74 Sttullex on Soil Protozoa 



with protozoa is veri/ marked and lies well outside the limits of experimental 

 error. The conclusion may safely be drawn, therefore, that the limiting 

 factor or at least one limiting factor (of Russell and Hutchinson) has 

 been inoculated into the sterilised soils and has produced its effects on 

 the numbers of bacteria. This limiting factor can thus be cultivated 

 on soil extract medium. That it has not simply been intic)duced into 

 the sterilised soils with the soil used for inoculation of the soil extract 

 ((.e. without having grown on the latter) is proved by the fact that for 

 the second experiment sub-cultures (made by inoculatioti of one loopful 

 of the original cultures on to fresh sterile medium) were used. Large 

 numbers of protozoa were observed in the solutions used for inoculation 

 and these organisms were cultivated once more on soil extract from 

 the soils which showed low bacterial counts. And, as it has been shown 

 that the protozoa are capable of reducing the numbers of bacteria in 

 solutions, it appears justifiable to con.sider them as the limiting factor 

 in soils. 



In conclusion I wish to thank Prof. Lohnis for having suggested 

 this work on the soil protozoa and for advice, ever at my disposal, 

 during the carrying out of it. 



[This paper was ■publisiicil in the Centralbl. f. Bakt. Abt. ii. of 

 August last, but owing to the war no copies of it have yet reached this 



country.] 



{Received December 2\st. 1011. 



