392 



THE POPULAR SCIENCE MONTHLY. 



The oxen make in increase but little more than one per cent of 

 their weight per week, the sheep make one and three fourths per cent, 

 and the pigs nearly six and one half per cent of their weight per week. 

 Nearly the same amount of dry substance of the food appears in the 

 manure of the different animals per week for each hundred pounds of 

 their live weight. In proportion to their weight, the pigs consume 

 more food, and a larger amount of food-constituents is actually used 

 in work of the system, but, from the greater rate of increase, the work 

 required to produce a pound of increase is less than one half of that 

 required in oxen. These facts are of particular interest in connection 

 with the differences already noticed (page 384), in the relative percent- 

 age weights of the digestive organs of oxen, sheep, and pigs. 



The dry substance of the food has alone been taken into the account 

 in the preceding table, but, if we trace the final disposition of its sev- 

 eral constituents in the system, we shall find marked differences in the 

 proportions of each that are stored up as increase, voided in manure, 

 or used in work of the system. The percentage of each group of food- 

 constituents stored up as increase and voided in the manure is given in 

 the next table : 



The nitrogenous substance and mineral matters, as will be seen, are 

 all accounted for in the stored-up increase and the manure, but there 

 remains from 77'4 to 81*7 per cent of the non-nitrogenous substances 

 that can not be found in the increase of the body or in the residual 

 manurial excretions, as they have been used in internal work and ex- 

 creted in the process of respiration. 



Sheep store up as increase a larger proportion of all the food-con- 

 stituents than oxen, and pigs store up a much larger proportion than 

 sheep. The percentage of nitrogenous constituents stored up as in- 

 crease or voided as manure will vary widely with different foods. We 

 have seen, as a result of these experiments, that but a small proportion 

 of nitrogenous substance was required in the food, and that the needed 

 amount was comparatively constant under varying conditions. If the 

 food contains but a moderate amount of nitrogenous substance, a larger 

 percentage of it will be required by the system, and the amount ap- 

 pearing in the manure will be so much diminished ; but with highly 

 nitrogenous foods a small percentage of the nitrogenous constituents 

 will suffice for the purposes of the system, and the excess will appear 

 in the manure. 



