WORKING OVER THE BODY'S INXOME 133 



Parotid 

 gland 



Blood 

 vessels 



Sublingual 



The peptones resulting from stomach digestion differ from pro- 

 teins chiefly in being soluble in water and capable of diffusing 

 through membranes. As the changing of proteins into peptones 

 goes on, the mixture in the stomach becomes more and more 

 liquid and more and more acid. From time to time a quantity 

 of the liquid passes into the intestine. After a while most of the 

 contents of the stomach has 

 been changed to a mixture 

 having the consistency of a 

 rather thick pea soup, and 

 all of it has passed on into 

 the intestine. 



111. The bowels or in- 

 testines. Among the high- 

 est animals the gut has two 

 distinct divisions. The first 

 is called the small intestine, 

 and in human beings it is 

 about one inch in diameter 

 and about twenty-four or 

 twenty-five feet long. This 

 opens rather abruptly into 

 the large intestine, which is 

 about two inches in diam- 

 eter and about five feet 

 long {seej,k, Fig. 74). 



You have probably handled a piece of pig gut or calf gut, 

 which is used as sausage casing. The wall of the intestine is 

 thin and soft. The Hning carries very small glands, and the 

 outer layer contains muscle cells. The muscle cells are ar- 

 ranged in rings: when they contract they simply reduce the 

 diameter of the intestine at any given point. The contraction 

 starts at the forward end (nearest the stomach) and passes 

 backward along the whole length of the small intestine, aided 

 by longitudinal muscles. As a result of these contractions some 

 of the thick mixture of food and digestive juices is moved along, 



Suhnaxillary 



Fig. 75. The salivary glands 



There are three sets of glands which produce 

 saliva : the parotid, in the cheek, just in 

 front of the ears; the submaxillary, under the 

 angles of the jaw; and the sublingual, under 

 the tongue. The more the food is chewed, 

 the smaller are the particles into which it is 

 broken, and the more thoroughly is the saliva 

 mLxed with these particles 



