INTELLECTUAL ACTIVITY.
once the external excitation is disseminated through the plexuses of the cortical substance, and in corporated in the sensorizini, developing in it the specific energies of the cerebral cells that have received this new medium itself comes into play, and reacts in the direct line of its latent capacities.
The sphere of psycho-intellectual activity then exhibits all its natural riches, all the stores of its awakened sensi bility. It is suddenly thrown into agitation, reacts, and thus develops the marvellous capacities with which it is fundamentally endowed. This new medium which comes into play, comprehends, as we have said, the sum of the purely psychical and purely intellectual phenomena of the living organism. It is the regio princeps of the organism, in which all ends, from which all begins, and which is the epitome of the vital forces of mental activity.
Now, how is this double sphere of activity, which from the dynamic point of view presents characters so dis tinctly marked, and yet so intimately fused together, constituted ? How may it be ideally conceived as re gards the cortical structure ? These are questions to which it is at present impossible to give a completely satisfactory reply. We merely know, from the anatomical data we have already laid before the reader, that the cerebral cortex is made up of a series of cells superposed in independent zones and yet united one with another ; and that these plexuses of cells directly receive external excitations, chiefly within a specially circumscribed region, thus forming a vast surface of reception for these excitations, and in the strict accepta tion of the word a true sensorium commune.
Now these plexuses of the sensorium, constituted by the different submeningeal zones of cortical cells, are not merely inert screens, nervous zones destined to receive and passively register the images of the external world. They are sensitive, living, emotional plexuses, which become erect in a peculiar manner in presence of the stimulating excitation, and which, on its arrival, like their fellows in the peripheral regions, give evi dence of the various manners in which they may be impressed. They live, they feel, and what is more, they remember ; for then it is that this new property of preserving records of past impressions, appearing in full force, gives a special character of permanence to all the excitations that arrive, and enables them to sur vive themselves, to prolong their existence in the form of memories, and to be marked in the calendar of our sensitive impressions with a special co-efficient of pleasure or pain.
Thus by these two fundamental conditions, the arrival of the external excitation, and the appropriate reactions of the cerebral medium in which it is received, new forces are created in the brain, a special sphere of nervous activity is developed, in which the natural sensibility of our being, our conscious personality, represented with all its elements (see p. 105) in the tissue of the sen sorium, comes to life, expands, and perfects itself, by the coming into play of the natural sensibility of the ele ments which compose it. Thus, consequently, former impressions are inevitably associated with recent ones ; the past life of diverse emotions, the memory of days of joy or sorrow, is incessantly in contact with the conceptive regions of mental activity ; and in fine, if the sphere of purely psychical activity be considered from a dynamic point of view, as the resultant of all the impressions of our sensibility present and past, associated with the events of our current life ; from an anatomical point of view, it may be conceived of as localized in all that series of nervous elements which constitute the plexuses of the seusorium.
On the other hand, if, up to a certain point, we have some precise data which permit us to suppose that certain regions of the cortex (the regions of the small cells) play the part of a common reservoir as regards the external impressions which are distributed among them, and consequently become the special territory of the phenomena of mental sensibility, it is as yet almost entirely impossible to obtain any precise data as to the real constitution and topo graphic situation of the field of intellectual activity proper. It is only artificially, and in a roundabout way, that we can succeed in grouping a few facts with regard to the subject.