Throughout the 18th and early 19th centuries, enslaved people who were transported across the oceans to work plantations, soldiers conscripted into vast wars across the world, and people undergoing rapid changes due to colonization, were directly observed, interviewed, or studied via records decades later. The data gathered from observations of countless individuals provided critical information that underlies development of modern medicine. Downs shows that the study of infectious disease depended on the unrecognized contributions of those conscripted, enslaved, and conquired populations with comprehensive research and captivating human stories.  Of interest to medical historians, with lessons for current times. The Belknap Press of Harvard University Press. 2021. Paper. NEW. $18.00