318 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



If we do this we obtain the series of curves shown in Fig. 89. These curves 

 are very different one from another, one of the reasons for this being that 

 the number of oxygen-binding groups varies from case to case. The oxygen 

 capacity, i.e. the quantity of oxygen in volumes per cent corresponding to 

 complete saturation of the carrier, in effect regulates the level at which the 

 curve flattens out. In order to compare the different curves with profit, it is 

 necessary to consider in each case, for different partial pressures, not only 

 the amount of oxygen combined with the carrier, but also the degree of 

 saturation of the latter. Thus, in Fig. 90 we have a series of curves whose 

 positions can be related to each other by noting the value of the partial 

 pressure of oxygen corresponding to 50% saturation (p^o)- The position 



Table XIX 



P02 = ± 150 (in air, or in water in equilibrium with air) 



Table XX 



and the shape of the curves in Fig. 89 correspond, in each case, to the 

 temperature and CO2 partial pressure of the arterial blood. In the case of 

 the ray the temperature is 10° and in man 38°. 



The partial pressure of CO2 is 8mm in the frog and 43mm in the case 

 of the Urodel Amphiuma. 



If the curves had been traced at the same^^Q^, and at the same tempera- 

 ture, the ^60 values would not have been those shown in Fig. 90. The 

 particular shape and form which correspond to physiological conditions is 



