360 ANNUAL REPORT OF THE Off. Doc. 



examined by the writer, with one exception, are aerobic, and yet they 

 all actively reduce nitrates. 



That active denitrification can take place in the presence of an 

 abundant supply of atmospheric oxygen is shown by the following: 

 A culture of B. pulvinatas was selected on account of its active denit- 

 rifying properties. 



The bacillus was grown in a solution of Witte's peptone containing 

 one gram of nitrate of soda to the litre. 



Provisions were made for continually passing sterile air through 

 the culture so as to provide an abundance of atmospheric oxygen. 

 Simultaneously with the above, a culture was made in an ordinary 

 flask, plugged with cotton wool, without aeration. At the end of 5 

 days 7.0 milligrams of nitrite of soda per 100 c. c. were found in the 

 aerated culture and 30.0 milligrams in the non-aerated. 



At the end of 10 days 20 milligrams of nitrite of soda were found 

 in the aerated and 40 milligrams in the non-aerated culture. 



In this case active denitrification took place even with abundant 

 and continual aeration of the culture, although the presence of large 

 quantities of atmospheric oxygen seemed to somewhat retard the 

 process. 



These results are in conformity with those of Stutzer and Maul.'" 

 B. denitrificans and B. coli-communis in a broth culture caused a 

 vigorous reduction of nitrates to nitrites, and in four days the ni- 

 trites had entirely disappeared, when, however, a constant stream 

 of air was passed through the culture, growth took place as before 

 but the nitrates had not entirely disappeared until after the tenth 

 day. 



It would, therefore, appear that denitrification can take place ac- 

 tively even in the presence of an abundant supply of atmospheric 

 oxygen, certain bacteria at least being capable of utilizing combined 

 oxygen equally with that supplied in the free state. 



Contrary results were obtained by Pfeiffer, Franke, Gotze and 

 Thurmann'^^ in their study of the loss of nitrogen in manures. They 

 found that denitrification was more active when air was drawn 

 through and over the manure than when air was excluded, the pres- 

 ence of atmospheric air apparently favoring the process, and it has 

 become a recognized principle that manures lose nitrogen less readily 

 when kept closely compacted than when loose. 



(5.) The Presence of Organic Matter. 



The effect of organic matter upon the development of the denitri- 

 fying organism was shown by Stutzer and Jensen in 1897.^^ The 

 experiments of the latter indicate that denitrification can take place 

 only in the presence of a suflBcient supply of assimilable carbon, 



