BACTERIA. 31 



cate straight or wavy filaments project. These are called 

 cilia or flagella, and seem to be organs of locomotion. 

 Sometimes they are observed projecting only from the 

 ends, or from one end; sometimes they are so numerous 

 and so regular in their distribution as to give the organ- 

 isms a woolly appearance. 



Messea ' has grouped the bacteria according to the ar- 

 rangement of their flagella into monotricha, with a single 

 terminal flagellum; amphitricha, with a flagellum at each 

 end; lophotricha, with a bundle of flagella at one end; 

 and peritricha, with a variable number of flagella round 

 about the body. 



Many of the bacteria which are thus supplied with 

 flagella are actively motile and swim about like mi- 

 croscopic serpents. In all probability the locomotory 

 powers of the bacteria are not entirely dependent upon 

 the presence of the flagella, but may sometimes be due 

 to contractility of the protoplasm within an elastic cell- 

 wall. The micro-organisms most plentifully supplied 

 with them are those of the rod and spiral shape. Only 

 one of the spherical forms, Micrococcus agilis of Ali- 

 Cohen, has been shown to have flagella. This and one 

 other species are probably the only motile cocci. Ob- 

 serving that the organisms known to be most active are 

 those best supplied with flagella, it is reasonable to con- 

 clude that the motility is dependent upon the flagella. 



The presence of flagella, however, does not necessarily 

 imply motility, for some of the bacilli amply provided 

 with these appendages are not motile. The flagella may 

 not only serve as organs of locomotion, and be of use to 

 the organism by conveying it from an area where the 

 nutrition is less to one where it is greater, but, as Wood- 

 head points out, may, in the non-motile species, serve to 

 stimulate the passage of currents of nutrient material 

 past the organism, so as to increase the food-supply. 

 The flagellate bacteria have a greater number of repre- 

 sentatives among those whose lives are spent in water 



1 Rivista d'igiene e sanita publica, 1890, ii. 



