Effects of certain Agents on Insects. 207 



coloured. During the first half hour the fly was active, and seemed 

 little affected ; after another half hour it was found motionless ; 

 whether it revived or not is not mentioned in the note of the ex- 

 periment. The experiment was repeated at the temperature of 

 the air of the room, 55°, on two flies (Heteromyza buccata); one, 

 which was feeble when put into the tube, became motionless in 

 about a quarter of an hour ; the other, in the same time, excepting 

 that it had become dull, seemed but little affected ; in about an 

 hour its gait was unsteady, as if its muscles were no longer under 

 control ; after four hours it was found motionless ; neither of 

 them revived. 



On the results described in the two last sections I beg to offer 

 in conclusion a few remarks. 



Comparing the effects of the several agents no two seem to have 

 acted precisely in the same manner ; and probably were a larger 

 number of experiments made, and with minute attention, each 

 agent would be found to possess some peculiarity in its influences. 

 Those most fatal to life appear to have been sulphuretted hydrogen, 

 ammonia, chlorine, nitric acid, iodine, camphor, oil of turpentine, 

 each varying in degrees of rapidity of effect, but so far analogous 

 that no perfect revival ensued on exposure to the air, after a 

 motionless state had once been induced. Those less fatal to life 

 appear to have been azote, hydrogen, carbonic acid, coal gas, 

 muriatic acid vapour, ether, chloroform, — all of them producing 

 immobility, and probably insensibility, with different degrees of 

 rapidity, but not commonly terminating in death, revival in most 

 instances following. Whether oxygen belongs to either is more 

 than doubtful ; it seems to stand alone, as regards its effects on 

 the functions of life, throughout all classes of animals. That 

 death sooner occurred in the trial with it than in that with atmo- 

 spheric air, may have been owing to exhaustion connected with 

 increased vital action of the insect, unsupported by nourishing 

 food. 



How the effects of the several agents are produced, it may be 

 difficult to explain in the present state of our knowledge. Some 

 of them probably act chemically, such as the strong acid vapour, 

 chlorine, iodine : some probably, chiefly, in suspending respiration, 

 or in preventing the due aeration of the fluids, such as azote, 

 hydrogen, carbonic acid ; and others, it may be, in a more com- 

 plicated manner, and in part through their action on the nervous 

 as well as the respiratory system, such as sulphuretted hydrogen, 

 ether, chloroform, alcohol, oil of turpentine, camphor. * 



It is worthy of remark, that most of the substances, which, even 



