On this day, 131 years ago, on August 25, 1894 (July 25, 1894 in the lunar calendar), Japanese biologists discovered the plague bacterium. On August 25, 1894, Japanese scholar Shisaburo Kitasuri and French bacteriologist A. Yerssen discovered almost simultaneously during the 1894 plague epidemic in Hong Kong that the pathogen of the disease was a bacterium. This bacterium was later named Yersiniapestis, also commonly known as Yersinia pestis. Plague, also known as the Black Death, is generally prevalent among mice or other rodent wild animals. Human plague is caused by rat fleas biting humans. The untreated case fatality rate of plague is as high as 50% to 70%. There have been several devastating plague pandemics in human history. Comments: Human progress