78 THE POPULAR SCIENCE MONTHLY. 



the two is reached, the osmose will stop. If the sac which has be- 

 come 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 re- 

 ceived 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 im- 

 pregnated 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 |)roof, however, is to be sought in chemical analysis. In the 

 course of an investigation conducted under the auspices of the United 



