When Francisco Pizarro's conquistadores began pushing their way up the coastal valleys of Peru, a fourth of them sickened and died of a strange fever. Others suffered for months from hideous warts.
In those same valleys, the fever and the warts still lingera threat to strangers, though seldom to the natives. One fever outbreak killed 7,000 workmen and stopped the building of a railroad. But for 300 years the connection between the fever and the warts was unrecognized. Then in 1885, Daniel Carrión, a medical student, inoculated himself with fluid from a patient's warts....