The article is “ A Small Piece of Spite” from the Daily Morning Call:
http://www.twainquotes.com/18640906d.html
More info is available in the annotations for the letter written 25 Sept.
1864 online at
marktwainproject.org
Barb
On Sunday, June 30, 2019, Clay Shannon <[log in to unmask]> wrote:
> In a 9/25/64 letter to his mother and sister, Sam wrote, "I published the
> wickedest article on them I ever wrote" ("them" being "Massey's undertaker
> establishment").
> Is this article extant?
>
> - B. Clay Shannon
>