Soil Organisms concerned in Nitrogen Cycle. 523 



respectively. The proportion of one part of bacterised peat in ten of soil is 

 that used practically throughout the experiment, but it was anticipated that, 

 since in all probability by no means the whole of the active substance is 

 separated by the phosphotungstic acid method, an addition of this fraction 

 equivalent to one part of peat in ten might possibly be too small to produce 

 the maximum effect. "For this reason, experiments were made with the 

 phosphotungstic fraction from double the amount of peat normally used, and 

 also from proportions of one-eighth and one-sixteenth the volume of soil. 

 The soils, incubated and sampled from time to time, gave the following 

 results : — 



Table X. 



Nitrate content (parts per million- 

 mean of three determinations). 



Originally. 



After 

 15 days. 



29 days. 



40 days. 



1. 

 2. 

 3. 

 4. 

 5. 

 6. 

 7. 

 8. 

 9. 

 10. 



Soil alone 



Soil + phosphotungstic fraction from 1 in 10 



1 in 10 

 1 in 5 . 

 1 in 5 . 

 „ 1 in 8 . 

 „ 1 in 8 . 

 1 in 16 

 1 in 16 



31 

 35 

 36 

 33 

 34 

 36 

 35 

 31 

 32 

 31 



50 

 48 

 84 

 90 

 112 

 105 

 83 

 85 

 49 

 53 



220 

 211 

 304 

 302 

 232 

 241 

 130 

 141 



112 

 120 

 320 

 309 

 462 

 448 

 346 

 335 

 198 

 205 



The addition, in sufficient quantity, of the phosphotungstic fraction thus 

 appears to increase the rate of nitrification in soils. It has, however, been 

 shown above that such addition also increases the nitrogen fixation, and the 

 possibility arises that the increase in nitrate content may be due to the 

 nitrification of the nitrogen fixed rather than to direct action upon the 

 nitrifying organisms themselves. 



This point could only be elucidated by examining the effect of the 

 auximone fractions upon nitrification in liquid culture. Accordingly, a 

 crude nitrifying culture was obtained by inoculating some good garden soil 

 into Erlenmeyer flasks, each containing 100 c.c. of the following medium : — 

 Tap water, 100 c.c. ; ammonium sulphate, 0'1 grm. ; dipotassium phosphate, 

 0"1 grm. ; basic magnesium carbonate, 0'2 grm. ; and incubating at 26° C. for 

 seven days. This was sub-cultured three times before any attempt was made 

 to experiment with the auximone fractions, but then it was found that the 

 addition of the phosphotungstic or silver fraction to the culture resulted in 

 the formation of the thick scum of some foreign organisms already described 



