THE MICROBES OF THE SOIL 285 



nitrous nitrogen, and can grow in ammoniacal solu- 

 tions devoid of organic matter. There is little 

 doubt that Frankland's and Winogradsky's microbes 

 are the same. Both sets of experiments prove that 

 the nitrous bacillus of the soil converts ammoniacal 

 into nitrous nitrogen, and not into nitric nitrogen. 



(3) Waringtoris researches. Mr. Warington has 

 also isolated, by the dilution method, a microbe 

 which converts ammonia into nitrous acid only ; 

 and confirms the investigations of Frankland and 

 Winogradsky. In addition to this, Warington has 

 apparently isolated a microbe from soil which con- 

 verts nitrites into nitrates. This microbe produces 

 neither nitrites nor nitrates in ammoniacal solu- 

 tions; in fact, it cannot oxidise ammonia. The 

 nitric microbe (Fig. 56 B) is a micrococcus, and 

 grows in a solution of potassium nitrite. 



'The nitrification effected by soil is thus ex- 

 plained as performed by two microbes, one of 

 which oxidises ammonia to nitrates, while the other 

 oxidises nitrites to nitrates. The first microbe is 

 easily separated from the second by successive 

 cultivations in solutions of ammonium carbonate. 

 The second is (probably) separated as easily from 

 the first by successive cultivations in solutions 

 of potassium nitrite containing monosodium car- 

 bonate.' 



' In soil the nitric microbe is equally active as 

 the nitrous, since soil never contains any but ex- 

 tremely weak solutions of ammonia, andsuper- 

 carbonates are always present.' 



