FAKMYAKD MANUKE 315 



into the " short or rotten " condition is called " making " 

 the manure. It is brought about by the action of micro- 

 organisms, and involves a numerous and complex series 

 of chemical changes which are collectively known as 

 fermentation. Some of the changes are well understood, 

 and are caused by known types of bacteria. Others are 

 more obscure, can only be followed in outline, and are 

 probably caused by many different types. The bacteria 

 may be classified as aerobic and anaerobic, but some 

 are indifferent and can act either in the presence or 

 absence of air. The changes affect both the nitro- 

 genous and the non-nitrogenous organic matter, and a 

 considerable proportion usually about 25 per cent, of 

 the dry matter disappears in the form of gases, and 

 heat is generated. The temperature developed depends 

 largely upon the rate at which fermentation takes place. 



Fermentation is at first of the aerobic type and takes 

 place very rapidly, the action of the bacteria being 

 favoured by the presence of air and of soluble carbo- 

 hydrates in the straw. A considerable rise of tempera- 

 ture is thus produced, but the carbohydrates are soon 

 all consumed and the further entrance of air is hindered 

 as the manure settles in the heap. The temperature is 

 reduced again as the fermentation gradually changes to 

 the anaerobic or putrefactive type and becomes much 

 slower. 



Fermentation 'of the Non-Nitrogenous Matter. The 

 non-nitrogenous matter of ordinary fresh manure consists 

 mainly of cellulose and other carbohydrates which, in the 

 presence of air, are oxidised, forming carbon dioxide and 

 water as final products. This change can, however, 

 only take place to a very limited extent as the supply 

 of oxygen is soon used up. In the absence of air, carbon 

 dioxide and water are also produced together with lactic, 

 butyric, acetic and other similar acids, methane and 



