484 



The farmer long before this, also, had realized the value of what 

 is known as " fallowing," in which sufficient food is allowed to ac- 

 cumulate for a period, to supply the bacterium with its food. 



From the fact, however, that these discoveries do not absolutely 

 explain or account for all the problems of soil fertility or lack of 

 fertility, we realize that these bacteria are merely another determining 

 factor in connection with the problem. 



These results have remained without intrinsic alteration till quite 

 recently, when we are brought in contact with another phase of the 

 ciuestion, the elucidation of which has been solved by Russell and 

 Hutchinson within the last year, viz., the partial sterilization of soil 

 as a means to increase its fertility. 



Here again we have the accumulated experience of ages of agri- 

 cultural practice explained by the results of scientific investigation. 



The effect of heat on soils has been known not only in European 

 agricultural practice but in other countries — notably India and I find 

 too that it is known to Javanese gardeners in this country, whose 

 common practice is to burn together a mixture of earth and dry 

 manure before using it in pots for horticultural purposes. When 

 asked why they practice this method — they reply that it is valuable' 

 although they ofler no reason why this is so. 



It is now known that partial sterilization of soils, not only by 

 lieat, but by certain antiseptics such as chloroform and carbon 

 Ijisulphide, has a very beneficial action, and the reason for this action 

 has been most ably explained by the above mentioned investigators. 



Crops grown on soils sterilized by heat become doubled in some 

 cases, and almost equally good results are obtained by treating with 

 antiseptics. The plants on analysis are also found to contain much 

 more nitrogen than those from undertreated soils, showing that the 

 result of the treatment has effected an increase of nutriment. 



Russell and Hutchinson found that (i) the nitrogen combined as 

 ammonia in the soil increased remarkably under the treatment (2) the 

 treatment did not effect complete sterilization (3) the bacteria in the 

 soil were greatly reduced in number at first (4) subsequently the bac- 

 teria increased to an enormous extent, and far beyond the original 

 number, {5) the nitrifying bacteria were destroyed. 



From these results they naturally concluded that the increased 

 ammonia content of soil treated in this manner was due to the increase 

 in bacteria, and the absence of nitrifying bacteria which enabled the 

 ammonia to accumulate ; but the real value and brilliancy of their 

 discoveries was the realization that the subsequent enormous increase 

 of the bacteria was due to the absence of some factor in the soil which 

 had been destroyed in the process of partial sterilization. 



