FUNCTIONS OF BLOOD 



95 



worms and in chironomids. In fishes, Amphibia, and reptiles 

 the values given are between 5 and 15, while in the warm- 

 blooded animals they are usually between 15 and 20, reaching 

 very high figures, even 40, in the divers. There is an unmis- 

 takable correlation between the call for oxygen of an organism 

 and the oxygen capacity of the blood, but the relations are 

 by no means clear-cut. 



Ojmm 89^ 



20 



25 



30 



35 



Fig. 53. Oxygen dissociation curves of various forms of life at different 

 temperatures. (Barcroft.) 



The affinity of blood or pure haemoglobins for oxygen is a 

 complex phenomenon, depending upon a number of condi- 

 tions, the most important of which are temperature and hydro- 

 gen ion concentration. The affinity is expressed by a dissocia- 

 tion curve or a set of such curves, connecting oxygen tension 

 in the blood with the percentage saturation of the haemoglobin. 



The curves in Fig. 53 illustrate the remarkable difference in 

 the dissociation curves of haemoglobin from different animals, 

 and give also some indication of the temperature effect, and 

 the curves in Fig. 54 illustrate the effect of a change in reac- 

 tion brought about by variations in the C0 2 tension, such as 



