There was once a time when humans viewed the insides of their bodies as being made of Earth, water, fire and air.
Agents of Metabolism
The Four Humors are the metabolic agents of the Four Elements in the human body. The right balance and purity of them is essential to maintaining health. The Four Humors and the elements they serve are as follows:
BLOOD - AIR PHLEGM - WATER YELLOW BILE - FIRE
BLACK BILE - EARTH
All four of these humors, or vital fluids, are present in the bloodstream in varying quantities: Blood, or the Sanguine humor, is the red, hemoglobin-rich portion. Phlegm, or the Phlegmatic humor, is present as the clear plasma portion. Yellow Bile, or the Choleric humor, is present as a slight residue or bilirubin, imparting a slight yellowish tint. Black Bile, or the Melancholic humor, is present as a brownish grey sediment with platelets and clotting factors.
The Earl of Newcastle had a special night cap with a hole in the top to vent
humours. That was the 17th Century.
Them Greeks knew what they were doing!