Born 20 December 1885, the youngest son of James Nowell Johnson, inspector of insurances, and his wife Elizabeth Burford. He was educated at the City of London School and St Thomas's Hospital, qualifying in 1908 and taking the Fellowship in 1911. In 1912 he entered the West African Medical Staff, intending to practise as a surgeon. On arrival in Africa, however, he became more interested in public health problems and was seconded in 1913 for research work with the Yellow Fever Commission. During 1914-15 he served as a temporary captain, RAMC, in the Cameroons. He began tsetse fly investigations in northern Nigeria in 1921, work which led to the establishment of the Trypanosomiasis Research Institute at Kaduma. Johnson was appointed Director of Medical and Sanitary Services for Nigeria in 1929, a post which he held with great distinction till 1936. He was created CMG in January 1933 and a Knight bachelor in June 1935. He was instrumental in establishing the Nigerian Medical School. After retiring he became Superintendent of the Botsabelo Leper Institute at Maseru in Basutoland, and was subsequently medical adviser to the High Commissioner for Basutoland, Bechuanaland, and Swaziland. Johnson was unmarried. His life and work were shared by his sister Miss Mary Johnson, MBE. They lived at The Thatch, Penhill Estate, Eersteriver, Cape Province, where he died on 5 July 1951, aged 65. Johnson was essentially a field worker, though also an able administrator. He was a man of abounding energy and goodwill, loved and admired by countless Europeans and Africans, and was known to his friends as Buff. He thought little of driving his Ford truck from Nigeria north to England or south to the Cape, accompanied by his sister. He was a big-game hunter and a fisherman, fond also of travel and of golf. He was a strong swimmer and nearly lost his life in a gallant attempt to rescue a friend off Lagos beach. Johnson was the author of many valuable official reports on yellow fever and trypanosomiasis. At the centenary meeting of the British Medical Association in London in 1932 he presided at some of the meetings of the section for tropical medicine.