identified the cause of the outbreak as water from the public pump at the junction of Broad Street (now Broadwick Street) and Cambridge Street (now Lexington Street), close to the rear wall of what is today the John Snow public house. Snow mapped the addresses of the sick and noted that they were mostly people whose nearest access to water was the Broad Street pump. He persuaded the authorities to remove the handle of the pump, thus preventing any more of the infected water from being collected. The spring below the pump was later found to have been contaminated with sewage. This is an early example of epidemiology, public health medicine and the application of science—the germ theory of disease—in a real-life crisis. Science writer Steven Johnson has written about the changes related to the cholera outbreak, and notes that almost every building on the street that existed in 1854 has since been replaced. A replica of the pump, with a memorial plaque and without a handle (to signify Snow's action to halt the outbreak) was erected in 1992 near the location of the original. Decline By the mid-18th century, the aristocrats who had been living in Soho Square or Gerrard Street had moved away, as more fashionable areas such as Mayfair became available. The historian and topographer William Maitland wrote that the parish "so greatly abound with French that is an easy Matter for a Stranger to imagine himself in France." Soho's character stems partly from the ensuing neglect by rich and fashionable London, and the lack of the redevelopment that characterised the neighbouring areas. The aristocracy had mostly disappeared from Soho by the 19th century, to be replaced by prostitutes, music halls and small theatres. The population increased significantly, reaching 327 inhabitants per acre by 1851, making the area one of the most densely populated areas of London. Houses became divided into tenements with chronic overcrowding and disease. The 1854 cholera outbreak caused the remaining upper-class families to leave the area. Numerous hospitals were built to cope with the health problem; six were constructed between 1851 and 1874. Businesses catering to household essentials were established at the same time. The restaurant trade in Soho improved dramatically in the early 20th century. The construction of new theatres along Shaftesbury Avenue and Charing Cross Road improved the reputation of the area, and a meal for theatre-goers became common. Public houses