GENERAL FUNCTIONS OF MICROBES 13 



That nitrification is the work of living creatures has been 

 proved by the celebrated experiment of Schlcesing and Miintz. 

 If a cylinder is filled with cultivated soil, ammonia poured on 

 the top appears at the bottom as nitrate of lime. But this 

 transformation no longer occurs if the earth is previously heated 

 to 100 C, or if it is impregnated with the vapour of chloroform 

 or of carbon bisulphide, i.e. t if the living organisms that it 

 contains are killed or paralysed. The soil recovers its activity 

 when the paralysing vapours have been removed by passing 

 through a current of air. 



Nitrification is a process of two stages, and is carried out by 

 two species of bacteria, each with its own function. In the 

 first phase, the ammoniacal salts are transformed into nitrites 

 by the microbes known as the nitrous ferment, e.g. Nitroso- 

 monas of Europe, Nitrosomonas of Java, and the Nitrosococcus 

 of America (Mexico and Brazil). In the second phase the 

 nitrites are turned into nitrates by the nitro-bacterium or nitric 

 ferment, the Nitrobacter of Winogradsky (figs. 4-6). 



Neither the nitrous nor the nitric ferments develop in 

 presence of organic matter. The activity of the nitrous 

 ferment is arrested by 0*3 per cent, of glucose, peptone or 

 asparagin. The nitric ferment, less sensitive, is stopped by 

 0-3 per cent, of glucose, 1^25 per cent, of peptone or i per 

 cent, of asparagin. The former is inhibited by 1*5 per cent., 

 the latter by 3 per cent, of sodium acetate. 



Now we are accustomed to the idea that bacteria live on 

 organic matter. Yet the bacteria of nitrification must, as we 

 have seen, get their nourishment elsewhere. They differ from 

 other bacteria in being capable of taking up carbon by decom- 

 posing carbonates, in being aerobic, and in behaving like chloro- 

 phyllous plants. They are not saprophytes in the same sense 

 as the majority of bacteria. 



In the laboratory, the two phases of nitrification can be 

 demonstrated separately by pure culture. But in nature they 

 are simultaneous. Under laboratory conditions ammonia 

 exerts an inhibiting action on the nitric ferment, whereas in 

 nature both the actions can occur in presence of quantities of 



