INADEQUACIES OF PRESENT NOMENCLATURE 



103 



cyclic formulas. In the bile pigments containing methene groups, 

 the double bond linking the carbon to the pyrrolic ring places the 

 methene hydrogen in the trans position to the pyrrole nitrogen : 



\\' 



H 



not in the cis position: 



H 



as the linear formulas suggest {168 Jf). The true linear formula for 

 bilirubin would thus be formula I rather than formula II in Figure 8. 



HO 



M 



M 



*-- ■KJ (^ VT L 



H H H. Ji H 



(I) 



M 



M 



P M M V 



TT^ /^ ApA A^A ApA A\ 



HO^ N 9. N k N h N OH 



H 



H 



H. 



(II) 



H 



H 



Fig. 8. Linear formulas of bilirubin. 



We shall nevertheless continue to use the linear formulas as a rule, 

 since they save space and are more readily visualized. For most 

 purposes, the difference is of no significance, but considerations of 

 complex salt formation should be based on the cyclic formulas. 



2. BILE PIGMENT CLASSES AND THE 

 PROBLEM OF NOMENCLATURE 



2.1. Inadequacies of Present Nomenclature 



The inadequate and inconsistent nomenclature of the bile pigments 

 has always added to the difficulties for the student, although this can 



