List of sources:
Burrows, E.H. A history of medicine in South Africa up to the end of the nineteenth century. Cape Town: Balkema, 1958.
Cape of Good Hope. Alexander McGregor Memorial Museum, annual report, 1909.
Cape of Good Hope Government Gazette, 16 September 1862, and 9 January 1885: List of licensed medical practitioners in the Cape Colony.
Daily Independent, 18 February 1882, p. 4, Medical notice.
Diamond Fields Advertiser, 11 July 1882, The meeting re the small-pox.
FamilySearch: Willem Jacobus Otto. https://www.familysearch.org/en/tree/person/about/M59J-744 AND https://www.familysearch.org/ark:/61903/1:1:CZRV-C1T2?lang=en
Grahamstown Journal, 21 January 1882, p. 3, Kimberley Medical Society.
Medical and pharmacy register for the Colony of the Cape of Good Hope, 1893, 1907.
Men of the times: Old colonists of the Cape Colony and Orange River Colony. Johannesburg: Transvaal Publishing Company, 1906.
National Automated Archival Information Retrieval System (NAAIRS). http://www.national.archives.gov.za/naairs.htm Documents relating to Otto, W.J. / Dr Otto.
National Union Catalogue, pre-1956 imprints. London: Mansell, 1968-1980.
Plug, C. Almost forgotten, never told: The Griqualand West Medical Society (1881). Adler Museum Bulletin, April 1992, Vol. 18(1), pp. 2-8.
South African medical directory for 1897. Cape Town: Cape Times, 1897.