Andrk\v Cunningham 73 



days in the 38° C. incubator to hasten evaporation, the flasks received 

 the inoculations shown in Table 20 and the water content of the soil 

 was brought up to 70%w.h.c. The water content was readjusted 

 once a week to this level and after 25 days bacterial counts were made 

 for the various soil samples. 



Table 20. 



Soil extract cultures were prepared from the soil samples as in 

 the last experiment. Those from Nos. 1-4 showed numerous active 

 flagellates after seven days at 22° C. In the remainder of the cultures 

 no protozoa were found. The controls 9 and 10 remained practically 

 sterile. They contained fewer than 10 bacteria per gram. The plates 

 poured for No. 5 remained sterile. The lowest dilution used was one 

 million. It is practically certain, however, that this must have been 

 due to a slip in the manipulation, and as the samples had been used for 

 soil extract cultures before it was discovered, the mistake could not be 

 rectified. At all events the soil extract culture showed quite as good 

 a development of bacteria as was got from samples 6, 7 and 8. 



The protozoa-free culture contained 184 milhons, the protozoa 

 culture 24 millions bacteria per c.c. and as the soils inoculated with 

 protozoa received in addition 1 c.c. of the protozoa-free culture they 

 contained at the beginning of the experiment about 24 millions more 

 bacteria than the soils inoculated with j)rotozoa-free culture alone. 

 But during the course of the experiment the conditions have become 

 reversed and the soils containing protozoa now show a bacterial content 

 of, on the average, about | that of the soils inoculated with protozoa- 

 free culture. The reduction in bacterial numbers in the soils inoculated 



