Summary

Bryson starts Chapter 12 with an overview of what the immune system contains, including earwax, skin, tears and a number of different kinds of immune cells. We have 300 different types of immune cells, although each person has a unique immune system. Immune systems respond to germs, but also to toxins, drugs, cancers, foreign objects and even our state of mind. Bryson makes the point that protecting us is a limitless challenge and, so, immune systems sometimes make mistakes. Diseases like multiple sclerosis, lupus, rheumatoid arthritis, Crohn’s disease and others are diseases of the immune system when it misfires. Five percent of people suffer from autoimmune diseases.

At its heart, the immune system is made up of five types of white blood cells, of which the most important are lymphocytes. Lymphocytes find unwanted invaders and mobilize a response. They come in two...