This was Arthur Coga, who had studied at Cambridge, and was said to be a bachelor of divinity. He was indigent, and “looked upon as a very freakish and extravagant man.” Dr. King, in a letter to the Hon. Robert Boyle, remarks “that Mr. Coga was about thirty-two years of age; that he spoke Latin well, when he was in company, which he liked, but that his brain was sometimes a little too warm.” The experiment was performed on November 23rd, 1667, by Dr. King, at Arundel House, in the presence of many spectators of quality, and four or five physicians. Coga wrote a description of his own case in Latin, and when asked why he had not the blood of some other creature, instead of that of a sheep, transfused into him, answered, “Sanguis ovis symbolicam quandam facultatem habet cum sanguine Christi, quia Christus est agnus Dei” (Birch’s “History of the Royal Society,” vol. ii., pp. 214-16). Coga was the first person in England to be experimented upon; previous experiments were made by the transfusion of the blood of one dog into another. See November 14th, 1666 (vol. vi., p. 64).
This text comes from a footnote on a diary entry in the 1893 edition edited by Henry B. Wheatley.