DIGESTION OF FOOD: THE INTESTINE 



105 



whitish, syrupy liquid, called chyle, in which there are but 

 few remnants of solid material. Its proteids have become 

 peptones or even simpler bodies; its starches are all sugars; 

 and its fats are either emulsified or are changed into fatty 

 acids and glycerine. It is not until the food has flowed 

 through a considerable section of the 

 intestine that digestion is complete. 



The walls of the small intestine, 

 shown in Figure 57, are composed 

 of muscles that force the food along, 

 of glands, the secretion of which re- 

 sembles that of the pancreas, and of 

 villi (described in the next chapter). 



THE LARGE INTESTINE 



The small intestine empties into 

 the large intestine in the lower right 

 side of the abdominal cavity. The 

 opening from one to the other is little 

 more than a slit, the sides of which 

 open easily in one direction but not 

 in the other; Fig. 58. Hence food 

 passes readily onward, but not back- 

 ward. The part of the large intestine 

 thus entered is the colon, and the 

 general shape of the course which 

 it takes is that of an inverted letter 

 U; i. e. beginning on the lower right side of the body cavity 

 it passes up that side as far as the liver (ascending colon); 

 then it crosses to the left side of the body (transverse colon), 

 and there passes downward (descending colon); Fig. 52. 



The small intestine opens into the side of the large intes- 

 tine (see Figs. 52 and 58); about two and a half inches of 

 the latter are thus left below the opening as a short section 

 ending blindly and called the coecum, a word meaning " blind." 



Muscles 



FIG. 57. A CROSS SECTION 



THROUGH THE WALL OP 

 THE SMALL INTESTINE 

 (Modified from Oppel). 



