FUNCTIONS OF BLOOD 



91 



Such a calculation is valid only if the balance of acids and 

 bases remains the same during the circulation cycle, and in 

 many cases, probably in a majority, this condition does not 

 hold. The failure may be due to actual variations in the 

 content of ions, but the normal reason, at least in vertebrates, 

 is a shift in the reaction of 

 haemoglobin by its combina- 

 tion with oxygen. Oxy- 

 haemoglobin is definitely 

 more acid than reduced 

 haemoglobin and at the same 

 tension arterial blood there- 

 fore contains less CO2 than 

 venous. The difference for 

 man — or rather for the sub- 

 ject J.S.H. — is illustrated in 

 the curves Fig. 52. The 

 thick line represents the act- 

 ual curve along which the 

 change in CO2 takes place, 

 provided the oxygen re- 

 moved by metabolism is re- 

 placed with 0.8 volumes of 

 CO2. A steep curve means 

 a reduced difference in 



tension between venous and arterial blood, and facilitates, as 

 Haldane points out, the regulation of the blood Ph. 



It does not seem possible at present to correlate in detail 

 the C0 2 absorption curves determined for many different 

 animals with the corresponding oecological conditions. 



Generally speaking, gill-breathing, and particularly marine, 

 animals are exposed to media with a very low CO2 tension of 

 at most a few mm, while the tension in lungs is much higher, 

 ranging up to 50 mm. The former utilize a portion of the 

 curve which is normally quite steep, and they can have low 

 total capacities, as pointed out by Winterstein (1909), and a 

 low content of protein or other weak acids. 



30 40 50 60 70 80 90 



PPESSUK of CO, in MM. H<j 



Fig. 52. C0 2 dissociation curves. 

 Upper curve blood of J. S. H. in pres- 

 ence of hydrogen and C0 2 . Middle 

 curve blood of J. S. H. in presence of air 

 and GO,. Lower curve blood of ox in 

 presence of air and C0 2 . Line AB 

 curve of actual dissociation within the 

 body of J. S. H. (Haldane.) 



