122 NATURAL MANURES. VI. 



case of the aerobic bacteria the compounds formed by 

 their vital processes are usually of a simple character, 

 e.g., water, carbon dioxide, and ammonia. Such fer- 

 mentation is sometimes called mouldering or decay and 

 is not attended by the evolution of foul-smelling gases. 



The anaerobic organisms, on the other hand, tend to 

 produce unoxidised products, some of which are highly 

 complex, and the gases evolved consist of methane, 

 CH 4 , hydrogen, sulphuretted hydrogen, &c., &c. Many 

 of these products are possessed of disagreeable smells 

 and the changes leading to their production are con- 

 sidered as true putrefaction. These putrefactive changes 

 can be brought about by a great number of different 

 organisms and the albuminoid substances are the chief 

 raw material for their activity. Many of the bad-smell- 

 ing gases evolved have not been identified. Among 

 other products, amines, e.g., trimethylamine, N(CH H ) 3 , 

 volatile acids, e.g., butyric acid, C H H 7 .COOH, and ca- 

 proicacid, C. 5 H n .COOH, and mercaptans, e.g., C 2 H 5 .SH, 

 have been detected. 



In a manure heap both aerobic and anaerobic orga- 

 nisms perform their functions, the former chiefly at 

 first and until the air in the interstices of the manure 

 has been exhausted, producing mainly carbon dioxide, 

 water, and ammonia. Then the anaerobic bacteria 

 begin to operate and evil-smelling gases come off. The 

 evolution of heat, which is aften considerable during 

 the life of the aerobic organisms, diminishes, 

 (d) Ammoniacal or urea fermentation. This has already been 

 briefly referred to (v. p. 65). The main reaction is 

 there given as 



CO(NH,\ 2 + 2H 2 = (NH 4 ). 2 C0 8 , 



thus giving ammonium carbonate ; in addition a reaction 

 expressed by the following equation : 



CO(NH. 2 ),+H 2 = NH 4 .O.CO.NH. 2 



Urea. Ammonium carbamate. 



resulting in the formation of ammonium carbamate, 

 has been detected. At least five or six different bacteria, 

 some micrococci, some bacilli, and even some moulds 



