32 HEMOLYMPH NODES OF THE SHEEP 
dated by these considerations than the current and more or less accepted 
statement regarding the circulatory conditions in the spleen is invalidated 
by similar considerations. To be sure, a purely mechanical explanation is 
not suggested as adequate or final; but since this conception not only 
harmonizes with the observed facts but quite satisfactorily accounts for 
most of the difficulties, it seemed justified. 
In the assumed case, then, in which practically all of the node is 
formed by a mass of lymphatic tissue containing a few blood cells, the 
supposition would be that there is a very slow movement of lymphocytes 
from the parenchyma into the blood stream, and a correspondingly slow, 
though not necessarily a purely passive movement of the blood cells in 
the opposite direction. Wherever local depletion of the parenchyma 
occurred blood islands and blood spaces would naturally form; and 
whenever a more or less general or local depletion of lymphatic tissue 
took place along the periphery of the node, a continuous or discontinu- 
ous peripheral blood space could also result. It is, of course, also prob- 
able that the accessory affluent veins sometimes present, may be in part 
responsible for the formation and persistence of a more or less continu- 
ous peripheral blood space, and that rapid depletion of the lymphatic 
tissue of the node might result in decreasing the size of the node. How- 
ever, since it is unlikely that the capsule and framework of the node can 
accommodate themselves rapidly to the altered conditions, an opportunity 
would be afforded for blood to occupy the depleted periphery and so 
form a peripheral blood space. Since the lymphocytes must be carried 
away by the blood stream, they would of course have a tendency to 
gather about the venous ostia of the lacunae, thus explaining the occur- 
rence of remnants of the lymphatic tissue about empty lacunae and near 
the periphery in depleted nodes, although it is unlikely that a purely me- 
chanical explanation is adequate. In depleted nodes the more or less stag- 
nant blood may then undergo degenerative changes ; and, since the frag- 
ments of the erythrocytes can probably pass out easier with the lympho- 
cytes than the intact cells, the presence of granular deposits in the lacunae 
would also be accounted for. If, in addition, it be recalled that some of 
the openings into the lacunae are undoubtedly obstructed partly or 
wholly by collapse of their walls through encroachment of the lymphatic 
tissue, the correctness of the above supposition regarding the post-em- 
bryonic genesis of such inconstant and transient structures as the blood 
spaces and blood islands is made still more probable. 
It is interesting to recall in this connection that Weidenreich [37] 
considered the blood as passing through the parenchyma between the 
blood spaces and lacunae under ordinary conditions, but assumed that 
