For centuries, doctors blamed almost every illness on four bodily juices
Blood, phlegm, yellow bile and black bile: Greek and Roman physicians believed health meant keeping these four fluids in balance, and illness came from too much or too little of one. Thanks largely to Galen's authority, the idea steered medicine for centuries, until the discovery of microbes finally disproved it.
The word humour translates the Greek chymos, meaning juice or sap. The notion may trace back to Egypt or Mesopotamia, and early Ayurvedic texts described three or four humours called doshas, but Greek thinkers turned it into a system. Alcmaeon of Croton, active around 540–500 BC, listed many humours; Hippocrates is usually credited with narrowing them to four bodily fluids and applying the scheme to medicine, though other Hippocratic writers accepted only two.
Galen, who lived from 129 to 201 AD, made the theory dominant through his commentary on the Hippocratic treatise On the Nature of Man. He tied each humour to qualities and seasons: blood hot and wet like spring, yellow bile hot and dry like summer, black bile cold and dry like autumn, phlegm cold and wet like winter. Warm foods were thought to breed yellow bile and cold foods phlegm, and geography mattered too, with cities exposed to hot winds supposedly prone to digestive troubles.
Besides an ideal balanced mixture, Galen described eight lopsided temperaments, but the four named after humours, sanguine, choleric, melancholic and phlegmatic, became the famous ones. For him temperament meant a bodily disposition that shaped susceptibility to disease as well as emotional leanings; the word only later shrank to mean personality. Oddly, he thought phlegm had no effect on character, while yellow bile brought sharpness and blood a certain simplicity.
Treatment aimed to drain the surplus by purging, inducing urination, or bloodletting. Bleeding was already common by the first century and gained importance once Galen declared blood the most plentiful humour; physicians took anything from a few drops to several litres over several days. The theory lost ground from the 17th century. Modern science still shares one broad idea with it: that the body is built from fundamental chemical substances.
Source: Humorism
