260 Natural Histot-^i/ 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 gradually 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, with greater or less celerity, 

 according to the intensity of the 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 far as is known, be removed 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. The 

 latter also make a red ink of it, a purpose to which it was 

 applied by the Byzantine writers, who esteemed it highly. * 

 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 Ii>dian ink, 

 so much used by artists. 



Amongst the Mollusca 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 

 ofiicinalis) still hold a precarious place in some pharmacopceias, 

 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 (Z/imax agrestis) boiled in milk, nor from sucking 



* This condensed history of the Purpura has been drawn up from the 

 following works : — Aristotle Hist. Animal.^ lib. v. cap. 13.; Plin. Hist. Nat., 

 lib. ix. ; Edinburgh Enci/clopcsdiay vol. viii. art. Dyeing ; Thomson's History 

 of the Royal SocietVy p. 67. &c. ; Beckman's Hist, of Inventions ^ vols. i. and ii. ; 

 Pennant's Brit. Zool., vol. iv. ; Montagu's Test. Brit. Suj)., p. 105 — 108. 

 120. &c. J Cook's VoyageSy vol. i. p. 18. 12mo. 



