BY R. GREIG-SMITH. 



645 



production of toxin, or by the gradual loss, by decomposition, of 

 the nutritive sugar added to the soil. 



At start ... 

 8 days 

 28 days . 

 57 days ... 



Bacteria in millions 



per gram of 



drv soil. 



Growth of soil-bacteria 

 in the soil-extract ; 

 water-control = 10. 



302 

 122 

 109 



84 



It is concluded from the experimental work detailed in this 

 paper that: — (1) The formation of toxins in the soil, free from 

 vegetation, occurs most rapidly when the temperature is near 

 28°, and the moisture-content is one-fourth of the vvater-holding 

 capacity. 



(2) The soil-extract is, as a rule, either nutritive or toxic 

 according to the volume of water, relative to the soil, used in 

 preparing the extract. It is most nutritive when the ratio of 

 soil to water is 1 : 0-5, and most toxic when it is 1 : 1. 



(3) A previous drying or chloroforming of the soil generally 

 causes the extract to be much more nutritive than when the raw 

 soil is used. 



(4) The addition of small quantities of dextrose to soil brings 

 about a more rapid production of toxin, while aeration of the 

 treated soil accelerates the formation and decay of the toxin. 



