Louis Pasteur’s 1881 vaccination experiment with sheep successfully prevented anthrax. At Pouilly-le-Fort in France, vaccinated animals survived exposure to virulent anthrax while the unvaccinated control animals died.
Pasteur and his collaborators used weakened anthrax preparations to stimulate protection without causing the full disease. The public demonstration became a landmark for the germ theory of disease and for the principle that deliberate exposure to a weakened form could protect against a dangerous infection.
The experiment included a crucial control group. Without unvaccinated animals exposed to the same challenge, survival in the vaccinated group would have been much harder to interpret. This comparison is one reason the event remains important in discussions of experimental design.
Pasteur later developed a rabies vaccine, but that was a different achievement. The famous sheep demonstration is specifically associated with anthrax, caused by the bacterium Bacillus anthracis.