The book ends in 1940, on the cusp of change that came with the militarization of the North during the Second World War and the Cold War. This was also when the Canadian government asserted greater control over the North, including over healthcare. Epidemics that arrived with resource workers, military, and state personnel, were interpreted by southern observers as ‘virgin soil epidemics’ in ‘isolated’ populations. These epidemics and their northern setting influenced biomedical research into the nature of immunity that was significant to the history of medicine.