Convict bodies contributed to knowledge and representations of criminality, race, and ethnicity, and tropical disease. Scientists used convicts to establish causal links between physique, criminal character, and sometimes race. They were especially interested in anthropometry, or the science of physical measurement, including through close analysis of the skull or other bodily features. By the third quarter of the nineteenth century, Italian positivist Cesare Lombroso, author of L’Uomo Delinquente (Criminal Man), had made the highly influential, though controversial, proposition that criminality was biologically determined, connected to hierarchies of race, and thus related to degeneration. Lombroso’s theory was particularly influential in Latin America, though the Russians, British, and French received it with more ambivalence. Later, scientists became interested in how both sensitivity to pain and in flows of blood (including to the face) might be physical manifestations of criminality. From the nineteenth century onwards, penal colonies were important spaces of medical research on morbidity and mortality, including studies of leprosy, hookworm, yellow fever, and malaria in places such as French Guiana and the Andamans. Such research fed into larger global investigations into mosquitos as vectors for sickness and disease. The era under consideration here also impacted on the purpose and method of convict studies.