In electrization, a source of electricity is of course necessary, and this is furnished by a cell or cells, with contained elements and chemicals; and, until a few years ago, it was impossible to get a _portable_ cell that remained always in order and ready for use.[7] [SN: Requisites of a Portable Battery.] The requisites of a portable battery are that it should be really portable, always ready for use, and little liable to get out of order. Such batteries may be divided into two classes: firstly, those in which the elements are either lowered into the exciting fluid or the fluid is lifted to them, as in the instruments of Stöhrer, Weiss, and almost all other makers; and, secondly, those in which the elements remain immovable in their cells, and of these the Leclanché, the Gaiffe-Clamond, and the chloride of silver, are to be generally preferred to any of the first-named construction, for they admit of the cells being so nearly sealed up that no fluid can be spilt by any movement except turning the battery quite upside down; while the somewhat common accident with batteries of the first-named construction--viz., destruction of the plates by leaving them in the acid, with its anything but agreeable result of a considerable expense to replace them, is obviously impossible. The only disadvantage they possess is that when exhausted it is necessary to send them to the maker to be recharged, _while the owner can keep the first-named variety in order himself_. Efficient cells are, however, but a first step to the perfection of electrical apparatus, and the mechanism by which the current is brought into use and graduated, and the general accessories of the instrument, are of at least equal importance. The instruments which I am about to describe, have been designed by myself, and may be obtained from Mr. Hawksley, Surgical Instrument Maker, Oxford Street. It is claimed for them that they place at the service of the busy practitioner a battery that with ordinary care (and no instrument will remain in order without this) may be kept upon his consulting-room table, always as available to his service as his stethoscope or ophthalmoscope. Three kinds of batteries are constructed:--A Voltaic battery, with any required number of cells, from 15 to 100; a Faradaic battery; and a Combined battery, uniting both Voltaic and Faradaic currents. [Illustration: FIG. 6. 40-Cell Voltaic Battery. A. Guard preventing the lid being shut, unless the needle of the dial points to “0”, and the instrument is out of action. B. Cells shown by the removal of the compartment, H, for sponges and accessories. C. Bolt to secure the element board, which moves upon the hinges, D. D, D. Hinges of element board. E. Dial plate regulating the strength of the current. The needle, when the battery is not in use, should cover the stud, “0,” seen to its left. F. Commutator of the poles. The poles, N and P, are seen through holes cut in the element board.