CHILD'S SENESCENCE AND REJUVENESCENCE 421 



istic expression, " Behavior is regulation." Indeed, one may 

 go further and maintain that regulation is the most character- 

 istic of all of the distinctive vital functions. There is nothing 

 which more clearly distinguishes a living body from a dead body 

 than the ability of the former to adapt its behavior to changing 

 environmental conditions, and yet during this adaptation to 

 maintain its structural and functional pattern without funda- 

 mental change. 



The method of learning and many of the other questions with 

 which students of animal behavior are concerned are, of course, 

 special problems of regulation in the wide sense of the term; 

 and it is therefore to be expected that any contribution to the 

 nature of regulation in general will bear directly or indirectly 

 upon the fundamental problems of comparative psychology. 

 Child's work, accordingly, has both theoretical and practical 

 value in the field of animal behavior. 



The two books here reviewed present successive chapters in 

 a single program of research. The first and larger volume on 

 Senescence and Rejuvenescence gives a detailed analysis of the 

 problem of organic constitution with experimental illustrations 

 of some of its factors, notably those centering about the life 

 cycle. The second book on Individuality in Organisms analyzes 

 in more general terms the nature of the biological individual 

 and the mechanistic factors which characterize it. Among the 

 theses which are elaborated, the following are of especial interest 

 from our point of view: 



1. In discussing living things static formulations are incom- 

 plete and meaningless without corresponding formulations in 

 dynamic terms. " Life is not any particular reaction nor any 

 particular substance, but a great system of processes and sub- 

 stances. Structure and function are then indissociable." ' In 

 other words, neither structure nor function is conceivable except 

 in relation to each other." The discussion takes its departure 

 from the following definition, "A living organism is a specific 

 complex of dynamic changes occurring in a specific colloid sub- 

 stratum which is itself a product of such changes and which 

 influences their course and character and is altered by them." 

 (Senescence, p. 26.) 



2. There are two factors in organic differentiation, (1) the 

 amount of metabolism, and (2) the complexity of organization. 



