MIXED NODES 
51 
be sure, that the above results demonstrate that the mere presence or 
absence of free blood in the form of blood islands or intermingled with 
the parenchyma cannot and does not convert a lymph node into a hemal 
node. For if this were the case then there could, of course, be no such 
organs as true hemal nodes. The fundamental difference between lymph 
and hemal nodes, as pointed out and reiterated by Weidenreich, is the 
presence or the absence of lymphatics. It does not consist of or lie in a 
mingling of the vascular and lymphatic circulations of the node, or in 
the possession of sinuses and blood spaces common to both; nor merely 
in the presence of blood in the lymph spaces of lymph nodes. Further- 
more, there is another fundamental difference between hemal and lymph 
nodes which has been overlooked so far, but to which attention was di- 
rected earlier in this discussion. It was emphasized in connection with 
injections that, as is well known, in mature lymph nodes injected from 
the vascular system, the transition from the artery to the vein is a very 
gradual one. These injections of the vascular system present many fine 
arborizations, as is characteristic of the vascular system in general. In 
the case of hemal nodes, on the contrary, there apparently is no such 
gradual transition by means of capillaries, but by very wide sinuses, 
devoid of reticulum and having walls like capillaries. These open di- 
rectly into the draining vein, and communicate with the parenchyma and 
indirectly with the blood spaces. Hence it is evident that in order to 
change a lymph into a hemal node it is not only necessary to remove the 
characteristic lymph sinuses and lymph vessels, but to profoundly alter 
the vascular system. This fact and the fact that the distribution of the 
blood spaces — the so-called peripheral and central sinuses of hemal nodes 
— which are considered comparable to the lymph sinuses in lymph 
nodes, have a wholly different distribution, and do not as a rule form 
a communicating system, is also overlooked by v Schumacher, who con- 
cluded that an alteration in or an obliteration of the lymphatics is all 
that is required to convert a lymph node into a hemal node. 
Hemal nodes in which the lymphatics ended blindly in the hilus, as 
reported by Helly, or in the capsule, as reported by v Schumacher and 
denied by Helly, or in which all stages of partial penetration of the nodes 
by lymph vessels occurred, were not found. Lymphatics were either 
present or wholly absent in all nodes examined experimentally or micros- 
copically; and whatever explanation or explanations it may be possible 
to give for the occurrence of so-called hemorrhagic lymph nodes, — the 
occurrence of which no one doubts — i. e., nodes in which blood cells 
are present in the lymphatic sinuses and parenchyma — it must be evi- 
