ALS in French, signed “L. Pasteur,” one page both sides, 5.25 x 8.25, October 30, 1888. Handwritten letter to a friend with important scientific content about cholera, in part: "We have just had a conference, Monsieur Marey and I, with Gamaleia…Ever since 1884 Chantemesse has maintained by successive cultures the Koch microbe taken from a choleraic body. Dr. Chantemesse will send it to you himself, since Gamaleia…will start the experiments under your supervision…to arrive, by the end of this week, at the hot virulence caused by the flight of pigeons." In very good to fine condition, with edge wear and light overall creasing.