From Draining Blood to Giving It

For over two thousand years, physicians prescribed bloodletting as the remedy for nearly every ailment. Hippocrates endorsed it in ancient Greece. Galen systematized it in Rome. Medieval barbers hung red-and-white-striped poles outside their shops to advertise the service. Generation after generation, doctors opened veins with lancets, applied leeches, and drained their patients — sometimes fatally — believing that removing blood would restore health.…