Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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nerve trunk that occasions tonic contractions of varied degrees, according to the resistance the given current meets in its way. Labile contractions can also be produced by directing one elec- trode so as to glide over the point of insertion of the tendon into the farther end of the fibres of the muscle. We are led to notice that, for instance, in lean persons, when the platysma myoides is caused to contract by Faradaic or Gal- vanic excitement, the skin of the neck is raised into sharp folds, over the contracted fibres of that muscle, from the transversal arrangement of the electrodes above the clavicle. Now, as soon as one of the electrodes is swept along, we get the labile con- tractions in the successive fibres over which it passes. But the contractions are still stronger if the electrodes are situated so as to be according to the anatomy of that muscle ; i. e., longi- tudinal with its fibres, if the electrode movements regard that mainly, although obliquely. In such muscles as are attached fleshily to the bones of the joints, the mechanical effect of the current is almost nothing when the electrode passes transversely across the fibres of them. But we can increase this effect, as, for instance, on the extensor muscles of the relaxed and down- hanging hand, by a proper position or support, as of the forearm, so that the current will then simply, from that little aid, produce a full lifting of the hand to a horizontal posture, while the elec- trode moves along rather obliquely across the direction of those extensor muscle fibres on the forearm, and thereby changing even the labile contractions into a gradually increasing tonic together-drawing of the fibres of the extensor muscles, and thus producing a good stretch of the hand. Sometimes we notice the labile contractions of the contractile tissues and muscle fibres will appear only at the moving, and not at all at the stationary electrode. This is according to the ex- citability of the contractile fibres that come respectively under the electrodes. If the trial is reversed, i. e., if the previously moving electrode is now held at rest, while the other one is caused to vary and move a little, then, even, will the very same fibres twitch which are under or near the electrode that is at rest. This can be tested in another way on a large scale, as