LYMPHATIC AND VASCULAR RELATIONS 
^5 
These paths apparently always lie through a narrow barrier of lymphatic 
tissue between venous lacunae and the blood spaces. It follows from 
this, and from other considerations, that the peripheral and central blood 
spaces or islands are not necessarily, or even usually, in direct open com- 
munication with the venous system in many nodes. Hence it is easy to 
understand why color changes are not more manifest in hemal nodes dur- 
ing the progress of injections from the vena cava or aorta or during 
bleeding, and why pressure exerted upon isolated excised nodes does not 
empty the filled blood spaces. Moreover, it also helps to explain why, in 
case of puncture injections, the injected fluid is usually seen in the vena 
cava before any recognizable change in appearance of the node takes 
place, if the injection is made slowly enough. The probable correctness 
of this explanation is further confirmed by the results obtained by injec- 
tion in series of a number of nodes lying in a row in excised tissue, by 
puncture from the largest of them. When, for example, nodes i, 2, 3 
and 4, having a common effluent, were injected with India ink from 
node 1 under a free outflow, a sequence of events was observed as fol- 
lows. The vein draining the adjoining nodes and tributary to the vein 
draining node 1, also became filled. Now if these nodes and their veins 
form a series of decreasing size, the resistances offered to the inflow cf 
ink necessarily vary ; and hence it may happen, as was actually the case, 
that node 2 becomes injected before, and more completely than nodes 
3 and 4. Consequently, node 2 showed external color changes, while 3 
and 4 did not do so, or did so but slightly. On cutting such an injected 
series, it was found that in node 2, which had turned black, the ink had 
penetrated into the peripheral and some of the central blood spaces, as 
shown in fig. 6. In node 3, on the contrary, which had undergone no 
color change, the ink was confined entirely to the venous lacunae or true 
venous sinuses ; while practically no ink at all had entered node 4, which 
had likewise undergone no color changes. It is evident, however, that 
an outward change in color would occur in all nodes, whether they con- 
tained a peripheral blood space or not, if a sufficient quantity of the in- 
jection mass penetrated the node. 
It follows, from these facts, that it is generally very easy to dis- 
tinguish between an arterial and a venous injection from sections of in- 
jected nodes ; and I fail to see why Drummond declared it to be impos- 
sible to do so. This would be true even in the case of a venous injection „ 
in which the lacunae, the blood spaces, and the veins were entirely empty 
before injection ; for in such a case the arteries would remain unin- 
jected, which would not be the case if the injection had been made from 
