- Technology - Koch’s assistant, Julius Richard Petri, invented the Petri dish. This enabled Koch to grow bacteria. He could then use industrial dyes to stain the bacteria. Finally, he could use powerful microscopes to identify the bacteria.
- Chance - Pasteur developed the chicken cholera vaccine when he left some cholera germs unrefrigerated before going on holiday. When his assistant, Charles Chamberland, injected these germs into a chicken on their return, the chicken did not become ill. Pasteur realised that the old germs had given the chicken immunity without making it ill.
- War - In 1870-1871, France and Germany were fighting each other in the Franco-Prussian War. This led to rivalry between Pasteur and Koch. Their respective governments invested in their research to show they had more advanced science and for national pride.
- Key individuals - Pasteur and Koch are both significant figures in the fight against disease. Their work relied on careful observation, scientific experiments, and years of work to develop new methods and treatments.