Many people are still deterred from sleeping out by a mistaken fear of night air and of the malaria which they imagine this dreaded night air may bring. To-day we know that malaria is communicated by the bite of the anopheles mosquito and never by the air. The moral of this is not to shut out the night air, but, when necessary, to shut out the mosquito by screens. The experiment has been made of sleeping out-of-doors _in screened cages_ in the most malarial of places and no malarial infection resulted, though those who were unprotected and were consequently bitten by mosquitoes contracted malaria as usual. The truth is that night air, especially in cities, is distinctly purer than day air, on account of the fact that there is much less traffic at night to stir up dust. [Sidenote: Protection From Cold] It is very important, in any sleeping balcony, to be protected from the wind by a sash on one or two or--in very windy places--three sides. But of course sleeping out-of-doors does not reach its maximum efficiency if there is too much protection, that is, if the sleeping-out place is so shut in that very free currents of air are not secured. An outdoor porch really ceases to be an outdoor porch, when enclosed on four sides. A roll curtain (preferably rolling from the bottom) can be arranged on the open side or sides, to be used in case of storms only. In cold weather a thick mattress, or two mattresses, should be used. It is not only what is over the sleeper, but also what is under him, that keeps him warm. The body should be warmly clad, and the head and neck protected by a warm cap or helmet or hood. To prevent the entrance of cold air under the bedclothes, one or more blankets should be extended at least two feet beyond the head, with a central slit for the head. Early awakening by the light may, if necessary, be prevented by touching the eyelids with burnt cork, or by bandaging the eyes with a black cloth or stocking. Sheets should be well warmed in the winter-time before being used. They can easily be warmed with a hot-water bag, flat-iron, or soapstone. Blankets next to the skin are not hygienic. [Sidenote: Sleeping-tents] Sleeping out is really much easier than most people imagine. In fact, few, if any, of the other cardinal rules of hygiene are so easy to obey. Where a sleeping-porch is not available, an inward window tent can always be had which puts the sleeper practically out-of-doors and at the same time cuts off his tent from the rest of the room. [Sidenote: Outdoor Tents]