Robert James Minnitt introduced the concept of self-administered analgesia, using an apparatus designed and built in conjunction with London scientific instrument-maker, Charles King. The Minnitt apparatus met with considerable success and led to further modifications, including the introduction of the Queen Charlotte gas-air analgesia apparatus in 1936, manufactured by the British Oxygen Company.
Black and white photograph of a Minnitt gas/air analgesia apparatus, in a Queen Charlotte case. The case is standing open with the apparatus inside. A label with instructions is on the left side of the case, and the apparatus is on the right side of the case. A nitrous oxide cylinder tank and valve is connected to a small box with a regulator. A tube with a breathing mask is attached to the box. The Queen Charlotte case has hinges on the side and a handle on the top.