impulse itself must be sufficient in intensity; the "points" (in railway-phraseology) must be "open," the line must be clear, and the circulation must be so balanced that it is ready to surge in the required direction. The outcome may be defective by the failure of any of these conditions, and an improved adjustment in some needed respect may at once enable a correct result to be got. Thus, a familiar name or word may escape the memory, and for a time every effort may fail to recall it. Then, for example, a more successful focusing of the circulation taking place in the ideational center, the word comes up without apparent effort. From this point of view, "unconscious cerebration" means simply "better adjustment."
If the radiation be toward a motor center, we find in the latter all the conditions favorable for liberating its energy. In the waking state, in the absence of fatigue or disease, the center requires little more than permission to do its work. All the potential conditions for discharge are already there. With the stimulus communicated from another center, we have simultaneously molecular agitation and vascular excitement. The latter acts in two ways. In the first place, by derivation, it removes the inhibitory action of other parts of the brain; and in the second place, it further directly stimulates the molecular movement. The immediate result is turgescence or orgasm in the center itself. Then, the general law in physics, that action and reaction are equal and contrary, must here hold good. If the surroundings, therefore, be stable, natural relief will be got by the overflow or discharge of energy into a motor nerve, and contraction of a muscle will be the result. On the other hand, if the support afforded to the center be insufficient, the vascular turgescence will to some extent spend itself in displacing the surrounding tissues, and the intended movement will either not take place, or it will fail in precision and strength.
My object in the present paper has been rather to give prominence to what I consider a neglected factor in cerebral physiology than to attempt its application to all possible instances. I shall be satisfied if I have said enough to show the importance of investigation in the direction I have indicated. Indeed, when one reflects on how much research is devoted to the minute structure of the brain itself, it seems surprising that so little attention is given to what may be called intracranial physics. We have here a field which is at least as likely to be fruitful in results as the attempt to measure and classify all the varieties of nerve-cell, or to unravel the complex network of nerve-fibers.
Within the skull we have an imperium in imperio, where, with loyal fealty to the interests and claims of imperial unity, the rights of "home-rule" are jealously conserved. As the speck of protoplasm requires the restraint of the cell-wall to enable it to develop and exercise some specific form of energy, so the brain-mass has its form molded, and its development directed, and, especially, its energies exercised under the severe repression of membrane and bone. Then,
