22 GENERAL SYSTEMATIC BACTERIOLOGY 



Cohn (1872, p. 229) named a spherical organism which he found in 

 smallpox lymph the Microsphaera vacciniae. Later the fact that this 

 generic name had been previously used for a genus of Ascomycetes 

 led him to change to the generic name Micrococcus. 



The first measurably adequate classification of bacteria following 

 the recognition of the fact that they were plants, not animals, was that 

 of Cohn (1872, p. 127). He defined the bacteria as having cells free 

 from chlorophyll, spherical, oblong or cylindric, straight or bent^ 

 multiplying exclusively by fission and either isolated or vegetating in 

 cell families. Four tribes with a total of six genera were recognized. 

 They may be differentiated by reference to the following key : 



Cohn's Classification of Bacteria (1782) 



A. Cells spherical Tribe I. Sphaerobacteria 



One genus only 1. Micrococcus 



B. Cells isolated short rods .Tribe II. Microbacteria 



One genus only 2. Bacterium 



C. Cells elongate or in filaments Tribe III. Desmobacteria 



1. Cells not flexuous 3. Bacillus 



2. Cells flexuous 4. Vibrio 



D. Cells spiral Tribe IV. Spirobacteria 



1. Cells not flexuous 5. Spirillum 



2. Cells flexuous 6. Spirochaete 



It will be noted that one new genus, Bacillus, was created with B, 

 sublilis as the type. Two other species, Bacillus ulna and B. anthracis 

 were included. 



Billroth (1874) in a volume entitled "Untersuchungen iiber die Veg- 

 etationsformen von Coccobacteria septica," revived in a modified form 

 the Hallier theory of pleomorphism. As the result of extended studies 

 he came to the conclusion that various bacteria which he observed were 

 different growth forms of the organism which he termed Coccobacteria 

 septica. To the various growth forms he gave names, such as Micro- 

 coccos, Mesococcos, Megacoccos, Microbacteria, Mesobacteria, Mega- 

 bacteria, Monococcos, Monobacteria, Petalococcos, etc. With a modified 

 spelling some of these names have been used by subsequent writers 

 as generic names for bacteria, and by some have been credited to Bill- 

 roth. This is incorrect as the names were not used by this author in 

 a generic sense, and had no species named. 



Cohn (1875, p. 141) later greatly extended and improved his classi- 

 fication of bacteria. He concluded that they belonged with the blue 

 green algae, differing principally in the absence of chlorophyll. His. 

 complete classification is as follows. 



