If you close all the windows and doors in the schoolroom and shut up the ventilators, you will soon find that you are not able to pay close attention to your studies, and in a little while you will begin to feel drowsy. This is because you have used up so much of the oxygen in the air that there is no longer enough to supply the demands of the little cells, and because, in addition, you are taking into your bodies the poisonous carbon dioxid that has been breathed out into the room. It takes a great deal of fresh air to supply the body with oxygen—about 1,250 cubic feet of air each hour. With thirty or forty children in a room, it does not take long to use up all the oxygen. So there should be a constant supply of fresh air coming into the room.
Fig. 25. Results of breathing good and bad air.
Methods of ventilation
It is not only in the schoolroom that you need oxygen. When you are out-of-doors you get an abundance of fresh air, but from a great many houses every bit of fresh air is shut out. It is always possible to let an abundance of fresh air into any house without causing a draft. A piece of board can be made to fit into a window frame so that when the window is raised, the air will be directed upward and will not cause a draft. Hot-air furnaces are made with cold-air pipes. The fresh air from outdoors comes through these cold-air pipes and, after being heated, is driven into the rooms of the house. Some people think they will save coal by closing these drafts. Not only do they not save coal (for the furnace does not give as much heat when this draft is closed), but they kill their body cells by refusing to give them oxygen. The cold-air pipe in a hot-air furnace should always be kept wide open.
In houses heated with steam or hot water, either the windows must be kept open, or some other way must be provided for admitting fresh air and taking out foul air. These arrangements constitute a system of ventilation. Houses heated with stoves must also be provided with some means of ventilation. The stove, by its draft, takes out a little of the foul air, but it will not take out more air than one person poisons.
Fig. 26. Restfulness: Effect of good ventilation in a sleeping-room, with the right position for sleeping.
Fig. 27. Restlessness: Effect of poor ventilation in a sleeping-room, with the wrong position for sleeping.