The theory of the four humours

Greek Medicine from Hippocrates to Galen: Studies in Ancient Medicine Edited by John Scarborough Philip J. van der Eijk Ann Ellis Hanson Joseph Ziegler states, 

“The theory of the four humours (blood, phlegm, yellow bile, black bile) first appears in a fifth-century bc Hippocratic treatise called The Nature of Man, the only treatise from the Hippocratic Corpus to which we can attribute an author’s name.”

“It is the work of Polybus, Hippocrates’ student and son-in-law. Here, we see for the first time a very clear expression of the idea that the nature of man consists of four humours, and that the properties of each of these correspond to each of the four seasons, each humour predominating in the season which shares the same nature: blood, hot and wet, predominates in spring; yellow bile, hot and dry, in summer; black bile, cold and dry, in autumn; and phlegm, cold and wet, in winter.”

“Good health is defined as the balance and mixture of the humours, whilst their imbalance and separation is the cause of disease. “

“To avoid this imbalance, the doctor recommends modifying one’s regimen according to the seasons. The predominance of the humours varies not only according to the seasons, but also according to age.”