BACTERIA AND ENZYMES IN AGRICULTURE 261 



Fertility of Soils. — Enough has been said to show the great 

 importance to the farmer of the bacterial life in the soil. 

 Dr. E. J. Russell has carried out important investigations 

 showing that the fertility of the soil is, under normal circum- 

 stances, actually proportional to the bacterial activity of the 

 soil. It is, of coxirse, obvious that bacterial activity is a 

 very wide term, and covers the many classes of action which 

 have been indicated in the foregoing paragraphs, but Dr. 

 Russell has found that the sum of these activities can be 

 measured, by determining the rate at which oxygen is taken 

 up by a given weight of soil, and also the total amount of 

 oxygen so taken up. This he determined by enclosing the 

 soil in a flask, connected on one side with a tube dipping into 

 mercury, and on the other with a small receptacle containing 

 strong potash solution, which served to absorb the carbon 

 dioxide produced by the oxidation of the organic matter. 

 The rise of the mercury in the side tube enabled the rate and 

 amoimt of oxygen absorption to be measured. A number 

 of these flasks, each containing soil, whose character as 

 regards fertihty was known, was placed in a common water- 

 bath, and maintained at a constant temperature, one flask 

 being left empty to serve as control. It was f oimd, as already 

 stated, that the absorption of oxygen, and consequently the 

 bacterial activity, increased with the fertility. 



In the face of these results, it appears surprising that 

 experiments, by Russell and others, should have shown that 

 partial sterilisation of the soil, either by antiseptics, such as 

 toluene, or by heat, should increase the fertility. 



An explanation of this apparent contradiction is afEorded 

 by a recent research by Russell and Hutchinson. They 

 efiected partial sterilisation either by heating to 98° C, or 

 by addition of 4 per cent, of toluene, which, at the end of 

 three days, was allowed to evaporate by spreading out the 

 soil in a thin layer. In a third series, the toluene was left in ; 

 in a fourth series, the soil was left untreated. The soils were 



