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 
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 
