638 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, xiii. 



but if it is feebly toxic, as on September 9tli, or virtually non- 

 toxic, as on September 5tb, drying brings about a greater solu- 

 bility of the nutrients if it does not destroy the bacteriotoxins.* 

 The number of soil-bacteria in the soil was tested on Septem- 

 ber 5th, and found to be as follows : — 



Raw soil ... 14 inillions per gram of dry soil. 



Air-dried soil... 3'6 millions per gram of dry soil. 



The Development of Soil-Toxins. — Although the development 

 of soil bacteriotoxins has been previously described in these Pro- 

 ceedings, some further work was done during the later months 

 of 1914 by way of confirmation. The garden-soil under grass 

 was passed through a coarse sieve (No. 13), and moistened with a 

 small quantity of water to bring the content up to 6%. It was 

 then heated in the oven until a thermometer, with its bulb in 

 the centre of the soil, registered 80° for 10 minutes. After 

 cooling down, the moisture was made up to 10%, and the soil was 

 incubated at 28°. As the soil was contained in an enamelled 

 bucket with a lid, the moisture did not fall rapidly, and any loss 

 was made good from time to time. Extracts were made in the 

 ordinary manner, and these were seeded with Bac. prodigiosus 

 and with a suspension of bacteria from the same bucket of soil. 



* Buddin (Journ. Agric. Sci., vi., 452) shows thai the air-drying of soil 

 causes an increase in the amount of nitrate formed during a period of three 

 months under laboratory conditions; and that a drying to 98 % of dry 

 matter gives a greater nitrate-increase than a drying to 96 %. In another 

 experiment, in which the drying diminished the bacteria from 10 to 4 or 5 

 millions, no difference was detected in the amount of ammonia and nitrate 

 immediately after treatment, but after an incubation of 4 months, the 

 soils which had not been air-dried contained 28 to 33 part^ of nitrate per 

 million, and those which were air-dried contained 41 parts. 



