26 



CELL STRUCTURES 



occasionally happens that water diffuses into the cell and 

 swells up the cytoplasm so much more rapidly than the cell 

 wall that the latter ruptures and some of the cytoplasm 

 exudes in the form of droplets on the surface of the cell 

 wall. This phenomenon is called plasmoptysis. Students 

 will seldom observe the distinction between cell wall and cell 

 contents, except that in examining living bacteria the outer 

 portion appears more highly refractive. This is chiefly due 

 to the presence of a cell wall, but is not a^proof of its exist- 

 ence. 



Fig. 18. — Cells of bacteria show- 

 ing plasmolysis. The cell sub- 

 stance of three of the cells in the 

 middle of the chain has shrunk 

 until it appears as a round black 

 mass. The cell wall shows as the 

 lighter area. 



Fig. 19. — Vacuoles in the bac- 

 terial cell. The lighter areas are 

 vacuoles. 



Nucleus.— Douglas and Distaso^ summarize the various 

 opinions with regard to the nucleus in bacteria as follows: 



1. Those who do not admit the presence of a nucleus or of 

 anything equivalent to it (Fischer, Migula, Massart) . 



2. Those who consider that the entire bacterial cell is 

 the equivalent of a nucleus and contains no cytoplasm 

 (Ruzicka) . 



3. Those who admit the presence of nuclein but say that 

 this is not morphologically differentiated from the proto- 

 plasm as a nucleus (Weigert). 



1 Centralblatt f. Bakteriologie, etc.. 1912, 63, I abt. orig., 4; idem, 19i: 

 66, I abt. orig., 323. 



