It’s true that modern sanitation and water treatment plays a very significant role in controlling the spread of disease-carrying organisms, but this is the result massive public works projects and modern, large scale, civic-funded programs. A physician dropped into the Dark Ages of Europe just isn’t going to have the wherewithal to effect public works on this scale (even though they had been done centuries before in China, Rome, and Constantinople). You might as well expect our time-traveling physician to put a stop to the spread of bubonic plague by isolating the rat population; he may well know what the vector of transmission is, but he’d have a very limited ability to do anything about it. A savvy doctor might be able to develop sulfa drugs or crude fungal antibiotics, and perhaps very limited innoculation, provided you could get people to accept the notion of rubbing cowpox pus into an open sore. Without modern laboratory apparatus, though, it would be largely guesswork and experimentation as to what he was getting from cultures.
Personal sanitation–particularly on the part of a physician going from one patient to another–would be a definite reduction in the transmission of disease, but only on a small scale. And the physician’s ability to treat major trauma, chronic illnesses, and malignancies without modern antibiotics, anesthesia, and other pharmaceuticals will be essentially limited to first aid. As Qadgop the Mercotan notes, most of the common ailments that physicians treat today, such as childhood diabetes, just aren’t going to exist, as they’re too debiliitating to allow the patient to survive into adulthood. Recommending good nutrition and preventative medicine are limited by available food sources, and few people are going to live long enough that the chronic illnesses of modern old age, like heart disease, are going to be the root cause of death.
I’d guess the major impact a physician would have in that circumstance is in childbirth and treatment of the illnesses and syndromes of early childhood. There are many serious complications in childbirth which can be lethal to both child and mother but are readily reduced by an experienced doctor, even equipped only with rudimentary tools. With careful precautions, sterile operating procedures, and at least some crude antibiotics, its possible that even Ceasarian sections might be conducted successfully. The illnesses of childhood, particularly chronic but not necessarily fatal illnesses like asthma or moderate diabetes, can also be treated via prevention or diet modification.
A good primer on this topic is the Hesperian Foundation book, Where There Is No Doctor, which is intended as a reference for health care workers in Third World countries. I’m not recommending it as any kind of replacement for modern health care and a qualified physician, but it does give an indication of what treatment is feasible outside of the context of modern pharmaceutical medicine.
Stranger
)- I’m sure there must be others that might have been growing wild. Coca for a local anesthetic, ephedra or ma huang as an antihistamine, cinchona against malaria, cannabis, valerian…