Collier's New Encyclopedia (1921)/Pearl

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PEARL, a peculiar product of certain marine and freshwater mollusks or shellfish. Most of the molluscous animals which are aquatic and reside in shells are provided with a fluid secretion with which they line their shells, and give to the otherwise harsh granular material of the shell a smooth surface, which prevents any unpleasant friction. The material in its hardened condition is called nacre by zoölogists, and by dealers mother-of-pearl. Detached and generally spherical or rounded portions of the nacre are often found on opening the shells, due to the intrusion of a grain of sand or other substance, which, by irritating the tender body of the animal, obliges it in self-defense to cover the cause of offense which it has no power to remove; and as the secretion goes on regularly to supply the growth and wear of the shell the included body constantly gets its share, and thereby continues to increase in size till it becomes a pearl. The true pearl of price is only found in the pearl oyster. The most famous pearls are those from the East; the coast of Ceylon or Taprobane, as it was called by the Greeks. They are, however, obtained now of nearly the same quality in Panama in South America, St. Margarita in the West Indies, the Coromandel coast, the shores of the Sooloo Islands, the Bahrien Islands, and the islands of Karak and Corgo in the Persian Gulf. The pearls of the Bahrien fishery are said to be even finer than those of Ceylon.

The single pearl which Cleopatra is said to have dissolved and swallowed was valued at $400,000, and one of the same value was cut into two pieces for earrings for the statue of Venus in the Pantheon at Rome. False pearls are manufactured extensively. The finest and costliest imitations could only be distinguished from the real by an expert. Roman pearls differ from other artificial pearls by having the coating of pearly matter on the outside, to which it is attached by an adhesive substance. The art of making these was derived from the Chinese.

The Chinese have long been in the habit of introducing grains of sand and little knots of wire into the shell of the pearl oyster, in order that the animal, to relieve itself from the irritation so caused, may coat the foreign substance with pearl.