The first, relates to the health of a family. It is a universal law of physiology, that all living things flourish best in the light. Vegetables, in a dark cellar, grow pale and spindling,[H] and children, brought up in mines, are wan and stinted. This universal law, indicates the folly of turning day into night, thus losing the genial influence, which the light of day produces on all animated creation.
There is another phenomenon in the physiology of Nature, which equally condemns this practice. It has been shown, that the purification of the blood, in the lungs, is secured, by the oxygen of the atmosphere absorbing its carbon and hydrogen. This combination forms carbonic acid and water, which are expired from our lungs into the atmosphere. Now all the vegetable world undergoes a similar process. In the light of day, all the leaves of vegetables absorb carbon and expire oxygen, thus supplying the air with its vital principle, and withdrawing the more deleterious element. But, when the light is withdrawn, this process is reversed, and all vegetables exhale carbonic acid, and inspire the oxygen of the air. Thus it appears, that the atmosphere of day is much more healthful than that of the night, especially out of doors.
Moreover, when the body is fatigued, it is much more liable to deleterious influences, from noxious particles in the atmosphere, which may be absorbed by the skin or the lungs. In consequence of this, the last hours of daily labor are more likely to be those of risk, especially to delicate constitutions. This is a proper reason for retiring to the house and to slumber, at an early hour, that the body may not be exposed to the most risk, when, after the exertions of the day, it is least able to bear it.
The observations of medical men, whose inquiries have been directed to this point, have decided, that from six to eight hours, is the amount of sleep demanded by persons in health. Some constitutions require as much as eight, and others no more than six, hours of repose. But eight hours is the maximum for all persons in ordinary health, with ordinary occupations. In cases of extra physical exertions, or the debility of disease, or a decayed constitution, more than this is required. Let eight hours, then, be regarded as the ordinary period required for sleep, by an industrious people, like the Americans. According to this, the practice of rising between four and five, and retiring between nine and ten, in Summer, would secure most of the sunlight, and expose us the least to that period of the atmosphere, when it is most noxious. In Winter, the night air is less deleterious, because the frost binds noxious exhalations, and vegetation ceases its inspiring and expiring process; and, moreover, as the constitution is more tried, in cold, than in warm, weather, and as in cold weather the body exhales less during the hours of sleep, it is not so injurious to protract our slumbers beyond the proper period, as it is in the warm months. But in Winter, it is best for grown persons, in health, to rise as soon as they can see to dress, and retire so as not to allow more than eight hours for sleep.