364 THE BIOLOGY OF THE SEASONS 



three generations of the animate engines who controlled 

 it, and we know that of two organisms, apparently equal in 

 complexity, one may be old in twelve months, and another 

 may be still young in twelve years. It is easy to speak of 

 accumulated debts, of diminished trophic activity of nerves, 

 of hampering superfluity of half-used products and of 

 diminishing activity of internal secretion, of the struggle of 

 parts within the organism and of the limitations to pro- 

 longed cell-divisions ; but why should it be so at all, and 

 why should the results be so different in different cases ? 



We are not surprised, therefore, to find a specialist on 

 senility (Dr. W. H. Allchin) declaring : " We do not 

 know why the body, after it has reached a state of maturity 

 and vigour, should gradually decline ; why, when once an 

 even balance between tissue-waste and restitution is estab- 

 lished, it is not maintained indefinitely." It is easy to 

 understand why individual human beings with poor 

 inheritance, unnatural environment, and vicious habits 

 should exhibit senile involution and die ; it is often difficult 

 to understand how they manage to live so long ! but these 

 abnormal, though frequent, cases do not touch the bio- 

 logical problem of normal senescence. All the signs of 

 human senility may be seen in a patient under twenty years 

 of age ; but this sad fact hardly touches the general problem 

 of normal senescence which is so elusive. 



As we think over such facts as we have hinted at, the 

 suspicion grows strong that we are apt to miss biological 

 truth by being too anthropocentric. Man is in many ways 

 a very artificial organism he is super-organic. He has 

 an external heritage not less important than that embodied 

 in his germ-plasm ; he has often a self-made environment 

 not less important than that which he was born into ; he 

 has peculiar functions and habits both for good and ill 

 which are all his own ; and there is good reason for sup- 



