John Scott Haldane was born in Edinburgh in 1860. He was the brother of statesman Richard Burdon Haldane (1856-1928), Viscount Haldane, and the father of both geneticist John Burdon Sanderson Haldane (1892-1964) and writer Naomi Mitchison (1897-1999). Haldane was educated at Edinburgh Academy and then studied medicine at Edinburgh University and in Jena, Germany. He graduated in 1884 and took up a position at Queen's College, Dundee, before becoming a Demonstrator in Physiology at Oxford University in 1887. There he lectured and researched in medicine, and became Reader in 1907. In 1905 he established that it was the high concentration of carbon dioxide in blood, not low concentrations of oxygen, which regulated the breathing rate, and in 1907 he developed stage decompression for bringing deep-divers to the surface, thus avoiding 'the bends'. During the First World War he worked on the identification of war-gases, and when he was Director of the Mining Research Laboratory in Doncaster (1912-1936) he improved mine-safety. He demonstrated the toxic effects of carbon monoxide and the use of rescue equipment, including the development of the Haldane Equaliser Device. John Scott Haldane died in March 1936 after research in Iran (then Persia) into heat stroke among oil workers.