THE CELL AND ITS ACTIVITIES 17 



thousands of generations of the slipper animalcule, 

 Paramecium, concludes that, as Weismann long ago 

 assumed, these creatures are 'potentially immortal, 

 and do not even require the supposed stimulating 

 effect of conjugation - - the union of the protoplasm 

 of two individuals. The fact that under natural con- 

 ditions myriads die from accidental causes or disease 

 has no bearing upon the question. We are obliged, in 

 the face of this evidence, to strike off death from the 

 list of phenomena necessarily accompanying life, and 

 therefore exhibited by every cell. 



6. Yet we must die, and the innumerable cells com- why we die 

 posing our bodies must die, excepting only those which 

 go to form a new generation. Early in the develop- 

 ment of the individual, certain portions of the proto- 

 plasm are set aside to form the germ cells, whose 

 function it is to start a new generation. On this fact 

 Weismann developed his theory of the continuity of 

 the germ protoplasm, or germ plasm, the living material 

 which is passed on from parent to offspring. This 

 germ plasm does not make any muscles, or nerves, or 

 other body structures while it is waiting for the time 

 when it will take part in the formation of a new in- 

 dividual. The other cells, on the contrary, divide 

 many times, and the final result is muscle cells, and 

 nerve cells, and connective tissue cells, and so forth. 

 This specialization of the cells is necessary, in order 

 that they may do the work required in a highly or- 

 ganized body; but as a result they are rendered quite 

 unfit for reproduction. They have sacrificed the 

 potentiality of new life for the sake of becoming special- 

 ists. The body as a whole has bought all those powers 

 and qualities which make it man rather than protozoan, 

 at the price of having to die. The race, however, does 



