STUDIES ON SOIL PROTOZOA 



175 



its effect upon the protozoa. Soil extract and hay extract cul- 

 tures made from untreated soil and incubated at 37°C. have 

 failed entirely to reveal the presence of any of the active types 

 of protozoa which have been mentioned as especially abundant 

 in soil. In such cultures only a very few types of protozoa 

 appear at all and these only slowly and in small numbers. 



The number of bacteria developing in sterilized soils reinoculated 

 with untreated and with partially sterilized soils 



The preceding experiments appear to demonstrate quite 

 conclusively that the beneficial effect of volatile antiseptics in 

 soil is not due to the destruction of a biological factor, unless 

 it be assumed that the treatment of soil so changes it that the 

 harmful organisms are no longer able to develop in it, even though 

 it is reinoculated with them. An experiment was planned in 

 order to see if this explanation is a true one. Two pots of sterile 

 soil were inoculated with 1 per cent of normal soil, while two 

 other pots were inoculated with 1 per cent of a soil which had 

 been treated with 2 per cent toluene. In case the antiseptic 

 really destroys a harmful factor that fact should be indicated 

 by a much greater number of bacteria in the soils inoculated 

 with the treated soil. This result, however, was not obtained ; 

 on the contrary, the counts made at thirty and forty-five days 

 after inoculation showed no practical difference between the 

 numbers of bacteria in the two soils, as is shown in Table XXXVI I. 



TABLE XXXVII 



The number of bacteria developing in sterilized soils inoculated with normal and 



with toluened soils 



