EXPERIMENT STATION BULLETINS. 479 



pupae which in the dormant stage had absorbed only 0.18 -j- of the 2.08 

 c. c. of gasoline vapor placed with the air used in the cold room test. 



When the nine pupae, used in Exp. 2, were removed from the gasoline- 

 vapor-air at the end of the test in the cold room, they had become quite 

 sensitive to touch. They would wriggle actively when touched. The 

 gasoline vapor seemed to have stimulated them. They were removed to 

 the warm room and kept there about 15 days before the second absorp- 

 tion test was run. In this experiment 1.96 c. c. of gasoline vapor was 

 present in the air at the beginning of the warm room test, and 0.45-|- 

 of this vapor was absorbed by the i^upae as against only 0.2 + of the 

 1.7 c. c. of vapor present in the air during the cold room test. About 

 80 c. c. of gasoline-vapor-air Avas present at the end of each test. The 

 ratio of the adsoihed gasoline vapor to the whole amount present was, 

 in both experiments, greatest in the warm room te^ts where the insects 

 were undergoing active development. All the pupae recovered at the 

 end of the tests, and the first moths began to emerge about five days after 

 the last tests in each experiment. Adults emerged from all the pupae, 

 although none were very perfect moths. After the above experiments, 

 it was decided to use adult Passalus cornutus in absorption-tests made, 

 first, when the beetles were quiet and dormant from cold, and again when 

 they had become active in the warm room. These beetles were chosen 

 because, as has been explained in Bulletin 11, all of the air could be 

 safely forced out from around these insects by mercury. Thus, it was 

 possible to introduce samples of the same stock of insecticide-vapor-air 

 into the container, unmixed with other air, in the cold room and in the 

 warm room. Air that was almost, but not quite, saturated with the 

 insecticide vapor at the cold room temperature was kept in a gas con- 

 tainer above mercury as the stock-supply. One could, in this way, be 

 sure that the percentage of insecticide vapor present, in both tests, was 

 exactly the same. With this assurance that the same percentage of the 

 insecticide vapor could be placed with the insects in the two different 

 tests, it was not necessary to use a vapor which would permit of accurate 

 quantitative estimations of the percentage present at the beginning and 

 end of each test. Thus, different apparatus and a different method might 

 be employed. The method of measuring the total rapid decrease in vol- 

 ume could be depended upon, it appeared, to show the volume of insecti- 

 cide vapor absorbed by the insects. Experience had shown that most of 

 the vapor-absorption would take place in an interval too short for 

 respiration to make an appreciable change in volume. Moreover, in the 

 short interval necessary, barometer and therometer readings remained 

 practically the same. The apparatus used for making the gas measure- 

 ments was the compensation-burette just referred to (Shown in Fig. 4, 

 Tech. Bull. 11, and a gas-container of the type shown at A., Fig. 7, Tech. 

 Bull. 11 of this station. 



A certain measure of the insecticide vapor to be used was transferred 

 from the stock supply into the compensation burette. The beetles were 

 floated, dorsal side up, on mercury in a gas-container, and the mercury 

 was raised until all air was expelled from around them. The container 

 Avas at once connected Avith the compensation gas-burette, and the ac- 

 curately measured sample of insectici'^-^ vapor was quickly drawn over 



