STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 



31 



Although it is usually impossible to discern chromosomes in such nuclei, it 

 is most frequently assumed that such nucleoprotein structures are neverthe- 

 less present. In support of such an assumption it has been asserted that the 

 cellular requirements of exact duplication and consequent genetic continuity 

 demand a continuity of substance. 



Fig. 3. Schematic representation of a parenchjo^iatous cell of rat liver (Novikofl 1957). 

 The following structures are represented: mitochondria (mt); basophilic material (er); 

 glycogen (g); nucleolus, nuclear membrane, nuclear "pores" {np); Golgi apparatus (go); 

 "dense bodies" (db); interlocking cell processes [cp); and bile canaliculus (be). 



Of course, it is precisely this kind of reasoning which has been called to 

 question in recent years by the data on transformation agents and on viruses. 

 The hfe cycle of a nucleoprotein does not require its structural continuity 

 since viral nucleic acid, appropriately placed within its host, is sufficient to 

 direct the subsequent production of not only nucleic acid but also a variety 

 of differentiated proteins as well, and to control their subsequent organization 

 into a protein-associated structure. It is, however, true that biology has not 

 yet developed a hypothesis concerning a mechanism, other than those 



VOL. I — 4 



