532 Miss F. A. Mockeridge. Effects of Auximones on 



This experiment was repeated several times, always with similar results. 

 At the conclusion of one of these repetitions 1 c.c. of the culture was 

 extracted from each of the flasks and diluted to 100 c.c, and 1 c.c. of each 

 of these was again taken and diluted to 100 c.c. A further similar dilution 

 was made, and then 1 c.c. of each of the 20 equally diluted cultures was 

 inoculated into a sterilised tube of the denitrifying medium, containing 

 1 per cent, of agar-agar. The inoculation was performed just before the 

 media solidified, the tubes being well shaken to ensure distribution of the 

 organisms. When this was accomplished, they were plugged with cotton 

 wool and incubated at 22° C. The number of bubbles of gas formed in the 

 solid media after a given time indicated the number of colonies in the 

 tubes, and these numbers were practically equal in the tubes inoculated 

 from the pure culture medium and in those from the water extract, very 

 much fewer in number in those from the alcoholic and phosphotungstic 

 fractions, these being again practically equal between themselves, while 

 those from the silver fraction were intermediate in number between these 

 two sets. These numbers bear out the figures obtained above, for it is to be 

 expected that the number of bacteria should be proportional to the activity 

 of the culture. 



Similar results having been uniformly obtained in all experiments with a 

 comparatively pure culture, the effect of the addition of the auximones upon 

 the denitrifying power of the soils themselves was examined. The soils from 

 Kew and Chelsea used in the above experiments were investigated, and the 

 culture flasks were prepared precisely as before. Instead of being inoculated 

 with a definite quantity of a pure culture, however, each was inoculated with 

 5 grm. of a finely sifted uniform sample of the soil to be tested, and was then 

 incubated in the usual manner. The results obtained were concordant 

 throughout with the figures given for the pure culture, a typical set of mean 

 results, obtained with a Chelsea soil, being as follows : — 



Gas formed in 

 48 hours. 



c.c. 



Culture solution — 



+ soil 63-0 



4- soil + water extract 05 grm. bacterised peat 64 - 



+ soil + alcoholic extract 1 grm. bacterised peat 9'5 



+ soil + phosphotungstic fraction 1 grm. bacterised peat 8"1 



+ soil + silver fraction 1 grm. bacterised peat 31*0 



From the results obtained it appears evident that while the water extract 

 of bacterised peat is practically without effect upon denitrification, the 



