These consist of long or short cylindrical cells, with rounded or sharply rectangular ends, usually not more than broad, but varying very greatly in length. They may be motile or non-motile. Where flagella occur, these maybe distributed all round the organism, or only at one or both of the poles {pseudomonas).
Several species are provided with sharply marked capsules (B. Pneumonia). In many species endogenous sporulation occurs. The spores may be central or terminal, round, oval, or spindle-shaped.
Great confusion in nomenclature has arisen in this group in consequence of the different artificial meanings assigned to the essentially synonymous terms bacterium and bacillus. Migula, for instance, applies the former term to non-motile species, the latter to the motile. Hueppe, on the other hand, calls those in which endogenous sporulation does not occur, bacteria, and those where it does, bacilli. In the ordinary terminology Of systematic bacteriology the word bacterium has been almost dropped, and is reserved, as we have done, as a general term for the whole group. It is usual to call all the rod-shaped varieties bacilli. And until the botanists themselves agree to adopt a common standard of nomenclature, it is preferable, we think, to retain the use of the older system throughout this site.
