Hippocrates (460–377 BC) postulated that the imbalance or excess of four fluids (called humors) within the body play a role in ones emotional and physical state. The chart below shows the four humors (row 1), the condition created by too much of each (row 2), and their respective emotions (row 3):


The Hippocratic theory of personality popularized the practice of bloodletting — opening a vein or applying leeches to "drain off" excessive amounts of the troublesome humor. In medieval Europe, it was common for barber-surgeons (whose professional practice relied on sharp instruments like knives and razors) to advertise their bloodletting services by posting a sign depicting a pale human arm traced with a crimson spiral of blood. (Remember that a ...