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 vertebrae. 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 vertebrae 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_.