. Electricity : its medical and surgical applications, including radiotherapy and phototherapy . Schematic representation of the distribution and density of the threads of current with regard totheir entrance deeply into the tissue (in this instance, into the spinal cord): n, when electrodes are inclose proximity; b, when far removed from one another. (Erb.) To affect a small superficial structure, such as one of the peripheralnerves, the active electrode should be small (Fig. 159) and well presseddown upon the nerve. The indifferent electrode (Fig. 159) should belarge. Fia. 159. S, S, represe
. Electricity : its medical and surgical applications, including radiotherapy and phototherapy . Schematic representation of the distribution and density of the threads of current with regard totheir entrance deeply into the tissue (in this instance, into the spinal cord): n, when electrodes are inclose proximity; b, when far removed from one another. (Erb.) To affect a small superficial structure, such as one of the peripheralnerves, the active electrode should be small (Fig. 159) and well presseddown upon the nerve. The indifferent electrode (Fig. 159) should belarge. Fia. 159. S, S, represents the skin; A^, N, a nerve trunk. The density of the current under the small ornegative electrode is much greater than that under the large or positive electrode. If very strong currents are to be passed through the skin, it is essentialthat the electrode in contact with the skin be large. Large electrodesdo not cause as much pain as small ones. Whenever the polar action(p. 132) is desired the indifferent electrode should be far removed fromthe part being treated (Fig. 116). 206 GENERAL RULES AND PRECAUTIONS DOSAGE When the galvanic current is employed the current strength employedcan be exactly estimated by means of the galvanometer or milliampere-meter (Fig. 44). By dividing this current strength, estimated in mil-liamperes by the diameter of the electrode, we obtain the current considers the limits of safe therapeutic dosage to lie and 50 milliamperes, with an electrode surface of from 3 to 500square centimeters. For most purposes 5 to 10
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