Plague doctor. Historical artwork of a doctor dressed in clothing to protect him from the plague. The long beak contained scented herbs, as the plague was thought to be caused by foul air. The shape of the hood led to these doctors becoming known as beak doctors". Plague occurred in epidemics in Europe in the Middle Ages, killing millions of people. It was caused by the bacterium Yersinia pestis, which was transmitted by the bites of infected fleas carried by rats. This illustration was made during the 1720 outbreak of plague in Marseilles, France."