138 Partial Sterilisation of Soil 



After nine days the proportions have somewhat changed:- 



* After 4 days ; 9 days' count lost by plates liquefying. 



§ 35. The differences shown by the flora of the tokiened and heated 

 soils are much more marked than between the toluened and untreated 

 soils and cannot in any case be correlated with the ammonia production 

 curves. Attention has also been directed to the apparent loss of activity 

 after toluening of the separate species examined (§ 26). We must 

 therefore conclude that the change in type is less significant than the 

 enormous increase in numbers of the decomposing organisms. 



§ 36. It does not appear that any bacterial factor causes the 

 comparative infertility of the untreated soil. Addition of the untreated 

 soil extract to toluened soil caused no depression in the production of 

 ammonia, or the number of organisms, but on the contrary a considerable 

 increase ; the organisms contained in the extract have no inhibiting 

 effect, but multiply side by side with those present in the toluened soil. 

 The extract was prepared by shaking 20 grams of soil with 100 c.c. of 

 water and filtering through cotton-wool: nor did inoculation with 

 B. jiuorescens, the most striking organism suppressed by toluene, have 

 any inhibiting effect. On the other hand addition of 5 per cent, of 

 untreated soil, although at first without apparent action, after a time 

 stopped the further increase in bacterial numbers and in ammonia. 

 The results are set out in Table 13 and Curve 3 (p. 140). 



