MLA

Cassirer, Ernst, 1874-1945. Unidentified. Box 6, folder 152. 1960, n.d.. https://collections.library.yale.edu/catalog/9998762.

APA, 6th edition

Cassirer, Ernst, 1874-1945. (["Box 6, folder 152"])(1960, n.d.)[Unidentified]. https://collections.library.yale.edu/catalog/9998762.