30 PRINCIPLES OF BACTERIOLOGY 



have a rather indefinite cell membrane surrounding the central proto- 

 plasm. This, according to Zettnow, contains a nucleus, or at least 

 the equivalent of the nucleus of the higher micro-organisms, lying 

 within a network of protoplasma. The nuclear substance takes the 

 chromatin stains and is often so abundant that the material holding it is 

 covered up. The plasma substance divides into the entoplasma and the 

 ectoplasma. The first is more or less intimately connected with the 

 nuclear substance, and is especially collected at the ends of the long 

 bacteria. This stains blue by the Romanowski method. The ecto- 

 plasma, or cell membrane, is a much more concentrated substance than 

 the entoplasma, and remains unstained ordinarily, but by special stains 

 appears as an external shell or flagella. The membrane surrounding 

 some bacteria is very slightly developed ; in others, as in tubercle bacilli, 

 it is well developed. It is never a cellulose envelope like the higher 

 plant cells, but by means of its chemical composition is differentiated 

 from the inner plasma, as shown in plasmolysis. Thus, when bacteria 

 are placed in 1 per cent, chloride of sodium the central body contracts 

 and separates itself in places from the capsule, as shown in Fig 13. 



THE CAPSULF. The capsule consists of an inner tougher portion 

 immediately surrounding the central body and which gradually passes 

 into a thinner and more watery outer portion which is uncolored by 

 ordinary staining method. 



This is indicated by the greater apparent diameter of bacteria when 

 stained with certain dyes beyond what they usually show. Certain 



bacteria, however, commonly known as 

 Fl - 14 capsule bacteria, as shown in Fig. 14, have 



the outer layers of the membrane so much 

 thickened that the bacteria seem to be 

 surrounded by a broad gelatinous envelope 

 or capsule, which is distinguished by a 

 diminished power of staining with the or- 

 dinary aniline dyes. The foim of the cap- 

 sule varies with different species (Fig. 12). 

 The demonstration of this capsule is often 

 of help in differentiating between certain 

 bacteria e. g., some forms of the strep- 

 capsule tococcus and pneumococcus. A peculi- 

 formation. arity of 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 

 milk, blood serum, bronchial mucus, etc.; grown on nutrient gelatin 

 agar or potato the capsule is only visible under very exceptional con- 

 ditions, and then not distinctly. 



ORGANS OF MOTILITY. The outer surface of bacteria, when occur- 

 ring in the form of spheres, is almost always smooth and devoid 

 of appendages ; but the rods and spirals are frequently provided with 

 fine, hair-like appendages, or flagella, which are their organs of motility 

 (Figs. 15 and 16). These flagella, either singly or in numbers, are 



