Mercury was used in the manufacturing of felt hats during the 19th century, causing a high rate of mercury poisoning among those working in the hat industry. Mercury poisoning causes neurological damage, including slurred speech, memory loss, and tremors, which led to the phrase "mad as a hatter". In the Victorian age, many workers in the textile industry, including hatters, often suffered from starvation and overwork, and were particularly prone to develop illnesses affecting the nervous system, such as central nervous system (CNS) tuberculosis, which is portrayed in novels like Alton Locke by Charles Kingsley and North and South by Elizabeth Gaskell, which Lewis Carroll had read. Many such workers were sent to Pauper Lunatic Asylums, which were supervised by Lunacy Commissioners such as Samuel Gaskell and Robert Wilfred Skeffington Lutwidge, Carroll's uncle. Carroll was familiar with the conditions at asylums and visited at least one, the Surrey County Asylum, himself, which treated patients with so-called non-restraint methods and occupied them, amongst others, in gardening, farming and hat-making. Besides staging theatre plays, dances and other amusements, such asylums also held tea-parties.