THE DIGESTION OF THE NUTRIENTS 45 



not only produces proteoses and peptones, but in addition, 

 it breaks up some of these compounds into peptids, which 

 are still simpler combinations of only a few amino acids, 

 and into the simple amino acids themselves. 



Erepsin completes the action upon the proteins by break- 

 ing up the proteoses, peptones, and peptids into the amino 

 acids. With the exceptions of casein, gelatin, fil^rin, and 

 a few other proteins, erepsin does not act upon the unchanged 

 proteins, but only upon the products of their partial de- 

 composition. 



Pancreatic amylase acts upon the starch of the feed. 

 Its action is mu.ch more pronounced than that of sahvary 

 amylase because it ordinarily has a longer time to act upon 

 the food and is present in greater abundance. Like sali- 

 vary amylase, it changes starch to maltose. 



Lipase acts upon the fats of the feed, breaking them up 

 into the fatty acids and glycerin of which they are com- 

 posed. Most of the fatty acids then unite with the alkaline 

 salts of the pancreatic juice and bile, producing soaps. (See 

 page 20). The resulting soap .solution, together with the 

 bile, forms a fine emulsion with the remaining fats and 

 enables the lipase to come in much closer contact with them 

 and complete their digestion. 



Maltase acts upon maltose with the formation of glucose. 

 Sucrase acts upon sucrose ^vith the formation of glucose and 

 fructose, while lactase acts upon lactose with the production 

 of glucose and galactose. 



The bile is a yellowish-green, alkaline, very bitter Uquid 

 secreted by the Hver and stored in the gall bladder, except 

 in case of the horse as noted on page 38. It contains no 

 enzymes, its chief digestiv^e function Ije^ing due to its solvent 



