ELECTROTHERAPEUTICS, or the treatment of disease by electricity, began to be a science with the work of Duchenne of Bou logne. Working chiefly with a faradic current he determined the motor points of the various muscles or the places upon the skin where the application of the current produces contrac tion of the individual muscles. And for a long time the testing and treatment of paralysed muscles was the principal function of the elec trotherapeutist. The burning and sometimes fa tal effect of lightning had always been lcnown and our countryman Benjamin Franldin had charged a Leyden jar w:th electricity collected from the clouds dunng a thunder storm. Frank lin, after whom static electricity is denominated Franklinic electricity, was among the first to ex periment with the shocks and muscular contrac tions produced by static electricity, One of the types of electrictty employed in electrotherapeutics and electrodiagnosis is Galvanic or Voltaic electricity or the constant direct current. This is obtained from a voltaic battery or from a storage battery, or from the direct current electric light circuit (suitably controlled) or from the alternating current electric light circuit employed to actuate a motor generator of direct current.
For various purposes the strength of the cur rent may be regulated in the case of a battery by selecting the proper number of cells, and in the case of the other sources of voltaic currents by rheostats or variable resistances placed in the path of the current or by volt controllers. The latter regulate the voltage at the terminals applied to .the body by offering the current a side path of variable resistance through which arg a greater or less part of the current may ass. A milliamperemeter to show the stren of current traversing the patient is essenti . For many purposes the current should have such or such a strength; and for all kinds of electro diagnosis we must be able to determine the strength of current required to produce certain physiological effects. Conducting cords or flexible insulated wires pass from the control table to electrodes in contact with the patient. The simplest example is a flat metal disk cov ered with fabric wet with a dilute solution of bicarbonate of sodium, preferable to salt which discolors the metal, and provided with an in sulated handle. Some other electrodes are a needle in an insulated handle; a carbon plate covered with a wet pad in a non-conducting tray partly filled with bicarbonate of sodium solution; a metal plate in an insulated bath tub of water; a metal sheet thickly covered with damp clay; or a bare metal cylinder which may be grasped in the hand. The galvanic or
voltaic current is a bipolar application, passing through the patient's body between two senarate electrodes, one the anode from the positive and the other the cathode from the negative pole of the battery or other generator. A switch is essential for turning the current on or off. A pole changer alters the polarity of the elec trodes by changing the connections at the con trol table by simply turning a switch. A pole detector is a necessary apparatus and a con venient one contains a colorless liquid which changes to red at the negative terminal.
Effects of the Galvanic One important effect is muscular contraction. This does not occur during the uniform passage of the current, but at the moment of any great variation in the strength of the current, as when a strong current is suddenly turned on or off. If the current were gradually increased from zero to the same maximum, no muscular con traction would result. In electrodiagnosis one electrode is called the indifferent one and is placed at some place remote from the region under examination. The other, active, electrode is applied to the skin either over the nerve at the place where the nerve is nearest the sur face, or over the muscle at the place where the motor nerve enters the muscle. These two places are called the motor points for the nerve and muscle respectively, because at these the application of electricity is most effective in producing muscular contraction. Figure 1 from a standard text-book is a chart of the motor points in the arm and is used as a guide in elec trodiagnosis or treatment. The threshold of excitability is the weakest strength of current which when suddenly turned on or off will cause muscular contraction. The reaction of degen eration takes place in many cases of paralysis and indicates a degeneration in the substance of the motor neuron itself. It occurs in polio myelitis, labioglossopharyngeal paralysis, and paralysis accompanied by lesions of the motor roots or of the motor nerves. In its complete form there is (1) abolition of galvanic and faradic excitability of the nerve; (2) abolition of the faradic excitability of the muscle; (3) hyper or hypoexcitability of the muscle with or without inversion of the normal formula, Ca C C > C C; (normally cathode closure contracture exceeds the anode, positive, closure contracture) but the muscular contraction is slow instead of the normal sharp jerk. The presence of the reaction of degeneration shows *hat nerves are affected and to what extent; and the return to a normal reaction indicates progress toward recovery of voluntary muscu lar power.