It's the first sign of life: that quick inhalation parents wait to hear their babies take, that reassuring gasp of air. From then, each of us breathes 19,000 times daily. That's 650 million inhalations over an average lifespan, all taken involuntarily. We might not give it a second thought, but Joe Sherman does.In his exhaustive review, Sherman traces the evolution of air as a science and as a concept, sketching short, fascinating biographies of obscure geniuses and modern-day wonders alike. Think of sixteenth-century homeopath Paracelus who introduced the idea that illnesses could be airborne. Or Lance Armstrong. Sherman visits a respiratory clinic and learns how his aerobic capacity differs from the famous cyclist's. Such portraits, along with a reasoned look at modern concerns  pollution, transmission of diseases like anthrax or SARS  offer air as a substance readers can hold in their minds as well their lungs.