= ee 
* * * In the tests with pyrethrum extracts, an effort was made to devise 
a technique that would give uniform results at high dilutions of the 
kerosene base, this having proved to be the principal difficulty en- 
countered in determining the relative toxicity of different extracts. 
Most of the tests were made with a kerosene extract representing ap-— 
proximately 12 percent of pyrethrum (1 pound of pyrethrum flowers to 
1 gallon of oil) and the preliminary emulsions were made with penetrol 
(a commercial sulphonated oil), glue, or a trimethylamine soap. Complete 
killing in all tests was obtained at a dilution of 1 gram of pyrethrum to 
400,000 cubic centimeters of water), but above this the results were 
quite erratic, complete or nearly complete killing occurring in some of 
the tests at 1 to 2,000,000, while other tests gave no kill at all. 
Therefore the diluting technique will require still further improvement." 
