Electricity, MEDICAL. The three forms of electricity—Static, Galvanic, and Faradic—are employed in medicine.
(1) Static.—This form has been little used of late years, chiefly owing to the inconvenience and uncertainty of the apparatus required for its production. The old frictional and even the Holtz machines were most uncertain in their action, and depended for their efficiency on various conditions of the atmosphere, &c. The recent invention of the Winshurst machine is increasing the interest in the use of static electricity for medicinal purposes. This instrument being independent of atmospheric conditions is specially well adapted for occasional use.
(2) Galvanic.—The current derived from the galvanic battery is largely employed in medicine. As in almost all cases the current requires to traverse the skin, the electrical resistance of which is high, a battery of a considerable number of elements is required to yield sufficient electric pressure. The elements usually employed are some form of the Leclanché or the bichromate element, and batteries containing from 30 to 50 of these are found most convenient. These should yield an electric pressure of from 40 to 70 volts when in good working order. As portability is a consideration, the cells are usually made small, and as the external resistance is considerable and the circuit closed for a comparatively short time, the smallness of the elements is not an objection. When, however, the external resistance is reduced by special appliances, and the current passed for a considerable period, as in the electrolysis of tumours, larger elements must be used, and those of pint or even quart capacity are found convenient. The battery should possess a collector by which the cells may be added to the circuit one by one; and the larger-celled batteries should also possess a reostat, by which the external resistance may be varied with perfect gradations so as to avoid the transmission of shocks while the current is being increased or diminished. Until recently the only measure of the amount of electricity employed was the number of cells in the circuit. This is obviously an unreliable guide. The electromotive force of the cells varies with the exhaustion of the fluid and polarisation of the plates, and the resistance of the external circuit varies with the condition of the skin as to moisture, vascularity, and locality, the size, distance between, and the polarisation of the electrodes. And as the amount of current passing depends on an absolute relation between the electromotive force and the resistance of the current, neither of which under these conditions can be known, this method is quite useless. The unit of current strength in ordinary electric measurement is the ampère. This is, however, much too large a unit for medical purposes, and the thousandth part of this, termed the milliampère, is employed. Galvanometers calibrated in milliampères are now largely made for medical purposes, so that when one of these is introduced into the circuit the exact amount of current passing at a given time can be read directly. As currents varying from 1 to 300 milliampères are now regularly employed, the instrument should be capable of indicating between those limits. Further, the instrument should be as near as possible aperiodic (dead-beat). Such an instrument should therefore be included in the circuit whenever it is advisable to estimate the current strength employed. Effects can only be compared provided we know the amount of current producing them, and this can only be determined by the milliampère-meter. The efficiency of the current depends, however, not only on its amount, but also on its density. This character depends on the diameter of the conductors which bring it in contact with the body. The current-density varies inversely as the sectional area of the conductor. Thus a current of 200 milliampères, conveyed to the body by two conductors whose terminals are 10 inches in diameter, may be borne with little inconvenience and produce little appreciable effect, but if one of the conductors be reduced to, say, 1 inch in diameter while the same current is passing, the density of the current at the electrode is greatly increased, the pain would be intense, and vesication and tissue destruction would follow in a very short time. Currents of large amount and of great density are thus employed in the electrolysis of tumours, &c.
Well-insulated flexible wires of suitable length are employed for conveying the current. These terminate in electrodes of various kinds and sizes according to the object in view. For ordinary purposes (galvanisation of muscle, nerve, &c.) discs, plates, or cones of brass or carbon covered with flannel or wash-leather are employed. For conveyance of large currents large pads of moist clay, flannel, sponge, &c., 10 or 12 or more inches in diameter, are employed externally, while the current is concentrated by a platinum or steel needle on the part to be affected. In all cases electrodes to be applied to the skin should be thoroughly soaked in a solution of salt in warm water in order to diminish the resistance of the circuit and the pain of the current.
(3) Faradic.—For the production of the faradic current a simple form of induction coil is employed. The primary coil of thick wire is wound round a tube in which slides a bundle of iron wire. The secondary coil of fine wire fits over this. In the best forms of instrument the strength of the current can be regulated both by the sliding of the iron bundle in and out of the primary, and also by the sliding of the secondary over, or off and away from the primary. Some form of simple magnetic interrupter (Neef's hammer) is connected with the instrument, and it is desirable that some means should be provided for regulating the rate of interruption. It must be borne in mind that at each movement of the interrupter two currents are generated in the secondary, the one, at the moment of making of the primary, in the opposite direction, and the other, at the moment of breaking, in the same direction as the primary current. The currents from a faradic machine are thus alternating. But further, these differ in strength; the breaking current being reinforced by the 'extra stream' of the primary, is considerably the stronger. The signs + and - sometimes marked on the terminals of the secondary, refer only to this stronger or breaking current.
Physiological Effects of the Galvanic Current: (a) On Sensory Surfaces.—When a current of from 10 to 15 milliamperes is applied to the skin by electrodes of 1 or 2 inches in diameter, a prickling followed by a burning sensation is experienced. If the current is gradually diminished and the electrodes removed, the skin will be found to be bright red, showing increased vascularity. While the current is being diminished it will be noticed that the sensation first disappears under the positive pole, and while being increased first appears at the negative one, thus indicating the greater exciting effect of the latter. (b) On Motor Apparatus.—If a large sponge electrode be applied to the spine in the dorsal region, and a smaller conical one be applied to such a muscle as the biceps in the upper arm, it will be found that if a current of sufficient strength be employed, the muscle will be thrown into contraction at the moment of making and breaking the current. The strength of current required to produce this effect will depend (1) on the pole applied to the muscle; (2) on whether the current is made or broken. In a state of health it is found that muscular contraction occurs with those conditions in the following order: (1) Current closed—negative muscle; (2) current closed—positive on muscle; (3) current opened—positive on muscle; (4) current opened—negative on muscle. Thus the weakest current capable of producing contraction will act when the current is closed with the negative on the muscle (1); and stronger currents will be required to produce contraction under the conditions 2, 3, 4. Or conversely, if a muscle contracts with an opening current, the negative being on the muscle (4), more and more powerful contractions will be obtained by altering the conditions with the same current to 3, 2, and 1.
Electrolytic Effects.—If a broad surface-electrode be applied to any part of the body and connected to one pole, and the other pole connected to a platinum or steel needle inserted into, say, a fibroid tumour of the uterus, or applied to any mucous surface, and a current of 15 to 250 milliamperes passed, tissue in contact with the electrodes will be decomposed. Owing to the extent of the external electrode and small density of the current, the result here will be inappreciable, but it is very obvious at the internal one. Thus, if the electrode is positive, the products of decomposition will be strongly acid in reaction (turning litmus red), and the tissue round the electrode will be condensed, and contract round it. If the internal electrode is now negative, the products of decomposition will be strongly alkaline in reaction, and the tissue will be rapidly broken up, a loose frothy material escaping from the electrode, which will move freely in a sinus formed by the electrolysis. The negative pole while liberating alkaline products has much more marked disintegrating influence than the positive.
Physiological Effect of Induced Currents: (a) On Sensory Apparatus.—When a weak current from the secondary is applied to the skin, the sensation is that of gentle prickling or tingling. As the strength of the current is increased the sensation becomes more and more painful, but has never the burning character of the galvanic current. (b) On Motor Apparatus.—If one or both poles are applied to a muscle, and a single shock of sufficient strength sent, a single muscular contraction will be produced. If the shocks are repeated with sufficient slowness, a series of single contractions will follow; but if the rate of transmission is increased, the muscle will be thrown into a state of tetanus or continued contraction, the effect of one shock not having passed before the next has reached the muscle.
Diagnostic Uses of Electricity.—Galvanic and faradic currents are employed in the diagnosis of various nervous and muscular disorders. In certain diseases of the spinal cord and the cerebro-spinal nerves it is found that the normal phenomena of muscular contraction are much altered. Thus it may be found that a muscle may fail to respond to faradic stimuli of any strength, and yet continue to respond to interrupted galvanic stimuli; and again it may respond to galvanic stimuli in an order different to that indicated in a previous paragraph as normal to health. These abnormal phenomena are termed the 'reactions of degeneration.'
Therapeutic Uses of Electricity.—Only the most general indications of these can be given. The static form is of value in the treatment of various nervous disorders—e.g. old-standing neuralgia, chorea, hemi-anæsthesia, hystero-epilepsy, and hysteria. Galvanism is used in acute neuralgias, such as tic-douloureux, sciatica, &c.; in atrophy of muscle following hemiplegia, diabetes, writers' cramp, &c.; in spinal irritation, chronic myelitis; in the enlarged and stiffened joints of chronic rheumatism and rheumatic arthritis, and in lumbago; in chronic pharyngitis, in glandular laryngitis (clergyman's sore throat), naso-pharyngeal catarrh, chronic tonsillitis; and in other diseases associated with chronic inflammation and defective nutrition. Faradism is employed in general nervous exhaustion associated with insomnia, in functional disorders of the generative organs, in the acute stage of articular rheumatism, giving great relief to the inflamed and painful joints, in incontinence of urine from atony of bladder and sphincter, in irritable and painful prostate, in hysterical aphonia, neurasthenia, &c.
Galvanism in Electrolysis.—Nævi and aneurisms are frequently cured by electrolysis of their contents. Needles insulated to within a quarter of an inch of their points are plunged into the tumour, and through these the current is passed. Coagulation takes place round the needles, and forms a nucleus round which further clotting occurs, resulting in obliteration of the nævus, or strengthening of the walls and filling of the sac in an aneurism. For uterine hemorrhage a current of 100 to 250 milliamperes is employed, a thick platinum wire carrying the positive current to the mucous membrane of the uterus, a large surface-electrode lying on the abdomen. The positive current is a powerful hæmostatic, and properly applied this method checks most cases of hemorrhage. So also fibroid tumours of the uterus are treated by similar high currents applied in the same way. But the disintegrating effect of the negative pole is preferred either lying in the uterine cavity or introduced into the substance of the tumour. Various inflammatory conditions both outside and inside the uterus are similarly treated. All these effects depend (1) on the strength of the current, which is obtained by the use of a sufficiently large pressure (30 to 40 cells = 40 or 60 volts), and a large surface external electrode which diminishes the resistance of the skin; (2) on the density of the current at the part to be affected, which is obtained by the use of an electrode consisting of a small platinum or steel needle.
In conclusion, a word may be said regarding the much advertised 'galvanic' and 'magnetic' belts. There is no doubt that galvanic chains, such as Pulvermacher's, are capable of giving a more or less continuous current of electricity, and it may be that in some cases their use has been followed by benefit. But the irregularity of their action, and the impossibility of directing or controlling the current, render their use entirely hazardous. Moreover, very troublesome ulcerations have been produced in the skin by prolonged contact of the negative pole. On the other hand, there is not the least evidence that the so-called 'magnetic belts' have any influence whatever on the tissues or functions of the body. They consist of pieces of watch-spring, or of crinoline steel, more or less magnetised, sewn between layers of flannel or other material, and adapted to different parts of the body. It has never been shown that even powerful magnets have any influence on the bodily functions, and it cannot be believed that these appliances are of any use whatever. Any relief from pain which may follow their application is most probably due to the heat-conserving property of the flannel or other material in which the bits of steel are sewn.