We hope you'll humor us as we mark the 1881 founding of the American Red Cross with a sanguine look at bloodletting. (来源：http://www.EnglishCN.com)

We used sanguine in its sense meaning "self-confident," but sanguine—from the Latin word for blood—also means "bloodthirsty; murderous;" as well as "extremely optimistic."

While it's easy enough to understand how the Latin word for blood developed into a word with senses meaning "murderous" and "bloody," the "extremely optimistic" sense may require a bit more explanation.

Blame it on humorism, the ancient theory that four bodily humors determine a person's health. According to practitioners, an excess of phlegm makes a person phlegmatic; too much black bile makes a man melancholic; a surfeit of yellow bile creates a choleric temperament; and a plethora of blood leads to sanguinity, high color, sturdiness, and cheerfulness.

Where does bloodletting fit in this scenario? As you might have suspected, bloodletting, the controlled release of blood, was once performed in order to help restore a person's balance of humors. And while a doctor would have recommended the bloodletting, the surgery itself would have been performed by a barber, as indicated by his red and white striped pole. The pole itself represents the staff squeezed by patients to make their veins dilate; the white and red represent a tourniquet and bloodied bandages respectively.