THE DIGESTION OF THE NUTRIENTS 41 



and is destroyed by more than a trace of acid. It is present 

 in only small amounts in the saliva of cattle and sheep, and 

 probably lacking in dogs. 



In addition to salivary amylase, the saliva contains a 

 small amount of maltase, an enzyme which changes maltose 

 to the .simple sugar glucose. 



In ruminants mastication is usually quite incomplete at 

 first but the food is later returned to the mouth for further 

 mastication or rumination. At least seven out of every 

 twenty-four hours are given to rumination. Inasmuch as 

 an animal does not ruminate while working or sleeping, a liard- 

 working ox may not have sufficient time in which to properly 

 masticate his feed. 



In the horse, mastication is usually quite complete when 

 the feed is swallowed. In the pig, mastication is quite in- 

 complete. 



After the feed has been masticated, it is swallowed, passing 

 by way of the esophagus or gullet into the stomach. 



Digestion in the Stomach. — During and immediately 

 following the entrance of the masticated feed, the entire 

 contents of the stomach are neutral or shghtly alkaline in 

 reaction on account of the large quantity of sahva with 

 which the feed is mixed. Thus salivary amylase and malt- 

 ase may continue to act for some little time after the 

 food reaches the stomach. 



The gastric juice, secreted by glands in the walls of the 

 stomach, begins to flow as soon as the masticated feed enters 

 the stomach. As the gastric juice contains 0.2 to 0.5 per 

 cent of hydrochloric acid, the contents of the stomach soon 

 become acid. The acid destroys any sahvary amylase 

 which may have been acting upon the starch and the enzymes 



