PHYSIOLOGICAL ASPECTS OF FLYING 203 



obtained by asking the subject to hold the breath in 

 a similar manner after graduated exercise. By means 

 of the exercise the heart beat is increased in rate, as it 

 is at high altitudes, and from the length of time the 

 breath is held, and from the sensations experienced, 

 an even better idea can be gathered as to the endurance 

 power of the subject at high altitudes. 



By examination of successful aviators it has also 

 been shown that the vital capacity that is, the 

 amount of air which can be taken into the lungs after 

 the fullest expiration and fullest possible inspiration, 

 should be sufficiently large. To test this, a special 

 modification of an ordinary gas-meter may be em- 

 ployed. After having filled the lungs in the manner 

 mentioned above, the subject is asked to expire as 

 deeply as possible through the meter, and the amount 

 of the respiratory capacity is thereby automatically 

 recorded. The average vital capacity of the successful 

 pilot is about 4000 cubic centimetres, and the vital 

 capacity of any flying officer should preferably not 

 fall below 3400 cubic centimetres, whatever his 

 physique. 



This method of measuring the lung capacity is 

 altogether more satisfactory than that of measuring 

 the chest, which may give totally deceptive results. 

 An apparently narrow-chested individual may often 

 have a larger vital capacity than a subject who, to all 

 appearances, has a large chest. 



It is important that the candidate for aviation should 

 have good chest movement, and a firm abdominal wall. 

 Preferably also he should be a deep breather. By 

 slow, deep breathing more air is taken in to the 

 lungs than by more rapid, shallow breathing. 



The importance of a firm abdominal wall for good 

 respiration cannot be overstated. Research in con- 

 nection with successful pilots has shown that those 



