556 STATE BOARD OF AGRICULTURE. 



gasoline and similar volatile oils will interfere with the absorption of 

 oxygen — sometimes preventing the absorption entirel}'. 



Having made sure that beetles and grasshoppers were able to extract 

 most of the oxygen from a limited amount of air, even in the presence 

 of the carbon dioxide given off from their bodies, it w^as decided to 

 try out the method of confining insects in a certain amount of air for 

 some given period — the carbon dioxide present, and the oxygen remain- 

 ing, both being estimated volumetrically at the end of that period. Of 

 course, the oxygen and carbon dioxide value of the air could be de- 

 termined at the beginning of the experiment and thus the oxygen used 

 and the carbon dioxide given off easily found. 



Trials of this method soon proved that reasonably constant results 

 could be obtained from insects even when the carbon dioxide content 

 of the air confined with them had risen to six per cent or more. In 

 actual tests of effects of insecticide vapors, however, the percentage of 

 carbon dioxide was never allowed to run so high. 



Accurate measurements of the air samples to be used in the gas- 

 analyses w^ere difficult to obtain. Since the interval between the meas- 

 urements of air samples for analysis at the beginning and at the end 

 of a series of exi)eriments on an insect was often one or two days it 

 was necessary to reduce all measurements to 0° 0. and 760 m. m. 

 mercury pressure. A simple compensation burette was sought, there- 

 for^, which w^ould enable this reduced reading to be made directly, with- 

 out the need of taking the actual reading of the thermometer and 

 barometer and computing every time a measurement was made. 



No complete outfit that was simple, conveniently adapted to this 

 special work and at the same time suflSciently accurate, could be found 

 on the market. But gradually, as the conditions to be met with became 

 better understood, fairly simple apparatus for determining the respira- 

 tory quotient of insects was devised. A brief description of this ap- 

 paratus and of its manipulation is necessary. The principal pieces 

 of the entire outfit may be described under three headings: (1) respira- 

 tion and gas-containers, for confining insects to be studied, transferring 

 gases, etc.; (2) a measuring-compensating gas-burette outfit, used for 

 taking accurate direct measurements of gases reduced to 0° C. and 

 760 m. m. pressure; (3) various gas pipettes in which absorptions of 

 different gases could be made during an analysis of any air-sample. 



The form of respiration container finally designed is represented by 

 "A" Fig. 7, page 60. It was made of strong^ clear glass. At the top of the 

 container was a two-way gas-tight glass stop-cock and at the lower 

 part, a wide mouth. One outlet of the gas-cock was surrounded by a 

 thimble device marked "th" which consisted of a rubber stopper "S," a 

 doubleweight rubber connecting-tube "r," and a wider glass tube (a little 

 longer than ''r") that formed the thimble ''th." This device enabled 

 pure gas samples to be transferred under either mercury or water seal. 



Insects were confined in the air of the container above mercury. An 

 aspirating bottle containing mercui'y was connected to the lower 

 mouth through a rubber stopper. About the wide neck, above the 

 mouth of the container, w^as a metal band bearing hooks by which 

 the rubber stopper could be securely fastened. The opening closed 

 by the stopper was large enough so that insects could be introduced 

 or the container cleaned readily. AYhen in use, the latter stood in a 

 iieavy glass Jar of suitable heigiit Avhere it could be held in an iipright 



