224 
NATURAL HISTORY. 
shews about half its length above the surface. 1 ms appear- 
ance, however, is instantaneous ; and, if the fisher does not 
seize the opportunity, the razor buries itself, with great ease, 
to its former depth/ There it continues secure ; no salt can 
allure it a second time ; but it remains unmolested, unless the 
fisher will be at the trouble of digging it out sometimes two 
feet below the surface. 
Such are the minute differences between bivalved shell- 
fish ; but in the great outlines of their nature they exactly 
resemble each other. It is particularly in this class of shell- 
fish that pearls are found in greatest abundance. The pearl 
seems bred from no disorder in the animal, but accidentally 
produced by the same matter that goes to form the shell. This 
substance, which is soft at first, uickly hardens ; and thus, 
by successive coats, layer over layer, the pearl acquires its di- 
mensions. If cut through, it will be found to consist of seve- 
ral coats, like an onion; and sometimes a small speck is seen 
in the middle, upon which the coats were originally formed. 
All oysters, and most shell-fish, are found to contain 
pearls; but that which particularly obtains the name of the 
pearl oyster has a large strong whitish shell, wrinkled and 
rough without, and within smooth, and of a silver colour. 
From these the mother-of-pearl is taken, which is nothing 
more than the internal coats of the shell, resembling the. pearl 
in colour and consistence. There are a great number of pearl 
fisheries in America and Asia. The chief of these is carried 
on in the Persian Gulph. 
The wretched people that are destined to fish for pearls, are 
either negroes, or some of the poorest of the natives of 
Persia. The divers are not only subjec^ to the dangers of the 
deep, to tempests, to suffocation at the bottom, to being de- 
voured by sharks, but from their profession universally labour 
under a spitting of blood, occasioned by the pressure of air 
upon their lungs in going down to the bottom. The most ro- 
bust and healthy young men are chosen for this employment, 
but they seldom survive it above five or six years. Their 
fibres become rigid ; their eye-balls turn red ; and they usu- 
ally die consumptive. 
It is amazing how very long they are seen to continue at 
the bottom. Some, as we are assured, have been known to con- 
tinue three quarters of an hour under water without breath- 
ing; and to one unused to diving, ten minutes would suffo- 
cate the strongest. They fish for pearls, or rather the oysters 
that contain them, in boats twenty-eight feet long ; and of 
these there are sometimes three or four hundred at a time: 
with each seven or eight stones, which serve for anchors. 
