166 AMERICAN MANURES. 



as those of one that is fattening, because the 

 growing animal requires nitrogen to make blood 

 and muscular fibre, also phosphoric acid for the 

 bones. On the contrary, the fattening animal 

 requires but little of these substances. Full 

 grown animals when in good condition require 

 only sufficient food to renew the waste of the 

 system. Horse manure is more valuable than 

 that of the cow, as the latter has to furnish 

 milk, which almost exhausts the food of its 

 nitrogen ; also an animal with young will nearly 

 exhaust its food, as it requires not only materials 

 for its own sustenance, but also a sufficient 

 amount to build up its young. Hence the food 

 will be exhausted not only of its nitrogen, but 

 also of phosphoric acid. In fact, the excrements 

 of animals, like other substances used as manures, 

 are valuable just in proportion to the amount of 

 ammonia, phosphoric acid and potash they con- 

 tain. The reader has been shown how varying 

 circumstances will affect the amounts of these 

 elements ; hence it is impossible to arrive at any 

 strictly correct estimate of the value of a given 

 weight of any animal manure. A general average 

 based on extended experiments is given in the 

 following Table, which shows the amount of 

 water, and of the valuable constituents only, 

 contained in lOOOlbs. in its natural undried 

 state : 



