MLA

Lewis, Sinclair, 1885-1951. "Black Blood". Box 35, folder 275. undated. https://collections.library.yale.edu/catalog/17116518.

APA, 6th edition

Lewis, Sinclair, 1885-1951. (["Box 35, folder 275"])(undated)["Black Blood"]. https://collections.library.yale.edu/catalog/17116518.