How did Robert Koch show that anthrax spores could survive for years?

Robert Koch demonstrated the longevity of anthrax through a series of meticulous laboratory experiments. By cultivating anthrax organisms in suitable media on microscope slides, he observed their growth into long filaments and identified the formation of oval, translucent bodies, which he recognized as dormant spores.1

Koch discovered that these dried spores could remain viable for years, even when exposed to harsh conditions. This finding provided a critical explanation for why the disease would reappear in pastures that had been unused for grazing for long periods: the dormant spores could develop into the rod-shaped bacteria, or bacilli, that cause anthrax when environmental conditions became favorable. This discovery of the anthrax life cycle offered the first definitive proof of a causal relationship between a specific microorganism and a specific infectious disease.1