398 



THE RESPIRATION 



lung alveoli (100 mm.) the blood becomes nearly saturated with 2 , 

 whereas at pressures below 50 mm. it readily loses 2 , so that at 10 mm! 

 there is nearly complete reduction. 



The question is: What are the environmental conditions under which 

 the hemoglobin in the blood so alters its combining power for 2 as to 

 produce such a difference in the dissociation curve? By experimenting 

 with hemoglobin solutions, three such factors have been found to come 



>00 



90 



80 



70 



60 



50 



40 



30 



20 



10 



100 



10 20 30 40 50 60 70 80 i 



Fig. 139. Dissociation curves of hemoglobin. 



; Ordinates Percentage saturation of hemoglobin. 

 Abscissa Tension of oxygen in mm. of mercury. 



I. Dissociation curve of hemoglobin dissolved in water. 



II. Dissociation curve of hemoglobin dissolved in 7% NaCl. 



III. Dissociation curve of hemoglobin dissolved in 9% KC1 

 Temperature 37-38 C. (From Joseph Barcroft.) 



into play: (1) the presence of inorganic salts, (2) the hydrogen-ion con- 

 centration (C0 2 tension) of the solution, and (3) the temperature. If 

 hemoglobin is dissolved in water containing the various salts of plasma 

 in the same proportion as in blood (artificial plasma), the dissociation 

 curve will be found to change so as to resemble that of blood (Fig. 139). 

 Since the plasmas of different animals contain different proportions of 

 salts, the artificial plasma required to secure the result is not always the 



