GBOWTH OF ANIMALS; ANIMAL FOOD. 145 



nourisMng the body and maintaining life. The change 

 of the food compounds or constituents into similar 

 animal products is accomplished in the living animal 

 by a series of what are termed ^^ nutritive processes or 

 functions/^ and include digestion, circulation, respiration, 

 secretion, and absorption. 



Digestion. — By digestion the solid matter of the food 

 is brought into a form capable of being absorbed by 

 the blood. Soluble food compounds, as sugar, are ab- 

 sorbed without digestion. Digestion is accomplished by 

 means of the digestive organs, — the mouth, stomach, and 

 intestines. In the mouth the food is ground fine and 

 mixed with the saliva, which, besides softening the food, 

 makes it alkaline, and starts a fermentation, which 

 changes the starch into sugar; when the masticated 

 food passes into the stomach — the fourth stomach in 

 the case of animals that chew their cuds — it comes in 

 contact with the gastric juice. This is an acid substance 

 which acts chiefly upon the albuminoids, converting them 

 into substances called ^^ peptones," which are capable of 

 passing through the lining membranes of the stomach. 

 The food remains in the stomach a sufficient time to 

 bring every portion in contact with the gastric juice; it 

 then passes into the first intestine, where it meets with 

 other alkaline secretions, pancreatic juice and bile, which 

 complete the digestion of the starch, albuminoids, and 

 fat. The absorption of the dissolved constituents of the 

 food now remaining takes place finally in the small in- 

 testines; the soluble product passes into the blood, which 

 then nourishes the whole body ; the undigested portion 

 is expelled in the form of manure. 



