36 



THE FUNDAMENTAL PRINCIPLES. 



THE MOTILITY OF BACTERIA. 



Motility, or the power of transporting themselves from 

 place to place, is possessed by a number of bacteria. This 

 is effected by filamentous or hair-like processes arising from 

 the body of the bacteria, and called flagella. It must not 

 be confounded with the peculiar whirling or dancing move- 

 ment so often seen under the microscope, even in inorganic 

 particles, and called the Brownian movements. Motility, 

 except in two instances, has so far been observed only in 

 bacilli and spirilla. Its rapidity depends on the particular 

 bacterium, its mode of cultivation, the age of the culture, 

 and other similar factors. Some bacteria after repeated arti- 

 ficial cultivation seem to lose their motility, which, however, 

 may be restored fully by passing through an animal. 



FIG. 8. 



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). (Abbott.) 



The flagella are hair-like processes consisting of the same 

 material as the bacterial cell-membrane, and are so minute as 

 scarcely to be visible under the highest power of the micro- 

 scope unless they are stained by special processes, as will be 

 described in the chapter on staining. Whenever there is 

 only a single flagellum at one of the poles of the bacillus, this 

 is said to be monotrocha ; whenever there is a single flagellum 

 at each pole of the bacterium, it is said to be amphitrocha ; 

 whenever there is a cluster of flagella at one pole, the bac- 

 terium is said to be lophotrocha ; and finally, when a varying 

 number of flagella seem to arise from different portions of 

 the body of the bacterium, it is said to be peritrocha. These 

 features are shown in Fig. 8. 



