GENERAL MORPHOLOGY AND PHYSIOLOGY OF BACTERU. 23 



1. Micrococcus. —Cells spherical or biscuit-shaped. Division in one 

 direction of space. With or without flagellae. A large genus, represented 

 by numerous species, pathogenic and non-pathogenic, chromogenic, zymo- 

 genic, etc. ' • • 



2. Streptococcus. — Generic limitation not clearly defined. Often merely 

 chain forms of above, resulting from cohesion of cells dividing in one direction 

 of space. 



3. Sarcina. —Bivision in three directions of space. Cells often in fours 

 (Tetracoccus) — as for example, the sarcina of the stomach. With or without 

 flagellse. 



II. Family Bacteriace^.— Bacilli. Cells more or less elongated, 

 cylindrical, straight ; some are somewhat curved or irregular in outline. With 

 or without flagellae. Endospore formation. Transverse septation. 



1. Bacillus. — Variable in size and length of cell. Numerous flageUfe. 

 Endospore formation common. A very large group, to which belong many 

 of the most important microbes. Includes the old genus Bacterium. 



2. Pseudomonas. — Said ffe have only polar flagellae. Doubtful genus, by 

 many relegated to the group bacillus. 



III. Family Spieillace^. — Spirillae. Cells elongated and spirally 

 twisted. Transverse septatiori. Body fixed, with polar flagellas. 



1. Spirillum. — Numerous polar flagellse. Large group. 



2. Microspira. — ^Few polar flagellae. A group Spirosoma is said to be 

 without flagellae. 



IV. Family Spikochetace^. — Spirocheta. Long, single-celled, flex- 

 ible,' spirally twisted threads without flagellae. One genus — Spirocheta. 

 (Some authorities place these organisms in the animal kingdord with the 

 Protozoa.) 



V. Family Mycobacteriace^. — ^Filamentous organisms, perhaps form- 

 ing a connecting link between bacteria proper and the lower filamentous 

 fungi. Cells filamentous but not enclosed in a sheath. To this family 

 belong the groups Mycobacterium and Actinomyces (ray fungus). No flag- 

 ellae have been observed. Mostly transverse septation. Gonidial (spore) 

 formation has been observed. 



VI. Family Chlamydobacteriace^. — Resembling above family, but 

 the cell filaments are enclosed in a sheath. The following not very clearly 

 defined groups are recognized: Cladothrix, Crenothrix, Phragmidiothrix, 

 and Thiothrix. 



VII. Family BeggiatoacEjE. — Beggiatoa. Family characters not clearly 

 defined^ Motile, though no flagellae have been observed. Beggiatoa is 

 the most important genus. 



The uncertainty in the systematic grouping of microbes need not cause 

 any worry, as even the leading specialists do not give the matter any con- 



