This section is from the book "A Practitioner's Handbook Of Materia Medica And Therapeutics", by Thos. S. Blair. Also available from Amazon: A Practitioner's handbook of Materia Medica and Therapeutics.
Gaultheria, Wintergreen. The oil is the most useful preparation, and contains about 90% of methyl-salicylic acid. Its dose is 5 to 10 I.. Salicylic acid prepared from true (not synthetic) oil of wintergreen is far safer and more efficient than the ordinary acid. The various tinctures of gaultheria are eligible ways for its administration in small doses for various forms of neuralgia, gonorrheal rheumatism, inflammation of the bladder, and hepatic congestion. Dose, ec. tr., 5 to 15 I.; tr., 30 to 120 I. Do not mix with aqueous menstrua until moment of administration.