SALICINE IN APHIDES. 195 



In other cases, I have found potash to evoke the violet 

 shade from specimens otherwise colourless. This dye 

 is fugitive, and, if discharged by an acid, cannot be 

 again recovered by the action of an alkali. Soda and 

 ammonia also bring out this colour. 



Advantage may be taken of the fact, that there is a 

 certain order in which the tissues resist the intrusion 

 of foreign matter, such as a dye. Thus the germinal 

 and most vitally endowed organs reject dyeing by 

 carmine, logwood, and such coal-colours as magenta ; 

 whilst the portions in process of exfoliation and 

 decay absorb it the most readily. For such purposes, 

 weak alcohol may be made slightly alkaline by 

 ammonia, and tinged with a little carmine or 

 cocchineal solution. 



Dilute chromic acid both tinges the tissues yellow 

 and renders them tough. Solutions of osmic acid 

 also may be used with advantage, and, in short, the 

 usual reagents employed for conducting minute 

 anatomy may be taken with due circumspection and 

 tenderness. 



For labelling specimens, paste will be found much 

 more adherent than gum. The former may be pre- 

 served for some months in a well-closed bottle, if a 

 little aqueous solution of corrosive sublimate be stirred 

 into it. 



11.— SALICINE IN APHIDES. 



Mr. C. T. Muller, of Eastbourne, informs me that 

 he has been able to prove the presence of salicine in 

 the juices of Lachnus viminalis. He digests the 

 insects in chloroform, which liquid subsequently, on 

 evaporation, leaves silky crystals, capable of polarising 

 light, and giving the characteristic red coloration 

 with sulphuric acid. 



If these crystals be salicine, the polarised ray should 

 have a rotation to the left. This experiment I have 



