154 BACTERIA 



ature. The nitrifying organism can act at a temperature as 

 low as 37° or 39"^ F. (3-4° C), but at a higher temperature 

 it becomes much more active. According to Schlosing and 

 Miintz, at 54° F. (12° C.) nitrification becomes really active, 

 and it increases as the temperature rises to 99° F. (37'' C), 

 after which it falls. A high temperature or a strong light 

 are prejudicial to the process. 



We are now in a position to consider shortly some of the 

 characters of these nitrification bacteria. They may readily 

 be divided into two chief groups, not in consideration of 

 their form or biological characteristics, but on account of the 

 duties which they perform. Just as we observed that there 

 were few denitrifying organisms which could break down 

 ammonia compounds to nitrogen gas, so is it also true that 

 there are few nitrifying bacteria which can build up from 

 ammonia to the nitrates. Nature has provided that this 

 shall be accomplished in two stages, viz., a first stage from 

 ammonia bodies to nitrites, and a second stage from nitrites 

 to nitrates. The agent of the former is termed the nitrous 

 organism, the latter the nitric organism. Both are con- 

 tributing to the final production of nitrates which can be 

 used by plant life.' 



The Nitrous Organism (Nitrosomonas). Prior to Koch's 

 gelatine method the isolation of this bacterium proved an 

 exceedingly difficult task. But even the adoption of this 

 isolating method seemed to give no better results, and for 

 an excellent reason : the nitrifying organisms will not grow 

 on gelatine. To Winogradsky and Percy Frankland belongs 

 the credit of separately isolating the nitrous organism on the 

 surface of gelatinous silica containing the necessary inorganic 



' The saltpetre beds of Chili and Peru are an excellent example of the indus- 

 trial application of these facts. Nitrates are there produced from the faecal 

 evacuations of sea-fowl in such quantities as to form an article of commerce. 

 A like form of utilisation of the action of these bacteria was once practiced on 

 the continent of Europe. Economic application is also seen in the treatment 

 of sewage referred to elsewhere. 



