THE FEEDING OF THE ANIMAL 241 



of its digestive processes, tears down these sub- 

 stances, setting free the energy and transforming 

 the matter into forms suitable to be incorporated 

 into animal tissue. 



430. Before the matter of the fodder can be 

 used, it is necessary that the animal expend energy 

 upon it during the processes of digestion and as- 

 similation. The profit of the fodder to the animal 

 is represented by the difference between the 

 amount of energy originally present in the fodder 

 and the amount of energy it is necessary for the 

 animal to expend upon it in order to make it 

 available. Some substances require so great an 

 expenditure of energy by the animal to digest or 

 partially digest them that they are useless as 

 fodders, although they may contain the proper 

 compounds in measurably proper proportions. 



431. Fodder is used by the animal (1) as fuel 

 to keep up the bodily heat, without which the 

 vital processes cannot go on; (2) to repair the 

 wastes of the various tissues, organs and fluids of 

 the body; (3) to form new tissues or organs, or 

 add to those already formed (especially in young 

 animals) ; (4) to produce young; and (5) to lay 

 up reserve stores in the form of fat or otherwise, 

 to secrete various products, or to perform muscu- 

 lar labor. Many of these reserves or products 

 are useful to man, as milk, wool and eggs. 



432. In general, if the amount of food is 



