MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Kesting, Edmund. Box 105, folder 2571. 1948-49, n.d.. https://collections.library.yale.edu/catalog/2015212.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 105, folder 2571"])(1948-49, n.d.)[Kesting, Edmund]. https://collections.library.yale.edu/catalog/2015212.