RESPIRATION 79 



oxygen capacity of Arenicolan blood. Bounhiol (1902) found 

 that the polychaetes with haemoglobin have a more active gas 

 exchange than those without haemoglobin. It cannot be 

 stated as yet with confidence that chlorocruorin performs an 

 essential role in the life of the worm ; for the blood circula- 

 tion is poorly developed and there appears no danger of oxygen 

 deficiency in the water in the life of Spirographis under normal 

 conditions. It is interesting to note that the earthworm will 

 survive perfectly well after all its haemoglobin has been con- 

 verted into carboxy -haemoglobin so that the blood pigment can 

 no longer function as a vehicle for the transport or a means for 

 storing oxygen. Chlorocruorin in many respects resembles the 

 haemoglobins. It forms a compound with carbon monoxide. 

 The oxidised form is reduced by potassium ferricyanide. It 

 acts as a peroxidase. It is possible to prepare a parallel series 

 of derivatives of chlorocruorin analogous to met-haemoglobin, 

 haematoporphyrin, haemochromogen, etc. 



Finally, mention must be made of a pigment allied to 

 haemoglobin in the liver of the crayfish and the gut of all 

 pulmonates except Planorbis, a genus in which haemoglobin 

 itself occurs in the blood. Helicoruhin, as this pigment is 

 called, has been investigated by Anson and Mursky (1925), 

 who find that it combines loosely with oxygen, its affinity for 

 the latter being increased, not as in the case of haemoglobin 

 decreased, by the acidity of the medium. These authors have 

 put forward a rather different view of the biochemical and 

 phyletic relationship of the haemoglobins from that hitherto 

 accepted and indicated earlier in this chapter. They regard 

 haemochromogen and its oxidised form haematin as themselves 

 conjugated proteins of which haemoglobin and oxyhaemoglobin 

 are respectively polymers. To the iron-pyrrol part of the 

 molecule Anson and Mirsky apply the term hcern. Haemo- 

 chromogen is a compound of haem and a nitrogenous sub- 

 stance, protein or otherwise. The haems of different haemo- 

 globins and of helicorubin are identical ; the specificity of the 

 haemoglobins depends on the nature of the conjugate globin 

 or the degree of polymerisation of the haemochromogen. The 

 separation of haem from its conjugate protein (or other 



