Bacteria are most conveniently classified according to their shape. Thus
we recognise (1) those that are globular--_cocci_; (2) those that
resemble a rod--_bacilli_; (3) the spiral or wavy forms--_spirilla_.
_Cocci_ or _micrococci_ are minute round bodies, averaging about 1 [micron]
in diameter. The great majority are non-motile. They multiply by fission;
and when they divide in such a way that the resulting cells remain in
pairs, are called _diplococci_, of which the bacteria of gonorrhoea and
pneumonia are examples (Fig. 5). When they divide irregularly, and form
grape-like bunches, they are known as _staphylococci_, and to this
variety the commonest pyogenic or pus-forming organisms belong (Fig. 2).
When division takes place only in one axis, so that long chains are
formed, the term _streptococcus_ is applied (Fig. 3). Streptococci are
met with in erysipelas and various other inflammatory and suppurative
processes of a spreading character.
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