146 SOILS AND FERTILIZERS 



The value of the manure can be approximately de- 

 termined from the composition of the food consumed. 

 Only a small amount of the nitrogen in the food is re- 

 tained in the body. The larger portion is used for re- 

 pair purposes. The nitrogen of the tissues which 

 have been renewed is voided as urea in the liquid ex- 

 crements. Some of the nitrogenous compounds of the 

 food are utilized for the production of fat, in which 

 case the nitrogen is voided in the excrements. The 

 fact that but little of the nitrogen of the food, under 

 ihost conditions, is retained in the body may be ob- 

 served from the figures of Lawes and Gilbert relating 

 to the composition of the flesh added to animals while 

 undergoing the fattening process. 54 



Increase during Fattening. 



Dry Nitrogenous 



Water. matter. Fat. matter. Ash. 



Ox 24.6 75.4 66.2 7.69 1.47 



Sheep 20.1 79.9 70.4 7.13 2.36 



Pigs 22.0 78.0 71.5 6.44 0.06 



The results of numerous digestion experiments 

 show that when the food undergoes digestion from 5 

 to 15 per cent, of the nitrogen is, as a rule, retained in 

 the body. The nitrogen of the food is utilized largely 

 to replace that which has been required for vital func- 

 tions. The nitrogen of the food enters the body, un- 

 dergoes digestion changes, is utilized for some vital 

 function, and is then voided in the excrements. 



The digestion of the food has been compared to the 



