Open main menu

Page:Popular Science Monthly Volume 32.djvu/88

This page has been proofread, but needs to be validated.

the two is reached, the osmose will stop. If the sac which has become distended is elastic, it will, after osmose has ceased, tend to come back to its normal size, the extra quantity of solution which it has received being driven out again.

We should expect these principles to apply to the oyster. Roughly speaking, the body of the animal may be regarded as a collection of membranous sacs. It seems entirely reasonable to suppose that the intercellular spaces, and probably the cells of the body, would be impregnated with the salts of the sea-water in which the animal lives; and this supposition is confirmed by the large quantity of mineral salts which the body is found by analysis to contain, and which amount, in some cases, to over fourteen per cent of the water-free substance of the body.

It seems equally reasonable to believe that osmose would take place through both the outer coating of the body and the cell-walls of the animal's body. As long as the oyster stays in the salt water, the solution of salts within its body would naturally be in equilibrium with the water outside. When the animal is brought into fresh or brackish water, i. e., into a more dilute solution, we should expect the salts in the more concentrated solution within its body to pass out, and a larger amount of fresh water to enter, and produce just such a distention as actually takes place in the floating. If this assumption is correct, we should expect that the osmose would be the more rapid the less the amount of salts in the surrounding water, that it would proceed more rapidly in warm and more slowly in cold water; that it would take place whether the body of the animal is left in the shell or is previously removed from it; that the quantity of salts would be greatly reduced in floating; and that, if it were left in the water after the maximum distention had been reached, the imbibed water would pass out again, and the oyster would be reduced to its original size. Just such is actually the case. Oyster-men find that the oysters "fatten" much more quickly in fresh than in brackish water; warmth is so favorable to the process that it is said to be sometimes found profitable to warm artificially the water in which the oysters are floated. Although oysters are generally floated in the shell, the same effect is very commonly obtained by adding fresh water to the oysters after they have been taken out of the shell; indeed, I am told that this is a by no means unusual practice of retail dealers. Oysters lose much of their salty flavor in floating, and it is a common experience of oyster-men that, if the "fattened"' oysters are left too long on the floats, they become "lean" again.

This exact agreement of theory and fact might seem to warrant the conclusion that the actual changes in the so-called fattening of oysters in floating are essentially gain of water and loss of salts. The absolute proof, however, is to be sought in chemical analysis. In the course of an investigation conducted under the auspices of the United