CHAPTER IX. 



BACILLUS (Desmobacterium, Colin). 



General Characters. Bacilli are cylindrical or rod-shaped 

 bacteria, which are rounded or square-cut at their extremities ; 

 they are longer in proportion to their thickness than bac- 

 terium termo, and divide .by fission, forming straight, curved, 

 or zigzag chains of two, four, six, or more elements. Many 

 species of bacilli in suitable nourishing materials grow by 

 repeated division into longer or shorter chains of bacillus- 

 filaments or leptothrix. 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 

 prepared, as "by drying and staining with anilin dyes, they 

 show themselves composed of shorter or longer cubical, cylin- 

 drical, or rod-shaped protoplasmic elements, contained in linear 

 series within the general hyaline sheath : between many of 

 the elements is a fine transverse septum. The isolated bacilli 

 are likewise composed of a membrane and protoplasmic con- 

 tents. These latter appear homogeneous or finely granular, 

 and when stained with anilin, absorb the dye very easily and 

 retain it better and longer than the membrane. According to 

 the stage and the rapidity of their growth, the bacilli vary much 

 in length ; this is the case not only with the single bacilli and 

 short chains, but also in an eminent degree with the elements 

 of a bacillus-filament or leptothrix. In each case, indeed, it 

 is possible to ascertain that all lengths occur from the cubical 

 or spherical element to the cylinder or rod. The former 

 elongate into the latter and then divide. According to whether 

 division occurs in a short or long element, the daughter- 

 elements are cubical or spherical in the former, cylindrical or 

 rod-shaped in the latter case. This applies to single bacilli, 

 to short chains, and to the leptothrix forma. 



