Hippocrates and Galen theorized that the human body contained four fluids, or humors - blood, phlegm, yellow bile, and black bile. A balance of these was required for good health, and disease was blamed on imbalance. This belief continued through the middle ages, and illustrations of the various natures caused by the humors appear in medical texts, including LJS 463, a 15th century collection of medical and astrological texts from Germany. Clockwise from top left: melancholy (black bile), phlegm (phlegmatic), sanguine (blood), choleric (yellow bile).