At the age of 17, Dellon, who is sometimes referred to as Gabriel Dellon, embarked as second surgeon aboard the ship La Force. He arrived at Darman, in the Portuguese Indies, in 1673, where he was doctor to Luis de Mendonça Furtado, a member of the government council, then viceroy. Dellon was denounced to the Inquisition, arrested and taken to Goa, before being taken to Lisbon three years later and released. Back in France, he finished his studies and became a doctor to the Prince de Conti.

Dellon's work is divided into 12 chapters: vomiting; scurvy or sore ear; colic from Madagascar; venereal disease in Isle Dauphine; diseases of the Indies, fevers; smallpox; snake bites; what the Portuguese call Bicho. Dellon deals with the main diseases observed and Pandite doctors, "people without study, without science" having received only a certain number of precepts but whose "long experience they have of the country that they often succeed better than the foreigners ". Delon reports the remedies used in India, to which he sometimes resorted. He cites the "weird" treatment of burning the feet (at the most calloused place) with a hot iron and using a pepper-based diet in the disease called mordechi (probable food poisoning). Dellon advocates, before Lind, the consumption of lemon juice to prevent scurvy: "Individuals should, if possible, make provision of lemon juice."

Dellon's book was translated into English in 1698 as A voyage to the East-Indies giving an account of the Isles of Madagascar, and Mascareigne, of Suratte, the coast of Malabar, of Goa, Gameron, Ormus : as also A treatise of the distempers peculiar to the eastern countries : to which is annexed an abstract of Monsieur de Rennefort's History of the East-Indies, with his propositions for the improvement of the East-India Company / written originally in French by Mr. Dellon ...