24 WHAT IS LIFE 



What happens ? The cell thus emptied of its 

 most important part does not immediately die. 

 For a time it will go on exhibiting what we shall 

 shortly learn is one of the most important and 

 characteristic activities of life, namely irritability. 

 But it has lost, and that permanently, all its former 

 powers of assimilation, of growth and of repair. 

 It is not dead but it is dying and nothing can 

 hinder or delay its final death. Hence, as Roux 

 and others claim, and it would appear justly claim, 

 the nucleus is the controlling agency in the 

 cell. 



But, on the other hand, if the cell cannot get 

 on without the nucleus, neither can the nucleus 

 get on without the cell, for it too perishes if it be 

 cut off completely from it. It seems as if the 

 cytoplasm, or cell-protoplasm in some way acts as 

 a stimulant to the nuclear protoplasm and hence, 

 though the nucleus is, or appears to be, the main 

 factor in division, it is possible that the cytoplasm 

 may "indirectly regulate the process of cleav- 



Cytoplasm then is necessary to nucleus and 

 nucleus to cytoplasm. If a unicellular organism 

 be so divided up that certain of the fragments into 

 which it is separated contain portions of the nucleus 

 and certain do not, those fragments which contain 

 1 Morgan, The Development of the Frog's Egg, p. 128, 



