Jean-Baptiste Denys

Jean-Baptiste Denys (ca. 1640–1704) was a French physician. He was the personal physician to King Louis XIV.

On June 15, 1667, Jean-Baptiste Denys administered the first fully-documented human blood transfusion. A 15 year old boy, bled too many times to count by other doctors because of a fever, was given nine ounces of lamb's blood. The boy recovered, but other attempts at transfusion failed and the practice was soon outlawed by the Parisian municipal council.