SECTION 20. In the first part of this work I have insisted upon the
great value of health as the chief and most important element in happiness. Let me emphasize and confirm what I have there said by giving a few general rules as to its preservation.
The way to harden the body is to impose a great deal of labor and effort upon it in the days of good health,—to exercise it, both as a whole and in its several parts, and to habituate it to withstand all kinds of noxious influences. But on the appearance of an illness or disorder, either in the body as a whole or in many of its parts, a contrary course should be taken, and every means used to nurse the body, or the part of it which is affected, and to spare it any effort; for what is ailing and debilitated cannot be hardened.
The muscles may be strengthened by a vigorous use of them; but not so the nerves; they are weakened by it. Therefore, while exercising the muscles in every way that is suitable, care should be taken to spare the nerves as much as possible. The eyes, for instance, should be protected from too strong a light,—especially when it is reflected light,—from any straining of them in the dark, or from the long-continued examination of minute objects; and the ears from too loud sounds. Above all, the brain should never be forced, or used too much, or at the wrong time; let it have a rest during digestion; for then the same vital energy which forms thoughts in the brain has a great deal of work to do elsewhere,—I mean in the digestive organs, where it prepares chyme and chyle. For similar reasons, the brain should never be used during, or immediately after, violent muscular exercise. For the motor nerves are in this respect on a par with the sensory nerves; the pain felt when a limb is wounded has its seat in the brain; and, in the same way, it is not really our legs and arms which work and move,—it is the brain, or, more strictly, that part of it which, through the medium of the spine, excites the nerves in the limbs and sets them in motion. Accordingly, when our arms and legs feel tired, the true seat of this feeling is in the brain. This is why it is only in connection with those muscles which are set in motion consciously and voluntarily,—in other words, depend for their action upon the brain,—that any feeling of fatigue can arise; this is not the case with those muscles which work involuntarily, like the heart. It is obvious, then, that injury is done to the brain if violent muscular exercise and intellectual exertion are forced upon it at the same moment, or at very short intervals.
What I say stands in no contradiction with the fact that at the beginning of a walk, or at any period of a short stroll, there often comes a feeling of enhanced intellectual vigor. The parts of the brain that come into play have had no time to become tired; and besides, slight muscular exercise conduces to activity of the respiratory organs, and causes a purer and more oxydated supply of arterial blood to mount to the brain.
It is most important to allow the brain the full measure of sleep which is required to restore it; for sleep is to a man's whole nature what winding up is to a clock.[30] This measure will vary directly with the development and activity of the brain; to overstep the measure is mere waste of time, because if that is done, sleep gains only so much in length as it loses in depth.[31]
30 ([a]return])
[ Of. Welt als Wille und Vorstellung, 4th Edition. Bk. II. pp. 236-40.]
31: ([a]return])
[ Cf. loc: cit: p. 275. Sleep is a morsel of death borrowed to keep up and renew the part of life which is exhausted by the day—le sommeil est un emprunt fait à la mort. Or it might be said that sleep is the interest we have to pay on the capital which is called in at death; and the higher the rate of interest and the more regularly it is paid, the further the date of redemption is postponed.]
It should be clearly understood that thought is nothing but the organic function of the brain; and it has to obey the same laws in regard to exertion and repose as any other organic function. The brain can be ruined by overstrain, just like the eyes. As the function of the stomach is to digest, so it is that of the brain to think. The notion of a soul,—as something elementary and immaterial, merely lodging in the brain and needing nothing at all for the performance of its essential function, which consists in always and unweariedly thinking—has undoubtedly driven many people to foolish practices, leading to a deadening of the intellectual powers; Frederick the Great, even, once tried to form the habit of doing without sleep altogether. It would be well if professors of philosophy refrained from giving currency to a notion which is attended by practical results of a pernicious character; but then this is just what professorial philosophy does, in its old-womanish endeavor to keep on good terms with the catechism. A man should accustom himself to view his intellectual capacities in no other light than that of physiological functions, and to manage them accordingly—nursing or exercising them as the case may be; remembering that every kind of physical suffering, malady or disorder, in whatever part of the body it occurs, has its effect upon the mind. The best advice that I know on this subject is given by Cabanis in his Rapports du physique et du moral de l'homme.[32]
32 ([a]return])
[ Translator's Note. The work to which Schopenhauer here refers is a series of essays by Cabanis, a French philosopher (1757-1808), treating of mental and moral phenomena on a physiological basis. In his later days, Cabanis completely abandoned his materialistic standpoint.]
Through neglect of this rule, many men of genius and great scholars have become weak-minded and childish, or even gone quite mad, as they grew old. To take no other instances, there can be no doubt that the celebrated English poets of the early part of this century, Scott, Wordsworth, Southey, became intellectually dull and incapable towards the end of their days, nay, soon after passing their sixtieth year; and that their imbecility can be traced to the fact that, at that period of life, they were all led on? by the promise of high pay, to treat literature as a trade and to write for money. This seduced them into an unnatural abuse of their intellectual powers; and a man who puts his Pegasus into harness, and urges on his Muse with the whip, will have to pay a penalty similar to that which is exacted by the abuse of other kinds of power.
And even in the case of Kant, I suspect that the second childhood of his last four years was due to overwork in later life, and after he had succeeded in becoming a famous man.
Every month of the year has its own peculiar and direct influence upon health and bodily condition generally; nay, even upon the state of the mind. It is an influence dependent upon the weather.