THE SCIENTIFIC MONTHLY
FEBRUARY. 1922
GROWTH IN LIVING AND NON-LIVING SYSTEMS
By Professor RALPH S. LILLIE
THE NELA RESEARCH LABORATORY, CLEVELAND, OHIO
GROWTH has perhaps a better claim than any other life-process
to be called "fundamental," since it is the indispensable
basis or condition of all vitality. This is true not merely in the
obvious sense that all organisms are products of growth ; even
when an animal or plant has ceased to "grow," i. e., add to its
total living or organized material, it continues automatically to
renew its own substance and to repair losses and damage; without
this continual renewal no life can persist. We may thus regard
the adult organism as still "growing," but the growth is "latent"
masked by the simultaneous loss inseparable from all vital activ
ity. Visible increase in size is thus not the only evidence of growth ;
whether an organism grows visibly or not is in fact determined
by the relative rates of two opposed processes, one of which builds
up and accumulates, while the other breaks down and dissipates.
In all life the primary or fundamental /process is the building-up
of the specifically organized living substance by constructive
metabolism; but this process is always accompanied by chemical
breakdown or destructive metabolism, with loss of material to the
surroundings. Briefly, therefore, we may describe the essential
situation as follows : when metabolic construction exceeds destruc
tion there is "growth" (in the ordinary sense of visible increase) ;
when the two are equal there is balance, or simple maintenance;
when destruction predominates there is regression or atrophy.
Visible growth represents simply the accumulated excess of con
struction over destruction.
This constant association of destruction and repair has long
been recognized as the essential or distinguishing peculiarity of
the living state ; while the organism * lives, the effects of loss or
destruction are continually being offset or compensated (often
over-compensated) by new construction. The life process is thus
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