BY K. GKEIG-SMITH. 



Experiment v. 



731 



Later experiments, with this specimen of air-dried soil, showed 

 that, upon the twenty-ninth clay of storage, the toxicity had dimin- 

 ished considerably. 



The effect of dilution upon a toxic soil-extract was studied, in 

 order to find out, if possible, the point of dilution at which the 

 added bacteria maintained their numbers, or, at any rate, equalled 

 the control or water-increase. Previous experiments had shown 

 that dilution so weakened the activity of toxin, that the nutrients 

 caused an increase. If a balanced action could be demonstrated, a 

 road might be found to estimate the toxicity of soils. The first 

 experiment in this direction was upon the same soil used in the last 

 experiment, but it had been stored for 29 days. 

 Experiment vi. 



The loss of toxicity, by this specimen of soil, is shown by the 

 thousandfold increase in the undiluted extract; 13 days before, the 

 toxicity had produced a hundredfold decrease. 



