David Thomson, born and educated in Edinburgh, received his M.D. and studied in Dresden before he became medical officer at the Derby County and then Camberwell asylums. He was senior medical officer at Surrey County Asylum and only 30 years old when appointed medical superintendent at Norfolk County Asylum on Boxing Day 1886. Yet he was already ‘favourably known’ to the lunacy commissioners, who had ‘some confidence that, under his charge, this Asylum will not fall back’. Thomson took up his position on 12 February 1887 and remained there until 1 May 1922, well beyond his due retirement date, because of emergencies created by the Great War. In that time he was mainly responsible for the extensive reorganisation of the asylum and its modernisation to standards considered comparable with best contemporary practice. He also supervised the asylum's conversion to a military hospital, the subject of the next chapter, and its eventual reinstatement and renaming as a mental hospital.

Thomson's arrival coincided with changes in the regulation of county asylums and a determined effort by the lunacy commissioners to secure improvements. Under the 1888 Local Government Act Norfolk County Council became responsible for maintenance of the asylum, from April 1889 renamed the Norfolk County Asylum and run by a committee of seventeen visitors appointed from the elected councillors. Four members of the new committee had been members of its predecessor, providing an element rather than any guarantee of continuity in its management. The 1890 Lunacy Law Amendment Act altered procedures for the certification of patients, requiring the approval of a qualified medical practitioner and the formal consent of a judge or justice of the peace, rather than a clergyman or poor law relieving officer. It also required the annual recertification of existing asylum patients by their medical superintendent. A further clause restricted any cash surpluses generated from private patient care to asylum building accounts but, as will be seen, the indirect and medium-term subsidy of certain asylum patients and ratepayers continued.

Initially, Thomson complained that legislative requirements consumed medical superintendents’ time and that ‘the treatment of patients … cannot help being in a greater measure delegated to their less experienced colleagues’. Although he remained accountable to the committee of visitors, he grasped the reform opportunities offered, initiated relevant policy-making and effectively assumed personal control of the asylum.