CHAPTER XVIII. 

 ABSORPTION. 



Absorption a Living Process. The layer of cells which 

 forms the inner surface of the mucous membrane is called 

 epithelium. These cells are moist, soft, and thin-walled. 

 They take up the digested foods, now in liquid form, and 

 pass them on to the lymph and so into the blood capillaries 

 that are thickly distributed just beneath the surface. 



Absorption from the Mouth. Sugar, and some other 

 substances, may be absorbed by the mouth as soon as it is 

 dissolved. But very little material is thus absorbed. 



Absorption from the Stomach. Some parts of the food 

 that are already digested, or such matters as are soluble, 

 e.g. water containing sugar, peptone, salts, etc., may be 

 absorbed immediately through the walls of the stomach 

 into the blood capillaries. Recent experiments show, how- 

 ever, that the amount of absorption from the stomach is 

 much less than was formerly supposed ; water, for instance, 

 " when taken alone, is practically not absorbed at all in the 

 stomach. As soon as water is introduced into the stomach 

 it begins to pass out into the intestine, being forced out in 

 a series of spurts by the contractions of the stomach." 



Absorption from the Small Intestine. Most of the 

 digested food is absorbed in the small intestine. 



Increased Surface for Absorption. The mucous mem- 

 brane of the small intestine is thrown into ridges, but, 

 unlike those of the stomach, they run crosswise. Again, 



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