839 



CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL- 

 FERTILITY, 



xii. The Action of Toluene upon the Soil-Protozoa. 



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



Society. 



In their experiments upon the partial sterilisation of soils, 

 Russell and Hutchinson, as a rule, employed toluene in the pro- 

 portion of from 0-5 % to 1 % of the soil, leaving it to act for 

 about 30 hours, and then allowing it to evaporate completely."*^ 

 They found that 1 % of toluene entirely suppressed the detri- 

 mental factor, which limits the growth of bacteria, when the 

 disinfectant was allowed to act for two days.f In richer soils, 

 however, the toluene often failed to kill all the protozoa, just as 

 it failed to destroy nitrifying organisms, and to cure soil-sickness. 

 The failure was traced to the low solubility of toluene, and its 

 consequent inability to penetrate any but the smallest particles 

 of soil, in the presence of much moisture or organic matter. | 

 Regarding certain discrepancies between laboratory and pot- 

 experiments, Russell and Petherbridge said that their experi- 

 ments showed that toluene acted best in finely sifted, fairly dry 

 soils, and lost much of its effectiveness in rich soils, when too 

 much moisture was present or the soil-particles were too coarse.§ 

 Yet, in their conclusions upon their work with sickness in glass- 

 house-soils, which, I submit, must be classed as "rich" soils, 

 they said that the factor, detrimental to bacteria, resembles in 

 every way that present in ordinary arable soil. It was put out 

 of action by antiseptics, and, in all respects, its properties agreed 

 with those of the protozoa. || 



In considering these various findings, one is driven to the 

 conclusion that, as protozoa cannot be trusted to be absent in 



* Journ. Agric. Science, v., p. 157. 

 + Op. cit. , p. 171. t Op. cit. , p. 190. § Op. cit. , p. 107. II Op. cit. , p. 1 1 1 . 



