In answer to the query about useful sources on Mark Twain and P. T. Barnum-- I highly recommend Neil Harris's book about Barnum, _Humbug: The Art of P. T. Barnum (Chicago: Chicago UP, 1973). While it's only about Barnum, Harris does a really good job locating Barnum in the cultural context of nineteenth-century America. The book would, at least, give you some useful background for speculating about connections between them. Susan Reed