seen that three kinds of somatic stimuli will be distinguished: the objective sensory stimuli which proceed from external objects, the inner states of excitation of the sensory organs, having only a subjective reality, and the bodily stimuli arising within the body; and we have also noticed that the writers on dreams are inclined to thrust into the background any psychic sources of dreams which may operate simultaneously with the somatic stimuli, or to exclude them altogether. In testing the claims made on behalf of these somatic stimuli we have learned that the significance of the objective excitation of the sensory organs- whether accidental stimuli operating during sleep, or such as cannot be excluded from the dormant relation of these dream-images and ideas to the internal bodily stimuli and confirmed by experiment; that the part played by the subjective sensory stimuli appears to be demonstrated by the recurrence of hypnagogic sensory images in dreams; and that, although the broadly accepted relation of these dream-images and ideas to the internal bodily stimuli cannot be exhaustively demonstrated, it is at all events confirmed by the well-known influence which an excited state of the digestive, urinary and sexual organs exercises upon the content of our dreams.

Nerve stimulus and bodily stimulus would thus be the anatomical sources of dreams; that is, according to many writers, the sole and exclusive sources of dreams.

But we have already considered a number of doubtful points, which seem to question not so much the correctness of the somatic theory as its adequacy.

However confident the representatives of this theory may be of its factual basis- especially in respect of the accidental and external nerve stimuli, which may without difficulty be recognized in the dream- content- nevertheless they have all come near to admitting that the rich content of ideas found in dreams cannot be derived from the external nerve-stimuli alone. In this connection Miss Mary Whiton Calkins tested her own dreams, and those of a second person, for a period of six weeks, and found that the element of external sensory perception was demonstrable in only 13.2 per cent and 6.7 percent of these dreams respectively. Only two dreams in the whole collection could be referred to organic sensations. These statistics confirm what a cursory survey of our own experience would already, have led us to suspect.

A distinction has often been made between nerve-stimulus dreams which have already been thoroughly investigated, and other forms of dreams. Spitta, for example, divided dreams into nervestimulus dreams and association-dreams. But it was obvious that this solution remained unsatisfactory unless the link between the somatic sources of dreams and their ideational content could be indicated.

In addition to the first objection, that of the insufficient frequency of the external sources of stimulus, a second objection presents itself, namely, the inadequacy of the explanations of dreams afforded by this category of dream-sources. There are two things which the representatives of this theory have failed to explain: firstly, why the true nature of the external stimulus is not recognized in the dream, but is constantly mistaken for something else; and secondly, why the result of the reaction of the perceiving mind to this misconceived stimulus should be so indeterminate and variable. We have seen that Strumpell, in answer to these questions, asserts that the mind, since it turns away from the outer world during sleep, is not in a position to give the correct interpretation of the objective sensory stimulus, but is forced to construct illusions on the basis of the indefinite stimulation arriving from many directions. In his own words (Die Natur und Entstehung der Traume, p. 108).

"When by an external or internal nerve-stimulus during sleep a feeling, or a complex of feelings, or any sort of psychic process arises in the mind, and is perceived by the mind, this process calls up from the mind perceptual images belonging to the sphere of the waking experiences, that is to say, earlier perceptions, either unembellished, or with the psychic values appertaining to them. It collects about itself, as it were, a greater or lesser number of such images, from which the impression resulting from the nerve-stimulus receives its psychic value. In this connection it is commonly said, as in ordinary language we say of the waking procedure, that the mind interprets in sleep the impressions of nervous stimuli. The result of this interpretation is the socalled nerve-stimulus dream- that is, a dream the components of which