Medieval urine wheel and the four humours. Labelled in Latin, this 15th century diagram shows possible colours of urine (flasks on outer edge of circle) to help doctors diagnose urine-related diseases. The four corner circles indicate the four humours (black bile, yellow bile, phlegm and blood). The inner circles indicate the different stages of percolation of the urine. Artwork from Fasciculus Medicinae, a collection of medieval medical manuscripts, published in Europe, that date from 1491.