There was a belief that sleeping in the cold was a good thing; but I cannot find any facts proving this theory, particularly no comparative observations about the wholesomeness of heated and unheated dormitories. It would be safer to say that experience proves that sleeping in the cold does not, generally, do harm. If a single person sleeps in a large cold room with shut doors and windows, it will do him no harm when he has a good bed. One person cannot deteriorate the air of an unventilated space as much as two or more. The bed is a garment, an apparatus, which is of great use for our heat-economy; it prevents our feeling cold even in the coldest dormitory, but the bed is no ventilating apparatus, and ventilation must be provided for in another way. He that wants to sleep safely in the cold must have a good bed and a large space, or bad windows and doors, or very porous walls, or he must keep his windows partly open in winter as well as in summer.
You have probably now the desire to hear from me how much air or ventilation a person wants in a stated time. After you have all the while heard from me that everything is full of air, that air penetrates everywhere, and that it is extremely difficult to prevent its passage, many among you will ask: "What need is there of special contrivances, if the air passes through each brick, through mortar, through wood? Would it not be rather desirable to protect ourselves against this universal aggression of the air?"
It is with air as with all things which we must have—as with money, of which we must not only have some, but sufficient—one must have as much as one requires. Some money is, after all, in everybody's possession, even that of the poorest beggar.
Till some time ago, ventilation was chiefly considered in its qualitative aspect: we wanted change of the air, and were satisfied if there was one aperture for it to go out, and another to come in. The question about the quantity of this air was never put; if it had been known how much was really wanted, and how it was to be procured, that amount of ventilation which was often paraded would have appeared beggarly. It is only during the last twenty years that we have acquired clear ideas on this subject.
We deteriorate the air of a closed space inevitably by using it for the maintenance of our respiration and perspiration. To which degree, then, may we alter or pollute by our emanations the air of a closed space, without going so far as to injure our health? This leads us to another preliminary question: What standard have we for measuring the deterioration of the air?
At all times people have been in the habit of making some estimate of the pollution of the air by the smell imparted to it by the respiration and emanations of the persons staying in it. This estimate is of the same value as that we have spoken of when on the subject of the water in the walls. The smell of a certain air need not be in any kind
