TRANSFORMATIONS OF CARBON AND NITROCJEN. /I 



same time being liberated in the form of water. These join 

 the atmosphere while the minerals remain behind as ash. 

 The carbon is thus brought back once more to its original 

 source and in its original form. Thus all forms of combustion 

 of carbonaceous material aid in keeping up the store of CO 2 in 

 the atmosphere, upon which plants can depend. 



But although direct oxidation may form a considerable part 

 of this process of food reduction, another very large factor is 

 due to the agency of microorganisms. Fires rarely occur in 

 nature unless started by man, and there must, therefore, be some 

 other means of oxidation. A slow oxidation of carbonaceous 

 material occurs in nature at all times, which has ordinarily 

 been attributed to direct chemical processes. It is quite doubt- 

 ful, however, whether this slow oxidation would occur were it 

 not for the agency of microorganisms. At all events, a*ton- 

 siderable part of the so-called slow oxidizing processes are 

 the direct result of their growth. 



There are various organisms which contribute to the gradual 

 destruction of the carbonaceous materials. The sugars, for 

 example, undergo an alcoholic fermentation, a process veiy 

 widely distributed in nature. This fermentation is produced 

 by the action of yeasts, and the fermentation which goes on 

 in nature is identical with that which occurs in the brewer's 

 vat The result of the fermentation is the formation of CO 2 

 and alcohol, the carbon dioxide passing into the atmosphere to 

 contribute to the store of this important food. The alcohol, 

 under normal conditions, also passes into the air and is even- 

 tually further oxidized into carbonic acid and water. Thus, the 

 sugars, by the agency of yeasts, aided by the forces of chem- 

 ical oxidation, are restored to the air. Starches have nearly 

 the same history since they are readily converted into sugars 

 and then fermented. 



Cellulose. For our subject a more significant feature of 

 chemical decomposition concerns that product of plant life 



