194 The Feeding of Animals 



RELATION OF FOOD TO PRODUCTION 



Another class of experiments somewhat more severe 

 in their requirements are those designed to give infor- 

 mation as to the relation between the constituents of 

 the food and the growth of the various tissues in the 

 animal body or the formation of milk solids. The ex- 

 periments conducted by Lawes and Gilbert on the for- 

 mation of fat with swine may be cited in illustration of 

 the methods used. These were planned so as to learn 

 the amounts of digested protein, carbohydrates and 

 fat consumed by the animal and also the quantities of 

 protein and fat stored in the body during a given 

 period. "In experiment No. 1, two pigs of the same 

 litter, of almost exactly equal weight, and, so far as 

 could be judged of similar character, were selected." 

 One was killed at once and its composition determined, 

 and the other was fed for ten weeks on a fattening 

 ration of known composition and then slaughtered and 

 analyzed. The quantity of protein and fat which the 

 pig's body had gained during the ten weeks as ascer- 

 tained from the composition and weight of the two 

 pigs was then compared with the food supply of simi- 

 lar compounds. It was assumed that a pound of food 

 fat could produce a pound of body fat and that 51.4 

 per cent of all the protein not stored in the body 

 as such could be used for fat formation. Even with 

 the most liberal allowances it was found that the pro- 

 tein and fat of the food could not possibly have been 

 the sole source of the new body fat, thus forcing the 

 conclusion that the carbohydrates are fat -formers. 



