MORPHOLOGY AND BIOLOGY OF BACTERIA. 19 



consists of a lining layer of protoplasm, and a loculated 

 space for the cell-fluid. Not rarely the protoplasm of the 

 bacteria contains granules that stain deeply with aniline 

 dyes. The significance of these so-called Babes-Ernst 

 bodies has not been established ; they have been looked 

 upon as the progenitors of spores, as nuclear structures, as 

 degeneration-products, and, finally, as reserve substances. 



The ground-substance of the bacterial cell is surrounded 

 by a cell-capsule or cell-membrane constituted of albuminoid 

 material, in rare instances of cellulose and of varying 

 amounts of a carbohydrate that stains blue with iodin. 

 When the outer layers of this mem- 

 brane possess the property of swelling 

 up greatly and becoming viscid and 

 gelatinous, an appearance is created as 

 if the bacterium possessed a special 

 capsule, and under such circumstances 

 it is customary, in view of the physi- 



! i f Fig. 4. Encapsulated 



cal appearance, to speak of an encap- bacteria. 



sulated bacterium, (Fig. 4.) This 



mucoid transformation of the capsule of the cell occurs in 

 the case of pathogenic bacteria usually only in the animal 

 body, and but seldom in artificial culture-media. 



The length of bacteria varies greatly from one to several 

 micromillimeters (twenty and more), while their thickness 

 is generally less than one micromillimeter. 



Bacteria are in part motile, in part nonmotile. When 

 motility is present, it is dependent upon special motor 

 organs so-called flagella (Fig. 5) which are connected 

 with the body of the cell in varying number and arrange- 

 ment. These represent protoplasmic structures of extreme 

 attenuation, which arise directly from the cell-membrane, 

 and do not extend into the actual ground-substance. The 

 following varieties of motile bacteria may be distinguished : 



1. Monotrocha, with a single flagellum at the pole of 

 the cell. 



2. Amphitrocha, with a single flagellum at each pole, 



3. Lophotrocha, with a cluster of flagella at one pole. 



4. Peritrocha, with a varying number of flagella sur- 

 rounding the body of the bacterium. 



The shape and length of these flagella are extremely 

 variable in the different varieties of motile bacteria. The 

 movement itself is forward, and is always combined with a 



