BACTERIA. 



77 



which may be of very varied length. A distinction may be 

 drawn between the motile (bacillus] and the motionless form 

 (bacterium). When the rods are swollen in the middle, and 

 thus form spindle shapes, we have the Clostridium form (/). 

 If the bacilli are elongated, so as to become more or less thread- 

 like, they are called Leptothrix (g), which may also occur as 

 pseudo-filaments when several bacteria are grouped length- 

 wise, or as Cladothrix, when they lie close to one another and 

 appear as irregular branching threads. The bacilli and 



n****j 



K\f/.*SS& 



S&j&Vfiyl' 



Fig. 16. Growth-forms of Bacteria (in part schematic). a, Cocci; b, diplococci and micro- 

 coccus ; c, streptococci ; <l, zoogloea ; e, bacteria ; /, clostridium ; </, pseudo-filament, lepto- 

 thriz, cladothrix ; h, vibrio, spirillum, spirochicte and spirulina ; i, involution forms ; k, bacilli 

 and spirilla, with cilia or flagella ; /, spore-forming bacteria ; //', germination of the spore 

 (Bacillug subtili). 



filaments frequently assume wavy or spiral forms (h) ; when 

 they are only slightly curved, we have the Vibrio form ; when 

 the spirals are more prominent, the Spirillum and Spirochcete 

 forms ; when they intertwine like a plait of hair, the form 

 called Spirulina is produced. 



The thickness of most bacteria is about T tjW mm. (I/*) J 

 the largest do not exceed 3 to 4 /x. The thickness may, how- 

 ever, vary extraordinarily in one and the same kind, and the 

 same is equally true of the length, because the cells elongate 

 before they subdivide. The limit may be placed at 10 to 12 /u ; 



