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. 



BACILLUS. 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 denned 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 zoogloea (differing from the zooglcea 

 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. 



SPIRILLUM. 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' 1 of Koch " Spirillum cholerae Asiaticae"; the spirillum of Finkler 

 and Prior " Vibrio proteus" ; the spirillum described by Gameleia "Vibrio 

 Metschnikovi,"etc. These microorganisms 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 Spirillum. 



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 microorganisms, 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 



