[8] _The Galvanometer as an aid to the Dosage of Electricity._--The dose of voltaic electricity is made up of two factors, (_a_) the strength of the current and (_b_), the time during which it is applied to the patient. [SN: The Galvanometer as an aid to the Dosage of Electricity.] The strength of the current is directly dependent upon the number of cells employed, but, unfortunately, cells of dissimilar construction evolve currents of very unequal strength; while cells that have been freshly charged are more powerful than similar ones that have been partly exhausted by use; and, therefore, to speak of a current from “so many cells,” though, practically, a convenient method of dosage, fails to convey any _exact_ idea of a measured and unvarying quantity. It is a comforting theory to electro-therapeutists that a galvanometer will enable them to administer their doses of electricity with as much exactitude as we daily prescribe so many grains, or so many minims of ordinary medicines; but, like some other theories which save us much trouble, when adopted as theories _only_, it fails us in practice (at least according to my experience), and chiefly so, because a galvanometer can be usefully employed only when it is included in the circuit of a continuous current, as, _e.g._, in aneurismal electro-puncture; and, I believe, I am within the mark in saying that electrizations, which even admit of its useful employment, are indicated in barely 5 per cent. of ordinary cases in electro-therapeutics; and that it is of no practical utility, where we most want aid, in measuring, not the current which leaves the battery terminals, but that which, after overcoming the very variable resistance of the human skin, really reaches the underlying muscular and nervous tissues, which, in 95 per cent. of our cases, we desire to influence, not by a constant, but by an interrupted Voltaic current; and the amount which really reaches these tissues depends largely upon the condition of the patient’s skin, and, I may also add, upon the kind and shape of the conductor, and its degree of moisture, &c.; and the operator will do well to graduate his dose of electricity by a consideration only of the three factors, number of cells, effect upon himself, and effect upon his patient, discarding entirely the use of any merely mechanical aids to graduation.