148 GENERAL BIOLOGY OF MICRO-ORGANISMS 



membrane. The motile bacteria possess exceedingly slender hair- 

 like 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 flagellum 

 at either end as amphitrichous. When there 

 ^ ft is a tuft of flagella at the end, the distribution 



($) ^ /^ K is said lobe lophotrichous, and when they are 

 distributed all over the surface the arrange- 

 ment is called peritrichous. The internal 



structure of the bacterial cell has received 

 FIG. 67. Bactena with 



capsules. comparatively little attention. The direct 



microscopic study of the living cells shows 

 them to be finely or coarsely granular, or sometimes nearly ho- 

 mogeneous. No constant internal structures can be distinguished. 

 Ordinary simple staining w'th the basic aniline dyes colors the bac- 

 terial cell diffusely and intensely, usually without any internal 

 differentiation. The cell membrane between 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 un- 

 evenly distributed in the cell, perhaps grouped at the ends of a rod, 



FIG. 68. Bacteria showing flagella. 



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. 



The recognition of the cell nucleus has received special atten- 

 tion. Zettnow, more especially, has shown that the chromatin or 

 essential nuclear substance is present in the bacterial cell as finer 



