MOTILITY. 



57 



cells as pale, transparent, oval bodies, surrounded by 

 the remainder of the cell, which has taken up the dye. 



A single cell produces but one spore. This may be 

 located either at an extremity or in the centre of the 

 cell. (Fig. 5.) 



Occasionally spore-formation is accompanied by an 

 enlargement of the cell at the point at which the proc- 

 ess is in progress. As a result, the outline of the cell 

 loses its regular rod shape and becomes that of a club, 

 a drum-stick, or a lozenge, depending upon whether 

 the location of the spore is to be at the pole or in the 

 centre of the cell. (See Fig. 5, e and d.) 



In addition to the property of spore-formation there 

 is another striking diiference between various species 

 of the rod-shaped organisms, namely, the property 

 of motility, by which some of them are distinguished. 

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



/^ 



Fig. 7. 



ah c 



u. Spiral forms with a, flagellum at only one end. b. 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). 



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 



