184 BIOLOGY OF SPECIALIZED GROUPS 



ammonia to nitrites, are known as the nitroso-bacteria. The 

 other class are the nitrifying bacteria proper (Fig. 43). 



The chemical changes brought about by the nitrifying 

 bacteria in the oxidation of ammonia is represented by the 

 _g_ following formula: - 



^ A 2 NH 3 + 6 O = 2 HNO 2 + 2 H 2 O. 





 :. 2 And the second stage is represented by the 



$? 4>^ formula : - 



2 HNO 2 -f2O = 2 HNO 3 . 



FIG. 43. Nitri- 

 fying bacteria. The energy obtained by this oxidation pro- 



(i) Nitrous fer- 



ments, (2) nitric cess enables these bacteria to make use or 

 ferments x 2000. ^e carbon and nitrogen in an inorganic form 



After Burri and 



Stutzer. (Lip- and thus to synthesize organic matter. 

 These bacteria not only do not require or- 

 ganic matter for food but, in pure culture at least, the organic 

 material interferes with their development. The process of 

 nitrification is strictly an oxidizing process, and, in order 

 that the process may go on, an abundant oxygen supply 

 must be available. Furthermore, the activity of these organ- 

 isms is checked by the presence of considerable amounts of 

 the acids, so that if the process continues, bases must be sup- 

 plied which will unite with the acids to form salts. The 

 nitrification of soils is dependent upon the action of these 

 bacteria, and our knowledge of the life history of these germs 

 is a matter of practical importance when it is applied to soil 

 fertility. Certain phases of this will be referred to in another 

 connection. These bacteria are widely distributed in the 



