REGULATION OF BREATHING 23 



The theory that the breathing is regulated merely 

 by the effects of alternate distention and collapse of 

 the lungs is also quite plainly absurd in view of what 

 is now known about the part played by the carbon 

 dioxide pressure in the alveolar air and arterial blood. 

 The observations of Hering and Breuer and of others 

 who have made experiments along the same lines are 

 none the less significant, however. Mr. Mavrogorato 

 and I have found that the main facts, apart from the 

 effects of section of the vagus nerves, can best be 

 observed and analysed in man. The subject breathes 

 through a wide bored tap which can be opened or 

 closed at any moment ; the nose is clipped ; and a pres- 

 sure-gauge is connected between the mouth and the 

 tap so as to show the inspiratory or expiratory pres- 

 sure. 



When the tap is closed at the end of inspiration it 

 will be noticed on the gauge that there is expiratory 

 pressure, slight at first, but afterwards increasing more 

 and more rapidly, till at last, after an interval occupy- 

 ing the time of several normal respirations, there is a 

 sudden inspiratory effort. The natural tendency of the 

 respiratory centre to discharge alternate inspiratory 

 and expiratory impulses thus breaks through the 

 prolonged expiratory effort. Similarly, if the tap is 

 closed at the end of inspiration there is a prolonged 

 and increasing expiratory effort. If, now, apnoea 

 is produced by forced breathing before the experiment, 

 there is inspiratory or expiratory pressure as before ; 

 but it is a very long time before this pressure begins 

 to increase. On the other hand if air containing CO 2 



