EFFECT OF PARTIAL STERILISATION 275 



Further investigations led to the following conclusions : * 

 1. Partial sterilisation of soil, i.e., heating to a temperature 

 of 60 C. or more, or treatment for a short time with vapours 

 of antiseptics such as toluene, causes first a fall, then a rise, in 

 bacterial numbers. The rise sets in soon after the antiseptic 

 has been removed and the soil conditions are once more 

 favourable for bacterial development ; it goes on till the 

 numbers considerably exceed those present in the original soil 

 (Tables XCIV. and XCV.). 



TABLE XCIV. Numbers of Bacteria and Amounts of Ammonia Production 

 in Partially Sterilised Soils. 



t After 4 days. 



TABLE XCV. Ammonia and Nitrate accumulating in a Soil kept twenty- 

 three days at about 15 C. in a moist condition; parts per million of 

 Dry Soil. 



2. Simultaneously there is a marked increase in the rate of 

 accumulation of ammonia. This sets in as soon as the 

 bacterial numbers begin to rise, and the connection between 



* The details are given in two papers by Russell and Hutchinson in J. Agric. 

 Sci., 3 (1909), 111-H4, and 5 (1913), 152-221. 



