In the Middle Ages, the study of medicine consisted largely of mastering the theories of Galen, a Greek physician active in the second century AD. Among his insights, he imagined that, just as the physical world was made up of the four elements fire, water, earth, and air, so also were humans were made up of four humors: blood, black bile, yellow bile, and phlegm. Each person had a unique combination of humors, which determined his personality; I like to point out that the adjectives sanguine,* melancholic, choleric, and phlegmatic derive from Galen’s theory of humorism (not that any of my students has ever heard of these words, alas). Illness was caused by your humors getting out of balance: unfortunately, a naturally melancholic person who had acquired an excess of blood did not get temporarily happy, he just got sick, and it was the doctor’s job to determine the person’s unique blend of humors, and to try to bring them back in proper balance. One way to do this was to prescribe a substance with the opposite qualities of the excess humor. Humors were either hot or cold, and either wet or dry, as illustrated by this table:
So if you had a disease that caused an excess of phlegm (cold and wet), you took something like pepper (hot and dry) to counter it. In the opposite direction, oil of earthworms was cold and wet, and so was useful against anything producing an excess of yellow bile, which was hot and dry. And so on.
Another way to counter an excess humor was to employ some way of removing it from your body. Getting bled by leeches (or simply by being cut by a barber) was a common way to get shed superfluous blood, while purgatives (either emetics or laxatives) took care of the others.
I suppose there may have been a placebo effect with such treatments but it’s easy to see how visiting a doctor in the Middle Ages was useless at best, and positively harmful at worst.
I don’t wish to condescend to the Middle Ages too much; I am a medievalist, after all, and part of my job is to rehabilitate them from the popular notion that it was a dark, ignorant, superstitious, and backward time. Some of their theories are models of subtlety, and they make complete internal sense. The main problem is that the theories were treated as ends in themselves – and did not actually have any relation to reality. Or rather, they “worked” enough that they just kept on going.** Only with the Scientific Revolution, which featured such things as the accurate collection of data and experimentation to test one’s hypotheses, were Galen’s (and Ptolemy’s, and Aristotle’s) theories seriously challenged. And even then humorism was not completely demolished until the nineteenth century.
But there’s nothing particularly medieval about devotion to elaborate and plausible-sounding theories that aren’t really true (e.g. Marxism, Freudianism, etc.).
* I recently read an interesting use of “sanguine” on Mitch Berg’s Shot in the Dark blog, about the Korean War defector No Kum-Sok:
Parts of the story were less sanguine; while his father was already dead and his mother had fled to the south before the war, No’s uncle and all members of his family apparently disappeared. And No’s commander and five other pilots were executed.
But this use of “sanguine” is somewhat ironic. “Sanguine” generally refers to something happy or jovial. But the disappearance of No’s family and the executions of his comrades were also “bloody” in the other, more usual sense. I would have picked a different word here.
** Theodore Dalrymple once wrote that:
The Galenical theory was an article of uncritical faith for university-trained physicians. Training consisted of indoctrination, memorization, and regurgitation. No deviation was permissible, and even refinement or elaboration was hazardous. Outright challenge was professionally dangerous. The theory therefore took many centuries to overthrow; mastery of it, and the treatments it entailed, distinguished real physicians from mere empiricks and quacks.