The deadly outbreaks of anthrax in the nineteenth century baffled farmers who were raising their cattle in fields that had been cleared of any infected animals. They did not understand the cause of the recurring outbreaks which killed farm animals as well as their handlers.

In humans, anthrax may manifest itself as malignant pustules (the cutaneous form of the disease), which could be contracted from the bristles of a shaving brush containing the spores, or from exposure to hides or blood of infected animals. Anthrax pneumonia (inhalation anthrax), or "wool sorter's disease," was prevalent among those working with hides and wool. An intestinal form of the disease resulted from eating anthrax-contaminated meat.

Rod-shaped organisms, Bacillus anthracis, were discovered in the blood of anthrax-infected animals as early as 1850 by French physician Casimir Joseph Davaine (1812-1882), who postulated that these organisms cause the disease. In 1876 Robert Koch, demonstrated that these...