BY R. GRKIG-SMITEI. 



81J 



In the experiments with soils, 20 gms. were moistened with 

 2 or 5 c.c. of suspension which was thoroughly incorporated. The 

 infected soil, or, in some cases, sand, was incubated overnight at 

 30°, as in the case of the infected extracts, and, in the morning, ib 

 was shaken up with 500 c.c. of sterile water for 30 minutes; 

 dilutions were then made. As a rule, those plates containing 

 from 40 to 400 colonies were reserved for counting. 



The Effect of Heat upon Air-drlkd Soils. 

 Experiment i. 



These tests show (Expt. i.) that the increase of the bacterial 

 activity is proportional to the temperature to which the soil lias 

 been heated, and (Expt. ii. 6) that soil, as compared with sand, 

 contains some substance which prevents the rapid growth of 

 bacteria. It is also shown that prolonged incubation may reduce 

 the number of bacteria, presumably by the development of auto- 

 toxins. 



