XVI LIFE-HISTORIES 337 



opened buds, and others which flower before they leaf, 

 so there are animals which have a long youth and others 

 a long maturity, some that are born old and others that 

 die young ; some which break down suddenly 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, and the question rises whether some of the 

 contrasts between different types may not have arisen 

 in the course of evolution by not very startling alterations 

 in the timing of life, in the rate and rhythm of metabolism. 

 Finally we would note that while man is a slowly 

 varying creature, changing but little from age to age in 

 the organic punctuation of his life, he is eminently plastic 

 or modifiable, and therefore able, probably to an extent 

 unsuspected, to lengthen out his youth, to prolong his 

 period of cerebral variability, and to shorten the days of 

 undesirable senescence. In all of which there is a great 

 hope. 



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