86 EVOLUTION 



Weismann called attention to the fact that 

 unicellular organisms are not subject to 

 natural death in the same degree as higher 

 animals are. They may be killed, of course, 

 in many ways, but they do not normally die. 

 Even against microbic infection many of 

 them seem proof; they digest the virulent 

 intruders, as do the phagocytes which form 

 our body-guard. But the point is, that in 

 natural conditions, where inter-crossing, for 

 instance, is readily feasible, they appear to 

 be exempt from that natural death which 

 in the higher organisms is due to the slow 

 mounting-up of physiological arrears. 



How is it that these simple pioneer organ- 

 isms are exempt from the penalty all other 

 flesh is heir to? The answer is twofold. On 

 the one hand, being relatively very simple, 

 in a strict sense without a "body" they are 

 able to sustain with persistent success the 

 vital equation between waste and repair. On 

 the other hand, their common mode of repro- 

 duction, by dividing into two or more units, 

 is inexpensive and not attended with any loss 

 of life. For although the individual A dis- 

 appears in giving rise to B and C, its daugh- 

 ter-cells, we can hardly speak of death when 

 there is nothing left to bury. On the one 

 hand, we reach the idea that death was the 

 price paid for a body; on the other hand, 



