Continuity of Life 35 



other individual that avoids this end ; but replacement of the 

 worn material by a reserve. 



It results that the continuity of life in the infusoria is in 

 principle much like that in ourselves, though with differences 

 in details. As individuals, the infusoria do not die, save by 

 accident. Those that we now see under our microscopes 

 have been living ever since the beginnings of life ; they come 

 from division of previously existing individuals. But in just 

 the same sense, it is true for ourselves that everyone that 

 is alive now has been alive since the beginning of life. This 

 truth applies at least to our bodies that are alive now ; every 

 cell of all our bodies is a piece of one or more cells that 

 existed earlier, and thus our entire body can be traced in 

 an unbroken chain as far back into time as life goes (see 

 the diagram, Figure 5). The difference is that in man 

 and other higher organisms there have been left all along 

 the way great masses of cells that did not continue to live. 

 These masses that wore out and died are what we call the 

 bodies of the persons of earlier generations; but our own 

 bodies are not descended by cell division from these; they 

 are the continuation of cells that have kept on living and 

 multiplying from the earliest times, just as have the existing 

 infusoria. From our own personal point of view it seems 

 unfortunate that the mass of cells which is next to wear out 

 and be left behind in the chain of life is that with which our 

 own selves seem to be bound up ; but certain samples of our- 

 selves may continue to live indefinitely,! like the infusorian. 

 The great mass of cells subject to death in the higher 

 animals dwindles in the infusorian to the macronucleus ; this 

 alone represents a corpse. But the dissolution of this corpse 

 occurs within the living body. It resembles much such a 

 process as the wasting away and destruction of minute parts 

 of our own bodies, which we know is taking place at all 



