304 Bacteria in Relation to Country Life 



of water, of soluble and insoluble nitrogen compounds, 

 and likewise of phosphoric acid, potash and lime, exerts 

 in each case a decided influence. The following table, 

 given by Beal, shows the average composition of manure 

 from different animals and may be taken as an illus- 

 tration of the natural differences affecting the bac- 

 terial processes: 



Water Nitrogen Phosphoric acid Potash 



Per cent Per cent Per cent Per cent 



Sheep 59.62 0.768 0.391 0.591 



Calves 77.73 0.497 0.172 0.532 



Hogs 74.13 0.840 0.390 0.320 



Cows 75.25 0.426 0.290 0.440 



Horses 48.69 0.490 0.260 0.480 



As is indicated by the analyses, the horse manure 

 contains much less water than the cow manure. In 

 consequence of this, it is more permeable to air and favors 

 the rapid growth of aerobic bacteria. The cow manure, 

 on the other hand, not only contains more water, but, 

 also, mucilagenous substances derived from the diges- 

 tive tract of the animal. These substances help to form 

 an impervious crust over the solid excreta and contribute, 

 thereby, to a more effective exclusion of air from the 

 interior of the mass. 



Mechanical constitution and bacterial change. — The 

 mechanical constitution of manure in so far as it is 

 determined by its content of water, becomes thus an 

 important factor in the bacterial changes that subse- 

 quently take place. The reference to horse and sheep 

 manure as being dry and hot, in contradistinction to 

 cow and pig manure may, therefore, be regarded from 

 the bacterial standpoint as indicating susceptibility 

 to decomposition processes. 



