260 Natural History of Molluscous Animals : — 
can remain concerning the identity of the modern with the 
ancient dye. 
It forms no part of my plan to describe the process of dye- 
ing with this fluid, but should you wish to procure it, remember 
that in the living animal it is not purple but whitish. When 
applied to linen, it appears at first of a pleasant green colour, 
and being exposed to the light, the green gr adually i increases 
in intensity, and at last changes to blue ; the blue soon acquires 
a tint of red, and at last becomes a fine purple of great intens- 
ity. Beyond this no further change is produced; and as the 
fluid attains this its ultimate tint, w vith greater or less celeri ity, 
according to the intensity of fire light to which the linen is 
exposed, there is reason to conclude that it consists of a base 
capable of uniting with various doses of oxygen, and of varying 
its colour, accordingly. 
Mr. Montagu strongly recommends the use of this secretion 
for the purpose of marking linen, since it grows brighter by 
washing, and cannot, so fav as is known, be remov ed by any 
chemical process. You may try the experiment; it will amuse 
you: but the Tyrian purple is ‘eclipsed by several dyes of the 
moderns, and is disregarded by nations who have made any 
considerable advance in the arts. It is still used, according 
to Ulloa and other travellers, by the natives on some parts 
of the coast of South America, and by the Chinese. ane 
latter also make a red ink of it, a purpose to which it 
applied by the Byzantine writers, who esteemed it ent * 
This reminds me that the ink of the ancients was sometimes 
prepared from the black liquor of the cuttle-fish; and from 
the same fluid the Chinese manufacture our black Indian ink, 
so much used by artists. 
Amongst the Molliasca there is not one which gives any 
essential aid to the physician, in his work of ministering to our 
ailments. In the Natural History of Pliny, indeed, there is a 
catalogue of medicines furnished by these animals sufficiently 
extensive and varied, but their reputation has passed away, 
For if oyster shells and the bone of the cuttle-fish (Sepia 
officinalis) still hold a precarious place in some pharmacopeeias, 
it is more from respect to ancient usage, than from a conviction 
of their utility. Nor is there any benefit to be got from swal- 
lowing slugs (Zimax agréstis) boiled in milk, nor from sucking 
* This condensed history of the Parpura has been drawn up from the 
following works :— Aristotle Hist. Animal., lib. v. cap. 13.; Plin. Hist. Nat., 
lib. ix. ; “Edinburg th Encyclopedia, vol. viii. are. Dyeing; iphomisoris s History 
of the Royal Soc ‘iety, p.67. &c.; Beckman’s Hist. of Inventions, vols. i. and i. ; 
Pennant’s Brit. Zool., vol. iv.; Montagu’s Test. Brit. Sup., p. 105—108. 
120. &c.; Cook's Voyages, vol.i. p. 18. 12mo. 
