568 STATE BOARD OF AGRICULTURE. 



readilv. Thus, the influence of this vapor upon the respiratory quotient 

 might be studied in a manner similar to that described already for 

 three other insecticides. A platinum wire heated in a suitable con- 

 tainer of the air-vapor mixture was used to effect the combustion. The 

 theory was good, but a series of experiments showed that it was ap- 

 parently impossible to control the amount of vapor used so as to ob- 

 tain satisfactory complete combustion. Always, some of the carbon 

 of the burning vapor was deposited as a black soot instead of being 

 completely burned to carbon dioxide. Besides, a terrific, uncontrolled 

 explosion sometimes occurred. This plan, therefore, had to be given 

 up. Neither could a satisfactory method be found for estimating both 

 carbon dioxide and oxygen in the presence of carbon disulphide vapor. 



One other method, however, seemed worthy of trial. It had been 

 noticed in case of all the vapors whose influence upon the insects was 

 decidedly anaesthetic or narcotic, that the effects were apt to continue 

 for a long while after specimens were removed from the presence of the 

 Insecticide vapor. This was especially trme of carbon disulphide and 

 nicotine when beetles had been brought deeply under their influence. 

 If specimens were treated with the right amounts of the vapor of either 

 of these fluids they might lie for many hours as if dead — showing, 

 perhaps, only a faint heart-beat at times or slight jerking movements 

 of the antennae and feet. 



Eecourse was therefore had, in the case of these two insecticides, to 

 the following method. First, the respiratory quotient was obtained 

 for two specimens of P. cornutus in air under controlled conditions. 

 Then the same specimens were treated with the vapors of the insecti- 

 cide until nearly dead, after which they are allowed to lie in the open 

 air for several minutes until the odor of the insecticide had disappeared. 

 Finally, they were placed in a respiration chamber again, in pure air. 

 Enough air was used so that, after about a half hour, a sample could be 

 taken for analysis. The respiration period was counted from the time 

 the sample was obtained — the percentages of oxygen, carbon dioxide, 

 and nitrogen found by its analysis being taken as the beginning values 

 of those component gases. Thus, the estimation served at the same 

 time as a check to show that no more of the insecticide vapor had been 

 given off from the insects to interfere with oxygen estimations. 



Obviously, in studying the effects of an insecticide vapor upon the 

 respiratory quotient, the best way would be to have some of the vapor 

 present in the respired air all through the experiment — the percent- 

 age of the vapor being accurately determined — as was done when 

 using gasoline, kerosene, and hydrocyanic acid. But as has already 

 been stated, the ilatter method could not be used successfully with the two 

 fluids in question. As it proved out, the method used did give some in- 

 teresting and instructive results. They are, therefore, recorded here in 

 Table VI. 



