Protozoa in Relation to Soil Bacteria. 309 



The drop in bacterial numbers in all three inoculated soils (T + C), 

 (T + M), and(T + F) is not, I think, to be attributed to protozoal activity. 

 The only curve which reaches well below the level of the (T + W) curve is 

 that for (T + F). Now in this sample there were, as the Table shows, about 

 1000 Amoiba Umax and 1000 flagellates per gramme, at the beginning of the 

 experiment, whilst in the other two soils there were much greater numbers 

 of protozoa. Moreover, towards the end of the experiment protozoal counts 

 showed that there had been no increase in numbers of protozoa in the 

 (T + F) soil, and from this it seems reasonable to infer that there had been 

 no activity of the amoebae and flagellates. Consequently the drop in the 

 numbers of bacteria must be attributed to some other influence than 

 protozoal action. This statement may appear to invalidate the previous 

 results, but reference should be made to p. 311 under "Discussion," where 

 an explanation is advanced which covers this and the similar cases from 

 the (T + C) and (T + M) soils. In the same way later protozoal counts for 

 (T + C) and (T + M) soils showed signs of increase in the numbers of protozoa 

 in only one case, and that is for Amceba Umax in (T + C), where the figure 

 for this organism has risen from 3000 to 20,000 per gramme. 



The ciliate cucullus in (T + C) has actually decreased from 1000 to 500 

 per gramme, and in like manner the other ciliates are not so numerous as 

 at the beginning of the experiment. 



4. Mass Inoculations of Bacteria-free Amceba Cysts. 



The last curves to be considered are those of the Toluened and twice- 

 heated soil plus amoebae free from bacteria (T + A), and the Toluened and 

 twice-heated soil (TH 2 ), which are shown in fig. 5. 



E 160 - 



33 Days. 



Fig. 5. 



The method by which the amceba cysts used in this experiment were 

 prepared has been described above (p. 300). The protozoal counts made 



2 c 2 



