The theory of the four Humours was created by Hippocrates. According to the theory, it said that illness developed when there was too much or too little of a certain humour. There were four humours, black bile, yellow, bile, phlegm and blood. To try and cure the patients, the doctor would either try to re-balance the humours by bloodletting, or by telling the patients to rest, take care over their diet and in general to let themselves get better naturally. The theory of the four humours was widely accepted for 1,500 years, until it was proved to be wrong by Galen.