Your body is an amazing machine. It can protect itself from many sicknesses. Often, when it does get sick, it cures itself.

But invisible enemies called germs attack your body all the time. The germs live in the air you breathe, in the food you eat, and even on the surface of your skin. But don't worry -- your body comes equipped with a good system to keep germs from doing harm.

To understand how your body's defense system works, imagine a video game. On the screen, you see a shape. It's your body. Suddenly, germs invade -- perhaps through the mouth, or through a cut on the knee. You've got to get rid of the germs!

To do that, you use a chemical called an antibody. White cells in your blood manufacture these chemicals. The antibodies race around the screen after the germs. They catch them, and wipe them out. You've won! The prize is good health.

Antibodies are the weapons your body uses to fight infection and sickness. They stay in your body, ready to fight invaders at any time. The defense system is so complicated that each germ you may get has a special antibody to fight it. Once your white cells have made an antibody, it stays in your system. If the same germ shows up again -- BOOM! The antibody takes care of it.

When you're born, you have some antibodies already. But you don't have enough to protect you from all the germs out there.

That's where shots -- also called immunizations or inoculations -- come in.

Let's let a doctor explain. Dr. George Cohen works at Children's Hospital in Washington. He knows a lot about germs.

Dr. Cohen sees many patients every day. Some of them come to him to get shots before starting a new school year.

"Germs cause certain diseases that can make kids very sick," he says. "A shot is medicine that will help your body make chemicals called antibodies to fight these germs. It hurts for a few minutes, but then it helps you keep certain sicknesses away for a long time."

When you get a shot, the doctor puts a liquid called a vaccine into your body. Vaccines contain germs that have been specially treated. The germs in the shot aren't strong enough to make you sick. But they are strong enough to make your white blood cells produce antibodies to fight the germs.

Vaccines can protect you from serious illnesses such as polio, measles, mumps and whooping cough.

When you go to your pediatrician to get a booster shot, you probably feel a bit scared. That's okay -- almost everybody feels that way.

When you're getting ready to go to your doctor's office, it might help to remind yourself that you're already an old pro at getting shots. By the time you were 1 1/2 years old, you had already received a whole bunch.

You probably don't remember getting them. After all, you were just a baby. But your parents are sure to have some stories to tell you about early visits to the family doctor. They may also have a list of the shots you've already had. Ask your mother or father to show you the record of your immunizations. It will make you feel good to know that your body is already hard at work -- keeping you well. Tips for Parent

Parents can help children cope with inoculations, suggests Dr. George Cohen, director of outpatient services at Children's Hospital National Medical center in the District, by leveling with them. Let them know what's happening and why. And don't say it's not going to hurt, because it is.

Before taking your children to the doctor, go over these points with them:

* Immunization is an important part of staying well.

* The procedure is going to hurt a little bit. Nobody likes getting shots.

* Parents and physicians are not giving the child shots because he's done something wrong.

* All children have to have injections before starting school.

Cohen doesn't object to offering a child some kind of treat after a shot.

"When you can offer that visible, tasteable symbol of your esteem and friendship, it helps," he says. "I think it's important to give children a token that says I love you."