Hallam,33 one of the latest observers, has collected examples showing the very opposite behaviour, and claims for the point the right of individual psychology.
The third and the most remarkable and incomprehensible peculiarity of the memory in dreams, is shown in the selection of the reproduced material, for stress is laid not only on the most significant, but also on the most indifferent and superficial reminiscences. On this point I shall quote those authors who have expressed their surprise in the most emphatic manner.
Hildebrandt35 (p. 11): "For it is a remarkable fact that dreams do not, as a rule, take their elements from great and deep-rooted events or from the powerful and urgent interests of the preceding day, but from unimportant matters, from the most worthless fragments of recent experience or of a more remote past. The most shocking death in our family, the impressions of which keep us awake long into the night, becomes obliterated from our memories, until the first moment of awakening brings it back to us with depressing force. On the other hand, the wart on the forehead of a passing stranger, of whom we did not think for a second after he was out of sight, plays its part in our dreams."
Strümpell66 (p. 39): "...such cases where the analysis of a dream brings to light elements which, although derived from events of the previous day or the day before the last, yet prove to be so unimportant and worthless for the waking state that they merge into forgetfulness shortly after coming to light. Such occurrences may be statements of others heard accidentally or actions superficially observed, or fleeting perceptions of things or persons, or single phrases from books, &c."
Havelock Ellis23 (p. 727): "The profound emotions of waking life, the questions and problems on which we spread our chief voluntary mental energy, are not those which usually present themselves at once to dream-consciousness. It is, so far as the immediate past is concerned, mostly the trifling, the incidental, the "forgotten" impressions of daily life which reappear in our dreams. The psychic activities that are awake most intensely are those that sleep most profoundly."
Binz4 (p. 45) takes occasion from the above-mentioned characteristics of the memory in dreams to express his dissatisfaction with explanations of dreams which he himself has approved of: "And the normal dream raises similar questions. Why do we not always dream of memory impressions from the preceding days, instead of going back to the almost forgotten past lying far behind us without any perceptible reason? Why in a dream does consciousness so often revive the impression of indifferent memory pictures while the cerebral cells bearing the most sensitive records of experience remain for the most part inert and numb, unless an acute revival during the waking state has shortly before excited them?"
We can readily understand how the strange preference of the dream memory for the indifferent and hence the unnoticed details of daily experience must usually lead us to overlook altogether the dependence of the dream on the waking state, or at least make it difficult to prove this dependence in any individual case. It thus happened that in the statistical treatment of her own and her friend's dreams, Miss Whiton Calkins12 found 11 per cent. of the entire number that showed no relation to the waking state. Hildebrandt was certainly correct in his assertion that all our dream pictures could be genetically explained if we devoted enough time and material to the tracing of their origin. To be sure, he calls this "a most tedious and thankless job." For it would at most lead us to ferret out all kinds of quite worthless psychic material from the most remote corners of the memory chamber, and to bring to light some very indifferent moments from the remote past which were perhaps buried the next hour after their appearance." I must, however, express my regret that this discerning author refrained from following the road whose beginning looked so unpromising; it would have led him directly to the centre of the dream problem.
The behaviour of the memory in dreams is surely most significant for every theory of memory in general. It teaches us that "nothing which we have once psychically possessed is ever entirely lost" (Scholz59); or as Delbœuf puts it, "que toute impression même la plus insignifiante, laisse une trace inaltérable, indéfiniment susceptible de reparaître au jour," a conclusion to which we are urged by so many of the other pathological manifestations of the psychic life. Let us now bear in mind this extraordinary capability of the memory in the dream, in order to perceive vividly the contradictions which must be advanced in certain dream theories to be mentioned later, when they endeavour to explain the absurdities and incoherence of dreams through a partial forgetting of what we have known during the day.
One might even think of reducing the phenomenon of dreaming to that of memory, and of regarding the dream as the manifestation of an activity of reproduction which does not rest even at night, and which is an end in itself. Views like those expressed by Pilcz51 would corroborate this, according to which intimate relations are demonstrable between the time of dreaming and the contents of the dream from the fact that the impressions reproduced by the dream in sound sleep belong to the remotest past while those reproduced towards morning are of recent origin. But such a conception is rendered improbable from the outset by the manner of the dream's behaviour towards the material to be remembered. Strümpell66 justly calls our attention to the fact that repetitions of experiences do not occur in the dream. To be sure the dream makes an effort in that direction, but the next link is wanting, or appears in changed form, or it is replaced by something entirely novel. The dream shows only fragments of reproduction; this is so often the rule that it admits of theoretical application. Still there are exceptions in which the dream repeats an episode as thoroughly as our memory would in its waking state. Delbœuf tells of one of his university colleagues who in his dream repeated, with all its details, a dangerous wagon ride in which he escaped accident as if by miracle. Miss Calkins12 mentions two dreams, the contents of which exactly reproduced incidents from the day before, and I shall later take occasion to report an example which came to my notice, showing a childish experience which returned unchanged in a dream.3
(c) Dream Stimuli and Dream Sources.—What is meant by dream stimuli and dream sources may be explained by referring to the popular saying, "Dreams come from the stomach." This notion conceals a theory which conceives the dream as a result of a disturbance of sleep. We should not have dreamed if some disturbing element had not arisen in sleep, and the dream is the reaction from this disturbance. The discussion of the exciting causes of dreams takes up the most space in the descriptions of the authors. That this problem could appear only after the dream had become an object of biological investigation is self-evident. The ancients who conceived the dream as a divine inspiration had no need of looking for its exciting source; to them the dream resulted from the will of the divine or demoniacal powers, and its content was the product of their knowledge or intention. Science, however, soon raised the question whether the stimulus to the dream is always the same, or whether it might be manifold, and thus led to the question whether the causal explanation of the dream belongs to psychology or rather to physiology. Most authors seem to assume that the causes of the disturbance of sleep, and hence the sources of the dream, might be of various natures, and that physical as well as mental irritations might assume the rôle of dream inciters. Opinions differ greatly in preferring this or that one of the dream sources, in ranking them, and indeed as to their importance for the origin of dreams.
Wherever the enumeration of dream sources is complete we ultimately find four forms, which are also utilised for the division of dreams:—
I. External (objective) sensory stimuli.
II. Internal (subjective) sensory stimuli.
III. Internal (organic) physical excitations.
IV. Purely psychical exciting sources.
I. The External Sensory Stimuli.—The younger Strümpell, son of the philosopher whose writings on the subject have already more than once served us as a guide in the problem of dreams, has, as is well known, reported his observations on a patient who was afflicted with general anaesthesia of the skin and with paralysis of several of the higher sensory organs. This man merged into sleep when
