752 



by the action of inorganic substances, particularly that of alkalies, 

 but this theory was opposed by the experiments of Landolt, Plath, and 

 Baumann,* which indicated that purely chemical agencies do not 

 suffice to explain the nitrification in the soil. Frank t replied, main- 

 taining his position and insisting upon the fact that he had isolated 

 and cultivated several microbes " by the ordinary methods," but 

 despite repeated efforts, had not succeeded in producing even traces of 

 nitrification by the pure cultures. 



In the following year Warington | studied a large number of bacteria 

 with reference to their ability to nitrifj", but without result. As he 

 secured the phenomena of nitrification when he used soil instead of 

 pure cultures, he concluded that the organism causing it must in the 

 course of time be found. 



Negative results were likewise secured in the experiments of P. and 

 G. Frankland, § with cultures of a number of soil organisms which were 

 carefully isolated and studied. The reduction of nitrates was several 

 times observed but in no case was ammonia oxidized. But when soil 

 from which these same organisms had been obtained was used for inocu- 

 lation, active nitrification was easily obtained. 



Up to the time Winogradsky || took up the study of the subject all 

 attempts to isolate from the soil organisms which it could be conclu- 

 sively proved were capable of producing nitrification, had, therefore, 

 been unsuccessful. Various investigations, including esi)ecially those of 

 Schlosing and Mlintz, pointed clearly to the existence of nitrifying organ- 

 isms in the soil. Wiuogradsky's previous experience had been such 

 as to confirm his belief in such organisms. He had discovered ferments 

 which caused the oxidation of hydrogen sulphide and which he had 

 designated as sulpho-bacteria,^] and others which caused the oxidation 

 of ferrous to ferric compounds and to which he gave the name ferro- 

 bacteria.** He reasoned that it was extremely probable tha t organisms 

 should exist in water and in the soil capable of availing themselves 

 of the abundant energy which would come from the oxidation of the 

 ammonium compounds therein contained. It seemed to him j)robable 

 that the number of species or varieties would be small, at least in 

 any given specimen of soil. It seemed to him that the way to secure 

 and study the nitrifying organisms would be, (1) to find a medium 

 and the conditions in which they would thrive, and by which the 

 growth of denitrifying organisms would be discouraged ; (2) to con- 

 tinue the culture by this method long enough to eliminate for the most 

 part the other (non-nitrifying or denitrifying) organisms; (3) when 

 the cultures of the oxidizing organisms should have been obtained 



'Landw. Jahrb., 1887, and Landw. Versuchs-Stationen, 38, 1888. 



t Ibid. 



t Report of experiments made in the Rothamsted Laboratory. London, 1888. 



§ Zeitsch. f. Hygiene, 6. 



II An. de I'lnstitut Pasteur, 1890. 



H Bot. Zeitung, 1887. 



** Ibid. 1888. 



