Robert Koch named the germ behind tuberculosis

On March 24, 1882, Robert Koch stood before the Berlin Physiological Society and announced he had found the cause of tuberculosis: a slow-growing bacterium later named Mycobacterium tuberculosis. Using more than 200 microscope preparations and a painstaking new staining method, he had made the elusive tubercle bacillus visible at last.

The stakes were enormous. Tuberculosis, then called consumption or the “white death,” was claiming roughly one-seventh of Germany’s population. Many believed it was inherited; Koch proved it was infectious, caused by a specific organism that could be grown and transmitted.

The lecture made him famous overnight and helped found modern bacteriology, supplying the rigorous logic now known as Koch’s postulates. He received the 1905 Nobel Prize in medicine for the work.

The World Health Organization later fixed the anniversary as World TB Day, a yearly reminder that a disease Koch diagnosed still kills over a million people annually.