204 BIOLOGICAL PROBLEMS 



who wear well have good expiratory force. From the 

 examination of successful pilots a standard expiratory 

 force has been fixed, namely, the height to which 

 a column of mercury can be blown. When flying 

 stress is supervening the power to blow up a column 

 of mercury is decreased. 



A variant of this test is to note the length of time 

 during which a definite pressure of mercury can be 

 sustained with the breath held. If necessary, the 

 behaviour of the pulse may also be watched, and, 

 from the nature of the response, valuable information 

 is obtained as to the condition of the subject under 

 examination. 



Soundness of heart is as essential as soundness of 

 wind. Over and above evidence of soundness by the 

 ordinary clinical examination, proof is obained that it 

 will respond efficiently to work. In flying, the heart 

 will have increased work thrown upon it, sometimes 

 in a much rarefied atmosphere, and the quicker the 

 heart beats, even at ground-level, the more oxygen 

 it requires. 



Under stress of work at ground-level the heart-beat 

 rises frequently to 100, but at great heights the rate is 

 often considerably more than this, which means that 

 under these circumstances an increased oxygen supply 

 is necessary, with a lessened supply available. For 

 this reason alone it is very important that the heart 

 should be sound. 



At the entrance examination for pilots for the Air 

 Force, therefore, a test is employed which has been 

 standardized by the examination of successful pilots. 

 This consists in raising the body on to a chair five 

 times in fifteen seconds. The standard increase of 

 pulse rate which takes place in good pilots is known, 

 and the time of the return to normal is also known, 

 and, from the figures obtained, an idea as to whether 



