The four humours. Diagram showing the relationship between the four humours, basic qualities of the body and its diseases, and nature and the seasons. This theory dates back to the time of the Ancient Greeks, and was also used in Arabic medicine and medieval Europe. In the nineteenth century, it was slowly replaced by modern medicine. The concentric circles surrounding health show: the life stages, the seasons, the four classical elements (Fire, Earth, Water, Air), the modern and ancient names of the four humours (yellow bile, choleric; black bile, melancholic; phlegm, phlegmatic; blood, sanguine) and the known heavenly bodies (Sun-Mars, Saturn, Moon-Venus, Jupiter). The quarters of hot, dry, wet and cold are also shown. The theory tried to explain diseases in terms of excesses of these four humours in the human body.