Onion. Cepa.—The bulk of Allium Cepa L. (Fam. Liliaceae.) Fourcroy and Vauquelin obtained from the ordinary onion a white, acrid, volatile oil containing sulphur; also albumen, much uncrystallizable sugar and mucilage, phosphoric acid, both free and combined with lime, acetic acid, calcium citrate, and lignin. The expressed juice is susceptible of the vinous fermentation. The oil is essentially the same in chemical composition as the oil of Allium sativum L., and consists largely of allyl sulphide, (C3H5)2S. (See A. Pharm., 1892, 434.) Perkin and Hummel found quercetin in the outer skin of onion bulbs, and the skins have been used in dyeing.
By virtue of its volatile oil the onion taken in moderate quantities is a stimulant to the stomach and promotes digestion, but in large quantities is apt to cause gastric uneasiness. It is slightly rubefacient, said to be diuretic, and belongs among those expectorants to be employed in the advanced stages of subacute bronchitis or in chronic bronchitis. Although the onion has been asserted to exercise a marked influence on nitrogenous metabolism it can scarcely be doubted that any apparent influence which it may exert in the direction spoken of is secondary to its action upon digestion.
Onion poultices are somewhat effective as a counter-irritant and nerve stimulant in cases of bronchitis or pneumonia in young children, with nervous symptoms. According to M. V. Pogrelaky, a decoction made with the outer reddish skin of the bulb is widely used in Russia for the production of abortion. He attributes the ecbolic effect to the presence of allyl sulphide. One or two tumblerfuls of the concentrated dark brown or dark red infusion are taken at a dose.