254 POPULAR SCIENCE MONTHLY. 



nervous system or of the fact that all these bodily activities which 

 are accompanied by modifications of his consciousness seem to be de- 

 inendent 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 in- 

 dependently 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 conscious- 

 ness of a given human individual increases in complexity and coordi- 

 nation 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 reject- 

 ing 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 less- 

 complex 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 sys- 

 tematized; 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. 



