This section is from the book "The London Dispensatory", by Anthony Todd Thomson. Also available from Amazon: PDR: Physicians Desk Reference.
"Take of marsh-mallow root, dried and bruised, four ounces; rasins, stoned, two ounces; water, seven pounds. Boil down to five pounds; set aside the strained liquor until the dregs have subsided, and then decant it."
Decoctum Althaeae, Dub. Decoction of Marsh Malloics.
The same as the Edinburgh formula.
Marsh-mallow roots contain a considerable quantity of mucus, which is thus extracted unaltered by water. The simple decoction of the roots is viscid, of a pale-yellow colour, sweetish, and has a peculiar odour resembling that of boiled turnips. In the above preparation, the raisins increase its sweetness, and render it more palatable.
Medical properties and uses. - This decoction is a useful demulcent in visceral inflammations, calculous affections, gonorrhoea, strangury, and other diseases of the urinary organs. The dose is a cupful, frequently taken; but in inflammation of the urinary organs, and in similar cases, it may be drunk ad libitum, as a common beverage.
 
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