They thus form that matrix, that regio princeps of the cerebral cortex, which constitutes the true sensorium commune, the common reservoir into which all the im pressions that have thrown our sensitive fibres into agitation, flow, and in which they subside. (Fig. 1—B, and Fig. 6-5, 1o, 15.) Thus, then, is constituted this region which receives into its sensitive tissue the resultant of all sensitive excitations, from the external world as well as from the vegetative life of the organism, and which, when thrown into agitation, sensitized in its turn, reacts in a thousand ways, dispersing in all directions the vibratory excitations which have developed the energies of its elements. It is its task gradually to transform the phenomena of sensibility, and finally to cause sensitive excitations, radiated from cell-plexus to cell-plexus, like a force in evolution which is incessantly transformed, to produce insensibly a motor phenomenon.
Thus we arrive at the conclusion that, from a phy siological point of view, the voluntary motor act which emanates from the brain is in all cases nothing more than the repercussion, more or less distant, of a pri mordial sensitive impression. (Fig. 6-6, II, 16.)
It should, however, be added, that although the act of voluntary motion is, as a general rule, only the indirect expression of the agitation of the sensorium, never theless, from the very fact that it is evolved throughout the plexuses of the cortical substance, laying its various zones under contribution, it is not a simple, purely reflex phenomenon, like those which occur in the similar plexuses of the spinal axis ; it is a complex synthetic phenomenon that resumes in itself the dif ferent elements which, taken together, constitute human personality. We may also say that if an act of the will be merely a phenomenon of transformed sensibility, it is, nevertheless, sensibility doubled, multi plied by all the cerebral activities in agitation, in a word, by the feeling and vibrating human personality, which comes into play in a somatic form, and reveals itself externally by a series of reflected and co-ordinated manifestations.