Maxwell Geismar's _Mark Twain an American Prophet_ also has interesting
comments on how Twain interchanged the usage of the word "negro" and
"nigger"
in Huck Finn.

Another sample of how Twain interchanged the two words even earlier in his
writing can be found in an newspaper report he wrote in 1865 that appears
in Paul Fatout's _Mark Twain Speaks for Himself_.  The report is entitled
"Immorality in San Francisco" and according to Fatout appeared in the
Downieville, California Mountain Messenger, 7/1/1865.

Other reports of his racial views have been reported in his daughter Clara's
books.

Barb