1892.] on Micro-organisms in tlieir Belation to Chemical Change. 523 



Experiments on Continuous Nitrification in Mineral Solutions. 



In carrying on this series of experiments it was soon evident that 

 although a number of forms foreign to the nitrification-process were 

 being eliminated, there were still some remaining alongside of the 

 nitrifying organisms, or, in other words, that a pure culture of the 

 nitrifying organisms had not been obtained. From various considera- 

 tions, however, we came to the conclusion that the nitrifying 

 organisms probably differed from the other forms which were still 

 present along with them in being Imable to grow on the common 

 cultivating medium employed by bacteriologists, and known as 

 gelatin-peptone. 



The separation from these foreign forms v;^as ultimately effected 

 by enormously diluting one of these nitrifying solutions, and then 

 taking out small portions of this diluted material and introducing 

 each of these portions into separate ammoniacal solutions. In some 

 of these nitrification was established, in others not, whilst amongst 

 those in which nitrification was established, some contained organisms 

 which grew upon gelatin, whilst one refused to give any growth on 

 the gelatin at all, although it was seen under the microscope to 



2 N 2 



