The Black Death The Black Death, also called Bubonic Plague, was a devastating disease that killed almost 50% of the population of Europe, and nearly one-fifth (%) of the world's population in the 1300's. At that time, most of Europe was ruled by a feudal system, in which a wealthy upper class owned much of the land, and poorer peasants farmed the land. The population of cities was also increasing at this time, but these Medieval cities did not have modern facilities that help maintain hygienic (clean) conditions for the inhabitants. For example, it was common practice for people to throw garbage and human waste directly into the streets. Population of Medieval Europe Year Percent Population in millions increase 1100 62.1 10 1200 68 9.5 1300 78.7 15.7 1400 78.1 -0.8 The Black Death occurred in the late 1340's Scientists have studied ancient skeletons from the Medieval period in Europe to better understand what might have happened during the plague. According to one such scientist, Dr. Sharon DeWitte, many of the people that died from the Black Death were elderly, frail, and malnourished. Based on an analysis of over 700 skeletal remains, "the disease apparently removed the weakest individuals on a very broad scale over much of Europe, whether their frailty was due to poor immune systems, prior disease, or malnutrition." The Black Death is caused by a bacterium called Yersinia pestis. Bacteria are microscopic organisms that live everywhere in our environment, as well as on and inside our bodies. Most bacteria are actually harmless, or even beneficial. However, some like Yersinia pestis, are pathogenic (cause disease). Yersinia pestis is often found in rodents like rats. Rats, which were common in Medieval cities, often had fleas on them. The fleas bit the rats, then jumped onto humans and bit them, which spread the disease to humans. Once the disease was in a person it was often able to spread from person to person through body fluid and coughing. Once inside the body, the bacteria quickly multiply and damage tissues in the lymphatic and respiratory systems causing fever, vomiting, and large boils on the body. Rat contracts the bacterium Yersinia Pestis Flea jumpe on al and bies Tand has a bibod in is mouth Flea jumps on human and bites mixing rat and human blood and giving human Yersinia Pestis