64. Allium Cepa, Linn.—The Onion
Sex. Syst. Hexandria, Monogynia.
History.—The onion was known and used in the most ancient times. By Fraas [Synops. Plant. Fl. Class. p. 291, 1845.] it is considered to be the κρομμνον; (see ante, p. 207) of Theophrastus [Hist. Plant. lib. vii. cap. 4.] and Dioscorides. [Lib. ii. cap. 181.] The σητανιον of Theophrastus was a variety of onion. By Pliny [Hist. Nat. lib. xix. cap. 32, ed. Valp.] the onion is called cepa. It was employed in medicine by Hippocrates. An onion taken from the hand of an Egyptian mummy perhaps 2000 years old has been made to grow. [Müller's Physiol. by Baly, vol. i. p. 29.]
Botany. Gen. Char.—Vide Allium sativum.
Sp. Char.—Stem fistulous, ventricose beneath; longer than the terete, fistulous leaves. Umbel capsuliferous, globose. Segments of perianth linear-elliptic, obtuse; shorter than the stamens and pistil. [Botanicon Gallicum.] Biennial. Flowers whitish. July.
Loudon [Encyclopadia of Gardening.] enumerates eighteen varieties deserving of culture.
Hab.—Egypt. Cultivated in kitchen gardens.
Besides A. sativum and A. Cepa, various other species of Allium are also cultivated for culinary purposes; as, A. Porrum, the Leek; A. ascalonicum, the Shallot; A. Schoenoprasum, the Chive; and A. Scorodoprasum or Rocambole. Their virtues are analogous to those of the onion and garlic.
Description.—The bulb (bulbus) is tunicated. When cut, it evolves an acrid principle, having a well-known odour, and a powerful action on the eyes, causing a flow of tears. Its taste is sweet and acrid. Onion juice is colourless, but by exposure to the air it becomes reddish.
Composition.—According to Fourcroy and Vauquelin, [Ann. Chim. lxv. 161, 1808.] the onion contains an acrid volatile oil, uncrystallizable sugar, gum, woody fibre, albumen, acetic and phosphoric acids, phosphate and citrate of lime, and water.
Oil of Onions (Oleum cepae) contains sulphur, and is probably similar in composition to oil of garlic, AllS=C6H5,S. It is acrid, piquant, and colourless.
Physiological Effects.—Analogous to those of garlic, but milder. The oil becomes absorbed, and communicates the well-known onion odour to the breath. By boiling onions the volatile oil is dissipated, and the bulb is deprived of its irritating qualities, and becomes a mild esculent substance.
Uses.—Extensively used as an article of food and as a condiment. It is very rarely employed in medicine, but is adapted to the same cases as garlic. Raw onions are occasionally taken as an expectorant, with advantage, by elderly persons affected with winter cough.
Administration.—A roasted onion is sometimes employed as an emollient poultice to suppurating tumours, or to the ear to relieve ear-ache. The expressed juice has been given to children, mixed with sugar, as an expectorant.