Blood transfusion is the process of transferring blood from one person into the body of another person. Folk medicine and ancient practice long considered blood to have beneficial, curative properties when swallowed. Actual transfusion was seldom attempted, however. Perhaps the earliest recorded case was that of Pope Innocent VIII (1432-1492), who was transfused in April 1492 with the blood of three young boys. The outcome indicated why transfusion attempts were rare and dangerous: the boys died.

After William Harvey (1578-1657) explained the mechanism of blood circulation in 1628, interest in transfusion was rekindled. An Italian physician, Giovanni Colle, gave the first concise description of a blood transfusion in 1628. An English clergyman, Francis Potter, seems to have experimented with transfusions in the 1650s. In the 1660s, the Royal Society of London sponsored a series of transfusion trials after Sir Christopher Wren (1632-1723), the famous architect, used a quill-and-bladder syringe...