BACILLUS 85 



commonest species. Both motionless and active forms are 

 found, the latter having a flagellum at each end. The 

 zooglaea condition is often assumed, and the rods are fre- 

 quently found united end to end so as to form filaments. 



Vibrio resembles Bacillus, but the rod-like cells (Fig. 18, A) 

 are wavy instead of straight. They are actively motile and 

 when highly magnified are found to be provided with a 

 flagellum at each end. Vibriones vary from 8/x to 2^ in 

 length. 



Spirillum is at once distinguished by its spiral form, the 



V 



* . 



\ ::&:. 4 



\ : :?#& 







% .?; ' 



V / .;: 



::: 



...... : 



Pf t ** O * 



FIG. 1 6. Micrococcus. I, single and double (dumb-bell shaped) 

 forms : 2 and 3, chain-forms : 4, a zooglsea. 



cells resembling minute corkscrews (Fig. 18, B & c) and 

 being provided with a flagellum at each end (c). The 

 smaller species, such as S. tenue (B) are from 2 to 5/x in 

 length, but the larger forms, such as S. volutans (c) attain a 

 length of from 25 to 3o/x. In swimming Spirillum appears 

 on a superficial examination to undulate like a worm or a 

 serpent, but this is an optical illusion : the spiral is really a 

 permanent one, but during progression it rotates upon its 

 long axis, like Hsematococcus (p. 25) and this double move- 

 ment produces the appearance of undulation. 



