DIGESTION OF THE FOOD 23 



dextrine, maltose, and grape sugar. In the case 

 of cooked or steamed foods, the ptyalin begins to 

 act in a quarter to half a minute, whilst the starch of 

 the coarse fodders only begins to be changed after 

 the saliva has acted for two to three minutes. 

 Saliva contains another ferment which splits up 

 proteins, but it appears to exercise very little in- 

 fluence. In the fourth stomach (abomasum) of 

 ruminants and in the simple stomach of other 

 mammals, a second digestive fluid, the gastric juice, 

 is poured out upon the mass of food. This gastric 

 juice is acid, for it contains free hydrochloric acid 

 and also lactic acid, and acts upon the proteins and 

 fats of the nutrients. Under the action of the pepsin 

 of the gastric juice the proteins are changed into 

 albumoses and peptones, both of which are soluble 

 and can easily enter into the blood and lymph of the 

 animal. Many proteins, such as the casein of milk, 

 are coagulated by another ferment (rennet) present 

 in the gastric juice before being digested in the 

 manner already mentioned. A third ferment 

 lipase acts upon the fats, splitting them up into 

 free fatty acids and glycerine (see p. 10). The other 

 nutrients of the food are not appreciably acted 

 upon by the acid gastric juice. 



The partly-digested food passes from the stomach 

 into the small intestine, where it is mixed with two 

 other digestive fluids the bile and the pancreatic 

 juice. The first of these, the bile, plays an import- 



