WHEN ARCHAEOLOGISTS translated 4500-year-old carvings on an Egyptian pyramid, they were surprised to discover medical advice that included the following item: “If a patient with a neck injury has loss of feeling in the arms and legs, it is because of a break in the spinal cord… . This condition cannot be treated” (New York Times, Sept. 30,1997, p. C1). Today, we still view spinal cord injuries as essentially untreatable for the simple reason that severed nerve tissues in the spinal cord do not regrow. It's as if you had cut off the limb of a tree-while the tree survives, the limb dies away and is lost. But trees can grow ...

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