CHAPTER IX 

 ABSORPTION AND ASSIMILATION 



122. Absorption of food. Digested foods which be- 

 come part of the body are peptone, glucose, and emulsified 

 fat. While they remain in the intestine, they are still 

 outside of the body proper. In order to nourish the body, 

 they must diffuse through the wall of the intestine and 

 become part of the blood. The process of taking any sub- 

 stance into the blood is absorption. 



The bodies of most cells are semi-fluid and jellylike. 

 The peptone and glucose, dissolved in water, will soak into 

 the soft epithelial cells lining the intestine, while the 

 original albumin and starch or sugar will not. Blood tubes 

 run so near the inner surface of the wall of the intestine, 

 that only a layer of epithelium and the capillary wall, 

 both together thinner than the thinnest paper, separate 

 the blood from the food in the intestine. The food soaks 

 through the epithelial cells and the walls of the blood tube, 

 and is washed away by the blood stream. So there is a 

 steady flow of digested food through the epithelial cells 

 toward the blood tube ; while the undigested food remains 

 behind. The cells are alive, however, and to a degree 

 select what they transmit. Common salt is necessary in 

 the process, and bile greatly aids it. Peptone and glucose 

 are thus absorbed from the intestine by every point of its 

 mucous membrane. The millions of villi projecting into 

 the intestine greatly increase the surface for absorption, 



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