68 BULLETIN 824^ U. S. DEPARTMENT OF AGRICULTTJEB. 



Gillette (96), in 1889, arrived at the same conclusions as to the 

 absence of toxic substances in the volatile oil of Pyrethrum. He 

 made practical tests upon insects, operating as follows: 



Two or 3 grams of the powder were first put in a test tube and the dust allowed to 

 settle for a few minutes. Then a loose cotton plug was pushed halfway down in each, 

 upon which were placed the insects, and the tubes were then tightly corked. Dipte- 

 rous, ichneumons, chalcids, cynipids, and aphids were subjected to this treatment, 

 and allowed to remain for different lengths of time, varying from 1 or 2 to 40 hours, 

 without showing any signs of being affected by the volatile oil. 



To see if the toxic principle of Pyrethrum would come off at a 

 higher temperature, Gillette made further tests: 



Two cynipids were then similarly inclosed in a tube with fresh powder and the lower 

 end of the tube was held for 10 minutes in a dish of boiling water, the upper end of the 

 tube being kept cool with a wet cloth. The insects were allowed to remain for a few 

 minutes after the boiling, but showed no signs of being affected by the treatment. 



. Another tube was then prepared in which were confined other cynipids in a manner 

 similar to the preceding, and the tube was held over the flame of an alcohol lamp and 

 constantly shaken until the powder was entirely browned, care being taken not to 

 burn it. The insects were unhurt by this treatment. 



Then a quantity of powder was put in a tube and held in the flame of a lamp until 

 the tube was filled with fumes. These fumes were poured ov^er into another tube 

 in which was an ichiieumon, on which they took immediate effect and death ensued ■ 

 in a very few minutes. 



Next, three ichneumons were enclosed in separate tubes. One was shaken up with 

 a small amount of fresh Pyrethrum powder, one with a small amount of the browned 

 powder spoken of in the second preceding experiment, and one in a small amount 

 of the partially burned powder spoken of in the preceding experiment. In each case 

 the insect was killed, the fresh and the browned articles acting alike, and the par- 

 tially burned powder acting somewhat slower. 



Three grams of the powder were then put in about 90 cc. of water in a retort and 

 boiled for one-half hour, the vapor being caught and condensed in a receiver. Soon 

 after boiling began a slight odor was noticed escaping about the mouth of the receiver 

 which the neck of the retott did not quite fill. A cynipid was entangled in a bit of 

 cotton and crowded into the opening, where it remained for 12 minutes without being 

 affected. 



About one-half of the liquid was sent over in the above experiment, and the distil- 

 late was clear, colorless, and almost tasteless and odorless, there being a slight taste 

 resembling steeped hay. The distillate and the residue were used to compare their 

 insecticidal properties with one another and with fresh powder extracted in cold 

 water for 24 hours. The results of these experiments were that the distillate used 

 pure killed but a very small percentage of the lice treated and that the residue was as 

 efficient as the same amount of powder extracted in cold water. 



Gillette found that ether extracted all the insecticidal principle 

 from Pyrethrum, as the extracted powder when dusted upon insects 

 had no effect. The greater part of the ether extract would dissolve 

 readily in water, and this water solution affected insects exactly as 

 if they had been treated with Pyrethrum. 



Zuco (296), in 1889, made an ethereal extract of the flowers of 

 Chrysanthemum cinerarisefolium. After repeated treatment of this 

 with aqueous and alcoholic potash a substance was left which formed 



