WHAT ARE BACTERIA ? 4! 



TRIBE i. 



A. Free cells arranged in pairs or fours. 

 Cells round chroococcus (Naegeli). 

 Cells cylindrical synechococcus (Naegeli). 



B. Cells united into zooglcea masses by homogeneous gelatinous sub- 



stance. 



a. Cellular membrane shading off into the intercellular substance. 

 Cells round micrococcus (Hallier). 



Cells cylindrical bacterium (Dujardin). 



b. Intercellular substance arranged in concentric layers. 

 Cells round glaeocapsa. 



Cells cylindrical glaeothece. 



C. Cells forming circumscribed zoogloea masses with a definite shape. 



a. Families arranged in flat layers in a single plane merismopedia. 



b. Cells rounded, arranged in a zoogloea mass forming a network 



clathrocystis. 



c. Cells cylindrical or wedge-shaped, the families divided by con- 



strictions coelospheerium . 



d. Cells forming families, dividing in several planes, colourless 



cubical cells with a quadrate arrangement sarcina. 



e. A large and indefinite number of colourless cells ascococcus. 



TRIBE 2. 



Filamentus forms in which the cells are thread-shaped. 



A. Without branching. 



1. Colourless cylinders with little sign of division, very delicate, when 



short bacillus, when long leptothrix. 



2. Similar filaments, but thicker and longer beggiatoa. 



3. Filaments deeply divided at intervals with colourless spore-bearing 



tissue and a well developed sheath crenothrix. 



4. Spiral filaments. 



Short and undulating vibrio. 



Short with rigid spirals spirillum. 



Long with flexible spirals and containing phycochrome spiro- 



chaete. 

 Filaments long and spirals flexible spirulina. 



5. Filaments in chains without phycochrome streptococcus (strepto- 



bacteria). 



6. Zoogloea masses or cylindrical cells. 

 When colourless myconostoc. 



In chains nostoc. 



Filaments thinner at one end rivolaria. 



B. Filaments with pseudo ramifications cladothrix. 



Cylindrical colourless filaments streptothrix. 



It may be of interest to some to glance over a few of the 

 classifications suggested by different authors, and to compare 

 the bases on which these classifications are made. Cohn, as 

 we have seen, classifies entirely according to the elementary 

 form of the organism, the nature of the membrane and the 

 mode of division. Van Tieghem founded his classification 



