326 Comparative Animal Physiology 



Function of Chlorocruorin 

 In a series of papers, Fox^**' "■ ^^ has reported studies of the function of 

 chlorocruorin in the sabellid worms, particularly in Spirographis. The oxygen 

 dissociation curve of this pigment is shifted to the right, with increase in 

 acidity and with a rise in temperature, just as in vertebrate hemoglobin. 

 The ti/2 sat is sufficiently high (27 mm. Hg at pH 7.7 and 20°) that the 

 pigment probably is deoxygenated in the tissues and oxygenated at the gills. 

 The oxygen consumption is reduced by CO over a wide range of oxygen 

 tensions (Fig. 80).^^ A variable fraction of the needed oxygen is supplied 

 by the blood pigments, the remainder is carried in solution. Chlorocruorin 

 is definitely an oxygen carrier functioning normally at high oxygen tensions. 



Function of Hemocyanin 



The blood pigment hemocyanin which occurs in many molluscs and arthro- 

 pods can combine reversibly with oxygen. The higher the hemocyanin content 

 of the blood as measured by the copper content, the greater the oxygen capacity 

 (Table 54). The physiology and biochemistry of hemocyanin have been well 

 summarized by Redfield.-^-^ 



In the cephalopod molluscs it has long been known that hemocyanin func- 

 tions as an oxygen carrier. ^'^ The blood of Octopus has an O2 capacity of 4.2- 

 5.0 volumes per cent,^^^ and Redfield and Goodkind^-^ found the blood of 

 Loligo to have an oxygen capacity of 4.2 volumes per cent. Arterial blood taken 

 from the heart of the squid contained on the average 4.27 volumes per cent 

 of oxygen and 3.82 volumes per cent of COo, whereas venous blood had 0.37 

 volumes per cent of Oo and 8.27 volumes per cent of COo. Thus approximately 

 92 per cent of the oxygen was removed in the course of circulation, approxi- 

 mately three times as much as in man. This high transfer of oxygen to the 

 tissues fails to provide much reserve against hypoxic stress. Similar data on 

 arterial blood in Octopus were obtained by Winterstein.^^^ The color of the 

 blood can be seen to change as it passes through the gills of a squid, so that the 

 oxygenated blood is distinctly blue. In the cephalopods COo and increased 

 acidity shift the oxygen dissociation curve to the right as with hemoglobin 

 (Fig. 8l).^-^' ^*^'^ A rise in temperature also raises the tensions of loading and 

 unloading (Fig. 73). The effect of CO2 upon dissociation of oxyhemocyanin 

 accounts for about one third of the respiratory exchange in the squid. The 

 tsat and ti/2 sat are in a reasonable range for physiological function (Table 

 56), although they are sufficiently high to make the squid sensitive to asphyxi- 

 ation. It is well established, then, that hemocyanin serves as an efficient 

 oxygen carrier in the cephalopod molluscs. 



In the gastropods, crustaceans, and arachnoids, however, evidence for func 

 tion of hemocyanin as an oxygen carrier is less convincing. No specific inhibi- 

 tor, as CO for hemoglobin, is known for hemocyanin. In Limulus the blood 

 always appears reduced (colorless) when the animals are bled, and it contains 

 only as much Oo as sea water does.- When saturated with air the blood ol 

 Limulus, of several crabs, and of Helix takes up only about 2 to 4 times as 

 much oxygen as sea water does (Table 56). The position of the oxygen dis- 

 sociation curve of Helix and Limulus (ti/o sat=6-12 mm. Hg) is within the 

 usual physiological range, but the curve of Homarus blood is far to the right 

 at blood pH (ti/2 sat=90 mm. Hg). 



