110 



RESPIRATORY MECHANISMS 



Limulus, but not so far outside these groups. They contain 

 copper and show in the oxidized state a blue colour which 

 disappears on removal of the oxygen. According to Bege- 

 mann (1924) they combine with oxygen in the proportion of 

 1 atom of Cu to 1 of oxygen, while haemoglobin takes up 2 

 atoms of oxygen for each atom of iron. The unit molecular 

 weight is equal to that of haemoglobin, but the actual molecules 

 are very large, containing from 36 to 288 units (Svedberg, 

 1933). Haemocyanin is always present in solution. The 

 oxygen capacities of haemocyanin bloods are never very high, 

 varying from a fraction of 1% in many bivalves, gastropods, 

 and crustaceans to a maximum of 5% in the very active cepha- 

 lopods. The dissociation curves are very similar to those for 

 haemoglobins and almost as variable among themselves, but 

 it would appear that the temperature effect is less pronounced 

 and extremely steep curves, adapted to very low oxygen ten- 

 sions, have not so far been observed. The following table 

 compiled from papers by Winterstein (1909), Wolvekamp 

 (1932, 1938), Redfield, Coolidge, and Hurd (1926), Begemann 

 (1924), Redfield and Ingalls (1933), shows some characteris- 

 tics of haemocyanin-containing bloods. In some respects 



Table 10 

 Respiratory characteristics of h^mocyanin-containing bloods 



these have a definite oecological significance, but others are 

 from this point of view obscure. The very active squids 

 {Loligo) living in the open sea have a high loading tension. 



