List of sources:
Cape of Good Hope Government Gazette, 9 January 1885. Government Notice No. 1295, 1884: List of licensed medical practitioners in the Cape Colony, corrected up to the 31st December, 1884.
FamilySearch: George Sandison Brock. https://www.familysearch.org/search/record/results?q.givenName=George Sandison&q.surname=Brock
Google scholar. http://scholar.google.co.za Publications by G.S. Brock.
Henning, M.W. Animal diseases in South Africa (2 vols). Central News Agency, 1932.
Medical and pharmacy register for the Colony of the Cape of Good Hope, 1893, 1907.
Melle, B.G. The Transvaal Medical Society. South African Medical Journal, 1937, Vol. 11, pp. 217-220.
Pietermaritzburg Archives Repository, Vol. NMC 34: [List of medical practitioners, dentists, and chemists and drugists in the Cape Province, as on 31 December 1915].
South African Medical Directory for 1897. Cape Town: Cape Times, 1897.
Staats-almanak der Zuid-Afrikaansche Republiek, 1896 (pp. 96-100) and 1898 (pp. 86-93): Naamlijst van de geadmitteerde genees-, heel- en verloskundigen... Pretoria: Staatsdrukkery.
Staats Courant der Z.A. Republiek, 2 April 1890, p. 298, Gouvernements Kennisgeving No. 90: Erratum [Lijst van toegelaten geneeskundigen...].