In straightforward text, a veteran science writer describes the system that makes it possible to inhale and exhale more than 20,000 times a day. Beginning with a quick explanation of the air around us, Simon goes on to describe its journey through your nose, pharynx, trachea and bronchi, and the subsequent movement of its oxygen into the blood. Other topics include lung movement, yawns, snores and sneezes, as well as respiratory problems and their detection. While the text is clear and the information appropriate, middle-grade readers may find some illustrations—brightly colored diagrams, computer-enhanced X-rays and other images—confusing. Not all full-page images are labeled; only a careful look at the index will reveal the point. In one, opposite the page explaining the difference in left and right lung sizes, only the left lung is visible in most lights. The “damaged lungs of a smoker” are horrific, but there is no similar image for comparison. Part of a long-standing and popular science series, however, this will be welcome in classrooms. (index, glossary, suggested reading, websites) (Nonfiction. 8-11)