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. ( i ) 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 is that the 

 curve of life is like a discontinuously elastic thread 

 wth fixed arcs here and there, and that the tension 



