Soil Organisms concerned in Nitrogen Cycle. 527 



are the two chief decomposition processes, ammonification and denitrification. 

 These result in the breaking down of the soil organic matter and nitrates, 

 with the liberation in the form of ammonia and free gaseous nitrogen of the 

 element which has been " fixed " and oxidised in the two processes of 

 nitrogen fixation and nitrification. As these two decomposition processes 

 involve reactions which are directly opposed to those concerned in the two 

 already considered, it was thought possible that an investigation of the 

 effect of auximones upon the bacteria concerned in them would give some 

 indication as to whether the auximones merely stimulate all classes of 

 bacteria equally, or whether they play some definite part in the building up 

 of the nitrogenous molecule. 



It was practically impossible to carry out experiments on ammonification 

 in a soil which had been mixed with bacterised peat, in the same way as had 

 been done for nitrogen fixation and nitrification, on account of the ammonia 

 content of the bacterised peat and the rapid nitrate formation and other 

 changes in the nitrogen compounds in such a mixture. The only alternative 

 was to depend upon the results obtained in liquid culture, and here again, 

 on account of the ammonia contained in the water extract of bacterised 

 peat, it became difficult to test the effect of this extract upon the process of 

 ammonification. It appears, however, from the results obtained in the 

 experiments recorded above, that the auximone fractions are largely 

 responsible for the increased activity of the bacteria hitherto investigated ; 

 hence tests were made of the effect upon the ammonifying organisms of the 

 alcoholic, phosphotungstic and silver fractions alone. 



An investigation was first made of the influence of the addition of these 

 fractions upon the " ammonifying " or " putrefactive " power of the soils 

 used in the previous experiments, this putrefactive power being determined 

 by the method in general use described by Eemy.* 



Sixteen flasks were prepared, each containing 100 c.c. of 1 per cent, 

 peptone solution and 10 grm. of fine air-dried Chelsea soil. To four of 

 these was added the alcoholic extract, to another four the phosphotungstic 

 fraction, and to a third four the silver fraction, of 1 grm. of bacterised peat. 

 The whole set was incubated at 22° C. for five days, then 2 grm. of calcined 

 magnesia and a few drops of paraffin (to prevent frothing) were added to 

 each. The contents of each flask were distilled, and the distillate received 

 in decinormal sulphuric acid, which was then titrated with decinormal 

 sodium hydrate solution. The figures obtained were : — 



* Eemy, ' Centr. Bakt. Par.,' Abt. II, vol. 8, pp. 657-662 (1902). 



