REJUVENESCENCE 153 



organs like brain and heart, liver and kidneys, for 

 a chain is no stronger than its weakest link. Others 

 have referred to the waning activity of the all- 

 important organs of internal secretion, and others 

 to the sobering fact that there is no multiplication 

 or replacement of the cells of our central nervous 

 system after a very early date in our life. It may be 

 pointed out, however, that most, if not all, of the 

 theories break down because they do not admit of 

 all-round application (thus it is plain that many 

 animals that are not troubled with a large intestine 

 nevertheless grow old), and furthermore that the 

 theories seize on symptoms rather than on causes; 

 for while it is good sense to refer to wear and tear, 

 the question arises why all animals do not exhibit 

 the perfect recuperation to which some at least have 

 attained. 



Professor Child has been working for fifteen 

 years or more with simple creatures called Planarian 

 worms, which he has come to know with con- 

 siderable intimacy. One of the features of their 

 life which he brought to light is their capacity for 

 periodically becoming young again. Thus it often 

 happens that a Planarian separates off the posterior 

 third or quarter of its body, which speedily grows 

 into a whole, while the diminished original heals 

 itself and grows a new tail. This is an old story, 

 but the new fact is that in the reconstitution of 

 the whole from the part there is a remarkable 

 process of rejuvenescence. Instead of the current 

 of life being slow, it is very rapid; the output of 



