44 BACTERIOLOGY. 



and devoid of appendages ; but the longer rods and 

 spirals are usually provided with fine hair-like append- 

 ages or flagella, which are their organs of motility. 

 These flagella, either singly or in numbers, are some- 

 times distributed over the entire body of the cell, or 

 they may form a tuft at one end of the rod, or only 

 one polar flagellum is found. The polar flagella 

 appear on the bacteria shortly before division. The 

 nature of flagella is little understood; they are believed 

 by some to be formed of protoplasmic material which 

 penetrates the cell membrane, and probably have the 

 property of protrusion and retraction. So far as we 

 know, the flagella are the only means of locomotion 

 possessed by the bacteria. They are not readily 

 stained, special staining agents being required for 

 this purpose. The envelope of the bacteria, which 

 usually remains unstained with the ordinary dyes, 

 then becomes colored and more distinctly visible than 

 is commonly the case. Occasionally, however, some 

 portion of the envelope remains unstained, when the 

 flagella present the appearance of being detached from 

 the body of the bacteria by a narrow zone. Unfor- 

 tunately, many of the methods employed for staining 

 flagella cause them to become degenerated, so that their 

 perfect demonstration is often very difficult. In cul- 

 tures of richly flagellated bacteria peculiar pleated 

 masses sometimes are observed, consisting of flagella 

 which have been detached and then matted together. 

 Bacteria may lose their power of producing flagella for 

 a series of generations. Whether their power be per- 

 manently lost or not we do not know. 



The vegetative reproduction of bacteria takes place by 

 division. When development is in progress a single 



