4'-t The Non-jjerMstence of Barferio-toxm.s in f/ic SoiJ 



Only in the case of iiii acid soil — from a barren heath — was any 

 improvement effected, and this we think can be explained more simply 

 on purely chemical grounds. Whereas the untreated extract from this 

 soil after filtration was clear and only slightly straw coloured, it became 

 distinctly turbid and of a reddish brown colour on being subjected to a 

 temperature of 94° for one hour. It thus became apparent that we had 



■ Heated E.xtract 



with Peptone 



24 48 



Time iu houis 



Cdrve III. Growth of Bac. prodiiiiosus iu beateil extract, and heated 

 extract with peptone. 



to deal with a soil of the " adsorptively unsaturated" type which has been 

 studied in detail by Daikuhara(o). Such soils on treatment with a neutral 

 salt solution yield an extract containing considerable quantities of iron 

 and alumina, and distinctly acid in reaction. In the case of the heath soil 

 used in our experiments it was possible to demonstrate the presence of 

 such compounds in the extracts. It is difficult, therefore, to avoid the 



