RESPIRATION 381 



that even in a complete vacuum the contained oxygen would still 

 have a pressure of 1 30 mm. There would then be no physiological 

 limit to the height attainable. 



The problem of going to very high altitudes with an oxygen 

 apparatus is similar to that of using a self-contained breathing 

 apparatus in mine air which is either intensely poisonous from 

 the presence of CO or H 2 S, or contains little or no oxygen. 

 This problem has been solved successfully, so that teams of 

 miners have worked daily for weeks or months at places a long 

 distance from where there was any oxygen in the air. The same 

 care as is needed and actually taken in the case of the mining 

 apparatus is even more necessary in the case of airmen at great 

 altitudes, but, owing to prevailing ignorance, has not yet been 

 applied. At 36,000 feet, for instance, with the barometric pres- 

 sure at a quarter the normal, an airman breathing pure oxygen 

 would be much nearer danger if, owing to some accident, he took 

 several breaths of the surrounding air, than a miner using a self- 

 contained breathing apparatus would be if he took several breaths 

 of an atmosphere of fire damp. The miner would have in his 

 lungs to start with a pressure of 700 mm. of oxygen, whereas the 

 airman would have only about 90 mm. To the airman at very 

 high altitudes it is therefore specially necessary to have an ap- 

 paratus which is perfect in its action and is used with all the 

 precautions which our existing physiological knowledge shows 

 to be necessary. 



