Hippocrates, an ancient Greek physician whose "Hippocratic Oath" is still in use today, is credited with developing the theory of the "four humours" of the body, which are elemental temperaments that must be kept in balance to prevent disease. The four humours are blood, phlegm, black bile, and yellow bile. Each relates to an element and a state of being (dry/damp, etc.), and shows some similarities to understandings of the body in Traditional Chinese Medicine (TCM). The theory of the humours first originated in Egypt and Mesopotamia.