MLA

Douglas, Norman, 1868-1952. Magnus, Maurice. Box 18, folder 272-74. 1917-1920. https://collections.library.yale.edu/catalog/16454712.

APA, 6th edition

Douglas, Norman, 1868-1952. (["Box 18, folder 272-74"])(1917-1920)[Magnus, Maurice]. https://collections.library.yale.edu/catalog/16454712.