18 CLASSIFICATION. 
or more elements, which remain associated in more or less regular 
cubical masses. 
BACILLI. 
General Characters.—Rod-shaped and filamentous (not spiral) 
bacteria in which there is ‘no differentiation between the extremities 
of the rods; reproduction by binary division in a direction trans- 
verse to the long axis of the rods, or by binary division and the for- 
mation of endogenous spores ; rigid or flexible ; motile or non-motile. 
BacILuus.—Characters as given above. 
Bacterium.—This genus, established by Dujardin, is now generally 
abandoned, the species formerly included in it being transferred to the genus 
Bacillus. As defined by Cohn, the generic characters were: Cells cylindri- 
cal or elliptical, free or united in pairs during their division, rarely in 
fours, never in chains, sometimes in zodgloea (differing from the zodgloea 
of spherical bacteria by a more abundant and firmer intercelluar substance), 
having spontaneous movements, oscillatory and very active, especially in 
media rich in alimentary material and in presence of oxygen. 
Clostridium.—Rod-shaped bacteria which form large, endogenous, and 
usually oval spores ; these are centrally located, and during the stage of 
spore formation the rods become fusiform. 
SPIRILLA. 
General Characters.—Curved rods or spiral filaments ; rigid or 
flexible ; reproduction by binary division, or by binary division and 
the formation of endogenous spores (or by arthrospores ?) ; move- 
ments rotatory in the direction of the long axis of the filaments. 
SprRILLUM.—Characters as above. 
Spirochcete.—Flexible, spiral filaments; movements rotatory. 
Vibrio.—Filaments flexible, straight or sinuous; movements sinuous. 
A considerable number of bacteria which are usually seen as short, curved 
rods, but which may grow out into long, spiral filaments, are described by 
some authors under the generic name Vibrio, e.g., the so-called ‘‘comma 
bacillus” of Koch—‘' Spirillum cholere Asiaticee”’; the spirillum of Finkler 
and Prior—‘‘ Vibrio proteus”; the spirillum described by Gameléia—‘‘ Vibrio 
Metschnikovi,” etc. These microdrganisms have not the characters which 
distinguished the genus Vibrio as established by Ehrenberg, and we prefer to 
follow Fliigge in describing them under the generic name §pirillum. 
The pathogenic bacteria now known belong to one or the other 
of the above-described genera, and the attention of bacteriologists 
has been given chiefly to the study of micrococci, bacilli, and spirilla. 
But the botanists place among the bacteria certain other forms which 
are found in water, and which, in a systematic account of this class 
of microérganisms, demand brief attention at least. These are in- 
cluded in Baumgarten’s second group, which includes the pleomor- 
phous bacteria. 
SPIRULINA (Hueppe).—The vegetative cells are sometimes rod- 
shaped and sometimes spiral; in suitable media they may grow out 
