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nervous system, producing at first, excitement, then uncertain move- 

 ments, then narcosis. Evidence seems to show that the vapours of 

 gasolene, kerosene and carbon bisulphide become effective after absorp- 

 tion, through a tendency to prevent oxygen absorption by the tissues. 

 These three gases, when at sufficient concentration, as well as heat of 

 certain intensities, affect the activities of certain enzyme-like bodies 

 in the tissues of the living insects. If the activity of these bodies is 

 of vital significance, then the disturbance of the balance of activities 

 must be an important, and perhaps in some cases the determining, 

 factor in causing the death of treated insects. Fat or fat-like mem- 

 branes absorb gasolene and chloroform vapour from air charged with 

 these gases, and the absorbed vapour renders the membrane less 

 permeable to oxygen. This may account for the fact that less 

 oxygen is used by an insect under the influence of gasolene, since 

 the living, oxygen-absorbing cells and the body fluids surrounding 

 them are impregnated with the vapour. Waxen membranes, after 

 treatment with lime-sulphur solution, have been found to become less 

 permeable to oxygen. Pupae of the luna moth and adults of Passohis 

 cormdus in a dormant condition arising from cold, were found to absorb 

 less gasolene or ether vapour in air than did the same insects w^hen 

 most active, at a warm temperature, in air charged with the same 

 percentage of gas. This lowered absorption capacity may furnish 

 the chief explanation of the fact that insects dormant from cold are 

 more difiicult to kill by ordinary fumigants and by those contact sprays 

 which depend partly on volatile insecticide ingredients for their 

 effectiveness. Certain non-volatile powders may act as insecticides 

 in some cases. They stick fast in exudations on parts of the body, 

 where they become partly dissolved and absorbed through the integu- 

 ment. Powdered borax and sodium fluoride may act in this way, but 

 normally they become stomach poisons, since insects such as cock- 

 roaches swallow some of the powder in cleaning it from their bodies. 

 A very fine, dry powder passes readily into all crevices and adheres 

 well ; similarly a weak surface tension enables a liquid insecticide to 

 flow into all irregularities. Extracts taken from the leaves and stems 

 of Saponaria officinalis were found to increase the spreading power 

 of lime-sulphur solution, and this fact may prove useful in orchard 

 spraying. Experiments with ammonia, derived from dry, liquefied 

 ammonia, as a fumigant for mill insects were not very successful ; 

 but the liquefied ammonia was easy to apply and might prove to be a 

 desirable fumigant in some instances. When carbon tetrachloride 

 was compared with carbon bisulphide as to its action on grain insects 

 in air-tight flasks, six times as much of the former was required for 

 effective fumigation. The carbon tetrachloride was vaporised by 

 heat and used at the rate of 3-55 lb. per 100 cubic feet to control moths 

 in fur ; fumigation was repeated every five weeks during the summer. 

 This strength killed adults of Tinea biselliella. Evidence indicates 

 that heat might be applied with advantage as an insecticide in many 

 cases in which it has not yet been used. It was found that the San 

 Jose scale [Aspidiotus perniciosus] on thickly infested twigs could be 

 killed by submerging for five minutes in water heated to 130° F. 

 Green apple aphis [Aphis 2)omi] was killed in half a minute by water 

 at the same temperature. Most household insects succumb readily 

 to heat. Adults of Tinea hisellicla are quickly killed at 119° F. 



