The four-humor story is more interesting than the usual “Hippocrates invented it and everyone believed it” version. A clear four-humor scheme of blood, phlegm, yellow bile, and black bile appears in the Hippocratic treatise On the Nature of Man, traditionally associated with Polybus, Hippocrates’ student and son-in-law. Health was explained as a proper mixture of these fluids; disease could result when their proportions or distribution went wrong.
But ancient Greek medicine was pluralistic. Historians emphasize that four-humor theory was only one of several competing fluid and disease models. It became a much more universal medical standard after Galen, the second-century physician whose enormous body of writing synthesized, commented on, and extended earlier Greek medicine. Galen’s influence helped bind humoral explanations to anatomy, diagnosis, diet, drugs, bleeding, and other therapies.
That later dominance is why this card’s quantitative lifespan begins in the Galenic era rather than with the first appearance of the four humors centuries earlier. Galenic medicine was transmitted through Byzantine, Islamic, and Latin scholarly traditions and became deeply embedded in medical education.
The collapse was correspondingly gradual. Anatomical discoveries, quantitative physiology, pathological anatomy, cellular theory, and germ theory did not replace humoral medicine in one stroke. Different pieces of the older framework lost explanatory power at different times. The card therefore represents the long dominance of Galenic four-humor medicine, not every ancient idea involving bodily fluids.