II. 



CLASSIFICATION. 



THE earlier naturalists Ehrenberg (1838), Dujardin (1841) 

 placed the bacteria among the infusoria; but they are now recog- 

 nized as vegetable microorganisms, differing essentially from the 

 infusoria, which are unicellular animal organisms. One of the prin- 

 cipal points in differentiating animal from vegetable organisms 

 among the lowest orders of living things is the fact that animal 

 organisms receive food particles into the interior of the body, assimi- 

 lating the nutritious portion and subsequently extruding the non- 

 nutritious residue ; vegetable organisms, on the other hand, are 

 nourished through the cell wall which encloses their protoplasm, by 

 organic or inorganic substances held in solution. 



Ehrenberg (1838), under the name of vibrioniens, established four gen- 

 era, as follows : 



1. Bacterium filaments linear and inflexible. 



2. Vibrio filaments linear, snake-like, flexible. 



3. Spirillum filaments spiral, inflexible. 



4. 'Spirochcete filaments spiral, flexible. 



Dujardin (1841) united the two genera Spirillum and Spirochcete of 

 Ehrenberg, and added to the description of the generic characters as fol- 

 lows: 



1. Bacterium filaments rigid, with a vacillating movement. 



2. Vibrio filaments flexible, with an undulatory movement. 



3. Spirillum filaments spiral, movement rotatorv. 



It will be seen that this classification leaves no place for the motionless 

 bacilli, such as the anthrax bacillus and many others, and does not include 

 the spherical bacteria, now called micrococci. 



The classification of Davaiue (18G8) provides for the motionless, fila- 

 mentous bacteria, but does not include the micrococci. This author first 

 insisted that the vibrioniens of Ehrenberg are truly vegetable organisms, 

 allied to the algae. He makes four genera, as follows: 



Filaments straight or bent, i Moving spontane- \ Rigid Bacterium. 

 but not in a spiral, ously, ) Flexible Vibrio. 



( Motionless, . Bacteridium. 

 Filaments spiral, Spirillum. 



Following Davaine, the French bacteriologists frequently speak of the 

 motionless anthrax bacillus as la bacteridie. 



Hoffman in 1869 included in his classification the spherical bacteria, 

 and pointed out the fact that motility could not be taken as a generic char- 

 acter, as it was not constant in the same species and depended to some ex- 

 tent upon temperature conditions, etc. 



