Erethism or
erethism mercurialis is a
neurological disorder which affects the whole central nervous system, as well as a symptom complex derived from
mercury poisoning. This is also sometimes known as the
mad hatter disease. Historically, this was common among old England felt-hatmakers who used
mercury to stabilize the wool in a process called felting, where hair was cut from a pelt of an animal such as a rabbit. The industrial workers were exposed to the mercury vapors, giving rise to the expression “mad as a hatter.” Some believe that the character
the Mad Hatter in
Lewis Carroll's
Alice in Wonderland is an example of someone suffering from erethism, but the origin of this account is unclear. The character was almost certainly based on
Theophilus Carter, an eccentric furniture dealer who was well known to Carroll.