THE CELL AND PROTOPLASM. 91 



are incapable of assimilating food and incapable 

 of reproduction, and hence their life cannot con- 

 tinue very long. Facts like these demonstrate 

 conclusively the vital importance of the nucleus 

 in cell activity, and show us that the cell, with its 

 power of continued life, must be regarded as a 

 combination of protoplasm with its nucleus, and 

 cannot exist without it. It is not protoplasm, 

 but cell substance, plus cell nucleus, which forms 

 the simplest basis of life. 



As more careful study of protoplasm was 

 made it soon became evident that there is a 

 very decided difference between the nucleus and 

 the protoplasm. The old statement that the 

 nucleus is simply a bit of dense protoplasm is not 

 true. In its chemical and physical composition 

 as well as in its activities the nucleus shows itself 

 to be entirely different from the protoplasm. It 

 contains certain definite bodies not found in the 

 cell substance, and it goes through a series of 

 activities which are entirely unrepresented in the 

 surrounding protoplasm. It is something entirely 

 distinct, and its relations to the life of the cell are 

 unique and marvelous. These various facts led 

 to a period in the discussion of biological topics 

 which may not inappropriately be called the 

 Reign of the Nucleus. Let us, therefore, see what 

 this structure is which has demanded so much 

 attention in the last twenty years. 



(b) Structure of the Nucleus. At first the nu- 

 cleus appears to be very much like the cell sub- 

 stance. Like the latter, it is made of fibres, which 

 form a reticulum (Fig. 23), and these fibres, like 

 those of protoplasm, have microsomes in intimate 

 relation with them and hold a clear liquid in their 

 meshes. The meshes of the network are usually 



