CHEMISTRY OF FOODS AND FEEDING. 1171 



CHARTER XXI. 



THE CHEMISTRY OK FOODS AND FEEDING.* 



IN order to understand this subject so as to make it of prac- 

 tical value, a little knowledge of the composition of the 

 animal body and the laws of nutrition is necessary. 



The carcass of a fat ox, exclusive of offal, contains in every 

 one hundred pounds about fifty-six pounds of water. A lean 

 animal contains a much larger percentage of water. The re- 

 mainder of the body is composed of three principal substances : 

 muscle and similar matter, fat, and bones. The dry substance 

 of muscle contains about fifteen per cent of nitrogen, and is 

 hence called nitrogenous matter; fat contains no nitrogen; and 

 the bones are composed of phosphate of lime, in connection with 

 a nitrogenous substance called gelatine. 



The animal lives, grows, and gets all its powers and facul- 

 ties from the food it consumes, and its tissues are built up 

 wholly out of the material contained in the food; and it is, 

 therefore, necessary that the food should contain all the sub- 

 stances which are to be contained in the animal body. The 

 animal can rearrange these substances, but has no power to 

 create any thing not contained in the food. 



Starch, sugar, and the other vegetable substances commonly 

 described as carbohydrates, are composed of three elements : 

 carbon, hydrogen, and oxygen. Fat is composed of these same 

 three, only arranged in a little different proportion ; muscle con- 

 sists of these three elements, and also of nitrogen. An animal, 

 therefore, can transform starch or fat into fat, but can not con- 

 vert them into muscle, as that contains a substance which nei- 

 ther of the other materials can supply. 



By R. S. THOMPSON. 



