I

20

Materia Medica.

Part II.

pure; but when a prejudice is once established against anyparticular article, it is difficult to efface it. The gum, in theabove-mentioned state, is used in all parts of the country, forcataplasms and fumigations. The sandy light soil which pro-duces the gum ammoniac, abounds in the north of Morocco.It is remarkable that neither bird nor beast is seen where thisplant grows, the vulture only excepted. It is, however, at-tacked by a beetle, having a long horn proceeding from itsnose, with which it perforates the plant, and makes the inci-sions whence the gum oozes out." t

Ammoriiacum has a nauseous sweet taste, followed by a bit-ter one; and a peculiar smell, somewhat like that of galba-num, but more grateful: it softens in the mouth, and acquiresa white colour upon being chewed. It softens by heat, butis not fusible -, when thrown upon live coals, it burns away inflame: it is in some degree soluble in water and in vinegar,with which it assumes the appearance of milk ; but the resin-ous part, amounting to about one-half, subsides on stand-ing.

Such tears as are large, dry, free from small stones, seeds,or other impurities, should be picked out and preferred for in-ternal use; the coarser kind is purified by solution, colature,and careful inspissation; but unless this be artfully managed,the gum will lose a considerable deal of its more volatile parts.There is often vended in the shops, under the name of strain-ed gum ammoniacum, a composition of ingredients much in-ferior in virtue.

Neumann extracted from 480 parts, 360 by alcohol, andthen by water IOS ; by water applied first 410, and then byalcohol 60. Alcohol distilled from it arose unchanged, butwater acquired a sweetish taste, and the smell of the ammo-niac. More modern chemists say that the spirit drawn fromit by distillation smelt strongly of the gum, and that a smallportion of a very pungent strong smelling' oil could be gotfrom it. The solution in alcohol is transparent; but on the ad-dition of water, becomes milky. It therefore seems to consistprincipally of a substance soluble both in water and in alcohol,combined with some volatile matter. Braconnot makes itconsist of TOO resin, 184 gum, 44 gluten, and 60 water.

Medical usr. —The general action of gum-ammoniac is sti-mulant. On many occasions, in doses of from ten to thirtygrains, it proves a valuable antispasmodic, deobstruent, or ex-pectorant. In large doses it purges gently, excites perspira-tion, and increases the flow of urine. It is used with advan-tage to promote expectoration in some pulmonary diseases,especially asthma and chronic catarrh; in dropsical affections,