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A

HANDBOOK

PHYSIOLOGICAL LABORATORY,

CONTAINING

AN EXPOSITION OP THE FUNDAMENTAL FACTS OF THE

SCIENCE, WITH EXPLICIT DIRECTIONS FOR

THEIR DEMONSTRATION.

HTSTOT Or1 V' PartB l and 1I- By B' Klein> m,d> Assistant Professor in the
Pathological Laboratory of the Brown Institute, London.

PHYSTOT OPT"' Part r' BL00D CIRCULATION, RESPIRATION AND
ANIMAL HEAT. By J. Burdox Sanderson, m.d., Pro-
fessor of Physiology, University College, London.

« Part II. THE FUNCTIONS OF THE MUSCLES AND

NERVES. By Michael Foster, m.d., Prelector of Physi-
ology, Trinity College, Cambridge; Author of a Text-boofc
of Physiology, etc.

ti . Part III. DIGESTION AND SECRETION. By T. Lauder

Bhunton, m.d., Lecturer on Materia Medica and Therapeu-
tics, St. Bartholomew's Hospital, etc.

EDITED BY

J. BURDON SANDERSON, M.D.

WITH

ONE HUNDRED AND THIRTY-THREE FULL-PAGE PLATES,

CONTAINING

353 BEAUTIFULLY EXECUTED ILLUSTRATIONS.
WITH BEFEBENCEfi \M> EXPLANATIONS

PHILADELPHIA:
BLAKISTON, SON & CO.,

No. 1012 Walm i Sti.-kjct.
188 I.

TO

WILLIAM SHARPET. M.D. LL.D. F.R.S. F.R.S.E.

PROFESSOR OF AS ATOMY AND PHYSOT.OGT IX CX1VERSITY COLLEOE LOXO X. ET

Dear Dr. Sharpey,

To you, who have been these many years the friend
of physiologists throughout the world, and who, by your
original work, by your teaching, by your generous aid and
judicious counsel, have been the mainstay of physiology in
England, we desire to dedicate this attempt to promote the
study of our science.

Accept it as a token of our personal regard, as well as of
the high value we set on your life-long labors.

Your devoted Friends,

MICHAEL FOSTER,
J. BURDON-SANDERSON,
T. LAUDER BRUNTON,
E. KLEIN.

Digitized by the Internet Archive

in 2010 with funding from
Columbia University Libraries

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EDITOR'S PREFACE.

This book is intended for beginners in physiological
work. It is a book of methods, not a compendium of
the science of physiology, and consequently claims a place
rather in the laboratory than in the study. But although
designed for workers, the authors believe that it will be
found not the less useful to those who desire to inform
themselves by reading as to the extent to which the
science is based on experiment, and as to the nature of
the experiments which chiefly deserve to be regarded as
fundamental.

The practical purpose of the book has been strictly kept
in view, both in the arrangement and in the selection of
the subjects. Many subjects are entirely omitted which
form important chapters in every text-book. They have
been left out either because they do not admit of experi-
mental demonstration, or because the experiments required
are of too difficult or complicated a character to be either
shown to a class or performed by a beginner.

The mode of arrangement will be found to be somewhat
different in the four sections into which the work is
divided. This difference, although in part attributable to
difference of authorship, is mainly due to the peculiarities
of the modes of demonstration required in the several sub-
jects.

As regards the physiology of nerve and muscle, it is
sufficient to refer the reader to the author's introduction
for an exposition of the method followed. Iu the his-
tological part will be found a purely objective description
of anatomical facts and methods. Substituting chemical
for anatomical, the same tiling might be said of the chap-
ters relating to tin- chemical functions. Ilere, where
minuteness of description is essential, great pains have
been taken to -jive the student the most ample details as

Vlll l'l'.KF ace.

regards materials for work, instruments, and methods. In
the chapter on the blood, the same object has been kept
in view, but in those relating to the mechanical functions

of circulation and respiration, where either man or the
higher animals must he for the most part the subjects of
observation, and where consequently the conditions of
experiment are complicated by the interference of the ner-
vous system to an extent which it is often difficult to
estimate, it has been found impossible to avoid entering
somewhat more largely into theoretical explanations.

In the chapters on digestion and secretion, and in the
remainder of the chemical part, those experiments or
methods which arc most important and hist suited for
demonstration are distinguished by two asterisks (**), the
less important by a single asterisk (*). The absence of an
asterisk at the beginning of a paragraph denotes either
that the experiment is unimportant or that it is difhVult
to perform. A dagger (f) is used, to draw special atten-
tion to a test or procedure.

I have to record Dr. Brunton's obligation to Dr. Arthur
Gamgee, F.R.S., for many important suggestions in the
preparation of the chapter on secretion. Dr. Brunton
further wishes me to state that, although he has recom-
mended no method as suitable for demonstration which
he has not himself tried, he has freely availed himself of
the well-known works of Hoppe-Seyler, Gorup-lU'sanez,
and Ivuhne, both in the arrangement of the sections and
in the selection of experiments.

It has been judged expedient by the Publishers to sepa-
rate the illustrations from the text. In this way full
justice has been done to the engravings of the Histologi-
cal part, which have been executed by Mr. Collings from
the original drawings of the author.

Most of the illustrations of the Physiological part are
the work of the same artist, both as regards drawing and
engraving. Of the remainder, several have been borrowed
(with the kind permission of the author) from Mr. Sut-
ton's work on Volumetrical Analysis.

CONTENTS.

HISTOLOGY.— PART I.
CHAPTER I.

PAGE

Blood Corpuscles '. . .17

CHAPTER II.
Epithelium and Endothelium 35

CHAPTER III.
Connective Tissues 4G

CHAPTER IV.
Muscular Tissue 65

CHAPTER V.
TISSUES of TnE Nervous System 70

HISTOLOGY— PART II.

CHAPTER VI.
Preparation op TnE Compound Tissues .... 100

CHAPTER VII.
Vascular System 110

CHAPTER VIII.
Lymphatic System 123

CHAPTER IX.
Organs of Respiration 133

X CONTENTS.

CHAPTER X.

PA(iK

Organs of Digestion 135

CHAPTER XI.

Skin, Cutaneous Glands, and Genito-1 binary Apparatus 141

CHAPTER XII.
Organs of Special Sense 150

CHAPTER XIII.
Embryology 158

CHAPTER XIV.
Appendix. — Study of Inflamed Tissues .... IG9

PHYSIOLOGY.— PART I.

Blood, Circulation, Respiration, and Animal Heat.

CHAPTER XV.
The Blood 175

CHAPTER XVI.
The Circulation of the Blood .2 17

CHAPTER XVII.
Respiration 298

CHAPTER XVIII.
Animal Heat S36

PHYSIOLOGY.— PART II.
Functions of Muscle and Nerve.

CHAPTER XIX.
General Directions 350

CHAPTER XX.
General Properties of Muscle at Rest .... 360

CONTENTS. XI

CHAPTER XXI.

PAGE

Preliminary Observations on the Stimulation op Nerve
and Moscle 364

CHAPTER XXII.
Phenomena and Laws op Muscular Contraction . . . 365

CHAPTER XXIII.
The "Wave of Muscular Contraction 369

CHAPTER XXIV.
Tetanus 371

CHAPTER XXV.
Electric Currents of Muscles 370

CHAPTER XXVI.

Electric Currents op Nerves 381

CHAPTER XXVII.
Electrotonus 382

CHAPTER XXVIII.
Stimulation of Nerves 383

CHAPTER XXIX.
Phenomena accompanying a Nervous Impulse . . . 393

CHAPTER XXX.
Various Forms op Stimulation op Muscle and Nerve . . 395

CHAPTER XXXI.
Dbar] Poisoning and Independent Muscular Irritability. 398

CHAPTER XXXII.
The Functions OF the Roots ok Spinal Nerves . . . 402

CHAPTER XXXIII.
Reflex Actions 406

CHAPTEB XXXIV.
ome Functions of Cebtaih Parts of the Ekcephaloh . 418

x'li CONTENTS.

PHYSIOLOGY— PART III.
Digestion and Secretion.

CHAPTER XXXV.

TA'iP.

Albuminous Compounds 1-'1

CHAPTER XXXVI.
Chemistry of the Tissues ....

44!

CHAPTER XXXVII.
Digestion **'"

CHAPTER XXXVIII.
The Secretions '-''

CHAPTER XXXIX.
Appendix.— Notes on Manipulation 561

HISTOLOGY.

By Dr. E. KLEIN.
PART I.-PREPARATION OF THE ELEMENTARY TISSUES.

CHAPTER I

BLOOD CORPUSCLES.

In the microscopical examination of the blood, we have to
do only with the study of the formed elements, namely, the
colorless corpuscles and blood disks.

Colorless Blood Corpuscles. — The colorless corpuscles
are elementary organisms which are endowed with the power of
spontaneous motion. This power belongs to them in virtue of
the material of which their bodies are composed. This mate-
rial is protoplasm. Their motion is of two kinds; it consists of
change of form and change of place. The latter results from
the former. As movements of this kind are seen in greatest
perfection in rhizopods and amoebae, they are called amoeboid.

Amoeboid Movements of Colorless Corpuscles. —
Very active movements are seen in the colorless blood corpus-
cles of the newt. The cells are large and easy of observation.
It is of the first importance, in beginning our study of them,
that they should be placed under conditions which, if not iden-
tical with, are not materially different from, those under which
they actually exist. The simplest method is the following: —

Take a clean glass slide and an absolutely clean cover-glass,
which, as we must use high powers (that is, objectives of which
the focal distance is short), must be thin. Take the newt out
of the water, dry the tail, cut off its end. If no blood comes,
squeeze the organ from the root towards the tip until a drop is
obtained. One of two methods may now be used: 1st, let the
blood drop upon the middle of the glass slide, and place the
cover-glass on it in such a way that one edge rests on its sur-
face, while the opposite edge is supported by the finger or for-
ceps. Then let the glass gradually down upon the drop. Or,
2

18 BLOOD CORPUSCLI ~.

2dly, collect the blood on the cover-glass by bringing it into
contact with the drop, then place it on the slide with its clean
surface upwards. By following either of these methods,
the introduction of air-bubbles will be avoided, which would
otherwise be a source of difficulty to the beginner. The drop
should be neither too small nor too large. The following in-
conveniences arise from its being too large: 1. The thin cover-
glass does not lie steadily in its place, but floats on the drop
in such a way that, by the slightest movement of the table,
currents are produced in the liquid which render observation
difficult or impossible. 2. If it is desired to keep the preparation
for a length of time under observation, it is necessary to adopt
some means to prevent the liquid from evaporating ; for, if this
is not done, it gradually dries from the edges, and soon be-
comes unfit for the observation of amoeboid movements, we
therefore inclose the preparation in oil, as will be immediately
described, and experience shows that, by so doing, the move-
ments may be watched for twelve hours or more continuously
— a time which is sufficient for a complete study of the phe-
nomena in question. This, however, cannot be done unless
the drop is very small. 3. If high powers are used, the front
glass of the objective comes into contact with the cover-glass,
and produces currents due to pressure.

If, on the other hand, the drop is too small, the elements
are pressed upon by the cover-glass, and thereby subjected to
unnatural conditions. No definite rule can be given as re-
gards the size of the drop, which must of course vary with
that of the cover-glass.

The mode of surrounding a preparation of blood with oil is
as follows : Take a drop with a glass rod or camel-hair pencil,
and let it fall at the very edge of the cover-glass in such a
way that, although most of it is on the surface of the slide, it
covers a little of the cover-glass also. Then incline the glass
slide slightly, and with the rod lead the oil from the drop
along the edge of the cover-glass, taking care not to press
upon the latter. If one drop of oil is insufficient, of course
another must be added. Take great care to avoid smearing
the cover glass too far; for by so doing, the space available
for observation may become inconveniently limited.

Having thus obtained a preparation of blood entirely pro-
tected from evaporation, we are ready to begin our study of
the colorless corpuscles.

Varieties of Colorless Corpuscles. — As soon as we
have brought a field containing blood into focus, we see, in
addition to a multitude of colored blood disks, to which we at
present pay no attention, a greater or less number of color-
less corpuscles, which themselves differ from one another both
in size and aspect, and in their property of spontaneous

BY DR. KLEIN. 19

movement. Three forms may be distinguished, which we
will examine in succession : —

1. Common Large Colorless Corpuscles. — Supposing
that a few moments have elapsed since the preparation was
made, some of these pale corpuscles are sure to be seen float-
ing hither and thither in the liquid with a rolling movement.
The}r are much more numerous than the other forms.

Fix the attention on one of these bodies, and observe, first,
that it is so transparent that, as it rolls over and 6ver, a single
granule embedded in its substance may be kept constantly in
view. Continuing the observation, notice that the surface of
the corpuscle, at first smooth, gradually becomes uneven.
The cause of the unevenness is this. The surface is beset
with a greater or less number of filamentous appendages,
varying in lengtL^ and distributed over the surface with
variable uniformity. These seem to consist of the same
material as the body of the corpuscle. When they are short
the}' may be compared to prickles, when longer they are often
bent at the point. Sometimes we see one of the processes
lengthen itself, while another disappears; sometimes a whole
group of processes push out on one side, while others are re-
tracted on the opposite side. Occasionally, from the small-
ness and great number of the processes, it is scarcely possible
to be sure as to the changes which occur. Here is a corpuscle
which appears to be graduall}' enlarging. Let us follow the
changes it will undergo. Already it covers a space three or
four times as great as before. Simultaneous!}' with this in-
crease of size, its form becomes irregular, and (as may be
ascertained by the fine-adjustment screw) its vertical measure-
ment is diminished, so that it now constitutes a thin layer
limited by a distinct contour. Soon, however, the circumfer-
ence thins out in certain directions, so that the edge can no
longer be discerned ; the only evidence of its existence in these
attenuated parts being that the field appears to be covered
with a granulous film.

In the layer of protoplasm we have now before us, some
parts are hyaline, or contain at most a few minute granules.
In others, you will notice, there are clear spots with well-de-
fined contours, which differ indefinitely in size, and have no
definite arrangement. Many of them are so clear that they
look like perforations. It is characteristic of them that they
are undergoing change, both as regards their relative position
and relative distinctness, some coming into view while others
are fading. These we call vacuoles. They are believed to be
cavities filled with liquid, the origin of which is due to the
fonstant commotion of the protoplasmic mass. If this be so,
it is easy to understand why it is that they appear and dis-
appear so rapidly. We next observe that at some part of the

20 BLOOD CORPUSCLES.

corpuscle (often, but not always, towards the centre) one or
more bodies may be distinguished of roundish, ovoid, or irre-
gular form, and tolerably distinct contour, somewhat less re-
fractive than the surrounding protoplasm, and containing one
or more granules. These bodies are commonly close together,
and arc called nuclei. The nuclei are usually invisible so long
as the colorless blood corpuscle is spheroidal ; when it spreads
out into a layer, they can be distinguished. But they can also
be observed when the lamina draws itself together into an irre-
gular clump ; and it may be then seen that they are subject to
continual change, both as regards form and relative position.

We now leave the corpuscle we have been hitherto studying
and observe another, which is roundish, and exhibits a very
few delicate processes. At present we see no nuclei. After a
time we notice that one of the processes suddenly becomes
longer and thicker, so that the corpuscle'is now club-shaped,
consisting of a tapering stalk ending in a knob. The stalk
incloses an oblong, compressed nucleus, and the knob two
such nuclei close together, the surfaces of both being shaggy,
with minute processes. We have not long to wait until the
body loses this form. A new process, towards which the two
nuclei tend, shoots out from the knob, at right angles to the
stalk. The knob becomes smaller in proportion to the growth
of the process, while the two nuclei gradually approach its ex-
tremity. The next change is, that each process lengthens out
in the direction of its axis into a filament, the two together
being of such a length as to stretch over the whole field.
These filaments spring from a small clump of granular proto-
plasm— the original knob above mentioned. Each filament
swells out at its end into a little mass, which, in the one case,
contains a single nucleus, in the others, two nuclei. Continu-
ing our observation, we notice that the clump at the junction
of the two filaments disappears, while the other masses, which
are now united \>y a straight thread of nearly equal thickness
throughout, get larger, and send out new processes. The
larger mass now creeps nearer the edge of the field ; the
smaller is drawn after it, but moves more slowly, so that the
hyaline thread which connects them gets thinner and longer.
But while we are watching it, the large mass undergoes
changes which are a repetition of what we before observed in
the original clump. A process shoots out from it at right
angles to the direction of the thread : into this process one of
the nuclei finds its way; it then stretches out into a filament,
wdiich is swollen at its extremity into a protoplasmic envelope
for the nucleus. Still later, we find that the filaments become
thicker and shorter; that the clumps between which they
stretch, again approach one another, until, in their confluence,
the original form reappears. A similar series of changes may

BY DR. KLEIN. 21

be witnessed in any corpuscle of the kind we have been
studying.

2. Granular Corpuscles. — Of the three kinds of pale cor-
puscles which, as before stated, are to be observed in the blood
of the newt, we have now to consider the granular cells. These
are larger, but much less numerous than the others, and are
distinguished by the large dark granules they contain. To
observe them we must make a fresh preparation, for they un-
dergo changes of form much more rapidly than the others.
The granular corpuscle is at first spheroidal. Very soon its
surface exhibits round and entirely hyaline prominences, into
which, however, granules appear shortly to find their way.
So long as the corpuscle presents this appearance, the only
changes of form observable consist in heaving movements of the
prominences. Eventualby, one of these suddenly shoots out
into a prong-like process, into which the granular mass of the
original cell flows. Soon the corpuscle throws out a second
similar process, into which the mass again gathers itself, and
in this way advances across the field, with more or less ra-
pidity. After this has gone on for a certain time the move-
ments change their type : the corpuscle lengthens itself out
into a thread, in which the movement of the protoplasm is
rendered visible by that of the dark granules which it contains.
The thread swells out at the end into a little mass, from and
towards which alternately the rolling motion of the granules
is seen to be directed. Often a granular corpuscle may be ob-
served to creep about among groups of colored blood-disks,
stretching out its process with the terminal knob, as if this were
a feeler. In other cases we may witness the whole series of
changes described in the preceding paragraph as occurring in
the ordinary form of colorless blood corpuscle ; the main
difference being that the transformations are accomplished
within shorter periods. Finally, it ma}' be noticed that in
granular cells, even when they are spheroidal, the nuclei often
show themselves as ovoid spaces free from granules. They
are, however, much more readily distinguished after the cell
has undergone changes of form.

3. Colorless Corpuscles of the third form. — In addi-
tion to the common colorless corpuscles and the granular cells
we have just had under observation, we notice a considerable
number of colorless elements of a different character. These
are of three kinds : (a) Small, well-defined bodies, resembling
nuclei, which retain only for a very short time the spheroidal
form which they had at first ; (b) larger corpuscles, consisting
of finely granular protoplasm, with jagged outline, containing
three or four distinct nuclei, which may be either roundish, or
flattened against each other, exhibit a double contour, and
contain a few fine nucleoli which arc relatively of a large size,

22 BLOOD CORPUSCLES.

so ranch so, that they often appear to be surrounded by a
narrow zone of protoplasm ; (<■) large masses of finely granular
protoplasm, which commonly are of irregular form, and in-
close bodies similar to the nuclei above described, varying in
number from five to twenty in each mass.1

Methods of Warming a Preparation. — As in our fur-
ther study of the blood corpuscles it will be necessary to em-
ploy artificially increased temperatures, we proceed to describe
the methods employed for applying heat to preparations whilst
under microscopic observation. These methods are of two
kinds. The first is used when we wish to subject the prepa-
ration for an indefinite period to an increased temperature, to
which it has been gradually raised ; the second when we wish
to warm it suddenly, but for a very short period. To accom-
plish the first of these objects, a very simple contrivance, shown
in Fig. 1, may be used. Take a cover-glass, and spread all
round the edge of its upper surface a thin layer of oil ; then
take another cover-glass of the same size as the first, place
on its centre the drop of the blood to be examined, and allow
it to fall on the glass previously prepared, edge to edge, with
the blood drop downwards. The drop will then occupy the
space between the two, inclosed by the layer of oil in such a
manner that it may be examined under high powers. The
preparation may then be readily lifted with the aid of a lancet-
shaped knife, and placed on the orifice of the copper plate (e).
The copper rod (g) is then gently warmed by means of a spirit-
lamp, a little cacao butter (or some other fat, the fusing point
of which nearly corresponds to the desired temperature) having
been previously placed on the copper plate, close to the prepa-
ration. As soon as the cacao butter begins to liquefy, the
flame of the lamp is diminished, or the lamp itself is removed
to a greater distance, until the heat communicated by it to the
plate through the rod is just sufficient to keep the fat from
solidifying. If it is desired to employ higher temperatures,
or to measure the temperature with greater exactitude, it is
necessary to have recourse to Strieker's warm stage.

Strieker's Warm Stage. — Of this there are two forms. In
one the mode of heating, and consequently of modifying the
amount of heat communicated, is that which has been already
described (see Fig. 2). From its simplicity it is well adapted
for the beginner, while it enables the more practised observer
to maintain any desired temperature within very inconsidera-
ble limits of variation. The other, in addition to the greater
exactitude which can be attained, has the advantage that, by

1 Free nuclei of colored corpuscles, which may be seen if the prepa-
ration has been subjected to pressure, must not be confused with these
structures.

BY DR. KLEIN. 23

its aid, it is possible to continue the observation for a long pe-
riod. It is this which is employed by Sanderson and Strieker
for the studjr of the circulation in mammalia. For our present
purpose we do not require the whole apparatus, so that it is
onlv necessary to refer to those parts of it which are shown in
Fig. 3.

In the employment of this apparatus several difficulties are
encountered. For instance, the temperature of the water re-
ceptacle is only in part controlled by the regulator. Then,
again, the temperature of the stage is subject to variation ac-
cording to the rate at which the water flows into and escapes
from it ; so that, if great care be not taken in the adjustment,
constancy cannot be relied on. Another practical difficulty
lies in the fact that the temperature of the water in the recep-
tacle is different from that in the stage, the rate of flow being
so inconsiderable that there is necessarily a great loss of heat
by radiation from the metal surface. If the stage be not fitted
with a thermometer, this difference of temperature may be de-
termined, once for all, by comparative measurements, so that
the true temperature of the stage can then be known at any
time by deducting the ascertained loss of heat, i. e., the ascer-
tained difference above referred to, from the temperature to
which the regulator is adjusted.

Method of varying the temperature rapidly. — In
connection with this apparatus, it is convenient to describe
the method employed for subjecting a preparation to sudden
alterations of temperature. With this view the following con-
trivance is used : A clip is placed on the tube leading from the
water receptacle (<7, Fig. 3), by means oX which the access of
warm water to the stage ma}r be interrupted. The end of the
escape-tube (D) is then allowed to dip into a vessel of cold
water. This done, cold water may be readily introduced into
the stage, so as to cool it suddenly, by suction through the
tube (C), which must be provided with a branch (not shown
in the figure) between the clip and the stage, for the purpose.
This, of course, at once lowers the temperature. To effect a
sudden rise, all that is necessary is to open the clip. For short
experiments, it is not necessary to have a water receptacle spe-
cially constructed for the purpose; a large flask, supported
over a lamp, and without a regulator, may be substituted for
it, provided that, in addition to the discharge-tube, a thermom-
eter is passed through the cork, in order that the variations of
temperature may be observed, and the application of heat mod-
ified accordingly.

Effects of Warmth on the Colorless Corpuscles. —
We now return to the study of the drop of newt's blood, in-
closed between two cover-glasses, with which we were occu-
pied. On subjecting the preparation to a temperature of 38°

24 BLOOD CORPUSCLES.

C, the first fact that we notice is that the movements of the
colorless corpuscles in general, and of the granular ones in
particular, art' much more active. We shall not, however, oc-
cupy ourselves at present with these, but shall direct our atten-
tion to the three kinds of corpuscles which we have included
in our third division.

On the warm stage we may observe in these bodies (which
differ only in size) two kinds of change. One of these consists
of alteration in the form of the protoplasm, from the surface
of which processes shoot out in all directions. This is more
particularly seen in the forms we have designated b and c.
In the form a, although the nucleus at first appears bare, it is
afterwards seen to be surrounded by a protoplasmic envelope ;
this may throw out a pointed process, which, after stretching
out to a considerable length, is retracted, to be succeeded by
others. If the preparation is kept for a length of time at 38°,
the elements of the form a undergo other remarkable altera-
tions. They become strongly refractive, lose their double
contour and sharplj'-defined aspect, and acquire a form which,
at first globular, subsequently exhibits constrictions; so that
they become in succession kidney-shaped, dumb-bell shaped,
and rosette-shaped, until they eventually assume a nodulated
aspect. In the course of the process it is common to observe
the furrows or constrictions forming, disappearing, and reap-
pearing repeatedl}'; but, sooner or later, they become more and
more distinct and complete, so that the body assumes the ap-
pearance of a clump of highly refractive minute globules. Con-
sidering the coincidence of the changes of form and aspect of
the nucleus with those which occur simultaneously in the cell,
it is scarcely possible to doubt the dependence of the former
upon the latter, especially if we bear in mind the concomitant
changes in optical properties. So that we must regard these
appearances as indicating that the nuclei take an active part
in the changes of form.

In the form c the cell-substance itself may be also the seat
of a process of division. In one instance at least I have, of
course after many hours of observation, witnessed the division
of a cell which originally contained five nuclei. The cell in
question in the first place exhibited a transverse furrow : this
became deeper and deeper, so that, eventually, two masses
were formed, united together by a neck, the smaller containing
two nuclei, the larger three. These nuclei had already under-
gone the process of cleavage above described. By the length-
ening, thinning out, and final rupture of the isthmus, the two
corpuscles came apart. In the larger of the two, which was
now exclusively observed, there appeared gradually two boss-
like prominences, each of which contained a number of small
bodies resulting from the cleavage of the nuclei. By the con-

BY DR. KLEIN. 25

striction of the base of each of these prominences it gradually
separated from the rest of the cell. One of them, after separa-
tion, sent out a process ; in the other, no alteration of form
could be observed. It is probable that the forms a and b are
the offspring of c.

On the warm stage, division can also be observed in the first
and second variety of colorless corpuscles. Thus, for example,
it sometimes happens that the process described only results
in actual separation by rupture of the filament. In other cases
a corpuscle undergoes division by a process of cleavage, pre-
ceded by the repeated formation, disappearance, and reappear-
ance of furrows. In all cases of real division it is to be
observed that the }'Oung cells produced exhibit very active
movements, changing thereb}' in form and place.

Colorless Corpuscles of Man. — The mode of examining
the colorless corpuscles of other classes of animals is similar
to that above described. It is, however, necessary to add some
observations as to the characters which these bodies present
in human blood. A drop of blood, taken from the finger, is
placed between two cover-glasses, as above described, and
examined on the warm stage at a temperature of 38° C. The
human colorless corpuscles are smaller than those of the newt,
and exhibit much less variety in their appearance. They are
either quite pale, or they contain a variable number of dark
granules. The movements are less active than those of newt's
blood, but sometimes are comparable with them. When they
are more active than usual, the mode in which their processes
are thrown out and retracted, and the characters of their pro-
gressive movement correspond witli the descriptions already
given. On one occasion I have observed movements which
were even more lively than those commonly seen in the newt,
and resembled those of rhizopods in the extreme rapidity with
which the successive protrusion of processes, and corresponding
interstitial fluxion of the protoplasm occurred. This happened
in the case of a patient suffering from hemorrhagic ansemia.

Feeding of Colorless Corpuscles. — We have now to
study the faculty possessed by the colorless corpuscles of
taking, by virtue of their amoeboid movement, solid particles
into their substance. For this purpose we emplo}^ either finely-
divided fatty substances or coloring matters. The subject is
of great interest in relation to the mode in which amoeboid
cells take in nourishment. To the histologist it is further of
Importance, as affording him a means by which to mark indi-
vidual corpuscles, so as to follow them in their wanderings
through the organism. The materials used are the following:
". Vermilion. Tins is prepared I13' prolonged trituration in
a half per cent, solution of common salt. b. Carmine. Car-
mine is dissolved in as little liquor ammonias as possible, in a

26 BLOOD CORPUSCLES.

small beaker, and filtered. Common concentrated (commer-
cial) acetic acid is then added with agitation, until a drop of
the mixture, when examined under a low power, is seen to con-
tain granules. If too much is added, the precipitate is not
fine enough. The latter is then to be separated by careful
decantation, and suspended in a half per cent, salt solution as
before. It is well to dilute the liquid with its bulk of serum
before using it. c. Aniline Blue is dissolved in common me-
thylated spirit, and filtered. Water or salt solution must then
be added gradually, so as to obtain a fine precipitate, the
resulting liquid being mixed with serum as above, d. Fresh
Milk.

If it is intended to watch the process of feeding, a small
drop of blood, to which one of the liquids above mentioned
has been added, is examined, either in the ordinary way, in the
case of amphibian blood, or on the warm stage if mammalian
blood is employed. If our object is merely to observe corpus-
cles already fed, the liquids in question may be injected either
into the jugular vein (of rabbits or guineapigs) or into the
abdominal vein (of frogs), care being taken to empio}' a suffi-
ciently large quantity. After 10-30 minutes, a drop of blood
may be taken for examination. (See Chapter VII., as to in-
jection into the veins, and Chapter VIII., as to the lymphatic
system.) Whichever plan is adopted, it is alike possible to
satisfy ourselves that the cells not only take in foreign bodies,
but that they also have the faculty of discharging them, and
further, that when one cell comes into contact with another, it
often gives up to it the solid bodies which it has itself before
ingested. In general, the tendencj7 to ingestion varies with
the activity of the amoeboid movement, for the first thing
observed is an adhesion, either of the surface of the central
part of the corpuscle, or of a process to the foreign body, fol-
lowed by a retraction of the adherent part into its substance.

Application of Liquid Reagents. — It is, in the first
place, of importance to ascertain what liquids can be added
without affecting the vital phenomena of the colorless corpus-
cles. Such are designated by the adjective indifferent, and
are those which are always to be used in the study of fresh
living tissues. For example, we may use fresh serum or tran-
sudation liquids, as also the aqueous humour of the eye, which
has the important advantage of being entirely free from formed
elements. The most commonly used indifferent liquid is the
half per cent, solution of common salt already mentioned,
which is of great value ; although, as may be readily under-
stood, it is not altogether without action on living tissues. In
the examination of blood, it is added as a preparatory step to
the addition of other reagents. With this view the solution
is dropped from a capillary pipette (Fig. 4) upon a slide; a

BY DR. KLEIN. 27

drop of newt's blood being then added to it and covered. It
is seen that the colorless corpuscles have undergone no mate-
rial change, but that, in some instances, their movements are
not quite so active. The colored corpuscles, which in our
previous examination we have disregarded, are now seen as
smooth oval elliptical disks, which, when looked at edgewise,
present an outline as if they were oblong rods. Those which
lie horizontally look, for the most part, like greenish-yellow
bodies of oval form; in some of which we can distinguish a
central elliptical nucleus. Soon, changes occur, in consequence
of which the color becomes unequally distributed, the margins
are more or less curved, or the surfaces marked with what look
like folds. These appearances are referable probably to a pro-
cess analogous to coagulation.

Method of Retarding Evaporation.— If it is intended
to keep a preparation of this kind long under observation, it
is necessary to add saline solution from time to time from a
pipette. If, however, as is often the case, it is of importance
to keep an individual corpuscle in the field, this method can-
not be employed without great risk of the object being carried
away by the stream. To avoid this result, it is a good plan
to place a drop or two of solution near each of two opposite
margins of the cover-glass. Ity these drops the liquid under
the glass is preserved from evaporation, because the space in
the immediate neighborhood of the margin is kept saturated
with moisture.

We may now proceed to study the action of other reagents
on blood already treated with saline solution. We use the
so-called method of irrigation. On one side of the cover-
glass a small strip of blotting-paper is placed, while the re-
agent is discharged from the pipette at the opposite edge.
When the paper has become saturated with liquid it is replaced
by another, and the process repeated, so that a constant cur-
rent is maintained through the preparation. If the colored
corpuscles are the special subject of study, it is best to wait
until they have shrunk, for we are then sure that many of
them will have had time to sink and adhere to the surface of
the slide. If this precaution is neglected, they are apt to be
swept away by the current.

Action of Distilled Water. — In blood preparations irri-
gated with distilled water, the movements of the colorless
blood corpuscles gradually cease. The inequalities, corre-
sponding to the processes, disappear, while the corpuscle en-
larges, and assumes the globular form. From one to four (or
even more) round vesicular nuclei come into view. Soon the
nuclei coalesce to form a single mass, also having a vesicular
character, which not un frequently exliibits a rotatory move-
ment within the corpuscle. The substance which surrounds

28 BLOOD CORPUSCLES.

the nucleus is pale. It contains numerous distinct granules,
which show active Brownian movement. It not unfrequently
happens, that a much-swollen spheroidal corpuscle, after re-
maining a length of time in its place without change, is torn
away from its attachment to the glass by the current, in which
case it may either divide into two masses, one < »f which con-
tinues adherent, while the other floats away, or it may float
away en masse, leaving behind it a long filament, b}' which it
is still connected with its original point of adhesion. By re-
newing the irrigation, the filament will probably be severed.
It is thus proved that the colorless corpuscle consists of a soft
viscous substance. The final result of the action of water on
the colorless corpuscles is always disintegration; the mass
suddenly disperses into the surrounding medium, all that re-
mains of the previously so active entity is a collapsed, form-
less clump, in which one or two motionless granules may be
seen.

In the colored blood disks, the first change is that their
surfaces become smooth, their contour becomes circular, the
nucleus rounder and brighter than before, the corpuscle paler
and paler, until its outline is scarcely distinguishable. Two'
phenomena are worth noticing before we proceed further.
The first is, that, at the commencement of irrigation with dis-
tilled water, it occasionally happens that, immediately their
surfaces have become smooth, the corpuscles suddenly assume
a rounder and smaller appearance, and are more intensely
colored: quickly returning, however, to the elliptical form,
and losing their color as before. The second will be explained
later: a colored corpuscle appears to have separated into two
parts, a pale elliptical disk and a yellow mass, occupying a
central, or, more frequently, an eccentric position within it,
from which colored processes often stretch out like rays
toward the periphery.

Strieker's Method. — There is another method of stiutying
the action of water on the colored corpuscles. Fortius pur-
pose wre require the warm stage (Fig. 2). A drop of water is
placed on the floor of the chamber, and on the middle of the
surface of the cover-glass a drop of blood, either pure or di-
luted with salt solution. The cover-glass is then inverted
over the chamber, the edges of which have been previouslj'
oiled, or surrounded with a ring of putty, so that it is air-
tight. By wanning the copper wire the water is made to
evaporate from the floor of the chamber, and becomes con-
densed on the under surface of the cover-glass. In this way
we are enabled to study the gradual action of water on the
corpuscles very advantageously.

Action of Salt Solution on the Blood Corpuscles of
Mammalia. — In mammalian blood which has been diluted

BY DR. KLEIN. 29

with salt solution, the naturally bi concave colored corpuscles
exhibit a remarkable alteration, which consists in their assum-
ing a form very similar to that of the fruit of the horse-chest-
nut. In those corpuscles which present their surfaces, the
processes which project from the margin look like the rays of
a star, while those which spring from the surface appear as
dark points. In such a preparation it is not difficult to float
away the colored disks altogether, by irrigating it immedi-
ately with salt solution. The colorless corpuscles sink very
rapidly, and stick to the glass, while the colored disks remain
suspended.

Let us seek for a field in which one or two colorless corpus-
cles only are to be seen. By discontinuing the irrigation, at
the same time replacing the bit of blotting-paper so as to with-
draw the fluid, we bring the cover so near the slide that it
compresses the corpuscles, which in consequence appear paler
and larger. The paper is now taken away, and salt solution
added at the opposite edge as before. The corpuscles at once
become smaller and more globular, and seem to contract; but,
immediately after, dilate again, as if they were relaxing. In
the resumption by the corpuscle of its original form after
compression, we have to do with a phenomenon which can only
be explained on the supposition that the colorless corpuscle is
elastic. The nature of the contraction and the subsequent re-
laxation lead us, however, to suppose that the contraction is,
at least partly, a result of the excitation produced by the irri-
gation with saline solution.

Action of Water on Mammalian Blood. — As regards
the action of water on the corpuscles of mammalian blood,
there is not much to be added to what has been said with re-
ference to newt's blood ; the colorless corpuscles discontinue
their movements, become globular in form, exhibit vesicular
nuclei and vibrating granules, and finally are disintegrated.
The colored disks lose their horse-chestnut form, become
smooth and pale, and eventual]}' disappear.

Action of Acids. — The general action of acids is so uni-
form that it is not necessary to refer separately to each. We
content ourselves with describing the action of acetic acid. A
special action of boracic acid will be noticed further on. The
final result of the action of acetic acid on the blood corpuscles
is the same, whether it is diluted or concentrated. The rapid-
ity witli which the changes take place is, however, different. It
is always better to begin with dilute acid. If a salt solution
preparation of newt's blood is, after the shrinking of the colored
corpuscles, irrigated with a liquid containing one per cent, of
the ordinary commercial acid, we observe, first, that the move-
ments of the colorless corpuscles cease, and that they enlarge
and display their nuclei as sharply-defined bodies, beset with

30 BLOOD CORPUSCLES.

granules. If the action of the acid 1ms been prolonged, each
corpuscle appears to consist of two parts — a distinctly gran-
ular mass, which immediately surrounds the nucleus, and a
bright transparent circle, with sharp outline, within which
that body is inclosed. The nuclei are furrowed in such a way
that their form is very variable, and, if the action has lasted
long enough, they look as if actually split into smaller par-
ticles. The colored corpuscles again become smooth, swell out
somewhat, become cellular in their contour, just as after the
addition of water, each showing an oblong granular nucleus,
which is at first smooth, subsequently uneven and rough.
Many of the blood disks return to their original elliptical form.
All eventuall}' lose their color, but possess, even when entirely
colorless, a much more distinct contour than those which have
been acted upon by water. Occasionally, it happens that the
nucleus becomes stained with coloring matter, and assumes a
yellow tint. In human blood, the colorless corpuscles exhibit,
after the action of acetic acid, the appearance of globular bodies,
in which two, three, or more small shrunken nuclei are visible.
The colored disks lose their stellate form and their coloring
matter, but their outlines are still distinct.

Action of Alkalies. — If a salt solution preparation is irri-
gated with an alkaline liquid, whatever be the source of the
blood used, the colorless corpuscles at first swell, and then
rapidly disappear. The colored disks also swell out at first —
those of mammalia becoming often what German authors have
designated napfformig (cup-shaped); eventually they lose
their color and disappear.

Action of Boracic Acid. — We have now to describe a
reaction which, especially in the blood of the newt, is of im-
portance, as serving to illustrate the intimate structure of the
colored blood disk. The action of a two per cent, solution of
boracic acid on the colorless corpuscles in general, and on the
blood disks of mammalia, does not differ from that of other
weak acids. If, however, a salt preparation of newt's blood, in
which the colored corpuscles have already sunk, is irrigated
with the solution in question, we observe that those bodies
swell and acquire a circular contour, showing, at the same time,
a pale oval nucleus. It is now seen that, as the disk grad-
ually pales, the nucleus becomes more and more spheroidal
and yellow, while, at the same time, it increases in size. At
first it is smooth, subsequently uneven. Here and there cor-
puscles are met with in which the yellow central body (zooid
of Briicke) is not round, but beset with processes which stretch
like rays towards the periphery. Occasional^', it can be made
out that the processes are withdrawn, so that the j'ellow centre
acquires a roundish form. The zooids eventually lose their
central position, and if the preparation is protected from evapo-

BY DR. KLEIN. 31

ration for a sufficient length of time, the observer is sure to see
man}' corpuscles in which the}7 lie, some parti}-, some entirely
outside of the outline of the pale disk. The latter (again fol-
lowing Briicke) we designate cecoid. Briicke teaches that the
zooid consists of the nucleus and the haemoglobin ; that it with-
draws from the cecoid which it previously, as it were, inhab-
ited, and collects itself around the nucleus, so as to form an
independent individual, capable of a separate existence. In
describing further on similar appearances observed during the
action of carbonic acid gas, we shall suggest another explana-
tion of the phenomenon.

Action of Tannin on Human Blood — Roberts's Re-
action.— The action of tannin on the colored corpuscles of
human blood resembles that of boracic acid on newt's blood.
When two per cent, solution of tannin is added to human
blood, the corpuscles, which have been already rendered star-
shaped by salt solution, acquire an even contour. Soon after,
a sharply-defined, yellowish-green, roundish body is seen, either
just within or at the margin of each corpuscle, or even out-
side of it, while the corpuscle itself has become colorless.

Action of Gases on the Blood. — For the study of the
action of oxygen and carbonic acid gas on the blood corpus-
cles, either of the movable stages represented in Figs. 2, 3,
and 16 may be used. Around the edge of the central chamber
we form an annular wall of putty. We then make on a cover-
glass a preparation of newt's blood, to which about half its
volume of distilled water has been added. The glass is then
inverted over the chamber (upon the floor of which a drop of
water has previously been placed) with the preparation down-
wards, so that its entire periphery presses evenly upon the
putty ring. The chamber is thus converted into an air-tight
cavity. In Fig. 3, two tubes (H, I), with India-r.ubber con-
nectors fitted to them, are shown, both of which communicate
with the chamber in such a way that when it is closed above
and below, a stream of gas passing in by the one escapes by
the other. By means of an apparatus in communication with
the tube H, the construction of which will be readily under-
stood from Fig. 5, the observer is able to fill the chamber at
will with carbonic acid gas or with air. This is accomplished
as follows: —

If the bottle containing hydrochloric acid is raised, the clip
n opened, and the India-rubber tube a shut between the teeth,
the carbonic acid, which is developed in M, after it has passed
through the wash-bottle V, flows into the chamber, and is dis-
charged by the tube b. By proceeding in this manner one
hand is left free, and can be used for adjustment. To inter-
rupt the current of gas, all that is necessary is to close N and

32 BLOOD CORPUSCLES.

to let down the bottle. The carbonic acid gas in the chamber
is easily replaced by air, by aspiration through the tube a.

Action of Carbonic Acid Gas. — The preparation having
been brought into focus, the gas is allowed to pass through
the chamber for a short time. At first, the only observable
effect is that the nuclei of the slightly smoother disks are more
distinct. If the carbonic acid is now replaced by air, the nuclei
again become indistinguishable. We have to do, therefore,
with a transitory coagulation of the substance surrounding
the nucleus. An excess of the gas brings the nuclei perma-
nently into view. If, however, we first add to our preparation
a quantity of water, sufficient not merel}' to swell the colored
disks, but to deprive them partly of their color, the result is
somewhat different. After a short action of the gas, the ap-
pearances are much as they have been already described ; but,
if an excess is admitted, bodies similar to the zooids above
described as produced by the action of boracic acid, come into
view.

Instead of the pale oblong nuclei, the areas of the decolor-
ized disks inclose relatively large, yellow, roundish bodies, both
the areas and the inclosed bodies being beset with fine gran-
ules. In those disks which have previously lost their color,
and are consequently scarcely visible, the nuclei become visi-
ble after the addition of excess of carbonic acid, as pale
granulous bodies, the disks themselves also containing nume-
rous granules. If we now replace the carbonic acid by air,
the corpuscles recover, in every respect, their previous aspect ;
those in which the zooids had come into view becoming smooth,
and of uniform color, so that neither nucleus nor granules can
be distinguished. Those disks which have lost their color by
the action of water become, as before, uniformly pale and in-
distinct. The experiment may be repeated several times. It
is not difficult to explain all these appearances by coagulation.

It is a very good plan, in order to study the action of car-
bonic acid on newt's blood, in all degrees of dilution, to
examine a salt solution preparation of such blood on the mov-
able stage (Fig. 2), which also serves the purpose of a gas
chamber. On warming the metal rod, water vapor is disen-
gaged from the floor of the chamber (into which a drop of
water has been previously introduced), and acts upon the cor-
puscles.

In order to study the action of carbonic acid on the colored
corpuscles of man, it is best to employ a drop of blood mixed
with salt-solution, taking care that the individual cells are as
much as possible separate from one another. If, as soon as
the corpuscles become horse-chestnut shaped in consequence
of the action of the salt-solution, the preparation is subjected
to the action of the gas, we at once observe that the acuminate

BY DR. KLEIN.

33

projections on the surface of the corpuscles become less marked
in consequence of the levelling up of the intermediate parts ;
and, although there are many which do not resume the bicon-
cave form, being still saucer-shaped, they all have even surfaces.
If the carbonic acid is replaced by air, the corpuscles again
become horse-chestnut shaped. This reaction may also be
witnessed several times in succession. The disappearance of
the stellate form may be explained on the supposition that a
spontaneously coagulated constituent is redissolved under the
action of carbonic acid. Colorless corpuscles show their nuclei
when acted on by carbonic acid, but are otherwise unaltered.

Action of Electricity.— If it is intended to subject blood
to the action of electrical discharges, or of the constant or in-
terrupted current, we place a small drop of blood on the slide
(Fig. 6) in such a position that, when it is covered, it spreads
between the two poles of tinfoil, which we connect by means
of either of the appliances shown in the figure with the secon-
dary coil of the induction apparatus.

According to Rollett, it is advisable, in using electrical dis-
charges, that the tinfoil points should be six millimetres apart.
The Leyden jar should have a surface of 500 square centi-
metres, and give a spark one millimetre long. If, then, the
discharges succeed each other at intervals of from three to five
minutes" the following changes are observed in the colored cor-
puscles of man. Firstly, the circular disks become slightly
crenate. This effect gradually increases, the corpuscles become
rosette-shaped, then mulberry-shaped, and finally, by the acu-
mination of the projections, horse-chestnut shaped. Later, the
processes are withdrawn, the blood corpuscle becomes round,
and, at last, pale. In the corpuscles of the newt and frog the
effects are not dissimilar. They become wrinkled and dappled,
but these appearances are very transitory, and they are again
seen to be circular and pale, while the nucleus becomes round
and sharply defined. Not unfrequently it happens that one or
more blood corpuscles coalesce before they lose their color, or
that (in amphibian blood) the nucleus is discharged while the
disk is still yellow. The effects produced by induction cur-
rents are altogether analogous to those ahove described. Un-
der the action of the constant current (a single Bunsen's cell)
the corpuscles next the electrodes undergo changes, which at
the negative pole correspond to the action of an acid, at the
positive, to that of an alkali. In a salt preparation of batra-
chian blood examined near the positive pole, the nucleus comes
fust into view, and then the corpuscles lose their color. In a
similar preparation of human blood in which the corpuscles
are horse-chestnut shaped already, they become smooth, lose
their color, and disappear.

The colorless corpuscles, when excited electrically during
3

34 BLOOD CORPUSCLES.

their amoeboid movements, assume the spheroidal form. Their
movements, however, are resumed as soon as the excitation is
discontinued. The motion is more undulating than before,
but soon recovers its former character. After repeated excita-
tion the corpuscles expand into lamina', but still exhibit
changes of form. Under the influence of successive shocks of
greater intensity, the colorless corpuscles swell out, their
granules exhibiting molecular movement, and finally disappear.

Blood Crystals. — In concluding this chapter, we propose
to give the most simple methods of obtaining crystals of luemo-
globin and hsemin for microscopic purposes, referring the reader
for more detailed information to Chapter XV.

Haemoglobin. — A large drop of blood is taken directly
from a living guineapig, and allowed to coagulate on a watch-
glass. We now add a small quantity of water, and then,
taking up the clot with the forceps, let fall on a glass slide
several small drops. As these drops evaporate haemoglobin
crystals of varying size shoot out from the edge, separately
and in bunches.

Another plan is to cut out the heart and great vessels of a
recently killed guineapig, placing them on a watch-glass in
saturated air for twenty-four hours. Then take some blood
from the heart by means of a capillary tube, and allow a very
small drop to fall into an equally small drop of water on a
slide. As it evaporates, crystals are formed as before. This
method does not answer with rabbit's blood.

Heemin Crystals. — The simplest method of obtaining
hsemin crystals is the following: A small quantity of dried
mammalian blood (human will do) is placed on a slide. A few
small crystals of common salt are then added, and a cover-
glass placed over. A drop of glacial acetic acid is then allowed
to enter from the side. On warming the preparation carefulty
until the greater part of the acid has evaporated, an immense
number of the reddish-brown crystals of hoemin are seen.

For a description of the corpuscles which occur in the lym-
phatic system, see the chapter treating of that subject. The
development of the blood corpuscles will be described in Chap-
ter VII.

BY DR. KLEIN. 35

CHAPTER II.

EPITHELIUM AND ENDOTHELIUM.

Under this heading are included the epithelium of the
mucous membranes, of the cornea and conjunctiva, and of the
integument, and the endothelium of the serous membranes.
The epithelium-like structures which are in relation with the
nerves of the various organs of sense will be examined in Part
II.

Ciliated Cylindrical Epithelium. — To investigate cili-
ated epithelium in the living state, a frog should be selected,
and its mouth opened with the handle of a scalpel. Then,
using either a lancet-shaped needle or the blade of a sharp knife,
we scrape from the projection in the roof of the oral cavit}',
corresponding with the floor of the orbit, a little of its epithe-
lial covering. This is transferred to a small drop of an indiffe-
rent fluid (half per cent, solution of common salt) on a glass
slide, slightly separated with needles, and covered in the usual
manner. In such a specimen we find not only masses of epi-
thelium in connection, but also smaller groups and single cells.
In the masses of epithelium we cannot distinguish quite clearly
the individual cells, but on the free border — on the coast, as
it were, of the epithelial island — we observe the exceedingly
lively movement of the cilia. In addition we see blood disks,
small round particles of protoplasm and granules driven quick-
ty along in the fluid ; and from these passing bodies we are
able to recognize the direction of the movement of the cilia,
an observation which could not otherwise be made, on account
of the extreme rapidity of that movement. In the smaller
epithelial groups we are able more easily to recognize the in-
dividual shorts-conical cells. These groups are in more or
less rapid rotation, the rotatory motion being due to the fact
that onlj7 one portion of their surface is furnished with cilia —
that, namely, which corresponds to the bases of the conical
cells.

Effects of Reagents on Ciliary Motion. — Dilute
Alkalies. — After some time we perceive that the cilia here
and there begin to strike more slowly, and, by-and-by, they
come to rest. In a specimen prepared as above described,
which has of course been prevented from becoming dry by the
occasional addition of a drop of half per cent, solution of com-
mon salt, if we choose a spot at which the ciliary movement

36 EPITHELIUM AND ENDOTHELIUM.

is either exceedingly languid or has ceased altogether, and
cautiousl}r allow a small quantity of a very delicate solution
of potash to act upon it by the irrigation process, we soon ob-
serve that the motion is renewed ; becoming equal in rapidity
to that seen in the perfectly fresh preparation. The restora-
tion of motion is not due to any special property of potash ;
nor can it be attributed to the influence of that reagent in dis-
solving coagulated material between the cilia, which might be
supposed to interfere mechanically with their movements.
This is proved bj' the fact that many other reagents act simi-
larly as stimulants of ciliary motion — e. g., distilled water, half
per cent, solution of common salt, dilute acetic acid, carbonic
acid, or the induced current (applied according to the method
described in Chapter I.). All these, if used with great care,
accelerate the movement in the first instance. The accele-
ration lasts only for a short time, and, in most cases, is quick-
I3* followed by cessation of movement, consequent upon the
destructive influence of the reagent used. After the addition
of dilute acetic acid (and still more rapidly with concentrated)
the bodies of the cells swell and become transparent, and their
nuclei well defined, in the same manner as after the addition
of water. The investigation of the respective actions of carbo-
nic acid gas and oxygen upon ciliary movement is a very im-
portant experiment. We make a preparation of the ciliated
epithelium from the throat of the frog, in a half per cent, solu-
tion of common salt upon a cover-glass, which is then placed
on a ring of putty over the gas-chamber of the movable stage
(Fig. 2). Into this chamber a drop of water has been previous-
ly placed to keep it moist, and if we now allow a stream of
carbonic acid to pass, we perceive, as has been already men-
tioned, that for a few moments the ciliary motion becomes
quicker, but, by-and-by, slower, until it finally ceases. On
now substituting atmospheric air (oxygen), we find that the
movement slowly recommences, and, before long, is quite as
active as before the passage of the carbonic acid. The experi-
ment ma}r be repeated several times with a like result, until at
last the motion can no longer be excited. Ox3'gen is there-
fore as essential for the continuance of motion in the indi-
vidual ciliated cell as for the maintenance of animal life in
general.

Study of Ciliary Motion in Situ. — To demonstrate
ciliary action on a membrane in situ, the most judicious plan
is to remove from a female frog or toad that portion of peri-
toneum which covers the cisterna hjmphatica magna, the so-
called septum of the cisterna. Or, instead of this, a portion
of the parietal peritoneum of the anterior abdominal wall of
the newt may be employed. In either case, the part removed
is to be quickly and carefully spread upon a glass slide with

BY DR. KLEIN. 37

needles (avoiding every kind of mechanical injury) in such a
manner that the peritoneal surface looks upwards : a drop of
half per cent, solution of common salt is then placed on the
under surface of the cover-glass, which is cautiously applied.
In such a preparation we find places in which a bird's-eye view
is obtained of the cilia in motion, as well as others, where, as
in the preparation from the throat of the frog, we see the same
in profile. The cells, which bear the cilia, are not cylindrical,
but form a pavement endothelium, the elements of which are
granular. We shall have occasion to return to these cells in
the description of the endothelium of the septum. The sto-
mata are almost always guarded by the cells above described.
If we are uncertain of the direction in which the cilia strike, or
if we wish to demonstrate this positively, we should transmit
through the preparation, by the method of irrigation described
in Chapter I., coloring matter, or some similar substance, in a
finely divided state, such as ground animal charcoal, cinnabar, or
Indian ink, suspended in half per cent, solution of common salt.
We shall then be able to recognize, from the direction in which
the particles are driven, the direction in which the cilia strike.

Forms of Ciliated Epithelium. — For the study of the
various forms of ciliated cells, we remove a mucous membrane
covered with these from a freshly-killed animal, and place
small pieces of it in a sherry-colored solution of bichromate
of potash. After they have lain in the liquid for twenty-four
hours or more, we scrape with a scalpel from the free surface
a little of the epithelium — place it on a slide in a small drop
of bichromate of potash solution or of common water, reduce
it to fragments with the handle of a needle and cover it. The
most suitable objects for such a studjr are the trachea of a
mammal, the bell-shaped extremity of the Fallopian tube of
the sow, and the mucous membrane of the mouth, throat, and
03Sophagus of the frog. By this mode of preparation the cells
are preserved very perfectly. In the long conical cells with
ciliated bases we have to notice the granular protoplasm which
composes the bod}', the bright basal border, the sharply-
defined ovoid nucleus, with its large single or double nucle-
olus ; the long filaments, simple or divided processes which
penetrate between the cells of the deeper layers, and finally
the cilia which pass out from the central protoplasm, perfora-
ting the basal border.

Besides these, we find intermediate forms of ciliated cells,
which are shorter and broader, and which run out into one or
two short, thick processes; and varying forms of spindle-
shaped cells, which, as we may convince ourselves, in large
flakes of epithelium, wedge themselves, by means of processes
of greater or less thickness, between the processes of the
ciliated elements. They possess, likewise, an ovoid nucleus.

38 EPITHELIUM AND ENDOTHELIUM.

Finally, there show themselves, here and there, long, conical
cells (goblet cells), which, like the first mentioned, run into a
Long process; and, in the thicker portion (Fig. 7«), are empty,
or contain only a very few granules. The ampullate, or flask-
shaped portion of these cells is bordered by a double-con-
tonred membrane, which, at the basal end. is open, so that we
have before us only the empty shell of the cell without the
basal lid. Among a number of such cells swimming about,
individuals occur in which the open ends of the goblets can
be seen, both obliquely and from the surface. In the deeper
and thinner part of the cell the protoplasm with the nucleus
is, in most cases, still present, as represented in the figure.
In a few examples part of the cell (Fig. lb) is torn off", so that
an empty funnel remains behind, in the extreme apex of which
a small bit of protoplasm remains. If we look over a series
of preparations we shall certainly find examples in which the
complete lid. or a portion of it, remains attached at one point
only of the circumference, and floats freely otherwise. The
appearances show that these goblet cells are nothing more
than products of changes which have occurred in the ordinary
conical ciliated cells. In the description of the epithelium of
the intestine we shall again have an opportunity of referring
to these cells.

Non-Ciliated Cylindrical Epithelium. — For the in-
vestigation of this form we use the epithelium of the papilla'
of the tongue of the frog, and that of the intestinal canal of a
mammal, either in the fresh condition or with the aid of re-
agents. From the dorsal surface of the frog's tongue a minute
portion is snipped with curved scissors, transferred b}- means
of a needle from the scissors on to a glass slide, and then,
either covered without addition, the glass being pressed lightly
down, or mounted in a drop of serum, or of half per cent, solu-
tion of common salt. The specimen must be examined with
high powers (as, e. (/., Hartnack's Xo 10 immersion). We see
the numerous, thin, conical papilla?, both from above and in
profile ; the latter especially at the borders of the preparation.
A papilla seen in profile exhibits on its surface a beautiful
mosaic of pale cells, composed of finely granular protoplasm,
marked off by sharp clear-shining lines of interstitial substance.
If we fix our attention upon the borders and apices of the
papilla?, we may convince ourselves that the mosaic is only the
surface view of the conical or cylindrical cells, which cover and
surround the papilla?. Here and there we may easily perceive
that these cells are coarsely granular, and that each contains a
clear oval nucleus. Such coarsely-granular cells increase in
number after the preparation has been mounted some time.
W may mention that the cylindrical cells around the bases of
the papilla1 are generally ciliated.

BY DR. KLEIN. 39

Epithelium of Villi of Intestine. — In the rabbit we
proceed as follows: The animal is killed, the small intestine
immediately opened, and from the borders (which then cnrl
outwards) we remove a small portion with curved scissors as
in the previous case. This is to be covered with the mucous
surface upwards. The villi seen exhibit, on their surfaces, a
regular mosaic of epithelium ; at their borders, where the epi-
thelium is in profile, it is seen to consist of regular cylindrical
cells. If the observation of the mosaic is continued for some
time, granular spherical bodies come into view ; at first singly,
but afterwards in numbers, which are raised above the general
surface of the cells, as may be learnt by using the fine adjust-
ment. These spherical bodies have escaped from the cylindri-
cal cells. We shall see that it is by this means that the goblet
cells already mentioned are produced. The epithelial cells on
the borders of the villi display distinctly the broad, finely-
striated border, which spreads over their ends like a cuticle.
Equally instructive specimens may be obtained from the intes-
tine of the cat, dog, guineapig, rat or hedgehog. The epithe-
lium of the villi ma}' be as successfully studied, while still
attached, in a preparation, mounted in serum, or half per cent,
solution of common salt. For more prolonged examination,
especially if we wish to study isolated cells, we put a piece of
intestine, cut from the rabbit, dog, or cat, into a sherry-yellow
solution of bichromate of potash, allow it to remain there for
one or more days, and make our preparation in the manner al-
ready described with regard to the trachea. In such speci-
mens we find not only numerous isolated cells, but also com-
plete villi, and parts of the same, on which the epithelium,
when its surface is viewed, resembles, as in the fresh prepara-
tion, a pavement of granular cells, each of which contains a
relatively large, sharply-bordered, and apparently round nu-
cleus. The lines of interstitial substance are sharp and dark.
At the edges of each villus the epithelial cells are cylindrical,
with finely-striated border. Each cell consists of granular
protoplasm, and contains a sharply-defined nucleus, in which a
distinct nucleolus is to be seen.

If we examine attentively the surface of a villus, or of a por-
tion of villus (especially in a preparation from the intestine of
the dog or cat, which has been allowed to remain in a solution
of bichromate of potash), we shall find, between the mosaic of
granular cells, roundish structures, either single or in small
groups, and with a diameter greater than that of the cells of the
mosaic ; these are quite clear in the centre, have a doubly-con-
toured membrane, and give the impression of vesicular'bodies.
If we search on the borders of the villi for a structure in profile
Corresponding to this surface appearance, we find between the
cylindrical cells, which are full of protoplasm, bodies of a bell-

40 EPITHELIUM AND ENDOTHELIUM.

or goblet-shape, containing in the part which is next the tissue
of the villus, a hit of protoplasm of variable size, refracting
light strongly; within this is included a compressed, nuclear

body. Amongst the isolated cells, also, we meet with nume-
rous goblet-shaped ones, which may be examined in various
positions. These cells are most numerous in the intestines of
the dog and cat, in which it often occurs in preparations which
have been kept in dilute chromic acid, or bichromate, that the
epithelium is almost entirely transformed into goblet cells. The
facts show that they are transformations of cylindrical epithe-
lial cells, and that they may either be produced spontaneously,
or, as more commonly happens, may be the product of certain
reagents.

Pavement Epithelium. — This variety is well known to
occur, chiefly as laminated epithelium, in the conjunctiva
corner, mucosa of mouth and pharynx of mammals, and in
the skin. In the urinary bladder of mammalia the epithelium
is not purely pavement, but is mixed with, and shades off into,
the cylindrical variety. We accordingly call it "transitional."
The epithelium of the frog's urinary bladder is a single layer
of pavement epithelium. That of the serous membranes, of
the membrana Descemeti, and of the iris, consists mostly of a
single layer of flat cells.

Fresh specimens of the epithelium of the mouth may be pre-
pared either with indifferent reagents or with very dilute solu-
tion of bichromate of potash ; but, if we wish to stud}' the
relation of the various layers of the laminated epithelium to
each other, it is needful to make vertical sections through the
superficial layers of the mucous membrane. To study the
forms of the various cells of the separate layers, we ma}' ob-
tain a thin shred from the surface of the tongue or gums of a
mammal by energetically scraping it with a scalpel. What is
removed is broken up with needles, and covered either in half
per cent, solution of common salt, or, what is quite as good, a
very weak solution of bichromate of potash. In the surface
layers of the epithelium, we find flat tablet-shaped cells, with
small, oblong, strongly refracting nuclei; the borders of these
cells are sharp and doubly-contoured. Their substance is
mostly clear, containing only a few granules, generally situated
in the immediate neighborhood of the nucleus. Their surface
is generally beset with irregular folds and furrows. If one of
these cells is seen edgewise it appears spindle-shaped, because
the thickness of the nucleus is greater than that of the cell.
Besides these we find smaller polyhedric pavement cells, which
consist of a nearly uniformly granular protoplasm, and possess
one, or very rarely two, roundish, clear, and sharply-define'd
nuclei, with one or two large granules — i. «., nucleoli — within
them. Finally, if we have scraped very energetically with the

BY DR. KLEIN. 41

scalpel, we meet with cells corresponding to the deepest layers,
which possess more of a cylindrical form, and contain an
oblong nucleus. Similar results may be obtained if we mace-
rate a portion of the mucous membrane in bichromate of pot-
ash solution.

To study the epithelium of the cornea in the fresh condition
we proceed in a somewhat similar wa}\ A frog is held by an
assistant, its nictitating membrane drawn down, and from the
anterior corneal surface a thin la3'er is scraped with a lancet-
shaped, or a cataract knife; the fragment removed is then
broken up and covered in aqueous humor, or in half per cent,
solution of common salt. Here we find not only isolated cells,
but connected masses of epithelium arranged in layers. By
means of the fine adjustment the individual cells of these layers
may be studied ; but we shall not at present occupy ourselves
further either with the epithelium of the anterior corneal sur-
face, or with the membrana Bescemeti, since they will be fully
described when we treat of the cornea.

The epithelium of the skin (epidermis), and especially of the
elements of the stratum corneum, may be readily brought under
investigation as follows : A small shred is raised from either
the back, or palm of the hand, and covered in water ; reagents
which act upon horny structures, as, e.g., dilute and concentrated
acids and alkalies, may then be added. For the study of the
cells of the Bete Malpighii, or portion of the epidermis which
lies upon the corium, or true skin, the pointed condylomata so
frequentl}r met with, are peculiarly suitable. Cancroid tumors
are equally to be recommended. We place these structures in a
sherry-colored solution of bichromate of potash, and let them
macerate ttiere for several days. At the end of this time we
scrape off a small portion of the epithelium with a scalpel,
transfer it to a drop of water or bichromate solution on a slide,
break it up with a needle-handle, and apply the cover-glass as
usual. In such preparations we meet with very striking forms
of the so-called ridged cells, i. e., polyhedric cells whose surfaces
are covered with ridges and intermediate furrows, and whose
borders therefore, when seen in profile, appear as if serrated.
Wherever two such surfaces are applied to each other, the
ridges of the one fit into the furrows of the other, the line of
adaptation being a zigzag one. The granular protoplasm of
the individual cells, the sharply-bordered, ovoid, single or double
nuclei, which sometimes lie in a vacuole in the protoplasm, and
the nucleoli are clearly seen. Very interesting are the nume-
rous cells in various stages of division. These are represented
by the following forms: 1. Ceils containing a single nucleus
constricted into an hour-glass shape, with two nucleoli. 2.
Cells which possess two nuclei lying quite close to each other,
each with a nucleolus. 3. Cells with two nuclei lying at a

42 EPITHELIUM AND ENDOTHELIUM.

distance from each other. Amongst those of the first form,
some possess a shallow constriction ; in some the constricting
furrow is so deep, that the two portions of the cell are con-
nected by a short bridge, which in others is reduced to a slender
filament. The division of the nucleus is not always into two;
it is not uncommon to find cellswhose nucleus is rosette-shaped.
Further, we meet with numerous huge, flat cells, belonging to
the most superficial layers, in whose interior is a vacuole of
variable size, and shut up in this a young brood of from two
or three, to eight or ten cells. This variety of proliferation is
known as endogenous.

Epithelium of the Bladder. — As we have already re-
marked, the epithelium of the mucous membrane of the
urinary bladder of mammals is laminated and transitional. A
thin shred from the internal surface of the urinary bladder
of the rabbit, guineapig, dog, or cat, in the fresh state, may
be covered in half per cent, solution of common salt in water,
or in a bichromate solution. If the bladder has been kept from
twenty-four to forty-eight hours in the latter liquid, specimens
are obtained in which the following appearances may be ob-
served: Firstly, large pavement cells, bounded by a double
contour, and consisting of a uniformly granular protoplasm
which contains from two to five clear vesicular nuclei, each
with a double contour, and possessing a large, shining nucleo-
lus. In these pavement cells we see that, as a rule, only one
of the surfaces is even ; that, namely, which corresponds to
the free surface of the mucous membrane. Of this we may
convince ourselves by examination of connected masses of
epithelium or of vertical sections. The deep surface of each
cell is marked by depressions with prominent ridges between
them, and is that by which it is in contact with the club-
shaped or conical cells of the subjacent layer, so that the
rounded summits of the latter fit into the depressions of the
former. The cells of the second layer consist of a uniformly
granular protoplasm, have a double contour membrane, and
each contains an oval vesicular nucleus, and within this a
shining nucleolus. They possess simple or divided processes
of varying length and thickness. Among tliem there are
spindle-shaped cells which insinuate themselves between the
processes of the former layer.

To study the single layer of epithelium of the urinary
bladder of the frog, consisting as it does of large granular
cells, we spread upon a slide a portion of this organ with the
free surface upwards, and cover it with a piece of thin glass,
on the under surface of which a small drop of half per cent,
solution of common salt has been placed. Wherever folds
occur in the mucous membrane the epithelial cells show them-

BY BR. KBEIN. 43

selves in profile ; where this is not the case, the surface view
alone is obtained.

The Endothelium of the Serous Membranes.— The
endothelium of the serous membranes, as well as that of the
membranes related to them (for example, those which cover
the posterior surface of the cornea and the iris of mammals,
and the septa and walls of the lymph sacks of amphibia), is
well known to consist of flat cells, the substance of which
appears homogeneous when fresh, but becomes finety granular
by the action of certain reagents. The nucleus is generally
single, and occasions a projection of the free surface. It is
usually oval and clear, and sometimes contains a nucleolus in
its interior. Some cells contain two nuclei. By reason of
the homogeneity of its protoplasm, the endothelium of the
serous membranes is, with difficulty, brought into view in the
fresh state. In folds, indeed, of a serous membrane which
has been spread out upon a slide in a solution of common salt
or in other indifferent reagents, the individual cells may be
recognized in profile. Again, on the omentum, and on certain
parts of the pleura of many animals, there occur bodies
(which were first described by Sanderson as structures re-
sembling lymph follicles, and which we shall describe at
length in another place), the endothelium covering which may
be seen in the fresh state to consist of granular cells which
are polyhedral, but rounded on their free surfaces, each in-
closing a rounded nucleus. On the fenestrated portion of the
omentum, also, spots are met with where granular cells of the
same form occur in groups, the elements of which appear to
sprout out as it were from a common stem. Cells of the same
kind are also found on the abdominal surface of the centrum
tendineum of the diaphragm, over the structures to be after-
wards described as lymph channels. Further, as we have
already had occasion cursorily to remark, there occurs, in the
mesentery and parietal peritoneum, and in the female of Bufo
and Rana, on the septum separating the cisterna lymphatica
magna from the peritoneal cavity, between the non-ciliated,
homogeneous, large and flat endothelial cells, others which are
ciliated, granular, small, and polyhedral, occuring either
singly or in groups. To bring these into view we have simply,
as we have said, to remove a portion of the membrane in
question from the recently killed animal, to spread it out
carefully upon a slide witli a couple of needles, avoiding all
unnecessary dragging, and to cover it quickly before it be-
comes dry, with a cover-glass, on which a small drop of
half per cent, solution of common salt, serum, or aqueous
humor has been placed.

The Silver Method. — The best method, however, and the
one most frequently employed for exhibiting endothelium, is

44 EPITHELIUM AND ENDOTHELIUM.

that of coloring by means of a solution of nitrate of silver.
This method consists in bathing the fresh membrane, which,
of course, has not been allowed to conic into contact with
blood or any injurious tluid, in a quarter or half per cent, so-
lution of nitrate of silver. After immersion in this for a few
minutes, it is washed out in ordinary water, which must be
renewed as often as it becomes turbid, and is then exposed to
the light until it assumes a brownish color. The portion of
membrane thus treated is spread out upon a glass slide and
covered, a small drop of glycerine having been previously
placed on the under surface of the cover-glass. On superficial
examination a system of dark lines is seen, which bound clear
spaces of various forms and sizes corresponding to the indi-
vidual endothelial cells. Hefore mounting such a portion of
membrane in glycerine, after having colored it with silver, Ave
may place it for a short time in very dilute ammoniacal car-
mine solution (to which, however, two small drops of acetic
acid have been previously added), and then wash it in slightly
acidulated water. We shall then find, on mounting the speci-
men, that nuclei appear in the spaces above mentioned : these
are sometimes central, but more often to one side, and are ob-
long in form. According to the duration of the action of the
carmine solution, and to its strength, they are more or less
intensely colored. By a modification of the silver method we
may demonstrate, not only the nuclei and dark lines, but also
the cell substance of the endothelia. This method always
succeeds with the endothelium which lines the lymph sacs of
the frog, and with that of the abdominal side of the diaphragm:
sometimes also with the endothelium of other serous mem-
branes. If we allow the membranes mentioned to lie for a
longer time (ten to fifteen minutes) in a half per cent, nitrate
of silver solution, and then simply wash them in water, and
mount them in glycerine after they have acquired a browrn
color, we shall be able to recognize, after an interval of from
twelve to twenty-four hours, or often even earlier, the sub-
stance of the endothelial cells as a 3'ellow or dark brown pre-
cipitation surrounding the clear oval nucleus. In preparing
specimens with silver it is in general much to be recommended
to mount the objects in glycerine, as soon as they have assumed
a brownish tint, and not to leave them exposed to the light for
an unnecessarily long time, otherwise they are apt to lose their
beauty and clearness, from the occurrence of dark precipitates.
In man}' parts of silver-colored serous membranes a peculiar
arrangement of the endothelium is observed, which consists in
the existence of dark or clear spaces of various forms, around
which the cells are set in a radiating manner. Each of these
small apertures occurs at the point of junction of three or
more endothelial cells, the interstitial lines of which radiate

BY DR. KLEIN. 45

from the aperture. Such an arrangement we find on the por-
tions of the abdominal side of the diaphragm, which corre-
spond to the so-called lymph channels, on certain parts of the
mesentery, and very abundantly in the pleura and omentum
on the structures already mentioned as resembling lymph fol-
licles. They are distinguished by the name of stomata, and
are looked upon as the recipient openings of canals which be-
long to the lymphatic system. In the case *of many of these
cells this has not yet been proved ; some of them have even
been regarded as small endothelial portions of larger cells ;
while others give the impression of being accidental forma-
tions. Of such openings, or stomata, those that occur on the
septum of the disterna lymphatica magna of the frog may
serve as the type. If we cut out this membrane from a frog
or toad, spread it out and mount it in a solution of common
salt, or in serum, or if instead we first color it in silver and
then mount it in glycerine, we shall find a proportionately
large number of roundish or oblong openings between large
radiating endothelial cells. These discontinuities represent
the openings to short canals, which pass through the mem-
branes and connect the abdominal cavity with that of the
cisterna lymphatica magna. These openings are bordered by
small granular cells, the convexities of which project into
them. They are compactly arranged together, and each pos-
sesses a roundish nucleus. If the spreading out of the speci-
men has not been accomplished with sufficient care, or the
membrane is too much shrunk, we miss the above-mentioned
regular openings, and there appear instead only groups of
small roundish cells — i.e., the openings are collapsed, and the
cells which line them have approached each other, so as to
come in contact. The nature of the small bodies which pro-
ject in the interior of the stomata has been disputed. It has
been believed that they are nothing more than the nuclei of
the large radiating endothelial cells which surround them.
But, as we ma}T convince ourselves both in fresh and in silver
preparations, they are really endothelial cells seen in profile,
which line the apertures. In female frogs and toads these
cells are provided with cilia. In the chapter on lymphatic
vessels we shall have an opportunity of making several addi-
tional remarks on the stomata.

We shall, in conclusion, endeavor to show that the lines
which are brought out by nitrate of silver in the serous mem-
branes are caused by precipitations for the most part in the
albuminous substance which connects the cells, and not merely,
as many authors believe, in an albuminous fluid which col-
lects between their surfaces. A serous membrane prepared
from an animal just killed may be spread upon a cork plate
and rinsed with one per cent, solution of sugar, or with a very

46 CONNECTIVE TISSUES.

dilute solution of glycerine, may even be brushed with a camel-
hair pencil moistened with water (of course not too vigorously),
without preventing the occurrence of the silver lines. Again,
in a section prepared from :i fresh mucous membrane, with
laminated pavement epithelium, which section has been colored
in silver, the silver lines corresponding to the borders of the
individual cells are distinguishable throughout all the layers.
Farther, silver lines corresponding with the borders of the in-
dividual muscle cells are met with in anstriped muscular tissue
which has been colored in silver, as, e.g., in the muscular coats
of arteries. These facts justify the assumption that the silver
lines are caused by precipitations in the albuminous intersti-
tial substance which bounds and separates the individual
cells.

CHAPTER III.

CONNECTIVE TISSUES.

Under this heading we include the fibrous tissues, with the
cellular elements which they contain, the elastic tissues, carti-
lage, and bone.

Fibrous Tissue. — Fibrous tissue consists of delicate gela-
tigenous fibres, which are connected by an interstitial albumi-
nous substance. The fibres form bundles of various thickness,
which either have a parallel arrangement, as in tendons and
fascia? ; or form a meshwork by the spliting and reunion of
neighboring bundles, as in the omentum, the submucous and
subcutaneous tissue; or, finally, have a felt-like arrangement
in which the bundles cross each other, or twist round one
another in the most complicated manner, as in the skin and
mucous membranes. Fibrous tissue may be studied in the
fresh state, or after maceration, or in hardened preparations.
To examine the tissue in the fresh state it is best to make a
preparation of a tendon \>y teasing. A small tendon (such as,
e. g., one of the extensors of the toes) having been cut out from
a recently killed frog or rabbit, is placed from ten to fifteen
minutes in a five to ten per cent, solution of chloride of sodium,
whereby the splitting of the tendon is considerabl}7 facilitated.

Process of Teasing. — In making preparations by teasing,
the following practical rules must be attended to: A very small
portion must be used; this must be placed on the glass in a
drop of the liquid to be employed, which must also be small,
for if in too great quantity the particles teased out, swim away

BY DR. KLEIN. 47

in the liquid, and lire difficult to seize upon with the needle.
On the other hand care must be taken, as the liquid evaporates,
to add more, so as not to allow the prepn ration to become dry.
In the preparation of tissues which consist of several parallel
bundles, such as nerves, tendons, or muscular tissue, our object
is to divide the fragments in the direction of the fibres into
smaller and smaller portions. Even when the tissue consists
of elements which tend in no particular direction, it is still
desirable to follow one direction in teasing — the object being
best attained by first fixing the fragment with one needle, then
piercing it with the other held in the opposite direction, and
finally drawing the two apart. It is further noteworthy that
the teasing must be performed on the centre of a slide, and
limited within an area which is not larger than the cover-glass.
The drop of fluid in which the preparation is to be mounted
should be placed on the cover-glass, which must then be in-
verted upon it. As the liquid evaporates it must be renewed
from time to time.

Action of Acetic Acid on Fibrous Tissues. — In a
teased preparation of tendon in salt solution, bundles of very
fine homogeneous-looking fibres are seen. If the preparation
is irrigated with weak acetic acid the bundles are seen to swell
out, become homogeneous, and completely disappear. If con-
centrated acid is used the effect is more rapid.

Areolar Tissue. — In a portion of fresh mesentery (of a
frog or of a small mammalian animal) spread out on a glass
slide and mounted in salt solution, we have the shining wavy
bundles forming a felt-work. In the omentum or pleura of a
guineapig or of a cat, prepared in a similar way, the arrange-
ment is that of a meshwork. From each larger bundle we see
several smaller ones splitting off, and then meeting with simi-
lar ones which are branches of other larger bundles in the
neighborhood. (See Fig. 8.) According to the abundance of
these collateral or secondary bundles, and the way in which
they run, the meshes vary in size and form, being round, rhom-
bic, or oblong.

Effect of Maceration. — For the purpose of macerating
fibrous tissue, ten per cent, solution of common salt, lime water,
baryta water, or solution of permanganate of potash may be
used. By all these reagents the interstitial albuminous sub-
stance is dissolved out, so that the bundles split into their con-
stituent fibres. All that is then necessary to display them is
to prepare a small fragment with needles. Diluted bichromate
of potash solution may also be used, but its action is very slow.

Elastic Tissue. — Elastic tissue is characterized specially
by the facts that the elementary fibres of which it consists do
not swell in acids, that they do not yield gelatin in boiling,
and that in general they are not united into bundles, but occur

48 CONNECTIVE TISSUES.

as sharply defined threads which run an isolated course, some-
times straight, sometimes contorted, or even spiral. By repeated
bifurcations and fusions of the branches again with one another,
they form a network. These facts may be demonstrated very
advantageously in a serous membrane, particularly in the meso-
colon of the rabbit, or in that part of the parietal peritoneum
of the same animal which lies on either side of the lumbar ver-
tebra. In both of these situations the elastic fibres are very
strongly developed. If preparations of these or similar mem-
branes are treated with acetic acid, the bundles of common
connective tissue disappear, so that the network of elastic
fibres becomes prominent.

To show the elastic fibres of the ligamentum nuchx, the best
way is to make preparations by teasing a portion of that of
the ox, in salt solution, either in the fresh condition, or after
maceration for a day or more in sherry-colored solution of
bichromate of potash. In either case we have before us thick,
solid, shiny cords of homogeneous substance, which branch
dichotomously, uniting by their branches so as to form a net-
work. The individual fibres, however, run mostly in one direc-
tion, and are so close to one another, that, on superficial exami-
nation, they exhibit the appearance of a reticular arrangement.
Such fibres as happen to be separated from the rest are often
rolled up like a watch-spring.

The dichotomously-branching elastic fibres of the pulmonary
substance can be shown, either by teasing fragments of fresh
lung (an operation which requires an immense deal of patience),
or in sections of fresh lung hardened by freezing, as will be
afterwards described. The elastic so-called fenestrated mem-
branes which exist in the tunica intima of the large arteries
may be demonstrated as follows: A part of the aorta of a rab-
bit or guineapig, having been cut out, is pinned down on a flat
cork with the internal surface upwards. The membrane having
been fixed at a certain point with a needle, the intima is raised
up close to the latter with sharp forceps, and then shreds as
long as possible are stripped off — a process which requires no
remarkable skill. Any one possessed of the requisite dexterity
may then strip off thin lamella from the deep surface of these
shreds ; these may be at once mounted, and are so thin that
the fenestrated membrane can be seen at the edges without
further preparation. If this does not succeed, the student
must content himself with teasing out the shreds first obtained.

Finally, a network of elastic fibres can be shown very beauti-
fully in the vocal cords of the frog. To any one who is suffi-
ciently acquainted with the general anatomical relations of the
parts, it is not difficult to remove those structures even from
the living animal. The easiest way is to place the vocal cord
for a few minutes in dilute acetic acid, and then to scrape off

BY DR. KLEIN. 49

the epithelium with a lancet-shaped needle— a process which is
much facilitated by the previous steeping in the acid. The
preparation is then mounted in glycerin.

Cellular Elements of the Connective Tissue. — These
are either amoeboid — i. e., migratory cells ; or branched — i. e.,
fixed cells ; the latter being distinguished further by the union
of their branched or simple processes, so as to form networks
of various densities.

Amoeboid Cells. — These are to be found in every form of
connective tissue. Normally, the}' occur only in small num-
bers, and are irregularly distributed; but, in inflammation,
they are numerous in proportion to the intensity of the process,
their multiplication being sometimes scarcely observable, while,
at other times, they are so numerous as to fill up the tissue.
Two kinds may be distinguished : the cells of the first form
entirely resemble the colorless blood corpuscles — i. e., they con-
sist of finely granular protoplasm, contain two or more nuclei,
exhibit amoeboid movements, and are similarly affected b}r re-
agents ; while those of the second form are large, coarsely
granular cells, which, like the granular cells of the blood, are
characterized by the rounded contour of their processes. The
former are to be found in every connective tissue, but the latter
are more common in the subcutaneous and submucous tissue,
in the intermuscular connective tissue, in the mesentery, in the
neighborhood of bloodvessels, in the septa of the subcutaneous
lymph sacs of the frog or toad, and in the neurilemma of the
larger nerve trunks of the frog. The two forms graduate into
each other.

The method of studying these cells in the living condition
consists simply in spreading out thin shreds of connective tis-
sue on a glass slide, and mounting them in indifferent liquids.
Where the integument is loose, as in the neck of mammalia, etc.,
it is easy to effect this, by first making a slit in the skin, and
then, with curved scissors, snipping away a thin lamella of
subcutaneous tissue. In the frog, the tongue ma}' be drawn
out and fixed by an assistant, while the operator snips out a
portion, so as to obtain a cut-surface, from which a thin la-
mella can be readily taken, as above. In either case the lamella
must be spread out, without loss of time, and with as little dis-
placement as possible, on the slide, and mounted in humor
aqueus or fresh serum. Blood corpuscles which exist on the
surface of the preparation do not interfere with the object, be-
cause the amoeboid cells are to be found in the interstices of
the clear transparent fibrillated mass of fibrous tissue. It is
somewhat more difficult to demonstrate the migratory cells of
the normal cornea. The method is as follows: A frog is held
by an assistant in such a way that the bulbus oculi is tense.
The membrana nictitans is then drawn back, and the bulb pene-
4

50 CONNECTIVE TISSUES.

trated with a cataract knife, just as in the operation for cata-
ract, at the limbus conjunctivae next the inner canthus. The
point of the knife is advanced until it approaches the limbus
of the opposite side, without puncturing it, and is then carried
outwards and upwards, so as to form a 11a}), consisting of the
upper half of the cornea. The extreme edge of the flap must
then be seized with the forceps, while the lower half of the
cornea is cut away with the aid of scissors curved in the direc-
tion of their edge. The cornea is next transferred to a drop
of humor aqueus (previously obtained by puncturing the oppo-
site eye) and spread out on the glass slide with the anterior
surface uppermost. In order to avoid folds, it is desirable
to make two or three radical incisions. The preparation is now
covered and inclosed in oil. If it is desired to study the mi-
gratory cells on the warm stage, the preparation must of
course be mounted between two cover-glasses, as before di-
rected.

If a cornea is thus prepared with great care, nothing is to
be seen excepting that a few pale lines of interstitial substance,
referable to the anterior epithelium, may be distinguished where
the membrane is folded. No other optical differences can be
made out. If the individual epithelial elements can be distin-
guished, this affords proof that the object has been injured in
preparation. Notwithstanding its homogeneity, it is possible
(with the No. 10 immersion objective of Hartnack) to find out
the upper and under surfaces of the cornea by means of colored
blood corpuscles, pigment, granules, or retina-elements which
may happen to be in contact with them. As time goes on, the
interstitial lines of the anterior epithelium come into view. If
we then adjust the microscope so as to bring into view the
most superficial layer of the propria, a few corpuscles of more
or less irregular form can be detected, each of which consists
of almost hyaline protoplasm, and contains a nucleus of ir-
regular form, apparently finely granular. If one of these cor-
puscles is watched carefully, it is seen that changes of form
take place, both in the protoplasm and in the nucleus. The
corpuscles throw out processes and retract them, and even per-
form a certain amount of locomotion. The nuclei become con-
stricted or compressed, and again resume their original form,
to undergo similar changes. By and by similar corpuscles
become visible in the depth of the cornea. On the warm stage
the movements are naturally more active. (See Chapter
XIY.)

If a preparation is made in humor aqueus of the fresh peri-
toneum (particularly the omentum) of the frog or of a mammal,
or of a septum of a subcutaneous lymph sac of the former, in-
numerable migratory cells are seen, especially in the neighbor-
hood of the vessels, which present transitions between small

BY DR. KLEIN. 51

pale corpuscles and large granular ones, all exhibiting distinct
amoeboid movements. But the best place for observing these
bodies is the tail of the tadpole. If a portion of the tail is
taken from the thin membranous part, and mounted in half
per cent, salt solution, migratory cells are to be found every-
where, consisting of finely granular protoplasm, and displaying
extreme^ active movements.

With reference to the g?-anular corpuscles it is not necessary
to add much to what has already been said. Among the best
examples are certain coarsely granular elements, which occur
in the intermuscular connective tissue of the frog. If the
transparent membrane which separates the muscles of the thigh
of the frog is spread out and examined in an indifferent liquid,
it is found that,besides active migrator}7 cells, there are coarsely
granular elements possessing oblong nuclei of the most various
forms, which move very sluggishly. Perfectly similar bodies
occur in the sheaths of large nerves of the frog. Another
situation for studying these cells in great numbers is the tongue
of the same animal. A living frog having been secured in the
supine position, its mouth is opened and the tongue is drawn
out by its two cornua. Thin shreds are then snipped from the
substance of the organ (the epithelium having been first re-
moved in the same way) and covered in fresh serum. In a
preparation thus made, an immense number of large coarsely
granular cells appear, presenting the most grotesque forms.
(See Fig. 9.)

Branched Cells (Connective Tissue Corpuscles). —
These bodies are flattened cells, consisting of finely granular
protoplasm: each contains a nucleus, which is also, for the
most part, flattened and oblong. The}7 possess a greater or
less number of processes ; and b}r these, which are sometimes
branched, sometimes single, they are in continuity with each
other, so as to form a network. In some connective tissues
the processes exhibit a more or less regular relation to the
body of the corpuscles ; in others, they are so short that the
corpuscles are almost in contact with each other, being sepa-
rated by scarcely any interstitial substance. In preparations
made in the way already recommended for the demonstration
of amoeboid cells of the subcutaneous connective tissue of the
rabbit, bodies are also found which are distinguished from the
others by their very irregular placoid form, greater size, and
hyaline appearance, as well as by the possession of oblong
nuclei. These cells contain very few granules, and those
mostly in the neighborhood of the nucleus. At first sight
these placoids seem to have only short projections, but, under
high powers, they are found to possess numerous long hyaline
radiating processes.

52 CONNECTIVE TISSUES.

Fixed Corpuscles of the Cornea.— In a cornea prepared
in the manner previously described, it is possible to recognize
the network of pale branched corpuscles at all depths, after
some time has elapsed. The}' ma}', however, be more distinctly
shown with the aid of certain reagents. p;irticularl3r wood
vinegar, nitrate of silver, chloride of gold, and some other
metallic salts. Of these, the first is now laid aside in favor of
the others. In preparations obtained by stripping off shreds of
a cornea (of the rabbit or frog), which has been macerated for
twenty-four hours in wood vinegar, the corpuscles are seen as
large flattened cells, consisting of granulous protoplasm, com-
municating with one another by processes. If vertical sections
are made of such a cornea, the cells seem to be spindle-shaped ;
but, if the section is made obliquely, it is found that the cor-
puscles appear the more flattened and the more branched, the
greater the obliquity of the section. This fact proves that the
corpuscles are flattened in planes parallel to the surface, and
that the processes also stretch out in similar planes.

Treatment of the Cornea with Nitrate of Silver. —
Nitrate of silver is used both in substance and in solution. In
substance it may be employed in two ways: a. The centre of
the cornea of a frog, which is held by an assistant in the
manner previously described, is firmly cauterized with a pointed
stick of lunar caustic. One or two drops of salt solution are
then allowed to flow over the cornea to decompose the excess
of nitrate of silver. About an hour after the cauterization,
the cornea is excised in the manner directed in p. 49, washed
in water for several minutes, and the surface of the slough
cleansed by pencilling it lightly under water. In the case of
the frog's cornea, the central cauterized part may be cut out
and mounted in gbycerin at once; but the rabbit's cornea is so
thick that it is necessary to split it into layers, with the help
of fine pointed forceps. If the preparation has been exposed
to daylight, clear spaces are seen on a brown, yellow, or dark
ground, which communicate with one another by clear channels,
either branched or single. These correspond in form and
configuration with the network of corpuscles above described.
This signifies that we have before us, as will be more com-
pletely shown afterwards, the spaces which the coi'puscles
occupy. This network of clear spaces represents the canalicular
system (Saftcan'dlchen System) of the cornea: it must not be
confused with Bowman's tubes, h. The second method of ap-
plying the nitrate of silver in substance has the advantage
that it shows the canalicular system in all parts of the cornea.
It consists in first scraping the cornea of a living frog or small
mammal with a sharp cataract knife, so as to remove the epi-
thelium completely. After a little practise, and provided the
bulb is properly fixed by an assistant, it is not difficult to per-

BY DR. KLEIN. 53

form this operation without injuring the substance of the cornea.
Thereupon the caustic is two or three times lightly rubbed over
the whole surface, after which the eye is, washed with saline
solution, and the animal is left to itself for twenty or thirty
minutes. The cornea is then excised, washed in ordinary
water for several minutes, and pencilled with a camel-hair
brush. The mode of preparation is as before, care being taken
to make one or two radial incisions, in order that the mem-
brane may lie flat on the glass surface. After the preparation
has been exposed for a few hours, the contrast between the
spaces and the yellowish-brown interstitial substance becomes
very obvious.

[The endothelium of Descemet's membrane, with its dark
interstitial lines, brownish-yellow cell substance, and clear
ovoid or lobed nuclei, is well seen. It is to be noted that all
preparations of this kind must be kept in the dark.]

Similar results are obtained by the use of the nitrate of
silver in solution. With this view the epithelium is either
pencilled off from the anterior surface with warm water, or
scraped off as above described. The cornea is then imme-
diately excised and immersed for fifteen or twenty minutes in
a half to one per cent, solution. It is then washed and pre-
pared as above. If, however, after washing the preparation
for a very short time, it is transferred to a ten per cent, solu-
tion of chloride of sodium for five or ten minutes, and is then
again washed in ordinary water and mounted in glycerin, the
appearance is very different. We have before us in most parts
the canalicular system marked out by a dark precipitate, while
the interstitial substance remains almost clear. In other parts
there are gradations of staining between this appearance and
the negative staining obtained by the ordinary method.

Preparation of the Cornea with Chloride of Gold.
— The fresh cornea of a frog or mammal is placed in as much
half per cent, solution of pure chloride of gold as is sufficient
to cover it, and left immersed until it acquires a straw-yellow
color — i. e., at most thirty minutes. Thereupon it is trans-
ferred to distilled water, or water slightly acidulated. The
preparation passes through pale gray, then dark gray, violet
gray, violet and reddish, to dark red — the time required for the
production of the last-mentioned color differing, cxteris paribus,
according to the time during which it was immersed, and the in-
tensity of the light. In the height of summer, twenty-four
hours, or oven less time, is sufficient ; but in winter several days
are required, in which case it is preferable to use distilled, rather
than acidulated, water, because the latter is apt to produce too
much swelling of the preparation. From a darkly colored
cornea bo prepared, the anterior epithelium is removed by strip-
ping it off from the cumulus conjunctivae inwards, with the aid

54 CONNECTIVE TISSUES.

of a sharp pointed forceps. If that of a frog, the cornea may
tlien lie mounted in glycerin without .farther preparation. The
rabbit's cornea must be prepared as before directed. In this
way one of the most beautiful preparations in the whole range
of histology is obtained. The bodies and processes of the cor-
puscles are seen to consist of a more or less granular proto-
plasm of various shades of violet. Each corpuscle contains a
flattened oblong, well-defined nucleus, which is of a violet
color, and incloses one or two large, round, dark colored nu-
cleoli. (Fig. 10.) Corneas stained with chloride of gold may
also be advantageously studied by vertical sections, and by
sections parallel with the surface : from such sections it is easy
for any one to satisfy himself that the structures seen actually
exist as such, and are not the products of the mode of prepara-
tion. It is, however, necessary to demonstrate that the cana-
licular network which we see with such distinctness in silver
preparations, corresponds to and coincides with the network
of branched corpuscles displayed in gold preparations, in such
a way as to make it certain that the latter lit into and fill
out the former. There are two modes of proof: a. A frog's
cornea is prepared and mounted, lege aiiis, on the glass slide
(Fig. 6), and is then examined with a No. 10 immersion, objec-
tive, while an induced current of moderate strength is caused
to act upon it. After the excitation, the system of branched
corpuscles becomes distinguishable, and each is seen to be
surrounded with a clear margin. After a time this appearance
is lost, but can be reproduced b}T repeating the excitation. It
admits of but one interpretation, viz., that the protoplasm
contracts, under the excitation, in such a wa}r as no longer to
fill out the space in which it is contained — again occup3'ing it
as soon as the contraction ceases, b. A rabbit's cornea is
gently rubbed with caustic until the epithelium is removed as
a slough. After from twenty to thirty minutes a few drops of
concentrated solution of chloride of gold are placed on the
cornea. The eye is left to itself for fifteen or twenty minutes,
after which time the cornea is shaved off with a razor, and
steeped for twenty-four hours in water feebly acidulated with
acetic acid. It is then not difficult to prepare from the parch-
ment-like cornea, with sharp forceps, thin lamellse ; or to make
thin sections, in planes parallel with the surface, with a razor.
In preparations of either kind mounted in glycerin, even when
examined with the naked eye, three different colors may be dis-
tinguished. There are patches of gray and others of violet:
and these two are separated from each other by intermediate
regions of a dull violet-red. Under the microscope the gray
parts exhibit the characteristic appearance of silver prepara-
tions— a clear canalicular sj-stem on a yellowish-brown inter-
stitial substance. In the violet parts the canalicular S3-stem is

BY DK. KLEIN. 55

also clear, but the interstitial substance is violet ; whereas in
the dull red parts, there are bluish or dull red corpuscles on a
clear ground. Both in the first and in the second, there are
transitions to the intermediate parts, i. e., the nearer the part
observed is to the edge of the dull violet-red parts, the more
possible is it to make out that the network of protoplasm
occupies the canalicular system. It is alwa}rs possible to find
points where the processes of protoplasm stretch from these
parts into clear canaliculi.

Branched Corpuscles of the Tail of the Tadpole.
— Another object in which it is easy to demonstrate the
branched corpuscles is the tail of the tadpole. In this organ,
when prepared in the fresh state, as above directed, a very
beautiful network of pale protoplasm, in a hj-aline interstitial
substance, may be demonstrated. The network consists of
nucleated cells, which communicate with one another by den-
dritic processes. It is most dense near the edges and toward
the tip of the tail. In order to obtain preparations of this
structure, it is best to place a portion of the organ of a tad-
pole (in which the posterior extremities have begun to sprout)
in half per cent, solution of chloride of gold for from thirty
to forty minutes. The preparation having been placed for
twenty-four hours in distilled water and exposed to light, the
epithelium of one side must be removed. For this purpose
the organ must be fixed by a needle in the middle line close to
the cut end : the epithelium, with the plexus of nerves and
bloodvessels of one side, can be stripped off with the fine-
pointed forceps in the form of a membrane — a process which
is much facilitated by first placing the preparation for fifteen
minutes in absolute alcohol. The separated structures are
then covered in glycerin. Such preparations are of great
value, serving not merely for the demonstration of the cells
with which we are now concerned, but also, as will be seen,
for the study of the structure and development of the capil-
lary bloodvessels, of the most minute nerve fibres, and the
relation of the lymphatic vessels to the connective tissue
elements. The description and mode of demonstration of the
branched cells of the serous membranes will be given in the
chapter on the lymphatic system, in connection with which
they are of most importance.

Branched Corpuscles of the Skin. — In order to de-
monstrate the branched cells of the cutis (or of the mucosa),
it is best to snip off folds or ribands from the fresh structure
with the curved scissors. These are placed in half per cent,
solution of chloride of gold until they acquire a distinctly
yellow tinge. They are then transferred into distilled water
until they are tinged dark violet and finally hardened in ordi-
nary alcohol. Sections must then be made parallel to the

56 CONNECTIVE TISSUES.

surface and covered in glycerin. Sections in this direction
are preferable, because the branching of the cells and their
mode of communication cannot be so well seen in others.
We shall return to these subsequently. In the membrana
nictitans of the frog there occur networks of large, coarsely
granulated cells, containing flattened oblong nuclei, and with
branches which run for the most part parallel with the surface.
This structure must be prepared with chloride of gold in
exactly the same way as the cornea.

Pigment Cells. — These are closely related to the fixed
cells now under consideration. They are more or less
branched corpuscles, which are sometimes isolated, sometimes
form a network. They are, in general, larger than the ordi-
nary connective tissue corpuscles. Each contains an oblong
clear nucleus, while both their bodies and processes are beset
with pigment granules. In mammalia they are found, as is
well known, especialh- in the skin, and in the sclerotic, iris,
and choroid. In the lower vertebrates, e.g.. in the frog, they
are very numerous, not only in the skin, but in the peritoneum,
and in several mucous membranes. Pigment cells can be
made to retract their pigmented processes when stimulated
either mechanically, chemically, or electrically, as well as
under the influence of light. Let us examine them (a) in the
web, (6) in the mesentery of the frog, (c) in the tail of the
tadpole, and (d) in the choroid of a mammal, (a) A common
frog (B. temporaria) is secured on a plate similar to that
shown in Fig. 11, and the toes are extended by ligatures at-
tached to their tips. With this view, the hole 0 is surrounded
by five or six small perforations into which wooden pins can
be stuck ; the ends of the ligatures are drawn through the
holes and fastened with the pins. In those parts of the web,
which appear to the naked eye dark, it is seen, even with a
linear magnification of 100, that the pigment cells are con-
nected by an extraordinary number of fine dark processes
which are either penicilliated or dendritic. Often the distinc-
tion between body and process is not marked ; it looks rather
as if the whole network were made up of processes. In other
parts, which are not so dark to the naked eye, groups of
pigment cells arc found in which the bodies are round or
oblong, and the processes broader and less numerous — the
latter being either in continuity with those of neighboring
corpuscles, or broken off abruptly by a gnawed edge. The
pigment granules do not extend to the end of these broad
processes ; so that it is possible to see that the substance in
which they are embedded is hyaline.

If the dark parts are touched once or twice with a camel-hair
pencil (especially if it has been dipped in oil of turpentine),
the processes are gradually retracted, while, pari pasm, the

BY DR. KLEIN. 57

skin becomes visibly paler. On resuming the observation, after
the lapse of one or two hours, it is found that the pigmented
network is as dense, and the processes are as numerous, as at
the beginning of the observation. It is a remarkable fact
that the projection of the processes is much accelerated by
the application of a drop of croton oil, with the aid of a
capillary pipette, to the irritated part. In certain places
where the cells are not entirely black, but have a more or less
3'ellowish-brown color, and possess only a few stumpy pro-
cesses, these last undergo spontaneous changes of form as
regards length and thickness. When the web is irritated,
these, like the others, retract their processes altogether. If
the circulation is arrested by placing a ligature around the
leg, the pigment cells on the same side acquire a brighter
color — the dull brownish-yellow tint returning with the resto-
ration of the circulation.

In the tail of the tadpole the pigment cells in several respects
resemble the ordinary branched cells. The most superficial
extend themselves by their processes between the epithelial
cells. In the tadpole of the toad, which is distinguished from
that of the frog b}r the breadth and shortness of the tail, they
are spindle-shaped, and form by their processes a tolerably
regular lattice-work, with nearly rectangular spaces, which is
uniforml}- distributed throughout the tissue ; immediately un-
derneath the epithelium, however, there are some cells, the
mode of branching of which is dendritic. In fresh prepara-
tions, or in preparations with chloride of gold, of the mesen-
tery of the frog, a greater or less number of pigment cells are
seen in the immediate neighborhood of the large bloodvessels,
and especially the arteries, and often form a complete sheath
around them. Isolated pigment cells occur also elsewhere in
the tissue. With high powers (No. 10 immersion) and with
dilute acetic acid, it is possible to make out in fresh prepara-
tions of the nictitating membrane and mesentery that the
whole cell is not pigmented, the pigment being confined to
certain parts of the body and to the axes of some of the pro-
cesses. In mammalia, the most varied forms of pigment cells
occur in the choroid and sclerotic, from the irregularly formed
cells with slight knob-shaped projections containing coarse
pigment granules, to cells with regular dendritic branching
and fine granules.

Fat Cells. — Fat cells are distinguished from ordinary
branched connective tissue corpuscles mainly by the fact that
they contain drops of fat. When an ordinary branched cell
undergoes conversion into a fat cell, the change commences
by the appearance of small droplets in the protoplasm. By
the confluence of these with each other a larger drop is formed.
As this increases, the protoplasm of the corpuscles is dis-

58 CONNECTIVE TISSUES.

tended more and more, until it forms around the globule a
thin investment, in which lies the clear oblong nucleus. In
well-developed fat cells, which usually lie together in groups,
it is not possible to observe processes. They rather resemble
closel}' packed globular structures.

Transition Forms between Connective Tissue
Corpuscles and Fat Cells. — If, in a rabbit, the skin and
subcutaneous tissue are divided over the inner (anterior) third
of the infra-orbital edge, and the thin membrane which stretches
over the infra-orbital fossa is severed, it is easy to remove,
along with the glandula infraorbitalis, a gelatinous hyaline
mass. If, from this mass, a very thin portion is snipped off
and placed in a drop of fresh serum on a glass slide and
covered, it is easy to distinguish, among the ordinary branched
cells, others which are larger and contain globules of fat. All
transitions may be seen between those which contain one or
two small droplets and those which are completely distended.
These structures will be referred to again, under another
heading. Fat cells are, as a rule, collected in masses around
bloodvessels.

Tendon Cells. — The cells of mature tendon tissue do not
essentially differ from those of ordinary connective tissue.
Like them, they are oblate branched masses of protoplasm,
which are in communication with one another by their pro-
cesses. They are not, however, flat, but curve themselves in
conformity with the surfaces of the individual bundles to
which they are applied. In order to study them, the best
material is afforded by the tail-tendons both of young and full-
grown rats or of rabbits, which can be examined either in the
fresh state in serum, or by steeping them for a few minutes in
silver solution, after they have been first pencilled with a
camel-hair brush dipped in fresh serum. Another material
which may be used is the centrum tendineum of the diaphragm.
In very young animals the caudal tendons present a peculiar
arrangement. If the tail of a very young rat is amputated,
and the tip torn asunder from the cut end, a great number of
isolated lengths of tendon are obtained, of almost microscopic
tenuity. These may be at once separated, and covered in very
dilute acetic acid. Such a preparation shows, between the in-
dividual bundles, chains of apparently quadrangular masses
of protoplasm, each containing a roundish nucleus. These
chains alternate in position with the bundles. If, however, a
single cylindrical bundle of fibrils is separated, it is seen that
it possesses an envelope of granulous protoplasm, which ex-
tends along one side of the bundle, covering nearly half of its
circumference ; in this envelope nuclei lie arranged in linear
series. If the preparations are treated with stronger acetic v
acid, the protoplasm between the nuclei exhibits cross lines of

BY DR. KLEIN. 59

interstitial substance. Hence it is evident that the sheath of
protoplasm with which nearly the half of each individual
bundle is surrounded consists of a series of hollow half-cylin-
ders with their ends in apposition. To preserve the prepara-
tions above referred to, the fresh tendon should be placed for
a very short time in acidulated water, until it begins to swell
just perceptibly ; it is then to be transferred to half per cent,
solution of chloride of gold for ten or fifteen minutes, and
washed in distilled water till it acquires a rich color, and then
to be mounted in glycerin. In cross sections through young
tendons of the rat or rabbit, in consequence of the anatomical
facts already stated, the bundles look as if they were contained
in the meshes of a network of protoplasm, with nuclei at the
nodes. Such sections may be hest prepared from the caudal
tendons, or from the T. Achilles treated with gold and then
hardened in common alcohol.

Adenoid Tissue. — It remains to describe the so-called
adenoid tissue. By this term is understood a dense reticulum
of branched cells, the processes of which are short but of great
delicacy. The younger the individual, the more the material
of which the reticulum is composed possesses the character
of protoplasm ; the older, the more homogeneous the processes
appear, and the smaller the quantity of protoplasm at the nodes,
which correspond to the bodies of the cells. There are great
differences between the several forms of adenoid tissue, which
it will be most advantageous to study in connection with the
tissues in which they are respectively met with, e. </., lymphatic
glands, intestinal mucosa, etc. The best objects for study are
the mesenteric glands or the thymus of the calf, and the lym-
phatic follicle of the intestine of the rabbit. These must be
hardened in Mailer's fluid or in diluted alcohol. As soon as
the tissue has become firm enough, thin sections are prepared,
which are agitated with water in a test tube, until they present
the appearance of a reticular membrane. They are then covered
in glycerin, with or without previous staining. For more
minute descriptions, see Chapter VI.

Development of Connective Tissue. — Fibrous connec-
tive tissue is developed from cells in two ways, as follows: —

At a certain stage of embryonal life, those organs which, at
birth and in the adult consist of fibrous tissue, are composed
exclusively of embryonal cells. As development proceeds,
these cells, which are originally roundish, arc either transformed
into a network of branched cells, or lengthened out, so as to
form bundles of spindle-shaped cells. At first both the bodies
and processes of the cells, whether branched or spindle-shaped,
consist of granulous protoplasm. The protoplasm subse-
quently undergoes a process of splitting, by which it is trans-
formed into fibrils. This change commences in the processes,

60 CONNECTIVE TISSUES.

progressing towards the body. The fibrils are united to one
another by an interfibrillar substance, which, at first granular,
afterwards becomes homogeneous. In this way the network of
branched cells is transformed into fine fibres, arranged in a
nicshwork ; while the spindle-shaped cells are converted into
collections of fibres, running in parallel bundles. A third mode
consists in the transformation of isolated spindle or branched
cells, which, according to the number of their simple or divided
processes, split into a corresponding number of bundles of fi-
bres. For the study of the process it is best to employ the
umbilical cord, the skin, tendons, or the mucous membrane of
the mouth or bladder of young embryos of man or animals.
The parts in question should be kept for some time in sheriy-
yellow solution of bichromate of potash, after which the tissues
may be prepared by teasing in a drop of the solution or in
water. It is also desirable, especialby as regards tendons, skin,
and mucous membrane of the bladder, to make thin sections,
after hardening in solutions of chromic acid or chromates. —
A splendid object is to be found in the abundant gelatinous
substance which covers the internal surface of the gravid
uterus of the sow, and extends from thence over the external
surface of the membranes of the ovum. If a very small por-
tion of this substance is placed in salt solution on a glass
slide, and covered without any further preparation, very re-
markable forms of large branched or spindle-shaped cells are
seen, which consist of evenly granular protoplasm, and con-
tain roundish or oblong sharply defined nuclei. The branches
are often so large as to stretch over the whole field (Xo. 8
Hartnack), and the\r may be seen to split out at their ends
into sheaves of the most delicate fibrils. From the abundant
submucous spongy tissue of the gravid uterus of the same
animal, instructive preparations maybe obtained (by stripping
off fine portions with the curved scissors), which merely re-
quire to be spread out with needles in salt solution. If the
preparation is to be kept, it may be placed in bichromate of
potash and afterwards transferred to glycerin. In the gela-
tinous substance previousby described as found in the infra-
orbital fossa of the rabbit, isolated delicate wavy bundles of
connective tissue occur, which, after a shorter or longer course,
is seen to be in close relation with processes of slender pale
cells which contain round nuclei.

Hyaline Cartilage. — For the study of hyaline cartilage, the
episternum of the frog and the thin expansion of the shoulder-
girdle of the newt are good objects. If the thin part of either
of these is prepared in half per cent, saline solution or in serum,
after the perichondrium has been carefully separated with the
aid of the sharp forceps, the oblong or spherical cartilage cells
are seen embedded in a hyaline or finely granular matrix. The

BY DR. KLEIN. 61

edges of the cells are sharply defined, their substance is clear,
or beset with a very few granules, their nuclei are also some-
what granulous. At all depths the intercellular substance
(ground substance or matrix) can be seen, under high powers,
to be divided into territories, each corresponding to a cell. So
long as the preparation is fresh, most of the cells completely
fill the cavities which they occupy in the matrix; these cavi-
ties are termed capsules. Only here and there can a clear
space be distinguished between the external surface of the cell
and the wall of the capsule. For the most part each cell
contains a single nucleus ; there are, however, some which
contain two nuclei. In the middle part of the preparation
they are found either singl}r and at equal distances from each
other, or in pairs, i. e., two in one capsule, united by straight
lines of contact. Occasionally two cells are seen placed
together in the same relative position to each other as the two
inclosed in the same capsule, but separated by a septum of
ground substance, so that each is inclosed in its own cavit}\
If, for the indifferent fluid, we substitute distilled water, the
cartilage cells separate themselves from the internal surface of
the cavity, while their protoplasm becomes turbid. If the
cartilage of the newt is subjected to the induction current in
the manner already described, a sudden shrinking of the cell
results, in consequence of which it assumes a coarsely granular
appearance, and a nodulated form, while the nucleus becomes
invisible. This condition is permanent, the cell never resum-
ing its former appearance; in some, however, the nucleus
becomes more or less invisible. A perfectly similar change is
produced by the addition of dilute acetic acid. In many parts
of the preparation, especially near the margin, where the
cartilage cells are closel}' packed, the change does not take
place. The cells become more transparent, while their edges
and those of the nuclei become more sharply defined.

Sections can be easily made of cartilage in the recent state,
and can then be examined in an indifferent liquid. The con-
dyles of the tibia or femur of a frog or mammal may be used
or the costal cartilages of the latter. The greatest variety is
found in different cartilages, and in different parts of the same
cartilage, in respect of the number and size of the cells. For
making permanent preparations of cartilage, the chloride of
gold method is better than any other. Thin fresh sections of
cartilage are placed for ten or fifteen minutes in a half per
cent, solution of chloride of gold, exposed to light in distilled
water for twenty-four hours or more, and then mounted in
glycerine. The matrix remains clear, or is only very slightly
stained violet, while the corpuscles display all transitions of
color between violet, violet-red, and dark red. The nuclei are
usually brightly stained, of a reddish tint. The method

62 CONNECTIVE TISSUES.

formerly used, which consisted in staining sections of cartilage,
previously steeped in chromic acid solution, may be dispensed
with ; the plan above recommended possessing the great ad-
vantage over it, that the cartilage cells retain their natural
form completely. Before leaving hyaline cartilage a word
must be said as to the arrangement of the cells in the carti
lages which occup}' the centre of the epiphysis of the tibia ot
the frog. If the tibia of a frog is enucleated from the knee-
joint, and sections are made at right angles to the axis of the
bone through the condyles, these exhibit concentric layers,
arranged around two centres corresponding to the two con-
dyles. Proceeding from without inwards, we have first articu-
lar cartilage, then an external periosteum, a ring of bone, an
internal periosteum, and, finall}r, a nucleus of cartilage on
either side, one corresponding to each condyle. These two
cartilages are hyaline, but each cell constitutes a rigid lamina,
which is separated from its neighbors b}7- little or no matrix.
Towards the diapl^ses each nucleus tapers away gradually ;
and, in its lower part there is a cavity which is continuous
with the medullary cavity of the diaphysis, and contains a
little liquid. The cells are here more separated from each
other than they are towards the condyles ; but, immediately
round the cavity, they are more densely arranged, are roundish
in form, and look like lymph corpuscles, consisting of finely
granular protoplasm.

In embryonal cartilage, the spindle-shaped or stellate branch-
ed cartilage cells, which consist of granular protoplasm, and
possess spheroidal nuclei, are crowded together in a hyaline
substance, penetrated throughout by bloodvessels (e. g., in the
patella or head of the femur of the human foetus). In the
immediate neighborhood of the vessels they possess more or
less the form of ordinary cartilage cells. They may be
prepared for observation in the same way as the others.

Yellow Cartilage differs from hyaline in the fact that its
matrix consists of a network of elastic fibres, in which there
are cavities occupied by cartilage cells, either isolated or in
groups. These are sometimes surrounded by a certain quan-
tity of li3-aline substance. The best objects for the study of
this tissue are the epiglottis and the cartilage of the external
ear; these may be examined fresh or in chloride of gold. In
addition to these forms, the so-called 2yarenchymatous cartilage
must be mentioned ; i. e., cartilage without matrix. This
occurs in the embiyonal chorda dorsalis, and in the tendo
Achilles of the frog. We have already studied an example of
it in the nucleus cartilage of the epiphyses of the frog's tibia.

Fibro-Cartilage. — In fibro-cartilage the structural ele-
ments of cartilage are intermixed with gelatigenous tissue, as
in the neighborhood of the insertions of tendons into bones, in

BY DR. KLEIN. 63

cartilages of the symphyses, etc. The mode of preparation is
the same.

Bone. — In the investigation of the structure of bone, one
of two courses may be followed, according as we have in view
the bony framework, i. e., the bone substance proper, or the
soft parts, viz., the periosteum, medulla, bloodvessels, and
nerves. The bone substance proper may be studied satisfac-
torily by means of thin sections, for the preparation of which
the method is as follows : A human long bone, a vertebra, or
one of the flat bones of the skull, is cleared of the soft parts
and dried. The bone is then fixed in a vise, and thin lamella?
are cut in various directions with the aid of a fine saw. These
are rubbed down with moist emery powdered on a ground-
glass plate, against which they are pressed either with the
finger alone, or with a bit of cork, or with a second glass
plate, until they are extremely fine. Having been polished
on a wet hone, they are washed in water and pencilled with a
camel-hair brush, in order to get rid of adhering dirt. They
must next be dried and placed under a cover-glass, either
without the addition of any liquid, or in glycerin. As ex-
amples, transverse and longitudinal sections of a human
radius may be taken. In the one, the Haversian canals are
seen cut across ; in the other, they appear as broad channels,
which communicate with each other by cross channels, the
latter running obliquely or at right angles to the former.

The clear ground substance consists of lamella? arranged
concentrically around the Haversian canals (primary lamellae),
and secondary lamellae, which run longitudinally in various
planes, occup3'ing the spaces which are left between contiguous
systems of concentric lamellae. The lamellae contain an im-
mense number of dark cavities (lacunae) at equal distances
from each other, which, as longitudinal sections show, are of
elliptical form. These communicate with each other by dark,
somewhat convoluted canaliculi, many of which run in the
same layer, but many also in such a direction as to form com-
munications between one lamella and the next. In dry prepa-
rations, the whole system of lacunae and canaliculi is filled
with air. We shall see afterwards that in the living state they
contain protoplasmic branching cells.

A second method of preparing bone is that of maceration.
A fresh bone is separated from the surrounding muscles and
placed in a large quantity of a quarter to half per cent, solu-
tion of chromic acid, to which a few drops of hydrochloric acid
have been added. The bone acquires a consistence suitable
for the preparation of sections with the razor in from a week
to a fortnight, according to its size. If too soft, it can be
placed in diluted alcohol. Bones prepared in this way may

64 CONNECTIVE TISSUES.

be used just as other tissues hardened in chromic acid (see
Chap. VI.).

For the study of the periosteum and of the compact bony
substance, i.e., of its lamellae and lacunae, with the cells con-
tained in them, sections of the long bones of man are very
suitable. The spongy substance can be best examined in the
metacarpal and metatarsal bones and in the phalanges of
children, or in those of rabbits or rats. Very instructive sec-
tions may also be obtained from the tibia of the frog, showing
the compact substance of the bone, as well as the pigment
cells, fat cells, medullary cells, and bloodvessels of the marrow.
Medullary tissue can be also advantageously studied in the
tongue bone of birds. The whole tongue is hardened in
chromic acid solution, after which sections are made through
the posterior part of the tongue, so as to pass through the
bone in question. Sections of bone prepared as above afford
evidence that the cells which occupy -the lacunae are strictly
analogous to the branched cells of other connective tissues,
so that the system of lacunae and canaliculi, seen in prepara-
tions of dried bone, corresponds entirely with the system of
canaliculi (Saftcan'dlchen) seen in silver preparations of the
cornea, serous membranes, etc. And it ma}' even be shown
in preparations of the flat bones of the skull, or of the tongue
bone of birds, that the cells are not only in continuity ex-
ternally with those of the periosteum (which, although really
branched, look spindle-shaped in section), but internally, i.e.,
towards the medulla, with cells which are also more or less
branched, but are arranged so regularly and so close together
against the bony surface, that they resemble an endothelial
lining. In the flat bones of the skull of human embiyos, the
same arrangement presents itself with great distinctness — the
cells, which line the medullary cavities, being then called
osteoblasts.

The medullary tissue of bone is rich in bloodvessels and in
cellular elements. The former are best seen in injected prepa-
rations (see Part II., Chapter VI.). After the injected part
has been one or two days in alcohol, the bone must be freed
from surrounding tissues, and steeped in chromic acid with
the addition of hydrochloric acid, as before. The medullary
cells, which differ in size and in the distinctness of their granu-
lation, may be examined in the fresh condition on the warm
stage, for the demonstration of their amoeboid movements, in
the manner several times described previously. In chromic
acid preparations, the individual medullary cells, as well as
the fat cells, retain their form and aspect.

Development of Bone-tissue. — For the study of the
development of bony tissue (whether from cartilage or from
fibrous tissue, as in the flat bones of the skull) the human

BY DR. KLEIN. 65

foetus is best adapted, after having been steeped in Miiller's
liquid, or in one-quarter to half per cent, solution of chromic
acid, for a few da}rs. The sections may be stained with car-
mine (see Chapter VI.). For studying the development and
growth of bone in the epiphyses, longitudinal sections may
be made through the epiphysis of the femur, or of the tibia, of
the metacarpal bones, or phalanges of newl}r born human
foetuses, or of young rabbits.

CHAPTER IV.

MUSCULAR TISSUE.

Section I. — Uhstriped Muscle.

The elements of this tissue are cells — the so-called " contrac-
tile fibre-cells" — of varying length, and for the most part
spindle-shaped, this form being often modified by a flattening
of the cells where they come in contact. Their ends are either
single or divided. Their substance is, in the fresh state, a pale
or finely granular protoplasm, sometimes longitudinally stri-
ated : in the thicker part of the cell lies an oblong, compressed
nucleus, rather rounded at the extremities (thus becoming
staff-shaped), or pointed. The nucleus contains one or two
large shining nucleoli : if single, the nucleolus lies in the centre
of the nucleus ; if double, one is found at each extremit}'.
External to the nucleus, and in a straight line with its longi-
tudinal axis, some small granules may sometimes be seen.
The unstriped muscular fibres are always arranged in bundles,
the elements of which are separated from each other by inter-
stitial substance. The bundles are held together by connective
tissue, in which they lie in such a way that the}' either form
membranes (as in the intestine) or meshworks (as in the blad-
der). In the former case, the bundles are parallel and mostly
undivided ; in the latter, they run in various directions, divide
frequently, and intercommunicate with each other.

The best materials for the stud}' of involuntary muscular
fibre, are the bladder of the frog, the mesentery of the newt, the
muscular coats of the intestines of the frog and mammalia, and
arteries, such as those at the root of the mesentery of the frog.
The}r may be demonstrated either in connection or isolated.

To show their arrangement, a portion of the bladder of the
frog may be spread on the glass slide with the mucous surface
downwards, and covered in half per cent, salt solution. In
5

6Q MUSCULAR TISSUE.

such a preparation it is seen that a mesh work is formed by the
repeated division of the bundles of fibres. If the bit is soaked
for a few minutes in one per cent, or two per cent, acetic acid,
the epithelium brushed off with a camel-hair pencil, and the
membrane then examined in water or glycerin, the individual
elements of the muscular bundles come very distinctly into
view ; those of the muscular coats of the arteries can also be
studied advantageously. The mesentery of the newt maybe
prepared in the same manner. Instructive preparations of
muscular tissue may be obtained by carefully excising the iris
of an albino rabbit just killed, and spreading it flat on the ob-
ject glass in an indifferent liquid. The muscular tissue of the
intestine can be prepared as follows: A short portion of the
small intestine of a rabbit, or mature fetus, is filled with half
per cent, salt solution by ligaturing one of the ends, and tying
into the other a glass tube with a canulated extremit}', through
which the liquid must be injected. The gut having been in
this way well distended, a second ligature is placed between
it and the canula. Thin shreds, consisting only of the perito-
neum and of the longitudinal muscular layer, are then stripped
off with the aid of pointed forceps from the surface of the in-
testine opposite to its mesenteric attachment. These strips
are carefully spread out and prepared in an indifferent liquid.
Of course care must be taken not to pierce the intestine with
the forceps. Another suitable object of study is the abdominal
extremity of the Fallopian tube, which, in some mammalia
(e. g., in the sow), is dilated into a large thin sac. It may be
prepared in the same way as the bladder of the frog. An ex-
cellent method of preparing unstriped muscle is to immerse the
tissue in half per cent, solution of gold, for which purpose the
bladder of the fi*og, the mesentery of the newt, the iris of the
eyes of albino animals, or the muscular coat of the intestine
of small mammalia may be used. The bladder of the frog is
prepared as follows : A frog is decapitated, and the upper
two-thirds of the abdominal cavity opened. A solution of chlo-
ride of gold is injected, either by means of a tube ten to fifteen
centimetres in length, which is drawn out at one end so as to
form a canula, and bent at an obtuse angle so as to facilitate
its introduction into the bladder, or, still better, with the aid
of a glass syringe furnished with a long beak. As soon as the
bladder is filled; a ligature is placed round its neck and tight-
ened round the canula, after which the organ may be excised
and placed in a capsule, containing a similar solution, for fif-
teen minutes. After this time it is cut into small sections,
which arc immersed in acidulated water and exposed to the
light. If this method is followed, there is no fear of folds or
shrinking, as the bladder is already more or less hardened.
As soon as the fragments have acquired a dark violet or dull

BY DR. KLEIN. 67

red color, the mucous membrane is pencilled away and the re-
mainder covered in glycerin. The mesentery of the newt, the
iris, or the muscular coat of the intestine of mammalia may
be prepared in the method already explained, and then treated
in every respect as just described. Chloride of palladium,
which has also been used for the coloring of muscular fibres,
has no advantage over the gold salt. In sections of unstriped
muscle, previously hardened in one-eighth to one-fourth per
cent, solution of chromic acid, and subsequently colored in pic-
ric acid, carmine, aniline, &c, the muscular bundles are dis-
tinctly seen, as well as their relations to each other, and to
the septa of connective tissue which surround and separate
them.1

In sections through the hardened intestine of the frog, rab-
bit, or rat, the muscular cells, where they are seen in longitu-
dinal section, appear to be separated from each other, not by
straight lines, but by marginal borders, which exhibit fine trans-
verse markings, referable to the existence of minute furrows,
which run in a direction vertical to the axis of the fibre.

To isolate the individual muscle-cells for the study of their
form and nuclei, macerating liquids, by which the interstitial
substance is disintegrated, are employed. Small fragments are
introduced into a dark sherry-colored solution of bichromate
of potash, two or three per cent, acetic acid mixture, nitx-ic
acid diluted with four times its volume of water, or thirty-five
per cent, potash solution. The arrangement of the nerves of
unstriped muscle will be described in a future chapter.

Section II. — Striped Muscle.

The tissue of striped muscles consists of long cylinders (mus-
cular fibres) which are united by connective tissue into bundles
(fasciculi) of varying length. The following parts have to be
considered : The contents of substance of the individual fibre
with its muscle-corpuscles; the sarcolemma ; and the junction
of muscle with tendon. The mode of ending of the nerves in
muscle will be described in the next chapter.

Proper Substance of Muscular Fibre. — The leg of a
water-beetle (Hydrophilus) is torn out, and its horny covering
removed. A snip is then taken from the exposed muscular
mass, with the aid of curved scissors, or a fine scalpel, and at
once covered without addition. If the cover-glass is then

1 Fine sections of structures containing numerous unstriped muscu-
lar fibres, which have been hardened in chromic acid, then placed for a
few days in diluted alcohol, and finally stained in a weak ammoniacal
solution of carmine, exhibit a striking contrast between the muscular
fibres and the connective tissue, the former being tinged yellow by the
chromic acid, the latter red by the carmine.

68 MUSCULAR TISSUE.

slightly pressed, so as to flatten out the object, arhoreseent
branchings of the tracheae first attract attention. These air-
tubes consist, like the trachea? of mammalia, of parallel rings,
and entwine the muscular fibres with a network of fine, dark
capillaries, each of which follows a winding or spiral course.
The muscular fibres themselves, which either run parallel, or
cross each other in various directions, are in active movement
In some fibres this movement resembles that of a wave, which
rapidly progresses in the direction of its length; in others,
when it is slower, it has a vermicular character. On more
careful examination it is seen that, during the progress of the
wave, the muscle swells, returning to its original thickness
immediately after. It is further observed that the dark paral-
lel striae come nearer together during the swelling, and that
the intervals return to their original width after the wave has
passed. In the contents of a muscular fibre, when in a state
of rest, the following parts can be distinguished: (a) the dark
parallel cross stripes, which as we shall find, correspond to
thin parallel disks of less refractive isotropous substance
(called interstitial disks) ; (b) the portion intervening between
these. This, again, appears to consist of two parts, viz., a
broader middle one of dull gray appearance, and on either side
of this a narrow, clear layer. The whole is made up of highly
refractive, anisotropous contractile substance, which is to be
regarded as the essential substance of the muscular fibre. The
dark cross-lines do not seem, under high powers, homogeneous,
but appear to consist of series of contiguous granules of equal
size. Many muscular fibres exhibit no other differences; in
others, it is possible to distinguish lines running longitudinally
of greater or less extent, and which are so arranged that twejr
come between what appear to be dark granules of the inter-
stitial striae. With reference to these granules, it is not to be
supposed that the}' actually exist as such ; the appearance is
rather to be regarded as expressive of the fact that the dark,
interstitial transverse stripes are interrupted b}r clear, longi-
tudinal lines, the interval between the latter remaining dark —
as, e.g., in a check of which dark transverse lines are covered
by light longitudinal lines. In a fresh muscular fibre, as seen
under the microscope, the transverse interstitial disks are not
placed vertically, as we can satisfy ourselves b}' using the fine
adjustment, but are set at an oblique angle with the long axis
of the muscular fibre. In this respect a muscular fibre ma}' be
compared to a roll formed of coins of different metals, so ar-
ranged that the thin dark disks alternate with thicker light
ones. If such a roll is laid on a plain surface, all the coins
lean in one direction, and present their edges to the eye, re-
garding them from above, just as the disks in a muscular fibre
do under the microscope.

BY DR. KLEIN. 69

We have now to consider the significance of the appearances
above described. The fact may be stated in limine, that the
whole of what intervenes between two interstitial stripes, i. e.,
the gray band and its two bright borders, affects polarized
light in the same way — that consequently the view according
to which only the borders are doubly refracting, is erroneous.
If a microscope is employed, of which the stage admits of ro-
tation around the vertical axis of the instrument, as in the
larger instruments of Hartnack, and these bright borders
(which should be distinct and regular) are observed, in a
muscular fibre, under No. 8 objective, and if the stage is slowly
rotated, so as to alter the course of the rays in relation to the
muscular fibre under observation, a remarkable change is seen
to take place in these borders. As the rotation is continued
the bright bands fade, first on one side of the interstitial line,
then on the other, coming into view again in the same order;
the changes do not, however, occur simultaneously through-
out the whole of the muscular fibre.

When fresh muscular tissue is placed in absolute alcohol,
and then steeped for a few minutes in oil of turpentine,
mounted in dammar varjiish, and covered, only two kinds of
substance can be distinguished in the fibres, i. e., dark inter-
stitial stripes and a dull gray substance between them, without
a trace of the clear borders. The longitudinal section of such
a muscular fibre may be represented diagrammatical^', as in
Fig. 15. In the diagram, the slightly refracting interstitial
substance is represented by a, the clear borders by b, the dull
gray b}r c. Let us endeavor to understand the course of the
rays which pass through b. Let $ be a ray which enters from
the mirror in the direction a /3, and penetrates at o into the
less refractive medium a, and passes through it in the direc-
tion o 6 — inasmuch as it deviates from the normal in a. Let
s' be another ray which enters b at the angle m', i. e., a greater
angle than that under which $ enters. Aeeordinglj*, the de-
viation it will undergo in the medium a will be greater than
the deviation undergone by $. And if it be assumed that it
is so great that the sine of the angle of deviation^/, the angle
being a right angle, the ray will pass out between a and b. If
the angle of incidence is greater than mf, the angle of deviation
is greater than a right angle, so that the ray does not enter a
at all, but is totally reflected through b. Hence the substance
b appears clearer than c, for more rays pass out at b than at c;
the excess consisting of those rays which, entering b in a di-
rection towards a, and at a greater angle than in', are totally
reflected in b, as above explained.

The bright borders of the proper substance present the same
characters and relations in the muscles of crabs after treat-
ment with gold. Occasionally they may be also seen in the

70 MUSCULAR TISSUE.

muscles of frogs, and in those of the tail of the rabbit, if quite
fresh. From these facts it is evident that the clear borders
of the proper substance need not be regarded as actually ana-
tomically distinct from the rest, but their presence can be ex-
plained as mere optical results of total reflection, i. e., provided
it be admitted that the interstitial substance and the proper
substance refract light in different degress.

In order to study the longitudinal stria? preparations must
be made in humor aqueus of the fresh muscular tissue of
Hydrophilus, of the sartorius of the frog, or of the muscles
of the back of the lizard, care being taken to separate the
muscular bundles slightly from one another. In such prepa-
rations it is seen that the substance which lies between two
adjoining transverse striae appears to be marked off into a
number of quadrangular areas which correspond to the sides
of the prismatic " sarcous elements."

A number of such sarcous elements, arranged in a linear
series parallel to the axis of the muscle, and connected each
to each by shorter disks of transparent intermediary substance,
together constitute a so-called primitive fibril. And, in ac-
cordance with this definition, we can conceive each muscular
fibre to be formed of primitive fibrils, along with the interme-
diary substance (corresponding to the longitudinal strife), by
which these fibrils are held together. It is no less possible to
conceive of the muscular fibre as consisting of disks (each
composed of a number of laterally contiguous sarcous ele-
ments, along with the intermediary substance by which they
are, as just remarked, held together), separated each from
each by thinner disks of intermediary substance. The best
demonstration that the sarcous elements are the elements of
the muscular substance which are arranged in disks trans-
versely, and in fibrils longitudinally, is to be obtained by the
method of Cohnheim. A muscular fibre of a frog, Hyrophilus,
or cray fish is exposed in a platinum capsule to a freezing
mixture, at a temperature of — G° C. to — 8° C. After a short
time the muscle acquires the consistence of wax. Fine sec-
tions are then made with the aid of a cooled razor, and are at
once examined in a drop of serum under a thin cover-glass,
care being taken to introduce slips of silver paper to avoid
pressure. Such a preparation, seen under Hartnack's immer-
sion objective No. 10, exhibits the following facts: Circular
or oval disks present themselves (cross sections of muscular
fibres), the margins of which are sharply defined and possess
a double contour (sarcolemma). Within the sarcolemma a
beautiful mosaic is seen, in which the triangular, four-sided, or
pentagonal areas appear to consist of dull-looking material,
separated by lines which are brighter, more transparent, and
refract light less strongly. These lines are, in general, of

BY DR. KLEIN. 71

extreme tenuity, but certain spots are always to be observed,
within which the areas of dulness are further apart; in other
words, the clear lines of demarcation are wider. Wherever
this is the case there exist sharply defined nucleus-like bodies,
which, as we shall find, are actually the nuclei of the muscle-
corpuscles. In cross sections of muscular fibres of Crustacea,
insecta, amphibia, and reptilia, nuclei, surrounded by spots in
which the clear lines are thicker than elsewhere, are met with
in all parts of the fibres ; but in mammalia they occur only in
the immediate neighborhood of the sarcolemma. In the
Crustacea and in Hydrophilus, the prevalent form of the
mosaic is pentagonal ; in the frog, four-cornered, and usually
rectangular. Provided that the preparation is protected from
pressure and evaporation, it remains unaltered for several
days. If a small quantity of water or very dilute acetic acid
is added to the fresh preparation, the disks swell out in a
remarkable manner; the polygonal areas become more trans-
parent and increase in size, while the intermediary substance
disappears.

A fresh section, obtained as above, may be placed for a few
minutes in diluted serum and then transferred for from ten to
thirty seconds to half per cent, silver solution ; finally, washed
in water slightly acidulated with acetic acid, covered in glyce-
rin, and exposed to light. A preparation is thus obtained in
which the sectional disks are colored of various shades, from
clear yellowish-brown to dark-brown. Clear white lines on a
brown ground are seen with great distinctness, which corre-
spond completely with the trellis-work of transparent lines
seen in the fresh preparation, from which appearance we learn
that the spaces of the mosaic are stained brown by silver.
Oblique sections, whether examined fresh or after staining
with silver, exhibit corresponding appearances. In longitudi-
nal sections, prepared according to the same method, small
brown rectangles, longer in the direction of the axis of the
muscle than in the transverse direction, which correspond to
the sarcous elements, are here and there visible. These
rectangles are separated from each other by clear narrow lines.
If a very small fragment of mammalian or frog muscle
(sartorius or mylohyoid of the frog, or the flat muscle in front
of the trachea of the rabbit), be steeped for fifteen or twenty
minutes in chloride of gold, then exposed to light for one or
two days in slightly acidulated water, and subsequently
hardened in common alcohol, sections can be made in planes
at right angles to the axis of the muscle. These exhibit
.-tjtpearances which coincide in every respect with those above
described, the only difference being that the rectangular sar-
cous elements exhibit a clear red or purple tinge, while the
interstitial substance is dark.

72 MUSCULAR TISSUE.

From all those facts we learn that the substance of a mus-
cular fibre consists, in the first place, of oblong prisms, i. e.,
sarcous elements, with their axes parallel to its axis, and
formed of a material which refracts light strongly, is stained
strongl}- with silver, slightly with solution of chloride of gold,
and swells out in the fresh state on the addition of water ; and,
secondlj', of a less refractive, transparent, interstitial substance,
occupying the remainder of the space ; which is not colored by
silver, but is intensely stained by chloride of gold, and dis-
appears in dilute acetic acid. This last reagent appears to
have the faculty of dissolving the interfibrillar part of the inter-
stitial substance, leaving the interstitial disks of the fibrils
almost intact. Similar facts are observed in muscles which are
subjected to the hardening influence of alcohol or chromic
acid. In sections of muscles so prepared, the fasciculi which
are cut transversel}' are seen to consist of disks, which are
either round or flattened against each other, and ma}' be easily
stained in carmine or picric acid. In such disks the double
contoured section of the sarcolemma includes a number of small
roundish corpuscles, each of which, as may be seen in longitu-
dinal sections, is a fibril cut across. Muscular fibres, cut lon-
gitudinally, seem to consist mereby of fibrils which are divided
b}T cross lines into small long rods placed end to end. In sec-
tions of hardened tongue of the frog, it is very easy to obtain
isolated fibrils : the}' are also to be seen in teased preparations
of other muscles hardened in alcohol and chromic acid.

The Sarcolemma. — Each muscular fibre is invested in a
structureless hyaline membrane. To demonstrate it, the readiest
method is to add water to a fresh preparation of Hydrophilus,
or, better, frog muscle. After a short time the sarcolemma
separates in transparent bulgings with double contours.
Greater lengths of sarcolemma can be shown, by carefully
teasing fresh frog-muscle in salt solution. In such a prepara-
tion, fibres are always to be found, which, over a greater or
less extent, are no longer striated, but consist of a finely
granular mass. Continuing the observation, it is seen that the
parts of the fibre on either side of such a spot become con-
tracted, as indicated by the approximation of the transverse
striae, and by the widening of the fibre. By virtue of this con-
traction, the granular muscular substance is torn asunder, the
sarcolemma being brought into view as a transparent tube.
Within this tube a greater or less number of granules are ob-
served in active molecular movement. As the disintegration
of the muscular substance progresses, an increasing quantity
of sarcolemma is brought into view. The broken up ends (if
muscular substance are always irregular in form, presenting
numerous projections, none of which exhibit striation. By and
by fresh spots become the seat of the same change, so that the

BY DR. KLEIN. 73

disintegrated parts are separated from each other only by
short intervals of normal muscle. By drawing asunder a small
number of muscular bundles, their opposite ends being seized
with fine forceps, a preparation may be obtained which shows
similar appearances in a larger proportion of fibres.

The extraordinary power of resistance of the sarcolemma
may be shown as follows : One of the hind legs of a tadpole is
amputated at the thigh. The animal is then replaced in water.
After fort3'-eight hours, the loosened muscular fibres hang from
the stump in long pencils. If these are cut off" close to the sur-
face of the stump with sharp scissors, and covered in water,
the}' are found to consist of a number of hyaline tubes, which,
when seen in profile, present doubfy contoured edges. Next
the cut edge some of them contain a plug of striped muscular
substance, or of coarsely granular material, which is divided
into a number of closely packed polyhedral cells. In the rest
of the tubes, coarsely granular young cells are seen sprouting
from the internal surface.

Muscle-Corpuscles. — In preparations of fresh muscle
(newt, frog, or Hydrophilus) numerous nuclei occur, which in
the Hydrophilus are roundish, in the frog oblong or staff-
shaped. If dilute acetic acid be added, the muscular substance
becomes swollen and transparent, and the nuclei are seen very
distinctly, each embedded in granular protoplasm, which has
the form of a spindle-shaped cell, the long axis of which is
parallel to that of the fibre. If, on the other hand, we examine
an oblique or cross section of frozen muscle, covered in dilute
acetic acid, it is easy to satisfy one's self that the nuclei in
question are not embedded in fusiform protoplasmic masses,
but in finely granular lamella?, which are seen to be dotted
about the whole thickness of the fibre, and may be either di-
vided or simple. The distribution of these lamellae in the
muscular fibre differs in different animals. In mammalia, they
are confined to the immediate neighborhood of the surface; in
the Hijdrophilus, crab, newt, and frog, they constitute a net-
work within the muscular fibre, exhibiting marked differences
in thickness, not only between different lamella?, but between dif-
ferent parts of the same lamella. In fresh muscle of Dytiscus
marginalia, the arrangement of these protoplasmic masses is as
follows: In some muscular fibres, the granular protoplasm has,
throughout the fibre, the form, more or less, of cylindrical bands,
in which roundish nuclei are arranged close together in linear
scries. Here and there, these nuclei are separated by distinct
marks, so that the whole cylinder seems as if divided into por-
tions, each corresponding to a nucleus. In other fibres, there
are. in place of an axial cylinder of protoplasm, two or three
lamella: which are continuous with each other by subordinate
lamella? of various extent. In these, roundish nuclei arc em-

74 MUSCULAR TISSUE.

bedded at various distances, and in cross sections they appear
thicker at the level of the nuclei. In an optical longitudinal
section, in which a lamina is seen in its whole length, it is ob-
served to be usually curved. In a transverse section it is also
often curved. We therefore conclude that these lamellae are
composed of placoid cells, each of which corresponds to a nu-
cleus, and constitutes a muscle-corpuscle, the limits of which
are indicated by the markings often seen between neighboring
nuclei. In Hydrophilus, muscular fibres are also met with, in
which the lamellae are replaced by cylinders.

In the individual muscular fibres of the tongue of the frog,
obtained by taking a snip from that organ near the surface,
and covering it at once with serum, chains of oblong nuclei, or
large groups of nuclei without definite arrangement, are to be
found here and there. In the latter case, the nuclei are not all
oblong; some of them are constricted and possess knobs. In
sections of tongue stained in gold, it is seen that these chains
and groups of nuclei are embedded in granular protoplasm,
which is continuous with the granular lamellae above described.
These bodies are therefore to be regarded as enlarged, many-
nucleated muscle-corpuscles.

Tendinous Insertions. — The transition from muscle to
tendon takes place in two ways: In one the transverse striae
cease, the whole muscular fibre passing into a tendinous bundle
of the same size, consisting of parallel wavy fibres. In the
other, the muscular fibre tapers to a blunt point, the sarco-
lemma extending beyond it as a thread-like structure of vary-
ing thickness, resembling, and becoming continuous with, a
slender bundle of connective tissue. Oblong cellular structures
may be seen in this fibre. The first form may be very easily
and complete!}' demonstrated in a teased preparation in serum
or saline solution, in the muscular layer which extends, in
Hijdrophilus, from the trunk to the first joint of the extremi-
ties, or in a similar preparation of the thoracic cutaneous
muscle of the frog. In the latter case, care will be necessary
to remove the tendinous insertions along with the muscle, and
to spread out the whole in serum or saline solution before
covering it. The second form can be studied in fresh teased
preparations of the muscles of the limbs of small mammalia,
or of the muscles of the larynx; but more easily in very thin
sections of the tongue of man or of mammalia, especially in
those fibres which radiate upwards towards the dorsal mucous
membrane. In sections of tongue hardened in chromic acid,
which are made across the long axis of the organ, bundles of
fibres are seen to pass upwards between the transversely cut
bundles of the longitudinalis linguae. Of these bundles it is
seen that certain of the muscular fibres stop short, the sarco-
lemma being prolonged into a thread, as above described. The

BY DR. KLEIN. 75

rest of the muscular fibres enter the mucosa, and end in ten-
dinous bundles of equal diameter, which again unite with the
mesh work of the mucosa.

Arrangement and Division of Muscular Fibres. —
They are grouped into bundles by septa of connective tissue,
which in general contain numerous amoeboid cells, and a net-
work of ordinary branched cells. From these septa thinner
lamellae spring, which are interposed between the individual
bundles. In a mature foetus a cross section of muscular bun-
dles, e.g., of the tongue, palate, or eyelids, shows that they are
intersected by a beautiful network of nucleated branched cells,
in such a way that each mesh is occupied by a single fibre. In
general, striated muscles do not divide: there are, however,
situations in which muscular fibres are seen to divide dicho-
tomously or dendritically. The best example is to be found in
the cardiac muscular fibres, of which a repeated dichotomous
division is characteristic, as also their union with one another
so as to form a network. In the tongue of mammalia, the
muscular fibres often divide before ending in tendons; but in
that of the frog the divisions occur much more frequently.
Both in recent preparations, and in sections made after hard-
ening, muscular fibres are seen which branch dendritically, as
they ascend towards the dorsal mucous membrane, the ulti-
mate branches being so small that they contain only a few
fibrils, which finally end in connective tissue fibres.

Examination of Muscular Fibre in Polarized Light.
— We assume the reader to be acquainted with the action of a
Nicol's prism, contenting ourselves with stating that the polari-
zation microscope is an ordinary microscope, in which one
Nicol is placed above the eye-piece or ocular (i.e. between the
eye-glass and the observer's eye), and a second between the
object and mirror. The upper Nicol is usually of one piece
with the ocular. The prism is so fixed that it can be rotated,
and that the axis of rotation is contained in its principal plane.
The degree of rotation is measured by a graduated circle.
The lower Nicol is surrounded by a condensing lens, and can
(in Ilartnack's microscope) be fitted into the tube which
ordinarily contains the diaphragm or condensor. In looking
through such a microscope, it is seen that the illumination of
the field varies according to the relative position of the two
prisms; so that, in rotating the upper one (which is called the
analyzer), it is darkened and lightened twice in each complete
rotation. The positions of greatest obscurity are those in
which the principal planes of the two Nicols are at right angles
to each other — of greatest luminousness, those in which these
planes are coincident. When the microscope is used 'with the
Nicol in the first-mentioned position, the object is said to be
observed between crossed Nicols.

76 MUSCULAR TISSUE.

Before proceeding to describe what is seen in muscle when
examined between crossed Nicols, the facts observed when
crystals which possess similar optical properties arc looked at
in the polarizing microscope, should be first carefully studied.
Muscular fibres can be shown to possess optical properties which
resemble those of doubly refractive, positive, uniaxial crystals,
such, e. jy., as those of rock crystal or quartz, etc. The meaning
of these expressions must be illustrated. If a number of doubly
refracting microscopical crystals of any kind are placed under
the polarizing microscope, it is seen that when the upper Xicol
(or analyzer) is rotated so as to make the field dark, the crys-
tals appear (according to their position) more or less illumin-
ated ; whereas this is not the case if the crystals are isotropous,
i. e., belong to the " regular" system of crystallization.

The degree of illumination of each crystal varies according
to its position. This may be readily shown by rotating the
object-glass, or stage on which it lies, without moving either
prism : it is then seen, as regards each crystal (supposing the
Nicols to be crossed), that four times in each complete rotation
it loses its luminousness altogether. These two positions are
called the inactive azimuths, because the body looks in these
positions as if it were isotropous — dark on the dark field.
This happens whenever the principal plane of the crystal lies
in the principal plane of either Nicol, and is consequently at
right angles to that of the other. In all other positions it looks
more or less illuminated, the degree of brightness increasing
and diminishing as the azimuth in which it is placed declines or
approaches; consequently, the crystal appears brightest when
its principal plane is inclined at an angle of 45° to the plane of
polarization. When the crystalline body is of a certain thick-
ness, the appearances are somewhat different. Thus, if a plate
of mica from one to two millimetres thick is placed on the ob-
ject-glass with the Nicols crossed, it is seen that the field is not
only luminous but colored, the color varying according to the
thickness of the plate — its intensity varying according to the
inclination of the principal plane of the mica to that of the
prisms, being brighest when that inclination is 45°. If now the
plate of mice is rotated, it is seen that in each rotation, as be-
fore, there are four azimuths of greatest brightness, and four
intervening ones of greatest obscurit}'. But, in addition to
this, it is observed that, in the bright azimuths, the colors dis-
played differ — the color of the field in any given position of the
plate being complementary to that seen when it is rotated 90°.
These facts are of great practical importance in all eases in
which it is desired to observe the doubly refractive parts of
transparent objects between crossed Nicols, without losing
sight of those parts which are isotropous. If such objects are
examined in the ordinary way in the dark field, it is obvious

BY DR. KLEIN. 77

that all those parts which are isotropous are invisible. If,
however, the field is colored, by placing a plate of mica or
selenite underneath the object, everything is seen as distinctly
as if the light were not polarized, with the difference that the
doubly refractive bodies are distinguished from others by their
color — the latter being of the color of the field, the former of a
color differing from it variously, according to their thickness,
their position, and their optical properties. In all doubby re-
fracting ciystals, there is at least one direction in which light
ma}r be transmitted without suffering double refraction — i. e.,
bifurcation. Those crystals in which there is only one such
direction are called uniaxial, e. g., Iceland spar, qtiartz, and
tourmaline. When such crystals are examined between crossed
Nicols, in such a position that the light is transmitted through
them in the direction above referred to (which is always that
of the axis of ciystallization), they are not seen. We shall find
that the same holds good as regards the anisotropous parts
of muscular fibre.

In a fresh muscular fibre seen between crossed Nicols, the
first fact that strikes one is that the appearances correspond
with those observed in doubly refracting bodies. Next it is
seen that all the muscular fibres under observation are not
equally illuminated. Those are brighest which are so placed
that the long axis forms an angle of 45°, the illumination di-
minishing as the angle diminishes, until it disappears at the
moment that the fibre axis lies in the plane of polarization of
either Nicol. It is further seen that all parts of the muscular
fibre are not doubly refracting, but only those parts which
were before described as sarcous elements. The interstitial
substance looks dark whatever be the position of the fibre, so
that between crossed Nicols it is invisible.

The method to be adopted for demonstrating these facts is
as follows : —

Method. — From a number of plates of selenite or mica, one
is selected which, when placed in the proper azimuth, gives be-
tween crossed Nicols a field of the tint which is known as
teinte de passage.1 Such a plate having been found, it is fixed
to the object-glass with a drop of dammar. Fresh muscular
fibres of the extremities of the crab, frog, or hydrophilus, are
placed in absolute alcohol for half an hour, or in ordinary al-
cohol for several days. As soon as the muscular tissues are
deprived of water, they are soaked in oil of turpentine. Of the

1 The teinte de passaged a peculiar purple violet, and lies between
red and blue in this sense, that if the plate possess a thickness a shade
greater than that which produces the tint required, the color is blue ; if
a shade less, red. These facts are of importance as aids in selecting
a plate.

70 MUSCULAR TISSUE.

muscle so treated, a preparation is made on the plate of mica
above mentioned, the muscular fibres being teased in such a
way that they lie in various directions. If the preparation is
now examined in the purple fU'ld (obtained as above described),
the different colors of the individual muscular fibres arc brought
out with the greatest distinctness. On rotation of the upper
Nicol they undergo changes: if the rotation extends to 'J0C,
each color is replaced by its complementary. In a cross section
of a muscle (of any animal) hardened in alcohol, and prepared
in dammar varnish after steeping in turpentine, the individual
fibres show various degrees of illumination. All transitions
present themselves between those which are bright between
crossed Nicols, and those which are completely invisible; and
it is found that the latter are those which are cut in planes at
right angles to their axis — the former, those cut at an angle of
45° to their axis. It is thus seen that the long axis of a mus-
cular fibre corresponds, in relation to its properties of double
refraction, to the axis of crystallization of a uniaxial crystal —
in short, that a muscular fibre is optically comparable to such
a crystal. Briicke has further demonstrated, not only that the
muscular fibres are uniaxial, but also that they are positive,
i. e., that they resemble those uniaxial crystalline bodies in
which the extraordinary index of refraction exceeds the ordi-
nary index. Inasmuch as the apparatus necessary for demon-
strating this is not to be found in most laboratories, and an
explanation of the mode in which it is accomplished would in-
volve a more general discussion of the subject of polarization
than our space allows, it has been omitted. The reader is re-
ferred to Briicke's article in Strieker's Histology for further
information.

If a teased preparation of the fresh muscle of a frog is
treated with water and covered, the ends of the muscles swell,
and the contents project as a transparent granular mass, in
which the strire are no longer visible. Between crossed Nicols
these parts are found to be doubly refractive, and look like a
silver-gray cloud of dust on the dark ground. The particles
of which the cloud consists are regarded by Briicke as the
real elements of the doubly refracting substance. They are
the constituents of the sarcous elements, and are called Dis-
diaklasts. The disaggregation of the sarcous elements is de-
termined by the water.

BY DR. KLEIN. 79

CHAPTER V.

TISSUES OF THE NERVOUS SYSTEM.
Section I. — Nerve Fibres.

According to the presence or absence of the medulla which
surrounds their central and essential part, viz., the axis-
cylinder, nerve fibres are distinguished as medullated and
non-racdullated. The presence or absence of the so-called
Schwann's sheath affords an additional and subordinate dis-
tinction. This sheath is a resistant, elastic, sometimes fibril-
lated, but more commonly homogeneous, membrane, contain-
ing a variable number of oval nuclei.

Axis-Cylinder. — All nerve fibres contain an axis-cylinder ;
it is a solid cylindrical structure, which, under the highest
powers, is seen to be made up of the most delicate fibrils
(primitive fibrils). It varies in size, in accordance with the
thickness of the nerve fibre. As it approaches the periphery,
it splits into its constituent fibrils by repeated division, or by
giving off smaller lateral branchlets. To demonstrate the
fibrillated structure of the axis-cylinder, a fresh nervous
bundle may be prepared from the lateral columns of the spinal
cord of a small mammal, from the optic nerve, the olfactory
nerve, or from some nerve belonging to the sympathetic sys-
tem. The preparation must be macerated for twenty-four
hours in iodized serum, and then further prepared by teasing
with needles. In the nerve fibres of the lateral columns of the
spinal cord, the structure of the axis-cylinder may also be
shown in preparations which have been steeped for several
days in diluted solution of bichromate of potash. In prepa-
rations thus obtained, many of the fibres are seen to exhibit
points at which the medullary sheath is broken, in conse-
quence of which the pale, finely striated axis-cylinder becomes
visible. Fibrillar structure may also be readily demonstrated
in the processes of the ganglion cells, and in the pale naked
axis cylinders of various thicknesses of the nervous centres.
Again, in the fresh tadpole's tail, as prepared in serum or in
half per cent, salt solution, fibrillar structures can be seen
with great distinctness in the peripheral branching axis-cylin-
der. This structure is not, however, peculiar to the peripheral
or central portions of the course of a nerve, but exists in other
parts. To show this, the best way is to place the fresh nerve

80 TISSUES OF THE NERVOUS SYSTEM.

in common alcohol for a few minutes, and to stain the prepa-
ration with carmine. It must then be put in absolute alcohol
for twenty to thirty minutes, after previously teasing it out
somewhat. If it is allowed to remain twelve hours or more in
oil of turpentine, and then covered in dammar varnish, it will
be found that all the nerve fibres are more or less completely
deprived of their medullary sheaths. The axis-cylinder ap-
pears in general to consist of granulous substance, but here
and there distinct longitudinal streaking can be recognized.
The axis-cylinder can also be freed of its medullary sheath if
chloroform or collodion be added to a teased preparation of
fresh nerve, which is as nearly dry as possible without being
thoroughly desiccated. Occasionally the primitive fibrils of
the non-medullated nerve fibres are beset with small varicosi-
ties at nearly regular intervals, which, when treated with cer-
tain reagents (perosmic acid, chloride of gold), become very
distinct.

Medullary Sheath. — In a teased preparation of a fresh
sciatic nerve of the frog, in half per cent, salt solution, the
individual nerve fibres are seen to be invested by a sheath of
transparent, highly refractive material, which, when it presents
its surface, appears hyaline, but, as seen at the edge of the
nerve, exhibits a double outline. Thus the medullary sheath
confers on the nerve fibre a dark edge or double contour; so
that these appearances in a nerve are characteristic of its
presence. Soon after the preparation has been made, it is ob-
served that the sheaths of many fibres become beset with drop-
like bodies of irregular form, which are either bright and
shining, or granulous and turbid. The}r are produced by a
coagulation of the medulla. In preparations made in iodized
serum, the fibres remain, however, for several hours quite
smooth, without undergoing this change. In the nervous
centres, the medullated fibres which possess no Schwann's
sheath often present a necklace-like appearance, due to this
coagulation of the medullary sheath (the so-called varicose
fibres). The medullary sheath exhibits a remarkable arrange-
ment at those points of the course of the nerve at which it
divides into two or more branches. At such points the sheath
becomes considerably attenuated, as well as contracted. To
show this, the membrana nictitans of a frog is carefully ex-
cised, spread out in a drop of humor aqueus, and covered —
care being taken to introduce strips of paper under the cover-
glass so as to prevent pressure. The thoracic cutaneous
muscle of the frog may be prepared in the same way. Where
a medullated nerve fibre passes into a non-medullated, as in
the objects above mentioned, the sheath is usuall}' thinned out
towards the point where it is about to cease, in which case
the thin portion ma}7 either extend up to the line at which it

BY DR. KLEIN. 81

abruptly terminates, or may end in a terminal thickened bor-
der. In other instances, more particularly in the striated
muscles, the sheath very often stops suddenly without any
previous attenuation.

Neurilemma. — In order to make out satisfactorily the
relation of the nerve fibres in a nerve trunk, sections must be
prepared, either of nerves hardened in alcohol, or in diluted
chromic acid, and must then be stained with carmine ; or tis-
sues known to be richly supplied with nerves must be em-
ployed, c-g-i tongue, oesophagus, trachea, urinary bladder, etc.
In cross sections of nerves, the nerve fibres are seen to be in-
closed in a well-defined connective-tissue sheath (neurilemma),
of thickness more or less proportional to that of the nerve
itself. Between the fibres of the neurilemma, cellular struc-
tures are met with. In many nerve trunks, septa stretch in-
wards from the sheath, by which the nerve fibres are divided
into a greater or less number of bundles. In such preparations
the cross sections of each nerve fibre exhibit an external ring
with double contour — the cut edge of the medullary sheath —
inclosing a body of circular outline which does not fill up the
whole of the space, and is readily stained by carmine. In a
longitudinal section of a nerve we observe, within the connec-
tive-tissue sheath, the double contoured fibres, running parallel
with each other, but following a more or less wavy course, and
showing the nuclei of their Schwann's sheaths. In newly-born
children the number of nuclei is much greater than in adults.
The spinal nerves, which in the frog find their way to the skin
from the spinal cord through the dorsal lymph sac, possess an
extraordinarily thick neurilemma ; this is covered by a layer
of endothelium, which can be demonstrated by staining with
nitrate of silver. In the neurilemma of many microscopical
nerves, fine capillary vessels can often be made out. For the
tracing out of medullated fibres, the use of osmic acid is of
great value; for the medullary sheath is, in consequence of
the fatty matter it contains, stained dark by this reagent.

Schwann's Sheath. — With the exception of the optic
and auditory nerves, the fibres of all peripheral nerves possess
a Schwann's sheath. The nuclei which the sheath contains
are seen, when examined in the fresh state in indifferent fluids,
to be pale, and more or less distinctly granular. When acted
on l»y acids or hardening reagents, they shrink. In freshly
prepared teased preparations (e.g., of the sciatic nerve of the
frog), the Schwann's sheath of the wide medullated fibres can
be recognized with great difficulty. In general, only the
nuclei can be made out. The sheath itself can be more easily
seen in the narrow non-medullated fibres. In the nerves of
Lbe tail of the tadpole, and of the membrana nictitans of the
frog, in those of the mesentery of the frog and of mammalia
6

82 TISSUES OF THE NERVOUS SYSTEM.

"whether in the fresh state or treated with gold, in the cornea
of t he frog or of mammalia treated with gold, in sections of
the epiglottis or of the mucous membrane of the mouth made
after treating the tissue with gold — the Schwann's sheath can
be often recognized as a more or less distinctly streaked mem-
brane. It generally ceases where the non-medullated fibres
split into their constituent fibrils.

Non-medullated Fibres. — Various methods must be
used for the demonstration of the non-medullated fibres, for
the same method does not answer equally well in all cases.
Among these, chloride of gold has, unquestionabl}', the first
place. In very many instances it affords the only means we
have of following these fibres to their finest ramifications, e.g.,
in the skin, mucosa, cornea, and striped muscular tissue, etc.
Osmic acid is also very useful. The silver method, or treat-
ment with certain acetic acid mixtures, is occasionally em-
ployed. In membranes which are prepared in the fresh state
in an indifferent liquid, individual non-medullated nerve fibres
can be seen, but their finer ramifications cannot be traced, even
in the most transparent, without the aid of the reagents above
mentioned.

Section II. — Nekve Cells.

Nerve Cells, i.e., ganglion cells, may be investigated (a)
in the ganglia which are attached to the spinal and certain
cerebral nerves ; (b) in the gray substance of the brain and
spinal cord ; (c) in ganglia belonging to the sympathetic
system.

(a) Ganglia of the Cranial and Spinal Nerves. — As
may be seen in sections of these ganglia (hardened in chromic
acid or Midler's fluid), each of them is inclosed in a capsule.
This capsule varies in thickness in different ganglia, and is
continuous with the neurilemma of the nerves which enter and
leave the ganglion. It consists of fibrillated connective tissue,
in which the cellular elements proper to that tissue ma}' be
distinguished. From it septa of connective tissue stretch in-
wards, and unite by anastomosis so as to form a meshwork.
This meshwork serves to support the rich vascular system with
which the ganglion is provided. Its meshes arc occupied by
the nerve fibres and b}r ganglion cells. These last consist of a
substance partly granulous, partly fibrillated, in which a
vesiculated, spheroidal, sometimes oblong, nucleus is em-
bedded, which itself incloses a shining nucleolus, the position
of which may be either central or eccentric.

For the study of these cells, teased preparations must be
used. The spinal ganglia of fish, particularly of the roach
and pike, the Gasserian ganglion of the frog, or the ganglion

BY DR. KLEIN. 83

through which in the same animal the auditory nerve passes —
are best suited for the purpose. If the first are used, the root
of the nerve with its ganglion is excised, and macerated in
iodized serum, dilute solution of bichromate of potash, or
Miiller's fluid, for twenty-four hours or more, after which the
cells may be teased out with needles. Good teased prepa-
rations can also be obtained of the ganglia of the spinal
nerves of fish or frogs in the fresh state. The ganglion cells
of fish and frogs, thus isolated, are mostly bipolar, less fre-
quently multipolar. The processes exhibit fibrillar streaking,
and, when a process is isolated for some distance, it is found
to become invested with a medullary sheath at a short distance
from its origin ; or, in other words, it assumes the characters
of a medullated nerve fibre. The Schwann's sheath of this
nerve fibre is continuous with the similar membrane which
forms the capsule of the ganglion cells from which it originates,
and in which, as in the Schwann's sheath, there are oblong
nuclei at regular distances. In the ganglion cells of the Gas-
serian ganglion of the frog, there are always masses of yellow
pigment. In the spinal nerve ganglia of the mammalia, it is
only possible to isolate unipolar cells. Good permanent pre-
parations of ganglion cells may be obtained after treatment
with chloride of gold. With this view the Gasserian ganglion
of the frog, freshly excised and cut into with fine scissors, is
placed for ten or fifteen minutes in chloride of gold, and then
exposed in slightly acidulated water to daylight, until it as-
sumes a darkish tinge. In preparations of ganglia thus treated
and teased in glycerin, the ganglion cell substance, along
with the axis-cylinder process, is violet red, while the nucleus
is pale.1

(b) Ganglion Cells of the Brain and Spinal Cord. —
The spinal cord of the calf or ox are the best objects for this
demonstration. The organ must be divided into small por-
tions, which must be placed in bichromate of potash solution,
for periods varying from a few da}Ts to several weeks. Then
a thin slice of gray substance is to be cut with the razor — pre-
ferably from the anterior horns — and teased in the liquid in
which it has been macerated. Any one who is practised in the

1 Preparation of the Gasserian Ganglion. — A frog having been
rendered ex-sanguine by slitting open the ventricle, the roof of the
skull is exposed, and then carefully raised from the occipital region for-
wards. This process is continued until the internal auricular foramen
of the petrous bone can be distinctly seen. Then the medulla oblon-
gata and pons are pushed aside with a needle, and the notch of the
pars petrosa cleared of fluid by dabbing it with a fragment of bibulous
paper. The fifth nerve is then readily seen. On it, close to where it
enters the bone, is a distinctly yellow swelling, which must be care-
fully exposed by removing the portion of bone which conceals it, and
excised with fine scissors.

#4 TISSUES OF THE NERVOUS SYSTEM.

use of the needle can also obtain good preparations by teasing
from fresh spinal cords, in iodized serum. In preparations of
this kind, in addition to the multipolar ganglion cells, mednl-
lated nerve fibres, of various diameters, possessed of irregular
or regular dilatations (varicosities), and axis-cylinders of va-
rious size with distinct fibrillar streaking, are to be met with.
In teasing spinal-cord preparations, it is always well to place
the glass on a black ground.

The ganglion cells of the anterior horns of the spinal cord
of the calf are remarkable for their size, and consist of a
granular cell substance, in which (as may be seen in prepara-
tions in iodized serum under very high powers) fibrils may be
distinguished. The large round vesicular nucleus which each
cell contains, has a double contour, and incloses a highly
refractive nucleolus: in its neighborhood there is usually a
mass of pigment. Each cell possesses processes of two kinds —
the so-called axis-cylinder process, and the branched processes.
The axis-cylinder process springs from a broad base, from
which it tapers to a fine filament. To whatever distance this
filament is traced, it is seen that it it does not branch, but
becomes thicker, and eventually assumes the character of a
medullated nerve fibre. The other processes are broad and
flattened, and soon divide dentritically. They consist of fibrils
embedded in a coarsely granular interstitial substance: the
fibrils can be followed distinctly into the ganglion cell. As
we shall see subsequently, the terminations of these processes
form a dense network of extremely minute filaments, which
network is in equally direct continuity with the endings of
the nerve fibres which enter the cord by the posterior roots.
The cells of the posterior horns are entirely similar, but some-
what smaller. If thin sections of the spinal cord of the pike
are hardened in bichromate of potash or chromic acid, washed
in water for twenty-four to forty-eight hours, and then placed
in diluted ammoniacal solution of carmine for a few hours or
a day, good permanent preparations can be obtained by teasing,
which can be mounted in glycerin. In the nuclei of Stilling,
in the intra-cranial part of the cord, cells occur resembling
those of the anterior horn of the spinal cord, and may be pre-
pared in the same way.

Gerlach's method of demonstrating the relation
between the ganglion cells and the network of non-
medullated nerve fibres in the spinal cord. — Longi-
tudinal sections, which must be as thin as possible, are made
through the anterior horns of the gray substance of a per-
fectly fresh spinal cord of the calf or ox ; these are transferred
as they are cut into very dilute solution of bichromate of
potash (one part in 5,000-10,000), and allowed to remain for
two or three days in a cool place. Thereupon they are placed

BY DR. KLEIN. 85

for twenty-four hours in very dilute solution of carmine; they
are then washed in distilled water, teased out- superficially on
the object-glass, and mounted in glycerin. I have also found
it possible to demonstrate the extremely fine network of non-
medullated nerve fibres, with the greatest distinctness, in
teased preparations of sections of the gray substance of the
spinal cord of the calf, after maceration for two or three weeks
in one per cent, solution of bichromate of potash.

Ganglion Cells of the Hemispheres. — If the cortical
substance of the mammalian brain be macerated in iodized
serum, bichromate of potash, or Midler's fluid, ganglion cells
of more or less conical form can be isolated, from the base of
each of which several arborescent processes stretch inwards
towards the white substance, while the small end of the cone
terminates in a process which is simple near its origin, but
eventually divides into fine branches, and exhibits everywhere
(in iodized serum preparations) fibrillar streaking. Permanent
teased preparations may be obtained in the way described
above as applicable to the spinal cord.

(c) Ganglion Cells of the Sympathetic System. —
The ganglion cells of the sympathetic system occur either as
distinct ganglia of various size (as is seen in the digestive
mucous tracts, and in the genital organs), or they are ar-
ranged in linear series, or are scattered in greater or less
number amongst and between the fibres of nerves. The sym-
pathetic ganglia (as, for example, those of the ganglionic cord
or the coeliac ganglion of mammalia) are best studied as fol-
lows : The structure is placed in Midler's fluid or bichromate
of potash, and allowed to remain several days until firm
enough. Fine sections are then prepared, and teased in gly-
cerin, either at once or after staining in solution of carmine.
Another plan consists in steeping sections prepared from
frozen ganglia, in chloride of gold for ten or fifteen minutes,
and making from them teased preparations, which may be
mounted in glycerin. Again, small fragments of fresh ganglia
may be steeped in one-tenth to one and a half per cent, acetic
acid, and left in it from twenty-four to forty-eight hours, and
then employed in the same way.

The aorta and the bulbus arteriosus of the frog afford excel-
lent preparations. For this purpose the vessel is ligatured at
the point of division, and filled with half per cent, solution of
chloride of gold by aid of a capillary tube. A second ligature
having been placed around the bulb, the part is cut out, and
steeped for ten minutes in the same solution. The tube is
then opened and exposed, two days or more, in acidulated
water, to the light. When of sufficiently dark color, it is
stuck out on a cork with pins. Thin lamella? may then be

86 TISSUES OF THE NERVOUS SYSTEM.

stripped off the external aspect of the vessel, spread out on an
object-glass, and covered in glycerin.

Meissner's Plexus. — The ganglionic nodules, occurring
in the course of the nerves which form Meissner's plexus, in
the submucosa of the intestine, may be studied as follows.
They are also well seen in longitudinal and cross sections of
intestine hardened in chromic acid, and still better in sections
parallel with the surface. Strips of intestine of the cat or clog
(after having been washed with half per cent, salt solution, or
water colored slightly with bichromate of potash) are steeped
for from forty minutes to an hour in half per cent, gold solu-
tion, and then exposed to light in distilled water, and finall}'
hardened in alcohol. Sections are then made in a direction
parallel to the serosa, of which of course those only are of
use which pass through the submucous tissue. Any one pos-
sessed of sufficient dexterity can obtain good preparations by
spreading bits of rabbit's intestine, excised and cleansed as
above described, on a piece of cork by aid of pins, with the
mucous surface uppermost. The mucosa is then Avorked off
as completely as possible with the fine-pointed forceps. Fine
flakes of loose tissue must be snipped with the aid of the
curved scissors, either from the deep surface of the mucosa, or
from the surface from which it has been severed. These are
either examined in salt solution in the fresh state, or treated
with gold for permanent preparations.

Auerbach's Ganglia. — The ganglia of Auerbach, which
are interposed between the transverse and longitudinal muscu-
lar layers, are demonstrated as follows : A portion of fresh intes-
tine of a rabbit or new-born foetus is blown out with the aid of
a glass tube. The operator must then try to strip off with the
forceps, from the external surface, a thin membrane, which will
be found to contain the serosa and the longitudinal muscular
layer. Strips of considerable extent ma}' be thus obtained with
a little practice, and must be then treated with gold in the
usual manner.

The ganglion cells, which occur in the genital organs, may
be best studied in sections or parts hardened in chromic acid,
or colored with gold and then hardened in alcohol. — Good
preparations of sympathetic ganglia can be obtained from the
bladder of the rabbit. Bits of the fresh bladder are colored
with chloride of gold, and then steeped in acidulated water until
they swell out into a gelatinous translucent mass. Thin mem-
branous fragments stripped off with the forceps, or snipped off
with the scissors, are spread out and covered in glycerin. To
these preparations we shall recur, in connection with the dis-
tribution of the nerves among unstriped muscular fibres.

Intimate Structure of the Ganglion Cells of the
Sympathetic System.— In each ganglion cell (with the ex-

BY DR. KLEIN. 87

ception of those of the ganglia of Auerbach) the following parts
may be distinguished ; the capsule, the body of the cell and its
nucleus, aud the processes. The capsule is beset with strong nu-
clei at even distances from each other ; in sections of fresh gan-
glia hardened by freezing, and treated with nitrate of silver,
markings may be seen in the capsule which indicate the exist-
ence of endothelium ; the elements of this endothelium are of
such size as to make it apparent that each of the nuclei above
mentioned belong to an individual cell. As in the ganglia of the
spinal nerves, the capsule is continued from the cell upon one
of the processes, with the Schwann's sheath of which it becomes
identified. The ganglion cells of the sympathetic system are
of various size, and are either globular or oblong. In the for-
mer case, they may be either without distinguishable processes,
or may have a single process (unipolar), or two in opposite
directions (bipolar) ; being in the former case pear-shaped, in
the latter spindle-shaped. Others occur which have two pro-
cesses in the same direction, or numerous processes in various
directions (multipolar cells). The substance of the ganglion
cell is for the most part finely granular, sometimes containing
clumps of pigment of various size. Each cell contains a single
vesicular nucleus (or two nuclei), which is usually eccentric,
and always contains a large, shining nucleolus. In the exami-
nation of a number of ganglion cells, one or two can generally
be found in which fine fibrils are distinguishable : these can
often be traced nearly to the nucleus, presenting an appearance
which seems to correspond with the network of fibres described
by some in the body of the cells.

Spiral Fibre Cells. — In the cells of the sympathetic gan-
glia of the frog, as well as of the coeliac ganglion of mammalia,
and in those of the bladder of the rabbit, pear-shaped or club-
shaped ganglion cells may be isolated, which possess two pro-
cesses, extending in the same direction. These processes differ
more or less in thickness from each other : they are contained
near their origin in a common sheath, which, at a greater
distance, divides into two, each investing one of the processes.
So long as they are in the common sheath, their arrangement
to one another is peculiar. Sometimes they merely cross one
another; at others, one of them, usually the thinner, twines
spirally round the other. Occasionally, this last is perfectly
straight ; sometimes it is apparently of the same substance with
the body of the cell ; at others, it seems to penetrate into its in-
terior tending towards the nucleus, without, however, being de-
monstrably united with it. The second process, viz., the so-
called spiral fibre, originates by a double or single root, which
can be followed to certain nucleolus-like structures, of oblong
form, of which from one to four are to be found in the neighbor-
hood of the pole from which the straight process springs. But

88 TISSUES OF THE NERVOUS SYSTEM.

whether the spiral fibre is connected with these nuclei, as hns
been supposed, by a network of extremely fine filaments from
which it appears to spring, cannot be determined any more
certainly than the question whether, in multipolar cells in gene-
ral, the processes spring entirely from the substance of the cell,
or one or other of them from the nucleus.

Reproduction of Ganglion Cells. — The ganglion cells of
the sympathetic system seem to undergo very active develop-
ment. This appears, first, from the frequency with which cells
containing two nuclei are met with ; secondl}', from the cir-
cumstance that frequently two, three, or four polyhedral cells
occur in a common capsule; thirdly, from the occasional oc-
currence of two club-shaped cells in one capsule, so placed that
they are in apposition by their flat bases, while their sharp
ends are continuous with processes; and finally, that in many
organs, as, e. </., in the (male) genital tract, and in Meissner's
ganglia of the newly-born foetus, groups (so-called " nests") of
extraordinarily small ganglion cells occur. If the Auerbach's
ganglia of the rabbit's intestine are prepared as directed above,
and covered in serum, they are found to consist of a network
of bands of various breadth, the nodes of which constitute
broad plates of irregular form, the whole being invested by a
sheathing in which nucleus-like structures are distinguishable.
The substance both of the nodes and of the bands which connect
them is finely streaked or granular. A greater or less number
of ganglion cells mostly globular inform, are embedded in this
substance, and arranged either in groups (in the nodes) or in
rows (in the bands). In the latter, the chains of cells are inter-
rupted at intervals; the former exhibit numerous perforations,
which are merely the interstices of a dense meshwork of bands.
In gold preparations, these facts can also be easily demon-
strated.

In preparations made in the same manner from the intestine
of a nearly mature human embryo, it is possible to make out
that, in the reticular sj'stcm above described, numerous small
cellular structures occur, embedded in the substance both of
the bands and nodes, in most of which all that can be seen is a
nucleus surrounded by a very narrow entourage of granular
substance: a few present the ordinary characters of ganglion
cells.

In sections of intestine of the rabbit hardened in chromic
acid (as we shall see in Part II.), the connection of these gan-
glia with the ganglionic masses of similar form which exist in the
circular fibres, and communicate towards the mucosa with the
ganglia of Meissner, can be well seen.

BY DR. KLEIN. 89

Section III. — Peripheral Nerve Endings.

Terminal Organs of Nerve Fibres.— Pacinian Bod-
ies.— The Pacinian bodies are oval or pear-shaped little mas-
ses which are found in the subcutaneous tissue of the skin of
the finger, and in that of the beak and tongue in birds (goose
and duck). In man they are met with also in the genital tract,
e. gr., in the labia majora, prostate, and corpora cavernosa : in
all these situations they can be best studied in sections. They
are most easily demonstrated, however, in the mesentery of
the cat, in which they are visible to the naked eye as elliptical,
transparent bodies, occurring mostly in the fatty parts. Pre-
parations are made as follows : A mesentery of a cat that
has just been killed is spread out on an object-glass and cov-
ered with a drop of serum or half per cent, solution of common
salt; or a portion of mesentery containing Pacinian bodies is
placed in solution of bichromate of potash for twenty-four
hours, and then covered in glycerine. We begin our study
with the medullated nerve fibre, which enters the corpuscle at
one end. From the point at which the nerve parts from the
twig from which it is a branch, its course is winding. As it
approaches the Pacinian body its sheath becomes thicker, and
acquires an appearance as if it consisted of several layers of
nucleated membrane. The dark-bordered nerve fibre is sepa-
rated from the sheath by a distinct, clear interspace, into
which oblong nuclei project at regular distances from the in-
ternal surface of the sheath, so as to resemble an endothelium.
The Pacinian corpuscle may be divided into the neck (the
point at which the nerve enters) and the body. In the neck,
the lamellae of the Schwann's sheath split repeatedly, becom-
ing further and further apart from each other, so as to form
the well-known concentric capsules of which the body is con-
stituted. Each capsule is beset with regularly arranged flat
oblong nuclei ; and, in the part of the body which is nearest
the neck, each capsule communicates with its neighbors by
cross lamelhe, which run obliquely from one to the other.
Elsewhere the capsules are discontinuous. In the neck, the
nerve fibre is dark-bordered and convoluted, but as it enters
the clear space which is contained in' the inmost capsule it
becomes straight, and at the same time pale and finely streaked.
In its course in the axis of this space it is separated from the
capsule by a clear interval, into which nuclei, arranged at
regular distances, project. Near the end of the axial space
the nerve fibre usually divides into two, occasionally into
three, branches, each of which ends in a pear-shaped enlarge-
ment (cell), containing a vesicular nucleus. Sometimes the
nerve fibre remains undivided, in which case the terminal cell
is relatively larger. In the mesentery of the cat I have seen

90 TISSUES OF THE NERVOUS SYSTEM.

Pacinian corpuscles in which the nerve fibre, instead of termi-
nating, passed out at the end opposite to that at which it
entered, eventually ending in another Pacinian body. In this
case the relation of the nerve fibre to the concentric capsules,
and of these to each other, in the neighborhood of the point
of exit of the nerve, was the same as in the neck. In the
most superficial of the concentric capsules, endothelial mark-
ing can be seen after treatment with nitrate of silver.

In connection with the Pacinian corpuscles we must mention
the so-called " Endkolben" (club-shaped endings), which are
described in the papillae of certain mucous membranes, and
are said to consist of an axis-cylinder, ending in an enlarge-
ment, surrounded by a thickened sheath.

Meissner's Bodies, or Tactile Corpuscles. — These
bodies occur in certain broad papillae of the skin of the volar
side of the fingers and of the palm in man. The}' can be best
demonstrated in vertical sections of portions of skin, made
across the parallel furrows, and either hardened in chromic
acid or in alcohol after treatment with gold. They are oblong
bodies, each occupying the axis of a papilla. Their outline is
often broken by deep notches. In each corpuscle numerous
cross markings are to be seen, which depend partly on the
existence of fine fibres, partly on the arrangement of spindle-
shaped nuclei. Into each body a medullated nerve fibre, pro-
vided with a nucleated Schwann's sheath, finds its way, and
then twines once or twice round it : the nerve may often be
followed to its upper extremity. Sometimes the fibre appears
to enter the corpuscle from one side, in which case it cannot
be traced further.

Peripheral Nerve Cells. — Fresh thin portions of human
skin (e. g., skin of the prepuce or of amputated extremities), or
small portions of the shaven skin of the rabbit's abdomen, are
placed for a few minutes in half per cent, acetic acid, and then,
after immersion for one or two hours in solution of chloride
of gold, are treated in the usual wa}\ In sections of such skin,
fine nerve fibres present themselves, which, after penetrating
the rete malpighianum, are seen to be connected with bodies of
an oblong or stellate form, which are strongly stained 03- gold,
and often contain each a distinct, clear, nucleus-like structure.
These nerve cells are not really, as has been supposed, terminal
organs, for fine fibres are seen not only to reach them, but to
pass beyond them, towards the surface. Similar nerve cells
exist in the epithelium of the mucous membrane of the mouth
and of the vagina. Again, in the network of delicate non-rae-
dullated fibres which branch under the epithelium of the tail-
pole's tail, the nerve fibres are continuous with the processes
of branched nerve-cells.

Recently, terminal bodies have been discovered by certain

BY DR. KLEIN. 91

authors in the mucous membrane of the epiglottis, from which
it would appear that nerve fibres, either medullated or others,
end under the epithelium in club-shaped bodies, consisting of
granulous substance, each of which contains one or two nuclei,
and is inclosed in a prolongation of the Schwann's sheath of
the nerve. In the mucous membrane of the frog's stomach it
is also stated that the nerve fibres end between the cylindrical
elements of the epithelium in oval or club-shaped swellings.
Again, in the connective tissue of the bladder of the frog, are
to be found cells which consist of a fine granulous protoplasm,
and contain several nuclei. In the skin of the wing of the bat,
and in the skin of the ears of mice, the medullated nerves come,
at certain parts, into remarkable relation with the papillae of
the hairs (See Chapter XI.).

Peripheral Branching of the Non-Medullated
Nerve Fibres in Different Tissues. — Under this head
will be described the termination of the nerves in the cornea,
conjunctiva, in the tail of the tadpole, in the skin in certain
mucous membranes, in unstriped muscular fibres, in striped
muscular fibres, in bloodvessels, and in glands. The nerve
endings of organs of special sense will be described hereafter.

Nerves of the Cornea. — In a living or recently killed
rabbit, the cornea is excised close to the limbus, and placed in
chloride of gold solution for three-quarters of an hour. The
preparation is then transferred to distilled water, in which it
remains until it has attained a steel-gray color, the time re-
quired varying, according to the season, from six hours to six-
teen or twenty. Thence the object is transferred to a small
wide-mouthed vessel, which contains a small quantity of nearly-
concentrated, filtered solution of tartaric acid. As soon as it
has had time to absorb the liquid, its color becomes deeper,
and changes to grayish-violet. If the bottle is then plunged
into water at a temperature of 40° to 50° C, to such a depth
that both liquids stand at the same level, the preparation as-
sumes, after a few minutes, an intense violet-red color, which
goes on increasing until it attains a dirty brownish-red, and
exhibits a velvety lustre. The cornea is now removed, and
steeped in distilled water for two hours or more. The epithe-
lium, along with a thin layer of corneal substance, is then
stripped off with the aid of the pointed forceps, beginning from
the sclerotic beyond the edge. In a preparation thus obtained,
it is seen that there exists in the anterior, i. e. most superficial,
layer of the cornea propria, a plexus of nerves of various
breadth ; each of these nerves consists of a bundle of minute
fibrils, invested in a pale Schwann's sheath with oblong nuclei,
within which they may either run parallel to each other, or wind
round each other in a more or less spiral manner. Wherever
a bifurcation occurs, or two nerves join, there is an enlarge-

92 TISSUES OF THE NERVOUS SYSTEM.

ment, in which the individual fibrils are distinct^' woven to-
gether into a network. From the nerves of this plexus, fibriH
are given off either alone or in tufts. Their general direction
is towards the surface. In taking this course they divide into
finer and finer filaments, so that the finest are scarcely dis-
tinguishable under the highest powers, and form, by repeated
anastomoses, a network which lies immediately under the epi-
thelium. The fibrils themselves are beset with minute granu-
lar varicosities. In either case these form a network, the
meshes of which are oblong or quadrangular. Corneas pre-
pared in the manner above described may be also advanta-
geously employed for the preparation of vertical and horizontal
sections.

The nerves of the substantia propria of the cornea of the
frog are best demonstrated as follows: A silk thread having
been passed through the centre of the cornea of rana esculenta
and brought out again at the sclerotic ring, the two ends are
knotted together. After the thread has remained from five to
eight hours, the cornea is excised and placed for twenty min-
utes or more in half per cent, solution of chloride of gold. It
is then transferred to distilled water, and exposed to light until
it acquires a dark violet-red, or reddish-brown color; the time
required for this purpose varying from one to three days, ac-
cording to the season. The epithelium must now be removed
with the aid of sharp-pointed forceps, along with a very thin
layer of corneal tissue, after which the cornea is to be mounted
in glycerin. In such a preparation it is seen that the nerve
trunks form a rich plexus by division and anastomosis in the
corneal substance. The branches of this plexus may be dis-
tinguished as nerves or bundles of the first order, and resemble
in their structure the corresponding nerves already described in
the cornea of the rabbit. From these, smaller bundles, not pos-
sessed of a nucleated sheath (nerves of the second order) are
given off. These run a course which is sometimes winding,
sometimes straight, and are connected by scanty anastomoses,
so as to form a plexus of large meshes. The}' give off, either
laterall}' or terminally, the fibrils of the third order.

Nerves of the Conjunctiva and Membrana Nicti-
tans. — For the study of the nerves of the mammalian conjunc-
tiva, the conjunctiva fornicis, or the plica semiluna?'is of the
eye of the pig, calf, or rabbit answers best. Portions of the fresh
plica semilunaris are treated in the same way as the cornea of
the rabbit. As soon as the proper degree of coloration is at-
tained, the preparation is hardened in diluted alcohol. Sec-
tions are then made in both directions, and covered in glycerin.
The conjunctiva fornicis is prepared free over a considerable
surface, and spread out on a cork with the free surface up-
wards. It may then be immersed in gold solution in a cup-

BY DR. KLEIN. 93

sule, or this liquid may be poured on it, after which it must
be treated as before. The demonstration of the fine nerves of
the conjunctiva is not so easy as of those of the cornea, so that
a general idea of their distribution can only be obtained by a
comparison of a number of preparations. The nerve trunks,
composed of medullated fibres, divide in the superficial layer
of the mucosa into small branches, each containing two or
three medullated fibres, in which varicosities occur here and
there. These mostly accompany bloodvessels, following a
winding course, and, by their communications, forming a plex-
us. They give off under the epithelium non-medullated fibres,
by the anastomosis of which a scanty sub-epithelial network
is formed. I have seen fibres originating from this network
making their way towards the surface among the epithelium
cells, and dividing dichotomously, but have been unable to
trace their further course.

The mode of preparing the membrana nictitans is the same
as that for the cornea. The fresh membrane is placed for
twenty minutes in chloride of gold, and then in distilled water
until it is of a dark color. The epithelium of the anterior sur-
face is then stripped off with the sharp-pointed forceps, after
which the preparation is covered in glycerin. The objects
which present themselves are (1) The flask-shaped glands (with
their short, narrow ducts) lined with spheroidal, granular, nu-
cleated cells ; they are surrounded by a layer of spindle-shaped
cells, not unlike muscle-cells. (2) Granular, large, flat, branched
cells, brightly stained, possessing oblong, flat nuclei, and send-
ing out processes which communicate in the same way as cor-
nea corpuscles. (3) Pigment cells, some of which are much
branched and communicate with each other, while others are
isolated and clump-shaped. (4) A rich network of bloodves-
sels. (5) Nerves. From the plexus of medullated nerves,
separate medullated nerve fibres spring, which, close to their
origin, lose their medullaiy sheaths. The non-medullated
fibres possess numerous oblong nuclei.

Nerves of the Skin. — We have already had occasion to
describe the method of preparation to be adopted for the study
of the nerves in the skin. It may, however, be well to add
that, immediately after removing the preparation from the
gold solution, it is possible to cut sections. The nerve trunks,
which find their way from the subcutaneous tissue towards
the epidermis, unite at the surface of the corium to form a
dense network of non-medullated fibres, from which fine fibrils
stretch vertically into the rete Malpighii either as isolated
fibrils which pass up into the epithelium between two neigh-
boring papillae, or as groups of several fibrils which pierce the
tips of the papilhe. In the rele Malpighii the nerve fibres often
divide, and occasionally communicate with their neighbors by

94 TISSUES OF THE NERVOUS SYSTEM.

horizontal brandies, or with processes of the deeply stained
branched cells above described. Isolated fibres may be traced
in the rete Malpighii to within a short distance of the horny
layer, where they either seem to lose themselves in swellings
of various size, or to divide dichotomously beyond ; eventually
returning towards the corium. The hair bulbs are also sur-
rounded by a network of fine non-medullated nerve fibres, the
further description of which will be found in another part.

Nerves of the Tadpole's Tail. — The best object for the
purpose is the tadpole of Hyla. The distribution to be now
described may be studied in recent preparations in half per
cent, salt solution or serum. It is, however, better to make
preparations by the method full}' described in the chapter on
connective tissue. The peripheral nerves of the tadpole's tail
are derived from a plexus which lies immediately underneath
the sub-epithelial hyaline layer ; the nerves which form it are
composed almost entirely of non-medullated fibres, which are
invested in a sheath beset with oblong nuclei. From this plex-
us similar fibres arise towards the epithelium, and by division
become smaller and smaller, anastomosing with each other
so as to form a second plexus nearer the epithelium than the
other. They also possess nuclei, the position of which in re-
lation to the fibre is sometimes lateral, sometimes apparently
axial. In the more superficial plexus, spindle-shaped enlarge-
ments are frequently seen at equal distances from each other.
These are distinctly granular, and each contains one oblong,
clear, sharply-defined nucleus, and nucleoli. They are to be
considered as bipolar ganglion cells, occurring in the course
of the fine non-medullated fibres. Immediately under the epi-
thelium the densest branching of the fine, pale fibres is seen.
These bifurcate repeatedl}*, displaying at tolerably regular dis-
tances, and especially at the points of division, numerous
granular swellings. The branchlets arising from this repeated
division join each other archwise, forming a very close network,
the meshes of which are round, or more often polyhedral, and
of such size that two or four of them can be covered by the
nucleus of an epithelial cell. In this network, nuclei and cells
are scattered, the former being sharply defined and of oblong
or irregular shape, exactly similar to those mentioned above
as occurring in the fine non-medullated fibres. The cells are
spindle- or (more frequently) star-shaped, flat, and finely granu-
lar, each containing a roundish nucleus. Their short pointed
processes are in continuity with the fibres of the nerve plexus.
They may be regarded as multipolar ganglion cells. (See p.
77, ■' peripheral nerve cells.") I could never find any connec-
tion between the pale nerve fibres and the well-known pale or
pigmented branched cells of the connective tissue. From
these facts we learn that the fine nerves of the tadpole's tail

BY DR. KLEIN. 95

terminate close to the epithelium in a dense network of pale
fibres, extending equally on both sides of the tail so as to form
a continuous sub-epithelial layer. As no nerve fibres can be
traced bej-ond this network, we are entitled to conclude that
the nerves terminate in it.

Nerves of the Mucous and Serous Membranes. —
Thin strips of fresh mucous membrane are cut from the vagina
or mouth of the dog or rabbit, and are placed for from forty-
five to sixty minutes in half per cent, solution of chloride of
gold, and are then, after having been washed with distilled
water, transferred to a solution of tartaric acid, hardened in
alcohol, and employed for the preparation of sections in the
manner already explained. The nervous trunks which are
distributed to the mucous membrane consist mostly of medul-
lated fibres, and give off branches which resolve themselves
into a network of fine non-medullated fibres, lying immedi-
ately beneath the epithelium, and the films of this network are
beset with nuclei, which are either far apart, as in the vaginal
mucous membrane of the dog, and in the oral and vaginal
mucous membrane of the rabbit, or more frequent, as in the
mouth of the dog. From this network, filaments having vari-
cosities of various sizes, find their way into the epithelium,
and give off branches to the different layers of epithelium
which combine into a network, some of which appear to end
in a knob-like swelling. In the middle layers they are in com-
munication with branched nerve-cells: there is no evidence
of an}r connection between them and the branched cells of the
mucosa.

Nerves of the Septum Cistern® and of the Mesen-
tery of the Frog or Newt. — It is comparatively difficult
to demonstrate non-medullated nerves in these parts by means
of the ordinary method of staining with gold. It can be
done in the following way successfully : The fresh membrane
is placed for from fort\T-five to sixty minutes in solution of
gold ; thereupon it is exposed to the light for several days in
distinctly acid water. As soon as the preparation has ac-
quired a markedly reddish or grayish-violet tint, it is pencilled
on both sides so as to remove the endothelium, and placed for
ten minutes in diluted, distinctly alkaline solution of carmine.
It is then washed in acidulated water and covered in glycerin.
From the winding nervous trunks which accompany the larger
vessels of the mesentery, numerous small twigs branch off in
great numbers, consisting of very numerous non-medullated
fibres, which combine to form a network. Although these
fibrils are much more numerous than has been hitherto sup-
posed, they never terminate by a free end, but always take
part in the formation of a network. (The numerous non-medul-

9t> TISSUES OF THE NERVOUS SYSTEM.

lated fibres which are distributed to the bloodvessels will be
described elsewhere.)

Nerves of the Peritonaeum. — For the demonstration
of the fine fibres of the peritonaeum of the rabbit, the follow-
ing is the best method: Three drops of concentrated acetic
acid are added to twenty cubic centimetres of distilled water.
To this mixture five drops of half per cent, solution of gold
is added. The fresh peritonaeum is immersed in the solution,
and allowed to remain exposed to the light for several days
until it becomes darkly stained. Very instructive prepara-
tions may be obtained by preparing in the same way the fold
in the peritonaeum, which stretches backward and to the left,
from the diaphragm to the upper surface of the stomach, close
to the cardia.

Nerves of Unstriped Muscular Fibres. — The bladder
of the frog, the small arteries of the same animal, the muscular
coats of the intestine, or of the vagina of the rabbit, may be
employed. The following methods are applicable : As regards
the bladder of the frog, the previously described method of pre-
paring the muscular fibres themselves, also serves for the de-
monstration of their nerves. In the bladder of mammalia, the
mixture of acetic acid and gold, mentioned above in relation to
the preparation of the nerves of the peritonaeum, answers well.
After the preparation is sufficiently stained, thin shreds of
muscular tissue are stripped from the external surface of the
swollen membrane, and prepared in glycerin. In the large
arteries of the mesentery of the frog, the method already em-
ployed for the demonstration of the non-medullated nerve
fibres of the mesentery generally, is to be used. The relatively
large arteries of the frog (as, e. g., those of the root of the me-
sentery) can, as a rule, lie advantageously prepared by placing
them for five minutes in half or one per cent, acetic acid, and
then either allowing them to stand in the gold solution twent}r
to thirty minutes, or transferring them to chromic acid solu-
tion of one-tenth per cent, for from thirty minutes to an hour.
For the unstriped muscular fibres of the intestine, uterus, etc.,
sections of frozen organs may be treated with acetic acid and
gold, or chromic acid, in the same way. Finally, small por-
tions of the same tissues may be steeped in gold solution,
washed in distilled water, treated with tartaric acid, hardened
in alcohol, and employed for the preparation of sections. The
facts thus demonstrated maybe summed up as follows : Nerve
trunks of various size run in the sheaths of connective tissue
which lie between the muscular bundles. These trunks consist
either of non-medullated fibres, or of medullated, or of both
kinds mixed, and form a plexus with wide meshes. In this
(which may be termed the principal plexus) the ganglion cells
which have been already described are intercalated. Its nerves

BY DR. KLEIN. 97

give off numerous fibres, some of which are medullated, but
soon lose the medullary sheath, others non-medullated. These
last are pale, streaked longitudinally, and have nucleated
sheaths. By their abundant ramifications, they form a network
of rhomboidal or oblong meshes, having nuclei at their points
of junction. This network involves the individual muscular
bundles, and is called the intermediary network. Fine fila-
ments, containing granules, spring from it, which penetrate be-
tween the muscular cells, and divide dichotomously in this
situation, forming by their connection the intra-muscular net-
work. In addition to the fibrils which lie between the fibres,
the network contains others, which penetrate the muscle-cells
and become connected with the nucleoli of their nuclei, in such
a wajr, however, that the nucleolus is not the end of the fibril,
but is intercalated in it. It is only in a few, out of a great
many successful preparations, that the iutra-muscular network
can be demonstrated. Most serve to show only the interme-
diary plexus.

Nerves of the Striped Muscles. — The demonstration
of the nerves of voluntary muscle has, hitherto, been accom-
plished only in fresh preparations; there are, however, one or
two cases in which the silver method can be used. It is, in
the first place, to be borne in mind that only muscles that are
still irritable are of any use for the purpose. Secondly, that
the greatest care must be taken in making the preparation,
especially to prevent the cover-glass from pressing, by strips
of paper.

Muscular Nerve Endings of the Water-beetle. — The
muscles of certain invertebrate animals, e. g., Dytiscus, or, still
better, Hydrophilus piceus, and particularly those which pass
from the thorax to the legs, are best suited for the purpose.
The. muscle is severed near its insertion with fine, sharp scis-
sors, and at once placed on the object-glass and covered, or
transferred to a drop of serum and spread out so as to sepa-
rate a few muscular fibres. It is easy to recognize the broad,
riband-shaped, medullated nerve fibres, each possessing a stri-
ated axis-cylinder, which rapidly divide into finer non-medul-
lated fibres, each distinctly streaked and beset with nuclei. A
single muscular fibre may receive several non-medullated nerve
fibres. At the point at which each enters the muscular sub-
stance, a more or less marked elevation is distinguishable, the
so-called Doyere's prominence. This consists of granular sub-
stance in which clear, roundish nuclei are embedded. The
prominence, with its nuclei, is lengthened out into processes in
directions corresponding with that of the axis of the muscular
fibre. These processes may either stretch along the surface of
the muscular fibre, or sink into its depth. Sometimes the
prominence is represented by a mere lamina of granular sub-
1

98 TISSUES OF THE NERVOUS SYSTEM.

stance, which does not project above the surface. The axis-
cylinder penetrates into the substance of the prominence, pass-
ing through the sarcolemma, with which its Schwann's sheath
becomes continuous. It usually divides dichotomously in the
prominence, each branch ending in a rounded extremity. The
prominence, therefore, consists of two parts, viz., the axis-
cylinder, with its two branches, and the nucleated granular
substance in which it is embedded. The granular substance
consists, in all probability, of the same material as that which
constitutes the so-called muscle-corpuscles.

Muscular Nerve Endings of the Frog. — In many
respects the nerves of the muscles of the frog differ from
those above described. In the first place, there are many
muscular fibres which are entered by only one nerve. In
order to make out this fact, it is a good plan to place portions
of muscle in a mixture of chlorate of potash and nitric acid
at 40° C. ; or, better,%to place the tissue for twenty-four hours
or more in diluted sulphurous acid, after which it is exposed,
still remaining in the liquid, to a temperature of 40° for a few
hours. If the muscle is then shaken with water in a test tube,
the individual fibres separate very readily from each other, and
may be covered without further preparation. For the study of
the finer relation of the muscular nerves, separate fasciculi of
the gastrocnemius may be employed, which must be cut out
with their tendons — those parts being chosen to which vessels
and nerves can be traced with the naked eye. The preparation
is covered in humor aqueus, after it has been spread out with
great care with needles. It is then possible to observe that a
medullated fibre comes into contact here and there with a
muscular fibre, and divides into several medullated branches.
Just as the branches approach the point at which they enter
the sarcolemma, in order to attain the surface of the muscular
substance, they lose their medullary sheath. At this point,
they resolve themselves into a number of small pale filaments,
which run parallel to the long axis of the muscle, keeping close
to its surface, and are beset with oblong structures resembling
nuclei. Eventually, each terminates abruptly in a rounded
end.

Another excellent object for demonstration of the muscular
nerves is the thoracic cutaneous muscle of the frog, which
must be divided along its insertions, and then severed from its
thoracic attachments, and carefully spread out in a drop of
humor aqueus and covered, care being taken to interpose strips
of paper underneath the edge of the cover-glass. It is also
possible to demonstrate the nerve endings in frog-muscles with
the aid of nitrate of silver — the same parts being used for the
purpose. The isolated fasciculi are placed in serum, to which
an equal quantity of distilled water has been added, for ten or

BY DR. KLEIN. 99

fifteen minutes. Thence they are transferred to a quarter per
cent, solution of nitrate of silver for thirty or sixty seconds,
and then exposed to the light until they acquire a brownish
color. They are further prepared in a drop of a mixture of
equal parts of ordinary acetic acid, glycerine, and "water. In
such preparations a s}'stem of clear lines shows itself in the
striped brown ground of muscular substance. These lines
correspond exactly, in their whole arrangement, with the intra-
muscular nerves above described.

Muscular Nerve Endings of Snakes and Lizards. —
The most beautiful muscular nerve endings with which we are
acquainted are those of the reptilia, e.g., Lacerta agilis, Lacerta
viridis, and Coluber natrix. In preparations of the muscle of
the thigh or of the back of the lizard in humor aqueus or
serum, it is seen that the medullated nerve fibres divide into
branches in the same way as in the frog. Here, as before, the
branches lose their medullary sheath just as they enter the
sarcolemma, and then resolve themselves into a beautiful digi-
tate or fringe-like expansion of pale fibres embedded in a
granular ground containing nuclei, resembling that described
in Hydrojohilus, but of a laminar form. In the subcutaneous
muscles of Coluber natrix, the terminal expansion forms a rich
network of riband-shaped fibres embedded in a granular ground.
The network is so close that it looks like a lamina in which
round and oval orifices have been punched out. In silver
preparations made as above directed, as well in the lizard as
in the snake, the same facts may be demonstrated — the intra-
muscular system of nerves exhibiting themselves as clear lines
on a brown ground.

The endings of the muscular nerves of mammals resemble
those of reptiles.

From the preceding details it appears that two forms of
muscular nerve endings may be distinguished. In the first
form, the ends of the axis-cylinder, or those of its branches,
lie in immediate contact with the muscular substance under-
neath the sarcolemma (frog). In the second, they are embed-
ded in a granulous ground {Hydrophilus, reptilia, mammalia).
The demonstration of nerve endings is one of the most difficult
tasks which can be undertaken by the histologist.

100 METHODS.

PART II.

PREPARATION OF THE COMPOUND TISSUES.

CHAPTER VI.
METHODS.

The methods of examining tissues in the fresh state, with
or without the addition of reagents, and of isolating the ele-
ments by the process of teasing with needles, have been fully
described in the First Part. We have also seen that, in trans-
parent structures, particularly membranes, the anatomical
relations of the elements may be studied, either by observing
them in the natural condition, or after preparation with the
solution of chloride of gold, or with that of nitrate of silver.
For the investigation of the compact tissues, other modes of
preparation are necessary, in order to bring them into such a
condition that fine sections can be made of them. It is the
purpose of this chapter to describe the method by which this
is accomplished.

Preparation of Sections of Fresh Tissues. — There
are a few organs or parts of organs which possess such a con-
sistence that it is possible, without preparation, to make micro-
scopical sections of them ; such as cartilage, some tumors,
skin, hypertrophied lymphatic glands, prostate gland, kidney,
liver, and under certain circumstances involuntary muscle.
Sections of these tissues serve either for the study of the con-
dition of the elements, or the action of reagents ; or are made
with a view of treating them with gold or silver. They are,
however, mainly useful as facilitating the preparation of the
individual elements by the process of teasing. For this pur-
pose the section may be either used in the fresh state with
indifferent liquids, or after maceration in iodized serum, Mid-
ler's fluid, or one per cent, solution of bichromate of potash.

For the study of the anatomical relation of fresh tissues,
other methods must be used. The simplest plan is to take the
object in the hand, and use a sharp section knife. It is some-
times recommended to fix the tissue between elder pith or

BY DR. KLEIN. 101

cork, by mechanical means. This is not advantageous on the
following grounds : Those tissues which are soft are so injured
by the pressure that their elements are in a completely un-
natural condition ; whereas, in the case of firm tissues, it is
quite easy to do without such assistance.

Preparation of Sections by Freezing. — For the pur-
pose of obtaining sections of tissue without any dislocation or
alteration of structure, the method of freezing is well adapted.
A freezing mixture is prepared by introducing alternately
small quantities of broken ice, or snow (not so advantageous),
and of finely powdered salt, into a large vessel, mixing the
two ingredients thoroughly after each addition. The tem-
perature should be determined by the introduction of a ther-
mometer. The object, which must be small, should be cut to
an oblong form, and placed on a flat cork, much wider than
itself. It must be pinned to this cork at the end opposite that
from which the sections are to be cut. In the case of a mem-
brane, the object must be folded, and fixed in the same way.
The whole is then placed in a platinum crucible, which has
been previously plunged into the freezing mixture. The cru-
cible must be at once covered, and a little of the freezing
mixture placed on the top of it. The section knife, which
must be sharp, is cooled by laying it on ice. As soon as it is
ascertained, by exploration with a needle, that the preparation
is firm enough, the knife is handed to an assistant, who wipes
it, and holds it in readiness. The cork is then taken out with
the forceps, and seized by the fingers of the left hand in such
a way that they do not come into contact with the preparation.
A succession of sections having been rapidly made, the num-
ber varying with the skill of the operator, the cork is replaced
in the crucible. The sections may be employed either for
immediate examination, or for teasing, or subjected to further
processes of preparation. As soon as the portion of tissue in
the crucible is again of the proper consistence, more sections
can be made. As regards the temperature which should be
employed, and the time during which the object should be
frozen, no definite rule can be given. It may be stated, in
general, that temperatures varying from — 6° to — 20° C. are
sufficient for all purposes. The time necessary for the attain-
ment of the proper degree of firmness is obviously dependent
on the temperature of the freezing mixture, on the thickness
of the object, and on the relative quantity of water it contains.
Accordingly the time is very variable, so that the proper
moment for removing the preparation can only be determined
by frequently repeated exploration ; by which means alone it
i~ possible to avoid the risk of carrying the hardening too
far — a result which is alike prejudicial to the structure of the
organ, and to the success of the section.

102 METIIODS.

Methods by which Tissues are Hardened for the
Preparation of Sections. — For the purpose of rapidly
hardening tissues, small portions may be advantageously
placed in the chloride of gold, osmic acid, or chloride of pal-
ladium, and kept till they are sufficiently consistent. Such
preparations must usually be embedded in the manner to be
hereafter described, before sections are made from them. The
sections themselves are then exposed to the light in distilled
water, and covered in glycerin. Half per cent, solution of
chloride of gold, solutions of perosraic acid varying from one-
tenth to two per cent., or solutions of chloride of palladium
from one-tenth to half per cent., are used.

Other agents and methods in use are the following : Alco-
hol, oxalic acid, boiling and drying, chromic acid and its com-
pounds, (a) For thin membranous tissues, hardening in alco-
hol answers well. It is more rapid than chromic acid, which,
however, has superseded it for many purposes for which it
was formerly employed. Absolute alcohol is used principally
for hardening brain, and for injected tissues. Common alco-
hol is also used for the hardening of pancreas, salivary glands,
and the glands of the stomach and intestine, and of objects
which have been already treated with gold or silver. Further,
when tissues have been partly hardened in chromic acid com-
pounds, the hardening can be accelerated and completed by
subsequent immersion in common alcohol, (b) The use of
oxalic acid and oxalates, and other similar salts, majr be en-
tirely dispensed with. If used, weak solutions of from a half
to two per cent, are preferable, (c) The process of boiling,
etc., is entirely relinquished. In former times it was employed
for intestine, kidney, trachea, and larynx. The intestine was
boiled in a mixture of water, creasote, and vinegar, stretched
on cork, and dried. Sections were made with scalpels, and
then steeped in acetic acid, (d) The chromium compounds
are the most valuable agents we possess for hardening — viz.,
chromic acid, in solutions varying in strength from one-tenth
to half per cent.; bichromate of potash, in solutions from half
to two per cent., and MiilLr's liquid, which consists of two
parts of bichromate, and one part of sulphate of soda, in 100
parts of water. These have the immense advantage that they
produce no marked shrinking or distortion of the tissues, so
that they retain for the most part their natural characters.
This is particularly the case as regards bichromate of potash
and Midler's liquid. Very small portions of tissue must be
used, particularly when chromic acid is employed, for it pene-
trates much less readily into the tissues than the others ; so
that if the preparation is too large, it is apt to become putrid
in the centre, while the outside is too hard. If the objects
are smeared with foreign matters, as, e. g., intestine by intes-

BY DR. KLEIN. 103

tinal contents, blood, or mucus, it is desirable to rinse them in
water colored \-ellow b}* bichromate of potash, before intro-
ducing them into the hardening liquid. The quantity of liquid
must be large in proportion to the size of the object. If the
process does not go on quickly enough, the liquid must be re-
newed. Chromic acid hardens much more rapidly than bi-
chromate or Midler's liquid, from two to five days being often
enough for the former, while as many weeks are required for
the latter. Its greatest disadvantage is that the tissue be-
comes brittle if it is left in it beyond the time that is neces-
saiy. It is, on this account, a good plan to transfer the
objects to common alcohol before they have acquired the
requisite consistence. The alcohol not only serves to com-
plete the hardening, but to preserve the objects in a state fit
for use. For some tissues, chromic acid is not suitable to
begin with, e. g., retina, ovary, or kidnej^s. For all these
organs, the bichromate of potash must be used. After two or
three weeks they are transferred to chromic acid or alcohol, to
complete the hardening.

Embedding. — It has been several times mentioned that
small portions of hardened tissues must be embedded. This
is effected by immersing the bits in a fluid mass, which can be
rendered solid either by cooling it or depriving it of water;
the purpose being, first, to render it possible to hold the bit,
and secondly, to facilitate the cutting of sections equally thin
throughout. Mixtures are used of stearin and oil, stearin and
wax, paraffin and oil, paraffin and wax, paraffin spermaceti
and oil, wax and oil, gum arabic, gelatin, gelatin and glycerin.
Among the fatty mixtures, the best, cheapest, and easiest to
prepare, is wax and oil. Next comes the mixture of paraffin
spermaceti and oil. For portions of tissue which have an un-
even surface, especiall}' if the inequalities are close together,
embedding in gelatin or gum is more to be recommended,
especially to those who have not had much practice.

Embedding in Wax and Oil. — For this purpose pure
white wax and pure olive-oil should be used. Equal quantities
of these ingredients are warmed in a capsule till all the wax is
fused; they are then thoroughly mixed with a glass rod. It
is better to prepare a considerable quantity at a time, although
only very little is required for one embedding. The propor-
tion of wax to oil depends on the consistence of the object to
be embedded ; the more wax being employed the firmer the
object, and vice versa. When sections of compact tissues (e. g.,
glands of the organs of digestion, trachea, larynx and muscle,
bone, the eye and its appendages) are to be made, the mode of
procedure is as follows: If the organ has been hardened in
alcohol, an oblong bit must be cut from it with a razor, in-
cluding the part of which it is desired to make sections. If

104 METHODS.

it has been hardened in any aqueous solution, e. g., chromic
acid or bichromate of potash, it must be first steeped in com-
mon alcohol. According to the size of the bit, a little box or
case, of paper or any suitable material, such, for example, as
zinc-foil, must be made, so that it will hold the fused mixture.
"When paper is used, the sides are joined with gum or paste,
or are merely pinned together. The box should be about half
as loiii; again as the object used. When read}-, it is filled with
the fused wax-mass to a depth sufficient to cover the object.
As soon as the mass begins to solidifj' at the sides, the bit is
introduced as follows: A needle is stuck slightly into the
end opposite to that from which sections are to be cut, and
the bit is plunged into the mass with its long diameter hori-
zontal, and in such a position that the end furthest from the
needle is near, but not in contact with, the side of the box,
and, consequently, the other end is at a considerable distance
from the side. In this way, although the whole is surrounded
with the wax mass, there is a greater thickness around the end
into which the needle is stuck, so that the whole can be se-
curely and conveniently held. The solidification can be accel-
erated by immersion in water or alcohol. If the portions of
tissue are compact enough, it is possible to perforate the bit
with a very slender needle, the point of which is stuck into the
table or cork on which the box rests; by this means the ope-
rator is saved the trouble of holding the needle till the wax-
mixture solidifies. In finally withdrawing the needle, the
greatest care must be taken to give it a twisting motion, as
otherwise, especially if the object is thin, it is apt to be dis-
placed. If the object contains a cavity communicating with
the surface by a single opening (e. g., the cochlea), it is neces-
sary first to fill the cavity with the mass : this is done either
by placing it in vacuo, or by making an additional opening.
If a thin membrane is to be embedded, of such tenuity that a
needle could not be introduced without danger of destroying
it, the following methods may be used: (1) A box is half
filled with the mass, and then, as soon as it begins to solidify,
the membrane is applied to the half-solid surface, in such a
position as is most suitable with reference to the direction in
which the section is to be made. The box is then filled with
a thoroughly fused mass, care being taken that it is not too
hot. (2) The fused mass is allowed to drop on an object-glass
or a thin flat piece of cork, so as to form a layer thick enough
to serve as a basis for the object, which is then laid upon it
and covered with an additional layer of wax-mass. If an
object-glass is used, it must be first covered with turpentine,
otherwise it will be difficult to remove the solidified mass from
it. In all cases the surface of the object must be nearly

BY DR. KLEIN. 105

dried before embedding, otherwise the mass will not adhere
to it.

As regards the other fatty masses, the only one which can
be recommended is a mixture of five parts paraffin, two parts
spermaceti, and one of lard. It is, however, decidedly inferior
to the mass of wax and oil.

Embedding in Gum or Gelatin. — It has already been
stated that objects with delicate projections in close proximity
to each other (e. g., papillae or villi), can be better embedded
in gum or gelatin than in wax and oil. The wax-mass, in
solidifying, does not penetrate between the projecting parts,
so that they are unsupported, and consequently are apt to be
broken off in making sections. Gum is solidified by immersion
in alcohol, gelatin by cooling : in both cases the process is so
slow that the mass has time to penetrate between the inequali-
ties of the surface of the object. The gum or gelatin solution
must be concentrated ; to the gelatin a little glycerin should
be added. I think gum preferable, first, because the consist-
ence of the solid mass can be varied according to the time it
is left in alcohol ; and even if it has already become too hard,
it ma}r be softened b}' adding to the alcohol a few drops of
water. No such modification is possible in the case of gelatin.
It is also more easy to make sections in gum than in gelatin,
the elasticity of which is a great disadvantage. On the other
hand, it is easier to embed in gelatin, and the time required for
solidification is much shorter. The method of embedding in
gum is as follows : A thick solution of powdered and sifted
gum arabic is prepared in a beaker, and allowed to stand in a
water-bath until all air-bubbles have collected at the surface in
the scum, which must then be removed by skimming ; after
which the solution may be used. A little box of paper is then
prepared, of suitable size, which is placed on a plate of cork.
The bit to be embedded is then stuck through with a needle,
the point of which is thrust into the cork through the bottom
of the box ; the same rules being followed as regards the posi-
tion of the bit in the box as in embedding in wax-mass. The
whole is then transferred to a glass capsule. As soon as the
bit is nearly dry at the surface, the solution is poured along a
glass rod into the box until it is full to the brim. Alcohol is
then carefully poured into the capsule, until the little box is
immersed to half its height. The whole must then be covered
over and left for two or more hours. As soon as the gum be-
comes opaque and white on the surface, which occurs in about
the time mentioned, the whole mass can be immersed in alco-
hol until it is brought to the required degree of solidity. The
process may be accelerated either by changing the alcohol
frequently, or by using absolute alcohol. If the mass is too
hard, it can be softened by adding a drop or two of water to

10G METHODS.

the alcohol, as has been already stated. When gelatin is used,
the mode of procedure, so far as relates to the preparation of
the solution, is similar. The bit having been fixed into the
box and surrounded with the solution, the whole is allowed to
stand until it becomes solid. Whichever material is used, the
mass is freed from the paper box as soon as it has acquired
sufficient firmness, and the ends of the needle are snipped off
above and below.

Preparation of Sections of Hardened Tissues. — For
making sections, razors are most used. Other instruments
are also employed, the purpose of which is to make up for
want of skill in the operator. The principal ones are Valentin's
knife, the microtome of Hensen, that of His, another micro-
tome lately described by Brandt, and the section cutter of
Stirling, lately improved by Rutherford. Of these, the most
useful is that of His, which has the advantage that it is possi-
ble to cut with it successive sections of an organ in equidistant
planes, parallel to each other, with the greatest exactitude.

The razor or section knife, in the hands of a skilful operator,
is superior to any of these contrivances. The knife I use is of
the form shown in Fig. 1 G. The blade measures eight inches ;
the wooden handle is massive, so that it can be firmly grasped.
One side of it is flat, the others slightly concave, it is thus ex-
tremely thin to a considerable distance from the cutting edge.
When sections are to be made of objects embedded in wax-
mass, the knife must be wetted with common alcohol, in which
liquid each section must be immersed as soon as it is made.
Sections of objects which have been embedded in gum or gela-
tin must be placed in water, but the knife wetted with alcohol.

Coloring of the Sections. — It is quite unnecessary to
refer to all the colored liquids which have been used for stain-
ing. It will be sufficient to describe the mode of using carmine
and anil in.

Carmine. — The most simple solution for the purpose is the
following: Two grammes of carmine in fine powder are tho-
roughly mixed in a beaker, with a few drops of water. Four
cubic centimetres of liquor ammonhe are then added, and forty-
eight cubic centimetres of distilled water. The liquid is filtered
into the stoppered bottle, in which it is to be kept. The bottle
is then left open for a few days, in order to get rid of the excess
of ammonia. One or two drops of this solution are introduced
into a watch-glass, and diluted with distilled water to such an
extent, that when it is placed on a written or printed sheet of
paper, the letters can onl}rjust be distinguished through it.
The sections are immersed in the diluted liquid till, on inspec-
tion, they appear to have the tint desired. Prolonged steeping
in dilute solution gives, as a rule, better results than rapid
straining in strong solution; for, in the former case, although

BY DR. KLEIN. 107

the color is less intense, the different tissues are rendered dis-
tinct by the different degrees to which they are stained. I use
the carmine solution for this purpose as follows: The sections,
having been allowed to remain for twenty or twenty-four hours
in a liquid consisting of one part of carmine solution and nine
to twelve parts of distilled water, are washed for a short time
in distilled water, and transferred either to glycerin (if it is in-
tended to mount them in this medium), or to alcohol (if they
are to be mounted in Dammar). If the sections have not been
previously in alcohol, it promotes the staining to put them for
a few minutes into that liquid. If it is intended to preserve
the sections in gtycerin, it is desirable to add a few drops of it
to the staining liquid. The well-known liquid used by Beale
for staining fresh tissues may be also employed for staining
sections; but, in preparing it for this purpose, the alcohol may
be omitted. The composition of Beale's liquid is as follows: —

Beale's Solution. — Ten grains of carmine are heated in
half a drachm of liquor ammonia?. As soon as the liquid is
cold, two ounces of distilled water, two ounces of pure glycerin,
and half an ounce of alcohol are added. The solution is then
either filtered or decanted from the undissolved carmine. This
liquid requires no dilution. A small quantity must be warmed
in a watch-glass to get rid of the ammonia, and it is then ready
for use. We shall find that, in the preparation of the mucous
membrane of the stomach, it is of special value.

Anilin — Anilin is used in aqueous and alcoholic solution ;
the former being most useful. It is obtained by treating anilin
blue with sulphuric acid. Two centigrammes of the soluble
product are dissolved in twenty-five centimetres of distilled
water, and twenty to twenty-five drops of alcohol. This solu-
tion colors sections which have been in alcohol very rapidly.

Picric Acid is used in very dilute solution for the purpose
of staining sections yellow. Sections may be first stained in
picric acid, then in carmine, in which case the muscles are col-
ored yellow. Whatever the staining liquid employed, the sec-
tions must be transferred, as soon as they are sufficiently col-
ored, to distilled water with or without the addition of a trace
of acid.

Methods of Mounting Sections. — Sections maybe cov-
ered either in glycerin, in mixtures of gelatin and glycerin, of
glycerin and acetic acid, of glycerin acetic acid and alcohol, in
Canada balsam, or in Dammar varnish. If glycerin is to be
used, the sections should, if they have been in alcohol, be pre-
viously placed in water. Glycerin alone, answers best for sec-
tions of tissues treated with gold or silver. Sections of organs
treated with osmic acid must be placed in acetate of potash.
Very thin unstained sections of glandular organs and of con-

108 METHODS.

nectivc tissue ma}- be temporarily mounted in glycerin, but
cannot be preserved for a length of time in that liquid.

All sections which are intended to be permanent, excepting
those of tissues prepared by the gold or silver methods, must
be mounted in Canada balsam or Dammar ; the last being
preferable, as more easy to manipulate. It is prepared as
follows: —

Preparation of Dammar Varnish. — Half an ounce of
gum Dammar in powder, is dissolved in an ounce and a half
or two ounces of turpentine, and half an ounce of gum mastic
in two ounces of chloroform. The two solutions are then
separately filtered and mixed. This varnish so obtained is
clear, and if exposed in a thin layer on a plate of glass solidi-
fies rapidly. The sections which are to be mounted must be
placed, for a quarter of an hour or more, in a capsule contain-
ing absolute alcohol, which should be provided with a cover.
Each section must be raised with the aid of a german-silver
or copper lifter (the blade of which is then placed on blotting-
paper, to remove the adhering alcohol), and transferred to a
watch-glass containing oil of cloves. B}r this means it be-
comes, in a few seconds, quite transparent. If it is colored,
the color becomes more intense; if it is unstained, it becomes
almost invisible. From the oil of cloves it is transferred by
the same means to a drop of Dammar varnish, previously
placed in the centre of an object-glass.1

If excessively delicate and thin sections are to be mounted,
such, e. g., as sections of the retina, or of any thin membrane,
it is not possible, without risk, to transfer them from one
liquid to another. In this case it is, therefore, necessary to
swim the section directly from the knife on to the object-glass,
in which position they must be treated with the several liquids
to be employed ; and each liquid must be allowed to fall on
to the section, and, after producing its effect, removed by in-
clining the glass, care being taken not to allow the object to
float away at the same time. All delicate sections must be
protected by the interposition, between the object and cover-
glass, of a square of silver paper, with a window cut in it
somewhat smaller than the latter.

Methods of Preserving Preparations permanently.
— Preparations which are to be preserved must be mounted

1 The lifter or spoon may be made by flattening the end of a copper
or german-silver wire, and bending it at right angles. It is desirable
to place the object-glass on a white ground if the object is stained, or
on a black ground if it is unstained, in order that the folds, if present,
may be seen and removed. If several sections are to be placed under
one cover-glass, each section may be pressed gently down on the sur-
face of the glass before covering ; the sections then adhere to the glass
sufficiently to keep in their places.

f

BY DR. KLEIN. 109

permanently. Those which are in liquids, such as glycerin,
acetate of potash, bichromate of potash, etc., must be sur-
rounded with cement, in order to fix the cover-glass. For
those which are in glycerin jelly, Canada balsam (neither of
which, however, are to be recommended), or Dammar varnish,
that is not neeessaiy. Various kinds of varnish are used for the
purpose, such as Frankfort lac, asphalt, etc. I use always
Dammar varnish. A streak of the varnish is placed on the edge
of the cover-glass and carried all round it, with the aid of a
glass rod drawn to a point, or a brush, care being taken that it
extends only a very little over the cover-glass. Before apply-
ing the varnish, the excess of liquid must be carefully removed
with blotting-paper from the edge of the cover-glass. I dis-
pense with the instrument frequently used for mounting, for the
following reasons : If the cover-glass is already fixed, as, e. g.,
in Canada balsam or Dammar preparations, any additional
mounting is unnecessary. If it is not fixed, i. e., when the
medium in which the preparation is contained is liquid, there
is much greater risk of displacement with the machine than
without it. It should always be borne in mind that the pre-
servation of the preparation is of more importance than the
outside setting. The other kinds of varnish may be used in-
stead of labels, for writing on the glass the name of the pre-
paration. If it is desired to preserve a preparation already
covered in water and solution of osmic acid, or bichronmte of
potash, etc., without removing the cover, so as to avoid risk
of displacement, the best way is to irrigate it with glycerin or
acetate of potash, until the one liquid is replaced by the other.
The excess of liquid must then be removed with blotting-
paper, and the cover-glass surrounded with Dammar varnish.
If, l>3' inadvertence, the upper surface of that part of the cover-
glass which is above the preparation has been smeared with
glycerin or Dammar varnish, and it is desired not to remount
it, the only way is to wait until the setting is dry. The spot
can then be removed with a camel-hair pencil soaked in water
if it be glycerin, or in turpentine and afterwards in alcohol if
it be Dammar.

110 VASCULAR SYSTEM.

CHAPTER VII.
VASCULAR SYSTEM.
Section I. — Methods of Injection. »

Before describing the structure of the bloodvessels and
lymphatics, an account will be given of the methods of inject-
ing. The processes of injection may be divided according as
they are used during life or after death.

Methods of Injecting during Life. — The method of
injecting the vessels of an animal during life has, hitherto, not
been much employed. It may be practised either for the pur-
pose merely of introducing into the circulation any suitable
liquid containing coloring matters, or other substances in
solution or suspension, or with a view to empt3*ing the vessels
of their contents and substituting another liquid. For ex-
ample, we have already seen that insoluble coloring matters
are introduced in order to feed the colorless blood corpuscles
and those of the connective tissue ; and we shall subsequently
see that hy the injection of colored solutions, a "natural
injection," produced by excretion of the ducts of certain
glandular organs, may be obtained. (See Chapter X.) The
most important insoluble coloring matters are vermilion, car-
mine, and anilin, which are used suspended in salt solution, as
described in Chapter I. p. 26. Insoluble Prussian blue, as
precipitated by the gradual addition of alcohol to the solution,
can also be used in the same way.

The methods are as follow : —

Injection of the Frog during Life. — In a large frog,
secured on its back, the abdominal vein is carefully exposed
under a dissecting lens, in its course up the middle line of the
anterior wall of the bell}'. A ligature is passed round the
distal end of the prepared part and tightened. A small clip
is then placed on the proximal end, and a ligature passed
under the vein between the two, which is looped, but not
tightened. The vein having then been opened just beyond the
loop, with a pair of sharp scissors, a fine glass canula is
introduced in the direction of the circulation. The loop is
then tightened round the canula and knotted. The canula
must now be filled, with the aid of a capillary pipette, with
salt solution, and connected by a bit of india-rubber tubing
with a brass syringe, in doing which great care must be taken

BY DR. KLEIN. Ill

not to tear the canula out of the vein. If it is desired to
continue the injection for some time, it is better to employ the
pressure of a column of liquid, for which purpose the following
arrangement must be used: A moderate-sized flask, contain-
ing the injection liquid, is supported on a retort-holder at a
height of about two or three feet above the table. The flask*
is fitted with a cork, in which two tubes are fixed, the one
being straight for the admission of air, the other bent so as to
form a syphon, the short leg of which dips under the level of
the liquid. To the other end an india-rubber tube, furnished
with a screw-clamp, is fitted, long enough to reach the canula.
A current is now produced along the tube by suction, which
can be regulated b}' the clamp so as to allow the liquid to flow
in a rapid succession of drops. The tube is then momentarily
closed b3r a second clip, and connected with the canula. The
clip on the tube is now opened and that on the vein removed.
As soon as the injection is finished the vein is ligatured on the
proximal side of the canula, which is then withdrawn. In
long injections, it is of course necessary to open the peripheral
end of the vein. If it is desired tq, estimate the quantity of
liquid injected, a cylindrical bottle is substituted for the flask,
which must be previously graduated. When the object in view
is to replace the blood completely with salt solution (with or
without coloring matter), it is better to introduce the canula
into the bulbus arteriosus.

Injection of small Mammalian Animals during life.
— The animal is secured with the aid of Czermak's holder.
(See Chapter XYI.) The external jugular is then exposed
by a sufficient incision, and cleared of the sorrounding tissue
with the aid of dissecting forceps. The vessel having been
ligatured at the distal end of the prepared part, and a clip
placed on it at the central end, the vein is opened by a small
incision, and a proper canula inserted and secured with a
ligature. The canula is then filled with salt solution with the
aid of a capillary pipette, and connected either with the
syringe or the tube of the syphon previously described.
Finally, the clip is opened, and the liquid allowed gradually
to enter the vein. As soon as the injection is completed, the
clip is immediately closed. Before the canula is removed, the
vein is of course ligatured. If the quantit}r to be injected is
small, it is simpler to use a small subcutaneous syringe, in
which case all that is necessary is to compress the vein imme-
diately above the clavicle, and to pierce it, when distended,
with the point of the canula. The pressure having been
discontinued, the liquid is at once injected. The aperture
must be seized by means of clip-forceps as the canula is with-
drawn, so as to prevent bleeding.

112 VASCULAR SYSTEM.

Injection after Death. — The materials used for this pur-
pose are Prussian blue, carmine, and nitrate of silver.

Prussian blue, like carmine, can be injected either in solu-
tion or suspension in water, or in solution in gelatin. Silver
is mostly used in solution in water. Soluble Prussian blue,
which is more used for injection than any other coloring
matter, is prepared according to the method of Briicke. 217
grammes of ferro-cyanide of potassium are dissolved in a litre
of water iu a large flask (Solution A). In another flask a
solution (B) of chloride of iron is prepared, containing one
part of the salt in ten parts of water. A third solution (C) is
prepared of sulphate of soda, which must be saturated. Equal
parts of the solutions A and B are mixed, each with twice its
bulk of C. The chloride of iron mixture is then poured slowly
into the mixture containing the yellow prussiate, care being
taken to stir constantly during the addition. The precipitate
having been allowed to settle, the greenish supernatant liquid
is poured away, and the residue thrown into a flannel strainer.
The blue liquid which passes through is returned to the
strainer until it become^ transparent. Thereupon what re-
mains on the filter is washed with water until what passes
through is of an intense blue color. The filter is allowed to
drain completely, and then placed between shreds of blotting
paper, and left to dry gradually in a sufficiently cool place. It
is then broken up into small fragments and kept in a glass
bottle. The blue material so prepared is perfectly and readily
soluble in water.

A two per cent, solution of this material may be used either
at the ordinary temperature or at the temperature of the bod\r.
It can be injected with great facility. When it is used with
gelatin, the mass is prepared by adding five parts of the fil-
tered solution above mentioned to one hundred parts of solu-
tion of gelatin, containing one part of gelatin to eight of
water. The gelatin is first dissolved in the water over a water-
bath in a porcelain dish ; the hot solution is then filtered
through flannel or fine calico, it is replaced on the water-bath,
and the blue liquid is gradually added to it with constant
agitation.

[There are some other blue liquids of the same kind in use :
"Beetle's Prussian blue fluid" is prepared as follows : Take
one ounce of common glycerin, one ounce of spirits of wine,
twelve grains of ferro-cyanide of potassium, one drachm of
tincture or solution of perchloride of iron, and four ounces of
water. The ferro-cyanide is dissolved in half an ounce each
of water and glycerin, and the iron mixed with similar quanti-
ties of both ingredients. The chloride of iron mixture is
thereupon added gradually to the ferro-cyanide, with constant
agitation. Finally, the spirits of wine, and the remainder of

BY DR. KLEIN. 113

the water are added gradually. " TurnbulV 's Blue." — Ten
grains of protosulphate of iron are dissolved in an ounce of
glycerin diluted with a little water. Thirty-two grains of ferro-
cyanide of potassium are dissolved in the same quantity. The
iron is then added to the red prussiate with constant agitation.
Beale modifies this formula by substituting five grains of sul-
phate of iron and ten of the red prussiate for the quantities
above stated, and adding to the mixture an ounce of water
and a drachm of alcohol.]

Carmine. — A mass which is fluid at ordinary temperature
is prepared, according to Beale, as follows : Take five grains
of carmine, half an ounce of glycerin containing eight or ten
drops of acetic acid, one ounce of pure glycerin, two drachms
of alcohol and §ix drachms of water. The carmine is first
mixed with a little water containing about five drops of ammo-
nia. Half an ounce of pure glj'cerin having been added to
this liquid, it is shaken in a flask, and then gradually poured
into the acidulated glycerin, with constant .agitation. If the
mixture is not distinctly acid, a trace of acetic acid is added to
the remaining half ounce of glycerin, which with the alcohol
and water is then gradually added to the rest. It is necessary
to prepare this mixture each time that it is used. The alcohol
may be omitted altogether without detriment. Carmine is
usuall}- emplo}'ed in solution of gelatin. The following liquids
are to be recommended : —

Ge7-lach,is Carmine Mass. — Sixty-nine grains of carmine are
dissolved in seventy grains of water with eight drops of liquor
ammoniae. The solution, having been exposed to the air for
several days, is mixed with a solution of one and a half drachm
of gelatin in one and three-quarter drachm of water. A few
drops of acetic acid are added to the warm mixture. Dr. Car-
ter's Carmine 3fass. — Take sixty grains of carmine, 120
grains of liquor ammonias, eighty-six minims of glaciai acetic
acid, two ounces of solution of gelatin, containing one part
in six, one and a half ounce of water. The carmine is dis-
solved in the ammonia and water and filtered. The filtrate is
added to one and a half ounce of solution of gelatin. The
other half ounce is mixed with the acetic acid, and added gut-
tali in to the rest, with constant agitation.

I found this mass answer extremely well with the following
modification: Four grammes of carmine having been sus-
pended in a few drops of water, eight cubic centimetres of
liquor ammonia? and forty-eight cubic centimetres of water are
added. As soon as the carmine is dissolved, the liquid is fil-
tered— a process which requires several hours. A gelatin so-
lution, containing one part in eight of gelatin, is next prei)ared
and filtered through fine calico. The carmine solution is added
gradually to two ounces of the filtrate, which is kept warm
8

114 VASCULAR SYSTEM.

over the water-bath. Forty or fifty minims of glacial acetic
acid are then added to another half ounce of warm gelatin solu-
tion, which is mixed gradually with the rest, with constant
agitation. Before the whole of the acid gelatin is added, the
mixture changes its color from bright red to dirty red. I>y
the addition of the last drops, the mass acquires the slight
acid reaction which is necessary to render it indiffusible in the
tissues.

Silver Solution. — The solution of silver used for injection
contains one-quarter or half per cent, of the salt.

Apparatus and Instruments. — Syringes of the ordi-
nary form answer well. They may be made of brass or
German silver. They are, however, now used only for special
purposes, e. g., for the injection of very small organs, and are
open to the objection that much practice is required in order
to regulate the pressure in such a way as to insure success;
deficient pressure rendering the injection imperfect, too much
producing extravasation. In general, and indeed in all cases
in which it is desirable that the pressure should be constant
throughout, the apparatus to be hereafter described must be
used. Canulas. — When the syringe is used, it is better to
employ metal canulas than glass ones. The former consist of
three parts (Fig. 17), viz., a collar, with two cross arms, and
a tubular beak. The beak is bevelled at the end, and is
grooved at a short distance from the bevelling. The dimen-
sions of the whole are accurately shown in the drawing. The
point must be carefully rounded. The nozzle of the syringe
is plugged into the collar, and is fitted with a stopcock, in
order to prevent the mass from returning after the injection is
completed. This object can also be answered by a ligature,
but in many cases this would be difficult from want of space.
Three or four such canulas with beaks of different calibres are
necessary. Glass canulas should be made of the following
form : A tube is drawn out in such a manner that it tapers to
a degree which varies according to the size of the vessel into
which it is intended to be introduced. The end must be trun-
cated and smooth, and must have a constriction at a distance
of about three millimetres. The large end should also be a
little drawn out, so that an India-rubber tube can be easily
slipped over it, and secured.

The various forms of apparatus for injection all depend on
the principle that the pressure which is required for injecting
is produced by the influx of water or mercury into a closed
vessel. The mechanical arrangements employed for this pur-
pose are as follow : A bottle containing water is suspended by
a pulley, so that it can be raised to any required height.
From a tubulature near the bottom a flexible tube issues,
which reaches to the table, and is connected with a glass tube,

BY DR. KLEIN. 115

■which is fitted by a cork into one of the tubulatures of a large
WoolfTs bottle, the bottom of which it almost touches. In
the other neck of the bottle a cork is also fitted, which con-
tains a short glass tube bent at the top ; this is connected by
a flexible tube with the stem of a T-shaped tube, one branch
of which leads to a manometer, the other to a second smaller
"WoolfTs bottle, in which the injection mass is contained. The
long flexible tube which leads from the suspended bottle must
be furnished with a clamp, and another is required on the tube
which connects the T with the injection-flask. Another ar-
rangement consists of a large flask holding several gallons, in
the mouth of which a large India-rubber stopper can be fitted.
At the bottom there is a side tubulature (for discharging the
water when necessary), into which a second stopper must be
fitted. The stopper contains a strong glass tube, having a bit
of India-rubber tube fitted to it, guarded by a strong clamp.
In the large stopper are two glass tubes, one of which is short,
not extending beyond the neck, and bent at the top; it is con-
nected with a T tube, which corresponds to the one employed
in the apparatus first described. The second tube is of the
same form as the first, and communicates with a supply-tap.
In other forms of apparatus rnercury is used. The apparatus
may then consist merely in a single WoolfTs bottle, into one
of the necks of which a rose funnel is fitted, reaching to the
bottom. The other neck contains a short bent glass tube,
which communicates with the T tube as before.' In all forms
of apparatus for injection, it is necessary to take the greatest
care to make all the junctions absolutely air-tight.

The injection mass is always contained as above described
in a WoolfTs bottle, which should be previously graduated, so
that the operator may know as he proceeds how much has
been injected. One of the necks of the bottle is in communi-
cation with the T tube, by means of a short glass tube fitted
with a caoutchouc connector, which does not reach below the
vulcanite stopper in which it is fixed. In the other, a long
tube is contained, the end of which reaches to the bottom of
the bottle, while the top communicates with the canula. If a
metal canula is used, the India-rubber tube is fitted on to the
stopcock. If the canula is of glass, it is guarded by a screw-
clamp.

When the organ or animal to be injected is small, it answers
well to use the syringe as a compression air-pump, by con-
necting it with the short tube of the WoolfTs bottle. The
superiority of this method over the direct use of the syringe

1 Of the more complicated forms of mercurial apparatus, that devised
by Hering (which is to be had of Heinitz, instrument maker in Vienna)
is undoubtedly the best, and answers all requirements. A description
of it will be found in the Wiener Sitzungsberichte.

116 VASCULAR SYSTEM.

is obvious. The inequalities of the pressure, which are its
chief disadvantage, are annulled by the elasticity of the air
contained in the bottle, which serves as a kind of cushion.
'While the operator fixes his attention on the canula, an
assistant gradually injects air into the bottle until the con-
tents of the syringe are discharged. The tube must then be
closed with a screw-clamp, and the operation, if necessary,
repeated.

"When warm masses are used, it is commonl}' necessary to
place the injection-bottle in a water-bath, kept warm by a
spirit lamp. It is also desirable to keep the object warm, for
which purpose it is placed on a plate of glass over a water-
bath ; or (as in Ludwig's arrangement) a warm chamber of
metal supported on a tripod is used, which is large enough to
hold both the animal and the bottle containing the injection.
It is furnished with a cover and air opening for the admission
of the compressed air.

In order to illustrate the method more completely, I will
describe three injections. In the first of these examples the
syringe is used in the ordinary way ; in the second it serves
as a pump for the injection of air into the "WoolrTs bottle con-
taining the mass; in the third, the apparatus is used. Sup-
pose that it is desired to inject the kidneys of a small mammal
with cold two per cent, solution of Prussian blue. The animal
having been just killed by bleeding, the abdomen is opened
and the whole mass of intestines pushed aside to the right.
The left renal artery is then separated from surrounding parts
with the aid of two pairs of ordinary forceps without any cut-
ting instrument. A silk ligature is placed round the artery,
and looped near to the point at which it enters the kidney.
The vein is next prepared in the same way, and a ligature
placed round it close to its junction with the vena cava. By
drawing on the renal vein, it is easy to make a valvular open-
ing with fine scissors. The artery is similarly opened short
of the loop, and the metal canula with its stopcock intro-
duced, the edge of the incision being held aside with the for-
ceps. In making the opening and inserting the canula, the
greatest care must be taken to avoid rupturing the artery or
cutting it through with the scissors. The moment that the
canula is in the artery, the loop must be tightened round the
groove. The canula and nozzle are then filled with half per
cent, salt solution with the aid of a capillary tube : the syringe
is charged with the liquid and connected with the nozzle. In
injecting, the piston must be slowly pushed forwards. As
soon as the organ becomes blue, and the liquid appears to pass
unmixed from the opening in the vein, I stop, and then direct
my assistant to close the vein with a clip, or to tighten a loop
previously placed round the vessel for this purpose. This

BY DR. KLEIN. 117

done, I make one push more with the piston, turn the stop-
cock of the nozzle, and take away the syringe.

I will next describe the injection of a whole animal, such as
a rat or a small rabbit, with carmine gelatin mass. The animal
is killed b}- inhalation of chloroform. A window is then cut
out in the left wall of the chest, just large enough to expose
the heart and the roots of the great vessels, taking care not to
carry these incisions so near the middle line as to endanger
the internal mammary artery. A fold of pericardium having
been taken up with the forceps and divided, the apex of the
heart is raised out of the thorax and pierced with a threaded
needle through both ventricles. By the thread which has been
brought through, the apex is then drawn downwards by an
assistant, while the root of the aorta is cleared with the aid of
two pairs of dissecting forceps. A ligature is then passed
round it close to its origin, and looped. Thereupon the wall
of the left ventricle is opened near its base, and as soon as
blood has ceased to flow, the canula is passed into the aorta,
to such a distance that its neck can be grasped by the ligature,
which is then tightened. The blood in the canula is then re-
moved with a capillary pipette, and filled with saline solution
with another pipette, and an opening is made in the right
ventricle. Up to this time the animal has been allowed to
remain on a plate. The plate is now placed on a support, at
a level which nearly corresponds with that of the WoolfFs
bottle, in which the mass is contained, which is kept warm by
immersion in a water-bath, heated by a spirit lamp. The noz-
zle having been connected with the discharge tube of the flask
by an India-rubber tube, and the syringe (the piston of which
has been drawn up) with the other opening in the WoolfTs
bottle, an assistant injects a little air so as to fill the discharge
tube up to the orifice of the nozzle. The stopcock is then
closed, and the point of the nozzle inserted in the canula.
The stopcock having been reopened, the assistant pushes on
the piston. As soon as the syringe is emptied, the screw-clamp
between it and the injection bottle is tightened. Air is again
injected, if necessary, in the same manner. If, however, a full-
sized syringe is used, it is seldom necessary to repeat the pro-
cess. When the vessels are sufficiently full, the heart is
seized with strong clip-forceps, as near the base as possible,
care being taken not to include the canula. The stopcock is
then closed.

As a third example may be taken the injection of the
abdominal organs of a rabbit. The animal is decapitated.
The whole of the left wall of the thorax is removed from the
flanks forwards as far down as the costal origin of the anterior
half of the diaphragm. The left lung and the heart having
been drawn aside to the right, the thoracic aorta is prepared

118 VASCULAR SYSTEM.

with two pairs of dissecting forceps as far down as possiMe.
A ligature having been passed round the vessel and looped,
and the vessel slit open, the canula is introduced and the
ligature tightened. The canula having been then cleared of
blood and filled with saline solution, the plate on which the
animal lies is put into the warm chamber which contains the
injection bottle. This bottle, which is charged with the warm
Prussian blue mass, is connected with the pressure bottle, the
manometer of which indicates a pressure of 00 to 120 milli-
metres. It is, however, not in communication with it, for the
connecting tube is closed by a clamp. This clamp is then
slightly opened for a moment, so as to fill the discharge tube
to the orifice, and immediately closed, the stopcock being
shut at the same time. The nozzle having been inserted into
the canula, the stopcock and clamp are simultaneously
opened. The cover of the chamber is put on and the injection
allowed to proceed, all that is required being to maintain the
pressure in the apparatus as nearly constant as possible.
When the injection is complete, a clip is placed on the vena
cava, near its mouth, and the stopcock shut. [The special
methods to be used for the injection of particular organs, and
the methods of double injection, will be given under the proper
heads.]

Injection with Solution of Nitrate of Silver. — It is
preferable for this purpose to work with the apparatus, as it
is necessary to employ a considerable pressure. As soon as
the injection is completed, it must be replaced by water. This
is effected by substituting a flask containing water fo rthat
used for the nitrate of silver solution. The vessels must be
thoroughly streamed with water, otherwise the endothelial
markings are concealed by the quantity of precipitate which
is formed.

Treatment of Injected. Tissues. — Organs injected with
colored masses must be suspended in ordinary alcohol in a
breaker. If a whole animal has been injected, the body must
be left to cool for half an hour or more. It must then be trans-
ferred to a large vessel containing common alcohol, to which
a few drops of glacial acetic acid have been added. It is a
good plan to transfer animals which have been injected with
gelatin masses to ice-cold alcohol, immediately after the com-
pletion of the injection; great care being taken in this, as in
every other case, to secure the artery and vein so as to avoid
all risk of escape of the mass.

Section II. — Structure op the Bloodvessels.

Endothelium. — The simplest method of demonstration is
to color the internal surface with silver. If the vessels are of

BY DR. KLEIN. 119

large size, they are prepared as follows: A portion of the
vessel taken from the freshly killed animal is washed with di-
luted serum and then dipped for a few minutes in half per
cent, solution of silver. Its internal surface is then exposed
to light until it acquires a brownish-yellow color. If the mus-
cular wall is thick, the intima must be separated by the meth-
od previously described (Chapter III. p. 48) and covered in
gh'cerin, with its endothelial surface upwards. If the vessel
is thin-walled, e. y., the vena cava of a small animal, it can be
covered without an}r preparation. For the endothelium of
capillaries in the kidney or bladder, or in the serous mem-
branes, the best results are obtained by injection of the solu-
tion of nitrate of silver. In the serous membranes, however,
e. <j., in the mesenter}", good preparations can be obtained by
first pencilling one or both surfaces with fresh serum in situ
(the animal having been bled to death) and then cutting out
the pencilled part and coloring in silver in the usual way

The endothelium of the large arteries consists of long nar-
row spindle-shaped \ lates. The nucleus is oblong, and usual-
ly in the middle of each plate. The interstitial lines are very
slightly sinuous. The endothelial elements of the veins are
relatively broader. If the staining is intense, the cell is filled
with brown precipitate, the nucleus remaining clear. The ca-
pillary vessels appear, when colored with silver, to consist
merely of oblong plates, the interstitial lines of which are com-
monly more or less sinuous. The oblong regular nuclei of the
walls of the capillaries seen in profile are those of the endo-
thelium elements. It is easy to color the nuclei by carmine,
in which case an acid solution must be used, i. e., an ammoni-
acal solution to which a sufficient quantity of acetic acid has
been added to render it distinctly acid. Larger vessels must
be immersetl in the solution, but for capillaries it is enough to
immerse the membrane in which they are contained. Ten
minutes' immersion is sufficient for the purpose: the prepara-
tion must then be washed in water and prepared in glycerin.
In preparations of mesentery of the frog or of a small mamma-
lian animal in bichromate of potash, the nuclei may be readily
recognized, not only in profile, but on the surface of the small
vessels.

The Intima- — The anatomical relations of the intima, i. e.,
of the internal longitudinal fibres, and the elastic membrane,
may be studied either in sections or in the fresh state. In
large arteries, the best method is to immerse the vessel in one
per cent, solution of bichromate for several days. The intima
is then peeled off in thin strips, which are teased in the same
liquid and covered with gl}rcerin. This is the only way of
showing the elastic network or the fenestrated membrane
which exists in certain arteries. In vessels of macroscopical

120 VASCULAR SYSTEM.

dimensions, e. g., in large arteries of the mesentery, the intima
is seen in profile both in fresh preparations and after treatment
with bichromate of potash, as a doubly-contoured, sharply de-
fined membrane; the surface view showing traces of longitu-
dinal fibres. In cross sections of smaller arteries, the intima
is seen as a wavy hyaline membrane, differing in thickness
according to the size of the artery. The intima of large veins
differs only in its thickness from that of the arteries.

Muscular Coat. — The muscular coat differs in its charac-
ters in different parts of the vascular system. In the arteries,
the muscular elements form layers which are connected to-
gether by the elastic lamella? interposed between them, the two
together constituting the tunica media. In many arteries
there are also bundles of muscular fibres in the intima, and in
others in the adventitia. In the minute arteries they form cir-
cular layers, the number of which varies according to the size
of the vessel. In such arteries the media is made up almost
entirely of muscular fibres.

The muscular fibres of large arteries may be studied either
by teasing preparations of vessels steeped in bichromate of
potash, or in sections hardened in chromic acid. The muscle-
cells of large arteries appear, when isolated, to be broader,
relatively, than ordinary muscular elements, and are often split
at their ends into processes. The oblong nuclei are more or
less staff-shaped. If a portion of fresh bladder of the frog is
treated with acetic acid in the manner already recommended
in the chapter on unstriped muscular fibres, or a portion of
mesentery of a frog or mammal with bichromate of potash or
acetic acid, the muscle-cells can be distinguished as trans-
versely arranged short spindles, inclosing long distinctl}* gran-
ular staff-shaped nuclei, which are arranged in rows alternating
with each other. In optical longitudinal sections of minute
arteries, such as occur very frequently in sections of hardened
tissues, the elements of the media exhibit the same appear-
ances as in cross sections of involuntary muscle in general ; as,
however, the muscle-cells are shorter, and their nuclei longer,
most ctoss sections exhibit a nucleus in almost every element.
In minute veins, muscular elements are seen which have a longi-
tudinal direction, but do not form a continuous layer.1

The intima and adventitia of the bloodvessels contain nu-
merous branched cells. To demonstrate them, sections must
be made of bloodvessels and treated with gold. They ma}r be
also shown in preparations made by the silver method. By this
method a rich network of lymphatics may be demonstrated in
the adventitia of the aorta of small animals.

1 For the special arrangements of the muscular fibres in particular
arteries, the reader is referred to larger treatises on general anatomy.

BY LR. KLEIN. 121

Nerves. — The rich plexus of non-medullated nerve fibres
which exists in the adventitia of large bloodvessels, can be
studied in the mesentery of the frog, which for this purpose
must be prepared in the manner directed in Chapter V. for the
demonstration of the nerves of the mesentery. In the same
organ it can be shown that the capillaries are also surrounded
by non-medullated nerve fibres. In the nictitating membrane
and tongue of the frog, the plexuses which surround the capil-
laries may be seen to give out fibrils which enter the walls of
the vessels themselves. For this purpose the tongue of the
frog must be colored in a half per cent, solution of chloride of
gold, and used, after hardening in alcohol, for the preparation
of sections. (See Chapter XII.)

The development of bloodvessels will be given in the chapter
on Embryology.

Section III.— Microscopical. Study of the Circulation.

Study of the Circulation in Cold-blooded Animals.

— The parts which may be used for this purpose are (1) the
web of the frog's foot, (2) the mesentery of the frog or toad,
(3) the tongue of the same animal, (4) the tadpole.

Web of the Frog. — If the animal is not curarized, the
arrangement must be employed which was described in Chap-
ter III. It is, however, better to employ curare, as described
in Chapter XVII. The animal is laid on an oblong plate of
glass, on which a cork disk is fixed with sealing-wax, which
should be three-tenths of an inch thick, and an inch and a
quarter wide. The disk must have a hole in the middle, which
should be about three-quarters of an inch wide. At the edge
of this aperture pins are stuck, to which ligatures attached to
the toes may be secured.

Mesentery". — The preparation of the mesentery is not so
simple. A snip is made in the right side of the belly, parallel
with the middle line. Before dividing the skin further, it is
raised to ascertain where there are no large veins ; the incision
is then continued upwards and downwards, in such directions
as to avoid bleeding. If, notwithstanding, a vein is divided,
the bleeding must be restrained by seizing the end of the in-
cision with the clip-forceps. The traces of blood having been
removed with filter paper, the muscles are divided in the same
vertical line. This having been done, the intestine and mesen-
tery are drawn out carefully, and laid on the anterior surface
of the belly. The next step is to place the animal on a in Fig.
19. (For this, however, a simple glass plate of similar size
may be substituted, nt the edge of which a cork is fixed, which
should have an aperture corresponding to c, covered with a
round cover-glass.) The frog having been pushed up against

122 VASCULAR SYSTEM.

rf, the intestine can be easily turned over on to b. The intes-
tine then lies in the trough c, while the mesentery rests on the
glass plate b. So much of the intestine as does not occupy the
trough must be replaced. If the observation is prolonged i as
in researches on inflammation), it is well to place in the trough,
outside of the intestine, a layer of Alter paper, on which half
per cent, solution of salt is dropped from time to time. It is
sometimes useful, when high powers are to be employed, to
cover the mesentery with thin glass. If the cork is used, it is
necessary to fix the intestine at two or three points with small
pins'.

Tongue. — The animal must be curarized as before. A plate
of glass, like that used for the web, is employed, with this
difference, that the cork, instead of having a round aperture,
is cut into the form of a horseshoe, the convexity of which is
towards the edge of the plate. If it is intended to study the
circulation on the lower surface of the tongue, the animal is
placed on its belly. If the papillary surface is to be examined,
it must be on its back. In either case, the tongue must be
drawn out by the cornua, around each of which a thread must
be secured. With the aid of these threads the organ is drawn
as forward as possible without affecting the circulation, and
secured to pins which are stuck horizontally into the edge of
the cork at each corner. It is sometimes necessary to extend
the organ further by means of pins stuck in the cork at the
sides.

Tail of the Tadpole. — The tail of the tadpole affords a
most instructive object. The animal is curarized by placing
it in a drop or two of solution in a watch glass. As soon as
it is motionless it is transferred to an object-glass and ex-
amined. The description of the phenomena of circulation as
seen in the batrachians, and of the methods employed for their
investigation in mammalia, will be found in Chapter XVII.

Observation of the Emigration of Colored and
Colorless Blood Corpuscles. — In the tadpole, emigration,
particularly of the colored corpuscles, may be witnessed in
various parts of the tail, if the observation is continued for
a short time.1 If the mesenteiy of a frog is exposed to the
air, or treated with any irritant, the emigration of colorless
corpuscles can be seen with the greatest ease, provided that
the observation is made with sufficient care. A small vein
must be sought out with a low power, and a point selected in
its course at which one or more colorless corpuscles have
attached themselves to the walls. These must then be watched
continuously under a higher power.

1 In the frog an abundant emigration of colored corpuscles takes
place after the injection of salt solution (two to six per cent.).

BY DR. KLEIN. 123

CHAPTER VIII.

LYMPHATIC SYSTEM.
Section I. — Lymphatic Vessels.

The tymphatic vessels may be studied either by coloring
with nitrate of silver or by injection. As those of the serous
membranes are most readily demonstrated, it will be con-
venient to refer to them first.

Lymphatics of the Centrum Tendineum of the
Diaphragm. — The pleural cavity of a rabbit or guinea-pig,
which has just been killed, is exposed by removing the sternum,
care being taken to avoid opening any large bloodvessels.
The pleura having then been divided along the edge of the
costal part of the diaphragm, the cava ascendens is ligatured
close to the atrium, and divided between the ligature and the
heart. The heart and lungs are then removed from the
thoracic cavit}7. The pleural side of the centrum tendineum is
then carefully brushed with a camel-hair pencil, moistened with
serum, after which a small quantity of half per cent, solution
of nitrate of silver is poured on the diaphragm, while the
animal is held vertically, with its head uppermost. After five
minutes or so, the silver solution is poured av,ray and replaced
bj* water, which should be changed several times. The centrum
tendineum may then be cut out and prepared in glycerin. Ac-
cording to another plan, the diaphragm is cut out immediately
after it has been brushed, and immersed in solution of nitrate
of silver. With this view the abdominal cavity is opened; the
ligamentum suspensorium is divided, and a ligature placed
round the vena portce. This vein, having been divided, the
whole diaphragm is cut out with the liver. In such a prepara-
tion clear channels are seen in the yellowish-brown ground-
substance, which are of various size, and of two kinds, and
exhibit endothelial markings. In the one kind — viz., in the
larger vessels — the endothelial elements are spindle-shaped;
in the other — i. e., the capillaries — they are more or less sin-
uous. The walls of all these vessels consist exclusively of
endothelium.

Before describing the arrangement of the lymphatics in the
centrum tendineum, it is desirable to give an account of the
structure of that organ. It consists of three parts, viz., pleura,
peritoneum, and tendon ; each serous membrane being made

124 LYMPHATIC SYSTEM.

up of endothelium and membrana propria. The tendon con-
sists of two layers, of which the one that is next the perito-
neum is formed of bundles of fibres which radiate from the
centre outwards; the upper Layer of bundles arranged circu-
larly. The bundles of each are separated from their neighbors
by splits or channels, of which there are two sets; those
between the abdominal layers being designated the superficial,
those of the pleural, the deep interfascicular channels of the
centrum tendineum. The membrana propria of the peritoneum,
where it stretches over the superficial channels, possesses a
special fenestrated structure (found also in one or two situa-
tions elsewhere). Between the propria of the pleural side and
the tendons, large lymphatic vessels exist which form numer-
ous ramifications, and communicate with a network of capil-
laries. All of the larger vessels are provided with valves,
with their corresponding dilatations. The capillaries may be
distinguished into those which lie in the pleural propria, and
have a more or less winding course, and those which are
straight and lie further from the pleural surface. The former
have saccular dilatations, which are called lymphatic sinuses.
The straight vessels are contained in the channels already
described, and may, therefore, be designated lymphatics of
the interfascicular channels. They may be further distin-
guished, according as they are contained in the peritoneal or
pleural layer, into superficial and deep. There are many
channels of both layers which do not contain them. The two
sets of vessels are in communication with each other. The
superficial interfascicular lymphatics pass, in the neighborhood
of the great vessels which perforate the centrum tendineum,
into winding lymphatic capillaries with saccular dilatations,
which are situated on the abdominal surface of the tendon,
where the}' form a network. On the other hand, the interfas-
cicular lymphatics freely communicate with the peritoneal
cavity by means of vertical channels, which, although they for
the most part extend only to the radiating tymphatics of the
superficial layer, can also, in many instances, be seen to pass
directly to those contained in the deeper, i. e., the circular
channels. By these canals the endothelium of the lymphatics
is continuous with that of the peritoneum. The endothelial
elements which guard the orifices of each vertical canal (the
stoma) have the characters of young cells, and differ from
those which adjoin them in being more granular, smaller, and
polyhedric. It has been already indicated, in Chapter II.,
that the endothelium which covers the channels consists of
smaller and apparent^ 3'ounger elements than those of the
general surface. These characters are much more marked in
the cells which surround and form the stomata. Iu diaphragms
which have been stained without brushing, they cannot be

BY DR. KLEIN. 125

made out. It is true that, among the small mosaic of certain
channels, there are dark or clear spots which have been de-
scribed by authors as stomata, with which, however, their
relation is very doubtful.

Method of Demonstrating the Stomata. — To demon-
strate them, the abdominal cavity of a rabbit just killed must
be opened, a ligature passed round the cardia, and another
round the bunch of vessels leading to the porta. This done,
the abdominal viscera, excepting the liver, may be cut away
and removed; great care being taken not to draw upon the
diaphragm in any part of the operation. The liver being then
held aside, water is poured over the abdominal surface of the
diaphragm. After a few seconds, silver solution is poured
once or twice over it in the same wa}', and the whole left to
itself for a few minutes. It is then again washed with water,
after which it may be cut out and subjected to microscopical
examination. In preparations so obtained rows of stomata
may be seen, both over the superficial interfascicular lymph-
atics, and occasionally in situations which correspond to the
circular ones ; which, exhibit, in all respects, the same anato-
mical characters as those of the septum cisternee magnee in the
frog. Each canal leading from a stoma to a subjacent lym-
phatic is seen to be lined by small granular cells of the same
character as those already described as guarding the orifice.
They are particularly distinct where the canal opens into the
13-mphatic, especially in those canals which are in communica-
tion with the lymphatics of the deeper, i. e., the pleural layer.
The lymphatic system of the diaphragm is divisible b}- the
middle line into two similar halves. Each half may be again
divided, according to the direction in which the lymph flows,
into two parts — an anterior and a posterior. The anterior
system is made up of the large lymphatic vessels to be found
on the pleural side, all of which converge towards the sternum,
discharging themselves into a single large lymphatic trunk,
which stretches in the form of an arch along the outer edge of
the sternum, accompanying the internal mammary artery and
vein.

Each of the trunks as it ascends divides into a plexus of
smaller vessels, by which the lymph is conveyed to the sternal
glands. These lymph vessels receive their tributaries from
the external border of the anterior half of the centrum, and
from the anterior third of the external border of the posterior
half. The lymphatic vessels of the remainder of the diaphragm
belong to the posterior system, which opens on either side by
a short, wide lymphatic trunk, which joins the thoracic duct
just after the latter has entered the throracic cavity. The
lymphatic interfascicular channels are all to be regarded as
tubes of communication between the two systems. From

126 LYMPHATIC SYSTEM.

these facts it ma}' he understood why the posterior half of
the diaphragm is more readily filled from the peritoneum than
the anterior.

Demonstration of the Lymphatic System of the
Diaphragm by Injection. — In a large or middle-sized rabbit,
which has been kept from sixteen to twenty hours without
food, ten cubic centimetres of a warm, five per cent, solution of
Prussian blue are injected into the abdominal cavity through
a small canula, with the aid of a glass tube drawn out at one
end. The liquid is allowed to flow in of itself. After three
hours and a half, the animal is bled to death by opening the
carotid arteiy, or killed by strangling. As soon as the body
is cool, the pleural cavity is opened, the cava ascendens is liga-
tured just before it enters the heart, while a second ligature is
tightened round the aorta, oesophagus, thoracic duct, and vena
azygos. The vessels having been divided above the ligatures,
the whole of the thoracic viscera are removed. With a lens the
arrangement of the vessels above described ma}r now be made
out, without removing the diaphragm. To obtain permanent
preparations, the peritoneal cavity must be opened, and the
suspensory ligament divided as before directed, the animal
being placed aslant. The vena cava and the cardia having
next been divided between the liver and the diaphragm, the
serous ligaments which connect the left lobe of the liver, the
stomach, and the spleen with the diaphragm, are severed, so
that these organs are complete^- detached. Thereupon the
abdominal surface of the centrum tendineum is brushed with a
camel-hair pencil moistened with warm water, after which the
ring of bone, cartilages, and soft parts, to which the diaphragm
is attached all round, is separated from the rest of the body,
immersed for a few minutes in silver, and washed in water.
Those parts which are intended for microscopical examination
can then be cut out and covered in glycerin. Anilin and milk
may be used in the same manner as Prussian blue, but do not
yield such certain results.

Another method of injecting the lymphatics of the diaphragm
may be mentioned, which is, however, not so successful. The
liquid employed consists either of one or two per cent, solution
of Prussian blue, in which a partial fine precipitation has been
determined by the addition of a small quantity of alcohol, or
of anilin with milk. A rabbit is bled to death by opening the
crural artery. A bent tube is then secured in the trachea, which
is connected with the apparatus for artificial respiration. The
abdominal cavity is then opened and the suspensory ligament
divided, as well as the fold of serous membrane which connects
the left lobe of the liver with the diaphragm. The cardia having
been exposed and tied, and a ligature passed round the vessels
contained in the omentum minus and the vena cava below the

BY DR. KLEIN. 127

liver, the organs are cut away below the ligatures, so that the
diaphragm is covered only by the liver. The lumbar part of
the spinal column is then severed, and the division completed
by continuing the incision forwards on either side to the middle
line. Threads are then attached to the cut edges, by which
the upper part of the body is suspended, head downwards, to
a ring of iron. The whole operation can be completed in from
three to five minutes. The next step is to pour the liquid to
be used (previously warmed) on to the diaphragm, in quantity
sufficient to cover it. For twenty or thirty minutes, artificial
respiration is maintained at regular intervals. The diaphragm
ma}' then be prepared as before for microscopical examination.

The Cellular Elements of the Centrum Tendineum
in their relation to the Lymphatic System. — The
pleural surface of the centrum lendineum of a rabbit, guinea-
pig, or any other small mammalian animal, is exposed as above
described, and carefully, but slightly, brushed with a camel-
hair pencil moistened with serum. Silver solution is then
poured over it, and, after a few minutes, water. Thereupon bits
are cut out for microscopical examination, which must be care-
fully separated from the parts in contact with their abdominal
surfaces. These must then be mounted in glycerin, with the
pleural side upwards. Immediately under the endothelium
of the surface there exist large, flat cells, which are more or less
branched. In the neighborhood of the large vessels which pass
through the centrum tendineum these are so close together that
they are marked off from each other by mere lines of interstitial
substance, and appear as if they formed a second layer of flat
endothelial elements subjacent to the one brushed off. Under
these cells branched cavities are seen to exist, hollowed out in
a yellow or yellowish-brown ground-substance. When the
examination is made with sufficient care, it is found, first, that
each of these cavities contains a nucleated mass of protoplasm,
which completely occupies it; and, secondly, that both the
cavities and their contents are in continuit}' with each other,
so as to form a network. This network of cavities was first
described by Recklinghausen, under the name of Saftcan'dlchen.
We propose to call it lymphatic canaliculi, and the more or
less branched cells contained in them, lymphatic cells.

If these are examined in a island of tissue surrounded by
lymphatic capillaries, it is seen that there are places in which
the cells are closer together and less branched than in others,
and that in such spots they are often arranged in linear series,
or in small groups, each cell being marked off from its neigh-
bors by interstitial lines, so that they resemble an endothelium.
This is particularly the case in the immediate neighborhood of
the lymphatic capillaries ; and here it can often be made out
that cells contained in canaliculi are in contact with the ele-

128 LYMPHATIC SYSTExM.

ments of the lymphatic endothelium. The canalicular cells are
also in communication with the flat cells which form the layer
immediately covered by the serous endothelium.

The anatomical relation of the canaliculi and lymph cells on
the abdominal side are the same as in the pleura. To demon-
strate them, the abdominal surface of the centrum tendineum
is prepared in the same way as last described. In the neigh-
borhood of the large vessels, the existence of a similar layer of
flat elements lying underneath the serous endothelium, resem-
bling in character those already described in the pleura, can be
demonstrated. The canaliculi and lymphatic cells of the pro-
pria have also the same relation to each other and to the super-
ficial network of lymphatic capillaries as in the pleura. Finally,
it is to be mentioned that in the tissue which occupies the
fascicular channels which contain no lymphatics, the same
character can be observed. Here the continuity of the lym-
phatic cells with the similar cells of the tendon-tissue, which,
as we have seen, are oblong branched placoids, and apply
themselves to the surfaces of the primitive bundles of fibrils,
can be demonstrated.

Pseudo-Stomata. — In examining carefully the pleural sur-
face of a diaphragm which has been treated with nitrate of
silver, without pencilling, it is seen that there are here and
there spaces between the endothelial elements which are occu-
pied by bodies of a more or less branched contour. These are
usually darker in color than the endothelium of the surface,
and often exhibit distinct nuclei. If the preparation has been
partly pencilled, it is often possible to observe, at the junction
of the pencilled and unpencilled part, that the bodies in ques-
tion are of the same kind with the flat branched cells which
are covered by the endothelium ; and it can be also made out
that even where they are covered, the cells of this layer send
up projections between the endothelial cells which reach the
surface. These projecting cells may be called pseudo-stomata.
The intimate relation which exists between the sub-endothelial
cells and those of the propria, and between these last and those
which line the lymphatic vessels, has been already referred to.
That these cells are also concerned in absorption is indicated
by the fact that, in chronic inflammation, and other conditions
in which absorption from the serous surface is more than usually
active, these pseudo-stomata and the canaliculi are the seat of
germination — and that if coloring matter in a state of fine
division has been previously introduced into the peritoneum,
they are found to contain it.

Lymphatic System of the Omentum and Mesen-
tery.— To demonstrate the lymphatic structures of the omen-
tum, the peritoneal cavity is opened in a rabbit just killed. The
large and small intestines having been pushed aside to the

BY DR. KLEIN. 129

right, the omentum, which usually lies on the anterior surface
of the stomach, is carefully brushed in situ, from below up-
wards, with a camel-hair pencil, moistened with peritonaeal
liquid. Half per cent, solution of silver is then allowed to drop
over the surface from a capillary pipette, until the membrane
is distinctly turbid. It must then be gently streamed with
water, and removed along with the stomach, and placed in
water exposed to the light. Portions of the membrane are
then cut out, and covered in glycerin with the pencilled surface
upwards. In preparations so obtained, an abundant network of
lymphatics presents itself. In addition to this, there are cer-
tain parts of the surface in which the lymphatic cells are
crowded together in patches. It is seen, in parts where the
endothelium has not been completely removed, that the cells
which lie immediately underneath it project so as to form
pseudo-stomata, and in other respects stand in the same rela-
tion to it and to those which line the lymphatic capillaries, as
on the surface of the diaphragm. It is also seen that in some
of the patches there are lymph sinuses which communicate with
the surface by true stomata. As was indicated in Chapter II.,
the endothelium which covers these lymphatic patches, particu-
larly that which surrounds stomata and pseudo-stomata, differs
from that of the general surface, by the smaller size, polyhedral
form, and granular appearance of the elements. The same
tissue also presents itself in the form of tracts alongside of the
larger vessels.

In the dog, guinea-pig, and cat, these tracts are particularly
well developed along the large vessels which are to found in
the trabecular of the membrane. Connected with these, there
are nodular structures which project more or less from the
surface. Both the tracts and the nodules consist of aggrega-
tions of lymphatic cells close together, richly supplied with
bloodvessels, and covered with an endothelium which has the
same characters as that which covers the patches. In the
neighborhood of the tracts, lymphatic vessels are usually'' to be
seen on one or both sides, which often communicate by cross
branches, and stand in the same relation to the lymphatic
elements as in the patches. The canaliculi of the tracts and
nodules sometimes contain what appear to be young cells,
which, from what has been observed in pathological conditions
of the structure, must be regarded even in the normal state as
to a great extent offsprings of the endothelial elements.

Mesentery. — In the mesentery treated in the same way as
that above described, in addition to the lymphatic vessels
which proceed from the intestine, numerous lymphatics with
dilatations (sinuses) can be demonstrated. The canaliculi with
which they are surrounded and in communication, pervades
the ground-substance of the mesentery in every direction. In
9

130 LYMPHATIC SYSTEM.

the cat and rabbit, tho endothelium of the mesentery exhibits
pseudo-stomata of the same character as in the omentum. In
that of the toad and common frog, the trabecular, in which the
large vessels run, split into a kind of meshwork of smaller
processes, the spaces of which are occupied by large lymphatic
sinuses, in which a beautiful endothelium with sinuous outlines
can be demonstrated by the silver method.

Injection of Lymphatic Glands and of Mucous
Membranes. — For the injection of the lymphatics of the
lymphatic glands, and of the mucous membranes, the " Einstich
Methode" (method of puncture) of Ludwig is the best. The
liquids used are either half per cent, silver solution or Prussian
blue. The animal to be employed must be perfectly fresh. A
very fine glass canula is used, which is connected either with a
syringe or with the apparatus described in the last chapter.
The method consists in penetrating any tissue in which there
are numerous lymphatics (e. g.} the submucosa of the mucous
membranes, the cortical substance of a gland, or the loose
tissue beneath the costal pleura), with a needle to a sufficient
distance. The needle having been withdrawn, the canula pre-
viously filled with the solution to be injected is introduced into
its track, and connected with the apparatus or syringe as the
case may be. The canula having been seized with ordinary
dissecting forceps, the liquid is injected. If it is seen that the
colored liquid is not contained in vessels but merely occupies
a bulging cavity in the tissue, the injection must be discon-
tinued as unsuccessful. In the case of the mesenteric or ingui-
nal glands of small animals, I succeeded in obtaining good
results with a tube drawn out at one end to a very fine point,
and bent near the point at right angles. This tube having been
filled with the liquid, was injected by the mouth. In the rabbit,
nothing can be easier than to insert such a tube into one of the
lymphatics of the mesentery, and in this way to inject the gland
to which it leads. — Lymphatic glands, after injection, must be
placed in alcohol and used for the preparation of sections.

Structure of the Lymphatic Vessels. — The structure
of lymphatic vessels may be further advantageously studied in
those of the mesenteiy. In small cats or rabbits, it is easy to
prepare the parts of the mesentery in which there ai*e abundant
lymphatic vessels leading to the mesenteric glands, by stretch-
ing them on cork and treating them with silver, after pencilling
away the endothelium of the peritonaeum with a camel-hair
pencil, moistened with serum. In these vessels, it is possible
to demonstrate the existence of transverse muscular fibres.

Structure of the Lymphatic Glands. — Mesenteric
Glands. — The best glands for the purpose of study are those of
the calf, ox, or cat. Small portions can be placed in Midler's
liquid, or in solution of bichromate of potash. After a few

BY DR. KLEIN. 131

days, it is possible to make thin sections of small extent. It is
easier, however, to make sections of glands which have been
steeped two or three days in common alcohol. The sections,
stained or unstained, are placed two or three together in a test
tube, half full of water, which must then be shaken regularly
but briskl}- until the sections acquire the characters of reticu-
lated membranes. The contents of the test tube are poured
into a shallow capsule, and prepared in the usual manner,
either for mounting in Dammar varnish or glycerin. It is well
not to continue the agitation longer than is necessary to get
rid of the medullary substance of the gland. The globular or
ovoid follicles which constitute the mass of the cortical sub-
stance, and are in continuity with the lymphatic cylinders, are
seen in such preparations to have the following structure : —
Each consists of a close network of fibres, the meshes of which
are of nearly equal size. It is further seen that the fibres are
thickened at the nodes, and that each thickening contains a
nucleus. The younger the animal, the more obvious it is that
the network consists of branched cells. The follicle also con-
tains numerous capillaries. From the network of branched
cells which forms the adventitia of each capillar}', spring fila-
ments which either stretch to neighboring capillaries, or form
a part of the general adenoid network of the follicles. These
filaments are alwa3rs broader at their bases than elsewhere,
and have thickenings which contain nuclei. In sections which
have not been agitated, the whole network is filled with small
roundish bodies (so-called lymph corpuscles). It can be readily
shown in glands which are injected from the lymphatics, that
each follicle is surrounded by sinuses, which are mere dilata-
tions of the different lymphatic vessels of the cortex, and are
in like manner lined with endothelium, as is seen in glands in-
jected with nitrate of silver. Outside of the follicles is a layer
of connective tissue which contains numerous bloodvessels, and
is continuous towards the hilus, with the trabecular, which form
the framework of the organ. Outwards it is intimately united
with the capsule. In glands of which the bloodvessels are in-
jected, capillary loops can be seen to penetrate into the follicles
from the rich network of bloodvessels with which each is in-
vested. The part of the gland between the cortical substance
and the hilus consists of lymphatic cylinders, and intervening
trabeculse. The former are united with each other so as to
form a network, and have the same intimate structure as the
follicles, as regards the adenoid network, the cells it contains,
and the capillaries. In general they possess only capillaries ;
occasionally, however, larger vessels enter them. The trabe-
cular consist of fine fibres which run mostly parallel to each
other; they are connected into a meshwork, the intervals of
which are occupied by the network of cylinders. There are,

132 LYMPHATIC SYSTEM.

however, between the outer surfaces of the cylinders and the
trabecular, spaces to which we shall revert immediately. In
sections which have been only slightly shaken, it is possible to
observe that fibres stretch at more or less regular intervals
from the external surface of the cylinders to the trabecular, by
which the intervening space is divided into sections. These
fibres appear to be offsets from the trabecular, and exhibit
either swellings containing nuclei, or distinct nucleated stellate
cells. In sections which have not been shaken, the whole me-
dullaiy substance appears to be uniformly full of lymph cor-
puscles. In the spaces, as we have seen, they can be shaken out
so readily, that it is evident they lie quite loosely ; whereas, in
the cylinders themselves, they are intimately united to the net-
work. The significance of this structural difference can be
demonstrated in glands in which the different lymphatics have
been injected, or, still better, in glands which have been injected
by the puncture method with nitrate of silver. In the former
case it is possible to trace the injection from the different ves-
sels of the cortex, through the lymph sinuses which surround
the follicles, to the spaces which separate the cylinders from
the trabecular, and thence to the different vessels at the hilus.
In the latter case, lymphatic sinuses are met with in the me-
dullary substance near the hilus, lined with endothelium, which
are continuous with the spaces surrounding the cylinders in
such a way that their endothelium can be distinctly traced on
to the surface of the trabecular.

Solitary and Agminated Follicles of the Intestine. — Folli-
cles such as we have just described in the cortical substance
of the lymphatic glands occur in the large intestine as solitary
follicular bodies, or in the small intestine, in groups (the so-
called Peyer's patches. See p. 125).

Thymus Gland. — This is to be regarded merely as an
aggregation of follicles of the same kind. Neither in their
structural elements, nor in the relation of these to the vessels
or lymphatics, can any difference be made out. In man, as
well as in the dog, the external surface of the capsules is
covered with an endothelium identical with that of the pleura.
The tonsils and follicular glands at the base of the tongue are
almost made up of aggregations of lymphatic follicles.

BY DR. KLEIN. 133

CHAPTER IX.

ORGANS OF RESPIRATION.

The structure of the larynx, trachea, and bronchi can be
completely studied in sections of organs hardened in chromic
acid. The epithelium has been already fully described else-
where. An animal having just been killed, the tubes are
opened, washed with very dilute solution of bichromate of
potash, and placed in the hardening liquid. In thin sections,
the relations of the mucosa submucosa with its glands, carti-
lages, perichondrium, muscular fibres, and ganglia, may be
completeby made out. The bloodvessels may be injected in the
ordinary way, and the lymphatics by puncture of the submu-
cosa. The network of elastic fibres which surround the alveoli
are most readily studied in thin sections of fresh-frozen lungs
of small mammalia. The sections are steeped in acidulated
water till the air-bubbles have escaped, and then spread out
on an object-glass and covered in glycerin. The structure of
the fine bronchi ma}7 be well studied as regards its epithelium,
minute glands, muscular coat, and innumerable large gangli-
onic masses, in sections of lungs of human foetuses of the
last months of pregnane}', which have been hardened in one-
tenth or one-eighth per cent, solution of chromic acid. The
flat epithelial elements of the alveoli, as well as those which
line the finest bronchial tubes, can be best examined in lungs
of small mammalia, prepared by placing a canula in the
trachea, removing the sternum, and then injecting the bronchi
with one-tenth to one-eighth percent, solution of chromic acid,
until the organ is moderately distended. The trachea is then
tied, and the lungs are carefully removed from the thorax
along with the heart, after separating them first from the
spinal column, and then from the diaphragm; the whole is
then placed in liquid of the same strength. Another method,
which, however, does not answer so well, is that of injecting
half per cent, solution of silver into the pulmonary artery.
Good injected preparations of lungs can be obtained by filling
the air-passages with cacao butter, and the bloodvessels with
gelatin-mass, simultaneously. A rabbit is killed by opening
the crural artery. The trachea having been prepared, a canula
fitted to a nozzle is fixed in it. The sternum is then removed,
and a second canula inserted in the pulmonary artery close to

134 ORGANS OF RESPIRATION.

its origin. As much air as possible is now pumped with a
syringe out of the trachea, and the stop-cock closed. The
apparatus for injection having been previously put in readi-
ness, all must be connected, and the pressure raised in the tube
to the required point, i. e., sixty to eighty millimetres, so that
at an}- moment the stop-cock of the nozzle may be opened and
the injection begun. A sufficient quantity of cacao butter
having been fused in a capsule, a middle-sized syringe is filled
with the hot liquid, and fitted into the nozzle, which is inserted
into the trachea, and the injection begun. The moment that
the cacao butter has begun to enter, an assistant opens the
stop-cock1 of the canula in the pulmonary artery. As soon as
the lung appears to be distended with the butter, the stop-cock
of the trachea is closed, but the injection of the bloodvessels
is continued. As soon as this appears to be complete, the left
auricle of the heart is comprised in a ligature, by tightening
which the pulmonar}' veins are completely closed. A few
moments later, the stop-cock in the artery is also closed, and
the animal placed in a basin so that the thoracic organs are
immersed in cold water. As soon as the lungs are seen to be
firm, they are taken out with the trachea and placed in common
alcohol. In two or three days, small portions may be cut out
and placed for a short time in absolute alcohol, and then
embedded for the preparation of sections. The sections must
be steeped in oil of turpentine or cloves, till the cacao butter
is dissolved out ; this may be ascertained by placing the watch-
glass containing them under a low power. Turpentine accom-
plishes this more quickly than oil of cloves. The sections
must be mounted in Dammar varnish. The relation between
the different bloodvessels and the capillary network of the
walls of the alveoli, are admirably seen in such preparations.
If it is intended to preserve the structure of the pulmonary
tissue unimpaired and at the same time to inject the blood-
vessels, half per cent, solution of salt or of bichromate of
potash may be substituted for the cacao butter, and two per
cent, solution of Prussian blue for the gelatin mass. The
organ must be placed in alcohol as before.

1 Great care must be taken to keep the tube leading from the bottle
containing the mass, as well as the nozzle, warm with hot sponges,
otherwise there will be great danger of the solidification of the gelatin
in those parts, during the time which intervenes between the prepara-
tion of the apparatus and the commencement of the injection.

BY DR. KLEIN. 135

CHAPTER X.
ORGANS OF DIGESTION.

Teeth. — Polished sections of teeth are prepared in the
same way as those of bone. They must be made in various
directions. For the study of the development of the teeth,
maxillary bones of human foetuses, softened in chromic acid
in the way previously directed, must be used. The reader is
referred for the description of the structure to the ordinary
handbooks of general anatomy.

Salivary Glands and Pancreas. — These organs must
be steeped several da}rs in half per cent, solution of bichro-
mate of potash and prepared b}r teasing. Small bits of the
fresh glands may be steeped for fort}^-eight hours in the dark,
in one-tenth to one-half per cent, solution of osmic acid, and
then either placed in water for a day or two, with a view to
preparation by teasing, or hardened in alcohol for the prepara-
tion of sections. In either case the preparations, if kept,
must be placed in concentrated solution of acetate of potash.
The arrangement of the alveoli and their ducts, and the
characters of the epithelium of each, can be best seen in
sections of glands hardened in alcohol, and stained with
dilute carmine. In such sections, the beautiful mosaic of the
pol\rhedral epithelial cells of the alveoli, each consisting of
granular protoplasm, forms a striking contrast to the cylindri-
cal epithelial lining of the ducts; the latter consisting of pale
slender cells, each of which appears streaked in the direction
of its length, and contains an oblong nucleus in its outer third.
The alveoli are united into groups (lobules) by delicate
bundles of connective tissue. In teased preparations, the
cellular and fibrous elements of the connective tissue, and the
ganglion cells which are met with here and there, can be studied.
In injected glands, each alveolus is seen to be invested by a
delicate and very abundant network of capillaries.

Mucous Membrane of Mouth, Tongue, Pharynx,
and (Esophagus. — The structure of these mucous mem-
branes can be well seen in sections of organs hardened in
chromic acid.1 For studying the epithelium, the papilla, the
glands, and muscles, this mode of preparation is sufficient.

1 As regards the tongue, see also the chapter on Organs of Special
Souse.

136 ORGANS CF DIGESTION.

The lymphatic vessels, e. g., in the pharynx and at the root of
the tongue, can be filled by the puncture method, after which
the injected parts must be hardened in alcohol, and used for
the preparation of sections. To see the loops of fine capil-
laries in the papilla of the mouth, tongue, and pharynx, these
parts must be injected. As regards the distribution of the
fine nerves, see Chapter V.

Stomach. — The relation of the muscularis mucosae, the
submucous tissue, the musculosa and the ganglia to each
other, can be well shown in sections of organs hardened in
chromic acid. For the study of the glands, the best method
is to open the stomach of the cat or dog immediately after
death, carefully inverting it so as to empty it of its contents,
and then to stream it gently with water. Thin folds of the
membrane must be snipped off with sharp curved scissors and
placed in common alcohol. After three or five days the ob-
jects are ready for the preparation of sections, the direction of
which must be parallel or vertical. The parallel sections must
be made at various depths. For the coloring of these sections
a staining liquid prepared after Beale's formula (omitting the
alcohol) answers well ; but it is necessary to free it from excess
of ammonia, either by careful neutralization with acetic acid
or by warming it in the water-bath. The sections having been
placed in this liquid in a watch-glass, it is put in a closed ves-
sel along with a second wratch-glass containing water with a
trace of ammonia. After twenty-four hours the sections are
removed, washed in dilute glycerin, and transferred to con-
centrated glycerin in another watch-glass, which is then placed
in the closed vessel along with a glass containing common
acetic acid. After twenty-four to twenty-eight hours the
sections may be finally covered in glycerin. In such prepara-
tions the gland tubes of the fundus (the so-called peptic
glands), with their two kinds of epithelium, are well seen.
Next the cavity of the gland it consists of C3Tlindrical cells
(the Hauptzellen of Heidenhain), which are scarcely colored
by the carmine, and are very finely granular. The nuclei of
these cells are occasionally colored, but usually not so. Un-
derneath them, i. e., next the membrana propria, both in
vertical and parallel sections, ovoid granular cells are seen
which are strongly stained. These last (the Belegzellen of
Heidenhain) do not form a continuous layer in either direc-
tion : they occur in small numbers in the half or two-thirds of
the gland next the muscularis mucosae, i. e., in the body of the
gland — more abundantly in the adjoining part, which is
usually called the neck, where thej' more or less conceal the
cylindrical layer. The short duct, in which usually two
tubes open, possesses an epithelium of the same kind as that

BY DR. KLEIN. 137

which covers the surface, consisting of slender cylindrical
elements.

When these structures are compared as seen in fed animals
and in animals in inanition, it is found that in the former the
staining extends both to the ovoid cells and to the columnar
cells. A difference of the same kind may be shown in similar
sections stained with anilin. An extremely dilute aqueous
solution is used. The sections must be placed in a watch-
glass containing the liquid, which is allowed to stand twenty-
four hours in a closed vessel, the air of which is kept saturated
with moisture. The preparations can then be at once inclosed
in glycerin. The only difference between the results of the
two methods is, that the cylindrical cells are here slightly
tinged even in inanition. The convoluted and much-branched
tubes which occur in the region of the pylorus contain only
cylindrical cells, which correspond to those of the same form
in the proper peptic glands. Between these last and the
branched glands, intermediate forms are met with, which
differ from each other in the number of ovoid cells (Belegzel-
len) which they contain, the number diminishing according
to the distance from the pylorus.

The processes of the muscularis mucosae, which stretch
towards the surface through the mucosa between the glands,
can be better seen in chromic acid preparations.

Small Intestine. — The characters of the epithelium of the
small intestine in the fresh state have been already described.
They may be further advantageously studied in sections of
hardened organs, which will also serve for the demonstration
of the following structures — the dense reticulum of the sub-
stance of the villi, with the round cells in its interspaces ; the
anatomical relations of the single or double central lymphatic
vessel which each villus contains ; the slender bundles of
longitudinal unstriped muscular fibres which run out around
the lymphatics towards the apex of each villus ; the reticular
tissue of the mucosa, identical in its characters with that of
the villi, in which the tubes of Lieberkuhn are sunk ; the mus-
cularis mucosae, with the distinct layers of which in many
parts it is seen to consist, and the bundles of fibres which ex-
tend from it, either towards the villi or between the glands ;
and, lastly, the submucosa and muscularis externa. The in-
testine should be treated as follows : The intestine of a cat,
dog, rabbit, rat, or hedgehog just killed is opened, small por-
tions are at once placed in water colored with bichromate of
potash, and washed. They are then transferred to a one-tenth
or one-eighth per cent, solution of chromic acid, and five or
six days later to dilute alcohol, in which they are steeped for
some days. Thereupon small portions are embedded in gum,
and colored and mounted as directed in Chapter VI.

138 ORGANS OF DIGESTION.

The Glands of Brunner. — These glands may be studied
in thin vertical sections of the duodenum of the cat or dog.
They lie in the submucosa, and consist of branched tubes,
which are much convoluted and are lined throughout with
cylindrical epithelium. Towards'the muscula?*is externa they
are invested by a special layer of unstriped muscular fibres,
originating from the muscularis mucosae. The ducts of these
glands, after penetrating the muscularis mucosae, diminish in
calibre as they pass outwards towards the surface between the
Lieberkuhn's tubes. The epithelium with which they are lined
exhibits a striking contrast to that of the tubes, the elements
being slenderer and much more readily stained with carmine.

Peyer's Follicles. — The best preparations are to be ob-
tained from the lower end of the ileum of the dog or cat. The
intestine of the rabbit may also be used. Thin sections of
these parts may be prepared as above directed, with the excep-
tion that the time occupied in each stage of the process of
hardening may be shortened. The hardened portions must,
moreover, be embedded in wax-mass rather than in gum. The
sections, whether stained or not, should be steeped for twent}--
four hours in water, and then shaken in the manner recom-
mended for the preparation of sections of the lymphatic
glands. They are finally mounted in glycerin. In this way
the recticular tissue both of the mucosa and of the follicle is
well shown. From sections of Peyer's patches, prepared in
the manner previously described, we learn that each follicle is
surrounded by a large lymphatic sinus — that each is deeply
embedded in the submucosa, sometimes approaching the mus-
cularis externa — that a small part of each penetrates the mus-
cula?-is mucosae and projects into the mucosa, some of the
summits losing themselves in its tissue without any defined
limit, others reaching up to the epithelium. When this is the
case, the epithelial elements are smaller, and consist of several
layers of polyhedral cells. Both in situations where there are
distinct patches, and in those regions in which (as occurs in the
ileum of the cat and dog) the whole of the submucosa is occu-
pied with follicles, the individual follicles are in continuity at
their widest part. The network of lymphatic vessels of the
submucosa, with which the sinuses of the follicles, as well as
the tymphatics of the villi, are in immediate communication,
can be readily filled with soluble Prussian blue, by the method
of puncture. It is most easilj- accomplished in large rabbits.
Half per cent, silver solution may be also used for the demon-
stration of the endothelial lining which all these vessels pos-
sess.

To prove that in the absorption of fat the network of the
stroma of the villi is concerned, a rat, hedgehog, or kitten is
allowed to remain without food for a day or two, and then fed

BY DR. KLEIN. 139

with milk (rat, kitten) or fat meat (hedgehog), and killed a few
hours afterwards by strangulation. The belly having been
opened, those parts which to the naked eye appear best filled
are ligatured without delay, and placed at once (without open-
ing them) into Midler's liquid, previously slightly warmed.
After a few days, small portions are cut out and immersed in
half per cent, solution of osmic acid, and then, twenty-four
hours later, replaced in Midler's liquid, or in one-tenth per
cent, chromic acid solution. Bits of the intestine so prepared
must finally be embedded in gum-mass for the preparation of
sections, which must be mounted in acetate of potash. In
sections which comprise villi, the epithelium, and the reticulum
and central lymphatic vessel of each villus are observed to be
filled with fat drops stained brown or black by the reagent.
When a villus is cut transverseby, it is seen that trabecular
beset with blackish or dark-brown fat drops, arranged in a
reticulate manner, radiate from the central lymphatic outwards
to the epithelium.

Bloodvessels. — The arrangement of the capillary networks
which surround the glands, and those of the villi, must be
studied in injected preparations.

Nerves. — Meissner's and Auerbach's ganglia have been
already referred to sufficiently in Chapter V.

Large Intestine. — The methods for studying the epithe-
lium, the Lieberkuhnian tubes, and the solitary follicles of the
submucosa, the mucosa and muscular structures, are the same
as those used for the small intestine. The agminate follicles,
with their lymphatic sinuses, may be particularly well seen in
the vermiform appendix of the rabbit. The muscularis and
glands of the mucosa are best seen in the wart-like prominences
of the colon. Good examples of the Lieberkuhnian tubes, the
muscularis mucosae, and the solitaiy follicles, are to be obtained
from the dog. The ganglia of Meissner are well seen in the
dog and cat, and in the human foetus.

Liver. — For the study of the liver, fine sections of the fresh
organ may be employed. By teasing these out with needles,
the characters of the elements of the connective tissue, and
the form of the liver-cells and their nuclei, can be satisfactorily
made out. The arrangement of the cells in the acini can be
demonstrated in sections of liver of human foetus, or of the
smaller domestic animals, hardened in solution of bichromate
of potash or very dilute solution of chromic acid. The best
plan is to steep very small portions of liver for four or five
days in a large quantity of one to two per cent, solution of
bichromate of potash, and then for twenty-four to forty -eight
hours in common alcohol. The sections so obtained are
stained in the usual way in carmine. In such preparations
the beautiful regular groups or oblong tracts of liver-cells,

140 ORGANS OF DIGESTION.

with the capillaries which separate them from each other, are
well seen. Here and there it is observed that an interstitial
hole or orifice appears to be formed by the apposition of two
semi-circular notches in the border of contiguous cells, or. in
other cases, bv three cells similarly notched. By comparing
these appearances with sections of organs in which the ulti-
mate bile ducts are injected, it is seen that the orifices cor-
respond to sections of these channels. They possess no special
wall, being apparently bounded immediately by the cell-sub-
stance. In such preparations the cylindrical epithelium of the
interlobular ducts can also be well seen. The bloodvessels
should be studied in organs in which the vena portse has been
previously injected with gelatin mass ; for which purpose the
liver of a rabbit, guinea-pig, or small dog, answers best. The
animal having been killed by bleeding, a canula is inserted in
the vein, and a ligature placed round the vena cava, in the
thorax. Before injecting the mass, it is best to send warm
half per cent, solution of salt through the organ, till it be-
comes colorless. Carmine-gelatin or Prussian-blue-gelatin mass
must then be injected in the manner directed in Chapter VI.
Before leaving off, the ligature on the cava is tightened, after
which a somewhat stronger impulse is given, so as to keep
the vessels distended. The vena portse having been ligatured,
the organ is treated as before directed. In such preparations
the whole course of the vessels from the interlobular veins,
through the capillary s3-stem of each acinus to the intralobular
vein, may be studied. If it is desired to inject the hepatic
artery and the portal system with different colors, this may be
accomplished by securing a canula at the same time in both
vessels ; the nozzle of the one canula being connected with
a Woolff s bottle containing carmine mass, that of the other
with a similar bottle containing Prussian blue. The connect-
ing tubes leading to the two bottles are adapted, one to each
arm of a T" tube, the stem of which is in communication with
the pressure apparatus, so that the same pressure is exerted at
the same time in both bottles. The bile ducts can be injected
naturally by the same method which is used for injecting the
urinary tubes, or in the ordinary way by the hepatic duct.
After ligaturing the cystic duct, two per cent, solution of Prus-
sian blue can be injected with such success that in parts the
capillary bile ducts are filled. The livers that answer best for
the purpose are those of mature foetuses, puppies, and rabbits.
As soon as a successful injection has been obtained (as may be
judged of by inspection), it is desirable to inject the portal
system with a different color.

The Spleen. — For the study of the elements of the pulp of
the spleen it is absolutely necessary to use the organs of ani-
mals just killed. Preparations may be made either by scraping

BY DR. KLEIN. 141

the sectional surface, or by teasing. The tissue of the trabe-
cular,the special sheaths of the arteries, the stroma of the pulp,
and that of the Malpighian corpuscles, are best studied as fol-
lows: Small bits of fresh spleen are steeped in one or two per
cent, solution of bichromate of potash till they are fit for
making sections. The thin sections are then washed in water
(after coloring if desired), and carefully shaken in a test tube.
They are then covered in glycerin. In organs successfully in-
jected and prepared in the usual way, it can be made out that
the vascular system is not definitely limited as in other tissues.
The circulating blood, before reaching the veins of the pulp,
passes through a system of channels without definite walls,
the so-called vasa serosa.

CHAPTER XL

SKIN, CUTANEOUS GLANDS, AND GENITO-URINARY
APPARATUS.

Section I. — Skin.

Methods of Study. — For the study of the structure of the
skin in general, the human integument is preferable to that of
the lower animals. Portions of skin with subcutaneous cellu-
lar tissue, obtained in as fresh a state as possible, are placed
in sherry -yellow solution of chromic acid, containing from one-
tenth to one-fourth per cent. After a week, or even sooner,
they should be transferred to common alcohol, and used for
the preparation of sections. As regards examination of the
epidermis, it is only necessary to add to the directions given
in Chapter II., that the best parts of the skin for the prepara-
tion of sections are the volar side of the fingers, the lips, the
alae of the nose, and the eyelids. Any part will answer equally
well for the investigation of the structure of the corium. If
it is desired to demonstrate the sweat glands, the palm of the
hand, the axilla, and after these the forehead, answer best.
Hairs can be examined in the skin of the scalp, the upper lip,
and eyelids. The sebaceous glands, whether those which open
into hair follicles, or those of which the orifices are free, can
be best prepared in the labia majora, prepuce, scrotum, or in-
ternal lining of the orifice of the nose or eyelid of new-born
children, and in the scalp of adults. The unstriped muscular
fibres of the skin, particularly the hairs, can be studied in the
scalp and scrotum, or in the skin which covers the anterior

142 SKIN.

and external aspect of the thigh. The bloodvessels can be
best studied in injected preparations, for which purpose the
best way is to inject one of the upper extremities of a new-
born foetus.

The lymph vessels can be made out most easiby in oedenia-
tous skin. The integument must be removed with the whole
of the subcutaneous tissue, and then sacrificed at one or two
points, and left twenty-four hours suspended, until much of
the liquid has drained awa}\ The vessels can then be injected
by the puncture-method.

The preparation of the nerves and cellular elements of the
corium and papillae by the gold method has been already de-
cribed. The Pacinian corpuscles and tactile corpuscles of
Meissner can be advantageously seen in thin sections of the
volar side of the finger or palm, after hardening in chromic
acid.

Sweat Glands. — The sweat glands are of two forms.
Those of the first form are long and slender tubes closed at
one end. The secreting part, or body of the gland, is convo-
luted, and is imbedded in the subcutaneous tissue at a variable
depth; the duct which passes through the corium to the sur-
face follows a slightly winding course. The gland, whether
seen in transverse or longitudinal sections, is found to be
limited by a fine membrane (membrana propria) lined by a
single layer of cylindrical epithelium, the free surface of which
forms the internal surface of the gland. In very thin sections,
in which it is possible to compare the epithelium of the ducts
with that of the bod}r of the gland, it is seen that the elements
of the former are more slender. In the duct it is further note-
worthy that the nucleus of each element is in its outer third,
and that the nuclei are regularly arranged. In the elements
of the body of the gland they lie in the middle of each cell.
In the epidermis, the duct is continued towards the surface as
a canal, which winds spirally, like a corkscrew. This is par-
ticularly the case when the epidermis is of some thickness.

In a section which shows the whole course of the canal, it
is seen that the membrana propria becomes continuous with
the most superficial layer of the corium, while the epithelium
of the duct becomes identified with the elements of the rete
Malpighii. This first form of sweat glands is met with over
the whole integument. The glands of the second form occur
along with the others in grown persons onl}r, and are subject
to great differences as regard their distribution. They are
always to be found in the skin of the palm of the hand, of the
axilla, and of the scalp. They are met with in some persons
in other parts of the body. They are distinguished from the
common form by the facts that they are three or four times
as large, that the tube is as much wider, and that the epithelium

BY DR. KLEIN. 143

consists of larger elements, which are coarsely granular, and
of polyhedral form, and occasionally contain yellowish-brown
pigment.

As the epithelium elements are often found separated from
the membrana propria, it may be inferred that the}' are much
more loosely attached to it than in the other form. Further,
it is to be noticed, that the membrana propria contains a con-
tinuous longitudinal laj'er of unstriped muscular fibres, which
seem to lie towards its inner surface. Wherever glands of this
form occur, they appear to be cpiiite distinct from the others,
for no intermediate or transition forms present themselves.
It is possible that these glands have a casual relation to the
offensive odor of perspiration in certain persons.

The orifices of the ducts of both kinds of sweat glands are
lined with laminated epithelium, which is in direct continuity
with the rete 3falpighii. The cells of the layer which lies on
the propria are of a polyhedral or rather pallisade form.
Those which lie next them are somewhat flattened, forming
layers which are more and more scanty the further the}' are
from the orifice ; they entirely cease where the duct joins the
gland. The membrana propria of the gland itself is lined by
a la}'er of polyhedral cells, which are of uniform size and ap-
pearance, and consist of protoplasm. These are readily stained
by carmine, and are continuous with the deepest la}'er of the
epithelium (the pallisade cells).

Sebaceous Glands. — The sebaceous glands consist of closed
tubes, which are usually branched, and receive a variable num-
ber of tributary sacculi. They either open at the surface, or
into hair follicles. In every sebaceous gland the secreting part
may be distinguished from the duct. The duct is lined with
pavement epithelium, which, when the orifice is at the surface,
can be, seen to be continuous with the rete Malpighii. In
glands which open into hair follicles, it is continuous with the
external sheath of the bulb. In passing from the duct to the
secreting part, the epithelium changes its character, being re-
presented by a layer of granular, cubical, or polyhedral ele-
ments which lines the propria. Besides these cells, the sacculi
contain larger elements, which are so closely packed together
as to be flattened against each other. In fresh preparations
these appear to be loaded with fat, but in preparations treated
with absolute alcohol and oil of cloves they exhibit a distinct
nucleus and investing membrane. The sebaceous glands can
be best studied in the skin of mature foetuses, e. g., in that of
the lips and nasal orifice, labia majora, prepuce, and scalp.
The acinous form is exemplified in the Meibomian follicles of the
eyelids. Sections of these parts hardened in chromic acid must
be made, which can be stained and mounted in Dammar var-
nish.

144 URINARY APPARATUS.

Hair. — With reference to the structure of hair, it is of im-
portance to notice that each follicle consists of a connective
tissue layer, and of a layer of muscular fibres. The former,
which is richly supplied with capillaries, is formed of fibres
which run mostly longitudinally, and seem to be merely a con-
densation of the surrounding tissue. In certain parts, this
layer is in immediate contact with the external hyaloid mem-
brane of the hair; in others, there exists between them a cir-
cular layer of plain muscular fibres, which varies in distinct-
ness in different varieties of hairs, but is always most strongly
developed in the neighborhood o'f the bulb. In the eyelash of
the mature foetus, the muscular la^'er is much stronger than
the connective tissue layer, and can be traced over the whole of
the bulb. As regards the structure of the hair itself, all that
is required will be readily understood from the description
given in the ordinary text-books.

The structural facts relating to the root of the hair can be
easily made out in chromic acid preparations. The structure
of the shaft can be best seen by preparing fresh hair (of the
scalp) in concentrated acetic acid, by which means the cuticle
and the elements of the medulla are brought into view. For
the isolation of the plates of the cuticle, and of the fibre-cells
of the substance of the hair, concentrated sulphuric acid is
used, at a temperature of 40° to 50° C, in which the hair must
be heated for about an hour. After steeping for several days
in two per cent, solution of caustic potash, the elements of the
medulla become very distinct. The development of the hair,
and of the sweat glands and sebaceous glands, may be studied
in embryos at various periods, in preparations hardened with
chromic acid. The most important point to notice is, that in
mature embryos, or even in the eyelashes of children, if the
section coincides precisely with the axis of the hair and4nvolves
the papilla, it is seen that that part of the external hyaline mem-
brane which extends over the papilla is uninterrupted^ covered
with the regularly arranged cells of the external sheath, and
that these cells occup\r the whole bulb to about half-way up
the root. It is common to find several stages of development
in a single preparation, from which it can be learnt that the
new hair takes its origin from the axial cells of the sheath of
the root, being formed by the lengthening of these elements.

Section II. — Urinary Apparatus.

Epithelium of the Kidneys.— For the study of the epi-
thelium of the kidneys, the pig, dog, or mature foetus may be
used. The fresh kidneys having been divided into two halves,
in the direction of the length of the organ, juice from the cut
surface may be employed for the study of the epithelium of

BY DR. KLEIN. 145

different parts. It is, however, better to cut one of the halves
transversely into a number of parts, which may be placed in a
large bottle filled with half or one per cent, solution of bichro-
mate of potash. After from eight to ten days, sections of the
cortex are prepared, as thin as possible. Some of these must
he made in the direction of the pyramidal processes (which are
readily seeu by the naked eye), others at right angles to these
processes, and parallel to the surface. Other sections com-
prising as much of the medullary substance as possible, must
in like manner be made in both directions. The cross sections
should be taken from various parts of the medullary substance,
some comprising the papillae, others the intermediate part.
The sections, having been washed in water for fifteen minutes
or more, may be either mounted at once in glycerin, or after
previous staining for twenty-four hours in diluted solution of
carmine. Such preparations show the characters of the epi-
thelium in the tubes throughout their whole extent, and in the
loops of Henle. It may be farther seen that in many of the
convuluted tubes of the cortex, the uniformly granular sub-
stance can be distinguished into distinct polyhedral cells, each
possessing a spheroidal nucleus. By teasing the sections ob-
tained as above, it is possible to isolate straight tubes or loops,
but this can be better accomplished by another method to be
described further on.

Epithelium of the Malpighian Capsules. — For the
demonstration of the epithelium which lines the internal
surface of each Malpighian capsule, and the surface of the
glomerulus, it is best to employ kidneys of mature or imma-
ture human foetuses. With this view the organ (which must
be as fresh as possible) must be divided into small portions,
and first placed for three to six days in one per cent, solu-
tion of bichromate of potash, and then transferred for one or
two days into one-fourth to one-eighth per cent, solution of
chromic acid. The sections are prepared in the ordinary way
after embedding. In such preparations it is seen that the
capsule of the glomerulus, which is characterized by its oblong
nuclei, extends continuously over it, and that it is lined with
a continuous layer of elements which are mostly cubical, but
sometimes columnar. The epithelium of the convoluted tubes
consists, in the human foetus, of spheroidal or cubical cells.
If a very small strip of the fresh kidney of the frog is pre-
pared in salt solution or serum, it is seen that the epithelium,
as well of the capsule as of the commencement of the con-
voluted tube leading from it, is beset with cilia of extraordi-
nary length.

Isolation of the Tubes. — Long slices of fresh kidney so
cut as to include both cortical and medullary substance, and
to extend from the surface to the papillae, are placed in a flask
10

146 URINARY APPARATUS.

containing a mixture of eight parts of common alcohol, and
two parts of hydrochloric acid. The flask is fitted with a cork,
through which a very long glass tube passes. It is kept
boiling for some hours, after which the liquid is poured away,
and replaced by distilled water. In this liquid (which should
be changed once or twice) the portions of kidney arc steeped
several days. They are then agitated in a test tube, contain-
ing a little water, by which means the tubes readily separate
from each other. They can now be prepared in the same
liquid for microscopical examination, or allowed to subside,
and then separated from the liquid and mounted in glycerin.
Pure hydrochloric acid is also used for the same purpose.
The slices of kidney, which must be taken from an animal
killed the day before, are steeped in hydrochloric acid of 1-120
sp. g., for five to twenty hours. Thereupon the portions are
carefully washed with distilled water. Of these methods, the
former is easier. By either it can be shown that the capsule
of the Malpighian body is first contracted, and then dilated so
as to form the convoluted urinary tubes, which are filled with
a substance, the division of which into cells is almost indis-
tinguishable. These tubes are continued onwards, first as the
narrower descending limb of the Henle's loop, and then as the
somewhat wider ascending limb. The latter again dilates, so
as to form the intercalated convoluted tube (Schaltsliick)
wdiich ends in a straight collecting tube. These last form the
pyramidal processes, and unite finally into single ducts, by
repeated junctions with each other at very acute angles.

The whole system of ducts ma}r often be injected from the
ureter. Injections can, however, seldom be carried beyond
the loops. The most suitable kidneys for the purpose are
those of the pig, dog, or rabbit. The animal must, if possible,
be killed by bleeding. A canula, having been secured in the
ureter, close to the point at which it leaves the pelvis of the
kidney, two per cent, solution of Prussian blue is injected,
under a pressure of from 60 to 100 millimeters. The ureter
having been ligatured, it is desirable to fill the artery with
carmine gelatin. The urinary tubes can be also injected
during life by what is called the natural method. A rabbit of
moderate size is allowed to lose 10 c. c. of blood from the
jugular vein, replacing it with a filtered solution of carmine,
containing two drachms of carmine, and one drachm of liquor
ammoniac in an ounce of water. If a dog of moderate size
is used, 25 c. c. are required. Immediately after the injection,
the ureters are ligatured, and the animal is allowed to live for
an hour, and then killed. The bloodvessels are then injected
with solution of Prussian blue in gelatin, and the organ is
placed in common alcohol containing a drop or two of glacial
acetic acid. Before placing the kidneys in alcohol, they must

BY DR. KLEIN. 147

be steeped for a short time in concentrated solution of chloride
of potassium. Instead of the carmine, solution of sulpho-
indigotate of soda, saturated in the cold, may be used in
exactly the same manner. The bloodvessels must, however,
be subsequently injected, not with Prussian blue, but with
carmine gelatin.

Pelvis, Ureter, and Bladder. — The laminated epithe-
lium of these parts may be studied in bichromate of potash
preparations. For sections, the membrane must be hardened
in chromic acid. The methods for the study of the epithelium,
muscular tissue, nerves, and ganglia, etc., have been already
fully described in Part I.

Section III. — Genital Organs.

Epithelium and Endothelium of Ovary. — It has

been recently shown by Waldeyer that the ovary is only
partly covered with peritoneum. Where this is the case the
surface is covered with endothelium. The remainder of the
surface possesses a cylindrical epithelium, to which the term
germinal epithelium is applied. This can be demonstrated in
the ovaries of the sow, bitch, and cat, and in the human
ovary. In the last it can be seen both in the mature foetus
and in the adult. In the fresh ovary the line of demarcation
can be made out, even with the naked eye. By scraping the
surface with a scalpel, shreds can be obtained which may be
at once prepared in salt solution. In those taken from the
peritoneal part, large endothelial plates can be shown, each
containing an oblong nucleus. In those from the other part,
cylindrical cells are seen, which consist of distinctly granular
protoplasm, and contain an ovoid nucleus and nucleolus.
These possess the character of epithelial elements. If an
ovary is placed a few minutes in silver solution and then
washed the usual way in water, and hardened in alcohol,
sections parallel with the surface of both parts may be pre-
pared. In such sections, if made close to the surface, and
covered in glycerin, the contrast between the two forms of
cellular investment can be completely demonstrated.

The anatomical relations of the germinal epithelium, and of
the tunica albuginea, stroma, and Graafian vesicles must be
studied in sections. For this purpose the fresh organ obtained
from any of the above-mentioned animals must be steeped in
one or two per cent, solution of bichromate of potash for
periods varying from four days to a week ; it must then be
transferred for a day or two to one-eighth or one-tenth per cent,
solution of chromic acid, and can afterwards be kept in com-
mon alcohol. Small ovaries, such as those of mature foetuses,
or of other young animals, can be embedded in toto. Larger
organs must be divided.

148 GENITAL ORGANS.

Stroma. — The most important peculiarity to notice is the
extraordinary frequency of bundles of spindle-shaped cells
which run across each other in various directions. Their claim
to be regarded as muscular or connective tissue cells is still
open to question. Both in the sow and bitch, there are
bundles of unstriped muscular fibres, which, along with blood-
vessels, run from the medullary part into regions in which
large follicles are to be met with, and form an investment of
the follicular wall. There are, however, many bundles in the
cortical substance which present no such definite characters.
But in the ovary of the guineapig, muscular bundles can be
distinctly recognized even in the stroma of the cortex.

Graafian Follicles. — The structure of these follicles can
be made out completely in the preparations above referred to.
For the study of their development, human fcetal ovaries and
those of the dog must be used. In the former, it is seen that
from that part of the surface which is covered with germinal
epithelium, blind tubes are sunk to various depths and in
various directions. These tubes are lined with an epithelium,
which is continuous with that of the surface, and identical
with it. It can further be made out that certain individual
elements of this epithelium have a special character, being
more readily stained with carmine, and that they are larger
than the others. Between these and ovules all transitions
can be observed. By the segmentation of a single tube into
several closed vesicles, Graafian follicles are formed, each of
which is lined with a layer of epithelium, and contains one or
two nucleated ovules, so that both stand in a definite develop-
mental relation to the germinal epithelium. These facts may
be demonstrated equall}* well in the ovaiy of the bitch ; a zone
of tissue exists under the germinal epithelium in which closed
tubes are met with, which run in very various directions.
Many of these look as if they were connected with each other
so as to form a network. Deeper, there is a zone in which
separate follicles exist.

Ovum and Discus Proligerus. — The ovum itself and
the cells of the Discus proligerus may be studied in fresh
ovaries. The contents of a large Graafian vesicle of the
rabbit's or guineapig's ovary are discharged on to an object-
glass for the purpose. The}' can also be well seen in the pre-
parations above described.

Fallopian Tubes, Uterus, Vagina, and External
Organs. — These may be best studied in sections of organs
hardened in chromic acid — the methods recommended in Bart
I. being employed for the study of the several tissues of
which they consist. Some special remarks are, however,
necessary relating to the glands of the uterus. They can be
best demonstrated in the cornua uteri of bitches or cats which

BY DK. KLEIN. 149

have already borne young. The fresh organ is placed in
common alcohol or dilute chromic acid, Avithout opening it;
after four or five days it is fit for making sections. Each
gland consists of long blind tubes, which may be either single
or divided. The glands are closety packed together. In each
tube two parts may be distinguished ; one of these, which may
be regarded as the duct, is straight, and possesses an epithe-
lium of slender pale cylindrical elements. The gland proper
is convoluted, and consists of shorter elements. If the sec-
tions are steeped twenty-four hours in very dilute carmine, it
is seen that this epithelium is much more stained than that of
the duct. In the sow's uterus, and in those of the rabbit and
mouse, it can be made out that the epithelium is ciliated.

The glands can be best prepared in lengths from the preg-
nant uterus of the sow. For the mode of preparation see
Chapter III., p. 60. It is scarcely necessary to observe that
for the study of the external organs, injected preparations are
important.

Male Genital Organs. — The general structural relations
of the testis and epididymis are best studied in sections of
fresh organs (frog or mammalia), hardened in common alco-
hol ; these must be stained and prepared in Dammar varnish
in the usual way. Preparations with the bloodvessels and
lymphatics injected must also be used. The latter are easily
obtained by the method of puncture. The characteristic epi-
thelium of the epididymis must be seen in fresh preparations
in serum, as well as in sections. The structure of the vasa
deferentia^ vesiculae seminales, prostate, urethra, and penis,
may be all studied in the organs of the fcetus or of children,
after hardening in chromic acid. The structure of the erectile
tissues cannot be demonstrated without good injected prepa-
rations. [For details see the author's paper in Strieker's
Hand-book. J

150 ORGAN OF BIGHT.

CHAPTER XII.
ORGANS OF SPECIAL SENSE.

Organ of Sight. — The epithelium, cellular elements, and
the finer nerves of the cornea have been already treated of
(Chapters II., III., and V.)« We have only to remark that,
in order to observe the relation of the cornea to the conjunc-
tiva, sclerotica, and ligamentum peclinatum, it is necessary to
harden the bulb entire, and to make sections which shall in-
clude all these structures. The best and simplest method
consists in placing the fresh bulb of a mature foetus, a rabbit,
a pig, or a calf, in one-tenth per* cent, solution of chromic acid,
for eight or ten days; having previously made two or three
punctures in it with a lancet-shaped needle. After two or
three daj-s of immersion, the bulb may be cut in two with a
razor, the crystalline lens and vitreous body removed with
forceps, and the anterior half of the bulb (containing the con-
junctiva, the cornea, the iris, and processus ciliares, the an-
terior segment of the sclerotic and choroid as well as the ora
serrata retinse, and zonula Zinii) put back in the solution.
The necessary consistence having been obtained, a portion is
cut off in such a way as to render it possible to make trans-
verse sections through the above-mentioned structures. The
sections ma}r be treated in the ordinary way ; and, if thin
enough, they will also be useful for the purpose of studying
the tissue of the sclerotic, choroid, ciliary processes, and iris,
as well as of the musculus tensor choroidese.

The cellular elements of the sclerotic may be further de-
monstrated in surface preparations as follows : The bulbus oculi
of a frog having been extirpated, is carefullj* freed from ad-
herent connective tissue on an object-glass ; the surface of the
sclerotic is then thoroughly touched with lunar caustic : after
a quarter of an hour small portions are cut off: these must be
pencilled on their inner surface with a camel-hair brush, so as
to remove any adhering pigment ; the preparations being
finally mounted in glycerin. Successful preparations exhibit
branched clear spaces — canaliculi — on a brownish-ground, such
as have been previously described.

Other portions of fresh sclerotic may, after pencilling, be
treated with a half per cent, solution of chloride of gold, and
employed both for vertical and horizontal sections. In the
former, the violet-colored cellular elements appear as spindle-

BY DR. KLEIN. 151

shaped cells, lying between the bundles of connective tissue of
the sclerotic; whilst, .in the latter, they exhibit forms which
correspond to the above-mentioned canaliculi. The sclerotic
of a young rabbit may be similarly treated with the gold and
silver solutions. For the study of the iris, choroid, and ciliary
processes, several methods are employed besides that of making
vertical sections through the hardened parts. The hexagonal,
pigmented epithelium covering the inner surface of the uvea,
which is considered to belong to the retina, can be removed
from the fresh membrane with a scalpel or sharp needle, in
small shreds : these must be spread out with needles and
mounted in salt solution. Preparations of the same kind can
also be obtained from bulbs which have been kept for a few
weeks in Muller's fluid ; they must be preserved in glycerin.
The more or less branched pigment cells which are to be found
in the substance of the uvea in different animals, but varying
in number and distribution, may be prepared from the fresh
tissue in a similar manner, but it is preferable to make thin
sections of the membrane. For the investigation of the mus-
culus tensor choroids, as well as the sphincter pupillse, verti-
cal sections of the human uvea from a bulb hardened in chro-
mic acid, are most important ; the sections must be immersed
in very dilute carmine for twenty-four hours.

To demonstrate the dilator et sphincter pupillse, the iris of
a small albino rabbit will serve. It must be cut out with great
care, and after having been pencilled on both surfaces with a
camel-hair brush, moistened with humor aqueus, must be im-
mersed in half per cent, solution of chloride of gold for from
thirty to forty minutes, whence it must be transferred to acidu-
lated water. There is also another plan which answers satis-
factorily : * The bulb of a similar rabbit is placed in Midler's
liquid for a few days, the cornea having been previously punc-
tured. The whole iris is then cut out, pencilled in the same
fluid with a camel-hair brush on both sides, and placed in spirit
for from fifteen to thirty minutes. The iris should then be
colored in dilute carmine, and portions should be mounted in
glycerin. With the exception of the muscles, the bloodvessels
form the most important part of the uvea. For their study,
injections witli gelatin, colored by carmine or Berlin blue,
should be made ; albino animals being preferred. For small
animals the canula should be tied into the root of the aorta,
the aorta ihoracica descendens being ligatured. For large
animals the common carotid may be employed ; of course, as
a general rule, onljr one eye will be injected. The bulb having
been kept in spirit for a few days, the whole uvea is carefully
isolated from the outer coats: in the case of a small rabbit,
one section may be mounted including a portion of the iris,
ciliary processes, and the anterior half of the choroid ; and

152 ORGAN OF SIGHT.

another including a portion of the posterior half of the choroid.
The circuit arteriosi iriili.< minor et major, the vessels between
these, the system of capillaries of the ciliary processes, and
their relation to the arterise ciliares posticse1 the system (ar-
terial) of the laminae Ruisehii, and the tributaries of the venae
vo> ticosae, are severally to be studied.

The crystalline lens, with its several parts (capsule, epithe-
lium lining the inner surface of the anterior portion, and the
constituent fibres of the lens itself) should be made the subject
of careful observation. The hyaline capsule, with the above-
mentioned epithelium, can be demonstrated in a perfectly fresh
preparation, in humor aqueus. The structure of the lens fibres
may be made out in preparations from the lens of a fowl, or of
some large mammal, macerated in very dilute sulphuric acid
(one or two per cent.). The fibres exhibit a striated appear-
ance, and, if they are sufficiently separated from each other,
it may be seen that each possesses a spherical nucleus.

In preparations of the same kind from the portion of the
lens which corresponds to the margin between the anterior
and posterior half of the organ, every stage of transition of
the epithelium which lines the anterior part of the capsule,
into true lens fibres, can easily be made out ; the elements be-
coming progressively more and more elongated, and their nu-
clei more and more distant from their bases. The best way
to ascertain these facts is by means of sections, which show
also that, posteriorly, the lens fibres are in immediate contact
with the capsule. Vertical sections display the very regular
mosaic due to the cutting across of the long, hexagonal fibres.
They may be made after the lens has been hardened in solu-
tion of chromic acid (one-tenth per cent.), or bichromate of
potash (one-half to one per cent.). The hardening ma}' also
be effected by exposing the lens to the air, and allowing it to
become almost dry : sections so obtained must be mounted in
glycerin. The structure of the corpus vilreum, consisting as
it does of a perfectly hyaline gelatinous matrix, with a few
extremely pale, small spheroidal cells imbedded in it, may be
investigated in the fresh organ, but better in sections made
after the bulb has been hardened in a one-eighth to one-half
per cent, solution of chromic acid. The staining of the sec-
tions with carmine or aqueous solution of anilin will prove
very useful for the demonstration of the cellular elements.

The retina presents, perhaps, a more difficult task to the
histologist than any other organ ; the investigation of even the
simplest relations of its constituent elements requiring much
time and patience. The introduction of the perosmic-acid
method of preparation, however, has, within the last few years,
considerably bridged over our difficulties in this respect.

BY DR. KLEIN. 158

The most useful preparations are those made with needles.
The carefully excised fresh eye of a frog, newt, rabbit, ox,
calf, or pig is divided into an anterior and posterior half.
The latter is placed for from twenty-four to forty-eight hours
in a one-tenth per cent, solution of perosmic acid, in the dark;
thence it is transferred to distilled water for twenty-four hours.
After this period small portions of the retina are snipped off
and teased in a drop of nearly saturated solution of acetate
of potash and mounted in the same fluid. The frog's retina
in particular is extremely valuable for the study of the rods
and cones with their outer and inner portions, the radial fibres,
the nuclei of the outer and inner granular layers, and the nerve
fibres and ganglion cells, all of which are much better seen
than in retinas which have been macerated in Midler's liquid.
When the object is to study the relations to each other of the
different strata in the retina, either of the two following pro-
cesses may be employed : —

1. The posterior half of the bulb (or, when small, the whole
bulb, after two or three punctures have been made in it), is
placed in a two per cent, solution of perosmic acid in the dark
for twenty-four hours : it is then removed, and small, oblong
pieces are cut from it with a razor (these including, of course,
besides retina, corresponding portions of sclerotic and choroid),
and placed in alcohol for twent3r-four hours or more, until they
have attained sufficient consistence for sections to be made
from them after embedding. The sections should be mounted
in acetate of potash as before. This method answers very
well for the retina of the rabbit, calf, or pig.

2. The other plan, which must also be looked upon as a
good one, is the treatment with Midler's liquid. The entire
bulb of one of the above-mentioned animals is placed in this
liquid, having previously been punctured at two or three
points. After from three to five weeks it is taken out, and cut
into an anterior and a posterior half. From the portion of
retina belonging to the latter, an oblong piece is removed
with fine, sharp scissors (it is generally pretty easy to do this
without involving the sclerotic and choroid, since the retina
has usually become more or less separated from the latter by
the action of the fluid), and transferred for a few days to ordi-
nary spirit. From this it is put into dilute carmine solution
for twenty-four hours, then washed in acidulated water, and,
finally, after half an hour's or an hour's immersion in absolute
alcohol, is embedded in the manner previously described
(Chapter VI.). The sections are transferred in the manner
there indicated from the razor to the object-glass, on which,
after proper treatment, they are to be mounted in Dammar.

A skilful manipulator can obtain good results with this
method. Very thin sections show, in a sufficiently clear man-

154 ORGAN OF HEARING.

ner, the general arrangement of the rods and cones, and their
illation to the elements of the outer granular layer, that of
the intermediate layer to the granules of the inner granular
layer; the finely granular layer, and the relation of its fine
fibrilla? to the fibrils of the inner granular layer on the one
side and the processes of the ganglion cells on the other; and
finally, the layer of nerve fibres. The general arrangement of
the radial fibres, or, rather, bundles of radial fibres, may be
also made out : each bundle, attached to the Umitans interna
by a broad basis, enters the finely granular layer, thence pass-
ing through the inner granular layer (where the bundles be-
come ramified, and inclose nuclei), then on through the inter-
mediate layer and outer granular layer (where again ramifica-
tions and junctions are met with) to become attached, finally,
to the Umitans externa. (See description of Figs. 139 and
140).

Organ of Hearing. — The outer part of this organ, including
the external ear, meatus, and Eustachian tube, should be
studied in portions taken from a 3'oung human subject. To
prepare the membrana tympani (human, or from a cat or dog),
it must be exposed b}" the aid of saw and bone-forceps — a
manipulation requiring an accurate knowledge of the topo-
graphical details of the temporal bone. This done, the mem-
brane is excised, and either stained with silver at once, to
show the epithelium of the two surfaces, or pencilled on its
outer surface with a brush moistened with serum, to show the
lymphatics. If the gold method is used, the epithelium is also
pencilled on the outer surface, and the membrane immersed in
the solution from half an hour to an hour. It must then be
treated in the usual way.

The study of the membranous labyrinth, especially the canal
of the cochlea and the semicircular canals — is a matter re-
quiring an immense deal of care and practice. It should be
undertaken both in foetal and adult organs. For the examina-
tion of it in the embyro, a foetal calf or pig from ten to fifteen
centimeters long may be used. The whole cartilaginous laby-
rinth may be readily separated from the rest of the skull after
the maceration of the latter in solution of bichromate of potash
(half to one per cent.) for a week or two. After separation it
is placed in spirit for a few clays. A second opening (besides
the already existing fenestra rotunda) should then be made
on the side opposite to it, or, better, at a point corresponding
to the top of the cochlea. The whole organ is now stuck on
a needle and immersed in a warm — but of course, not hot —
mixture of wax and oil, so as to fill up, at least in part, the
canals which exist in the organ ; this is then embedded in the
ordinary way, marks being made on the mass for the purpose
of indicating the exact position of the preparation. Sections

BY DR. KLEIN. 155

are then made in succession across the axes of the several
canals, and are stained in weak carmine. Such sections, being
readily obtained in a perfect state in the foetus, serve as a
most valuable key to the stud}' of the adult organ.

The fully-developed organ is best studied in the ear of a small
dog, guineapig, or new-born child. From the fresh jaw of the
guineapig the whole of the petrous portion of the temporal bone
can readily be removed, and placed for a week or fortnight in
a half to a quarter per cent, solution of chromic acid, to which
a few drops of hydrochloric acid has been previously added,
the liquid being changed once or twice during that time. The
cochlea is then removed, and after remaining in spirit for a
few days, is filled with a mixture of wax and oil under the
air-pump. Sections are prepared as before, after embedding.
A second mode should also be employed, which is as follows :
A horizontal section is made through the organ after removal
from the spirit, so as to expose all the turns of the cochlear
canal. Both halves are then embedded in gelatin solution, to
•which a few drops of glycerin has been added, as mentioned in
Chapter VI. The transparency of the gelatin enables us to be
sure of the direction of our sections. These are placed first in
warm water, to remove the gelatin. They may be then mounted
in glycerin, or replaced for a short time in spirit, stained with
carmine, and mounted in Dammar. I would, however, advise
the student not to risk the manipulation required for the latter
process, but to mount in glycerin at once after the warm water ;
for the section, if it is as thin as it should be, would stand a
considerable chance of injury.

For the stud}'' of the organ of Corti, thin vertical parts of
sections must be sought for in which the lamina spiralis near
that organ is seen to be cut exactly across: this is more par-
ticularly the case when the situation of the rods of the arch of
Corti, the arrangement of the cells of Deiter and the ciliated
cells, and the distribution of the nerves of the membrana basi-
laris, are .under examination. To show the elements of the
membrana reticularis, and the epithelium of Reissner's mem-
brane, more obliquely cut parts of the section are to be chosen,
or even portions where a surface view of these structures is
obtainable.

Organ of Taste. — For the study of the organ of taste the
tongue of the frog or rabbit may be used. In the former, our
attention may be confined to the papillae fungiformes, the most
important subject of observation being the topographical rela-
tions of their cellular covering. The perfectly fresh organ is
spread out with pins on a plate of cork, care being taken to
avoid unequal stretching, and placed in very dilute chromic
acid. Vertical sections are then made in the usual way.
Another way is to color the fresh organ, spread out on cork as

156 OROAN OF TASTE.

above, in chloride of gold. Half an hour's steeping in half
per cent, solution is sufficient ; but it is necessary, before cx-
posing the preparation in water, to stream it thoroughly with
the same liquid, in order to avoid the subsequent formation of
colored deposit on the surface. As soon as the tongue has
assumed the proper color, it must be hardened in alcohol, for
the preparation of sections which must be prepared in glycerin.
In vertical sections of fungiform papillae the following parts
are seen : In the axis of the papilla, along with the vessels, a
nerve twig is observed, consisting of medullated fibres, which
ascends towards the summit of the papilla, and there pencils out
into nerve fibres. Each of these is seen eventually to end in a
non-medullated fibre. Along the border of each papilla are
seen muscular fibres which divide dendritically as the}' ascend.
The covering of the flattened summit consists of a relatively
thick layer, in which two strata can be distinguished. The more
superficial of these is thicker and paler, and is finely striated
in the direction of the long axis of the papilla. In thin sec-
tions it can be recognized that this material consists of pale
longitudinally striated cylinders. The deeper and thinner
stratum consists of a ground-substance deeply stained both by
gold and carmine, in which several layers of nucleus-like struc-
tures are embedded. It can be made out in very thin sections
(and also in teased preparations) that the cylindrical nucleated
cells take part in the formation of both layers, the outer seg-
ment of each cell contributing to form the outer stratum, the
other, which contains the nucleus, the inner stratum. The
outer segment of each cell is pale and finely streaked longitu-
dinally, while the inner segment, which consists of granular
protoplasm, is divided towards the papilla into branched pro-
cesses, which unite with each other and with those of neighbor-
ing cells. In preparations successfully stained with gold, it
can further be made out, that the non-medullated fibres re-
solve themselves into a network of extremely fine fibrils, which
spread under the stratum of cells. No connection, however,
has been demonstrated to exist between this network and the
anastomosing branched processes above mentioned. The forms
of the cylindrical cells should be also studied in teased prepara-
tions. Strips of fresh mucous membrane are placed in the
dark for from twent3'-four to fort3'-eight hours, in one-tenth
per cent, solution of perosmic acid. The object having been
steeped in water one or two daj's, shreds must be torn off the
free surface of each strip of membrane, with fine sharp needles.
Each of these shreds, having further been teased carefully with
needles, must then be mounted in a drop of acetate of potash.
Another method consists in macerating similar strips in iodized
serum, solution of bichromate of potash, or very dilute solution

BY DR. KLEIN. 157

of chromic acid (one-twentieth per cent.). The teased prepara-
tions must be mounted in glycerin.

At the edge which unites the dorsal and lateral surfaces of
the tongue of the rabbit, a round or oval depression is seen,
on the surface of which an arrangement of furrows with inter-
mediate ridges are visible to the naked eye. If a vertical sec-
tion is made of this part, in a tongue hardened in one-tenth per
cent, chromic acid, in such a direction that the plane of section
crosses the ridges, a meshwork of trabecular of striped muscular
fibres, in the spaces of which the numerous mucous glands are
embedded, can be recognized. The short ducts of these glands
rise for the most part vertically, but occasionally obliquely to
the surface ; alwa3rs opening into the splits between the ridges.
So much of the mucosa as lies underneath the furrows and
ridges, contains a great number of non-medullated nerve-fibres.
Each ridge is covered with a laj'er of epithelium which becomes
thicker upwards, i. e., towards the arete ; and on either aspect
of each ridge, certain bodies are seen, embedded in the surface
b}T which it looks towards its neighbor : to these the term taste
goblets (Geschmacksbecher) has been applied. They are, as
the term indicates, bell or cup-shaped structures, which are
limited by a special layer of flattened epithelium cells, which in
profile look spindle-shaped. Into the space inclosed within
this layer, there projects from the mucosa a bunch of oblong
spindle-shaped cells, which towards their bases appear to be
divided. Each contains an oblong nucleus. The forms of the
elements just described, and of those which constitute the outer
wall or investment of each goblet, should be studied in teased
preparations. The circumvallate papillae of the human tongue
and of other mammalia exhibit similar structures.

Organ of Smell. — Teased preparations can be obtained
by macerating the olfactoiy mucous membrane of the frog
or of mammalia in one-twentieth per cent, chromic acid, in
Miiller's liquid, or iodized serum, or perosmic acid. The whole
of the head of the frog, after removing the lower jaw, and
opening the nares, is placed in the liquid. In mammalia, the
nares can be opened in the middle line, after Avhich portions of
the olfactory tract can be removed. For the preparation of
sections, the parts must be kept in one-fifth per cent, solution
of chromic acid, which must be renewed as often as necessary
till the bone becomes soft. In teased preparations it is seen
that there is no marked distinction between the ordinary coni-
cal epithelial cells and the special spindle-shaped cells, recog-
nized as olfactory epithelium: for they are connected together
by a continuous series of transitional forms. The most char-
acteristic form of the olfactory cells is drawn out at both ends,
viz., towards the mucosa into an extremely slender filament,
which exhibits granular swellings ; and towards the surface

158 EMBRYOLOGY.

into a somewhat stouter fibre, which is streaked longitudinally,
like the ordinary epithelial element, and like it, bears at its
extremity a bunch of cilia ; but, as has been already said, exam-
ples are met with, in which the special peculiarities arc wanting.
In the frog, the processes of the epithelial elements appear
to penetrate the mucosa, so as to form a network of fine trabe-
cular The finest branches of the olfactory nerve are seen to
tend towards this network, but have not been traced into actual
continuity with the extremities of the so-called olfactory cells.
The mucosa and its glands must be studied in sections.

CHAPTER XIII.
EMBRYOLOGY.

In treating of the methods which are commonly employed
in the study of general embiyology, we shall follow the same
plan as in special histology ; noticing only those points which
are of importance to the beginner.

As is well known, three parts are distinguished in every
mature egg: the vitelline membrane, the yolk or vitellus, and
the germ. The last-mentioned is the essential part, and as-
similates itself to the general idea of the cell, viz., an organism
composed of protoplasm, which possesses the capability, under
certain conditions, of performing amoeboid movements. In
the protoplasm of the germ the germinal vesicle, a body
analogous to the nucleus of other cells, is embedded; and
within this lies the germinal spot, the analogue of the nucleo-
lus. According as the two elements of the egg, which are
inclosed by the vitelline membrane, viz., germ and yolk, exist
separately from one another, or form a single bod}', eggs are
subdivided into two large groups, viz., meroblastic eggs, in
which the germ is separate from the }'olk — such as those of
the bony fishes, scaly reptiles, and birds ; and holoblastic eggs,
in which the germ itself contains the elements of the yolk —
those of the cartilaginous fishes, amphibia, and mammals.

In eggs of the first group, the germ lies upon the yolk in
the form of a disk; for which reason it receives the name of
blastoderm : formerly it used also to be termed (after Reichert)
" formative yolk," while the yolk itself was called " nutritive
3'olk." The first process that claims the attention of the
embryologist is cleavage. The fertilization of the egg sets
this process going. It is called cleavage because the germ
divides into two cleavage masses, each of these again into two,

BY DR. KLEIN. 159

and so on, until the whole germ is divided into a number of
globules, each of which consists of protoplasm inclosing a
vesicular nucleus, and, like the entire germ, is endowed with
the capability of performing amoeboid movements. These
cleavage globules are called " embryo cells." Only the germ
or blastoderm takes part in the cleavage, since this alone is
endowed with amoeboid movement. Consequently in mero-
blastic eggs the cleavage is said to be partial. In the holo-
blastic, on the other hand, the whole egg divides, for the whole
is germ ; it is, therefore, said to exhibit total cleavage.

Study of the Process of Cleavage in the Ova of
Fish and Amphibia. — The cleavage process should be
studied, in the first place, in the entire ovum ; the knowledge
thus gained being completed by sections of the germ at the
cleavage time. Of meroblastic eggs, those of the trout are
best suited for this study. Several such eggs are examined
under the microscope in a watch-glass, in the water in which
the}' have lain since undergoing fertilization, strong trans-
mitted light and a weak magnifying power (90-100) being
employed (see figs. 159-163). At the tenth hour after fertiliza-
tion, the blastoderm appears, lying upon the yolk like a lid
over a saucer-shaped depression ; the yolk, which forms the
bottom of this cavitj', contains closely packed oil globules,
which have become aggregated at this pole of the yolk since
the time of fertilization. In the blastoderm amoeboid move-
ments are observable. About the twelfth hour, the first cleav-
age line appears. About the twenty-seventh, almost all the
eggs show two cleavage lines crossing each other. Between
this time and the end of the second day, eight segments may
be distinguished ; so that four cleavage lines are now seen on
the surface of the blastoderm. At the end of the seventh
day the process of cleavage has progressed so far that the
surface of the blastoderm appears beset with a number of
bosses, like a mulberry. The cleavage process is far more
easily studied in the holoblastic eggs of amphibia. If eggs of
the frog or toad, freshly spawned, are placed under the micro-
scope, in a small cell, which may be conveniently prepared upon
a slide by means of putty, it is seen (especially in the case of
the latter, where they are placed one behind the other in rows
in gelatinous strings), that only a very few are spherical:
generally one part of the surface is flattened: so that it
frequently happens that, in a long row of eggs, alternating
conical ones are met with. About the sixth or seventh hour
after spawning, it can be seen by transmitted light that most
of the eggs have become round. As this period of time ap-
proaches, the amoeboid movement of the germ becomes more
distinctly visible, presenting the appearance of an oscillation
at some point or other within the vitelline membrane. This

160 EMBRYOLOGY.

appearance gradually increases, until a slight indentation like
a notch is seen at some part of the margin by transmitted
light. This first notch fills up, but soon a similar notch occurs
in another spot, which is permanent. By strong reflected light,
if the egg lies in such a position that the white pole is directed
downwards, a crater-like dimple may be seen on the surface.
This dimple extends itself over the margin of the hemisphere,
diminishing at the same time gradually in depth. It is called
the plaited band (Faltenkranz), because a number of smaller
creases proceed from it at right angles. This appearance owes
its name to the erroneous impression that it is due to a folding
of the vitelline membrane, but in reality it merely depends on
the amoeboid movement of the germ. In fact, it is possible,
by close observation, to convince one's self that the furrows
of the plaited band are subject to active changes, for succes-
sive groups of them disappear, again crop up, become more
extensive and deeper, and then again retire. After a longer
or shorter time — commonly one hour from the appearance of
the first dimple — one of the folds of the plaited circle becomes
deeper, and spreads itself more and more towards the periphery
of the hemisphere, whilst the others gradually disappear.
Eventually a deep cruciform furrow is apparent in the hemi-
sphere we have hitherto had under observation, and which, as
previously stated, is on the opposite side to the white pole.
We will call this the upper hemisphere. At this time, only
a single shallow furrow is seen in the lower hemisphere.
Subsequently the furrowing proceeds somewhat more rapidly ;
for the third, or equatorial furrow, occurs half an hour after;
other furrows then appear at right angles to the three first
formed, generally in the same succession in which the principal
furrows have originated; from these secondaiy furrows of the
first order proceed others of the second, and from these, others
of the third, and so on. The upper hemisphere divides much
more quickly than the lower.

The ova of the trout are prepared as follows : The egg is
placed upon an object-glass between the points of a broad pair
of forceps, so that the blastoderm is uppermost ; the forceps
are held with their blades at a fixed distance from each other,
while the egg is pierced near its equator with a lance-shaped
knife. On rapidly withdrawing the knife it generally happens
that the blastoderm in loto, with a large part of the tenacious
semi-fluid yolk, spirts out. The object must now be surrounded
with a ring of putty and covered. The attention of the ob-
server should be directed to the appearance of the elements,
their amoeboid movement, and to the various forms of cleavage.
The preparation of the ova of Batrachia is far simpler. The
egg is placed upon an object-glass, and as much as possible of
the gelatinous investment is removed with the aid of forceps

BY DR. KLEIN. 161

and scissors. The vitelline membrane is ruptured by means of
needles, and a small portion of the escaping contents is spread
out in a very thin layer. If the egg is not more than three
days old, it can be investigated under low powers (Hartnack's
5 or 7) without a cover-glass. The yolk disks should be espe-
cially observed, and the active movements of the pigment
granules with which the embryo cells are filled. Attention
should be further directed to the hyaline prominences which
the latter send out and retract, particularly after the addition
of a very small drop of distilled water.

The Cleavage Cavity. — The second important point, to
which the embryologist should direct his attention, is the
cleavage cavity. In the trout, this comes into existence towards
the end of the cleavage pi*ocess. The blastoderm appears to
be separated from the yolk of the saucer-shaped depression by
a cavity which gradually increases in width and depth. The
blastoderm is not, however, entirely detached from the yolk,
but remains connected with it here and there by chains of cells.
These chains of cells — " sub-germinal processes" — may be com-
pared to columns by means of which the blastoderm rests
upon the yolk (see fig. 167). The cells of the sub-germinal
processes, like those of the deeper layer of the blastoderm, are
larger and more coarsely granular than those of the more
superficial layers. By degrees the cells of the sub-germinal
processes become separated from the blastoderm, and lie upon
the floor of the cleavage cavity. The elements which are found
in this position are characterized by their greater size, and by
their distinctly granular appearance ; they are products of the
blastoderm, which are either left lying on the floor of the cavity
when it is formed by the raising of the blastoderm from the
yolk, or fall to the bottom of the cavity as it increases in size.

For the study of the formation of the cavity, that is, of the
elements which are to be found on its floor (the destination'of
which we shall again have occasion to mention) and of the
simultaneous expansion of the blastoderm over the cavity,
sections are alone available. Eggs of the requisite stage (10-
14 days) are placed in a very dilute (one-tenth per cent.) solu-
tion of chromic acid, the liquid being frequently changed.
After a few days the eggs will have become almost black and
quite friable. An egg is now pierced with a lance-shaped needle,
and the vitelline membrane carefully torn open at one place
by means of sharp forceps, the rent being extended in a hori-
zontal direction until it describes a complete circle ; the mem-
brane is then removed from the upper hemisphere, which con-
tains the blastoderm. Thereupon the blastoderm, together
with the whole of the yolk of the saucer-shaped depression, is
separated by a sharp scalpel and placed in dilute alcohol, where
it may remain for any length of time. It is, however, ready
11

162 EMBRYOLOGY.

for further treatment in one or two hours. It may he stained
by steeping it for twenty-four hours in very dilute carmine
(see Chapter VII.), anil it is then washed in weakly acidulated
water. The object is now placed in absolute alcohol for from
half an hour to an hour. After this, it is embedded in the
following manner: A layer of the mass used for embedding
(wax and oil) is poured upon aflat piece of glass, wood, or cork,
or into a little box, and is allowed to harden ; the object, after
its surface has been earefull}' dried, is placed in the desired
position upon this mass, and a further layer is poured around
and OArer it, which must be warm, but not too hot. When the
mass is thoroughl}- solidified, sections are made as follows:
The razor is moistened, by means of a small brush, with oil of
cloves or with turpentine, and a section made, which is floated
off from the razor to an object-glass with oil of cloves. When
the section is thoroughly transparent, a process which occupies
a few seconds, or at most minutes, if the object has been long
enough in absolute alcohol before embedding, the excess of oil
of cloves is to be carefully soaked up with strips of filter-paper.
A window is cut out of fine tissue paper, and applied to the
preparation in such a way as to afford protection from the
pressure of the cover-glass. A drop of Dammar varnish is
allowed to fall upon the preparation thus inclosed b}r the paper,
and the whole is covered. The eggs having been placed in
one-tenth per cent, solution of chromic acid until the gelatinous
investment is entirely dissolved, they are transferred to common
alcohol for two or three days and then preserved in glycerin.
They may be used even after an interval of months.

For the study of the cleavage-cavity of Batrachia, sections
should be made of the eggs of Bufo, beginning with the stage
at which the first furrows are already formed. The egg is
taken, by means of a spoon, out of the glycerin, dried with
filter-paper, and embedded according to the method above
described. The razor in this case is to be moistened with
absolute alcohol, and the sections floated on to the object-
glass, with the same liquid. The alcohol is removed by filter-
paper, and the section moistened with a drop of oil of cloves,
after which the process is the same as above. Batrachian
eggs require great care and attention, both in making and
handling the sections; first, because the ovum is less easily
fixed than is the case with the disk-like germ of the trout or
chick, and, further, because it is extremel}r friable, so that
sometimes, out often sections, only one will be brought entire
under the cover-glass. The first indication of a cavity may
be traced shortly after the appearance of the first two furrows.
In sections made at this stage, it is seen that the upper two
quarters of the germ, that is to say, those furthest removed
from the white pole, and which are always smaller than the

BY DR. KLEIN. 163

two lower, are rounded off at their inner angles, i.e., those
turned towards the centre of the germ, as if they had retracted
from it ; the lower two, also, are somewhat rounded at their
inner angles, but not so markedly as those above : by this
means a small cavity is formed, which lies just in the place
where the four segments meet. In sections of progressively
later stages, it will be observed, in the first place, that the
upper segments have undergone cleavage much more rapidly
— in other words, that their elements are considerably smaller ;
and, secondly, that the cavity becomes enlarged at the expense
of the upper half of the germ. In a still later stage of cleavage,
forms will be met with in which the cavity takes up the greater
part of the space occupied by the upper segments. The cavity
is spanned by a thin dome, consisting of only two or three
layers of small elements; whilst its floor is flat and lined by
larger elements belonging to the lower segments. Under-
neath these elements, which still contain pigment, elements
occur which become larger as the white pole is approached.
At this time it may be observed, that these large elements —
which may be termed ''formative elements" — spread upwards
from the floor of the cavity over the under surface of the dome,
until at last a stage is reached at which the whole of that sur-
face is covered with them. In the middle part of the dome
these formative elements are disposed in a single layer ; on
the parts which are in closer proximity to the floor of the
cavity, the number of layers is greater. The dome consists,
therefore, at this stage, in the first place, of two or, at most,
three layers of small elements which originally belonged to it
(and which are also continuous with the cortex of the rest of
the germ) ; and secondly, below these, in its central part, of a
layer of larger elements, which before formed part of the floor
of the cavity.

Simultaneously with the changes just mentioned, another
important change occurs at the white pole, as may be ascer-
tained by the stud}' of sections at different stages. This pole
has been getting gradually smaller, and now presents the
appearance of a sharply bounded white patch of the size of a
pin's head — the so-called yolk-plug (Dotterpfropf ). A fissure
occurs, which constantly extends further and further upwards,
increasing at the same time in width, until it gradually ex-
pands to a cavit}', which is eventually only separated from the
cleavage-cavity by a single layer of the larger elements. As
this cavity (called the visceral cavity, Rusconi's cavity,
Leibeshohle) increases, the cleavage-cavity diminishes. In
consequence of these changes, the position of the egg is
altered ; that which before was the upper half now becoming
the lower. (As regards the formation of the cleavage and
visceral-cavities, compare figs. 169-173.)

1G4 EMBRYOLOGY.

Formation of the Lamellae of the Blastoderm. —
From a comparative study of sections of the egg of the trout
at successive stages, from that at which the blastoderm begins
to form a cover over the saucer-shaped depression, consisting
of a middle thinner, and a peripheral thicker part (marginal
swelling — Randwulst), to that at which it lias already grown
round a quarter of the yolk and exhibits the first trace of the
formation of an embyro, the following facts ma}- be made out:
The large elements found on the floor of the cavity gradually
tend towards the periphery of the blastoderm, where they form
the peripheral thickening, or marginal swelling already men-
tioned (see fig. 168). As this occurs the central part of the
blastoderm by degrees becomes so thin, that it consists at
length of only two layers of cells, an upper lamella of flattened
elements, and a lower containing loosely arranged spherical
elements (in single or, here and there, in double series).
These two layers are continuous with the marginal swelling,
the upper layer of which also consists of flattened elements,
the lower of one or two strata of more or less cylindrical cells.
In the marginal swelling two other strata exist underneath
these layers, each of which consists of large spherical elements,
and is at least two cells deep. We have therefore in the mar-
ginal swelling, by the thickening of which the rudiment of the
embyro is formed, four layers, the upper or corneal layer
(Hornblatt) ; a second, or, as it may be termed, nervous
stratum, because out of it is formed the central nervous sys-
tem ; a third or motor-germinative ; and a fourth, or epithelial
glandular layer (Darmdr'ilsenblatt). Of these four layers the
two lower must be attributed to the formative elements which
come from the floor of the cavity.

To the conditions just described those found in the batra-
chian egg are analogous. The mode in which, during the
formation of the cleavage-cavity, formative elements spread
from its floor over the under surface of the dome, adding a
third stratum to the two of which it alread}' consists, has been
already described. This third layer then splits into two,
whilst the visceral cavity is growing upwards into the dome.
At a point which corresponds to the central part of the cavity
the cortex becomes thicker: this thickening, which is formed
at the cost of the second layer, is the rudiment of the central
nervous system of the embyro. We find the same four layers
in the egg of Batrachia — the corneal, the nervous, the motor-
germinative, and the epithelial glandular (Darmdrusenblatt) :
the last two of which, as in the ovum of the trout, are derived
from the formative elements of the floor of the cleavage-cavity
(see fig. 1 73).

Cleavage Cavity of the Chick. — For the study of the
cleavage process and formation of the cleavage-cavity, in the

BY DR. KLEIN. 165

blastoderm of the chick, it is necessary to intercept the eggs
in their passage through the Fallopian tube ; for in eggs which
are already laid, these processes have been gone through.
The investigation of these phenomena is expensive, and de-
pends somewhat on chance. Hens known to be in the habit
of laying eggs in spring and summer must be sacrificed.
Eggs may be examined in which the shell is either absent or
consists of a very thin parchment-like structure, or is in pro-
cess of calcification. They are placed for a few days in a deep
capsule containing a one per cent, solution of bichromate of
potash, and are hence removed to a one-sixth per cent, chro-
mic acid solution for one or two days. After this time the
part of the yolk which has the blastoderm resting on it, is cut
off with a razor and laid in common alcohol, in which with due
precaution the vitelline membrane can be readily stripped off
from the blastoderm. The subsequent processes are the same
as with the blastoderm of the trout.

If eggs in the different stages of their passage through the
Fallopian tube have been obtained, it is eas}^ to make out in
prepared sections, that, during the formation of the cleavage-
cavit}-, the large coarse^ granular elements (filled with the
coarse granules of the yolk) which compose the deeper la}'ers
of the blastoderm, remain lying in large numbers upon the
floor of the cleavage-cavity; that these are most numerous
towards the area opaca, that is, where the peripheral part of
the blastoderm lies upon the white yolk (yolk-rim, Keimwall)
and that they here become continuous with the large coarsely
granular elements of the deeper laj'ers of the blastoderm.
These elements lying on the floor of the cavity and derived
from the blastoderm during the formation of the cavity, corre-
spond to the formative elements on the floor of the cleavage-
cavity of the trout's egg, and those elements which, in the
batrachian egg, stretch up from the floor of the cavity to the
under surface of the dome (see fig. 175).

Lamellae of the Blastoderm of the Chick. — The study
of the layers of the embryo of the chick must be commenced
with fresh laid eggs. The egg is held with its long axis hori-
zontal ; the shell is cracked at its upper pole ; the bits of shell
in this place are removed with a forceps, and the outer mem-
brane torn off the exposed part ; the shell is then broken in
two, and the contents are let out into a flat capsule. With
the aid of scissors and forceps, the egg (using the word in its
more restricted sense) is freed from the investing albumen,
which is carefully poured off. After having, by means of a
lens, acquired a general notion of the grosser anatomical re-
lations as they present themselves on a surface view (such as
the Area pellucida, A. opaca, Pander's " nucleus of the white
yolk," etc.), we pour into the capsule in which the egg lies a

1GG EMBRYOLOGY.

small quantity of one per cent, solution of bichromate of pot-
ash, which, after one or two days, is replaced by from one-sixth
to one-tenth per cent, chromic acid solution. In two or three
days more, the segment of yolk which hears the blastoderm is
cut off and transferred to spirit ; the vitelline membrane is
then carefully removed. Afterwards the object, which may or
may not be stained, is treated with absolute alcohol, embedded,
and employed for sections in the manner above described.
This method may be employed during the first twenty-four
hours of incubation. At a later period, or at all events after
thirty-six hours, the egg must be treated in the following
manner : —

After the yolk is freed from albumen, the vitelline mem-
brane is snipped with scissors at a point in its periphery as
far removed from the blastoderm as possible; part of the yolk
flows out through the opening, while the blastoderm adhering
to the vitelline membrane remains in position. The vitelline
membrane is then cut around the blastoderm, the circular
piece not only including the blastoderm, but the vitelline mem-
brane over it, together with a portion of yolk under it. This
is placed in a small flat watch-glass, which is held by forceps,
and is brought into a glass capsule containing a very weak
solution of bichromate of potash. After from ten to fifteen
minutes, the edge of the vitelline membrane is seized by for-
ceps, and gently swayed to and fro in the liquid till that mem-
brane is loosened and removed. The blastoderm, with the
yolk adhering to its area pellucida, is thus completely iso-
lated.

In the superficial portion of the germ disks thus isolated,
especially those of the early part of the second day of incuba-
tion (provided that they are normally developed as is usually
the case in spring and summer), the primitive streak, the rudi-
ments of the central nervous sj'stem, of the chorda dorsalis, of
the proto vertebrae, of the heart and great vessels, of the eyes,
of the auditory vesicles, and of the olfactory pits, may be ob-
served. For this purpose, the blastoderm is floated from the
watch-glass on to an object-glass, and examined with a low
power. For studying the first vessels it is necessaiy to use
higher powers. The object, in solution of bichromate of potash,
or in a mixture of this and glycerin, should be surrounded by
a ring of zinc foil, wax mass, putty, or sealing wax, and
covered. The whole germ disk of the second day of incuba-
tion, which is very suitable for the demonstration superficially
of the rudiments of the organs just named, may be preserved
for a considerable time, if the wall of sealing-wax surrounding
the blastoderm is high enough. The mixture consists of one
part of one-sixth per cent, chromic acid, two parts of one-half

BY DR. KLEIN. 167

per cent, bichromate of potash, and one part glycerin. The
cover-glass is fixed by means of sealing-wax.

Sections through the nnincubated germ-disk show that it
consists of two layers, besides the formative elements which
are to be found on the floor of the cleavage-cavity, and at the
yolk-rim. (See fig. 176.) Sections made during the first half
of the first day teach that these formative elements find their
way from the yolk-rim in between the two la3?ers of the germ,
so as to form, first (seventeenth hour), the central part of the
middle layer of the area pellucida, and afterwards (at the
twenty-third or twenty-fourth hour), the remaining portion of
that layer. Thus, at the end of the first day, the germ-disk,
which before consisted of two layers, consists in the area jjellu-
cida of three — upper, lower, and middle — the last originating
from the formative elements which had previously rested on
the floor of the cleavage-cavity.1

As the central nervous system is developed from the central
portion of the upper layer, the remainder of this layer giving
rise to the epithelium of the skin and of the cutaneous glands,
it follows that the upper layer in the chick represents the upper
and nervous layers in fish and Batrachia ; it is therefore simply
called corneal la3'er: the middle layer in the chick corresponds
to the third in the trout and in Batrachia, and is therefore
termed motor-germinative ; the lowest la}rer in the chick cor-
responds to the fourth in the germ of trout and Batrachia, and
is termed the epithelial glandular layer.

AVhen the central part of the middle germinal layer is formed
(seventeenth hour), the upper one is seen to be thickened at its
middle portion ; it consists of cylindrical cells. At the same
time, this middle portion of the upper layer is more or less
fused with the just deposited central part of the middle layer.
This condition shows on a surface view the primitive streak
(Axenstrang). Along with the formation of the primitive
streak, the dorsal groove is also developed, a differentiation of
the middle layer of the germ takes place into the notochord
and protovertebroe, and the dorsal laminae begin to project.
In the first hours of the second day of incubation, the dorsal
lamina; are seen to be already approaching one another, so that
in the region of the neck they almost touch ; at the tail end
they are still a considerable distance apart, so that the dorsal
furrow is very shallow. A short time afterwards, the dorsal
lamina? in the cervical region are observed to be completely
closed, and the dorsal furrow is changed into a canal — the cen-
tral canal of the central nervous system. (Figs. 117, 178.)

In sections made later in the second day of incubation, the

1 The corneal, motor-germinative, and epithelial glandular layers cor-
respond to the epiblast, mesoblast, and hypoblast of Huxley. — En.

168 EMBRYOLOGY.

rudiments of the notochord and of the protovertebrrc appear in
the central part of the middle layer of the germ ; the two
outer portions of this same layer — the ventral laminae (Seiten-
platten) — split into an upper parietal (Hautmuskelplatte) and
a lower visceral lamella (Darmfaserplallc) ; between the cleft
or split thus formed is the rudiment of the pleuro-peritoneal
cavity. (Figs. 180-182.)

At the same time, the rudiment of the Wollfian duct ap-
pears on the upper surface of the middle laj-er of the germ,
where the rudiments of the protovertebrae abut on the ventral
laminae. In sections through the blastoderm made during the
second day (3G-48 hours), the protrusion of the primary optic
vesicles out of the anterior cerebral vesicles may be studied as
well as the intrusion of the secondary eye vesicle into the
primary (see fig. 185 b), which proceeds simultaneously with
the formation of the rudiment of the lens by the thickening
and subsequent separation by constriction of the intruded
part of the corneal laj'er. Similarly the auditory vesicle pre-
sents itself as a pit-like depression of the same layer ; this pit
gradually deepens whilst the margins rise up and grow until
they fuse into one another, so as to form the auditory vesicles.
We may further notice the extrusion of the visceral lamella in
the region of the neck, which forms the wall of the heart vesi-
cle. Sections made on the second and the commencement of
the third day serve for the study of the development of the
amnion, as a fold-like elevation of the corneal and parietal
Layers, as well as that of the intestinal groove, and of the
fovea cardiaca ( Vorderdarm) by the closing in of the epithelial
glandular la}Ter (.see fig. 181). The extrusion of the two pri-
mary hepatic ducts out of the tube so formed, its partition
into a posterior oesophageal and an anterior tracheal-tube, and
the extrusion of the lungs from the latter must be followed at
later stages of incubation.

BY DR. KLEIN. 169

CHAPTER XIV.

(appendix.)
STUDY OF INFLAMED TISSUES.

Inflammation of Epithelium.— The inflammatory
changes of the epithelial elements of the cornea may be
studied 03- abrading the epithelium over a limited surface in
several frogs, and examining the organ at various periods after
the injury. The cornea must be studied in the fresh state
(with and without irrigation with serum), as well as after pre-
paration with gold and hardening in alcohol. Sections in both
directions must be made of the preparations so obtained.
Evidence is thus obtained (1) of the division of the nuclei of
the epithelial cells, (2) of the overgrowth of the bodies of the
cells, and (3) of their subsequent division.

The examination of the catarrhal secretions of any inflamed
mucous membrane which is covered with pavement epithelium,
is very instructive. If a small drop taken from the surface of
such a membrane is examined, either without any addition, or
diluted with a drop of serum, it is seen that among a great
number of amoeboid young cells (pus cells) a few larger struc-
tures are to be found, consisting of granular protoplasm,
which, as regards their form and size, and the characters of
their nuclei, resemble epithelial cells. Some of them contain
vacuoles of very various size, each exhibiting in its wall a well-
defined nucleus, which either shows constrictions or is already
divided. In those vacuoles which are largest there are pus-
corpuscles. Besides these, thin-walled vesicular bodies are
seen, of great size, filled with pus-corpuscles ; and between
them and the cells containing vacuoles there are all transitions.
If vertical sections are made of a bit of the inflamed mucous
membrane after treatment with gold, it is learnt that these
structures correspond to the cells of the superficial layers. In
fresh preparations taken in such a wa}r as to include the ele-
ments of deeper layers, large epithelial cells are seen which
exhibit very distinct indications of division both in their
bodies and nuclei. On the warm stage these cells may be
seen actually dividing. To obtain permanent preparations,
the fresh inflamed mucous membrane must be placed in two
per cent, solution of bichromate of potash. After two or
three days, sections may be made by shaving off a portion of

170 STUDY OF INFLAMED TISSUES.

the mucous membrane, and comminuting it in a drop of
glycerin with a blunt instrument. It need scarcely be added,
that both those cells of the deeper layers which are in the
natural state, and those which exhibit appearances of division,
have the ridged character. Similar changes can be studied in
certain chronic diseases of the skin, as in acuminated condy-
lomata. (See Chap. II.)

Inflammation of Endothelium. — As regards the endo-
thelium of the serous membrane, the changes consequent on
inflammation have been already referred to. In the blood-
vessels, the inflammatory changes may he studied by cauter-
izing the external surface of any superficial vein (e.g., the ex-
ternal jugular or femoral), or even by simply ligaturing the
vessel. Three or four days after the injury, the vessel is ex-
cised and hardened in chromic acid, or treated with gold and
hardened in alcohol, for the preparation of sections. When
the vessel is very thin-walled, it can be studied at once, with-
out preparation, after straining with gold or silver. The
appearances correspond to those observed in the serous mem-
branes.

Inflammation of Cartilage. — Germination of the cells
of hyaline cartilage can be studied after mechanical injury of
articular cartilages. The best method is to pass a needle into
the knee-joint of a rabbit, in such a way that it penetrates into
the tibia. A few days after, sections are made of the fresh
cartilage, and stained in gold. It is more difficult to observe
inflammatory changes of the cartilage cells in the frog. Much
can be learnt from cartilages of human joints in a state of
chronic inflammation.

Inflammation of Bone. — Germination of the cells of bone
may be induced in the long bones of mammalia by passing a
red-hot needle as deeply as possible into a bone, previously
freed of the soft parts covering it, and then cauterizing the
hole with a pointed stick of nitrate of silver, or by violent
fracture. After a week or more the bone is excised. Scale-
like bits are then split off from the immediate neighborhood of
the injury, and steeped in chloride of gold, and then placed in
water acidulated with acetic acid till the}' are soft enough to
render it possible to make sections, which must be prepared
in glycerin. Another plan is to place the part in solution of
chromic acid (§- to £ per cent.), to which hydrochloric acid has
been added, as described fully in Chap. II. The sections
should be so made as to comprise the transition between in-
flamed and normal conditions. Human inflamed bones can
often be studied in amputated limbs. In all of these cases the
lacunne are seen to contain groups of young cells, instead of
the ordinary branched cells.

BY DR. KLEIN. 171

Inflammatory Changes in the Liver Cells. — Inflam-
mation of the tissues of the liver may be induced by passing
a needle into the organ. Twenty-four to forty-eight hours
after the injury, the animal must be killed. The liver cells
exhibit distinct appearances of division and germination.
Similar appearances are seen in the neighborhood of the so-
called psorosperm nodules in the liver of the rabbit.

Inflammation of the Cornea. — Inflammation of the
cornea may be studied in the frog in two ways : The cornea
may be cauterized at the centre, to such a depth as almost to
perforate it, or a thread may be drawn through it entering at
the centre and passing out through the sclerotic, be3Tond the
margin, the ends of which are then tied. After cauterization
it is necessary to wash the part with a few drops of solution
of common salt. In either case the animal is placed in a
beaker glass, with some moist blotting-paper at the bottom of
it. To study the successive stages of the process, half a dozen
corneas should be prepared in this way at a time, which can
then be excised after 8, 12, 18, 24, 36, and 48 hours. The best
preparations are obtained from rana esculenta, during the
summer months, from 8 to 24 hours after the introduction of
a silk thread, as above described. The cornea should be
studied first in the fresh state, and then stained with gold.
It is excised in the manner directed in Chapter II. and pre-
pared in humor aqueus, care being taken to protect it from
pressure by inserting slips of fine paper under the edges of the
cover-glass. The contrast between a cornea twelve hours after
injury and a normal one lies, first, in the immense number of
migrating cells it contains, and, secondly, in the marked dis-
tinctness of the branched corpuscles. The migrating cells are
most numerous towards the periphery, occurring more and
more scantihr towards the centre. They are masses of proto-
plasm of irregular form, beset with knob-like prominences,
and exhibit very active amoeboid movement. To study their
changes, the preparation must be irrigated with serum. For
this purpose, a frog is decapitated and the blood received in
a porcelain capsule and allowed to coagulate. The serum is
collected in capillary glass tubes. The irrigation is performed
as before directed (Chapter I.), a very small strip of blotting-
paper being used. Under the immersion objective, the most
active motions can then be observed; and if a single corpuscle
is kept under observation for a length of time, it is sometimes
possible to make out an appearance as if it were about to di-
vide. A line presents itself on the surface, which after a time
assumes the character of a furrow. Occasionally the furrow
is seen to deepen till the two parts are severed. In other
cases, one of the knob-like prominences enlarges and separates
itself. As regards the branched cells, some of them appear

172 STUDY OF INFLAMED TISSUES.

to be larger than natural, while their processes become thicker
and less branched. Immediately under the epithelium, as well
as under the endothelium of the posterior surface, the pro-
cesses often exhibit node-like enlargements. Occasionally
corpuscles occur which possess processes only on one side,
while on the other they merely exhibit slight prominences. If
a cornea of this kind is immersed in solution of chloride of
gold for twenty minutes and treated as usual, the corpuscles
are seen to be much more stained in certain parts than in
normal corneas, although the latter may have been immersed
twice as long. If a comparison is made between different
parts, it is easy to satisfy one's self, that the strongly colored
corpuscles are larger and look as if they were swollen, and
that their processes are fewer in number and thicker. The
nuclei of these corpuscles exhibit the most various phases;
constrictions and bulgings are seen in some, complete division
in others.

This is by no means the final stage of the alteration of the
corpuscles. It may be demonstrated at a later period that in
some parts no branched corpuscles can be distinguished, their
place being taken by a trellis-work of spindle-shaped cells,
presenting the aspect of parallel streaks of granular protoplasm,
running in two directions at right angles to each other. In
each streak there are thickenings at intervals. Each thicken-
ing ma}' contain either a few deeply stained small nuclei, re-
sembling those of the neighboring migratory cells, or nuclei
with constrictions which resemble those which are character-
istic of the cornea corpuscles. Between these larger swellings
containing nuclei, the streaks are beset with small nodosities
of various sizes. If these streaky parts are compared with
others, it is seen that there are all transitions between the
streaks and regularly branched oblong cornea corpuscles, while
in other directions their relation can be traced with chains of
young cells, which run in the same direction as the streaks.

The entrance of migratory cells, and even a beginning of
the changes above described in the cornea corpuscles, may be
imitated in an excised healthy cornea, as follows : Inflammation
is produced in one eye by cauterization, and then, twenty-four
hours after, a portion of the cornea of the other eye is excised,
spread out carefull}', and lodged between the membrana nic-
titans and the cornea of the injured eye. The membrana nic-
titans is then drawn up and secured by two or three ligatures
to the skin. After twentj'-four hours more, the sac is opened
and the cornea taken out. It may be examined in the fresh
state, and after preparation with gold.

Corneas prepared in other ways (e. </., by gentle friction with
solid caustic, as directed in Chapter II., or by holding the
head over hot water, and brushing the surface with a camel-

BY DR. KLEIN. 173

hair pencil) and then excised and stained in silver solution,
may be placed, in the manner above described, in an inflamed
conjunctiva. If the preparation is taken out after twenty-four
hours, and studied immediately on the warm stage, we are able
to satisfy ourselves that, in those parts which exhibit the char-
acteristic silver staining, 3'oung cells are actually found in the
canaliculi, and pass along them.

Of mammalia, young rabbits answer best for studies of the
cornea. Inflammation is excited by the same methods. The
results are also similar. In a cornea excised twenty-four hours
after thorough cauterization,. and stained with gold, parts are
found in the strips which are obtained by the method previously
described, in which the canaliculi assume the character of
channels of even width, which, as well as the cell cavities, are
lined with chains of small cells, arranged in linear series, so
as to resemble endothelial elements. From these appearances,
we are justified in concluding that both the bodies and the pro-
cesses of the cornea corpuscles have split into young elements,
changing, at the same time, their form.

Inflammation of the Tongue of the Frog. — In the
tongue, cell division can be studied both in the corpuscles
peculiar to the organ and in migratory cells. For this purpose,
the tongue is prepared as for the study of the circulation. The
mucous membrane covering the large lymphatic sac of the under
surface is snipped off with curved scissors. The observation
is necessarily tedious, often lasting for forty-eight hours. It
is therefore desirable to replace the tongue in the mouth for a
time after each examination.

Inflammatory Changes in the Tadpole's Tail. — The
inflammatory changes which take place in branched cells may
be studied in those of the tadpole's tail. In a curarized tad-
pole, the required degree of irritation can be produced either
by simply pencilling the surface, or by allowing a drop of am-
monia to fall on it from a capillary pipette, or, finally, by piercing
it witli a needle. The research must be continued often for
many hours. The results are similar to those observed in the
cornea, and may be studied either in the fresh state or in gold
preparations.

PHYSIOLOGY.

PART I.-BLOOD, CIRCULATION, RESPIRATION, AND
ANIMAL HEAT.

By Dr. BURDON-S ANDERSON.

CHAPTER XV.

THE BLOOD.

Section I.— The Liquor Sanguinis, or Plasma.

The blood is not a liquid, in the strict sense, but consists
of colored and colorless corpuscles suspended in liquor san-
guinis. It is necessary, in order to examine the liquor san-
guinis, to separate the corpuscles from it by mechanical meth-
ods— i. e., by subsidence and decantation, or filtration. As,
however, it is not possible, under ordinary circumstances, to
remove blood from the body without its undergoing that re-
markable change which we call coagulation, neither of these
methods can be applied to the blood unless by some means or
other it can be kept in a fluid state during the process of fil-
tration. The earliest successful attempt to accomplish this
was made by Johannes Muller. His experiment consists in
allowing a frog to bleed into a solution of sugar (half per
cent.), and then rapidly filtering the mixture. The large cor-
puscles of the frog's blood are retained, and the liquid passes
transparent, and free from corpuscles. After a time it solidi-
fies to a trembling jell}-, which eventually contracts into a clot
surrounded by serum. This experiment was, for a long period,
the only proof of the existence in the blood of a liquid possess-
ing the properties of plasma — that is, of the fact that the liq-
uor sanguinis solidifies when left to itself, quite independently
of the corpuscles. It does not, however, enable us to study
the properties of this liquid completely, because in Midler's
filtrate it is diluted with saccharine solution.

176 THE BLOOD.

1. Filtration of the Blood of the Frog.— Of three test
tubes (Fig. 190), each capable of holding about two drachma
of liquid, No. 1 is filled to about one-fifth of its depth with a
solution of sulphate of soda obtained by mixing one volume
of saturated solution with one of distilled water ; No. 2 con-
tains about half a drachm of half per cent, solution of sugar;
No. 3, half per cent, solution of chloride of sodium. Several
frogs are then selected, in each of which the pericardium is
exposed and divided as directed in § 40, and a snip made in
the ventricle with fine scissors, the integument having been
dried with filtering paper before making the first incision.
The blood is allowed to flow into No. 1 until four times as
much blood has been added to the quantity of solution as the
tube previously contained. To each of the liquids in No. 2
and in No. 3 an equal volume of blood is added. Each of the
liquids is gently agitated and then thrown on a filter made of
strong close-fibred paper prepared for its reception, and corre-
spondingly numbered. In each instance we obtain a clear and
colorless filtrate, the whole of the colored part of the blood,
i. e., the corpuscles, being collected on the filter. The three
filtrates have, however, different characters. From filter No.
1 is obtained a liquid which remains fluid at ordinary temper-
atures, i. e., provided that the room is moderately cool. From
filter No. 2 we have a liquid which coagulates immediately.
From No. 3 a liquid which coagulates after a time : its coagu-
lation will be much accelerated if it is placed in a bath, at a
temperature approaching that of the body.

In the sulphate of soda filtrate the appearance of a clot is
postponed indefiniteby. It is, how-ever, not the less certain
that it really contains the immediate principles of which fibrin,
the material of the gelatinous mass seen in the other tubes, is
formed. This may be demonstrated by diluting the liquid
with distilled water. If the original solution had been satu-
rated, water might have been added gradually for some time
without producing any apparent change. In the present in-
stance, the solution employed contains one part of saturated
solution to one of distilled water. If water is added to the
mixture in the proportion of one-fifth of its volume, it is suffi-
cient to render it coagulable, whereas six or seven volumes
would have been required if the solution had been concen-
trated. As, therefore, saturated solution of sulphate of soda
contains fifty per cent, of the crystalline salt, this last must,
in order to the prevention of coagulation at ordinary tempera-
ture, be present in a proportion of not much less than five per
cent.

In these experiments it has been shown (1) that the colored
blood corpuscles of the frog are so large that they do not pass
through close filtering papers ; (2) that in the filtrate, even

BY DR. BURDOX-SANDERSON. 177

when it is diluted with its volume of solution ot sugar, a
gelatinous clot forms immediately, under ordinary tempera-
tures ; (3) that the process of coagulation is held in check by
certain neutral salts, and in particular by sulphate of soda.
A similar influence is exercised by sulphate of magnesia,
nitrate of soda, borax, and some other neutral salts.

2. Separation of the Corpuscles from the Liquor
Sanguinis or Plasma in the Blood of Mammalia, by-
Subsidence and Decantation. — It is not possible to filter
mammalian blood in the way above described ; for the cor-
puscles are so small that they will run through the finest filter-
ing paper. We must, therefore, have recourse to subsidence.
The difficulties of separating the liquor sanguinis from the
corpuscles by subsidence depends on the length of time which
the corpuscles take to settle, as compared with the rapidity
with which the blood coagulates. In consideration of both
these circumstances we select the blood of the horse as
preferable to any other. In horse-blood the specific gravity
of the globules is 1105, that of the liquor sanguinis 1027-1028
(Hoppe-Seyler) : the difference is considerable, and somewhat
greater than in other animals. But it is of more importance
still that horse-blood coagulates more slowly than that of
other animals.

If blood is received into one of two similar jars from a
bullock, into the other from a horse, it is seen that after an
hour or two both have coagulated firmly. In the former, the
clot is all of one color ; in the latter, it is divided by a tolera-
bly defined horizontal line into an upper colorless, and a lower
deeply colored, part, the upper being a little more than half
the depth of the other. In the one case the corpuscles have
had time to descend through the upper stratum of liquid before
it solidified, whereas in the other their descent is anticipated
by the coagulation of the plasma. In the horse this appear-
ance is always observed when the blood taken from a blood-
vessel is allowed to stand. In other animals, and particularly
in man, it occurs onlj' under abnormal conditions (particularly
inflammatory fever). It is spoken of as the "buffy coat."

In the experiment above described, the object we have in
view has not been attained. The corpuscles have subsided
more or less completely, but the plasma no longer exists as
such. It has separated into clot and serum. To succeed,
coagulation must not only be delayed but prevented — for
which purpose there is but one means available, i. e., cold. At
the temperature of freezing, coagulation is indefinitely post-
poned. The blood must, therefore, as it flows from the
animal, be subjected to this temperature, and kept under its
protective influence. For this purpose a cylindrical vessel
made of tinplate, of the form shown in Fig. 191, is used.
12

178 THE BLOOD.

This vessel is not only surrounded with ice externally, hut
contains in its axis a smaller cylinder, closed at its lower end,
which is also filled with ice. Between the external surface of
the smaller cylinder and the internal surface of the larger,
there is an interval which does not exceed half an inch in
width, so that the whole of the liquid which occupies it is kept
at freezing temperature. In the course of two hours or less
the blood has separated into two layers, of which the lower
contains all the corpuscles. The upper stratum consists
entirely of plasma — a liquid which, in its general aspect,
resembles ordinar}' serum, but is not so transparent. The
most obvious as well as the most important property which it
possesses is that of coagulation. So long as it is kept at 0° C.
it remains liquid ; but if the temperature is allowed to rise
even a few degrees above freezing point, the whole mass is
converted into a gelatinous clot.

3. Experiments Illustrative of the Properties of
Plasma and Fibrin. — 1. Transfer some of the plasma, with
the aid of a cooled pipette, to a small narrow test glass,
surrounded with ice and water contained in a small beaker.
As the ice gradualh' wastes, the liquid becomes gelatinous.
The surface by which the mass adheres to the glass is so
extensive as compared with its volume, that the adhesion is
permanent. Consequently, if the tube is examined after
having been left to itself for several hours, it is found that
the plasma has not (as in other cases of coagulation) separated
into clot and serum, but that it appears to be entirely semi-
transparent and gelatinous.

2. Another quantity of plasma is allowed to coagulate in a
wide vessel. At first the process seems to go on in a similar
manner, and for a time the mass adheres to the sides of the
vessel. Afterwards, as it contracts, drops of serum collect,
first on the surface, then between the clot and the sides of the
glass. Soon the clot detaches itself wholly from the vessel, at
the same time diminishing in volume. Eventually we have a
clear liquid (serum) in which an opaque white cast of the
beaker floats. As, in consequence of the adhesion of the
coagulum to the sides, contraction is more resisted in the
horizontal direction than in the vertical ; the upper surface
always becomes more or less concave.

3. Preparation of Fibrin. — a. The clot from 2 is removed
from the liquid, divided into small fragments, and washed with
water until it is absolutely colorless. In this condition it
differs strikingly from the semi-transparent gelatinous mass
which is obtained in 1. It is dense, fibrous, and opaque, and
extreml}- clastic. b. A fresh portion of plasma is briskly
agitated with a rod of whalebone or other suitable implement.
In this case the fibrin is obtained in fine fibres, which may also

BY DR. BURDON-S ANDERSON. 179

be rendered white by washing. In a the fibrin has passed
through a previous condition in which it was gelatinous. In
o it is obtained directly in the fibrillated state.

4. Some plasma is diluted with one hundred times its
volume of ice-cold water, or three-quarter per cent, salt solu-
tion, and allowed to stand. After twenty-four hours, it will
be found that there are long delicate filaments of fibrin, .which
stretch across the mass of liquid in every direction, from one
side to the other of the vessel in which it is contained. These
filaments, the extremities of which adhere to the glass surface,
are in the highest degree elastic. If they are separated from
their points of attachment, they shrivel up into little lumps of
fibrin. If these again be drawn out into lengths, they resume
their original form when let go, as completely as a bit of
India-rubber would do.

5. The fibrin prepared in 3 is placed in water containing one
per thousand of hydrochloric acid. At first it swells out into
a bulk}' hyaline mass. If it is then placed in the air bath,
and kept at a temperature of from 40° to 60° C, it wastes
awa}- at a rate which varies according to the temperature.
In undergoing solution the fibrin has been transformed into
another albuminous compound, sj'ntonin or acid-albumin.1
If the liquid is carefully neutralized, the syntonin is precipi-
tated, but the precipitate is redissolved in a slight excess of
alkali or alkaline carbonate.

6. Another portion of the same fibrin is soaked in solution
of peroxide of hydrogen. It is then placed on a sheet of fil-
tering paper, which has been previously soaked in tincture of
guaiacum. It soon becomes surrounded with a border of blue,
in consequence of the oxidation of the guaiacum. Another
method consists in first steeping a fragment of fibrin in alco-
hol, then in tincture of guaiacum, and finally immersing it in
the solution of the peroxide: the fibrin becomes blue. The
same thing happens if the fibrin is dipped in a mixture of the
tincture and the solution. This reaction signifies simply that
fibrin decomposes peroxide of hydrogen: it affords no proof
of the presence of ozone.

4. Experiments relating to the so-called Fibrin
Factors — Paraglobulin and Fibrinogen. — In every act
of coagulation, fibrin appears to be produced by the combina-
tion of two albuminous substances closely allied as regards
their chemical characters, both of which are to be found in
plasma as obtained by any of the methods above described.
Fifty cubic centimetres or thereabouts of the plasma, which
has been kept at a freezing temperature, are added, in a beaker,

1 The ending in is adopted here and elsewhere to denote that the
word is used in a stcechiological sense. Albumen is white of egg.

180 THE BLOOD.

to five hundred centimetres of distilled water. A current of
carbonic acid gas is allowed to pass through the liquid until
it becomes turbid; much froth collects on the surface. On
discontinuing the current, it is found that a distinctly granular
precipitate has been formed. This is paraglobulin. After
decanting off most of the liquid, the precipitate is collected
on a filter and washed with water saturated with carbonic
acid. It is insoluble in water which has been boiled, but
soluble in water containing air or oxygen ; it decomposes per-
oxide of hydrogen in the same way as fibrin. It is character-
istic of the solution that when mixed with a solution of a sub-
stance to be spoken of immediately under the name of
fibrinogen, fibrin is produced. This property is denoted by
the term Jibrmoplastic, which is applied both to the substance
and to the solution.

2. After the precipitate has had time to subside, the clear
liquid is decanted off, diluted with twice its own bulk of ice-
cold water. A stream of carbonic acid gas is again passed
through it. At first it remains clear, but after a time a some-
what viscid scum begins to collect on the surface of the liquid
and on the sides and bottom of the glass. This precipitate is
fibronogen. This process involves an immense expenditure of
ice. and occupies a great deal of time.

3. Fifty cubic centimetres of serum of ox-blood are mixed
with half a litre of distilled water. A stream of carbonic acid
gas is passed through it as before. A granular precipitate is
formed, which, like that obtained from plasma, is fibrino-
plastic.

4. Fifty cubic centimetres of hydrocele fluid or pericardial
fluid are diluted with water and treated with carbonic acid
gas as before. A slimy white substance is formed in very
small quantity, which collects on the surface of the liquid and
on that of the glass.

5. The granular precipitates in 1 and 3 may be obtained in
the same form by adding to the same diluted liquids acetic
acid, the quantity of which must be so small that the liquid
still retains a trace of alkalinity. The precipitate has the
characters described in 1.

6. Twenty cubic centimetres of filtered hydrocele or peri-
cardial fluid are placed in a beaker in the air bath at a tem-
perature of 40° C. The liquid does not coagulate, but on
adding serum a firm clot is formed.

7. A second quantity of the same liquid which has been
ascertained by the preceding experiment to be fibrinogenic,
i. e., to have the property of coagulating on the addition of a
fibrinoplastic liquid, is saturated with pure chloride of sodium
by adding the salt gradually in fine powder. As the point of
saturation approaches, the previously clear liquid becomes

BY DR. BURDON-5 ANDERSON. * 181

cloudy, and on standing, a flocculent deposit separates. This
deposit is fibrinogen. It must be collected on a filter and well
washed with saturated solution of common salt. If the sub-
stance so prepared is dissolved in a small quantity of distilled
water, and the liquid filtered, a clear solution of fibrinogen
and chloride of sodium is obtained. It possesses the property
of coagulating on the addition of serum, especially at a tem-
perature approaching that of the body.

8. Filtered serum of blood treated in precisely the same way
yields a similar product containing paraglobulin. The filtrate
obtained determines coagulation in hydrocele liquid when
added to it. Coagulation may be also expected to occur when
the fibrinoplastic filtrate obtained in 8 is added to the fibrino-
genic filtrate obtained in 7. The result of this experiment is,
however, uncertain.

9. If plasma is saturated with chloride of sodium in the
manner above described, a precipitate is obtained which con-
tains both paraglobulin and fibrinogen. If this is washed with
saturated solution of salt as before, dissolved in distilled water,
and rapidly filtered, a clear fluid passes through, which after a
while coagulates, and which has the characters of fibrin.

10. If the transudation liquids above mentioned cannot be
obtained, a liquid may be prepared by adding to plasma a solu-
tion of a neutral salt, such as sulphate of magnesia or sulphate
of soda, so as to prevent coagulation. If the quantity of
neutral salt added is just sufficient for the purpose, the addi-
tion of a little paraglobulin at once determines the formation
of a clot. Blood is received directly from the circulation into
one-third of its volume of ice-cold saturated solution of sulphate
of soda or of sulphate of magnesia. The mixture is allowed to
stand in ice till next day, in order that the corpuscles may com-
pletely or in great measure settle. The clear liquid (plasma
and neutral salt solution) is then removed hy decantation with
a capillary syphon, and used as follows : a A small quantity is
placed in an eprouvette, in the warm chamber, at 40° C. b
Other quantities are diluted with proportions of distilled water,
varying from 4 parts to 10 parts, and kept at the ordinary tem-
perature, a Coagulates at once. Of b the more dilute coagu-
late spontaneously, even at the ordinary temperature. To
those that do not so coagulate, paraglobulin is added, when it
U found that in the more concentrated quantities the addition
determines the formation of a clot. Kuhue recommends for
this experiment a solution of sulphate of magnesia containing
1 part of the salt to 3£ of water. Plasma mixed with this
solution in the proportion of '.> parts to 1, and then diluted with
8 parts of water, coagulates on the addition of paraglobulin.'

1 Lehrbuch der pbysiol. Chemie, p. 172.

182 THE BLOOD.

11. Diluted plasma which has been treated with carbonic
acid gas docs not coagulate, even when Bhaken with air and

subjected to the temperature of the bod}- (40° C).

From the above experiments we learn that plasma contains
two albuminous compounds, precipitable by carbonic aeid gas
and by aeetic aeid; that one of them (paraglobulin) exists
alone in serum in considerable quantity ; that the other (fibrin-
ogen) exists alone in liquids effused into uninflamed serous
cavities in very small quantity; that when paraglobulin is
added to these effusion-liquids they become coagulable, justas
serum may be made coagulable by the addition of fibrinogen.

5. Heynsius's Experiment.1 — From the properties of
blood plasma demonstrated in the above experiments, we are
apt to infer that this liquid is the exclusive source of the fibrin
formed when blood coagulates. There is reason, however, for
believing that a very considerable quantity of fibrin-producing
material is contained while the blood is circulating, in the col-
ored or colorless corpuscles, for it can be shown that if these
elements arc separated as complttelyas possible by subsidence
and decantation from a known quantity of blood, and added
to a similar quantity of serum, this serum acquires the pro-
perty of coagulating ; and the quantity of fibrin produced bears
a very considerable proportion to the whole quantity which the
blood would have yielded. Fifty cubic centimetres of blood
are received directly from the vein of a horse or ass into a
measuring tube surrounded with ice. The blood is immediately
afterwards poured into a tall narrow glass cylinder, which
ahead}7 contains half a litre of a two per cent, solution of com-
mon salt, previously cooled by standing in ice. In this vessel
the mixture is allowed to remain until the corpuscles have sub-
sided, after which the liquid must be drawn off with the aid of
a capillary pipette or syphon. The remainder is then mixed
with a similar quantity of salt solution, again left to itself sur-
rounded by ice, and the process repeated. Fifty centimetres
of serum of ox blood previousl}- prepared, having been then
added to the corpuscles which remain at the bottom of the
vessel, the mixture is placed in water at a temperature of 40°
C. Alter two or three minutes coagulation takes place. The
clot is collected and washed, dried and weighed. In the mean
time the fibrin yielded by an equal quantity of blood is deter-
mined. On comparing the weights, it is found, as before stated,
that the coagulum obtained from the mixture of serum and cor-
puscles alone, is nearly equal to that obtained from the whole
blood (corpuscles and plasma). It has been further shown by
Heynsius, that if blood is received in an ice-cold, half per cent.,
or one per cent., solution of common salt, the quantity of fibrin

1 Pfluger's Archiv. B. III. p. 419.

BY DR. BURDON-SANDERSON. 183

yielded by the plasma is much less (so to speak) than it ought
to be, i. e., much less than that yielded b}r a corresponding
quantity of blood. This fact, taken in connection with the
result of our experiment, leads us to regard it as probable that
in circulating blood, the liquor sanguinis contains less of the
fibrin factors than it does immediately after its removal from
the body. If this inference is correct, there can be little doubt
that it somehow or other, in leaving the living vessel, acquires
fresh properties of coagulation from its formed elements.
Heynsius believes that the colored blood disks are alone con-
cerned in this action, and attributes it to the discharge into
the plasma of certain of their constituents. His results are,
however, quite as consistent with the belief that the colorless
elements are the chief agents, in favor of which several facts
may be demonstrated. Vaccine and blister fluid are both co-
agulable ; they contain no colored blood corpuscles, but always
many colorless corpuscles. If the process of coagulation is
watched in either of these liquids under the microscope, it is
seen, not merely that it begins from these elements, but that
it occurs nowhere in the liquid excepting where they are pre-
sent. Again, if a ligature is drawn through a vein in which
blood is circulating, as e. gr., through the external jugular of
a rabbit or guineapig, and allowed to remain there for a time,
and then removed and examined microscopically, it is found
that the threads of the ligature are crowded, and its surface
encrusted, with colorless corpuscles. These bodies are held
together by fibrin, which appears to grow from their surface
into the blood-stream.

iox II. — Conditions wnicn Affect the Coagulation of the
Blood.

Although the circulating blood contains either in its colored
corpuscles or plasma both the fibrin factors, i. e., the imme-
diate principles necessary for its coagulation, it does not co-
agulate. In other words, the blood, so long as it forms part of
the normal living body, contains no fibrin. This remarkable
fact is dependent on the maintenance in the corpuscles of those
chemical changes which constitute their life. And inasmuch
as these changes cannot continue in the absence of the physical
and chemical conditions to which the blood is subjected, so
long as it is contained in healthy bloodvessels, an}' derange-
ment of those conditions leads to the formation of a clot. It
can Ik: proved experimentally (1) That blood does not coagu-
late in the living heart or in a living bloodvessel, even when
tin; circulation is arrested; (2) That although normal blood
ordinarily coagulates as soon as it is withdrawn from the body,
there are certain circumstances under which the act of coajni-

184 TIIE BLOOD.

lation cither does not take place, or is accomplished in so im-
perfect a manner, that the clot is scarcely recognizable as
such.

6. The following is a modification of an experiment of
Briicke, devised by my friend Dr. Durante. In a rabbit, two
small incisions are made across the course of the external jugu-
lar vein, (see § 48) one near the clavicle, the other near t he
origin of the vessel — great care being taken not to go deeper
than is necessary in order to see the vessel through the fascia.
A small needle is then passed under the vein near the proxi-
mal incision, in a direction at right angles to that of its axis,
and corresponding to that of the incision, but deeper. A
second needle is then laid in the course of the incision, and
drawn tightly towards the first by a ligature at either end, by
which means the blood current is entirely arrested, while the
coats of the vein are absolutely protected from injury. A
second pair of needles is then inserted at the distal incision,
and secured in a similar manner, so as to shut in the blood
with which the vein becomes distended after the tightening of
the first ligature. After the lapse of a couple of days, the
ligatured portion of the vein is exposed at some part of its
course, and punctured with a glass pipette, by means of which
the blood is withdrawn from it by suction in a perfectly liquid
state. On removing the needles the natural circulation is at
once restored. This result, however, is onh/ obtained when t he-
greatest care is used to avoid injury to the coats of the vein.
This may be readily proved by repeating the experiment
(which, in a practical point of view, is of great importance) in
a different wa}r. If, instead of using needles, ordinary liga-
tures are placed on the points indicated, a coagulum is formed,
so that on pinching the vein no blood flows. On opening such
a vessel it is found to be occupied by two clots (thrombi), each
of which is thickest and firmest at the ligature, and becomes
thinner and looser towards the middle of the deligated part.
Dr. Durante has shown that, in this experiment, this absence of
coagulation depends on the integrity of the endothelium.
Wherever the endothelium of a vein is irritated so as to
undergo germination, a clot is formed which is co-extensive
with the alteration of the endothelial elements.

7. The arterial trunks leading from the heart of a frog or
tortoise are first tied, and then (as soon as the heart has be-
come distended) the venous trunks. The heart full of blood
is removed from the bod}- and suspended in a small flask by
one of the ligatures. The flask is allowed to stand so long as
the heart continues to pulsate. If, then, before the pulsations
have entirel}' ceased, the blood is allowed to flow from the
heart by removing the arterial ligatures, it is seen to be fluid.

BY DR. BURDON-SANDERSON. 185

As soon as it escapes it coagulates. This is also an experi-
ment of Briicke.

8. Recklinghausen's Experiment. — A small porcelain
crucible is heated to redness, and allowed to cool without re-
moving the cover. The pericardium of a frog is then exposed
and divided, and a snip made in the ventricle with absolutely
clean scissors, the frog being held in such a position that the
blood discharged from the wound in the heart may be received
in the prepared crucible without coming in contact with the ex-
ternal surface of the body. The quantity of blood used should
not exceed ten drops. The crucible (without its cover) is then
placed on a ground-glass plate, and covered with a wide bell-
glass, the edge of which is also ground, so that it fits the glass
plate perfectly. The blood coagulates immediately, but during
the course of the next twenty-four hours it apjjears to become
liquid again. If the experiment has been carefully performed,
the blood remains unaltered (its colorless corpuscles retaining
their vital activity) for many daj's: it is, however, necessary
to renew the air contained in the bell-glass, by lifting it care-
fully from time to time. This experiment may be also made writh
mammalian blood, provided that a temperature is maintained
equal to that of the body, for which purpose v. Recklinghausen
uses an air bath furnished with a Bunsen's regulator. The
capsule is heated to redness, because, if it were not so, the or-
ganic matter adherent to the surface of the porcelain would
determine changes in the blood, which would be fatal to the
vitality of its elements. With a similar view every possible
precaution is used against other modes of contamination,
whether from the air or from surfaces with which the blood is
brought into contact. The liquefaction of the coagulum in the
preceding experiment is onl}r apparent. To prove this, the
process must be observed microscopically under otherwise
similar conditions. The following method, suggested by cer-
tain experiments of Schlarewski (who, however, does not appear
to have understood their significance), I owe to my assistant,
Mr. Schafer. Several very thin walled capillary tubes, not
more than \ millimeter in diameter, are filled with blood as it
flows from the artery of a frog, and at once placed under the
No. 9 immersion objective of Hartnack. The contents of the
tube can be seen with perfect distinctness. At first the Avhole
of the space inclosed in the tube is occupied by colored blood
disks. After a few minutes it is seen that coagulation has oc-
curred, and that the cylindrical mass in which the corpuscles
arc contained is separated from the glass, by a transparent
border in which there are no corpuscles. Next, the colorless
corpuscles begin to squeeze themselves out of the coagulum
and swim in the serum (see Fig. H)2). From the activity of
the amoeboid movements which these corpuscles exhibit imme-

186 THE BLOOD.

diately after their expulsion, the observer is inclined to attri-
bute their escape from the clot to these movements ; this notion
is, however, proved to be erroneous by what follows. In a
short time (usually about forty-five minutes after the com-
mencement of the observation), the colored corpuscles begin
to participate in the process, and escape from the still sharply-
defined edge of the clot in such numbers that the liquid becomes
so crowded with them, that microscopical examination is no
longer possible. If now the tube is removed from the stage
and placed vertically, it is seen, after a time, that the corpuscles
subside to the bottom of the tube, leaving a clear space con-
taining serum above. Here, then, we have a process which we
might at first sight be disposed to regard as a resolution of the
eoagulum ; the appearance is, however, deceptive, for if the
tube is discharged into a watch-glass and examined under a
low power, the eoagulum is easihT found as a thin cord of fibrin
floating in the liquid. In short, the whole process of emigra-
tion of the corpuscles and liquefaction, of the clot is the conse-
quence of the contraction of a reticulum of fibrin of such extreme
looseness, that it is incapable of retaining the corpuscles in its
meshes.

9. The two experiments last related prove, as regards the
blood of the frog, that, under certain conditions, coagulation
occurs very imperfectly, even though the blood be removed
from the body, and consequently that Briicke's inference, that
the circulating blood is prevented from coagulating by the in-
fluence of the living A'essel, need no longer be maintained. The
following experiment, devised by Mr. Schafer, which has been
repeated a great number of times in the laboratory of Univer-
sity College, proves this much more conclusively and satisfac-
torily. A glass tube, three or four inches long, is drawn out
atone end into an arterial canula of the usual form and of
suitable size. A frog having been secured in the usual way
(see § 46) in the prone position, the heart is exposed and the
right aorta ligatured. A clip is then placed on the left aorta
at its origin from the bulb. The canula (Fig. 103, a) is then
inserted and secured in the left aorta, and the tube supported
vertically by a suitable holder. This done, and the clip having
been removed, the blood is allowed to flow into the tube. It
rises to a height which varies according to the vigor of the
animal and the quantity of blood which its vascular sj'stem
contains, the blood column oscillating with the contractions of
the heart. If now the tube is left to itself, no coagulation takes
place. In a very few minutes the corpuscles begin to subside,
leaving an upper layer of clear liquid, the depth of which gradu-
ally increases. If it is removed with a capillary pipette and
submitted to examination, it is found to possess all the proper-

BY DR. BURDON-SANDERSON. 187

ties which are characteristic of plasma. It contains scarcely
an}' colored but a considerable number of colorless corpuscles.

Section III. — The Coloring Matter.

10. Methods by which the Blood can be rendered
Transparent or Laky. — It has long been known that,
when water is added to blood in quantity, the blood corpuscles
are apparently dissolved in the diluted liquor sanguinis. This
solution is, however, only partial ; for, if the liquid is examined
under the microscope, each corpuscle is seen to be represented
by a colorless spheroidal residue. This residue was formerly,
described as the membrane of the corpuscle, rather in con-
formity to the notion that, being a cell, it must have a mem-
brane, than because the structure in question possessed mem-
branous characters. We now recognize it, not as a membrane,
but as the porous structure fully described in the histological
part as the cecoid.

There are many other methods by which the zooid may be
compelled to relinquish its dwelling without altering the den-
sity of the serum at all. So long ago as 1851, Dr. De Chaumont
discovered that the vapor of chloroform had this effect. That
of ether acts in the same way, but not so rapidly. More re-
cently, it has been shown by Rollett that the same effects are
produced by freezing, as well as by electrical discharges and
induction currents. In all these cases (as has been already
seen as regards some of them) the blood undergoes a remark-
able change of appearance. In the natural state, blood, even
in the thinnest layers, is opaque. One may judge of this by
looking at it either by transparent light (as, e. g., in a very
thin capillary tube) or by reflected light, spread out in a thin
layer over the surface of a porcelain capsule. In the former
case the blood presents the appearance of a solid-looking band
in the axis of a glass rod,- in the latter it appears as a bright
scarlet patch, completely concealing the white surface, and
obscuring the light which would otherwise be reflected by it.
If, however, the blood has been subjected to any of the pro-
cesses above mentioned, the appearance it presents in the two
cases are materially altered. The blood in the tube looks
bright, because it is translucent, whereas that on the porce-
lain looks as dark as if it were venous, because the corpuscles
from which the light shone, reflected by countless convex sur-
faces, arc now scarcely more refractive than the liquid in
which they are immersed. In other words, blood in the natu-
ral state lias the character of an opaque pigment, such as ver-
milion ; whereas in the altered state it resembles a lake — a
fact which Rollett, who, as I have stated, has studied these
changes with great exactitude, expresses by the terms deck-

188 THE BLOOD.

farbig and lackfarbig, as applicable to the former and the
latter respectively. Blood may lie rendered transparent or
laky by exposing it cither to extreme cold or to a temperature
a little above G0° C. ; by subjecting it to the action either of
induced currents or of shocks of frictional electricity. A
similar effect, as already stated, is produced by the addition of
water and of various other liquid reagents, such as ether, chlo-
roform, and solutions of the bile acids in combination with
alkaline bases.

11. Action of Cold. — A platinum capsule containing a
couple of cubic centimetres of defibrinated blood is exposed
to a temperature of — 6° to — 10° C.,1 by placing it in a vessel
previously filled with alternate layers of pounded ice and salt,
and leaving it in contact with the freezing mixture until it is
completely frozen through. The solid mass of blood is then
slowly thawed and poured into a beaker, which should be of
such size that the blood contained in it is not more than half
an inch deep. If readily crystallizable blood has been cm-
ployed, as, for example, that of the guineapig, a sediment of
crystals forms on the bottom. It is seen from the first that
the freezing has completely altered its appearance. It has
become darker in color, and if we place some of it on the sur-
face of a white plate with a pattern on it, the pattern is visible
with more or less distinctness through it, whereas if ordinary
blood were employed it would be completely concealed. It
is scarcely necessary to add that the crystallization is depend-
ent on the discharge of the haemoglobin from the corpuscles
into the liquor sanguinis.

12. Action of Heat.— (Method of Max Schultze.) This
is a method which is only applicable to small quantities of
blood. In experiments with the warm stage (see Chap. I., p.
22). Max Schultze found that when blood is heated from 60°
C. to G4° C, the blood corpuscles dissolve in the plasma.
The same effect is produced if a small quantity of blood is
subjected to similar temperatures in a hot chamber, furnished
writh Bunsen's regulator. Here, as in the former case, if the
blood is derived from an animal in which the haemoglobin
crystallizes readily, crystals are obtained. According to
Preyer, remarkably fine crystals of haemoglobin ma3r be pre-
pared by warming the colored corpuscles separated by subsi-
dence and decantation from the defibrinated blood of the
horse, in the manner above described. To insure success,
care must be taken to maintain the temperature of the quan-

1 The effect of subjecting blood to the temperature of a freezing mix-
ture was first studied by llewsou. His experiment was similar to that
described in the text. His purpose was to show that cold is not the
cause of coagulation. He was not aware that frozen blood loses its
opacity.

BY DR. BURDON-SANDERSON. 189

tity of blood operated on within the limits of temperature
above mentioned.

13. Action of Electricity. — The effects both of shocks of
friction al electricit}r and of induced currents have been de-
scribed in the histological part. To what is there stated, it
may be added, as regards induced currents, that the most
marked effects are produced when the current is most analo-
gous in its characters to a discharge of statical electricity, and,
consequently, that the direct induced current which accompa-
nies the opening of the primary current is more effectual than
in the inverse one. In the results observed, it is important to
distinguish between the direct action of the shock or shocks
on the corpuscles, and the electrolytic action indicated b}' the
liberation of gases at the tinfoil points (see Fig. 194). In so
far as electrolysis occurs, the results may be in part attributed
to the development of acid reaction at the positive pole, con-
sequent on the decomposition of the salts of the blood. A dis-
tinction ought also to be drawn between those effects which
are only produced when the corpuscles are in a living state,
and those which are manifested also in dead blood. The
discharge of the coloring matter from the corpuscles is a phe-
nomenon of the latter class, but there are other effects which
manifest themselves only when the blood emploj'ed still retains
its vital properties.

14. Action of Water on the Blood. — The mode of action
of water on the corpuscles is full}' described in Chapter I. The
coloring matter is entirely discharged, and probably the greater
part of the globulin. That the whole is not expelled seems
evident from an old experiment, made more than twent3'-five
years ago b}r Dr. Buchanan, of Glasgow, who observed that
the solid residue left behind, even when repeatedly washed
with distilled water, still retained the power of determining
coagulation in serous effusion-liquids, when added to them in
small quantity. Again, when blood which has been acted on
by water is subjected to a stream of carbonic acid gas, the
stromata of the corpuscles show changes which indicate that
they still retain a substance precipitable by that gas.

15. Action of Crystallized Ox-bile. — On the addition of
a dilute solution of ;' bile crystals," i. e., crystals of glyco-cho-
late and tauro-cholate of soda to blood, a great number of the
corpuscles are dissolved, so that the blood becomes distinctly
laky; and if it is derived from a suitable source, and not too
much diluted, the coloring matter crystallizes.' On this fact
one of the numerous methods of obtaining hsemaglobin is
founded. With reference to the mode of obtaining " bile
crystals," see Chap. XXXVI.

16. Preparation of Haemoglobin. — Any method by which
the coloring matter can be caused to quit the corpuscles without

100 THE BLOOD.

undergoing chemical change, or in other words, any of the
methods by which the blood can be rendered transparent or
laky, may be used for obtaining crystalline haemoglobin. Many
of these methods yield the product very readily, when the blood
is derived from one of those animals in which the coloring
matter is prone to crystallize. There arc, however, only one
or two of them by which pure haemoglobin can be obtained in
considerable quantity.

Thus by the method of freezing, large well-formed crystals
cau be obtained from the blood of the guineapig or dog. In
like manner the blood of the same animals crystallizes readily
after it has been rendered laky b}r warming or by the trans-
mission of induction shocks.

When it is intended to prepare considerable quantities in a
state of purity, it is best to emplo}' water as a solvent, and
then to determine crystallization in the liquid by the addition
of alcohol, in such proportions that the mixture is only just
capable of retaining the coloring matter in solution. To insure
success, it is to be borne in mind that the coloring matter
crystallizes as oxyhemoglobin (see § 17), that crystallization is
much impeded b}r the presence of non-crystallizable organic
compounds, particularly albumin, and that haemoglobin is
prone to undergo change when exposed in solution to tempe-
ratures above that of freezing. To insure complete oxidation,
the blood must be freely exposed to air. To obviate the
interfering influence of albumin, the coloring matter must be
derived, not from the whole of the blood, but in as far as pos-
sible from the corpuscles alone. To obviate the risk of che-
mical change, i. e., of the splitting of the haemoglobin into
other products, the liquids must be subjected, as far as pos-
sible, during the whole operation to a low temperature. These
indications are fulfilled in the following process, devised by
Preyer, which gives good results, when the weather is cold
and when blood is used of which the coloring matter is com-
paratively insoluble in water at 0° C, e. g., that of the dog or
cat. The haemoglobin of the blood of the horse, on the other
hand, is very soluble at all temperatures. It cannot therefore
be prepared by Preyer's method. Blood to be employed is
allowed to flow from a vein or artery into a porcelain capsule.
It is then placed in a cool cellar to coagulate. On the follow-
ing day most of the serum is poured off, and the remainder
removed with the aid of a pipette. The clot is then cut into
small fragments and placed on a filter of fine calico, on which
it is washed repeatedly with ice-cold distilled water, until the
washings give scarcely any precipitate .with a solution of cor-
rosive sublimate. [This indicates that the clot is tolerably
free from serum-albumin. The water must be ice-cold, because
at freezing temperature haemoglobin is sparingly soluble.]

BY DR. BURDON-S ANDERSON. 191

Then on the filter the clot is treated with distilled water at a
temperature of about 35CC, the filtrate being allowed to drop
into a measure-glass cooled in ice. It is of great importance
that this part of the process should be carried out with as little
loss of time as possible. I have found it a good plan to in-
close the clot in the filterer, and then to knead it repeatedly in
small quantities of warm water contained in the capsule; the
products of all the extractions being collected on the same
filter, and received in the cooled beaker. A measured portion
(say ten cubic centimetres) is then transferred, with the aid of
a pipette, to a test-glass, to which alcohol is added drop b}'
drop from a burette. The precipitate formed by the first drops
of alcohol redissolves on shaking or stirring: as more alcohol
is added the precipitate at last remains undissolved. [By this
means the proportion of alcohol required, in order to diminish
the solvent power of the liquid sufficiently to render it prone
to crystallize, is determined.] Alcohol is then added to the
whole liquid, in proportion somewhat less than is required to
produce a permanent precipitate. The clear solution on being
left to itself, surrounded with iced water, soon begins to
crystallize. The crystals are separated by filtration and washed
on the filter with ice-cold water containing a little spirit, and
subsequent^ with ice-cold water alone. To obtain the sub-
stance in a state of purity it must be subjected to recrystalli-
zation. For this purpose the crystals must be dissolved in
distilled water at 40 °C. and evaporated in vacuo, the process
being repeated until a product is obtained which on incinera-
tion leaves pure oxide of iron without trace of phosphoric
acid.

Dr. Gamgee recommends the following process, which was
recently communicated to him by Professor Kuhne, and has
been successfulby emploj^ed by him on three separate occasions.
Five hundred cubic centimetres of defibrinated blood of a dog
are mixed in a flask with 31 c. c. of pure ether, and thoroughly
shaken at intervals of a few minutes during an hour and a half
or two hours. The mixture is then placed in a cellar for about
twentj'-four or thirty-six hours. The flask containing the lake-
red liquid is now surrounded with ice (not a freezing mixture)
for twelve hours, at the end of which time it is found to have
become converted into a magma of haemoglobin crystals. Dr.
Gamgee states that the only objection to this method consists
in the great difficulty of filtering the crystalline from the viscid
serous portion of the mixture. In laboratories where the cen-
trifugal apparatus is to be found, the magma may be placed in
tubes and submitted to. excessively rapid rotation for three or
four hours, at the end of which time the haemoglobin will have
separated as a soft cake from the serum, which can be decanted.
Where no centrifugal apparatus can be obtained, the magma of

192 THE BLOOD.

crystals ma}' be diluted by the addition of an equal volume of
a mixture consisting of one part of ninety per cent, alcohol and
four parts of distilled water. The whole must be filtered
through calico, and the soft haemoglobin freed from the greater
part of the adhering water and spirit by being placed on a
porous brick and exposed to a current of cold air. Whichever
method of separating the crystals is used, they must be purified
by recrystallization.

The best method of obtaining haemoglobin crystals in small
quantities, for microscopical purposes, is one founded on the
same principles. A teaspoonful of defibrinated blood is treated
with a sufficient quantity of water to render it transparent.
A quarter of its bulk of alcohol having been added to it, the
mixture is introduced into a platinum capsule, and plunged in
a mixture of pounded ice and salt. A relatively abundant
crop of crystals is obtained. The mere freezing and thawing
the blood, as directed in § 11, will also give satisfactory re-
sults. Another method consists in passing the vapor of chloro-
form through the blood, which has alwaj^s the effect of render-
ing it laky, and in some animals determines crystallization.

17. Chemical Properties of Haemoglobin. — Solubility.
— The solubility of haemoglobin in water differs according to
the species of animal from which it is derived. Thus the color-
ing matter of the dog and cat are very soluble at 40° C;
sparingly soluble in ice-cold water. That of the guineapig
dissolves with relative difficulty at all temperatures, and crys-
tallizes more readily than that of any of the common domestic
animals. All kinds of haemoglobin are more soluble in warm
water than in cold. Diffusibility. — Haemoglobin, although
crystallizable, is indiffusible. This can be easily shown by
placing a solution of blood or haemoglobin in a diffusion-cell,
the septum of which is of good parchment paper.1 If an animal
membrane is substituted, a certain amount of coloring matter
passes from the solution into the water. The fact of the
diffusibility of haemoglobin perhaps stands in relation with
the enormous weight of its molecule. Coagulability. — Aque-
ous solutions of haemoglobin coagulate when heated, just in
the same way as albumin, and at about the same temperature
(64° C). When this occurs, the haemoglobin splits into an
albuminous compound and an insoluble coloring matter. Pre-
cipitation by Alcohol. — Small quantities of alcohol ma}' be
added to solutions of blood or haemoglobin without producing
an}' appreciable change. In continuing the addition a precipi-
tate is formed, which at first is redissolved on shaking, after-
wards becomes permanent. Relation to Oxygen. — In a solution

1 For method of preparing and testing a diffusion-cell, see Chapter
on Chemical Methods.

BY DR. BURDON-SANDERSON. 193

freel}' exposed to air, the haemoglobin is always combined with
oxygen (oxyhemoglobin). Consequently, whenever haemo-
globin is spoken of, it is understood to mean oxyhaemoglobin.
This oxygen is so loosely combined, that it begins to separate
itself from the haemoglobin as soon as the pressure of that
gas in the gaseous atmosphere to which it is exposed falls
below a certain point, recently determined by Worm Mullet* to
be about twenty-five millimetres of mercury. So that when
blood is subjected to the air-pump, the haemoglobin it contains
begins to part with its oxygen as soon as the pressure is reduced
to about a sixth of an atmosphere. This is expressed by say-
ing that the tension of oxj'gen in the blood is about twenty-
five millimetres Hg. Haemoglobin in solution can be deprived
of its oxygen by the addition to the liquid of certain reducing
agents (see § 18). In animals completely deprived of air, the
haemoglobin in the blood loses its oxygen completely in less
than a minute (see § 111). This is, no doubt, owing to the
rapid accumulation in the blood of oxidizable products. When
blood or solution of haemoglobin is subjected to the barometer
vacuum (see Gases of the Blood), it parts with the whole of
its oxygen. Haemoglobin has the property of oxydizing tinc-
ture of guaiacum. If a drop of concentrated solution of guaiac
resin in absolute alcohol is dropped on to filtering paper, and
the alcohol allowed to evaporate, and then a drop of solution
placed on the brown spot, a deep blue ring is formed round
the edge of the drop. This reaction must not be confused
with that observed when fibrin steeped in peroxide of hydro-
gen produces a similar effect. In the latter case, all that is
shown is, that fibrin decomposes the peroxide; in the former,
the reaction a fiords evidence of the presence of nascent oxy-
gen. Action of Carbonic Acid — Blood which has been satu-
rated with carbonic oxide is entirely deprived of its oxj-gen,
which is replaced by an equal volume of carbonic oxide. On
this fact is founded the excellent method of Bernard for the
gasometrical determination of the oxygen of the blood (see
§ 32). The carbonic oxide combines with haemoglobin in the
same way that oxygen does. Action of Oxide of Nitrogen. —
When oxide of Nitrogen is passed through a solution of blood
which has been freed from oxygen, by subjecting it to an atmos-
phere of hydrogen in such a manner as to exclude atmospheric
air during the process, the dark blood acquires a carmine color.
Here, as in the case of carbonic oxide, a new compound is
formed with haemoglobin, which crystallizes in the same form
as oxyhemoglobin. The solution, however, undergoes no
change when treated with reducing agents. Action of Nitrites.
— Dr. Gamgee has shown that the blood of animals poisoned
with nitrites, as e.g., nitrite of amy], assumes a chocolate
color. This color may be observed strikingly if a few drops
13

194 THE BLOOD.

of nitrite of amy! are added to a solution of haemoglobin. The
color of the latter almost instantly becomes brown. On adding
reducing agents to solutions so altered, reduced haemoglobin
(see § 18) appears — a fact which seems to square hest with the
assumption that the action of the nitrites on haemoglobin is to
peroxidize it, and that on reduction, oxyhemoglobin is first
formed, then reduced. The precise nature of the reaction is
still matter for investigation.

18. Optical Properties of Haemoglobin. — Crystals. —
The crystals are doubly refractive, ?'. e., they look luminous
when examined with the aid of the polarization microscope (see
Part I., Chap. IV.), between 'crossed Nicols. They shine in
sunlight with a lustre compared by Preyer to that of silk.
When formed in liquids freely exposed to air or ox}rgen, they
are of the color of arterial blood, but have the wonderful pro-
perty of becoming dark without altering their form when placed
in vacuo at a low temperature. They then exhibit two colors,
looking green along the arUts^ purplish-red elsewhere. On the
admission of air or oxygen, the color is restored. If a glass
plate to which crystals of hiemoglobin adhere is placed in front
of the slit of the spectroscope, two characteristic absorption
bands (Hoppe-Seyler) are seen in the 3'ellow between the Frau-
enhofer's lines D and E (see Fig. 195, 1). Solution. — The bands
just mentioned are also seen when solution of haemoglobin or
of blood corpuscles is placed in the same position : they can
be distinguished even when the solution contains only one ten-
thousandth of its weight of coloring matter. The bands differ,
however, in their characters according to the degree of dilu-
tion. According to the experiments of Prej'er, solutions vary-
ing in strength from one to five per 10,000, show both bands
faintly ; in solutions of six per 10,000, it can be distinguished
that the band next the line P is the darker of the two, the other
being broader and fainter (see Fig. 195,5); in solutions of
thirty per 10,000, the violet end of the spectrum is completely
absorbed, and the blue partially. As the concentration is in-
creased the two bands approach each other, until finally (when
the solution contains seventy per 10,000) they form a single
band, while the whole of the more refrangible rays are absorbed,
so that the spectrum does not extend beyond the limits of the
green (see Fig. 195, ft).

In 18G2 it was discovered by Stokes that haemoglobin exists
•in the blood in two states of oxidation, which are distinguished
alike bjr color and by the spectroscope; that the oxygenized
haemoglobin, or (as it has since been called) oxyhemoglobin, is
deprived by reducing agents of its oxygen, and that when it
has been so reduced, it can be restored to its original state by
agitation with air. The nature of the change of color is ex-
pressed in two facts, which can be observed with the aid of the

BY DR. BURDON-SANDERSON. If' 5

spectroscope. The first is, that when solutions of haemoglobin,
or of blood, are deprived of oxygen, either by placing them in
vacuo or by the addition of reducing agents, the more refran-
gible rays (blue and violet) are much less absorbed, and the
green more absorbed than they were before. The second fact
is, that in solutions so concentrated that most of the spectrum
is extinguished, the last color winch is transmitted is orange-
red if the blood is arterial, red if it is venous. These two facts
may be shortly expressed by saying that the color of arterial-
ized blood consists of orange-red plus green, of venous blood-
red plus blue.

These differences, however, are not the most remarkable
which are observed when oxydized and reduced solutions of
blood or its coloring matter are compared spectroscopically.
The most striking change produced by reduction relates to the
two bands of absorption in the yellow part of the spectrum
whieh have been already mentioned. This change is most
readily demonstrated by following the directions given by
Stokes in his original paper. A solution of protosulphate of
iron, to which a sufficient quantity of tartaric acid has been
added to prevent its being precipitated by alkalies, is rendered
decidedly alkaline by the addition of ammonia, and is intro-
duced into the solution of blood. "The color is almost in-
stantly changed to a much more purple red, as seen in small
thicknesses, and a much darker red than before, as seen in
greater thickness. The change of color, which recalls the dif-
ference between arterial and venous blood, is striking enough,
but the change in the absorption spectrum is far more decisive.
The two highly characteristic dark bands seen before, are now
replaced by a single band, somewhat broader and less sharply
defined at its edges than either of the former, and occupying
nearly the position of the bright band separating the dark bands
of the original solution (see Fig. 195, 2). The fluid is more
transparent for the blue, and less so for the green than it was
before. If the thickness be increased till the whole of the spec-
trum more refrangible than the red be on the point of disap-
pearing, the last part to remain is green, a little beyond the
fixed line 6, in the case of the original solution ; and blue, some
way beyond F,in the case of the modified fluid. If the purple
solution be exposed to the air in a shallow vessel, it quickl}'
returns to its original condition, showing the same two char-
acteristic bands as before; and this change takes place imme-
diately, provided a small quantity only of the reducing agent
were employed, when the solution is shaken up with air. if
an additional quantity of the reagent be now added, the same
effect is produced as at first, and the solution may thus be
made to •uy through its changes any number of times." [Stokes,
On the Reduction and Oxydation of the Coloring Matter of

196 THE BLOOD.

the Blood. Proceedings of the Roy. Soc., vol. xiii. p. 355.]
The same facts can be demonstrated quite as advantageously,
and perhaps with greater ease, if the solution of the sulphhy-
drate of ammonium is substituted for the solution of sulphate
of iron used by Stokes. The change is, however, not so rapid:
it is accelerated by subjecting the liquid to a temperature of
40° C.

19. Methaemoglobin. — If a pure solution of haemaglobin
is left to itself at the ordinary temperature, it gradually loses
its brightness, and if it is then examined spcctroscopically, it
is seen that a new band has appeared in the orange at a point
where in ordinary blood there is least absorption. This band
is due to the presence of a new coloring matter, called by
Hoppe-Seyler methaemoglobin. The same change occurs under
other circumstances, e.g., when carbonic acid gas is passed
through dilute solutions of haemaglobin, or when glacial acetic
acid is added to dilute solution of defibrinated ox-blood, in ex-
tremely small quantity. [In larger proportions, acetic acid
determines the formation of haematon. — See § 22.] Haemoglo-
bin undergoes the same transformation when acted on by per-
manganate of potash. If a crystal of pure permanganate is
dissolved in distilled water, and the solution added to very
dilute solution of blood, before the slit of the spectroscope, at
a temperature of about 25° C, the haemoglobin bands gradu-
ally disappear. In their place we have a spectrum, in which
there are not only the band mentioned above, but two others,
of which one nearly corresponds in position to the second hae-
moglobin band, while the other lies half way between the lines
E and F. Methaemoglobin is a substance of which the chemi-
cal constitution and relations are imperfectly ascertained. Its
presence is indicated spectroscopically in all collections of
blood which have been for some time extravasated within the
body, e. g., in thrombi, sanguinolent transudation liquids, etc.

20. Preparation of the Crystalline Coloring Matters
■which result from the Decomposition of Haemoglo-
bin, and Demonstration of their Absorption Spectra. —
Hasmin. — When dried blood is treated with glacial acetic acid
and warmed to the temperature of the body, a solution is ob-
tained which yields crystals of a new coloring matter, of re-
markable properties, which has been designated haemin. The
erystals vary extremely in shape, sometimes occurring as
rhombic plates, sometimes as rods crossing each other at vari-
ous angles. They are not soluble without decomposition in
any liquid excepting hydrochloric acid, and are so little liable
to chemical change that they may be kept for years, exposed
to a moist atmosphere, without undergoing any change. Hae-
min difl'ers from haematin (§ 21) in containing an additional
equivalent of hydrochloric acid, on which account it is also

BY DR. BURDON-SANDERSON. 197

called hydro-chlorate of haematin. Its carbon, nitrogen, and
iron are in the same relative proportions as in haematin, but
necessarily it contains a little less iron per cent, than that
body.

The mode of preparing the so-called Teichmann's crystals —
in other words, the mode of obtaining haemin for the purpose
of demonstrating its crystalline form microscopically — has
been fully described in the histological part (Chap. I., p. 34).
Haemin majr be obtained from blood in quantity, as follows,
but the process is one which appears to present great difficulty,
as it frequently fails. Defibrinated blood is diluted with a vol-
ume and a half of distilled water. The transparent liquid is
then precipitated with neutral acetate of lead, for the purpose
of separating the albumin. The excess of lead (with respect
to which it is desirable to be careful not to add more than is
necessary) having been got rid of by the addition of a con-
centrated solution of carbonate of soda, the liquid is filtered,
and the filtrate evaporated to dryness either in the air or in
vacuo. The dry residue is then finely powdered and rubbed
up with fifteen times its own weight of glacial acetic acid, to
which a trace of chloride of sodium has been added. The
brown liquid thus obtained is introduced into a flask and
warmed in the water bath until it is entirely dissolved, and the
solution is mixed with five times as much distilled water, and
allowed to stand for many days, protected from evaporation.
The crystals collect on the bottom of the beaker and may be
readily purified by repeatedly treating them with distilled
water, allowing them to subside and then decanting. As hae-
min contains chlorin, it cannot be prepared from haematin
unless chlorides be present. When it is prepared from blood,
the quantity of chloride of sodium present is sufficient, so that
the addition of that salt is not essential. The solution of hae-
min in hydrochloric acid gives no characteristic spectrum.

21. Haematin. — Haematin can only be obtained in a state
of perfect purity from the crystals of haemin, the mode of pre-
paration of which has just been given. The process is simple :
the haemin crystals are dissolved, i. e., decomposed in ammonia.
The solution of haematin thus obtained is evaporated to dry-
ness, the residue is then extracted with water, which removes
the chloride of ammonium, and dried. The product is pure
haematin. It is insoluble in water, alcohol, and ether, soluble
in alkalies and alkaline carbonates, but not soluble in acids
without decomposition.

In the impure state, haematin may be obtained in various
ways. The change occurs more gradually at ordinary tem-
peratures in solutions of blood, or haemoglobin, which are de-
cidedly alkaline, whether the alkalinity is derived from potash,
soda, ammonia, or their carbonates. Solutions of haemoglobin

108 TIIE BLOOD.

which have undergone this last change exhibit, when placed
before the slit of the spectroscope, in place of the haemoglobin
bands, a less distinct and paler bund on the opposite side of
the D line, i. t\, in the orange. This change is characteristic
of the presence of hsematin. It is attended with an obvious
darkening of the color of the liquid.

When an alkaline solution of haematin is subjected to the
action of reducing agents, such as sulphuret of ammonium or
protosulphate of iron, it exhibits, when examined spectroscopi-
cally, two much more distinct bands (Fig. 195, 4), one of which
is exactly opposite the bright space which separates the two
haemoglobin bands ; the other, which is less intense, is close to
Frauenhofer's line, E, i. e., nearer to the blue end of the spec-
trum than the broader of the two haemoglobin bands. If the
solution is fresh and dilute, and the quantity of the reducing
agent small, these bands can be made to vanish b}' agitation
with air, giving way to the so-called oxyhaematin band above
described. All these facts ma}7 be as readily demonstrated in
solutions of blood corpuscles ; i. p., of cruor, as in solutions of
haemoglobin. Blood rendered distinctl}r alkaline either by soda,
potash, ammonia, or their carbonates, shows the absorption
band of oxyhaematin. After addition of sulphuret of ammo-
nium, this is replaced by the more distinct spectrum of reduced
hsematin.

22. Haematoin. — When acetic acid is added to blood, the
iron of the haemoglobin is separated and takes the form of a
protosalt, and a new coloring matter remains in solution, the
spectrum of which was first described by Professor Stokes, and
has been subsequently known as acid hsematin. More recently,
Preyer has shown that it is not identical with hsematin, but
with the body to which Hoppe-Seyler gave the name of iron-free
hsematin. It is produced whenever concenti'ated sulphuric
acid acts on haematin. According to Hoppe-Se3Tler, it is pre-
pared by rubbing up finely powdered hsematin in concentrated
sulphuric acid. A liquid is obtained which is green in thin
layers, reddish-brown in thicker layers, and gives a brown pre-
cipitate when diluted with water. This precipitate is easily
dissolved in ammonia. On evaporating the ammoniacal solu-
tion, a bluish-black residue with metallic lustre is left, wdiich is
free from iron. It may be obtained in like manner by acting
on methaemoglobin by sulphuric acid. The solution of haema-
toin in ammonia exhibits four absorption bands. It is ad-
mirably shown b}r the method recommended by Professor
Stokes, i. e.< by extracting with ether blood which has been
mixed with acetic acid. The ethereal liquid thus obtained ex-
hibits a four-banded spectrum. Of these bands, three onl}' are
easy to recognize — one in the orange, nearer to the red than
the reduced hsematin band ; a rather broad band in the green;

BY DR. BURDON-S ANDERSON. 199

and a narrow but well-defined one in the blue. (See fig.
195, 3.)

23. Quantitative Analysis of the Blood, with refer-
ence to its Corpuscles, Serum, Fibrin, Haemoglobin,
Albumin, and Salts. — The following summary of the order
of proceeding in the analysis of the blood, will be found
sufficient for the guidance of those who have been previously
trained in quantitative methods. The student who has not
learnt accuracy by practice, in the analysis of bodies of known
composition in the chemical laboratory, should not attempt
the quantitative determinations relating to the blood or other
animal liquids, partly because the operations are complicated,
but principally because the operator has no means of detecting
his mistakes. The blood to be analyzed is received in four
vessels, the contents of which are as follow: 1. Ten or
twelve centimetres of blood are allowed to flow into a weighed
porcelain capsule and covered with a weighed watch-glass:
After weighing, the blood is evaporated in a water-bath, dried
in the air-bath at 120° C, and the residue used for the deter-
mination of the total albuminous constituents, fat and salts, as
follows: After standing till it is cool in a receiver over sul-
phuric acid, it is weighed. The weight, deducted from that of
the capsule and watch-glass, gives the total solids. The dry
residue is then pulverized in a glass or porcelain mortar with
common alcohol (Sp. G. 890) and transferred to a small beaker,
the mortar being subsequently carefully washed with alcohol,
and the washings added to the quantity in the beaker. This
done, the contents of the beaker are boiled, and the alcoholic
solution thus obtained is poured into a small previously
weighed filter. What remains in the beaker is similarly
treated with a second quantity of alcohol, which is thereupon
poured into the same filter. After carefully washing the filter
with boiling alcohol, the filtrate together with the washings
is evaporated on the water-bath, dried at 110° C, allowed to
cool over sulphuric acid, and weighed. The weight gives the
solids soluble in alcohol a.

Distilled water is added to the residue in the beaker, which
is warmed in the water-bath. The water-extract is then poured
on to the filter last used, and the filtrate collected in a weighed
covered capsule, evaporated on the water-bath, dried at 110°,
cooled over sulphuric acid, and weighed. The weight, minus
that of the capsule, is that of the solids soluble in water . b.

The remainder on the filter is dried at 110°, and then over
sulphuric acid, and weighed repeatedly, till it is found no
longer to lose weight. For this purpose it must be inclosed
between two watch-glasses, held together by a clamp. The
weight, minus that of the watch-glasses, filter, etc., is that of
the insoluble solids c.

200 THE BLOOD.

The fats of the blood are contained in a, from which they
are extracted by repeatedly treating it with ether and evapo-
rating the ethereal extract. The residue is washed into a
small platinum capsule for incineration.

b is incinerated in the capsule in which it was weighed ; c,
with the filter in which it is contained, is incinerated in another
capsule. The ash of a and b represents the soluble salts of
the blood, viz., the chloride of sodium (five-sixths of the
whole), phosphate, sulphate, and carbonate of soda ; chloride
and sulphate of potash. The ash of c consists of phosphates
of lime and magnesia.1

2. A second quantity of twenty-five centimetres is used for
the determination of the fibrin. For this purpose a small
beaker is used, over the top of which a vulcanized India-rubber
cap with a single neck (see Fig. 190) can be drawn without
difficulty. Through the neck or tubulature, a rod of whale-
bone, which, at its lower end, widens out into a blade, is
grasped by the tubulature. The blood is received into the
beaker, covered at once with the cap, and immediately agitated
very briskly with the blade of the whalebone, the purpose of
the whole arrangement being to prevent loss of weight by
evaporation during the process. As soon as coagulation is
complete, the beaker and its contents are weighed. The
weight, minus that of the beaker, its cover and the oar, is that
of the quantity of blood used. The cover is then removed
and the beaker filled with water, to which a trace of chloride
of sodium has been added. After agitation and subsidence
the clear liquid is poured off, and the fibrin again treated with
as much more water with a trace of salt. The fibrin is then
collected on a weighed filter, and washed with distilled water

1 In incinerating, it is of importance that the capsule or crucible
should be large enough to hold four or five times as much material as is
used. Platinum vessels are preferable. If the substance contains much
organic matter, and at the same time much soluble salts, e. g., chlorides,
it is necessary to perform the operation in two stages, i. e., first to car-
bonize the substance, then extract the ash with boiling water, collect
the insoluble part on a filter free from ash or containing a known
weight of ash. The filter, after careful washing, must be dried at
110° C, and gradually heated to whiteness until the carbon is entirely
destroyed. Almost the whole of the soluble salts are contained in the
extracts. Thus the decomposition of the alkaline carbonates and
chlorides, which occurs at a higher temperature, is avoided. In incine-
ration of the total solids of the blood this interruption of the process is
desirable, if for no other reason, on account of the extreme difficulty of
getting rid of the carbon in presence of so great a quantity of alkaline
salts. If, however, the method described in the text is followed, these
difficulties are got rid of in another way. For, on the one hand, the
watery and alcoholic Extracts contain very little organic matter ; on
the other, the insoluble residue (c) is free from alkaline salts. In both
cases, therefore, the incineration can be proceeded with continuously.

BY DR. BURDON-SANDERSON. 201

until the filtrate is colorless. The pink fibrin thus obtained is
then finally washed on the filter with boiling alcohol, dried
first in the air-bath, then over sulphuric acid, and finally
weighed.

3. A third portion of blood is received in a similar apparatus,
defibrinated, and the defibrinated blood strained through a
calico filter and weighed. The filtrate is then mixed in a tall
jar, with ten volumes of a solution of salt, prepared by adding
nine volumes of water to one of saturated solution. After a
day, the corpuscles having subsided, the liquid is decanted
off, and replaced by a second similar quantity of saline solu-
tion. Again the corpuscles are allowed to subside, and the
liquor removed by decantation. The deposit is then washed
with water into a porcelain capsule, evaporated on the water-
bath, dried, pulverized with alcohol, and then proceeded with
for the separation of the albuminous compounds from the
soluble constituents, as in the first quantity. The weight of
the insoluble residue (c), minus the weight of its salts, corre-
sponds to that of the albumin and haemoglobin of the whole
blood.

4. The fourth quantity is allowed to coagulate in a capsule.
The serum is then poured off, and the albumin contained in
a weighed quantity determined by the method already de-
scribed.

The results stand as follows : From 3, we learn the propor-
tion in a known weight of blood, of albumin and haemoglobin
contained in the corpuscles ; from 1, the corresponding pro-
portion of albumin and haemoglobin contained in the corpus-
cles and plasma together; and hence, by deducting the former
from the latter, the proportion of albumin in the plasma.
From 4, the proportion of albumin contained in the serum is
known, and thereby that of the serum in the blood. The
weight of the plasma is equal to the weight of the fibrin (2),
plus that of the serum. Finally, by deducting the weight of
the plasma from that of the blood, we have that of the corpus-
cles in the moist.

24. Quantitative Determination of the Haemoglobin
contained in Blood. — It is often of great importance to be
able to determine the proportion of haemoglobin in a small
quantity of blood ; such, for example, as may be obtained by
cupping. This is accomplished by making a solution of a
measured or weighed quantity of blood in water, and then
ascertaining, with the aid of the spectroscope, what degree of
dilution is necessary in order to bring it to such a strength
that only the red rays are transmitted {see § 18). The point
of dilution at which the green is entirely extinguished, has
been found by Preyer to be so constant, that it may be used
as a basis for quantitative determinations.

202 THE BLOOD.

The determination of the percentage of haemoglobin which
is required to yield the spectroscopic result above described,
is accomplished by introducing a concentrated solution of a
known weight of pure haemoglobin crystals into a glass cham-
ber ( so-called hannatinomcter), of which the parallel sides are
one centimetre from each other. . The chamber is then placed
in front of the slit of the spectroscope, the source of light
being a paraffin lamp. Distilled water is then carefully added
from a finely divided burette, so \omx as all of the spectrum is
extinguished excepting the red. The moment that the green
begins to appear, the operation is ended. The volume of the
diluted solution is determined ; and the exact conditions, viz.,
the distance of the lamp and chamber, and the width of the
slit, are carefully noted. The percentage of haemoglobin con-
tained in the solution is that at which, uncle?' the given condi-
tions, complete absorption of the green takes place. It may
be designated k.

In order to ascertain the percentage of haemoglobin con-
tained in any given specimen of blood, all that is required is
to repeat the process just described. A small quantity of
fresh blood, which has been well agitated with air and defibri-
nated, is introduced into a finely graduated small pipette,
from which exactly one centimetre is delivered into the glass
chamber above mentioned, and diluted before the slit of the
spectroscope (the liquid being carefully stirred after each
addition) until the green begins to appear. At this moment
the liquid contains a percentage of haemoglobin equal to k.
If the volume of distilled water including the centimetre
originally added, be designated c, and the original volume of
blood 6, the percentage of haemoglobin which the blood con-
tains is readily calculated according to the formula

CC I) -J— 0 ■ . T

— =_J_ Whence, if the quantity of blood used, as above
k b H J '

supposed, be one centimetre, we have x=k (1 + c).

25. Determination cf the Quantity of Haemoglobin
in Blood, by the Estimation of its Iron. — Assuming
that haemoglobin contains 0.42 per cent, of iron, and that the
whole of the iron of the blood is contained in its coloring
matter, it is evident that if the percentage of iron existing in
any quantity of blood is known, the percentage of haemoglobin
can be readily calculated. Although the process has disad-
vantages as compared with that last described, both as regards
the time required for carrying it out, and the accuracy of the
results, it cannot be omitted, as, under man}* circumstances
(e.g., when the blood to be investigated is not perfectlj- fresh),
the spectroscopic method is inapplicable. To ascertain the
proportion of iron in blood, a weighed or measured quantity
of the liquid must be incinerated. The ash must then be dis-

BY DR. BURDON-SANDERSON. 203

solved in pure dilute hydrochloric acid, and the iron deter-
mined volumetricalty with permanganate of potash. This is
accomplished as follows : —

The volumetrical solution of permanganate which is usual-
ly employed, is prepared by dissolving the pure crystals in
distilled water, in the proportion of 3.16 grammes to the litre.
It is of such strength that 17.85 centimetres correspond ap-
proximatively to one-tenth of a gramme of metallic iron. It
is, however, necessary, before using it, to determine its exact
strength, by means of a weighed quantity of solution of the
double sulphate of iron and ammonia. The mode of preparing
this salt will be found in Sutton's " Volumetrical Analysis."
It contains exactly one-seventh of its weight of iron, so that
0.7 gramme represents 0.1 gramme of iron. The mode of ap-
plying it is as follows: —

0.7 gramme of the salt having been dissolved in a beaker in
distilled water, and five or six c. c. of dilute (1 : 5). sulphuric
acid added, the permanganate solution is delivered from a bu-
rette, having a glass stopcock, until a point is reached at which
the rose color no longer disappears on shaking. As the per-
manganate must be slightly in excess to produce a percepti-
ble color, a correction should be made by ascertaining experi-
mentally how much of the salt is required to produce the
observed intensity of color in the quantity of liquid used.
This quantity should then be deducted from the result. The
number of cubic centimetres used for 0.7 gramme of the
double sulphate, (i. e., 0.1 gramme of metallic iron) must be
marked on the bottle. As the method depends on the con-
version of the iron from the lower to the higher stage of oxi-
dation at the expense of the permanganate, it is obviously
necessary that the whole of the iron in the liquid to be ope-
rated upon should be in the condition (to use modern lan-
guage) of a ferrous salt. For this reason, the first step in
dealing with the hydrochloric acid solution of blood ash, is to
reduce it. With this view, the solution of ash is first intro-
duced into the flask already mentioned, in which it is gently
boiled with a few pieces of zinc until the latter is dissolved
and the liquid is colorless. It is then allowed to cool and
diluted to fifty centimetres, after which the solution of per-
manganate is added to it from the burette, as before, until
the rose color becomes permanent after agitation. For each
centimetre of the red liquid emplo3'ed in attaining this result,
the quantity of solution in the flask contains 0.0056 gramme
of iron.

204 TIIE BLOOD.

Section IV. — Gases of the Blood.

1. The gases of the blood are oxygen, carbonic acid and
nitrogen. The knowledge we possess of the conditions under
which they are contained in the blood, and of the relative
quantities of each, is founded entirely on the researches of
Ludwig and his pupils, published during the first }rear of the
last decade.

As regards ox}rgen,a correct method (that of displacement
by carbonic oxide) had already been employed by Claude
Bernard ; but, as regards carbonic acid, the methods previous-
ly used were imperfect and the results erroneous.

2. In round numbers, one hundred volumes of arterial blood
deliver to the Torricellian vacuum about twenty volumes of
oxygen (estimated at 760 millimetres pressure and 0° temper-
ature)— venous blood about twelve volumes. Of the quantity
of oxygen so extracted, by far the greatest part is in combina-
tion with haemoglobin — in other words, in the concrete state.
The proportion of free oxygen in blood is so small that oxygen
is absorbed from any atmosphere containing it in which its
tension is greater than from twenty to twenty -five millimetres
— in other words, from any space in which it exists in a pro-
portion greater than about one-eighth of the proportion in
which it exists in the atmosphere. Consequently, in subject-
ing blood to the air-pump, no oxygen is given off till the press-
ure sinks to about 125 millimetres (t. e., about a sixth of an
atmosphere) ; whereas, in the case of other liquids (e. g.,
water), oxygen, with the other contained gases, begins to be
disengaged, pari passu, with the reduction of pressure, in a
quantity determinable according to Dalton's law. These facts
are expressed by saying (1) that the absorption of oxygen by
the blood is independent of Dalton's law, and (2) that the ten-
sion of oxygen in the blood is from twenty to twenty-five
millimetres of mercury.

3. When blood is subjected to the Torricellian vacuum, the
disengagement of oxygen is complete. The blood is converted
into froth, and rapidly assumes a dark color. This appear-
ance is due partly to the discharge of the coloring matter from
the corpuscles, partly to the complete reduction of the haemo-
globin which accompanies the extraction from the liquor san-
guinis, of its free oxygen.

4. When blood is subjected to an atmosphere which con-
tains no oxygen, the result, so far as relates to the extraction
of oxygen, is the same as if it were exposed to the vacuum.
This is particularly the case if the gas employed be one which
has the power of combining with haemoglobin. The gas which
pre-eminently enjoj's this faculty is carbonic oxide. When
blood is subjected to an atmosphere of this gas, the oxygen it

BY DR. BURD0N-S ANDERSON. 205

contains, "whether free or combined, escapes from it, its place
being taken by carbonic oxide. The blood-coloring matter in
combination with this gas acquires optical and other characters
which remarkably resemble those of oxyhaemoglobin.

5. Carbonic acid gas may be extracted from arterial blood
by the Torricellian vacuum in the proportion of about 35 vol-
umes (as estimated at TGO millimetres pressure and 0° tempe-
rature) to 100 volumes of blood. Venous blood may yield 43
volumes, asphj'xial blood 50 volumes. Of this quantity a cer-
tain but very varying proportion is merely absorbed, the rest
is in loose combination, principally with the sodic carbonates
of the plasma. It is probable that some of it is held by the
bibasic sodic phosphate of the blood, and perhaps some other-
wise. Hence it may be readily understood that serum con-
tains as much carbonic acid gas as a corresponding volume of
blood.

6. When a fixed acid, e. gr., tartaric acid, is added in vacuo to
blood which has been already deprived of its absorbed and
loosely combined carbonic acid (which together constitute
what may be called its inexhaustible carbonic acid), an addi-
tional quantity of carbonic acid may be obtained from it, which
previously existed in the blood in the condition of neutral car-
bonate, principally if not entirely sodic.

Every apparatus for extracting the gases of the blood must
consist of two parts, a mercurial pump and a recipient. The
form and character of the latter necessarily depend upon those
of the former. The most important forms of pump in use are
those of Dr. Geissler, and others similar, employed in Ger-
many, and of M. Alvergniat, in Paris. In this country, under
the direction of Professor Frankland, Mr. Cetti has constructed
a Sprengel's pump for the purposes of extracting the gases of
water. Dr. Gamgee, of Edinburgh, has applied this form of
pump to the extraction of the gases of the blood with complete
success.

26. Alvergniat's Pump. — A long barometer tube, the
scale of which is divided into millimetres, is fixed to a vertical
board on a suitable stand. This tube is dilated at the top into a
large bulb (a, Fig. 197), and is then continued upwards until it
ends in a three-way stopcock (d), surmounted by a funnel. To
the right, the stopcock is in communication with a glass tube,
ending in a bulb (jy), and possessing a flexible joint at/. To
the lower end of the barometer tube is fitted a long tube of
thick-walled vulcanized caoutchouc, which ends in a globular
mercury-holder (o). The vertical board is fitted at regular in-
tervals with perforated shelves, on one of which the mercury-
holder is resting. The pump is worked as follows: v having
been filled with mercury, the metal enters the vulcanite tube,
and rises to the same heijjht in the tube a c as in v. If v is

206 THK BLOOD.

raised from its present level to that of the highest of the
shelves, the stopcock being :it the same time turned so that
the vertical tube communicates with the external air. but not
with the bulb, the mercury will rise till the whole of the verti-
cal tube is occupied. The stopcock is now turned so as to
make communication only between a c and the bulb, and the
mercury-holder is replaced in its original position. As the re-
sult of this manipulation, tin: air previously contained in the
bulb and the tube leading from it occupies the whole cavit}',
and (according to Marriotte's law) is expanded, i. e., dimin-
ished in density in the same ratio that the volume occupied by
it is increased. In other words, the density of the air in the
bulb, before the depression of u, is to its density after as the
capacity of the barometer plus the bulb is to that of the bulb
alone. To repeat the operation, the stopcock must first be
placed in such a position that all channels are closed, v is
then raised and the stopcock again turned as at first — viz.,
the horizontal way closed, the vertical way open. The ait-
contained in a c having been discharged, the stopcock is again
opened horizontally and closed vertically, and v depressed.
The air remaining in the bulb is again expanded in the same
proportion as before. If the capacity of the tube, together
with its dilatation, be equal to that of the bulb and its tube,
it is obvious that the effect of each stroke of the pump will be
to halve the density of the air in the bulb ; consequently, if
the operation is repeated ten times, the density of the air con-
tained in the bulb (supposing it to be dry, and to have an ori-
ginal density of 160 millimetres) becomes 760x(i),0=0.74 mil-
limetre. By filling the bulb and the tube leading to it, before
attaching it, with water deprived of its gases by boiling, the
process of exhaustion can be very much shortened. No sooner
does the mercury sink in the vertical tube (a c) than the water
follows it, and can be discharged b}r raising the mercury-
holder with the stopcock open vertically and closed horizon-
tally, as before. A vacuum which is almost perfect is thus
obtained at a single working of the pump. In the pumps
recently made by M. Alvergniat, he has substituted a movable
support which works up and down the vertical board by a
winch.

27. Geissler's Pump — The instrument (see fig. 198) con-
sists, like that just described, of a fixed vertical tube (a), which
is dilated into a large bulb near the top and communicates near
its lower end by means of a flexible tube of thick walled caout-
chouc with another vessel (b) which can be moved up and down
by turning a winch. Above the bulb, the vertical tube, which
is nearly a metre in length, ends in a stopcock (g), so con-
structed that the bulb can be completely shut off, or may be
brought into communication either, with the external air or with

BY DR. BURDON-SAXDERSON. 207

the cavity to be exhausted. The pump is worked in the same
manner as that just described. In order, if necessary, to dry
the vacuum, a Pfliiger's drying apparatus is interposed between
the pump and the recipient. This may be described as a U
tube, the bend of which is dilated into a bulb (c). It is so
constructed that the fragments of pumice or the glass* balls
moistened with sulphuric acid which are used for drying can
be readily introduced into either limb. The tube leading from
the dessicator to the pump communicates with a vacuum gauge
(m). The advantage which this instrument possesses consists
in the relatively large size of the bulb, the perfection of the
workmanship (particularly of the stopcocks) and the arrange-
ment whereby the vacuum obtained is dry.

28. Frankland-Sprengel Pump— Sprengel's pump as
modified b}r Frankland, consists essentially of a vertical glass
tube (o Fig. 199) about four feet long, with thick walls and nar-
row bore, the lower end of which is bent up in such a way that,
if filled with mercury, and closed at the top, it would constitute
a barometer. At its upper end, however, it is not closed, but
is continuous by a bend with the second vertical tube (g) or
ascending limb of the Sprengel (the supply tube), which is of
wider bore, and runs parallel to the first. At the top, or con-
vexity of the bend, a third tube, about four inches in length
(the exhaustion tube), is sealed on, by which the barometer
tube or descending limb communicates with the cavity to be
exhausted. The ascending limb communicates by a flexible
tube, strengthened by a covering of strong canvass and
guarded by a screw clip, with the descending limb of another
bent tube (c) of similar construction to the first; the only dif-
ference between it and the one just described being that it com-
municates at the bend, not with any cavity, but merely with a
bulb (d) closed at E by mercury. Its other limb finally com-
municates by a second flexible tube with a reservoir of mer-
cury (b), the arrangement of which will be best understood from
the figure. It consists of two glass funnels, each having long
stems, the relative sizes of which are such that the one can be
contained within the other. To work the pump, the exhaust-
ing tube of the first bent tube must be connected with the cavit}'
to be exhausted by means of a junction of vulcanized caout-
chouc, guarded by a chamber filled with glycerin. Mercui^ is
then poured into the inner funnel (the tube leading to the first
bend having been previously closed) until it rises in the space
between it and the outer to the same level. This done, the
clip is opened, and a stream of mercury is allowed to flow over
the two bends in succession, great care being taken that the
stream is not so abundant as to cause the mercury to ascend
in tin; exhausting tube above the level of the bend. The flow
must then be gradually diminished with the aid of the clip,

208 TIIE BLOOD.

until the column of mercury in the descending limb of the
Sprengel tube is broken into fragments by intervening spaces
containing air. This happens whenever the quantity of mer-
cury which readies the bend by the ascending limb in any given
time, is less than that which leaves it by the descending limb.
In a time which varies according to the capacity of the cavity
to be exhausted, vacuum is attained. No more bubbles are
discharged at the lower end of the Sprengel. Each drop of
mercury as it falls produces a peculiar click, and if the current
is stopped, it is seen that the height of the column in the de-
scending limb is less than that of the barometer at the time,
by a number of millimetres which is equal to the tension of
aqueous vapor at the temperature. The apparatus is so
arranged that the bend of the first tube is supported at a level
several inches higher than that of the second. Consequently,
as the process of exhaustion approaches, the bulb with which
it communicates becomes emptied of mercury, the vacuous
space thus formed gradually extending till the level of the mer-
cury in the descending limb coincides with that of the bend of
the second tube.

We next pass to the description of the method of obtaining
blood from an artery or vein, and of transferring it to the
vacuum. Although it is not possible to produce a vacuum
with the Sprengel pump above described, as rapidly as with
the ordinary mercurial pump,1 its action in other respects is
very satisfactory. It completely fulfils the conditions enume-
rated by Ludwig as essential to an efficient blood-pump. The
vacuum produced is perfect; it is bounded by mercury which,
having previously passed through a vacuum (in the first tube),
is completely deprived of air; and it can be renewed any num-
ber of times after the blood is introduced.

29. Method of Transferring the Blood to be Ex-
hausted from the Artery or Vein to the Vacuum. — It
is essential that the transference should be effected without
contact with air; the blood must therefore either flow as directly
as possible from the artery or vein into the vacuum tube: or,
if it is intended to de fibrin ate it, it must be received in a space
previously occupied by mercury. Before describing the mode
of transferring, an account must be given of the chamber or re-
cipient in which the blood is exhausted, and of tiie mode in
which it communicates with the pump. The exhaustion tube
(sec Fig. 199, ii) is connected by a vulcanite union, inclosed in
an external tube containing glycerin, with a long nearlj' capil-
lary tube, of such form and length as to reach the table by the
side of which the pump stands. Near its lower end it is bent

1 The instrument probably admits of considerable improvement in this
respect.

BY DR. BURDON-SANDERSON. 209

at an obtuse angle, so that the last few inches are horizontal.
A little above the bend there is a bulb: the horizontal part is
firmly supported on a block. With this tube the recipient is
united either by a mercurial joint (i) or by a connector of vul-
canized India-rubber, inclosed in a glycerin chamber. The
recipient is a large glass tube (j), of about an inch and a
quarter diameter, and forty inches long. At its lower end it
terminates in a capillar}' tube, which is guarded by a stopcock
(l). Its capacitj' is about 250 centimetres, consequently six-
teen times that of the blood it is intended to receive.

In selecting a method of transference, preference ought to be
given to those plans which are least complicated and most rapid
in execution. The method I have found to answer is as fol-
lows: The animal having been secured, a canula fitted with an
India-rubber connector is inserted in the vessel, which is closed
by a clip lege artis. For receiving the blood as it flows from
the artery or vein, a straight-glass tube (Fig. 199, m) of known
capacity is used ; one end of this tube is guarded b\' a stop-
cock, while the other is drawn out, and so formed that it can
be accurate!}' stopped by the finger. A trough having been
filled with mercury, completely freed from air by passing
through the pump, the narrow end of the tube is dipped into
it. The tube is then easily filled up to the stopcock by aspira-
tion and the stopcock closed. It having been ascertained that
the tube is perfectby full, it is placed in an inclined position,
with the stopcock end downwards, and the open end at such a
distance from the canula that the India-rubber tube can be
easily slipped over it at the required moment. This having
been accomplished, and the other end of the tube having been
fitted with a bit of India-rubber tubing of sufficient length to
conve}' away the mercury to a convenient receptacle, all is
ready. The clip on the canula is opened, and blood allowed to
flow freely from the tube for a few moments while the mercuiy
tube is grasped by the operator. The warmth of the hand
causes the mercury to expand and project from the open end
of the tube: at that moment the India-rubber connector from
which blood is flowing is slipped over it, and the connection is
completed without the slightest risk of the introduction of air.
Withont a moment's loss of time the stopcock is opened, and
the blood allowed to replace the mercury. The stopcock having
been closed, the India-rubber connector is slipped off, and the
open end of the tube closed with the finger. The tube is now
placed with its open end downwards in the mercurial trough
(u i, the finger being still kept on the orifice, while an assistant
fills the bit of capillary tube beyond the stopcock with boiled
distilled water, and connects it with the corresponding end of
the recipient by means of an India-rubber connector. The mo-
ment that this is accomplished, the finger is removed from the
14

210 THE BLOOD.

orifice of the tube, and both stopcocks are opened. The blood
passes rapidly into the recipient, followed by a column of mer-
cury, and is at once converted into froth. A few drops of mer-
cury having been allowed to enter, the stopcocks are finally
closed. It will be understood from the figure that the joint
between the measuring tube and the recipient, as well as the
stopcocks, are under water, the purpose of which arrangement
is, it need scarcely be said, to obviate the risk of the entrance
of air.

At first the water in the wooden trough (n, which is not in-
troduced until M has been joined to l) is kept cool with frag-
ments of ice, in order to prevent the blood from coagulating
during the preliminary operations. As soon as all is complete,
hot water is graduall}' added until the temperature rises to
about 40° C, care being taken not to expose the stopcocks to
the air during the process. The only moment in the process
at which air can be admitted, is that of joining the measuring
tube to the recipient. For this reason it is desirable, before
opening the second stopcock of the measuring tube, to keep the
pump in action for a few minutes so as to be certain that the
vacuum is unimpaired before admitting the blood. This is not-
attended with inconvenience, ifthe blood is kept at a tempera-
ture approaching that of freezing.

When it is desired to defibrinate the blood before exhausting
it, it must be collected over mercury. This is best effected in
Ludwig's recipient. This recipient is a tube closed at one end
and furnished with a Geissler's stopcock having a remarkably
large way. The tube is inverted over mercury, with the stop-
cock open, and the blood allowed to flow directly from the ves-
sel into it until it is nearl}7 filled. It is then closed by the hand,
defibrinated by vigorous shaking with mercury, and replaced
in the trough. The stopcock is now closed, and the tube, from
which the blood contained outside of the stopcock has been
washed, is united with the recipient of the pump by an India-
rubber joint. To carry out this method, Sprengel's pump is
scarcely applicable ; for, inasmuch as the process of exhaustion
cannot be begun until the connection is made, a long time must
elapse before the tap can be opened. Blood alters so rapidly
after removal from the body — the oxygen diminishing, the car-
bonic acid increasing — that if much time is lost the results are
of little value.

30. Method of Analysis. — In France most of the analy-
ses which have been published by Bernard and his pupils have
been made by a method which, although rapid, is inexact. In
Germany the analyses of Ludwig and his pupils, as well as
those of Pfliiger, have been made according to the accurate
methods first introduced by Bunsen, and commonly known by
his name. Bernard's method is practised in the physiological

BY DR. BURDON-SANDERSON. 211

laboratory of the Jardin des Plantes, in Paris. The analysis
is made in a circular mercurial trough, in the centre of which
is a well sixteen inches deep, and large enough to contain
about 12 lbs. of mercury. The gas having been transferred
from the tube in which it is collected from the pump, to a
eudiometer, the latter is plunged into the mercury, in order
that its contained air may acquire the temperature of the
metal. It is .then raised with the aid of a wooden tube-holder
until the level of the mercuiy inside is the same as that out-
side. The quantity of gas having been measured, a fragment
of caustic potash is introduced, which rapidly dissolves in the
few drops of water which always float on the surface of the
mercury. The column of mercury is then gentty agitated by
alternately raising and lowering the eudiometer, which, after
the completion of absorption, is again plunged into the mercury.
The gas having been again measured, about a centimetre of
strong solution of pyrogallic acid is introduced with the aid
of a pipette with a bent beak. The agitation is repeated and
continued for some time. As soon as the absorption of the
ox}Tgen appears to be complete, the tube is transferred to a
basin containing water, into which the mercury with the pyro-
gallate of potash is allowed to fall. The residue, consisting of
nitrogen, is read over water. The results obtained by this rough-
and-ready method must necessarily be erroneous, not only be-
cause the measurements are inaccurate, but because the absorp-
tions must always be incomplete. If, however (as in certain
pathological inquiries), it is more important that the analy-
ses should be numerous than that they should be exact, it may
be available. For class illustrations of the general nature of
the blood gases, it is completely adapted.

For more exact purposes the process of gas analysis has
been during the last few years much shortened by Frankland,
Russell, and others. With a view to the analysis of the gases
of drinking water, Frankland has introduced an apparatus of
great simplicity (see Fig. 200), the working of which will be
readily understood by the diagram. It consists of two parts,
viz., a laboratory tube (&), in which the gas to be analyzed is
first received, and a measuring apparatus to which it can be
transferred from the laboratory, in order that its volume may
be determined before and after each absorption. The measur-
ing apparatus consists of two tubes (a, 6), fixed vertically side
by side in a stand, surrounded by a chamber containing
water (n). They communicate below both with each other
and (by the long flexible tube) with a mercury-holder (t), like
that of Alvergniat's pump. One of them can be brought into
communication by the arm (g) with the laboratory tube ; the
other (b) is open at the top. A scale of millimetres is en-
graved on it, the zero of which is opposite o. A corresponding

212 THE BLOOD.

scale, starting from a zero at the same level, is engraved on
the measuring tube. The apparatus is filled with mercury by
raising the mercurj'-holder (/) to a sufficient height, the stop-
cock (f) remaining open ; in doing which the surface of the
mercury in t must not be more than a few millimetres higher
than the tap. As soon as the mercury appears at g, the stop-
cock is closed. The next step is to fill the laboratory tube.
Having inverted it in the trough, which has been previously
raised to the proper height, the operator draws out most of
the air by means of a bent tube, the point of which rises to
the top of the laboratory tube, and shuts the stopcock as soon
as the mercury rises. The removal of the air is completed by
joining g and g' so as to connect the laboratory tube with the
measuring apparatus, and then causing the air contained in
the former to pass over into the latter, by depressing t. The
stopcock h must now be closed and g and g' disconnected to
allow of the expulsion of the air from a. This having been
accomplished, g and g' are again brought together and care-
fully secured. The whole apparatus is now full of mercury ;
as soon as it has been ascertained that the joint is air-tight at
all pressures, it is ready for use. Before proceeding further,
however, the measuring tube, which, as already stated, is
graduated in millimetres measured from an arbitrary zero line
near the bottom, must be calibrated. In other words, it must
be ascertained as regards each principal mark of the gradu-
ation, what volume of air or water (as the case may be) the
tube contains, when the upper convex surface of the mercury
stands exactly level with it. For this purpose the orifice a is
connected by means of an India-rubber tube with a reservoir
(a funnel) containing distilled water. The mercurial column
is then allowed to descend until it stands exactly at zero. A
weighed beaker having been then placed under a, water is ex-
pelled till the column stands at a height of fifty millimetres,
and the beaker again weighed. In a similar manner the out-
flow of water corresponding to a rise of the mercurial column
from fifty to one hundred millimetres is determined, until the
capacit}' which corresponds to each fiftj' millimetres of the
scale is ascertained. To insure accuracy', the process must be
repeated several times. If the results, after correction for
difference of temperature, are in close accordance, the means
may then be taken as expressing the capacities required. In
the upper part of the tube, calibration must be made at short-
er intervals. In calibrating, as in all subsequent measure-
ments, the height of the column must be read horizontally
through a telescope, so adjusted that its axis is at the same
height as the surface of the mercury. The temperature is
read by a thermometer suspended in the cylinder of water by
which the barometer and measuring: tube are surrounded.

BY DR. BURDON-S ANDERSON. 213

31. Introduction of the Gas to be Analyzed. — The

measuring and laboratory tubes having been brought into con-
nection in the manner described above, and both filled with
mercury, the gas to be analyzed is introduced into the labo-
ratory tube from the test tube to which it has been discharged
b}7 the Sprengel. It is then at once transferred to the mea-
suring tube by depressing t until the mercury rises in the
laboratory tube as far as the stop-cock g'. This done, the
stop-cock g is closed, and t raised or depressed till the column
stands at one of the marks of the graduation, in reference to
which the capacity of the tube has been determined. The
temperature is then observed, and the pressure determined by
adding the difference between the height of the column in the
measuring tube and that in the pressure tube, to the reading
of a barometer which stands by. A few drops of solution of
caustic potash having been introduced into the laboratory
tube, the gas is returned from the measuring tube. Absorption
takes place rapidly. It is accelerated by slightly agitating the
trough, and by allowing the mercury to stream into the labo-
ratory tube after the gas has passed. The measurement of
the gas after absorption is performed in the same manner as
before. About half a centimetre of strong solution of pyro-
gallic acid is then introduced in the same way as the potash,
and the gas again returned. After absorption of the oxj'gen,
what remains is nitrogen. In analysis of blood gases, the
proportion of nitrogen is nearly constant, viz., about 2.5 vol-
umes in 100 volumes of blood. If a larger quantity is obtained,
the fact indicates that air has entered. Whatever method of
analysis is employed, the results must be reduced to 0° tem-
perature and 760° millimetres pressure — t. e., they must be
expressed as if the measurements had been made under those
conditions. A further deduction must be made from each
measurement in respect of the aqueous vapor which the gas
contains (the measuring tube being always moist). This is
accomplished by the following well-known formula : —

v = J!_ H'-/

1 + t 0-00367 760

V denotes the corrected volume; V the volume read; t the
temperature; H' the observed pressure; and f the tension of
aqueous vapor at the temperature t. The values of 1 -f t 0.003G7
and / are always obtained from tables. For these, and many
other important practical details relating to the performance
of gas analysis, the reader is referred to Mr. Sutton's " Volu-
metrical Analysis,'' whom I have to thank for two of the
woodcuts with which this section is illustrated. To illustrate
the application of the method to the analysis of the gases of
the blood,! give the following example: —

214

TIIL BLOOD.

Analysis of Gases of Arterial Blood of Dog.

2d Measurement

1st Measure nt.

After absorption

.'id Measurement.

Total quantity

of carbonic acid

After absorption

of gas extracted.

gas,

of oxygen.

Height of column in measur-

ing-tube

230.0

270.0

450.0

Height of column in pres-

sure-tube

312.8

369.0

320.0

Difference

82.8

99.0

—130.0

Reading of barometer

7G4.0
846.8

764.0

764.0

H'=

863.0

634.0

Tempcrature=19.8°C.=t.

Tension of aqueous vapors

from table=f=

17.2

17.2
845.8

17.2

H'— f=

829.6

626.8

Volume of gas as measured

in cubic centimetres=V —

11.822

3.865

0.562

1 + t 0.00367 (from table)
Hence from the first measurement we have —
11.822 829.6

1.0725.

V =

V.

1.0725

From second measurement —
3.865
1.0725 '
From third measurement —
y 0.562

760

845.8

= 12.030.

760

= 4.010.

626.8

= 0.432.

1.0725 760

Thus the total volume of gases obtained as measured at 0° C.
and 760 in. m. was 12.030 cubic centimetres ; of carbonic acid
gas was 12.030 — 4.010 = 8.02 c. c.; of oxygen 4.010 — 0.432 =
3.578 c. c, and of nitrogen 0.432 c. c.

As the volume of blood employed was 20.266 cubic centime-
tres, we have the following final result : —

In 100 volumes of blood —

Carbonic acid <^as 39.585 volumes

8.020

Oxygen
Nitrogen

Total

17.652

2.138

59.375

0.20266
3.578

0.20266
0.432

0.20266
12.030

0.20266

(=

vols.

vols.

vols.

vols.

BY DR. BURB-ON-SANDERSON. 215

In the preceding example such variations of temperature
and barometric pressure as may occur during the analysis are
disregarded. The readings are taken immediately after the
absorption of the carbonic acid gas ; as the time occupied in
the analysis up to this point is very short, the error arising
from the variations in question is inconsiderable. As regards
the absorption of oxygen, the error might be of more conse-
quence, were it not that the residue of nitrogen is so small.
As it is, it can be easiljr shown that it would require a differ-
ence of pressure amounting to three millimetres, and a dif-
ference of a degree of temperature, to make an error of one-
hundredth of a percentage in the result as regards nitrogen or
oxygen. Within these limits, therefore, the errors arising from
this source may be regarded as trivial.

Although determinations of oxygen made by absorption
with hydrate of potash and pyrogallic acid are not entirely
free from objection on the score of accuracy, the results ob-
tained by the method above described are quite accurate enough
for most of the purposes of physiological research, for the small
errors are practically inappreciable, as compared with the varia-
tions hi the proportion of oxygen contained in the blood to be
analyzed, produced by what might be regarded as very trifling
differences in the mode of collecting it. If it is desired to have
recourse to explosion with hydrogen, the best methods for the
purpose are those of Dr. W. Russell, and of Frankland, and
Ward. The following short description of the latter will be
readily understood from what has preceded. The apparatus
(Fig. 201) consists of two parts, corresponding to the labora-
toiy-tube and measuring-tube of the instrument previously de-
scribed. The measuring-tube communicates, as in that instru-
ment, with a second tube (the one most to the right in the
figure) containing a column of mercury, by the height of which
the pressure to which the gas to be measured is subjected, can
be estimated. The chief difference is that, whereas in the for-
mer more simple instrument the pressure-tube is open at the
top, so that if air is contained in the measuring-tube, and the
stopcock by which it communicates with the laboratory-tube
is closed, the difference between the heights of the two columns
indicates the difference between the tension of the gas in the
measuring-tube and that of the atmosphere; in the instrument
now before us the tube is closed, and constitutes a barometer,
so that the difference expresses the actual tension of the gas in
inches of mercury. In the horizontal channel, by which the
measuring-tube and barometer communicate at the bottom, is
a three-way stopcock (not shown in the figure), by which they
may lie brought into communication cither with a vertical
escape-tube, the end of which dips into a receptacle containing
mercury several feet below, or with a tube open at the top (the

216 THE BLOOD.

middle and longest in the figure), called the filling-tube. In
this way the gas can be expanded or compressed at the will of
the operator, and consequently can (in most analyses) be
readily brought to the same volume after each successive ope-
ration. The convenience of this is very great, for obviously
the tensions of different quantities of gas when expanded to
the same volume are proportional to the volumes they would
assume if they were all under the same pressure, so that the
original volume of gas to be analyzed being known, the rela-
tion between that volume and the volume of the other quanti-
ties to be measured can be readily calculated, the several vol-
umes being proportional to the corresponding readings of the
barometer. The original volume of gas to be analyzed is mea-
sured as before described, with this difference, that the absolute
pressure to which it is exposed is known without reference to
the barometric pressure outside at the time. The explosion is
effected in the eudiometer, into the upper end of which two
platinum wires are fixed for the purpose ; the arrangement of
these wires is the same as in Bunsen's eudiometer. As to the
mode of preparing and introducing pure hjdrogen, and of ex-
ploding the mixture, the reader will find sufficient information
in Roscoe's translation of Bunsen's Gasometry.

32. Bernard's Method of Determining the Propor-
tion of Oxygen combined "with the Coloring Matter
of the Blood by Displacement with Carbonic Oxide. —
As was before stated, the property which carbonic oxide pos-
sesses of displacing the oxygen combined with the coloring
matter of the blood, has been used by Bernard, as a substitute
for the vacuum, for the determination of the quantity of free
and combined oxygen contained in the blood. Bernard's
-method consists in agitating the. blood to be analyzed in a
tube half filled with carbonic oxide. The carbonic oxide to be
used must be perfectly pure. The tubulated retort into which
the oxalic and sulphuric acid are introduced must l>e cleared
of atmospheric air, by passing a stream of carbonic acid
through it, before heat is applied. The gas is best collected
in flasks, over water containing potash in solution. Two re-
sults are produced. In the first place, the oxygen of the hae-
moglobin is replaced by cai'bonic oxide ; and, secondly, the
atmosphere of carbonic oxide acts on the blood as if it were a
vacuum, the displaced oxygen and other gases passing out
into it until equilibrium is established. Inasmuch as the pro-
portion in wdiich oxygen is absorbed is very small, as com-
pared with the quantity held in combination by haemoglobin,
nearty the whole is discharged, so that if the proportion of
that gas contained in the gaseous mixture which fills the place
originally occupied by the carbonic oxide be determined, it is
found to fall very little short of the proportion obtained from

BY DR. BURDON-S ANDERSON. 217

the same blood by exhaustion. The remainder of the mixture
contains, in addition to the excess of carbonic oxide, nitrogen
and carbonic acid gas, derived from the blood, but the propor-
tions of these gases discharged are very variable. As regards
oxvgen, the method has yielded, in the hands of Bernard, re-
sults of the greatest value. It has the immense advantage
that it can be carried out without a mercurial pump, and for
pathological purposes is sufficiently accurate.

CHAPTER XVI.

THE CIRCULATION OF THE BLOOD.

In commencing the study of the circulation of the blood, it
is desirable to direct our attention first to that part of the
circulatory apparatus in which the phenomenon presents itself
in its simplest form. In systematic physiological treatises the
heart is usually described first; but for our present purpose,
considering that the heart is an organ of very complicated
structure, that it is constantly influenced by ever-varying
conditions of the vessels on the one hand, and of the nervous
centres on the other, it is much better to begin with the
arterial system.

Part I The Arteries.

At the commencement of the period of relaxation of the
heart — t. e., of the period which intervenes between one con-
traction and its successor — the progressive movement of the
blood in the aorta all but ceases. At that moment, and during
the remainder of the time which precedes the bursting open
of the aortic valve, the pressure exercised by the wall of the
vessel on its contents is the only cause of the continuance of
the blood-stream. During each ventricular systole the aortic
pressure is reinforced by the motion communicated to the
blood by the contracting ventricle. Consequentl}', if, for the
sake of facilitating our understanding of the matter, we
assume the heart to be a mere pump, acting regular^, and
discharging at each stroke an invariable quantity of liquid, we
have the force by which the circulation is carried on at any
moment expressed by the tension of the arteries, and varying
with that tension; or if, on the other hand, we assume the
tension of the arterial system to remain constant, then the
quantity of work done varies with the mean velocity of the

218 CIRCULATION OF THE BLOOD.

stream at the commencement of the aorta — in other words,
with the quantity of blood delivered by the heart per minute.
The work done by the heart in maintaining the circulation,
manifests itself in the aorta in two modes, those of pressure
and progressive motion of the blood. These two phenomena
are not, however, collateral results, i. e., they do not stand in
the same relation to the agent which produces them. The
former is rather the efficient cause of the latter; for so long
as the arterial pressure continues, i. e., so long as the pressure
in the aorta is greater than that in the vense cava*, progressive
movement also continues. As soon as equilibrium is estab-
lished, circulation stops. Systemic death consists in decline
of aortic pressure. This decline may occur rapidly, as in
syncope ; but usually, even in deaths by violence, it is very
gradual. In deaths from disease it may last for days, weeks,
or even months.

Section I.— Arterial Pressure.

33. The arterial pressure, although in the mean remarkably
constant, almost as constant as the temperature of the body,
is subject to recurring variations — ?'. t?., alternate augmenta-
tions and diminutions, which are of three orders. Of these,
the first is dependent on the rhythmical injection of blood into
the arteries by the contraction of the heart ; the second, on the
influence which the respiratory movements, or rather the alter-
nate acts of breathing, exercise on the circulation; the third,
on augmentations or diminutions of what is called the tonus of
the arteries, by virtue of which they are constantly undergoing
changes of diameter, consequent on varying conditions of the
nervous system.

In the measurement of the arterial pressure we have, there-
fore, two distinct problems. The first is the determination of
the mean or average pressure, which, as I have said before, is
almost as constant as the temperature in the same animal so
long as it remains in a natural state; the second is the investi-
gation of the variations due to the heart's action, to respira-
tion, or to arterial contractility, respectively.

For the determination of the mean arterial pressure, and of
those variations which belong to the secontl and third class,
preference is to be given to the ordinary mercurial manometer,
one branch of which is connected with the artery to be investi-
gated, while the other is open. This instrument, as so applied,
constitutes what Poiseuille designated by the term hsemadyna-
mometer. It was employed in this simple form until Ludwig,
in 1848, by his invention of the kymograph, laid the foundation
of the more exact methods of investigating blood-pressure
which are now in use. Just as the first method of Poiseuille
originated in the ruder experiments of our countryman Hales,

BY DR. BURDON-SANDERSON. 219

so the notion of the kymograph is said to have been suggested
by a contrivance of Watt's for registering the pressure of the
steam-engine.

The principle of the kymograph consists in causing a pen,
fixed horizontally at the upper end of a vertical rod, the lower
end of which rests by a floating piston on the surface of the
mercurial column in the distal open limb of the manometer, to
write the up and down movements of the column on a surface
of paper progressing horizontally at a uniform rate by clock-
work. Since the time that Ludwig first employed it, the con-
trivance has developed into a method now commonly known as
the graphic method.

Description of the Kymograph and Accessory Ap-
paratus now used in the Laboratory of University
College.1 — 1. The arterial canula is a T-shaped tube of glass,
of the size and form shown in fig. 193, c. By its stem it is con-
nected with the manometer; one branch is drawn out and
bevelled, the other is of the same size as the stem, and when in
use is fitted with a short bit of caoutchouc tubing, guarded by
a steel clip.

The canulated end is made as follows: The tube which it is
intended to use for the purpose is first softened in the flame of
the gas blow-pipe, and drawn out gently at the softened part.
It is then allowed to cool, and again heated in a pointed flame
at x, and drawn out so as to make it assume the form 193, b.
It is then scratched with a sharp three-cornered file opposite
x, and sundered by drawing the one end of the tube from the
other in the direction of its axis. The last step in the process
consists in filing off the cut end in the direction of the dotted
line, and smoothing the edges b}r touching them with the
border of an ordinary gas flame. A tube of this kind can be
inserted with great ease into an artery of considerably less
diameter than itself. Canulae of glass are always to be pre-
ferred to those of silver, not merely on the ground of facility
of introduction, but because a glass surface is much less apt
than one of metal to determine coagulation of the blood which
comes into contact with it.

2. The stem of the arterial canula communicates with the
proximal arm of the manometer (see fig. 202) by a tube (c), of
which the part next the canula only is of India-rubber. The
rest is of lead; the purpose of the arrangement being to avoid
a certain modification of effect due to the yielding of the wall
of the tube, which becomes appreciable if the whole connector
is elastic.

1 This instrument was made for me by Mr. Ilawksley, of Blenheim
Street, and has advantages over any other form with which I am
acquainted.

220 CIRCULATION OF THE BLOOD.

3. The proximal arm of the manometer communicates at its
end, by means of along flexible tube (b) guarded by a clip, with
a " pressure bottle" containing solution of bicarbonate of soda.
A horizontal arm, which springs from it near the top, is con-
tinuous with the lead tube already mentioned.

4. The manometer is fixed to the edge of the small mahogany
table on which the recording apparatus stands by means of
a brass clamp, which admits of its being raised or lowered at
will. The floating piston and rod (a) are made of black vul-
canite. The piston is in the form of an inverted cup, which
embraces the convex surface of the mercurial column. The
rod is quadrangular, and works in a guide, fixed at a height of
six inches above the upper end of the tube, b}r which it is kept
vertical. The writer, a fine sable miniature pencil, is supported
on the rod by a horizontal arm of thin wire, one-third of an inch
in length. One end of the wire is coiled round the rod, the
other round the stem of the pencil. From the guide just men-
tioned springs a horizontal arm, from which a silk plummet-line
is allowed to fall in such a way that it rests against the hori-
zontal part of the wire. By this means the point of the writer
is kept in constant contact with the paper, without exercising
too much pressure.

G. The recording apparatus consists of a single cylinder,
which revolves at a constant rate of one revolution per minute.
The clock-work by which it is moved is constructed b}' Mr.
Hawksley on the model of the so-called " Foucault's Regula-
tor." To the right of the cylinder, as seen in the drawing, is
shown a large brass bobbin, of the same width as the cylinder,
on which a riband of paper is tightly rolled b^y machineiy, of
sufficient length to serve for many hundred observations.
From the bobbin the paper riband is drawn off by the cylinder
as it revolves, against the surface of which it is accurately
applied, furnished with ivory friction wheels.

34. Rules and Precautions to be observed in mak-
ing a Kymographic Observation. — Before commencing,
it is necessaiy to see that the manometer is in proper order.
The mercury in the distal column must be clean and dry, and
the writing pencil moist and free from the remains of the ink.
To insure this, it should always be steeped in water after each
observation.

To dry mercury, the best Swedish filtering paper is used.
It is cleaned by straining it through calico, or still better
through chamois leather. If the latter is used, it must be
strained under a considerable pressure. The system of tubes
communicating with the proximal limb of the manometer
must now be filled with solution of bicarbonate of soda. To
accomplish this, the arterial tube is first closed by a clip, and
the solution introduced with the aid of a pipette into the open

BY DR. BURDON-SANDERSON. 221

end of the proximal limb. Some of the solution is then
allowed to flow from the bottle by the long communicating
tube (b) so as to fill it completely, after which its end is
brought into communication with the manometer. If any air
bubbles are introduced, they are readily got rid of through
the artery tube. According to the height to which the press-
ure bottle is raised above the level of the manometer, the
mercurial column in the distal limb rises above that in the
proximal. It must be adjusted so that the difference between
the two is a little less than the probable arterial pressure of
the animal to be used. This having been accomplished, and
the communication between the manometer and the pressure
bottle closed, all is ready.

The only arteries which are used for observations of arterial
pressure are the carotid and the crural. On the whole, the
latter is preferable ; for the carotid cannot be exposed without
some risk of disturbing the vagus nerve. In the rabbit, the
carotid is prepared as follows : The animal having been
secured on Czermak's rabbit-board, and the fur clipped, the
skin is pinched up between the finger and thumb on either
side of the upper end of the trachea, so as to form a horizontal
fold, which an assistant divides vertically. As soon as any
slight bleeding has ceased, the wound is dabbed with a sponge
moistened with saline solution, and the fascia, which stretches
from the edge of the sterno-mastoid to the middle line, is
seized with blunt forceps and opened with knife or scissors.
The opening having been enlarged with the aid of a second
pair of blunt forceps, the sterno-mastoid is slightly drawn
aside, so as to bring the artery, with its three accompanying
nerves, the vagus, the depressor, and the sympathetic, into
view. The sheath having been opened, the artery is raised on
a blunt hook, and easily cleared from its attachments to a
distance of three-quarters of an inch in either direction. The
distal end of the prepared part is tied, and the proximal end
closed by a clip. A splinter of wood, or a bit of card of
similar shape, is slipped under the artery close to the ligature,
and a second ligature looped round it. Finally a V-shaped
snip is made in its wall with scissors which cut well at the
point ; the canula is inserted, and the ligature tightened round
the constriction. The whole operation ought to be accom-
plished in three minutes ; it is desirable to have an assistant.
The instruments required are indicated by the italics. (See
fig. 203.) They must be placed in readiness on the table of
the kymograph. Czermak's rabbit supporter is shown in fig.
204. It consists of a strong wooden board, about 8 inches
wide and 30 inches long. At one end it is strengthened with
an iron plate, into which a strong vertical stem is screwed.
This stem bears a sliding block of brass, in which an iron rod

222 CIRCULATION OF THE BLOOD.

also slides horizontally. Near its base it is bent twice at
right angles, so that the upper part on which the block slides
is not in the same line with the lower part. Consequently the
rod, while still remaining horizontal, can be moved in four
different ways. It can be shortened or lengthened, heightened
or lowered, rotated round its own axis, rotated round the axis
of the stem, or moved from side to side without change of
direction. It ends in a kind of forceps the blades of which,
when kept closed by the adjusting screw, seize upon the head
of a cat or rabbit in such a manner as to hold it firmly without
inflicting the slightest injury. The neck of the animal rests
on a cylindrical cushion, covered with water-proof cloth, and
the rest of the body on a mattress of similar material. Along
the edges of the board there are convenient attachments for
the extremities.

The preparation of the crural artery is even more simple than
that of the carotid. The skin having been divided in a line
leading from the middle of Poupart's ligament towards the inner
side of the knee by first pinching up a fold of skin as above
directed, the pulsation of the artery is felt by the finger in the
hollow between the adductor muscles and those which cover the
femur. The sheath of the vessels having been exposed from
Poupart's ligament downwards, the vein and crural nerve are
seen, the artery lying behind and to the outer side of the former.
On drawing the vein inwards it is easily got at, and must he
prepared from the origin of the arteria j)rofunda close to Pou-
part's ligament, nearly to the point at which it enters the ad-
ductor ; first giving off the arteria saplwna, which accompanies
the saphenous nerve and veins. The lower of the two circum-
flex arteries which are given off within a short distance from
the profunda must be tied doubly and divided hetween the liga-
tures, as it is desirable to place the clip as high as possible.
In the dog or cat, the operation is equally simple, but requires
more time on account of the greater abundance of fat in these
animals.

The canula having been inserted, the next step is to bring
the artery into communication with the manometer. The clip
on the artery remaining closed, that on the stem of the canula
is opened for a couple of seconds. At once the soda solution
fills the canula and passes out bj' its open branch. In doing
this, great care must be taken not to allow the solution to flow
into the wound. Air bubbles, if they exist, are got rid of by
passing a thin rod of whalebone into the canula, which must
then be closed by means of the terminal clip. All being now
ready, the stem of the canula is finally opened, and the clip re-
moved from the artery. The mercurial column at once begins
to oscillate ; but no record should lie taken until a minute or
two have elapsed, for it often happens that a small quantity of

BY DR. BURDON-S ANDERSON. 223

soda solution enters the artery and produces a slight and transi-
tory disturbance of the circulation. If, indeed, the previously
existing pressure in the artery tube is somewhat less than that
of the artery, no such effect occurs; but inasmuch as we have
no means of knowing the arterial pressure of any particular
animal beforehand, it is usually unavoidable.

A kj-mographic observation may last a few minutes or several
hours, according to the question to be investigated. In the
latter case, tracings are taken at intervals. Two persons are
required, one of whom performs the experiment, while the other
undertakes the charge of the writing apparatus, and notes on
the paper-roll, with a soft pencil, the events as they occur and
the times of beginning each tracing. In this wa}- the roll
stands in the place of a protocol, and is less liable to errors of
'time and order than any other kind of record.

35. Measurement of absolute Arterial Pressure at
any given moment during the period of observation.
— For this purpose it is necessary to draw the abscissa of the
pi*essure curve, i. e., the horizontal line which the writer would
have drawn had the arterial pressure been equal to that of the
atmosphere. This is accomplished immediately after the ter-
mination of the experiment, by closing the stem of the canula
and then removing it from the artery, and immersing it iu a
capsule containing soda solution, standing at a level equal to
that of the artery. The clip having been opened, the clock-
work is set in motion for a moment, and a horizontal line drawn
which coincides with the abscissa required. In this line the
paper is then pierced with a pointed instrument in such a wa}r
as to perforate the several layers of paper at the same level.
By removing the roll from the cylinder and connecting the
holes, a horizontal straight line is obtained which runs from
end to end of the record. By drawing an ordinate from any
point in the tracing to this line, measuring its length in milli-
metres and doubling the result, the absolute arterial pressure
at the corresponding moment is obtained in millimetres of
mercury.

The mean arterial pressure is obtained by drawing ordi-
nates at regular intervals and measuring the length of each.
The mean of the lengths corresponding to the period investi-
gated, multiplied by two, is the mean pressure required. [I
never use paper divided into squares — in other words, with the
ordinates ready measured — finding by experience that they do
not tend to accuracy. Moreover, such paper is expensive, and
thereby furnishes an inducement for an undesirable economy
in its use.] In all normal kymographic records it is seen that
the arterial expansions due to the contractions of the left ven-
tricle are indicated by oscillations which differ very materially
in form, and that these differences are dependent on their fre-

224 CIRCULATION OF THE BLOOD.

qucncj\ (See Fig. 206.) When extreme]}- frequent, they are
mere undulations; but when the intervals are longer, they ex-
hibit forms which, as we shall afterwards see, have a definite
relation to the changes of tension which actually occur in the
arteries during each cardiac period. It is further seen that
there are larger waves which correspond, not to the beats of the
heart, but to the respiration — the valley and ascending limb
of each of these greater undulations corresponding to inspira-
tion, the summit and descending limb to expiration and to the
pause. These and other details will be referred to in future
sections.

Section II. — Observation op the successive Changes of Arte-
rial Tension wnicn occur during each Cardiac Period.

In studying tracings obtained by the mercurial kymograph,
it is to be borne in mind that what is inscribed on the cylinder
is not the record of the actual movement of the artery, but of
the oscillations of the mercurial column. It is true that the
latter are the immediate results of the former, and that the
elevation of the distal column produced by each arterial ex-
pansion has some relation to the increase of lateral pressure,
of which the expansion is the expression ; but the curve drawn
is not that#of the arteiy, but of the manometer. The artery
expands suddenty, the mercury rises comparatively slowly, so
that at the moment it attains its acme the artery has already
collapsed. Consequently, if the interval between each pulsa-
tion and its successor is very short, the extent of oscillation
(or, as it is usually called, the excursion) of the manometer
is relatively too small ; and converse^*, if the interval is much
prolonged, the excursion is relatively too great. The descent
of the column is almost entirely independent of the collapse
of the artery. It falls back to equilibrium, and describes a
curve, which (as may be learnt by comparison) has the same
characters as that made by the lever in returning to its origi-
nal position, by whatever wa}T — as, e. g., by squeezing the con-
necting-tube— the equilibrium of the manometer may have been
momentarily disturbed.

This being the case, it is eas}' to understand that no conclu-
sion can be derived from observations with the mercurial mano-
meter, either as to the duration of the effect produced by each
contraction of the heart, or as to the relative duration of the
periods of expansion and collapse. The use of the instru-
ment is limited to the investigation of the mean pressure, and
of those varieties of pressure of which the periods of recur-
rence are long enough to prevent their being interfered with
by the proper oscillations of the instrument.

BY DR. BURDOX-SANDERSOX. 225

36. The Spring Kymograph. — If we desire to obtain a
record of the complicated succession of variations of arterial
pressure which constitute an act of pulsation, precisely as
they occur as regards order, duration, and degree, or of the
exact interval of time between the close of one arterial expan-
sion and the commencement of the next, the instrument with
which we write must be of such a nature that it shall transmit
the movements communicated to it without mixing with them
any movements of its own. The most perfect of such instru-
ments is the so-called Federkymographion of Professor Fick.
The construction of the instrument will be readily understood
with the aid of Fig. 205. It consists essentially of a C-shaped
hollow spring of thin metal. The cavity of the spring is filled
with spirits of wine, and communicates with the arteiy by means
of a connecting-tube containing bicarbonate of soda. As the
pressure increases, the crescentic spring tends to straighten,
and vice versa. Hence, if the proximal end is fixed, the distal
end performs movements which follow exactly the variations
of arterial tension. These movements are of very small ex-
tent, but they are so exact that the slightest and most transi-
tory variations are expressed by them. Before they are writ-
ten on the cylinder they must be enlarged by a lever.

It is not necessary to make any remarks as to the mode of
connecting the spring kymograph with an artery, the modus
operandi being the same as that described in § 34. It is, how-
ever, to be noted, that if it is intended to use the tracing ob-
tained by it for the purpose of determining the absolute arte-
rial pressure, the instrument must be first graduated by com-
parison with a mercurial manometer. This is effected as
follows : The kymograph being placed so as to write on the
recording cylinder, its artery tube, which communicates by a
side opening with a pressure bottle, is united with the proxi-
mal arm of the manometer. The pressure bottle is first
lowered until the liquid it contains stands at the same level
as the mercuiy in the proximal arm. A tracing is made on
the cylinder, which is the abscissa. The bottle is then raised
till the distal mercurial column is ten millimetres higher than
the proximal, and a second tracing taken, and so on at suc-
cessive increments of 10 mill, pressure, up to 150 mill, or
more. LJy measuring vertically the distances in millimetres
between the horizontal lines so traced and the abscissa, a
series of results are obtained which express the values of the
ordinates of the tracing in millimetres of mercurial pressure.

In tracings obtained by the spring kymograph it is seen
that the ascent of the lever, which corresponds to the period
during which the artery is acted on by the contracting ven-
tricle, is abrupt — indeed, nearly vertical ; that towards the
vertex the tracing changes direction, gradually approaching
15

22«3 CIRCULATION OF THE BLOOD.

a horizontal line touching it at the highest point; that the
line of descent — much more oblique than that of ascent — ter-
minates in the same way by gradually approaching a horizon-
tal line touching the curve at its lowest point. (See fig. 207.)

37. Observation of the Expansive Movements
■which accompany the successive Changes of Arte-
rial Pressure above described. — When an artery is ex-
posed in a living animal, as, e. ;/., when it is prepared in the
manner described in § 34, two kinds of motion are seen. The
bit of artery which is separated from the surrounding parts
lengthens, and its diameter visibly increases each time it is
acted on by the contracting heart. Of these two phenomena,
the first is commonly called locomotion, because in certain
superficial arteries of the human bod}- (especially when 1 1 1 c- v
are enlarged in advanced life), the artery, as it lengthens, is
compelled to bend to one side or the other, and thereby
visibly changes its place each time that it is distended. The
other, viz., the expansive movement, is called pulsation, and
is practically of great importance, seeing that it is the only
phenomenon of the arterial circulation which admits of being
investigated without exposing the artery, and consequent!}7
affords the only direct means by which we can judge of its
ever-varying conditions in man.

Arteries being elastic, their changes of diameter express all
changes of the pressure exercised by their liquid inelastic con-
tents on their internal surfaces. J f. therefore, the expansive
movements of an exposed artery were to be measured and re-
corded graphical^7, the record would correspond closely with
that of the pressure obtained by Fick's k3Tmograph. For just
as in that instrument the variations of pressure are converted
by the C-shaped spring into nearl}' rectilinear movements, the
artery expands with every increase of pressure on its internal
surface, and contracts with eveiy diminution of it, so that any
point taken on its surface is constantly performing, in relation
to its axis, orderly successions of rectilinear movements in
opposite directions.

In both cases — that of the spring and that of the arteiy —
the expansion, and the pressure which produces it, vary in
the same directions during the same times, but not in the same
degree. As regards the spring, we can readily determine the
relation of expansion to pressure by the method of graduation
described in the preceding paragraph, and so use the former
as an expression for the latter. In the case of the artery, no
such empirical graduation is possible. The expansion of an
artery, or any other elastic tube, due to any given increase of
pressure against its internal surface, depends upon the degree
in which the tube is already distended at the commencement
of the act of expansion. The greater the original distension,

BY DR. BURDON-SANDERSON. 227

the less will be the effect ; so that the condition of an artery
in which the expansive movement is relatively greatest, is that
in which its walls, when the expanding agency is suspended,
are in the state of elastic equilibrium, i. e., when the minimum
pressure is least. A moment's consideration teaches us that
there are two circumstances which must diminish the minimum
pressure in the arteries, viz., diminution of the mean arterial
pressure, and prolongation of the period which intervenes be-
tween one expansive act and its successor. In other words,
the less frequent the contractions of the heart and the lower the
arterial pressure, the greater the expansion in proportion to
the expanding force which produces it.

38. The Sphygmograph. — In man, no artery can be di-
rectly measured either as regards pressure or expansion. In
feeling the pulse, we attempt to measure both by the sense of
touch, and obtain results, which, although incapable of nu-
merical expression, are sufficiently exact to be of great value.
In the sph\-gmograph, an attempt has been made to obtain the
same kind of information by a mechanical contrivance, which
the physician obtains by the tactus eruditus ; the supposed
advantage of the instrumental results over the others being,
that they can be estimated by measurement and weighing, and
that they are unaffected by variation in the skill and tactile
sensibility of the observer.

The purpose of the sphygmograph is to measure the com-
plicated succession of alternate enlargements and diminutions
which an artery undergoes whenever blood is forced into it
b}r the contracting heart, to magnify those movements, and to
write them on a surface, progressing at a uniform rate by
watch-work.

The construction of the instrument is so well known, that
it is scarcely necessary to give a detailed description of it. It
consists essentially of three parts: a frame of brass which is
applied along the outer edge of the volar aspect of the fore-
arm, in such a way that it is maintained in a fixed position
with reference to the bones of the wrist and radius — a steel
spring which, when the instrument is in use, presses upon the
radial artery and receives its movements — and lastly, mechani-
cal arrangements for magnifying these movements and record-
ing them. Both of these ends are accomplished by means of a
light wooden lever (a a', fig. 208) of the third order, which is
supported by steel points (c). There is a second lever of the
same order (b b) which has its centre of movement near the
attachment of the spring (at E). It terminates in a vertical
knife-edge (n),and is traversed by a vertical screw (t). When
the extremity of the screw (\) rests upon the spring above the
ivory plate, every movement of the plate is transmitted to this
lever (b e), and, by means of the knife edge, to the wooden

228 CIRCULATION OF THE BLOOD.

lever (a a'). The purpose of the screw (t) is to vary at will
the distance between the wooden lever and the upper surface
of the spring, without interfering with the mechanism by which
the movement is transmitted. As the distance between the
steel points (c) and the knife-edge (d) is much less than the
length of the lever, the oscillations of the extremity of the
lever (a7) are much more extensive than the vertical move-
ments of the spring. The lever ends in a metal point, which
writes on a glass plate blackened by passing it rapidly back-
ward and forward through the flame of a spirit-lamp trimmed
with paraffin.

When this instrument is applied in the proper manner to
the wrist, the radial artery is compressed between the surface
of the radius and a spring, the bearing of which is in a fixed
position in relation to that surface. This being the case, the
spring performs movements which are more or less conform-
able with the variations of the diameter of the artery. These
movements are transferred in a magnified, but otherwise little
altered, form to the lever. As regards the relative and actual
duration of the movements, the correspondence is exact; but
as regards their extent, this is true only in so far as the lever
follows the movements of the spring with precision,1 and as
the strength of the spring, i.e.., the pressure exercised by it on
the artery, is adapted to the antagonistic pressure exerted by
the blood stream on the internal surface, and to the extent of
the movements it is intended to measure.

The relation between the pressure of the spring and its effect
on the artery is a complex one, and need only be considered
here in so far as is necessary for the interpretation of sphyg-
mographic results. To facilitate our understanding of it, let
us call the position which the spring takes when left to itself
its equilibrium position ; and as regards the artery, let us de-
signate a plane parallel to the surface of the skin, and touch-
ing the surface of the artery, when most dilated, the plane of
expansion; and a plane in similar relation to it, when least
expanded, the plane of collapse ; and to simplify the problem,
let us suppose that the artery is not covered by skin. It is
evident that, if the sphygmograph accomplished its professed
end completeby, the under surface of its spring would coincide
with one of these planes at the moment of the pulse, and with
the other during the interval. The question is, How ought
the spring to be set, in order to obtain a movement which shall
approach this standard of perfection as nearly as possible ?
We may proceed one step towards answering this question
without difficulty. It should be set so that if the spring were
in the equilibrium position its under surface would lie within

1 See note on p. 235.

BY DR. BURDON-SANDERSON. 229

the plane of collapse — i. e., nearer the axis of the artery. For
if it were further from the artery it would be affected by the
arterial movement only during its period of expansion, remain-
ing the rest of the time motionless. If, on the other hand, it
were much nearer, the vessel would be flattened against the
bone during the period of collapse, so that in this case, as in
the other, there would be no motion (of the spring) during
diastole. Hence it is easy to understand how it happens that
the tracings obtained with excessive and defective pressure are
very similar to each other in their general characters. Stating
the same tiling in other words, we arrive at the general rule
that the spring must be so set that the ivory plate on its under
surface is at such a distance from the opposed surface of bone
that the artery is pressed upon at all degrees of expansion, j-et
not so strongly pressed upon as to bring its wails into contact
even when it is relaxed. Within these limits, the variations
of form of the tracing — in other words, its departure from
truth — are very inconsiderable ; so that observations made on
the same individual at different times yield closely correspond-
ing forms. As, however, the results obtained by strong press-
ure are less subject to accidental error than those obtained
with weaker ones, it is better always to begin with a pressure
sufficient to flatten the artery, and then to weaken the spring
until the effects of over-compression disappear — i.e., until it is
found that the lever continues to descend until the very end
of diastole.

39. Use of the Sphygraograph as a Means of Appre-
ciating those Changes of Mean Arterial Pressure
which occur in Disease. — We have already seen that the
sphygmograph is of no use as a gauge of arterial pressure. It
is possible, however, by the comparison of observations made
at successive periods on the same individual, to determine
whether the arterial tension has changed, and in what direc-
tion the change has taken place. We have seen that if the
spring is so strong that the artery is either partially or en-
tirely flattened against the radius, the fact is indicated b}' tire
cessation of the motion of the lever. The strength of spring
which is required to bring about this result varies with the
pressure; by which the artery is distended ; so that if in any in-
dividual the arterial pressure is increased, a greater tension of
the spring is required to compress it than was required before.
With Marey'a sphygmograph, as imported, it is not possible
for the observer to avail himself of this principle, because the
instrument is not graduated — i.e., there is.no means by which
the pressure exerted by the spring at any moment can be ascer-
tained. I have therefore modified that instrument as follows
(see Fig. 20'.». a : The brass frame, instead of being bound on
to the arm by bandages, rests firmly on the bones of the wrist

230 CIRCULATION OF THE BLOOD.

(particularly the scaphoid) by a plate of brass, the under sur-
face of which is covered with ebonite. In the middle of the
upper surface of this plate is a socket for the reception of the
point of a finely-cut screw, which revolves in it freely. Above,
the screw ends in a milled head (y), between which and its
point it passes, first loosely through a guide, which is of the
same piece with the brass plate; and, secondly, through a hole
in the end of the brass frame of the sphygmograph (f), in
which it fits closely. This being the construction, it is scarcely
necessary to explain that, by turning the milled head, the dis-
tance between the ebonite surface and the frame is varied
according to t lie direction of revolution, and that in this way
the pressure on the arteiy may be readily modified when.the
instrument is in use. The extent of the modifications thus
produced, however, still remains undetermined, for they vary
according to the form of the limb and the relative position of
the arm and forearm at the time of observation. To measure
them, we must have recourse to another method which is at
once simple and accurate. It is obvious that, provided that
the spring is firml}- and immovably fixed in its place, the press-
ure which it makes against any object pushed against it from
below is determinable by the force which is exerted in pushing
it. If, for example, I turn the instrument upside down, and
place a weight of 200 grammes on what was before the under
surface, now the upper surface, of the spring, I push it back
some fraction of an inch from its position of equilibrium; I
learn that, whenever it is pushed back to this extent, the press-
ure it exerts on the surface opposed to it is that of 200
grammes' weight. Repeating the experiment with a series of
other weights, I can in a similar way obtain other measure-
ments of distance corresponding to them, and thus, by com-
bining the results, accomplish the graduation of the spring in
.such a way that the pressure made by it can be alwaj's known
from the extent of its deflexion. The most convenient wa}r of
determining this deflexion is either to measure the distance
between the head of the steel screw, the point of which rests
on the upper surface of the spring, and the surface of the brass
lever, with a scale (as shown in Fig. 210); or, better still, to
have the screw itself graduated. In either case, care must be
taken to fix the writing lever in the proper position — i.e., in a
direction which coincides with the direction of movement of
the writing surface — before making the measurements.

40. The Artificial Artery or Arterial Schema. — The
phenomena of arterial pulsation can be best studied in a well-
constructed schema or artificial artery, consisting in an elastic
tube through which water is propelled by an artificial heart,
i. e., by a pump of such construction that it discharges its
contents into the tube in a manner which mechanically

BY DR. BURDON-SANDERSON. 231

resembles that in which the heart discharges its blood into the
arteries. Several instruments of this kind have been con-
trived, from the simple schema of E. H. Weber, to the com-
plicated " artificial heart" of Marey.

It may be stated generally that those forms of schema are
most instructive which are of the simplest construction ; and
inasmuch as the object in view is not to illustrate but to
explain, it is of no importance whatever that the schema
should have any outward resemblance to the organs of circu-
lation for which it stands. What is essential in a schema is,
that as regards the quantity of liquid discharged at each
stroke of the pump, the period occupied in the discharge, the
distribution in time of the pressure exercised on the mass of
liquid expelled, and the resistance opposed to the terminal
outflow of liquid from the elastic tube, the representation
should resemble, as closely as possible, the thing represented.
To the student, it is far from an advantage that the resem-
blance should extend beyond this to the details of external
form and arrangement; for his attention is thereby apt to be
drawn oft" from the essential conditions of the act, to the
accessory peculiarities of the machine which produces it. Two
kinds of schema may be usefully employed for the study of
the phenomena of the pulse, which differ from each other in
the construction of the pump which does the work of the
heart. The first is represented in fig. 211. Here the pump
consists of a glass tube (a), closed at the upper end, and
connected below by two branches — on one side with a cistern,
at a level of some eight or ten feet above the table ; on the
other, with the experimental tube which represents the artery.
These communications are controlled by valves, placed at the
opposite ends of a horizontal lever (e, d) of such construction
that the same act which closes the one must necessarily open
the other ; so that, as regards their actions, one represents the
semilunar, the other the auriculo-ventricular valves of the
heart. By means of a spring (shown in the figure to the right
of d), when the apparatus is not working, i. e., during the
period corresponding to diastole, the former is kept closed,
the latter open. Under these circumstances, the water rises
in the tube, compressing the column of air which it contains
in a proportion which is determined by Marriotte's law. If,
as in the present instance, the pressure is about one-third of
an atmosphere, the volume of the inclosed air is diminished in
the proportion of 2 : 3, and so on. When, by depressing the
opposite end of the lever, the aortic valve is opened, and the
mitral closed, the compressed air suddenly expands, and forces
the water which the tube contains into the aorta. We shall
see, when we come to consider the modes of contraction of
the heart, that the above is as close an imitation as could be

232 CIRCULATION OF THE BLOOD.

made by any artificial means. Just as, when the heart con-
tracts, it compresses its contents most energetically at the
outset, while its force rapidly diminishes towards the end of
the systole, so here the most rapid movement of the column is
at the first moment after the depression of the lever.

The arterial tnhc where it passes under the valve D is ahout
four lines in thickness. Soon it divides into two branches of
smaller diameter, each of which is several yards long. One of
these tubes passes under the spring of the sphygmograph,
which is fixed at ri in such a manner that tracings may be
conveniently taken. Both open finally into a waste basin ;
but each is provided with screw clamps, by which it can be
compressed or constricted at any desired distance from the
pump. The purpose of the bifurcation is, that the observer
may be enabled, without interfering in any way with the con-
dition of the tube, of which the expansive movements are re-
corded sphygmographically, to vary the quantity of liquid
which is discharged through it per minute. To experiment
with the schema satisfactorily, it is desirable to leave the
working of the lever to an assistant, or, still better, to arrange
the apparatus so that the work can be done by an electro-
magnet. The observer is then at liberty to watch the effect of
modifications of resistance, etc., on the form of the tracings
while they are in progress. The most important facts to be
demonstrated with the aid of the schema, as above described,
are the following: —

1. It is shown that the artificial and the natural pulse resemble
each other closely, each consisting in a succession of expansive
and contractile movements which always occur in the same
order (.see Fig. 212, a). In describing these movements, it is
convenient to speak of the experimental tube as the artery, and
to assume that elevation of the lever of the sphygmograph is
equivalent to expansion of the tube, and depression to contrac-
tion. This granted, the tracing shows that when the valve D
is opened, a sudden expansion of the artery takes place; that
so long as the heart continues to act the vessel remains full,
and that the cessation of the injection of liquid from behind de-
termines a contraction of the artery which is as rapid as the
previous expansion. Xo sooner has the artery accomplished
its contraction than it begins a second expansion inferior to
the first both in extent and rapidity ; and then finally contracts,
continuing to get smaller until the aortic valve again opens.

2. It can next be shown that just as the expansion of the
lever is consequent on the opening of the aortic valve, so its
descent is consequent (not on the closing of the valve, but) on
the cessation of the injection of liquid by the pump, i. e., the
cessation of the systolic contraction of the ventricle.' To prove
this, I use a contrivance which will be readily understood from

BY DR. BUBDON-SANDERSON. 233

the figure. Its purpose is to write on the plate of the sphyg-
mograph the duration of the injection of liquid. It consists of
a cylinder of box-wood (Fig. 211, h), the steel axis of which rests
horizontally on bearings so placed that the cylinder revolves in a
direction at right angles to that of the movement of the plate at
a short distance from it. From one side of the cylinder a steel
needle projects, which, when the cylinder turns, makes a mark
on the smoked surface. Hound one side of the cylinder runs
it cord of spun silk, the two ends of which stretch, one from
either side of it, to the point of a vertical arm (l) ; this arm
springs from the wooden lever already described, by which the
valves are opened and shut. Of the two cords, the upper one
is rendered partly elastic by the interposition of a short length
of caoutchouc. So long as the aortic valve is closed, the needle
remains in contact, but the moment the valve is opened, it is
withdrawn, and we obtain, first, an upper horizontal line, broken
at regular intervals — which are, of course, limited in time by
the opening and closing of the aortic valve — and, secondly,
a pulse-tracing (Fig. 212, 6), which may be compared with
it. This exact correspondence between the length of time the
heart is acting and the time which elapses between the begin-
ning of the expansion and the commencement of the contrac-
tion, affords evidence that the latter is dependent on the
former.

3. Lastl}*, it can be shown that the second expansion is not,
as might be supposed, connected with the closure of the com-
munication between the pump and the elastic tube (the shut-
ting of the aortic valve), but is a consequence of the disturb-
ance of equilibrium produced in the tube itself by the act of
distension. To demonstrate this, the second expansion must
be studied under various conditions and by various methods;
among the best is the following: A narrow tube, closed at one
end, and containing air, is connected by means of a T-piece
with the experimental tube or artery. The volume of air con-
tained in the tube varies with the pressure, indicating its varia-
tions with great sensitiveness. If the surface of the liquid in
the tube is watched during the action of the pump, it is very
easy to see that the volume of air is diminished as the valve D
opens, enlarges for a moment, and again contracts after the
injection has ceased. If now the action of the pump is so modi-
fied that, after opening the valve D, the discharge of liquid is
continued for some seconds (both valves remaining open), we
learn that the first expansion is followed by a second just as
before. If the same experiment is made with the sphygmo-
graph, a tracing is obtained in which the ascent due to the open-
ing of the valve is succeeded by a momentary descent, then a
second ascent, the lever finally assuming a position correspond-

234 CIRCULATION OF THE BLOOD.

ing to the increased pressure produced by tlie continuous cur-
rent which is now passing through the tube.

From tins experiment we learn, as regards the artificial
artery, first, that the second beat of the pulse is not, as has
been sometimes imagined, a mere product of the instrumental
method we employ to demonstrate it, for it can be shown quite
as distinctly in other ways ; and secondly, that it is a result
of the disturbance produced in the tube by the sud len disten-
sion of its proximal end, independently of any subsequent move-
ment or action of the pump.

41. Experiments -with the Schema relating to the
Form of the Arterial Pulse. — In the schema, the injection
of liquid by the artificial heart into the proximal end of the
elastic tube produces two effects, which can not only be dis-
tinguished in the tracing, but can be proved experimentally to
be independent of each other. One of these consists in the
transmission of a series of vibratory movements of the liquid
(t. e., movements in alternately opposite directions) from the
proximal to the distal end; the other, in the communication
of the pressure existing in the artificial heart at the moment
that the valve D is opened to the contents of the arterial tube.
The first of these effects can be readily demonstrated on the
schema.

If you take an elastic tube, distended with water, and closed
at both ends, and give it a smart rap with a hammer at one end,
an effect is transmitted along the tube which, although of an
entirely different nature to that which constitutes the pulse, yet
mixes itself up with it under certain conditions. This effect is
called, from its mode of origin, a percussion-wave. To produce
it, close the communication between the schematic heart and
artery, and arrange the lever (Fig. 211) in such a manner that,
by striking on it with a hammer (at d), the required percus-
sion may be produced. The tube being placed under the spring
of the sphj'gmograph (at Q), in such a position that the length
of tubing between the point of percussion (d) and the spring
(o) is equal to two metres, a succession of percussion-waves is
produced, and a tracing obtained similar to those shown in Fig.
213, in which the interruptions in the upper line indicate the
moment of percussion, the vertical ascents in the lower line the
effects. In the figure, the interval of time between cause and
effect corresponds to the portion of the horizontal line, (in the
lower tracing) which lies between the short vertical scratch and
the commencement of the ascent. The rate of movement of
the clock-work during the experiment being 8 centimetres per
minute, this distance corresponds to about a fifteenth of a
second.

The other effect, the communication of pressure from the
artificial heart to the elastic tube, may be readily illustrated

BY DR. BURLON-SANDERSON. 235

with the aid of a schema in which the heart is represented by
an elastic bag of such size that it can be squeezed with the hand.
This bag communicates at one end with a long elastic tube
representing the arterial system, at the other with a vessel con-
taining water, the apertures being furnished with valves which
open in directions corresponding to those of the heart. If
three levers, like those we have just been using, are so arranged
as to receive the successive expansion-waves — produced by
repeatedly squeezing the bag — at different distances from their
origin, the three tracings are obtained which are represented
in Fig. 214. It is instructive to observe that these tracings have
no resemblance to those of the arterial pulse. The reason is,
that the contracting hand is entirety unlike the contracting
heart. The real heart, like the schematic heart used in the pre-
vious experiments, contracts suddenly, exerting its greatest
vigor at the commencement. The hand contracts gradually,
and is, moreover, incomparably weaker, as compared with the
resistance to be overcome, than the heart. Hence the expan-
sion of the tube is slow, lasts a long time, and is followed by
no rebound. This very slowness of the process enables one to
see the steps of it better. In the distal part of the tube, to
which the upper tracing corresponds, the expansion culminates
later than in the proximal part, because the motion commu-
nicated to its contents by the grip of the hand at the outset
does not begin to tell on the former (distal) until the latter is
fully expanded.

In the pulse tracings obtained with the schema arranged as
in Fig. 211, so as to imitate the natural pulse, the two effects
produced in the preceding experiments separately, are combined
with each other. Thus in Fig. 212 a, the abrupt initial ascent
of the lever is the first of a series of vibratory movements of
the same kind as those shown in Fig. 213, and is instantly fol-
lowed by a recoil. In the same tracing, the more gradual ac-
cumulation of arterial pressure manifests itself in the fact that
the lever jerked up1 by the vibration does not (as in Fig. 213)
descend to its previous position, but remains elevated for a
period, which, as already seen, depends on the duration of the
injection of liquid.

This combination of effects is seen with equal distinctness in
the natural radial pulse. The abrupt line of ascent with which

1 In the sphygmographs, lately made by Bregnet, the movement of
the spring is communicated to the writing lever by a mechanism shown
in Fi'_r. 209 b, more simple and effectual than that described on p. 237.
'Die screw is hinged to the, upper surface of the spring in such a way
thai it presses gently against the axis of the lever, and acts upon it as a
rack on its pinion. In this way the lever follows the movements of the
screw much more exactly, and the jerk is diminished. (See Garrod on
Spliygmography. Journ. of Anat. and Phys., May, 1872, p. 399.)

236 CIRCULATION OF THE BLOOD.

every normal tracing begin-, expresses not the more or less
gradually increasing arterial distension, but the antecedent
transmission of a vibration.

42. Postponement of the Pulse. — There is :i sensible dif-
ference in time between the beat of the carotid artery and that
of the radial. Any one can satisfy himself of the fact by feel-
ing his own carotid with the left thumb and forefinger, while
he feels the left radial with the other hand. The reason why
time is lost in the transmission of the expansion from the centre
to the periphery, is that the arteries are elastic. Let us sup-
pose a tube. A, b, c, to represent

the arterial system — A the proximal end, c the distal. At the
instant that blood bursts suddenly out of the contracting heart
into a, it yields to the pressure against its internal surface and
expands. In tins expansion great part of the sensible motion
of the blood momentarily disappears, and consequently, so long
as the expansion lasts, produces comparatively very little effect
in distending b; but immediately that A becomes tense, the
lost, or rather converted, motion again becomes sensible, and
adds itself to the motion which the contracting heart is still
communicating. And, inasmuch as B deals with the accumu-
lated effect which it receives from a in exactly the same way as
a dealt with that which it received from the heart, c is as far
behind b in attaining its maximum of distension as b was
behind a. This being the case, it is easy to see that the loss
of time between A and c, or between aorta and radial, depends
on the yieldingness (extensibility) of the tube by which the two
points are connected. If the tube is absolutely rigid, there is
no postponement; if, though elastic, it is tense at the moment
that it receives the discharge, there is scarcely any ; whereas
that condition of the tube is most favorable to postponement,
in which it is longest in attaining its maximum of distension,
or in which the time taken by any part of it to expand to the
uttermost is longest.

The preceding explanation relates exclusively to so much of
the pulsation as is due to the communication of pressure. As
regards the antecedent vibration-effect, we have also time occu-
pied in transmission, but the rate of propagation is so rapid
that in the case of an artery, or of an elastic tube of similar
length, it is inappreciable. This fact enables us to explain
how it is that in some persons the pulse seems to be much
more postponed than in others. The reason of tins is, not that
there is more time lost in the former case than in the latter,
for even if this were so the difference would be certainly too
inconsiderable to be judged of by the finger, but that in some

BY DR. BURDON-SANDERSON. 237

individuals, and under certain conditions of health, the instan-
taneously transmitted vibration-effect is more felt by the fin-
ger; in others, the moment at which the artery attains its
greatest extension. Thus a pulse of the form shown in Fig.
215 a seems to the finger delayed, because the vibration-effect
is in abeyance on account of the existence of an obstruction
between the heart and the wrist; whereas, in the pulse re-
presented in b, the initial shock is so intense that it masks
the other.

43. Cause of the Second Beat. — The facts relating to
the postponement of arterial expansion are also the key to the
understanding of the phenomenon of dicrotism. In applying
them in explanation of the production of the second expansion
in arteries which, like the radial, are not far from the periphery,
there are two facts to be borne in mind: first, that these arte-
ries, as they become smaller, become more distensible; and
secondly, that in the capillaries themselves the resistance to
the passage of blood is much greater than any which is en-
countered in the arteries. Just as the expansion of the aorta
determines that of the radial, the radial expansion determines
and is followed by that of the peripheral arterioles. Hence at
a certain moment the radial is subsiding, while the arterioles
are still swelling; so that, when they are at their acme of dis-
tension, the pressure is greater at the periphery than in the
radial itself. From the other fact — the resistance to the flow
of blood in the capillaries — it results that, immediately behind
this resistance, pressure accumulates so long as blood enters
the arterioles from behind more rapidly than it is discharged
in front. The state of the arterial circulation during the period
of cardiac diastole may therefore be described as follows: The
arterial system is closed by the aortic valve behind, and vir-
tually closed in front by the capillary resistance. In the
largest arteries the expansion is ebbing, in the smallest it is
culminating; so that, for an instant, the pressure is greater in
the latter than in the former. There is but one effect possible.
The restoration of equilibrium must take place by increase of
pressure towards the heart and diminution towards the peri-
phery. This restoration of equilibrium constitutes the second
beat. It may manifest itself in very different degrees, accord-
ing to the yieldingness of the arteries. When, as in health,
the arteries are tense, it is seen merely in a slight arrest or in-
terruption of the arterial collapse — a break in the descending
limb of the tracing. In fever, when the arteries are relatively
much more distensible, the second expansion is separated by
so distinct an interval of relaxation from the first that the pulse
feels double to the finger. To facilitate the comprehension of
the subject, the S3'nchronous conditions of central, peripheral,
and intermediate arteries may be stated in parallel columns.

238 CIRCULATION OF THE BLOOD.

Carotid. Ra<li;il. Peripheral Arterioles.

Fully expanded . Expanding . . Collapsed.

Contracting . Expanded . . Expanding.

Again expanding . Contracting . . Expanding.

Stationaiy . Again expanding . Slowl}- contracting.

Contracting . Contracting . Contracting.

Hence, as sphygmographic tracings show to be the case, the
second expansion in the great arteries lasts longer than in the
smaller ones ; for, although it commences the sooner the nearer
the heart, the subsidence is simultaneous throughout the whole
arterial system.

Rules for Sphygmographic Observation. — 1. The
forearm should be supported on a table or other similar sur-
face, with the back of the wrist reposing on a firm, well-padded
cushion, of such a height that the dorsal surface of the hand
makes an angle of from 20° to 30° with that of the forearm.

2. The spli3rgmograph must be placed on the wrist in a di-
rection parallel with that of the radius, in such a position
that the block rests upon the trapezium and scaphoid, and
the extremity of the spring is opposite the styloid process of
the radius.

3. In beginning an observation, adjust the instrument so
that the pressure exerted by the spring is sufficient to flatten
the arteiy against the radius ; then weaken the spring until the
effects of over-compression disappear — i.e., until yon find that
the lever continues to descend until the end of diastole. Note
the pressure at which this result is attained, as well as that
which is required to flatten the artery, and take tracings at
each of the two pressures.

Section III. — Phenomena of tiie Circulation in the smallest

Arteries.

The smallest arteries may be studied during life with the
aid of the microscope, in fish, batrachians, and mammalia.

44. For the microscopical study of the circulation in fish, a
contrivance devised by Dr. Caton, of Liverpool, is used (fig.
21 G). It consists of an oblong box of gutta percha, open at
one end, closed at the other, and just large enough to hold the
bod}7 of a minnow or stickleback very loosely. This box
forms part of a plate of gutta percha, which is fixed on to the
stage of the microscope in such a position that the tail of the
fish contained in it covers a perforation in the plate prepared
for its reception. The tail is held securely in its place b}r a
ligature, and the caudal fin which rests on a square of glass is
further secured by a couple of fine springs. The box itself,
which incloses the head and gills of the fish, contains water,
which is constantly renewed by means of the two tubes, of

BY DR. BURB-ON-SANDERSON. 289

■which the upper, guarded by a screw-clamp, communicates
"with a vessel at a higher level, the lower conveys the water
away as fast as it is supplied. The excellency of this method
lies in the fact that the animal can be kept under observation,
without the use of any narcotizing drug, for a long time in a
perfectly natural condition. The frog is used both in the larval
and adult state. To observe the circulation in the tail of the
tadpole, the animal is placed in a moderately strong solution
of curare, care being taken to remove it before it is completely
paralyzed — the moment, in short, that its motions become
sluggish. It is also possible to secure it, without the aid of
curare, in a holder of construction similar to that of the in-
strument I have just described — a method which has this great
advantage, that the animal is in a more normal condition ; for
even when curare is given with the greatest care, the action
of the heart is weakened by it. For most purposes the adult
frog is more useful than the tadpole, particularly when it is
desired to observe not merely the circulation as it is, but to
witness the modifications which the phenomena undergo under
the influence of conditions acting on the bloodvessels through
the nervous sj'stem.

There are three transparent parts of the frog — the mesen-
tery, the web, and the tongue — each of which has its special
advantages for the purposes of study. For a first view of the
relation between arteries, capillaries, veins, and lymphatics, the
mesentery is superior to either of the other two. The frog
must be placed under the influence of curare, the dose of
which, for the ordinary specimens of rana temporaria, is about
smooth of a grain. The solution of curare is prepared by
weighing out five milligrammes of the substance, and rubbing
it up in a glass mortar with a little alcohol. The proper
quantity of water — that is, sufficient to make up ten cubic
centimetres — is then added, and a straw-colored, nearly limpid
liquid is obtained, a single drop of which is a sufficient dose.
It is injected under the skin of the back with an ordinary
subcutaneous syringe, and answers best when the effect does
not manifest itself for some time after the injection. The
most convenient apparatus for the purpose of exposing the
mesentery is that shown in fig. 21*7. The manipulation is ;
fully described in Chapter VII. It is always desirable to
commence the examination with a low power. It is then seen
that the arteries are smaller than the veins, the latter exceed-
ing the former in diameter by about a sixth ; that the arterial
stream is quicker than the venous ; that it is accelerated
appreciably at each beat of the heart ; and that in every
artery a space can be distinguished within the outline of the
vessel, which is entirely free from corpuscles. The arterial
stream, indeed, is so quick that the forms of the corpuscles

2-40 CIRCULATION OF THE BLOOD.

cannot be discerned, but in the veins both colored and color-
less corpuscles can be distinguished ; and it is soon noticeable
that, while the former are confined to the axial current, the
latter show a tendency to loiter along the inner surface of the
vessel, like round pebbles in a shallow but rapid stream. The
observation may be continued without material change for
many hours; but if any artery is measured from time to time
micrometrically, it will be found that after a while it becomes
wider. On this dilatation of the arteries follows a correspond-
ing though less marked enlargement of the veins, and, if the
attention of the observer is fixed upon these last, it is seen
that the circulation, which was before so active, undergoes a
marked and almost sudden slowing. This slowing indicates
that the membrane, in consequence of its exposure to the air,
is becoming inflamed; simultaneously with it, the colorless
corpuscles, instead of loitering here and there at the edge of
the axial current, crowd in numbers against the venous walls.
In this way the vessel becomes lined with a continuous pave-
ment of these bodies, which remain almost motionless, not-
withstanding that the axial current still sweeps by them,
though with abated velocity. If, at this moment the atten-
tion is directed to the outer contour of the vessel, it is seen
that minute, colorless, button-shaped elevations spring from it,
each of which first assumes the form of a hemispherical pro-
jection, and is eventually converted into a pear-shaped body,
attached by a stalk to the outer surface of the vein. This
body, which has thus made its way through the vascular mem-
brane, is, I need scarcely say, an amceboid colorless corpuscle.
It soon shows itself to be so by throwing out delicate prongs
of transparent protoplasm from its surface, especially in the
direction from which it has come.

The methods to be employed for the study of the circulation
in the tongue and in the web are fully described in Chapter
VII. For investigations relating to the innervation and con-
tractile movements of the smallest arteries, the tongue is of
little value, though superior to the mesentery and web for the
study of inflammation. The web, on the other hand, is pre-
ferable, for the purposes first mentioned, to either the tongue
or mesentery.

45. Capillary Circulation in Mammalia. — The study
of the capillary circulation of mammalia under the micro-
scope is attended with great difficulty — in the first place, be-
cause (if we except the wing of the bat) there is no external
part sufficiently transparent for observation under high power ;
and, secondly, because if internal parts are used, the injurious
effects of exposure are much greater than those which occur
in batrachians. To overcome these difficulties it is necessary

BY DR. BURDON-SANDERSON. 241

to have recourse to more complicated appliances and appa-
ratus.

The mesenteries of small rodents have been repeatedly used
for the demonstration of the mammalian capillary circulation.
These, however, are not to be compared, as subjects of obser-
vation, with the omentum, and particularly with that of the
guineapig. This structure forms a delicate membranous ex-
pansion of from twelve to fifteen cubic centimetres in extent,
which is attached by its upper margin to the greater curvature
of the stomach. It differs from the organ of the same name in
man in consisting, for the most part, of only two la}rers of
peritonaeum, in being much more delicate in its structure, and
containing very little fat. Hence, from the simplicity of the
anatomical relations, and particularly from its being attached
by one side only to the stomach, from its perfect transparency,
from its abundant vascularity, and, lastly, from its containing
not only vessels but living cells, it is obvious that this mem-
brane offers a good field for research.

The observations hitherto made on the mammalian mesen-
tery have been without practical result, the reason being that
so vulnerable a tissue as that of the peritonaeum cannot be
exposed, even for a few minutes, without injury; so that,
although the greatest care is taken in demonstration, only a
momentary glimpse can be obtained. To obviate this difficulty,
the arrangements for placing the membrane under the micro-
scope must be of such a nature, that the structure is bathed
during the whole period of observation in a liquid at the tem-
perature of the body. It need scarcely be said that water,
from its destructive influence on living tissues, would not
answer the purpose. Serum would probably be best, if it were
always at hand ; but, practically, solution of common salt of
the strength ordinarily used (f per cent.) answers the purpose
perfectly. The temperature is maintained by keeping the
glass trough, in which the membrane is spread out, over the
warm stage, the construction of which has been already de-
scribed.

The mode of procedure is as follows: The guineapig is first
placed under the influence of chloral by injecting that sub-
stance in solution under the skin, three grains being required
for an animal about lib. in weight. It is then laid on a sup-
port, the upper surface of which is on the same horizontal
plane as that of the microscope-stage. An incision not more
than an inch in length is next made, extending outwards from
the edge of the left rectus muscle a little below the end of the
ensiform cartilage. The muscles having been divided, and the
peritonaeum cautiously opened for about half an inch, or even
less, the free edge of the omentum is carefully drawn out. It
must then be floated in the warm bath prepared for it, and is
16

242 CIRCULATION OF THE BLOOD.

ready for examination. Tt is, however, found very advanta-
geous to cover those parts of it which do not lie under the
microscope with sheets of blotting-paper, for by this means
the risk of exposure is diminished, and the undulating move-
ments of the water are prevented ; so that the object is
rendered much steadier than it would otherwise be. So long
as low powers are employed, this arrangement is sufficient ;
but if it is desired to use objectives of short focal distance, it
is necessary to warm the objective by allowing a stream of
water from the same source as that which supplies the stage
to pass round it.

The objects which present themselves to the observer are
manifold. Veins and arteries may be studied of various di-
ameters, some of which are free, while others are surrounded
by sheaths of tissue in which there are lab}-rinths of capillaries
of surpassing beauty. Several new observations have already
been made by this method. One of the most important, phy-
siologicallj-, is the fact that the maintenance of the capillary
circulation is wonderfully dependent on temperature ; and, in
particular, that any rise of temperature above the normal is in
the highest degree injurious, parti}', perhaps, from its direct
influence on the blood corpuscles, but mainly because it pro-
duces changes similiar to those we have already noticed as
occurring in batrachians after long exposure — viz., arrest of
the capillary blood-stream and escape of the liquor sanguinis
and corpuscles into the surrounding tissue.

46. Artificial Circulation. — For many purposes of re-
search, it is desirable to observe the circulation independently
of the action of the heart. This is accomplished either in the
whole body or in an organ, by injecting blood, or a liquid
which may be substituted for it, in a constant stream into the
arterial system, at the same temperature and under the same
pressure as that which naturally exists in the arteries. In the
case of batrachians, this is accomplished without difficulty,
for the temperature of the bod}' differs little from that of the
atmosphere, and the nutritive processes can be maintained for
long periods, not only without respiration, but without the
agent by which oxygen is combed to the tissues — haemoglo-
bin. Consequently the conditions to be observed are very
simple. The requirements for the purpose are as follows: —

1. The liquid to be injected may be either serum, defibri-
nated blood, or f per cent, solution of chloride of sodium.
When serum is used, it must be absolutely fresh. For this
reason, the serum obtained from the slaughter-house is usually
not to be depended upon. It is therefore necessary to use a
small rabbit for the purpose. In order to obtain a sufficient
quantity of blood from this animal, a canula must be care-
fully secured in the carotid, and a clip placed on the artery.

BY DR. BURDON-SANDERSON. 243

The connector adapted to the canula must be of sufficient
length to reach an absolutely clean flask or capsule destined
for the reception of the blood. If serum is required, the cap-
sule must be allowed to stand in a cool place until it is coagu-
lated. If defibrinated blood, the flask must be agitated brisk-
ly imniediateby after it is collected. The blood should be taken
in successive portions, for in this way a much larger quantity
is obtained than would be yielded if the animal were allowed
to bleed to death at once.

2. The apparatus for injection consists of a funnel, supported
on a holder at a height of about two feet from the table, to
the stem of which a flexible tube, guarded by a clip, is adapt-
ed. In addition to this, two Canute must be prepared, one
for the bulbus arteriosus, the other for the vena cava inferior.
Both should be made of thin fusible glass, and of the size and
form shown in figure 218. The arterial canula must be con-
nected by an India-rubber tube of the same width as itself
with a glass joiner, and its end must be supported by a holder
which can be best made of a strip of sheet lead bent to the
proper form. The funnel having been filled with the liquid
to be injected, and connected with the canula by the joiner, a
sufficient quantity is allowed to flow into the tube to occupy
it completely, and the clip closed. All being now ready, a
frog, previously slightly curarized, is fixed on the table in the
supine position. The integument is divided over the sternum
in the middle line, and the anterior wall of the upper part of
the visceral cavity removed, so as to expose the pericardium,
great care being taken not to injure the abdominal vein, or
any other large vessel. The ventricle is then opened, and the
canula passed through the opening into the bulb, and secured
b}' a ligature. This done, the heart is drawn upwards, and to
the right (after severance of the small vein which stretches
from the back of the ventricle to the pericardium), so as to
expose the sinus venosus, which is then opened in the line of
junction between it and the auricles. By this opening, the
canula for the vena cava is easily introduced into the funnel-
shaped dilatation (see fig. 228 6), and pushed into the vein.
If the canula is of proper size, a ligature is unnecessary. On
opening the clip on the tube leading from the funnel, the cir-
culation is restored. The blood contained in the vascular
system of the animal is soon replaced by the liquid injected.

The most instructive observations, relating to frogs in
which the circulation is maintained artificially (sometimes
called salt or serum frogs, according to the liquid used), are
made with the aid of the microscope. The examination of the
web shows us that even when saline solution is used, the ves-
sels and the circulation through them remain unaltered for
some time. If serum is used, this period is longer, provided

244 CIRCULATION OF THE BLOOD.

that it is perfectly fresh. A very slight admixture, however,
of kept scrum is fatal to the experiment. After a time, de-
cline of tissue life manifests itself by a change in the appear-
ance of the preparation, the elements losing their plumpness
and distinctness of outline. Along with this change, the ves-
sels, and particularly the arteries, become relaxed, and the
normal exchange between the liquid inside and that outside
of the vessels is perverted, the latter increasing in such a way
as to render the whole animal oedematous.

If, while the circulation is still normal, an injur}' is inflicted
on a part of the web — as, for example, by applying mustard
to a spot on its surface — it is seen that in the injured part
changes occur suddenly which are analogous to those which,
as tissue death approaches, affect the whole bod}'. These
changes are known by the term stasis, and form part of the
process of inflammation — a word which is used as a general
expression for the local effects of injuring living parts to such
a degree as not to destroy their vitality at once. They are
best studied when serum which contains a few corpuscles, or
defibrinated blood diluted with saline solution, is employed.
It is then seen that in any part of the web to which a so-called
irritant is applied, as, e. g., mustard — the blood stream is re-
tarded, and the corpuscles crowd together in the dilated ves-
sels. This is not due to any property of mutual attraction
peculiar to the corpuscles, for the same thing happens if milk,
diluted with saline solution, is substituted for blood ; so that,
whatever be the nature of the change, its seat is not in the
circulating liquid itself, but in the vessels or surrounding tis-
sues.

Section IV. — Functions of Vasomotor Nerves.

In the proceeding section the arteries have been regarded
merely as passive elastic tubes, dilating or contracting accord-
ing to the pressure exercised upon them by the circulating
blood. They must now be studied as not only elastic but
contractile.

The arteries owe their contractility to the unstriped muscu-
lar fibres which they contain. These fibres shorten under the
influence of impressions conveyed to them by the vascular
nerves, which nerves, together with the automatic centre from
which they radiate, constitute the vasomotor nervous system.
Of the centre which governs arterial contraction, nothing is
known anatomically ; for there is no point or tract in the brain
or spinal cord to which vascular nerves can be traced back.
All that is known has been learnt exclusively by experiment.

That there is a vasamotor centre, and that it is intracranial,
we learn by observing, first, that if the medulla is divided im-

BY DR. BURDON-SANDERSON. 245

mediately below the cerebellum, all the arteries are relaxed,
and that a similar effect is produced if certain afferent nerve
fibres, which lead to the intracranial part of the cord, are ex-
cited. Its position has been lately determined with great pre-
cision in the rabbit by Ludwig and Owsjannikow, who have
found by experiments, to which further reference will be made,
that it is limited towards the spinal cord by a line four or five
millimetres above the calamus scriptorius, and extends
towards the brain to within a millimetre of the corpora
quadrigemina.

That the vasomotor centre is in constant automatic action,
is shown b}' the paralyzing effect of section, whether of the
spinal cord, or of any nerve known to contain vascular fibres.
If the action of the centre were not constant, division could
not produce arterial relaxation. In relation to this constancy
of action, the word tonus is used. Arterial tonus means that
degree of contraction of an artery which is constant and nor-
mal. It is maintained only so long as the artery is in com-
munication with the vaso-motor centre.

47. Experiments relating to the Influence of the
Cerebro-Spinal Nervous Centres of the Vascular Sys-
tem.— (1.) Destruction of the Nervous Centres. — Two
frogs are slightly curarized, and placed side by side on the
same board, in the supine position. In both, the heart and
great vessels are exposed, as in the preceding section. It
having been ascertained that the circulation is normal in each
animal, and the frequency of the contractions having been
noted, the brain and spinal cord are destined in one of the
frogs, Iry inserting a strong needle into the spinal canal imme-
diately below the occipital bone, and then passing it upwards
and downwards. This may usually be accomplished without
much loss of blood. If now the frog which has been deprived
of its nervous centres is compared with the other, it is seen
that in the former, although the heart is beating with perfect
regularity and unaltered frequency, it is empty, and in conse-
quence, instead of projecting from the opening in the anterior
wall of the chest, it is withdrawn upwards and backwards
towards the oesophagus.

The emptiness of the heart is not limited to the ventricle and
bulb. The auricles are alike deprived of blood ; and if the
heart is drawn forwards by the apex, it is seen that the sinus
venosus and vena cava inferior are in the same condition.
The state of the heart is therefore not dependent on any cause
inherent in itself, but on the fact that no blood is conveyed to
it by the veins. To make this still more evident, the rest of
the visceral cavity may be opened, when it is seen that, although
the vena cava is collapsed, the intestinal veins are distended.
The second frog, which is no longer required for comparison,

246 CIRCULATION OF THE BLOOD.

should now be pithed in the same manner as the first. A
canula is then introduced into the abdominal vein, with its
orifice towards the heart, and connected, by an India-rubber
tube guarded by a clip, with a funnel containing three-fourths
per cent, solution of chloride of sodium. The heart having
been exposed, and its empty condition noted, the clip is
opened. Its cavities at once distend, and it acts as vigorously
and effectually as before the destruction of the nervous cen-
tres. The experiment may be varied thus : Two frogs are
suspended side by side, one of which has been pithed in the
manner above described. In both, the heart is exposed and
the ventricle cut across. In the pithed frog, a small quantity
of blood escapes, the quantity contained in the heart itself and
the commencement of the arterial system. In the other, blood
continues to flow for some minutes, in consequence of the con-
tinued contraction of the arterial system. To what extent the
veins may participate in it is uncertain.

These simple experiments show, first, that in the frog the
arteries, unaided by the heart, continue the circulation for a
certain time after equilibrium of pressure has been established,
by virtue of their contractility ; and secondly, that in this ani-
mal the influence of arterial contractility in aid of the circula-
tion is so considerable that, when it is abolished, circulation is
no longer possible.

It may be well to point out that this fact affords no ground
for supposing that the arteries take any active part in main-
taining the circulation. All that is proved is, that in the re-
laxed state the vascular system of the frog is relatively so
capacious that it is more than large enough to contain the
whole mass of the blood, which consequently comes to rest in
it out of reach of the influence of the heart. During life, the
arterial tonus is usually constant ; so long as, and in so far as
this is the case, the function of the arteries is a passive one,
the motion they give to the blood-stream during diastole being
a mere restitution of that received by them from the heart
during systole. On the other hand, whenever they contract,
they originate motion of themselves ; but in this case the dura-
tion of the effect is limited by that of the contraction, and can
never be continuous.

48. (2.) Direct Excitation of the Spinal Cord in the
Frog. — The requirements are as follows : a. A thin board of
soft wood about 8 inches long and 2 inches broad, one end of
which has a V-shaped notch cut out of it, corresponding in form
and size to one of the interdigital membranes of the web of the
frog's foot. b. A pair of common strong sewing-needles ;
around the blunt end of each of these needles, the end of a
length of thin copper wire is closely coiled ; they are then cov-
ered nearly to their points with a protective and insulating

BY DR. BURDON-SANDERSON. 247

coating of soft sealing-wax, for which purpose it is necessary
to warm them in the flame of a lamp. In doing this, care must
be taken not to heat the point, c. A battery and Du Bois's
induction apparatus and key. The key must be interposed in
the secondary circuit.

A frog having been curarized just sufficiently to paralyze its
voluntary muscles, a straight line is drawn from the notch
along the upper surface of the board in a direction parallel to
its edges. Two small perforations are made in this line, a
couple of millimetres from each other, at a distance from the
notch equal to that from the web of the frog to its occiput.
Through these perforations the needles are thrust, so as to pro-
ject about 5 millimetres, after which the board is arranged in
such a way on the microscope, that the V-shaped notch rests
over the stage aperture, and the opposite end on a support at
the same level. All being now ready, the integument is opened
along the middle line of the back of the neck, and the occipital
bone perforated in the middle line with a fine awl, close to its
posterior margin. The frog is then laid, back downwards on
the board, in such a position that one of the needles enters the
cranium through the hole in the occipital bone, the other the
spinal canal. The web is then laid on a plate of glass which
covers the notch, and secured if necessary by fine pins. Finally,
the heart is exposed as before.

On opening the key for a moment, so as to allow the induced
current to pass through the needles, it is seen that all the arte-
ries of the web at once contract, the contraction increasing for
four or five seconds and then gradually subsiding. If the ex-
citation is continued for several seconds, the circulation stops.
To judge of the effect accurately, it is desirable, first, to fix
upon an artery for observation beforehand, and bring it well
into view ; and secondly, to measure its diameter before, during,
and after excitation. For this purpose, a sheet of paper is
placed on a board in such a position that its surface is at right
angles to the direction in which the image is thrown by the
prism (see fig. 219), and at a distance of about 10 inches from
it. The outlines of the vessel are then traced on the paper with
a fine hard pencil. During and after excitation, other tracings
are made in the same way ; by comparison of which the changes
of the diameter of the vessel can be accurately estimated. The
microscope must of course be so placed that light is received
from the side, and that the surface of the paper is sufficiently
illuminated to enable the observer to distinguish the point of
the pencil. To insure success in this fundamental experiment,
the following precautions must be attended to. The dose of
curare must be very small, and should therefore be given an
hour or two before the observation is made. One at least of
the electrodes must be inserted within the cranium : for if both

248 CIRCULATION OF THE BLOOD.

are lielow the occipital bone, the effect is uncertain. Lastly,
great cart' must be taken to use feeble currents, and not to pro-
long the excitations, for the vasomotor nervous system of the
frog is very readily exhausted.

49. (3.) Excitation and Section of the Spinal Cord in
the Rabbit. — The requirements and preliminary preparation
for this experiment are the following : A canula and subcuta-
neous syringe for injecting 20 per cent, solution of curare into
the jugular vein ; apparatus for a kymographic observation of
arterial pressure ; apparatus for artificial respiration ; a needle
for ligaturing the muscles, in addition to the ordinary instru-
ments. The canula for the jugular is shown in fig. 220 An
India-rubber tube is fitted to it, the end of which is closed by a
ligature. It is inserted as follows: The rabbit having been
placed in the usual way on Czermak's rabbit supporter, with
the cushion under its neck, the integument is divided in the
middle line from the pomum Adami downwards, as directed in
Section I. On drawing the edge of the incision to either side,
the jugular vein is readily seen as it crosses the sterno-mastoid.
It is then carefully cleared of the platysma fibres and fascia
which cover it, and of its sheath to the extent of an inch or
more, with the aid of two pairs of blunt forceps. A clip having
been placed on the proximal end of the cleared part, a ligature
is looped round the distal end, which is tightened as soon as
it is seen that the vein is distended. This being accomplished,
a second ligature is placed round the vessel between the first
ligature and the clip, and then a V-shaped incision is made in
the vein immediately beyond it. Finally, the canula, which has
been previously filled with saline solution, is slipped into the
vein and secured in its place by the ligature prepared for it.
When it is intended to inject, the point of the subcutaneous
syringe is shrust through the closed tube of India-rubber. On
withdrawing it no liquid escapes. The plan has the advantage
that successive quantities may be injected with the greatest
facility. The mode of preparing the carotid artery, and of con-
necting it with the kymographic canula, has been described in
§ 34. For the present purpose it is necessary to free the artery
from its connections to a greater extent than usual. The canula
having been secured in the artery, and the latter divided beyond
the point of insertion, the canula is turned back and fixed to
the animal's thorax (by tying it to the fur) in such a position
that the artery forms a loop, with its convexity towards the
head. The purpose of this arrangement is to prevent the artery
from being strained when the animal is turned. The apparatus
for artificial respiration has not yet been described. It is re-
quired because the animal being under the influence of curare,
its voluntary muscles are paralyzed. Asa substitute for natu-
ral breathing, air must be injected in the proper quantity at

BY DR. BURDON-SANDERSON. 249

regular intervals, which correspond with the previous frequency
of the respiratory acts. In the absence of self-acting apparatus,
the best instrument to use is the caoutchouc blower and ex-
panding regulator sold by Messrs. Griffin for working the gas
blow-pipe (see fig. 221). The blower is worked by means of a
squeezer. It consists of an oblong board or lever, 16 inches
long, 3 inches wide, and f inch thick. This board is hinged in
the middle to a fulcrum, in such a way as to admit of a see-saw
movement. The fulcrum is firmly screwed to the table. When
it is in use, the blower is placed under one end, i. e., between
it and the table, the degree of compression being limited by a
strong cord attached at the opposite end to the table. By
varj'ing the length of the cord, the quantity of air injected at
each stroke is regulated. The blower communicates with the
respiratory cavity by a tracheal canula. No valve is required,
the expired air passing out freely during the intervals between
each injection and its successor, by a hole in the tube. The
quantity of air discharged by the blower at each stroke must,
therefore, considerably exceed the quantity which is required
for respiration. This contrivance can be worked with much
less fatigue than bellows. The time must be regulated by a
metronome. The self-acting appa?*atas consists of two parts
— a constantly acting blower or expirator, and an arrange-
ment for interrupting the current of air at regular intervals.
The best constant blower is that known as Sprengel's blowpipe,1
the structure of which will be understood at once from fig. 222.
The essential part of it is the vertical tube c7, with its branch
e, the lower end of which opens into a bottle having two other
openings. Of these, one, which communicates with the top of
the bottle, is for the efflux of air; the other, near the bottom,
for the escape of water. If a continuous current of water is
caused to pass through d, e remaining open, it carries with it a
quantity of air which passes down into the bottle; and if the
screw clamp c is so adjusted as to allow the water to flow out
of the bottle at the same rate that it flows in from <7, the water
in the bottle remains at the same level, and a constant stream
of air escapes from b. The interruption of the stream of air so
produced is effected by means of an electro-magnet, which is so
arranged that each time the voltaic current is closed, a weight
by which the tube is compressed is lifted, and thus air is in-
jected so long as the magnet is in action. The voltaic current
may be closed aud opened either by a metronome or by the
mercurial breaker, shown in fig. 223. Two copper wires, one
of which is connected with the battery, the other with the mag-
net, run along the top of the wooden bridge, nearly meeting at

1 A somewhat more complicated apparatus (Waxxarluftpumpc zur
Erzeugunrj conqiriiuirler Lujfl) is sold by Desaga of Heidelberg.

250 CIRCULATION OF THE BLOOD.

the crown of the arch ; here the}- descend parallel to each other,
but not in contact. Below the arch is a flat vulcanite bag, on
the upper surface of which a U tube is supported vertically,
with its concavity upwards. The ends of the two wires are
received into the two limbs of the U- As the bend contains
mercury, it is obvious that whenever the bag expands the cir-
cuit is closed, and broken when it contracts. The rest of the
mechanism is so arranged that the tube is closed beyond the
breaker whenever the magnet is not acting, and open so long
as the current passes. This condition can, however, never be
permanent; for after an interval of time, which can be very
readily regulated by altering the quantity of mercury in the U
tube, the bag becomes sufficiently distended to close the cir-
cuit. When this happens, the magnet acts and opens the tube,
allowing the distended bag to discharge itself. This contriv-
ance answers particularly well for the artificial respiration of
rabbits. The needles for exciting the cord are constructed in
the same manner as those described in the preceding paragraph ;
they should, however, be thicker and stronger.

The canulffl having been placed in the trachea and external
jugular vein, and the apparatus for artificial respiration being
in order, three-tenths of a centimetre of a one percent, solution
of curare is injected. As soon as respiration ceases, air is in-
jected at regular intervals by the metronome, the beats of which
express the previous frequency of breathing. The carotid
artery is now connected with the kymograph, and the animal
placed in the supine position, the head-holder being so arranged
that the head is very much flexed on the cervical part of the
spinal column, so as to make the space between the occipital
bone and the atlas as wide as possible. In doing this, great
care must be taken not to strain or twist the artery, or kink the
air tube. This done, an observation must be made of the arte-
rial pressure, and the atlanto-occipital membrane exposed with
as much dispatch and as little bleeding as practicable. This
is best effected with the aid of the notched needle, fig. 203/.
With the help of this needle, three ligatures are passed under-
neath the muscles which stretch vertically on either side of the
spine of the atlas, its point being directed towards the occipital
spine as close to the bone as possible. It is usually necessary
to pass two such ligatures in line on either side, the upper
entering where the lower passes out. The ligatures having
been tightened and the muscles divided in the middle line, it
is easy to expose the posterior tubercle of the atlas, the mem-
brane, and the edge of the occipital bone, without hemorrhage.

The next step is to expose the cord by dividing the atlanto-
occipital membrane; this is best done with scissors and for-
ceps. While a tracing of the arterial pressure is taken by an
assistant, the cord is divided: at once the mercurial column

BY DR. BURDON-S ANDERSON. 251

sinks from, say, 100 millimetres to 20 or 30. One needle is
then inserted in the middle line above the posterior tubercle
of the atlas, the other below it, the key being closed. On
opening the latter so as to direct the induced current through
the needles, the arterial pressure rises to a height which at
first equals, if not exceeds, that at which it stood before sec-
tion.

The effects of exciting the cord in increasing the arterial
pressure are seen with equal distinctness when the cord is not
previously divided. In both cases the ascent is accompanied
with an increase of the frequency of the contractions of the
heart, the cause of which will be investigated in a future sec-
tion.

Direct Observation of the Arteries during Excitation of the
Cord. — That the increase and diminution of arterial pressure
observed is in great part, if not entirety, dependent on con-
traction of the arterial systems, can be shown in several ways.
The most direct consists in the observation of the arteries
themselves. In the rabbit, the arteria sajrfiena, which, after
leaving the femoral, just as that vessel enters the adductor
sheath, takes a superficial course towards the inner side of the
knee, may be observed with great facility. All that is neces-
sary is to divide carefully, first the skin, and then the fascia
which covers it : the two saphena veins which lie on either
side of it serve to determine its exact position. In this
artery it can be readily seen that as the pressure rises the
vessel contracts. To observe the effect of vascular conti-ac-
tion on the heart, that organ must be exposed. In a curarized
animal, this can be effected without interfering materially with
the vital functions. Ligatures of fine copper wire having
been passed, with the aid of a curved needle (fig. 203, e),
around the 3d, 4th, 5th, and 6th cartilages, close to the left
edge of the sternum, and a second vertical series of ligatures
around the corresponding ribs at a sufficient distance outwards,
the portion of the thoracic wall which lies between the two
series can be removed without hemorrhage. It is then seen
that after section of the cord, the heart is flaccid and empty,
and that its cavities fill and its action becomes vigorous when
the vascular contraction caused by excitation of the peripheral
end forces the blood forwards so as to fill the right auricle.

[For the experimental proof that the effects of excitation
of the cord above described are not dependent on the increased
vigor of the contractions of the heart, see §§ 80, 81.]

50. (4.) Section of the Medulla Oblongata in the
Rabbit, within the Cranium. — The recent experiments of
Ludwig and Owsjannikow have shown that the medulla m:iy
be divided within the cranium with the same results as regards
arterial pressure as are obtained when it is severed immediately

252 CIRCULATION OF THE BLOOD.

below the occipital foramen. For this purpose, the occipital
bone must he perforated with a small trephine (fig. 203, d) in
the middle line between the occipital protuberance and the
occipital spine (see fig. 224). By this opening, a thin-bladed
knife is introduced in the middle plane, with its edge outwards,
by which the medulla is divided, first on one side, then on the
other. If the division is made as much as five millimetres
above the calamus scriptorius, the diminution of arterial press-
ure produced is as great as after section outside of the
cranium. In experiments in which the division was made
higher, the effect was found to be lessened, disappearing when
a point was reached about a millimetre below the corpora
quadrigemina.

Experiments relating to the Refeex Excitation of the Vaso-
motor Centre.

The vasomotor centre, although constantly in activity, may
be stimulated by impressions received by it through afferent
nerves. This can be shown both in the frog and in mammalia.

51. Reflex Excitation of the Medulla Oblongata in
the Frog. — For this purpose, the nerves in question may be
excited either with the aid of the ordinary excitor (fig. 225),
or bj' the application of a metallic brush to the skin. In the
latter case, one of the wires which form the secondary circuit
ends in a point which is inserted into the muscles; the other,
in the brush which is kept in contact with the skin in the im-
mediate neighborhood. The effect should be observed in the
web, in the mesentery, and in the great vessels leading to the
heart. The currents employed must be feeble when the nerves
are excited by the direct application of the electrodes to the
sensory nerves, but strong when it is intended to excite their
cutaneous or mucous endings. The periods of excitation
should always be very short. The experiment may be varied
as follows: a. A frog having been carefully curarized, with
the same precautions as were recommended for studying the
effect of direct excitation of the medulla, and arranged for the
microscopical observation of the circulation in the web, the
points of the excitor are placed upon the tongue, the mouth
being kept open for the purpose. On opening the key, the
same changes exactly are observed in the vessels as are pro-
duced by direct excitation. At the first moment the blood-
stream in the arteries is accelerated, but immediately after,
the arteries begin to contract sensibly. The contraction
increases gradually but rapidly for one or two seconds, and is
attended with slowing, and finally witli arrest, of the circula-
tion. A maximum of narrowing having been attained, the
effect passes off as it came on. Even if the excitation is

BY DR. BURDON-S ANDERSON. 253

continued, the arteries do not remain contracted, but often
exhibit alternations of contraction and relaxation at irregular
intervals. For observing the changes of rate of movement in
the velocity of the blood-stream, the veins should be preferred ;
for in them the initial acceleration is not quite so transitory as
in the arteries, while the subsequent slowing is as distinct. If
it is desired to make a more exact observation, the method
devised by Dr. Riegel must be used. It consists in comparing
the movements of the blood corpuscles in a selected artery or
vein, with that of a current of water containing solid particles
in suspension, which passes through a horizontal glass tube
fixed in the eye-piece of the microscope at such a distance from
the eye-glass as to be distinctly seen by the observer. One end
of the tube communicates with a large bottle placed on a shelf
at a higher level than the table, containing the liquid ; the
other, with the discharge tube of the movable warm stage
represented in fig. 3. Ity varying the height of the dropper,
the rate of flow through the eye-piece can be readily regulated.
The rate of flow is learnt by measuring the quantity of liquid
discharged per second, and dividing it by the product of the
lumen of the glass tube and the magnifying power of the
microscope. Thus, if the rate of discharge were a cubic centi-
metre in 15 seconds, i. e., 6.6' cubic millimetres per second, the
lumen of the tube 0.8 square mill., and the magnifying power
300, the velocity of the current would be 30Qy0.8= 0.02775 mill.
The determination of the absolute velocity is of little import-
ance, the object being rather to appreciate, with exactitude and
certainty, the changes of rate which occur during the period
of observation, b. If, instead of the tongue, the surface of
the skin is excited with the brush, the appearances observed
are very similar. The initial acceleration of the blood-stream
is more easily observed by this method than by the other, c.
Direct Excitation of a Sensory Nerve. — A frog having been
curarized, the integument is divided along the outer and
posterior aspect of the thigh in a line which corresponds in
direction with the slender biceps muscle, or leather with the
groove between the muscular mass which covers the front of
the femur (triceps femoris) and the bulky semi-membranosus.
The sciatic nerve, accompanied by the sciatic artery and vein,
lies immediately underneath the biceps, between it and the
semi-membranosus. In order to separate it from the vessels,
it is best to bring it into view by raising the biceps on a blunt
hook. Both webs having been arranged for observation under
the microscope, the nerve is divided a little above the knee,
and the central end laid on the copper points. The secondary
coil having been placed at a considerable distance from the
primary, and the eye fixed on an artery of the web of the un-

254 CIRCULATION OF THE BLOOD.

injured limb, the key is opened. The same scries of phe-
nomena present themselves as before — contraction and slowing
of the circulation, preceded by a much less obvious accelera-
tion. If now the other web is brought under the microscope,
it is seen that the contraction of the arteries is very inconsider-
able, the acceleration is more distinct. The explanation of
this is easy. The sciatic nerve being the channel by which
most of the vasomotor fibres find their way to the arteries of
the web, those vessels are in great measure (but not entirely)
paralyzed by its division. Consequentl}-, of the three effects
produced by excitation of the vasomotor centre — viz., increased
vigor of the contractions of the heart, increase of arterial press-
ure, and contraction of the arteries — the first two only mani-
fest themselves in acceleration of the blood-stream. In the
other limb, the vasomotor nerves being intact, the phenomena
present themselves in their completeness. The effect of
direct and indirect excitation of the medulla on the vessels of
the mesentery has as yet been imperfectly investigated. It is
certain that in general the contraction of the mesenteric
arteries is much less marked than of those of the web. It is
often entirely absent, the only change observed during excita-
tion being that the stream is accelerated. These facts do not
indicate that these arteries are out of the control of the
cerebro-spinal centres, but merely that the nerves excited are
not in reflex relation with them.

52. Reflex Excitation of the Medulla Oblongata in
Mammalia. — The vasomotor centre may be stimulated in
the dog, rabbit, or cat, by the electrical excitation of any sen-
sory nerve. The most convenient for the purpose is the sciatic.
The requirements are the same as for an ordinary kymographic
observation. If it is intended to excite the trunk of the sciatic
nerve, the animal must rest on its side. It must first be ren-
dered insensible by opium or chloral, and subsequently curar-
ized. In order to expose the sciatic nerve, an incision must
be made from a point half way between the trochanter and
the promontory of the ischium towards the tendon of the
biceps. Such an incision runs nearly parallel to the inner
and posterior edge of the long head of the muscle just named,
which edge must be found and drawn outwards. In the upper
third of the thigh, the nerve lies between the biceps and the
adductor inagnus, further down, between the biceps and the
semi-membranosus. If it is desired to stimulate the nerve
near its distribution, the peromeal nerve may be found very
readily in front of the ankle, on the fibular side of the com-
mon extensor of the toes. It is often called the n. dorsalis
pedis.

Excitation of the central end of the divided sciatic or of the
peronoeal nerve produces effects which are indistinguishable in

BY DR. BURDON-SANDERSON. 255

kind from those of direct excitation of the medulla, although
the augmentation of arterial pressure and other concomitant
phenomena are less considerable. In the case of the doi'salis
pedis, however, and other nerves to be immediately referred
to, there is a marked difference between the condition of the
arteries in the region to which the excited afferent nerve is
distributed, and those of the rest of the body.

Experiments showing that the same Degree of Excitation
op a Sensory Nerve wuicn produces General Contraction
op the Arteries in other Parts op the Body, diminishes
the Tonus of the Arteries of the Part to which the Ex-
cited Nerve is Distributed.

53. (1.) Excitation of the Nerves of the External
Ear of the Rabbit. — The ear of the rabbit derives its sensi-
bility from two nerves, both of considerable size. One of
these, the posterior auricular, approaches the surface at the
back of the neck, very near the middle line, and runs forwards
and outwards, under a thin covering of muscle, to the root of
the ear, where it penetrates a process of cartilage, easilj* felt
in passing the finger from the occiput outwards. By making
an incision between this process and the occipital spine, the
nerve can be very easily found. The other nerve (n. auricu-
laris maynus, see fig. 226) springs from the anterior branches
of the second and third cervical nerves ; it becomes superficial
at the posterior edge of the sterno-mastoid, and then runs up-
wards, covered only by integument, towards the thin edge of
the external ear, where it soon divides into two branches. It
is most easily found at the root of the ear, just before it di-
vides.

The animal having been curarized, the apparatus for artificial
respiration is connected with the trachea, and the manometer
of the kymograph with the carotid artery. The great auricu-
lar nerve is then carefully exposed, separated from the sur-
rounding parts with the aid of two pairs of blunt forceps, and
divided. The next step is to arrange the lobe of the ear in
such a way that the central artery can be well seen. With
this view, if sunlight is not at command, a paraffin lamp
should be so placed that its light may be thrown on the ear
from behind by a condensing lens, while the lobe itself is sup-
ported vertically by a suitable holder. Before beginning the
experiment, the central artery should be carefully observed,
attention being particularly directed to the rhythmical changes
of diameter which it undergoes. Its condition having been
carefully noted, and a preliminary kymographic tracing having
been taken, for the purpose of preserving a record of the pre-
vious arterial pressure, the central end of the nerve is laid
upon the points of the excitor, and the key opened for a couple

25$ CIRCULATION OF THE BLOOD.

of seconds. If no increase of arterial pressure takes place, the
secondary coil, which in beginning the experiment must be
distant from the primary one, is cautiously brought nearer to
it until this effect is produced. As soon as this is the case,
it is usually observed that the artery of the ear, instead of
contracting, dilates, and that the whole lobe obviously con-
tains more blood than it did before. Frequently, however, it
happens that, notwithstanding the increase of arterial press-
ure, no increased vascular injection is observable. In this
case, recourse must be had to the posterior auricular nerve,
the excitation of the central end of which is almost certain to
be followed by the effect in question. The augmentation of
arterial pressure and the dilatation of the auricular artery
appear to be collateral phenomena, both increasing gradually
during the few seconds which succeed the commencement of
electrical excitation. If care is taken neither to prolong the
excitation unduly nor to use too strong currents, the reaction
may be witnessed a great number of times in the same animal.

54. (2.) Excitation of the Dorsalis Pedis. — When the
central end of the divided dorsal nerve of the foot is excited,
phenomena occur of a similar nature. To enable the observer
to judge of the effect, the saphenous artery must be exposed
in its course down the inner side of the lower half of the thigh,
as recommended in § 49. It is then seen that during and
after excitation of the central end of the divided nerve, the
artery gradually dilates, subsequently regaining its former
dimensions.

The general result of the preceding experiments may be
expressed b}' sa}'ing that the afferent nerves to which the}r
relate (in common probably with other sensoiy nerves) con-
tain fibres so endowed that, when they are excited, the action
of the vasomotor centre is inhibited or suspended, as regards
certain regions with which the nerves in question are in close
anatomical relation. In its relations to the vasomotor ner-
vous system, the words " inhibitory" and "depressor," both
of which are used bj- physiologists to denote the case in which
arterial tonus is diminished by excitation of an afferent nerve,
may be regarded as equivalent.

Experiments relating to the effects of direct Excitation
and Division of the Vasomotor Nerves.

When a vasomotor nerve is excited directly, the arteries of
the region to which it is distributed contract. When it is
divided, they become permanently larger, and remain unaffect-
ed bj' changes in the condition of' the vasomotor centre,
whether these are determined by direct or reflex excitation.

BY DR. BURDON-SANDERSON. 257

55. (1.) Demonstration of the Vasomotor Functions
of the Cervical Portion of the Sympathetic Nervous
System in the Rabbit. — In 1852, Brown-Sequard showed
that when the sympathetic nerve is divided in the neck, the
central artery of the ear dilates, and the organ becomes vascu-
lar ; and that when the peripheral end is excited, the same ar-
teries contract ; and in the same year he demonstrated that
the former effect was dependent on paralysis, the latter on
spasm of the muscular walls of the vessels.

A rabbit having been placed on the support in the prone
position, about four cubic centimetres of a five per cent, solu-
tion of chloral (obtained by diluting a stronger solution with
the required proportion of the ordinary solution of chloride of
sodium) is gradually injected into the crural vein. [For the
method of exposing the crural vein and of inserting the canula,
see § 49]. As soon as the animal is insensible, an incision is
made about two inches in length parallel with the trachea; so
as to expose the edge of the sterno-mastoid muscle on one
side. The carotid artery is then brought into view, separated
from the vagus, and drawn forward from beneath the edges of
the muscle with the (fig. 203, c) hook, when it is seen that two
small nerves, both much smaller than the vagus, are drawn
forward with it, embedded in the membranous sheath (fig.
227). Of these two nerves, one, which is the smaller of the
two, is the depressor — an important cardiac branch of the
vagus; the other is the s3-mpathetic. To discriminate between
them, all that is necessary is to trace them both upwards. It
is then seen that the depressor arises by one root from the
vagus trunk, by another from the superior laryngeal; whereas
the sympathetic continues its course upwards alongside of the
artery. The sympathetic is also distinguishable by its gray
color. A loose ligature having been placed round the nerve,
the condition of the posterior auricular artery should be care-
fully observed, and noted in the manner recommended in the
previous paragraph. On dividing the nerve, it is seen that
the artery dilates, the rhythmical movements cease, and the
whole vascular network of the ear rapidly becomes injected
with blood. The change in the condition of the organ is very
similar, both in degree and in kind, to that observed after ex-
citation of the central end of the auricular nerve, but differs
from it in being more permanent. If after a few minutes the
ears are held, one in each hand, it is felt that that of the in-
jured side is warmer than the other. If now the peripheral
end of the divided nerve is placed between the copper points
and the key opened, the artery contracts and the congestion
of the car disappears.

This experiment shows conclusively that most of the spinal
vasomotor nerves which are distributed to the arteries of the
17

258 CIRCULATION OF TIIE BLOOD.

integument of the head, must reach their destination by pass-
ing through the superior cervical ganglion. As, however, the
superior ganglion is also in direct communication with the
spinal cord, the vascular paralysis is incomplete unless this
communication is broken by the extirpation of the ganglion.
To accomplish this, the incision must be continued upwards
in the angle of the jaw (see fig. 227). The carotid artery and
the vagus which accompanies it, having been brought into
view as far upwards as the stylohyoid muscle, are drawn for-
wards and towards the middle line with the blunt hook by an
assistant, while the sympathetic trunk is followed upwards
behind the artery with the aid of two pairs of blunt forceps.
The space in which the ganglion lies is crossed by the trunk
of the hypoglossal nerve, and by the st3'lohyoid muscle. The
latter should be divided. The extirpation of the ganglion is
best effected with blunt-pointed scissors. After section of the
sympathetic trunk in the neck, the normal condition of the ear
is gradually restored ; but if the ganglion is destroyed, the
effect is permanent.

56. (2.) Demonstration of the Vasomotor Functions
of the Splanchnic Nerves. — The splanchnic nerves con-
tain (in addition to those fibres which govern the peristaltic
movements of the intestine, with which we have at present no
concern) sensory and vasomotor fibres. The vasomotor fibres
are distributed to the arteries of the abdominal viscera. Their
importance depends on the fact that these arteries receive so
large a share of the systemic blood-stream (especially in the
rabbit), that the resistance offered by the arterial system to
the discharge of blood from the heart is largely affected by
any alteration of their calibre. The sensory part of the nerve,
in common with other sensory nerves, contains fibres by which
the vasomotor centre is influenced. It is also, as will be seen
in a future section, in reflex relation with the heart through
the vagus. The splanchnic nerve in the rabbit leaves the sympa-
thetic trunk at the 8th or 9th ganglion, passes downwards in
front of the psoas major muscle, receiving branches from the
other thoracic ganglia. At the level of the tenth thoracic
vertebra, the two nerves lie on either side of the descending
aorta, and accompany it downwards until it reaches the dia-
phragm, at which point the right splanchnic is further away
from the vessel than the left. After entering the belly, the
left splanchnic retains the same relation to the aorta as before,
ending in the lower of the two caeliac ganglia, which is easily
found above the left supra-renal capsule on the front of the
aorta. The right nerve is more difficult to find from its lying
further from the aorta, separated from it by the breadth of the
vena cava. It ends at the level of the right supra-renal cap-
sule, in the superior caeliac ganglion which lies in front of the

BY DR. BURDON-SANDERSON. 259

vein. The splanchnic nerve may be reached either in the ab-
domen or in the thorax. In very exact experiments, and es-
pecially in those that relate to the functions of the afferent
fibres, it is obviously desirable that these organs should not
be exposed b}r opening the peritonoeal cavity; but for the pur-
pose of demonstrating the vasomotor functions of the nerve,
this precaution is unnecessary. When one of the splanchnic
nerves is divided in the rabbit, the arterial pressure sinks ; on
electrical excitation of the divided nerve, it rises to a height
which far exceeds the normal limits. Section of the other
nerve is followed by further reduction, which, however, is not
so considerable as that produced by division of the first. The
reduction of pressure after section is attended with increase,
the elevation of pressure after excitation with decrease of the
frequency of the pulse. These facts are demonstrated as fol-
lows : —

A chloralized rabbit having been secured in the prone
position, and one carotid connected with the kymograph, the
abdominal cavity is freely opened in the linea alba. The in-
tegument is then carefully divided by a transverse incision,
which extends outwards from the first incision a little below
the edge of the ribs. A curved needle, of the form shown in
fig. 203 e, guarded by the left forefinger, is then passed under
the abdominal wall in the direction of the incision. Its point
having been brought out about two and a half inches from the
linea alba, the ligatures are tightened in such a way that the
muscles are constricted at different levels. The part between
the ligatures is then divided by a horizontal incision, which
may be continued in the same direction without hemorrhage.
This done, the left splanchnic nerve is plainly seen running
down parallel to the aorta on its left side, towards the supra-
renal capsule. The space in which it lies is occupied by very
loose cellular tissue covered by peritoneum, which must be
broken through to get at the nerve.

Immediately after the abdominal cavity is opened — that is,
before the nerves are touched — there is a very considerable
rise of arterial pressure, which is accompanied with slowing
of the pulse. These effects are, however, only transitory, the
mercurial column sometimes sinking immediately afterwards
below its original level. After division of the left splanchnic
it sinks very considerably, often as much as forty millimetres
(i.e., more than an inch and a half ). On placing the peri-
pheral cut end between the copper points of the excitor and
opening the key, the column suddenly rises. The sinking pro-
duced by section of the right nerve is comparatively incon-
siderable. As it is very difficult to get at, its division may be
omitted, all that is essential in the experiment being observ-
able after section of the left.

260 CIRCULATION OF THE BLOOD.

The following numerical results are derived from one of
Lndwig and Cyon's experiments: Previous arterial pressure,
90 millimetres; after division of left splanchnic, 41 mill.;
during excitation of peripheral end of divided nerve, 115 mill.;
after division of right splanchnic, 31 mill. After section of
both nerves, the vessels of all the abdominal viscera are seen
to be dilated. The portal system is filled with blood ; the
small vessels of the mesentery, and those which ramify on the
surface of the intestine are beautifully injected, the vessels of
the kidneys are dilated, and the parenchyma is hyperoemic; all
of which facts indicate, not merely that by the relaxation of
the abdominal bloodvessels a large proportion of the resist-
ance to the heart is annulled, but that a quantity of blood is,
so to speak, transferred into the portal system, anil thereby as
completely discharged from the systemic circulation as if a
great internal hemorrhage had taken place.

Part II. — The Heart.

Section V.— The Movements of the Heart.

The method of demonstrating the movements of the heart,
stated in the order of their importance, are the following: 1.
Exposure of the contracting heart in situ. 2. Application of
instruments to the prsecordla, for the purpose of measuring the
cardiac movements of the wall of the chest. 3. Listening to
the sounds of the heart. 4. Imitating the movements of the
living heart by the production of similar passive movements
in the dead heart.

57. Study of the Movements of the Heart in the
Frog. — Before beginning the study of its movements, an ade-
quate knowledge of the form and anatomical relations of the
organ must be gained by dissection. For this purpose, the
heart and great vessels should be filled with some solid sub-
stance which can be rendered fluid by warming it; such, for
example, as cacao butter or the ordinary gelatin mass (see
Chap. VI.). This must be injected by the vena cava inferior
in sufficient quantity to fill the heart and great vessels (see
fig. 228). It is then seen that the organ, as a whole, is egg-
shaped ; but is more or less flattened from side to side by a
furrow which crosses the heart nearly at right angles to its
axis, but inclines downwards towards the left; it is divided
into an upper globular (formed of the two auricles) and a
lower conical part (the ventricle). On its anterior aspect, the
ventricle is continuous with a cylindrical prominence (the
bulb), which projects from the anterior aspect of the right
auricle, and terminates above by dividing into two arteries, the

BY DR. BURDON-SANDERSON. 261

right and left aorta. Of these aortfe, which part from eacli
other at the middle line, the left is the larger. The posterior
wall of the right auricle extends backwards into a club-shaped
appendage, the sinus venosus. This body may be described
as the dilated end of the large vena cava inferior. It first
extends vertically upwards in the middle line, in continuity
with that vein, applying itself against the oesophagus behind,
and opening towards the front into the right auricle, from
which it is separated by a slight furrow. At the top it re-
ceives on either side the two venae cavae superiores, which,
however, are relatively small. The two auricles are separated
from each other b}' a septum, which stretches as a curtain from
before backwards, between them. This curtain ends below in
a crescentic margin, beneath which the two cavities communi-
cate freely. The orifice leading from the sinus venosus into
the right auricle is guarded by a well-marked Eustachian valve,
which hangs downwards and towards the right. The auriculo-
ventricular valve consists of an anterior and a posterior cur-
tain, both of which are continuous at their edges with the
auricular septum.

The mode of exposing the heart has already been described.
The facts to be observed when the pericardium is opened are
the following : The series of muscular movements which are
performed b}' the heart each time it contracts is seen to begin
at the upper end of the vena cava inferior and sinus venosus.
From the sinus the peristaltic wave extends to the auricles;
but it is not until the auricular contraction is complete that
the ventricle suddenly draws itself together. Before this last
act is accomplished, it is asually seen that the sinus venosus
is fall, and the auricles are already filling. In a moment they
become distended and contract, transferring the blood they
contain to the now empty and flaccid ventricle, which in its
turn forwards it onwards to the bulbus aortas and arterial
system. In consequence of the fact that during the contrac-
tion of the ventricle the auricles are already filling with blood,
and that the ventricle does not fill until the auricle contracts,
the successive appearances presented by the heart during each
cardiac period are very much as if there were a constant ex-
change of blood between the two great chambers into which
the organ is divided, and at once suggest the notion that the
auricles and ventricle dilate and contract alternate^', the one
seeming to contract while the other dilates, and vice versa.
It is easy, however, for any one who possesses the faculty of
observation to satisfy himself that this is not the case, and
that, while the ventricular contraction is determined by the
auricular, and the auricular by that of the sinus, the last
originates of itself — i. e., independently of any previous
movement.

262 CIRCULATION OF THE BLOOD.

The precise time between the successive acts above described

may be measured by arranging a lever of the second order in
such a way that, while it rests near its bearings on the con-
tracting heart, and follows its movements, its distal end in-
scribes those movements on the cylinder of the recording ap-
paratus. In this way a tracing is obtained (Fig. 220), in
which the relaxation of the heart is marked by a rapid descent
of the lever, the auricular contraction by a first ascent, the
commencement of that of the ventricle by a second, and its
continuance by a slow subsidence, suddenly ending in the
rapid diastolic descent already mentioned. Thus, in the ex-
ample given, the interval between the vertical lines a and b cor-
responds to the auricular s}'stole ; that between b and c to the
contraction of the ventricle — so that the auricles are in dia-
stole from b to a, the ventricles from c to b.

58. Study of the Movements of the Heart in Mam-
malia.— For this purpose a rabbit must be completely chlo-
ralized. The trachea having been connected with the appa-
ratus for artificial respiration, and the frequency and quantity
of the inflations carefully regulated, the chest is opened in the
manner already indicated in § 49. The facts to be studied are
the following : a. At the beginning of the period of relaxation,
the heart is so flaccid that it obeys the law of gravitation, and
is consequently flattened from side to side, just as we usually
see it in the dead body. It does not follow, from this observa-
tion, that the relaxed heart has the same form when inclosed
in the thorax, but on other grounds it probably is so, for its
form within the chest when in the flaccid condition is mani-
festly determined partly by gravity, partly by the shape of the
space in which it is contained; and inasmuch as the space is
a wedge-shaped one, bounded anteriorly b}' the sternum and
ribs, posteriorly by the diaphragm, but virtually unlimited
towards either side, we may be quite sure that the organ is at
least as much flattened antero-posteriorly in the natural state,
as it is seen to be when the chest is open. b. During the re-
mainder of the diastole the ventricles are still flaccid and per-
fectly passive, but the conditions are changed. While gradu-
ally filling with blood, they go through those changes of form
which are exhibited by a bladder contained in a basin when it
is gradually filled with water, c. At the end of diastole fol-
lows a very short period, during which, although the ventricles
are still soft, active muscular movements can be observed.
This is known as the prse-systolic period. Systole has in re-
ality begun; but the auriculo-ventricular valves not having
yet had time to close, the ventricular contraction is unresisted.
The heart, like any other muscle, so long as it contracts with-
out opposition, is soft. cl. The moment that the valves close,
the heart hardens and becomes globular, slightly twisting

BY DR. BURDON-SANDERSON. 263

round its axis, -while the apex is thrown forward, and at the
same time approaches the base. If at the moment of ventri-
cular hardening the attention is fixed on the aorta, that great
artery is seen to undergo the same changes of form which we
have already studied in the arterial pulse — changes due partly
to lateral expansion, i. e., increase of diameter ; partly to axial
expansion, i. e., increase of length. The "locomotive" move-
ment, which results from the axial expansion of the aorta, has
its influence on the heart, for it compensates for the axial
shortening which occurs when the heart gathers itself up into
a globe to overcome the arterial resistance which is opposed
to it at the moment that it begins to force its contents into
the already distended arteries.

In the preceding paragraphs the attention of the student has
been directed entirely to the arterial side of the heart, i. e., to
the movements of the ventricles and great arterial trunks.
These having been mastered, he must next observe those of
the auricles, with special reference to the order of time in
which they occur.

At the commencement of the period of ventricular relaxa-
tion the whole heart is flaccid. The duration of this period
varies inversely as the frequenc}7 of the pulse, so that no
general statement can be made with respect to it. As long
as it lasts, blood enters the auricles from the systemic and
pulmonaiy veins. At a moment which anticipates the harden-
ing of the ventricles (in the rabbit) by something like a fifth
of a second, the auricles harden, while the ventricles, which
have alread}' received a certain quantity of blood through the
open auriculo-ventricular orifices, fill much more rapidly.
This hardening of the auricles is not, however, to be compared
either in vigor or suddenness to that of the ventricles ; it
docs not affect the whole auricle at once, but rather seems to
spread from the vena? cava? towards the ventricles as a wave
of contraction. While the auricle is still contracting, the pre-
paratory " prae-s}Tstolic" movements begin in the ventricles,
culminating, as already described, in the ventricular shock, or
heart pulse.

To complete the stud}r of the movements of the heart in
situ, they should be observed under various abnormal condi-
tions, e. g., under the influence of section and excitation of
the vagi, in dyspnoea, and after hemorrhage. The appear-
ances then seen will be referred to under the proper heads.

59. The Cardiac Impulse. — It has been already stated
that the ventricular part of the heart is contained, both in
man and in the lower mammalia, in a somewhat wedge-shaped
ipace, the posterior wrall of which formed by the diaphragm is
more or less resistant. Consequently, when the ventricles
suddenly harden and become globular, they knock against the

2G4 CIRCULATION OF THE BLOOD.

wall of the chest with more or less violence. This knock is
called the cardiac impulse. It is precisely coincident with the
complete closure of the auriculo- ventricular valves, and deter-
mines the bursting open of the sigmoid valves. If the base
of the heart, ?'. e., the roots of the great arteries, were fixed,
the shortening of the ventricular axis, which, as we have seen,
occurs at the moment of hardening, would determine a with-
drawal or retraction of the apex from the position occupied
by it in diastole. As, however, this shortening is attended
with lengthening of the aorta, its retractive effect is more or
less neutralized, so that the seat of impulse — in other words,
the centre towards which the muscular mass of the ventricles
draws itself together — is not far from the position occupied
by the apex of the heart when in a state of relaxation. This
can be demonstrated both in man and in the lower animals.
In a rabbit or dog rendered insensible by opium or chloral, a
number of long slender needles are introduced into the heart
in the following positions: No. 1 is inserted vertically into
the ventricle at the point at which its knock can be felt by
the finger most distinctly. From this point a line is drawn
upwards and inwards towards the root of the aorta, along
which Nos. 2, 3, and 4 are inserted in a similar manner in the
intercostal spaces. In like manner, Nos. 5 and G are inserted
at equal distances on either side of the impulse in the same
intercostal space. The movements executed by these several
needles differ according to their relation to the central one,
No. 1, which, although it is affected by the ascent and descent
of the diaphragm, is indifferent as regards the heart. Of the
series, Nos. 2, 3, and 4, the free end of each performs an in-
stantaneous upward movement, the extent of which is in pror
portion to its distance from No. 1 ; and finalljr, Nos. 5 and 6
oscillate more or less horizontally, their free ends receding
from each other, as well as from No. 1, at the moment of the
impulse. From these facts we learn that, whereas that part
of the ventricular mass which knocks against the chest is
nearly stationary, the base of the heart moves downwards,
and to the left at the moment of the ventricular hardening,
i. e., of the aortic pulse; and that the other parts of the ven-
tricles are drawn towards the impulse in a degree proportional
to their distance from it.

In man, the same facts are demonstrated with the aid of the
cardiograph. The word cardiograph has been applied by
various writers to a variety of instruments, which differ from
each other both in their form and in the principles on which
they are constructed, but agree in the purpose which they are
intended to fulfil. This purpose is the recording of the cardiac
movements of the wall of the chest by the graphic method.

BY DR. BURDON-SANDERSON. 265

60. The Cardiograph. — The cardiograph I use is shown
in fig. 230. Its' most important part is a hollow disk, the rim
and back of which are of brass ; the front is of thin India-
rubber membrane. This disk is called a tympanum. To the
brass back a flat steel spring is screwed, which is bent twice at
right angles in the same direction, in such a way that it over-
hangs the India-rubber membrane. The extremity of this
spring, which is exactly opposite the centre of the face of the
tympanum, is perforated by a steel screw, the point of which
rests on the membrane, while its head is surmounted by an
ivory knob. The tympanum is further provided witli three
adjusting screws, by which, when in use, it rests on the wall
of the chest, with its face parallel to the surface, and can be
approximated or withdrawn at will. It is evident that when
the screws are so adjusted that the spring presses on the chest,
whatever movements of expansion or retraction are made by
the surface to which it is applied are communicated to it, and
by it to the India-rubber membrane with which its point is in
contact. The cavity of the disk communicates by a vulcanized
India-rubber tube with a second tympanum, represented in fig.
231, in such a way that the two tympana and the tube inclose
an air-tight cavity. The result of this arrangement is, that
whatever movement is performed by the first is simultaneously
reproduced, but in the reverse direction, by the second. If
the tympana are of equal area, the extents of the primary and
secondary movements are equal. When, as is usually the
case, the areas are unequal, the extent of movement is approxi-
mate^- inversely proportional to the areas. The movement of
the second tympanum is magnified and inscribed on the regis-
tering cylinder by a lever in the manner explained in a pre-
vious paragraph. By this apparatus a tracing is obtained,
which is an exact representation of the movements of the sur-
face against which the spring is applied, so that, if the instru-
ment is graduated, it may be used not only for the purpose of
estimating the relative duration of those movements, but for
measuring their extent.

For the purpose of studying the cardiac impulse in the hu-
man chest, the subject should be allowed to rest supine on a
flat surface, with his head on a pillow. The impulse is sought
for in the normal position, i.e., in the space between the fifth
and sixth ribs, about half an inch nearer the sternum than the
mammary line (the line which passes vertically through the
nipple). On applying the cardiograph in this position, with
the ivory knob pressing against the seat of impulse, a tracing
is always obtained which has the general characters exhibited
in Fig. 232a, in which the moment of hardening is indicated
by a sudden ascent of the lever, and the end of the ventricular
systole by an equally marked, but not so sudden, descent. If

266 CIRCULATION OF THE BLOOD.

now the cardiograph is shifted towards the sternum, the
character of the tracing is entirely altered. '(See Fig. 2326).
The ventricular hardening is still, indeed, indicated by a jerk
upwards of the lever; but this is immediately succeeded by a
descent of such a character as to afford evidence that at the
point investigated the thoracic wall, instead of bulging, is re-
tracted during the systolic effort. This phenomenon, which
is well known to pathologists, being so marked in some con-
ditions of disease that it is easily appreciated b}' the unaided
hand or eye, has been called the " negative impulse." It means
that the heart, which, when gradually filling with blood applies
itself to the whole prsecordia, gathers itself from all directions
towards the centre of impulse — in bedside language, commonly
miscalled the apex. If the cardiographic tracing of the im-
pulse is compared with that obtained manometrically by a
method to be immediately described, it is obvious that the two
correspond with each other very closely ; so that we are per-
fectly safe in assuming, as has been done above, that the ascent
denotes the beginning, the descent the end, of the ventricular
effort. We can thus determine with the greatest precision the
moment at which the mitral and tricupsid valves close. The
moment of the closure of the arterial valves is not so certain,
for it does not coincide with the end of the systole. It is
sometimes marked b}T an up-and-down movement of the lever,
due to the vibration into which the chest wall is thrown at the
moment that the curtains of the aortic valve come together.
The auricular contraction is often indicated by a slight eleva-
tion, which precedes the impulse by a distinct interval.

61. Investigation of the Sounds of the Heart. — The
sounds of the heart can be studied both in man and in the
lower animals. The first or dull sound coincides with the
hardening of the ventricles, the complete closure of the
auriculo-ventricular valves, and the bursting open of the arte-
rial orifices.

It is caused principally by the sudden distension of the ven-
tricles, but can be proved experimentally to be also in part of
the same nature with the noise made by all muscles in the act
of contracting against a resistance. The second or sharp sound
is coincident with and caused by the closure of the sigmoid
valves. This is proved by the observation that if the valve is
injured, or prevented from closing by mechanical means, the
sound is no longer heard. In studying the sounds of the heart
in the lower animals, particularly in the dog, the student of
medicine should direct his attention specially to the modifica-
tions of the sounds under known conditions — e.g., in dysp-
noea, when the heart is distended with blood ; after hemorrhage,
when the ventricles are insufficiently filled in diastole ; after
section of the vagi, when the frequency of the contractions is

BY DR. BURDON-SANDERSON. 267

so great that the aortic valves have not even time to close, or
under the various conditions in which these nerves are directly
or indirectly excited. From all these modifications, the effi-
cient causes of -which are known and understood, lessons ma3r
be learnt which may be applied directly at the bedside as aids
in the interpretation of analogous phenomena when they pre-
sent themselves in man.

62. Study of the Action of the Valves in the Dead
Heart. — Although this method forms no exception to the
general rule that little can be learnt in physiology by teleo-
logical inferences from the properties of dead organs or tis-
sues, it is yet of great value to the student for the purpose of
illustrating the purely mechanical part of the action of the
heart. The heart of any mammalian animal may be used, that
of the pig being most suitable. The simplest method of imi-
tating the conditions which actually exist in the circulation,
consists in bringing one or other of the ventricles into commu-
nication with a reservoir placed at a sufficient height above it
b}r means of two flexible tubes. The most convenient form to
be given to the reservoir is that of a glass funnel, the stem of
which communicates by one of the flexible tubes with the aorta.
The other tube ends in a large glass canula, which is secure^
tied into the ventricle near its apex ; its opposite end is fitted
to a glass s}'phon, the short leg of which dips into a funnel ;
the tube is guarded by a clip. The funnel and syphon having
been filled with water, and the clip closed, the apparatus is
ready. On opening the clip, water flows into the right ven-
tricle and distends it ; on closing it and compressing the ven-
tricle with the hand, its contents are forced upwards through
the aorta into the funnel, while the tricuspid valve is distended.
To observe the action of that valve, all that is necessary is to
cut away part of the wall of the right auricle. It is then seen
that, when the ventricle is squeezed, the liquid contained in it
tends to rush outwards by the auriculo-ventricular opening,
carrying the valve with it. In a moment the curtains become
distended, meeting by their borders so as to form a tense mem-
branous dome, which projects into the auricle. The time which
intervenes between the commencement of the compression and
the tightening of the valve varies according to the vigor of the
contractions, the quantit}' of blood contained in the ventricle,
and the previous position of the valve, but must alwa3's be ap-
preciable. It corresponds to the praesystolic period previously
referred to. All these facts are learnt much more impressively
by introducing the index finger into the right auricle of a large
animal. In the horse this can be done easily by an opening
of such size that the finger is tightly grasped by it. The valve
bulges out as a tense membranous dome into the auricle at the
moment of auricular contraction. In observing the action of

268 CIRCULATION OF THE BLOOD.

the tricuspid valve in the dead heart, it is important to notice
what are the conditions which render the valve incompetent,
i. e., prevent it from closing completely. The most important
of these conditions is over-distension of the ventricle, by which
the ostium becomes too large to be covered by the valve.
When this occurs during life, the phenomenon known as the
venous pulse presents itself. The right ventricle being still in
communication with the venous system at the moment that it
hardens, blood is injected by it backwards. When, in the
human subject, this condition is permanent, it leads first to
dilatation of the great veins, and, secondly, to similar incom-
petence of the vein-valves nearest the heart. In such persons
two large swellings are seen on either side of the neck — the
distended jugular veins — which pulsate nearly synchronously
with the heart.

Section VI. — Endocardial Pressure.

By this term is understood the pressure exercised by the
blood contained in the heart, against its internal surface. It
can be measured in the frog and in mammalia.

63. Investigation of the Endocardial Pressure in
the Heart of the Frog under various Conditions. — In
the frog the action of the heart is maintained unimpaired after
the separation of the organ from the cerebro-spinal nervous
centres. It is not even necessary that it should be supplied
with blood. Serum (if perfectly fresh) of another animal may
be substituted for it, without apparently affecting either the
vigor or regularity of the cardiac contractions. These two
facts render it possible to use the heart of the frog for the solu-
tion of a number of problems, in reference to which it is desira-
ble to investigate the mechanical functions of the heart inde-
pendentty of the influence of the nervous S3rstem.

The method of preparing the heart for such experiments is
that first employed by Dr. Coats, of Glasgow, in an investiga-
tion relating to the mechanical work done by the heart in a
given time, in Lud wig's laboratory. It has been since used
with various modifications by Bowditch, Brunton, Blasius, and
others. The brain and spinal cord having been destroyed by
the introduction of a needle, the body of the frog is cut across
below the liver. The sternum with the anterior extremities
are removed, great care being taken to reserve on one side a
large flap of skin which ma,y be used as a cover for the nerves
and the heart. The heart is then freed of its pericardium, and
the little serous ligament by which it is connected witli the
posterior surface of that membrane is ligatured and divided.
The next step is to tie one branch of the aorta, and then to pass
a canula through the other and the bulb into the ventricle. The

BY DR. BURDON-S ANDERSON. 269

suspensory ligaments of the liver are then severed so as to ex-
pose the vena cava inferior. A ligature is passed round that
vessel, which is then slit open so as to allow a large canula to
pass into the right auricle. The canula having been secured,
the liver and lungs are removed, the stomach is severed through
the middle, and a stout glass rod, tapering at either end, is
passed from the mouth down the oesophagus. This rod should
be as large as possible, as the stretching of the parts between
the heart and the spinal column which is thus produced mate-
rial^ facilitates their satisfactory exposure. The end of the
glass rod which projects from the mouth must then be fixed in
a support, and the tube which is inserted in the right auricle
be fitted with a flexible tube and connected with a glass reser-
voir (for which purpose one of the patent syphon inkstands
does best) filled with reddish rabbit serum. The aorta is in
like manner connected with a manometer of the form indicated
in fig. 233, from which the general arrangement of the heart,
reservoir, and manometer will also be best understood.

The heart is charged with serum and brought into action by
filling the reservoir. From thence the liquid fills the right
auricle, passes therefrom to the ventricle, and is discharged by
it into the manometer. As soon as it is seen that no more air
bubbles pass through the proximal limb of the manometer
(the upper end of which is connected with a flexible tube for
the purpose of conveying the liquid pumped by the heart to a
suitable receptacle), the apparatus is ready. The mode of ex-
periment may be varied according as it is intended merely to
measure the variations of endocardial pressure which occur
during a cardiac period, or to observe the modifications which
that pressure undergoes under different mechanical conditions.

64. a. Variations of Endocardial Pressure which occur
during each Cardiac Period. — To observe these, the heart
must communicate exclusively with the manometer, the prox-
imal limb of which with the tube leading to it from the ven-
tricle, and the ventricle itself, must form one cavity filled with
serum and closed towards the auricles by the valve, and in
the opposite direction by the mercurial column and a clip, by
which the tube connected with the upper end of the proximal
limb is guarded. The manometer should be at such a height
that when the pressure is greatest the top of the proximal
column is at the same level as the heart ; and the quantity of
mercury it contains must be adjusted, by addition or subtrac-
tion, with the aid of a capillary pipette, so that when the heart
is in diastole the distal column is still about a millimetre
higher than the other. The reservoir for the supply of serum
must now be placed at such a height above the heart that the
auricle is equal to that existing during diastole in the ven-
tricle ; and inasmuch as this has been already arranged at a

270 CIRCULATION OF THE BLOOD.

millimetre of mercury, the height of the venous column of
serum must be about half on inch = 12 millimetres, the spe-
cific gravity of mercury being about twelve times that of serum.
In the distal column of the manometer is a glass piston, the
upper end of which bears a horizontal arm arranged in the
same way as that which bears the writing pencil in the ordi-
nary k3'mograph — the main differences being that in this case
the manometer is much smaller, and that, in order to avoid
friction, the tracing is recorded, as in the sphygmograph, on
glazed paper, blackened by passing it over the flame of a
paraffin lamp. The record so obtained is shown in fig. 234.
On account of the relative slowness of the movements and the
inconsiderable lumen of the manometer, the curve is very little
modified by the oscillation proper to the mercurial column, and
is therefore a true representation of the succession of changes
of pressure which take place in the ventricle. We learn from
it that in the frog the pressure exercised by the ventricle on
the blood it contains arrives at its acme somewhat gradually,
and persists for an appreciable period ; and that when the heart
relaxes, the subsidence of pressure is at first extremelj- rapid,
but subsequently somewhat more gradual. The rate of move-
ment of the paper being 40 centimetres per minute, the dura-
tion of each systole can be easily measured.

65. b. Modifications of the Endocardial Pressure Curve
under various Conditions. — For the purpose of investigating
the influence of various mechanical conditions on the action of
the heart, and particularly of changes in the relation of the
pressure in the veins and that in the arteries, the apparatus
must be so modified that the ventricle, instead of communi-
cating exclusively with the manometer, pumps the liquid, con-
stantly supplied to it from the venous reservoir, along a tube
or system of tubes representing the arterial system. To fulfil
these conditions, all that is necessary is, (1) to insert the arte-
rial canula, not in the bulb, but in the left aorta (the right
being tied), so as not to interfere with the play of the aortic
valve ; and (2) to join to the proximal limb of the gauge an
India-rubber tube, dilated near the junction into an elastic
bulb, and ending in a nearly capillary beak of glass, the pur-
pose of the latter being to furnish the required resistance, that
of the former to render the discharge as nearly equable as pos-
sible— in short, to replace the elasticity of the arteries.

The advantage of this arrangement does not lie in the cir-
cumstance that the mode of action of the heart is more natural,
for it makes little difference to that organ whether the liquid
it discharges at one contraction returns to it during the next
relaxation or is pumped forwards, provided that the pressures
to which it is subjected are the same in systole as in diastole.
It is rather that when the heart is so arranged that liquid is

BY DR. BTJRDON-SANDERSON. 271

pumped through it continuously, the observer has it in his
power to modify the arterial pressure (by altering the resist-
ance) without modifying the venous pressure, and vice versa,
and so to reproduce conditions which actually exist and exer-
cise a most important influence in the living body.

It is obvious that if the pressure on the venous side of the
heart is nil, no progressive movement will occur, whatever may
be the resistance in the arteries ; and, on the other hand, that
if the pressures on the two sides of the heart are equal, there
must also be no movement, for, the auriculo-ventricular valve
remaining open, the heart would act as in the previous experi-
ment, receiving back again in diastole whatever liquid it dis-
charged during s}rstole. Between these two extremes, that of
equalit}' of venous and arterial pressures and that of total
want of pressure in the auricles, a mean relation exists which
is most advantageous to efficient action, and cannot be de-
parted from in either direction without impairment of effect.
The existence of this ratio of greatest efficiency has been lately
demonstrated experimentally by Blasius;1 and it has been found,
first, that for every value of arterial resistance, it is possible by
successive trials to ascertain what venous pressure enables the
heart to contract with the greatest effect ; and, secondly, that
for every heart there is a certain value of arterial resistance
which is most advantageous. The mean result of numerous
observations is, that the frog's heart (rana esculenta) does most
work when it is opposed by an arterial pressure of about 35
millimetres of mercury. If the resistance is greater than this,
the heart becomes over-distended, and its valves incompetent.

66. Application of the preceding Methods to the
Investigation of the Problem of the Mechanical
Work done by the Heart in a given Time. — In the
preceding paragraph, the expressions, mechanical " effect" of
the heart's contractions, and " work" done by the heart, have
been used without explanation. Before proceeding further, it
is necessary to define them. The work done by the heart in
any given time is equal to the product of the aortic pressure
and the quantity of blood which passes through the aortic
orifice in the same time. To illustrate this, it is necessary to
revert to the experiment described in § 46, in which the circu-
lation is maintained artificially in the frog b}^ substituting for
the heart a column of serum of sufficient height. In this case,
so long as the height of the column remains unaltered, the
work done in carrying on the circulation truly represents that
of the heart. If it is allowed to diminish, the rate of flow
diminishes with it. To maintain constancy in the circulation,

1 Am. Frosch-ITerzen angestellte Versuche uber die Ilerz-Arbeit, etc.
Fick'a Arbeiten, Wurzburg, 1872, p. 1.

272 CIRCULATION OF THE BLOOD.

the liquid discharged by the sinus venosus must he constantly
replaced in the funnel as it flows out. The work which is ex-
pended in doing this per minute is the work by which tin; cir-
culation is carried on. Thus, supposing the height of the
column of serum to be 400 millimetres, and that it is found
that the level of the liquid in the funnel begins to subside
when not supplied at such a rate that the weight of serum
flowing through the aorta during one second is equal to one-
fifth of a gramme, then the force expended per second would
be that required to raise one-fifth of a gramme 400 rnillimetres,
i.e., one gramme to the height of a metre in 12.5 seconds, or
0.08 grammes to the same height in one second ; and this re-
sult has been arrived at in accordance with the proposition
with which we started, by multiplying the aortic pressure
(expressed in the height of a column of blood corresponding
to it) by the quantity discharged in the given time.

If exact information were attainable as to the quantity
which the heart actuall}- discharges at a stroke, it would be
possible to measure the quantity of work done by the heart in
the maintenance of the circulation in a mammalian animal,
and inferentially in man ; but inasmuch as no such method at
present exists, no estimate can be given which possesses even
approximate value. In the frog, however, a reliable estimate
can be made b}r the methods described in § 63, whichever form
of experiment is employed. Thus, when the heart communi-
cates exclusively with the manometer, the work which the
heart is made to do is to raise whatever quantity of mereur3r
is contained in the manometer between the level at which it
stands during diastole and that to which it rises in systole, to
the mean height height £, where h denotes the difference in
millimetres of the two levels. For evidently, of the whole
number of particles of mercury in the distal column, the sur-
face of which is caused to rise /( millimetres above the surface
in the proximal column, it is only the top particles which are
raised h millimetres above the level of the proximal column ;
those in the exact middle are raised only half h ; those above
and below, less or more in proportion to their distance from
the middle ; so that the mean elevation is half/?. The weight
is easily known if we know the aera, i. e., lumen, of the tube,
and the specific gravity of the mercur}'. If we designate the
former as a and the latter as s, we have the weight lifted by
the heart in each contraction to the height £, expressed by a
s h, and the work done (that is, the product of the weight
lifted and the height to which it is lifted) — ". If it is desired
to obtain perfectly accurate results, a manometer must be used
of which the area of the surface of the mercury in the proximal
limb is relatively very large. In the other form of experiment,
§ 64, i.e., when a continuous current of serum is pumped by

BY DR. BURDOX-SANDERSON. 273

the heart along a tube representing an arterial System, the
problem assumes a somewhat different form. The rate of flow
through the tube must be first ascertained by measuring the
discharge from its terminal orifice. This being known, the
answer to the question is arrived at by considering what
height of column of serum would, if substituted for the heart,
be sufficient to determine the same rate of efflux. This can
be learnt most accurately by a comparative experiment; it
can be deduced approximately from the measurement of the
mean pressure actually existing in the aorta. Here, as before,
the mechanical Avork done by the heart is the work which
would be required to raise the quantity of serum discharged
per second to the height corresponding to the pressure, i. e.,
to a height something like twelve times that indicated by the
mercurial manometer.

67. Investigation of the Endocardial Pressure in
Mammalia. — As this mode of investigation can only be prac-
tised on animals of large size, and has already perhaps yielded
all the results which can be expected from it, it will be suffi-
cient to give a cursory account of it here, referring the reader
to the papers of its author, Professor Chauveau, for detailed
information. The method consists in lodging in one or other
of the cavities of the heart of an animal, an India-rubber bag,
or ampulla, which communicates by a long narrow tube with a
manometer. The introduction of the instrument in question
(which has received the name of cardiac sound) into the right
cavities through the external jugular vein is perfectly easy, and
can be effected in the horse, as I can testify from my own ob-
servation, without occasioning the animal the slightest suffer-
ing or even inconvenience — a fact easily enough understood
when we reflect that the internal surface of the vascular system
is not supplied with sensory nerves. The ampulla does not
come in contact with the surface of the heart. The left ven-
tricle is reached through the carotid artery with somewhat
greater difficult}'. The left auricle is of course inaccessible.

The most important results have been obtained by a cardiac
sound so constructed that the variations of pressure can be
recorded in the. right auricle and ventricle simultaneously. By
means of this instrument, M. Chauveau has been able to demon-
strate the order of succession of the movements of the heart,
and the intervals of time which separate them from each other,
with an exactitude which would have been otherwise unattaina-
ble. Thus he has shown that in the horse the interval between
the hardening of the auricle and that of the ventricle is just
about a tenth of a second, and that the duration of the ven-
tricular systole is about three-tenths, whatever be the number
of contractions per minute; so that frequency of the pulse de-
pends not on the time taken by the heart to accomplish each
18

274 CIRCULATION OF THE BLOOD.

contraction, but on the interval of relaxation which separates
one systole from its successor. {See fig. 2o.r).)

Chauveau found the systolic pressure in the horse to be about
128 millimetres in the left ventricle, and 25 millimetres in the
right. These numbers express the relative values of the me-
chanical work done by the two ventricles. The absolute values,
as has been already stated, are unknown, from the impossibility
of determining the quantity of blood which Hows through the
heart in a given time.

Section VII. — Intrinsic Nervous System of TnE Heart.

Nothing is as yet known either as to the anatomical distribu-
tion of nervous elements in the hearts of mammalia, or as to
the functions which they perform. In the frog, both have
been the subject of minute and repeated investigation. We
have already had frequent occasion to observe that the frog's
heart continues to beat after its removal from the body, and
that this rhythmical movement often goes on for hours or even
for days, under favorable circumstances. From this it is evi-
dent that its maintenance is dependent on conditions which are
contained within the heart itself.

68. Proof that the Ganglion Cells contained in the
Heart are the Springs of its Automatic Movement. —
It is objected b}^ some physiologists that the rhythmical con-
tractions go on not merely in the whole heart when deprived
of blood and severed from the cerebro-spinal nervous system,
but also in mere fragments of the muscular substance which
cannot be admitted to contain ganglion cells. The answer lies
in the results of the following experiments: —

The heart of a frog just removed from the body is placed in
a watch-glass containing serum, or three-fourths per cent, saline
solution, in which it will continue to pulsate for many hours.
Small portions of muscular substance are then taken either from
the sinus venosas, the auricles, or the ventricle, and observed
in a drop or two of the indifferent liquid, under a low power.
It is then seen that portions taken from the sinus, the auricles,
or that part of the ventricle which is in the immediate neighbor-
hood of the auriculo-ventricular constriction, pulsate rhythmi-
cally, but that similar portions taken from the ventricle near
the apex do not pulsate. The pulsating bits may be further
divided with sharp scissors under the dissecting microscope,
until preparations are obtained which consist of only a few
muscular fibres. Many of these still contract rhythmically,
each fibre becoming shorter and thicker at each contraction, but
not losing its rectilinear contour. If now the pulsating and
non-pulsating shreds are submitted to microscopical examina-
tion, it will be found that, whereas ganglion cells cannot be

BY DR. BURDON-SANDERSON. 275

seen in the latter, they exist as a rule in the former. In the
recent state, indeed, it is quite impossible to demonstrate their
presence in either case, but they can be detected after prepara-
tion with chloride of gold in the manner directed in Chap. IV.

69. Description of the Intrinsic Nervous System of
the Heart of the Frog. — The heart of the frog is not known
to receive nerves from any source excepting the vagus. The
cardiac branches of this nerve, as they enter the heart (see §
73), apply themselves to the superior vena cava close to its
origin, and then, after giving numerous branches beset with
ganglionic cells to the sinus venosus, the two nerves combine
to form a plexus at the upper part of the septum, between the
auricles. From this plexus two filaments descend, the smaller
along the anterior edge of the septum, the larger along the
posterior. On approaching the auriculo-ventricular orifice,
each of them exhibits a distinct bulging (Bidder's ganglia),
from which radiating streaks may be seen to spread towards
the ventricle.

So long as the nerves are still outside of the heart they do
not contain any ganglion cells, nor give off any branches ; but
as they approach the plexus they become beset with cells, and
give off numerous filaments to the sinus venosus. The two
branches (anterior and posterior) have no special relation to
the two rami cardiaci from which they in common originate,
although Bidder finds that the anterior contains more fibres
from the right side, the posterior from the left. In their
course, both filaments give off branches, which ramify in the
septum or pass into the wrall of the auricles. In order to see
these nerves, the heart must be exposed by opening the peri-
cardium. Its point must then be drawn upwards, the two
aortse divided, and the ligamentous shred which connects it
with the posterior surface of the pericardium cut through.
The two vense cavae must then be divided as far from the heart
as possible, and the heart removed. If the organ is now
stretched on a wax plate by means of fine pins stuck into the
vena? cavae, one into the vena cava inferior, and one into each
vena cava superior, and examined under water, the two vagi
(rami cardiaci) can be seen where they are in relation with
the vena cava superior. If now the apex is drawn to the right
and fixed by a fourth pin, the side of the left auricle is ex-
posed, and may be slit open with fine scissors, so as to bring
into view the septum, which must then be cleared of the outer
wall of the auricle by careful dissection. Fig. 236 shows the
appearance of the septum prepared in this wa}r.

70. Demonstration of the Special Functions of the
Ganglia. 1. Slannius's Experiment. — The heart of a frog
having been exposed in the usual way, a short glass rod is
introduced into the oesophagus. All the other organs may

276 CIRCULATION OF THE BLOOD.

now be removed in the manner directed in § 03, care being
taken to avoid interfering with tlie vena- cava*. The glass
rod having now been fixed horizontally on the table, and the
oesophagus secured by pins stuck through it into the table so
as to prevent it from slipping on the rod, the apex of the
heart is seized with blunt forceps and drawn forwards and to
the right. A silk ligature is then passed, with the aid of the
needle shown in fig. 203£>, between the vena cava inferior and
the ventricle, and between the vena; cava? superiores and the
right auricle, in such a position that when it is tightened it
will grasp the line of junction between the sinus venosus
and the right auricle. The ligature having been looped by an
assistant and carefully adjusted in the proper position, the
heart is left to itself. As soon as it is seen that it is con-
tracting regularl}', the ligature is tightened. After one or two
beats, the heart stops in a state of relaxation. The pulsations
of the sinus, however, continue at the same rate as before.
After a time the ventricle also begins to beat ; but on com-
paring its rhythm with that of the sinus, it is seen that they
do not agree.

2. In another heart, prepared in the same manner, the sinus
is cut off from the right auricle, the line of amputation corre-
sponding with that of the ligature in 1. In doing this, the
heart must be drawn forwards with the forceps by its apex as
above directed. The result is more striking when the scissors
used are not very sharp.

3. If in either of the above experiments the ventricle is cut
off from the auricles immediately after the ligature or amputa-
tion, as the case may be, it begins to beat again at once.

4. In a third heart, the line of ligature, i. e., the junction
between the sinus venosus and the right auricle, is excited by
the induced current. For this purpose Du Bois Reymond's
induction apparatus is used. The points of the excitor must
be very close to each other. The effect resembles that of the
ligature. If the electrodes, instead of being placed so as to
include the sinus, are applied to the auricles, no effect is
produced.

5. In another animal, TTn>o °f a grain of atropin (or less) is
injected underneath the skin. After a few minutes the heart
is removed, and experiment 4 is repeated. The electrical exci-
tation produces no effect, the ganglion of the septa being para-
lyzed. Experiment 1 is then repeated. The heart stops as
before.

All the preceding results can be obtained in the separated
heart. The method recommended facilitates the manipulation
without in the slightest degree impairing the value of the re-
sults. Stannius's experiment admits of two different explana-
tions, which are not, however, inconsistent with each other: —

BY DR. BURDON-SANDERSON. 277

1. The arrest of the heart may be regarded as a result of
the excitation of the ganglion of the septum, i. e., the mechani-
cal irritation of that part produced by the scissors or ligature ;
in other words, as an effect of the same nature as that pro-
duced in experiment 4, where that centre is subjected directly
to electrical stimulation; or,

2. It is dependent on the severance of the sinus venosus
from the rest of the heart. In this case it must be regarded
as of a different nature from the arrest produced by electrical
excitation.

If it were not for experiment 5, we should be inclined to
adopt the former of these views : for it is very easy to imagine
that it is not likely to make much difference whether we
squeeze the ganglion with a ligature, nip it between the blades
of a pair of scissors, or excite it by Faradaic electricity. In-
deed, any one who compares the two results — the arrest of
the heart by electrical excitation of the sinus on the one hand,
and that produced by ligature across the upper part of the
auricles on the other — would probably at once decide on their
identity. By previously subjecting the heart to the influence
of atropin, we are enabled to demonstrate that such a conclu-
sion would be erroneous ; for if the effect of ligature were of
the same nature, it would be counteracted by the same agency.

In order to explain the phenomena, it is necessary to assume,
what has not }Tet been proved anatomically, namely, that the
venous sinus contains an automatic motor centre. By this
term we understand (in accordance with the general notions
entertained as to r3rthmical action) a ganglionic centre, in which
energy tends to accumulate and discharge itself in the form
of motion at regular intervals, the length of which varies (a)
with the resistance to the discharge, and (b) with the rapidity
of accumulation.

The phj'siological ground for this assumption of the exist-
ence of a motor centre in the sinus venosus is, first, that the
succession of acts which make up a cardiac contraction com-
mences distinctl}' in the sinus, and that it is the only part of
the heart which contracts independent!}', i.e., without being
affected by the action of any other part of the organ; and,
secondly, that electrical stimulation of the sinus induces in-
creased frequency of the contractions of the whole organ. Ad-
mitting the existence of such a centre, and assuming also that
the ganglion of the vagus, situated, as we have seen it to be,
close to the line of ligature or amputation on the auricular
Bide of it, has the power of inhibiting, i.e., increasing the re-
sist ance to the discharges from that centre, and further that
it exercises a similar inhibitory influence on the motor ganglia
at the base of the ventricle, we are enabled to harmonize the
experimental results completely thus: In the ligature and am-

278 CIRCULATION OF THE BLOOD.

putation experiments, the heart stops for two reasons: first,
because the ventricle is separated from the motor centre; and,
secondly, because, by the pressure or mechanical irritation of
the ligature or blunt scissors, the vagus ganglion is excited.
In electrical excitation, on the other hand, the second of these
effects is produced without the first ; consequently, when under
the influence of atropin, the vagus ganglion is paralyzed — the
influence of ligature and amputation, in so far as they are de-
pendent on severance of the sinus from the rest of the heart,
are unaltered, but electrical excitation is without result.

On this subject the student will do well to consult the ori-
ginal papers, the references to which are as follows : As regards
the anatomy of the ganglia, the most important paper is that
of Bidder, in Midler's Archiv, 1852, p. 1G3; as regards their
functions, Stannius (Midler's Archiv, 1852, p. 85), Nawrocki
(Der Stanniusche Herzversuch, Heidenhain's Studien, 1861, p.
110), and Schmiedeberg (Untersuch. liber einige (jiftwirkungen
am Froschhcrzen. Ludwig's Arbeiten, 1871, p. 41).

71. Study of the Influence of Changes of Tempe-
rature on the Heart. — (a) In the Frog. Inasmuch as the
influence of temperature is obviously dependent on the in-
trinsic nervous system, the present is the proper time for con-
sidering it. The modes of investigation are the same as those
already described in the section on endocardiac pressure. Ex-
act and extended researches have been made by both of the
methods there given, the first having been employed by Cyon,
the second by Blasius. Of the two, the latter is preferable, on
account of the greater ease with which the work done can be
measured. The general result is, firstl}', that the quantity of
mechanical work which can be done by the heart in a given
time increases with the temperature up to a certain point
(about 20° C, but it differs in different animals, and no doubt
also at different seasons), so that it may be doubled or trebled
by a gradual rise from ordinary winter temperature to that of
summer; and, secondly, that under the same circumstances
the frequency of the contractions increases in much greater
proportion than the mechanical effect. Hence it results that,
although the total quantity of work done in a given time is
less at lower temperatures than at higher, the effect of each in-
dividual contraction is much greater.

If it is desired merely to observe the effect of changes of
temperature on the frequency of the pulse, much simpler ap-
paratus will answer the purpose. Either the whole heart may
be used or a part of it. In the former case, the organ having
been removed from the body is suspended by a thread attached
to the aorta in the interior of a tolerably wide test-tube fur-
nished with a cork, through the centre of which the thread is
drawn. At the bottom of the tube there is a bit of blotting-

BY DR. BURDON-SANDERSON. 279

paper, soaked with water. The " moist chamber" so prepared
is immersed vertically in a test tube filled with cold water,
which also contains a thermometer. The water in the beaker
is then very gradually warmed, while its temperature and the
frequency of the contractions of the heart are noted from time
to time. It is then seen that the frequency gradually increases
up to about 34° C, above which the contractions become ir-
regular, and are difficult to count with exactitude, until at last
the condition known as " heat rigor" (with reference to which
see Chapter XX.) supervenes. Similar observations may be
made with respect to portions of the heart, as, e. #., the base
of the ventricle or the sinus venosus. For this purpose it is
convenient to place the fragment on a cover glass in a drop
of serum, and invert it over the chamber of Strieker's warm
stage.

72. (b) In Mammalia. — From the observation of the very
remarkable effects which diminution and increase of the in-
ternal temperature of the body respectively produce, the one
in diminishing, the other in increasing, the frequency of the
pulse inrabbits and dogs, it seems probable that the mammalian
heart is more sensitive to temperature changes than that of the
amphibia. As, however, it is not possible to eliminate the in-
fluence of the central nervous system, this cannot be proved
experimentally.

Section VIII. — The Inhibitory Nerves of the Heart.

73. 1. Demonstration of the Influence of the Vagus
Nerve on the Heart in the "Frog.— Description of the
Vagus Nerve. — The vagus nerve originates in the frog from
the posterior aspect of the medulla oblongata by three or four
roots, the lowest (analogous to the spinal accessory) being
more to the front than the rest. The nerve passes out of the
cranial cavity through the condyloid foramen of the occipital
bone, outside of which it forms a ganglion, and is in close
relation with the sympathetic trunk. After leaving the sym-
pathetic (see fig. 237), it divides into two branches, of which
the anterior contains the glossopharyngeal, the posterior the
nerves which are distributed to the heart, lungs, and other
viscera. The vagus itself and its cardiac branch run along-
side of and in the same direction with the lower of the three
petrohyoid muscles, as far as the extremity of the posterior
horn of the hyoid bone, into which the muscle is inserted.
During this part of its course it is accompanied "by the laryn-
geal nerve, which leaves it just before it reaches the insertion
of the muscle. At about the same point it crosses the apex of
the lung, passing behind the pulmonary artery, and gives off
pulmonary branches which accompany that vessel. Having

280 CIRCULATION OF THE BLOOD.

crossed the lung, the nerve finds its way directly to the sinus
venosus, but is so surrounded with gray-looking connective
tissue, that in small frogs it is difficult to trace it. As it
enters the heart it is closely applied to the superior vena cava
and to the wall of the sinus.

74. Method. — A frog, having been slightly curarizcd or
rendered motionless by section of the medulla, is fixed in the
prone position. The sternum is then divided in the middle
line, and the two halves of the wall of the chest drawn to
either side, so as to expose the pericardium and lungs, while a
stout glass rod is passed down the oesophagus. The following
objects (.see fig. 237) are then seen : 1. The two aorta?, parting
from each other in the middle line, ascend outwards and up-
wards close to the cartilaginous tips of the posterior horns of
the hyoid bone. 2. From each of these horns muscular fibres
are seen to stretch backwards and upwards, towards the
occipital region; these are the petrohyoid muscles already
mentioned, which originate from the petrous bone, and are
inserted into the cartilaginous processes just referred to. The
lower of these nearly parallel bundles of fibres, is the guide
to the vagus nerve, which always lies along its lower edge. 3.
Following the muscles backwards, they are seen to be crossed
by a white nervous cord (the hypoglossal nerve), which ascends
upwards and inwards towards the muscles of the tongue.
Nearer the middle line, lying somewhat further from the
surface, but following the same general direction, another
nerve is seen, the glossopharyngeal. 4. Crossing upwards to
the larynx, over the tip of the inferior horn of the hyoid, the
laryngeal nerve is seen. This is the onl}' nerve which is likely
to be mistaken for the vagus ; it must therefore be traced back
for a short distance from the cartilage and divided. It is
convenient also to get rid of the hypoglossus.

The vagus, with the muscular slip which accompanies it, can
now be readily placed on or between the electrodes. On
opening the ke}', the heart usually stops in diastole, with its
cavities full of blood, the arrest not being preceded by any
previous slowing. If, however, Helmholtz's arrangement of
the induction apparatus is used, and the secondary coil is
placed at a sufficient distance, a degree of excitation ma}' be
attained which, while it falls short of stopping the heart, is
enough to diminish its frequency. With reference to this
effect, it is to be noticed that, although it is mainly due to
mere lengthening of the diastolic intervals, it is also accompa-
nied with an impairment of the vigor of the ventricular
systole; so that if the heart is connected with a manometer
(see § G3), the manometer rises less during the period of slow-
ing than it did before. Another interesting and important

BY DR. BURDON-SAXDERSON. 281

fact is, that the effect does not attain its maximum till several
seconds after the commencement of the excitation.

[In this and all other experiments in which it is desired to
note the time which elapses between the application of a
stimulus and its effect, we use the electrical indicator. It is
an arrangement exactly similar to an electrical bell, with the
exception that the hammer, instead of striking a bell, writes
on the recording cylinder of the kymograph. By a simple
mechanical arrangement, the same act which opens the Du
Bois' key closes another circuit, of which the electro-magnet
of the indicator forms part, and vice versa. This being the
case, the instrument makes vertical strokes on the cylinder at
the moment that the excitation of the nerve begins and ends.]

75. 2. Demonstration of the Influence of the Vagus
Nerve on the Heart in Mammalia.— In mammalia, the
inhibitor}' nerves contained in the vagi are in constant action,
consequently division of both vagi produces acceleration of
the contractions of the heart. In the dog, this effect is much
more considerable than in the rabbit, and is attended with an
increase of the arterial pressure, which in the latter is absent
(see fig. 238). On the other hand, electrical excitation of the
vagus, whether previously divided or not, retards the contrac-
tions of the heart in all animals, and, if the induced current is
strong enough, arrests the organ in diastole. (See fig. 239 a, 6.)

To show these facts in the rabbit, all that is necessary is to
narcotize the animal, to insert a needle in the heart at the
upper part of the praecordia (i. e., about an inch to the left of
the middle line, at the level of the third cai'tilage), and to ex-
pose the vagi on both sides of the neck. If, now, either
nerve is placed between the electrodes, and the key opened,
the movement of the needle either stops, becomes irregular,
or is mereby retarded and diminished in extent, according to
the strength of the current. To observe the effect of section,
loose ligatures must be placed round both nerves, and the
animal then left to itself, while the number of pulsations per
fifteen seconds is carefully counted. The two nerves are then
divided at once, and the countings repeated. The increase of
frequency usually amounts to about twenty percent. Finally,
the peripheral end of one nerve is excited, and the same effects
produced as by excitation of the undivided trunk.

In demonstrating the influence of the vagus on the heart in
the dog, it is desirable to connect the carotid or crural artery
with tlic kymograph ; for the most important effects are those
which relate to the changes in the arterial pressure. The pre-
liminary steps of the experiment are those described in § 34.
Loose ligatures having been placed round both vagi, and a
kymographic observation made, to determine the normal arte-
rial pressure and frequency of the pulse, both nerves are

282 CIRCULATION OF THE BLOOD.

divided simultaneously. The mercurial column at once rises,
mid the contractions of the heart become so frequent, that the
oscillations can no longer be followed by the eye, all that can
be distinguished being a vibratile movement of the column.
On exciting the peripheral end of either vagus, the same effects
are produced as in the rabbit. If the current is sufficiently
strong to stop the heart, the mercurial column sinks rapidly,
inscribing a parabolic curve on the paper (fig. 2:>!)/;). the exact
form of which depends on the condition of the arterial system ;
the rate of descent varing inversely as the arterial resistance
encountered by the blood in its progress towards the veins.
On discontinuing the excitation, the heart begins to beat
again, at first at long intervals, subsequently more frequently,
the pressure rapidly increasing until (for a few moments) it
exceeds that observed before excitation. In man, the trunk
of the vagus may in some persons be excited by pressure, and
results produced which correspond with those of electrical ex-
citation in animals. Prof*. Czermak, of Leipsic, is able, by
making pressure at the proper spot on the right side of the
neck, to arrest the action of his heart for a few moments.1

76. 3. Demonstration of the Influence of certain
Afferent Nerves, in reflex Relation with the Inhibi-
tory Nerves contained in the Vagus, on the Heart.
Bernstein's Experiment. — The inhibitory heart nerves
contained in the vagus are in intimate relation, through the
heart centre in the medulla oblongata, with certain afferent
fibres contained in the sympathetic system ; so that when
these fibres are excited, the same effects are produced as if
the vagus itself was directly acted upon. This may be shown
in the frog as follows: A frog is secured in the supine position.
The pleuro-peritoneal cavity is then opened, and the intestines
and other viscera are removed, great care being taken not to
injure the mesentery or the vessels and nerves which it con-
tains. Nothing now remains excepting the heart resting upon
the oesophagus. By carefulljr dividing the double layer of
serous membrane which forms the lateral wall of the cisterna
magna on both sides (see Chap II.), the ganglionic chains
(fig. 240) are brought into view along with the rami com-
mutneantes b}r which the ganglia are severally connected with
the anterior roots of the corresponding spinal nerves. In the
thoracic part of the visceral cavity the two aortas are seen
converging downwards, till at the level of the sixth vertebra
the}' meet to form one trunk, from which at its origin the me-
senteric artery is given off, to be distributed to the stomach
and intestines. If now the two aortas are raised near their
junctions, with the point of the forceps, it is seen that one of

1 Populare Vortrage, p. 27.

BY DR. BURDON-SANDERSON. 283

the ganglia of the cord sends towards the mesenteric arter}r a
branch which meets with its fellow from the corresponding
ganglion of the opposite side, to form a plexus of nerves
which surrounds the artery; and that from or through this
plexus a nerve or nerves (nervi mesenterici) can be traced
which follow the vessel towards its distribution. It is in these
nerves that the fibres which are in reflex relation with the
vagus are contained. To excite them, the best method is to
raise the aortae with the forceps from the bodies of the verte-
brae, drawing upwards with them at the same time the two
ganglionic cords; then to divide the abdominal aorta and the
two cords at the level of the seventh or eighth vertebra, sever-
ing at the same time some of the rami communicantes on
either side; and lastly, to place the two aortse and the cords
which accompany them, on the excitor in such a position that
the two ganglia next the junction are in contact with the
electrodes. On opening the key, the heart is arrested in dias-
tole, beginning to contract again rhythmically as before, when
the excitation is discontinued. To demonstrate that the
channels by which stimulation of the mesenteric nerves affects
the heart are the vagus nerves and their centres in the me-
dulla oblongata, the experiment must be thrice repeated; first,
after section of both vagi ; secondby, after destruction of the
medulla oblongata; and thirdly, after destruction of the brain,
the medulla remaining intact. In the first and second cases
the effect is annulled, in the third it is unaltered.1

77. Reflex Excitation of the Vagus of the Frog, by
Mechanical Means: Goltz's Klopfversuch. — It is now
many years since it was discovered by Goltz that excitation of
the ends of the mesenteric nerves by mechanical means produces
the same effect as the electrical excitation of their trunks. To
show this, a frog is secured on its back, the pleuro-peritoneal
cavity opened, and the heart exposed as before. The surface
of the intestine is then smartly tapped. After a few moments
the heart is arrested in diastole. If the ganglionic cord is then
divided on each side opposite the junction of the two aortae, and
the experiment repeated, no effect is produced. Another frog
is prepared in the same way, with the exception that both vagi
are divided. On repeating the tapping, the result is negative.
The same thing happens if, instead of dividing the vagi, the
cord is divided immediately below the medulla.

78. Reflex Excitation of the Vagus in Mammalia. —
The constant action of the inhibitory heart nerves in the higher
animals is dependent on the constant action of the centripetal
nerves in reflex relation with them. This may be shown as fol-

1 " Unterrachtrogen fiber den Mcchanismus dee regulatorischen Herz-
nerrensy stems." Archiv f. Anat. u. Physiol., 18G4, p. G14.

284 CIRCULATION OF THE BLOOD.

lows : Tn a rabbit, the trachea is connected with the apparatus
for artificial respiration, and the vagi arc exposed in the neck.
Thereupon the spinal cord is divided immediately below the
medulla oblongata. On the cessation of breathing, artificial
respiration is commenced. The cervical sympathetica are
then divided, and a needle is inserted in the heart. A succes-
sion of observations of the frequency of the heart's action is
then made, and both vagi are divided. No acceleration of the
pulse rate occurs.

The purpose of the experiment is to show that when the affer-
ent sympathetic nerves which are known to be in reflex relation
with the vagus heart nerves are severed, the same effect is pro-
duced on the vagus as if it were itself divided. There is no way
of accomplishing this directly, without such interference with
other nerves as would affect the heart, and thereby render the
result ambiguous. The most complete method would be to
remove the whole, ganglionic cord on both sides. Without
reference to the extreme difficulty of such an operation, it is
clear that it would involve the accelerator nerves (see § 80),
and thereby perhaps produce an effect the opposite of that which
we intended — a slowing instead of an acceleration of the pulse.
So also, when the spinal cord is divided immediately below the
medulla oblongata, the effect is modified not only by the de-
struction of the accelerator nerves, but b}r the general paralysis
of the vasomotor system. Consequently no answer to the
question is to be obtained by direct observation of the changes
which are produced by any such operation in the rate ofpulsa-
tion of the heart, so that the end we have in view can only he
accomplished indirectly. We already know that both vagi are
in constant action, i. e.. that the heart is constantly under their
inhibitory control; and that when this control is removed by
dividing them, the frequency of the pulse increases. It is ob-
vious that this effect can only be witnessed so long as the con-
trol is in actual exercise ; in other words, that if the vagi are
not acting, it would make no difference as regards the heart
whether they are divided or not. The consideration of this
fact suggests the method which is employed in the experiment
above described, which shows that in an animal in which the
spinal cord has been divided below the medulla, the rate of the
pulse is the same before and after section of the vagi.

Bernstein has further shown that the same thing happens
after destruction of the whole ganglionic cord, or of the cervi-
cal part, provided that the spinal cord is at the same time
severed at the seventh vertebra. In the dog, section of the
cord generally diminishes the frequency of the pulse. There
is no such effect in the rabbit. The difference can only be ex-
plained by supposing that in the former the activity of the
accelerator nerves is less, as compared with that of the nerves

BY DR. BURDON-SANDERSON". 285

in reflex relation with the vagus, than in the latter. In the
frog, section of the sympathetic at the level of the junction of
the aorta? has no direct effect on the frequency of the pulse, for
the same reason, viz., that in this animal the heart-beat is not
quickened by section of the vagi.

The influence of reflex excitation of the vagus through the
fifth nerve may be easily shown in the rabbit by causing the
animal to smell ammonia. The effect is immediate. Accord-
ing to the strength of the ammonia, the heart is arrested in
diastole, or the diastolic intervals are lengthened. The inha-
lation of chloroform, which is so apt to be fatal to rabbits, stops
the heart in the same way. When sudden death occurs in a
man by a blow on the epigastrium, or by drinking a large
quantit}' of cold water, the heart is arrested in diastole by the
agency of the same nerves as in Goltz's experiment.

79. Demonstration of the Influence of Increase or
Diminution of the Arterial Pressure on the Fre-
quency of the Contractions of the Heart. — The pulse is
retarded by increase, accelerated by diminution of arterial
pressure. That these effects are mainly dependent on the in-
hibitory heart nerves, can be shown in the rabbit as follows :
Ligatures having been passed round the vagus nerve on each
side, and a needle inserted in the heart, the fingers of the right
hand are placed under the animal's back, while the thumb is
firmly pressed upon the aorta, the beats of the needle having
been previously counted. On making pressure, the frequency
of the contractions of the heart is diminished, and this effect
continues so long as the pressure lasts.

Both vagi are now divided and the experiment repeated.
The frequency of the pulse is still slightly diminished, but the
degree of diminution is not to be compared with the previous
effect. This experiment can be made with greater exactitude
by applying the pressure to the aorta directly, at the same
time connecting the carotid artery with Fick's kymograph.
To accomplish the first of these objects, the abdominal cavity
is opened in a chloral ized rabbit in exactly the same way as
for excitation of the left splanchnic nerve. It is then easy to
place the thumb directly on the aorta as it passes between the
crura of the diaphragm. Tracings are thus obtained which
show that, during obstruction of the aorta, the arterial press-
ure is doubled, or even trebled, and the pulse rate much di-
minished, the status quo being re-established when the thumb
is removed from the aorta. After division of the vagi, the
effect as regards pressure is of course as marked as before, but
there is scarcely any slowing of the pulse.

The fact that the effect of aortic obstruction in diminishing
the frequency of the pulse is so markedly weakened by section
of both vagi, shows that these nerves bear a large part in its

286 CIRCULATION OF THE BLOOD.

production, and therefore that the relation between cause and
consequence is in this case not dependent on the lengthening
of the systole by resistance, as supposed hy Marey. The
question, however, remains, whether the mechanical explana-
tion may not be accepted as regards the remainder of effect
which is observed after the vagi are divided. There are two
reasons why this is not possible. One is, that here, as in other
cases when the pulse rate is retarded, the retardation does not
signify that the systole is lengthened, but that the diastolic
intervals are more protracted. The other reason is, that even
after section of the vagi, the retardation of pulse produced by
increased arterial pressure is postponed, whereas if it were
merely mechanical it would certainly be immediate. We must
therefore turn to the nervous system for its explanation —
either to some influence exercised on the heart by means of
accelerator nerves, which after section of the vagi are the only
channel by which the heart is in communication with the cere-
brospinal centres, or to excitation of the inhibitory nerves in
the heart itself. Considering that in the frog the same effects
are produced by exciting the ganglion of the vagus in the cut-
out heart as by exciting the vagus itself, and that we have
no reason to believe that increased pressure produces any
paralyzing influence on the accelerators, we need have little
hesitation in concluding that the effect of increased blood-
pressure in retarding the heart's rl^-thm is exercised entirely
through the inhibitory heart-nerves ; and that it is due princi-
pally to the increased supply of blood to the intra-cranial vagus
centre — i. e., to the medulla oblongata, but partly also to the
influence of the increased endocardial pressure on the vagus
ends in the heart itself.

80. Demonstration of the Functions of the Accele-
rator Nerves. — It has been already seen that when, after
severance of the spinal cord just below the medulla oblongata,
the organ is excited electrically below the section, two effects
are produced — the arterial pressure, reduced by the section, is
enormously increased, and the heart beats much more fre-
quently. Bczold thought that both of these effects were due
to the direct action of the spinal cord on the heart. Ludwig
and Thiry showed that, as regards arterial pressure, this was a
mistake. They also showed that the acceleration of the pulse
was in part a secondary effect of the increased resistance to the
flow of blood ; for they found that even after the complete
severance of all nervous communication between the heart and
the spinal cord, the pulse became markedly more frequent on
excitation of the cord. Hence Ludwig was led to doubt
whether, after all, the central nervous system exercised any
direct accelerative influence on the heart. We now know that
while v. Bezold was wrong in believing that the spinal nerves

BY DR. BURDON-SANDERSON. 287

have any power of augmenting the energy of the heart's con-
tractions, or of causing it to do more work in a given time,
there are certain nerves by which the distribution of its efforts
in time may be modified in the direction of greater frequency.
By the following experiment it can be shown that the accele-
ration of pulse which is produced b}' electrical excitation of
the severed spinal cord is independent of increase of arterial
pressure.

In a curarized rabbit in which respiration is maintained arti-
ficially, the spinal cord is severed from the medulla, and the
vagi, sympathetica, and depressors are divided. The arterial
pressure of course sinks to about an inch of mercury, and the
pulse becomes slower. The cord is then excited electrically.
The pressure rises at once to four or five inches, the rate of
the heart's contractions also increasing, but not in proportion
to the rise of pressure. As soon as the effects of stimulation
have subsided, and the circulation has had time to resume its
former condition, both splanchnics are divided, in consequence
of which the pressure again sinks a few millimetres. The ke\r
is opened : again we have acceleration of the pulse, but this
time, the verm pressores having been divided, the excitation
produces hardly an}r effect on the arterial tension. The results
of one of Ludwig's experiments are as follows : After section
of the depressors, vagi, and sympathetics, arterial pressure 60
millimetres, pulsations in 15 seconds, 52 ; after section of cord,
arterial pressure 20 millimetres, pulsations 45 ; during excita-
tion of cord, arterial pressure 80 millimetres, pulsations 61;
after section of splanchnics, arterial pressure 10 millimetres,
pulsations 27; during excitation of medulla, arterial pressure
12 millimetres, pulsations 42.

81. Proof that the Inferior Cervical Ganglion is
the Channel by •which the Direct Influence of the
Spinal Cord on the Heart is exercised. — Before pro-
ceeding to describe the experiments by which this is shown,
it will be necessary to give an account of the anatomical rela-
tions of the lowest cervical ganglion in the rabbit and dog.
It is obvious, from what we know of the anatomy of the
cardiac nerves as well in man as in the lower animals, that,
with the exclusion of the vagus, the only channels by which
the spinal cord can influence the heart directly are the rami
communicantes, by which it is united with the ganglia. By
experiment we learn that the communicating filaments by
which the accelerating influence of the cerebro-spinal centres
is transmitted, are those which enter the inferior cervical
ganglion.

In the rabbit, the trunk of the cervical sympathetic ends at
the root, of the neck, in the inferior ganglion. This ganglion
lies deeply on the surface of the muscles which cover the spinal

2S8 CIRCULATION OF THE BLOOD.

column (longus colli), and consequently to the inner side of
the tendinous origins of the scalenus milieus from the trans-
verse processes. It has the oesophagus on its inner .side, the
vertebral artery on its outer, and lies behind the carotid artery
and internal jugular vein. The following are the best guides
to its discovery: Superficially, the junction of the external
jugular vein and subclavian vein to form the vena innominata,
in the angle between which vessels the phrenic nerve appears
lying on the scalenus anticus ; more deeply, the origins of the
scalenus anticus, from the two last cervical transverse pro-
cesses; and particularly the vertebral artery where it passes
to the inside of these insertions, to enter the foramen trans-
veraarmm of the sixth cervical vertebra. The upper end of
the ganglion is to be found close to the artery on its inner
side. The ganglion receives from above, in addition to the
sympathetic trunk, communicating branches from the brachial
plexus and from the vagus, and a branch (the so-called radix
brevis) which accompanies the vertebral artery. Downwards,
the ganglion sends (besides those leading to the first thoracic
ganglion) branches wdiich go towards the heart. One of the
most internal of these is the continuation of the depressor
nerve, to be hereafter mentioned, which rather passes by the
ganglion than springs out of it, and looses itself in the plexus
of nerves between the aorta and pulmonary artery. The com-
munication between the lower cervical and the first thoracic
ganglion takes place by two nerves, one of wdiich passes in
front of, the other behind, the subclavian artery, before that
arteiy gives off the vertebral. The accelerator fibres enter
the ganglion by the vertebral nerve, and thence find their way
to the heart through the cardiac plexus already mentioned.
(See explanation of fig. 241.)

In the dog, the arrangement of the accelerator nerves is
somewhat different. In this animal, as in the rabbit, the
lower cervical ganglion lies on the longua colli immediately to
the inner side of the vertebral artery, and above the subclavian.
It is connected with the first thoracic ganglion by two twigs,
one of wdiich passes behind the subclavian and vertebral arte-
ries, the other in front of them. Of its cardiac branches, of
which three have been distinguished by Cyon, the most im-
portant accompanies the recurrent nerve until that nerve
bends upwards to its distribution, and then follows the sub-
clavian or innominate artery to gain the cardiac plexus. From
above, the ganglion receives, first, the combined trunk of the
vagus and sympathetic, which here separate from each other,
the former continuing its course into the thorax ; and secondly,
two branches corresponding to those described in the rabbit.
The accelerator fibres are very variously distributed among
these several branches, sometimes finding their way to the

BY DR. BURDON-SANDERSON. 289

heart from the inferior cervical ganglion along the vagus, or
the recurrent, but most frequently by the cardiac branch
above described. For further details, see the explanation of
fig. 242.

Before entering on an}' experimental inquiry relating to the
accelerator nerves, it is absolutely necessary to make several
dissections. The mode of experiment is as follows: In a cu-
rarized rabbit in which artificial respiration is maintained in
the usual way, an incision is made in the middle line extending
from the upper third of the sternum to the upper end of the
trachea. The external jugular vein of one side is then brought
into view, tied in two places, and divided between the liga-
tures. The steruo-mastoid muscle is also divided between
ligatures : a strong, threaded aneurism needle is thrust under
the sterno-clavicular ligament and the upper fibres of the
pectoral muscles ; these, with the ligament, are divided be-
tween ligatures, and the cut ends drawn aside. By this pro-
ceeding, the carotid artery, the internal jugular vein, and the
subclavian vein, are brought into view. These veins and the
vena anonyma are tied and divided in the manner already in-
dicated, and any other vessels which come in the way are se-
cured. A simpler and more rapid mode of performing the
operation is the following : The superficial parts having been
exposed by two lines of incision, one of which is in the middle
line, while the other extends from it on either side in the di-
rection of the sterno-clavicular ligament, and the jugular vein
having been divided between ligatures, the next step is to find
the pneurnogastric nerve at the upper part of the wound, and
free it from the surrounding tissues. This done, a blunt aneu-
rism needle is threaded and passed carefully, with its convexity
backwards, along the course of the nerve, between it and the
carotid artery. Its point is then made to penetrate the sheath
and fascia immediately above the long, cord-like, sterno-clavi-
cular ligament. The thread is then severed, and the ends
having been drawn out to a sufficient length, the two ligatures
are tightened, the one inside and the other outside of the
aneurism needle, after which the whole of the tissues which
are tied off between the ligatures, including the great veins,
may be raised on the needle and divided. The needle, which
has been carefully kept in its place, is now again threaded,
and its point pushed downwards under the edge of the pectoral
muscles, as far as the upper surface of the first rib. The point
is then pushed outwards and forwards through the muscles,
the thread is again severed, and the muscles are divided be-
tween the two ligatures in the manner already described. By
this proceeding a deep hollow (see fig. 243) is exposed, in
which, among other important parts, the ganglion inferiics
lies, covered by a layer of fascia. This hollow is bounded
19

290 CIRCULATION OF THE BLOOD.

below by the crescentic upper border of the first rib, behind
and to the outside by the scalenus anticus, and to the inside by
the trachea and (on the right side) by the oesophagus. In the
depth of the hollow, to the outside, lies the subclavian artery
on its way to cross outwards over the first rib : the vertebral
artery springs from it just as it is about to leave the hollow
space. This vessel is the guide to the ganglion which lies on
its inner side concealed in a good deal of cellular tissue. To
find it, the most certain method is to seek for the trunk of the
sympathetic in the upper part of the space where it lies con-
cealed behind the carotid artery, and then to trace it down to
the ganglion. All this having been accomplished without
bleeding, there is no difficulty in passing a ligature round the
ganglion, so that at any desired moment it may be extirpated.
The same operation is then performed on the opposite side of
the body. Both ganglia having been thus prepared with as
little loss of time as possible, the sympathetic and vagus are
divided (so as completelj' to sever the nervous connection be-
tween the heart and the central nervous system), and one of
the carotids is connected with the kymograph.

The medulla oblongata is then divided, and comparative
observations are made, in the manner already directed, as to
the effect of excitation of the peripheral end of the spinal
cord on the arterial pressure, and on the frequency of the pulse
before and after extirpation of both ganglia. In the one case,
the rise of pressure is attended with acceleration ; in the other,
the frequency of the contractions of the heart remains un-
altered. This result proves, first, that the accelerative influ-
ence of the cordon the heart is conveyed by nerves which pass
through the ganglia; and secondly, that these nerves are not
in constant action. Although the cord, when excited, acts
throughout by means of them, their destruction produces no
effect on the heart when the cord is quiescent. To complete
the proof that the nerves which pass to the heart from the
sympathetic trunk, and particularly those which spring from
the ganglion, are concerned in shortening the diastolic inter-
vals, direct observations are necessary. Such observations
were first made by the brothers Cyon, who found that both in
the dog and rabbit most of the accelerator fibres reach the
ganglion by the nerve which accompanies the vertebral artery.
In both animals, but especially in the dog, as has been already
stated, the path followed by these fibres from the ganglion to
the heart varies considerably in different individuals. The
experiments by which these facts have been established are
among the most difficult in physiology, and consequently the
description of them lies beyond the scope of this work.

From the preceding experiments and observations, we learn
that it is the function of the accelerator nerves to shorten the

BY DR. BURDON-S ANDERSON. 291

diastolic interval, and thus, indirect^, to render the individual
contractions of the heart feeble and less effectual. How they
act, and what is their anatomical and physiological relation
either to the ganglion cells, or to the vagus of which they are
the antagonists, it is not at present possible to explain. As
has been already stated, the heart of the frog does not receive
any accelerator nerves. From the following experiment, how-
ever, it appears that the vagus nerves in that animal contain
accelerator fibres. To demonstrate this, the animal must be
placed under the influence of nicotin, which alkaloid, as lately
shown by Schmiedeberg, possesses the power of paralyzing the
terminations of the inhibitory fibres contained in the trunk of
the vagus, without affecting the intrinsic inhibitory ganglia of
the heart. If in a frog, into which about a thirtieth of a grain
of nicotin has been injected, one vagus nerve is excited, the
excitation, instead of arresting the heart in diastole, or dimin-
ishing its frequency, accelerates its contractions. And if,
instead of injecting the solution under the skin, the heart is
prepared after Dr. Coats's method, supplied with serum con-
taining nicotin, and connected with the kymograph, and
observed before, during and after excitation of the vagus,
tracings are obtained which show that the frequency of the
heart-beats is increased sixty per cent.; that the acceleration
commences about four seconds after the opening of the key,
and lasts about a minute and a half after the cessation of the
excitation; and that it is due to shortening, or rather annull-
ing, of the diastole, each systole following immediately on the
close of the preceding one (see fig. 244).

82. Demonstration of the Functions of the Depres-
sor Nerve. — In the rabbit as well as in the cat, a cardiac
branch separates itself from the vagus at the level of the thy-
roid cartilage, high in the neck, and ends in the inferior cervical
ganglion. In the rabbit, the nerve commonly originates in
two roots, one of which springs from the superior lar}'ngeal,
the other from the vagus itself, near the point at which the
laryngeal leaves it ; but very often it is derived exclusively
from the superior laryngeal. In its course towards the inferior
cervical ganglion, it is close to the carotid artery, and still
closer to the sympathetic trunk, from which it is distinguished
by its smaller size and whiter aspect. From the ganglion the
fibres of the depressor are continued downwards, forming the
two most internal of the filaments which in the rabbit pass be-
tween it and the heart. They can be traced to the connective
tissue between the origin of the aorta and pulmonary artery.
The depressor contains centripetal fibres, the function of which
is to diminish the activity of the vasomotor centre, and thereby
diminish the arterial pressure.

A rabbit is chloralized ; one carotid is connected with the

202 CIRCULATION OF THE BLOOD.

kymograph, and the vagus of the same side divided opposite
the thyroid cartilage. The depressor is isolated, and a loop
of thread passed round it. An observation is then taken of
the arterial pressure and pulse rate, after which the depressor
is divided. There is no alteration either in the height of the
mercurial column, or in the number of pulsations per ten
seconds. On exciting the peripheral end, there is still no
effect ; but on exciting the central end the pressure sinks to
about two-thirds of its previous height, and the pulse often be-
comes slower. On discontinuing the excitation, the status quo
is gradually restored.

The results of such an experiment are shown in the tracing
(fig. 245). It i3 seen that the excitation produces no change
whatever either in the character or frequency of the pulsations,
the only effect produced being diminution of pressure. In other
instances there is perceptible slowing, but the variations of the
two effects are never parallel. In the observation recorded in
the tracing, the vagus of the side opposite to that on which the
depressor was excited, was left intact ; consequently the heart
was still partly under the control of the intracranial inhibitory
centre. Notwithstanding this, the slowing was not appreci-
able. When it does occur, it must be attributed, without doubt,
to reflex excitation of the inhibitory heart centre, the effect of
which is conveyed to the heart by the undivided vagus.

The diminution of the arterial pressure cannot be referred
to any direct influence exercised by excitation of the depressor
on the heart, but to diminution of the resistance in the arterial
system ; i. e., to relaxation of the minute arteries. This may
be shown in the same animal which is used for the preceding
experiment, if the left splanchnic is divided (see § 56) and the
depressor excited as before. The mercurial column, which has
already fallen, sa3r, to two-thirds of its former height, is further
depressed during excitation ; but the amount of sinking is
much less than it would have been if the splanchnic had not
been divided.

The same conclusion is confirmed by two other observations,
viz., (1) that if the aorta is obstructed so as to raise the arterial
pressure and conceal any changes in the state of contraction
of the abdominal vessels, the effect of the excitation of the de-
pressor is imperceptible : and (2) that if the abdominal organs
are exposed and inspected during excitation of the depressor,
they are seen, according to Cyon, to become congested. The
effect is most perceptible in the kidneys, which (if care is taken
to avoid the previous occurrence of congestion from exposure
or other conditions) change color from pale to red, and back
again, as the induced current is closed or opened.

BY DR. BURDON-SANDERSON. 293

SUPPLEMENT.

Absorption by the Veins and Lymphatics.

Under this head, certain experiments will be referred to re-
lating to the mode in which soluble and insoluble substances
find their wa}- into the vascular system from the tissues. This
kind of absorption may be termed, in order to distinguish it
from that which takes place at the cutaneous and mucous sur-
faces, internal absorption. The other kind will be dealt with
in succeeding Chapters.

It is obvious, so far as relates to the bloodvessels, that con-
sidering that the whole vascular system, with the exception of
that of the spleen, the medulla of bone, and some other smaller
tissues, is lined with a continuous membrane, no substance can
enter them excepting in a state of solution, and consequently
that the process of venous absorption is one of filtration or
diffusion; and that, of these two, the former is excluded by the
fact that the pressure inside of the vascular system is every-
where greater than the pressure outside. As regards the lym-
phatic system, on the other hand, the anatomical facts des-
cribed in Chap. VIII. will show that there is no obstacle to the
entry of solid substances, provided that they are in a state of
extremely fine division ; so that we are led to infer that,
whereas it is the function of the bloodvessels to absorb sub-
stances which are soluble and diffusible, those which are inca-
pable of diffusion are taken up by the lymphatics.

From experiments we learn, not merely that this inference
is correct, but that the process of absorption from the tissues
by the veins is, like the analogous process of secretion (Chap.
XXXVI.), dependent on the nervous system.

83. Proof that Solid Matters in a State of Extremely-
Fine Division are Absorbed from the Tissues by the
Lymphatics. — In Chapter VIII. it has been shown that,
without reference to the origin of the lacteals from the mucous
membrane of the intestine, or to the stomata, by which the
lymphatic system communicates with the serous cavities, the
absorbent S3rstem originates from those forms of interstitial
tissue which for the present we designate lymphatic, the char-
acteristic of which is that they consist of ground substance,
riddled in all directions by cavities containing protoplasm
masses — z. «., cells, these cavities being in communication with
each other, as well as with the lymphatic capillaries, by a net-
work of channels (lymphatic canaliculi or Saftkanalchen).
The distribution in the body of interstitial tissue having these
characters has not yet been sufficiently investigated ; for it is
only during the last year or two tWat its anatomical relations
have been more or less completely made out. We already

294 CIRCUF.ATION OF THE BLOOD.

know, however, that it is to be found almost everywhere, par-
ticularly in the tunica adventitia of bloodvessels, underneath
the endothelial lining of serous cavities, and of the vascular
system, and on the surface and in the inter-fascicular splits of
tendons and aponeuroses ; and that, wherever it occurs, it is in
anatomical relation with lymphatic capillaries. The proof
that the absorption of solid matters in line division takes place
mechanically, has already been given in Chapter VIII., where
it is shown that the lymphatics leading from the peritonaeum
can be filled with Prussian blue or other coloring matters in
suspension, by injecting'the liquid charged with them into
the peritomeal cavity; and that if the mechanical conditions
are favorable, the injection takes place in the same manner in
the dead body as in the living. It has also been shown in the
same Chapter, that in order to obtain good anatomical pre-
parations of lymphatic capillaries, the best method is that
there described as the method of puncture, the reason being
that, wherever these vessels are abundant, they are in open
communication with the canaliculi, and, consequently, that it
is impossible to introduce the point of a syringe into the tissue
between them without penetrating many of these cavities.
This may be instructively shown as follows.

84. Method of Showing the Mode of Entry of Col-
ored Liquids into the Lymphatic Vessels. — The best
tissue for the purpose is the mucous membrane of the larynx
and trachea ; those of an ox or sheep may be used. An ordi-
nary subcutaneous syringe, with as fine a point as possible, is
charged with solution of alkanet in spirits of turpentine. The
point is then inserted horizontally into the mucous membrane,
at some part where it rests upon cartilage. A drop of the
liquid is then pushed out into the tissue as slowly as possible.
If the operation is successful, it at once fills the lymphatic net-
work, the character of the result varying according as the
point of the S3rringe has entered the submucosa or has not
penetrated beyond the mucosa. That the liquid progresses
along the vessels by capillarity is learnt by observing that the
injection continues to spread long after all pressure from the
syringe has ceased. The alkanet solution is employed in this
and similar experiments, because it is quite incapable of pass-
ing through organic membranes, is immiscible with water, and
enters capillary channels with extraordinary facilit}'.

The further progress of liquids along the lymphatics towards
the venous system is due partly to capillarit}-, partly to the
fact that the lymphatics pass through spaces in which the
pressure is less than that in which their capillaries originate,
and partly to the variations of pressure due to muscular action,
to which they are subjected,. That in certain parts of the body

BY DR. BURDON-SANDERSON. 295

the lymphatic trunks are subjected to a less pressure than their
absorbing orifices, does not need special experimental proof.
Thus, for example, it is certain that the h/niphatics of the peri-
toneum enter the thorax, i. e., pass from a cavity where the
pressure is usually greater, to another where it is much less
than that of the atmosphere. The influence of muscular move-
ments admits of being demonstrated by the following experi-
ment, which at the same time affords a striking confirmation
of the evidence already given as to the mechanical nature of
lymphatic absorption.

In a large dog, which has been just killed by opening one
carotid, the skin, costal cartilages, and muscles of the flank are
severed by a transverse incision, which extends from the ensi-
form cartilage as far as the middle line on either side. The
wall of the abdomen is then split vertically in the linea alba,
and the diaphragm cut away from the ribs. The bladder hav-
ing been squeezed empty, two ligatures are tightened round
the rectum, which is divided between them. Ligatures must
now be placed round the cardia, the hepatic vessels, and duct,
and the mesentery, so as to remove the stomach and intestines
en manse without bleeding. This having been accomplished,
the vena cava is tied above and below the liver, and that organ
removed, after which the body is bisected by sawing through
the eighth vertebra, and completing the division of the soft
parts. Finally, a glass canula, fitted with a flexible tube
guarded by a clip, is inserted in the thoracic duct and secured
with a ligature.

If now the spinal column is fixed near the edge of the table,
and the lower limbs alternately flexed and extended by an as-
sistant, the lymph flows freely and may be received in a test
tube. If the passive movement is discontinued and then re-
sumed from time to time, the quantity of lymph collected is very
considerable, so that it is easy to fill several test tubes ; but
none is discharged during the intervals of cessation. The lymph
which is collected at first, resembles ordinary lymph both in
its microscopical characters and in its composition. It is ob-
vious that it is the liquid which at the moment of death occu-
pied the canaliculi of the tissues from which it is gathered.
The course taken by the lymph stream can be further demon-
strated in the same preparation, by introducing solution of
alkanet, by puncture, into the intertendinous splits of the
lower part of the fascia lata. If a sufficiently fine syringe is
used, it is easy to produce in this way a satisfactory injection,
first, of the tymphatic capillaries contained in the splits them-
selves, and secondly (if the passive movements are continued),
of the rich net-work of lymphatics which exists in the " cellular
membrane" which covers the aponeurosis on its cutaneous

29G CIRCULATION OF THE BLOOD.

aspect.1 Soon the discharge from the thoracic duct is reddened
by the alkanet. It has been shown by Ludwig that in the ex-
tremities, the tendons and aponeuroses are the special seat of
the net-works of capillaries by which the lymphatics commence,
and that they have here an arrangement similar to that observed
in the central tendon of the diaphragm. The experiment proves
that even passive movements of the limbs, by alternately tight-
ening and relaxing these structures, press forwards the lymph
stream. The influence of active movements must be much
greater.

85. Internal Absorption by the Veins. — The propo-
sition stated at the beginning of the section, that substances
in solution enter the capillaries from the tissues by a process
of absorption, which is under the immediate control of the
nervous system, may be strikingly illustrated as follows : —

Two frogs having been slightly curarized are prepared thus:
The heart having been exposed lege artis ; a small opening is
made in the skin in the occipital region. In one of the frogs,
the brain and spinal cord are completely destroyed by passing
a needle upwards and downwards from the occipital region,
and then both are hung vertically on a board, side by side.
looking in the same direction. A small funnel, the stem of
which is drawn out into a narrow beak, is now passed from the
incision downwards under the skin of each animal, till its end
reaches the dorsal Emphatic sac. This done, the bulbus
aortse is divided in both animals, and the results are observed.
In the frog deprived of its central nervous system, only a few
drops of blood escape — the quantity, that is to say, previously
contained in the heart and in the beginning of the arterial
system. In the other, the bleeding is not only more abundant,
but continues for several minutes after the section. As soon
as bleeding has ceased, a quantity of saline solution (say, 5 to
10 centimetres) is injected into the lymphatic sac of each animal
until it is distended, and the exact quantity used carefully
noted. In the frog in which the central nervous system is
intact, the discharge of blood from the opening in the bulb
begins again, and goes on increasing; while the liquid, which
at first is nearly pure blood, becomes more and more diluted
with serum. The discharge of sanguineous liquid goes on for
one or two hours ; and if, during the progress of the experi-
ment, the vasomotor centre is stimulated reflexl\- by exciting
a sensory nerve or the surface of the skin, it is seen that the
rate of flow is at once augmented, but becomes less after the
cessation of the excitation than it was before. This last fact

1 Colored drawings of the injections so obtained "will be found in Lud-
wig and Schweigger-Seidel's beautiful monograph on the lymphatics of
tendons and aponeuroses.

BY DR. BURDON-SANDERSON. 297

is thought by Goltz,1 the author of this experiment, to indicate
that when a sensory nerve is excited, venous absorption is in-
creased. It may perhaps be attributable rather to the contrac-
tion of the vessels which is determined by the excitation. To
render the observation of the result as accurate as possible,
the quantity discharged should be measured. The quantity
found in the test-glass in which the mixture of blood and serum
is collected should, together with the residue remaining in the
lymph sac, be equal to the quantity originally injected. — In
the other frog there is no discharge. The heart remains flaccid
although contracting regularly, and the skin dry from the arrest
of the secretion of the cutaneous glands. In this experiment
it may be supposed, either that the liquid contained in the
lymph sac passes into the circulation directly, or that it first
diffuses out into the surrounding tissue, and is then absorbed
by the veins. The first supposition is negatived b}r the obser-
vation that the contractions of the lymph hearts have ceased
in both frogs, and that consequently the mechanism by which
alone the liquid could be directly transferred to the venous
system is wanting. We are, therefore, compelled to admit that
it enters the blood-stream by the only other channel open to
it; and the conditions of the experiment prove that it does so
under the direct influence of the nervous system.

The precise nature of the agency by which the living ele-
ments which surround the bloodvessels determine the diffusion
of liquid into the blood in opposition to pressure, cannot at
present be stated. In the instance before us, two sets of effects
may be distinguished as referable to one cause, i. e., destruc-
tion of the central nervous system — those due to paralytic
relaxation of the bloodvessels, and those which are attributable
to absence of absorption. In how far those of the second
kind are the immediate result of the others, may perhaps be
open to question. They do not, however, afford any explana-
tion of them, for there is no reason why a relaxed vessel
should not absorb quite as much as a contracted one ; the fact
of relaxation affords no explanation whatever of the absence
of absorption. Both are manifestations of properties enjoyed
by the living elements only so long as they are in communica-
tion with cerebro-spinal nervous centres.

1 " Ueber den Einfluss dcr Nervencentren auf die Aufsangung,"
Pflugers Arcbiv. B. v. p. 53.

29S RESPIRATION.

CHAPTER XVII.

RESPIRATION.

Section I. — Preliminary Study of the External Movements
of Respiration.

86. Respiratory Movements of the Frog. — To ob-
serve the respiratory movements in the frog, the animal must
be fixed on its back. It is seen that that part of the floor of
the pharyngeal cavity which corresponds to the submaxillary
space, e. e.. to the space which lies between the episternal car-
tilage, and the two branches of the lower jaw bone, alternately
rises and falls at intervals of about one or two seconds. On
more attentive examination, it is found that these movements
are clue to the alternate retraction and advance of the body of
the hyoid bone, the general form of which can be readily dis-
tinguished under the skin. To study their nature, the skin
must be divided in the middle line from the mouth to the
sternum, and detached from the subjacent muscles as far out-
wards on either side as the jaw. In this way a view is ob-
tained of all the muscles attached to the hyoid bone, without
interfering with the mechanism of respiration (see fig. 246).
By its long and slender anterior horn, the hyoid bone is con-
nected with the skull (t. e., with the cartilaginous part of the
petrous bone) in such a manner that, although the two car-
tilages are not united by a joint, the hyoid works on the
petrous bones as if it were hinged to them. This being borne
in mind, it is easy to understand the action of the muscles
which are attached to it. Those which come from the sternum
and bones connected with it, in drawing the hyoid backwards,
cause it, at the same time, to descend in such a way as to in-
crease the space between its upper surface and the roof of the
mouth and pharynx, and to extend that part of the submax-
illary space which intervenes between the arch of the hyoid
and that of the lower jaw. On the other hand, those muscles
which stretch from the chin (the genio-hyoid), and from the
petrous bones (the petrohyoid muscles) to the bod}* of the
bone, combine in drawing it upwards and forwards, to such a
degree, indeed, that when the latter are in action, the sub-
maxillaiy space becomes concave. All this can be readily
seen in the living animal; for although the muscles above-
mentioned are covered by the submaxillary or mylohyoid

BY DR. BUR DON-SANDERSON. 299

muscles, this muscular membrane is so thin that they can be
easily perceived through it.

To investigate the part taken by these movements in the
mechanism of respiration, it is necessary to ascertain in what
relation they stand to the influx and efflux of air. This is
accomplished by inserting a suitable glass canula into one of
the nostrils and connecting it with the tympanum, shown in
fig. 231. In this way the curve is obtained, which is copied in
fig. 246 bis. By watching, at the same time, the motions of
the hyoid bone and of the lever, it is easy to satisfy one's self
that the retraction of the former towards the sternum corres-
ponds with the depression of the latter, and with the entrance
of air into the pharyngeal cavity. It is further seen that the
motions are by no means uniform, and that in connection with
this want of uniformity they present certain peculiarities which,
from their intimate connection with the mechanism by which
air is introduced into and expelled from the lungs, require
careful attention. The tracing enables us to divide the respira-
tory acts into two kinds, viz., smaller alternative movements
(a a a), which occur at pretty regular short intervals, and larger
movements (bbb), which differ from the others in this respect,
that the less energetic expiratory act by which the movement
begins, terminates in a sudden expulsion of air, indicated by a
more rapid rise of the lever, and determined by a more vigor-
ous contraction of those muscles which connect the body of the
hyoid bone with the skull. This sudden elevation of the floor
of the pharynx is the act by which the frog injects air into its
lungs. The student must now fix his attention on the nostrils,
when he will see that whereas during the small movements
(a a) those organs are motionless, the sudden expulsions (b b)
are accompanied by contraction of the little constrictor mus-
cles of the nares, and, consequently, that the latter differ from
the former not merely in their greater vigor, but in their being
executed witli the nostrils more or less closed, so that the air,
instead of passing freely out, is injected through the glottis into
the lungs. To prove this, watch the expiratory muscles of the
flanks (the external oblique particularly). At the first moment,
it will perhaps appear as if the sudden contraction of these
muscles were coincident with the closure of the nares, but it is
soon seen that the former movement follows the latter at an
interval of time, which, although very short, is not difficult to
appreciate even without instruments. This may be demon-
strated graphically by puncturing the anterior wall of the vis-
ceral cavity, and introducing through the puncture a canula
in such a way that it communicates with the cavity of one lung.
The canula being connected with a tympanum, a tracing is ob-
tained, which shows that the period during which the air is
contained in the lungs is extremely short, that the entry of air

300 RESPIRATION.

into the lungs coincides with the closure of the nares, and is
determined by the approximation of the body of the hyoid
bone to the roof of the pharynx, and that the expulsion of air
from the lungs by the contraction of the Hanks occurs while
the hyoid is still drawn upwards, so that the two muscular
movements form part of the same act.

87. External Respiratory Movements of Man and
Mammalia. — The alternate emptying and filling of the air
cells of the lungs, which is the final cause of respiration, is
effected by the alternate enlargement and contraction of the
chest. If the whole of the thorax were occupied by the air
cells, these changes of capacit}' could be measured by the quan-
tity of air entering and leaving the respiratory cavity in each
act of breathing. As, however, in addition to the lungs, the
chest contains various other organs, some of which alter their
volume very considerably, according to the degree of expansion
of the cavity in which they are contained, there is no constant
relation between the enlargement or diminution of the available
intra-thoracic air space and the external enlargement or dimi-
nution of the thorax.

There is no practicable method of determining the changes
of volume which the chest undergoes in respiration with exacti-
tude. As, however, the imperfect methods we possess differ
from most of those employed in physiology, in being quite as
applicable to man as to the lower animals, and are sufficiently
accurate to yield valuable results in the study of disease, they
are well worthy of the attention of the phj'sician, though of
comparatively little interest to the physiologist.

88. The external movements of the human chest maybe in-
vestigated by recording the variations either of its diameters
or of its circumference, at different parts, or of both simulta-
neously. For the graphic measurement of the circumference,
an instrument contrived by Marey, and much improved by
Bert, is used. It consists of an air-tight cylinder of brass and
India-rubber, of the shape and construction of a common drum,
the cylinder being of brass and the membranous ends of India-
rubber. The cylinder communicates by a flexible tube with a
tympanum, the lever of which records its variations of capacity.
To the centre of each of the two terminal membranes a metal
disk is attached, which is furnished with a hook, and is thus
connected with one of the ends of an inelastic cincture, which
encircles the circumference to be measured. As the circum-
ference augments, the membranes are extended, and the ca-
pacity of the drum increased, and vice versa. It is obvious
that before the instrument is used it must be graduated. The
mode of accomplishing this will be given further on.

89. The graphic measurement of the diameters of the chest
is much more simple, inasmuch as it merely involves the trans-

BY DR. BURDON-SANDERSON. 301

lation to the paper of the movement produced by the alternate
recession from each other, and approximation to each other,
of two points in the chest wall at the opposite extremities of
the diameter to he measured ; so that if either of these points
be taken as fixed, the recording of the movement of the other
point amounts to nothing more than the conversion of one
rectilinear movement into another. This is readily accom-
plished by the contrivance we have already employed for re-
cording the external cardiac movements (see § 60), that is, by
the employment of two tympana, the one for receiving the
movement to be investigated, the other for inscribing it on the
cylinder. The receiving tympanum must be so placed that
the distance of its India-rubber membrane from the fixed
extremity of the diameter to be investigated, is subject to no
variation during the period of measurement, and that its ivory
button is applied to the movable end in such a way that the
diameter, if produced beyond the surface of the chest, would
coincide with its axis. All these conditions are completely
fulfilled in the instrument I use. It consists of two parallel
bars of iron, the opposite ends of which are screwed firmly at
right angles into a cross bar, so as to form a rigid frame re-
sembling in shape the Greek letter n. The diameter to be
investigated is placed between the extremities of these bars.
One of these carries an ivory knob, similar to that of the
cardiograph, the convexity of which looks towards the oppo-
site arm. Its distance may be varied by a screw. The other
arm beai's the receiving tympanum, the knob of which faces
the knob just mentioned, their axis being in the same line.

The mode of application of the instrument, which may be
conveniently called a recording stethometer, varies according
to the diameter to be measured. The most important diame-
ters are those which connect the 8th rib in the axillary line
with the same rib of the opposite side, the manubrium sterni
with the 3d dorsal spine, the lower end of the sternum with the
8th dorsal spine, and the ensiform cartilage with the 10th dor-
sal spine. The mode of application for the first of these diame-
ters is shown in fig. 247. The subject stands or sits, as is
most convenient, and the stethometer is hung over his neck
by a broad band, the length of which can be regulated by a
buckle. The movements recorded are not those which the
middle of the 8th rib performs in relation to its stdrnal and
vertebral attachments, but those which the one end of the
diameter executes in relation to the other, which is for the
moment regarded as a fixed point. In measuring the diame-
ters which lie in the middle plane, it is most convenient to
take the vertebral spines as fixed points, although, of course,
the results would not be affected by doing otherwise. The
records obtained by the stethometer are of value for two pur-

302 RESPIRATION.

poses, viz., for the appreciation of the relative and absolute
duration of the respiratory acts, and for the measurement of
their extent. For the latter purpose, the instrument must be
graduated every time that it is Used. To facilitate this pro-
cess, I employ a set of five standard wooden measures of
length, differing from each other by two millimetres. With
these, the graduation is effected in less than five minutes. The
recording and receiving tympana having been brought into
communication, and the whole system tested as regards the
perfection of the joints, and found to be air-tight, one of the
wands (the one of which the length is equal to the mean of the
five) is placed between the two buttons of the stcthometer,
which are then approximated until the India-rubber membrane
of the tympanum is slightly concave. A horizontal tracing
having been drawn on the cylinder, the two next longest and
shortest wands are substituted for the first, and the process is
repeated in respect of each, and then the next two, until five
parallel horizontal lines have been drawn, by comparison with
which, the variations of the diameters investigated may be
estimated in millimetres from the vertical measurements of the
tracings. By this method we learn, for example, that in a
healthy muscular j-oung man, aged 22, the diameters above
given vary respectively in each respiration as follows : Upper
sternal diameter= 146, varies one millimetre; the lower ster-
nal diameter = 203, varies 1.5 — 1.8 millimetre; the transverse
costal diameter = 228, varies 1.7 — 2.0 millimetres.

As regards the duration and succession of the respiratory
acts, the most instructive curves are the costal and lower
sternal (see fig. 248). It must be carefully borne in mind
that they apply strictly to natural respiration. In forced
breathing, the thoracic movements acquire a different char-
acter. Dr. Arthur Ransome, who has studied the subject
with great accuracy, allows me to refer to his measurements.
He has found that the variations of the antero-posterior diame-
ters of the upper part of the chest are very extensive, and
that the whole thoracic framework participates in them — the
ends of the upper ribs moving horizontally forward, i. e., in a
plane parallel to the middle plane of the body, from 12 to 30
millimetres; the advance of the third rib is greater, by
several millimetres, than that of the fifth. Dr. Ransome con-
siders that this advance cannot be otherwise accounted for
than b}' an actual bending of the ribs.

We shall see afterwards that the difference between natural
and forced breathing consists partly in increased constriction
of the chest during expiration, partly in increased expansion
during inspiration. In the meantime, it is sufficient to note
that when the thoracic movements become excessive, the
change affects the antero-posterior diameters of the upper part

BY DR. BURDON-SANDERSON. 303

of the chest more than of the lower part, so that the normal
.relation between the two is reversed.

90. Measurement of the Intra-Thoracic Pressure.
—In consequence of the elasticity of the lungs, and of the
fact that they are contained in a cavity of which the capacity
is much greater than the volume which these organs assume
in their unextended condition, and that their external surface
is inseparably applied to the inner surface of the cavity, the
pressure to which the heart, arteries, veins, and other intra-
thoracic organs are subjected, is considerably less than that of
the atmosphere. What is required to measure the difference
is to connect one pleural cavity with a manometer. This is
easily effected in the following manner : A glass tube of about
three millimetres in diameter is sealed at one end, and drawn
out to a blunt point. A hole is then cut with a sharp three-
cornered file on one side of the tube, close to the sealed end,
and the open end temporarily closed with a plug of wax. A
rabbit having been secured on the rabbit support, the skin is
perforated with a scalpel close to the left edge of the middle
of the sternum. This having been done, the point of the tube
is easily passed into the right pleura by pushing it in a hori-
zontal direction behind the sternum, with its point against the
posterior (i. e., as the animal is placed, the under) surface of
the thoracic wall. The wax plug is then removed, and the
open end is connected with a water manometer; but while this
is being done, great care must be taken to keep the side of the
tube on which the orifice is, firmly but gently applied against
the chest wall. The quantity of water in the manometer is
then increased or diminished until the two columns stand at
the same level. If now the tube is twisted round so that its
orifice looks towards the cavity of the chest, the distal column
sinks, the difference between the heights of the two columns
in millimetres being about thirteen times as great as the dif-
ference in millimetres of mercury between the atmospheric
pressure and that to which the thoracic organs are subjected
in the animal under observation. The intra-thoracic pressure
may also be measured indirectly immediately after death, by
connecting the trachea air-tight with a manometer, and then,
after seeing that the two columns stand at the same level,
opening both pleural cavities. This time the distal column
rises above the proximal. The difference between them, if the
same kind of animal is used, will be the same, though in the
opposite direction. If it is desired to obtain a record of the
variations of intra-thoracic pressure during the respiratory
acts, it is easily done by bringing the tube into communica-
tion with a Marey's tympanum, by means of a somewhat thick-
walled India-rubber connector. In this way the tracing, fig.
249, is obtained.

>04 RESPIRATION.

Section II. — Study of tiik Mode of Action of the Muscles of
Respiration.

In man, the entry of air into the chest in tranquil breathing
is accomplished exclusively by the diaphragm. In the dog, it
is effected partly by the descent of the diaphragm, partly by
the widening of the chest. In the rabbit, the respiratory
movements resemble in their general character those of man,
on which account this animal is preferable to any other for
the purposes of study. From the fact just stated, it is ob-
vious that in our examination of the action of the muscles of
respiration, we must not confine ourselves to the normal
breathing, for if we were to do so, our studies would relate
almost exclusively to one muscle. To observe the action of
the others, we must direct our attention to the excessive tho-
racic movements of animals affected more or less with dyspnoea,
the phenomena of which condition, so far as they relate to
the action of muscles, must therefore be entered upon here,
although its nature and cause will form the subject of a special
section.

The muscular movements by which the chest is expanded,
must be studied in their relation to a certain definable position
of the thorax, which is called the position of equilibrium. It
is the position assumed by it at the end of normal expiration.
For as no muscle takes part in the normal expiratory act, the
whole thoracic muscular apparatus is at that moment in a
state of rest, the bones and cartilages assuming that position
which results from the balance of the opposed elastic forces,
which act upon them from within and from without. Of these
elastic forces, the most important is that of the lungs ; which
organs, being contained in a cavity much larger than they are
themselves, to the inner surface of which their external sur-
face is inseparably applied, constantly draw together its walls
with a force to be investigated in a future paragraph. Next
in importance is the elasticity of the ribs and cartilages, by
virtue of which the thoracic wall ever tends to be larger than
it is, in opposition to the contractile influence of the lungs.
Co-operating with these, we have, thirdly, the "tonus" of the
thoracic muscles, different indeed in its nature, but indis-
tinguishable as regards its action. All the muscles by which
the chest is enlarged beyond the position of equilibrium are
called inspiratory ; all those by which it is contracted to a
capacity less than that which it possesses when in equilibrium
are called expiratory.

91. Inspiratory Muscles. — The Diaphragm. — To demon-
strate the action of the diaphragm, several methods may be
used. The most striking is to expose it in an animal made
completely insensible by the injection of from twenty to forty

BY DR. BURDON-SANDERSON. 305

minims of a ten per cent, solution of chloral into the crural
vein. For this purpose the abdominal cavity must be opened
in the linea alba, immediately below the ensiform cartilage, and
then two incisions must be made, extending from the opening
in opposite directions parallel to the edges of the costal car-
tilages, according to the instructions given in § 56. Another
method consists in merely making an opening in the linea alba,
close to the ensiform cartilage, sufficient to receive the finger,
the tip of which must be pressed against the centrum tendi-
neum, when the movements can be appreciated with great ex-
actitude. The plan most used consists in introducing a long
and slender needle into the chest through the ensiform carti-
lage, close to the lower end of the sternum, the direction of
which is such, that it grazes the upper surface of the diaphragm,
if possible piercing it at one or two points, so as to be in some
part of its course on the abdominal side of the membrane.
For this experiment, the rabbit must be carefully chloralized,
and secured on Czermak's supporter in such a way that the
spinal column is immovable. A long silk thread is then passed
through the eye of the needle and connected with the little
bow-wood pulley shown in fig. 250, the movements of which
are inscribed by means of the horizontal lever on the blackened
cylinder. The tracing so obtained enables us not only to de-
termine to what relative distance the dome of the diaphragm
descends in each inspiratory act, but also the mean relaxation
of the muscle, i. e., the mean height to which it ascends during
each expiration. This, as we shall see further on, is much
affected by conditions which act on the muscle by its motor
nerve.

92. Intercostal Muscles. — To demonstrate the action of the
intercostal muscles, a rabbit is used which has been deprived
both of voluntary motion and of sensibility by the ablation of
the cerebral hemispheres as well as of the corpora striata and
thalami optici. This operation is performed as follows : The
animal having been rendered insensible by chloroform, both
carotids are tied. It is then secured on the supporter in the
prone position. The calvarium is now exposed by an incision
extending from the occiput to the frontal region in the middle
line, and the integument drawn aside in either direction. The
parietal bones having been first perforated with the trephine,
to allow of the introduction of the cutting pliers, the roof of
the cranium is rapidly removed so as to expose the hemi-
spheres completely. These organs are then scooped out with
the ivory handle of a scalpel, an assistant being at hand with
the actual cautery to arrest the bleeding. The animal at once
passes ii'to a state resembling deep sleep, breathing regularly,
bat much more slowly than before the operation. The action
of the respiratory muscles of the chest can now be investigated
20

306* RESPIRATION.

without any misgiving as to the infliction of suffering, by re-
moving the integument and superficial layer of muscles 80 as
to expose the ribs and intercostal Bpaces.

The first lesson to be learnt relates to normal breathing. It
it seen that so long as air enters the chest freely, ami the res-
piratory apparatus is not interfered with, there is no appreci-
able expansive movement of the ribs, ami the intercostal mus-
cles, in so far as they are visible, do not contract. Dyspnoea
may now be produced, either by letting air into one or both of
the pleural cavities, by diminishing the opening by which the
chest communicates with the atmosphere, or by combining the
two methods. It is most convenient to begin with puncturing
one pleura.

The effect of this operation is to increase the respiratory
movements, and to alter their character by bringing the tho-
racic muscles into action. The upper ribs, particularly the
second, third, and fourth, which were before motionless, move
upwards and outwards in each inspiration, while the external
intercostal muscles, and the intercartilaginous parts of the in-
ternal intercostal, are seen to grow hard in contraction at the
same moment.

To produce a higher degree of dyspnoea, the other pleura
may be opened; the principal effect observed is that the upward
and outward movement of the upper ribs is increased, and that
the scaleni, which were before inactive, now begin to contract
in concert with the external intercostals. These muscles,
although from their anatomical arrangement the}' must act as
elevators of the ribs, cannot be shown to be so experimentally ;
for there is no appreciable diminution of the costal movement
when they are divided.

The function of the external intercostals and intercartilagi-
nous muscles, having been proved by direct observation in the
manner above described, at a very earl}' period in the history
of physiology, has never been seriously disputed. This is not
however the case as regards the interosseous part of the internal
intercostals — that part of those muscles which is covered by the
external intercostals. In the rabbit, the interosseous intercos-
tals differ from the intercartilaginous, both in being less oblique
and in being somewhat thinner. The experimental evidence
as to their function is negative — that is to say, it can be shown
that the}' do not contract with the external muscles, but it
cannot be shown that the}' act antagonistically to them. It
admits of demonstration as regards any of the lower ribs, from
the fourth to the eighth or ninth, that if all the muscles at-
tached to it from above are removed, excepting the external
intercostals and the levatores costarum breves (muscles which
connect each transverse process with the rib next below it, and
can be seen to contract with the external intercostals), the rib

BY DK. BURDON-S ANDERSON. 307

still rises outwards in inspiration; but if these muscles are
completely severed, no more costal movement is perceptible ;
nor is there any hardening of the exposed intercostal muscles
at the moment of inspiration. In a word, it must still be ad-
mitted that the action of these muscles is as }ret undetermined.
Most probably they may be regarded as constrictors of the
chest — as the agents of forced expiration.

93. Movements of the Nares and Larynx. — In the
rabbit, the nostrils dilate with each ordinary inspiration, and
contrast in expiration; but from their frequency these move-
ments are very difficult to observe. To study them satisfac-
torily, the student must avail himself of the excessive and in-
frequent respirations of animals in which both vagi have been
divided. It is then seen that the dilatation of the nares is
the first act of inspiration. It precedes by a distinct interval
the expansion of the chest, and appears even to precede the
contraction of the diaphragm. Whether it actually does so
is very difficult to determine. The muscles b}' which this
movement is effected are, the subcutaneous faciei which springs
from the lateral surface of the intermaxillary bone, and from
the anterior supraorbital process of the frontal bone, to be in-
serted into the skin of the nose and forehead, and the levator
nasi, which springs from the lower edge of the orbit, and is
also inserted by a long tendon into the skin, covering the
edge of the nose. Of the two, the former is the more super-
ficial.

The respiratory movements of the larynx in the rabbit are
scarceby perceptible in perfectly natural breathing; but the
slightest interference with the access of air to the chest is suf-
ficient to produce them. The larynx is drawn downwards in
inspiration hy the muscles connecting it with the sternum,
and returns to the position of muscular equilibrium in expira-
tion. One of these muscles, the sterno-thyroid, has also the
effect of tilting forwards the thyroid cartilage, so as to bring
its lower edge nearer the cricoid.

94. To study the intrinsic respirator}' movements of the
larynx, the rima glottidis must be exposed to observation, by
making a suitable opening either above or below. The best
view of the movements is obtained by dividing the hyothyroid
membrane. The skin having been carefully divided in the
middle line, lege ariis, the membrane must be exposed with
the aid of two pairs of forceps. The veins (which are the
principal source of difficulty) can then be readily seen, and
must be carefully secured above and below by ligatures, be-
tween which the membrane may be cut across without risk of
hemorrhage. The head must of course be so supported that
a strong light is thrown on the vocal cords. If now the epi-
glottis is drawn forwards, the motions of the vocal cords and

308 RESPIRATION.

of the arytenoid cartilages are well seen — the chink becoming
wider in inspiration, narrower in expiration. To observe the
motions of the arytenoid cartilages, the best way is to excite
the recurrent nerves, when it is seen that during excitation
the vocal cord of the same side approaches the middle line.
If both recurrents are excited, the rima is completely closed,
the arytenoid cartilages applying themselves to each other
just as they do in the production of a musical note. Con-
sidering that the recurrent nerve is distributed to all the
muscles, and not merely to those which act as constrictors
{aryteenoidei and crico-arytsenoidei laterales), and that the
movements produced are of the same nature as those which
occur in ordinary expiration, though much more vigorous, we
arrive at the inference that in both cases the widening of the
glottis is a condition of general muscular relaxation, or, in
other words, that all the intrinsic muscles of the larynx are
expiratory — their combined effect manifesting itself in ap-
proximation of the vocal cords, not because the posterior
crico-arytenoid muscles and the other dilating muscles do not
act with the rest, but because they are overpowered by them.

Section III. — Measurement of the Quantity of Air respired in
a given Time, and of the Volume of Air inhaled in each Re-
spiratory Act.

95. The apparatus for this purpose consists of three parts,
viz., (a) a receiver or chamber in which the air to be breathed
during the period of observation is contained; (b) a face-piece
and tube for connecting the receiver with the respiratory
cavit}^ of the subject of observation; (c) arrangements for
supplying fresh air to the receiver, to take the place of the
air breathed.

To obtain results which are reliable, the first and most im-
portant condition is that the air should be respired without
the slightest effort. To insure this, the receiver must be of
such construction that the pressure to which the air contained
in it is subjected should be the same as that of the atmos-
phere. Consequently, it must have the form either of a gaso-
meter, the cylinder of which is accurately counterpoised, or
that of a membranous bag, the material of which is so thin
that it offers no resistance either in contracting or expanding.
The best material for the latter purpose is vulcanized India-
rubber; it is, however, difficult to obtain bags of this descrip-
tion which are perfect. Whatever be its form, the receiver
must have two openings, one communicating with the face-
piece, the other for the reception of air. It must be also so
constructed that the moment at which it is full may be easily
and accurately observed.

BY DR. BURDON-SANDERSON. 309

The receiver is brought into communication with the expira-
tory cavity of the subject of experiment by means of a face-
piece or mask of very perfect construction, furnished with two
valves, by one of which the air is expelled, while the other,
opening inwards, guards the orifice of a tube about an inch in
width, which leads from the receiver.

By its second opening, the receiver communicates with a
gasometer filled with air, under a pressure somewhat greater
than that of the atmosphere. Between the gasometer and the
receiver, the tube of communication passes first through a
stop-cock of brass, the aperture of which can be regulated
very accurately by means of a long handle, and then through
an accurately graduated gas meter, specially constructed for
the purpose. Each observation lasts ten minutes. The gas-
ometer is kept full of air by means of a pair of bellows, which
must be worked by an assistant (in default of other motor)
during the whole period; while the quantity of air which is
driven through the meter to the recipient is so regulated with
the aid of the stop-cock, that the receiver is kept exactly at
the same degree of fulness.

The chief mechanical source of inexactitude in this appara-
tus is to be found in the imperfect closure of the valves, and
imperfect fitting of the face-piece. These defects may be
obviated by substituting for the face-piece a couple of tubes of
ivory, which accurately fit the anterior opening of the nostrils.
The wide tube with which these ivory nose-pieces are connected,
at once divides into two branches. Of these, one is guarded
by a mercurial valve leading outwards, the other by a similar
valve leading inwards for inspiration, the arrangement of these
valves being the same as that shown in fig. 251 to be imme-
diately described.

96. In making observations of the same nature on the
lower animals, it is convenient to use an apparatus which not
only admits of accurate measurement of the quantity of air
breathed, but renders it possible to modify its composition by
the introduction of definite proportions of other gases or
vapors. And inasmuch as in such investigations it is, as a
rule, of more importance that the conditions should be
accurately known than that they should be identical with
those normally existing, the principle of completely avoiding
resistance, which was regarded as fundamental in the con-
struction of the apparatus described in the preceding para-
graph, must be abandoned ; for it is a mechanical impossibility
to construct valves which, while they close with perfect
accuracy, work without resistance. The apparatus to be now
described is so constructed that any gaseous mixture may be
kept in it for a length of time without change of composition
by diffusion, and the valves act so perfectly that the experi-

310 RESPIRATION.

mentcr is absolutely certain that the whole of the air which
leaves the receiver, and no more, is actually used in respiration.

The receiver may he constructed us follows: Two glass
cylinders are selected, about eight inches in length, open at
both ends, one of which is about half an inch wider than the
other; the outer is about three inches in width, the inner (e
fig. 251) two and a half inches. Both of them are cemented
in the most perfect manner possible, with their axes in the
same vertical line into a circular horizontal plate, so that they
are separated from each other by a narrow space of the same
width everywhere. This space is to be filled with mercnry.
Through the central part of the plate rise three vertical tubes
of glass, of about a quarter of an inch internal diameter.
Underneath the plate, which is supported on a tripod, each of
these tubes passes downwards for a short distance, and is
then bent horizontally at right angles. A third cylinder (o),
closed at one end and made of iron carefully protected, con-
stitutes the bell of the gasometer. Its diameter is the mean
of the diameters of the two cylinders of glass, so that it
descends without touching them into the space containing
mercury, by which they are separated from each other. It is
suspended by a silk cord, pulley, and counterpoise. The
counterpoise consists of a cup containing shot, and there is a
second and similar cup on the top of the cylinder. Of the
three tubes which enter the receiver from below, one (a) com-
municates with the atmosphere (when in use), a second (b)
with the respiratory cavity of the animal, the third (c) is
usually closed. The India-rubber tubes by which these com-
munications are made, are guarded by the simple contrivances,
known as Midler's mercurial valves. Each such valve consists
of a rather wide bottle containing a shallow column of mer-
cury, and closed air-tight with an India-rubber stopper.
Through the stopper pass two tubes, one of which is of such
length that its end dips just below the surface of the mercury;
the other is much shorter. The valve (a) is so placed that the
short tube is in direct communication with the receiver, the
long one with the atmosphere ; in (c) this arrangement is re-
versed. To complete the apparatus, all that is required is a
T tube and a third valve. The stem of the T tube communi-
cates with the respiratory cavit}- b}' means of a canula secured
air-tight in the trachea; the one arm with the receiver, and the
other with the valve (b), through which the expired air is dis-
charged into the atmosphere. The quantity of air used by
the animal during any given period of observation must be
measured in the same way as before.

The objection to which this apparatus or any other of
similar construction is liable, lies, as has been already hinted,
in the resistance offered by the mercurial valves, which is

BY DR. BURDON-SANDERSON. 311

sufficient to retard the respiratory movements to a sensible
degree. As, however, the most important applications of the
method are those which relate to the influence of variable con-
ditions on the quantity of air breathed, this fact is of little
consequence; for the error arising from it may be entirely
eliminated b}- substituting, as a standard of comparison, the
respiration already modified by the resistance, for normal
respiration. For the purpose of obtaining such a standard,
the animal must be allowed to breathe common air through
the apparatus for some time before making any other observa-
tion.

Section IV. — Determination of the Quantity op Carbonic
Acid Gas discharged by an Animal from the Lungs and Skin
in a given Time.

97. There are two leading methods by which this can be
accomplished. One of them is that of Regnault and Reiset,
which, with important modifications, has been used by Ludwig
and his pupils. The animal under observation is contained in
an air-tight chamber, which communicates with a second
chamber containing oxj-gen. The chamber communicates
with an absorbing apparatus, through which the air passes in
a continuous current, so that the expired carbonic acid gas is
removed from it as rapidly as it is formed, its place being
taken up by exactly the same volume of oxygen, so that the
constitution of the air remains unchanged. The quantity of
carbonic acid gas absorbed is calculated from the increase of
weight of the absorbing apparatus during the period of obser-
vation. As improved by Ludwig, the method is the best
suited for exact experiments. The apparatus is described in
Ludwig's Arbeiten for 1869.

The second method, which is much simpler, and sufficiently
exact when for comparative investigations as to the influence
of various physiological and pathological conditions on the
discharge of carbonic acid gas, is that of Pettenkofer. It is
applicable either to large animals or small. A short account
of Pettenkofer's complete apparatus will now be given, as an
aid to the understanding of the application of the same method
to the small animals in common use for physiological and
pathological investigations. Pettenkofer's apparatus consists
of three parts, viz., a chamber in which a man can sit or stand
comfortably; a large wet gas meter, which communicates with
the chamber by a tube ; a double-action air-pump, by which
air is continuously drawn through the meter from the cham-
ber ; and, lastly, clockwork, by which the pump is worked.
The chamber, which is of metal and glass, communicates with
the external air during the period of observation by the inter-

312 RESPIRATION.

stices round the door, which serve for the entrance of air, and
by the tube, which leads to the meter. The quantity of air
which is drawn through it by this tube amounts to about
20,000 litres (706.4 cubic feet) per hour, a quantity not merely
abundantly sufficient for ventilation, but to prevent loss or
error by diffusion into the air through the chinks round the
door. It is quite unnecessary to describe the aspirating appa-
ratus excepting in so far as to state that the clockwork is
moved by a weight, which, by a well-known mechanical con-
trivance, is constant^ wound up by a steam-engine.

To obtain a result, we must be able to determine with accu-
racy, first, the duration of the period of observation, and,
secondly, the quantitj' of carbonic acid gas contained in the
air which passes out of the chamber during that period. The
latter object ma}' be attained either by estimating the total
weight of carbonic acid discharged, or by measuring the
volume of air aspired, and, simultaneously, the proportion by
volume of the same gas contained in it. In the apparatus
above described, the quantity of air discharged is so large
that it would not be possible to analyze the whole of it, so
that the second of the two alternatives must be adopted.
This is effected not by taking one or more specimens of the
discharged air from time to time and analyzing them (for this
plan, unless a very great number of analyses were made, would,
in consequence of the constant irregularities which occur in
the rate of discharge, give wrong results), but by causing a
definite proportion of the used air to pass through an absorb-
ing apparatus, and measuring the total quantity of carbonic
acid gas contained in it by a volumetrical method to be imme-
diately described. This division of the aspired air into two
parts, one to be measured and analyzed, the other merely to
be measured, is a matter of great difficulty ; for it obvioush/
involves the carrying on during the period of observation of
two continuous measurements — i. e., the employment of two
meters instead of one, each of which must give results which
are not only accurate in themselves, but must correspond
exactly with those of the other. As, in applying the method
to animals so small that the whole quantity of air can be
analyzed, this difficulty is not met with, it is not necessary to
say anything as to the means of obviating it, or the errors
which, in spite of all precautions, it occasions.

98. Application of Pettenkofer's Method to the
Determination of the Discharge of Carbonic Acid
Gas in Small Animals. — The apparatus consists of a metal
chamber of iron, which communicates in one direction with
the Bunsen's water air-pump; in the other, with the apparatus
for the absorption of carbonic acid gas. Its lid closes air-
tight by means of a mercurial joint. For a guineapig or rat,

BY DR. BURDON-SANDERSON. 313

it should have a capacity of about 500 cubic inches (8193 c. c).
Between the blower and the chamber is interposed a flask of
about 6 oz. capacity, through the cork of which two tubes
pass ; of these, one is prolonged nearly to the bottom ; the
other, the exit tube, ends just below the under surface of the
cork. This flask is filled with pumice, moistened with solu-
tion of potash. In this way the chamber is supplied with a
constant and perfectly steady stream of air, free from carbonic
acid. As, however, the quantity of air supplied by the blower
is much larger than is required, it must be diminished by
allowing a certain quantity to waste. For this purpose a T
tube is" interposed between the blower and the potash flask,
the stem of which is connected by an India-rubber tube with
a kind of safety-valve, the construction of which is the same
as that of valve b, in fig. 251 ; the waste of air may be in-
creased or diminished by raising or lowering the longer of the
two tubes. The absorbing apparatus consists of two or a
greater number of absorption tubes (fig. 252), which are
charged with absorbing liquid. When each tube is placed at
its proper inclination, and the difference between the pressure
on opposite sides of the column of liquid is not too great, the
air, which enters the short limb by an end of India-rubber
tube which reaches nearly to the bend, passes up the long arm
in a regular succession of bubbles so small that it is thoroughly
acted on b3r the liquid. The two tubes are charged with a
solution of baryta, which in the longer is three times as strong
as in the shorter. The strengths of both solutions are deter-
mined volumetrically by a standard solution of oxalic acid
before and after every period of observation.

Preparation of the Solutions of Baryta and Oxalic Acid. —
Of the two solutions of baryta which are in use, the stronger
contains about 21 grammes of hydrate of baryta in a litre,
the other 7 grammes; the former is obtained by adding suf-
ficient distilled water to 420 cub. cent, of saturated baryta
water to make up a litre ; the latter contains 140 cub. cent, in
a litre. These liquids must be kept in bottles which have no
communication with the air, excepting through a flask or ab-
sorption tube filled with pumice, moistened with potash. The
oxalic acid solution must be prepared with the utmost accuracy.
It must contain 2.8636 grammes of pure well-crystallized
oxalic acid, free from efflorescence, in a litre. Before making
the solution, it is necessary to dry the crystals over sulphuric
acid for a few hours. The strength of this solution stands in
the ratio of exactly 1 to 22 to that of the ordinary volumetri-
cal solution of the pharmacopoeia. It keeps badly, being apt
to become mouldy, so that if a large amount is required, it
is better to keep the weighed quantities of oxalic acid than the
liquid.

314 RESPIRATION.

Mode of determining the Strength of the Baryta Solution. —
Thirty centimetres of baryta water having been introduced

into a small flask, the solution of oxalic arid is cautiously
added from a finely graduated burette. Between each addi-
tion, the flask is closed with the thumb and shaken. As an
indicator, Pettenkofer has found that turmeric paper gives
better results than litmus. The paper must be prepared by
digesting turmeric root in weak alcohol, and dipping strips of
Swedish filter paper into it, which must then be dried in a
dark place, and kept in the dark. "When the liquid is so nearly
neutralized that it does not brown a strip of paper dipped
into it, a drop is placed with a rod on the strip. If there is
still a trace of alkaline reaction, a brown line appears at the
periphery. As soon as this is no longer the case, the point of
complete neutralization has been attained. This reaction is so
delicate, that it is sensibly affected by the presence of one-
tenth of a cubic centimetre of solution of oxalic acid, i. e.,
one-tenth of a milligramme of carbonic acid gas, so that the
results of two determinations of the same liquid ought not to
differ from each other by more than the quantity named. It
is well, in order to save time, to make a first experiment with
a small quantity (say 5 cub. cent.). It is of great practical
importance to notice that the baryta solution must contain no
trace of caustic potash, or soda, the smallest quantities of
which render the determination impossible — for the oxalate of
potash or soda formed in this case reacts on the carbonate of
baryta present, so as to produce oxalate of baryta and carbo-
nate of soda. Consequently, the liquid never loses its alkaline
reaction, for each renewed addition of oxalic acid re-converts
the alkaline carbonate into oxalate, which is again decomposed
by the carbonate of baryta as before.

Mode of preparing and filling the Absorption Tubes. — Tfie
short arm of each tube is filled air-tight with an India-rubber
cork, pierced with a tube. The larger tube is connected at its
opposite end with the smaller, from which the air finall}' escapes
through an India-rubber tube, guarded by a screw-clip. By
adjusting this clip, the size of the bubbles is regulated, their
magnitude varying inversely as the resistance. To fill the
tubes, the required quantities of liquid are introduced into
flasks, fitted with air-tight corks, having necks sufficiently wide
for the introduction of a pipette. The strength of the solution
having been determined in thirty centimetres, as above de-
scribed, the stronger solution is to be delivered into the first
absorption tube in three quantities of 45 centimetres, and two
such quantities of the weaker into the second. [Tubes of the
size required for these quantities are made by Cetti & Co.,
of Brooke Street, Holborn.] The tubes are then closed and
adjusted to the proper inclination (previously ascertained by

BY DR. BURD0N-5ANDERS0X. 315

trial). At the close of the experiment, the liquids are trans-
ferred once more to flasks, similar to those above described, and
their strength determined as before. The calculation of the
result is simple. The quantity of carbonic acid absorbed by
each 30 cub. cent, of the liquid is indicated by the difference
between the corresponding quantities of oxalic acid solution
used, before and after absorption. This quantity must be mul-
tiplied in the one case by 133q5 = 4.5, in the other by f£=3. The
sum of the two products is the total quantity of carbonic acid
disengaged during the period of observation. If an animal
larger than a guineapig is used, it is necessary to employ two
sets of absorbing tubes, or a greater number.

Section V. — Innervation of the Respiratory Movements.

The rhythmical movements of respiration depend on the
activity of a centre contained in that part of the floor of the
fourth ventricle from which the roots of the vagus nerve
spring. The proof of this fact lies in the fundamental ex-
periment of Legallois, by which he showed that the cerebrum,
the cerebellum, and even part of the medulla oblongata itself
may be removed, without arresting respiration. This experi-
ment has already been described in § 92.

By motor nerves this centre is in relation with the muscles
of which the combined rhythmical actions have been studied in
the same paragraph. Its discharges of energ}', like those of
the motor centres of the heart, are automatic, but their rhythm
is constantly subject to modification by impressions received
through the afferent fibres of the vagi. Consequently, the study
of the innervation of the respiratory movements resolves itself
into experiments relating to the respiratory functions of these
nerves. The results of such experiments ma}* be divided accord-
ing as they relate to the effects of section of both vagi, to ex-
citation of the central end of the divided nerves, or to excita-
tion of the superior laryngeal nerve.

99. Section of both Vagi in the Neck. — In the para-
graph relating to the functions of the vagus as a heart-nerve,
directions have been given as to the mode of preparing it. The
rabbit is preferable to the dog or cat, for in those animals the
vagus is united in one trunk with the sympathetic. Section
of the vagi is the simplest and at the same time one of the most
instructive experiments relating to the physiology of the ner-
vous system. The animal having been secured in the usual
way on Czermak's rabbit support, a ligature is passed round
each nerve a little below the cricoid cartilage. The ends of
each ligature are then knotted together, so as to facilitate their
being found at any moment. To observe the effect, the animal
should be placed before and after section, under the same cir-

316 RESPIRATION.

cumstances. If it is not intended to record the results graphi-
cally, it may be allowed to run about while the respirations arc
counted, and careful observations are made as to the respira-
tory movements. For more exact observations various methods
may be used, each of which is of some value. The first consists
in recording the movements of the diaphragm on the kymo-
graph, as directed in § 91.1 The second and third are so con-
trived as to show not only the duration and rhythm of the
respiratory movements before and after section, but the extent of
the respiratory exchange of air. The apparatus for this purpose
is constructed as follows: A large bottle, capable of holding
five gallons or more, is closed air-tight with an India-rubber
cork, into which the stem of a glass "|" tube is carefully fitted.
Of the two branches of the T tube, one communicates with the
respiratory cavity of the animal, by a connector of India-rub-
ber and a glass canula secured air-tight in the trachea, the other
is left open and can be readily closed with the finger. The
bottle also communicates by a second glass tube which passes
through its India-rubber stopper, with a Marey's tympanum,
the lever of which writes on the blackened cylinder of the k}'mo-
graph. This tube is controlled by a screw clamp. So long as
the arm of the T piece is left open, the animal of course breathes
the external air freely. On placing the finger against the aper-
ture, it begins to breathe the air of the bottle, but inasmuch as
the capacity of this vessel is 250 times as great as the respira-
tory cavity of the rabbit, it can do so for some time without
the slightest dyspnoea, as is proved by the observation that the
depressors of the larynx do not come into action. The resist-
ance is, however, sufficiently great to affect the lever of the
tj'mpanum, the rise and fall of which in each respiratory act is
in exact proportion to the quantity of air breathed. The animal
having been chloralized and both nerves prepared as above de-
scribed, a few tracings should be taken of the normal respira-
tion. This done, the clockwork is again set in motion and botli
nerves are divided at the same moment. In this way a tracing
(fig. 253) is obtained, which strikingly exhibits the effects of
section, both as regards the rhythm and extent of the thoracic
movements.

Another method consists in measuring the quantity of air
inspired in a given time with the aid of the apparatus shown
in fig. 251. In this way the effect of section on the respiratory
exchange can be estimated with much greater precision than
in any other, but obviously no information is obtained as to
the respiratory movements.

100. The most important results are as follows: 1. In the

1 The tracing so obtained is shown in the first (normal) part of fig.
255.

BY DR. BURDON-SANDERSON. 317

adult rabbit, the number of respirations per minute diminishes
from 120—140 to 40—50. That this is only to a very slight
extent dependent on the narrowing of the glottis due to the
relaxation of the intrinsic muscles of the larynx, is proved by
the fact that if the two recurrents are divided, the retarding
effect of the operation is very inconsiderable, while the re-
tarding effect of section is diminished in no appreciable degree
by previous tracheotom}\ 2. The mechanism of breathing is
completely altered. Each respiration is about five times as
deep as it was before. This depends partly on increased action
of the diaphragm, partly on the participation of the accessory
muscles in the inspiratory act. The belly is projected and the
larynx drawn down by the sternal muscles in each inspiration,
while the upper ribs, which before were motionless, are drawn
upwards and outwards by the external intercostals and inter-
cartilaginous muscles. The inspiratoiy expansion of the
upper part of the thorax lasts for several seconds, at the end
of which it suddenly collapses, expelling the air with such
force as to make an audible sonorous noise in the air-passages,
often accompanied, if the trachea has not been opened, with
a coarse rale. This sudden collapse, which is a non-muscular
act, is followed by a long pause, the existence of which is
characteristic. At the end of it there usually occurs a short
expiratory movement, attended with hardening of the muscles
of the abdominal wall, which is the immediate precursor of the
inspirator}7 act. The mode of breathing just described is that
of dyspnoea; but there is this important difference between
ordinary dyspnoea and that produced by section of the vagi,
that whereas in the former the frequency of the respiratory
movements is increased, in the latter it is diminished ; with
this exception, all the characteristics of dyspnoea are present.
3. The quantity of air breathed per minute is as great after
section of both vagi as before, the diminished frequency of
the respirations being counterbalanced Irv the increased depth
of the respiratory act. This is proved by measuring the
quantity of air breathed in a given time in the manner above
directed. 4. These facts afford ground for inferring that
although section of both vagi does not materially either in-
crease or diminish the work done in a given time by the re-
spiratory muscles, it interferes very considerably with the
accomplishment of the purpose of their movements — the ar-
terialization of the blood. Notwithstanding the vigor of the
respiratory movements, the blood becomes more or less venous.
101. Death after Section of both Vagi. — Rabbits in
which both vagi have been divided, commonly die before the
end of the first day. Dogs live longer — often two or three
days. After death, the lungs are found in an altered condi-
tion, of which the following are the leading features: The

318 RESPIRATION.

mucous lining of the air-passages is reddened (especially in
dogs), the color being due to the injection of the capillaries of
the mucosa with blood. The lungs collapse much less than
naturally when the chest is opened. The pulmonary paren-
chyma is, to a greater or less extent, devoid of air. The air-
less parts are soaked with a brownish-red serous liquid, and
here and there choked with a grayish-white material, which, on
microscopical examination, is found to consist of young cells
(pus corpuscles). Similar cells are seen in the serous liquid
along with numerous blood corpuscles. These changes may
be accounted for as follows: When the vagi are divided, all
the parts to which the branches below the point xof section are
distributed are affected, e. g., the larynx, air-passages, lungs,
oesophagus, etc. 1. The glottis is partially closed, just as it is
after death. 2. The mucous lining of the air-passages is de-
prived of sensibility, so that, when it is irritated, no cough is
produced. 3. The muscular fibres of the oesophagus are para-
lyzed, so that regurgitation of food from the stomach is apt
to take place; the muscular fibres of the bronchial tubes are
in a similar condition. With reference to these co-efficients in
the production of the lung affection we have the following
facts, showing that the first two are at all events the only ones
which are of importance: (a) A lung affection of the same
nature as that induced by section of both vagi, though of in-
ferior intensity, follows section of the inferior laryngeal
nerves, (b) In animals with divided vagi, life is prolonged
by tracheotomy, the degree of prolongation depending on the
efficiency of means used to prevent the entrance of foreign
bodies into the air-passages, (c) In animals of which the vagi
are intact, a lung affection is produced b}' injecting mucus
from the pharynx into the air-passages which is of the same
nature with that now under consideration. The combination
of these facts leads to the inference that the inflammation of
the lungs of which animals with divided vagi die, is dependent
on the intrusion of foreign bodies from the pharynx into the
air passages and lungs, rather than to an}' direct effect of the
section on the lung tissue.

102. Demonstration of the Respiratory Functions
of Afferent Fibres of the Vagus, by Excitation of the
Central End of the Divided Nerve. — The method of
preparing the nerve has been already described. The excitor,
shown in fig. 225, is used. It is better to employ Helmholtz's
side wire (see next paragraph), but not necessary ; for even
when strong unmodified induced currents are used, there is
little danger of unipolar effects, the extent to which the nerve
can be separated being such, that there is no difficulty in inter-
posing a considerable air space between it and the surrounding
parts.

BY DR. BURDON-SANDERSON. 319

The phenomena which accompany excitation of the central
end of the divided vagus vary according to the state of the
animal and the state of the nerve. It will be convenient to
describe them under heads corresponding to these conditions:
1. Animal breathing naturally. To observe what may be re-
garded as the normal results of excitation, care must be taken
that the subject of experiment is not exhausted, and that, in
placing it on the support, nothing is done which can interfere
with its breathing. The movements of the diaphragm must
be recorded1 either with the aid of the apparatus, fig. 250, or
in the manner described in the preceding paragraph ; but for
the present purpose, by far the best method is to introduce
into the peritonaeal cavity, by means of a small opening in the
linea alba close to the ensiform cartilage, a small flat bag of
India-rubber, of such size that it can be conveniently slipped
between the diaphragm and liver. If this bag is slightly dis-
tended with air and connected with a Marey's tj'mpanum, it
gives excellent tracings of the diaphragmatic movements. To
the student who witnesses the experiment for the first time, a
still more convincing mode of appreciating the effect of ex-
citing the central end on the diaphragm is to feel the con-
traction of the muscle with the finger during the period of ex-
citation. The nerve having been prepared, and the excitor
placed under it, a preliminary tracing must be taken of the
normal respiration. In a tracing, taken by the method de-
scribed in § 99, it is seen that in each respiratory act three parts
may be distinguished, one of which, the ascent, expresses in-
spiration, or active contraction of the diaphragm ; the whole
of the remainder of the period corresponds to relaxation or
that muscle. Sometimes the part of the curve which imme-
diately precedes the ascent indicates that towards the close of
the period of relaxation air neither enters nor leaves the chest.
If a straight line is drawn through the angle formed in each
curve at the point corresponding to the commencement of in-
spiration, it ma}' be taken as indicating the position of the
lever when the diaphragm is at rest after an ordinary expi-
ration. So long as air is passing out of the chest, the lever
keeps below this line, but as soon as the outflow ceases, pro-
vided that the diaphragm is still relaxed, it returns to it.
Hence the line corresponds to the position of equilibrium.
These facts are well seen in the first (normal) part of tracing,
fig. 255.

The tympanum having now been connected with the bag
between the diaphragm and liver, as above described, and the
secondary coil placed at a considerable distance from the pri-
mary, the key which has been connected with the telegraph is

1 See fig. 254a.

320 RESPIRATION.

opened. The effect cannot be predicted with certainty.
Probably the respiratory movements will be quickened, the
lever assuming a somewhat higher position during the period
of excitation than it did before. This indicates that the dia-
phragm descends further in each inspiration, and does not
relax quite so much in expiration.

The secondary coil must now be gradually brought up
nearer, while the excitation is repeated after each shifting,
until it is observed that the lever ascends and remains station-
ary each time the key is opened, drawing a nearly horizontal
line at a much higher level than that of the previous part of
the tracing. (See fig. 254 &.') If the excitation is continued
only for a few seconds, the elevation of the lever which indi-
cates contraction of the diaphragm not only continues during
the whole time, but lasts a second or two after it. The lever
then gradually falls, and after a few moments resumes its up-
and-down movements, always beginning with a descent. In
other words, the diaphragm, after a period of contraction,
which somewhat exceeds its cause in duration, is for a moment
relaxed before it assumes its rhythmical action. The conduct
of the other respiratoiy muscles should be carefully watched
(by another observer) during these experiments. It will be
seen that, provided that the animal is breathing perfectly
naturally at the moment that the key is opened, the descent
of the diaphragm determined by the excitation of the vagus
is not attended by any other muscular movement, and in par-
ticular, that the upper ribs remain as motionless as before,
and that the larynx does not descend.2 2. Animal in the
state of apneea. In a rabbit of which the blood has been sur-
charged with oxygen by excessive artificial respiration, the
effect of exciting the central end of the vagus is negative.
No respiratory movement is produced. To demonstrate this,
experiments must be made before, during, and after apnoea.
It is found that the same current which tetanizes the dia-
phragm in the normal state, has no effect when the blood is
over-arterialized. This is an experiment of fundamental im-
portance, because it shows that the relation between the vagus

1 Fig. 2545 shows that during the whole period of excitation (indi-
cated by the horizontal line below) the diaphragm remained contracted ;
then followed a few irregular movements, after which the rhythmical
movements were resumed with a slightly increased frequency. The
period of contraction was interrupted, as frequently happens, by a
momentary relaxation.

2 Fig. 254a was obtained in the same animal as 2546 with the aid of
the apparatus, Fig. 250. The tracing shows that the rhythmical move-
ments were not resumed until a second or two after excitation had
ceased. They were at first somewhat more frequent than before, and
the diaphragm was in a lower position. In less than a minute the pre-
vious conditions were restored in both respects.

BY DR. BURBON-SANDERSON. 321

and the motor nerves of respiration (and particularly the
phrenic) is entirely different from that which exists between
the afferent and efferent nerve in the ordinary case of reflex
action. 3. Animal in the state of dysjmoea. When the blood,
instead of containing too much oxygen, contains too little, the
effect of excitation of the central end extends itself to all the
extra muscles which are at the time in action ; consequently,
J;he greater the dyspnoea, the greater is the number of muscles
which respond to the stimulus. This is best seen in an animal
in which after perforation of one side of the chest, respiration
is maintained artificially ; the same rabbit which has served
for the other experiments may be used. The result may be
varied according to the degree of dyspnoea produced, by regu-
lating the frequency and quantity of the injections of air. If,
for example, the dj'spncea is sufficient to bring into action the
external intercostals, intercartilaginei, and scaleni, all these
muscles contract simultaneously with the diaphragm when the
central end is excited, so that the chest remains during the
time that the key is open, in a state of tetanic expansion.

103. Excitation of the Central End of one Vagus after Sec-
tion of both. — By very careful graduation of the induced cur-
rent (with Helmholtz's modification), it is sometimes possible
to supply the precise degree of excitation to the vagus centre,
which is required to make up for the loss sustained by the sec-
tion of its afferent fibres, and in this way to restore the normal
respiratory rhj'thm. More frequently the experiment fails,
and effects are produced which correspond to those described
above.

Exceptional Cases. — It very frequently happens, particularly
in animals under the influence of chloral, that effects are pro-
duced by excitation of the central end which are just the oppo-
site of those whic,h we regard as normal. The diaphragm, in-
stead of contracting, relaxes, and remains relaxed during the
whole time (see Fig. 255') that the key is open. The imme-
diate cause of this generally is that the nerve is exhausted.
The reason why it happens is that the vagus contains (in addi-
tion to the fibres which, when excited, act on the vagus centre
in such a way as to lessen the hypothetical resistance by which
it is normally prevented from discharging itself in muscular
contractions) other fibres, which in the language of physiolo-

1 The tracing, Fig. 2o.r>, was obtained by the method described in
U 90. During the whole period of excitation the diaphragm remained
stationary in the position of ordinary expiration ; almost immediately
after, the rhythmical movements were resumed, the first movement be-
ing an ordinary inspiration. The period was interrupted by a single
respiratory movement, caused by the accidental removal of the elec-
trodes from the nerve. The notches in the horizontal part of the tracing
express cardiac pulsations.
21

322 RESPIRATION.

gists arc "inhibitory" — t. c, tend to increase the resistance
above referred to. In the fresh state of the nerve, the influ-
ence of these fibres is completely overbalanced by that of the
others. In the exhausted state, this relation is reversed, so
that the two sets of afferent fibres are as much distinguished
from each other by their difference of endurance as by their
differences of function. Recent experiments (Burkhart) make
it probable that the "inhibitory" fibres come mostly from the
recurrents.

104. Excitation of the Superior Laryngeal Nerve. —
The experimental investigation of the superior laryngeal is
much more difficult than that of the trunk of the vagus, partly
because the nerve is difficult to reach and runs a short course,
partly because it is very slender. To expose it in the rabbit,
an incision should be made extending from the side of the tra-.
chea, at the level of its first and second rings, to the hollow
between the angle of the jaw and the laiynx. After severing
the skin in the usual way, the fascia which extends forwards
from the edge of the sterno-mastoid muscle must be carefully
broken through with the aid of two pairs of dissecting forceps,
so as to expose the parts seen in Fig. 227. The space is di-
vided into two by the artery, the direction of which coincides
exactly with that of the original incision. Near its lower end
the arteiy gives off its thyroid branch. At the top the space
is limited by the tendon of the stylohyoid muscle, and the pos-
terior cornu of the hyoid bone. Immediately below the muscle
is the trunk of the ninth nerve, which arches forwards towards
the tongue. The descending branch of that nerve passes down-
wards and forwards to reach the muscles which cover the front
of the trachea, giving communicating branches to the cervical
plexus, and a branch which arches forwards over the artery to
gain the muscles which draw the larynx upwards. Before pro-
ceeding to expose the deeper nerves, it is well, in order to avoid
confusion, to remove the descendens noni; the next step is to
draw the larynx well to the side opposite to that chosen for
the incision, so as to widen the space between it and the caro-
tid artery. This done, the exposure of the superior laryngeal
becomes eas}-. Its exact position is indicated in the figure ; its
course is much twisted, so as to allow of the up-and-down
movements of the laiynx. In preparing it, no cutting instru-
ments must be used. It must be freed from the surrounding
structures with the aid of two pairs of forceps, any veins in
the way having been divided between two ligatures. Care
must be taken, however, to leave a certain quantity of cellular
tissue about it to serve as a kind of protective sheath, and
make it somewhat less liable to get dry. The nerve having
been prepared, a ligature must be tied round it as near as pos-
sible to the thyrohyoid membrane, after which it must be di-

BY DR. BURDON-S ANDERSON. 323

vided beyond. In the dog or cat the mode of preparation is
very much the same as in the rabbit. In the cat, the compara-
tive thickness of the nerve facilitates the manipulation.

In exciting the superior laryngeal, the great source of
difficulty is the proximity of the vagus and the consequent
liability of that nerve to be acted on by the induced current
in a unipolar way. This accident, which is of course fatal to
the success of the investigation, the functions of the two
nerves being opposite, is to be avoided, not by the use of
complicated arrangements for the insulation of the nerve, but
b}- placing it in such a way on the ordinary copper points that
the part acted on is separated by a considerable air space from
the surrounding tissues. Before beginning the excitation, the
secondary coil must be shifted to a distance from the primary,
and the primary current divided by means of Helmholtz's side
wire into two branches, one of which only passes through the
breaker. The other is led directly from the battery to the coil,
so that the primary current is never entirely opened. In this
way the opening induction shock, which, in the ordinary
arrangement of the induction apparatus, possesses a much
greater tension than that of the closing shock, is so reduced
that the two become nearly equal to each other.' Conse-
quently, as the risk of unipolar action varies with the maxi-
mum intensity of the current, it is very much diminished by
this contrivance — so much so, indeed, that if care is taken to
prepare the nerve properly, even nioderateby strong currents
ma}' be used without any effects referable to unipolar excita-
tion of the vagus manifesting themselves. Excitation of the
central end of the superior laryngeal produces, according to
the strength of the current used, either diminution of fre-
quency of the respiratory movements or complete relaxation
of the muscles of inspiration. The most advantageous way
of judging of its effect on the diaphragm, is to expose that
muscle in the way directed in § 91. It is then seen that that
muscle becomes absolutely flaccid during excitation of the
nerve, and it is drawn up by the elastic contraction of the
lungs, so as to assume its highest possible position. When
the excitation is discontinued, the relaxation either gives way
to natural breathing or is immediately succeeded by one or
two vigorous inspirations. If the current is so feeble that it
merely diminishes the frequency of the respirations, without
arresting them, the tracings show that there is no diminution
of the duration of the inspiratory acts, and that the slowing
is entirely due to a prolongation of the intervals, i. e., of the

1 For a fuller explanation of the difference between the two induced
currents and of the effect of Helmholtz's modification, see Rosenthal,
"Electricitatslehre," p. 120.

324 RESPIRATION.

periods during which the diaphragm remains in the position
assumed by it at the elose of ordinary expiration. To record
the effects graphically, any of the methods recommended in
the preceding paragraphs may be used. If the method de-
scribed in § 99 is employed, a tracing is obtained which
exactly resembles fig. 255. The tracing, fig. 250, ' was drawn
by inserting a bag between the diaphragm and the liver.

Section VI. — Influence of the Respiration on TnE Circulation.

105. If the stethoscope is applied to the prsecordia of a dog,
it is easity observed, especially if the animal has been narco-
tized, that the rate at which the contractions of the heart
succeed each other is subject to rhythmically recurring varia-
tions, and that the acceleration follows each expansion of the
chest, lasting during the first part of the succeeding expiration ;
while during the latter part of the expiratory period — the
period during which, as we have seen, air is expelled very
slowl}r — the diastolic intervals become longer. These facts
admit of much more precise demonstration by the graphic
method. For this purpose the most convenient instrument is
that shown in fig. 257.

It is a kymograph so constructed as to record the arterial
pressure and respiratory movements simultaneously. The
mercurial manometer consists of two limbs of equal length,
one of which, the distal (A), is much wider than the other
near the top, the relation between the lumen of the one and
that of the other being 1 : 10. The float wdiich rests on the
distal column is of boxwood. Its under surface is concave, so
as to fit the convex surface of the mercury. By the vertical
rod it is connected with a light lever, d, about two feet in
length, which is counterpoised by a weight suspended to it on
the other side of the brass bearing, e. At its thin end, the
lever carries a pen, the distance of which from d is such, that
for every inch of variation of difference between the two col-
umns of the manometer, it rises or falls three-tenths of an
inch. It will be readily understood that the movement of the
pen, instead of being rectilinear, is circular; consequently, it
is vertical only when the lever is horizontal ; for which reason
the fulcrum, e, which is so constructed as to slide up and down
on the brass uprights, must alwa}^ be placed in such a posi-
tion that the lever is horizontal. The height of the mercurial

1 The tracing, fig. 256, shows that during the whole period of excita-
tion the diaphragm remained motionless in the position of expiration,
with the exception that at gradually lengthening intervals it executed
momentary contractions. When, after the cessation of excitation, the
respiratory movements were resumed, they were slower hut more ex-
tensive than before.

BY DR. BURDON-SANDERSON. 325

column corresponds to the average arterial pressure. That
part of the instrument which is intended for recording the re-
spiratory movements, consists of a Marey's tympanum, c, and
a lever, F, similar to D, and of the same length, with which it
is connected. The tube, H, of the tympanum may be either
brought into communication with one arm of a glass T tube,
the stem of which is inserted in the trachea, or with a stetho-
meter applied to the chest. The lever of the tympanum is
connected with the recording lever by a vertical rod seen in
the drawing. In this way two tracings are obtained simul-
taneously, of which fig. 258 is an example. The arterial trac-
ing is marked A p, the respiratory r. In the latter, the begin-
ning of inspiration is indicated by the vertical stroke a; of
expiration by b; of the pause b}' c. The coincident points in
A P are indicated by similar strokes. The break is made by
removing both pens from the paper by the same act. In man,
the variations of frequenc}' (which, of course, can alone be in-
vestigated) are absent in most healthy persons, although very
obvious in certain conditions of disease. In the rabbit they
are much less marked than in the dog. They are regarded by
most physiologists as dependent on variations of activity of
the intracranial centre of the cardiac vagus: until very re-
cently it has been assumed, by way of explanation, that the
respiratory movements affect the cerebral circulation in such a
way that during the period of relaxation of the muscles of
respiration, the supply of blood to the medulla oblongata is
diminished, and increased during their contraction — and that
the inhibitory nervous system of the heart is affected by these
changes. This explanation has always appeared unsatisfactory,
and could only be accepted provisionally; for it seemed ex-
tremely improbable that there was any appreciable difference
in the supply of blood between the inspiratory and expiratory
periods. We now know that the respiratory variations in the
arterial pressure and in the frequency of the contractions of
the heart, are not necessarily dependent on the mechanical
effect of the respiratory movements on the heart, inasmuch as
they persist when these movements are abolished; and that
they have their primary source in the vasomotor and cardiac-
inhibitory centres, which act rhythmically, not because they
are subject to any rhythmical excitation, but because they
have periods of waxing and waning activity which correspond
to those of the respiratory centre. A very little consideration
■hows that this inference carries the admission that the cardiac-
inhibitory centre and the vasomotor centre act alternately, for
it can lie seen in every tracing that the increase of arterial
tension determined by increased vascular tonus, alternates
with the retarded pulse and diminished tension produced by
" vagus excitation." In other words, the phase of maximum

326 RESPIRATION.

activity of the inhibitory centre always coincides with that of
minimum activity of the vasomotor centre. The experiment
by which it is proved that the respiratory phases of arterial
pressure and pulse frequency are independent of the thoracic
movement, consists in curarizing a dog by the injection into
the venous system of a dose of curare only just sufficient to
paralyze the respiratory muscles (5 to 10 millig. for a dog of
10 lbs. weight), and observing graphically the changes of ar-
terial pressure which occur during the gradual extinction of
the respiratory movements, with the aid of the apparatus de-
scribed above. The tracings, figs. 259-261, show what is ob-
served at three different stages of curarization. Curve 259
was drawn when the animal's muscles were still active. It
may be regarded as normal. Curve 2601 corresponds to a
period at which each inspiration and expiration is represented
by a scarcel}' perceptible contraction and dilatation of the
chest. Curve 261 to a still later condition, in which the inspi-
ratory movements are indicated by a mere vibration of the
lever, produced (as was observed at the time) by momentary
contraction of certain inspiratory muscles which were not yet
completely parabyzed. We learn from these observations, that
during the gradual extinction of the respiratory movements,
the intervals between them correspondingly lengthen ; and
that at first the variations of arterial pressure and pulse fre-
quency exhibit the characters which closely correspond to
those they exhibit normally. Subsequently, the ascents and
descents of the mercurial column become much more gradual,
and the changes of frequency less abrupt. Finally they as-
sume, so far as relates to arterial tension, the characters of the
variations known as Traube's curves, to be described in the
next paragraph.

106. Traube's Curves. — This term is applied by physio-
logists to the rhythmical variations of arterial pressure which
occur in curarized animals, after complete cessation of the re-
spiratory movements, and section of both vagi. They can be
demonstrated in the rabbit, cat, or dog, but most readily in
the last. Traube described them as the}' occur in the absence
of artificial respiration, i. e., when the inflations are for a time
discontinued. During the gradual rise of arterial pressure
which, as we have already seen, takes place under those cir-

1 In fig. 260 the notches in the lower tracing represent rudimentary
inspirations and expirations. The expiratory movements, e e e, are
only traceable, however, in the last half of the tracing ; they follow the
inspiratory, i i i, at an interval of about five mill. = 1£ sec. In fig.
201. the expiratory movements are wholly indistinguishable. All the
tracings of this series are reduced one-half to save space. The distance
between the respiratory and arterial tracing is also diminished for the
same reason.

BY DR. BURDON-SANDERSOST. 327

cnrastances, the arterial pressure-curve exhibits the undula-
tions in question. It has, however, been lately shown by
Hering, that the state of asphyxia is far from being essential,
and that the most certain way of producing the phenomenon
is to bring the blood of the animal into a state which corre-
sponds to dyspnoea, not b}r stopping the artificial respiration
altogether, but by gradually diminishing the quantity injected
at each stroke. In the arterial tracings so obtained it is seen
that the cardiac intervals are of uniform duration — in other
words, that there are no variations of pulse-frequency, the vagi
having been divided. When these nerves are left intact, curves
are obtained (fig. 2621) in which the variations of the pulse
intervals exhibit the same relation to those of the arterial
tension as in the normal condition — the pulse-frequency being
greater in the ascending limb of each respiratory wave than
in the descending. From this we learn that the variations of
frequency are dependent on the integrity of the vagi. The
proof that the variations of pressure are vascular in their
origin, and depend on corresponding changes of arterial tonus,
is shown by two experimental results, viz. : (a) that although
after section of the spinal cord, arterial pressure is still sub-
ject to variations which are no doubt dependent on changes
of arterial tonus, these are very irregular ; and (6) that the
rhythmical variations of pressure persist after the influence of
the heart has been eliminated. The latter fact has been de-
monstrated b)r Hering, who has shown that if circulation is
maintained artificially, independently of the heart, in an ani-
mal which is placed in other respects in conditions favorable
to the production of " Traube's curves," they exhibit them-
selves with the same distinctness as when the heart is in action.
The conclusion to be derived from the preceding experiments
may be expressed as follows: The rhythmical variations of
arterial pressure which are associated with the respiratory
movements, are dependent on corresponding variations of
arterial tonus, but the variations of the frequency of the con-
traction of th£ heart are governed by the inhibitor}' nervous
sj-stem of that organ. In accepting this proposition, it must
not be forgotten that under normal conditions the thoracic

1 The tracings, fig. 2G2, are those of a curarized dog with undivided
vagi, in which air is injected into the lungs at regular intervals, but in
insufficient quantity. The arterial curve differs from "Taube's" only
in this respect — that in the ascending limb of each wave, the wavelets
which express the arterial pulsations are more frequent than in the
descending. In the lower tracing the ascents mark the strokes of the
artificial respiration apparatus, which was working at intervals of five
seconds ; the variations of arterial pressure shown in the upper tracing
follow the rhythm of the natural respiratory movements, and conse-
quently do not correspond with the inflations.

328 RESPIRATION.

movements co-operate in the most powerful manner in the pro-
duction of the result; for in every inspiration, so long as the
pleural cavities remain closed, the diastolic impletion of the
heart is favored by the filling of the venie cavae, and thereby
the vigor of the succeeding contractions of the heart is in-
creased. This is particularly the case in animals which (like
the dog and cat) breathe thoracically.

Section VII. — Apncea, Dyspncea, and Asphyxia.

The terms apncea, dyspnoea, and asphyxia, are applied in
physiology to the states of functional disorder which are
produced by excess and defect of oxygen in the blood, the
differences between them being — in accordance with a gene-
ralization so well established that it may be regarded as a law
— that the activity of the respiratory movements varies in-
versely as their effect on the blood.

107. Apncea. — When the blood is saturated with ox3rgen,
respiratory movements cease, and the animal is said to be in a
state of apncea. The fact can be demonstrated with great
ease in the rabbit by the ordinary method of artificial respira-
tion. If the intervals between the inflations of the lungs
are gradually shortened, the inspiratory movements become
shallower and shallower, and finally cease. The heart con-
tinues to beat vigorously and somewhat more frecpaently than
before. The visible mucous membranes present a perfectly
natural appearance. The eye closes instantly when the con-
junctiva is touched, and the state of the pupil is normal. In
short, all the functions excepting the respiratory movements
go on as before.1

108. Dyspncea. — We have already studied the phenomena
of dj'spncea so far as relates to the muscular movements. We
have seen that in the rabbit, when the access of air to the cir-
culating blood is gradually diminished, other muscles begin to
co-operate wdth the diaphragm in the inspiratory act, in an
order which, as a rule, is a follows: Inter costale$ externi, leva-
tores costarum breves, intercartilaginei, scaleni, serrati jyostici.
As external signs of dyspncea, the drawing down of the larynx
in inspiration by the muscles which cover the trachea, and the
expansion of the upper part of the chest by the intercartilagi-

1 The fact of apncea was first demonstrated by Hook, before the
Royal Society in October, 16G7. His experiment consists in opening
the chest of a dog, distending the lungs witli bellows, and keeping up
a constant stream of air through the organ through punctures made in
its surface for the purpose. He found that, although "the eyes were
all the time very quick, and the heart beating regularly," there were
no respiratory movements. The term "apncea" was first applied to
this condition by Rosenthal, in 1864.

BY DR. BURDON-SANDERSON. 329

nous muscles and external intercostals, are the most important,
as indicating successive stages. For a comprehensive study
of dyspnoea, as it affects not merely the respiratory movements,
but the circulation and the functions of the nervous system,
those experiments are best in which the disorder can be watched
from its beginnings in mere increase of functional activity (hy-
perpncea), to its issue in asphyxia or suffocation. These may
consist, either in complete obstruction of the air-passages, in
which case death occurs very rapidly (in 4-5 minutes in the
dog, a shorter time in the rabbit), in allowing the animal to
breathe out of a bag with which its respiratory cavitj- is in
air-tight communication, or from a gasometer (the instrument
represented in Fig. 251), into which definite mixtures of gases
can be continuously introduced.

109. Asphyxia by Complete Occlusion of the Tra-
chea.— For this purpose, a canula must be fixed air-tight in
the trachea, the mouth of which is of such form that it can be
plugged with a cork. If it is desired to obtain a tracing of the
variations of tension which the air so inclosed in the respira-
tory cavity undergoes, the cork must be perforated and fitted
with a tube which communicates with a mercurial manometer,
the movements of which are recorded on the cylinder of the
kymograph, simultaneously with the variations of pressure
in the crural artery. The tube must be of small bore and have
thick walls. The phenomena, as they present themselves in
the dog, may be enumerated as follows: First minute. — Ex-
cessive respiratory movements, in which at first the expansive
efforts of the thoracic muscles, afterwards the expulsive efforts
of the muscles of the abdominal wall, are most violent. During
this period the arterial pressure increases, but it is extremely
difficult to measure it, on account of the modifying influence
of the thoracic movements. Towards the close of the first
minute the animal becomes convulsed. These convulsions must
be attentively studied, because they are the type, by compari-
son with which all other convulsions of the same order are de-
scribed or defined. The prominent fact with respect to these
convulsions is that they are expiratory. At first, indeed, they
seem to be nothing more than exaggerations of the previous
expulsive efforts. Afterwards, the contractions of the proper
expiratory muscles are accompanied by more or less irregular
spasms of the muscles of the limbs, particularly of the flexors.
Second minute. — Early in the second minute the convulsions
cease, often suddenly; simultaneously with their cessation, the
expiratory efforts become indistinguishable. The iris is now
dilated to a rim ; the eye does not close when the corneals
touched, nor does the pupil react to light ; all reflex reaction
to stimuli has ceased. All the muscles, except those of inspi-
ration, are flaccid, and the animal lies in a state of tranquil-

830 RESPIRATION.

lity, which contrasts in the most striking way with the storm
which preceded it. The condition of the circulation at this
stage can be best judged of by the tracing, Fig. 2036. ' Inspi-
rations occur at long but tolerably regular intervals, and eacli
inspiratory act is accompanied, not, as in normal inspiration,
by an increase of arterial pressure, but by a marked diminu-
tion. The mean arterial pressure, which at the beginning of
the second minute is far above the normal, sinks considerably
below it towards the end. Third and fourth minutes. — As
death approaches, the thoracic and abdominal movements,
which are entirely inspirator}', become slower and slower as
well as shallower. The diminution of frequenc}' is, however,
never uniform, the inspirations occurring, for the most part,
in successions of two or three efforts, with long pauses between
them. In each act the accessory muscles of inspiration co-
operate with the diaphragm in the production of the result,
and towards the close other muscles come into spasmodic
action which are not usually regarded as inspiratory muscles
at all, although, in all probability, they act by virtue of motor
impulses originating in the inspiratory centre. In these
spasms, which accompany the final gasps of an asphyxiated
animal, the head is thrown back, the trunk straightened or
arched backwards, and the limbs are extended, while the mouth
gapes and the nostrils dilate. They are called by pli3rsiologists
stretching convulsions, and must be carefully distinguished
by the student from the expiratory convulsions previously
described.

110. Asphyxia by Slow Suffocation. — When an animal
is allowed to breathe the same quantity of air repeatedly
and continuously out of a bag, the process being of much
longer duration, the phenomena can be studied with greater
facility. As, however, its duration depends on two variable
conditions, viz., the respiratory capacity of the animal and the
capacity of the receptacle from which it breathes, it is not pos-
sible to describe the phenomena with reference to periods of
fixed duration. It is sufficient to divide the process into two
stages, the limits of which will be readily understood from the
preceding paragraph. The first may be called that of hyper-
pnoea. The respiratory movements, at first natural, are gradu-
ally exaggerated, both as regards their extent and frequency,
while the arterial pressure rises. Towards the end of the
period, as in the former case, the expiratory movements gain
in vigor, both absolutely and relatively to those of inspiration,
so that each inspiratory act is immediately followed by a sud-

1 Fig. 2636 is taken toward the end of the second minute of asphyxia
by occlusion. The mean arterial pressure is gradually sinking; each in-
spiration is accompanied by a depression of arterial pressure.

BY DR. BURDON-SANDERSON. 331

den tightening of the anterior abdominal wall, accompanied by
convulsive twitchings of the limbs. The second stage begins
by a change in the phenomena quite as marked as when the
exclusion of air is complete. Suddenly, the violent expulsive
efforts cease, and the inspiratory movements assume the charac-
ter already described, consisting in spasmodic contractions of
the diaphragm, accompanied by gasping movements of the
head and neck, the most marked difference being that the arte-
rial pressure, instead of sinking with each inspiratory effort,
rises, the rise being accompanied by an equally considerable
acceleration (see Fig. 263a1). In the dog this phenomenon is so
obvious that it can be judged of quite as well by watching the
mercurial column of the manometer as by the tracing. As re-
gards the gradual diminution of the frequency of the contrac-
tions of the heart during the first part of the period of collapse,
and their gradual acceleration as extinction approaches, the
phenomena are the same whatever be the mode in which
asphyxia is produced. As regards the final respiratory move-
ments, and the stretching convulsions which are associated
with them, nothing need be added to the description previously
given.

The preceding facts may be summed up as follows: In the
first stage of asphyxia (understanding by the term, that part
of the process which culminates in the struggle), the phenomena
are of two kinds. At first, we have merely over-activity of the
respiratory apparatus (hyperpncea) ; at the end, expiratory
convulsion. The convulsive movements are so distinct from
those proper to expiration, that we are compelled to assign
their origin to a special centre. This centre is often called the
''convulsion centre." It is probably identical with that from
which the co-ordinated expiratory movements of dyspnoea (hy-
perpncea) spring; for in asphyxia we see that these last pass
into convulsions by insensible gradations.3 When the struggle
with which the first stage closes is succeeded by the calm of
the second, all voluntary muscles, excepting those which are

1 Fig. 2G3« is taken at the beginning of the second stage of slow
asphyxia. Almost every inspiration is immediately followed by two or
three cardiac contractions, succeeding each other at very short in-
tervals.

2 It is important to notice that the convulsion of asphyxia is identical
with that produced in Kussmaul and Tenner's experiment, both having
the expiratory character. If that experiment is performed in an animal
in the state of apncea, the arrest of the arterial circulation in the intra-
cranial nervous centres at once induces respiratory movements; and if
the closure of the arteries continues, the animal passes through the suc-
cessive stages of dyspnrea, and finally becomes convulsed just as in as-
phyxia. If at this point the arteries are released, the animal relapses
gradually, after one or two vigorous inspirations, into the condition of
apncea.

332 , RESPIRATION.

either inspiratory or associated in their action with inspiration,
become relaxed. The inspiratory muscles, on the contrary, act
with great vigor.

111. State of the Circulation in Asphyxia. — This may
be best studied by actually observing the condition of the heart
and great vessels in a narcotized animal, of which the chest has
been opened while respiration is maintained artificially. In a
perfectly chloralized animal, the heart may be exposed very
rapidly, as follows: The integument covering the left side of
the chest having been turned hack, a series of strong ligatures
are passed round the costal cartilages, close to the left edge of
the sternum, in such a way that each ligature enters the thoracic
cavity by one intercostal space and passes out by the next; a
second set of ligatures are passed in a similar manner round the
ribs in a vertical line outside of the prsecordia. The ligatures
having been tightened, the quadrangular space between them
can be cut away without any bleeding. The pericardium having
then been opened, the thoracic organs can be perfectly well seen.
If now after continuing the artificial respiration till apnoea is
produced, it is suspended, all the degrees of respiratory activity,
viz., apncea, natural breathing, hyperpnoea, dyspnoea, convul-
sion, asphyxia, will be witnessed in the order in which they have
been mentioned, and it will be seen that no very obvious change
in the condition of the heart and great vessels will occur until
the last stage (corresponding to what I have called the second
stage of asphyxia) is approached. During the convulsive strug-
gle, and particularly towards its close, the heart enlarges to
something like the double of its former dimension, this enlarge-
ment being due (as the attentive observer will have no difficult}'
in satisfying himself) to the lengthening of the diastolic inter-
val and to the quantity of blood contained in the great veins,
which in fact are so distended, that if cut into they spirt like
arteries. If at this point air is again injected, the heart begins
after a few seconds to contract more rapidly, and in a moment
or two, emptying itself of its overcharge of blood, resumes its
former size. The effect of these changes on the arterial pres-
sure can be best studied in a curarized animal, of which the
crural or carotid has been connected with the kymograph. If,
in such an animal, artificial respiration is discontinued till the
arterial pressure, after first increasing, sinks as low as 20 to 40
millimetres, the tracing shows that the diastolic intervals are
much lengthened. If then air is injected, the arterial pressure
after an interval of 5 or 6 seconds suddenly rises, while the
curve expressing the rise indicates the extreme frequency of
the contractions by which the heart empties itself of its con-
tents, or rather pumps on the blood contained in the over-full
veins to the arterial system. (See fig. 2G4, in which i indicates
the moment of injection of air.) During this effort, the mer-

BY DR. BURDON-SANDERSON. 333

curial column usually rises above the normal, but after it is
over, subsides to a height which is nearly the same as that
about which it oscillated before artificial respiration was sus-
pended. The explanation of these phenemena may be given in
a few words. One of the effects of diminishing the proportion
of oxygen in the circulating blood is to excite the vasomotor
centre, and thus determine general contraction of the small
arteries. The immediate consequence of this contraction is to
fill the venous S3rstem, in the production of which result the
contraction of the expiratory muscles of the trunk and extremi-
ties powerfully co-operates. The heart being abundantly sup-
plied with blood, fills rapidly during diastole and contracts
vigorously, in consequence of which and of the increased resist-
ance in front, the arterial pressure rises. This last effect is
however temporary ; the diastolic intervals being lengthened
by the excitation of the inhibitory nervous system, and the
heart itself weakened by defect of oxygen, the organ soon
passes into the state of diastolic relaxation already described.
Its contractions become more and more ineffectual till they
finall}' cease, leaving the arteries empty, the veins distended,
its own cavities relaxed and full of blood. That the small arte-
ries are contracted in asphyxia we learn by inspecting them
(see § 49). The narrowing is as marked as it is during elec-
trical excitation of the medulla oblongata. In both cases the
contraction induces increased arterial pressure, but there is
this difference, that whereas in the latter case the heart is not
interfered with, in the former its functional activity is much im-
paired by the condition of the blood. Consequently, the rise
of the arterial pressure is much greater in proportion to the
degree of contraction of the arteries during excitation of the
medulla than in asphyxia.

112. Examination of the Heart after Death by-
Asphyxia. — If the heart is rapidly exposed immediately
after death by asphyxia, and a strong ligature tightened round
the roots of the great vessels, the organ may be readily cut
out without allowing any blood to escape from its cavities.
The quantity of blood contained in the right and left side re-
spectively may be measured by carefully opening the ventri-
cles and allowing their contents to flow into separate measure
glasses. It is always found that all the cavities of the heart
are filled to distension, the quantities in the right and left
cavities respectively, usually being to each other about in the
proportion of 2 to 3. The lungs are always pale; if, however,
the body is kept for a few hours, those parts of the organs
which are lowest becomes airless and soaked with sanguino-
lent liquid.

113. Demonstration of the Chemical Changes -which
occur in the Blood in Dyspnoea and Asphyxia. — It

334 RESPIRATION.

being known that in suffocation two changes take place in the
chemical condition of the blood — diminution of oxygen and
increase of carbonic acid gas — it is obviously not unreasonable
to attribute the phenomena either to the one or the other of
these changes, or to the combination of both. In the preced-
ing pages it has been assumed that the}' are due to the dimi-
nution of oxygen. The chief proofs that this is so are as fol-
lows: In order to demonstrate in a striking way and in one
experiment that diminution of ox}-gen in the air breathed
does, and that excess of carbonic acid gas does not, produce
the phenomena of dj'spncea, the following method, devised by
Rosenthal, may be employed. The mercurial gosometer (fig.
251) is filled with oxj-gen. The animal is then allowed to
breathe the gas in the way described (§ 95) until it ma}' be
reasonably supposed that the air contained in the air-passages
is displaced by it. This occurs in the rabbit in about ten
respirations. The communication is then opened between the
valve B and the receiver, while the exit tube is clipped so that
the animal both inspires from the gasometer and expires into
it. As the experiment goes on, it is obvious that the propor-
tion of carbonic acid increases and must continue to increase,
until that gas attains such a tension in the gasometer that no
further escape from the blood is possible. At first the volume
of gas in the gasometer undergoes no sensible diminution,
for the animal expires nearly as much of carbonic acid as it
inspires of oxygen ; afterwards, as the quantity of carbonic
acid gas given off becomes less and less, the cylinder sinks in
each inspiration more and more. As soon as this is the case
it is of course absolutely certain that the animal is breathing
an atmosphere containing a large excess of carbonic acid gas,
yet notwithstanding, there is no sign of asphyxia, the reason
being that the oxygen still exists in the mixture in a propor-
tion exceeding that in which it exists in the atmosphere, or at
all events, not falling far short of it. When at a still later
period the breathing begins to be excessive, the dyspnoea can
at first be relieved by increasing the pressure to which the
gases contained in the gasometer are exposed. This, of course,
while it favors the absorption of oxygen, equally favors that of
carbonic acid gas ; that the latter has no physiological effect
cannot be maintained, but the experiment proves that its
effect is very inconsiderable.

The direct proof that dyspnoea is dependent on defect of
oxygen, is obtained by the analysis of the gases of the blood
in an animal which has been asphyxiated by the inhalation of
pure nitrogen. Pfluger has found that an animal (dog) breath-
ing nitrogen becomes hyperpnoeic in 15 seconds. In 20 seconds
the struggle is at its height, the blood being already very dark.
In Pfluger's experiments, blood was allowed to flow from an

BY DR. BURDON-SANDERSON. 335

artery into a recipient for the analysis of its gases, at from half
a minute to a minute after the beginning of the inhalation of
nitrogen, the animal being already in the second stage of as-
phyxia. It was found, for example,' that the blood of an animal
which before breathing nitrogen contained 18.8 per cent, per
vol. of ox}rgen (at 760 millim. and 0° C), contained after breath-
ing nitrogen for one minute a mere trace of oxygen (0.3 per
cent.) ; during the same period the carbonic acid gas had dimin-
ished from 47.2 per cent, to 39.4 per cent. These experiments
are referred to here on account of their fundamental importance.
The}^ are much too difficult for repetition.

114. Demonstration that the Pulmonary Termina-
tions of the Vagus Nerves are Excited by Distension
of the Lungs. — It was long ago surmised by physiologists
(particularly by Rosenthal) that the pulmonary branches of
the vagus nerves contain afferent fibres, which are excited by
the expansion of that organ, and that these fibres take part in
the regulation both of the movements of the heart and those of
respiration. The proof of this has been lately given by Hering.
A dog having been narcotized with morphia or opium, one arm
of a T-shaped canula is secured in the trachea, the other being-
connected with a mercurial manometer. To the stem an India-
rubber connector is fitted, which is guarded by a screw clip,
and ends in a blowing tube: a canula is placed in the carotid
and connected with the kymograph. These preparations having
been made, an observation of arterial pressure is taken. The
clockwork being still in motion, the experimenter distends the
lungs of the animal until the distal column of the manometer
stands about 30 or 40 millimetres above the other, and then
closes the clip. Two important results are produced. In the
first place, the inspiratory muscles are thrown out of action,
and remain relaxed so long as the distension lasts, while those
of expiration are brought into continuous and energetic con-
traction ; and secondly, the frequency of the contractions of
the heart is more than doubled. In the preceding experiment
the circulation is considerably affected by the increased pres-
sure exercised by the distended lungs on the heart and great
veins ; consequently, the increased frequency of the pulse might
be attributed in whole or in part to this circumstance rather
than to the pulmonary distension. To meet this objection, the
experiment may be modified as follows: A dog is narcotized
and respiration maintained artificially, the apparatus being so
arranged that at any moment the lungs may be distended as
in the last case. This done, the thoracic organs are completely
exposed by removing the anterior wall of the chest in the man-
ner described in § 49 : it is then seen that the effect of inflation

1 Pfliiger's Archiv., vol. I. p. 94.

336 ANIMAL HEAT.

on the heart is just the same as when the thorax is closed.
These results are sufficient to show the pulmonary distension
and acceleration of the contraction of the heart, stand in the
relation to each other of cause to effect. That the influence of
the former on the latter is exercised through the nervous sys-
tem, and consequently through the vagi (these being the only
known channel by which the lungs are in communication with
the nervous centres) is sufficiently obvious. Accordingly, we
should expect that if this channel were interrupted the effect
would be annulled, and experiment proves that it is so. The
demonstration is, however, very difficult, for in the dog the
pulsations of the heart are already so rapid after section of the
vagi that no further acceleration is possible ; a negative result,
therefore, would mean nothing. Hering has met this difficulty
by carefully exciting the peripheral end of one of the divided
nerves after section of both (using Ilelraholtz's modification),
so as to reduce the frequency of the heart's action, and repeat-
ing the pulmonary distension under these altered conditions ;
the result was still negative. These experiments teach us two
important facts relating to the innervation of the lungs, viz.,
that the pulmonary branches of the vagus contain afferent
fibres, the excitation of which by pulmonary distension tends
to weaken or paralyze both the inspiratory and cardiac centres
in the medulla oblongata ; the one action showing itself in the
complete cessation of the rhythmical efforts of the inspiratory
muscles, the other in the shortening of the diastolic intervals
of the heart. The subject requires much fuller investigation
than it has yet received.

CHAPTER XVIII.

ANIMAL HEAT.

The temperature of the body is dependent on the relative
activit}T of two sets of processes, viz. : those by which heat is
produced or generated, and those by which it is destroyed or
lost. The subject admits of being correspondingly divided
into two parts — the study of the processes, and the stud}' of
the resulting state. The former is based on the measurement
of the quantity of heat set free at the surface during a given
period (Calorimetry) ; the second on the measurement of the
temperature existing in the circulating blood and the tissues
at the moment of observation (Thermometry).

BY DR. BURDON-SANDERSON. 337

Section I. — Calorimetry.

The production of heat is one of the essential functions, of
living tissue ; consequently, wherever there are living cells,
heat is generated at all times. We assume, at the outset, that
the source of production is the sum of the chemical processes
which take place in the body ; and that under all circum-
stances, so long as the tissues are neither growing nor wasting,
the quantity of heat produced by the oxidation of the food
consumed is equal to the quantity which would have been
produced had the same quantity of oxidizable substance been
converted into similar more or less oxidized products out of
the bod}7.

115. There are two distinct methods by which a theoretically
complete determination of the quantity of heat products in
the body in a given time can be arrived at. The first consists
in deducting the heat-producing power (heat value) of the
substances discharged from the body in a given time, from the
heat value of the substances consumed. The second is based
on the actual measurement of the quantity of heat discharged
in a given time. In the former case the difference obtained
expresses the amount of heat produced in the period, 'provided
that the animal is in a state of nutritive equilibrium — i. e.,
that its tissues are neither growing nor wasting. In the latter,
the measurement gives the desired result, provided that the
discharge is exactly equal to the production of heat — i. e., that
the temperature of the body remains the same.

With reference to the first method, as it reposes entirely on
chemical and .physical operations, some of which do not fall
within the scope of this work, while others will be described
under other heads, all that is necessary is to make clear the
principles of its application. So long as an animal is in
nutritive equilibrium (see above) the combustible material
actually consumed, i. <?., oxidized in its body in a given time,
may be known by deducting, from the quantity of such
material actually swallowed, the quantity discharged in the
fieces. This determination is, therefore, purely a question of
chemical analysis.

The heat-producing powers of the chief constituents of food
have been determined approximative^ by Frankland, who
finds, for example, that one gramme of albumin; in under-
going complete combustion into water, carbonic acid, and
ammonia, produces heat enough to raise 4998 grammes of
water one degree centigrade. This fact we express by stating
that 4998 is the heat value of albumen. In like manner
Frankland has found the heat value of lean beef to be 5103,
and of the fat 9069. If, therefore, it were possible to
determine how much of any of these substances is consumed,
22

338 ANIMAL HEAT.

say per diem, it is clear that we could readily calculate how
much heat would be produced, provided that the consumption,
i, e., oxidation, were complete. As regards the albuminous
elements of food, no such complete oxidation takes place, for
the elements of these compounds do not leave the organism in
the form of ultimate products of oxidation, but in great part
in the form of urea and other imperfectly oxidized organic
constituents of urine. The quantity of heat actually pro-
duced by a given weight of albumin, therefore, falls consider-
ably short of its heat value. In order to arrive at this
quantity, the deduction previous!}' referred to must be made:
i. e., from the heat value of the albumin consumed, the heat
value of the nitrogenous excreted substances into which it is
transformed must be taken: the difference expresses theoreti-
cally the exact number of heat units actually generated by its
elements in their passage through the body. As regards the
hj'dro-carbons, no such deduction is necessar}', so that in the
case of animals which feed exclusiveljr on these compounds —
e. g., bees — the quantity of heat produced is at once obtained
by estimating the heat value of the food consumed.1

Another chemical method of estimating the rate of produc-
tion of heat in the body of an animal, is founded on the esti-
mation of the discharge of carbonic acid from the lungs and
skin. In carnivorous animals this method is of little value,
for, as we have seen, so much of the food consumed as consists
of albuminous compounds is incompletely oxidized, so that
there is no definite relation between the consumption of albu-
minous products and the amount of oxidation. In such ani-
mals, however, as can be fed entirely on hydro-carbons of
known composition, the carbonic acid gas discharged ma}' be
taken as an exact index of the heat production — not because
the quantity of heat produced, as was at first erroneously as-
sumed, is equal to the heat which would be disengaged by the
oxidation of the quantity of carbon actually contained in the
carbonic acid, and of the quantity of hydrogen contained in
the corresponding quantity of water — but because in such an
animal the whole of the material consumed is completely oxi-
dized ; so that the quantity of carbon discharged as carbonic
acid is always equal to the total quantity of the same element
oxidized. On this account bees, which can be fed exclusively

1 No results can be obtained by this method unless the animal is in a
state of perfect nutritive equilibrium. For this reason, it can be seldom
applicable in the investigation of physiological or pathological questions
relating to heat ; for, on account of the length of the periods over which
the determinations must necessarily extend, it gives little or no informa-
tion as to the variations in the production of heat, the appreciation of
Which is practically more important than the determination of the means
of the quantities produced per hour or day.

BY DR. BURDON-SANDERSON. 339

on hydro-carbons, and have the additional advantage that,
although they are of variable temperature, their heat produc-
tion is as active as that of warm-blooded animals, are specially
adapted for the investigation of the relation between heat pro-
duction and oxidation.

Under many circumstances which preclude the use of this
method alone, it is of value in combination with that of direct
measurement, to be immediately described ; for the informa-
tion it affords, even when the nutritive substances consumed
are parti}' nitrogenous, is trustworthy. If the ingestion of
nutritive material is regular and uniform, it affords a rough,
but otherwise reliable, indication of whatever variations may
occur in the activity of the chemical vital processes.

It will be readily understood, that these indications occur
later than the causes which produce them ; so that it is not
until some time after any increase or diminution of oxidation,
that the corresponding increase or diminution of the discharge
of carbonic acid manifests itself. The mode of gauging the
discharge of carbonic acid in the animal bod}- has been de-
scribed in the previous chapter. In the application of the re-
sults of such determinations, it must not be forgotten that the
absolute values obtained are meaningless. Their use is limited
to the interpretation of direct calorimetrical measurements.

116. Direct Estimation of the Quantity of Heat
produced by an Animal in a given Time. — The second
method (to which alone the term Calorimetry is strictly appli-
cable), consists in the direct estimation of the quantity of
heat (heat units) given off by an animal in a given time. The
subject of observation is placed for a measured period in a
chamber, which is so constructed that while it is continuously
supplied with air for respiration, it is surrounded on all sides
by a mass of water, the weight and temperature of which are
known. The construction of such a chamber (Calorimeter)
can be readily understood from the diagram, fig. 265.

A, is a box of zinc plate, in which the animal is placed, the
size varying according to the animal it is intended to receive.
If for rabbit or small dog, it is 15^ inches long by 12 inches
wide, and 13 inches high. It possesses two openings, one of
which is in the lid and communicates with a large gasometer,
into which air is constantly injected by a Bunsen's water air-
pump. The other is in one end, and opens into an exit tube
(D;, which after surrounding the box twice, terminates in a
flexible connector, by which the air which has passed through
the chamber escapes. The section of this tube, the purpose of
which is to secure the condensation of the aqueous vapor dis-
charged from the lungs and skin, is oblong and rectangular;
in order that it may present to the water by which it is sur-
rounded as large a surface as possible. The inner box (A) is

340 ANIMAL HEAT.

surrounded by another, which is of such dimensions that the
external surface of the former is separated from the internal
surface of the latter by a space of an inch and a half in every
direction. This space contains water the weight of which can
be readily known. The inner box can be fixed into its place
by a simple mechanical arrangement. The water-chamber (B)
is contained in a wooden case (C), which however is so large
that a considerable space intervenes, which is closely packed
with tow, the purpose of which is to prevent loss or gain of
heat by radiation or conduction, and thus to render the tem-
perature of the interior of the apparatus entirely independent
of that of the surrounding media. For the same reason the
external surface of the water-chamber is of bright tinplate.
The interior of the water-chamber is japanned. The zinc inner
chamber for the reception of the animal is left as it is.

The temperature of the animal having been measured by
passing a thermometer an inch and a half into the rectum, it
is placed in the box, the exit tube of which has been previously
brought into communication with an aspirator. The lid is then
rapidly but carefully closed with putty, and the whole placed
without loss of time in the water-chamber. The water-chamber
is then closed and immediately covered with a layer of tow.
In its lid there are two oblong openings for the introduction
of stirrers.1 The water having been agitated immediately
after the introduction of the box containing the animal, a
thermometer is introduced by one of the openings already
mentioned, which after three minutes is read. The time having
been noted, the apparatus is left to itself for fifteen minutes,
half an hour, or an hour, and the temperature is again ob-
served after agitation of the water. The results having been
noted, the animal is withdrawn with as little delay as possible
from the case containing it, and the thermometer is introduced
into the rectum to the same distance as before, and read after
the same interval of time.

In this way obviously four readings are obtained — those of
the animal and of the calorimeter at the beginning and end of
the given period. To interpret them we must take into ac-
count, not only the relative weights of the animal and of the
calorimeter, but their several capacities for heat. In the case
in which the temperature of the animal remains the same, the
amount of production being equal to that of discharge, all
that is required is to know how much heat has been communi-
cated during the period of observation to the calorimeter. In
the opposite case we must, in order to judge of the quantity

1 I have lately adopted a better method of agitation, consisting in the
injection of air into the space below the chamber A. The construction
is such that the whole of the air so used finds its way into the chamber.

BY DR. BURDON-SANDERSON. 341

of heat produced, add to or deduct from the quantity commu-
nicated the quantity it has borrowed or given off from its own
body. If the animal loses heat while it is in the chamber,
the "heat it gives off is only partially generated, the remainder
being abstracted from its own body. If it gains, the quantity
of heat generated is only partially given off; the remainder is
added to its own temperature. To make this deduction or
addition, as the case may be, two questions must be answered.

1. How much heat does the calorimeter require in order that
its temperature may be raised one degree?

2. How much does the bodjr of the animal require for the
same purpose ?

In both cases the quantity required is equal to the specific
heat multiplied by the weight. The mean specific heat of the
calorimeter is obtained by adding together the products of the
specific heat and weight of the parts of which it is composed
— i. <?., the iron case and the water.

Supposing, e. g., the iron to weigh 3800 grammes and the
*water 8600 grammes, the specific heat of iron being 0.114, the
product in question is for the iron casing 419.5, while that for
the water is 8600.0. Consequently 9019.5 gramme-units' of
heat are required to raise the whole one degree of temperature.
Apptying the same method to the animal body, the specific
heat of which is estimated to be 0.83, we have of course 0.83
gramme-units as the quantity to be added or deducted for each
gramme of weight and degree of variation of temperature.

The whole process will be readily understood from an ex-
ample, the weight of the calorimeter being that given above.

Temperature of calorimeter — at beginning 9°.l C, at end
9C.7 C.

Temperature of animal — at beginning 39°.2 C, at end
38°.3 C.

Weight of animal, 3200 grammes.

From these results we obtain : —

1. Units of heat communicated to the calorimeter 9019.5 x

1.6 = 14431.

2. Units of heat borrowed from the body of the animal

3200 x 0.83 x 0.9 = 2390.
Result 14431 —2390 = 12041.

That is to say, the animal, during the period of observation
gave off 12,041 gramme-units of heat.

In calorimetrical experiments, the temperature of the water

1 The absolute amount of heat (in gramme-units) required to raise
the calorimeter 1° C. of temperature may be ascertained empirically by
introducing into the calorimeter (in place of the animal) a metal vessel
containing a known weight of water at a known temperature — say 40°
C. — and determining on the one hand the loss of heat sustained by the
water, and on the other, the gain by the calorimeter in a given time.

342 ANIMAL HEAT.

should, as a rule, be a little higher than that of the surround-
ing atmosphere. Not only is this the condition most favour-
able to the accuracy of the observations, but it is most advan-
tageous as regards the state of the animal observed. If the
temperature is too high, the disengagement of heat from the
surface is relatively lessened, so that unless completely com-
pensated for b}- increased evaporation, the bodily temperature
of the animal will rise. If, on the other hand, the tempera-
ture of the calorimeter is lower than that of the surrounding
air, that of the animal sinks so quickly that its condition is
no longer normal. It is obviously of great importance that
the observations should be made in a room of even tempera-
ture, and it is desirable that it should not be too cold.

The method above described may be applied not only to the
investigation of periodical and other physiological variations
of the process of nutrition, but to the investigation of many
abnormal states and alterations, such for example as those of
fever changes affecting the condition of the surface of the
body, changes affecting the circulation, respiration or nervous"
system, and changes produced by the action of various drugs.1
— For the investigation of fever, the pyrexial state may be pro-
duced experimentally, either by injecting into the venous sys-
tem small quantities (5 to 15 minims) of the exudation liquids
of certain acute inflammations; or by producing a local in-
flammation, e. (/., by applying croton oil to the surface. Al-
though the increase of temperature produced bj* these methods
has been carefully investigated by the thermometer, no suffi-
cient investigations have as yet been made as to the quantit}'
of heat produced in a given time. Among other subjects
which admit of calorimetrical investigation, that of the remark-
able effects produced in rabbits by the process of " varnish-
ing" may be referred to.

111. Increased Discharge of Heat of "Varnished"
Rabbits. — It is well known that rabbits when smeared over
the clipped surface with gelatin or any other similar material,

1 Considering that it is not possible, even with the utmost care, to
keep the animal in a perfectly natural condition during a calorimetrical
observation, and that there are certain sources of error inseparable from
the method itself, which do not admit of being corrected for, it is advi-
sable in employing the calorimeter for physiological investigations to
estimate the value of the results obtained not by calculation but by
comparative experiments, e. g., (1) by comparing the result obtained
under the condition to be investigated with the result obtained in the
normal state of the same animal ; (2) by employing in each observation
two calorimeters, in one of which the animal is placed, while the other
remains unoccupied, but in all other respects under the same conditions.
In this case, the loss of heat, if any, during the period of observation
in the empty calorimeter is to be added to the gain in the one in which
the animal is contained.

X

BY DR. BURDON-S ANDERSON. 343

die ; the pulse and respiration being first accelerated and then
diminishing. Associated with this last change is a veiy rapid
loss of temperature, while the urine becomes albuminous.
Formerly it was supposed' that these changes were dependent
on the suspension of respiration. It is easy, however, to prove
experimentally that it is not so by placing the animal in a
chamber at a temperature of about 30° C, when it is seen
that as the temperature of the body rises the other symptoms
disappear. Even if the animal has been allowed to cool as
low as 21°.l C. it can be restored by warmth. By placing a
varnished rabbit in the calorimeter, it can be shown that al-
though its temperature is actually 10° or more below that of
the surrounding air, it gives off a great deal more heat than a
normal rabbit. Thus I find that a rabbit, which in the normal
state gives off only 3000 heat units in ten minutes, gives off
about 20,000 after varnishing, notwithstanding that in the
former case its temperature was constant at 39.5° C, while in
the other it sank from 36 c to 25°.

Section II. — Thermometry.

The temperature of the animal body is measured either by
the mercurial thermometer or thermo-electrically : —

118. Measurement of Temperature by the Mercu-
rial Thermometer. — The mercurial thermometer used for
ph}-siological (as well as for pathological) purposes should
have the following characters. The proportion between the
quantity of mercury contained in the bulb and the lumen of
the tube must be such that the difference of length of the
column produced by any given increase of temperature shall
be as great as possible. One degree of the centigrade scale
should be sufficiently distant from another to render it possi-
ble to read easily to a tenth. On this account the range of
graduation is necessarily limited. It is sufficient if it extends
from 30° to 45° C. The bulb must expose a large surface in
proportion to the volume of mercury it contains ; for which
reason it is made cylindrical. The most celebrated thermo-
meters are those of Dr. Geissler, Of Bonn. They are 32 centi-
metres ( = 12 inches) long, and relatively exceedingly narrow
— only a line and a half in diameter. The cistern is no wider
than the stem, and is eight-tenths of an inch long. Mr. Hawks-
ley, of Blenheim Street, has recently constructed for me in-
struments which are very similar and comparable in quality
to those of (Teissier. The bulbs and stems are of equal diame-
ter throughout, not exceeding three millimetres. They are
extremely sensitive, and the graduation is so fine that to the
practised observer it is easy to read accurately to the 50th of
a degree of Celsius.

344 ANIMAL HEAT.

For many purposes, it is desirable to employ maximum ther-
mometers, ?. e., thermometers in which the capillary tube pos-
sesses a narrowing at one part, which, while it allows the mer-
cury to ascend, prevents its return to the cistern ; so that the
instrument, wdien removed from the part, still shows the tem-
perature to which the bulb has been exposed. Maximum
thermometers are constant^ used for clinical purposes in this
country, and are also valuable to the physiologist.

If it is intended to observe the temperature in the interior
of the heart, or in any of the great cavities of the bod}-, the
animal must be of large size, and must be curarized. To ob-
serve the temperature in the right ventricle, the bulb of a long
stemmed thermometer must be introduced through the exter-
nal jugular. To observe that of the aorta, or left ventricle,
the carotid must be opened. If a large dog is used, a thermo-
meter introduced into the right side of the heart ma}-, if the
tube be long enough, be easily pushed onwards into the vena
cava. In the rabbit it is scarcely possible to do this, but it is
easy with one of the thermometers mentioned above to mea-
sure the temperature of the heart in this animal.

119. Electrical Measurement of Temperature. — If
a magnetic needle is set in an oblong quadrangular frame, of
which one of the long sides is of bismuth and the other three
sides are of copper, the two metals being soldered together at
the two junctions in such a manner that the needle can swing
freely in a plane at right angles to that of the frame, and so
placed that the frame is in the magnetic meridian, it can then
be observed that if one of the junctions is warmed, the magnet
is made to decline from its normal position — the degree of
deflection varying with the difference of temperature of the two
junctions, and continuing until they again resume the same
temperature. The deflection of the magnet indicates that in
the quadrangle a current exists, and the direction of the de-
flection shows that the current flows from the bismuth to the
copper, beginning at the warmer of the two junctions. Similar
results are obtained when other combinations of two metals
are substituted for bismuth and copper. According to the
electro-motive force yielded by each, the metals may be ar-
ranged in what is called the thermo-electrical series ; in which
series those metals are placed furthest apart which 3'ield the
greatest quantity of electricity at their junctions. Bismuth is
at one end, antimony at the other ; close to bismuth comes
German silver, and close to antimoii}7 iron. Iron and German
silver yield, therefore, nearly as much electro-motive force per
degree of difference of temperature as antimony and bismuth,
and are much more workable. Being further apart in the
thermo-electrical series than bismuth and copper, they are
preferable to those metals on that ground also.

BY DR. BURDON-SANDERSON. 345

On these facts are based the electrical method of measuring
temperature. Instead of the quadrangle, we give to our junc-
tions a convenient form for introducing them into the situa-
tions at which we desire to make our measurements. Instead
of the magnet, we use the instrument known as a multiplier.
This consists essentially of a magnet, surrounded by numerous
coils of copper wire, in which the current due to difference of
temperature between, the two junctions flows. We have to de-
scribe first the junctions, then the multiplier. As one of the
reasons for preferring the electrical to the ordinary method of
measurement is that the measuring instrument can be intro-
duced with exactitude into spaces which are too small for a
thermometer bulb, the form usually given to the junctions is
that of a needle. These needles are generally made of iron and
German silver, i. e., each needle consists of two wires of iron
and German silver respectively, which are soldered together at
and near their points, so that the junction may be completely
buried in any tissue into which the needle is thrust. The two
needles forming one element are connected together, metal to
metal — the iron wire forming part of both, while the two Ger-
man silver wires communicate each with the two ends of the
coil of the multiplier, thus completing the circuit. As the
needles require to be handled by the experimenter, it is neces-
sar}' to protect the upper ends by covering them with silk and
varnish ; and the two wires must be carefully isolated from
each other everywhere excepting at the points where they are
soldered together.

For the purpose of making clear the mode of using the ther-
mo-electric needles, let us suppose that it is required to measure
the difference of temperature between two symmetrical parts
on opposite sides of the bod}7, one of which is inflamed, the
other in the normal state. One or any number of thermo-ele-
ments may be used, each of which consists of a pair of needles
with their wires arranged as above described. If only one ele-
ment is employed, one of its junctions is placed in each of the
tissues of which the temperature is to be investigated ; the iron
wire of each needle being in communication with that of the
other, and the German silver wires with the ends of the multi-
plier. If several pairs are used, an equal number of needles
must be placed in each of the parts to be compared, the ar-
rangement of which is as follows : Let us designate the needles
on the right side a, b, c, those on the left a', b', and c'. The
German silver ends of a and c' being connected with the multi-
plier, the iron end of a is connected with that of a', the iron
end of b with that of b', and that of c with c', and the German
silver end of a' with that of b, and that of b' with that of c.
It is scarcely requisite to say that the junctions need not
assume the form of needles ; each may consist of two wires of

346 ANIMAL HEAT.

different metals soldered together endwise, in which case it is
of course necessary to transfix the part to be investigated with
the joined wire, placing it in such a position that the junction
is at the point to be investigated.

The multiplier consists essentially of a magnetic needle, sus-
pended horizontally in the centre of a coil of wire along which
flows the current which requires to be measured. In conse-
quence of this arrangement, the needle, if it is in the same
plane with the coil which surrounds it, will be deflectdl in
accordance with Ampere's law, whenever a current passes along
the wire, and will be acted on similarly by all parts of the coil.
In order to enable the needle to act under the direction' of the
coil without being affected by terrestrial magnetism, it is made
astatic. Twomagnetic needles of equal powers, placed parallel
to each other, are rigidty united by a copper wire passing
through their centres of gravity in such a manner that the north
pole of the one is opposite the south pole of the other, and vice
versa. The united needles are hung at such a level that the
one swings above the coil, the other in its centre. From this
arrangement it results not only that the influence of earth-
magnetism is neutralized, but that both needles are affected in
the same way by the current.

The construction of the most important parts of the instru-
ment (which is represented in fig. 265, bis) is as follows : The
wire is coiled round a frame of wood, represented at a, the two
pieces x and y are hollow. In the cavity of the horizontal
piece, x, the lower of the two magnets swings, and can be
introduced through the vertical slit in y. The magnets are
shown at b. The copper wire is carefully covered with silk,
and varnished. As the resistance of the coil must be low, the
wire is not longer than from 20 to 25 feet, and its thickness is
considerable (0.5-1 millim.). The end of the coil terminates
in the screws seen on the right side in the drawing. The nee-
dles are^hung by a cocoon fibre to the centre of the frame, the
mode of attachment being such that by raising or depressing
the knob the height at which they are suspended can be varied.
When the instrument is used, the lower needle must swing
freely in the horizontal split, the upper above the graduated
circle. Having raised the needles by the cocoon fibres till they
swing freely, adjust the instrument with the levelling screws so
that the fibre hangs exactly in the centre of the circle, then
rotate the coil until the upper needle points to 180° and 0°,
and connect the screws with the thermo-elements, with the
intervention of a single "plug-key." If the temperatures of
the junctions are different, the needle is deflected on opening
the key.

In using the multiplier, it must be remembered that although
the deflection of the needle varies with the intensity of the cur-

BY DR. BURDON-SANDERSON. 347

rent, find consequently with the difference of temperature be-
tween the two junctions, the variations are not proportional, so
that, e. g., a deflection of 30° does not indicate a current twice
as strong as a deflection of 15°. The relation between the read-
ings and the intensities of the currents they indicate is different
in each instrument, and consequently, must be determined once
for all for each. Of the various modes which may be adopted
for this purpose, the simplest is the empirical method devised
originally b}r Melloni, an account of which will be found in all
treatises on physics ; the operation can be best done in a physi-
cal laboratory. Within twent}' degrees the deflection is usu-
ally so nearly proportional to the strength of the current, that
the error may be disregarded. For deflections beyond this
point the results of the graduation must be recorded in a table
of the following form, which must be kept with the instrument.

Deflection. Intensity of Current.

20° . 20.0

24° 25.0

28° 31.5

32° 39.6

36° 49.5

etc. etc.

The above numbers are taken from the example given by
Melloni. In the second column the starting number 20, stands-
for the intensity of current indicated by a deflection of 20°.
This being assumed, the other numbers represent the intensities
corresponding to the deflections opposite to which they stand.

The instrument having been graduated, it is still necessary
to determine for each element the constant, by which the start-
ing number must be multiplied in order to give the temperature
difference. Thus, if with a certain element a deviation of 20°
is produced by a difference of temperature amounting to 0.10
C, the temperature corresponding to any other deviation is
obtained by multiplying the number opposite to it in the table
by 0.005, which is therefore the constant required. This deter-
mination the physiologist must make for himself. It is effected
by immersing the junctions into two large vessels containing
water or oil, the difference of temperature between which is
measured by accurate and sensible thermometers. To avoid
error, it is of course necessary to repeat the observation many
times.

[For the accurate measurements of temperature which are
required in some physiological and pathological researches the
multiplier is not adapted. We substitute for it a true galvano-
meter. The instrument used in Germany is the Spiegelbussole
of Wiedemann, a description of which will be found in Rosen-
thal's " Electricitatslehre fur Mediciner." In England, the

348 ANIMAL HEAT.

preference is given to the galvanometer of Sir William Thom-
son. In both of these instruments the deviation of the needle
has a definite relation to the intensity of the current, the inten-
sities of any two currents being proportionate to the tangents
of the angles of the deviation they produce; so that, so long
as the same junctions are used, if the deviation produced by
an}' known difference of temperature has been ascertained em-
pirically, the values of other readings can be deduced from it.]
120. Distribution of Temperature in the Body. — The
principal purpose to which the therm o-electrical method is
applied in physiology, is that of measuring the differences of
temperature which exist between different parts of the body.
These differences vary according to the proximity to, or dis-
tance from, the surface of the point where the measurement is
made, and according to the supply of blood which the adjacent
tissues or organs receive. Taking as a standard of comparison
the temperature of blood in the aorta, the facts hitherto ascer-
tained as to the temperature of other parts are as follows: —

1. The blood of the inferior vena cava is warmer, that of the
superior, colder ; but in the former this is true only of the
upper part of the vein just as it passes through the diaphragm.

2. The temperature of the skin and subcutaneous tissue is
always considerably lowrer than that of the aorta, but varies a
good deal.

3. The temperature of the lungs also varies. Near the dia-
phragm it is higher than that of the aortic blood, but elsewhere,
and particularly near the costal surfaces, it is lower.

4. All the abdominal organs have a higher temperature than
that of the aortic blood, those in the upper part of the abdomi-
nal cavity being the warmest.

5. The blood contained in the right ventricle is somewhat
warmer than that in the left, the difference varying from 1° C.
to 3° C. This difference is not dependent on the cooling of the
blood as it passes through the lungs; for it is just as marked
when an animal is made to breathe warmed air saturated with
moisture. Moreover, such an hypothesis is rendered untenable,
by the fact that the lungs themselves are scarcely cooler than
the blood in the aorta. Its real cause is, doubtless, that the
wall of the right ventricle is in contact with the diaphragm and
abdominal organs, while the left is surrounded by lung.

The recent introduction of thermometers of extreme sensi-
tiveness and accuracy has rendered the method less important
to the physiologist than it seemed to be a few years ago. This
may be illustrated by the remarkable fact, that the long con-
troversy as to the relative temperature of the two sides of the
heart has been at last set at rest, not electrically, but by the
thermometer.

PHYSIOLOGY.

PART II.— FUNCTIONS OF MUSCLE AND NERVE.
By Dr. MICHAEL FOSTER.

INTRODUCTORY.

In the following part of this work, the object chiefly kept in
view has been to limit the directions as much as possible to
such observations and experiments as the student may be
reasonably expected to perform for himself under due super-
vision. The ordinary phenomena of muscle and nerve are
consequent^ dealt with at far greater length than are the
properties of the central nervous system. The latter are, to
say the least, but imperfectly known, the experiments on which
our knowledge rests difficult and complex, and too often bring-
ing out uncertain or even contradictory results. The former,
on the other hand, may be studied with approximate exacti-
tude ; the methods of experiment and observation are becom-
ing, year by year, more physical in character, and the observa-
tions themselves, fundamental in their nature and having the
widest bearings in all the higher branches of physiology, may,
for the most part, be conducted on frogs, may be repeated any
number of times without difficulty or expense, and so serve
usefully as a means of training students in physiological study
and inquiry. The phenomena in question are so fully treated
of in various text-books, that space in the following chapters
has been devoted to detailed instructions as to how to proceed
in the various observations rather than to complete explana-
tions of what the observations are intended to show or prove.

Instructions concerning the various special pieces of appara-
tus required in this part of the subject are thrown together,
for convenience sake, in the first chapter. The succeeding
chapters deal with the general properties of muscle and nerve;
while such observations as the student may be expected to

350 GENERAL DIRECTIONS.

make on the central nervous system are contained in the two
last chapters.

No special chapters on the senses have been introduced, as
there seemed to be no mean between the common simple
observations on the one hand which are found in all the text-
books and such elaborate instructions on the other as would
hardly come under the scope of this work.

CHAPTER XIX.
GENERAL DIRECTIONS.

I. The Nerve-Muscle Preparation. — Having pithed a
frog and destroyed both its brain and spinal cord, lay it on its
bell}' and make an incision through the skin along the middle
line of the back of the thigh, from the knee to the end of the
coccyx, and carry the incision along the back about midway
between the coccyx and ileum (fig. 266, line &, m, n). On
drawing back or removing the skin, there will come into view,
on the outside of the thigh, the triceps femoris (fig. 267 a),
on the median side the semi-membranosus c, and between these
the small narrow biceps femoris b. With the " seeker" sepe-
rate gently b and c ; the sciatic nerve and femoral vessels will
be found running between them. Gently tear away, with the
seeker, the connective tissue round the nerve, beginning near
the knee (where it divides into two branches), and working
upwards till the muscle n is reached. Be careful to touch the
nerve itself as little as possible, and on no account seize it
with a pair of forceps. Carefully cut through the pyrilbrm
muscle n and the connective tissue in which the nerve is em-
bedded at this point, divide the iliac-coccygeal muscle d, right
through, and follow the three nerves (which come into view
when the muscle is removed, and which go to form the sciatic
and other nerves) right up to the vertebral column. Cut the
column across just above the last lumbar vertebra, and bisect
lengthways the piece so cut off. Hold the bony fragment with
the forceps, lift it up and free it from the tissues around, and
then follow with the scissors the nerves right down to the
knee, cutting away their various branches and removing any
tissue which still may be clinging to them.

Now remove the skin from the leg; the gastrocnemius (fig.
267 g) will at once be recognized : cut through the tendo
Achillis at /, below the thickening at the heel. Holding the
cut tendon with a pair of forceps, it will be easy, with a few

BY DR. MICHAEL FOSTER. 351

strokes of the seeker, to free the muscle right up to its at-
tachment to the end of the femur, at h. The branch of the
sciatic nerve going to the gastrocnemius will be readily seen
when the muscle is turned over, as also another branch which
runs along its under surface, but which ends in other muscles.
Carefully avoiding any injury to the former nerve, but disre-
garding the latter, cut away the whole of the tibia and fibula
from the femur. Clear away, carefully avoiding the nerve, all
the muscles of the thigh from the lower end of the femur so
as to leave the bone tolerably bare, and cut the bone across at
its lower third. There is left merely the end of the femur, to
which is attached the uninjured gastrocnemius, with the whole
length of the nerve from the muscle up to its entrance into
the spinal canal. The muscle attached to the fragment of
femur, with its prepared nerve, is represented in fig. 268.
(The vertebral fragment is not shown.)

II. The Lever. — In order to study the contraction of a
muscle, it is advantageous to employ a lever.

The myographion of Helmholtz and Pfluger is shown in fig.
269. The lever a moves on the fulcrum b and is balanced by
the counterpoise c. At d is either a fine brush to write on
paper, or a fine style to scratch smoked glass or paper. The
rod e bearing the style, moves on a hinge at/*, and also carries
a counterpoise g. Hence the writing point describes a straight
line, while the actual end of the lever itself is describing the
arc of a circle. The silk thread coming from the tendon of
the muscle is attached at h. The small pan is to receive
weights for loading the muscle.

For ordinary purposes, the simple lever of Marey, shown in
the lower part of fig. 270, is much more convenient for use,
while at the same time the momentum of the heavy lever of
the myographion is avoided. The portion next to the fulcrum
is of metal, perforated or notched to receive the hooks, etc.,
by which the muscle is attached above, and the weight below.
This is prolonged by a thin slip of wood or piece of straw, at
the end of which is a fine brush, placed horizontally at an
angle of about 60 degrees to the long axis of the lever, or a
thin slip of gutta-percha bearing a fine needle for tracing on
smoked glass or paper.

To get rid of the momentum, the weight may be replaced
by a long weak spiral spring. This spring must be graduated
beforehand, i. e., the amount of force determined which is re-
quired to extend it to a given amount. The spiral may be
replaced by a simple slip of main-spring pressing on the lever
in a direction opposite to that of the movement given to it by
the muscle.

III. The Moist Chamber. — In order to prevent the
muscle and nerve from drying, they must be kept damp.

352 GENERAL DIRECTIONS.

Moistening either muscle or nerve, and especially the nerve,
even with Na. CI. .75 p. c. is undesirable, as it tends to intro-
duce errors. It is necessary, therefore, so to place the nerve
and muscle that they may be experimented upon in an atmo-
sphere kept uniformly damp. This is effected by means of
the moist chamber (fig. 270).

This consists of a platform of hard wood or ebonite, which
slides up and down, and can also be turned from side to side
and clamped in any position, on an upright. Let into the
platform are two or more pairs of insulated binding screws for
receiving the various wires for the electrodes, as well as
clamps into which the leaden electrode bearers are fixed. The
upright on which the platform slides also carries above a
sliding arm, with a clamp for holding the femur of the nerve-
muscle preparation, and below a similar sliding arm to which
the lever is fixed. The attachment of the muscle to the lever
is carried through a slit in the platform. A common glass
shade, fitting into a rim in the platform, covers everything ;
and when several pieces of wet blotting-paper are placed inside
the cover, the atmosphere within may be kept saturated with
moisture for any length of time.

IV. Nerve Chamber. — When the phenomena of electro-
tonus (Chap. XXVII.) are being studied, it is very desirable
to have a smaller chamber than the ordinal moist chamber to
work in. This may be gained by having a small glass trough,
about three inches long and one broad, with a movable top,
and the glass of one of the sides replaced by a piece of India-
rubber sheeting with a slit along the middle. The electrodes
may be introduced through the slit at the side (the India-
rubber closing on them), the nerve placed in position on the
electrodes, a few morsels of wet blotting-paper inserted (so as
not to touch the nerve), and the cover laid on. The nerve
ma}' thus be kept from drying for a considerable time.

V. Electrodes. — For many purposes the ends of the
copper wires may be used without any special arrangement.
The two wires may be kept separate, or they may be fixed at a
definite distance from each other in an insulating handle of
bone, wood, gutta-percha, etc. (fig. 271). It is often con-
venient to have the ends of wires completel}' covered, except
just at one point in each to which the nerve may be applied
(fig. 271). In this case it is also frequently an advantage to
have the ends somewhat curved. Such a pair of electrodes
can easily be made at once by fastening two wires, bent as
desired, on either side of a slip of wood, or other non-conduct-
ing material, of the thickness required to separate the wires
sufficiently, coating the whole with melted paraffin, and, when
the paraffin has cooled, scraping a little away at one spot till
a point of each wire is exposed. Platinum wire, or slips of

BY DR. MICHAEL FOSTER. 353

platinum foil, may be advantageous^ substituted for the
terminal portions of the copper wires.

VI. Non-Polarizable Electrodes. — In many cases, how-
ever, it will be absoluteljr necessary to have non-polarizable
electi'odes. The most convenient form is that of Du Bois
Reymond, modified by Donders (fig. 212).

A glass tube a (about one-third inch diameter is the most
convenient size) is plugged at one end by a plug b of china
clay, worked into a firm putt}' with .75 p. c. sol. of Na. CI.
A few drops of a saturated solution of sulphate of zinc c are
carefull}' introduced into the tube. A slip of zinc, or piece of
zinc wire 2, thoroughly amalgamated at the tip but covered
with varnish over the greater part of its length, is introduced
into the tube, and so placed that the amalgamated end dips
into the zinc solution as far as two or three millimetres above
the clay plug. The other upper end of the wire is bent round
the upper open end of the tube, and brought to the binding
screw of the brass collar d, which is movable up and down the
outside of the tube, and can be clamped at will. The copper
wire e is fastened in the same binding screw.

Several such electrodes of different forms should be pre-
pared. The tube may be cut off straight at the lower end,
and the clay plug brought out in the form of a cone (fig. 273
a), or in any other shape that may be desirable. It is often
convenient that the end of the tube should be cut obliquely,
witli the clay plug not projecting at all (fig. 273 c). The end
of the tube ma}' be of the same diameter as the rest of the
tube, or may be brought more or less to a point. Where the
electrodes require to be applied to nerves, it is convenient to
have the form fig. 273 b ; the end of the tube is bent round,
and the extreme point closed ; near the end, on the upper
surface, a small hole is drilled ; consequently the plug b is only
exposed at b'.

Electrodes of different lengths should be prepared ; those
required for working in the moist chamber need not be more
than two inches long ; otherwise, five or six inches is a con-
venient length.

The most convenient electrode-bearer is represented in fig.
272. The piece of leaden wire k ends in the brass head h',
which bears the two arms f f, each of which holds an elec-
trode tube by means of a spring collar. The two arms move
round the point //, and can be clamped in any position. The
points of the electrodes may thus be brought near to or apart
from each other, as may be desired. The extremely flexible
but non-elastic leaden wire (a cylindrical wire being far better
than a flat piece of lead), the far end of which is fixed in a
clamp, permits the pair of electrodes to be placed without re-
23

354 GENERAL DIRECTIONS.

bound, and therefore with great accuracy, in any position
whatever.

VII. Commutator. — This is useful for changing the direc-
tion of a current when the effects of constant currents are
being studied. Any form of commutator may be used, pro-
vided that the current can easil}- be cut off altogether, as well
as reversed in direction. A very convenient form is that
represented in fig. 297, in which, when the handle is horizontal,
the current is cut off from the electrodes altogether; and a
different direction given to the current according as the handle
is raised or lowered. The wires from the battery should be
brought to the upper, and those from the electrodes to the
lower binding screws.

VIII. Rheoehord. — This instrument is directed to be used
in the following pages simply for the purpose of causing defi-
nite changes in the amount of a constant current under use.
Fig. 298 represents a convenient form of the rheoehord of Du
Bois Reymond.

Bring the wires from the battery to the binding screws at
the top of the board and those from the electrodes to the same
screws. If all the plugs are in place and the travelling mer-
cury cups close up to the top of the board in direct contact
with the brass, the resistance to the current from the battery
offered by the rheoehord compared with that offered by the
circuit of the electrodes is practically nil, and consequently all
the current passes through the former and none through the
latter. If the mercury cups be moved on their platinum wires
a little distance down the board, there will be no passage for
the current from one side of the rheoehord to the other, ex-
cept through such a length of the two platinum wires as lies
between the cups and the brass plate. But these thin wires
offer a certain resistance to the passage of the current, and
consequently a proportionate fraction of the total current from
the battery is thrown into the circuit of the electrodes. By
sliding the mercury cups various distances down the graduated
board, small differences of resistance in the rheoehord are es-
tablished, and consequent!}' slightly differing fractions of the
total current thrown into the circuit of the electrodes. If one
of the plugs be removed, a certain amount of resistance is
suddenl}' introduced into the rheocord, and consequently a
certain amount of the current is suddenty thrown into the
circuit of the electrodes. With the different plugs different
amounts of resistance are introduced into the rheoehord, and
different amounts of the current thrown into the circuit of the
electrodes. The several plugs are all numbered as multiples
of the resistance offered by the total length of the platinum
wires on which the cups travel. Thus if the resistance offered
by the rheoehord when the cups are quite at the bottom of the

BY DR. MICHAEL FOSTER. 355

board, but all the plugs in place, be taken as the unit, the re-
moval of the plug marked 5 will suddenly introduce in addi-
tion five times that amount of resistance, and so send a pro-
portionate amount of the current through the circuit of the
electrodes.

IX. The Double Key or Wippe. — This is very con-
venient when it is desired to throw a given current from one
pair of electrodes into another. It is represented in fig. 299,
in which it is seen that the mercury cups belonging to the
binding screws 1 and 2 are connected by a handle of which the
central part is of insulating material, the ends of thick copper
wire. Each of the copper wires is crossed just as it enters
the handle by an arch of the same material ; one end of each
arch dips into one of the mercury cups 3 and 4, when the
handle is thrown to the right as in the figure. The wires from
one pair of electrodes are to be brought to the binding screws
3 and 4, those from the other to the screws 5 and 6. The small
cups on the surface are to be filled with mercury, and the wires
from the battery or induction coil, etc., brought to the screws
1 and 2, and the straight cross wires between 3 and 6 and 4
and 5 taken awa3r. By throwing the handle to the right, the
current from the battery is sent into the wires connected with
the screws 3 and 4; by throwing the handle to the left, into
the wire connected with the screws 5 and 6.

X. The Marking "Lever. — This is a two-armed, flat,
metal lever, fig. 275 a a\ working vertically on the. pivot 6, the
arm a being considerably heavier than a'. The pivot is elec-
trically continuous with the small brass pillar c, where binding
screws receive a wire or wires from a battery, induction coil,
electrode, etc. The pillar c is placed on one side of the sup-
port d, made of non-conducting material, which by e can be
clamped to any stand, either vertically or horizontally. On
the other side of the support is a similar pillar/ (also bearing
binding-screws), on which the arm a of the lever rests ; g is a
weak spring, which serves to catch the end of the lever when
thrown up ; h is a slip of gutta-percha or India-rubber at the
end of the lever bearing the marking needle or pen.

If c be connected with one of the poles of the battery, and
/ with one end of the primary coil, when the lever is down and
horizontal, the arm a being in close contact with the pillar, the
current passes along the lever from c to /. When, therefore,
the arm a of the lever is suddenly tilted up, which can easily
be done with the point of the finger, the current is suddenly
broken ; and the moment of the breaking is indicated on the
registering surface by the descent of the marking point of the
lever. When it is desired to mark the making rather than the
breaking of a current, the two positive (or negative) wires
must be brought to the binding screws of/, and the two nega-

356 GENERAL DIRECTIONS.

tive (or positive) to those of c. The tilting up of a will then
correspond to the making of a current as in Du Bois Rej-
inond's key. (See below.)

XI. Arrangement of Apparatus for Experiment. —
The electrodes being charged and fastened in their bearers, the
bearers secured in the clamps, and the wires from the electrodes
brought to the binding-screws of the platform of the moist-
chamber, fasten the femur of the nerve-muscle preparation
securely in the clamp, in such a way that the muscle* hangs
vertically downwards over the slit. Seize the vertebral frag-
ment with the forceps, and gently lodge the nerves on the
electrodes. Firmly fasten the tendo Achillis in a Kronecker's
clamp (fig. 274), and with a strong silk thread of appropriate
length connect the Kronecker with the lever, the silk passing
through the slit. Adjust the arm bearing the muscle, and that
bearing the lever, in such a way that the muscle hangs per-
fectly vertical, and, without being actually on the stretch, is so
attached to the lever (which should be in a perfectly horizontal
position) that the slightest contraction of the former will move
the latter.

Bring the wires from the battery, induction coil, etc., to the
binding-screws which carry the wires of the electrodes. Place
the glass shade over the platform, with wet blotting-paper
inside, being careful that the wet paper touches neither the
nerve-muscle nor the wires.

Prepare weights for loading the lever; the most convenient
are 5, 10, 20, 30, 50, 150, 200, and 300 grammes. Place the
whole apparatus so that the point of the lever touches the
registering surface.

Where it is required to study the muscle without removing
it from the circulation, another method must be adopted,
which may be followed in other cases as well. The upper
surface of the platform should in this case be provided with a
thick layer of cork.

Having pithed the frog, pin it firmly, bell}' downwards, on
the cork of the platform, fixing the thigh of one side espe-
cially tight ; one of the pins should be passed close to the
femur, on the anterior surface of the thigh, just above the
knee. Make a slight longitudinal slit along the tendo Achillis,
which divide low down, and carefully dissect out for a few
millimetres; put a small but strong S hook, with a silk thread
attached, in the tendon, pass the silk over one of the small
double-cone pulleys which are fixed on to the platform, and so
through the arms of the T slit to the lever below.

The sciatic nerve may now be dissected out in the thigh
without injuring the bloodvessels, and the curved electrodes
slipped beneath it.

Where the recording cylinder used rotates on its horizontal,

BY DR. MICHAEL FOSTER. 357

and not on its vertical, axis, the simple lever must be fixed in
a horizontal position at the front of the platform, and the silk
brought in a straight line to it from the tendon. Resistance
to the action of the muscle may then be gained by means of
the light spring, or a weight passing over another pulley. As
a rule, it is best, when possible, to do without a pulle}*-.

XII. Recording Tuning-Fork. — For measuring small
intervals of time in plrvsiological observations, it becomes
absolutely necessary to make use of tuning-forks of known
rates of vibration. Fig. 277 is a figure of a tuning-fork
arranged by Konig for recording its vibrations on a revolv-
ing surface. A massive stand bears the fork A firmly secured
in it. The two coils c c' (which by means of the arrangement
k can be slid up and down the stand, so as to accommodate
themselves to tuning-forks of different lengths) project over
the two ends of the fork, and each bears a screw d which can
be screwed as desired up to or away from the ends of the fork.
The upper arm of the fork bears at its end a rod a with plati-
num point which dips into the mercury cup b.

The tuning-fork B, which must have the same rate of vibra-
tion as A, is fixed into a light movable stand, so that it can
be placed in such a position that the light elastic marker g
may touch with the least excess of friction the recording sur-
face. This fork is placed in the same manner as A, with its
ends between the coils e e', bearing similarly the screws f f.

One wire from a battery w is connected with a binding
screw at the handle of the tuning-fork A, and is thus in electric
continuity with the rod a. The mercury cup b is connected by
a wire z with the coil e of the fork B. The other pole of the
battery is connected by x with the coils c c' of A, and thence
by y with the coil e' of B.

The screws d d, f f being brought rather near to their re-
spective forks, place a small quantity of mercury covered by a
little spirit in the cup 6, and having set the fork A vibrating a
little, screw the rod a up or down until magnetic interruption
is fairly established. B will then be found vibrating synchro-
nously with A, and the point g will be found tracing curves
on the recording surface, the interval of time corresponding
to each curve being determined by the pitch of the fork.
Screw the d d, / '/' ', as far away from their respective forks as
can be done without stopping the current altogether.

XIII. Arrangement of Electrical Apparatus. — Con-
stant Current. — Place the nerve (or muscle, when muscle
alone is the subject of experiment) on the electrodes, taking
care that the nerve is actually in contact with each electrode.
When the non-polarizable electrodes are used, their plugs must
be kept damp with the normal saline solution: avoid making

358 GENERAL DIRECTIONS.

them too wet, and especially do not let a bridge of fluid form
along the nerve between the two electrodes.

Bring the wire from each electrode to the outer binding screw
on each side of a Du Bois Raymond's key (fig. 300). Bring
the wires from the battery to the inner screws of the same key.
Let the positive wire, the wire connected with the copper,
carbon, platinum, etc., of the battery be colored of some defi-
nite color, e. g., red; let the wire fastened to the same side of
the key have the same color. The electrode connected with
this wire will be the positive electrode, or anode. Let the two
other wires connecting the zinc of the battery with the key,
and that side of the key with the other electrode which there-
fore becomes the negative electrode or kathode, be colored of
some other color, e. g., blue.

When the key is down, the brass plate offers such little re-
sistance to the passage of the current, compared with that
offered by the nerve, etc., that the whole current will pass
through the bridge of the ke}r, and none through the nerve.

Consequently, opening the key is equivalent to throwing a
current into the nerve ; shutting the key, to removing the cur-
rent from the nerve ; during the whole time that the key is
open, the nerve, etc., is exposed to the action of the current.

When the kathode (negative pole) is placed at a point on the
nerve nearer the muscle than the anode (positive pole), the
current is said to be descending ; when the anode is the nearer,
the current is said to be ascending.

Single Induction Shock. — Connect each wire from the
battery (Fig. 276 B), a key b intervening, with one of the two
screws on the top of the primary coil C. Connect the secondary
coil D with the electrodes E E', a key a intervening.

Whenever the key b is opened, and the current from the
battery allowed to pass from the primary coil, a current is in-
duced for the instant in the secondary coil ; another current
is similarly induced in the secondary coil when the same key
is shut; but in the interval there is no current produced in
the secondary coil provided that the current in the primary
coil be constant.

If the key a is kept open while the key b is being opened or
shut, at each opening or shutting of b a single "induction
shock" is sent through the nerve.

If a be kept open when b is opened, i. e., when the current is
allowed to pass into the primary coil (when the current is
made), but closed before b is closed again, a " making or closing
induction shock" only will be sent through the nerve.

If the key a be kept closed while b is opened, and opened
before b is shut (and the current in the primary coil is broken),
a "breaking or opening induction shock" only is passed through
the nerve.

BY DR. MICHAEL FOSTER. 359

In determining the direction of the induction shock, it must
be remembered that, at making the current in the primary coil,
the current induced in the secondary coil is opposite in direc-
tion to that of the primary, but that on breaking it, it is in the
same direction.

Interrupted Current. — For ordinary tetanizing purposes,
the magnetic interruptor of Du Bois Reymond's apparatus is
used (see Fig. 293). Connect the end of the positive wire of
the batteiy with the brass column g, and the negative wire
with a ; the current then enters by y, passes along the German
silver spring, which when not in action is in contact, by a little
plate of platinum soldered on to its upper surface, with the
platinum point of the screw f. From f the current passes
through the brass block e, with its binding screw d, to the pri-
mary coil c ; after traversing it, it reaches the electro-magnet
6, and then returns to the battery through the binding screw a.
The anchor h is supported over the electro-magnet by the end
of the German silver spring; the moment that the current
passes through &, the anchor with the spring is drawn down
so as to break the current at f. Thereupon, the magnet
ceasing to act, allows the spring to return to its former posi-
tion. By sliding the secondary coil to a greater or less dis-
tance from the primary, the strength of the induced current
can be varied at will.

When it is specially important to avoid unipolar action, the
apparatus must be modified in the manner recommended by
Helmholtz. With this view, connect the column g with the
binding screw d by a side wire also marked g, and heighten
the tip of the column a by means of the milled rim. This
arrangement is shown in Fig. 294. The current enters as be-
fore, but in its course to the primary coil it passes partly
through f and partly through the side wire g. When the an-
chor is drawn down, as seen in the figure, the spring rests
upon the summit of a, so that the current passes directly back,
as indicated by the arrow, to the battery. The moment this
is the case, the current through the electro-magnet becomes so
feeble that it is insufficient to keep down the anchor, the spring
rising again comes into contact with f, and so on. The modi-
fication of effect is as follows : 1. The induced currents are
weaker, for the variations of the strength of the current are
less. 2. The intensity of the opening induction current, which
in the ordinary arrangement is much greater than that of the
closing, is reduced so that the two are nearly equal.

If it is desired to allow the current from the battery to tra-
verse the primary coil without passing the interruptor, so as,
e. g., to use the apparatus for producing single opening or
closing induction shocks, connect the positive wire of the bat-
tery with e, and the negative, as before, with a.

360 GENERAL PROPERTIES OF MUSCLE AT REST.

It is often advisable to use a key both between the battery
and the induction coil, and between the secondary coil and the
electrodes.

Current "with Definite Interruptions by Means of
the Metronome. — Arrange as for a single induction shock,
except that, in place of the key b, insert the electrical metro-
nome, an instrument which may be described as a key which
is opened and closed by clock-work at regular intervals of
time, the length of interval being varied at will. The key a
may be dispensed with, as, unless a special provision be made,
the shocks given will be both opening and closing.

Current interrupted by Means of an Oscillating
Rod. — Bring one wire straight from the battery to the pri-
mary coil, connect the other wire with a slip of thin elastic
steel (the length will be determined by the rapidity of inter-
ruption required), one end of which is made fast, while at the
other a needle, at right angles to, but in electrical continuity
with, the steel slip, hangs over a mercury cup at such a dis-
tance, that when the steel slip is at rest, the needle is quite
clear of the mercury, but that when the slip is made to oscil-
late, with each oscillation the needle dips in and out of the
mercuiy. Connect the mercuiy of the cup with the other
binding screw of the primary coil. At each oscillation of the
slip, the current will accordingly be made and broken.

CHAPTER XX.
GENERAL PROPERTIES OF MUSCLE AT REST.

I. Elasticity. — Obs. I. Take a gastrocnemius, prepared
as directed in Chap. XIX., sec. I., except that the nerve may
be neglected wholly ; fasten the femur in the clamp of the
moist chamber, and attach the muscle to the lever, as directed
in sec. XI. Let the lever be perfectly horizontal.

Draw on the recording surface a straight line, on which
make a mark for zero, and mark off abscissas in the proportion
of 10, 30, 50, 100, 150, 200, 300, 400, etc.

Disregarding the weight of the lever (or of the pan, etc.,
when Helmholtz's arrangement is used), the muscle may be
supposed to have its natural length when no weight is brought
to bear upon it. This may be indicated by bringing the re-
cording point of the lever to touch the zero point on the re-
cording surface. Xext shift the recording surface until the
point of the lever touches the point corresponding to 10.

BY DR. MICHAEL FOSTER. 361

Then place 10 grammes in the pan, or hang a 10 gramme
weight on the lever. The point of the lever will move clown-
wards, describing a line of a certain length. This indicates
the amount of extension which the muscle has suffered in con-
sequence of being loaded with the 10 gramme weight.

Remove the weight carefully ; the point of the lever will re-
turn to the point where it was before the weight was applied.

The distance of the point of attachment of the muscle and
that of the point of the lever from the fulcrum being known,
the actual extension of the muscle with 10 grammes may be
calculated from the length of the line marked on the cylinder.

"Ifuscle possesses very little elasticity (i. e., is very extensi-
ble) ; but that little is very perfect ; i. e., on withdraival of the
extending force, the muscle returns very rapidly and com-
pletely to Us previous length.''1

Obs. II. Now move the recording surface till the lever point
stands at the mark 30; load the pan with 30, and proceed as
before. Repeat at 50, 100, 200, etc. Before trying the heavier
weights (300, 400), see that everything is secure, especially the
clamps on the femur and on the tendon. As a general rule,
the attachment of the muscle to the femur at last gives way.

With the heavier weights it will be found that the muscle
returns after extra extension and upon removal of the weights
towards its former length, at first very quickly, and then more
and more slowly — and that even after waiting for some minutes,
it does not regain its former length completely.

This falling short of a complete return is due to exhaustion
(commencing death, see Obs. IV.). The student had better,
in one set of observations, start in each case from the point of
the ordinate to which the lever had returned after the previous
extension, but of course from the next point on the abscissa,
and in another set bring down the recording surface in each
case so that the lever may start afresh from the abscissa line.
The lever should be horizontal at the beginning of each trial.
The pan or weight should also be allowed to descend very
gradually and slowly, to avoid momentum. Where there is
no arrangement for keeping the recording point in a straight
line, a horizontal line drawn through the end of each curve will
cut off from a vertical line, drawn through the starting-point,
a line equal to the vertical distance traversed by the lever
point.

If now the lines so obtained be examined, it will be found
that though with the greater weights there is greater extension,
yet the increase of extension caused by increase of weight gets
less and less. The extension increases not in direct propor-
tion to the weight, but with continually diminishing increments.
If a line be drawn through the points which in each case mark
the limit of extension, that line will not be a straight line as it

3G2 GENERAL PROPERTIES OF MUSCLE AT REST.

would he if the extension were in direct proportion to the
weight, but will he a curve, sinking very rapidly at first, hut
afterwards more and more slowly, and so continually tending
to run parallel to the ahscissa line ; in fact, it will he an hyper-
bola.

Obs. III. Neither of the ahove set of observations is quite
correct : to eliminate the effects of exhaustion, the observations
should he repeated on the muscle within the body (see Chap.
XIX., sec. XL), and time allowed between each observation
for the muscle completely to recover itself.

Obs. IV. Kill the muscle (either the same or a fresh one) by
immersing it in water at 40° C. for five minutes.

Repeat Obs. I. and II. on the muscle so killed. It will be
found that there is far less extension of the muscle, which, after
the load has been removed, does not return to its original
length.

The dead muscle, as compared with the living one, is more
elastic, i. e., is less extensible ; but its elasticity is very imper-
fect, i. e., the original length is not regained.

II. Reaction. — Obs. V. Having pithed a frog, place a ca-
nula in the aorta, slit open the right auricle, and drive all the
blood out by injecting the normal saline solution, which should
be perfectly neutral. Dissect out the gastrocnemius of one
side with clean instruments, and with a very clean knife cut it
across through the middle of its belly. Take two slips of lit-
mus paper, one faintly red, the other faintly blue ; press the
cut end of one-half of the muscle on one piece, and the other on
the other. On the red litmus paper will be left a distinct blue
mark where the muscle was pressed ; on the blue litmus paper
there will be no mark at all, or, if any, a change in the direc-
tion of red, which is distinctly less red than the blue mark on
the red litmus is blue.

The reaction of living muscle, freed as much as possible from
blood, is faintly alkaline.

Obs. VI. Kill the corresponding muscle in the other leg by
immersion in water at 40° C. Test as in 06s. V. The blue
litmus paper will be marked most distinctly red ; the red not
altered. For this a much stronger blue paper may he used.
The reaction is permanent, and therefore is not due to carbonic
acid.

Muscle, in dying, on entering into rigor mortis, becomes dis-
tinctly acid.

Obs. VII. Keep any of the above rigid muscles covered in a
damp warm place. Test the reaction from time to time. The
acid reaction gives way to an alkaline one, which increases
rapidly in intensity, and soon far exceeds the natural alkaline
reaction. This secondary alkalinity arises from decomposi-
tion.

BY DR. MICHAEL FOSTER. 363

At the same time the muscle will be found to have become
very extensible, with scarcely any elasticity.

06s. VIII. Divide a fresh muscle in two. Immerse for a
few minutes one half (A) in water at 40° C. ; the other (B) in
boiling water. Test the reaction of both.

A will be acid, from development of rigor mortis.

B will be alkaline. Before rigor mortis had time to set in,
the albumin of the muscle was coagulated. This coagulation
set free a quantity of alkali (see Chap. XXXV.) ; hence its re-
action.

III. Transparency. — Obs. IX. Take from a frog a portion
of any one of its thin flat muscles. The mylohyoid is the most
convenient, but the sartorius (fig. 278 s.), or any other thin
muscle, will do as well. The muscle must be perfectly fresh
and irritable, and care must be taken that at least the middle
portion of muscle is not in the least injured. Place the muscle
in normal saline solution, or serum, on the unheated " warm
stage," and examine with a quarter-inch object-glass.

Focus down through the middle (least injured) portion of
the muscle, upon some object (bloodvessel, etc.) underneath
the fibres. The distinctness with which this object is seen will
be a measure of the transparency of the muscular tissue.

Keeping the eye fixed upon the above-mentioned object, heat
the stage. It will be found that when the temperature of the
muscle has risen to 40° C. (or a little below), the object is no
longer so distinct as before, or has even become totally invisi-
ble.

On entering into rigor mortis, the muscular fibre becomes
opaque.

Living muscle is very extensible, with perfect elasticity, of
alkaline reaction, and considerable transparency. On enter-
ing into rigor mortis it loses its extensibility, its elastieitjr
becomes imperfect, its reaction acid, and its transparency
gives place to opacity.

864 STIMULATION OF NERVE AND MUSCLE.

CHAPTER XXI.

PRELIMINARY OBSERVATIONS ON THE STIMULATION
OF NERVE AND MUSCLE.

I. Electrical Stimulation. — Obs. I. Get reacty a nerve-
muscle preparation and place the nerve on a pair of common
electrodes ; or simply lay bare the sciatic nerve, slip the elec-
trodes underneath, and watch the leg for any movements indi-
cating muscular contractions. Connect the electrodes with a
battery of one, two, or three cells, a key intervening. Open
the key, and after a few seconds shut it again ; this is equiva-
lent to making and then breaking a current in the nerve. It
will be found that either at the breaking or at the making, or
at both making and breaking of the current, a single muscular
contraction is produced ; but that during the passage of the
current (provided the intensity be uniform) there is no con-
traction at all.

Obs. II. Instead of a constant current, employ a single
induction shock. Each application of a single induction
shock (if strong enough), whether it be an opening shock or a
closing shock, will produce a single muscular contraction.

Obs. III. Instead of a single induction shock, employ a
series of shocks rapidly following each other. These produce
a continued contraction, a tetanus, which lasts during the
whole time of the application of the currents, or until the
muscle is completely exhausted. For this purpose use the
apparatus of Du Bois Reymond.

Obs. IV. Lay bare the gastrocnemius or any other muscle,
apply the electrodes directly to the muscle instead of to the
nerve, and repeat the above observations. The results will be
the same.

II. Mechanical Stimulation. — Obs. V. Pinch the nerve
sharply with a pair of forceps, prick the muscle with a needle ;
in either case a contraction will take place.

III. Thermal Stimulation.— Obs. VI. Touch lightly
either nerve or muscle with a hot needle ; a contraction will
follow.

IV. Chemical Stimulation. — Obs. VII. Dip the end of
the nerve into a strong solution of common salt ; after a little
while a series of contractions running into tetanus will be ob-
served in the muscles supplied by the nerve.

Obs. VIII. Kill the muscle and nerve by immersion for a
few minutes in water at 40°. The above stimuli applied to
either muscle or nerve will produce no contraction.

BY DR. MICHAEL FOSTER. 365

CHAPTER XXII.
PHENOMENA AND LAWS OP MUSCULAR CONTRACTION.

I. The Muscle Curve.' — In order to study the muscle
curve, the recording surface must travel with sufficient
rapidity. (The chief features of the curve may be seen when
Secretan's cylinder with Foucault's regulator revolves on the
second axis.)

Obs. I. Arrange a muscle preparation in the moist chamber.
The electrodes should be placed at some little distance from
each other on the muscle itself; the nerve consequently need
not be prepared. Load with 10 or 15 grms. Underneath the
point of the lever bring the recording tuning-fork to bear on
the cylinder.

Arrange for a single opening induction shock, but instead
of the ke}' b (Chap. XIX., sec. XIII.), insert the marking kej',
simply introducing it into one wire from the batteiy, so that
when the lever is down the current passes, but when it is
raised (and the point depressed) the current is broken (Chap.
XIX., sec. X.). The point of the marking key must be
brought close under the recording point of the lever but
above the recording point of the tuning-fork. Place all three
recording points very carefully in the same vertical line.

The marking key being closed, and the tuning-fork vibrat-
ing, open the key a, and remove the break from the governor
of the clock-work , when the cylinder is approaching the end
of the first revolution, open the marking key, and as soon as
possible afterwards stop the cylinder.

On the cylinder there will now be seen three lines of mark-
ing (see fig. 279) ; a is the line of the marking key, and the
point where it descends indicates the moment at which the
current broke into the muscle ; b is the line of the tuning-fork,
and each complete curve denotes a certain fraction of a second
(determined by the pitch of the tuning-fork) ; c is the line of
the muscle-lever, m1 marks the moment of the beginning of
the contraction, m2 the curve's highest point, m? its termina-
tion. Draw a straight vertical line m through the point where
the line a descends, and similar vertical (parallel) lines m, m1,
ra2, m3, cutting a b and c.

m — m1 will give by measurement off b the duration of the
latent period m1 — m9, of the rise ; m2 — ms, of the fall ; and m1
— m', of the total contraction.

306 LAWS OF MUSCULAR CONTRACTION.

The rapidity of Se"cretan's second axis is hardly sufficient
to bring out the latent period with sufficient distinctness; but
the other characters of the curve may be very well shown.

The third, swiftest, axis may be used, but there are diffi-
culties in managing it. Care must be taken to reduce the
friction of the various recording points to a minimum; and
the observation should not be taken till towards the end of
the second revolution. Before that, the cylinder is far from
reaching its maximum (uniform) speed ; after that, the over-
lapping curves of the tuning-fork are difficult to decipher.

Better results are obtained if the cylinder be used horizon-
tally (the natural position of the apparatus) instead of verti-
cally. The lever tuning-fork and marking key will of course
have to be arranged accordingly.

When the heavier mj'ographion lever is emplo3red, the effect
of the inertia of the lever will make itself manifest in a secon-
dary curve, at the end of the muscle curve.

(For more exact observations than are furnished by Fou-
cault's second axis, it is better to employ the pendulum myo-
graphion, see Wundt Mechanik der Xerveu, p. 6.)

A muscular contraction, even when produced by an instan-
taneous electric shock, takes a measurable time for its com-
plete development. The contraction does not begin at the
moment when the stimulus breaks into the muscle, but is pre-
ceded by a latent period. The contraction curve rises at first
very rapidly, but afterwards more slowly, and having reached
a maximum, declines at first slowly, afterwards more rapidly,
and lastly more slowly again.

The advanced student may determine by the same method
the variations in the character of the muscle curve, caused
by:-

1. Exhaustion. — Obs. II. Having determined with a single
induction shock the natural curve, exhaust the muscle b}r pro-
longed or repeated stimulation with the interrupted current,
and then repeat again with the same single induction shock as
before. The curve will be not only of less height, but will be
longer, i.e., the contraction will be slower, and the latent period
especially will be prolonged.

2. Heat and Cold. — Obs. III. The temperature of the
chamber may be raised or lowered by introducing a current
of moist hot air or pieces of ice into it.

It is more convenient, however, to use the frog in a hori-
zontal position, simply laying bare the gastrocnemius, and
dividing its tendon (see Chap. XIX., sec. XI.), and then
placing the muscle in a double trough, made by bending a
piece of leaden tube. Having determined the natural curve,
pass hot or ice-cold water through the tube, and determine the
curve at various temperatures.

BY DR. MICHAEL FOSTER. 367

At higher temperatures than the normal, the muscle curve
is much shortened ; at lower, lengthened.

3. Poisons : Veratrin, etc. — 06s. IV. Arrange the frog
as directed for observations on muscles in the living body
(Chap. XIX., sec. XI), and having determined the natural
muscle curve, inject a small quantity of veratrin (^V-sV mgrm.)
beneath the skin of the back, having previously divided the
sciatic nerve near the knee without injury to the bloodvessels.
Determine the curve at given intervals after the introduction
of the poison; the duration of the contraction will be enor-
mously prolonged.

II. The Contraction as a Function of the Stimulus.

Obs. V. Arrange the nerve muscle preparation in the moist
chamber ; place the nerve over a pair of electrodes. Load the
muscle with about 10 grammes. Arrange for a single induc-
tion shock, using in the same series of observations the same
either opening or closing shock. Draw an abscissa line on the
recording surface.

Slide the secondary coil as far away as the sliding board
will allow from the primary coil. Send a shock through the
nerve. If there is no contraction (and most probably there
will be none), move the secondary coil some centimetres nearer
the primary; repeat the shock. Advance in this way, gradu-
ally bringing the secondary coil nearer and nearer to the pri-
mary, until the first visible contraction is gained.

By sliding the secondary coil backwards and forwards,
accurately determine this "minimum stimulus" for the muscle
and nerve under the circumstances of the case.

Advance now steadily on, moving the secondary coil a
definite distance nearer the primary each time, and record
each contraction as an ordinate on the abscissa line, at dis-
tances proportionate to the distances the secondary coil is
moved, in a manner similar to Chap. XX., Obs. II.

The contractions will go on for a while increasing as the
strength of the current increases; but at last it will be found
that increasing the stimulus no longer increases the contrac-
tion, i. e., the ''maximum contraction" for the muscle and
nerve under the circumstances has been reached. Determine
accurately the relative positions of the two coils at which this
point is reached.

If with the battery employed to start with the maximum
contraction is not reached, increase the number of cells.

The student in making the above observations is nearly sure
to meet with very great irregularities, which will tend very
much to confuse the results. These may be partly due to
imperfections in the apparatus. He will therefore carefully
examine these, and see that everything is in order, and espe-
cially that the battery is working steadily.

3G8 LAWS OF MUSCULAR CONTRACTION.

But the variations will in most cases be due to the fact that
the nerve after stimulation, and the muscle after stimulation
and contraction, are for a variable period of time in a different
condition from what they were before. They are suffering
from more or less exhaustion, reaction, etc. To eliminate
these entirely is a task of considerable difficulty. They may
be more or less reduced by waiting a sufficiently long time
between each two trials, by working backwards from the
stronger shocks to the weaker, as well as from the weaker to
the stronger, etc. etc.

The student, however, will see sufficient to enable him to
state that the amount of contraction does increase with the
increase of the strength of the shock {increase of stimulus),
at first rapidly, then more and more slowly, and finally, when
the maximum is reached, ceasing to increase any more.

III. The Contraction as a Function of the Resist-
ance.

Obs. VI. Everything being arranged as in the last observa-
tion, place the secondary coil in such a position as to give a
shock about midway between the maximum and minimum
stimulus.

" First let there be no load to the muscle ; record the contrac-
tion as an ordinate on the abscissa line. Then load succes-
sively with 10, 30, 50, 100, etc. etc., grammes; recording the
several contractions at proportionate distances along the ab-
scissa line.

Repeat with a minimum stimulus and also with a maximum
stimulus.

With the same stimulus the amount of contraction decreases
as the load is increased ; but not regularly. At first, as the
load is increased from zero upwards by small increments, the
contraction increases; as the load continues to be increased,
the increment diminishes, and finally gives place to a decre-
ment. The initial increase of contraction is most prominent
when the stimulus lies within a certain range of intensity.

IV. The Work Done.

06s. VII. The dimensions of the lever being known, deter-
mine from the ordinates of contraction the actual shortening
of the muscle itself during each contraction. This multiplied
into the weight will give the ivork done in each case.

Draw an abscissa line and mark off from it distances propor-
tionate to the loads employed in Obs. VI. Draw as ordinates
the actual work done in the case of each load. A line drawn
through the summits of the ordinates will give the curve of
the icork done with the same stimulus and increasing loads.

With the same given stimulus and an increasing load, the
work done increases up to a maximum, and then declines.

BY DR. MICHAEL FOSTER. 369

The maximum is not the same with all intensities of stimulus.

There is a definite relation of load, muscle, and stimulus,
by which the greatest amount of work can be got out of a
given muscle.

CHAPTER XXIII.
THE WAVE OF MUSCULAR CONTRACTION.

Obs. I. Place a nerve-muscle preparation in a horizontal
position, so that the gastrocnemius rests on some flat surface
(e. g., a glass plate) over which it can glide freely ; clamp the
femur fragment tight ; b}r means of a pulley attach the tendon
to a lever, etc., with a load of 10 or 15 grammes. Bring over
the middle of the muscle the button of a light cardiograph
connected with a Marey's tambour (see p. 265, fig. 230). If
the button is large, attach to its under surface a conical piece
of cork or some other material, which can be brought into
contact with a small portion of the surface of the muscle.

Bring the recording point of the tambour lever to mark on
the cylinder, a little distance below the other lever.

Place the nerve on the electrodes of an induction coil.

While the cylinder (first or second axis) is revolving, and
the two levers are describing parallel lines, send induction
shocks of various strengths through the electrodes.

The direct lever will indicate the shortening of the muscle,
the tambour lever its thickening. It will be seen that they
both take place at about the same time, and that with the
various strengths of current the movement of one lever in-
creases or decreases with the other.

06s. II. Poison a frog completely with urari, so as to eli-
minate as much as possible the influence of nerves. Dissect
out carefully one of the large muscles of the thigh ; for in-
stance, the rectus interims major (fig. 278, r. i). Cut away
with it the piece of the pelvis, to which its origin is attached.
Leave as much of the tendon of insertion as possible.

Lay the muscle in a small trough (fig. 280) (one can easily
be made of gutta-percha), and place over it, as far apart as
possible, two levers. The levers must be so arranged that
their points write on the cylinder one below the other in ex-
actly the same vertical line. Fix the one end of the muscle
1)}' clamping the piece of pelvis, and attach by means of a
pulley a load of 5 or 10 grammes to the tendon.

Bring two pointed electrodes from an induction coil, to one
24

370 THE WAVE OF MUSCULAR CONTRACTION.

end of the muscle, so that they touch the muscular fibres close
to the end.

Bring the levers to trace on the cylinder rotating on its
swiftest axis. While the two points of the lever are describ-
ing two parallel lines on the cylinder, send a single induction
shock through the lever.

Each of the two levers will describe a curve, each curve in-
dicating the thickening of the muscle under the lever during
the contraction. But these curves will not be exactly one
under the other ; one, viz., that described by the lever nearer
the electrodes, will be a little earlier than the other. The dif-
ference in time between the commencement of the two curves
will be more marked in an exhausted muscle, or in a muscle
exposed to a low temperature, than in a fresh and very irri-
table muscle.

The contraction then does not take place in the vihole fibre
at the same time, but travels with a certain velocity from the
point at which the electrodes are placed along the fibre.

Obs. III. Repeat the observation ; placing the electrodes on
the muscle close to the tendon of insertion instead of close to
the origin.

The results are just the same; the wave of contraction
travels in either direction.

Obs. IV. Instead of resting the levers on the muscle as di-
rected above, the muscle may be placed on a piece of cork
with holes in it and two slips of thin foil looped round two
distant parts of the muscle, each slip being connected with a
lever below, as in fig. 281.

If the tuning-fork be brought to trace on the cjdinder be-
low the levers, the interval of time between the commence-
ments of the two contractions may be exactly determined,
and the distance between the two levers on the muscle bein«:
accurately measured, the velocity of the wave of contraction
mav be calculated.

BY DR. MICHAEL FOSTER. 371

CHAPTER XXIV.
TETANUS.

1. The Curve of Tetanus. — 06s. I. Having arranged
the nerve-muscle preparation, etc., in the moist chamber as
usual, draw first, if not read}7 at hand, the curve of a simple
muscular contraction, for comparison.

Then connect the electrodes with the induction machine
using the magnetic interruptor ; insert between the secondary
coil and the electrodes the marking key with double circuit;
raising the marking key will now allow an interrupted current
to fall into the nerve ; on pressing the key down the current
will be shut off.

All being arranged (the slow axis of Secretan's instrument
will give sufficient speed), allow an interrupted current of
very moderate intensity (i. e., the secondary coil hardly, if at
all, overlapping the primary with a weak battery) to break
into the nerve, and in a few seconds shut it off again.

A curve similar to that shown in fig. 282 will be obtained ;
where the plumb line m drawn through the first a marks the
commencement both of the stimulation and contraction (the
speed not being sufficient to show the latent period), and the
line m2 through the second a marks the end of the stimulation,
and m3 the end of the contraction.

It will be seen that the curve rises at first very rapidly,'
afterwards more slowly, and speedily reaches a maximum, which
it maintains during the whole time of the stimulation. Upon
the cessation of the stimulus at m2, the curve at once falls, at
first very rapidly, but afterwards more slowly, and in its later
phases very slowly.

If the stimulus is allowed to act upon the muscle for more
than a few seconds, the curve begins to decline, even while the
stimulus is still acting ; but, even after very prolonged stimu-
lation, the cessation of the stimulus is indicated by a sharp
fall in the curve.

Tetanus from an ordinary interrupted current is a continued
contraction rapidly reaching a maximum, continuing (within
limits) in that condition so long as the current is passing, and
followed by a gradual relaxation upon the current being cut
of.

1 In the figure the curve does not rise rapidly enough.

372 TETANUS.

Obs. II. Arrange for a single induction coil, hut replace the
key b by the oscillating interruptor (Chap. XIX., sec. XI 11.).
Use the first or the second axis of Secretan, and the needle of
the interruptor being clear of the mercury, open the key a,
and set the cylinder revolving. When uniformity of speed
has been reached, suddenly set the interruptor vibrating, and
after some ten vibrations or so have taken place, close the key a.

The tracing on the cylinder will be a curve of the character
shown in fig. 283.

In general features it resembles the curve, fig. 282. There
is the same rise, maximum, and fall ; but instead of being, as
in fig. 282, apparently a simple curve, it is evidently composed
of a series of curves. Each of these component curves cor-
responds to a contraction caused by a breaking or a making
of the primary current through the needle dipping into or
coming out of the mercury. It will be seen that the second
contraction began before the first was completed, and is, so to
speak, placed on the top of it; in the same way, the third
comes on the top of the second, and so on. The amount of
rise contributed by each subordinate curve to the total rise is
greatest in the first, and goes on diminishing until the maxi-
mum is reached.

By varying the length of the oscillating slip, a series of
curves may be obtained, showing the various steps between a
series of quite separate contractions, each being completed
before the next begins, and one in which (as in the tetanus
produced with the magnetic interruptor) the individual con-
tractions follow each other so rapidly, that no trace of their
separate existence is visible on the recording surface.

Tetanus really consists of a series of simple muscular con-
tractions fused together.

II. The Effects of Exhaustion.

Obs. III. Throw a muscle, with the electrodes applied to the
muscle itself, into tetanus, with a strong interrupted current.
Record the movement on the cylinder. Continue the current
for some minutes. The curve will gradually fall from the maxi-
mum down to very nearly the abscissa line ; but even after
very prolonged action, a sudden fall will mark the shutting off
the current.

Obs. IV. Send through a muscle a single induction shock of
a certain strength. Record the contraction. Then tetanize
the muscle by means of the interrupted current for ten or
twenty seconds. Apply again the same induction shock as
before. There will be either a much slighter contraction than
before, or none at all. After waiting some minutes, repeat the
shock again. The contraction will now be much nearer its
former dimensions.

BY DR. MICHAEL FOSTER. 373

By contraction, especially hy tetanus, irritability of a muscle
is diminished; after a period of rest, the irritability returns
even in a muscle removed from the blood current.

Obs. V. Repeat the observation on a muscle still connected
with the blood current. The return of irritability will be much
more rapid and complete.

With a Du Bois Reymond's induction apparatus, the transit
tion from a single induction shock to an interrupted current
may easily be effected thus : The apparatus being arranged for
an interrupted current, the key a being open, press the spring
of the magnetic interruptor up to the platinum point, and open
the key b. The current breaks into the primary coil, and a
single (making or closing) induction shock is the result. On
letting go the spring, an interrupted current is at once ob-
tained. This may be stopped at any moment by pressing
down the spring, and then a single shock is again obtained
b}1, letting it rise once against the platinum point, and keeping
it there.

III. Phenomena Attending Muscular Contraction.

These can only be satisfactorily determined by studying
tetanus. The changes in a single contraction are too slight
and transitory to be distinctly appreciated.

Obs. VI. During contraction there is no appreciable change
of bulk.

Take the whole leg, or, better still, both legs, of a frog, in-
cluding the attachment of the thigh muscles to the ilium and
coccyx, and remove the skin. Tie a thin platinum wire round
each end of the leg. Place the thigh in a bottle filled with
normal saline solution, insert a cork in the mouth, bring the
platinum wires through the cork, and in the centre of the cork
insert a narrow glass tube. Fill the tube up to a certain height
with the saline solution, make sure that no air bubble remains
below the cork or entangled in the leg, and that the cork is
tight. Place a scale behind the glass tube in order that the
level of the solution may be exactly determined, and bring the
platinum wires into connection with an induction coil arranged
for an interrupted current.

Tetanize the leg with a strong current ; even at the height
of the tetanus, no perceptible change of level in the fluid in the
tube will take place.

Obs. VII. During contraction the elasticity of the muscle is
diminished^ i.e., its extensibility is increased.

Load a muscle with 50 grammes, and record the amount of
extension. Kemove the load and tetanize the muscle. At the
height of tetanus, load the muscle again with the 50 grammes
and record the extension. This will be found to be much
larger in the second instance than the first. If tracings of the
extension be taken on a revolving cylinder, curves similar to

374 TETANUS.

those shown in Fig. 284 will be obtained. When the muscle is
at rest and unloaded, the recording point of the lever describes
the straight line o, x. The sudden application and speedy re-
moval of the load produces the curve ./', o, the muscle in this
instance failing to return to its original length. On being
tetanized, the muscle shortens from the level of x' a to the
level of o; and the application of the same load as before pro-
duces the long curve o' a'.

Obs. VIII. During contraction there is a diminution, a nega-
tive variation, of the natural muscle current.

This is shown by the galvanometer {see Chap. XXV.,
Sec. II.).

It may also be shown by using the variations in the mus-
cular current as a means of stimulating a nerve supplying
another muscle.

Get ready two nerve-muscle preparations as irritable and as
little injured as possible; one may be the whole of the under
leg, with the femur cut off close to knee, and as long a sciatic
nerve as possible (Fig. 285 a); the other should include the
muscles of the thigh as well, the skin being in both cases re-
moved (Fig. 285 b).

Place b on a glass plate, and let the extreme (central) end
of the nerve rest on a pair of electrodes connected with an in-
duction coil.

Lay the nerve of a over the muscles of the thigh of b, as in
the figure.

Send a single induction shock through b; there will be a
single contraction of the muscles of b, and almost at the same
time a single contraction of the muscles of A.

Send an interrupted current through the electrodes of b.
The muscles of b will be thrown into tetanus. So also will
those of a.

The single contraction of the muscles of b causes a single
variation in the natural currents of the muscles of b; this acts
as a single stimulus to the nerve of a, and so causes a single
contraction in the muscles of a.

When the muscles of b are thrown into tetanus, each con-
stituent contraction of which that tetanus is made up causes a
corresponding variation in the natural current, which therefore
during the tetanus is undergoing a succession of variations.
Each such variation acts as a stimulus to the nerve of A, and
accordingly the muscles of A are thrown into a tetanus, the
constituent contractions of which correspond exactly with
those of the muscles of b.

In the galvanometer we have no such series of variations in
the position of the needle; the negative variation during teta-
nus appears as a steady backward swing of the needle. This

BY DR. MICHAEL FOSTER. 375

is because the inertia of the needle prevents its responding
with sufficient rapidity to the variations in the current.

The proof that the negative variation of tetanus is thus
really made up of a succession of variations is supplied not by
the galvanometer, but by the above experiment with the frog's
muscle, or, as it is often called, the " rheoscojnc frog."

The above observation will frequently fail unless the nerves
are perfectly fresh and irritable.

06s. IX. Satisfactory results having been obtained, liga-
ture tightly in one case the nerve of b between the muscles
and the electrodes, and in another the nerve of a between its
muscles and the part of the nerve lying on the muscle of b.

In either case, the secondary contraction in a should be
entirely absent. If they are present, they are due to an escape
of the current; and the observation must be repeated on fresh
muscles and nerves, greater precautions being taken to pre-
vent the escape of the current.

Obs. X. During contraction, muscle becomes acid.

Prepare two muscles, either the gastrocnemius or rectus, or,
perhaps better still, take the whole of the thigh muscles.
Leave one, a, alone ; tetanize the other, b, repeatedly. Make
an incision through each and test their reaction.

A will be found to be neutral or alkaline ; b will be found to
be distinctly acid.

Obs. XL During contraction, the temperature of the vius-
cle rises.

Prepare a whole leg with sciatic nerve ; choose a large,
health}', strong frog. From the thigh resect the femur in its
middle for the greater part of its length, injuring the nerve
and muscles as little as possible.

In place of the removed femur, place the bulb of a thermo-
meter reading one-tenth of a degree centrigrade at least ; wrap
the muscles carefully round the bulb ; surround the thigh with
cotton-wool, and wait till the level of the mercury is constant.
The thermometer should be fixed very firmly and steady. Now
send an interrupted current through the nerve. The muscles
will be thrown into tetanus, and the mercury in the thermo-
meter will rise.

(For determining more exactly the changes of temperature
in a muscle during contraction, it is better to use thermopile
needles with a galvanometer of little resistance (see Chap.
XVIII., p. 344) ; or for still finer observations, in which it is
desirable to avoid the effects of friction, the swinging appa-
ratus of Heidenhain may be employed. (See Heidenhain-
Mechan. Leistung, Wcirmeentivickelung, etc., bei der Muskel-
thdliglceil.)

376 ELECTRIC CURRENTS OF MUSCLES.

CHAPTER XXY.
ELECTRIC CURRENTS OF MUSCLES.

I. The Natural Currents. — Obs. I. Place the galvanome-
ter A and scale b east and west (with lamp lighted) about three
feet apart, level the galvanometer with the levelling screws c,
carefully set the mirror free if needful by gently raising the
milled head seen on the top of the galvanometer when the
glass cover is removed,1 and adjust the height of the lamp
by pulling in and out its brass neck, or moving it from side to
side until the light falls well on the mirror.

The most convenient galvanometer for the purpose is Sir
William Thomson's. The one represented in the figure (fig.
286) is a differential one, but should be used as a single one
in the following observations by connecting the two central
binding screws a a with a piece of wire.

Having put on the glass cover, screw the adjusting magnet
d with its upright e on to the top of the galvanometer. Let
the magnet, with its north pole directed towards the magnetic
north, be at first at the top of the upright ; gradually bring it
down, moving it from side to side, and carefully watching the
spot of light as it travels to and fro on the scale. Before the
magnet lias descended very far, the student will have so far
gained command over the mirror, as, by moving the magnet
to a certain position right or left, to be able to bring the spot
of light nearly to zero.

This done, shift the scale away from or towards the galva-
nometer, until the image of the slit/ through which the lamp
shines is well focussed on the scale. (If not provided on the
scale, affix an upright wire in the middle of the slit ; have the
slit wide, and use the shadow of the wire seen in the broad
spot of light, to determine the position of the mirror.)

Now bring the magnet very gradually still lower down.
keeping the spot of light as near as possible to zero, and
watching attentively the rapidity with which the spot oscil-
lates on either side of that point. It will be found that as the
magnet descends the oscillations become slower and slower.
This indicates that the influence of the earth's magnetism is
becoming more and more neutralized by the magnetism of the

1 If possible, the galvanometer should be carefully levelled and set
once for all, and kept so in some place where it need not be disturbed.

BY DR. MICHAEL FOSTER. 377

adjusting magnet. On continuing to lower the magnet, the
point of neutralization is soon passed, and then the influence
of the adjusting magnet on the needle becomes stronger than
that of the earth. The needle, consequently, which previously
had its north pole under the north pole of the magnet, would,
if free to turn, swing half round in the attempt to bring its
south pole under the north pole of the magnet ; and indeed
does swing round as far as the arrangements of the apparatus
will allow, the spot of light rapidly travelling quite beyond
the limits of the scale. When this had been found to occur,
the magnet must be raised again up to or rather above the
point of neutralization. The oscillations of the needle will
now be at their minimum of rapidity, and the needle will be
at its maximum of sensitiveness. Bring the spot of light ex-
actly to zero. The magnet may be at first moved with the
hand, but this will be found to be too coarse a method. Finer
adjustment is gained by turning the milled head/*.

The wires convej'ing the current through the galvanometer
are to be attached to the outer binding screws b b.

To determine which direction of current is indicated by the
movement of the spot of light, try the effect of a very feeble
cell upon the galvanometer. But be' careful not to use the
whole of the current proceeding from the cell; cut off the
greater part of it by means of the shunt. (Fig. 287.)

Bring the wires from the cell to the binding screws of the
shunt. With the plug placed in the hole between the binding
screws, there is no resistance offered by the shunt. The whole
current consequently flows through the shunt, none going
through the circuit of the galvanoraetei\ The shunt may thus
be used as a key, and it will not be necessary to have another
key between the galvanometer and the electrodes. If a plug
be inserted in the hole marked 1-0, and the plug between the
binding screws be withdrawn, such resistance is offered by the
.shunt, that one-tenth of the total current of cell goes through
the galvanometer. Similarly with the plug in the hole marked
1-99, instead of in the hole marked 1-9, 1-1 00th goes through
the galvanometer; so also with 1-909.

By means of the shunt send 1-lOOOth of the current from a
cell through the galvanometer, and mark the direction in
which the light travels. Note which screw of the galvanome-
ter is connected with the kathode, and which with the anode,
and the relation of the direction of travel of the spot of light,
to that of the current is known. Most probably it will be
found that the light travels in the same way as the current.

Obg. II. Prepare two non-polarizablc electrodes with trun-
cated ends, or with the plug projecting; connect them with
the shunt, using it as a key.

The plug being in the shunt and the spot of light at zero,

378 ELECTRIC CURRENTS OF MUSCLES.

place the two electrodes so that the plugs touch each other,
or place a morsel of thread or paper, moistened with normal
saline solution, over the two plugs, and open the key. The
needle should remain at zero. If any deviation occurs, it is
an indication of a current in the electrodes themselves. If
the deviation is slight and constant, its direction and amount
in degrees must be noted, and all subsequent observations
corrected by it. This may be done by shifting the scale a
little, so as to bring the spot of light to zero, or by bringing
the spot of light to zero by means of the adjusting magnet. If
it be large, a fresh pair of electrodes must be prepared, which
shall give no such deviation.

06s. III. The muscle may now be prepared. Take one of
the large muscles of the thigh, e. g., the triceps (fig. 2G7 a);
with a sharp clean knife or scissors cut the tendon of inser-
tion clear away with a transverse cut; similarly make a
transverse cut at the origin. Place the muscle thus prepared
on a glass plate with the electrodes under a moist chamber.
The muscle will have a natural longitudinal surface and two
artificial transverse surfaces. Place one electrode on the
longitudinal surface at a point as near as possible midway
between the two ends, and the other as near as possible in the
centre of one of the transverse sections. Connect the elec-
trodes with the binding screws of the shunt, the plug of the
shunt being in place between the screws. Remove the plug.
A deviation of the needle will take place. Most probably the
spot of light will swing right out of sight beyond the limit of
the scale. If this is so, replace the plug; when the needle has
returned to zero, shunt by means of the second plug ; for
instance, put the second plug in the hole marked 1-99 and
thus allow only 1-lOOth of the muscle current to pass through
the galvanometer, and then remove the first plug. The deflec-
tion will be far less. Note its direction and amount (number
of degrees of scale).

A current will be found passing through the galvanometer
from the mid-point of the longitudinal surface to the central
point of the transverse section. Replace the plug, so as to
shut off all the current from the galvanometer.

Ob*. IV. Keeping the one electrode still on the transverse
section, shift the other electrode from the mid-longitudinal
point to some point nearer that transverse section ; remove
the plug. The deflection of the needle will indicate a current
in the same direction as before, but of less strength. Replace
the plug.

Obs. V. Place the electrodes in the following positions,
always replacing the plug (serving as key) between the binding
screws of the shunt after each observation, and always being

BY DR. MICHAEL FOSTER. 379

careful that the amount of contact between the electrodes and
muscle is as nearly as possible the same in all cases: —

One electrode on the mid-longitudinal point, the other at
the other transverse section. The current will he, as before,
from the longitudinal surface to the transverse section.

Obs. VI. One electrode on or near the mid-longitudinal
surface, the other at a point nearer either transverse section.
The current will be slight, and its direction will be from the
point on or near the mid-longitudinal point to the one farther
off.

06s. VII. The two electrodes on the longitudinal surface
on either side at unequal distances from the middle point or
equator. The current will be slight, and from the point nearer
the middle to the point farther off.

Obs. VIII. The two electrodes on the longitudinal surface
at equal distances from the middle point on either side ; there
will be little or no current at all.

Obs. IX. By using very pointed electrodes, evidence of a
current may be obtained on the transverse section from the
electrode farther from the centre to that nearer to the centre.

Obs. X. The student may repeat these observations on a
muscle to which an artificial longitudinal surface has been
given by a clean section, and also on a muscle, the tendons of
origin and insertion of which have been divided without injury
to the muscular fibres, i. e., on a muscle with natural trans-
verse surfaces as well as a natural longitudinal surface.

In all cases the following result will come out more or less
clearly: —

In any muscle, or piece of muscle, with natural or artificial
longitudinal and transverse surf aces, evidence may be obtained
of a current passing through the electrodes from the middle of
the longitudinal surface {from the equator) to the centre of
either transverse section, and from any point nearer the equa-
tor to any point nearer the centre of either transverse section ;
the current is stronger the farther apart these two points lie
(see fig. 288, where the direction of the currents obtainable
from a piece of muscle of rectangular form is indicated by the
arrows, and the intensity by the sweep of the curves. The
points a a, equidistant from the equator, give no current).

Obn. XI. Immerse the muscle, on which you have been
experimenting, in water at 40°, in order to kill it. As soon
as it is cool, repeat the above observations. No currents at
all, or very trifling ones, will be obtained, if the muscle be
perfectly and completely "rigid."

The currents obtainable from a living muscle disappear
when rigor mortis is complete.

In all eases examine the electrodes by themselves, after any
scries of observations, as well as before, in order to be sure

380 ELECTRIC CURRENTS OF MUSCLES.

that no changes have taken place in them during the observa-
tions, such as would give rise to a current.

II. Negative Variation. — Obs. XII. Get ready a nerve-
muscle preparation, and make a transverse section through the
lower end of the muscle. Lay the muscle on a glass plate ;
connect the equator and transverse section of the muscle by
non-polarizable electrodes with the shunt and so with the gal-
vanometer ; lay the end of the nerve (as far away from the
muscle as possible) on another pair of electrodes. Connect
this second pair, or "exciting electrodes," as the}' may he
called, with an induction coil arranged for an interrupted cur-
rent. Let the induction coil be as far as possible away from
the galvanometer, and before commencing the observation
ascertain that the setting the induction machine in action does
not affect the needle.

The spot of light being at zero, remove the plug of the shunt,
and when the spot has come to rest (using a shunt if the cur-
rent is too great for the scale), send a moderately strong inter-
rupted current through the exciting electrodes. The muscle
will become tetanized; at the same time the spot of light .will
travel back a certain distance toward zero, i. e., the current
obtainable from the muscle at rest is diminished, or suffers a
negative variation during tetanus. Shut off the tetanizing cur-
rent; the needle returns towards its former position. If the
muscle be laid flat on the glass plate, considerable tetanus may
be called forth without the electrodes at all shifting their posi-
tion in relation to the muscle, especially if they be pressed
somewhat firmly on to the muscle to start with.

Obs. XIII. Having determined the negative variation as
above, tie a piece of wet silk or thread tightly round the nerve
between the muscle and the exciting electrodes, being very
careful to disturb nothing else. Now send the same inter-
rupted current as before through the exciting electrodes.
There will be no tetanus and no negative variation. The liga-
ture, having destroyed the vital continuit}' of the nerve, lias
prevented the passage of nervous impulses along the nerve to
the muscle.

Should any influence on the galvanometer be observable, it
is an indication that an escape of current from the exciting
electrodes to the galvanometer electrodes has taken place.
The ligature of the nerve does not destroy the electrical con-
tinuity of the nerve, though it does its vital continuity.

The exciting electrodes must be removed further from the
muscle, or a weaker current used, so as to prevent this escape
of current, and the observation then repeated.

BY DR. MICHAEL FOSTER. 381

CHAPTER XXVI.
ELECTRIC CURRENTS OF NERVES.

I. Natural Currents. — Obs. I. Bring the galvanometer
into as sensitive a condition as possible. The shunt will he
unnecessary in this case except to he used as a key. Prepare
as long a piece of nerve as possible with the least possible
injury. Hang the middle of the nerve over a bent non-polari-
zable electrode, and bring both ends to rest on the plug of
another electrode, as represented in fig. 289. In this way,
one electrode will be in contact with the equator, and the other
with both transverse sections. The current from the equator
to each transverse section being the same in direction, the re-
sult of this arrangement will be to double the effect on the
needle.

The current in the nerve, far feebler than that in muscle, is
as in the muscle from the equator (or mid-longitudinal point)
to the. transverse section.

Obs. II. By doubling a long piece of nerve and laying
different points on the electrodes, it may be determined that
the arrangements of the currents are the same in one case
as in the other. Naturally, the various points in the minute
transverse section cannot be examined.

II. Negative Variation in Nerve. — Obs. III. Prepare
as long a piece of nerve as possible ; lay the transverse section
of the central. end and a point in the longitudinal surface at
some little distance from that end on the pair of galvanometer
electrodes. Lay any two points at the other end (peripheral)
of the nerve on a pair of exciting electrodes connected with an
interrupted current.

Determine the amount of deflection given by the natural
current. Send an interrupted current through the exciting
pair. There should be a slight but distinct diminution, a slight
negative variation, of the current. When a nerve is excited,
the natural current suffers a negative variation.

Obs. IV. Repeat the observation, placing the peripheral end
of the nerve on the galvanometer electrodes, and the central on
the exciting electrodes.

There will be, as before, a diminution, a negative variation
of the current.

382 ELECTROTONUS.

The negative variation travels along the nerve in either di-
rection.

Obs. V. Ascertain as before, by ligature, that the effects
witnessed are not due to any escape of current.

CHAPTER XXVII.
ELECTROTONUS.

Obs. I. Prepare as long a piece of nerve as possible. Get
ready two pair of non-polarizable electrodes. Place the thicker
(central) end of the nerve, on one pair of electrodes, a a' fig.
290. This figure is intended to represent diagrammatic-ally
the effects of a polarizing current, p p\ acting on the centre
of a piece of nerve, as seen by testing either end with a gal-
vanometei*. It will serve, however, to illustrate the simpler
case of Obs. I., if the electrodes bb' he. supposed to be removed
and p p' brought nearer to that end of the nerve. Let one
electrode be on the transverse section of the nerve, and the
other on the longitudinal surface at some distance, so as to
obtain a tolerably good current. Connect this pair of elec-
trodes with the galvanometer, putting in a key or using the
shunt.

Place the other end of the nerve on the other pair of elec-
trodes, p p' ; connect these electrodes with a cell, which may
be called the polarizing cell, interposing a commutator (Chap.
XIX., sec. VII.). Cover the nerve with a shade, or put it with
the electrodes in the nerve chamber (Chap. XIX., sec. IV.), to
protect it against evaporation.

Both keys being down, and the needle of the galvanometer
being at zero, open the key of a a', and note the deflection of
the needle. The current will of course pass through the gal-
vanometer in the direction of the arrow in the figure from a to
«', and the circuit may be supposed to be completed by the
current passing inside the nerve in the direction of the arrow.
Shut the key of a a'.

Obs. II. Now open the commutator of the polarizing cell in
such a way that the current of the cell passes from p to ;/, in
the direction of the arrows in the figure, i.e., flows in the same
direction as the natural nerve current flows through the gal-
vanometer. Open the key of a a'. Note again the deflection
of the needle; it will be found to be greater than it was before.

Shut the key of a a' and shut off the polarizing current.

BY DR. MICHAEL FOSTER. 383

Then reopen a a'. The needle will be found to return to the
position it had in Obs. I.

Obs. III. Repeat the observation, but reverse the polarizing
current; let it flow from p' to p, that is, in a direction con-
traiy to the natural nerve-curreut. The needle of the galvano-
meter will now be found to have suffered a diminution of de-
flection instead of an increase.

" When a constant current is allowed to break into a nerve,
the natural nerve current., even at some distance from the
electrodes, is affected during the whole time of the passage of
the constant {jiolaTiziag) current; when the natural and
polarizing currents have the same direction, the natural cur-
rent is increased ; when contrary directions, the natural cur-
rent is diminished.'''1

This condition of the nerve, maintained during the whole
passage of the current, is known as electrotonus.

Obs. IY. Tie the nerve very tightly with a ligature between
the polarizing and the galvanometer electrodes ; or divide it,
and place the ends carefully in exact opposition, and repeat
the observations. It will be found that the natural current is
in no way affected by the polarizing current.

The phenomena, therefore, are not due to any escape of the
battery current : something more than mere physical continu-
ity is required for their development.

Obs. Y. Repeat the observations, placing the thinner (peri-
pheral) end of the nerve on the galvanometer electrodes, and
the thicker on the polarizing electrodes.

The results are the same ; electrotonus is established equally
well in either direction.

Obs. YI. The same result may be better shown in the fol-
lowing way: Take three pair of electrodes. Place the polar-
izing pair p p' , fig. 290, in the middle of the nerve, and connect
the other two pair with the two cut ends, as shown in the figure.
Bring the wires from a a' to a key, and those from b b' to
another key ; then the wires from both keys to the same bind-
ing screws of the galvanometer. By opening the key of a a'
while that of b b' is shut, or vice versa, the amount of natural
current in a a' or b b' may be respectively determined. (Or
use the double key, as directed in Chap. XIX., sec. IX.).
Determine both before the key of p p' is opened. Then open
the key of p p' and determine the amount of deflection both in
a a' and b b'.

It will be found that when the current passes from p to p'
in the direction of the arrow, as in the figure, the current at
l> !>' is diminished (in the neighborhood of the kathode), while
that at a a' is increased (in the neighborhood of the anode).
If the direction of the polarizing current be reversed, if it be

384 ELECTROTONUS.

made to flow from p' to p, then a a' will be diminished and b b'
increased.

Ob*. VII. Repeat the observation, placing the galvanometer
electrodes, not at the cut ends as before, but on any two
points from which a natural current can be obtained. Similar
results will be observed.

With most dispositions of the electrodes the natural current
is increased in the neighborhood of the positive and diminished
in that of the negative pole. The region of the negative pole
is said to be thrown into katelectrotonus, that of the positive
into anelectrotonus.

Obs. VJII. Having determined the amount of diminution of
b b' and the amount of increase of a a' when the polarizing
electrode is exactly in the middle line between the other two
pair, shift the polarizing electrodes nearer to b b'. Be very
careful that the electrodes in their new position are exactly the
same distance from each other as before, and that the nerve
touches the plugs of the electrodes exactly as before, so that
the only difference established is that a different part of the
nerve is placed between the electrodes. Be careful also not to
disturb the position of the nerves on the two pair of galvano-
meter electrodes. If all has been done properly before the
polarizing current is allowed to break into the nerve, the
amount of deflection at a a' and b b' should be the same as
when the polarizing electrodes were in the middle. Now open
the key of the polarizing current and determine the deflection
at a a' and b b'. The diminution of deflection at b b' should
be greater, and the increase at a a' less, than when the polar-
izing electrodes were in the middle. Reverse the direction of
the polarizing current. The increase at b b' will be greater,
the decrease at a a' less, than when the electrodes were in the
middle.

Obs. IX. Shift the electrodes (carefully as before) towards
a a/ instead of towards b &', and repeat as in Obs. VIII. It
will be found, as before, that the nearer the galvanometer
electrodes are to the polarizing electrodes, the greater the effect
either in way of decrease or increase, as the case may be, of
the natural current.

The amount of electrotonic increase or decrease is greater
the nearer the points tested lie to the polarizing electrodes.

Obs. X. Having determined the amount of electrotonus es-
tablished by the passage of a current from a single cell, use
two cells (keeping everything just the same), and compare the
results ; then three cells ; then four.

The amount of electrotonic increase or decrease of the
natural current increases with an increasing intensity of the
polarizing current.

Obs. XI. Determine the electrotonic increase and decrease

BY DR. MICHAEL FOSTER. 385

■with a given current on a perfectly fresh nerve from a strong
frog. Allow the nerve to remain for some time exposed in the
moist chamber, and repeat the observation. The electrotonic
effects will be found to be less.

The amount of electrotonic variation is dependent on the
vital conditions of the nerve.

CHAPTER XXVIII.
STIMULATION OF NERVES.

Other things being constant, we ma}' now take variations
in the contraction of the muscle of a nerve-muscle preparation
as a measure of variations in the condition of the nerve. A
muscular contraction is a token of a nervous impulse passing
along the nerve, the extent and character of the one being a
measure of the extent and character of the other: a tetanus in
the muscle indicates a series of impulses in the nerves, follow-
ing each other with not less than a certain velocit}'.

1. The Effects of the Constant Current.— Obs. I. Ar-
range a nerve-muscle preparation in the moist chamber, with
the nerve on non-polarizable electrodes, the muscle loaded
with 10 or 15 grammes, lever attached, recording surface pre-
pared, etc.

Have a battery of two or more cells, and between the battery
and the electrodes introduce the rheochord (Chap. XIX., sec.
VIII.). Let all the plugs be in, and the travelling mercury
cups close up.

The resistance now offered by the rheochord, compared with
that offered by the electrodes, is practically nil ; consequently
none of the current from the battery will pass through the
latter; there will, therefore, be no contraction in the muscle.

Remove one of the plugs, viz., that one the removal of which
tli rows the least resistance into the rheochord. A certain
fraction of the current will now pass through the electrodes on
account of the resistance thrown into the current through the
rheochord by the removal of the plug. If a contraction be
the result, let it be recorded ; if none, let that fact be recorded
too, noting on the recording surface the plug removed. Re-
move the plugs one by one, recording the result each time.
Replace the plugs one by one, also noting the results.

It will be found that a contraction of the muscle takes
place, a nervous impulse is originated, only at the moment
when the plug is withdrawn or replaced. It may be present
25

386 STIMULATION OF NERVES.

at both withdrawal or reinsertion, or at either, or at neither;
but no contraction occurs in the interval during which the
plug or plugs remain away from the board or in their place,
provided that the current in the battery be constant and the
condition of the nerve-muscle normal.

A nervous impulse is generated in a nerve only when there is
a sudden change in the intensity of a constant current passim/
through it {including the changes from and to zero, i. e., the total
breaking and making of the current). So long as the current
remains uniform in intensity, there is no contraction of the
muscle, no uervous impulse generated in the nerve.

The contractions so obtained are simple contractions, indica-
tive of the advent of a single nervous impulse. Very often,
especially in working with winter frogs in early spring, the con-
tractions thus obtained by variations in the intensity of a con-
stant current are not simple, but tetanic. This is an abnormal
result, which has not yet been investigated.

The contractions obtained above are not only variable, inas-
much as they come either at a diminution (breaking) or increase
(making) of the current, or at both, but also differ in extent,
i. e., the nervous impulses differ in intensit}r.

These variations depend on the strength of the current
(amount of variation of the current), the direction of the cur-
rent, and the condition of the nerve.

II. Law of Contraction. — Obs. II. Arrange in the moist
chamber a nerve-muscle preparation as fresh and lively as pos-
sible. Place the nerve on a pair of non-polarizable electrodes,
about a centimetre apart. Insert between the electrodes and
a battery of two or more cells, first the commutator, and
then the rheochord. Let the positive and negative wires have
different colors, the same throughout the whole apparatus in
each case, and arrange so that when the handle of the commu-
tator is raised, the current is ascending in the nerve ; when
depressed, descending.

The handle of the commutator being horizontal, and the plugs*
of the rheochord all in, withdraw the mercury cups a few de-
grees of the scale, and depress the handle of the commutator.
If there be any contraction, record it. This is equivalent to
the making in the nerve of an extreme^ feeble descending cur-
rent. Then bring the handle of the commutator horizontal,
and so break this feeble current, recording any result.

After waiting a few minutes, repeat the observation, using
an ascending current instead of a descending. Thus will be
obtained the effects of breaking and making an extremely feeble
constant current both ascending and descending.

Then shift the mercury cups several degrees, and repeat the
whole observation. This will give the effects of making and

BY DR. MICHAEL FOSTER. 387

breaking a still feeble but yet rather stronger descending and
ascending current.

Proceed in this way, shifting the mercury cups by stages,
until the}7, are brought to the other end of the board ; then
remove the plugs one by one, the removal of each plug mark-
ing a corresponding augmentation of the strength of the current
sent through the electrodes on the nerves.

Wait some minutes between each observation to allow the
nerve to recover itself. Tabulate the results. They should be
such that, throwing the various intensities of current into four
categories, they illustrate the following law: —

Descending.
Make. Break.

Ascending
Make. Break.

Weakest

Yes

No

No No

Weak

Yes

No

Yes No

Moderate

Yes

Yes

Yes Yes

Strong

Yes

No

No Yes

where " Yes" means a contraction ; " No," none.

The making of the descending current is the first to make
itself manifest by its effects, and maintains its pre-eminence
throughout the series as the most certain and strongest
stimulus.

Next, the making of the ascending current also becomes effi-
cient; then the breaking of the descending ; lastly, the break-
ing of the ascending ; so that with a certain intensity of current
which we here call " moderate," a contraction is called forth
both by making and breaking both ascending and descending
currents.

With a further increase of intensity, the contraction which
follows upon the making of the ascending current gets less,
and finally disappears altogether. The contraction due to
breaking the descending current suffers subsequently the same
fate, so that wijh a " strong" current we have only a single
contraction with each current; but it is a contraction on mak-
ing in the case of the descending, on breaking in case of the
ascending.

We have seen that when a constant current is sent into a
nerve, katelectrotonus is established at the negative pole, ane-
lectrotonus at the positive. Both conditions remain during the
whole time of the passage, and both disappear (with more or
less rebound) when the current is broken.

It is evident from the above observations that the rise of a
nervous impulse is connected with the transition of a nerve from
its ordinary condition into that of either katelectrotonus or
anelectrotonus, or both, or with its return from katelectrotonus
or anelectrotonus into its normal condition, and not witli its
being or remaining in either katelectrotonus or anelectrotonus.

388 STIMULATION OF NERVES.

Further, it is evident from the different results of breaking
and making, that the entrance into katelectrotonus and ane-
lectrotonus has not the same relation to the origin of a nervous
impulse as has the exit from those states.

Lastly, from the different behavior of the ascending and
descending currents, it appears that the effect of the entrance
into katelectrotonus is not the same as that of the entrance
into anelectrotonus, and that the effects of the exits from these
states likewise differ.

III. Electrotonus as affecting Irritability. — Arrange
a nerve-muscle preparation in the moist chamber, with lever,
etc. Prepare two pair of non-polarizable electrodes. Place the
end of the nerve on one pair, about 1 or 2 cm. apart ; connect
this, the polarizing pair, with a batteiy of one or two cells,
the commutator intervening. Place the second pair between
the first pair and the muscle, and connect this, the exciting
pair, with an induction coil.

When the polarizing current is made a descending one, the
portion of the nerve on which the exciting electrodes rest, will
be in the region of katelectrotonus ; when ascending, in anelec-
trotonus.

Obs. III. The polarizing current being shut off (the handle
of the commutator horizontal),- pass a single induction (open-
ing) shock through the " exciting" pair, and record the con-
traction. Shift the secondary coil, if necessary, until a con-
traction of moderate excursion is obtained, and note the dis-
tance of the secondary coil from the primary.

Now let the polarizing current ascend in the nerve (through
the polarizing pair of electrodes) ; the exciting pair will ac-
cordingly now be in the region of anelectrotonus.

Neglect the contraction which may be caused by the making
(and subsequent breaking) of the constant polarizing current ;
and while the current is thus passing in an ascending direc-
tion, send a single induction shock of the same strength as
before through the exciting pair, and record the contraction.

Shut off the polarizing current, and after a few minutes'
rest, send a third time the same induction shock through the
exciting pair.

Of the three contractions thus called forth by the same
stimulus (the induction shock) under different circumstances,
it will be found that the second is much smaller than the first,
but the third nearly of the same size (it may be larger) as the
first.

During the passage of a constant current, the irritability of
a nerve is lessened in the anelectrolonic region, the same stimu-
lus giving rise to a weaker nervous impulse, and so to a smaller
contraction.

Obs. IV. Shift the secondary coil until it reaches such a

BY DR. MICHAEL FOSTER. 889

position that the induction shock given becomes the mini-
mum stimulus required to produce a muscular contraction,
that is, any further removal of the secondary from the pri-
mary coil will lead to the absence of all contractions. This
minimum stimulus then giving, in the absence of the polarizing
current, a slight but obvious contraction, send an ascending
polarizing current through the nerve ; the contraction will be
wholly absent. Remove the polarizing current, and excite
again ; the contraction will again make its appearance.

Obs. V. Remove the secondary coil a little further away
from the primary, so that an induction shock gives no con-
traction where the polarizing current is cut off from the nerve.
Pass a descending current through the polarizing pair, i. e.,
throw the portion of nerve in which the exciting pair rest
into katelectrolonus. Again pass the same induction shock as
before : a contraction will follow.

Shut off the polarizing current, and after waiting a few
minutes, send the induction shook through the exciting pair a
third time. No contraction, or at best a very slight one, will
be obtained.

During the passage of a constant current, the irritability is
increased in the region of katelectrotonus.

Obs. VI. The other arrangements being the same, put the
magnetic interruptor into connection with the primary coil.
Record the movements of the lever on the revolving cylinder.

With a not very strong interrupted current, throw the mus-
cle into tetanus, and as soon as tetanus is established, send
an ascending current through the polarizing electrodes for a
few seconds only, and afterwards close the key of the inter-
rupted current.

The curve of the tetanus on the recording cylinder will ex-
hibit a marked fall (down even to zero if the polarizing current
be strong enough) at the moment when the polarizing current
breaks into the nerve, and a corresponding rise when the
polarizing current is shut off.

This is simply another way of showing the diminution of
irritability in an electro ton us.

Obs. VII. Repeat the observation, using a very weak teta-
nizing current, and let the polarizing current be descending.
The making of the polarizing current will be marked by a rise,
and the breaking by a corresponding fall in the tetanus curve,
indicating, as before, an increase of irritability in katelectro-
tonus.

Obs. VIII. Ligature the nerve between the two pair of elec-
trodes, and repeat all the observations. The polarizing current
will have no effect at all upon the results of the exciting cur-
rent. Otherwise, part of the effects described above will have

390 STIMULATION OF NERVES.

been due not to vital changes in the nerve, bat to escape of
current or simple electrical changes.

Obs. IX. Having arranged a nerve-muscle preparation with
the polarizing, but without the exciting pair of electrodes, let
the nerve between the electrodes and the muscle hang down
in a loop.

Let the extreme end of the loop dip into a drop of concen-
trated solution of common salt. As soon as the irregular
tetanic contractions resulting from the action of saline fluid
on the nerve make their appearance, pass an ascending current
through the electrodes. The tetanic spasms will be much less-
ened, or cease altogether.

Pass a descending current through the electrodes, the spasms
will be increased.

The general irritability, therefore, of the nerve is affected
in electrotonus, not simply its susceptibility to electrical modi-
fications.

Obs. X. By introducing a rheochord between the battery
and the polarizing electrodes, and by varying the number of
cells used, the student will ascertain that the amount of in-
crease of irritability in katelectrotonus and decrease in anelec-
trotonus depends on the strength of the polarizing current,
being greater with the stronger.

Obs. XI. B3' placing the polarizing electrodes at a variable
distance from each other, it will be found that, with the same
strength of current, the effect is greater the longer the piece of
nerve between the polarizing electrodes.

Obs. XII. By shifting the exciting electrodes nearer to and
farther from the polarizing electrodes, it will be found that
the effects of both anelectrotonus and katelectrotonus are
greatest in the immediate neighborhood of the polarizing
pair, and diminish the farther the exciting pair is from the
polarizing.

In all the above observations, the stimulus, whether electric
or chemical or other, is brought to bear on the nerve between
the polarizing pair and the muscle.

Obs. XIII. They may be repeated with the polarizing pair
placed between the exciting pair (or chemical stimulus) and
the muscle. An ascending current will now throw the region
of the exciting pair into katelectrotonus, a descending into
anelectrotonus.

The general results will be the same, but they will not come
out with the same distinctness, for the following reason:
When the exciting pair is placed nearer to the muscle than the
polarizing pair, the nerve between the exciting pair and the
muscle is simply in a state of katelectrotonus, the intensity of
which diminishes towards the muscle onwards. There is
nothing between the exciting electrodes and the muscle to

BY DR. MICHAEL FOSTER. 391

moilify the increase of impulse due to katelectrotonus. When
the exciting pair is on the other side of the polarizing pair,
and the region of the exciting pair thrown into katelectroto-
nus, for instance, the increased impulse due to katelectrotonus
after passing through the region of katelectrotonus has to
make its way through a region of anelectrotonus before it can
reach the muscle — it has to struggle in this region against an-
tagonistic influences, and whether it reaches the muscle as an
impulse greater than, or less than, or simply equal to, that
which occurs in a nerve not electrotonized, will depend on the
relative amounts of the katelectrotonic increase of irritability
and the anelectrotonic decrease of conductivity.

This will be found to depend largely on the intensity of the
polarizing current.

If the current be weak, the katelectrotonic increase over the
normal impulse (of the non-electrotonized nerve), though less-
ened by having to pass through an anelectrotonic region, will
be evident as a larger contraction in the muscle.

If the polarizing current be strong, the contraction caused
b}- the impulse originated in the katelectrotonic region will
not only not be greater than the normal but will even be less,
or may be absent altogether with a very strong (three or four
Grove cells) polarizing current, owing to the impulse being
completely blocked in the anelectrotonic region.

Mutatis mutandis, the same results are witnessed when the
effect of an anelectrotonic decrease has to pass through a kate-
lectrotonic region on its way to the muscle.

Obs. XIV. By placing the polarizing electrodes sufficiently
far apart from each other, the exciting pair may be inserted
into the intrapolar region, and the following results ob-
tained : —

In the intrapolar region, as in the extrapolar, there is an in-
crease of irritability in the neighborhood of the negative, and
a decrease in the neighborhood of the positive pole.

The increase and decrease respectively are greatest close to
the poles, and diminish towards a neutral point situate between
the poles.

With a weak current, this neutral point lies rather nearer
to the negative pole than the positive. By increasing the
strength of the current it is driven nearer and nearer to the
positive pole.

IV. Other Variations in Irritability. — The farther
from the muscle the part of the nerve excited, the greater the
contraction.

Obs. XV. Arrange a nerve-muscle preparation with two pair
of eleel rodes, one dose to the muscle, the other near to the cut
<-u<l of the nerve.

Connect both electrodes with a double key (Chap. XIX.,

392 STIMULATION OF NERVES.

sec. IX.), and the double ke}- with an induction coil. Arrange
for single opening induction shocks.

By means of the double key, put the lower electrodes next
the muscle in connection with the secondary coil, and find
what strength of the current (what position of the secondary
coil) just falls short of causing a contraction.

Then connect the upper electrodes with the secondary coil,
in place of the lower ones. Send through these a shock of
the same strength as that which sent through the lower elec-
trodes produced no contraction. A distinct contraction will
follow.

Once more send the same shock through the lower elec-
trodes. There will be, as before, no contraction, or a very
slight one.

The same stimulus produces, therefore, more effect when
applied to a point farther from the muscle.

Obs. XVI. This is partly due to the section of the nerve
trunk above the higher electrodes.

Having thoroughly destroyed the spinal cord of a frog, and
laid bare the sciatic nerve without dividing it, place a pair of
electrodes under the main sciatic trunk, send a feeble single
induction shock through them, and record the amount of con-
traction in the gastrocnemius, or determine the position of the
secondary coil, which gives a shock just falling short of the
strength required to cause a contraction.

Divide the sciatic nerve a little distance above the electrodes,
and determine, at intervals of 15 minutes, the contractions
which result from the application of the same stimulus as
before ; or determine the position of the secondary coil for a
minimum stimulus.

It will be found that the effect of the section is first to in-
crease, and afterwards to diminish, the irritability of the
portions of the nerve lying immediately below the section.

In the above observations, the student must make sure that
the electrodes are exactly similar, so that the differences which
come out are not due to an}- differences of resistance in the
two pair of electrodes or to the electrodes of one pair being
further apart from each other than those of the other, etc.

For this purpose it will be as well, after a series of observa-
tions, to exchange the electrodes, putting the one pair in the
former position of the other, and repeat the series.

Obs. XVII. On the sciatic nerve of a frog in which the
brain and spinal cord have been destroyed, and the heart
removed so as to stop the circulation, place three pair of
electrodes, one near the gastrocnemius, another close to the
central end of the nerve, and a third between the other two.
Divide the nerve above the upper pair.

Arrange the preparation carefully in the moist chamber.

BY DR. MICHAEL FOSTER. 393

Send a single weak induction shock through each pair of
electrodes, and record the contraction ; or determine the
minimum stimulus for each pair of electrodes.

Repeat the observation at intervals during the day.

It will be found that after the temporary increase due to
section, the irritabilit}' gradually diminishes from the central
cut end towards the periphery, the extreme muscular branches
being the last to die.

Be careful that no part of the nerve is more exposed than
others.

Obs. XVIII. Repeat the observation in a frog whose brain
and spinal cord have been destroyed, but the blood current
not interfered with.

The irritability will disappear much more slowly, but in the
same centrifugal manner.

CHAPTER XXIX.
PHENOMENA ACCOMPANYING A NERVOUS IMPULSE.

The only phenomenon definitely and certainly known to
accompany the passage of a nervous impulse is the negative
variation of the nerve current (see Chap. XXVI., sec. II.).

in the case of muscle, the negative variation shown in teta-
nus by the galvanometer was proved by the rheoscopic frog to
consist of a series of successive negative variations (see Chap.
XXIV., sec. III.).

At first sight a similar proof seems to be afforded by the be-
havior of nerves.

Obs. I. Prepare a nerve-muscle, and also a separate piece of
nerve as long as possible. Place the nerve-muscle B (fig. 291)
on a glass plate ; place the nerve A over the nerve of B, in either
of the positions shown in fig. 291, 1. II. ; connect the end of A
with an induction coil.

A single shock sent through A will produce a contraction in
b; an interrupted current will throw b into tetanus.

Obs. II. Ligature A between the electrodes and the end touch-
ing b. No contractions will appear in B on sending shocks
through the electrodes. This proves that the results of Obs.
I. were not due to any simple electrical conduction through a
or to any escape of the current to B by other means.

The same thing is shown in the so-called "paradoxical con-
traction."

Obs. III. In the leg of a frog, the sciatic nerve divides at the

394 PHENOMENA ACCOMPANYING A NERVOUS IMPULSE.

lower end of the thigh into the peroneal and tibial branches.
Dissect out one, say the peroneal, and divide it at its periphery;
Divide the sciatic trunk high up, and place the peroneal branch
on the electrodes of an induction coil. This will virtually con-
vert the leg into a preparation similar to fig. 201, III.; the
peroneal and tibial branches running, so to speak, side by side
in the sciatic trunk.

Irritating the peroneal nerve A, with an interrupted current,
will produce contractions in the muscles to which the tibial b
is distributed.

All these "secondai^ contractions" cease when the nerve a
is ligatured between the electrodes and the nerve b.

With each making (competent to give rise to a nervous im-
pulse) of the exciting current through a, two events take place
which must be kept distinct in the mind of the student.

First, there is the electrotonic increase (in the anelectrotonic
region) or decrease (in the katelectrotonic region) of the
natural nerve current. This increase or decrease remains
during the whole time of the passage of the exciting current,
and disappears with the breaking.

Secondly, there is the negative variation of the natural cur-
rent which travels with the nervous impulse indifferently in
either direction, and which, in any given point of the nerve, is
over and gone in an exceedingly short time after the act of
making the exciting current.

During the time of the passage of the (uniformly constant)
current, there is no negative variation, as there is no nervous
impulse.

On breaking the exciting current, a fresh negative variation
sweeps along the nerve, if the current is of such a character
that the breaking of it gives rise to a nervous impulse.

With a single induction shock there is also the double event
of a negative variation, and, as well, of a momentary electro-
tonus ; with an interrupted current there is a succession of
such double events.

In both these cases the secondary contraction, as in Obs. I.,
II., III., may be due to either half of the double event: to the
negative variation, or to the electrotonic change; or to both.
To which of them it is really due cannot be decided by the use
of such currents only.

If, however, the electrotonic increase is itself competent to
cause a secondary contraction, the contraction ought to be ob-
tainable at any period during the passage of an exciting con-
stant current, at a time when the negative variation is absent.

Obs. IV. Connect a (placed on a glass plate) with a constant
current of two cells, the positive pole towards the long free end ;
suspend the nerve of B in such a manner over A that, when de-
sired, it can be let fall so as to lie upon a in the position I. or
II. (fig. 291).

BY DR. MICHAEL FOSTER. 395

The exciting current being made, a negative variation sweeps
over A and is gone. There remains, however the anelectrotonic
increase of the natural current of a along the whole region from
the positive pole to the free end. Now let fall b as directed.
A contraction in the muscle of b will follow.

This can only be due to theelectrotonically increased natural
nerve current of a acting as a stimulus to the nerve of b when
the circuit is closed by a portion of b, and so causing a nervous
impulse just as the closing of any other galvanic current
would.

And inasmuch as the electric intensity of the electrotonic
increase (or decrease) is much greater than that of the negative
variation, the secondary contractions in the Obs. I., II., III.
are chiefly due to this cause.

CHAPTER XXX.

VARIOUS FORMS OF STIMULATION OF MUSCLE AND

NERVE.

I. Mechanical Stimulation. — A blow, sufficient^ strong
and sudden, applied to either muscle or nerve, will produce a
contraction ; and a series of such blows repeated sufficiently
rapidly will produce a tetanus.

This may be roughly shown by striking simply b}^ hand,
with some thin but blunt instrument, either muscle or nerve.

For more exact purposes, the tetanomotor of Heidenhain may
be used, and can be applied equally to muscle or nerve. For a
description, see. Rosenthal, Electrieitatslehre, p. 116.

A simpler method is that of Marey's, with a tuning-fork.

Obs. I. Get ready a nerve-muscle preparation. Place the
nerve on a small piece of India-rubber sheeting stretched quite
tight over a ring of wood or metal. The object of the elastic
India-rubber is to soften the violence of the' blows given. Ar-
range a tuning-fork on a stand, in such a position that the
vibrations of the tuning-fork shall take place at right angles to
the nerve. Set the fork going, and bring it in slight contact
with the nerve. The muscle will at once be thrown into teta-
nus, which may be recorded on the cylinder.

Obs. 1 1. A muscle (gastrocnemius, or, better, one of the recti)
of a frog poisoned with urari, may be placed on the caoutchouc
in place of the nerve.

Tetanus will be then obtained by direct mechanical irritation
of the muscle itself, without intervention of the nerves.

396 VARIOUS FORMS OF STIMULATION.

II. Idio-Muscular Contractions. — 06s. III. Place on

some flat surface a nerve-muscle preparation which has heeu
much exhausted by treatment or by long removal from the
body.

Strike the muscle sharply with some thin but blunt instru-
ment (handle of scalpel), across the middle of the bell}', at
right angles to its long axis.

A contraction will probably follow — a contraction which, as
usual, travels along the whole length of the fibres.

When the contraction, however, has passed awa}', the line
where the blow fell will be marked by a wheal, i. e., by a local
shortening and thickening, which lasts for several seconds, but
finally disappears. This wheal, this local thickening and short-
ening, is the idio-muscular contraction.

Obn. IV. Wait till neither muscle nor nerve give any (ordi-
nary) contraction with an electric stimulus. Strike as before;
the idio-muscular contraction will still make its appearance.
The relaxation becomes slower the nearer the advent of rigor
mortis, with the onset of which the idio-muscular contraction
disappears.

III. Chemical Stimulation of Muscle. — 06s. V. Care-
fully dissect out the sartorius muscle in the front of the thigh
(fig. 278 .s), injuring it as little as possible, and taking away
with it a piece of the pelvis from which it has its origin. Clamp
the piece of pelvis, avoiding any entanglement of the fibres of
the sartorius itself, and attach the clamp to a stand so that the
muscle hangs vertical. If it be desired to record the contrac-
tions, thrust a fine needle through the middle of the muscle,
and either bring the muscle to bear directly on the recording
surface, steadying it with a shotted thread as in the kymo-
graphion (Chap. XVI., § 33), or make the needle part of a
delicate lever. With a sharp pair of scissors, cut off the ten-
don of insertion so as to lay bare a transverse section of mus-
cular fibre.

Place a drop of any or each of the below-mentioned fluids on
a rather greasy glass plate (so as to have a good convex sur-
face of fluid), and very gradually raise the plate until the fluid
comes in contact with the muscular surface. Immediately, or
very shortly after contact, spasmodic contractions of the
muscle will begin.

The following substances applied directly to muscular fibres
produce contractions: —

Mineral acids, even when extremel}' diluted; solutions of
metallic salts ; strong solutions of neutral salts of the alkalies ;
lactic acid ; glycerin, even diluted to a considerable extent.

Obs. VI. The vapor of ammonia, even in mere traces, acts as
a powerful stimulus. Place a few drops of ammonia in a small,
flat, wide-mouthed bottle ; cover the top with a greased glass
plate. Protect the muscle from all extraneous vapor of am-

BY DR. MICHAEL FOSTER. 397

monia, and bring the closed bottle immediately under it. The
muscle exhibiting no contractions (there being no escape of
ammonia), slip away the glass cover from the top of the bottle ;
contractions will at once follow.

In the above observations, a fresh surface of muscle must be
cut after each trial, as the body used as stimulus destroys the
layer of muscle with which it is immediately in contact.

Apply the substance under trial as soon as possible after
making the section, as the surface exposed soon dies.

IV. Chemical Stimulation of Nerve.— Obs. VII. Pre-
pare a nerve-muscle with as long a piece of nerve as possible.
Fasten the muscle in the clamp, and support the nerve so that
the end hangs freely down in a vertical position. Bring a drop
of one of the below-mentioned fluids, on a glass plate, in con-
tact with the end of the nerve, allow some millimetres at least
of the nerves to be fully immersed in the fluid ; and either take
a fresh nerve-muscle for each experiment or cut away each
time all that portion of the nerve which had been previously
exposed to the action of the fluid.

The movements of the muscle may be recorded as usual.
Do not load the muscle with anything more than the lever
itself.

The following substances applied to a nerve produce con-
tractions in its muscles: —

Mineral acids, in considerable concentration only ; neutral
salts of the alkalis and metallic salts, in considerable concen-
tration only; lactic acid, only when concentrated; glycerin,
only when concentrated.

Ammonia hardly acts at all as a stimulus to nerve; in
making trial with this, care must be taken to protect the
muscle from all ammonia vapor.

V. Thermal Stimulation of Muscle.— 06s. VIII. Hav-
ing arranged a sartorious muscle, as in Obs. V., bring to the
lower cut surface a thin slip of heated metal. On contact
taking place, a contraction will result. In this case the heat
is applied to a part only of the muscle.

Obs. IX. Attach a gastrocnemius to a lever (either with
the origin of the muscle downwards and the tendon upwards,
or in the ordinary position with the tendon playing round a
pulley) in such a way that the whole muscle may readil}' be
immersed in fluid. Fig. 202 represents a convenient arrange-
ment for this and other purposes. The muscle a is fastened
to the clamp e, which is part of the bent holder d. This
holder moves on the same upright as the lever e. The tendon
of the muscle is attached by the thread b to the lever, so that
its contractions pull the lever down. The lever is counter-
balanced by weights carried over a pulley. The muscle can
thus be readily immersed in or withdrawn from any fluid.
Counterbalance the lever with 10 or 15 grammes.

398 INDEPENDENT MUSCULAR IRRITABILITY.

Immerse the whole of the muscle in a small vessel filled with
normal saline solution, and around the small vessel place a
large one, through which send a stream of hot water.

By means of a thermometer, ascertain the temperature of
the saline solution close to the muscle. When the tempera-
ture rises to 38°-40° C, the muscle is thrown into tetanus.
In this case the temperature of the whole muscle has been
raised at as nearly as possible the same time.

Immediatel}' that tetanus has set in, withdraw the muscle
from the saline solution. The tetanus will speedily pass away,
and the muscle will i*emain alive and irritable.

Repeat the observation, but allow the muscle to continue at
the temperature of 40° for about two minutes. On removing
the solution, the muscle will still remain in a state of tetanic
contraction, as indicated by the position of the lever, and
from that contraction no relaxation will take place. No
stimulus, however strong, will be able to call forth any further
contraction. The reaction of the muscle will be found to be
acid, and its extensibility diminished. In fact, the muscle will
be found to have passed from a state of tetanus into a state of
rigor mortis.

VI. Thermal Stimulation of Nerves. — Obs. X. Ar-
range the nerve-muscle preparation with the nerve dependent
as in Obs. VII.

Bring a hot surface to bear on the end of the nerve, or dip
the end of the nerve into a hot normal saline solution, or place
the end of the nerve in a small quantity of the normal saline
solution, the temperature of which gradually raise.

In all cases contractions in the muscle will follow.

CHAPTER XXXI.

URARI POISONING AND INDEPENDENT MUSCULAR
IRRITABILITY.

Obs. I. Introduce beneath the skin of the back of a strong
frog a drop or two of a solution of urari. (The exact strength
of the solution and the dose required will depend on the source
from which the urari has been obtained.) In a short time the
frog will be found perfectly motionless, with its respiration
arrested, but its heart still beating.

La}' bare the sciatic nerve in the thigh, slip under it a pair-
of electrodes connected with an induction coil, and stimulate
the nerve with an interrupted current, taking care that there is

BY DR. MICHAEL FOSTER. 399

no escape of the current into the surrounding muscles. This
may be effected by slipping under the electrodes a small piece
of India-rnbber sheeting.

If the animal has been thoroughly poisoned, no contractions
whatever in the muscles of the leg will follow upon the appli-
cation of a stimulus, however strong, to the nerve. If con-
tractions do make their appearance, the poisoning is not com-
plete; and the student must wait or inject a further quantity
of the poison.

The nerve having been proved to be insensible to stimuli,
la}T bare any of the muscles of the leg and apply the electrodes
directly to them. Contractions will be manifest upon the ap-
plication of a ver}r slight stimulus.

The effect of urari is to destroy {or suspend) the irritability
of nerves but not that of muscles.

Obs. II. In a strong frog make an incision through the skin
between the ilium and coccyx along the line k, wt, fig. 266
Cut cautiously through the ileo-coccygeal muscle (fig. 267 d)
until the peritoneal cavity is reached. The three nerves (fig.
295, 7' 8' 9'), which go to form the sciatic nerve, will come into
view when the sides of the wound are held apart. Very cau-
tiously, by means of a small aneurism needle, pass a thread
under these nerves, putting it under from the outside and
bringing it out again on the median side. Be very careful not
to wound the bloodvessels.

Repeat the same process on the other side, passing the same
thread under the nerves of that side too, but putting it in at
the median side and bringing it out at the outside. The thread
will now be in the position of the line o p q in fig. 266, with
the nerves of one side lying over it between o and p, and those
of the other side over it between p and q. Tie the thread very
tightly round the abdomen, so as to check entirely the flow of
blood to the lower limbs. All this may be done under a slight
dose of chloroform. The nerves thus form the only means of
communication between the hind limbs and the trunk, the
vascular communication being entirely stopped. Now inject
a small quantity of urari into the back, and wait until the
poison has had time to produce its effects in that part of the
body to which alone it h:is access, viz., the part above the liga-
ture.

The following facts may then be determined : —

Though there are no voluntary movements in the body, head,
or fore limbs, some slight (voluntary?) movements may some-
timefl be witnessed in the hind limbs.

Pinching, or otherwise stimulating, either hind foot may
produce movement* in either one or both hind limbs, but in no
other part of the body.

Pinching, or otherwise stimulating, the skin of the head,

400 INDEPENDENT MUSCULAR IRRITABILITY.

fore limbs or trunk above tbe ligature may produce movements
in the hind limbs, but in no other part of the body.

These facts are intelligible only on the hypothesis that the
urari has destroyed (or suspended) the irritability of the
motor nerves in that part of the body to which, by means of
the blood current, it has had access, but has not destroyed the
irritability of the sensory nerves or of the central nervous sys-
tem. Pinching the skin of the fore limb gave rise to an affe-
rent nervous impulse which, either by volition or by reflex
action, gave rise in turn to efferent impulses which were unable
to manifest themselves through the poisoned motor nerves of
the fore limbs and trunk, but found vent through the unpoisoned
motor nerves of the hind limbs.

In order to bring these results out well, the dose of poison
must not be more than sufficient to poison the motor nerves.
Subsequent or stronger action of the poison affects the central
nervous system as well.

Obs. III. In a fresh, strong frog, lay bare the sciatic nerve
on one side — say the right — in its lower course, place a ligature
under it near where it divides into its two branches, and tie the
ligature tightly round the leg above the knee. The circulation
of the lower right leg will thus be completely arrested ; but in-
asmuch as the nerve is not included in the ligature, there will
be complete nervous connection between the right lower leg and
the rest of the body. Poison with urari. As soon as the
animal has come under the influence of the poison, determine
the following facts : —

Complete absence of spontaneous movements, except per-
haps some feeble stirring of the right lower leg.

Stimulation of the right lower foot may produce movements
in the right lower leg, but will not produce movements in any
other part of the body.

Stimulation of any part of body may produce movements in
the right lower leg, but in no other part of the body.

If the two sciatic nerves be laid bare along their whole
course, it will be found that stimulation, however strong,
applied to the left sciatic nerve, produces no contractions
whatever in the muscles to which its branches go; while
stimulation, even slight, of the right sciatic nerve, whether
applied above or below the level of the ligature, and even
close up to the spinal cord, produces contractions in the mus-
cles of the right lower leg, but in none other.

Now the whole of the trunk of the right sciatic nerve, being
supplied with poisoned blood, has been as much subject to the
influence of the urari as the left sciatic. Nevertheless, while
the trunk of the left sciatic seems to have entirely lost its
irritability, that of the right seems to have suffered very little
indeed. The difference really is, that the left sciatic trunk

BY DR. MICHAEL FOSTER. 401

cannot manifest its irritability because all its branches are
poisoned; the right sciatic can, b}- means of those branches
which through the ligature have been removed from the in-
fluence of the poison-bearing blood.

With moderate doses of urari, the small branches appear to
be poisoned and to have lost their irritability, ivhile the trunks
are still intact.

Obs. IY. In a fresh, strong frog, dissect out a gastrocne-
mius (or any other single muscle), dividing both insertion and
origin and ligaturing its bloodvessels, thus leaving it connected
with the rest of the bod}- by its nerve onty. Poison the frog
with urari.

It will be found that stimulation of the nerve fibres supply-
ing the muscle at any part of their course, whether close to
the muscle, or in the sciatic trunk as far away as possible from
the muscle, will produce contractions in the muscle, though all
the other motor nerves in the bodjr seem to have lost their
irritability.

In a similar way it may be proved that if only the portion
of nerve immediately next to the muscle be kept from the in-
fluence of the poison, however much the rest may have been
subjected to the action of the poison, the muscle may be
thrown into contractions by stimuli applied to any part of the
course of the nerve. The presumption is, that urari acts on
the extreme ends only of the nerve, possibly on the end-plates.

Yet, as we have seen, however much the muscles themselves
be exposed to the action of the poison, they do not lose their
irritability. These two facts (1), that urari poisons the ex-
treme peripheral ends of the nerves, and (2), that the muscles
themselves do not under urari lose their irritabilit}', form to-
gether a very strong argument for the view that muscles pos-
sess an independent irritability of their own.

06s. Y. Get ready a nerve-muscle preparation. Place one
pair of electrodes (A) (as far apart as practicable) on the
muscle itself, another (B) on the nerve near the muscle, and a
third (non-polarizable) pair (C) on the nerve also, a little
higher up than B. Connect A and B with induction coils,
and determine the minimum stimulus required to be sent
through each pair of electrodes in order to produce a contrac-
tion in the muscle. It will be as well to record the contraction
by means of the lever, etc. The irritability of the nerve (elec-
trodes 15) and of the muscle and nerve together (electrodes A)
will thus be respectively determined.

Now pass through C a strong ascending constant current ;
and while the current is passing, determine as before the mini'
mum stimulus for A mid B. By the ascending constant cur-
rent the portion of nerve between the electrodes C and the
muscle has been thrown into a state of anelectrotonus ; and it
26

402 THE FUNCTIONS OF THE ROOTS OF SPINAL NERVES.

will be found that the irritability of the nerve in this region
has been very considerably lowered ; or, if the polarizing cur-
rent be strong enough, and the pair of polarizing electrodes
far enough apart, has been suspended altogether. Contractions
in the muscle are either entirely a'bsent when a shock is sent
through B, or only appear when the shock is very strong. At
the same time it will be found that the minimum stimulus of
A is not very different from what it was before. A rather
stronger stimulus is required to produce a contraction, but the
difference is strikingly less than that in the case of the elec-
trodes B, and even this difference may be accounted for by
considering that the electrodes A stimulate both the muscular
fibres and the intra-muscular nerve fibres, and that the com-
bined effect is therefore greater when the intra-muscular nerves
are intact than when they are paralyzed b}r the ascending cur-
rent.

Thus the ascending current will, if strong enough, suspend
the irritability of. the nerve fibres supplying a muscle, and yet
will leave the muscle but little altered in its susceptibility to
direct stimulation. This again is an argument in favor of
" independent muscular irritability."

The same view is supported by the facts that the chemical
irritants of nerve and muscle are not identical (see Chapter
XXX., Obs. V.-VII.) ; that the lower part of the sartorius
of young frogs in which no nerve fibres can be detected, is
susceptible of chemical stimulation ; and that the idio-muscu-
lar contraction may be called forth in muscles the nerves of
which have completely lost their irritability. (Chapter XXX.,
Obs. IV.)

CHAPTER XXXII.
THE FUNCTIONS OF THE ROOTS OF SPINAL NERVES.

The posterior root of a spinal nerve is said to be sensory,
i. t?., to serve as the path along which alone centripetal influ-
ences pass on their way from the peripheral nerve terminations
to those central organs, in which the3' become transformed
into sensations, or give rise to reflex actions, etc. The anterior
root is said to be motor, i. e., to serve as the path along which
alone centrifugal impulses pass, on their way from the central
organs to the nerve terminations in muscles, etc. The truth
of this absolute distinction in function between the two roots
may readily be shown in the frog.

The results are most clear and distinct when the organs of

BY DR. MICHAEL FOSTER. 403

consciousness are intact, and the ordinary tokens of sensation
are used to determine whether the impulses caused by stimu-
lation of the peripheral terminations reach the conscious cen-
tral nervous sj-stem or not. But the facts may also be readily
shown in the absence of the brain, when reflex action is taken
as a proof of a centripetal impulse having reached the spinal
cord. In the former case, the frog should be placed under
chloroform during the laying bare of the roots. In the latter
the medulla should be previously divided in the neck (see
Chap. XXXIII.).

The frog being placed on its bell}', make an incision in the
middle of the back, from the upper end of coccyx to the level
of the limbs, see fig. 26G g h. Having hooked back the flaps
of skin, carry the median incision down to the spines of the
vertebrae, and dissect away the longitudinal muscles on either
side, so as to lay bare the bony arches, and then hook back
the muscles on either side, or cut them away altogether.

With a small but strong blunt-pointed pair of scissors, cut
through, on either side, the arch of the last (eighth) vertebra
(be careful not to thrust the scissors in too deep), and remove
the piece so loosened. Proceed then to the next arch above,
and so remove three arches. The roots of the nerves will be
seen lying in the spinal canal. Snip away the remains of the
arches on each side, until the last three (or four) roots are
quite clear, being very careful not to touch the nerves with
the scissors. The bleeding may be disregarded. The posterior
roots lie superficialby, are large, and hide the anterior roots.
The several roots may be separated from each other by pass-
ing with great care the blunt seeker lengthways between them.

Very gently pass a fine aneurism needle, armed with thin silk
(ex. gr., a fine sewing-needle, with the head slightly bent, and
the point fixed in a handle), under a conspicuous posterior root
which seems to be the last. This will be the ninth ; the tenth
is much smaller, and runs closer to the filum terminale, see fig.
295. The seventh, eighth, and ninth form the ischiatic, from
which the crural, Ne, and sciatic, Ni, nerves are given off, the
seventh supplying most of the fibres of the crural. Tie the silk
loosely round the nerve, near its entrance into the cord. Care-
fully avoid compressing the nerve.

068. I. The frog being completely at rest, draw the ligature
tight, observing the frog all the while. If the animal be in good
condition, some movements will be visible in some parts of the
body as evidence either of sensibility or reflex action. Xow cut
tin: nerve between the ligature and the cord ; some movement
will probably be again witnessed.

06*. II. Lift the peripheral stump of the nerve carefully up
by means of the ligature, and slip it upon the curved shielded
electrodes (fig. 271) which may be held in the hand, or, better,

404 THE FUNCTIONS OF THE ROOTS OF SPINAL NEIIVES.

fixed on a movable stand. To prevent any escape of the cur-
rent, slip a fragment of India-rubber sheeting beneath the nerve
and electrodes, so as to isolate these from the cord and from
the rest of the nerves. Pass a moderately strong interrupted
current through the electrodes. If there be no escape of the
current, the animal will not move in the slightest.

Obs. I'll. Repeat the observation with the nerve-root next
above (the 8th), with this difference; place the ligature as near
as possible to the walls of the spinal canal ; divide the nerve
between the ligature and the wall, and place the central instead
of the.peripheral stump on the electrodes.

Ligature and section, as before, produce movements. A
very moderate interrupted current applied to the central stump
will produce verj considerable movements in various parts of
the body, i. e., signs of sensation or reflex action, as the case
may be.

Ligature or section of the posterior roots of spinal nerves
jiroduces movements in various p>arts of (he body. Stimulation
of the peripheral stump produces no movement whatever ; stimu-
lation of the central stump produces considerable movement*.
These movements, be they simple re flex actions or more compli-
cated voluntary movements set going by conscious sensations, are
evidences of centripetal sensor impidses, excited in the posterior
sensory roots.

Obs. IV. Examine now the sensibility of the hind limb on
which you have been operating. It will be found that pinching
the toes or the skin of the hind surfaces of the limb produces
little or no reflex action. The anterior surface of the leg, how-
ever, still retains considerable sensibilit}'.

Obs. V. Divide the posterior roots of the 7th and 8th nerves,
and also that of the small 10th nerve. The whole limb will
now be found to be totally insensible. Movements of the leg,
however, may readily be called forth by pinching the skin of
the back, or any other part of the body except the leg itself.

Division of the posterior roots stops the passage of sensory, but
not of motor impidses.

Obs. VI. Carefully cut away the posterior roots on which you
have been experimenting. The anterior roots, which are thin-
ner than the posterior, will now come into view.

Repeat on one of these anterior roots (9th nerve) Obs. II.
Mere touching the nerve will probably produce a movement of
the hind limb of that side. This result will at all events follow
upon ligature and section.

Stimulation of the peripheral stump, with even a very feeble
stimulus, will produce tetanus in the limb.

Obs. VII. Repeat on the anterior root next above Obs. III.

No effect whatever will be produced by stimulating the cen-
tral stump.

BY DR. MICHAEL FOSTER. 405

The anterior roots convey motor impulses centrifugally, but
not senso7~y impulses centripetally.

Obs. VIII. In a fresh, strong frog lay bare the roots of the
spinal nerves and divide the posterior roots of the 7th, 8th, 9th,
10th nerves on the right side and the corresponding anterior
roots on the left side.

The left leg will remain motionless, being simply dragged
along by the rest of the bod}*, but never moving of itself. [If
the brain has been previously destroyed or separated from the
spinal cord, the right leg will be drawn up as usual (see Chap.
XXXIII.), but not the feft leg.]

Pinching the right foot, or otherwise irritating the right leg,
will give rise to no movement whatever in any part of the body,
will call forth no signs of sensation.

Pinching the left foot, or otherwise irritating the left leg, or
an}' part of the body except the right leg, will produce move-
ments which ma}' occur in any part of the body except the left
leg itself.

In this case the right leg has had all its posterior, the left all
its anterior, roots divided. No centripetal impulses pass up
from the right leg to the central nervous system ; no centrifugal
impulses pass down from the central nervous system to muscles
of the left leg.

The posterior i-oots are the channels of the centripetal (sen-
sory), the anterior of centrifugal (motor) impulses.

Recurrent Sensibility. — This is never witnessed in the
frog. It can only be shown in the higher animals, the cat or
dog being best adapted for the purpose. The method adopted
is very similar to the above — the arches of one or two verte-
brae being carefully sawn through or cut through with the bone
forceps, and the exposed roots being very carefully freed from
the connective tissue surrounding them. If the animal be
strong, and have thoroughly recovered from the chloroform
and from the operation, irritation of the peripheral stump of
the anterior root causes not only contractions in the muscles
supplied by the nerve, but also movements in other parts of
the body indicative of pain or of sensations. On dividing the
mixed trunk at some little distance from the junction of the
roots, the contractions of the muscles supplied by the nerve
cease, but the general signs of pain or of sensation still re-
main. These disappear when the posterior root is also divided.
Hence it is inferred that fibres conveying centripetal impulses
pass downward along the anterior root to the mixed trunk,
and thence, turning round, run back again to the central ner-
vous organ along the posterior root. (For further details, see
Iicrnard, Lecons sur la Phys. clu Systeme Nervcux, Vol. I.,
p. 02 et seq.)

40G REFLEX ACTIONS.

CHAPTER XXXIII.

KEFLEX ACTIONS.

Reflex actions are best studied in the frog, the brain hav-
ing first been removed, or at least separated from the spinal
cord. The strongest and healthiest frogs should be chosen for
the purpose. The student should make himself acquainted
with the general form of the dried frog's skull. This having
been done, the position of the occipito-atlantal articulation
may readily be recognized on the living animal.

Division of the Medulla Oblongata. — Having wrapped a cloth
round the hind legs and body of the animal, clasp the fore legs
round the ring finger of the left hand, and hold them in posi-
tion by the middle and little fingers, which should also hold
tight the cloth. Press down the tip of the frog's nose with the
thumb of the same hand, so as to bend the neck as much as
possible. If the fore-finger of the right hand be now made to
glide over the roof of the skull, exactly in the mid-line from
before backwards, a slight but distinct depression will be felt
in the neck at the point where the occiput ends, and where the
medulla is covered, not by bone, but by the occipito-atlantal
membrane. It lies in a line drawn across the skull at a tan-
gent to the hinder borders of the two membrana tympani. (Fig.
266, line a-b.)

The position of this point being satisfactorily ascertained,
with a sharp-pointed scalpel make a small transverse incision
across it about a few millimetres long. The incision should
not be carried too far on either side. If the blood, which comes
freely, be rapidly taken up with a sponge, and the neck be kept
well bent, the medulla will be clearly seen. This should now
be completely cut across, and the wound be rapidly sponged,
in order that the division ma3T be ascertained by actual inspec-
tion to be complete. The encephalon may then be completely
destroyed by introducing a blunt piece of wire into the wound,
and eviscerating the skull. If the wound be then left to itself
the bleeding will, in most cases, soon cease ; if not, a small plug
of wood (the sharpened end of a lucifer match) ma}' be thrust
into the skull. This, however, should be avoided if possible.
It is better to conduct the operation in this way, seeing clearly
what is being done, than to divide skin, membrane, and medulla
by one thrust, without being able to tell exactly whether the
division is complete.

BY DR. MICHAEL FOSTER. 407

Decapitation. — Introduce one blade of a strong pair of
scissors into the mouth, and bring it, transverse to the long
axis of the head, as far back as possible. Bring the other
blade down to the skin behind the occiput, and quickly cut off
the head, being careful that neither blade slips forward.
Simple inspection will, at once, determine whether the whole
of the encephalon has been removed or no. The bleeding, in
man}' cases, is excessive, and must be staunched by astringents
or by the actual cautery. Indeed, where decapitation seems
desirable, it is far better to employ the galvanic cauture,
introducing the loop of platinum wire into the mouth, and
bringing it out through the occiput along the line a-&, fig. 266.

For the general study of reflex actions, division of the
medulla is preferable to decapitation. The large amount of
bleeding, the exposure to the air, and possibly other causes,
often lead, in the latter case, to abnormal results, ex. gr.,
pseudo-voluntary movements on the one hand, and lack of
reaction on the other.

Obs. I. Place the frog, immediately after the division of
the medulla, on its belby, with its legs extended. In most
cases the legs will remain extended, and at first no movements
will be produced by stimuli applied to any part of the body.
The animal (or rather its spinal cord) is in a state of shock,
consecpuent upon the operation.

If the animal be watched, it will be found that after a while
the hind legs, apparently without the intervention of any
external stimulus, are suddenly, first one and then the other,
drawn up to the body, and assume the wonted flexed posture.
This is a token that the condition of shock has passed away.
If now one of the legs be pulled out, and then let go again, it
will be immediately drawn up once more under the bod}r.

After the shock has passed away, the legs having been
drawn up, the animal will appear to have assumed a natural
posture. On observing it more closety, however, it will be
found that the posture is not quite natural. The line of the
back is too horizontal, the head lies flat, with the neck almost
touching the table, and the fore limbs spread out; whereas an
entire frog keeps the head and neck raised high up on the
almost vertical fore limbs, and the line of the body makes a
large angle with the plane of the table.

If left to itself, the frog will exhibit no movements whatever,
will not stir from the spot in which it is placed unless sbme
external stimulus be brought to bear upon it. This absence
of spontaneous movements is most marked, when sudden
variations of temperature are avoided, and the skin is not
allowed to get dry. Eence it is advisable to place the animal
on ;i dish containing a small quantity of water, and to cover it
with a glass shade.

408 REFLEX ACTIONS.

If turned over and placed on its back, it remains for an
indefinite period in that position, without making any attempt
to regain its natural posture. While on its back, the heart
may be observed beating, but the respiratory movements will
be wholly absent.

If thrown into a basin of water, it will sink to the bottom
like a lump of lead (unless the lungs be too much distended
with air), without making any attempt whatever to swim.

15y irritating it in various ways, it may be made to execute
a variety of movements (see following observations), but can-
not, by any means, be made to leap or spring forward.

Obs. II. With the point of a needle gently stroke the
abdominal walls on one side. A slight twitching of the
muscles of the region so stroked will be witnessed. This is
one of the simplest forms of reflex action. Contraction takes
place in muscles on that side of the body only, the afferent
nerves of which are affected by the stimulus, and it will be
found that the afferent and efferent nerves concerned in the
action belong tolerably exactly to the same segment of the
spinal cord.

On increasing the stimulus gradually by stroking more
forcibly, the twitchhigs will be seen to spread over a wider
and wider area, to invade the other side, and finall}' to pass
into the hinder and fore limbs.

With a stimulus, sufficiently slight, of an afferent nerve, a
definite small group of efferent fibres are alone affected by
reflex action. On increasing the intensity of the stimulus, the
effect spreads into a larger and larger number of efferent fibres.

Obs. III. Pass an S hook through the lower jaw, and thus
suspend the animal on a suitable upright, with the legs and
body hanging freely down.

Or, take a piece of thin wood, about an inch broad and five
long ; place the frog, belly downwards, on it, in such a wa}r
that the wood reaches no farther down than the lower part of
the abdomen, and secure the frog to it by two slight India-
rubber bands, one immediately below the fore limbs, and the
other a little above the thighs. If the wooden slip be now
fastened vertically in an upright, the hind limbs will hang
freely down, completely loose, while the body will be held
sufficiently firm.

For most purposes the former simpler method is sufficient.
When it is desired to study the movements of the legs alone
with some accuracy, the latter method must be adopted.

The legs hanging freely down, and the bod}' being com-
pletely at rest, with a smooth pair of forceps gentl}- pinch the
tip of one of the toes. The leg will immediateljr be drawn
sharply up, and after being kept in the flexed position for a
variable time, will be slowly dropped again.

BY DR. MICHAEL FOSTER. 409

Repeat the observation on the other leg. Only that leg, the
toes of which are pinched, is drawn up : and if the toes be not
too roughly treated, no other movement than the drawing up
of the leg is witnessed.

Obs. IV. With more force pinch the folds of the skin around
the anus. Both legs will be suddenly complete^' drawn up,
so that the toes of both feet are brought above the forceps, and
are then as suddenly and completely extended again. This
movement of sudden flexion and extension, that is of kicking,
may be repeated rapidly several times as the result of one for-
cible pinching of the region in question.

Obs. V. Pinch with some force the skin at a point on one
side of the loins. The leg of the same side will be suddenly
flexed over the back, and brought round back again with a
sweeping movement.

Obs. VI. The hind limbs hanging down as before, place a
watch or other small glass containing very dilute sulphuric
acid (one drop to 20, 30, or 50 CCm, strong enough to give an
acid taste) underneath the frog, and bring it close up to one
of the feet, so that the extreme tip of the longest toe just dips
into the acid. Within a short time, the exact length of time
being determined by the strength of the acid and the condition
of the frog, the leg will be flexed, and the foot withdrawn.
Very frequently the movement, even after the fluid has been
taken quite out of the wa}', is not confined to a single flexion
followed by a relaxation, but consists of a series of flexions
and relaxations, each succeeding flexion being less marked than
its predecessor.

Repeat the observation with varying degrees of acidity,
beginning with simple distilled water, and gradually adding
acid. Be careful to wash the foot carefully with water after
each observation, to wait some minutes between each applica-
tion, and to dip only the tip of the toe, and that to the same
extent in each case.

.Measure by means of a metronome, beating very rapidly, the
exact time intervening between the actual entrance of the toe
into the fluid, and its withdrawal.

With an acid of a given strength, applied to the same frog
under varying circumstances, the duration of this interval may
be taken as a measure of the power of reflex action. The shorter
the interval, the more prone is the cord to reflex actions. In
making observations on the length of this interval, it is as well
to use very dilute acid, such as will only just give a sensation
of acidity when applied to the tongue.

Obs. VII. Simple water of a sufficiently high temperature
(25°- 35°C.) may be used instead of the acid. It has the ad-
vantage of being less likely than the acid to produce a perma-
nent action on the skin. The difficulty, however, of keeping

410 REFLEX ACTIONS.

up exactly the same temperature renders it unsuitable for com-
parative experiments.

In all the above experiments the movements produced bear
marks of purpose. As the result of stimulation of a particular
region of the surface of the body, we find a complicated move-
ment, a movement brought about by the contraction of certain
muscles and sets of muscles, acting in a definite combination
and sequence. The movement thus produced is apparently
directed towards an end. Thus when the foot is pinched or
irritated by the acid, the resulting movements appear at least
directed towards, and frequently actually effect, the withdrawal
of the foot from the offending object ; when the flank is pinched,
the movement is such as tends to thrust away the points of the
forceps ; when the anus is pinched to kick away the forceps,
and so on.

This purposeful character of reflex actions may be still more
conveniently shown b}r adopting the following method : —

Obs. VIII. Arrange the frog with the legs alone free ac-
cording to the second method given above. Cut small pieces
of blotting-paper about 1 or 2 millimetres square, dip them in
strong acetic acid, remove from them all superfluous acid, and
then place them on definite regions of the skin. In this wa}' the
stimulus may be limited to very small areas chosen at pleasure ;
and it will be found that very different movements of the hind
limbs will be produced by applying the morsel of paper to dif-
ferent regions of the body. Thus if the morsel be placed on
the heel of one foot, both feet will be violently rubbed together,
while the legs remain foreibty extended. If the morsel be
placed on one flank, it will be rubbed off by the foot of the
same side ; if it be placed in the mid-line of the back, either or
both feet will be employed to remove it, and so on.

The student will do well to map out the limbs and bod}r of
the frog into small areas, and to determine the characters of
the movements, which result from the stimulation of each
area. He will in this way find abundant instances of an appa-
rent purpose.

06s. IX. It has been seen that where the morsel of acid
paper is placed, say on the right flank, it is the right leg, and
the right leg only, which under ordinary circumstances is used
to rub off the paper. Choosing a strong frog, in which reflex
action has been found to be highly developed, suspend it ac-
cording to the second method, hold the right leg firmly down,
or load it with a greater weight than the leg is able to lift, and
apply a morsel of acid paper to the right flank. Twitchings
and convulsive movements of the right leg are first witnessed,
and then the left leg is brought up to rub the right flank.

Place a similarly strong frog with powerful reflex capabilities
on its back on the table.

BY DR. MICHAEL FOSTER. 41 1

If a morsel of paper were now placed on the surface of the
right thigh, the right foot would be brought up to rub away
the paper, the left foot remaining quiet. Hold tight the right
foot, or better still, place a ligature below the right knee, and
cut away the whole lower leg and foot. If the acid paper be
now placed on the right thigh, convulsive twitching of the
stump (ineffectual as far as the removal of the paper is con-
cerned) will follow, and then the left foot will be brought
across to rub the paper away. %

In both these cases we have instances of an apparent power
of the organism, even in the total absence of the brain, to
change its customary proceeding and to adapt itself at once
to new circumstances, instances which have led some to speak
of a conscious intelligence residing in the spinal cord.

Obs. X. As an instance tending directly to the contrary
supposition, the following experiment may be performed: —

In a shallow glass or porcelain dish, place enough water to
reach up to the head of a frog. Line the sides and bottom
of the vessel inside with felt or blotting-paper.

Place an unmutilated frog in the water, and then graduall}"
raise the temperature. Cover the top of the vessel with a
piece of gauze or netting, to prevent the escape of the frog.

As the temperature rises the frog becomes uneasy, and after
20° C or 30° C is reached makes violent attempts to escape.

Place in exactly similar circumstances a frog whose medulla
has been divided ; the water should cover the whole of the
animal up to just below the wound in the neck (care being
taken that the water gains no access to the spinal cord).

Up to 30° or above, no movement of any kind is visible.
About 35°, slight twitch ings may be observed in some of the
muscles of the limbs and flanks. At 38°-40° the whole body
becomes rigid (rigor caloris), and the frog is dead without
having made the slightest attempt to escape from the hot
water.

This observation goes quite as far to prove that the frog, in
the absence of the brain, has no consciousness or volition as
Observation IX. seems to point to the contrary. Both obser-
vations are probably to be explained without any reference,
negative or positive, to consciousness or volition.

Oba. XI. As a useful exercise, the student may lay bare the
roots of the 7th, 8th, 9th, and 10th spinal nerves as directed
in Chap. XXXII., the medulla having previously been divided.
Let him now divide the posterior root of say the tth nerve,
and determine on what parts of the skin the acid papers may
be placed without producing reflex actions. In this way he
may ascertain the distribution in the skin of the sensory fila-
ments of that nerve ; and in the same way with the other
nerves.

412 REFLEX ACTIONS.

068. XIT. Having divided the medulla, make a tran verse
incision over the spine a little below the level of the fore limbs
(fig. 2C>C), line c-d) cut through very carefully a vertebral arch
on each side of the middle line and remove the piece. With
a sharp-pointed scalpel, the spinal cord may be divided right
across.

After the shock has passed away, it will be found that reflex
actions xmxy be called forth in the fore limbs by stimulating
the skin of the fore limbs or of the fore part of the body,
without any movement whatever being produced in the hind
limbs ; and vice verm. By the operation, the body hns be-
come divided into two segments, which, as' far as all reflex
actions are concerned, are quite independent one of the other.
Sometimes, when the movements of one segment are very
violent, the other segment becomes displaced, the displace-
ment serves as a stimulus, and a reflex action is thereby indi-
rectly brought about. But this will not be confounded with
direct reflex actions, which can only be called forth by stimu-
lating the respective segments.

Obs. XIII. In any of the above frogs which have shown
good reflex actions, destroy the spinal cord entirely by thrust-
ing a wire or blunt needle down the spinal canal. All reflex
actions will at once and for ever cease.

Obs. XIV. The orderly and purposeful character of reflex
actions may be modified by the action of certain poisons, more
particularly by strychnia.

Having divided the medulla in a frog, suspend the animal
as in Obs. III. and determine the readiness with which reflex
action is produced by mechanical stimulation. This may be
taken as a measure of the reflex excitability of the spinal cord
(the acid method being unsuitable in this case).

Introduce into the back of the frog a ^oVff or Wott °f a
grain of strychnia sulphate and determine again after a short
interval the effects of mechanical stimulation. They will be
found to be increased, i. e., the reflex excitability has become
heightened.

Now inject a larger quantity of the poison, and in a very
short time a very marked change becomes obvious. The
movement resulting from the stimulus is no longer a simple
movement, for instance, a simple withdrawal of the foot, but
a tetanic extension of the leg, which becomes more and more
violent and prolonged.

Soon each application of the stimulus will give rise to a
prolonged tetanic movement which is no longer confined to
the limb, or even to the side stimulated. The hind limbs are
forcibly extended, the fore limbs bent over the sternum, and
every muscle of the trunk is thrown into a state of prolonged
tetanic contraction.

BY DR. MICHAEL FOSTER. 413

After a while these contractions pass off and the body and
limbs become once more relaxed. With each application of
the stimulus the same tetanus of the whole body is called forth,
no matter to what part of the body the stimulus be applied, or
what be the character of the stimulus. The purposeful nor-
mal reflex actions are lost in a complete spasm of the whole
body.

It is possible to conceive that this result might be brought
out by an abnormal intensity of the impulses generated in
the afferent nerve by the stimulus, or by an abnormal irrita-
bility of the total muscular system, or by an abnormal condi-
tion of the spinal cord. That the last and not either of the
former two is the real cause, is shown by the following obser-
vation.

Obs. XV. In a frog with divided medulla, ligature the hind
limbs, leaving the nerves free as directed in Chap. XXXI. for
urari, and afterwards inject a small dose of strychnia.

In spite of the absence of the blood-current in the lower
limbs, the reflex actions will be as manifest in them, and as
easily brought about by stimulating them, as under ordinary
circumstances. But by the ligature the strychnia has been
prevented from having access to either the sensory nerves or
the motor nerves and muscles of the hind limb. Hence the
tetanic character of the reflex actions produced in them must
be due entirely to the changed conditions of the spinal cord
itself.

CHAPTER XXXIV.

ON SOME FUNCTIONS OF CERTAIN PARTS OF THE
ENCEPHALON.

Most of the experiments illustrating this part of the sub-
ject, like those having to do with the conduction of impulses
through the spinal cord, are of a kind which the student can-
not be expected to perform for himself, and are consequently
not introduced here. Several observations, however, of a very
instructive character may be made on the frog.

The brain of the frog may be considered, for present physio-
logical purposes, as consisting of three segments. We have
first the medulla oblongata (fig. 296 M. 0), and small cerebel-
lum c. next the optic lobes, L. Op., easily recognized in an
operation by the pigment contained in their pia mater, and
lastly, the cerebral hemispheres H. C lying over the corpora

414 ON SOME FUNCTIONS OF THE ENCEPHALON.

striata, with the small optic thalami Th. 0 between them and
the optic lobes.

The position of the optic lobes pretty well corresponds to
the hind part of the fron to-parietal bones, which are distinctly
seen when the skin over the skull is removed. A transverse
incision made through the skull with a narrow strong blade.
in a line which runs as a tangent to the anterior borders of
the membranse tympani, will separate the cerebral from the
optic lobes. This may be done without removing even the
skin. In most cases, however, it is better to remove the roof
of the skull and to see the parts of the brain which are being
operated on.

The frog being placed under chloroform, make a longitudi-
nal incision over the mid-line of the skull from behind the
nose backwards, and convert it into a T incision by a trans-
verse cut immediately behind the membranse tympani (fig. 266,
e.f a b.). Hook back the flaps. With a pair of fine bone
forceps or strong scissors cut right across the fronto-parietal
bones where they overlap the ethmoid. Each bone may then
be easily seized by its front end and torn away without any
injury to the cerebrum below. That being done, the blade of
a pair of scissors may be carefully slipped under eacli parietal
bone close to its external border and the bone cut through.
The bones may then be carefully seized at their front border
with a pair of forceps, lifted up and torn away. If the blood-
vessels at the side have been avoided, there will be but little
bleeding, and what does occur will soon cease. The cerebrum
may now be simply divided from the optic lobes by a trans-
verse incision and removed. A better method, in order to
prevent any injury to the optic nerves and optic thalami, is to
cut across the cerebral lobes at their junction with the olfac-
tory lobes, fig. 296 L. oh, to lift up their cut ends and so to
remove them carefully, working gradually backwards. To
separate the optic lobes from the medulla, nothing more than
a simple transverse incision is necessary, taking care not to
injure the cerebellum ; but it is as well to remove all the parts
in front of the incision. The flaps of skin may then be
brought together and united by a couple of sutures, and the
animal left to recover from the operation. All plugging, etc.,
should be avoided.

Obs. I. The phenomena of a frog when the animal possesses
the medulla oblongata and cerebellum as well as the spinal
cord, but all the rest of brain has been removed. The follow-
ing facts may be observed after the animal has completely
recovered from the operation, and should be compared with
the phenomena of a frog possessing a spinal cord only.

The attitude is completely normal, quite different from that

BY DR. MICHAEL FOSTER. 415

of a frog possessing the spinal cord only. The head is well
raised on the fore limbs.

Respiration goes on in an almost normal manner.

If left to itself, and protected from all external stimuli, the
animal will remain perfect^ motionless. For some little time
after the operation has been performed, movements apparently
voluntary, that is, occurring without any obvious cause, are
frequently witnessed. These, however, generally cease after a
little while, and if the animal lives long enough for the wound
to heal, entirely disappear.

The animal will not feed of itself. Flies, worms, etc., may
be placed close to it, and even introduced between the teeth,
without any notice being taken of them. If, however, the
mouth be opened and a morsel be introduced into the pharynx,
it is swallowed. In this way the animal may be kept alive for
an indefinite period, being fed on pieces of worm or flesh ; frog's
flesh does very well ; care must be taken not to introduce too
large pieces, and not to feed too often.

If the skin round the anus be pinched, the animal does
more than simply kick out its hind legs : it leaps forward, often
repeating the leap several times, and springing forward a con-
siderable distance ; sometimes it crawls instead of leaping, and
not unfrequently does both. If placed on its back, it imme-
diately turns over again to its normal position. This it does
instantly and with vigor. It has to be held down forcibly in
order to keep it on its back for any length of time.

If thrown into a basin of water, it at once begins to swim,
and continues swimming about with considerable energy till
it finds some resting-place. Having found a suitable support,
it crawls upon it, and assumes the normal attitude, and there
remains motionless until again disturbed.

If the cerebellum be removed, all these movements and
habits become much impaired, much feebler, and less striking;
or may (with the exception of the respiratory movements) be
wholly absent, but it is difficult to remove the entire cerebellum
without injury to the medulla. Hence the share taken bjT each
organ in keeping up these powers of executing complicated
movements cannot be readily ascertained.

The above facts all point to the existence in this part of the
brain of some mechanism connected with the co-ordination of
movements. The crawling, leaping, swimming, and turning
over on to the belly all demand a more complex nervous
machinery than is needed for the purely spinal reflex actions,
intricate as many of these are.

The persistence of what we have called the normal attitude
is very remarkable. Strictly speaking, the natural frog varies
its attitude constantly, but its most common posture, the one
into which it naturally falls when at rest, is the one we have

41G ON SOME FUNCTIONS OF THE ENOEPHALON.

described. This attitude is the one to which the frog with
cerebellum and medulla clinga most rigidly, to which it always
returns after being disturbed, and in which it eventually dies
if left alone and not fed.

Obs. II. Influence of the presence of optic l<>l,r.<, — Remove
the parts in front of the optic lobes as directed ; the best re-
sults are obtained when the animal is allowed to remain per-
fectly quiet for a day, or for several hours at least, after the
operation.

All the facts mentioned in Obs. I. may also be observed in
this case ; in addition, there are certain phenomena which are
only witnessed when the optic lobes are present.

Goltz's Balancing Experiment. — Place the frog on a rough
board (about eight or nine inches square), somewhat near to
one of the edges. Hold the board horizontal, and the frog
will remain motionless in the normal attitude.

Tilt the board gradually up, with that edge uppermost which
is farthest away from the frog, and towards which he should
be looking. Up to an angle of about 45° and beyond no
change will be observed in the frog. As soon, however, as
the board becomes so much inclined that the centre of gravity
of the frog is thrown outside the lower edge, the frog will
begin to creep up the board. As the inclination proceeds, the
frog moves higher and higher up, until, wdien the board at last
becomes vertical, the frog will be found seated in the normal
attitude, on the upper edge. On continuing the movement
of the board, so that what was the upper surface becomes the
lower, the frog will move from the edge downward over the
now upper surface ; and when that surface, by the continuance
of the revolving motion, again becomes inclined upward, will
again creep over it as before towards the new upper edge.

Evidently here the disturbance of the centre of gravity pro-
duces such an effect as to give rise to movements which are
directed towards the re-establishment of equilibrium, and which
are continued until that result is achieved. At first sight this
may appear very much like an act of conscious intelligence, but
if the student carefully observes the different behavior of an
entire frog and of a frog in this condition, the contrast between
the two will be found very striking. This frog does nothing
but crawl, and stops crawling as soon as the stimulus of the
disturbed equilibrium passes away. When the experiment is
successful, he remains perched motionless on the edge of the
vertical board, and never leaps away. The entire frog leaps
away at once.

Goltz's Croaking Experiment. — Place the frog on the table,
and with the thumb and forefinger gently stroke down the
flanks on either side. A little very gentle pressure must be ex-
ercised. As the thumb is thus carried backward along: the

BY DR. MICHAEL FOSTER. 417

sides of the animal, he will utter a single distinct, sharp, short
croak, and as often as the movement is repeated the croak will
be heard.

This again is very different from the behavior of the entire
frog. The entire frog, when thus stroked, may or may not
croak; for a single stroke he may croak several times, or not
at all. The frog without the cerebral hemispheres, but posses-
sing the optic lobes, and otherwise in good condition, croaks
at every stroke, and croaks once only for each stroke.

One seems driven to regard this behavior as the result of a,
so to speak, croaking mechanism ; and not as the act of a con-
scious intelligence.

Obs. III. The cerebral hemispheres having been carefulby re-
moved, in such a way as to leave intact the optic nerves, the
student may attempt the following experiment of Goltz to test
the persistence of any visual sensations.

Place the frog on the table, with his head towards the
window, and some six or eight inches in front of him place a
large book, or other thoroughly opaque mass. Gently pinch
him behind, in any spot which is exactly in the median line of
his body. Under ordinary circumstances, he would spring for-
ward in a straight line, and, in the absence of all vision, would
strike his head against the book. It will be found in this case,
however, if the experiment be successful, that instead of spring-
ing forward in a straight line, he turns a little to the right or
to the left, so as to avoid the book.

If he turns to the left, shift the book to the left and then
repeat the experiment. He will now move in a straight line or
to the right. In the same way, if the book be to the right he
will incline to the left.

The student will do well to try this experiment, but it fre-
quently fails. Care should be taken to have the light coming
into the room as directly in front of the animal as possible, in
order to exaggerate the shadow cast by the book. Apparently
the image of the opaque book produces some sort of visual im-
pression sufficient to guide the movements of the animal. But
it would be hazardous to say that the animal sees, for it is diffi-
cult, or rather impossible, to obtain any other evidence of the
influence of vision in a frog in such a condition.

These observations arc; introduced to illustrate the fact that,
in the absence of the cerebral hemispheres, whether the optic
lobes be present or no, the frog possesses no volition. He exe-
cutes none of those so-called spontaneous movements which we
are in the babit of attributing to volition. This leads us to infer
the absence of at least that amount of consciousness which we
find inseparably connected with volition. At the same time,
we learn that the presence of certain parts of the brain lying
behind the cerebrum, determines the nature of the movements
27

418 ON SOME FUNCTIONS OF TIIE ENCEPIIALON.

which arc called forth by external stimuli, rendering them very
complicated and delicate, especially giving them features which
cause them closely to resemble ordinary voluntary movements,
and suggesting the idea of intricate arrangements within certain
parts of the brain, of afferent (including nerves from the sense
organs) and efferent nerves and nervous centres, winch maybe
set into action by volition on the one hand, or by some external
stimulus on the other.

Obs. IV. Inhibitory Influence of parts of the Brain over the
Reflex Actions of the Spinal Cord.

The reflex actions of the cord much more readily occur, and
are much more vigorous and complete, in the absence than in
the presence of the brain. The brain, therefore, must in some
way or other prevent reflex actions.

Irritation of the optic lobes. — Having prepared a frog, as in
Obs. II. etc., ascertain the intensity of the reflex activity by the
sulphuric acid method. (Chapter XXXIII., Obs.'YI.).

Touch with a small crystal of sodium of chloride, or with the
point of a brush dipped in saline solution, the cut surface of
the optic lobes and determine, after a few seconds before con-
vulsions, which may occur, have set in, the duration of the
interval between the exposure of the foot to the acid and its
withdrawal. It will be found to be greatly prolonged. In
other words, irritation of the optic lobes has interfered with, or
partially inhibited, the reflex action of the eord. If the optic
lobes be removed, and the medulla irritated instead, the result
will be much less marked.

Obs. V. Having prepared a frog with optic lobes, and deter-
mined the reflex interval as above, inject into the back \ grain
of quinine sulphate, and determine the interval again from time
to time. It will be found to be much prolonged.

Having prepared a frog with divided medulla (Chapter
XXXIII.), and determined the duration of the reflex interval,
inject the same quantity of quinine, and again determine the
interval as before. No prolongation of the interval will be ob-
served. These results may be explained bj* supposing that the
quinine is unable to act directly on the reflex activity of the
cord, but is able either to stimulate an inhibitory mechanism
in the brain, or at least to affect the brain in such a manner as
to interfere with the reflex actions of the cord.

Obs. VI. Removal of the Cerebral Hemispheres in the Bird. —
Select a vigorous pigeon, so young as to be just able to fly well.
Keep it on dry food for a few days, in order to avoid an excess
of bleeding.

Having placed it under chloroform, using as little chloro-
form as possible, make an incision in the median line over the
roof of the skull, and hook back the two flaps of skin. The
thin skull may now be easily cut through with a pair of scis-

BY DR. MICHAEL FOSTER. 419

sovs. and the roof removed. Without waiting to stop the
bleeding, draw the cerebral hemispheres gently forward, and
cany a traverse incision from side to side with a blunt-
pointed bistoury through the brain in front of the corpora
bigeminal, and with a narrow spatula remove the hemispheres
en masse from behind forwards. Place the animal on a perch,
and leave it to itself. Do not attempt to plug or staunch the
bleeding ; a clot will soon form and serve as the best protec-
tion against further bleeding. Postpone putting sutures into
the flaps of skin until the bleeding has wholly ceased.

If it be desired to keep the animal alive for any length of
time, it will be as well to allow it to remain perfectly quiet for
some time after the operation, avoiding all observations and
experiments upon it. Only on the second or third day begin
to feed it gradually with a few grains of softened barley or
of rice.

Otherwise, observations may be begun as soon as the bleed-
ing has ceased.

The bird so deprived of its cerebral hemispheres (together
with its corpora striata and optic thalami), if placed on the
finger or on a perch, will settle itself in a balanced position,
and remain thus for an indefinite period motionless, or all but
motionless, except as far as the breathing is concerned. It
seems to be plunged in the most profound sleep, with the head
drooping and the ej'elids closed.

If irritated, it appears to awake; it opens its eyes, raises its
head, and more or less opens its wings, and otherwise moves
its bod}' or limbs.

If, while in a state of complete rest, perched on the fore-
finger, the finger be gently revolved, so as to throw the centre
of gravity outside the finger, the wings will immediately spread
out as if for the act of flight.

If thrown into the air, it will actually fly for some little dis-
tance, eventually settling down into its lethargic but balanced
condition. If in its flight it meets any objects it blindly strikes
against them.

For a detailed description of the phenomena exhibited by
such a bird, see Flourens's Systome Nerveux, p. 123.

06*. VII. Removal of the Cerebral Hemispheres in the Mam-
mal.— A young rabbit, about two months old, is the most suit-
able animal to operate upon. It should be fed for some days
previouslj- on dry food. The method of operating is very
much the same as in the bird. Fasten the animal on a Cer-
mak's rabbit-holder (Fig. 204), which should be raised at an
angle of 60° or so, in order that the head may be as high as
possible, and, consequently, the bleeding diminished. The
removal of the roof of the skull will be facilitated by first
making a small hole in each parietal with a trephine about a

420 ON SOME FUNCTIONS OF THE ENCEPIIAL0N.

third of an inch in diameter, and thou slipping the blade of the
scissors from one hole to the other between the bone and the
dura mater, and cutting the bone through. The rest of the
roof may then be removed piecemeal. Carefully avoid wound-
ing the venous sinuses, and carry the operation through as
speedily as possible. The amount of ether or chloroform given
should be no more than is absolutely necessary just to send
the animal off. Previous ligature of the carotid does very
little good, and only complicates the operation.

The animal will not survive the operation very long, but for
several hours after the operation the phenomena of complicated
movements consequent on stimulation, with total absence of
volition, may be witnessed as in the bird and in the frog.

Obs. VIII. Division of the Semi-circular Canals. — This is
best performed on the bird, ex. gr., a young pigeon'. The stu-
dent should first make himself acquainted with the position and
relation of the ganals in a dead bird. Make a vertical incision
along the back of the head, hook back the flaps of skin, scrape
away the insertion of the muscles of the neck, remove the outer
tablet of the diploe of the skull behind each ear, and pick away
in minute pieces with a small pair of forceps the cancellous
bone, embedded in which the hard bony canals will then easily
be found.

Having thus determined their exact position in the dead bird,
the student will find no great difficulty in reaching them by a
similar proceeding in the living bodj'. Having found them, cut
one o,r, better still, two on each side right through with a pair
of small but strong scissors. The bleeding, which is generally
excessive, may be staunched by styptics.

Immediately after the operation, and for an indefinite time
afterwards, the bird exhibits the utmost disorder in its move-
ments. Though able apparently to move each and every mus-
cle of its body, it has completely lost the so-called co-ordina-
ting power. For a particular account of this condition, see
Flourens's Systeme Kerveux, p. 454, and Goltz Pfluger's Archiv.
Vol. III. p. 172.

PHYSIOLOGY.

PART III -DIGESTION AND SECRETION.

WITH INTRODUCTORY CHAPTERS ON THE ALBUMINOUS
COMPOUNDS, AND ON THE CHEMISTRY OF THE
TISSUES.

By Dr. LAUDER BROTTOK

CHAPTER XXXY.
ALBUMINOUS COMPOUNDS.

Section 1. — Properties of Albumin.

1. Albuminous bodies occur in all the tissues of the higher
animals, and form the chief part of their bulk. They derive
their name from white of egg, which may be taken as a t3rpe of
the group, and they all resemble one another very closely, both
in properties and composition. They contain 52.7-54.5 per
cent, of carbon, 6.9-7.3 per cent, hydrogen, 20.9-23.5 per cent,
oxygen, 15.4-16.5 per cent, nitrogen, and 0.8-1.6 sulphur. In
the body they occur partly in a solid form and partly in solu-
tion. The herbivora derive them from vegetables in which
they are contained, and the carnivora from the animals on which
they feed. They do not diffuse, and only a small part of the
albuminous matter taken as food passes through the walls of
the alimentary canal into the circulation unchanged. The
greater portion is converted into diffusible bodies nearly allied
to albumin, called peptones, which are readily absorbed.

The organism not 011I3' possesses the power of transforming
albuminous bodies of one kind into those of another, so that,
e. fj., the casein of milk is converted into the muscles of the
sucking infant, but of combining them with other substances,
BO as to form such compounds as the haemoglobin of blood, and
of altering them in such a way as to obtain from them the so-

4-2:2 ALBUMINOUS COMPOUNDS.

called albuminoids of which connective and elastic tissue, carti-
lage, and epithelium are composed.

Alter serving their purpose in the organism, the}' are ex-
creted, not, however, in the form of albumin, but in that of
urea. It is extremely improbable that they are converted di-
rectly into urea, but rather into leucine and tyrosine, uric acid,
kreatin and [creatinine, and other substances, from which urea
is produced by further decomposition. Lately, some have
seemed inclined to put forth the opinion that peptones, after
their absorption, instead of being raised again to the rank of
albuminous bodies, undergo still further decomposition, and
yield hydro-carbons, which serve as fuel to the body, and nitro-
genous substances, which are rapidly converted into urea and
excreted, while the waste of the tissues proper is supplied by
albumin absorbed as such from the alimentary canal (Fick).

* * 2. Preparation of a Solution of Albumin to be
used in testing. — Egg Albumin. — In order to get a solu-
tion of albumin for examination, pour the whites of two or three
hen's eggs into a beaker, and cut them up with a pair of scis-
sors, so as to liberate the albumin from the network of line mem-
branes in which it is inclosed ; stir the viscous fluid vigorously
with a glass rod, and then press it through a piece of linen.
Mix it with an equal quantity of water, allow it to stand at
rest for some time, and then filter it. It passes very slowly
through the filter and chokes it very quickly. Several small
filters should therefore be used in preference to one or two
large ones, and they should be changed as soon as they get
choked. The filtration should also be quickened by the use of
the air-pump (see Appendix, § 211).

This filtrate contains inorganic salts as well as albumin, but
it will serve perfectly well to show most of the properties of
albumin. For some purposes, however, serum albumin is to be
preferred (.see § 18).

* 3. Preparation of Pure Albumin. — If pure albumin
is wanted, it may be prepared by separating the inorganic salts
from it by dialysis, and this operation is also useful in showing
that albumin does not diffuse.

Before subjecting the diluted and filtered albumin to dialysis,
it is advisable to concentrate it by evaporation at 40° C, so as
to quicken the diffusion of the salts. Then place the concen-
trated liquid in a dialyser (App. § 212), and let it remain over
distilled water. Change the water every six hours, till the water
no longer gives a turbidity with silver nitrate. As sodium
chloride is the chief salt contained in the egg albumin its ab-
sence in the ditfusate may be regarded as a sign that the albu-
min is free from all salts which diffuse. The vessels used must
be perfectly clean, and the distilled water tested beforehand, as
this test is very delicate. The albumin still retains a certain

BY DR. LAUDER BRUNTON. 423

proportion of inorganic salts, but there is no way known of
removing them without completely altering its constitution.

4. Preservation of Albumin. — If kept in solution,
albumin will quickly decompose, and it is inconvenient to
prepare it from eggs every time that a solution is required.
It may. however, be preserved for a long while by evaporating
the solution to dryness at 40 c C. (see App. § 208). The dry
albumin forms a j-ellowish transparent glassy substance, which
may be kept in a stoppered bottle, and dissolved as required.

5. Serum Albumin. — Preparation: Add very dilute
acetic acid, drop by drop, to serum of blood or hydrocele fluid,
stirring it constantly all the time, till a flocculent precipitate
is produced. Filter. Add a dilute solution of sodium carbo-
nate to the filtrate till it is nearly neutralized ; evaporate it to
a small bulk at 40° C. ; separate the salts by diffusion, and
evaporate the solution at 40° C. to dryness, in the same way
as directed for egg albumin. It still contains small quantities
of salts, but it is almost impossible to separate them from it.

6. Differences between Serum Albumin and Egg
Albumin. — Serum albumin agrees with egg albumin in most
of its characters, but it differs from it in the following re-
spects:—

1. Its solutions are not coagulated by ether.

2. It is more easi^ precipitated from its solution by hydro-
chloric acid.

3. It dissolves more readily in concentrated nitric or hydro-
chloric acid, and the precipitate thrown down by dilution from
the solutions in these acids, as well as that thrown down by
these acids from solutions in other menstrua, is readiby and
completely soluble in the concentrated acids, while the pre-
cipitate of egg albumin is not.

When injected under the skin of an animal it does not
appear in the urine, while egg albumin does so either when
injected under the skin or introduced in large quantities into
the stomach or rectum (Stockvis).

* 7. Solubility of Dry Albumin.— In testing the solu-
bility of albumin or other substances to be afterwards men-
tioned, they ought first to be pulverized and then agitated or
stirred with the liquid. If the powder runs into masses, these
ought to be broken up with a glass stirring rod ; this ma}' be
done much more easily if the rod is very thick or has a bulb-
ous end.

If simple agitation or heat suffices to dissolve a substance,
it may be placed in a test-tube, but if it requires stirring it
should be put in a test-glass (as the rod is apt to break the
tube), and afterwards transferred to a tube if heat is to be
applied.

The fact of a substance being soluble in a liquid is ascer-

424 ALBUMINOUS COMPOUNDS.

tained by the quantity which was at first put in becoming
gradually less, and finally disappearing. When it is only
sparingly soluble no diminution in the substance may be
observable, and the liquid is then to be decanted or filtered off,
and something added or done to it which will indicate the
presence of the substance, if any has become dissolved. It is
sometimes more convenient, especially when alcohol and ether
are employed as solvents, to evaporate the filtered liquid to
dryness, and see whether it leaves any residue or not.

Pulverize a little albumin in a Wedgwood mortar. Put a
little of it in several test-tubes, and test its solubility in the
following reagents: —

fl. Water: The albumin will dissolve, and may be shown
to be present in solution by boiling, when it will be precipi-
tated.

f 2. Liquor Potassse : The albumin will dissolve, and may
be precipitated from the solution by neutralizing.

3. Alcohol.

4. Ether : The albumin does not dissolve either in alcohol
or ether. The clear liquid, when filtered and evaporated, will
leave no residue.

f 5. Acetic Acid dissolves albumin. On adding potassium
ferrocyanide to the solution, a precipitate falls.

fO. Concentrated Hydrochloric Acid: The albumin dis-
solves, and the solution gradually becomes blue, then violet,
and, lastly, brown. Test this with one portion at the tempera-
ture of the room, and with another heated over a spirit-lamp.
The same changes will occur in both, but much more quickly
in that which is heated. A precipitate falls when either solu-
tion is neutralized.

7. Concentrated Sulphuric Acid : The albumin dissolves,
and more quickly if heated.

8. Concentrated Nitric Acid : The albumin dissolves, form-
ing a yellowish solution. When boiled it dissolves more
quickly. When the solution is allowed to cool, and ammonia
added to it, it becomes orange colored.

** 8. Coagulation of Albumin. — One of the most re-
markable properties of albumin is its precipitation from neutral
solutions as an insoluble coagulum by boiling.

In heating albuminous solutions care must be taken not to
hold them too near the flame, and also to shake or stir them
about, as otherwise the coagulum sticks to the tube and be-
comes burnt, and the test-tube cracks. Boil a watery solution
of albumin in a test-tube; a coagulum separates.

Alkali ajypears to be set free during Coagulation. — Add a few
drops of neutral solution of litmus to a solution of albumin and
boil. The color will become more decidedly blue.

BY DR. LAUDER BRUNTON. 425

Circumstances ivhich influence Coagulation. Temperature
at ivhich Coagulation occurs. — Although solutions of albumin
are generally boiled in order to produce coagulation, it takes
place much below the boiling point. The temperature at which
it occurs sometimes serves to separate albuminous bodies which
could not otherwise he distinguished (see § 60). The method
of ascertaining it is as follows : Put some aqueous solution of
albumin in a test-tube; place it along with a thermometer in a
beaker containing water, and apply heat very gradually till
coagulation begins to take place and the solution grows milky
from the formation of a precipitate. Then note the tempera-
ture of the water. If the liquid is heated over a naked flame,
it cannot be so equally and gradually warmed throughout, nor
the temperature at which coagulation occurs so accurately
ascertained.

Effect of Acids and Alkalis on the Temperature of Coagula-
tion.— The addition of very dilute acetic or phosphoric acid
causes coagulation to take place at a lower temperature. The
addition of a very little sodium carbonate pi'events coagulation
from taking place till the solution has been raised to a higher
temperature than is necessary in neutral solutions. A large
quantity will prevent it altogether.

Put some albumin solution into three test-tubes, acidulate
one slightly with very dilute acetic or phosphoric acid, add to
another a drop or two of a solution of sodium carbonate, and
keep the third without any addition, for the purpose of com-
parison. Put a drop or two of litmus solution into each, so
that they may be distinguished by their color, or attach a small
label to each. Place all three in a beaker, and warm them as
in the previous experiment. As the temperature rises coagu-
lation Avill occur, first in the acid, next in the neutral, and lastly
in the alkaline solution.

Effect of neutral Alkaline Salts on the Temperature of Co-
agulation.— The addition of neutral alkaline salts, such as
sodium chloride or sulphate, to a solution of albumin causes it
to coagulate at a lower temperature than it would otherwise
do. The salts produce this effect in neutral, in acid, and in
alkaline solutions of albumin.

Repeat the previous experiment, dividing each solution into
two parts and adding to one of them some saturated solution
of sodium sulphate. In each case coagulation will take place
at a lower temperature in the solution to which the salt has
been added than in the corresponding one to which no addition
has been made.

As the acetic acid alone lowers the temperature of coagula-
tion, and the addition of neutral salts does so still further, the
solution to which both have been added will coagulate first.
J5y adding a large quantity of the salt and of acetic acid coagu-

426 ALBUMINOUS COMPOUNDS.

lation may be produced at a temperature between 20° C. and
30° C. (Hoppe-Seyler).

f Coagulation is not due to heat alone, but to the presence of
Water. — Take some perfectly dry albumin, put it in a test-tube,
cover the mouth of the tube and plunge its lower end into
boiling water. Keep it there sufficiently long to be certain that
the albumin has been heated to 100° C. Take it out, let it
cool, and then add water to the albumin. It will be found solu-
ble. Plunge the tube a second time into the boiling water, and
the solution will be coagulated.

** 9. Precipitation of Albuminous Bodies. — Though
the action of the following reagents may be conveniently tried
with a solution of egg albumin, their power of precipitating
albumin is not limited to that obtained from eggs, but extends
equally to all other albuminous bodies.

Take a solution of albumin in water, put some of it into ten
test-tubes and add the following reagents. They all precipitate
albumin.

fl. Concentrated nitric acid.

2. Concentrated lrydrochloric acid.

3. Concentrated sulphuric acid.

f4. Acetic acid, or a little hydrochloric acid, and afterwards
a solution of potassium ferrocyanide.

5. Acetic acid and a considerable quantity of a concentrated
solution of sodium sulphate. [Other neutral salts of the alkalis
or alkaline earths as well as gum arabic or dextrin have a simi-
lar action to sodium sulphate.]

6. Basic lead acetate.

7. Mercuric chloride.

8. Tannic acid.

9. Powdered potassium carbonate thrown into the solution
till it is almost saturated.

10. Alcohol.

** 10. Detection of Albumin. — The three tests ordina-
rily used to detect the presence of albumin in a fluid are

1st. Its precipitation when boiled and acidulated with nitric
acid.

2d. Its precipitation by acetic acid and ferrocyanide of
potassium.

3d. Its precipitation when boiled with acetic acid and a strong
solution of neutral salt.

The student should first try these tests with a solution
known to contain albumin, so as to become familiar with tlu2tn,
and afterwards with a solution which may or may not contain
it.

1. Put some of the fluid in a test-tube and heat it over a
spirit-lamp or Bunsen's burner till it boils. Add a drop or
two of nitric acid so as to give it a most distinctly acid reac-

BY DR. LAUDER BRUNTON. 427

tion. If a precipitate is formed by boiling and is unchanged
by the nitric acid, or if one forms after the addition of the
acid, the fluid contains albumin.

The acid is added for two reasons, (a) To dissolve any
substance which might be present in the solution, and being
precipitated by boiling might simulate albuminous coagula-
tion. Such substances are calcium phosphate which is present
in human urine, and calcium carbonate in the urine of herbi-
vora. As this test is very frequently used for detecting albu-
min in urine, these substances might very easily lead to error.
Albumin which has been coagulated b}r heat is not soluble in
nitric acid, and if the precipitate produced in the fluid by
boiling disappears on the addition of acid, no albumin is
present.

(b) To neutralize alkali which might hinder the albumin
from being precipitated by boiling.

Take some solution of albumin in water, add a few drops of
liquor potassoe and boil. No precipitate occurs. Add one
drop of dilute nitric acid — any precipitate which forms disap-
pears on shaking the tube. Add sufficient to make the fluid
very distinctly acid, and a permanent coagulum will he pro-
duced. The quantity of acid added must therefore not be too
small, or some albumin may remain in the solution. Some-
times, instead of using nitric acid, the fluid is kept boiling,
and acetic acid added very gradually till the fluid is neutral.
Unless very great care is taken to neutralize the fluid exactly,
this method may fail, for if an excess of acetic acid be added
it will retain the albumin solution. If neutralized exactly,
the albumin will be precipitated, and may be separated from
the fluid by filtration.

2. Acidulate the fluid strongly with acetic acid, and then
add several drops of a solution of potassium ferrocyanide. If
albumin be present, a white flocculent precipitate will occur.

3. Add acetic acid to the fluid till it is very distinctly acid,
mix it with its own volume of a strong solution of sodium sul-
jmate, and heat to boiling. If albuminous bodies are present,
a permanent precipitate will be formed.

This last method enables us not only to discover albumin
when present, but to separate it from the solution, so that
tests for other substances, such as sugar, with which the pres-
ence of albumin would have interfered, may then be applied
to it.

11. Separation of Albuminous Bodies from other
Substances in solution. — 1. The usual way of separating
albuminous bodies from solutions is by boiling, so as to coagu-
late the albumin. If the solutions are already acid, they are
boiled without adding anything, but if not, a little dilute

428 ALBUMINOUS COMPOUNDS.

acetic acid is to be added before boiling, excess being carefully
avoided.

2. If complete coagulation is not produced by boiling with
acetic acid alone, an equal volume of concentrated solution of
sodium sulphate may be added, and the liquid again boiled.

** 12. Tests for traces of Albumin in solution. — 1.
Caustic Potash and Copper Test. — It is advisable, before try-
ing this test, which is also used for the detection of sugar, to
become acquainted with the reaction presented when a caustic
alkali is added to a solution of cupric sulphate, and the mix-
ture heated without any foreign substance being present in
the solution. Put a little distilled water into a test-tube, with
a drop or two of a dilute solution of cupric sulphate. Pour
into it some liquor potassa?, and a light blue precipitate of
hydrated cupric oxide will be thrown down. Boil the liquid,
and the blue precipitate will be converted into a black powder,
which is anhydrous cupric oxide. If it is gently warmed, in-
stead of boiled, the powder will be dark brown.

The hydrated cupric oxide is not soluble in excess of ordi-
nary liquor potassa?, but is slightly soluble in very concen-
trated solutions of potash, and imparts to them a light blue
color. The presence of certain organic substances renders
hydrated cupric sulphate soluble in weaker alkaline solutions.
Put some water and cupric sulphate solution in a test-tube ;
add a small crystal of tartaric acid, or a few drops of its solu-
tion, and then liquor potassa?. Either no precipitate will form,
or it will redissolve, and, on shaking the tube, the liquid will
become of a bright blue color. Boil it: no precipitate will fall,
and no change in the color will take place.

Application of this Test to Albumin. — Put some solution of
albumin in a test-tube ; add a drop or two of cupric sulphate
and liquor potassa? ; an excess of liquor potassa? does not inter-
fere with the reaction. Either no precipitate will fall, or it
will be dissolved on shaking the tube, the liquid assuming a
violet color. Boil it. No precipitate falls, but the violet
color will become deeper.

** 2. Xanthoprolein Reaction. — Add to the fluid some con-
centrated nitric acid, and boil. Let the liquid cool, and then
add a little ammonia. If albumin is present, an orange color
will be produced. This is one of the most delicate tests for
albuminous substances.

** 3. Millon's Reaction.— KM to the fluid a little of Mil-
Ion's reagent and heat. If albumin be present in considerable
quantities, a white precipitate will fall and become red on heat-
ing ; if only a trace be present, the fluid will become red. The
red color is produced even at ordinary temperatures, but it is
increased by heating.

To prepare Millon's reagent take two beakers, one of which

BY DR. LAUDER BRUNTON. 429

may be considerably larger than the, other ; place one on each
pan of a pair of scales, and add shot or weights to the pan
containing the lighter beaker till the other is counterbalanced.
Four into the smaller beaker a little mercury, and into the
other the same weight of nitric acid (sp. gr. 1042). Dissolve
the mercury in the nitric acid at first without, and afterwards
with gentle warmth. Pour the solution into a graduated glass
measure, and add to it twice its volume of water. Let it stand
for some hours, and then decant the fluid from the crystalline
deposit.

Section II. — Alteration of Albumin by Alkalis.
Ew albumin is converted into alkali-albuminate when it is

CO

dissolved in caustic potash or soda, or when they are added to
its solutions. Alkali-albuminate is the substance first described
b}' Mulder under the name of protein. He considered it to be
the essential part of all albuminous bodies, and regarded them
as compounds of it.

Albuminous bodies are not converted immediately into
alkali albuminate, but they undergo this change when allowed
to stand with caustic alkalis, and it is greatly accelerated by
the application of heat.

Alkali albuminate is not coagulated by heat. It is soluble
in weak alkalis. It is precipitated when the alkaline solutions
are neutralized by acids. It is soluble in very dilute acids,
especially hydrochloric acid, and when the acid is added in
excess to an alkaline solution, the precipitate which was
thrown down by its neutralization is again dissolved very
readily by the acid. When the acid solution is neutralized
by an alkali the albumin is again precipitated.

If the alkali albuminate is precipitated by neutralization,
and the precipitate immediately dissolved in acid, it is quickly
converted into syntonian. If it is precipitated, and allowed
to stand for some time, it will still be dissolved by dilute
acids, but not so readily as immediately after precipitation,
and it must be warmed with them to 60° C. in order to convert
it into syntonian.

If alkaline phosphates are present in the solution, alkali
albuminate is not precipitated by neutralization. When just
sufficient acid has been added to a solution of alkali albumi-
nate to convert the basic phosphate into acid phosphate, the
slightest excess of acid, or even C02 will produce a precipitate.
In studying the action of alkalis on albumin, it is as well to
begin with their action on solution of albumin, and afterwards
to examine the solid alkali albuminate.

** 13. Alkali Albuminate. — Dissolve some albumin in
water in a beaker ; add to it a few drops of liquor potassaj, and

430 ALBUMINOUS COMPOUNDS.

put a little of the mixture into four test-tubes. The, Alkali
Albuminate is not formed immediately. — To the solution in
the first tube add a drop of watery solution of litmus (see
App. § 217). Then add very dilute acid till the blue color of
the litmus begins to change to red. No precipitate, or only a
very slight one, will take place. Boil the neutral liquid ; a
precipitate is produced showing that much unchanged albumin
is still present. If a precipitate falls, the presence of much
unchanged albumin may still be demonstrated by filtering and
boiling the filtrate, or adding tannin to it, when a precipitate
will be produced. It is quickly formed when heat is applied.
It is not coagulated by boiling. Gently warm the fluid in the
second test-tube till it boils ; no precipitate forms. Let it
cool, add a drop of litmus to it, and neutralize. Just when
the blue begins to change to red the fluid will become turbid
from the precipitation of the alkali albuminate. Let the pre-
cipitate settle, and filter the fluid. Boil the filtrate ; no pre-
cipitate is formed, showing that the whole of the albumin has
become insoluble in water, and has been precipitated b}' neu-
tralization. It is soluble in dilute acids. Warm and neutral-
ize the solution in the third tube as in last experiment, then
add an excess of hydrochloric acid to the neutralized solution,
and the liquid will again become clear. On neutralizing the
solution a second time the precipitate re-appears. It is formed
at ordinary temperatures, but more slowly. Let the solution
in the fourth tube stand for some time, and then neutralize it.
The precipitate will be greater than in that which was neutral-
ized immediately after adding the potash. Filter and test the
amount of albumin in the filtrate by adding tannin. It will
vary, being greater or less, according to the shorter or longer
time the solution has been allowed to stand.

* 14. Preparation of Solid Alkali Albuminate. — a.
From esrafs. Put the white of one or two esus in a beaker, cut
it up with scissors and shake it vigorously with air in a flask
until the membranes separate and come to the top with the
foam. Filter it through a piece of linen. Add strong solu-
tion of caustic potash to it drop by drop, until the whole mass
becomes transformed into a stiff' jelly. Cut it into pieces
about the size of a horse-bean and throw them into a large
quantity of distilled water. Stir them round and round a few
times and then pour off the water, keeping back the pieces bjr
a piece of gauze stretched across the mouth of the beaker.
Wash the albuminate with fresh water several times in order
to remove the free alkali until the pieces begin to turn white
at the edges and exhibit only a faint though distinct alkaline
reaction. As the albuminate is soluble in water containing
alkali, a good deal of it is lost in the process. When deprived

BY DR. LAUDER BRUNTON. 431

of its alkali by prolonged washing or by soaking in dilute
acids it forms 2)seild°fibrin. Like fibrin this substance is
elastic, and it swells but does not dissolve in dilute hydro-
chloric acid. Unlike fibrin it contains no ash, and when put
into ln'drogen peroxide does not readily decompose it ; so that
few hubbies of gas appear.

b. From milk. Alkali albuminate may be prepared from
milk by shaking with caustic potash and ether, removing the
ether, precipitating the albuminate by acetic acid and washing
the coagulum with water, alcohol, and ether.

15. Properties. — Boil some pieces of albuminate in water;
it still contains alkali, and is soluble in boiling water, forming
a feebly alkaline solution. Let it cool, divide it into several
portions and apply the following tests : —

1. Pass CO., through the solution and a precipitate will fall.
No precipitate is produced if the solution is strongly alkaline.

2. Add alcohol to the solution ; no precipitate is produced.

3. Add magnesium sulphate in substance till the solution is
saturated. The albuminate will be precipitated. Calcium
chloride will have the same effect.

It is precipitated by metallic salts like other albuminous
solutions. It is precipitated by neutralization, and behaves
to alkaline phosphates like the solution of alkali albuminate
prepared by heating solutions of albumin with potash.

* It is not precipitated by Neutralization in presence of
Alkaline Phosphates. — A very small quantity of acid is suffi-
cient to give a distinctly acid reaction to a pure solution of
alkali albuminate, but if sodium or potassium phosphate is
present a considerable amount of dilute acid may be added to
the liquid after the point of neutralization has been reached
without given it a very distinctly acid reaction ; for the acetic
acid and neutral phosphate react on each other, forming-
sodium or potassium acetate and acid phosphate. Whenever
the solution becomes distinctly acid, the albumin is precipi-
tated, whether sodium phosphate be present or not. If suffi-
cient acid has been added to convert all but a trace of the
sodium phosphate present into acid phosphate, the further
addition of C02will cause a precipitate. Heating the solution
will also cause a precipitate, for it converts the acid phosphate
into neutral phosphate, and by thus liberating free acid acts
just as the addition of more acid would do.

Put some solution of alkali albuminate into two test-tubes ;
add solution of sodium phosphate to one of them, and color
them both equally witli solution of litmus.

Neutralize them both with very dilute acetic acid. Very
little acid will neutralize the pure solution of albuminate, and
the slightest excess will at once turn the litmus red. A

432 ALBUMINOUS COMPOUNDS.

greater quantity may lie added to the other without turning it
red. and till it turns red no precipitate will fall.1

16. Alkali Albuminate should contain no Sulphur.
— The sulphur which is contained in albumin is said to he re-
moved by the alkali used in converting it into alkali albumi-
nate, and it therefore differs from casein and syntonin, in both
of which sulphur is present. The presence of sulphur is thus
tested: Put a piece of alkali albuminate into liquor potassa?,
add a drop of solution of lead acetate and boil. The solution
should not become brown, as it would do from the formation
of lead sulphide, if sulphur were present in the alkali albumi-
nate. The sulphur is, however, by no means always removed
during the preparation, and it is very probable that a brown
color will be got.

Section III.— Alteration of Albumin by Acids. Acid Albumin
or Syntonin.

When a solution of albumin is treated with very dilute acids,
or when solid albumin is dissolved in concentrated acids, it is
converted into acid albumin, which is identical with syntonin,
or, at any rate, appears to be so. Myosin, vitellin, and fibrin
are quickly dissolved by dilute acids, and converted into
syntonin. It is soluble in very dilute acids, but is insoluble in
water, and it is, therefore, precipitated by neutralization. It
is redissolved by excess of alkali, as it is soluble in alkalis
and alkaline carbonates. Unlike alkali albuminate, its pre-
cipitation is not prevented by the presence of alkaline phos-
phates. It is not precipitated from decidedly acid solutions
by boiling, but when the solutions are nearly neutralized, and
only very faintly acid, boiling precipitates it.

1 It is usually stated that alkali albuminate is precipitated by neutral-
ization. In the text I have made use of this expression, which is per-
haps a convenient one, since the quantity of acid necessary to produce
precipitation being extremely small and the precipitate soluble in excess,
the direction to neutralize rather than to acidulate is more likely to
lead to the desired result, I believe the student will readily convince
himself that alkali albuminate is not precipitated from its solutions by
exact neutralization, and is only thrown down when a slight excess of
acid is present. I am inclined to think that the sodium phosphate acts
simply by preventing the inadvertent addition of a slight excess of acid,
which is extremely liable to occur in solutions of alkali albuminate, and
that syntonin is precipitated by neutralization in presence of sodium
phosphate, while alkali albuminate is not, because the point of slight
acidity at which the albumin is precipitated is reached before that of
neutralization in the former case, so that, before neutralization is
effected, the albumin is thrown down ; while in the latter, the solution
does not become acid, and the albumin is therefore not precipitated,
till after neutralization. On this subject compare Rollett, Wien. Sitz.
Ber. XXXIX. p. 547, and Molcschott's Untersuch, VII. p. 230, also'
Soxhlet, Journ. f. pract. Chemie, N. F. 1872, VI. p. 1.

BY DR. LAUDER BRUNTON. 433

** 17. Preparation of a Solution of Acid Albumin
or Syntonin. — Put some solution of albumin in water into
a beaker and mix it with its own bulk of dilute hydrochloric
acid (four cubic centimetres of strong commercial acid in one
litre of water). Pour some of the mixture into several test-
tubes. The dilute acid does not convert the albumin immedi-
ately into syntonin. Add to the fluid in the first test-tube a
drop of litmus solution, and then neutralize it exactly with
dilute liquor potassae. Little or no precipitate will fall. If
any should be produced, filter, and boil the filtrate or add tan-
nin to it. A copious precipitate will appear, showing that
there is much albumin in the solution. The prolonged action
of the acid converts it into syntonin, which is precipitated by
neutralization. Let one tube stand for some hours, and then
examine it, or prepare it some hours before, and examine it
at the same time as the rest. Put a drop of litmus into it,
divide the liquid into two parts and then neutralize one part
exactly. The whole of the albumin will be precipitated from
the liquid. To show this, filter and boil the filtrate; no precipi-
tate will be produced. Acid albumin is not precipitated from
acid solutions by boiliyig. Boil the other part of the liquid.
The albumin in it has been already shown to be converted into
syntonin. No coagulation will occur. The formation of acid
albumin is accelerated by heat. Warm a test-tube containing
albumin solution mixed with acid gently to boiling. Add a
drop of litmus solution, and neutralize. The albumin will be
completely precipitated, and the solution, when filtered, will
give no precipitate on boiling.

f Syntonin is precipitated from its solutions by neutraliza-
tion, even though alkaline phosphates be present. Repeat the
last experiment, adding a little sodium phosphate before
neutralizing. The S}rntonin will be precipitated as before.

** 18. Behavior of Syntonin with Acids. — Syntonin
is solnble in concentrated mineral acids ; it is insoluble in
them when they are moderately dilute, and it is soluble in them
when very dilute.

Heat a watery solution of albumin gently to boiling, with
its own bulk of very dilute hydrochloric or nitric acid (four
parts of commercial acid in 1000 of water). No coagulum
will be produced. Add a small quantity of strong acid and a
precipitate will form which will dissolve in a large quantity of
the acid, especially when heated.

Put a little serum albumin into three test-tubes, and add to
one concentrated nitric acid, to another hydrochloric, and to a
third sulphuric acid. Dissolve the albumin in the acid by
heating.

Dilute the solutions with twice their volume of water, and a
precipitate will fall. Let it settle, and pour off the superna-
28

434 ALBUMINOUS COMPOUNDS.

tant liquid or filter it ; throw the precipitate, still moist with
acid, into water, and it will dissolve. This is not a solution in
water, but in dilute acid, for a considerable quantity of acid
still remains in the precipitate. Egg albumin differs from
serum albumin in its behavior with acids, and this, and its
coagulability by ether, form the chief distinctions between
them.

Repeat the last experiment with egg albumin. It will not
dissolve so readily in nitric or hydrochloric acid, and when
precipitated by dilution will dissolve slowly and imperfectly
in more water, instead of doing so readily, like serum albumin.

The precipitate from hydrochloric acid will be brittle and
fibrous if the solution has been recently made, but if the solu-
tion is boiled until it begins to become violet, or allowed to
stand for some days, the precipitate will be flocculent and
soluble, like that of serum albumin.

* 19. Preparation of Syntonin. — (a.) From serum or
ess; albumin. Neutralize the solution in dilute acid, obtained
in last experiment, with dilute liquor potassa- ; a gelatinous
flocculent precipitate of pure syntonin will fall.

(&.) From fibrin. Dissolve it in concentrated hydrochloric
acid ; filter the solution if necessary, and then proceed as with
serum albumin.

(c.) From muscle. Mince some muscle, wash it with water,
add to it a considerable quantity of dilute hydrochloric acid
(four cubic centimetres of strong acid to one litre of water),
and let it stand for several hours, stirring it frequently. Fil-
ter it through a plaited filter. Dilute the filtrate with water,
neutralize it with a solution of sodium carbonate, and wash
the precipitate with water.

20. Characters. — When freshly precipitated, syntonin
forms a sticky jell}', but it is not tenacious.

Solubility. — It is insoluble in water, and in dilute XaCl
solution. It is readil}" soluble in lime water, in dilute hydro-
chloric acid, and weak alkaline solutions. It is not soluble in
a solution of six parts of potassium nitrate in 100 of water.

Its solutions behave like those made by heating albuminous
solutions with dilute acids.

21. Tests. — Dissolve some syntonin in lime-water and boil
it. Coagulation will occur.

Add magnesium sulphate or calcium chloride to a cold alka-
line solution of syntonin. Unlike alkali albuminate, it will
not be precipitated. Boil the solution, and precipitation will
occur.

Boil an alkaline solution of syntonin, and then add magne-
sium sulphate or calcium chloride, and a precipitate will fall
at once. This would seem to be due to the syntonin being
converted into alkali albuminate bv boiling.

BY DR. LAUDER BRUNTON. 435

22. Syntonin contains Sulphur. — Dissolve some syn-
tonin in liquor potassre, add a drop of a solution of lead acetate
to it, and boil. It will become brown from the formation of
lead sulphide.

23. Distinction between Alkali Albumin and Syn-
tonin.— If a solution of alkali albuminate contains an alkaline
phosphate, the alkali albumin is not precipitated when the
solution is neutralized, but syntonin is precipitated from its
solutions b}' neutralization whether an alkaline phosphate be
present or not.

Synopsis of the Chief Albumixoes Bodies. (Hoppe-Seyler.)

24. I. Albumins. — Albuminous bodies which are soluble
in water, and are not precipitated by very dilute acids, alka-
line carbonates, NaCl, or platino-hydrocianic acid. Their
solutions are coagulated by boiling.

1. Serum Albumin. — Not coagulated by shaking with ether.
Readily soluble in concentrated hydrochloric acid ; water
added to this solution causes a precipitate which is readily
dissolved by more water.

2. Egg Albumin. — Precipitated by ether. Less readily solu-
ble in concentrated hydrochloric acid : water added to this"
solution causes a precipitate which dissolves with difficult}* in
a large quantity of water.

25. II. Globulins. — Albuminous substances, insoluble in
water, soluble in dilute NaCl solution. The solution is coagu-
lated by beat. Very dilute hydrochloric acid dissolves them
and converts them into syntonin.

1. Vitellin. — Not precipitated by the addition of NaCl in
substance to the solution until it is saturated.

2. Myosin. — Precipitated from its solution in dilute NaCl
solution by the addition of NaCl in substance.

3. ttbrinogenic Substance and —

4. Fibrinoplastic Substance {Paraglobulin) agree with myosin
in their reactions, but together in neutral solutions they form
fibrin.

26. III. Fibrins. — Insoluble in water or in NaCl solution.
In dilute acids they swell, and also in solutions of soda, though
to a less extent. The swollen substance is coagulated by heat.

27. IV. Albuminates. — Insoluble in water or in NaCl
solution. Easily soluble in very dilute hydrochloric acid and
in alkaline carbonates. The solutions are not altered by boil-
ing. They are not precipitated from their solutions by neutrali-
zation if alkaline phosphates are present.

1. Casein yicids potassium sulphide when allowed to stand
with liquor potassce, and still more quickly when heated with it.

436 ALBUMINOUS COMPOUNDS.

2. Alkali albuminates (Proteins) do not yield potassium sul-
phide with liquor potassse.

28. V. Acid Albumins, or Syntonin.— Insoluble In
water or in NaCl solution. Easily soluble in dilute hydro-
chloric acid. Precipitated from solution by neutralization,
even in presence of alkaline phosphates.

29. VI. Amyloid. — Insoluble in water, dilute hydrochloric
acid and sodium carbonate ; in solutions of NaCl it does not
perceptibly swell. It is colored reddish-brown or violet by
iodine. It is not digested by gastric juice at the temperature
of the blood.

30. VII. Coagulated Albuminous Bodies. — Insoluble in
water, very dilute hydrochloric acid and sodium carbonate; in
NaCl solutions thejr do not swell up perceptibly. They are
colored yellow by iodine. They are readil}' converted into
peptones by gastric juice at the temperature of the blood.

31. VIII. Peptones. — Soluble in water, not precipitated
from the solution by acids, alkalis, or heat.

33. Decomposition of Albumin. — The decomposition of
albumin by various agencies is of great interest, as it is only
by a study of the way in which it splits up that a knowledge
of its constitution can be obtained.

When treated with powerful oxidizing agents albuminous
bodies yield formic, acetic, propionic, butyric, valerianic, ca-
proic, and benzoic acids and the corresponding aldeli3Tdes, am-
monia, and volatile organic bases.

Such substances are, however, too far removed from albumin ;
it is not from these final products of its decomposition that
much information is to be got, but rather from those bodies of
a tolerably complex nature into which it first splits up when
treated with less active decomposing agents. These may after-
wards undergo further decomposition, and yield substances of
a simple constitution.

The most important decomposition is that which albuminous
bodies undergo when boiled with water or with acids, or when
subjected to the action of one of the pancreatic ferments. Under
such circumstances peptones are first formed, and afterwards
split up, yielding leucine and tyrosine.

34. Peptones. — These are distinguished from other albu-
minous bodies by not being precipitated by boiling, by alkalis
or acids, nor by acetic acid and potassium ferrocyanide. They
are precipitated by alcohol. Unlike albumin, they diffuse easily
through vegetable parchment. With caustic potash and a
trace of cupric sulphate, the}- give a precipitate, which dissolves
on shaking, and forms a solution of a red color, becoming violet
on the addition of more copper sulphate.

Bodies which closely resemble the peptones formed during
digestion may be prepared by boiling albuminous bodies, such

BY DR. LAUDER BRUNTON.

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as fibrin, for along time with water, especially under pressure,
in a Papin's digester, in a sealed glass tube, or in a soda-water
bottle. By boiling with dilute sulphuric acid or concentrated
hydrochloric acid, they are produced in a shorter time. The
production of peptones by the digestive ferments will be con-
sidered a ft e r w a rds.

35. Leucine. — Preparation. — It may be obtained by boil-
ing fibrin with dilute acid for a long time, or by digesting it
with pancreas, but it is more usually got from horn chips.
Boil two parts of horn shavings with five parts of sulphuric
acid, previously diluted with thirteen parts of water, for twenty-
four hours, loss of water by evaporation being prevented by
the arrangement shown in fig. 329. Saturate the fluid while
hot, with chalk, filter, evaporate the filtrate to half its bulk, add
oxalic acid to precipitate the lime, filter and evaporate till a
scum forms on the surface, and then set it aside to crystallize.
A considerable amount of tyrosine will crystallize out first.
Pour off the liquor, let it stand till crystals of leucine form.
Purify them by boiling with water and lead hydrate, filter, re-
move the lead by sulphuretted hydrogen, filter, evaporate the
filtrate in a water-bath to dryness: dissolve the residue in hot
weak alcohol, and let it cool and evaporate till crystallization
takes place.

Leucine can be formed synthetically, and if wanted pure,
this is the best way of obtaining it.

For this purpose a mixture of valeral-ammonia, hydrocyanic
and hydrochloric acids are boiled together in a retort till the
oil}' ammonium compound has disappeared. The liquid is then
evaporated to dryness, the residue is boiled with water and
lead hydrate, and the product purified as already directed.

Characters. — Leucine forms extremel}" slender, white, glisten-
ing plates. Allow a drop of a solution in water or alcohol to
evaporate on an object-glass and examine it under the micro-
scope. It will form round balls, which arc either hyaline, and
strongly resemble fat globules, or exhibit radiating lines. Or
it may appear as very thin plates grouped in a radiating fashion.
They differ from urates presenting a similar form in not being
strongly refractive.

Solubility. — 1. Water: Pure leucine dissolves slowly, and is
soluble in about twent3*-seven parts of cold water. It dissolves
more easily in hot water. When impure it is more easity solu-
ble.

2. Alcohol: Pure leucine dissolves in 1040 parts of cold,
and in 800 of hot alcohol. If impure, it is much more soluble.

3. In Liquor potassa>, 4, ammonia, and 5, dilute acids, it is
readily soluble.

6. Concentrated hydrochloric or sulphuric acids. It is dis-

BY DR. LAUDER BRUNTON. 439

solved without decomposition. Neutralize them, and it is
precipitated.

f Effect of Heat. — At 170° C. it sublimes unchanged : a
higher temperature decomposes it.

Put a little leucine into a dry test-tube and heat it gently.
It will rise in white clouds and be deposited on the cool part
of the tube. Heat the deposit strongly and a strong smell of
amylamine will be perceived.

Decomposition. — When decomposed by heat it yields C02
XH3, and amylamine.

To show this put a portion of leucine into a hard glass bulb,
and connect this by means of India-rubber tubing with a glass
tube long enough to reach to the bottom of a test-tube. Pre-
pare two other similar pieces of glass tubing and three test-
tubes, the first of which should be about half filled with caus-
tic baryta solution, the second with Nessler's reagent, and the
third with water. Heat the bulb containing the leucine, apply-
ing the heat first to the upper part of the bulb and gradually
moving it downwards, so that as the leucine sublimes its vapor
may be strongly heated and decomposed. Pass the fumes into
the baryta solution, then disconnect the glass tubing, and after
attaching a clean piece, pass them into Nessler's reagent and
then into water. The baryta will be precipitated as white car-
bonate, the Nessler's reagent will become brown, showing the
presence of ammonia, and the water in the third test-tube will
acquire the peculiar smell of amylamine and an alkaline reac-
tion. Add to the barium solution a little nitric acid. It will
become clear and evolve gas, showing that the precipitate was
barium carbonate. A minute quantity onljr of NH3 is disen-
gaged when leucine is heated alone, and the coloration of Ness-
ler's reagent is therefore very slight. If a little lime and caus-
tic soda or potash are heated with the leucine much more NH3
is given off.

36. Preparation of Nessler's Reagent. — Dissolve 4
grammes of potassium iodide in 250 cub. cent, of distilled
water. Set aside a few cub. cent, and add a cold saturated solu-
tion of mercuric chloride to the remainder, till the precipitate of
mercuric iodide is no longer dissolved on stirring. Add that
part of the potassium iodide solution which was set aside, to
the rest, so as to dissolve the remaining precipitate, and then
add mercuric chloride again very gradually, till a slight per-
manent precipitate is produced. If a few cub. cent, of the
potassium iodide solution were not set aside, great caution
would be required in adding the mercuric chloride so as to
avoid excess. Dissolve 150 grammes of potassium hydrate in
1 50 'ul). cent, of distilled water, allow the solution to cool, and
arid it gradually to the potassium iodide solution. Pour the
mixture into a measuring-glass or flask, and add distilled water

440 ALBUMINOUS COMPOUNDS.

to make up a litre. Pour it into a large well-stoppered bottle,
taking care that there is no ammonia near it at the time. It
will deposit a brown precipitate, and become quite clear and
of a pale greenish-yellow color. It is then ready for use ; a
little of it should be poured into a smaller bottle when wanted.

37. Detection of Leucine in Tissues. — In order to de-
tect the presence of leucine, cut up the organ (the pancreas of
a sheep or ox, for example) into small pieces with a large knife
or sausage-making machine. Mix it with water and let it stand
for a little while, stirring it frequently ; filter it through a piece
of cloth, and press out the water first with the hand, and then
with a screw-press. Extract it with water a second time in the
same way. Mix the watery extracts together, acidify slightly
with acetic acid, and boil, to coagulate the albumin. Filter:
add a solution of lead acetate to the filtrate. Filter: pass sul-
phuretted hydrogen through the filtrate to remove the excess
of lead. Filter : evaporate the filtrate to dryness. Extract
the residue with boiling alcohol. Filter: evaporate the filtrate
to a syrup, and set it aside for several days to crystallize. If
leucine is present, it will crystallize in a day or two in balls or
knots, or, possibly, in shining plates, but will not form good
crystals. It is not pure, but is mixed with a number of other
substances. In order to free it from these, the following method
is recommended by Hoppe-Seyler. Dissolve it in ammonia,
add lead acetate till no further precipitate is produced. Filter:
wash the precipitate with a little water. Suspend it in water,
and pass sulphuretted hydrogen through it. Filter, and
evaporate the filtrate in the water bath.

38. Tests for Leucine. — The formation of round lumps or
plates is not sufficient to prove that a substance is leucine, and
other tests must be applied to them. Before doing so, the}'
should be purified by drying them between two folds of blot-
ting-paper, dissolving them in boiling alcohol, and letting them
crystallize out again. The following tests may be applied: —

1. Put a portion into a dry test-tube and heat it over a
Bunsen's burner or spirit-lamp. If it consists of leucine, it
will emit the smell of amylamine.

2. Scherer's Test: Put a small portion of the supposed
leucine with a drop of nitric acid on a piece of platinum foil,
and evaporate it gently. If it is pure leucine, a colorless,
almost invisible, residue will remain on the foil. Add a few
drops of liquor potassa: to it, and heat. It will become yellow
or brownish, and then form an oily drop, which runs about
upon the foil without adhering to it.

39. Tyrosine. — Prej>aration. — Boil horn shavings with
dilute sulphuric acid, crystallize out the tyrosine, as directed
in the preparation of leucine, wash the crystals with cold

BY DR. LAUDER BRUNTON. 441

■water, dissolve them in ammonia, and allow the solution to
evaporate, until the tyrosine cr3rstallizes.

It forms fine colorless microscopic needles, with a silky
lustre, and without taste or smell.

Or digest fibrin with pancreas, see § 171.

Characters. — Let a drop of a solution of tyrosine in hot
water evaporate on an object-glass, and examine it under the
microscope. Long needle-like crystals will be seen which are
often united in single tufts, or in radiating groups of tufts.

Solubility. — 1. Cold water dissolves it with difficulty. 2.
Boiling water dissolves it easily. Almost all the tyrosine
crystallizes out on cooling. It is insoluble in, 3. Absolute
alcohol, 4. Ether. It is easy soluble in, 5. Ammonia, 6. Liq-
uor potassse, 7. Concentrated solution of potassium or sodium
carbonate, 8. Alcoholic solution of caustic potash, 9. Concen-
trated 113-drochloric or sulphuric acid, and, 10. Dilute mineral
acid. 11. Acetic acid dissolves it with difficult}'. 12. Nitric
acid dissolves it. Let the solution stand a while. A yellow
ciystalline powder of nitro-tyrosine will separate. Pour off the
liquid and add liquor potassse to the powder. It will dissolve
and form a red solution.

40. Detection of Tyrosine. — Treat the organ exactly
as described in the process for the detection of leucine. The
dried residue, after it has been extracted with boiling alcohol
to remove the leucine, consists of tyrosine. Dissolve it in boil-
ing water or ammonia, and let it ciystallize out.

41. Tests fcr Tyrosine. — It is distinguished b}r its micro-
scopic appearance, and by the following reactions.

1. Hoffmann's Test. — Put a little of the solution supposed
to contain tyrosine in a test-tube ; add some water, and a few
drops of mercuric nitrate solution. Boil it for a little while.
If tyrosine is present, the liquid will become rose-colored, and
will afterwards deposit a red precipitate.

2. Piria's Test. — Pour a few drops of concentrated sulphu-
ric acid on two or three pieces of t3rrosine the size of a pin's
head in a wTatch-glass. Gently warm it for a little. Let the
solution cool. Mix it with a little water, and add chalk or
barium carbonate till all effervescence has ceased. Filter.
Evaporate, if necessary, to a small bulk at a gentle heat, and
add a few drops of a neutral solution of ferric chloride. The
fluid will become of a beautiful violet.

•';. Scherer's Test. — Put a little of the supposed tyrosine,
witli a drop or two of nitric acid, on a piece of platinum foil,
and evaporate gently. If it is really tyrosine, it will quickly
become of a bright yellow color, and will leave a deep yellow
shining residue. Add a few drops of liquor potasses to it, and
it will form a yellowish-red solution. Evaporate, and it will
leave a brown residue.

442 CHEMISTRY OF THE TISSUES.

CHAPTER XXXVI.

CHEMISTRY OF THE TISSUES.

42. Epithelial Tissues. — The epithelial tissues — nails,
hair, epidermis, and epithelium, as well as horns and feathers
— contain a small quantity of fat, and a substance which con-
stitutes the chief part of their bulk, and to which their form is
due. To this substance the name of keratin has been given.
It is prepared by removing the fat, etc., from any of the epi-
dermal tissues by boiling with ether, alcohol, water, and dilute
acid. As the elementary anatyses of it do not agree, it is rpiite
possible that it is a mixture of several substances, but this is
not yet certainly made out. It is nearly allied to albumin, as
is shown by its yielding the same products, leucine and tyro-
sine, when decomposed by boiling with dilute sulphuric acid
(.see § 35). It contains sulphur, which seems to be in a very
loose state of combination. Hair, as is well known, becomes
blackened by lead sulphide when a leaden comb is used. To
show the presence of sulphur, put a few parings of nails into
a test-tube; add a little liquor potassre, and boil. Add a little
hydrochloric or sulphuric acid to the solution thus obtained.
Hydrogen sulphide will be given off", and may be recognized by
the smell.

43. Connective Tissue. — In the group of tissues so desig-
nated, there are several which do not seem very like one another.
Such are mucous tissue, reticular and ordinary connective tis-
sue, adipose tissue, cartilage, bone, and dentine. Their close
relation to one another is shown by their being linked together
by intermediate forms, by one tissue sometimes passing into
another so that the boundary between them cannot be defined,
and \>y one occasionally replacing another. Thejr all contain
substances which* are either derived from albumin or are nearl3r
connected with it, and have received the name of albuminoids.

44. Albuminoids. — These are nitrogenous, and resemble
albuminous bodies in composition, but differ from them in their
behavior with acetic acid, potassium ferrocyanide, nitric and
hydrochloric acids. The}' are mucin, gelatin, and chondrin.

** 45. Mucin. — This is found in foetal connective tissue,
and although not present in the fasciculi is an important con-
stituent of tendon tissue. It occurs also in all mucous secre-
tions, and gives them a tenacious character. It is distinguished
by its solutions not being coagulated or rendered turbid by

EY DR." LAUDER BRUNTON. 443

boiling ; by giving with acetic acid a precipitate which shrinks
together in pure acid, instead of swelling and dissolving as
albuminous bodies do. The addition of potassium ferrocyanide
to the acetic acid prevents it from precipitating mucin, so that
no turbidity is produced unless albuminous substances are also
present. It gives no precipitate with mercuric chloride ; when
heated with liquor potassas and cupric sulphate, the solution
remains of a clear blue.

Preparation, (a) From Saliva?~y Glands. — Wash the sali-
vary glands of an ox or sheep well. Cut them up into small
pieces. Wash away any remaining blood with a little water.
Mix the glandular substance well up with a considerable quan-
tity of water, and filter through linen. Add acetic acid gradu-
ally to the filtrate, till a precipitate parti}' fibrous and partly
flocculent is obtained. Filter through linen. Wash the pre-
cipitate with water, and then with alcohol and ether, to remove
the fat.

(b) From Tendons. — Free the sinews of the legs of an ox or
sheep from muscle. Wash them well, and cut them up in small
pieces. Extract them with water. Put them into a large quan-
tity of lime or baryta water, and let them stand in a closed ves-
sel for several days. Filter. Add acetic acid in excess to the
filtrate to precipitate the mucin. Wash the white flocculent
precipitate with dilute acetic acid and then with dilute alcohol.

(c) From Ox Gall. (See § 134).

Solubility. — 1 . Water : — It does not dissolve, but swells very
much; when the mixture is filtered, part of the mucin often
passes through, forming a turbid filtrate. The mixture with
water is not tenacious, and no foam is produced on shaking it.
2. XaCl solution. Add a little solid NaCl to a mixture of
mucin and water. It will become clearer. Put a glass rod into
the liquid. It will now be found to be tenacious, and on with-
drawing the rod a long thread will follow it from the fluid.
Shake it, and foam will form. Add a large quantity of water
to the solution or mixture (for it is not certain which it is), and
the mucin will be precipitated. 3. Very dilute hydrochloric
acid of less than 1 per cent., or other mineral acid, does not dis-
solve mucin. 4. Dilute hydrochloric acid of 5 per cent, partly
dissolves it. Shake the solution and it foams. Add a little
NaCI to it, and the mucin will dissolve much more readily.
"i. Concentrated hydrochloric, or other mineral acid, dissolves
it completely. 6. Liquor potassae dissolves it; add a little to
some mucin, but not enough to dissolve the whole of it. Filter.
The filtrate is not tenacious, and is neutral, t. Baryta and
limewater dissolve mucin, and when used in small quantity
give, like liquor potassse, a neutral filtrate.

Precipitation of Mucin. — f 1. Boil the neutral or slightly
alkaline solution. It will not be altered.

444 CHEMISTRY OF TIIE TISSUES.

f 2. Add acetic acid. A precipitate will fall. Let it settle.
Pour off the liquid and pour on glacial acetic acid. Generally
it will not dissolve.

f 3. Add acetic acid with solution of potassium ferrocyanide.
If the mucin is pure no turbidity will appear at first, but will
do so after the solution has stood for some time.

4. Add mercuric chloride. No precipitate.

5. Add basic lead acetate. A copious precipitate will form.
f Reaction with Cupric Oxide. — Add liquor potassre and a

little cupric sulphate to a solution of mucin. The cupric hy-
drate will be dissolved. Boil. The liquid will still remain of
a clear blue color. This distinguishes mucin from albumin,
pepsine, and gelatin, which give a violet or red color.

** 46. Ordinary Connective Tissue. — Tendons. —
Gelatigenous Substance, or Collagen. — This substance
forms the organic basis of bones and teeth, and the principal
or fibrous part of connective tissue, tendons, ligaments, and
fascire.

Preparation, (a) From Bones Soak some bones in hydro-
chloric acid diluted with 8 or 9 times its bulk of water, chang-
ing the acid several times. This will remove the inorganic
salts which are deposited in the bone and impart hardness to
it; so that when they are entirely removed, the bone will retain
its original shape, but be quite soft and pliable. The time
during which the bones must be soaked in order to remove the
whole of the salts they contain, varies with their size ; but if
the bones be cut into small pieces, or thin bones such as ribs
are used, a dajr or two is sufficient. Wash them well with
water to remove the acid and dry them over the water bath.

(b) From Tendons. — After removing the mucin from tendons
by means of lime or baryta water {see § 45), wash the swollen
pieces first with water, and then with a little acetic acid much
diluted, so that they contract and do not again swell. Then
soak and wash them for a while in water, changing it several
times.

Characters. — When fresh, it is soft, but it shrinks and be-
comes hard when it is dried or alcohol is added to it.

Solubility. — 1. In cold water, it will not dissolve. 2. Boil
the water. It will dissolve and be converted into gelatin.
On cooling, it will form a jell}'. 3. In cold dilute acetic or
other acid, it will swell up. 4. In boiling dilute acids, it is
dissolved and converted into gelatin still more readily than
b}7 water. 5. In hot liquor potassae, it dissolves tolerably
easily.

47. Gelatin. — Preparation. — Boil collagen obtained from
bones or siuews in the manner already described. Filter the
solution hot. Divide the filtrate into three parts. Allow one
of them to cool; it will form a jelly. Evaporate another to

BY DR. LAUDER BRUNTON. 445

dryness on the water bath. Use the third for testing various
precipitants.

Solubility. — 1. Cold water. Dried gelatin will swell, bnt
will not dissolve. 2. Boil the water, it will dissolve. 3. Cold
dilute acids, and 4. Cold dilute alkalis, will dissolve it readily.

Precipitation. — It is precipitated by 1, tannic acid ; 2,
mercuric chloride. Unlike albumin, pure gelatin is not pre-
cipitated by, 1, acetic acid and ferrocyanide of potassium ; 2,
man}' metallic salts, as lead acetate, cupric or ferric sulphate.
It is not precipitated by acids or alkalis.

Alteration by Boiling. — Boil a solution of gelatin for some
time with an acid or alkali and let it cool. It will remain
fluid and will not form a jelly. Test its reactions. They will
be found the same as before. The same effect is produced by
prolonged boiling with water alone.

48. Elastic Tissue. — Elastin. — The elastic fibres which
occur in the connective tissue in various parts of the bod}",
and are especially abundant in the middle coats of the aorta
and large arteries, and in the ligamentum nuchas, and ligamenta
subjlava, are supposed to consist of elastin.

Preparation. — Remove the adhering cellular tissue from the
fresh ligamentum nuchee of an ox. Cut it into small pieces,
and boil it with alcohol and ether to remove the fat. Boil it
for 24 hours with water, to dissolve the collagen, renewing the
water as it evaporates, or preventing evaporation (see § 207).
Boil the residue with concentrated acetic acid for a consider-
able time ; remove the acetic acid by boiling with water, and
then boil with moderately dilute liquor soda? or potassre till it
begins to swell. Remove the alkali by boiling with dilute
acetic acid, then with water. Put the residue into cold hydro-
chloric acid ; let it remain for 24 hours, and then wash it with
water till the washings have no longer an acid reaction and
leave no residue on evaporation.

Characters. — The elastin which remains after the treatment
just described is yellowish and elastic while moist, but when
dry becomes hard and brittle.

Solubility. — 1. Put a piece of dry elastin in' water. It will
swell up but will not dissolve. 2. Boil the water. Unlike the
collagen of connective tissue, it will not dissolve. It does not
form gelatin, and the water will not gelatinize on cooling. 3.
It does not dissolve in alcohol, ether, or acetic acid, though it
swells in the latter. 4. Boil it with a strong solution of
caustic potash ; it will dissolve.

Precipitation. — Neutralize the solution in potash with hy-
drochloric or other acid. No precipitate will fall. Add tannin
to the neutral solution. A precipitate will be produced. No
other acids cause a precipitate.

Reactions. — 1. Xanthoprotein reaction. Put a piece of elas-

440 CHEMISTRY OF THE TISSUES.

tin in concentrated nitric acid, and let it stay some time. It
will swell up, then become yellow, and lastly form a mucilagi-
nous solution. Add ammonia, and it will become a deep
orange-red. 2. Millon's reaction. Test a piece of elastin with

Millon's reagent. It will become slightly red.

Decomposition. — On boiling elastin with concentrated sul-
phuric acid, it is decomposed and yields leucine, but no
tyrosine.

** 49. v Cartilage. — Chondrogen. — The intercellular sub-
stance of hyaline cartilage, and that which lies between the
fibres of fibrocartilage, consists mainly of chondrogen, so
named because it is dissolved b}' boiling in water and forms
chondrin.

Solubility. — Take a piece of costal cartilage of a sheep or ox
and test its solubilitj' in the following reagents : 1. Cold water.
It is insoluble. "When allowed to dry before it is put in water,
it swells up slightly. 2. In boiling water, it dissolves. On
cooling, it forms a jelly. 3. In acetic acid it is insoluble.
When dry, it swells very little in acetic acid.

50. Chondrin. — Preparation — Boil the costal cartilages or
trachea of a sheep or ox in water till the perichondrium strips
easily oft", Bemove the perichondrium. Cut up the cartilages
into very small pieces, and boil them with water for several
hours. If a Papin's digester is at hand, boil them in it under
a pressure of 2-3 atmospheres. Filter while hot. The fil-
trate will be strongly opalescent. Put part of it into a beaker
and allow it to cool. It will form a jelly. To the remainder
of the filtrate add acetic acid, and the chondrin will be pre-
cipitated.

Solubility. — Test the solubility of chondrin, using either
that precipitated b}r acetic acid, or the jelly which formed on
cooling, in the following reagents: 1. In cold water it is in-
soluble. Heat it, and it is dissolved. It is soluble in 2. Solu-
tions of alkaline salts, as sodium sulphate, and is easily solu-
ble in 3. Dilute mineral acids, 4. Liquor potassa?, and 5. Liquor
ammoniae. It is insoluble in G. Alcohol, and 7. Ether.

Precipitation. — Add to a warm solution of chondrin in
water, f 1. Acetic acid. It will be precipitated, f 2. Add to
this a little sodium chloride or sulphate. The precipitate will
redissolve. 3. Add sodium sulphate to a watery solution of
chondrin, and afterwards acetic acid. No precipitate will fall.
4. Dilute hydrochloric or other mineral acid. The chondrin is
precipitated and is dissolved by excess of acid. 5. Alum pre-
cipitates chondrin ; excess dissolves it. 6. Lead acetate, 7. Sil-
ver nitrate, 8. Chlorine water, all precipitate chondrin.

Effect of Boiling. — Boil a watery solution of chondrin for a
long time. Let it cool, and it will be found to have lost its

BY DR. LAUDER BRUNTON. 447

power of gelatinizing, but it will give the other reactions just
as before.

Decomjiosition of Ghondrin. — By boiling with concentrated
hydrochloric acid, chondrin is decomposed, and yields grape
sugar, and certain nitrogenous substances. The presence of
grape sugar may be tested by the reactions given in § 17
or § 155.

51. Distinctive Characters of Mucin, Chondrin,
Gelatin, and Albumin.

Mucin. — Precipitated by acetic acid, the precipitate is not
dissolved by sodium sulphate.

Chondrin. — Precipitated by acetic acid, the precipitate is
dissolved by sodium sulphate.

Gelatin. — Not precipitated by acetic acid, nor by acetic acid
and potassium ferrocyanide.

Albumin. — Dissolved by acetic acid, the solution is precipi-
tated b}' potassium ferrocyanide, or by the addition of
alkaline salts and heat.

Gelatin and Chondrin are most generally recognized by their
hot solutions forming a jelly on cooling ; but as they are both
deprived of this property by long boiling or boiling with acids,
this test is not always to be depended on.

** 52. Bone. — When bone is subjected to the action of
acids, the earthy salts are removed. The remainder, to which
the name ossein has been given, consists chiefly of gelatigenous
substance. The earthy salts are tribasic calcium, and magne-
sium phosphates, calcium carbonate, and small quantities of
calcium fluoride.

To remove the earthy salts, and leave the ossein, place a bone
for some time at a low temperature in very dilute hydrochloric
acid. When treated with warm dilute hydrochloric acid, bone
gives out CO., and is apt to separate into lamellae. The ossein
is soft, flexible, and elastic while moist, but becomes hard
when dry. It retains the form of the bone. In its chemical
characters it resembles the arelatisenous substance from con-
nective tissue.

To get the earthy salts, incinerate the bone, when the organic
substance will be consumed, and they will remain behind, mixed
with other salts formed during the combustion, for here as in
other cases the salts in the ash differ considerably from those
which exist in the tissue.

** 53. Adipose Tissue. — Fats. — Fats differ from each
other in appearance and consistence. Their general properties
may be conveniently studied in olive oil, for which cod liver oil
or train oil may be substituted, if an animal fat is desired.

8olubility^—F&tB are insoluble in 1. Water, and 2. Cold al-
cohol, f 3. Hot alcohol. Warm a test-tube containing oil
and alcohol over a spirit-lamp or Bunsen's burner. As the

448 CHEMISTRY OF THE TISSUES.

spirit becomes warm, part of the oil will be dissolved. Pour
off some of the clear alcoholic solution into another tube and
cool it. It will become milky from tin- deposition of oil. f 4.
Cold ether. Shake a little oil wit h ether and it will dissolve
readily. The test-tube containing the ether must not he
brought near a flame, as its vapor is readily inflammable. ;">.
Chloroform ; 6. Oil of turpentine, and other volatile oils, also
dissolve fat readily.

* JEmulaionizing of Fats. — Shake a little oil with a solution
of albumin in a test-tube. The oil will become finely divided,
and form a milky-looking fluid or emulsion. Put a drop of
this under the microscope, and it will be found to consist of
minute globules of fat. The globules in the emulsion unite
again and form large globules, but very slowly. Add a little
acetic acid to the emulsion and shake it. The globules will
unite much more quickly. Repeat the experiment with a solu-
tion of gelatin. This also will emulsionize the fat.

Reaction. — Wash a piece of lard in water and press a piece
of litmus paper against it, or melt it in a test-tube, and put a
drop of it or of olive oil on the paper. Its reaction will be
neutral.

Composition of Fats. — Fat consists of a triatomic radicle,
propenyl or glyceryl, combined with three atoms of a mona-
toinic fatty acid. The glyceryl may be displaced by inorganic
bases, such as potassium, lead, etc., and glyceryl hydrate, or
glyceryl alcohol (glycerin) is produced. The replacement of
glycerin by other basis is termed saponification.

Boil two and a half grammes of olive oil with one gramme
of very finely powdered lead oxide, and about fifty cubic centi-
metres of water in a beaker or evaporating dish for some
hours, stirring the mixture well to prevent the lead oxide from
falling to the bottom, and replacing the water as it evaporates.
The lead will combine with the fatty acid in the oil, forming a
slightly yellowish mass, and the glycerin will be set free. To
obtain the glycerin, filter the fluid ; pass sulphuretted l^drogen
through the filtrate, add a little animal charcoal to decolorize
it; let it stand for a while in a warm place ; filter and evapo-
rate the filtrate.

54. Glycerin. — Gl3"cerin is a S}*rup3- fluid, with a sweet
taste and a neutral reaction.

Solubility. — 1. With water, and, 2, with alcohol, it mixes
very readily. 3. With ether it does not.

Solvent Foiver — It dissolves many metallic oxides. Add a
little liquor potassae to a solution of copper sulphate or lead
acetate, a precipitate will fall. Add a little glycerin, and the
precipitate will redissolve.

It also acts to some extent as a solvent for fatty acids.

Decomposition. — Put a little glycerin, free from water, into

BY DR. LAUDER BRUNTON. 449

.1 test-tube, with glacial phosphoric acid or acid potassium
sulphate, aud heat. The glycerin will be decomposed, aud yield
water and acrolein or acrol, a body which has an extremely
unpleasant smell, and causes great irritation of the nose and
eyes.

Test for Glycerin. — As no other body yields acrolein when
decomposed in the way just mentioned, its formation serves as
a test for glycerin ; and as it is very pungent, small quantities
of glycerin can easil}' be detected.

55. Muscle. — For the structure of muscle, see Chap. IV.
Reaction. — Muscles which have been at rest have an amphi-

cromatic reaction ; i. e., they change red litmus to blue, and
also blue litmus to red. They do not alter the color of blue
litmus so much as that of red, and they are therefore alkaline.
Alteration in the Reaction by Contraction. — The reaction
changes to acid after contraction of the muscle or after death.
See Chap. XX., Obs. YI.

56. Composition of Muscle. — The Sarcolemma is
usually said to agree with elastic tissue in its characters, and
to yield no gelatin, but it has been recently stated to be solu-
ble, though slowly, in alkalies and acids, as well as in gastric
juice, and would thus more nearly resemble connective tissue.

51. Sarcous Elements. — Little is known regarding the
chemical composition of the sarcous elements, except that
they swell slightly, and lose their power of double refraction
when boiled or when heated with alkalies or very dilute acids.
Alcohol does not alter them.

f 58. Muscle Plasma. — When muscles are subjected to
pressure at 0° C, a fluid termed muscle plasma is obtained.
The plasma of muscles resembles the plasma of the blood, in
possessing the power of coagulating spontaneously, and sepa-
rating into a clot, and serum. To this clot, corresponding to
the fibrin of the blood, the name myosin has been given. Co-
agulation of the plasma causes the muscles to lose their elas-
ticity and become stiff and hard, and thus gives rise to rigor
mortis. After some time, decomposition sets in, and the mus-
cles again become soft and flexible. Muscle plasma is some-
what troublesome to obtain, as it coagulates too quickly in the
muscles of warm-blooded animals to allow of its preparation
from them, and the muscles of frogs, in which it coagulates
more slowly, are not always to be had in sufficient quantity.

Preparation. — Prepare a freezing mixture by mixing to-
gether equal parts of salt and snow, or pounded ice. Intro-
duce it into a large beaker, and plunge a platinum crucible or
small tin box into it. Fill another beaker with half per cent,
salt solution, and put it in a vessel containing snow or ice.
Prepare several frogs in the following manner: Open the thorax,
cut off the apex of the heart, push a canula up into the aortic
29

450 CHEMISTRY OF. THE TISSUES.

bulb, and inject a half percent, salt solution through it, in the
manner directed tor artificial circulation in Chap. XVI. § I-"'.
till the fluid which issues from the veins is quite colorless.
Cut away the muscles close to their attachments, and wash
them with half per cent, salt solution cooled to 0° C. When
washed, squeeze them tightly together into a ball, and tie them
up in a piece of thin linen ; put them into the crucible or tin
box. As the muscles of each frog are prepared add them to
those in the crucible, and let it remain in the freezing mixture
until they are all frozen quite hard. Take a sharp knife and
cool it in the freezing mixture; cut the frozen mass of muscle
into very thin slices; throw them into a mortar cooled in the
same way, and break them up small. Tie them up in a piece
of strong linen, and put them into a strong screw-press. As
the temperature of the muscle is gradually raised by the
warmth of the room to 0° C, the frozen plasma melts and
issues from the press. It must be collected in a vessel cooled
in ice, and filtered through paper moistened with cold half per
cent, salt solution, and collected in a cold beaker. The funnel
may be kept cold during filtration by placing it in a double cop-
per filtering stand of the form shown in fig. 336, but filled with
snow or pounded ice, instead of hot water. As the filters get
soon choked, they must be frequently renewed. The filtered
plasma is a slightly yellowish and opalescent, syrupy, but not
tenacious, fluid.

Reaction. — Its reaction is alkaline, like that of muscle.

Coagulation of Muscle Plasma. — Transfer a little plasma
from the beaker to cooled test-tubes and observe the following
facts : —

It will coagulate spontaneously when allowed to stand at
the temperature of the room, and form a gelatinous clot, which
will begin at the sides of the tube, and extend inwards.

B}' stirring, a coagulum is obtained, which is flocculent, and
not fibrous like the fibrine of blood.

Heat greatly accelerates its coagulation, and at 40° C. it
coagulates almost instantaneous^.

Cold water coagulates it at once, so that the plasma when
dropped into it, forms white elastic balls. Cold NaCl solution,
of fifteen per cent., also coagulates it, but a solution of five
per cent., does not. Dilute hydrochloric acid of ten per cent,
coagulates it at once, but dissolves the coagulum, and forms
syntonin almost immediately.

** 59. Examination of the Aqueous Extract of
Muscle. — In order to obtain an aqueous extract of muscle, a
dog must be killed by decapitation, and the blood removed
from the vessels of the lower extremities by artificial circula-
tion. For this purpose open the abdomen quickly, and insert
a canula iu the aorta. Inject ten per cent. NaCl solution into

BY DR. LAUDER BRUNTON. 451

it till the blood returns colorless by the vena cava. Cut off
some of the muscles of the thigh quicklj", and mince them up
small. This is best done by a sausage-making machine. Mix
the mass with distilled water, stir it up well, and let it stand
for a quarter of an hour. Filter it through linen, aiding its
filtration by pressure.

** 60. Albuminous Substances in Muscle. — Alkali
Albuminate. — The watery extract thus obtained contains
alkali albuminate. It is at first alkaline or neutral, but after-
wards becomes acid, and the alkali albuminate is then thrown
down as a flocculent precipitate. The source of the acid is
not known. If the extract has been made from muscle which
has already become acid, this precipitate will not fall.

To a portion of the extract add dilute hydrochloric, acetic,
or lactic acid very gradually. A flocculent precipitate will
fall.

Repeat the last experiment, using exactly the same quanti-
ties of extract and acid, but add a little sodium phosphate to
the extract before acidulating it. No precipitate will fall.
See § 15.

Albumins. — Besides alkali albuminate, the extract contains
two other albuminous substances, one of which coagulates at
45° C, the other at 75? C. Filter the fluid from which the
alkali albuminate has been precipitated either by the develop-
ment or the addition of acid. Put some in a test-tube and
warm it in a water bath to 45° C. A precipitate will form.
The coagulation is not affected at all by previously rendering
the liquid neutral or alkaline. Let the fluid stand till the
precipitate subsides, and then remove it by filtration, and
warm the filtrate to 70° C. A second coagulation will take
place.

** 61. Myosin. — Free the remainder of the muscles from
fascia, tendons, fat, nerves, and vessels, and cut them up small.
Put the mass of finely-divided muscle into five or six times
its weight of water and stir it well. Let it stand for several
hours and then strain it through a linen cloth, and express
the fluid with the aid of a screw-press. Treat the muscles a
second time with water in the same way, and strain and press
again. Unite all the fluids thus obtained and keep them for
examination. Wash the muscle, which remains on the linen,
with water, as before, till it becomes of a grayish color, and
the water is no longer colored.

Throw it into a mortar, and rub it up with ten per cent, salt
solution in sufficient quantity to prevent it from being too
thick and to allow it to flow tolerably easily. Let it stand for
several hours ; filter, first through linen, then through paper,
and add to the filtrate several pieces of rock salt. As the salt
dissolves, the myosin, which is insoluble in a concentrated NaC

452 CHEMISTRY OF THE TISSUES.

solution is precipitated in flocculi. If any salt remains undis-
solved after the myosin seems fully precipitated, remove it, and
then filter the solution. The myosin which contains a large
amount of NaCl remains on the filter. In order to free it from
this, dry it as well as possible by pressing it between folds of
filtering paper ; dissolve it in a little water, and throw the solu-
tion into a large beaker full of water, when it will again be pre-
cipitated. Let it stand for a day, pour off the clear fluid as well
as possible, and then collect the precipitate on a filter. After
the greater part of the water has passed through the filter, but
while the precipitate is still moist, remove it into a beaker, as
it cannot be separated from the filter after it becomes dry.

Solubility. — Test the solubility of the moist myosin in the
following reagents : f 1. Ten per cent. NaCl solution. The
myosin will dissolve. Put some sodium chloride in substance
into the solution. As it dissolves, and the solution becomes
saturated, the myosin will be precipitated. It is soluble in 2.
Solution of sodium sulphate or other neutral salt ; 3. Very
dilute liquor potassa? ; and 4. Very dilute h}-drochloric acid.

Action of Acids and Alkalies. — Dilute acid and alkalies dis-
solve myosin, as has just been seen. At first it is simply dis-
solved, but is very soon converted into acid albumin or alkali
albuminate. Divide the solutions of myosin in dilute liquor
potassoe and dilute lrydrochloric acid just made, into two por-
tions, add salt solution immediately to one portion of each, put
in a drop of litmus, and neutralize both. No precipitate will
fall, for the myosin being unchanged is soluble in the salt solu-
tion. Let the other portions stand for ten minutes, and then
treat them in the same way. A precipitate will fall on neutral-
izing them, for the myosin, being now converted into alkali al-
buminate and syntonin, is no longer soluble in NaCl solution.

Coagulation of Myosin. — 1. Boil a NaCl solution of myosin ;
it will coagidate. 2. Add alcohol to its NaCl solution, and a
similar coagulum will form.

Effect of Drying. — Dried myosin is tough and difficult to
powder, and almost insoluble in NaCl solution.

** 62. Extractive Matters in Muscle.— The cold
watery extract of muscle contains, beside the albuminous mat-
ters, creatine, creatinine, hypoxanthine (sarkin), xanthine, uric
acid, inosic acid (apparently not always present), glucose, ino-
site, salts of lactic acid, and volatile fatty acids and acid phos-
phates of the alkalies. Unless a large quantity of muscle can
be got, it will be better to use Liebig's extract for the prepara-
tion of these substances. Put the wateiy extract of muscle in
a tin kettle; heat it quickly to boiling, so as to coagulate the
albumin. Filter it through a linen cloth. Let the filtrate be-
come quite cool, and add acetate of lead to it as long as a pre-
cipitate is formed. Excess of lead must be avoided as much as

BY DR. LAUDER BRUNTON. - 453

possible. Collect the precipitate on a filter, and keep it for after
examination. . ...... (a)

63. Creatine. — Precipitate any lead present in the filtrate
b}' hydrogen sulphide : filter ; evaporate the filtrate to a thin
syrup on the water-bath. Put it in a cool place for several
daj's, and the creatine will separate in short colorless crystals.
Let it stand till no more crystals are deposited ; pour off the
mother liquor from the crystals, and add to it two or three times
its volume of alcohol of 88 per cent., so as to cause the sus-
pended creatine to be deposited. Filter it, and wash the crys-
tals with a little alcohol. Wash off the crystals which still re-
main on the evaporating dish with the alcohol which drops
from the filter, throw them also on the filter, and wash them
with a little alcohol. Collect the filtrates, mix them and put
them aside. ......... (b)

Dissolve the ciystals in a little boiling water, and allow the
solution to cool, when the creatine will crystallize out in color-
less transparent and lustrous oblique rhombic prisms, which,
when gently heated on a piece of platinum foil, lose water of
crystallization, and become dull and whitish.

Solubility. — Creatine is sparingly soluble in cold water ;
easiby soluble in boiling water ; almost insoluble in strong alco-
hol ; insoluble in ether.

Reaction. — The solution in hot water has a neutral reaction,
and bitter taste.

Test. — Creatine has no very characteristic reactions, and it
is best recognized by converting it into creatinine. If it is
pure, no precipitate will fall on the addition of zinc chloride to
its solutions, but if mixed with creatinine a precipitate will be
produced.

Decomposition. — When it is boiled for a considerable time
with caustic baryta, creatinine decomposes into urea and sar-
cosin. If the boiling is continued still longer, the urea decom-
poses into carbonic acid and ammonia. This reaction is very
interesting as indicating one source of urea in the body. When
boiled with water for a long time or with acids, it loses water
and is converted into creatinine.

64. Creatinine. — Boil creatine for half an hour with dilute
hydrochloric acid ; neutralize with h}*drated lead oxide ; filter ;
evaporate the filtrate to dryness on the water-bath. Extract
the residue with alcohol, and evaporate the extract. The crea-
tinine will crystallize in colorless lustrous prisms, which, when
heated on platinum foil, do not dry like creatine.

Solubility. — It is soluble in water, especially when hot. Un-
like creatine, it is soluble in hot alcohol.

Reaction. — Test the watery solution with litmus or turmeric
paper ; it will be found strongly alkaline. It has a taste like
dilute ammonia.

454 CHEMISTRY OF THE TISSUES.

Characters. — Creatinine nets like a strong alkali, and forms
double salts with metals. Themosl importanl is its compound
with zinc chloride. Add to an alcoholic or not very dilute
watery solution of creatine, a concentrated Byrupy solution of
zinc chloride free from hydrochloric acid ; a precipitate of
warty granules will fall at once if the solution is concentrated :
but if dilute, groups of needles will slowly form. The granules
are seen under the microscope to consist of radiating groups
of fine needles. They are very sparingly soluble in cold water ;
more so in hot ; insoluble in alcohol ; but very soluble in mine-
ral acids.

This test is sufficient to distinguish creatinine. It is fur-
ther precipitated by silver nitrate, by mercuric chloride, and
by mercuric nitrate with the gradual addition of sodium carbo-
nate.

65. Sarkin (Hypoxanthine). — Evaporate the alcohol
from the filtrate (b) upon the water-bath ; dilute it with water ;
render it alkaline by ammonia, and then add an ainmoniacal
solution of silver nitrate. Sarkin will be precipitated. Let the
flocculcnt precipitate subside ; wash it several times by decan-
tation with water containing ammonia; throw it on a smooth
porous filter, and wash it thoroughly ; push a glass rod through
the bottom of the filter, and wash the precipitate with nitric
acid of 1.100 sp. gr. into a small Bask. Heat it to boiling, and
add more nitric acid till the whole is dissolved. The fluid
should be kept nearly boiling. Sometimes a few flakes of
silver chloride remain undissolved. Decant the liquid from
them into a beaker, and let it stand for six hours. A double
nitrate of silver and hypoxanthine will crystallize out.

Decant the liquid (c) from the crystals and preserve it for
the preparation of xanthine. Wash them with an ammoniacal
solution of silver nitrate to remove the free acid. Suspend them
in water, and pass hydrogen sulphide through it. Filter from
the silver sulphide, and evaporate the filtrate. The hypoxan-
thine will crj-stallize out.

In its reactions it resembles xanthine, but differs from it in
being precipitated by silver nitrate.

66. Xanthine. — To the mother liquor (c) of the hypoxan-
thine add ammonia in excess. A flocculent precipitate of nitrate
of silver and xanthine will fall. Wash it by decantation ; sus-
pend it in boiling water, and decompose it by hydrogen sul-
phide. Filter and evaporate. The xanthine will separate as a
scaly film.

I'ests. — Put a little xanthine in ammonia. It will dissolve.
Add a little nitric acid to a portion of xanthine in a porcelain
capsule; evaporate to dryness. A yellow residue will remain.
Add a drop of caustic soda to it, and it will become red. Heat
it, and the color will change to purple red.

BY DR. LAUDER BRUNTON. 455

Put liquor soda? in a watch-glass with a little chloride of
lime ; stir it, and introduce a portion of xanthine. A ring will
form round it, at first dark green, but soon becoming brown,
and then disappearing.

67. Uric Acid. — Suspend the lead precipitate (a) in water ;
decompose it complete^ by hydrogen-sulphide ; filter; concen-
trate the filtrate in a water-bath. Uric acid will separate gradu-
ally.

Filter, and set the filtrate aside (d). Wash the crystals on
the filter with a little water and then with alcohol. If desired,
they may be further purified by dissolving them in a little
liquor sodae, precipitating by ammonium chloride ; filtering and
decomposing by dilute hj-drochlorie acid.

Jfurexide Test. — Put a small portion of uric acid on a watch-
glass, with one or two drops of nitric acid, and evaporate to
dryness at a moderate temperature. A yellow residue will re-
main, which becomes red when quite dry. Put a drop of am-
monia on the side of the glass, and let it run gently down to
the uric acid, which will then become of a beautiful purple. If
a drop of liquor potassre or liquor sodas is used instead of am-
monia, a bluish-violet color will be produced.

Inosite. — Evaporate the filtrate (d) till a permanent tur-
bid it}r is produced by the addition of alcohol. Then add its
own volume of alcohol to it and warm it, when the turbidity
will disappeai*. Set it aside for several days. Inosite ma}'
then crystallize out. If it does not, add ether ; and if still no
crystals form, evaporate almost to dryness ; add a little nitric
acid, evaporate to dryness; moisten it with calcium chloride,
and evaporate to dryness again. If inosite is present, a rosy
red spot will remain.

If crystals have been formed, dissolve some in water, in which
they are easily soluble, and apply the same test.

68. Brain. — The brain contains cholesterin, lecithin, and
cerebrin, besides albuminous substances, which chiefly form the
axis cylinders, and are insoluble in water. Cerebrin probably
belongs to the white substance of nerves.

The specific gravity of the brain may be ascertained in the
manner directed in A pp. § 210, and the amount of water it
contains by weighing it, drying it in a hot chamber, or over
sulphuric acid, and estimating the loss. To separate the sub-
stances contained in the brain, remove the membranes and ves-
sels as much as possible from it, wash its surface with water,
and rub it to a paste in a mortar. Mix it with great excess of
alcohol, and let it stand for several days, stirring it frequently.
Separate the alcohol by filtration, and set it aside for the pre-
paration of lecithin. ....... (a)

Knit up the brain again, and extract it with large quantities
Of ether, as long as they take up much lecithin or cholesterin.

456 CHEMISTRY OF THE TISSUES.

This is known by evaporating a small quantity of the ether
each time it is taken from the brain. Put the ether aside ; ex-
tract the brain with hot alcohol several times, and filter it hot.
On cooling, cerebrin will crystallize out, mixed with lecithin.

69. Cerebrin. — Purification. — Filter off the alcohol from
the crystals, wash them with cold ether, and boil them for an
hour with baryta water. Pass C0.2 through the liquid to pre-
cipitate the excess of baryta ; filter, and wash the precipitate
first with cold water and then with cold alcohol. Put the pre-
cipitate in a beaker with alcohol and heat it, to extract the
cerebrin from it, and filter it hot. On cooling, crystals of
cerebrin will be deposited, which should be again dissolved in
hot alcohol, allowed to crystallize out again, washed with ether,
and dried at a moderate temperature.

Cerebrin forms a white hygroscopic powder. Put a little on
a piece of platinum foil and heat it. It will become brown,
melt, and then burn.

From the mode of preparation, it is evident that it is inso-
luble in cold but soluble in hot alcohol, and that it is not de-
stroyed by boiling with baryta water.

Put it in water. It will slowly swell up, somewhat like
starch.

70. Lecithin. — Add to the alcoholic extract (a) a solution
of platinum chloride, acidified with hydrochloric acid. A }'el-
low flocculent precipitate of lecithin platinum chloride will
fall. Filter, and dissolve the precipitate in ether ; pass hydro-
gen sulphide through the solution to precipitate the platinum.
Filter and evaporate. Lecithin chloride will remain a waxy
mass.

Decomposition. — When treated with acids or with boiling
baryta water it is decomposed, and yields glycerophosphoric
acid, neurin, and fatty acids.

Dissolve some lecithin chloride in alcohol and pour it into
boiling baryta water. It will be decomposed, and a smeary
precipitate will fall.

71. Neurin. — Filter ; pass CO., through the filtrate to re-
move the baryta ; filter ; evaporate to dryness ; extract with
alcohol. Add to the alcoholic extract platinum chloride, and
a precipitate of neurin platinum chloride will fall. The pla-
tinum may be removed by hydrogen sulphide and the neurin
chloride obtained, but it is with difficulty crystallizable.

BY DR. LAUDER BRUNTON. 457

CHAPTER XXXVII.

DIGESTION.

Section I. — Saliva and its Secketions.

72. Mode of obtaining Mixed Saliva. — To obtain a
sufficient quantity of human saliva for examination, the secre-
tion of the salivary glands must be stimulated artificially.
For this purpose anj7 of the mechanical or chemical stimuli to
be mentioned in § 85 may be used. To avoid the risk of the
saliva becoming altered by mixture with the substance used
to quicken its secretion, the mechanical stimuli should be pre-
ferred. There is no objection, however, to the employment of
ether vapor.

** 73. Examination of Mixed Saliva — Appearance. —
Saliva is transparent or opalescent. It sometimes deposits a
white precipitate almost immediately after it has been col-
lected. When poured from one vessel to another, it is seen
to be more or less viscid, in consequence of which it is gen-
erally filled with air-bubbles. If none are present, they are
readily produced by blowing into the liquid through a
narrow glass tube, when it is seen that they take a long time
to subside. If the saliva is allowed to stand long, a thin pelli-
cle of carbonate of lime forms on its surface. Microscopical
Examination. — Saliva contains numerous air-bubbles, paAre-
ment epithelium cells from the mouth, and round cells (sali-
vary corpuscles) resembling tyrnph corpuscles, within which
are numerous granules in constant movement.

** 74. Determination of the Amount of Water and
of Solids. — Take a small porcelain crucible with a lid, dry it
in an air-bath at 100° C, put it under a bell-jar over a dish
containing strong sulphuric acid till it is quite cool, then
weigh it immediately and note its weight carefully. After
weighing it, replace it in the air-bath for another hour, cool it
and weigh it again as before. If the weight is less the second
time than the first, the process must be repeated till no further
loss of weight occurs. Introduce some saliva into it and
Weigh again. The amount of saliva used is ascertained by de-
ducting the weight of the crucible alone from the weight of
the crucible and its contents, thus : —

458 DIGESTION.

Wright of crucible and saliva 33.562 grm.
Weight of crucible alone 23.296 grin.

10.2GG = weight of saliva used.

Evaporate the saliva to dryness either in the air-bath or over
a water-bath, but finish the desiccation in the air-bath. Cool
and weigh the crucible as before. The amount of solid residue
is determined in the same way as that of the saliva itself,
thus : —

Weight of crucible and dried residue 23.342 grm.
"Weight of crucible alone 23.200 grin.

Difference .046 grm. = weight

of residue.

The amount of water is found by subtracting the weight of
the solid residue from that of the saliva used, thus : —

Weight of saliva used 10.266

"Weight of solid residue .046

10.220 weight of water.

10.220 x 100 nft . ,
Hence percentage of water = •— = yy.O and

7> -,.-,., 0.046 x 100 n ..

Percentage of solid residue = — . =0.44

10.266

* 75. Qualitative Investigation of Inorganic Con-
stituents.— For this purpose the saliva must be filtered so
as to separate the epithelium and mucus. It contains carbo-
nates, chlorides, phosphates and sulphates of potassium,
sodium, calcium, and magnesium, and in most cases also
potassium sulphocyanide. The presence of these several salts
may be demonstrated as follows : Carbonates. — If a drop of
saliva is placed on an object-glass and covered in the usual
way, and a drop of acetic acid added, bubbles of gas will be
seen to form under the cover-glass. Chlorides. — The saliva
is acidulated strongly with nitric acid, after which solution of
silver nitrate is added ; the precipitate formed is insoluble in
excess of acid, but dissolves readily in ammonia. Sulphates.
— The turbidity produced b}r solution of barium, chloride, or
nitrate does not disappear when nitric acid is added, and the
liquid is boiled. Potassium. — If a little saliva is gently evapo-
rated on a platinum wire and then heated in the flame of a
Bunsen's lamp, the flame seen through blue glass exhibits a
violet color. Sodium. — Without the glass it presents the well-
known yellow color due to the presence of sodium. Calcium
may be precipitated as oxalate by the addition of ammonium
oxalate. Magnesium as ainmoniaco-magnesian phosphate. To
obtain the latter, ammonium chloride, and ammonia must first

BY DR. LAUDER BRUNTON. 459

be added, then sodium phosphate. Potassium Sulphocyanide.
— This is generally, though not invariably, present in mixed
saliva. It is derived from the saliva secreted b}^ the parotid
gland, and is not contained in that of the submaxillary gland.
To show its presence, add a drop of solution of perchloride of
iron, so very dilute as to be almost colorless, to a little saliva,
in a porcelain crucible or capsule, and stir it. A reddish color
is developed, which remains unchanged after the addition of
hydrochloric acid, but is at once removed by a solution of cor-
rosive sublimate. Perchloride of iron gives a similar color
with acetic acid and with meconic acid, but the color produced
in the former case is destnryed by h3'drochloric acid and in
the latter by mercuric chloride. When undiluted perchloride
of iron is used, the color is deep red, and ma}' be shown to
persons at a little distance. If the test does not at first suc-
ceed, the saliva should be evaporated to one-third of its bulk,
and the test then applied.

To determine the percentage of inorganic salts, the dry resi-
due must be incinerated (see § 214), weighed, and calculated,
as in § 74.

* 76. Organic Constituents. — These are albumin, mucin,
ptyalin. Albumin. — If saliva is strongl}' acidified with nitric
acid, it becomes turbid, but no precipitate is formed. On then
boiling it becomes clearer, and the color changes to yellow ;
the addition of ammonia changes the yellow to orange-red.
If to another portion a mixture of acetic acid and potassium
ferrocyanide is added, a white precipitate is produced. Saliva
contains two albuminous bodies — albumin proper dissolved in
salts, and globulin. Globulin is precipitated from dilute solu-
tions by CO,,, ordinary albumin is not. To separate them, a
stream of carbonic acid gas must be passed through saliva, di-
luted with a large quantity of water, for some time. A very
fine flocculent precipitate is formed, which tends to disappear
when the turbid liquid is agitated with air. After the precipi-
tate has settled, the liquid may be decanted off with a syphon,
and, if needful, filtered ; it can then be proved to contain albu-
min by the addition of acetic acid and ferrocyanide of potas-
sium. This process requires considerable care. Mucin. — To
this body is due the stickiness and tenacity of saliva. If acetic
acid is gradually added to saliva while it is stirred with a
glass rod, it becomes more and more tenacious, and finally the
mucin separates in white stringy flakes ; these must be washed
with water and acetic acid, and tested by the reactions given
in § 45.

** 77. Action of Saliva on Starch Paste. — Saliva con-
verts starch into sugar. To show this, prepare some thin
mucilage by rubbing up a little starch with cold water into a
smooth paste and pouring a large quantity of boiling water

460 DIGESTION.

over it (one grain of starch to one hundred centimetres of
water), or by boiling it in a flask or large test-tube, and then
allowing it to cool. Filter the saliva to be used, and distribute
it in three test-tubes, introducing into the first, starch mucilage
alone — into the second, saliva — and into the third, saliva with
about three times its bulk of starch paste. Mix them well
together by agitation. Then put all three for a few minutes
into a water-bath at 40° C, or warm them gently over a spirit-
lamp. Add to each of them liquor potassee in excess, and a
drop or two of solution of cupric sulphate. In the first and
second, a light blue precipitate will be thrown down, and the
liquid will remain colorless ; but in the third, the precipitate
just formed will be redissolved, and give a blue solution. If
now the liquids are boiled, the precipitate in the first tube,
containing starch paste, alone will be blackened, but the liquid
will remain colorless. In the second, containing saliva, the
precipitate will be partly dissolved, and give to the fluid a
violet color, due to albumin in the saliva, § 12. In the third,
a yellow or orange precipitate will be formed. This reaction,
which is known as Trommer's test, shows that there is no
sugar either in the saliva or starch used, but that it is formed
by the action of the one on the other. Rapidity of concertina
of starch into sugar. — Bidder and Schmidt erroneousl}- con-
sidered that the conversion of starch into sugar was almost
instantaneous. To illustrate this view, introduce saliva into a
small beaker. Place it in a water-bath at 40° C, and when it
is warmed through, let a little dilute starch mucilage, colored
with iodine, fall into it drop by drop. As each drop falls it
becomes decolorized. The disappearance of the blue color is
not dependent on the conversion of starch into sugar, but on
the conversion of the iodine into hydriodic acid. Other or-
ganic fluids, such as the urine of dogs, according to Schiff, ex-
hibit the same reaction, which is probably due to their con-
taining deoxidizing substances, for the same effect is produced
by sulphurous acid or morphia, both of which absorb oxygen
readily. This ma}r be shown by putting starch mucilage
colored with a little iodine into a test-tube and diluting it till
it forms a clear blue transparent solution. If it is now placed
in the warm bath at 40° C., it will remain unaltered, but will
at once lose its color on the addition of either of the reducing
agents above mentioned.

* 78. Effect of Temperature on the Diastatic Action
of Saliva. — Take four test-tubes, and carefully introduce a
little saliva into each with a pipette. Put the first into a mix-
ture of snow or ice and salt, the second into a test-tube rack
on the table, the third into a water-bath at 40° C. ; boil the
fourth briskly for two or three minutes, and then allow it to
cool. Theii add starch paste to each of them, and allow them

BY DR. LAUDER BRUXTOX. 461

lo remain where they are for five or ten minutes. Take a part
of the fluid from each, and test it for sugar, either by Trom-
mer's or Moore's tests. (See § 155.) Xone will be found in
the first or fourth, a little in the second, and more in the third.
Thus we learn that saliva does not act, or acts very slowly, at
the freezing point, that it acts at the temperature of the air, and
still more quickly at the temperature of the body. Now place
the first and fourth test-tubes in the water-bath at 40 C, allow
them to remain for several minutes, and test again for sugar.
It will be found in the first but not in the fourth. This shows
that the power of saliva to transform starch into sugar, is
merely suspended by exposure to a very low temperature, but
is totally destroyed b}- boiling.

* 79. Influence of Acids and Alkalies on the Dias-
tatic Action of Saliva. — Dilute acids do not arrest the
action of saliva upon starch ; stronger acids do so for a time,
but when they are neutralized the action again goes on.

Take three test-tubes, and put into each equal parts of
saliva and starch paste. Add to the first its own bulk of
water, to the second a similar proportion of distilled water,
containing 0.65 per cent, of commercial hydrochloric acid, and
to the third the same quantity of dilute acid of 10 per cent.,
and keep them for five minutes at 40° C. Add liquor potassae
to the first and second, and test for sugar. It will be found
in nearly equal quantity in both. Take part of the fluid in
the third tube, and test it for sugar. Xone will be found.
Neutralize the remainder with .carbonate of potash, carefully
avoiding excess, and replace the test-tube in the water-bath
for a little while. On again testing it, sugar will be found to
be present. — As the greater part of the starch we eat is uot
transformed into sugar in the mouth, but is swallowed un-
changed, it is important for us to know whether the trans-
formation goes on in the stomach or whether it is arrested by
the acid gastric juice. The strength of the dilute acid just
employed (0.2 of real hydrochloric acid) is nearly the same
as that of the gastric juice, and the experiment shows that in
the healthy stomach the conversion of starch into sugar may
go on rapidly. In some pathological conditions the acidity
of the gastric juice is abnormally increased, and the action of
the saliva may be suspended so long as the food remains in
the stomach, but when the acid is neutralized by the intestinal
secretion, the action will go on again.

Alkalies. — Caustic potash and soda, when added to the
saliva in excess, put a stop to its action on starch, and its
diastatic power is not restored by neutralization. Its action
is suspended by sodium and potassium carbonates, ammonia
and lime-water, but restored by neutralization. Put saliva in
two test-tubes and add to one several drops of liquor potassie.

4G2 DIGESTION.

and to the other a few drops of a solution of potassium car-
bonate, mix a little starch mucilage with both, and let them
stand in a water-bath at 40° C. for half an hour. Test a small
portion of the liquid from both tubes, and having ascertained
that neither contains sugar, put a drop of litmus solution in
each, and neutralize with dilute hydrochloric acid. After both
have stood for another half hour, sugar will be found in the
one to which the carbonate was added, but not in the other.

* 80. Action of Saliva on Raw Starch. — As has been
seen, the saliva rapidly converts starch mucilage into sugar,
but it does not act so quickly on raw starch. The starch
granules consist of a number of layers arranged in an eccentric
manner round a point called the hilum. These laj'ers consist
alternately of two substances which have been termed respec-
tively, starch-cellulose and starch-gran ulose. The latter is
colored blue by iodine alone ; the former is not colored unless
the granules have been previously acted on by sulphuric acid
or zinc chloride. When starch is digested with saliva, the
granulose onty is dissolved, and although the starch granules
still retain their form, they are no longer colored blue by
iodine.

To show this, potato starch must be mixed with saliva, and
subjected for two or three days to a temperature of 35° C.
The saliva used must be decanted off, and a fresh quantity
added every two or three hours. The starch is prepared for
the purpose by placing a quantity of the pulp obtained by
scraping the cut surface of a raw potato on a bit of calico
stretched over the mouth of a beaker, and theu washing it
with a gentle stream of water. The starch granules pass
through into the beaker, leaving a fibrous residue on the
calico.

81. Artificial Saliva.— As ptyalin is present, ready
formed, in the salivary glands, a fluid which, like saliva, will
convert starch into sugar, can be obtained by making an infu-
sion of the glands.

Take the salivary glands of an ox, sheep, rabbit, or guinea-
pig. Remove the cellular tissue from them, chop them up fine,
and let them stand with a little water upon them for several
hours. Strain through muslin and filter. The filtrate may
be used instead of saliva for the experiments already described.

* 82. Preparation of Ptyalin from the Salivary
Glands. — Ptyalin may be separated from the infusion of the
glands in the same manner as from saliva, but as it dissolves
very readily in glycerin, it is much more advantageous to ex-
tract it by that agent. For this purpose prepare the salivary
glands of an ox or sheep, as above directed. Place the well-
minced gland in a flask, and cover it with absolute alcohol.
Cork the mouth of the flask, and let it stand for twenty-four

BY LR. LAUDER BRUNTON. 463

hours. Then, having poured off the liquid, squeeze the re-
mainder in a cloth, so as to get rid of as much of the alcoholic
extract as possible. The cake so obtained must now be mixed
with as much glycerin as will cover it in a beaker, and allowed
to remain for several days, during which the mixture may be
occasionally stirred. At the end of this period, the whole
must be strained through muslin, and then filtered through
paper. In the filtrate, ptyalin is precipitated by the addition
of alcohol in excess. The precipitate, after having been col-
lected by subsidence and decantation, must be dried over sul-
phuric acid.

83. Separation of Ptyalin from Saliva. — The method
emploj-ed for separating ptyalin as well as other ferments from
the secretions in which they are contained, depends on the fact
that when a copious precipitate is produced in the fluid, the fer-
ment adheres to the particles of the precipitate, and is carried
down along with them. It does not, however, adhere very
closely to the precipitate, and can readily be washed off. The
precipitate employed to carry down ptj'alin is calcium phos-
phate. This carries down with it not onty the ptyalin, but
also the albumin in the saliva. The albumin, however, adheres
more closel}T than the ptyalin to the precipitate, so that the
ptyalin is dissolved away by the first wash -water, while the
albumin remains adherent. Collect a considerable quantity of
saliva by filling the mouth with ether; while fresh, acidify it
strongly with phosphoric acid, so that the precipitate to be pro-
duced may be voluminous; then add milk of lime till the fluid
has a faintly alkaline reaction, and filter. When the fluid has
drained from the precipitate, remove the latter into a fresh
beaker, add to it a little water, not exceeding in amount the
saliva originally employed, stir it well and filter again. Add
to the filtrate an excess of alcohol. After some time a fine
white flocculent precipitate will separate, which must be col-
lected in a filter and dried over sulphuric acid. It then forms
a snow-white powder, and consists of pt3'alin mixed with some
inorganic salts. To obtain it free from ash, dissolve it in water,
and precipitate it again by absolute alcohol. Pour off the alco-
hol, dissolve again in water, and precipitate again. Repeat this
several times, collect the precipitate on a filter, wash with dilute
alcohol, and then with a little water, and finally dry it at a low
temperature, under a bell-jar over sulphuric acid.

* 84. Properties of Ptyalin. — The reactions of ptyalin
may be examined either in the filtered aqueous solution of the
calcium phosphate precipitate, or in solutions of pure ptyalin.
Ptyalin differs entirely from albumin in its reactions.

1. Add nitric acid; there is no precipitate. Boil the liquid,
allow it to cool, and add ammonia. No yellow color is produced.

2. Add to several portions in test-tubes, mercuric chloride;

4G4 DIGESTION.

tannic acid ; acetic acid and solution of potassium ferrocyanide ;
platinum chloride; solution ofiodine. No precipitate appears
in any case, but the iodine produces a yellow color.

3. Add lead acetate, and to another quantity basic lead ace-
tate. In both cases a precipitate is formed after a time, and on
filtration it is found that the filtrate is without action on starch,
the ptyalin having been carried down with the precipitate.

4. Add liquor potassaiand cupric sulphate. No reduction of
the copper oxide occurs.

** 85 Secretion of Saliva. — The secretion of saliva goes
on very slowly or ceases entirely when the glands are not under
the influence of some stimulus. The stimulus may be either
mechanical, chemical, electrical, or mental. The student may
estimate the effect of different stimuli by experiments on him-
self, thus : Swallow all the saliva contained in the mouth, so as
to empty it completely. At the end of two minutes spit out
the saliva which has collected in the mouth into a small beaker
previously counterpoised (see § 215) and weigh it. Again
empty the mouth, apply the stimulus and collect the saliva
for two minutes more, and weigh as before. B}' the comparison
of the two, the action of the stimulus may be judged of. The
best modes of stimulation are the following: —

1. Mechanical Roll a pebble or glass stopper in the mouth,

and attempt to chew it.

2. Chemical. — Touch the tongue (1) with a crystal of tartaric
or citric acid, or (2) of sodium carbonate; (3), fill the mouth
with ether vapor, allowing it to pass back into the pharynx,
and retaining it for some time in the mouth.

3. Electrical. — Touch the tongue and inside of the cheeks
with the electrodes of Du Bois Reymond's induction coil.

The effect which a stimulus applied to the mouth produces
in man, on the secretion from the parotid and submaxillary
glands, may be studied with greater precision by means of a
canula or syringe. If a syringe is used, its nozzle must end in
a funnel-shaped dilatation. This is applied to the papilla at
the orifice of Wharton's or Stenson's ducts, and gentle traction
made upon the piston. A stimulus may be applied to the
mouth, and the rate at which the saliva flows afterwards ob-
served. It is, however, more satisfactoiy to use a canula, which,
with a little practice, can be introduced into the ducts with
great ease.

*86. Mode of Collecting the Secretions of the Sali-
vary Glands unmixed in Man. — Insertion of a Canula
into the Submaxillary Duct. — Draw out a narrow glass tube to
a fine point, and at the place where it seems small enough to
enter the orifice of the duct, notch it with a triangular file,
break it off, round the edges at the border of a glass flame and
allow it to cool. To insert a canula thus prepared into his own

BY DR. LAUDER BRUNTON. 465

submaxillar}' duct, the student must now place himself before a
mirror, with a bright light directed into the mouth. Fill the
mouth with vapor of ether, or chew a piece of pyrethrum. Turn
the end of the tongue back against the palate. At the root of
the frsenum linguae a papilla with a little black dot is seen at
each side of the middle line. From these two dots, which mark
the orifices of Wharton's ducts, the saliva will be seen to issue.
Insert the end of the canula into one of them, and hold it
steadily in its place. The entrance of the canula is attended
with an unpleasant sensation, not amounting to pain. At first
the canula fills pretty rapidly, but as the effect of the ether
passes off, the flow soon diminishes. If it is desired to collect
the secretion, a piece of India-rubber tubing must be attached
vto the wider end of the canula before inserting it.

Insertion of a Canula into the Parotid Duct. — As it is
hardly possible to insert a canula into one's own parotid duct,
a second person must be employed, who should sit opposite a
good light and chew pyrethrum root as before. The method
is as follows: Draw one angle of the mouth outwards and
forwards so as to stretch the cheek. Opposite the second
molar tooth of the upper jaw the small papilla is seen which
marks the orifice of Stenson's duct. Insert the canula and
hold it steadily but carefully in its place, then a third person
may blow into the mouth some vapor of ether, or introduce a
little diluted tincture of pyrethrum.

By these methods a sufficient quantity of secretion can be
collected for the investigation of the leading properties of the
two secretions. Both possess the property of determining the
transformation of starch and sugar.

87. Study of the Secretions of the Salivary Glands
in Rabbits. — The ducts of the salivary glands in rabbits
are too small to allow of the easy introduction of a canula,
but the secretion may be readily studied by cutting the duct
across. The saliva escapes from the cut end and collects in
drops. When the secretion is slight, it may be rendered readily
visible by putting over the end of the duct a piece of bibulous
paper reddened with litmus. The saliva is absorbed by the
paper, and produces a blue spot, which increases in size, more
or less rapidly, according to the rate of secretion.

* Parotid Gland. — The duct runs from behind forwards
across the masseter muscle about its middle, covered by fascia.
It lias branches of the facial nerve on each side of it, and is
parallel with the transverse facial artery. At the anterior
edge of the masseter it takes a direction towards the middle
line, in order to enter the mouth.

If a vertical incision is made in a line with the cornea
through the skin and fascia of the cheek down to the masseter,
30

466 DIGESTION.

the facial nerves and transverse facial artery are cut across as
well as the duct.

As soon as the bleeding has ceased, the discharge of saliva
from the cut end may be investigated in the manner directed
in § 90.

88. Investigation of the Secretions of the Salivary
Glands in the Dog. Permanent Salivary Fistulae. —
Permanent fistulae may he made either with or without insert-
ing a canula in the duct. In the method to be described, that
of Sch iff, no canula is used. Permanent Submaxillary Fis-
tula.— The animal having been placed on the table, and its
head secured with the aid of Bernard's holder, it is put under
the influence of chloroform.1 Shave the hair from the under
surface of the lower jaw. Make an incision akuig the inner
border of the ramus of the lower jaw, extending forwards
from the anterior margin of the digastric muscle, and dividing
the skin and platj-sma. Secure every vein that presents it-
self with two ligatures, and divide it between them. Divide
the mylohyoid muscle cautiously. Underneath it will be found
the submaxillary and sublingual ducts, which run side by side,
the submaxillary being somewhat larger and nearer the ramus
of the jaw. Isolate the duct and divide it as near as possible
to its entrance into the mouth. Close the wound with sutures,
leaving the end of the duct projecting. To prevent its retrac-
tion, pass a suture through it. When the wound heals, the
end of the duct will come away, leaving a fistulous opening.
Examine it daily, and if it has a tendency to close, pass a fine
probe into it and along the duct.

Permanent Sublingual fistula. — This is made in the same
way as a submaxillary fistula, and the same animal may be
used for both, but the two fistulae should be on opposite sides
of the head.

89. Parotid Fistula. — The animal having been secured
and placed under chloroform as before, the hair is clipped from
the cheek between the orbit and the angle of the mouth. On
running the finger along the lower border of the z3-gomatic
arch from behind forwards, its anterior and inferior root is
felt at its insertion into the superior maxilla, forming an arch,
of which the convexity is directed backwards. At the end of
this arch, between its insertion into the maxillary bone and
the alveolus of the second molar tooth, a little depression-is

1 In administering chloroform to a dog, great care must be taken that
the vapor is sufficiently diluted with air, and that the sponge does not
come into contact with the muzzle. The breathing must be carefully
watched during the period of administration, and if it fails it must be
continued by alternately compressing and relaxing the thorax. If this
does not succeed, no time must be lost in opening the trachea and com-
mencing artificial respiration.

BY DR. LAUDER BRUNTON. 467

felt. Exactly on a level with this depression, and in a line
with the insertion of the zygomatic arch, make an incision
through the skin, cutting obliquel}' in a direction from the
inner canthus of the eye towards the angle of the mouth. On
dividing the subcutaneous cellular tissue, the facial vein and
artery, a nerve, and the parotid duct will be found all together.
The duct lies most deeply and runs from behind forwards,
while the artery, with its accompanying vein, pass from above
downwards. It is of a pearly white color. Isolate it, and
divide it as near the mouth as possible. The wound must be
closed round the duct, and the duct secured in it by a suture,
just as in the case of the submaxillary gland.

* 90. Effect of Stimuli on Secretion. — In animals with
permanent fistulse, whether parotid or submaxillary, it can be
demonstrated that these glands do not secrete excepting when
secretion is excited by stimulants. The stimulation ma}- con-
sist in the introduction into the mouth of sapid substances,
such as vinegar (which, in common with acid substances in
general, acts most on the parotid), quinine, or coloc3rnth, or
of ether, or in electrical excitation of the tongue. The action
of mental stimuli may be also shown, as, e. g., by placing a bone
before the nose of a fasting dog without allowing him to reach
it. From SchifTs experiments, it appears that this kind of
stimulation has no effect on either the parotid or submaxillary.
The mastication of a bone produces an abundant secretion from
both glands, but mastication of a tasteless substance, as, e. g.,
a piece of wood, has no effect on the parotid, and a very slight
one on the submaxillary. For rabbits a piece of hard biscuit
should be used in place of a bone.

Experimental Investigation op the Functions of the
Submaxillary Gland.

91. Owing to its comparatively exposed position, the sub-
maxillary gland has been more completely studied than either
of the other two. The investigation of its functions has yielded
results which have acquired an importance far beyond that
which they possess as bearing on the secretion of saliva. They
form, indeed, the basis of all that is known as to the nature of
glandular action, and of the influence exercised on it by the
nervous system. Before proceeding to describe the methods
employed, it will be necessary to give a short account of its
anatomical relations, and particularly of the bloodvessels and
nerves which are distributed to it.

Nerves. — The gland receives nerve fibres from three sources,
viz., from the facial, from the submaxillary ganglion, and from
the cervical sympathetic. The branch of the facial (known as
the chorda tympani) reaching the neighborhood of the duct, as
part of the trunk of the lingual nerve, leaves that nerve as it

468 DIGESTION.

crosses the duct, in order to accompany the latter to the gland
(see fig. 307). In the angle which it thus forms with the lin-
gual lies the submaxillary ganglion or ganglionic plexus above
mentioned. From it fibres originate which reach the gland
along with the chorda. The sympathetic fibres are derived
from the superior cervical ganglion.

Physiologically, the nerves derived from the submaxillary
ganglion cannot be distinguished from those of the chorda.
When the chorda is irritated, the arteries of the gland dilate,
the blood-stream becoming much more rapid ; consequently,
the veins leading from the organ pulsate, and if they are opened
they jet like an artery. At the same time, the secretion dis-
charged from the duct becomes copious and watery. When
the sympathetic fibres are excited, the arteries contract, and
the circulation in the gland is retarded, and if the veins are
opened, they discharge " black" blood in a slow stream. The
secretion becomes scanty and tenacious.

It was first demonstrated experimentally by Ludwig that the
increased secretion produced by excitation of the chorda is
immediately dependent on increased activity of the function of
the secreting elements of the gland, and not on changes in the
bloodvessels; in other words, that in the submaxillary gland
the process of secretion is not a mere filtration, but is effected
by changes which go on within the gland itself, of such a nature
as to determine a current from the circulating blood towards
the duct. This conclusion was based by Ludwig on the ob-
servation : first, that if the duct is constricted, secretion con-
tinues, notwithstanding that the pressure in the interior of the
gland is greater than that in the arteries ; and, secondly, that
secretion continues after circulation has ceased, e. g.} after the
head has been severed from the body.

More recent observations make it probable that by the chorda
tympani two kinds of fibres find their way to the gland, viz.,
fibres by which secretion is influenced directly, and others
which are " vaso-inhibitory," i. e., diminish arterial tonus.
Among the most important observations bearing on this ques-
tion are those lately published by Heidenhain, who has found
that injection of atropiainto the arteries or veins of an animal
deprives the chorda of its power of over-secretion, without in-
terfering with its vaso-inhibitory function ; and the earlier ex-
periments of Gianuzzi, made under Ludwig's directions, in
which a similar effect was produced by the injection of solution
of quinine, half per cent, hydrochloric acid, or five per cent,
solution of sodium carbonate into the gland itself.

** 92. Demonstration of the Functions of the Chorda
Tympani and Sympathetic Fibres of the Submaxil-
lary Gland in the Dog. — The animal having been secured,
as directed in § 88, and placed under chloroform, with the

BY DR. LAUDER BRUNTON. 469

usual precautions, the hair is clipped from the jaws and neck,
and the skin cleaned with a wet sponge. This having been ac-
complished, proceed according to the following

Directions. — 1. Make an incision along the inner boi'der of
the lower jaw, beginning about its anterior third, a little in
front of the insertion of the digastric muscle, and extend it
backwards to the transverse process of the atlas, dividing the
skin and platysma {see figs. 308 and 310). — 2. Expose the
jugular vein at or near the point where it divides into two
branches (j' and j"), and lay bare those branches also. One
of them (j') passes upwards behind the gland ; the other
(j") passes forwards below it, and then subdivides into two
branches. The gland itself has two veins. One of them (d'
fig. 308) issues from its posterior aspect and enters the vein
j'. The other (d) comes from its lower side and enters the
vein j". Sometimes one vein (d) is larger, sometimes the
other (d'). — 3. Tie both branches of the lower division of
the jugular opposite 3" (fig. 310). Tie the upper branch
where it crosses the ramus of the jaw, and remove the part
between the ligatures. — 4. Tie the other division (J') on the
distal side of the place where it receives the vein (d' fig. 308)
from the gland. — 5. Remove the cellular tissue from the surface
of the digastric muscle, and from the groove between it and
the masseter. Be careful not to injure the facial artery, and
the duct of the gland which passes forwards and inwards
between the muscles. — 6. Separate the digastric muscle by
means of a director or aneurism needle from the facial artery.
Tie the arterial twig which supplies the muscle. Separate the
muscle from its attachment to the jaw, or divide it about its
anterior third, cutting it through very carefully, so as not to
injure the duct and nerves which lie below it. — 7. Lay hold of
the lower end of the digastric with a pair of artery forceps,
and draw it backwards. This brings into view a triangular
space, whose apex is directed forwards, and whose base is
formed by the reflected digastric. Its lower margin (the dog
being supposed to be in the upright position, as in the figures)
is formed by the genio-hyoid muscle, and its upper one bj' the
ramus of the jaw and the lower edge of the masseter. The
anterior half of its floor is formed by the mylo-hyoid muscle,
on which some nerves ramify. The carotid artery enters the
triangle at its lower angle, and runs along its base, giving
off first the lingual artery, secondly the facial. Just as the
carotid begins to pass in front of the digastric, it is crossed by
the hypoglossal nerve P, and is accompanied by filaments of
the sympathetic tt'. At the upper angle of the triangle, several
structures pass from it to the hilus of the gland close to the
margin of the digastric. These are — 1, the duct; 2, the nerves ;
3, the principal artery of the gland. The artery is given off

470 DIGESTION.

by the facial at the upper angle of the triangle. It lies beneatli
the nerves, but is easily reached by drawing them aside. — 8.
Carefully isolate the digastric by a director or aneurism needle
from all the structures just mentioned. Divide it close to its
insertion into the temporal bone. — 9. Divide the mylo-hyoid
muscle, cutting its fibres across about their middle, and reflect
the upper half, taking care not to injure the mylo-hyoid never
■which lies upon it, and tying all the veins which come into
view on its surface with a double ligature. This brings into
view the lingual nerve L, which issues from under the ramus
of the jaw just opposite the groove between the masseter and
digastric muscles, and after passing across the floor of the
triangle towards the middle line, enters the mucous membrane
of the mouth — 10. Draw the parts a little towards the middle
line with the fingers, and follow the lingual nerve to the
ramus of the jaw. A small twig T will then be seen, which
passes off from its posterior aspect, bends down, making a sort
of loop, and then runs backwards to the gland in close relation
to the duct. This nerve is the chorda tympani. In the angle
between .the corda and the lingual lies the submaxillary gan-
glion.— 11. Isolate the chorda tympani, pass a thread under
it, and tie the two ends together, so that the nerve may be
raised from its place at will. — 12. Isolate the lingual nerve
close to its entrance into the mouth, and pass a thread under
it. — 13. To reach the sympathetic, divide the hypoglossal nerve
P just where it crosses the carotid, and raise up its central
end. Close to the inside of the carotid lies the vagus, and
when this is raised the sympathetic is seen underneath and
inside of it. The sympathetic separates from the vagus at
this point and goes to the superior cervical ganglion (see fig.
309). From the ganglion, fibres accompany the carotid and
enter the gland, some along with the chief artery (0), and
others with the other arteiy P'. The ganglion can easily be
found by following the carotid filaments backwards. — 14. Place
a canula in the submaxillary duct. The ducts of the sub-
maxillary and sublingual glands pass along the middle of the
triangle close to each other. The submaxillar}' duct lies nearer
the ramus of the jaw, and is larger than 'the sublingual duct.
Isolate it slightly with an aneurism needle. Pass under it a
thread for the purpose of tying in the canula. Place under
the duct a smooth splinter of wood or a piece of card half an
inch long by one-eighth of an inch wide, on which it may rest.
Close the duct as near the mouth as possible with a clip, or
tie a thread round it so as to obstruct it. Pvaise the chorda
by the thread which has been passed round it, irritate it by a
weak interrupted current; the purpose of this is to distend
the duct witli secretion, and thus render the introduction of a
canula much easier. Let an assistant lay hold of one edge of

BY DR. LAUDER BRUNTON. 471

the duct with a pair of fine forceps while the operator lays
hold of the other just over the splinter of wood on which it
rests; open the duct between them with sharp-pointed scissors.
Insert the canula into the duct and tie it in. — 15. Put a liga-
ture round the jugular vein half an inch or an inch below its
bifurcation, so as to be able readily to introduce into it a
canula when necessary.

In the preceding directions, all the steps of the operative
procedure required for the complete investigation of the func-
tions of the submaxillary gland during life are detailed. The
method may, however, be modified, according as it is intended
to limit the observation to the influence of direct or reflex ex-
citation of chorda tympani on the secretion of the gland, or to
extend it to this investigation of the vascular changes and to
the functions of the vascular nerves.

93. Direct and Reflex Excitation of the Chorda
Tympani. — Proceed as above directed, omitting 13 and 15.
2, 3, and 4 may also be omitted, provided that all such veins
as are necessarily involved in the succeeding steps are doubly
ligatured and divided between the ligatures. Reflex Excitation.
— Divide the lingual nerve close to its entrance into the mouth,
and excite its central end with the secondary coil at a con-
siderable distance from the primary. The secretion of saliva
is increased. The animal must previously be allowed to recover
from the chloroform, or no increase will be observed. The
reflex action of the lingual is abolished during narcosis by
opium, as well as by chloroform. ** Direct Excitation. —Divide
the chorda close to the point at which it leaves the lingual, and
place the peripheral cut end on theexcitor (fig. 225), removing
the secondary coil to a considerable distance from the primary.
On opening the key, saliva is discharged from the canula (to
which an end of India-rubber leading into a test-tube has been
fitted). It begins to flow a few seconds after the excitation,
but not immediately. By repeating the excitation at regular
short intervals, the discharge can be maintained, and a con-
siderable quantity collected.

** 94. Demonstration that the Pressure produced
by Secretion in the Duct of the Submaxillary Gland
-when it is Obstructed is greater than the Arterial
Pressure. — A canula having been placed in the carotid of the
opposite side of the body and connected with a mercurial ma-
nometer, a second manometer is connected with the canula in
the duct of the gland. The pressure indicated by the latter
gradually increases until it attains a height greater than that
indicated by the former. In this experiment it is desirable
that the tube of the manometer connected with the duct should
be narrow. Its proximal arm should be connected by a side
opening with a pressure bottle at a height of about four feet

472 DIGESTION.

from the table, the arrangement being the same as in the man-
ometer of the kymograph. In this way a mercurial pressure
of about 50 mill, of mercury is produced in the duct before
excitation is commenced. On exciting the chorda tympanic it
rises, as above stated, to double that height or more. For this
experiment the same preparations are required as for the pre-
ceding, and the same animal may be used. The ineasureinent
of the arterial pressure in this experiment may be advanta-
geously omitted. The pressure in the particular case may be
assumed to be equal to the average.

** 95. Excitation of the Vascular Nerves. — If the
filaments which accompany the carotid or principal artery of
the gland are excited, a few drops of secretion may be dis-
charged, but the quantity is so small that unless care is taken
that the canula and duct are quite full before the key is opened,
the effect will be scarcely perceptible. The secretion thus ob-
tained is so thick and viscid, that the canula is apt to become
ch'oked b}r it.

** 96. Demonstration of the Influence of Excitation
of the Chorda, and of the Vascular Filaments on the
Circulation of the Submaxillary Gland. — For this pur-
pose it is necessary to insert a canula into the jugular vein,
which has been exposed fortius purpose (see direction 15). In
doing so. great care must be taken that the vein is not twisted,
and that the canula is properly inserted so as to allow the blood
to flow freely out of it from the gland; it will be remembered
that all the tributaries of the vein, excepting those from the
gland, have been previously tied. On exciting the chorda, the
blood flows from the canula more rapidly, and acquires a
brighter color. The opposite effect is produced by exciting the
vascular filaments.

97. Simultaneous or Alternate Excitation of the
Chorda Tympani and Vascular Filaments of the Sub-
maxillary Gland. — The same degree of excitation of the
chorda which is sufficient to induce a marked increase of the
secretion of the gland, is without effect if the sympathetic fila-
ments are excited at the same time. Hence it is concluded
that the functions of the two sets of fibres are antagonistic to
each other, not only in relation to the circulation of the gland,
but as regards their direct influence on secretion. The experi-
mental proof of this consists in first exciting the chorda with
the secondary coil at such a distance that the effect produced
is only just appreciable, and then repeating the excitation while
the vascular filaments are excited at the same time. In the
latter case, the effect of the excitation of the chorda is annulled.
If with a Pohl's commutator the same induced currents are
directed alternately through the chorda and the sympathetic
filaments at short intervals, the preventive influence of excita-

BY DR. LAUDER BRUNTON. 473

tion of the latter manifests itself in the same way as if the ex-
citation were simultaneous. Here, as before, the effect must be
verified by comparative experiments.

98. Simultaneous Section of the Chorda Tympani
and Vascular Nerves. — Paralytic Secretion. — After divi-
sion of both nerves, the secretion of the submaxillary gland,
which in the normal state only goes on when the gland is
directly or reflexly excited, becomes constant and abundant.
This effect does not occur until some time after section, and
may last for days or weeks. A similar condition of the gland
is produced by the introduction of curare into the blood, which
is supplied to the gland by its arteries. To show this, proceed
as follows : Find the facial artery and prepare it. Then insert
and secure a canula, to which an end of India-rubber tubing
has been previously fitted in the usual way. Fill the canula
with saline solution, and connect it with the nozzle of a Pravaz's
syringe previously chai'ged with one per cent, solution of curare,
taking care that the India-rubber tube is firmly tied round the
nozzle. Open the clip, inject five divisions (about two milligr.
of curare), and then close the clip. The same mode of injection
may be used for the introduction of solution of atropin, if it is
desired to repeat the experiments of Heidenhain previously
referred to.

99. Function of the Submaxillary Ganglion. —
Bernard found that excitation of the central end of the lingual,
when divided near the mouth, produces effects similar to those
of excitation of the chorda, i. e ., causes the submaxillary gland
to secrete even when the trunk of the lingual and chorda has
been severed at a point nearer the brain than that at which it
is in relation with the ganglion.

From this, Bernard concluded that the submaxillary ganglion
acts as a reflex centre, independently of the central nervous
system. More recent observations render it probable that
Bernard's result derives its explanation from the anatomical
fact that a filament of the chorda exists, at all events in some
animals, which accompanies the lingual nerve for about an
inch and a half beyond the point at which the chorda separates
from it. The effect in question is to be attributed to excitation
of this filament, which runs back parallel with the lingual nerve
to the submaxillary plexus, and so to the gland. (On this
subject, nee Schiff, Physiol, de la J)igestion, t. I., p. 288, and
Haartman's Thesis, 1846. Helsingtbrs, p. 37, and PI. I. 142.)

100. Parotid Glands. — In most animals the parotid, like
the submaxillary gland, does not secrete unless the nerves
which regulate its secretion are stimulated, but in the sheep it
is said by Eckhard to secrete constantly. Secretion occurs
when sapid substances are applied to the posterior part of the
tongue, and still more when they are chewed ; but the mere

474 DIGESTION.

motion of the jaws in chewing a tasteless substance does not
induce secretion. The gland receives two secreting nerves,
one of which is derived from the facial, and the other from the
sympathetic. The branch from the facial is the lesser superfi-
cial petrosal nerve, which leaves the facial in the petrous por-
tion of the temporal bone, passes to the otic ganglion, and
thence to join the auriculo-temporal branch of the fifth, in
which it proceeds to the gland. These facts have been experi-
mentally ascertained by observing, first, that irritation of the
roots of the facial within the cranium determines flow of saliva
from the parotid gland ; secondly, that excitation of the fifth
nerve within the cranium has no such effect ; and, thirdly,
that after section of the facial nerve at its exit from the stylo-
mastoid foramen, the application of stimuli to the mouth de-
termines secretion from the parotid as before. These facts,
taken in combination, show that the secreting fibres for the
parotid are given off by the facial in its passage through the
petrous part of the temporal bone. This conclusion receives
direct confirmation from an experiment of Bernard, who found
that destruction of the facial nerve in the temporal bone stops
the secretion of the parotid.

Of the three nerves given off" bjr the facial in its passage
through the temporal bone, viz., the chorda lympani, the greater
superficial petrosal and the lesser, the last-mentioned was
proved by Bernard by exclusion to contain the secreting fibres
for the parotid, for he showed that the chorda could be divided
in the tympanum without affecting the parotid secretion ; and
as regards the greater superficial petrosal, it was known ana-
tomically that it did not go to the parotid, and also found ex-
perimentally that excision of Meckel's ganglion had no effect
on that gland. Bernard's conclusion has received direct con-
firmation from later experiments, which have shown, first, that
the secreting function of the parotid gland is much impaired
by the extirpation of the otic ganglion, and entirely annulled
1>3' section of the auriculo-temporal nerve. After division of
this nerve, Schiff has shown that discharge of saliva cannot be
induced by the application of stimuli to the mouth, and that
electrical excitation of the peripheral end excites secretion just
in the same way as excitation of the chorda tympani.1

1 For a description of the method of dividing the facial at its exit from
the stylomastoid foramen, see Eckhard's Beitr'age zur Anatomic und
Physiologic, Bd. III. p. 49. Section of the facial within the temporal
bone is described in Bernard, Lecons sur la Physiol, et la Pathol, du
Syst. Nerv., II. pp. 58 and 141. As regards section of the chorda in
the tympanum, excision of the sphenopalatine ganglion, and division
of the lesser superficial petrosal nerve, see Schiff, Physiol, de la Diges-
tion, torn. I. p. 229. Excision of the otic ganglion, do. p. 227. For
the method of exciting the auriculo-temporal nerve, see Nawrocki Stud,
d. Physiol. Inst, zu Breslau, lit. IV. p. 185.

BY DR. LAUDER BRUNTON. 475

** 101. Secretion of Saliva after Decapitation. —

Make a parotid fistula in a rabbit; decapitate it; split the
head in the middle line by a knife and hammer; remove the
brain from that half of the head on which the fistula has been
made, apply a piece of filter-paper colored red by litmus to the
orifice of the duct, and irritate the roots of the facial as they
enter the internal auditory foramen, either electrically or by
touching the nerve with a drop of acid. A blue spot will appear
on the paper, showing that saliva has been secreted.

Section II. — Digestion in the Stomach.

102. In the stomach the albuminous constituents of the food
which were unaffected by the saliva are dissolved by the gas-
tric juice, and to a great extent converted into peptones. If
they were merel}T dissolved, they could only be absorbed in
very minute quantities, for albumin will hardly diffuse through
animal membranes. The peptones into which the albuminous
substances are converted, on the contrary, diffuse very readily,
and are thus easily absorbed. The gelatinous substances in
the food are also changed somewhat h}' the gastric juice, so
that after the}' have been acted on by it they no longer gela-
tinize. The transformation of starch into sugar by the saliva,
which was begun in the mouth, also goes on in the stomach,
the acidity of the gastric juice being too slight to arrest it.

Unlike saliva, gastric juice cannot be readily obtained from
man or animals, at any rate in a state of purity, without an
operation. It is therefore necessary to establish a gastric
fistula in a dog in order to collect a sufficient quantity of gas-
tric juice for examination.

** 103. Establishment of a Gastric Fistula.— The
object of making a gastric fistula is twofold : 1st, to obtain
gastric juice for examination ; and, 2d, to observe the process
of secretion within the stomach itself.

The method adopted by Bassow was simply to make an in-
cision in the abdominal parietes, to sew the stomach to the
edge of the wound, and then to make an-opening in the stomach
itself. The fistula was plugged with a piece of sponge. It
was, however, very liable to close, and was too small to allow
the interior of the stomach to be observed. Blondlot pre-
vented the wound from closing by placing in it a canula, which
was closed with a cork, so that the gastric juice and products
of digestion might not be lost during the intervals between
his observations.

This method, as improved by Bernard, is the one usually
employed. Bernard's canula consists of two tubes, each of
which lias at one end a broad flange. One tube screws into
the other, so that the distance between the two flanges can be

470 DIGESTION.

altered at will. This- is effected by means of a key which fits
on two projecting points in the inner tube, and turns it round,
while the outer one is held fast by the fingers. The advantage
of this form over a simple tube with a shield at each end, is
that the cicatrix of the wound often thickens in healing, and
if the tube is not proportionately lengthened the outer plate
presses on the skin and causes ulceration. The disadvantage
of Bernard's canula is, that it is too small to allow the in-
terior of the stomach to be conveniently observed, and also, I
think, that the edge of the wound comes into contact with the
screw of the inner tube, and not with a smooth surface.

These advantages may be readily obviated by increasing the
diameter of the tube and the width of the flange, and adapting
a key to the projecting points by which the outer tube may be
placed in the stomach and turned round as necessary. Such a
canula is represented in fig. 311.

104. Operation for Gastric Fistula. — Give the dog a
hearty meal, so as to distend its stomach completely and make
it lie close against the intestinal walls.1 Anaesthetize the
animal by chloroform, taking care that the vapor is mixed
with a sufficient proportion of air. Lay it on its back on the
table, shave off the hair from the epigastric and hypochondriac
regions, and remove the hairs carefully by a sponge, so as to
prevent the risk of their getting into the peritoneal cavity.
Make a vertical incision about an inch and a half to one side
of the linea alba, preferably the left, and parallel to it, extend-
ing downwards from the lower edge of the costal cartilages to
a distance somewhat less than the diameter of the flange of the
canula. Divide the muscles parallel to the course of their
fibres. Tie every bleeding point before opening the perito-
neum, so that no blood shall get into its cavity. Open the
peritoneum on a director. Lay hold of the stomach with a
pair of artery forceps at a point where there are not many ves-
sels, and draw it forwards. Pass two threads with a curved
needle into the gastric walls at a distance from each other
about equal to the diameter of the tube of the canula, and
bring them out again at a similar distance from the points
where they were introduced. Make an incision into the gastric
walls, between the two threads, rather shorter than the diame-
ter of the tube of the canula. Put a pair of forceps, with the
blades together, into the incision, and then dilate it by sepa-
rating the blades till it is large enough to allow the canula to
be introduced. Push the canula into the stomach up to its
outer plate. Tie the stomach to it by the threads, and then

1 Holmgren recommends the inflation of the stomach with air, by
means of a tube passed down the oesophagus, as preferable to distend-
in? it with food.

BY DR. LAUDER BRUNTON. 477

pass their ends through the edges of the wound in the abdo-
minal wall in such a way as to fasten the stomach to it, and
at the same time to keep the cut edges in apposition. No
other suture is required. Leave the canula uncorked for at
least half an hour after the operation is finished, for when the
dog recovers from the chloroform it will vomit, and if the ca-
nula be corked, the fluid contents of the stomach are apt to be
forced past the side of the canula into the abdominal cavity.
Feed the dog on milk for one or two days, and if the operation
be performed in winter, keep it in a place warmed night and
day. The day after the operation the edges of the wound will
be much swollen, but the swelling will subside in a day or two.
After the wound has begun to heal, the cicatrix may thicken,
and the outer plate of the canula begin to press too much on
the skin, so that it ulcerates. If this should occur, the canula
must be lengthened by screwing the two flangs further apart.
The canula may be closed by an India-rubber stopper, or by a
cork. If the dog tears out the cork with his teeth, soak it in
decoction of colocynth, or put a little phosphoric acid on its
outer end.

In order to collect the juice, let the animal fast for several
hours, so that its stomach may be quite empty, but not for
more than a da}-, as the mucous membrane would become
covered with a thick coating of mucous. Let an assistant pat
the dog, and keep him quiet ; withdraw the cork from the
canula, and tickle the inside of the stomach with a feather tied
to a glass rod. Put a small beaker underneath, so that the
end of the rod rests on its bottom : the gastric juice will flow
into it down the sides of the rod.

** 105. Examination of Gastric Juice.— The gastric
juice is thin, almost colorless, very faintly opalescent, and has
a faintly acid taste. Its specific gravity is nearly the same as
that of water. Its reaction is strongly acid; blue litmus paper
becoming bright red when dipped into it.

Composition. — In the dog, it contains three per cent, of
solids; in man, only one per cent. About two-thirds of this
is organic matter, consisting of pepsin and peptones ; and one-
third of inorganic matter, consisting of chlorides of potassium,
sodium, ammonium, calcium, and phosphates of calcium, mag-
nesium, and iron. The specific gravity and amount of solids,
organic and inorganic, are to be determined in the same way
as those of saliva.

The acidity of the gastric juice is really due to free acid,
and not to acid salts. To show this, the amount of bases and
of acid contained in it must be determined. When this is
done, it is found that the quantity of acid is more than suffi-
cient to form acid salts with all the bases present which are
capable of forming such salts ; it must, therefore, exist partly

478 DIGESTION.

in a free state. For the details of this process, consult Bidder
and Schmidt, Verdauungssafte, u. Stoffweehsel, 1852, p. 44; or
Hoppe-Seylei's Handbuch d. Chemischen Analyse, third edi-
tion, p. 434.

106. Estimation of the Acid in Gastric Juice. — Fill
a burette with dilute standard solution of soda (one part in
ten), letting- the standard solution flow gently into it, so as to
avoid air-bubbles, till it is filled above the zero mark. Then
place it in the stand, and take care that it is perfectly vertical.
If any bubbles of air arc present they must be allowed to
break or be removed by a glass rod. Let the fluid flow out by
pressing the clip till its level corresponds to the zero mark on
the burette. Measure out 10 cubic centimetres of gastric juice
into a beaker, and add a little litmus solution to it till a dis-
tinct red color is produced. Place the beaker containing it
under the burette, and let the alkaline solution flow gradually
into it at first, and at last only drop by drop, stirring all the
time till the red color of the litmus changes to a violet. Then
note exactly the level at which the surface of the fluid stands
in the burette. The difference between this level and the zero
mark gives the number of cubic centimetres used. Calculate
the amount of soda contained in this quantity. One hundred
cubic centimetres of the original soda solution contained four
grammes, or one-tenth of an equivalent of soda. One hundred
cubic centimetres of the diluted solution, therefore, contains
one-tenth of this amount, 0.04 grammes, or one-tenth of an
equivalent.

Let us suppose that the amount of soda solution actually
used to neutralize the gastric juice is 21.6 cubic centimetres.
Then, as 100 cubic centimetres contain 0.04 grammes ( = 0.01
equivalent), this quantity will contain only 0.00G grammes
( = 0.00216 equivalent). The quantity of gastric juice neutral-
ized was 10 cubic centimetres. Had we used 100 cubic centi-
metres of juice instead of 10, we should have required ten
times as much soda to neutralize it, i.e., 0.0216 equivalent.
One hundred cubic centimetres of the juice, therefore, contains
0.021 of an equivalent of acid, supposing that the acid be
monobasic. If the acid be bibasic or tribasic, an equivalent
of soda would only saturate a half or a third of an equivalent
of acid, and the proportion of acid would be 0.015 or 0.00?.

107. To Determine the Nature of the Acid.— The
gastric juice is introduced into a large retort connected with
a Liebig's condenser, and distilled till the fluid in the retort
becomes very concentrated, and clouds begin to form in it.
To remove the excess of water from the distillate, it must be
neutralized with sodium carbonate, evaporated to dryness over
a water-bath, extracted with absolute alcohol and filtered.
The filtrate is then evaporated to dryness on a water-bath, and

BY DR. LAUDER BRUNTON. 479

the residue dissolved in a small quantity of water. A little of
the solution is now put in a test-tube, and a few drops of a
neutral solution of ferric chloride added. If acetic acid is
present, the fluid will become of a dark red color, and when
boiled will deposit a 3'ellow precipitate. A solution of silver
nitrate ma}' be added to second portion. If hydrochloric acid
is present, a white precipitate will fall, and will not be dis-
solved on adding nitric acid, but will be dissolved by ammonia.
To the remainder, dilute sulphuric acid is added, and the
mixture allowed to stand for some time. If butyric acid is
present, a smell like rancid butter will be perceived. The
residue of the gastric juice, which remained in the retort after
the hydrochloric and other acids were distilled off', is poured
into a large test-tube or flask, and agitated with ether. The
ethereal layer is then decanted off and evaporated over a water-
bath. If acetic acid be present in the gastric juice, it will
remain as an acid residue. Crystals of zinc lactate (square
prisms with one or two oblique surfaces at the ends) may be
obtained on allowing the residue to stand after the addition of
zinc, oxide, and water.

108. Action of Gastric Juice. — The power of gastric
juice to dissolve coagulated albuminous substances is best
shown by using fibrin from blood. To prepare fibrin the blood
is to be stirred, as it flows from the vessel, with a rough stick
or piece of ragged whalebone, and the fibrin collected and
washed till it is perfectly white. It may be preserved for a
considerable time under glycerin, from which it must be
washed before it is used. Put a small piece of fibrin into a
test-tube along with gastric juice, and place the tube for an
hour or two in the water-bath at 35° C. The fibrin will swell,
become somewhat transparent, and then dissolve, forming an
opalescent fluid, which is not precipitated by boiling, and
slight^, or not at all, by neutralization. As no other fluid
except gastric juice has this action on fibrin, the production
of all these effects is used as a test for it, and is called the
pepsin test. Pepsin alone will not produce them, however,
unless free acid be present as it is in gastric juice. In this
process, boiled fibrin ma}' also be used as recommended by
Kiihne.

** 109. Artificial Gastric Juice. — All the actions of gas-
tric juice can be more conveniently studied with an artificial
juice than with the natural secretion, as the former can be ob-
tained in much larger quantities. The method of preparing it
is as follows : Open the stomach of a newly-killed pig or rabbit,
or the fourth stomach of a calf, remove its contents and wash
it thoroughly with a gentle stream of water without much rub-
bing. Lay it on a piece of board with its mucous surface up-
wards, fasten it down with a few pins, and then with the back

480 DIGESTION.

of a knife or an ivory paper-cutter, scrape off all the mucus from
the surface. Rub it up in a mortar with clean silicious sand
or powdered glass and water, let it stand some time, stirring
it from time to time, and then fdter it. The filtrate is gastric
juice in a state of very considerable purity. It is slightly opa-
lescent, and contains a large quantity of pepsin and but little
peptone. When acidulated with its own bulk of dilute hydro-
chloric acid of 0.2 per cent., it digests fibrin with great rapidity.
It may be kept in a bottle for a long time, and though fungi
grow on its surface, it still retains its digestive powers.

A much stronger gastric juice, though not so pure, is ob-
tained by scraping the mucus from the stomach as in the first
process, or by dissecting off the whole mucous membrane from
the muscular layer, cutting it into small pieces, then rubbing
it up with dilute hydrochloric acid of 0.1 per cent, and filtering.
The gastric juice so readil}' prepared by this method is very
strong, and does very well for experiments on digestion, al-
though it contains a good deal of albumin which is dissolved
in the acid. It maj- be freed in a great measure from albumin
b}' putting it into the water-bath at 35° C, for several hours,
so as to convert the albumin into peptones, and then transfer-
ring it to a dialyzer, and changing the water several times.
The peptones will diffuse out into the water, a great part of
the pepsin will remain in the dialyzer.

** 110. To Prepare Hydrochloric Acid containing
0.2 per cent, of real HC1. — The ordinary strong hydrochlo-
ric acid sp. gr. 1.16 contains 31.8 per cent, by weight of II CI.
gas. To prepare a dilute acid, containing 0.2 per cent, of real
HCL, measure out with a graduated pipette 6.25 cubic centi-
metres of such acid into a litre flask ; fill the flask up to the
neck with distilled water, and shake so as to mix thoroughly.

** 111. To Prepare a Solution of Pepsin in Glycerin.
— The solubility of digestive ferments in glycerin was dis-
covered by Yon Wittich ; and by its means they may be ob-
tained with great facility. Cut open the stomach of a pig
or rabbit (best when newly killed), and wash the mucous
membrane as directed ; cut off the pyloric part ; stretch the re-
mainder on a piece of board, and dissect off the mucous mem-
brane from the muscular layer. Cut up the mucous membrane
into small pieces and put it into a beaker, with sufficient gly-
cerin to cover it. It will acquire peptic properties in a few
hours, but it is as well to let it remain for several days. Then
strain off the glycerin and put on a fresh quantity. This may
be repeated several times, and each time the glycerin will take
up a fresh quantity of pepsin.

An artificial gastric juice may be readily prepared whenever
it is wanted by adding a little of the glycerin extract to hydro-
chloric acid of 0.1 per cent.

BY DR. LAUDER BRUNTON. 481

** 112. Preparation of Pure Pepsin from Glycerin
Solution. — Let the mucous membrane, prepared and cut into
pieces, as already directed, lie for 24 hours in absolute alcohol.
Filter off the alcohol ; dry the pieces of mucous membrane with
a cloth or filtering paper, cover them with glycerin, and let them
stand for several days or weeks. Filter the glycerin, first
through linen and then through paper. Add a large excess of
absolute alcohol to the filtrate and a flocculent precipitate will
fall. Filter off the alcohol, pour IIC1. of 2 per cent, over the
precipitate on the filter, and it will dissolve. Boil a little of
the solution with strong nitric acid, and after cooling, add am-
monia. It should not give the slightest trace of the xantho-
protein reaction. Let a piece of fibrin, either boiled or un-
boiled, remain in another portion of the solution for several
hours, at 40° C, and it will be digested. Apply the other
tests mentioned in § 118. Very probably no precipitate may
be occasioned by platinum chloride.

113. Preparation of Pepsin (Brucke's Method). — The
process by which Briicke separated pepsin, and thus for the
first time succeeded in isolating any of the digestive ferments,
depends on their being tarried down from their solutions along
with precipitates produced in them. This has already been
mentioned when speaking of saliva, from which Cohnheim
separated ptyalin by Brucke's process. Separate the mucous
membrane from the stomachs of two pigs, and cut it up into
small pieces, as directed in § 109. Digest it at 40° C. with a
considerable quantity of dilute phosphoric acid, of the British
Pharmacopoeia, mixed with its own bulk of water (it thus con-
tains 5 per cent, of acid). If necessary, remove the acid, and
add fresh portions till the whole of the stomach has been dis-
solved, with the exception of a slight residue, continuing the
process till the liquid which passes through on filtering gives
no precipitate with potassium ferrocyanide. Filter the liquid,
put a little of the filtrate aside in a test-tube, and add lime-
water to the remainder till it turns blue litmus paper slightly
violet. Collect the precipitate on a cloth filter, press all the
fluid out of it with the aid of a screw-press, and dissolve it while
still moist, in water, with the addition of dilute hydrochloric
acid (50 cubic centimetres of commercial acid in a litre- of
water).

Precipitate the solution a second time with lime-water, col-
lect the precipitate on a cloth filter, press out the liquid, pour
a little water on it while still moist, and add phosphoric acid
to it in small quantities and at long intervals. The pasty tri-
basic phosphate Ca((P04)., is thus converted into sandy bibasic
phosphate Ca II P04. Filter off the fluid; it contains pepsin
still mixed with albuminous substances. Test its digestive
power by adding a few drops of it to 0.1 per cent, hydrochloric
31

482 DIGESTION.

acid, and digesting fibrin in it. It will be found still to give
the xanthroprotein reaction, though not quite so strongly as
the original solution. Wash the precipitate upon the filter
several times with distilled water, plug the funnel, and pour on
dilute phosphoric acid, so that a part of the Ca II P04 is dis-
solved, Ca II4(POJ.,, being formed. After several hours remove
the plug and let the fluid run off. It will digest fibrin, and lias
a still weaker xanthoprotein reaction. Wash the precipitate
several times with distilled water, plug the funnel again, pour
on fresh phosphoric acid, and repeat this several times. At
last a fluid is obtained which, although it digests, gives scarcely
any xanthoprotein reaction. To prepare pure pepsin in sub-
stance, prepare a solution with phosphoric acid and lime-water,
as directed above. After precipitating a second time with lime-
water, and pressing the precipitate, dissolve it in dilute hy-
drochloric acid and filter it into a large flask. Prepare a cold
saturated solution of cholesterin in a mixture of 4 parts of alco-
hol of 808 sp. gr. and one part of ether. Put a long funnel
which will reach to the bottom of the flask into it, and pour in
the cholesterin solution in small quantities. It will separate
and form a thick scum on the surface of the fluid. After it has
attained the thickness of about an inch, take out the funnel,
close the mouth of the flask and shake it well, so that as much
pepsin as possible may stick to the cholesterin. Filter and
wash the precipitate, first with water acidulated with acetic
acid, and then with pure water. Continue the washing until
the wash-water no longer has an acid reaction, nor gives a pre-
cipitate with silver nitrate. Put the moist cholesterin into a
precipitate glass, and shake it with some ether which has been
previously agitated with water to free it from alcohol. The
ether will dissolve the cholesterin, and the adhering water will
separate and form a turbid layer at the bottom of the glass.
Pour off the ether and shake the watery solution with new
quantities of ether several times, until a few drops of the ethe-
real solution no longer leaves behind crystals of cholesterin
when evaporated. Then let the glass stand open, to allow the
last thin layer of ether, which cannot be poured off*, to evapo-
rate. Filter; a small quantity of a slimy substance remains in
the filter, but the filtrate is clear. It is a concentrated solution
of pepsin, and the following reactions may be tried with it, or
with the solution of pepsin obtained directly from the lime pre-
cipitate.

* 114. Reactions of Pepsin. — To show the following reac-
tions the solutions referred to in §§ 112 or 113 may be employed.
It is not precipitated bj- — 1, concentrated nitric acid ; 2, tannic
acid; 3, iodine ; 4, mercuric chloride. It is precipitated by — 1,
platinum chloride; 2, lead acetate, both neutral and basic.

If absolutely pure, it gives no xanthoprotein reaction. When

BY DR. LAUDER BRUNTON. 483

allowed to evaporate over sulphuric acid, it leaves a grayish
amorphous body, which contains nitrogen, and is not hygro-
scopic. It is sparingly soluble in water, more readily in dilute
acids, and digests fibrin.

115. Digestive Action of Pepsin. — Neither pepsin alone
nor dilute hydrochloric acid alone will digest fibrin, but when
mixed together they do so readily. Pepsin alone has no action
on fibrin whatever ; hydrochloric acid of 0.2 per cent, alone
causes it to swell up, but does not dissolve it for days, or even
weeks, at ordinary temperatures. At 35°-38° C, it dissolves
fibrin readily in from twent3'-four to forty-eight hours, but only
converts it into syntonin, so that the whole of the albuminous
matter (with the exception of a trace which Von Wittich says
is really converted into peptone), may be precipitated by neu-
tralization. Pepsin with dilute hydrochloric acid likewise
causes fibrin to swell and dissolves it, forming at first an opa-
lescent solution of syntonin which can be almost entirely pre-
cipitated by neutralization, a little peptone only remaining in
solution. Its action does not stop here, for it very quickly con-
verts the syntonin (parapeptone) into peptones which are not
precipitated by neutralization nor coagulated by boiling, but
are precipitated by alcohol, and possess all the characteristic
reactions of albuminous bodies.

116. Products of the Digestion of Albuminous Com-
pounds.— During digestion several substances are formed, to
which the names of parapeptone, dyspeptone, and metapeptone
have been given by Meissner.

Parapeptone. — Briicke considers that albuminous bodies are
converted into syntonin, and that the syntonin is transformed
entirely into peptones during digestion, but Meissner thinks
that the syntonin, instead of undergoing this transformation,
splits up iuto peptones and parapeptones. Parapeptones
agree with syntonin in every respect, except that they cannot
be converted into peptones by any amount of digestion, while
syntonin can be digested. When an albuminous body is sub-
jected to the action of gastric juice, the solution first obtained
yields, on neutralization, a precipitate of syntonin, which,
when again treated with gastric juice, is converted into pep-
tones. After digestion has gone on a little longer, the pre-
cipitate consists, according to Meissner, partly of syntonin
and partly of parapeptones, for he states that if this precipitate
is digested with fresh gastric juice, a less proportion of it than
of the former precipitate is converted into peptones, and that
this proportion diminishes more and more as digestion goes
on, and the remaining syntonin is split up. Briicke and others
have found, however, that fibrin can be completely converted
into peptones; consequently, Meissner is not correct in sup-
posing that syntonin splits up into peptones and parapeptones.

484 DIGESTION.

Sometimes, however, several clays are required to convert the
whole into peptones.

Dyspeptone. — The dyspeptone of fibrin is a part of the syn-
tonin or parapeptone, which becomes insoluble in 2 per cent,
hydrochloric acid, and therefore falls as a fine precipitate. It
also, according to Meissner, is incapable of further digestion,
and only differs from parapeptone in being insoluble in dilute
alkalies and dilute acids, and therefore is precipitated sponta-
neously from gastric juice without neutralization.

The dyspeptone of fibrin still requires investigation. The
dyspeptone of casein has lately been examined by Hoppe-
Seyler and Lubavin ; as it consists partly, at least, of a non-
albuminous substance, they consider casein to be composed,
like haemoglobin and vitellin, of an albuminous, combined with
a non-albuminous, body.

Metapeptone is merel}- an intermediate stage between syn-
tonin and peptone.

Peptones. — There are several kinds of peptones, but they
still require further investigation. Meissner distinguishes
three sorts, which he names a, b, and c peptones ; c is the
final product, the others being probably only preliminary
stages in its production ; a is precipitated from neutral solu-
tions by concentrated nitric acid, and from solutions slightly
acidulated with acetic acid by potassium ferrocyanide ; b is
not precipitated by concentrated nitric acid, but is precipitated
by acetic acid and potassium ferrocyanide; c is not precipitated
by either of these reagents.

** 117. Demonstration of the Digestive Action of
Pepsin. — Take three test-tubes, and put into the first, water
with a few drops of glycerin extract of pepsin ; into the second,
0.1 per cent, hydrochloric acid; and into the third, the same
acid with a few drops of the glycerin extract. Throw into
each a small piece of fibrin, taking great care to choose pieces
not only of the same size, but of the same texture, as hard
pieces are much more slowly acted on either by acid or by
gastric juice. Label each, or note the number of the hole in
the rack in which each is placed, and put them all in the water-
bath at 40° C. (fig. 331). In order to obtain a sufficient
quantity of solution of peptones for testing, is is desirable at
the same time to put a larger quantity of fibrin in a beaker
with dilute acid, and when it has swollen up and become
transparent, add some gh'cerin extract to it, and place it with
the rest. Look at the test-tubes again in five minutes or so,
and if the pepsin extract is strong,, the bit of fibrin in the gas-
tric juice will be partly dissolved, while the one in the acid
will have swollen and become translucent, still retaining its
form, while that in pepsin alone will be unchanged. Filter
the artificial gastric juice from the residue of fibrin. Put a

BY DR. LAUDER BRUNTON. 485

drop of litmus in the nitrate and neutralize it; a precipitate
of syntonin or parapeptone will fall. Filter the liquid: the
neutral filtrate containing peptones will not be precipitated by
boiling, but it will give the xanthoprotein reaction strongly,
and will give a precipitate with tannin.1

For the further examination of the products of digestion,
filter the solution in the beaker from any undissolved residue.
Neutralize, and parapeptones will be precipitated. Let the
precipitate settle, and then filter : the filtrate will contain pep-
tones. Test for a and b peptones. If they are present, put
the beaker back in the bath for a while, and then test for
them again. If they are no longer present, apply the follow-
ing tests : —

** 118. Reactions of Peptones. — True or c peptones
possess the following characteristics : They are not precipitated
by (I) neutralization, (2) boiling the solution, either neutral
or acid, (3) nitric acid either in the cold or on boiling, (4)
hydrochloric acid in the cold, (5) acetic acid and potassium
ferrocyanide — (after standing, the fluid becomes turbid and
gives a precipitate) — (6) copper sulphate in small quantity
(if more is added it causes turbidity, which partly disappears
on adding excess). They are precipitated by (1) tannic acid,
(2) silver nitrate, (3) mercuric chloride, (4) platinum chloride,
(5) lead acetate, both neutral and basic. (The precipitate is
soluble in excess.)

The solution, when treated with caustic potash and an
extremely minute quantity of copper sulphate, or a drop of
diluted Fehling's solution, gives a precipitate which dissolves
on shaking, and forms a red solution. If more copper sul-
phate is then added, it becomes violet. Peptones thus differ
from albumin, which gives a violet at once.

** 119. DifFusibility of Peptones. — Put a solution of
peptones into a small dialyzer, and let it diffuse into distilled
water for an hour or two. Then test the water by the tests
given above, and peptones will be found to be present. In
this they differ from albumin, which, as has been already seen,
hardly diffuses at all.

* 120. Action of Gastric Juice on Gelatin. — Pepsin,
with dilute hydrochloric acid, deprives gelatin of its power to

1 For showing the action of pepsin to a class, Griinhagen's method
maybe employed. A piece of moist fibrin is placed in 0.2 per cent.
hydrochloric acid till it swells to a stiff jelly. It is then, laid on a funnel,
either with or without a filter, and after the superfluous acid has drained
off, a few drops of glycerin solution of pepsin, or artificial gastric juice,
are added to it. The rapidity with which the fibrin is converted into
peptone is shown by the number of drops which fall from the funnel.
By using two similar lilt"rs, the power of different digestive fluids may
he compared, and the effect of temperature shown by using Planta-
mour's funnel.

486 DIGESTION.

form a jelly sooner than dilute hydrochloric acid alone. Soak
gelatin in cold water till it swells up completely, and then add
sufficient boiling water to it to form a concentrated solution.
Put some of it into two test-tubes, and add to each its own
bulk of 0.2 per cent, hydrochloric acid. Put into one test-
tube a little glycerine solution of pepsin, and into the other
the same amount of glycerin, and place them in the water-
bath at 40° C. Take them out after an hour or so. and let
them cool. If both gelatinize, replace them for a while, and
then cool them again, repeating the experiment if necessary.
In this way the gelatin in the gastric juice will be found to
lose its power of gelatinizing somewhat sooner than the other.

* 121. Effect of Temperature on Digestion. — A low
temperature arrests the action of pepsin temporarily, but does
not destroy its activity. It acts more and more rapidly as the
temperature increases, until it attains its maximum between
30° C. and 50° C. Above this the action becomes slower. It
is completely annulled by boiling. The activity of a dilute
solution of pepsin is destined by exposure to a temperature
of 70° C. for two minutes, and by a still lower temperature
when exposed for a longer time. The activity of a concen-
trated solution is not so readily destroyed, and that of an
undiluted glycerin solution is retained after being exposed to
80° C. for two minutes.

To show the action of temperature, take four tubes, and put
into each equal quantities of 0.1 per cent, hydrochloric acid,
to which a little gtycerin solution of pepsin has been added.
Put one in pounded ice, the second in a test-tube rack on the
table, the third in the water-bath at 40° C, and boil the fourth,
and then put it also in the water-bath. Put into each a bit of
fibrin, and let them stand. The fibrin in the third tube will
dissolve quickly, that in the second much more slovvlj'-, that in
the first and fourth not at all. After a while — say half an
hour — take the tube out of the ice and put it in the water-
bath. The fibrin will then dissolve quickly, showing that the
activity of the pepsin has been only suspended. That in the
fourth will not dissolve at all, showing that the pepsin has
been destro}*ed.

* 122. Strength of Acid required for Digestion. —
The strength of acid with which albuminous bodies are most
quickly digested by pepsin varies with the nature of the body,
and also with the amount of pepsin present. Very dilute
solutions of pepsin digest best with veiy dilute acids, while
more concentrated pepsin solutions act more quickly with a
somewhat stronger acid. There seems, indeed, to be a definite
relation between the amount of pepsin and the strength of the
acid, though what this is has not yet been determined. The
proper strength of acid for any albuminous body may be

BY DR. LAUDER BRUNTON. 487

ascertained by placing a number of test-glasses in pairs, the
first pair containing very dilute acid, and each succeeding pair
a stronger acid. In each glass is placed a little of the albu-
minous substance, and to one of each pair au equal quantity
of solution of pepsin is to be added. They are then allowed
to stand, and the rapidity with which digestion goes on in each
is noted. The glasses with acid alone are required for the
purpose of comparing its effects with those of the pepsin and
acid together.

It can be shown as follows that digestion is hindered when
the acid is either too weak or too strong: Take three test-
tubes, and put into the first 10 cubic centimetres of 0.1 per
cent, hydrochloric acid, mixed with three times its bulk of
water ; into the second the same quantity of a similar acid
undiluted; and into the third 9^ cubic centimetres of this acid,
and half a cubic centimetre of commercial hydrochloric acid.
Place in each a bit of fibrin, and put them all in the water-
bath at 40° C. The fibrin in the second one will be quickly
digested ; that in the first and third tube much more slowly.
The reason of the slow digestion in the third tube will be seen
in the next experiment.

* 123. Influence of the Swelling of Fibrin on its
Digestion. — If fibrin is prevented from swelling up under the
action of gastric juice, either by mechanical means, such as a
thread tied round it, or by chemical agents, such as salt solu-
tions or too strong acids, its digestion is much retarded. Put
about 10 cubic centimetres of 0.1 percent, hydrochloric acid into
four test-tubes, and add to that in the fourth test-tube half a
cubic centimetre of commercial hydrochloric acid. Take four
bits of fibrin as nearly as possible of equal size. Wind a
thread firmly round one of them, and drop it into the third
test-tube. Put another piece into each of the other tubes.
As soon as that in the second tube begins to swell, add a
saturated solution of sodium chloride to it till it shrivels again.
Then add to the fluid in each tube half a cubic centimetre of
glycerin-pepsin, and let them stand. The fibrin in the first
tube, which merely serves for comparison, is soon digested,
and dissolves from without inwards. The bit in the second
tube does not swell again, but dissolves from within outwards;
so that a sort of shell remains, which, on shaking, falls to
pieces. That in the third tube, which has been tied with a
thread, behaves in the same way. That in the stronger acid,
in the fourth tube, swells incompletely, but dissolves from
without inwards, like the first.

** 124. Pepsin is not destroyed during Digestion. —
Although the aigesti-oe power of pepsin appeal's to be indefinite,
yet a limited quantity of gastric juice will not dissolve an nn-
1 1 in ittd quantity of fibrin — Adda little glycerin-pepsin and a

4S8 DIGESTION.

quantity of fibrin to some 0.2 per cent, hydrochloric acid in a
test-tube, and place it in the water-bath at 4o 0. for several
hours. If all the fibrin is digested, add more, and repeat the
addition until at last it remains undissolved, however long it
may be digested.

The arrest of digestion in this experiment is not due to de-
struction of the pepsin '., but to the accumulation of the products
of digestion in the liquid, andto the want of acid. Dilute the
mixture with water, and put it in the water-hath again, and di-
gestion will go on for a while and then stop. Jf again diluted,
it will go on again, but the action will be slow from the dilu-
tion of the acid. If more aeid be added, digestion will proeeed
more quickly, and by adding fresh quantities of acid, a very
large quantity of fibrin may be digested.

The same thing may be shown by putting the fibrin and di-
gestive fluid in a dialyzer and letting the peptones diffuse out.
The digestive fluid is then to be evaporated to its original bulk,
and acidulated, when it will digest the same amount of fibrin
as it did at first. It is well to keep an excess of fibrin always
in the dialyzer. This experiment is interesting, because diges-
tion in the stomach takes place under somewhat similar con-
ditions, the peptones being absorbed by the gastric vessels.
A stronger acid is required for digestion if the products of di-
gestion are present in guanti/;/ in the solution. When digestion
stops, as in the previous experiment, it may be renewed by
acidulating the solution more strongly with hydrochloric acid
instead of diluting with water, and when it stops a second time
a second addition of acid will set it on again. As too strong
hydrochloric aeid arrests digestion, a limit is soon put to the
addition of acid, but if phosphoric acid is used instead, diges-
tion may be kept up for a considerable time by fresh additions
of acid.

* 125. Pepsin Test. — The power of pepsin to dissolvealbu-
minous substances and convert them into peptones, has been em-
ployed as a test for its presence. For this purpose either fibrin
or coagulated white of egg maybe used. The process is given
by Briicke in " Moleschotts Untersuchungen" for 1860, p. 490,
and from this the following description has been taken: —

f Pepsin Test with Fibrin. — To test for the presence of pep*
sin in any substance or organ (as for example, any part of the
digestive system of an invertebrate animal), it must be finely
divided, treated with distilled water, and then allowed to stand
for some time, with frequent stirring, and filtered. If the filtrate
is alkaline it must be neutralized, after which as much hydro-
chloric acid must be added to it as will bring the percentage
of acid to one-tenth. A bit of fibrin is then thrown into it; if
it swells it is allowed to stand, but if it does not swell, dilute
acid is added by drops at intervals till the edges and free fibres

BY DR. LAUDER BRUNTON. 489

of the hits of fihrin hecome translucent. If the filtrate is acid,
a hit of fihrin is thrown into it; if it swells up, it is allowed to
stand, if not, acid is added as before directed till it does swell :
the digestion is then allowed to go on at the temperature of
the room, and the result observed.

The residue which remains on the filter is introduced into a
beaker covered with 0.1 per cent, hydrochloric acid, and placed
in the water-bath at 40° C. for an hour and a half or two hours,
or allowed to stand 24 hours at the temperature of the room,
with frequent stirring. It is then filtered, and the filtrate used
in the same manner as before. The reason why Briicke recom-
mends that the watery extract should be tested separately from
the acid extract, is that by this means pepsin already excreted
from the peptic cells can be distinguished from pepsin still con-
tained in them, inasmuch as the former is easily taken up by
water alone, while the latter is taken up with difficulty by
water, but easily by dilute acid. This process has also the ad-
vantage that when soluble albuminous bodies are present in
any quantity, the}' are, for the most part, removed by the
watery extract. If neither of these objects is of importance,
the substance may be at once treated with dilute hydrochloric
acid, and when it is small, as, for example, the salivary glands
of insects, it may be at once thrown with a bit of fibrin into
dilute hydrochloric acid, and digestion looked for. If a fluid
is to be examined it must be filtered, and the filtrate and residue
treated as above directed for solids.

Pepsin Test with White of Egg. — White of egg is more readily
got than fibrin, but it dissolves mere slowly, so that the test
takes a longer time. Hard boiled white of egg, cut into dice,
may be left for a long time in dilute hydrochloric acid without
undergoing any changes, but the coagulum which is produced
by boiling white of egg diluted with water undergoes partial
solution pretty rapidly. The free alkali contained in white of
egg is the cause of this difference in its -behavior when prepared
in these different ways, and the inconstancy of its amount ren-
ders it difficult to determine what degree of acidity must be
given to the liquid. To obviate this, add acetic acid to white
of egg diluted with water until it turns blue litmus paper violet,
but not red. Filter from the precipitate; test the reaction of
the filtrate again, and correct it if necessary. Then coagulate
it in the water-bath, wash it with water, and use it like fibrin,
but iimj an acid of 0.15 per cent. If pepsin is present, diges-
tion will go on just as with fibrin. The acid alone will not dis-
solve the albumin for many days.

126. Theory of Pepsin Digestion. — It has already been
leen that neither pepsin alone, nor hydrochloric acid alone,
will digest. 0. Schmidt supposes they do so when mixed, by
forming a compound acid — pepto-hydrochloric acid, lie thinks

490 DIGESTION.

that digestion consists in the combination of this acid with
albuminous bodies, and explains the fact that digestion can
be renewed by the addition of hydrochloric acid after it has
ceased, by supposing that the pcpto-hydrochloric acid, thus
liberated, is enabled to begin to digest anew.

The combination of pepsin and hydrochloric acid to form a
new acid is supported by several facts, and is very generally
believed, but Schmidt's hypothesis regarding its mode of
action is open to the objection that it is not merely a com-
pound of albumin with acid which is formed during digestion,
but peptones. It therefore seems more probable that the pep-
sin acts as a ferment only in acid solutions, causing the albu-
minous bodies to take up water and split up.1

That pepsin and hydrochloric acid mutually combine when
mixed, as in digestive liquids, is rendered probable, not only
by the fact already shown that they produce effects together
which neither is capable of producing separately, but that in
such mixtures the characters of both are modified.

This is seen by comparing the action of dilute hydrochloric
acid alone with that of hydrochloric acid pepsin. The former
extracts all the salts and leaves a gelatinous substance, while
the latter extracts this substance and leaves a brittle mass
containing a large proportion of inorganic salts. As regards
pepsin, a modification of property is shown in Yon Wittich's
observation, that, although pepsin alone does not diffuse
through vegetable parchment, pepsin with hydrochloric acid
does so readily. That the decomposition of albuminous sub-
stances is essentiall}' connected with their taking up water, is
rendered probable by the fact that digestion does not take
place in its absence, and that products similar to those of
digestion can be obtained by boiling albuminous bodies with
water for a very long, time, or for a shorter time with dilute
acid.

The former of these facts can be easily demonstrated by
treating fibrin which has been soaked in glycerin and not
washed at 40° C. with a glycerin solution of pepsin undiluted
with water, acidulated to the proper degree by the addition of
a few drops of strong acid ; under these circumstances the
fibrin is not digested. The latter may be shown by boiling
fibrin with dilute sulphuric acid for an hour or two, and then
neutralizing the liquid, filtering and testing the filtrate for
peptones.

* 127. Secretion of Gastric Juice. — Pepsin is contained
in all parts of the peptic glands, but free acid is only formed
near their orifices. To show this, kill a pigeon, open it imme-

1 For a clear account of the probable mode of action of ferments, see
" Betrachtungen iiber die Wirkungsweise der ungeforinten Fermente,"
by Dr. G. Hufner ; Barth, Leipzig, 1872.

BY DR. LAUDER BRUNTON. 491

diately and dissect off part of the muscular layer from the
proventriculus, which lies between the crop and gizzard. The
ends of the gastric glands are thus laid bare. With a pair of
curved scissors snip off the ends of the glands, taking care not
to cut much below the surface. Squeeze the shred so obtained
between two bits of blue litmus paper. It will have a neutral
or at most an extremely weak acid reaction, while the inside
of the stomach will be found to be strongly acid. The pres-
ence of pepsin in the part of the glands where little or no acid
is contained may be shown by dissecting oft* this part along
with the muscular layer, and placing it in a test-tube with 0.1
per cent, hydrochloric acid in the water-bath at 40° C. Part
at least of the muscular la}7er will be digested. The presence
of acid only on the surface of the stomach can be shown, also,
b}r injecting first a solution of half a gramme of ferric lactate,
and then a solution of potassium ferrocyanide into the jugular
vein of a rabbit, killing it about an hour afterwards, and open-
ing the stomach immediately. These two salts form Prussian
blue onl}7 in the presence of an acid. On making a section of
the wall of the stomach, it is seen that the blue color is en-
tirely confined to the surface, the deeper part of the mucous
membrane remaining colorless.

After Death Acid continues to be formed in the Glands. —
Thus, if the stomach of a pig or rabbit is cut in pieces, washed
until it no longer gives a trace of acid reaction, and then left
to itself, it is found after a time to be again acid.

* 128. Digestion of the Stomach by itself.— If there
is only a small quantity of acid present in the stomach it will
not be completely digested after death ; but if it contains
anything which will supply acid, not only the stomach, but a
great part of the adjoining organs may be digested. Give a
cat a quantity of milk, or introduce the. same liquid into the
stomach of a rabbit or guineapig by means of a Byringe and a
gum-elastic catheter. For this purpose a perforated cork
should be placed between the animal's teeth, and the catheter
passed through the hole into the stomach. In an hour after kill
the animal, and let it lie in a warm place for twenty-four hours.
The whole of the stomach will probabty be found digested.
The stomach is not digested during life, because the alkalinity
of its walls is preserved by the circulation of blood in them.

* 129. Digestion of the Stomach during Life. — When
the circulation of the blood is arrested in one part of the organ,
it becomes digested, and ulceration occurs. This is best shown
by Sharpey's modification of Pavy's original experiment. The
method consists in opening the stomach of a rabbit, narcotized
by subcutaneous injection of chloral, by a longitudinal incision,
seizing a part of its posterior wall with a pair of artery forceps
and drawing it forward. This having been done, a ligature is

I

492 DIGESTION.

passed round the part seized, so as to include a piece of about
half an inch in diameter. Finally, the wound in the stomach
ami that in the abdominal wall are sewn up. and the animal
placed in a warm place for some hours.

130. Influence of Nerves upon the Secretion of the
Stomach. — The stomach, like the submixillary gland, has two
secretions; one thin, watery, and acid — the gastric juice proper ;
the other thick, tenacious and alkaline — the gastric mucus.
The latter is secreted and accumulates on the surface of the
gastric mucous membrane during fasting, while the former is
only secreted when an irritant is applied to the inside of the
stomach. The irritant may be mechanical, e. <?., the friction
caused by food, or any firm or hard substance introduced into
the stomach, tickling with a feather, or rubbing with a glass
rod. The most active chemical irritants are alkalies, which
produce, even in very dilute solutions, an abundant secretion.
This continues even after the alkali has been neutralized by
the gastric juice or washed away by a stream of water. The
saliva which is swallowed by the animal thus excites the se-
cretion of gastric juice. Other stimulants are alcohol, ether,
pepper, and cold water. When an irritant is applied, the gas-
tric mucous membrane, which is of a pale color, immediately
becomes red ; its vessels dilate those of the submaxillary gland,
and the watery-looking gastric juice oozes rapidly from its
surface. The nerve centres, on which secretion is dependent,
are present in the walls of the stomach itself, for it takes place
even after all the nerves which enter the viscus from without
have been divided. These centres are, however, as Ave shall
see, much influenced by the vagi.

The Action of the Vagus on the stomach is still much dis-
puted, but it would appear from the experiments of Bernard
and Rutherford that it contains afferent fibres, the irritation of
which, as, e. g., during digestion, causes reflex dilatation of the
gastric vessels. Bernard found that section of the vagi during
digestion caused the stomach to become pale, and that in one
or more experiments, irritation of these nerves reddened it, and
induced an abundant secretion. He did not, however, deter-
mine whether this effect was due to afferent or efferent fibres,
but Rutherford found that, while section of the vagi during di-
gestion caused the stomach to become pale, irritation of their
central ends generally reddened it. This effect was, however,
sometimes preceded by its opposite, the organ becoming pale at
first and afterwards red. a result which indicates that the vagus
contains two sets of afferent fibres, one of which increases,
while the other diminishes the degree of contraction of the gas-
tric vessels.'

From the observation of Bernard and Blondlot, that gentle excita-
tion increases the secretion of gastric juice while violent irritation stops

BY DR. LAUDER BRUNTON. 493

** 131. Effect of Stimuli on the Secretion of Gastric
Juice. — To see the effect of stimuli applied to the mucous
membrane, a dog with a gastric fistula should be allowed to
fast for six or seven hours, and then laid on its side in such a
position that a good light falls into the canula. The observa-
tion consists in noting the color of the membrane, and then in-
jecting a little dilute solution of sodium carbonate, or tickling
the surface with a feather, and observing the effect. The effect
of irritation on the amount of secretion ma}' be estimated by
letting the dog stand while the beaker is held under the canula,
and bjr measuring the juice which flows from it in a given time
before and after irritation.

** 132. Demonstration of the Action of the Vagus
and Splanchnic on the Stomach.— The proof that the
vasomotor nerves of the stomach are derived from the splanch-
nics is founded on the observation that, when the left splanch-
nic is irritated in the rabbit, as directed at page 259, the arte-
ries at the great curvature may be seen to contract. This may
be still better seen in the cat.

The vagus is the sensory nerve of the stomach and contains
afferent fibres, the irritation of which produces reddening of
the gastric mucous membrane. — It also contains motor-fibres
which are distributed to the muscular coats of the organ. To
show these facts, a cat must be placed under chloroform, after
which both vagi are prepared, and the stomach exposed. If,
now, the animal having partially recovered from the anaesthetic,
the stomach is seized between the thumb and forefinger, and
subjected to traction in the direction of its length, slight but
unequivocal signs of uneasiness are perceived. The vagi are
then divided, after which it may be observed, first, that the
stomach is paler than before, and secondly, no sign of uneasi-
ness is produced b}r traction.

On irritation of the central end of one of the divided nerves,
the color of the mucous surface is more or less completely re-
stored. On irritation of the peripheral end, the walls of the
stomach often begin to contract, but this effect is not constant
when either splanchnic is intact. When both are divided, irri-
tation of either vagus is invariably followed by movements of
the stomach (Ilouckgeest).

Experiments on vomiting have been omitted, as they do not
succeed in narcotized animals.

it and causes vomiting, it appears probable that some of the gastric nerves
are more easily excited than others. See Carpenter's Physiology, edited
by Power, 7th edition, p. 128.

494 DIGESTION.

Section III. — Functions of the Liver.

133. General Characters of the Bile. — Bile as it flows
from the liver is a thin liquid, but when it stays some time in
the gall bladder it becomes mixed with mucin, the presence of
which renders it tenacious. In man, it is, when fresh, of a
golden-yellow color, like yolk of egg, as may be seen when it
is vomited; but after death the bile in the gall bladder is
generally brownish. In the dog it is also yellow, in the herbi-
vora it is green, but very frequently it has a decided brown
tinge in both. Its specific gravity and composition are not
alwa3rs the same even in the same animal.

Sj)ecijic Gravity and Solids. — The specific gravity and
amount of solids, organic and inorganic, in bile are determined
in the same way as in saliva. The ash has a reddish tinge,
due to the presence of iron. For the method of determining
the amount of iron, see page 202.

* Reaction. — Bile discolors litmus so much as to hide the
reaction, it must therefore be first diluted and the reaction
tested afterwards. In fresh bile it is always alkaline.

134. Composition of Bile. — When obtained from the gall
bladder, the bile contains, 1, mucin ; 2, bile pigments; 3, sodium
salts of biliary acids; 4, cholesterin; 5, lecithin ; 6, phosphates
of sodium, calcium, and iron, sodium chloride, and generally
traces of copper.

* Mucin. — Add common alcohol to bile, obtained from the
gall bladder of an ox; wash the abundant precipitate so ob-
tained with dilute alcohol ; add water, and the precipitate will
dissolve; add acetic acid, and a precipitate of mucin will fall
with traces of bile pigment adhering to it. For the reactions
of mucin, see § 45.

Bile Pigments The yellow color of fresh bile in man and

carnivora is due to a coloring matter termed Bilirubin ; the
green color possessed by the bile in herbivora, or acquired by
the bile of carnivora after standing, is due to Biliverdin, a pro-
duct of the oxidation of Bilirubin. When the bile is long in
the gall bladder, a small quantity of a third pigment, Biliprasin,
may also be present.

** 135. Test for Bile Pigments (Gmellin's Test.)—
When strong nitric acid, which has been exposed to light, and
therefore contains nitrous acid, is added to a solution of bili-
rubin, it becomes oxidized, and the products of oxidation
which are successively produced, present the colors of the
rainbow. First, biliverdin is produced, and tlte yellow color
of the bilirubin solution changes to green and then becomes
successively blue, violet, red, and lastly dirty yellow. If a so-

BY DR. LAUDER BRUNTON. 495

lution of biliverdin is used instead of bilirubin, the same
changes of color occur, but the first change is of course to
blue. In the reaction above described, the oxidation is most
complete at the point of contact of the two liquids, the degree
of action diminishing as the distance from this point increases.
If, therefore, the two liquids are brought into contact without
agitation, successive zones of color are formed by the products
of oxidation in the same order as before, viz., green, blue, violet,
red, and dirty ^yellow, the last mentioned being nearest the
acid. In order to apply the test to a fluid supposed to contain
bile pigment, pour it in a thin layer on a white porcelain plate,
and place two or three drops of nitric acid in contact with its
edge. Or pour nitric acid containing a little nitrous acid into
a test tube: hold it obliquely, and let the fluid to be tested
flow gently down the side of the test-tube and over the surface
of the acid. Fix the test-tube in the same oblique position,
without shaking, in a holder, and let it stand ; see from time
to time whether the rainbow-colored zones have appeared at
the point of junction in the proper order. Brucke's method is
to mix the fluid to be tested with very dilute nitric acid, and
then to let a little strong sulphuric acid run gently down the
side of the test-tube. Dilute nitric acid alone does not act on
the bile pigment, but after the addition of the sulphuric acid
t he colored rings spread from its upper surface. Ox-gall does
not exhibit the colored zones, even when treated with strong
nitric acid, unless it contains much nitrous acid.

To show them, pour a little ox-bile on one part of a porce-
lain plate, and on another near it some very strong nitric acid,
containing much nitrous acid, or nitric acid, previously mixed
with concentrated sulphuric acid, and let the bile and acid
gently come in contact.1

1 When the urine of a patient suffering from jaundice is tested for
bile pigments with nitric acid, the color reaction sometimes cannot be
obtained, even though the urine be so dark that the foam on its surface,
after shaking it, is quite yellow. Tins negative result generally occurs
in cases where the temperature of the patient is high, and more espe-
cially when it has continued high for some time. It is then advisable,
instead of testing the urine directly with nitric acid, to use the method
recommended by Huppert. Precipitate the urine with milk of lime,
throw the precipitate on a fluted filter, and allow the fluid to drain away.
Take a piece of the precipitate, about the size of half a hazel-nut, place
it in a test-tube, fill the tube half full of alcohol, and then add dilute
sulphuric acid in such quantity that the fluid, after being shaken, has an
acid reaction. Warm the tube : the fluid will extract the color from the
precipitate ; filter and boil the filtrate. If bilirubin is present in the
urine, it will combine with the lime and be precipitated ; but it will be
again set tree by the sulphuric acid, and be dissolved by the warm aci-
dulated alcohol, forming a yellowish-^reen solution. This solution will
become dark green on boiling, anil tin; more free acid present, the sooner
will it do so. When long boiled, it sometimes becomes blue.

496 DIGESTION.

Fallacies to be avoided in using Gmelin's Test. — This test
must never be applied to a fluid containing alcohol, as the
alcohol alone will cause abundant formation of nitrous acid,
and produce the colored rings, although no bile pigment is
present.

Jn using it for the detection of bile pigment in urine, the
presence of indican may lead to error. This is avoided if care
is taken to observe that the green, violet, and red zones are all
present, as urine containing much indican may exhibit green
and yellow zones alone, or green and yellow with blue between,
but never exhibit all of the colors in the right order.

* 136. Bilirubin. ClfiH18N,();. — Synonymes : Bilifulvin,
Biliphain, Cholepyrrhin, Haematoidin.

Preparation from Bile. — Put some fresh dog's bile in a
small flask, acidulate it with acetic acid, add chloroform till
the flask is almost full, warm it in a water-bath, and shake.
The chloroform takes up the bilirubin and settles at the bot-
tom of the flask. Remove it with a pipette, and evaporate it
quickly. The red residue is bilirubin. Add alcohol to it to
dissolve out the impurities ; pour it off after it has stood some
time ; dissolve the bilirubin again in chloroform, and again
evaporate. To obtain it pure, this may be repeated once or
twice. When crystallized, it is of a red color. During crys-
tallization, a part of it is apt to become oxidized with biliver-
din, on which account it is easier to obtain it pure by precipi-
tating it from the choloroform solution by the addition of
alcohol. The precipitate is amorphous, and of an orange
color.

The amount of bilirubin which can be obtained from the
bile of a single dog is very small. To obtain it in greater
quantities, biliary calculi may be used.

Preparation of Bilirubin from Gall Stones. — Reduce the
gall stone to powder, and extract it first with ether, to free it
lrom fat and cholesterin, so long as any of the powder is dis-
solved; next boil it with water, to free it from admixture of
bile ; and lastly, treat it with dilute hj^drochloric acid, to
remove lime and magnesia. Dissolve the residue in warm
chloroform. Filter (preserving the undissolved part), distil,
or evaporate off the chloroform ; extract the residue with abso-
lute alcohol (preserving the alcoholic extract, see § 147), and
then witli ether. Dissolve the residue in a second quantity of
chloroform, and evaporate until the bilirubin begins to sepa-
rate, and then precipitate it with alcohol.

Properties of Bilirubin. — The orange-colored precipitate is,
1, quite insoluble in water; 2, very slightly soluble in ether;
3, springly soluble in alcohol, but rather more soluble than in
ether ; 4, soluble in chloroform, especiall}' when warm, and in
a less degree in benzol and bisulphide of carbon, amyl-alco-

BY DR. LAUDER BRUNTON. 497

hol, and glycerin. Its solutions have a yellow or brownish-red
color, which is so intense that it is distinguishable in a layer
1.5 centimetres thick of a solution containing one part in
500,000.

Bilirubin combines with alkalies, forming compounds which
are soluble in weak alkaline liquids, which are precipitated by
neutralization. They are insoluble in chloroform, the chloro-
form solution bilirubin being precipitated by alkalies. For
this reason it is necessary to acidity bile before extracting the
bilirubin with chloroform. Bilirubin also combines with Lime.
— If bilirubin is dissolved in ammonia, and the solution pre-
cipitated with calcium chloride, a rusty-red flocculent precipi-
tate is obtained, which is a calcium compound of bilirubin.

* 137. Biliverdin. C16H20N.,O, or C^H^N^.— Preparation.
— Put an alkaline solution of bilirubin in a flat shallow vessel,
and let it stand exposed to the air for a considerable time,
until it becomes green. Precipitate it with hydrochloric acid,
wash the precipitate with water, dissolve it in alcohol, filter,
and evaporate. The biliverdin is left as an amorphous body.
The reaction by which bilirubin is converted into biliverdin is
considered by Staedeler to be CI6HlfeN2O3-|-H,O-|-O = C16H.0

NsOs«

Properties. — It is insoluble in water, ether, and chloroform.
It is soluble in — 1, alcohol (and can thus be separated from
bilirubin, which is insoluble), 2, dilute liquor potassae, or 3,
ammonia, and 4, strong sulphuric acid. It is precipitated from
its alkaline solution by acids, or by salts of calcium, barium,
or lead. It is precipitated unchanged from its solution in sul-
phuric acid by the addition of water. Nitric acid oxidizes bili-
verdin in alkaline solutions, and produces the same series of
colors as with bilirubin. Sulphurous acid, which is a powerful
deoxidizing agent, causes alkaline solutions of biliverdin, espe-
cially when warmed, to become yellow ; when the j'ellow solu-
tion is treated with nitric acid, it behaves just like a solution
of bilirubin.

138. Relation of Bile Pigments to Haemoglobin. — Bili-
rubin is generally believed to be formed from haemoglobin,
which becomes altered during the passage of blood through
the liver. The grounds for this belief are the apparent identity
of bilirubin, and the pigment called haematoidin, found in old
extravasations of blood, and the observation that bile pigments
appear in the urine after the injection into the veins of solu-
tions of haemoglobin or of any substance which will dissolve
the blood corpuscles, and liberate haemoglobin, such as water
(Herrmann), bile acids (Frerichs Kiihne), or ether (Tiegel).
They also appear after prolonged inhalation of ether (Noth-
nagel), or chloroform (Bernstein). Further support is also
lent to this view by the destruction of haemoglobin, which
32

498 DIGESTION.

appears to take place in the blood during its passage through
the liver (Grehant). Though a positive result has been
obtained by so many observers, Naunyn failed to detect bile
pigments in the urine of rabbits after the injection of haemo-
globin, either subcutaneously or into the jugular vein, and
attributed the success of others to their experiments having
been made on dogs, in whose urine bile pigment is normally of
frequent occurrence. Tie noticed them, however, in rabbit's
urine, when blood in which the corpuscles had been destroyed
by freezing or ether, was injected into the intestine, so that
the haemoglobin absorbed from it, or set free by the action of
the ether on the blood of the portal vein, passed through the
liver before reaching the general circulation. Nannyn's experi-
ments, also, have been repeated by Wolff and Wickham Legg,
with a negative result.

In performing them proceed as follows: Narcotize a rabbit
with chloroform, shave the hair from the belly, make an incision
about 1^ centimetres in length in the linea alba a little above
the middle point, between the base of the xiphoid cartilage and
the symphysis pubis. Seize a coil of small intestine with a pair
of artery forceps, and hold it opposite the wound, without draw-
ing it forward more than is just necessaiy. Inject 2 cub. cent,
of ether into the intestine close to the points of the forceps with
a subcutaneous syringe. Tie a ligature round the point
wounded by the syringe and forceps ; attach the intestine by
it to the abdominal wall, and close the wound with a point of
suture. The inhalation of chloroform is too short to produce
of itself bile pigment in the urine, and it greatly facilitates the
operation.1 Examine the urine of the rabbit for bile pigments
an hour or two after the operation, and again next morning.
To get the urine, hold the rabbit over a large beaker, compress
the abdomen with the palm of one hand, and press with the
thumb of the other on the bladder just above the pubes, push-
ing it well down into the pelvis.

139. Relation bet-ween the Coloring Matter of Bile
and that of Urine. — The urinary pigment is supposed to be
derived from that of bile, as a substance which presents similar
spectroscopic characters can be extracted from bile, or produced
by deoxidation from bilirubin. In the organism, bile pigments
are probably reduced by hydrogen, or other reducing agents
present in the intestine.

When dog's bile is extracted with dilute hydrochloric acid
and filtered, the filtrate has a reddish or reddish-yellow color,
and on spectroscopic examination presents a band close to F,

1 The writer has failed to observe bile pigments in the urine, either
after the injection of bile acids into the veins, or of ether or dissolved
blood corpuscles into the intestines.

BY DR. LAUDER BRUNTON. 499

between it and 5, which disappears on the addition of liquor
sodae, and is replaced by a narrower band, also between 6 and
F, but nearer 6, the filtrate at the same time assuming a yel-
lowish color. If the solution is only very slightly alkaline,
both bands ma}T be seen at once. . Ammonia produces similar
changes in the color of the fluid, but the second band is very
faint when it is employed. On acidulation, the alkaline liquid
regains its red color, and the first band re-appears. By treat-
ing it with chloroform, a solution is obtained in which the first
band is visible, but is somewhat nearer b.

Urine, especially when high-colored, exhibits the band at F,
though not very distinctly; but it may be clearly seen by pre-
cipitating the urine with lead acetate, decomposing the precipi-
tate by an acid, and examining the filtrate spectroscopicallj\
The addition of sodium hydrate causes the other band faintly
to appear, and when treated with .chloroform in the same way
as bile, the solution and the position of the band seen in the
chloroform solution is altered in a similar manner.

A substance presenting a similar band is obtained by acting
on a solution of bilirubin in liquor potassse or liquor sodae with
sodium amalgam, for several days, with exclusion of air (Maly).

** 140. Bile Acids. — The bile acids are taurocholic and
glycocholic acids. In the bile of the pig another acid, hyocho-
lic acid, is present. In the bile they are combined with soda,
and their soda salts form the so-called crystallized bile. These
acids are conjugate acids, composed of cholic acid in combina-
tion with taurine and glycocine. The presence of cholic acid
or its compound is recognized by a reaction known as

Pettenkofer's Test. — This test shows the presence only of
bile acids, but not of bile pigments or other constituents of bile.
Dilute some ox-bile with water and filter it. Put a little in a
test-tube, with a small piece of sugar or a little strong syrup.
Then add concentrated sulphuric acid drop by drop, shaking
the tube after each addition ; the temperature of its contents
should be kept as near 70° C. as possible, either by warming it
if necessaiy, or putting it in cold water if it gets too hot.
Cholic acid is first precipitated and then dissolved by the sul-
phuric acid, the solution assuming a cherry-red and then a
beautiful purple color, which becomes gradually darker when
the liquid is allowed to stand. The reaction is hindered by
the presence of much pigment, oxidizing substances, and albu-
minous bodies, or bodies readily decomposed by sulphuric acid.
It is therefore better to use a solution of crystallized bile, if it
is at hand, than diluted bile. This reaction cannot be relied
on alone as positive proof of the presence of bile acids, for
amylic alcohol and other organic substances give a similar col-
oration. To show this, put a solution of albumin, or rather of
syntonin (§ 7), into a test-tube with a little syrup, and add

500 DIGESTION.

strong sulphuric acid. A purple color is developed. To dis-
tinguish between the purples given by bile and by albumin, ex-
amine the test-tubes by the spectroscope. The bile acids give
four hands; the first at I), the second and third between D and
E (the second being nearer I), the third close to E), the fourth
at F. If the solution is dilute, the third band is seen sharply,
the second less distinctly, and the other indistinctly. The col-
ored albuminous solution gives only one band between E and F.

Detection of Bile Acids in the Urine. — They are usually
present only in small quantities in the urine, even in severe
cases of jaundice. Various methods of applying Pettenkofer's
test have been proposed, one of which (Strassluirg's) is applied
as follows: Add a little cane sugar to some urine containing
bile acids, dip a piece of filtering paper into it, let it dry com-
pletely, put a drop of pure sulphuric acid upon it, and allow
the acid partially to run off.. In a quarter of a minute a beau-
tiful violet color appears, which is best seen by holding up the
paper to the light and looking through it. In all doubtful
cases, and whenever accurate results are required, the bile
acids should be separated before applying the test, see § 204.

* 141. Crystallized Bile. — Mode of Preparation. —
Evaporate bile to a quarter of its volume, mix it with a con-
siderable quantity of animal charcoal, rub them thoroughljr
together, and then heat the mixture on a water-bath till it is
perfectly dr}'. Put it immediately, while still warm, into a
flask, cover it with absolute alcohol, cork the flask, and let it
stand for a good while, shaking it occasionally so that the
alcohol may dissolve out all the bile salts. Filter, and pour
the filtrate into a perfectlj7 dry stoppered bottle, large enough
to hold four times as much. Add ether to it, until no further
precipitate is produced ; then replace the stopper, and put the
bottle aside for a few days. If the alcohol and ether are both
anhydrous, the precipitate which falls consists of microscopic
crystals, but generally it forms a resinous mass at the bottom
of the flask, which after several days, or weeks, begins to
crystallize, and groups of silky needles appear.

To preserve the crystals, pour off the mixture of alcohol find
ether, wash them with pure ether, evaporate the adhering ether
from them in vacuo, and replace the stopper in the bottle.
The crystals, if left exposed, take up moisture, and form a
resinous mass, which is eventually converted into a syrupy
fluid. Crystallized bile is very soluble in water and in alco-
hol, hut insoluble in ether.

Composition of Crystallized Bile Crystallized bile consists

of the sodium salts of glycocholic and taurocholic acids. To
separate these two acids from the base and from eaeli other,
dissolve the ciTstals or the resinous precipitate in water, and
add first solution of neutral lead acetate, and then a little basic

BY DR. LAUDER BRUNTON. 501

lead acetate. This combines with the glycocholic acid, and
forms an insoluble lead-glycocholate. Filter, and add to the
filtrate lead acetate and ammonia, and a precipitate of lead-
tanrocholate will be formed. Filter; the filtrate contains the
soda which has been set free, and also the excess of lead.
The nature of the base may be shown by precipitating the
lead from the solution by hydrogen-sulphide, and filtering ;
the filtrate when evaporated to dryness leaves sodium acetate.

* 142. Glycocholic Acid (C2RH45NOH) is abundant in
ox-gall, but is only present in small quantities in human bile,
and absent from the bile of the dog and cat. Preparation. —
Dissolve the lead-gl3'cocholate obtained in last experiment in
hot alcohol ; precipitate the lead with hydrogen-sulphide, con-
centrate the alcoholic solution by evaporation, and then pre-
cipitate the glycocholic acid by adding water.

Another and easier plan is that of Gorup-Besanez. Evapo-
rate ox-gall nearly to dryness in a water-bath, and exhaust
the residue with alcohol of ninety per cent. (sp. gr. 822).
Distil or evaporate off the alcohol, dilute the residue if neces-
sary with water, add milk of lime to it and warm it gently.
The greater part of the coloring matter will be precipitated by
the lime. Filter, allow it to cool, and add dilute sulphuric
acid to it (avoiding excess), until a permanent turbidity is
produced. Let it stand for a few hours, and the fluid will in
most cases become a mass of crystals of glycocholic acid.
Occasionally this conversion does not take place till after
some days, or even weeks. Throw the mass on a filter con-
nected with the water air-pump, wash with cold water, and
press it between folds of blotting paper, first with the hand
and then with a screw-press. It may be obtained in a still
purer condition by dissolving it in a large quantity of lime-
water, and adding dilute sulphuric acid until the ghycocholic
acid again separates. It crystallizes in long thin white needles.
The crystals are sparingly soluble in cold water, more readily
in warm, from which it crystallizes out on cooling. It is Tery
sparingly solid tie in ether, readity in alcohol. When water is
added to the alcoholic solution, the acid is precipitated first
as a turbidity, and then in flakes and drops, which become
gradually con verted into crystals.

* 143. Glycocine or Glycocol. — Glycocholic acid can
be decomposed, and glycocine obtained from it by boiling it
for a long time with strong hydrochloric acid.1 On then

' Glycocine is more readily prepared from hippuric acid, which is
contained in large quantities in the urine of herbivora, and consists of
glycocine in combination with benzoic acid. Preparation, of Hippuric
Acid. — Milk of lime is added to horse's or cow's urine ; the mixture is
boiled, filtered, neutralized with hydrochloric acid, and evaporated to
a small bulk. On acidulating with hydrochloric acid, hippuric acid

502 DIGESTION.

allowing it to eooi, a resinous mass (cholalic acid and dyslysin)
separates. The fluid is poured off from the resin and evapo-
rated. The residue is then dissolved in water wanned with
hyd rated lead oxide, and filtered ; the filtrate decomposed by
hydrogen-sulphide, filtered, and the filtrate evaporated.

The transparent rhomboidal crystals of glycocine thus ob-
tained are then washed with absolute alcohol. They have a
sweet taste, and are readily soluble in cold water ; almost in-
soluble in ether and alcohol.

* 144. Taurocholie Acid (C2fiH45NS07) is present along
with glycocholic acid in ox-bile ; it is the chief acid in human
bile, and the only one in that of dogs. Preparation Sus-
pend the lead taurocholate obtained from crystallized bile in
alcohol, and decompose it by hydrogen-sulphide : filter ; evapo-
rate the filtrate at a moderate temperature to a small bulk,
place it in a stoppered bottle, and precipitate by a great excess
of ether. The acid is precipitated as a syrup. After standing,
it changes, if the process is successful, to fine silky crystals,
which, when exposed to air, dissolve, or form a syrup.

Taurocholie acid is soluble in water and alcohol, insoluble
in ether. It is recognized as a bile acid by giving Petten-
kofer's reaction, and is distinguished from glycocholic acid
by not being precipitated by lead acetate alone, but by lead
acetate and ammonia, and from any other bile acid b}' yielding
taurin when decomposed by boiling with hydrochloric acid.
It may be prepared from taurocholie acid or from crude bile.

145. Taurine (C2H.NS03). — Preparation. — Boil ox-gall
with dilute hydrochloric acid for several hours. The bile
acids are thus decomposed : Taurine and glycocine combine
with the hydrochloric acid, and remain in solution, cholic acid
separating as a resinous mass. Filter the fluid, evaporate the
filtrate to dryness, extract the residue with absolute alcohol to
remove the glycocine-hydrochlorate, dissolve the residue in
water, and allow it to stand and crystallize. In order to
purify it, dissolve it in spirit, precipitate it with lead acetate,
decompose the precipitate with hydrogen-sulphide, filter, evapo-
rate the filtrate to dryness, extract the residue with absolute
alcohol, dissolve the taurine which remains in a very little
water, and allow it to crystallize. Taurine is soluble in fifteen

crystallizes out in rhombic prisms resembling thick needles (fig. 318).
Glycocine is prepared by boiling hippuric acid with strong hydrochloric
acid for several liours, and evaporating tbe solution almost to dryness.
The hippuric acid is decomposed, yielding benzoic acid and glycocine.
The residue is extracted with cold water, which dissolves but little of
the benzoic acid. To the watery extract hydrated lead oxide is then
added, to remove the hydrochloric acid. The liquid is filtered, and the
lead precipitated from the filtrate by hydrogen sulphide. The precipi-
tate having been removed by filtration, the filtrate is evaporated to a
small bulk.

BY DR. LAUDER BRUNTON. 503

or sixteen parts of cold water, and in a much smaller quantity
of hot water. In cold alcohol it is sparingly soluble, more
easily in warm alcohol. It is insoluble in absolute alcohol and
ether. Taurine is recognized by its crystalline form, and by
its containing sulphur. Its crystals are colorless, transparent,
six-sided prisms, with four to six-sided pointed ends (fig. 312).
Taurine is proved to contain sulphur as follows: If a crystal
is heated on platinum foil, it swells, becomes brown, and fuses,
giving off fumes in which sulphurous acid is recognized by
its smell. If the crystals are ignited with sodium carbonate,
and a little acid is poured over the residue, hydric-sulphide is
evolved. If they are dissolved in caustic potash, and the
solution concentrated by boiling, ammonia is given off, and
potassium sulphate and acetate left in solution.

146. Cholic Acid (C.>tHm05). — Preparation.— Boil bile
(or solution of gtycocholic acid) with strong solution of caustic
potash, or hot saturated solution of baryta water, for twelve
or fourteen hours, precipitate by hydrochloric acid, wash the
precipitate with water, dissolve it in a little liquor potassre,
add ether, precipitate by hydrochloric acid, and allow the
liquid to stand for several days. The ether causes it to become
crystalline, and form quadrilateral prisms with pyramidal ends.
Pour off the ether, dry the crystals between folds of blotting
paper, dissolve them in hot alcohol, and add a little water
until a turbidity just commences. Cholic acid crystallizes
out on cooling in tetrahedra. Cholic acid exists in two con-
ditions. In one it is soft and waxy, and somewhat soluble in
water ; in ether tolerably, and in alcohol very readily soluble.
In the crystalline condition it is insoluble in water and ether,
but tolerably soluble in alcohol. When heated on platinum
foil, it becomes brown, melts and burns, giving off incense-like
fumes. Heat, or boiling with sulphuric acid, converts it into
resinous-looking substances, choloidinic acid and dyslysin.

* 147. Cholesterin. — Cholesterin is not generally pre-
pared directly from bile, but from gall-stones, most of which
consist chiefh' of cholesterin, along with a little bile pigment
and earthy salts. Preparation. — Extract pulverized gall-
stones with boiling alcohol, and filter while boiling. Crystals
of cholesterin separate from the filtrate when cool. In order
to purify it, boil the crystals with alcoholic solution of caustic
potash. On cooling they will again separate. Wash the pro-
duct .with cold alcohol, and then with water; dissolve it in a
mixture of alcohol and ether; allow it to evaporate. Crystal-
lized cholesterin forms rhombic, plates, the corners of which
are often broken (fig. 314). It is quite insoluble in water and
in cold alcohol. In boiling alcohol it dissolves with ease. Cho-
lesterin may be conveniently prepared from the ethereal extract
of gall stones obtained in the preparation of bilirubin by evapo-

504 DIGESTION.

ration. The crystals must be purified as above directed.
Reactions. — (1) Put a few crystals of cholesterin under the
microscope ; add a drop of a mixture of Ave volumes of sul-
phuric acid and one of water, and warm the object-glass gently.
The edges of the crystals will acquire a carmine color. If
three parts of acid arc used to one of water, the edges are
violet, and if it is still more dilute they become lilac and dis-
solve in the acid. (2) Add to some crystals strong sulphuric
acid, with a little iodine or zinc chloride ; they acquire a tint
which varies from greenish-blue to violet. (3) Put a drop of
concentrated nitric acid on a costal in a porcelain capsule,
and evaporate to dryness at a gentle heat ; touch the residue
with a drop of ammonia. A deep red color is produced. (4)
Rub up cholesterin with strong sulphuric acid, and add chlo-
roform. A solution varying in color from blood-red to purple
is produced, which, after changing successively into violet,
blue, and green, finally disappears.

* 148. Action of Bile. — The bile appears to aid the ab-
sorption of fat. Lenz, Bidder, and Schmidt found that, after
ligature of the gall duct, a dog absorbed less fat than before,
and that the chyle in the thoracic duct contained veiy little
fat. They calculated the amount absorbed by comparing the
quantity of fat eaten with the amount passed with the freces.
The bile emulsionizes fat, as can be seen by shaking a little oil
with it. It is doubtful, however, whether it is to this property
that the absorption is due. In forcing oil through animal mem-
branes or filter-paper, either by pressure or by suction, it passes
with much greater facility if it has been previously mixed with
bile.

149. Bile precipitates Syntonin and Pepsin. — Digest
a piece of fibrin with artificial gastric juice, and then add a
large quantity of bile to it; a precipitate is at once produced.
Filter, put another piece of fibrin in the filtrate, and acidulate
with hydrochloric acid to the proper degree. The pepsin having
been precipitated, the fibrin is not digested. Unless the quan-
tity of bile is large, the whole of the pepsin will not be thrown
down. It is not known what purpose is served by the pre-
cipitation of the chyme by the bile in the duodenum. In the
stomach the presence of bile must be injurious.

150. Secretion of Bile. — The secretion of bile goes on
constantly, but is more rapid at one time than another. It is
accelerated after taking food, usually attaining its maxjmum
from two to four hours after each meal. The secretion is
observed by tying the gall duct and introducing a canula into
the gall bladder. A detailed account of the method of perform-
ing this operation on dogs is given by Rutherford and Gamgee in
the report of the British Association for 1868. The principal
facts may be demonstrated in the guineapig, as follows : —

BY DR. LAUDER BRUNTON. 505

** 151. Mode of Producing Biliary Fistula in
Guineapigs. — Chloroform the animal and secure it on the
rabbit-support. Make an incision from an inch to an inch and
a quarter long through the abdominal parietes in the linea
alba from the xiphoid process downwards. The pyloric end of
the stomach is thus exposed. Pull gently on the stomach
until the duodenum is brought into view. The part correspond-
ing to the superior transverse part in man forms a loop with
its convexity directed towards the diaphragm, into the top of
which convexity the ductus choledochus enters. Tie the duct in
this situation, then seize the gall bladder with a pair of forceps.
It is always full, and cannot be missed if the forceps are passed
immediately under the edge of the costal cartilages. Make a
small incision into the gall bladder, introduce a canula and tie
it in. The diameter of the canula should be from two to three
centimetres, and the end to be inserted should have a project-
ing rim. This can be made very readily by heating the end of
a piece of glass tubing of the proper size, and pressing it, while
hot, against a flat piece of iron. Sew up the wound, leaving
the free end of the canula outside. The bile in guineapigs is
secreted in very large quantities, being as much as 7.3 grammes
in an hour per kilogramme of body weight. It contains a very
small proportion of solids, about 1.3 per cent. When the bile
duct is tied the guineapigs die in less than twentj'-four hours,
but when it is not tied they will live for a week. The bile is se-
creted under a very low pressure. For estimating this pressure,
prepare a manometer by attaching a piece of glass tubing,
eighteen inches long, to a wooden or pasteboard scale. Fit an
India-rubber tube to its lower end, fill the manometer and tube
with water, and close the latter with a clip. Tie the ductus
choledochus of a guineapig, and secure a canula in its gall
bladder. Having ascertained that the water in the manometer
stands at about 100 millimetres above the zero point, place the
tube in a horizontal position at the same level as the canula.
Connect the India-rubber tubing with the canula, and remove
the clip. As the bile is secreted, the column of water advances,
and the rapidity of secretion is thus indicated. When it
reaches 150 millimetres on the scale, raise the tube to a vertical
position. If the maximum pressure under which secretion
occurs in the animal experimented on be used, the water will
descend in the tube, but if not, it will continue to rise.

** 152. Absorption by the Liver. — The bile which has
been secreted by the liver is re-absorbed either when the pres-
sure is diminished in the bloodvessels, or when it is increased
in the bile capillaries (Heidenhain) ; jaundice may thus be pro-
duced in two ways. To show absorption from diminished
pressure in the bloodvessels, compress the aorta just under-
neath the diaphragm. The pressure in the manometer some-

506 DIGESTION.

times falls, but as the vena cava and other parts are generally
compressed likewise, the result is not constant. To show ab-
sorption from increased pressure in the ducts, replace the water
in the manometer by aqueous solution of indigo-carmine, taking
care that the column of fluid stands several inches above the
highest level previously attained by it. The solution is gradu-
ally absorbed, muscular tremors occur, and the animal dies
just as if water had been injected into the veins. At the same
time the surface becomes colored blue by the indigo-carmine.
The experiment enables us to understand how a very slight
obstruction to the orifice of the bile duct is sufficient to deter-
mine re-absorption, and the production of jaundice.

GLYCOGEN.

153. It would form a marked exception to the economical
use of material which we find in the body if the liver, the
largest gland in it, had as its sole function the secretion of
bile; a fluid of much less importance in digestion than the
gastric or pancreatic juices. This, however, is not the case,
for, in addition to secreting bile, the liver has the power of
forming glycogen, a substance which resembles dextrin in its
reactions, and like it, can be converted into sugar by the action
of ferments. It is always present in the liver in larger amount
during digestion than during fasting. What the materials
from which it is formed actually are is uncertain. Its amount
is increased by the use of starchy food ; but as it continues to
be formed in considerable quantity when the food consists of
flesh alone, it is evident that it can be produced from albumin-
ous bodies. In support of its origin from albumin, it has
been argued that the increased amount which is met with after
the administration of starchy food, is due to the sugar derived
from the starch being burnt off instead of albumin, in con-
sequence of which more albumin remains to be converted into
glycogen. The experiments of Cyon (if the}7 are to be relied
upon) make it probable that urea is formed in the liver. As
the amounts of sugar and urea excreted by diabetic patients
fed on an animal diet, run parallel with one another, it might
be supposed that when the diet is exclusively albuminous,
glycogen is formed by albumin or peptones splitting up and
yielding glycogen and urea. Again, when the diet consists of
starch and sugar, glycogen is formed abundantly, and at the
same time a deposit of fat takes place in the liver. From this
it might be supposed that the sugar absorbed from the intes-
tine is decomposed so as to yield glycogen and fat. Glycogen
seems to be of great importance for cell growth, for it is found
wherever this is going on actively, as in new formations, or in
embryonic tissues. A remarkable experiment of Hoppe-Seyler

BY DR. LAUDER BRUNTON. 507

shows that it is an ingredient of colorless blood corpuscles so
long as they are active, but that when they lose their power of
motion their glycogen disappears, and is replaced by sugar.1
In early foetal life, the muscular fibres and lungs contain much
glycogen, which subsequently diminishes. The liver and other
glands, and the nervous system of the embryo, contain little
or no glycogen ; but it is found in large quantities in the pla-
centa. After birth it is confined almost entirely to the liver
and muscles. In the latter it seems to have some relation to
the work done b}r them, for the quantity present in them is
diminished by activity. The glycogen of the liver does not
remain in it long, but is soon converted into sugar, so that the
large quantity which is present after a meal is quickly dimin-
ished by fasting, and disappears altogether during starvation,
while that present in the muscles does not increase so much
after food, nor is it so quickly lessened by starvation (Weiss).
Although both the liver itself and the blood contain a fer-
ment which transforms glj'cogen into sugar, its conversion is
probably effected in great measure by the blood, for it takes
place more rapidly when the circulation through the liver is
quickened. It is uncertain what the use of the sugar in the
organism is, but possibly it, as well as glycogen, has some-
thing to do with muscular action, since the quantity of sugar
(or a substance reducing copper) in blood becomes much dimin-
ished in its passage through the vessels of contracting mus-
cles (Genersich). While Bernard considers that the formation
of sugar goes on in the liver constantly during life, this has
been denied by Pavy, Ritter, Meissner, and Schiff, who hold
that it only occurs after death, or under pathological condi-
tions, such as disturbance of the respiration or circulation
during life. They base their opinions on the observations that
the liver contains little or no sugar when examined imme-
diately after death, and that the blood of the hepatic vein does
not contain more sugar than that of the portal or jugular veins.
It is quite true that sugar is found only in very small amount
in fresh livers ; but the smallness of the quantity is in all pro-
bability due to the constant circulation through the liver
during life, washing the sugar out of it as soon as it is formed
(Flint). The statement that the blood of the portal contains
as much sugar as that of the hepatic vein, rests on experiments
vitiated by the omission to place a ligature on the former while
removing the liver, so that the hepatic vein having no valves,
the blo«d from it flowed back into the portal S3rstem. When
this fallacy is avoided, sugar is found in much larger propor-
tion in the hepatic than in the portal vein. To meet the objec-

1 For the details of this experiment see Med. Chem. Untersuch., 1871,
p. 480.

508 DIGESTION.

tion that BUgai thus found has been formed after death, blood
has been taken from the right side of the heart, or vena cava,
and the quantity of sugar it contained compared with a similar
specimen of blood from the jugular vein. Every precaution
was taken to avoid disturbance of the circulation, yet the
sugar in the former was found to exceed that in the latter con-
siderably (Lusk).

** 154. Mode of demonstrating the Glycogenic
Function of the Liver. — The Liver contain* Sugar which
can be removed by Washing. — Kill a large rabbit in full diges-
tion, by decapitation with a long knife. Open the abdomen,
remove the liver, and place it in a large flat dish, such as is
used for photographic purposes. Tie a canula into the portal
vein, and another into the hepatic vein. Pass a stream of
water through the portal vein. This may be effected by a
syringe ; but a more convenient method is to connect the
canula in the portal vein by means of India-rubber tubing with
a pressure-bottle containing water. (See page 1 14.) Proceed
in every respect as in injecting the liver for anatomical pur-
poses, using a pressure of two or three feet of water. The
liquid which flows from the hepatic vein as the water enters
the portal vein, will be at first blood, then blood diluted with
water, and, lastl}', pure water. Collect portions of each of
these fluids in small beakers as they flow out. The remainder
which is not collected is allowed to run into the dish in which
the liver lies. Test each of the fluids for grape sugar. It will
be found in the portions first collected, the quantity gradually
diminishing as the washing is continued. Eventually it disap-
pears. Allow the stream to flow until none can be detected by
any of the tests described in the next paragraph.

As soon as this is the case, disconnect the canula without
loss of time, and cut the liver into three pieces. Mince one of
them as rapidly as possible, put it immediately into water boil-
ing briskly, and acidulate it very slightly with acetic acid, to
coagulate the albumin. Put another into strong alcohol for a
minute or two, pour off the alcohol, and squeeze the remainder
of it from the liver. Then cut it up small, cover it with abso-
lute alcohol and let it stand. Allow the third piece of liver to
lie on the table. After the liver has been boiled for a few min-
utes filter the water from it. The filtrate is milky. Test it for
sugar. If the operation has been rapidly performed, little or
none will be found, showing that all the sugar has been re-
moved from the liver.

Sugar is again formed in the Liver after its removal by
Washing. — After the third piece of liver lias lain on the table
for some time, cut it up and boil it like the first ; filter, and test
for sugar ; in most cases it will be found. As there was none

BY DR. LAUDER BRUNTON. 509

in the other piece, this sugar must have been formed after the
liver was cut in pieces.

The Liver contains Glycogen, a Substance whieh can be
changed into Grape Sugar by the action of Ferments. — Take
a little of the milky filtrate obtained by boiling the liver which
has been already found to contain no sugar. Add to it a little
saliva, and let it stand in the water-bath at 35° C. for a few
minutes, or warm it gently over a spirit-lamp. Then add liquor
potassas and cupric sulphate, and boil ; sugar is found. Evapo-
rate the milky remainder of the filtrate to a small bulk, and
add alcohol in excess. A white flocculent precipitate of gly-
cogen is formed.

The Liver also contains a Diastatic Ferment. — From the
other piece of liver which has been placed in alcohol prepare a
glycerin solution, as directed in § 160. Add some of this to a
solution of glycogen, let it remain in the water-bath at 40° C,
and test small portions of it from time to time. Sugar will at
length be found, but very many hours may be necessary.

155. Mode of Testing for Sugar in Blood. — As the
albumin and coloring matter of the blood would interfere with
the reaction, they must be removed before the test is applied.
Bernard's method is as follows: Put the blood, if pure, in a
mortar, and rub it up with a quantity of animal charcoal, suffi-
cient to form a dry paste. Add a little water, rub it up again,
and throw the mixture on a filter. The water filters through
quite clear, holding in solution any sugar which may be pre-
sent, and Trommer's test may then be applied to it. If the
blood is diluted, agitate it well with sufficient animal charcoal
to form a thick paste ; filter it, and test as before.

Another method, which is preferable if the quantity of sugar
is to be estimated, is to mix the blood with three or four times
its bulk of strong spirit, and after allowing it to stand for some
time, to filter. The residue is then extracted with much alco-
hol, and after the addition of the extract to the filtrate, the
alcohol is evaporated off and the residual liquid tested. Trom-
mer's test answers for saliva, but in the present case it is inade-
quate, as many other substances capable of reducing cupric
oxide might be present. Other tests are therefore required.

Moore's Test. — Put the solution in a test-tube and add suffi-
cient liquor potassoe or liquor sodae to make it strongly alka-
line. Heat it gently to boiling. If sugar is present in con-
siderable quantit}r, the fluid will become first yellow, then
reddish-brown, and, lastly, dark brown or black ; but if there
is only a little sugar, the color will only become yellow or red-
dish-brown.

Bottehers's Test. — Put the solution in a test-tube, and add to
it as much bismuth oxide or subnitrate as will lie, on the point
of a knife, and a considerable excess of a very strong solution

510 DIGESTION.

of caustic potash or soda, and boil for some time. If sugar is
present, the bismuth oxide will be reduced and become at first
gray, and lastly black. If only traces of sugar are present, a
small quantit}' of bismuth must lie used, or the whole will not
be reduced; if a first trial gives only a gray color, it should
be repeated with a smaller quantity of bismuth.

Fermentation Test. — A solution of grape sugar mixed with
yeast should at once ferment and give oil" carbonic acid. A
convenient apparatus for testing this is described by Bernard.
It consists of a test-tube, about three inches long, fitted with a
tight cork, through which a piece of small glass tubing passes
to the bottom. The tube is to be completely filled with the
fluid to be tested, mixed with a little yeast, and then put in
the water-bath at 35° C. If sugar is present, carbonic acid is
given off, and as it cannot escape, it drives the fluid out through
the small tube. As the yeast may contain sugar itself, a similar
tube should be filled with yeast and water for comparison with
the first. The gas may be shown to be carbonic acid by shak-
ing it with baryta water. The fluid which escapes should be
collected by means of a piece of India-rubber tubing attached
to the upper end of the small tube, and tested for alcohol by
boiling it with a little potassium bichromate and sulphuric acid.
If alcohol is present the fluid becomes green.

** 156. Preparation of Glycogen. — In order to obtain a
large amount of glycogen from a liver, the animal must be
healthy, and must be killed during digestion, as otherwise the
liver would contain but little glycogen. Conversion into sugar
after death must be prevented by rendering the ferment which
acts on it inactive, as quickly as possible ; this is done by heat-
ing the liver to 100° C.

Kill a large and well-fed rabbit an hour or two after it has
had a full meal, by decapitation with a long knife. Open the
abdomen instantly, tear out the liver, chop it into pieces as
quickly as possible with a few strokes of the knife, and throw
it into a capacious capsule containing water, which is kept
briskly boiling by a large Bunsen's burner. The burner must
be large, because the liver cools the water into which it is
thrown, and unless ebullition be kept up briskly it may be some
time before the pieces of liver are heated to 100u C. throughout,
in which case the transformation of glycogen into sugar will
go on in those parts which are insufficiently heated. Let the
liver boil briskly for a short time ; then pour the liquid out of
the capsule into a large beaker, and put the liver into a mortar.
Return the liquid to the capsule, rub the liver to a fine pulp,
put it back into the capsule and boil it again. Then filter the
liquid and cool the filtrate rapidty, by placing the vessel con-
taining it in iced water. The filtrate contains a considerable
quantity of albuminous substances, which must be removed in

BY DR. LAUDER BRUNTON. 511

order to get the gtycogen pure. This is best done by precipi-
tating them with potassio-mercuric iodide, as recommended by
Briicke. This solution is made by precipitating a solution of
mercuric chloride with potassium iodide, washing the precipi-
tate and adding it to a boiling solution of potassium iodide till
the latter is saturated.

When the filtrate from the liver is cool, add hydrochloric acid
and potassio-mercuric iodide solution to it alternately, as long
as they cause any precipitate. Stir the mixture, let it stand
about five minutes, and then filter. Add alcohol to the filtrate
till glycogen begins to be copiousl}' precipitated, taking care
not to add an excess of alcohol, lest other substances be also
precipitated. The glycogen is best precipitated when the mix-
ture contains 60 per cent, of absolute alcohol. Collect the gly-
cogen in a filter, wash it, first with dilute alcohol, then with
strong alcohol of 90 per cent. (sp. gr. 822), which makes it more
easy to separate from the filter. Extract it with ether and dry
it rapidly on a flat plate. Instead of separating the albumin
from the glycogen by potassio-mercuric iodide, the boiling solu-
tion of glycogen may be slightly acidulated with acetic acid
and filtered. The filtrate is then quickly evaporated to half its
bulk and mixed with its own volume of strong alcohol of 90
per cent. The glycogen is precipitated along with a little glu-
tin. To separate it from this it is boiled with liquor potass*
for an hour or more, neutralized with acetic acid, precipitated
with alcohol, collected on a filter, washed first with strong alco-
hol and then with absolute alcohol till all traces of water have
been removed, and then the alcohol displaced by absolute ether.
The glycogen remains as a white powder. It is to be quickly
dried by spreading it in a thin layer on a warm porcelain plate
and passing a current of air over it. If the glutin has not been
perfectly removed, or if the water has been incompletely dis-
placed by the alcohol and ether, the glycogen in drying becomes
converted into a gummy mass, instead of forming, as it ought
to do, a white powder.

* 157. Properties of Glycogen. — Glycogen is amorphous,
colorless, and tasteless. In water it is readily soluble. The
solutions are strongly opalescent, and when concentrated are
quite milky. They are, apparently, true solutions, as the}7 pass
unchanged through filters and through animal charcoal, and no
particles can be observed in them by the microscope. Briicke,
however, considers that they are not true solutions, but merely
suspensions of particles of glycogen swollen up in the fluid. The
opalescence disappears on the addition of caustic alkalies,
although the alkali does not destroy the glycogen. In alcohol
and in ether it is insoluble. It contains no nitrogen. When
burnt on platinum foil, it does not give off the peculiar smell
of nitrogenous bodies, nor does it leave any ash.

512 DIGESTION.

Glycogen is colored red by solution of iodine. The best
solution for this purpose is made by putting a little iodine in
water and adding potassium iodide very gradually to it, with
constant agitation, until the fluid assumes a wine-red color. If
caustic potash is added to a solution of glycogen, and then a
drop of cupric sulphate, the copper oxide is redissolved. The
oxide is not reduced on boiling.

158. Influence of Food on the Amount of Glycogen
in the Liver. — If two rabbits, one of which is fed abandantly
with corn, the other sparinglj' with green food, are kept other-
wise in the same conditions and killed at the same period of
digestion, it is found that the liver of the former contains much
more gtycogen than that of the latter.

** 159. Conditions "which determine the Conver-
sion of Glycogen into Grape Sugar. — Glycogen can be
changed into dextrin and grape sugar: —

1. By Ferments. — Take a watery solution of glycogen and
mix some saliva with it. Put the mixture into two test-tubes
and place them in the water-bath at 37° to 40° C. Take out
one immediately after the milkiness of the solution has dis-
appeared. Add alcohol to it: a precipitate of dextrin is
formed. Filter, and wash the precipitate with alcohol. Put
the precipitate in water : it becomes transparent and dissolves,
forming a solution perfectly free from opalescence. Test a
little of the solution with liquor potassaa and cupric sulphate ;
no reduction takes place on boiling. To another portion add
iodine solution ; a red color like that of glycogen appears.
Test the alcoholic filtrate with liquor potassae and cupric sul-
phate: it is reduced. This shows that the glycogen has been
converted partly into dextrin and partly into grape-sugar by
the salivary ferment. Let the other test-tube stand for some
time in the water-bath. Add alcohol. If it has stood long
enough, no precipitate is produced. Test it. On applying
Trommer's test a great reduction of cupric oxide will occur.
This shows that the glycogen has been entireh* converted into
sugar by the prolonged action of the salivary ferment.

Blood contains a Ferment which converts Glycogen. — A
ferment possessing the same action is contained in the blood.
Add a little blood to a solution of glycogen, and let it stand
for some time at 37° C. Then remove the albumin and test
for sugar in the manner ahead}' described.

2. By Acids. — Mix a solution of glycogen with dilute hydro-
chloric or sulphuric acid and boil. Then add liquor potassae
in excess and copper sulphate, and boil ; sugar is found. All
specimens of glycogen can be converted into sugar by acids,
but they are not all alike in their behavior to ferments, some
specimens requiring a longer time than others.

BY DR. LAUDER BRUNTON. 513

160. Separation of a Diastatic Ferment from the
Liver. — Cut off the head of a rabbit and remove the liver as
quickly as possible. Mince it and wash it with water several
times to remove the blood. Then squeeze it tolerably dry, put
it into absolute alcohol, and let it remain for twenty-four
hours. Filter off the alcohol, wash the liver with alcohol, and
then put the mass, for several days, in glycerin. Filter it
through muslin. The filtrate is free from sugar, but contains
a ferment which converts glycogen and starch into sugar.
Take a little of the glycerin extract in each of three test-
tubes ; put into one a little glycogen, and into another a little
starch paste, and let them stand for a quarter or half an hour.
Then test all three for sugar with copper sulphate and potash.
No sugar will be found in the tube containing the glycerin
extract alone, the sugar found in the liver immediately after
death having been removed by the alcohol before the glycerin
was added. Both the other tubes will contain sugar. Diluting
the glycerin extract does not alter the effect.

After the Ferment has been extracted by Glycerin, the Mass
still contains Glycogen. — Extract the mass several times with
fresh glycerin. Take two test-tubes : then introduce a little of
it. with water in each, and let them into two test-tubes. Test
one of them for sugar : none is found. Add to the other one
a little of the glycerin extract, which has already been found
to contain no sugar, and let it stand at 40° C. for some time,
after which it will be found to contain sugar. A similar
ferment can be extracted from bile by precipitating it with
alcohol, washing the precipitate with alcohol on a filter, and
then extracting it with glycerin in the way already mentioned
(Von Wittich).

161. Glycosuria. — It is still disputed whether sugar is a
normal constituent of the urine or not. But in the diseased
condition, to which the term Diabetes Mellitus is applied, it
appears in considerable quantities. Bernard first showed that
its appearance in the urine can be induced by certain lesions
of the nervous system, and finding that they caused, at the
same time, dilatation of the vessels of the liver, he attributed
the appearance of the sugar to the increased circulation
through that organ. His views have lately been confirmed;
the nervous mechanism by which the vessels become dilated
has been discovered by Cyon and Aladoff, from whose re-
searches it appears that the vasomotor nerves of the hepatic
vessels pass from the vasomotor centre in the medulla oblon-
gata down the cervical part of the spinal cord, which they
leave at its lower end. Thence they accompany the vertebral
arteries to the last cervical ganglion, finding their way by the
two fibres, which pass in front and behind the subclavian
artery (forming the annulus of Vieussens) to the first dorsal

33

514 DIGESTION.

ganglion. Thence the}' proceed in the gangliated cord of the
sj'mpathetic and the splanchnic nerves to the liver. When
these vasomotor fibres are severed, either by dividing the
fil ins on the vertebral artery or those forming the annulus of
Yienssens, or by extirpating the third cervical or first dorsal
ganglion, the hepatic vessels dilate, and diabetes occurs. It
is of great importance to notice that section of the sympa-
thetic cord or the splanchnic nerves does not produce diabetes,
although the vasomotor nerves of the liver are thus divided.
The reason of this probably is that the vasomotor nerves of
the intestine, being divided at the same time, so much blood
goes to the intestinal vessels that the circulation in the liver
is not increased. The vessels can be dilated reflexly by irrita-
ting the central ends of the cut vagi, or the roots of the vagus
in the fourth ventricle. Section of the splanchnics or sym-
pathetic cord prevents the occurrence of diabetes when the
fourth ventricle is afterwards punctured, but does not remove
it when already present. Diabetes may also be produced by
the inhalation of carbonic oxide ( Schmiedeberg), chloroform,
or nitrite of amjd, or by the injection of curare. As regards
carbonic oxide, it has been ascertained that the action is not
prevented in the dog by section of both splanchnics, but in
rabbits it does not produce diabetes at all (Eckhard).

Increased proportion of sugar in the blood determines glj'co-
suria. To show this, expose the jugular vein in a healthy rab-
bit, having first weighed it and ascertained that its urine is free
from sugar. Then slowly inject 5 to 10 per cent, solution of
grape sugar into the vein. About two grammes of sugar should
be used for eveiy kilogramme of body weight. Sugar is found
in the urine shortly after, but next da}r it will have disappeared.
It has been found that if the amount of sugar in the blood does
not exceed a half a gramme for each kilogramme of body weight,
it may not appear in the urine.

** 162. Production of Glycosuria by Puncture of
the Floor of the Fourth Ventricle. — The part of the
fourth ventricle the puncture of which is followed by the most
abundant appearance of sugar in the urine is limited superiorly
by a Hue joining the origin of the auditory nerves, and inferi-
orl}- by one joining the origins of the vagi ; a puncture higher
up, or to either side, may, however, produce more or less glyco-
suria. It has been ascertained by Bernard that it is essential
to the result, that the olivary fasciculi should be injured, and
that it is not produced by injury of the superficial, i. e., poste-
rior sensory layers. The instrument used for puncturing the
ventricles consists of a small steel chisel (.see Fig. 315), about
four millimetres broad, and having a style in the middle which
projects about two millimetres beyond the cutting edge. This
chisel is pushed on through the occipital bone and the cere-

BY DR. LAUDER BRUNTON. 515

bellum until its further progress is arrested by the point com-
ing in contact with the basilar process of the occipital bone.
In this wa}r the edge of the chisel is prevented from injuring
the anterior motor fibres of the medulla, and thus producing a
disturbance of the motor functions which would complicate the
experiment.

Mode of Operation. — Place a rabbit in the prone position on
Czermak's rabbit-support, and fix the head to the upright at
the side. Feel for the occipital protuberance, and make an in-
cision over it about half an inch long. Fix the point of the
chisel in the middle line of the skull just behind the protube-
rance, and bore through the bone, moving the handle of the
instrument from side to side, in order to assist its passage, but
not pressing with too great a force. When the skull has been
penetrated, push the chisel downwards and forwards through
the cerebellum in such a direction as to cross a line joining the
two auditory meatus (see Fig. 31fi) until it is stopped by the
basilar process, and then gently withdraw it. Remove some
of the urine in half an hour or an hour afterwards (§ 138), and
test it for sugar.

Section IV.— Digestion in the Intestines.

PANCREATIC JUICE.

163. Pancreatic juice may be obtained either by a temporary
or permanent fistula. It is usually stated that the secretions
from these two kinds of fistula differ much from each other, a
normal juice being obtained only from a temporary fistula,
while that yielded by a permanent one is watery and destitute
of some of the properties possessed by the other. Ludwigand
Bernstein, however, have, by an improved method of making a
permanent fistula, succeeded in obtaining a normal juice from
it also.

164. Method of itiaking a Temporary Fistula. — In
the dog there are two pancreatic ducts, one of which opens into
the duodenum along with the ductus choledochus. The other
duct, which is larger, and enters the duodenum about two cen-
timetres below the one first mentioned, is exclusively employed
for the operation. It is not necessary to ligature the first.
Bernard prefers for the purpose large dogs, sheep dogs being
best, as they are less subject to peritonitis than others. Five
or six hours before the operation, the animal should get a large
meal of bread and meat. The operation, which must be per-
formed as quickly as possible, consists in laying the dog on its
left side, and making an incision five centimetres long in the
right hypochondrium from the projecting point of the last false
rib downwards, parallel with the linea alba. The bleeding
should be stopped before the peritoneum is opened. The duo-

516 DIGESTION.

denum lies opposite the wound. As soon as it is exposed it is
drawn out, and the pancreatic duct looked for about two centi-
metres below the ductus choledochus. The part of the pancreas
in which the duct lies is generally closely attached to the duo-
denum, and somewhat overlaps it. The largest and lowest of
the bundles of vessels which pass from the duodenum to the
pancreas, lies over the duct. These vessels are to be pushed
aside, and a thread passed under the duct, which is recognized
by being larger and paler than the vessels. Care must be taken
not to injure the vessels and cause bleeding, and the pancreas
must be pulled or pressed as little as possible. The duct is
opened with scissors, and a plain silver canula, about five mil-
limetres in diameter, and 10 or 12 centimetres long, pushed
into it up to its first division, which is generally visible; the
ligature is then tightened; another thread is passed through
the serous coat of the duodenum, and the canula fixed to the
intestine by it. The ends of these threads, and the end of the
canula, are kept outside the wound, the duodenum returned
to the abdominal cavity, and the wound closed by first sewing
together the muscles, and then the skin. A small India-rubber
bag. furnished with a stopcock, is then tied to the outer end of
the canula. emptied of air. and the stopcock closed. The
juice then collects in it, and is drawn off by the stopcock (see
Fig. 317). Generally, it flows abundantly; but if it does not.
a little ether should be injected into the stomach by a stomach-
pump. The juice may be collected for several hours; but
after the expiration of twenty-four hours, the character of the
secretion changes. In a few hours more, the canula and
threads should be gently drawn out. The wound generally
heals quickly.

165. Method of making a Permanent Fistula. — For
permanent fistulpe, Ludwig and Bernstein choose small dogs,
as in them the duodenum is more easily reached from the mid-
dle line, and is not drawn so far from its natural position by
the fistula as in larger animals. The dog must be kept fasting
on the day of the operation, as the pancreatic vessels are full
during digestion, and bleed easil}-. Narcotize the animal by
injecting opium into the tibial vein, and open the abdomen by
an incision about two centimetres long in the linea alba, mid-
waj' between the ensiform cartilage and the umbilicus. The
duodenum is then searched for, and drawn out of the wound
along with the attached pancreas, and a thread looped round
the duct. Instead of then putting in a canula, a piece of lead
wire is inserted into the duct, so that one end of it passes into
the intestine and the other into the gland to a considerable dis-
tance. The middle part of it is twisted together, and projects
through the wound. Owing to the T shape thus given to the
wire, it cannot either slip out or move about in the duct; but

BY DR. LAUDER BRUNTON, 517

wire being chosen which does not fill it up, the flow of the juice
is not hindered. Three threads having then been passed
through the wall of the duodenum near the duct, the intestine
and omentum are replaced in the abdomen, and the duodenum
fastened by the threads to the abdominal wall. The wound is
then sewed up, care being taken that the twisted part of the
lead wire passes through the wound. Twenty-four hours after
the operation, the stitches are taken out, but the wire left in.
In two or three days afterwards the juice can be collected. For
this purpose, the animal must be supported by two straps, which
pass under its belly, and are attached to a horizontal bar hung
from the roof by a cord and pulley. The dog is thus suspended
over a table at such a height that it can barely touch it with
its toes, in which position it remains perfectly still. A funnel
is then attached under the fistula, and the juice collected in a
glass below.

The normal juice obtained from a temporary fistula is a col-
orless transparent tenacious fluid, with a strongly alkaline re-
action. "When cooled under 0° C, a coagulum separates from
it. The j nice from permanent fistulas is more watery, and yields
no coagulum when cooled. In the former, it often contains
about 10 per cent, of solids, but the amount may be as low as
2 per cent. ; and in the latter, the percentage is frequently from
2 to 5. Their amount is determined in the manner described
in § 74. Pancreatic juice contains an albuminous body, an
alkali-albuminate, leucine, t}Trosine, fats, soaps, inorganic salts,
and three ferments. One of these converts starch into sugar,
another splits up fats, liberating fatty acids, and the third con-
verts albuminous bodies, first into peptones, and then into leu-
cine and t}'rosine. On account of the presence of this third
ferment, the reactions of the juice, after it has been allowed to
stand, differ from those which it presents when fresh, the albu-
min of the fresh juice itself being digested by the ferment in
it, and yielding peptones, leucine, and tyrosine. When fresh
juice is heated to 72° C, the albumin coagulates, and after the
coagulum has been separated, acetic acid precipitates the alkali-
albuminate. The watery extract of the gland may be used for
showing man}- of the properties and actions of pancreatic juice,
instead of the juice itself.

** 166. Artificial Pancreatic Juice. — For this purpose,
the pancreas from an animal killed in full digestion must be em-
ployed. Take the pancreas of an animal which has been killed
about six hours after a full meal. Wash off the blood, cut it
into moderately small pieces, pour about four times its weight
of water at 25° C. over it, and let it stand for two hours in the
water at that temperature, above which it must not be allowed
to rise more than four or five degrees at most. Filter it first
through linen, and then through paper. The filtrate generally

518 DIGESTION.

has an acid reaction from the presence of fatty acids, liberated
by the ferment from the fats in the pancreas, and is opalescent
from the presence of fat in a state of emulsion. Boil a little of
the fluid ; a precipitate of albumin is formed. Filter, and neu-
tralize by acetic acids, and a further precipitate of alkali-albu-
minate will be produced. The presence of leucine and tyrosine
may be shown by removing the albumin by boiling and acidu-
lating, and then separating them as described in § 35. To show
that leucine is present in the juice as secreted, and is not due
to changes in it afterwards, it must be received in alcohol as it
flows from the fistula.

* 167. Glycerin Solution of Pancreatic Ferments. —
After cutting up the pancreas, as in the previous experiment,
lay it for a day or two in absolute alcohol, and after express-
ing the alcohol let it lie several days in glycerin, then filter.

** 168. Actions of Pancreatic Juice. — It emulsionizes

Fat Shake up some of the watery extract with olive oil, an

emulsion is formed. This is due to the albumin it contains,
for by adding liquor potassae to the mixture so as to dissolve
the albumin, and shaking, the drops of fat may be made to
run together again.

2. It decomposes Fats, liberating Fatty Acids. — The extract
of pancreas contains fat : hence when it is kept for an hour in
the water-bath at 40° C, without any addition, its acid reac-
tion increases. To show its action on fats, carefully neutralize
some of the watery extract and add to it a little olive oil or
fresh butter, whose reaction must also be neutral. Put the
mixture in the water-bath for some time, put a drop from the
bottom of the tube on blue litmus paper and let it run off. A
red and somewhat greasy spot is left.

3. // converts Starch into Sugar. — Mix some of the extract
with starch mucilage and let it stay for some minutes in the
water-bath at 40° C. ; then apply Trommer's test, and sugar
will be found.

4. It digests Fibrin, forming Peptones, and afterwards de-
composes them, Leucine and Tyrosine being produced. — Before
dissolving boiled fibrin, the pancreatic juice converts it into a
soluble albuminous substance, very much like raw fibrin. This
is then dissolved and is present in solution, either as albumin,
coagulable by heat, or as an albuminate. The dissolved albu-
min is next converted into peptones. If the digestion is
allowed to go on, the quantity of peptones in the solution
diminishes, while that of leucine and tyrosine increases. Bodies
which give the reaction of naphthilamine and indol (Kiihne)
are also formed, and when the digestion goes on for a long
time the indol is formed in considerable quantities, and emits
a most disagreeable faecal odor, which was attributed to putre-
faction till Kiihne showed its true nature. Boil several bits of

BY DR. LAUDER BRUNTON. 519

fibrin in a large test-tube, pour off the water, add artificial
pancreatic juice or glycerin extract of pancreas, and put the
tube in the water-bath at 40° C. At first it will not be altered,
but after two hours or more the bits will be found to be easily
torn by stirring, and the smaller ones will disappear, and if
two or three are taken out and washed with water they will
be seen to be corroded, not swollen as in gastric juice. To
show that the coagulated fibrin has been converted by the
pancreatic juice into a body resembling raw fibrin in its pro-
perties, put a bit into 0.1 per cent, of hydrochloric acid. It
dissolves veiy cpiickly, forming a solution of syntonin. Rub
up a second bit with 10 per cent, salt solution, and filter. The
filtrate contains albumin in solution. Add nitric acid to one
portion of it and boil another ; a precipitation occurs in both.
If boiled fibrin is tested in the same way, it is found to be
insoluble in these reagents. Even raw fibrin is much less solu-
ble than the boiled fibrin which has been acted on by pancreatic
juice.

Take part of the solution of fibrin in pancreatic juice and
boil it. Neutralize another portion with acetic acid ; a precipi-
tate is formed in both. Let the rest stand for two or three
hours longer, then acidulate it with acetic acid and boil, to
coagulate any albumin present. Filter. Evaporate the filtrate
at 60° to 70" C, and add alcohol to it while still hot, till the
peptones are precipitated. Let it stand for twenty-four hours
and filter. Dissolve the precipitate of peptones in water and
apply the tests given in § 118. Evaporate the filtrate to a
moderately small bulk and let it cool. Tyrosine crystallizes
out. Pour off the mother liquor, evaporate it to a small bulk,
and leucine will crystallize out. In order to purify the tyro-
sine, put it on a filter and wash it, first with ice-cold water till
the filtrate is colorless, and then with spirit, next with abso-
lute alcohol, and lastly with ether. To purify the leucine, put
the crystals on a filter, which must be allowed to stand in a
cool place until not a drop more runs from it. Then wash it,
first with ice-cold water until the filtrate is colorless, next
with common alcohol, then with absolute alcohol, and lastly
with ether. It is of great importance that the mother liquor
should be allowed to drain away completely before the wash-
ing, as otherwise the crystals would dissolve in the water used.
Test the mother liquor for naphthilamine and indol. In test-
ing for the former, dilute naphthilamine is indicated by the
appearance of a rose-red color when chlorine water is added
gradually to the mother liquor diluted with water. To prove
the presence of indol, dilute some of the mother liquor, boil it
in a test-tube, add a little dilute sulphuric acid and a drop or
two of a dilute solution of a nitrite ; or of very dilute nitrous
acid, a red color is produced. The dilute nitrous acid for this

520 DIGESTION.

purpose may be conveniently obtained by boiling a small piece
of grape sugar with nitric acid in a test-tube, and when the
tube is filled with red fumes emptying out the acid and filling
the test-tube writh water.

* 169. Separation of the Pancreatic Ferments from
the Glycerin Extract. — Precipitate the glycerin extract by
absolute alcohol; filter; treat the precipitate again for a week
or two with glycerin, and filter; let the filtrate fall drop by
drop into a tall cylinder filled with absolute alcohol. The
ferment is precipitated in white flocculi. After the precipita-
tion is complete, let it stand one or two days under a mixture
of alcohol and ether. Filter by means of Bunsen's pump, and
wash several times with alcohol and ether. Let the precipitate
dry over sulphuric acid, and then pulverize it (Hiifner).

170. Isolation of the Pancreatic Ferments. — Two of
the pancreatic ferments have been separated by Danilewsky ;
but that which splits up fat is removed or destroyed by the
magnesia he employs. His method is as follows: "Wash the
pancreas of a dog which has been killed six hours after a full
meal thoroughly from blood, and rub it to a fine pulp in a
mortar, with about a quarter of its bulk of magnesia, and
four times its bulk of water. Put the mixture in a beaker,
and let it stand for two hours at 25° in the water-bath. After
it has cooled, and the pulp and magnesia have nearly subsided,
filter the fluid, but do not put the sediment on the filter, as it
chokes it, and, at the same time, partly passes through. Neu-
tralize the filtrate with dilute hydrochloric acid, and put it
into a flask large enough to hold three times as much. Pour
into it without stirring ^-^ of its volume of thick collodion,
and shake it sharply for several minutes, and repeat the shaking
several times. Pour the liquid into a large beaker, and stir
it constantly, so as to favor the escape of ether and prevent
the collodion from separating in large lumps. When the col-
lodion presents the appearance of small rounded granules,
filter through linen, and evaporate the ether from the filtrate
in vacuo. Then treat the liquid with collodion a second time,
filter through the same piece of linen, unite both filtrates, and
put them aside (a)

Wash the precipitate several times with spirit (60 to 10 per
cent.), and dry it without removing it from the linen between
double folds of blotting paper. Spread it out with a spatula,
and leave it exposed to the air till it is dry. Then shake it in
a tall narrow glass with ether, to which a little absolute alcohol
has been added, till the precipitate is dissolved and a turbid
solution obtained. Let it stand for two days, and then decant
the turbid fluid from the precipitate, and after diluting it witli
ether, pour it into two tall glasses and let it stand for several
days till a new precipitate subsides. Collect that which then

BY DR. LAUDER BRUNTON. 521

remains suspended by filtration through Swedish paper. Re-
move the collodion from each precipitate by agitating it with
ether several times, and then dry it in vacuo. Treat the
yellowish residue (which consists of an admixture of coagu-
lated albumin with that pancreatic ferment which acts on
fibrin) with cold water, and filter. The ferment will be dis-
solved and the albumin left. Test the digestive power of the
filtrate on a bit of fibrin.

Evaporate the filtrate (a) in vacuo, filter from the collodion
that separates, heat to 43°-44° C. in a water-bath, in order to
separate an albuminous body contained in it which coagulates
at this temperature. Filter; evaporate the filtrate in vacuo to
one-sixth of its bulk, and add a large quantity of absolute
alcohol. It is advisable to let the precipitate thus produced
remain under the alcohol for some days, as it is thus rendered
more insoluble in water. Collect the precipitate on a filter,
and wash it several times with strong spirit. Then treat it
with a mixture of one part of strong spirit and two parts water,
in order to dissolve the ferment and leave the albumin. Filter ;
evaporate the filtrate to dryness in vacuo, and dissolve the
residue in water. The solution converts starch quickly into
sugar, and digests fibrin, but not very quickly, the ferment
having this latter action not having been completely removed
by the collodion. It contains also leucine and tyrosine, but
the greater part of these may be removed by dialysis at 4° C.
The ferment should then be dried in order to keep it.

171. Preparation of Tyrosine by Pancreatic Diges-
tion.— Take out the pancreas of an animal which has been fed
five or six hours before being killed, weigh it, cut it in small
pieces, and rub it up with ten times its weight of raw fibrin,
and add to the whole twelve or fifteen parts of water at 45 °C.
Keep the whole at this temperature for four to six hours,
stirring frequently ; then add a little acetic acid, and boil to
coagulate albumin. Filter through a piece of linen, and evapo-
rate the filtrate quickly to a syrup. Pour it, while still hot,
into a flask, and add strong spirit to it till a distinct flocculent
precipitate occurs. Let it cool ; filter, and distil the filtrate
till it forms a thick pulp while still warm. Let it stand for a
day in the cold to allow complete crystallization to take place ;
then throw it on a filter, and let the mother liquor drain com-
pletely away ; wash the residue with a little cold water, and
then put it into a large quantity of water at 50° C, which will
dissolve the leucine and leave the tjM-osine. Dissolve the
tyrosine in hot water, let it crystallize out, and then dissolve
it again in ammonia and re-crystallize.

522 DIGESTION.

INTESTINAL JUICE.

172. Intestinal juice was first obtained pure by Thiry, who
divided the jejunum or ileum in two places at a distance of 10
to 15 centimetres from each other, sewed up one end of the
piece thus isolated, and attached the other to the wound in
the abdominal walls. The short cul-de-sac of intestine formed
in this manner remained attached to the mesentery, and its
vessels and nerves being uninjured, it yielded a normal secre-
tion which could thus be collected without admixture with
other digestive secretions and products. The continuity of
the alimentary canal was restored by sewing together the
divided ends of intestine.

173. Intestinal Fistula. — The method employed by
Thiry has been somewhat modified by Paschutin, who prefers
the duodenum and the beginning of the jejunum, a part of the
small intestine which yields a very active secretion. In
making a fistula by his method, the hair must be carefully
removed from the skin, and an incision 3 to 5 centimetres
long made in the linea alba. The duodenum is drawn out and
two stout ligatures passed round it about two and a half cen-
timetres beyond the spot where it separates from the pancreas.
The ligatures having then been separated from each other and
tightened, the intestine is divided between them. The upper
end of the duodenum is then replaced in the abdomen.

The next step in the operation is to divide the jejunum in a
similar manner. The most obvious method of accomplishing
this would be to follow the intestine down to the point at
which the second division is to be made. This is, however,
rendered impossible b}r the extreme shortness of the mesentery
at the point where the duodenum ends in the jejunum. It is,
therefore, necessaiy to find the jejunum independently, by
following the intestine upwards from any loop which may
present itself in the wound. It is obvious, however, that be-
fore this can be done, the operator must find out in what di-
rection the intestine must be followed. For this purpose, the
loop being held tight between the finger and thumb, a quantity
of half per cent, salt solution is injected into the lower cut end
of the duodenum, by a syringe with a conical nozzle, which is
passed through the tightened ligature. As the fluid passes
downwards until it meets the obstruction presented by the
fingers, the upper part of the loop is at once recognized by its
becoming full. The distended gut is then followed up till the
beginning of the jejunum is reached, which is recognized by
the mesentery becoming shorter. Two ligatures are passed
round it, and the intestine divided between them as before.
The under end is replaced in the abdomen, and the upper end
closed by sutures so as to form the cul-de-sac. Before doing

BY DR. LAUDER BRUNTON. 523

so, the bundle of mesenteric vessels leading to the part con-
stricted by the ligature must be compressed between the finger
and thumb, while the constricted part is cut off. As it is
necessary that the serous surfaces should be in apposition,
the mucous membrane, which is turned outwards by the con-
traction of the muscular coat, must be first turned inwards,
and the closure affected by sutures, applied as shown in fig.

318. The closed end is then replaced in the abdomen, and the
continuity of the intestine again restored by joining the cut
ends of the duodenum and jejunum. In doing this, the two
ligatures, with the parts constricted by them, must be cut off
in the manner previously directed. The ligatures applied to
the vessels should include a little of the adjoining intestinal
wall, so as to give them a firmer hold. The two cut ends are
now brought into apposition, and the ligatures firmly tied to-
gether so as to retain the ends in their proper relation, and
held in the hand of an assistant The first stitch is put through
the intestines in such a way as to include both bundles of ves-
sels, and should be drawn very tight and tied, so that it not
only unites the ends, but serves as an additional ligature for
the vessels.

To prevent the ligature from cutting the intestine, it should
either be made of very thick soft silk, or of two or three fine
ligatures used together. Five or six similar stitches made at
a little distance from each other on each side of the first are
sufficient to join the mesenteric edge of the two pieces of in-
testine, which then lie with their axes parallel (fig. 318). To
complete the junction, the two ends must be brought into the
same straight line and sewn together. The application of the
final sutures is a matter of considerable difficulty, principally
on account of the tendency of the mucous membrane to become
everted. The mode of applying the sutures so as to accomplish
this object, will be at once understood by a reference to fig.

319. Several threads, each with a needle at each end, must be
prepared. For the first suture, one needle enters the intestine
from its serous aspect at a, and is brought out at b, the other
enters at a', and is brought out at b'. The two ends, b and &',
are drawn tight and knotted together. For the second suture,
one needle enters at b, and is brought out at c, the other enters
at b', and is brought out at c', and so on. To conclude the
operation, the wound in the abdominal wall is brought together
by sutures, and the open end of the cul-de-sac sewn into it.
It is also desirable that the junction of the divided intestine
should be secured to the wound by a suture, in order to pre-
vent the induction of general peritonitis by its locomotion.

** 174. Artificial Intestinal Juice. — Remove the small
intestine from a pig, dog, or rabbit, as soon after death as
possible ; put a ligature round its upper end, attach the lower

524 DIGESTION.

end to the tap, and fill it with water under pressure. Close
the lower end by compressing it between the finger and thumb,
and raise, first the one end, and then the other, so that the
water may loosen the contents of the intestine from its walls.
Empty out the water, and repeat the process three or four
times, until what flows from the intestine is either transparent
or only slightly opalescent, and is not at all tinged with bile.
Five minutes' washing is generally sufficient to cleanse the in-
testine thoroughly. It should not be continued longer than
is necessary, as otherwise a great part of the intestinal ferment
may be removed. Slit up the intestine, and separate the mu-
cous membrane from the muscular layer. Cut the mucous
membrane into small pieces with scissors, or rub it up in a
mortar with sand or pounded glass, then mix it with three to
six times its bulk of water, and let it stand for a quarter of an
hour to two hours. Filter the infusion through muslin, and
then through paper.

** 175. Actions of Intestinal Juice. — 1. It converts

Starch into Sugar Add a little of the artificial juice to some

starch mucilage, warm it, and test for sugar as described in § 77
or 155. The mucilage and juice alone should also be tested, in
order to be sure that neither of them contains sugar. 2. It con-
verts Cane Sugar into Grape Sugar. — Dissolve some cane
sugar in water, and apply Trommer's test to a portion of the
solution. No reduction of the copper will occur as it would
do if grape sugar were employed. Add some artificial intesti-
nal juice to another portion of the solution. Let it stand at
40° for a short time, and then apply Trommer's test ; a re-
duction of the copper will take place. A similar conversion
of cane into grape sugar is produced by boiling with acids, as
may be shown by boiling a little of the syrup with dilute sul-
phuric acid, and then applying Trommer's test.

* 176. Moreau's Experiment. — When all the Nerves
going to a part of the Intestine are^divided, it secretes a very
large Quantity of a ivatery Intestinal Juice. — This is shown by
letting a large dog fast for at least twenty-four hours, so that
its intestines may be empty. It is then put under chloroform,
an incision made in the linea alba, and a loop of intestine drawn
out. Two ligatures are tied firmly round it at a distance of
four or five inches apart, so that the piece of bowel between
them is completely isolated from the rest of the intestine. All
the nerves in the mesentery belonging to this piece are then
carefully divided, leaving the vessels uninjured. Another liga-
ture is then tied round the intestine on each side of the first
two, and about four or five inches from them, so that a piece of
intestine similar to the first is isolated on each side of it, but
the nerves going to them are left untouched. The intestine is
then returned to the abdominal cavity, the wound sewn up, and

BY DR. LAUDER BRUNTON. 525

the animal left for four or five hours. It is then killed, and
the intestines examined. The part of which the nerves have
been divided is found perfect^* full of fluid, while the piece on
each side of it is empty. The fluid contained in the distended
loop has been ascertained by Kiihne to resemble in composition
diluted intestinal juice.

177. Movements of the Intestine. — The influence of
the nervous s}'stem on the movements of the intestine has not
yet been completely investigated. Peristaltic action is in all
probability produced by the ganglia in the intestinal walls, as
it continues in an excised portion ; but it may be increased by
the action of the vagi, and lessened or arrested by the splanch-
nics. The ganglia are stimulated and movements excited by
the presence of venous blood in the intestinal vessels (Maier
and Von Basch), or their distension by arterial blood (Nasse).
The splanchnics are inhibitory nerves for the intestine, and
its movements are arrested by their irritation (Pfluger and
Westphal). At a certain period after death, however, they ex-
cite movements (Ludwig and Spiess). It is uncertain whether
they exert an inhibitor}' action directly on the ganglia as the
vagus does in the heart, or act only indirectly through the ab-
sence of blood which they produce by causing contraction of
the vessels. For a description of the method of showing the
action of the splanchnics, see Ludwig and Spiess ; Sitzungsbe-
richte der Wiener Academie, xxv. 1857, p. 580. Their inhibi-
tory power is said by Koliker to be destroyed by curare, and
the writer has been unable to observe it in several experiments
on animals narcotized by chloral. Irritation of the vagi causes
movements of the intestine, beginning in the stomach. This
occurs only occasionally when one or both splanchnics are in-
tact, but almost invariably after both have been divided
(Houckgeest). In performing this experiment, as well as
others on the intestine, it is advisable to employ Sanders-Ezn's
method, of opening the abdomen under f per cent, salt solution
warmed to 35° C, in order to avoid the irritation to the intes-
tines which is occasioned by their exposure to air. For this
purpose, a bath of tin or zinc, 32 inches long, by 9£ broad, and
8^ deep, provided with a Geissler's regulator at one end, is
used, into this thirty-five litres of water at 35° C. are poured,
and sufficient salt added to make a | per cent, solution. In-
stead of measuring out the water each time, it is more conven-
ient to mark on the sides of the bath the height to which it
should be filled. The animal, being laid on a piece of board
with Czermak's holder attached to it, instead of the usual sup-
port, is placed in the bath, and the lower end of the board is
kept immersed by attaching a weight to it. For detailed ex-
periments with this method, see Houckgeest Pfiiiger's Archiv.
vi. p. 266.

526 THE SECRETIONS.

CHAPTER XXXVIII.

THE SECRETIONS.
Section I. — Milk.

178. Characters of Milk. — Newly-drawn milk is an
opaque fluid of a white or yellowish-white color. Its color
and opacity are due to its being an emulsion, i. e., to its con-
sisting of little globules of fat suspended in a solution of
albumin, milk, sugar, and organic salts. Each globule of fat
is covered by a thin coating of casein. When the milk is
allowed to stand, the fat globules, being lighter than the fluid
in which they swim, rise in great part to the top, and form
cream, and the lower part of the fluid often acquires a bluish
tinge. A similar separation also takes place in the milk gland
itself, so that the milk last drawn is richest in cream. The
globules of fat are prevented from uniting by the thin albumi-
nous coating which surrounds each ; but when this is broken
bj- agitation, they coalesce, forming butter. Changes also
occur in the milk, sugar, casein, and fats of the milk, more or
less quickly, according to the higher or lower temperature to
which it is exposed. The milk-sugar becomes converted, ap-
parently through the agency of a ferment, into lactic acid.
This gives the milk an acid reaction, and precipitates the case-
in, causing the milk to curdle. The coagulum, or curd, in-
closes the fat globules. The liquid from which it is separated,
a solution of milk, sugar, and salts, is known as whey. The
curd, when completely separated from the whey, is called
cheese.

Microscopical Examination. — Examine milk under the mi-
croscope. It will be seen to consist of a colorless fluid, con-
taining large numbers of minute fat globules. Add a drop of
acetic acid, so as to dissolve the coating of casein : the globules
will coalesce. Besides these globules, cells containing much
fat ma}r be seen, and also masses of fat similar to those within
the cells, but destitute of an envelope. These cells are found
much more frequently in the milk (called colostrum) which is
secreted for the first few days after parturition, and they have,
therefore, received the name of colostrum corpuscles. They
sometimes exhibit contractile movements.

Reaction. — The reaction of human milk is always alkaline,
and that of cows' milk is generally so. Free lactic acid always

BY DR. LAUDER BRUNTON. 527

exists in the fresh milk of the carnivora, and occasionally in
that of the cow and goat.

Specific Gravity The specific gravity may be taken by

the specific gravity bottle or by a hydrometer. Before using
either, the milk should be well shaken and air-bubbles removed.

With a view to the detection of adulteration by water, a
special hydrometer is used, which is known as Quevenne's
lacto-densimeter. It is furnished with a scale indicating
specific gravities from 1042 to 1014. The highest specific
gravity of milk yet observed is 1040 to 1041, and the average
specific gravity of milk mixed with 50 per cent, of water is
1014 to 1016. The instrument is graduated for use at 15° C,
and when employed at a different temperature, a correcti*i
must be made in the specific gravity indicated by it. Tables
for this purpose are to be found in Gorup-Besanez's Zoochemie,
3d edition, p. 468. The quantity of water mixed with a
sample of milk may be approximately estimated by the sub-
joined tables.

The specific gravit}r of milk, with the cream thoroughly
mixed with it by shaking, is first ascertained, and if the result
is doubtful, another observation is made after the cream has
been removed.

Table for estimating the quality of milk by its specific
gravity before the removal of the cream : —

Specific Gravity.

1033 to 29 = Pure milk.
1029 " 26 = Milk with 10 per cent, of water.
1026 " 23 = " 20 " "

1023 " 20 = " 30 " "

1020 " 17 = " 40 " "

1017 " 14 = " 50 " "

Table for estimating the quality of milk from which the
cream has been removed, by its specific gravity : —

Specific Gravity.

1037 to 1033 = Pure milk.

1033 " 1029 = Milk with 10 per cent, of water.

1029 " 1026 = " 20 " "

1026 " 1023 = " 30 " "

1023 " 1020 = " 40 " "

1020 " 1016 = " 50 " "

**179. Constituents of Milk. — Casein. — Casein closely
resembles alkali-albuminatu' in its characters. It is not pre-

1 Casein is usually regarded as identical with alkali-albuminate. The
recent researches of Hoppe-Seyler and Lubavin on its digestion in gas-
tric juice, tend to show that it consists of an albuminous, in combina-
tion with a non-albuminous, organic body.

528 THE SECRETIONS.

cipitated by boiling. It is soluble in alkaline solutions, and is
precipitated from them by neutralization, but this precipitation
is prevented by the presence of alkaline phosphates. It dis-
solves in excess of hydrochloric acid, and also, but not so
readily, in acetic acid. Milk does not coagulate when it is
boiled in a test-tube, but if it is boiled in an evaporating basin,
the casein near the surface becomes somewhat dried and forms
a scum on the surface; and if this is removed another appears.
When milk stands in a warm place, it becomes sour and curdles.
»If common salt is added to fresh milk, it becomes sour on stand-
ing, but does not curdle, for the albumin, separated from the
casein by the acid, is kept in solution by the neutral salt. If
tfl!e solution is boiled, the albumin is coagulated.

Mode of Separating Casein. — As alkaline phosphates are
contained in milk, it must be not merely neutralized but ren-
dered distinctly acid, in order to precipitate the casein. The
precipitation is not complete unless the milk is diluted.

Add a little acetic acid to milk and warm it to 40° C. The
casein and the greater part of the fat separates in large flakes.
Moisten a plaited filter with water, and lilter the milk ; put the
filtrate aside, wash the coagulum thoroughly with water, and
remove the fat by exhausting it with a mixture of alcohol and
ether in the apparatus described in App. § 207. Put this solu-
tion aside; the remaining coagulum is casein.1

Mode of Separating Albumin. — Boil the filtrate from which
the casein has been precipitated. A precipitate of albumin
will be produced. Albumin may also be separated by filtering
milk through a porous cell or cone by exhausting the air. A
clear fluid will pass through which will not be precipitated by
acetic acid, showing that no casein is present, but will be pre-
cipitated by boiling or by nitric acid. In the acid liquid from
which the coagulable albumin has been removed by boiling, a
precipitate is produced by Millon's reagent, although none is
occasioned by the addition of nitric acid or mercuric chloride.

Milk-Sugar. — Filter the rest of the fluid in which the albu-
min has been coagulated. Shake it with ether to dissolve out
the fat ; remove the ether with a pipette, and then evaporate
the fluid to a thin syrup. The milk-sugar will crystallize out
gradually in rhombic prisms. It differs from glucose in its
crystalline form (the latter generally occurring in warty crumb-
ling masses), in fermenting less readily, and in being insoluble
in absolute alcohol.

The Inorganic Salts of milk are chlorides, sulphates, phos-

1 The casein in human milk cannot be readily precipitated by hydro-
chloric or acetic acids, and in order to obtain it, magnesium sulphate
must be added until the casein is precipitated, and the precipitate must
be washed with a strong solution of this salt, and then with alcohol and
ether.

BY DR. LAUDER BRUNTON. 529

pbates and carbonates of the alkaline and earthy bases. They
can only be investigated in the ash. For the method of igni-
tion see § 214.

Fats. — The fats may be separated by either of the following
methods: 1. Evaporate the mixture of alcohol and ether with
which the coagulum was exhausted, and the fat remains.

2. Add to 15 or 20 c. c. of milk, 10 c. c. of a moderately strong
solution of caustic soda; shake it vigorously with twice or
thrice its volume of ether. Remove the laj^er of ether, and
evaporate it in a water bath, and the fat remains. Ether does
not remove the fat from fresh milk, as the casein envelops the
globules, and protects the fat from its action ; but soda dis-
solves these envelopes. Ether will remove 90 per cent, of the
butter from milk which has become acid by standing.

** 180. Mode of Estimating the Quantity of Butter
Contained in Milk. — A rough method of doing this, is to
measure the cream which separates from it by Chevallier's cre-
mometer. This is a cylindrical vessel, graduated into a hun-
dred parts. The percentage amount of cream is indicated by
the number of divisions it occupies when the vessel is filled with
milk to the zero point. This method is quite unreliable.

VogeVs Test. — A much more exact method is that devised
by Vogel, which depends on the fact that the opacity of milk
is due to the globules it contains, and is in proportion to their
number.

The apparatus required for this test are — 1. A cylindrical
bottle, in which to mix the milk and water. It should hold
about 200 c. c, and have a mark on the side at the height of
100 c. c. 2. A test-glass, with parallel glass sides, exactly ^ a
centimetre apart, and supported vertically on a metal foot. 3.
A pipette graduated in fifths of a cubic centimetre.

Application of the Test. — Before applying this test, it must
be ascertained by microscopical examination that the milk does
not contain starch granules, or any other impurity in suspen-
sion which might increase its opacity. Fill the bottle up to
the 100 c. c. mark with clear spring water. Fill the pipette up
to zero with milk (App. § 217), and let 3 c. c. run into the bottle.
Mix it well with the water, and fill the test-glass with the mix-
ture. Put it in a tolerably dark room, place a stearine candle
at a distance of about three feet from it, and look at the candle
through the glass. If the contour of the flame can be readily
perceived, pour the liquid back into the bottle, add another ^
c. C. of milk to it, shake it, and look at the candle through it
again. Repeat this till the outlines of the flame can no longer
be recognized. Then add together the different quantities of
rnilk, so as to find the total amount which has been added, and
then ascertain by the following table how much butter the milk
contains : —
34

530 THE SECRETIONS.

1.0 c. c. milk, corresponds to 23.43 per cent, of butter.

1.5

tt

u

15.46

tt

tt

2.0

tt

u

11.83

tt

tt

2.5

tt

u

9.51

tt

tt

3.0

If

u

7.96

tt

tt

3.5

tt

u

6.86

tt

tt

4.0

t(

((

6.03

tt

tt

4.5

l(

t(

5.38

tt

tt

5.0

tt

tt

4.87

tt

tt

5.5

u

u

4.45

tt

tt

6.0

u

11

4.09

tt

tt

6.5

tt

u

3.80

tt

tt

7.0

tt

u

3.54

tt

tt

7.5

tt

u

3.32

tt

tt

8.0

tt

u

3.13

tt

tt

8.5

It

u

2.96

tt

tt

9.0

u

u

2.80

tt

. tt

9.5

tt

t<

2.77

tt

tt

10.0

u

u

2.55

tt

tt

11

tt

((

2.43

tt

tt

12

tt

a

2.16

tt

tt

13

u

((

2.01

tt

tt

14

it

(C

1.88

tt

tt

15

u

u

1.78

tt

tt

16

tt

u

1.68

tt

tt

17

u

a

1.60

tt

tt

18

tt

u

1.52

tt

tt

19

tt

u

1.45

tt

tt

20

tt

u

1.39

tt

tt

22

u

u

1.28

tt

tt

24

tt

u

1.19

tt

tt

26

u

(t

1.12

tt

tt

28

tt

I.

1.06

tt

tt

30

u

(4

1.00

tt

tt

35

tt

tc

0.89

tt

tt

40

tt

u

0.81

tt

tt

45

u

11

0.74

tt

tt

50

tt

u

0.69

tt

tt

55

u

11

0.64

tt

tt

60

tt

a

0.61

tt

tt

70

it

it

0.56

tt

tt

80

u

tt

0.52

tt

tt

90

u

it

0.48

tt

tt

100

u

tt

0.46

tt

tt

If cream is to be tested, only one cubic centimetre is to be
added at first, and a half c. c. at a time afterwards.

Vogel found that about 6 c. c. of pure cow's milk, or 3.7 of

BY DR. LAUDER BRUNTON. 531

cream, added to 100 c. c. of water, were sufficient to form a mix-
ture which quite obscured a caudle flame. When 8 c. c. are
required, the milk contains about 30 per cent, more water than
it ought to do, either from the addition of water, or of creamed
milk. When 12 c. c. are necessary, the milk contains 50 per
cent, too much water.

THE URINE.

** 181. Characters of Urine. — The healthy urine of man
is a clear liquid of a golden color, possessed of a characteristic
odor, and having a specific gravity which generally varies from
1018 to 1023, although it may sink as low as 1005, or rise, under
opposite circumstances, as high as 1030.

The reaction of the mixed urine of man under normal circum-
stances is acid. By the term mixed urine, we understand a
mixture of the different portions of urine passed during twenty-
four hours.

When urine is allowed to stand for some hours, it deposits a
slight cloudy sediment, which is called the mucous cloud, and
which consists of mucus holding in suspension a few epithelial
cells, derived from the genito-urinary passages. It is usually
affirmed that the urine, on exposure to the air, in clean vessels,
becomes, after some hours, much more acid than it was when
passed. To this change the name of the acid fermentation has
been given. There are no facts which prove the constant occur-
rence of this acid change. When the urine is, however, placed
for periods which vary very greatly, in open vessels, exposed to
air, it ultimately invariably undergoes the so-called alkaline
fermentation, i.e., its reaction becomes exceedingly alkaline, it
emits an ammoniacal odor, and it becomes turbid, in conse-
quence of the precipitation of phosphate of magnesium aud am-
monium, of phosphate of calcium, and urate of ammonium.

The acid reaction of healthy human urine is probably due, in
great part, to free carbonic acid, to uric and to hippuric acids ;
it has been commonly believed, however, that acid phosphate
of sodium exists in urine, and that the acidity of the fluid is
chiefly due to its presence.

The alkaline reaction of urine which has become decom-
posed is undoubtedly due to carbonate of ammonium. Un-
der the influence of putrescent animal substances it may be
observed that perfectly fresh urine becomes, in the course of
an hour or two, intensely foetid. Under these circumstances,
the urea contained in urine combines with the elements of
water and is transformed into ammonium carbonate CH4N20-f
H,0=»(NH4),CO^ The following experiments throw much
light on the proximate causes of the alkaline fermentation of
urine : —

532 TUE SECRETIONS.

Collect 200 cubic centimetres of perfectly fresh urine in a
vessel which has been carefully washed with dilute sulphuric
acid, and afterwards with distilled water. Examine the reac-
tion of the fluid, which will be found acid, then divide it in four
equal parts: 1st. Pour fifty cubic centimetres into a clean
beaker, and set it aside to serve as a standard with which to
compare the other portions.

2d. Place fifty cubic centimetres in a clean beaker, and add
to it a few drops of urine which lias been allowed to become
foetid. After twent3'-four hours compare this sample with the
first, determining the following points: o, smell, which will
have become ammoniacal in the second, unchanged in the first ;
6, clearness. The second sample will have become opalescent,
or a considerable deposit will have fallen ; c, reaction will be
strongl}' alkaline in the second, and still acid in the first. The
alkaline reaction may be shown to be due to the presence of a
volatile alkali by heating the test-paper which has been used,
and observing that the reaction which indicated alkalinity dis-
appears on the application of heat ; thus the blue color pro-
duced when reddened litmus paper was plunged into the fluid,
will disappear, and again give place to red when the paper is
heated.

3d. A third quantity of fifty cubic centimetres is placed in
a Florence flask and boiled briskly for some time, then a plug
of clean cotton wool is inserted into the neck of the flask
whose contents are still boiling, and is thrust down by means of
a glass rod. The urine is allowed to boil for some minutes
after the insertion of the plug, the flask is then allowed to
cool, set aside for many weeks and then examined.

The flask containing boiled urine and protected by the plug
of cotton wool, will, if the operator have been sufficient^
expert, retain its transparency and its acidity, and when
examined with the microscope will present no animal or vege-
table forms. On, however, exposing the contents of the flask
to the air, the alkaline fermentation will soon occur.

182. Enumeration of the normal constituents of
the Urine. — The normal urine of man consists chiefly of a
watery solution of urea and common salt, mixed with smaller
though important quantities of other substances, viz., hippuric
acid, creatinine, uric acid, coloring matters yet not accurately
investigated, indican, traces of fat, besides ammonium and
potassium chlorides, sulphates of potassium and sodium, phos-
phates of calcium and magnesium, acid phosphate of sodium,
silicic acid and iron. To the list of organic substances pres-
ent in urine, we may add unknown substances which contain
sulphur and phosphorus in an unoxidized condition, besides
well-known bodies which are certainly present in the urine in

BY DR. LAUDER BRUNTON. 533

certain cases of disease, but which cannot positively be classed
among the normal constituents.

The abnormal urine of man may contain albumin, grape-
sugar, lactic acid and lactates (?), bile coloring matter and bile
acids, blood serum and blood cells, haemoglobin, pus serum
and pus cells, carbonate of ammonium, sulphuretted hydrogen,
oxalate of lime, xanthine, hypoxanthine, leucine, tyrosine, and
inosite.

The urine may contain, in addition to the substances which
have been previously named, others which have been intro-
duced into the bod}' as drugs or poisons, and which, being
excreted b}' the kidneys, find their way into the urine ; this is
the case with many, although probably not with all the metallic
salts, with most alkaloids, and with organic bodies of different
constitution, as carbolic acid, alcohol, and various vegetable
coloring matters.

183. Urinary deposits. — Owing to deficiency in the quan-
tity of the urinary water, excess in the quantity of normal
ingredients, or presence of substances which are not normally
present, we are apt to have urinary sediments or deposits, some
of which are composed of structural elements, not usually
present, others of the normal or abnormal proximate princi-
ples. Amongst such sediments we find most frequently uric
acid, urates, ammoniaco-magnesian phosphate, calcium phos-
phate, calcium oxalate, blood corpuscles, mucus, epithelium,
pus, etc.

** 184. Reactions of Urine treated -with some com-
mon reagents.

Before commencing a systematic account of the mode of
separating the chief constituents of urine, the student may
with advantage study the action on this fluid of a few of the
common reagents which indicate the presence of the chief
ingredients contained. Put about 15 cubic centimetres of
urine into a series of test-tubes, and try the following experi-
ments:—

1. Add about 5 cubic centimetres of^strong nitric acid. No
precipitate will occur, either immediately or after standing for
some time. The color of the urine will, however, become
darker.

2. To a portion of fresh urine in a test-tube add an equal
volume of liquor potassae. After some time a transparent
flaky precipitate will be observed, which separates on boiling,
leaving the supernatant fluid of its original color.

By other experiments it may be shown that solutions of am-
monia and caustic soda likewise induce this precipitate, which
consists of car//ii/ phoaphMes.

3. Add to 15 cubic centimetres of the urine, about 5 c.c. of
a solution of silver nitrate (1-10) ; an abundant curdy precipi-

584 THE SECRETIONS.

tate will fall. This consists of chloride of silver and phosphate
of silver ; and adding nitric acid to the mixture, the phosphate
of silver is dissolved, leaving a quantity of perfectly white,
chloride of silver, which, after the test-tube has. been shaken
for some time, sinks to the bottom, leaving a clear supernatant
fluid.

4. To 15 cubic centimetres of urine which have been strongly
acidulated with nitric or hydrochloric acid, add two or three
c.c. of a solution of barium chloride. A precipitate of barium
sulphate will fall.

5. Pour a strongly acid solution of ammonium molybdate
into a test-tube, add a few drops of urine and boil ; the fluid
will become yellow, and a canary-yellow precipitate will fall,
composed of phospho-molybdate of ammonium ; this indicates
the presence of phosphoric acid.

6. To 15 cubic centimetres of urine, in a test-tube, add an
equal quantity of a solution of caustic baryta. An abundant
precipitate will fall, composed chiefly of barium sulphate and
phosphate.

7. To the same quantity of urine add about one-third of its
volume of a solution of acetate of lead. A white precipitate,
consisting of chloride, sulphate and phosphate of lead, will
fall ; and it will be observed that the urine is to a great extent
decolorized.

On the methods of Separating, and on the Reaction of TnE
Principal Organic Constituents of Urine.

** 185. Preparation of Urea (CH4N20) from Urine.

— Take 100 cubic centimetres of urine, and add to it 50 cubic
centimetres of a solution made by mixing one volume of a
saturated solution of nitrate of barium, with two volumes of a
saturated solution of caustic baryta.

A precipitate will form, which is chiefly composed of phos-
phate and sulphate of barium. On filtering, a clear fluid is
obtained which is evaporated to dryness on awrater bath. The
residue is treated with hot spirits of wine, and the alcoholic
solution is likewise evaporated to dryness. On now adding
absolute alcohol to the residue the urea is separated, and is
obtained from the solution by evaporation. To purify it further
from traces of other organic and saline matters, the crystals
of urea must be colleeted on blotting-paper, strongly pressed
between folds of filtering paper, dried on a porous tile, and, if
necessary, again dissolved in spirit and re-crystallized.

Although urea can be readily obtained from urine, it is more
convenient to make use of artificial urea in the experiments
which are required to demonstrate its characteristic properties.

As it is altogether beyond the province of this book to refer

BY DR. LAUDER BRUNTON. 585

to matters which concern pure chemistry, it may be merely
stated that the artificial urea, which can now be readily pur-
chased, is prepared by mixing, in certain proportions, aqueous
solutions of potassium cyanate and ammonium sulphate, eva-
porating to dryness and extracting the residue with alcohol.
During the process ammonium cyanate is first formed, and sub-
sequently this is transformed into its isomer, urea. In order to
determine the chief reactions of urea, perform the following
experiments : —

1. Take a crystal of urea, and placing it in a water-glass add
a few drops of distilled water. It will dissolve with great
readiness. Take a couple of drops of the solution and allow
it to crystallize on a glass slide, which may be gentl}- heated.
A residue is obtained which presents to the naked eye a crys-
talline appearance, and which under the microscope is seen to
be formed of transparent four-sided prisms, terminated by one
or two oblique facets (Fig. 322).

2. Place a fragment of urea on the tongue, and observe that
it possesses a cool, nitre-like taste.

3. Heat a fragment of urea on a piece of platinum foil, or on
a platinum spatula, over a gas or spirit-lamp. The urea will
first melt, then solidify, and ultimately burn away rapidly
without leaving a trace of ash or unburned carbon.

4. Place a tiny crystal of urea on a glass slide; dissolve it
in distilled water, and then add a drop of strong and perfectly
colorless nitric acid. Crystals will form which consist of a
compound of nitric acid and urea (CH4Nv!0,HN0.1). These are
much less soluble than crystals of urea. Nitrate of urea is
comparatively insoluble in dilute nitric acid. Nitrate of urea
crystallizes generally in the form of six-sided tables (Fig. 323).

From highly concentrated urine of man, large quantities of
nitrate of urea may be sometimes obtained, without any pre-
vious evaporation, by inerety adding pure nitric acid. In any
case, however, nitrate of urea may be obtained in a crjrstalline
form by evaporating urine nearly to a S}rrupy consistence, de-
canting the liquid from the salts which have separated out, and
then adding an equal volume of pure nitric acid.

5. Perform an experiment similar to the preceding one,
substituting a solution of oxalic acid for the nitric acid. A
crystallization of oxalate of urea (CH^N^OjC^H^Oj is obtained
(Fig. 324).

6. Take one cubic centimetre of a solution of pure urea (con-
taining 5 grammes dissolved in 100 grammes of distilled water).
Then add cautiously a solution of mercuric nitrate; a curdy
white precipitate forms, which consists of combinations of urea
with mercuric oxide. On adding a drop of the mixture of urea
and mercuric nitrate to a drop of a cold saturated solution of
sodic carbonate no reaction will be observed until an excess of

f>:5lj THE SECRETIONS.

the mercuric salt has been added. Then there is produced a
very characteristic 3'ellow color, due to the precipitation of
mercuric hydrate. On this reaction is based Liebig's method
for the determination of urea.

7. Place one cubic centimetre of a solution such as that used
in the last experiment, in a test-tube, and then fill the latter
exactly with a solution of sodium hypochlorite. Invert the
tube once or twice, and plunge it into a basin containing mer-
cury. A most vigorous evolution of gas takes place ; this con-
sists of nitrogen.

The reaction which occurs is illustrated by the following
equation : —

CH4N20 + 3NaC10=3NaCl + C02+2n20 + 2N.

The carbonic acid which is generated in the reaction is absorbed
by the solution of sodium hypochlorite.

Instead of sodium hypochlorite, the similar salt of potassium
or calcium might be used in this experiment.

** 186. Separation of uric acid (C5H4N403) from
Urine. — Place 200 cubic centimetres of urine in a narrow glass
cylinder, and add two or three cubic centimetres of pure nitric
acid. After twenty -four hours a brick colored or brown sedi-
ment will have subsided, which consists of crystals of uric acid,
strongly tinted with the coloring matter of urine. These pre-
sent, under the microscope, the most various forms, the more
common being rhombic tables or columns and lozenge-shaped
crystals ; the yellow or brown color which such crystals pos-
sess is very characteristic of uric acid.

Decant the urine from the red sediment of uric acid, which
maybe freely washed with distilled water, as uric acid requires
14,000 times its weight of cold and 1800 times its weight of hot
water to dissolve it. The sediment may then be collected on
filtering paper and subjected to the following tests : —

1. Place a small quantity of the crystals on a microscopic
slide, and add a drop of liquor potassre. The crystals dissolve,
and a solution of urate of potassium is obtained (C^H^K.^OJ.

Now add carefully an excess of nitric or hydrochloric acid,
when uric acid will be again obtained in the form of crystals,
which may be further examined.

It may be well to state that uric acid often occurs as a de-
posit in urine which has not been artificially acidified, and that
the crystallographic characters of the substance are very various
and sometimes puzzling. The typical crystals of uric acid are
undoubtedly rhombic plates with extremely obtuse angles ; the
typical form is, however, very frequently modified ; thus spin-
dle-shaped figures are formed by the rounding of the obtuse
angles, or the primary form is so modified that needles are
formed which occur in groups (fig. 305). Not at all unfrequently

BY DR. LAUDER BRUNTON. 537

wc have the primary form so modified that the crystals resemble
hexagonal plates. Experience gained by a frequent comparison
with accurate drawings of the various forms of crystals of uric
acid, can alone enable the observer rapidly to identify uric acid.
When any doubts exist as to the identity, it is well to dissolve
the suspected crystals in liquor potassae, and to proceed as
directed above, for by neutralizing an alkaline urate with acid,
some of the commoner, and therefore easily identified shapes of
uric acid ciystals, are obtained.

2. Place a very small quantity of the reddish ciystalline
deposit in a watch glass ; add four or five drops of nitric acid
and heat very cautiously over a small spirit-lamp flame. The
uric acid will dissolve, and on evaporating to dryness, a red-
dish-yellow residue is obtained. On exposing this residue to
the vapor of ammonia, or adding, by means of a thin glass rod,
a small quantity of solution of ammonia, a beautiful purple-
red color is developed, which, on the subsequent addition of a
little solution of caustic potash, assumes a violet tint. This
reaction has received the name of the Murexide Test.

*187. Separation of Hippuric Acid (C9H9NCg.— After
urea, hippuric acid is the organic compound present in largest
quantity in the urine of man, the mean quantity excreted per
diem amounting at least to one gramme. The difficulties at-
tending the separation of hippuric acid from the urine of man
are, however, great, and it is therefore advisable that the stu-
dent should learn to isolate this substance when it is present in
larger quantities than normal in the urine. As the urine of
herbivora contains large quantities of hippuric acid, it may be
advantageous to use for the experiment to be described cows'
or horses' urine, or the urine of men in whom an excessive
excretion of hippuric acid has been induced ; this may be done
by administering to a man ten or fifteen grammes of benzoic
acid ten or twelve hours before the urine is collected.

It is a fact worthy of remembrance that when benzoic acid is
administered to healthy men, large quantities of hippuric (ghy-
co-benzoic) acid are excreted. There appears to be always in
the system a quantity of glycocine (C.^H., (NH2) OJ. which al-
though it is never excreted as such, is capable of being seized
upon by the radical of benzoic acid, so as to yield hippuric acid.
By comparing the formula? of glycocine and hippuric acid, ex-
hibited below, it will be seen that the latter can be represented
as derived from the former by the substitution of (C7ILO) for
II, thus:—

Glycocine 02H,(NHB)Os

Hippuric acid C,II,(NIIJ (C.II50)0,.

Take 200 cubic centimetres of the fresh urine of the cow
and concentrate it, by beating an the water-bath, to forty cubic

538 THE SECRETIONS.

centimetres. Then add hydrochloric ;ici<l, and set aside until
next day. A large quantity of hippuric acid will have separa-
ted in the form of a brown crystalline mass. Wash with cold
water, press the crystalline mass between folds of filtering
paper; dissolve in as little boiling water as possible, add a
little pure animal charcoal (i. p., animal charcoal which has
been in contact with dilute hydrochloric acid for many days,
and then thoroughly washed with water), and filter. The
filtrate should be concentrated and allowed to crystallize.
(For other methods of separating hippuric aeid, especially
when existing in small quantities, the reader is referred to
Hoppe-Seyler's " Handbuch der physiologisch- und patholo-
gisch-chemischen Analyse, 1870, p. 157).

Having obtained nearly pure hippuric acid, the following
experiments may be tried : —

1. Dissolve a fragment in boiling water, and allow a drop
of the solution to crystallize on a microscope slide. The acid
usually separates in the form of transparent prisms which are
single, or occur in radiating groups, and generally present four
sides parallel to their long axis ; their ends are terminated by
two or four planes. Their primary form is a right rhombic
prism (fig. 313).

2. Heat a fragment of hippuric acid in a small glass tube,
with a little soda-lime ; the ammonia which is given off, and
which can readily be detected by its odor, proves that the body
under examination contains nitrogen.

3. Mix a fragment of hippuric acid with strong nitric acid
in a small porcelain crucible. Boil and then evaporate to
dryness; on heating the residue, a very characteristic odor of
nitro-benzol is developed.

* 188. Separation of Creatinine (C4H7NsO) from
Urine. — To 300 cubic centimetres of urine add milk of lime
until the reaction of the fluid is decidedly alkaline. Then add
a solution of chloride of calcium as long as a precipitate falls.
After the precipitate has been allowed partially to subside,
filter, evaporate the filtrate to dryness in a basin or the water-
bath, and add to the yet warm residue thirty or forty cubic
centimetres of 95 per cent, alcohol. Stir and decant the con-
tents of the basin into a beaker, taking care to add the alco-
holic washings of the basin. Set aside the beaker in a cool
place. Filter and wash the insoluble residue with a little more
spirit. If the filtrate and washings amount to more than 50
c. c, concentrate at a gentle heat to that volume. Allow the
fluid to cool, and then add half a cubic centimetre of an alco-
holic solution of chloride of zinc, absolutely free from the least
trace of acid, and stir for some time. Set the beaker aside for
three or four days in a cellar. At the end of that time the
whole of the creatinine will have separated in combination

BY DR. LAUDER BRUNTON. 539

with zinc chloride. It should be collected on a filter and
washed with pure spirit; the substance left on the filter con-
sists of chemically pure chloride of zinc-creatinine (C4H7N30).2,
ZnCl„. This most characteristic compound is very slightly
soluble in cold water and insoluble in cold alcohol ; it crystal-
lizes from urine in the form of bundles of needles.

From chloride of zinc-creatinine, the pure substance is
obtained by boiling with freshly pi'epared and thoroughly
washed h}rdrate oxide of lead for half an hour or longer. On
filtering the fluid, and evaporating to dryness, creatinine is
obtained, which may be dissolved in alcohol and crystallized.

Creatinine is very soluble in cold alcohol. The following
experiments may be performed with it : —

1. When a few drops of a solution are allowed to evaporate
spontaneously, colorless prisms are obtained (fig. 302).

2. The taste of the solution is strongly alkaline.

3. The reaction to test-paper is intensely alkaline.

4. A concentrated solution of chloride of zinc added to
creatinine, causes the immediate precipitation of the zinc com-
pound, which is always crystalline.

** 189. Separation of the Coloring matters of
Urine. — Under various names, among others that of Urohae-
matine, different writers have described the substance, or
mixture of substances, which they considered to be the cause
of the color of healthy urine (Scherer, Harle}7, Heller). We
are now perfectly convinced that no one coloring matter, capa-
ble of accounting for the normal, golden, or amber color of
human mine, has been separated.

The following experiments maybe performed, as they throw
some light on the reactions of the normal urinary coloring
matter : — »

1. Take 200 cubic centimetres of urine and precipitate with
neutral acetate of lead ; an abundant precipitate falls, which
consists of lead salts of acids present in the urine, and which
contains a portion of the urinary coloring matter. Filter, and
observe that the filtrate from this precipitate is not altogether
colorless. Add to the filtrate basic acetate of lead, when a
further precipitate will form, which, when separated, leaves a
colorless filtrate.

Now unite the precipitates caused by neutral and basic
acetates of lead, and treat the mixture with alcohol acidulated
with hydrochloric acid. A red fluid will be obtained, which,
on filtration and evaporation, yields a reddish-black residue,
insoluble in water.

That this is not, as was supposed, the coloring matter of
urine, is now admitted. The researches of Dr. Harley, although
failing to discover any one normal urinary coloring matter, show

540 TI1K SKCRKTIONS.

that the so-called urohiematinc contains a mixture of several
pigmentary substances.

2. Passing from urohrcmatine, the student's attention is to
be drawn to the constant presence in urine of a very well-
defined body — viz., indican, or white indigo (C,8H12N,0,) —
which may readily be converted into indigo-blue and indigo-
red. To the indican present in urine, Heller, who first dis-
covered its presence, without, however, being aware of its
nature, gave the name of Uroxanthine, and to the indigo-blue
and indigo-red obtained from it, the names of Uroglaucine and
Urrhodin respectively.

For the method of obtaining indican, the reader is referred
to Hoppe-Seyler (op. cit. p. 163) ; it will be sufficient if the
student performs the following experiments: —

Precipitate 100 cubic centimetres of perfectly fresh urine
with acetate of lead. The fluid is filtered. The filtrate con-
tains the whole of the indican. A strong solution of ammonia
is added, which precipitates hydrated lead oxide, together
with indican. The precipitate is collected on a filter, washed
with water and dilute dydrochloric acid. Very often the
filter is seen to contain blue particles, in consequence of the
production of indigo-blue, which contrasts with the chloride of
lead with which it is mixed.

The filtrate, when left to itself for twenty -four hours, gener-
ally becomes covered with a bluish-purple film, consisting of
indigo.

3. Several hundred cubic centimetres of pure urine are pre-
cipitated by acetate of lead and then filtered ; the filtrate is
treated with excess of sulphuretted hydrogen, boiled and
filtered; the filtrate is now poured into an equal volume of
pure and strong hydrochloric acid. The fluid becomes either
violet or indigo-blue ; it is allowed to stand for twelve hours,
and diluted with an equal volume of water. After about
twenty-four hours, a deposit will generally have formed, which
is collected on a filter, washed, and dried. When treated witli
ether, the deposit will generally yield to it a red coloring
matter, whilst indigo is left behind, and is to be purified by
solution in boiling alcohol.

The student will remember that indigo-blue only differs from
indican in the possession of two additional atoms of hydro-
gen,—

Indican, or white indigo ClfH].iN.!0.!.

Indigotin, or blue indigo C^II^N.^O.^.

In the production of indigo-blue from indican there are
other substances formed, such as a form of sugar, which is an
isomer of glucose, but unfermentable, and the imperfectly

BY DR. LAUDER BRUNTON. 541

investigated body, indigo-red, which has already been alluded
to.1

The following reactions may be tried with indigo-blue : —

(a) Shake a fragment of indigo-blue with ether ; the sub-
stance is found to be veiy scantilj7 soluble. Ether, however,
dissolves enough to acquire a faint blue tint.

(b) Place a fragment in a narrow glass tube and heat ; it
will sublime and be deposited in the cool part of the tube. If
the latter be very narrow and thin, it may be examined
microscopically. The sublimate of indigo is then seen to con-
sist of microscopic needles and plates.

Methods fok the Quantitative Analysis op Urine.

** 190. Determination of the total quantity of Urine
passed in a given time. — Before describing briefly the
methods which are employed for the determination of the more
important urinary constituents, attention must be drawn to
the fact that, as a general rule, quantitative analj'sis of urine
throws little or no light on the rate and character of the tis-
sue changes going on in the animal body, unless the analysis
be made of a specimen of urine which represents the average
excretion of a known period, during which the conditions of
the animal have been ascertained as accurately as possible.

These remarks will be better understood when it is stated
that we can obtain the most valuable information relating to
the urinary secretion if we collect, mix, and then measure the
whole of the urine passed in twenty-four hours. Having
ascertained the total volume of urine passed in twenty-four
hours, two hundred cubic centimetres will suffice for the great
majority of quantitative analyses.

The urine of man must be collected in perfectly clean glass
vessels which in accurate experiments, should, before being
used, be washed with dilute sulphuric acid, and then with
water. The collecting-vessel ma}' be graduated or not ; in the
latter case, the urine is carefully poured, if necessary, in suc-
cessive portions, after being mixed, into a cylinder capable of
holding a litre of water, and divided into 200 parts; so that
each division indicates 5 cubic centimetres.

It is frequently of use to collect the urine of dogs and rab-
bits, especially when experiments are made on the physiological
action of drugs.

1 In many cases of disease, urine contains so much indican, that the
following reaction may be observed : —

To five cubic centimetres of fuming hydrochloric acid, add from one
to two cubic centimetres of urine. A violet color is produced, which
passes into red.

542 THE SECRETIONS.

In those cases, cages are employed, whose walls are made
partly of sheet iron or zinc, and partly of wire netting. The
floor of the cage should he made of thick glass rods (about
four-tenths of an inch in diameter), placed very closely together.
These rods are so arranged that the spaces between them will
allow urine to trickle away, whilst the solid excreta are re-
tained.

The glass rods are firmly inserted into the wooden base of
the cage ; this is furnished with a drawer, into which is accu-
rately fitted a flat glass or porcelain dish, such as is used by
photographers in washing photographs. The dish is perforated
by a hole, in which a tube (preferably of glass) is accurately
fitted, and leads to the collecting vessels outside.

If care be taken to wash the glass-rod bottom of the cage
and the collecting-glass dish placed beneath it, the urine may
be collected in a state of great purity.

** 191. Determination of the specific gravity of
Urine. — This may be effected in either of the two ways de-
scribed in App. § 216, for the determination of the specific
gravity of fluids, viz., by means of a hydrometer or with the
specific gravity bottle.

The hydrometer employed for taking the specific gravity of
urine is called a urinometer ; in this country its stem is usually
divided so as to indicate densities ranging from 1000 to 1060
(water being 1000) ; it is preferable to use two urinometers :
one indicating densities from 1000 to 1030, the other from
1030 to 1060. The length of the stem being the same as that
of the ordinary instruments, the accuracy of the reading will
be much increased. Before using a urinometer, its accuracy
should be checked by immersing it in fluids of known specific
gravity. If the specific gravity of three samples of urine be
accurately taken with the bottle, data are obtained for checking
the accuracy of the urinometer.

Although, under certain circumstances, important informa-
tion may be obtained by a determination of the specific gravity
of an isolated sample of urine, generally it is only when the
specific gravity of a sample of the mixed and measured urine
of the twenty-four hours is ascertained, that we learn much
from the experiment.

A knowledge of the specific gravity enables one to form a
near approximation to the total quantity of solid matter ex-
creted by the kidneys in a given time.

It has been empirically determined that the specific gravity
of urine generally bears a close relation to the solid matters
which it contains in solution. Sir Robert Christison pointed
out, many years ago, that if the whole numbers which express
the difference between the density of a sample of urine and the
density of water (expressed as 1000) be multiplied by the factor

BY DR. LAUDER BRUNTON. 543

2.33, the product represents very closely the weight of the
total solids contained in 1000 parts, by weight, of urine.
Subsequent observers have determined that whilst Christison's
formula yields very correct results when applied to urines of
specific gravities above 1018, for urines of lower specific gravity
greater accuracy is obtained by substituting the factor -2 for
2.33.

The following example will suffice to show the method of
calculating approximately the total solid matter excreted in
the urine in twentjT-four hours : —

A man passes in twenty-four hours 1575 cubic centimetres
of urine of specific gravity 1023, and it is desired to obtain an
approximate estimate of the total urinary solids.

1st. We find the total solids (expressed in any particular
units of weight) contained in 1000 par,ts (expressed in the
same units of weight) by Dr. Christison's formula, thus, if the
unit be the gramme, and the quantity of solid matter in 1000
grammes be represented by x,

x = (1023 — 1000) 2.33 = 53.59.

2d. We require to know the weight of the whole of urine.
As its density is 1023, and the quantity 1576 cubic centimetres,
the weight in grammes is at once found by the following
proportion : —

1000 : 1023 :: 1575 : x

x = 1023x 1575 = 16n>

1000

3d. Knowing the weight in grammes of the urine of twenty-
four hours, and the approximate weight of total solid matters
in 1000 parts, by weight, of urine, we obtain the total solids
passed in twenty-four hours expressed in grammes: —

1000 : 53.59 :: 1611 : x
x = 86.33 grammes.

It is to be noted that the result obtained by such calcula-
tions is merety an approximation to the actual number which
would be ascertained by the direct method, to be immediately
described ; the approximation is, however, sufficiently close to
be useful.

192. Determination of the Total Solid Matters con-
tained in Urine. — If we know the total volume of urine
passed in twenty-four hours, and it be desired to ascertain, by
direct weighing, the total quantity of solid matter contained
in it, 10 or 15 cubic centimetres of the mixed urine are poured
from a very accurately graduated pipette into a weighed porce-
lain or glass capsule, which is heated over the water-bath,

544 THE SECRETIONS.

or in the water oven (fig. :{:!!>), until a nearly dry residue is
obtained. The capsule with its contents is then heated in an
air oven whose temperature is maintained at 120° C. The
capsule is, after some time, allowed to cool in an exsiccator
(fig. 340) and rapidly weighed. The drying and weighing
should be repeated until the weight of the capsule and residue
is constant. In order to secure accuracy, the capsule in which
the evaporation is carried on should be fitted with a ground
glass plate, which should be placed over it, when it is trans-
ferred from the air oven to the exsiccator, and from the ex-
siccator to the balance.

It is absolutely essential that the weighing should be con-
ducted with the greatest possible rapidity, as the dried urinary
solids are highly hygroscopic.

Instead of measuring the urine used in the analysis, a
weighed quantity may be taken.

** 193. Determination of the Amount of Chlorine
contained in Urine.

By Liebig's Method — It has been already mentioned that
when a solution of mercuric nitrate is added to a solution of
urea, a dense white precipitate is formed, which consists of
compounds of urea with mercuric oxide.

If the solution of mercuric nitrate be sufficiently diluted,
and be added in sufficient quantity, the compound formed con-
tains four molecules of mercuric oxide for each molecule of
urea.

If, however, a solution of mercuric nitrate be added to a
solution of urea and chloride of sodium, no precipitate will at
first be formed, the reaction between the urea and oxide of
mercury not occurring until the double decomposition between
the mercuric nitrate and sodium chloride has been completed,
thus: —

Hg 2N03 + 2NaCl=Hg Cl,+ 2NaN03.

As soon, however, as this has occurred, a white precipitate
of the mercuric oxide and urea compound falls.

Liebig's method of determining the amount of chlorine in
urine is based upon the reactions which have been referred to.

In order to enable the student to determine the amount of
chlorine by Liebig's method, we shall describe, in the first
place, the method of preparing the standard solution of nitrate
of mercury, and, in the second place, the method to be fol-
lowed in determining by its aid the quantity of chlorine in
urine.

Preparation of standard solution of mercuric nitrate for
the estimation of chlorine in Urine.

The following solutions are required : —

1st. A solution of mercuric nitrate of such a strensth that

BY DR. LAUDER BRUNTON. 545

one cubic centimetre shall correspond to 10 milligrammes
(0.010 grm.) of sodium chloride.

This solution may be made by dissolving twenty grammes
of perfectly pure metallic mercury in boiling nitric acid, until
a drop of the acid fluid does not cause a precipitate when added
to a solution of common salt. The acid fluid is concentrated
by heating over a water-bath until it is of syrupy consistence.
It is then diluted with nearly a litre of distilled water.

Unless a great excess of nitric acid has remained after the
evaporation, a white precipitate, consisting of a basic nitrate
of mercury, will fall, and must be separated by filtration. Be-
fore performing the latter operation, a few drops of nitric acid
may, however, be added, as they will cause the re-solution of a
considerable part of the precipitate, without rendering the
liquid too acid. The solution of mercuric nitrate thus made
must be set aside until the other reagents which are required
for determining its strength are prepared.

2d. A solution made by dissolving in distilled water 20
grammes of pure sodium cloride and diluting to one litre. The
salt is fused before being weighed.

Ten cubic centimetres of this solution contain 0.200 grm. of
NaCl.

3d. A solution made by dissolving 4 grammes of pure urea
in distilled water and diluting to 100 c. c.

4th. A solution of sodium sulphate, saturated at ordinary
temperatures.

In order to determine the strength of the solution of mer-
curic nitrate, it is poured into a burette (preferably a Mohr's
burette, with glass stopcock) of a capacity of 50 cubic centi-
metres, and divided into lOths of a cubic centimetre.

Ten cubic centimetres of the standard solution of chloride
of sodium are then measured by means of a pipette, and poured
into a glass beaker.

To this is added 3 cubic centimetres of the solution of urea,
and 5 cubic centimetres of the solution of sulphate of sodium.
The solution of nitrate of mercury is now allowed to flow
gently into the beaker; as the drops fall into the fluid con-
tained in the latter, a white precipitate is seen to form, which,
however, dissolves at once, or when the fluid is stirred. On
adding more of the solution of nitrate of mercury, the fluid
becomes opalescent but no precipitate occurs until the reaction
is completed, i. e., until the whole of the chloride of sodium
has been decomposed.

The number of cubic centimetres of the solution of mercuric
nitrate which has been added is read off; if, for example, 12.7
cubic centimetres of the solution had to be added in order to
induce a permanent precipitate, we conclude that this quantity
of solution contains the quantity of mercuric nitrate required
35

546 THE SECRETIONS.

to decompose 0.200 gramme of NaCl. As it is convenient to
have a solution of which 10 cubic centimetres shall be equiva-
lent to 0.100 gramme of NaCl, we must take our solution and
dilute it to the required extent. In the assumed case, 12.7
cubic centimetres contained as much of the mercurial salt as
correspond to 0.200 gramme of NaCl, i. e., as much as would
be required in 20 cubic centimetres of solution. If we there-
fore diluted 12.7 cubic centimetres with 7.3 cubic centimetres
of water, we should obtain 20 cubic centimetres of a solution
of which 10 cubic centimetres would be exactly capable of de-
composing 0.100 gramme of NaCl.

But as in preparing such a standard solution we deal with
large quantities of fluid, it is well to effect the dilution of the
whole at once.

Thus let us suppose that we have 800 cubic centimetres of
the solution, of which 12.7 cubic centimetres are equivalent to
0.200 gramme of NaCl.

As 12.7 cubic centimetres require the addition of 7.3 cubic
centimetres of water, it is easy to find how much 800 cubic
centimetres require, viz., 459.8 cubic centimetres. If we then
measure out very accurately this quantity of distilled water,
and add it to our solution, we obtain 1259.8 cubic centimetres
of a solution of which 10 cubic centimetres represent 100 milli-
grammes of NaCl, or 60.65 milligrammes of CI.

Having made the standard solution of nitrate of mercury
for the estimation of chlorine, we must, before analyzing urine,
prepare a solution which we shall designate as Baryta Mixture.

This is prepared by mixing two volumes of a solution of
barium nitrate, saturated in the cold, with one volume of a
solution of caustic baryta (barium hydrate), similarly saturated.

Two volumes of the urine to be analyzed (say 40 cubic centi-
metres) are now mixed with one volume (say 20 cubic centi-
metres) of baryta mixture. An abundant precipitate falls,
consisting chiefly of a mixture of phosphate, sulphate, and car-
bonate of barium. (This removal of phosphates is essential,
as these salts are precipitated by the solution of nitrate of
mercury.)

The fluid in which the precipitate has formed is filtered, care
being taken that the filter is not moistened.

As the filtrate contains one-third of its volume of baryta
mixture, it is convenient to take for analysis 15 cubic centi-
metres. This quantity will exactly correspond to 10 cubic cen-
timetres of urine. It is convenient, therefore, to have, in addi-
tion to pipettes graduated so as to deliver 20 and 40 cubic
centimetres, one which delivers exactly 15 cubic centimetres
of fluid. The measured portion of filtrate is very slightly
acidified by adding, drop by drop, exceedingly dilute nitric
acid, and then the solution of nitrate of mercury is allowed to

BY DR. LAUDER BRUNTON. 547

flow in, at first rather rapidly, afterwards guttatim, until a per-
manent and dense cloud, not affected by vigorous stirring,
makes its appearance.

The number of cubic centimetres used, multiplied by 0.010.
indicates the amount of chlorine, in fractions of a gramme, cal-
culated as NaCl, contained in 10 cubic centimetres of urine.
Thus, if 8.56 cubic centimetres of the standard solution of
chlorine were added, the quantity of CI, calculated as NaCl,
in 10 cubic centimetres, would be 0.085 gramme.

It must be remarked that if a urine contains albumin, this
substance must be removed by boiling and filtration before the
determination of chlorine bjr Liebig's method can be effected.

194. Determination of chlorine by means of nitrate of silver.
— In cases where the quantity of chlorine is exceedingly small,
the following method is much to be preferred to that already
described.

Ten cubic centimeti'es of urine are placed in a platinum cap-
sule, together with 2 grammes of pure potassium nitrate (quite
free from chlorine), and evaporated to dryness. The residue is
ignited at a moderate heat until the whole of the carbon has
disappeared.

The crucible is allowed to cool, and the saline mass which it
contains is dissolved in distilled water, a little nitric acid being
added. The estimation of chlorine may then be effected by
those methods which are to be found described in text-books
on chemical analysis. The chief of these methods consist (a)
in precipitating the chlorine as chloride of silver, etc., washing,
burning, and weighing the precipitate; and (6) in adding to
the neutralized solution of the chloride, mixed with a drop of
potassium chromate, a standard solution of nitrate of silver.
Thfr nitrate of silver causes a white precipitate of chloride of
silver, when added to such a solution, until the whole of the
chlorine has been precipitated. Then, however, the addition
of a single drop more produces a deep salmon-red color, due
to the formation of silver chromate.

** 195. Determination of the amount of Urea found
in Urine.

I. By Liebig's Method In order to determine the amount of

urea by Liebig's method, we require (a) baryta mixture as used
in the determination of the amount of CI in urine, and (b) a
standard solution of nitrate of mercury, prepared in the same
manner as that used for CI determinations, but containing
much more mercury. In making this solution, dissolve about
75 grammes of pure mercury in pure nitric acid, adopting all
the precautions previously suggested, and dilute to the volume
of oik; litre.

In order to grade the solution of mercuric nitrate for uren,
we must pour into a beaker 10 cubic centimetres of a standard

548 THE SECRETIONS.

aqueous solution of pure urea, containing 2 grammes of per-
fectly pure urea in 100 cubic centimetres. The quantity of so-
lution in the beaker will then contain 0/200 gramme of urea.

The solution of mercuric nitrate is then added and the fluid
stirred ; an abundant snow-white precipitate falls. When the
precipitation appears to be nearly completed, a drop of the fluid
holding the precipitate in suspension is added to a drop of
solution of sodium carbonate on a porcelain slab. If the urea
be not completely precipitated, no change of color will be ob-
served when the two fluids are mixed. The mercuric nitrate
solution is then added drop by drop, and the process of testing
with the solution of Na^CO., on the slab repeated from time to
time. At last a 3rellow color will appear. This will indicate
that the solution of mercury has been added in excess. The
number of cubic centimetres of solution added indicates the
number of c. c. which are equivalent to 0.200 gramme of urea.
As it is convenient to have a solution of mercuric nitrate, of
wdiich 10 cubic centimetres shall precipitate 100 milligrammes
of urea (0.100), or 1 cubic centimetre 10 milligrammes, it is
essential to dilute the solution which has been prepared, in the
same manner as was indicated in the case of the solution for
the determination of chlorine.

Having prepared the solution of mercuric nitrate for urea,
and the baryta mixture, the analysis of urine can be rapidly
effected. 40 cubic centimetres of urine are mixed with 20 cubic
centimetres of baryta mixture; 15 cubic centimetres of the fil-
trate are precipitated with the mercury solution, until a yellow
reaction with solution of Na2C03 is obtained.

The number of cubic centimetres of the mercury solution
used, minus 2 and multiplied by 0.010 gramme, indicates very
closely the amount of urea, expressed in fractions of a gramme,
contained in 10 cubic centimetres of urine, provided that the
urine be of average composition, i. e., that it contains no ab-
normal substances, that the amount of chlorine in it be about
the average, and that it be neither very concentrated nor very
dilute.

The statements made in the preceding paragraph indicate
many circumstances which have to be taken into account, and
many corrections which have to be introduced in order to give
to Liebig's method the accuracy of which it is capable.

In pointing out these corrections, an explanation must be
given of the empirical statement, '■'•that the number of cubic
centimetres of mercury solution used, minus 2, and multiplied
by 0.01 grm., indicates very closely the amount of urea, ex-
pressed in fractions of a gramme, contained in 10 cubic centi-
metres of urine." The reason for subtracting 2 cubic centi-
metres is, that in average urines this volume of the solution is

BY DR. LAUDER BRTJNTON. 549

required to decompose the chlorides, and does not, therefore,
take part in the urea reaction.

If this correction be constantly introduced in a series of ob-
servations, and, as has been ahead}7, pointed out, the urine be
not of very exceptional composition, results are obtained which
are very nearly correct, and which are comparable the one with
the other. If, however, the urine in cases of pneumonia or of
fevers were under investigation, the error introduced by the
application of this arbitrary correction would generally be very
great.

In such cases we must adopt a more scientific method of
avoiding the error introduced by the presence of chlorides. We
must in the first place determine, by the standard solution of
mercuric nitrate for chlorine, the amount of chlorine, calcu-
lated as NaCl present in 10 cubic centimetres of the urine, i.e.,
in 15 cubic centimetres of the filtrate obtained on mixing two
volumes of urine with one volume of baryta mixture, and we
must then remove the whole of the CI from a fresh quantity
of filtrate by a standard solution of nitrate of silver. To do
this we require a solution of nitrate of silver exactly equivalent
to the solution of nitrate of mercury Which has been used. If
11.601 grammes of fused silver nitrate be dissolved in distilled
water, and diluted to the volume of 1 litre, the solution will be
of the required strength, i. e., 1 cubic centimetre will exactly
precipitate 0.010 gramme of chloride of sodium.

Take 30 cubic centimetres of the filtrate from the mixture of
baryta mixture and urine, and, having added a drop of nitric
acid, pour in from a burette, or from a finely divided pipette,
twice, as many cubic centimetres of the nitrate of silver solu-
tion as the number of cubic centimetres of nitrate of mercury
solution required in the chlorine determination. A precipitate
of chloride of silver will fall, and the filtrate may now be sub-
jected to analysis for urea.

An example will help to make the course of these operations
clear.

Forty cubic centimetres of the urine of a boy suffering from
typhus fever were mixed with 20 cubic centimetres of baryta
mixture, and the fluid was filtered. 15 cubic centimetres of the
filtrate was placed in a beaker, and the standard solution of
mercury for chlorine was added, until a permanent and dense
cloud had formed. The number of cubic centimetres added
was 4.5. As each cubic centimetre of the standard solution
corresponds to 0.010 gramme of CI calculated as NaCl, the
quantity in 10 cubic centimetres amounted to 0.045 gramme.
30 cubic centimetres of the filtrate from the baryta mixture
and urine were now taken and treated with 4.5 X 2, i. e., 9 cubic
centimetres of nitrate of silver solution. The fluid was filtered.
Now 39 cubic centimetres of the mixture of urine, baryta so-

550 THE SECRETIONS.

lution, and silver nitrate solution, contained 20 cubic centi-
metres of urine. On, therefore, taking :y or 19.5 cubic centi-
metres of the filtrate, after the precipitation of the chloride of
silver, we obtained a quantity of fluid which contained all the
urea present in 10 cubic centimetres of the original urine.

It may be well to state that when, as in many cases of acute
disease, the amount of chlorine present is very small, nearly
accurate results are obtained, if no correction for chlorine be
introduced.

Other corrections must be introduced into Liebig's method
under peculiar circumstances : these will be stated dogmati-
cally, the student being referred to larger books for their ex-
planation.

1st. "When, in determining the amount of urea in 15 cubic
centimetres of mixture of urine and baryta solution, the num-
ber of cubic centimetres of mercury solution added exceeds 30,
we must repeat the operation, adding to 15 cubic centimetres
of the fluid a quantity of distilled water equal to the difference
between 30 and the number required in the first operation.

2d. When the amount of solution of nitrate of mercury
added to 15 cubic centimetres of the filtrate from the mixture
of urine and baryta mixture, is less than 30 cubic centimetres,
0.1 cubic centimetre must be subtracted from the amount of
mercury solution required, for every 5 cubic centimetres less
than 30 cubic centimetres.

This correction is of little importance.

II. Davy's method for the determination of Urea.

This excellent method is based upon the fact already men-
tioned, that when a solution of urea (CH4'Nv,0), such as urine,
is treated with a solution of hypochlorite, it splits up into car-
bonic acid, water, and nitrogen gas. If the mixture be effected
in a long graduated tube, and this be inverted and placed over
mercury, the whole of the N accumulates on the surface of the
fluid, the carbonic acid being absorbed by the solution of \\y-
pochlorite used. From the volume of X evolved the quantity
of urea present may be calculated. (For details of this method
the reader is referred to a Treatise on the Pathology of the
Urine, by Dr. Thudichum, London: Churchill, 1858.)

Davy's process is, like Liebig's, not absolutely correct. Uric
acid, and other nitrogenous substances present in urine, are de-
composed by hypochlorites ; as their quantity is, however, com-
paratively very small, the error introduced is not large. The
writer can vouch, from personal observations, of the great accu-
racy of this method when applied to solutions of pure urea, and
believes that, if carried out with the apparatus devised by Dr.
Hiifner for the determination of urea by solutions of alkaline
hypobromites, it would prove the most useful and reliable
method for the determination of urea.

BY DR. LAUDER BRUNTON. 551

* 196. Determination of the Amount of Uric Acid
in Urine. — Uric acid is usually determined by precipitation
with dilute nitric or hydrochloric acid, the crystalline precipi-
tate being washed, dried, and weighed.

Take 200 c. c. of the urine and add to it 5 c. c. of dilute hy-
drochloric acid of density 1.11. Set aside in a cellar for 24
hours. Collect the uric acid on a weighed filter, and wash
thoroughly with distilled water. Dry the filter and uric acid
in a water oven at a temperature of 100° C. Allow the dried
filter to cool under an exsiccator (in watch glasses, etc.) and
weigh. The weight of the filter and uric acid, minus the weight
of the filter paper, gives the amount of uric acid precipitated.
To this must, however, be added the quantity of uric acid
which has been held in solution by the urine and hydrochloric
acid, and by the washings of the filter. The whole of these
fluids are therefore mixed and measured, and for every 100 c. c.
0.0038 grammes of uric acid must be calculated (Neubauer).
The number thus calculated, added to that of the uric acid col-
lected on a filter, gives the amount of uric acid contained in
the urine. The number is, however, only an approximation to
the truth.1

**197. Determination of the Amount of Phosphoric
Acid contained in Urine. — The phosphoric acid contained
in urine exists partly in a state of combination with the alka-
line earths, magnesia, and lime, but chiefly in combination with
alkalies. If we render the urine alkaline by the addition of am-
monia, the former are precipitated, leaving the alkaline phos-
phates in solution. It is customary to state the amount of
phosphoric anhydride corresponding to phosphoric acid in the
urine. In determining the quantity of phosphoric acid in urine,
we may merely determine the total quantity existing in the
fluid, or we may determine the total quantity first, and then
the quantity which remains after the precipitation of the earthy
phosphates.

The volumetric method for the determination of phosphoric
acid in urine is based upon the following reactions: —

(a) When a solution of a phosphate acidulated with acetic
acid is treated with a solution of nitrate or acetate of uranium,
a precipitate falls which is composed of uranium phosphate.

(6) When a soluble salt of uranium is added to a solution of
potassium ferrocyanide, a reddish-brown precipitate or color is
developed.

Preparation of Standard Solutions of Uranium, etc. — Before
preparing this solution, it is advisable to make a standard solu-

1 The reader is referred to the recent researches of Dr. Salkowsky, in
Virchow's Archiv. Bd. 52, and of Maly, Pfluger's Archiv. 1872, vol. vi.
p. 201.

552 THE SECRETIONS.

tion of a phosphate. For this purpose, 10.085 grammes of well
crystallized sodium phosphate (XaHI'O, 4- 1211,0) are dis-
solved in distilled water, and the solution diluted to one litre.
Fifty cubic centimetres contain 0.1 gramme of P,Os.

Then 100 grammes of sodium acetate are dissolved in 900 c.c,
of distilled water, and 100 c.c, of acetic acid added.

The solution of uranium acetate is made b}T dissolving com-
mercial uranic oxide in acetic acid, diluting and filtering; or,
instead, a solution of uranium nitrate may be made hy dissolv-
ing the crystallized salt in water, and diluting. The solutions
are intended to contain 20.3 grammes of uranic oxide in one
litre of solution.

Having obtained the solution of uranium acetate or nitrate,
its strength is determined in the following manner: 50 c.c. of
the standard solution of sodium phosphate are placed in a
beaker, and 5 c. c, of the acid solution of sodium acetate added.
The uranium solution is poured from an accuratel}7 graduated
burette, until precipitation ceases. Then a few drops of a
solution of potassium ferrocyanide are placed on a porcelain
slab, and after each addition of uranium solution to the phos-
phate, a drop of the mixture is taken up by means of a glass
rod and brought in contact with the ferrocyanide. As soon as
an excess of uranium solution has been added, the character-
istic reddish-brown color of uranium ferrocyanide is observed.

It is convenient to graduate the solution of uranium so that
20 cubic centimetres shall be exactly equal to 50 c. c. of the
standard solution of phosphate of soda, i.e., to 0.1 gramme of

PA-

In analyzing urine by means of solutions of uranium, it is
convenient to operate on 50 c. c. This quantity of urine is
treated with the acetate of sodium solution and heated on the
water-bath to a temperature approaching 100° C. ; it is then
treated with the solution of uranium as previously described.

198. Determination of the Quantity of Sulphuric
Acid in Urine. — The quantity of sulphuric acid in urine is
best determined by precipitating with chloride of barium and
weighing the dried and burned precipitate of barium sulphate ;
from this the amount of sulphuric acid can be calculated. It
is usual to state the amount of sulphuric anhydride (S03) cor-
responding to the sulphuric acid existing in the urine.

For details as to the precaution to be used in determining
the amount of sulphuric acid by precipitation, the student is
referred to Fresenius's Quantitative Analysis. The manipula-
tions involved in such an analysis, however simple it may be,
can only be learned in a laboratoiy devoted to pure chemistry.

It has been suggested that the sulphuric acid in urine should
be determined by means of a standard solution of chloride of
barium ; the method is one, however, which is tedious, and

BY DR. LAUDER BRUNTON. 553

which cannot be recommended, even on the score of rapidity,
as preferable to the one first described.

** 199. Detection of Su^ar in Urine.— It is still a mat-
ter of doubt whether the urine in health contains sugar; the
processes which have been suggested, for the separation of this
substance, by those who maintain its constant occurrence in
healthy urine, are, however, complicated ; and, as they have led
to veiy various results in the hands of different observers,
their consideration would be out of place in this book. (See
Pfliiger's Archiv. fur Physiol. V. pp. 359 and 375.)

When present in abnormal quantities in urine, as in diabetes,
glucose ma}' be very readily detected. The following experi-
ments will be sufficient to make the student acquainted with
the more common reactions.

Experiment 1. Take 5 cubic centimetres of diabetic urine, or
of a solution of grape-sugar, and add to it two or three drops
of a solution of copper sulphate, so that a very slight green
tinge is perceptible ; then add to the fluid a solution of caustic
soda, or potash, until the precipitate of hydrate copper oxide,
at first formed, is redissolved.

The fluid, which has assumed a blue tint, is now boiled, when
an abundant precipitate of cuprous oxide falls ; before this has
separated, the fluid in which the precipitation is effected be-
comes opaque, and presents a reddish-yellow color. This is
known as Trommer's test (.see § "IT and § 12).

2. To five cubic centimetres of urine add nearly an equal
volume of a solution of caustic soda, or potash, and boil. The
fluid will assume at first a light-yellow, then an amber, and
lastly a dark-brown coloration. Tins is known as More's test.

3. Some diabetic urine is mixed with a little brewer's yeast,
and the mixture is poured into a test-tube half full of mercury ;
the orifice of the tube is closed with the thumb, and the tube
is inverted into a capsule containing mercury.

After a period of twent}T-four hours, at ordinary tempera-
tures, the test-tube will be found to contain large quantities of
carbonic acid gas, which can be readily absorbed by passing
up into the tube a fragment of caustic potash.

In addition to these tests, the student may with advantage
determine, by means of a polariscope, that diabetic urine pos-
sesses the property of rotating the plane of polarized light to
the right.

** 200. Determination of the Quantity of Sugar in
Urine. — Tins may be best effected b}r one of the two follow-
ing methods : firstly, by determining to what extent a known
depth of the saccharine fluid rotates the plane of polarized
light to the right; or, secondly, by determining the quantity
of urine which has to be boiled with a standard solution of

554 THE SECRETIONS.

a cupric salt, in order to reduce the whole of the copper to
the condition of red cuprous oxide.

In order to determine the quantity of sugar by the last
method, which is known as that of Fehling, we require to
prepare a standard solution in the following manner : 34.65
grammes of pure and well crystallized copper sulphate are
dissolved in about 1G0 cubic centimetres of water, and 173
grammes of Rochelle salts (tartrate of potash and soda) are
dissolved in about (iOO cubic centimetres of solution of caustic
soda, having a specific gravity of 1120. The solution of sul-
phate of copper is added gradually to the alkaline solution of
Rochelle salts, the fluid being continually stirred. A deep
blue solution is thus obtained, which is diluted with distilled
water to the volume of one litre. Ten cubic centimetres of
this solution are reduced by 0.05 gramme of diabetic sugar.

The following is the process which has to be followed in
determining the quantity of sugar in urine: —

The urine to be examined is diluted to a known extent;
thus in the case of a diabetic urine, having a specific gravity
of 1040, 100 cubic centimetres are diluted with distilled water
to the volume of 1000 cubic centimetres.

Ten cubic centimetres of the standard copper solution are
then accurate^ measured out and poured into a porcelain
capsule. Forty cubic centimetres of distilled water are added,
and the solution in the capsule boiled.

The previously diluted urine is then allowed to flow in from
a burette ; after a few cubic centimetres have been added, the
fluid in the capsule is briskly boiled, and then the application
of heat discontinued for a few seconds.

The solution, which, after the saccharine fluid has been
boiled with it, assumes a red color, deposits a red sediment of
cuprous oxide, whilst the supernatant fluid retains a more or
less blue color, in consequence of a portion of the copper
remaining in solution.

Successive portions of the diluted urine are then added, and
the fluid boiled after each addition. As the operation proceeds,
the addition of the diluted urine is performed with great care,
only a few drops being poured in at a time. A point is at last
reached when the bottom of the capsule is coated with a de-
posit of red cuprous oxide, and when, on tilting the capsule
so as to bring the fluid, which it contains, over the clean white
sides, no tint of blue is perceived.

The number of cubic centimetres of sugar solution added is
then read off and marked. It is advisable, however, to pur-
sue the operation one step further. A few more drops of
diluted urine are added to the contents of the basin, which
are again boiled, and if necessary, the addition is repeated
until the boiled fluid becomes faintly opaque and of a yellowish

BY DR. LAUDER BRUNTON. 555

color. These appearances prove that a slight excess of sugar
solution has been added. The number of cubic centimetres of
diluted urine added is again read off. If the arithmetic mean
of the first and second results be now taken, a number will be
obtained which represents, very accurately, the volume of the
dilute urine, in cubic centimetres, which was capable of re-
ducing the whole of the copper in ten cubic centimetres of
the standard solution employed. Now, as this volume of
copper solution is reducible by exactly 0.05 gramme of dia-
betic sugar, this quantity must have been present in the
volume of diluted urine made use of. An example will render
the calculations required intelligible : The urine of a diabetic
patient was found to have a specific gravity of 1035. 100
cubic centimetres were placed in a litre flask, and distilled
water added until the fluid exactly measured 1000 c. c. Ten
cubic centimetres of standard copper solution required 30.49
c. c. of the diluted urine in order to be completely reduced, or
30.49 c. c. of the diluted urine contained 0.05 gramme of sugar.
As the urine had been diluted to ten times its original bulk,
the same volume of the undiluted urine would contain ten
times as much sugar, i. e., 0.5 gramme of sugar. From these
data we can easily ascertain how much sugar was passed in
the twentj'-four hours.

Thus, if the quantity of urine passed in twent3'-four hours,
in the case under consideration, amounted to 3000 cubic
centimetres, the amount of sugar passed during the same
period would be at once found by the following proportion : —

30.49 : 0.5 : : 3000 : x

= 49.19 grammes.

The student, in carrying out the process just described, must
be careful to dilute the urine to a sufficient extent. In cases
where the percentage of sugar is very large, it is, for instance,
convenient to dilute the urine twenty times instead of ten.

** 201. Detection of Albumin in Urine. — Except in
very exceptional cases, which need not be alluded to here, the
only albuminous body proper which appears in urine possesses
the reaction of serum albumin. Accordingly, when albumi-
nous urine is boiled, it is found to be coagulable, i. e., the
albumin separates in the insoluble form, and the coagulated
albumin is insoluble in nitric acid. Nitric acid, when added
alone to urine containing albumin, likewise precipitates that
substance, and the precipitate is not dispelled by heat. It
must be stated, however, that in certain cases, when nitric acid
produces a mere haze, this may disappear on boiling, although
it be really due to a trace of albumin. Albuminous urine
possesses the property of rotating the plane of polarization to
the left.

556 Till: SECRETIONS.

* 202. Determination of the Amount of Albumin in
Urine. — A known volume of the urine, say 50 or 100 cubic
centimetres, is boiled ; if the reaction is alkaline or neutral, a
trace of acetic acid being previously added, the albumin sepa-
rates freely and is collected on a weighed filter. The substance
on the filter is repeatedly washed with boiling water, and
after being allowed to drain, it is dried, first in a water oven at
100° C, and afterwards in an air oven at 120° C. The weight
of the filter and albumin, minus the weight of the filter, fur-
nishes us with the quantity of albumin (with adhering salts)
present in the quantity of urine taken for analysis.

When a large number of determinations of albumin in urine
have to be made, it is advisable to make use of the polariscope.
The extent to which the plane of polarized light is rotated to
the left bears a strict relation to the quantity of albumin present
in a fluid, providing the depth of fluid examined be the same,
and that no other substance (e. g., sugar) be present, exerting
an opposite action on polarized light.

** 203. Detection of Bile-coloring Matter in Urine.
— When a large quantity of bilirubin is present in urine it may
be separated from it by agitating the fluid with chloroform,
decanting, evaporating the chloroform solution, dissolving the
residue in pure chloroform, and allowing the fluid to evaporate
spontaneously. In this way red rhombic prisms of bilirubin
may be obtained.

In all cases where bile-coloring matter is present, we can de-
tect it by the well known reaction with nitric acid (Gmelin's
reaction). If strong nitric acid, containing nitrous acid, be
added to a thin stratum of urine containing bile, in a flat por-
celain dish, a succession of beautiful tints is perceived. The
fluid is seen at first to be green, then blue and violet ; it then
assumes a rather dirty claret, and ultimately a dirty yellow
color (.see § 135).

In cases where a very satisfactory search for traces of bili-
rubin is to be made, it is advisable to separate it from the urine,
by means of chloroform, and then to test the evaporated residue
with nitric acid. A property which is very characteristic of
urine or other animal fluids colored by bile pigment, is that of
staining, of a yellow color, linen which is moistened with it.

** 204. Separation and Detection of Bile Acids in
Urine. — Four or five hundred cubic centimetres of urine
are treated with acetate of lead until a precipitate ceases to fall,
and then solution of ammonia is added. The precipitate is
collected on a filter, washed with water, and allowed to drain.
The filter paper, with the very bulky precipitate which it con-
tains, is then boiled in a flask, with alcohol, and the solution is
filtered whilst hot. A few drops of solution of sodium carbo-
nate being added, the fluid is evaporated to dryness on the

BY DR. LAUDER BRUNTON. 557

water-bath. The residue is boiled with absolute alcohol, and
the solution is concentrated to a small volume. On adding an
excess of ether to the alcohol, a precipitate occurs which con-
sists of the soda salts of the bile acids, and which, if set aside
for some time, often crystallizes.

This precipitate may be obtained by decanting from it the
supernatant mixture of alcohol and ether. It is soluble in
water ; a few drops of the aqueous solution ma}' be evaporated
to dryness in a porcelain capsule and then subjected to Petten-
kofer's test. This consists in adding a few drops of pure sul-
phuric acid, and then a trace of solution of cane sugar to it,
and heating very gently. After some time, an exceedingly
beautiful purple-violet coloration is developed.

Bile acids may be detected in the urine without previous
separation b}- employing Strasburg's method (see §140), but
Hoppe-Seyler's method just described is much more reliable.

205. Detection of Blood in Urine. — Urine which con-
tains blood, on being allowed to stand, usually furnishes a de-
posit in which characteristic blood corpuscles may be discovered
without difficult}'.

On examiningsuch urine by means of the spectroscope, there
is usualty no difficulty in observing the spectrum of haemoglo-
bin or of hsematin.

Urine which contains haemoglobin furnishes, when boiled, a
precipitate of albumin and haematin.1

1 Although it has been considered adivisable to devote some space to
the mode of detecting a few of the more important abnormal constituents
of urine, it would be beyond the object of this book to give a complete
account of the properties of, and mode of separating, all the substances
which occur in urine in a state of disease. Any additional information
on these subjects is to be found in the very valuable " Handbuch der
physiologisch- und pathologisch-Chemischen Analjrsen of Professor
Hoppe-Seyler, to which reference has been already made.

APPENDIX.

CHAPTER XXXIX.

PRACTICAL NOTES ON MANIPULATION.

208. Manipulation of Glass Tubing. — Most laboratories contain
a glass-blower's table ; in its absence the mouth gas blowpipe must be
used. The difficulty of keeping up a continuous blast of air with this
instrument can be readily overcome by practice, provided that the orifice
is not too wide. The blowpipe flame (fig. 325) consists of two parts, an
inner blue cone («) which is the deoxidizing or reducing flame, and an
outer envelope (5) which surrounds it. The hottest part of the flame
is a very little in front of the tip of the blue cone. The reducing flame
is so called because the unburnt gasses present in it have at that high
temperature a great tendency to take oxygen from any substance con-
taining it. In the outer envelope, on the contrary, the supply of oxy-
gen is abundant ; it is therefore called the oxidizing flame. Ordinary
English glass tubing contains oxide of lead : when it is heated in the
reducing flame, black stains of metallic lead form on its surface. To
avoid this, it should always be heated in the extremity of the outer flame.
German glass is free from lead, and much less fusible than English glass,
and is generally preferable to it. Tubes of German glass may be dis-
tinguished from English by looking through them lengthwise ; the for-
mer has a greenish color, while the latter looks dark. In drawing out
a glass tube so as to form a pipette (see fig. 326), care must be taken to
soften the part to be drawn completely and equally, and to remove it
from the flame before extending it. If this precaution is neglected, the
drawn-out part will collapse and close. When heating a tube for the
purpose of bending, it is important to use as low a temperature as is
sufficient to soften it, and not to begin to bend until a considerable ex-
tent of the part to be bent is equally softened. For this reason, it is best
to use a large flame (that from a gas jet being preferable to a Bunsen's
lamp or blowpipe), in which the tube must be moved up and down
until the object is attained. Before bending, it must of course be re-
moved from the flame. In bending a thin tube, especially, if it be
heated too strongly, it is difficult to avoid its becoming wrinkled at the
bend. To avoid this, it is a good plan to close one end air-tight
and blow in gently at the other during flexion. Large tubes are bent
more easily by filling them with clean dry sand and heating them over
incandescent charcoal, supported on wire netting. To seal a tube, it
must be thoroughly softened at a short distance from its end, and drawn
out quickly to a thread. The capillary part of a tube already drawn out
is sealed instantaneously by directing the point of a small blowpipe
flame upon it and extending the heated part (fig. 327). To close a tube
at its end, another piece of the same kind of glass must be joined to it

5G0 APPENDIX.

by fusing the ends of both in the same flame. As soon as the joining
has cooled slightly, the tube to be closed is heated again at a short dis-
tance from its end, and drawn out as before

Annealing. — After glass has been strongly heated it must be allowed
to cool as gradually as possible, in order to anneal it.

Manipulation of Corks. — To fit properly, a cork must be somewhat
larger than the opening it is intended to fill. Before pushing it in, it
should always be reduced by compression, either with a cork squeeze!
or, in its absence, by rolling it on the floor (protected by a covering of
paper) under the foot. For shaping corks, a shoemaker's knife which
has been sharpened on a rough stone answers best. Any knife with a
keen edge will do. To perforate a cork, a piece of brass tubing, the
edge of one end of which is sharpened, is used. It is best to work the
borer from the opposite ends, the two bore-holes meeting in the middle.
As the holes always require finishing with a rat's tail file, a borer
smaller than the intended channel should be used.

207. Solution and Ebullition. — The different solubility of various
organic substances in reagents, such as water, ether, alcohol, acids,
alkalies, and saline solutions, not only serves as a means of separating
them from each other, but in many instances, as in the case of albumi-
nous bodies, furnishes a characteristic by which one substance may be
distinguished from others nearly allied to it. Tests are also more gene-
rally and conveniently applied to solutions than to bodies themselves.
Solution takes place more readily when the body to be dissolved is finely
divided. Dry and hard substances are therefore generally pulverized by
pounding and rubbing in a Wedgewood mortar. If too large to be con-
veniently triturated at once, they may be previously broken in an iron
mortar, or by wrapping them loosely in brown paper and pounding
them with a hammer. If the substance is constantly shaken or stirred
about so as to bring it continually into contact with fresh portions of the
solvent, it will dissolve much more quickly than if allowed to remain
at rest.

For preparing Solutions. — A beaker is for most purposes the most
convenient vessel, as its contents can be stirred at the same time that it
is subjected to heat, which always accelerates solution. To avoid risk
of fracture, the beaker must not be heated over a naked flame, but must
be placed on a piece of wire gauze or sand bath (fig. 328), supported on
a tripod. Flasks may be employed instead of beakers for solution or
boiling when stirring is not required. They have the advantage of
preventing loss of fluid during the process of ebullition, as any particles
which spurt up are caught against the sides of the flask, especially if
it is placed in an inclined position, instead of falling outside as in a
beaker.

To prevent Loss by Evaporation. — Various methods may be used. One
of these consists in placing a small funnel in the mouth of the flask ;
the fluid condenses in the funnel and runs back into the fiask. Another
method is to close the neck of the flask with a cork, through which a
wide glass tube, drawn out to a capillary opening at its upper end, is
passed. A considerable part of the vapor passing from the boiling liquid
is condensed in the tube and falls back into the flask. If the boiling
is long continued, the tube gets very hot and a great deal of vapor
escapes. To avoid this, the escape tube is prolonged and surrounded
by a Liebig's condenser, for which purpose it must be bent at an angle
of about 120u, as seen in fig. 329.

To exhaust a substance with ether, the ether and the substance should
be placed in one flask, with which a second is connected by a bent glass
tube which passes through the cork of both. The tube, which scarcely
projects beyond the under surface of the cork in the first flask, reaches

BY DR. LAUDER BRUNTON. 561

to the bottom of the second. The first flask being then placed in a
beaker of warm water and the second in cold, the ether distils over
from the former into the latter and is condensed. When a large quan-
tity of the ether has passed over, the flasks are transposed, when the
whole of the ether rushes back into the first flask. The process may be
repeated indefinitely.

In connection with this subject, an arrangement may be described
which is chiefly used for washing precipitates. It is also applicable for
the purpose of replacing loss by evaporation when liquids are boiled, or
to keep the water at a constant level in a water-bath. (See fig. 331.)
It consists of a large flask, a, fitted with a cork, through which pass
two tubes. One of these, b, c, is straight and open at both ends ; the
other, d, e, g, f, is bent so as to form a syphon, the limbs of which are
of equal length. Both ends of d, e, g, /, are at a somewhat lower level
than the lower end of b, c. The end is placed in the funnel or water-
bath at such a height that the level of the lower end of b, c, coincides
with that at which it is desired that the surface of the fluid shall remain.
The effective difference in the limbs of the syphon is the space between
c and d. Whenever the surface of the liquid in the funnel or bath is on
a level with c, the tube d, e, g, /, ceases to act as a syphon ; but as soon
as it falls, d, f, again acts, and liquid runs into the funnel till the surface
is again level with c.

208. Evaporation. — Evaporation of watery liquids is usually con-
ducted in shallow basins of Berlin porcelain, heated either directly in a
sand-bath or over a water-bath. An ordinary saucepan answers per-
fectly as a water-bath. (See fig. 330.) If the naked flame is used, it
ought not to be allowed actually to touch the bottom of the basin. The
process is greatly accelerated by constant stirring.

If it is important that none of the substance be lost, the liquid must
not be heated to boiling, as it is then apt to spirt over the sides. In
evaporating a solution to dryness, its surface often becomes covered
towards the end of the process with a pellicle, which hinders the vapor
below from escaping easily, and thus both retards evaporation and
causes the vapor to issue in jets which may occasion loss of material.
The formation of the pellicle is best prevented by stirring the fluid con-
stantly with a glass rod. It may also be prevented by covering the
evaporating basin loosely with another somewhat smaller one, or with
a concave glass with the concavity downwards, but this retards evapo-
ration. Solutions in alcohol, ether, and chloroform must be evaporated
in beakers. Solutions in the two latter menstrua must never be evapo-
rated over a naked flame, but always on a water-bath, as their vapor is
inflammable.

Krciporation at a Constant Medium Temperature. — It is sometimes
desirable to evaporate a liquid at a constant medium temperature, such
as 40° C. This may be done roughly by placing the evaporating basin
in a sand-bath, and carefully regulating the size of the flame by a
thermometer. Unless, however, it is constantly watched, the tempera-
ture is apt to rise or fall too much, and the solution may get spoiled.
This difficulty is avoided by using a water-hath heated by a gas-lamp,
which is connected with a Bunsen's gas-regulator. For this purpose I
find a water-bath of the accompanying form (fig. 331) a convenient
one. It is made of galvanized zinc, is eleven inches in diameter, and
five deep. At one side it bulges out, and in the projecting part thus
formed the thermometer and regulator are placed. The top of the bath
is covered by a zinc plate perforated by several large holes, in which
evaporating basins may be put; or by a series of concentric copper
rings, "no or more of which maybe removed so as to accommodate
evaporating basins of different sizes. The regulator, as modified by
36

562 APPENDIX.

Gcissler (fig. 332), consists of a wide glade tube, a, divided into two
parts, an upper and a lower, by a horizontal septula. In the middle of
the septum is an opening, from which a tube runs down nearly to the

bottom of the lower division. The tube is closed by a perforated cork
or India-rubber stopper. Through this passes a tube, is, with a hori-
zontal limb, e. Inside B is a smaller and shorter tube, C, which has a
very small opening opposite r>. The sides of n and < are luted together
with cement at v. In using this regulator, a quantity of mercury is
poured into a, and of course runs down into the lower division, partly
filling it, and partly compressing the air it contains.

The mouth of a is then closed by the cork, and the tube c connected
by India-rubber tubing with a gas-pipe, and the tube e with a small
gas-burner. The gas passes down the tube c through its lower open
end, up again between it and B, and out at E, and thence to the burner.
The regulator and a thermometer are then immersed in the water-bath,
the gas lighted, and the bath warmed till the thermometer indicates
40° C., or any other desired temperature. The tubes B and c are then
pushed down till the mercury touches the lower end of c and closes it.
The gas is thus prevented from passing onwards to the burner, and the
flame would go out entirely were it not that the small bole in c, oppo-
site D, allows sufficient gas to pass through it to preserve the flame from
being completely extinguished. As soon as the flame' is thus diminished,
the water-bath and the regulator immersed in it begin to cool, and the
mercury, and still more the air in the regulator, conserpiently contracts.
The mercury, therefore, sinks, and leaves the mouth of c open, so that
the gas again passes freely through it. the flame increases, and the tem-
perature of the bath again rises. The mercury and air again expand ;
and as soon as the temperature is reached to which the regulator was
adjusted, the mercury again closes the mouth of c, and cuts off the gas
till the temperature again falls. In this way the temperature may be
kept for months at 40° without varying much more than half a degree.
Unless the mercury is very clean, however, it will adhere slightly to
the lower end of c, and the variations will thus be greater. The water
in the bath must also be kept at a constant level, as otherwise the part
of the regulator heated by it is sometimes greater and sometimes less.
The mercury consequently does not always expand in the same pro-
portion to the rise in the temperature of the water in which it is par-
tially immersed, and variations of several degrees may thus be produced.

209. Precipitation. — Iu precipitating a substance by the addition
of another, the reagent is generally added a little at a time, and mixed
by means of a stirring rod, till a further addition of the reagent, produces
no perceptible increase iu the amount of the precipitate. In order to
ascertain that the precipitation is complete, a little of the liquid is tested
by throwing it on a filter, and the reagent added to the clear filtrate.
If no further precipitate occurs, the precipitation is complete ; but if
one is formed, the filtrate is again mixed with the rest of the fluid and
the process repeated.

210. Washing of Precipitates on Filters. — Precipitates are gene-
rally collected on a filter and washed by directing a stream of water or
alcohol on them by means of a wash-bottle. The filter should never be
filled up to the top, as the upper part of the precipitate cannot then be
properly washed. It is always advisable to let the precipitate settle in
the beaker, and to allow the clear liquid to passs through the filter
before throwing the precipitate itself upon it ; and the whole of the
fluid from which the precipitate has subsided must be allowed to pass
through the filter before the washing is begun. A stream of water is
then directed on the part of the precipitate nearest the edge of the filter,
by which it is gradually washed towards the centre. The stream

BY DR. LAUDER BRUXTOX. 563

should not be too strong, nor should it strike the filter or precipitate
perpendicularly, as it is then apt to scatter the precipitate or tear the
filter. When the filter is nearly full of water, the whole should be
allowed to run through, and the washing again repeated.

Washing of Precipitates by Decantation. — "When a precipitate sub-
sides quickly, it is more readily washed by decantation than on a filter.
Granular and gelatinous precipitates are not easily washed completely
on a filter, and it is better to wash them as well as possible by decanta-
tion, and to finish the operation on a filter. In washing by decantation,
the precipitate is placed in a tall beaker, and stirred well with a quantity
of water, alcohol, or other washing liquid. It is then allowed to sub-
side, and the supernatant liquid carefully poured off or removed by a
syphon (see fig. 333) ; this is repeated till the washing is complete. In
order to prevent any of the precipitate being carried off in the washing
and lost, the liquid used for washing may be collected and passed
through a filter. Any part of the precipitate retained by the filter may
then be washed, and the rest of the precipitate added to it.

211. Filtration. — Filtration is the separation of insoluble substances
from liquids bypassing the latter through a porous material which keeps
the former back. When the substance to be removed is in large pieces,
or when the liquid is thick and viscid, and will not pass easily through
paper, it may be filtered through linen or gauze. The linen may either
be stretched over the mouth of a beaker or placed in a porcelain strainer
in the form of a hollow cone, with numerous perforations near its apex.
The removal of the last portions of the liquid may generally be hastened
by squeezing the linen either with the hand or in a press (fig. 334).
Fine precipitates are usually separated by filters of unglazed porous
paper, made specially for the purpose. To make a filter, take a round
or square piece of paper of the proper size, and fold it twice at right
angles. If a square piece has been used, it must now be cut round.
Open it in the form of a cone, and place it in a funnel. If the funnel is
of proper form (its sides sloping at an angle of 30° to its axis), the filter
will fit it exactly. If it does not, the angle at the apex of the paper cone
must be modified. The filter should always be a little smaller than the
funnel, and never project above its edges. Before pouring in the liquid
to be filtered, the paper must be moistened with distilled water, alcohol,
or ether, according as the liquid is aqueous, alcoholic, or ethereal. If
this is not done, the first portions of the fluid which pass through are
apt to be muddy, but they may be cleared by pouring them back on the
filter and making them pass through a second time. To avoid breaking
the filter at the apex, the liquid should be poured on it so as to fall on
its Bides, which are supported by the funnel, and the stream directed by
a glass rod. The filtrate is generally collected in a beaker; it is well
to let the end of the funnel touch the side of the glass, so that the liquid
may run down it without splashing If the filtrate only is wanted, fil-
tration may be quickened by using a ribbed or plaited filter. To make
this, take a circular piece of filter paper and fold it into quadrants, and
then into half quadrants, making all the folds towards one side. Then
make a fold towards the other side between each two of those already
made.* aiid push the paper into the funnel, pressing the point down into
the neck of the funnel : then pour in the liquid, when it will open com-
pletely. Instead of this, three glass rods, bent at the top so as to hook
on to the edge of the funnel, may be laid inside it at equal distances
from each other. These are useful both in quickening the filtration and
in supporting the bottom of the filter, especially when the funnel is
badly made and its tube i- too wide :it its junction with the cone. When
albuminous liquids are filtered through paper, the pons become very
quickly choked up, and it is therefore better to use a number of small

564 APPENDIX.

filters than one large one ; and when the fluid ceases to pass through
one set of filters, to pour it into fresh ones.

Filtration by liniment ramp. — Filtration may be much accelerated
by filtering the liquid into a partial vacuum. This is done by fixing the
tunnel air-tighl in one neck of a Woulfe's bottle, and exhausting the air
through the other by an ordinary exhausting Byringe. It can. however,
be more conveniently effected by means of a Bunsen's water air-pump
(fig. 335).

The principle oi this instrument is the same as that of SprcngcTs pump,
with this difference, that water is substituted lor mercury. It consists of
a wide air-tight tube, through which water descends in a constant stream
to a depth which (if it is desired to produce a complete vacuum) must
not be less than thirty-two feet. Into the axis of this tube, close to its
upper end, a second tube of much smaller bore projects, the open end
of which looks downwards, i. c, in the direction of the stream. Through
this tube, if it is open, air is constantly drawn ; any closed cavity with
-which it is in air-tight communication is rapidly exhausted. It may
thus he used either as an aspirator or as an air-pump. If, however, the
height of the column of water is less than thirty-two feet, its exhausting
power is limited to the production of a diminished pressure, which is
expressed by the difference between the height of the columnand thirty-
two feet. The usual way of employing it in filtration is to attach the
extraction tube 11 to a piece of bent glass tubing, which passes through
an India-rubber stopper in one neck of a "Woulfe's bottle, in the other
neck of which a funnel is fixed in a similar manner. The air inside the
bottle being exhausted by the air-pump, the fluid is forced rapidly
through the filter by the pressure of the external atmosphere. I find it
more convenient to use a strong bell jar, with a tubular opening at the
top. Into this opening an India-rubber stopper, which is perforated for
the funnel and exhausting tube, is fitted. The beaker in which the fil-
trate is to be received is placed on a ground-glass plate. The ground
edge of the bell jar having been smeared with resin ointment, it is set
on the plate in such a position that the funnel is exacttyover the beaker.
The fluid is then p\>ured into the filter, and the air exhausted from the
bell jar. The pressure of the air would force the liquid through the
filter and tear it away unless it were supported in some way. This is
done by taking a semicircular piece of platinum foil of suitable size. A
snip having been made at the centre of the straight edge, and at right
angles to it, the bit of foil is heated in the blowpipe flame, and allowed
to cool. It can then be smoothed out, bent at the snip, and the edges
brought together so as to overlap each other slightly. The hollow cone
thus formed is next placed in an iron mould with a conical cavity, and
pressed firmly in with a conical plug. The funnel used must be chosen
with sides sloping at the proper angle, and the tube must not be too wide
at the junction with the cone. The platinum foil is placed in the bottom
of the funnel, and pressed with the finger, so as to fit the funnel smoothly.
Instead of platinum foil, fine wire gauze or parchment paper is some-
times used. The filter is then folded and placed with its apex resting in
the platinum, moistened with water, and pressed gently against the sides
of the funnel so as to make it fit tightly to it. and prevent air from get-
ting down into the receiver between them. Milk, albuminous solutions,
and glycerin can be filtered much more readily through porous earthen-
ware than through paper. For this purpose the top of a porous cell,
such as is used for galvanic batteries, is closed by an India-rubber cap
with two openings. One of these is connected by a short glass tube and
strong India-rubber tubing with the pump. Through the other a glass
tube passes nearly to the bottom of the c}Tinder, and is closed at its
upper end by a piece of India-rubber tubing and a strong clip. This

BY DR. LAUDER BRUNTON. 565

serves as a pipette to remove a little of the fluid occasionally from the cell
for the purpose of testing it. The cell is placed in a glass cylinder, little
more than wide enough to admit it, and the fluid to be filtered is poured
into the cylinder until it covers the lower part of the India-rubber cap.
The air being then exhausted from the cell, the fluid filters into it from
the cylinder. Instead of cells, cones of porous earthenware may be used
as filters. A short piece of wide India-rubber tubing is stretched over
the top of a funnel, and into its upper end, which lies flat across the
opening of the funnel, a porous cone is inserted {see fig. 335). In order
to keep liquids hot during the process of filtration, Plantamour's funnel
is used. This is a hollow funnel of copper containing water, which is
kept hot by a flame applied to a projecting part. A better plan is to
use a water-bath with a funnel-shaped opening in it (fig. 336). This
has the advantage that it may be kept at any required temperature with
the aid of a Bunsen's regulator.

212. Dialysis. — Almost all crystalline bodies, with the notable ex-
ception of haemoglobin, pass readily, when in a state of solution, through
animal membranes or through vegetable parchment. The great ma-
jority of non-crystalline bodies, such as albumin, do not pass through at
all, or only with very great difficulty. In this way the diffusible may
be separated from non-diffusible substances. Such a separation is
termed dialysis. Graham, the discoverer of the process, gave to the
diffusible bodies the name crystalloids, to the non-diffusible the name
colloids, as he thought all crystalline bodies diffused and all non-crystal-
lizable did not ; but these names are open to objection since the dis-
covery that hannoglobin will not diffuse, although it forms crystals,
while peptones diffuse, although they do not crystallize. Dialysis is
effected by placing the liquid which is to be dialysed in a cylinder, of
which the bottom consists of vegetable parchment. This cylinder,
called a dialyser, is then placed in a shallow vessel containing distilled
water. The diffusible substances pass through the parchment into the
water, while the non-diffusible remain behind. Two forms of dialyser
are in ordinary use. For dialysing small quantities, bell-shaped glass
jars are used. For quantities of seven or eight ounces or upwards, a
dialyser is employed which consists of two gutta-percha hoops, one of
which is two inches deep, the other only one. The deeper hoop is
Blightly conical, so that the other hoop slips over its smaller end.

Before using this contrivance, both hoops must be washed thoroughly
with distilled water. A piece of vegetable parchment, about three
inches wider than the smaller end of the deep hoop, must then be
steeped for a minute in distilled water and stretched over it. After
applying 'he edges of the parchment carefully to the outside of the
smaller hoop, the larger one is slipped oyer it, so as to fix it tightly.
The dialyser must next lie tested, to ascertain that the parchment is
free from holes. It must be filled to the depth of a quarter of an inch
with distilled water, and placed for a short while on a piece of blotting-
paper. If there are any holes in the parchment, the water will come
through and leave a wet spot on the blotting-paper, in which case either
a fresh piece should be put on or the holes closed up. This may be
done by sticking a piece of vegetable parchment over the holes on the
under surface of the dialyser with white of egg, and then passing a
smooth hot iron over the patches. This done, the dialyser must be,
again tested. After having been ascertained to be perfect, it maybe
tilled ; the Liquid to be dialysed must not cover the bottom to a greater
depth than half an inch. It must then be floated in about five times as
much water as it contains of liquid 'tig. 337), and gently agitated from
time to time.

The bell-shaped dialysers are used in the same way, but the paper is

566 APPENDIX.

fixed over the wide end with a piece of fine cord, and the dialyser,
instead of being floated <>n the water, is suspended so thai the parch-
ment is just below the surface. This is effected by strings which pass
from its neck to a glass rod laid over the mouth of a cylindrical
jar containing the water (fig. 338). Diffusion is prompted by using a
large Burface of parchment, or by frequentlj gently shaking the dialyser.
The process may be further accelerated by heat and by evaporation, for
which purpose the basin containing the dialyser may be advantageously
placed in tlic warm chamber or bath al a temperature of 37 I '.

213. Drying. — Glass vessels, in which substances are to be weighed,
are dried by beat. In the case of flasks and tubes, this may be done by
warming them over the flame of a spirit-lamp, then blowing air through
them "with the bellows. For most purposes the hot-air bath is used — a
copper vessel either cubical or cylindrical in shape, and provided with
a door or movable cover (fig. 339). It is heated by a lamp or burner,
and must be furnished with a thermometer, so fixed as to indicate the
temperature of the air of the chamber. For all purposes which re-
quire a temperature not exceeding 100° C, the hot-air bath must con-
sist of two casings, the space between which is filled with water.

Drying and Cooling over Sulphuric Arid. — When substances, espe-
cially hygroscopic powders, are dried in the air-bath and then allowed
to cool, they take up moisture and gain weight. To prevent this, they
must be allowed to cool under a bell jar, under which is a dish con-
taining sulphuric acid (fig. 340). The acid absorbs moisture with
avidity, and keeps the air under the jar dry. The acid may be placed
in a shallow dish, and the substances to be dried supported over it on a
sheet of perforated zinc, winch rests on the edges of the dish or on a
small tripod. Another method is to put the acid in a beaker, covered
with a ground-glass plate greased at the edges, and to supporl the cru-
cible on a leaden support ; the support is made of a bit of strong leaden
wire by bending one end of it into a circle which lies at the bottom of
the beaker, and the other end into a smaller circle which rises above
the surface of the acid and holds the crucible. To prevent dried hydro-
scopic substances from taking up moisture during weighing, they
should not be placed in an open vessel, but inclosed between two watch-
glasses held together by a spring.

When it is desired to dry substances without the aid of heat, they are
to be placed under the receiver of an air-pump and over sulphuric acid.
as just mentioned.

Precipitates maybe rapidly dried by supporting the funnel containing
them over a very small flame by means of a beaker with the bottom
out. a triangle of iron wire and a piece of wire gauze, arranged as in
fig. 041.

214. Ignition. — Substances are exposed to a red beat in order to dry
them thoroughly, to drive away volatile matters, or to burn off organic
constituents, and allow the fixed inorganic solids to fie determined. A
small quantity of a substance may be ignited on a piece of platinum
foil or in a platinum spoon, larger quantities in porcelain or platinum
crucibles. Platinum vessels should not lie used if the substance to be
ignited contains iodine, bromine, phosphorus, or easily reducible
metals, such as copper, lead. sHver, gold, or tin. Wjien precipitates
collected in a filter are ignited, they must be first carefully dried. The
crucible is then to be placed on a piece of glazed paper, the precipitate
loosened from the filter by rubbing the sides together, and then shaken
gently into the crucible. The tiller is then either (bided and placed in
the crucible, or it is set tire to and held over it by a pair of forceps, so
that the ashes may fall into it. Any ashes or precipitate that has fallen
on the paper having been collected and added to the rest, the crucible

BY DR. LAUDER BRUNTON. 567

is placed in a triangle of platinum wires stretched on a larger one of
iron wire (fig. 342), and heated over a Bnnsen's lamp. The cover
should be laid on the crucible at first to prevent any loss, and the heat
raised very gradually. The cover may be removed during part of the
process to allow freer access of air, but towards the end it should again
be replaced so that the heat within the crucible may become greater.
With the same view, the blowpipe flame may be substituted for that
of the Bunsen's burner. The crucible is then allowed to cool somewhat
on the triangle, but while still warm must be placed over sulphuric
acid, and left there till cold. The weight'of ash left by a good filter is
very inconsiderable ; but it may be ascertained by burning a dozen
filters and dividing the weight of the ash by the number. Filters may
be almost completely deprived of ash by extracting them with dilute
hydrochloric acid, and washing them with water till the acid reaction
completely disappears.

215. Weighing. — The balances most useful in a plrysiological labora-
tory are a fine analytical balance to carry 100 grammes in each pan, and
turn easily with half a milligramme or less, and a large balance to carry
seventy kilogrammes, aud turn with a few grammes. Fine balances
are always protected by glass covers, to prevent the access of dust and
protect the instrument from draughts of air, etc. Inside this, a vessel
containing chloride of calcium is often placed to keep the air dry. The
doors of the case should be only opened when the substance or weights
are to be adjusted, and should be closed while the beam is oscillating.
It is convenient to lay the weights on a sheet of paper on the floor of
the balance, and to mark the weight of each on that part of the paper
where it lies. They must never be touched with the fingers, only with
forceps. It is advisable always to place the weights in the same pan
(the right) of the balance, aud the substance to be weighed in the
other. The placing of heavy weights on a fine balance should be
avoided, even though they may not exceed the weight which the instru-
ment is constructed to carry. Nothing should be placed on the pans or
taken from them while the beam is oscillating. It is not necessary to
wait each time till the index stops moving in order to see whether there
is any difference between the weights in the pans ; for this is ascer-
tained much more axactly by observing whether the index oscillates
farther on one side of the zero mark than ori the other, than by noticing
its position when at rest. After weighing, add together the weights
which are absent from their places on the paper. Note down the weight
"/ <///rv, and cheek it by adding the weights together as they are lifted
from the pan and replaced. No weight should ever be allowed to remain
on the balance after weighing. Substances are generally weighed in
watch-glasses, small crucibles or small flasks. These may be either
weighed separately, and their weight deducted from the total weight, or
they may lie counterpoised. To save the trouble of weighing them each
lime, they may lie carefully weighed once for all, and their weight noted
and marked on them with a diamond, or, if they arc of porcelain, in
ink. When a crucible with its lid is used, it is usual to put correspond-
ing marks on the crucible and its lid, so that the same may be used each
time. Counterpoises may he made in various ways. The most con-
venient is to choose a piece of brass of about the size of the brass weight
which corresponds most closely to the weight of the vessel to be coun-
terpoised, and reduce if by careful filing till the weights are exactly
equal. If only required for temporary use, a pill-box partly filled with
small shot will suffice.

216. Specific Gravity. — The specific gravity of a solid or liquid is
it- weight compared with that of an equal bulk of distilled water.
Water and other liquids, however, shrink when cooled, and expand

568 APPENDIX.

when heated, so that the weight of a given bulk varies with the tempe-
rature. It' a vessel containing, for example, a cubic inch is filled with a

fluid at a moderate temperature and cooled, the liquid will shrink, and
more must be poured in to till up the space. If, on the contrary, it be
wanned, the liquid will run over. The weight of the cubic inch of cold
liquid will be greater than that of the liquid at the original temperature
by the quantity poured in, while that of the hot liquid will be less by
that which has run over. It is therefore absolutely necessary to com-
pare the weights of bodies at the same temperature. Specific gravities
are in this country estimated "at 15 0. or GO- F.

Specific Gravity of Liquids. — The specific gravity of a liquid maybe
ascertained by the use of the specific gravity bottle, the hydrometer, or
specific gravity beads.

The Sjjectfic Gravity Bottle. — This is a small bottle which contains a
known volume of liquid ; one form of bottle (fig. 343) contains its pro-
per quantity when it is filled perfectly full, another form (fig. 344) when
filled up to a mark on the neck, which is long and thin. The bottle hav-
ing been charged with the liquid, of which the specific gravity is to be
determined, the weight of its' contents is determined by the balance, for
which purpose it must first be counterpoised. The quotient obtained by
dividing the weight of the liquid by the weight of the same bulk of
water at the same temperature is its specific gravity. It is difficult to
fill an ordinary bottle completely and to put in the stopper without get-
ting in an air-bubble, which would of course alter the weight of the
contents and so give false results. To obviate this difficulty, the stop-
per of a specific gravity bottle has a hole bored up through its middle,
so that when the bottle is filled and the stopper put in, any air or fluid
that may be present in the neck passes up through the hole, and thus
both the bottle and the hole in the stopper are completely filled with
fluid. Before weighing the empty bottle or making a counterpoise for
it, it must be thoroughly dried. Specific gravity bottles of this kind
are usually constructed to contain from 50 to 100 grammes of distilled
water at 15° C. Counterpoises are always sold with them. Before
using them, the accuracy both of the counterpoise and of the capacity
of the bottle must be tested. For the latter purpose, the bottle must be
filled and then immersed in a beaker containing distilled water at a tem-
perature a few degrees higher than 15° C, and allowed to remain until
a thermometer standing in the water indicates that the required tempe-
rature has been reached. The bottle must then be removed from the
beaker and weighed against the counterpoise, its outside having been
first carefully wiped dry. The weight is that of the distilled water
contained in the bottle at 15° C. In weighing the contents of the bot-
tle when charged with any liquid of which the specific gravity is to be
determined, the same method is to be followed, with the exception that
the bottle must not be completely immersed in the liquid contained in
tin' beaker. If then w indicate the weight of the water and w' that of
the same volume of the other liquid at the same temperature, its specific
gravity =^,'.

Sometimes it is difficult to get a sufficient quantity of liquid to fill the
specific gravity bottle just described. When this is the case, a specific
gravity bottle may be made out of a test-tube, by drawing it out, as in
the accompanying figure (fig. 345), and then flattening the bottom so as
to make it stand by heating it and pressing it against a piece of iron.
A scratch is to be made on the narrow part of the neck, up to which
the bottle is to be filled with water at 15 : C and weighed against a
counterpoise as before. In all other respects the procedure is that which
has been already described.

BY DR. LAUDER BRUNTON. • 569

The Hydrometer. — The hydrometer is an elongated glass bulb which
is weighed at one end so as to make it float upright, and is prolonged at
the other end into a stem, graduated in such a manner that the number
of the division up to which the instrument sinks expresses the specific
gravity of the liquid in which it is placed. As every instrument reads
accurately only at the temperature for which it is constructed, the
liquid must be brought to the proper temperature before the instrument
is used. In using the hydrometer, the liquid must be placed in a cylin-
drical glass vessel, deep enough and wide enough to allow the instru-
ment to float freely in it without coming in contact with the sides or
bottom. The froth, if any, is then to be removed from the surface with
a piece of blotting-paper, and the hydrometer allowed gently to sink
into the liquid. The mark on the scale, which coincides with its sur-
face, indicates the specific gravity. To read this correctly, the eye
must be brought to a level with the surface of the liquid. When this
is the case, the surface presents the form of a meniscus, assuming the
aspect of an ellipse when the eye is either raised or lowered. To insure
accuracy, the reading should be repeated once or twice, the hydrometer
being down in the liquid between each two observations.

Specific Gravity of Solids. — The specific gravity of a solid mass, the
substance of which is insoluble, is ascertained by weighing it first in air
and then in water. The difference between these weights is equal to
the weight of its own bulk of the water which it displaces. The specific
gravity is therefore got by dividing the weight of the solid in air by the
difference between its weight in air and water. The weight of solids
may also be ascertained by immersing them in fluids of known density
till thej'- float. Thus the best way of ascertaining the specific gravity of
the substance of the brain, or any other organ, is to prepare a graduated
series of solutions of common salt of different densities, and to immerse
the solid, first in one, and then in another, till a solution is found in
which it floats indifferently at any height.

217. Volumetrical Analysis. — For volumetrical analyses, measuring
flasks, measuring glasses, pipettes, burettes, and other accessory appa-
ratus are required.

Measuring Flasks. — These flasks, of the form shoAvn in fig. 346, are
used for dissolving substances for the preparation of standard solutions,
etc. They should have tolerably wide mouths, and be furnished with
well-fitting stoppers, so that they may be shaken without risk of loss.
The graduation mark should be just below the middle of the neck.
Flasks are used of capacities varying from 100 centimetres to a litre.
Graduated cylinders, such as that shown in fig. 347, generally called
test-mixers, are used for the same purpose.

l'ipcttes.—h. pipette is a glass tube of the shape shown in fig. 348, and
when tilled up to the mark on the neck it should deliver the exact quan-
tity «)!' fluid which is marked upon it. Some pipettes are graduated so
as to let the exact quantity run out by its own weight ; others, to de-
liver the right amount only when the liquid is blown forcibly out. The
former are to be preferred. Another kind of pipette is graduated along
the greater part of its length, so as to deliver different quantities at will,
but it ,is not so accurate as the others. In using pipettes, the liquid to
lie measured is to be put into a test-glass or small beaker ; the lower
end of the pipette is then immersed in the liquid, which is to be sucked
up till it stands somewhat above the mark on the neck of the pipette.
Tin upper cad of tiie pipette must then be quickly covered with the
moistened tip of tin' forefinger, so as to prevent the liquid from flowing
out. 'lie- mark on the neck is next brought to a level with the eye, and
the tip of the finger gently raised so as to allow the liquid to escape slowly
till it stands opposite the mark. It is then allowed to run out into a clean

570 APPENDIX.

beaker, and the last few drops removed from t lie point of the pipette by
touching it againsl the Bide of the beaker.

Burettes.- -These are used for delivering standard solutions. There
arc several forms of burette, but the most convenient is that of Mohr.
It consists of a graduated tube, to whose lower end an india-rubber tube
is attached, which can be opened and shut by a spring clip (fig. 349), so
that the operator can lei the solution rim out or stop it at will. The bu-
rette is supported in an upright position on a stand made for the purpose
(fig. 852). To prevent dust getting in, a polished marble should be
placed on its upper end. In many cases the spring clip answers well,
but when nitrate of mercury is used it attacks the clip, and bichromate
of potash destroys the India-rubher. For such liquids a burette fur-
nished with a glass stopcock is to be preferred. A burette should he
filled by allowing the liquid to How gently into it while it is held in an
inclined position in the hand till it stands above the zero mark. The in-
strument is then replaced. If any air-bubbles are present, they musl be
allowed to break, or removed by a glass rod. The solution is then al-
lowed to flow out till its level corresponds to the zero mark on the burette.

Eulesfor Reading Burettes and other Graduated Instrument* used in
Volumetrical Analysis. — When liquid is contained in a narrow tube, its
surface is higher at the edges where it touches the ulass than elsewhere ;
and if we examine the curved surface by transmitted light, it seems to
be formed of several zones or bands, the lowest of which is dark (tig.
850). To avoid errors and uncertainty, the under border of the dark
zone is always regarded as indicating the level at which the liquid stand-.
In reading, the eye must of course be exactly level with the surface,
otherwise the reading will be cither too high or too lowr. The under
surface of the liquid is incur easily seen if a card, with its under half
blackened, while its upper half remains white, be held behind the liquid,
so that the division between the black and white parts is about one-eighth
of an inch below its surface. The lower surface of the liquid then seems
to be bounded by a sharp black line (Sutton). Burettes may be read
very easily and with great accuracy by using Erdmann's float (fig. :i"i1 .
This is an elongated glass bulb, 'weighted with mercury at its lower end.
so that it floats upright. Its diameter being a very little less than the
calibre of the burette which contains it, it moves freely, but at the same
time steadily, up and clown. A horizontal mark round its middle is
taken as indicating the height at which the liquid stands, the absolute
height being disregarded.

Litmus Solution. — The solution used in the neutralization of albumi-
nous liquids is prepared by dissolving a little litmus in distilled water,
decanting the liquid from the sediment, and diluting it as required. For
determinations of the strength of acid, the litmus solution is made by
putting 10 grammes of solid litmus into half a litre of distilled water, let-
ting it stand for a few hours in a warm place, decanting the clear fluid,
adding a few drops of dilute nitric acid so as to produce a violet color,
and preserving it in an open bottle with a narrow neck. If the color
should at any time partially disappear, it may be restored by exposing the
liquid to the air in an open bottle (Sutton).

Volumetric Solution of Soda. — Fill a burette with solution of soda,
and cautiously drop thisinto 0.3 grammes of purified oxalicacid in crys-
tals, quite dry but not effloresced, dissolved in about 70 c. c. of distilled
Water, until the acid is exactly neutralized, as indicated by litmus. Note
the number of grain measures (n) of soda solution used, and having
then introduced 900 c. c. of it into a graduated jar, augment this quantity

900x140
by the addition of water until it becomes cc If, for example,

n

?i=93, the 900 cub. cent, should be augmented to ! * =907.7

Jo

BY DR. LAUDER BRUNTON. 571

cub. cent. 100 cub. cent, contain ^th of an equivalent in grammes (4
grammes) of hydrate of soda, and will neutralize ^th of an equivalent
in grammes of an acid.

Soda solution for estimating the acidity of gastric juice is made by di-
luting 100 c. c. of the above solution to the bulk of a litre.

218. Polariscope. — There are several organic substances Avhose
solutions possess the power of circumpolarization, i. e., of rotating to one
side or another the plane of polarization of a ray of polarized light passing
through them. Some of them, such as glucose, cane sugar, and tartaric
acid, turn it to the right hand, while others, such as albumin, uncrystal-
lizable sugar, and oil of turpentine, turn it to the left. As the amount of
rotation increases in proportion to the concentration of the solution and
the thickness of the stratum through which the ray passes, if is easy to
ascertain the quantity of a substance held in solution by simply observing
the extent to which a ray is rotated in passing through a stratum of a de-
finite thickness. The apparatus used for this purpose is shown in fig. 353.
It consists of a stand in which are placed two Xieol's prisms, a and b.
The prism b is fixed, but that at a is movable, and the extent to which
it is rotated is indicated on a graduated circular disk s s by an index z.
When the two prisms are placed exactly in the same position, the ray,
which has been polarized by b passes readily through «, and the field of
vision of an observer, looking into the instrument at «, is illuminated.
As a is turned round on its axis, the field becomes dimmer and dimmer
till the two prisms are turned crosswise to each other, when the polar-
ized ray by b is entirely stopped by a, and the field consequently be-
comes quite dark. At this time the index stands at zero. If a glass
tube, containing a solution of sugar or albumin, is then placed in the
space oo, the polarized ray will pass through it, and in doing so will
have its plane of polarization more or less rotated, so that it will no
longer be entirely stopped by the prism a. In order, therefore, to stop
it again and produce a dark field, this prism must be rotated to a corre-
sponding degree, and the extent of rotation is read off on the graduated
disk. As it is difficult to determine exactly the position of a, at which
the field is darkest, some additions have been made to this instrument
by Boleil and Ventzke, which make their saccharimeter more complica-
ted, but greatly increase its exactitude. The first of these is a plate of
quartz, q, composed of two pieces, whose line of junction is exactly in
the middle of the field of vision. One piece rotates light to the right
hand, while the other turns it to the left. When a solution of sugar
is placed in the space o o, it increases the action of that half of the plate
which rotates to the right, and lessens the action of the other halfwhich
rotates to the left, and the two halves of the field of vision become of a
different color. This difference can be removed by turning the prism
a. but this is more easily effected by means of the compensator /'. The
chief parts of tins are figured separately. It consists of two equal
prisms (rand r') of left -handed quartz, whose surfaces (c and c') are
ent perpendicularly to the optic axis of the crystal. Taken together
they form a plate bounded by parallel surfaces, and they can be made
to slide on one another by means of a rack and pinion, », so as to in-
crease or diminish its thickness at will. One of the frames in which
these is fixed has a Male, /. ami the other a vernier, n. When the zero
of this corresponds to the zero on the scale, the left-handed rotation of
the two prisms is compensated by a plate of right-handed quartz, ]'. and
the field then appea rs of an uniform color, but as soon as the prions are

moved this compensation ceases, and the two halves become differently
colored. The Name effecl is produced by putting a solution of sugar

into o o. The screw '' i-i then turned fill the effect of tin- sugar is counter-
balanced and the amount of rotation read off on the scale. At this end,

K79

APPENDIX.

a, is a telescopic adjustment, to enable the division between the two
halves of the quartz to be clearly seen.

In using this instrument, the end h should be placed opposite the
brightest part of a lamp Mame, and it is advisable to cover the flame
with an earthenware cylinder having an aperture which just admits
the end of the saceharimeter, so as to shut off all light excepl that which
passes through the instrument. The zero of the- vernier having been
placed opposite! that of the scale, the operator looks into the end <(, and
adjusts the telescope till the dark line in the centre of the field is clearly
defined. If the two sides of the field are of exactly the same tint, he
may proceed with the operation, but if they are not, he must adjust
them by means of a screw and key, which are not represented in the
engraving. The tube is then to be filled with the fluid to lie examined,
and its end closed by a piece of glass and a metal cap, which should
not be screwed too tightly. The fluid must be transparent, and as
colorless as possible. A light yellow color does not interfere with the
accuracy of the determination, but a red or brown color impairs it
seriously. Three tubes, 1, 2, and h a decimetre in length, are generally
supplied with each instrument, and the longer the tube used, the more
exact is the determination. Dark fluids may be examined in the
shorter tubes, but if very dark they should be diluted before examina-
tion. The tube is then placed in the space o o, and the rack r is turned
till the two halves of the field present exactly the same tint. By turn-
ing the prism a, different colors of the field may be obtained ; a pale
rose color is that in which differences of the two halves can be most
readily observed. The distance to which the zero of the vernier has
been moved from that of the scale to one or other side, indicates the
amount of dextro- or loevo-rotation. The compensator is so graduated
that each degree of the scale corresponds to one gramme of sugar or
albumin in 130 cub. cent, of fluid when a tube one decimetre long is
used. When tubes of a different length are employed, the number of
degrees must be divided by the length of the tube in order to find out
the strength of the solution. As sugar and albumin rotate the rays in
a different direction, their amount cannot be determined when both are
present in a solution, the instrument then indicating merely the differ-
ence between their rotating power. In such a case the albumin must
be removed and the amount of sugar determined. The difference
between the rotation caused by the sugar alone and the sugar and
albumin together, will then of course give the rotation due to albumin.
This instrument may also be used for distinguishing between substances,
such as albuminous bodies, which nearly resemble each other in their
general characters and reactions, but have different powers of rotation
or specific rotation. The specific rotation of a substance is the extent
to which a solution of one gramme in one cubic centimetre, contained
in a tube one decimetre long, will rotate a ray of light passing through
it. To indicate rotation of light to the right, a -f- is prefixed to the
number of degrees through which the beam is turned, and a — to indi-
cate rotation to the left. The specific rotation of sugar is + 56° ; that
of albumin — 5G°. To find out the specific rotation of any substance
with the saceharimeter, the following formula is used (Hoppe-
Seylerj : —

•^ pi

( a j is the usual symbol for the specific rotation for yellow light, a is
the rotation indicated on the scale, p the weight of the substance in
grammes contained in 100 cub. cent, of the solution, and I the length

BY DR. LAUDER BRUNTOX. 573

of the tube employed. The specific rotation of different albuminous
bodies for yellow light, as given by Hoppe-Seyler for serum albumin,
is — 56°, and for egg albumin — 35°. 5. The conversion of serum albumin
into acid albumin by phosphoric or acetic acid increases its specific
rotation to — 71°, and a solution in hydrochloric acid has a rotation
of — 78°. 7. Serum albumin, treated with caustic potash, has a rotation
of— 86°; egg albumin, — 47°; and coagulated egg albumin, treated in
the same way, — 58°. 8, for yellow light.

574 LIST OF INSTRUMENTS, ETC.

The Instruments and Apparatus referred to in
this Work may be obtained from Jas.W. Queen
& Co., Opticians, 924 Chestnut St., Philad'a.

I. HISTOLOGY,

Microscopes.— "Continental" Models of various makes; English and
American Models, including Bausch & Lomb, Queen's Acme,
Crouch, Zentmayer, Beck, or any other spe'cial make preferred.

Warm Stages, Injecting Apparatus, Syringes and Oanulse,
Fine Scissors and Forceps, Spring Clips, etc.

Hatching Oven.

Soluble Prussian Blue.

Gelatin, plain, and prepared for Injecting.

Chemicals.

II. PHYSIOLOGY OF THE CIRCULATION AND RESPIRATION.

Gas Pumps.— Made by Alvergniat et Freres, Dr. Geissler, and Cam-
bridge Scientific Instrument Co.

Sprengel's Pump, Frankland and Macleod's Apparatus,
Recipients and other Apparatus for Analysis of Blood Gases.
— Manufactured by Dr. Geissler.

Kymograph, Arterial Schema, Cardiograph, Marey's Tym-
pana and Levers, Recording Stethometer, Czermak's
Rabbit Support, Manometer, and Support for Coats'
Apparatus, Delicate Thermometers, Aneurism Nee-
dles, Blunt Hooks, Clips, Screw Clamps, and other
Instruments. — Made by C. Verdin, Cambridge Scientific Instru-
ment Co., and Hawksley.

Bernard's Holder. — Manufactured by Cambridge Scientific Instru-
ment Co.

LIST OF INSTRUMENTS, ETC. 575

Pick's Spring Kymograph.— Made by Verdin, and Cambridge

Scientific Instrument Co.
Sphygmograph. — Made by C. Verdin.
Bunsen's Compressed Air Water-Pump. — See De Saga and Dr.

Geissler.
Calorimeter.— Salleron.

III. PHYSIOLOGY OF THE NERVOUS SYSTEM.

Galvanometers and Shunts, Du Bois Reymond's Induction
Apparatus, Rheochord, Commutator, Wippe, and
other Electrical Apparatus. — Manufactured by Elliott Bros., J.
Carpentier, Hartmann & Co., and M. Th. Edelmann.

Moist Chamber, Marking Key, Marey's Myograph. — Made
by Cambridge Scientific Instrument Co., Hawksley, Verdin, etc.

Batteries. — Jas. W. Queen & Co.

IV. DIGESTION AND SECRETION.

Gastric and other Canulse. — Made by Cambridge Scientific Instru-
ment Co., Verdin, and Hawksley.

Bunsen's Regulator.— Jas. W. Queen & Co.

"Water-Baths for Digestion. — Jas. W. Queen S- Co.

Beakers, Test-Tubes and Glass Apparatus. — Jas. W. Queen
cfr Co.

Chemical Apparatus. — Jas. W. Queen & Co.

Soleil's Polarization Apparatus, as adapted by Ventzke, for the
Quantitative Determination of Grape Sugar and Albumin : also
Polariscopes, by Laurent and Duboseq. — Jas. W. Queen <f*
Co., Agents in North America.

Apparatus for Volumetric Analysis and Titrated Solu-
tions.— Jas. W. Queen & Co.

INDEX.

Absolute arterial pressure, Measure-
ment of, 22o
Absorption by the liver, 505
internal, by veins, 296
by veins and lymphatics, 293
Accelerator, Nerves of heart, 286
Acetic acid, Action of, on fibrous tis-
sues, 47
Acid albumin, or syntonin, 432
albumin, 436

Preparation of solution of,
433
Acids, Action of, on blood, 29
Adenoid tissue, 59
Adipose tissue, Chemistry of, 447
Albumin, Alteration of, by acids, 432
by alkalies, 429
Coagulation of, 424
Decomposition of, 436
Detection of, 426
in urine, 555
Determination of amount of, in

urine, 556
Dry, solubility of, 423
Mode of separating, from milk,

528
Preservation of, 423
Properties of, 421
Pure, preparation of, 422
Solution to be used in testing,

422
Tests for traces of, in solution,
428
Albuminates, 435
Albuminoids, Chemistry of, 442
Albuminous bodies, Coagulated, 436
in solution, 437
Precipitation of, 424
Separation of, from otber
substances in solution,
427
Synopsis of, 435
compounds, 421

Products of digestion of, 483
substances in muscle, 451
37

Alkali albuminates, 429, 435

and syntonin, Distinction be-
tween, 435
should contain no sulphur,
432
Alkalies, Action of, on blood, 30
Alvergniat's pump, 205
Amoeboid cells, 49
Amyloid, 436

Analysis of blood gases, 210-214
Aniline for coloring sections, 107
Animal heat, 336
Apnoea, 328
Areolar tissue, 47
Arterial pressure, 218

Changes of, in each cardiac

period, 224
Expansive movements ac-
companying change of,
220
Influence of, on frequency of
heart contractions, 285
pulse, Experiments with schema
relating to forms of, 234
schema or artificial artery,
230
Arteries, Observation of, during ex-
citation of the cord, 251
Circulation in, 217
smallest, Phenomena of circula-
tion in, 238
Artery, Artificial, or arterial schema,

230
Asphyxia by complete occlusion of
the trachea, 329
by slow suffocation, 330
State of circulation in, 332
Auerbach's ganglia, 86

Beale's solution for coloring sections,

107
Bernard's method of determining

oxygen in blood, 216
Bernstein's experiment, 282
Bile, I'M

578

INDEX.

Bile ocids, 199

Separation and detection of,

in urine, 556
Pettenkofei's test for, 499
Action of, 604
Composition of, 19 I
General character of, 494
pigments; Relation of, to uromo-
globin, 497
Tests for, 494
precipitates, syntonin and pepsiu,

5! 1 1
Secretion of, 504
Biliary listula, Mode of producing, in

guineapigs, 505
Bilirubin, 196

Preparation of, from bile, 496

from gall stones, 496
Properties of, 496
Biliverdin, 497

Properties of, 497
Bladder. Epithelium of, 42
Blastoderm, Formation of lamella: of,
104
of chick, Lamellic of, 165
Blood, 175

Action of acids on, 29
of alkalies on, 30
of boracic acid on, 30
of carbonic acid gas on, 32
of cold on, 188
of crystallized ox-bile on, 189
of electricity on, 33, 189
of gases on, 31
of heat on, 188
of water on, 189
Chemical changes of, in dyspnoea

and asphyxia, 333
Circulation of, 217
coloring matter, 187
Condition affecting coagulation

of, 183
corpuscle of mammalia, Action of

.salt solution on, 28
crystals, 34

Detection of, in urine, 559
Gases of, 204

method of analysis, 210
method of rendering laky or

transparent, 187
Method of transferring, from
artery or vein, to vacuum, 208
Mode of testing for sugar in, 509
of frog, Filtration of, 170
Quantitative determination of hae-
moglobin in, 192
Quantitative analysis of, 199
Bloodvessels, Endothelium of, 118

Bloodvessel?, Muscular coat of, 120
Nerves of, 121
of intestine, 189

Structure of, 1 18

Bone, 63

Chemistry of, 447
Development of, fi 1
Inflammation of, 1 70
Preparation of gelntigenous sub-
stances from, i 1 1
Boracic acid. Action of, on blood,

30
Brain and spinal cord, Ganglion cells
of, 83
Chemistry of, 455
Ganglion cells of, hemispheres,
85
Branched cells (connective tissue cor-
puscles), 51
corpuscles of skin, 55
of tail of tadpole, 55
Brunner's glands, 138

Calorimetry, 337

Capillary circulation in mammalia,

240
Carbonic acid gas, Action of, on blood,
32
Discharge of, by an ani-
mal in a given time,
311
Cardiac impulse, 203
Cardiograph, 265

Carmine, Coloring of sections by, 106
for injecting, 113
Mass, Gerlach's, 113
Cartilage, hyaline, 60
inflammation of, 170
Yellow, 02
Casein, 435

Mode of separating, from milk,
528
Cells, Amoeboid, 49
Fat, 57
Nerve, 82
Pigment, 56
Tendon, 58
Cellular elements of centrum tendi-
neum in relation to lymphatics, 127
Cellular, Elements of, connective tis-
sue, 49
Centrum tendineum, Cellular elements

of, 127
Cerebral hemispheres, Removal of, in

bird, 417
Cerebrin, 450

Cerebro-spinal nervous centres of vas-
cular system, influence of, 246

INDEX.

579

Changes of arterial pressure during

each cardiac period, 224
Chick, Cleavage cavity of, 104

Lamellns of blastoderm of, 105
Chloride of gold, Preparation of cor-
nea with, 53
Chlorine, Determination of, in urine,

503
Cholesterin, 503
Cholic acid, 503

Chondrin, Decomposition of, 447
Chondrin, Effect of boiling on, 44G
Precipitation of, 446
Preparation of, 440
Solubility of, 440
Chondrogen, 440

Solubility of, 440
Chorda tympani and vascular fila-
ments of submaxillary gland, Simul-
taneous section of, 472
Chorda tympani, Direct and reflex

excitation of, 471
Ciliary motion, Effects of reagents on,
35
Stud}- of, in situ, 36
Ciliated cylindrical epithelium, 35

epithelium, 37
Circulation, Artificial, 242

Capillary, in mammalia, 240
in arteries, 217

Influence of respiration on, 324
Microscopical study of, 121
Phenomena of, in smallest arte-
ries, 238
State of, in asphyxia, 332
Study of, in cold-blooded ani-
mals, 121
Study of, in mesentery, 121
in tail of tadpole, 122
in tongue, 122
in web of frog's foot, 121
Cleavage cavity in ova of fish and
amphibia, 101
of chick, 104
process in ova of fish and am-
phibia, 159
Coagulation of albumin, 424
of blood, 183
of muscle plasma, 450
of myosin, 452
Cold, Action of, on blood, 188
Cold-blooded animals, Study of cir-
culation in, 121
Coloring of sections, 106
Colorless blood corpuscles, 17
Colorless corpuscles, Action of dis-
tilled water on, 27
Amoeboid movements of, 17

Colorless corpuscles, Application of
liquid reagents to, 20
Effects of warmth on, 23
Feeding of, 25
of man, 25
Varieties of, 18
Commutator, 354
Conjunctiva and membrana nictitans,

Nerves of, 92
Connective tissue, Cellular elements
of, 49
corpuscles, 51

and fat cells, Transition
forms between, 58
Development of, 59
tissues, 46

Chemistry of, 442
Constant current, Arrangement of

electrical apparatus for, 357
Contraction as a function of stimulus,

307
Contractions, Idio-muscular, 305
Cornea, Fixed corpuscles of, 52
Inflammation of, 171
Nerves of, 91
Preparation of, with chloride of

gold, 53
Treatment of, with nitrate of
silver, 52
Corpuscles, Branched, of skin, 55
of tail of tadpole, 55
Fixed, of cornea, 52
Granular, 21
Corpuscles of blood, Separation of,
from liquor sanguinis, by subsi-
dence, 177
Cranial and spinal nerves, Ganglia of,

82
Creatine, 453

Decomposition of, 453
Reaction of, 453
Solubility of, 453
Tests for, 453
Creatinine, 453

Characters of, 454

Reaction of, 453

Separation of, from urine,

538
Solubility of, 453
Crystallized bile, 500

composition, 500
Action of, on blood, 189
Curare, Poisoning by, 398
Current, electric, interrupted by

means of an oscillating rod, 360
Current, electric, with definite inter-
ruptions by means of the metro-
nome, 300

580

INDEX.

Cylindrical ciliated epithelium, 86
epithelium, non-ciliated, 38

Dammar varnish, Preparation of, 108
Death, after section of both vagi, 317
Development of bone tissue, G4

of connective tissue, 50
Dialysis, 505

Diaphragm, demonstration of lym-
phatics by injection, 126
Diaphragm, Lymphatics of centrum

tendineum of, 123
Diastatic action of saliva, Effect of

temperature on, 400
Digestion, 457

and secretion, 421
Effects of temperature on, 486
in the stomach, 475
intestines, 515

Method of making a

temporary fistula, 515

Digestion in the intestines, Method of

making a permanent fistula, 516
Digestion of the stomach by itself,
491
during life, 491
Organs of, 135

Strength of acid required for,
486
Digestive action of Pepsin, 483
Discus proligerus and ovum, 148
Dorsalis pedis, Excitation of, 256
Drying, 566
Dyspeptone, 484
Dyspnoea, 328

Egg albumin, 435
Elastic tissue, 47

Chemistry of, 445
Elastin, 445

Characters of, 445
Decomposition of, 446
Precipitation of, 445
Preparation of, 445
Reactions of, 445
Solubility of, 445
Electric currents of muscles, 376
Natural, 376
Negative variations of,
380
of nerves, 381
Natural, 381
Negative variations of,
381
Electrical measurement of tempera-
ture, 344
stimulation of nerve and muscle,
364

Electricity, Action of, on blo<
Electrodes, 852

Non-polarizable, 353
Electrotonus, 382

as affecting irritability, 8
Embedding in gum and gelatine, 105
in wax and oil, 108
of tissues for cutting sections. 1 1 '■'•
Embryology, 158
Endocardial pressure, 268

curve, Modifications of, 270
in mammalia, 27^1
Investigation of, in heart of

frog, 268
Variations of, during each
cardiac period, 269
Endothelium and epithelium, 85
Inflammation of, 170
of bloodvessels, 118
of serous membranes, 43
Silver method of exhibiting, 43
Epithelial tissues, Chemistry of, 442
Epithelium and endothelium, 35
of ovary, 147
Ciliated forms of, 37
Cylindrical ciliated, 35

non-ciliated, 38
Inflammation of, 169
of bladder, 42
of kidneys, 144
of malpighian corpuscles. 145
of villi of intestines, 39
pavement, 40
Excitation and section of spinal cord
in rabbit, 248
Direct, of spinal cord in frog, 246
of dorsalis pedis, 256
of nerves of external ear of rab-
bit, 255
of superior laryngeal nerve, 322
of central end of one vagus after

section of both, 321
of vascular nerves of submax-
illary gland, 472
Extractive matters in muscle, 452
Evaporation, 561

Method of retarding, 27

Fallopian tubes, 148

Uterus and vagina, 148
Fat cells, 57

and connective tissue cor-
puscles, Transition forms
between, 58
Fats, 447

Composition of, 448
Emulsionizing of. 1 18
Reactions of, 4 is

INDEX.

581

Fats. Solubility of, 447
Feeding of colorless corpuscles, 25
Fibre cells. Spiral, 87
Fibrin and plasma, Properties of, 178
Influence of swelling of, on its
digestion, 487
Fibrinogen and paraglobulin, Experi-
ments relating to, 179
Fibrinogenic substance, 435
Fibrino-plastic substance, 435
Fibrins, 435
Fibro-cartilage, 62
Fibrous tissue, 40

tissues, Action of acetic acid on,
47
Effect of maceration on, 47
Filtration, 563

of frog's blood, 176
Fixed corpuscles of the cornea, 52
Follicles, Graafian, 148

of intestine, Solitary and agnii-

nated, 132
of Peyer, 138
Frankland-Sprengel pump, 207
Frog, Injection of, during life, 110
Muscular nerve endings of, 98
Piespiratory movements of, 298
Study of movements of heart in,
260

Ganglia, Auerbach's, 86

of the cranial and spinal nerves, 82
Ganglion cells of brain and spinal
cord, 83
of hemispheres of brain, 85
of sympathetic system, 85
Reproduction of, 88
Gases, Action of, on blood, 31

of arterial blood of dog, Analysis

of, 214
of blood, 204
Gastric fistula, Establishment of, 475

Operation for, 470
Gastric juice, Action of, 479
on gelatine, 485
Artificial, 479

Effects of stimuli on secre-
tion of, 493
Estimation of acid in, 478
Examination of, 477
Secretion of, 490
To determine the nature of
acid in, 478
Geissler's pump, 206
Gelatin, 444

Action of gastric juice on, 485
Alteration of, by boiling, 445
Precipitation of, 1 1"j

Gelatin, Preparation of, 444

Solubility of, 445
Gelatigenous substance, 444
Characters of, 444
Preparation of, from bone,

444
Preparation of, from ten-
dons, 444
Solubility of, 444
Genital organs, 147

of male, 149
Gerlach's carmine mass, 113
Gland, thymus, 132
Glands, Lymphatic, system, 130
of Brunner, 138
Parotid, 473

Salivary and pancreatic, 135
Sebaceous, 143
Sweat, 142
Globulins, 435
Glycerin, 448

Decomposition of, 448
Solubility of, 448
Solvent powers of, 448
Test for, 449
Glycocholic acid, 501
Glycogen, 506

Conver'n of, into grape sugar, 512
Influence of food on amount of,

in liver, 512
Preparation of, 510
Properties of, 511
Glycogenic function of liver, Mode of

demonstrating, 508
Glycosuria, 513

produced by puncture of floor of
fourth ventricle, 514
Graafian follicles, 148
Granular corpuscles, 21
Gum or gelatin, Embedding in, 105

H?ematin, 197
Ilrematoin, 198
Haemin, 196

crystals, 34
Haemoglobin, 34

Chemical properties of. 192

Determination of quantity by es-
timation of its iron, 202

Optical properties of, 194

Preparation of, 183

Quantitative determination of, in
blood, 201
Hair, 144
Hardened tissues, Preparations of

sections from, 100
Hearing, Organ of, 154
Heart, 260

582

INDEX.

Heart, Examination of, after death by
asphyxia, 338

Function of depressor nerve of,

291
Inhibitory nerves of, 279
Influence of temperature on, 278
Intrinsic nervous system of, 274
Movements of, 260
sounds, Investigation of, 266
Study of movements of, in frog.
200
in mammalia, 262
Heat, Action of, on blood, l^s

produced by an animal in a given
time, Estimation of, 339
Hemispheres of brain, Ganglion cells

of, 85
Heynsius' experiment, 182
Hippuric acid, Separation of, from

urine, 537
Hofmann's tests for tyrosine, 441
Hyaline cartilage, GO
Hypoxanthine, 454

Idio-muscular contractions, 395
Ignition, 560
Impulse, Cardiac, 263
Inflammation of bone, 170
of cartilage, 170
of cornea, 171
of endothelium, 170
of epithelium, 169
of tongue of frog, 173
Inflammatory changes in liver cells.
171
in tadpole's tail, 173
Inflamed tissue, Study of, 160
Inhibitory influence of parts of the
brain on reflex actions of the spinal
cord, 418
Inhibitory nerves of the heart, 279
Injected tissues, Treatment of, 118
Injecting with carmine, 113
with Prussian blue, 112
Injection after death, 112

Apparatus and instruments for,

114
of lymphatic glands and mucous

membranes, 130
of the frog during life, 110
of the small mammalia during

life, 111
of solution of nitrate of silver, 1 1 8
Innervation of respiratory movements,

315
Inosite, 455

Inspiratory muscles: Diaphragm, 304
Intercostal, 305

Internal absorption by veins 296
Interrupted electric current, 359

Intestinal fistula. 622
juice, 522

Actions of, 524
Artificial. 528
Intestine, epithelium of villi, 39
Large. 139
Movements of, 525
Small, 137

Solitary and agminated follicles
of, 132
Intrathoracic pressure, Measurement

of, 303
Intrinsic nervous system of the heart,
274

Kidneys, Epithelium of, 144
Isolation of tubes of, 145

Kymographic observation, Rules and
precautions in, 220

Kymograph, Mercurial, 219
Spring, 225

Lecithin, 456
Leucine, 438

Tests for, 440
Liquor sanguinis, 175
Liver, 139

Absorption by, 505

Functions of, 494

Influence of food on amount of
glycogen contained in. 512

Glycogenic function of, 508

Separation of diastatic ferment
from, 513
Lymphatic glands, Structure of, 130

system, 123

vessels, Stomata of, 125
Structure of, 130
Lymphatics of diaphragm, 126

of omentum and meseutery, 128

Male genital organs, 149
Malpighiau corpuscles, Epithelium

of, 145
Manipulation, Practical notes on. 559

of glass tubing, 559
Marking lever. 355
Mechanical stimulation of muscle and

nerve, 364, 395
Medulla oblongata, Division of. 406
Excitation of, 262-25 I
Section of, within the cra-
nium, 251
Medullary sheath of nerve fibres, 80
Meissner's bodies or tactile corpus-
cles, 90

INDEX.

583

Meissner's plexus, 80

Metnbrana nictitaus and conjunctiva,

Nerves of, 92
Mesentery, 129

and omentum, Lymphatic system

of, 128
Study of circulation in, 121
Metapeptone, 484
Methaemoglobin, 190
Microscopical studj' of circulation,

121
Milk, 52G

Characters of, 526
Constituents of, 527
Fats of, 529

Microscopical examination of, 52G

Mode of estimating butter in, 529

separating albumin from,

528
separating casein from, 528
Sugar in, 528
Moreau's experiment on intestinal

secretion, 524
Motion, Ciliary study of, in situ, 30
Mouth, Mucous membrane of, 135
Mucin, 442
Mucous and serous membranes,

Nerves of, 95
Mucous membrane of mouth, tongue,

pharynx, and oesophagus, 135
Murexide test for uric acid, 435
Muscle, Albuminous substance in, 451
and nerve, Mechanical stimula-
tion of, 395
Aqueous extract of, 450
Chemical stimulation of, 396
Chemistry of, 449
corpuscles, 73
curve, 365
Exhaustion of, 300
Striped, 67
Unstriped, 65
plasma, 449
Reaction of, 449
Thermal stimulation of, 397
Muscles of respiration, Action of, 304
Muscular coat of bloodvessels, 120
Muscular contraction, Influence of
temperature on, 300
Influence of veratrin, etc.,

on, 867
Phenomena and laws of, 365
Wave of,
work done, 3G8
Muscular fibre, Arrangement and di-

vi-ion of, 75
Muscular fibres, P^xamination of, in
polarized light. 75

Muscular fibres, Substance of, 67
Nerves of, 96

nerve endings, 97-99

tissue, 65
Myosin, 435

Nares and larynx, Movements of, 307
Nessler's reagent, Preparation of, 439
Neurilemma, 81
Neurin, 450
Nerve cells, 82

Peripheral, 90
chamber, 352

Chemical stimulation of, 397
endings, 89
fibres, 79

Axis-cj'linder, 79
Medullary sheath, 80
non-medullated, 82
Schwann's sheath, 81
Nerves, Influence of, on secretion of

stomach, 492
Nerves of bloodvessels, 121

of conjunctiva and membrana

nictitans, 92
of cornea, 91
of mucous and serous membranes,

95
of peritoneum, 96
of septum cisternal of mesentery

of frog and newt, 95
of skin, 93
of striped muscle, 97
of tadpole's tail, 94
of unstriped muscular fibre, 96
Stimulation of, 385
Thermal stimulation of, 398
Vasomotor functions of, 244
Nervous system, Tissues of, 79

Omentum and mesentery, Lymphatics

of, 128
Optic lobes, Irritation of, 418
Organs of digestion, 135
of respiration, 133
of special sense, 150
Ova of fish and amphibia, Process of

cleavage in, 159
Ovary, Epithelium and endothelium
of, 147
stroma of, 148
Ovum and discus proligerus, 148

Pancreas and salivary glands, 135
Pancreatie ferments, Glycerin solu-
tion of, 518
Pancreatic ferments, Isolation of, 520
juice, 515-521

;84

INDEX.

Pnraglobulin and fibrinogen, Experi-
ments relating to, 179
Parapeptone, 488

Parotid duct, Insertion of cauula in,
405
fistula, 4G6

glands, 473

Peritoneum, Nerves of, 96

Peyer's follicles, 138

Phosphoric acid, Estimation of, in
urine, 551

Picric acid, Coloring of sections by,
107

Pigment cells, 56

Piria's test for tyrosine, 441

Plasma, or liquor sanguinis, 175

Polariscope, 571

Polarized light, Examination of mus-
cular fibres in, 75

Precipitates, Washing of, on niters, 205

Precipitation, 562

Pressure, Arterial, 218
Endocardial, 208
produced by secretion, 471

Prussian blue for injecting, 112

Pseudo-stomata, 12s

Ptyalin, 402-3

Pulse, Arterial, experiments relating
to forms of, 234

Pumps, Alvergniat's, Geissler's, and
Franklaud-Sprengel, 207

Recording tuning-fork, 357
Recurrent sensibility, 405
Keflex actions, 400

excitation of medulla oblongata,
252-254
of vagus, 283
of vaso-motor centres, 252
Respiration, 208

Influence of, on circulation, 324
Organs of, 133
Respiratory movements, Innervation
of, 315
of frog, 298
Roots of spinal nerves, Functions of,
402

Saliva and its secretion, 457
Action of, 459-462
Artificial, 402
Effect of temperature on dias-

tatic action of, 400
Inorganic constituents of, 458
Organic, 469
Secretion of, after decapitation,

475
Separation of ptyalin from, 403

Salivary fist nice, 166

glands and pancreas, 185

Preparation of mucin from,

1 18
Secretion of, in rabbit, 465
secretion, Stimulation of, 16 I
Sarcolemma, 72
Sarcous elements, 449
Sarkin, 454
Scherer's test for leucine, 1 10

tyrosine, 441
Schwann's sheath, 81
Sebaceous glands, 143
Secretion of gastric juice, 400
of saliva, 464

of stomach, Influence of nerves
on, 492
Section of both vagi in the neck, 815
of medulla oblongata within the
cranium, 251
Sections, Coloring of, 100
Mounting of, 107
of fresh tissues, Preparation of,

1(H)
of hardened tissues, Preparation
of, 100
Semicircular canals, Division of, 420
Sensibility, Recurrent, 405
Serous membranes, 43
Serum albumin, 423
Skin, 141

Branched corpuscles of, 55
Nerves of, 93
Sight, Organ of, 150
, Silver, Solution for injecting, 114, 118
Smell, Organ of, 157
Sounds of the heart, 200
Special sense, Organs of, 150
Specific gravity, 567
Sphvgmograph, 227

"Uses of, 229
Spinal and cranial nerves, Ganglia of,
82.
cord, Excitation of, 240, 248.
Spiral fibre cells, 87
Splanchnic nerves, Vaso-motor func-
tions of, 258
Spleen, 140

Spring kymograph, 225
Starch paste, Action of saliva on. 459
Stimulation of muscles and nerves,

304, 385.
Stomach, 130

Digestion of, during life, 491
Strieker's warm stage," 22
Striped muscle, 67

Nerves of, 97
Stroma of ovary, 148

INDEX.

585

Submaxillary fistula, 4G6

ganglion, Functions of, 473
gland, Excitation of vaso-motor
nerves of, 471
Investigation of functions of,
467
Sugar, Detection of, in urine, 553

Testing for, in blood, 509
Sweat glands, 142

Sympathetic system, Ganglia of, 85,86
nerve, Vaso-motor functions of
cervical portion of, 257
Syntonin, or acid albumin, 432

Tactile corpuscles, 90
Tannin, Action of, on blood, 31
Taste, Organ of, 155
Taurocholic acid, 502
Taurine, 502
Teeth, 135

Temperature, Distribution of, in body,
348

Electrical measurement of, 344
Tendons, Preparation of gelatigenous
substance from, 444
of mucin from, 443
Tetanus, 371

Curve of, 371

effects of exhaustion, 372
Thermal stimulation of muscle and

nerve, 364, 397-8
Thermometry, 343
Thymus gland, 132
Tissues, Chemistry of, 442

Process of teasing, 46
Tongue, Mucous membrane of, 135

of frog, Inflammation of, 173

Study of circulation in, 122
Traube's curves, 326
Tuning-fork, 857
Tyrosine, 440

Preparation of, by pancreatic
digestion, 521

Tests for, 441

Unstriped muscle, 65

Nerves of, 96
Urari, Poisoning by (see also Curare),

Urea, Determination of, in urine, 547

1'reparation of, from urine, 534
Ureter, pelvis of kidney, and bladder,

147
Uric acid, 466

Determination of, in urine,
661
Urinary apparatus, 144
deposits, 683
38

Urine, 531

Detection of blood in, 557
Constituents of, 534
Determination of albumin in,
556
of chlorine in, 549
of phosphoric acid in, 551
of sugar in, 553
of sulphuric acid in, 552
of urea in, 547
quantity passed in a given time,

541
Reactions of, 531, 533
Separation of bile acids from,
556
of coloring matters from,

539
of creatinine from, 538
of hippuric acid from, 537
Specific gravity of, 542
Uterus, Fallopian tubes, and vagina,
148

Vagus and splanchnic nerves, Influ-
ence of, on stomach, 493
nerve, Influence of, on heart,

279-80
Reflex excitation of, 283
Valves, Study of, in dead heart, 267
Varnished rabbits, Increased dis-
charge of heat from, 342
Vascular system, Methods of inject-
ing, 110
Vasomotor, Centre reflex excitation
of, 252
functions of splanchnic nerves,
258
of cervical portion of the
sympathetic, 257
nerves, Excitation and division
of, 250
Functions of, 244
Veins and lymphatics, Absorption by,
293
Internal absorption by, 296
Villi of intestine, Epithelium of, 39
Vitellin, 435
Volumetrical analysis, 569

Warm stage, 22

Wax and oil, Embedding in, 103

Web of frog's foot, Circulation in,

121
Weighing, 567

Xanthine, 454

Yellow cartilage, 62

LIST OF ILLUSTRATIONS

PLATE I.

Fig. 1. Simple Arrangement for warming an Object under the Microscope.
" 12. Similar but more complicated Apparatus.
" 2. Strieker's Warm Stage.
" 13. Rod for Heating Stage.
" 16. Object Support with Gas Chamber.

PLATE II.

Fig. 3. Mode of warming an Object under the microscope by means of Current
of Hot Water.
" 4. Capillary Pipette.
" 14. Strieker's Stage for warming a Preparation by Voltaic Current.

PLATE III.

Fig. 5. Carbonic Acid Apparatus.
" 6. Microscope Stage with Strieker's Electrodes.

PLATE IV.

Fig. 17. Injecting Syringe.
" 11. Support for Study of Circulation in Web of Frog's Foot.
" 20. Injecting Canuloo.
" 21. Section Knife.
" 18. Nozzle of Injection Syringe.
" 19. Support for Studying Circulation in Mesentery.

PLATE V.

Fig. 22. Large Colorless Corpuscle of Newt.
" 23. Granular Corpuscle of Newt.
" 24. Action of different Reagents on Blood Corpuscles.

PLATE VI.

Fig. 2(5. Action of Heat on Colorless Corpuscles of Human Blood.
" 7. Epithelial Cells from Trachea of Cat.

PLATE VII.

Fig. 2G. Epithelial Cells from Bladder of Rabbit.
" 27. " of Bete Malpighii from Pointed Condyloma.

" 28. Superficial Cells of the same Preparation.

" 2'J. Jagged Epithelial Cells of Gum.

PLATE VIII.

Figs. 30 and 32. Abdominal Surface of Centrum Tendineum of Rabbit.
Fig. 31. Pleural

PLATE IX.

Fig. 33. Omentum of Guineapig treated with Silver.
" 34. Fenestrated Portion of Omentum of Ape.

IV LIST OF ILLUSTRATIONS.

PLATE X.

Pig. 35. Omentum of Ape, showing Group-; of germinating Endothelial •'■■ll--.
" 37. Silver Preparation of Septum of Cisterna Lymphaticn of Female Frogs.

FLATE XI.

Fig. 37. Germinating Endothelium of Pleural Mediastinum of Cnt.

" 38. Mesogastrium of Frog covered with Ciliated germinating Endothelium.

PLATE XII.

Fig. 39. Cornea of Frog treated with Lunar Caustic.
" 40. Horizontal Preparation of Cornea of Frog colored with Chloride of Gold.

PLATE XIII.

Fig. 41. Horizontal Preparation of Cornea of Rabbit treated with Lunar Caustic
and Salt Solution.
" 42. Membrana Nietitans of Frog treated with the Chloride of Gold.
" 43. Surface of Inflamed Mesentery of Ape.

" 44. " " " " showing Branched Cells of Ca-

nalicular System filled with Fat Globules.
" 45. Fat Cells, Omentum of Rat.

PLATE XIV.
Figs. 46 and 47. Cells of Gelatinous Substance of Infra-orbital Fossa of Rabbit.

PLATE XV.

Fig. 48. Cells of Parietal Peritoneum of R'abbit with Chronic Peritonitis.
" 49. " of Submucous Tissue of Gravid Uterus of Sow.
" 50. " of Gelatinous Substance of Infra-orbital Fossa of Rabbit being
converted into Fat-cells.

PLATE XVI.
Fig. 51. Branched Cells of Omentum of Rabbit.

PLATE XVII.
Fig. 52. Cells of Caudal Tendon of young Rat ; Silver Preparation.
" 53. " " " of full-grown Rat.

" 54. " " of young Rut ; Gold Preparation.

" 55. Transverse Section of Tendon from Tail of Rabbit.
" 8. Connective Tissue Trabeculaj from Omentum of Guineapig.

PLATE XVIII.

Fig. 5G. Elastic Fibres from Mesentery of Rabbit.
" 57. Intervertebral Cartilage of Tail of Rabbit.

PLATE XIX.
Fig. 58. Transverse Section of Epiphysis of Femur of Human Foetus.

PLATE XX.
Fig. 59. Longitudinal Section of Epiphysis of Femur of Human Foetus.

PLATE XXI.

Fig. GO. Transverse Section of Diaphyaifl of Femur of Human Foetus.

LIST OF ILLUSTRATIONS. V

PLATE XXII.
Fig. 61. Vertical Section of Parietal Bone of a Child.

PLATE XXIII.

Fig. 62. Longitudinal Section of Epiphysis of Metatarsal Bone of Rabbit.
PLATE XXIV.

Fig. 15. Diagram to illustrate the Course of a Ray of Light transmitted through
a Muscular Fibre.
" 63. Longitudinal section of Muscular Coat of Fallopian Tube of Sow.
" 64. Transition of Striped Muscular Fibre into Tendon in Tail of Rabbit.
" 65. Muscular Fibre of Hydrophilus Piceus.

PLATE XXV.

Fig. 66. Section of Injected Muscle.
" 67. Smooth Muscular Fibre.
" 68. Striped Muscular Fibre of Frog.

PLATE XXVI.

Fig. 69. Group of Ganglion Cells of a Sympathetic Nerve Trunk from Bladder of
Rabbit.
" 70. Ganglion Cells with Spiral Fibres.

PLATE XXVII.

Fig. 71. Ganglion Cells from Spinal Cord of Calf.
" 73. Superficial Intra-epithelial Network of Non-medullated Nerve Fibres

from Cornea of Rabbit.
" 74. Sub-epithelial Nerve-plexus from Cornea of Rabbit.

PLATE XXVIII.

Fig. 72. Branched Ganglion Cell from Spinal Cord of Calf.
11 75. Nerves of Substantia Propria of Cornea of Rabbit.

PLATE XXIX.

Fig. 76. Intra-epithelial Non-medullated Nerve Fibrils of Cornea of Rabbit.
" 77. Auerbaclrs Plexus from small Intestine of Human Foetus.

PLATE XXX.

Fig. 78. Sub-epithelial Nerve Branchings of Cornea of Guineapig.
" 79. Non-medullated Nerve Fibres from Cornea of Rabbit.

PLATE XXXI.

Fig. 80. Superficial Intra-epithelial Network of Non-medullated Nerve Fibres,
Cornea of Guineapig.
" 81. Non-medullated Nerve Fibres from Cornea of Frog.

PLATE XXXII.

Fig. 82. Nerve Fibres of Substantia Propria of Cornea of Frog.
" 83. Bab-epithelial and deep Intra-epithelial Nerve Fibrils from Cornea of
Babbit.

PLATE XXXIII.

Fig. 84. Deep Intra-epithelial Network of fine Non-medullated Nerve Fibres of
Cornea of Babbit.
" 85 Superficial [ntra-epithelial Nerve Fibres of Cornea of Rabbit.
" 86. Nerve Fibre* and Corpuscles of Cornea of Frog.

VI LIST OF [LLUSTRAT1

PLATE XXXIV.

Fig 87. Non-medullated Nerve Fibres of a Capillary Bloodvessel.

" 8S. Nerve Fibres of Mesentery of Frog.

PLATE XXXV.
Fig. 89. Nerve Fibres and Capillary Bloodvessel from Tail of Tadpole.

PLATE XXXVI.

Fig. 90. Plexus (if Non-medullated Nerve Fibres round Capillary Bloodvessel from

Mesentery of Frog.
" 91. Non-medullated Nerve Fibres surrounding Capillary Bloodvessel from

Tongue of Frog.
" 92. Plexuses of Non-medullated Nerve Fibres surrounding Bundles of Un-

striped Muscle from Vagina of Babbit.

PLATE XXXVII.

Fig. 93. Distribution of Non-medullated Nerve Fibres from Base of a Gland of
Membrana Nictitans of Frog.
" 9. Non-medullated Nerve Fibres surrounding small Artery of Tongue of
Frog.

PLATE XXXVIII.

Fig. 94. Sub-epithelial Non-medullated Nerve Fibres of Vagina of Rabbit.

" 95. Non-medullated Nerve Fibres in Adventitia of large Vein from Mesen-
tery of Frog.

•' 96. Non-medullated Nerve Fibres in Adventitia of large Artery from Mesen-
tery of Frog.

PLATE XXXIX.

Fig. 97. Sub-epithelial Non-medullated Nerve Fibres of Membrana Nictitans of
Frog.
" 98. Bloodvessels of Injected Mesenteric Gland of Guineapig.

PLATE XL.

Fig. 99. Longitudinal Section of Branch of Pulmonary Artery from Lung of
Guineapig.
" 100. Transverse Section of Artery from Skin of Guineapig; Gold Preparation.
" 101. Omentum of Rabbit, showing Development of young Capillaries.
" 102. Capillary Bloodvessel extending into a Branched Cell.

PLATE XLI.

Fig. 103. Endothelium of a large Vein and Artery of Omentum of Rabbit ; Silver
Preparation.

PLATE XLII.

Fig. 104. Endothelium of Capillary Bloodvessel of Omentum of Rabbit.

PLATE XLIII.

Fig. 105. Capillary System of Mucosa from Injected Stomach of Rat.
" 106. Fat Tract from Injected Omentum of Goineopig.

" 107. Superficial Capillary Meshworkof Mucous Membrane, Injected Uterus
of Guineapig.

PLATE XLIV.

Fig. 108. Superficial Arteries, dense Network of Capillaries, and deep Veins of
Mucous Membrane of Stomach of Rat.
" 109. Masses of Tubercle from Injected Omentum of Guineapig.

LIST OF ILLUSTRATIONS. Vll

PLATE XLV.
Fig. 110. Bloodvessels of Striped Muscle from Injected Tongue of Rabbit.

PLATE XLVI.

Fig. 111. Stomata of Mesentery of Frog.
" 112. Stomata of Septum Cisternal Lymphaticse Magna; of Frog.

PLATE XLVII.

Fig. 113. Germination of Endothelium round Stomata of Mesentery of Guinea-
pig affected with Chronic Inflammation.

PLATE XLVIII.

Fig. 114. Stomata of Peritoneal Surface of Centrum Tendineum of Rabbit.
•• 115. Stomata on a Lymph Vessel of Mesentery of Guineapig.

PLATE XLIX.

Fig. 116. Germination of Endothelium on Mesentery of Guineapig affected with
Chronic Inflammation ; Silver Preparation.

PLATE L.

Fig. 117. Lymph Capillaries of Peritoneal Serosa of Centrum Tendineum of
Rabbit.
" 118. Lymph Vessels of Pleural Serosa of Centrum Tendineum of Guinea-
pig-

PLATE LI.

Fig. 119. Pleural Surface of Centrum Tendineum of Rabbit, showing rich Net-
work of Lymph Vessels.

PLATE LII.
Fig. 120. Lymphatics of Centrum Tendineum of Rabbit.

PLATE MIL

Fig. 121. Lymphatics of Omentum of Rabbit; Silver Preparation.

PLATE LIV.

Fig. 122. Surface of Omentum of Rabbit, showing Distribution of Lymph Ves-
sels j Silver Preparation.

PLATE LV.

Fig. 123. Pleural Side of Centrum Tendineum of Guineapig affected with Chronic
Inflammation.

PLATE LVI.
Fig. 124. Pleural Side of Centrum Tendineum of Rabbit; Silver Preparation.

PLATE LVII.

Fig. 125. Lymph Vessels of Pleural Side of Centrum Tendineum of Rabbit.

PLATE LVII I.

Fig. 120. Artery and Lymphatic Vessel of Omentum of Rabbit ; Silver Prepara-
t [on.
" 127. Adenoid Tissue of Mesenteric Gland of Ox.

Y1U LIST OF ILLUSTRATIONS.

PLATE LIX.
Fig. 12S. Natural Injection of Lymphatics of Centrum Tendineuni of Rabbit.

PLATE LX.
Fig. 129. Section of Medullary Substance of Mesenteric Gland of Ox.

PLATE LXI.

Fig. ISO. Alveolus from Section of Lung of Rabbit.
'• 132 Section of Lung of Rabbit Injected.
" 133. Trabecule of Liver Cells of Guineapig.

PLATE LXII.

Fig. 134. Section of Liver of Dog Injected from Vena Porta).
" 130. Section of Liver of Rabbit, the Portal Vein and Hepatic Duct of which
are Injected.

PLATE LXIII.

Fi£. 130. Section of Injected small Intestine of Rat.

" 137. " " Villus of small Intestine of Cat.

" 138. " " Filiform Papilla) of Tongue of Rabbit.

" 139. " " Large Bronchus of Human Foetus.

PLATE LXIV.

Fig. 140. Injected Follicles of Section of Peyer's Patches from small Intestine
of Rabbit.
" 141. Section of Ileum of Dog.

PLATE LXV.

Fig. 142. Section of Acinus from Liver of Rabbit.
" 143. Section of Injected Kidney of Rat.
" 144. Urinary Tubes of Pyramidal Substance of Injected Kidney of Pig.

PLATE LXVI.

Fig. 145. Transverse Section of Injeoted Kidney of Rat.

PLATE LXVII.

Fig 14fi. Transverse Section of Pyramidal Substance of Kidney of Pig.
'• 147. Preparation from Kidney of Pig showing a llenle's Loop.
" 148. Similar Preparation, showing Portion of Collecting Tube in Pyramidal

Process.
" 149. Section of Malpighian Corpuscles of Kidney of Human Foetus.

PLATE LXVIII.

Fig. 150. Convoluted Tube of Kidney of Pig.
" 151. Section of Eyelash of newly-born Child.
,; 152. Meibomian Follicle from Section of Human Eyelid.

PLATE LXIX.

Fig. 153. Tubular Glands of Human Prostate.
" 154. Section of Cortical Substance of Kidney of Six Months' Human Fcetus.
" 155. Tubular Glands of Human Eyelid; Vertical Section.

PLATE LXX.

Fig. 156. Cornea of Rabbit j Vertical Section.
" 157. Diagram of Connective Substance of Retina.
" 158. " Nervous Elements of Retina.

LIST OP ILLUSTRATIONS. IX

PLATE LXXI.

Figs. 159-163. Blastoderm of Egg of Trout, Various Stages of Cleavage in.
'• 164. Germ of Egg of Trout in an early Stage of Cleavage.
" 165. Blastoderm of Egg of Trout at the Third Day; Vertical Section.
" 166. Similar Preparation at the Sixth Day.

PLATE LXXII.

Fig. 167. Blastoderm of Egg of Trout, Twelfth Day ; Vertical Section.
" 169-172. Sections of Egg of Bufo Cinerus.

PLATE LXXIII.

Fig. 168. Blastoderm of Trout's Egg at Fourteenth Day.
" 173. Section through Rudiment of Emhryo of Bufo Cinereus.

PLATE LXXIV.

Fig. 174. Section showing the Four Embryonal Coats of Rusconi's Cavity.

" 175. Blastoderm of Fresh-laid Hen's Egg.

" 176. Blastoderm of Hen's Egg at Fifteenth Hour of Incubation.

" 177. Section of Rudiment of Embryo at Twenty-sixth Hour after Incubation.

PLATE LXXV.

Fig. 178. Section of Rudiment of Embryo at Thirty-sixth Hour.
•■ 179. " Area Opaca and Area Pellucida at Thirtieth Hour.

" 180. Embryo of Chick at Thirtieth Hour ; Section of Cervical Portion.

PLATE LXXVI.

Fig. 181. Embryo of Chick, Second Day, showing Development of the Heart.
" 187. Development of Blood in Blastoderm of Chick.

PLATE LXXVII.

Fig. 1S2. Embryo of Chick at Forty-eighth Hour; Section of Posterior Part of
Body.
" 183. Section of Anterior Cerebral Vesicle and Primary Optic Vesicle.

PLATE LXXVIII.

Figs. 184-1S6. Transformation of Primary into Secondary Optic Vesicle and De-
velopment of Crystalline Lens.
" 188. Development of Blood in Chick.

PLATE LXXIX.

Fig. 190. Test Tube with Foot.
" 191. Vessel for collecting Blood and keeping it at 0° C.
'• 192. Coagulation of Blood of Frog in a tine Capillary Tube.
' 193. Canula for Schiifers' Experiment.
" 194. Object Glass for Studying Action of Induction Shocks on Blood.

PLATE LXXX.

1 fig. 195. Absorption Spectra.

196. Hoppe-SeyJer's Bottle for Preparing Fibrin.

" 197. Alvergniat's Pump.

" 198. Geissler'fl Mercurial Pump.

PLATE LXXXI.

Pig, 199. Frankland-Sprengel Pump.
•• 203. Needles for posting Ligatures under Vessels ; BrUcke's Blunt Hook;
and Trephine.

X l.I-T OF ILLUSTRATIONS.

PLATE LXXXII.
Fig. 200. Frankland's Apparatus for Analysis of Gases by Absorption.

PLATE LXXXIII.

Fig. 204. Czermak's Rabbit Sui>port.
" 201. Frankland and Ward's Apparatus for Analysis of Gases by Explosion.

PLATE LXXXIV.

Fig. 202. Mercurial Kymograph.
" 206. Normal Tracing obtained with Mercurial Kymograph.

PLATE LXXXV.

Fig. 205. Fick's Spring Kymograph.
" 207. Normal Tracing obtained with Spring Kymograph.
" 207a. Tracing obtained after Excitation of Vagus.
" 208. Mechanical Arrangement of Sphygmograph.

PLATE LXXXVL

Fig. 200. End View of Block by which Sphygmograph rests on the Wrist.
" 209A. Breguet's Improvement.
" 210. Mode of Measuring Pressure.
" 211. Arterial Schema.

PLATE LXXXVII.

Fig. 212. Tracing obtained with Arterial Schema.
" 213. Percussion Waves.

" 21-1. Tracings showing the Contractions and Expansions of an India-rubber
Tube, along which Water is propelled in an Intermitting Stream.
" 215. Sphygmographic Tracings.
" 216. Dr. Caton's Fish Trough.

PLATE LXXXVIII.

Fig. 217. Stage for Mesentery of Frog.

" 218. Canules for Aorta and Vena Cava of Frog.

" 219. Diagram of Arrangement for Measuring Objects under Microscope.

il 220. Canula for Injecting Liquid into a Vein.

" 221. Griffin's Blower and Expanding Regulator.

PLATE LXXXIX.

Fig. 222. Sprengel's Blower.
" 223. Mercurial Breaker for Artificial Respiration.
" 224. Skull of Rabbit seen from behind.
" 225. Excitor.

" 226. Parts exposed in Rabbit by an Incision from Thyroid Cartilage to
Root of Left Ear.

PLATE XC.

Fig. 227. Carotid Artery of Rabbit and Parts in relation with it.

" 228. Heart of Frog.

" 230. Cardiograph.

" 231. Marey:s Tympanum and Lever.

PLATE XCI.
Fig. 233. Coats1 Apparatus.

LIST OF ILLUSTRATIONS. XI

PLATE XCII.

Fig. 235. Tracings recording simultaneously Variations of Pressure in Right
Auricle, Right Ventricle, and Left Ventricle.
" 236. Septum Auricularum of Frog.
" 237. Dissection of Vagus Nerve of Frog, right side.

PLATE XCIII.

Fig. 240. Sketch illustrating Relations of Ganglionic Cord in Visceral Cavity of
Frog.
" 241. Heart, Lungs, and great Vessels of Rabbit.
" 242. Dissection of lower Cervical Ganglion of Dog.

PLATE XCIV.

Fig. 243. Inferior Cervical Ganglion of Rabbit.
" 244. Tracing showing Effect of Electrical Stimulation of Vagus of Frog

under the Influence of Nicotin.
" 246. Respiratory Muscles of Frog.
" 247. Recording Stethometer.

PLATE XCV.

Fig. 250. Pulley for recording Movements of Needle inserted in the Diaphragm.
" 251. Rosenthal's Apparatus with W. Mailer's Valves.
" 252. Pettenkofers Tube for Absorption of Carbonic Acid Gas.

PLATE XCVI.

Fig. 257. Lever Kymograph.
" 258. Tracing obtained with Lever Kymograph.

PLATE XCVII.

Fig. 265. Calorimeter.
" " Galvanometer.

•' " Wooden Frame on which Galvanometer Wire is coiled.
" " Magnets of Galvanometer.

PLATE XCVIII.

Fig. 229. Tracing drawn by Lever applied to Apex of Heart of Frog.

" 232a. " obtained with Cardiograph applied to Seat of Impulse of Hu-
man Heart.

" 2325. " obtained with Cardiograph applied outside Seat of Impulse of
Human Heart.

" 234. " of Endocardial Pressure of Heart of Frog.

" 238a & b. Tracings of Arterial Pressure and Respiratory Movement of Air
in Trachea before and after Section of both Vagi.

" 239a <fc b. Tracing of Arterial Pressure of Rabbit during Excitation of Peri-
pheral End of Divided Vagus.

" 245. Tracing of Arterial Pressure during Excitation of Central End of De-
pressor Nerve.

PLATE XCIX.

Fig. 246&*. Tracing of Respiration of Frog.
••' 248. " obtained with the Stethometer.

" 219. '' of Intrathoracic Pressure.

" 253. Tracings of Respiration of Cat, before and after Section of both Vagi.
" 263a. Tracing of Arterial Pressure and Respiratory Movements in Second

Stage of Asphyxia by Occlusion.
" 2634. Slow Asphyxia.

XI] LIST OF II.U STRATIONS.

PLATE C.

Figs. 259-61. Tracings of Respiratory M"vements of Dog, before ami after
Curarization.

" 262. Tracings of Artificial Respiration and Arterial Pressure, showing
Traube's Curves with Vagi intact.

" 264. Effect of Single Injection of Air in a Curarized Dog after Discontinu-
ance of Artificial ltespiration.

PLATE CI.

Figs. 254-55. Excitation of Central End of Vagus in the Rabbit.
" 256. Excitation of Central End of Superior Laryngeal Nerve.

PLATE OIL

Fig. 266. Diagram of Frog, showing Lines of Incision necessary in various Ob-
servations.
" 267 Diagram of Muscles of Leg of Frog.
" 268. Nerve-Muscle Preparation.

PLATE Cm.

Fig. 269. Myographion of Pfliiger.
" 270. Moist Chamber, with Nerve-muscle Preparation.
" 270£/j. Simple Spring Myograph of Marey.

PLATE CIV.

Fig. 271. Ordinary Electrodes.
" 272. Non-polarizable Electrode in Bearer.
" 273. Ends of Non-polarizable Electrodes.
" 274. Kronecker's Forceps.
" 275. Marking Lever.

" 276. Diagram of Apparatus for Studying the Effects of Electrotonus or Ir-
ritability.

PLATE CV.

Fig. 277. Recording Tuning-fork.

" 278. Diagram of Muscles of Thigh of Frog.

" 279. " " Muscle Curve.

" 280. Muscle in Trough bearing Levers, to show the Wave of Muscular Con-
traction.

" 281. Another arrangement of the Levers to show the Wave of Muscular
Contraction.

PLATE CVI.

Fig. 282. Diagram of the Curve of Tetanus.
" 283. Curve of Tetanus, showing individual Contractions.
" 284. Curves illustrating Extensibility of a Muscle during Tetanus.
" 2S5. Muscles and Nerves arranged for the Experiment of the Rheot
Frog.

PLATE CVII.

Fig. 286. Sir W. Thomson's Galvanometer and Scale.

" 287. Galvanometer Shunt.

" 288. Diagram of " Natural " Current in Muscle.

" 289. Arrangement of Nerve on Non-polarizable Electrodes.

" 290. Diagram illustrating Electrotonus.

LIST OF ILLUSTRATIONS. xin

PLATE CVIII.

Fig. 291. Muscle and Nerves arranged to show Use of Electrotonic Changes in
one Nerve as a Stimulus for another.
" 292. Apparatus to show the Effects of varying Temperatures on a Muscle.
" 293. Induction Apparatus of Du Bois Reymond.
" 294. Scheme of Du Bois Reymond's Induction Coil.

PLATE CIX.

Fig. 295. Diagram of Nervous System of Frog.
" 296. Brain of Frog seen from above. ,

" 297. Commutator.

PLATE CX.
Fig. 298. Rheochord.
" 299. Double Key.
" 300. Du Bois Reymond's Key.

PLATE CXI.
Fig. 301. Creatine Crystals.
" 302. Creatinine "

" 303. Nitrate of Hypoxanthine Crystals.
" 304. Hydrochlorate of Xanthine "
" 305. Uric Acid Crystals.

PLATE CXII.

Fig. 306. Starch Granules.
" 307. Nerves of Sub-maxillary and Sub-lingual Glands of Dog.
" 308. Veins of Sub-maxillary Gland.

PLATE CXIII.

Fig. 309. Nerves of Sub-maxillary Gland of Dog.

PLATE CXIV.

Fig. 310. Parts exposed in Operations on the Sub-maxillary Gland.
" 311. Gastric Canula seen in Section, and Key.
" 312. Taurine Crystals.
" 313. Hippuric Acid Crystals.

PLATE CXV.
Fig. 314. Cholesterin.
" 315. Bernard's Instrument for puncturing Fourth Ventricle.
" 316. Section of Rabbit's Head, showing direction of Instrument in order to
puncture the Fourth Ventricle.

PLATE CXVI.

Fig. 317. Canula in temporary Pancreatic Fistula.
" 318. Diagram to show arrangements of Stitches in Thiry's Fistula
" 320. Milk Globules.
" 321. Colostrum.

PLATE CXVII. *

Fig. 322. Urea.
" 323. Nitrate of Urea.
" 324. Oxalate "

" 325. Blowpipe Flame.

" 326. Glass Tube drawn out to form a Pipette.
•'-"• " in order to seal it.

Beaker supported on Wire Gauze to prevent it from Cracking.
' 320. Apparatus to prevent Loss by Evaporation during prolonged Ebulli-
tion.

XIV

LIST OF [LLUSTR VTIONS.

PLATE CXVIII.

Fig. 330. Saucepan used as Water-bathi

331. Bnnsen's Gas Regulator aa modified by Geiasler.

" 332. Water-bath for evaporating nl a constant lemperatnre.

" 333. Use of Syphon in Washing Precipitates.

PLATE CXIX.

Fig. 334. Screw-press.
" 335. Bunsen's Water Air-pump.

33(3. Plantaraour'fl Funnel for keeping Fluids Hot during Filtration.

337 Dialyser of Gutta-percha

PLATE CXX.

Fig. 338. Dialyser suspended in Water.

" 339. Hot-air Bath.

" 340. Ball-jar and Dish for drying and cooling Substances.

" 341. Method of drying Precipitates.

" 342. Platinum Triangle for Ignition.

" 343-4. Specific Gravity Bottles.

" 345. " " " for small Qiantities of Fluid.

Fig. 346. Measuring Flask.
'« 347. Test Mixture.

Fig. 348. Pipettes.
" 349. Mohr's Burette.

PLATE CXXI.

PLATE CXXII.

PLATE CXXIII.

Fig. 350. Stand for Burettes.
" 351. Elliptical Appearance of Surface of Liquid in Burette.
" 352. Erdmann's Float.
" 353. Saccharometer.

NOTE

The letter-press descriptive of the illus
to specific pages of the text. Inasmuch
that of the English edition, we subjoin a
of the two editions is seen at a glance.

trations in this work contains references
as the paging of this edition differs from
table in which the corresponding paging

Plate I.

F.ng. Ed.

Am. Ed.

Eng.
Plate XX.

Ed.

Fig. 1,

page 6, see page 22

Fig 59, page

49,

" 2

" 14,

31

Plate XXI.

Plate II.

Fig. 60,

50,

Fig. 4,

" 11,

" 26

Plate XXII.

Plate III.

Fig. 61,

50,

Fig. 5,

16,

31

Plate XXIII.

6,

17,

" " 33

Fig 42,

50,

Plate IV.

Plate XXIV.

Fig. 11,

" 42,

' " 56

Fig. 63,

53,

" 19,

" 10S,

' " 121 •

" 61, "

61,

Plate V.

" 15, "

56,

Fig. 22,

3,

" 19

" 65, "

51,

" 23,

" 5, '

' " 21

Plate XXV.

" 21,

" 13-15,

' " 2S-31

Fig. 68,

61,

Plate VI.

'• 67,

52,

Fig. 2.5,

9, '

' " 25

Plate XXVI.

11 7,

" 23,

38

Fig. 69, "

72

Plate VII.

" 70,

72,

Fig. 2(5,

" 27 '

42

Plate XXVII.

" 28,

2t,

41

Fig. 71,

60,

Plate VIII.

" 73,

78,

Fig. 30,

" 29-112, '

" 44, 125

" 74, "

78,

Plate IX.

Plate XXVIII.

Fig. 33,

33,

47

Fig. 72, "

1 o,

" 31,

" 29,

' " 44

" 75, "

78,

Plate X.

Plate XXIX.

Pig.

28,

43

Fig. 70,

78,

Plate XII.

" 77,

73,

Fig. 30,

38,

52

Plate XXX.

" 40,

40,

54

Fig. 79, "

7S,

Plate XIII.

" 7S,

78,

Fig. 42,

" 41,

Plate XV.

41,

3S, '

52

Plate XXXI.
Fig. 80,

" 81,

7>,
78,

Fig. 4S,
" 40,

44,

46, '

5S
00

Plate XXXII.

Plate XVII.
Pig 53,

41,

5S

Fig. S3,

" S2,

78,
78,

" s*,

41,

" 58

Plate XXXIII.

8,

33, '

47

Fig. 81,

77,

XVIII

" S6,

78,

Fig.

3 J,

< « 48

Plate XXXIV.

Plate XIX.

Fig. 87,

70,

Fig. :/■,,

40,

" 63

" 8S,

82,

66

7t
69
67

74
6.5

So
85

S2
91
91

82
91

91
SO

91
91

91
91

91
91

91
91

92
95

XVI

NOTE.

Eng.

Ed.

Am. Ed.

Eng

Ed.

An, E.I.

Plate XXXV.

Plate LXI.

Fig. i

60, boo page 91

1'ii.'. 130, page

120, gee page 133

Plate XXXVI.

" 132,

120,

" 133

Fig. 90-fll "

83,

98

" 133, "

12o,

"

" 92,

83,

96

Plate LXI I.

Plate XXXVII.

Fig 134, "

126,

" 139

Fig. 93,

79,

' " 92

" 135,

120,

ii

" 9,

37-S3,

" 51,96

Plate LXIII.

PLATE XXXVIII.

Fig. 136, "

124,

"

Fig. 94,

83,

96

" 137,

124,

" 137

" 13S, "

122,

" "

Plate XXXIX.

Fig. 97,

79,

' " '.' 2

" ,39' "

120,

" 133

" 9S,

118,

" 131

Plate LXIV.

Plate XL.

Fig 140,

125,

" 133

Fig. 99, "

106,

" 119

" 141,

126,

" 139

" 100, "

106,

" 119

Plate LXV.

Plate XLI.

Fig. 1 13,

134,

" 146

Fig. 103,

105,

' " 118

" 142,

l-;,

" 139

" 141, "

134,

" 146

Plate XLIII.

Plate LXVI.

Fig. 105} "

12-3,

" 139

Fig. 145, "

134,

" 146

Plate XLIV.

Plate LXVII.

Fig. 109, "

28,

" 43

Fig 146, "

132,

ii ]U

" 109, "

115,

" 128

" 14S, "

132,

" 114

Plate XLVI.

" 149, "

132,

" U4

Fig. Ill, "

112,

" 125

Plate LXVI1I.

• " 112,

112,

" 125

Fig. 150, "

132,

ii 1U

Plate XLVII.

" 151,

131,

" ill

Fig 113,

112,

" 125

" 152, "

131,

" 144

Plate XL VIII.

Plate LX IX.

Fig. 115,

111,

" 12.)

Fig. 153,

137,

" 149

" 114,

112,

" 125

" 154,

132,

" 144

Plate L.

Plate LXX.

Fig. 117,

114,

" 127

Fig. 156, "

13S,

" 150

" IIS, "

114,

" 127

" 15S, "

142,

" 154

Plate LI.

Plate LXX I.

Fig. 119, "

114,

ii 127

Fig. 159, "

14S,

" " 159

" 160, "

14.3,

" 159

Plate LI I.

" 161, "

US,

l.V)

Fig. 120, "

114,

" 127

ii 102) "

148,

" 159

Plate LI 1 1.

" 163, "

14S,

" 159

Fig. 121, "

115,

" 128

Plate LXXII.

Plate LIV.

Fig. 163-1 72, "

152,

'• " 163

Fig. 122,

115,

' " 12S

Plate LXXIII.

Fig. 173, "

153,

" " 164

Plate LVI.

Fig. 124,

114,

ii 127

Plate LXXV.

Fig. 178,

156,

"

Plate LVII.

Plate LXXVII.

Fig. 125,

114,

" 127

Fig. 183, "

157,

" " 16S

Plate LX.

Plate CX.

Fig. 129, "

117,

" " 130

Fig. 298, "

347,

" " 354

Plate I.

FIG. i. — Simple arrangement for warming an object under the microscope. It consists of a copper
plate (c) with a central orifice which is cemented to'a common object-glass. From the edge of the
plate a copper rod (g) projects, the end of which can be heated by a spirit lamp. p. 6.

FIG. 12.— A similar but more complicated apparatus. The copper plate 6 is square. The rod e
projects from its under surface (upper as seen in the drawing), and fits in a groove cut in the glass.
The groove ends in a hole into which the pin d fits.

FIG. 2.— Strieker's warm stage (simple form). It consists of a block of black vulcanite about 3
inches long by VA wide, and % inch thick. The central chamber (4) is closed below by a glass plate,
and surrounded at the top by a perforated copper dish («), the orifice of which is of the same size
as the chamber. The chamber is cylindrical. The cistern of the thermometer surrounds the cham-
ber, as shown by the dotted line Id). Its capillary tube lies in a trough, one side of which is
formed by the back of the block and the other by a metal plate screwed on to it, the form of
which is shown in the figure. The tube (r) leads into the chamber. A second tube leads from it

through tin- proji ctinj Ilic arm shown at the tup of the figure. This arm, which is of one piece

witli the disk In), is of such size that the rod, tig. 13, fits on to it. By means of this rod the chamber
is heated in the way already explained, In experiments with gases the gas enters by c and passes
out through the projecting arm. p. 14.

FIG. 13.— A rod <7) Intended to lit on the projecting arm of fig. 2 by means of a spiral (/). It
answers the same purpoM al ';/' in tit-, t. A ilmllar but much lighter rod is used for fig. 12.
fig. 16. object rapport "i I measuring finches by 1, with central gas chamber a,

. ,. 1. 1, . I hi block when in use is fixed with putty on to an
ordinary object-glass, and the chamber clo»ud .it the Urn with a cover-glass.

Plate II.

FIG. 3. — Strieker's warm staee. In the vessel ABC the water is maintained at a constant level {indicated by the
dotted line), and at boiling temperature. A, supply tube ; B. waste tube ; 0, tube leading to the stage ; D, tube by
which the hot water leaves the stage, terminating in a conical dropper, E ; F, funnel for collecting the drops which
fall from E; G, waste. The rate of flow is determined by varying the height of E, by means of the sliding screw ou
which it is supported It admits of more exact adjustment by means of a fine screw which works in the axis of the
vertical column, on which the escape tube is supported. This column is firmly fixed in the stage of the microscope ;
its axial screw terminates above in a milled head, K.

FIG. 4.— Capillary pipette, p. 11.

Fig. n— A similar stage by Strieker, in which the chamber b is warmed by a voltaic current, //are two

topper plates u, which Strieker's electrodes, represented in Bg. '., an applied, .■ a platli wire by which these

two plates are iii communication. It coils round the obtern "f the thermometer d. The electrodes are in connec-
tion with the opposite pules of a suitable battery, the elements ol which mu>-t present a large surface.

PtATE III.

FlO. s.— Carbonic acid apparatus. A. Bottle containing hydrochloric acid. M. Bottle containing fragments of
marble on a stratum of broken glass. V. Wash-bottle. H. Object support, fig. 16. G. T-tube which communicates
with the gas ai>pajatus by the tube F, which is guarded by a clip, and in the opposite direction with H. By its stem
it is in direct communication with the mouth of the operator by a tube on which there is also a clip. When the
first clip is closed, carbonic acid collects in M and drives back the hydrochloric acid into A ; a current of air can
then be drawn through G and H. If the clip on the mouth-tube is closed and that on F opened, carbonic acid
passes through H. p. i6.

Via. &— Microscope stage on which the object-glass is held ill position by Strieker's electrodes. Each electrode
■ i by being screwed Into aii ivory knob which is let into the stage plate of the microscope. The electrodes
are connected (with the Interposition of a key) with ti.e secondary coil of a Dm Bois Beymond'e induction appa-
ratus. The key i- i' pi' 'lit. 'I open. The upper surface of the object-glass is covered with tinfoil, leaving a apace,
ft, for the reception of the object, p. 17.

Plate IV.

FIG. ii.— Support for the study of the circulation in the web of the frog. It must be so arranged that the large
hole is just opposite the stage aperture of the microscope. {See description in text, p. 42.} It may also be used for
the study of the tongue. For this purpose half of a ring of cork must be fixed with brass pins round the hole on
the side next the end of the board. To this cork the cornua of the tongue may be attached.

FIG. 20. — a A b. Injection cannulas, actual sizes.

Fig. 21.— Section knife. In the left-hand corner transverse section of the blade.

Fro. 18,— Nozzle of injection syringe, actual size.

Fig. 19.— Support for mudying the circulation in the mesentery of the frog. /v. Board on which the frog lies.
C. Glaus dink on which tin: mesentery red 6 TrOB b tm tbe reception Of the coU Of intestine, d, Object-glass
covered with cork. [In the text, p.' iu£, 0 and c are transposed,]

Plate V.

FIG. 32.— Common large colourless corpuscle of the newt, a to h. Successive forms assumed by the same
cell in the course of an hour, in a preparation enclosed in oil, without the addition of any reagent, p. 3. (Hart"
nack: Ocular, No. 3; Objective, No. 8.)

Fli;. 23. — A granular corpuscle in the same preparation, a to h. Successive forms assumed by the same cell
in the course of fifteen minutes, p. 5. (Ocular, No. 3; Objective, No. 8.)

O Q

FIG. 24.— a and b. Coloured bl ol the newt, after the addition ol - per cunt, boracic acid.

idiowing tb 1 - Coloured corpuscle ol human hi 1, after the additl 1 i~ 1 cent, tannin

■olntion, i, Co] 1 corpuscle of newt's id 1, ai'ti-i ihf aiiditioii of diluted

with water, and then ■objected to the action ol COa. ,/'. The same, a small

CO It had ■ endered pale by treatment with water. </. Colourless

dilute acetic acid. 7«. Colourless corpuscle of human blood, after
the addition of dilute acetic acid, pp. 13-15. (Oc, 3; Obj., 8.)

Plate VI.

FIG. 25. — Oil preparation of human blood, as observed on the warm stage. A colourless blood corpuscle is
seeu, showing the changes of form it has undergone in twenty minutes, p. 9. (Hartuack: OcuJ., 3; Obj., 8.)

Pi<; 7.— Varlotu tormi of epithelial oelli fr <.m the trachea "f test, tttt 1 of bichromate

of |».U»I. '. to th« left, p. -.1. Ill,-, i, Obj., 8.)

I'LATE VII.

FIG. 26.— Epithelial cells from the urinary bladder of a
rabbit, after maceration in solution of bichromate of potash
p. 27. (Oc, 4; Obj.. 8.)

m!k

'-■;i

',':,/

J9B

Via. 27.— Epithelial cells didged cells) of the rote malpigliii from a pjiuted condyloma, macerates in sjlution
of bichromate of 1 Ua are in various stages of division. (Oc, 3 ; Obj., 8.)

I

1 ■' the Jni'l<ll>! I: .lit . |.i thtl I UKl froll

Obj., h.)

vertical action 01 tbt

Plate VIII.

Fl<i. go.— Abdominal surface x,t centrum tendinenm of rabbit, slightly coloured with silver, a. Endothelium
of the seros* where no lymph vessel is seen. b. The same, showing an interfascicular lymph channel under-
lying the endothelium, in which a capillary lymph vessel runs. c. A "stoma" (?). pp. 29, 112. {Oc.,2; Obj., 4.)

.

I

m

FIG. 31.— Pleural surface of centrum tendineum of rabbit, more strongly coloured with silver, a. Dark silver
lines of the interstitial substance of the endothelial cells ; 0. cell substance ; c. nucleus. (Oe., 3; Obj., 5.)

Via. 32,— The iome aa fig. 30, kUH more Intensely colotued. (Oc., \\ Obj., 71

Fm. 33— Omentum of guineapig treated with silver. A. One of the principal trabecular, containing blood
vessels and fat cells, n. Fenestrated portion, the trabecular of which are covered with flat endothelium, p. 33,
where it is referred to as fig. 8. (Oc, 3; Obj., 7. Tube of the microscope not drawn out.)

•

^

torn ol

the endothelium which 00 | rah 1 li [8>. 11 re and there cells at in which have germlnatlre

characters; ami branded cells, a. Meshwo'-k of trundles of fibrous connective tissue, p. 29.

Plate X.

^

FIG. 35. — A similar preparation ir,..Lu the same omentum as fig. 34, showing groups of germinating endothe-
lial cells amongst the ordinary large endothelial elements which cover the trabecula (6).
(In Figs. 34 and 35, Oc. 3, Obj. 5. Tube half drawn out.)

/»>

x^%-.

Yv. -j, 11. .11 of the teptnm ■ •/ tbi eUterna IpmpJtatiea magna In a, Bndo>

uumte ot peril •!" i mrtace having germinating character!, fc. A tree trabecula projecting above t/..-

rarfaee, severed tbeUonj t Pigment celli. p [Oi Obj., 8, Tube do! drawn

Platk XI.

FIG. 38. — Bud-shaped structure of uiesogastriuin of frog, treated with silver, covered with ciliated polyhedral
germinating endothelium. In the ground-substance of the bud-shaped structure are groups of young amoeboid
cells; and in addition to these are vacuole cells beset with cilia on their internal surface— i.e. that turned
towards the cavity of the vacuole. There is also a large vacuole cell, the wall of which has become changed
into endothelium. (Oc, 3; Obj., 8.)

7.— Stiver preparation of fenestrated portion oi anterior mediastinum in the 1 ri ben germtnatli

Obf., 7-1

Plate XII.

—Horizontal prepara'ion of cornea of frog coloured with chloride of gold, showing the network of
branched cornea corpuscles. The ground-substance is completely co'ourlesB. p. 40, referred to as fig. 10. (Oc. 3;

obj., a)

iX

$m&-< ■rV I

1. ( malty$tem). 1 place

1 in wen ; in two othei 1 11 uwUcolai

1 1 !■> which sonnacl the

(0 Obj., /. Immenion.)

Plate XIII.

FIG. 42.— Membrana nic titans uf frog, treated with
chloride of gold. a. Branched pigment cells. 6.
Unpigniented portion of the body of the cell.
il. Depigmented process. c. Nucleus of pigment
cell. e. Ordinary unpigmented branched flattened
cell. p. 41. (Oc., 4; Ohj., 10; immersion — reduced to
11 ilf.)

FIG. 43— Surface of chronically inflamed me-
sentery of ape. peucilled ana treated with silver.
Canalicular system : Migratory cells are seen
upon the flat branched cells, which, on account
of their nuclei and size, are probably not to be re-
garded as colourless blood corpuscles. (Oc, 3;
Obj., 8. Tube not drawn out.)

FIO. 44.— The same preparation, showli the canal , , . ailed with fat globules

m of cornea of . I first with lunar caustic, and afterwards placed

I 11 I" .1 oul l>y a dark

granular pi 1 that shown In Bg. .. I l ■■■ on ■ 1 ich other as the

photograph, p. (0 Obj., 7. Tube not drawn out.)

Plate XIV

of infni.-orl.ital fossa of rabbit, freshly prepared in serum, a. Bundles of
connective tissue. I. Flat branched cells, c. The same seen in profile, d. Cells of doubtful character

1 i on the lurface. i

luictly (ibrill ,i

Plate XV.

V

PIG. 43.— The same cells as in fig. 47 being converted into fat cells, p. 44. (Oc, 3; ObJ., 9 ; immersion.)

■ ol gravid uterus of sow, maceialed in bichromate of po1
Blanched cells, more or loss spindle-shaped. b. Bundles of connective tissue, p. 46. (Oc, 3; Obj., 8. Tube
lialf drawn out.)

, tal peritoneum from thelnmbai region of a rabbit with chronic

tive tissue COt]
ObJ., 8.)

Plate XVI.

i i [ omentum of rabbit, pencilled and treated with silver, a. The flat

branched granular structnn . fch b nuclei art narplj

defined, and In .,,.!, &. Migratoi

free, irhile othen grow '">*• ""|" the flat celJ ol the canalicular syi ben latter, the

formation of a vacuole La seen at c. d. II the wall "f which i ad Into endothelial

[Oc, 3 ; ObJ., 9, f in i<

Plate X.

FIG. 35. — A similar preparation from the same omentum as fig. 34, showing groups of germinating endothe-
lial cells amongst the ordinary large endothelial elements which cover the trabecula (b).
(In Figs. 34 and 35, Oc. 3, Obj. 5. Tube half drawn out.)

, . preparation ■•( the leptnin ol tbi eliterna lymphatica magna In 1 1 Endo

having germinating character*. i>. A bee trabecula projecting above the
covered with germinating endothelium, 0 Pigment culls, p. -•«. (Oc, ;; Ob]., 8. Tube not drawn

Platk XI.

FIO. 38.— Bud-shaped structure of mesogastrium of frog, treated with silver, covered with ciliated polyhedral
germinating endothelium. In the ground-substance of the bud-shaped structure are groups of young amoeboid
cells; and in addition to these are vacuole cells beset with cilia on their internal surface— I.e. that turned
towards the cavity of the vacuole. There isjilso a large vacuole cell, the wall of which has become changed
into endothelium. (Oc, 3; Obj., 8.)

,

I rated portion oj aterioi mediael i In tbe cal e ten prminatfoa

101 ial] ">■ ■ ■ Obi., 7->

Flate XII.

-Horizontal prepara'ion of cornea of frog coloured with chloride of gold, showing the network uf
branched cornea corpuscles. The ground-substance is completely co'ourless. p. 40, referred to as fig. in. (Oc 3;

obj., a >

1 a. Canallcul 0 analiyittm) h place

■ branched, Battened conn 1 i» wen; in two other ar< lacuna ol the canalicular

corpuscle*. <f. Migratory cell i Branched channel) which connect the

( the canalicular eyetei dark p |Oi Ob] 1 1 lei Ion.)

Plate XIII.

-^

Fig, 45.— Ordinary fat cells of a
fat tract in the omentum of a rat.
(Oc, 3; Obj., 7)

FIG. 42.— Menibrana Qictltane of frog, treated with
chloride of gold. a. Branched pigment cells. 6.
Unpigmented portion uf the body of the cell.

d. Unpigmented 1 :ess. c. Nucleus of pigment

cell. c. Ordinary unpigmented branched flattened
cell. p. 41. (Oc, 4; Obj., 10 j immersion— reduced to
about half.)

FIG. 43.— Surface of chronically inflamed me-
sentery of ape, pencilled an A treated with silver.
Canalicular system : Migratory cells are seen
upon the flat branched cells, which, on account
of their nuclei and size, are probably nut to be re-
gar ltd as colourless blood corpuscles. (Oc, 3;
Obj., S. Tube nut drawn out.)

' Uw eanallculai ,yrt< m Oiled with Cat lol

irda placed

rim tm •■ :""!''1 ■ 1 1

(noolu p md that thown tberaathe

oi>j.. 7. Tube Dot 'Ira

Plate XIY.

FIG. 46.— Gelatinous substance 01 infra-orbital fossa of rabbit, freshly prepared ill seiiim. a. Bundles of
connective tissue, b. Flat branched cells, c. The same seen in profile, rf. Cells of doubtful character

' from the surface. They appeal rithoblonj

tinctly ilbrili ■■ b then figure*.)

Plate XV.

PIG. 40 — Portion of submucous tissue of gravid uterus of sow, maceiated
Branched cells, 1 ped b. Bundli oi connective tissue.

hall drawn out.)

bichxoiuate of potash. *r.
46. (Oc, 3; Obj., 8. Tube

I

11.. 1. , 1.

Plate XVI.

if

I [ omentum of i obit, pencilled and treated with silver, a. The Sat

i ■ b finely granular . I racl tiri : their am li I are barplj

of 'li\ Idlog. /.. M l| rat ore of it bich are

free, while othen grow out from ili.r flat celli of the cai m, i one of the latter, the

formation ..f a \ i U lis roll of which i, alreadj changed Into endothelial

elemeuU. (Oc., '\\ oi.j., 9. Inn

Plate XVII.

I 11 ti. I

Fig. 52.— Caudal tendon of a young
treated with silver. The spaces occup
cells are clear, while the intercellula
stance is seen as dark lines.

itcr.-titial sub-

FIG. 53.— Similar pre] aration from a full grown
at. p. 44- (Oc j ; Obj., 7.)

(.1,. 54.— Caudal tend >' young rat, treated first with dilute acetic acid, and then with chlori

the arrangement, form and structure of the tendon cells, p. 44. (Oc, 2; Obj., 8.)

--Tniiisvi-r-e aecMon of tendon from

at 250.)

m of 11
Bundli ■ ■ !

Plate XVIII.

FIG. #.— Network of elastic fibres from the fresh mesentery of i
a the network is more superficial than in 6. p. 34. (Oc, 3; 01>j.,

rabbit, treated
7)

itll dilute acetic acid. I I

PIO. 57.— Longitudinal section ..f Intervertebral cartllag. -1 thi tall of a rabbit. Tb< preparation was

■olonied with chloride <>i gold, then macerated in dilute chromic acid, and hardened mi alcohol. '/. Clear

irtilage. " Border between hyaline and (e) 1 1 1 cartilage Heri thi (ro 1 ubsti ■

tendon) of bund 1. ae. instead ■■< flai tend ells, an otheri whichtt

a ol 1 1. ni 1 and Iructnral ehajrac

led a* cartilage cells. "*,

Plate XIX.

"^SSft^^fc

^

<?\

piphysig in the neighbourhood of the diaphysis of the femur of
;i human ■ till covered with hyaline cartilage, a. Superficial

portion of hyaline cartilage. 6. The . i, with lai i ubatance of which ate is

e. d. Fine fibrous tiaaue, rich in cell elements and bl 1-

work of Hie bone trabecules, p. 49. (Oc, •.; ObJ.,7.)

Plate XX.

io>:M?i:

»)i^.'«** ,t:

i epiphysis of the same preparation. \ and B. Porehyalli artlloge ■ ■( the Joint.

■ •■•< ■ "i I.e., where U Hi b i I diminished-

,\t i> the cellelen

order peripherally ; the Intercello U farther dixoli i Into Don j trabe

embryonal bone I I ! i ! e apace*, which answer to the cartllagi

oayadM <rf the previous layer D.hs ,,. ,.,. (0o.,4; ObJ., j Tube not drawn

out.)

Plate XXI.

!>Vi

1$i^iSm

QW:*f$.

^■■«/.

PIO. 60.— Transverse flection ot the dlaphysia of thefei anUma \, macerated with chromic acid, a. Con-

cc-utri«: |.-i '■ urn >> I: lies nf connective tissue uj' the periosteum which run

longitudinally, cat across, c. Loose la] Lnflei oal periosteum, rich is blood-vessels and young cellsi which is in

on into ''. the Arab 0 its rich medullar; tissue. The latter alum mis in

md and between the trabecule. The cells of the loose

tissue ut 1 I'cll (1 ■■■•■> Tii I-m) lumul in the bone tra«

becukv, «-.*■■ trabecules, and with those in the medullary tissue. In;*
similar manner tin I periosteal layer (more or less distinct fibrous con-

nective tissue) are continuous with that of tin il», and of the spaces between them* p. 50, (Oc.,3i

ObJ.,5. Tuhhah drawn

Pl.ATF, XXII.

<- &r£?

^y

'2 if

S>, . o'

^rv-r^ : , lip

k'^'.* ,1. XI. P.. ... ^jf ':'« ,- , 1

FIC. 6r.— Vertical section of the parietal bone of tlie sknll of a child, macerated in chromic acid, showing the bone

Izabecuta of the diploe. a. B i trabecule, covered bj [e)o teoblasts. e. Medullary tissue (in outline), d. Spaces,

artificially occasioned by the yielding of the lamella! of the bone trabe.iike. p. 50. (how power.)

Plate XXIII.

wdmr

r 5 $u# 1

'

1 ; i linal bi piphynitj of the

1 I oi a rabbli i rated in chromic

acid. a. 1 M b Iht dulla, a'. System <.f

; an Uled up
«ith medullar; tl ue, i ii b to ci Uulai elemenj i he ■
element! mednllary celli are in continuity wiil

■■ hich have a coluuinai arrange*

era [es begin

to enlai ■ transii Ion Into the tubular

L'fTllli-

ii.ii.-. The intercellular nibstance which bounds the

Ca] I, p. .. I LOU i N I

Plate XXIV.

FIG. 63.— Longitudinal section of muscular coat of fallopian tube iu a sow. a. Connective tissue trabecule- which
form the septa between the bundles of unstriped muscular fibre, b. Transverse layer of unstripcd muscular fibres,
cut across, c. Connective tissue which contains the large blood-vessels, and separates the transverse muscular
layer 6 from the longitudinal muscular layer d. c. Outermost, or serous, covering of the fallopian tube. p. 53.
Oc, 3; Obj.,s)

FIG. 64.— Fresh isolated preparation covered in serum from the tail of a rabbit, showing the transition of trans-
versely striped muscular fibre into a connective tissue bundle, i.e., into tendon, p. 61. (Oc, 2 ; Obj., 5.)

\

h

/,

0

W*

a.

w

Fig. 15. — Diagram t,,, llhutrate the ■
a ray of lighl transmitted tin a
fibre. 18m

'lated nil unlaj Sbrt ■>< Bydrophllu
a. Muncular labetaace. (. Entering non-medullary nerve fibre, c. Doyore' i" Ii

\ with nans\ 111 11:
p. St. Oc, (; Ohj..?.)

Plate XXV.

Fir;, 66.— Section oi an injected muscle of the extremities of a rat, showing the distribution of blood-vessels in the
transversely striped muscular tissue, a. Arteriole, b. Vein. d. Capillary between them. c. Muscular libre with
transverse striae. (Oc, 3; Obj., 5.)

FIG. 68.— Isol Oed muscular fibre with transverse strias from an oblique section of the tougue of a frog coloured
with chloride of gold. The muscle cells are distinctly shown, and three are visible, each containing several nuclei.
p. 61. (Oc, 3; Obj., 8.)

' "' ""■ ,"'11 '"*• Hue of a cat, macerated In bichromate of potash. The

nUataoce of the cell 1 longitudinally striated, the nuclei ore staff-shaped and well defined, p. 52. (Oc.,3; obj., 7.)

Plate XXVI.

PIG. 70.— Three ganglion cells with spiral fibres in a preparation of the same kind as fig. 69. Each ganglion
cell exhibits a nucleated capsule, p. ?2. (Oc, 4; Obj., 8.)

FJC. 69.— Group of ganglion cells of ■ a me trunk of the urinary bladder of a rabbit, Isolated

a coloured in gold and then treated with dilute acetic acid. p. ja. (Oc, 3; Obi -1

Plate XXVII.

Fir;. 73.— Horizontal section of cornea of rabbit coloured wit'i
chloride of gold, showing the superficial intra-epithelial i.etwork
of fine non-medullated nerve fibres, seen from the surface.
(Magnified 3oodiam.)

PM 71 —Ganglion ce't bom teasel preparation of spinal cord of olf, mart-rated in bichromate of potash,
i 11 cell may be called bipolar; its distinctly flbrillated structure, and tin- large nucleus enclosed in

a distinct men, 1. ran.-, with its large nucleolus, are specially to be noted, p. </,. (Oc., 3; ObJ., 8.)

Horizontal preparation of cornea "f rabbit coloured in (raid, showing a portion of the sub-epithe-
lial nerve-plexus, with a, its coarse non-mednliated nerve trunks, an 1 i, sma'l bundles of non-medollated
nerve fibres, p. 7?. (Oc, 3; Obj., 7 )

Plate XXVIII.

FIG. 72.— A many-branched ganglion cell from the same preparation as fig. 71. All the processes are
branched, with the exception of a tingle pale one— the axis-cylinder process, which is also distinguished from
the others by its more delicate lungitudinal streaking, and the absence of any granular substance between the
stripes, p. 69. {Oc, 3; Obj., 8.)

4 r-

Ki'. 7 ,. -Horizontal

-■ - propria a. Coai e oon-inedullated uerve trunk.
Magnified y>> dlam.)

. blorldd r,i gold, ihowing ti

b. Fine null-Jin .liill.Ltcil nerve fibruH.

if the

Plate XXIX.

-Horizontal section of cornea pi rabbit coloured in chloride of gold, showing a, the coarser non-
uiedullated nerve trunks of the sub-epithelial plexus; b, the fine non-medullated nerve fibres; and c, tufts
of the finest nerve fibrils, p. 78. (Magnified i'jo diain.)

^C~

r

W \ '<u

I taerbach'i pl^xuw »>( muU Intestine ><f human tetui <-.,i<.ur<-<i with gold. The i

idi ap '-f trabecnUe "f ration* thiol m 11 ■ In Largi plncold

Vaclena-lika elementi (unformed ganglion cell*) and ganglion cell* are embedded in tin- plexus, the whole oi

Wbiefc i- frri<:l'.-.nj in a nncleati Oi -■ ; ObJ., 7 i

Plate XXX.

PIG. 79. — Horizontal preparation of cornea of rabbit coloured with chloride of gold, a. Larger, b, smaller
non-medullated nerve fibres ; and c, the smallest fibrils of the sub-epithelial network, p. 78. (Oc„ 3; Obj., 10.
Immersion.)

btaneblngi
U*u»d nerve

Horizontal lection "f cornea oi 1 ired in chloride <>f gold, sin 1 wing the BUb-epH delial nerve

". Coarse non-medtiUated nerve trunk oi the sub-epithelial plexus, b, Fine, and c finer non-meduJ
fibres oi the subepithelial ui >diam.)

Plate XXXI.

FIG. 8o.-Horizonta1 preparation of cornea of guineapig, showing the superficial intraepithelial network of non
medullated nerve fihres as seen from the surface, p. 78. (Magnified 300 diam. ; reduced.)

PlO. 81.— Horizontal preparation of cornea of fro I. showing the dl trih

ihi r .i port 1 'i uea. a. Com e non medullated 111 rve I

■ order. '■ and c, Non-tnedullated oerre fthrei of the second and third order, p, 7 :- (Oc, 1: OhJ.,7.)

FIG. 84. — Horizontal preparation of the same kind as fig. 83. showing the deepintra-epithelial network of fine non-
medullated nerve fibres viewed from the surface, a. Contours of deepest cells of anterior epithelium, b. Nerve
fibres, p. 7 [Oc, 3; 01)]"., 7. Tube not drawn out.)

Fig. 85.— Horizontal section of cornea of rabbit coloured with chloride of gold, exhibiting more swellings than in
fig. 73, which are due either to the mode of preparation or to the appearance of foreshortened nerve fibres passing
upwards or downwards into other layers. (Oc.3; Obj.,7. Tube half drawn out. }

I col hlorlde of gold, a. Large non-medullated nerve

trunk", im ■ ""' 0. Nerve fibres of the third order. I cornea

corpunelen. p 8.)

Plate XXXIV.

'*%r?P:' f*

FIG. 87.— Horizontal preparation of nictitating membrane of frog in chloride of gold, showing the distribution of
non-inedullated nerve fibres to, a , capillary blood-vessels. 6. Coarse non-medullated nerve fibres giving off fine
branches c, which form a plexus around the vessel, p. 79. (Oc, 3; Obj., 8.)

ted with cbioridi <<t gold a Large trunl at medullar d nam abree, b. a tingle

. \,,,i.,,,mii belonging to the mtmbrwna propria

of the u.enentery. /. Nucleus of fine non-raedalUted nerve fibre g. Capillar] bl < P (0o.,3; ObJ.,8.)

Plate XXXV.

FIG. 89.— Horizontal prep .ration of (lit tail of the tadpole treated with chloride of gold. a. Capillary blood-vessel.
0. Coarse non-medullated nerve trunks, a Flnenon medullated nerve fibres, d. Minute fibrils of the ultimate sub-
epithelial network, in which cells and nuclei, e, are scattered. In one part of the preparation the surface epithelium
is left, which shows the relative size of t!ie meshes of the sub-epithelial network, p. 80. (Oc., 3 ; Obj., 7. Tube not
drawn out.)

Plate XXXVI.

PIG. 91.- Horizontal section of tongue of frog treated
with chlorideof gold, showing the distribution of non-
lnedullated nerve fibres to a capillary blood-vessel: a.
Capillary vessel. 6. Coarse non-niedullated nerve fibres,
c and d. Fine non-medullated nerve fibres funning a
plexus which surrounds the vessel like a sheath, d.
Non-inedullated nerve fibres in the wall of the vessel
p. 83. (Oc.,3; Obj.,8.)

PIO. 90.— Mesentery of frog prepared in chloride of
bowing the distribution of non medullated
nerve fibre* t.» h capilli

non-inedullated nerve Bbre giving <'ir ftnei branches,
which fonn a plexus round rb<- capillary. Borne <>f-

Flo. 92.— Tnwuverfte Mction of mocouf membnuieoi vagina "i rabbit pre] id with

the plexuses of non-medullated nei ol unstriped muscular fibre, p.

Obj., B. Tube not drawp oat 1

Plate XXXVII.

FIG. 93. — Horizontal preparation of the base of a gland of the membrana nictitans of the frog stained with chloride
of gold, showing the distribution of non-med dilated nerve fibres to the eland, -a. Membrana / roj via of glan/I,
6. Coarse non-medullated nerve trunk, c. Fine non-medullated nerve fibres, which form a plexus round the gland.
From these fibres, fine fibrils proceed, which penetrate between the epithelial cells, d, of the gland, p. 79. [Oc.,3;

Obj.,8.)

■ .
Many «f thete contain nuclei

utiofi of non-medul*
. . In ..!, two capillarii Clrculai mu culai flbn
■ ■ 1 1 ■ thi in terra v alar 1 11 Coara non-medul-

d. Pine t

ObJ.,7.)

Plate XXXVIII.

ntal sect.:. .11 of mucous membrane of vagina of rabbit stained with chloride < : .
distribution of the lion med tinted nerves under the surface epithelium, a. Coarse nerve trunks b. 0
the deepest epithelial cell . c. Non-niedullated nerve fibres forming a plexus Ii eta maybe

seen, which, leaving tlie di identified with ti.e interstitial substance of the deepc-t epithelial cells.

Oc, 3: Olij., 8. I •■ ont 1

1 irith chloride of gold, giving U
. . with the plexn Bon-medallated nerve 8 in the adventii

m'lar fibres in the adveutltu of a large artery. (Oc.. 3

oy.,7.)

Plate XXXIX.

PIG. 07.— Horizontal preparation of nictitating membrane uf frog, coloured in chlori<le<>£ gold; showing the- distri-
bution of tlie non-medullated nerve fibres under the epithelium of the posterior surface, a. Larger, 6 smaller
• • smallest non-medullated nerve fibres, p. 79. (Oc, 3; Obj., 8.)

mtlon ol the bli

layer. '/ Medullar] lajri r. ft Largi '"' 1 I

Plate XL.

a

FIG. loo.— Transverse section of an artery from a
vertical section of the skin of a guineapig, coloured
with gold. a. Lumen of ihe vessel. 6. Endothelium
seen in profile, c. Intima. d. Circular muscles,
e. Adventitia. /. Cellular elements of adveutitia.
p. 106. (Oc.,3; Obj., 7.)

PIG. 99.— Longitudinal section of a branch of the pulmo-
nary artery, from the lung of a guineapig, the bronchia; of

which were injected with dilute chromic acid. a. Intima.
6. Circular layer of unstriped muscular fibres, cut across*
c. Adventitia. p. 106. (Oc, 3; Obj., 7.)

FIG. 102.— A capillary
blood-vessel, the ca-
vity of which is extend-
ing into a branched
cell. (Oc, 3 Obj., 7.)

Fin. bu*— Preparation from tbe normal omentum oj a rabbit, fin t pencilled and then treated with silver, showing

the development of young capillaries, a. Capillary blood-vessels, i>. Capillaries only Just hollowed out; this pro*

.1 the branched conned Lve tissue cells, d, which are Ln relation with the capillary

wail. c. Vacuoles In the branched cells. 0, Branched cells of the ground ubstanccC f, Migrator) cells. (Oc.,3

obj.. 7.)

Plate XLI.

Flo. 103.— Omentum of rabbit coloured In silver, a. One of the larger arteries, shoving the spindle-shaped endo-
thelium and transverse muscular fibre. I>. One of the larger veins, showing the endothelial elements, which are not
■o elongated a* in the artery, 0. Endothelium of one oi the surfaces of the membrane, p. 105. (Oc, 3 ObJ., 5.)

Plate XLII.

MO, i<v4_— Part of the name preparation as tig. 103. a. Endothelium of one of the surfaces, b. An arteriole
bnoohing riesd, which are continued into a capillary vein c. The endothelium ia clearly shown in

all the vensels. (Oc, 3; OhJ., 7 1

Plate XLIII.

F!<;. 105. — Vertical section of mucosa and sul. mucosa
of injected stomach of a rat, showing the rich capillary
system of the mucosa which contains the peptic glands.
p. 126. (Oc.,3; Obj., 2.)

PIG. 107.— Horizontal preparation "f mueona inenibn I

Injected uterus of gnlni 1 ;|1 dense

capillary meabwork, the lb, and tin- Mill deepei

[0 ■., 3 ; 0I1J..2.)

FIG. 106. — A fat tract from the omentum
of an injected jiiii" ii'iL'. a. Artery, b.
Vein. r. Denaeaysti m of capillary vessels
of true fatty tissue. (Or., 2 ; OhJ., 2.)

Plate XLIV.

—Surface preparation of the mucous membrane of the stomach of a rat, injected ; showing the superficial
arteries, the dense network of capillaries, and the deep veins, which are pale. (Oc, 3 ; Ohj., 2.)

WU. loo.— Him* of tubercle fwm the Injected omeftt .fa galneaplg, artificially infected with tub

(chronic inflammation of the MrOUl in. -ml/ran. ... Artery.

b. Vein. Between then to a lieb capillary tyetem, i the dumm of tnberela. pp. s8 and 115. (Oc, 3
ObJ., 2.)

Plate XLV.

Fir,, no — Vertical Bection of injected tongue of rabbit, showing the rich system of vessels with which the
transversely striped muscular substance is provided. (Oc, 3; Obj., 2.)

Plate XLVI.

FIG. in.— Mesentery of frog coloured in silver, a. Ordinary surface endothelium, b. Endothelial cells sur-
rounding a simple true stoma. These cells have the germinating character, are distinctly granular, and are
not flat like those which surround them. p. 112. (Oc, 3; Obj., 5. Tube not drawn out.)

Fl';. ii2.—S'j,tu.rn cltterna lymphatlca magna of frog, coloured iu silver. A. View of peritoneal surface.

B. view of surface of lymph s»c. The »tomat», »ome of irhli ih ue open, ton lUp ed, are surrounded 1 v

IBIIllllnllllQ endothelium, which is ciliated if the subject is a female, p. 112. (Oc, 3; ObJ., 5.)

Plate XL VI I.

Fig. in.— Surface view 01 mesentery, coloured in silver, of :i guineapig affected with chronic [nflam-
,,i : 1 1 i 1 1 1 . ■ i ; . ! [ -, induced tuberculoslB. Proliferation of the surface

an which lurroaiida ■• • rminatlng endothelium. «. True »t a, open.

the endothelium of which is exposed because the Btomata belonging to them are
wide open. c. Proliferating endothelium, d. Ordimiry surface endothelium. i>. 112. (Oc, 3; Obj., 5.)

Plate XLVIII.

*m

FIG. 115.— Peritoneal surface of centrum tendineuin of rabbit, treated willi water and then coloured in silver.
In the middle of the preparation a lymph vessel, !, appears below the surface endothelium, i.e.. the system
of lines of interstitial substance. On both sides of the lymph vessel are tendon trabecular, t. The endothe-
lium which coverd the lymph channels consists of smaller elements. Five true stomata are shown which pass
through the "vertical lymph channels" into the Ij'inph vessel below. Two of the stomata. are open, and
three collapsed; all are surrounded by germinating endothelium, p. m. (Oc, 3; Obj., 5. Tube not drawn
out.)

ai c_

FIC. 114.— Similar preparation, c. A wide lymph vessel which can be seen through the surface endotheliums.
An artery, d, and a nervi through the lymph vessel (perivascular lymph vessel) c, and within

the field of vision are ten distinctly open true stomata 0. The surface endothelium bordering the
germinating, p. 112, (Oc, 3, Obj., 5.)

Plate XLIX.

Via. 116.— Mesentery, coloured in Bilver, of guineapig affected in the same manner as in fig. 113. a. Surface
endothelium, d. The freely exposed upper wall of a lymph sinus, the endothelial marking of which is seen.
On the periphery, however, answering to the free surface of the serous membrane, two distinctly open true
• tomata, 6, are shown. These communicate in an oblique direction with the lymph sinus. On the right a
closed stoma caa be seen. The endothelium, c, which borders the stomata is in germination. (Oc, 3; Obj., 7.)

Plate L.

Fig. 117. — Peritoneal surface of centrum tendineum of rabbit, pencilled and coloured in silver, showiDg the
lymph capillaries of the abdmi'nal serous covering iu the neighbourhood of the large blood-vessels which
pas* through the diaphragm. The sinuous endothelium of the lymph capillaries is distinctly bhown. p. 114.
Oe., 3; Obj., 4. Tube halt drawn out.)

PIO. 1 tH.— Pleural surface of centrum tendin'um of guineapig, pencilled and coloured in silver. A. Lymph
ve-seli of the p'eural side, the larger trunks having iptDdU-lliaped 1 mi ■■llielium, and being provided with
valve*. Only a few capillaries are to be seen — that is to say, few vessels with sinuous endothelium.
B. Principally lymph caplllaiies which run between the tendinous bundles, p. 114. (Oc, 3; Obj., 4. Tube not
dmwu out.)

Plate LI.

9Va. 119.— Similar preparation of ■ rabbit. Bleb netwoik of lymph vessels of tlie pleural Bide. a. Large
• ranks of lymph vessels, having spindle-shaped endothelium and provided with va'ves. h. Lymph capillaries,
c. Lymph capillaries which penetrate deeply, i.e., which bend towards the abdominal s.ile in order to run
i>etwe«-u the bnndlM of tendon. i> m. [Oc, -;; Ohj., 2.)

Plate LI I.

1 ii. ill.-il iiinler water and then bathed in silver,

while an 1 1 u m being carried mi. The l.w,.,. risible in the Bllghtly-ioloured

(found ai dutinet and very ilnuoue tabes, the endothelium ..f which is sharply defined. <i. Trunks of
r/nrpo reeseli ol b. Lymph capillaries which, ai "strahjhl Interfu ciculu lymph . .

run between the ten. Ion ban I to Um abdominal tide. p. [14. (<>• , :; ObJ,, 5.)

Plate LIII.

Pi'.. i2i.— Omentum of rabbit, pencilled anil coloured in silver, a. ArLery. b. Capillary Mood-vessel.
<?. Network of lymphatics, recognized a lariee )>y tbeir sinuous endothelium and the a

Lymphatic canalienll oi the ground ratmance; in most of them the nuclei of the cells contained
in them are se*-n. p. n> (Oc, ^; ObJ., 5. Tube ba'f drawn out.)

Tr-ATE LTV

■Surface of omentum of rabbit, pencilled and coloured In Hilver. allowing the distribution of the
lfin\i\t jeuelB. a. Lymph reaaeU, •bowing their endotbellnm. h. Valve*, c. IuilicateK the position of vessels
eiiel<«u-<l iu a tra/.-t. the de'alll "f which, an well as th*>se of the gr.mnd-sufoHtance '/. are omitted. p. 115.
ObJ., 51

Plate LV.

Flo. 123.— Pleural Bide ef pencilled centrum tendineam of n. guiueapig, in which there was chronic inflain-
matiult of the serous DUMIllUMIM, in eunse4tieaofl of artificially iuduced tuberculosis, a. Lymph capillaries of
the pleural serosa surrmndmx an island of $r jund-suhstance. In the litter is the canalii. ■ ilar system, with
the nucleated flat cells, b, which it contains. These cells, in var.ous pla:es, are seen to lie dividing; and
most of them are branched, e. The Endothelium of the lymph capillaries is distinctly seen in sevir.il places
Vj he in continuity with the cells of the canalicular system. (Oc, 3; Ohj., 7. Tu^e not drawn out.)

Plate LVI.

no. 124.— Pleural side of centrum tendineum of rabbit, pencilled and coloured in silver. I. Lymph capil-
laries showing their endothelium. The system of lymphatic canaliculi, c, stands out sharply from the dark
col ,ured ground-substance of the pleural serosa; in many places the lacuna: of the canalicular system are
separated from each other by mere lines, and a trace of nucleus 1 is to be seen; the placoid cell to which
the nucleus belongs is not visible. At r. the canalicular system is passing ovtr into endothelium of the
lymph capillaries, p. 114. (Oc, 3; ObJ., 7. Tube half drawn out.)

Plate LVII.

<JN

Fni. 125.— Similar preparation t<> flg 124, «. Lymph vessels with valves, paining over Into '<, lymph
cAp'lUrieti. c. Inlands of ground nulieUnce ihowing the canalicular s) stem, p. 114, (Oc, 3; ObJ., 5.)

Plate LVIII.

FIG. 127.— Section oi cortical layer of mesenteric gland of ox, which has been hardened in Miiller'd liquid
and then shaken, a. Capillary blood-vessel. 6. Nucleated cells representing the nodes of the delicate reticulum
—adenoid tissue. (Oc.. 3; Ohj.. 7.)

inentwn ■>( rabbit, pencilled and coloured In silver, a. Lymphatic capillary in the

h .<,.! o( u. an artery, c. Capillary bl 1 vhii h la evidently to continuity with

ti,'- numerous branched eell (arm , d, in the ground thi endothelium ol the lymphatic

capillary U •imilarl) mtlnultjr irltb. thi (Oc, 3; ObJ., 7.)

Plate LIX.

_LkJ

k

fev .1 fl 'Mfjjifg,','t'Jf

FlO. 128.— Centrum tendineutu o! rabbit, Been from the abdominal side. Berlin blue had been introduced into
the peritoneaii] by "natural injection." f>. Straight interfascicular Lymphatics between the bundles of tendon
of the abdominal side. a. Lymph vessels of the pleural side, showing the valves, with corresponding dila-
tttioiM. The 1; Lit lymph vessels are as completely injected as the first. (Oc, 3 ; Obj., 4. Tube not drawn out.)

Plate LX.

-Section "f medullary substance of n ad of ox, which has been hardened in miller's

liquid and then partially shaken. Thi the lymphatic cylinders containing bl 1-vessels, sup

rounded b; i ed lymph corpuscles, bfai One] .,i cell between

tliem. The blank i the trabecule and the cylindei repre en< the Bystem of lymph sinuses, the

lymph corpuscles ol which have for the mostpArl b su bakpn out. p, 117. (Oc, 3; Obj., 8. Tube not drawn
out.)

Plate LXI.

FIG. 130.— Alveolus from a section of lung of rabbit, frozen and coloured in silver, a. Inter alveolar septa
of elastic fibres, b. Epithelium of the alveolus, seen from the surface. The epithelial cells are seen edgewise
on the borders of the alveolus, p. 120. (Oc, 3; Obj., 7.)

FIG. 132.— Section of a lung of a rabbit, injected
through the pulmonary artery. ". Bfancn "f the
pulmonary artery' losing itself in h, a dense capil-
lary »y»teiu. p. 120. (Oj., 3; Obj., 2.)

Fig. 133.— Section of livr-r ol goineapig harflfnH In bichromate of potash, showing tlie cylindrical trabecules

■ Us. The spaces between tb>- cylindrical cell* correspond to capillary blood-vessels. The little

opening* b n-tituent cells of a cylinder are capillary bile ducts cut.across. p.120. (Oc., 3; Obj., 8.)

Plate LXII.

FIG. 134.— Horizontal section of liver of dog, the vena porta of which has been injected, a. Trunk of inter-
lobular vessel, b. Trunk of intralobular vessel, or vena centralis. A dense system of capillary vessels is
between them. p. 126. (Oc, 3; Obj., 2.)

Fin. n?.— Vertical lection >.f liver of 1 1 1. thi portal vein and hepatic it of which aro injected, a. In-
terlobular blood-veeeels. t. Interlobnlai bile d 1 network. a Intralobular capillary i>l<md-veasel«.
a. Intralobular bill 1 ipl larl . 1 . ■ lei "f which are deeply itained with carmine, p. 126.

Plate LXIII.

FIG. 136.— Vertical section of injected small intestine of rat. a. Villus showing its epithelium and dense
system of capillary vessels, which is developed from a central artery d, and terminates in two peripheral
veins, •■. b. Mucosa, c. Portion of muscuZaru externa, p. 124. (Oc, 2; Obj., 2.)

FIG. 137.— Vertical section of a villus of the small intestine of a cat, hardened id chromic acid. a. Streaked
basal border of epithelium, b. Cylindrical epithelium, c. Goblet cells, d. Central lymph vessel, e. Smooth
muscular fibres which lie nearest to the lymph vessels. /. Adenoid struma of the villas in which lymph
corpuscles lie. p. 124. {Oc, 3; Obj., 8.)

.1 iiiif.inii papilla ol tongue "f rabbit, a. Epithelial covering ol papilla?.
b. Capillar; loop ol papilla, e. Ve ell ol the mucosa, d. Vessels of longitudinal muscles, p. 122. (Oc, 2;

Obj., .: .

1 1 . : ., ■ > large bronchus ol human Castas, bom b Lung hardened In chromic acid.

cylindrical epithelium in layers. '«. Uueosa. 0. Bundles '.1 onstrlped muscular fibre, d. Sub-

■1 -int. showing Portion i cartilaginous ring, /. <m the left, an

• through ; on the right, below, » »eln. g. Trnnks "f inedullated oerve liiire out through, h. Section

•il ganglion, p. 1 10 Obj., 4. Tubs not drawn out.)

1 a* rigs. 157 and

Plate LXIV.

Fig. 140.— Two injected follicles from transverse section of Fever's patches of small intestine of rabbit. Out
of the plexus of large vessels which surrounds the follicle, numerous capillaries are developed, which tend
towards the centre of the follicle, and for the most part turn hack so as to form loops, p. 125. (Oc, 3
Obj., 2.)

/

T .'' '• r.'^'p, !'/?(fP\ '., %/ ..,.- •;'■ , >i ;v. ;

Y\<:. 141.— Vertical lectl >t portion ..f Uenm "f dog, baidaned bj chromic acid. «. Villus, showing its

cylindrical epithelium with tbicli basal border. The troma at the villus Menu to I oiely-paetod

lymph oorpusclas; botwi at onstriped muscular ftbre. '-. Mucosa with Lleoerkohnlan crypts.

I Ich the nimmil ol the follicles, ■/. project, bo order to

reach the epithelium oi U .;■,., ... ,,/ „„.,,, ,, which the follicle are olomly packed,

> as to form a Payer' patch lit th. baas of tl Hides the lymph sinuses, «,

mmnd them 010 i« seen. /. Portion of circular muscular layer of the muicuiurit vxurna. p. izf.

Oc, 3; Obj., x)

Plate LXV.

Fig. 143.— From a longitudinal section of the injected kidney of a rat. a. Arterial trunk, i. Venous
trunk, c. Glomerulus, d. Vas afferens of the glomerulus, e. Vas efferens. /. Capillaries which twine round
the convoluted tubes, g. Capillary vessels of the pj-raniidal processes, p. 134. (Oc, 3; Obj., 4.)

FKi. 142— Section, parallel with the surface, at an acinus at the same preparation as fig. 735. a. Into*
lobular aipfUary blood-veueL b. intralobular capillary bile duet c Liver cells, p. 126. (Oc.,3; Obj., 7.) (.see
aluo fig. 135.)

Fi<;. i44.~Froni a kidney of pig Injected from the ureter, ihawtng Che arrangement • ■! the tul*f in the
pyramidal anbitaace, a Collecting tubei t Henb/a loope, p. 134- t(>c, 3; obj., 2.)

Plate LXVI.

1 I ■■ ■ I ■' tl ted kidney of a rat, Li I aw mu the bundla at

■ the pyramid*, B. Cortical ubatance, p i, (Oo., i; Ob]., a.)

Plate LXYII.

Fig. 146 —Transverse section of pyramidal substance of kidney of pig, the blood-vessels of which are injected.
a. Large collecting tube, cut across, lined with cylindrical epithelium, b. Branch of collecting tube, cut
across, lined with epithelium with shorter cylinders, c and d, Henle's loops cut across, e. Blood-vessels cut
across. D. Connective tissue ground-substance, p. 132.

FIG. 147.— Teased preparation from a section of kidney of pig, hardened in bichromate of potash, showing a
HenW'a loop. a. Membrana propria, b. Epithelium.

PIO. i4''— The a portion of a collecting tube m the pyramidal px sees of the corttcolU. \

ahowi the lumen '•>' the tube; '', the membrana propria; «. the cylindrical epithelium, p. 132. (oc, 3.)

FlO. 149.— Section of cortical substance of kidney of human foetus, hardened in bi.hr ate of potash.

«. Glomerului with lb) IU membruna propria, ; and c, the epithelium of polyhedric ci 1; covering the glome-
1. d, thi ii.ii.-n.-d epithelium which Uee upon the inner surface of
the Bowm /• Convoluted urinary tube ou( ro 1 1 12. ISru also fig. 155.)

Plate XLVIII.

FIG. iis— Peritoneal surface of centrum tendineuin of rabbit, treated wilh water and then coloured in silver.
In the middle of the preparation a lymph vessel, J, appears below the surface endothelium, i.e., the system
of lines of interstitial substance. On both sides of the lymph vessel are tendon trabecular, t. The endothe-
lium which covers the lymph channels consists of smaller elements. Five true stomata are shown which pass
through the "vertical lymph channels" into the lymph vessel below. Two of the stomata are open, and
three collapsed; all are surrounded by germinating endothelium, p. ill. (Oc, 3; Obj., 5. Tube not drawn
out.)

a c_

Fr<.. 114.— Similar preparation, c. A wide lymph vessel which can be seen through the surf:*' 1 ad
An artery, d. and a nerve trunk, e, pan through the lymph vessel (perivascular lymph renal) c, and within
the field of vi»iou are ten distinctly open true stomata b. The Burface endothelium bordering the (ton kta ll
germ mating, p. 112, (Oc, 3, Obj., 5.)

•Plate LXIX.

j£52E£i'7t£:

FIG. 153. — Tabular glands of human prostata, hardened in chromic acid, showing the cylindrical epithelium
which covers them. p. 137.

FIG. 154.— Section of cortical substance of kidney of six months' human foetus, hardened in bichromate of
potash, a. Glomerulus, b. Membrana propria, which extends over the glomerulus, and which is a direct
continuation of Bowman's capsule. At the point of section it appears as if it consisted of spindle-shaped
elements placed together, c. The epithelium of cylindrical elements which covers the glomerulus, d. Epithe-
lium -.f polyhedral cells which lines Bowman's capsule. /. Convoluted urinary tube cut through transversely.
p. 132. {See also fig. 14).)

1 section "f human eyelid, showing the tabular glands which are embedded In that part
bos, which la i I Dioxide of gold preparation, har-

dened in alcohol, a. Conn rich in branched cells, In which the tubular glands (£)

are embedded. These are shown cat through in rarloui direction We bi • rselv, as at <■, it

is seen that the epithelium oorering them consists of cylindrical nucleated cells, (OoM 3; OhJ.i **.)

Plate LXX.

FIG. 156.— Vertical section of cornea of rabbit, hardened in chromic acid. a. Anterior layer of pavement
epithelium, b. Substantia propria of the cornea, consisting of connective tissue fibres in more or less parallel
bundles, between which are the cornea corpuscles. These, in vertical sections, appear spindle shaped, c. The
posterior lamina elastics , or Descemet's membrane, and the endothelium of polyhedral cells, d which covers
it. p. 13K.

WW'

FIG. 157. — Diagram of the connective
substance of the retina.

FIG. 158. — Diagram of the nervous ele-
ments of the retina (after Max Schultze),
These two diagrams must be supposed to
fit into one another in such a way that
the nervous elements fill corresponding
spaces in the connective substance. In
157, the lower line represents the limitans
interna ; the line 8 the Umilant externa,
2. Layer of nerve fibres. 3. Layer of
ganglion cells. 4. Inner finely granular,
or, more correctly, finely ribrillated layer
which really Conns an extremely close
network 01 very tine fibres int<j which,
on the one hand, the processes, of the
ganglion cells penetrate; out of which,
on the other hand, the fibres of the inner
granular layer, s. proceed. The outer
processes of the elements of this layer

similarly terminate in a cl

fibrillar network, 6, the intermediate
granular layer or outer flnelj
or, iii.,1-.; correctly, finely fibi Ulai
Out of this proceed the Inner 1
of the outer granular layer, 7, which ter-
minate as rods and cones, 9. p. 142.

Plate LXXI.

- -163.— Various stages of cleavage of the egg of the trout, a. Germ. 6. Section of yolk ou which
the germ lies. p. 148. (These figures are referred to in the text, by error, as 146-150.)

FIG. 164.— Germ iu an early stage of cleavage,
<i. Vitelline membrane. 6. Germ. c. Yolk.

Flo. 165.— Vertical section of blastoderm of the egg of a trout
at the third day. a. Germ, already split into a large number of
elements, in some of which the dark yolk granules can be dis-
tinctly recognized, 6. Yolk of the saucer-shaped depression, filled

Wwk

made at the sixth day. The blastoderm, whirl the jrolk like a cushion,

consists, a li 1 ■ '<'•< element . The deeper elemento, those not ao

Ur adraiu

Plate LXXII.

FIG. 167.— Similar preparation at the twelfth day. The blastoderm has increased considerably in width, and
shows at a a marginal thickening. Opposite the thinner central portion, d, the blastoderm is separated from
the yolk, e, by a hollow space, the cleavage cavity, b. It is still, however, connected with the yolk by
columns of cells, the sub-germinal processes.

n

%
B !£'"£ "3 it

ggssag //,

no. i'/, 172.— Sections of the egg of bnfo cinereus, intended relations between the cleavage

cavity and Bnaeoni's cavity, eventually the viscera] cavity (after Strieker). B. The dorsal aspect of

B. The vejitral aspect. I N. In 169. and 170, Etusconi's cleft; in ■ ;., Knsooni's cavity

:-. Dome of the <vage, and

original upper pole ol U Oi dally In 171

and I-L-. Bcker'e yolk ping. 2. 1 ...:. of the cleai centra] yolk mi

larger, that la, less ad than the elements in the dome "f the cleavage

cavity or of *U making their way alon rface of the oovi

the nppei pole. They answer to the formative elements of the tront'a i-xx. Rusconi's

cleft adrai " 171. where the olefl has become :i cavity, they an.- separated

by a layer "I I • ,it». 1. in 172, owing to tin- alteration in its centre of

the egg has Chan th.- white pole being now nearly uppermost, p. 152.

Plate LXXIII.

FIG. 168.— Vertical section oJ peripheral part of blastoderm of trout's egg at the fourteenth day. 6. Margina
thickening, c. Central thin portion of blastoderm, showing superficially a layer of flattened elements, under
which is a layer of spheroidal elements, ,t. The blastoderm rests on the yolk by means of the sub-germinal
processes, as in fig. 167. The formative elements, e, on the floor of the cleavage cavity, a, are derived from
the blastoderm; either from the sub-germinal processes, or from the lower layer, d, of the central portion.
f. Yolk of the saucer-shaped depression, g. Vacuoles (fat globules?).

Flo. 173.— Vertical lection of the dona] furrow oi th dnereui. </. Cornea

layer, b. Donal furrow, c. Commencing central uervi Perl

liberal portion of nervous layer. /. Peripheral p 9 1 lb "i-

epithelial glandular layer, h. Buwsoni's cavity. 11. 1 ! central yolk mass. k. The re-
mainder oi the cleavage cavity, p. 153.

Plate LXXIV

FIG. 174. — Section of the cover or dome of Euaconi's cavity (Bufo). a. Corneal layer. b. Nervous
layer, c. Motor-genniuative layer, d. Epithelial glandular layer, c and d are the offspring of formative
elements.

FIG. 175.— Vertical section of a portion of the area peUucida and area opaca of the blastoderm of a fresh-
laid hen's egg. In the section corresponding to the area peUucida, the blastoderm consists of two distinct
layers, a the upper, and 6 the lower; the latter looser and consisting of larger elements, cc. Formativ
elemeuts lying on the floor of the cleavage cavity F, which have originated from the germ, and are filled with
yolk granules. These elements are continuous with similar ones in the area opaca.

—Section of blastoderm of hen's egg, at the fifteenth hour of incubation, a. T'pier, and i lower
ayer. c. Cleavage cavity. </. Toll rim. /. Formative elements on the floor of the cleavage cavity, g. Similar
elements which have already migrated in between the layers of the blastoderm.

WUk 177. flection of comment I the twenty-aixtfa hour after Incubation a. I ppi r. 0 middle,

c under Uyer. '/. Central portion of the middle layer, vrbica itli Um upper layer. *-. Primitive

groo\ e. 1

Plate LXXV.

Fig. 178. — Similar preparation at the thirty-sixth hour. a. Upper layer, b. Parietal lamella, lamina ven~
tmlis [ffautontukelpUUte). c. Lamina serosa, visceral lamella [Darntfaserpiatte), d. Lower layer. /. Central
nervous system, g. Chorda dorsalis. h. Proto-vertebne. ;". Wollfian body. ft. Pleuro-peritoneal fissure. 0, c,
k, i, g, are products of differentiation of the middle layer, p. 156.

Fig. 179.— Section of area opaca, and a portion of area pettucida of blastoderm (caudal end), at the thirtieth
hour. Ap. Area peUucida. Ao. Area opaca. b. Upper, c under. M middle layer of germ, <■. Lamina ven-
trolls, d. Lamina serosa, f. Uluud-vessels. g. Elements which belong to the middle layer, and particularly to
the lamina serosa, h. Yolk of the inner yolk rim.

1 j n srtlou through the cervical pa] ...... <.f the chicle eth hour <>f

" 1 ppex layer oi th< era 6 Central doti ■■ tern c. C) — la dorsalU d Pi'oto'vertebraj,

c. Lamina oentraUs, / Lamina terosa. a. Lower layer.

Plate LXXYI.

Fig. 181.— Section of embryo of chick at the beginning <>£ the second day, in the neighbourhood of the

heart, a. Upper or corneal layer. '>. Centra] Canal of the central nervous system, d. Under or epithelial

glandular layer. D. Anterior intestine (Vorderdann), e. Lamina serosa, f. Lamina ventralis. g. Aort:e. *. rente

m. Fold of amnios. //. Pleuro-peritoneal cavity, h. Heart cavity, h. Endothelium of wall of

heart, e'. Proper wall of heart. /;. Bluud corpuscles.

MS

—Transition of the tin i bhi fcod indothelial n Iclee containing blood

enons development of bl I corpuscles), i. Coarsely granular formative element in which

l*.,iai'-d fin- lei, a, are found. a f ew bl od corpnscli , a, are distinguishable, while b

peripheral zone, i rest ol the cell. In }. the peripheral ileated layer

[i i mi [rely <>\ coloured

d .. '.• Icle lined with endothelium and filled with bl I corpusoles,

II uely granular protoplasm, With Its more or less regularly arran ed I

endothelium of a I

Plate LXXVII.

—Section of the posterior part of the body of the embryo of the chick at the forty-eighth hour.
«. Central nervous system, b. Proto-vertebrae. c. Chorda dorsalU. d. Upper or corneal layer, e. Serous, and/,
ventral lamina, g. Wollfian duct. h. AorUe. i. Pleuro-peritoneal cavity, k. Lower layer. D. Intestinal
furrow, a. Amniotic fold. !. Bl.iod vessels.

n of anterior ■ -. ■ inlddli • >!" the pecond day. a. Cavity of

//. Wui! of cerebral reticle, c. Primary optic :•■ lole, and d tta wall. e. Upper

layer of :■ olng of the opp r. Middle lsyei /«. :.Tnu
optical. !

Plate LXXVIII.

FIGS. 184-186.— Various stages in the transition of the primary into the secondary optic vesicle, and the
development of the lens at the end of the second and during the third day.

186. a. Cavity of secondary optic vesicle, b. Rudiment of retina, c. Rudiment of pigment epithelium of the
choroid, d. Nermu opticus, e. Lens. /. Upper or corneal layer.

184. a. Primary optic vesicle, and 6 its wall. c. Ncrnis opticus, d. Upper or corneal layer, e. Beginning of
lens.

185. a. Primary optic vesicle. 6. Saucer shaped cavity, which subsequently becomes the secondary optic
vesicle, c. Xervus opticus, d. Outer wall, and e inner wall, of primary optic vesicle, f. Upper or corneal layer.
g. Rudiment of lens.

FIG. 188.— Other forms of elements, in which blood corpuscles arc produced, a, a, are the cavities of vesi-
cular structure*, produced by the formation of vacuoles, in originally solid cells. The wall of the vesicle 6,
! 11 (top] '" 1 pre Bnts the endothelium of the future vessel, for whirl, reason these
vesicles may 1* called endothelial vesicles. At,/, blood oorpuscles arc detaching themselves from Die inner
portion of a vesicli m element at another kind, in which blood corpuscles are formed. It is a

spindle-shaped m d e,i], the central portion of which becomes hluud corpuscles, and the peri-

pheral portion endothelium. bat in rig. 187.

i formative elemente Ol M I 10 communication with each other by

■olid oflkboots. They have this in common, that io jUI a peripheral layer of nucleated protoplasm is dif-
iterior, which contains s number of blood corpuscles. The interiors of

neighbouring elements eventually be, ,.,,,1, each other by tie oris] 1. oi communicating

threads above mentioned, which becomi hollowed out, and thus give rise to a system of tubes, the blood-vessels.

Plate LXXIX.

HO. 190.— Test tube, with foot, used for subsidence of small quantities of blood (§ 1).

WO. • [tin plate for collecting blood and keeping it at OOC |§ 2).

WO. lOx-Coagulatlon of blood of frog Id ■ fine capillary tube, ffartnack. (Ob]. 0; immersion. Oc. 3.)

-a. Oammla Cot Bchafert experiment, i shows the form into which a tube is drawn rat for the

d of an arterial cannula (§ 9); the tube is first severed at one of ti utrlctions, and then filed

away m the direction of the oblique line. c. T-shaped arterial cannula; the horizontal tube is in communica-
tion with the manometer of the kymograph (§ 33).

I tor studying the action of induction shock! on blood. The drop of blood to I va-

in.n.-d U placed between the tinfoil pointa on the under surface of the fixed square cover glass. The chamber
i» closed by placing a second ordinary object-glass below it (§ 13).

Plate LXXX.

FIG. 196. — Hoppe-Seyler's bottle for preiraring
fibrin (§ 23).

FIG. 195.— Various absorption spectra. 1. o'4 per
cent, solution of haemoglobin. 2. Reduced haemo-
globin (§ 18). 3. Hrematoin (§ 22). 4. Reduced htematin
(§ 21). 5- °'°6 per cent, solution of hfeinoglobiu.
6. 07 per cent, solution of the same (§ 24).

;-.-.--;-' v.

F10. 198.— Ueissler's mercurial pump |? 27)

li'.. I-..?.— Alvergniai'i minimal pump

Plate LXXXI.

Fro. 199.— FiantlanJ-Sprengel pump (5

Fig. 201— '< ud b. tfeedlM Cm pairing UfCri . ,.. Urilcke's blunt liwk. d. Tre-

liljii,': e. Curved needle. /. Cured and 11..1

Plate LXXXII.

FIG. aco.— FrHiiklaud's api>aratuB for the analysis oi gases by absorption (| 30). [From Button's Volum. Analysis.)

Plate LXXXIII.

F"^

Fl«. 204. — Czeruiak's rabbit support (§ 34).

FIG. 201.— Frankland and Ward's apparatus for explosion <§ v)- (From Button's Volum. Analysis.)

Plate LXXXIV.

PIG. 20Z.— The mercurial kymograph, a. Vulcanite rod of floating pistou. b. Tube which conummicates
with the pressure bottle, c. Tube wliich communicates with the artery, d. Feeding cylinder, i. First axis,
which revolves once in a minute. 2. Second axis, which revolves once in ten seconds. 3. Third axis, in a
second and a half (§ 33). The instrument is furnished with other cylinders suitable for the reception of
single liands of glaztd paper, the surface of which can be blackened after they are fixed on to the cylinders,
by causing the latter to revolve over the flame of a petroleum lamp. These cylinders can be fitted ou to
either of the axes 1. 2, or 3, and are always used when it is necessary to employ a rapidly-moving surface,
ui, *'..'/., for tracing the curves of muscular contraction.

Yu.. 206.— Normal tracing of arterial pressure obtained with the mercurial kymograph (rabbit).

Plate LXXXV.

FIG. 205. — Pick's spring kymograph. A. C -spring, bb. Suppo
of the spring to the lever 1), and thus to the writing-needle 1
spring is in communication with the artery.

C. Rod which communicates the movements
K. Leaden tube by which the cavity of the

Firr. 207

Ficr 207a

Fl'i. 207.— Normal arterial tracing obtained with the spring kymograph (dog under curare).

1'i'.. -.;■/.— Tracing of Bame animal after exhaustion of vagus by repeated excitations; dicrotoua pulse.

Via, 206.— Meohanical arrangement of the sphygmograph {§

Plate LXXXVI.

Fig 209.— End view of the block by which the sphygiuograph rests on the bones of the wrist, showing the
screw. G, by which the pressure exercised by the spring on the artery can be varied (§ 39).
FIG. 2096.— Breguet's improvement |§ 39).
PIG 2io. — Mode of measuring pressure (§ 39).

PIQ. 211.— Schema f r demonstrating the nature of the arterial movements. A. Glass tube which represents
the heart. B. The tul.e by which A communicates with a cistern at a height of ten or twelve feet above it. (A.
much smaller head of water is sufficient.) C. The lever by which the two valves K and L> are worked, the
same act which shuts the one opening tin- other. 1'. Oommenceinent of the experimental tube, which is of
black vulcanite. At 9 the tut.e communicates with a long vertical tube of glass, only part of which is seen;
It is closed at the top, and usually shut off from K t>y a pinohcock. At (l tin? tube passes under the spring of
the sphygmograph, the frame of which rests on a block (below t<). By error, the tube has bean drawn on the
wrong side of the block, II. The blackened plate of the iphygmograph. To the left of it is seen the cylin-
der, with its needle for recording the time which intervenes between the opening ami closing of the aortic
valve, D. I.. A rod which is lirmly fixed in the lever, and is connected by two cords, ono of which is elastic
with the cylinder 1$ 40).

Plate LXXXVII.

-Tracings obtained with the arterial schema (§ 40).

FIG. 2126.— Natural pulse.

FIG. 213.— Percussion waves (§ 41.)

rami:*

Fin. 2U.— Tracings showing the contractions and expansions of an india-rubber tulle, along which water is
propelled in an intermitting stream hy squeezing with the hand at regular intervals of time an elastic bag
provided with valves, with which the tube is in communication; the bag thus represents the heart. The three
tracings are drawn simultaneously, and exhibit the expansive movements of the tube at three different dis-
tanees from the bog;, the upper tracing being taken at the greatest distance (§ 41).

Fn;. 21C — Dr. OMon'i (Uh-trongb i« |4l. It 1 be naed with the mlaraoope itage Inclined ■) an ingle ..f

kbonl i .

Plate LXXXYIII

FIG. ar;.— Stage for mesentery of frofi {§ 44).

Fig. 218.— Cannulas for aorta and vena cava of frog.
The right-hand figure represents the arterial cannula.
They are of size suitable for large specimens of It.
eteulenta (§ 46).

PIO. 219.— Diagram of arrangement for measuring
objects seen under the microscope, a. Axis of tube
at microscope, t. Pri in, tj. Direction in which the
object \> ' board, which should

be at a 1 utimeters] from the

eye. The angle* of tbi | 1 ial, the angle

($ 48).

31.— Griffin's bl ae used fox gas blow-pipe. The blower la used (or artificial

respiration (tee i vi).

, ■,.,!.. liquid into

Plate LXXXIX.

FIG. 224.— Skull of rabbit seen from behind, p p. Parietal
bones ; i, interparietal bone ; below i, occipital tubercle ; above
P, occipital protuberance. Half-way between the tubercle and
the protuberance is the point at which the bone must be per-
forated in the operation for producing glycosuria (§ 50).

Fir;. 222— Bprengel'i blower (5 49).

Fir;. 225.— Exettor. The wires are of oopper, with platinum print!. Their sheaths aro made of bits of flexible
catheu-r. ami are bound together with raxed »ilk (§ 51).

1 in the rabbit by an in. 1 Ion extending from the thyroid cartilage to the root of
Bifurcation '.r tin- |ugulai rein; /</".•, poeterioi buriaJ vein; p a », poeterloi anrloular

vein; a/r, anterior (acta] vein ; num.. great ;■ ni.n nerve, where it emerge! at the posterior edge of

1 mtucle (} w).

FIG. 227.— Carutid artiry of rabbit, and parte m relation with it. c, Carotid;
c ?», cornti m ijus hi hyoid bom ; 8 ft, stylohyoid muscle; ft, hypoglossal nerve;
f, sympathetic; v, vagus nerve; i. points to superior laryngeal nerve where,
close to its origin from the vagus, it passes behind the carotid ; p, pharyngeal
artery; f m, edge of sterno-inastoid muscle; t ft, thyroid artery; s I ft, sterno-
hyoid muscle ; I, laryngeal artery the nerve which crosses it is the descendem
noni (§ 56).

I c 1

PIG. 22a— Heart of froj (aftel Frittche); front vien t.. the left, back \i

the right. .1 .1. Anrt.e ; v.r.*., vena earns tuperioret ; At.t, left auricle;

ri^ht auricle ; fen., ventricle; li.m-.. Bulbut arteriosus: 8.V., sin 113 venosue; I'.c.i.

Inferior ; v.h., vena hepatica : V.p., vena pulmonale! (§ 57).

It.i/,
rena

in. ' apanam and lei Beu ug in H liich th< '

be rained or depressed at «iii, by means of the little adju tin level th«
backwards and slightly downwards b opal /, tube

; 1,1 II, 1 I. 1

long arm of which i

bj \\ lii'-li its cavity c

ude.

ith the cardiograph; thii tube enters the tyn paiiuin by a horizontal metal tul u Its further

Plate XCI.

I . 'i ■!>,/■. na caw

■ Simula in wi Hon with the manometer; i tub uarded bj

clip, by which proximal end "I manonu rte, which record the distal

column »l Hi'- iiiaii./iiK-i'T on 'In: cylinder; n. heart; K, ligature, by irhlch the tnbe la eeoured tu the

>i« ; I., bolder, by « bich the ulan* red J Is supported (S 63). ,

Plate XCII.

■■■ill

llll

llll

llll
llll

attain

!ll kill

■■■■■■ H»l

FIG. 237. — Dissection of the parts in relation with
the vagus nerve of the frog on the right side. The
oesophagus is distended with a glass tube about half
an inch in width. The object is represented of about
twice the actual size, a. Right aorta ; B, bitlbus
aortCB ; c, posterior horn of hyoid bone ; g.h., genio-
hyoid muscle ; h.g., hyoglossus muscle ; p, lowest of the
three petrohyoid muscles; H, ninth nerve; G, glosso-
pharyngeal nerve; r, vagus ; 6, larynx ; s&h& oh., point
to the space occupied by the origins of the large muscle
(sternohyoid) which connects the hyoid with the ster-
num, as well as by the omohyoid ; both of these muscles
have been cut away (§ 73).

-Tracings obtained by recording simultaneously on the same cylinder the variations of pressure in

the right auricle, right
ventricle, and left ven-
tricle, respectively. The
interval between each
vertical line and the
next corresponds to
about a tenth of a se-
cond. The second ver-
tical line is just before
the completion of the
systole of the auricles.
The contraction of the
ventricles falls be*
tween the third and
fourth lines. It ends
between the seventh
and eighth ; conse-
quently, in the horse,
the interval of time
between the auricular
systole and that of
the ventricles is about
o'iS sec, and the
duration of the ventri-
cular systole is about
o"4 sec. (After Chau-
veau ; see § 67.)

FIG. 236. — Septum
auricularum of frog, a,
Muscular fibres ; 6, endo-
cardium ; c, free edge of
septum ; dd, wall of ven-
tricle; e, right cardiac
brooch of vagus ; /, left
branch; h, anterior
nerve of upturn ; *',
posterior nerve; kkt
Didder's ganglia; //,
ganglia of ventricle;
§ 69. {After Bidder,)

Plate XCIII.

FIG. 240.— Sketch to illustrate the relations of the
ganglionic cord in the visceral cavity of the frog.
The septum citlemce magna having been divided on
the right side, the right kidney is turned over towards
the left, so as to expose the parts concealed by it, viz.,
the aorta and the ganglionic cord of the same side.
The stomach and the first coil of intestine are also
turned over, so that the posterior surface of the
former organ is presented. In this way the origin of
the mesenteric artery from the junction of the right
and left aorta? is brought into view. On its surface
nervous filameuts, which spi-ing from the ganglionic
Cord, may 1* traced. These [nerri metenterici) com-
bine to form a plexus with similar filaments from
•he corresponding ganglion of the other side. (.See fig.
295.) I, Liver; rl, right lung; », stomach; *, kidney.

Fir.. 241.— Heart, lungs, and gTeat vessels of the rabbit,
with the nerves In relation willi thrni. (After Ludw ig,
■lightly altered.) V.c.d., v.c.t.. Kit-lit and left venaeemt
tuperiortt ;the li represented as if cut

away, in order to Show the m-rv. ' < ... . „ • ervicate
inf.riiin j m, sympathetic ; i>. vagus; d, depressor. The
dotted Unas on each side indict p " of the

(I 81).

1 .Dissection of the lower cervical ganglion hi tin- .log. and of the parts in relation with it. (Alter

Behmledeh mimon trunk of the ^agus and sympathetic ; fcphrenici «l

■ ■ • rlorcei deal ganglion (6)

B, flr-t I. rale ganglion; 0, ratntw cardiac. h mptrtor ; 11, trunk of
', it).

Plate XCIV.

FIG. 244. — Tracing (after Schuiiedeberg) showing the effect of electrical stimulation of tlie vagus of a frog under
the influence of nicotin. The line ending in asterisks indicates the duration of the period of excitation
1$ 81).

FIG. 243.— Dissection of in-
ferior cervical ganglion of
rabbit. The pectoral mus-
cles and sterno-clavicular
ligament have been divided,
and other more superficial
parts removed. The dotted
line indicates the middle line
of the body, g I, A lym-
phatic gland in contact with
the apex of the lung ; a x,
sub-claviau artery ; a v, ver-
tebral artery ; v, vagus nerve ;
*, sympathetic ; pt phrenic
(§ 81J.

FIG. 246.— Respiratory mus-
cles of frog (after Ecker).
smt, submental is ; g h, ge-
niohyoideus ; h g, hyo-
glOBBUB ; k m. submaxillaris ;

* m", anterior horn of the
hyoid hone ; p k, petrohy-
oidei ; oh, omohyoidens;

* h, sternohyoideus.

FIG. 247.— Recording Stethometer.
A.Tynipanuin ; B, ivory knob; B'rod
which carries the knob opposed to
B. C, T-tube, by which A communi-
catee, on the one hand with the re*
cording tympanum, on the otherwith
an elastic bag D. The purpose of the
Twg is to enable the observer to vary
tlie quantity of air in the cavity of
the tympana at will. The tube lead*
i tiK (" K [1 closed by a clip when the
Instrument u in nee. ($ Pq).

tlatk xcv.

Fig. 250.— Boxwood Pulley for recording the movements of a needle, Inserted in the diaphragii
is attached to the horizontal arm {§ 91).

Fit:. 251. — Rosenthal's apparatus, with W. MU11er*8 valves l§ <&>.

txmlc bu td i';is itj 96),

Plate XCVI.

no. 257.— The lever kymograph, fur recording the respiratory and arterial movements simultaneously (§ 105).

PIG. as&— Tracing trbtalnad with the tov« kymograph 1$ 105),

Flate XCYII.

FIG. 265.— The calorimeter ({ 116).

ultlpller, for thermo-electric currents (J 119).

Fl,. ... „ (ram ■ on which i>»- wire It colled

!

EXPLANATION OF PLATES XCYIII. TO CI.

FIG. 229.— Tracing drawn by a lever applied directly to the apex of the heart of the frog.

Fig, 2^4.— Tracing of endocardial pressure of heart of frog, obtained by Coats' method.

Fins. 238a and ©. — Synchronous tracings of arterial pressure, and respiratory movement of air in trachea,
taken (a) immediately before, and (M one minute after, section of both vagi. The lever kymograph (fig. 257)
was employed. Arterial pressure before section about igo m.iu., after suction about [80 in in. Pulse rate
before section no, after section 260. Respirations before section 24, after section 10. The characteristic violence
of the expiratory movements after section is well shown.

FIG. 239.— a. Tracing of arterial pressure of rabbit, obtained with Fick's kymograph (fig. 205) during
excitation of peripheral end of divided vagus, with feeble induced currents (secondary coil far removed
from primary). Duration of excitation of nerve indicated by asterisks, b. The same, with secondary coil
brought nearer.

Flii. 245.— Traeiug of arterial pressure with Fick's kymograph during excitation of the central end of the
depressor nerve (§ 82).

FIG. 233.-11. Tracing obtained with the cardiograph, when the button is applied to the seat of impulse of
the human heart, b. Tracing obtained when the button is applied either outside of the impulse or nearer the
sternum. The line of sudden descent in b coincides with that of sudden ascent in a. Both are coincident
with the sudden hardening of the ventricle, i.e., with the complete closure of the mitral and tricuspid
valves (§ 60).

FIG. 246 bis.— Tracing of respiration of frog {§ 86).

FIG. 249.— Tracing of intrathoracic pressure (§ 90).

FIG. 248. — Tracing obtained with the stethometer when applied as in fig. 247. i. Inspiration ; e, expiration.
Immediately after n, a notch in each of the curves occurs, the descending limb of which expresses the
moment of cardiac impulse. Compare fig. 2326 {§ 89).

FiG. 253.— Respiration of the cat before and after section of both vagi. The tracing expresses the variations
of pressure which occur in the air passages during each respiratory act. In b the horizontal Hue is that
drawn by the lever when at rest ; consequently, when the pressure in the air passages is less than that of
the atmosphere the lever rises, when it is greater it falls. The sudden expiratory movement which is the
most marked characteristic of the mode of breathing after section of both nerves commences at e. (§ 92).

FIG. 263a. — Tracing of arterial pressure and respiratory movements in the second stage of asphyxia by OCCluslon,
a p. Arterial pressure ; i, respiration. Both tracings express the movements of mercurial manometers (S 109).

FIG. 2636.— Slow asphyxia. The lower tracing expresses the movements of an elastic bag in communication
with the trachea (§ no),

FIGS. 259-261.— Tracings of respiratory movements of the dog before and after CUrarization (j 105),

FIG. 262.— Tracings of artificial respiration and arterial pressure, showing Traube's curves, as seen with vagi
intact (§ 106).

Fit:. 264.— Effect of a single injection of air in a curaiized dog, after long discontinuance of artificial respiration
(§ in).

FIGS. 2^4 and 255.— Excitation of the central end of the vagus in the rabbit (§§ 102 and 103).

FIG. 256.— Excitation of the central end of the superior Laryngeal nerve (§ 194).

\Plate 98. Ficr. 229

Fi£.238.«

Fig-. 232 6

Plate /OQ.

Fior.259.

S\l\f~

itafr-resji

Fig. 260

Fig. 261

a^aaaaa/ ^aaaaaat ^^vvvvw^^Aaj^

arf.resjo

Fig. 262,

Fig. 264.

\art.ye.yj.

Plate CI I.

266.— Diagram of a frog, to show the lines of incision necessary in various orxervati ins.

FIG. 267. — Diagram of the uraa-
he leg of a frog, pi

ma femoris ; 6,
in.-r.s; e, seiei a

■■ coocygeo-iliacn ; 1 /.
tendo achillii 1 g, gastrocne-
mius ; h. bead ol gastrocnemins :

•us (the muscle also
marked £ in front <-f and partly
hidden by the preceding is the
tibialis 1 ins In-

ternal ; ">. glntarai ; ». pyri-

; a. ilium ; ./',

The ni 1 1
.0 l , end "f lemur ;
nerve : 1. tendo aohlllla;
f. attachment "i ■mailer tend in
Ixocnemlni to femur.

Plate CIII.

FIG. Myographion of Pfliiger.

The moist chamber, which is sup-
ported by the large pillar, and from
Which the thread h descends, is nut
shown. The lever " moves freely on
the t«o pillars bb. At /the rod 6,
bearing the movable style </, with
lis movable c ainterpoise ;j, swings
easily. At the opposite end of the
lever is theheavy counterpoise c. The
milled head on the side of one of the
pillars b rotates the lower of the
two bars connecting b and b. A silk
thread is carried from -• to thi.s bar.
By turning the milled head the style
may thus he allowed to fall upon or
remove away from the recording
surface as desired

I G —The moist

chamber, with the
uezi e-muscle prepar-
ation, non-pularizaMe
electrodes, electrode-
bearer, and lever in
position ready for
an observation. Tin:
glass cover is not
shown.

FI<;. 270 bis. — Simph
spring myograph of M.-ire'*
arranged horizontally

(See ch. xix.)

Plate CIV.

FIG. 271. — Ordinary electrodes. The pair 011 the right band being the pail spoken of in the text as curved and
shielded.

FIG. 272.— A non-polarizable electrode in the bearer.

FIG. :;;.— Ends of non-polarizable electrodes. A, with the clay plug 6 projecting beyond the glass tube; B, with
the end "f the glass tube closed and bent, a hole being drilled in the tube at b', to expose the ping ; C, oblique end
with the clay plug flush with the glass tube.

FIG. 274. — Kronecker's 1

rf apparatus for «tudyiii ' ' '■■ *■ *•

1) the polarizing 1 by thee mutator 1 with the two celled

>\ fed ' "' "" ' ",,l",v "■'l "■

' . Ills pri

Plate CV.

PIG. 277.— The recording tuning fork.

<**$.l.

FlG. 278.—
Diagram of
the muscles of
the thigh of a
frog, anterior
surface. $, gar*
torius ; ad.m.,
adductor mag-
nus ; r.i., rec-
tus intemus

FIG. 23o.— Muscle iu a trough bearing two levers, in order
to show the wave of muscular contraction. To the left
are seen the pointed electrodes and the clamp fastening the muscle. At the other end uf the
thread connected with the lever.

Fig. 23i.— A different disposition of the
levers, intended to show the same thing.
The levers seen below the platform on to
which the muscle is fastened, are connected
with slips which pass round the muscle
at different parts of its length.

FIG. 279. — Dia-
gram oi a muscle
curve asdrawn on a
travelling surface.
c,the line described
by the point of the
lever connected
with tho muscle ;
11 , the Line described
by marking lever;

■ id

by the tuning-
fork. The verticil
Line "' marks the
m uuenl - 1 stlmu-
Latlon, m' the he-
ginning, ma the
tin, and m \
tl I of the

on of tba

Plate CVI.

Fig. 282.— Diagram of the curve of teta-
nus. 4, the Hue drawn by the point of
the lever connected with the muscle ; o.
the liue of the marking lever. The record-
ing surface is supposed to be moving
slowly. The line m marks the commence-
ment of stimulation, and also of the con-
traction (the movement not being suffi-
ciently rapid to show the latent period);
mi, the cessation of stimulation and the
commencement of relaxation ; m3, the
return of the muscle to its former length.
The straight line, which is the continua-
tion of 4 from m to m3, is the line
which would have been described by the
muscle in the absence of all contraction.

FIG. 283. — Lower part of large figure.
Curve of tetanus, showing the individual
contractions. Below are seen the vibra-
tions of a recording tuning-fork.

FIG. 284.— Upper part of large figure.
Curves illustrating the increased extensi-
bility of a muscle during tetanus.

Fig. 285.— MnselM and uervea at bog,
mi m 1 tor the Mcperlmant of the
" rheoaooplc frog."

Plate CVII.

Thomson's galvanometer and scale,

FIG. 287.— The shunt
of the galvanometer.

FIG. a88.— Diagram

illustrating the "natu-
ral " current in a piece
61 muscle. The equator
is marked by the posi-
tive sign, and the mid-
points of the transverse
sections by the negative.
The arrows denote the
direct. on of the current
through the galvano-
meter. The larger curves
denotethe stronger cur-
rents, and lice versd.
aa, are two points on the longitudinal surface equidistant from the
equator ; between them, therefore, there is no current.

(2

®rf

ZB

/;

1 11 \ 1 rani '" "' ■ ' ' "" ' ,"'1'" l'';l,'l,' ' lectrode iliu 1 q be»i

ration of the natural current* In a uerve,

Via. -.■■:■ 0 igi ",, Ulu I rati '■ I rotonu p », thi polai Iziai 1 I

,, /./,.. 1, 1 1 1 0 placed .-is i" »ho« the eft < 1 ■ • al ' on

... .,, al I ol •'• n ■ l>ea the arizing current is in

n ..1 Hi.' 1 hi iin i' . the "■ 1 ■ " I "i n

11 I- iin p I-.'., hil-ii, while Hi." of I 'i

■ Ign.

Plate CVITI.

FIG. 291.— Diagram of a muscle ami nerves, arranged to
show the use of the eleetrotonic change in "lie nerve. A, as
a stimulus for another, B. I. II. two different modes ol
placing the nerve of A on I! ; III. the so-called " para-
doxical contraction."

FIG. 292.— Apparatus for showing the effects of varying temperatures on a muse]

FIG 233.— The induction aopsratus of Do Bois Eeymond, with the magnetic interrupter.

Via ' me of above

Plate CIX.

/Mi

— Diagraujof the nervous system of a frog— anterior (or Inferior) v iiw. i, :•, 3, *,&, I" [0, Cranial nerves

in order. 7a, ophthalm palatine nerve; Ye, luperlor maxillary; Vd, inferior maxillary j Ft

tympanic nerve, which, after Joining withtheromi q form/*, the facial serve*

• '.7. ganglia I 1 1. branohea of teuthpalri ,ting branch with tympanic nerve; X2

I :, nerves '■■ rtomaoli and lute tlna ; 1 1. on X '-', ganglionof vagus

Jf, spinal cord: mpathetli in lla, nninbered a rdlng to the

ritb which tbey communicate; A' c, crural 1 joker, slightly altered.)

! 1 frog from above, enlarged. Col, olfai rebral hemlBphara

(;./,. pineal body ; /'■*< oplie thalaml \ /..•>/>. optic lobe*; ft oerabeUum ; If.o. Medulla oblongata ; fl.rft. sinus
rhoroboidaUa.
i

Plate CX.

Fin. 298.— The Rbeochord. The diagram represents the end of the board on which the resistance wires are
stretched, a, b, c. d, e,f, g, are brass blocks which would, if it were not for the wires, be insulated. From the
block b a german silver wire (the course of which is indicated by the dotted line}, after turning round an ivory pin
at 1, returns to c. From c a similar wire of exactly the same length returns to d. From d a wire three times the
length returns to e ; e and /are connected by a wire five times as long. From each of the blocks a and 6 platinum
wires extend to the further end of the board, a distance of more than a metre, which are insulated at their
extremities. They are, however, in metallic connection by means of a slide (" travelling mercury cups ") shown in
the diagram. According to the distance of the slide from a and 6, which can be measured by a scale ontheboard,
the resistance between a and b can be varied. "When the slide is as far as it will go, the resistance is equal to that
between 6 and c, or c and d. Wheu the slide is pushed up to a b, the total resistance of the rheochord is twenty
times as great as between 6 a«d c. If plugs {not shown in the dagram) are inserted between each block and its
neighbour, the resistance is nil. (See p. 347.)

FIG. 299.— Double key.

FIG. 300.— I>'i Boll Kryi.i'.n.]'. k> y.

Plate CXI.

W

FIG. 301.— Creatine.

FIG. 302. — Creatinine.

FIG. 303.— Nitrate of hypoxanthine.

: — Hyilr'K.lilxnttc '.f xanthine.

FIG. 305.— I til !

Plate CXII.

FIG. 306.— P, potato starch ; W, wheat starch ; R, rice starch; A, arrowroot' starch.

Fh;. 307. — After Bernard. Nerves of the submaxillary and sublingual glands of the dog. N. Submaxillary
Gland. O. Sublingual gland. .1 M. Wharton's duct, in which a cannula has been placed. J L. Duct of the sub-
lingual gland, also furnished with a cannula. T, s, s'. The lingual branch of the fifth nerve. F. The facial nerve.
c. Chorda tynipani. g. The submaxillary ganglion, q. The superior cervical ganglion. P. Sympathetic twig
passing from the ganglion to 'the submaxillary gland, j. Internal maxillary artery. V. Vidian nerve. (.Branch
of the lingual nerve ramifying in the breccal mucous membrane.

1 Paint at the submaxillary gland. 11. Submaxillary gland, J. Jugular \ < in, dividing

,/aud/', which pan along the l«. mi. 1 "l ill.' gland, 1/. Anterior vein, and •' DOlt v. in.

bDSB Qm gland.

Tlate CXIII

*■"• •' ■■' Ountmt -t the rabnuxillaiy gland in the dog <■■ Bnfamaxlllan

gland, from irhicl > k, accompanied al fliel by the total* of .]„■ mblingual (land, which farther on

"' ' ' t. Ungual :irt-ry. 0. Artery of tli- gland, It »].ni.K* ir..ni the

In from the acta IB", The bypogloeia] nerve, . „i ecroai to upon the

superior cervical gang i which Ilea beneath It (r. The vagus, p. A evinpathetlc filament, which li oonneoted

ganglion, ami j.,in» the ragna town down. i>. Branch ol the flrai oer
lug with the superior cervical ganglion, it it. Glossopharyngeal nerve, i. Anterior branch! ol the
sopertora tomiing the inter-carotid plexna which imal oarotld artery, p. A

■mall sympathetic twin which aacendi to the iabma»lllary gland, a ipauylngal Bid the Inferior artery O.and

indular aitarjr !•'. ■/. BympaUu „>,,„. ,i„. fata] artery and

wnnlngni I tta mylohyoid branch, of the fifth, a. Thi Ungu posterior atpect ol

1,1 d to Hi- glaud forming anaatot

filaments of the «ym|*thetlc t. Bxternal division ol the spinel acceseory nerve.

Plate CXIV.

FIG. 310.— After Bernard. Anatomy of the parts exposed in operations on the submaxillary gland. The pos-
terior half of the digastric muscle has been removed. M. Anterior half of the muscle drawn aside by a hook.
M . Insertion of the posterior half, which has been removed in order to expose the carotid artery, t V. Sympathetic
filaments. G. Submaxillary gland drawn aside by a hook in order to show its deep surface. H. Submaxillary
and sublingual ducts. J. Trunk of the external jugular vein. J'. Branch of the jugular vein passing behind the
gland. J". Branch of the jugular vein passing in front of the gland, cut across. D. A vein issuing from the sub-
maxillary gland. 1 1'. Carotid artery accompanied by a sympathetic filament on either side ; only one filament, f,
>s distinctly shown in the engraving. F. Origin of the inferior artery of the gland. P. Hypoglossal nerve.
L. Lingual nerve. T. Chorda ty 11 ipani going to the submaxillary gland. S S'. Mylo-hyoid muscle, cut across to
show the lingual nerve and the salivary ducts which lie beneath it. U. Masseter muscle covering the angle of the
lower jaw. z. Origin "f the mylohyoid nerve, which is hidden by the reflected digastric and mylo-hyoid muscles.

Fig. 311.— -Qastric cannula seen in section, and key. A, outer flange; B, inner flange; C, projecting points
by which the outer can be screwed round on the inner tubi .■■■■> m to Increase the distance between the flanges.
d, i). 1- the key by which the tube Is t 1 n t, ..f a .in I.- of metal, with two slits, ]> and i>, into

which the projections 0 pass. It is attached by a CrOSB-har to a handle K, which is about six or eight inches long,
though cut short, in the engraving.

!

m Ipptueo :"'"i

Plate CXV.

Fic:. 314.— Cholesterin.

PIG. 315.— Point of the instrument used fur puncturing the fourth ventricle to produce diabetes,

Fk;. •)(<;.— Aft<r Bernard. Section of i rmbuit'i bead, ihowlng Che direction taken oy the Inttromenl In
a, earabaUum; r>, origin ol the levantb oatrai o, pinji] cord; d, ori

vagua; e, i».iut w] ■ .1 ; g, the fifth uerre j Ik, Iltorj

(■IMl ; <, I ■ . 1 1 . 1 .1 U limn ;

*, ooelplta] raoooi ilnae; ', corpora quadrigemiiiA ; .. .,, , U

Plate CXYI.

V-,

Fn;. 317.— Arrangement of the cannula in a temporary pancreatic fistula. A, the chief pancreatic duct of
the dog directed transversely; a, insertion of the pancreauc ducts into the intestine; the insertion of the
smaller duct is higher up. and is marked by a line without a letter; a', a branch of the larger duct within the
Bland; a", ligature, fastening the cannula T to the intestine;//, is a thread by which the cannula is fastened
pancreatic duct; 1, is the intestine; P P\ the pancreas ; T, the silver cannula; B, the stopcock, for
letting out juice which has accumulated in the india-rubber hag ; V, an india-rubber bag, tied

mter end of the cannula, and used for collecting the .juice.

-The left-hand diagram shows the method of stitching up the end r,f the divided intestine ao
in Thiry's fistula. The right ban. I figure shows the method ol ether the divided

The two black dots in the middle of the pieces already Joined, Indlc&tethe position of the mesenterl
tionld surround these vessels and serve as a ligature for them. Five or six similar

to Join the ..lie edge, as shown here. The two ends of intestine are then pulled into
iwn in fiir. 319.
I the method of applying the tin loin the divided Intestine in Thiry's fistula. The

represented a* entirely apart, but the other half of the circumference must i« undi 1 1 1

t„ 1* air ether in the manner ihown In tig. 318.

.v. "a

°?

o 3 o OOjO

3 ' -a

S3 »

<8fo

B*.

- ■

O'
1 Milk.

' m

°0l

.0. ' V',
Kill. 3ji. 1

Plate CXVII.

FIG. 326. — Piece of glass drawn out to furm a pipette.

FIG. 327. — A tube drawn out in order to seal it. The operation is completed by directing the point of a blowpipe
name 011 the point a, and drawing the two ends of the tube rapidly apart.

MB jA— flotation. The beaker Uiupported on win gauw In order to prevent it bom cracking.

, Uon during prolonged ebullition, k, the flank in which

U,e liquid condeneer;/, a glaee tube, wb andr; ( end *, two india-rubber

1., ud from the I In t, end

rmu taek into X, Any of the oondsnied liquid that ad the bend of the gltm tube p, which li 1

Ui the nj'iH-r endof f«ii eolleoted in tbeexnal] 0, [rnwttit '<» the

M any quantltj " tlatei ■" it, the flame may iw rem ■ raouum then

form* In K, and the liquid ruiliei back luto it.

Platk CXVIII.

FIG. | used as a water-bath.

FIG. 331. — Bun iilator as m...i .

Qelssler. a, is a wide glass tube divided into two
parts, an upper and" lo we: atal septum, from

which a tube runs down nearly to the bottom of Che
lower one. The upper division and paarf of the L
is filled with mercury. 6, is a glass tube passing through
the cork of a, and f and * with the g pipe

and the burner, c, is an inner glass tube whose edges
are luted to those of & at/, (/, is a small hole in <•,
allowing suffii ii ■ through it to 1 1

the flame from being extinguished. The gas enters
at / and passes through the inner tube c to the burner
bye, or vice versd. The instrumeul isset by warming
it to the desired temperature, and then pushing down
b till the end of c touches the mercury. The gas
is then prevented from passing through <*, and only
enough passes through the hole d to keep the flame
alive, till, the instrument becoming cooler, the mercury
contracts, and allows the gas again to pass through
the lower end of c.

FIG. 332.— Water-bath for experi-
ments mi digestion, o) fur evapor-
ating a1 a constant temperature.
This consists "i" two parts, the
bath itself , i, and an apparatus, a,

for keeping the water in the bath
at a constant level, (i, I-. .
flask containing water, b, c, is
i -lass tube open at hoth
ends. d,e,f, is a bent tube with
limbs of equal length. The end.
e, ispnf at the level at which the
watei in 'Ii.- bath, i, is to remain.
Both ends, d and/, are about an
inch below c, ami thus form a

5 S p] I difference

qi verti-
cal distance between c and </, t>r
about an inch. Whenever the
water in i falls below the level
of c, thesyphon arts, and water

runs through it nnl il the level in

/ i as high as c, when it ceases.
ff, is opposite a thermometer for

temperature of

the i«ath. //, is a gas regulator.
The on.- represented here differs

somewhat trom thai in fig, ; ;i, hut.

re expensh e and has no

advantage 0 a fcheol her. t, is

anc or in). The dotted line

it . covered ....;. 1 .- plati perforai <l with boles, in which bi it .on

basins can be put. The

rhe perforated pi 1 ; toved, and a large

dialyzer, flg. v;7, put in Its place, when dig tion and dlarj are bo bi a sd or ai the ami in,..'. /, 1. b tin

in which dj m pla 1 d 1 he boli in the apper plate oi the nu 1 are

numbered '" ' '"' ,! '" tlie

lower plate are much small* 1 than In the upper, and lerve only to prevenl the tubes from Up]

1 -,- of the syphon in v.

Plate CXIX.

FIG. 334-— Screw-press. The substance from which the
fluid is to be expressed is wrapped iu strong flannel or
calico, and the liquid which oozes out is collected as it
runs from the small spout.

tPtG-335' — Bunsen's witter air-pump. This consists of a
wide glass-tube at into which another tube b,b',b", passes
air-tight, c. is au india-rubber tube connecting a with the
w;tter Supply, d, is a clamp to stop the flow of water
through c. e, is another clamp to regulate the flow. /,
is a reservoir to prevent any water which may accidentally
come over from getting into J. <f, is a plug to let out
any water from /. 7*. is a screw for connecting a air-tight
to a piece of tubing, which should pass 32 feet, if jwssible,
below the level of a. i, is a piece of strong india-rubber
tubing to connect the air-pump withy, the bell-jar, to be
exhausted. The water rushes in at c and down h, carrying
bubbles of air with it, as shown opposite a, till the exhaus-
tion is complete, a is represented as half full of water.
k, a funnel fixed air-tight in the india-rubber stopper of j.
I, a small cone of platinum foil to prevent the filter

from being broken, m, a plate of ground glass, n, a beaker to receive the filtrate. N, a manometer to measure
the degree of exhaustion, o. apiece of platinum foil <>f the proper, size and shape to make the cone, /. #, a mould,
and t, a stamp, to give the proper Bhape to the cone, Z. /», is a cone of porous earthenware used as a funnel. 7, is a
piece of wide india-rubber tubing stretched over the funnel r, and holding the cone j> air-tight, r, is a
funnel inserted into the Btoppex Of a bell-jar. The bell-jar may either be exhausted by means of a tube in the
stopper* like j, or by ■< tubulature in tin- side, as is supposed to be the case with thai holding r.

l\ Iso 1 1 bo keep liquldsatthe

I then Luini 1 Om ol
•enlng above, mi below, which la closed b b the tube

.

lee with which the metal fui I Oiled, rh< """' '""" bae a copper fu 1 of the dotted Mue

itn,j ^ o,, ■ I ■ ' oded by the water oi Ice

then tore xuA <■■ removed n Ith great

place whirl, lei* ■ n the othei form [seni] ■'

■ he The uppi r figure si tysei e*lth the 1 1 n1 papt - tret bed

Plate CXX.

Fig. 339. — Hut ait bath fur drying precipi-
tates, &c.

FIG. 340.— Bell-jar aud dish, containing sulphuric acid
for drying aud cooling substances.

FIG. 342.— Platinum triangle stretched
upon a larger iron one for ignition.

FIG. 343.— Specific gravity bottle.

FIG. 344. — Specific gravity bottle.

FIG. 345. — Bottle for taking the spe-
cific gravity of small quantities of
liquids.

1

Plate CXXI.

- tie nulDi fl»»k. {tram Huit.ui» Handbook "f Volumetric Aoalyil*.)
■tat mixer. (From Button'! Handbook ol Volumetric AnalyiU.)

Tlate CXXII.

50 CC

10 CC

3

PBj. 3(8.-1 ! " Bnthm'i Handbook "f Volumetric ArmlyniH.)

Bandbook of 7oluin*trio Ajwlyrii.]

Tlate CXXIII.

Pig. 350

Fir;. 351.

FI8. 350. From Sutton's Handbook of Volumetric Analysis. The figure to the left shows the elliptical appear-
ance presented by aline round a burette or by the surface of fluid in it. when the eye of the observer is above
it. The figure to the right shows the curved surface of fluid in a tube. In reading off its level, the lower border
of the dark zone must coincide with the graduation of the burette as ill the figure, where the dark line stretch-
ing across the tube indicates one of the graduated lines upon it.

FIG. 351.— Erdmann's float. (From Sutton's Handbook of Volumetric Analysis.)

! " PiF-

" t:ji

1

llr

^-=^j

|ii..mni"imi

i' ii-'n

i<

V *"■"•'> >'•"!»

no

PIO. 352.— Stand for burettes. (From Sntton's rTaudbookof Volumetric Analj I |

Kii;. 35 (.- , harameter. a and 0 are two N I's prisms, of which, i, is fixed, and the other, a, U movable'

t, ii an Indicator t., show the position "f a. « », Is a circular graduated disk lor measuring the rotation ■•! •<. g, Is I

nompoa doi two pieces, v. Is a single plate "f quartz. Sand ". are the soak and vernier of thi mpen-

sator. r, the screw bj which thee mi ensatoi Ii ai - '. ars the two quarts prisms of whioh the com-

ug the tube of fluid for examination.

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THE POLYCLINIC. Vol. V.

A Monthly Journal of Medicine and Surgery. Doubled in Size Without Increase of Price.

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EDITOR-IN-CHIEF, HENRY LEFFMANN, M. D.

The Polyclinic for 1888 will Contain

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number of articles on practical subjects will also appear. A series of articles by Dr. J. Henry C.
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REGULAR CONTRIBUTORS.— Chas. H. Burnett, m.d. (Otology), Arthur Van Har-
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Clinical Lectures, Papers and Original Articles appeared by the following gentlemen during
1887:—

Goodell (Prof. Win.), Univ. of Penna. Bantock (Geo. Granville, f.r.c.s.), London.

Meigs (Dr. A. V.), Phys. to Penna. and Child. Hosp. ] Pepper (Win., m.d. ), Prof. Pract. of Med. Univ. of Pa.

Osier (Prof. Wm.), Univ. of Penna. Carter (Dr. Landon Gray), Prof, of Men. and Nerv.

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Longstreth (Dr. Morris), Pathologist to Jefferson

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Ashhurst (John, Jr.), Prof. Clin. Surg., Univ. of Pa.
Packard (Dr. John H.), Surg, to Penna. Hospital.
Parvin (Theophilus), Prof. Obst. and Dis. of Women,

Jefferson Med. Coll.
Wyeth (John A.), Prof, of Surg., N. Y. Polyclinic.
Reese (Dr. John J.), Prof, of Med. Jurisprudence,

Univ. of Pa.
Spender (John Kent, m.d.), Bath, England.

Browne (Lennox, f.r.c s.), London.

Brubaker (Dr. A. P.), Dem. of Physiology Jefferson

Med. Coll.
Steele (D. A. K., m.d.), Prof. Orth. Surg. Coll. Phys.

and Surg., Chicago.
McMurtrie (Dr. L. S.), Danville, Ky.
Tyson (Dr. Jas), Prof. Pathology, Univ. of Penna.
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