40 



THE MUSEUM. 



Gwyn Jeffreys, tell us that in most 

 cases the irritation is caused by the 

 presence of a minute parasite in the 

 muscles cf the mollusc. Dr. Kelaart 

 says that the frustule of a diatom or 

 even one of the ova of the mollusc may 

 be the source of irritation. That the 

 disturbing object is a minute parasite 

 seems the more probable. Experienc- 

 ed pearl fishers say that pearls • are 

 more often found in oysters of stunted 

 growth, irregular shape and honey- 

 combed by boring parasites. It seems 

 improbable that a grain of sand, or 

 ova, or other than a parasite would 

 effect the growth or shape of a mollusc. 



The substance of the pearl is essen- 

 tially the same as that which lines the 

 interior of many shells and known as 

 mother-of-pearl. The iridescence of 

 this substance is an optical phenome- 

 non, as first shown by Sir. D. Brewster, 

 due to the interference of rays of light 

 reflected from corrugations of the sur- 

 face. 



Only a few molluscs yield true pearls 

 although a large number secrete 

 mother-of-pearl. 



The finest pearls are found in the 

 so-called "pearl-oyster," Avicula {Me- 

 leagi ina) niargaritifcra. Fresh-wat- 

 er pearls are produced by the "pearl- 

 mussel," Unio (^Margariiana) niargar- 

 etifcriis. Fresh water pearls are 



greatly inferior to those of marine ori- 

 gin, possessing a dull leaden hue. 



The shape of the pearl depends 

 largely upon its manner of attachment 

 in the mollusc. It is readily seen that 

 a perfectly spherical pearl must have 

 remained loose in the soft tissues of the 

 mollusc. Frequently the pearl be- 

 comes attached to the interior of the 

 shell, the point of attachment interfer- 

 ing with its symmetry. The nacreous 



deposits which it receives in this posi- 

 tion, will in time, form a pearl of hem- 

 ispherical shape, flat on one side and 

 convex on the other. During its 

 growth the pearl may become involv- 

 ed in the general deposit of mother-of- 

 pearl, and be buried in the substance 

 of the shell. Very fine pearls are oc- 

 casionally found by cutting up the moth- 

 er-of-pearl. 



A perfect pearl must be of delicate 

 te.xture, free from specks or flaws, of a 

 clear or translucent white color with 

 subdued iridescent sheen. It should 

 be perfectly spherical or symmetrical 

 pear-shaped. The most perfect pearl 

 in existence is in the museum of Zos- 

 mia in Moscow, it being perfectly glob- 

 ular and of singular beauty, weighing 

 28 carats. The largest pearl in exis- 

 tence is in the South Kensington mu- 

 seum. It is irregular in shape, weighs 

 three ounces and has a circumference 

 of four and one-half inches. 



Clarence W. Miller, 



Frankfort, Ind. 



Tanning. 



To tan Mink, Muskrat, Martin, etc.: 

 Before tanning, all skins should be 

 thoroughly cleansed in warm — not hot 

 — water and all flesh andfat removed; 

 then stretched on a board and smear- 

 ed with a mi-xture of 2 oz. each of salt 

 and alum, 3 gills of water and i 

 drachm of sulphuric acid. This should 

 be thickened with wheat bran or flour 

 and allowed to dry on the skin, after 

 which scrape off with a spoon. Next 

 take off the board, roll with fur inside 

 and draw it quickly through an iron 

 ring, unfold and roll again the opposite 

 way. Repeat until the skin is soft 

 and flexible. 



