692 CONTRIBUTIONS TO OUR KNOWLEDGK OP SOIL-FERTILITY, iv. 



Experiment xv. 



In the experiments wliich have been recorded, the develop- 

 ment of the heat-toxins and their solubility in water pre- 

 vented the action of the agricere being clearly shown. Ac- 

 cordingly, another method of endeavouring to demonstrate 

 the solvent action of the disinfectants upon the agricere was 

 adopted. This had for its principle the pasteurisation of the 

 soil. It is exceedingly unlikely* that the protozoa can sur- 

 vive exposure to a moist heat at 75° C, for 10 minutes, and, 

 in view of the previous experiments, that any appreciable 

 amount of heat-toxin will be develojjed. 



A garden-soil was moistened with water, and heated in the 

 water-oven. In two hours, the temperature of the soil, as 

 recorded by a thermometer with its bulb in the middle of the 

 soil, reached 75", and 10 minutes later it had risen to 78°. 

 The dried layer of soil on the top was rejected, and the lower 

 moist soil was spread out upon a sheet of glass, and allowed to 

 cool and dry in the air. Portions weighing 20 gr. were taken, 

 and tested with and without previous treatment with ether 

 (Merck). 



•Russell and Golding, Journ. Soc. Chem. Ind. xxx. 1911, p.741, say 

 that the protozoa are completely destroyed at 60°. 



