fully acting sensory and motor stimuli of different sorts remain without effect during sleep. I can perceive a sensation during sleep through and through sleep, as it were, which happens as a rule with painful stimuli, but without weaving the pain into the texture of the dream ; thirdly, I can awaken on account of the stimulus in order to obviate it. Only as a fourth possible reaction, I may be impelled to dream by a nerve stimulus; but the other possibilities are realised at least as often as that of dream formation. This could not be the case if the motive for dreaming did not lie outside of the somatic sources of dreams.
Taking proper account of the defect in the explanation of dreams by somatic stimuli which has just been shown, other authors—Scherner,58 who was joined by the philosopher Volkelt72—have tried to determine more exactly the psychic activities which cause the variegated dream images to arise from the somatic stimuli, and have thus transferred the essential nature of dreams back to the province of the mind, and to that of psychic activity. Scherner not only gave a poetically appreciative, glowing and vivid description of the psychic peculiarities which develop in the course of dream formation; he also thought he had guessed the principle according to which the mind proceeds with the stimuli that are at its disposal. The dream activity, according to Scherner—after phantasy has been freed from the shackles imposed upon it during the day, and has been given free rein—strives to represent symbolically the nature of the organ from which the stimulus proceeds. Thus we have a kind of dream-book as a guide for the interpretation of dreams, by means of which bodily sensations, the conditions of the organs and of the stimuli may be inferred from dream images." Thus the image of a cat expresses an angry discontented mood, the image of a light-coloured bit of smooth pastry the nudity of the body. The human body as a whole is pictured as a house by the phantasy of the dream, and each individual organ of the body as a part of the house. In 'toothache-dreams' a high vaulted vestibule corresponds to the mouth and a stair to the descent of the gullet to the alimentary canal; in the 'headache-dream' the ceiling of a room which is covered with disgusting reptile-like spiders is chosen to denote the
