Soil Organisms concerned in Nitrogen Cycle. 531 



and each was closed by a well-fitting cork, through which passed a glass 

 tube, reaching almost to the bottom of the flask, and bent at an angle of 

 about 60° just above the cork. The corks were all coated with melted 

 paraffin to render them air-tight. The process of denitrification is an 

 anaerobic one, and the inert gases collected at the top of the flasks, forcing 

 the liquid out through the bent tube and maintaining the anaerobic 

 conditions. 



When a crude culture had been obtained in this way, it was sub-cultured 

 four successive times into fresh media before being used for purposes of 

 experiment, and a comparatively pure culture of mixed denitrifying 

 organisms was thus obtained; 1 c.c. of this culture was then transferred 

 to each of the 20 flasks shown in the Table below, and after filling with 

 their respective solutions these flasks were all corked, great care being 

 taken that none of the medium should be spilt, and at the same time that 

 all air bubbles should be excluded. 



After 36 hours' incubation at 22° C, the corks were carefully removed, 

 and the volume of gas which had collected in each was measured approxi- 

 mately by filling each flask again with water from a burette. 



The results obtained were : — 



Table XV. 



Flask. 



Contents. 



Gas formed in 

 36 hours. 



1 Culture solution 



2 „ 



I :. : 



Culture solution + water extract ot" *5 gnu. bacterised peat 



9 Culture solution + alcoholic extract of 1 grm. bacterised peat. 



PP 99 St 99 39 99 ; , ?, 



» 99 IJ jj 99 



12 



13 Culture solution + phosphotungstic fraction of 1 gim. bacterised peat 



14 I » 

 15 

 16 



17 Culture solution + silver fraction of 1 grm. bacterised peat 

 18 

 19 

 20 



49" 



50 



• 5 "2 



• 3-0 



29 ~) 



30 J 



