112 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



period is the time for performance and for the 

 assumption of necessary physical risks. And this 

 is also the time for reproduction. In middle life, 

 physical vigor begins to decline, although the body 

 tends to accumulate reserves of energy which show 

 themselves in a disposition to obesity, where nutri- 

 tion is good. Judgment receives the benefit of the 

 increment due it from long experience. Well- 

 founded self-confidence tends to mitigate aggres- 

 siveness and to allay suspicion of others, while the 

 mellowing process is still further accelerated by a 

 recognition and acceptance of personal limitations 

 and by the perception that the margin of life's 

 expectation is no longer a broad one. The value of 

 life is, in this period, the greatest of all, for it is the 

 time of that conservative and ripe judgment unmixed 

 with timorousness, which is so needed to correct the 

 impulsive and erroneous tendencies of youth and to 

 encourage and reenforce its true ones. The decline 

 of sexual passion directs life processes more and 

 more into somatic and intellectual channels, without 

 depriving the individual of the humanizing experi- 

 ences of past sexual life experiences. The period 

 of senility is one of accelerated wasting of the body 

 and relatively slow failure of the mental processes. 

 The reason for the divergence in the rate of decay 

 of body and mind probably lies in some definite 

 physical characteristic of the brain. This immunity 

 of the brain substance to the effects of retrogressive 

 metabolism is only a relative one, and memory, 



