This volume on the control mechanisms in cellular processes
consists of papers presented at the symposium of the Society of
General Physiologists at its annual meeting in 1960. It will, we trust,
prove useful as a report to the diverse mechanisms now known to act
as regulatory systems.

Biologists have often felt that biochemists take a homogenized
and quite unregulated view of cellular events. In fact, the feeling
has been expressed that biochemists view cells simply as sacks full
of enzymes. There is, of course, some truth in this statement; the
elucidation of biochemical events has indeed required the use of cell-
free material. Such investigations, however, have proved singularly
rewarding; we now enjoy detailed knowledge of the precise mecha-
nisms involved in energy transfer, in the biosynthetic processes con-
cerned with the formation of substrate molecules, and in the synthesis
of such macromolecules as enzymes and nucleic acids. We have
come to an era in which fruitful consideration can be given not only
to the integration of separate biochemical events but to the coordi-
nate regulation of cellular biochemistry. In addition, consideration
can now be given these subject areas, in part at least, at the molecular
level.

Multicellular animals have characteristic developmental stages.
Growth and development are intrinsic properties of biological sys-
tems; the biochemical characteristics of diverse differentiated cells
are clearly different. Even in bacteria, biochemical differences have
been noted at different stages in their growth cycle. These are bio-
logical facts which must be accounted for, and the answer presum-
ably could in part be deduced from an understanding of the systems
which regulate cellular biochemistry. What are the regulatory sys-
tems known at present?

A classic agent of cellular regulation is, of course, the gene. In
the past decade magnificent work from many laboratories has given
clear experimental proof that one action of genetic material is the

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