French microbiologist and chemist who demonstrated the germ theory of disease and developed techniques of inoculation, most notably the first vaccine against rabies. ANS in French, signed “L. Pasteur,” one page, 3.5 x 3.5, May 11, 1888. Translated from the French, in full: “I have the honor to respond to the favor of your request for my signature.” Loosely matted with a sepia portrait of Pasteur to an overall size of 13.5 x 9.75. In fine condition, with horizontal fold through the bottom of the paraph. COA John Reznikoff/PSA/DNA and R&R COA.