How did Robert Koch investigate the life cycle of anthrax?

Robert Koch investigated the life cycle of anthrax by addressing the mystery of why the disease reappeared in pastures that had been unused for long periods. While previous researchers had identified rod-shaped organisms in the blood of infected animals, the full natural history of the disease remained unknown.1

Koch conducted a series of laboratory experiments where he cultivated anthrax organisms in suitable media on microscope slides. He observed the bacteria growing into long filaments and discovered the formation of oval, translucent bodies, which he identified as dormant spores. Koch demonstrated that these dried spores could remain viable for years under exposed conditions.1

This discovery explained the recurrence of the disease: the dormant spores could develop into the rod-shaped bacteria (bacilli) that cause anthrax when conditions were right. By documenting this process, Koch provided the first convincing proof of a definite causal relationship between a specific microorganism and a specific disease, effectively completing the understanding of the anthrax life cycle.1