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 vibrios (Fig. 



441 442 



Figs. 438-442. — Typical forms of bacteria: 438, coccus type; 439, the same, 

 hanging together in chains ; 440, rod-shaped bacteria (bacillus type), the clear areaa 

 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., spirillum). 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 



