9 Editor's Note: This brief and provocative review derives from a lecture presented
at the symposium “Frontiers of Science and the Liver,” held on June 5, 1979, at The
Mount Sinai Medical School of the City University of New York in honor of Dr. Hans
Popper. Several of the intriguing speculations have subsequently proved to be correct,
and the text therefore provides a timely current review of this aspect of heme metabolism.
