PRESIDENTIAL ADDRESS. 69 



Air-drying and liming coagulate the slime of the sewage- 

 sick soil, and possible also destroy the causative bacteria. 

 The surviving bacteria doubtless attack the coagulated 

 slime, and the sickness disappears. On this account, volatile 

 disinfectants by disturbing the original flora may eliminate 

 the sickness. 



The effect of Air-drying the Soil. 

 With regard to the simple air-drying of soils, there 

 appears to be no doubt that the chemical and bacterio- 

 logical activities are considerably increased. Heinze 1 

 found that air-dried soil was about 20% more active than 

 moist. It formed 20% more acid from glucose, 20% more 

 gas was evolved in the presence of carbonate of lime, and 

 in solutions of peptone and urea, 20% more ammonia was 

 formed. The fermentation, as shown by Ritter, x was quicker 

 and more intensive, but the difference became obliterated 

 later on. Rahn 2 showed that the acid production was 

 greatest during the first twelve days, but was quite evident 

 on the sixtieth day. Buhlert and Pickenday 1 found that 

 even a slight drying increased the nitrate reaction. It has 

 been found that a slowly dried soil is more active than one 

 which has been rapidly dried. The activity appears to 

 rapidly disappear upon again moistening the soil, for in 

 twenty-four hours the greater part has gone. The bacteria 

 are greatly decreased in numbers; I found that air-drying 

 reduced the bacteria from 14 millions to 3*6 millions. 3 



The reason for the increased activity is difficult to 

 explain. It cannot be due to a physical difference in the 

 structure, for a dry soil is more difficult to wet than a 

 moist one, and even if so, the small quantity of soil added 

 to a comparatively large quantity of culture fluid would 

 annul any physical difference. It may be that the mineral 



1 Cent. Bakt. 2 te, 33, 116. a Ibid., 20, 38. 

 3 Proc. LinD. Soc. New South Wales, 1915, 63S. 



