11 



CHAPTEE II. 



THE CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 



THE following description of the cellular elements will be incomplete, 

 as they will be considered in many ways in the chapter on lymphatic 

 and blood-vessels. The most instructive and simple object for the 

 investigation of the cellular elements of the ground*substance is the 

 omentum of rabbits, this being flatter, and, for the most part, very 

 slightly fenestrated compared with that of the guinea-pig, dog, cat, 

 and monkey. 



If one compares the omenta of various rabbits, one finds, on mi- 

 croscopical observation, some not immaterial differences. One finds, 

 namely, a great number of omenta of full-grown animals in which 

 there are richly distributed opaque tracts of different breadth, forming 

 a network : some of these tracts consist of a row of patches of different 

 size, mostly oblong, sometimes roundish, which coalesce with each 

 other more or less. 



There are numerous patches which are situated laterally to these 

 tracts, as well as perfectly isolated ones. Seen under a lens, the tracts 

 generally follow the course of the larger blood-vessels. In young 

 animals the network of opaque tracts is less developed than the 

 isolated patches. But also, on the same omentum, there exists a 

 difference between different parts ; while that part of the omentum 

 which lies upon the anterior wall of the stomach, viz. between the 

 large and small curvature, contains very abundantly isolated patches 

 up to such a size that they are hardly visible to the naked eye, we 

 find on those portions which lie along the great curvature and upon 

 the pylorus, besides these, also large tracts of fused patches. It may 

 be said in general, the younger the animal the more isolated small 

 patches are to be met with ; the older the animal the larger they are, 

 and the more confluent to tracts. It must not be understood, however, 



