It is often desirable to bring the entire parts of the patient, through which the current is made to pass, under one and the same kind of influence—such as shall make them all more positive or more negative. Especially is this true in many cases where we wish to run through but a short space. For this purpose, there is frequent advantage in using conducting cords of unequal length. As my views on this point have been disputed in certain quarters, I will endeavor here to place them in such a light that they shall not be rejected for want of being rightly understood.
I have previously remarked[C] that, for practical purposes, it is sufficiently exact to consider the magnetic circuit as extending only from the positive post, around through the conducting cords, the electrodes, and the person of the patient, to the negative post. We will so regard it at present. This circuit may be viewed as one continuous magnet, made up of several sections or shorter magnets placed end to end—the positive end of the first to the negative end of the second, and the positive end of the second to the negative end of the third. In this arrangement, the negative end of the first section is the negative pole of the one whole magnet, and the positive end of the third section is the positive pole of the whole magnet. The minimum quantity of the magnetism is supposed to be at the negative pole, and the maximum quantity at the positive pole; and the quantity is supposed to increase, by regular graduation, from the negative to the positive pole. This being so, the quantity is the same in the positive end of either section and the negative end of the adjoining section, at their point of contact.
Now, in practice, the body of the patient, or so much of it as is embraced between the two electrodes, may be regarded as the second section in this magnet; and the cord connected with the positive post, together with its electrode attached, may be counted the first and most negative section; and the cord connected with the negative post, along with its electrode, may be the third and most positive section. And if this whole magnet be more and more positive, by regular degrees through all the sections, from its negative to its positive end or pole, then the nearer any given part of it, say the second section—the patient's person, may be to its positive pole in the negative post, so much the more positive that section or part will be. And the nearer such part or section may be to the negative pole in the positive post, so much the more negative it will be. If the cords be of equal length, the central point in the circuit or magnet will be in the second section—the person of the patient, midway between the electrodes; and that section will be charged with the mean quantity of the magnetic fluid. The central point will hold exactly the mean quantity. But if the cord in the first section be two yards long, and that in the third section be four yards, then section second—the patient's parts under treatment—will be nearest to the negative pole in the positive post, and consequently will be charged with much less than the mean quantity of the fluid, and will therefore be made so much the more negative. If, on the other hand, the cord in section first be four yards in length, and that in section third be only two yards, then the patient's body—section second—will be brought nearest to the positive pole in the negative post, and of course be charged with much more than the mean quantity of the magnetic fluid, and hence will be made so much the more positive.
It is true that the positive and negative poles of section second—the parts of the patient between the electrodes—will not be reversed by any such changes in the length or relative positions of the conducting cords; nor is such reversal required in those cases where the use of the long cord is indicated. The only change of polarization called for in such cases, is that all the parts through which the current is to pass should, in greater or less degree, be affected alike, as being made more positive or more negative. Of course these parts will be so affected in different degrees—those nearest to the short cord the most; those nearest to the long cord the least.
The class of cases where the use of the long cord is more especially advantageous, comprises those in which it is desirable to run the current out of the patient at the shortest admissible distance from the positive electrode. For example, in treating cynanche tonsillaris, (quinsy), if treating with the positive pole in the mouth, we would not wish to run the current further than to the back of the neck; or, if treating externally, we would not wish to carry the negative electrode further from the positive than from side to side. Here the long cord, with the negative electrode, would be a special advantage in subduing the inflammation. We would not care to increase the inflammatory action, as we should necessarily do on the positive side of the central point, by using cords of equal length.
Again, if treating a case of acute enteritis—inflammation of the intestines—we would not wish, while treating the abdomen with the positive pole, to increase the inflammation in the lower parts, by using equal cords and placing the negative pole at the sacrum or the coccyx. Neither would we wish to reduce the strength of the lower limbs by carrying the negative pole to the feet. Nor, yet again, would we care to endanger the thoracic viscera by running the current from the abdomen up to the dorsal or cervical vertebræ. The true way, in such a case, would be to connect the negative electrode with a long cord, and then to run the current through the inflamed parts, and out somewhere from the lumbar vertebræ to the coccyx, by treating over the abdomen with the positive pole, and placing the negative pole on the lower parts of the spine.
As the cords that accompany the machine from the manufacturer are usually cut about two yards in length, every practitioner should supply himself with an extra cord, of at least three yards, to be used as the long cord.
THE INWARD AND THE OUTWARD CURRENT.
I have already said that when the conducting-cords are of equal length, as for the most part they should be, the central point of the circuit will be in the person of the patient, about midway between the two electrodes. Now, since the current always runs from the positive to the negative pole, and makes its whole circuit in that direction, it will be readily seen that, from the place on the patient where the positive pole is applied, inward as far as to the central point, the direction of the current may properly be said to be inward; and that, from the central point to the place of the negative electrode, where the current comes out, its direction may be said to be outward. When, therefore, a part is treated with the positive pole, or when the part under treatment appears anywhere between the positive pole and the central point, it is not unusual to say, It is treated with the inward current. And when a part is treated with the negative pole, or when it appears between the central point and the negative pole, it is often spoken of as being treated with the outward current.