attached, until at last we come to a condition of things symbolized by the larger ellipse, which may be taken to stand for some rather massive and slow process of tension and discharge in the cortical centres, to which, _as a whole_, the feeling of musical tone symbolized by the line at the top of the diagram _simply and totally_ corresponds. It is as if a long file of men were to start one after the other to reach a distant point. The road at first is good and they keep their original distance apart. Presently it is intersected by bogs each worse than the last, so that the front men get so retarded that the hinder ones catch up with them before the journey is done, and all arrive together at the goal.[170] [Illustration: FIG. 26.] On this supposition there _are_ no unperceived units of mind-stuff preceding and composing the full consciousness. The latter is itself an immediate psychic fact and bears an immediate relation to the neural state which is its unconditional accompaniment. Did each neural shock give rise to its own psychic shock, and the psychic shocks then combine, it would be impossible to understand why severing one part of the central nervous system from another should break up the integrity of the consciousness. The cut has nothing to do with the psychic world. The atoms of mind-stuff ought to float off from the nerve-matter on either side of it, and come together over it and fuse, just as well as if it had not been made. We know, however, that they do not; that severance of the paths of conduction between a man's left auditory centre or optical centre and the rest of his cortex will sever all communication between the words which he hears or sees written and the rest of his ideas. Moreover, if feelings can mix into a _tertium quid_, why do we not take a feeling of greenness and a feeling of redness, and make a feeling of yellowness out of them? Why has optics neglected the open road to truth, and wasted centuries in disputing about theories of color-composition which two minutes of introspection would have settled forever[171] We cannot mix feelings as such, though we may mix the objects we feel, and from _their_ mixture get new feelings. We cannot even (as we shall later see) have two feelings in our mind at once. At most we can compare together _objects previously presented_ to us in distinct feelings; but then we find each object stubbornly maintaining its separate identity before consciousness, whatever the verdict of the comparison may be.[172] SELF-COMPOUNDING OF MENTAL FACTS IS INADMISSIBLE. But there is a still more fatal objection to the theory of mental units 'compounding with themselves' or 'integrating.' It is logically unintelligible; it leaves out the essential feature of all the 'combinations' we actually know.