Hedeoma. Pennyroyal. American or Mock Pennyroyal. Squawmint. Mosquito Plant. Berbe de Pouliot Americaine, Fr. Amerikanischer Polei, G.—The U. S. VIII recognized "The dried leaves and flowering tops of Hedeoma pulegioides (Linne) Persoon (Fam. Labiatae)." U. S. VIII.

This plant is entirely distinct from Mentha Pulegium, or European, pennyroyal. It is probable that various other species of the genus are used in the localities in which they grow. Thus, H. piperita Bentham is said to be used in Mexico as a substitute for peppermint, and H. thymoides Gray, in Texas as an aromatic diaphoretic.

Hedeoma pulegioides (L.) Pers. (1807) [Cunila pulegioides L. (1762); Melissa pulegioides L. (1753)] is an indigenous annual plant, from nine to fifteen inches high, with a small, branching, fibrous, yellowish root, and a pubescent, quadrangular stem, which sends off numerous slender erect branches. The plant is common in the Eastern and Middle Western United States, preferring dry grounds. Hedeoma was officially described as "branchlets quadrangular, with numerous spreading hairs; leaves opposite, short-petioled, oblong, 15 to 35 Mm. long, thin, obtuse, obscurely serrate, glandular-hairy beneath; flowers in axillary fascicles, with a tubular-ovoid, bilabiate and 5-toothed calyx, and a pale blue, spotted, bilabiate corolla containing two sterile and two fertile, exserted stamens; odor strong, somewhat mint-like; taste aromatic and pungent." U. S. The activity of hedeoma depends upon a volatile oil. The oil of hedeoma (Oleum Hedeomae, U. S. VIII, Oil of Pennyroyal), is "A pale yellow, limpid liquid, having a characteristic, pungent, mint-like odor and taste. Specific gravity: 0.920 to 0.935 at 25° C. (77° F.). It should form a clear solution with 2 volumes or more of 70 per cent. alcohol. It is dextrogyrate, the angle of rotation varying from about +18° to +22° in a 100 Mm. tube, at a temperature of 25° C. (77° F.)." U, S. VIII. Its chemical composition was investigated by E. Kremers (A. J. P., 1887, p. 535) and F. W. Franz (A. J. P., 1888, p. 161). Each of them found a body of the composition C10H18O, boiling at 217° to 218° C. (422.6°-424.4° F.) (constituting, according to Franz, about 33 per cent. of the oil). For this the name hedeomol was proposed. Franz also found a body of the composition

C10H17O, boiling at 220° to 225° C. (428°-437° F.), and constituting 12 per cent. of the oil; likewise a body of the composition C6H12O, boiling at 165° to 170° C. (329°-338° F.), and constituting about 0.7 per cent. of the oil. Both investigators found formic and acetic acids, and Kremers considers isoheptoic acid also to be present. Beckmann and Pleissner (Ann. Ch. Ph., cclxii, p. 1) found in American as well as in Spanish and Algerian pennyroyal oil a ketone, C10H16O, to which they gave the name of pulegone. This compound forms with hydroxylamine an oxime, C10H16NOH.H2O, crystallizing in beautiful needles melting at 157° C. (314.6° F.), and with hydrogen bromide a crystalline compound melting at 40.5° C. (104.9° F.). The two compounds of the formula C10H18O, discovered by Kremers (Ph. Rund., ix, p. 130), are also ketones and yield corresponding oximes.

American pennyroyal is a gently stimulant aromatic, and may be given in flatulent colic and sick stomach, or to qualify the action of other medicines. Like most of the aromatic herbs, it possesses the property, when administered in warm infusion, of promoting perspiration, and of exciting the menstrual flow when the system is predisposed to the effort. A large draught of the warm tea is in popular practice often given at bedtime, in recent cases of suppression of the menses, the feet having been previously bathed in warm water. The drug may be given in doses of two drachms (7.7 Gm.). The oil in doses of two to ten minims (0.12-0.6 mil).

The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.