A dispensatory, or commentary on the pharmacopoeias of Great Britain : comprising the natural history, description, chemistry, pharmacy, actions, uses, and doses of the articles of the materia medica / by Robert Christison.

  • Christison, Robert, Sir, 1797-1882.
Date:
1842
Catalogue details

Licence: Public Domain Mark

Credit: A dispensatory, or commentary on the pharmacopoeias of Great Britain : comprising the natural history, description, chemistry, pharmacy, actions, uses, and doses of the articles of the materia medica / by Robert Christison. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    the natural constitution of active vegetable drugs is supposed to be less altered in this form than in any other. The reason is a questionable one. In some instances expressed juices do not con- tain the whole active constituents of plants,—as in the case of monkshood, where most of the acrid principle is left behind. And in others, such as hemlock, the making of an extract by inspissa- tion of the juice is attended with the risks which are apt often to arise from the concurrent influence of water and heat. These risks have been already discussed under the head of Decoctions, and con- sist in the dissipation of volatile matters,—the conversion of fixed soluble principles into insoluble and therefore more inactive com- pounds,—and the transformation of active constituents into prin- ciples totally different, and wholly inert. All these objections to the form of watery decoction apply with tenfold force to the form of extract, as it is usually prepared. Some extracts indeed may be correctly obtained in this way, such as extract of gentian, calum- ba, liquorice-root, rhatany-root, pareira, log-wood, dandelion, quassia, colocynth, and nux-vomica,—more especially if the heat be applied through the medium of boiling water or steam at 212° But others are thus greatly deteriorated or altogether spoiled, such as the extracts of most narcotic vegetables; and this result is cer- tain if the heat be either continued too long, or raised above 212°. The extract of hemlock, for example, when kept for even a few minutes too long over the vapour-bath after the inspissation of the - juice is nearly completed, exhales ammonia of a peculiar heavy odour, and becomes soon inert from the conversion of its active al- kaloid into an inactive resin. Various means have in consequence been proposed for securing the due preparation of such extracts. In the first place something may be accomplished by taking care that the heat be not allowed to exceed 212°, nqr the liquor at any time to boil,—that the mate- rial be diligently stirred towards the close,—and that the concen- tration be stopped the moment the odoui- exhaled becomes ammo- niacal, or undergoes any other change. These measures however are not always sufficient; and more ex- tensive alterations of procediue have been recently adopted, with imquestionable advantage. Of these the simplest, and perhaps one of the best, is the substitution of spontaneous evaporation at ordi- dinary atmospheric temperatures. Some years ago I made some experiments on this method, chiefly in consequence of the represen- tations of Mr Cheyne, at the time an intelligent driiggist of this city. About the same period similar inquiries were made in Lon- don and elsewhere. The genei-al result is, that many, probably indeed all, expressed juices, which do not owe their virtues to a vo- latile oil or other principle expelled or destroyed by drying, may be convei-ted with little loss of activity into the form of firm extract, by evaporating them without artificial boat in shallow vessels ex- posed to a current of air, and protected from dust and insects by i