of the horizontal
optic fibres (i) of the stra-
tum fibrillosum (Corti, Re-
mak, Koelliker, H. Muller,
Schultze, Hasse, and others),
while protoplasm processes,
on the other hand, are given off
externally (g\ and it is sup-
posed undergo repeated sub-
division here, forming in the
delicate spongy tissue of -the
molecular layer a tangle of
the most delicate, and pro-
bably varicose filaments.

Finally, commissural pro-
cesses have been stated to
exist between adjacent gan-
glion cells ( Corti, Koelliker) ;
but this has lately been again
questioned by many.

The depth of the stratum,
cellulosum (figs. 586 and
587, 6) varies in the most
interesting way, according to
locality. It is greatest op-
posite the yellow spot, where
several rows of cells, some-
times from 6 to 10, may be
observed lying one over the
other. Here it may present
a thickness of 0'0999 mm.,
except in the fovea centralis,
where it is much less. With
the distance from the macula
lutea the ganglionic layer
decreases more and more in
depth, until but two rows of
cells are to be seen, and then gradually one alone. In the vicinity of the
ora serrata, finally, the ganglionic corpuscles are only met with singly, and
with an ever-increasing interval between them.

In the middle portion of the retina the quantity of sustentacular con-

Fig. 596.

642 MANUAL OF HISTOLOGY.

nective-tissue found between these cells is small, while anteriorly the
fibres of Muller, becoming more and more numerous as we advance in
that direction, form regular compartments for their accommodation.

(8.) We turn now to the expansion of the optic, nerve, the stratum
ftbrillosum. The nerve tubes of the options, which, with Schultze, we
believe to be possessed of no primitive sheath, and which must conse-
quently be of the same nature as the nerve tubes of the centres, lie in the
trunk of the former in bundles, separated by interstitial connective-tissue.
Here they are to be seen as dark fibres 0'0045-0-0014 mm. in thickness,
and frequently varicose ; and in this form they pass through the lamina
cribrosa. In their passage through the funnel-shaped opening in the
sclerotic, and as far as the collicuius nervi optici (i.e., that slight eminence
projecting internally at the point of entrance of the nerve), they lose this
dark-edged medullated appearance. Here they commence to spread
out, forming a membranous layer of pale fibres, that is, of naked axis
cylinders covering the inner surface of the retina (Bowman, Remak,
Schultze), but still associated in groups. Diverging now more and more,
the bundles are seen to anastomose at very acute angles, forming one of
those characteristic plexuses so frequently to be met with immediately
before the termination of nerves. Tracing up this expansion of the fibres
towards the ora serrata, we find the fasciculi becoming thinner and
thinner, and the distance increasing between them. Finally, scattered
nerve tubes alone are to be seen. These are extremely delicate and
marked with slight varicosities, and decrease in number more and more
the further we advance forwards. Throughout the whole retina they
probably terminate by sinking into the multipolar ganglion cells of the
layer already described. From what we have just seen we should expect
to find great inequality in the thickness of various parts of the stratum
fibrillosum ; and so it is ; thus, in the neighbourhood of the entrance of
the optic nerve, the layer is 0'29 mm. in depth, sinking rapidly to 0-099
mm., and decreasing so much anteriorly that close to the ora serrata it is
only 0-0026 mm.

The occurrence of dark-bordered medullated fibres in some retinae is
remarkable. Thus, in the eyes of certain of the rodentia they exist
normally, as in the rabbit and hare, where they present themselves in the
form of two bands of white fibres streaming into the retina. The same
medullated retinal fibres have not unfrequently also been observed in the
eye of the dog, and in a few cases in that of the ox (H. Muller) and man
( Virclww).

The expansion of the optic fibres takes place between the extremities
of the fibres of Muller, as they are about to be inserted into the mem-
brana limitans internet. These fibres, as we have already remarked in
speaking of the stratum cellulosum, are at the fundus of the eye narrow
and fine, as they lie between the massive bundles of fibres situated here,
but become more and more bulky anteriorly, thus affording extra support
with their broad expanded bases to the nerve fibres, where the latter de-
crease in number, and seem specially to require it.

(9.) The membrana limitans interna has been already described above.

§ 318.

There now remains for our consideration the special structure of two
spots in particular in this complicated structure, the retina ; these are the
macula lutea and ciliary or anterior border.

ORGANS OF THE BODY.

643

The yellow spot, or macula lutea (fig. 597), from the fact of its being
the most sensitive portion of the retina, and also from its peculiar texture,
possesses for the histologist the highest interest.

Fig. 597. — Diagram of the macula lutea and fovea ccntralis of the human retina, In vertical section
(after Schultze). a, pigmentary; b, columnar; and c, external granular layer; d, inferior fibrous
portion of latter; /, internal granular layer ; g, molecular stratum ; A, stratum cellulosum ; », layer
of optic fibres.

If we examine the different layers of this locality (in which the susten-
tacular matter is in general but ill developed), in order from within out-
wards, we remark that the layer of the optic fibres (i) disappears very
early, so that even at a considerable distance from the fovea centralis the
stratum of the ganglion corpuscles is in contact (its six or seven layers of
cells (h) accommodated to one another like epithelium) with the mem-
brana limitans interna. The latter stratum, also, is much thinned, as it
passes into the fovea centralis, so that only about three rows of cells (h)
are to be seen at the border (H. Muller). These, moreover, are for the
most part bipolar over the macula lutea (Merkel, Schultze). The central
portion of the fovea is destitute of ganglion cells according to Schultze
(and before him Bergmanri). The molecular layer (<?) diminishes like-
wise considerably in depth here, and in the very centre possibly disap-
pears. This is certainly the case with the internal granular layer (/).

The remarkable change in the proportion existing between the rods
and cones as we approach the macula lutea, and in the latter itself, has
been already alluded, to (§ 316). In fig. 597, b, we see that here the rods
fall in number more and more, until eventually, in the yellow spot, cones
alone are to be found (Henle), which increase regularly in length towards
the centre of the fovea, up to upwards of O100 mm., diminishing at the
same time in thickness.

We must now deal with these facts, however, somewhat more in detail.

]n man the bodies of the cones, in most parts of the retina, present a
diameter of 0'007-0'006 mm., falling, however, at the edge of the macula
lutea to 0 -005-0 -004 mm. More towards the centre of the latter, where
rods no longer exist (fig. 598, a, V), they become still narrower, and in
the fovea centralis their diameter is only 0 '002— 0 '002 5 mm., probably
only 0-0028-0-0033 mm. when quite fresh (Schultze, with H. Mutter and
Welcker). Here, then, we have cones almost of the same thickness as

644

MANUAL OF HISTOLOGY.

the rods. The cone styles sink at the same time, perhaps, to 0'0009 and
O'OOl mm. in diameter, while the cone fibres, on the other hand, pre-
serve their original thickness.

Over the fovea centralis the pigment cells are higher and darker, and
enclose the cone styles in long pigmentary sheaths.

Another point deserves notice here, namely, that as we approach the
yellow spot the retina increases in thickness, the distance between mem-

brana limitans externa and internal
granular layer becoming greater. And
while the thicker cones increase, the
slender rods diminish in number, giv-
ing rise to a change also in the external
granular layer. In the first place,
there are absolutely fewer corpuscles
necessary here, while, on the other
hand, owing to the large number of
cones, the corpuscles of the latter no
longer find room in one plain to lie
side by side. Thus, the rod and cone
fibres present themselves as a purely
fibrillated stratum beneath the granules,
the latter no longer lying upon the
intergranular layer as in other parts of
the retina. In this deeper portion of
the layer in question, which is destitute
of granules, and which has received
from Herile the name of external fibre
layer, the bacillary and cone fibres
commence to abandon their perpendi-
cular arrangement more and more as
we approach the inner part of the fovea
centralis. Here they may be observed
to run obliquely downwards and out-
wards (Bergmann, H. Miiller), and in
the centre of the fovea almost hori-
zontally (fig. 597, d), so that it is only
after a long course that the cone fibre
reaches at last the intergranular layer.
At the same time the fibrillated half
of the external granular layer increases
in thickness about the periphery of the yellow spot, but becomes rapidly
thinner in centre of the fovea itself (Schultze).

According to the latter's observations, farther, it is not only the internal
surface of the fovea turned towards the vitreous humour that is concave,
but also the opposite side facing the membrana limitans externa. Owing to
this the choroidal ends of the fovea cones are inclined towards each other,
and consequently more approximated than would be possible were they
still arranged perpendicularly, — a circumstance which bears upon the
delicate sensitiveness of this region. ' The adjacent portion of the retina
also takes part in this peculiar curvilinear arrangement of the light-
perceiving elements.

Let us now turn to the ciliary edge of the retina.

Anteriorly towards the ora serrata the thickness of the latter decreases

Fig. 598. — Cones from the human macula
lutea and fovea centralis. a, with half
decomposed external member; b, with
resolution of the latter into disks (after
Schultze).

ORGANS OF THE BODY

645

more and more, its nervous constituents commence to disappear, while
the sustentacular matter gains the preponderance. The optic fibres cease
gradually to constitute a separate layer, the ganglion cells appear at wider
intervals, the granular layers become shallower, and the rods and cones
shorter &c. (Muller, Merkel, Schultze). Finally, the nervous elements
disappear entirely from the membrane, leaving behind reticula of con-
nective-tissue fibres, which give way in their turn to a nucleated and
eventually non-nucleated homogeneous substance. This becomes, then,
still thinner, until, about 2 mm. from the ora serrata, the retina terminates
by fusing with the membrana hyaloidea. This is the relation of parts as
described by Hitter, .while other observers seem to have come to different
conclusions on the point. Thus Koelliker states that the membrana linii-
tans extends in the form of a system of cylindrical cells decreasing in height,
over the ciliary processes (intimately united to them and to the zonula
%innii) as far as the external border of the iris. Briicke and H. Muller,
on the other hand, suppose them to reach as far as the edge of the pupil.

Schultze found several forms of these cells, but did not observe any
transition into the fibrous matter of the zonula Zinnii (§ 313). He
regards the cells as corresponding to the radiating sustentacular fibres.

The blood-vessels of the retina (fig. 584) are derived from the arteria
and vena centralis, enclosed within the optic nerve. They thus consti-
tute a separate vascular system of the bulb, which forms, however, con-
nections in the manner described in § 312 with the vessels of the ciliary
system (e). From the splitting
up of the artery just mentioned
"is formed a delicate wide-
meshed network of capillaries
0-0056-0-0045 mm. in dia-
meter (fig. 599, b). This vas-
cular plexus lies chiefly in the
internal portion of the retina,
but extends, however, as far as
the internal granular layer. It
was formerly supposed by many
that at the ora serrata this
retinal system of vessels com-
municate with that of the
choroid ; but this is not really
the case (H. Muller, Leber).
In the yellow spot numerous
capillaries are to be seen, but
no vessels of any size.

The optic nerve itself only re-
ceives small twigs from the art.
cent., but, on the other hand,
numerous branches from the in-
ternal sheath (fig. 584, 1), and
a few from the external sheath.

A highly developed network of this kind does not, however, occur
in the retina of all mammalia. In the horse, for instance, we only find
a narrow belt of delicate radiating vessels around the entrance of the
optic nerve. The retina of the hare and rabbit, also, only presents a
narrow vascular zone corresponding, as a rule, with that of the medullated

Fig. 599.-

Vessels of the human retina, a, arterial; c,
venous twig ; 6, capillary network.

646 MANUAL OF HISTOLOGY.

nerve fibres. At the edge of this zone the most exquisite recurrent
capillary loops may be seen. In birds, amphibia, and fishes the .retina
is even entirely devoid of vessels, but the membrana hyaloidea is fed by
a network which probably also supplies the retina (ffyrtl, H. Miiller).

The question now arises at the conclusion of this long description of
the retina, What is the arrangement and connection of its nervous
elements ? and here we have only hypotheses to offer. That the rods and
cones may be regarded as the terminal perceptive elements of the mem-
brane is to our mind a point upon which there can be now but very little
doubt. Bacillary cells, besides, we know have recently been recognised
as the terminal structures of other nerves of special sense. Another ques-
tion arises here also from which we cannot refrain, although a physio-
logical one, namely, What are the relative purposes of "the rods and cones 1

We hav* learned from the foregoing description, that the point at
which the power of perception is most intense, the fovea centralis, pre,-
sents only cones in the human eye. Mammals of more. nocturnal habits
(§ 316) have, on the other hand, rods alone throughout the whole retina.
It is to be remembered, also, that towards the external border of the retina
the nervous fibrous mass undergoes considerable and progressive diminu-
tion.

The probability has been pointed out by Schuttze, that the latter
structures are endowed with the powers of perceiving quantitative differ-
ences in light and in distance, while the cones, besides possessing both
these, are sensible to colours also, that is, to qualitative differences in
light. The fibres, then, of both these retinal structures, which traverse
the external granular layer, may be regarded as nervous elements together
with the corpuscles. The efforts, however, of earlier investigators to
follow up these nervous fibres in a direct perpendicular course through
the internal layers, down to the stratum of the ganglion cells, are to be
looked upon as fruitless. Since the provisional ending of both rod and
cone fibres in the inter-granular layer, consequently in the very middle
of the retina, has been pointed out by Schultze, and also the apparent
origin of another set of the finest fibrillae pursuing an altered course
inwards, it seems vain to hope to demonstrate, with our present modes
of investigation, and through such a complicated system of fibres, the
connection between the cones and ganglion cells and optic fibres. In
this respect the grey matter of the nervous centres and retina resemble
each other.

There has been no lack, however, of other views regarding the retina
in recent times.

Thus Henle contrasts the external half of the membrane, as far as the
inter-granular layer, under the name of "mosaic, stratum" (musivische
Schicht), with the internal half or "true nervous layer." We fail to per-
ceive any great advantage in this.

An effort has recently been made also by Krause to prove that the
retina, down to the inter-granular layer, his membrana fenestrata, is by
no means of nervous nature. Apart from anatomical considerations, he
bases his views upon the fact, that some weeks after section of the optic
nerve, the nerve fibres and ganglion cells of the retina may be observed
to have undergone fatty degeneration, but the whole rod and cone apparatus
to remain unaltered.

As to the composition of the retina we know but little. Some investi-
gations by C. Schmidt have brought into notice a substance contained in

ORGANS OF THE BODY.

647

it, giving the reactions neither entirely of albumen nor of glutinous bodies,
but exhibiting properties to some degree intermediate between the two.

§ 319.

Before passing on from the globe of the eye, we must bestow a few
words upon its lymphatic vessels.

From Schwalbe's investigations it would appear that the lymph formed
in the ball of the eye is carried off in three directions. That produced in
the iris and ciliary processes is collected, in the first place, in the anterior
chamber. This with the absorbents of the conjunctiva and corneal
tissue may be said to belong to the first part, or anterior lymphatic circula-
tion of the eye.

All the lymphatic spaces situated behind the ciliary processes empty
their contents in two other directions. Those of the sclerotic and choroid
open near the points of exit of the venae vorticosse, while the absorbents
of the retina, on the other hand, are independent of these, and leave the
globe of the eye through the optic nerve. Here, then, we have what we
may call a posterior lymphatic circulation.

Let us consider this posterior lymphatic circulation first (fig. 600).
Both the sclerotic and choroid seem destitute of special lymphatic vessels.
Instead of these the shell-like interspace between the two coats appears
to possess the nature of a lymph receptacle. This occupies the position of
the supra-choroidea, as is well known (§ 310). To this receptacle, which
is crossed by connective-tissue net-
works, the name of " pericho-
roidal space " (p) has been given by
Schwalbe, who describes it as lined
by endothelium. From this (at
about the height of m.r. in our
figure) that communication with
" Tenon's space " (t) takes place
which has been already alluded to.
The latter lies between Tenon's
sheath and the external surface of the
sclerotic. The oblique intercom-
municating canals invest, as a rule,
the venae vorticosae like sheaths.
This lymphatic space of Tenon is
continuous behind with the "supra-
vaginal" (spv) of Schwalbe, which
latter invests the external optic
nerve sheath "like a sheath." In
it, also, there is apparently a lin-
ing of endothelial cells.

By Key and Retzius it was found
(§ 300), that from the subdural
space of the cranium another space
between the external and internal
sheath of the optic nerve may be
injected, and that from this the
perichoroidal interval may be filled, which would seem to show that the
latter is a prolongation of the first. Between the internal sheath and
the connective-tissue immediately investing the optic nerve fibres, injection
42

Fig. 600.— Posterior lymphatic circulation in the
eye of a pig (diagram after Schwalbe). e, con-
junctiva; m.r. recti muscles; m. retr. retractor
bulbi ; a, layer of fat; v, external sheath of optic
nerve; t, "'Tenon's" space opening behind into
the "supravaginal" tpv; sbv, "subvaginal"
space between the internal and external optic
nerve sheath; p, "perichoroidal" space com-
municating by oblique passages with Tenon's
space.

648 MANUAL OF HISTOLOGY.

fluid may also be driven, and moreover from the subarachnoidal space of
the brain. Sclnvalbe, however, states that his " subvaginal " space (sbv)
between the internal and external optic sheath does not communicate
with the perichoroidal interval.

The lymphatics of the retina are said to invest the capillaries and veins
like sheaths in the adventitial layers, but to pass along side by side with
the arteries. They enter the optic nerve, as already stated above. We
are still in want of details here.

Turning now to the anterior lymphatic circulation, we have already
remarked that the anterior chamber is regarded as a reservoir for the
lymph produced in the iris and ciliary processes.

In the first place, according to Schivalbe, the lymphatic fluid passes by
a series of slits out of the canal of Petit into the posterior, and from
thence into the anterior chamber.

But the supply flowing from Montana's space, through the system of
slits in the ligamentum iridis, is of more importance still. This space
receives the lymph of the ciliary processes and iris apparently.

At the border of the membrane of Descemet the opening into the
circular canal of Sclilemm takes place, according to Schwalbe. This may
be filled with even very slight pressure, and, whether we deny it the
nature of a venous vessel or not, certainly does communicate with the
venous system.

This reminds us of a similar arrangement of parts described in the
brain by Key and Retzius.

§320.

Turning now to the accessory structures of the eye, we may pass over
the four recti and two oblique muscles as requiring no farther description.

Many years ago an analogue to the orbital muscle of many mammals
was discovered by Mutter in man. This is a greyish-red mass, closing
up the fissura orbitalis inferior, consisting of bundles of unstriped muscle
fibres, most of which possess elastic tendons. It is supplied by pale, non-
medullated nervous filaments from the sphenopalatine ganglion.

The eyelids, palpebrce are formed of the tarsal cartilages (§ 109),
enclosed in a thin skin quite devoid of fat. Imbedded in this cartilage
a series of peculiar modified sebaceous glands is to be found, known as the
Meibomian glands. In man from 30 to 40 of these may be counted in the
upper lid, and 20 or less in the lower. In form they are tubes about
0*1128 mm. in diameter, with round vesicles attached along the sides.
They are somewhat less in length than the tarsal cartilages are in height,
and open with contracted mouths on the posterior edge of the free border
of the lid. The vesicles of these glands are enveloped in a beautiful net-
work of medium-sized capillaries. Their contents, with the exception of
a laminated lining of flattened cells in the excretory duct, is the same as
that of the sebaceous glands of the skin (§ 304).

The secretion of the Meibomian glands is a thick, whitish-yellow matter
containing much fat, and hardening on exposure to the air. It is known
as the sebum palpebrale,, and serves to keep the free border of the lid in a
greasy condition.

The orbicularis palpebrarum muscle belongs to the striped class.
Associated with it, however, are membranous layers of smooth fibres,
forming reticulated fasciculi (H. Mutter), and constituting a ?n. palpe-
sup. and inf.

ORGANS OF THE BODY.

649

The posterior surface of the eyelids, and anterior portion of the sclerotic,
with the cornea, are covered by a thin, soft, mucous membrane, known as
the conjunctiva. This is generally divided into the c. paJpebrantm, the c.
bulbi, or that passing from the' latter to the ball of the eye; and the
inferior part, the c. scleroticce and cornece. The latter portion, however,
deserves no longer the name of mucous membrane, from the fact of its
being represented merely by a laminated flattened epithelial covering.

The substratum of the palpebral conjunctiva is formed of reticulated con-
nective-tissue containing lyuiphoid cells (Henle). This Stieda asserts to
be separated from the epithelial layer by a homogeneous elastic membrane.
The epithelium in the cleft between the lids, derived from, the cuticular
layer of the skin, was formerly erroneously supposed to be ciliated (Henle).
It consists, on the contrary, of several layers of pavement cells.

Numerous depressions, pits, and clefts, of the most diverse forms, which
occur in this mucosa, are, strange to say, lined by a kind of columnar
epithelium, producing the deceptive appearance of true glands ; indeed, such
were described here by Henle. Among the ordinary epithelial elements
of the part there occur also, in the conjunctiva palpebrarum, those struc-
tures known as beaker cells (Stieda). We also meet here with tactile
corpuscles, according to Krause, the terminal structures of the nerves of
sensation (§ 185). The conjunctiva bulbi is a continuation, not only of the
epithelial cellular layer, but also of the subjacent connective-tissue. The
first extends over the whole cornea (§ 292), but not so the latter, which
is lost at the periphery of the cornea in the tissue of the same, after having
become very thin. The plica semilunaris, finally, is a duplicature of the
conjunctiva bulbi, and contains in its caruncula lacliryinalis ordinary
sebaceous glands. Scattered fasciculi of unstriped muscle
also occur here (H. Mutter).

The glands of the conjunctiva are of various kinds.

In man, and in certain of the mammalia, in the first
place, small racemose glandules are to be found, known
generally as mucous glandules (" accessory lachrymal
glands" of Henle). They are situated in that portion of
the conjunctiva passing from the tarsus to the bulb, and
are seen to the number of 42 in the upper, while from
2 to 6 only occur in the lower lid. They are irregularly
scattered, imbedded in the mucous membrane or sub-
mucous tissue. They are most crowded in the transition
fold. The contents of their acini, which are about 0'0564
mm. in diameter, present fatty particles.

Among the ruminants, but not in man, there occurs,
as was discovered some years ago by Meissner, a second
very interesting form of gland in the conjunctiva of the
eyeball, and particularly in that part encircling the cornea
below and internally. This belongs to the convo-
luted tubular class (tig. 601) like the sweat glands of
the skin, but each gland opens with a bulbous dilata-
tion. The number of such convoluted glandules, how-
ever, is very small, only amounting in each eye to from
6 to 8.

At the outer border of the cornea of the pig another
third species of gland was found by Manz. IP this form we have simple,
round, or oval sacs, measuring 0-067-0-2 mm. in diameter, made up of

601.— A convo-
luted gland from
the conjuuctivu
bulbi of the calf
(after Manz).

650

MANUAL OF HISTOLOGY.

Fig. 602. — Trachoma gland from the ox, with injected
lymphatic canals: vertical section, a, submucous
lymphatic vessel ; c, splitting up of the same round
the follicle, ft.

concentric layers of connective-tissue, and containing cells and a granular
matter. They have been named by histologists, after their discoverer,
the glands of Manz.

In addition to these secreting organs of the conjunctiva we meet with

lymphoid follicles, or, as they
have been named by ffenle,
trachoma glands (fig. 602). They
are to be found in man, in nume-
rous mammals, and in several
birds. They usually occupy,
but not in all animals, the inner
angle of the eye, especially in
the transition fold of the under
and third lid, or plica semi-
lunaris, and are sometimes scat-
tered, sometimes aggregated.
An enormous collection of
them, strongly resembling one
of Peyer's patches, may be ob-
served in the under eyelid of the ox (plaque of Bruch). In the human
conjunctiva they a're only met with irregularly and sparsely scattered.

The structure of these bodies is that of
other lymphoid follicles (fret/, Hugue-
nin). Their vascular network is thin and
irregular (§ 227). Around them, even with-
out injection, lymphoid lacunae may be
recognised.

As regards the blood-vessels of the con-
junctiva bulbi, we find its capillary supply
derived from branches of the palpebral and
lachrymal arteries, as well as twigs given
off from the anterior ciliary vessels (comp.
§ 312). The capillary system of the pal-
pebral conjunctiva is much more dense
and more extensive.

The lymphatics of the conjunctiva were
discovered many years ago by Arnold, and
have been since observed by Teichmann.
A delicate zone of the same, about 0*9
mm. broad, encircles the cornea, and is con-
tinuous peripherally with the network of
wider canals of the sclerotic conjunctiva.

The trachoma glands are likewise rich in
lymphatic vessels, as may be learned from
injection (Frey).

In Bruchs plaque in the ox (fig. 602)
knotted lymphatics of considerable size,
ranging from 0*377 to 0-1511 mm., may
be observed traversing the submucosa
obliquely or perpendicularly (a). These form, at the under surface of
the follicle, a very complicated network of canals 0 -0744-0' 11 28 mm.
in breadth, and give off other finer vessels, 0-02 mm., which are also
arranged in a retiform manner, ascending through the narrow-meshed

Fig. 603.— Termination of the nerves of
the conjunctiva in end-bulbs. 1. From
the calf. 2. From man.

OHGANS OF THE BODY. 651

connecting layer of the follicle, and forming, on their part, a net-like
covering (c) around the same (b). The most superficial part of this
network, namely, that underlying the epithelial layer, runs more or less
horizontally beneath the latter, giving off numerous fine terminal twigs of
0*0282-0'0113 mm. in diameter, which ascend still farther for a short
distance, and then end blind under the epithelial covering.

The nerves of the conjunctiva (fig. 603, c) terminate, in the first place
(as has been shown by Krause), in man and other mammalia in those
end-bulbs (a), already described (§ 184). Again, as we have learned from
Cohnheiiris and Hoyer's interesting discovery, the cornea! nerves extend
into the overlying epithelium, or so-called conjunctiva corneae (§ 309).
For the rest we refer the reader to § 184.

The lachrymal glands, whose sp. gr., according to Krause and Fischer,
is 1*058, consist of aggregations of racemose glands, which, as far as the
shape of both lobuli and vesicles, and their nucleated cells, composed of
finely granular protoplasm, is concerned, present nothing peculiar for
our consideration. Their excretory canals, 7 to 10 in number, made up
of fibrous tissue lined with columnar epithelium, perforate the conjunc-
tiva. In the walls of these we meet again with those flattened stellate
cells already alluded to, § 194 (fig. 329). The nerves of the organ are
supposed to penetrate through the limiting structures of the acini, and
terminate between the gland cells in the same manner as in the sub-
maxillary gland (Boll). The arrangement of the capillaries here is as
usual in such structures.

The structures composing the apparatus for carrying off the tears are
not alike throughout. In the lachrymal canals the tissue of the mucosa
is rich in elastic fibres, while in the lachrymal sac and duct a reticulated
connective substance, containing lymphoid cells, presents itself (Henle).
From the lining membrane of the nose small mucous glands extend
upwards, and occur not only in the wide nasal duct, but also in the
mueosa of the canaliculi (R. Maier). In regard to the species of epithe-
lium lining the lachrymal passages there still exists much diversity of
opinion. Non-ciliated columnar cells are stated to occur throughout
them by Maier. Henle, on the other hand, mentions having found
flattened epithelium in the canaliculi, ciliated in the lachrymal sac and
nasal duct, merging into the flattened formation of the nose.

We turn now to the tears, the secretion of the lachrymal glands, which,
with a small quantity of aqueous humour, which exudes through the
cornea, bathe the front of the eye. This fluid has a strong alkaline
reaction and slightly saltish taste. Chemical analysis, instituted long
ago by Frericlis, shows about 1 per cent of solid matters (0*9-1 '3 per cent.)
Among these albumen appears in combination with soda (the " lachry-
mirie " of earlier investigators), together with traces of fats, extractives,
and mineral matters. Of the last chloride of sodium is the most import-
ant, phosphates of the alkalies and earths appearing in but small amount.
Under ordinary circumstances the tears are carried off by the canaliculi
into the nose, but when the secretion is too abundant it overflows the
lower lid. The psychical significance in the human being of tears has
long been recognised.

§321.

The development of the eye, to which we will only devote a few words
tere, takes place from three different portions of the rudimentary embry-

652 MANUAL OF HISTOLOGY.

onic body. The first trace is seen in the form of a hollow stalked process
of the anterior portion of the brain, the primary optic vesicle, which is
destined in its farther development to transformation into the retina and
pigmentary epithelium of the choroid, while the pedicle becomes the optic
nerve. We have already seen that the lens springs from that portion of the
corneous germinal layer which lies over the rudimentary eye, growing in-
wards in the form of a thick-walled hollow sphere (comp. § 161). Besides
the latter, and underneath it, there presses into the primary optic vesicle
the vitreous humour, a production of the middle germinal layer, i.e., of the
dermal tissue of the head. These two organs thus double in the optic vesicle
into itself, after which, as in the serous sacs, two lamellae of formative
cells may be distinguished, a thicker internal one, the future retina, and
an external thin layer destined to form the pigmentary epithelium. "We
now have before us what is known as the secondary optic vesicle. The
fibrous layer of the choroid, the ciliary body and muscle, the iris, sclerotic,
and cornea, all spring from the adjacent portions of the middle germinal
layer of the rudimentary embryonic head.

That the whole retina, with the exception of the pigmentary epithelium,
takes its rise from the internal lamella of the secondary optic vesicle, is a
fact observed long ago by Remak and Koellilter, which has been con-
firmed more recently by Babiichin and Schultze. The first elements to
be recognised, according to Babuchin, are the rudiments of the fibres of
Muller, in the form of fusiform cells, terminating at either end in the
limiting membranes (external and internal) which are formed from them.
After the fibres of Muller the ganglion cells are next developed, and
then the stratum fibrillosum. The molecular and inter-granular layers, as
well as that of the rods and cones, appear almost simultaneously ; the first-
mentioned layer, however, precedes the others somewhat in formation,
and the stratum bacillosum brings up the rear. The rods, cones, and
cone-bodies are produced, according to Babuchin, in the tadpole as pro-
cesses or outgrowths from cells. They thus constitute with their cells
("granules" or " corpuscles") an inseparable whole.

The development of the central portion of the retina, moreover, hurries
on in advance of that of the periphery (Babuchin, Schultze).

A number of delicate hemispheroidal growths were recognised by
Schultze in the chick projecting from the outer surface of the membrana
limitans externa. These are stated by him to be developed later on into
rods and cones.

The outer halves or members of the rods, which also undoubtedly
belong to the internal wall of the secondary optic vesicle, are formed
much later than the inner members.

In connection with the late development of the rods there is a point of
much interest mentioned by Schultze. Animals which are born with
closed eyes — as, for instance, cats and rabbits — do not at birth possess
those retinal elements, while in man and the ruminants they are already
fully developed when born.

The external layer of the so-called secondary optic vesicle is formed by
a single row of perpendicular, and originally elongated, but later more or
less cuboid cells, which become eventually flattened. This is gradually
transformed into pigmentary epithelium, as has been already remarked,
by the absorption of molecules of melanin. This layer is generally
reckoned among the laminae of the choroid, whereas it belongs in reality
to the retina.

ORGANS OF THE BODY. 653

The histogenic occurrences in connection with the development of the
cooroid, iris, and sclerotic require further investigation. The rudimentary
chrnea has been already alluded to, § 133, and the mode of origin of the
fibres of the lens has been dwelt upon in the section quoted above.

The lachrymal glands are developed in the same manner as most other
racemose secreting organs ; their cellular constituents springing from the
corneous germinal plate. The Meibomian follicles are developed at
rather a late period.

§322.

We come now, finally, to the consideration of the organs of hearing,
the last of the apparatuses of special sense which shall occupy our
attention.

On each side of the head we have an internal ear, consisting of the
labyrinth, which receives the impressions of sound, a midde ear for the
conducting of the waves of sound ; and an external ear, separated from
the last by the tympanum.

We will commence our description with the latter.

The outer ear is made up of the pinna and external auditory meatus.
The texture of its cartilage has been already described § 108. The exter-
nal skin, likewise, which is here closely attached to the latter; and which
is quite destitute of fat, except in the lobe of the ear, needs no farther
notice. In the pinna of the ear we find numerous downy hairs, and
often considerable sebaceous follicles (§ 304), as well as small sudoriferous
glands (§ 302), especially on the posterior aspect. The peculiarities of
the glandule cerminosae of the outer passage, in which sebaceous follicles
are also present, have been likewise dealt with in an earlier portion of our
work (§ 302). The muscles of the pinna belong to the striped class
(§ 164).

The membrana tympani consists of a fibrous plate clothed externally
by the cutis, and internally by the mucous membrane of the middle ear.
Through the so-called annulus cartilagineus it is continuous with the adja-
cent periosteum. The coat derived from the skin presents a thin fibrous
layer, quite devoid of glands and papillae, which may be found, however, in
its immediate neighbourhood. The fibrous plate consists of an external
lamina of radiating fibres, and an inner sheet of circular bundles. The
elements are those of ill-developed connective-tissue, exhibiting flat anasto-
mosing bands with connective-tissue corpuscles (Gerlacli), and perhaps also
a few smooth muscle fibres (Prussak). The mucous membrane of the inner
surface possesses likewise a very thin fibrous portion, and usually a covering
of simple flattened epithelium. The latter extends also into the several
depressions of the tympanum, and into the mastoid cells. The rest of the
cavity of the tympanum is lined with doubly laminated ciliated epithe-
lium. The vascular network of this diaphragm consists of several portions
(Cferlach) of an external web formed of radiating elongated meshes of
fine tubes belonging to the dermal layer, an internal with rather small
meshes supplying the mucous membrane, while the middle fibrous layer
of the tympanum, which was formerly said to be devoid of vascularity,
presents a third set of vessels according to Kessel. Lymphatics are also
present here in large numbers, and nerves likewise, but the mode of
termination of the latter has not yet been ascertained.

The whole of the middle ear, with its various parts and adjoining cavi-
ties, is lined bv the same thin, vascular, probably glandless, mucous mera-

654 MANUAL OF HISTOLOGY.

brane. In the Eiistacliian tube its ciliated cells are of the columnar kind
interspersed with beaker cells (Schultze).

The vascular system of the tympanic cavity is remarkable for present-
ing a few very slightly ramifying arterial feeding tubes, forming but a
very ill-developed arterial capillary network. The venous portion, on
the other hand, is highly developed. Here we meet with considerable
vessels forming strong networks. The circulation of the cavity is char-
acterised by being very rapid, and subject to small pressure (Prussak).

The lymphatics of the cavity resemble those of the tympanum (Kessel).

The nerves require closer attention. On the tympanic branch nume-
rous ganglia have been observed, formed of larger or smaller collections
of cells, or even of single elements between the medullated fibres (Krause).
Numerous nervous networks are also found here.

The small bones of the ear consist of compact osseous substance, present-
ing numerous Haversian canals (Rildinger, Brunner). Between the hammer
and ambos only is there a joint. The first of these is covered as far as it
is united to the tympanum (i.e.) on its short process, and the so-called
handle with a thin coat of hyaline cartilage (Cfruber).

The union of the short process of the ambos (which is clothed with
cartilage) with the side of the cavity is effected by strong connective-
tissue, that between ambos and stapes by a symphysis of hyaline cartil-
age, with a diaphragm of fibrous tissue in the middle. The cartilaginous
borders of the foot of the stirrup, arid of the foramen ovale, are joined by
strong connective-tissue (Brunner).

The muscles of the ossicular auditus are of the striped kind (§ 164).

We conclude this section with a glance at the Eiistacliian tube.

Its cartilage has been already considered, § 108. Its mucous membrane
bears a double layer of ciliated epithelium, and contains racemose mucous
glands, varying in size and position, however, in diiferent localities. The
gland vesicles are lined with columnar cells. The mucous tissue may in
parts be infiltrated with lymphoid cells (Riidinger). A nervous plexus with
groups of ganglion cells is also to be seen in the Eustachian tube (Krause).

§ 323.

The internal, and proper organ of hearing, consists of the vestibule,
semicircular canals, and cochlea. The whole is occupied by certain mem-
branous bags and canals, containing a watery fluid ; in these the auditory
nerves terminate, surrounded by the fluid. The distribution of these
nerves is twofold, — first, to the ampullae and sacculi of the vestibule, and
then to the spiral plate of the cochlea.

Both the vestibule and internal surface of the semicircular canals are lined
with periosteum. The transparent serous fluid with which they are filled
is known as the perilymph, or aqunla Cotunii. According to Schwalbe,
they may be injected from the subarachnoidal space of the brain through
the porus acusticus internus. The periosteum, with the mucous mem-
brane of the cavity of the tympanum, constitute the membr. tympani
secundaria, resembling in their structure, as a whole, the true drum of the
ear in many respects.

The walls of the saccul'us hemielltpticus and rotundus and c. semicir-
cularis membranacei, with their ampulla3, suspended in the perilymph,
but always attached at definite points to the periosteum, consist of an
external undeveloped connective-tissue, composed of stellate corpuscles,
and an internal elastic transparent layer, containing numerous nuclei. In

ORGANS OF THE BODY. 655

the membranous semicircular canals, which lie excentrically, that is,
attached to the convex aspect of the long passages (Riidinger), this elastic
lamina is maintained by the same observer to project in the form of
numerous tufts into the lumen. These, however, appear to be in man
pathological products (Lucae). Again, internally these present a thick
covering of epithelium (0'0068 mm. deep), made up of pavement cells, from
O'OOOO to 0'0180 mm. in diameter. From the usually numerous blood-
vessels of these walls a second watery
fluid is secreted, known as endolymph.
or aquula vitrea auditiva, which fills the
space contained within them.

The otolithes (fig. 604), enclosed with-
in a special membrane, present them-
selves in the form of white specks at
those points where the terminal fila-
ments of the auditory nerves are spread
out in the sac of the vestibule. These
are probably small columnar crystals,
whose size varies to a remarkable extent,
their diameter ranging from O0090 to
0-0020 mm. and less. A few of them
«re also contained within the membran- Fig. 604.— otolithes, consisting of carbonate
ous semicircular canals. They consist

principally of carbonate of calcium, but leave behind, according to the
observations of many investigators, an organic substratum, after having
been treated with acids.

§324.

There now remains for our consideration the mode of distribution of the
acusticus to the two sacs of the vestibule and the membranous ampullae.
The nerve fibres for the sacculus hemiellipticus and ampullae are derived
from the n. vestibuli ; those for the sacculus rotundus from the so-called
n. saccularis minor, a branch of the cochlear division of the auditory.
They enter the duplicatures of the walls, which are especially distinct and
prominent in the ampullae, projecting into the cavity in the form of par-
titions. Here they divide into branches, and run towards the internal
free surface of the walls, still ramifying in their course. All the
nerve fibres are, however, confined to this projection, known as the
septum nerveum ; none of them extend into the adjacent parts of the
ampullae.

It was formerly supposed, from the early investigations of Valentin and
Wagner, that the filaments of the auditory nerve were arranged in termi-
nal loops. The incorrectness of this view, however, is now generally
recognised ; and we know that the ends of the nerves undergo still farther
subdivision. It was Schultze, however, who first arrived at definite con-
clusions here in regard to the arrangement of parts, which latter is of the
highest interest, manifesting as it does such close relationship to the mode
of termination of the higher nerves of special sense (fig. 605). These
conclusions were not drawn from investigation of the structure of the
human ear, but from that of rays and sharks.

If the septum nerveum be very minutely examined, its projecting
margin (crista acustica of Schultze) presents on either side a thick covering
of soft pultaceous matter, resembling, in transverse section, the cap of a

656

MANUAL OF HISTOLOGY.

mushroom. Under the microscope we may easily recognise the fact, that
the ordinary simple pavement epithelium of the internal ear has given
way to another species, namely, to a deeply laminated, whose uppermost
elements (a), which are cylindrical in shape, and dotted with yellowish
granules, have a strong resemblance to the cells met with in the regie
olfactoria (§ 307).

It is between these cylinders on the septum nerveum that the fibres of
the auditory nerve terminate, in a manner similar to that of the olfactory
and gustatory nerves.

The structure of this portion of the organ of hearing is, however, very
complicated, and by no means as yet fully understood.

The first thing remarked — in fishes, such as young tritons (Schulze) —
over the free surface of the whole yellow layer, is a multitude of extremely
long (O0902 mm.) stiff filaments, projecting beyond the surface (the
" auditory filaments"), whose relation, however, to the cells below requires
farther investigation. Deeper down, seated on the fibrous substratum,
there appears another kind of cell (b), supported upon an expanded base
(basal cell of Schuttze). Finally, we meet with small colourless cells in

great number, which give off a process at
either pole of their rounded or fusiform
bodies (c) ; these are the fibre cells of
Schultze. The superior process (d) is the
thickest, and of rod-like form, ending on
the surface of the complex epithelial
stratum, with truncated extremity. The
inferior (e) is thinner, and dips down to-
wards the connective-tissue substratum.
The nerve fibres (/) appear at first sight
to terminate at the border of the fibrous
layer, under the epithelial covering, but
only merge here into pale axis cylinders,
which enter the latter (g), and after split-
ting up into a large number of branches,
disappear eventually from view. It is not
improbable, although not yet proven, that
these terminal fibres are continuouswith the
inferior processes of the fibre cells (Schultze).
/Schultze maintains, and possibly with per-
fect right, that the divided non-medullated
axis cylinder is prolonged directly into the
long hairs already mentioned.
The same structural relations, with shorter hairs, however, have been
observed in the otolith sac of fishes.

Statements have also been made to the same effect as regards other
vertebrates ; but the opinions of investigators still differ widely.

The two nervous projections of the human vestibular saccules, or
maculce acusticcB, as Henl.e calls them, are less marked than the septa
nervea of the ampullae, but are wider, and present a larger surface on the
other hand.

These maculae acusticae were very accurately described some years ago
by Odenius. In the utriculus a complicated plexus of nerves spreads out
towards the surface through the connective-tissue substratum, terminating
finally in delicate axis cylinders, which penetrate into the epithelial layer.

Fig. 605. — From the critta acustica of
the ampulla of raja clavatu (after
Schultze). a, cylinder cells; 6, basal
cells ; c, fibre cells, with an upper rod-
like process d, and lower filiform e ;
/, nerve fibres, passing into pale axis
cylinders at g.

ORGANS OF THE BODY. 657

The arrangement of nervous elements in the sacculus rotundus varies in
some points, though in the main the same.

In approaching the macula, the low cylindrical elements covering the
walls of the saccule are observed to give place to long, columnar, distinctly
nucleated cells, with yellowish contents, above whose free border filaments
are seen to project.

Minute examination reveals that of these very decomposable elements
there are at least two forms, probably corresponding to the cylinder and
fibre cells of Schultze. These were also seen and sketched by Koelliker
in the saccus hemiellipticus of the ox years ago. One species present
long, narrow fusiform bodies without nuclei, but bearing on their ends those
filaments 0'0221-0'0226 mm. long, which, as we have already seen, pro-
ject beyond the surface of the nerve epithelium. These auditory filaments
were discovered long ago by Schultze in mammals, and from Odenius we
learn that they are also to be found in the septum nerveum of the human
ampullae.

The connection of these filamentous bodies with the axis cylinders,
which certainly penetrate into the epithelium, requires, however, further
proof in our opinion.

§325.

Let us turn now finally to the consideration of the cochlea (fig. 606).

This spiral canal, which performs in the human ear two and a half
turns, is divided into two passages, which have long been known as the
scalce, — the upper, named scala vestibuli (V), and the lower, scala tympani
(T), — by a spiral plate, the lamina spiralis (q-i). Besides these, it pre-
sents also a third and more important intermediate space, the canalis coch-
learis of Reissner (Cf).

The lamina spiralis (from q to i) consists of an internal bony and an
external soft or membranous portion. The first of these, an outgrowth from
the modiolus or central pillar, is about half the breadth of the whole leaf.
It is not, however, alike in all the turns, being broadest in the first, and
becoming gradually narrow as it ascends, until it finally terminates in the
last half in a hook, hamulus.

This osseous spiral plate, lamina spiralis ossea, presents two lamellae of
compact bony tissue — the upper facing the scala vestibuli, the lower the
scala tympani, and between these, porous tissue, through which run the
freely intercommunicating passages for the transmission of vessels and
nerves. Near the junction with the membranous portion these passages
unite to form a single fissure, bounded by the two osseous lamellae, both of
which terminate together here likewise.

The membranous portion is directly and horizontally prolonged outward
from the bony partition. It is known as the lamina spiralis membranacea,
or memlrana bas-ilaris. It presents about the same breadth throughout
(O45 mm.), and is attached to the inner surface of the outer wall of the
cochlea.

But as we first learned from Reissner and Koelliker, there springs
further, within the scala vestibuli, and near the line of junction of the
lamina ossea with the membranacea («), another membrane (R), which
ascending obliquely upwards and outwards reaches the inner surface of
the external wall of the cochlea, where it is attached. This is known
as the membrane of Reissner.

Thus, a narrow passage is cut off from the scala vestibuli, lying external

658 MANUAL OF HISTOLOGY.

to it, and holding, of course, a spiral direction likewise. In cross-section
it is almost triangular. This is the canalis cochlearis, already mentioned
above ((7). Its three sides are consequently formed, below, by the lamina
spiralis membranacea (tympanic wall), above, by the membrane of Reissner
(vestibular wall), and externally by the parietes of the cochlea. Above, at
the hamulus, the canalis cochlearis ends in a blind sac (" Kuppelblind-

Fig. 606.— Vertical section through the tube of the coclilea and adjacent parts from a
foetal calf at an advanced period. V, Scala vestibuli; T, Sc. tympani; C, canal of the
cochlea; R, membrane of Reissner, with its attachment (a) to a projection on the so-
called habenula sulcata (c) ; b, connective-tissue layer, with a vas spirale on the under
surface of the membrana basilaris; c', teeth of the first row; d, sulcus spiralis, with
thickened epithelium, which extends to the organ of Corti (/), still in process of forma-
tion; c, habenula perforata; Cm, membrane of Corti (1, its inner and thinner; 2, its
middle thicker portion; 3, its external end); g, zona pectinata; h. habenula tecta; *,
epithelium of the z. pectinata; k', external wall of the cochlea; k" habenula sulcata; I,
ligamentum spirale (i, transparent portion of the same, connecting it with the zona pecti-
nata); m, slight elevation; «, cartilaginous plate; o, stria vascularis; p, periosteum of
the zona ossea; p>, transparent external layer of the latter; q, bundles of cochlear nerve
fibres; s, point of termination of the meduHated nerve fibres; t, position of the axis cylin-
ders in the hab. perforata ; r, tympanal periosteum of the zona ossea.

sack") (Hcnsen, Reichert), and below also practically, in a vestibular sac
(" Vorhofs' blind sac "), although there does exist a communication
between it and the sacculus rotundus (Hensen, Reichert, Henle). This
is a short and fine tubule, opening at right angles into the lower end of
the canalis cochlearis, in the same way as does the oesophagus into the
stomach. We name this the canalis reuniens. The latter, like the two
blind sacs, is only lined with cubical epithelial cells, and is destitute of
the acoustic nerve fibres present elsewhere.

Both scala tympani and scala vestibuli are lined by a fibrous coat.
The membrane of Reissner is also formed of fibrous connective-tissue

ORGANS OF THE BODY.

659

...-E

...J7

covered underneath, but not above, with a single layer of epithelium.
The outer wall of the canalis cochlearis is likewise formed by a coat of
periosteum overlaid with similar cells (&'). In it, also, may be recognised
a peculiar eminence (m), a layer of cartilage situated higher up (n), and a
vascular streak (0).

The floor of the canalis cochlearis, i.e., the upper surface of the lamina
spiralis membranacea, exhibits a very complex structure ; while the under
surface, or that facing the scala tympani, presents nothing remarkable for
our consideration, with the
exception of the so-called
vas spirale (b), enveloped
in a thin coating of connec-
tive-tissue.

The very important struc-
tures to be seen here were
in part discovered by Corti,
who was succeeded by Reiss-
ner, Claudius, Bottcher,
Scnultze, Deiters, Koelliker,
and Hensen (without men-
tioning many others), by
whom the wonderful ar-
rangement of parts was
further and further un-
veiled, at the same time
that its complexity was ren-
dered so evident as to
baffle all hopes of arriv-
ing at anything like de-
finite conclusions for the
present.

According to Corti, the
membranous spiral plate
may be divided into two
zones, — an internal zona
denticulata, and an external
z. pedinata (<?).

The zona denticulata has
been again subdivided into
two portions, namely, into
the habenula internet, or sul-
cata (c), or labium superius
of the sulcus spiralis, and
into the h. externa, s. den-
ticulata (e, h).

The first of these presents
itself as a high eminence,
the crista spiralis, project-
ing into the canalis coch-
learis with comb-like ridges

... A

Fig. 607.— The organ of Corti from the dog, after Waldeyer.
seen on its vestlbular aspect, the membrane of Reissner
and the so-called membrana tectoria having been removed.
A, Crista spiralis ; B, epithelium of the sulcus spiralis; C,
pillar heads of the fibres of Corti; D, lamina reticularis;
E, external epithelium of the membrana basilaris ; a, cells
of the sulcus spiralis shining through the acoustic teeth; 6,
corresponds to the outer boundary line of these teeth ; e,
cuticular meshwork between the internal epithelial cells;
d, vas spiral! ; e, internal hair cells; /, heads of the inter-
nal pillars, or fibres of Corti; fi, their head plates; g,
boundary line between the external and internal pillars ;
/», heads of the external pillars shining through the head
plates of the internal fibres of Corti (the clear circle is the
optical transverse section of the external fibre or pillar) ; I,
phalangcal head-plate of the external pillar or the first
phalanx ; k, m, o, first, second, and third rings of the lamina
reticularis, with the hairs or filaments of the first, second,
and third rows of hair or tufted cells; n and p are the
second and third phalanges ; r, supporting cells (Hensen) ;
g, cuticular network between the epithelial cells or the
framework of Deiters.

and grooved external bor-
der. The furrow is known as the semicanalis or sulcus spiralis (d).
The whole structure results from the peculiar disposal of the periosteum

660 MANUAL OF HISTOLOGY.

of the spiral bony plate. Under the microscope it is seen to be made
up of simple, either homogeneous or streaked, connective-tissue, with
imbedded cells and scattered capillaries. For the rest, this eminence
decreases, both in height and breadth, as we ascend through the canal
of the cochlea.

Upon the upper surface of this peculiar pectiniform structure (fig.
607, A) a number of not less remarkable longitudinal and bifurcating
ridges present themselves. These are the teeth of the first order of
Cortij or acoustic teeth of Huschke.

In the first turn of the cochlea their length is 0*0451 mm., and diameter
0-0090-0-0113 mm. ; these dimensions fall, however, as we ascend. Inter-
nally, towards the modiolus, they become shorter and shorter, ceasing
suddenly; while externally they increase in length, overhanging with
their extremities the sulcus spiralis already mentioned.

With this last structure the second division of the zona denticulata
commences, namely, the habenula denticulate, or externa, as it is called.

It is again subdivided by Koelliker (and, indeed, unnecessarily so) into
two secondary divisions, — an internal, which he calls the liabenula per-
forata (fig. 606, e) ; and an external (h), the liabenula tecta. The latter
is identical with the habenula arcuata of Deiters.

The habenula perforata constitutes the floor of the sulcus spiralis,
that is, of its labium inferius, and increases in breadth as the summit of
the cochlea is approached throughout the turns of the canal, while the
habenula sulcata becomes narrower at the same time.

It consists of simple connective substance, and is covered on its surface
facing the canal of the cochlea by closely set row of longitudinal emi-
nences, 0 '0226-0 '01 128 mm. broad ; these are the apparent teeth of CortL

Between the outer ends of these apparent teeth, which are completely
hidden by the teeth of the first order in the first, but only partially so in
the subsequent turns of the cochlea, small slits exist for the passage
of the cochlear nerves (fig. 608, h).

Here, then, we have the boundary between the habenula perforata and
habenula tecta or arcuata.

Its wall, or the membrana basilaris (fig. 608, a, b) (formed by a prolonga-
tion outwards of the habenula perforata and tympanal periosteum), sup-
ports upon its upper surface the organ of Corti, — a structure of the most
remarkable kind, whose physiological significance is as yet by no means
understood (figs. 607, 608). This is also known as the papilla siriralis, —
a name proposed by Huschke, and employed after him by Hensen.

In this extraordinary organ may be distinguished two species of form
elements, namely, peculiar fibres and no less characteristic cells.

The first of these, the fibres or pillars of Corti, consist of two rows of
band or pillar-like elements standing upon the surface of the membrana
basilaris, which is somewhat thinned here, and converging obliquely
above, where they meet with pointed extremities. Collectively they pre-
sent the appearance of a puffy elevation, holding a spiral course through
the coils of the cochlea. The whole being hollow, has not inaptly been
likened to a tunnel.

Thus, in the organ of Corti, we have to distinguish between internal
(ft, m) and external (o) pillars. Both kinds of elements are not present,
however, in the same number. Two of the external pillars may usually
be counted to three of the internal (Claudius),

ORGANS OF THE BODY.

661

The internal pillars, separated from one another by narrow clefts, all
spring up in the same line, external to the holes in the lidbenula per-
forata. They rest upon the membrana basilaris with a slightly expanded
base (n), which covers a mass of nucleated protoplasm. This is a remnant
of the original formative cell of the pillar.

The upright portion of our internal pillar becomes, at first, somewhat
narrowed (down to 0-0034-0-0045 mm.), but terminates above in a

v* 18«-H|1«§S)

! 5-3.82-S-Sgs

bs—

slf l»?l~"l

iMIfffif

5 .S aj— * ,-H 3

t£i5f*i!i

B^aorf^SS*:

sZsgSi'**!

*.5§'5'S'8fl."S

bulbous swelling 0'0054 mm. in diameter (?n). Into a depression on the
outer aspect of the latter, the upper end or " head" of the external pillar
of Corti (o) (0-0079 mm. across) fits.

This external pillar springs, with a similar expansion, from the mem-
brane upon which it rests, and presents here also the same nucleated
protoplasm as the internal. These protoplasmic cell-residues taken collec-
tively, are known as the " granular layer."

662 MANUAL OF HISTOLOGY.

The form of the external pillar is allied to that of the internal, although,
by no means quite the same. A glance at fig. 608 will render any further
description unnecessary.

These remarkable structures are composed of a transparent homoge-
neous substance, offering but slight resistance, however, to the action of
reagents.

But the cellular elements of the organ of Corti are no less remarkable.

Commencing from within from the sulcus spiralis, we may observe that
the epithelial cells become higher, so that at about the middle of the
internal pillars of Corti a high ridge of epithelium (g) is formed. Here,
then, we come upon a peculiar structure, known as the internal " hair cell"
or tufted cell of Deiters. We shall frequently have occasion again to refer
to the cells in question, which, taken all together, naturally form a spiral
row.

Now, just as the internal hair cell lies in a slanting direction upon the
internal pillar covering it, so do the external hair or tufted cells or cells of
Corti of earlier observers (p, q, ?•), of which there are three or four rows,
cover the external pillars, similarly inclined. They are said, however,
by the most recent observers (Gottstein and Waldeyer) to be double cells,
and the pillars of Corti are, probably, also developed from such twin
cells likewise.

External to the outer hair-cell spiral we next come upon columnar
epithelial elements, the so-called " supporting cells " of Hensen (fig. 608,
z; 607, r). Beyond this, the latter become shorter and shorter, until
they gradually merge into the simple cubical epithelium of the zona
pectinata (fig. 606, k).

Let us now bestow a glance upon that wonderful fenestrated covering
membrane, known as the lamina reticularis of Koellilcer or I. velamentosa
of Defers, essential to our gaining a comprehensive idea of the whole.

In fig. 608 the position of this covering membrane is represented in
side view from I to l'f but its remarkable structure can only bo recognised
from above, as in fig. 607.

From as far inwards as the internal pillars, the epithelial cells give
off a cuticular annular limiting border (c). Above this, then, the internal
hair-cells (e) reach the same height as the organ of Corti.

Each internal pillar of the latter, then, is prolonged into a pretty broad
horizontal plate, which rests upon the top of an external pillar. In fig.
607 these internal "head plates" are represented at/, i. Beneath them
lie the head plates of the external pillars, likewise horizontal (607, I ;
608, m). These plates have a long narrow neck, and present an oar-
shaped figure. They constitute the first phalanges of the lamina reti-
cularis. In these head plates the latter cuticular formation has its
commencement.

A glance at fig. 607 will convey a more rapid idea of the annulary con-
dition of this lamina reticularis than any description, however minute
(k, m, o). With the first phalanx we are already acquainted. At n and
p, the second and third rows of phalanges are to be seen. K, m, o, indi-
cate the tufts of hairs of the three spiral ranks of the so-called external
hair cells. Finally, at E, descending again, we come upon the external
epithelial cells of the tnembrana basilaris. But between these also
further prolongation of this cuticular mesh-work may be recognised.
This is the so-called "terminal frameivork" of Deiters (q).

The zona pectinata (fig. 606, g), i.e., the external portion of the lam.

ORGANS OF THE BODY. 663

spiral, memb. commences at the outer border of the organ of Corti, and
remains — one might almost say happily — free from further accessory
structures. Formed of the two periostea! laminae of the memb. basilaris
it presents a perfectly smooth under surface towards the scala tympani,
while the upper appears finely streaked as if fibrillated. The outer
border of the zona pectinate^ reaches the bony wall of the cochlea (fig.
606, i). Here opposite a low bony ridge (m), which Huschke has named
the lamina spiralis accessoria, it unites with the so-called ligamentum
spirals (I). The latter, a vascular mass, consists of an upper fibrillated
portion, and an under cellular part facing the scala tympani (Hensen).

§ 326.

There still remain for our consideration the epithelial lining of the
canalis cochleae, and the mode of termination of its nerves.

In the foetus this canal (fig. 606, C), is originally lined throughout
with epithelial cells (Koelliker). These present themselves as a single
layer of pavement elements, except in two localities, namely (1), at the
sulcus spiralis (d), and so-called habenula sulcata, and (2) in the position
of the organ of Corti (/). In the first of these positions the cell-layer is
stratified and overlaid with a membrane, the membrane of Corti (Cm). At
the spot indicated by (b), the epithelial mass forms a ridge which sup-
plies, according to Koelliker, material for the formation of the organ of
Corti, of the hair-cells, and as a cuticular structure of the lamina reticu-
laris also.

If the membrane of Corti be closely examined in the full-grown
animal, it will be found to present (in the ox, for instance) a thickness
of 0'045 mm., and finely fibrous appearance. It commences upon the
habenula sulcata at about the same spot as that at which the membrane
of Reissner, already mentioned, arises. Its mode of termination exter-
nally is still a matter of controversy. According to Hensen, Gottstein,
and Waldeyer, it reaches to the organ of Corti, terminating very much
thinned in the neighbourhood of the external hair-cells. It rests immedi-
ately upon the lamina reticularis.

The epithelium of the fully developed canalis cochleae consists, upon the
membrane of Reissner of a layer of large flat pavement cells. Smaller
and thicker cells are to be found on the outer parts of the canal and zona
pectinata, as far as the neighbourhood of the organ of Corti, where large
spheroidal, and at last perpendicularly elongated elements present them-
selves the "supporting" (Stiitzzellen) of Hensen, Under Cortfs mem-
brane, upon the habenula sulcata, it probably only occurs, on the other
hand, interruptedly, and in the sulcus spiralis Hensen only found a
single layer.

The cochlea is supplied by numerous capillary networks situated in the
periosteum and lamina spiralis. Above the so-called ligamentum spirale,
especially, may be seen a peculiarly vascular streak, the stria vascularis
of Corti (fig. 606, o). Within the lamina spiralis the bony tissue and
nervous ramifications are traversed by a complex network, which com-
municates with a spiral vessel situated upon the under surface of the
plate, i.e., that facing the scala tympani.

As regards lymphatic spaces, in the internal ear, we have only to
remark that injections from both subdural and subarachnoidal spaces
of the encephalon penetrate into the labyrinth (Key, Retzius).

Turning now to the distribution of the corhlear nerve, the first point to
43

664 MANUAL OF HISTOLOGY.

be observed is that bundles of fibres, made up of medullated tubes
0'0031 mm. in thickness, radiate from the modiolus into the lamina
spiralis ossea, forming a dense plexus in its complicated passages. At
one particular spot, namely, at the point of exit from the bony portion of
the spiral plate, there is imbedded (as was first observed by Corti} in the
course of the primitive fibres a ganglion cell (ganglion spirale of Corti}.
Preserving their plexiform arrangement, the nerve fibres still pursue a
course outwards, passing eventually through the apertures in the habe-
nula, after having dwindled down to non-medullated axis cylinders.
Arrived now in the canalis cochlearis they present themselves as extremely
delicate pale fibrillse.

From this on two different sets of fibres may be distinguished, namely
(a}, one for the internal, and (b) one for the external hair cells.

The axis cylinders of the internal set (0'0015-0'002 mm. thick) are
supposed to penetrate into the apices of the internal hair cells (fig. 608).
The external, which are much finer, to pass across the " tunnel " of the
organ of Corti, about midway between floor and roof (Gottstein, Wal-
deyer) to unite with the external hair cells (w). These views are, how-
ever, still but very feebly supported.

While we leave the greater part of the development of the organs of
hearing to the special works on embryology, we may here mention a few
general facts on the subject in conclusion.

The labyrinth makes its first appearance as a vesicular structure, known
as the labyrinthine or auditory vesicle, a multilaminar infolding of the
corneous layer (Remak), which subsequently receives from the middle
germinal plate a fibrous, and then over that a cartilaginous covering in
the form of a capsule.

The semicircular canals and the canalis cochlearis are then formed
from the auditory vesicle as secondary outgrowths.

The canalis cochlearis, at first only a slight eminence, grows out into a
curving horn, which acquires in its further development the spiral pas-
sage (Koelliker). The two scalar, that of the tympanum and that of the
vestibule, are tertiary formations produced by the liquefaction of the con-
nective-tissue adjoining the canalis cochlearis.

INDEX.

Acetic acid, 24
Acids (fatty), 23
nitrogenous, 36
n on -nitrogenous, 34

Acinus of glands, vid. Glandular Tissue
of thymus, vid. CIRCULATORY APPARA-
TUS

Acoustic teeth, vid. SENSORY APPARATUS
Addison's Disease, relation to supra-renal

bodies, vid. CiRC. APP.
Adenoid Connective-Tissue of His, 193
Agminated glands, 420
Air-cells of lungs, vid. RESPIRATORY APP.
Albumen, 14

of several organs, vid. latter
Albuminous Compounds, 12
albumen, 14
casein, 17
composition of, 13
crystalliu, 17
ferments, as, 14, 17
fibrin, 15
fibrinogen, 15
fibrinoplastin, 15
globulin, 17
haemoglobulin, 18
histogenic derivatives from, 21
chondrin, 22
chondrigen, 22
collagen, 22
colloid, 21
elastin, 23

glutin- yielding substances, 21
glutin, 22
keratin, 21
mucin, 21
myosin, 16
peptones, 17
properties of, 13
syntouin, 16

Amides. Amido-Acids, Organic Bases, 40
allantoin, 44
cholin (neurin), 48
cystin, 50
glycin, 48
guanin, 43
hypoxanthin, 43
kreatin, 44
kreatinin, 45
leucin, 45
neurin, 48

relations and constitution of, 40
sarkin, 43
taurin, 48
tyrosin, 47
urea, 40
nitrate of, 41
oxalate of, 41
xanthin, 43

Ammonium Salts, 62

carbonate of, 62

chloride of, 62

urate of (acid), 37
Amoeboid cells, vid. Cells
Amoeboid motion, vid. Cells and Blood
Amyloid degeneration of cells, vid. Cells
Amyloid matter, 29
Anatomy, general, 1

study of same with microscope, 2

without latter, 2
APPARATUSES OF BODY, 399

bony,

circulatory, 402

digestive; '458

generative, 536

muscular, 573

nervous, 574

respiratory, 448

sensory, 603

urinary, 514
Aqua Cotunii (perilymph) of internal ear,
vid. SENS. APP.

vitrea auditiva (eudolymph) of internal

ear, vid. SENS. APP.
Arachnoid of brain, vid. NERV. APP.
Areola of breast, vid. GEN. APP.
Arrector pili, muscle of hair follicle, vid.

Hair
Arteriae helicinse of cavernous organs, vid.

GEN. APP., male
Arteries, vid. VESSELS
Arteriolae rectas of the kidneys, vid. URINARY

APP.
Articulations, vid. BOXY APP.

cartilages of, vid. BONY APP.
Auditory filaments, vid. SENS. APP.
Aiterbac/i's plexus myentericus, vid. Nerv.

Tiss. and DIGEST. APP.
Auricles of heart, vid. CIRC. APP.
Axial canal of spinal cord, vid. NERV. APP.
Axial stream of blood-vessels, vid. VESSELS
Axis cylinder, vid. Nerve Tiss. and NERV.

APP.
Axis-cylinder process of ganglion cells, vid.

Nerve Tiss. and NERV. APP.
Axis fibres, vid. Nerve Tiss.
Axis fibrillae, vid. Nerve Tiss.

Bacillary layer of retina, vid. SENS. APP.
granules, vid. SENS. APP.

Bacilli (rods) of retina, vid. SENS. APP.

Bartholin's glands, vid. GEN. APP. (female)

Basement membrane (intermediate mem-
brane), vid. Cells

Bases, organic, vid. Amides, &c.

Beaker cells, vid. DIGEST. APP. and Epithe-
lium

Bellini, tubes of, vid. URIN. APP.

666

INDEX.

Benzole acid, 38

BicJiat, X., 2

Bile, vid. DIGEST. APP.

Biliary capillaries of liver, vid. DIGEST.

APP.
Biliary passages, vid. DIGEST. APP.

glands of, vid. DIGEST. APP.
Biliary pigments, 53
Bilifuscin, 54
Bilihumin, 54
Biliprasin, 54
Bilirubin, 54
Biliverdin, 54
Bladder, vid. URIN. APP.
Blood, 105

amount of, in body, 105

analysis, chemical (present state), 115

anatomical, 105

cells, conditions of, during life, 127
coloured or red (human), 106
compared with those of lower ani-
mals, 109

composition of, 11 7
differences of, in vena porta and

vena hepatica, 108
effects of electrical discharges on,

107

of gases on, 122
of heat on, 108
of several reagents, 107
number of, 106
origin of, 114

passage of, through walls of unin-
jured vessels, 128
rouleaux of, 123
shape of, 106
size of, 106
volume of, 106
weight of, 106
colourless, white, pale, 110
amoeboid motion of, 112
composition of, ]34
number (normal) compared with

red and in leucaemia, 113
nuclei of, 111

origin of, 113 ; from bone medulla,
spleen, and lymphatic glands,
128; in the embryo, 129.
passage of, through walls of vessels,

129

segmentation of, 129
transformation of, into red cells,

114, 128
circulation of red and white corpuscles

in living vessel, 113
coagulation of, 124
buffed coat, 127
causes of, theories, 127
crassamentum, 126
crusta phlogistica, 127
variations in process of, 126
composition of (chemical), 114
arterial of, 121
intercellular fluid of, 118
menstrual of, 121
splenic artery and vein of, 121
venous of, 121

vena porta and hepatica of, 121
corpuscles, vid. Cells
crystals, 117

development of, in embryo, 129
of, 118-120

o Ti
Uss< ils8'

Blood, odour of, 105

physical properties of, 105-106

plasma of, 106

temperature, 105'

Blood-vascular glands, vid. CIRC. APP.
Blood-vessels, vid. VESSELS

of organs, vid. same
Bodies of cells, vid. Cells
Bone, vid. Oss. Tiss.

canaliculi of, vid.

cartilage, vid.

earths, vid.

lacunae of, vid.
Bones of ear, vid. SENS. APP.
BONY APPARATUS, 510

Articulation (modes of), 570
diarthrosis, 570
sutures, 570
symphyses, 570
synarthrosis, 570

Cartilage of, 570

ill-developed osseous tissue under-
neath, 170

Formation of, 570

Half-joints, 570

Haversian glands, 571

Medulla (conversion of cells of, into red
blood corpuscles), 573

Myeloplaxes, 573 and 71

Nerves of, 572

Plicse vasculosae, 571

Vessels of, 571
Boundary layer of Henle in kidneys, vid.

URIN. APP.
Jiowman's glands of olfactory regions, vid.

SENS. APP.

Brain, vid. NERV. APP.
Breast, vid. GEN. APP. (fern.)
Bronchi, vid. RESPIR. APP.
Bruch's agminated follicles (plaques) of

conjunctiva, vid. SENS. APP.
firunner's glands, vid. DIGEST. APP.
Buccal glands, vid. DIGEST. APP.
Bulb of eye, 617
Bulb olfactory, 597
Bulb of urethra, 566
Butyric acid, 24

Calcification of cells, vid. Cells

Canal, semicircular, of ear, vid. SENS. APP.

Canal of Petit of eye, vid. SENS. APP.

Canal of Schlemm of eye, vid. SENS. APP.

Canaliculi of bone, 243

Canalis cochlearis, vid. SENS. APP.

Canals, Haversian, 240

Capillaries, vid. VESSELS

Capillary canals, vid. VESSELS

Capillary vessels, vid. VESSELS

Capillary looped networks, vid. VESSELS

Caprinic acid, 25

Capronic acid, 25

Caprylic acid, 25

Capsula lentis, vid. Lens Tiss.

Capsule of cells, vid. Cells

Caput epididymis, vid. GEN. APP.

Carbohydrates, 30

Cardiac ganglia, vid. Ganglia

Carotid ganglion, vid. Ganglia

Cartilages, 166

articular, 167, 174

calcification of, 171

capsules, 169

INDEX.

667

Cartilages —
cells, 163

fatty infiltration of, 171
cells of (medullary), 171

segmentation of, 170
chemical analysis of, 183, 184
classification of, 167
connective-tissue, vid. fibro-cartilage
early appearance of, 186
ekchond roses, 186
elastic, 179
enchondroma, 186
fibro, 180, 225

colloid nuclei of intervertebral liga-
ments, 182
fibro-reticular, 179
hyaline, 166

portions of adult bodies still consist-
ofit, 173, 174

preformation of fcetal skeleton in, 173
intercellular substance, 169

source of, 169
liquefaction of, 173
medulla of, 251
membraniform, 167
neoplasmata of, 186
permanent, 167

respiratory apparatus, of, 176, 448
reticular, 179
significance of, in adult and foetal body,

185

temporary, 167
Casein, 17

Cauda epididymis, vid. GEN. APP.
Cavernous passages of lymphatic glands, vid.

CIRC. APP.
Cells, 63

amoeboid motion in, 75
body of, 64

material of, 66
calcification of, 95
capsule of, 83
casting off of, 94
chemical constitution of, 72
ciliated, the, 78
colloid metamorphosis of, 94
component parts of, 66
containing red blood- corpuscles, vid.

CIRC. APP.
contractile, 75
cytoblastema, 87
decay of, 94
derivatives of, vid. Cells, as parent of

other structures
division of, 88
envelope, 64

structure of, 68
enveloping sphere of, 92
fatty metamorphosis of, 95
flattened, 65
formed products of, 82

basement membranes, 84

ground substance, 86

intercellular substance, 86

intermediate membrane, 84

membrane propria, 85

tissue cement, 86
fusiform, 66
generation of, within larger and older

cells, 94

giant (multinuclear), 71
granulated, 69

Cells, growth of, 78

interchange of material of, 80

mature, 66

membrane of, 64

multinuclear, 71

multiplication of, 88

networks of, vid. Cells, as parent of

other structures and, 98
nucleolus, 64, 70
nucleus, 64, 69

absence of, 71

gemmation of, 91
ova, perfect examples of, 64
parent, 89
parents of other structures as, 95

of cellular networks, 98 .

of connective substances, 98

of connective-tissue fibres, 89

of elastic fibres, 89

of nerve fibres, 100

of smooth muscle fibres, 95

of striped muscle fibres, 96

of vascular cells, 97
physiological properties of, 64

decay of, 101
pore canals of, 83
protoplasm of, 66

deposit of strange matters in, 67
psorospermia in, 92
reception of solid particles into interior

of, 77

Remak's discoveries concerning, 93
ridged, 69
segmentation of, 88

of naked cells, 88

of encapsuled, 89

of parent, 89

of daughter, 89

of yelk, 90
senescent, 66
shape, 65

single-celled organisms, 64
size of, 65
smooth-edged, 69
solution of, 94
spheroidal, 65
spinous, b'9

spontaneous generation of (Schwann), 92
stellate, 66

tall narrow species of, 66
tuberculisation of, 95
vital properties of (amoeboid motion), 75
wandering of, through the body, 78

significance of latter process in inflam-
mation, 79
Cellular networks, vid. Cells, as parent of

other structures
Cement, vid. Dent. Tiss.
Central organs of NERV. SYS. (brain and

cord), vid. NERV. APP.
Cerebellum, vid. NERV. APP.
Cerebra ganglia, vid. NERV. APP.
Cerebrum, vid: NERV. APP.
Cerumen, vid. SENS. APP.
Ceruminous glands, vid. SENS. APP.
Chemistry of tissues, 5

physiological, 6
liloride of ammonium, 62
of calcium, 58
of iron, 62
of magnesium, 59
of potassium, 61

668

INDEX.

Chloride of sodium, 60

Cholestearin, 30

Cholic acid, 39

Cholin (neurin), 48, and Nerve Tiss.

Chondrigen, 22

Chondrin, 22

Chorda dorsalis, vid. Cartilage

Choriocapillaris, vid. SENS. APP.

Choroid coat of eye, vid. SENS APP.

Chorion (zona pellucida) of ovum, vid. GEN.

APP.
Chyle, vid. Lymph

vessels, vid. VESSELS
corpuscles, vid. Lymph
in intestinal villi, vid. DIGEST. APP.
Ciliary arteries, vid. SENS. APP.
Ciliary motion, vid. Epithelium
Ciliary muscles, vid. SENS. APP.
Ciliary nerves, vid. SENS. APP.
Ciliary processes, vid. SENS. APP.
Ciliated cells, vid. Epithelium
CIRCULATORY APPARATUS, 403
Blood-vascular Glands, 440
carotid gland (ganglion intercaroti-

cum), 448

coccygeal gland, 447
structure of, 447
vessels of, 447
pituitary body, 446
glandular structure of anterior lobe,

446

suprarenal body, 443
Addison's Disease, 416
blood-vessels of, 445
composition of, 446
cortical substance of, 443
development of, 448
envelope of, 463
lymphatics of, 445
medullary substance of, 444
pathological changes in, 446
thyroid, 440

colloid metamorphosis of, 442
composition of, 442
development of, 443
goitre in, 442
lymphatics of, 441
nerves of; 442
stroma of, 441
vesicles of, 441
Heart, 403
auricles of, 405
endocardium of, 405
fibres of Purkiiy'e of, 405
ganglia, 406

muscular substance of, 403, 292
nerves of, 403, 406
pericardium of, 403
valves of, 406
vessels of, 406
Lymphatic Glands, 407
'follicles of, 407

of cortical layer, 407
of medullary mass, 407
investing spaces of, 408, 410
structure of, 408
hilus-stroma of, 411
lymphatic passages of, 415
epithelial lining of, 417
lymph tubes of, 411, 412
origin of, 413
termination of, 413

CIRCULATORY APPARATUS—
Lymphatic Glands —
medullary substance of, 407
nerves of, 418

nucleus of, vid. hilus-stroma
septa of, 408
substance of, 411
vas atferens of, 407
vas efferens of, 407
vessels of, 414
Lymphoid Organs, 420

lenticular follicles of stomach, 420
lingual follicles, 420
lymphoid follicles, 420

investing spaces of, 421

lymphatic passages of, 422

structure of, 420
lymphoid glands, 420

agminated, 420

solitary, 420
spleen, 426

arteries of, 427

capillaries of, 431

capillary husks, 431

cavernous splenic veins, 434

cells containing blood corpuscles, 43

composition of, 439

development of, 440

envelope of, 446

follicles of, 430
gradual formation of same, 431

intermediate pulp passages of, 436

lymphatics of, 438

lymphoid portion of, 427

Malpighian corpuscles of, 427

morbid changes in, 440

nerves of, 438

penicilli, 427

pulp, 427

pulp tubes, 432

pulp cords, 432

septa, 427

trabeculse, 427

transition of arterial into venous
circulation in, 435

vascular sheaths of, 429

veins of, 434

venous system of, 434

wall-less passages of, 435
thymus, 423

acini of, 424

central canal of, 423

composition of, 425

concentric bodies of, 424

degeneration of, 425

development of, 425

granules, 424

lobules, 423

lymphatics, 425

vessels, 424
tonsils, 420
trachoma glands, 420
Circulus arteriosus iridis major and minor,

vid. SENS. APP.
Circulus arteriosus niusculi ciliaris, vid.

SENS. APP.

Clitoris, vid. GEN. APP. (fern.)
Coagulation of nervous matter, vid. NKKV.

APP.

Coccygeal gland, vid. CIRC. APP.
Cochlea, vid. SENS. APP.
Cochlear nerve, vid. SENS. APP.

INDEX.

669

Cohnheim's fields in transverse sections of

muscle, vid. Mus. Tiss.
observations on wandering of white

blood-corpuscles, 129
Collagen, 22

Colliculus seminalis, vid. GEN. APP.
Colloid matter, 21
Colloid metamorphosis of thyroid gland, vid.

CIRC. APP.
of cells, vid. Cells
Colloid nucleus of intervertebral ligament,

rid. Cart.

Colon, follicles of, vid. DIGEST. APP.
Colostrum, vid. GEN. APP. (fern.)
corpuscles, vid. GEN. APP.
formation of, vid. Gland. Tiss.
Colouring matters (animal), 50.
Columnar layer of retina, vid. SENS. APP.
Commissures, ant. and post, of spinal cord,

vid. NERV. APP.

Conarium (pineal gland), vid. NERV. APP.
Concentric bodies of thymus, vid. CIRC. APP.
Cone granules, vid. SENS. APP.
Cones of retina, vid. SENS. APP.
Coni vasculosi, vid. GEN. APP.
Conjunctiva of eye, vid. SENS. APP.
Conjunctival glands, vid. SENS. APP.
Connective substance, its origin from cells,
vid. Cells, parents of other structures
cytogenous, vid. Gelat. Tiss.
reticular, 187

sustentacular of nervous system and re-
tina, 188, 196
Connective-tissue, 205
bundles

elastic limiting layers of, 210

primary, secondary, and tertiary, 207

cartilage, vid. fibro-cartilage

cells, vid. corpuscles

cornea of eye, 220

canal work of, 222

corpuscles, 222

elastic laminae of (ant. and post.), 220

epithelium of, 220

tissue of, 220

corpuscles, 212

amoeboid motion of, 213
immigration of, into tissue of cornea
under inflammatory irritation
Cohnheim's and v. RecTdinghaMS
ens experiments, 222
in an inanimate state, 214
stellate pigmentary, 219
change of form of, 219
cutis vera, of, 228
dental pulp, of, 218
elastic, elements of, 208
nucleus fibres, 208
origin of, in embryo, 237
structures of respiratory organs, 229
tissue, so-called, 2H)
fasciae, 226

fibres, vid. Cells, as parents, and, 205
fibrillae, 205

more closely considered, 206
fibromata, 234
fibrous membranes, 225
formed, 219
ligaments, 225

ligamentum flavae of spinal col. , 229
ligamentum nuchae, 229
mode of occurrence, of, 216

Connective-tissue, loose areolar, 217
mucous membranes of, 228
neurilemma, 226
origin of, in the embryo, 235
perichondrium, 226
perineurium, 226
periosteum, 226
physiological pui poses of, 232
plasmatic circulation (suppositions) in,

223

relationship to other tissues, 233
serous membranes of, 226
subarachnoid spaces of, 227
subcutaneous, 218
submucous, 218
subserous, 218
suppuration in, 234
sy no vial bursae of, 227

sheaths of, 227
tendons of (in the infant), 224

(in the adult), 224

tunics of blood and lymph vessels, 229
* varieties of, 205
vascular membranes of (pia mater and

choroid plexus), 229
Contour (double) of nerves, vid. Nerve Tiss.
Contour lines of dentine, vid. Dental Tiss.
Contractility, vital, of cell, vid. Cells
Convoluted glands of conjunctiva, vid. SENS.

APP.

Copper, 62.

Cord, spinal, vid. NERV. APP.
Cornea, vid. Con. Tiss. and SENS. APP
Corneal tubes, vid. SENS. APP.

nerves, vid. SENS. APP.
Corneous layer of epidermis, vid. Epithe-
lium, and SENS. APP.
Cornification of flattened epithelium, vid.

Epithelium

Comu ammonis, vid. NERV. APP.
Cornua of spinal cord

accessory of medulla oblongata

corpuscles, vid. Con. Tiss.

germinal layers (epibla^t, mesoblast, and

hypdblaai)
layer of epidermis

Corpora cavernosa, vid. GEN. APP. (male)
Corpora quadrigemina, NERV. APP.
Corpora amylacea, 29

quadrigemina, vid. Nerv. Tiss.
Corps momine" of testicle, vid. GEN. APP.

(male)

Corpus ciliare of eye, vid. SENS. APP.
Corpus dentatum of cerebellum, vid. NERV.

APP.

of olivary body, vid. NERV. APP.
Corpus epididymidis, vid. GEN. APP.
Corpus Highmori of testicle, vid. GEN. APP.

(male)

Corpus luteum, vid. GEN. APP. (female)
Corpus striatum, vid. NERV. APP
Corpus vitreum, 189

Cortex corticis of kidney, vid. URIN. APP.
Cortis fibres in cochlea, vid. SENS. APP.
cells of, vid. same,
organ of, vid. SENS. APP.
Cowper's glands, vid. GEN. APP.
Crura cerebelli

ad corpora quadrigemina
ad medullam oblongatam
ad pontem, vid. SENS. APP.
Crura cerebri ad pontem, vid. SENS. APP.

670

INDEX.

Crusta petrosa, vid. Dent. Tiss.

Crystallin, vid. Globulin, 17

Cumulus proligerus of ovary, vid. GEN. APP.

(female)

Cuticula of hair, vid. Hair
Cyanogen compounds, 54
Cystin, 50

Cytoblastema, vid. Cells
Cytogenic connective-tissue of KoeUiker, 193

Daughter cells, vid. Cells

Decidua of uterus, vid. GEN. APP. (female)

Dehiscence of glands, vid. Gland. Tiss.

of ovarial follicles, vid. GEN. APP.

(female)

Deiter's cells, vid. SENS. APP.
Dental tissue, 260
cement, 264

composition of, 265
formation of, 271
lacunae of, 265
crusta petrosa, 265
dental canaliculi. 261
cup, 271
fibres, 264
follicles, 266
germ, 266
groove, 267
ridge, 267
dentine, 261
cells, 254

composition of, 265
contour line, 263
globules, 262
ground-substance, 262
interglobular spaces, 262
enamel, 261
germ, 268
membrane, 269
organ. 266
odontoblasts, 264

layer of, 270

pathological conditions of, 272
pulpa dentis, 263
teeth, 260

development of, 266
tooth 260
crown of, 260
germ, vid. dental germ
neck, 260
root of, 260
Tomes' fibres. 264

layer, 262 '

Dental germ, vid. Dent. Tiss.
Dental cells, vid. Dent. Tiss.
Dentine, vid. Dent. Tiss.
Uiarthrosis, vid. BONY APP.
DIGESTIVE APPARATUS, 458
Colon, 497
blood-vessels of, 498
development of mucous coat, 499
lymphatics of, 498
lymphoid follicles of, 497
tubuli of, 497
Intestine (small), 484
development of, 497
glands of, 486
firunner's, 486
Lieberkuhn's, 488
racemose, vid. Urunner's
juices of, 499
lymphatics of, 495

DIGESTIVE APPARATUS—
Intestine (small) —

lymphatics of, arrangement in mucous
membrane and sub-inucous tis-
sue, 496
in Peyer's plaques, 496

AuerbacKs inteiiaminar plexus of
496 * '

in villi and muscular tunic, 495

radicles of, 495
lymphoid follicles of, 489

agminated, 489

base, 490

cupola, 490

form of, 490

mesial zone of, 490

parts of, 490, 491

Peyer's plaques, 489

position of, 489

ridge of mucous rnemb. of, 491

structure of follicles, 491
mucous membrane of, 484
nervous apparatus of, 492

Auerbach's plexus rnyentericus, 494

Remak's and Meissner's sub-mucous

plexus, 492
succus entericus, 499
valvulae conniventes, 484
vascular supply of, 493
villi, 484

capillary network of, 485

chyle radicles of, 486

structure of, 485
Liver, 502

bile, a secretion of, 512
bile, composition of, 512

gases of, 513

pigments of, 53, 513

quantity of, 513

secretion of, 513

uses of, 514
bile ducts, 506

glands of, 510
bile capillaries, 506

relation of, to cells, 507

walls of, 509
cells, 502

arrangement of, 502

contents, 502

cuticular border of, 509
cirrhosis of, 502
composition of tissue of, 511
development of, 514
gall bladder, 509

vasa aberrantia of, 510
lobules of, 502

arrangement of vessels in, 504

capillaries of, 504 '

demarcation of, 504

sustentacular tissue of, 505
lymphatics "of, 510
nerves of, 511
vena hepatica, 504
vena intralobularis, 504
vena interlobularis, 504
vena porta, 504
Mouth, 458
glands of, 459

buccal, 459

lingual, 459

palatal, 459
lymphoid organs of, 469

INDEX.

671

DIGESTIVE APPARATUS—
Mouth-
mucus of, 464
mucous membrane of, 458
submucosa, 458
(Esophagus,
glands of, 472
lymphatics of, 473
nerves of, 473
vessels of, 473
Processus vevmiformis, 499
Pancreas, 499

development of, 500
juice of, 501

composition of, 501
nerves of, 500
secreting tubules of, 500
structure of, 500
Phamyx, 472
lymphatics of, 472
lymphoid organs of, 472
vessels of, 472
Saliva, 463

composition of, 463
uses of, 464
Salivary glands, 460
parotid, 462
secretion of, 465

effectof irritation of nerves on, 465
subm axillary glands, 460
blood-vessels of, 461
border cells of, 465
crescents of, 465
excretory ducts of, 461
lymphatics of, 461
mucus of, 465

nerves of (termination of), 4til
secretion of, 464
corpuscles of, 465
effect of nerve irritation on, 464
varieties of cells of, 460
sublingual glands, 462

secretion of, 465
Stomach, 473
cells, 477

development of, 482
glands of, 475
cells of, 475
adelomorphous, 478
delomorphous, 478
membrana propria of, 475
mucous of, 479
peptic, 475
racemose, 479
juices of, 482
action of, 482
composition of, 482
mucous membrane of, 474
muscularis mucosas, 474
lenticular follicles of, 480
lymphatics of, 481
nerves of, 481
peptones of, 483
serous covering of, 473
vascular system of, 480
Tongue, 466
development of, 469
fibre-cartilage of, 466
glands of, 469
lingual follicles, 469
lymphatics of, 468
mucous membrane of, 469

DIGESTIVE APPARATUS—
Tongue —

mucous membrane of, lymphoid infil-
tration of, 469
muscular substance of, 466
nerves of, 468, and SENS. APP.
papillae of, 467
circum vail ate, 467
filiform, 467
fungiform, 467
Tonsils, 470
lymphatics of, 471
vessels of, 470
Diglycerides, 24

Dilatator pupillze, vid. SENS. APP.
Disks, vid. Mus. Tiss.
Ductus ejaculatorii, vid. GEN. APP.
Ductus thoracicus, vid. Vessels
Dura mater, vid. NERV. APP.
Duvemey's glands, vid. GEN. APP. (female)

Ear (internal), vid. SENS. APP.
Ekchondroses, vid. Cartilages
Elain, vid. Triolein, 26
Elaidic acid, 25
Elastin (elastic material), 23
Elementary parts of body, 63
Elements of composition of body, 11
Enamel of teeth, vid. Enamel Tiss.
Enamel columns, vid. Enamel Tiss.
Enamel cuticle, vid. Enamel Tiss.
Enamel fibres, vid Enamel Tiss.
Enamel germ, vid. Dent. Tiss.
Enamel membrane, vid. Enamel Tiss.
Enamel organ, vid. Dent. Tiss.
tissue of, vid. Gelat. Tiss.
Enamel prisms, vid. Enamel Tiss.
Enamel tissue, 273
columns, 273

cuticle (membrana praeformativa), 276
composition of, 275
development of, 275
fibres of, 273
prisms of, 273

Enchondroma, vid. Cartilages
End-bulbs, vid. Nerv. Tiss.
End-capsules of gland nerves, vid. Nerv. Tiss.
Endocardium, vid. CIRC. APP.
Endogenous cell growth, vid. Cell
Eudolymph of internal ear, vid. SENS. APP.
Endothelium, vid. Epith. and Vessels
Envelopes of fine nerve twigs, vid. Con.

Tiss. and Nerve Tiss.
Envelopes of the central organs of nervous

system, vid. NERV. APP.
Ependymal thread of spinal cord, vid. NERV.

APP.

Epidermis, vid. Epith.
Epididymis, vid. GEN. APP. (male)
Epithelium, 137

Cells (varieties of), 138

action of alkalies upon, 151

beaker, vid. goblet

ciliated, 138

columnar, 138

flattened, 139

goblet, 148

occurrence of mucous and pus-cor-
puscles in, 153

pavement, 138

pigmentary, 138

ridged, 141, 142

672

INDEX.

Epithelium —

Cells, relationship to gland cells, 152
spinous, 141, 142

Ciliated, 148

Ciliary motion of, 156

Columnar, 146
thickened border of, 84, 147
pore canals in, 84, 147

Composition of, 150

Development of, 137

Endothelium, 159

Epidermis, 144
corneous layer of, 144
cornification of, 150

Goblet cells in, 150

Keratin of, 151, 152

Laminated, 139

Mucus of, 154

Pavement, 139

Physiological significance of, 152

Rete Malpighi, 144

Synovia a secretion of, 155
Erection of penis, vid. GEN APP.
Eustachian tube, vid. SENS. APP.
Extractives, 54 (note)
Eyelids, vid. SENS. APP.

Faries' milk, 554

Fallopian tubes, vid. GEN. APP.

Fats, 23

cerebral, 28

neutral, 26

of several organs and tissues, vid. same

purposes of, 27

Fat-cells containing serum, vid. Fatty Tiss.
Fat-cells poor in fat, vid. Fatty Tiss.
Fatty acids, 23

Fatty degeneration of muscle, vid. Mus. Tiss.
Fatty metamorphosis of cells, vid. Cells
Fatty tissue, 198

blood-vessels of, 200

development of, in embryo, 203

distribution of, through the body, 200

fat cells, 198

deprived of fatty matter, and contain-
ing serum, 199, 200
formation of, from connective-tissue
corpuscles, 203

fatty tumours, 201

panniculus adiposus, 200

physiological purposes of, 202
Fatty tumours, 201

Fermentation of urine, vid. UKIN. APP.
Ferments, 14, 17

Fibre-cell contractile, vid. Muscle Tiss.
Fibres (elastic), vid. Cells, as parent ot

tissues and Con. Tiss.
Fibrin, 15

coagulation of, 16
Fibrinogen, 15
Fibrinoplastin, 16
Fibroma, vid. Con. Tiss.
Fibro-cartilage, vid. Cartil. and Con. Tiss.
Fibro-reticular cartilage, vid. Cartil.
Fluoride of calcium, 58
Follicles,

of colon, vid. DIGEST. APP.

Graafian, vid. GEN. APP. (female). •

of lymphatic glands, vid. CIRC. APP.

lymphoid, vid. CIRC. APP., and several
organs

Malpighian, vid. CIRC. APP.

Follicular rudiments of ovary, vid. GEN.

APP. (female)

Forked cells, vid. SENS. APP.
Form elements of body, 63
Form, change of, in amoeboid cells, vid. Cells
Formatio granulosa of ovarial follicle, vid.

GEN. APP. (female)
Formatio reticularis of med. oblong., vid.

NERV. APP.
Formic acid, 24

Fovea centralis of retina, vid. SENS. APP.
Fundamental lamellae of bone, vid. Oss. Tia.s

Gall bladder, vid. DIGEST. APP.
Ganglia of different organs, vid. same
cardiac, vid. CIRC. APP.
cells of, vid. Nerve Tiss.
apolar, vid. Nerve Tiss.
bipolar, vid. Nerve Tiss.
multipolar, vid. Nerve Tiss.
unipolar, vid. Nerve Tiss.
ramifying in anterior cornu of spinal

cord, vid. Nervous App.
cerebral, vid. Nervous App.
corpuscles, vid. Nerve Tiss.
structure, vid. Nerve Tiss.
Ganglion iutercaroticum, vid. CIRC. APP.
Ganglion spirale of Corti, vid. SENS. APP.
Ganglionic cell layer of retina, vid. SENS. APP.
Ganglionic plexuses

of submucosa of intestine, and of mus-
cular tissue, vid. Nerv. Tiss. and
DIGEST. APP.

Gegenbaur's osteoblasts, vid. Oss. Tiss.
Gelatinous and Reticular connective sub-
stance, 187
forms of, 187

mucoid of enamel organ, 191
of vitreous humour of eye, 189

composition of, 190
of gelatin of Wharton, 191
neuroglia, 197
reticular, 187, 193
forms of, 194
where found, 193
sustentacular of Nervous System an«l

Retina, 187, 190

GENERATIVE APPARATUS (female)
Constituents of, 526
Corpus luteum, 545
degeneration of, 546
formation of mode of, 546
structure of, 546
true and false, 547
Decidua, 549
Fallopian tubes, 547
Formatio granulosa, 540
Hymen, 550
Mammary glands, 557
areola of, 552
development of, 552
excretory ducts of, 552
nerves, 551
nipple, 552
sacculi lactiferi, 552
structure of, 551
in male, 553
in child, 552
in mature body, 553
in virgin, 553
vascular supply of, 551
Milk, 553

INDEX.

673

GENERATIVE APPARATUS (female) —
Milk, colostrum corpuscles of, 554

composition of, 554

corpuscles of, 553

globules, 553

mode of generation of, 555

purposes of, 555
Ovary, 540

blood-vessels of, 540

cortical zone, 538

development of, 542, from Wolffian
bodies .

germinal epithelium, 537

Graafian, follicle of, 539
bursting of, 545

cumulus proligerus (ovigerus), 540
liquor folliculorum, 540
membrana granulosa, 540
membrana follicula, 539
theca folliculi, 539

hilus stroma of, 537

lymphatics of, 544

medullary substance of, 537

nerves of, 544

sustentacular matter of, 537
Ova chains, 513
Ovum (ovule), 540

chorion of, 540

destiny of, 545

discharge of, 545

germinal vesicle of, 540

germinal spot of, Wagner, 540

macula germinativa, 540

vitellus (yelk), 540

segmentation of, 545 ; and Cells
Parovarium, 541
Primordial follicles, 543
Primordial ova, 542
Pudenda, 550

blood-vessels of, 550

clitoris, 550

genital corpuscles of, 551

glands of Ijartholin, 550
of Duverney, 551

nerves of, 551

nymphse, 550

vestibulum, 550
Purkinje's vesicle, 540
Uterus, 547

aileries of, 548

during menstruation, 549
pregnancy, 549

glands of, 548

lymphatics of, 548

nerves of, 549
Vagina, 550

nerves of, 550

vascular supply of, 550
Wolffian bodies, development of ovary

from, 542

Zona pellucida, 540
Zone of primordial follicles, 540
GENERATIVE APPARATUS (male), 555
Constituents of, 555
Colliculus seminalis, vid. Urethra, 566
Corps innomine', vid. Testis, 555
Cowper's glands, 566
Ductus ejaculatorius, 565
Erection, theory of, 570
Epididymis, 555

caput of, 556

cauda of, 557

GENERATIVE APPARATUS (male) —
Epididymis, corpus, 557

vasa aberantia, 557 >
Hydatids of Morgagni, 559
LMre's glands, vid. Penis
Organ ot Giraldes, 559
Parepididymis, 559
Penis, 566

corpora cavernosa, 567
arteriae helicinoe of, 569
lymphatics of, 569
nerves of, 569
vessels of; 568
erection of, 570
glands of Tyson, 567

of Littre, 567
skin of, 567
structure of, 566
Prostate, 565

calculi of, 566
Semen, 560

composition of, 561
Smegma preputii, 567
Spermatozoa, 560
composition of, 560
development of, 561
movements of, 563
penetration of into ovum, 564
structure of, 560
under actions of reagents, 563
Testis, 555
coverings of, 555
coni vasculosi of, 556
corpus Highmoriani, 556
development of, 559
lymphatics of, 558
nerves of, 559
rete testis, 556
structure of, 557
sustentacular tissue of, 557
tubulus rectus, 556
vasa efierentia, 556
vessels of, 558

Tyson's glands, vid. penis, 567
Uterus masctilinus, 566
Urethra, 556

colliculus, seminalis of, 556
Vasa deferentia, 564
Vesiculae seminales, 565
Germinal layers of embryo, 129, 137
Germinal vesicle of Purkinje, vid. GEN.

APP. (fern.), Ovum
Germinal spot of Wagner of ovum, vid. GEN.

APP. (fern.)
Giant cells (of medulla of bone), vid. Cells

and BONY APP.
Giraldes, organ of, vid. testis, GEN. API*.

(male)

Glandulae agminate, 429
Glandular Tissues, 353
Composition of, 359
Glands, 353
acini of, 348
blood-vessels of, 353
capsules shut, 348
cells of, 345

part taken by, in secretion, 351
transitoriness of, 351
varieties of, 349
compound, 349
dehiscence of, 349
excretory passages of, 354

674

INDEX.

Glandular Tissues—

Glands, general comparison of, 359

lobules of, 348

lymphatics of, 354

memhrana propria of, 345
anatomically, 348
physiologically, 348
structure of, 348

muscular elements, 354

nerves, 354

simple, 349

tubular, 349

vesicles, 348
shut, 348

Gland capsules, vid. Gland. Tiss.
Gland cells, vid. Gland. Tiss.
Gland nerves, vid. Nerv. Tiss. end capsules

of, 327

Gland tubules, vid. Gland. Tiss.
Gland vesicles, vid. Gland. Tiss.
Globulin, 17
Glomerulus, vid. Vessels
Glutin, 22 ; glutin-yielding substances, 21
Glycerin, 23

Glycerophosphoric acid, 24
Glycin, 48
Glycocholic acid, 39
Glycogen, 31

Goitre of thyroid gland, vid. Cmc. APP.
Goll, band of, in spinal cord, vid. NERV.

APP.

Graafian follicle, vid. Ovary, GEN. APP.
Granular layer of retina, vid. SENS. APP.
Granules of cerebellum, vid. NERV. APP.
Granules of retina, vid. NERV. APP.
Grape sugar, 32

Ground lamellae, vid. General Lamellae
Ground substance, vid. Cells
Growth of cells, vid. Cells
Guanin, 43

Gustatory buds, vid. SENS. APP.
Gustatory cells, vid. SENS. APP.
Gustatory organ, (tongue), vid. SENS. APP.
Gustatory papillae of tongue, vid. DIGEST.

APP.

Habenula interna (sulcata) externa (denti-
culata) perforata and tecta of the coch-
lea, vid. SENS. APP.
Haematin, 50
Haematoglobulin, 18
Haematocrystallin, 18
Haematoidin, 51
Haerain, 50
Haemoglobulin, 18
Hair, 388

arrectores pilorum, 389
bulb, 388

structure of, 391
composition of, 349
development of, in embryo, 396
follicle, 388
layers of, 389
muscles of, 389
growth of, 396
Henle's layer, 391
Huxley's layer, 391
papilla of, 390

physiological purposes of, 395
regeneration of, 397
roots of, 338 »

root-sheath, 388

Hair--
root-sheath, external, 390

internal, 390
shaft, 388

cortical portion of, 391
cuticle of, 392
hair scales of, 392
medulla of, 393
structure of, 391
Hair bulb, vid. Hair
Hair follicles, vid. Hair
Hair scales, vid. Hair
Haversian canals, vid. Oss. Tiss.
Haversian glands (so called) of bones, vid.

BONY APP.

Haversian lamellae, vid. Oss. Tiss.
Haversian spaces, vid. Oss. Tiss.
Heart, vid. CIRC. APP.

ganglia of, vid. CIRC. APP.
muscle of, vid. CIRC. APP. •
nerves of, vid. CIRC. APP.
valves of, vid. CIRC. APP.
vessels, vid. CIRC. APP.
Hemispheres of cerebrum, vid. NERV. APP.
Hemispheres of cerebellum, vid. NERV. APP.
Henle's investigation on structure of kidney,

vid. URIN. APP.

ffenle's layer of inner root- sheath, vid. Hair
Hepatic vein, blood of, vid. Blood.
Hilus stromaof ovary, vid. GEN. APP. (fern.)
Hilus stromaof lymphatic glands, vid. CIRC.

APP.
Hippuric acid, 33

in urine, vid. URIN. APP.
Histochemistry, 4
Histogenesis, 4
Histology, 1

comparative, 4
general, 1
pathological, 4
topographical, 7

Humor aqueus of eye, vid. SENS. APP.
Humor vitreus of corpus vitreus, vid. Gelat.

Tiss.
Huxley's layer of internal root- sheath, vid.

Hair

Hydrochlorate of haematin, 50
Hydrochloric acid, 57
Hymen, vid. GEN. APP. (fern.)
Hypophysis cerebri, vid. CIRC, and NERV.

APP.
Hypoxanthim (sarkin), 43

Indican, 52

Indigo, 52

Infundibula of lung, vid. KESP. APP.

Inosinic acid, 36

Inosite, 33

Intercellular substance, vid. Cells

Interchange of material of cells, vid. Cells

Interglobular spaces, vid. Dental Tiss.

Intergranular layer of retina, vid. SENS.

APP.
Intestinal glandular geiminal layer, 129,

137, 349

Intestinal juice, vid. DIGEST. APP.
Intestinal villi, vid. DIGEST. APP.
Investing spaces of lymph follicles, vid.

CIRC. APP.

Investing sphere, vid. Cells
Iris, vid. SENS. APP.

nerves of, vid. SENS. APP.

INDEX.

675

Iron, 62

in different organs and tissues, vid. same

in haemoglobulin, 18

in haematin, 50

in melanin, 52

phosphate of, 62

protochloride of, 62

salts of, 62
Ivory, vid. Dental Tiss.

Joints, vid. BONY APP.

Keratin, 21

Kerkring's folds of intestines, vid. DIGEST.

APP.

Kidney, vid. URIN. APP.
Kreatin, 44
Kreatiuin, 45

Lachrymal glands, vid. SENS. APP.

Lachrymal passages, vid. SENS. APP.

Labial glands, vid. DIGEST. APP.

Lacteals, vid. Vessels

Lactic acid, 34

Lamellae of bone, vid. Oss. Tiss.

Lamina elastica anterior of cornea, vid.

Con. Tiss.
Lamina fusca ( supra- chorioidea) of eye, vid.

SENS. APP.

Lamina spiralis of cochlea, vid. SENS. APP.
Lamina spiralis accessoria of cochlea, vid.

SENS. APP.

Larynx, vid. RKSP. APP.
Lateral accessory cornu of med. obi., vid.

NERV. APP.
Lenticular glandules of stomach, vid.DiGE&r.

APP.

Lens, tissue of,
capsule, 276
composition, 278
development, 279
fibres or tubes, 276

arrangement of, 277
membrana capsulo pupillaris, 280
relation of, to corneous germinal layer,

279

stars, 277

Lens capsule, vid. Lens Tiss.
Lens tubes, vid. Lens Tiss.
Lens stars, vid. Lens Tiss.
Lecithin, 28

Leeuwenhoek, A. van, 2.
Leucaemia, vid. Blood
Leucin, 45
Lieberkuhn's follicles of small intestine, vid.

DIGEST. APP.
Ligamenta ciliare (ciliary muscle), vid. SENS.

APP.
Ligamenta flava of spinal column, vid. Con.

Tiss.
Ligamenta intervertebralia (symphyses of

vertebral bodies), vid. Cartil. Tiss;
Ligaments, vid. Con. Tiss.
Ligamentum nuchae, vid. Con. Tiss.
Ligamentum pectinatum mdin,vid. SENS. APP
Ligamentum spirale of cochlea, vid. SENS.

APP.

Lime compounds, 57
Limiting layers on connective-tissue bundles,

vid. Con. Tiss.

Lingual follicles, vid. DIGEST. APP.
Lipoma, vid. Fatty Tiss.

Liquor folliculi of ovary, vid. GEN. APP.
Liver, vid. DIGEST. APP.

cirrhosis of, vid. DIGEST. APP.
cells of, vid. DIGEST. APP.
lobules of, vid. DIGEST. APP.
sustentacular substance of, vid. DIGEST.

APP.

Loosening of cells, vid. Cells
Lungs, vid. RESP. APP.

alveoli of, vid. RESP. APP.
infundibula of, vid. RESP. APP.
vesicles of, vid. RESP. APP.
Lunula of nail, vid. Nail Tiss.
Lymphatic circulation, vid. VESSELS
Lymphatic glands (nodes), vid. CIRC. APP.

of various organs, vid. same
Lymphatic canals, vid. Vessels
Lymphatics of several organs, vid. same
Lymphatic passages of lymphatic glands,

vid. CIRC. APP.

Lymphatic vessels, vid. Vessels
Lymphatic radicles, vid. Vessels
Lymphatic vessels in intestinal villi, vid.

VESSELS and DIGEST. APP.
Lymphatic vessels in tadpole's tail, vid.

VESSELS
Lymph (and Chyle), 131

amount of, in system, 134
blood-corpuscles in, 133
cells of, 132

first appearance of in embryo, 137
source of, 133

composition of lymph and chyle, 134--1EG
elementary granules of, 13'J
molecules of, 133
physiological significance of, 131
Lymph corpuscles, vid. Lymph
Lymph corpuscles of blood, vid. Blood
Lymph corpuscles as elements of reticular
connective substance, vid. Gelat. Con.
Sub.

Lymph nodes (glands), vid. CIRC. APP.
Lymphoid cells, vid. Lymph
Lymphoid follicles of conjunctiva (trachoma

glands), 420 and SENS. APP.
Lymphoid organs, vid. CIRC. APP.
Lymph sheaths of vessels, vid. VESSELS
Lymph tubes of lymphatic glands, vid. CIR.
APP.

Macula genninativa of ovum, vid. GEN

APP. (female)

Macula lutea of eye, vid. SENS. APP.
Malpighi, M., 2
Malpighian glomerulus of kidney, vid

URIN. APP. and VESSELS
Malpighian corpuscles or follicles of spleen,

vid. CIRC. APP.
Malpighian pyramids of kidney, vid.

URIN. APP.

Malpighian cells of lungs, vid. RESP. APP.
Mammary glands, vid. GEN. APP. (fern.)
Manganese, 92

M anz's glands of conjunctiva, vid. SENS. APP.
Margaric acid, 26
Margarin, 36

Medulla of nerve fibres, vid. NERVE Tiss.
Medulla oblongata, vid. NERV. Tiss.
Medulla spinalis, vid. NERV. APP.
Medulla of bone, vid. BONY APP.

foetal, vid. Osseous Tiss.
Medullary canals of bone, vid. Oss. Tiss.

676

INDEX.

Medullary pyramids of kidney, vid. URIN.

APP.

Medullary radii of kidneys, vid. URIN. APP.
Medullary sheaths of nerves, vid. Nerv. Tiss.
Medullary spaces of bone, vid. Oss. Tiss.
Medullary substance of lymphatic glands,

vid. CIRC. App.

Meibomian glands of eyelids, vid. SENS. APP.
Melanin, 52

in the lungs, vid. RESP. APP.
Memtrana capsulopupillaris, we?. SENS. APP.
Membrana Descemetica of cornea, vid. Con.-

Tiss.
Membrana fenestrata of retina, vid. SENS.

APP.
Membrana follicularis of ovary, vid. GEN.

APP.

Membrana granulosa of ovary, vid. GEN. APP.
Membrana hyaloidea of eye, vid. SENS. APP.
Membrana limitans, ext. and int., of retina,

vid. SENS. APP.
Membrana propria of glandular structures,

vid. Cells and Gland. Tiss.
Membrana tympani, vid. Sens. App.
Membrana tympani secundaria, md. SENS.

APP.

Menstrual blood, vid. Blood
Metabolic force of cells, 82
Microscope, invention of, 2
Middle germinal layer, 129
Milk, vid. GEN. APP. (female)
Milk globules, vid. GEN. APP.

formation of, vid. Gland. Tiss.
Milk receptacles, vid. GEN. APP. (female)
Mineral constituents of body, 55

of several organs and fluids, vid. same
Molecular layer of retina, vid. SENS. APP.
Molecules foreign in muscle fibres, vid. Mus.

Tis.

Monoglycerides, 24
Morgan and Tomes, vid. Tomes
Morgagni's hydatids, vid. GEN. APP.
Mother cells, vid. Parent Cell
Motus vibratorius, vid. Epithelium
Mouth, vid. DIGEST. APP.
Mouths, open, of lymphatics, 378
Mucin, 21

Mucous glands of stomach, vid. DIGEST. APP.
Mucous membranes, vid. Con. -Tiss.
Mucous sheaths of muscles, vid. Mus. Tiss.
Mucous sheaths of tendons, vid. Con. -Tiss.
Mucus, 154

corpuscles, presence of, in interior of

epithelial cells, 91, 153
MiMer's, If., radiating sustentacular fibres

of retina, vid. SENS. APP.
Muscle bundles, vid. Mus. Tiss.
Muscle fibres, vid. Mus. Tiss. and Cells as

parents of tissues
Muscle fibrillae, vid. Mus. Tiss.
Muscle fibrin, vid. Mus. Tiss.
Muscle Tissue, 280
composition of, 293

constituents, 298
contractile fibre-cells, 281

striped, 283

structure of, 282
in mature animal, 282
in embryo, 282
where found, 283
contraction of, 299
decay of, 303

Muscle Tissue-
development of, 301
growth of, 303

mode of union of, with tendons, 291
muscle sugar, 33, 298
myosin, 296
neoplasis of, 305
pathological changes in, 304, 305
perimysium, 293
physiology of, 299
plasma of, 296
ramifying fibres of, 292

arrangement of, in bundles, 292
rigor mortis of, 300
sarkolemma, 302
smooth, 281
striped, 283

accessory disks, 289

cementing matter, 287

Cohnheim's mosaic, 290

disks of Bowman, 286

fibres of, 283

fibrillse of, 285

fleshy substance of, 285

foreign deposits in, 291

middle disk of Hensen, 289

muscle, caskets of, 289

muscle, corpuscles of, 284

primitive bundles, 283

primitive sheath, 283

sarkolemma, 283
formation of, 302

seen with polarised light, 290

transverse plate of transparent zone of
Krause

transverse marking on, 285

zones transparent and dark, 288
syntonin, 16, 297
unstriped, 281
vessels of, 291

voluntary and involuntary, 281
Muscle caskets, vid. Mus. Tiss.
Muscle corpuscles, vid. Mus. Tiss.
j Muscles, lymphatics of, vid. Mus. APP.
nerves of, vid. Nerv. Tiss.
plasma of, vid. Mus. Tiss.
Muscle sugar (inosite), 33, and Mus. Tiss.
MUSCULAR APPARATUS, 573
Blood vessels, 574

of tendons, 573
Lymphatics of, 574
Mucous bursas, 573
Mucous sheaths, 573
Sesamoid bones, 573
Sesamoid cartilages, 573
Muscular elements, md. Cells, parents of

other structures, and Mus. Tiss.
Myelin, 29

Myeloplaxes, vid. BONY APP.
Myosin, 16, and Mus. Tiss.

Nail, 160.

cells, 162

composition of, 163

embryonic development of, 164

lunula of, 162

matrix of, 161

root, 161
Nerve fibres, vid. Cells, parents of other

structures, and Nerv. Tiss.
Nerve loops, vid. Nerve Tiss.
Nerve sheath (perineurium), vid. Nerve Tiss.

INDEX.

677

Nerve Tissue, 305

axis, cylinders of, 307

fibrillar structure of, 310
cellular elements of (corpuscles), 311
apolar, -unipolar, bipolar, &c., 316
body (structure of), 311, 319
envelopes of, 311, 312
processes (axis, cylinder, protoplasm)

315

purposes of, 312
spiral, 315
composition, 338

constituents of, 338, 339
development of, in embryo, 341
elements, cellular and fibrous (general
arrangement of, in nervous centres),
317

fibres, vid. Nerve Fibres
ganglia, structure of, 333
course of nerves through, 334
most minute, 335
perineurium of, 333
spinal, 334
sympathetic, 334
ganglion cells or corpuscles, 305
ganglionic plexuses, 336
myentericus (plexus) ofAuerbach, 336
submucous, 336
medulla (nervous), 306

coagulation of, 306
nerve fibres (varieties of), 305
anastomoses of, 318
coarse, 305

double contour of medullated, 306
fine dark-edged, 305
medullated, 305
neurilemma of, 307
non-medullated, 308
perineurium, 318
primitive fibrillse, 310
primitive sheath, 306
Remotes, 308

structure of, 307
sympathetic, 319
termination of (motor), 320
in glands, 326
in loops (supposed) 319
in neural eminences, 322
in non-medullated fibres, 320
in salivary glands, 326
in special terminal structures, 320
in striped muscle, 322
in terminal plates, 322
in unstriped muscle, 324
transverse sections of, 308
nerve tubes, vid. Nerve Fibres
physiology of, 339
plexuses, 318

repair of nerves after section, 343, 344
sensory nerves, 326
terminal structures, 326
bulb of Krause, 327
end capsules of gland nerves, 327
genital corpuscles, 327
Pacinian bodies, 329
tactile corpuscles of skin, 328
termination of simply sensitive
nerves, 331

in corneal epithelim, 332
in dental pulp, 333
varicosities, 308
Nerve tubes, vid. Nerve Tiss.

Nerves of several organs and tissues, vid.

\inder same

NERVOUS APPARATUS, 574
Cerebellum, 590
cortical layer of, 591
grey layer of, 592

ganglion cells of, 592
nerve fibres of, 590
nucleus dentalus of, 591
rust brown layer of, 591

granules of, 591
Cerebrum, 594
arachnoid of, 599
blood-vessels of, 601
cerebal ganglia, 594
cerebro-spinal fluid, 599
cornu ammonis, 597
corpora quadrigemina, 594
corona radiata, 595
corpus striatum, 594
crura cerebri ad pontem, 94
development of central organs, 602
dura mater, 598
hemispheres, 595

cortex of (structure of, &c.), 595
membranes of, 598
olfactory bulb, 597
optic nerves (origin of), 594
Pacchionian granulations, 600
peduncli cerebri, 594

"base "of, 594

"cap "of, 594
pia mater, 599
pineal gland, 598

pituitary body, 598, and CIRC. APP.
plexus chorioidea, 600
sabulous matter in, 601
subarachnoid spaces, 599
substantia nigra, 594
thalami optici, 594
Medulla Oblongata, 583
blood-vessels of, 590
columns of spinal cord in, 586
cranial nerves arising from, 586
crura cerebelli ad med. oblong., 589

ad corp. quad. , 590

ad pontem, 589
formatio reticularis of, 585
lateral accessory cornu of, 585
lateral nervous tract of, 586
nuclei of (specific, &c.), 584
olivary bodies of, 589
pyramids of, 589
several constituents of, 583
systems of fibres of, 585

structure of, 585
tractus intermedio lateralis, 585
Pons Variolii, 590
Spinal Cord, 577
anterior cornua, 578

multipolar ganglion cells of, 578

processes of ganglion cells, 578
anterior nerve roots of, 578
axial canal, 574 »

bands of Goll of, 578
blood-vessels of, 576
columns of, 574
commissures of, 574
ependyraal thread of, 575
ganglion cells, 582
GolUs bands, 578
grey matter and cornua, 574

678

INDEX.

NERVOUS APPARATUS —

Spinal Cord, nervous elements of, 577
arrangement of. in white substance,

577
differences in thickness of, in

several columns, 577
horizontal, 577
longitudinal, 577
oblique, 577
neuroglia, 575

perivascular canals, 577, 365
posterior cornua, 581
posterior roots, 581

relation to cornua, 581
substantia gelatinosa of Rolando, 574
sustentacular substance of, 575
of grey and -white matter, 576
transverse commissure of, 582
Nervous nuclei of med. oblong., vid. NERV.

APP.

Nervous plexuses, vid. Nerve Tiss.
Nervous tracts (lateral) of med. oblong., vid.

NERV. APP.
Nervous tracts of spinal cord, vid. NERV.

APP.

Neural eminence, vid. Nerve Tiss.
Neurilemma (primitive sheath), vid. Nerve

Tiss.

Neurin (cholin), 48, and Nerve Tiss.
Neuroglia, vid. Gel. Tiss. and NERV. APP.
Neutral fats, vid. Fats
Nitrogen, 56

Non-vascular organs, 371
Nose, cavities and accessory cavities of, vid.

SENS. APP.
Nucleus, vid. Cells
Nucleus fibres, vid. Con. Tiss.
Nucleus fibrous of lymphatic glands, vid.

CIRC. APP.
Nucleolus, vid. Cells
Nymphae, vid. GEN. APP. (female)

Odontoblasts (dentine cells), vid. Dent. Tiss.

(Esophagus, vid. DIGEST. APP.

Oleic acid, vid. Elaidic acid

Olfactory nerves (ramification and termina-
tion of, in regio olfactoria), vid. SENS.
APP.

Olfactory cells of regio olfactoria, vid. SENS.
APP.

Olfactory filaments, vid. SENS. APP.

Olfactory bulbs, vid. NERV. APP. and SENS.
APP.

Olfactory organs, vid. SENS. APP.

Olfactory roots, vid. NERV. APP.

Olivary bodies, vid. NERV. APP.

Oilier 's views on functions of periosteum in
formation of bone, 257

Openings (free) of lymphatics, vid. 378

Optic nerve, vid. SENS. APP.

expansion of same to form retina, vid.

SENS. APP.
origin of, vid. NERV. APP.

Ora serrata of retina, vid. SENS. APP.

Orbital muscles, vid. SENS. APP.

Organs of the body, 403

Organ of Giraldes, vid. Corps innomine

Organs of Hearing, vid. SENS. APP.

Organ of Sight, vid. SENS. APP.

Organ of Smell, vid. SENS. APP.

Organ of Taste, vid. SENS. APP.

Organ of Touch, vid. SENS. APP.

Osseous Tissue, 238

bone cartilage, 239

bone cells, 246

bone earths, 247

canaliculi, 243

cartilage before ossification, 251

cartilage medulla, 251

classification of bones, 239

composition of, 247

development of, 250

dotted appearance of, 243

formation of, from periosteum, 256

glutin-yielding substratum, 247

growth of, 256

Haversian canals of, 240

Haversian spaces of, 242

lacunae, 244

lamellae, 241
formation of, 254
fundamental, 241
general, 241

special (Haversian), 241
subsequent absorption of, in newly-
formed bone, 256

medulla (foetal), 253

medullary canals, 240

medullary spaces (formation of), 252.
253

neoplasis (pathological) of, 260

ossein, 240

ossification, 250
direct, of cartilage, 256
direct, of connective-tissue, 259
points of, 251

osteoblasts, 254

ostoklasts, 258

physiological purposes of, 249

preformation of, in cartilage, 250

regeneration of, for repair, 259

regeneration from periosteum, 260

secondary bones, 256

Sharpens fibres, 244
Ossein (bone cartilage), vid. Oss. Tiss.
Ossification process, vid. Oss. Tiss.
Osteoblasts, vid. Oss. Tiss.
Osteogenesis, vid. Oss. Tiss.
Ostoklasts, vid. Oss. Tiss.
Otoliths, vid. SENS. APP.
Ova chains, vid. GEN. APP. (female)
Ova primordial, vid. GEN. APP. (female)
Ovarial follicles, vid. GEN. APP. (female)
Ovary, vid. GEN. APP. (female)
Ovigerms, vid. GEN. APP. (female)
Ovum (ovulum), vid. Cells and GEN. APP.
Oxalic acid, 35
Oxygen, 56
Oxyhaemoglobin, 20

Pacchionian granulations, vid. NERV. APP.
Pacinian corpuscles, vid. Nerv. Tiss.
Palatal glands, vid. DIGEST. APP.
Palmitic acid, 25
Palpebrae, vid. SENS. APP.
Pancreas, vid. DIGEST. APP.
Pancreatic juice, vid. DIGEST. APP.
Panniculus acliposus, vid. Fatty Tiss.
Papilla spiralis (of organ of Corti), vid.

SENS. APP.
Papillae circumvallatae of tongue, vid.

DIGEST. APP.
Papillae filiformis (conicae) of tongue, vid.

DIGEST. APP.

INDEX.

679

Papillse fungiformis (clavatse) of tongue,

vid. DIGEST. APP.
Papillae renales, vid. URIN. APP.
Papillae of skin, vid. SENS. APP.
Papillie of tongue, vid. SENS. APP.
Paralactic acid, 34

Paraovarium, vid. GEN. APP. (female)
Parent cells, vid. Cells
Parepididymis, vid. GEN. APP. (male)
Parietal stream of blood-vessels, vid. VES-
SELS

Parotid gland, vid. DIGEST. APP.
Parotid saliva, vid. DIGEST. APP.
Pavement epithelium, vid. Epithelium
Pedunculi cerebri, vid. NERV. APP.
Penicillii of splenic artery, vid. CIRC. APP.
Penis, vid. GEN. APP. (male)
Pepsin, 18, and DIGEST. APP.
Peptic gland cells, vid. DIGEST. APP.
Peptones, 17, and DIGEST. APP.
Perichondrium, vid. Cartilage and Con. Tiss.
Pericardium, vid. CIRC. APP.
Perilymph (aquula Cotunii), vid. SENS.

APP.

Perimysium, vid. Mus. Tiss.
Perineurium, vid. Con. and Nerve Tiss.
Periosteum, vid. Con. Tiss.

functions in ossification, vid. Oss. Tiss.
Perithelium (endothelium), vid. Epithelium

and VESSELS
Perivascular canal system in spinal cord and

brain, vid. NERV. SYSTEM
Perspiration, vid. SENS. APP.
Petit, canal of, vid. SENS. APP.
Peyer's glands, 420, and DIGEST. APP.
Pharynx, vid. DIGEST. APP.

tonsil of, vid. DIGEST. APP.
Phenol, 36

Physical properties of blood, vid. Blood
Pia mater, vid. Con. Tiss. and NERV. APP.
Pigmentary epithelium, vid. Epithelium
Pigmentary metamorphosis of cells, vid.

Cells
Pigment cells (polyhedral), vid. Epithelium

stellate, vid. Con. Tiss.
Pineal gland, vid. NERV. APP.
Placenta sanguinis, vid. Blood
Plasmatic vascular system, vid. Vessels
Pleura, vid. RESP. APP.
Plexus chorioidea of brain, vid. Con. Tiss.

and NERV. APP.
Plexus myentericus, vid. NERV. APP. and

DIGEST. APP.

Plexus (formation of), vid. Nerv. Tiss.
Plica semilunaris of eye, vid. SENS. APP.
Plicae vasculpsae, vid. BONY APP.
Pons Varolii, vid. NERV. APP.
Pore canals of Cecils, vid. Cells
Potash compounds, 61 and 62
Primitive fibrillae

of con. tiss. vid. Con. Tiss.
of muscles, vid. Mus. Tiss.
of nerves and axis cylinders, vid. Nerv.

Tiss.
Primitive sheath (sarcolemma) of muscle,

vid. Mus. Tiss.

Processus ciliares of eye, vid. SENS. APP.
Processus vermiformis, vid. DIGEST. APP.
Prostate gland, vid. GEN. APP. (male)
Prostatic vesicle (uterus masculinus) vid.

GEN. APP. (male)

Prostatic calculi, vid. GEN. APP. (male)
44

Protagon, 29

Protein bodies, vid. Albuminous Compounds
immediate derivatives of, 15
remote derivatives of, 21
Protoplasm, 66
Protoplasm processes of ganglion cells, vid.

Nerve Tiss. and NERV. APP.
Psorospermi.i in interior of columnar epithe-
lium, 91

Pudenda, vid. GEN. APP. (female)
Pulpa dentis (dental germ), vid. Dent. Tiss.
Pulp tubes of spleen, vid. CIRC. APP.
Purkinje's, germinal vesicle of, vid. GEN.

APP. (female)

fibres of heart, vid. CIRC. APP.
Pus corpuscles in interior of epithelial celJs,

91, 153
emigrated lymphoid cells, 129, 91,

153

in connective tissue, 234
Pyramids, vid. NERV. APP.
Pyramid processes of kidney, vid. URIN.

APP.
Pyramids, decussation of, vid. NERV. APP.

Recklinghausen, von, on formation of red

blood cells, 114

Kegeneration of several tissues, vid. same.
Regio olfactoria, vid. SENS. APP.
Reisner's membrane of cochlea, vid. SENS.

APP.

Remak's views on cell theory, vid. Cells
Remak's fibres, vid. Nerve Tis.
BESPIRATORY APPARATUS, 443.
Bronchi (structure of), 450
Composition of pulmonary tissue, 457
Larynx, 448

cartilages of (structure of), 176
lymphatics of, 449
nerves of, 449
structure of, 448
vessels of, 449
Lungs, 450
air-cells of, 451
alveoli (structure of), 451
arrangement of vessels in, 453
development of, 458
epithelium of, 455
infundibula of, 451
lobes of, 450
lymphatics of, 455
pigmentary deposit in, 452
vesicles, 451
Neoplasms in, 458
Nerves oi» 456
Pathological changes in, 458
Pleura, 456

absorption from cavity of, 457
Trachea, 449
several parts (nerves, lymphatics,

vessels), 449

Rete Malpighi, vid. Epithelium
Rete testis, vid. GEN. APP. (male)
Retina, via. SENS. APP.
Rhodanide of potassium, 55
Ridged and spinous cells, vid. Cells
Rods of retina, vid. SENS. APP.
Rolando (substantia gelatinosa of), vid.

NERV. APP.

Rod granules of retina, vid. SENS. APP.
Roots of hair, vid. Hair
Root sheaths (int. and ext. ), vid. Hair

680

INDEX.

Sacculi lactiferi, vid. GEN. APP. (fern.)
Sacculus ellipticus, vid. SENS. APP.
Sacculus rotund us, vid. SENS. APP.
Saliva, vid. DIGEST. APP.
Salivary glands, vid. DIGEST. APP.
Sarcous elements, vid. Mus. Tis.
Sarkolemma, vid. Mus. Tis.
Sarkin, vid. Hypoxanthin
Scala media tympani and vestibuli of coch-
lea, vid. SENS. APP.
Sclerotic of eye, vid. SENS. APP.
Schlemm, canal of, vid. SENS. APP.
Schneiderian membrane, vid. SENS. APP.
Schwann, Th., 3
Schwann's sheath of nerve fibre, vid. Nerve

Tis.
Sebum cutaneum, vid. SENS. APP.

formation of, 351 and 2
Sebum palpebrale, vid. SENS. APP.
Segmentation of cells, vid. Cells
Semen (sperma), vid. GEN. APP. (male)
Semicircular canal, vid. SENS. APP.
Seminal filaments, vid. GEN. APP.
Seminal tubules, vid. GEN. APP. (male)
Seminal vesicles, vid. Versiculae Seminales
Semicanalis (sulcus) spiralis of cochlea, vid.
SENS. APP. .

SENSORY APPARATUS, 603
Organs of Hearing, 653
development, 664
external ear, 653
Eustachian tube, 654
ossicula auditus, and muscles of, 654
pinna, 653
tympanum, 653
internal ear, 654
cochlea, 657

canalis cochlearis of Reissner t 657
epithelium of, 663
termination of nerves in, 663
canalis reunions, 658
Corti, cells of, 660
Corti, fibres (pillars) of, 660

heads of, 661
Corti, organ of, 659
external and internal pillars of,

660

hair or tufted cells of, 662
habenula externa and interna, 659
habenula perforata and tecta, 660
lamina spiralis, 657
lamina spiralis accessoria, 663
ligamentum spirale, 663
membrane of Reissner, 657
scala tymph. and vestib. , 657
sulcus spiralis, 659
teeth of first order, 660
zona denticulata, 659
zona pectinata, 662
endolymph (aquula vitrea auditiva),

655
nerves, acoustic, distribution of,

655

in fishes and mammals, 656
otoliths, 653 and 58
perilymph (aquula, Colunii) 654
Sacculus ellipticus and rotund us, 654
semicircular canals, 654.
septem nerveum, 655
auditory filaments, 656
crista acustica, 655
fibre cells of Schultze, 606

SENSORY APPARATUS —
Organs of Hearing —

internal ear, vestibule, 654
Organs of Sight, 617
aqueous humour, 629
bulbus occuli (various parts of), 617

vascular system of, 618
canal of Petit, 630
ciliary arteries, vid. Iris (below),
cornea, 618 and 220
conjunctiva of, 618
lymphatics of, 619
nerves of, 619
vessels of, 619
conjunctiva of eye, 649
glands of —

Bruch's plaques, 650
convoluted, 649
lymphoid, 650
lymphatics of, 650
nerves of, terminating in epithe-
lium, 650
palpebral, 649
plica, semilunaris of, 649
vessels of, 650
development of eye, 651
iris, or diaphragm of eye, 622
ciliary arteries, 624
dilatator pupillse, 623
ligamentum pectinatum iridis, 623
nerves of, 623 and 624
sphincter pupillse, 622
vascular system of iris and choroid,

624
circulus arteriosus iridis major,

626

cir. art. irid. minor, 626
cir. art. muscul. cil. , 626
vessels of choriocapillaris, 625
lachrymal glands, nerves or lympha-
tics of, 651
lens, 629

lymphatics of eye, 647
Meibomian glands, 648
muscles of eye, 648
palpebrae, 648
retina, 631

composition of, 647
blood-vessels of, 645
fovea central is, 632
layers of, vid. strata
macula lutea, 632
structure of, 643
medullated retinal fibres, 644
membrana fenestrata of Krause,

646

membrana limitans exter., 633
membrana limitans interna, 632
ora serrata, 632 and 644
properties of several constituents,

646

radiating fibres of Milller, 632
stratum bacillosum, 634
bacillary ellipsoids, 635
constituents of, in different ani-
mals, 634
cones, 636

of macula lutea, 637
supposed functions of, 646
cone granules, 636, 638
cone styles, 6.36
cone twins, 637

INDEX.

681

SENSORY APPARATUS —
Organs of Sight —
retina, 634
fibres of Ritier, 636
rods, 634.

supposed functions of, 646
rod granules, 635
stratum bacillosum, 634
stratum cellulosuni of, 641
stratum fibrillosum of, 642
stratum granulosum ext. of, 638
stratum granulosum int. of, 640
stratum intergranulosum of, 638
stratum moleculare of, 640
sclerotic, 618 and 625
canal of Sehlemm of, 618
vessels and nerves of, 618 and 628
sebum palpebrale, 648
tears, 651

uvea (tunica vasculosa), 621
choroid (structure of), 621

transparent limiting layer of, 621
lamina fusca, 621
memb. choriocapillaris, 621
musculus ciliaris, 621
processus ciliaris, 621
suprachorioidea, 621
tensor chorioidea, lig. cil., 621
veins of, 627

venae vorticosae, 628
vitreous humour, 630

membrana hyaloidea of, 630

with its relations to zone of Zinn

and canal of Petit
zonula Zinnii, 630
Organs of Smell, 612

nose (cavities of, and accessories), 612
regio olfactoria, 613
epithelium of, 614
glands of Bowman of, 614
olfactory cells of, 615
olfactory filaments of, 615
olfactory nerve, 615

supposed termination of, 616
structure of, 613
Organs of Taste, 610
gustatory buds of, 610
gustatory cells of, 611
gustatory nerves (termination of),

610

in papillae of tongue, 610
papillae foliatae of, 610
papillae of frog's tongue, 612 '
bowl cells of, 612
cylinder cells of, 6] 2
forked cells of, 612
Organ of Touch (Skin), 603
blood-vessels of, 604
cutis (thickness of), 603

development of, 603
epidermis (thickness of) 603

development of, 605
glands of, 605
ceruminous, 607

cerumen of, 607
circumanal, 607
sebaceous, 609
development of, 610
sebum cutaneum of, 610
structure of, 609
sweat, 605
sweat (composition of), 606

SENSORY APPARATUS —
Organ of Touch —
glands, sudorific, where found, 608
lymphatics of, 604
papillaj of, 603
perspiration from, 607
Septum . ner veum. vid. SENS. APP.
Serum sanguinis, vid. Blood
Sesamoid bones, vid. Mus. APP.
Sesamoid cartilages, vid. Mus. APP.
Shafts of hair, vid. Hair
Sharpens fibres, vid. Oss. Tiss.
Sheaths of nerves, vid. Nerve Tiss.
Silicic acid, 57
Skin (as tactile organ), vid. SENS. APP.

secretions, vid. SENS. APP.
Small intestine, vid. DIGEST. APP.
Smegma preputii, vid. GEN. APP.
Sodium compounds, 40, 59.
carbonate of, 60
chloride of, 60
glycocholate of, 40
phosphate of, 61
sulphate of, 61
taurocholate of, 40
Solitary glands of intestine, vid. 407 and

DIGEST. APP.
Special lamellae (flaversian) of bone, vid.

Oss. Tiss.

Sphincter pupil lae, vid. SENS. APP.
Spinal ganglia, vid. Nerve Tiss.
Spinous (and ridged) cells, vid. Cells
Spiral fibres of ganglionic nerve cells, vid.

Nerve Tiss.

Spiral (so-called) elastic, vid. Con. Tiss.
Spleen (&c.), vid. CIRC. APP.
Splenic blood, vid. Blood
Spontaneous generation of cells, vid. Cells
Stearic acid, 25
Stelluise Verheyenii of ludney, vid. URIN.

APP.

Stomach, vid. DIGEST. APP.
Stomach, juices of, vid. DIGEST. APP.
Stomachal glands, vid. DIGEST. APP.
Stratum bacillosum of retina, vid. SENS.

APP.

cellulosuni of retina, vid. SENS. APP.
fibrillosum of retina, vid. SENS APP.
granulosum (internal and external) of

retina, vid. SENS. APP.
intergranulosum of retina, vid. SENS.

APP.

moleculare of retina, vid. SENS. APP.
Struma (goitre), vid. CIRC. APP.
Subarachnoidal spaces, vid. Con. Tiss.
Sublingual gland, vid. DIGEST. APP.
Sublingual saliva, vid. DIGEST. APP.
Submaxillary gland, vid. DIGEST. APP.
Submaxillary saliva, vid. DIGEST. APP.
Submucous ganglionic plexus of Remak and

Meissner, vid. DIGEST. APP.
Substantia gelatinosa of Rolando, of spinal

cord, vid. NERV. APP.
Substantia nigra of brain, vid. NERV. APP.
Succus entericus, vid. DIGEST. APP.
Succus gastricus, vid. DIGEST. APP.
Sudor (sweat), vid. SENS. APP.
Sugar of grape, 32
Sugar of milk, 33
Sulcus (semicanalis) spiralis of cochlea, vid.

SENS. APP.
Sulphocyanogen, 54

682

INDEX.

Suprachorioidea (lamina fusca) of eye, vid.

SENS. APP.

Suprarenal body, vid. Cine. APP.
Sustentacular substance (nervous), me?. Gelat.

Tiss. and NERV. APP.
SAveat, vid. SENS. APP.
Sweat glands, vid. SENS. APP.
Sympathetic cord, vid. Nerve Tiss,
Sympathetic fibres, vid. Nerve Tiss.
Sympathetic glands, vid. Nerve Tiss.
Symphyses, vid. BONY APP.
Symphyses of vertebras, vid. Cart. Tiss.
Synovia, 155

Synovial sheaths of tendons, vid. Con. Tiss.
Syntonin, vid. Muse. Tiss.
Systems of the body, 399

Tactile corpuscles, vid. SENS. APP.

Tannin, 48

Taurochloric acid, 40

Taurylic acid, 36

Tears, vid. SENS. APP.

Teeth, vid. Dent. Tiss.

Tendons (vessels of), vid. Con. Tiss.

Tensor chorioidea (ciliary muscle), vid.

SENS. APP.

Terminal plates, vid. Nerve Tiss.
Terminal structures of nerves, vid. Nerve

Tiss.

Testis (testiculus), vid. GEN. APP. (male)
Thalami optici, vid. NERV. APP.
Theca of ovarian follicle, vid. GEN. APP.
Thymus gland, vid. CIRC. APP.
Thyroid gland, vid. CIRC. APP.
Tissues, 1

simple, 102

cement of, vid. Cells

classification of, 102, 103

composite, 103

elements of, 1
Tomes and De Morgan's Haversian spaces,

vid. 242 and Oss. Tiss.
Tome's layer of dentine, vid. Dental Tiss.
Tongue, vid. DIGEST. APP.

follicular glands of, 420

glands of, vid. DIGEST. APP.

muscles, vid. Mus. Tiss.

papillae, vid. DIGEST. APP.
Tonsils, 420, and DIGEST. APP.
Touch corpuscles, vid. SENS. APP.
Trachea, vid. BESP. APP.
Trachoma glands, 420, and SENS. APP.
Tractus intermedio lateralis of med. oblong,

vid. NERV. APP.

Traetus olfactorious, vid. NERV. APP.
Tractus opticus, vid. NERV. APP.
Tr.Lbmtyrin, 25
'Trigiycerides, 24
Trimargarin, 26
Trioleia, 26
Tripalmitin, 25
Tristearin, 25

Tubae FaLlopii, vid. GEN. APP. (female)
Tuberculisation of cells, vid. Cells
Tubuli seminiferi, vid. GEN. APP.
Tubuli uriniferi, vid. URIN. APP.
Tympanum, vid. SENS. APP.
Tyrosin and crystals, 47
Tyson's glands, vid. GEN. APP. (male)

Umbilical artery, vid. VESSELS
Umbilical cord (tissue of), vid. Gelat. Tiss.

Ureter, vid. URIN. APP.
Urethra (female), vid. URIN. APP.
URINARY APPARATUS, 514
Bladder, 536
Kidney, 514

arteriolse rectse, 528
.Bellini, tubes of, via. tubuli uriniferi
boundary layer of Henle, 518
blood-vessels of, 526
arrangement of, in superficial layer

of cortex, 528
composition of, 530
convoluted tubes of, 520
structure of, 520

termination of, in glomerulus, 521
cortex corticis of, 521
cortical pyramids of, 520
cortical substance of, 515
development of, 529
glomeruli of, 527
capsule of, 521
vasa afferent-ice of, 527
vasa efferentise, 527
Henle's investigations, 515, 516
looped tubes of Henle, 516
lymphatics of, 529
Malpighian pyramids of, 515
medullary py rain ids of, 515
medullary radii of, 519
collecting tubes of, 522
relation to ascending and descend-
ing arms of looped tubes, 525
minute anatomy of, 522
nerves of, 529
open tubes of, 516
structure of, 517
papillae renales, 516
pyramidal processes, 519
stellulse Verheyenii of, 528
straight tubules of, 519
sustentacular substance of, 526
tubuli uriniferi of, 515

differences in med. and cort., 515
general sketch of course from glomer-
ulus outwards, 525
vasa recta, 528
Urinary passages, 536
bladder, 536
calyces, 536
pelvis, 536
ureter, 536
urethra (female), 536
Urine, 530

constituents of, 531
abnormal, 534
occasional, 534
proportion of, 531
fermentation of, 534
physiology of, 535
Uroerethrin, 52
Urohsematin, 52
Uterine glands, vid. GEN. APP.
Uterus, vid. GEN. APP.
Uterus masculinus (vesicula prostatica), vid.

GEN. APP. (male)
Uvea of eye, vid. SENS. APP.

Vagina, vid. GEN. APP.

Valves of vessels, vid. VESSELS

Valvulae conniventes, Kerkringii, of small

intestine, vid. DIGEST. APP.
Varicosities of nerves, vid. Nerve Tiss.

INDEX.

683

Varolii pons, vid. NERV. APP.

Vas aberrans Halleri, vid. GEN. APP. (male)

Vas afferens and efferens of lymphatic glands,

vid. CIRC. APP.

Vas deferens of testicle, vid. GEN. APP.
Vasa aberrantia of liver, vid. DIGEST. APP.
Vasa afferentia and efferentia of the glome-

rulus of kidney, vid. URIN. APP.
Vasa recta of kidneys, vid. URIN. APP.
Vasa serosa (plasmatic vessels), vid. VES-
SELS

Vasa vasorum, vid. VESSELS.
Vascula efferentia of testicle, vid. GEN. APP.
Vascular cells, vid. Cells, parents of other

structures, and VESSELS
Vascular convolutions, vid. VESSELS
Vascular membranes, vid. Con. Tiss.
Vascular nerves, vid. VESSELS, and 324
Vascular Tissue, vid. VESSELS
Veins, vid. VESSELS
Venae interlobulares of liver, ma. DIGEST.

APP.
Venae intralobulares (central vein) of liver,

vid. DIGEST. APP.

Venae vorticosae of eye, vid. SENS. APP.
Vernix caseosa of infant, 160
Vesicula prostatica (uterus masculimis) vid.

GEN. APP.

Vesiculae seminales, vid. GEN. APP.
VESSELS (Vascular Tissue), 362
Arteries, 362
nerves of, 370 and 324
structure of, 369
umbilical, 369
Blood-vessels, 362
Capillaries, 362
development of, 385
lymph sheaths of, 365
structure of, 363
Capillary canals or lacunae, 362
Capillary system, 370
convolutions, 373
glomerulus, 373
loops, 373
networks, 371
elongated, 372
looped, 373
round, 372

Circulation of blood, 382
axial and parietal stream, 383
rapidity of, 383
Development of early, late, 384

pathologic, 387
Ductus thoracicus, 279
Lymphatic system, 373
commencement of, in villi, 374

Vessels-
Lymphatic system —
in other organs, 374
in tadpole's tail, 374
larger vessels of, 378
Lymphatic canals, 373
communication of. with serous sacs,

377

development of, 377
pathology of, 388

relation of, to blood capillaries, 376
texture of finer tubes, 377
Perivascular canal system, 377
Physiological relations of larger vessels,

382

of capillaries, 382
Plasmatic vessels, 382
Primary vascular membrane, 364
Vasa serosa or plasmatic vessels, 382
Vasa vasorum, 370
Vascular cells (perithelium endothe-

lium), 363
Veins, 362

structure of, 366
valves of, 368

Vestibule of ear, vid. SENS. APP.
Vestibulum vaginae, vid. GEN. APP.
Villi iutestinales, vid. DIGEST. APP.
Vitellus (yelk) of ovum, vid. GEN. APP.

segmentation of, vid. Cells
Vitreous humour, vid. SENS. APP.

Wagner's germinal spot on ovum, vid. GEN.

APP.
Water, 56

proportion of, in tissues and organs, vid.

same

Wharton, gelatin of, vid. Gelat. Tiss.
Wolffian bodies (primordial kidneys), vid.
GEN. APP.

Xanthin, 42

Yelk (vitellus) of ovum, vid. GEN. APP. and

Cells

segmentation of, vid. Cells
Yellow spot of retina, vid. SENS. APP.

Zinn, ligament of, vid. SENS. APP.
Zona denticulata of cochlea, vid. SENS. APP.
Zona pectinata of cochlea, vid. SENS. APP.
Zona pellucida (chorion) of ovum, vid. GEN.

APP.

Zonula Zinnii of eye, vid. SENS. APP.
Zoochemistry, 6

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progressive mind of this country, and ought to be
widely circulated."— New York Evening Post.

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to popularize science in the pages of a monthly." —
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tive."— Philadelphia Age.

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promises which the publishers made in the pro-
spectus of publication."— Niagara Falls Gazette.

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ablest men of science throughout the world write
about their meditations, speculations, and discov-
eries."—Providence Journal.

" This is a highly-auspicious beginning of a use-
ful and much-needed enterprise in the way of pub-
lication, for which the public owe a special debt of
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terested in the laudable effort of diffusing that in-
formation which is best calculated to expand the
mind and improve the conditions and enhance the
worth of life."— Golden Age.

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fore it was capable of reasoning." — The American
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the hands of some compiler."— TheWriting Teacher
and Business Advertiser ', New York.

THE POPULAR SCIENCE MONTHLY is published in a large octavo, handsomely printed
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D. APPLETON $- CO., Publishers,

549 & 551 Broadway, New York.

DESCRIPTIVE CATALOGUE

OF

MEDICAL WOEKS

D. APPLETON & CO.,

PUBLISHERS AND IMPORTERS,

549 & 551 BROADWAY, NEW YORK.
1875.

INDEX OF SUBJECTS.

PAGE

Anatomy 15

Anaesthesia 25

Acne 81

Body and Mind IT

Cerebral Convolutions 7

Chemical Examination of the Urine In Dis-
ease 8

Chemical Analysis 18

" Technology 80

Chemistry of Common Life 16

Clinical Electro-Therapeutics 10

" Lectures 81

Comparative Anatomy 6

Club-foot 24

Diseases of the Nervous System 11

u « « Nerves and Spinal Cord .... 81

" " Bones 18

" Women 25, 26

" the Chest 25

" Children 28,81

" the Eectum 28

" the Ovaries 80

Emergencies „ 14

Electricity and Practical Medicine. 19

Foods... .. 24

Galvano-Therapeutics 22

Hospitalism 25

Histology and Histo-Chemistry of Man. ... 81

Infancy 6

Insanity in its Relation to Crime 10

Materia Medica and Therapeutics 22

MedicalJournal... 82

Mental Physiology 5

Midwifery 25,26

Mineral Springs 29.

Neuralgia 8

Nervous System 12

Nursing 22

Ovarian Tumors 28

" Diagnosis and Treatment 30

Obstetrics 4, 8, 25

Physiology 9,10

Physiology of Common Life 16

Physiology and Pathology of the Mind 17

Physiological Effects of Severe Muscular

Exercise 11

Pulmonary Consumption 5

Practical Medicine 20

Physical Cause of the Death of Christ 24

Popular Science 82

Puerperal Diseases 2

Reports.... 4

Eecollections of Past Life 14

" of the Army of the Potomac ..16
Responsibility in Mental Diseases 18

Sea-sickness 2

Surgical Pathology 5

" Diseases of the Male Genito-Uri-

nary Organs 27

Surgery 7

Syphilis 27

Science 80, 32

Skin Diseases... .. 21

Uterine Therapeutics 2

6

Winter and Spring 4

CATALOGUE

OF

MEDICAL WORKS

ANSTIE.

Neuralgia, and Diseases which resemble it.
BY FRANCIS E. ANSTIE, M. D., F. R. C. P.,

Senior Assistant Physician to Westminster Hospital ; Lecturer on Materia Medica in "Westminster
Hospital School; and Physician to the Belgrave Hospital for Children; Editor of "The
Practitioner" (London), etc.

1 vol., 12mo. Cloth, $2.50.

" It is a valuable contribution to scientific medicine."— The Lancet (London).

BARKER.
The Puerperal Diseases, cumcai

delivered at Bellevue Hospital.

BY FORDYCE BARKER, M. D.,

Clinical Professor of Midwifery and the Diseases of Women in the Bellevue Hospital Medical
College; Obstetric Physician to Bellevue Hospital; Consulting Physician to the New York
State Woman's Hospital; Fellow of the New York Academy of Medicine ; formerly.Presi-
dent of the Medical Society of the State of New York ; Honorary Fellow of the Obstetrical
Societies of London and Edinburgh; Honorary Fellow of the Royal Medical Society of
Athens, Greece, etc., etc., etc.

1 vol., 8vo. Cloth. 526 pages. Price, $5.00.

" For nearly twenty years it has been my duty, as well as my privilege, to give clinical lect-
ures at Bellevue Hospital, on midwifery, the puerperal and the other diseases of women. This
volume is made up substantially from phonographic reports of the lectures which I have given
on the puerperal diseases. Having had rather exceptional opportunities for the study of these
diseases, I have felt it to be an imperative duty to utilize, so far as lay in my power, the advan-
tages which I have enjoyed for the promotion of science, and, I hope, for the interests of human-
ity. In many subjects, such as albuminuria, convulsions, thrombosis, and embolism, septicaemia,
and pyaemia, the advance of science has been so rapid as to make it necessary to teach something
new every year. Those, therefore, who have formerly listened to my lectures on these subjects,
and who now do me the honor to read this volume, will not be surprised to find, in many par-
ticulars, changes in pathological views, and often in therapeutical teaching, from doctrines before
inculcated. At the present day, for the first time in the history of the world, the obstetric de-
partment seems to be assuming its proper position, as the highest branch of medicine, if its rank
be graded by its importance to society, or by the intellectual culture and ability required, as
compared with that demanded of the physician or the surgeon. A man may become eminent as
a physician, and yet know very little of obstetrics; or he may be a successful and distinguished
surgeon, and be quite ignorant of even the rudiments of obstetrics. But no one can be a really
able obstetrician unless he be both physician and surgeon. And, as the greater includes the less,
obstetrics should rank as the highest department of our profession."— From Author's Preface.

On Sea-sickness.

BY FORDYCE BARKER, M. D.
1 vol., 16mo. 36 pp. Flexible Cloth, 75 cents.

Reprinted from the NEW YORK MEDICAL JOURNAL. By reason of the great demand for the
number of that journal containing the paper, it is now presented in book form, with such pre-
scriptions added as the author has found useful in relieving the suffering from sea-sickness.

4 D. Appleton & CoSs Medical Publications.

BARNES.

Obstetric Operations, including the Treatment
of Hcemorrhage.

BY ROBERT BARNES, M. D., F. R. C. P., LONDON,

Obstetric Physician to and Lecturer on Midwifery and the Diseases of Women and Children at
St. Thomas's Hospital; Examiner on Midwifery to the Eoyal College of Physicians and to
the Eoyal College of Surgeons; formerly Obstetric Physician to the London Hospital, and
late Physician to the Eastern Division of the Eoyal Maternity Charity.

WITH ADDITIONS, by BENJAMIN F. DAWSON, M. D.,

Late Lecturer on Uterine Pathology in the Medical Department of the University of New
York ; Assistant to the Clinical Professor of Diseases of Children in the College of Physicians
and Surgeons, New York ; Physician for the Diseases of Children to the New York Dis-
pensary ; Member of the New York Obstetrical Society, of the Medical Society of the
County of New York, etc., etc.

Second American Edition. 1 vol., 8vo. 503 pp. Cloth, $1.50.

" Such a work as Dr. Barnes's was greatly needed. It is calculated to elevate the practice
of the obstetric art in this country, and to be of great service to the practitioner/1— Lancet.

Bellevue and Charity Hospital Reports.

The volume of Bellevue and Charity Hospital Reports
for 1870, containing valuable contributions from.

ISAAC E. TAYLOE, M. D., AUSTIN FLINT, M. D., LEWIS A. SAYEE, M. D., WIL-
LIAM A. HAMMOND, M. D., T. GAILLAED THOMAS, M. D., FEANK H. HAMIL-
TON, M. D., and others.

1 vol., 8vo. Cloth, $4.00.

" These institutions are the most important, as regards accommodations for patients and
variety of cases treated, of any on this continent, and are surpassed by but few in the world.
The gentlemen connected with them are acknowledged to be among the first in their profession,
and the volume is an important addition to the professional literature of this country." — Psycho-
logical Journal.

BENNET.
Winter and Spring on the Shores of

the Mediterranean ; or, the Riviera, Mentone, Italy,
Corsica, Sicily, Algeria, Spain, and Biarritz, as Win-
ter Climates.

BY J. HENRY BENNET, M. D.,

Member of the Eoyal College of Physicians, London ; late Physician -Accoucheur to the Eoyal
Free Hospital; Doctor of Medicine of the University of Paris; formerly Eesident Physician
to the Paris Hospital (ex- Interne des Hopitaux de Paris), etc.

This work embodies the experience of ten winters and springs passed by Dr. Sennet on the
shores of the Mediterranean, and contains much valuable information for physicians in relation
to the health-restoring climate of the regions described.

1 vol. 12mo. 621 pp. Cloth, $3.50.

"Exceedingly readable, apart from its special purposes, and well illustrated." — Evening
Commercial.

" It has a more substantial value for the physician, perhaps, than for any other class or pro-
fession. . . . We commend this book to our readers as a volume presenting two capital
qualifications — it is at once entertaining and instructive." — N. Y. Medical Journal.

D. Appleton <& Go's Medical Publications. 5

BENNET.
On the Treatment of Pulmonary Con-

sumption, by Hygiene, Climate, and Medicine, in its
Connection with Modern Doctrines.

BY JAMES HENRY BENNET, M. D.,

Member of the Royal Colle/e of Physicians, London ; Doctor of Medicine of the University of

Paris, etc., etc.

1 vol., thin 8vo. Cloth, $1.50.

An interesting and instructive work, written in the strong, clear, and lucid manner which
appears in all the contributions of Dr. Bennet to medical or general literature.

" We cordially commend this book to the attention of all, for its practical common-sense views
of the nature and treatment of the scourge of all temperate climates, pulmonary consumption."
— Detroit Review of Medicine.

BILLROTH.
General Surgical Pathology and The-

rapeutics, in Fifty Lectures. A Text-book for Students
and Physicians.

BY DR. THEODOR BILLROTH.

Translated from the Fifth German Edition, with the special permission

of the Author, by
CHARLES E. HACKLEY, A. M., M. D.,

Surgeon to the New Tork Eye and Ear Infirmary; Physician to the New York Hospital;
Fellow of the New York Academy of Medicine, etc.

1 vol., 8vo. 714 pp., and 152 Woodcuts. Cloth, $5.00; Sheep, $6.00.

Professor Theodor Billroth, one of the most noted authorities on Surgical Pathology, gives in
this volume a complete resume of the existing state of knowledge in this branch of medical
science. The fact of this publication going through four editions in Germany, and having been
translated into French, Italian, Russian, and Hungarian, should be some guarantee for its standing.

" The want of a book in the English language, presenting in a concise form the views of the
German pathologists, has long been felt ; and we venture to say no book could more perfectly
supply that want than the present volume. . . . We would strongly recommend it to all who
take any interest in the progress of thought and observation in surgical pathology, and surgery."
— The Lancet.

'• We can assure our readers that they will consider neither money wasted in its purchase,
nor time in its perusal." — The Medical Investigator.

CARPENTER
Principles of Mental Physiology, with

their Applications to the Training and Discipline of the
Mind and the Study of its Morbid Conditions.

Br WM. B. CARPENTER, M. D., LL. D., F. R. S., F. L. S., F. G. S.,

Registrar of the TJniversity of London : Corresponding Member of the Institute of France and
of the American Philosophical Society^ete., etc.

u Among the numerous eminent writers this country has produced, none are more deserving
of praise for having attempted to apply the results of Physiological Research to the explanation
of the mutual relations of the mind and body than Dr. Carpenter. To him belongs the merit of
having scientifically studied and of having in many instances supplied a rational explanation of
those phenomena which, under the names of mesmerism, spirit-rappine. electro-biology, and
hypnotism, have attracted so large an amount of attention during the last twenty years. . " . We
must conclude by recommending Dr. Carpenter's work to the members of our own profession as
applying many facts, that have hitherto stood isolated, to the explanation of the functions of the
brain and to psychological processes g-enerally.'1— The Lancet.

6 D. Appleton & CoSs Medical Publications.

COMBE.
The Management of Infancy,

cal and Moral. Intended chiefly for the Use of
Parents.

BY ANDREW COMBE, M. D.
REVISED AND EDITED

BY SIB JAMES CLARK, K. C. B., M. D., P. R. S.,

Physician-in-ordinary to the Queen.

First American from the Tenth London Edition. 1 vol., 12mo. 302 pp.

Cloth, $1.50.

"This excellent little book should be in the hand of every mother of a family; and, if some
of our lady friends would master its contents, and either bring up their children by the light of
its teachings, or communicate the truths it contains to the poor by whom they are surrounded,
we are convinced that they would effect infinitely more good than by the distribution of any
number of tracts whatever. . . . We consider this work to be one of the few popular medical
treatises that any practitioner may recommend to his patients ; and, though, if its precepts are
followed, he will probably lose a few guineas, he will not begrudge them if he sees his friend's
children grow up healthy, active, strong, and both mentally and physically capable."— The
Lancet.

CHAUVEATL
The Comparative Anatomy of the

Domesticated Animals.

BY A. CHAUVEAIJ,

PEOFE880B AT THE LYONS VETERINARY SCHOOL.

Second edition, revised and enlarged, with the cooperation of S. ARLOING,
late Principal of Anatomy at the Lyons Veterinary School; Professor at the
Toulouse Veterinary School. Translated and edited by GEORGE FLEMING,
F. R. G. S., M. A. I., Veterinary Surgeon, Royal Engineers.

1 vol., 8vo. Cloth. 957 pp., with 450 Illustrations. Price, $6.00.

OPINIONS OF THE PRESS.

" This is a valuable work, well conceived and well executed by the authors, MM. Chauveau
and Arloing, and well translated by Mr. Fleming. It is rather surprising how few works exist,
in any language, in which the anatomy of the commoner animals, domestic and otherwise, is
given with any approach to detail. Systematic works there are in abundance, but, if the student
be desirous <>f ascertaining any particular point, such as the position and branches of the
pneumogastric or sympathetic nerves, or the homologue of a given muscle in several different
animals, he may search all day ere he find it. The work before us appears to be well adapted to
meet this difficulty.

" The illustrations are very numerous, and Mr. Fleming has introduced a large number that
are not contained in the original work.

" Taking it altogether, the bfok is a very welcome addition to English literature, and great
credit is due to Mr. Fleming for the excellence of the translation, and the many additional notes he
has appended to Chauveau's treatise."— Lancet (London).

"The want of a text-Jbook on the Comparative Anatomy of the Domesticated Animals has
long been felt. . . . The descriptions of the text are illustrated and assisted by no less than 460
excellent woodcuts. In a work which ranges over so vast a field of anatomical detail and de-
scription, it is difficult to select any one portion for review, but our examination of it enables us
to speak in high terms of its general excellence. . . . The care and attention with which hippot-
omy has been cultivated on the Continent are illustrated by every page in M. Chauveau's wortr
—Medical Times and Gazette (London).

D. Appleton & CoSs Medical Publications. 7

DAVIS.

Conservative Surgery, as exhibited in remedying
some of the Mechanical Causes that operate wjurir
ously both in Health and Disease. With Illustrations.

T3y HENRY G-. DAYIS, M. D.,

Member of the American Medical Association, etc., etc.
1 vol., 8vo, 315 pp. Cloth, $3.00.

The author has enjoyed rare facilities for the study and treatment
of certain classes of disease, and the records here presented to the pro-
fession are the gradual accumulation of over thirty years' investigation.

" Dr. Davis, bringing, as he does to his specialty, a great aptitude for the
solution of mechanical problems, takes a high rank as an orthopedic surgeon,
and his very practical contribution to the literature of the subject is both valu-
able and opportune. We deem it worthy of a place in every physician's library.
The style is unpretending, but trenchant, graphic, and, best of all, quite intelli-
gible."— Medical Record.

ECKER
The Cerebral Convolutions of Man,

represented according to Personal Investigations, es-
pecially on their Development in the Foetus, and with
reference to the Use of Physicians.

By ALEXANDER ECKER,

Professor of Anatomy and Comparative Anatomy in the University of Freiburg.

Translated from the German by Robert T. Edes, M. D.

1 vol., 8vo. 87 pp. $1.25.

" The work of Prof. Ecker is noticeable principally for its succinctness and
clearness, avoiding long discussions on undecided points, and yet sufficiently
furnished with references to make easy its comparison with the labors of oth-
ers in the same direction.

" Entire originality in descriptive anatomy is out of the question, but the
facts verified by our author are here presented in a more intelligible manner
than in any other easily-accessible work.

" The knowledge to be derived from this work is not furnished by any other
text-book in the English language." — Boston Medical and Surgical Journal,
January 20, 1873.

D. Appleton & Co.'s Medical Publications.

ELLIOT.

triC CliniC. A Practical Contribution to the
Study of Obstetrics, and the Diseases of Women and
Children.

By the late GEORGE T. ELLIOT, M. D.,

Late Professor of Obstetrics and the Diseases of Women and Children in the Bellevue Hospital
Medical College ; Physician to Bellevue Hospital, and to the New York Lying-in Asylum ;
Consulting Physician to the Nursery and Child's Hospital; Consulting Surgeon to the State
Woman's Hospital; Corresponding Member of the Edinburgh Obstetrical Society and of the
Eoyal Academy of Havana ; Fellow of the N. Y. Academy of Medicine ; Member of the
County Medical Society, of the Pathological Society, etc., etc.

1 vol., 8vo. 458 pp. Cloth, $4,50.

This work is, in a measure, a resume of separate papers previously
prepared by the late Dr. Elliot ; and contains, besides, a record of nearly
two hundred important and difficult cases in midwifery, selected from
his own practice. It has met with a hearty reception, and has received
the highest encomiums both in this country and in Europe.

" The volume by Dr. Elliot has scarcely less value, though in a different direction, than that
of the Edinburgh physician (Dr. Duncan, 'Eesearches in Obstetrics ')."— Lancet.

"There is no book in American obstetrical literature that surpasses this one."— Edinburgh
Medical Journal.

" It ought to be in the hands of every practitioner of midwifery in the country." — Boston
Medical and Surgical Journal.

" It has no equal hi the English language, as regards clinical instruction in obstetrics."—
American Journal of Obstetrics.

FLINT.
Manual of Chemical Examination of

the Urine in Disease. With Brief Directions for the
Examination of the most Common Varieties of Urinary
Calculi.

BY AUSTIN FLINT, JR., M. D.,

Professor of Physiology and Microscopy in the Bellevue Hospital Medical College ; Fellow of the
New York Academy of Medicine ; Member of the Medical Society of the County of New
York; Eesident Member of the Lyceum of Natural History in the City of New York, etc.

Third Edition, revised and corrected. 1 vol., 12mo, 77 pp, Cloth, $1.00.

The chief aim of this little work is to enable the busy practitioner to
make for himself, rapidly and- easily, all ordinary examinations of Urine;
to give him the benefit of the author's experience in eliminating little
difficulties in the manipulations, and in reducing processes of analysis
to the utmost simplicity that is consistent with accuracy.

" We do not know of any work in English so complete and handy as the Manual now offered
to the profession by Dr. Flint, and the high scientific reputation of the author is a sufficient
, guarantee of the accuracy of all the directions given/'— Journal of Applied Chemistry.

"We can unhesitatingly recommend this Manual."— Psychological Journal.
w Eminently practical"— Detroit Review of Medicine.

J9. Appleton & CoSs Medical Publications. 9

FLINT.

The Physiology of Man. Designed to rep-
resent the Existing State of Physiological Science as
applied to the Functions of the Human Body.
By AUSTIN FLINT, JB., M. D.,

Professor of Physiology and Microscopy in the Bellevue Hospital Medical College, and in th«
Long Island College Hospital; Fellow of the New York Academy of Medicine ; Microscopist
to Bellevue Hospital

In Five Volumes. 8vo. Tinted Paper.
Volume I. — The Blood} Circulation; Respiration.

8vo. 502 pp. Cloth, 84.50.

" If the remaining portions of this work are compiled with the same care and
accuracy, the whole may vie with any of those that have of late years been pro-
duced in our own or in foreign languages." — British and Foreign Medico- Chirurgi-
cal Review.

" As a book of general information it will be found useful to the practitioner,
and, as a book of reference, invaluable in the hands of the anatomist and physi-
ologist."— Dublin Quarterly Jounced of Medical Science.

" The complete work will prove a valuable addition to our systematic treatises
on human physiology." — The Lancet.

" To those who desire to get in one volume a concise and clear, and at the
same time sufficiently full resume of ' the existing state of physiological science,'
we can heartily recommend Dr. Flint's work. Moreover, as a work of typographi-
cal art it deserves a prominent place upon our library-shelves. Messrs. Appleton
& Co. deserve the thanks of the profession for the very handsome style in which
they issue medical works. They give us hope of a time when it will be very
generally believed by publishers that physicians' eyes are worth savins:. " — Medi-
cal Gazette.

Yolume II. — Alimentation • Digestion / Absorption /
I/ym/ph and Chyle.

8vo. 556 pp. Cloth, $4.60.

** The second instalment of this work fulfils all the expectations raised by the
perusal of the first. . . . The author's explanations and deductions bear
evidence of much careful reflection and study. . . . The entire work is one
of rare interest. The author's style is as clear and concise as his method ia
studious, careful, and elaborate." — Philadelphia. Inquirer.

" We regard the two treatises already issued as the very best on human physi-
ology which the English or any other language affords, and we recommend them
with thorough confidence to students, practitioners, and laymen, as models of
literary and scientific ability." — A'. Y. Medical Journal.

" We have found the style easy, lucid, and at the same time terse. The prac-
tical and positive results of physiological investigation are succinctly stated,
without, it would seem, extended discussion of disputed points." — Boston Medical
and Surgical Journal.

" It is a volume which will be welcome to the advanced student, and as a
work of reference." — The Lancet.

" The leading subjects treated of are presented in distinct parts, each of which
is designed to be an exhaustive essay on that to which it refers." — Western Jour-
nal of Medicine.

10 D. Appleton & Co.'s Medical Publications.

Flint's Physiology, Volume HI— Secretion; Ex-
cretion; Ductless Glands y Nutrition; Animal Heat ;
Movements ; Voice and Speech.

8vo. 526 pp, Cloth, $4.50.

" Dr. Flint's reputation is sufficient to give a character to the book among the
profession, where it will chiefly circulate, and many of the facts given have been
verified by the author in his laboratory and in public demonstration." — Chicago
Courier.

" The author bestows judicious care and labor. Facts are selected with dis-
crimination, theories critically examined, and conclusions enunciated with com-
mendable clearness and precision." — American Journal of the Medical Sciences,

Y^lume IV. — The Nervous System.
8vo. Cloth, $4.50.

This volume embodies the results of exhaustive study, and of a long and
laborious series of experiments, presented in a manner remarkable for its strength
and clearness. No other department of physiology has so profound an interest
for the modern and progressive physician as that pertaining to the nervous
system. The diseases of this system are now.engaging the study and attention
of some of the greatest minds in the medical world, and in order to follow their
brilliant discoveries and developments, especially in connection with the science
of electrology, it is absolutely necessary to obtain a clear and settled knowledge
of the anatomy and physiology of the nervous system. It is the design of this
work to impart that knowledge free from the perplexing speculations and uncer-
tainties that have no real value for the practical student of medicine. The
author boldly tests every theory for himself, and asks his readers to accept noth-
ing that is not capable of demonstration. The properties of the cerebro-spinal,
nervous, and sympathetic systems are treated of in a manner at once lucid,
thorough, and interesting.

Although this volume is one, perhaps the most important one, of the author's
admirable series in the Physiology of Man, it is nevertheless complete in itself,
and may be safely pronounced indispensable to every physician who takes a pride
and interest in the progress of medical science.

Volume Y. — Special Senses ; Generation.

8vo. Cloth, $4.50.

" The present volume completes the task, begun eleven years ago, of preparing
a work, intended to represent the existing state of physiological science, as ap-
plied to the functions of the human body. The kindly reception which the first
four volumes have received has done much to sustain the author in an under-
taking, the magnitude of which he has appreciated more and more as the work
has progressed.

" In the fifth and last volume, an attempt has been made to give a clear account
of the physiology of the special senses and generation, a most difficult and delicate
undertaking. . . .

" Finally, as regards the last, as well as the former volumes, the author can
only say that he has spared neither time nor labor in their preparation ; and the
imperfections in their execution have been due to deficiency in ability and oppor-
tunity. He indulges the hope, however, that he has written a book which may
assist his fellow-workers, and interest, not only the student and practitioner of
medicine, but some others who desire to keep pace with the progress of Natural
Science." — Extracts from Preface.

D. Appleton <& CoSs Medical Publications. 11

FLINT.
On the Physiological Effects of Severe

and Protracted Muscular Exercise. With Special ref-
erence to its Influence upon the JExecretion of Nitrogen.

By AUSTIN FLINT, JE., M. D.,

Professor of Physiology in the Bellevue Hospital Medical College, New York, etc., etc.

1 vol., 8vo, 91 pp. Cloth, $2.00.

This monograph on the relations of Urea to Exercise is the result of a thorough and careful
investigation made in the case of Mr. Edward Payson "Weston, the celebrated pedestrian.
The chemical analyses were made under the direction of R. O. Doremus, M. D., Professor of
Chemistry and Toxicology in the Bellevue Hospital Medical College, by Mr. Oscar Loew, his
assistant. The observations were made with the cooperation of J. C. Dalton, M. D., Professor
of Physiology in the College of Physicians and Surgeons; Alexander B. Mott, M. D., Profess-
or of Surgical Anatomy ; W. H. Tan Buren, M. D., Professor of Principles of Surgery ; Austin
Flint, M. D., Professor of the Principles and Practice of Medicine ; W. A. Hammond, M. D.,
Professor of Diseases of the Mind and Nervous System — all of the Bellevue Hospital Medical
College.

" This work will be found interesting to every physician. A number of important results
were obtained valuable to the physiologist."— Cincinnati Medical Repertory.

HAMILTON.
Clinical Electro-Therapeutics. (Medical

and Surgical.) A Manual for Physicians for the
Treatment more especially of Nervous Diseases.
By ALLAN McLANE HAMILTON, M. D.,

Physician in charge of the New York State Hospital for Diseases of the Nervous System ;
Member of the New York Neurological and County Medical Societies, etc., etc.

With Numerous Illustrations. 1 vol., 8vo. Cloth. Price, $2.00.

This work is the compilation of well-tried measures and reported cases, and is intended as
a simple guide for the general practitioner. It is as free from confusing theories, technical
terms, and unproved statements, as possible. Electricity is indorsed as a very valuable remedy
In certain diseases, and as an invaluable therapeutical means in nearly all forms of NEBVOITS
DISEASE ; but not as a specific for every human ill, mental and physical.

HAMMOND.
Insanity in its Relations to Crime.

A Text and a Commentary.

By WILLIAM A. HAMMOND, M. D.
1 vol. 8vo. 77 pp. Cloth, $1.00.

" A part of this essay, under the title ' Society versus Insanity,1 was contributed to Put-
nam's Magazine, for September. 1870. The greater portion is now first published. The im-
portance of the subject considered can scarcely be over-estimated, whether we regard it from
the stand-point of science or social economy ; and, if I have aided in its elucidation, my object
will have been attained.1'— From Author1 8~ Preface.

12 D. Appleton & (70. 's Medical Publications.

HAMMOND.

A Treatise on Diseases of the Nervous

System.

By WILLIAM A. HAMMOND, M. D.,

Professor of Diseases of the Mind and Nervous System, and of Clinical Medicine, in the Bellevue
Hospital Medical College ; Physician-in-Chief to the New York State Hospital for Diseases
of the Nervous System, etc., etc.

FOURTH EDITION, REVISED AND CORRECTED.

With Forty-five Illustrations. 1 vol., 8vo. 750 pp. Cloth, $5.00.

The treatise embraces an introductory chapter, which relates to the
instruments and apparatus employed in the diagnosis and treatment of
diseases of the nervous system, and five sections. Of these, the first
treats of diseases of the brain ; the second, diseases of the spinal cord ;
the third, cerebro-spinal diseases ; the fourth, diseases of nerve-cells ;
and the fifth, diseases of the peripheral nerves. One feature which may
be claimed for the work is, that it rests, to a great extent, upon the per-
sonal observation and experience of the author, and is therefore no mere
compilation.

This work is already universally popular with the profession ; their
appreciation of it may be evidenced by the fact that within two years
it has reached the fourth edition.

" That a treatise by Prof. Hammond would be one of a high order was what we anticipated,
and it affords us pleasure to state that our anticipations have been realized."— Cincinnati
Medical Repertory,

" This is unquestionably the most complete treatise on the diseases to which it is devoted
that has yet appeared in the English language ; and its value is much increased by the fact that
Dr. Hammond has mainly based it on his own experience and practice, which, we need hardly
remind our readers, have been very extensive."— London Medical Times and Gazette.

" Free from useless- verbiage and obscurity, it is evidently the work of a man who knows
what he is writing about, and knows how to write about it." — Chicago Medical Journal.

" This is a valuable and comprehensive book ; it embraces many topics, and extends over a
wide sphere. One of the most valuable parts of it relates to the Diseases of the Brain ; while
the remaining portion of the volume treats of the Diseases of the Spinal Cord, the Cerebro-
spinal System, the Nerve-Cells, and the Peripheral Nerves."— British Medical Journal.

" The work before us Is unquestionably the most exhaustive treatise, on the diseases to
which it is devoted, that has yet appeared in English. And its distinctive value arises from
the fact that the work is no mere rafficiamento of old observations, but rests on his own ex-
perience and practice, which, as we have before observed, have been very extensive." — Ameri-
can Journal of Syphilography.

" The author of this work has attained a high rank among our brethren across the Atlantic
from previous labors in connection with the disorders of the nervous system, as well as from
various other contributions to medical literature, and he now holds the official appointments of
Physician to the New York State Hospital for Diseases of the Nervous System, and Professor
of the same department in the Bellevue Hospital Medical College. The present treatise is the
fruit of the experience thus acquired, and we have no hesitation in pronouncing it a most valu-
able addition to our systematic literature.1'' — Glasgow Medical Journal.

D. Appleton c5 (70. 's Medical Publications. 13

HOFFMANN.
Manual of Chemical Analysis, G3 applied

to the Examination of Medicinal Chemicals and their
Preparations. A Guide for the Determination of their
Identity and Quality, and for the Detection of Impuri-
ties and Adulterations. For the use of Pharmaceutists,
Physicians, Druggists, and Manufacturing Chemists, and
Pharmaceutical and Medical Students.

BY FRED. HOFFMAXX, PHIL. D.
One vol., 8vo, Bichly Illustrated. Cloth. Price, $3.

SPECIMEN OF ILLIT6TBATION8.

•This volume is a carefully -prepared work, and well nptothe existing state of both the science
and art of modern pharmacy. It is a hook which will find its place in every medical and phar-
'utical laboratorv and library, and is a safe and instructive puide to medical students and
practitioners of medicine."— American Journal of Science and Arts.

In America this work has already met with general and unqualified approval; and in Europe
is now heinor welcomed as one of the best and most important additions to modern pharmaceu-
tical literature.

Send for descriptive circular. Address

D. APPLETON & CO., 549 & 551 Broadway, N. Y. City.

14 -Z). Appleton & Co.'s Medical Publications.

HOLLAND.

Recollections of Past Life,

By SIR HENRY HOLLAND, Bart, M. D., F. R. S., K. C. B., etc.,
President of the Royal Institution of Great Britain, Physician-in-Ordinary to the Queen,

etc., etc.

1 vol., 12mo, 351 pp. Price, Cloth, $2.00.

A very entertaining and instructive narrative, partaking somewhat of the nature of
autobiography and yet distinct from it, in this, that its chief object, as alleged by the
writer, is not so much to recount the events of his own life, as to perform the office of
chronicler for others with whom he came in contact and was long associated.

The "Life of Sir Henry Holland " is one to be recollected, and he has not erred in Div-
ing an outline ot it to the public."— The Lancet.

"His memory was— is, we may say, for he is still alive and in possession of all hid
faculties— stored with recollections of the most eminent men and women of this cen-
tury. ... A life extending: over a period of eighty-four years, and passed in the most
active manner, in the midst of the best society, which the world has to offer, must neces-
sarily be full of singular interest; and Sir Henry Holland has fortunately not waited until
his memory lost its freshness before recalling some of the incidents in it ''"'—The New
York Times.

HOWE.
Emergencies, and How to Treat Them.

The Etiology, Pathology, and Treatment of Accidents,
Diseases, and Cases of Poisoning, which demand
Prompt Attention. Designed for Students and Prac-
titioners of Medicine.

By JOSEPH W. HOWE, M.D.,

Clinical Professor of Surgery in the Medical Department of the University of New York ;

Visiting Surgeon to Charity Hospital; Fellow of the New York Academy

of Medicine, etc., etc.

1 vol., 8vo. Cloth, $3.00.

"This work has a taking title, and was written by a gentlemen of acknowledged ability, to
fill a void in the profession. ... To the general practitioner in towns, villages, and in the
country, where the aid and moral support of a consultation cannot be availed of, this volume
will be recognized as a valuable help. "We commend it to the profession.— Cincinnati Lancet
and Observer.

" This work is certainly novel in character, and its usefulness and acceptability are as marked
as its novelty. . . . The book is confidently recommended."— Richmond and Louisvi lie Med-
ical Journal.

" This volume is a practical illustration of the positive side of the physician's life, a constant
reminder of what he is to do in the sudden emergencies which frequently occur in practice.
. . . The author wastes no words, but devotes himself to the description of each disease as if
the patient were under his hands. Because it is a good book we recommend it most heartily to
the profession."— Boston Medical and Surgical Journal.

" This work bears evidence of a thorough practical acquaintance with the different branches
of the profession. The author seems to possess a peculiar aptitude for imparting instruction
as well as for simplifying tedious details. ... A careful perusal will amply repay the student
and practitioner.' —New York Medical Journal"

D. Appleton & Co.'s Medical Publications. 15

HUXLEY AND YOUMANS.
The Elements of Physiology and

Hygiene. With Numerous Illustrations.

BY THOMAS H. HUXLEY, LL. D., F. R. S., and
WILLIAM JAY YOUMANS, M. D.

New and Revised Edition. 1 vol., 12mo. 420 pp. $1.75.

A text-book for educational institutions, and a valuable elementary
work for students of medicine. The greater portion is from the pen of
Professor Huxley, adapted by Dr. Youmans to the circumstances and
requirements of American education. The eminent claim of Professor
Huxley's " Elementary Physiology " is, that, while up to the times, it
is trustworthy in its presentation of the subject ; while rejecting dis-
credited doctrines and doubtful speculations, it embodies the latest
results that are established, and represents the present actual state of
physiological knowledge.

" A valuable contribution to anatomical and physiological science." — Religious Telescope.

"A clear and well-arranged work, embracing the latest discoveries and accepted theories."
—Buffalo Commercial.

" Teeming with information concerning the human physical enconomy." — Evening Jour-
nal.

HUXLEY.
The Anatomy of Vertebrated Animals.

BY THOMAS HE^RY HUXLEY, LL. D., F. R. S.,

Author of "Man's Place in Nature," "On the Origin of Species," "Lay Sermons and

Addresses," etc.

1 vol., 12mo. Cloth, $2.50.

The former works of Prof. Huxley leave no room for doubt as to the impor-
tance and value of his new volume. It is one which will be very acceptable to
all who are interested in the subject of which it treats.

" This long-expected work will be cordially welcomed by all students and teachers of Com-
parative Anatomy as a compendious, reliable, and, notwithstanding its small dimensions, most
comprehensive guide on the subject of which it treats. To praise or to criticise the work of so
accomplished a master of his favorite science would be equally out of place. It is enough to
say that it realizes, in a remarkable degree, the anticipations which have been formed of it ;
and that it presents an extraordinary combination of wide, general views, with the clear, accu-
rate, and succinct statement of a prodigious number of individual facts." — Nature.

16 I>. Appleton <& Co.'s Medical Publications.

JOHNSON.
The Chemistry of Common Life.

Illustrated with numerous Wood Engravings.
By JAMES F. JOHNSON, M. A., F. R. S., F. G. S., ETC., ETC.,

Author of "Lectures on Agricultural Chemistry and Geology," "A Catechism of Agricultural
Chemistry and Geology," etc.

2 vols., 12mo. Cloth, $3.00.

It has been the object of the author in this work to exhibit the
present condition of chemical knowledge, and of matured scientific
opinion, upon the subjects to which it is devoted. The reader will not
be surprised, therefore, should he find in it some things which differ
from what is to be found in other popular works already in his hands or
on the shelves of his library.

LETTERMAN.
Medical Recollections of the Army of

the Potomac.

By JONATHAN LETTERMAN, M. D.,

Late Surgeon TJ. S. A., and Medical Director of the Army of the Potomac.

1 vol., 8vo. 194 pp. Cloth, $1.00.

" This account of the medical department of the Army of the Poto-
mac has been prepared, amid pressing engagements, in the hope that
the labors of the medical officers of that army may be known to an in-
telligent people, with whom to know is to appreciate ; and as an affec
tionate tribute to many, long my zealous and efficient colleagues, who,
in days of trial and danger, which have passed, let us hope never to re-
turn, evinced their devotion to their country and to the cause of hu-
manity, without hope of promotion or expectation of reward." — Preface.

" We venture to assert that but few who open this volume of medical annals,
pregnant as they are with instruction, will care to do otherwise than finish them
at a sitting." — Medical Record.

" A graceful and affectionate tribute." — N. Y. Medical Journal.

LEWES.
The Physiology of Common Life.

By GEORGE HENRY LEWES,

Author of "Seaside Studies," "Life of Goethe," etc.

2 vols., 12mo. Cloth, $3.00.

The object of this work differs from that of all others on popular
science in its attempt to meet the wants of the student, while meeting
those of the general reader, who is supposed to be wholly unacquainted
with anatomy and physiology.

D. Appleton <& (70. 's Medical Publication. 17

MATTDSLEY.
The Physiology and Pathology of the

Mind.

By HENRY MAUDSLEY, M. D., LONDON,

Physician to the "West London Hospital; Honorary Member of the Medico-Psychological Society
of Paris ; formerly Resident Physician of the Manchester Eoyal Lunatic Hospital, etc,

1 vol., 8vo. 442 pp. Cloth, $3.00.

This work aims, in the first place, to treat of mental phenomena from
a physiological rather than from a metaphysical point of view ; and,
secondly, to bring the manifold instructive instances presented by the
unsound mind to bear upon the interpretation of the obscure problems
of mental science.

" Dr. Maudsley has had the courage to undertake, and the skill to execute,
what is, at least in English, an original enterprise." — London Saturday Review.

" It is so full of sensible reflections and sound truths that their wide dissemi-
nation could not but be of benefit to all thinking persons." — PsychalogicalJournal.

" Unquestionably one of the ablest and most important works on the subject
of which it treats that has ever appeared, and does credit to his philosophical
acumen and accurate observation." — Medical Record.

" We lay down the book with admiration, and we commend it most earnestly
to our readers as a work of extraordinary merit and originality — one of those
productions that are evolved only occasionally in the lapse of years, and that
serve to mark actual and very decided advances in knowledge and science." —
N. Y. Medical Journal.

Body and Mind : An Inquiry into their Con-
nection and Mutual Influence, especially in reference
to Mental Disorders ; an enlarged and revised edition
to which are added Psychological Essays.

By HENKY MAUDSLEY, M. D., LONDON,

Fellow of the Eoyal College of Physicians; Professor of Medical Jurisprudence In University Col-
SSNfeBtei Pl^S dent-elect of the Medico-Psychokgical Association; Honorary Member of
the Medico-Psychological Society of Paris, of the Imperial Society of Physician^ of Vienna,
and of the Society for the Promotion of Psychiatry and Forensic Psychology of F Vienna-
formerly Eesident Physician of the Manchester Eoyal Lunatic Asylum, etc., etc?

1 vol., 12mo. Io5 pp. Cloth, $1.00.

The general plan of this work may be described as being to bring
man, both in his physical and mental relations, as much as possible with-
in the scope of scientific inquiry.

" A representative work, which every one must study who desires to know
is doing in the way of real progress, and not mere chatter, about mental
physiology and pathology."— The Lancet.

SteP ln the progre8^ of scientific psychology."— Tht

18 I>. Appleton & Co?s Medical Publications.

MATTDSLEY.
Responsibility in Mental Diseases.

BY HENRY MAUDSLEY, M. D.,

Fellow of the Koyal College of Physicians, Professor of Medical Jurisprudence in University
College, London, etc., etc. Author of " Body and Mind," " Physiology and Pathology of the
Nervous System."

"This book is a compact presentation of those facts and principles which re-
quire to be taken into account in estimating human responsibility — not legal
responsibility merely, but responsibility for conduct in the family, the school, and
all phases of social relation in which obligation enters as an element. The work
is new in plan, and was written to supply a widely-felt want which has not
hitherto been met."— The Popular Science Monthly.

MARKOE.

A Treatise on Diseases of the Bones.

BY THOMAS M. MARKOE, M. D.,
Professor of Surgery in the College of Physicians and Surgeons, New York, etc.

WITH NUMEROUS ILLUSTRATIONS.

1 vol., 8vo. Cloth, $4.50.

This valuable work is a treatise on Diseases of the Bones, embracing their
structural changes as affected by disease, their clinical history and treatment, in-
cluding also an account of the various tumors which grow in or upon them. None
of the injuries of bone are included in its scope, and no joint diseases, excepting
where the condition of the bone is a prime factor in the problem of disease. As
the work of an eminent surgeon of large and varied experience, it may be regarded
as the best on the subject, and a valuable contribution to medical literature.

"The book which I now offer to my professional brethren contains the substance of the
lectures which I have delivered during the past twelve years at the college. ... I have followed
the leadings of my own studies and observations, dwelling more on those branches where I had
seen and studied most, and perhaps too much neglecting others where my own experience was
more barren, and therefore to me less interesting. I have endeavored, however, to make up the
deficiencies of my own knowledge by the free use of the materials scattered so richly through
our periodical literature, which scattered leaves it is the right and the duty of the systematic
writer to collect and to embody in any account he may offer of the state of a science at any given
period." — Extract from Author's Preface,

D. Appleton & CoSs Medical Publications. 19

MEYER.

Electricity in its Relations to Practical

Medicine.

By DE. MORITZ MEYER,

Eoyal Counsellor of Health, etc.

Translated from the Third German Edition, with Notes and Additions,
A New and Bevised Edition,

By WILLIAM A. HAMMOND, M. D.,

Professor of Diseases of the Mind and Nervous System, and of Clinical Medicine, in the BeUevua
Hospital Medical College; Vice-President of the Academy of Mental Science^ National
Institute of Letters, Arts, and Sciences ; late Surgeon-Genera U. 8. A., etc.

1 vol., 8vo. 497 pp. Cloth, $4.50.

" It is the duty of every physician to study the action of electricity,
to become acquainted with its value in therapeutics, and to follow the
improvements that are being made in the apparatus for its application in
medicine, that he may be able to choose the one best adapted to the
treatment of individual cases, and to test a remedy fairly and without
prejudice, which already, especially in nervous diseases, has been used
with the best results, and which promises to yield an abundant harvest
in a still broader domain." — From Authors Preface.

OF DLLTTSTBATIOira.

Saxton-EttinghanBen Apparatus.

" Those who do not read German are under great obligations to William A.
Hammond, who has given them not only an excellent translation of a most ex-
cellent work, but has given us much valuable information and many suggestions
from his own personal experience." — Medical Record.

" Dr. Moritz Meyer, of Berlin, has been for more than twenty years a laborious
and conscientious student of the application of electricity to practical medicine,
and the results of his labors are given in this volume. Dr. Hammond, in making
a translation of the third German edition, has done a real service to the profession
of this country and of Great Britain. Plainly and concisely written, and simply
and clearly arranged, it contains just what the physician wants to know on the
subject." — N. Y. Medical Journal

"It is destined to fill a want long felt by physicians in this country." — Journal
of Obstetrics.

20 D* Appleton & (70. 's Medical Publications.

NIEMEYER
A Text-Book of Practical Medicine.

With Particular Reference to Physiology and Patho-
logical Anatomy.

By the late Dr. FELIX VON NIEMEYER,

Professor of Pathology and Therapeutics ; Director of the Medical Clinic of the University of

Tubingen.

Translated from the Eighth German Edition, by special permission of

the Author,

By GEORGE H. HUMPHREYS, M. D.,

lAta jne of the Physicians to the Bureau of Medical and Surgical Belief at Bellevue Hospital for
the Out-door Poor; Fellow of the New York Academy of Medicine, etc.,

and
CHARLES E. HACKLEY, M. D.,

One of the Physicians to the New York Hospital; one of the Surgeons to the New York Eye
and Ear Infirmary ; Fellow of the New York Academy of Medicine, etc.

Eevised Edition. 2 vols., 8vo. 1,528 pp. Cloth, $9.00 ; Sheep, $11.00.

The author undertakes, first, to give a picture of disease which shall
be as lifelike and faithful to nature as possible, instead of being a mere
theoretical scheme; secondly, so to utilize the more recent advances
of pathological anatomy, physiology, and physiological chemistry, as to
furnish a clearer insight into the various processes of disease.

The work has met with the most flattering reception and deserved
success ; has been adopted as a text-book in many of the medical colleges
both in this country and in Europe; and has received the very highest
encomiums from the medical and secular press.

"It is comprehensive and concise, and is characterized by clearness and
originality." — Dublin Quarterly Journal of Medicine.

" Its author is learned in medical literature ; he has arranged his materials
with care and judgment, and has thought over them." — The Lancet.

"As a full, systematic, and thoroughly practical guide for the student and
physician, it is not excelled by any similar treatise in any language." — Appletons'
/burnal.

" The author is an accomplished pathologist and practical physician ; he is not
only capable of appreciating the new discoveries, which during the last ten years
have been unusually numerous and important in scientific and practical medicine,
but, by his clinical experience, he can put these new views to a practical test, and
give judgment regarding them." — Edinburgh Medical Journal.

" From its general excellence, we are disposed to think that it will soon take
its place among the recognized text-books." — American Quarterly Journal of
Medical Sciences.

" The first inquiry in this country regarding a German book generally is, * la
it a work of practical value ? " Without stopping to consider the justness of the
American idea of the ' practical,' we can unhesitatingly answer, ' It is ! ' " — New
York Medical Journal.

" The author has the power of sifting the tares from the wheat — a matter of
the greatest importance in a text-book for students." — British Medical Journal.

" Whatever exalted opinion our countrymen may have of the author's talents
of observation and his practical good sense, his text-book will not disappoint
them, while those who are so unfortunate as to know him only by name, have in
store a rich treat." — New York Medical Record.

D. Appleton & CoSs Medical Publications. 21

NEUMANN.
Hand-Book of Skin Diseases.

By DR. ISIDOR NEUMANN,
Lecturer on Skin Diseases in the Royal University of Vienna.

Translated from advanced sheets of the second edition, furnished by the
Author ; with Notes,

By LUCIUS D. BULKLEY, A. M., M. DM

Surgeon to the New York Dispensary, Department of Venereal and Skin Diseases ; Assist-
ant to the Skin Clinic of the College of Physicians and Surgeons, New York; Mem-
ber of the Ne« York Dermatological Society, etc., etc.

1 vol., 8vo. About 450 pages and 66 "Woodcuts. Cloth, $4.00.

SPECIMEN OP ILLUSTRATIONS.

Section of skin from a bald head.

Prof. Neumann ranks second only to Hebra, whose assistant he was for many yean
and his work may be considered as a fair exponent of the German practice of Dermatolo-
gy. The book is abundantly illustrated with plates of the histology and pathology of the
skin. The translator has endeavored, by means of notes from French, English, and Ameri-
can sources, to make the work valuable to the student as well as to the practitioner.

u It is a work which I shall heartily recommend to my class of students at the Univer-
sity of Pennsylvania, and one which I feel sure will do much toward enlightening the pro-
fession on this subject." — Louis A. Duhring.

" I know it to be a good book, and I am sure that it is well translated ; and it is inter-
esting to find it illustrated by references to the views of co-laborers in the same field/1 —
Erasmus Wilson.

" So complete as to render it a most useful book of reference."— T. Me Call Anderson.

" There certainly is no work extant which deals so thoroughly with the Pathological
Anatomy of the Skin as does this hand-book."— ,#". T. Medical Record.

"The original notes by Dr.. Bulkley are very practical, and are an important adjunct to
the text. ... I anticipate for it a wide circulation."— Silas Durkee, Boston.

" I have already twice expressed my favorable opinion of the book in print, and am
glad that it is given to the public at last."— James C. White, Boston.

" More than two years ago we noticed Dr. Neumann's admirable work in its original
shape : and we are therefore absolved from the necessity of saying more than to repeat
our strong recommendation of it to English readers."— Practitioner.

22 D. Appleton & Co? a Medical Publications.

NEFTEL.

GalvanO-TherapeutlCS. The Physiological and
Therapeutical Action of the Galvanic Current upon
the Acoustic, Optic, Sympathetic, and Pneumogastric
Nerves.

By WILLIAM B. NEFTEL.
1 vol., 12mo. 161 pp. Cloth, $1.50.

This book lias been published at the request of several aural sur-
geons and other professional gentlemen, and is a valuable treatise on
the subjects of which it treats. Its author, formerly visiting physician
to the largest hospital of St. Petersburg, has had the very best facili-
ties for investigation.

" This little work shows, as far as it goes, full knowledge of what Las been
done on the subjects treated of, and the author's practical acquaintance with
them." — New York Medical Journal.

" Those who use electricity should get this work, and those who do not
should peruse it to learn that there is one more therapeutical agent that they
could and should possess." — The Medical Investigator.

NIGHTINGALE.

N OtCS On N lirsing : What it is, and what it is not.

By FLORENCE NIGHTINGALE.

1 vol., 12mo. 140 pp. Cloth, 75 cents.

Every-day sanitary knowledge, or the knowledge of nursing, or, in
other words, of how to put the constitution in such a state as that it will
have no disease or that it can recover from disease, takes a higher place.
It is recognized as the knowledge which every one ought to have — dis-
tinct from medical knowledge, which only a profession can have.

PEKEIKA.

Dr. Pereira's Elements of Materia

Medica and Therapeutics. Abridged and adapted
for the Use of Medical and Pharmaceutical Practi-
tioners and Students, and comprising all the Medi-
cines of the British Pharmacopoeia, with such others
as are frequently ordered in Prescriptions, or re-
quired by the Physician.

Edited by ROBERT BENTLEY and THEOPHILUS REDWOOD.

New Edition. Brought down to 1872. 1 vol., Eoyal 8vo. Cloth, $7.00 ;
Sheep, $8.00.

Z>. Appleton & Go's Medical Publications. 23

PEASLEE.

Ovarian Tumors ; Their Pathology, Diagnosis,
and Treatment, with reference especially to Ovariotomy.
By E. E. PEASLEE, M. D.,

Professpr of Diseases of Women in Dartmouth College; one of the Consulting Physicians to
the New York State Woman's Hospital ; formerly Professor of Obstetrics and Diseases of
Women in the New York Medical College ; Corresponding Member of the Obstetrical
Society of Berlin, etc.

1 vol., 8vo. Illustrated with many Woodcuts, and a Steel Engraving of Dr.
E. McDowell, the "Father of Ovariotomy." Price, Cloth, $5.00.

This valuable work, embracing the results of many years of successful experience in the
department of which it treats, will prove most acceptable to the entire profession ; while the
high standing of the author and his knowledge of the subject combine to make the book the
best in the language. It is divided into two parts : the first treating of Ovarian Tumors, their
anatomy, pathology, diagnosis, and treatment, except by extirpation ; the second of Ovariot-
omy, its history and statistics, and of the operation. Fully illustrated, and abounding with
information the result of a prolonged study of the subject, the work should be in the hands of
every physician in the country.

The following are some of the opinions of the press, at home and abroad, of this great
work, which has been justly styled, by an eminent critic, " the most complete medical mono-
graph on a practical subject ever produced in this country"

" His opinions upon what others have advised are clearly set forth, and are as interesting
and important as are the propositions he has himself to advance ; while there are a freshness,
a vigor, an authority about his writing, which great practical knowledge alone can confer." —
The Lancet.

41 Both Wells's and Peaslee's works will be received with the respect due to the great repu-
tation and skill of their authors. Both exist not only as masters of their art, but as clear and
graceful writers. In either work the student and practitioner will find the fruits of rich expe-
rience, of earnest thought, and of steady, well-balanced judgment. As England is proud of
Wells, so may America well be proud of Peaslee, and the great world of science may be proud
of both." — British Medical Journal.

" This is an excellent work, and does great credit to the industry, abih'ty, science, and
learning of Dr. Peaslee. Few works issue from the medical press so complete, so exhaustive-
ly learned, so imbued with a practical tone, without losing other substantial good qualities."
— Edinburgh Medical Journal.

" In closing our review of this work, we cannot avoid again expressing our appreciation of
the thorough study, the careful and honest statements, and candid spirit, which characterize it
For the use of the student we should give tlie preference to Dr. Peaslee's work, not only
from its completeness, but from its more methodical arrangement." — American Journal
of Medical Sciences.

" Dr. Peaslee brings to the work a thoroughness of study, a familiarity with the whole
field of histology, physiology, pathology, and practical gynaecology, not excelled, perhaps, by
those of any man who ever performs the operation." — Medical Record.

" If we were to select a single word to express what we regard as the highest excellence of
this book, it would be its thoroughness.'1'1— New York Medical Journal.

" We deem its careful perusal indispensable to all who would treat ovarian tumors with a
good conscience." — American Journal of Obstetrics.

" It shows prodigal industry, and embodies within its five hundred and odd pages pretty
much all that seems worth knowing on the subject of ovarian diseases."— Philadelphia Medi-
cal Times.

" Great thoroughness is shown in Dr. Peaslee's treatment of all the details of this very ad-
mirable work."— .Boston. Medical and Surgical Journal.

"It is a necessity to every surgeon who expects to treat this disease."— Leavenworth
Medical Herald.

" Indispensable to the American student of gynaecology."— Pacific Medical and Surgical
Journal.

tt There is not a doubtful point that could occur to any one that is not explained and an-
swered in the most satisfactory manner." — Virginia Clinical Record.

" The work is one the profession should prize ; one that every earnest practitioner should
possess." — Georgia Medical Companion.

" Dr. Peaslee has achieved a success, and the work is one which no practical surgeon can
afford to be without."— Medical Investigator.

24 D. Appleton & CoSs Medical Publications.

SAYKE.

A Practical Manual on the Treatment

of Club-Foot.

By LEWIS A. SAYRE, M. D.,

Professor of Orthopedic Surgery in Bellevue Hospital Medical College ; Surgeon to Bellevue
and Charity Hospitals, etc.

1 vol., 12mo. New and Enlarged Edition. Cloth. $1.00.

" The object of this work is to convey, in as concise a manner as possible,
all the practical information and instruction necessary to enable the general
practitioner to apply that plan of treatment which has been so successful in my
own hands." — Preface.

" The book will very well satisfy the wants of the majority of general practitioners, for
whose use, as stated, it is intended."— New York Medical Journal.

SMITH.

On Foods.

By ED WARD SMITH, M. D., LL.B., F.R.S.,

Fellow of the Eoyal College of Physicians of London, etc., etc.
1 vol., 12mo. Cloth. Price, $1.75.

Since the issue of the author's work on " Practical Dietary," he has
felt the want of another, which would embrace all the generally-known
and less-known foods, and contain the latest scientific knowledge re-
specting them. The present volume is intended to meet this want, and
will be found useful for reference, to both scientific and general read-
ers. The author extends the ordinary view of foods, and includes
water and air, since they are important both in their food and sanitary
aspects.

STKOUD.
The Physical Cause of the Death of

Christ^ and its Relations to the Principles and Prac-
tice of Christianity.

By WILLIAM STROIJD, M.D.

With a Letter on the Subject,

By SIR JAMES Y. SIMPSON, BART., M.D.
1vol., 12mo. 422pp. Cloth, $2.00.

This important and remarkable book is, in its own place, a masterpiece, and
will be considered as a standard work for many years to come.

The principal point insisted upon is, that the death of Christ was caused by rupture or lacer-
ition of the heart. Sir James Y. Simpson, who had read the author's treatise and various com-
ments on it, expressed himself very positively in favor of the views maintained by Dr. Stroud.
—Psychological Journal.

D. Appleton <& Co?s Medical Publications. 25

SIMPSON.
The Posthumous Works of Sir James

Young Simpson, Bart., M. D. In Three Volumes.

Volume I. — Selected Obstetrical and Gynaecological Works of
Sir James Y. Simpson, Bart., M. D., D. C. L., late Professor of Midwifery
in the University of Edinburgh. Containing the substance of his Lect-
ures on Midwifery. Edited by J. WATT BLACK, A. M., M. D., Member of
the Royal College of Physicians, London ; Physician- Accoucheur to Char-
ing Cross Hospital, London ; and Lecturer on Midwifery and Diseases of
Women and Children in the Hospital School of Medicine.

lvol.,8vo. 852 pp, Cloth, $3.00.

This volume contains all the more important of the contributions of
Sir James Y. Simpson to the study of obstetrics and diseases of women,
with the exception of his clinical lectures on the latter subject, which
will shortly appear in a separate volume. This first volume contains
many of the papers reprinted from his Obstetric Memoirs and Contri-
butions, and also his Lecture STotes, now published for the first time,
containing the substance of the practical part of his course of Mid-
wifery. It is a volume of great interest to the profession, and a fitting
memorial of its renowned and talented author.

" To many of our readers, doubtless, the chief of the papers it contains are familiar. To
others, although probably they may be aware that Sir James Simpson has written on the sub-
jects, the papers themselves will be new and fresh. To the first class we would recommend
this edition of Sir James Simpson's works, as a valuable volume of reference; to the latter, as
a collection of the works of a great master and improver of his art, the study of which cannot
fail to make them better prepared to meet and overcome its difficulties."— Medical Times and
Gazette.

Volume IL — Anaesthesia, Hospitalism, etc. Edited by Sir
WAXIER SIMPSON, Bart.

lvol.,8vo, 560pp. Cloth, $3.00,

" "We say of this, as of the first volume, that it should find a place on the table of every
practitioner; for, though it is patchwork, each piece may be picked out and studied with pleas-
ure and profit-"— The Lancet (London).

Volume III. — The Diseases of Women. Edited by ALEX. SIMP-
SON, M. D., Professor of Midwifery in the University of Edinburgh.
1 vol., 8vo. Cloth, $3.00.

One of the best works on the subject extant. Of inestimable value to every physician.

SWETT.
A Treatise on the Diseases of the Chest.

Being a Course of Lectures delivered at the New
York Hospital.

By JOHN A. SWETT, M. D.,

Professor of the Institutes and Practice of Medicine in the New York University ; Physician
to the New York Hospital; Member of the New York Pathological Society.

1vol., 8vo. 587pp. $3.50.

Embodied in this volume of lectures is the experience of ten years in hospital and private
practice.

20 D. Appleton <£ CoSs Medical Publications.

SCHROEDER
A Manual of Midwifery, including the

Pathology of Pregnancy and the Puerperal State.
By Dr. KARL SCHROEDER.

Professor of Midwifery and Director of the Lying-in Institution in the University of Erlangen.

Translated from the Third German Edition,
By OHAS. H. CARTER, B. A., M. D., B. S. Lond.,

Member of the Eoyal College of Physicians, London, and Physician Accoucheur to St. George's,
Hanover Square, Dispensary.

With Twenty-six Engravings on Wood. 1 vol., 8vo. Cloth.

" The translator feels that no apology is needed in offering to the profession a translation
of Schroeder's Manual of Midwifery. The work is well known in Germany and extensively
used as a text-book; it has already reached a third edition within the short space *>f two years,
and it is hoped that the present translation will meet the want, long felt in thia country, of a
.manual of midwifery embracing the latest scientific researches on the subject

TILT.
A* Hand-Book of Uterine Therapeu-

tics and of Diseases of Women.

By EDWARD JOHN TILT, M. D.,

Member of the Koyal College of Physicians ; Consulting Physician to the Farringdon General
Dispensary ; Fellow of the Koyal Medical and Chirurgical Society, and of several British
and foreign societies.

1 vol., 8vo. 345 pp. Cloth, $3.50.

Second American edition, thoroughly revised and amended.

" In giving the result of his labors to the profession the author has done a great work. Our
readers will find its pages very interesting, and, at the end of their task, will feel grateful to
the author for many very valuable suggestions as to the treatment of uterine diseases."— The
Lancet.

"Dr. Tilt's 'Hand -Book of Uterine Therapeutics1 supplies a want which has often been
felt. ... It may, therefore, be read not only with pleasure and instruction, but will also be
found very useful as a book of reference."— The Medical Mirror.

" Second to none on the therapeutics of uterine disease."— Journal of Obstetrics.

VAN BTTKEK

Lectures upon Diseases of the Rectum.

Delivered at the Bellevue Hospital Medical College.
Session of 1869-70.

By W. H. VAN BUREN, M. D.,

Professor of the Principles of Surgery with Diseases of the Genito-Urinary Organs, etc., in the
Bellevue Hospital Medical College ; one of the Consulting Surgeons of the New York Hos-
pital, of the Bellevue Hospital ; Member of the New York Academy of Medicine, of the
Pathological Society of New York, etc., etc.

1 vol., 12mo. 164 pp. Cloth, $1.50.

" It seems hardly necessary to more than mention the name of the author of this admirable
little volume in order to insure the character of his book. No one in this country has enjoyed
greater advantages, and had a more extensive field of observation in this specialty, than Dr.
Van Buren, and no one has paid the same amount of attention to the subject. . . . Here is the
experience of years summed up and given to the professional world in a plain and practical
manner."— Psychological Journal.

I). Appleton <& CoSs Medical Publications. 27

VAN BUBEN AND KEYES.

A Practical Treatise on the Surgical

Diseases of the Genito- Urinary Organs, including Syphi-
lis. Designed as a Manual for Students and Practition-
ers. With Engravings and Cases.

BY W. H. VAN BUREN, A. M., M. D.,

Professor of Principles of Surgery, with Diseases of the Genito-TJrinary System and Clinical

Surgery, in Bellevue Hospital Medical College; Consulting Surgeon to the New York

Hospital, the Charity Hospital, etc. ; and

E. L. KEYES, A. M., M. D.,

Professor of Dermatology in Bellevue Hospital Medical College ; Surgeon to the Charity Hospi-
tal, Venereal Division ; Consulting Dermatologist to the Bureau of Out-Door Belief,
Bellevue Hospital, etc,

1 vol., 8vo. Cloth, $5.00; Sheep, $6.00.

This work is really a compendium of, and a book of reference to, all modern
works treating in any way of the surgical diseases of the genito-urinary organs.
At the same time, no other single book contains so large an array of original
facts concerning the class of diseases with which it deals. These facts are
largely drawn from the extensive and varied experience of the authors.

Many important branches of genito-urinary diseases, as the cutaneous mala-
dies of the penis and scrotum, receive a thorough and exhaustive treatment that
the professional reader will search for elsewhere in vain.

Both to the specialist and the general practitioner the work commends itself
as one of inestimable value.

The work is a marvel of conciseness, and very rarely is so much condensa-
tion accomplished without loss of any valuable points of detail. A glance at
the table of contents will give an idea of the scope of the volume, but only a
careful perusal of the work will convince the reader that full justice has been
done to all the various branches of this highly-interesting class of diseases.

The work is elegantly and profusely illustrated, and enriched by fifty-five
original cases, setting forth obscure and difficult points in diagnosis and treatment.

" The first part is devoted to the Surgical Diseases of the Genito-Urinary
Organs; and part second treats of Chancroid and Syphilis. The authors 'ap-
pear to have succeeded admirably in giving to the world an exhaustive and
reliable treatise on this important class of diseases.' " — Northwestern Medical and
Surgical Journal.

" It is a most complete digest of what has long been kncfwn, and of what has
been more recently discovered in the field of syphilitic and genito-urinary dis-
orders. It is perhaps not an exaggeration to say that no single work upon the
same subject has yet appeared, in this or any foreign language, which is superior
to it." — Chicago Medical Examiner.

" The commanding reputation of Dr. Van Buren in this specialty and of the
great school and hospital from which he has drawn his clinical materials, together
with the general interest which attaches to the subject-matter itself, will, we
trust, lead very many of those for whom it is our office to cater, to possess them-
selves at once of the volume and form their own opinions of its merit." — Atlanta
Medical and Surgical Journal.

28 D. Appleton <$; CoSs Medical Publications.

VOGEL.
A Practical Treatise on the Diseases

of Children. Second American from the Fourth
German Edition. Illustrated T>y Six Lithographic
Plates.

By ALFEED VOGEL, M. D.,

Professor of Clinical Medicine In the University of Dorpat, Russia.
TRANSLATED AND EDITED BY

H. RAPHAEL, M. D.,

late House Surgeon to Bellevue Hospital ; Physician to the Eastern Dispensary for tiw DloeaaoB
of Children, etc., etc.

1 vol., 8vo. 611 pp. Cloth, $4.50.

The work is well up to the present state of pathological knowledge ;
complete without unnecessary prolixity; its symptomatology accurate,
evidently the result of careful observation of a competent and experi-
enced clinical practitioner. The diagnosis and differential relations of
diseases to each other are accurately described, and the therapeutics
judicious and discriminating. All polypharmacy is discarded, and only
the remedies which appeared useful to the author commended.

It contains much that must gain for it the merited praise of all im-
partial judges, and prove it to be an invaluable text-book for the stu-
dent and practitioner, and a safe and useful guide in the difficult but all-
important department of Paediatrics.

" Rapidly passing to a fourth edition in Germany, and translated into three
other languages, America now has the credit of presenting the first English ver-
sion of a book which must take a prominent, if not the leading, position among
works devoted to this class of disease." — N. Y. Medical Journal.

" The profession, of this country are under many obligations to Dr. Raphael
for bringing, as he has dona> this truly valuable work to their notice." — Medical
Record.

"The translator has been more than ordinarily successful, and his labors
have resulted in what, in every sense, is a valuable contribution to medica*
science." — Psychological Journal.

"We do not know of a compact text-book on the diseases of children more
complete, more comprehensive, more replete with practical remarks and scientific
facts, more in keeping with the development of modern medicine, and more
worthy of the attention of the profession, than that which has been the subject
of our remarks." — Journal of Obstetrics.

D. Appleton & CoSs Medical Publications. 29

WALTON.
The Mineral Springs of the United

States and Canada, with Analyses and Notes on the
Prominent Spas of Europe, and a List of Sea-side
Resorts. An enlarged and revised edition.

By GEORGE E. WALTON", M. D.,

Lecturer on Materia Medics in the Miami Medical College, Cincinnati.
1 vol., 12mo. 390 pages, with Maps. Price, $2.00.

The author has given the analyses of all the springs in this country and
those of the principal European spas, reduced to a uniform standard of
one wine-pint, so that they may readily he compared. He has arranged
the springs of America and Europe in seven distinct classes, and de-
scribed the diseases to which mineral waters are adapted, with refer-
ences to the class of waters applicable to the treatment, and the pecul-
iar characteristics of each spring as near as known are given — also, the
location, mode of access, and post-office address of every spring are men-
tioned, In addition, he has described the various kinds of baths and
the appropriate use of them in the treatment of disease.

EXTRACTS FROM OPINIONS OF THE PRESS.

"... Precise and comprehensive, presenting not only reliable analyses of
the waters, but their therapeutic value, so that physicians can hereafter advise
their use as intelligently and beneficially as they can other valuable alterative
agents." — Sanitarian.

"... Will tend to enlighten both the profession and the people on this
question." — N. Y. Medical Journal.

" . . . Contains in brief space a vast amount of important and interesting
matter, well arranged and well presented. Nearly every physician needs just
such a volume " — Richmond and Louisville Medical Journal.

"... Fills this necessity in a scientific and pleasing manner, and can be read
with advantage by the physician as well as layman." — American Jour, of Obstetrics.

OP YiBGimA, June 9, 1878.

GENTLEMEN : I have received by mail a copy of Dr. Walton's work on the
Mineral Springs of the United States and Canada. Be pleased to accept my
thanks for a work which I have been eagerly looking for ever since I had the
pleasure of meeting the author in the summer of 1871. He satisfied me that
he was well qualified to write a reliable work on this subject, and I doubt not
he has met ray expectations. Such a work was greatly needed, and, if offered
for sale at the principal mineral springs of the country, will, I believe, com-
mand a ready sale. Very respectfully yours,

J. L. CABELL, M. D.

30 D. Appleton & CoSs Medical Publications.

WELLS.
Diseases of the Ovaries ; Their Diagnosis

and Treatment.

By T. SPENCER WELLS,

Fellow and Member of Council of the Eoyal College of Surgeons of England ; Honorary Fellow
of the King and Queen's College of "Physicians in Ireland ; Surgeon in Ordinary to the
Queen's Household ; Surgeon to the Samaritan Hospital for Women ; Member of the Im-
perial Society of Surgery of Parts, of the Medical Society of Paris, and of the Medical Soci-
ety of Sweden ; Honorary Member of the Eoyal Society of Medical and Natural Science
of Brussels, and of the Medical Societies of Pesth and Helsingfors : Honorary Fellow of
the Obstetrical Societies of Berlin and Leipzig.

1 vol., 8vo. 478 pp. Illustrated. Cloth, Price, $4.50.

In 1865 the author issued a volume containing reports of one hundred and
fourteen cases of Ovariotomy, which was little more than a simple record of
fact8. The book was soon out of print, and, though repeatedly asked for a
new edition, the author was unable to do more than prepare papers for the
Royal Medical and Chirurgical Society, as series after series of a hundred cases
accumulated. On the completion of five hundred cases he embodied the results
in the present volume, an entirely new work, for the student and practitioner,
and trusts it may prove acceptable to them and useful to suffering women.

" Arrangements have been made for the publication of this volume in Lon-
don on the day of its publication in New York." French and German transla-
tions are already in press.

WAGNER
A Hand-book of Chemical Tech-

nology.

By RUDOLPH WAGNER, Ph. D.,

Professor of Chemical Technology at the University of Wurtzburg.

Translated and edited, from the eighth G-erman edition, with extensive

additions,

By WILLIAM CROOKES, F. R. S.
With 336 Illustrations. 1 vol., 8vo. 761 pages. Cloth, $5.00.

Under the head of Metallurgic Chemistry, the latest methods of preparing Iron, Cobalt,
Nickel, Copper, Copper Salts, Lead and Tin, and their Salts, Bismuth, Zinc, Zinc Salts, Cad-
mium, Antimony, Arsenic, Mercury, Platinum, Silver, Gold, Manganates, Aluminum, and
Magnesium, are described. The various applications of the Voltaic Current to Electro-Metal-
lurgy follow under this division. The preparation of Potash and Soda Salts, the manufacture
of Sulphuric Acid, and the recovery of Sulphur from Soda Waste, of course occupy prominent
places in the consideration of chemical manufactures. It is difficult to over-estimate the mer-
cantile value of Mond's process, as well as the many new and important applications of Bisul-
phide of Carbon. The manufacture of Soap will be found to include much detail. The Tech-
nology of Glass, Stone-ware, Limes, and Mortars, will present much of interest to the Builder
and Engineer. The Technology of Vegetable Fibres has been considered to include the prep-
aration of Flax, Hemp, Cotton, as well as Paper-making; while the applications of Vegetable
Products will be found to include Sugar-boiling, "Wine and Beer Brewing, the Distillation of
Spirits, the Baking of Bread, the Preparation of Vinegar, the Preservation of Wood, etc.

Dr. Wagner gives much information in reference to the production of Potash from Sugar
residues. The use of Baryta Salts is also fully described, as well as the preparation of Sugar
from Beet-roots. Tanning, the Preservation of Meat, Milk, etc., the Preparation of Phospho-
rus and Animal Charcoal, are considered as belonging to the Technology of Animal Products.
The Preparation of Materials for Dyeing has necessarily required much space ; while the final
sections of the book have been devoted to the Technology of Heating and Illumination

NEW MEDICAL WORKS IN PRESS.

Hand-Book of the Histology and Histo-

Chemistry of Man. By Dr. HEINRICH FREY, of Zurich. Illustrated with
500 Woodcuts.

Clinical Lectures on Diseases of tlie

Nervous System. Delivered at the Bellevue Hospital Medical College, by
WM. A. HAMMOND, M. D. Edited, with Notes, by T. M. B. Cross, M. D.

; its Pathology, Etiology, Prognosis, and Treatment By L. DUNCAN
BULKLEY, A. M., M. D., New York Hospital

A monograph of about seventy pages, illustrated, founded on an analysis of two hundred
cases of various forms of acne.

Compendium of Children's Diseases, for

Students and Physicians. By Dr. JOHN STEINER.

Diseases of the Nerves and Spinal Cord.

B Dr. H. CHARLTON BASTIAN.

D. APPLETON & CO.,

549 & 561 BROADWAY, NEW YORK.

31

THE NEW YORK MEDICAL JOURNAL.

JAMES B. HUNTER, M. D., Editor.
Published Monthly, Volumes begin in January and July,

" Among the numerous records of Medicine and the collateral sciences published in America,
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" One of the best medical journals, by-the-by, published on the American Continent." — Lon-
don Medical limes and Gazette.

"A very high-class journal.1'— London Medical Mirror.

" The editor and the contributors rank among our most distinguished medical men, and each
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"Full of valuable original papers, abounding in scientific ability." — Chicago Medical Times.

44 We know no other periodical that we would rather present as a specimen of American skill
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The press all over the land is warmly commending it. We subjoin a few encomiums from
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" Just the publication needed at the present day."— Montreal Gazette.

New York Medical Journal and Popular Science Monthly, $8 00

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U.C. BERKELEY LIBRARIES