PORPHYRINS 

 Let us double once more and we obtain^ 



(Hans Fischer.) 



This is clearly the skeleton, so to speak, to which the soft parts in the 

 way of side chains are attached. On this skeleton are built up not only 

 all the porphyrins but so far as is known all vertebrate blood pigments. 

 Let us fill in the "soft parts." 



CH=CH, 



HOOC-CHrCH, 



This probably represents the brown pigment of the egg-shell: its 

 relation to the blood pigments is a matter of exchanging for two 

 hydrogens the group FeOH thus: 



CH=CH, 



HOOC-CH-CH 



which is hsematin, or by FeCl which gives haemin. 



^ Kuster had published an alternative linkage of the four pyrrols which Fischer, 

 since the above went to press, has adopted. [Berichte Jahrg. LX. Seite 2611, 1927.] 



