SELECTION AND CARE OF LIVE-STOCK. 87 



produces animal heat and muscular energy. In fact, 

 no force, or energy, can be exerted by an animal 

 without the destruction or consumption of material, 

 and the heat of the body, like the heat of a fire, can 

 not be maintained without the burning of fuel of 

 some kind. 



195. In cold weather, therefore, animals require 

 more substantial food than in warm weather, in order 

 to keep up a proper temperature of the body. Work- 

 animals also require more food than those that do no 

 work, in order to supply the necessary force, or en- 

 ergy. A certain amount of food is required to keep 

 up the ordinary heat, and sustain the daily " wear 

 and tear " of the body ; if the animal is expected to 

 grow or become fat, an additional supply is neces- 

 sary. All farmers know that hogs fatten faster, oth- 

 er things being equal, when kept in close pens, and 

 not allowed to run at large. The physical exercise 

 consumes much of the food that would otherwise go 

 to form fat. On the same principle, the stall-feeding 

 of cattle is economical. 



196. Some years ago, Liebig, a noted German 

 chemist, divided the food of animals into two kinds, 

 heat-forming and flesh-forming. The first con- 

 tains no nitrogen, like sugar, starch, and fat; the 

 second contains nitrogen, like gluten and albumen. 

 Liebig taught that the first kind is used altogether 

 for keeping up the animal heat and forming fat, 

 while the second supplies force, and forms flesh, or 

 muscle. It is now believed that this theory is not 



