The application of electricity as a test of the nature of a neuralgia has been employed by Benedikt,[34] who lays down certain laws as the result of his researches. He says that (_a_) in idiopathic peripheral neuralgias the nerves are not sensitive to the current; (_b_) in neuralgias dependent on neuritis or hyperæmia of the nerve-sheath there is general electric tenderness of the nerve; (_c_) in cases where the pain has been set up by morbid processes in tissues surrounding the nerve, there is electric tenderness only at the site of these changes. I may, in general terms, express concurrence in these statements; but I must add that, as diagnostic rules they apply only to the early stages of neuralgia; for the occurrence of secondary complications may and does altogether change the condition of electric sensitiveness. It need hardly be said that the above remarks on diagnosis apply for the most part only to the superficial neuralgias, which, however, include an immense majority of the cases of neuralgias. The diagnosis of visceral neuralgias is, it need hardly be said, in most cases, a far more difficult and complicated matter. In these diseases we have often little more to guide us, in the actual symptoms, than (_a_) the intermittence of the pain, and (_b_) the absence of commensurate constitutional disturbance, especially the complete freedom from sense of illness in the intervals between the pains. We shall be obliged to rely greatly on such historical facts as the presence or absence of neurotic tendencies in the patient and his family; the possibility of his having been exposed to blood-poisoning (_e. g._, from malaria or chronic alcoholic excess, or extreme over-smoking); the circumstance that he has been habitually overworked, or greatly exposed to agitating psychical influences; perhaps that he has been subject to a combination of several of these morbific momenta. To say truth, the diagnosis of visceral neuralgias must, at the best of times, be a difficult and anxious matter, and we can hardly ever thoroughly satisfy ourselves until we have procured some decided results from treatment; fortunately, however, it happens tolerably often that we can do this, and sometimes in a very striking way. _Prognosis._--The prognosis of neuralgia varies exceedingly, according to the form and situation of the disease, and many other considerations. There are, of course, in the first place, certain neuralgias in which the prospect is perfectly hopeless as to cure; such are the cases in which the nerve is involved in a continuously growing tumor (especially within a rigid cavity, like the skull), or a slow but persistent ulcerative process. Supposing, however, that the case is none of these, the very first prognostic consideration is that of age.