46 RESPIRATION 



the breathing was interrupted by an expiration, repeated after- 

 wards at gradually diminishing intervals. The diminution in 

 these intervals was evidently due to the fact that CO 2 was ac- 

 cumulating in the lungs; and this interpretation is confirmed by 

 Figure 13. 



Figure 14 shows a corresponding effect with a negative pressure 

 applied, so as partially to deflate the lungs. In this case the ap- 

 parent pause was much shorter, as CO 2 began to accumulate very 

 rapidly, owing to the facts that not only had no fresh air been 

 introduced, but the volume of air in the lungs was diminished. 



Figure 14. 



Effects of partial deflation. Crosses show beginning and end of 

 deflation. To read from left to right. Time-marker = i second. 



The supposed apnoeic pause produced by distention or inflation 

 of the lungs is simply a prolonged inspiratory or expiratory effort. 

 This effect is produced regardless of the chemical stimulus to the 

 center. Thus Lorrain Smith and I showed that it is even produced 

 when the lungs are distended with air containing 20 per cent of 

 CO 2 , though the prolongation is much curtailed in such a case. 3 



It is thus clear that the continuance of an inspiratory or ex- 

 piratory discharge of the respiratory center depends on the extent 

 to which actual inspiration or expiration accompanies the dis- 

 charge. If the movements of inspiration or expiration are not 

 accomplished the ordinary respiratory rhythm is replaced by a 

 prolonged and increasingly powerful inspiratory or expiratory 

 discharge, tending to overcome the obstruction. The respiratory 

 center does not act independently of the lung movements, but 

 inspiratory or expiratory discharge of the center goes hand in' 

 hand with actual inspiration or expiration, as if the center were 

 one piece with the lungs. The term "vagus apnoea" is evidently 

 an entire misnomer, as prolonged inspiratory or expiratory effort 

 cannot be called apnoea. The tracings which apparently demon- 

 strate the existence of apnoea are only one-sided, and therefore 

 misleading, records. 



Hering and Breuer found, as already mentioned in Chapter I, 

 that after section of both vagi the association of discharge of the 



1 Haldane and Lorrain Smith, Journ. of Pathology, I, p. 168, 1892. 



