230 H^MOCYANIK 



oxygen which is displaced from a given weight of methsemoglobin 

 when it is treated with nitric oxide. 1 We may probably say, 

 therefore, that under certain conditions, without our being able 

 to state exactly what has taken place, the oxygen loosely united 

 to hemoglobin as oxy-hsemoglobin becomes more stably combined, 

 and is now not removable by either a vacuum, or carbon-monoxide, 

 or a current of hydrogen, and further that the resulting substance 

 (methpemoglobin) has the same composition and crystalline forms 

 as oxy-haemoglobin, and may be reconverted into the latter body 

 by suitable means, such as reduction by ammonium sulphide and 

 subsequent oxidation. 



7. Hsemocyanin. 2 As previously stated (p. 217) the blood- 

 plasma of many invertebrates contains haemoglobin in solution ; 

 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 hsemocyanin has been given. Hence the 

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

 venous is colourless. 



Hcemocyanin is a proteid of the globulin class ; it is therefore 

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

 tion of its solutions with sorh'nm p.h1nr[rjp and completely by satu- 

 ration with magnesium sulphate. 3 Unlike haemoglobin it has not 

 yet been crystallised ajid contains copper, presumably as a con- 

 stituent of its molecule, in place of the iron characteristic ^f 

 haemoglobin. 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. 4 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 hasmocyanin in its general properties, and is only men- 

 tioned here because it contains copper, as does the former pigment. 

 It is slightly soluble in water, readily soluble in dilute alkalis, the 

 solutions in either of these solvents showing two absorption bands be- 

 tween D and E very similar to, though not identical with, the bands 

 of oxy-haenioglobin and a third faint broad band at F. It is not how- 

 ever a respiratory pigment. 



1 Hiifner u. Kiilz, Zt.f. phi/siol. Chem. Bd. vn. (1883), S. 366. 



2 For literature see' Halliburton, Chem. Phi/sioi. and Pathol. 1891, p. 321. 

 Details of previous work to date (1880) are given by Krukenberg, Vergleich.-physiol. 

 Studien, in. Abth. (1881), S. 66. 



3 Halliburtou, ,//. of Phi/siol. Vol. vi. (1884), p. 319. 



* Church, Phil. Trans. Vol. CLIX. (1870), p. 627. Cf. Ber. d. d. chem. Gesell. Bd. IT. 

 (1869), S. 314; in. (1870), S. 459. See later Krukenberg, Veryl.-pht/siol. Stud. 

 v. Abth. (1881), S. 72; 2 Reihe, i. Abth. (1881), S. 151. The same work (2 Reihe, 

 Abth. n. n. in. 1882, Sn. 1 u. 128) contains elaborate observations on other pigments 

 from feathers. 



