Across many cultures, humans have regarded blood as a substance with important regenerative properties since long before blood transfusions became feasible as a form of medical therapy. The idea of transferring new blood to a sick person to restore his or her health is quite old, but until the modern era it was only possible in the realm of myth. In the Odyssey, for example, Odysseus is able to temporarily revitalize shades in the underworld—allowing them to communicate with him—by giving them the blood of a sacrificed animal.
The two scientific breakthroughs that made blood transfusion conceivable as a medical treatment were William Harvey’s pioneering description of the circulation of blood through the body, published in 1628, and Christopher Wren’s invention of a syringe for injecting substances intravenously around 1659. Soon physicians in England and France began experimenting with transfusions between animals. In 1666 the English physician Richard Lower performed the first successful transfusion between animals.
On June 15, 1667, the first direct blood transfusion to a human was performed by the physician Jean-Baptiste Denis, when he gave a feverish young man approximately 12 ounces of blood taken from a lamb. The young man recovered quickly. Shortly afterward, Denis performed another transfusion that also appeared to be successful. The third and fourth transfusion patients fared badly, though. The third died shortly after having a transfusion, and the fourth died while a transfusion was in progress. The fourth patient’s wife accused Denis of murder. He was brought before a court and cleared of wrongdoing, but the court also ruled to ban blood transfusions. The French parliament, the Catholic Church, and the Royal Society soon passed their own bans on blood transfusions, and the procedure ceased to be used in mainstream medicine until the mid-19th century.
We now know that there was no way to perform a blood transfusion safely prior to Karl Landsteiner’s discovery of blood types in 1900–01. Mixing blood from two non-compatible blood types causes an immune response that can be fatal. It’s possible that this caused the death of one or both of Denis’s patients, although we can’t be certain.