A frog frozen solid, heart stopped, that restarts when it thaws
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Imagine an animal whose heart stops, whose breathing vanishes and whose body becomes encased in ice, only to get going again quietly when spring arrives. This is the routine of the wood frog in North America.
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When frozen, it shows no detectable sign of life: no heartbeat, no breathing, no blood circulation. Roughly 65 to 70 percent of its body water turns to ice, mostly outside the cells. The freeze can last for weeks, even months.
Much of the secret lies in a sugar made by the liver. Glucose protects the inside of the cells and reduces the amount of ice in the body. In a laboratory experiment on frogs from Ohio, those that had received glucose survived at -5 °C, while all the control animals died.
Tolerance also depends on the season: frogs collected in autumn survived a two-week freeze, while those collected in summer did not. Cell damage still occurs, so recovery is not perfect.
