MICROSCOPIC STRUCTURE 
41 
on nodes from three pigs. Meek says that "On microscopical examina- 
tions they (the glands) are seen to possess a very thin capsule and in 
some cases a distinct capsule cannot be said to exist, the peripheral sinus 
of the gland being directly contiguous with the periglandular fat, and the 
cellular tissue of the sinus spreading between the contiguous fat cells. 
This condition much resembles that seen in the marrow of the long bones 
at the junction of cellular and fatty marrow." These observations of 
Meek are similar to those made on sheep by Clarkson [2], who stated 
that the cells of the surrounding fat are often in contact with the adenoid 
tissue. It is particularly interesting in connection with Meek's observa- 
tions that v Schumacher failed to find hemolymph (hemal) nodes in the 
pig. Both he and Baum and Hille, who according to v Schumacher first 
directed attention to the matter, and also Baum, found fat cells bordering 
the marginal sinus in most of the lymph nodes of the pig. Baum regarded 
this as fat formation on part of the reticulum, beginning from the per- 
iphery and leading to complete atrophy of the node, as due to age ; but v 
Schumacher found that fat is already present at six months. The latter 
also called attention to the well-known fact that similar changes occur in 
other animals, and that erythrocytes are normally present in the lymph 
sinuses of lymph nodes of the pig. 
Intra-capsular sinuses, or blood spaces, as described by Robertson 
[24] as extending one-fifth of the distance around the gland, were not 
seen ; although it is not rare to find free blood in the looser portions of 
the capsule. Neither did nodes which were almost depleted of lymphatic 
tissue, and which might perhaps be considered as undergoing retrogres- 
sion, show the least sign of fatty degeneration. However, Warthin [33], 
in writing of the marrow lymph nodes of man, reported the finding of 
fat cells throughout this type of node, and also maintained [34 and 35] 
the development of hemolymph nodes from fat and their degeneration 
into fat ; but Vincent and Harrison [28] reported that "In no instance did 
we find any fat cells inside the capsule" in the sheep and ox. 
The conclusion that the blood islands and blood spaces, both per- 
ipheral and central, are transient, and perhaps even quite incidental 
structures, seems amply justified. Present now and absent then, found in 
this node and not in that, their usual presence in developing nodes even, 
does not signify, it seems to me, that they are indispensable constituents 
of hemal nodes. It is not uncommon, for example, to find a portion of a 
node containing many follicles which are in a state of proliferation, and 
which encroach upon both the peripheral and the central blood spaces or 
blood islands. That such a process must often result in the complete obli- 
