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 

 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 



Fig. 139. Curve to show the degree of variations occurring in the Oa dissociation curve for 



the blood of man in atmospheres containing carbon dioxide in the same percentage as present 



in the alveolar air of the individuals examined. Along the abscissae are given the pressures of 



oxygen in mm. Hg. and along the ordinates the percentage saturation of the blood with oxygen. 



.(From Barcroft's Respiratory Function of the Blood.) 



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 

 same. It differs, for example, for the dog and man. Potassium salts 

 are particularly efficient in causing hemoglobin to absorb 2 . The in- 

 fluence of varying hydrogen-ion concentrations of the solution may 

 be conveniently studied by adding varying percentages of C0 2 to the 

 gas mixture in the tonometers, when it will be found that the curve be- 

 comes lowered in proportion to the amount of C0 2 present. This is shown 

 in Fig. 140. 



