DECOMPOSITION IN THE BOIL 7! 



gradual degradation of organic matter by microorganisms. 



No single form can act on an organic compound and 

 change it into the final products of decomposition. Many 

 forms are concerned in the complete decomposition of the 

 simplest forms of organic matter. The various organisms 

 concerned may br-ar different relations to one another. The 

 most common and the most important of these relations is 

 that already discussed, to which tfce term metabiosis is ap- 

 plied. It is to be noted, from the example of metabiosis 

 given on page 59, that the processes of hydration are first 

 involved, later dextrose is split into alcohol and carbon- 

 dioxide, and this is followed by oxidation. The former 

 processes can take place in the absence of free oxygen 

 under the influence of facultative organisms. The com- 

 pletion of the decomposition process must be occasioned by 

 aerobic forms. This fact is noted also in the decomposition 

 of all organic matter; the final stages are always due 1o 

 aerobic organisms. This fact implies the accumulation <>f 

 partially decomposed organic matter under conditions 

 where oxygen is not abundant, a phenomenon of the utim^' 

 importance in the soil. 



The degradation of starch does not always occur on the 

 lines laid down: from sugar, acids rather than alcohol may 

 be formed. Lactic, acetic, formic, butyric, and propionic 

 acids are the most common. The formation of acids from 

 sugar and alcohol is chiefly due to bacteria, while yeasts are 

 the prime factors in the production of alcohol. 



It is to be noted that, in the decomposition of carbohy- 

 drates, acids of varying strength are formed, down to the 

 weak carbonic acid. This accounts for the acid reaction in 

 decomposing organic matter in which carbohydrates pre- 

 dominate over proteins, which in their decomposition yield 

 ammonia. The reaction of decomposing protein will be 

 alkaline, as exemplified in eggs and meats. It may be 



