198 THE LIVING ORGANISMS OF THE SOIL [chap. 



observers, particularly Deherain and Maquenne (1882), 

 with regard to soils, confirmed these results and showed 

 that they were due to bacterial action. In a paper 

 published in 1882, Warington described an experiment 

 in which sodium nitrate was applied to a soil saturated 

 with water ; after standing for a week, the nitrate was 

 washed out of the soil, part of it had disappeared, and 

 part had become nitrite. The total of both nitric and 

 nitrous nitrogen only amounted to 20-9 per cent, of that 

 which had been originally applied. That the nitrate 

 had been reduced to gaseous nitrogen was seen by the 

 development of transverse cracks filled with gas in the 

 soil, and it was concluded that some of the nitrogen 

 applied in manures and unaccounted for in crop and 

 soil may well be due to the reduction of nitrates to 

 gas, by the combustion of organic matter with the 

 oxygen of the nitrate, especially in ill-drained soils in 

 wet weather. Gayon and Dupetit, in 1886, isolated two 

 organisms from sewage which would reduce nitrates 

 to gas in the presence of organic matter, the action 

 being chiefly carried on when oxygen was absent; it 

 came to a standstill when plenty of air was supplied, so 

 that the organism had no need to attack the nitrate 

 to obtain oxygen. Both in their experiments and in 

 others, the presence of an abundant supply of soluble 

 organic matter was one of the necessary conditions 

 for the destruction of the nitrates. The denitrifying 

 bacteria are widely distributed. Warington found, out 

 of thirty-seven species of bacteria examined, only 

 fifteen failed to reduce nitrate, twenty-two reduced 

 it to nitrite, and one of them liberated gas. P. F. 

 Frankland, again, found that fifteen out of thirty 

 organisms derived from dust or water would reduce 

 nitrate to nitrite. In fact, a large number of bacteria, 

 when deprived of oxygen and in contact with abundant 



