402 Our Surroundings 



called the peritoneum, and the inner surface is lined, like the other 

 parts of the canal, with mucous membrane. 



Glands of the Stomach. In the mucous membrane of the 

 stomach there are numerous minute glands which secrete a diges- 

 tive fluid called the gastric juice. The gastric juice is made from 

 material supplied by the blood in the capillaries of the membrane. 

 This juice is a yellowish fluid, composed largely of water, holding 

 in solution hydrochloric acid and two ferments, rennin and pepsin. 



Peristalsis in the stomach helps to mix the food thoroughly 

 with the gastric juice. This action is sometimes called the churning 

 motion of the stomach. Normally about three quarts of gastric 

 juice are produced daily. 



Work of the Gastric Juice. The gastric juice is of prime 

 importance, for it is the first main factor in making the protein 

 food soluble. It contains ferments, or enzymes, which change 

 protein food to a soluble form. This is effected by the pepsin 

 and hydrochloric acid in the juice. Pepsin acts only in an acid 

 solution ; hence the importance of the hydrochloric acid. The acid 

 also renders soluble, or digests, mineral matter in the food and is 

 said to destroy many bacteria and prevent fermentation. 



Rennin, the other ingredient of gastric juice, curdles the pro- 

 teins in milk so that the pepsin can change them to soluble forms. 

 Rennin is especially important in aiding digestion in children as 

 they drink so much milk. The gastric juice does not digest starch 

 and fat, but makes protein food soluble. The food as it leaves the 

 stomach is called chyme. A little of it is absorbed through the 

 stomach walls but most passes on into the small intestine, where 

 it is further digested and absorbed. 



The Small Intestine. The small intestine consists of a tube 

 twenty feet or more long, covered, like the stomach, with peri- 

 toneum, and lined with mucous membrane. The important work 

 of digestion that goes on in this organ is the mixing of the food 

 with three kinds of fluids, pancreatic juice, bile and intestinal juice. 

 The pancreatic juice and the bile are made in two large glands 

 which are just outside the small intestine, and are poured into 

 the intestine through small openings. These glands pour their 

 secretions into the small intestine in a way similar to that of the 



