The Black Death was an infamous plague causing an estimated 20 million deaths in Europe. Its spread and impact is disputed, but it does give an insight into a medieval way of life. All the conditions were right for an epidemic. Doctors were powerless against infectious disease. People were weakened by war and harvest failures. Germs, the fleas which carried them, and the rats which carried the fleas, flourished in the dirty towns. Busy trade routes carried the plague from one place to another. The plague arrived at Melcombe Regis in Dorset in June 1348 and it spread throughout the south of England. In 1349 it reached Wales, Ireland and the north of England. By 1350, it had made it to Scotland. Estimates suggest as much as half the population died. More
Poor medical knowledge. Medieval doctors did not understand disease, and had limited ability to prevent or cure it. So, when the plague came, doctors were powerless to stop it.
Medieval European medicine was very different from our modern concept of medicine. There was no knowledge of germs, and only relatively basic tools to diagnose and treat illness. Much of medicine was, at best, based on ancient Roman and Greek ideas of the 'humours'. The ideal was to balance specific fluids known as 'black bile', 'yellow bile', blood and phlegm (the fluids made by your ear, nose and throat). To be in a bad or good humour was evidence of how healthy you were! Other doctors would release "evil spirits" by trepanning (drilling a hole in your head to release them). In this context it is not surprising that the causes listed below emerged.
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