First off, what we think of as doctors was really two disparate professions. Barber surgeons performed minor surgeries, and were generally not wealthy. On the other hand there were trained medical professionals from european universities. Germ theory was nonexistent, but medieval people were not stupid, and understood the concept of contagion. This was generally understood through the miasmic model, where disease was believed to be spread by bad odors and vapors. Many believed these vapors were released via earthquakes. These earthquakes were caused by celestial conjunctions, eclipses, etc, which were caused by God.

As for "cures" and treatment, medical knowledge was largely preventative. Plague doctors (who by the way did not wear the stereotypical mask until the 17th century) wrote consilia for individual italian city states, states, or individual nobles. Consilia means "plan" in latin, and this is pretty much what they were. The consilia laid out, to the best of their ability, all the medical knowledge gathered on the plague i.e. how it was understood to be spread (miasma), and how one could avoid it. Avoiding plague basically amounted to avoiding bad odors, and practicing moderation in exercise, food, drink, and sex. This was due to the galenic theory of humors, and it was believed that people with out of balance humors were more susceptible to plague. This also took on a moral component, as people who did not practice moderation in these things were seen as drawing God's ire. Consilia were not always written for individuals, and were also prescriptions for society at large. These measures largely consisted of keeping the streets clean, particularly of organs and excrement. Other doctors wrote that there should be large fires in the streets, so to combat the diseased air with smoke. The consilia also advised restrictions on the movement of people and goods, particularly goods like clothing which were believed to be able to absorb plague odors.

One example of a consilia is Gentile da Foligno's consilia contra pestilentiam, meaning "plan against pestilence". It consisted of four parts 1) causes 2) prevention 3) cure and 4) dubia which Arrizabalaga states, "...were written to stimulate the wits of medical students"

So to conclude, its hard to say whether they "made a difference". Doubtless, there was probably at least one victim of plague who died of blood loss from blood letting and was recorded as a plague death. At the same time, the consilia of plague doctors did contain useful information on avoiding plague, even if that information sometimes amounted to "run away". My personal thoughts on the matter are that they did the best they could with what they had, and were remarkably scientific despite knowing nothing of germ theory.

​

For further reading, I recommend reading Arrizabalaga's article "Facing the Black Death: Perceptions and Reactions of University Medical Practitioners". This is where most of my information is from. Shona Kelly Wray also examines the roles and perceptions of doctors in "Boccaccio and the doctors: medicine and compassion in the face of plague". I can point to other further reading on the Black Death that is not as relevant, but is still interesting if asked.

​