66 R. GREIG-SMITH. 



bacteriotoxins, while that of the disinfectant is to liberate 

 nutrients. Goodey furthermore found that the addition of 

 a Vorticella sp. showed a bacterial curve akin to that of 

 the untreated soil, and that the addition of Colpoda sp., of 

 amoebae and of flagellates, gave numbers always higher 

 than the untreated soil, from which he naturally concluded 

 that the addition of protozoa, with the inevitable bacterial 

 impurity, did not bring about a diminution of the soil 

 bacteria. 



Russell and his colleagues believe that 1% of toluene 

 destroys all protozoa, and, although this is the case gener- 

 ally, many of their experiments show that the treatment 

 had not eliminated the protozoa. Gainey found that toluene 

 depressed the soil bacteria more than the protozoa, and 

 from his experiments he could not account for Russell and 

 Hutchinson's results. Very early in my experiments, I 

 found that even 20% of disinfectant did not destroy the 

 microfauna, and, in work undertaken to discover the reason, 

 I found that much depended upon the moisture content of 

 the soil. When soils are prepared for experimental work 

 it is usual to partly dry them to enable them to be 

 thoroughly mixed, and to furnish a representative sample. 

 If the drying is allowed to proceed so far as to bring the 

 moisture below one-twentieth of the water-holding capacity 

 of the soil, the protozoa are not destroyed by the volatile 

 disinfectants. 1 Yet in such soils the protozoa do not appear 

 to have any influence in reducing the bacteria. In the 

 research, I showed that the toluening of moist soils not 

 only destroyed the protozoa, but also destroyed the sulphur- 

 oxidising bacteria, with the result that in certain culture 

 media, traces of sulphuretted hydrogen are produced which 

 prevent the growth of protozoa. This is a point that should 

 not be lost sight of when proving the absence or presence 

 of protozoa in treated soils. 



1 Proc. Linn. Soc. New South Wales, 1914, 839. 



