In ancient times, the body was said to be controlled by four humours, related to the body fluids blood (sanguine/red), phlegm (phlegmatic), yellow bile (choleric), and black bile (melancholy). In addition to predisposition to certain diseases, an excess of one or another humor was associated with a particular appearance, personality, and/or personality disorder. While the theory is long discredited, the descriptions carry through to today: a sanguine personality is friendly and outgoing; a phlegmatic one, slow-moving or lazy; a choleric one, quick to anger; and a melancholic one, prone to sadness, discontent, or depression. (Interestingly, I haven't been able to find a relationship between diabetes — either major type — and an imbalance of one or more humours.)
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