Villagers are as a rule healthier than people who live in towns. One reason for this is that country air is fresher than the air in smoky cities. The villager is out all day in the fields, breathing fresh clean air; but the air the townsman is breathing is always full of smoke and dust, and germs of disease.
We cannot live without air. If we are stopped from breathing even for five minutes, we die. No air means death at once; but bad air means bad health and certain kinds of illnesses, which may kill us in the end, though they may not kill us at once.
We all know what unpleasant feelings we soon get if we stay a long time in a shut-up, crowded room. After a time, we begin to feel very sleepy, and can hardly keep our eyes open. Then our heads begin to ache, and the longer we stay there the worse we feel. What a relief it is when we get out into the fresh air outside!
Why is this? Well, the air we breathe into our lungs purifies our blood and gives it more life. The air we breathe out is full of all kinds of dirt from our bodies, and especially a kind of gas which is poisonous. The air we breathe in is like the clean water we pour into a basin for washing our hands; the air we breathe out is like the dirty water we pour away after our hands are washed. If we are always breathing fresh air, no harm is done, because the bad air we breathe out is blown away by the wind. But if the air we breathe in is, like the air in a smoky town or a shut-up room, impure air, it cannot purify our blood; and in a shut-up room, we are always breathing again the bad air we, and the other people, breathe out.
We must, therefore, keep our windows open, so that the air in our rooms is always fresh; and we are as much as we can in the open air, for people who breathe bad air for a long time often get very ill and die of lung diseases.