ABSORPTION AND ASSIMILATION OF FOODSTUFFS 141 



laws of osmosis is due to the activity of the epithelial cells. 

 This view is supported by the fact that when the intestinal 

 epithelial cells are rendered functionless by sodium fluoride 

 (which does not destroy the cells anatomically), absorption 

 follows the law of osmosis. 



The seat of absorption is chiefly the intestine ; in a less 

 degree, the stomach. Pure water is not absorbed from the 

 stomach; on the contrary, water is passed by the mucous 

 lining into the stomach. Aqueous solutions of salts, sugar, 

 and peptones are absorbed when they are very concentrated. 

 Absorption from the stomach is favored by table-salt and 

 spices, such as mustard, peppermint, pepper. Alcohol and 

 other narcotics also favor absorption because they paralyze 

 the resistance which the epithelium of the stomach offers to 

 the absorption of foodstuffs. 



Most of the absorption takes place in the small intestine, 

 where the surface for absorption is very large. The villi of 

 the mucous membrane of the intestine increase the absorp- 

 tion surface to twenty-three times what it would be if no 

 villi were present. One sq. cm. of the intestinal mucosa 

 contains about 2500 villi. 



The epithelial cells of the intestinal mucosa are cylindri- 

 cal. The free surface of these cells is striated. Each villus 

 contains a central lacteal, and between this lacteal and the 

 outside border of the villus are the blood vessels, a mass of 

 capillaries, and the afferent and efferent vessels. The lac- 

 teal is surrounded by smooth muscle-fibres, by the contrac- 

 tion of which the villi are shortened, the lacteal is pressed 

 together, and the contents emptied into the lymph vessels. 



In the large intestine also considerable absorption takes 

 place. Among other things water is here absorbed whereby 

 the contents of the intestine become more solid. Food is 

 also absorbed in the large intestine when, in soluble form, 

 it is forced through the anus into the intestine as nutritive 

 clyster. 



The path of the absorbed food from the intestine is two- 

 fold: (i) The portal vein; (2) the lymph vessels. 



