WHAT ARE BACTERIA ? 39 



than about twice its diameter, it is usually spoken of as a 

 Bacillus : — the length of a bacillus may be eight or ten times 

 the diameter, which ranges from i/* to 2/j. In some cases 

 these bacteria take the shape of short stout spindles or lemons, 

 especially during the stage of spore formation, when they are 



Photo-micrograph of Proteus Vulgaris Bacillus, in the form of short rods, x looo. 



spoken of as Clostridium forms, of which an exceedingly 

 good example is the spore-bearing Bacillus butyricus. 



Bacilli increase in length, and, becoming more or less 

 jointed as vegetative division takes place, form the long 

 delicate jointed threads which are spoken of as Lepto- 

 thrix forms when there is no apparent branching, but if 

 pseudo-ramifications, such as are found in Cladothrix dicho- 

 toma and are due to vertical division taking place in one of 

 the terminal cells, are present, we have the Cladothrix form. 



