CHAPTER VIII. 



BACTERIUM (Microbacterium, Cobn). 



BY this name Cohn 1 designates a class of minute schizo- 

 mycetes, which are slightly elongated and oval, or short and 

 cylindrical, with rounded ends. They divide by fission, 

 like the micrococci, the individuals elongating and becoming 

 constricted in the middle. They are capable of sponta- 

 neous locomotion, being possessed of a flagellum at one or 

 both ends, with which they perform active spinning and 

 darting movements (Dallinger). Engelmann has shown 

 that these movements are only possible in the presence of 

 oxygen. Bacteria are found also as dumb-bells, i.e. in the 

 act of dividing, and then appear as rods constricted in the 

 middle. Occasionally, after rapid division, several remain 

 connected, thereby forming a short chain. In this state the 

 terminal elements are flagellate. Bacteria, like micrococci, 

 are capable of forming zoogloea, the interstitial gelatinous 

 substance being, as a rule, more copious than in the zoogloea 

 of micrococci. In this state they form pellicles, in which 

 the elements are without flagella ; but from the margin of 

 the pellicles one constantly sees elements separating, be- 

 coming flagellate, and moving away. In some species 



1 Biologic d. Pflanzen, ii. (1872), p. 167. 



