You feel awful. You’re sneezing. Your throat hurts. Your nose is dripping. Your body is under attack. Germs have invaded! Don’t worry. Help is on the way.


Parts of your body are fighting back. It’s your immune system to the rescue! Let’s learn how it works.


Meet the Invaders It starts with germs. Germs are so small, you can’t see them. Yet they are trouble. T ey can make you sick. Germs are all around you. T ey’re


on your skin. Sometimes, they get inside your body. T ey float in the air you breathe. T ey ride on the food you eat. Biting insects can infect you with germs. Sick people may pass on germs, too. Once inside your body, germs make more germs.


This virus is ready to attack your body.


Unwanted Guests Two kinds of germs can harm your body. T e first is bacteria. Bacteria are living things made up of one cell. Cells are the tiny building blocks of all living things. Bacteria swim inside your body


and can make you sick. T ough not all bacteria are bad. Some help you digest your food. Some kill the bad bacteria that make you sick. T e other harmful germ is a virus.


Viruses live in many places. T ey live on things you may touch. T ey may live on people’s hands. Viruses can travel through the air. If someone close to you sneezes, watch out! A virus may land on you and attack. Viruses cause many diseases. T ey


don’t swim around in your body. T ey move into your body’s cells.


12 NATIONAL GEOGRAPHIC EXPLORER


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