38 BACTERIOLOGY. 



II. Barter iacece, producing in the vegetative condition 

 rod-forms which are grouped in chains or filaments. 



1. Arthrobacterium, forming arthrospores, or Bac- 

 terium, forming no endospores (Fig. 3). 



2. Bacillus ; with endospore formation (Fig. 18). 

 Sub-genera^. Bacillus; straight rods. 



b. Clostridium ; spindle-shaped rods. 



c. Plectridium ; drumstick-shaped rods. 



III. Spirobacteriacece, in vegetative condition forming 

 short curved rods (comma-shaped, S-shaped) which 

 may elongate into spiral filaments. 



1. Spirochcete, without endospores and with arthro- 

 spores (Fig. 19). 



2. Vibrio, with endospores ; the cell changes in 

 shape during spore-formation. 



3. Spirillum, with endospores ; the cell does not 

 change its form. 



IV. Leptothrichecz, forming in the vegetative stage rods 

 which unite in filaments. 



1. Leptothrix is distinguished from the filamentous 

 chains of arthrosporous bacteria by the fact that 

 the filaments are differentiated into base and 

 apex. 



2. Beggiatoa, filaments without sheath ; the cells 

 contain sulphur granules (Fig. i, i and 5). 



3. Phragmidiothrix ; the threads are segmented 

 into shallow disks which may fall apart into 

 half-disks, quadrants and finally spheres. 



4. Crenothrix ; the thread possesses a sheath in 

 which there is usually a deposit of iron (Fig. 



13). 



V. Cladothrichea ; the vegetative cells belong to the 

 rod-forms, the rods have a sheath and show branch- 

 ing. 



Cladothrix (Figs. 5 and 21). 



