Midwife giving a woman gas and air The gas and air machines used by midwives were portable and easy to use. This photograph, showing a midwife applying the mask, was produced for promotional purposes by the British Oxygen Company who supplied the gases used with the machines. Machines donated by the National Birthday Fund carried plaques indicating their provenance. Source: National Birthday Trust Fund Papers, c. 1950s. Reproduced with kind permission of BOC.