della Casa states “It does not befit a modest, honourable man to prepare to relieve nature in the presence of other people, nor do up his clothes afterward in their presence. Similarly, he will not wash his hands on returning to decent society from private places, as the reason for his washing will arouse disagreeable thoughts in people.” Historian Lawrence Stone contends that the development of these new behaviours had nothing to do with problems of hygiene and bacterial infection, but rather with conforming to increasingly artificial standards of gentlemanly behaviour. These standards were internalized at an early age. Over time, much that had to be explained earlier was no longer mentioned, due to successful social conditioning. This resulted in substantial reduction of explicit text on these topics in subsequent editions of etiquette literature; for example, the same passage in Les règles de la bienséance et de la civilité Chrétienne by Jean-Baptiste de la Salle is reduced from 208 words in the 1729 edition, to 74 words in the 1774 edition. The first modern flush toilet had been invented in 1596, but it did not gain popularity until the Victorian era. When hygiene became a heightened concern, rapid advancements in toilet technology ensued. In the 19th century, large cities in Europe started installing modern flushing public toilets. George Jennings, the sanitary engineer, introduced public toilets, which he called "monkey closets", to the Crystal Palace for The Great Exhibition of 1851. Public toilets were also known as "retiring rooms." They included separate amenities for men and women, and were the first flush toilet facilities to introduce sex-separation to the activity. The next year, London's first public toilet facility was opened. Underground public toilets were introduced in the United Kingdom in the Victorian era, in built-up urban areas where no space was available to provide them above ground. The facilities were accessible by stairs, and lit by glass brick on the pavement. Local health boards often built underground public toilets to a high standard, although provisions were higher for men than women. Most have been closed as they did not have disabled access, and were more prone to vandalism and sexual encounters, especially in the absence of an attendant. A few remain in London, but others have been converted into alternative uses such as cafes, bars and even dwellings. Hong Kong In the early days of the colony of Hong Kong, people