Chadwick's Report on the Sanitary Condition of the Labouring Population (1842) argued that disease rose from filth, foul air and stagnant water, and that removing them by drainage, water supply and ventilation would cost less than the destitution epidemics caused. Miasma theory was wrong about mechanism but produced the right instruments: trunk sewers, piped supply, wide streets, open space, minimum room volumes and window areas. Snow's Broad Street work in 1854 and then Pasteur's and Koch's isolation of specific organisms between 1876 and 1882 replaced bad air with identifiable pathogens and definite transmission routes. Sanitary reasoning narrowed accordingly - from cleansing the whole environment to intercepting particular routes through filtration, pasteurisation, screening, notification and later vaccination.
The miasma phase justified the largest civil works and the widest regulatory reach in urban history, and hygienist urbanism - the boulevard, the interceptor sewer, the by-law street, the open block, the sun-and-air prescription - is its physical residue. When germ theory withdrew the general environmental rationale, planners kept the forms and had to find new arguments for them, a hangover visible in modernist doctrine and again in COVID-era ventilation debates.
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