PRESIDENTIAL ADDRESS. 



57 



I clearly showed that the extracts could be toxic to a 

 bacterium such as Baa. procligiosus, and that so far as the 

 soil bacteria were concerned, the toxic extracts, while not 

 actually destroying them, yet decidedly hindered their 

 multiplication. 1 In the soil-extract there is, as it were, a 

 contest between the nutrients and the toxins, and the 

 ultimate victory will depend upon the preponderance of 

 the one or the other. 



The nutrients are probably fairly constant in amount, 

 while, on account of their instability, the toxins are vari- 

 able. It is therefore not to be expected that the extracts 

 will always be directly toxic. An indirect toxic action, 

 however, can, as a rule, be shown by heating the extract 

 and comparing it with an unheated portion. The heated 

 extract usually gives an enhanced growth of bacteria. I 

 showed that the toxins are rapidly decomposed by heat, by 

 storage in aqueous solution and by the action of sunlight. 2 

 They are soluble in water and are easily washed out of the 

 soil by rain, 3 and, on this account, direct evidence of toxicity 

 may be difficult to obtain in some soils, especially in those 

 of moist climates. 



The Agricere of the Soil. 

 It is not at all probable that any one reason will explain 

 the cause of the enhanced fertility of soils that have been 

 treated with volatile disinfectants. Russell and Hutchinson 

 showed that there was an instantaneous production of a 

 small quantity of ammonia upon the soil being toluened. I 

 have shown that the disinfectant, acting as a fat-solvent, 

 dissolved the soil- wax or fat (agricere), and instead of depo- 

 siting it again in the original position on the evaporation 

 of the solvent, it is carried with the liquid disinfectant and 

 deposited near the surface of the soil. 4 It is deposited on 



1 Proc. Linn. Soc. New 8outh Wales, 1910, 814. 2 Ibid., 1910, 822. 

 3 Ibid , 1911, 685. * Ibid., 1910, 817; 1911, 699. 



