They shrink, go inside his body, and travel in his bloodstream to his sore throat. The kids find out what's making Ralphie sick, and see his white blood cells fight the bacteria in a raging battle. But there's one problem. Now the white blood cells think the Magic School Bus is a germ. The Magic School Bus gets inside Ralphie's body by going through a cut on his leg.
Germs can get in the body that way, too.
But usually the skin protects the body. Set up this activity to show how skin protects our bodies the way apple skin protects an apple. Label the sheets of paper A and B. Wash hands and the apples. Place one apple on each sheet. Watch the apples for a week.