A laboratory manual of electrotherapeutics . s thought desirable. The Indirect Spark (Fig. 48.)—In order to get theindirect spark the machine must be grounded. This isdone by putting the negative prime conductor or pole ofthe machine in communication with the earth by means ofa conductor running from it to a convenient gas pipe orwater-pipe. The electrode used for the purpose of draw-ing sparks should also be grounded. This has the effectof increasing the quantity of electricity which the machinegenerates and improving the constancy of its action. Thespark is likely to have more volume and is
A laboratory manual of electrotherapeutics . s thought desirable. The Indirect Spark (Fig. 48.)—In order to get theindirect spark the machine must be grounded. This isdone by putting the negative prime conductor or pole ofthe machine in communication with the earth by means ofa conductor running from it to a convenient gas pipe orwater-pipe. The electrode used for the purpose of draw-ing sparks should also be grounded. This has the effectof increasing the quantity of electricity which the machinegenerates and improving the constancy of its action. Thespark is likely to have more volume and is cleaner, withless irritating properties, It is more satisfactory, there- 134 LABORATORY MANUAL fore, when using the spark treatment to have the machinegrounded. A sputtering series of sparks is very disagree-able to most patients and irritates the sensory nerves andshould always be avoided except when this effect is soughtfor, as in the case when counter-irritation or skin excita-tion is desired. It insures a clean, full, individual spark. Fig. 16, to have the machine well grounded and then make the ballelectrode approach the part of the charged body suddenlyto within the proper distance and as suddenly withdraw it. The purpose and manner of the treatment with the in-direct spark is the same as that with the direct spark, butthe effect differs because of the physical and physiologicaldifferences which they possess. The Friction Spark.—This is used mainly for ex-citation of the skin or the superficial blood vessels and is,a convenient method for applying mild patient is insulated as with the spark treatment. Aroller electrode is provided for this application but is notnecessary since the large ball electrode will serve the same OF ELECTROTHERAPEUTICS. 135 purpose. The only physical difference between this andthe direct or indirect spark is that the dielectric is thinneddown to a layer which is represented by the thickness ofthe patients clothing. The r
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