124 MANUAL OF BACTERIOLOGY. 



with tetanus bacilli (Fig. 44). When a bacillus assumes a 

 spindle shape on account of having the middle part bulged 

 through the formation of a spore it is called a clostridium. 

 With rare exceptions, a single bacillus contains but one 

 spore. Under favorable conditions the spores germinate, as 

 it is called, and develop to the adult form of the organism. 

 This may be witnessed in hanging-drop preparations. 



Motility. Motility is rarely exhibited by micrococci ; 

 some bacilli possess it and some do not; while nearly all 

 of the spirilla are motile. The phenomenon is observed in 

 the hanging-drop. The degree of motility is variable, being 



FIG. 45. 



Bacteria showing Flagella. 



sometimes slight and sometimes very active. When seen 

 under a high power the little particles taken from a cul- 

 ture of a motile organism may look like a writhing mass 

 of maggots or like tadpoles in a pool. The motility is most 

 active in young cultures. The movement results from the 

 vibration of little processes, or flagella (Fig. 45). Of these 

 there may be one or several. They may be placed singly 

 or in groups, at the end, or scattered around the sides. They 

 are extremely difficult to demonstrate except by special stain- 

 ing methods, which, furthermore, are decidedly capricious. 

 After the flagella have been stained, the bacteria appear 

 somewhat larger than when stained by the ordinary 

 methods. The flagella upon the bacilli of typhoid fever are 

 numerous and form a very striking picture. 



Chemotaxis. Motile bacteria possess the property of 

 being attracted by certain substances (positive chemotaxis) 



