First English edition of a treatise on the medicinal use of Spanish fly (Lytta vesicatoria, traditionally classified in the family Canthardiae). Joannes Groenevelt (1648-1715/16)) was a Dutch-born physician, practising in London from 1675 on. Spanish fly was known for centuries as an aphrodisiac, but was also extremely dangerous, overdoses sometimes causing death. Greenfield, as he called himself in England, strongly advocated the use of Spanish fly, primarily for the treatment of gout and of bladder and kidney diseases. One of his patients accused him of malpractice and Groenvelt was fined and sent to Newgate prison, but obtained permanent freedom through William III's general pardon in 1691. He published the present treatise on the use of Spanish fly as a vindication of his methods. It includes a laudatory poem by Bernard Mandeville, detailed descriptions of the various medicinal uses of Spanish fly, followed by medical observations and several recipes. Blake, p. 187; ESTC T64914; for the author: Cook, "Groenevelt, Joannes (bap. 1648, d. 1715/16)", in: ODNB (online ed.).