32 BACTERIA, GENERAL CONSIDERATIONS, MORPHOLOGY 



known that this motion of very small solid particles in fluid is due 

 to the fact that the adjacent particles of gaseous or liquid matter 

 surrounding them are in constant violent motion, and these lively 



FIG. 16 



FIG. 17 



Spirillum of Asiatic cholera, showing single 

 flagellum. (Kolle and Zetnow.) 



Spirillum volutans, showing flagella at 

 either end of the bacterium. 



molecules bumping constantly against the small, not truly motile 

 bacteria keep them in a continued state of trembling agitation. It 

 was formerly believed that the Brownian movement depended upon 

 surface tension, but this is not the case. 



Multiplication or Propagation. 



Under 



bacteria 



material 



FIG. 18 



suitable conditions 

 take up nutritive 

 and multiply very 

 quickly. This process is so 

 rapid that a single bacterium, 

 if circumstances are favorable, 

 may in twenty-four hours have 

 increased to many millions. It 

 has been ascertained that several 

 of the disease-producing bac- 

 teria under the most favorable 

 conditions divide once in less 

 than thirty minutes. 



Binary Division or Fission. 

 It is characteristic of bacteria 

 that they always multiply by 

 dividing in the middle and the 

 elongated forms namely, bacilli 

 and spirilla always divide at right angles to their long axis. This 

 mode of multiplication is called binary division, or fission, and often 

 causes bacteria to group themselves in a very characteristic manner, 



Bacillus proteus vulgaris, showing numerous 

 fla^ella around the entire body of the bac- 

 terium. 



