A less well-known source for the quote you desire is a letter written by SLC to Joseph Twichell from Vienna in 1897, soon after his arrival there. As Carl Dolmestch discuesses in his exemplary _Our Famous Guest: Mark Twain in Vienna_, Viennese religious prejudice ripped society in half, with the anti-Semites on one side and everyone else -- a minority, sadly -- on the other. SLC, in part because of his Old Testament first name and in part because he sympathized with the politics of the Jews in Vienna, was presumed a Jew and castigated in the anti-Semitic press. Out of that experience, and his friendship with Theodor Herzl (SLC translated his play _The New Ghetto_), SLC wrote "Concerning the Jews." Before that, right after he arrived in Vienna, he wrote a letter to Twichell, quoted in part by Dolmetsch and more or less completely in Paine's edition of _Mark Twain's Letters_ which gives a more raw account of how he felt after being thrown into this lion's den of racial and religious politics. Hope this helps.