Ancient medicine was based on the four elements (air, earth, wind, and fire). The human body turned these elements into humors. All people belonged to one of four humors: sanguine, choleric, melancholic, and phlegmatic. People who were sanguine, for example, were thought to have more blood than people who were choleric, who were thought to have more bile. A sanguine person was calm, which was a function of the blood, whereas choleric people were easily angered, which was a function of the bile. To cure a sanguine person of a disease required bloodletting.
According to this passage,

