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The Straight Dope 

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Do fish sweat? --Bill Bow, San Francisco

No. Lord knows I'd love to leave it at that, but as usual there's a little more to it. The primary purpose of sweating in mammals is to cool the body by means of evaporation, obviously a matter of no relevance to your typical fish. An incidental result of sweating, however, is the shedding of salt, and it turns out certain fish do possess special cells that enable them to unload extra sodium chloride.

The bodily fluids of saltwater fish are less salty than the seawater they swim in. Because of osmosis, the mechanics of which I won't bore you with here, saltwater fish are continually losing water. They have to replace this by (ahem) drinking like fish. Any excess salt they pick up in the process they get rid of through "salt cells" located in the gills.

Freshwater fish have the opposite problem. They're saltier than the water around them and thus have a tendency to absorb water. They combat this by absorbing what salt they can through special cells and getting rid of extra water by excreting large amounts of, well, pee. This can be a real problem if you are traveling with a freshwater fish on a long car trip. On the plus side, freshwater fish never (well, almost never) drink. If you get a little hammered some night and are presented with the choice of having fish from Sheboygan or Jersey City drive you home . . . well, not to cast aspersions, but I know which one I'd pick.

SPEAKING OF FISHY PHENOMENA

Cecil read with interest recent declarations in the newspapers that the famous eelskin wallet controversy, discussed in this column some months ago, has at last been solved. (The wallets had been blamed for demagnetizing automatic bank teller cards.) Unfortunately the newspapers, with their unerring instinct for the meaningless, managed to omit such details as what exactly the solution was, technically speaking. So I called up Katie Jarman, an assistant vice president at the Bank of America in San Francisco, to determine the facts. To my delight, I discovered that Katie, in the great tradition of Straight Dope Home Science, had undertaken an experimental regimen that would have done this column proud.

After a sudden rash of complaints about bad cards from eelskin-wallet owners, Katie and her colleagues examined the magnetic stripe on several failed cards and found that magnetic information had in fact been erased. They further noted that most of the complainers were women who used eelskin wallets with large magnetic clasps. As an experiment, Katie ran a variety of magnetic items over some test cards. Sometimes the cards became demagnetized, sometimes not. But when she ran an eelskin-wallet clasp over the cards, they always became demagnetized, even at a distance of two inches. A call to the fellow who owned the patent on the special donut-shaped magnet used on eelskin wallets confirmed that the magnet was unusually strong. Why you need a heavy-duty magnet on an eelskin wallet has not been made clear to me, but hey, not my problem.

Katie and company then ran a variety of eelskin products that didn't have magnetic clasps over the test cards. (Her boss, a sucker for kitsch, had picked up a boatload of souvenirs during a trip to Korea.) All the cards continued to operate normally. Conclusion: it's the clasp, not the eelskin itself, that does the demagnetizing. (The eel in question, by the way, is the hagfish, not an electric eel.) The Bank of America now advises its customers to keep their teller cards in a separate place to avoid demagnetization. It's also developing a protective jacket for the cards made of the antimagnetic coated paper used for computer disk sleeves.

Meanwhile, eelskin-wallet makers are scrambling to save their hides, so to speak. Katie says at least one company has come out with a polyester clasp. But for some it's too late. Two companies reportedly have already gone belly up. A slimy business, if you ask me. I think the whole thing stinks.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

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