The steady decline of wet nursing that began in the nineteenth century concluded in the twentieth century with the transformation of human milk into a commodity. In 1900 wet nurses occupied several small niches – suckling foundlings in institutions or working for well-to-do private families. By the 1910s and 1920s the number of wet nurses in these venues had decreased, although new opportunities arose for women willing to suckle abandoned babies in their homes or premature infants in hospitals. At the same time, a new career opened for lactating mothers: expressing and selling their breast milk for use in homes and hospitals. This procedure proved so successful that by the 1930s wet nurses had almost entirely vanished, replaced by bottled human milk. As one physician described it, human milk had become “therapeutic merchandise.”

In the case of human milk, commodification – the process by which things come to have economic value – was configured by the long history of wet nursing. Not surprisingly, traditional ideas about milk and character uncoupled slowly. The personal characteristics of wet nurses – their health, morals, willingness to obey authority, emotional ties to their own children – had long been crucial measures of their worth. So too were women who sold their milk judged by more than just the product that they made. In the end, however, commodification transformed the meaning of breast milk.