Jean-Baptiste Denys administered the first documented human blood transfusion on June 15, 1667. He transfused sheep's blood into a 15-year old boy, who had been bled with leeches 20 times. The boy's condition improved. Later, however, another patient died after receiving a transfusion, & Denys was tried for murder & acquitted. It was later determined that the patient's wife had poisoned him with arsenic. Denys left medicine following this incident.