penny saved is a penny burned.

And all that corrosion may cause upset tummies or even ulcers for children and pets that happen to swallow modern copper coins, which are minted mostly with zinc, researchers are warning. Zinc and hydrochloric acid produce the same chemical reaction that occurs in car batteries.

Parents shouldn't panic when their child gulps down a penny, the scientists say. But if the coin hasn't passed in a day or two -- as is usual -- a child who is vomiting or having stomach pain probably should go to the emergency room, physicians from Duke University Medical Center warned last week in Chicago at the annual meeting of the Radiological Society of North America.

The Duke team became aware of the potential problem when a two-year-old boy came to the hospital with an upset stomach. An X-ray revealed a small disc, which was the remains of a 1989 penny ingested four days earlier. The boy had a small peptic ulcer where the coin had lodged.

Curious, the physicians bathed coins in a solution of hydrochloric acid, which the stomach produces to help digest food. They found that pennies made before 1982, which are primarily made of copper, remained mostly intact. But those produced after 1982, which are zinc with a thin copper plating, began dissolving immediately, the researchers said. Other coins are made of noncorrosive metals.

Last year, about 21,000 children were brought to U.S. emergency rooms after swallowing coins.

-Dallas Morning News