David Traill, medical practitioner, qualified as Bachelor of Medicine (MB) and Master in Surgery (ChM) at the University of Edinburgh in 1883. At some time he also obtained the degrees Bachelor of Science (BSc) and Master of Arts (MA). He was an exceptionally well-read man and a deep thinker, interested in philosophical studies. In 1899, at the beginning of the Anglo-Boer War (1899-1902), he came to the Cape Colony where he was registered to practice in November that year and was appointed medical officer to the British troops. In 1904 he became district surgeon at Richmond, Northern Cape. However, later that same year he was appointed as railway medical officer at Beaufort West. He retired from this position in 1919 and went to Kakemas, but in 1926 commenced practice at Ladismith in the Western Cape, where he remained for the rest of his life. After his retirement in 1928 he lived with his only daughter, Mrs Bosman, on the farm Buffelskloof near Ladismith.
Traill was a member of the South African Association for the Advancement of Science for some time around 1910. In that year he delivered a paper at the association's annual congress on 'Atmospheric variation as a factor in organic evolution' which was published in the association's Report (1910, pp. 299-305). The next year he delivered two further papers, 'Additional notes on evolution' and 'Theories of atmospheric variation'. Only abstracts of these papers were published in the Report for 1911 (pp. 405-406). In the medical field he contributed a paper on 'The cause of the declining death rate from tuberculosis' to the South African Medical Record (1913, Vol. 11, p. 241).