Jean-Baptiste Denys, personal physician to France’s Louis XIV, is generally credited with performing the first human blood transfusion, although some sources award that distinction to Englishman William Lower. What is not in dispute is the year — 1667 — and the patient — a 15-year-old boy who had been bled so much by his doctor that he required an infusion of blood.
The source is also not under dispute: Whoever the physician was, he used a sheep’s blood. And, somehow, the kid recovered.
Subsequent transfusions using sheep’s blood were not as successful, however, and the practice was eventually banned. Science was unaware of the danger not only of interspecies transfusions but of the fact that human beings possessed different, generally incompatible, blood types.
The four major blood groups were not identified until 1907.
Another discovery that advanced the science of blood transfusions occurred in 1901, when Viennese physician Karl Landsteiner demonstrated the presence of agglutinins and iso-agglutinins in the blood. Landsteiner’s work earned him a Nobel Prize.