SIZE AND STRUCTURE OP THE BACTERIAL CELL. 31 



The higher animal and plant cell always contains a 

 nucleus within the protoplasm. The nucleus unquestion- 

 ably plays a most important part in the division of the cell. 

 .So much so that it has been considered essential to repro- 

 ductive changes. Inasmuch as bacteria possess the power 

 of multiplication, it might be expected that they would 

 contain, like higher forms, a well denned nuclear body. 



The direct examination of a bacterial cell fails to reveal 

 the presence of any form analogous to a nucleus. Usually, 

 the cell appears perfectly homogeneous, and the closest 

 examination will not bring out a structure. The question 

 -of the existence of nuclei in bacteria has been the subject 

 of numerous extensive investigations which have led to 

 very different conclusions. In fact, it may be said that the 

 presence of a nucleus is not demonstrated. 



There are some who consider bacteria as wholly devoid 

 -of nuclei. The minute granules which are not infrequently 

 present, especially in older cells, are believed by some to 

 be the first indication of the formation of a nucleus. 



Some have endeavored to show the existence of a cen- 

 tral body which, while it is not a nucleus in the sense that 

 this term is usually employed, nevertheless possesses certain 

 properties of a nucleus, and may therefore be considered as 

 -a rudimentary form of that body. On the whole the opinion 

 prevails that bacteria consist essentially of nuclear matter 

 surrounded by a very thin protoplasmic layer and by the 

 cell-wall. It is well known that in embryonic cells the 

 nucleus almost fills the cell. 



This view is especially strengthened by the behavior 

 of bacteria to anilin dyes. The bacterial cells stain readily 

 and intensely, like the nuclei of higher cells. This is 

 assumed to be due to the presence of similar chemical sub- 

 stances such as nucleins. The presence of a nuclein com- 

 pound in the bacterial cell is indicated by the fact that 

 nuclein bases and even a protamin-like body have been 

 isolated. 



