124 BACTERIOLOGY. 



circular, but are flattened or facetted where they 

 are opposite to each other. They gradually 

 become rounded off, and each daughter cell is then 

 ready to divide in its turn. In other cases the 

 cocci after division only form irregular heaps or 

 collections like bunches of grapes. This form is 

 sometimes distinguished as staphylococcus, but it 

 cannot be considered an important feature. Where 

 we find irregular masses or balls embedded in a 

 copious gelatinous matrix, the extent of the latter 

 affords a characteristic condition described as 

 ascococcus. 



Another type is the rod, characteristic of bac- 

 terium and bacillus. The rods may vary con- 

 siderably in length. The very short rods with 

 rounded ends are very difficult to distinguish from 

 the oval cocci, but differ in that a rod, however 

 short it may be, must have at least two sides 

 parallel. The vibrio or bent rod may be considered 

 as the connecting link between the rods and the 

 corkscrew forms or spirilla. Lastly we have the 

 filamentous forms, which may be straight, leptothrix, 

 or wavy, spirochceta (Fig. 50), or the wavy thread 

 may be looped and entwined on itself, spirulina 

 (Plate I., Fig. 37). 



By involution forms we signify certain irregular 

 shapes which result especially in exhausted culti- 

 vations. They are peculiar, oval, pear-shaped, or 

 irregular enlargements (Plate I, Figs. 31 to 36). 



Movement. Many bacteria are devoid of move- 



