The four humours, coloured historical artwork. Here, the head of Christ is surrounded by four male figures, who are personifications of the four humours. These are the essential bodily fluids: black bile (Melancholic, upper left), blood (Sanguine man, upper right), phlegm (Phlegmatic, lower right) and yellow bile (Choleric, lower left). It was thought that imbalances in these humours led to illness, but that they could be redressed by changing the diet, taking medicine and by undergoing surgery or bloodletting. This illustration is originally from the Guild Book of the Barber- Surgeons of York, which was printed in the 16th century in York, England.