Before leaving this subject of spontaneous sleep-waking states I ought briefly to mention a form of trance with which we shall have to deal more at length in a later chapter. I speak of trance ascribed to _spirit-possession_. As will be seen, I myself fully adopt this explanation in a small number of the cases where it is put forward. Yet I do not think that spirit-agency is necessarily present in all the trances even of a true subject of possession. With all the leading sensitives--with D. D. Home, with Stainton Moses, with Mrs. Piper and with others--I think that the depth of the trance has varied greatly on different occasions, and that sometimes the subliminal self of the sensitive is vaguely simulating, probably in an unconscious dream-like way, an external intelligence. This hypothesis suggested itself to several observers in the case especially of D. D. Home, with whom the moments of strong characterisation of a departed personality, though far from rare, were yet scattered among tracts of dreamy improvisation which suggested only the utterance of Home's subliminal self. However we choose to interpret these trances, they should be mentioned in comparison with all the other sleep-waking states. They probably form the best transition between those shallow somnambulisms, on the one hand, which are little more than a vivid dream, and those profound trances, on the other hand, in which the native spirit quits, as nearly as may be, the sensitive's organism, and is for the time replaced, as nearly as may be, by an invading spirit from that unseen world. This brief review of non-hypnotic somnambulisms has not been without its lessons. It has shown us that the supernormal powers which we have traced in each of the preceding chapters in turn do also show themselves, in much the same fashion, in spontaneous sleep-waking states of various types. We must now inquire how far they occur in sleep-waking states experimentally induced. And here the very fact of _induction_ suggests to us a question specially applicable to the hypnotic state itself. Is hypnosis ever supernormally induced? Can any one, that is to say, be thrown into hypnotic trance by a telepathic impact? or, to phrase it more generally, by any influence, inexplicable by existing science, which may pass from man to man?