THE CYANIDE BOTTLE. 



^9 



cyanide of potassium, used as described, affect any colour except 

 green ; but, with a treatment of wet cyanide, I have seen some 

 startling "varieties" of Lepidoptera produced. Greens are 

 among the most interesting of insect colours. Some, as in lodis 

 lactearia, appear to depend upon the supply of oxygen in life, 

 and are therefore probably held in the circulatory tiuid, as red is 

 in that of the human subject. It has been suggested that this 

 form of insect green is heightened by the wing-scales producing 

 polarised light. Some greens are iridescent, as in the case of 

 dragonflies, and are proof against dry cyanide. Others are not 

 greens at all, as on the under wing- surfaces of Pieris rapan and 

 P. napi, but optical delusions resulting from a mixture of black 

 and yellow scales. The green of such an insect as Geometra 

 papilionaria may be taken as the type of a fourth class where 

 a strong pigment seems present. Most of the lepidopterous 

 greens, and certainly all the examples quoted, are peculiarly 

 susceptible to the action of cyanide of potassium, and quickly 

 change to a suggestive ochreous. Therefore, when it is recol- 

 lected what a strong "affinity" cyanogen exhibits for certain 

 metals, and that iron exists in animal circulatory Huids, it is not 

 too much to suppose that these greens contain iron.* 



After trying various methods, including the use of ammonia, 

 for killing G. papilionaria so as to preserve the colour, I adopted 

 the least of the evils, and carefully exposed the moth to no more 

 than a fatal dose of the cyanide bottle, that is to say, whilst 

 doing nothing more than terminating the respiratory functions, 

 I removed the insect at once, so as to prevent cyanide saturation 

 of the wing-tissue. The body of the moth, however, through 

 spiracular inhalation of cyanogen, always turned ochreous, 

 whilst the wings retained their natural green ; but by-and-bye 

 the rays assumed the ochreous tint. I am not acquamted with 

 the Catopsilia referred to by Mr. Radley, but I strongly suspect 

 that the reason why the "nervures" even "go green" is con- 

 nected with the above illustration. This green may arise from 

 contact of the cyanogen with some other ingredient than iron, 

 the cyanogen reaching only the uervures, or rays, containing 

 the main channels of transmission. 



I have now reached Mr. Eadley's last interesting query : "Is 

 there any way," asks Mr. Eadley, "to prevent them [green 

 Noctuse and GeometrseJ changing colour?" I can thoroughly 

 recommend for this purpose the "Killing Fluid" of Messrs. J. & 

 L. Davis. I have used it constantly in the field during the past 

 season, and therefore claim to be acquainted with its many 

 merits. It disturbs no greens ; it is quick in dealing with insects 

 which appear to defy even the cyanide bottle, and it leaves the 

 insect perfectly relaxed and fit for setting. 



Chester, Dec. 12th, 1893. 



- Dry specimens might be burnt as a test for metal vapours.— J. A< 



