With regard to memory, as with regard to sensation, we seem in waking life to be dealing with a selection made for purposes of earthly use. From the pre-conscious unselective memory which depends on the mere organisation of living matter, it is the task of consciousness, as it dawns in each higher organism, to make its own appropriate selection and to develop into distinctness certain helpful lines of reminiscence. The question of self-preservation—What must I needs be aware of in order to escape my foes?—involves the question, What must I needs remember in order to act upon the facts of which I am aware? The selected currents of memory follow the selected avenues of sensation; what by disuse I lose the power of noticing at the time, I also lose the power of recalling afterwards.
For simpler organisms this rule may perhaps suffice. Man needs a more complex formula. For it may happen, as we have already seen, that two or more phases of personality in one man may each select from the mass of potential reminiscences a special group of memories of its own. These special groups, moreover, may bear to one another all kinds of relations; one may include another, or they may alternate and may be apparently co-exclusive.
From these dissociations and alternations of memory there will be many lessons to learn. The lesson which here presents itself is not the least important. What is the relation of the sleeping state to these dissociated, these parallel or concentric memories? Is it the case that when one memory includes another it is the waking memory—as one might expect from that state's apparently superior vividness—which shows itself the deeper, the more comprehensive record?
The answer of actual experience to these questions is unexpectedly direct and clear. In every recorded instance—so far at least as my memory serves me, where there has been any unification between alternating states, so as to make comparison possible—it is the memory furthest from waking life whose span is the widest, whose grasp of the organism's upstored impressions is the most profound. Inexplicable as this phenomenon has been to observers who have encountered it without the needed key, the independent observations of hundreds of physicians and hypnotists have united in affirming its reality. The commonest instance, of course, is furnished by the ordinary hypnotic trance. The degree of intelligence, indeed, which finds its way to expression in that trance or slumber varies greatly in different subjects and at different times. But whensoever there is enough of alertness to admit of our forming a judgment, we find that in the hypnotic state there is a considerable memory—though not necessarily a complete or a reasoned memory—of the waking state; whereas with most subjects in the waking state—unless some special command be imposed upon the hypnotic self—there is no memory whatever of the hypnotic state. In many hysterical conditions also the same general rule subsists; namely, that the further we get from the surface the wider is the expanse of memory which we encounter.
If all this be true, there are several points on which we may form expectations definite enough to suggest inquiry. Ordinary sleep is roughly intermediate between waking life and deep hypnotic trance; and it seems a priori probable that its memory will have links of almost equal strength with the memory which belongs to waking life and the memory which belongs to the hypnotic trance. And this is in fact the case; the fragments of dream-memory are interlinked with both these other chains. Thus, for example, without any suggestion to that effect, acts accomplished in the hypnotic trance may be remembered in dream; and remembered under the illusion which was thrown round them by the hypnotiser. Thus Dr. Auguste Voisin suggested to a hypnotised subject to stab a patient—really a stuffed figure—in the neighbouring bed.[44] The subject did so; and of course knew nothing of it on waking. But three days afterwards he returned to the hospital complaining that his dreams were haunted by the figure of a woman, who accused him of having stabbed and killed her. Appropriate suggestion laid this ghost of a doll.
Conversely, dreams forgotten in waking life may be remembered in the hypnotic trance. Thus Dr. Tissié's patient, Albert, dreamt that he was about to set out on one of his somnambulic "fugues," or aimless journeys, and when hypnotised mentioned to the physician this dream, which in his waking state he had forgotten.[45] The probable truth of this statement was shown by the fact that he did actually set out on the journey thus dreamt of, and that his journeys were usually preceded and incited by remembered dreams.
I need not dwell on the existence, but at the same time the incompleteness, of our dream-memory of waking life; nor on the occasional formation of a separate chain of memory, constructed from successive and cohering dreams. It should be added that we do not really know how far our memory in dream of waking life may have extended; since we can only infer this from our notoriously imperfect waking memory of past dreams.
A cognate anticipation to which our theory will point will be that dream-memory will occasionally be found to fill up gaps in waking memory, other than those due to hypnotic trance; such so-called "ecmnesic" periods, for instance, as sometimes succeed a violent shock to the system, and may even embrace some space of time anterior to the shock. These periods themselves resemble prolonged and unremembered dreams. Such accidents, however, are so rare, and such dream-memory so hard to detect, that I mention the point mainly for the sake of theoretical completeness; and must think myself fortunate in being able to refer the reader to a recent case of M. Charcot's which affords an interesting confirmation of the suggested view.[46]
I pass on to the still more novel and curious questions involved in the apparent existence of a dream-memory which, while accompanying the memory of ordinary life, seems also to have a wider purview, and to indicate that the record of external events which is kept within us is far fuller than we know.
Let us consider what stages such a memory may show.