The Hippocratic On the Nature of Man, and more particularly Galen's commentary on this text, forms the starting-point for the tradition on humoral theory. One of the reasons why this humoral theory became such a success (there were others around in antiquity) seems to be because of the authority of Galen.

The existence of fundamental biochemical substances and structural components in the body remains a compellingly shared point with Hippocratic beliefs, despite the fact that current science