E. J. Russell and H. K Hutchinson 



183 



the amount of decomposition they bring about when inoculated into 

 peptone solution. The bacteria present in the extract of the toluened 

 soil are more effective than those in the extract of the untreated soil ; 

 the results are : 



Similar results are obtained when other nitrogenous compounds are 

 substituted for peptone. Casein, gelatine and lucerne hay infusion were 

 all decomposed more readily by the toluened than by the untreated 

 soil. 



It is thus clear that the flora which survives the process of partial 

 sterilisation and developes when the conditions again become favourable 

 is more effective in producing ammonia from complex nitrogen compounds 

 than the original flora of the soil. 



§ 26. This conclusion however only applies to the community of 

 organisms considered as a whole. If we isolate any individual species 

 of organism we find that the cultures made from the toluened soils are 

 actually less potent than cultures of the same organism from untreated 

 soils. The amounts (in mgms.) of ammonia produced from peptone 

 solution in 7G hours were found to be : 



It is clear that we must not explain the efifects of partial sterilisation 

 by assuming that the separate organisms or group of organisms are 

 rendered more virulent, or more effective by loss of weaker members, 

 or that they are stimulated for any long period by the temporary action 

 of the toluene. The contrary indeed happens, and the individual species 

 rather suffer by the treatment. An interesting point brought out is 

 that the brown and white streptothrix possess very similar decom- 

 posing powers. 



