CHEMICAL CHANGES 123 



Nitrification proper, or the production of nitrates, is due to 

 me or more organisms capable of growing in culture solutions 

 ^hich are practically free from organic carbon. But under 

 latural circumstances they act in succession to nitrous 

 organisms, and in the presence of organic material, which they 

 do not, however, by themselves decompose.^ Some of the 

 difficulties of the subject have been cleared up by the researches 

 of Adeney, who, by cultivation in known solutions, has elimi- 

 nated disturbing factors. His conclusions are : 



1. In inorganic solutions containing ammonia nitrous 

 organisms thrive, but nitric organisms gradually lose their 

 vitality. 



2. Nitrous organisms cannot oxidize nitrites to nitrates in 

 inorganic solutions. 



3. Nitric organisms thrive in inorganic solutions containing 

 nitrites. 



4. The presence of peaty or humous matter appears to pre- 

 serve the vitality of nitric organisms during the fermentation of 

 ammonia,^ and establishes conditions whereby it is possible for 

 the nitric organisms to thrive simultaneously in the same solu- 

 tion as the nitrous organisms. 



In corroboration of this, Beddies^ cultivated nitrifying 

 bacteria in a nutrient solution containing i per cent, of a 

 strong solution of humus and 0*25 per cent, of sodium silicate, 

 and found the organisms much more stable than those obtained 

 by Winogradsky in the absence of organic matter (p. 76). Four 

 stable varieties of nitric and three of nitrous bacteria were 

 isolated, the stronger forms being singularly unaffected by 

 changes of temperature, and growing freely together without 

 interference. When nitrifying organisms are abundant, deni- 

 trification is hindered, and there is no loss of free nitrogen ; 

 but when the denitrifying forms predominate, the nitrifying 

 bacteria are injured, especially if aeration is limited. This is 

 in accordance with what we have observed in connection with 

 some bacterial filters. 



In an effluent which is properly prepared and well aerated 

 nitrification can often be encouraged by seeding with a small 



^ Winogradsky, Centr. Bakt. Par., 1896, (2), ii., 415 and 449. Omeliansky, ibid., 

 1S99, II-, v., 473. See also Ccntr. Bakt., 1899, 652 ; Mitt. Landw. Breslau, (i), 75 ; 

 (2), 197; Comptes rendus, 1899, 566. 



^ As to the production of peaty matter by B. mesentericns, see Julius Stocklasa 

 {Bied. Centr., 1899, xxviii., 588). Streptothrix chromogena is a humus-producing 

 organism in soils {Journal of the Chemical Society, 1900, ii., 425). 



^ Chem. Zeit., 1899, xxiii., 645. 



