X.] COMPOSITION OF FOOD. 85 



CHAPTER X. 

 FOOD OF FARM STOCK. 



177. The food of farm stock comprises numerous 

 substances, which differ very widely in their character 

 and composition. The extent to which cultivation, 

 soil, climate, and manure affect the nutritive value of 

 our crops, is a subject of the deepest importance for 

 the consideration of farmers, and it may be hoped 

 that, as the principles regulating vegetable growth 

 become more generally known, we shall be able to 

 increase the value of the food employed. We have 

 already (32) referred to the several substances which 

 we find in vegetable matter, and shown that they 

 are divided into two groups nitrogenous and non- 

 nitrogenous. 



178. The non-nitrogenous bodies starch, gum, 

 sugar, and oil have two distinct duties : 



The maintenance of the warmth of the body, and 

 The production of fat. 



It is from the food, that the blood obtains its supply 

 of the materials, by which the warmth of the body is 

 kept up by the respiration of the lungs. It is more than 

 probable that when starch, gum, and sugar are present 

 in the food, these are first acted upon for the produc- 

 tion of animal heat, but if these substances are absent, 

 then the oily matter of food has to perform this ser- 

 vice. These bodies may therefore be regarded as the 

 heat-producing matters in food. 



179. The nitrogenous substances in food albu- 

 men, casein, and fibrin have two other perfectly 

 distinct duties to perform. They have 



To repair the waste of the body, and 

 To develope muscular growth. 



