Mother-of-Pearl and its Uses. 391 



The true cause of the production of pearls is supposed 

 by many to be a disease in the animal, for the following 

 reasons : In the first place, wheresoever a pearl fishery 

 is found of which the oysters grow to great size, with a 

 clean, smooth outer surface, free from knots, humps, worm 

 holes, or other blemishes in fact, presenting every appear- 

 ance of healthy and uninterrupted development (which is 

 particularly noticeable in lagoons where the shells are wide 

 apart) there will the pearls be extremely scarce ; so much 

 so that it would not pay to prosecute such a fishery for the 

 profit to be derived from the pearls alone, although the 

 shell is proportionately more valuable. On the other hand, 

 where shells are closely crowded together, deformed by 

 pressure, abnormally thickened about the base, having 

 laminae of which their outside is composed forced at their 

 edges into an unnatural contact, so as to induce a belief 

 that their growth had been stunted, as likewise being 

 studded with warts and knots of a scabby appearance, 

 being, moreover, honeycombed with small worm holes 

 which penetrate more or less deeply into the nacre there 

 will pearls most exceedingly abound. It is not uncommon 

 for as many as 100 pearls to be found in such a shell, 

 though the presumption is that where they exist in such 

 great numbers, very few, and frequently none whatever, 

 will possess any market value. 



But of the presence of the conditions necessary to the 

 production of a pearl inside of an oyster there is one very 

 significant and certain sign, the faculty of detecting which 

 can only be acquired by practice. While the animal is alive, 

 the two flat surfaces which appear at the back of the hinge 

 present very beautiful prismatic colours ; the cable which 

 attaches it to the rock is in like manner remarkable. When 

 the shell contains pearls, the prevailing colour of these 



