This is easily accounted for. Uneducated persons, who are deprived of one or more of the senses, are isolated from the world in which they live. The book of nature is open before them, but they are unable to peruse it. The simplest operations constantly going on around them are locked in mystery. They are an enigma to themselves. Even those who are endowed with inquisitive minds are perplexed with the existing state of things. They know nothing of the physical organization of the planet we inhabit, of its political and civil divisions, and of the whole machinery of human society, and are profoundly ignorant of the past history and future destiny of the race to which they belong. It is not remarkable that mind so unnaturally and peculiarly circumstanced—with its usual inlets of knowledge so obstructed, and deprived of external objects to act upon—should prey upon itself, and thus superinduce insanity in its usual forms, and more especially when unaided and undirected by education.
Keeping the same principle in view, we shall not be surprised to find that want of exercise of the brain and nervous system, or, in other words, that inactivity of intellect and feeling, is a very frequent predisposing cause of every form of nervous disease, even with those who have not been deprived of any of their senses. 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 call 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 nervous weakness, which not only deprives them of much enjoyment, but subjects them to suffering, both of body and mind, from the slightest causes.
In looking abroad upon society, we find innumerable examples of mental and nervous debility from this cause. When a person of some mental capacity is confined for a long time to an unvarying round of employment, which affords neither scope nor stimulus for one half of his faculties, and, from want of education or society, has no external resources, his mental powers, for want of exercise to keep up due vitality in their cerebral organs, become blunted, and his perceptions slow and dull. Unusual subjects of thought become to him disagreeable and painful. The intellect and feelings not being provided with interests external to themselves, must either become inactive and weak, or work upon themselves and become diseased.
But let the situation of such persons be changed; bring them, for instance, from the listlessness of retirement to the business and bustle of a city; give them a variety of imperative employments, and place them in society so 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 acuteness will take the place of former insipidity and dullness. In such instances, it would be absurd to suppose that it is the mind itself which becomes heavy and feeble, and again revives into energy by these changes in external circumstances. The effects arise entirely from changes in the state of the brain, and the mental manifestations and the bodily health have been improved solely by the improvement of its condition.
The evils arising from excessive or ill-timed exercise of the brain, or any of its parts, are numerous, and equally in accordance with the ordinary laws of physiology. When we use the eye too long or in too bright a light, it becomes bloodshot, and the increased action of its vessels and nerves gives rise to a sensation of fatigue and pain requiring us to desist. If we turn away and 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 sight, or even blindness, may ensue, as often happens to glass-blowers, smiths, and others who are obliged to work in an intense light.
Precisely analogous phenomena 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 in those of the eye. Sir Astley Cooper had a young gentleman 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." Sir Astley hence concludes that, in the treatment of injuries of the brain, if you omit to keep the mind free from agitation, your other means will be unavailing.
A still more remarkable case is said to have occurred in the hospital of Montpellier in 1821. The subject of it was a female who had lost a large portion of her scalp, skull-bone, and dura mater. A corresponding portion of her brain was consequently bare, and subject to inspection. When she was in a dreamless sleep, her brain was motionless, and lay within the cranium; but when her sleep was imperfect, and she was agitated by dreams, her brain moved and protruded without the cranium. In vivid dreams the protrusion was considerable; and when she was awake and engaged in active thought or sprightly conversation, it was still greater.
In alluding to this subject, Dr. Caldwell remarks, that if it were possible, without doing an injury to other parts, to augment the constant afflux of healthy arterial blood to the brain, the mental operations would be invigorated by it. This position is illustrated by reference to the fact that when a public speaker is flushed and heated in debate, his mind works more freely and powerfully than at any other time. And why? Because his brain is in better tune. What has thus suddenly improved its condition? An increased current of blood into it, produced by the excitement of its own increased action. That the blood does, on such occasions, flow more copiously into the brain, no one can doubt who is at all acquainted with the cerebral sensations which the orator himself experiences at the time, or who witnesses the unusual fullness and flush of his countenance, and the dewiness, flashing, and protrusion of his eye.
Indeed, in many instances, the increased circulation in the brain attendant on high mental excitement reveals itself by its effects when least expected, and leaves traces after death which are but too legible. Many are the instances in which public men have been suddenly arrested in their career by the inordinate action of the brain induced by incessant toil, and more numerous still are those whose mental power has been forever impaired by similar excess.
It is generally known that the eye, when tasked beyond its strength, becomes insensible to light, and ceases to convey impressions to the mind. The brain, in like manner, when much exhausted, becomes incapable of thought, and consciousness is well-nigh lost in a feeling of utter confusion. At any time in 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 injury is more easily produced by injudicious treatment than at any subsequent period. In this respect, the analogy is complete between the brain and the other parts of the body, as we have already seen exemplified in the injurious effects of premature exercise of the bones and muscles. 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, and even with the best management, the child passes the first years of its life constantly on the brink of active disease. Instead, however, of trying to repress its mental activity, as they should, the fond parents, misled by the promise of genius, too often excite it still further by unceasing cultivation and the never-failing stimulus of praise; and 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 a luster on their name. But in exact proportion as the picture becomes brighter to their fancy, the probability of its becoming realized becomes less; for the brain, worn out by premature exertion, either becomes diseased or loses its tone, leaving the mental powers feeble and depressed for the remainder of life. The expected prodigy is thus, in the end, easily outstripped in the social race by many whose dull outset promised him an easy victory.