SOIL FERTILITY 125 



hypothesis which fits the known facts so closely as 

 to deserve at least a provisional acceptance. This 

 hypothesis may be described as an inversion of 

 MetchnikofFs doctrine of phagocytosis. Whereas 

 white blood cells phagocytes maintain the health 

 of the human body by destroying intruding patho- 

 genic microbes, the protozoa of the soil, according 

 to Russell's hypothesis, by a similar phagocytic 

 action depress the fertility of the soil. A certain 

 number of bacteria is good for a soil and if the 

 numbers fall off the soil becomes sick. As by 

 cauterisation a wound is cleansed, so by partial 

 sterilization the soil is restored to a fertile state. 

 In the former case the bacteria are the sufferers, 

 in the latter the protozoa. In soil and in body 

 alike the struggle is the same but the roles of the 

 protagonists are reversed. In order to verify the 

 hypothesis and to extend our knowledge of the 

 protozoa of the soil, applied science has most 

 properly applied to zoologists trained in the methods 

 of pure science. On their work must depend much 

 of the success which will attend this novel and 

 promising line of enquiry. Thus in both cases 

 the dramatic hypothesis of the zoologist Metch- 

 nikoff, which emerged from a study of the trans- 

 parent body of a sick water flea, and the elegant 

 hypothesis of Russell pure science was present 

 at inception and denouement. It allured to brighter 

 worlds and led the way. 



As a last example of the contribution of pure 



