554 STATE BOARD OF AGRICULTURE. 



An examination of Tables III A. and B. will show that where the 

 insecticides were used in small amounts (either when the liquids were 

 applied as such, or in the vapor form only) the rate of excreting car- 

 bon dioxide was increased. Even when the insects were partly stupe- 

 fied the rate of giving off carbon dioxide might remain, for a time, 

 higher than the normal in pure air. Note that a grasshopper, with 

 all the spiracles on one side of the body plugged, gave off, in spite of 

 that, as much carbon dioxide as was usually excreted in pure air when 

 all spiracles were free. Large amounts of the liquids or of the vapors, 

 when suflScient to bring the insect near death, caused a decided reduc- 

 tion in the rate of excreting carbon dioxide. In later respiration ex- 

 periments it was found that hydrocyanic acid gas, the vapor of To-bak- 

 ine, and the vapor of carbon disulphide produced very similar effects — 

 except that small amounts of these insecticides did not cause nearly 

 so large an increase in the excretion rate of carbon dioxide as did 

 gasoline. 



When using the aspirating pump method, in no case did any pre- 

 cipitate appear in the wash flask ''b." Also, an experiment was run 

 for eight hours with 2 c. c. of gasoline in flask "C" (no beetle in the 

 respiration chamber) in order to find whether any carbon dioxide was 

 given off from the gasoline or whether the vapor passing with the 

 air through the barium hydrate solution interfered in any way with 

 its titration. At the end of that time titrations were made, and the 

 amount of ^ acid required was within 0,05 c. c. of the required 



amount for the standard solutions — a difference within the limit of 

 error in manipulation. Therefore, all carbon dioxide caught in the 

 experiments with insects must have come from the insects, alone. 



It should be stated further, that the beetles used for the ex- 

 periments recorded in Table III A. were all taken from the same lot. 

 The beetle used in the experiment recorded in Table III B. was taken 

 from a fresh lot of ver\' active specimens just collected. Different lots 

 of beetles varied in their vitality and activity — specimens in the same 

 lot even varied somewhat. But it is believed that the experiments were 

 such as to leave no doubt as to the effects, as thev are stated above, 

 of the insecticides used. 



EFFECT OF CERTAIN GASES AND VAPORS UPON THE RESPIRATORY QUOTIENT. 



The influence of the contact insecticides studied upon the rate of 

 carbon dioxide excretion made perfectly plain the desirability and im- 

 portance of determining the effect of these insecticides upon the rate 

 of oxygen absorbed by the insects during the same period of time. The 

 one determination might serve as a valuable check upon the other; but 

 more than that, it would make possible a study of the effects of an 

 insecticide upon the respiratory quotient of an insect under varying 

 conditions of amount or length of time the agent were used. In other 

 words, a comparison could be made between the ratio of carbon dioxide 

 given off to oxygen absorbed by an insect in air, and the corresponding 

 ratio made by the same insect under the influence of an insecticide — • 

 other conditions being as nearly as possible the same. Such a compari- 

 son would be of value, of course, only if the respiratory quotient in air 

 were a practically constant quantity for the insect, under controlled 

 conditions — as has been found to be the case for higher animals. 



