THE GASES OF THE BLOOD 



253 



60 



40 



observations is the influence of the carbon dioxide of the blood on 

 the binding power of haemoglobin for oxygen. It has been shown 

 that the presence of carbon dioxide increases the dissociation ten- 

 sion of oxyhaemoglobin, or, what is a different way of expressing 

 the same thing, diminishes the quantity of oxygen taken up with 

 a given oxygen partial pressure (Bohr, Barcroft, Fig. 121). The 

 influence of salts is also considerable. The form of curve obtained by 

 Hiifner (an equilateral hyperbola, Fig. 119) is only found when the 

 haemoglobin solution is thoroughly freed from salts. But even when 

 allowance is made for all these factors, the discrepancies seem still 

 sufficiently definite to warrant the conclusion, which is also sup- 

 ported by other facts, that the substance in blood with which the 

 oxygen is loosely united, although, of course, intimately related to 

 the haemoglobin which can be 

 artificially prepared from it, is IC 

 yet not absolutely identical with 

 the crystalline product. Some 

 writers for this reason prefer to 

 give the special name haemo- 

 chrome to the native blood-pig- 

 ment as it exists within the 

 unaltered corpuscles, reserving 

 the term haemoglobin for the 

 more or less artificial though, 30 

 perhaps, only slightly altered 20 

 product. Jo 



The Distribution and Condition 

 of the Carbon Dioxide in the 

 Blood. The question is much 

 more complicated than for the 

 oxygen, which is practically con- 

 fined to one of the morphologi- 

 cal elements of the blood (the 

 erythrocytes), and exists in the form of a single compound. Carbon 

 dioxide is distributed over the entire blood in important amounts, 

 and is present is several forms. The serum yields a larger per- 

 centage of carbon dioxide than the clot, but this percentage is not 

 great enough to allow us to assume that the whole of the carbon 

 dioxide is contained in the plasma. Somewhat more than a third 

 of it belongs to the corpuscles. 



As regards the condition of the carbon dioxide, it is known that 

 some of it is simply dissolved in the plasma and corpuscles; but 

 although this fraction, on account of the relatively high coefficient of 

 absorption of the gas (p. 246), is much greater than the corresponding 

 oxygen fraction, it is insignificant in comparison with the quantity 

 chemically combined. Carbon dioxide is united in dissociable 



(0 SO 30 40 50 60 /O 60 90 lOO 



Fig. 121. Dissociation Curves of Blood, 

 with Different Tensions of CO 2 (o, 3, 

 20, 40, and 90 mm.). Ordinates = 

 percentage saturation. Abscissae =* 

 oxygen pressure. (After Barcroft.) 



