96 RESPIRATION 



siderable capacity for absorbing CO2. Hence it will take some 

 time for the blood to saturate the tissues and lymph up, or de- 

 saturate them down, to a new CO2 pressure. Here we have a 

 second, and very powerful, buffer action, tending to smooth out 

 the influence on the respiratory center and other tissues of all 

 variations of short duration in the CO2 pressure of the arterial 

 blood, and also to prolong the influence of variations of longer 

 duration. 



This subject was investigated by t)ouglas and myself.^^ The 

 following table shows the results we obtained on determining the 

 alveolar CO2 pressure at various times after holding the breath. 

 In order to throw out disturbing eff"ects due to the action of oxy- 

 gen want on the respiratory center, some of the experiments werel 

 made after a few normal breaths of oxygen had been taken, so that 

 there should be plenty of oxygen in the lungs up to the end of the 

 stoppage of respiration. 



Figure 29 is a stethographic tracing of the respirations during 

 an experiment, and shows that the breathing returns gradually 

 to normal after the hyperpnoea following the stoppage. 



The table is extremely instructive, and shows very clearly what 

 a long period of increased breathing, with the alveolar CO2 pres- 

 sure distinctly below normal, is required in order to compensate 



" Douglas and Haldane, Journ of Physiol., XXXVIII, p. 420, 19 19. 



