I also read about how lead poisoning was what
made the Hat makers go mad and is where the
expression "Mad Hatter" came from.

Thats widely believed to be due to mercury,
not lead, as mercury-based compounds were
used in the manufacture of felt hats in the
18th and 19th century.

From what little I'v read on the subject, lead
poisoning causes dimentia and sympotoms of general
illness such as abdominal pain whereas mercury
can cause more severe psychotic symptoms such
as hallucinations.

Bob