BACTERIAL POWERS OF MOTION 11 



non-liguefaciens (green); B. pyocyaneus (green); B. ^prodigiosus 

 (blood-red). 



Motility. — When a drop of water containing bacteria is placed 

 upon a sUde, a clean cover-glass superimposed, and the specimen 

 examined under an oil immersion lens, various rapid movements will 

 generally be observed in the micro-organisms. These are of four 

 chief kinds : (1) A dancing, stationary motion known as Brownian 

 movement. This is molecular, and depends in some degree upon heat 

 and the medium of the moving particles. It is non-progressive, and 

 is well seen in gamboge particles. (2) An undulatory, serpentine 

 movement, with apparently little advance being made. (3) A 

 rotatory movement, which in some water bacilli is very marked, and 

 consists of spinning round, sometimes with considerable velocity, and 

 maintained for some seconds or even minutes. (4) A progressive, 

 darting movement, by which the bacillus passes over some con- 

 siderable distance. 



The conditions affecting the motility of bacteria are but partly 

 understood. Heating the slide or medium accelerates all movement. 

 A fresh supply of oxygen, or indeed the addition of some nutrient 

 substance, like broth, will have the same effect. There are also the 

 somewhat mysterious powers by which cells possess inherent 

 attraction or repulsion for other cells, known as positive and negative 

 chemiotaxis. These powers have been observed in bacteria by 

 Pfeiffer and Ali-Cohen. 



The essential condition in the motile bacilli is the presence of 

 jlagella* These cilia, or hairy processes, project from the sides or 

 from the ends of the rod, and are freely motile and elastic. Some- 

 times only one or two terminal flagella are present ; in other cases, 

 like the bacillus of typhoid fever, five to twenty may occur all round 

 the body of the bacillus, varying in length and size, sometimes 

 being of greater length even than the bacillus itself. It is not yet 

 established as to whether these cilia are prolongations of capsule 

 only, or whether they contain something of the body protoplasm. 

 Migula holds the former view, and states that the position of 

 flagella is constant enough for diagnostic purposes. They are but 

 rarely recognisable except by means of special staining methods. 

 Micrococcus agilis (Ali-Cohen) is one of the rare cases of a coccus 

 which has flagella and powers of active motion. 



Modes of RepPOduetion. — Budding, division, and spore formation 

 are the three chief ways in which Schizomycetes and Saccharomycetes 

 (yeasts) reproduce their kind. Budding occurs in many kinds of 

 yeast-cells, and generally takes place when the nutriment and 



* Aflagellum is a hair-like process arising from the poles or sides of the bacillus. 

 It must not be confused with a, filament, which is a thread-like growth of the bacillus 

 itself. 



