232 THE LIVING ORGANISMS OF THE SOIL [chap. 



generally attributed to the washing out of the autumn- 

 formed nitrates, but it is more probable that the shortage 

 of nitrogen is due to denitrification consequent upon 

 water-logging. Indeed denitrification and the evolution 

 of gaseous nitrogen, rather than leaching is probably 

 the main source of the loss of nitrogen to soils. 



The Protozoa of the Soil. 



A number of isolated experiments are on record, in 

 which it was found that ordinary soil, which had been 

 subjected to some form of treatment resulting in a 

 disturbance of the organisms living in the soil, became, 

 for a time at any rate, more fertile. For example, in 

 connection with the fumigation of the soil of vineyards 

 with carbon bisulphide in order to get rid of phythoxera, 

 an increased crop-producing power had been noticed to 

 follow in the soil itself. Again, attempts to sterilise 

 soil by heat gave similar results. 



The question remained vague and without explana- 

 tion, until the publication, in 1909, of a systematic 

 investigation by E. J. Russell and H. B. Hutchinson. 

 Russell established the prime facts that soil which had 

 been heated for an hour or so to the temperature of 

 boiling water, gave, in the next crop, something like 

 double the produce that a control of unheated soil did. 

 The effect persisted, though to a smaller degree and 

 with a steady decline, in the succeeding two or three 

 crops. Similar results, though the initial increase was 

 not so marked, were obtained when the soil was only 

 heated to temperatures between 55 and 70 C. In 

 other experiments the moderately dry soil might be 

 mixed with 0-5-1 per cent, of some volatile antiseptic 

 like toluene, carbon disulphide, or chloroform, left closed 

 up with the antiseptic for some thirty hours, and then 

 freely exposed to the air until the antiseptic had entirely 



