The discovery and rediscovery of oxygen.

The therapeutic use of oxygen was pioneered in the early 20(th) century by the respiratory physiologist John Scott Haldane. His work followed Claude Bernard's description of the toxic effects of carbon monoxide. Haldane, having also observed the effects of carbon monoxide poisoning, became aware of the therapeutic benefits of oxygen in this condition. He was also an advocate of oxygen as a therapeutic agent in other respiratory illness, and made efforts to define how the gas could best be administered. The history of identification of oxygen as a chemical element is convoluted. In the 17(th) century, the controversial John Mayow suggested that only a portion of air was necessary for sustaining life. Mayow's work was largely overlooked during his lifetime, and his insight was subsequently eclipsed by the phlogiston theory, an erroneous concept widely believed for nearly a century after his death. This theory was ultimately disproved by Joseph Priestley in 1774. Although the point of primacy is somewhat contentious, Priestley shares the distinction of discovering elemental oxygen with Antoine-Laurent Lavoisier, the French chemist, and Carl Wilhelm Scheele, the Swedish apothecary.