6 



Drs. Russell and Hutchinson embarked upon a complete investigation 

 of the condition of the soil after treatment, both from the bacterial 

 and chemical standpoints. 



The present paper deals with the causes of this increased 

 productivity, and has revealed a new factor in the life of the soil, 

 and one which promises to be of extreme interest and perhaps of 

 practical importance. Various theories have been advanced to 

 account for the increased availability of the plant food in the soil 

 which results from treatment of this kind. S. U. Pickering, for 

 example, has shown that the heating, and even the treatment with 

 antiseptics, are followed by a marked increase in the amount of soluble 

 nitrogen compounds that can be extracted from the soil, which extra 

 available plant food he regarded as sufficient to account for the 

 increase of crop. More generally it was supposed that some change 

 in the bacterial flora of the soil had been effected which resulted in 

 a greater availability of the original stock of nitrogen, but the 

 mechanism was not clearly understood. Russell and Hutchinson, 

 began by finding, in common with other observers, that the treatment 

 to which the soil was subjected by no means effected complete 

 sterilisation. The numbers of bacteria were enormously reduced by 

 the process if they were counted immediately afterwards, but when 

 the soil was moistened and put under conditions suitable for growth, 

 the numbers gradually mounted up again, and eventually reached a 

 magnitude which is never attained under normal conditions in the 

 untreated soil. For example, one of the Rothamsted soils contained 

 at the outset about 7,000,000 organisms per gram, a number which 

 remains comparatively constant on storage ; after heating, the 

 number had fallen to 400 per gram ; and after treating with toluene, 

 to 2,600,000. After four days, however, these small numbers had 

 risen in the case of the heated soil to over 6,000,000, after which it 

 ceased to be possible to count the colonies ; in the case of the toluene 

 the numbers rose to 40,000,000 in nine days. Pari passu with this 

 increase in the number of the bacteria in the soil came an increase 

 in the rate at which ammonia was produced by the breakdown of the 

 more complex carbon compounds of nitrogen that were present in 

 the soil. When no plants were present to take up the ammonia, it 

 accumulated in the soils, because the bacteria which convert nitrites 

 and nitrates had been completely destroyed. It thus appeared pretty 

 clear that the increased fertility of the treated soils was due to the 

 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 

 abnormal multiplication of the ammonia-splitting organisms which 



