This is Twain's offensive article in THE GALAXY (September 1870):

http://cdl.library.cornell.edu/cgi-bin/moa/pageviewer?frames=1&coll=moa&view=50&root=%2Fmoa%2Fgala%2Fgala0010%2F&tif=00432.TIF&cite=http%3A%2F%2Fcdl.lib
rary.cornell.edu%2Fcgi-bin%2Fmoa%2Fmoa-cgi%3Fnotisid%3DACB8727-0010-55