50 JOUIINAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



organs are kept moist and brought immediately into pure air or oxy- 

 gen again. 



It is believed that these experiments upon the action of contact 

 insecticides justify the following statements: 



Contact insecticides as a rule effect the death of the insect through 

 more than one cause. 



Alkaline insecticides, such as the strong soap washes pass rather 

 slowly through the chitinous walls of insects and dissolve the proteids 

 and fats of the tissue cells. 



Corrosive sublimate and similar substances, which in solution pre- 

 cipitate proteids, pass slowly through the chitinous walls of insects and 

 precipitate the proteids of the tissue cells. 



Most gases penetrate the chitinous walls of insects into the body, 

 rapidly — much more rapidly than liquids. 



Gases and liquids may enter the trachese through the spiracles and 

 there penetrate the walls of the trachese into the body tissues of the 

 insect more rapidly than through the outer chitin. Apparently the 

 more feeble the surface tension of the liquid, the more readily is it able 

 to enter the spiracles of the insect. 



In the case of gasoline, kerosene, carbon disulphide and many such 

 insecticides which are volatile, the volatile portions penetrate the 

 body through the trachese and through the outer chitin, thus affecting 

 the insect long before the liquid alone would have time to do so. Such 

 insecticides may plug the trachese to some extent, but they appear to 

 be effective principally through their ability to interfere, in some way, 

 with the processes of oxidation in the tissue cells. 



SOME PROPERTIES THAT MAKE LIME-SULPHUR WASH 

 EFFECTIVE IN KILLING SCALE-INSECTS. 



{Abstract) 

 By G. D. Shafer, East Lansing, Mich. 



In making a study of how the lime-sulphur wash kills scale-insects, it 

 was found that after treatment with the spray, for several hours before 

 death results, many of the insects lie under their scale coverings in a 

 more or less comatose condition. During this time, if the scale is 

 removed, the insect speedily recovers the ability to respond when 

 touched with a needle. Of course after a few hours in dry air the 

 delicate bodied insect would shrivel and die, but fresh air seemed to be 

 the thing that revived it when the covering Avas first removed. 



Haywood ('07) showed that lime-sulphur sprays contain polysul- 



