The narrator is on his way to deliver some important nutrients to the patients at the hospital. He's been waiting for a long time, and finally he's there. He wants to check on the patients' reactions to the nutrients. He notices that they're all freaking out. The narrator doesn't know what's going on, but he does know that the patients are freaking out because they've been exposed to a lot of chemicals. He also knows that the histamine in the blood is a chemical that's released by the mast cells, which are the body's "antigens" . The mast cells are supposed to release histamine when they see foreign things, but they don't react well to chemicals that are harmful to them. The histamine is a mediator that helps the immune system fight off foreign invaders, but it's hard to know exactly what the histamine is for, since the immune cells aren't really trained to react to chemicals. It's not just the histamine, though, that helps fight off the invaders: it also helps the body fight off other invaders, like the mosquito, which can cause Dengue fever, a disease that can lead to fever and headaches.