GENERAL CHARACTERISTICS OF BACTERIA. 39 
unequal at different portions. Spore formation also 
causes an irregularity of the cell outline (Fig. 12). 
The bacilli divide only in the plane perpendicular to 
their long axis. A classification, therefore, of bacilli 
Fie. 5. Fig. 6, 
Bacilli, single and in pairs. Bacilli, single and in threads. 
Small bacilli, mostly in pairs. 
according to their manner of grouping is much simpler 
than in the case of the cocci. We may thus have bacilli 
as isolated cells, as pairs, or as longer or shorter chains. 
3. Spiral Form, or Spirillum. The members of the 
third morphological group are spiral in shape, or rather 
