I knew that Koch was the first to conclusively demonstrate that bacteria caused diseases (tho he didn't discover the specific bacterium), but I had no idea that this was based on experiments with anthrax.
I also had no idea about this:
As Koch’s experiments went on, his backyard menagerie began to thin out; his daughter, Gertrud, grew concerned that she was losing all her pets. He needed a new pool of animals to experiment upon. Koch and Emma set live mousetraps in the horse barn behind their house. They caught a bounty and stuffed them into tall glass jars with some holes poked in the lid for air. When he needed an animal, he’d pull one out, tail first, using an old bullet extractor he’d saved from the war. After the mouse had died, ostensibly from the microbes, Koch would dissect it, searching for the bacteria—and then dispose of the cadaver by burning it in the oven. Later, he found a more dependable source of animals, after a friend sent Gertrud some white mice as pets. The animals began reproducing rapidly, and Koch began using the extra supply in his lab. These became one of his most iconic contributions to science: the white lab mouse.