RESPIRATION BEYOND THE LUNGS 



399 



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

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

 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 



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.) 



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- 

 gas apparatus. To obtain the rate of oxidation, a mixture of N 2 or H 2 

 and 2 is bubbled through the blood with the partial pressure of the 

 2 the same as that which obtains in alveolar air namely, about 95-100 

 mm. Hg; and to obtain the rate of reduction pure N 2 or H 2 gas is bub- 

 bled through. 



The rates of reduction or of oxidation as thus determined are then 

 plotted in curves constructed with the percentage saturation of the 

 hemoglobin on the ordinates and the time in minutes along the abscissae 

 (Fig. 141). Even if we use blood in this experiment and therefore make 



