532 THE RESPIRATORY EXCHANGE 



to contain a mixture of different haemoglobins, which vary not only 

 in different animals, but even in the arterial and venous blood of 

 the same individual. 



^^ There remains considerable doubt about the validity of these 

 views. Hiifner maintains that in ox-blood there is only one 

 kind of haemoglobin, 1 grm. of which absorbs about T34 c.c. of 

 carbon monoxide or oxygen measured at and 760 mm. This 

 contention is supported by the following considerations. The 

 haemoglobin of ox-blood contains 0*336 per cent, of iron, and its 

 molecular weight, on the assumption that one molecule contains 

 one atom of iron, would be 16,669 ; its capacity to combine with 

 oxygen appears to depend upon the iron, one atom of which holds 

 two atoms of oxygen, and calculated from the percentage of iron 

 this value should be 1'34 c.c. of oxygen absorbed by 1 grm. 

 of haemoglobin. Direct experiments by Hiifner gave an average 

 of T26 c.c. of carbon monoxide per grm. of haemoglobin, a 

 figure which became 1'34 c.c. when it was corrected for incom- 

 plete saturation and for the coefficient of absorption of carbon 

 monoxide. This figure has been generally accepted by physio- 

 logists, but recently Haldane has raised doubts about its correct- 

 ness ; he points out that the results of Hiifner' s individual 

 experiments vary by as much as 10 per cent, from one another, 

 and the corrections applied are hypothetical. Further experi- 

 ments must decide the question. The general percentage of iron 

 in the blood of different warm-blooded animals is 0-335 per cent. 

 Further, the amount of haemoglobin in human blood is about 

 14 per cent., and if 1 grm. can absorb T34 c.c. of oxygen, it follows 

 that the amount of oxygen combined in arterial blood should be 

 about 19 volumes per cent., a figure which agrees well with the 

 results of actual experiments. 



The foregoing remarks show that it is possible to give another 

 interpretation to the question of " specific oxygen capacities." 

 They may depend not upon different kinds of haemoglobin, but 

 upon mixtures of pure and partly decomposed haemoglobin, for it 

 has been shown by various observers that the use of alcohol in 

 the preparation of the crystals will affect their absorptive power 

 for oxygen ; it may be that methaemoglobin, haematin, and haemo- 

 chromogen are present as impurities. 



The Carbon Dioxide in Blood. The conditions under which 

 carbon dioxide is present in blood are even more complex than 



