68 



PHYSIOLOGY OF NUTRITION 



acid, are presented below. The soil without oxygen thus lost its whole content 

 of nitrate, and those supplied with oxygen formed additional amounts, the 

 quantity formed increasing with the amount of oxygen supplied. 



Nitrification in soils is due to bacterial action, as Schlösing and Müntz 1 have 

 shown. These authors took a large-bore glass tube a meter long, filled it with 

 a mixture of sand and lime and allowed sewage water containing ammonia to 

 percolate slowly through it. After some days nitrate could be indentified in 

 the filtrate. The ammonia of the water was oxidized in its passage through 

 the tube. They also subjected the soil contained in the tube to the action of 

 chloroform vapor during the percolation, to determine whether this oxidation 

 was effected by the soil itself or by microorganisms contained therein. The re- 

 sult was a cessation of nitrification, the filtrate containing ammonia instead 

 of nitrates in this case. Since the chloroform probably only repressed the 

 vitality of the soil bacteria, without influencing purely chemical processes, 

 Schlösing and Müntz concluded that the process of nitrification in the soil is 

 caused by bacteria. 



After many investigators had vainly endeavored to obtain the nitrifying 

 bacteria of soil in the pure culture, Vinogradskii 2 was at length successful in 

 this, as have been mentioned above (page 48). 



Further investigations by Vinogradskii showed that the nitrification of 

 ammonia and ammonium salts to nitrates is effected in the soil not by one 

 but by two species of bacteria. One form produces nitrites (N0 2 ) from 

 ammonium salts, and the other produces nitrates from nitrites. Vinogradskii 

 proposed to reserve the term Nitrobacteria for all those bacteria that have to 

 do with converting ammonium into nitrate. Investigation of the morpho- 

 logical characteristics of nitrite-formers from different sources shows that they 

 belong to different species. The difference between the nitrite-formers of 



1 [Schloesing, Th., and Müntz, A., Sur la nitrification par les ferments organised. Compt. rend. Paris 

 84:301-303. 1877. Idem, same title. Ibid. 85 : 1018-1020. 1877. Idem, same title. Ibid. 86: 892- 

 89s. 1878.] 



2 Winogradsky, S., Recherches sur les organismes de la nitrification. I, II, III, IV and V, 1890. [See 

 note 1, p. 48.] Idem. Contributions ä la morphologie des organismes de la nitrification. [Russian and 

 French.] Arch. sei. biol. St. -Petersbourg 1 : 87-137. 1892. 



