MLA

MacDonald, George, 1824-1905. Matheson, William. Box 1, folder 22. [1873 Oct. ?]. https://collections.library.yale.edu/catalog/16474482.

APA, 6th edition

MacDonald, George, 1824-1905. (["Box 1, folder 22"])([1873 Oct. ?])[Matheson, William]. https://collections.library.yale.edu/catalog/16474482.