Koch and the anthrax bacillus

Anthrax was common among farm animals around Wollstein, where Robert Koch was district medical officer from 1872 to 1880. Pollender, Rayer and Davaine had already described the anthrax bacillus, and others had passed the disease on with the blood of sick animals. Koch, cut off from libraries and other scientists and working around a busy practice, set out to prove that the bacillus itself caused the disease.

His laboratory was the four-room flat where he lived, and apart from a microscope his wife gave him he supplied his own equipment. Using home-made slivers of wood, he inoculated mice with material from the spleens of animals that had died of anthrax. Those mice died, while mice given spleen blood from healthy animals stayed well. The Science Museum's account adds that he repeated the transfer through 20 generations of mice.

That still left open whether the bacillus alone was responsible. Koch grew it in pure culture in the aqueous humour of ox eyes, watched it multiply, and drew and photographed what he saw. When conditions turned against them, especially for lack of oxygen, the bacilli formed round, resistant spores, which became bacilli again when conditions improved. Bacilli kept for several generations in culture, with no contact with any animal, could still cause anthrax.

Koch took his results to Ferdinand Cohn, professor of botany at Breslau, who called colleagues, among them the pathologist Cohnheim, to watch a demonstration. Cohn published the paper in 1876 in the botanical journal he edited, and Koch became famous almost at once. He stayed in Wollstein four more years, improving ways to fix, stain and photograph bacteria, and he later made solid growth media from broth set with gelatine or agar, which others used to find the causes of tetanus and plague.