March 24, 1882

Robert Koch

Robert Koch demonstrates the bacterial cause of tuberculosis

Koch did not stop at seeing the organism. He grew it, gave the culture to guinea pigs, reproduced the disease, and recovered the bacillus again.

24 March 1882: a reading room in Berlin

Robert Koch addressed the Physiological Society of Berlin in the reading room of the city's Physiological Institute on 24 March 1882, announcing the discovery of the tuberculosis pathogen.

His case rested on making slender bacilli appear blue against brown-stained tissue — a selective stain he had developed for the purpose.

A chain, not a glimpse

In 'The Aetiology of Tuberculosis' Koch presented linked evidence: specially stained bacilli appeared in tuberculous lesions; the organisms could be cultivated, with colonies taking 10–14 days to appear; cultured organisms produced tuberculosis when inoculated into guinea pigs; and the organism could be recovered from the resulting lesions.

He concluded that the bacilli caused tuberculosis and characterised the disease as infectious, giving public-health measures against transmission a specific microbial target.

Ehrlich leaves with a sample

Paul Ehrlich was in the audience. He obtained material from Koch after the lecture and immediately began improving the staining procedure.

The lecture was published in Berliner Klinische Wochenschrift on 10 April — seventeen days later — circulating the evidence well beyond the room.

Sources

Researched 23 Aug 2026 8 sources 3 audit passes

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

What the sources leave uncertain

The date, venue and substance of the announcement are well documented. The modern binomial Mycobacterium tuberculosis was not the name Koch used that evening; he referred to tubercle bacilli or the tuberculous agent.