DIGESTIVE ACTION OP THE ENZYMES 115 



arations contained in glass vessels. The results of such 

 experiments may be svtmmarized as foUows: 



The proteid thus treated first swells and softens and 

 then is slowly transformed into a soluble form of proteid 

 known as peptone, 



This peptone is the result of the combined action of the 

 pepsin and hydrochloric acid, the food proteids being 

 broken gradually into simpler and simpler forms, until 

 finally the soluble peptone results. 



Peptic digestion is fovmd to take place best at a tem- 

 perature of from 98° to 102° Fahrenheit. 



The action of peptic digestion is confined wholly to the 

 proteid parts of the food, and does not directly affect 

 any other nutrient. In fat meats the albuminous pockets 

 are dissolved away in this action, and the result is the 

 liberation of the fat globules inclosed by the pockets, 

 but the pepsin does not change the fat in any way. In 

 similar manner starch grains held in albuminous pockets 

 may be liberated, but the starch itself is not affected. 



All these actions of the pepsin and acid which are ob- 

 served in experiments with glass vessels take place nor- 

 mally under similar conditions in the stomach. 



Rennin. (See Ex. XXXVIL, b.) Gastric juice con- 

 tains a second enzjone called rennin. This enzyme plays 

 an important part in the digestive action of the gastric 

 juice upon the particular form of proteid found in milk. 

 When milk proteid (caseinogen) comes in contact with 

 gastric juice, the rennin enzyme causes it to coagulate 

 and separate from the rest of the milk as curd or casein. 

 This action is exactly similar to the curdling of milk by 

 acid when it sours. This separation of milk proteid by 

 the rermin prepares it for the action of the pepsin and 



