MLA
Miller, H. V. M. (Homer Virgil Milton), 1814-1896. Letter from Chief Surgeon Homer Virgil Miller to W. W. Wilson[?] - July 28, 1861. July 28, 1862. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/443nvx0m74-cor.
APA, 6th edition
Miller, H. V. M. (Homer Virgil Milton), 1814-1896. (July 28, 1862)[Letter from Chief Surgeon Homer Virgil Miller to W. W. Wilson[?] - July 28, 1861]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/443nvx0m74-cor.
Chicago
Miller, H. V. M. (Homer Virgil Milton), 1814-1896, Letter from Chief Surgeon Homer Virgil Miller to W. W. Wilson[?] - July 28, 1861, July 28, 1862, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/443nvx0m74-cor.