It is possible that if we could discern the minute psychology of this long series of changes, ranging from modifications too minute to be noted as abnormal to absolute revolutions of the whole character and intelligence, we might find no definite break in all the series; but rather a slow, continuous detachment of one psychical unit or element of consciousness after another from the primary synthesis. It is possible, on the other hand, that there may be a real break at a point where there appears to our external observation to be a break, namely, where the personality passes into its new phase through an interval of sleep or trance. And I believe that there is another break, at a point much further advanced, and not to be reached in this chapter, where some external intelligence begins in some way to possess the organism and to replace for a time the ordinary intellectual activity by an activity of its own. Setting, however, this last possibility for the present aside, we must adopt some arrangement on which to hang our cases. For this purpose the appearance of sleep or trance will make a useful, although not a definite, line of demarcation.
We may begin with localised psychical hypertrophies and isolations,--terms which I shall explain as we proceed; and then pass on through hysterical instabilities (where intermediate periods of trance may or may not be present) to those more advanced sleep-wakings and dimorphisms which a barrier of trance seems always to separate from the primary stream of conscious life. All such changes, of course, are generally noxious to the psychical organism; and it will be simpler to begin by dwelling on their noxious aspect, and regarding them as steps on the road--on one of the many roads--to mental overthrow.
The process begins, then, with something which is to the psychical organism no more than a boil or a corn is to the physical. In consequence of some suggestion from without, or of some inherited tendency, a small group of psychical units set up a process of exaggerated growth which shuts them off from free and healthy interchange with the rest of the personality.
The first symptom of disaggregation is thus the _idée fixe_, that is to say, the persistence of an uncontrolled and unmodifiable group of thoughts or emotions, which from their brooding isolation,--from the very fact of deficient interchange with the general current of thought,--become alien and intrusive, so that some special idea or image presses into consciousness with undue and painful frequency.