EXPERIMENT STATION BULLETINS. 575 



EFFECT OF SERIOUS MECHANICAL INJURY UPON r^^ OF P. CORNUTUS. 



Four experiments were rim to determine how the respiratory ratio 

 would behave in case of beetles mechanically injured and dying in pure 

 air from the effects of the injury — i. e., "mechanical injury" was sub- 

 stituted for the insecticide. 



In the first case, the head of the beetle w^as crushed; in the next two 

 experiments, the heads and prothoraxes were crushed ; and in the fourth 

 experiment the head was pithed in every direction with a hot steel needle. 

 Death was brought about in periods ranging from 10 to 24 hours. The 

 effect upon the respiratory quotient was comparatively uniform. The 

 average quotient in air before injury was 0.72, after injury it was 0.53 

 and after death when decay had begun the average had risen to 0.87. 



These results are added evidence that the rise in the respiratory quo- 

 tient during the time beetles are deeply under the influence of gasoline, 

 etc., must be due to some peculiar effect of such insecticides on the 

 respiration of living tissues. 



CO 

 EFFECT OF STARVATION UPON .-■ ^ OF P. CORNUTUS. 



In making all these respiration studies, it was necessary to exclude 

 any food from the respiration chamber. Now since it was important to 

 first obtain the respiratory quotient for the beetles in air, and after- 

 ward to make two or three determinations under the influence of the 

 insecticide, they had to be without food, often for 24 to 48 hours or 

 longer — sometimes, even as long as four dajs. However, the experi- 

 ments were always carried on in a moist atmosphere, and whenever 

 possible, the beetles were placed with food (partly decayed wood) be- 

 tween experiments for a short time. But the question might naturally 

 arise as to the possible effect of this enforced fast, itself, upon the 

 respiratory quotient. A few ''starvation exijeriments" were therefore 

 carried out in order to know whether this question might have anv 

 bearing upon the results obtained in connection Avith the influence of 

 insecticide vapors on the respiratory quotient. 



For each experiment, a strong healthy specimen was taken from food 



OO 



and the — ^^ in air determined. The specimen was then con- 

 fined in a moist place without food for a time, when the quiotient was 

 again determined ; and so on at intervals until after death. Results were 

 comparatively uniform. The respiratory quotient remained almost con- 

 stant for six to seven days, and then began to decline in value. Within 

 about two weeks (a little more or less) it had fallen from 0.71 or 0.74 to 

 0.54 or 0.50 and remained about that low until death, which did not oc- 

 cur in one case until the end of the twenty-fourth day — Avhen the heart 

 had entirelv ceased beating. Verv soon after that, as soon as decav had 

 begun, the quotient rose to 0.85 to 0.89. Sometimes the quotient for a 

 decaying insect ran a little higher. 



It will thus be seen that all the respiration work with insecticides 

 was well within the period when the respiratory quotients of the beetles 

 (without food) in air remain constant. 



