This novel was "groundbreaking with its treatment of the contentious theme of medical ethics. It has been credited with laying the foundation in Great Britain for the introduction of the NHS a decade later.
"For his fifth book, Dr. Cronin drew on his experiences practising medicine in the coal mining communities of the South Wales Valleys, as he had for The Stars Look Down two years earlier. Specifically, he had researched and reported on the correlation between coal dust inhalation and lung disease in the town of Tredegar. He had also worked as a doctor for the Tredegar Medical Aid Society at the Cottage Hospital, which served as the model for the National Health Service" (Wikipedia article on The Citadel (novel) accessed 04-2018).