840 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, xii., 



rich soils, which have been treated with toluene, all work done 

 upon such soils cannot be taken as indicating the inactivity or 

 otherwise of the protozoa. The bulk of the %vork was done, as 

 they say, with 1 % of toluene, and it was taken, generally, that 

 the protozoa had been eliminated, yet their latest work contains 

 many footnotes to the effect that the protozoa had not been 

 destroyed. 



There is so much claimed for the protozoa by Russell and his 

 co-workers, and, at the same time, there are so many points 

 wherein they safeguard themselves, while pushing forward the 

 protozoal hypothesis, that it appeared to be opportune to examine 

 the limits of the action of the volatile disinfectant, toluene. 

 This was all the more desirable, as I had already found that even 

 10 % of toluene did not kill off all the ciliates in soil. 



In the experimental work embodied in this paper, the general 

 procedure consisted in sifting the soil through sieves varying 

 from 12, for damp soils, to 30 meshes to the inch, for dry soils. 

 Weighed portions were put into bottles, treated with varying 

 amounts of toluene (Kahlbaum), and thoroughly stirred with a 

 sterile wire. Disinfection was allowed to act for two days. The 

 soils were then spread on paper, and returned to their bottles 

 when the toluene had evaporated. About five grams of each 

 portion of the soil were put into inch test-tubes, containing 10 

 c.c. of culture-fluid, and these were incubated at 22°. At con- 

 venient intervals, generally 3, 5, 7, and 10 days, a small quantity 

 of the fluid was carefully pipetted from the surface-edge of the 

 liquid, while the point of the capillary pipette was rubbed against 

 the o-lass wall of the tube. This was done with the intention of 

 dislodging the amoebae, and allowing them to be sucked up in the 

 pipette. The teat was then pressed, and the drop blown upon a 

 glass-slide, which was dusted with fine sand, and a cover glass 

 was placed over the drop. When the amo^b^ had been given 

 time to settle and attach themselves to the surface of the slide, 

 the film was examined. 



Many culture-fluids were tried. At first, an infusion of French 

 beans was used, but an improvement was found in dilute nitrate 

 bouillon, containing one part of ordinary nitrate bouillon to seven 



