In practice electrodes having quite a considerable area are em ployed and care is taken to wet them in a ten or twenty per cent. solu tion of chloride of sodium before they are applied to the skin. It has been taught that the electrodes should be applied at parts corre sponding to the insertion of the muscles, and the current passing between them will then excite muscular contractions, the intensity and extent of which present variations of considerable interest. The following, however, is the method usually employed at the present day : An electrode of large area, known as the indifferent electrode, is placed upon the sternum; the other, the differential electrode, is brought in contact with the integument covering the muscle to be ex amined. The current passes and the circuit is then closed; when the electrode is removed the circuit is opened. I need not more than refer to the necessity that may exist for attaching to the exploratory apparatus an instrument for indicating the intensity of the current.
In order to simplify the recording of the modifications observed under the influence of the electrical current, it has become customary to employ a certain number of conventional signs, designating the positive and negative poles, the opening and closing of the current, and the reaction (shock or contraction) which results. But for all these details I must refer the reader to one of the numerous special treatises on medical electricity. We need only add that, after having tested the muscle directly by means of the negative pole, the cor responding electrode should be used as the indifferent one, the posi tive electrode then becoming the one by which the reactions are tested. By this substitution we may obtain differences in reaction of
some diagnostic value.
In the normal state, the faradic current excites independent contractions when the interruptions are not very rapid; when these are increased the muscle becomes tetanically contracted. The neg ative pole always produces stronger contractions than the positive. When we galvanize a healthy muscle we obtain weak localized con tractions at the instant of opening or closing the circuit, and we note also that the negative pole excites to stronger contractions than the positive.
I have already spoken of the difficulty that is met with in disso ciating electrization of the muscles from that of the nerves. We should take care not to place the electrode over the points of entrance of these nerves, a matter of relative ease in the case of certain muscles such as the biceps, the deltoid, the anterior muscles of the leg, etc. Furthermore the points of election for application of the electrode have been determined in the case of each muscle and are pictured in many works on the subject.
In disease of the muscles we often find a diminution or even a complete abolition of the electrical contractility. This abolition of reaction indicates a destruction of the muscular element. In certain cases there is, so to say, a dissociation of the electro-muscular con tractility, and we find that the continuous current will still excite con tractions while faradization produces no effect.
After this brief consideration of the general symptomatology of diseases of the muscles, in a certain measure necessary by way of introduction, we will take up the study of the various forms of in flammation of muscular tissue.