FARM MANURES 591 



In practice, then, it is this agricultural evaluation which 

 must be especially watched. Its expression should be 

 not only in net yield to the acre, but also in net return 

 to a ton of manure applied. 



494. The fermentation of manure.^ — During the 

 processes of digestion the food of animals becomes more 

 or less decomposed and decayed. This condition comes 

 about partly because of the digestive processes and 

 partly from the bacterial action that takes place, largely 

 in the lower intestines. Of these two influences within 

 the animal, bacterial activities are probably of the greater 

 importance as far as the breaking-up of the complicated 

 foodstuffs is concerned. The fresh excrement, then, as 

 it comes from the stable, consists of decayed or partially 

 decayed plant materials, with a certain amount of broken- 

 down animal tissue and mucus. This is more or less 

 intimately mixed with litter and the whole mass is wetted, 

 or moistened, with the liquid excrement, carrying, as it 

 does, considerable quantities of soluble nitrogen and 

 potash. This mass of material, ranging from the most 

 complex compounds to the most simple, is teeming with 

 bacteria, especially those that function in decay and putre- 

 faction. The number very often runs into billions to a 

 gram of excrement. In such an environment it is of 

 little wonder that biological changes go on so rapidly. 



Although so many different groups of organisms live 

 and function in manure, and although so many products, 

 both simple and complex, are continually being split 

 off, for convenience and simplicity the bacteria may be 



1 Good discussions may be found as follows : Lipman, J. G. 

 Bacteria in Relation to Country Life, pp. 303-356. New York. 

 1911. Hall, A. D. Manures and Fertilizers, pp. 184-210. 

 New York. 1910. 



