REPRODUCTION OF BACTERIA 43 



creases in size to the normal adult, then divides by fission as the 

 parent did. Not infrequently fission takes place before the 



FIG. 31. Diagram illustrating fission of bacterial cells (bacilli and cocci). 



After Npvy. 



adult stage is reached. Involution forms may be produced 

 by this means. Before any constrictions appear in the cell 

 wall the protoplasm within shows evidences of being constricted 

 into two parts. Some writers claim that a membrane forms 

 at the point of division which separates the parent cell into 

 two distinct parts. This in all probability is not always the 

 exact condition, although in some species of bacteria an un- 

 stained line does appear in the protoplasm at the point of di- 

 vision. It is claimed by some that this dividing membrane 

 is cellulose, but recent research shows that no such sub- 

 stance as the cellulose of higher plant cells occurs among the 

 lower bacteria. Bacilli and spirilla always divide in a direc- 

 tion transverse to the long axis of the cell. The cocci divide 

 irregularly as regards a definite direction. 



Rate of Multiplication. A bacterium may reach the adult 

 form and divide in from twenty minutes to an hour, varying 

 with the species. Bacteria are very prolific when the requi- 

 site conditions of food, temperature, and gaseous environment 





