Does there really exist a perfect unity? Evidently not in the strict, mathematical sense. In a relative sense it is met with, rarely and incidentally. In a clever marksman in the act of taking aim, or in a skilled surgeon performing a difficult operation all is found to converge, both physically and mentally. Still, let us take note of the result: in these conditions the awareness of real personality disappears; the conscious individual is reduced to an idea; whence it would follow that perfect unity of consciousness and the awareness of personality exclude each other. By a different course we again reach the same conclusion; the ego is a co-ordination. It oscillates between two extreme points at which it ceases to exist: viz., perfect unity and absolute inco-ordination. All the intermediate degrees are met with, in fact, and without any line of demarcation between the healthy and the morbid; the one encroaches upon the other. Even in the normal state the co-ordination is often sufficiently loose to allow several series to coexist separately. We can walk or perform manual work with a vague and intermittent consciousness of the movements, at the same time singing, musing; but if the activity of thought increases, the singing will cease. With many people it is a kind of substitute for intellectual activity, an intermediate state between thinking and not-thinking. The unity of the ego, in a psychological sense, is, therefore, the cohesion, during a given time, of a certain number of clear states of consciousness, accompanied by others less clear, and by a multitude of physiological states which, without being accompanied by consciousness like the others, yet operate as much as, and even more than, the former. Unity, in fact, means co-ordination. The conclusion to be drawn from the above remarks is namely this, that the consensus of consciousness being subordinate to the consensus of the organism, the problem of the unity of the ego is, in its ultimate form, a biological problem. To biology pertains the task of explaining, if it can, the genesis of organisms and the solidarity of their component parts. Psychological interpretation can only follow in its wake. 2. Personality as a Complex[70] Ideas, after being experienced in consciousness, become dormant (conserved as physiological dispositions) and may or may not afterward be reawakened in consciousness as memories. Many such ideas, under conditions with some of which we are all familiar, tend to form part of our voluntary or involuntary memories and many do not. But when such is the case, the memories do not ordinarily include the whole of a given mental experience, but only excerpts or abstracts of it. Hence one reason for the fallibility of human memory and consequent testimony.