the process of
reproduction the cell protoplasm may be extruded, leaving the empty tube
unaltered in shape.

[Illustration: FIG. 85.--Dragrammatic sketch of composite bacterium to
illustrate details of anatomical structure.]

[Illustration: FIG. 86.--Plasmolysis.]

3. _Cell Contents._--Protoplasm (mycoprotein) contains a high percentage
of nitrogen, but is said to differ from proteid in that it is not
precipitated by C_{2}H_{6}O. It is usually homogeneous in
appearance--sometimes granular--and may contain oil globules or sap
vacuoles (Fig. 85, d), chromatin granules, and even sulphur granules.
Sap vacuoles must be distinguished from spores, on the one hand, and the
vacuolated appearance due to plasmolysis, on the other.

The cell contents may sometimes be differentiated into a parietal layer,
and a central body (e. g., beggiotoa) when stained by haematoxylin.

4. _Nucleus._--This structure has not been conclusively proved to
exist, but in some bacteria chromatin particles have been observed near
the centre of the bacterial cell and denser masses of protoplasm
situated at the poles which exhibit a more marked affinity than the rest
of the cell protoplasm for aniline dyes. These latter are termed polar
granules or _Polkoerner_ (Fig. 85, e). Occasionally these aggregations
of protoplasm alter the colour of the dye they take up. They are then
known as metachromatic bodies or _Ernstschen Koerner_ (e. g., B.
diphtheriae).

5. _Flagella_ (Organs of Locomotion, Fig. 85, a).--These are
gelatinous elongations of the cell protoplasm (or more probably of the
capsule), occurring either at one pole, at both poles, or scattered
around the entire periphery. Flagella are not pseudopodia. The
possession of flagella was at one time suggested as a basis for a system
of classification, when the following types of ciliation were
differentiated (Fig. 87):

[Illustration: FIG. 87.--Types of ciliation.]

1. Polar: (a) _Monotrichous_ (a single flagellum situated at one pole;
e. g., B. pyocyaneus).

(b) _Amphitrichous_ (a single flagellum at each pole; e. g.,
Spirillum volutans).

(c) _Lophotrichous_ (a tuft or bunch of flagella situated at each
pole; e. g., B. cyanogenus).

2. Diffuse: _Peritrichous_ (flagella scattered around the entire
periphery e. g., B. typhosus).

~PHYSIOLOGY.~

~Reproduction.~--_Active Stage._--Vegetative, i. e., by the division of
cells, or "fission."

1. The cell becomes elongated and the protoplasm