I 



Cfses of Carhohydrates 155 



four -fifths of the fat stored by pigs must have had 

 its origin outside the food protein and fat. Besides 

 all this, the common experience of feeders that foods 

 highly non- nitrogenous are often the most efficient for 

 fattening purposes is good common -sense evidence that 

 fat formation is not greatly dependent upon the pro- 

 tein supply. Nevertheless, the possibility of producing 

 animal fat from protein is not disproved, and there are 

 several considerations which make it seem probable 

 that under certain conditions this does occur. 



Protein can unquestionably serve as fuel, or, in other 

 words, as a source of energy. The amount so used 

 depends much upon the animal fed and the character 

 of the ration. In the case of a dog eating an exclusive 

 meat diet or of a fattening animal which receives a 

 ration liberally nitrogenous, probably the greater part 

 of the protein eaten is not stored but is used as fuel. 

 With milch cows or young animals growing vigor- 

 ously, a much larger proportion escapes oxidation. 

 The fuel value of protein will be discussed later under 

 another head. 



FUNCTIONS OF CARBOHYDRATES 



Carbohydrates are usually characterized as the fuel 

 portion of the food, or that part which is burned to 

 produce the various forms of energy. This conception 

 of the function of these bodies is correct in the sense 

 that in the case of ruminants they constitute the 

 larger part of the fuel, although not the whole of it. 

 For instance, in the case of a cow eating daily sixteen 



