INTRODUCTORY LETTER TO SENATOR MOSSOxvii 



intricate science so much time was absorbed, that I 

 was forced to give up the hope with which I started 

 out, and have only the present book to offer as a 

 fragment towards the fulfilment of the original plan 

 of researches upon general biological phenomena. 



If one starts with the purpose of getting nearer a 

 solution of the final problem of life, it is not difficult 

 to devise numerous researches which would be likely 

 to gain for us insight into the fundamental phenomena 

 of biology. It was from the indicated standpoint 

 that it seemed to me that one of the most promising 

 opportunities for attack was offered by the changes 

 which age effects in organisms. These changes had 

 been then, and indeed have been since, very little 

 studied in a systematic way or from any general 

 standpoint. It is assuredly one of the most general 

 phenomena in the life history of organisms that they 

 become old. From the age of zero at the moment 

 of sexual impregnation, animals and plants, broadly 

 speaking, both pass through a series of changes until, 

 barring accidents, they reach their limit of life ; by 

 which we mean the maximum longevity achieved 

 by each individual under the optimum of conditions. 

 Organisms are created young and grow old, and the 

 old produce young successors. Senescence is a pro- 

 blem of living matter, and, so far as known, has no 

 parallel in non-living matter. It is an essential feature 

 of life. It finds its most familiar expression in the 

 gradual loss of the functional powers of the organ- 

 ism, its end is death. My book is the outcome of an 



