In early twentieth-century Latin America, doctors, technocrats, and citizens alike looked for “proof” in new places. Technology, epistemologies, and the physical body all seemed to offer such confirmation, albeit in distinct ways. This panel brings together historians of the Andes, Mexico, Central America, and the United States to interrogate varied practices of meaning-making and their implications for local practices of science. Even more, these papers interrogate how local scientific practices compelled distinct social responses. Bianca Premo’s paper examines how Peruvian physicians, working in conjunction with government officials, attempted to establish the proof of an anomaly of the human body, and hence a kink in the natural order of the passage of time, focusing on medical imaging and photography. Karin Rosemblatt probes medical studies of diet and nutrition to uncover prevailing ideas regarding bodily plasticity. Scientists asked how distinct cultures and natural environments, including foodways and agricultural practices, shaped bodies and therefore forms of distinction that were etched on the body. Heather Vrana’s paper reads patient case files and medical journals from Guatemala and El Salvador to show how conditions like epilepsy, alcoholism, psychosis, and leprosy enabled medical specialization and professionalization through patient observation, surveys, and statistics The measurement of population (especially the assessment of curability) and state management became hallmarks of professional medicine. Adam Warren’s paper draws on an unusual catalog of photographs published by Lima’s Society for Public Beneficence to ask how members of the society sought to understand and depict medical modernity. He focuses especially on the way in which such photographs decenter the body of the patient in favor of depicting various aspects of institutions. Ultimately, each of these papers interrogates the boundary work of knowledge, emphasizing how social relationships shaped the practices of science and medicine and, in turn, how science shaped what contemporaries knew, or could know. The papers place particular emphasis on the first decades of the twentieth century, a moment when interest and training in the sciences expanded rapidly in the region. This expansion was largely due to governmental interest and economic prosperity, additional themes that the panelists examine. For some time, Latin America has not been seen as a source for the export of raw data and import of knowledge. But these papers mark a new moment in Latin American Science and Technology Studies, providing views of research as a contact zone where elites, often urban medical professionals, professionals-in-training, and anthropologists, encountered “the masses” and formulated norms and predictions about them, which then circulated among global health networks. Frida Gorbach and Carlos López Beltrán have implored historians that “to think about the sciences today means to understand them as knowledges, in other words, cultural practices inserted into complex relations of power.” These papers take up that call.