This historical survey in two parts analyses the history of inhalative oxygen therapy and its interactions with the history of anaesthesiology. For this purpose, we will start with illustrating "the long way of oxygen" from its first isolation by Carl Wilhelm Scheele (1772) and Joseph Priestley (1774) to its breakthrough for therapeutic application in the 20th century. We will show that the two main factors delaying the successful implementation of a truely rational oxygen therapy were of technical nature: The complicated and costly production of the gas and insufficient means to apply it continuously and with reliable and sufficient dosages to the patients. Both problems could not be satisfactorily solved until 1902. From this year on, however, the "Linde Process" allowed cheap mass-production of oxygen. Simultaneously, various inventions of modern pressure gas technology allowed to solve the application problems. Here, a special significance is to be awarded to pressure reducing valves. These were first introduced into medical technology by Draeger Inc. (Lijbeck/Germany) on a significant scale, proving particularly successful in anaesthesia and rescue-devices (e.g. in the "Roth-Draeger Anaesthesia Apparatus" [1902]). Critically discussing earlier research on the history of oxygen therapy, we therefore propose a historical reassessment, accepting the year 1902 as the internationally decisive "turning point" towards the development of modern oxygen therapy.
