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.
Acidum Salicylicum (From Oil of Wintergreen ). This is the substance upon which the reputation of salicylic acid is based, and many discriminating physicians will not employ the synthetic acid internally. Synthetic oil of wintergreen has been prepared and synthetic salicylic acid purporting to be true acid has been made from it. This is a fraud upon the part of the maker that has vastly complicated the already much involved therapy of salicylic acid. A conservative view of the matter makes it appear that the natural acid produces less irritation than does the synthetic, is eliminated more rapidly, and has a more regular and reliable influence where the temperature is elevated. Salicylic acid produces tinnitus, a reduction of reflex action, depression of cerebration, reduces temperature, is diaphoretic and antiseptic, and is apt to irritate the kidneys. The unaltered acid is employed in ulcerations and cancerous conditions of the stomach and in foul breath and offensive expectoration. It is also used locally in various conditions. The average dose is about 7 or 8 grains. Sodium salicylate is usually preferred for internal administration in rheumatism, sciatica, lumbago, and for its supposedly alterative properties. In small doses salicylic acid is employed in tonsilitis, giving I or 2 grains every two hours. It is highly efficient where there is a septic influence or the follicles of the tonsils are involved. Homeopathic physicians assert that 1-10 gr. doses relieve many of the symptoms of Meniere's disease. Externally, salicylic acid is used in the treatment of indolent ulcers, cold abscesses, chilblains, pruritus, and many skin affections.