Active Ingredients. - The particular ingredients of the rhizome of the Filix-mas are a volatile oil, a fatty fixed oil, and a resin, besides which there are tannin, filicic acid, coloring matter, some starch, gum, uncrystallizable sugar, and other subordinate substances. Bock represents the proportion of the fixed oil to be that of 60.0 in 1000 of the dried rhizome, while the volatile oil exists to the extent only of 0.4. The active principles of the plant, which are probably identified with the oils, or with one of them, are separable by means of ether, in which they are soluble. The ethereal extract, termed " oil of male-fern," contains also the resin; it is blackened by the presence of coloring matter, and retains the peculiar odor of the rhizome.

Physiological Action. - Filix-mas is of very ancient repute as a vermicide. It appears to act as a direct poison to the worms, though the expulsion of the dead creatures has generally to be accomplished through some other agency, the natural action of the intestines fulfilling its own part. Besides the essentially vermicidal action, there is a slightly purgative one.

Therapeutic Action. - The chief success of the oil of male-fern appears to have been found in connection with tape-worm, and most especially in cases of the presence of Bothriocephalus lotus. Its value in such cases can hardly be over-estimated, and an additional good feature is the smallness of the dose required. The patient should fast before receiving the medicine, or, at all events, take it upon an empty stomach; and after an interval, say from five to six hours, it should be followed by a gentle laxative. If the alimentary canal be occupied by food, the medicine is too much diluted to be operative, concentration being always very important in regard to vermifuges. A dose of castor oil the night before taking the medicine is often preferable to a laxative subsequently.

Preparations and Dose. - Oleoresina Filicis, gr. x. - xxx. (.60 - 2.); Extract. Filicis Liquidum (B. Ph.), xv. - xxx. (1. - 2.).