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Oxygen was discovered in the late 18th century chiefly through the work of three scientists. Joseph Priestley, a minister in England, made his discovery after attempting to melt mercuric oxide using a magnifying glass and the sun’s rays. The vapor that was produced by this melting allowed a candle to burn brighter, and Priestley later discovered the vapor could be used in place of air to keep a mouse alive. He first published his findings in 1775. In a similar way to Priestley (i.e., by burning mercuric oxide), Carl Scheele, a pharmacist in Sweden, independently made the same discovery earlier in 1772, but did not publish his results until 1777.1 After being told about this new vapor during a 1774 visit to Paris by Joseph Priestley, the French chemist Antoine Lavoisier devised quantitative experiments that he used to prove the existence of this element and its role in combustion. He named the element “oxygen,” meaning “sharp-begetter”—“oxy” meaning sharp, “gen” meaning begetter—as he believed the element was a necessary element to form acids and published his research in 1777. Scheele beat Priestley by several years but was deprived of priority because Lavoisier denied receiving a letter Scheele later claimed to have sent in September 1774 describing his 1772 discovery of what he called “fire air.” Scheele’s claim of priority remained unconfirmed, until his missing letter (received on October 15, 1774) was finally made public in 1992 in Paris, 218 years later. It now resides at the French Academie de Sciences. Lavoisier’s guilt was kept secret in the effects of his wife and scientific assistant, Madame Lavoisier. Lavoisier failed on several occasions to credit either Priestley or Scheele for contributing to the one of the most important discoveries in the history of medicine and science.1

Soon after its discovery, oxygen began to be used as a medicine and cure-all for many respiratory diseases, including “dropsy,” “consumption,” and asthma. However, suspicions about the safety of oxygen therapy were raised almost as soon as it was discovered and even before the element was named. In 1775, Joseph Priestley wrote of oxygen: “A moralist, at least, may say that the air which nature has provided for us is as good as we deserve.”2

Rigorous scientific evaluation of the potential toxicities of oxygen did not occur until the work of James Lorrain Smith, an Edinburgh pathologist, who first published the pulmonary pathologic alterations associated with oxygen exposure in 1899. It was also recognized around this time that under ambient air, the arterial blood was already at near-maximal oxygen-carrying capacity, putting into doubt the utility of further increasing the fraction of inspired oxygen. Following these observations, the use of therapeutic oxygen fell into some disrepute.

In the early 1920s, supplemental oxygen therapy was reevaluated. This was occurring as the detrimental effects of tissue hypoxia were being recognized, along with their reversibility with supplemental oxygen. Since the ...

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