134 SCHIZOMYCETES 



culture of the same bacillus, but grown under different 

 conditions, may consist almost entirely of long fila- 

 ments or threads. This variation in morphology is 

 known as "pleomorphism." 



Some of the factors influencing pleomorphism are : 



1. The composition, reaction, etc., of the nutrient 

 medium in which the organism is growing. 



2. The atmosphere in which it is cultivated. 



3. The temperature at which it is incubated. 



4. Exposure to or protection from light. 



The various points in the anatomy morphology and 

 physiology of bacteria upon which stress is laid in the 

 following pages should be studied as closely as is possible 

 in preparations of the micro-organisms named in con- 

 nection with each. 



ANATOMY. 



1. Capsule (Fig. 85, b). A gelatinous envelope 

 (probably akin to mucin in composition) surrounding 

 each individual organism, and preventing absolute con- 

 tact between any two. In some species the capsule 

 (e. g., B. pneumonias) is well marked, but it cannot be 

 demonstrated in all. In very well marked cases of 

 gelatinisation of the cell wall, the individual cells are 

 cemented together in a coherent mass, to which the 

 term "zoogloea" is applied (e. g., Streptococcus mesen- 

 teroides) . In some species colouring matter or ferric 

 oxide is stored in the capsule. 



2. Cell Wall (Fig. 85, c). A protective differen- 

 tiation of the outer layer of the cell protoplasm; 

 difficult to demonstrate, but treatment with iodine or 

 salt solution sometimes causes shrinkage of the cell 

 contents " plasmolysis " and so renders the cell wall 

 apparent (e. g., B. megatherium) in the manner 

 shown in figure 85. Stained bacilli, when examined 

 with the polarising microscope, often show a doubly 



