42 MORPHOLOGY OF BACTERIA 



The speed with which they travel, being magnified to the same 

 extent as are the organisms, makes them appear to be travelling 

 with enormous speed, insomuch that Leeuwenhoek, who first 

 described it, stated that "they seemed to tear through each other." 

 The actual speed, however, is not great for the typhoid bacillus 

 may travel a distance of 4 mm. or about 2000 times its own length 

 in one hour, whereas the cholera spirillum has been known to attain 

 a speed of 18 cm. per hour. Some organisms are motile if grown on 

 one cultural media, and non-motile if grown on another ; for example, 

 the colon bacillus is usually motile if examined from young cultures 

 grown on gelatin or agar, but non-motile if taken from boullion. 



Organs of Locomotion. The protoplasmic threads called organs 

 of locomotion are flagella or cilia. A cilium differs from a flagellum 

 in that the former has a simple curve whereas the latter has a com- 

 pound curve, like a whip lash. The size, the number, and the 

 arrangement of the flagella are characteristic of the organism. 

 Most bacteria possess flagella rather than cilia. Differences exist in 

 respect to the number and position of the flagella on the cell body. 

 Some forms possess only a single flagellum at one pole and are 

 called monotricha, others a flagellum at each pole (amj^jtricha), 

 others a tuft of flagella at one pole (lophotricha), otheiHtgella 

 projecting from the whole body of the cell (peritricha) ; a8^ s ^i\\ 

 others possess no flagella and are known as atricha. 



FIG. 11. Pneumococci with unstained capsules. From pneumonia sputum, 

 stained with carbol-fuchsin and differentiated with weak acid alcohol. Magnifica- 

 tion 1000. (Karg and Schmorl.) 



Cell Wall (Ectoplasm). The cell wall is the slightly differentiated 

 outer portion of the cell substance. Many writers prefer to call it 

 "ectoplasm." Early in the history of bacteriology it was con- 

 sidered that the absence of cellulose in bacteria indicated that they 

 belonged to the animal rather than to the plant kingdom. But 

 cellulose or hemicellulose has been identified in bacteria from pus, 



