52 The Noii-perxiMence of Bacteria -toxins in. the Soil 



Table IV. Woburn Soil (uninanured). 



Relative Number of Cells in the Extracts after 



Untreated Extract 

 Heated Extract . 

 Heated Extract + Peptone 



= 6 pts. N per million of 



Extract .... 1000 — I'tBO 212.000 .373,000 373.000 



Table V. Millhrook Soil. 



Relative Number of Cells in the Extracts after 



Table VI. Rothamsled Soil {unmanured). 



Relative Number of Cells in the Extracts after 



Marked diflieiences appear to exist between the values of the un- 

 treated extracts of the various soils and these allow of a useful comparison 

 with the suitability of the original soils for plant growth. From other 

 experiments where some of the soils were used for pot culture the 

 following results were obtained : 



There is thus some relation between the crop producing power of a 

 soil and the capacity of its extract to support bacterial growth: the 

 more fertile the soil, the more abundant the growth of organisms in the 

 soil extract. Although all the soil extracts showed some reduction in 

 bacterial numbers in^mediately after inoculation, the organisms appear 

 to have adjusted themselves after 48 hours in the case of the allotment 

 soil and 72 hours in that of the Chelsea and Broadbalk manured soils; 

 their numbers showed, therefore, an upward tendency. With the extracts 



