Chapter XX

., Part First, that leaves take from the lungs of animals, giving them back good air in return. You see, then, how important it is that this gas shall get from us to the leaves, and that the good gas from the leaves shall come freely into our lungs. But this can not be done unless there is a free circulation of the air. When people are shut up in a close room, a great deal of this bad gas is made in a little while, and unless it is let out of the room it does harm. It does not often kill any one at once, but it injures the health; and the poisonous effect repeated every day, though it be but a little, after a while may destroy life. A few persons are killed quickly by this gas made from burning charcoal; but a great many are killed slowly by it as it is given out from their lungs, because they do not take enough pains to let it escape.

_Questions._--In what things is the gas that we burn like air? In what does it differ from air? What is said about the smell of gas? In what two ways is life sometimes destroyed by gas? What is flame in a common wood or coal fire? Tell about the blowing we sometimes see in wood on the fire. What is said about the making of gas? What is said about the gas that comes from burning charcoal? How are people sometimes killed by it? What is said about its being in wells? Tell about the Grotto of the Dogs. What is said about the lungs giving out this gas? How does it often do harm when given out in this way? Which kills the most people, the gas that comes from burning charcoal or that which comes from people’s lungs?

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