Avsnitt 14

You are not a person, you are a planet, made of roughly 40 trillion cells. There is so much of you, that if your cells were human-sized, you would be as big as 20 Mount Everests. For your creepy-crawly inhabitants, this makes your body an ecosystem, rich in resources and warmth and space. A perfect place to move into and have a family. While some of these guests are welcome, most are not . Your immune system is the guardian of this planet, the force tasked with protecting yourself against the constant danger of invasion.