I7O FEEDING FARM ANIMALS 



brevity, it is usual to speak of all the nitrogenous substance 

 of the body as flesh, as distinguished from fat and bone. 

 For a similar reason the word fat is used to denote all the 

 non-nitrogenous substance of the body, both the real fat 

 and the other substance. Likewise the word bone is fre- 

 quently used to denote only the mineral constituents of 

 bone, although much of the substance of bone is nitroge- 

 nous organic matter. The flesh of the animal body is also 

 referred to as protein substance and the fat as non-protein 

 substance. It should be remembered that these various 

 terms are only close approximations to the truth. 



The discussion of the various food factors in feeding 

 stuffs should not close without some reference to their 

 functions in producing heat and in sustaining muscular ex- 

 ertion. The influence which they exert on milk production 

 is touched upon elsewhere (see p. 413). 



Heat in the animal body results from the constant proc- 

 ess of oxidation or burning of waste tissue and of food sub- 

 stance which is going on everywhere in every part of the 

 body to which the blood reaches. The heat supply is de- 

 pendent on the food supply, for the tissues that are oxidized 

 or burned come orignially from the food. This oxidation is 

 maintained with no gain of substance but of loss, as the 

 products of the combustion, carbonic acid gas, water and 

 urea must be gotten rid of by the excretory organs. It is 

 estimated that of the whole quantity of food eaten by an 

 animal for maintenance about four-fifths are required to 

 sustain the demand occasioned by the production of heat. 



Since the nitrogenous substance, the fats, and the car- 

 bohydrates of the food are all oxidizable, they may be all 

 used as sources of heat. But the fats and the carbohy- 

 drates are the most suitable since their oxidation in the 

 blood is much more readily effected than that of the ni- 

 trogenous substance. They are also on the whole much 

 cheaper, as previously intimated (see p. 168). 



Regulation of animal heat. How the heat of the ani- 

 mal body is regulated cannot be discussed here. But in 



