THE CURVE OF LIFE 147 
in their prime and others that seem to have no 
limit (save violent death) to their persistent growth. 
It is a question of vital punctuation. 
Just as there are many novels but only a few 
plots, so amid an apparent multiplicity of life- 
histories we discern but a few main types. The 
details may seem very different, but they are often 
interpretable as due to a lengthening out here and 
a condensation there, to a changing of the time of 
the tune. Let us briefly consider three corollaries of 
this proposition. (1) Just as there are in organisms 
architectural variations which find expression in 
spatial rearrangements of materials (comparable 
to those we see a schoolboy effecting with his 
“mechano” toy, out of which he constructs now a 
crane and again a bridge, to-day a railway truck 
and to-morrow an aeroplane), so there are temporal 
variations which find expression in changes in the 
rate of growth and development, or in alterations 
in the rhythm or punctuation of life. In this con- 
nection it is interesting to remember that in the 
internal secretions (of back-boned animals at least) 
there is a means by which the rate of growth and 
development can be automatically regulated. How 
suggestive, for instance, is the result of Guder- 
natsch’s experiments on tadpoles, that a thyroid 
diet stimulates differentiation and hinders growth, 
while a thymus diet inhibits differentiation and 
lets growth go on. (2) The general idea 1s that the 
curve of life is like a discontinuously elastic thread 
wth fixed arcs here and there, and that the tension 
