X.] 



TAX UPON FOOD. 



restored, and this necessitates the unproductive use of 

 a certain quantity of nitrogenous matter. It is a sort 

 of life tax which has to be paid in order that the ani- 

 mal may be kept in health and strength to perform 

 some useful duty. 



192. In order that some idea may be formed of the 

 extent to which the elements of food are used for the 

 maintenance of the body in health, independent of any 

 production of flesh, we will take the case of a cow in 

 milk, which received a known quantity of food during 

 twenty-four hours and (assuming, as may fairly be done, 

 that she remained the same weight at the end of the 

 day as at the beginning) disposed of it in the following 

 manner. The food given consisted of 120 Ibs. of 

 water, 30 Ibs. of potatoes, and 15 Ibs. of grass. (Bous- 

 singault.) 



In this case we have 



17 Ibs. utilized as milk. 

 57 Ibs. indigestible matter. 

 91 Ibs. the waste of the body. 



165 Ibs. weight of food given. 



193. The food which is necessary for supplying 

 the waste of the body is variable, because the cir- 



