INTESTINAL ABSORPTION. 



195 



to control the passage of the fluid from the serous cavity into 

 the lymph vessels. These stomata may be regarded as the com- 

 mencement of the dense network of lymph capillaries, which 

 lie in the subserous tissue. 



II. Intestinal Absorption. 



The intestinal absorbents are merely a special department of 

 the lymphatic system, which, on account of the white chyle they 

 carry being seen through their trans- 

 parent walls, have been called lac- FIG. 89. 

 teals, their function being to take up 

 the nutrient fluid from the intestinal 

 cavity, as well as to drain the tissue 

 in which they lie. In order to fulfil 

 their function, they are arranged in 

 a particular way, especially adapted 

 to the peculiar construction of the 

 mucous membrane lining this part of 

 the alimentary tract, which must be 

 briefly described before the mechan- 

 ism of absorption can be understood. 



The most striking characteristic of 

 the lining membrane of the small in- 

 testine is the existence of villi, which 

 are only found in this part of the ali- 

 mentary tract. They consist of nip- 

 ple-shaped processes projecting into 

 the intestinal cavity, so closely set that 

 they have the appearance of the pile 



of velvet; and being just visible to the naked eye, they give the 

 mucous membrane, when washed and held under water, a pecu- 

 liar velvety look. On account of these villi, and also of the 

 ring-like folds of mucous membrane in the upper part of the 

 small intestine, the extent of surface over which the chyme has 

 to travel is greatly increased. 



The surface of the villi is covered over with a simple layer of 

 columnar epithelial cells in continuity with the epithelium lining 



Diagram of relation of 

 the epithelium to the lac- 

 teal radical in villus. The 

 protoplasmic epithelial 

 cells supposed to be con- 

 nected to the absorbent 

 vessel by adenoid tissue. 

 (After Funke.) 



