"Citations taken from secondary sources. To cite a source from a secondary source ("quoted in...") is generally to be discouraged, since authors are expected to have examined the works they cite. If an original source is unavailable, however, both the original and the secondary source must be listed."
1. Louis Zukofsky, "Sincerity and Objectification," Poetry 37 (February 1931): 269, quoted in Bonnie Costello, Marianne Moore: Imaginary Possessions (Cambridge, MA: Harvard University Press, 1981), 78.
(Chicago Manual of Style, 17th ed., p. 868).