H. B. Hutchinson and A. C. Thaysen 59 



from tbe soil during digestion, for the control soil was digested with an 

 equal amount of water. The absence of any apparent restriction of 

 bacterial growth in the former soil, even within the first 24 hours after 

 treatment, makes it extremely improbable that toxins were at all operative 

 in this soil. As might be anticipated, the improvement in the soil con- 

 ditions is not confined to bacterial growth alone, but is also reflected 

 in a greatly increased crop dry matter production. In this respect the 

 following data obtained from pot experiments may be of interest. 



Hai'peniJen Common Soil: Crop, Barley 

 Untreated Soil Soil + CaCOa 



Dry matter in Crop 1-05 grams 17-05 grams 



The limitation of bacterial and plant growth appears therefore to 

 be determined more by chemical than bacterial conditions. 



In submitting this explanation of the observed facts we do not, 

 however, wish to imply that the toxicity of the extracts is solely due 

 to the acidity of the soil itself. It is in fact conceivable that in soil 

 possessing an acid reaction, the protein degradation changes may be 

 arrested and incomplete, just as the process of nitrification in these 

 soils is restricted, or the decomposition of carbonaceous residues only 

 partially takes place. 



The Behaviour of B. jirodigiosus toivards it.i otvn Products of Growth. 



In conjunction with the foregoing experiments, which are based on 

 the supposed susceptibility of B. prodigiosus to the by-products of the 

 mixed bacterial flora of the soil, we also determined the behaviour of 

 this organism towards its own by-products. 



As the conventional media, such as dextrose broth, are unduly 

 concentrated and are apt to yield complex results on account of acid 

 formation from the sugar, recourse was had to the use of an extract 

 of toluened Chelsea soil, wliich had been found to support vigorous 

 growth of the organisms. The extract was prepared by the usual method 

 and inoculated with a suspension of B. prodigiosus in saline solution. 

 Growth was allowed to take place at 28° C. for 10 days, by which 

 time no further increase could be found. The extract or culture 

 was then divided into two portions, one of which was filtered by passage 

 through a Berkfeld candle, while the other was pasteurised at 70° for 

 half an hour. The two portions were then inoculated with 4200 and 



