VITAL PHENOMENA OF BACTERIA. 79 



ammonia into nitrites and the other converts nitrites 

 into nitrates. 



Conversion of Nitrous and Nitric Acids into Free Nitrogen. 

 This process is performed by a number of bacteria. The 

 special nitrate- ferment ing bacteria, however, were first 

 accurately described by Barri and Stutzer. In their 

 exhaustive investigation they first isolated from horse- 

 manure two bacteria, neither of which was alone capable 

 of producing nitrogen from nitrates, but which together 

 in the presence of oxygen, but never without it entirely, 

 decomposed nitrates energetically. Later a second 

 denificating bacillus was found, B. denitrificans II., 

 which by itself was able to produce nitrogen from 

 nitrates. 



The practical importance of these organisms is that 

 by their action large quantities of nitrates in the soil, 

 and especially in manure, may become lost as plant- 

 food by being converted into nitrogen. 



Nitrogen Combination. The bacillus radicicola of 

 Beyerinck, which was isolated by him, has the power of 

 assimilating nitrogen from the air. This bacillus is found 

 in the small root-nodules of various leguminous plants 

 (pease, clover, etc.), and can be obtained from these in 

 cultures. Different varieties exist in different kinds 

 of legumes, each kind of legume apparently having a 

 special variety of bacteria adapted to it, and not every 

 variety is capable of producing nodules in all legumes. 

 There are certain " neutral " varieties, however, existing 

 free in the soil and not adapted to any special legume, 

 and these seem to be able to form nodules in different 

 legumes. 



By the aid of these root-bacteria, which gain entrance 

 to the roots and there produce this nodular formation, 



