262 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



moistened, and kept for definite periods in bottles, stoppered 

 with cotton wool, at the ordinary laboratory temperature. 

 Determinations were then made : 



(a) Of the production of ammonia ; 



(6) Of the production of unstable nitrogen compounds ; 



(c) Of the proportion of humus ; 



(d) Of the nitrification; and 



(e) Of the total amount of nitrogen. 



The effect of partial sterilisation was found to be : 



(1) An increase in the amount of ammonia ; 



(2) Cessation of nitrification. 



Besides the chemical observations, they determined the 

 total number of bacteria ; and they found that the increased 

 ammonia production, due to partial sterilisation, was accom- 

 panied by an increased number of bacteria. The problem 

 resolves itself into finding out why the bacteria increase so 

 much more rapidly in the partially sterilised than in the un- 

 treated soil. They found that if untreated soil were added to 

 partially sterilised soil, the rate of ammonia production was 

 reduced, but this was not the case if an extract of the un- 

 treated soil, filtered, but still containing bacteria, was added 

 to the partially sterilised soil. This would indicate that the 

 inhibiting agent was something which affected bacterial 

 growth, but which could be removed by a coarse filter. Such 

 an agent would be found in large organisms capable of feeding 

 upon bacteria. As a matter of fact, upon examination, 

 many of these were found in the untreated soil. 



Russell and Hutchinson therefore conclude that the 

 large organisms, that is, protozoa of various kinds, are an 

 important factor in limiting the bacterial activity, and there- 

 fore the fertility of untreated soil. When toluene is added to 

 the soil, or when the soil is heated to 98 C., these phagocytic, 

 or bacteria-consuming, organisms are destroyed, but the 

 bacterial spores are not. On removing the toluene, and 

 adding moisture, the spores germinate, and the other bacteria 



