28 
HEMOLYMPH NODES OF THE SHEEP 
venous lacunae as it penetrates deeper and deeper into the lymphatic 
tissue, apparently without the intervention of venules or capillaries. 
The above considerations and observations seem to indicate quite 
clearly that the blood which enters a hemal node, wholly devoid of blood 
islands and a peripheral (sinus) or subcapsular blood space, through 
the artery, passes through arterioles and capillaries directly into the 
venous lacunae or true sinuses. From here it may, in some cases at least, 
at once enter the larger central venous spaces, if present, and hence pass 
directly to the vein ; or it may in the absence of a main intra-nodal vein 
enter the efferent vein directly from the lacunae. Since in the above 
case the absence of blood islands and blood spaces has been assumed, the 
relation of these structures to the circulatory conditions will be consid- 
ered farther on. Consequently the only thing open to question in the 
above premises is the manner of termination of the arteries, their rela- 
tion to the blood spaces or areas when present, and to venous lacunae, 
and the relation of the latter to the vein. That the arteries end in capil- 
laries, is easy to demonstrate ; but it is very difficult to demonstrate satis- 
factorily that these capillaries communicate directly with the venous 
lacunae, except experimentally. The presence in arterial injections of 
the injection mass in the lacunae is, of course, alone sufficient evidence 
to establish a direct connection between the latter and arteries ; but it 
must be admitted that the actual demonstration of a direct continuation 
of an injected capillary into an injected lacuna is only very occasionally 
possible. This fact may, to be sure, be accounted for by the contractil- 
ity of the small arterial endings, and especially by shrinkage of the node, 
as a result of which the injection material contained in the fine arteries 
is forced out into the relatively very much larger venous lacunae. The 
direct communication of the lacunae with the larger venous spaces, or 
with the veins, can, however, be seen easily, and can be demonstrated 
satisfactorily in both injected and non-injected specimens, even in the 
case of some very depleted nodes. Since the lacunae form a venous 
plexus of widely varying calibre, which must usually be many times the 
volume of the arterial tree, a decided disproportion between the size and 
volume of a capillary and the lacunae into which it empties naturally 
exists. Consequently it is evident that a decided slowing of the blood 
current must also take place here. 
Although all attempts to demonstrate the existence of an endothelial 
lining in the lacunae by means of silver stains have so far been futile, 
it cannot be doubted from microscopical examination of the ordinary 
specimens alone that such an endothelium exists. For, except at points 
