The Magic School Bus - Inside Ralphie - Ep. 12

The class needs Ralphie to give them a story idea for Broadcast Day, but he is sick. His mother (Tyne Daly), who is a doctor, refuses to allow him to go to school. When Ms. Frizzle says that there is an amazing battle going on inside him, the class decides Broadcast Day should be about whatever is making him sick. After shrinking and going into his veins through a cut on his leg, they travel to his sore throat to see what is making him sick. Then, after they forget to stay out of the crossfire, his white blood cells see the bus as a threat and attempt to devour it.