Why did Robert Koch shift his research from algae to disease-causing organisms?

Robert Koch initially studied algae while working as a district surgeon in Wollstein, where he had established a small laboratory equipped with a microscope and other basic tools.1

His shift toward researching pathogenic (disease-causing) organisms was driven by his interest in the theory—previously proposed by his teacher Friedrich Gustav Jacob Henle—that infectious diseases are caused by living microscopic organisms. Koch was specifically inspired to investigate anthrax after observing that the disease recurred in grazing animals despite no apparent source of infection. His subsequent experiments, which successfully mapped the life cycle of the anthrax bacillus, provided the first convincing proof of a causal relationship between a specific microorganism and a disease. This breakthrough established him as one of the founders of bacteriology, leading him to dedicate his career to identifying the agents responsible for other major illnesses, such as tuberculosis and cholera.12345