Let us now return to that analogy of the piano and the unseen player and see if we can get some more light from it than has yet appeared. In view of the last considerations which were urged in this connexion—the possibility of effecting not merely the ruin of the instrument but the more vital change of the character of the music it will perform, we must slightly alter one of the terms of the comparison. The analogy will be a strikingly close and suggestive one if we bring into view the latest development in musical mechanism, the pianola. Suppose that the music-rolls of a pianola were made of different sizes and shapes according to the different classes of music. There would then, let us say, be one kind of roll for classical music, another for Italian opera, another for Palestrinian polyphony, another for music-hall ditties, and subvarieties of all these. Now let us suppose that each pianola were so constructed as to take some particular type of music easily, other types with more difficulty, and others, again, not at all, and let us assume that all these types are continually being presented for performance. The construction of the pianola will then correspond to the physical constitution of the brain. This constitution, in each case, is the material equivalent of the dominance of a particular kind of personality, or what we have called above _aura_. But the records which have lately been so much studied of cases of what is called ‘multiple personality’ tend to show that in each of us there _are_ several distinct personalities—or if that word seems to beg an important question as to the unitary character of personality, let us say streams of consciousness—which are pressing for manifestation. The brain selects automatically among these, and normally keeps one particular type to the front. But just as a mechanical alteration in our hypothetical pianola might entirely change the type of music it would play, so a lesion or shock of any kind might change, more or less, the type of personality which a particular brain was fitted to express; and such cases are, of course, well known to occur. But now we come to a fact than which none is better known, none more absolutely verifiable in experience, but to which there is nothing in the least analogous in the pianola or any other piece of mechanism taken by itself. I can, with time and toil, with patience and resolution, _change the structure of my brain_ and make easy for it that which before was difficult or impossible. Within limits which cannot be defined (because human life is too short), I can even adapt it to the expression of a new type of personality. No musical instrument can do that to itself. One would have to call in for that purpose the initiating and controlling force of the man who made it.[135]