LOCOMOTION AND LOCOMOTORY ORGANS 



15 



then appear deeply coloured. Both bacteria and their cilia are by this 

 process made to look thicker than they really are, and appear therefore 

 more clearly. 



According to the arrangement of the cilia upon the cell the bacteria may 

 be divided into three groups — monotricha, lophotricha, and peritricka(\0). 

 The members of the first division bear a single flagellum at one end of the 

 cell (Figs. 8, a, and 23) ; examples are the cholera germ and other vibrios, 

 and B. pyocyaneus. The lophotrichous bacteria have in place of the 

 single flagellum a brush or tuft of cilia {Spirillum, many putrefactive 

 bacteria ; Figs. 8, b ; 22, a; 12) and the peritrichous forms have their whole 

 surface beset with cilia more or less thickly arranged, so that they appear 

 almost as though they had a shaggy coat (B. typhi, B. coli communis, some 

 butyric ferments, B. subtilis, B. pro- 

 tens, and many others ; Figs. 8, c, e, and 

 11, 13, 22, 24, 28). The arrangement 

 of the cilia is constant in each species, 

 and even the number of cilia united to 

 form the terminal tuft has a taxo- 

 nomic value. 



Functionally and structurally the 

 cilia of bacteria correspond to the 

 analogous organs in other groups, 

 such as the swarm-spores of algae and 

 fungi, the infusoria, and the ciliated 

 cells of metazoa. They consist of long 

 delicate threads of protoplasmatic sub- 

 stance, which vibrate to and fro and 

 propel the bacterium through the water 

 as a boat is propelled by oars. They 

 grow out slowly from the body of 

 the cell (Fig. 8, d), and are not re- 

 tractile. The shrinkage of the cell- 

 contents during plasmolysis leaves the 



cilia unaffected, so that they would seem to be fairly independent organs. 

 They receive their nourishment and vis viva from the protoplasm, with 

 which they are connected through minute pores in the cell- wall. 



The cilia are very sensitive to injury, unfavourable conditions causing 

 them to be thrown off. When shed in this way they sometimes become 

 disintegrated and disappear in a few minutes. As a result a preparation 

 made from a culture containing actively mobile bacteria frequently shows 

 not a single cilium, and this is particularly the case when old cultures are 

 employed, the bacteria they contain being especially sensitive. Not infre- 

 quently the cilia become rolled up or looped before they are shed, and 



Fig. 8. Types of ciliation. a, monotrichous 

 {Vibrio choleras) ; b t lophotrichous (Spirillum un~ 

 dula)\ c, peritrichous (typhoid bacilli); d, develop- 

 ment during fission of the cilia tuft of Spirillum 

 undula ; <r, partial and (to the right) complete 

 looping; of the cilia in Bac* subtilis. Magn. a-e 

 2250. In Figs, a, 3, c, the structure of the cell-con- 

 tents has been taken from iodine preparations 

 (Fig. 5) in order to illustrate the structure of bac- 

 teria as far as is known at the present time. In 

 Figs, d and e the contents are schematically shaded, 

 for in these preparations (stained by Loeffler's 

 method) the precipitation of colour on the cell- 

 surface conceals the structure. See also Figs. 11, 

 12, 13, 17, 22, 23 ; 24, 26 and 28, which give further 

 examples of various ciliation. 



