By the 1890s the Metropolitan Asylums Board’s massive archipelago of fever hospitals had completely reshaped the everyday experience of many of the most common infections and “childhood diseases”—this despite the very real contagious dangers that lurked in the hospitals themselves. This chapter examines the controversies about hospital infection that served to remake the isolation hospitals into epidemiological laboratories and sites for the investigation and construction of the hygienic body. The fever hospital emerged as an institution dedicated to the public. It became a place not only for establishing external perimeters but also internal partitions and blockades—seen in practices of “isolation within isolation” such as partial walls, glass partitions, and rituals of barrier nursing.