Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by ...

Galen, a Greek physician, is born. He develops the theory of the four "humors": blood, phlegm, yellow bile and black bile. Good health is thought to result from a balance of the humors ...

Through this method, he made important discoveries about the circulation of blood and the workings of ... on Hippocrates's theories of the four humours. His medical writings were very influential ...