386 



THE RESPIRATION 



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. 



The effect of temperature on the dissociation curve is twofold: (1) on 

 the rate with which equilibrium is established at the given partial pres- 



10 20 30 40 00 CO 70 80 90 100 



Fig. 140 Dissociation curves of human blood, exposed to 0, 3, 20, 40 and 90 mm. CO 2 . Ordinate, 

 percentage saturation. Abscissa, oxygen pressure. (From Joseph Barcroft.) 



sure of 2 , and (2) on the position of the curve; the lower the tempera- 

 ture, the higher the curve. 



The Rate of Dissociation. Though it is now clear that the three con- 

 ditions namely, saline content, C H , and temperature are capable of 

 altering the dissociation curve of a pure hemoglobin solution so as to 

 make it correspond with that of blood, this does not entirely solve our 

 problem, for we have yet to show how the cooperation of these forces 

 renders it possible for the rate at which hemoglobin takes up 2 in 

 the lungs to correspond exactly with that at which it gives up its 2 

 to the tissues. To study this problem a somewhat different kind of 

 experiment must be undertaken. The hemoglobin solution is placed in 

 a tube and the gas mixture slowly bubbled through it, samples of the 

 solution being removed at intervals for analysis in the differential blood- 



