116 Partial SteriUsation of Soil 



ammonia in the treated soils, or (2) to the removal b}' the treatment of 

 some agent, other than the nitrifying organisms, which is always con- 

 suming ammonia in the untreated soil. The second supposition falls 

 to the ground, because when small quantities of ammonium salts are 

 added to untreated soils the whole of the added nitrogen is recovered 

 as ammonia and nitrate. (§ 21, Table 8.) 



Hence we conclude that the treatment has induced an increased 

 production of ammonia. 



II. The part played by bacteria. 



§ 4. We have confirmed Hiltner and Stormer's discovery that 

 bacteria multiply more rapidly and reach far higher numbers in the 

 partially sterilised than in the untreated soils. Our untreated soils 

 usually contained about 5 to 9 million organisms per gram, a number 

 which remained fairly constant. Treatment with toluene effected 

 a considerable reduction, but subsequently, when the toluene had gone 

 and moisture was added, a period of rapid multiplication set in, and 

 the numbers rose to 40 millions or more. The numbers of bacteria 

 increase pari passu with ammonia production, and we may therefore 

 associate the increased ammonia production with the increased numbers 

 of bacteria. (§ 22, Table 9.) 



§ .5. Examining this conclusion in some detail, there is no evidence 

 that the species surviving the treatment have received a stimulus 

 which makes them more active or that they are the more active sur- 

 vivors of a mixed race. The contrary is rather the case ; for instance, 

 B. mycoideSy and the brown and white streptothrix, were isolated from 

 the toluened soil, and all proved less active than the same organisms 

 obtained from the untreated soil. (§ 26.) On the other hand we 

 obtained considerable evidence that the whole surviving flora is more 

 active than the original one in effecting the decomposition of nitro- 

 genous organic substances such as peptone, etc., and in hydrolysing 

 urea. (§§ 24 and 27, Table 10.) 



Not only is the whole soil with its flora more active, but also the 

 flora carried in an aqueous extract of the soil. (§ 25.) The extract is 

 prepared at ordinary temperatures by shaking soil with water and 

 filtering through cotton-wool; it contains all organisms that are readily 

 detached from the soil and sufficiently small to pass through the filter. 

 Such an extract prepared from the partially sterilised soils proved 

 more active than extracts of untreated soil in decomposing peptone. 



