THE NITROGEN CYCLE 219 



solution containing only nitrate. During the course of the 

 experiment the bottle should be kept as far as possible in 

 darkness, to prevent the formation of green algae growths, 

 which combine with the nitrogen of the ammonia or the 

 nitrate, and so confuse the progress of the reaction. 



Experiments of this kind were carried out by Munro in 

 1883, who showed that practically every form of nitrogenous 

 organic matter was capable of undergoing this series of 

 changes. 



We are indebted to the labours of Warington for the 

 exhaustive study of the conditions under which nitrification 

 occurs. 



He showed that the power of nitrification could be com- 

 municated to solutions, which otherwise did not nitrify, by 

 inoculating them from solutions in which nitrification was 

 taking place. 



He further confirmed the results of Schlosing and Muntz 

 by showing that nitrification could be inhibited by the intro- 

 duction of antiseptics such as chloroform and carbon bisulphide. 



The following were the conditions which Warington found 

 to be essential for nitrification, and his results are in harmony 

 with those of other observers, among whom may be especially 

 mentioned Munro and Winogradski. 



1. It was found that phosphates are the essential element 

 of the food of the organism of nitrification. In fact, the very 

 interesting observation was made that these organisms could 

 thrive on purely inorganic material, and even that the presence 

 of organic matter appears to have an inhibiting effect. This 

 question will be further considered in the light of more recent 

 investigations. 



2. The presence of oxygen is essential to the activity of 

 the nitrifying organisms. 



3. The presence of a base is also essential to neutralise 

 the nitrous and nitric acids as they are formed ; at the same 

 time there must not be an excessive alkalinity. 



