576 THE POPULAR SCIENCE MONTHLY 



age and on conjugation leads to a unified result, and one that is in 

 most respects in consonance with what we observe in higher animals. 

 But in one respect there is a difference, and this brings us back to the 

 question with which we began. Is death a necessary accompaniment 

 of life ? Do the life processes necessarily take such a course that they 

 must lead to death ? 



To this question the work on the infusoria answers No! The evi- 

 dence that was supposed to show that the life processes must gradually 

 run down and end in death had been shown by the work of Woodruff 

 not to lead to any such conclusion. Woodruff appears to be clearly 

 justified in his recent statement that these organisms " have the poten- 

 tiality to perpetuate themselves indefinitely by division/' and my own 

 studies on the effects of conjugation furnish the complement to this re- 

 sult, agreeing with it fundamentally. 



All that Weismann meant by saying that such creatures are poten- 

 tially immortal has shown itself correct. Death is not necessarily in- 

 volved in life. 



But why, then, in higher animals and in ourselves, even when there 

 is no accident and conditions are good, do we find death coming as a 

 natural end to life? Why should there be this tremendous difference 

 in such an essential point between the lower organisms and the higher 

 ones ? Is there any possibility of mistake as to the necessity in the case 

 of higher organisms? 



To find a ground for this difference, we shall do well to follow the 

 usual procedure in science, and examine other differences between these 

 lower creatures and the higher ones, to see if these may not give us the 

 clue. And here I touch upon a matter that had been fully developed by 

 Minot and others; it is worth while to speak of it briefly, because work 

 bearing upon the matter has recently appeared. 



The most striking other difference between these lower organisms 

 and the higher ones, is evidently the fact that in the higher organisms 

 the body becomes large, complex and differentiated into a number of 

 diverse parts ; different cells of the body have taken on themselves dif- 

 ferent functions and different structures. This appears to, involve a 

 correlative loss of the power of carrying on the fundamental vital proc- 

 esses ; the cell that has become filled with lime, or that has transformed 

 into muscle, no longer retains the vital elasticity of the cell in which 

 the diverse functions remain well balanced. Products of metabolism 

 are no longer perfectly removed; other processes necessary to life be- 

 come clogged. The final result of this is a complete cessation of the 

 processes; age and death follow upon differentiation. This, as you 

 know, is the theory of Minot. According to it, the welfare of the in- 

 dividual cell is as it were sacrificed to that of the body as a whole, and 

 this in turn involves the final destruction of the body itself, so that a 



