Less than a century ago, physicians, scientists, and cultural commentators became fascinated by the endocrine glands and the effects of their secretions on our bodies and minds. Of all the characteristics supposed to be governed by them, the attributes of sex evoked the wildest interest. The gonads, it was revealed, secreted chemicals that not only influenced the biological expressions of sex, but seemed to generate the vitality and energy that made life worth living. Through a series of case studies drawn from Central Europe, the United States, and Britain, The Most Secret Quintessence of Life explores how the notion of sex hormones enabled scientists to remap the human body, encouraging hopes that glandular interventions could cure ills, malfunctions, and even social deviance in ways inconceivable to previous generations. Many of these dreams failed, but their history, Chandak Sengoopta shows, takes us into the very heart of scientific medicine, revealing how even its most arcane concerns are shaped by cultural preoccupations and anxieties.