Before the eighteenth century the demographic impact of the profession of medicine remained negligible. Relatively few persons could afford to pay a doctor for his often very expensive services; and for every case in which the doctor's attendance really made a difference between life and death, there were other instances in which even the best available professional services made little difference to the course of the disease, or actually hindered recovery.... Only with the eighteenth century did the situation begin to change; and it was not until after 1850 or so that the practice of medicine and the organization of medical services begin to make large-scale differences in human survival rates and population growth.

Ch.6. - Plagues and Peoples (1976)