E. J. Russell and H. B. Hutchinson 115 



3. If the toluene is loft in the soil there is only a slow production 

 of ammonia and never a rapid rate ; the curve is more nearly linear. 

 The action of micro-organisms is here excluded, but enzymes may still 

 act. 



4, The rapid period sets in only when the soil is sufficiently moist. 

 (Table 2.) 



(b) The production of unstable nitrogen compounds, which may 

 be regarded as intermediate products in the general decomposition, 

 is also accelerated by partial sterilisation. (§ 17, Table 8.) 



(c) The humus, on the other hand, appears to be but little affected ; 

 if anything there is a small increase, rather than a decrease, in the 

 amount of humic nitrogen. It does not appear that the ammonia has 

 been produced in the partially sterilised soils at the expense of humic 

 nitrogen. (§ 19, Table 5.) 



(d) Nitrification. The nitrifying organisms are destroyed by either 

 method of partial sterilisation, but there is a very important difference 

 between the two cases to which subsequent reference will be made. 

 Toluene simply destroys the organisms : if they are again introduced 

 after the toluene has been removed they at once begin to act. Heat 

 not only destroys the organisms but brings about some change whereby 

 the soil is rendered unsuitable for their development ; they now no 

 longer act even when re-introduced into the soil. (§ 31.) It appears 

 that an inhibitory substance is formed by heat. References to Table 2 

 show that the untreated soil gains in nitrate whilst the toluened and 

 heated soil do not. 



(e) The change in the total amount of nitrogen is not great, even 

 over a long period. There appears to be a small net loss from the 

 partially sterilised soils as compared with the untreated soil : whether 

 this result is due to diminished nitrogen fixation or to increased loss of 

 nitrogen cannot be determined, but at any rate it disposes of the 

 hypothesis that partial sterilisation is followed by an increase in the 

 total nitrogenous matter in the soil. (§ 18, Table 4.) 



§ 3. The two significant changes induced by partial sterilisation 

 are thus seen to be (1) an increase in the amount of ammonia, (2) cessa- 

 tion of the nitrifying process. 



The accumulation of ammonia which we have shown to take place 

 in the treated soils is not simply due to the cessation of nitrification, 

 for the amount of ammonia produced is greater than the sum of the 

 ammonia and nitrate in the untreated soils after the same period. This 

 accumulation may be due either (1) to an increased production of 



