GENERAL CHARACTERISTICS OF BACTERIA. 43 



bacteria, however, commonly known as capsule bacteria, 

 as shown in Fig. 2, the cell membrane or the outer layers 

 of the membrane are so much thickened that the bacteria 

 seem to be surrounded by a gelatinous envelope or cap- 

 sule, which is distinguished by a diminished power of 

 staining with the ordinary aniline dyes. The demonstra- 

 tion of this capsule may be of help in differentiating 

 between certain bacteria e. g., some forms of the 

 streptococcus and pneumococcus. A peculiarity of 



FIG. 10. 



Faintly stained flagella attached to heavily stained bacilli. 



the capsule bacteria is that, except very rarely, they 

 exhibit this envelope only when grown in the animal 

 body or in special' culture media, such as liquid blood 

 serum, bronchial mucus, etc. ; grown on nutrient 

 gelatin, agar, or potato the capsule is only visible under 

 very exceptional conditions, and then not distinctly. 



The outer surface of bacteria when occurring in the 

 form of spheres and short rods is almost always smooth 



