The imperative necessity of maintaining flyers at the highest possible efficiency was brought home to the aviation authorities through studying the reports of English air-casualties during the first year of the war. The records divided these as follows: 2 per cent were due to the enemy, 8 per cent were due to the plane, and 90 per cent were due to the men, which clearly indicated that something was radically wrong with the personnel and that prompt action was necessary. A thorough study of the situation disclosed the fact that practically all of the flying personnel was suffering from what is known to scientists as oxygen fatigue, caused by flying for many hours a day at high altitudes where there was not enough oxygen to feed the body. As a result of this discovery, Lieutenant-Colonel Dreyer, of the Royal Army Medical Corps, designed an oxygen apparatus for use by the British air forces, the manufacture of which was immediately begun in Paris. So pressing was the need for these apparatus that an automobile was kept waiting at the plant where they were being manufactured to rush each one to the front as soon as it was finished. An original model of this apparatus was brought to the United States shortly after we entered the war, but as it was made entirely by hand, it had to be redesigned to meet our manufacturing conditions. The perfected oxygen equipment, as used in the American Air Service, consists of a small tank, or tanks, according to the amount of oxygen carried, a pressure device, a face-mask covering the mouth and nose, and a tube connecting the mask with the oxygen reservoir. The American mask has combined with it the interphone whereby the pilot and observer can converse with each other while in the air and, in certain cases, the receiver of the radio telephone. In May, 1918, six complete apparatus were sent overseas by special messenger to be tried out under battle conditions, and when the war ended 5,000 had been manufactured and accepted. All American military planes flying at an altitude of over 10,000 feet are now fitted for the installation of oxygen equipment. This includes day-bombing, pursuit, and chase planes, and a percentage of night-bombing and observation machines. So much importance was attached by the military authorities to supplying our flying-men with oxygen that a special oxygen division was organized and sent to France for the purpose of installing the apparatus in the planes. Yet, as I have previously remarked, the flyers themselves persist in regarding the apparatus, probably because of the discomfort involved in wearing it, with amused scepticism. * * * * *