I2 THE GENERAL CHARACTERS OF MICROORGANISMS 
formed bacteria. These are either long, coiled spirals, or very 
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 
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 satisfactorily. The question of their motility is, however, 
Fic. 8.—Showing bacteria with flagella; a, peritrichic; b, lophotrichic; c, monotrichic. 
usually determined without staining, by the study of the living 
bacteria (Experiment No. 8). These flagella are differently dis- 
tributed 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, ’)—lophotrichic; and some- 
times there is a covering of flagella over the whole body of the 
bacterium (Fig. 4, «)—peritrichic. 
Spore-production.—A further point of importance in dis- 
tinguishing the different kinds of bacteria is spore-production, a 
matter which will be more fully discussed later (page 16). Many 
of the rod-shaped bacteria have the power of producing a tiny 
spore within the rod (see Fig. 11) which is more resistant to heat 
and drying than-the rod itself. The ability to produce these 
‘spores is used in some classifications of bacteria. 
