242 PURPLE SECRETIONS. 



that, in drying, the secretion assumes the beautiful deep 

 hue of the sweet scabious (Scabiosa atro-purpurea, Linn.), 

 and remains unaltered by long exposure to the air. Nitric 

 acid, in small quantity, heightened the tint, but a larger 

 dose changed it to a dirty aurora ; and potash changed it to 

 a dirty vinous grey colour : both the acid and alkali preci- 

 pitated many white flakes from the fluid. The smell is 

 faint : there is nothing peculiar in the taste ; nor has it any 

 irritating quality, for it may be applied a long time to the 

 skin with perfect impunity. * The liquid of our native 

 species is a beautiful purple when exuded. In dyeing it 

 becomes of a brown colour; and if a tincture is made by 

 macerating the Aplysia in whiskey, the purple colour is 

 retained for some time, but ultimately the tincture assumes 

 a tint much like port-wine. 



The excretion which approaches apparently nearest to 

 this in its character is that of the lanthinae ; but I am not 

 aware that any analysis has been made of it. Planorbis 

 corneus (Fig. 42), also, when irritated by any means, or, as 

 Fig. 42. Wallis translates a passage from Lister, 



by "an injection of a grain of salt, pep- 

 per, or ginger, into its mouth," pours 

 forth a purple fluid from the sides, be- 

 tween the fork and margin of the 

 cloak ; but the colour is of so fugitive a 

 nature, that no acid or astringent has 

 hitherto been found sufficient to preserve 

 the elegancy of its tint, and from turning to an unpleasant 

 rusty hue.f In this respect it agrees with the liquor dis- 

 charged by Scalaria clathrus, of which Montagu has given 

 us an interesting history. " The purple juice," he tells us, 

 " may be collected either from the recent or dried animal, 

 by opening the part behind the head ; and as much can be 

 procured from five individuals as is sufficient, when mixed 

 with a few drops of spring-water, to cover half a sheet of 

 paper." Neither volatile nor fixed alkali materially affects 

 it ; mineral acids turn it to a bluish green, or sea-green ; 

 sulphuric acid renders it a shade more inclining to blue ; 

 vegetable acids probably do not affect it, since cream of tartar 

 did not in the least alter it. These colours, laid on paper, 

 were very bright, and appeared for some months unchanged 

 by the action of the air or the sun; but, being exposed, for 

 a whole summer, to the solar rays, in a south window, they 



* M6m. ix. 7. 



t Wallis, Nat. Hist. North., i. 371. Lister, in his Anim. Ang. 144, 

 gives a full and very good account of this liquor. 



