Page:Popular Science Monthly Volume 67.djvu/260

254 nervous system or of the fact that all these bodily activities which are accompanied by modifications of his consciousness seem to be dependent upon modifications of the activities of this nervous system. But coincidently with the advance of knowledge in reference to the structure of the nervous system modern psychologists have quite independently reached the conclusion that human consciousness itself is systemic in its nature. As the nervous system of a given man is looked upon as a closed or definitely bounded physical system; so is his consciousness looked upon as a closed or definitely bounded psychic system.

Furthermore, we have learned that in a general way the consciousness of a given human individual increases in complexity and coordination pari passu with the increase of complexity and coordination in his nervous system, in the course of his development from birth to the life of full intelligence.

It is natural for us then to conclude that wherever we find in an animal a closed nervous system of greater or less complexity we have good ground for the assumption of the existence of some form of consciousness of a corresponding greater or less complexity; and this accords, as we have seen, with the every-day assumption of the common man. It is true, as we have said above, that many of our biologists hesitate to accept this commonly accepted view: but it is also true that they fail altogether to furnish to us any valid reasons for rejecting it, being utterly at a loss to give us any satisfactory mark by which to distinguish between animals which are certainly conscious and those which certainly are not.

Modern students of neurology have discovered a further fact of importance to our consideration, viz., the fact that among all animals subject to our study, excepting possibly the very lowest forms in which nervous systems exist, each nervous system is really a more or lesscomplex system of minor nervous systems. The sympathetic nervous system in man, for instance, has a distinct individuality of its own, although it is at the same time a part of the whole broad system: and more or less of such individuality is traceable in connection with many other minor systems within the whole nervous system.

It is interesting then to note that the psychologist also finds himself compelled to look upon human consciousness not only as a psychic system, but as a broad system of minor psychic systems. For instance, our ocular sensations and their resultants are in themselves systematized; and our aural sensations and their resultants are also, although differently, systematized; while at the same time they are both parts of the whole psychic system which we call consciousness. Each group has a measure of individuality, each forms a minor system, within the broader conscious system.