CHAPTER III 



MORPHOLOGY AND CLASSIFICATION OF THE BACTERIA 



MORPHOLOGY OF BACTERIA 



Shape. Bacterial cells are usually one of four shapes, 

 straight rods, curved rods, spheres, or filaments. A 

 straight rod is termed a bacillus; a curved rod a spirillum; 

 a spherical cell a coccus; the filamentous forms are some- 

 times termed trichobacteria. 



Bacteria not infrequently develop cells which are not of 

 the normal size and shape. In some cases these are prob- 



FIG. 1. SHAPES OF BACTERIA. A. Spherical bacteria (cocci). B. 

 Rod-shaped bacteria (bacilli). C. Spiral bacteria (spirilla). 



ably degenerate types, cells produced as a result of growing 

 under abnormal or unfavorable conditions. In other cases 

 they may represent special developmental phases of the life 

 history of the organism. In general, such unusual cells are 

 termed involution forms. Some authors insist that this 

 term should be used only for those which represent de- 

 generate types and not those which represent phases in the 

 normal life cycle. 



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