E. J. Russell and H. B. Hutchinson 



Table 7. Relative absorption of oxygen in 10 days 

 untreated soil = 100. 



129 



§ 21. The increased amount of ammouia in the partially sterilised 

 soil is not in itself a sufficient pi'oof of increased ammonia production : 

 it might equally arise from a diminished ammonia assimilation if we 

 assume the presence of some ammonia or nitrate consuming organism 

 in the untreated soil, but not in those partially sterilised. We failed, 

 however, to find any evidence of such a process. Periodical deter- 

 minations of the ammonia and nitrate in soils to which known quantities 

 of ammonium sulphate had been added always accounted for all or more 

 than all of the added ammonia. Some of the results obtained are as 

 follows : 



Table 8. Effect of adding ammonium sidphate to soil. 



These experiments show that (1) the increased productiveness of a 

 partially sterilised soil is due to an increase in the amount of ammonia 

 present, 



(2) the increased amount of ammonia is the result of bacterial 

 action, 



(3) it is not due to a diminished assimilation of ammonia or 

 nitrate but to an actual increase in the rate of ammonia production. 



§ 22. Tike total number of bacteria capable of developing on gelatine 

 plates. The first effect of partial sterilisation is to reduce considerably 

 the number of these organisms present, but when the soil is subsequently 



9—2 



