ACTIVE FORCES OP MEDICINES.

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using mercurials in fever. The homceopathists assert, and with trath, that thestudy of the effects of medicines in the healthy State is the only way of ascer-taining the pure or palhogenetic efFects of medicines—since when we administerour remedies to invalids " tlie Symptoms of the natural disease, then existing,mingling with those which the medicinal agents are capable of producing, thelatter can rarely be distinguished with any clearness or precision." (Hahne-mann's Organon, translated by C. H. Devrient, p. 190.)

CIIAPTER II.— OF THE ACTIVE FORCES OF MEDICINES.

The produetion of effects, by the application of medicines to the living body,depends on the existence of two classes of powers or Forces; the one residing inthe medicine, (and called the aclive. forces of medianes,) the other in theorganism.

Bodies act on each other in one or more of three ways; viz. mechanically, bytheir weight, coliesion, externa! form, and motion; chemically, by their mutualaffmities; and dynamically, by agencies which are neither mechanical nor che-mical mercly. Hence we may examine the actions of medicines under the threeheads of mechanical, chemical, and dynamical.

1. Mechanical. —The alterations of cohcsion, of form, of relative position,&c., caused by medicines, are dcnominated their mechanical effects. They arefrequently attended or followed by organic changes; consequently a medicinewhose action is simply mechanical, may preduce two classes of effects—the onemechanical, the other vital; and the whole of its Operation may be denominatedmechanico-vilal.

Müller {Elements of Physiology, translated by Baly, p. 59.) considers that mechanicalagents rnay give rise to chemical changes in the tissucs. " Mechanical influence in frietions,"hc observes, " acts under certain eircumstances, as a vivifying Stimulus; it has this effect,probably, by inducing in the composition of the tissucs, slight chemical changes, as a conse-quence of which the afftnity of the tissucs for the general vital Stimuli alrcady in the organismis inereased."

Formerly most of the articles of tlie Materia Medica werc supposed to act on the organismmechanically merely. " I doubt not," says Locke, (Essay concerning Human Understanding,book iv. chap. iii.) " but if we could discover the figure, size, texturc, and motionof the miauteconstituent parts of any two bodies, wo should know, without trial, several of their Operationsone upon another, as we do now the propertics of the Square or a triarigle. Did we know themechanical affections of the particlcs of rhubarb, hemlock, opium, and a man, as a watch-maker does those of a watch, whereby it performs its Operations, and of a fite, which, by rub-bing on thern, will alter the figure ofany of tlie whccls, wo should be ablc to teil before-handthat rhubarb will purge, hemlock kill, and opium tnake a man sleep." These mechanical no.tions of Locke harmonized well with those of the iatromechanical or iatromathematieal seet ofthe agc in which he lived ; a sect which ranked amongst its supporters Borclli (its founder,)Bellini, and others, in Italy ; Sauvages, in France; and Pitcairn, Keill, Mead, and Frcind,in England. The fonetions of the body, the produetion of diseases, and the Operation of me.dicincs, were explained on mechanical principles. The action of stimnlants, for example, wassupposed to depend on tlie pointed and needle-like form of their particlcs, and the Operation ofemollicnts on their globular form. (Sprengel, Hisl. de Medec. by Jourdan, t. v. p. 131, et seq.)I need hardly say, the existence of particlcs with the peculiar shapes assumed, is quite imagi-nary; and, indeed, if, for the sake of argutnent, we admit their existence, the action of medi-cines is, notwithstanding, quite incxplicable. We can, indeed, easily believc that a ball ofglass may be swallowed with impunity, and that the samc substance, reuueed to the form ofa coarsc powder, might cause Irritation by the mechanical action of the angular particlcs onthe tender alimentary tube ; but we could not, on this hypothesis, explain why one medicineacts on one part of the body, and a seeond on another part.

There are very few medicinal agents now in use whose remedial efficaey canbe solely referred to their mechanical influence. Indeed, several of the processesto which medicines are subjeeted before they are administered, have for theirprineipal objeet the prevention or diminution of this influence. Among the me-dicines still 'employed, on aecount of their mechanical action, are the hairs of thepods of Mitcwia pruriens, quicksilver, and, perhaps, powdered tin; the first and