902. Now this seems a strange doctrine to have reached after so much disputation. For it simply brings us back to the creeds of the Stone Age. We have come round again to the primitive practices of the shaman and the medicine-man; - to a doctrine of spiritual intercourse which was once oecumenical, but has now taken refuge in African swamps and Siberian tundras and the snow-clad wastes of the Red Indian and the Esquimaux. If, as is sometimes advised, we judge of the worth of ideas by tracing their origins, no conception could start from a lower level of humanity. It might be put out of court at once as unworthy of civilised men.

Fortunately, however, our previous discussions have supplied us with a somewhat more searching criterion. Instead of asking in what age a doctrine originated - with the implied assumption that the more recent it is, the better - we can now ask how far it is in accord or in discord with a great mass of actual recent evidence which comes into contact, in one way or another, with nearly every belief as to an unseen world which has been held at least by western men. Submitted to this test, the theory of possession gives a remarkable result. It cannot be said to be inconsistent with any of our proved facts. We know absolutely nothing which negatives its possibility.

Nay, more than this. The theory of possession actually supplies us with a powerful method of co-ordinating and explaining many earlier groups of phenomena, if only we will consent to explain them in a way which at first sight seemed extreme in its assumptions - seemed unduly prodigal of the marvellous. Yet as to that difficulty we have learnt by this time that no explanation of psychical phenomena is really simple, and that our best clue is to get hold of some group which seems to admit of one interpretation only, and then to use that group as a point de repere from which to attack more complex problems.

Now I think that the Moses-Piper group of trance-phenomena cannot be intelligently explained on any theory except that of possession. And I therefore think it important to consider in what way earlier phenomena have led up to possession, and in what way the facts of possession, in their turn, affect our view of these earlier phenomena.

If we analyse our observations of possession, we find two main factors - the central operation, which is the control by a spirit of the sensitive's organism; and the indispensable prerequisite, which is the partial and temporary desertion of that organism by the percipient's own spirit.

Let us consider first how far this withdrawal of the living man's spirit from his organism has been rendered conceivable by evidence already obtained.

903. First of all, the splits, and substitutions of phases of personality with which our second chapter made us familiar have great significance for possession also.

We have there seen some secondary personality, beginning with slight and isolated sensory and motor manifestations, yet going on gradually to complete predominance, - complete control of all supraliminal manifestation.

The mere collection and description of such phenomena has up till now savoured of a certain boldness. The idea of tracing the possible mechanism involved in these transitions has scarcely arisen.

Yet it is manifest that there must be a complex set of laws concerned with such alternating use of brain-centres; - developments, one may suppose, of those unknown physical laws underlying ordinary memory, of which no one has formed as yet even a first rough conception.

An ordinary case of ecmnesia may present problems as insoluble in their way as those offered by spirit-possession itself. There may be in ecmnesia periods of life absolutely and permanently extruded from memory; and there may be also periods which are only temporarily thus extruded. Thus on Wednesday and Thursday I may be unaware of what I learnt and did on Monday and Tuesday; and then on Friday I may recover Monday's and Tuesday's knowledge, as well as retaining Wednesday's and Thursday's, so that my brain-cells have taken on, so to say, two separate lines of education since Sunday - that which began on Monday, and that which began on Wednesday. These intercurrent educations may have been naturally discordant, and may be fused in all kinds of ways in the ultimate synthesis.

These processes are completely obscure; and all that can be said is that their mechanism probably belongs to the same unknown series of operations which ultimately lead to that completest break in the history of the brain-cells which consists in their intercalary occupation by an external spirit.

904. Passing on to genius, which I discussed in my third chapter, it is noticeable that there also there is a certain degree of temporary substitution of one control for another over important brain-centres.

We must here regard the subliminal self as an entity partially distinct from the supraliminal, and its occupation of these brain-centres habitually devoted to supraliminal work is a kind of possession, which illustrates in yet another way the rapid metastasis of psychical product (so to term it) of which these highest centres are capable. The highest genius would thus be the completest self-possession, - the occupation and dominance of the whole organism by those profoundest elements of the self which act from the fullest knowledge, and in the wisest way.

905. The next main subject which fell under our description was sleep. And this state - the normal state which most resembles trance - has long ago suggested the question which first hints at the possibility of ecstasy, namely, What becomes of the soul during sleep? I think that our evidence has shown that sometimes during apparent ordinary sleep the spirit may travel away from the body, and may bring back a memory, more or less confused, of what it has seen in this clairvoyant excursion. This may indeed happen for brief flashes during waking moments also. But ordinary sleep seems to help the process; and deeper states of sleep - spontaneous or induced - seem still further to facilitate it. In the coma preceding death, or during that "suspended animation" which is sometimes taken for death, this travelling faculty has seemed to reach its highest point.