Jean-Baptiste Denys (1643 – 3 October 1704) was a French physician notable for having performed the first fully documented human blood transfusion . Denys administered the first fully documented human blood transfusion on June 15, 1667. He transfused about twelve ounces of sheep blood into a 15-year-old boy, who had been bled with leeches 20 times. The boy survived the transfusion. Denys performed another transfusion into a labourer, who also survived. Both instances were likely due to the small amount of blood that was actually transfused into these people,