Ancient Ideas - The Work of Galen
Galen (born AD129) took Hippocrates' ideas and ran with them. This Roman doctor developed the theory of opposites - essentially a treatment manual for balancing the four humours.
Galen made genuine discoveries through animal dissection, like proving the brain controls speech. However, his reliance on animals instead of human bodies led to serious mistakes. He wrongly claimed blood passed through tiny holes in the heart's wall, when it actually flows through veins and arteries.
Medieval people had access to both natural and supernatural treatments. Supernatural methods included prayer, astrology, and trepanning (drilling holes in skulls). Natural treatments, encouraged by Hippocrates and Galen, included bloodletting and herbal remedies.
Remember: Galen's mistakes weren't corrected until much later because dissecting humans was forbidden, so doctors had to rely on his animal-based observations.