CHAPTER IV. 



CELL GROUPINGS. 



It has been stated that bacteria reproduce by trans- 

 verse division, that is, division across the long axis. Fol- 

 lowing repeated divisions the new cells may or may not 

 remain attached. In the latter case the bacteria occur as 

 separate isolated individuals. In the former, arrangements 

 characteristic of the particular organism almost invariably 

 result. These arrangements are best described as cell 

 groupings, or growth forms. 



Fig. 40. — Streptoapirillum grouping. Fig. 41. — Diplobacillus grouping. 



In the case of spiral forms it is obvious that there is only 

 one possible grouping, that is, in chains of two or more 

 individuals adherent end to end. A chain of two spirilla 

 might be called a diplospirilluvi (5i7rX6s = double); of 

 three or more, a streptospirillum (a-TpeirTds = necklace, chain) 

 (Fig. 40). These terms are rarely used, since spirilla do 

 not ordinarily remain attached. Likewise the bacillus can 

 grow only in chains of two or more, and the terms diph- 

 bacillus (Fig. 41), bacilli in groups of two, and streptobacUlus 

 (Fig. 42) , bacilli in chains are frequently used. Still the terms 

 thread, filament, or chain are more common for streptobacillus. 



