6Y R. GRfelG-SMITtt. 



16b 



The numbers show that the addition of the moulds and of the 

 toxic bacteria had a small though consistent effect in leducing 

 the numbers of bacteria after an interval of some thirty days; 

 for when the counts are plotted, the control-curve is generally 

 higher than the others. The reduction of the numbers, however, 

 was not pronounced, and we must therefore conclude that the 

 moulds and bacteria used in the experiment do not constitute 

 what is recognised as the limiting factor. This had not been 

 completely eliminated from the soils, for its effect was made 

 evident between the 125th and the 357th day. 



Shortly after the start of the last experiment, another w^as 

 prepared to determine the effect of three of the micro-organisms 

 upon raw, toluened and heated soils. The moisture of a garden- 

 soil was raised to 6% with sterile distilled water, and the soil 

 was divided into three portions. One was treated for two days 

 with 2% of toluene, and aired off. A second was heated for two 

 and a half hours at 97'', and, with the third portion, was aired 

 so as to give all three portions the same air-treatment. The 

 portions were subdivided, treated with the respective organisms, 

 and had the moisture-contents raised to 10%. 



Bacteria in millions per gram of dry soil. 



The experiment confirms the previous one in showing that the 



