VOLTAISM OR GALVANISM.
Voltaism.
The Voltaic current is a continuous current. Unless artificially interrupted, the electricity flows in an unbroken stream until the battery is exhausted. The current will gradually lessen in power until it ceases, but there will be no break in it, and no change in its direction, which is uniformly from the positive to the negative pole. |Points of distinction between the Voltaic and Faradaic Currents.| It is important to recollect these points, for they constitute the chief physical distinction between the Voltaic and the Faradaic—or, as it is sometimes called, the Induced current. This latter is not, strictly speaking, a “current,” but a rapid discharge or succession of momentary shocks, each perfectly distinct in itself, and separated by an appreciable interval of time from its fellows.
Voltaic Cells.
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]
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.
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.
G. Key by which the current can be shut “off” or “on,” without change of position of the conductors. It can also be used by vibrating it backwards and forwards as an “interrupter.”
I, I. Binding screws, to which are attached the conducting wires and sponge-holders, &c.
The Voltaic Battery.
The Voltaic Battery (see [Fig. 6], p. 20) has its cells arranged in the interior of a mahogany case, and in use they are hidden from view and from danger, but I now partially expose them by removal of the tray for holding the sponges and accessories. Their connecting wires are brought across the under surface of the element board, which is made to move upon hinges that, when necessary, the cells may be examined, but at other times this element board is held in position by a bolt, and it should never be needlessly disturbed. These wires conduct the current through the graduating dial, and the position of the needle of this dial determines from how many of the cells the electricity shall be allowed to reach the binding screws, and from them, by way of the conductors, sponge-holders, or electrodes, the body of the patient,[8] or whether it shall be entirely shut off, as is the case when the battery is not in use, and when the needle stands at “0” ([Fig. 7]). When the needle points to any stud numbered on the dial, the number of cells marked on that stud are brought into action, and the needle is made just wide enough to touch one of the studs before it breaks contact with the preceding one, and thus the current may be increased or decreased in power without shock, and while the electrodes are held applied to the patient; but if it were not so made a series of painful shocks would be communicated whenever the current was increased or decreased. Should the needle, from forgetfulness, be left when out of use in any other position than at “0,” a guard upon the lid of the instrument prevents its being shut, and the operator has his attention called to his inadvertence. A Voltaic alternative, or change of direction of the current, is sometimes required in treatment, and the commutator of the poles enables this to be accomplished without alteration in the position of the conductors. By pushing forwards or backwards the handle which moves a lever working below the element board the current is instantly reversed, and the alternation of the letters “P” and “N” seen through holes cut in the element board indicates at once not only that there has been a change of poles, but which pole is at the moment negative or positive; whereas in all previous instruments, when the poles have been changed, there has either been no letter marking them, or this letter has really been wrong, and one has had to remember this; and under such circumstances, and examining patients in rapid succession, momentary confusion of the poles was very liable to occur, even to a practised operator. A key enables the current to be shut off or on without removal of the conductors. Dirt is a non-conductor of electricity, and the studs of the dial must be kept clean with emery paper or plate-powder, as also the under surface of the needle, key, and binding screws, which unscrew to admit of removal. In the daily use of a battery the chief work is usually thrown upon the first half (say in a battery of forty cells, upon the first twenty-five), and various arrangements have been added to batteries by ingenious instrument-makers to enable the operator to vary his selection of the cells to be brought into use, and thus to relieve the first half of his battery, or, in other words, to equalize its work. But this unequal work question is more a theoretical than a practical evil; for if the initial cells grow weaker a greater number can be placed in use. I have carefully studied all the proposed modifications, and have found in all of them the remedy worse than the disease, unless the graduating dial be doubled (an original suggestion of my own), so that the initial cells of one week may be made the terminal cells of the next.
Fig. 7. Graduating dial with needle at “0”.
When desired batteries can be constructed with this double dial [(Fig. 8)], but it adds to the complexity of the instrument, and I do not myself use it.
Fig. 8. New form of Graduating Dial.
In [Fig. 9] a similar battery is shown to that just described; but the elements consist of carbon and zinc, and are lifted into and out of a bichromate solution. As it can be recharged by the owner without the necessity of sending it to the maker, it is especially suited for country and colonial practitioners.
Fig. 9. 40-Cell Voltaic Battery with zinc and carbon elements, and lifting apparatus.
Essentials of a Medical Voltaic Battery.
To recapitulate. The essentials of a medical Voltaic battery are—
a. A constant supply of electricity of sufficient quantity and quality.
b. A means by which this electricity may be administered in measured doses.
c. A means by which the direction of its current may be changed.
d. A means by which it may be instantly discontinued.