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

metal most attacked is the positive, and the second fact, that the metal least attacked is the negative, we must not lose sight of the third fact, that the positive electricity comes out of the battery by the negative or copper metal after having passed through the liquid of the battery, and consequently the other, or negative electricity, comes out by the positive or zinc metal, so that in these batteries the zinc pole is negative while the copper pole is positive. Besides, we should take the terms positive and negative simply in the sense of electro-motive power, — the positive as predominating over the negative, and constituting a prevailing stream or current. But we must also recollect, that although it is true that the metal most attacked is the starting point for the current direction, yet the mere gal- vanic series of metals do not of themselves and under all circum- stances determine the route of the current absolute; for this is likewise dependent upon the nature of the liquid that is em- ployed as an exciter or oxidizer. Faraday found a very curious and interesting variation of the current when he placed a gal- vanic pair of copper and silver in a solution of sulphuret of potassium; the current first setting out from the copper, the silver is not the least tarnished, and soon the action dies down to a low degree. But this is soon seen to be followed by an increasing action that is now on the silver, which gives rise to a current running in the opposite direction, while the sil- ver is becoming more and more coated with the sulphuret; and at the same time the film that was at first formed on the copper is as rapidly dissolved off; in a few minutes more and the needle of the galvanometer drops to near zero, but as soon again begins to rise, reversed, showing an increasing but changed current direction, and the copper again becomes posi- tive, and coats over. Thus the chemical action and the direc- tion of the current change simultaneously. Quantity and Intensity. Electricity, when in the current form, has two very distinctive and important characteristics, which must never be unheeded or