Round about cities and large towns there are certainly more people than
there are trees, but in many other parts of the world there are a great
many more trees than there are people.
I have heard of forests in South America so thick and so large, that the
monkeys might run along the tops of the trees for a hundred miles. So
you see there are plenty of trees in the world to do the work.
But then, how does all the bad air leave the towns and cities where men
live, and get to the forests and meadows?
The air is constantly moving about; rising and falling, sweeping this
way or that way, and traveling from place to place.
Not only the little particles out of our breath, but any thing that
gives the air any smell, does it some harm. Even nice smells, like those
of roses, are unhealthy, if shut up in a room for some time.
Dirty walls, ceilings, and floors give the air a musty, close, smell; so
do dirty clothes, muddy boots, cooking, and washing. Some of these ought
not to be in the house at all; others remind us to open our windows
wide.
All the things I have been saying to you about pure air, apply still
more to sick people than to healthy ones.
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