4 PRACTICAL DAIRY BACTERIOLOGY 



common microscopical preparation no internal structure can be 

 seen, the bacteria appearing as faint stained balls. The cocci, 

 however, differ somewhat in their method of growth, thus 

 enabling the microscopist to distinguish different kinds, as will 

 be mentioned presently. 2. The rod formed bacteria. (Fig. 3, 

 e, f, g.) These organisms are longer than they are broad, some- 



FIG. 3 SHAPES OF BACTERIA 



a. Spirillum. b. Microcpccus. c. Micrococcus. (/. Streptococcus 

 e /i. Rod-shaped bacteria, i and /. Divisions 



times only slightly so, but at other times very much longer, 

 forming, indeed, long, slender threads. 3. The spiral formed 

 bacteria. These are either a long coil spiral or a very short 

 one with only a single turn. (Fig. 3, a.) The type is rare in 

 milk, and it is not likely that the dairyman will ever run across 

 them, even if he makes extended microscopic studies. 



Motility. 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. 4.) The flagella are so delicate that they 

 cannot ordinarily be seen in the living bacteria, and they do 

 not stain by the ordinary method of staining. They are, there- 



