176 



JAMES M, SHERMAN 



The effect of carbon bisulphide on the number of bacteria in sterilized 

 soils reinoculated with normal soil and with protozoa-free soil 



Another experiment performed in order to detect the presence 

 of the "harmful factor" was to inoculate soils sterilized by 

 steam with normal soil and with the protozoa-free soil described 

 in an earher part of this paper. These soils were allowed to 

 stand three weeks and were then treated with 1 per cent of car- 

 bon bisulphide. Bacterial counts were made before the soils 

 were treated and then at fifteen and thirty days after treatment. 

 According to the phagocytic theory, it would be expected that 

 the number of bacteria in the soil inoculated with normal soil 

 would subsequently be greatly increased while the soils inoculated 

 with the protozoa-free soil should not be appreciably affected. 



As in the previous experiments, the results of this test give 

 no indication that there exists in soil a biological factor which 

 is harmful to the bacterial flora. It will be seen upon examina- 

 tion of Table XXXVIII that the soils free of protozoa and those 

 containing protozoa behaved in exactly the same way. 



TABLE XXXVIII 



Effect of CS2 upon sterilized soils inoculated with normal soil and with protozoa- 

 free soil 



The results of this test add further weight to the preceding 

 experiments all of which point to the non-existence of a detri- 

 mental biological factor in soil. The fact that volatile antiseptics 

 have no appreciable effect in soils which have been steriHzed 

 by steam and then reinoculated with normal soil would appear 

 to indicate that the beneficial effects derived by the use of these 



