MLA

Brush, George Jarvis, 1831-1912. Eichwald, Julius (6). Box 2, folder 41. 1861-1862. https://collections.library.yale.edu/catalog/32512666.

APA, 6th edition

Brush, George Jarvis, 1831-1912. (["Box 2, folder 41"])(1861-1862)[Eichwald, Julius (6)]. https://collections.library.yale.edu/catalog/32512666.