THE INTESTINES. 



515 



a peculiar structureless coat, like the cuticle of plants ; by its longer 

 action, however, or by that of the intestinal fluids, the bursting of the 



Fig. 211. 



pnwz 



cells produces apertures in them, or they become distended into large 

 pyriform clear vesicles. 



We may here refer to the changes which the epithelial cells and the 

 mill in general undergo during digestion. The most striking circum- 

 stance is the occurrence of fat in different parts of the villi, which may 

 always be observed during the formation of a fatty, milk-white chyle. 

 The succession of the morphological steps, at least as I have observed 

 them in animals, is as follows: The fat contained in the chyme at first 

 enters only isolated epithelial cells in different regions of the villi, so 

 that in each we soon observe a large ovate shining drop. The number 

 of these fat-cells rapidly increases, and then the villi acquire a very 

 peculiar appearance, often as if beset with pearls, from the irregular 

 alternation of cells filled with fat and consequently bright and shining, 

 with those which are empty and pale. In the end, all the cells become 

 filled with these drops and the epithelium appears quite dark by trans- 

 mitted, but whitish by reflected light, giving its aspect to the whole 

 villus^ With the repletion of the entire epithelial covering of the villus 



Fio. 211. d, two villi, with their epithelium, from the Rabbit; magnified 73 diameters: 

 a, epithelium; b, parenchyma of the villus. B, a detached sheet of epithelium, magnified 300 

 diameters : a, membrane raised up by the action of water. C, single epithelial cells, mag- 

 nified 350 diameters : a, with, b, without, a raised-up membrane ; c, a few cells from the 

 surface. 



