8

ELEMENTS OF MATERIA MEDICA.

catty, by agencies which are neither mechanical, nor chemical merely.Hence we may examine the actions of medicines under tire three heads ofmechanical, chemical, and dynamical.

a. Mechanical. —The alterations of cohesion, of form, of relative posi-tion, &c. caused by medicines, are denominated their mechanical effects.They are frequently attended or followed by organic changes; conse-quently, a medicine, whose action is simply mechanical, may producetwo classes of effects—the one mechanical, the other vital; and thewhole of its operation may be denominated meclianico-vital.

Muller (Elements of Physiology, translated by Baly, p. 59) considersthat mechanical agents may give rise to chemical changes in the tissues.“Mechanical influence in frictions,” he observes, “acts under certaincircumstances as a vivifying stimulus; it has this effect, probably, byinducing in the composition of the tissues, slight chemical changes, as aconsequence of which the affinity of the tissues for the general vitalstimuli already in the organism is increased.”

Formerly most of the articles of the Materia Medica were supposed toact on the organism mechanically merely. “ I doubt not,” says Locke ,“ but if we could discover the figure, size, texture, and motion of theminute constituent parts of any two bodies, we should know, without trial,several of their operations one upon another, as we do now the propertiesof the square or a triangle. Did we know the mechanical affections ofthe particles of rhubarb, hemlock, opium, and a man, as a watchmakerdoes those of a watch, whereby it performs its operations, and of a file,which, by rubbing on them, will alter the figure of any of the wheels, w r eshould be able to tell before-hand that rhubarb will purge, hemlock kill,and opium make a man sleep.”—( Essay concerning Human Understanding,book iv. chap. 3.) These mechanical notions of Locke harmonizedwell with those of the iatromechanical or iatromathematical sect of theage in w hich he lived; a sect which ranked amongst its supporters Ilorelli(its founder,) Bellini, and others, in Italy ; Sauvages, in France ; and Pit-cairn, Keill, Mead , and Freind, in England. The functions of the body,the production of diseases, and the operation of medicines, were explainedon mechanical principles. The action of stimulants, for example, wassupposed to depend on the pointed and needle-like fonn of their particles,and the operation of emollients on their globular form.—( Sprengel, Hist.Medec. by Jourdan, t. 5, p. 131, et seq.) I need hardly say, the existenceof particles with the peculiar shapes assumed, is quite imaginary; and,indeed, if, for the sake of argument, we assume their existence, the actionof medicines is, notwithstanding, quite inexplicable. We can, indeed,easily believe that a ball of glass may be swallowed with impunity, andthat the same substance, reduced to the form of a coarse powder, mightcause irritation by the mechanical action of the angular particles on thetender alimentary tube ; but we could not, on this hypothesis, explainwhy one medicine acts on one part of the body, and a second on anotherpart.

There are very few medicinal agents now in use wiiose remedial effi-cacy can be solely referred to their mechanical influence. Indeed, severalof the processes to which medicines are subjected before they are admi-nistered, have for their principal object the prevention or diminution ofthis influence. Among the medicines still employed, on account of theirmechanical action, are the hairs of the pods of Mucuna pruriens, quick-