4 Shells as evidence of tlie Migraiiems. 



A ven- curious fact concerning this dye, which was 

 noted also to some extent by the ancients, is the trans- 

 formation through which it passes on exposure to 

 sunlight. The fluid is at first colourless, but on exposure 

 to the action of the sun it becomes of a bright yellow, 

 speedily turns to a pale green, and continues to change 

 imperceptibly until it assumes a bluish cast and then a 

 purple red. These changes of colour, which are faster or 

 slower according to the intensitj' of the sun's light, are 

 accompanied by the production of a disagreeable foetid 

 odour, similar to that of essence of garlic. 



This peculiarity was well known to the ancients and 

 is referred to by Pliny. It was probably the cause of the 

 extravagant use of perfumes bj- the wearers of " the 

 purple " in classical times. 



The Sources of the Puri'lk. 



The vague descriptions of the Greek and Latin writers 

 has led to much discussion as to the exact species of 

 shell-fish used in the manufacture of the dye. 



Pliny speaks of two kinds that produce the purple 

 colour. The smaller "fish," he tells us, was called the 

 "buccinum," from its resemblance to the conch by which 

 the sound of the buccinus or trumpet is produced ; the 

 other " fish " was known as the " purpura," or purple, and 

 was studded with points up to the very apex, differing in 

 this respect from the first kind. 



'The earliest attempt to discover the source of the 

 ancient purple seems to have been made by William Cole 

 of Bristol, in i686,» who conducted experiments on shell- 

 fish [Purpura lapillus) found on the shores of Somerset- 



'Phil. Trans. Roy. Soc, T.oud., xv., pp. 278—86, and plate. 



