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COMPARATIVE PHYSIOLOGY 



practically a linear function of the partial pressure for all 

 values of the latter, and the carbon dioxide capacity of the 

 blood is not greater than that of sea-water. In the case of 

 the tunicate that of the whole blood is rather less ; but the 

 capacity of the plasma is somewhat higher than that of the 

 whole blood, and the difference is probably correlated with 

 the distinctly acid reaction of the corpuscles which, according 

 to Henze, may contain as much as 3 per cent, free sulphuric 

 acid. In marked contrast with the carbon dioxide capacity 

 of these comparatively inactive forms are the curves derived 



50 60 70 



Fig. 22. 



from the blood of the crustacean and cephalopod (Fig. 22). 

 Here the uptake of CO2 by the blood increases steeply up to a 

 tension of about 15 mm. Hg ; and within this Hmit the reaction 

 remains well on the alkaline side of neutrality. The steep 

 portion of the curve is much less protracted than in the 

 mammal ; but according to Parsons and Parsons there is never 

 more than about 3-10 c.c. of COo per 100 c.c. of blood in these 

 animals as against 50 c.c. in 100 c.c. of mammalian arterial 

 blood. The more stable reaction and greater carbon dioxide 

 capacity of the blood in the crustacean and cephalopod as 

 contrasted with the condition in Aplysia is that the blood of 

 the former is rich in haemocyanin and other proteins. The 



