CHAPTER IX 

 BACILLUS [Des?nobacterium, Cohn) 



General Characters. — Bacilli are cylindrical or rod-shaped 

 bacteria, which are rounded or square-cut at their extremi- 

 ties ; they are longer in proportion to their thickness, and 

 divide by fission, forming straight, curved, or zigzag chains 

 of two, four, six, or more elements. Many species of bacilli 

 in suitable nourishing material grow by repeated divi- 

 sion into longer or shorter chains of bacillus — filaments or 

 leptothrix — while other species have little or no tendency to 

 form filaments. These appear straight or wavy and twisted, 

 isolated or in bundles ; and, although in the fresh condition 

 they appear of a homogeneous aspect, when suitably pre- 

 pared, as by drying and staining with aniline dyes, they show 

 themselves composed of shorter or longer cubical, cylindrical, 

 or rod- shaped protoplasmic elements, contained in linear 

 series within a general hyaline sheath ; between many of the 

 elements is a fine transverse septum. The isolated bacilli 

 are likewise composed of a membrane and protoplasmic 

 contents. These latter appear homogeneous or finely 

 granular and, when stained with aniline dyes, absorb the 

 dye very easily and retain it better and longer than the 

 sheath, 



