III.

ELECTRO-PHYSICS.

BY A. J. BAKER, M.D., BOSTON, MASS.

MR. PRESIDENT, GENTLEMEN AND LADIES, In introducing this, a comparatively new subject, before this Society, I must beg your indulgence, first, for the uninteresting matter one is obliged to introduce into foundations which are expected to support substantial structures; second, if I dwell upon preliminaries longer than seems profitable or interesting, encouraging you with the hope of future interest in clinical results.

It was not a

The subjects usually presented here are those, the preliminaries of which we are, or should be, familiar with; but in this subject of electricity it is quite different. part of our college education, but a separate and special study; and, because of its primary principles having in the past been neglected, it is the more essential that we begin as nearly right as possible. I have therefore decided to confine myself, in this paper, chiefly to electro-physics, taking up in their order, in future, the different subjects of the science as applied to therapeutics. In doing this I shall be obliged, in this department of the work particularly, to quote various authorities: I could not otherwise give you electro-physics.

The differences of opinion on the therapeutic value of electricity are readily understood, if we bear in mind that the mode of application has an all-important bearing upon the result (it is true, that, even by a careless employment of it, a few accidental successes have been obtained): hence it can

only be expected to be of service in the treatment of disease, if we are guided in its use by an exact knowledge of the physiological effects which it will invariably produce. The profession have now too widely employed electricity in the treatment of disease, and with too frequent success, to deny it a place among prominent therapeutic agents. The only questions concerning it now are those which relate to the versatility of its power, the scope of its useful applicability, and the principles which must govern in its administration.

The general subject embraced in these questions is one in which suffering humanity has a right to claim that physicians shall be at home; and yet I think you will bear me out in saying, that in the exhibition of electricity, more than almost any other therapeutic agent, medical practitioners feel uncertain as to what shall be its effect.

Now and then it acts as they expected it to do; sometimes it pleasantly surprises them, again it offensively disappoints them: its action on the living organism appears to them to be largely veiled in mystery.

There is, again, another class of physicians who say they do not believe in the agent as one possessing any therapeutic advantages. I can no better explain such assertions coming from learned men, than by referring to the anecdote concerning Charles Lamb, who, when asked to be introduced to certain persons, stammered, "I don't like them."-"But you do not know them, Mr. Lamb." "I know I do not know them, and that is why I do not like them."

It may be asked, What if it be true that these things can be done with electricity? They are also done with medicines, which are more quickly and conveniently administered: what, therefore, is the practical utility of your electric system above the ordinary method of practice, especially if we include, in the latter, electricity as occasionally employed by the most of respectable physicians?

This is an important question; one, too, which I think can be appreciated by those who have used electricity to any extent in their practice: for it is true that a physician can pre

scribe medicine for half a dozen or more patients in the time required to treat one electrically. First, then, in not a few diseases, and these among the most dangerous or distressing, the electric current, skilfully employed, is able to reach, control, and cure with facility, where medicines are but slowly and in some instances imperfectly successful, or fail altogether.

This is perhaps most often exemplified in neuralgic, rheumatic, and paralytic affections. Cases often come under my notice, also, of inflammatory action, more particularly where it is internal, which medicines have failed to subdue, and which electricity controls with almost infallible certainty.

Why is it that the mass of those who use electricity do so with no knowledge, or next to none, of the versatility of action, of which the electric current is capable? They appear to suppose that the point to be immediately aimed at, as a means of cure, is to get the electricity from the machine into the affected parts; whereas it should be, to change by correction the polarization of the parts, and, if there be virus present, to neutralize it.

Equally unacquainted are they generally with the diverse physiological action of the several modifications of the electric force, — galvanism, magnetism, Faradism, and frictional electricity, — and generally little or no better acquainted with the distinctive effects on the system of the positive and negative poles of the instrument. There is, therefore, plainly no science in their electrical practice: every thing is done at random, all is empirical.

"In England," says Professor Jenkin, "at the present time, it may almost be said that there are two sciences of electricity, one that is taught in ordinary text-books, and the other a sort of floating science known more or less perfectly to practical electricians. It is not a little curious that the science known to the practical electro-therapeutist is, so to speak, more scientific than the science of the text-books. These latter contain an apparently incoherent series of facts; and it is only by considerable mental labor, that, after reading the long roll of disjointed experiments, the student can even approximately understand any one experiment in its entirety. The author is content to say, under such and

such circumstances, a current flows, or a resistance is increased; the practical electrician must know how much current, and how much resistance, or he knows nothing: the difference is analogous to that between qualitative and` quantitative analysis. This measurement of electrical magnitudes absolutely requires the use of the word and idea potential, and of various units, each with an appropriate name, in terms of which each electrical magnitude can be expressed."

I repeat, then, the rational practice of electro-therapeutics is impossible, without some knowledge of the physical conditions under which we act.

"Electricity, then, like the other forces of nature, is a form of molecular motion. Many of its phenomena can be represented under the likeness of a fluid in motion, of a current flowing; and, in order to realize more vividly its manifestations, we may trace some analogies between a stream of water and a current of electricity. Such a current may be continuous, as in the case of the galvanic cell; or intermittent, and consist of a series of small currents or sparks, as in the case of the frictional machine or the induced coil: but it must be firmly remembered that the identical laws which govern the one, also govern the other.

"Galvanism, however, offering the mere typical instance, I shall confine myself to the phenomena presented by the so-called constant current. The fundamental condition of the existence of a stream of water is a difference of level between two points. If we wish to produce a flow of water from point to point, we must make one point higher than the other. In precisely the same manner, if we wish to have a flow of electricity between two points, we must create a difference of level between them, actually or by analogy. This difference of electrical level is called difference of potential. A galvanic element consists essentially of a vessel containing a liquid in which two plates of dissimilar metals, say zinc and copper, are immersed. To the top of each plate or electrode is fixed a copper wire. If, now, these wires are successively brought into contact with an instrument called a quadrant electrometer, constructed so as to measure differences of potential, we find that such a difference exists between the two wires. Next, if we attach the wire to the terminals of a sensitive galvanometer, immediately we notice a deflection of the needle a current flows through the galvanometer. Further, we notice that this deflection is not temporary, but lasting a more or less considerable time. Hence we conclude that our cell has the power, not only of producing difference of potential between two insulated points, but also of keeping up this difference when these points are connected through a conductor. As in hydrostatics we take the level of the sea as standard level for our measurements, so in electrics we take the potential of the

earth as standard with which we may compare the potential of any point of the body. In fact, we assume the earth to be in a state of electrical rest, as we do the sea to be at a uniform level.

“And, as the one is a practically unlimited reservoir of water, so the other is of electricity; small additions or subtractions of fluid having no perceptible effect in altering the level in either case. The potential of a body may therefore be defined as 'the excess or defect of its potential above or below that of the earth.' In illustration of this conception, we may adduce the thermometrical measurements of temperature. Our zero point having been fixed as that of the freezing-point of water, we measure the temperature of bodies by referring them to the standard so chosen.

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As, then, we have levels above and below that of the sea, and temperatures above and below freezing-point of water, so we have potentials above and below the earth's potential. The former are called positive potentials; the latter, negative potentials. When, therefore, we say that a point is at a positive potential, we imply, that, if connected with the earth, electricity will flow from it to the earth; and, conversely, that if a point is at a negative potential, electricity will, under the same circumstances, flow from the earth to the point.

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Therefore the expression of the potential, positive or negative, of a body, coincides with the statement that it is charged with 'positive' or 'negative' electricity. But it frequently happens that we have to compare the potentials of two points, irrespective of their relation to the earth's potential; and we then speak of them as being positive and negative respectively, though both may be, absolutely speaking, positive, or both negative. But this does not constitute an exception to the general law that the flow of electricity always takes place from the higher to the lower potential,—from the more positive to the less positive if both are above, from the less negative to the more negative if both are below, the earth's potential. Exactly the same thing occurs in the case of temperatures heat flows from the warmer to the colder point. Whether both be above, or both below zero, between two cisterns at different levels either above or below that of the sea, the stream invariably follows the same direction.

"If, by means of an appropriate instrument, we test the terminals of a galvanic element, we find that the wire connected with the copper is electrified positively, and the wire connected with the zinc negatively : hence the names of positive and negative poles of the cell; and the direction of the current which flows in a conductor uniting the two poles is accordingly found to be from copper to zinc.

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"When the two wires are placed in mutual contact, or in contact with a conductor, we say that the 'circuit is closed,' implying by this expression that the current of electricity does not simply flow from positive to