In the precise sense in which the remedy is here considered, electricity acts merely by exciting sensation. In regard to its influences in general, it is a universal stimulant, and has been treated of, along with heat, under the general head of stimulation. The various methods of applying it have there been considered. Here we have only to do with the influence of its shock, in other words, with the sensation it excites when applied so as to make a painful impression upon the nervous centres, which painful impression is the source of the remedial influence. For this purpose, it may be applied in two modes, either by the discharge of a Leyden jar, or by rapid intermissions of the current by means of the different coil machines. The latter is the more effective method, as the impression is sustained, and can be graduated exactly to the requisitions of the case. The therapeutic effect aimed at by thus exciting sensation, is to rouse the functions from torpor by the diffusive stimulation which such an impression produces, when not overwhelmingly violent. It is not in the prostration from long-continued disease, or that which often attends the progress and close of febrile and inflammatory affections, that the remedy is indicated. There is here not force enough to sustain the excitement after it has been produced; and a continuance of the measure would only further exhaust the excitability. The cases in which electricity is applicable, upon this principle, are those in which the system has been suddenly prostrated into more or less complete insensibility through impressions on the nervous centres, and in which the excitability remains unexhausted. Such are attacks of syncope or asphyxia, especially after the cause has ceased to act. The cases of poisoning by opium, before referred to (see page 537), in which the electro-magnetic machine aroused sensation in the advanced stage, when the direct symptoms of the poison had been followed by great prostration, and in which life appeared to be saved in consequence, are examples of this kind. The apparently comatose state of hysteria is another condition which indicates the use of the remedy. It would, probably, moreover, serve an excellent purpose in some cases of malingering.