WHAT ARE BACTERIA ? 4I 



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 liomogeneous gelatinous sub- 



stance. 

 a. Cellular membrane shading off into the intercellular substance. 



Cells round — micrococcus (Hallier). 



Cells cylindrical — bacterium (Dujardin). 

 h. Intercellular substance arranged in concentric layers. 



Cells round — glseocapsa. 



Cells cylindrical — glseothece. 



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



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



b. Cells rounded, arranged in a zooglcea mass forming a network — 



clathrocystis. 



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



strictions — coelosphaerium . 



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- 

 chsete. 



Filaments long and spirals flexible — spirulina. 

 J. Filaments in chains without phycochrome — streptococcus (strepto- 



bacteria). 

 6. Zooglcea 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 siiggested by diflferent 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 



