202 Dr. John Davy on the 



oxygen. Twenty-four hours after it was standing dry on the side 

 of the tuhe, as if in common air, and in like manner on the 31st. 

 On the 1st February it was found swimming on the water; by 

 inclining the tube it got out of the water, attaching itself to the 

 side of the glass; on the following day it was found motionless, 

 and it did not revive on being taken out. There was a slight 

 diminution of the volume of the oxygen, many times the bulk of 

 the fly. 



Coal Gas. — Put a fly (Heteromyza buccata) into a tube half-full 

 of water, above which was common air, and introduced a little 

 coal gas as it was generated by the action of heat : no sooner had 

 a few bubbles come in contact with the fly floating on the surface 

 of the water, than from a state of activity it became motionless. 

 Taken out without loss of time, and exposed to the air, it revived 

 in about ten minutes. The same fly, exposed to the action of the 

 gas nearly pure, became motionless in two or three seconds. 

 Taken out after about a minute, it gave no signs of life for half 

 an hour ; three hours later, a feeble movement of its legs was per- 

 ceptible, soon terminating in death. 



Sulphuretted Hydrogen. — On the 31st December immersed the 

 same flies, that had been exposed to the action of hydrogen on the 

 preceding day, in sulphuretted hydrogen, as it was slowly dis- 

 engaged in a tube by the action of dilute muriatic acid on sul- 

 phuret of iron. After a few seconds both flies were motionless ; 

 and they did not revive when taken out, and that immediately. 

 The effect was the same on another (Heteromyza buccata), and as 

 rapidly. 



On the 1st January immersed a fly (Musca hortorum) in a mix- 

 ture of sulphuretted hydrogen and common air : in a few seconds 

 it became motionless, and though instantly taken out it did not 

 revive. On the same day repeated the experiment on a Hetero- 

 myza, and with like effect : the air in the tube consisted of about 

 two parts common air and one sulphuretted hydrogen. On the 

 same day introduced into the tube in which the gas was in process 

 of being generated, two flies (Trichocera hiemaUs, very active, 

 Musca vomitoria, less so). After about an hour both were motion- 

 less ; nor did they revive when taken out. So small was the pro- 

 portion of sulphuretted hydrogen, that, when an attempt was made 

 to ascertain it, it was hardly appreciable. 



On the 20th March introduced an active honey bee, just taken, 

 into a mixture of sulphuretted hydrogen and atmospheric air. 

 The very instant it entered it dropt motionless ; and not the 



