This cultural biography of Mary Putnam Jacobi (1842–1906) illustrates how American women came to embrace scientific principles in the post-Civil War period. Historians of women and medicine have focused on how nineteenth-century men of medicine worked against the interests of women by pathologizing the female body. This study offers an alternative perspective by examining how Mary Putnam Jacobi adopted science as a cultural authority and enrolled medicine in the campaign for women's rights. Ultimately, this project provides a gendered perspective to the stories of secularization and medicalization in American life, and shows how American women moved from the “cult of true womanhood” in Victorian America to “scientific motherhood” in the early twentieth century.