A STUDY OF THK MICROSCOPIC PHENOMENA OF INFLAMAT- 
ION, WITH SPECIAL REFERENCE TO DIAPEDESIS OF THE 
WHITE BLOOD CORPUSCLE. 
Bv Charges F. Craig, M. D. A STUDY OF THE MICROSCOPIC PHENOM- 
ENA OF INFLAMMATION, WITH SPECIAL 
REFERENCE TO THE DIAPEDESIS OF 
THE WHITE BLOOD CORPUSCLE. 
Charles F. Craig, M. D., Danbury, Conn, 
Away back, in the olden times, observers noticed that a 
majority of the diseases of mankind were accompanied by 
certain symptoms, and these were constant and formed an un- 
broken chain in many instances. These symptoms were: swelling, 
redness, pain and heat in the diseased part or organ, and also, at 
times, an increase in the pulse rate and a rise in the general 
temperature of the body. 
We, to-day, have no difficulty in recognizing here the charac- 
teristics of inflammation and fever. The tissue which was red, 
swollen and painful was said to be inflamed, while if there were 
an increased pulse rate, higher temperature, and a change in the 
chemical activities going on within the body, there was said to 
be fever. 
The connection between the two was generally easily seen, but 
sometimes one occurred without the visible presence of the other, 
and their connection became obscured, but there came a day 
when the microscope was introduced into medical research and 
then the production of inflammation and fever were closely 
studied and light was shed on what was before darkness. 
By careful experiment the following facts have been proved 
regarding the origin of inflammation. First, there is, on irri- 
tating the tissue experimented upon, a contraction, followed by 
a dilation of the capillaries, then a migration through the capil- 
lary walls of leucocytes or white blood corpuscles, which spread 
into, and increase in the surrounding tissue ; then a blood stasis 
in the dilated capillaries and a congestion in the inflamed area. PROCEEDINGS OF THE 
These are accompanied by disturbance in the nutritive processes 
and a heightened temperature. 
With the thought in my mind that we learn new things only 
by more carefully and patiently observing old ones, I spent 
nearly all of the three months in the Summer of ’93 in studying 
beneath the microscope the following phenomena of commencing 
inflammation : dilatation of the capillaries, slowing of the blood 
stream, and the escape of the leucocytes or white blood corpuscles 
from the blood vessels into the surrounding tissue. 
I made these observations with but little hope of discovering 
any new facts where such observers as Cohnheim, luster, Strieker, 
Bottcher and others had so carefully and scientifically worked but 
simply to convince my own mind of the truth of their revelations, 
and to decide, if possible, certain points regardingthe diapedesis cf 
the leucocytes which are still in dispute. 
It will hardly be necessary for me to state that my results con- 
firmed their observations, and in one or -two points, my observa- 
tions, although differing somewhat from theirs, have cleared up 
to my own mind, disputed questions, the principal of which is 
that regarding the part taken by the leucocyte in its passage 
through the vessel wall. 
I do not wish to put forward any new theory, but simply state 
that which I observed, leaving to others the task of working out 
the theory which will accord with the facts. My observations 
were made upon the foot-webs and mesenteries of ten frogs and 
in this paper I do not intend to give a description of each individ- 
ual experiment which would be but repetition, but simply to state 
my general results and conclusions. 
The drawings inserted were made free hand, without a camera 
lucida, which will account for their crudity and comparative sim- 
plicity. 
METHOD. 
The method I have followed is simple in the extreme. 
First, I constructed a platform for the stage of my microscope, 
on which to place the frog. This consisted of the parts which 
the diagram on the opposite page shows. 
A is a piece of cork, twelve inches long, four inches wide and 
half an inch in thickness. At the center of its long diameter and AMERICAN MICROSCOPICAL SOCIETY. 
167 
an inch from its side I cut a hole about two inches long and an 
inch wide, as at B. Over this I placed a glass slide, such as is 
used in microscopy, sinking its two ends, (a and b in cut) even 
with the surface of the cork. As will be seen the slide entirely 
covers the hole in the cork, which reaches from cto d. The 
circle drawn in the center of the slide at f merely indicates the 
situation of the aperture in the stage of the microscope, through 
which the light comes when the apparatus is placed upon it. 
Fig. 1. 
A quarter of an inch, from the outer edge of the slide (at g) I 
cut a groove in the cork running a little beyond the ends of the 
slide and parallel with it, and a quarter of an inch from each end 
of this groove, another groove at right angles to it, which is con- 
nected with a rubber pipe (m) to allow for drainage, if needed. 
The cut is drawn as the apparatus looks when it lies upon the 
stage of the microscope, the posterior portion of which is seen at 
S. This apparatus is simply fastened upon the stage of the mic- 
roscope, seeing that the glass slide covers the aperture in the 
stage, and the frog arranged upon it, after being curarized by in- 
jecting a little of a watery solution of the poison in the dorsal 
lymph sac. 
If the*web of the foot is to be examined it is simply stretched 
across the slide at “ f ” and held in place by felted pins, placed 
between the toes but not piercing them. 
If the mesentery is to be examined, the frog is placed on the PROCEEDINGS OF THE 
apparatus after being curarized, the abdomen carefully opened and 
the intestine gently lifted out with felted forceps and placed in the 
groove “ e ” thus stretching the mesentery smoothly over the 
slide at “ f,” where it can be easily examined. My method was 
to get a fresh frog from a pond near by, each time I needed one. 
On the first ten frogs I made no observations whatever of the 
mesenteries, but only of the foot webs, while on the last ten I 
observed the changes in the mesenteries only. I tried to observe 
as carefully and as long at a time as I could, and I would say 
here that it is only by watching this process of inflammation from 
the time it commences until we can no longer follow it with our 
microscopes, can we hope to see and understand all its phenomena. 
I found it intensely tiresome to observe longer than eight consecu- 
tive hours at a time so that I probably missed much that I might 
otherwise have seen had I had greater endurance and patience. 
EXAMINATIONS OF FOOT-WEBS. 
In examining the foot-web of a frog with a medium power, say 
a two-thirds inch objective, we will notice a condition of affairs 
which I have tried to illustrate in Fig. i. The first thing noticed 
is the great number of vessels and capillaries, filled with a 
swiftly moving current of blood ; so swiftly indeed does it move, 
that the constituents of the blood can not be distinguished, and 
we see it only as a never ending motion, without known compo- 
sition. 
At various situations in the field beautifully branched pigment 
cells are seen (d Fig. 2), and on carefully focusing we can distin- 
guish the cells of the surface epithelium, each cell containing a 
barely distinguishable nucleus (e, Fig. 2). This is the appearance 
of the web before it is acted upon by an irritant, and such will be 
the appearance for hours, if the part is kept moistened and not 
irritated. 
But on touching the web lightly with nitrate of silver, or even 
scratching it with a needle, we get an entirely different appear- 
ance, and the process of inflammation begins. At once* there is a 
dilatation of the arteries, this dilatation extending gradually to 
the veins and capillaries. As far as I could determine this dilata- 
tion was not preceded by any contraction, and affected the arteries AMERICAN MICROSCOPICAL SOCIETY. 
169 
mostty, and the capillaries but slightly, although the ratio may 
have been alike. This dilatation seemed to increase steadily for 
about six hours, although Cohnheim states that it steadily and 
slowly increases for twelve hours. 
At the beginning of this dilatation there was an acceleration in 
the flow of blood plainly noticeable, but this, after lasting only 
about an hour, resulted in a considerable retardation of the flow, 
the vessels still remaining dilated. This is shown in Fig. 3. 
After an hour, and sometimes in the smallest capillaries, much 
sooner, pulsation became evident and the current of blood so slow 
that, in the small veins and capillaries, the individual corpuscles 
became distinguishable. They can first be distinguished in the 
veins. In two of my observations, this dilatation took place and 
subsided without any of the other phenomena of inflammation 
occurring, but, afterwards, a second dilatation with slowed stream 
came on slowly, which was constant, lasting as long as the caues 
operated. This last dilatation was, no doubt, the vascular change 
of the inflammation, due to the irritation. Returning to the time 
when the corpuscles are first to be distinguished, the following 
phenomena were observed. Using now a one-sixth objective. 
As the blood stream became slower, white corpuscles or leucocy- 
tes were seen in the plasmatic .layer in the smaller veins, rolling 
along sticking here and there, coming to a stand still for a few 
seconds, then rolling on again, and at last often sticking fast to 
the vessel wall, resisting all attempts of the current to dislodge 
them. A vessel at this time presents the appearance illustrated 
in Fig. 3 and 4, the white corpuscles being scattered here and 
there along the vessel wall, while the central canal of the vessel, 
enclosed on each side by the plasmatic layer in which the leucocy- 
tes lie is filled with the red corpuscles which can be distinguished 
very readily as the stream gets slower and slower. One of two 
things now generally occurred, either the leucocytes continued to 
accumulate on the vessel wall or else the vessel became so thickly 
packed with corpuscles as to present the appearance of a red in- 
jection mass, all movement ceasing. (See Fig. 5.) The contents 
of the vessel sway forwards and backwards with the impulse 
transmitted to the stream by the beating of the heart. This is 
known as the stage of oscillation and is succeeded by a complete 
stagnation, called stasis, in which no movement of any kind oc- PROCEEDINGS OF THE 
curs. I have spoken of the accumulation of leucocytes along 
the vessel wall, as though in this last instance it did not occur ; 
by this I mean that in my observations the vessel filled so rapidly 
that the accumulation of leucocytes was hidden from view, al- 
though if the field thus obscured be watched long enough the 
leucocytes are found congregating outside the vessel, thus show- 
ing that diapedesis still goes on. Where, however, the blood 
stream still continues to move on, the leucocytes accumulate more 
and more, until the vessel wall in some cases, becomes lined with 
them often two or three cells in thickness, as in Fig. 4. If 
such a small vein be watched very carefully for a varying space 
of time, from half an hour to several hours the following phe- 
nomena are seen to take place. (It is not necessary, however, 
that the vessel wall be lined with leucocytes in order that these 
phenomena take place, for in all those observations in which I 
obtained the clearest and best view of the process the leucocytes 
were only situated here and there upon the vessel wall.) As the 
vessel wall is watched, the leucocytes are seen to gradually pene- 
trate its wall, and finally to emerge upon the other side, having 
passed entirely through the vessel wall into the surrounding 
tissues. This process seems to be divided into four distinct acts 
which I have tried to roughty illustrate by Figs. 3to 9. At first the 
leucocyte is seen to adhere to the vessel wall, as in Fig. 3 and 4, 
then it sends a process into and through the wall, as in' Fig 6, fol- 
lowing this, the remainder of the cell is drawn after or follows 
this process, at one time in its passage appearing, constricted in 
the middle in Fig. 7 and finally, the leucocyte passes completely 
through the wall, and moves into the surrounding tissue, by 
virtue of its amoeboid movements. 
In these four acts, the process, known as the diapedesis of the 
white blood corpuscles or leucocytes consists and it is said to be 
due partly to the independent motility of the leucocytes themselves 
and partly a filtration of the colloid mass of the cell by the force 
of the blood pressure and probably taking place through the 
spaces between the endothelial cells, the vessel wall itself hav- 
ing been altered in some way, by the process of inflammation. 
In my observations, I very carefully watched all of the phen- 
omena and could observe nothing peculiar during the first 
stage, i. e., adherence to vessel wall, but, in the second stage, AMERICAN MICROSCOPICAL SOCIETY. 
171 
i. e., when the cell sends out its process into the wall, I observed 
a strange thing, namely : that the process sent into the wall by 
one cell was almost identical with the process that any other cell 
sent out both in size and general outline. 
This process was a cone shaped rather pointed one, wdiich 
seemed to wTork its way into the w7all of the vessel, and in fact, it 
seemed to quietly and steadily push its way on and in, until at 
last it emerged upon the other side of the vessel. I also observed 
in every case which I observed, where, after adhering the leuco- 
cyte was swept from its hold and carried on in the current, that it 
retained its penetrating process, (see Fig. 9 a and b) and did not 
as long as I could see it, regain its irregularly circular shape. 
From these two facts it seems more than probable that this 
penetrating process is due to the action of the cell itself rather 
than that it is such a one as would be produced by the blood 
pressure acting upon the soft colloid material of the cell and 
pressing it into the vascular wall, for a process so formed would 
disappear as soon as the leucocyte was swept off into the current. 
Again, the uniformity of the shape of the process tends to 
favor the view that the leucocyte penetrates the vessel wall mostly 
by its own independent power of locomotion. 
Now. as the leucocytes penetrate the vessel in greater and 
greater numbers, as serum accumulates also, the surrounding tis- 
sues become infiltrated as in (Fig. 9) and the field observed 
through the microscope becomes covered by a false membrane 
composed of leucocytes, connective tissue cells, film and serum. 
The above facts constitute the phenomena of inflammation which 
I observed in the web of the frog’s foot ; I did not carry my ob- 
servations further, as I mostly wanted to study the diapedesis of 
leucocytes, and I found that owing to the amount of material in 
the field, other than blood vessels, i. e., pigment cells, epithelial 
cells, etc., I could not obtain a good clear view of the process, 
and I accordingly conducted all my other observations upon the 
mesenteries of frogs, and obtained, I believe a much more accu- 
rate view of every step of the process as far as a microscope will 
reveal it. From the foot-web of a frog then I observed besides 
the process usually described as the adherence to and penetration 
through the vessel wall of the leucocyte two distinct and charac- 
teristic phenomena. 172 
PROCEEDINGS OF THE 
1. The process, which any leucocyte sends into the vessel wall 
in penetrating it, is almost identical in size and shape, with that 
which any other leucocyte sent off in the same act, or in other 
words, the leucocytes all send off similar processes into the wall 
of the vessel before penetrating it. 2. In all the cases which I ob- 
served, if a lencocyte, after sending off such a process, is swept 
from the vessel wall by the current it always retains that process 
and does not return to its former shape, providing it had really 
began penetrating the wall, as long as it remain in the field of 
vision. 
OBSERVATIONS ON THE MESENTERIES 
At this point I transferred my "observations to the mesenteries 
of frogs, but before doing so I made a thorough examination of 
the corpuscles of the frog’s blood with the following results ; Be- 
sides the oval red corpuscles I found there are two distinct kinds 
of white corpuscles present in the frog’s blood. See Fig. 10. 
1. The most numerous are large, about TyVo in- in diameter, 
irregular in outline, having fine projections from their surface 
and finely granular. They have two, or generally, three nuclei 
or three part nucleus. 
2. The second variety is less numerous, more coarsely granular, 
smaller and contain but one nucleus. The granules in the pro- 
toplasm are sometimes seen to rush from one side of the corpus- 
cle to the other. They both have active amoeboid movement. 
Unfortunately I could not distinguish these varieties in my ob- 
servations, on the process of ‘inflammation for the following rea- 
sons : 
1. In the small vessels, which I preferably watched, the white 
corpuscles were so few in number that the two varieties did not 
happen, in the cases I observed, to occur together, while if the 
leucocytes were present in larger numbers, they were so crowded 
that the difference could not be distinguished. 
2. The nuclei of the leucocytes cannot be readily distinguished 
without using reagents, which would have interfered with the 
process of inflammation. 
I found it necessary, as I have stated, in order to clearly de- 
fine the neuclei to use reagents. Adding to the blood a little di- 
lute acetic acid, clears up the surrounding protoplasm and brings AMERICAN MICROSCOPICAL SOCIETY. 
173 
the nuclei very clearly into view. Magenta may now be added 
which gives a, very fine stain. Adding dilute alcohol will also 
bring the nuclei into view. 
Having now thoroughly examined the blood, I next examined 
my field of operation, the mesentery. This is composed of the 
following elements, being a most typical example of all serous 
membranes. It is transparent and consists of : 
1. Very delicate connective tissue fibres. 
3. Some elastic fibres, the whole being traversed by a beautiful 
net-work of lympatics and blood vessels. In order to watch for 
a long time, the process of inflammation in the mesentery, it is 
necessary to keep it moistened by a weak salt solution per 
cent.) 
2. Connective tissue cells. 
Carefully opening the frog’s abdomen and spreading the mesen- 
tery over the slide as described, I observed the following phe- 
nomena ; 
A slight inflammation is caused by simply exposing the mesen- 
tery to the air and there is a slight dilatation of the arteries with 
an accelerated current, and we get an appearance like that in 
Fig. 11. 
The stream of blood is so rapid that it is impossible to distin- 
guish the individual corpuscles, hut gradually, the irritation being 
kept up, in from four to five hours, if in a medium sized vein the 
stream begins to grow slower, and soon the corpuscles become 
distinguishable, first in the smaller vessels, (see Fig. 12). 
This slowing occurred sooner in the mesentery than in the web 
of the foot, and more rapidly the greater the irritation. 
As the stream grows slower the same phenomena are observed 
as in the web, i. e., the red corpuscles occupy a central position 
in the vessel said to be due to their greater specific gravity, for in 
1868, Schklarewsky showed by physical experiment that particles 
of least specific gravity in glass capillaries are pressed toward the 
capillary wall, while the ones of greater specific gravity remain 
in the center of the stream. 
On either side of the stream of red corpuscles is a zone of 
plasma in which most, but not all, of the white corpuscles are 
moving. In the smallest capillaries the red corpuscles move 
along in single file, sometimes being compressed between the walls, PROCEEDINGS OF THE 
but regaining their former shape by virtue of their elasticity on 
reaching larger vessels. The white corpuscles are plainly seen 
rolling along, sticking here and there on the vessel wall, some- 
times being swept off again by the axial current. There is now 
an appearance like that sketched in Fig. 12 the red corpuscles be- 
ing plainly distinguishable, and the white ones adhering here and 
there to the vessel wall. 
At this point the leucocytes begin to penetrate the vascular 
wall, and as I carefully watched the process, in nearly a hundred 
different locations in the mesenteries, from nearly all of them I 
obtained the following results. 
1. After a leucoc3de has remained for a variable length of time 
upon the vessel wall, and just before it can be seen to send a pro- 
cess into the wall, the granular matter in its protoplasm all seems 
to be in motion and congregates thickly at that portion of the 
leucocyte furthest from the vessel wall, or, in other words, nearest 
the axial stream of the vessel. (See Fig. 13). 
2. The leucocyte next sends off a process which was almost 
exactly the same in outline and size, in every case which I ob- 
served, being composed of protoplasm entirely free from granules, 
and which seems to gradually push or work it’s way into the wall. 
See Fig. 13. 
3. Now -occurs a most singular thing. As the vessel wall at 
last gives way and the process of the leucocyte emerges upon the 
outer side of the vessel, the granules, which have, during the 
penetration of the wall, been congregated at the point in the leu- 
cocyte furthest from the wall, these granules fly swiftly through 
the passage thus made in the vessel wall by the protoplasm of the 
cell, from the interior of the vessel to the furthest point of the 
process outside the wall, leaving the part of the leucocyte not yet 
through the wall, free of granular matter. This now passes 
through and the leucocyte regains its former shape, the granules 
becoming distributed over its surface. See Figs. 14 and 15. 
In several instances while the leucocytes were in the act of 
penetrating the vessel wall, they were swept from it by the blood 
current but the granules still held their position in the part of the 
cell away from the penetrating process, and more than this, in 
one case, a leucocyte so swept away adhered again to the wall 
while still in the field and penetrated it with the self same process, AMERICAN MICROSCOPICAL SOCIETY. 
175 
passing through all the stages mentioned. These phenomena in- 
dicate to my mind that the leucocytes penetrate the vessel wall 
largely by their own activity, and I am convinced that such is the 
fact. 
As the blood-stream becomes slower and slower the process 
becomes obscured by the accumulation of leucocytes, and when 
at last the current stops, the vessel becomes filled with them and 
diapedesis can no longer be watched. 
To sum up, then, the following facts are those which I think 
are most important, and which I have not as yet seen any other 
account of: 
1. The leucocjdes, in penetrating a vessel wall, send off pro- 
cesses similar in shape and size. 
2. If a leucocyte, while in the act of penetrating the vessel 
wall, be swept off into the blood current, it retained its penetrat- 
ing process, as long as it remained in the field. 
3. The granular matter in the leucocytes becomes massed in 
the portion of the cell furthest from the penetrating process, so 
that the process contains only clear protoplasm. 
4. If the leucocyte be swept away while penetrating, the 
granules still retain their position, and in one case, the leucocyte 
was seen to again attach itself to the wall, and use the same pro- 
cess in penetrating it. 
5. The clear protoplasmic process works its way through the wall 
and in the channel of protoplasm thus formed, the granular mat- 
ter rushes through the wall and occupies the clear process which 
is now outside the vessel, leaving clear the portion of the leuco- 
cyte still within the vessel. 
6. This clear portion soon comes through the vessel wall, and 
the leucocyte regains its original shape, the granules being distri- 
buted over its surface. (See Fig. 16.) 
The thought came to me that perhaps it was the granu- 
lar corpuscles, heretofore described, in which the granules are 
seen to change their position, that were the ones which penetrated 
the wall, but when I considered the small number of this variety 
as compared with the large number of leucocytes so escaping, I 
am forced to conclude that it is probabty the finely granular 
variety which constitute the larger part of the escaped leucocytes. 
Of course the phenomena described give rise to many interesting 176 
PROCEEDINGS OF THE 
questions, but to me it seems evident that the condition brought 
about by irritation, causes in the leucocyte a certain abnormal ac- 
tivity which is manifested by these phenomena, and when we 
know that even in health some leucocytes escape from the ves- 
sels, it looks as if this was simply an exaggeration of a normal 
process. I could not determine as to whether the escape took 
place through the stomata or not. 
In conclusion I would say that while some of the phenomena 
described are exceptional to hitherto made observations, still, in 
the words of Claude Bernard, “In physiological (or other) 
studies we must always carefully note any fact that does not ac- 
cord with received ideas, for it is always from the examination 
and discussion of this fact that a discovery will be made, if there 
is one to be made.” 
WORKS REFERRED TO. 
Billroth, Theodor. Die allgemeine cbirurgisclie Pathologic andTherapie. 
Cornil ET Ranvier. Manual d’Histologie Pathologique. 
Cohnheim.- Vorlesungen liber allgemeinen Pathologic. 
Foster, M. Text Book of Physiologic. 
GREEN. Pathological Anatomy, 
LESTER, J. On the Early Stages of Inflammation. Philosoph. Trans.,lBs9. 
Landois and Stirring. Text Book of Physiology. 
Paine. General Pathology. 
PAGET, Sir J. Lectures on Surgical Pathology. 
Recklinghausen. Handb. d. allg., Path., in Deutche Chirurgie. 
Sanderson, J. Burdon. Inflammation, in Holmes Surgery. 
STRICKER. "Studies in Wein. 1869. 
Virchow. Die Cellular Pathologic. 
Woodhead. Manual of Pathology. 
YEO. Manual of Physiology. PLATE I. 
2 
Observations on Foot-ioeb 
3 
4 
■red corpuscles. 
-leucocyte. AMERICAN MICROSCOPICAL SOCIETY. 
177 
PI,ATB I. 
Fig. 2. The web of a frog’s foot as seen under a medium power, 
a, an artery. 
c, a capillary. 
d, pigment cells. 
e, surface epithelium, which can be seen by focussing. 
The stream is so swift that the individual corpuscles cannot be seen. 
Fig. 3. A vein, as it appears when the current begins to slow. The red cor- 
puscles can be seen in the central portion of vessel, while the 
white corpuscles or leucocytes creep slowly along vessel wall, 
sticking here and there. 
Fig. 4. Showing a vessel in which the current has nearly come to a stand- 
still, and the leucocytes are seen arranged in rows along its wall. 178 
PROCEEDINGS OF THE 
PLATE 11. 
Fig. 5. A vessel in which the corpuscles have accumulated to such a decree 
that the current is blocked, and the vessel seems simply to con- 
tain an injection mass. 
Fig. 6. Showing the leucocytes sending forth processes into the vessel wall 
which resemble each other in shape and size. 
Fig. 7. Leucocytes partly through vessel wall, showing constriction in their 
center. 
Fig. 8. Leucocytes after penetrating vessel wall, showing their power of 
regaining their former shape. 
Fig. 9. Appearance of a vessel and surrounding tissue after the process has 
gone on for some time. 
At a and b leucocytes may be seen which have been swept from vessel 
wall, while penetrating it, showing how they retain the process. 
OBSERVATIONS ON MESENTERIES. 
Fig. 10. The two varieties of white corpuscle in the blood of the frog. 
a, large corpuscles, having a bi-or tri-part nucleus, finely gran- 
ular. 
b, small corpuscle, having single nucleus and coarsely granular, 
and in which the granules may be seen to rush from one side 
to the other of the corpuscle. 
Ffig. 11. Appearance of mesentery of frog under a medium power, at time 
of exposure, 
a, artery. 
b, vein. 
c, capillaries. 
The current is so swift that the corpuscles cannot be distinguished. I 
have drawn the mesentery proper simply as a homogeneous mass. ’ PLATE II 
5 
6 
7 
S 
9 
20 
11 PIvATE 111. 
14 
1Z 
13 
15 
16 
JBLood Capillary. AMERICAN MICROSCOPICAL SOCIETY. 
179 
PLATE 111. 
Fig. 12. 
Stage of slowing of stream in mesentery. 
a, an artery in which the current is still swift. This should have 
been shown as in Fig. 11. 
b, a small vein, in which the current is slow, and the red and 
white corpuscles can be distinguished. 
Fig. 13 
Small vein of mesentery. Leucocytes may be seen sending off 
process, which is clear of granules, (a and b.) 
Small vein of mesentery. The leucocytes are seen partly through 
vessel wall, the penetrating part being clear, and some are seen 
in which the granules are flying through the passage made by 
clear protoplasm of the cell. 
Small vein of mesentery. Showdng leucocytes which have pene- 
trated and the granules are again distributed over entire cell, and 
also some which are nearly through wall and in which the gran- 
ular matter is in the part which is entirely without the vessel 
Fig. 14. 
Fig- 15 
wall, as at A. 
Fig. 16, 
Diagram illustrating the points made, 
a, leucocyte before penetrating. 
b, leucocyte sending off process, and granules beginning to with- 
draw to farther end of cell. 
c, leucocyte partly through wall, granules at upper end of cell. 
d, granules flying through passage made by clear process. 
e, granules arranged in portion of leucocyte farthest from vessel. 
f, leucocyte after penetrating, resuming its original appearance. 
g, leucocyte swept from wall showing retention of the clear pen- 
etrating process.