WHAT IS PHYSICAL LIFE 



are non-motile, or can scarcely be said to 

 move at all, but the cholera vibrio squirms 

 so incessantly that no snapshot of it can 

 be taken, all its micro-photographs being 

 blurred because it will not keep still. 

 Meantime, each of these agents kills its 

 victims in wholly dissimilar ways. Some 

 of them will attack the same person only 

 once, while others find a previous attack 

 makes another all the easier. And so we 

 might go on enumerating many other ab- 

 solute and fixed characteristics which dis- 

 tinguish these unicellular forms of life 

 from one another, but enough has already 

 been adduced to establish the fact that no 

 forms of life anywhere are so individual 

 and specific in their kinds as the unicellular 

 forms. x 



In this respect they markedly differ 

 from all other plants and animals. In the 

 unicellular forms but few and relatively in- 

 complete variations occur, such as between 



