578 STATE BOARD OF AGRICULTURE. 



present; the sliglit decrease in volume npon transferring to this pipette 

 was no doubt due to the water taking up a little carbon dioxide. 



The experiment given is an average one as carried out by this method 

 with hydrogen and nitrogen gases. 



A word of explanation is due as to the means of forcing all the gas 

 out of the respiration container from around the beetles. 



When mercury had been brought up to the top — i. e., to the two-way 

 cock of the container — the cock was closed, and the aspira ting-mug of 

 mercury connected with the respiration container was then lowered six 

 inches. Bubbles clinging around the wing covers would at once rise. 

 The mercury-mug was raised again, the cock was opened and these last 

 bubbles of gas could be forced over. By using care to bring the mercuiry- 

 mug down the same distance each time when causing the last bubbles to 

 rise, three successive measurements of a quantity of gas might be made 

 with a variation less than 0.1 c. c. It was surprising to find how little 

 the beetles were injured, under proper precautions, during the opera- 

 tion. Even in the case of active beetles from air, mercury was seldom 

 forced into the tracheal system or into the digestive tract and when the 

 beetles had first been rendered quiet with nitrogen (or other gas) such 

 an accident scarcely ever occurred. 



When it had thus been found perfectly possible to measure all the 

 air used with the beetles at the beginning and at the end of an experi- 

 ment, the question was tested out with the beetles in pure air. 



(Exp.) Used one beetle, wt. 1.89 grms. 



Air at beginning 81.7 c. c. measured by the burette (Fig. 4.) 



81.1. c. c. after 5% hours with insect. 0.6 c. c. loss. 

 79.17 c. c. after absorption of OOj with KOH. 

 1.93 c. c. — = 2.37% CO, 

 64.73 c. c. after Phosphorus-pipette = nitrogen at 



end, 79.81% N. 

 14.44 c. c. oxygen remaining = 17.8% O2 



The nitrogen percentage of the air used at the beginning was 79.2. 



81.7 c. c, X 79.2 = 64.70 c. c. nitrogen at beginning ; an amount which 

 corresponds almost exactly with that found at the end — i. e., 64.73 c. c, 

 (Also, experiments of this kind afford opportunity to compare the res- 

 piratory quotient, given by the percentage method already described, to 

 the quotient given when the actual number of cubic centimeters of car- 

 bon dioxide given off is divided by the actual number of cubic centi- 

 meters of oxygen absorbed. The quotients given by the two methods 

 agree within two hundredths.) 



Now, since the volume of nitrogen at the end was the same as at 

 the beginning, the 0.6 c. c. loss in air-volume, found by actual meas- 

 urements, must have been due, alone, to the fact that a volume of oxygen 

 was absorbed by them greater than the voluime of carbon dioxide ex- 

 creted. 



By the same method the question was tested out with specimens of 

 Melanoplus femoratns — a species which was used in some of the respira- 

 tion work — and within the limits of the possibility of error of the 

 method the amount of nitrogen remained the same in every case. When 

 the carbon dioxide in 76.9 c. c. of air confined with six of the grass- 



