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 as the Renaissance anatomist Andreas Vesalius.

This was done to ensure that recorded effects, such as eye movement, food consumption, and the weights of the subjects were consistent among all three dogs and did not change due to outside elements.

On March 9, 1667, he made an announcement in the journal des sçavans, stating his intention to publicize his anatomical and experimental demonstrations of blood transfusion as a therapeutic tool.

Denys would go on to announce his successes to the European scientific community through written reports submitted to the Journal des sçavans, which enabled him to start a correspondence with Henry Oldenburg, and consequently the Philosophical Transaction.

He believed the next step was initiating a radical new procedure between humans and animals, utilizing as a prime example the lamb, the symbol of the blood of Christ, hence the purest form.

With the assistance of Paul Emmerez he transfused about twelve ounces of lamb blood into the veins of a 15-year-old boy who had suffered from uncontrollable fevers for two months and had been consequently bled with leeches 20 times by a barber-surgeon, to no effect.

This was the final proof for Denys, who immediately publicized his success, firstly by writing to Oldenburg, who published the letters received on the February 10, 1668 edition of the Philosophical Transactions[3] (original and translated).

Denys was convinced that his transfusions did not cause Mauroy's death, and that this trial was rather a consequence of his decision to pursue research against the will of the King's Academy of Sciences as well as that of the major players of the conservative Parisienne Faculty of Medicine.

In an attempt to prove his innocence, Denys described his medical experiments to Commissioner Le Cerf and explained their safety, which was supported by the many survivors willing to witness in his favor.

Finding sufficient grounds for concern, La Cerf forwarded the case to the Criminal Lieutenant, the Honorable Jacques Defita, for a full hearing.

Arsenic poisoning was known to harm the nervous system and cause symptoms such as tremors, seizures and delirium; this could therefore explain Mauroy's intense delusional behavior prior to the third transfusion.

The only transcript of the hearing suggests that the argument made by Denys’ lawyer, Chrétien de Lamoignin, was considered a masterpiece; yet, the whole procedure was surprisingly short followed by no discussion.

Interest within the medical field grew after accounts of his successful demonstrations were reported in ‘Philosophical Transactions’, a publication by the English Royal Society dating back to mid-1673.

Denys' 'essence', of which the contents are unknown, is believed to contain a mixture of potassium alum and sulfuric acid, would be applied to arterial and venous wounds in order to staunch the bleeding.

The first fully documented experiment using Denys’ blood staunching liquor was carried out on May 30, 1673 in London by English physician Walter Needham and surgeon Richard Wiseman.

Under the order of King Charles II, the two proceeded to test the liquor on patients at the St Thomas' Hospital in Southwark, London; the same results were obtained.