655 '**^^ 



CONTRIBUTIONS TO OUR KNOWLEDGE OF SOII^ 



FERTILITY. 



vi.The Inactivity of the Soil-Protozoa. 



By R. Greig-Smith, D.Sc, Macleay Bacteriologist to the 



Society. 



In jDapers i., iv., and v. of this series, I have shown that soils 

 contain bacteriotoxins, and fatty substances collectively named 

 agrieere. These are affected differently by heat and by the vola- 

 tile antiseptics. Heat destroys the baeteriotoxins more or less, 

 theextentof the destruction depending naturallyupon the tempei'a- 

 ture and the exposure, but there is an interference through the pro- 

 duction of certain toxins developed in some unknown manner 

 during the heating. While, therefore, a moderate heat destroys 

 the natural baeteriotoxins that are in the soil, a higher tempera- 

 ture, or possibly a longer exposure, produces toxins that were not 

 originally present. The volatile disinfectants, on the other hand, 

 have no direct action upon the baeteriotoxins. They act upon the 

 agrieere, carrying it to the surface, where it is irregularly de- 

 posited upon the angular fragments of soil. Indirectly, the 

 nutrients are rendered more accessible to the solvent action of 

 soil-water, and especially to the attacks of the bacteria, while the 

 baeteriotoxins are more easily dissolved, and, therefore, more easily 

 decay. 



By their protozoal hypothesis, Russell and others claim that the 

 soil-bacteria are prevented from multiplying freely by such soil- 

 protozoa as the ciliates (among which Colpoda cucullus is very 

 active), and as the soil-amoebas. The action of heat and of the 

 volatile disinfectants, according to these authors, is chiefly to 

 destroy the protozoal phagocytes, other agencies having only a 

 slight effect. 



In the present paper, I have endeavoured to test the action of 

 the soil-phagocytes by adding them purposely to soil, and by using 

 the extracts of raw soil, as was done by Russell and Hutchinson. 



62 



