Well, if you can find in a library somewhere, a copy of the book, Treatise of Melancholie, by English doctor Timorhy Bright, and published in 1586, that would be a good primary source, as he explains the humoral theory of medicine in all its aspects. Also, Robert Burton’s Anatomy of Melancholy, published in 1621.
Other references:
A History of Medicine, by Henry E. Sigerist
A Brief History of Medicine: From Hippocrates’ Four Humours to Crick and Watson’s Double Helix, by Paul Strathern
The Four Temperaments, A Rediscovery of the Ancient Way of Understanding Health and Character by Randy Rolfe
