共用题干 Tiny Invaders
The human body is truly amazing.It allows us to sense the world around us,to do work and have fun,and to move from place to place.In fact,the human body does its work so well that most people don"t think about it very much一until they get sick.
The germs（致病菌）that make people sick are everywhere.You can"t see them, but they"re there.They"re sitting on your desk.They"re hiding on your computer"s keyboard.They"re even in the air that you are breathing.There are two types of germs:viruses and bacteria（细菌）.Viruses are germs that can only live inside animals or plants.Viruses cause illnesses such as flu and measles（麻疹）.Bacteria are tiny creatures.Some bacteria are good.They can help your stomach break down food.Other bacteria aren"t so good.They can make you sick.Bacteria can cause sore throats（喉痛）and ear infections.
How can you stop these tiny invaders from making you sick?Your skin is the first de-fense against germs.You can prevent some illnesses simply by washing,with soap and wa-ter.But germs can still enter the body through small cuts in the skin or through the mouth, eyes,and nose.
Once germs are inside your body, your immune（免疫的）system tries to protect you.It looks for and destroys germs.How does it do that?Special cells patrol your body.Some of these cells actually eat germs!Other cells make antibodies.An antibody sticks to a germ.There is a different antibody for each kind of germ.Some antibodies keep germs from making you sick.Others help your body find and kill germs.After a germ is destroyed,the antibodies stay in your body.They protect you if the same kind of germ comes back.That way you will not get the same illness twice.
You can keep your body healthy by eating a nutritious（有营养的）diet to make your immune system strong.You can also help your immune system fight germs by getting vaccinated（接种）.Vaccines are medicines.They contain germs that have been killed or weakened.
The dead germs can"t make you sick.Instead,they cause your body to make antibodies.If the same germ ever shows up again,then your antibodies attack it. Germs can enter the body through the eyes.