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, which allowed them to withstand the allergic reaction. Denys' third patient to undergo a blood transfusion was Swedish Baron Gustaf Bonde. He received two transfusions, and died after the second. In the winter of 1667, Denys administered transfusions of calf's blood to Antoine Mauroy, a madman. Mauroy died during the third transfusion. Much controversy surrounded his death. Mauroy's wife asserted Denys was responsible for her husband's death, and Denys was charged with murder. He was acquitted, and Mauroy's wife was accused of causing his death. After the trial, Denys quit the practice of medicine. It was later determined that Mauroy actually died from arsenic poisoning. Denys' experiments with animal blood provoked a heated controversy in France, and in 1670 the procedure was banned. It wasn't until after Karl Landsteiner's discovery of the four blood groups in 1902 that blood transfusions became safe and reliable.