MICROSCOPIC STRUCTURE 
37 
In addition to the large venous spaces in direct communication with 
the vein, usually located near the center of the node, when present, there 
are small and more numerous ones, termed venous lacunae' by Weiden- 
reich [37]. These dilated empty, or nearly empty, spaces are apparently 
most numerous and conspicuous in nodes which contain much more blood 
than lymphatic tissue (figs. 17 and 19). Indeed in such nodes they are 
frequently so numerous, so large, and so devoid of celluar content that 
they may give an almost fenestrated appearance to a section. In these 
specimens — and in general, for that matter — they are most evident near 
the periphery (figs. 8 and 11). In depleted nodes this fact can, to be sure, 
be easily accounted for by the fact that most of the remnants of the lym- 
phatic tissue are for some reason found in this location (fig. 18) ; but why 
they should be more evident here than elsewhere in the more typical nodes 
(fig. 8) is not so obvious. Although the configuration of these lacunae or 
true venous sinuses is an extremely irregular one, and although their boun- 
daries are not always well defined, it was nevertheless quite often possible 
to pass from one lacuna to another, along almost the whole circumference 
of a section of uninjected nodes. If, however, they were small, their com- 
munication, and in fact their continuity with other lacunae, was not so 
evident, although such communications and continuity undoubtedly 
existed. This apparent absence of inter-communications between lacu- 
nae can probably be explained by the fact that when the walls of the lacu- 
nae are in contact it is very difficult indeed, or impossible even, to dis- 
tinguish the latter from apposed reticulum fibers. Nor does the fact that 
no lacunae whatever were visible in sections of some nodes which had the 
appearance of splenic tissue, for example, necessarily imply that none 
existed ; for a hemal node — other than a completely depleted one — without 
lacunae would seem to be an impossibility, because of the probable or 
even necessary circulatory conditions which their absence would seem to 
imply. The absence of lacunae would practically transform the vascular 
system. Moreover, if the results of the many injections of the venous 
system of nodes can be used as a criterion, it is certain that lacunae are dis- 
tributed throughout the entire node, with the possible exception of the fol- 
licles ; unless, as seems improbable to me, the occasional presence of India 
ink in the latter can be taken as satisfactory proof of their existence here. 
Since, of course, the lacunae contain no reticulum, they must, I believe, 
be regarded as practically permanent structures which are an integral part 
of the venous system and intermediate in position in the circulation. 
Many of them persist until the last remnants of lymphatic tissue dis- 
appear (fig. 18). Moreover, whatever their relation to the arteries, since 
