Robert Koch: Proving Germ Theory

Robert Koch (1843-1910) was a poor country doctor in Germany. One day his life took a new direction when an epidemic struck the local farm animals. The culprit was anthrax. Even though Koch was a doctor for humans, he decided to study this disease that is commonly associated with animals.

The Germ

Anthrax is a disease that can strike suddenly and seemingly without warning. Animals will be healthy one day and dead the next. It was also possible for the disease to sicken and kill humans. There was no cure for the disease outside of killing the animals.

Koch began his research on anthrax with a microscope his wife had given him and no other equipment. If he needed something, he would make it himself or use common everyday items such as dinner plates. As Koch examined the blood of the dead animals, he continued to notice the presence of a bacteria in the blood of the dead animals. He never found these bacteria in healthy animals.

At this time, there was still controversy over whether germs caused disease. Therefore, it was not clear if the bacteria were causing anthrax. This means that Koch had to investigate more closely as to what the bacteria in the blood meant. To confirm his findings, Koch conducted an experiment.

The Experiment

The experiment involved growing anthrax outside of the blood. Then the cultured anthrax was placed inside living mice. The mice were killed by anthrax with their blood containing the bacteria. This was the proof Koch needed that anthrax was the killer.

Koch also found that the bacteria could survive outside a liquid in a state Koch called spores. In this state, anthrax could survive extreme conditions—this helped to explain how contagious the disease. Killing animals was not enough. They needed to be burned or buried deep in the ground to prevent infection.

Sharing Results

The next step for Koch was to take pictures of the bacteria. Then he decided to share his findings. Koch was an outsider to academic life, and working in the countryside did not warrant the respect he needed at this moment. Nevertheless, he contacted a university, and they agreed to let him share his results. Koch didn’t lecture; instead, he repeated his experiments at the university. Students and teachers saw the mice die along with the pictures of anthrax.

The impact was unquestioned. Koch had shown that germ clearly caused disease. This laid to rest what was, at one time, a controversial idea that unseen microbes could make people sick. These ideas are far removed from what Galen was proposing several thousand years ago.


Koch did not necessarily find a cure for anthrax. Instead, he was able to confirm the theory of germs. This may not have been the goal, but it was a significant contribution to medicine that convinced skeptical experts. The person who would defeat anthrax was Louis Pasteur, the same person who developed germ theory.

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