786 



THE CHANGE OF COMPOSTTION OF ALVEOLAR AIR 



AFTER THE STOPPAGE OF NORMAL 



BREATHING. 



By H. S. Halcro Wardlaw, D.Sc, Linnean Macleay 

 Fellow of the Society in Physiology. 



(With two Text-figs.) 



Introduction. 



The tensic)!! of carbon dioxide in the alveolar air of man is 

 maintained, under conditions of rest and normal breathing, at a 

 definite value in each individual, from which it deviates only 

 slightly. The constant values for different individuals vary over 

 a wider ranf^e. These facts were first established bv Haldane 

 and Priestly (1905), and by FitzGerald and Haldane (1905). 

 Campbell, Douglas, and Hobson (1914) have recently shown that 

 an increase of 2 nira.Hg in the alveolar tension of carbon dioxide 

 is sufficient to double the amount of ventilation of the lungs. 

 Under ordinary conditions of rest, then, the amount of air 

 breathed in a given time is so adjusted as to keep the alveolar 

 tension of carbon dioxide practically constant. Haldane and 

 Priestly also showed that the alveolar tensions of oxygen may 

 be varied widely by breathing atmospheres containing different 

 percentages of oxygen, without sensibly affecting the amount of 

 ventilation of the lungs. Within wide limits, therefore, the 

 ventilation of the lungs is regulated solely by the alveolar tension 

 of carbon dioxide, and is independent of the alveolar tension of 

 oxygen. 



When, however, the normal ventilation of the lungs is stopped 

 l)y holding the breath, or by rebreathing the same air, thecaibon 

 dioxide given off by the blood will accumulate in the lungs, while 

 the oxygen present will tend to disappear. The first investiga- 

 tion of the change of composition of the air in the lungs, when 

 the breath is held, seems to be that of Becher (1S55), who held 

 the breath for various periods ranging up to 100 seconds, after 



