H. B. Hutchinson and A. C. Tiiaysen 



49 



conclusion that the improvement of the extract on being subjected to 

 heat was more directly connected with the precipitation of these com- 

 pounds than with the destruction of toxins. Even if one disregards the 

 complications introduced by the peculiar behaviour of this soil on treat- 

 ment with salt solutions and assumes toxins to have been present in 

 the extracts, it is impossible to contend that this heath soil represents 



■5 1.000 



500 



Extract, of Untreatud Soil 



-— Extract of Toliiencti Soil 



4 8 



48 



72 



24 



Time in hours 

 Cdbve IV. Growth of Bac. prodiii'iostis in extracts of untreated and toluened soils. 



the normal type. Treatment of the soil with calcium carbonate entirely 

 removes its toxic power. 



III. We conclude from our observations that the unsuitability of 

 the heated extracts of normal soils is simply due to the lack of bacterial 

 nutrients. The addition of a minute quantity of food material (equal to 

 six parts of peptone nitrogen per million of the extract) leads to an 

 immediate and complete recovery of its suitability for growth. These 

 results are given in Curve III. 



Journ. of Agrio. Sci. ix 4 



