88 OYSTERS, AND ALL ABOUT THEM. 



The green oyster, the Parisian delicacy, is brought from 

 Brittany ; but the same flavour and colour can be produced 

 by putting oysters into pits where the water is about three 

 feet deep, in the salt marshes, and where the sun has great 

 power. In these they become green in three or four days ; 

 for these colours (as elsewhere stated) are derived from the 

 elementary substance on which they feed not, however^ 

 that it produces any peculiar difference as to flavour. 



The inner part of an oyster shell is a great contrast to 

 its exterior. As we examine it, we cannot fail to be struck 

 with its silver-like hue and its exquisite smoothness, so 

 completely adapted to the form and comfort of the little 

 in-dweller ; and when held to the light, a slight iridescence 

 is frequently discoverable. The hard, silvery, brilliant 

 internal layer of several kinds of shells reminds us of those 



described by Landor : 



" Of pearly hue 



Within, and they that lustre have imbibed 

 In the sun's palace porch, where, when unyoked, 

 His chariot wheel stands midway in the wave;" 



and the internal layer of oyster shells is often variegated 

 with changing purple and azure. 



The cause of this effect has been fully explained by 

 Sir David Brewster, as suggested to him accidentally. He 

 had fixed a piece of mother-of-pearl to an instrument for 

 measuring angles by a cement of resin and bees-wax. On 

 removing it from the cement when in a hard state, by 

 insinuating the edge of a knife, and making it spring up, 

 he found that the plate of mother-of-pearl had left a clean 

 impression of its own surface, and had actually given the 

 cement the property of exhibiting its own colours. The 

 discovery was therefore made, to his great surprise and 

 delight, that the cause, whatever it might be, of the colours 



