Let us then, in this place, return to the sublime conjecture of Franklin, a man habitually conversant with the system of the external universe, and by no means propense to extravagant speculations, that "mind will one day become omnipotent over matter." The sense which he annexed to this expression, seems to have related to the improvements of human invention, in relation to machines and the compendium of labour. But, if the power of intellect can be established over all other matter, are we not inevitably led to ask, why not over the matter of our own bodies? If over matter at however great a distance, why not over matter which, ignorant as we may be of the tie that connects it with the thinking principle, we seem always to carry about with us, and which is our medium of communication with the external universe?
The different cases in which thought modifies the structure and members of the human body, are obvious to all. First, they are modified by our voluntary thoughts or design. We desire to stretch out our hand, and it is stretched out. We perform a thousand operations of the same species every day, and their familiarity annihilates the wonder. They are not in themselves less wonderful, than any of those modifications we are least accustomed to conceive. Secondly, mind modifies body involuntarily. To omit, for the present, what has been offered upon this subject by way of hypothesis and inference, there are many instances in which this fact presents itself in the most unequivocal manner. Has not a sudden piece of good news been frequently found to dissipate a corporal indisposition?
Is it not still more usual for mental impressions to produce indisposition, and even what is called a broken heart? And shall we believe that that which is so powerful in mischief, can be altogether impotent for happiness?
How common is the remark, that those accidents, which are to the indolent a source of disease, are forgotten and extirpated in the busy and active?
I walk twenty miles in an indolent and half determined temper, and am extremely fatigued. I walk twenty miles, full of ardour, and with a motive that engrosses my soul, and I arrive as fresh and alert as when I began my journey. Emotion, excited by some unexpected word, by a letter that is delivered to us, occasions the most extraordinary revolutions in our frame, accelerates the circulation, causes the heart to palpitate, the tongue to refuse its office, and has been known to occasion death by extreme anguish or extreme joy. There is nothing of which the physician is more frequently aware, than of the power of the mind in assisting or retarding convalescence.
Why is it that a mature man loses that elasticity of limb, which characterises the heedless gaiety of youth? The origin of this appears to be, that he desists from youthful habits. He assumes an air of dignity, incompatible with the lightness of childish sallies. He is visited and vexed with the cares that rise out of our mistaken institutions, and his heart is no longer satisfied and gay. His limbs become stiff, unwieldy and aukward. This is the forerunner of old age and of death.
A habit peculiarly favourable to corporeal vigour, is cheerfulness.
Every time that our mind becomes morbid, vacant and melancholy, our external frame falls into disorder. Listlessness of thought is the brother of death.
But cheerfulness gives new elasticity to our limbs, and circulation to our juices. Nothing can long be stagnant in the frame of him, whose heart is tranquil, and his imagination active.
A further requisite in the case of which we treat, is clear and distinct apprehension. Disease seems perhaps in all instances to be the concomitant of confusion. When reason resigns the helm, and our ideas fluctuate without order or direction, we sleep. Delirium and insanity are of the same nature.
Fainting appears principally to consist in a relaxation of intellect, so that the ideas seem to mix in painful disorder, and nothing is distinguished.
He that continues to act, or is led to a renewal of action with perspicuity and decision, is almost inevitably a man in health.
The surest source of cheerfulness is benevolence. To a youthful mind, while every thing strikes with its novelty, the individual situation must be peculiarly unfortunate, if gaiety of thought be not produced, or, when interrupted, do not speedily return with its healing virtue. But novelty is a fading charm, and perpetually decreases. Hence the approach of inanity and listlessness. After we have made a certain round, life delights no more. A deathlike apathy invades us. Thus the aged are generally cold and indifferent; nothing interests their attention, or rouses their sluggishness.
How should it be otherwise? The objects of human pursuit are commonly frigid and contemptible, and the mistake comes at last to be detected. But virtue is a charm that never fades. The mind that overflows with kindness and sympathy, will always be cheerful. The man who is perpetually busied in contemplations of public good, can scarcely be inactive. Add to this, that a benevolent temper is peculiarly irreconcilable with those sentiments of anxiety, discontent, rage, revenge and despair, which so powerfully corrode the frame, and hourly consign their miserable victims to an untimely grave.
Thus far we have discoursed of a negative power which, if sufficiently exercised, would, it is to be presumed, eminently tend to the prolongation of human life. But there is a power of another description, which seems entitled to our attention in this respect. We have frequently had occasion to point out the distinction between our voluntary and involuntary motions.