6 OUTLINES OF BACTERIOLOGY 



attached. In accordance with these facts the rod-shaped bacteria are 

 classified as follows : 



I. Bacterium. Immotile (Fig. 7 a). 



II. Bacillus. Motile, the cilia being arranged all round the 

 organism (Fig. 7b). 



III. Pseudomonas. Motile, the cilia being found only at the poles 

 (Fig. 7c). 



These three genera include all the rod-shaped bacteria, the individuals 

 of which are normally quite free. Sometimes under certain conditions 

 the rods form in rows, end to end, like a string of sausages. This is a 

 characteristic mode of growth of Bac. anthracis (Fig. 8). 



The third fundamental type is the Spirillum or spiral form. In the 

 first place, each individual of a species may assume the form of a 



FIG. 8. FIG. 0. Vibrio form. 



" bent " rod. This is known as the Vibrio form of growth (Fig. 9). 

 It is exhibited in the dreaded organism which causes cholera. This is 

 not strictly a spiral, but rather an intermediate form between the true 

 rod shape and the true spiral, arid is best included here. 



It will readily be seen that those bacteria, which exhibit twists, will 

 show a variety of different forms, according to the number of the 

 twists, and the closeness or looseness of the spirals. The classification 

 of these forms is based, like that of the rod-bacteria, on the presence or 

 absence of cilia. 



We have 



I. Spirosoma. Spiral cells without organs of motion (Fig. 10). 

 II. Microspira. Spiral cells with 2-3 cilia at the poles (Fig. 11). 

 III. Spirillum. Spiral organisms with 5-20 polar cilia (Fig. 12). 



groups, examined by him, could, by appropriate cultivation be made motile. As 

 the supposed iion-motility of Micrococcus and Sarcina is the only characteristic 

 separating them from Planococcus and Planosarcina respectively, it is extremely 

 probable that the five groups mentioned above must be reduced to three, viz. 

 Streptococcus, Planococcus (or Micrococcus), and Planosarcina (or Sarcina). The 

 author has also found that all the Streptococcus species examined by him could 

 be rendered motile by appropriate cultivation (CentralUatt fur Bakteriologie y 

 Abth. ii. Bd. ix.). 



