42 
HEMOLYMPH NODES OF THE SHEEP 
teration of both peripheral and central blood spaces seems very likely in- 
deed. Moreover, since the blood spaces are usually engorged with 
blood, which cannot be expelled from them by external pressure 
even when they are large, further proof is given that they probably 
are not as a rule in free direct communication with the veins. For these 
and other reasons, I have come to regard the blood islands — the blood 
spaces including, as a rule, the peripheral or subcapsular blood space — as 
very largely representing areas in which the parenchyma of the node has 
become depleted of lymphocytes, whose place has either wholly or partly 
been taken by blood. Since, however, this blood is usually in an appar- 
ently good state of preservation, it seems to follow that these areas when 
large must nevertheless have fairly good communications with the vas- 
cular system. That they are probably not in free communication with the 
arteries, however, seems to be suggested by the fact that no such com- 
munications could be demonstrated microscopically, and that they were not 
injected from the aorta ; unless the supposition that the blood contained 
in them prevented the entrance of the injection mass, can be accepted 
as an adequate explanation. The adequacy of the latter explanation seems 
doubtful, however, since, as already stated, it is usually impossible to 
demonstrate arterioles or capillaries opening directly into the blood spaces, 
although the direct communication of the latter with veins is occasionally 
seen. For even in the case of the small and definitely circumscribed blood 
islands, which are completely surrounded by lymphatic tissue and which 
lie more or less distant from neighboring blood spaces, a direct communi- 
cation with the arterial system could not be demonstrated. Consequently 
it is difficult to believe that such a direct communication, if it occurs at 
all, represents normal or at least common conditions. 
The Cellular Content 
For the purpose of studying the cellular content of hemal nodes, 
blood smears and cover-slip preparations from fresh nodes and from the 
blood of the vein draining the node were also examined. In order to be 
certain that the veins from which the blood was taken actually drained a 
hemal node, injections into the node were made later. Although no full 
discussion is here intended, the large number of nodes examined and the 
many different staining methods used, afforded every opportunity for a 
comprehensive study of the cellular content. 
As is well known, the ordinary lymphocytes form the great bulk of 
the parenchyma of most nodes. Small areas in which they mingled in 
anything like equal proportions with erythrocytes were only rarely found, 
