H. B. HUTCIIINSON AND A. ('. TlIAYSEN 51 



each soil four separate determinations were carried out: counts were 

 made in the untreated soil extracts and also in another portion which 

 had been heated to 91° C. for one hour. These were compared with an 

 extract of soil which had been partially sterilised by means of toluene, 

 and lastly we included an extract of untreated soil which had been 

 boiled, and to which minute quantities of food nuiterial (peptone) had 

 been added. For the sake of conformity B. prodigiosus was used as a 

 test organism with each soil, but with the Broadbalk unmanured and 

 Woburn soils recourse was also had to the use of B. fluorescem luju-faciois; 

 this is one of the commonest soil forms, it is non-sporogenic, and owing 

 to the non-formation of zoogloea is suitable for quantitative work. 



The data obtained from these experiments are set out in Tables I-VI 

 below, from which it will be seen that the extracts of the various soils 

 differ very appreciably in their suitability for bacteria! growth. The 

 results are calculated on a bacterial content of 1000 cells per cubic centi- 

 metre at the beginning of each experiment. 



Table I. AUolmenl. Soil. 



Relativi^ Number of Cells in the Extracts after 



Table II. Chelsea soil. 



Relative Number of Cells in the Extracts after 



Untreated Extract 

 Heated Extract 

 Extract of Toluened Soil 

 Heated Extract + Peptone 



= 6 pts. N per miUion of 



Extract .... 1000 1610 2310 8770 283,000 452,000 



Table III. Roihamsted Soil (manured). 



Relative Number of Cells in the Extracts after 



Untreated Extract 

 Heated Extract . 

 Extract of Toluened Soil 

 Heated Extract + Peptone 



=6 pts. N per million of 



Extract .... 1000 32 16 16 1080 11,300 



