W. F. Cooper and W. A. B. Walling 173 



namely, the power of taking up or "adsorbing" substances. This 

 property is possessed by sawdust but not by ordinary coarse sand. 

 Wool has this property of adsorbing substances to a marked degree: 

 further, this property is selective, inasmuch as wool adsorbs basic 

 compounds more readily than acidic ones, the dyeing of wool being 

 based upon this property. For this reason many basic substances are 

 included in our list of possible toxic agents as pyridine, aniline, nicotine, 

 jS-naphthylamine, ^-nitraniline. 



(a) Powder experiments. 



A definite number of larvae were shaken with the powder so as to 

 be well covered with it, then carefully transferred to a glass jar 

 containing sand or sawdust. The jar was covered with muslin and the 

 number of flies which developed noted. The results are given in 

 Table III. The powder consisted of the toxic agent diluted with dry 

 precipitated chalk; the percentage of the toxic agent in the powder 

 is given in column 2. 



TABLE III. 



Showing the different effect of sawdust and sand basis. 

 Larvae shaken in powder and then placed in satvdust or sand. 



