150 GENERAL BIOLOGY OP MICRO-ORGANISMS 



drical bacteria, in which motility is of frequent occurrence. 

 Other terms in common use as generic names for certain cocci 

 are Diplococcus and Staphylococcus. A diplococcus is a double 

 coccus, two spheres attached together. This grouping by twos 

 is very common and the generic term Diplococcus is employed 

 for those forms in which it is a prominent characteristic. The 

 term Staphylococcus is applied to those micrococci which are 

 grouped in an irregular mass resembling a bunch of grapes. 



Cylindrical Bacteria. — The cylindrical bacteria, BacteriacecB, 

 have been subdivided by Migula into three genera, Bacterium, 

 Bacillus and Pseudomonas. The genus Bacterium includes 

 those members of the family which are without flagella and 

 are non-motile. Bacillus includes those forms possessing flagella 

 distributed over the surface, and Pseudomonas is the generic 

 term for those forms with flagella situated at the extremities 

 only (polar flagella) . 



BACTERIACE^— Cells cylindrical, straight, non-motile 

 or motile by means of flagella. 



Bacterium— Cells without flagella, non-motile. 



Bacillus^ — Cells motile with flagella distributed over the 

 surface. 



Pseudomonas — Cells motile with polar flagella. 

 These genera have not been generally adopted by bacteri- 

 ologists, and there are serious reasons for dissatisfaction with 

 such a classification of the rod-shaped bacteria. In the first 

 place the names Bacterium and Bacillus are unfortunate. The 

 former has long been employed as a general term designating 

 any member of the Schizomycetes and its plural. Bacteria,- 

 is ever}rwhere the common term employed in designating this 

 large group of micro-organisms. Its use in the narrower sense 

 by Migula has not displaced the former signification, and its 

 use in the sense of Migula must necessarily result in confusion. 

 The latter term, Bacillus, has long been used very generally by 

 bacteriologists to designate any member of the Bacteriacese 

 or rod-shaped bacteria, regardless of the motility or distribution 



