Robert Koch Identifies the Bacterium Behind Tuberculosis

On 24 March 1882, German physician and microbiologist Robert Koch addressed the Berlin Physiological Society to announce that he had identified the microorganism responsible for tuberculosis. At the time, the widespread and fatal affliction was frequently believed to be an inherited disorder rather than an infectious disease. Koch presented evidence demonstrating that a slow-growing rod-shaped bacterium, later classified as Mycobacterium tuberculosis, was the true causative agent behind the condition.

Koch had joined the Imperial Health Office in Berlin as a government advisor in 1880, bringing innovative laboratory techniques developed during his earlier career as a district physician. To visualize the pathogen, he utilized specialized staining methods, exposing tubercular matter to methylene blue in an alkaline potash solution before counterstaining with a brown dye. Under the microscope, the distinct blue bacilli stood out clearly against the surrounding tissue.