Electricity is a powerful agent in many forms of nervous disease, especially in the treatment of paralysis and neuralgia.

Three forms of electricity are employed, viz: The induced current, the galvanic current, both of which are dynamical, and the static current, which is frictional.

Galvanic electricity - galvanism, and induced electricity - faradism, are the two forms generally employed, frictional electricity being but seldom applied. What is known as electro-magnetism is a form of induced current, generated by the rotary instrument, and is not reliable. Faradism, so-called from its discoverer, is generated by an instrument which is capable of applying slow or rapid shocks, and giving what is denominated a fine, strong, induced current. It consists of coils of wire; a small hammer of soft iron, attached to a spring; a pole containing a platinum-pointed screw, the hammer breaking the current in the coil of wire, and by rapid vibration producing shocks.

"The galvanic current is generated by a series of cells, sufficient in number to cause a current of tension, which is the resistance offered to the passage of a current.

"One cell supplies a current, the poles of other cells being alternately joined, and there are finally but two terminal poles." As the current from the first cell passes through the remaining cells, its power is increased and the effect is governed by the number of cells belonging to the circuit. There is also what is dominated a current of " quantity," which is generated by a large metallic surface in the battery cell, the tension current being generated by a number of small metal plates. The " tension current" serves the best purpose for medical use, while the "quantity current" furnishes heat, and is, therefore, adapted to purposes of electro-surgery. The modified Bunsen galvanic cell is the best for medical purposes, although what is known as the Siemens and Halske cell is extensively used; "it consists of an outer cell of glass, with elements of zinc and copper, a diaphragm of porous earthenware, and a diaphragm of papier mache, between the solutions." The Holtz electric instrument furnishes the best static current.

The Ruhmkorff coil is also employed, in the use of which but one wire is brought in contact with the patient, the other conductor being formed by the air, and a spark, similar to the ordinary spark from the friction machine, being produced.

When electricity is applied to the body, sponges of different sizes, or polished metallic surfaces, known as "electrodes," the metallic being the best, are employed, the effect upon the skin being similar to what is caused by puncturing with many small needles. The theory of electro-therapeutics is dependent upon the following effects: -

"If a portion of a motor nerve is included between the poles of a galvanic battery, it is said to be polarized, and in a state of electrotonus. At the positive pole, the irritability of the nerve is diminished, while at the negative it is excited and more susceptible to stimulation. The condition at the positive pole is called anelectrotonus, and that at the negative catelectrotonus. The positive pole is known as the anode; the negative, the cathode, and these give the name to the states described. A nerve is said to be tetanized when the muscle supplied is thrown into a state of permanent tetanic contraction by a rapidly intermittent current. The passage of a number of these shocks for some time will diminish the irritability of the nerve to such an extent that, finally, there will be no further response. As an ascending current causes a greater irritability in a nerve than a descending one; a descending one depresses excitability. The stimulus is felt at the negative pole when the current commences, and when it is broken it is felt at the positive pole. A shock is felt at the opening of the weak currents; with moderately strong ones it is felt both at the opening and the closure. With very strong currents, it is impossible to tell the points of sensation, as the power of the nerve is impaired." The action upon involuntary muscles is less than upon the voluntary, and, as regards the latter, it is the same, or nearly so, as long as the integrity of their immediate nerve supply is concerned.

Degenerations and atrophies of muscles interfere to a considerable extent with their susceptibility to electric currents; hence, it is better, in diseased conditions, to pass the current through the nerve trunk which supplies them. The faradic current has but a local effect, the deeper muscles and nerves escaping.

When a metallic or sponge electrode is applied to the moistened skin, a pricking sensation follows, attended with redness and tingling, and this impression on the cutaneous nerves and muscles is known as electro-muscular sensibility. The galvanic current occasions a sensation of warmth, like that produced by a local stimulant, such as a mustard plaster, and when the faradic current is applied to the dry skin, or when the electrodes are but lightly applied, there is produced a sensation of pain, and the pain is the greater when caused by rapidly succeeding shocks than by slow ones.

The galvanic current causes deeper impressions than the faradic, and also electrolytic changes different from the faradic, producing absorption and changing the structure of the different tissues, and beneficial results have resulted from its application in diseases of the brain. The physical effects of the galvanic current upon the sympathetic nerve are dilatation followed by contraction of the pupil, diminished frequency of the pulse, and a lowering of the tension of the carotid arteries. When electricity is used for the purpose of diagnosis, the existence of local tenderness, exalted sensibility, anaesthesia, paralysis, diseases of the brain, spinal cord, etc., may be ascertained. It has also been used to determine the question of doubtful death, whether certain affections are recent or of long standing, and to detect malingering. As various nervous diseases are associated with the loss of such functions of muscles as contraction and sensation, or the reverse, electricity determines the extent of such changes.

When employing the electric current, the anatomy of the part affected should be well understood; for example, for neuralgia of the fifth pair of nerves one pole should be applied as near as possible to the point of exit of the nerve from the cranium, and the other pole to the remote parts of distribution.

Galvanism and faradism are employed for the relief of pain and spasm to improve the nutritive processes, and to restore deficient muscular power, to stimulate sensation in nerves, to stimulate secretion, to influence circulation, to cause absorption of fluids, to bring about the absorption of morbid growths and deposits, to induce sleep, and in surgery, in the form of the galvanic cautery. The galvanic current is considered to be the most useful for the mediate, and the faradic current for the immediate application, the former proving serviceable in all forms of neuralgia, and especially in facial neuralgia, and the latter in headaches, especially those of a rheumatic nature.

Galvanism is also employed with advantage in sciatica, spinal irritation and hysteria, also tumors, such as aneurisms and goitre, these morbid products being dispersed by connecting the two poles of a galvanic battery with needles which are thrust into the morbid growth and generate a process known as electrolysis. In such operations bubbles of hydrogen gas are disengaged at the negative pole, which separate mechanically the adjacent tissues, breaking them up in such a manner that the disintegrated particles may be taken up by the circulation. Oxygen is disengaged at the positive pole, which forms an acid with certain elements of the tissue, and the albumen is coagulated, forming a clot if this occurs in a cavity filled with blood.

For obtunding sensitive dentine and controlling peridental inflammation by electrolysis, Dr. F. McGraw suggests the following method: "To a 12 per cent. solution of cocaine add an equal amount of absolute alcohol. In connection with this use the galvanic current, varying the power as the needs of each case may indicate." The method of application is as follows: "After applying the rubber-dam, wet a pledget of cotton in the solution; place it in the cavity of the tooth; press the point of the positive pole on to the cotton, and the negative pole, with sponge attachment, to the cheek, turning on the current. An application of three minutes, with an interval of like duration, and then another three-minute application, is sufficient in the majority of cases, although it is occasionally necessary to make the third application. Then dry the cavity thoroughly and begin excavating." In case of peridental inflammation use a stronger current, which tetanizes the vessels and causes a diminished flow of blood to the parts and thus lessens congestion. The same current longer continued will cause electrolytic decomposition. "The medicinal agents he uses for peridental inflammation and for blind abscesses are a saturated solution of the chloride of sodium seven ounces, tincture of ergot, one ounce. The treatment of blind abscesses requires a stronger battery power in order to obtain the full effect of the electrolysis. Dr. Weeks has used this method successfully in the painless removal of pulps. (See Cataphoresis.)