List of sources:
FamilySearch: Arthur Inglis Girdwood. https://www.familysearch.org/ark:/61903/1:1:6Z5P-YZCT
Google scholar. http://scholar.google.co.za/ Publications by A.I. Girdwood.
Malan, M. In quest of health: The South African Institute for Medical Research, 1912-1973. Johannesburg: Lowry, 1988.
Medical, Dental and Pharmacy Directory of South Africa, 1926-1927. Pietermaritzburg: Ewald Herbert, 1926.
Medical and Pharmacy register for the Colony of the Cape of Good Hope, 1907 (see Girdwood, William). Cape Town: Townshend, Taylor & Snashall.
Pietermaritzburg Archives Repository (NAB). Volume NMC 34. List of medical practitioners, etc., registered in the Cape Province, 31 December 1915.
Pietermaritzburg Archives Repository (NAB). Volume NMC 34. List of medical practitioners, dentists, chemists and druggists, etc., registered [in the Transvaal], 31 December 1914.
Supplement to the London Gazette, 25 September 1918, p. 11393, at http://www.london-gazette.co.uk/issues/30919/supplements/11393/page.pdf
University of the Cape of Good Hope. Supplement to the University Calendar, 1903/4.