Lewis Intratracheal Apparatus, an anaesthetic machine from 1931. This is a modified version of the continuous flow anaesthetic machine introduced in 1917 by Dr. Henry Boyle (1875-1941). It has the main elements which are still present in modern machines; providing an accurate and continuous supply of medical gases such as oxygen and nitrous oxide, mixed with an accurate concentration of anaesthetic vapour (such as chloroform and ether), delivered to the patient at a safe pressure and flow. Anaesthesia was delivered via a tube into the trachea (windpipe) of the patient. Gas flow meters and a pressure gauge are visible at the front of the apparatus.