John of Burgundy

Upon the arrival of the Black Death, the fourteenthcentury physicians of Europe found themselves completely at a loss. Bacteria and viruses were still unknown, and nobody realized that the disease was being transmitted among people and animals by the bite of infected fleas. The only certain prevention seemed to be complete isolation, as it was certain that people who came into contact with the sick were more likely to get the disease than those who held themselves aloof or escaped the affected cities altogether.

Nevertheless, many leading doctors did make an effort to apply the medicine they knew to this mysterious sickness. In 1365, John of Burgundy wrote one of the most thorough medical tracts concerning the Black Death. He theorized that the plague took the form of evil vapors which took root in the heart...