56 ELEMENTS OF MATERIA MEDICA.

Generates de Medecine, t. ii. p. 432,) and. in 1833 by M. Fabre-Palaprat,{Arch. Gen. ll me serie. t. ii.; also, Becquerel, Traite de Electricite, t. iv.p. 321.) The principle on which galvanic electricity has been employedis, that the poles (electrodes) of a voltaic battery have attractive and re-pulsive powers for certain substances: thus the positive pole (anelectrode)attracts oxygen, chlorine, and iodine,—while the negative pole (cathelec-trode) attracts hydrogen and the metals. M. Fabre-Palaprat asserts, thatby the aid of galvanism he can cause certain chemical agents to traversethe body and appear at some distant part. He bound on one arm a com-press, moistened with a solution of ioduret of potassium, and covered bya platinum disk, connected with the negative pole (cathelectrode) of avoltaic battery of thirty pairs of plates. On the other arm was placed acompress, moistened with a solution of starch, and covered by a plati-num disk, connected with the positive pole (anelectrode) of the battery.In a few minutes the starch acquired a blue tinge, shewing that the iodinehad been transported from one arm to the other.

But the idea entertained by Davy, that the poles (electrodes) possessattractive or repulsive powers, has been shown by Faraday to be incor-rect. It is, indeed, true, that if we place a solution of ioduret of potas-sium in a glass tube (fig. 27, a.) closed atthe lower extremity by a piece of bladder,and immerse the tube in a glass vessel con-taining a solution of common salt and starch,we may, by connecting the liquid in the tubewith the negative pole (cathelectrode) (c,)and the outer or starch liquid -with the po-sitive pole (anelectrode) (d) obtain the blueiodide of starch in the outer liquid, shewingthat the iodine must have transuded thebladder. But the transudation is effected byexosmosis or imbibition, and not by the ac-tion of the battery, since the iodine may berecognised in the external liquid by appro-priate tests, when no voltaic apparatus hasbeen employed. The positive pole (anelectrode) does not, therefore,a'tract the iodine through the bladder, but merely sets it free when theioduret has transuded.

I have twice repeated M. Fabre-Palaprat’s experiment,—once on mypupil, Mr. John Smith, and a second time on my assistant, Mr. Scofiem,but though I employed fifty pairs of plates dining fifteen minutes, I wasunable to obtain the least Pace of the passage of iodine through the body.

It is not improbable, however, that electricity may promote absorption,either by increasing endosmosis, or by acting as a stimulus to the blood-• vessels and lymphatics.

10. Classification of Medicines.

In some works on Medical Botany, which contain figures of the plantsemployed in medicine, the authors have not followed any arrangement; inconsequence, I presume, of the impossibility of procuring specimens inregular order. This is the case in the following works :—

W. Woodville, M.D. Medical Botany, 3 vols. 4to. London , 1790. A Supplement tothe Medical Botany, 4to. London , 1794.

J. Bigelow, M.D. American Medical Botany, 3 vols. 8vo. Boston , 1817-18-20.