From comparison of a series of similar dreams, M. Simon endeavoured to formulate certain rules for the influence of the organic sensations on the determination of the resulting dream. He says (p. 34): "If any organic apparatus, which during sleep normally participates in the expression of an affect, for any reason merges into the state of excitation to which it is usually aroused by that affect, the dream thus produced will contain presentations which fit the affect."
Another rule reads as follows (p. 35): "If an organic apparatus is in a state of activity, excitation, or disturbance during sleep, the dream will bring ideas which are related to the exercise of the organic function which is performed by that apparatus."
Mourly Vold has undertaken to prove experimentally the influence assumed by the theory of bodily sensation for a single territory. He has made experiments in altering the positions of the sleeper's limbs, and has compared the resulting dream with his alterations. As a result he reports the following theories:—
1. The position of a limb in a dream corresponds approximately to that of reality, i.e. we dream of a static condition of the limb which corresponds to the real condition.
2. When one dreams of a moving limb it always happens that one of the positions occurring in the execution of this movement corresponds to the real position.
3. The position of one's own limb may be attributed in the dream to another person.
4. One may dream further that the movement in question is impeded.
5. The limb in any particular position may appear in the dream as an animal or monster, in which case a certain analogy between the two is established.
6. The position of a limb may incite in the dream ideas which bear some relation or other to this limb. Thus, e.g., if we are employed with the fingers we dream of numerals.
Such results would lead me to conclude that even the theory of bodily sensation cannot fully extinguish the apparent freedom in the determination of the dream picture to be awakened.
IV. Psychic Exciting Sources.—In treating the relations of the dream to the waking life and the origin of the dream material, we learned that the earliest as well as the latest investigators agreed that men dream of what they are doing in the day-time, and of what they are interested in during the waking state. This interest continuing from waking life into sleep, besides being a psychic tie joining the dream to life, also furnishes us a dream source not to be under-estimated, which, taken with those stimuli which become interesting and active during sleep, suffices to explain the origin of all dream pictures. But we have also heard the opposite of the above assertion, viz. that the dream takes the sleeper away from the interests of the day, and that in most cases we do not dream of things that have occupied our attention during the day until after they have lost for the waking life the stimulus of actuality. Hence in the analysis of the dream life we are reminded at every step that it is inadmissible to frame general rules without making provision for qualifications expressed by such terms as "frequently," "as a rule," "in most cases," and without preparing for the validity of the exceptions.
If the conscious interest, together with the inner and outer sleep stimuli, sufficed to cover the etiology of the dreams, we ought to be in a position to give a satisfactory account of the origin of all the elements of a dream; the riddle of the dream sources would thus be solved, leaving only the task of separating the part played by the psychic and the somatic dream stimuli in individual dreams. But as a matter of fact no such complete solution of a dream has ever been accomplished in any case, and, what is more, every one attempting such solution has found that in most cases there have remained a great many components of the dream, the source of which he was unable to explain. The daily interest as a psychic source of dreams is evidently not far-reaching enough to justify the confident assertions to the effect that we all continue our waking affairs in the dream.
Other psychic sources of dreams are unknown. Hence, with the exception perhaps of the explanation of dreams given by Scherner, which will be referred to later, all explanations found in the literature show a large gap when we come to the derivation of the material for the presentation pictures, which is most characteristic for the dream. In this dilemma the majority of authors have developed a tendency to depreciate as much as possible the psychic factor in the excitations of dreams which is so difficult to approach. To be sure, they distinguish as a main division of dreams the nerve-exciting and the association dreams, and assert that the latter has its source exclusively in reproduction (Wundt, p. 365), but they cannot yet dismiss the doubt whether "they do not appear without being impelled by the psychical stimulus" (Volkelt, p. 127). The characteristic quality of the pure association dream is also found wanting. To quote Volkelt (p. 118): "In the association dreams proper we can no longer speak of such a firm nucleus. Here the loose grouping penetrates also into the centre of the dream. The ideation which is already set free from reason and intellect is here no longer held together by the more important psychical and mental stimuli, but is left to its own aimless shifting and complete confusion." Wundt, too, attempts to depreciate the psychic factor in the stimulation of dreams by declaring that the "phantasms of the dream certainly are unjustly regarded as pure hallucinations, and that probably most dream presentations are really illusions, inasmuch as they emanate from slight sensory impressions which are never extinguished during sleep" (p. 338, &c.). Weygandt agrees with this view, but generalises it. He asserts that "the first source of all dream presentations is a sensory stimulus to which reproductive associations are then joined" (p. 17). Tissié goes still further in repressing the psychic exciting sources (p. 183): "Les rêves d'origine absolument psychique n'existent pas"; and elsewhere (p. 6), "Les pensées de nos rêves nous viennent de dehors..."
Those authors who, like the influential philosopher Wundt, adopt a middle course do not fail to remark that in most dreams there is a co-operation of the somatic stimuli with the psychic instigators of the dream, the latter being either unknown or recognised as day interests.
We shall learn later that the riddle of the dream formation can be solved by the disclosure of an unsuspected psychic source of excitement. For the present we shall not be surprised at the over-estimation of those stimuli for the formation of the dream which do not originate from psychic life. It is not merely because they alone can easily be found and even confirmed by experiment, but the somatic conception of the origin of dreams thoroughly corresponds to the mode of thinking in vogue nowadays in psychiatry. Indeed, the mastery of the brain over the organism is particularly emphasized; but everything that might prove an independence of the psychic life from the demonstrable organic changes, or a spontaneity in its manifestations, is alarming to the psychiatrist nowadays, as if an acknowledgment of the same were bound to bring back the times of natural philosophy and the metaphysical conception of the psychic essence. The distrust of the psychiatrist has placed the psyche under a guardian, so to speak, and now demands that none of its feelings shall divulge any of its own faculties; but this attitude shows slight confidence in the stability of the causal concatenation which extends between the material and the psychic. Even where on investigation the psychic can be recognised as the primary course of a phenomenon, a more profound penetration will some day succeed in finding a continuation of the path to the organic determination of the psychic. But where the psychic must be taken as the terminus for our present knowledge, it should not be denied on that account.