Andricw Cunningham 



oo 



therefore, yields useful results which, after all, is the best justification 

 it can have. 



The results of the experiments on the effect of heat quoted above 

 probably rather exaggerate its injurious action. In this connection 

 three points must be kept in mind: 



(1) It must be remembered that in those cases in which the 

 cysts failed to excyst after heating to 58° C. pure cultures were dealt 

 with. In the results of experiments on the effect of heat on cysts, 

 described in the previous paper, the thermal death point of the most 

 resistant cysts found in soil is given as T2° C. This does not, however, 

 exclude the possibility of the presence of forms with less resistant 

 cysts. 



(2) In the experiments on the effect of drying, the desiccation 

 itself may have had an injurious action on the cysts and as a conse- 

 quence 'may have rendered them a more easy prey to the injurious 

 influence of the heat. 



(3) In the potash experiment, protozoa which had been culti- 

 vated on an artificial medium (soil extract) and thus probably rendered 

 less resistant, are dealt with. 



III. The Occurrence and Activity of Protozoa in Soils 



AS INDICATED BY THE DILUTION MeTHOD. 



The relative occurrence of the flagellates and amoebae in soil is 

 indicated in Table 5. 



Table 5. 



The flagellates are seen to occupy first place. The amoebae are 

 rather fewer in number but this may be due to the fact that they are 



