In 1667, a French doctor transfused lamb blood into a human patient — and it somehow worked. Then his third patient died, and a murder trial followed.
In 1667, France and England were racing to be the first to achieve a successful human blood transfusion. The French Academy of Sciences and Britain's Royal Society were both conducting experiments, starting with dog-to-dog transfers. French physician Jean-Baptiste Denys and surgeon Paul Emmerez decided to move directly to humans.
On June 15, 1667, Denys transfused approximately twelve ounces of lamb blood into a 15-year-old boy suffering from severe fevers. By modern medicine, this should have killed the patient — human and animal blood are incompatible, causing catastrophic immune reactions. The boy appeared to recover. A second transfusion on a butcher also seemed successful, for reasons that likely had more to do with the tiny amounts used than any actual compatibility.
In November 1667, a nobleman named Antoine Mauroy was brought to Denys after suffering what we might now recognize as psychiatric episodes. His wife hoped transfusion might calm him. The first two procedures produced alarming symptoms — vomiting, dark urine, nosebleeds — but Mauroy survived. When his wife insisted on a third transfusion, Mauroy died the following day.
Denys was put on trial for murder. During investigation, it was discovered that Mauroy's wife Perrine had been secretly administering arsenic to her husband. The judge cleared Denys entirely — and imprisoned Perrine instead. But the ruling came with a condition: all future blood transfusions would require approval from the Parisian Faculty of Medicine, which effectively ended the experiments.
France's parliament banned human blood transfusion in 1670. England and the Pope followed with similar prohibitions. It would be 150 years before blood transfusion would be seriously attempted again, and another century beyond that before doctors understood blood types and why compatibility matters. Denis's reckless, lethal, and occasionally successful experiments were the beginning of a long road.