i8 
HEMOLYMPH NODES OF THE SHEEP 
node from another probably was mainly due to the presence of blood, 
and to some condition within the nodes which prevented a re-flow of 
this blood to the arterial side. Such conditions alone, it seemed, could 
explain the above facts, for a system of filled tubes could naturally not 
receive more fluid without further distention of the vessels of the node, 
or of leakage or rupture. Consequently, the fat in the lumbar region, 
including the great vessels, containing especially numerous nodes, was 
excised en masse, as Weidenreich had done. By means of puncture in- 
jections of the nodes it was now found a very easy matter to force the 
injected fluids into adjacent or occasionally distant nodes, even if the 
flow toward the excised vena cava was unobstructed. Hence Weiden- 
reich's observations were easily confirmed by using similar methods. 
But these results now required an explanation ; for why should there be 
such difficulty in injecting one node from another with the nodes un- 
disturbed in situ in the carcasses? Although I have no wholly satis- 
factory explanation, it is probable, it seems to me, that the manipulation 
incident to excision of the tissue emptied the veins which drained the 
nodes, sufficiently to permit the injected fluid to enter. Besides, as shown 
by the many points of leakage when injections were made into nodes 
contained in excised tissue, the numerous anastomosing veins which are 
severed during removal of the tissue also gave opportunity for relief of 
pressure in several directions. Hence the condition of a system of closed 
tubes partially or totally filled with fluid no longer existed. It is evident, 
of course, that it is not essential that the vein which drains a node be 
completely full of blood to prevent the injected fluid from entering 
the node, or, on the contrary, that it and the node must be com- 
pletely empty before any injection mass can enter. All that is mani- 
festly necessary is that a sufficient quantity of blood be contained in the 
main or in the anastomosing veins to completely fill, or perhaps to suf- 
ficiently distend, the venous spaces within the node to make further in- 
jection impossible. For in case of a small node even a fraction of a drop 
of blood in advance of the injected fluid might effectually prevent a suc- 
cessful injection, unless the veins and venous spaces within the node are 
partially or totally empty. Since these conditions probably obtain more 
or less in excised tissue, it was possible to inject a series of three or four 
nodes lying in a row from one of their number, with a few drops of 
fluid. It was also occasionally possible to inject incidentally a network 
of minute retro-peritoneal veins — not lymphatics — from nodes in the ex- 
cised tissue; although such a result was never obtained in the many 
injections made directly into nodes in situ on carcasses. These veins, 
