PEARLS AND PARASITES 



Know you, perchance, how that poor formless wretch 

 The Oyster gems his shallow moon-lit chalice ? 



SIR EDWIN ARNOLD. 



CERTAIN Eastern peoples believe that pearls are due to 

 raindrops falling into the oyster-shells which con- 

 veniently gape to receive them. 



* Precious the tear as that rain from the sky 

 Which turns into pearls as it falls on the sea,' 



as the poet Moore writes. This belief is of ancient 

 origin, and is probably derived from classical sources, 

 since Pliny tells us that the view prevalent in his time 

 was that pearls arise from certain secretions formed 

 by the oyster around drops of rain which have some- 

 how effected an entrance into the mantle cavity of the 

 mollusc. Probably this theory of the origin of pearls 

 has ceased to be held for many centuries except in the 

 East, where tradition has always received more credit 

 than experiment. In the West it has long been 

 known that pearls are formed as a pathological secre- 

 tion of the mineral arragonite, combined with a certain 

 amount of organic material, formed by the oyster or 

 other mollusc around some foreign body, whose pre- 

 sence forms the irritant which stimulates the secre- 

 tion. This secretion is of the same chemical and 

 mineralogical nature as the mother-of-pearl which 



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