one

pitmary current. When these windings run near another, their action is inductive, and they produce what is called the extra current. That this is really so, may be easily seen if we take a simple galvanic battery and close it, at first with a short, and then, for comparison, with a long spirally-wound wire. In the first case we will observe a very weak, in the second a much stronger emission of sparks. From the extra current-which was also known to Faraday, but for a thorough acquaintance with which we are, however, indebted to Dove'-originates also an induced current. It arises, as such, at the opening and closing, and takes at the closing a direction opposite to, at the opening a direction corresponding with, the primitive current. That it nevertheless, at the closing, has no effect on a body introduced, that is not so good a conductor, is due to the fact that the current in this case finds in the battery itself a closed metallic conductor, and consequently leaves the secondary connecting body unaffected. At the opening, on the contrary, the action is decided, because here the primary current is interrupted, and consequently the extra current flows through the body that has been introduced in its full intensity. A considerable increase of the extra current will be noticed if we put into the hollow of the wooden cylinder a piece of iron, or better, a split iron cylinder, or better still, a bundle of varnished wire. (Bachhoffner and Sturgeon, in "Annals of Electricity," vol. i., p. 481.)'

1 Poggendorf's Annalen, Band lvi., Pag. 251.

The cause of these phenomena, it was formerly thought, lay in the fact that the metal of which wire is made is softer than a piece of ordinary iron, and consequently susceptible of greater magnetism. Magnus (“Poggendorf's Annalen," vol. xlviii., p. 95) corrected this error. He showed, by the deviation of the magnetic needle, that the bundle of wire was not more strongly magnetized than the piece of iron by the current. He found, moreover, that the physiological action of a bundle of wire was stronger, and was still further strengthened by covering some pieces of the wire with varnish. Magnus's explanation was the following: The current surrounding the iron generates in the iron, at the moment it arises, a counter electric current; during its continuance the iron is maintained in a state of magnetic polarization; when it stops, a current

Here the galvanic current renders the soft iron at first magnetic, and thereby enables it in turn to induce electric currents in the spiral wire. The intensity of the current depends, on the one hand, upon the power of the battery, upon the other on the length of the inductive spiral, the thickness of the wire used, and the size of the bundle of wire. The wire for the inducing current is generally shorter and larger, that for the induced current longer and smaller. The reason will be given in the fifth chapter, where we shall go more into detail with regard to the difference in the action of the two currents. We will now simply observe that the extra current induces currents and causes shocks only when the . circuit is opened, while the secondary current does so both when the circuit is opened and closed.

We call a galvanic battery consisting of one or two helices a volta-electric or galvano-electric apparatus. As the induced current produced by such a battery is of only short duration, steps must be taken in order to secure continued generation for medical purposes, to frequently interrupt the primary current. This can be effected either mechanically, by introducing, according to the directions of Sprenger and Aldini, a toothed wheel, the teeth of which, as the wheel is turned, continually open or close the circuit, as in Güterbrock's, Rauch's apparatus, etc., or, much better, by the so-called Neefe's hammer, originally constructed by J. P. Wagner, in Frankfort, a clever contrivance, that secures the opening and closing by using the temporary magnetism of the bundle of

corresponding in direction with the primary current is produced. This current, however, retards the disappearance of the magnetism, and thereby weakens the action to be anticipated from the sudden discontinuance of the magnetism. What, therefore, operates to lessen the power of this current in the iron, increases the action of the extra current. But the action of this current will evidently not be so powerful on separate, and especially isolated wires, as on a solid piece of iron. Consequently, in a current induced by a bundle of wire, a given quantity of electricity will be more quickly compensated, and thereby more energetic in its action, than in a current induced by a piece of iron of the same dimensions. A similar result will be obtained with a split cylinder.

wire within the helix. This little hammer, of soft iron, was formerly attached to a steel spring, so that, by drawing it back and letting it strike, the battery could be opened and closed in continued succession. To these self-acting voltaelectric batteries belong those of Neef, Wagner, Klöpfer, Romershausen, Hassenstein, Danwerth, Duchenne, Du BoisReymond, Ruhmkorff, Erdmann, and others. The more important ones will be discussed in Fifth Section.

Faraday found, further, that, by simply placing a magnet and a closed conductor in close proximity, a stronger current, running counter to the current of the magnet, was induced in the conductor, and that, by removing the magnet to a distance, a weaker current was induced in the conductor, corresponding in direction with the current of the magnet. The continued renewal of the induced current, for medical purposes, is generally secured in the batteries constructed on this principle by winding the ends of an iron, bent in the form of a horse-shoe (or two short bars of iron that rest at right angles on an iron plate), with a copper wire in such manner that the spirals run in opposite directions, and then setting these two pieces of iron with their spirals in motion, by means of a crank, and letting them turn in a circle before the poles of a horse-shoe magnet, lying in a horizontal position. The action of the steel magnet on the spiral is here not direct, but is induced by the magnetism of the soft iron, that appears and disappears with each half revolution. This magnetism in its turn generates a current in the helices. This takes place independently of the fact that the iron is most powerfully magnetized when the helices stand opposite the poles of the magnet, and are always at the moment when the rollers move away from the two poles of the magnet, before which they stood, toward the opposite side, because the inductive action is produced only at the moment of the appearance and disappearance of the current, and not by the magnetism already generated. Saxton was the first to explain the phenomena of the extra current of the so-called

magneto-electric apparatus, and consequently the physicists named the apparatus the Saxton battery, which, however, was subsequently changed for the meaningless name of rotary apparatus. It should be stated that the intensity of its current increases with the power of the magnet, the length of the inductive spiral, the proximity of the soft iron, the rapidity of the revolutions, etc. To this class of machines belong those of Pixii, Saxton, Keil, Ettinghausen, Stöhrer, the Bréton brothers, Dugardin, Duchenne, Palmeret, and Hall, etc. (See Chapter V.)

CHEMICAL AND THERMAL ACTION.-The chemical action of induction electricity enables us, by means of the induced current, to decompose water, and a solution of the iodide of potassium, and to effect other electrolytic processes; also, to bring to a glowing heat a short, thin platina wire. But all these phenomena are more slowly and less perfectly accomplished than with the continued galvanic current.

Duchenne called induction electricity Faradism, after its discoverer, Faraday; its action he called Faradic, and its application Faradization, a terminology which has its justification in the nomenclature of contact electricity and its foundation in the difference of the action of contact and induction electricity.

THIRD SECTION.

OF THE ELECTRO-MOTOR PROPERTIES OF THE ANIMAL BODY.

E. Du Bois-Reymond, Untersuchungen über thierische Electricität, vol. i. and ii., 1848, 1849. C. Ludwig, Lehrbuch der Physiologie des Menschen, vol. i., 1852, pp. 316, et seq. C. Eckhard, Grundzüge der Physiologie des Nervensystems, 1854, pp. 40, et seq. A. Fick, die medicinische Physik, 1856, pp. 411, et seq. [Morgan, Electro-Physiology and Therapeutics, etc., New York, 1868.]

In order to have a clear understanding of the changes produced by the action of the electric current on the various animal tissues, we shall, in this chapter, speak of the inherent currents that are present in the animal body, as well as of the changes the tissues undergo in their molecular arrangement, during the production and action of the electric current.

Nobili, in 1827, discovered an electric current in the frog, the so-called frog-current, which he-starting on the supposition that nerves, on account of their small mass when compared with the muscles, cool more rapidly through evaporation-mistook for a thermo-electric current. Subsequently Matteucci corrected this mistake, as well as the error that the current is of electro-chemical origin, and proved that the connection of the two points in the long axis of the frog, of which, however, only one must be on the trunk of the animal, shows the presence of an inherent electric current flowing in the same direction. E. Du Bois-Reymond, however, was the first to succeed in demonstrating the presence of specific muscle and nerve currents, by the deflection of the