The means for the prevention of this form of vitiated air are obvious. Large, airy, well ventilated and lofty apartments are essential, if many persons must be put together; and, where that is not necessary, it is advisable to have them separated in several different chambers, where due ventilation is strictly maintained, by retaining the windows more or less open through the day, or by other equally effective means. By the sleeping of many persons in one apartment, the atmosphere is deprived to a great extent of its more vital fluid, and becomes unfit to support respiration in its integrity; and the health of the inmates is not unfrequently injured in consequence. The sleeping of many persons in one bed-room, therefore, should be avoided, where it is possible; but, where that is not practicable, it becomes necessary to lessen the evil consequences, and this may be done by keeping a door or window partially open during the night, when the weather is not too inclement to forbid that procedure. At all times, exhalations to a great extent are proceeding from the bodies of men; and, where individuals are much confined to one apartment, and where that is small, close, and ill ventilated, they fasten or adhere to the furniture, curtains, carpets, and the very walls. During sleep, the amount of these exhalations, it would appear, is increased. It is then that the pores of the entire system, as well upon the internal as the external surfaces, are most freely laid open, and that they pour forth their respective fluids most abundantly. The quantity of watery vapour which issues during sleep from the lungs is prodigious; and the large quantity of water which is sometimes seen collected on the panes of windows in the morning, and which is condensed vapour, affords some idea of the vast quantity of fluid which is exhaled during sleep. With this watery vapour, other ingredients of a hurtful nature are conjoined, and, like it, adhere to the furniture and clothes. When these exhalations are permitted to remain, they impart to the room a disagreeable odour, cause the bed-clothes to be damp and unwholesome, which, with the progress of fermentation, at length emit offensive effluvia. In order to avoid these hurtful consequences, the following measures should be adopted. When the bed-room is left in the morning, the window or windows should be opened, and the bed-clothes freely exposed to the air for some time: the constant passing of fresh air over the clothes and through the apartment, will shortly carry off the greater part of the exhalations which may have adhered. The window should be left open during a part of the day, if the atmosphere without is not particularly damp, as the removal of impurities, when they have adhered to solid bodies, is not effected at once, or so immediately as is generally believed.