SUGAR IN THE NUTRIENT MEDIUM. 147 



10. Conversion of Nitroiis and Nitric Acids into Free 

 Nitrogen. 



This process is carried on by an entire series of 

 bacteria. Burri and Stutzer (C. B., Part II., Yol. 

 I., No. 7 et seq.) were the first to describe special ni- 

 trate fermenters in such an accurate manner that they 

 could again be recognized. They first isolated from 

 horse manure two bacteria, of which each alone was 

 unable to produce nitrogen from nitrate, but did this 

 vigorously when combined, and when the supply of 

 oxygen was abundant or scanty but never when it was 

 absent. These two synergetic bacteria are : (1) Bac- 

 terium coli (this may be replaced by bacterium typhi) , 

 and (2) a short rod described as bacillus denitri- 

 ficans I. Later these writers found a bacillus deni- 

 trificans II., which alone effected the entire decom- 

 position of nitrate into nitrogen. We found that 

 bacterium pyocyaneum also converts saltpetre into 

 nitrogen. 



The practical importance of these organisms lies 

 in the fact that through their agency considerable 

 amounts of nitrates in the soil, but particularly in 

 manures, may be lost for the nourishment of plants 

 on account of their conversion into nitrogen. 



11. Assimilation of Nitrogen. 



According to our present knowledge no other vege- 

 table family is able to assimilate the nitrogen of the 

 air, but this power does inhere in one form of bac- 

 teria, the bacillus radicicola Beyerinck. This bac- 

 terium is found in the small root knobs of various 



