STUDIES ON SOIL PROTOZOA 



173 



TABLE XXXIV 

 Effect of reinoculation of treated soil with untreated soil {treatment 2 per cent CS2) 



Incubation period after reinoculation: 2 months. 



soil has any effect it is to increase the number of bacteria rather 

 than to decrease it. However, the data on this point are doubt- 

 less within the boundaries of experimental error. It is difficult 

 to reconcile these findings with the theory of Russell and Hutch- 

 inson. 



The number of bacteria in partially sterilized and normal soils 

 at different temperatures 



One of the strongest points in the evidence produced by Rus- 

 sell and Hutchinson to prove that the soil contains a harmful 

 biological factor was the difference in the behavior of untreated 

 and partially sterilized soils when incubated at different tem- 

 peratures. Their results indicated that the maximum develop- 

 ment of bacteria in the untreated soil was at low temperatures 

 (5° to 12° C), while in treated soil the greatest number was 

 found at 20°C., and at 30°C. there was a marked increase over 

 that found at 12°C. — the maximum in the case of the untreated 

 soil. This phenomenon they claim shows that the bacteria 

 under normal conditions are limited by the detrimental factor 

 and that their maximum development takes place under 

 conditions unfavorable for the harmful factor. 



This point has been tested by the comparison of toluened 

 and normal soils at 10°, 22°, and 37°C. The treated soil used 

 had been treated with 2 per cent toluene three months previously. 

 These soils were incubated for one month at their respective 

 temperatures and then sampled and their bacterial counts de- 

 termined. The results are given in Table XXXV. 



