Now we believe that there are certain vessels which contribute to nervous energy, perhaps by secreting a nervous fluid in the brain, or by concentrating electricity, which Dr. Faraday believes may constitute the _animal_ portion of the nervous system. This influence may be profusely accumulated in a waking state; the resolution to act has been formed; or, there may be a rapid production in sleep of this energy. Then, when sleep occurs, _this impression becomes uncontrolled_. The third form of insanity of Spurzheim, irresistibility, exists, and the night-walk takes place. And indeed it may form an interesting analogy to that satiety of the voluptuary, “Childe Harold,” “Who e’en for change of scene wou’d seek the shades below,” and to one unhallowed story related in “Salmonia.” From this excess there is the stimulus of _pain to move_; one of the most powerful motives of human action. Cardan, if we may believe in his “Opera et Vita,” was at least a monomaniac; and he “was wont instinctively, as it were, to relieve this tendency of his mind by the excitement of bodily pain.” I may assure you that I have, during my professional studies, often witnessed (and indeed have sometimes suggested) a remedy on this knowledge: you may be aware, that a severe and painful disorder will mitigate, if not entirely dissipate, that apathetic misery which springs from a vacant or unoccupied mind. In contrasting childhood and age, we witness these curiosities in the restless activity of youth and early manhood, for at these periods we are very constant somnambulists; not so in the passive state of old age, in which sleep-walking is very rare. Something of this we see also in the _growing pains_ and _fidgets_ of girls and those whose duties are sedentary. Exercise is the relief for all this. Now when the sleep-walk has exhausted this excess of irritability or electricity (if it be so), the dreamer returns to bed and sleep. A hint is here thrown out to us, that if powerful exertion be employed previous to sleep, the night-walk might not ensue. Lethargy often terminates in somnambulism. If I may for another moment still prose over the intricate, but deeply interesting question of the pathology of somnambulism, I will observe, that we often find it one symptom of madness or idiocy, and we know that somnambulism not seldom terminates in epilepsy.