3 6 MORPHOLOGY 



cur separately and become surrounded by a thin sheath of 

 a clear, jellylike, highly refractile substance, which is usually 



FIG. 26 Capsules. Bact. pneumonicum (Friedlander). After Weichselbaum. 



many times broader than the bacterial cell. To this sheath 

 of gelatinous material the name capsule has been applied. 

 Capsule-producing bacteria do not produce capsules under all 

 conditions. The necessary and particular nutrient material 

 must be available for capsule formation. Bacillus capsulatus 

 in milk produces the most typical capsules, while on agar-agar 

 it produces none. Bacterium anthracis on ordinary culture 

 media such as gelatin, agar-agar, beef broth, etc., produces 

 no capsules, while in the blood of an animal infected with an- 

 thrax the capsules are very typical. Sometimes several bac- 

 terial cells appear to be surrounded by a single capsule, e.g. Mic. 

 pneumoniae. In all probability this appearance is due to 

 the amalgamation of the capsules of the several cells. It is 



