
neonatology
considerable progress has been made in the
knowledge of bilirubin metabolism since the char-
acterization of "direct" (conjugated) bilirubin as an
ester glucuronide.  the metabolic pathway involved
in this hepatic conjugation is now well established
and has been the subject of excellent reviews by
sherlock and billing.
sherlock's diagrammatic representations of biliru-
bin metabolism (fig. 1) and of the possible mecha-
nisms of jaundice (fig. 2) are reproduced here
because they furnish a clear picture to serve as a
reference point for the discussion to follow.
it is interesting to re-examine current concepts of
the etiology of physiologic jaundice with this dia-
gram in mind.  jaundice may occur for a number of
reasons, described below.
