226 GENERAL SYSTEMATIC BACTERIOLOGY 



Plump rods, without spores, Gram-negative, motile by means of peritrichous 

 flagella, or non-motile, liquefying gelatin very slowly or not at all. Usually show- 

 ing marked power to ferment carbohydrates, frequentlj'^ with gas production. 



The type species is Bacterium coli Escherich. 



The genus is a large one, including many species. It is generally divided into 

 subgroups based primarily upon the fermentative reactions. It may be conven- 

 ient to recognize these as subgenera separated from each other by the charac- 

 teristics noted in the following key: 



Key to the subgenera of Bacterium 



A. Organisms which show a maximum of fermentative power, including fermenta- 

 tion of lactose, rarely pathogenic, some forms slowly liquefy gelatin. 



Subgenus 1. Aerohacter (or Eu-Bacterium) . 



B. Organisms not showing maximum fermentative power, never producing gas 

 in lactose, frequently pathogenic, never liquefying gelatin. 



1. Producing acid and gas from glucose, sometimes other sugars, but not 



from lactose Subgenus 2. Salmonella. 



2. Producing gas from none of the carbohydrates, acid sometimes 



formed Subgenus 3. Eberthella. 



Breed, Conn and Baker (1918, p. 445) suggest that the name be 

 dropped, or at most regarded as a general designation for insufficient!}^ 

 described organisms, 



Winslow et al. (1920, p. 211) in the final report of the Committee use 

 the following definition : 



Gram-negative, evenly staining rods. Often motile, with peritrichic flagella. 

 Easily cultivable, forming grape-vine leaf or convex whitish surface colonies. 

 Liquefy gelatin rarely. All forms except B. alcaligenes and the B. abortus group 

 attack the hexoses and most species ferment a large series of carbohydrates. 

 Acid formed by all, gas (CO2 and H2) only by one series. Typically intestinal 

 parasites of man and the higher animals although several species may occur on 

 plants and one (B. aerogenes) is widely distributed in nature. Many species 

 pathogenic. 



Type species, B. coli Escherich 1885, p. 518. 



Castellani and Chalmers (1919) have broken up the genus Bacterium 

 into a large number of genera, apparently dropping this generic name 

 entirely. In this they have been followed by Bergey et al. (1923). 



It is evident from the preceding analysis of the important literature 

 bearing on the subject that the various diagnoses of the genus Bacterium 

 with their principal advocates may be grouped as follows: 



1. Pre-Cohnian conceptions. Relatively rigid cells or chains of cells, 

 not flexible, motile, oscillating. First species described Bacterium trilo- 

 culare'Ehr. No type species designated. No species described at pres- 



