10 



BACTERIA 



by a peculiar amoeboid motion, or by an undulating membrane. 

 On loolfing at bacteria known to have no powers of voluntary 

 motion, they are seen to oscillate, tremble or move slightly. Sus- 

 pensions of india-ink in water are seen to do the same thing, as are 

 other inanimate suspensions. This molecular movement is known 

 as the Brownian motion. There are bacteria that are considered 



FIG. 8. Spirillum undula with polar 

 flagella. (Kolle and Wassermann .) 



FIG. 9 Bacillus prolius vul- 

 garis, showing peritrichous fla- 

 gella. (Kolle and Wassermann.) 



non-motile, on which it is possible to demonstrate flagella. By 

 ordinary staining methods, and in preparations of living bacteria 

 known to be flagellated, these organs of locomotion cannot be seen, 

 as a rule. Occasionally, however, one may be seen under either 

 condition. Generally, strong solutions of aniline dyes, to which 

 powerful mordants have been added, are necessary to stain the 

 capsule of bacteria and the attached flagella. The motion or 

 bacteria varies from a simple rotatory, on one axis, to a swinging, 



