In 1854, there was a major cholera outbreak in Soho, a neighborhood in London that Judith Summers described as full of “cow-sheds, animal droppings, slaughterhouses, grease-boiling dens and primitive, decaying sewers.” At the time, the cause of the outbreak was unknown because germ theory was still being developed and disease transmission was not well understood. Miasma theory was the dominant hypothesis, and it proposed that diseases, including cholera and the plague, were spread by foul gasses emitted from decomposing organic matter.