The son of Dr James Duncan, a well-known practitioner of Henrietta Street, Covent Garden. He was educated at Cholmeley School, Highgate, under the head master John Dyne; at King's College, London; Vienna, Strasburg, and Berlin. He entered King's College Medical Department as Warneford Scholar in 1868, won, among many awards, the Leathes Prize and Final Senior Scholarship, and eventually graduated with great success at the University of London. He became House Surgeon to Sir William Fergusson, John Wood, and Henry Smith in 1873, and in 1874 was appointed House Physician at the Seamen's Hospital, Greenwich. Here the systematic study of tropical diseases had only just begun. In 1875 he became House Surgeon to the Carey Street Dispensary and Medical Registrar to Charing Cross Hospital, and in 1876 was elected Surgical Registrar to King's College Hospital. At St Mary's Hospital he was Medical Tutor and Pathologist during 1877-1878, and might have gained a place on the staff of a teaching hospital when he decided to enter the Indian Medical Service, and passed in second in the list. All his home appointments were given up and he went to Netley, where he gained the Parkes Medal in 1885. In India he soon saw service, and in 1879-1880 was with Lord Roberts in the Afghan Campaign, being mentioned in despatches and receiving the Medal and Clasp. In the Battle of Charasiab he was dangerously wounded. Though severely affected in his general health he served also in the Black Mountain Campaign in 1891. In 1900 he retired with the rank of Lieutenant-Colonel after twenty-one years' service, and returned to England as an invalid. His strong convictions, which were expressed fearlessly, affected his advancement in the Indian Medical Service. Shortly after joining the Indian Medical Service he wrote a paper entitled "The Insanitary Tendencies of State Sanitation", in which he criticized severely the views of the chief sanitary officials of the Indian Government. This was considered an act of insubordination, and he was punished for it in various ways. He himself believed, and all his friends were certain of it, that his advancement in the service was blocked at every turn; there is no doubt that he was regarded as a difficult and troublesome man - the fate of all young reformers. However, his opportunity came in 1885 when the subject chosen for the Parkes Memorial Prize Essay was "The Prevention of Disease in Tropical Campaigns". He sent home his original essay with additions, and was awarded the prize. Duncan returned to professional life in London with so high a reputation that he soon received many appointments. Amongst others he became Physician to the Seamen's Hospital, Albert Docks, and to the Western General Dispensary, Examiner in Tropical Medicine for the University of London, and Lecturer on Tropical Medicine at Westminster Hospital Medical School and the London School of Tropical Medicine. He died after a long illness on Oct 17th, 1912. He had resided and practised at 24 Chester Street, SW. Lieut-Colonel Crawford gives his promotions as follows: Surgeon, Bengal Army, March 30th, 1878; Surgeon Major, March 30th, 1890; Lieutenant-Colonel, March 30th, 1898; retired, Feb.1st, 1900. Publications:- *The Prevention of Disease in Tropical and Sub-tropical Campaigns*, 8vo, London, 1888. This is the enlarged Parkes Memorial Prize Essay. *The Practitioner's Guide*, of which he was joint author. *Guide to Sick Nursing in the Tropics*, 8vo, London, 1908. Articles on "Dysentery" and "Kala-azar" in Quain's *Dictionary of Medicine*, 3rd ed. "Heat Stroke." - *Edin. Med. Jour.*, 1908, n.s. xiii, 217. "The Stools in Dysentery." - *Ibid.*, 1904, n.s. xv, 349. "Tropical Dysentery." - *Internat. Clin.*, series 13, iv, 70. "Military Surgery" in Treves's *System of Surgery*, 1895. He was for many years a valued collaborator upon the literary staff of the *Lancet*, to which journal he sent some signed articles.