This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is the herb of Hedeoma pulegioides, a small indigenous annual, growing in all parts of the United States, usually preferring dry, Sterile, or impoverished fields, and sometimes, from its abundance, scenting the air for a considerable distance. Both fresh and dried, it has an agreeable aromatic odour,resembling somewhat the European pennyroyal from which it derived its name, and a warm, pungent, camphorous taste. These properties reside in a volatile oil, which may be separated by distillation. The oil is lighter than water, of a light pale-yellow colour, and a smell and taste similar to those of the plant. The herb imparls its virtues to hot water, but more freely to alcohol.
The effects of hedeoma upon the system are very analogous to those of the mints; and, like these, it may be used to correct nausea, relieve flatulent pains, and cover the taste or correct the action of other medicines. When given in the form of hot infusion, in large draughts, it often, like most other aromatic herbs, produces perspiration, and promotes the flow of the menses. Hence, it is considerably employed, in domestic practice, in commencing catarrh and rheumatism, and to promote menstruation; the feet being at the same time well soaked in hot water, and the patient covered warmly in bed. There is no doubt that the remedy, thus aided, is not unfrequently successful. As an emmena-gogue it is most efficient in recent cases, and given at the regular monthly period, when it comes in aid of the tendencies of the system. It has little effect in obstinate cases. It has been used also, like the European herb of the same name, in hysteria and hooping-cough. The Infusion may be made in the proportion of half an ounce to the pint, and given in doses of from two to four fluidounces or more. The Volatile Oil (Oleum Hedeomae, U S.) is officinal, and may be employed with the same objects as the infusion, in the dose of from two to ten drops. It is sometimes used externally as a rubefacient. A water and spirit or essence of pennyroyal may be prepared from the oil, in the same manner as the similar preparations of the mints, and used in the same way.