BY R. GREIG-SMITH. 



849 



Another soil with 0*5 % of moisture was treated at the same 

 time, and sown in hay-infusion. Ciliates, amoebae, and monads 

 were found in all the tests, from none up to 20 %. There was 

 only a suspicion of sulphide in all the tubes, with the exception 

 of the control, 3 %, and 4 %, which were free from any trace. 



The same light-coloured soil, with 11 '6 % of moisture, was 

 toluened, and subsequently sown in 1 % ha\^-infusion, with and 

 without the addition of O'l % potassium nitrate. 



In these experiments, we see that, after toluening a damp soil 

 and adding it to 1 % hay-infusion, there is a formation of sul- 

 phuretted hydrogen similar to what was obtained in dilute 

 dextrose nitrate bouillon. 



The presence of potassium nitrate in Giltay's solution and in 

 the nitrate hay-infusion prevented the formation of ferrous 

 sulphide, but it did not accelerate the development of the ciliates. 

 The ciliates were destroyed by the toluene, and it was immaterial 

 whether sulphuretted hydrogen was formed in the culture-medium 

 or not. 



Sulphides \Vere found in media containing easily reducible 

 organic matter, such as 1 % hay-infusion and dilute dextrose 

 nitrate bouillon, but not in Giltay's solution or in hay-infusion 

 with nitrate, even although the latter never became acid to 

 litmus-paper. 



Regarding the action of toluene upon the bacteria, there is 

 indicated, in the formation of the sulphide, the probability that 

 certain oxidising organisms in the wet soils are, by the treat- 

 ment, either destroyed or overwhelmed in numbers by the 

 surviving reducing bacteria. In dry soil, this does not occur. 



