606 EXPERIMENT STATION RECORD. 



New York Cornell Experiment Station, have reported experiments 

 showino: that while steamin": soil under two atmospheres pressure for 

 two to four hours appai'ontly i^roduced substances which were at 

 first injurious to plant growth, a luxui-iaiit growth took place later 

 on the sterilized soil. 



Russell and Hutchinson found that, although the treatment with 

 heat or volatile antiseptics (toluene) enormously reduced the numl)cr 

 of bacteria present, it did not effect complete sterilization, and that 

 when the conditions were again made favorable for growth in the 

 partially sterilized soils the number of bacteria rapidly increased and 

 eventually became much more numerous than they had ever been 

 under normal conditions in the untreated soil. 



In a summary of these investigations. Director Hall states that 

 " with this increase in the number of bacteria in the soil came an 

 increase in the rate at which ammonia was produced by the break- 

 down of the more complex carbon compounds of nitrogen that were 

 present in the soil. When no plants were present to take up this 

 ammonia, it accumulated in the soils, because the bacteria which con- 

 vert nitrites and nitrates had been completely destroyed. It thus 

 appeared pretty clear that the increased fertility of the treated soils 

 was due to their greater power of breaking down the complex organic 

 matter of the soil to the state of ammonia, a form in which plants 

 can assimilate nitrogen ; and this increased production of ammonia 

 was due to an exceptional multiplication of the ammonia-splitting 

 organisms which constitute so large a proportion of the normal bac- 

 terial flora of the soil. 



" The authors then carried out various experiments, which showed 

 (1) that no stimulus could be supposed to have taken place through 

 the treatment which would make the bacteria remaining in the soil 

 more active; (2) that there had been no selective destruction of 

 organisms which would leave behind a population of a more active 

 type than the usual mixed flora of the soil. By other steps which 

 need not be here set out, it became clear that the difference between 

 the treated and untreated soils was due to some factor in the latter 

 which normally limits the number of bacteria, and therefore the rate 

 of production of ammonia. Search for this unknown factor disclosed 

 the presence, in all soils so far examined, of numbers of protozoa and 

 ameba which live on bacteria and keep their numbers down to the 

 comparatively low limit specified. The heat*'^"" -• treatment with 

 antiseptics kills off all these large organisms, but leaves unhurt some 

 spores of the ammonia-producing bacteria, which afterwards can 

 develop to a much greater extent than in the untreated soil because 

 they are freed from their normal check. 



" The theory as it stands then assumes that, putting aside its 

 physical characteristics, the fertility of a soil is determined by the 



