m 



Studies oil Soil. Froluzua 



This nietliod of inoculation, although it has jiiven quite good results, 

 is not entirely satisfactory. The difticulty lies in the uncertainty as 

 to whether the protozoa will develop after inoculation. This is probably 

 due to the fact that the inoculum is very small compared with the bulk 

 of the medium. The protozoa are thus forced to encyst until the 

 bacteria develop and during this process the bacteria very frequently 

 appear to take the upper hand. 



Another method of inoculation was tried. The medium (-4 % 

 bloodmeal, unfiltered, + -05 % K2HPO4 in 100 c.c. quantities in Erlen- 

 meyer flasks) was inoculated from a protozoa-free bloodmeal culture, 

 each flask receiving a loopful. After two days at 22° C. some of the 

 flasks received in addition a loopful of a bloodmeal culture containing 

 protozoa from soil, so that from the beginning they contained more 

 bacteria than the protozoa-free cultures. The development of the 

 protozoa was now much more regular. Bacterial counts were made 

 after 10 and 20 days and the numbers of active protozoa were deter- 

 mined roughly by the microscopic method. The results are shown 

 in Table 15. 



Table 15. 



After 10 days 



No. 

 of ' 

 Expt. j Bacteria 

 alone 



480 

 790 



830 

 870 



Bacteria 4- Protozoa 



After 20 day.? 



Bacteria •• Protozoa 



Bacteria Protozoa 



260 

 420 

 440 

 600 

 480 

 780 



Bacteria 

 alone 



Bacteria Protozoa 



30,000 F 

 5,000 F 

 5,000 F 

 10,000 F 

 25,000 F 

 20,000 A 



167 

 260 



.110 

 420 



156 

 358 

 2.'i5 

 320 

 90 

 ISO 



10,000 F 







.4,11 encysted 



All encysted 



60,000 F 

 All encysted 



Quite a marked reduction in the bacterial numbers is obtained as 

 a result of the presence of the protozoa in all si.\ experiments. The 

 reduction is, however, somewhat variable and even varies during the 

 course of the individual experiments. In 2, for e.xample. although the 

 protozoa have caused a great reduction in the numbers of bacteria 

 after 10 days, after 20 days the number of bacteria in the protozoa 

 culture is actually higher than in the protozoa-free culture. The 

 protozoa present in this case were large flagellates. But after 20 days 



