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RESPIRATION 



several factors contribute to modify considerably the 

 combination of hsemoglobin with oxygen. These we shall 

 now consider. 



Factors Influencing the Dissociation of Oxyhsemoglobin 



A. Inorganic Salts. — When the curves of dissociation of 

 pure haemoglobin and of blood are compared (Fig. 21), a 



100 



20 



30 



40 oO CO 70 00 £50 100 



Fig. 21. — The dissociation curves of haemoglobin (H) and of Blood (B). 

 Ordinates; percentage saturation of haemoglobin ; abscissae: pres- 

 sure of oxygen in mm. (From Barcroft, The Respiratory Functions 

 of the Blood.) 



great difference is noted between them. While the former 

 is rectangular the latter is more complex, the two differing 

 in such a manner that at low oxygen tension dissociation 

 takes place more easily from blood than from haemoglobin, 

 while at high oxygen tension more oxygen is in combination 

 with the blood than with haemoglobin. This means that 

 the oxygen-carrying power of the blood from a place of 



