Nothing is easier than to symbolize all these facts in terms of brain-action. Just as the echo of the _whence_, the sense of the starting point of our thought, is probably due to the dying excitement of processes but a moment since vividly aroused; so the sense of the whither, the foretaste of the terminus, must be due to the waxing excitement of tracts or processes which, a moment hence, will be the cerebral correlatives of some thing which a moment hence will be vividly present to the thought. Represented by a curve, the neurosis underlying consciousness must at any moment be like this: [Illustration: FIG. 27.] Each point of the horizontal line stands for some brain-tract or process. The height of the curve above the line stands for the intensity of the process. All the processes are _present_, in the intensities shown by the curve. But those before the latter's apex _were_ more intense a moment ago; those after it _will be_ more intense a moment hence. If I recite _a, b, c, d, e, f, g,_ at the moment of uttering _d_, neither _a, b, c,_ nor _e, f, g,_ are out of my consciousness altogether, but both, after their respective fashions, 'mix their dim lights' with the stronger one of the _d_, because their neuroses are both awake in some degree. There is a common class of mistakes which shows how brain-processes begin to be excited before the thoughts attached to them are _due_--due, that is, in substantive and vivid form. I mean those mistakes of speech or writing by which, in Dr. Carpenter's words, "we mispronounce or misspell a word, by introducing into it a letter or syllable of some other, whose turn is shortly to come; or, it may be, the whole of the anticipated word is substituted for the one which ought to have been expressed."[233] In these cases one of two things must have happened: either some local accident of nutrition _blocks_ the process that is _due_, so that other processes discharge that ought as yet to be but nascently aroused; or some opposite local accident _furthers_ the _latter processes_ and makes them explode before their time. In the chapter on Association of Ideas, numerous instances will come before us of the actual effect on consciousness of neuroses not yet maximally aroused. It is just like the 'overtones' in music. Different instruments give the 'same note,' but each in a different voice, because each gives more than that note, namely, various upper harmonics of it which differ from one instrument to another. They are not separately heard by the ear; they blend with the fundamental note, and suffuse it, and alter it; and even so do the waxing and waning brain-processes at every moment blend with and suffuse and alter the psychic effect of the processes which are at their culminating point. * * * * *