December, '11] COLEMAN: HYDROCYANIC ACID GAS 531 



The four lots are designated by letters of the alphabet and in each 

 capsule containing an insect is placed a small label bearing, in pencil, 

 the letter and serial number designating the exact place in the series 

 of that particular insect. The four lots run through under each 

 percentage of gas are allowed to remain in the gas for periods of fiftecm, 

 thirty, forty-five and sixty minutes respectively, the time being 

 recorded on the card opposite each lot. We thus have the entire 

 record for each series, with checks, on one card. For each stage or 

 condition of the insect treated we run through at least nine of these 

 entire series, representing as many different percentages of gas, in one 

 day. 



These series of treated insects and living checks are placed in glass 

 tumblers or in common white envelopes for future examination or 

 storage. The series are examined from time to time and careful 

 records made on the cards of the recovery of any treated insects or 

 death of the checks, so that when complete the results may be tabu- 

 lated direct from these card records. 



In preparing the insects for treatment they are handled as little 

 as possible. The scale insects being treated mostly in situ on the 

 twig, simply cutting the twig into short pieces holding one or more 

 insects and one piece placed in each capsule. We have also treated 

 the eggs and young en mass by placing large numbers in each capsule, 

 and usually, where material will permit, a large number are treated 

 in the Novy's jar as a check for those treated in vials for each percentage 

 and also to record the effect on parasites. 



For some series we use the gas as it comes from the generator 

 saturated with moisture while for others it is dried by passing through 

 a calcium chloride tube. Other entire series are placed in the large 

 refrigerator in the basement of the Entomological building during 

 treatment in order to record the effect at different temperatures. 



For these experiments we require thousands of specimens of the 

 various species of Coccidse found in California. Many of these have 

 already been collected, or their collection arranged for by Professor 

 Woodworth on a recent trip through the Santa Clara Valley and the 

 southern Cahfornia citrus district for this purpose. 



While it is desirable to obtain as large an amount of data as possible 

 before tabulating the results of our experiments, they have been 

 sufficiently comprehensive to show that the percentage of hydrocyanic 

 acid gas necessary for killing the eggs, larvae and adults of most species 

 of Coccidae where there is no leakage is less than .025 per cent or 

 about one sixteenth the dosage used at present in fumigation work. 



