EXPERIMENT STATION BULLETINS. 543 



The temperature of these experiments ranged from 68° to 72° F. 

 The use of barium hydrate as an absorbant for carbon dioxide is so 

 well known that but little review is needed here. Sulphuric acid 

 ( ~i^ ) ^"^'^^^ rosalic acid as an indicator seenftd most convenient for 

 use in the titrations. After a little practice, with proper care, constant 

 titrations accurate to a drop could be obtained. If only a very slight 

 precipitate of barium carbonate was found in the barium hydrate flask, 

 the titration could be made directly. If the precipitate were consider- 

 able, it was necessary to filter before titrating in order to determine 

 the exact end-point with certainty. The hydrate was filtered boiling 

 hot into a flask containing a little boiling water. The precipitate was 

 Avashed thoroughly; and the whole operation was carried out in an 

 atmosphere containing a minimum of carbon dioxide. By determin- 

 ing the value of the barium hydrate solution at the beginning and at 

 the end of the experiment, the value of the carbon dioxide absorbed by 

 it, in terms of (^) acid, could be found. Each cubic centimeter of 

 (t5") carbon dioxide is equal to 0.0022 gram of carbon dioxide. 



From Table 1 it may be seen that the beetles were able to recover 

 after many hours confinement in hydrogen. During this confinement 

 in pure hydrogen small amounts of carbon dioxide were given off. 

 After death the rate of giving off this carbon dioxide increased a little. 

 For the experiments in which insects were confined in carbon dioxide, 

 that gas was obtained in its purest form from the action of weak sul- 

 phuric acid dropping on pure sodium bicarbonate which was packed 

 into the bottom of the generator in the form of a paste. By this meanf 

 a current of carbon dioxide over 99.5% pure could be obtained. The 

 results secured on beetles with this gas were very similar to those in 

 which hydrogen was used except that the heart action lasted longer in 

 carbon dioxide. When Passalus coimutus was confined in this gas, the 

 heart-beat at first quickened and became irregular. It then slowed and 

 ceased, usually in about three minutes, only to begin again after about 

 twenty minutes, slowly, at sixteen to twenty beats per minute. Alter- 

 nate ceasing and beating again occurred thus for several hours but the 

 periods of beating gradually became shorter, farther apart, and the heart 

 weaker until finally it ceased altogether. Recovery in case of this 

 species, was scarcely ever complete after a longer period of exposure 

 than twenty-four hours. A ])upa of PhlegetJioritius celeus, however, 

 recovered perfectly within twelve hours after an exposure to carbon 

 dioxide of ninety-six hours. Several other insects, among which were 

 crickets, grasshoppers, certain Diptera and caterpillars were also tried. 

 All would quickly become motionless, but all could recover again in 

 fresh air after several hours confinement in the absence of oxygen. 

 (Caterpillars could endure the confinement for fully as long periods as 

 the beetles and then recover afterward. None of the experiments, how- 

 over, showed that insects could live longer in hydrogen than in carbon 

 dioxide. 



After searching some of the older literature on the subject of respira- 

 tion, it was interesting to find several experiments recorded years ago 

 (and practically lost sight of) which point to this same fact— viz. 

 that insects are by no nicaiis easily suffocated. Burmeister^ in 1836 



1, Burmeister; A Manual of Entomology; Trans, by Shuckard, London, 183G. 



