9. Describe the method of control of the circulatory and digestive processes. How do reflex actions protect the body?

10. Compare voluntary and reflex action. In what sense are all the activities of the body reflex?

11. In what sense is walking voluntary? In what sense is it reflex?

12. How does secondary reflex action lessen the work of the nervous system?

13. State the special functions of the nerves, ganglia, spinal cord, bulb, cerebellum, and cerebrum.

14. State the importance of the formation of correct habits.

[Fig. 143]

Fig. 143-Nerve board for demonstrating nerve pathways.

PRACTICAL WORK

*To demonstrate Nerve Pathways.*-A smooth board, 2x6 ft., is painted black, and upon this is drawn in white a life-size outline of the body.

Pieces of cord of different colors and lengths are knotted to represent mon-axonic and di-axonic neurons. These are then pinned or tacked to the board in such a manner as to represent the connections in the different kinds of nerve pathways. Fig. 143 shows such a board with connections for a reflex action and a voluntary action of the same muscle.

*Study of the "Knee Jerk" Reflex.*-A boy is seated on a chair with the legs crossed. With a small pointer he is given a light, quick blow on the upper margin of the patella at the point of connection of the tendon. The stroke will usually be followed by a reflex movement of the foot. Does this take place independently of the mind? (The one upon whom the experiment is being performed should a.s.sume a relaxed condition and make no effort either to cause or prevent the movement.) Can the movement be inhibited (prevented)? Repeat the experiment, effort being made to prevent the movement, but not by contracting opposing muscles.

Other reflex actions adapted to cla.s.s study are those of the eyes, such as the closing of the lids on moving objects near them and the dilating of the pupils when the eyes are shaded. The involuntary jerking of the head on bringing the p.r.o.ngs of a vibrating tuning fork in contact with the end of the nose is also a reflex action which can be studied to advantage.

*To determine the Reaction Time.*-Have several pupils join hands, facing outwards, making a complete circle, excepting one gap. Give a signal by touching the hand of one pupil at the end of the line. Let this pupil communicate the signal, by pressure of the other hand, to the next pupil and so on around, having the last pupil raise the free hand at close of the experiment. Note carefully the time, preferably with a stop watch, required to complete the experiment and divide this by the number of pupils, to get the average reaction time. The experiment may be repeated with boys only and then with girls, comparing their average reaction time.

*Reflex Action of the Salivary Glands.*-Place a small pinch of salt upon the tongue and note the flow of saliva into the mouth. Try other substances, as starch, bits of wood, and sugar. What appears to be the natural stimulus for these glands? Compare with reflex actions of the muscles.

CHAPTER XIX - HYGIENE OF THE NERVOUS SYSTEM

The far-reaching effects and serious nature of disorders of the nervous system are sufficient reasons for considering carefully those conditions that make or mar its efficiency. Controlling all the activities of the body and affecting through its own condition the welfare of all the organs, the hygiene of the nervous system is, in a large measure, the hygiene of the entire body. Moreover, it is known that some of our worst diseases, including paralysis and insanity, are disorders of the nervous system and are prevented in many instances by a proper mode of living.

*The Main Problem.*-Many of our nervous disorders are undoubtedly due to the age in which we live. Our modern civilization, with all its facilities for human advancement and enjoyment, throws an extra strain upon the nervous system. Educational and social standards are higher than ever before and life in all its phases is more complex. Since we can hardly change the conditions under which we live, and probably would not if we could, we must learn to adapt or adjust ourselves to them so as to secure for the nervous system such relief as it requires. This adjustment is sometimes difficult, even when the actual needs of the nervous system are known.

The healthful action of the nervous system requires, on the one hand, exercise, but on the other hand, a certain condition of quietude, or _poise_-a state which is directly opposed to that of restlessness. The conditions of modern life seem able to force upon the nervous system all the exercise that it needs, and more (whether it be of the right kind or not), so that the main problem of to-day seems to be that of conserving, or economizing, the nervous energy and of preventing nervous waste.

*Wasteful Forms of Nervous Activity.*-There are without doubt many forms of activity that waste the vital forces of the body and lead to nervous exhaustion. Take, for example, the rather common habit of worrying over the trivial things of life. Certainly the nervous energy spent in this way cannot be used in doing useful work, but must be counted as so much loss to the body. One who would use his nervous system to the best advantage must find some way of preventing waste of this kind.(108)

Undue excitement, as well as pleasurable dissipations, also tend toward nervous exhaustion. And while the fact is recognized that pleasurable activities supply a necessary mental exercise, the limit of healthful endurance must be watched and _excesses of all kinds avoided_. Intense emotional states are found to be exhausting in the extreme; and the suppression of such undesirable feelings as anger, fear, jealousy, and resentment are of immense value in the hygiene of the nervous system.

*The Habit of Self-control.*-Much of the needless waste of nervous energy, including that of worrying over trivial matters, may be prevented through the exercise of self-control. From the standpoint of the nervous system, the present age differs from the past mainly in supplying a greater number and variety of nerve stimuli. Self-control means the ability to suppress activities that would result from undesirable stimuli and to direct the bodily activities into channels that are profitable. Self-control, therefore, is not only to be exercised on occasions of great emergency, but in the everyday affairs of life as well. It is even more important that the daily toiler at his task be able to keep the petty annoyances of life from acting as irritants to his nervous system than that he keep cool during some great calamity. The habit of self-control is acquired mainly through the persistent effort to prevent any and all kinds of petty annoyances from affecting the nerves or the temper.

*Nervousness.*-Self-control is much more easily practiced by some than by others. This is due partly to habit, but is also due to an actual difference in the degree of sensitiveness, or irritability, of the nervous systems of different people. One whose nervous system tends to respond too readily to any and all kinds of stimuli is said to be "nervous." This condition is in some instances inherited, but is in most cases due to the wasteful expenditure of nervous energy or to the action of some drug upon the body. Excess of mental work, too much reading, long-continued anxiety, eye strain, and the use of tea, coffee, alcohol, tobacco, or other drugs, including many of those taken as medicines, are known to cause nervousness. Nervousness is not only a source of great annoyance, both to one's self and to others, but is a menace to the general health.

The first step toward securing relief from such a condition is the removal of the cause. The habits should be inquired into and excesses of all kinds discontinued. In some instances it may be necessary to _have the eyes __examined_ and gla.s.ses fitted by a competent oculist.(109) The nervous energy should be carefully economized and the habit of self-control diligently cultivated. Special exercises that have for their purpose the equalizing of the circulation and the strengthening of the blood vessels of the neck and the brain also have beneficial effects.

*Nervous Overstrain.*-Both mental and physical overwork tends to weaken the nervous system and to produce nervousness. Where hard mental work is long continued, or where it is carried on under excitement, a tense nervous condition is developed which is decidedly weakening in its effects. The causes which lead to such a condition, and in fact overwork of all kinds, should if possible be avoided. Where this is not possible, and in many cases it is not, the period of overwork should be followed by one of rest, recreation, and plenty of sleep. To the overworked in body or in mind, nothing is more important from a hygienic, as well as moral, standpoint, than the right use of the _one rest day in seven_. The best interests of our modern civilization _require_ that the Sabbath be kept as a quiet, rest-giving day.

*Disturbed Circulation of the Brain.*-Nervousness not infrequently is accompanied by an increase in the circulation of the brain and disappears when this condition is relieved. Though mental work and excitement tend naturally to increase the circulation in the brain, this should subside with rest and relief from excitement. When there is a tendency for this condition to become permanent, effort should be made looking for relief.

Increasing the circulation in the lower extremities by hot or cold foot baths, or by much walking, is found to be most beneficial. Special exercises of the muscles of the neck are also recommended as a means of relieving this condition.(110)

*Hygienic Value of Work.*-Within reasonable limits, both mental and physical work are conducive to the vigor of the nervous system. Through work the energies of the body find their natural outlet, and this prevents dissipation and the formation of bad habits. Even hard work does not injure the nervous system, and severe mental exertion may be undergone, provided the proper hygienic conditions are observed. The nervous disorders suffered by brain workers are not, as a rule, due to the work which the brain does, but to violation of the laws of health, especially the law of exercise. Such persons should observe the general laws of hygiene and especially should they practice daily those forms of physical exercise that tend to counteract the effects of mental work.

*Physical Exercise* properly taken is beneficial to the nervous system through both direct and indirect effects. A large proportion of the nerve cells have for their function the production of motion, and these are called into play only through muscular activity. Then, as already suggested, physical exercise counteracts the unpleasant effects of mental work. Hard study causes an excess of blood to be sent to the brain and a diminished amount to the arms and to the legs. Physical exercise redistributes the blood and equalizes the circulation. Light exercise should, therefore, follow hard study. The student before retiring at night is greatly aided in getting to sleep and is put in a better condition for the next day's work by ten to fifteen minutes of light gymnastics. A daily walk of two or three miles is also an excellent means of counteracting the effects of mental work. The brain worker should, however, avoid violent exercise or the carrying of any kind of exercise to exhaustion.

*Sleep*, and plenty of it, is one of the first requirements of the nervous system. It is during sleep that the exhausted brain cells are replenished.

To shorten the time for sleep is to weaken the brain and to lessen its working force. No one should attempt to get along with less than eight hours of sleep each day and most people require more. Children require more sleep than adults. Those under six years should have from eleven to twelve hours of sleep per day. Children between six and ten years should have at least ten hours.

*Insomnia*, or sleeplessness, on account of its effects upon the nervous system, is to be regarded as a serious condition, and hygienic means for relieving it should be diligently sought. Having its cause in nervousness, a disturbed circulation of the brain, or some form of nervous exhaustion, it is benefited through relieving these conditions and in the manner already described. Of course the external conditions for aiding sleep should not be overlooked. The bed should be comfortable, and the room should be cool, well ventilated, dark, and quiet. The inducing of sleep by means of drugs is a dangerous practice and should never be resorted to except under the direction of the physician.

*Effects of Heat and Cold.*-Heat and cold both have their effects upon the nervous system. Heat increases the nervous irritability, while cold acts as a natural sedative to the nerves. A nervous person is made more nervous by an overheated atmosphere, but derives beneficial effects from exposing the body freely to cold air and water. The tonic cold bath (page 273), if taken with the usual precautions, can be used to good advantage in diminishing nervousness. The taking of outdoor exercise in cold weather is, for the same reason, an excellent practice.

*Effect of Emotional States.*-We have already noted the effect of certain emotional states upon the digestion of the food (page 162). Emotional states are also known to interfere with breathing and with the action of the heart. Such effects are explained through the close relation of the mind to the work of the nervous system in general. While certain emotional states, such as fear, anger, melancholia, and the impulse to worry, interfere seriously with the normal action of the nervous system, others, such as contentment, cheerfulness, and joy, are decidedly beneficial in their effects. How important, then, is the habit of suppressing the states that are harmful and of cultivating those that are beneficial. From a hygienic, as well as social, standpoint a cheerful, happy disposition is worth all the effort necessary for its attainment.

*The Nervous Condition of Children* should be a matter of deep concern on the part of both parents and teachers. In the home, as well as in the school, the child may be "pushed" until the nervous system receives permanent injury. Exhaustion of nerve cells is produced through too many and too vivid impressions being made upon the immature brain. The child should be protected from undue excitement. He should have the benefit of outdoor exercise and should be early inured to cold. He should be shielded from the poisoning effects of tea, coffee, tobacco, alcohol, and other drugs. He should have impressed upon him the habit of self-control. He should not be indulged in foolish caprices or whims, but should be taught to be content with plain, wholesome food and with the simple forms of enjoyment.

*Influences at School.*-School life is necessarily a great strain upon the child. Night study added to the work of the day makes a heavy burden for elementary pupils to bear. Though the legal school age is usually fixed at six years, delicate children should be kept out of school until they are seven or eight years old, provided they have good homes. In addition to the excitation incident to studying and reciting lessons, conditions frequently arise both in the schoolroom and upon the playground that create a feeling of fear or dread in the minds of children. Quarrels and feuds among the children and the bullying of big boys on the playground may work untold harm. All conditions tending to develop fear, uneasiness, or undue excitement on the part of children should receive the attention of those in authority.

*Excessive Reading* is a frequent cause of injury to the nervous systems of children. This has a bad effect, both on account of too many impressions being made upon the mind and also on account of the strain to the eyes. Then if the reading consists mostly of light fiction, the mind is directed away from the really important things of life. The reading of children should be thoughtfully controlled, both as to quality and quant.i.ty. Exciting stories should, as a rule, be excluded, but a taste for biography, historical and scientific writings, and for the great works of literature should be cultivated. Simple fairy tales which have a recognized value in developing the imagination of the child need not be omitted, but it is of vital importance that the "story-reading habit" be not formed.

*Effects of Drugs.*-Because of its delicacy of structure a number of chemical compounds, or drugs, are able to produce injurious effects upon the nervous system. Some of these are violent poisons, while others, in small quant.i.ties, are mild in their action. Certain drugs, in addition to their immediate effects, bring about changes in the nervous system which cause an unnatural appet.i.te, or craving, that leads to their continued use. This is the case with alcohol, the intoxicating substance in the usual saloon drinks, and with nicotine, the stimulating drug in tobacco.

The same is also true of morphine, chloral, and several other drugs used as medicines. The _danger of becoming a slave_ to some useless and pernicious habit should dissuade one from the use of drugs except in cases of positive emergency.

*Alcohol and the Nervous System.*-Alcohol, as already shown, injures practically all portions of the body; but it has its worst effects upon the nervous system. Through its action on this system, it interferes with the circulation of the blood, produces a condition of "temporary insanity"

called intoxication, weakens the will, and eventually dethrones the reason. Worst of all, it produces a condition of "chronic poisoning" which manifests itself in an unnatural craving, and this causes it to be used by the victim even when he knows he is "drinking to his own destruction."

Though its use in small quant.i.ties does not, as a rule, produce such marked effects upon the nervous system, it develops the "craving," and this is apt in time to lead to its use in larger quant.i.ties. But even if this does not occur, the practice is objectionable for its unhygienic effects in general.(111) Tippling with such mild solutions of alcohol as light wine, beer, and hard cider is, for these reasons, a dangerous pastime.

*Alcohol and Crime.*-It is sometimes stated that no one who leaves alcohol alone will be injured by it. This is true only of its direct effects; not of its indirect effects. Whenever a crime is committed somebody is injured, and alcohol is known to be a chief cause of crime. Alcohol causes crime through the loss of self-control, seen especially in intoxication, and also because of the moroseness and quarrelsomeness which it developes in certain individuals. Indirectly it causes crime through the poverty which it engenders and through its influence in bringing about social conditions out of which crime develops. Everything considered, the free use of alcohol is incompatible with the nervous health and moral tone of a community.

*Nicotine and the Nervous System.*-Nicotine is an oily substance which is extracted from the tobacco plant. Its action on the nervous system is in general that of a poison. Taken in small quant.i.ties, it is a mild stimulant and, if the doses are repeated, a habit is formed which is difficult to break. Tobacco is used mainly for the stimulating effect of this drug. While not so serious in its results as the alcohol and other drug habits, the use of tobacco is of no benefit, is a continual and useless expense, and, in many instances, causes a derangement of the healthy action of the body.(112) With the bad effects of the nicotine must be included those of questionable substances added to the tobacco by the manufacturer, either for their agreeable flavor or for adulteration.

*Relation of Age to the Effects of Nicotine.*-The use of tobacco by the young is especially to be deplored. In addition to the harmful effects observed in those of mature years, nicotine interferes with the normal development of the body and lays, in many instances, the foundation for physical and mental weakness in later life. The cigarette is decidedly harmful, especially when inhalation is practiced, its deadening effects being in part due to the wrappers, some of which have been shown to contain a.r.s.enic and other poisonous drugs. While dulling the intellect and weakening the body, cigarette smoking also tends to make criminals of boys.(113) Parents, teachers, school officers, and all who have the good of mankind at heart should take every precaution, including that of setting a good example, to prevent the formation of the tobacco habit by those of immature years.

*Habit versus Self-control.*-The power of self-control, already emphasized for its importance in the economical expenditure of the nervous energy, is of vital importance in its relation to the habits of the body.

Self-control is the chief safeguard against the formation of bad habits and is the only means of redemption from such habits after they have once been formed. The persistent cultivation of the power to control the appet.i.tes and the pa.s.sions, as well as all forms of activity which tend to injure the body or debase the character, gives a tone to the nervous system which increases the self-respect and raises the individual to a _higher plane of life_. The worst habits _can_ be broken and good ones formed in their stead, if only there is sufficient determination to accomplish these results. Failure comes from not having the mind thoroughly "made up" and from not having, back of the desire to do better, "the strong will of a righteous determination."

*Effects of External Conditions.*-While the inner life and habits have most to do with the hygiene of the nervous system, a certain amount of attention may properly be given to those conditions outside of the body which affect directly or indirectly the state of this system. Noise, disorder, and confusion act as nervous irritants, but quiet, order, and system have the opposite effect. There is, therefore, much in the management of the office, factory, schoolroom, or home that has to do with the real hygiene of the nerves as well as with the efficiency of the work that is being done. The suppression of distracting influences not only enables the mind to be given fully to the work in hand, but actually prevents waste of nervous energy. Although the responsibility for securing the best conditions for work rests primarily with those in charge, it is also true that each individual in every organization may contribute to the order or disorder that prevails.

*Social Relations.*-In considering the external conditions that affect the nervous system, the fact must not be overlooked that man is a social being and has to adjust himself to an established social order. His relations to his fellow-men, therefore, affect strongly his nervous condition and theirs also. For this reason the best hygiene of the nervous system is based upon _moral_ as well as physical right living. Along with the power of self-control and the maintenance of a correct nervous poise, there should be a proper regard for the welfare of others. On account of the ease with which one individual may disturb the nervous state of another, those social forms and customs which tend to establish harmonious relations among men are truly hygienic in their effects, and may well be carried out in spirit as well as "in letter."

It is also a fact that a given mental state in one person tends to excite a like state in those with whom he a.s.sociates. How important, then, that each and all cultivate, as habits, the qualities of cheerfulness, kindness, and good-will, instead of the opposite states of mind.