Fig. 508.—Direct Current Switch Board or Wall Plate.
Whether the street or battery current is used with such a plate makes no difference except that with a battery circuit the lamp is not used. The connections are given in [Fig. 509].
Fig. 509.—Wall-Plate Connections.
It will be observed that a current changing switch has been added to the wall plate. This is included in the circuit to permit of changing the poles to the patient without interfering or disconnecting the electrodes if desired at any time during treatment.
Portable Batteries.—The above instruments and circuits refer to those to be used in the operating room and are stationary. The physician may be called upon to treat a patient at a distance and for this purpose must have a portable battery.
There are many such instruments on the market of both dry and moist cell type. The moist cells usually require a bichromate of soda or potash solution and are so constructed that the carbon and zinc poles are taken out of the electrolyte or solution and placed into water-tight compartments provided for them. Such an apparatus is shown in [Fig. 510a].
Fig. 510a.—Portable Wet Cell Direct Current Apparatus.
The best cell for this purpose is the silver chloride battery. It is compact, light in weight, and gives a steady current. The only objection is the high cost.