x HEMOGLOBIN 483 



oxygen) Hiifner makes the two assumptions, that carbonic oxide at 

 a tension of about 500 mm. does not saturate haemoglobin to more 

 than about 93 per cent, while at a tension of about 700 mm. the 

 saturation becomes complete. This assumption is inadmissible in 

 view of the work of Haldane and Lorrain Smith, 1 who showed that 

 the affinity of carbonic oxide for haemoglobin is a very powerful one. 

 Haldane continues : " Moreover, as the dissociation-curve of CO- 

 hsemoglobin is undoubtedly a rectangular hyperbola, even if we were 

 to admit that the saturation is a good way from being complete at 

 500 mm. tension of carbonic oxide, we should also have to admit that 

 at 700 mm. the incompleteness of saturation is nearly as great. 

 Hiifner's second assumption is that the coefficient of absorption of 

 carbonic oxide in a 3 or 4 per cent solution of haemoglobin, as deduced 

 from his actual experiments, is incorrect, and that a value about 10 

 per cent lower is correct. The haemoglobin solutions employed by 

 Hiifner were dilute, and consequently the correction needed on 

 .account of the coefficient of absorption of carbonic oxide amounted to 

 .as much as 50 per cent of the result. The hypothetical correction 

 introduced thus makes a considerable difference in the value obtained." 

 Haldane believes that the uncertainty of the determinations of the 

 .oxygen capacity of haemoglobin from electro-photometric observations 

 is the cause of the want of agreement between the results Hiifner 

 .obtained with the ferricyanide method (see next paragraph) and with 

 the spectro-photometer, though possibly there may also have been an 

 .error due to bacterial decomposition of the haemoglobin. 



Determination of the Oxygen Capacity of Mood by Ferricyanide 



Haldane 2 was the first to show that the percentage of oxygen 

 .capable of being taken up in combination with the haemoglobin of 

 blood may readily be determined by chemical means, as the combined 

 .oxygen is liberated rapidly and completely on the addition of a 

 solution of potassium ferricyanide to laked blood, and that the 

 liberated oxygen may easily be measured with an apparatus similar 

 to that used by Dupre 3 for determining urea in urine. In a second 

 paper Haldane 4 gives a full description of the modified Dupr6 

 apparatus used by him in determining the oxygen capacity of blood, 

 .and also precise information as to the treatment of the blood. The 

 result obtained by the ferricyanide method represents only the 



1 J. Haldane and Lorrain Smith, Journ. of Physid. 22. 253 (1898). 



2 John Haldane, ibid. 22. 298 (1898). 



3 Dupre, Journ. Chem. Soc. 1. 534 (1877). 



4 John Haldane, Journ. of Physiol. 25. 295 (1899-1900). 



