10 



HEMOGLOBIN 



To return from the digression on the pyrrol structure of porphyrin, 

 I had pointed out that the essential difference between haematin and 

 ooporphyrin was the replacement of the FeOH group of the haematin 

 by two hydrogen atoms, and further I had said that the replacement 

 could be effected by the action of certain bacteria, at aU events when 

 blood was used as the starting-point. The usual method, however, of 

 removing the iron from hsemin is by the action of strong sulphuric 

 acid, or better by hydrobromic acid ; in that case the FeCl is replaced 

 not merely by two hydrogen atoms, but two molecules of water 

 are added at the same time. The substance is not ooporphyrin but 

 hsematoporphyrin, C34H38N4O6. The hydration takes place in the 

 two groupings indicated below: 



-CH='CH, 



Put in two molecules of water H.OH and you might get: 



■i-Crfj-CHOH 



but equally if the water went in to the same groupings in another 

 way, the following might be obtained : 



CHOH-CH, 



