When the Celtic and Germanic tribes of Europe converted to Roman Christianity, they adopted a long-established written tradition of scientific principles. Their own herb lore continued, probably in many cases without reference to the new “science.” But it became, increasingly, the medicine of the countryside and the poor. Aristocrats wanted medical men trained in the Roman sciences.
The first underlying principle of Greco-Roman medicine was that each person is unique, in health as well as in sickness. We’re slowly coming back to partial acceptance of this idea with DNA definitions of how people differ. However, for a long time, one of our bedrock ideas has been that healthy people are fundamentally alike, and the diseases that make sick people different are also fundamentally alike. We deal in forests, not trees.
Greco-Roman medical practice identified diseases, but it focused more on balancing the four humors that every person was made of. In that one way people were alike, I suppose: they were made up of the same four elements, though in different combinations. The essence of disease was imbalance.
The physical world was already divided into earth, air, water, and fire. The body was similarly made of liquids that corresponded to these four elements. To a Roman doctor, we are made of blood, phlegm, yellow bile, and black bile. Every healthy person had a personal balance of these liquids, and every disease showed itself in signs of imbalance of humors.
The physical world also could be defined by the attributes of heat and water, and lack of heat (coldness) and of water (dryness). The four humors could be described in these terms also. Blood was hot and wet, while phlegm was cold and wet. The two kinds of bile were both perceived as dry; the black bile was additionally cold.
A healthy man could be defined by the humors that dominated in his system. If he was sanguine, it meant literally that he was full of blood. It would be considered normal for him to feel too warm frequently, and to be optimistic. Blood corresponded to air, which was warm and dry. The phlegmatic man had too much phlegm and was cold and wet, like water; he was resistant to action. The melancholy man had more black bile and was both cold and dry, like earth. The choleric man had yellow bile, was warm and dry, and got angry easily, like fire.
When doctors prescribed, they had to take into account the patient’s fundamental system as well as his symptoms of imbalance. Fever was a hot, dry symptom; diseases characterized by fever, like measles, were hot, drying disorders. They needed to be cooled and watered, to bring the system into balance again. A choleric man with a fever needed extra consideration; the fever might be a result of his system having cooled too much, so instead of cooling and hydrating, he might need more warming and drying.
The Greco-Roman system had the great advantage of logic. It organized everything neatly in basically one 2 by 2 table. Our culture may have a tendency to love binary options so much that we simply cannot resist a binary split by another binary.
The drawback was that the system had no factual basis; it was all theory.