Technology & Medicine › Electric age › Germ theory of disease
Robert Koch
1843–1910; anthrax 1876, TB 1882· Person· Germs, drugs & genetics
Well documentedSolid records, physical evidence or scientific consensus.
German country doctor turned microbiologist who proved specific bacteria cause anthrax, tuberculosis and cholera, and set rules for proving it.
See it on the Technology & Medicine map →How it works
Working from a home lab in Wollstein (now Wolsztyn, Poland), Koch showed in 1876 that a bacterium causes anthrax, tracing its full life cycle. He developed ways to grow pure cultures on solid media such as gelatin and agar, and to stain and photograph bacteria. On March 24, 1882, in Berlin, he announced the tuberculosis germ; TB then caused about one in seven deaths in Europe. In 1883–84 he identified the cholera germ in Egypt and India. He won the 1905 Nobel Prize.
Why it mattered
Koch turned germ theory from argument into method. His rules and lab techniques let others find the causes of diphtheria, typhoid, plague and more within about 20 years.
Think of it like
His postulates work like a chain of custody: find the germ in every case, isolate it, reproduce the disease, then recover the same germ.
Legacy and how we know
His published papers and 1882 Berlin lecture; his photographs of bacteria; the postulates as written up by his student Friedrich Loeffler in 1884; the Robert Koch Institute in Berlin, which carries his name.
Still unknown or debated
Historians weigh his 1890 fiasco, a secretive TB 'cure' called tuberculin that failed, against his achievements; tuberculin survives as a TB skin test.
Connections (4)
▸Microscope revealed the germs identified by Robert KochMostly agreed
The connection
Bacteria are a few thousandths of a millimeter long, so finding them took good lenses. Koch traced the fairly large anthrax germ in 1876 and stained and photographed bacteria from 1877. From 1878 he used Ernst Abbe's oil-immersion lens and light condenser, made by Zeiss, which let him find the much smaller tuberculosis germ in 1882.
When and how
Wollstein and Berlin, Germany, 1876–1882, with lenses from Carl Zeiss's workshop in Jena, designed by physicist Ernst Abbe.
How sure are we?
Koch's papers credit the Abbe condenser and oil-immersion lens, and his 1877 paper included some of the first photographs of bacteria taken through a microscope.
Debates and open questions
Leeuwenhoek saw bacteria in 1676, two centuries earlier; why linking them to disease took so long involves ideas and lab methods as much as lenses.
▸Robert Koch gave rigorous proof to the Germ theory of diseaseWell documented
The connection
Pasteur made germ theory persuasive; Koch made it provable. He linked one microbe to one disease, grew it in pure culture, and showed it caused the disease in animals. Those steps, later called Koch's postulates, became the standard test, and his 1882 tuberculosis discovery won over most remaining skeptics.
When and how
Germany and abroad, 1876–1884: anthrax in Wollstein (1876), tuberculosis in Berlin (1882), cholera in Egypt and India (1883–84).
How we know
His published papers and lectures, and the rapid identification of other disease germs by his students and rivals using his methods.
Debates and open questions
Some germs, such as those of leprosy and syphilis, fail his postulates because they are hard to grow; in 1892 rival Max von Pettenkofer drank cholera broth to disprove Koch, and survived.
▸Robert Koch identified the TB germ targeted by Streptomycin and the cure for TBWell documented
The connection
In 1882 Koch identified Mycobacterium tuberculosis as the cause of TB, then the deadliest disease in Europe. Knowing the exact germ meant drugs could be tested against it in the lab. Waksman's team checked soil microbes against the TB bacterium, and streptomycin was the first they found that stopped it and was safe enough to treat patients.
When and how
Berlin, March 24, 1882 (Koch's announcement, now marked as World TB Day); Rutgers University and the Mayo Clinic, 1943–45.
How we know
Koch's 1882 paper and the 1944 streptomycin papers, which report lab tests against the TB germ Koch had described.
Debates and open questions
Koch's own TB 'cure', tuberculin (1890), failed badly. Why the TB germ resists drugs so well, partly thanks to its waxy cell wall, still shapes research.
▸Stethoscope (Laennec) diagnosed the TB whose germ was found by Robert KochWell documented
The connection
Laennec's stethoscope, and the chest sounds he catalogued, let doctors diagnose tuberculosis in living patients and match it to lung damage seen at autopsy. He argued its many forms were one disease. Koch confirmed this in 1882 by finding its single cause, the tubercle bacillus.
When and how
Paris, Necker Hospital, 1816–26 (Laennec, who himself died of tuberculosis in 1826); Berlin, March 24, 1882 (Koch).
How we know
Laennec's 1819 book 'On Mediate Auscultation' describes TB in detail; Koch's 1882 lecture names the germ. The link is diagnostic and conceptual.
Debates and open questions
Laennec's view that all forms of TB were one disease was disputed in his day, and how TB spreads within households was argued for decades after Koch.