Nitrous oxide was first produced by the English chemist and Presbyterian minister, Joseph Priestley, in 1772 and further investigated by Humphrey Davy in 1800 at the Pneumatic Medical Institution in Bristol. In his book on nitrous oxide, Davy recorded that breathing the gas helped to relieve toothache - from which he was suffering at the time - and suggested: 'it may probably be used with advantage in surgical operations'. But the pain-relieving properties of nitrous oxide were not explored any further until nearly fifty years later. Initially, society was more interested in nitrous oxide as a source of amusement and entertainment. It is for this reason, no doubt, that nitrous oxide was commonly called 'Laughing Gas'. (This term has always seemed rather odd to the author, because in his experience, laughter is rarely observed!)

Although nitrous oxide was the first anaesthetic ever to be used, it was soon replaced by ether and chloroform. This was because the latter were more potent and convenient to use. Because they were more potent, however, ether and chloroform were more dangerous - especially if consciousness was lost. It was soon appreciated that they were not safe for use during labour except when given by someone experienced in anaesthesia: even then, tragedies sometimes occurred.

It was in response to this challenge that Dr Minnitt invented his Gas and Air machine in 1933. It was designed to deliver a mixture of nitrous oxide and room air in suffficient concentrations to relieve pain - but not, loss of consciousness. Minnitt's machine proved to be very effective and soon became available for midwives to use during labour. Gas and Air remained popular in Britain for many years - until it was replaced by machines which delivered nitrous oxide in oxygen - instead of air.