THE DIGESTION OF FOOD 



117 



165. How Food is absorbed. The souplike mass which 

 left the stomach under the name of chyme has now been 

 changed into a thick cream called chyle. Squeezed slowly 

 along the intestines by the wavelike motions of the mus- 

 cular walls, the food materials that have been digested and 

 turned into a soluble form are absorbed. In other words, 

 they pass from the inside of the intestines into the blood 

 vessels and the lacteals lying 



in the intestinal walls. 



The process by which the di- 

 gested materials are taken into 

 the blood is called absorption. 

 It is by no means a process 

 that is confined to the alimen- 

 tary canal, but one that is going 

 on in every tissue of the body. 



This is done chiefly by two 



sets of vessels, first, by the FIG. 76. Glands and Villi of the 

 lacteals, or lymphatics ; second, 

 by the blood vessels. 



166. The Work done by the 

 Lacteals. The inner surface 

 of the small intestine is not 



smooth and shiny, like the outside, but has a velvety 

 appearance. This is because it is crowded with millions 

 of little club-shaped threads which project into the cavity 

 of the intestine. 



These projections are called villi, meaning tufts of hair. 

 They are tiny threads, about one thirtieth of an inch long ; 

 and a five-cent piece would cover five hundred of them. 

 They are set side by side not unlike the pile on velvet. 

 These villi are not found in the large intestine. 



Small Intestine. 

 Magnified 40 diameters. 



A, B, glands seen in vertical section 

 with their orifices at C opening 

 upon the membrane between the 

 villi ; D, villus. 



