ASSIMILATION OF NITROGEN 



6 9 



the Old World and of the New is so great that it has even been necessary to 

 distinguish two different genera, each with several species. The nitrite bac- 

 teria of the Old World constitute the genus Nitrosomonas, with two species 

 (N. europcea, N. javanensis) and local varieties. Those of the New World form 

 the genus Nitrosococcus. A third genus, Nitrobacter, 1 includes those bacteria 

 that oxidize nitrites to nitrates. 



The work of Vinogradskii led to the supposition that these organisms might 

 get their carbon as magnesium carbonate, but Godlewski 2 showed that such is 

 not the case. Even with magnesium carbonate (MgC0 3 ) present, no carbon 

 assimilation occurs in an atmosphere devoid of carbon dioxide. The nitrify- 

 ing bacteria are thus shown to obtain their carbon from the carbon dioxide of 

 the air. 



Further investigations of Vinogradskii and Omelianskii 3 cleared up the re- 

 lation of nitrifying organisms to various organic compounds that check their 

 growth. In the following table are given, for each of the two kinds of bacteria 

 and for several organic compounds, the concentrations of the latter that just 

 begin to retard growth and those that check it completely. 



Vinogradskii and Omelianskii state: "The action of the above-named sub- 

 stances, in preventing nitrification, is so pronounced and becomes evident at 

 such low concentrations, that these substances are not to be considered even as 

 neutral in this case, although they are usually regarded as nutrients in bacteri- 

 ology; on the contrary, their action is quite analogous to that of the substances 

 that are known as antiseptics." 



If the presence of organic substances checks the process of nitrification, then 

 no nitrifying of organic nitrogenous compounds is to be expected in pure cul- 

 tures of nitrobacteria. According to Omelianskii 4 these organisms are entirely 

 lacking in ability either to break down organic nitrogenous compounds by split- 

 ting off ammonia, or to oxidize the nitrogen of these compounds directly. Or- 



1 On methods for pure cultures of nitrifying bacteria, see: Omeliansky, 1899. [See note I, p. 50.] 



2 Godlewski, Emil, O nitryfikacyi ammoniaku. Krakow. 1896.* 



3 Winogradsky, S., and Omeliansky, V., L'influence des substances organiques sur le travail des microbes 

 nitrificateurs. Arch. sci. biol. St. -Petersbourg 7 : 233-271. 1899. 



4 Omeliansky, V., Sur la nitrification de l'azote organique. Arch. sci. biol. St. -Petersbourg 7: 272-290. 

 1899. 



