Medicine: System for Survival

One sultry weekend, David Barr, 24, of Joliet, Ill., headed for Crab Orchard Lake in the southern part of the state. In his impatience to escape the heat, Barr dived right in without first testing the depth of the water, plummeted to the bottom and broke his neck.

Such critical accidents are not uncommon. "Trauma"—which in medical parlance includes injuries from all accidents—trails only heart disease and cancer as the nation's leading killer, and claims more than 100,000 American lives a year. However, Barr was more fortunate than most accident victims: he lived in...