Divers experience the ‘raptures of the deep’ when breathing high-pressure nitrogen, which affects their nervous system and, ultimately, their behaviour. Nitrogen narcosis was first described in 1930 by Leonard Erskine Hill and John James Rickard Macleod (1876–1935). It usually occurs during deep dives. Symptoms appear for some at a depth of 30 metres; by -60 metres they are unavoidable.