Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

battery. If a vessel is nearly filled with acidulated water, and into it we plunge a plate of very oxidizable metal, such as zinc, for example, and also another plate that is much less oxidizable in that liquid, as platinum, and then we unite the two dissim- ilar metals merely by means of a wire brought up out of the liquid, then the positive electricity that is acquired by the liquid, from the effect of the chemical action, is able, by traversing the connecting and conducting wire, to return and reunite with the negative electricity that the attacked metal has retained. For thus the greater portion of the two electricities, negative and positive, become neutralized through this peculiar process and order, instead of taking place locally, directly at the place of contact of the liquid with the metal that is oxidized, and which Faraday has termed local action. Here, then, we see the rationale of the electric current or stream of the batteiy with which we shall have so much to do. And this peculiar associa- tion or relation of any two dissimilar metals in a liquid, whose power for oxidization and conduction is peculiarly or exclu- sively for one of the metals rather than for the other, is termed a galvanic pair or battery ; and when a number of these are connected, they are then termed a pile, or so many elements, or a " compound battery." Philosophers teach us that we may also regard the two metals of any voltaic or galvanic pair as separately, but mutually, giv- ing rise to two opposite and unequal currents, one of which — and it is always that arising from the metal most attacked — is the more intense, while the other, arising from the metal least attacked, is the more feeble; that each of the two metals also serves as a conductor to the current of the other. The current, then, that is accumulated is the difference between the two partial and unequal currents, as they would be perfectly null if these two opposite and simultaneous currents were absolutely equal — a condition, as M. De la Rive says, next to an impossibility, even if we employ two metal plates as similar as can be in every respect. It is, therefore, a law that the metal of the battery that is most attacked determines that current direction. But while we attempt to establish in our minds the first fact, that the