The Dark Ages (2007): Discovering the Plague
Medieval cities are full of rats and therefore full of fleas. These fleas can carry yersinia pestis, a bacteria believed to be one of the sources of the Black Death in the form of Bubonic plague Infections in the lung could cause pneumonic plague. Scientists still debate the source of the Black Death as the shear speed and scale of the devastation is difficult to attribute to Bubonic plague. Cutting edge investigations, including examinations of DNA in tooth pulp, continue.