130 



Partial Sterilisation of Soil 



moistened an enormous increase takes place. This fact was first observed 

 by Hiltner and Stormer and has been repeatedly confirmed during the 

 course of our investigations; as an instance the following figures may 

 be quoted : 



Table 9. 



* After 4 days, 9 days' counts lost by plates liquefying. 

 Soil 2. Rich garden soil containing '592 per cent, of nitrogen. 



Untreated soil 



Toluene evaporated. 

 Heated soil 



At beginning After 10 days 



4,200,000 



1,306,000 



40 



10,600,000 



31,680,000 



7,360,000 



After 38 days 



13,850,000 



38,200,000 

 17,600,000 



Plate IX, Figs. 4 and 5 show the photographs of the plates. 



The rapid rate of increase in the partially sterilised soils is not 

 maintained indefinitely, but even after some months the toluened soil 

 contains more organisms than the untreated soil, the actual excess 

 depending on the conditions that have obtained in the meantime. 



A very important relationship is brought out by the above figures. 

 It will be noticed that the increase in the number of organisms runs 

 parallel with the increase in the amount of ammonia : v/e may therefore 

 infer that the increased ammonia production is associated with the 

 increase in the number of bacteria. 



§ 23. The production of ammonia by soil bacteria from nitrogenous 

 compounds. For the elucidation of this problem we had recourse in 

 the first instance to a method devised by Remy which, after suitable 

 modifications, gave very useful results. 



§ 24. The production of ammonia from peptone. In Remy 's method 

 10 grains of soil are inoculated into 100 c.c. of a culture solution 

 containing 1 per cent, of peptone besides nutrient salts, but no ammonia, 



