On this day 133 years ago, a young German physician stood up before the members of the Physiological Society of Berlin and announced he had found the cause of tuberculosis.
It is hard to overstate the importance of that day, and what Dr. Robert Koch did for the understanding of infectious diseases.
University of Michigan physician and medical historian Dr. Howard Markel says at the time of Koch's discovery, TB was probably the leading cause of death for anyone between 20 and 50 years of age.
Koch had been a country doctor, but after his work on anthrax, the city of Berlin made him head of the Imperial Health Institute.
With this position Koch had "the Cadillac of labs," as Markel calls it, surrounded by aspiring researchers and the best equipment.
Markel says Koch locked himself in his lab for months until he had found a way to pinpoint the micro-bacteria that caused TB.
Koch continued to make discoveries, including discovering the cause of cholera a few years later. His legacy was commemorated when he received the Nobel Peace Prize in 1905.