Ferrihaemoglobin in Normal Blood 



the total iron of blood with its carbon monoxide capacity, which he 

 called ' oxygen capacity determined by the carbon monoxide method '. 

 He used an accurate volumetric method for his iron determinations 

 and the usual Van Slyke technique, which is well known to give highly 

 reproducible results, for his carbon monoxide estimations. He found 

 that the carbon monoxide capacity of his specimens was usually 

 2-5 per cent less than that calculated on the assumption that the 

 whole of the blood iron was present as ferrohaemoglobin. This not 

 only suggests the inaccuracy of such an assumption, but at the same 

 time imposes a maximum concentration for ferrihaemoglobin, which 

 in any given specimen could not be greater than the discrepancy 

 between the carbon monoxide capacity and the iron content. Other 

 evidence leading to a similar conclusion is contained in the introduction 

 to the paper of Cox and Wendel 5 , who stated that ferrihaemoglobin 

 was not demonstrable spectroscopically (by means of the absorption 

 band of acid ferrihaemoglobin at 631 my.) in normal blood specimens 

 from nearly a dozen species. The method used was devised by 

 Wendel 5 , and will detect ferrihaemoglobin in a mixture with oxy- 

 haemoglobin when the mixture contains only 4 per cent of the former 

 pigment. This again indicates that there cannot be more than 4 per 

 cent ferrihaemoglobin present in the total pigment of normal blood, 

 so that the whole question turns out to be one of rather delicate 

 analysis. In fact, the present author feels that the critical investigation 

 of the analytical methods involved may well prove in the end to be 

 the most important aspect of the whole matter. 



More specific evidence has been provided by making use of the fact 

 that although ferrihaemoglobin does not combine with oxygen or 

 carbon monoxide, reducing agents such as Na 2 S 2 4 or alkaline 

 solutions prepared from TiCl 3 will readily convert it to ferrohaemo- 

 globin, which does combine with these gases. D. D. Van Slyke and 

 A. Hiller 9 described a method for the determination of ferrihaemo- 

 globin as the difference in the carbon monoxide capacities before and 

 after reduction with Na 2 S 2 4 ; some years later this technique was 

 applied by E. Ammundsen 10 to the examination of 82 normal blood 

 specimens, with the interesting result that in 40 per cent of these there 

 appeared to be a significant difference between the two carbon 

 monoxide capacities. Occasionally reduction caused an increase of 

 as much as 2-5 vols CO per cent, or 12-15 per cent of the total pigment, 

 but much more commonly the increase was less, only about 0-5-1 vol 

 per cent. The author discussed the possibility that the difference 

 might be due to the presence of ferrihaemoglobin, but preferred, in 

 the absence of further evidence, to use the phrase ' inactive haemo- 

 globin ', since it was possible that some compounds other than 



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