THE N1TRO-BACTERIA 233 



During the oxidation processes the bacteria are protected from injury 

 by the presence of bases which take up the acids with which the 

 ammonia was initially combined, and also neutralize the resulting 

 nitrous or nitric acid. Calcium carbonate performs this function excel- 

 lently in the soil. Free alkali is unsuitable here for the fixation of the 

 acids, because if present in quantity it would be injurious to the bacteria. 

 In artificial cultures Winogradsky replaces the calcium carbonate by 

 magnesium carbonate (Lafar's Tech. Mycology, 204-). 



THE NITRO-BAOTBRIA. 

 NITROSOMONAS EUROP^EA (WINOGRADSKY). 



Found in all samples of European, African, and Japanese earth 

 examined. 



Microscopical Appearances. They occur in short chains of three 

 to four individuals. 



Spore Formation absent. 

 Motility present (Monotricha). 



Biological Characters. For method of isolating this organism 

 see Technique, 156. 



On Silicic Acid Media the colonies are at first compact, with a sharp 

 contour, brownish colour, sometimes resembling a spindle with blunt 

 ends. In ten to fourteen days, round, clear, unstained masses, with 

 irregular offshoots, consisting of motile monas, extend from the growth. 



In Fluid Cultures, when quiescent, they collect in zooglcea, forming a 

 sediment especially around the precipitated carbonate. In seven days or 

 less the fluid becomes cloudy, and in twenty-four to forty-eight hours the 

 motile monas again sink to the bottom. The process of growth and the 

 nitrite formation is now finished. 



NITROSOMONAS JAVANIENSIS (WINOGRADSKY). 



Found in Java earth, and very similar to the above organism. 



NITROSOCOCCUS BRAZILIENSIS. 



Found in the soil of Campinas, Brazil. They do not form zooglcea, 

 and possess no cilia, and attain a diameter of 2 /x. The species grown 

 from Melbourne soil is indistinguishable from that found in Brazil ; 

 while that obtained from Quito (Ecuador) is a coccus, 1*5 to 1*7 />t in 

 diameter. 



