The notion of draining blood from a patient in the theory it will make them feel better only made sense when people believed that disease was caused by four bodily “humors” — blood, phlegm, yellow bile and black bile. Purging, starving, vomiting and bloodletting were ways to restore humor imbalances.

It was all in vein. Case in point: Dr. Benjamin Rush, one of the signers of the Declaration of Independence, was a strong advocate. In 1799, he treated his good friend George Washington for acute laryngitis by draining nine pints of blood in 24 hours. The average adult holds eight to 12 pints of blood. Washington died soon afterward.