164 



SOILS AND FERTILIZERS 



INCREASE DURING FATTENING 



The results of numerous digestion experiments show 

 that when the food undergoes digestion only 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 functions ; it enters the body, undergoes digestion 

 changes, is utilized for some vital function, and is then 

 voided in the excrements. 



The digestion of food has been compared to the 

 combustion of fuel : the undigested products of the 

 solid excrements represent the ashes, and the urine 

 represents the volatile products. When wood is burned 

 the nitrogen is converted into volatile products. When 

 food is digested and utilized by the body the digestible 

 nitrogen is mainly converted into urea, while the indi- 

 gestible nitrogen is voided in the dung. In the solid 

 and liquid excrements of animals from 80 to 95 per 

 cent of the nitrogen, phosphoric acid, and potash of the 

 food consumed is present. 



184. Comparative Composition of Solid and Liquid Ex- 

 crements. --In composition the liquid excrements differ 



