H. B. Hutchinson and A. C. Thaysen 57 



(c) Tulueiied soils yield extracts containing increased amonnts of 

 soluble organic nitrogen and are consequently of greater value for 

 growth than the untreated soil extracts. 



(d) The low value of heated extracts may be full}' restored by the 

 addition of suitable quantities of peptone. 



(e) The type of result obtained varies largely with the character of 

 the soil itself and according to the te.st organism, but in no instance has 

 it been possible to obtain definite indications of the presence of toxins 

 either with fresh samples of soil from the field or in those stored in the 

 laboratory in a moist condition. 



The Extracts of " Abnormal " Soils. 



In addition to the six soils mentioned in the foregoing pages, a 

 seventh sample was examined in the prescribed manner and as the 

 results are of such a manifestly different order it appeared desirable to 

 give them separate consideration. 



Whilst the majority of the soils studied are normally under cultiva- 

 tion, the remaining soil was derived from heath land and is generally 

 under a cover of either gorse (Ulex eiiropaeus) or of sorrel (Rumex 

 acelosella). As might be presumed from the occurrence of this type of 

 vegetation, the soil is markedly acid in character and is unsuited for 

 the growth of cereals, e.g. barley. In spite of this, the extract of the 

 untreated soil was found to be more suitable for the growth of B. pro- 

 digiosus than those of the relatively more productive Millbrook and 

 Rothamsted (unmanured) soils. Considerable growth occurred in the 

 heated extract (the relative numbers were 450,000 after 72 hours) and 

 thus approached more closely to the behaviour observed by Greig 

 Smith. 



Table X. 



Relative Number of Cells of B. prodigiosus 

 in the Extracts after 



The addition of peptone to the heated extract is followed by the 

 usual response, but the lack of growth in the extract of toluened soil is 

 peculiar and at present inexplicable. In contradistinction to the extracts 

 of the other soils examined, the extract of this soil became, on being 



