32 CONDITIONS OF FERMENTATION. 



complete absence of oxygen, and which, when exposed 

 to oxygen, die known as anaerobies. 



In the fermentation of the manure-heap, therefore, 

 we must conceive of the two classes of organisms as 

 the active agents. In the interior portion of the 

 manure-heap, where the supply of oxygen is neces- 

 sarily limited, the fermentation going on there is 

 effected by means of the anaerobic organism i.e., 

 the organism which does not require oxygen ; while 

 on the surface portion, which is exposed to the air, 

 the aerobic (or oxygen-requiring) organism is similarly 

 active. Gradually, as decay progresses, the aerobic 

 organisms increase in number. It is through their 

 instrumentality that the final products of decomposi- 

 tion are largely produced. The functions of the anae- 

 robic organisms may be, on the contrary, regarded as 

 largely preparatory in their nature. By breaking up 

 the complex organic substances in the manure into 

 new and simpler forms, they advance the process of 

 putrefaction through the initial stages, and when this 

 is accomplished, they die and give place to the aero- 

 bic, which, as we have just seen, effect the final trans- 

 formation of the organic matter into such simple 

 substances as water and carbonic acid gas. 



The conditions influencing the fermentation of farm- 

 yard manure may be summed up as follows : 



1. Temperature. The higher the temperature the 

 more rapidly will the manure decay. 



2. Openness to the air. Of course it will be seen 



