154 GENERAL BIOLOGY OF MICRO-ORGANISMS 



forms of bacteria become enclosed in a gelatinous capsule. This 

 seems to be a viscid material secreted by the cell through the cell 

 membrane. The motile bacteria possess exceedingly slender hair- 

 hke processes, called flagella, which serve as organs of locomotion. 

 These processes apparently take origin from the cell membrane. 

 Bacteria without flagella are spoken of as 

 atrichous, those with a single flagellum at 

 one end as monotrichous, those with a flag- 

 ellum at either end as amphitrichous. When 

 there is a tuft of flagella at the end, the dis- 

 tribution is said to be lophotrichous, and 



capsules. . '■ ' 



when they are distributed all over the sur- 

 face the arrangement is called peritrichous. The internal 

 structure of the bacterial cell has received comparatively Uttle 

 attention. The direct microscopic study of the living cells 

 shows them to be finely or coarsely granular, or sometimes nearly 

 homogeneous. No constant internal structures can be distin- 

 guished. Ordinary simple staining with the basic aniline dyes 

 colors the bacterial cell diffusely and intensely, usually with- 

 out any internal differentiation. The cell membrane between 



Pig. 70. — Bacteria showing flagella. 



two cells in a chain may remain relatively colorless and so be 

 differentiated from the protoplasm on either side. At times the 

 stainable substance is unevenly distributed in the cell, perhaps 

 grouped at the ends of a rod, or in granules or bands. Under 

 special conditions some bacteria show internal granules of special 

 composition, distinguishable as pigment granules or by their 

 microchemical reactions. Granules which stain with iodine, so- 

 called granulose or glycogen granules, are important features 

 of some kinds of bacteria. 



