Hypnagogic imagery, there can be little doubt, is not a purely ocular phenomenon, even when it is stimulated by ocular fatigue. It is a mixed phenomenon, partly retinal and partly central. That is to say that the eye supplies entoptic glimmerings, and the brain, acting on the suggestions thus received, superposes mental pictures to those glimmerings.[27] They are thus analogous to the pictures we may see in the fire or in the clouds. It must be added that the other senses also furnish corresponding rudiments which are filled in by the central activity; this is notably the case with faint buzzings and sounds in the ear, and in addition, muscular twitches and internal visceral sensations, all these becoming more prominent as the attentive activity of waking life subsides.[28] What is the relation of hypnagogic imagery to dreams? Johannes Müller, the great physiologist, long ago identified them, as previously had Gruithuisen and Burdach, while Maury--who himself possessed, however, a somewhat abnormal and irritable nervous system--regarded hypnotic imagery as furnishing the whole of the formative element of dreams, as being 'the embryogeny of dreams'; he frequently found that images which appeared to him in this way before going to sleep reappeared in dreams. This is supported by Mourly Vold, who made experiments on himself, and by fixing images as he fell asleep dreamed of the same images. Goblot, however, while regarding hypnagogic imagery as analogous with dream imagery, denies that it is identical. Since the hypnagogic state is the porch to sleep and dreams--the praedormitium, as Weir Mitchell terms it--we can scarcely fail to admit with Maury that hypnagogic imagery presents us with the germinal stuff of dreams. If it is not identical with the fully formed dream, it is still the early stage of dreaming. This is certainly the view suggested by my own experience, even though I have never definitely recognised a dream as related to a previous hypnagogic image. It has, however, occasionally happened to me that as I have begun to lose waking consciousness a procession of images has drifted before my vision, and suddenly one of the figures I see has spoken. This hallucinatory voice occurring before I was fully asleep has startled me into full waking consciousness, and I have realised that, while yet in the hypnagogic stage, I was assisting at the birth of a dream.