1AL COMPOSITION OF FOOD-FISHES. 
849 
salts of the sea water in which the animal lives; 
"nd this supposition is confirmed by the large quantity of mineral salt 
which the body is found by analysis to contain, and which amounts in 
some cases to over 14 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 solu- 
tion 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 distension 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 
distension had been reached, the imbibed water would pass out again 
and the oyster would be reduced to its original size. Just such is actu- 
ally the case. Oystermen find that the oysters u 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 arti- 
ficially the water in which the oysters are floated. Although oysters 
are generally floated in the shell, the same effect is very commonly ob- 
tained by adding fresh water to the oysters after they have been taken 
out of the shell; indeed, I am told that this is by no means an unusual 
practice of retail dealers. Oysters lose much of their salty flavor in 
floating and it is a common experience of oystermen that if the “ fat- 
tened w 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 
the investigations which have been described on the preceding pages 
I improved the opportunity to test this matter by some analyses of 
oysters before and after floating. I give here the main results, prefac- 
ing by brief accounts of the process of u floating 77 oysters as actually 
practiced by oystermen. 
The following very apposite statements* are by Prof. Persifor Frazer, 
jr., who attributes the changes mentioned to dialytie action : 
The oysters brought to our large markets on the Atlantic seaboard are generally first 
subjected to a process of “ laying out,” which consists in placing them fora short 
time in fresher water than that from which they have been taken. 
* “Note on Dialysis in Oyster Culture,” in “ Proceedings of Philadelphia Academy 
of Sciences,” 1875, p. 472. 
H. Mis. 274 54 
