EV. It is equally curious that a concentration of nervous energy, which is here the result of unconsciousness, should also be produced _by_ fear in some cases, which, in others, _paralyses_; but this is indeed a slight degree of heroism, or energy of despair. Thus we leap far higher, and run much faster, when danger threatens, than we could believe. These are all very apt illustrations of somnambulism. I will check myself in quotations of more, as the phenomena may closely resemble each other. But what is its philosophy, and how can I venture on its explanation, which involves the most intricate pathology of the nervous system? unless, with the self-complacency of quaint old Burton, I cut the Gordian knot by this affirmation,—“There is nothing offends but a concourse of bad humours, which trouble the phantasy. These vapours move the phantasy, the phantasy the appetite, which, moving the animal spirits, causeth the body to walk up and down, as if it were awake.” Thus much I may expound to you, if I am again allowed to run up our scientific scale. The philosophy of the dream and of incubus refers to the activity of the brain with a _passive_ body; for somnambulism, we require an _active_ body, with an _unconscious_ brain. Now there are _four_ sources of nervous influence:—the brain and _cerebellum_, within the skull; the marrow in the spinal canal; and the nervous bundles in the large cavities, termed _ganglia_. It is on the independent or unconscious function of the marrow, chiefly, that those mysterious actions, which do not seem to be willed by a conscious mind, depend. In the day-dream, a thought or form shall present itself, even at a time when the mind is employed on subjects of a contrasted nature. These thoughts, or forms, are usually fraught with a high degree of pleasure or of pain, or refer to events of vital importance, to the dreamer;—such are the objects of the lover’s idolatry, the anticipation of misfortune, or subjects of prospective felicity. Under this excitement, the influence of external objects is often for a time lost; the _retina_ may be struck by a ray, or the _membrana tympani_ by a vibration, but the mind shall fail in its perception,—no _internal_ impression being made. This cannot arise from a point of the _retina_, or the expansion of the auditory nerve being pre-occupied, as some have supposed. The idea of material impression must fail in explanation; for, on the instant that the mind is awakened, the external impression is again perceived. The external sense, in this case, is not in fault; nor is its direct influence on the _sensorium_ suspended; for we find that a person will continue to read in this state, as it were _mechanically_; but the attention is _diverted_ by deep thought, so that the reader, at the end of his task, may have no remembrance of what he has been reading.