698 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITV, iv., 



Experiment xxii. 



Extracts prepared from the different layers of soil after 

 antiseptic treatment, should contain more toxin in the lower 

 than in the upper strata. This proved to be the case. In the 

 following, the usual method of extraction was adopted — 500 

 gr. of soil were moistened in a beaker with ether, and exposed 

 to the air until all odour had gone : the top 200 gr. and the 

 bottom 200 gr. were each treated with 200 c.c. of tap-water 

 in a mortar. After an hour, the extracts were filtered through 

 paper, and then through porcelain. The extracts were diluted 

 with an equal volume of sterile tap- water, and 10 c.c. portions 

 of full and half streng'th extract were seeded with 1 c.c. of a 

 suspension of Bac. ■prodiyiosuH, and incubated overnight. 



Experiment xxiii. 



