The Secret of Sound Health.--"Half the secret of life," says _MacMillan's Magazine_, "we are persuaded, is to know when we are grown old; and it is the half most hardly learned. It is more hardly learned, moreover, in the matter of exercise than in the matter of diet. There is no advice so commonly given to the ailing man of middle age as the advice to take more exercise, and there is perhaps none which leads him into so many pitfalls. This is particularly the case with the brain workers. The man who labors his brain must spare his body. He cannot burn the candle at both ends, and the attempt to do so will almost inevitably result in his lighting it in the middle to boot. Most men who use their brains much soon learn for themselves that the sense of physical exaltation, the glow of exuberant health which comes from a body strung to its full powers by continuous and severe exercise, is not favorable to study. The exercise such men need is the exercise that rests, not that which tires. They need to wash their brains with the fresh air of heaven, to bring into gentle play the muscles that have been lying idle while the head worked. Nor is it only to this class of laboring humanity that the advice to take exercise needs reservations. The time of violent delights soon passes, and the effort to protract it beyond its natural span is as dangerous as it is ridiculous. Some men, through nature or the accident of fortune, will, of course, be able to keep touch of it longer than others; but when once the touch has been lost, the struggle to regain it can add but sorrow to the labor. Of this our doctor makes a cardinal point; but, pertinent as his warning may be to the old, for whom, indeed, he has primarily compounded his _elixir vitae_, it is yet more pertinent to men of middle age, and probably it is more necessary. It is in the latter period that most of the mischief is done. The old are commonly resigned to their lot; but few men will consent without a struggle to own that they are no longer young. All things are not good to all men, and all things are not always good to the same man. The man who confines his studies within one unchanging groove will hardly find his intellectual condition so light and nimble, so free of play, so capable of giving and receiving, as he who varies them according to his mood, for the mind needs rest and recreation no less than the body; it is not well to keep either always at high pressure. One fixed, unswerving system of diet, without regard to needs and seasons, or even to fancy, is not wise. The great secret of existence after all is to be the master and not the slave of both mind and body, and that is best done by giving both free rein within certain limits, which, as the old sages were universally agreed, each man must discover for himself. Happy are the words of Addison, and happily quoted: "A continual anxiety for life vitiates all the relishes of it,