254 EXPERIMENTAL GENERAL SCIENCE 



to its length, is much bent and coiled. It occupies most of the 

 abdomen. The combined length of the two intestines is nearly 

 thirty feet. The small intestine empties into the large intes- 

 tine at the lower right side of the body. Near this point, 

 a small tube two or three inches long, called the appendix, 

 projects downward from the large intestine. This is often the 

 seat of a serious inflammation called appendicitis. The large 

 intestine passes upward on the right side, across the body 

 below the stomach and downward on the left side and so on 

 to the surface of the body. In all animals, no matter what the 

 structure of the alimentary canal, it invariably begins in the 

 head with the mouth. 



218. Digestive Juices. When food is taken into the 

 mouth it is mixed with the saliva, a juice poured out by six 

 glands, three on each side of the head. The glands are simply 

 groups of cells which have the power to secrete saliva, the 

 material for which is taken from the blood. The disease called 

 mumps is caused by an inflammation of some of these glands. 

 The chief use of the saliva is to moisten the food and facilitate 

 its passage through the throat and esophagus to the stomach, 

 though it also contains a ferment called ptyalin which changes 

 some of the starch in the food to sugar. In the stomach the 

 food comes in contact with the gastric juice and, by a peculiar 

 churning movement of the stomach walls, is thoroughly mixed 

 with it. The gastric juice contains pepsin and rennin as 

 well as about .02 per cent, of hydrochloric acid. The acid kills 

 many germs in the food and renders the contents of the 

 stomach acid, thus promoting the working of the enzymes in 

 the gastric juice which cease their activities in an alkaline 

 medium. The pepsin changes some of the protein to more 

 soluble forms called peptones and also prepares the fats for 

 digestion by breaking up the tiny pouches in which they are 

 found. The rennin curdles milk. As the food, now a thin, 

 watery mixture, passes into the small intestine, the powerful 



