[Illustration: FIG. 25.--Inside view of a fire extinguisher.]
51. Carbon. Although carbon dioxide is very injurious to health,
both of the substances of which it is composed are necessary to life.
We ourselves, our bones and flesh in particular, are partly carbon,
and every animal, no matter how small or insignificant, contains some
carbon; while the plants around us, the trees, the grass, the flowers,
contain a by no means meager quantity of carbon.
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