_Observation._ Among some of the reigning families of Europe, particularly the Spanish, the folly of intermarriage among themselves is strongly ill.u.s.trated. The high and n.o.ble talents that characterized their progenitors are not seen, but there is now exhibited, among their descendants, imbecility and the most revolting forms of nervous disease.

796. "Unhappily, it is not merely as a cause of disease, that hereditary predisposition is to be dreaded. The obstacles which it throws in the way of permanent recovery are even more formidable, and can never be entirely removed. Safety is to be found only in avoiding the perpetuation of the mischief."

797. "Therefore, if two persons, each naturally of excitable and delicate nervous temperament, choose to unite for life, they have themselves to blame for the concentrated influence of similar tendencies in destroying the health of their offspring, and subjecting them to all the miseries of nervous disease, madness, or melancholy." The command of G.o.d not to marry within certain degrees of consanguinity, is in accordance with the organic laws of the brain, and the wisdom of the prohibition is confirmed by observation.

_Observation._ The inhabitants, females particularly, of the sea-girt islands of America, are more affected with nervous diseases, than those who reside upon the mainland. The prevalence of these affections is ascribed to the frequent intermarriage of persons closely related by blood.

What is one cause of nervous disease among the higher cla.s.ses? What is true of some of the reigning families of Europe? 796. Why is hereditary predisposition to be dreaded? 797. Is the prohibition of G.o.d respecting intermarriage in accordance with the organic laws of the brain? What is said of the inhabitants of the sea-girt islands of America?

798. _The brain requires a due supply of pure blood._ This organ receives an unusually large supply of blood, in comparison with the rest of the body. It is estimated that one tenth of all the blood sent from the heart goes to this organ. If the arterial blood be altogether withdrawn, or a person breathes air that is filled with carbonic gas, the brain ceases its proper action, and sensibility with consciousness becomes extinct.

_Ill.u.s.trations._ 1st. If a person lose a considerable quant.i.ty of blood, dizziness and loss of consciousness follow. This results from the brain not receiving a sufficient amount of blood to sustain its functions.

2d. When an individual descends into a well or pit that contains carbonic acid, the blood is not changed or purified in the lungs, and loss of consciousness and death soon follow.

799. The slighter variations in the state of the blood have equally sure, though less palpable effects. If its vitality is impaired by breathing an atmosphere so much vitiated as to be insufficient to produce the proper degree of oxygenation, the blood then affords an imperfect stimulus to the brain. As a necessary consequence, languor and inactivity of the mental and nervous functions ensue, and a tendency to headache, fainting, or hysteria, makes its appearance.

_Observations._ 1st. Let a person remain, for a time, in a crowded, ill-ventilated, hall or church, and headache or faintness is generally produced. This is caused by the action of impure blood upon the brain.

2d. If a school-teacher wishes to have his pupils, on the day of examination, appear creditably, he will be careful to have the room well ventilated. Ventilating churches might prevent the inattention and sleepiness that are observed during the afternoon service.

798. Why does the brain require a due supply of pure blood? What is the effect when a person loses a considerable quant.i.ty of blood? What causes the loss of consciousness when carbonic acid is breathed? 799.

What effects are produced by slight variations in the quality of the blood? From the following observations, give some of the effects of impure blood on the brain.

3d. In many instances, the transmission of imperfectly oxygenated blood to the brain, is an influential cause in the production of nervous disease and delicacy of const.i.tution. The only efficient remedy for these conditions is a supply of pure blood to the brain.

800. _The brain should be called into action._ This organ, like the muscles, should be used, and then allowed to rest, or cease from vigorous thought. When the brain is properly called into action by moderate study, it increases in size and strength; while, on the other hand, if it is not used, the action of this organ is enfeebled, thereby diminishing the function of all parts of the body.

801. The brain, being an organized part, is subject, so far as regards exercise, to the same laws as the other organs of the body. If it is doomed to inactivity, its size diminishes, its health decays, and the mental operations and feelings, as a necessary consequence, become dull, feeble, and slow. If it is duly exercised after regular intervals of repose, the mind acquires readiness and strength. Lastly, if it is overtasked, either in the force or duration of its activity, its functions become impaired, and irritability and disease take the place of health and vigor.

802. The consequences of inadequate exercise will first be explained.

We have seen that by disuse the muscles become emaciated, the bones soften, and the blood-vessels are obliterated. The brain is no exception to this general rule. It is impaired by permanent inactivity, and becomes less fit to manifest the mental powers with readiness and energy. Nor will this surprise any reflecting person, who considers that the brain, as a part of the same animal system, is nourished by the same blood and regulated by the same vital laws as the muscles, bones, and arteries.

800. Why should the brain be called into action? 801. What is the effect if the brain is doomed to inactivity? 802. Show the consequences of disuse of the organs mentioned in preceding chapters. Does the same principle apply to the brain?

803. It is the weakening and depressing effect which is induced by the absence of the stimulus necessary for the healthy exercise of the brain, that renders solitary confinement so severe a punishment, even to the most daring minds. Keeping the above principle in view, we shall not be surprised to find that _non-exercise_ of the brain and nervous system, or, in other words, inactivity of intellect and feeling, is a very frequent predisposing cause of every form of nervous disease.

804. For demonstrative evidence of this position, we have only to look at the numerous victims to be found among females of the middle and higher ranks, who have no calls to exertion in gaining the means of subsistence, and no objects of interest on which to exercise their mental faculties, and who, consequently, sink into a state of mental sloth and nervousness, which not only deprives them of much enjoyment, but subjects them to suffering, both of body and mind from the slightest causes.

805. But let the situation of such persons be changed; bring them, for instance, from the listlessness of retirement to the business and bustle of the city; give them a variety of imperative employments, and so place them in society as to supply to their cerebral organs that extent of exercise which gives health and vivacity of action, and in a few months the change produced will be surprising. Health, animation, and energy, will take the place of former insipidity and dulness.

806. An additional ill.u.s.tration, involving an important principle in the production of many distressing forms of disease will be found in the case of a man of mature age, and of active habits, who has devoted his life to the toils of business, and whose hours of leisure have been few and short. Suppose such a person to retire to the country in search of repose, and to have no moral, religious, or philosophical pursuits to occupy his attention and keep up the active exercise of his brain; this organ will lose its health, and the inevitable result will be, weariness of life, despondency, or some other variety of nervous disease.

803. What renders solitary confinement so severe a punishment to the most daring minds? What is a predisposing cause of nervous disease?

804. In what cla.s.ses do mental and nervous debility prevail? 805. How can this be counteracted? 806. Give another ill.u.s.tration, showing how disease of the brain is induced.

807. One great evil attending the absence of some imperative employment or object of interest, to exercise the mind and brain, is the tendency which it generates to waste the mental energies on every trifling occurrence which presents itself, and to seek relief in the momentary excitement of any sensation, however unworthy. The best remedy for these evils is to create occupation to interest the mind, and give that wholesome exercise to the brain, which its const.i.tution requires.

808. _The evils arising from excessive or ill-timed exercise of the brain, or any of its parts, are numerous._ When we use the eye too long, or in too bright a light, it becomes bloodshot. The increased action of its vessels and nerves gives rise to a sensation of fatigue and pain, requiring us to desist. If we relieve the eye, the irritation gradually subsides and the healthy state returns. But, if we continue to look intently, or resume our employment before the eye has regained its natural state by repose, the irritation at last becomes permanent, and disease, followed by weakness of vision, or even blindness, may ensue.

809. Phenomena precisely a.n.a.logous occur, when, from intense mental excitement, the brain is kept long in a state of excessive activity.

The only difference is, that we can always see what happens in the eye, but rarely what takes place in the brain; occasionally, however, cases of fracture of the skull occur, in which, part of the bone being removed, we can see the quickened circulation in the vessels of the brain, as easily as those of the eye.

807. What is one great evil attending the absence of some imperative employment to exercise the mind and brain? What is the true remedy for these evils? 808. From what other cause do evils arise to the brain?

Explain the evil of it by the excessive use of the eye. 809. What is the only difference in the a.n.a.logy of the phenomena of the eye and brain? Has the a.n.a.logy been verified?

810. Sir Astley Cooper had a young man brought to him, who had lost a portion of his skull, just above the eyebrow. "On examining the head,"

says Sir Astley, "I distinctly saw that the pulsation of the brain was regular and slow; but at this time he was agitated by some opposition to his wishes, and directly the blood was sent with increased force to the brain, and the pulsation became frequent and violent."

811. Indeed, in many instances, the increased circulation in the brain, attendant on mental excitement, reveals itself when least expected, and leaves traces after death, which are very perceptible.

When tasked beyond its strength, the eye becomes insensible to light, and no longer conveys any impressions to the mind. In like manner, the brain, when much exhausted, becomes incapable of thought, and consciousness is almost lost in a feeling of utter confusion.

812. _At any time of life, excessive and continued mental exertion is hurtful_; but in infancy and early youth, when the structure of the brain is still immature and delicate, permanent mischief is more easily produced by injudicious treatment than at any subsequent period. In this respect, the a.n.a.logy is as complete between the brain and the other parts of the body, as that exemplified in the injurious effects of premature exercise of the bones and muscles.

813. Scrofulous and rickety children are the most usual sufferers in this way. They are generally remarkable for large heads, great precocity of understanding, and small, delicate bodies. But in such instances, the great size of the brain, and the acuteness of the mind, are the results of morbid growth. Even with the best of management, the child pa.s.ses the first years of its life constantly on the brink of active disease.

810. Relate the case detailed by Sir Astley Cooper. 811. May the increased functional action of the brain change its structure? 812. At what age particularly is excessive and continued mental exertion hurtful? 813. What is said of scrofulous and rickety children?

814. Instead, however, of trying to repress its mental activity, the fond parents, misled by the early promise of genius too often excite it still further, by unceasing cultivation, and the never-failing stimulus of praise. Finding its progress for a time equal to their warmest wishes, they look forward with ecstasy to the day when its talents will break forth and shed l.u.s.tre on its name.

815. But in exact proportion as the picture becomes brighter to their fancy, the probability of its being realized becomes less; for the brain, worn out by premature exertion, either becomes diseased, or loses its tone, leaving the mental powers imbecile and depressed for the remainder of life. The expected prodigy is thus easily outstripped in the social race by many whose dull outset promised him an easy victory.