848 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, Xll. 



Lethal Tkmperatdres of Soil-protozoa. 



Moist soil, No.2 ... 

 Moist soil. No. 1 

 Air-dried soil, No.4 

 Air-dried soil, No.4 



Culture-fluid. 



Giltay 

 Giltay 

 Giltay 

 l%ha3'-infusion 



Ciliates. 



Amoel)fB. 



under 54° 

 56° 

 54° 

 50° 



63° 



over 62° 



70° 



64° 



Flagellates. 



under 54° 

 over 62° 



58° 

 58° 



The low lethal temperature in hay-infusion, as compared with 

 Giltay's solution, was traced to the presence of sulphuretted 

 hydrogen. On the twelfth day of cultivation, a slight deposit of 

 ferrous sulphide was noted lying on the surface of the soil, in the 

 tube which had been heated at 50°, while, at 52° and all higher 

 temperatures, the deposit of the black sulphide was pronounced. 

 The sulphide films were not seen in Giltay's solution. 



The development of sulphuretted hydrogen in the hay-infusion 

 indicates that this medium is not suitable for demonstrating the 

 effect of heat upon the protozoa. It is the medium which has 

 been used by many investigators for work connected with the 

 action of heat and volatile disinfectants upon the protozoa. As 

 it is unsuited for showing the action of heat, it is possible that 

 it may also be unsuitable for growing the fauna, that survive in 

 soils, treated with volatile antiseptics. A test was made, there- 

 fore, with two light-coloured soils. But for the use of such pale- 

 coloured soils, the films of ferrous sulphide would probably never 

 have been detected. 



A light-coloured soil, with a W.H.C. of 25, contained 7*5 % of 

 moisture when toluened. After treatment, it was sown in tubes 

 of hay-infusion and of Giltay's solution, and the suspensions were 

 examined on the 2nd, 7th, and 11th days. 



