140 DESTEUCTIVE INSECTS OF VICTORIA I 



" We then perfected an apparatus for putting the tent on tall trees 

 quickly. This occupied a great deal of time, but we finally succeeded 

 so well that we could change the tent from one tree to the other in less 

 than two minutes. Mr. A. B. Chapman and Mr. L. H. Titus, of San 

 Gabriel, became impatient at the delay and requested Professor Hilgard, 

 of the State University, to send them a chemist, and they would pay his 

 expenses. In the month of April, 1887, Mr. F. W. Morse was dele- 

 gated for this purpose, and he, too, finally discovered that hydrocyanic 

 acid gas would kill the scales ; but Professor Coquillett had made the 

 same discovery over six months previously, so that the credit of this 

 discovery belongs to this latter gentleman. Much credit is also due to 

 Mr. J. W. Wolfskill for the great amount of time and money that he 

 has devoted to this cause. 



"ALEXANDER CRAW." 



I am not aware that either of the other experimenters mentioned 

 above have ever published the results of their experiments, nor have 

 I been able to obtain any notes from them upon the subject. 



Many years ago Dr. George Dimmock, one of the editors of Psyche, 

 made a number of interesting experiments with pure gases on various 

 insects, and his account of these experiments is given in the March- 

 April number of that journal for 1877. The results obtained by him 

 are briefly as follows : 



" Carbonic acid gas (carbon dioxide) did not prove fatal to beetles 

 confined in it for one or two moments, but several sow-bugs (Oniscus) 

 confined in it from twenty to thirty minutes never recovered. Mixed 

 with oxygen in the proportion of three parts of the former to one of 

 the latter, it did not prove fatal to a beetle confined in it three minutes. 

 When mixed in the proportion of sixty-six parts of the carbonic acid 

 gas to thirty -four parts of oxygen, it did not prove fatal to a beetle 

 confined in it five minutes, nor to a wire-worm (Elateridce) confined in 

 it thirty minutes, and of several sow-bugs ( Oniscus} confined in it fifty 

 minutes, to some it proved fatal, while to others it did not. 



" Carbonic oxide gas (carbon monoxide) did not prove fatal to 

 beetles confined in it ten minutes, nor to butterflies confined in it thirty 

 minutes. 



" Hydrogen did not prove fatal to a beetle and butterfly confined in 

 it five minutes. 



" Oxygen did not prove fatal to a spider confined in it one hour, nor 

 to a beetle confined in it for three days. 



" Nitric oxide (NO) proved fatal to a beetle confined in it only 

 fifteen seconds, while several sow-bugs ( Oniscus) confined in it from 

 forty to sixty seconds never recovered." 



My own experiments with the nitric oxide mixed with air did not 

 prove as successful as those made by Dr. Dimmock with the pure gas ; 

 in fact, the brown fuming tetroxide proved more fatal to the Icerya 

 than did the colourless oxids. 



I first began experimenting with gases in the month of September, 

 1886, and have since continued it at intervals up to the present time ; 



