INTRODUCTION 5 



My investigation of senescence and rejuvenescence has been 

 closely connected with an attempt to determine the physiological 

 nature of the reproductive processes in organisms, and I believe 

 that some such conception of senescence and rejuvenescence as 

 that presented here is essential for the physiological analysis of 

 reproduction, since senescence, reproduction, and rejuvenescence 

 are very closely connected. But while some discussion of the 

 nature of various reproductive processes will be necessary in the 

 course of the present study, a full consideration of the problem of 

 reproduction is postponed .to another time. 



Our conception of the nature of these various processes, growth, 

 differentiation, senescence, reproduction, and rejuvenescence, must 

 depend upon our conception of the organism. It seems necessary, 

 therefore, to consider briefly in certain of its aspects the problem 

 of the constitution of the organism by way of clearing the ground 

 for consideration of the particular features of organic constitution 

 which form the subject of the book. 



