THE DIGESTION OF THE NUTRIENTS 43 



thoroughly mixed and the fibrous substances are mascerated 

 and broken up by a slow churning movement. Also there 

 is considerable digestion of the crude filxu-, pentosans, and 

 starch by means of bacteria which cause them to ferment, 

 with the formation of lactic, acetic, and butyric acids, and 

 carbon dioxide and methane gases. The acids may be 

 utilized as food by the animal body, but the gases are useless 

 and are excreted through the lungs and the digestive tract. 

 However, the digestion of the cellulose sets free such nutrients 

 as protein, starch, and fat which are inclosed in cells whose 

 walls, as has been stated, are composed of cellulose. If the 

 fermentation becomes too extensive and the gases are formed 

 faster than they are removed from the body, as is often the 

 case after large amounts of fresh grass are eaten, the animal 

 '' bloats." 



The finer and more liquid part of the feed tends to accu- 

 mulate in the reticulum, which regulates its passage into the 

 abomasum. The reticulum also furnishes water to moisten 

 the feed when it is regurgitated, and regulates its passage 

 into the esophagus when it is returned to the mouth for 

 rumination. 



The food may find its way into the omasum either directly 

 from the esophagus after remastication or from the rumen or 

 reticulum. The main function of the omasum is to com- 

 press and break up any remaining coarse parts of the feed, 

 which it does by crushing and rasping between its powerful, 

 horny, muscular leaves. Its contents are always rather 

 dry, as the liquid portion of the feed is squeezed out imme- 

 diately and forced on into the abomasum or true stomach. 

 The abomasum secretes the gastric juice whose enzymes 

 act practically the same as in 3ase of the horse and hog al- 



