MICROSCOPIC STRUCTURE 
39 
it is coarser here where it comes into relation with the capsule, and be- 
cause it is generally obscured much less here by the presence of celluiar 
elements. In the deeper portions of the node it is much finer, denser, 
much less cellular, and sometimes not at all apparent in the follicles in 
sections stained in the ordinary way. The size of the meshes of the retic- 
ulum also vary markedly in different portions of the node. They are 
largest where the fibers are coarsest, and smallest where they are of great- 
est tenuity. Although some very fine fibres can be found in practically all 
portions of the parenchyma, it is in the follicles where the finest reticulum 
is found. Here the meshes are often so small in section that they contain 
but a single cell. As in the follicles of lymph nodes, the reticulum is less 
evident in the center, where only an imperfect network can be demon- 
strated. Were this difference less constant it might possibly be due to 
variations in staining power of the reticulum, or to a faulty technique , but 
the same results were obtained by the special stains used. Near the per- 
iphery of the follicle, on the contrary, the fibers seem crowded together, 
and consequently are generally very evident, because they are coarser and 
have a rather circumferential arrangement. The finest reticulum fibers 
noticed were so minute that they appeared as extremely fine lines under 
the highest magnification used (x 1340). 
In the center of many good-sized blood islands, or in blood spaces, 
reticulum could never be demonstrated by the Bielschowsky or any other 
method. Moreover, in empty or in partially empty nodes many of the 
coarser reticulum fibers in the empty blood spaces seemed to end abruptly, 
as though they had been forced asunder. Nor was it difficult to find 
cells with six or more processes, some of which terminated in free ends 
a short distance from the cell. At the border of large blood islands, or 
of blood spaces, a very definite bounding or confining layer of coarse 
reticulum, from which branches extended into the blood islands, was fre- 
quently present. In some cases these walls of reticulum were formed 
by several parallel fibers, which looked as though they had been crowded 
together more or less, and which very closely simulated conditions found 
at the periphery of the follicles. Were it not for the fact that this wall of 
reticulum which separates the blood islands from the lymphatic tissue gives 
off branches which are directly continuous with the adjacent reticulum on 
both sides, it would be very difficult indeed, or impossible even, to distin- 
guish the walls of some empty blood spaces from those of empty venous 
lacunae. However, generally only a portion of the circumference of a blood 
island was thus bounded, the remainder of the boundary being formed by 
the parenchyma of the node, in the bounding area of which a gradual 
