THE PHYSIOLOGY OF MUSCULAR WORK 239 



may be shown by the following examples from experiments upon 

 three healthy men : 



The causes of hyperpno3a and dyspnoea have been the subject 

 of many experiments and much controversy, and even at the 

 present time it is impossible to maintain that the question is closed. 

 It is generally admitted that the work of Haldane and Priestley ( M ) 

 has shown that the factor which regulates the respiratory move- 

 ments during rest is the pressure of the carbon dioxide in the 

 blood, as gauged by the pressure of that gas in the pulmonary 

 alveoli. The rate of breathing may be altered, but the subject 

 of the experiment will also change the depth, so that the mean 

 pressure of the carbon dioxide remains almost the same, as shown 

 by the following results obtained by these authors : 



During muscular work Haldane and Priestley found that there 

 was a slight but distinct rise in the percentage of carbon dioxide 

 in the alveolar air. Their results are given in the next table. 



