308 PRACTICAL COURSE IN BOTANY 
the different shapes you see. Some appear as slender 
chains or filaments, but this is due to the individual cells’ 
adhering together for a time before breaking up and begin- 
ning an independent existence. The small, rounded bodies, 
like a period (Fig. 438), are cocci; the slender, rod-shaped 
ones — sometimes slightly curved (Fig. 440) — are bacilli 
(sing., bacillus) ; the comma-shaped ones, and those gener- 
ally showing a slight spiral curvature, are wbrios (Fig. 
441 442 
Fics. 438-442. — Typical forms of bacteria: 438, coccus type; 439, the same, 
hanging together in chains; 440, rod-shaped bacteria (bacillus type), the clear areas 
in some of these are spores; 441, forms of vibrio ; 442, forms of spirillum. 
441); the spirally twisted ones, like a corkscrew (Fig. 442), 
are spirilli (sing., spirdllum). These are the principal forms 
which it is important to distinguish and remember. The 
names are applied very loosely, however, in practice, bacillus 
being often used as a general term applicable to almost any 
kind, — the spirillum of cholera, for instance, being com- 
monly known as the cholera bacillus, while by some authors 
vibrios are ranked as a variety of spirillum. 
349. Life history of a typical bacterium. — A pure culture 
of the Bacillus subtilis can easily be obtained by boiling 
some of the hay infusion for half an hour and then leaving 
