METILEMOGLOBIN 583 



it may easily be seen how contradictory results may enter 

 into the subject at once. 



Importance of the Iron in the Blood Coloring Matter. 

 Before going further the question of the importance of the 

 iron in the coloring matter of the blood may be briefly dis- 

 cussed. In a previous lecture (v. Vol. I of this series, p. 213, 

 Chemistry of the Tissues) it was stated that according to 

 William Krister's investigations iron is present both in 

 haemin and in haematin in the ferric state ; the f erri chloride 

 group, FeCl=, in hsemin and the ferri hydroxide group, 

 FeOH=, in haematin replacing the hydrogen atom in the 

 imido group of pyrrol complexes. The ferri compound, 

 haematin, can be reduced to the ferro compound, haemo- 

 chromogen. It seems, however, that haematin is not a com- 

 ponent of oxyhaemoglobin, but of methaamoglobin, which has 

 all the characters of a ferri compound. According to Kiister 

 the following connections exist : 



Haemoglobin = Globin + Haemochromogen R>Fe 

 Oxyhaemoglobin = Globin + Haemochromogen peroxide 



E>Fe....0 2 

 Methaemoglobin = Globin + Haematin R>Fe OH ; 



and he is unable to recognize any force in Manchot's argu- 

 ments that haemoglobin is a ferri compound. 12 



Methcemoglobin. According to this view, the iron of 

 methaemoglobin 13 is trivalent ferric iron, which is no longer 

 able to loosely fix oxygen and is much more stable than 

 oxyhaemoglobin. The latter has a tendency to become met- 

 haemoglobin, and even in the living blood it is well known 

 that a number of poisons are able to induce this transition. 

 By a reducing agent (as ammonium sulphide or Stokes 7 

 reagent) methaemoglobin can be reconverted into haemoglo- 

 bin. Hiifner succeeded, it may be mentioned in passing, in 



12 W. Kiister, Zeitschr. f. physiol. Chem., 66, 248, 1910; 71, 104, 1911; 

 W. Manchot (Wiirzburg), ibid., 70, 230, 1910. 



18 Literature upon Methaemoglobin : 0. Cohnheim, 1. c., 345-349. 



