n the air again. We should use
either a damp cloth, or a dry duster made of tufts of wool, so that
the dust will stick to the duster.

[Illustration: =House fly, magnified.=

The hairs on its body and legs catch dirt and disease germs.]

=209. Foul air.=--If we live in a closed room, the air soon becomes
foul and dusty, and is likely to have disease germs in it. Foul air is
one of the greatest of the causes of sickness. We should change the
air of a room often so as to keep it fresh and free from dust and
disease germs (pp. 65-67).

=210. House flies.=--House flies come from garbage heaps and filth of
all sorts. So they carry disease germs on their bodies. They light on
our food and on our faces, and so they often make us sick. They are
often the cause of typhoid fever, stomach aches, and stomach sickness
in babies.

[Illustration: =Life history of house flies.=]

Flies are hatched in manure piles and garbage heaps. At first they
look like white worms, and are called _maggots_. Every maggot is a
young fly. We can get rid of flies by cleaning up every garbage heap
and manure pile.

[Illustration: =Young mosquitoes hanging head downward in water.=]

=211. Mosquitoes.=--Mosquitoes carry malaria and yellow fever from
sick persons to the well. If there were no mosquitoes, there would be
no malaria or yellow fever.

Mosquitoes are hatched in water, and the young are called _wigglers_.
We may often see them in rain barrels. We may get rid of mosquitoes by
emptying all rain barrels and pails and cans of dirty water, at least
once a week, and by drying up swamps and marshes.

WHAT WE HAVE LEARNED

1. We catch a fever by taking disease germs into the body.

2. Disease germs cannot be seen without a strong microscope.

3. The germs may be found in dust and dirt.

4. Slops from our houses are often full of the germs.

5. You may take germs into your body by putting pencils and other
things into your mouth, and by drinking from a public
drinking cup.

6. Spitting on the floor or pavement may scatter disease germs.

7. House flies and mosquitoes often spread diseases.

CHAPTER XVII

PREVENTING SICKNESS

=212. How our body kills disease germs.=--We take disease germs into
the body in three ways: first, through the mouth, second, through the
nose, and third, through the skin. So we should watch the purity of
our food, drink, and air, and should b