In 1877, Pasteur demonstrated that anthrax could be transmitted through infectious material containing the disease organism and its spore-forming stage. His experiments helped establish that anthrax was caused by a living microbe rather than by a vague chemical poison or spontaneous process.
Pasteur and Jules Joubert cultured anthrax organisms from the blood of infected animals and transferred the cultures into healthy animals. Repeated cultivation and inoculation showed that the infectious agent could multiply outside the original host and still reproduce anthrax.
The result built on Robert Koch’s 1876 work identifying Bacillus anthracis and tracing its development, including spore formation. Pasteur’s contribution was to strengthen the experimental case for microbial transmission and later apply the findings to vaccination.
The famous anthrax-vaccine demonstration came afterward. In 1881 at Pouilly-le-Fort, vaccinated sheep survived exposure to virulent anthrax while unvaccinated animals died. That experiment proved protection, not the original transmission principle.