x CN-HJEMOGLOBIN 505 



Cyan-methsemoglobin or CNHb 



Robert 1 showed that a substance which he calls cyan-methsemo- 

 globin is formed by acting with hydrocyanic acid or one of its salts 

 on a solution of methsemoglobin. In doing so the brown solution of 

 methsemoglobin is changed into a bright -red colour with a distinct 

 yellow tinge specially well seen in thin layers. 



Haldane 2 has shown that cyan-methaemoglobin is identical with 

 Bock's 3 photo-methsemoglobin. The formation of the latter is not 

 directly due to the action of light on methsemoglobin but to the 

 action on methsemoglobin of hydrocyanic acid liberated in consequence 

 of the decomposition, by the action of light, of ferricyanide present 

 in the methsemoglobin, for photo-methsemoglobin is only obtained from 

 methsemoglobin in the preparation of which ferricyanide has been 

 used, as, notwithstanding repeated crystallisation, ferricyanide cannot 

 be got rid off. The HCN liberated by the action of light acts on 

 methsemoglobin. It does not displace the oxygen of the latter but 

 becomes linked on to some other radical of the haemoglobin or hsemo- 

 chromogen molecule. When the oxygen is taken out of the cyan- 

 methsemoglobin molecule, the CN" is eliminated also, but not so if 

 the oxygen is taken out of the cyanhsematin molecule. If blood 

 solution, to which ferricyanide has been added, be allowed to stand 

 for two or three days, cyan-methsemoglobin is formed in consequence, 

 perhaps, of putrefactive changes leading to decomposition of the ferri- 

 cyanide. Amylnitrite added in excess may also give rise to the CN- 

 hsemoglobin spectrum on account, doubtless, of the presence of traces 

 of HCN in the reagent. 



Hoppe-Seyler's cyanhsematin is not identical with cyan-methsemo- 

 globin, as asserted by Szigeti. 4 



Cyanhsematin, according to Haldane. is formed by adding an 

 excess of cyanide to an alkaline solution of hsematin. Its spectrum 

 is narrower and less diffuse than that of cyan-methsemoglobin. On 

 the addition of ammonium sulphide to cyanhsematin the spectrum is 

 changed immediately as the single band is replaced by two bands, 

 resembling those of oxyhsemoglobin as regards position and relative 

 breadth, but the two bands are not so well separated as in oxyhsemo- 

 globin, and they are also slightly nearer the violet end of the spectrum. 



1 R. Robert, Cyanmethamoglobin und der Nachweis der Blausiiure, Stuttgart, 1891 ; 

 Pflilger's Arch. 82. 603 (1900). 



2 J. Haldane, Journ. of Physiol. 25. 230 (1900) ; see also R. v. Zeynek, Zeitschr. 

 f. physiol. Chem. 33. 426 (1901). 



3 J. Bock, Skandmav. Arch. f. Physiol. 6. 229 (1895). 



4 Szigeti, Malys Jahresb. 1893, p. 620. 



