RESPIRATION 225 



be as full of pitfalls in practice as the use of the blood pump, 

 aerotonometer, or spectrophotometer. What misled us most were : 

 (i) the assumption that Hiifner's oxyhaemoglobin dissociation 

 curve, then and for many years later quoted in every textbook, 

 was at least approximately correct; (2) the assumption that all 

 haemoglobin is alike as regards its relative affinities for oxygen 

 and CO; (3) ignorance at first of the powerful action of bright 

 light on the dissociation of CO haemoglobin, and of the influence 

 of temperature; (4) failure at first to realize how long it takes 

 to saturate blood or blood solution outside the body with air con- 

 taining low percentages of CO. There were probably also some 

 errors in the colorimetric titrations, owing chiefly to our not taking 

 precautions which subsequent experience showed to be necessary, 

 against decomposition of blood solutions during long experiments. 

 The first experiments were made by Lorrain Smith and my- 

 self 15 on men, the subject of the experiment going through the 

 lengthy process of breathing air containing a definite small per- 

 centage of CO, until absorption of CO ceased, as shown by the 

 analyses of blood samples. The results led us to the conclusion 

 that the normal resting arterial oxygen pressure was considerably 

 above that of the alveolar air; and corrections, made afterwards 

 for the causes of error just referred to caused this conclusion to 

 stand out still more clearly. Subsequent experience leads me to 

 the conclusion that we had become acclimatized more or less to 

 want of oxygen by frequently breathing CO, so that at the time 

 we were no longer ordinary normal subjects. We were at any 

 rate breathing with complete impunity a percentage of CO which 

 would under ordinary circumstances cause very unpleasant symp- 

 toms. On trying the next year and once or twice subsequently to 

 repeat one of the experiments, we were surprised to find that the 

 former percentages were too high for us, and we suspected that 

 there must have been some error about the percentages breathed 

 in the first series of experiments. On reconsidering the matter I 

 cannot see how there could have been an error about the per- 

 centages breathed. It now seems practically certain that we had 

 become acclimatized, and had consequently developed during 

 the experiments a considerably higher arterial oxygen pressure 

 than normal persons would have had, or than we ourselves would 

 have had, if we had not absorbed so much carbon monoxide as in 

 the experiments, and thus become somewhat short of oxygen. 



"Haldane and Lorrain Smith, Journ. of Phystol., XX, p. 497, 1896. 



