Take, for example, the following case, which, in its history of twenty-three years, presents a fair example of a type of trigeminal neuralgia which I believe to be the rule rather than the exception, though the trophic changes were somewhat unusually varied and interesting. The following would be the pathological order of events, according to the radiation theory: First or true migrainous stage; failure of nutrition of a portion of the sensory root of the right fifth nerve within medulla oblongata, lesser degree of the same condition in the adjoining and closely-connected vagus root (hence supra-orbital pain, local anæsthesia and vomiting); extension of the morbid process to the motor root (hence vaso-motor paralysis and secretory and trophic changes in the cornea, superciliary periosteum, etc). Second period: recovery, to a large extent, of the nutrition of the posterior root of the trigeminus, complete recovery of the root of the vagus (hence alteration of the type of recurrence of the pains, which now occur at increasingly long intervals, and needed special provocation, _e. g._, excessive fatigue, to bring them on; hence, also, disappearance of the stomach symptoms); continuance of the affection of the motor portion of the nerve (hence, continuance of the tendency to trophic, secretory, and vaso-motor changes); development of the true points douloureux during and after the paroxysms, instead of the diffused tenderness following the old attacks of migraine. Third stage: neuralgic attacks become rare and comparatively unimportant; tendency to trophic changes greatly lessened; local anæsthesia persists. Presumption, that the nutrition of the nerve-centre has nearly recovered itself, but that that centre is still the _locus minimæ resistentiæ_ of the central nervous system, liable to suffer from any cause of general nervous depression.