228 RESPIRATION 



We then repeated the old experiments with oxygen which had 

 disappointed Lorrain Smith and me so much. The results were 

 as follows: 



It will be seen that as long as the saturation of the blood with 

 CO did not exceed about 60 per cent, the arterial oxygen pressure 

 was about 7 per cent below that of the inspired air, just as the 

 alveolar oxygen pressure would be. With over 60 per cent satura- 

 tion, however, the animals began to suffer from oxygen want, 

 and the arterial oxygen pressure went just as high above that of 

 the inspired air as in animals breathing ordinary atmospheric 

 air. The old experiments were wrongly calculated, because the 

 relative affinities of haemoglobin for oxygen and CO are on an 

 average different in mouse blood from what they are in human 

 blood or in the ox blood which we then took as a fixed standard. 

 This led us to calculate the arterial oxygen pressure about 50 per 

 cent too high in both the ''normal" and the oxygen experiments. 

 Moreover the "normal" experiments were not normal, since the 

 percentage saturations of the blood were about 40 per cent, and 

 therefore too high to give normal results such as those of the first 

 five experiments in the previous table. If one recalculates the 

 average results of the old experiments in the light of this new 

 knowledge they give just the same result as the new experiments. 



The general, and absolutely sharp and definite, result of these 

 experiments is that with very low percentages of CO there was 

 no evidence of active secretion of oxygen inwards, but that with 

 higher percentages of CO there was perfectly clear evidence of 

 active secretion. This active secretion began to show itself as soon 

 as the CO percentage was sufficient to cause symptoms of CO 

 poisoning, which symptoms, as shown in Chapter VII, are simply 



