"The KidHaven Science Library introduces young readers to a wide array of inventions and natural phenomena that touch our lives today. Topics range from microscopes and lasers to tide pools and cells. Within each volume, readers will find important concepts and ideas explained in clear, simple language, and illustrated with vivid examples. Each book includes a glossary, bibliography, and full-color photographs. When the body's physical barriers against injury and infection are breached, the cellular and chemical components of the immune system take over. Yet these protective forces sometimes make mistakes. This book describes elements of the immune system, problems that can occur, and man-made ways to supplement the immune process.