William Harvey had been appointed physician to St. Bartholomew’s Hospital in 1609, and already in 1616 as Lumleian lecturer had stated his theory of the circulation, but not until its publication twelve years later could it be generally known. His treatise entitled _Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus_, which appeared in 1628, may therefore be regarded as the point from which blood transfusion first arose. It has often been stated in the literature of the subject that the first transfusion was performed in 1492, when the blood of three boys is supposed to have been transfused into the veins of the aged Pope Innocent VIII.[1] This, however, seems to have been a mis-statement of the facts. Actually a Jewish physician prepared a draught for the Pope from the blood of three boys, who were bled to death for the purpose.[2] The drinking of blood was not a new idea; this particular incident is of no special interest, and may now be allowed to sink into oblivion. It is not until after the middle of the seventeenth century that authentic references to blood transfusion are to be found. The first is in the writings of Francesco Folli, a Florentine physician, who claims to have demonstrated the operation of transfusion of blood on August 13, 1654, to the Grand Duke Frederick II. There does not seem to be any confirmation of this in the writings of others. A few years later experimental work tending in the same direction was being done in England, and the inception of this was due to the ingenious Sir Christopher Wren, who in this connexion has not hitherto received the recognition that is his due. Dr. Wren, as he was designated at the time, was one of the most active members of the recently formed Royal Society, and was responsible for many new experiments in several sciences. It is clear from references in the _Philosophical Transactions_ that his first experiments were done in 1659, and the following statement is made by Dr. Thomas Sprat in his _History of the Royal Society_, published in 1667: “He was the first author of the Noble Anatomical Experiment of Injecting Liquors into the Veins of Animals. An Experiment now vulgarly known; but long since exhibited to the Meetings at Oxford, and thence carried by some Germans, and published abroad. By this Operation divers Creatures were immediately purg’d, vomited, intoxicated, kill’d, or reviv’d according to the quality of the Liquor injected: Hence arose many new Experiments, and chiefly that of Transfusing Blood, which the Society has prosecuted in sundry Instances, that will probably end in extraordinary Success” (p. 317).