Hygiene (Gr.Hygiene 090062 healthy), the science and art of preserving health, by the appropriate nourishment of the body and the proper regulation of its surrounding conditions. The first subject of importance in a hygienic point of view is always the location or residence of the individual, family, or community whose interests are involved. Other conditions may be altered or modified with comparative readiness, but the place and character of the habitation, when once fixed, usually remain so for a considerable time, and thus exert a continued influence for good or evil. The habitation, when in the country, should always be placed upon such an elevation as to secure a thorough natural drainage. This is the first requisite; for there is no other single cause of disease so hurtful and insidious as the slow accumulation and stagnation of the refuse matters, in however small quantity, which are daily produced in and about an occupied habitation. Even standing pools, or hollow basins without an outlet, the result of a depression in the surface of the ground, should not be allowed in the immediate neighborhood of the house; for although it is only the rain water which at first collects in them, yet there is always more or less accumulation of organic matter from vegetable growth and from the aquatic animals and birds which make such places their resort; and as a pool of this kind is alternately filled and dried up, sometimes several times a year, the effluvia exhaled during this process will always become more or less injurious, and may be even dangerous to life.

When a large number of inhabitants are collected within a small space, as in towns and cities, the question of drainage becomes of course still more important. The production of refuse materials is here exceedingly rapid, and corresponding provision should be made for their immediate and complete removal. Besides the necessary provisions for drainage, the house and apartments should also be fully and completely ventilated. Effluvia and organic vapors of various kinds necessarily become developed in every occupied dwelling, from the daily culinary operations and the organic matters of the food and their remains. These effluvia are harmless when fresh; but they are subject to early decomposition, and at once become noxious if allowed to accumulate and stagnate. Every house, accordingly, should be swept throughout each day by a current of fresh air, sufficient to renovate its atmosphere and remove all vestiges of impurity. A free opening of the windows on opposite sides, early in the morning, is the best way of accomplishing this.

In addition, each inhabited apartment should be constantly ventilated in such a manner as to remove the carbonic acid and other products of respiration, by open fires or other effectual means. - Proper clothing, adapted to the season and the degree of individual exposure, is also an important element of hygiene. There are few causes of disease more prolific than undue exposure to cold and dampness, and particularly to sudden changes of weather or draughts of cold air upon unprotected parts. The clothing should be so regulated, as a general thing, that the ordinary vicissitudes of the weather shall not be felt by the individual in such a way as to make a permanent impression upon the system. A sufficient suit of woollen underclothing is the best protection in this respect. It is important to remember, however, that for a person in health exposure to cold and dampness is seldom injurious so long as the body is in a state of muscular activity. It is remaining in a cold apartment in an inactive condition, or keeping on the wet or damp clothing after muscular exertion has ceased, that gives rise to dangerous consequences. - The quality and quantity of the food, and the regularity with which it is taken, are of the next importance in a hygienic point of view.

The food, as a rule, should be simple in character, but nutritious, and each article of the best possible quality and properly cooked. An imperfect or careless mode of cooking may often injure materially the nutritious and digestible qualities of an article of food, originally of the best kind. Individual peculiarities are to be consulted in regard to the kind of food used by each person; certain articles being sometimes more or less indigestible for one person, which are quite harmless for another. The natural and healthy appetite is the best general criterion in regard to the quantity of food to be used, provided it be simple and nutritious in character. It is of great importance, finally, that the food be taken with regularity at the accustomed time, that it be properly masticated, and that its digestion be not interfered with by hurry, anxiety, or any unusual mental or physical disturbance at and immediately after the time of meals. - A regular and sufficient bodily exercise should be taken every day to keep all the organs in a healthy state of activity.

The exercise should be neither deficient nor excessive in amount; for bodily exertion which is so violent or so prolonged as to produce a sense of exhaustion and fatigue, instead of being beneficial to the system, is positively injurious to it. Neither can a deficiency of muscular exertion during one period be compensated by an excessive amount taken at another. It is the necessary and appropriate quantity of exercise, taken regularly day by day, which preserves the vigor of the system, and keeps it in a condition to resist the attacks of disease. The periods of exertion, furthermore, should alternate daily with periods of repose; and especially the natural amount of sleep should always be taken with regularity, and in apartments which are not too confined and the ventilation of which is properly provided for. It is during sleep that the main process of the nutrition and restoration of the nervous and muscular systems takes place; and if an individual deprive himself of sleep, wholly or even partially, for one or two nights in succession, he will invariably experience its damaging effects in the consequent temporary failure of the vital powers.

An imprudence or neglect, like either of those mentioned above, may bo counteracted in a strong and healthy person by subsequent care, so that he may recover from its immediate and more perceptible effects ; but it is a principle which lies at the basis of hygiene, that causes of disease, however slight, by constant repetition day after day, or even at longer intervals, will certainly at last undermine the health, and produce a permanent and often irremediable injury. The easiest as well as the surest way of avoiding such a result is a constant and regular attention to all the necessary hygienic conditions. (See Aliment, Bath, Dietetics, and Gymnastics.)