[macleod-page] oxygen UNSATURATION OF BLOOD 53 



it must depend on the appearance by incompletely oxidised acid 

 substances in the tissues and blood and that these stimulate the 

 respiratory centre by raising the H-ion concentration of the blood. 

 To test this hypothesis it will be necessary to make very careful 

 measurement of the H-ion concentration of the blood at various 

 stages in anoxaemia. 



It will be observed that it is only about in one half of the animals 

 that increased breathing became developed during the later stages of 

 anoxaemia, and that in the others (Group I) the opposite occurred, 

 namely, a gradual decline. This decline in breathing was associated 

 with a decided decrease in the saturation of the blood with oxygen 

 and we believe that a gradual failure of the respiratory centre is 

 responsible for the result. It is significant that the animals of this 

 group did not recover from the anoxaemia, after being allowed to 

 breathe outside air, nearly so well as those of Group II. In No. 49 

 the breathing became very slow and the blood remained unsaturated 

 in one half hour after the anoxaemia; in No. 43 marked Traube- 

 Hering waves developed on the blood pressure tracing and the breath- 

 ing became markedly periodic; and in 42 the respirations suddenly 

 ceased shortly after disconnecting the animal. 



References 



1. Fraser, Lang and Macleod — Amer. Jour. Physiol., 1921, Iv, 159. 



2. Douglas, Haldane, Henderson and Schneider — Phil. Trans. Roy. 



Soc, 1912, ciii, B. 



3. Macleod, J. J. R.— Trans. Roy. Soc. Canada, 1919. 



