THE CHEMISTRY OF " OYSTER-FATTENING:' yj 



it lives in water and has a body so constituted as to readily permit the 

 inflow and outflow of water and solutions of salts, may be easily used 

 for experiments. The results of the experiments have a practical as 

 well as scientific interest, since they confirm the common explanation 

 of the increase in bulk of oysters by "floating," and show that it is 

 essentially a process of watering in w^hich the bulk is increased with- 

 out any corresponding increase, but rather, if anything, a loss of nu- 

 tritive material.* 



It is a common practice of oyster-dealers, instead of selling the 

 oysters in the condition in which they are taken from the beds in salt 

 water, to first place them for a time — forty-eight hours, more or less — 

 in fresh or brackish water, in order, as the oyster-men say, to " fatten" 

 them, the operation being called " floating " or " laying out." By this 

 process the body of the oyster acquires such a plumpness and rotund- 

 ity, and its bulk and weight are so increased, as to materially increase 

 its selling value. 



The belief is common among oyster-men that this " fattening " is 

 due to an actual gain of flesh and fat, and that the nutritive value of 

 the oyster is increased by the process. A moment's consideration of 

 the chemistry and physiology of the subject will make it clear, not 

 only that such an increase of tissue-substance in so short a time and 

 with such scanty food-supply is out of the question, but that the in- 

 crease of volume and weight of the bodies of the oysters is just what 

 would be expected from the osmose which would naturally take place 

 between the contents of the bodies of the oysters as taken from salt 

 water and the fresh or brackish water in which they are floated. 



If we fill a bladder with salt water, and then put it into fresh wa- 

 ter, the salt water will gradually work its way out through the pores 

 of the bladder, and, at the same time, the fresher water will enter the 

 bladder ; and, further, the fresh water will go in much more rapidly 

 than the salt water goes out. The result will be that the amount of 

 water in the bladder will be increased. The bladder will swell by tak- 

 ing up more water than it loses, while at the same time it loses a por- 

 tion of the salt. 



It does this in obedience to a physical law, to which the terms os- 

 mose and dialysis are applied. In accordance with this law, if a mem- 

 branous sac holding salts in solution is immersed in a more dilute solu- 

 tion, or in pure water, the more concentrated solution will pass out, 

 and at the same time the water, or more dilute solution, will pass in, 

 and more rapidly. The escape of the concentrated and entrance of 

 the dilute solution will be, in general, the more rapid the greater the 

 difference in concentration and the higher the temperature of the two 

 solutions. After the osmose has proceeded for a time, the two solu- 

 tions will become equally diluted. "When this equilibrium between 



* The following statements are adapted from a paper presented to the last meeting of 

 the American Fisheries Association. 



