RESPIRATION 



75 



tein nature, and contain in organic combination a metal 

 which, however, is not iron but copper. 



There is no doubt that the haemocyanin of molluscs and 

 Crustacea is a reversibly oxidisable pigment. Octopus blood 

 saturated with air was found by Winterstein (1908) to take 

 up 4-5 per cent, of oxygen. The oxygen capacity of the blood 

 of Palinurus was decidedly less — about 1*5 per cent., a differ- 

 ence possibly correlated with the lower haemocyanin content 

 of the blood in Crustacea. The blood of the Arachnid, 

 Limulus, like Crustacean blood contains a bluish pigment 

 which is a colloidal compound of copper, to which the term 

 haemocyanin has also been extended. Alsberg and Clark 

 (19 10-19 14) have, however, stated that the oxygen capacity of 

 the blood of Limulus or of a lo-per-cent. solution of Limulus 

 '' haemocyanin " is not significantly greater than that of sea- 

 water. Their observations have further shown that the com- 

 position of Limulus haemocyanin is not the same as that 

 of the haemocyanin of Octopus as determined by Henze 

 (1904). 



Notable additions have recently been made to our Imow- 

 ledge of haemocyanin as a respiratory pigment through the 

 researches of Dhere (1916-1921), and of Quagliariello (19 10- 

 1923), who have obtained haemocyanin from a number of species 

 in crystalline form. Haemocyanin of cephalopods can be 

 prepared by precipitation with concentrated (NH4)2S04, 

 that of the snail and rock-lobster by crystallisation of the 

 supernatant serum dialysate in ice. Oxy-haemocyanin so pre- 

 pared in crystalline form is a protein, completely precipitated 

 by dialysis, coagulated by heat and alcohol, behaving as an 

 amphoteric electrolyte with a minimal solubility at its 

 isoelectric point (pH. 47 in the case of Octopus). The oxy- 

 haemocyanin of cephalopods crystallises in needles of a greenish- 



