MLA

Wolff, Kurt, 1887-1963. Kollwitz, Käthe. Box 5, folder 186. 1917. https://collections.library.yale.edu/catalog/2021332.

APA, 6th edition

Wolff, Kurt, 1887-1963. (["Box 5, folder 186"])(1917)[Kollwitz, Käthe]. https://collections.library.yale.edu/catalog/2021332.