My attention was first drawn to the medicinal qualities of formic acid by a semi-secret preparation styled by its manufacturer, Hensel, "Ferrum formicarum oxidatum oxydulatum." This was in 1888. The same or a similar preparation is now sold by a homeopathic drug house under the name of "Hensel's tonicum."
There is no doubt in my mind that Hensel's formic acid compound is a latter-day transformation of Hoffmann's "Vinegar of Magnanimity," in which a preparation of ants played the leading rôle. In the seventeenth century this famous vinegar had found entrance in all European courts and was employed by men and women as a general tonic, stomachic and diuretic, and probably also as an aphrodisiac. For formic acid seems to possess certain qualities stimulating sexual appetite (in South America a species of large ants are consumed), and the proprietary tonics demanding a good sale, as a general rule, are
STERN H. SIXTEEN YEARS' EXPERIENCE WITH FORMIC ACID AS A THERAPEUTIC AGENT.. JAMA. 1906;XLVI(17):1258-1262. doi:10.1001/jama.1906.62510440012001b