8 HEMOGLOBIN 



certain bacteria, and so, naturally, the question arises: What is the 

 relation between ooporphyrin and the simplest crystalline product 

 of the haematin family — haemin for instance? So far as their em- 

 pirical formulae are concerned the relationship would be as follows : 



Ooporphyrin C34H30N4O4 . Hg 



Haemin C34H3oN404FeCl 



Haematin C34H3oN404FeOH. 



Here let me make a short digression to point out the essential nature 

 of these formulae. Written as graphic formulae they, at first sight, 

 look almost as alarming as the modem "cross-word puzzle." Yet a 

 moment's consideration will show that in their main features they 

 are easily grasped. 



The fundamental grouping of atoms on which the whole pivots is 

 the pyrrol ring, consisting of four carbon atoms and one nitrogen 

 atom joined together in the form of a five -pointed figure 



H-c 



-C-H 



I I pyrrol itself being ^_^ ^.^ 



The above is written in an abbreviated form 



NH 



It is when two such rings are joined together in the following way 

 that the molecule takes on the first vestige of porphyrin character: 



