e milk from the hands of those who have
nursed the sick, these will grow into immense numbers in a single day.
Many of those who use the milk will then become ill. Hundreds are made
sick in this way every year.

PRACTICAL QUESTIONS

1. Why is milk a good food?

2. What does a gallon of milk contain?

3. What is cream?

4. How is butter made?

5. For whom is milk specially good?

6. How does milk become poisonous?

7. Why is dirty milk more poisonous in hot weather?

8. Tell what harm unclean milk does.

9. How may milk be kept clean?

10. Explain how milk is heated to make it safe for use.

11. Show how flies may cause fever.

12. Tell how milk may carry diphtheria into our homes.

CHAPTER VII

HOW THE BODY USES FOOD

=Organs for making ready the Food.=--Before the food can get into the
blood and be carried over the body to feed the muscles and the brain,
it must be made into a fluid. This changing of the solid food into a
liquid by the stomach and other organs is called _digestion_. The
organs which do this work are known as _digestive organs_. They
consist of a _food tube_ and several bodies called _glands_.

=The Food Tube.=--The food canal is about thirty feet long. Its first
part, the _mouth_, opens back of the tongue into the throat, named the
_pharynx_. This leads into a tube, the gullet, passing down through
the back part of the chest into the _stomach_ below the diaphragm. The
stomach is a bent sac opening into a tube over twenty-five feet long
called the _bowels_ or _intestines_. This tube is folded into a bunch
which fills a large part of the cavity of the abdomen.

[Illustration: FIG. 23.--The plan of a gland. _a_ carries blood to the
gland and _v_ takes it away after the gland has taken out what it
needs. On the right side the top of the gland has been cut off.]

=The Glands or Juice Makers.=--A gland is a little tube closed at one
end, or a bunch of such tubes, which can take something out of the
blood and make it into a juice. A gland under each ear and four others
near the tongue make the juice called _saliva_ which flows into the
mouth through tubes.

A long, flat, pink gland back of the stomach is called the _sweetbread_
or _pancreas_. This and a large brown gland, the _liver_, empty their
juices into the intestines. The whole inner surface of the stomach and
intestines is lined with tiny tubes, the glands. The