Page:Popular Science Monthly Volume 55.djvu/530

512 will be the resultant of any given present impression modified by others previously received and treasured up in memory, as we say. To accomplish this really great feat, Nature had to devise an elaborate contrivance, interposed between incoming messages and outgoing impulses, to act as a moderator or transformer of a very extraordinary and intricate character—the central nervous system, comprising the brain and spinal cord. That it may be able to meet the requirements of its office, this system must be equipped with two principal kinds of apparatus—cells, which will serve as storehouses of energy to be employed in keeping the machinery running, and association fibers or pathways, which will put any one cell into communication with others in the cerebral community.

The item which will engage our attention principally here relates to the primary function of the nerve cell—to store up vital forces in the form of highly unstable chemical compounds, which may upon slight disturbance be broken down, the static energy represented in their union thus becoming dynamic. Those who have given special attention to the matter seem to agree that all activity, physical as well as mental, involves the expenditure of a portion of this energy. It may perhaps be mentioned in passing that when this conception was first being presented some persons hastily constructed the theory that what people had been calling mind was nothing more nor less than a certain mode of manifestation of this mysterious but yet physical force. While abundant evidence, gained from various sciences by recent research, leads one to the conviction that in some unknown manner psychical and neural processes are closely co-ordinated, yet not a single investigator of standing claims that they are identical. There is doubtless among some in our day too great a tendency, unconscious though it may be for the most part, to declare that a description of the physical correlates or antecedents of mental phenomena fully accounts for the latter in respect alike of their nature and their modes of manifestation; but those who find themselves coming to such conclusions might be both interested in and benefited by examining the opinions of great naturalists and psychologists who have reflected long and profoundly upon the world-old problem of the connections between body and mind—such men as Lotze, Darwin, Romanes, Wallace, Fiske,