In response to Susanna Ashton's question:  you can search Twain's works
at the "Mark Twain in His Times" site maintained by Stephen Railton.
The address is
http://etext.virginia.edu/railton/index2.html
Another good place to search (perhaps even better, in fact) is the
"Twain's World" CD-ROM, which, with shipping charges, can be obtained
from Amazon.com or Barnes & Noble for about $20.  However, if you don't
know exactly what you're looking for, electronic searching may not be
the answer.

Jim Leonard