Born 25 March 1866, third child and second son of Arthur Edward Durham, consulting surgeon to Guy's Hospital, and his wife Mary, daughter of William Ellis (see *DNB*), economist and founder of the Birkbeck secondary technical schools. He was thus born into a remarkable family. The only brother who, with him, survived their father, Colonel Frank Rogers Durham, after a distinguished career as a civil and military engineer, became (1926) secretary of the Royal Horticultural Society. Of his sisters, Mary Edith Durham, FRAI (1863-1944), made her name first as an artist, and later as Balkan traveller and anthropologist, and champion of Albania; another sister became Mrs Hickson and her daughter Joan Durham Hickson was the wife of W H Trethowan, FRCS; the third sister, Caroline Beatrice (who died 13 April 1941), married William Bateson, FRS, the famous geneticist, and wrote the classic life of her husband. H E Durham was educated at University College School, London, and King's College, Cambridge, of which he was Vintner exhibitioner 1885; he took first-class honours in part 1 of the Natural Sciences Tripos 1886 and a second-class in part 2, 1887. He then worked for two years as John Lucas Walker student in the University laboratories of zoology and physiology. His medical training was at Guy's, where his father was the leading surgeon, and he qualified from Cambridge in 1887. He took the Fellowship, though not previously a Member, in 1894, but did not practise surgery. He served as resident obstetric officer and assistant in the throat department at Guy's, and was Gull research student there 1894. He was also medical officer to the North Eastern Fever Hospital at Tottenham. In 1894 he went to work under Max Gruber (1853-1927) in the Hygienisches Institut at Vienna. With his master he recognized the practical potentialities for diagnosing infectious diseases available from the effect, already observed by others, of agglutination of pathogenic organisms by the serum of animals immunized against those particular organisms. Durham reported this suggestion to the Royal Society of London on 3 January 1896. But it was first applied clinically in enteric fever by Fernand Widal (1862-1929), of Paris, in June and July of the same year (*Bulletin, Société médicale des Hôpitaux de Paris*, 1896, 13, 561) and by A S F Grünbaum (afterwards Leyton) (1869-1921), of Liverpool, during September-December (*Lancet*, 1896, 2, 806 and 1747). Gruber's communication is in *Münchener medizinische Wochenschrift*, 1896, 43, 285. The reaction is variously known by the names Widal, Gruber, and Durham. In 1896 Durham served on the Royal Society's tsetse-fly commission in Africa, and the following year was appointed Grocer's Company Research Fellow at Cambridge. He reported his observation of a common group agglutinating reaction between closely allied bacteria, and also introduced the "Durham tube", the small inverted test-tube placed in bacterial media to collect gas produced by fermentative organisms (*Brit med J*. 1898, 1, 1387), which was very generally adopted. In 1900 he took to Brazil the yellow-fever expedition, sponsored by the Liverpool School of Tropical Medicine. He and his colleague, Walter Myers (1872-20 January 1901), both contracted yellow-fever, and Myers died of it at Para. The expedition's results were published as the School's *Memoir* No 7, 1902. From 1901 to 1903 Durham headed the London School of Tropical Medicine's beriberi expedition in Malaya and Christmas Island, where he lost the sight of one eye. Durham was the first to bring back to England from Malay the poisonous plant *Derris elliptica*, which came into wide use as a horticultural insecticide. He described it in J D Gimlette's *Malay poisons*, 3rd edition, 1939. He was also associated with Sir Ronald Ross in his researches on malaria. Durham was hindered by his partial loss of sight from returning to bacteriological research, and therefore readily accepted the invitation of a friend, Fred Bulmer, director of H P Bulmer and Co, cider manufacturers, at Hereford, to superintend their chemical department. The Bulmer family had long been connected with Durham's old college, King's. Durham spent thirty useful years, 1905-35, at Hereford, working on fermentation, and also did much for the improvement of fruit trees and was active in the acclimitization of new plants. He served as president of the Herefordshire Association of Fruitgrowers and Horticulturists, and was also president of the Woolhope Naturalists Club. He lived at Dunelm, Hampton Park, Hereford. In 1935 he retired to Cambridge, where he continued his active horticultural work particularly in raising rare culinary plants, of which he contributed accounts to the *Dictionary of Gastronomy*. He was, too, a draughtsman of talent and a skilled woodworker, who designed ingenious modifications of his lathe. He was a medallist of the Royal Photographic Society in 1927. He was a retiring, modest man, though of adventurous originality and much charm. Durham married on 25 September 1907 Maud Lowry, daughter of Captain Harmer, 81st Regiment. Mrs Durham survived him, but without children. He died at 14 Sedley Taylor Road, Cambridge, on 25 October 1945, aged 79, having been well and happy the previous day. He left, subject to his widow's life-interest, bequests to the Royal Medical Benevolent Fund, King's College, Cambridge, and the Schools of Tropical Medicine in London and Liverpool. His outstanding publications are mentioned above.