GENERAL CHARACTERS OF BACTERIA. 



II 



short ones, with only a single turn (Fig. 7, c). This type is of less 

 importance than the others. 



Motility of Bacteria. The next point of distinction among 

 bacteria is based upon their motility. Some bacteria are capable 

 of an active swimming motion, others are stationary. The motion 

 is produced- by minute, extremely delicate, vibrating hairs, called 



FIG. 7. General shape of bacteria, a, spheres; b, rods; c, spirals. 



flagella (Fig. 8). The flagella are so delicate that they cannot often 

 be seen in the living bacteria, and they do not stain by the ordinary 

 method of staining. Therefore, they are never seen in the usual 

 microscopic preparations. They may be seen by special methods, 

 but these are so difficult that the beginner cannot use them satisfac- 

 torily. The question of their motility is, however, usually determ- 



FIG. 8. Showing bacteria with flagella; a, peritrichic; &, lophotrichic; c, monotrichic. 



ined without staining, by the study of the living bacteria (Experiment 

 No. 8). These flagella are differently distributed upon different 

 bacteria. Sometimes there is a single one on the end of a rod 

 (Fig. 8, c) monotrichic; sometimes a small tuft at one 'or both ends 

 of a rod (Fig. 8, b) lophotrichic; and sometimes there is a cover- 

 ing of flagella over the whole body of the bacterium (Fig. 4, a) 

 peritrichic. 



