PHYSIOLOGICAL CLASSES OF MEDICINES.

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On account of their acrid and heating properties, spices are objection-able in inflammatory conditions of the alimentary canal, and in febrileconditions of system.

d. The fourth group includes four sub-groups formed respectively bythe solid resins, the oleo-resins, the balsams, and the foetid gum-resins.As these differ not only in their chemical composition, but also to acertain extent in their effects and uses, they will require separateexaminations. But being so closely related to each other, they couldnot, with propriety, be formed into distinct groups.

a. Resins (resinee ).—Under this head I include elemi, mastic, and guaia-cum, obtained respectively from the orders Burseracece, Anacard.iacece,and Rutacea . They exude either spontaneously or from incisions madeinto the stems of the plants yielding them. Common resin obtained as aresidue in the distillation of the turpentines, may, in regard to its chemi-cal and medicinal qualities, be placed in'-the same sub-group with thenatural resins. These bodies agree in the following properties:—Theyare fusible and inflammable, and consist of resin principally combinedwith a small quantity of volatile oil: they are insoluble in water, butdissolve either completely, or nearly so, in alcohol, ether, and volatileoils : they combine with alkalies, saturating them as weak acids. Theirlocal action is irritant: applied to the skin they act as rubefacients,and when swallowed in large doses, produce heat of stomach, nausea,vomiting, or even purging. Their constitutional effects are those ofstimulants. Thus they occasion thirst, quicken the pulse, raise thetemperature of the surface, and promote the secretions, especially of theskin and kidneys. Elemi and mastic are rarely employed in medicine :their effects are analogous to the turpentines, but much milder. Guaiacumis used as a stimulant and sudorific.

(}. Oleo-resins (oleo-resince; liquid resins; balsams devoid of benzoic acid;terebinthinates). —These arc oleo-resinous, semi-liquid, or glutinous juices,which flow spontaneously, or by incisions, from various vegetables, espe-cially those belonging to the orders Coniferce, Burseracce, Anacardiacem,and Amyridacea;. Their liquidity or semi-liquidity, their odour, andmost of their medicinal activity, are owing to the volatile oil which theycontain, and which may be procured from them by distillation. Fromthe true balsams they are distinguished by the want of benzoic acid.They have a strong odour, which, in some, is very fragrant,—in others,so peculiar as to be taken as the type of certain odours under the nameof terebinthinate. Those oleo-resins, employed in medicines, are theturpentines,copaiva,andopobalsamum (commonlytermedMeccabalsam).Their taste is hot and acrid. They are all local irritants, causing rube-faction when applied to the skin; and some of them giving rise to activeinflammation. When swallowed they occasion more or less irritation ofthe alimentary canal, according to the dose in which they are taken ; thesymptoms being epigastric heat, loss of appetite, nausea, or even vomit-ing ; and, sometimes, when the quantity swallowed is large, griping orpurging.

The constitutional effects are thirst, dryness of the mucous membranes,increased frequency and fulness of pulse, and great heat of skin, fre-quently accompanied with sweating. The oleo-resins exercise a stimu-lant influence over the urinary organs, which is manifested by uneasinessin the region of the kidneys, increased desire of passing the urine, heat