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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 conveniently gape to receive them.

‘Precious the tear as that rain from the skyWhich 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 somehow 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 secretion of the mineral arragonite, combined with a certain amount of organic material, formed by the oyster or other mollusc around some foreign body, whose presence forms the irritant which stimulates the secretion. This secretion is of the same chemical and mineralogical nature as the mother-of-pearl which

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