Page:Philosophical Review Volume 1.djvu/543

No. 5.] fundamental. In witness of this are the pleasure functions of sex and of nutrition. We may now say, rather, that pleasure was duly preserved to the performance of these sensory functions. We intimated, also, the possibility of pleasure nerves yet preserved in all our special sense-organs, and of the kinds of general occurrence that are likely there to reach and to stimulate these submerged fibres. The morphologic bearing of all these matters will now, I think, be sufficiently obvious for our present sketch, without further comment on them.

We now are able to understand why our pleasure sense, if it be our primary sense, does not occupy that quantitative share of our present mental life which, under our postulate, its various multiplications by newly rising sense associations at first seemed to promise. The surface and even the interior of our body has been usurped by a varied set of new sense systems, which now mediate the majority of our efferent experiences. Our primary sense now mediates but few original sensations. The lack of positive demonstration that it mediates any at all, with the fact that so many fundamental functions of the primary sense have been usurped from it, leads us to inquire more closely as to those functions which have been preserved to it, and for what reasons they have been preserved.

Why, under the foregoing wide-spread specialization and substitution, has not our primary sense been eliminated entirely? Our answer is that by the very order and manner of origin and development of our various sense systems the primary sense was peculiarly developed to fitness for centro-neural functions. It has, therefore, been specialized to that function. We have already noted that each new sense must be joined to old motor paths, in order to become of service. The complex nature of our higher nervous centres, which is required to bring about the proper adjustments of the infinite variety of our present sensory experiences to appropriate co-ordination with a nearly equal variety of possible muscular combinations, is too common a subject of modern knowledge to need more than mention here. This vast central co-ordination of sensory paths to motor paths has itself become a special function of our neural organism of