20 AGE, GROWTH, AND DEATH 



body produces less. How this is accomplished we 

 are unable to say, but constantly we see evidence of 

 this purposeful accommodation on the part of the 

 body what is called by the physiologists the teleo- 

 logical principle, the adaptation of the reaction of 

 the body to its needs. There are innumerable illus- 

 trations of this, many of which are of course perfectly 

 familiar to us, although perhaps we do not think of 

 them as illustrations of this great law of nature ; as, 

 for instance, when we eat a meal, and the presence of 

 food in the stomach calls into action the glands in the 

 wall of the stomach by which the digestive juice is 

 secreted. The juice is produced exactly at the time 

 when it is needed. Innumerable, indeed, are the 

 illustrations of this fundamental principle. 



There is another class of phenomena characteristic 

 of the very old which will perhaps seem a little sur- 

 prising to you after the general tenor of my previous 

 remarks. I refer to the power of repair. This, 

 modern surgery especially has enabled us to recog- 

 nise as being far greater in the old than we were 

 wont to assume ; and we know that there is a certain 

 luxury, a certain excess reserve in the power of re- 

 pair, and that we may go far beyond the ordinary 

 necessities of our life in our demands upon our or- 

 ganism, and still find that our body is capable of 

 making the necessary response. 1 Ordinarily the 



1 A most valuable and suggestive study of the excess supply of physiological 

 resources has been made by Dr. S. J. Meltzer, " The Factors of Safety in Animal 

 Structure and Animal Economy," Journal Amer. Med. Assoc., vol. xlviii, 

 PP- 655-664. 



