As a true renaissance man, Samuel Pepys was interested in everything, from the affairs of the Parliament and the Admiralty, to the almost mundane events of mid-17th century Britain. The entries of Pepys’ diary, preserved to the modern age, provide an invaluable glimpse into life 350 years year — a tumultuous period that included the Great Plague of London, and the Great Fire of London — but not only for historians. Pepys recorded in fine detail one of the first attempts at blood transfusion to take place.

On this day, November 14, in 1666, Pepys described a transfusion between two dogs. This was just the second such attempt on record, and came just months after the discovery of blood circulation mechanisms through the heart.

The transfusion went semi-successfully: as happened in the first experiment, the donor dog did not survive the loss of blood. Pepys remained convinced the technique could be refined and adapted to be “of mighty use to man’s health, for the amending of bad blood by borrowing from a better body,” but it would take another two centuries until blood types would be discovered, to make the first human-to-human blood transfusion possible.