The Lower East Side of New York was one of the most densely populated square miles on the face of the earth in the 1890s. The photo-essayist Jacob Riis famously described it as a world of bad smells, scooting rats, ash barrels, dead goats, and little boys drinking beer out of milk cartons. Six thousand people might be packed into a single city block, many in tenements with sanitary facilities so foul as to repel anyone who dared approach. City health inspectors called the neighborhood “the suicide ward”; one tenement was referred to—in an official New York City Health Department report, no less—as an “out and out hog pen.”1

Diarrhea epidemics blazed through the slums each summer, killing thousands of children every week. In the sweatshops of what was then known as “Jewtown,” children with smallpox and typhus dozed in heaps of garments destined for fashionable Broadway shops. Desperate mothers paced the streets trying to soothe their feverish children, and white mourning cloths hung from every story of every building. A third of the children born in the slums died before their fifth birthday.

In the European farming villages where many of these immigrants came from, people spent most of their time outdoors in the fresh air and sunshine, and most never encountered more than a few hundred people in a lifetime. “Crowd diseases”—measles, dysentery, typhoid, diphtheria, trachoma, and so on—were rare, and the immigrants had little idea of how to prevent them. Some parents vainly tried to administer folk remedies; others just prepared the little funeral shrouds in silence.2

It was in the 1890s that Sara Josephine Baker decided to become a doctor. Not the Josephine Baker who would become celebrated as a cabaret star and dance at the Folies Bergère in a banana miniskirt but the New York City public health official in a shirtwaist and four-in-hand necktie, her short hair parted in the middle like Theodore Roosevelt, whom she admired. By the time Baker retired from the New York City Health Department in 1923, she was famous across the nation for saving the lives of 90,000 inner-city children. The public health measures she implemented, many still in use today, have saved the lives of millions more worldwide. She was also a charming, funny storyteller, and her remarkable memoir, Fighting for Life, is an honest, unsentimental, and deeply compassionate account of how one American woman helped launch a public health revolution.3

Born in 1873, Baker grew up in a modestly prosperous Poughkeepsie family and studied medicine at the Women’s Medical College in Manhattan, run by Emily Blackwell, the sister of the more famous Elizabeth, America’s first woman doctor. Baker graduated second in her class. The only course she failed was “The Normal Child,” taught by Dr. Annie Sturges Daniel, a pioneer health…