26 



of this reaction is very marked. After twenty-four hours 

 the surface of the liquid is covered with foam, and at the end 

 of two days very little nitrite remains. Those cultures in 

 which the evolution of gas was most pronounced, evolved 

 disagreeable odors; while those which developed but slight 

 activity were comparatively odorless. But few species of 

 bacteria reduce nitrites to free nitrogen in straight peptone 

 media. The fluorescens group are of special importance in 

 producing this change. Representatives of this class were 

 isolated from many of these soils and were probably indigenous 

 to all. 



TABLE X 



