RESPIRATION 



379 



the war for instance in the very high flights needed for bombing 

 London. It is of course necessary to use liquid oxygen. Simple 

 liquid air would evidently be quite useless ; but if ordinary liquid 

 air is allowed to evaporate for a sufficient time the nitrogen dis- 

 tills off, leaving a residue very rich in oxygen. It was this residue 

 that was employed by von Schrotter and Berson. 



To improve upon the simple tube hitherto used, von Schrotter 

 strongly recommended the use of a face piece, and figures the 

 first form used. The face piece covers both mouth and nose, and 

 the oxygen passes into it through a tube in a constant stream. 

 This arrangement was introduced for aeroplanes before the war, 

 and is now extensively used. The airman can inspire or expire 

 air freely, but always receives a certain amount of oxygen, and has 

 not to think of his breathing. The amount of oxygen, whether from 

 a steel cylinder or from a Dewar flask of liquid oxygen, can be 

 adjusted according to the height, but it is simpler to arrange for 

 a constant supply which is sufficient, or more than sufficient, up 

 to a certain height. About half the oxygen is wasted, as it reaches 

 the face piece during expiration. This waste can be prevented by 

 an arrangement similar to that already described (Figure 49) in 

 connection with the administration of oxygen to patients. Priest- 

 ley and I found in steel-chamber experiments that with this ar- 

 rangement about I liter a minute (measured at sea-level pressure) 

 was sufficient up to a height of 28,000 feet during rest ; but at least 

 2 liters were needed for such exertions as an aeroplane observer 

 or pilot has to make. With the light steel cylinders or large Dewar 

 flasks now in use the waste of oxygen with the ordinary arrange- 

 ment of mask does not greatly matter, however. 



A height as great as Berson and Siiring reached in a balloon 

 has quite recently (March, 1920) been reported as reached in an 

 aeroplane by Major Schroeder of the American Army Air Service, 

 who, however, also became unconscious, and had a very narrow 

 escape. How it was that the oxygen supply became insufficient in 

 this remarkable ascent has not yet been reported. 



The heights hitherto attained represent by no means the limit 

 which Paul Bert's experiments on animals indicated when pure 

 oxygen is breathed. All that is shown by them is that the oxygen 

 supply was insufficient. At 36,000 feet a man breathing pure 

 oxygen would be quite unaffected by the altitude. The barometric 

 pressure is about 1 80 mm. In the alveolar air there would be a 

 pressure of 47 mm. of aqueous vapor and 40 mm. of CO 2 - Hence 

 (by difference) there would be 93 mm. of oxygen pressure; and in 



