By Prof. M. V. O'SHEA.
I.
Modern studies in neurology have contributed much to our knowledge of the function of the nervous system as a whole and of its several parts, and also of the relation of psychical activity to cerebral conditions and processes. The architecture of the neural mechanism delineated by these investigations is not only interesting in itself on account of the marvelous unity of things apparently diverse, but it is at the same time suggestive respecting its office as the physical instrument through which mind must express itself in this world. Psychologists now quite generally conceive of a living being, human or otherwise, as a reacting organism, receiving impressions from its environment and responding to them in some characteristic manner. To be fitted for this office an individual must be provided with appliances alike for the reception of stimulations and for their transformation into incitements to muscular activity. In the human species Nature has ordained that action need not follow immediately and inevitably upon any sense stimulus; fortunately, it may be deferred, so that when it does finally occur it 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,[17] 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.[18] 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,[19] Darwin,[20] Romanes,[21] Wallace,[22] Fiske,[23] Drummond,[24] Wundt,[25] and many others of equal scientific attainments.
The architecture and chemical constitution of the neural elements indicate unmistakably, it seems, that they were so constructed that in their functioning they would be amenable to the law of the conservation of energy, and recent investigations have produced some experimental evidence in support of this view. Hodge,[26] who succeeded in making microscopical examinations of living nerve cells while under stimulation, demonstrated that the cell by this treatment was depleted of its contents, as revealed in the gradual reduction of its size. In corroboration of these results it was found that the cerebral cells in animals were larger in the morning than after a day's activities, indicating that depletion must have taken place during waking life, followed by recuperation in sleep. Some interesting data relating in a way to this matter are easily gained in the laboratories by the use of the plethysmograph, which is designed to record the degree of blood pressure in different parts of the body. This instrument may be put upon the wrists and head, for instance, and it may be observed, when a person is subjected to certain influences whether, there is any alteration in blood supply in either region. It may be noticed, as a matter of fact, that when one is required to think diligently upon any problem, or being asleep is awakened or even disturbed by a noise in his environment, the volume of blood decreases in the wrist and increases in the head.[27] This same phenomenon is shown by experiments with the scientific cradle.[28] The inference from these data seems reasonable, that mental activity causes an expenditure of nerve force, which Nature seeks to replenish by inciting an unusual flow of nutritive-bearing fluid to the cerebral cortex. It has been shown, in further illustration of this law, that thought increases the temperature of the head, indicating that heat is generated through molecular activity; and also that psychical action increases waste products in the system, which may be derived only from the degradation of substances in nerve cells.[29] So information obtained from various other sources points toward the conclusion that in all activity energy stored in nerve cells is dissipated.
Recent experimental studies have given us reasons for believing that nerve cells in different individuals yield up their energy in response to stimulation with varying degrees of readiness.[30] Experience corroborates what Professor Bryan[31] has said: that some persons possess a leaky nervous system, wherefrom their vitalities flow away without issue in useful results. In such individuals activity will be likely to be in excess of that which the stimulus occasioning it should normally produce. Every one must have seen children, and adults as well, who when they hear a slight noise, for instance, which others do not mind, react with great vigor by jumping or screaming; or, when spoken to unexpectedly the face flushes, the lip quivers, and they become physically uncontrolled in a measure. In these instances the persons are unduly profligate in the expenditure of their means, and, in consequence, their capital is relatively soon exhausted.[32]
The writer last year conducted some experiments upon school children which yielded results that appear to confirm the view here set forth. Scripture's steadiness gauge was used in one test. This is designed to investigate stability of control by requiring a person to direct a light rod under guidance of the eye upon a point several feet distant, failure to accomplish this being announced by the ringing of an electric bell. The subject is usually required to make the trial fifteen times at a single test, and the number of successful attempts is taken to be in a way, although not always reliable, an index to his power of co-ordination. But more important than the success or failure in accomplishing the task is the index it affords of the nervous condition of the subject as revealed in the expressions of face and body. Tests were made in the morning, shortly following the opening of school, and again at half past eleven o'clock, or thereabouts, after the pupils had been working over their lessons for about two hours. One boy of eleven years, A. M., is a fair illustration of what might not inappropriately be called an exhaustive type, wherein nervous energy is readily depleted because of incessant waste. In the morning tests he was well controlled and accurate. A record of five tests made at half past eleven all show that after four or five attempts to place the rod upon the point the hand became very unsteady, the lips compressed, the region about the eyes showed unusual constraint, and the hand not being used was tightly clinched. Ten trials were usually sufficient to produce twitchings or tics in the face and body, although nothing of this was ever noticed at other times. This boy invariably made hard work of the task, and all the physical accompaniments indicated excessive motor stimulation following, of course, upon an unduly excited condition of the cerebral cells. At the close of the experiments he generally seemed exhausted, and upon three occasions it was thought best not to permit him to make the entire fifteen trials.
Another pupil, W. R., two years younger, illustrates a different type. In the morning trials he was no better than A. M., but he, too, was subjected to five different tests at half past eleven, with the result that he could in every instance complete the task without any apparent fatigue. There was no constraint apparent in the face or hands, no unusual effort to co-ordinate the muscles of the body, and no twitchings of any kind. Now, it seems probable that in the case of W. R. the brain was able to adjust effort in right degree to the needs of the occasion, while with A. M. there was such prodigality in the expenditure of energy in various irrelevant motor tensions and activities that it not only defeated its purpose, but it was soon largely spent. A. M. showed this tendency to nervous extravagance in all the work of the school. While an unusually bright boy, he yet became fatigued in the performance of duties that W. R. could discharge with no evidence of overstrain; indeed, the latter boy seemed never to reach a point beyond which he could not go with safety if he chose.
Further illustrations of this principle of individual differences in the conservation of nervous energy were afforded by another simple experiment. The apparatus employed consisted of a plate of smoked glass set in a frame so that it could be moved horizontally. Just touching the glass, and adjusted to it by a delicate spring, was a fine metal point which could be maintained at any height by a silk thread to be held in the fingers of the subject to be experimented upon, who stood with closed eyes endeavoring to keep his hand perfectly quiet for one half minute. During the test the glass was moved slowly in the frame, the metal point thus tracing a line which was a faithful index to most of the movements, at any rate, of the subject's hand. Five sets of experiments were made upon a number of pupils in the morning soon after the opening of school, and again just before the noon recess. The accompanying tracings are reproductions of those gained at one of the tests, and are typical examples. The first two were secured from a girl, M. L. R., eleven years of age. The one made at half past eleven, after two and a quarter hours' work in school, shows a significant phenomenon which could be easily witnessed during the experiment. She had become so fatigued that all muscular expressions were unusually constrained. During the short period while the experiment continued one could observe the arm and fingers contracting, which accounts for the upward direction of the tracing. The body swayed almost to the point of falling, the fingers of the hand not employed were clinched, and all the expressions indicated great tension. The second set of tracings, gained from a girl, E. H., twelve years of age, shows evidences of marked fatigue after a few hours' work; but the effect upon the bodily activities is quite in contrast with that of the case just mentioned. Here there was relaxation of the muscles, a general letting go of the whole body, revealed in the tracings taking an abrupt downward direction. The third group of tracings was gained from W. R., whose characteristics have already been adverted to, and who indicated here, as in the other tests, that his morning's duties had had no serious effect upon his nervous energies.
