1 08 Life and Health 



162. Digestion in the Stomach. When the food, thor- 

 oughly mixed with saliva, has entered the stomach, the 

 cardiac end of that organ is closed, as well as the pyloric 

 valve, and the muscular walls contract on the contents. A 

 spiral wave of motion begins, becoming more rapid as diges- 

 tion goes on. The food is thus constantly churned about in 

 the stomach and thoroughly mixed with the gastric juice. 



163. The Action of the Gastric Juice. The gastric juice is 

 a thin, almost colorless fluid, with a sour taste and odor. 



B 



D 



FIG. 52. The Stomach. 

 A, cardiac end ; B, pyloric end ; C, lesser curvature ; D, greater curvature. 



Its reaction is distinctly acid. Its chief constituents are 

 two ferments called pepsin and rennin, free hydrochloric 

 acid, mineral salts, and 95 per cent of water. 



Pepsin, the most important constituent of the gastric 

 juice, has the power of dissolving the proteid foodstuffs, 

 converting some into what are called peptones, which are 

 both soluble and capable of filtering through membranes. 



Pepsin can do this only in the presence of an acid. Hence 

 the importance of the hydrochloric acid of the gastric juice. 



