Eldest son by the second marriage of John Firth, who was in the educational department of the HEICS, and of Maria, his wife, daughter of Major Robert Hammill, 18th Royal Irish Regiment, was born in Bombay, 1 December 1857. He was educated privately by the Rector at Ware, Herts, and then at University College, London, and he matriculated from Oriel College, Oxford, but never graduated, as his studies were interrupted by a visit to a brother in South America. He joined the Army Medical Department as a surgeon on 3 August 1883, becoming colonel AMS 13 November 1912, and retiring 25 December 1917. He was awarded the Alexander memorial prize and medal in 1888 and in 1891, and the Parkes memorial prize and medal for hygiene in 1889 and again in 1892. His first tour of foreign service was in India, where he served with the Hazara expeditionary force in 1888, receiving the medal and clasp. In 1892 he was appointed assistant professor of hygiene at the Army Medical School, Netley, and held the post until 1897, J Lane Notter being professor. On completing his five years' tenure as assistant professor, Firth returned to India, and took part in the operations during the Tirah expedition on the North-West Frontier 1897-98 and gained the medal with two clasps. Having by this time become known for his work on hygiene, for he had published conjointly with Lane Notter a standard work on *The theory and practice of hygiene*, he was detailed to investigate the causes of an increase in sickness due to enteric fever amongst the troops at Rawalpindi, and was subsequently sent to Lucknow to work at the bacteriology of dysentery. The results of his investigations were published in the *British Medical Journal*, 1902, 2, 936 and 1094, under the title "The influence of soil, fabrics, and flies in the dissemination of enteric infection", and "A comparative study of some dysentery bacilli" in the *Journal of the RAMC*, 1903, 1, 436. The latter paper was issued jointly with Major W H Horrocks and is extremely well illustrated. In 1906 he was appointed instructor at the School of Army Sanitation, when it was first established at Aldershot, and in that position he laid the foundations of the knowledge which was used to such good effect in the war of 1914-18. He proceeded again to India on the termination of his appointment, and on his return filled for a time the position of Sanitary Officer at Army Headquarters, a post which was abolished on 1 December 1912, the title being ADMS (Sanitary). In March 1915 he became ADMS of the 20th Division of the British Expeditionary Force in France, and in September 1915 he was appointed DDMS of the 11th Corps, a position he held until May 1917, when he retired on reaching the age limit and was transferred to the Havre base. For his services he was mentioned three times in despatches, received the Victory and Allied medals, was decorated CB (mil) in 1918 and was invested KBE (mil) in 1919. He was a Grand Officer of the Order of Avis of Portugal, and in 1919 received a silver medal from the municipality of Havre in recognition of the medical services rendered to the civil population of the town. In 1924 he was awarded a well-earned "good service reward". He was for many years a member of council and examiner at the Royal Sanitary Institute, a member of council of the Royal Institute of Public Health, and a Fellow of the Society of Medical Officers of Health. From 1927 to 1931 he was president of the Army Medical Officers' Widows and Orphans Fund. He was also a member of the Société de Médecine militaire française and at the annual meeting of the British Medical Association held at Swansea in 1903 he held office as vice-president of the section of state medicine. He married on 15 March 1884 Mary, eldest daughter of William Knight, solicitor, of Cardiff and Appledore, Devon, who died before him leaving one daughter. He died on Saturday, 6 June 1931, at his house in Finchley Road, NW. Firth carried on the tradition of Army sanitation which began with Parkes and it was largely due to the interest in his subject which he excited in officers of the combatant forces during the time he was in charge of the School of Army Sanitation at Aldershot that the British forces maintained so good a record of health during the war of 1914-18. Publications:- *The theory and practice of hygiene*, with J Lane Notter. London, 1896. This work practically replaced the excellent *Manual of practical hygiene* prepared especially for use in the medical service of the Army, which was written by E A Parkes in 1864 and was edited from the fifth edition in 1878 by Professor de Chaumont. The third edition of *The theory and practice of hygiene*, published in 1908, was brought out by Firth alone; the ninth edition appeared in 1921. *Practical domestic hygiene*, with J L Notter. London, 1897. *Military hygiene, a manual of sanitation for soldiers*. London, 1908. *Musings of an idle man*. London, 1919. Editor of the *Journal of the RAMC*. vol. 1, 1903. The succeeding volumes were edited by David Bruce.