x METELfiMOGLQBIN 493 



able in this reaction doubtless passes into the haemoglobin molecule. 

 The whole process may be provisionally represented by the following 

 equation when ferricyanide is acting on reduced haemoglobin : 



Hb + 4Na 3 (Cy 6 Fe) + 4NaHC0 3 = Hb0 2 + 4Na 4 (Cy 6 Fe) + 4C0 2 + 2H,0. 



In this equation the symbol Hb0 2 represents methaemoglobin. When 

 the ferricyanide is acting on cxyhaemoglobin, the following equation 

 represents the supposed process : 



Hb/^ + 4Na 3 (Cy 6 Fe) + 4NaHC0 3 = 

 X 



0, + Hbf + 4Na 4 (Cy 6 Fe) + 4C0 + 2R,O. 

 X 



/ ^ 



In this case Hb/ represents oxyhaemoglobin, and Hbf met- 



X X 



haemoglobin. The reason for employing these different symbols is 

 that there are some grounds for believing that in oxy haemoglobin 

 the oxygen atoms are united together, whereas in methaemoglobin 

 this is probably not the case (see also p. 483). 



The conversion of oxyhaemoglobin into methaemoglobin by 

 indifferent media or simply by the ' time-factor ' might be explained 

 through the migration of hydrogen atoms, analogous to the transition 

 of a ketone into an enole modification, as described by Briihl. 1 The 

 increasedly acid character of methaemoglobin agrees well with this 

 conception, as pointed out by v. Zeynek. 



By reducing agents, and especially by ammonium sulphide and 

 Stokes' reagent, methaemoglobin is converted far more readily than is 

 oxyhaemoglobin 2 into reduced haemoglobin, and the latter is changed 

 instantly into oxyhaemoglobin, provided free oxygen is present, but 

 not otherwise, as Haldane has shown. 3 



The peculiar action of another reducing agent, namely, nitric 

 oxide, on methaemoglobin has been studied by Hiifner and Kiilz, 4 who 

 found that, although methaemoglobin does not yield oxygen to the 

 blood-pump (Gamgee), it parts with exactly the same amount of 

 oxygen as does oxyhaemoglobin when subjected to NO, and that 

 therefore both methaemoglobin and oxyhaemoglobin must contain the 

 same amount of readily dissociable oxygen. 



1 J. W. Briihl, Zeitschr. f. physiol. diem. 30. 1 (1899). 



2 J. Haldane, Journal of Physiol. 22. 298 (1898). 



3 J. Haldane, ibid. 22. 302 (1898). 



4 Hiifner and Kiilz, Zeit. f. physiol. Chem. 7. 366 (1883). 



