NOTES ON THE COLOUEING MATTER OF APHIDES. 169 



Their bodies were crushed under a small quantity of 

 water, and the infusion, after standing some time, was 

 filtered from the insoluble residue. The solutions 

 showed a decided epipolism or fluorescence, the 

 brownish-red tint, seen by reflected light, being 

 changed into a greenish hue by transmitted light. 

 The colour is extracted from the solution much more 

 readily by boiling alcohol ; and carbonic disulphide 

 again takes it up, as with chlorophyl. 



The tinctorial properties of Aphides is most mark- 

 edly shown amongst the Lachnina?, but it also obtains 

 amongst the Aphidince and SchizoneuriuEe. In the 

 order commencing with the more pronounced charac- 

 teristics we have — Lachnus longipes, L. saligna, L. 

 pinicola, L. picea, L. juniperi, Schizoneura Janigera, 

 Aphis rumicis, A. padi, Dryohins croaticus, and Melan- 

 oxanthus salicis. 



The purple colouring matter of these insects appears 

 to be a quasi-living principle, that is, it is an educt 

 from the living mass, not a product by a subsequent 

 chemical oxydizing process. This view does not 

 militate against Mr. Sorby's investigations with the 

 spectroscope, but merely supplements them. 



Very shortly expressed, the chemical reactions are 

 as follows : — Lead acetate produces a sparing whitish 

 precipitate. Mercurous nitrate produces a pretty 

 abundant brown precipitate. No characteristic pre- 

 cipitate can be obtained by the joint solutions of an 

 alumina and stannous salt, which treatment is the 

 method employed for producing carmines from infu- 

 sions of Coccus cacti. 



Hydrochloric or nitric acids turn the solutions 

 yellow, and then bleach them. A marked reaction, 

 however, is observable by the addition of an alkali. 

 Aqueous potash strikes a deep purple, or rather a 

 port-wine red ; a colour which permanently stains paper 

 or cotton, but the dye is at once discharged by a weak 

 acid, and does not reappear by recurrence to the 

 alkali. 



