Effects of certain Agents on Insects. 199 



2. On the Effect of certain Gases. 

 Carbonic Acid Gas.— On the 19th December placed a fly (Musca 

 stabulans) in a tube in which this gas was in process of being rapidly 

 generated by the action of dilute nitric acid on fragments of lime- 

 stone. The fly was supported by a perforated diaphragm, so as 

 to be kept above the fluid, and the tube was corked, but not so tight 

 as to prevent entirely the escape of gas, and immersed in water. 

 In a few seconds the fly became motionless : taken out after two 

 • hours, it seemed dead, it did not move even when placed on the 

 warm hand, and breathed on for a minute or two ; soon after, the 

 breathing on it being continued, a slight tremulous motion was 

 perceived in its feet, and in a few minutes more decided animation 

 was restored, and it moved when touched, and walked. 



December 21st, put a fly (Heteromyza buccata) into a tube full 

 of carbonic acid gas. It became instantly motionless. Kept in 

 the gas about two minutes, it revived in about five minutes after 

 being taken out, and seemed not less active than before. Replaced 

 in the gas after an interval of twenty-four hours, in a few seconds 

 it became motionless ; left in the gas another twenty-four hours, 

 it was found dead when taken out. 



On the same day, a small fly (an Anthomyia), confined in a wine 

 glass inverted on a plate of glass, was so active (the temperature 

 of the room 56°) as to fly from side to side. Introduced a bit of 

 limestone, and added a little nitric acid ; the fly at the time was 

 standing on the side of the glass ; in two or three seconds, without 

 making any efforts to escape, it lost its hold, and fell into the 

 effervescing fluid, where it was motionless. Taken out after about 

 two minutes, in two or three minutes more it began to move its 

 legs, and shortly was tolerably active, considering its clogged state 

 from its wet wings and legs. 



On the 25th December, put a fly (Musca lanio) in an active state 

 at the temperature of the room into the tube, with carbonic acid 

 gas. It immediately became motionless ; taken out after twenty- 

 four hours, it was found to be dead. 



On the same day put into the gas a small fly of the gnat kind. 

 In two or three seconds it became motionless ; after about three 

 or four hours exposure to the gas, on being taken out, and placed 

 on the warm hand and breathed upon, a slight motion of the legs 

 was perceived, but this only for a minute or two, when all marks 

 of life ceased. 



On the 26th December, placed two flies, both of them pretty 

 active, (a Heteromyza buccata and a Musca lanio,) in carbonic acid 



