. A text-book of physiology : for medical students and physicians . and thence to the active electrode. Asthe threads of current condense to this latter electrode they passthrough the motor nerve which lies under it, and if sufficiently in- THE PHENOMENON OF CONDUCTION. 91 tense, will stimulate the nerve. The arrangement is represented inthe accompanying schema (Fig. 34), showing the disposition of theelectrodes for stimulating the median nerve. At the indifferentelectrode the sensory nerves of the skin are of course stimulated, butno motor response is obtained, as no motor nerve lies immediat
. A text-book of physiology : for medical students and physicians . and thence to the active electrode. Asthe threads of current condense to this latter electrode they passthrough the motor nerve which lies under it, and if sufficiently in- THE PHENOMENON OF CONDUCTION. 91 tense, will stimulate the nerve. The arrangement is represented inthe accompanying schema (Fig. 34), showing the disposition of theelectrodes for stimulating the median nerve. At the indifferentelectrode the sensory nerves of the skin are of course stimulated, butno motor response is obtained, as no motor nerve lies immediatelyunder the skin. Moreover, the large size of this electrode tends todiffuse the current and thus reduce its effectiveness in active or stimulating electrode is small in size, particularlywhen induction currents are employed, so that the current may becondensed and thus gain in effectiveness. The dry surface of theskin is a poor conductor of the electrical current, and to reduce theresistance at the points at which the electrodes come in contact. _ Fig. 34.—Schema to show the unipolar method of stimulation in man. The anode,+, is represented as the stimulating pole, applied over the median nerve. The cathode,—, is the indifferent pole. with the skin each is covered with cotton or chamois skin keptmoistened with a dilute saline solution. Motor Points.—By means of the unipolar method nearly everyvoluntary muscle of the body may be stimulated separately. Allthat is necessary, when the induced current is used, is to bring theactive electrode as nearly as possible over the spot at which themuscle receives its motor branch. A diagram showing these motorpoints for the arm is given in Fig. 35. In the same way the 92 THE PHYSIOLOGY OF MUSCLE AND NERVE. nerves of the brachial plexus and other nerve trunks may. bestimulated very readily through the skin. When the inductioncurrent is used no distinction is made between the cathodic andanodic effects. When, however, t
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