stomach"), accidental bodily position, and little occurrences during sleep, exercise upon the formation of dreams, and he seems not to suspect that even after the consideration of all these factors there still remains something unexplained.
We have explained at length in the introductory chapter (p. 16), what a rôle in the formation of dreams the scientific literature credits to the account of somatic exciting sources, so that we need here only recall the results of this investigation. We have seen that three kinds of somatic exciting sources are distinguished, objective sensory stimuli which proceed from external objects, the inner states of excitation of the sensory organs having only a subjective basis, and the bodily stimuli which originate internally; and we have noticed the inclination on the part of the authors to force the psychic sources of the dream into the background or to disregard them altogether in favour of these somatic sources of stimulation (p. 32).
In testing the claims which are made on behalf of these classes of somatic sources of stimulation, we have discovered that the significance of the objective stimuli of the sensory organs—whether accidental stimuli during sleep or those stimuli which cannot be excluded from our dormant psychic life—has been definitely established by numerous observations and is confirmed by experiments (p. 18); we have seen that the part played by subjective sensory stimuli appears to be demonstrated by the return of hypnogogic sensory images in dreams, and that although the referring of these dream images and ideas, in the broadest sense, to internal bodily stimulation is not demonstrable in every detail, it can be supported by the well-known influence which an exciting state of the digestive, urinary, and sexual organs exercise upon the contents of our dreams.
"Nerve stimulus" and "bodily stimulus," then, would be the somatic sources of the dream—that is, the only sources whatever of the dream, according to several authors.
But we have already found a number of doubts, which seem to attack not so much the correctness of the somatic theory of stimulation as its adequacy.
However certain all the representatives of this theory may have felt about the actual facts on which it is based—especially
