MLA

Stein, Gertrude, 1874-1946. Blake, Christopher. Box 98, folder 1873. 1944-46. https://collections.library.yale.edu/catalog/10268242.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 98, folder 1873"])(1944-46)[Blake, Christopher]. https://collections.library.yale.edu/catalog/10268242.