C. RIMINGTON 



a precursor of haematin. It was found to be present in bone marrow, 

 reticulocytes, the developing chicken's egg, etc. 



All experience has gone to show that the organism can readily 

 and rapidly synthesize the porphyrin nucleus of haemoglobin. There 

 is no conservation of its constituents as there is of iron. 



Little information has been gained from the study of excretion 

 products ; in fact, the recognition of two isomeric series of porphyrin 

 derivatives as a result of Fischer's work has only made the problem 

 more difficult. 



All porphyrins may be regarded as derivable from porphin, acid 

 or alkyl groups taking the place of any or all of the 8 hydrogen 

 atoms in the p positions of the pyrrole rings. Fischer's formula for 

 porphin together with a key indicating the constitution of the more 

 important porphyrins is reproduced below. 



1 



H 



1 



H 



HC 



/ 



, H 

 V/NV 



IV 



7 



H 

 C- 



H 



H 



II 

 H 



i,H 



N / 



CH 



III 



JH 



5 



In normal urinary porphyrin both coproporphyrins I and III are 

 present but no haem or natural prosthetic group has been discovered 

 belonging to the I series. All natural ferriprotoporphyrin derivatives 



242 



