MLA

Pound, Ezra, 1885-1972. MacKintosh, George Lewis. Box 31, folder 1326. 1907. https://collections.library.yale.edu/catalog/17122590.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 31, folder 1326"])(1907)[MacKintosh, George Lewis]. https://collections.library.yale.edu/catalog/17122590.