1296 JLEMOCHROMOGEK 



in a few cases this is united to special corpuscles in the blood. 

 But in the case of other invertebrates this respiratory pigment 

 is replaced by another to which, since it turns blue on exposure 

 to air (oxygen), the name hiemocyanin has been given. Hence 

 the arterial blood of those animals in which it occurs is blue, 

 while the venous is colourless. 



Haemocyanin is a proteid of the globulin class ; it is there- 

 fore partially precipitated by a current of carbon-dioxide, by 

 saturation of its solutions with sodium chloride and completely 

 by saturation with magnesium sulphate. Unlike haemoglobin 

 it has not yet been crystallized, and contains copper, presumably 

 as a constituent of its molecule, in place of the iron character- 

 istic of hemoglobin. It exhibits no absorption bands when 

 examined spectroscopically. 



Another animal pigment is known, into whose composition copper 

 (5 8 p.c.) enters ; this .is the substance called turacin. It gives the 

 characteristic colour to the plumage of certain African birds known 

 as Touracos or Plantain-eaters, whence the name turacin. It differs 

 entirely from hsemocyanin in its general properties, and is only 

 mentioned here because it contains copper, as does the former pig- 

 ment. It is slightly soluble in water, readily soluble in dilute 

 alkalis, the solutions in either of these solvents shewing two absorp- 

 tion bands between D and E very similar to, though not identical 

 with, the bands of oxy-hsemoglobin and a third faint broad band at 

 F. It is not however a respiratory pigment. 



8. Haemochromogen. C 34 H 36 N 4 FeO 5 (?). 



When (reduced) haemoglobin is treated with acids, or, better 

 still, with alkalis in the entire absence of oxygen it is decom- 

 posed into a proteid and a coloured substance to which the name 

 haemochromogen is given. When alkalis are used in its prep- 

 aration the solution obtained is of a brilliant purplish-red colour 

 and is characterized by two marked absorption bands, the 

 stronger lying halfway between D and E, the other and fainter 

 between E and b. These are identical with the bands of 

 Stokes' reduced haematin in alkaline solution (see Fig. 90, 

 No. 3). When exposed to the air (oxygen) the solution rap- 

 idly loses its brilliant colour, becomes dichroic, viz. red in thick 

 and greenish in thin layers and now yields an absorption spec- 

 trum which exhibits one not very strongly marked band in the 

 yellow, to the red side of D and touching the latter line. This 

 is the spectrum of haematin in an alkaline solution (see Fig. 90, 

 Nos. 1 and 2). When the decomposition of the haemoglobin is 

 brought about by acids instead of alkalis, the coloured product 

 is similarly hsemochromogen, but in this case unless special 

 precautions are taken some of the haemochromogen is itself 

 further decomposed and yields lucmatoporphyrin or iron-free 



