ELEMENTARY CHEMICAL PHYSIOLOGY 



249 



If the solution of methsemoglobin be rendered alkaline with 

 ammonia, the colour changes to a more distinct red, and the absorp- 

 tion band in the red disappears and is replaced by a band immedi- 

 ately on the red side of the D-line (Spectrum 15 in Chart). 



By the action of nitric oxide on oxyhsemoglobin, a product is formed called 

 nitric oxide haemoglobin. This is characterised by two bands, which are 

 between the D and E lines ; the band on the red side is somewhat nearer 

 the red end than the corresponding band of oxyhsemoglobin (Spectrum 16). 



12 



13 



FIG. 181. Absorption-spectra. 



12, Methsemoglobin (strong solution) ; 13 and 14, Methsemoglobin (weak solutions) ; 15, 

 Methsempglobin (alkaline solution) ; 16, Nitric oxide haemoglobin ; 17, Mixture of methsemoglobiii 

 and nitric oxide haemoglobin. 



If oxyhsemoglobin be treated with a nitrite, as sodium nitrite or 

 amyl nitrite, 1 there is formed a certain amount of methaemoglobin 

 and a certain amount of nitric oxide haemoglobin . The combination 

 of the two gives a spectrum very similar to simple methaemoglobin 

 (Spectrum 17 in Chart). 



1 Care must be taken to avoid excess of amyl nitrite, or so-called photo- 

 methsemoglobin, characterised by one broad band between D and E, will be 

 formed. 



