246 



ganisms on their rootlets it is possible that the actual stores of available 

 nitrogen may be increased. This fact explains the observation which has 

 frequently been made that in the fields which are not cultivated , but 

 which remain in grass, there may be found an actual increase in the 

 total amount of nitrogen which is available for plant growth. As will 

 be seen further along, the soil is also infested with an organism which 

 is capable of destroying nitric acid and returning the nitrogen which it 

 contains in the air in a free state. It seems almost certain that in every 

 complete decomposition of a nitrogenous organism a part of the nitro- 

 gen which it contains escapes in the free state. "Were it not, therefore 

 for the fact that this free nitrogen can be oxidised and made available 

 for plant growth, the total stores of organic nitrogen in existence would 

 be gradually diminished, and the time would ultimately come when 

 their total amount would not be sufficient to sustain a plant life abun- 

 dant enough to supply the food of the animal kingdom. Thus the earth 

 itself, even without becoming too cold for the existence of the life which 

 is now found upon it, might reach a state when plant and animal life 

 would become practically impossible by reason of the deficit of nitrogen- 

 ous foods. 



Much less is known concerning the character and activity of the or- 

 ganisms that oxidize free nitrogen than of those which feed upon organic 

 nitrogen. It cannot be doubted, however, that these scarcely known 

 ferments are of the greatest importance to agriculture, and the further 

 study of their nature and the proper methods of increasing their activity 

 cannot fail to result in the greatest advantage to the practical farmer. 



FERMENTS INIMICAL TO AGRICULTURE. 



It has been noticed by many observe! s that when nitric acid is sub- 

 jected to certain fermentative processes it becomes decomposed and 

 gradually disappears. In studying the causes which lead to this decom- 

 position it is found that it is due to the action of a micro-organ sm or 

 ferment, which, by reason of the result of its functional activity, is 

 called a denitrifying organism. While it is true that in numbers and 

 activity this denitrifying organism does not equal its nitrifying relation, 

 yet it is a matter of no inconsiderable importance to know fully the laws 

 which govern its existence. As in the case of the bacteria which are 

 found in ripening cream, where some produce evil and some good ef- 

 fects, so it is also with those in the soil. The favouring organisms, 

 whose functional activity prepares nitrogen in a form suited for plant 

 food, are accompanied by others, doubtless nearly related to them, whose 

 funtcional activity tends to destroy the work which the first have ac- 

 complished. It thus happens that in the fermentation of nitrogenous 

 bodies there is danger of losing, as has already been said, a part of the 

 nitrogen, which may either escape as gaseous oxides unsuited for the 

 sustenance of plants, or even as free nitrogen. The object, at least the 

 practical object, of the investigation of these denitrifying organisms 

 should be to discover some process by which their multiplication could 

 be prevented and their activity diminished. At the present time all that 

 is known is that in favouring circumstances these organisms are not de- 

 veloped in sufficient number to prove very destructive. It has already 

 been mentioned, however, that in case of a very great excess of organic 

 nitrogenous matter a considerable quantity of the nitrogen therein con- 



