FERTILITY IN SOILS 



361 



surviving: the treatment have become more active — indeed the 

 contrary is rather the case, since organisms isolated from the 

 partially sterilised soils proved less active than others of 

 the same kind from the untreated soil. Nor can the difference 

 in the rate with which ammonia is produced be attributed to 

 a change in the type of bacterial flora. Examination of the 

 gelatine plates showed that the flora which becomes established 

 in the soil after heating is altogether different from that originally 

 present ; on the other hand, the flora of the soil treated with 

 toluene did not appear to have altered very much. The curves 



50 



H 



T3 



40 • 



B 30- 



V 



a 

 o 



.2 

 'c 



1 20 



bo 

 O 

 u 



■a 10+ 







, ' '' Toluene Eva*-** 



.-• • — v 



..■"■ • 



Toluene left in 



Untreated soil 



12 



16 



"20" 



24 



days 



Fig. 3. — Amount of ammonia in variously treated soils. 



showing the amount of ammonia produced in the soil treated 

 with toluene and in the heated soil (fig. 3) are very much 

 alike but the bacterial flora of the soils is very different ; the 

 curves for the untreated soil and the soil treated with toluene 

 are fundamentally different, whilst the bacterial flora is not. 

 Our experiments indicate that the increased production of 

 ammonia in the partially sterilised soil is due to the increased 

 numbers of the bacteria rather than to any other cause ; the 

 problem reduces itself to finding out why the bacteria can 

 increase so much more rapidly in the partially sterilised than in 

 the untreated soils. 



