Born 24 August 1877 at Frogmoor House, High Wycombe, Bucks, in the house where his grandfather, William Hayden, LSA 1837, MRCS 1856, and his father, William Gallimore Hayden, MRCS 1863, had successively practised medicine. His mother was Elizabeth Matilda, daughter of William Falconer, who founded the Union Castle line to South Africa, and he was the fourth child of the marriage. Educated at the Grammar School, High Wycombe, when George Peachell was headmaster, he entered St Mary's Hospital, London, with the entrance scholarship and acted as a prosector at the Royal College of Surgeons. He served as house surgeon and assistant anaesthetist at St Mary's Hospital and as pathologist at the County Asylum, Winwick, Lancashire. He was gazetted lieutenant in the Indian Medical Service on 1 September 1905, and during his course in the Army Medical School won the Montefiore medal for military surgery and the Martin gold medal. Proceeding to India he was promoted captain on 1 September 1908, but was placed on temporary half pay on 23 January 1910 after an attack of poliomyelitis, which obliged him ever afterwards to use a mechanical chair for locomotion. He retired on 23 January 1912. Returning to England he undertook work at St Mary's Hospital as pathologist to the venereal disease department and as an assistant in the inoculation department. He married Ruth Lacey on 14 April 1912; she survived him with two sons and a daughter. He died on 8 March 1940 at 4 Graham Road, Hendon, NW4. Publications:- An inquiry into the influence of the constituents of a bacterial emulsion on the opsonic index. *Proc Roy Soc Lond*. 1911, B, 84, 320. Relative value of human and guinea pig complement in the Wassermann reaction. *Brit J exper Path*. 1922, 3, 151. **See below for an expanded version of the original obituary which was printed in volume 2 of Plarr’s Lives of the Fellows. Please contact the library if you would like more information lives@rcseng.ac.uk** Arthur Falconer Hayden was a surgeon in the Indian Medical Service who, after contracting polio, later joined the inoculation department at St Mary’s Hospital, London, where he worked under the influential immunologist Sir Almroth Wright. Hayden was born on 24 August 1877 at Frogmoor House in High Wycombe, Buckinghamshire. Both his father, William Gallimore Hayden, and paternal grandfather, William Henry Hayden, were doctors. William Gallimore Hayden trained at Charing Cross Hospital, qualified in 1863, and became the medical officer at the Little Marlow District and Workhouse Wycombe Union. William Henry Hayden was a medical officer for the 12th District Wycombe Union. Hayden’s mother was Elizabeth Matilda Hayden née Falconer. Hayden was educated locally in High Wycombe and then studied medicine at St Mary’s Hospital Medical School with an entrance scholarship. He was a prosector at the Royal College of Surgeons of England. He qualified with the conjoint examination in 1900, and subsequently gained a MB degree with honours in materia medica and forensic medicine, and a BS in 1904. He was an assistant demonstrator of anatomy, chemistry and pathology and a prosector in anatomy at St Mary’s, and went on to become a house surgeon at Newport and Monmouthshire Hospital and an assistant medical officer and pathologist at the County Asylum, Winwick. He was subsequently an assistant anaesthetist and house surgeon back at St Mary’s. He joined the Indian Medical Service on 1 September 1905 as a lieutenant. During his studies at the Army Medical School he won the Montefiore medal and prize for military surgery and the Martin gold medal for tropical medicine. He gained his FRCS in 1906 and became a specialist in advanced operative surgery. On 1 September 1908 he was promoted to captain. His military career came to end when he caught poliomyelitis. He was placed on half pay on 23 January 1910 and retired from the Indian Medical Service two years later. He returned to St Mary’s, where he was recommended for a job in the inoculation department by his friend Alexander Fleming. In 1917 Hayden became a pathologist in the newly opened venereal diseases department at St Mary’s, taking over from Fleming who had returned to military service. Hayden wrote ‘An inquiry into the influence of the constituents of a bacterial emulsion on the opsonic index’ *Proc Roy Soc Lond* 1911 B 84 320 and ‘Relative value of human and guinea pig complement in the Wassermann reaction’ *Brit J Exper Path* 1922 3 151. In 1939 he wrote ‘Acute conjunctivitis caused by a gram-negative diplococcus resembling the gonococcus’ *Brit J Vener Dis* 1939 Jan; 15(1):45-54 with his son. Hayden died on 8 March 1940 in Hendon, Middlesex. He was 62. He was survived by his widow Ruth Campbell Hayden née Lacey, originally from New Jersey, whom he had married in 1912, and their sons Arthur Falconer and Roger Keith, who both qualified as doctors. Hayden and his wife also had a son, William John, who died in 1916 aged just one month. Sarah Gillam