The theory of the origin of dreams just stated has been the favourite with all medical authors. The obscurity which conceals the essence of our being—the "moi splanchnique," as Tissié terms it—from our knowledge and the obscurity of the origin of the dream correspond too well not to be brought into relation with each other. The train of thought which makes organic sensation the inciter of the dream has besides another attraction for the physician, inasmuch as it favours the etiological union of the dream and mental diseases, which show so many agreements in their manifestations, for alterations in the organic sensations and excitations emanating from the inner organs are both of wide significance in the origin of the psychoses. It is therefore not surprising that the theory of bodily sensation can be traced to more than one originator who has propounded it independently.
A number of authors have been influenced by the train of ideas developed by the philosopher Schopenhauer in 1851. Our conception of the universe originates through the fact that our intellect recasts the impressions coming to it from without in the moulds of time, space, and causality. The sensations from the interior of the organism, proceeding from the sympathetic nervous system, exert in the day-time an influence on our mood for the most part unconscious. At night, however, when the overwhelming influence of the day's impressions is no longer felt, the impressions pressing upward from the interior are able to gain attention—just as in the night we hear the rippling of the spring that was rendered inaudible by the noise of the day. In what other way, then, could the intellect react upon these stimuli than by performing its characteristic function? It will transform the stimuli into figures, filling space and time, which move at the beginning of causality; and thus the dream originates. Scherner,58 and after him Volkelt,72 attempted to penetrate into closer relations between physical sensations and dream pictures; but we shall reserve the discussion of these attempts for the chapter on the theory of the dream.
In a study particularly logical in its development, the psychiatrist Krauss39 found the origin of the dream as well as of deliria and delusions in the same element, viz. the organically determined sensation. According to this author there is hardly a place in the organism which might not become the starting point of a dream or of a delusion. Now organically determined sensations "may be divided into two classes: (1) those of the total feeling (general sensations), (2) specific sensations which are inherent in the principal systems of the vegetative organism, which may be divided into five groups: (a) the muscular, (b) the pneumatic, (c) the gastric, (d) the sexual, (e) the peripheral sensations (p. 33 of the second article)."
The origin of the dream picture on the basis of the physical sensations is conceived by Krauss as follows: The awakened sensation evokes a presentation related to it in accordance with some law of association, and combines with this, thus forming an organic structure, towards which, however, consciousness does not maintain its normal attitude. For it does not bestow any attention on the sensation itself, but concerns itself entirely with the accompanying presentation; this is likewise the reason why the state of affairs in question should have been so long misunderstood (p. 11, &c.). Krauss finds for this process the specific term of "transubstantiation of the feeling into dream pictures" (p. 24).
That the organic bodily sensations exert some influence on the formation of the dream is nowadays almost universally acknowledged, but the question as to the law underlying the relation between the two is answered in various ways and often in obscure terms. On the basis of the theory of bodily excitation the special task of dream interpretation is to trace back the content of a dream to the causative organic stimulus, and if we do not recognise the rules of interpretation advanced by Scherner,58 we frequently find ourselves confronted with the awkward fact that the organic exciting source reveals itself in the content of the dream only.
A certain agreement, however, is manifested in the interpretation of the various forms of dreams which have been designated as "typical" because they recur in so many persons with almost the same contents. Among these are the well-known dreams of falling from heights, of the falling out of teeth, of flying, and of embarrassment because of being naked or barely clad. This last dream is said to be caused simply by the perception felt in sleep that one has thrown off the bedcover and is exposed. The ream of the falling out of teeth is explained by "dental irritation," which does not, however, of necessity imply a morbid state of excitation in the teeth. According to Strümpell,66 the flying dream is the adequate picture used by the mind to interpret the sum of excitation emanating from the rising and sinking of the pulmonary lobes after the cutaneous sensation of the thorax has been reduced to insensibility. It is this latter circumstance that causes a sensation related to the conception of flying. Falling from a height in a dream is said to have its cause in the fact that when unconsciousness of the sensation of cutaneous pressure has set in, either an arm falls away from the body or a flexed knee is suddenly stretched out, causing the feeling of cutaneous pressure to return to consciousness, and the transition to consciousness embodies itself psychically as a dream of falling. (Strümpell, p. 118). The weakness of these plausible attempts at explanation evidently lies in the fact that without any further elucidation they allow this or that group of organic sensations to disappear from psychic perception or to obtrude themselves upon it until the constellation favourable for the explanation has been established. I shall, however, later have occasion to recur to typical dreams and to their origin.
From comparison of a series of similar dreams, M. Simon63 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 Vold73 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.6
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