MOTILITY 71 



in some way converted directly into a vegetating cell. It 

 evinces no motion other than the mechanical tremor common 

 to all insoluble microscopic particles suspended in fluids, 

 and it remains quiescent until there appear conditions favor- 

 able to its subsequent development. 



By the ordinary methods of staining, spores do not become 

 colored, so that they appear in the stained 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. 6). 



Occasionally spore-formation is accompanied by an en- 

 largement of the cell at the point at which the process is 

 in progress. As a result, the cell loses its regular rod 

 shape and becomes that of a club, a drum-stick, or a loz- 

 enge, depending upon whether the location of the spore 

 is to be at the pole or in the centre of the cell. (See 

 Fig. 6, c and d.) 



Motility. — In addition to the property of spore-formation 

 there is another striking difference between various species 

 of bacteria, namely, the property 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 cells possessing them are propelled 

 through the fluid. In some cases the flagella are located at 

 but one end of the organism, either singly (monotrichic) or 

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

 the bacillus of typhoid fever, they are given off from the 

 whole surface of the rod (peritrichic). (See Fig. 7.) 



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 



