244 DENITRIFICATION 



into lactic acid, alcohol, and carbon dioxid. The nitrate is reduced 

 to nitrous acid and this in turn is reduced to ammonia or element- 

 ary nitrogen. The oxygen so obtained is utilized by the microorgan- 

 isms for the further oxidation of the carbohydrates, and it is in this 

 manner that the organism obtains its requisite energy. 



Stoklasa and Vitek believe that nitrous acid is always the inter- 

 mediate product in the reduction of nitrates. They consider that 

 carbon dioxid and hydrogen are produced from the carbohydrates 

 or organic acids of the cultural media and the nascent hydrogen 

 combines with the oxygen of the nitrates to form water and thus 

 reduces the latter to nitrites. Gayon and Depetit give this formula: 



5C 6 Hi 2 O6 + 24KNO 3 = 24KHCO 3 + 6CO 2 + 18H 2 O + 12N 2 



The process is probably due to enzymes. Fred was able to demon- 

 strate the production of both oxidases and peroxidases by B. 

 denitrificans. Hulme considered that reduction may be divided into 

 two parts: the bacterial reduction and the enzymatic reduction. 

 However, we are led to doubt whether either is due to a true enzyme, 

 for the enzymes which have been obtained in impure forms are not 

 affected by heat and the reducing substances are not specific, as is 

 the case with most enzymes, for they reduce chlorates to chlorids, 

 arsenates to arsenites, and ferricyanids to ferrocyanids in the same 

 manner as nitrates are reduced to nitrites. 



Influence of Water. Many of the results obtained on denitrifica- 

 tion were with the use of liquids, and it is now known that denitrifica- 

 tion in soils progresses differently from that in liquids, depending 

 upon the nature of the bacteria and the physical conditions of the 

 medium in which they are situated. In liquids and very wet soils 

 from which oxygen is excluded, the bacteria take their oxygen from 

 the nitrates present in the soil and thus liberate nitrogen, but in 

 well aerated soils this does not occur, as the bacteria can use the 

 oxygen of the air. 



The author failed to find any evidence of denitrification in a highly 

 calcareous soil to which had been added from to 25 tons per acre 

 of manure and from 12.5 to 22.5 per cent, of moisture, as may be 

 seen from the following : 



Nitric Gain in 



nitrogen total nitrogen 



Treatment. (per cent.) (per cent.). 



1 2 . 5 per cent, of water 1 100 100 



15 118 108 



17.5 121 102 



20.0 121 104 



22.5 123 108 



The results may vary with different soils, but Lemmermann found 

 that in three greatly dissimilar soils it was greatest when the soil 

 was saturated. 



Therefore, when the moisture exceeds certain limits, it may 



1 The soil containing 12.5 per cent, of water was taken as producing 100 per cent. 



