R J Minnit (1889-1974), with the help of Arthur Charles King (1888-1965), developed a modification of an existing anaesthetic apparatus to replace chloroform as a pain reliever for mothers during childbirth. Once the potentially toxic nature of chloroform had become apparent, it was used far more cautiously. In this device, nitrous oxide fills the rubber bag underneath the glass, which as it expands lifts the metal plate to close off the supply of gas. As the patient inhales through the mask, the nitrous oxide is mixed with air. The portable box was designed so mothers could self-administer the gas and air. Gas and air are still used today. This model is known as the ‘Walton-Minnit’ and was first sold in 1936.
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Glossary: nitrous oxide
Nitrogen oxide. A colourless, odourless gas that is used as an anaesthetic and analgesic. High concentrations cause a narcotic effect and may replace oxygen, causing death by asphyxia. It is also used as a food aerosol in the preparation of whipping cream.
Glossary: anaesthetic machine
An agent that causes insensitivity to pain. Applied to either the whole body (general anaesthetic) or a particular area or region (local anaesthetic).