De l'Atténuation des virus, avec la collaboration de MM. Chamberland, Roux et Thuillier. Quatrième Congrès international d'hygiène et de démographie. Séance du 5 Septembre 1882.

In his seminal 1880 paper, Sur les maladies virulentes, et en particulier sur la maladie appelée vulgairement choléra des poules, GM-2537, Pasteur developed the idea of a protective inoculation by attenuated living cultures, and subsequently adopted this principle with anthrax, rabies, and swine erysipelas. His work laid the foundations of the science of immunology. However, in that paper Pasteur did not reveal his method of attenuation until this paper presented in September 1882, and first published in 1883. The method developed by Pasteur and his team was  "heating the anthrax bacillus at exactly between 42 and 43 degrees centigrade for at least 5-6 hours.” Toward the end of his paper they stated, “It cannot be doubted that we possess a general method of attenuation…."

(Thanks to Juan Weiss for this reference and its interpretation.)