I came across a reference to Gary Scharnhorst's article:
Gary Scharnhorst (2004) Mark Twain's "How to Remove Warts and Tattoo
Marks" Authenticated, ANQ: A Quarterly Journal of Short Articles, Notes
but I have been limited to reading the first page and trying to obtain a
copy from ANQ has proved to be almost futile (six or seven weeks just to
be cleared), so I'm hoping someone might have a pdf copy they could send
me. The topic is not particularly geographic in nature but I do find
the subject to be intriguing.