184 Bacteria in Relation to Country Life 



tury, a number of investigators were already familiar 

 with the fact that such reductions of nitrate are likely to 

 take place in the presence of organic matter. They were 

 not a little puzzled at the apparently contradictory 

 properties of soils. 



The fact that the reduction of nitrates in the soil 

 is more likely to occur when the latter contains an ex- 

 cess of moisture, or an excess of organic matter, was 

 recognized by these men. They did not know, however, 

 that microscopic organisms in the soil are intimately 

 connected with the reduction processes. The German 

 scientist, Schonbein, suggested in 1868 that the reduc- 

 tion of nitrates might be due to fungi and bacteria. 

 A few years later his views were confirmed by the ob- 

 servations of others, particularly as to the reduction 

 of nitrates in sewage and in drinking-water. 



The cause of denitrification. These views found strong 

 support in the studies of the French investigators, 

 Gayon and Dupetit. They actually observed, at the 

 beginning of the eighties, cultures of a bacillus, or 

 " ferment," as they called it, that was found capable 

 of reducing nitrates with the production of nitrogen 

 gas. In 1886, they described two denitrifying ferments 

 that they had isolated and studied under varying con- 

 ditions. Cultures of a denitrifying bacillus were also 

 prepared by Giltay and Aberson in Holland. The 

 latter found that when grown in meat broth or other 

 solutions containing nitrate, this organism is capable of 

 reducing nitrate with the transformation of almost all of 

 its nitrogen into gas. It was thus demonstrated that 

 soil contains bacteria that cause reduction of nitrates. 



