From a sanitary point of view, the gymnasium, as usually located and managed, is by no means equivalent to out-of-door sports and contests, although it is often the best substitute for them. The form of exercise most used by men whose occupation does not involve bodily labor is walking, and next to this riding. Whatever mode be selected, it is very desirable that it should be taken for some other object than that of the mere making muscular exertion, or otherwise it will soon come to be looked upon as an unpleasant task, the time spent upon which is given grudgingly; and it will be partially or wholly abandoned as soon as the immediate discomfort which induced its use has ceased. It is not an uncommon error among men engaged in mental work to suppose that they can, and ought to, take the same amount of exercise which gives good results in those whose occupations involve physical rather than mental effort, or to think that the more exercise they take the more study or writing they are equal to. This is a grave mistake. Expenditure of brain-tissue is not to be repaired by muscular exertion, but by sleep and food, and exercise in the fresh air sufficient to produce appetite and sufficient weariness to ensure restful sleep is all that is necessary. For a time it is true that the student or writer who has a well-developed body can continue to burn the candle at both ends, and win literary honors while also standing high as an athlete; but this surely leads to physiological bankruptcy in the end. It is to be remembered that good muscular development is not necessarily synonymous with health, and that strength is not a guarantee against disease. And, while it is true that in this, as in most other matters of individual hygiene, each man must to a great extent be a law to {200} himself, and learn by experience what kind of exercise and how much of it he requires, yet the physician can often supply the motive which was wanting, or check undue effort. Exercise for the sake of health and comfort is not an end, but a means; yet if this means can be made to secure to the patient an end agreeable and pleasant in itself, so much the better. XI. CONTAGION AND DISINFECTION.--By "contagion" we mean the communication of disease from one person to another, either by direct contact or through some medium, such as air, water, etc. It therefore includes "infection," which is now generally used as a synonym for it. The so-called infective diseases of modern German writers (Infections-Krankheiten) include, besides what are commonly termed in English, contagious diseases, the so-called miasmatic diseases.