Whether growing nerves will reconnect properly--ensuring that a signal sent to a leg doesn't wind up at an arm--has always been a cause for concern. But there may be little reason to worry. Researchers now believe that advancing nerve endings carry chemical markers that guide them straight to receptors at their destination. "It's as if the body wants to be whole," says Reeve.

Skeptics warn against too much giddy hope that damaged spines will become whole anytime soon. Treatments may be many years off, they caution, and only incrementally helpful--restoring wrist motion to a person who has none, for example. Most researchers, though, are more optimistic. Over the course of 10 years, they say, the riddles of the cord have been solved. The question now is not what the treatments for an injured spine should be, but how best to implement them. At hospitals such as the Karolinska Institute in Sweden and the University of Florida, human trials are already getting under way. Studies at other hospitals are sure to follow. Says Black: "The astounding progress over the past decade dwarfs the progress of the past 5,000 years." Reeve may not stand up the day he turns 50, but the real possibility does exist that he will spend a future birthday on his feet.

Senior writer Jeffrey Kluger's latest book, about moons, is called "Journey Beyond Selene"

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