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 was introduced into the secondary catalogue of the U. S. Pharmacopoeia at the recent revision. The whole herb is used. It is the product of Achillea Millefolium, often called milfoil, from the great number and minuteness of the divisions of the leaves. Though a native of Europe, it is now abundant in this country, in which it has become completely naturalized. The herb has a feeble though rather agreeable odour, which is retained after drying, and a bitterish, pungent, somewhat astringent taste. The aromatic properties are somewhat stronger in the flowers than the leaves. In the latter the astringency and tonic property predominate. The active principles are volatile oil, tannic acid, and a bitter substance which has not been isolated. There is also a peculiar acid, called the achilleic; but how far this possesses any therapeutic properties has not been ascertained. The volatile oil, separated by distillation, has a beautiful blue colour, and the odour of milfoil. The virtues are extracted by water and alcohol.
Yarrow is a mild aromatic tonic and astringent. It has been used in intermittent fever, flatulent colic, and hysterical disorders. M. Richard, of Soissons, in France, finds it efficacious in low conditions of the exanthematous fevers with imperfect eruption, in colic, infantile convulsions and dysmenorrhoea, using it at the same time as a drink in the form of infusion, as an injection in the same form, and in fomentation. Dr. B. H. Coates, of Philadelphia, confirms the old opinion as to its efficiency in hemorrhages. (Trans. of College of Phys. of Philadelphia, N. S., ii. 334.) Dr. Joly, of France, considers it an excellent emmenagogue, and has obtained advantageous results from it in suppression of the lochia. (Bullet. Gen. de Therap., Mars, 1857.) The most convenient form of administration is that of infusion, which may be made in the proportion of an ounce to the pint, and given in the dose of a wineglassful. The dose of the volatile oil is twenty drops.