Gantillon was a medical doctor.
Gantillon's only contact with Whistler was in 1867 when he committed James Traer, Whistler's friend, and the medical partner of F. Seymour Haden, to hospital in Paris.
He was the author of a book published both in English and French on the diseases of the womb in 1868.
Gantillon is recorded as a doctor at 204 Rue de Rivoli in Paris in 1865, and at 12 Rue Montholon in 1866; he remained at that address until at least 1881. In 1884 he was at 32 Mont-Thabor, and by the following year at 10 Castiglione with a home address at 35 Rue Garnier, Neuilly. Between 1896 and 1902 he was listed at 8 Rue Rossini (8e).
Bottin, Sebastien, Almanach du Commerce de Paris ..., Paris, 1865-1902; British Library on-line catalogue (accessed 2004).