His new idea was based on the recently discovered chemistry of respiration. His concept was that inhaled gases, ‘factitious airs’, by entering the bloodstream via the lungs, could alter and improve the whole constitution, and thereby cure major diseases. On 31 October 1794 he wrote to Davies Giddy: ‘Incontestable proof has been given that the application of airs or gases to the cure of diseases is both practicable and promising.
