MOTILITY. 61 



MOTIIITY. In addition to the property of spore-for- 

 mation there is another striking difference between vari- 

 ous species of the rod-shaped organisms, namely, the prop- 

 erty of motility, by which some of them are distinguished. 

 This power of motion is due to very delicate, hair- 

 like appendages or flagella, by the lashing motions of 

 which the rods possessing them are propelled through 

 the fluid. In some cases the flagella are located at 

 but one end of a bacillus, either singly (monotrichic) or 

 in a tuft (lophotrichic) ; and in some cases, especially 

 Nvith the bacillus of typhoid fever, they are given off 



FIG. 7. 



a o c 



a. Spiral forms with a flagellum at only one end. 6. Bacillus of typhoid 

 fever with flagella given off from all sides, c. Large spirals from stagnant 

 water with wisps of flagella at their ends (spirillum undula). 



from the whole surface of the rod (peritrichic). (See Fig. 

 7.) In a few instances similar locomotive organs have 

 been detected on spherical bacteria i. e., motile micro- 

 cocci have been observed. 



For a long time this property of independent motion 

 could only be assumed to be due to the possession of 

 some such form of locomotive apparatus, because similar 

 appendages had been seen upon some of the large motile 

 spirilla found in stagnant water, but it was not until a 

 few years ago that the accuracy of this assumption was 



