1 54 DENITRIFICATION 



species and grow well enough in bouillon when supplied 

 with free oxygen, but do not reduce nitrates to more 

 than a slight extent under such circumstances. When 

 cultivated anaerobically or with a diminished supply of 

 air they take oxygen from nitrates or nitrites, using it 

 for the respiratory combustion of comparatively large 

 amounts of organic carbon compounds. That the want 

 of oxygen is the chief cause of denitrification may be 

 deduced from the cultivation of Bact. pyocyaneum, or a 

 similar organism with and without nitrite in the presence 

 and absence of air respectively. Growth and multiplica- 

 tion take place in alkaline nitrite bouillon under aerobic 

 conditions without decomposition of the nitrite, but when 

 cultivated as an anaerobe the nitrite disappears rapidly 

 with the evolution of free nitrogen. Without the nitrite 

 under anaerobic conditions little or no growth occurs, 

 and respiration is stopped even when suitable oxidizable 

 material is available. The power of utilizing organic 

 compounds apparently as the source of energy for the 

 reduction of nitrates which takes place in the denitrifica- 

 tion process, varies considerably with different species 

 of bacteria. Some of these can oxidize certain carbo- 

 hydrates and acids which are not attacked by other 

 species. For instance, Salzmann found that Bact. 

 Hartlebii made use of xylan, glucose, lactose, and 

 maltose, but none of these were of service for the growth 

 o^Bact. Stutzeri. 



The amount of nitrate decomposed is proportiorial 

 to the amount of easily assimilated carbon compounds 

 available. Those substances which serve best for 

 the denitrifying species of bacteria are neutral salts 

 of organic acids, especially butyric, lactic, and citric 

 acids ; acetic, propionic, valerianic, and other acids are 



