ANIMAL FOOD 



requires only one third as much oxygen and develops less 

 heat and energy. So food rich in fat yields more heat 

 and energy than a food rich in sugar or starch. 



Fourth. Liability to ferment. A food requiring a long 

 time in digestion is more liable to ferment than one which 

 is digested in a short time. Sugar and starch ferment 

 easily, while fat ferments only with difficulty. 



157. Milk. Among all the different kinds of food milk 

 seems to be most perfectly adapted for man and for many 

 animals. The average cow's milk consists of 



Water 86 per cent. 



Albumin 4 



Fat 4j " 



Sugar 5 



Mineral matter -|- " 



Milk thus contains all the five different kinds of food 

 substances, which, moreover, are in about the proper pro- 

 portions to support life best. 



The albumin, fat, and sugar of milk each re- 

 quires little time and energy in its digestion, and 

 leaves but little undigested residue. Milk is more J? 

 liable to undergo fermentation than some other o 

 kinds of food, but the quickness of its digestion 

 overcomes this objection. It develops heat and 

 energy in amounts best suited to support life. Fat globules in milk 

 Milk is thus an ideal food, and can be digested (X 300). 



when all other kinds of food are rejected. 



158. Caseine. The albumin of milk is called caseine. 

 In its digestion the rennin ferment in the stomach coagu- 

 lates it in fine flakes, which the acid and pepsin dissolve to 

 peptone. When much acid is present in the stomach, as 

 after a meal, or when fermentation has occurred, the 

 caseine is apt to be coagulated in hard lumps which dis- 



