The concept of four humors may have origins in Ancient Egyptian medicine[REF] or Mesopotamia,[REF] though it was not systemized until ancient Greek thinkers[REF] around 400 BC directly linked it with the popular theory of the four elements: earth, fire, water and air (Empedocles).
Fåhræus (1921), a Swedish physician who devised the erythrocyte sedimentation rate, suggested that the four humours were based upon the observation of blood clotting in a transparent container.