466 
DR. HERBERT WATNEY OH THE MINUTE 
of a Peter’s patch 1 It is very important to be clear on this point, as it is certain that 
fat-absorption cannot be properly understood unless we perfectly understand the structure 
of the villi, a fact which has been much lost sight of. The difference between the tissue 
of the villus on the one hand and of a follicle of a Peyer’s patch on the other, is not to 
be found in the reticulum (which is identical or very similar), but in the cells contained 
in that reticulum. 
In the lymphatic follicles, and in parts of the mucosa, the cells are entirely lymph- 
corpuscles*. In the villi, though lymph-corpuscles are always present and may be 
almost the chief constituent (as in the . sheep), or an important constituent (as in the 
rabbit), yet in some animals they are few in number (as in the dog and cat), or even 
rare (as in the monkey), in this situation. 
What, then, is the character of the cells of the villi 1 They are polygonal cells com- 
posed of a very pale protoplasm with an oval nucleus. These cells differ from lymph- 
corpuscles : — first, in size, they are more than twice as large ; secondly, they differ in 
having a large zone of protoplasm around the nucleus ; and thirdly, they differ in regard 
to their nuclei, which are oval and stain very lightly, as contrasted with the spherical 
deeply staining nuclei of the lymph-corpuscles. Let the reader compare the two kinds 
of cells in fig. 13 (Plate 39). Nevertheless, as can be seen in fig. 21 (Plate 41), the cells 
of the upper part of the villus are larger than those near the base ; and it is no doubt 
true that there is every transitional form between the lymph-corpuscles of a lymphatic 
follicle and the cells of the upper part of the villus. 
These cells of the villi are seen in sections to be arranged almost like an endothelium 
(see figs. 21 & 22) ; and in the upper part of the villus they are very similar to the 
endothelial cells of the membrana propria, of the veins, and of the chyle-vessel. See 
fig. 13, where the cells of the villus are not to be distinguished from those of the membrana 
propria; and see fig. 19, where there is great similarity between the endothelial cells of 
the vein and the cells of the villus. We have already noticed in fig. 21 that in the upper 
part of the villus the endothelial cells of the chyle-vessel and the cells of the villus are 
continuous and similar. 
We have seen above that the mucosa is composed of a reticulum containing cells in 
its meshes; these cells are (a) lymph-corpuscles and ( b ) large flat cells similar to endo- 
thelial cells : the latter may therefore be considered to be connective-tissue corpuscles. 
We have further seen that there is a gradual transition from the one kind of cell to the 
other. 
It has now been demonstrated that there is everywhere a reticulum holding all the 
elements of the mucous membrane in its meshes ; and if this account of the minute 
anatomy of the mucosa be correct, fat-absorption can only take place by means of the 
reticulum, or by the cells, or through both. Though my researches on fat-absorption 
have not been numerous, yet, as they show the fat to be in a reticulum, and as that 
reticulum is attached to the muscles and to the chyle-vessels in exactly the same way 
* I have already defined the cells which are spoken of in this paper as lymph-corpuscles. See page 459. 
