water look milky. This shows that the gas in your breath is not like
the air about you; because air was all over the top of the limewater,
yet did not change it at all. The milky look is caused by carbon
dioxid, one of the poisons in your breath.

When some people come close to you, you want to turn away your head,
because you do not like the smell of their breath. Even when one is
quite well, the breath has a queer "mousey" odor, so that we never
like to breathe the breath of another person. This disagreeable odor
comes not only from the lungs but from the teeth.

We are always breathing out poisons into the air. One of these you can
see in the milky limewater, and others you can smell when you happen
to come close to anyone else.

[Illustration: PROVING THAT THE BREATH IS NOT LIKE THE AIR]

If you blow on your fingers, you feel that your breath is much warmer
than the air. If people are crowded together in rooms with doors and
windows shut, their breath soon heats and poisons the air, until they
begin to have headache, and to feel dull and drowsy and uncomfortable.
If they should be shut in too long, without any opening to let in the
fresh air, as in a prison cell, or in the hold of a ship during a
storm, the air would become so poisonous as to make them ill, and
would even suffocate them and kill them outright. Even the bees found
this out thousands of years ago; and in their hives in hot weather
they station lines of worker-bees, one just behind another from the
door right down each of the main passages, whose business it is to do
nothing but keep their wings whirring rapidly, so that they fan a
steady current of fresh air into every part of the hive.