Active Ingredients. - In composition, oil of pennyroyal is believed to resemble oil of spearmint, i. e., to be an oxidized hydrocarbon, containing camphor in solution. The color is pale yellow; the odor corresponds with that of the recent plant, which is peculiar and agreeable; the taste is warm, aromatic, and somewhat bitter. The sp. gr. is 0.95; the boiling point, 395° F. Pennyroyal contains tannin in small quantity, with other ingredients apparently of little or no importance.

Physiological Action. - The operation of pennyroyal corresponds pretty nearly with that of the larger species of Mentha. Some persons consider it to be very specially antispasmodic and emmenagogue.

Therapeutic Action. - The chief medicinal value of this little herb is found in the directions just named, viz., as an antispasmodic and emmenagogue. It is also esteemed in whooping-cough and hysterical complaints.

Preparations And Dose. - None officinal. Preparations analogous to those of the other mints may be made and administered in corresponding doses.