RESPIRATION 27 



ventilation of the lungs is not affected by ordinary interruptions. 

 This is strikingly shown by experiments which we made on the 

 effects of voluntarily varying the frequency of breathing. 



The frequency of breathing varies considerably among normal 

 individuals, or in the same individual at different times ; and it is 

 easy to vary the frequency while leaving the depth of breathing 

 to regulate itself in a natural manner. On making experiments of 

 this kind Priestley and I found the following percentages of CO 2 

 in the alveolar air : 



In a recent series, made on myself ten years later, 11 the fre- 

 quency was varied within much wider limits, with the following 

 results : 



It will be seen that in spite of variations from 3 to 36 per minute 

 in the frequency of breathing the alveolar CO 2 percentage re- 



"Haldane, Amer. Journ. of PhysioL, XXXVIII, p. 20, 1915. 



