i.j INDIVIDUALITY AND AGE 19 



for example, with the larvae of insects and Crustacea. 

 On the other hand, in an organism such as our own, crises 

 like puberty or the menopause, in which the individual 

 is completely transformed, are quite comparable to changes 

 in the course of larval or embryonic life — yet they are part 

 and parcel of the process of our aging. Although they occur 

 at a definite age and within a time that may be quite short, 

 no one would maintain that they appear then ex abrupto, 

 from without, simply because a certain age is reached, just 

 as a legal right is granted to us on our one-and-twentieth 

 birthday. It is evident that a change like that of puberty 

 is in course of preparation at every instant from birth, 

 and even before birth, and that the aging up to that crisis 

 consists, in part at least, of this gradual preparation. 

 In short, what is properly vital in growing old is the in- 

 sensible, infinitely graduated, continuance of the change 

 of form. Now, this change is undoubtedly accompanied 

 by phenomena of organic destruction: to these, and to 

 these alone, will a mechanistic explanation of aging be 

 confined. It will note the facts of sclerosis, the gradual 

 accumulation of residual substances, the growing hyper- 

 trophy of the protoplasm of the cell. But under these 

 visible effects an inner cause lies hidden. The evolution 

 of the living being, like that of the embryo, implies a con- 

 tinual recording of duration, a persistence of the past in 

 the present, and so an appearance, at least, of organic 

 memory. 



The present state of an unorganized body depends ex- 

 clusively on what happened at the previous instant; and 

 likewise the position of the material points of a system 

 defined and isolated by science is determined by the po- 

 sition of these same points at the moment immediately 

 before. In other words, the laws that govern unorganized 

 matter are expressible, in principle, by differential equations 



