b. Faradisation; Electro-Magnetism; Magneto Electricity.

c. Galvanism; Voltaic Electricity.

These three varieties of the same agent, although closely allied, yet differ somewhat in their special therapeutic uses and action. All the forms of Electricity act as stimulants to the nervous system, and, unlike other remedies of the class, the stimulation they produce is not followed by subsequent depression. Common or Frictional Electricity may be obtained for medical purposes from the ordinary electrical machine, in which it is produced by the friction of a glass plate or cylinder on a rubber. Frictional Electricity is not so much used in the present day as formerly. In addition to its action as a nervine stimulant, it may be employed to produce counter-irritant effects. A common mode of using it is as follows: - "The patient is placed upon an insulating stool, and made to take hold of the prime conductor of the electrical machine. Sparks are then drawn from the body, either by the hand of the operator or by metallic conductors. By this proceeding a sharp pricking or pungent sensation is produced at the points touched; and after a time the skin is reddened, and an eruption resembling lichen urticatus breaks out."t Faradisation is the term applied by Duchenne to indicate the application to therapeutical purposes of Faraday's discovery, "That electric currents of instantaneous duration are induced in conducting-wires by the passage of an ordinary galvanic current (electro-magnetism), as well as by the approach to, and withdrawal from, conducting-wires, of a permanent magnet of steel (magneto-electricity)," The Faradic or induction current is an interrupted current, and differs in its physiological, chemical, and physical effects from the ordinary Galvanic or continuous current. The difference in the physiological effects of the interrupted (Faradic) and continuous (Galvanic) currents are exemplified by applying each in turn to the face: the continuous galvanic current will be found to excite the retina, producing the sensation of a flash of light, whilst it has but little action on the facial muscles; on the other hand, the interrupted galvanic current has little or no action on the retina, but produces a powerful effect on the muscles.* The continuous galvanic current always moving in the same direction produces considerable chemical effects, whilst induction currents, which move alternately in different directions, have only a slight chemical action. Dr. Althaus, therefore, observes, "that if we wish to make use of the chemical effects of electricity, it follows that the continuous galvanic current alone should be used." This observation applies to the treatment of Aneurisms and Varices by electricity. For the production of the ordinary galvanic current, Dr. Althaus recommends that Daniell's, Grove's, or Bunsen's batteries be employed. For Electro-magnetism and Magneto-electricity, the induction machines used for medical purposes are either volta-electric or magneto-electric (rotatory). The latter are generally preferred on account of their being cleaner and always ready for action.

* Dict. Pract, Med., vol. ii. p. 411. Althaus on the Treatment of Paralysis and Neuralgia by Galvanization and Faradisation, p. 3. Op. cit., p. 9.

If electricity be applied to animals in too large quantities, or in too great a degree of intensity, death ensues; and, as in some constitutions, there is a peculiar susceptibility to its action, and as there are no means of distinguishing beforehand those with whom it disagrees, it is always advisable to use it in the first instance cautiously, commencing with weak currents or slight shocks. It is, as a rule, a purely chronic remedy, applicable only to chronic diseases, and required to be continued for several weeks in succession. Common electricity should be used with caution in inflammatory and plethoric states of the body, and in pregnancy, as miscarriage might be produced.

Electricity, as an anaesthetic agent, was first introduced by Dr. Richardson, but in this character its field of action is very limited, being applicable only to the induction of local anaesthesia, as in tooth-drawing, &c, and even here it is inferior to congelation, &c.