Jean-Baptiste Denys (1643 – 3 October 1704) was a French physician notable for having performed the first fully documented human blood transfusion, a xenotransfusion. He studied in Montpellier and was the personal physician to King Louis XIV. Early life Jean Baptiste Denys was born in the 1630s, although his birth had gone unnoticed and undocumented. He was born in a family of modest means, in fact, his father was an artisan who specialized in water pumps, which was seeing an increase in popularity with new elaborate systems being introduced. The passion of Denys towards Medicine was also induced by his medical condition, in fact, he suffered from Asthma. Education Despite his family's humble origins, he obtained a bachelor in theology at the College des Grassins and a medical degree at the Faculty of Medicine in Montpellier, when barely thirty. Denys’ ambition drew him to attempt a career in Paris, however, the bad reputation and its location made him an outsider to the Parisian moneyed scientific elite. In Paris, he settled among the medical students in the Latin Quarter, to whom he would give anatomy lessons, encouraging the same hands-on approach of the Renaissance anatomist Andreas Vesalius. The lectures provided him with little income, but he gave them in an effort to establish important relationships with the Paris medical community. General Context The years between 1667 and 1668 were characterized by the growing frenzy over the possibility of blood transfusion. The French and English were the main contestants in the battle to master blood's secrets and perform the first successful human blood transfusion. Members of the British Royal Society began by injecting doses of fluids into the veins of animals, proceeding with dog-to-dog transfusion. Similarly, the French Academy of Science tried canine experiments, but was unable to replicate the English success. The general context of the time regarding blood transfusion, had Denys paid particular attention to the English successes that were taking place, and to which he would read about on the French Journal des Sçavans, which would translate articles written by Henri Oldenburg on the topic, originally published on the english Philosophical Transaction. Attempts at Blood Transfusion Denys started a collaboration with the barber-surgeon Paul Emmerez (?-1690), to undertake blood transfusion, as there were announcements of the progress the English were making regarding the topic, so much so that, during one of his dissection, he shared with his students his