116 DIGESTION 



acid, and once separated, peptic digestion takes place as 

 with ordinary proteid. In children whose diet is almost 

 entirely of milk this rennin action becomes very important. 



Hydrochloric acid. (See Ex. XXXIX.) Aside from 

 the aid which this acid gives in peptic digestion its pres- 

 ence is important in that it destroys the germs of fermen- 

 tation and disease, and probably dissolves some mineral 

 salts. Its action in destroying germs permits the food 

 to be stored in the stomach for some time without under- 

 going decay. In this way the stomach may act as a 

 storehouse of food. While proteids are practically the 

 only nutrients digested in the stomach, it is also true that 

 some of the preparatory actions upon other nutrients take 

 place here. For example, the heat of the stomach is 

 sufficient to liquefy the fats of the food, and the digestion 

 of the proteid covers of starch and fat particles liberates 

 these nutrients and prepares them for future digestive 

 changes. Sugar and certain mineral salts may also be 

 dissolved here by the water and acid of the gastric juice. 

 The mixture of all these substances together with the 

 digested and undigested particles of food and the gastric 

 juice results in the formation of a milky fluid called chyme. 

 This chyme is from time to time forced out of the stomach 

 into the small intestine. 



Mechanical action of the stomach. — Once in the 

 stomach the food is entirely cut off from the rest of the 

 alimentary canal by the contraction of the cardiac and 

 pyloric sphincter muscles. It was long thought that dur- 

 ing the period of stomach digestion the food was forced 

 in continuous circulation round and round the stomach 

 until sufficiently ground, and mixed with gastric juice to 

 permit of its discharge into the intestine. Later investi- 



