THE BIOLOGICAL ACTIVITIES OF BACTERIA 65 



bacteria appear as oval bodies, which swim actively about and 

 develop flagella at one end. Upon the solid media in ordinary use 

 they can not be cultivated. Special solid media suitable for their 

 cultivation and composed of silicic acid and inorganic salts have 

 been described by Winogradsky and by Omeliansky. 29 



Other nitrite-forming bacteria have since been described by 

 various observers, all of them more or less limited to definite locali- 

 ties. Some of these are similar to nitrosomonas in that they exhibit 

 the flagellated, actively motile stage. In others, this stage is absent. 



The nitrite-forming bacteria, apart from their great agricultural 

 importance, claim our attention because of their unique position in 

 relation to the animal and vegetable kingdoms. Extremely sensitive 

 to the presence of organic compounds, they are able to grow and 

 develop only upon media containing nothing but inorganic material ; 

 and this entirely without the aid of any substances comparable to 

 the chlorophyll of the green plants. The source of energy from 

 which this particular class of bacteria derive the power of building 

 up organic compounds from simple substances is to some extent a 

 mystery. The carbon which they unquestionably require for the 

 building up of organic material may be, as Winogradsky believed, 

 derived to a certain extent from ammonium carbonate. But it is 

 also quite certain that they are capable of utilizing directly atmos- 

 pheric C0 2 . In the absence of chlorophyll or of any highly or- 

 ganized chemical compound, it seems likely that the energy neces- 

 sary for the utilization of the carbon obtained in this simple form 

 is derived from the oxidation of ammonia during the process of 

 nitrification. 



The conversion of nitrites into nitrates is carried on by other 

 species of bacteria also discovered by Winogradsky. These bacteria 

 are much more generally distributed than nitrosomonas and prob- 

 ably include a number of varieties. The organism described by 

 Winogradsky is an extremely small bacillus with pointed ends. Cap- 

 sules have occasionally been demonstrated. It may be cultivated 

 upon aqueous solutions containing: 



Sod. nitrite 1 per cent. 



Potass, phosphate 05 " ' ' 



Magnesium sulphate 08 < l ' ' 



Sodium carbonate : . . .1 ' ' ' ' 



Ferrous sulphate 04 " " 



29 Omeliansky, Cent. f. Bakt., II, 5, 1899. 



