DIGESTION 393 



coarser feed than animals which have only simple stomachs. 

 Fermentation takes place in the first stomach of ruminants, since 

 temperature and other conditions are very favorable to the action 

 of bacteria. Lactic acid is produced from soluble carbohydrates, 

 proteids are split up, amides are affected, and even crude fiber 

 may undergo some slight change. Carbon dioxide, hydrogen, 

 marsh gas, acetic acid, butyric acid, and lactic acid are some of 

 the products of the fermentation. This process dissolves some 

 of the nutrients, and breaks up the cell walls, thereby allowing 

 the entrance of digestive juices. It also softens the materials and 

 so favors the disintegration of hard vegetable structures when 

 chewed again in the mouth. The acids which are formed grad- 

 ually decrease the fermentation, until they finally stop entirely 

 the action of the bacteria, since an acid medium is unfavorable 

 to their activity. 



Stomach Digestion. When food enters the true stomach, the 

 gastric juice is slowly poured upon it. The gastric juice contains 

 hydrochloric acid, lactic acid, and three enzymes, which can act 

 only in an acid medium. Pepsin splits up the proteids into 

 albumoses and peptones. Rennin which is found largely in the 

 stomach of young animals, coagulates the casein of milk and 

 other proteids. Lipase splits fats and oils into glycerol and fatty 

 acids. Proteids are digested chiefly in the stomach, though the 

 fats are also split up and digested to some extent. The proteids 

 are converted into peptones and albumoses, which are soluble 

 and can pass through the membranes of the stomach. Even 

 water-soluble proteids are split up during digestion. 



Intestinal Digestion. When the food enters the intestines, it is 

 gradually mixed with bile, the pancreatic juice, and intestinal 

 juices, and, being alkaline, they put an end to the action of 

 the gastric juice. 



Bile acts chiefly to form soaps with the fatty acids and to 

 emulsify the fats and oils. The emulsion consists of minute 

 drops of fat, suspended in the liquid, and both the emulsified fat 

 and the soaps can be absorbed. Bile is also able to convert starch 

 into sugar. 

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