THE INSTINCT OP SURVIVAL 121 



Why do so many drop by the way, or attain the goal 

 exhausted? Many factors enter into the outcome 

 - the primitive vigor of the cells, good habits of 

 life, good fortune in avoiding accidental infections. 

 The facts may be stated a little differently. We 

 may say that the vigor of the cells, cooperating with 

 careful habits of husbanding the energy of these 

 cells, are most potent influences in helping the body 

 to evade the dangers of bacterial infection. If it 

 were possible to live without such infection, there is 

 no doubt as to the effect on human life. Supposing, 

 for a moment, that such a thing were possible, we 

 should expect the cells of the body machine to 

 deteriorate only very slowly, with the result that the 

 duration of life would be, on the average, far hi 

 excess of what it now is. For we may consider that 

 at the time of conception the possibilities, with 

 regard to the future physical vigor of the cells, are 

 expressed in the protoplasm of the new being. The 

 events of impregnation are, indeed, not unlike the 

 winding of a clock, newly endowed with the power 

 to run for a quite definite period. Many things may 

 happen to check the course of the clock, or to shorten 

 its time of action, but under ideal conditions its 

 run cannot exceed the course made possible by its 

 organization. In exactly the same way, the span of 

 each human life has set to it a definite limit in organ- 

 ization, imposed at the instant of impregnation. 

 Many things may happen to rob the individual life 

 of a portion of the life possible to it, but man knows 



